JPS63188825A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To prevent blocking so as to enhance the traveling property in recording and reproducing apparatus and to facilitate film conveyance in a production process by providing a polyimide coating layer on one face of a polyimide film and forming a magnetic recording layer on the other face. CONSTITUTION:The PI coating layer 2 is disposed on one face of the polyimide (PI) film 1 and the magnetic recording layer 3 is formed on the other face. A substrate is made into the laminated structure consisting of the PI film 1 without contg. the inorg. particles and the layer 2 dispersed with the inorg. particles in such a manner. Since the mechanical strength depends on the PI film 1 occupying the greater part of the thickness, the adequate surface characteristic and sufficient mechanical strength are imparted to the coating layer; in addition, the magnetic recording layer 3 side has good smoothness. The conveyability of the film is, therefore, good in stages for a subsequent pretreatment, layer formation of the magnetic recording layer 3, and if necessary, other layer formation and post treatment, etc. Blocking during preservation of the raw sheet of the film is hardly generated. The layer 2 has high heat resistance and sufficiently withstands heating in the later processes. The good traveling property is thereby obtd. in the recording and reproducing apparatus.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a magnetic recording medium that uses a polyimide film as a base film and has excellent running properties.

[Prior Art] Conventionally, as magnetic recording media, thin film magnetic recording media using thin film deposition methods such as vacuum evaporation, sputtering, or plating, and magnetic powder coated magnetic recording media are known. . In particular, thin-film magnetic recording media are seen as promising as next-generation recording media because they can improve recording density compared to magnetic powder-coated recording media that are currently widely used.

On the other hand, when manufacturing this thin film type magnetic recording medium, the base film suffers heat loss due to radiant heat from the evaporation source and incident particle energy. In addition, Co-C of perpendicular magnetic recording media
In some cases, such as r-alloy, it is necessary to form a film at a high temperature in order to obtain sufficient magnetic properties. As described above, the substrate is required to have good heat resistance, so for example, polyimide film, which has better heat resistance than general polyester, is suitable for flexible substrates for tapes and floppy disks.

[Problems to be Solved by the Invention] Incidentally, in order to improve recording density, it is necessary to reduce the gap between the head and the medium. Calendar treatment or surface polishing is applied to achieve this.

However, in thin-film magnetic recording media, the hardness of the magnetic layer is high, and the smoothing treatment used in the coated magnetic recording media cannot be applied.In other words, in thin-film magnetic recording media, the smoothness of the substrate surface is Since it controls the smoothness of the recording medium, it is necessary to improve the smoothness of the substrate. On the other hand, if the surface smoothness of the substrate or the magnetic recording medium during manufacturing or after completion is too good, wrinkles may occur in each roll, adhesion between films (blocking), width misalignment or winding during film transport during the manufacturing process. There is a problem that unevenness or running problems within the recording/reproducing device are likely to occur.

The present invention was made to solve the above-mentioned problems.
The object of the present invention is to provide a magnetic recording medium that has excellent surface smoothness and runnability, and is also easy to handle during the manufacturing process.

[Means for Solving the Problems] Means taken in the present invention to achieve the above object will be explained with reference to the accompanying drawings. This means that it is used as a medium.

The above-mentioned magnetic recording medium of the present invention is produced by casting a polyamic acid solution obtained by polymerizing aromatic diamine and aromatic tetracarboxylic acid in a solvent onto a flat surface and removing the solvent. Polyimide coating layer 2 with inorganic particles dispersed on one side, obtained by applying a polyamic acid solution in which particles are dispersed, followed by desolvation and imidization.
The magnetic recording layer 3 can be manufactured by forming the magnetic recording layer 3 on the opposite side to the inorganic particle dispersion side of the polyimide film 1 having the following. A protective layer, a lubricating layer, or both may be laminated on the magnetic recording layer 3 of the resulting magnetic recording medium.

The polyimide film 1 having the polyimide coating layer 2 in which inorganic particles are dispersed is formed by casting polyamic acid, which is obtained by polymerizing aromatic diamine and aromatic tetracarboxylic acid in a solvent, onto a flat surface, and then removing the solvent by evaporation. A polyamic solution containing inorganic particles, which will become the polyimide coating layer 2, is applied onto the polyamic acid film thus formed, and then polymerization imidization is carried out at a high temperature, thereby achieving strong adhesion between the polyimide film 1 and the polyimide coating layer 2. It will be done.

As a method for forming the polyimide coating layer 2, a coating method such as a roll coating method such as gravure or reverse coating, a bar code method, or a spin code method can be used, and the dry coating film thickness is preferably about several liters.

Then, the substrate (
A certain surface roughness is formed on the laminated films 1 and 2).

Inorganic particles include carbon and metal fine particles, A, f)
203.5i02. Fine particles of metal oxides such as TiO2 and MgO are used. The particle size and content of the inorganic particles are adjusted by the value of the surface roughness to be formed, and the ten-point average roughness Rz (measured with Talystep, manufactured by Taylor-Hola 6son) is 0.05. ~0.5 gta and a protrusion density of 104 pieces/112 or more is preferable.

It does not matter which side of the polyimide film 1 the polyimide coating layer 2 is formed on, as long as it forms unevenness. A polyimide film obtained by casting a polyamic acid solution onto a flat support such as stainless steel, followed by solvent removal and polymerization imidization.
The surface roughness of the surface in contact with the support reflects the surface properties of the support.

Even if the support surface is a highly precisely polished stainless steel surface, it is difficult to achieve the flatness required for the surface of the magnetic recording layer 3 of the magnetic recording medium. Therefore, it is preferable for a magnetic recording medium to form the polyimide coating layer 2 on the side of the polyimide film l that contacts the support, and form the magnetic recording layer 3 on the side of the polyimide film 1 that does not contact the support (free side). .

The magnetic recording layer 3 formed on the polyimide film 1 having an uneven surface by the method described above is made of Fe.
A ferromagnetic alloy, a ferromagnetic oxide, or a ferromagnetic nitride thin film containing Co, etc. as a main component is preferable. That is, Fe
, Go, Go-Ni, Go-P, co-Pt.

Coercive force formed by plating method is 3000a or more, film thickness 0.
It is a ferromagnetic thin film of 05 to Ig. Among them, Go-Cr, which has perpendicular magnetic anisotropy in the easy-axis direction perpendicular to the film surface;
Go-C: r-Ta, Go-V, Co-Rh, C
O-0g and the like 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 have a laminated structure with magnetic or nonmagnetic layers.

The thermal expansion coefficient α of the magnetic recording layer 3 is approximately 1 to 2 × 10
-5, and α of the base polyimide film 1 is also preferably close to the above value, specifically in the range of 0.7 to 2.5 Xl0-5.

The metal, oxide, or nitride thin film magnetic recording layer 3 cannot be said to have sufficient corrosion resistance or abrasion resistance against sliding with a head or a member of a recording/reproducing device by itself. Therefore, a protective layer or lubricant layer of metal oxide, nitride, carbide, boride, or carbon film, higher fatty acid, higher fatty acid ester, fluorine oil, perfluorocarboxylic acid, fluororesin, etc. is formed on the magnetic recording layer 3. It is preferable. Specifically, 5i02. AI! 2(h, Co30
a. TiN.

5i3Na, BN, SiC, WC, ZrB2. H
fB2. Examples include layers of stearic acid, stearic acid metal salts, perfluoroalkyl polyethers, PTFE, FEP, acrylic ester compounds, and the like. The protective layer or lubricant layer material may be used alone, or may be used in combination.

The polyimide film 1 is usually produced by casting a polyamic acid solution obtained by polymerizing an aromatic tetracarboxylic acid and an aromatic diamine onto a flat surface, removing the solvent, and then imidizing the solution at a high temperature. Examples of aromatic tetracarboxylic acids include pyromellitic dianhydride, 3.3', 4.4'-biphenyltetracarboxylic dianhydride, and pyridine-2,3,5,6-
Aromatic diamines such as tetracarboxylic dianhydride and 2,3,6.7-chlorophthalenedicarboxylic dianhydride include
Examples include para-phenylene diamine, diaminodiphenyl ether, diaminodiphenylmethane, diaminodiphenylsulfone, diaminonaphthalene, and the like. Medium is preferred. These may be polymerized individually, but
Furthermore, by copolymerizing three or four of the above four components, it is possible to produce a polyimide film having desired mechanical or thermal properties as a magnetic recording medium.

In order to make the mechanical and thermal properties suitable for the magnetic recording medium, the diamine component used to produce the aromatic polyamic acid should be about 40 to 95 mol%, especially about 40 to 95 mol % based on the total cyamine component. The amount of PPD used is in the range of 45 to 90 mol%, and about 5 to 6% of the total diamine component is used.
I)A in a usage proportion of 0 mol %, in particular 10 to 55 mol %
It is preferable to consist of two components with DE. In addition, the tetracarboxylic acid component for producing the aromatic polyamic acid is BPDA in a usage ratio of about 10 to 90 mol%, particularly 15 to 85 mol%, based on the total tetracarboxylic acid component,
Approximately 10 to 90 mol% based on the total tetracarboxylic acid components,
In particular, it is preferable to use PMOA in an amount of 15 to 85 mol %.

The polyamic acid of the polyamic acid solution containing inorganic particles (the polyimide coating layer 2 after imidization) to be coated on the polyamic acid film (the polyimide film 1 after imidization) is the same material as the polyimide film 1. The same effect can be obtained even if there is one or a different one. If the polyamic acid solution is applied onto the polyimide film 1 that has already been polymerized and imidized, it is difficult to obtain a film with sufficient adhesion. Therefore, after casting a polyamic acid solution in which tetracarboxylic acid and diamine are mixed in a solvent onto a flat metal or glass surface, the solvent is evaporated to form a polyamic acid film, and then inorganic particles such as a polyimide coating layer 2 are applied. It is preferable to apply a polyamic solution containing the polyimide and then polymerize and imidize it at a high temperature because strong adhesion between the polyimide film 1 and the polyimide coating layer 2 can be obtained.

In addition, fluororesin, fluorine-containing compounds, fatty acids,
The ease of activation can be further improved by applying a material having lubricity such as a fatty acid metal salt or a fatty acid ester.

[Function] The advantage of forming the base polyimide film 1 into a laminated structure of a layer containing no inorganic particles and a layer containing dispersed inorganic particles, as in the present invention, is that the polyimide film 1 as a base has a laminated structure consisting of a layer containing no inorganic particles and a layer containing dispersed inorganic particles. It is important not to cause a decrease in the mechanical strength of the film caused by dispersing it in a large amount. In other words, if more than a few percent by volume of inorganic particles is mixed into the entire film in order to achieve the desired surface properties (surface roughness), the tensile strength of the film will decrease, making it undesirable as a magnetic recording medium. Become.

On the other hand, according to the configuration of the present invention, since the mechanical strength depends on the layer that does not contain inorganic particles and occupies most of the thickness, it is necessary to have the desired surface properties and sufficient mechanical strength surface roughness. However, if inorganic particles are dispersed throughout the film, the surface of the magnetic recording layer 3 will also have a similar surface roughness, which is not preferable for high-density recording. According to the present invention, it is possible to realize a magnetic recording medium in which the magnetic recording layer 3 side is extremely smooth and only the back surface has an appropriate surface roughness.

Furthermore, compared to the back coat layer conventionally used for magnetic tapes, etc., surface irregularities are formed at the base film stage, so it is difficult to perform subsequent pretreatment, formation of the magnetic recording layer, protective layer, and lubricating layer. The film has good running properties during post-processing and other processes, and blocking during storage of the original film is less likely to occur. Furthermore, the layer providing the unevenness (polyimide coating layer 2) has high heat resistance and can sufficiently withstand heating in subsequent steps.

[Example code] Hereinafter, Mokushuo will be explained in detail based on examples.

Example 1 Obtained by dissolving 30 mol% of paraphenylene diamine, 70 mol% of diaminodiphenyl ether, 50 mol% of biphenyltetracarboxylic dianhydride, and 50 mol% of pyromellitic dianhydride in N,N-dimethylacetamide. The polyamic acid solution was cast onto a smooth stainless steel belt.
The solvent was removed at 0° C. to produce a polyamic acid film about 15 μm thick. A polyamic acid solution having the same composition as above in which TiO2 fine particles having an average particle size of 0.2 gm were dispersed was applied to the stainless steel belt contacting surface of the polyamic acid film using a gravure roll, and the solvent was dried at 120°C. This laminated polyamic acid film was completely imidized in a heating furnace at 400°C to obtain a polyimide film with a total thickness of approximately 9 meters. The surface roughness of this polyimide coating layer is 0.147 pm in ten-point average roughness, and the protrusion density is 4
It was 104 pieces 10n+2.

On the opposite side to this polyimide coating layer, Go-Cr20wt was formed as a magnetic recording layer by high frequency sputtering.
% film was formed at a thickness of 0.3)tm, and a CO oxide film mainly composed of CO3O4 was formed on top of it as a protective layer at a thickness of 12OA.
This was cut into a width of 8 mm to produce an 8 mm videotape. Regarding this prototype tape, on the surface opposite to the magnetic recording layer, the friction coefficient against 4 mcaφ SUS m was measured, and the drop error h (-16 dB, 15 μs) when recorded and reproduced with an 8 mm VTR was measured. As shown in the table, the friction coefficient was small both for the first time and after the 100th measurement, and there were few dropouts. This prototype tape not only runs stably on a VTR, but also prevents blocking and running unevenness during each tape manufacturing process.
There was no uneven winding and it was easy to handle. Furthermore, no peeling of the polyimide coating layer was observed in a peeling test using a plastic film adhesive tape.

Example 2 In Example 1, the inorganic particles had an average particle size of 0.0814.
An 8 mm videotape was produced using the same materials and steps as in Example 1, except that 5i02 was used. This tape.

Comparative Example 1 A polyimide film without a polyimide coating layer with the same composition as in Example 1 and dispersed with inorganic particles was used as the substrate, and a magnetic recording layer and a protective layer were formed using the same material and the same process as in Example 1. !1m videotape was produced. This comparative tape had uneven winding and wrinkles during the tape manufacturing process, and the yield of non-defective tape was extremely low. Also, as shown in the table, due to the large coefficient of friction, the running performance inside the deck was poor, and the cassette reel caused the tape to slip and cause tape edges.

Example 3 The same method as in Example 1 was used except that the aromatic diamine was only paraphenylene diamine, and the aromatic tetracarboxylic acids were 80 mol% of biphenyltetracarboxylic dianhydride and 20 mol% of pyromellitic dianhydride. The total thickness is 9 gm, which is laminated with a polyimide coating layer in which inorganic particles are dispersed.
A polyimide film was produced. Using this polyimide film as a base, 20 wt.
% was obliquely deposited to form a magnetic recording layer with a thickness of 0.157 zm. At this time, by reacting the upper layer of the Go-Ni film with oxygen during deposition, the surface area of the magnetic recording layer is approximately 200 Å.
was used as a Go-Ni oxide layer. Furthermore, on the magnetic recording layer,
FEP was formed as a lubricating layer by the same vacuum deposition method to an average thickness of 15A, and an 8-inch videotape was produced.

Comparative Example 2 The same material as in Example 3 was used, and a polyimide coating layer was formed on the surface opposite to the contact surface of the stainless steel belt.On the surface opposite to the polyimide coating surface of a polyimide film,
A magnetic recording layer and a lubricating layer were formed using the same materials and the same steps as in Example 3, and an 8 mrn videotape was produced. When the magnetic tapes of Example 3 and Comparative Example 2 were subjected to the same measurements as Example 1, there was no difference in the coefficient of friction and runnability on a deck, but the tape of Comparative Example 2 had more dropouts and Comparative Example 3 In Example 3, a magnetic tape was produced using a polyimide film, in which a polyimide coating layer was formed on a polyimide film that had been completely imidized, as a substrate. This magnetic tape exhibited the same performance as Example 3, but the polyimide coating layer peeled off in a peel test.

(Leaving space below) [Effects of the invention] As explained above, a polyamic acid film is coated with a polyamic acid solution in which inorganic particles are dispersed, and then the polyimide film obtained by desolvation and imidization is coated with a magnetic layer on the side opposite to the coated surface. A magnetic recording medium on which a recording layer is formed is not only less likely to cause blocking and has good runnability in a recording/reproducing device, but also facilitates film transport during the manufacturing process.

[Brief explanation of the drawing]

The figure is an example of a schematic cross-sectional view of the magnetic recording medium of the present invention. l...polyimide film, 2... polyimide coating layer, 3...Magnetic recording layer.

Claims (1)

[Claims] 1) A magnetic recording medium comprising a polyimide film having a polyimide coating layer in which inorganic particles are dispersed on one side and a magnetic recording layer formed on the other side.