JPH0766523B2 - Magnetic recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to a magnetic recording medium using a polyimide film as a base film.

[Prior Art] Conventionally, as a magnetic recording medium, a thin film type magnetic recording medium using a thin film deposition method such as a vacuum deposition method, a sputtering method, or a plating method, and a magnetic powder coating type magnetic recording medium are known. . In particular, the thin film type magnetic recording medium is capable of improving the recording density as compared with the magnetic powder coating type recording medium which is currently widely used, and is regarded as a promising next-generation recording medium.

On the other hand, when the thin film magnetic recording medium is manufactured, the heat of the base film is lost due to the radiation heat from the evaporation source and the incident particle energy. Further, as with the Co—Cr alloy of the perpendicular magnetic recording medium, there are cases where film formation at high temperature is necessary to obtain sufficient magnetic characteristics. As described above, since the substrate is required to have good heat resistance, it is said that a polyimide film, which has better heat resistance than general polyester, is suitable for a flexible substrate for tapes and floppy disks.

[Problems to be Solved by the Invention] In a magnetic recording medium, it is needless to say that it is necessary to bring out the performance of the recording layer and maintain it for a long period of time. Therefore, in addition to the characteristics of the magnetic recording layer, the surface property of the medium and protection or lubricity are important.
In particular, since the surface properties of the thin-film magnetic recording medium easily reflect the surface properties of the substrate, it is extremely important to finely control the surface irregularities of the substrate in terms of improving the output, durability, and running property of the magnetic recording medium. is there.

The surface of the magnetic recording layer is preferably flat in order to obtain a high output in recording / reproducing a short wavelength signal, but if the surface smoothness of the substrate or the magnetic recording medium during manufacture or after completion is too good, winding Wrinkles, winding tightness, adsorption between films (blocking), width deviation during film transport in the manufacturing process, winding unevenness, running defects in recording / playback equipment, etc. are likely to occur, and these conflicting requirements must be met. There are problems that must be addressed.

The present invention has been made to solve the above problems,
An object of the present invention is to provide a magnetic recording medium which is excellent in output characteristics, durability and running property, and is also excellent in handling in a manufacturing process.

[Means for Solving the Problems] The means taken in the present invention for achieving the above object will be described with reference to the accompanying drawings.
A polyimide film 3 having a polyimide coating layer 4 in which inorganic particles 2 are dispersed on one side is formed, and a magnetic recording layer 6 is formed on the other side. In the polyimide film 3, inorganic particles 2 dispersed in the polyimide coating layer 4 are formed. A measure is taken to obtain a magnetic recording medium in which inorganic particles 1 having a smaller average particle diameter are dispersed.

In the magnetic recording medium of the present invention, an aromatic diamine and an aromatic tetracarboxylic acid are polymerized in a solvent, and the inorganic particles 1
The polyamic acid solution in which the inorganic particles 2 having a larger average particle diameter than the inorganic particles 1 are dispersed is applied onto a polyamic acid film prepared by casting a polyamic acid solution in which is dispersed on a flat surface and removing the solvent. It can be produced by forming the magnetic recording layer 6 on the surface of the polyimide film 3 opposite to the polyimide coating layer 4 containing the inorganic particles 2 obtained by desolvation and imidization. A protective layer, a lubricating layer, or both may be laminated on the magnetic recording layer 6 of the obtained magnetic recording medium.

The polyimide film 3 is usually produced by casting a polyamic acid solution obtained by polymerizing an aromatic tetracarboxylic acid and an aromatic diamine on a flat surface, removing the solvent, and then imidizing at a high temperature. Examples of the aromatic tetracarboxylic acid include pyromellitic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, pyridine-2,3,5,6-tetracarboxylic dianhydride. Examples of aromatic diamines such as 2,3,6,7-naphthalenedicarboxylic acid dianhydride include paraphenylenediamine, diaminodiphenyl ether, diaminodiphenylmethane, diaminodiphenylsulfone, diaminonaphthalene and the like. Among them, as tetracarboxylic acid, pyromellitic dianhydride (PMDA) or 3,
It is preferable to use paraphenylenediamine (PPD) or diaminodiphenyl ether (DADE) as the 3 ', 4,4'-biphenyltetracarboxylic acid (BPDA) and diamine. Although these may be polymerized individually, it is possible to produce a polyimide film having desired mechanical properties or thermophysical properties as a magnetic recording medium by further copolymerizing three or four of the above four components. Is.

In order to make the mechanical and thermal properties suitable for magnetic recording media, the diamine component used to form the aromatic polyamic acid is about 40 to 95 mol% based on the total diamine component, especially It is preferable that the PPD is used in a proportion of 45 to 90 mol%, and DADE is used in a proportion of about 5 to 60 mol%, particularly 10 to 55 mol%, based on all diamine components. The tetracarboxylic acid component for producing the aromatic polyamic acid is about 10 to 90 mol% of the total tetracarboxylic acid component, particularly 15 to 85 mol% of BPDA, and the total tetracarboxylic acid component. About 10 for ingredients
It is preferably composed of PMDA in an amount of ˜90 mol%, particularly 15 to 85 mol%.

The same material may be used for the aromatic diamine and the aromatic carboxylic acid that compose the polyimide film 3 of the substrate 5 and the polyimide coating layer 4 used in the present invention, or different materials may be used. It is possible to achieve the object of the present invention.

The inorganic particles 1 contained in the polyimide film 3 are SiO ₂ , T
Oxide fine particles such as iO ₂ , Al ₂ O ₃ and MgO, CaCO ₃ , BaSO ₄ or fine particles of nitride or carbide can be used and can be uniformly dispersed in the polyamic acid solution forming the polyimide film 3.

The inorganic particles 1 form fine irregularities on the surface of the polyimide film 3 and contribute to the running property and durability when the film is used alone or as a magnetic recording medium. Since the magnetic recording layer 6 is formed on the surface having fine irregularities made of the inorganic particles 1, the average particle size and the addition amount of the inorganic particles 1 are determined as to the output of the magnetic recording layer 6 and the running and durability. Determined to be satisfied. That is, if the height of the surface roughness formed by the inorganic particles 1 is too large, the spacing loss causes a reduction in short wavelength output, and if it is too small, the effect of improving the running property and durability is small. In addition, when the projection density of the unevenness is low, the effect of improving durability is small, and when a large amount of the inorganic particles 1 is added to increase the density, the inorganic particles 1 aggregate with each other to become coarse particles, and the density is rough. Generates high protrusions. The preferred surface roughness for a magnetic recording medium is a ten-point average roughness (made by Taylor Hobson, measured by Taristep) of 100 to 600Å and a protrusion density of 10 ⁵ to 10 ⁸
The range is pcs / mm ² . That is, the average particle size of the inorganic particles 1 is preferably 200 to 1000Å, more preferably 300 to 800Å.

The polyamic acid solution in which the above-mentioned inorganic particles 1 are dispersed is usually cast on a smooth surface made of stainless steel, and the solvent is removed at a temperature of 100 to 150 ° C to prepare a polyamic acid film. On this polyamic acid film, a polyamic acid solution in which inorganic particles 2 having an average particle size larger than that of the inorganic particles 1 is dispersed is applied by a coating method such as a gravure coating method or a bar coating method. The laminated polyamic acid film thus obtained is imidized at a higher temperature to produce Expectation 5.

The surface irregularities formed by the inorganic particles 2 are higher than the surface irregularities formed by the inorganic particles 1, but the height is preferably 0.05 to 0.5 μm in terms of ten-point average roughness, and the protrusion density is , 10 ⁴ pieces / mm ² or more are preferable. Further, the material of the inorganic particles 2 may be the same as that of the inorganic particles 1, or other materials selected from those listed as the materials of the above-mentioned inorganic fine particles 1 and the like, the effect is not changed.

The polyimide coating layer 4 may be formed on either surface of the polyamic acid film, but is preferably formed on the surface in contact with the casting support. The reason is that the casting support made of stainless steel or the like is flat and smooth, but is rougher than the surface smoothness required for the surface of the magnetic recording layer 6 and has scratches or the like attached during use. As a result, coarse protrusions exceeding 0.1 μ are often generated. Since such a coarse protrusion becomes a dropout, it is desirable to form the magnetic recording layer 6 on the surface opposite to the surface contacting the casting support. Further, by applying the polyamic acid solution to be the polyimide coating layer 4 onto the polyamic acid film before imidization, strong adhesion between the polyimide coating layer 4 and the polyimide film 3 can be obtained.

By the method described above, the magnetic recording layer 6 formed on the substrate 5 having different irregularities on each surface is a ferromagnetic alloy or ferromagnetic oxide containing Fe, Ni, Co or the like as a main component, and a strong oxide. Magnetic nitride thin films are preferred. Ie Fe, C
o, Co-Ni, Co-P, Co-Pt, Co-Cr, Co-Cr-Ta, Co-V, Co-
Rh, Co-O, Co-Ni-O, Co-N, Fe-N, etc. formed by vacuum evaporation method, sputtering method, plating method with a coercive force of 300 Oe or more and a ferromagnetic thin film with a thickness of 0.05-1μ. is there. Among them, Co-C having perpendicular magnetic anisotropy in which the direction perpendicular to the film surface is easy
The r, Co-Cr-Ta, Co-V, Co-Rh, and Co-O films have good high-density recording characteristics and are useful as magnetic recording media. The magnetic recording layer 3 may be a single layer or may be laminated with a magnetic or nonmagnetic layer.

The thermal expansion coefficient α of the magnetic recording layer 6 is approximately 1 to 2.0 × 10 ⁻⁵ , and the α of the substrate 5 is close to the above value, specifically 0.7 to
The range of 2.5 × 10 ^-5 is preferable.

The metal or oxide or nitride thin film magnetic recording layer 6 itself does not have sufficient corrosion resistance or abrasion resistance against sliding with a head or a member of a recording / reproducing device. Therefore, a metal oxide, a nitride, a carbide, a boride or a carbon film, a protective layer or a lubricating layer of higher fatty acid, higher fatty acid ester, fluorine oil, perfluorocarboxylic acid, fluorine resin or the like is formed on the magnetic recording layer 6. It is preferable. Specifically, SiO ₂ , Al ₂ O ₃ , Co ₃ O ₄ , TiN, Si ₃ N ₁ , BN, SiC,
Examples thereof include layers of WC, ZrB ₂ , HfB ₂ , stearic acid, stearic acid metal salt, perfluoroalkyl polyether, PTFE, FEP, acrylic ester compound and the like. The protective layer or the lubricating layer material may be used alone, or a plurality of materials may be used in combination.

Further, on the surface of the polyimide coating layer 4 which is the back surface of the magnetic recording medium, a fluororesin, a fluorine-containing compound, a fatty acid,
The lubricity can be further improved by applying a material having lubricity such as fatty acid metal salt or fatty acid ester.

[Operation] According to the present invention, by the inorganic particles 1 contained in the polyimide film 3, the traveling property of the polyimide film 3 alone, and the magnetic recording layer 6 after the magnetic recording layer 6 is provided to form a magnetic recording medium. It is adjusted so that desired output characteristics and durability are simultaneously satisfied. In addition, the inorganic particles 2 contained in the polyimide coating layer 4 provide the substrate 5 and the running property as a magnetic recording medium. Therefore, the magnetic recording medium of the present invention is not only excellent in recording / reproducing characteristics but also excellent in practical performance such as running property and durability, and further, formation of magnetic recording layer, protective layer, lubricating layer, post-treatment, etc. The film has good running property during the process of (2), and blocking during storage of the original film is unlikely to occur. Further, the polyimide coating layer 4 having irregularities has high heat resistance,
It can sufficiently withstand the heating in the subsequent step.

[Examples] Hereinafter, the present invention will be described in detail based on Examples.

Example 1 Paraphenylenediamine 30 mol%, diaminodiphenyl ether 70 mol%, biphenyltetracarboxylic dianhydride 50 mol%, pyromellitic dianhydride 50 mol% were added to N, N
-Dissolved in dimethylacetamide, and as the inorganic particles 1, SiO ₂ having an average particle size of 200Å, 400Å, 600Å, 800Å, 1000Å
The polyamic acid solution in which fine particles were dispersed was cast on a smooth stainless belt and the solvent was removed at 120 ° C. to prepare a polyamic acid film having a thickness of about 15 μm. A polyamic acid solution having the same composition as the above in which TiO ₂ fine particles having an average particle diameter of 0.2 μm are dispersed as inorganic particles 2 on the stainless belt contact surface side of this polyamic acid film is applied by a gravure roll.
The solvent was dried at 0 ° C. This laminated polyamic acid film was completely imidized in a heating furnace at 400 ° C and the total thickness was about 9 μm.
A polyimide film of was obtained. The surface roughness of this polyimide coating layer surface was 0.14 μm in ten-point average roughness, and the protrusion density was 4 × 10 ⁴ pieces / mm ² .

A 0.3% Co-Cr 20 wt% film was formed as a magnetic recording layer on the opposite side of this polyimide coating layer by high frequency sputtering.
and μm formed mainly Co ₃ O ₄ as a protective layer thereon to be
A Co oxide film consisting of 120 Å was formed and cut into 8 mm gold to produce an 8 mm video tape. With respect to this trial tape, on the surface opposite to the magnetic recording layer, the friction coefficient against a 4 mmφSUS rod was measured, and the RF output value, still durability, and dropout (-16 dB, 15 μS) when recorded / reproduced with an 8 mm VTR were measured. As a result, as shown in the table, the friction coefficient is small, the still durability is good, and the dropout is small. This prototype tape was not only stable in running on the VTR, but also easy to handle without blocking, running unevenness, or winding unevenness during each tape manufacturing process.

Comparative Example 1 Example 1 was repeated except that the inorganic particles 1 were SiO ₂ having an average particle size of 400 Å and the inorganic particles 2 had an average particle size of 0.03 μ.
8mm video tape was made with the same material and the same process.

Example 2 The same material as in Example 1 was used, except that the inorganic particles 1 were SiO ₂ having an average particle diameter of 400Å and the average particle diameters of the inorganic particles 2 were 0.08 and 1.0 μ in Example 1, and an 8 mm video tape was used in the same process. Two types were prepared.

Comparative Example 2 A polyimide film having the same composition as that of Example 2 and having inorganic particles dispersed therein and having no polyimide coating layer was used as the substrate, and the same material as that of Example 1 was used to form a magnetic recording layer and a protective layer in the same process to obtain 8 mm. A video tape was made. This comparative tape had uneven winding and wrinkles in the tape manufacturing process, and the yield of non-defective tape was extremely poor. Further, as shown in the table, since the friction coefficient is large, the running property in the deck is poor, and the tape reel is hindered from being wound by the cassette reel, and the tape edge is not practical.

Example 3 Paraphenylenediamine was the only aromatic diamine, and 80 mol% of biphenyltetracarboxylic dianhydride and 20 mol% of pyromellitic dianhydride were used as aromatic tetracarboxylic acids.
And the inorganic particles 1 are TiO ₂ fine particles with an average particle size of 450Å,
Inorganic particles 2 and TiO ₂ fine average particle size 0.2 [mu] m, in Example 1 and the same method, to prepare a polyimide film having a total thickness 9 .mu.m. Using this polyimide film as a substrate, Co—Ni 20 wt% was obliquely vapor-deposited on the surface opposite to the polyimide coating layer by an electron beam continuous vapor deposition apparatus to form a magnetic recording layer having a thickness of 0.15 μm. At that time, by reacting the upper layer of the Co-Ni film with oxygen during the deposition, the surface of the magnetic recording layer
200Å was used as the Co-Ni oxide layer. Further, FEP as a lubrication layer was formed on the magnetic recording layer by an average thickness of 15Å by the vacuum evaporation method to prepare an 8 mm video tape.

[Effects of the Invention] As described above, after coating the polyamic acid solution in which the inorganic particles larger than the inorganic particles are dispersed in the polyamic acid film in which the inorganic particles are dispersed, the polyimide film obtained by desolvation imidization is obtained. A magnetic recording medium with a magnetic recording layer formed on the side opposite to the coating surface has excellent durability, is less likely to cause blocking, and has good runnability in re-recording equipment, as well as easy film transport within the manufacturing process. It is something that can be done.

[Brief description of drawings]

 The figure is an example of a schematic sectional view of the magnetic recording medium of the present invention. 1, 2 ... Inorganic particles, 3 ... Polyimide film, 4 ... Polyimide coating layer, 5 ... Substrate, 6 ... Magnetic recording layer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenji Suzuki 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) References JP-A-60-261015 (JP, A)

Claims (1)

[Claims] 1. A magnetic recording layer is formed on the other surface of a polyimide film having a polyimide coating layer in which inorganic particles are dispersed on one surface, and the polyimide film is more average than the inorganic particles dispersed in the polyimide coating layer. A magnetic recording medium comprising inorganic particles having a small particle size dispersed therein.