JPH0573883A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide the magnetic recording medium which exhibits the output of a high frequency range equiv. to the high-frequency range of a vapor deposited tap in spite of a coating type and simultaneously has a good head contact, excellent preservable stability and traveling durability and a low drop- out and block error rate(BER). CONSTITUTION:This magnetic recording medium has at least >=2 layers of the plural layers constituted by at least the lower nonmagnetic layer in which nonmagnetic powder is dispersed in a binder on a nonmagnetic base and the upper magnetic layer in which ferromagnetic powder is dispersed in a binder on the lower layer before the above-mentioned lower nonmagnetic layer is still moist. The average value (d) of the dry thickness of the above-mentioned upper nonmagnetic layer is required to be <=1mum and the average valve DELTAd of the thickness fluctuation at the boundary between the above-mentioned upper magnetic layer and the lower nonmagnetic layer is required to have a relation DELTAd<=d/2. More preferably, the standard deviation a of the average value of the measured value of the dry thickness of the above-mentioned lower nonmagnetic layer is required to be <=0.2mum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, and more particularly to a very thin magnetic recording medium having a magnetic layer of 0.1 .mu.
More specifically, the present invention relates to a magnetic recording medium having excellent electromagnetic conversion characteristics and excellent production characteristics with good yield. In particular, the present invention relates to a magnetic recording medium, particularly a high density thin layer magnetic recording medium having a magnetic layer thickness of 1.0 μ or less. The present invention relates to a magnetic recording medium having improved runnability and durability.

[0002]

2. Description of the Related Art Conventional magnetic recording media such as video tapes, audio tapes and magnetic disks have a magnetic layer in which ferromagnetic iron oxide, Co-modified iron oxide, CrO ₂ , ferromagnetic alloy powder and the like are dispersed in a binder. A non-magnetic support coated with is widely used. In recent years, the recording wavelength tends to become shorter as the recording density becomes higher, and the problem of thickness loss at the time of recording / reproduction such as a decrease in output when the thickness of the magnetic layer is large becomes more serious. Therefore, the magnetic layer has been thinned. However, when the magnetic layer is thinned to about 2 μm or less, the surface property of the support is likely to appear on the surface of the magnetic layer, and the electromagnetic conversion characteristics tend to be deteriorated. ..

Therefore, by providing a nonmagnetic thick lower layer on the surface of the nonmagnetic support and then providing the magnetic layer on the upper layer, the problems due to the surface roughness of the support described above are solved and the magnetic layer is made thin. Has proposed an attempt to reduce the thickness demagnetization and achieve a high output. For example, in JP-A-62-154225, the thickness of the magnetic layer is 0.5.
In order to prevent the surface electric resistance of the magnetic layer from becoming higher as well as μm or less, a magnetic underlayer having a thickness including the conductive fine powder equal to or larger than the thickness of the magnetic layer is provided between the magnetic layer and the substrate. Recording media have been proposed. Also, JP-A-62-222
No. 427, a film containing a support and an undercoat layer provided on the support and containing an abrasive having an average particle size of 0.5 to 3 μm, and a ferromagnetic powder provided on the undercoat layer. 1μ
A magnetic recording medium having a magnetic layer of m or less has been proposed, but this has a function of cleaning the magnetic head of the magnetic recording medium because part of the abrasive in the undercoat layer protrudes into the magnetic layer. Is. In this way, the magnetic layer is made thin to achieve high density recording, and at the same time, carbon black is included in the lower non-magnetic layer to prevent static electricity, and an abrasive is added to improve cleaning characteristics and durability. is doing.

However, in the conventional technique, the lower non-magnetic layer is first coated on the non-magnetic support, dried, and optionally calendered before the upper magnetic layer is provided. It was complicated and had the following problems. That is, in order to make the magnetic layer thinner, it is conceivable to reduce the coating amount or to add a large amount of solvent to the magnetic coating liquid to reduce the concentration. If you take the former,
If the coating amount is reduced, there is not enough time for leveling after coating, and the drying starts, which causes a problem of coating defects such as streaks and marking patterns, resulting in very poor yield. When the latter method is used, if the concentration of the magnetic coating solution is low, the resulting coating film has many voids,
There are various problems such as not being able to obtain a sufficient filling degree of the ferromagnetic powder and insufficient strength of the coating film due to the large number of voids. As one means for solving these problems, as described in Japanese Patent Laid-Open No. 63-191315, a non-magnetic layer is provided as a lower layer by using a simultaneous multi-layer coating method to prepare a magnetic coating solution having a high concentration. A method of thin coating has been proposed.

In the case of the simultaneous multi-layer coating method or the sequential wet coating method, that is, in the case of the so-called Wet on Wet coating method in which the upper layer is coated simultaneously or sequentially while the lower layer is in a wet state, various magnetic layers already formed in the multi-layer structure. Are being studied. However, even if this technique was applied to the lower non-magnetic layer, similarly good results were not obtained. In other words, when the lower non-magnetic layer and the upper magnetic layer were provided by Wet on Wet, the interface between them was disturbed, pinholes were formed, and repulsion of the magnetic layer was produced.

When a nonmagnetic thick lower layer is provided on the surface of the support and then the magnetic layer is provided as the upper layer, the influence of the surface roughness of the support can be eliminated.
There was a problem that head wear and durability were not improved. This is because a non-magnetic lower layer has conventionally used a thermosetting (curing) resin as a binder, so that the lower layer is cured and contact between the magnetic layer and the head or other members is unbuffered. It is considered that this is because the magnetic recording medium having such a lower layer is somewhat inflexible. In order to solve this, it is possible to use a non-curable (thermoplastic) resin as a binder in the lower layer, but in the conventional method, when the lower layer is applied and dried and then the magnetic layer is applied as the upper layer, the lower layer is applied. Swells with the organic solvent of the upper layer coating solution, causing turbulence in the upper layer coating solution, which deteriorates the surface properties of the magnetic layer and causes problems such as deterioration of electromagnetic conversion characteristics.

Further, in order to improve the recording density of the magnetic recording medium, short wavelength recording has been advanced, and the recording wavelength of 8 mm video tape has reached 0.54 μm. As a magnetic recording medium corresponding to this, one using a ferromagnetic metal thin film has been put into practical use. Since the metal thin film magnetic recording medium has a very thin magnetic layer, the loss due to the thickness is small, and therefore a medium having a very high output can be obtained. However, these media are inferior in mass productivity as compared with the conventional coating type magnetic recording media because they are manufactured by vapor-depositing metal on a non-magnetic support, and because they are metal thin films, they are oxidized for a long time. There is a problem in terms of storability. In order to solve these problems, it has been desired to thin the magnetic layer of the conventional coating type magnetic recording medium.

However, in order to coat the upper magnetic layer with a thin layer of 1.0 μm or less, the magnetic liquid must be diluted with a large amount of solvent, which easily promotes aggregation of the magnetic liquid.
Also, since a large amount of organic solvent evaporates during drying, the orientation of the ferromagnetic powder is likely to be disturbed, and performance can be secured to some extent in media that are not longitudinal recording, such as magnetic disks, but in tape-shaped magnetic recording media. Poor orientation,
Even if a thin layer is achieved, it is difficult to secure sufficient electromagnetic conversion characteristics due to deterioration of orientation and deterioration of surface property. In addition, since the magnetic film was weak because the excessive drying caused many voids, the running durability was also insufficient. If the organic solvent to be diluted is reduced in order to improve the orientation and to reduce the voids in the coating film, the coating stability will be deteriorated.

As a means for dealing with such a problem, it has been proposed to include a non-magnetic granular abrasive or a filler in the undercoat layer. (JP-A-62-222427, JP-A-2-257424) However, a problem with these techniques is that when a magnetic layer and a non-magnetic layer are simultaneously coated to orient the magnetic material in the upper layer, a magnetic material with a magnetic field is applied. Due to the rotational movement of the above, mixing occurs at the interface between the upper and lower layers, and not only is there not sufficient surface property,
Since the orientation is not performed sufficiently, sufficient electromagnetic conversion characteristics cannot be obtained.

It has been proposed to improve the orientation of the upper magnetic particles by forming a conductive intermediate layer using graphite as the non-magnetic scaly particles.
(Japanese Patent Laid-Open No. 55-55438) However, although such a substance can improve the orientation, graphite itself does not have a reinforcing effect on the film and is insufficient in durability. Proposals to mix powders have also been made. (JP-A-60-125926) Further, it has been proposed to improve the orientation of the upper magnetic particles by forming a reinforcing layer using acicular oxalate as the non-magnetic acicular particles. .. (Japanese Patent Publication Sho 58-51
327).

Although these proposals improve the orientation and ensure the durability, the scale-like particles are likely to cause stacking at the stage of actually producing the medium, and the substance such as oxalate disperses in the binder. It was found that the smoothness of the magnetic surface was impaired because of the poor quality. Further, the magnetic recording medium is required to have a very smooth surface property in order to reduce the spacing loss with the head for higher density and higher output.
For this reason, the lower non-magnetic layer which is not directly exposed on the surface has good dispersibility as much as possible, and there is an increasing need for the surface property to be smooth when simultaneous multilayer coating is performed. Further, as described above, when the magnetic layer is made thin, the dispersibility of the lower non-magnetic layer further contributes to the surface property in the case of simultaneous superposition. As a result of earnest study, even if the dispersibility of only the lower layer is improved,
As a result of simultaneous layering, it was found that the surface became rough.

When the coercive force of the magnetic layer is low, self-demagnetization loss is large and it is not suitable for short wavelength recording. Therefore, it is necessary to have a considerable Hc. As means which can be used for such a purpose, the gap between the non-magnetic support and the magnetic layer is 0.5 μm to 5.
It has been proposed to provide an undercoat layer of 0 μm and Hc of the magnetic layer to 1000 Oe. (JP-A-57-19853
6) However, the conventionally known technique has the following problems in achieving this object. The above-mentioned JP-A-57-198.
In the technique disclosed in No. 536, when the simultaneous multilayer coating of the upper and lower layers, which is the feature of the present invention, the upper and lower layers are mixed, the surface property is not good, and the orientation is disturbed. Further, as a technique for improving the orientation in simultaneous multi-layer coating, JP-A-3-490
Although it has been disclosed that a layer in which carbon black is dispersed in 32 is used as a lower layer to perform multi-stage orientation, a filler having a small true specific gravity such as carbon black is used for simultaneous multi-layer coating due to the rotational movement of the magnetic substance during orientation. Sometimes the interfaces between the upper and lower layers were disturbed, and the SQ measured in the in-plane direction was high, but the improvement of the residual coercive force in the direction normal to the magnetic layer, which is the purpose of this case, was insufficient.

As a known technique for such a technique, there is JP-A-62-1115. However, the application of this known technique in simultaneous multi-layer coating as in the present application has the following problems. That is, in the case of simultaneous multi-layer coating using a non-magnetic lower layer low specific gravity carbon black,
In the coating process or orientation process, the non-magnetic lower layer and the magnetic layer are mixed with each other, or turbulent flow causes turbulence at the interface between the two layers. Such mixing and turbulence between the two layers extremely reduces the orientation of the magnetic material in the magnetic layer.

Further, since a magnetic material having a short major axis length and a small acicular ratio is less likely to be flow-oriented, the orientation of the magnetic material is further deteriorated and sufficient electromagnetic conversion characteristics cannot be obtained. In recent years, the magnetic material contained in the magnetic layer has been made finer to increase the density. By using fine particles, the strength of the magnetic layer becomes inferior, and for example, if a high tension is applied in the manufacturing process or in the video deck, the tape will be elongated and skew (SKEW) distortion will be increased. In order to prevent this, it has been attempted to reduce the heat shrinkage rate or increase the strength of the support, but there is a limit. Further, when the simultaneous multi-layer coating method is adopted, the heat shrinkage rate becomes larger and Skew strain increases as compared with the sequential multi-layer coating method, which is also a problem. This is because in the case of sequential multilayer coating, the lower layer was hardened by a calendering or curing treatment after coating the lower layer to make the medium less likely to expand and contract, but in the simultaneous multilayer coating method, the lower layer and the upper layer are coated at the same time. This is because the expansion and contraction of the medium cannot be suppressed by the lower layer. JP-A-63-187418 and JP-A-63-191315 disclose inventions based on the simultaneous multi-layer coating method, but have such drawbacks.

Similarly, there is a tendency for the tape thickness to be reduced in order to prolong the time. When the tape thickness is reduced, the tape stiffness is reduced, and good contact with the head cannot be maintained, resulting in deterioration of electromagnetic conversion characteristics. In particular, 8mm video tapes and VHs that have become popular in recent years
Since the total length of the long-time tape of S is as thin as 14 μm or less, it is difficult to secure the head contact. Conventionally,
For thick media, it was rather effective to lower the strength of the lower non-magnetic layer to maintain a smooth contact state.
In a thin tape used in a recording / reproducing apparatus using a rotary head in recent years, it is difficult to secure head contact unless the stiffness of the lower non-magnetic layer is increased. There is also a method of controlling this stiffness by a stretching method of the non-magnetic support, but the stiffness in the width direction is reduced, which is not preferable for running durability.

As shown in JP-A-63-191315, it was confirmed that the lower non-magnetic layer did not contain polyisocyanate in order to improve the contact with the head.
As a result, the storage stability at high temperature and high humidity is poor. Therefore, it is effective in a system that does not emphasize storage, but is difficult to use in a system that emphasizes storage such as business use or data storage. JP-A-63-18741
Regarding No. 8 as well, it is disclosed that the magnetic layer is similarly thinned to improve the electromagnetic conversion characteristics. However, in the present invention, there are still insufficient electromagnetic conversion characteristics. JP-A-50-8
No. 03 has an invention that a fine granular non-magnetic pigment having a Mohs hardness of 6 or more is provided between the magnetic layer and the support. The purpose is to increase the flatness of the substrate.

Further, it is difficult for these methods to meet the demand for thinning of the magnetic recording medium due to the recent increase in time and density, and these methods provide excellent electromagnetic conversion characteristics and running durability. There was insufficient compatibility. In particular, in order to improve running durability with a thin tape, it is necessary to reduce tape edge damage.
The inventions of No. 15 and JP-A-63-187418 were insufficient.

Next, various patent applications have been filed for obtaining a magnetic recording medium in which the upper layer is a magnetic layer and the lower layer is non-magnetic, and the method is Wet on Wet. For example, in JP-A-50-104003, there is a description suggesting Wet on Wet, but the non-magnetic layer is an example of only carbon black, and the structural viscosity is too strong, and the interface disorder is severe.

Further, Japanese Laid-Open Patent Publication No. 62-129222 (US
Japanese Patent No. 4916024) discloses a magnetic recording medium in which a conductive layer (intermediate layer) contains 5% to 25% of ferromagnetic powder of carbon black. This is added to improve the dispersibility of carbon black,
Since the ferromagnetic powder to be added to the intermediate layer is the same as that used in the magnetic layer, the disturbance at the interface could not be satisfactorily prevented. Further, in JP-A-62-214524, each coating solution composition is selected so as to have mutual solubility in the solvent and solute of each coating solution composition of a plurality of adjacent layers.
A method for manufacturing a magnetic recording medium which is coated with Eton Wet and dried is disclosed. However, although there is an example of a combination of an upper magnetic layer and a lower non-magnetic layer, it is an example of only a binder, and suggests that carbon black is also contained in the intermediate layer. It was not possible to eliminate the disorder of the interface. Also, JP-A-62-2411
No. 30 (US Pat. No. 4,839,225) is a magnetic recording medium in which the intermediate layer contains at least one binder containing a hydroxyl group and / or an amino group, and the magnetic layer contains an isocyanate compound. To improve the adhesion strength between the intermediate layer and the magnetic layer. Although it is stated that carbon black may be added to the intermediate layer and the intermediate layer may be applied by the Wet on Wet method, such a disclosure could not solve the interface fluctuation.

Further, JP-A-63-88080 (US
No. 4,854,262) discloses a coating device having an improved doctor edge. Although there is a disclosure of viscosity at a high shear rate (10 ⁴ sec ^-1 ) in this, only the viscosity of the upper layer and lower layer liquids is shown, and such a disclosure cannot sufficiently suppress the interfacial fluctuation. It was In addition, JP-A-6
Japanese Patent Laid-Open No. 3-146210 discloses a magnetic recording medium in which the binder of the lower magnetic layer or the non-magnetic layer is a non-curable binder and the binder of the uppermost magnetic layer is an electron beam curable resin. There is. However, only the example in which the lower non-magnetic coating material contained carbon black could not solve the disorder of the interface. Further, in Japanese Patent Laid-Open No. 63-164022, a non-magnetic liquid layer having a viscosity lower than that of the magnetic liquid layer is formed in the center of the slot of the extrusion type head on the front and rear wall surfaces of the slot, and extrusion coating of multiple layers is performed. A method of applying a magnetic liquid is disclosed. The inventors have invented that a high-viscosity magnetic layer liquid is wrapped with a low-viscosity non-magnetic layer binder solution to improve high-speed thin layer coating properties, and the purpose is to reduce the gap between the magnetic layer coating liquid bead and the Giessor. It was not possible to sufficiently solve the disorder of the interface only by such disclosure. Further, JP-A-63-187418 (US4863)
No. 793) discloses a magnetic recording medium in which the ferromagnetic powder contained in the upper magnetic layer has an average major axis length of less than 0.30 μm by a transmission electron microscope and a crystallite size of less than 300Å by an X-ray diffraction method. Has been done. It is disclosed that the lower non-magnetic layer may contain carbon black, graphite, titanium oxide, etc., and specific examples include α-Fe ₂
A combination of 100 parts by weight O ₃ and 10 parts conductive carbon is disclosed. However, since the amount of carbon used is small and the particle size of α-Fe ₂ O ₃ is not described, the disclosure of these publications cannot sufficiently solve the disorder of the interface.

Further, JP-A-63-191315 (U
S4963433), the binder of the lower layer is a thermoplastic binder, and the thickness of the lower layer is 0.5μ in dry thickness.
A magnetic recording medium having a size of m or more is disclosed. Specific examples of the non-magnetic powder contained in the lower non-magnetic layer include α-Fe ₂ O ₃ 10 as in the above-mentioned JP-A-63-187418.
A combination of 0 parts by weight and 10 parts of conductive carbon is disclosed. However, the amount of carbon used is small α-
Since the particle size of Fe ₂ O ₃ is not described, the disclosure of these publications cannot solve the disorder of the interface.

Further, in Japanese Unexamined Patent Publication No. 2-254621, a non-magnetic layer containing carbon black as a main component is provided, and a magnetic layer containing Fe--Al based ferromagnetic powder is formed thereon by a wet-on-wet multi-layer coating method. A formed magnetic recording medium is disclosed. However, the lower layer is exemplified only by carbon black, and the structural viscosity was too strong to solve the disorder of the interface.

Further, Japanese Patent Laid-Open No. 2-257424 discloses a magnetic recording medium containing a filler having an average particle diameter of 50 mμ or more in a non-magnetic layer. As the filler, abrasives such as carbon black, Al ₂ O ₃ and SiC are listed. However, the specific example is the use of only carbon black, only Al ₂ O _{3, and} only SiC, and such a combination could not solve the interface disorder.

Next, in JP-A-2-257425, the dynamic friction coefficient is 0.25 or less and the surface specific resistance is 1.
A magnetic recording medium provided with a plurality of layers of 0 × 10 9 Ω / sq or less is disclosed. However, examples of the non-magnetic powder in the lower layer are SnO ₂ only and carbon black only,
It was not possible to solve the disorder of the interface. In addition, JP-A-2
-260231 discloses a magnetic recording in which a first non-magnetic layer, a first magnetic layer, a second non-magnetic layer and a second magnetic layer are laminated in this order on a non-magnetic support. A medium is disclosed. This non-magnetic layer is only an example of the binder, and the disorder of the interface could not be resolved.

Further, JP-A-3-49032 (US5
No. 051291), the thickness of the magnetic layer is 1.5 μm.
The following is disclosed and a magnetic recording medium in which the squareness ratio of the magnetic layer is 0.85 or more is disclosed. This is to improve the squareness ratio by multi-stage orientation, but the lower layer is a layer using only carbon black, and the structural viscosity was too strong to solve the interface disorder.

In recent years, studies on Hi8 tapes have been made, and the ultimate need is to satisfy both the merits of ME (vapor deposition) tapes and MP (metal) tapes. The most important issue was how to achieve high C / N in the short wavelength region (luminance signal in the high frequency range) of the vapor deposition tape while maintaining the running property, durability, and production suitability. ..

Conventionally, the double coating technique is the VTR
Focusing on the signal recording mechanism, that is, the recording depth of each signal, the performance has been improved by designing the optimum upper and lower magnetic layers for each. The VHS double coating has a two-layer structure in which ferromagnetic powders having different sizes and magnetic properties are used for the upper layer and the lower layer, respectively, and high output and low noise have been realized in all bands of brightness, color and sound.

In the Hi8MP multilayer tape, the upper magnetic layer is made of a metal magnetic material suitable for high density recording, and the lower magnetic layer is made of an iron oxide magnetic material excellent in middle and low frequency characteristics.
The so-called high grid double coating, which uses a completely different type of magnetic material, was developed, and the image quality was greatly improved by producing highly sharp images and vivid colors.

However, in order to pursue further ultra-high density recording with Hi8MP and dramatically improve the high frequency characteristics, there is a limit only by the conventional techniques and ideas. Therefore, the present inventors have conducted an analysis and research into the principle and mechanism of the magnetic recording itself, and have conducted earnest studies in order to realize a high frequency characteristic higher than that of a vapor deposition tape.

[0030]

SUMMARY OF THE INVENTION A first object of the present invention is to provide a high density magnetic recording medium which, while being a coating type, exhibits a high frequency output comparable to that of a vapor deposition tape and has running durability and storage stability. Is to provide. A second object of the present invention is a coating type, and a first object of the present invention is to provide a thin layer magnetic recording medium excellent in electromagnetic characteristics such as output, C / N ratio, etc. with high yield and high production efficiency. Another object of the present invention is to provide a thin-layer magnetic recording medium having good head contact and good storage stability.

A third object of the present invention is to provide a magnetic recording medium having good electromagnetic conversion characteristics and excellent running durability. Especially, the output in short wavelength recording is high, and
An object of the present invention is to provide a magnetic recording medium having a good yield in production. A fourth object of the present invention is to provide a magnetic recording medium having high RF output, excellent running durability, few dropouts, and low block error rate (BER).

A fifth aspect of the present invention is to provide a magnetic recording medium having a good electromagnetic conversion characteristic and a good running property. In particular, the simultaneous multilayer coating method has a good surface roughness and a high electromagnetic conversion characteristic. It is to provide a magnetic recording medium. A sixth object of the present invention is to provide a magnetic recording medium having a good electromagnetic conversion characteristic, and having a small heat shrinkage ratio,
A magnetic recording medium having excellent long-term storage stability. A seventh object of the present invention is to provide a magnetic recording medium having a good electromagnetic conversion characteristic and a medium excellent in running durability with little edge damage due to repeated running.

[0033]

Means for Solving the Problems As a result of intensive investigations by the present inventors, although the conventional simultaneous multi-layer coating technique is partially based, it exceeds the frame and becomes larger as the wavelength becomes shorter. It was found that there are two important points: development of a new magnetic material and high packing density in order to reduce the magnetic field of the magnetic layer to a minimum, and to make the magnetic energy of the magnetic layer as high as possible. It was First of all, the signal loss was thoroughly reduced. In magnetic recording, various "losses" occur during the recording / reproducing process. However, by reducing the "self-demagnetization loss", which the present inventors have thought to be inevitable with MP (metal) tapes, it is possible to increase the loss. We have found a completely new idea that has never existed before, which is to improve the range characteristics.

That is, the first point of the present invention is to make the interface of the upper magnetic layer and the lower non-magnetic layer to have the same or similar chicken tropic properties by adjusting the shape of the lower non-magnetic powder. By eliminating the mixed region, a uniform thin magnetic layer with a magnetic layer thickness of 1 μm or less, an average value of thickness variation of 1/2 or less, and a standard deviation of thickness measurement values of 0.2 μm or less was realized. , The self-demagnetization loss in the short wavelength region is greatly reduced.

Further, the second point of the present invention is to suppress the disturbance of the above-mentioned interface to an extremely low level and to control the size and shape of the ferromagnetic powder in the upper magnetic layer and the size of the non-magnetic powder in the lower non-magnetic layer.
By adjusting the shape and adding an invention for improving the dispersibility to the non-magnetic powder itself, a more uniform interface with less fluctuation was realized and an ultra-smooth magnetic layer surface was completed. This smooth surface of the magnetic layer drastically eliminated "space loss" and improved high-frequency output.

The third point of the present invention is to increase the energy of the magnetic layer. It has been found that high magnetic energy and high coercive force can be achieved by using a fine ferromagnetic powder having both Hr and Hc increased for the upper magnetic layer, and a high band output equal to or higher than that of an ME (vapor deposition) tape can be exhibited. Fourth of the present invention
The point of is high density packing. In the conventional technology, if the magnetic layer is simply thinned, the low-frequency output is lowered and the color characteristics are deteriorated.However, in the present invention, the fine particle inorganic powder having extremely high rigidity in the thickness direction greatly enhances the filling effect by the calendar treatment. It has been found that by improving and packing high-energy ferromagnetic powder with high density, excellent middle and low frequency characteristics can be realized.

Further, the fifth point of the present invention lies in the properties such as viscoelasticity, adhesion strength, steel ball wear, residual solvent, sol fraction, etc., which ensures excellent durability that cannot be achieved by ME (vapor deposition) tape. As described above, the first to fifth points of the present invention act on each other in an organically complementary manner, in a complementary manner, and in a comprehensive manner.
It achieves super high filling and achieves epoch-making high frequency characteristics, which were difficult with conventional single layer coating technology, and excellent middle and low frequency characteristics.

First, the first point of the present invention will be described. That is, the above object of the present invention is to provide a lower non-magnetic layer in which at least a non-magnetic powder is dispersed in a binder on a non-magnetic support, and the ferromagnetic powder is bound to the lower non-magnetic layer in a wet state. In a magnetic recording medium having a plurality of at least two layers provided with an upper magnetic layer dispersed in an agent, a dry thickness average value (d) of the upper magnetic layer is 1 μm or less, and the upper magnetic layer and the lower layer are This can be achieved by a magnetic recording medium characterized in that the average value Δd of the thickness variation at the interface of the non-magnetic layer has a relationship of Δd ≦ d / 2.

That is, the first point of the present invention is to realize an ultrathin magnetic layer. From the principle of self-demagnetization, the smaller the cross-sectional area of the magnetic layer, the smaller the loss. Therefore, it was discovered that it is essential to make the magnetic layer ultra-thin in order to increase the output of short-wavelength signals. Moreover, when the thickness is 1 μm or more, the effect is small, and the effect becomes greater as the effective recording thickness, which is generally called ¼ of the recording wavelength, is approached, that is, as the saturation recording is approached. is necessary.

With the conventional single-layer coating technique, it is difficult to coat a thin layer in the submicron region itself, and it is difficult to secure a uniform thickness and super-smooth as the layer becomes thinner. It was extremely difficult to do. However, by innovating the conventional double coating technology and providing a non-magnetic layer containing fine-particle inorganic powder in the lower layer by Wet on Wet, the average value of the thickness variation of the magnetic layer is less than 1/2 of the thickness, and the standard deviation of the magnetic layer thickness is By setting the thickness to 0.2 μm or less, the breakthrough ultra-thin magnetic layer reduces self-demagnetization loss, which is 1/3 to 1/10 or less of the conventional general Hi8 MP tape, which was difficult with the conventional technology. In this way, the brightness signal output is greatly improved.

The principle of self-demagnetization is as follows. The magnetic poles of a magnetized magnet create a magnetic field not only outside the magnet, but also inside. The magnetic field inside the magnet is in the direction opposite to the direction of magnetization and acts in the direction of decreasing the magnetization. This internal magnetic field is called "demagnetizing field", and the decrease in magnetization caused by this is "self-demagnetization".

The size of the magnet depends on the shape of the magnet. That is, the smaller the cross-sectional area and the greater the distance between the magnetic poles, the smaller the demagnetizing field, and the less self-demagnetization occurs. Taking a sewing needle and a pachinko ball, which are completely different in shape, as an example, both are made of iron and stick to a magnet. Since the magnetism is large, it has the property that it is hard to become a magnet.

When this is replaced with a magnetic tape, the demagnetizing field is small in long wavelength (low range) recording, but short wavelength (high range).
As the recording is performed, the distance between the magnetic poles of the magnetization becomes smaller, the demagnetizing field increases, and the loss due to self-demagnetization increases. This is one of the major factors that deteriorate the high frequency characteristics of the tape. In order to reduce the self-demagnetization loss, it is effective to reduce the cross-sectional area according to the principle of self-demagnetization, that is, reduce the thickness of the magnetic layer. Moreover, the self-demagnetization loss becomes smaller as it approaches saturation recording and the output improves, so that it approaches the effective magnetic layer thickness, which is said to be ¼ of the recording wavelength. An ultra-thin layer in the submicron region is required.

The shortest recording wavelength of Hi8 is 0.49 μm,
The wavelength is extremely short, which is one of the reasons why it has excellent high-frequency characteristics similar to an ME (evaporation) tape having an extremely thin magnetic layer thickness of about 0.2 μm. On the other hand, the thickness of the magnetic layer of the coating type MP tape is about 3 μm, and the coating method used up to now has to be considerably thicker than the recording wavelength. It was an inevitable large wall.

However, according to the present invention, such a wall is largely broken. Space loss is also an important factor. Along with self-demagnetization, space loss is another major cause of deterioration in high frequency characteristics. The shorter the wavelength, the weaker the magnetic flux emitted to the surface of the tape, and even the slightest spacing between the tape and the video head causes a large loss. Space loss includes microscopic ones due to the roughness of the magnetic layer surface and macroscopic ones due to the rigidity of the tape. In the former case, how to achieve super smoothness and secure stable running performance is an issue.
As described above, the importance becomes extremely high in the high density recording in which the shortest recording wavelength is about 40% of VHS. The latter is so-called "head contact", and the issue is how to achieve both excellent tape strength and flexibility. This is not limited to short-wavelength recording, and the image quality is greatly affected. The present invention solves this space loss problem all at once.

Next, the second point of the present invention will be described. That is, in the present invention, the dry thickness d of the upper magnetic layer is 1.0 μm or less, and the root mean square roughness R of the surface of the upper magnetic layer is measured by a scanning tunneling microscope (STM) method.
_rms is 30 ≦ d / with the dry thickness d of the upper magnetic layer.
It is preferable that there is a relationship of R _rms .

The second point of the present invention is super smoothing of the magnetic layer surface. The double coating technology is originally a technology that can achieve excellent smoothness. This is because the lower magnetic layer absorbs irregularities on the surface of the base film, and it is difficult to convey the influence of the irregularities to the upper layer. But 0.5
When a slight space loss at a shorter wavelength of less than μm is taken into consideration and further smoothness is aimed at, there is a limit only in the conventional technique.

Due to the recording mechanism, it is necessary to use an ultrafine particle magnetic material excellent in high frequency characteristics in the upper layer, and even a very small disturbance of the upper and lower layer interfaces in particle size units caused by a relatively large lower nonmagnetic powder. , Because it is necessary to thoroughly pursue. In particular, as the upper layer is made ultra-thin, the smoothness of the interface has a greater effect on the smoothness of the surface of the magnetic layer, and the solution of this problem was even more important.

In the present invention, in order to achieve ultra-smoothness of the interface between the upper and lower layers, the non-magnetic particles in the lower layer were made into ultrafine particles and the packing thereof was dense. On the other hand, however, since it is extremely fine particles, it is difficult to fill it uniformly and in high density as it is. Therefore, by applying a special surface treatment to each surface of the ultrafine particles to enhance the dispersibility, high density filling is achieved. And the smoothness of the interface between the upper and lower layers has been dramatically improved.

Further, since this non-magnetic layer is a high-density packing layer, it has a high degree of freedom in the surface direction of the tape, and while it has excellent flexibility, it is well-suited to the force in the thickness direction. It exhibits high rigidity and further enhances the smoothing effect of calendering. As a result, Hi8
20% smoother than MP-DC,
The surface roughness of the magnetic layer was 2.5 nm. The ultra-smoothness realized only by Wet on Wet having the non-magnetic layer as the lower layer can greatly reduce the space loss in the short wavelength region and improve the high frequency characteristics.

Next, the third point of the present invention will be described. That is, according to the present invention, the ferromagnetic powder contained in the upper magnetic layer has a major axis length of 0.3 μm or less and an Hc of 15 or less.
Needle-shaped ferromagnetic alloy powder of 00 Oe or more or plate diameter 0.3
It is preferable that the powder is a powder having a particle size of μm or less and a plate-like ferromagnetic powder having Hc of 1000 Oe or more.

That is, the third point of the present invention is the high output and low noise of the magnetic layer, which is the basis of the technology for improving the performance of the magnetic tape. In order to thoroughly pursue improvement of characteristics at short wavelengths, in addition to minimizing signal loss, the magnetic layer itself has high output and low noise due to "ultrafine particles of magnetic material, high energy and high density packing". Ization is essential. Next, the fourth point of the present invention will be described.

That is, according to the present invention, it is preferable that the ratio SMD / STD of the application direction stayness SMD of the magnetic recording medium and the width direction stayness STD of the application direction is 1.0 to 1.9. Specifically, the inorganic powder contained in the lower non-magnetic layer has a Mohs hardness of 6 or more and an average particle size of 0.
It is preferably composed of spherical to cubic polyhedral inorganic powder having a particle size of 15 μm or less.

The present invention also relates to the magnetic recording medium of 80
The heat shrinkage ratio at 30 ° C. for 30 minutes is preferably 0.4% or less. Specifically, the dry thickness of the lower non-magnetic layer is 1 to 30 times the dry thickness of the upper magnetic layer. The difference between the powder volume ratio of the lower non-magnetic layer and the powder volume ratio of the upper magnetic layer is preferably in the range of -5% to + 20%.

That is, the fourth point of the present invention is high density packing, and it is the lower non-magnetic layer that enables high density packing of the magnetic material of the present invention. The non-magnetic layer, which is smooth and has extremely high rigidity in the thickness direction, is made of Super HDP.
(High Density Packing) It firmly receives the strong pressure of the calendar and realizes an epoch-making high-density packing that has never been seen before.

Further, if the high frequency characteristics are thoroughly pursued by making the magnetic layer ultra-thin, the characteristics of the middle and low frequencies are deteriorated by the conventional technology.
Excellent color characteristics cannot be obtained. However, the lower non-magnetic layer of the present invention enables an epoch-making high packing of the high energy magnetic material which solves this problem, and at the same time, the high output is greatly improved, and at the same time, the high middle and low range characteristics are secured. It was possible to achieve excellent color output.

That is, according to the present invention, it is possible to achieve high-density recording comparable to vapor-deposited tape, which was conventionally thought to be impossible with a coating type magnetic recording medium. This is because the lower non-magnetic layer is in a wet state. By the so-called Wetton Wet method in which the upper magnetic layer is provided, a uniform upper magnetic layer can be formed as a thin layer having a dry thickness of 1.0 μm or less, and a conventional magnetic recording medium by such a Wet on Wet method. The average value of the dry thickness of the upper magnetic layer, which has not been achieved by the method, is 1 μm or less, and the average value Δd of the thickness variation at the interface between the upper magnetic layer and the lower non-magnetic layer has a relationship of Δd ≦ d / 2. By doing so, it was for the first time that a high-density recording medium which was practically applicable and was comparable to a vapor deposition tape was obtained. Conventional dry thickness 1.
Magnetic recording media having an upper magnetic thin layer of 0 μm or less and a lower non-magnetic layer are only occasionally found as patent applications, and no product which has ever been actually marketed has been found.
The present invention is an epoch-making invention that breaks such conventional wisdom for the first time.

Here, the definition and measuring method of Δd are as follows. Here, the method of obtaining the thickness of the upper magnetic layer and the interface variation Δd is as follows. That is, the magnetic recording medium is cut out to a thickness of about 0.1 μm with a diamond cutter in the longitudinal direction, and a magnification of 10,000 to 1 is obtained with a transmission electron microscope.
It was observed at a magnification of 00000 times, preferably 20000 to 50,000 times, and the photograph was taken. The print size of the photograph was A4 to A5. After that, the interface was visually judged by observing the shape difference between the magnetic substance and the non-magnetic powder in the upper magnetic layer and the lower non-magnetic layer, and the surface of the magnetic layer was also black. After that, Zeiss image processing device IB
The length of the space between the trimmed lines was measured by AS2. Thus, the average value of the thickness of the upper magnetic layer was obtained. The length of the space was measured by segmenting a space having a length of 21 cm into 100 to 300.

The average value Δd of the thickness variation at the interface between the upper magnetic layer and the lower nonmagnetic layer is the peak formed by the bordered interface between the magnetic layer and the lower nonmagnetic layer having a length of 20 μm (actual length). The distance (Δd _i ) between the bottom of the crest and the valley in the thickness direction was determined at 10 to 20 points (all in 20 μm), and the average value of the sums was calculated. That is, in the present invention, the curve forming the interface is ideally a straight line with a constant d, which is the most preferable mode. However, in reality, the amplitude is smaller and the interval between peaks and valleys is smaller than the conventional one. It is preferable that a curve similar to a long smooth sine curve is formed, and the number of peaks and valleys is 2
It is preferable to limit the length to 0 μm to a maximum of 10 to 20 each (see FIG. 1).

That is, Δd is obtained from the following equation. Δd = (Δd ₁ + Δd ₂ + ... + Δd _m ) / m (m = 1
The distance (L) between the peaks of the curve formed by the interface is preferably 1 μm or more, particularly preferably 2 μm or more. Further, in the present invention, the standard deviation σ can be obtained by using exactly the same value as the thickness of each magnetic layer segmented into 100 to 300 as used in the statistical processing. This standard deviation σ is preferably 0.2 μm or less.

A first point of the present invention is to provide a lower non-magnetic layer in which at least a non-magnetic powder is dispersed in a binder on a non-magnetic support, and the lower non-magnetic layer is wet on the lower non-magnetic layer. In a magnetic recording medium having a plurality of at least two layers provided with an upper magnetic layer in which ferromagnetic powder is dispersed in a binder, the average dry thickness (d) of the upper magnetic layer is 1
It can be achieved by a magnetic recording medium characterized in that the average value Δd of the thickness variation at the interface between the upper magnetic layer and the lower non-magnetic layer has a relationship of Δd ≦ d / 2, and preferably, This can be achieved by a magnetic recording medium characterized in that the standard deviation σ of the average value of the measured dry thickness of the upper magnetic layer is 0.2 μm or less.

There are the following two concrete means for achieving the above-mentioned regulation. The first aspect is to control the thixotropic properties of the magnetic coating material of the magnetic layer and the respective dispersion liquids of the lower non-magnetic layer so as to approximate each other, and the second aspect includes the lower non-magnetic layer and the magnetic layer. This is to control the size and shape of the powder to be mechanically controlled so as not to mechanically generate a mixed region in the upper and lower layers.

As a concrete method of the first embodiment, a dispersion obtained by dispersing a non-magnetic powder in a binder has a thixotropic property and a shear stress A at a shear rate of 10 ⁴ sec ^-1.
Shear stress at 10 ⁴ and shear rate 10 sec ^-1 A10
The ratio A10 ⁴ / A10 is 100 ≧ A10 ⁴ / A10 ≧
It is to adjust to 3. There are the following four specific means for having such thixotropy. The magnetic recording medium of the present invention is not limited to these four, and the essence thereof is to make the thixotropic property of the dispersion liquid equal to or close to the thixotropic property of the magnetic paint, More specifically, it is within the range of the value of A10 ⁴ / A10. (A) The powder of the lower non-magnetic layer contains at least carbon black and an inorganic powder having an average primary particle diameter smaller than the dry thickness of the lower non-magnetic layer, and thermosetting polyisocyanate is used for the lower non-magnetic layer and the upper magnetic layer. 10 in the binder
~ 70% by weight. (B) The powder of the lower non-recording layer has an average primary particle diameter of 0.08 μm
Including a non-metallic inorganic powder having a particle size of m or less. (C) The dry thickness of the upper magnetic layer is 1.0 μm or less, and the saturation maximum magnetic flux density Bm of the lower nonmagnetic layer is 30 to 50.
Use a magnetic powder that imparts thixotropic properties such that it is 0 gauss. However, the lower non-magnetic layer does not participate in recording. (D) The ferromagnetic powder in the upper magnetic layer has a major axis length of 0.3 μm or less and a crystallite size of 300 μm or less, and the lower layer is made of nonmagnetic metal oxide powder as nonmagnetic powder and an average particle size of 20 n.
containing carbon black of less than m in a ratio of 95/5 to 60/40, and at least 3 OH in one molecule in the lower layer.
Including a polyurethane having a group and a polyisocyanate compound.

These (A) to (D) are A10 ⁴ / A
10 shows suitable means for adjusting 10 to the above range. However, these are related to the following factors (including duplicated description), for example, and variously selected to obtain desired A10. ^{It is possible} to obtain a dispersion having ⁴ / A10 and a magnetic coating material, and thus to manufacture a magnetic recording medium having desired properties.

Examples of the factor include (1) particle size (specific surface area, average primary particle diameter, etc.), (2) structure (oil absorption amount, particle morphology, etc.), for inorganic powder or magnetic powder to be dispersed. (3) Properties of the powder surface (pH, loss on heating, etc.), (4) Particle suction force (σ _S, etc.), etc. With regard to (1) type (polarity etc.), (2) binder solubility, (3) solvent formulation amount, etc., water content etc. can be mentioned.

Next, as concrete means of the second aspect, the following (E) to (G) can be mentioned. The essential point is that the mixed region is between the lower non-magnetic layer and the upper magnetic layer. , And these are merely examples. (E) Longest axial length r _{1 of the} non-magnetic powder contained in the lower layer
That the ratio r ₁ / r ₂ of the shortest axial length r ₂ to 2.5 or more. (F) The non-magnetic powder has an acicular ratio of 2.5 or more, and the average diameter of the longest axial length of the ferromagnetic powder is 0.3 μm or less. (G) The lower non-magnetic layer contains scale-like non-magnetic powder and a binder containing an epoxy group having a molecular weight of 30,000 or more, and the upper magnetic layer contains needle-like ferromagnetic powder or plate-like ferromagnetic powder. To let.

In order to prevent a mixed region from occurring at the interface between the lower non-magnetic layer and the upper magnetic layer, needle-like non-magnetic powder or scale-like non-magnetic powder is used in the lower non-magnetic layer. Compared with conventional granular non-magnetic powder, when needle-shaped non-magnetic powder is present in an array, it forms a strong coating film even in the undried state, and even if the ferromagnetic powder in the upper magnetic layer rotates, it will form an interface at the interface. No mixing occurs. Another means for preventing the mixed region from occurring is to use scale-like non-magnetic powder in the lower non-magnetic layer and spread it in a so-called tile shape. When the ferromagnetic powder rotates, no mixing occurs at the interface.

When the tile is spread, it is preferable to use a binder containing an epoxy group having a molecular weight of 30,000 or more in order to improve the dispersibility. By using a non-magnetic powder having a characteristic shape in the lower non-magnetic layer and providing the upper magnetic layer on the non-magnetic powder in this way, no mixed region occurs at the interface, and therefore, an extremely thin and smooth magnetic layer is obtained. A layer is obtained.

Further, in the magnetic recording medium of the present invention, the dry thickness average value d of the magnetic layer is λ / 4 ≦ d with respect to the shortest recording wavelength λ.
≦ 3λ and the surface roughness Ra of the magnetic layer is Ra ≦ λ / 50.
It is preferable that The preferred powder structure for this is that the ferromagnetic powder in the magnetic layer has a major axis length of 0.3 μm.
The following needle-like ferromagnetic powder or a plate-like ferromagnetic powder having a plate diameter of 0.3 μm or less, and the non-magnetic powder in the lower non-magnetic layer is granular particles having an average particle size of λ / 4 or less, or long particles. Needle-like particles having an axial length of 0.05 to 1.0 μm and an acicular ratio of 5 to 20, or plate particles having a plate diameter of 0.05 to 1.0 μm and a plate ratio of 5 to 20. Preferably.

The achievement of such surface properties of the present invention is based on the invention based on the invention in which the standard deviation of the average thickness of the upper magnetic layer is 0.2 μm or less.
This can be achieved by the four means (J). (H) The nonmagnetic powder contained in the lower nonmagnetic layer contains an inorganic powder having a Mohs hardness of 3 or more, and the ferromagnetic powder contained in the upper magnetic layer is an acicular ferromagnetic powder, and the average particle size of the inorganic powder is 1/2 to 4 of crystallite size of needle-like ferromagnetic powder
Be double. (I) The non-magnetic powder contained in the lower non-magnetic layer contains an inorganic powder having a Mohs hardness of 3 or more, and the ferromagnetic powder contained in the upper magnetic layer is a needle-like ferromagnetic powder, and the average particle diameter of the inorganic powder is Is 1/3 or less of the major axis length of the acicular ferromagnetic powder. (J) The ferromagnetic powder contained in the upper magnetic layer is a hexagonal plate-shaped ferromagnetic powder having an easy axis of magnetization in the direction perpendicular to the flat plate,
Further, the non-magnetic powder contained in the lower non-magnetic layer contains an inorganic powder, and the average particle size thereof is equal to or smaller than the plate diameter of the ferromagnetic powder contained in the upper magnetic layer. (K) The inorganic powder contained in the lower non-magnetic layer contains the inorganic non-magnetic powder having a surface layer coated with an inorganic oxide.

The respective operational effects described above are as follows. First, (H) will be described. 1 upper magnetic layer
Wet multi-layer coating is required to coat an ultra-thin layer of less than μm. At that time, the particle size of the inorganic powder contained in the lower non-magnetic layer and the crystallite size of the ferromagnetic powder contained in the upper magnetic layer. Fine surface roughness is determined in association with In the case of needle-shaped ferromagnetic powder, the crystallite size corresponds to the minor axis diameter. If the average particle size of the inorganic powder in the lower non-magnetic layer is less than 1/2 of the crystallite size of the acicular ferromagnetic powder, dispersion itself becomes difficult and a smooth lower surface cannot be obtained. The surface smoothness of the recording medium also becomes insufficient. On the contrary, when the average particle size of the lower layer inorganic powder exceeds 4 times the crystallite size of the ferromagnetic powder, the interparticle distance between the lower layer powder particles increases, so that the upper layer ferromagnetic powder affects the surface properties of the lower layer. As it receives, it cannot obtain sufficient surface property.
As shown in the examples, in order to obtain a sufficient surface property, an inorganic powder having an average particle size of 1/2 to 4 times, more preferably 2/3 to 2 times the crystallite size of the upper needle-like ferromagnetic powder is used. It is preferable. The shape of the inorganic powder is preferably spherical or dice. The Mohs hardness is 3 or more, preferably 4 or more, more preferably Q or more.

The volume filling rate of the lower layer of the inorganic powder is preferably 20 to 60%, more preferably 25 to 55%. In order to reduce the surface roughness due to the relationship between the particle size of the lower non-magnetic powder and the crystallite size of the upper ferromagnetic powder, the volume packing ratio of the lower powder has a preferable range. When the volume filling rate is 20% or less, the distance between the lower layer powder particles becomes large, the surface of the upper magnetic layer is affected by the roughness of the surface of the lower layer powder, and the upper layer ferromagnetic powder is present in the lower layer. It will also be mixed in and the surface will become very rough. In addition, the squareness ratio is also reduced. Further, when the volume filling rate is 60% or more, the viscosity of the dispersion becomes very high, and it becomes substantially impossible to apply the dispersion.
Even if applied, problems such as powder falling from the viewpoint of running durability will occur. In addition, the inorganic powder is 60% by weight of the nonmagnetic powder.
% Or more, and the inorganic powder is preferably a metal oxide, an alkaline earth metal salt, or the like.
Further, since it is possible to expect a known effect (for example, to reduce the surface electric resistance) by adding carbon black, it is preferable to use it in combination with the above inorganic powder, but carbon black has very poor dispersibility. ,
Carbon black alone cannot secure sufficient electromagnetic conversion characteristics. In order to obtain good dispersibility, 60% by weight or more must be selected from metal oxides, metals and alkaline earth metal salts. If the inorganic powder is less than 60% by weight of the non-magnetic powder and the carbon black is 40% or more of the non-magnetic powder, the dispersibility becomes insufficient and desired electromagnetic conversion characteristics cannot be obtained.

Next, (I) will be described below. It is necessary to increase the squareness ratio in order to maintain good electromagnetic conversion characteristics in wet multi-layer coating, but if the average particle size of the inorganic powder in the lower non-magnetic layer is larger than that of the upper ferromagnetic powder, the gap between the lower particles becomes large. Becomes larger, and the orientation of the ferromagnetic powder is disturbed particularly at the interface between the upper layer and the lower layer, and the surface property of the magnetic layer is deteriorated as in (H). In order to reduce the disorder of the orientation, it is necessary to arrange fine non-magnetic powders in the longitudinal direction of the ferromagnetic powder so as to support the orientation of the ferromagnetic powder in the longitudinal direction. When the requirements therefor were experimentally confirmed, it was found that the squareness ratio was equivalent to that of the single-layer magnetic layer in the case of needle-like ferromagnetic powder, 1/3 or less of the major axis length, and more preferably 1/3 to 1 / When 20 inorganic powders are used, good surface properties and squareness ratio can be obtained.

Further, in (J), when hexagonal plate-like ferromagnetic powder is used in place of the above-mentioned needle-like ferromagnetic powder, the hexagonal plate-like ferromagnetic powder is oriented in the vertical direction to reduce the disorder of the interface and increase the squareness ratio. be able to. The inorganic powder used for the lower layer is
The plate diameter or less, more preferably the plate diameter or less to 1 / the plate diameter
It is preferably 5 or more. In (I) and (J),
For the same reason as (H), the volume filling rate in the lower layer of the inorganic powder is preferably 20 to 60%.

When the thickness of the magnetic layer is 5 times the major axis length or less, the filling degree by the calendar is remarkably improved, and a magnetic recording medium having more excellent electromagnetic conversion characteristics can be obtained. Preferred types and properties of the inorganic powder are the same as those of (H). Next, (K) will be described. The inorganic oxide with which the surface of the inorganic powder contained in the lower non-magnetic layer is coated is preferably Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ ,
SnO ₂ , Sb ₂ O ₃ , ZnO and the like are preferable, and Al ₂ O ₃ , SiO ₂ and ZrO ₂ are more preferable. These may be used in combination or may be used alone. Depending on the purpose, a co-precipitated surface treatment tank may be used, or a structure in which the surface layer is first treated with alumina and then the surface layer is treated with silica, or the reverse structure may be employed. The surface treatment layer may be a porous layer depending on the purpose, but it is generally preferable that the surface treatment layer is homogeneous and dense.

For example, the surface treatment of non-magnetic inorganic powder is
After dry pulverizing the non-magnetic inorganic powder material, water and a dispersant are added, and wet pulverization and centrifugation are performed for coarse particle classification. After that, the fine particle slurry is transferred to a surface treatment tank, where the surface coating of the metal hydroxide is performed. First, a predetermined amount of Al,
An aqueous salt solution of Si, Ti, Zr, Sb, Sn, Zn or the like is added, and an acid or alkali for neutralizing the same is added,
The surface of the inorganic powder particles is coated with the produced hydrous oxide.
By-produced water-soluble salts are removed by decantation, filtration and washing, and finally the slurry pH is adjusted and filtered,
Wash with pure water. The washed cake is dried with a spray dryer or band dryer. Finally, the dried product is crushed with a jet mill to obtain a product. Also,
Not only water-based but also AlCl ₃ and SiCl ₄ vapors are passed through the non-magnetic inorganic powder, and then steam is introduced to allow Al, S
It is also possible to perform i surface treatment.

For other surface treatment methods, see "Charac
terization of Powder Surfaces ", Academic Press can be referred to. In this embodiment, the magnetic layer surface roughness is defined by defining the optimum thickness range of the magnetic layer according to the recording wavelength and the thickness variation at the interface between the lower non-magnetic layer and the magnetic layer (that is, the variation width in the thickness direction of the interface). Is defined and improved, and the magnetic layer is formed thin, uniform, and uniform, so that even if the recording wavelength becomes short, reproduction output fluctuation and amplitude modulation noise are prevented, and high reproduction output and high C / N are achieved. Can be realized.

In other words, conventionally, when the recording wavelength becomes shorter when the magnetic layer becomes thinner, the entire magnetic layer contributes to recording and reproduction, so that when the thickness of the magnetic layer changes, reproduction output fluctuation and amplitude modulation noise are observed. However, the present invention solves this drawback.

In the present invention, the shortest recording wavelength λ varies depending on the type of magnetic recording medium.
5 μm, and 0.67 μm for digital audio.

The range of the thickness d of the magnetic layer of the present invention is λ / 4.
≦ d ≦ 3λ, preferably λ / 4 ≦ d ≦ 2λ (ie,
0.25 ≦ d / λ ≦ 2). The average thickness d of the magnetic layer of the present invention is usually in the range of 0.05 μm ≦ d ≦ 1 μm, preferably 0.05 μm ≦ d ≦ 0.8 μm.

The thickness of the magnetic layer can be obtained by actual measurement as described above. A magnetic layer sample having a known thickness is measured by an fluorescent X-ray for an element uniquely contained in the magnetic layer to prepare a calibration curve. Then, the thickness of the sample of the unknown material can be obtained from the intensity of the fluorescent X-ray. In the present invention, Δd is d /
2 or less, that is, Δd / d is 0.5 or less, preferably,
It is controlled to 0.3 or less, more preferably 0.25 or less.
The range of Δd is 0.001 to 0.5 μm, preferably 0.03 to 0.3 μm, and more preferably 0.05 to
It is 0.25. Thereby, the uniformity of the magnetic layer thickness is ensured and the surface roughness Ra is Ra ≦ λ / 50, that is, λ /
Ra can be regulated to 50 or more, preferably 75 or more, more preferably 80 or more. Further, in the present invention, Ra represents a value obtained by measuring the center line average roughness measured using an optical interference roughness meter.

The magnetic recording medium of the present invention is formed by coating the upper magnetic layer while the lower non-magnetic layer is in a wet state. It may be present, but simultaneous multilayer coating is preferred.

That is, according to the present invention, for example, when the magnetic layer having a thickness of 1 μm or less is simultaneously coated with the lower non-magnetic layer to thin the magnetic layer by itself, or the lower non-magnetic layer is sequentially laminated in a dry state. In this case, a coating defect which is a problem can be prevented.

In the present invention, it cannot be said that the thickness of the magnetic layer needs to be simply reduced, and the present inventors have found that there is an optimum range for the shortest recording wavelength λ. That is, when the thickness of the magnetic layer becomes thinner than λ / 4, the magnetic flux that contributes to the reproduction decreases and the output decreases. Moreover, since the short-wavelength component is demagnetized by the deep recording magnetic field of the component having a long recording wavelength which is recorded at the same time as exceeding 3λ, the output is reduced. Therefore, d ≦ 3λ, and preferably d ≦ 2λ.

When the C / N, which is the basic performance of the medium, is taken into consideration, in addition to the unevenness (so-called surface roughness) on the surface of the magnetic layer which has been a problem in the conventional thick film magnetic layer, the non-magnetic layer And the thickness variation at the magnetic layer interface becomes a problem. This is because when the magnetic layer thickness d is in the range of λ / 4 ≦ d ≦ 3λ, the reproduction output is affected by the magnetic flux amount of the entire magnetic layer. This is not a problem with the conventional thick magnetic layer. The present invention has found that, with respect to this problem, the average value Δd of the thickness variation at the interface between the lower non-magnetic layer and the magnetic layer is required to be 1/2 or less of the magnetic layer thickness d. Also,
The surface roughness of the magnetic layer is required to be smooth like the conventional thick film magnetic layer, and the surface roughness Ra is Ra ≦ λ / 5.
It is necessary to satisfy the relationship of 0.

According to the present invention, the treatment in a vacuum is a prerequisite, there is no problem of productivity and reliability of the metal thin film medium which is vulnerable to corrosion, the electromagnetic conversion characteristics are comparable to those of the metal thin film, and the productivity is excellent. A high performance coating type magnetic recording medium can be obtained. A second aspect of the present invention is that the root mean square roughness R _{rms of the} surface of the magnetic layer by the scanning tunneling microscope (STM) method is 30 ≦ between the mean value of dry thickness d of the magnetic layer and 30 ≦ There is a relationship of d / R _rms .

When the thickness of the magnetic layer is reduced, the self-demagnetization loss should be reduced and the output should be improved. The roughness increases. In order to improve output by reducing self-demagnetization loss, S that satisfies the relation of the above equation
Surface roughness by TM is preferred. R by AFM
_{The rms} is preferably 10 nm or less. It is preferable that the optical interference surface roughness Ra measured by 3d-MIRAU is 1 to 4 nm, and the PV value (Peak-Valley) value is 80 nm or less.

The glossiness of the surface of the magnetic layer is preferably 250 to 400% after calendering. In order to achieve the third point of the present invention, the ferromagnetic powder contained in the upper magnetic layer is a needle-like ferromagnetic alloy powder having a major axis length of 0.3 μm or less and Hc of 1500 Oe or more. Plate diameter 0.3 μm or less, powder, and Hc of 100
It is preferably a plate-like ferromagnetic powder of 0 Oe or more.

As the ferromagnetic powder, acicular ferromagnetic alloy powder, plate-shaped hexagonal ferrite-based ferromagnetic material (Ba ferrite, Sr ferrite, etc.), and plate-shaped Co alloy powder can be used. Hc and saturation magnetization (σ _S ) may be appropriately selected, but Hc of 1500 (Oe) or more is particularly preferable for short wavelength recording with a shortest recording wavelength of 1 μm or less. The size of the magnetic substance is generally needle-like for adapting to high-density recording and has a major axis length of 0.3 μm or less, and plate-like one having a plate diameter of 0.3 μm or less.

In order to achieve the fourth point of the present invention, the magnetic recording medium application direction stability SMD and the width direction relative to the application direction (longitudinal direction) STD.
It is preferable that the ratio SMD / STD of the above is 1.0 to 1.9. In order to obtain the above-mentioned stability, the inorganic powder contained in the lower non-magnetic layer is a polyhedral inorganic powder having a Mohs hardness of 6 or more and an average particle diameter of 0.15 μm or less, from spherical to cubic. It is preferable.

The mechanism of action of the invention of stiffness is as follows. This aspect controls the mechanical characteristics of the magnetic recording medium by controlling SMD / STD of the magnetic recording medium,
This is to improve the head contact of a magnetic recording medium and to improve the electromagnetic conversion characteristics particularly in short wavelength recording. That is, this embodiment controls SMD / STD to 1.0 to 1.9.

The stiffness SMD in the coating direction and the stiffness STD in the width direction can both be measured by using a commercially available stiffener tester. For example, a loop stiffener tester manufactured by Toyo Seiki Co., Ltd. is used, and a manufactured magnetic recording medium having a width of 8 mm and a length of 50 mm is used for the SMD measurement so that the sample length direction is the same as the coating direction of the magnetic recording medium. For STD measurement, a sample was cut out so that the length direction of the sample was the same as the width direction of the magnetic recording medium, and this was cut into a ring,
The values required to give a displacement of 5 mm at a displacement rate of 3.5 mm / sec in the inner diameter direction expressed in mg can be used as SMD and STD.

Here, SMD / STD is 1.0 to 1.9,
It is preferably controlled to 1.1 to 1.85. Further, in the magnetic recording medium having a total thickness of 13.5 ± 1 μm, SMD is
50-200 mg, preferably 50-150 mg, STD
Is 40 to 150 mg, preferably 50 to 130 mg. The means for controlling the SMD / STD value is not particularly limited, but it is preferable to select the shape and Mohs hardness of the lower layer inorganic powder, and the inorganic powder contained in the lower layer has a Mohs hardness of 6 or more, preferably 6 or less. It is desirable to select a spherical to cubic polyhedral inorganic powder having a particle size of 0.5 or more and an average particle size of 0.15 μm or less, preferably 0.12 μm or less.

To improve the head contact of the magnetic recording medium, it is necessary to increase the stiffness of the tape to some extent. For that purpose, the hardness of the powder to be blended is preferably hard. If the Mohs hardness is less than 6, each stiffness becomes low, and good head contact cannot be secured. In addition, the smaller the average particle size is 0.15 μm or less,
Good head contact. This increases the number of contact interfaces with the binder, making it more resistant to deformation and increasing the stiffness S.
It is considered that MD and STD are improved. In the present invention, this SMD / STD is adjusted within the above range.

In particular, the effect on the electromagnetic conversion characteristics is high.
TD is close to SMD, that is, close to 1. When the inorganic powder contained in the lower layer has a polyhedral shape from spherical to cubic, the mechanical properties of the coating film become isotropic, which is convenient for improving STD. Here, the polyhedron shape specifically means a regular polyhedron or a non-regular polyhedron selected from one or more kinds of regular n-gons such as spherical, one-sided square, regular pentagon, regular hexagon, etc. or simple n-gons. Although it can be illustrated, it is preferable that the two axial ratios selected arbitrarily are in the range of 0.6 to 1.4, preferably 0.7 to 1.3.

Another aspect for achieving the fourth point of the present invention is that the heat shrinkage ratio of the magnetic recording medium at 80 ° C. for 30 minutes is 0.4% or less,
Specifically, the dry thickness of the lower non-magnetic layer is 1 to 30 times the dry thickness of the upper magnetic layer, and the powder volume ratio of the lower non-magnetic layer and the powder volume ratio of the upper magnetic layer. Is in the range of -5% to + 20%, the crystallite size of the ferromagnetic powder contained in the upper magnetic layer is 300 angstroms or less, and the average of the inorganic powder contained in the lower nonmagnetic layer is It is a granular material having a particle size of less than 0.15 μm or a needle-shaped material having an average major axis diameter of less than 0.6 μm, and the inorganic powder contained in the lower non-magnetic layer is titanium oxide, barium sulfate, calcium carbonate, At least one selected from strontium sulfate, silica, alumina, zinc oxide, and α-iron oxide, the lower nonmagnetic layer has an average particle size of 30 mμ or less, and a DBP oil absorption of 30 to 300. In l / 100 g, BET specific surface area is with respect to the inorganic powder 100 parts by weight of carbon black is 150 to 400 m ² / g as a second component, is that a proportion of less than 50 parts by weight.

In this embodiment, a coating type magnetic recording medium having a magnetic layer thickness of 1 μm or less and having improved self-demagnetization loss can be manufactured with high productivity without coating defects such as pinholes and stripes, and the heat of the magnetic recording medium can be improved. The shrinkage is suppressed below a predetermined value. That is, in this embodiment, by controlling the heat shrinkage ratio after storage at 70 ° C. for 48 hours to 0.4% or less, the skew distortion is improved or reduced, and the magnetic conversion characteristics comparable to those of the ferromagnetic metal thin film are obtained. A recording medium is provided.

In other words, the present embodiment has found that a magnetic recording medium having an extremely thin magnetic layer can be manufactured with high productivity, and an appropriate strength of the magnetic recording medium for reducing skew distortion can be defined by the heat shrinkage ratio. Is. Here, the heat shrinkage ratio is 100 × (length of magnetic recording medium at room temperature before heating-length after holding magnetic recording medium for 48 hours in an environment of −70 ° C.) / (Heating The length of the magnetic recording medium at room temperature before).

In this embodiment, means for controlling the heat shrinkage ratio is not particularly limited, and any method can be applied. As the control means, specifically, the following examples are preferable. The dry thickness of the lower non-magnetic layer is controlled to be 1 to 30 times, preferably 2 to 20 times the dry thickness of the upper magnetic layer, and the expansion / contraction of the magnetic recording medium is controlled by the film strength of the lower and upper layers. Is mentioned. If the thickness ratio is 1 or less, it is impossible to prevent an increase in heat shrinkage ratio due to strength deterioration due to finer magnetic layer. On the other hand, if the thickness ratio is 30 times or more, the coating thickness becomes thicker, so that the residual solvent increases and the film is plasticized.

As means for adjusting the film strength of the lower layer and the upper layer, the difference between the powder volume ratio of the lower non-magnetic layer and the powder volume ratio of the upper magnetic layer is -5% to + 20%, preferably Controlling in the range of 0 to 15% can be mentioned. Here, if it is -5% or less, it is not possible to suppress an increase in the heat shrinkage rate of the magnetic layer, and if it is increased by 20% or more, the medium itself becomes too hard, and powder is often dropped, which is not preferable.

In the present invention, the powder volume ratio of the upper layer is, for example, 10 to 50%, preferably 20 to 45%, and the powder volume ratio of the lower layer is 20 to 60%, preferably The range of 25 to 50% is exemplified. The powder volume ratio of each layer can be controlled by changing the amounts of the powder to be added and the binder, and by controlling the particle size and shape of the powder of each layer. Increasing the amount of binder relatively decreases the powder volume ratio. Further, the finer the particle size of the powder is, the more effective it is in reducing the heat shrinkage, but if it is too fine, the dispersion becomes difficult.

In this embodiment, as a preferable embodiment, for example, the particle size of the ferromagnetic powder has a crystallite size of 300 Å or less, preferably 100 to 250 Å,
The average major axis diameter is 0.005 to 0.4 μm, preferably 0.1.
The range of 1 to 0.3 μm is desirable, and the average major axis diameter / crystallite size is in the range of 3 to 25, preferably 5 to 20. The specific surface area of the ferromagnetic powder measured by the BET method is 25 to 80 m ² / g, preferably 30 to 70 m ²
/ G. Below 25 m ² / g, noise becomes high,
When it is 80 m ² / g or more, it is difficult to obtain surface properties, which is not preferable.

Regarding the particle size and shape of the lower layer inorganic powder, the average particle size is less than 0.15 μm, preferably 0.005 to 0.7 μm, and the average major axis diameter is less than 0.6 μm. Preferably, it is 0.1 to 0.3 μm, and the acicular ratio represented by the average major axis diameter / minor axis length is 4 to 50,
A needle-like material having a size of preferably 5 to 30 is exemplified. As the inorganic powder, rutile type titanium oxide, α-iron oxide and goethite are preferable.

As the powder used in the lower layer, carbon black can be mentioned. The carbon black has an average particle size of 30 mμ or less, preferably 5 to 28.
mP and DBP oil absorption is 30 to 300 ml / 1
00 g, preferably 50-250 ml / 100 g, B
Specific surface area by ET method is 150 to 400 m ² / g, preferably 170 to 300 m ² / g, pH is 2 to 10, water content is 0.1 to 10%, tap density is 0.1 to 1 g / cc.
Is preferred.

This carbon black is less than 50 parts by weight, preferably 13 parts by weight, based on 100 parts by weight of the inorganic powder.
It is preferably added to the lower layer in a proportion of about 40 parts by weight. The carbon black is an antistatic agent for magnetic recording media,
In addition to the function of strengthening the film strength, it is also used for controlling the powder volume ratio of the lower layer by controlling the porosity.
That is, when the porosity is high, the powder volume ratio is relatively reduced. As carbon black for controlling such a porosity, it is effective to use carbon black having a structure or hollow carbon black.

The porosity of the lower layer is preferably within the range of ± 10% of the porosity of the upper layer. The porosity of the lower layer is preferably in the range of 10 to 30%. The fifth point of the present invention relates to durability. The Young's modulus of the magnetic recording medium of the present invention measured by a tensile tester is 300 to 2000.
Kg / mm ² , preferably 400-1500 Kg / m
m ² , and the Young's modulus of the magnetic layer is 400 to 5000
Kg / mm ² , preferably 500 to 4000 Kg / mm
² , yield stress is 3 to 20 Kg / mm ² , preferably 4 to
It is desirable that the yield elongation is 18 Kg / mm ² and the yield elongation is 0.2 to 8%, preferably 0.5 to 5%.

This influences the durability because the ferromagnetic powder, the binder, the carbon black, the inorganic powder and the support are involved. The bending rigidity (annular stiffness) of the magnetic recording medium of the present invention is preferably 40 to 300 mg when the total thickness is more than 11.5 μm, and the total thickness is 10.5 ± 1.
In μm, preferably 20 to 90 mg or the total thickness is 9.5 μm
When thinner, it is preferably 10 to 70 mg.

This is mainly related to the support and is important for ensuring durability. The cracking elongation of the magnetic recording medium of the present invention measured at 23 ° C. and 70% RH is preferably 20% or less. Further, the Cl / Fe spectrum α of the magnetic layer surface of the magnetic recording medium of the present invention measured with an X-ray photoelectron spectroscope is preferably 0.
3 to 0.6, N / Fe spectrum β is preferably 0.0
It is 3 to 0.12.

This is related to the ferromagnetic powder, the inorganic powder and the binder, and is important in obtaining durability. Further, the glass transition temperature Tg of the magnetic layer of the magnetic recording medium of the present invention measured using a dynamic viscoelasticity measuring device (maximum point of loss elastic modulus in dynamic viscoelasticity measurement measured at 110 Hz) is preferably 40 to. 120 ° C. and storage elastic modulus E ′ (50 ° C.) is preferably 0.8 × 10 ^{11 to} 11 × 10 ¹¹ dyne / cm.
² , and the loss elastic modulus E ″ (50 ° C.) is preferably 0.5 × 10 ¹¹ to 8 × 10 ¹¹ dyne / cm ² . The loss tangent is preferably 0.2 or less. If the loss tangent is too large, sticking failure tends to occur. These are important properties associated with the binder, carbon black, and solvent, and associated with durability.

The 180 ° adhesion strength of the 8 mm width tape at 23 ° C. and 70% RH between the non-magnetic support and the magnetic layer is preferably 10 g or more. Further, the abrasion of the steel ball at 23 ° C. and 70% RH on the surface of the upper magnetic layer is preferably 0.7 × 10 ^{−7 to} 5 × 10 ⁻⁷ m ³ . This is a measure of the durability that is directly related to the wear of the surface of the magnetic layer and is mainly related to the ferromagnetic powder.

Further, five magnetic recording media of the present invention were photographed with a SEM (electron microscope) at a magnification of 50,000 times, and the number of abrasives on the surface of the magnetic layer was preferably 0.1 per μm ^2.
The above is desirable. The abrasive present on the end face of the upper magnetic layer of the magnetic recording medium of the present invention is 5/100 μm
² or more is preferable. These are the scales that are affected by the abrasive and binder in the magnetic layer and exert an effect on durability.

The residual solvent of the magnetic recording medium of the present invention measured by gas chromatography is preferably 50 mg / m ² or less. The residual solvent contained in the upper layer is preferably 20 m.
g / m ² or less, more preferably 10 mg / m ² or less, and it is preferable that the residual solvent contained in the upper layer is smaller than the residual solvent contained in the lower layer.

Further, it is desirable that the sol fraction, which is the ratio of the soluble solid content extracted with THF from the magnetic recording medium of the present invention to the magnetic layer weight, is 15% or less. This is influenced by the ferromagnetic powder and the binder,
It is a measure of durability. The magnetic recording medium of the present invention was recorded in the upper magnetic layer at a short wavelength of 1 MHz, magnetically developed using ferri colloid, and continuously recorded in a 5 mm wide sample observed at 10 times using a differential interference microscope. It is preferable that the number of black or white lines is within 5.

Friction coefficient (μ) of the magnetic recording medium of the present invention
Is preferably 0.15 to 0.4 on the magnetic surface, particularly preferably 0.2 to 0.35, and 0.1 to 0.4 on the back layer surface.
5 to 0.4 is preferable, and 0.2 to 0.3 is particularly preferable.
It is 5. The contact angle of the magnetic recording medium of the present invention is 60.
Is preferably 130 to 130, and more preferably 80 to 120. Further, in the case of methylene iodide, preferably 10 to
It is 90 °, particularly preferably 20 to 70 °.

These contact angles are values particularly determined by the lubricant and dispersant. The surface free energy of the magnetic layer and the back layer of the magnetic recording medium of the present invention is 10 to 100 dye.
n / cm is particularly preferred. The surface electric resistance of the magnetic recording medium of the present invention is 1 × 1 on both the magnetic layer surface and the back layer surface.
It is preferably 0 ⁹ Ω / sq or less, and particularly preferably 1 × 10 ⁸ Ω / sq or less.

General items that can be selected by the present invention will be described below. The non-magnetic inorganic powder that can be used in the present invention,
For example, metal, metal oxide, metal carbonate, metal sulfate,
Non-magnetic inorganic powders such as metal nitrides, metal carbides, and metal sulfides can be used. Specifically, TiO ₂ (rutile, anatase), TiO _x , cerium oxide, tin oxide, tungsten oxide, ZnO, ZrO ₂ , SiO ₂ , Cr
₂ O ₃ , α-alumina, α-alumina, α-alumina, α-iron oxide, goethite, corundum, which has an α-conversion rate of 90% or more,
Silicon nitride, titanium carbide, magnesium oxide, boron nitride, molybdenum disulfide, copper oxide, MgCO ₃ , CaC
_{O 3, BaCO 3, SrCO 3} , BaSO 4, silicon carbide, and titanium carbide is used alone or in combination. The shape, size, etc. of these inorganic powders are arbitrary,
If necessary, different inorganic powders may be combined, or a single non-magnetic powder may have a selected particle size distribution and the like.

The particle size is preferably based on the specific method described in (A) to (K) above, but is generally 0.01 to 0.7 μm in the case of granular, spherical or polyhedral shape. It is preferable that the wavelength is ¼ or less of the shortest recording wavelength λ. In the case of needles or plates, the major axis length is 0.05 to 1.0
μm, preferably 0.05 to 0.5 and needle ratio of 5 to 2
0, preferably 5 to 15, or a plate diameter of 0.05 to 1.
0 μm, preferably 0.05 to 0.5 μm, and a plate ratio (ratio of plate diameter to thickness) of 5 to 20, preferably 10 to 20.
What is used.

The following are preferred as the inorganic powder. The tap density is 0.05 to 2 g / cc, preferably 0.2 to 1.5 g / cc. Water content is 0.1-5%, preferably 0.2-3%. The pH is preferably 2 to 11, particularly preferably 4 to 10. The specific surface area is 1 to 100 m ² / g, preferably 5 to 70 m ² / g, and more preferably 7 to 50 m ² / g.
Is. The crystallite size is preferably 0.01 μm to 2 μm. The oil absorption using DBP is 5-100 ml / 100
g, preferably 10 to 80 ml / 100 g, more preferably 20 to 60 ml / 100 g. The amount of SA (stearic acid) adsorbed is 1 to 20 μmol / m ² , and more preferably ² to 15 μmol / m ² . The roughness factor of the powder surface is preferably 0.8 to 1.5, more preferably ² to 15 μmol / m ² . The heat of wetting with water at 25 ° C. is preferably 200 erg / cm ^{2 to} 600 erg / cm ² . Further, a solvent having a heat of wetting in the range can be used. The amount of water molecules on the surface at 100 to 400 ° C is appropriately 1 to 10 / 100Å. The pH of the isoelectric point in water is preferably between 3 and 9. Specific gravity is 1
-12, preferably 3-6.

The above inorganic powder does not necessarily have to be 100% pure, and the surface thereof may be treated with other compounds such as Al, Si, Ti, Zr, Sn, Sb and Zn depending on the purpose. , Those oxides may be formed on the surface. At that time, if the purity is 70% or more, the effect is not reduced. The loss on ignition is preferably 20% or less.

Specific examples of the inorganic powder used in the present invention include UA5600 and UA560 manufactured by Showa Denko KK
5, Sumitomo Chemical Co., Ltd. AKP-20, AKP-30, AKP
-50, HIT-55, HIT-100, ZA-G1,
Nippon Kagaku Kogyo G5, G7, S-1, Toda Kogyo T
F-100, TF-120, TF-140, R516,
Ishihara Sangyo Co., Ltd. TTO-51B, TTO-55A, TTO
-55B, TTO-55C, TTO-55S, TTO-
55S, TTO-55D, FT-1000, FT-20
00, FTL-100, FTL-200, M-1, S-
1, SN-100, R-820, R-830, R-93
0, R-550, CR-50, CR-80, R-68
0, TY-50, titanium industry ECT-52, STT
-4D, STT-30D, STT-30, STT-65
C, T-1 manufactured by Mitsubishi Materials, NS- manufactured by Nippon Shokubai Co., Ltd.
O, NS-3Y, NS-8Y, MT-100 manufactured by Teika
S, MT-100T, MT-150W, MT-500
B, MT-600B, MT-100E, FI made by Sakai Chemical Co., Ltd.
NEX-25, BF-1, BF-10, BF-20, B
F-1L, BF-10P, Dowa Kogyo DEFIC-
Y, DEFIC-R, Y-LOP manufactured by Titanium Industry Co., Ltd., and a product obtained by firing the same.

As the non-magnetic inorganic powder used in the present invention, titanium oxide (particularly titanium dioxide) is particularly preferable. Hereinafter, the production method of this titanium oxide will be described in detail. Titanium oxide is mainly produced by the sulfuric acid method and the chlorine method. In the sulfuric acid method, a raw illuminite ore is distilled with sulfuric acid to extract Ti, Fe and the like as sulfates. Iron sulfate is removed by crystallization, and the remaining titanyl sulfate solution is purified by filtration and then subjected to thermal hydrolysis to precipitate hydrous titanium oxide. After filtering and washing this,
After removing contaminants by washing and adding a particle size regulator etc.,
If it is fired at 80 to 1000 ° C., it becomes crude titanium oxide. The rutile type and the anatase type are classified according to the kind of the core material added at the time of hydrolysis. This crude titanium oxide is prepared by crushing, sizing, surface treatment and the like. For the chlorine method, natural ore natural rutile and synthetic rutile are used. Ore is chlorinated under high temperature reduction conditions, Ti for TiCl ₄ and Fe for FeCl ₂
And iron oxide that became solid by cooling is liquid TiC
Separated from l ₄ . The obtained crude TiCl ₄ is purified by rectification, then a nucleating agent is added, and it is instantaneously reacted with oxygen at a temperature of 1000 ° C. or higher to obtain crude titanium oxide. The finishing method for imparting pigmentary properties to the crude titanium oxide produced in this oxidative decomposition step is the same as the sulfuric acid method.

In the present invention, carbon black can be used in the lower layer, and R _S (surface electric resistance), which is a known effect, can be lowered. Furnace for rubber, thermal for rubber, black for color, acetylene black, etc. can be used as the carbon black. The specific surface area is 100 to 500 m ² / g, preferably 1
50-400, DBP oil absorption is 20-400 ml / 10
It is 0 g, preferably 30 to 200 ml / 100 g.
The average particle size is 5 m-80 m, preferably 10-50 m
μ, and more preferably 10 to 40 mμ. pH is 2
10, water content is 0.1-10%, tap density is 0.1
1 g / cc is preferred.

Specific examples of the carbon black used in the present invention include BLACKPEAR manufactured by Cabot Corporation.
LS 2000, 1300, 1000, 900, 80
0, 880, 700, VULCAN XC-72, Mitsubishi Kasei Kogyo's # 3050, # 3150, # 3250,
# 3750, # 3950, # 2400B, # 2300,
# 1000, # 970, # 950, # 900, # 8
50, # 650, # 40, MA40, MA-600, manufactured by Columbia Carbon Co., CONDUCTEX SC, R
AVEN 8800, 8000, 7000, 575
0, 5250, 3500, 2100, 2000, 180
0, 1500, 1255, 1250, Ketjen Black EC manufactured by Akzo and the like. The carbon black may be surface-treated with a dispersant or the like, may be grafted with a resin, or may be partially graphitized. Further, the carbon black may be dispersed with a binder in advance before being added to the non-magnetic coating material. These carbon blacks can be used alone or in combination.

The carbon black usable in the present invention is
For example, (“Carbon Black Handbook”, edited by Carbon Black Association) can be referred to. The non-magnetic organic powder used in the present invention is an acrylic styrene resin powder,
Examples thereof include benzoguanamine resin powder, melamine-based resin powder, and phthalocyanine-based pigment, and polyolefin-based resin powder, polyester-based resin powder, polyamide-based resin powder, polyimide-based resin powder, and polyfluorinated ethylene resin powder are used. The manufacturing method is disclosed in JP-A-62-18564.
Nos. 60-255827 and 60-255827 can be used.

These nonmagnetic powders are usually used in a weight ratio of 20 to 0.1 and a volume ratio of 10 to 0.
Used in the range of 1. In general magnetic recording media, an undercoat layer is provided, but this is provided in order to improve the adhesive force between the support and the magnetic layer and has a thickness of 0.5 μm. The following is different from the lower non-magnetic layer of the present invention. Also in the present invention, it is preferable to provide an undercoat layer in order to improve the adhesion between the underlayer and the support.

As the ferromagnetic powder used in the magnetic layer of the present invention, magnetic iron oxide FeOx (x = 1.33 to 1.5), C
Known ferromagnetic powders such as o-modified FeOx (x = 1.33 to 1.5), ferromagnetic alloy powder containing Fe or Ni or Co as a main component (75% or more), barium ferrite, and strontium ferrite can be used. Further, ferromagnetic alloy powder is more preferable. .. These ferromagnetic powders contain Al, Si, S, Sc, Ti, V, Cr, C in addition to the specified atoms.
u, Y, Mo, Rh, Pd, Ag, Sn, Sb, Te,
Ba, Ta, W, Re, Au, Hg, Pb, Bi, L
a, Ce, Pr, Nd, P, Co, Mn, Zn, Ni,
It may contain atoms such as Sr and B. These ferromagnetic powders may be previously treated with a dispersant, a lubricant, a surfactant, an antistatic agent, etc., which will be described later, before dispersion. Specifically, Japanese Patent Publication No. 44-14090
No. 4, Japanese Patent Publication No. 45-18372, Japanese Patent Publication No. 47-2206
No. 2, JP-B-47-22513, JP-B-46-284
No. 66, Japanese Patent Publication No. 46-38755, Japanese Patent Publication No. 47-42
No. 86, Japanese Patent Publication No. 47-12422, Japanese Patent Publication No. 47-17
284, Japanese Patent Publication No. 47-18509, Japanese Patent Publication No. 47-1
No. 8573, Japanese Patent Publication No. 39-10307, Japanese Patent Publication No. 48-
39639, U.S. Pat. Nos. 3,026,215 and 303.
No. 1341, No. 3100194, No. 3242005
No. 3,389,014 and the like.

Among the above ferromagnetic powders, the ferromagnetic alloy powder may contain a small amount of hydroxide or oxide.
What was obtained by the well-known manufacturing method of a ferromagnetic alloy powder can be used, and the following method can be mentioned.
A method of reducing a complex organic acid salt (mainly oxalate) and a reducing gas such as hydrogen, a method of reducing iron oxide with a reducing gas such as hydrogen to obtain Fe or Fe—Co particles, a metal carbonyl compound Pyrolysis method, reduction method by adding a reducing agent such as sodium borohydride, hypophosphite or hydrazine to an aqueous solution of ferromagnetic metal, evaporation of metal in a low pressure inert gas to form fine powder. How to get it. The ferromagnetic alloy powder thus obtained is subjected to a known gradual oxidation treatment, that is, a method of immersing it in an organic solvent and then drying it, and immersing it in an organic solvent and then feeding an oxygen-containing gas to form an oxide film on the surface and then drying it. It is possible to use any of the above method and the method of forming an oxide film on the surface by adjusting the partial pressure of oxygen gas and inert gas without using an organic solvent.

BET was used for the ferromagnetic powder of the upper magnetic layer of the present invention.
The specific surface area according to the method is 25 to 80 m ² / g,
It is preferably 40 to 70 m ² / g. When it is 25 m ² / g or less, noise becomes high, and when it is 80 m ² / g or more, surface properties are difficult to obtain, which is not preferable. The crystallite size of the ferromagnetic powder of the upper magnetic layer of the present invention is 450 to 100Å, preferably 350 to 100Å. The σ _{S of the} iron oxide magnetic powder is 50 emu / g or more, preferably 70 emu / g or more, and in the case of the ferromagnetic metal powder, 100 emu / g or more is preferable, and more preferably 110 emu / g to 170 e.
mu / g. Coercive force is 1100 Oe or more, 2500
It is preferably Oe or less, and more preferably 1400 Oe or more and 2000 Oe or less. The acicular ratio of the ferromagnetic powder is preferably 18 or less, more preferably 12 or less.

The r1500 of the ferromagnetic powder is preferably 1.5 or less. More preferably r1500 is 1.
It is 0 or less. The r1500 indicates the percentage of the remaining magnetization amount without being reversed when a magnetic field of 1500 Oe is applied in the opposite direction after saturation magnetization of the magnetic recording medium. The water content of the ferromagnetic powder is preferably 0.01 to 2%.
It is preferable to optimize the water content of the ferromagnetic powder depending on the type of binder. The tap density of γ iron oxide is 0.5 g / cc
The above is preferable, and 0.8 g / cc or more is more preferable. In the case of alloy powder, 0.2 to 0.8 g / cc is preferable, and if it is used at 0.8 g / cc or more, oxidation easily proceeds in the consolidation process of the ferromagnetic powder, and sufficient saturation magnetization (σ _S ) can be obtained. Becomes difficult. If it is 0.2 cc / g or less, the dispersion tends to be insufficient.

When γ iron oxide is used, the ratio of divalent iron to trivalent iron is preferably 0 to 20%, more preferably 5 to 10%. The amount of cobalt atom to iron atom is 0 to 15%, preferably 2 to 8%.
The pH of the ferromagnetic powder is preferably optimized depending on the combination with the binder used. The range is 4-12,
It is preferably 6 to 10. Ferromagnetic powder, if necessary,
The surface treatment may be performed with Al, Si, P or an oxide thereof. The amount is 0.1 with respect to the ferromagnetic powder.
It is preferably 10%, and when the surface treatment is performed, the adsorption of the lubricant such as fatty acid becomes 100 mg / m ² or less, which is preferable. The ferromagnetic powder may contain soluble inorganic ions such as Na, Ca, Fe, Ni, and Sr, but if it is 500 ppm or less, the characteristics are not particularly affected.

The ferromagnetic powder used in the present invention preferably has few voids, and the value is 20% by volume or less, more preferably 5% by volume or less. The shape is selected from needle-like, granular, rice-like, plate-like, etc. so as to satisfy the above-mentioned conditions. SFD of ferromagnetic powder 0.6
In order to achieve the following, it is necessary to reduce the distribution of Hc in the ferromagnetic powder. For that purpose, there are methods such as improving the particle size distribution of goethite, preventing the sintering of γ-hematite, and slowing the deposition rate of cobalt for cobalt-modified iron oxide as compared with the conventional method.

In the present invention, a hexagonal plate-like ferromagnetic powder having an easy axis of magnetization in the direction perpendicular to the flat plate is exemplified by plate-like hexagonal ferrite, and barium ferrite, strontium ferrite, lead ferrite, calcium ferrite Hexagonal Co powder such as each substitution product and Co substitution product can be used. Specific examples include magnetobranbite-type barium ferrite and strontium ferrite, and magnetobranvite-type barium ferrite and strontium ferrite containing a part of a spinel phase.
Particularly preferred are barium ferrite and strontium ferrite substitutes. In addition, in order to control the coercive force, Co--Ti, C is added to the hexagonal ferrite.
o-Ti-Zr, Co-Ti-Zn, Ni-Ti-Z
A material to which an element such as n or Ir-Zn is added can be used.

When barium ferrite is used, the plate diameter means the plate width of hexagonal plate-like particles and is measured by using an electron microscope. In the present invention, the plate diameter is 0.001 to 1 μm.
In m, the plate thickness may be ½ to 1/20 of the diameter. The specific surface area (S _BET ) is preferably 1 to 60 m ² / g, and the specific gravity is preferably 4 to 6. As the binder used in the lower non-magnetic layer and the upper magnetic layer of the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins and mixtures thereof are used. As a thermoplastic resin, the glass transition temperature is -1.
00 to 150 ° C, number average molecular weight of 1000 to 20000
0, preferably 10,000 to 100,000, and the degree of polymerization is about 50 to 1,000. Such examples include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic acid ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester, styrene, butadiene, ethylene, vinyl butyral, vinyl acetal, There are polymers or copolymers containing vinyl ether, etc. as a constituent unit, polyurethane resins, and various rubber resins. Further, as the thermosetting resin or the reactive resin, a phenol resin, an epoxy resin,
Polyurethane curable resin, urea resin, melamine resin, alkyd resin, acrylic reaction resin, formaldehyde resin, silicone resin, epoxy-polyamide resin, mixture of polyester resin and isocyanate prepolymer,
Examples thereof include a mixture of polyester polyol and polyisocyanate, a mixture of polyurethane and polyisocyanate, and the like.

These resins are described in detail in "Plastic Handbook" published by Asakura Shoten. It is also possible to use a known electron beam curable resin for the lower layer or the upper layer. These examples and the method for producing them are described in detail in JP-A-62-256219.

The above resins can be used alone or in combination, but are preferably selected from the group of vinyl chloride resin, vinyl chloride vinyl acetate resin, vinyl chloride vinyl acetate vinyl alcohol resin, vinyl chloride vinyl acetate maleic anhydride copolymer. Examples thereof include a combination of at least one of the above and a polyurethane resin, or a combination of these with a polyisocyanate.

As the structure of the polyurethane resin, known structures such as polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane and polycaprolactone polyurethane can be used. For all of the binders shown here, in order to obtain better dispersibility and durability, -COO is added as necessary.
_{M, -SO 3 M, -OSO 3} M, -P = O (OM 1)
(OM ₂ ), -OP = O (OM ₁ ) (OM ₂ ), -NR
₄ X (where M, M ₁ and M ₂ are H, Li, Na,
K, -NR _4, shows a -NHR _3, R represents an alkyl group or H, X is a halogen atom. ), OH, N
R ₂ , N ⁺ R ₃ , (R is a hydrocarbon group), epoxy group, S
It is preferable to use at least one polar group selected from H, CN, etc. introduced by copolymerization or addition reaction. The amount of such a polar group is 10 ^-1 to 10 ^-8 mol / g, preferably 10 ^-2 to 10 ^-6 mol / g.

The vinyl chloride-based copolymer is preferably an epoxy group-containing vinyl chloride-based copolymer,
Vinyl chloride repeating unit, a repeating unit having an epoxy group, optionally _{-SO 3 M, -OSO 3 M,} -COO
M and --PO (OM) ₂ (wherein M is a hydrogen atom,
Or a vinyl chloride copolymer containing a repeating unit having a polar group such as an alkali metal). When used in combination with a repeating unit having an epoxy group, an epoxy group-containing vinyl chloride copolymer containing a repeating unit having —SO ₃ Na is preferable.

The content of the repeating unit having a polar group in the copolymer is usually in the range of 0.01 to 5.0 mol% (preferably 0.5 to 3.0 mol%). The content of the repeating unit having an epoxy group in the copolymer is usually in the range of 1.0 to 30 mol% (preferably 1 to 20 mol%). And the vinyl chloride polymer is
Usually from 0.01 to 1 mol of vinyl chloride repeating unit
It contains 0.5 mol (preferably 0.01 to 0.3 mol) of a repeating unit having an epoxy group.

The content of the repeating unit having an epoxy group is lower than 1 mol%, or the vinyl chloride repeating unit 1
The amount of the repeating unit having an epoxy group is 0.
If it is less than 01 mol, it may not be possible to effectively prevent the release of hydrochloric acid gas from the vinyl chloride-based copolymer, while on the other hand it is higher than 30 mol% or has an epoxy group per 1 mol of vinyl chloride repeating units. When the amount of the repeating unit is more than 0.5 mol, the hardness of the vinyl chloride-based copolymer may decrease, and when this is used, the running durability of the magnetic layer may decrease.

Further, if the content of the repeating unit having a specific polar group is less than 0.01 mol%, the dispersibility of the ferromagnetic powder may be insufficient, and if it is more than 5.0 mol%, the copolymerization weight may decrease. The coalescence becomes hygroscopic and the weather resistance may decrease. Usually, the number average molecular weight of such a vinyl chloride copolymer is in the range of 15,000 to 60,000.

The vinyl chloride copolymer having such an epoxy group and a specific polar group can be produced, for example, as follows. E.g., having an epoxy group, in the production of -SO ₃ Na and is introduced in which vinyl copolymer chloride polymer as the polar group, a reactive double bond, and -SO ₃ Na as a polar group 2 Sodium (meth) acrylamido-2-methylpropanesulfonate (a monomer having a reactive double bond and a polar group) and diglycidyl acrylate are mixed at low temperature, and this is mixed with vinyl chloride under pressure at 100 ° C. It can be produced by polymerizing at the following temperature.

Examples of the monomer having a reactive double bond and a polar group used for introducing a polar group by the above method include the above-mentioned sodium 2- (meth) acrylamido-2-methylpropanesulfonate. In addition to, 2- (meth) acrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid and its sodium or potassium salt, ethyl (meth) acrylic acid-2-sulfonic acid and sodium or potassium salt, (anhydrous) maleic acid and Examples thereof include (meth) acrylic acid and (meth) acrylic acid-2-phosphate ester.

For introducing the epoxy group, glycidyl (meth) acrylate is generally used as a monomer having a reactive double bond and an epoxy group. In addition to the above-mentioned production method, for example, a vinyl chloride-based copolymer having a polyfunctional -OH is produced by a polymerization reaction of vinyl chloride and vinyl alcohol, and the copolymer and the polarities described below. A method in which a group and a compound containing a chlorine atom are reacted (dehydrochlorination reaction) to introduce a polar group into the copolymer can be used.

ClCH ₂ CH ₂ SO ₃ M, ClCH ₂ CH ₂ OSO ₃ M, ClCH ₂ COOM, ClCH ₂ PO (OM) ₂ , and epichlorohydrin is usually used to introduce an epoxy group utilizing this dehydrochlorination reaction. .

The vinyl chloride copolymer may contain other monomers. Examples of other monomers include vinyl ether (eg, methyl vinyl ether, isobutyl vinyl ether, lauryl vinyl ether), α
-Mono-olefins (eg ethylene, propylene), acrylic acid esters (eg (meth) acrylic acid esters containing functional groups such as methyl (meth) acrylate, hydroxyethyl (meth) acrylate), unsaturated nitriles (eg , (Meth) acrylonitrile), aromatic vinyl (eg, styrene, α-methylstyrene), vinyl ester (eg, vinyl acetate, vinyl propionate, etc.).

Specific examples of these binders used in the present invention include Union Carbide: VAGH and V.
YHH, VMCH, VAGF, VAGD, VROH, V
YES, VYNC, VMCC, XYHL, XYSG, P
KHH, PKHJ, PKHC, PKFE, Nisshin Chemical Industry Co., Ltd .: MPR-TA, MPR-TA5, MPR-TA
L, MPR-TSN, MPR-TMF, MPR-TS,
MPR-TM, MPR-TAO, manufactured by Denki Kagaku: 100
0W, DX80, DX81, DX82, DX83, 10
0FD, manufactured by Zeon Corporation: MR105, MR110, M
R100, 400X110A, made by Nippon Polyurethane Company:
Nipporan N2301, N2302, N2304, manufactured by Dainippon Ink and Chemicals: Pandex T-5105, T-R30
80, T-5201, Burnock D-400, D-21
0-80, Crisbon 6109, 7209, Toyobo Co., Ltd .: Byron UR8200, UR8300, UR860
0, UR5500, UR4300, RV530, RV2
80, manufactured by Dainichiseika Co., Ltd .: Daifuelamine 4020, 502
0, 5100, 5300, 9020, 9022, 702
0, Mitsubishi Kasei: MX5004, Sanyo Kasei: Sampren SP-150, Asahi Kasei: Saran F310, F
210 and the like.

The binder used in the upper magnetic layer of the present invention is used in the range of 5 to 50% by weight, preferably 10 to 35% by weight, based on the ferromagnetic powder. When a vinyl chloride resin is used, it is preferably used in a range of 5 to 30% by weight, a polyurethane resin is used in a range of 2 to 20% by weight, and a polyisocyanate is used in a range of 2 to 20% by weight.

The binder used in the lower non-magnetic layer of the present invention is in the range of 5 to 50% by weight based on the total amount of the non-magnetic powder.
It is preferably used in the range of 10 to 35% by weight. Further, when using a vinyl chloride resin, 3 to 30% by weight, when using a polyurethane resin, 3 to 30% by weight,
The polyisocyanate is preferably used in combination within the range of 0 to 20% by weight.

When an epoxy group-containing resin having a molecular weight of 30,000 or more is used in the present invention in an amount of 3 to 30% by weight based on the nonmagnetic powder, a resin other than the epoxy group-containing resin is added in an amount of 3 to 30% by weight based on the nonmagnetic powder. %, When using a polyurethane resin, 3 to 30% by weight and 0 to 20% by weight of polyisocyanate can be used, but the epoxy group is 4 × 10 ^{−5 with respect} to the total weight of the binder (including the curing agent). ~ 16x1
It is preferably contained in the range of 0 ⁻⁴ eq / g.

In the present invention, when a polyurethane resin is used, the glass transition temperature is −50 to 100 ° C., the elongation at break is 100 to 2000%, and the stress at break is 0.05 to 10 kg.
/ Cm ² , and the yield point is preferably 0.05 to 10 Kg / cm ² . The magnetic recording medium of the present invention comprises two layers. Therefore,
Binder amount, vinyl chloride resin, polyurethane resin, polyisocyanate, or other resin content in the binder, molecular weight of each resin forming the magnetic layer, polar group amount, or the physical properties of the resin described above. Of course, it is possible to change the characteristics and the like between the lower magnetic layer and the upper magnetic layer as required.

As the polyisocyanate used in the present invention, tolylene diisocyanate, 4-4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,
Isocyanates such as 5-diisocyanate, o-toluidine isocyanate, isophorone diisocyanate, and triphenylmethane triisocyanate, products of these isocyanates and polyalcohols, and polyisocyanates produced by condensation of isocyanates are used. can do. Commercially available trade names of these isocyanates are: Coronate L, Coronate HL, Coronate 2030, Coronate 2031, Millionate M, manufactured by Nippon Polyurethane Company.
R, Millionate MTL, Takeda Yakuhin: Takenate D
-102, Takenate D-110N, Takenate D-2
00, Takenate D-202, Sumitomo Bayer Co., Ltd .: Desmodur L, Desmodur IL, Desmodul N, Desmodul HL, and the like. These are used alone or by utilizing the difference in curing reactivity. The lower non-magnetic layer and the upper magnetic layer can be used in combination.

As the carbon black used in the upper magnetic layer of the present invention, rubber furnace, thermal rubber, color black, acetylene black and the like can be used. Specific surface area is 5 to 500 m ² / g, DBP oil absorption is 10 to 400 ml / 100 g, and particle diameter is 5 mμ to 300.
It is preferable that mμ, pH is 2 to 10, water content is 0.1 to 10%, and tap density is 0.1 to 1 g / cc. Specific examples of carbon black used in the present invention include: BLACKPEARLS 2000, 130 manufactured by Cabot Corporation.
0, 1000, 900, 800, 700, VULCAN
XC-72, Asahi Carbon Co., Ltd .: # 80, # 60, # 5
5, # 50, # 35, manufactured by Mitsubishi Kasei Kogyo: # 2400
B, # 2300, # 900, # 1000, # 30, # 4
0, # 10B, manufactured by Conlon Via Carbon Co .: CONDU
CTEX SC, RAVEN 150, 50, 40, 1
5, etc. The carbon black may be surface-treated with a dispersant or the like, may be grafted with a resin, or may be partially graphitized. Further, the carbon black may be dispersed with a binder in advance before being added to the magnetic paint. These carbon blacks can be used alone or in combination. When carbon black is used, it is preferably used in an amount of 0.1 to 30% of the amount of the ferromagnetic powder. Carbon black has the functions of preventing electrification of the magnetic layer, reducing the coefficient of friction, imparting light-shielding properties, improving film strength, etc. These differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention have different types, amounts, and combinations in the lower layer and the upper layer, and can be used according to the purpose based on various characteristics such as particle size, oil absorption, electric conductivity and pH. Of course, it is possible to use them properly. The carbon black that can be used in the upper layer of the present invention can be referred to, for example, "Carbon Black Handbook" (edited by Carbon Black Association).

As the abrasive used in the upper magnetic layer of the present invention, α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond having an α conversion of 90% or more, Known materials having a Mohs hardness of 6 or more such as silicon nitride, silicon carbide, titanium carbide, titanium oxide, silicon dioxide, and boron nitride are used alone or in combination. Further, a composite of these abrasives (abrasive surface-treated with another abrasive) may be used. These abrasives may contain compounds or elements other than the main component, but the main component is 9
If it is 0% or more, the effect is the same. The particle size of these abrasives is preferably 0.01 to 2 μm, but if necessary, it is possible to combine abrasives having different particle sizes, or to use a single abrasive to broaden the particle size distribution and obtain the same effect. .. Tap density is 0.3 to 2 g / cc, water content is 0.1 to 5%, pH is 2 to 11, specific surface area is 1 to 30 m.
² / g is preferred. The shape of the abrasive used in the present invention may be needle-like, spherical, or dice-like, but those having a corner in part of the shape are preferable because of high abradability.

Specific examples of the abrasive used in the present invention include AKP-20, AKP-30, manufactured by Sumitomo Chemical Co., Ltd.
AKP-50, HIT-50, Nippon Kagaku Kogyo Co., Ltd .: G
5, G7, S-1, manufactured by Toda Kogyo: TF-100, TF
Examples include −140, 100ED, 140ED and the like.
It is of course possible to use the abrasives used in the present invention in different types, amounts and combinations for the lower layer and the upper layer, and to use them properly according to the purpose. These abrasives may be dispersed in a binder in advance and then added to the magnetic paint.

As the additive used in the present invention, those having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect, etc. are used. Molybdenum disulfide, tungsten disulfide, graphite, boron nitride, fluorinated graphite, silicone oil, polar group silicone, fatty acid-modified silicone, fluorine-containing silicone, fluorine-containing alcohol, fluorine-containing ester, polyolefin, polyglycol, alkylphosphoric acid Ester and its alkali metal salt, alkyl sulfate ester and its alkali metal salt,
Polyphenyl ethers, fluorine-containing alkyl sulfates and their alkali metal salts, monobasic fatty acids having 10 to 24 carbon atoms (which may contain unsaturated bonds or may be branched), and these metal salts ( Li, N
a, K, Cu, etc.) or a monovalent one having 12 to 22 carbon atoms,
Dihydric, trihydric, tetrahydric, pentahydric, hexahydric alcohol (may contain unsaturated bonds or may be branched), alkoxy alcohol having 12 to 22 carbon atoms, 10 to 24 carbon atoms
A monobasic fatty acid (which may contain an unsaturated bond or may be branched) and a monovalent or divalent one having 2 to 12 carbon atoms,
Any one of trihydric, tetrahydric, pentahydric, and hexahydric alcohol (may contain unsaturated bonds or may be branched)
A mono-fatty acid ester, a di-fatty acid ester or a tri-fatty acid ester, a mono-alkyl ether fatty acid ester of an alkylene oxide polymer, and a carbon number of 8 to
22 fatty acid amides, aliphatic amines having 8 to 22 carbon atoms,
Etc. can be used. Specific examples of these include lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, butyl stearate, oleic acid, linoleic acid,
Linolenic acid, elaidic acid, octyl stearate, amyl stearate, isooctyl stearate, octyl myristate, butoxyethyl stearate, anhydrosorbitan monostearate, anhydrosorbitan distearate, anhydrosorbitan tristearate, oleyl alcohol. , Lauryl alcohol.

Further, nonionic surfactants such as alkylene oxide type, glycerin type, glycidol type, alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, phosphonium or Cationic surfactants such as sulfonium, anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid ester group, phosphoric acid ester group, amino acid, aminosulfonic acid, sulfuric acid of amino alcohol or the like. Amphoteric surfactants such as phosphoric acid esters and alkylbedine type can also be used. These surfactants are described in detail in "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.). These lubricants, antistatic agents, etc. are not necessarily 100% pure, and may contain impurities such as isomers, unreacted products, by-products, decomposed products, and oxides in addition to the main components. The content of these impurities is preferably 30% or less, more preferably 10% or less.

These lubricants and surfactants used in the present invention may be used in the lower non-magnetic layer and the upper magnetic layer in different types and amounts according to need. For example, fatty acids with different melting points are used to control bleeding to the surface in the lower non-magnetic layer and upper magnetic layer, bleeding to the surface is controlled using esters with different boiling points and polarities, and the amount of surfactant is adjusted. By doing so, it is conceivable that the stability of coating is improved, the amount of lubricant added is increased in the lower non-magnetic layer, and the lubricating effect is improved, and of course, the present invention is not limited to the examples shown here.

All or a part of the additives used in the present invention may be added in any step of the magnetic coating production, for example, when mixed with a ferromagnetic powder before the kneading step, the ferromagnetic powder is added. There are cases where it is added in the kneading step using a binder and a solvent, when it is added in the dispersion step, when it is added after dispersion, and when it is added immediately before coating. Examples of commercial products of these lubricants used in the present invention include: NAA-102, NAA-415, NAA-31 manufactured by NOF CORPORATION.
2, NAA-160, NAA-180, NAA-17
4, NAA-175, NAA-222, NAA-34,
NAA-35, NAA-171, NAA-122, NA
A-142, NAA-160, NAA-173K, castor-cured fatty acid, NAA-42, NAA-44, cation SA, cation MA, cation AB, cation BB, Nymeen L-201, Nymeen L-202, Nymeen S-202. , Nonion E-208, Nonion P-20
8, nonion S-207, nonion K-204, nonion NS-202, nonion NS-210, nonion HS
-206, nonion L-2, nonion S-2, nonion S-4, nonion O-2, nonion LP-20R, nonion PP-40R, nonion SP-60R, nonion O
P-80R, Nonion OP-85R, Nonion LT-2
21, nonion ST-221, nonion OT-221,
Monogly MB, Nonion DS-60, Anone BF, Anone LG, Butyl stearate, Butyl laurate, Erucic acid, Kanto Chemical Co., Ltd .: Oleic acid, Takemoto Yushi Co., Ltd .: FA
L-205, FAL-123, manufactured by Shin Nippon Rika Co., Ltd .: NJ Erb LO, N Jorb IPM, Sanso Sizer E4
030, manufactured by Shin-Etsu Chemical Co., Ltd .: TA-3, KF-96, KF-
96L, KF-96H, KF410, KF420, KF
965, KF54, KF50, KF56, KF-90
7, KF-851, X-22-819, X-22-82
2, KF-905, KF-700, KF-393, KF
-857, KF-860, KF-865, X-22-9
80, KF-101, KF-102, KF-103, X
-22-3710, X-22-3715, KF-91.
0, KF-3935, Lion Armor Co., Ltd .: Armide P, Armide C, Armoslip CP, Lion Yushi Co., Ltd .: Duomin TDO, Nisshin Oil Co., Ltd .: BA-41
G, Sanyo Chemical Co., Ltd .: Profan 2012E, New Pole PE61, Ionette MS-400, Ionette MO
-200, Ionet DL-200, Ionet DS-
300, Ionet DS-1000, Ionet DO-
For example, 200 is given.

The organic solvent used in the present invention may be any ratio of ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone, tetrahydrofuran, methanol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol. , Alcohols such as methylcyclohexanol, esters such as methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, glycol acetate, glycol dimethyl ether, glycol monoethyl ether, dioxane, glycol ethers such as benzene, benzene, Aromatic hydrocarbons such as toluene, xylene, cresol, chlorobenzene, methylene chloride, ethylene chloride, carbon tetrachloride, chlorine Chloroform, ethylene chlorohydrin, dichlorobenzene, chlorinated hydrocarbons and the like, N,
Those such as N-dimethylformamide and hexane can be used. These organic solvents are not necessarily 100% pure, and may contain impurities such as isomers, unreacted substances, by-products, decomposition products, oxides, and water in addition to the main components. The content of these impurities is preferably 30% by weight or less, more preferably 10% by weight or less. The organic solvent used in the present invention is preferably the same in the upper layer and the lower layer if necessary. You may change the addition amount. It is important that a solvent having a high surface tension (cyclohexanone, dioxane, etc.) is used for the lower layer to improve the stability of coating, and specifically, the arithmetic average value of the upper layer solvent composition does not fall below the arithmetic average value of the lower layer solvent composition. In order to improve the dispersibility, it is preferable that the polarity is strong to some extent, and the solvents used in the coating solutions for the lower non-magnetic layer and the upper magnetic layer both have a solubility parameter of 8 to 11 and a dielectric constant at 20 ° C. It is preferable that 15% or more of the solvent is contained in 15% or more.

The thickness constitution of the magnetic recording medium of the present invention is such that the non-magnetic support is 1 to 100 μm, preferably 4 to 80 μm, the lower layer is 0.5 to 10 μm, preferably 1 to 5 μm, and the upper layer is 0.05 μm or more. 0 μm or less, preferably 0.05
μm or more and 0.6 μm or less, more preferably 0.05 μm
It is m or more and 0.3 μm or less. The upper magnetic layer is preferably thinner than the lower non-magnetic layer. The total thickness of the upper layer and the lower layer is 1/100 to 2 times the thickness of the non-magnetic support. Further, an undercoat layer may be provided between the non-magnetic support and the lower layer to improve the adhesion. The thickness of these is 0.01 to 2 μm, preferably 0.05 to 0.5 μm.
m. Further, a back coat layer may be provided on the side of the non-magnetic support opposite to the side of the magnetic layer. This thickness is 0.1
˜2 μm, preferably 0.3 to 1.0 μm. Known undercoat layers and back coat layers can be used.

The non-magnetic support used in the present invention is a known polyester such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, polyamideimide, polysulfone, aramid and aromatic polyamide. The film can be used. These supports may be previously subjected to corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment, dust removal treatment, and the like. To achieve the object of the present invention, the non-magnetic support has a center line average surface roughness of 0.03 μm or less, preferably 0.02 μm or less, and more preferably 0.01 μm.
You need to use: Further, it is preferable that these non-magnetic supports have not only a small center line average surface roughness but also no large protrusions of 1 μ or more. Also,
The roughness shape of the surface is freely controlled by the size and amount of the filler added to the support, if necessary. An example of these fillers is C
In addition to oxides and carbonates such as a, Si, and Ti, organic fine powders such as acrylics can be used.

Further, the F of the non-magnetic support in the tape running direction is
The -5 value is preferably 5 to 50 Kg / mm ² , the F-5 value in the tape width direction is preferably 3 to 30 Kg / mm ² , and the F-5 value in the tape longitudinal direction is the F-5 value in the tape width direction.
Generally, the value is higher than 5 values, but it is not limited to this value especially when the strength in the width direction needs to be increased. Also, 100 ° C. in the tape running direction and width direction of the non-magnetic support 3
The heat shrinkage percentage at 0 minutes is preferably 3% or less, more preferably 1.5% or less, and the heat shrinkage percentage at 80 ° C. for 30 minutes is preferably 1% or less, more preferably 0.5% or less.
The breaking strength in both directions 5 to 100 kg / mm ^2, the elastic modulus is preferably from 100 to 2,000 kg / mm ^2.

The step of producing the magnetic coating material for the magnetic recording medium of the present invention comprises at least a kneading step, a dispersing step, and a mixing step provided before and after these steps, if necessary. Each process may be divided into two or more steps. All raw materials such as ferromagnetic powder, binder, carbon black, abrasive, antistatic agent, lubricant and solvent used in the present invention may be added at the beginning or in the middle of any step. In addition, the individual raw materials may be divided and added in two or more steps. For example, polyurethane may be divided and added in the kneading step, the dispersing step, and the mixing step for adjusting the viscosity after dispersion.

In order to achieve the object of the present invention, it goes without saying that conventionally known manufacturing techniques can be used as a part of the steps, but a strong kneading force such as a continuous kneader or a pressure kneader is used in the kneading step. The high Br of the magnetic recording medium of the present invention can be obtained by using the material having the same. When a continuous kneader or a pressure kneader is used, all or part of the ferromagnetic powder and the binder (however, 30% by weight or more of the total binder is preferable) and the ferromagnetic powder 100
Kneading is performed in the range of 15 to 500 parts per part. For details of these kneading treatments, see JP-A-1-106338.
And JP-A-64-79274. When preparing the lower non-magnetic layer liquid, it is desirable to use a dispersion medium having a high specific gravity, and zirconia beads and metal beads are suitable.

In the present invention, by using the simultaneous multi-layer coating method as shown in JP-A-62-212933, the production can be carried out more efficiently. The following constitution can be proposed as an example of an apparatus and method for coating a magnetic recording medium having a multilayer constitution as in the present invention. 1. The lower layer is first coated by a gravure coating, a roll coating, a blade coating, an extrusion coating device or the like which is generally used for coating a magnetic paint, and when the lower layer is in a wet state, JP-B-1-46186 and JP-A-60-46186. -23
The upper layer is coated by the support pressure type extrusion coating apparatus disclosed in JP-A-8179 and JP-A-2-265672. 2. JP-A-63-88080, JP-A-2-17921
No. 2,265,672, the upper layer and the lower layer are coated almost simultaneously by a single coating head having two slits for passing the coating liquid therein. 3. The upper layer and the lower layer are coated almost simultaneously by the extrusion coating apparatus with a backup roll disclosed in JP-A-2-174965. In order to prevent the deterioration of the electromagnetic conversion characteristics of the magnetic recording medium due to the aggregation of the ferromagnetic powder, JP-A-62-95174 and JP-A-1-23
It is desirable to apply shear to the coating liquid inside the coating head by the method disclosed in No. 6968. Further, regarding the viscosity of the coating liquid, Japanese Patent Application No. 1-312659
It is preferable to satisfy the numerical range disclosed in the publication.

In the present invention, the above-mentioned lower layer coating solution is applied on the non-magnetic support by a so-called wet-on-wet coating method in which the coating solution is superposed in a wet state. The wet-on-wet coating method used to provide the lower layer and the upper layer in the present invention is a so-called sequential coating method in which the first layer is first coated and then the next layer is coated thereon as quickly as possible in a wet state, and a multilayer coating method. At the same time, it refers to a method of applying the extrusion coating method and the like. As the wet-on-wet coating method, the magnetic recording medium coating method described in JP-A-61-139929 can be used.

FIG. 1 is an explanatory view showing an example of a sequential coating method used for providing both layers in the present invention, in which a flexible support 1 such as polyethylene terephthalate running on a coating machine ( A) 3 is pre-coated with the lower layer coating liquid (a), and immediately thereafter, the smoothing roll 4 is used to smooth the coated surface, and another extrusion coating machine (B) is used while the coating liquid 2 is in a wet state. 6 the following upper layer coating liquid (b)
Apply.

FIG. 2 is an explanatory view showing an example of an extrusion type simultaneous coating system which is preferably used for providing both layers in the present invention. The state in which the lower layer coating liquid (a) 2 and the upper layer coating liquid (b) 5 are simultaneously coated will be described. After applying both layers, magnetic field orientation, drying and smoothing treatment are performed to obtain a magnetic recording medium.

In order to obtain the medium of the present invention, it is necessary to perform strong orientation. It is preferable to use a solenoid of 1000 G (Gauss) or more and a cobalt magnet of 2000 G or more in combination, and it is preferable to previously provide an appropriate drying step before orientation so that the orientation after drying becomes the highest.
Further, when the present invention is applied to the disk medium, an orientation method that randomizes the orientation is rather required.

Further, as the calendering roll, a heat-resistant plastic roll such as epoxy, polyimide, polyamide, or polyimideamide is used. Further, it is possible to perform processing by using metal rolls. The treatment temperature is preferably 70 ° C or higher, more preferably 80 ° C or higher. The linear pressure is preferably 200 kg / cm, more preferably 300 kg / cm or more, and the speed is 20 m / min.
The range is 700 m / min. The effect of the present invention can be further enhanced by a linear pressure of 300 kg / cm 2 or more at a temperature of 80 ° C. or more.

After the calendering treatment, a thermotreatment at 40 ° C. to 80 ° C. may be performed in order to accelerate the curing of the magnetic layer, back layer and non-magnetic layer. The coefficient of friction of the upper layer and the opposite surface of the magnetic recording medium of the present invention with respect to SUS420J is preferably 0.5 or less, further 0.3 or less, the surface resistivity of the magnetic layer is 10 ⁴ to 10 ¹¹ ohm / sq, and the lower layer alone. When applied, the surface resistivity is preferably 10 ⁴ to 10 ⁸ ohm / sq, and the surface electric resistance of the BC layer is preferably 10 ³ to 10 ⁹ .

Both the upper layer and the lower layer have a porosity of preferably 30% by volume or less, more preferably 20% by volume or less. The porosity is preferably small in order to achieve high output, but it may be better to secure a certain value depending on the purpose. For example, in a magnetic recording medium for data recording, where repeated use is important, running durability is often preferable when the porosity is large. It is easy to set these values in an appropriate range according to the purpose.

The magnetic characteristic of the magnetic recording medium of the present invention is the magnetic field 5
When measured with KOe, the squareness ratio in the tape running direction is 0.
It is 70 or more, preferably 0.80 or more, more preferably 0.90 or more. The squareness ratio in the two directions perpendicular to the tape running direction is preferably 80% or less of the squareness ratio in the running direction. The SFD of the magnetic layer is preferably 0.6 or less.

The magnetic recording medium of the present invention has a lower layer and an upper layer, but it is easily presumed that the physical properties of the lower layer and the upper layer can be changed according to the purpose. The magnetic recording medium of the present invention basically comprises two layers of an upper magnetic layer and a lower non-magnetic layer, but may have three or more layers. As a structure of three or more layers, the upper magnetic layer is composed of a plurality of two or more magnetic layers. In this case, the general concept of a plurality of magnetic layers can be applied to the relationship between the uppermost magnetic layer and the lower magnetic layer. For example, the idea of using a ferromagnetic powder having a higher coercive force in the uppermost magnetic layer and a smaller average major axis length and a smaller crystallite size than the lower magnetic layer can be applied. Further, the lower non-magnetic layer may be formed of a plurality of non-magnetic layers.
However, it is roughly classified into an upper magnetic layer and a lower non-magnetic layer.

[0175]

EXAMPLES Next, the present invention will be described more specifically by showing Examples and Comparative Examples. In each example, “part” means “part by weight” unless otherwise specified.

A coating liquid for the upper magnetic layer and a coating liquid for the lower non-magnetic layer were prepared according to the following formulations. Example 1 Formulation of coating liquid for upper magnetic layer Ferromagnetic powder: Fe alloy powder 100 parts Composition: 93% by weight of Fe, 3% by weight of Ni, 3% by weight of Co, other Zn, Cr, etc. Hc 1600 Oe, σ _S 135 emu / g Major axis length 0.18 μm, acicular ratio 9 vinyl chloride copolymer 10 parts —SO ₃ Na, epoxy group-containing polyurethane resin 5 parts —SO ₃ Na-containing, molecular weight 45000 α-alumina (average particle size 0.2 μm) 5 parts Cyclohexanone 150 parts Methyl ethyl ketone 200 parts After mixing and dispersing the above composition in a sand mill for 6 hours,
A polyisocyanate (Coronate L), 5 parts of stearic acid and 10 parts of butyl stearate were added to obtain a magnetic coating solution.

Coating liquid formulation for lower non-magnetic layer Granular TiO ₂ 100 parts Average particle size 0.09 μm Carbon black 5 parts Average particle size 20 mμ Vinyl chloride copolymer 8 parts —SO ₃ Na, epoxy group-containing molecular weight 50000 Polyurethane resin 5 part -SO ₃ Na content, after 4 hours mixed and dispersed in a sand mill molecular weight 45000 alpha-alumina (average particle size 0.2 [mu] m) 5 parts cyclohexanone 150 parts Methyl ethyl ketone 50 parts the above composition,
5 parts of polyisocyanate (Coronate L), 1 part of stearic acid and 1 part of butyl stearate were added to obtain a coating liquid for the lower non-magnetic layer.

The above coating solution was applied in a wet state by using two doctors having different gaps, and after orientation treatment with a permanent magnet, it was dried. As the non-magnetic support, a 9.8 μm polyethylene terephthalate film was used, and a back layer containing carbon black was provided on the surface of the support opposite to the magnetic layer. After that, a super calendar treatment was performed. Coating thickness is 0.3 μm for magnetic layer and 3.0 μm for non-magnetic layer
Met. The original fabric thus obtained was cut into a 3.81 mm wide piece, and the digital audio tape of Example 1-1 (D
AT).

In addition, in Examples and Comparative Examples, tapes were prepared by changing the factors shown in Table 1 with respect to Example 1-1. These tapes were evaluated by the following methods, and the results are shown in Table 2. Magnetic layer average value d, standard deviation σ of d: Cross-section of tape was photographed with a transmission electron microscope (TEM) (magnification: 20000)
) And determined according to the definition above. Average value of thickness variation (Δd): A cross section of the tape was photographed with a transmission electron microscope (TEM) (magnification: 20,000 times), the displacement of the magnetic layer and the lower non-magnetic layer in a length of 20 μm (actual length) was measured, The average value of the displacement difference between the peak and the valley was calculated and set as Δd.

The sequential multi-layer of the comparative example means that the lower non-magnetic layer is applied, and after drying, the upper magnetic layer is applied. Electromagnetic conversion characteristics Deck used: Sony DTC-1000 reproduction output: A signal with a single frequency of 4.7 MHz was input, the reproduction signal was output to a spectrum analyzer, and the peak value of the signal was read.

C / N: A noise spectrum was taken at the time of reproducing output measurement, and the reproducing output and the central recording frequency (4.7 MH) were measured.
From the noise level ratio 0.1 MHz away from z), C /
I asked for N. The spectrum analyzer is HP-358
5A and 0 dB are tapes of a single magnetic layer of Comparative Example 1. BER (block error rate): BER (block error rate): BER is the number of error flags in 10000 tracks and is represented by the following formula.

BER = error flag / 10,000 × 128 blocks The DAT signal structure encodes an analog signal, one code is 8 bits, and one block is 32 symbols × 8 bits = 25.
Since it is 6 bits, one track is composed of 128 blocks. The signals of 2 tracks, that is, 128 × 2 blocks are fetched into the memory, shuffled, and the error is detected. A DAT deck manufactured by Sony Corporation was used, and an HP5328A manufactured by Hewlett-Packard Co. was used as a counter, and the measurement was performed by connecting to a personal computer.

Dropout: A signal with a single frequency of 4.7 MHz was input, and a dropout with a threshold (DO) level of −10 dB and a length of 0.5 μSEC was measured with a dropout counter.

[0184]

[Table 1]

[0185]

[Table 2]

The shortest recording wavelength λ of the created DAT is 0.
67 μm. Therefore, from λ / 4 ≦ d ≦ 3λ, the thickness range of the magnetic layer is 0.17 μm ≦ d ≦ 2.01 μm, but the present invention is in the range of 0.17 μm ≦ d ≦ 1 μm. Further, there is a relationship of Δd / d ≦ 0.5 from Δd ≦ d / 2.

In Examples 1-1 to 1-3, the lower nonmagnetic layer thickness and the upper magnetic layer thickness were kept constant and the upper and lower layer thickness ratios were changed. Example 1
-2 is set to the middle of the same thickness, and Example 1-3 is set to almost the upper limit. Example 1-4 has a configuration in which the thickness of the lower non-magnetic layer is reduced to near the lower limit. Examples 1-5 to 1-7
Is an example in which the type of non-magnetic powder in the lower non-magnetic layer is changed, and it is understood that Ra is affected within the definition of the present invention. Examples 1-8 are examples using barium ferrite as the ferromagnetic powder. Example 1-9 is an example in which the thickness of the upper magnetic layer is close to the upper limit, and this system is inferior in characteristics to other examples.

Comparative Example 1-1 is a magnetic recording medium having a single-layer thick magnetic layer. Comparative Example 1-2 is a case where the thickness of the lower non-magnetic layer is thin, and the formability and Ra are poor. In Comparative Example 1-3, coarse red iron oxide (average particle size of 0.25, λ / 4 = 0.167) was used as the non-magnetic powder of the lower non-magnetic layer.
(Larger than 5) is used, the Δd is large and the C / N is poor. Comparative Example 4 uses needle-shaped red iron oxide with a long major axis, and therefore has a large Δd and an inferior Ra. Comparative Example 5 is an example in which the magnetic layer thickness is below the lower limit, and the various properties are inferior. Comparative Example 6 is an example of successive layers and has many pinholes.

Examples 1 to 8 are d, Δd, σ, and Ra.
Since each range is satisfied, it is understood that all of the reproduction output, C / N, BER, DO, and coating moldability are superior to the comparative example.

According to the present invention, by coating a thin magnetic layer (3 times or less of the shortest recording wavelength) with a lower non-magnetic layer at the same time, it is possible to prevent a coating defect which is a problem when the magnetic layer is thinned alone. At the same time, the reproduction output is improved by optimizing the thickness of the magnetic layer for the shortest recording wavelength according to the recording system, the thickness variation of the thinned magnetic layer is reduced, and the surface of the magnetic layer is smoothed. / N is improved.

According to the present invention, an electromagnetic conversion characteristic comparable to that of a metal thin film magnetic recording medium can be obtained, and at the same time, a coating type magnetic recording medium which solves the problems of productivity and storage reliability of the metal thin film magnetic recording medium can be provided. You can Example 2 A coating liquid for the upper magnetic layer and a coating liquid for the lower non-magnetic layer were prepared with the following formulations. Coating liquid for lower non-magnetic layer Inorganic powder TiO ₂ 90 parts Average particle size 0.035 μm Crystalline rutile TiO ₂ content 90% or more Surface treatment agent Al ₂ O ₃ BET specific surface area 35-45 m ² / g DBP oil absorption 27 to 38 g / 100 g pH 6.5 to 8 carbon black 10 parts Average particle size 16 mμ DBP oil absorption 80 ml / 100 g pH 8.0 Specific surface area by BET method 250 m ² / g Volatile content 1.5% Vinyl chloride-vinyl acetate- vinyl alcohol copolymer 12 parts ^{_{-N (CH 3) 3 + Cl}} - 5 polar groups × 10 ^-6 eq / g containing composition ratio 86: 13: 1 degree of polymerization 400 polyester polyurethane resin 5 parts neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1 -SO 3 Na group containing 1 × 10 ^-4 eq / g butyl stearate 1 part Stearic acid 1 part Methyl ethyl ketone 200 parts Cyclohexanone 80 parts Coating liquid for upper magnetic layer Ferromagnetic metal fine powder composition Fe / Zn / Ni = 92/4/4 100 parts Hc 1600 Oe BET specific surface area 60 m ² / g crystallite Size 195Å Average major axis length 0.20 μm, acicular ratio 10 Saturation magnetization (σ _S ): 130 emu / g Vinyl chloride copolymer 12 parts —SO ₃ Na group 1 × 10 ⁻⁴ eq / g, polymerization degree 300 Polyester polyurethane resin 3 parts Neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1-SO ₃ Na group 1 × 10 ^-4 eq / g-containing α-alumina (average particle size 0.2 μm) 2 parts Carbon black (average particle size 0.10 μm) 8 parts Butyl stearate 1 part Stearic acid 2 parts Methyl ethyl ketone 2 For each 0 parts The above two paints, after kneading the respective components in a continuous kneader and dispersed using a sand mill. To the obtained dispersion liquid, 1 part of polyisocyanate was added to the coating liquid for the lower non-magnetic layer, 3 parts to the coating liquid of the upper magnetic layer, and 40 parts of butyl acetate was further added to each to have an average pore diameter of 1 μm. Filtration was performed using a filter to prepare coating solutions for the lower non-magnetic layer and the upper magnetic layer, respectively.

The thickness of the obtained lower non-magnetic layer coating liquid was 7 μm so that the thickness after drying was 3 μm and immediately thereafter the thickness of the upper magnetic layer was 0.5 μm. Simultaneous multilayer coating was performed on a polyethylene naphthalate support having a central average surface roughness of 0.01 μm. While both layers were still wet, a cobalt magnet having a magnetic force of 3000 gauss and a solenoid having a magnetic force of 1500 gauss were used. After being oriented and dried, it was treated at a temperature of 90 ° C. with a seven-stage calender composed of only metal rolls and slit into a width of 8 mm to produce an 8 mm video tape of Example 2-1.

Similarly, the factors shown in Tables 3 to 4 were changed to prepare samples, Examples 2-2 to 2-10, and Comparative examples 2-1 to 2-2.
-7 was prepared and the performance was evaluated as follows, and the results are shown in Tables 3 to 4. 1. Volume Ratio (Filling Ratio) of Lower Layer Inorganic Powder A medium was cut out to about 0.1 μm with a diamond cutter to prepare a test piece, which was observed with a transmission electron microscope. From this transmission electron micrograph image, the number of inorganic powder particles per 1 μm ^{2 is} counted, the thickness of the cut out test piece is calculated, and the number of inorganic powder particles contained per unit volume is measured. The volume ratio of the inorganic powder was determined by determining the volume per particle from the powder particle diameter obtained from the same photograph and multiplying by the number of inorganic powder particles contained per unit volume. The calculation formula is as follows.

Volume ratio of lower layer inorganic powder = 4π / 3 (D / 2) ³ (n / t) × 100 (%) D: Particle diameter of powder (μm) obtained from section photograph n: Obtained from section photograph Number of powders contained per unit area (pieces / μm ² ) t: Thickness of section (μm) 2. Powder volume ratio of upper magnetic layer The ferromagnetic powder density can be obtained from the following formula.

DM = Bm / 4πσ _S where Bm (gauss): residual magnetic flux density dM (g / cc): ferromagnetic powder density σ _S (emu / g): magnetization amount of the ferromagnetic powder of the ferromagnetic powder The volume ratio in the upper layer can be obtained by dividing the above density by the specific gravity of the ferromagnetic powder. Also, the density of other powder components and binder in the magnetic layer is calculated from the magnetic layer prescription amount, and divided by the specific gravity of each powder component to obtain the volume ratio of each powder component, and sum these. By
The powder volume ratio of the upper layer is obtained. 3. Average Particle Size of Inorganic Powder The average particle size along the long axis was determined by a transmission electron microscope. 4. Crystallite size of ferromagnetic metal powder It was determined from the spread of the half-value widths of the diffraction lines of the (1,1,0) plane and the (2,2,0) plane by X-ray diffraction. 5. Surface Roughness R _rms Scanning Tunneling Microscope (STM) is measured by Digital In
tunnel current 10 using Nanoscope II manufactured by strument
Scanning was performed in the range of 6 μm × 6 μm under the condition of A and bias voltage of 400 mV, and the value was obtained from the following formula 1.

[0196]

[Equation 1]

6. σ: The same method as in Example 1. 7.7 MHz Output A FUJIX8 8 mm video deck manufactured by Fuji Photo Film Co., Ltd. was used to record a 7 MHz signal, and the 7 MHz signal reproduction output when this signal was reproduced was measured with an oscilloscope. The reference is an internal reference of Fuji Photo Film Co., Ltd. 8. Pinholes After coating the magnetic layer and before coating the back layer, the magnetic layer was visually observed with transmitted light to measure pinholes per 100 m ² . It is desirable that the number is 1 or less per 100 m ² .

[0198]

[Table 3]

[0199]

[Table 4]

As shown in Tables 3 and 4, in the example samples, the average particle size of the inorganic powder contained in the lower non-magnetic layer was 1/2 times the crystallite size of the ferromagnetic powder contained in the upper magnetic layer. Four
The surface roughness R _rms is small because it is double, and d / R
It is an excellent magnetic recording medium in which a magnetic layer having a uniform _rms of 30 or more and σ of 0.2 μm or less and excellent surface properties is formed, the reproduction output is high, and pinholes are extremely small. On the other hand, in Comparative Example 2-1, ( _rms particle size of inorganic powder / crystallite size of ferromagnetic powder) is too large than the predetermined range, so R _rms becomes large and the reproduction output is not improved. In Comparative Example 2-2, the average particle size of the inorganic powder / the crystallite size of the ferromagnetic powder was too small than the predetermined range, and therefore R _rms
Becomes larger and the playback output is not improved. Comparative Example 2-3
The reproduction output is slightly inferior because the thickness d of the magnetic layer is as thick as 1.2 μm. Comparative Example 2-4 is a single-layer magnetic recording medium having only a magnetic layer. In Comparative Example 2-5, R _rms was large because the amount of the inorganic powder added was small, and the value of σ was 0.2 or more, and the electromagnetic conversion characteristics were not improved. Comparative Example 2-6
Since the volume ratio of the powder is too small, R _rms is large and the electromagnetic conversion characteristics are not improved. Comparative Example 2-7 could not be applied because the volume ratio of the inorganic powder was too large.

Example 3 A coating solution for the upper magnetic layer and a coating solution for the lower non-magnetic layer were prepared according to the following formulations. Lower non-magnetic layer; same as in Example 2-1, coating liquid for upper magnetic layer Co-modified γFe ₂ O ₃ 100 parts Hc 700 Oe Specific surface area by BET method 42 m ² / g Crystallite size 300 Å Saturation magnetization (σ _S ) 75 emu / g -SO ₃ Na group 1 × 10 ^-5 eq / g containing 9 parts of vinyl copolymer chloride polymer, polymerization degree 300 particulate abrasive (Cr ₂ O, an average particle diameter of 0.3 [mu] m) 7 parts toluene 30 parts Methyl ethyl ketone 30 parts the above After kneading the composition (1) with a kneader for about 1 hour, the following composition was further added and dispersed with the kneader for about 2 hours.

Polyester polyurethane resin 5 parts Neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1-SO ₃ Na group 1 × 10 ^-4 eq / g content average molecular weight 35000 toluene 200 parts methyl ethyl ketone 200 parts The following carbon black and coarse particle abrasive were added, and the dispersion treatment was performed with a sand grinder.

Carbon black (average particle size 20 to 30 mμ) 5 parts Ketjenblack EC coarse particle abrasive made by Lion Akzo 2 parts α-alumina (AKP-12 made by Sumitomo Scientific Co., average particle size 0.5 μm) The composition was added, and the mixture was dispersed again in a sand grinder to obtain a coating liquid for the upper magnetic layer.

Polyisocyanate (Coronate L manufactured by Nippon Polyurethane Co.) 6 parts Tridecyl stearate 6 parts The coating liquid for the upper magnetic layer and the coating liquid for the lower non-magnetic layer obtained as described above were applied to polyethylene terephthalate having a thickness of 75 μm. First, the lower non-magnetic layer coating liquid was applied first, and then the upper magnetic layer coating liquid was applied in a wet state, and the back surface was treated in the same manner. The dry thickness was such that the thickness of the lower non-magnetic layer was 1.5 μm and the thickness of the magnetic layer was 0.5 μm. Then, calendar processing was performed to obtain a magnetic recording medium. Thereafter, this magnetic recording medium was punched out into 3.5 inch, put into a 3.5 inch cartridge with a liner installed inside, and added with predetermined mechanical parts. I got a disc. Similarly, Table 5
Samples, Examples 3-2 to 3-5, by changing the factors described in 1.
Comparative Examples 3-1 to 3-3 were prepared, the performance was evaluated as follows, and the results are shown in Table 5. 1. Volume ratio (filling ratio) of lower layer inorganic powder; same as in Example 2. Average particle size of inorganic powder; same as in Example 2. Crystallite size of iron oxide magnetic powder; by X-ray diffraction,
It was calculated from the spread of diffraction lines of the (4.4.0) plane and the (2.2.0) plane. 4. Surface roughness R _rms ; same as in Example 2. σ: The same method as in Example 1. 6. Innermost circumference 2F output relative value (%); calculated as the initial 2F output value of Example 3-1. The drive used is PD211
It is manufactured by Toshiba Corporation.

[0205]

[Table 5]

As is clear from Table 5, the example samples are
Since the average particle size of the inorganic powder contained in the lower non-magnetic layer is 1/2 to 4 times the crystallite size of the ferromagnetic powder contained in the upper magnetic layer, the surface roughness R _rms is small, and d /
It is an excellent magnetic recording medium in which R _rms is 30 or less and σ is 0.2 μm or less, a magnetic layer having a uniform and excellent surface property is formed, the reproduction output is high, and pinholes are extremely small.
On the other hand, in Comparative Example 3-1, since (average particle diameter of inorganic powder / crystallite size of ferromagnetic powder) is larger than the predetermined range, R _rms becomes large and the output is not improved. In Comparative Example 3-2, the average particle diameter of the inorganic powder / the crystallite size of the ferromagnetic powder was too small than the predetermined range, so that the R _rms became large and the output was not improved. In Comparative Example 3-3, the reproduction output is slightly inferior because the thickness d of the magnetic layer is as thick as 1.2 μm.

Example 4 In the same coating solution composition for the upper magnetic layer and the lower non-magnetic layer as in Example 2-1, the factors shown in Tables 6 to 7 (particularly the average particle diameter of the inorganic powder of the lower non-magnetic layer and the upper layer) were used. Various samples were prepared by changing the ratio of the major axis length of the ferromagnetic powder in the magnetic layer, and the performance was evaluated in the same manner as in Example 2, and the results are shown in Tables 6 to 7.

Squareness ratio: The coating direction Br / Bm when measured at Hm 5 kOe using a vibrating sample type magnetometer (VNM; manufactured by Toei Industry) was taken as the squareness ratio.

[0209]

[Table 6]

[0210]

[Table 7]

As is clear from the above table, the example samples are
Since the average particle size of the inorganic powder contained in the lower non-magnetic layer is 1/3 or less of the major axis length of the ferromagnetic powder contained in the upper magnetic layer, d / R _rms is 30 or more, and Δd is d / 2
It is an excellent magnetic recording medium in which a uniform magnetic layer is formed, the reproduction output is high, and pinholes are extremely small. On the other hand, Comparative Example 4-1 (average particle diameter of inorganic powder /
Since the (major axis length of the ferromagnetic powder) is larger than the predetermined range, Δd becomes large and the output is not improved. Comparative Example 3-
In No. 2, the reproduction output is poor because the thickness d of the magnetic layer is as thick as 1.3 μm. Comparative Example 3-3 is an example of a single magnetic layer, and since there is no lower non-magnetic layer and d is thin, the coatability and electromagnetic conversion characteristics are poor. In Comparative Example 4-4, the coating properties are not improved because the layers are successively laminated after the lower layer is dried. In Reference Example 4-1, since the magnetic layer is a single layer and d is thick, the coatability is good, but the electromagnetic conversion characteristics are not improved. In Comparative Example 4-5, since no inorganic powder was used in the lower layer, the interface fluctuation between the upper layer and the lower layer was large, and thus Δd was high and the electromagnetic conversion characteristics were poor. In Comparative Example 4-6, since the volume ratio of the lower layer inorganic powder is low, Δd is also high and the electromagnetic conversion characteristics are poor.

Example 5 Co-modified γ in the composition of the coating liquid for the upper magnetic layer of Example 3-1
Example 3 except that Fe ₂ O ₃ was changed to the following ferromagnetic powder
The same coating liquid as the coating liquid for the upper magnetic layer and the coating liquid for the lower non-magnetic layer of Example 3-1 were prepared to prepare the sample of Example 5-1.

Ferromagnetic Powder (Hexagonal Barium Ferrite) Average Plate Diameter 0.05 μm, Plate Ratio 4 Specific Surface Area by BET Method 39 m ² / g Hc 1100 Oe In addition, the factors described in Table 8 (particularly the inorganic material of the lower non-magnetic layer) The ratio of the average particle diameter of the powder and the average plate diameter of the ferromagnetic powder of the upper magnetic layer) was changed, and the samples, Examples 5-2 to 5-3 and Comparative examples 5-1 to 5-1.
5-2 was prepared, the performance was evaluated in the same manner as in Example 3, and the results are shown in Table 8.

Vertical squareness ratio: Br / Bm in the direction perpendicular to the coated surface was measured using a vibrating sample type magnetometer. D50 (kfci): output of long wavelength recording / reproducing output 50
Recording density in%. This D50 is a measure of the maximum recording density that can be realized as a device.

[0215]

[Table 8]

From Table 8, the samples of Examples have a vertical rectangular shape because the average particle diameter of the inorganic powder contained in the lower non-magnetic layer is equal to or smaller than the average particle diameter of the plate-like ferromagnetic powder contained in the upper magnetic layer. A uniform magnetic layer having a high ratio and Δd of d / 2 or less is formed. Therefore, the example sample is an excellent magnetic recording medium having a high D50 and very few pinholes. On the other hand, in Comparative Example 5-1, since the average particle diameter of the inorganic powder is larger than the average plate diameter of the ferromagnetic powder, Δd becomes large and D50 is not improved. Comparative Example 5-2 is an example of a single magnetic layer without a lower non-magnetic layer, and has a poor D50.

Example 6 A coating liquid for the upper magnetic layer and a coating liquid for the lower non-magnetic layer were prepared with the following formulations. Example 6-1 Coating liquid for lower non-magnetic layer Inorganic powder TiO ₂ 80 parts Average particle size 0.035 μm Crystalline rutile TiO ₂ content 90% by weight Inorganic powder surface treatment layer Al ₂ O ₃ (10% by weight) BET method Specific surface area by 40 m ² / g DBP oil absorption amount 27-38 g / 100 g pH 7 carbon black 20 parts Average particle size 16 mμ DBP oil absorption amount 80 ml / 100 g pH 8.0 BET specific surface area 250 m ² / g volatile matter 1.5% vinyl chloride - vinyl acetate - vinyl alcohol copolymer 12 parts ^{_{-N (CH 3) 3 + Cl}} - polar groups of 5 × 10 ^-6 eq / g containing composition ratio 86: 13: 1 degree of polymerization 400 polyester polyurethane resin 5 parts neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1 -SO 3 Na group 1 × 10 ^-4 eq / g Containing butyl stearate 1 part Stearic acid 1 part Methyl ethyl ketone 100 parts Cyclohexanone 50 parts Toluene 50 parts Coating liquid for upper magnetic layer Ferromagnetic metal powder composition Fe / Zn / Ni = 92/4/4 100 parts Hc 1600 Oe BET method ratio Surface area 60 m ² / g Crystallite size 195 Å Average major axis length 0.20 μm, acicular ratio 10 Saturation magnetization (σ _S ): 130 emu / g Surface treatment agent: Al ₂ O ₃ , SiO ₂ vinyl chloride copolymer 12 parts —SO ₃ Na group 1 × 10 ⁻⁴ eq / g content, polymerization degree 300 Polyester polyurethane resin 3 parts Neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1 —SO ₃ Na group 1 × 10 ^{− 4} eq / g containing α- alumina (average particle size 0.3 [mu] m) 2 parts carbon black (average particle size 0.10μ ) For each of 0.5 parts Butyl stearate 1 part Stearic acid 2 parts Methyl ethyl ketone 90 parts Cyclohexanone 50 parts Toluene 60 parts The two paints, after kneading the respective components in a continuous kneader and dispersed using a sand mill. To the obtained dispersion liquid, 1 part of polyisocyanate was added to the coating liquid for the lower non-magnetic layer, 3 parts to the coating liquid of the upper magnetic layer, and 40 parts of butyl acetate was further added to each to have an average pore diameter of 1 μm. Filtration was performed using a filter to prepare coating solutions for the lower non-magnetic layer and the upper magnetic layer, respectively.

The thickness of the obtained lower non-magnetic layer coating liquid was 7 μm so that the thickness after drying was 2 μm and immediately after that the thickness of the upper magnetic layer was 0.5 μm. Simultaneous multilayer coating was performed on a polyethylene terephthalate support having a central average surface roughness of 0.01 μm, and while both layers were still in a wet state, a cobalt magnet having a magnetic force of 3000 gauss and a solenoid having a magnetic force of 1500 gauss were used for orientation. Then, after drying, it was treated at a temperature of 90 ° C. with a seven-stage calender composed of only metal rolls, and slit into a width of 8 mm to manufacture an 8 mm video tape of Example 6-1.

Similarly, the factors shown in Tables 9 to 10 were changed, and the samples, Examples 6-2 to 6-12, and Comparative examples 6-1 to 6-1 were changed.
6-3 was prepared, the performance was evaluated in the same manner as described above, and the results are shown in Tables 9 to 10. The relative speed of the 8 mm video is 38 m / sec, and the recording wavelength of 7 MHz is 0.54 μm.
m. Therefore, λ / 50 is 10.8 nm. Centerline average surface roughness (Ra): TOYO3D manufactured by WYKO
Area of about 250 × 250 nm by MIRAU method using
a was measured. Spherical correction at measurement wavelength of about 650 nm.
Cylinder correction was added.

[0220]

[Table 9]

[0221]

[Table 10]

As is clear from the above table, the example samples are
Since the surface of the inorganic powder contains a treatment layer of Al ₂ O ₃ , SiO ₂ , ZrO _2, etc. as shown in the above table, the dispersibility is improved,
Ra is low, λ / 50 (10.8 nm) or less, and electromagnetic conversion characteristics are good. In Comparative Example 6-1, since the treatment layer is not included in the inorganic powder, the dispersibility is poor, Ra, σ, and Δd are high, and the electromagnetic conversion characteristics are poor. Comparative Example 6-
In No. 2, the magnetic conversion characteristics are poor because the magnetic layer is thick. In Comparative Example 3, a sample could not be prepared due to the successive layers.

Example 7 A coating liquid for the upper magnetic layer and a coating liquid for the lower non-magnetic layer were prepared by the following formulations. Example 7-1 Lower non-magnetic layer coating solution; same as in Example 6-1 Upper magnetic layer coating solution Co-substituted barium ferrite 100 parts Specific surface area by BET method 35 m ² / g Average particle size 0.06, plate-like The ratio 5 vinyl chloride copolymer 9 parts -SO ₃ Na group 1 × 10 ^-5 eq / g containing, polymerization degree 300 particulate abrasive (Cr ₂ O, an average particle diameter of 0.3 [mu] m) 7 parts toluene 30 parts Methyl ethyl ketone 30 Parts After kneading the above composition with a kneader for about 1 hour, the following composition was further added and dispersed with the kneader for about 2 hours.

Polyester polyurethane resin 5 parts Neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1-SO ₃ Na group 1 × 10 ^-4 eq / g content average molecular weight 35000 methyl ethyl ketone 200 parts cyclohexanone 100 parts toluene 80 parts Next, the following carbon black and a coarse particle abrasive were added, and a dispersion treatment was carried out for 2000 hours with a sand grinder for about 2 hours.

Carbon black (average particle size 20 to 30 mμ) 5 parts Ketjen Black EC coarse particle abrasive made by Lion Akzo 2 parts α-alumina (AKP-12 made by Sumitomo Chemical Co., average particle size 0.5 μm) The composition was added, and the mixture was dispersed again in a sand grinder to obtain a coating liquid for the upper magnetic layer.

Polyisocyanate (Coronate L manufactured by Nippon Polyurethane Co., Ltd.) 6 parts Tridecyl stearate 6 parts The coating liquid for the upper magnetic layer and the coating liquid for the lower non-magnetic layer obtained as described above were applied to polyethylene terephthalate having a thickness of 75 μm. First, the lower non-magnetic layer coating liquid was applied first, and then the upper magnetic layer coating liquid was applied in a wet state, and the back surface was treated in the same manner. The dry thickness was such that the thickness of the lower non-magnetic layer was 1.5 μm and the thickness of the magnetic layer was 0.5 μm. Then, calendar processing was performed to obtain a magnetic recording medium. Thereafter, this magnetic recording medium was punched out into a 3.5-inch floppy disk, placed in a 3.5-inch cartridge having a liner installed inside, and a predetermined mechanical component was added to the 3.5-inch floppy disk of Example 7-1. I got a disc. Similarly, Table 1
Samples, Examples 7-2 to 7-, in which the factor described in 1 is changed.
7, Comparative Example 7-1 was prepared, the performance was evaluated, and the results are shown in Table 11.

Initial innermost 2F output: Calculated as a relative value with the sample of Example 7-1 as 100. The drive used is PD211 (made by Toshiba Corp.). The recording wavelength is
It is 1.428 μm. Therefore, λ / 50 is 28.5n
m. Surface roughness: Ra was measured by the same method as in Example 6.

[0228]

[Table 11]

From the above table, in the same manner as in Example 6, the sample of Example has Al ₂ O ₃ , SiO ₂ and ZrO _{2 on the} surface of the inorganic powder.
Since such treatment layers as described above are included as shown in the table above, the dispersibility is improved, Ra is low, and the electromagnetic conversion characteristics are good. Comparative Example 7
In the case of -1, since the inorganic powder does not include the treatment layer, the dispersibility is poor, Ra, σ, and Δd are high, and the electromagnetic conversion characteristics are poor.

Example 8 A coating liquid for the upper magnetic layer and a coating liquid for the lower non-magnetic layer were prepared with the following formulations. Example 8-1 Coating liquid for lower non-magnetic layer Inorganic powder TiO ₂ 80 parts Average particle size 0.035 μm Crystalline rutile TiO ₂ content 90% or more Specific surface area 40 m ² / g DBP oil absorption 27-38 g / 100 g pH 7 Carbon black 20 parts Average particle size 16 mμ DBP oil absorption 80 ml / 100 g pH 8.0 BET specific surface area 250 m ² / g Volatile content 1.5% Vinyl chloride-vinyl acetate-vinyl alcohol copolymer 12 parts -N (CH ₃ ) Containing 5 × 10 ⁻⁶ eq / g of polar group of ₃ ⁺ Cl ⁻ Composition ratio 86: 13: 1 Polymerization degree 400 Polyester polyurethane resin 5 parts Neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1-SO ₃ Na group 1 × 10 ^-4 eq / g-containing butyl stearate 1 part Stearic acid 1 part Methyl ethyl ketone Ton 200 parts Upper magnetic layer Ferromagnetic metal fine powder Composition Fe / Zn / Ni = 92/4/4 100 parts Hc 1600 Oe BET specific surface area 60 m ² / g Crystallite size 195 Å Average major axis diameter 0.20 μm, acicular Ratio 7 Saturation magnetization (σ _S ): 128 emu / g Vinyl chloride copolymer 12 parts —SO ₃ Na group 1 × 10 ⁻⁴ eq / g content, degree of polymerization 300 Polyester polyurethane resin 3 parts Neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1 -SO 3 Na group containing 1 × 10 ^-4 eq / g α- alumina (average particle size 0.2 [mu] m) 2 parts carbon black (average particle size 0.10 .mu.m) 0. 5 parts Butyl stearate 1 part Stearic acid 2 parts Methyl ethyl ketone 200 parts For each of the above two paints, open kneader each component Kneaded and dispersed in a sand mill. To the obtained dispersion liquid, 1 part of polyisocyanate was added to the coating liquid of the lower non-magnetic layer, 3 parts of the coating liquid of the upper magnetic layer, and 40 parts of butyl acetate were added to each to add 1 μm.
The coating liquids for the lower non-magnetic layer and the upper magnetic layer were prepared by filtering with a filter having an average pore size of 1.

The thickness of the obtained lower non-magnetic layer coating liquid was 7 μm so that the thickness after drying was 3 μm and immediately thereafter the thickness of the upper magnetic layer was 0.5 μm. Simultaneous multilayer coating was performed on a polyethylene terephthalate support having a center average surface roughness of 0.01 μm, and while both layers were still in a wet state, a cobalt magnet having a magnetic force of 3000 gauss and a solenoid having a magnetic force of 1500 gauss were used for orientation. Then, after drying, it was treated at a temperature of 90 ° C. with a seven-stage calender composed of only metal rolls, and slit into a width of 8 mm to manufacture an 8 mm video tape of Example 8-1.

Similarly, the factors shown in Tables 12 to 17 were changed to prepare samples, Examples 8-2 to 8-6, and Comparative Examples 8-1 to 8-1.
8-4 was created. In addition, Example 8-4 and Comparative Example 8-1
A continuous kneader was used for kneading the magnetic layer in order to increase the packing density of the ferromagnetic powder. The characteristics of the sample were evaluated, and the results are shown in Tables 16 and 17. Evaluation Method 7 MHz Output A 7 MHz signal was recorded using a FUJIX8 8 mm video deck manufactured by Fuji Photo Film Co., Ltd., and a 7 MHz signal reproduction output when this signal was reproduced was measured with an oscilloscope. The contrast is 8 mm tape SAG made by Fuji Photo Film Co., Ltd.
P6-120.

C / N ratio A FUJIX8 8 mm video deck manufactured by Fuji Photo Film Co. was used to record a 7 MHz signal, and the noise generated at 6 MHz when this signal was reproduced was measured with a spectrum analyzer. The ratio was measured. Tape heat shrinkage The sample tape was stored in a constant temperature bath at 70 ° C for 48 minutes, and the change in length before and after that was taken as the heat shrinkage. The tape length was about 100 mm, and the length was measured with a comparator. No tension was applied during storage in a constant temperature bath.

Skew Distortion A color bar signal was recorded in advance and then stored in a constant temperature bath at 70 ° C. for 48 hours, and after confirming that the temperature was sufficiently returned to room temperature, reproduction was performed to display the color bar signal on the screen. Obtained from the change. One color bar is 7.48 μsec. Running Durability The sample is P6-in 10mm 8mm VCR FUJIX8 made by Fuji Photo Film Co. in an atmosphere of 23 ° C and 70% RH.
The 120 was run 100 times. During that time, the output decrease was measured, and the stains on various parts in the deck after running were evaluated. ○
Indicates that the area with stains is within 5 places, △ indicates that there are 5 or more places with stains, but there is no actual damage due to clogging, and × indicates There are 5 or more spots with stains, which indicates that there is actual damage due to clogging. In addition, ◯ Δ means a performance intermediate between ◯ and Δ.

[0235]

[Table 12]

[0236]

[Table 13]

[0237]

[Table 14]

[0238]

[Table 15]

[0239]

[Table 16]

[0240]

[Table 17]

From the above table, the magnetic recording media of the present invention shown in the respective examples have smaller skew distortion than the comparative examples,
Since σ and Δd were also small, the reproduction output, C / N ratio, and running durability were good. In Comparative Example 8-1, the lower layer powder volume ratio is small, the powder volume ratio difference is small at −6.23%, the heat shrinkage ratio is high at 0.45%, and the skew distortion and σ are large.
Comparative Example 8-2, on the contrary, is an example in which the lower layer powder volume ratio is very large and the powder volume ratio difference is 23.47%, and although skew distortion is improved, σ and Δd are high and running durability is high. Is poor. In Comparative Example 8-3, since the upper layer thickness is as thick as 1.2 μm, the electromagnetic conversion characteristics are inferior.

In this example, the magnetic recording medium at 70 ° C. and 48 °
By controlling the heat shrinkage ratio in time to 0.4% or less, skew distortion is reduced and running durability, and C
/ N, it is a coating type magnetic recording medium having an extremely thin magnetic layer, which has excellent characteristics capable of ensuring good reproduction output, and can be manufactured in large quantities without coating defects. Example 9 A coating liquid for the lower non-magnetic layer and a coating liquid for the upper magnetic layer were prepared according to the following formulations. Coating liquid for lower non-magnetic layer Inorganic powder TiO ₂ 80 parts Average particle size 0.035 μm Crystalline rutile TiO ₂ content 90% or more Specific surface area by BET method 40 m ² / g DBP oil absorption 27-38 g / 100 g pH 7 Carbon black 20 parts Average particle size 16 mμ DBP oil absorption 80 ml / 100 g pH 8.0 BET specific surface area 250 m ² / g Volatile content 1.5% Vinyl chloride-vinyl acetate-vinyl alcohol copolymer 12 parts-N (CH ₃ ) Composition ratio of 86: 13: 1 containing a polar group of ₃ ⁺ Cl ⁻ of 5 × 10 ⁻⁶ eq / g 400 Polyester polyurethane resin 5 parts Neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1 -SO ₃ Na group containing 1 × 10 ^-4 eq / g butyl stearate 1 part 1 part of methyl ethyl stearate Ton 200 parts the upper magnetic layer (a) a ferromagnetic metal powder composition Fe / Zn / Ni = 92/ 4/4 100 parts Hc 1600 Oe BET method specific by surface area 60 m ² / g Crystallite size 195Å average major axis length 0.20μm , Acicular ratio 10 Saturation magnetization (σ _S ): 130 emu / g Vinyl chloride copolymer 12 parts —SO ₃ Na group 1 × 10 ⁻⁴ eq / g content, degree of polymerization 300 Polyester polyurethane resin 3 parts Neopentyl glycol / Caprolactone polyol / MDI = 0.9 / 2.6 / 1-SO ₃ Na group 1 × 10 ^-4 eq / g-containing α-alumina (average particle size 0.3 μm) 2 parts Carbon black (average particle size 0.10 μm ) 0.5 part Butyl stearate 1 part Stearic acid 2 parts Methyl ethyl ketone 200 parts For each of the above two paints, each component was continuously kneaded. After kneading with a dough, it was dispersed using a sand mill. To the obtained dispersion liquid, 1 part of polyisocyanate was added to the coating liquid for the lower non-magnetic layer, 3 parts to the coating liquid of the upper magnetic layer, and 40 parts of butyl acetate was further added to each to have an average pore diameter of 1 μm. Filtration was performed using a filter to prepare coating solutions for the lower non-magnetic layer and the upper magnetic layer, respectively.

The thickness of the obtained lower non-magnetic layer coating liquid was 7 μm so that the thickness after drying was 2 μm and immediately thereafter the thickness of the upper magnetic layer was 0.5 μm. Simultaneous multilayer coating was performed on a polyethylene terephthalate support having a center average surface roughness of 0.01 μm, and while both layers were still in a wet state, a cobalt magnet having a magnetic force of 3000 gauss and a solenoid having a magnetic force of 1500 gauss were used for orientation. Then, after drying, it was treated at a temperature of 90 ° C. with a seven-stage calender composed of only metal rolls, and slit into a width of 8 mm to manufacture an 8 mm video tape of Example 9-1.

Similarly, the factors shown in Tables 18 to 19 were changed, and samples, Examples 9-2 to 9-7 and Comparative Examples 9-1 to 9-1.
9-4 was created. Further, the samples of Examples 9-8 were prepared by using the following paints as the upper magnetic layer. Upper magnetic layer (b) Ferromagnetic metal fine powder Composition BaFe (barium ferrite) 100 parts Hc Specific surface area by BET method m ² / g Crystallite size Å Plate diameter μm, Plate-like ratio Saturation magnetization (σ _S ): emu / g -SO ₃ Na group containing 1 × 10 ^-4 eq / g vinyl chloride copolymer 12 parts, polymerization degree 300 polyester polyurethane resin 3 parts neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1 - SO ₃ Na group 1 × 10 ⁻⁴ eq / g content α-alumina (average particle size 0.3 μm) 5 parts Carbon black (average particle size 0.10 μm) 0.5 part Butyl stearate 1 part Stearic acid 2 parts Methyl ethyl ketone 200 parts The above samples were evaluated and the results are shown in Tables 18-19. SMD, STD, Stiffness ratio Using a loop stiffener tester manufactured by Toyo Seiki, a sample with a width of 8 mm and a length of 50 mm was cut out for SMD and STD, and this was used as a ring, and the displacement rate in the inner diameter direction was 3.5 mm /
Each force required to give a displacement of 5 mm in seconds is SMD in mg,
The stiffness ratio SMD / STD was determined by determining STD. Envelope flatness A FUJIX8 8mm VCR made by Fuji Photo Film Co. was used to record a 7 MHz signal, and when this signal was reproduced, the 7 MHz signal reproduction output was observed with an oscilloscope.
Expressed by the difference between the maximum output and the minimum output in the field. 7 MHz Output A 7 MHz signal was recorded using a FUJIX8 8 mm video deck manufactured by Fuji Photo Film Co., Ltd., and a 7 MHz signal reproduction output when this signal was reproduced was measured with an oscilloscope. The contrast is 8 mm tape SAG made by Fuji Photo Film Co., Ltd.
P6-120. C / N ratio A FUJIX8 8mm VCR made by Fuji Photo Film Co., Ltd. was used to record a 7MHz signal, the noise generated at 6MHz when this signal was reproduced was measured with a spectrum analyzer, and the ratio of the reproduced signal to this noise was measured. did. Running Durability Measurement Method A sample was used at 23 ° C. and 70% RH atmosphere, 8 mm biodecks FUJIX8 made by Fuji Photo Film Co., Ltd., and P6-1 were used.
20 was run 100 times. During that time, the output reduction was measured.

◯: Output decrease within 2 dB Δ: Output decrease 2-4 dB ×: Output decrease 4 dB or more or clogging occurred Pinhole After applying the magnetic layer and before applying the back layer, the magnetic layer was irradiated with transmitted white light. Was visually observed to measure pinholes per 100 m ² . One or less is preferable per 100 m ² .

[0246]

[Table 18]

[0247]

[Table 19]

From the above table, the examples of the present invention are SMD / STD
Is controlled to 1.0 to 1.9, the head contact is improved and the envelope flatness is small as compared with the comparative example. In addition, it can be seen that in the examples, since there are no coating defects and σ is small, running durability, output and C / N are excellent. Comparative Example 9-1 has a low STD and a predetermined SMD / because the lower layer uses carbon having a Mohs hardness of 2 instead of the inorganic powder.
STD cannot be obtained, and envelope flatness, σ, and running durability are not improved. In Comparative Example 9-2, the predetermined SMD / STD was not obtained because the inorganic powder having a large average particle size was used, and the envelope flatness and σ were not improved. Comparative Example 9
-3 is an example in which the lower layer is not provided, and a coating defect occurred in the magnetic layer, and an evaluation sample could not be made. In Comparative Example 9-4, since the thickness of the magnetic layer was as thick as 1.2, the electromagnetic conversion characteristics were inferior to those of the other Examples, but the envelope flatness and running durability were improved.

Example 10 As a non-magnetic powder, polyethylene terephthalate (thickness 1
0 μm, F5 value: MD direction 20 Kg / mm ² , TD direction 14 Kg / mm ² , Young's modulus: MD direction 750 Kg
/ Mm ² , TD direction 470 Kg / mm ² ) or polyethylene terenaphthalate (thickness 7 μm, F5 value: MD
Direction 22 Kg / mm ² , TD direction 18 Kg / mm ² ,
Young's modulus: MD direction 750 Kg / mm ² , TD direction 7
50 Kg / mm ² ) was used and the following formulation was stirred with a Dispa stirrer for 12 hours to prepare an undercoat liquid.

Polyester resin (containing —SO ₃ Na group) 100 parts Tg 65 ° C. Na content 4600 ppm Cyclohexanone 9900 parts Using the obtained undercoat liquid, it was applied on the non-magnetic support by bar coating to a dry thickness of 0.1 μm. did.

On the other hand, a coating liquid for the upper magnetic layer and a coating liquid for the lower non-magnetic layer were prepared with the following formulations. Formulation of coating liquid for upper magnetic layer Ferromagnetic powder: Fe alloy powder (Fe-Co-Ni) 100 parts Composition; Fe: Co: No: Ni = 92: 6: 2 Al ₂ O ₃ is used as a sintering inhibitor Hc 1600 Oe, σ _S 119 emu / g major axis length 0.13 μm, acicular ratio 7 crystallite size 172 Å, water content 0.6 wt% vinyl chloride copolymer 13 parts —SO ₃ Na 8 × 10 ⁻⁵ eq / g, -OH, epoxy group-containing Tg 71 ° C, degree of polymerization 300, number average molecular weight (Mn) 12000 weight average molecular weight (Mw) 38,000 polyurethane resin 5 parts -SO ₃ Na 8 x 10 ^-5 eq / g content -OH 8 x 10 ^-5 eq / g containing Tg 38 ℃, Mw 50000 α-alumina (average particle diameter 0.15 [mu] m) 12 parts ^{_{S BET 8.7m 2 / g, pH}} 8.2, water content 0.06 wt% cyclohexanone 150 parts menu After 6 hours mixed and dispersed in a sand mill ethyl ketone 150 parts The above composition,
5 parts of polyisocyanate (Coronate L), 1 part of oleic acid, 1 part of stearic acid and 1.5 parts of butyl stearate were added to obtain a coating liquid for the upper magnetic layer.

Coating liquid formulation for lower non-magnetic layer TiO ₂ 85 parts Average particle size 0.035 μm Crystalline rutile TiO ₂ content 90% or more Surface treatment agent Al ₂ O ₃ S _BET 35 to 45 m ² / g True specific gravity 4. 1 pH 6.5-8.0 Carbon black 5 parts Average particle size 16 mμ DBP oil absorption 80 ml / 100 g pH 8.0 S _BET 250 m ² / g Coloring power 143% Vinyl chloride copolymer 13 parts-SO ₃ Na 8 × 10 ⁻⁵ eq / g, —OH, epoxy group-containing Tg 71 ° C., degree of polymerization 300, number average molecular weight (Mn) 12,000 weight average molecular weight (Mw) 38,000 polyurethane resin 5 parts —SO ₃ Na 8 × 10 ⁻⁵ eq / g containing -OH 8 × 10 ^-5 eq / g containing Tg 38 ℃, Mw 50000 cyclohexane 100 parts Methyl ethyl ketone 100 parts the above composition in a sand mill After 4 hours mixed and dispersed,
5 parts of polyisocyanate (Coronate L), 1 part of oleic acid, 1 part of stearic acid and 1.5 parts of butyl stearate were added to obtain a coating liquid for the lower non-magnetic layer.

The above coating solution was applied in a wet state using two doctors having different gaps, and then the permanent magnet 3
Alignment treatment was performed using 500 gauss and then solenoid 1600 gauss, and then dried. Then, a metal roll and a super calender treatment with the metal roll were performed at a temperature of 80 ° C. Coating thickness is 0.3 μm for magnetic layer and 3.0 μm for non-magnetic layer
Met.

Next, a coating solution was prepared according to the following formulation. BC layer formulation Carbon black 100 parts S _BET 220m ² / g Average particle size 17mμ DBP oil absorption 75ml / 100g Volatile content 1.5% pH 8.0 Bulk density 15 lbs / ft ³ Nitrocellulose RS1 / 2 100 parts Polyester polyurethane 30 Parts Nipolan (manufactured by Nippon Polyurethane Co.) Dispersant Copper oleate 10 parts Copper phthalocyanine 10 parts Barium sulfate (precipitation) 5 parts Methyl ethyl ketone 500 parts Toluene 500 parts The above composition was pre-kneaded and kneaded with a roll mill. Next, with respect to 100 parts by weight of the above dispersion, 100 parts by weight of carbon black S _BET 200 m ² / g average particle size 200 mμ DBP oil absorption 36 ml / 100 g pH 8.5 α-Al ₂ O ₃ (average particle size 0.2 μm) Disperse with a sand grinder with a composition added with 0.1 part,
After filtration, the following composition was added to 100 parts by weight of the above dispersion to prepare a coating liquid.

Methyl ethyl ketone 120 parts Polyisocyanate 5 parts The obtained coating liquid was applied on the opposite side of the non-magnetic support provided with the magnetic layer to a dry thickness of 0.5 μm by a bar coater. The raw fabric thus obtained was cut into a width of 8 mm to prepare 8 mm video tapes of Sample 1 (PET support) and Sample 2 (PEN support).

The following measurements were performed on the obtained 8 mm video tape, and the measurement results were obtained. (1) TEM (Transmission Electron Microscope) An ultrathin section of the magnetic layer was observed. The medium was cut to a thickness of about 0.1 μm with a diamond cutter, observed with a transmission electron microscope, and photographed. The interface between the upper and lower layers of the photographed image and the surface of the magnetic layer were removed, the thickness of the magnetic layer was measured with an IBASII image processing device, and the average value d and the standard deviation σ were determined.

The average thickness d of the magnetic layer was 0.45 μm. Practically 1 μm or less, particularly preferably 0.6 μm
It turned out to be: The standard deviation σ of the thickness variation of the magnetic layer was 0.08 μm or less. Practically, σ is 0.2
It has been found that the thickness is less than or equal to μm, particularly preferably less than or equal to 0.1 μm. Similarly, in Example 2-4, d was 0.28 μm,
σ was 0.06.

The magnetic tape was stretched so that the magnetic layer floated from the support, and the magnetic layer was peeled off by squeezing with a cutter blade. 500 mg of the peeled magnetic layer was added to 1N-NaO.
The binder was hydrolyzed by refluxing in 100 ml of H / methanol solution for 2 hours. Since the ferromagnetic powder has a large specific gravity and sinks to the bottom, the supernatant liquid was removed. Then, it was washed with water 3 times by decantation, and then with THF 3 times. The obtained ferromagnetic powder was dried in a vacuum dryer at 50 ° C. Next, the obtained ferromagnetic powder was dispersed in collodion and observed with a TEM at a magnification of 60,000. As a result, the major axis length of the ferromagnetic powder was 0.13 μm, and the acicular ratio was 10. Similarly, in Example 2-2, the major axis length was 0.25 μm, and the acicular ratio was 15. It has been found that the particle major axis length needs to be 0.4 μm or less for practical use, and is preferably 0.3 μm or less. Further, it has been found that the acicular ratio needs to be 2 to 20, and preferably 2 to 15 in practical use. (2) AFM (Atomic Force Micro)
Scope) The surface roughness R _rms was measured. The surface of the magnetic layer is Digita
l Instrument Nanoscope II
Using a tunnel current of 10 nA and a bias voltage of 400 m
The V was scanned over a range of 6 μm × 6 μm. For the surface roughness, R _rms in this range was obtained.

As a result, R _rms was 6 nm. It was found that 20 nm or less is necessary for practical use, and preferably 10 nm or less. Similarly, Example 2 can be referred to. (3) Surface roughness meter The surface roughness was measured using 3d-MIRAU. WYK
Approximately 250 × by MIRAU method using TOPO3D manufactured by O company
Ra, R _rms , Peak-Vall of 250 mm area
The ey value was measured. Spherical correction and cylindrical correction are added at a measurement wavelength of about 650 nm. This method is a non-contact surface roughness meter that measures by optical interference. Ra was 2.7 nm. In practice, Ra was found to be preferably 1 to 4 nm, more preferably 2 to 3.5 nm. R _rms was 3.5 nm. It was found that 1.3 to 6 nm is preferable for practical use, and more preferably 1.5 to 5 nm. The PV value was 20 to 30 nm. 80 in practice
It was found that the thickness is preferably not more than nm, more preferably 10 to 60 nm. (4) VSM (Vibration Sample Type Magnetometer) The magnetic characteristics of the magnetic layer of the magnetic tape obtained by using VSM were measured. It was measured at Hm 5 kOe using a vibrating sample type magnetometer manufactured by Toei Industry Co., Ltd.

As a result, Hc is 1620 Oe and Hr (9
0 °) is 1800 Oe, Br / Bm is 0.82, SFD
Was 0.583. Practically Hc is 1500-25
00 Oe is required, preferably 1600 to 2000 Oe
Was found. Hr (90 °) is practically 100
0 to 2800 Oe is required, preferably 1200 to 25
It was found to be 00 Oe. It has been found that Br / Bm needs to be 0.75 or more for practical use, and is preferably 0.8 or more. It has been found that the SFD is practically required to be 0.7 or less, and preferably 0.6 or less.

Similar results were obtained in Example 4. (5) X-ray Diffraction X-ray diffraction was performed using the ferromagnetic powder taken out from the magnetic layer in (1) above. The magnetic tape was directly applied to an X-ray diffractometer, and it was determined from the half-width broadening of the diffraction lines of the (1,1,0) plane and the (2,2,0) plane. As a result, it was found that the crystallite size was 180Å. Practically preferably 400 Å or less, particularly preferably 100 to 300 Å
I found out. Similarly, when Example 6-2 was measured, it was 280 Å. (6) Tensile test Young's modulus, yield stress, and yield elongation of the magnetic tape obtained by the tensile tester were measured. Tensile tester (Universal tensile tester STM-T-50B manufactured by Toyo Baldwin Co., Ltd.
P) was used in an atmosphere of 23 ° C. and 70% RH at a pulling rate of 10% / min.

As a result, the Young's modulus of the magnetic tape was 700.
Kg / mm ^2, yield stress 6~7Kg / mm ^2, yield elongation was 0.8 percent. Practically preferably Young's modulus is 4
00-2000 Kg / mm ² , particularly preferably 500-
It was found to be 1500 Kg / mm ² . It has been found that the yield stress is practically preferably 3 to 20 Kg / mm ² , and particularly preferably 4 to 15. Practically, the yield elongation is preferably 0.2 to 8%, particularly preferably 0.
It was found to be 4-5%. (7) Bending rigidity, circular stiffness Using a loop stiffener tester, width 8 mm, length 5
A 0 mm sample is used as a ring, and the force required to give a displacement of 5 mm at a displacement rate of about 3.5 mm / sec is expressed in mg.

As a result, the 8 mm p6-120 tape had a thickness of 10.5 μm and a stiffness of 40 to 40.
It was 60 mm. It was found that when the thickness is practically 10.5 ± 1 μm, the stiffness is preferably 20 to 90 mg, particularly preferably 30 to 70 mg. When the thickness is 11.5 μm or more, practically preferably 40 to
It was found to be 200 mg. It was found that when the thickness is 9.5 μm or less, it is practically preferably 10 to 70 mg. (8) Stretch failure The crack elongation was measured at 23 ° C. and 70% RH.

The both ends of the test piece having a tape length of 10 cm were set to 0.
It is pulled at a pulling speed of 1 mm / sec, and the surface of the magnetic layer is observed under a microscope at 400 times to measure the elongation at which 5 or more obvious cracks are generated on the surface of the magnetic layer. Similarly, Example 8-4 was 12%. As a result, the elongation at occurrence was 4%. It was found that it is practically preferably 20% or less, and particularly preferably 10% or less. (9) ESCA Cl / Fe spectrum α and N / Fe spectrum β were measured.

An X-ray photoelectron spectrometer (manufactured by PERKIN-FLMER) was used for the measurement of α and β. The Mg anode was used as the X-ray source, and the measurement was performed at 300 W. First, the lubricant of the video tape was washed off with n-hexane and then set on the X-ray photoelectron spectrometer. The distance between the X-ray source and the sample was 1 cm. Five minutes after the sample was evacuated to vacuum, Cl-2P spectrum, N-1S spectrum and Fe-
The 2P (3/2) spectrum was integrated for 10 minutes and measured.
The bath energy was constant at 100 eV. The integrated intensity ratio between the measured Cl-2P spectrum and the Fe-2P (3/2) spectrum was obtained by calculation and designated as α.

The N-1S spectrum and Fe-2P (3
/ 2) The integral intensity ratio with the spectrum was calculated and set as β. As a result, α was 0.45 and β was 0.07. Further, when Example 3-5 is measured, α is 0.32,
β was 0.10. Practically α is preferably 0.3
It was found that it was ˜0.6, and particularly preferably 0.4 to 0.5. Practically, β is preferably 0.03 to 0.
It was found to be 12, and particularly preferably 0.04 to 0.1. (11) Rheovibron The dynamic viscoelasticity at 110 Hz was measured.

The viscoelasticity of the tape was measured at a frequency of 110 Hz using a dynamic viscoelasticity measuring device (Rheovibron manufactured by Toyo Baldwin Co., Ltd.). Tg is the peak temperature of E ″. This method applies vibration from one end of the tape and measures the vibration propagating to the other end. As a result, Tg was 73 ° C and E '
(50 ° C) is 4 × 10 ¹⁰ dyne / cm ² , E ″ (5
(0 ° C.) was 1 × 10 ¹¹ . It has been found that Tg is preferably 40 to 120 ° C., and particularly preferably 50 to 110 ° C. for practical use. Practically E '(50 ℃) is 0.8 × 10
It was found that it was ^{11 to} 11 × 10 ¹¹ dyne / cm ² , and particularly preferably 1 × 10 ^{11 to} 9 × 10 ¹¹ dyne / cm ² . Practically, E ″ (50 ° C.) is preferably 0.5 × 10 ¹¹ to 8 × 10 ¹¹ dyne / cm ² ,
Particularly preferably 0.7 × 10 ^{11 to} 5 × 10 ¹¹ dyne /
It was found to be cm ² . (12) Adhesion Strength The adhesion strength between the support and the magnetic layer was measured by the 180 ° peeling method.

A tape having a width of 8 mm was attached to a 3M adhesive tape, and 180 peel strength was measured at 23 ° C. and 70% RH. The result obtained was 50 g. or,
When measured in the same manner as in Example 3-1, it was 25 g. It was found that the adhesion strength is preferably 10 g or more, and particularly preferably 20 g or more in practical use. (13) Wear The wear of a steel ball at 23 ° C. and 70% RH on the surface of the magnetic layer was measured.

The sample was fixed by adhering both ends of the sample on a prepared glass with adhesive tape, and a steel ball of 6.25 mmφ was slid by applying a load of 50 g. At that time, after traveling once for a distance of 20 mm at a speed of 20 mm / sec, the steel ball was moved to a new magnetic surface and the same operation was repeated 20 times. Then, observe the sliding surface of the steel ball with a microscope of 40 times,
The diameter was calculated assuming that the surface was a circle, and the amount of wear was calculated from the diameter.

The obtained results are 0.7 × 10 ^{-5 to} 1.1.
It was × 10 ^-5 mm ³ . In addition, Example 3-2 is 4 ×
It was 10 ⁻⁵ mm ³ . Practically preferably 0.1-10
^{-5 to} 5 × 10 ^-5 mm ³ , particularly preferably 0.4 ×
It was 10 ^{−5 to} 2 × 10 ⁻⁵ mm ³ . (14) SEM (Scanning Electron)
The surface state of the magnetic layer was observed by ic Microscope SEM.

Magnification 50 with Hitachi electron microscope S-900
Five pieces were photographed at 00 times to measure the polishing agent on the surface. As a result, the number of abrasives was 0.2 / μm ² . Moreover, when Example 4-6 was measured, it was 0.4 pieces / mm ² . In practice, it was found that the number of abrasives was 0.1 / μm ² or more, particularly preferably 0.12 / μm ^{2 to} 0.5 / μm ² . (15) GC (Gas Chromatography) The residual solvent of the magnetic tape was measured by GC.

Gas chromatography GC manufactured by Shimadzu Corporation
Using -14A, a 20 cm ² sample was heated to 120 ° C. and the residual solvent in the medium was measured. As a result, the residual solvent was 8 mg / m ² . Moreover, it was 18 mg / m < ² > when Example 1-1 was similarly measured. Practically, it is preferably 50 mg / m ² or less, particularly preferably 20.
It was found to be mg / m ² or less. (16) Sol Fraction The ratio of the soluble solids extracted with THF from the magnetic layer of the magnetic tape to the weight of the magnetic layer was determined. As a result, the sol fraction was 7%. Moreover, it was 5% when Example 1-1 was similarly measured. Practically, the sol fraction is preferably 15
It has been found that the content is 10% or less, and particularly preferably 10% or less. (17) Magnetic development pattern The obtained 8 mm wide magnetic recording medium was used as a VTR manufactured by Sony Corporation.
Using EVO-9500, short wavelength recording of 1 MHz was performed, only the recorded portion was slit to a width of 5 mm, ferri colloid (about 100 Åφ) (manufactured by Taihou Kogyo Co., Ltd.) was poured, and magnetic development was carried out. The one subjected to the immersion treatment for 24 hours was photographed at a magnification of 10 using a differential interference microscope manufactured by Nihon Kogaku Co., Ltd. with the interference color being blue. When the photograph is visually observed, a black or white line does not appear in the sample in which the thickness of the magnetic layer is averaged, but a black or white line appears as the thickness variation of the magnetic layer increases. This line is a portion having uneven thickness, and it is preferable that the number of such black or white lines is within 5 within a width of 5 mm. Further, the density difference between the black and white lines measured by a microdensitometer for those lines is preferably 0.2 or less, and particularly preferably 0.1 or less. (18) Friction coefficient (μ) 2 mm of 8 mm wide tape and sus420J, 4 mmφ rod
The tension (T2) required for running the tape at a speed of 14 mm / sec under these conditions was measured by contacting with a tension of 0 g (T1) at a wrap angle of about 180 °, and calculated by the following formula.

Μ = (1 / π) ln (T1 / T2) As a result, μ of the magnetic surface was 0.3. In practice, it has been found that μ of the magnetic surface is preferably 0.15 to 0.4, particularly preferably 0.2 to 0.35. Further, μ of the back layer surface was 0.2. In practice, the back layer surface has a μ value of preferably 0.15 to 0.4, particularly preferably 0.2 to 0.4.
It was found to be 0.35.

The friction coefficient is determined in relation to the magnetic substance, abrasive, carbon black, lubricant, dispersant and the like. (19) Contact angle Water and methylene iodide droplets were dropped on the magnetic layer, and the contact angle was measured with a microscope. In the case of water, it was 90 °.
Practically, it is preferably 60 to 130 °, particularly 80.
It has been found that ~ 120 ° is preferred.

In the case of methylene iodide, the contact angle is 20.
It was °. Practically, it is preferably 10 to 90 °,
It was particularly preferably 10 to 70 °. These contact angles are values determined by the lubricant or dispersant. (20) Surface Free Energy of Magnetic Layer and Back Layer JP-A-3-119513, DK 0wens, J. App
l. polymer Sci., 13 (1969) and J. Panzer J. Colloid &
Based on the method described in Interfacial Sci., 44, No1.

As a result, both the magnetic layer and the back layer are 40d.
It was yne / cm. Practically 10-100 dynes /
It has been found that cm is particularly preferred. This surface free energy is a value that is particularly determined by the lubricant and dispersant. (21) Surface electrical resistance A sample with a width of 8 mm has a quadrant cross section with a radius of 10 mm.
It was passed over two electrodes placed at an interval of mm and measured by a digital surface electric resistance meter TR-8611A (manufactured by Takeda Riken).

As a result, both the magnetic layer surface and the back layer surface were 1 × 10 ⁶ Ω / sq. Practically 1 × 10 ⁹ Ω /
It was found that sq or less is preferable, and 1 × 10 ⁸ Ω / sq or less is particularly preferable. This surface electric resistance is a value determined by the ferromagnetic powder, the binder, the carbon black and the like.

An 8 mm video tape having the above-mentioned method and characteristics was compared with a tape currently on the market, and the results are shown in Table 20.

[0279]

[Table 20]

The evaluation method was the above-mentioned method or a general method. The criteria for judgment are as follows. Jitter: ○ Less than 0.2 μsec × 0.2 μsec or more Storage stability: ○ No rust after storage at 60 ° C, 90% RH for 10 days × Generation of rust after storage at 60 ° C, 90% RH for 10 days Durability: When 50 passes were run on an 8mm video deck. ○ No clogging lasting for 30 seconds or longer.

Clogged for 30 seconds or longer. Scratch: Run in still mode for 10 minutes. ○ No scratches are visually observed. × A scratch is visually observed.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a method for measuring Δd of a magnetic recording medium of the present invention.

FIG. 2 is an explanatory view showing an example of a sequential coating method used for providing the lower layer and the upper layer by the wet-on-wet coating method in the present invention.

FIG. 3 is an explanatory diagram showing an example of a simultaneous multilayer coating method.

[Explanation of sign]

 1 flexible support 2 coating liquid (a) 3 coating machine (A) 4 smoothing roll 5 coating liquid (b) 6 coating machine (B) 7 backup roll 8 simultaneous multi-layer coating device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoru Hayakawa 2-12-1, Ogimachi, Odawara-shi, Kanagawa Fuji Photo Film Co., Ltd.

Claims (17)

[Claims] 1. A lower non-magnetic layer in which at least non-magnetic powder is dispersed in a binder is provided on a non-magnetic support, and ferromagnetic powder is used as a binder while the lower non-magnetic layer is in a wet state. In a magnetic recording medium having a plurality of at least two layers provided with dispersed upper magnetic layers, the average dry thickness (d) of the upper magnetic layers is 1 μm or less, and the upper magnetic layers and the lower non-magnetic layers are A magnetic recording medium characterized in that the average value Δd of the thickness variation at the interface of the layers has a relationship of Δd ≦ d / 2. 2. The dry thickness average value d of the upper magnetic layer is λ / 4 ≦ d ≦ 3λ with respect to the shortest recording wavelength λ, and the surface roughness Ra of the magnetic layer is Ra ≦ λ / 50. The magnetic recording medium according to claim 1, wherein: 3. The relationship between the root mean square roughness R _{rms of the} surface of the upper magnetic layer by the scanning tunneling microscope (STM) method and the dry thickness d of the magnetic layer is 30 ≦ d / R _rms . The magnetic recording medium according to claim 1, wherein: 4. The magnetic recording medium according to claim 1, wherein the thermal contraction rate of the magnetic recording medium after storage at 70 ° C. for 48 hours is 0.4% or less. 5. The dry thickness of the lower non-magnetic layer is 1 to 30 times the dry thickness of the upper magnetic layer, and the powder volume ratio of the lower non-magnetic layer to the powder volume of the upper magnetic layer. The magnetic recording medium according to claim 4, wherein the difference from the ratio is in the range of -5% to + 20%. 6. The ratio SMD / STD of the staying direction SMD to the coating direction (longitudinal direction) of the magnetic recording medium and the staying direction STD in the width direction with respect to the coating direction is 1.0 to 1.
9. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is 9. 7. The non-magnetic powder contained in the lower non-magnetic layer contains an inorganic powder, and the inorganic powder has a Mohs hardness of 6 or more and an average primary particle diameter of 0.15 μm or less from a spherical shape to a cubic shape. 7. The magnetic recording medium according to claim 6, which is made of an inorganic powder. 8. The non-magnetic powder contained in the lower non-magnetic layer is an inorganic powder having a Mohs hardness of 3 or more, and the average particle size thereof is the crystallite size of the needle-like ferromagnetic powder contained in the upper magnetic layer. The magnetic recording medium according to claim 1 or 3, wherein the magnetic recording medium is 1/2 to 4 times as large as the magnetic recording medium. 9. The major axis length of needle-like ferromagnetic powder contained in the upper magnetic layer, wherein the non-magnetic powder contained in the lower non-magnetic layer is an inorganic powder having a Mohs hardness of 3 or more 4. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is 1/3 or less. 10. The surface of the upper magnetic layer is 3d-MIR.
Ra is 1-5 nm and R is the optical interference surface roughness measured by AU.
_{The rms} satisfies 1.3 to 6 nm and the PV value satisfies at least one value of 80 nm or less.
Or the magnetic recording medium described in 3. 11. The bending rigidity (annular stiffness) of the magnetic recording medium is 4 when the total thickness is thicker than 11.5 μm.
0 to 300 mg, and 2 when the total thickness is 10.5 ± 1 μm
The magnetic recording medium according to claim 1 or 3, wherein the magnetic recording medium has an amount of 0 to 90 mg, and an amount of 10 to 70 mg when the total thickness is thinner than 9.5 µm. 12. The magnetic recording medium at 23 ° C. and 70% R
The magnetic recording medium according to claim 1 or 3, wherein the crack generation elongation of the magnetic layer measured by H is 20% or less. 13. The Cl / Fe spectrum α of the surface of the upper magnetic layer of the magnetic recording medium measured by an X-ray photoelectron spectrometer is 0.3 to 0.6, and the N / Fe spectrum β is 0. The magnetic recording medium according to claim 1 or 3, wherein the magnetic recording medium has a thickness of 03 to 0.12. 14. The surface of the upper magnetic layer at 23 ° C. and 70%
4. The magnetic recording medium according to claim 1, wherein the wear of the steel ball of RH is 0.7 × 10 ^{−5 to} 5 × 10 ⁻⁵ mm ³ . 15. The number of visually observed abrasives on the surface of the upper magnetic layer is 0.1 / μm ² or more when 5 sheets of the magnetic recording medium are photographed with an SEM (electron microscope) at a magnification of 50,000 times. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is a magnetic recording medium. 16. The upper magnetic layer of the magnetic recording medium comprises 1M
Recorded at a short wavelength of Hz, magnetically developed with ferri colloid, and observed with a differential interference microscope at 10 times 5 mm.
4. The magnetic recording medium according to claim 1, wherein the number of continuous black or white lines in the width sample is 5 or less. 17. The in-plane squareness ratio in the coating direction (longitudinal direction) of the upper magnetic layer of the magnetic recording medium is 0.7 or more, and the squareness ratio in the vertical direction is 0.6 or more. The magnetic recording medium according to claim 1.