JPH11273051A - Magnetic recording media - Google Patents

Abstract

(57) [Problem] To provide a high-output magnetic recording medium in which the surface state is controlled without performing a polishing step of a magnetic layer and the spacing loss is reduced. SOLUTION: In an elemental analysis of an upper magnetic layer surface measured by X-ray photoelectron spectroscopy using a needle-shaped ferromagnetic metal powder mainly composed of Fe having a major axis length of 100 nm or less, the X-ray photoelectron spectroscopy measuring apparatus is used. 5 ° angle between detector and the surface
And the ratio of the number of atoms of iron to carbon is 0.05 or more, and the center line average roughness Ra of the upper magnetic layer is
Is 8 nm or less, the thickness is 0.05 μm or less, and the longitudinal squareness ratio of the magnetic recording medium is 0.88 or more.

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 having an improved output from a low frequency to a high frequency and a reduced amount of wear of a magnetic head.

[0002]

2. Description of the Related Art As one means for reducing the spacing loss between a magnetic layer and a magnetic head during recording and reproduction of a magnetic recording medium and improving reproduction output, a magnetic recording medium has It is common practice to polish the surface of the magnetic layer in the finishing step, to adjust the thickness of the lubricant layer covering the surface of the magnetic layer, or to control the surface shape of the magnetic layer. However, since such polishing is generally performed mechanically using a polishing tape or a blade, it is not easy to precisely control the thickness of the lubricant layer and the surface shape of the magnetic layer, In some cases, the surface may be roughened and the output may be reduced. Therefore, means for controlling the surface state without performing a polishing step has been desired.

[0003] As a conventional technique relating to the surface state of a magnetic layer, as described in JP-A-8-138232 and JP-A-9-16949, elemental analysis by X-ray photoelectron spectroscopy is used. There is known a magnetic recording medium in which the distribution of various elements on the surface of a magnetic layer is controlled. However, the technique described in Japanese Patent Application Laid-Open No. 8-138232 does not measure the distribution state of carbon on the surface of the magnetic layer, that is, the state of presence of organic substances. No knowledge about the thickness of the layer can be obtained, and the spacing loss cannot be reduced. Further, the technology described in Japanese Patent Application Laid-Open No. 9-16949 only focuses on the gradient of the abundance of the lubricant, and cannot obtain knowledge on the thickness of the lubricant layer or the thickness of the organic material layer. Pacing loss cannot be reduced.

Accordingly, it is an object of the present invention to provide a high-output magnetic layer which can control the surface state without performing a polishing step of the magnetic layer, reduce spacing loss, and have good wear resistance and head wear resistance. It is to provide a recording medium.

[0005]

Means for Solving the Problems The present inventors have found that the ratio of a specific element on the surface of a magnetic layer measured by X-ray photoelectron spectroscopy is a measure of spacing loss, and has further studied. As a result, when a ferromagnetic powder having a major axis length less than or equal to a specific value is used, the ratio at the pole surface of the magnetic layer is set to a specific value or more, and the surface roughness and thickness of the magnetic layer are increased. Each below a certain value,
Further, it has been found that the above object can be achieved by setting the squareness ratio of the magnetic recording medium to a specific value or more.

The present invention has been made on the basis of the above-described findings. On one surface of a support, a lower layer containing a powder and a binder, an acicular ferromagnetic metal powder mainly composed of iron, a binder and In a magnetic recording medium provided with an upper magnetic layer containing a lubricant in this order, the ferromagnetic metal powder having a major axis length of 100 nm or less is used, and the upper magnetic layer is measured by X-ray photoelectron spectroscopy. In the elemental analysis of the surface of the magnetic layer, iron (F) was measured when the angle between the detector of the X-ray photoelectron spectroscopy measuring apparatus and the surface was set to 5 °.
e) and the ratio of the number of atoms of carbon (C) (Fe / C) is 0.0
5 or more, and the center line average roughness Ra of the upper magnetic layer is 8 nm or less and the thickness is 0.5 μm or less;
Further, the above object has been attained by providing a magnetic recording medium characterized in that the squareness ratio in the longitudinal direction of the magnetic recording medium is 0.88 or more.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the magnetic recording medium of the present invention will be described below with reference to the drawings. here,
FIG. 1 is a schematic diagram showing an example of the configuration of the magnetic recording medium of the present invention, and FIG. 2 is a schematic diagram showing the state of the surface of the upper magnetic layer.

In the magnetic recording medium 1 shown in FIG. 1, a lower layer 3 is provided on one surface of a support 2 adjacent to the support 2 and adjacent to the lower layer 3 as an uppermost layer. An upper magnetic layer 4 is provided. A back coat layer 5 is provided on the other surface of the support 2. Lower layer 3
The upper magnetic layer 4 contains a powder such as a nonmagnetic powder and a binder, and the needle-like ferromagnetic metal powder mainly composed of iron, a binder and a lubricant.

The magnetic recording medium shown in FIG.
(1) to (4). (1) As the ferromagnetic metal powder contained in the upper magnetic layer 4, one having a major axis length of 100 nm or less is used. (2) In elemental analysis of the surface of the upper magnetic layer measured by X-ray photoelectron spectroscopy (hereinafter referred to as XPS), when the angle between the detector of the XPS measuring device and the surface is set to 5 °, and the measurement is performed. The ratio of the number of atoms of iron (Fe) to the number of atoms of carbon (C) (Fe / C) is 0.05 or more. (3) The center line average roughness Ra of the upper magnetic layer 4 is 8 nm or less and the thickness is 0.5 μm or less. (4) The squareness ratio Sq in the longitudinal direction of the magnetic recording medium 1 is 0.88
That is all. By satisfying all of the above requirements (1) to (4), the condition of the surface of the upper magnetic layer 4 in the magnetic recording medium 1 is improved, the spacing loss is reduced, the output is improved, and the wear of the magnetic head is improved. The present inventors have found for the first time that is reduced. Such a magnetic recording medium eliminates the need for polishing in a finishing step in the manufacture of the magnetic recording medium and wiping off polishing debris generated by the polishing, thereby simplifying the manufacturing process and reducing the manufacturing cost. Is also played. Hereinafter, the above requirements (1) to (4) will be described in detail.

The requirement (1) specifies that the ferromagnetic metal powder 7 contained in the upper magnetic layer 4 should have a major axis of 100 nm or less. Long axis length is 1
The above-mentioned ferromagnetic powder having a size of 00 nm or less is suitable for high-density recording. However, since the ferromagnetic powder 7 having such a small particle diameter is liable to cause agglomeration between particles, if a thin magnetic layer is formed using a paint containing such a powder, the presence of the magnetic powder on the surface of the upper magnetic layer The amount becomes extremely low, and the surface roughness becomes large, so that the space loss increases and high output cannot be obtained. Therefore, in the magnetic recording medium of the present invention, by satisfying the requirements (2) to (4), aggregation between particles is prevented without impairing the properties of the ferromagnetic powder 7, The goal has been achieved. A preferred range of the long axis length is 60 to 95 nm, and a more preferred range is 65 to 85 nm. The needle ratio of the ferromagnetic metal powder 7, that is, the ratio of the major axis to the minor axis is 3 to
8 is preferable and 2 to 7 are more preferable. Further, the BET specific surface area is 30 to 70 m ² / g, particularly 40 to 70 m ² / g.
It is preferred that The major axis length of the ferromagnetic metal powder is determined from an average value of n = 100 by observation with a transmission electron microscope.

Next, the requirement (2) will be described. XP
S is a method of performing elemental analysis of an irradiated portion by measuring the energy of electrons generated from atoms irradiated with X-rays. In the present invention, the elemental analysis of the extreme surface from the outermost surface of the upper magnetic layer to a depth of several nm is performed by setting the angle between the detector of the XPS measuring apparatus and the surface of the magnetic recording medium to 5 ° ( (See FIG. 2).

As shown in FIG. 2, in the upper magnetic layer 4, a needle-like ferromagnetic powder 7 mainly composed of iron is present in a state where its periphery is covered with a binder or a lubricant. The Fe atom observed in the above measurement is derived from the ferromagnetic powder 7 and is
Since the atoms are derived from a binder, a lubricant, etc., the observed F
The value of e / C means the abundance of the ferromagnetic powder 7 with respect to the binder, the lubricant and the like on the extreme surface of the upper magnetic layer.
When the value of Fe / C is 0.05 or more, a high output can be obtained in the magnetic recording medium of the present invention having a thin upper magnetic layer. When the value of Fe / C is 0.05 to 0.2, particularly 0.07 to 0.1, the abrasion resistance of the medium is improved, and the head abrasion resistance is reduced.

With respect to the magnetic properties of the ferromagnetic metal powder 7, the coercive force is 120 to 250 kA / m, particularly 150 kA / m.
２５０250 kA / m, and its saturation magnetization is 100-150 Am ² / kg, particularly 110-150 A
It is preferably m ² / kg.

Preferred examples of the ferromagnetic metal powder 7 include those in which the metal content is 70% by weight or more and 60% by weight or more of the metal content is iron. Co, Fe-Ni, Fe-Al, Fe-Ni
Alloys mainly composed of iron, such as -Al, Fe-Co-Ni, Fe-Ni-Al-Zn and Fe-Al-Si.

The ferromagnetic metal powder 7 may be subjected to various surface treatments, if necessary, for example, the surface treatment described in JP-A-9-35246, column 4, lines 9 to 24, or a transition metal such as aluminum or lanthanum. Surface treatment using an element may be performed.

The above requirement (3) defines that the center line average roughness Ra of the upper magnetic layer 4 is 8 nm or less. Together with this requirement (1) and (2),
The surface properties of the upper magnetic layer 4 become extremely good, and spacing loss between the upper magnetic layer 4 and the magnetic head is reduced. A preferred range of the center line average roughness Ra is 6.0 to 1.0 nm, and a more preferred range is 3.0 to 1.5 nm. The center line average roughness Ra is measured by a Zygo Laser Interferometric Mi.
It was measured using the croscope Maxim 3D Model 5700 under the following conditions. -Filter: Fixed-Remove: Cylinder-Filter Freg: 4.0 (1 / mm)-Filter Wavelength: 0.250 (mm)-Trim: 0-Trim Move: All-Lens: Fizeau x 40

The above requirement (3) also stipulates that the thickness of the upper magnetic layer 4 is 0.5 μm or less. That is, the upper magnetic layer 4 is an extremely thin magnetic recording layer. By making the upper magnetic layer 4 thin, self-demagnetization hardly occurs, and a high-density magnetic recording medium having high electromagnetic conversion characteristics can be obtained.
The preferable range of the thickness of the upper magnetic layer is 0.05 to 0.2 μm.
m, more preferably 0.05 to 0.15 μm, and still more preferably 0.08 to 0.12 μm.

The above requirement (4) specifies that the squareness ratio Sq in the longitudinal direction of the magnetic recording medium 1 is 0.88 or more. This requirement serves as a measure of the orientation state of the ferromagnetic metal powder 7 and the output characteristics of the magnetic recording medium 1. A combination of this requirement and the requirements (1) to (3) provides a favorable result. A magnetic recording medium having a surface property and a high output can be obtained. The squareness ratio Sq is preferably 0.90 or more,
More preferably, it is 0.92 or more. In the present specification, the “longitudinal direction of the magnetic recording medium” means the longitudinal direction of the tape when the magnetic recording medium is in a tape shape.
When the magnetic tape is used in a helical scan type recording / reproducing drive, the writing direction of the track is also included. When the magnetic recording medium is in the form of a disk, it means the longitudinal direction of the long magnetic recording medium before punching on the disk.

Preferred methods for obtaining a magnetic recording medium satisfying the above requirements (1) to (4) include, but are not limited to, the following. (i) The upper magnetic layer 4 does not contain a curing agent. This prevents the hardener from excessively seeping out to the surface of the upper magnetic layer, and improves the seepage of the lubricant from the lower layer. As described below, the lower layer may contain a curing agent as needed. (ii) In the paint for the upper magnetic layer, only fatty acids are used as lubricants,
The lower layer paint contains fatty acids and fatty acid esters,
Optimizes the amount of lubricant leached into the upper magnetic layer. (iii) As a powder contained in the lower layer, a powder having a particle size of 80 nm or less is used in an amount of 70% by weight or more, preferably 90% by weight or more based on all powders contained in the lower layer. Thereby, the roughness of the interface between the upper and lower layers can be suppressed, and the lubricant contained in the lower layer can be supplied to the upper magnetic layer in a favorable state. (iv) Control the magnetic field orientation and calendar processing conditions during the production of the medium. As a result, the upper magnetic layer is prevented from being roughened, and the ratio of the ferromagnetic powder present on the surface of the upper magnetic layer to an organic substance such as a lubricant or a binder, that is, the value of Fe / C can be controlled well. The above-mentioned means (i) to (iv) may be used in any combination of two or more.

Next, details of each layer and the support constituting the magnetic recording medium 1 shown in FIG. 1 will be described. The upper magnetic layer 4 is the uppermost layer of the magnetic recording medium 1 and contains the ferromagnetic metal powder, a binder and a lubricant. Among these components, the ferromagnetic metal powder has already been described, and therefore will not be described here. As the binder, for example, a vinyl chloride resin, a polyurethane resin, or a nitrocellulose resin is used. These binders include hydroxyl groups, carboxyl groups, sulfo groups, phosphate groups, nitro or nitrate groups, acetyl groups, sulfates, epoxy groups, nitrile groups, carbonyl groups, amino groups, alkylamino groups, alkyl It is also preferable to contain a polarizable functional group (a so-called polar group) such as an ammonium base, a betaine structure such as sulfobetaine and carbobetaine. In particular, when a combination of a vinyl chloride resin containing a hydroxyl group, an epoxy group, a sulfo group or a sulfate group and a polyurethane resin containing a hydroxyl group or a sulfo group is used, the dispersibility of the ferromagnetic metal powder is good. This is preferable because a magnetic recording medium satisfying the above requirements (1) to (4) can be easily obtained. in this case,
The weight ratio of the two (the former / the latter) is from 20/80 to 70/30.
Is preferred from the viewpoint of further improving dispersibility. The binder is preferably blended in an amount of 1 to 30 parts by weight, particularly 2 to 15 parts by weight, based on 100 parts by weight of the ferromagnetic metal powder, from the viewpoint of further improving dispersibility.

As the lubricant, it is preferable to use a fatty acid as described in the above (ii). Fatty acids include those having 8 to 28 carbon atoms, and examples thereof include myristic acid, palmitic acid, stearic acid, isostearic acid, and oleic acid. The lubricant is used in an amount of 0.1 to 5 parts by weight, especially 0.5 to 5 parts by weight, based on 100 parts by weight of the ferromagnetic powder, in order to further control the degree of leaching.
Preferably, it is added in an amount of up to 2 parts by weight.

In addition to the above-described components, components that can enhance various performances of the magnetic recording medium 1 may be added to the upper magnetic layer 4 if necessary. For example, an abrasive material (particles of an inorganic substance having a Mohs hardness of 8 or more, such as alumina or chromium oxide) that can increase the durability of the magnetic recording medium 1, can improve the running property of the magnetic recording medium 1, and can provide an antistatic property. Carbon black or the like can be added. The abrasive and carbon black are each based on 100 parts by weight of the ferromagnetic metal powder.
2 to 20 parts by weight, especially 3 to 15 parts by weight, and 0.1 to 1
0 parts by weight, particularly preferably 0.1 to 5 parts by weight, is blended.

The upper magnetic layer 4 is formed by applying a coating material for the upper magnetic layer, in which the above-described components are dispersed in a solvent, on the lower layer 3 and drying the coating. The paint for the upper magnetic layer is preferably prepared as follows. That is, the ferromagnetic metal powder and the binder are put into a Nauta mixer or the like together with a part of the solvent and preliminarily mixed to obtain a mixture. The mixture is kneaded by a continuous press kneader or the like or a twin screw kneader. At this time, by kneading under conditions of high shear, for example, kneading at a shear rate of 1000 [1 / s] or more, the dispersibility of the ferromagnetic metal powder is improved, and the above requirement (1) is satisfied. The upper magnetic layer 4 can be easily obtained. Next, the mixture is diluted with a part of the solvent, subjected to dispersion treatment using a sand mill or the like, and finally filtered to be prepared.

The lower layer 3 is formed by dispersing various powders in a binder, and may be magnetic or non-magnetic. As the powder, a ferromagnetic powder, a non-magnetic powder, an abrasive, carbon black or the like is used. As described in (iii) above, these powders have a particle size of 80%.
It is preferable that the particles having a diameter of not more than nm be used in an amount of 70% by weight or more based on the total amount of the powder.

As the ferromagnetic powder, in addition to the ferromagnetic metal powder contained in the upper magnetic layer 4, a ferromagnetic iron oxide powder such as γ-iron oxide and a ferromagnetic powder such as a plate-like hexagonal barium ferrite can be used. Examples thereof include hexagonal ferrite powder, metal soft magnetic powder and oxide soft magnetic powder.

The nonmagnetic powder is used for controlling the magnetostatic characteristics of the lower layer 3 or controlling the film rigidity. Specific examples of the non-magnetic powder include inorganic powders having a Mohs hardness of less than 8 described in column 9, line 44 to column 10, line 7 of JP-A-9-35246. As the inorganic powder, α-iron oxide, titanium oxide and calcium carbonate are preferred. The inorganic powder preferably has a needle-like shape. Its particle size is 5-100 nm, especially 5-8
It is preferably 0 nm. When the lower layer 3 is a layer having magnetism, that is, when the lower layer 3 contains the ferromagnetic powder, the ferromagnetic powder and the non-magnetic powder
It is preferable to mix at a weight ratio of ８０80/20. By setting the blending amount of the nonmagnetic powder in the above range in relation to the blending amount of the ferromagnetic powder, aggregation between the ferromagnetic powders in the lower layer 3 is suppressed, and leakage of magnetic flux from the lower layer 3 is improved. Thus, the effect of improving the output is increased and the disturbance at the interface between the lower layer 3 and the upper magnetic layer 4 can be suppressed.

Other powders contained in the lower layer 3 include, as in the case of the upper magnetic layer 4, abrasives (here, those having a Mohs hardness of 8 or more) and carbon black. As these powders, the same components as those contained in the upper magnetic layer 4 can be used. Therefore, although the details of these components are not particularly described here, the detailed description regarding the powder contained in the upper magnetic layer 4 is appropriately applied. Preferred amounts of these powders are as follows with respect to 100 parts by weight of the nonmagnetic powder or 100 parts by weight of the total amount of the ferromagnetic powder and the nonmagnetic powder. Abrasive material: 1 to 30 parts by weight, especially 1 to 12 parts by weightCarbon black: 0.5 to 30 parts by weight, particularly 1 to 2 parts
0 parts by weight

As the binder contained in the lower layer 3, the same binder as that contained in the upper magnetic layer 4 can be used. In particular, it is preferable to use a combination of the above-mentioned vinyl chloride resin and the above-mentioned polyurethane resin as a preferable binder contained in the upper magnetic layer 4.
The binder is preferably blended in an amount of 1 to 50 parts by weight, particularly 2 to 25 parts by weight, based on 100 parts by weight of the nonmagnetic powder or 100 parts by weight of the total of the ferromagnetic powder and the nonmagnetic powder.

The lower layer 3 preferably contains a lubricant. As the lubricant, it is preferable to use fatty acids and fatty acid esters as described in (ii) above. As the fatty acid, the same fatty acid as that contained in the upper magnetic layer 4 is used. Examples of the fatty acid ester include an alkyl ester of the fatty acid, and those having a total carbon number of 12 to 40 are preferable. Fatty acid and fatty acid ester have a weight ratio (former / latter) of 10/1 to 1/10, particularly 5/1.
It is preferred that the content be contained so as to be １ ／ of that, because the degree of leaching of the lubricant is further controlled. The lubricant is used in an amount of 1 to 2 parts by weight based on 100 parts by weight of the nonmagnetic powder or the total amount of the ferromagnetic powder and the nonmagnetic powder of 100 parts by weight.
0 parts by weight, particularly preferably 3 to 10 parts by weight, is blended.

The lower layer 3 may contain a curing agent, if necessary. In this case, the curing agent is added in an amount of 0.1 to 8 parts by weight, particularly 0.5 to 4 parts by weight, based on 100 parts by weight of the nonmagnetic powder or 100 parts by weight of the total of the ferromagnetic powder and the nonmagnetic powder. Is preferred.

The lower layer 3 is formed by applying a lower layer coating material in which the above-mentioned components are dispersed in a solvent on the support 2 and drying it. And the dry thickness of the lower layer 3 is 0.1.
It is preferably from 5 to 2.0 μm, particularly preferably from 0.8 to 1.2 μm. When the dry thickness is less than 0.5 μm, the coatability of the lower layer paint is deteriorated and dropout may increase. When the dry thickness is more than 2.0 μm, the entire thickness of the magnetic recording medium is increased, so that it is used as a magnetic tape. In this case, the winding diameter becomes large, and the recording becomes unsuitable for a long time.

The back coat layer 5 is formed by applying a back coat paint mainly containing a binder and a powder (for example, carbon black or various inorganic powders) on the back surface of the support 2 and drying it. As the binder and carbon black, those similar to those used in the upper magnetic layer 4 and the lower layer 3 can be used. In particular, it is preferable to use a combination of the above-described polyurethane-based resin and the above-mentioned vinyl chloride-based resin as exemplified for the description of the upper magnetic layer 4 as the binder. Further, it is also preferable to use two types of carbon black having an average particle diameter of 1 to 50 nm and an average particle diameter of 50 to 700 nm. The total amount of the powder containing carbon black is preferably 5 to 100 parts by weight, particularly preferably 10 to 70 parts by weight, based on 100 parts by weight of the total binder contained in the back coat layer 5. The thickness of the back coat layer 5 is set to 0.05 in consideration of the balance with the thicknesses of the upper magnetic layer 4 and the lower layer 3.
It is preferably from 0.8 to 0.8 μm, particularly preferably from 0.1 to 0.7 μm.

Incidentally, as for the points which are not particularly described with respect to the back coat layer 5 and the lower layer 3, the detailed description regarding the upper magnetic layer 4 is appropriately applied.

As the support 2, a known support can be used as long as it is for a magnetic recording medium. Specifically, those described in column 2, lines 30 to 42 of JP-A-9-35246 can be used.
Among these, polyethylene terephthalate (PE
Nonmagnetic materials such as T), polyethylene naphthalate (PEN) and polyamide (PA) are preferred. The thickness of the support 2 is preferably 8 μm or less, particularly preferably 6 μm or less, in order to increase the capacity of the magnetic recording medium. Further, a different adhesive layer may be provided on the surface of the support 2 to enhance the adhesiveness with the lower layer 3 and the back coat layer 5.

With respect to the magnetostatic properties of the magnetic recording medium 1 composed of the above-described layers and the support, the squareness ratio Sq is as described above. The coercive force is 120 to 270 kA / m,
In particular, it is preferably 150 to 250 kA / m, and the saturation magnetic flux density is 0.35 to 0.55 T, particularly 0.4 to 0.
It is preferably 5T.

Next, an outline of a preferred method of manufacturing the magnetic magnetic recording medium 1 shown in FIG. 1 will be described. First, a coating for the upper magnetic layer forming the upper magnetic layer 4 and a coating for the lower layer forming the lower layer 3 are simultaneously coated on the support 2 by a wet-on-wet method so that each layer has a predetermined thickness. To form a coating film of the upper magnetic layer 4 and the lower layer 3. That is, the upper magnetic layer 4 is preferably applied and formed when the lower layer 3 is wet. Next, after performing a magnetic field orientation treatment on these coating films, a drying treatment is performed and the film is wound. By appropriately controlling the conditions of the magnetic field orientation treatment, the degree of orientation of the ferromagnetic metal powder becomes appropriate, and
(4) A magnetic recording medium having (4) can be easily obtained. Preferred conditions for the magnetic field orientation treatment are as follows:
The condition is such that the magnet passes through a solenoid magnet of 0T, especially 0.5 to 0.8T. Thereafter, a calendar process is performed. By appropriately controlling the conditions of the calendering process, the surface state of the upper magnetic layer 4 can be controlled, and a magnetic recording medium satisfying the above requirement (3) can be easily obtained. Preferred conditions for calendering are
Temperature 80-120 ° C, especially 90-110 ° C, linear pressure 300
~ 600kgf / cm, especially 400 ~ 500kgf / c
m. Next, a back coat paint is applied on the back surface of the support 2 to form a back coat layer 5. Alternatively, after forming the back coat layer 5, the upper magnetic layer 4 and the lower layer 3 may be formed. Then, 6-1 at 40-80 ° C.
Aging treatment is performed for 00 hours. For example, in the case of manufacturing a magnetic tape, slitting is performed to a desired width. In the conventional method for manufacturing a magnetic recording medium, polishing of the surface of the magnetic tape and wiping of polishing debris generated by the polishing were performed as a finishing step. Since the surface properties are good, there is no need to perform these steps. Therefore, there is an advantage that the manufacturing process is simplified and the manufacturing cost is reduced.

Although the magnetic recording medium of the present invention has been described based on the preferred embodiments, the present invention is not limited to the above-described embodiments, and various changes can be made without departing from the spirit of the present invention. . For example, the magnetic recording medium 1 of the embodiment shown in FIG. 1 is further provided with a primer layer between the support 2 and the lower layer 3 or the back coat layer 5 or corresponds to a hard system using a long wavelength signal. Another magnetic layer or another layer for recording a servo signal or the like may be provided. Further, the magnetic recording medium of the present invention is suitable as a magnetic tape such as an image / audio recording tape such as an 8 mm video tape, a DAT tape, and a DVC tape, and a data recording tape such as a DDS tape and a 1/4 inch data cartridge (QIC) tape. However, the present invention can be applied to other magnetic recording media such as a magnetic disk such as a flexible disk.

[0038]

The present invention will be described in more detail with reference to the following examples and the effectiveness thereof will be illustrated. However, the scope of the present invention is not limited to such an embodiment.
In the following examples, "parts" and "%" mean "parts by weight" and "% by weight", respectively, unless otherwise specified.

Example 1 The following components (excluding the curing agent) were kneaded in a kneader, dispersed by a stirrer, finely dispersed by a sand mill, and filtered by a 1 μm filter. With respect to the lower layer paint, a curing agent was added last to prepare an upper magnetic layer paint, a lower layer paint, and a back coat paint. In addition, the shear rate at the time of kneading was 3000 [1 / s] for both paints. In addition, the lower layer paint contains powder having a particle size of 80 nm or less in the total powder.
6% was included.

<Coating for upper magnetic layer> 100 parts of acicular Fe-based ferromagnetic metal powder (coercive force: 187 kA / m, saturation magnetization: 150 Am ² / kg, major axis length: 85 nm, X-ray particle size: 15 nm)・ Α-alumina (average particle size: 0.3 μm) 5 parts ・ Carbon black (average particle size: 40 nm) 1 part ・ Sulfo group, epoxy group and hydroxyl group-containing vinyl chloride resin 10 parts ・ Sulfo group-containing polyurethane resin 3 Parts-palmitic acid 2 parts-methyl ethyl ketone 150 parts-toluene 150 parts-cyclohexanone 150 parts

<Coating for lower layer> 100 parts of α-Fe ₂ O ₃ (acicular, major axis length: 80 nm) 7 parts of α-alumina (average particle diameter: 0.3 μm) 7 carbon black (average particle diameter: 2 parts ・ Sulfo group, epoxy group and hydroxyl group-containing vinyl chloride resin 10 parts ・ Sulfo group-containing polyurethane resin 4 parts ・ Palmitic acid 2 parts ・ Butyl stearate 2 parts ・ Isocyanate type curing agent 0.5 parts ・ Methyl ethyl ketone 150 parts ・ Toluene 150 parts ・ Cyclohexanone 150 parts

<Coating for backcoat layer> 65 parts of carbon black (average particle diameter: 17 nm) 15 parts of carbon black (average particle diameter: 50 nm) 70 parts of nitrocellulose resin 10 parts of polyurethane resin 10 vinyl chloride Resin 30 parts ・ Stearic acid 2 parts ・ Isopropyl stearate 2 parts ・ Methyl ethyl ketone 150 parts ・ Toluene 150 parts ・ Cyclohexanone 150 parts

The resulting upper magnetic layer coating material and lower layer coating material were coated on a PET support having a thickness of 6.5 μm by die coating so that the lower layer dry thickness was 1.0 μm and the upper magnetic layer dry thickness was 0.2 μm. At the same time. Next, while the upper magnetic layer changes from a wet state to a dry state,
A magnetic field orientation treatment was performed by a solenoid having a magnetic field strength of 0.5T. Further, the coating film was dried by blowing hot air at 80 ° C. at a speed of 10 m / min in a drying furnace. 90 ℃ after drying, 3
A 7-stage super calender treatment was performed under the condition of 00 kgf / cm, and the above-mentioned back coat paint was further applied on the surface on the opposite side of the support so as to have a dry thickness of 0.4 μm.
It dried at ° C and formed the back coat layer. Finally, 6.
A magnetic tape having a structure shown in FIG. 1 was manufactured by slitting to a width of 35 mm. In the finishing step, the upper magnetic layer was not polished.

Example 2 A magnetic tape was obtained in the same manner as in Example 1 except that the shear rate during kneading of the two paints was 2000 [1 / s].

Example 3 A kneaded Fe-based ferromagnetic powder having a shear axis of 1000 [1 / s] and a major axis length of 100 nm was used as the acicular Fe-based ferromagnetic powder contained in the coating for the upper magnetic layer. A magnetic tape was obtained in the same manner as in Example 1 except that the magnetic tape was used.

Example 4 In both coatings, the shear rate during kneading was set to 1000 [1 / s], the magnetic field strength during the magnetic field orientation treatment was set to 0.3 T, and the needle-like Fe contained in the coating for the upper magnetic layer was used. A magnetic tape was obtained in the same manner as in Example 1 except that a long axis length of 100 nm was used as the system ferromagnetic powder.

Example 5 In place of 100 parts of α-Fe ₂ O ₃ contained in the lower layer paint of Example 1, 60 parts of the same α-Fe ₂ O ₃ were used.
-Fe ₂ O ₃ and 40 parts of hexagonal barium ferrite (coercive force: 180 kA / m, saturation magnetization: 60 Am ² / k
g, plate diameter: 30 nm, and plate ratio: 7), except that magnetic tape was obtained in the same manner as in Example 1.

Comparative Example 1 To the coating material for the upper magnetic layer of Example 1, 2 parts by weight of a curing agent was added to 100 parts by weight of the acicular Fe-based ferromagnetic powder. Fe
_A magnetic tape was obtained in the same manner as in Example 1 except that a long axis length of 120 nm was used as ₂ O ₃ .

Comparative Example 2 The procedure of Example 3 was repeated except that the amounts of the vinyl chloride resin and the polyurethane resin contained in the coating material for the upper magnetic layer of Example 3 were changed to 14 parts by weight and 8 parts by weight, respectively. To obtain a magnetic tape.

Comparative Example 3 A magnetic tape was obtained in the same manner as in Example 3 except that the conditions of the calender treatment in Example 3 were changed to 80 ° C. and 200 kgf / cm.

Comparative Example 4 A magnetic tape was obtained in the same manner as in Example 3 except that a magnetic field orientation treatment was performed by applying a magnetic field of 0.1 T in place of the magnetic field direction processing conditions in Example 3.

<Evaluation of Performance> The magnetic tapes obtained in Examples and Comparative Examples were subjected to elemental analysis in the depth direction of the surface of the upper magnetic layer measured by the XPS method to obtain θ = 5.
The value θ of Fe / C when set to ° was measured by the following method. The center line average roughness Ra of the upper magnetic layer was measured by the above-described method, and the squareness ratio Sq of the magnetic tape was measured.
Was measured by the following method. Further, the output of the magnetic tape and the wear amount of the magnetic head were measured by the following methods.
Table 1 shows the results.

<Element analysis method by XPS method> VG SCIEN
The measurement was performed using MICROLAB 320-D manufactured by TIFIC. The sample was fixed with carbon tape and the inside of the chamber was 1.5
Vacuum evacuation was performed to about 3.0 × 10 ⁻⁶ Pa, and measurement was performed 60 minutes later. The measurement was performed using Mgkα radiation as the X-ray source, irradiation energy of 200 W, and a distance between the sample and the X-ray source of 1 cm. C-1s spectrum for carbon atoms, Fe-2p ^3/2 spectrum for iron atoms, 1 for each
Scanning was performed 0 times at a time, and an integrated intensity was obtained with an integration time of 9.2 minutes. The channel of the detector was 100 ms and the path energy was 20 eV. Note that a straight line was used for the background.

<Measurement of Squareness Ratio Sq> VS manufactured by Riken Denshi Co., Ltd.
M was measured. The measurement condition is that the maximum applied magnetic field is 10
kOe (796 kA / m), sweep was 10 minutes / 1 loop.

<Output> A commercially available DVC camcorder was modified and measured. The relative speed between the tape and the head is 1
0.2 m / s. Measurement is in the low band (frequency 10.5M
Hz, wavelength 0.98 μm) and high frequency (frequency 21 MH)
z, wavelength 0.49 μm).

<Amount of Wear of Magnetic Head> As shown in FIGS. 3A and 3B, a sendust square member 20 having a square cross section of 0.5 cm on a side and a length of 2.5 cm is used. Sendust is generally used as a magnetic material for a magnetic head. The surface of the magnetic layer is brought into contact with one edge of the sendust square member 20 at a wrap angle θ = 12 ° so that the longitudinal direction of the magnetic tape 21 is orthogonal to the longitudinal direction of the sendust square member 20. Next, at 23 ° C, 50
% RH in an environment of 40 to 45 g / c.
At 200 mm / sec under a tension of m. The tape running length was 50 m × 10 times. The ridge is worn by running. The wear width W of the ridge (see FIG. 3B) is observed and measured from above the ridge using an optical microscope. The wear width W is used as a measure of the wear amount of the magnetic head.

[0057]

[Table 1]

As is clear from the results shown in Table 1, the magnetic tape of the example (the product of the present invention) has a higher output in both the low and high frequency ranges than the magnetic tape of the comparative example. Is obtained. It can also be seen that the amount of head wear is small due to the smooth surface.

[0059]

As described above, according to the present invention,
The surface state is controlled without performing the polishing step of the magnetic layer, and a high-output magnetic recording medium with reduced spacing loss can be obtained. According to the present invention, a magnetic recording medium having good wear resistance and good head wear resistance can be obtained. Further, according to the present invention, the manufacturing process is simplified,
A magnetic recording medium with reduced manufacturing costs can be obtained. Also,
According to the present invention, it is possible to obtain a magnetic recording medium with reduced calendar contamination in the manufacturing process.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of a configuration of a magnetic recording medium of the present invention.

FIG. 2 is a schematic diagram showing a state of a surface of an upper magnetic layer.

FIGS. 3A and 3B are schematic diagrams showing a method of measuring the wear amount of a magnetic head.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnetic recording medium 2 Support 3 Lower layer 4 Upper magnetic layer 5 Back coat layer 6 Detector 7 Needle-like ferromagnetic metal powder mainly composed of iron 8 Coating 9 Lubricant layer

Claims (1)

[Claims] 1. A lower layer containing a powder and a binder, and an upper magnetic layer containing a needle-like ferromagnetic metal powder mainly composed of iron, a binder and a lubricant on one surface of a support. In the magnetic recording medium provided in this order, a ferromagnetic metal powder having a major axis length of 100 nm or less is used. In the elemental analysis of the upper magnetic layer surface measured by X-ray photoelectron spectroscopy, the X The ratio of the number of atoms of iron (Fe) to the number of atoms of carbon (C) when the angle between the detector of the X-ray photoelectron spectrometer and the surface was set to 5 ° (Fe /
C) is 0.05 or more, the center line average roughness Ra of the upper magnetic layer is 8 nm or less, the thickness is 0.5 μm or less, and the squareness ratio in the longitudinal direction of the magnetic recording medium is 0. A magnetic recording medium having a diameter of 88 or more.