JPH0291811A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To allow the formation of a nearly uniformly coated film having <=0.2mum film thickness and to contrive the decrease of noises and the drastic decrease of electrical defects by applying a magnetic coating compd. prepd. by dispersing fine particles of ferromagnetic powder into a high-polymer binder on a substrate. CONSTITUTION:An epoxy resin, phenolic resin, etc., which are the binder for dispersion of magnetic powder are made into a powdery resin of <=20mum grain size. After this powder is previously sufficiently mechanically mixed with the ferromagnetic powder having specific surface area of >=40m<2>/g BET value, a proper ratio of a solvent is added to the powder to swell the powdery resin. The mixture is then kneaded under high shearing stress and is uniformly kneaded with the ferromagnetic powder by a ball mill. The nearly uniformly coated film having <=0.015mumRa surface roughness before working and <=0.2mum recording film thickness is obtd. if this magnetic coating compd. is applied on the substrate. In addition, the noises are decreased by >=30% and the resolving power is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording medium, a magnetic recording/reproducing device, and a method for producing a magnetic paint for forming a magnetic recording layer of a magnetic recording medium.

[Conventional technology]

In recent years, with the demand for higher density magnetic recording media such as magnetic disks, coating films containing ferromagnetic powder are becoming thinner. That is, the thickness of a magnetic coating film, which was conventionally 1 μm or more, has recently been reduced to 0.5 μm or less. Such a magnetic disk uses ferromagnetic powder as a binder,
For example, it can be manufactured by applying a coating material dispersed in a resin composition consisting of an epoxy resin, a phenol resin, and a vinyl resin onto a substrate to form a coating film, and then curing the coating film. (Japanese Unexamined Patent Publication No. 63-48612) Furthermore, as the density of magnetic disks increases, the floating distance between the magnetic disk and the magnetic head has become narrower. As a result, the magnetic disk coating surface is required to be smoother. The above-mentioned conventional technology made it possible for the first time to form a thin film of 0.2 μm (thickness of the magnetic layer before processing) by coating, but because the surface roughness of the paint film was as large as 0.03 μmRa, By processing the film by 0.1 μm, the roughness on one side is 0.01 μmRa and the coating thickness is 0.1 μm.
A 1 μm magnetic disk was obtained.

[Problem to be solved by the invention]

In the magnetic paint manufactured by the above-mentioned conventional technology, the particle size of the magnetic powder in the magnetic paint is large (specific surface area, BET value 22y).
d/g) and the magnetic powder was insufficiently dispersed, it was virtually impossible to form a thin film with a film thickness (before processing) of less than 0.2 μm due to the occurrence of electrical defects with this magnetic paint. The surface roughness of the processed surface before processing is 0.03 μm Ra
It was a big thing.

Therefore, when obtaining a thin magnetic disk with a coating thickness of 0.2 μm or less, approximately 1/2 of the coating film actually formed by coating is required.
I had to cut out 2.

However, when the amount of coating film processing becomes large in this way, the coating film processing time increases and electrical defects due to the occurrence of a large number of scratches occur. Ideally, the coating film on a magnetic disk can be used unprocessed, and even if the coating film is processed, it is considered desirable that the film thickness be at most 20% or less of the film thickness before processing.

The object of the present invention is to improve the dispersion state of magnetic powder in the paint by improving the manufacturing method of magnetic paint. As a result, by reducing the surface roughness of the coated surface of the magnetic disk before processing, it is possible to reduce the noise of the magnetic disk medium, reduce the amount of coating film processing as much as possible, and reduce the electrical damage caused by scratches. Reduce defects. Another object of the present invention is to obtain a magnetic disk medium with a small surface roughness as described above and a uniform thickness of 0.2 μm or less before processing on the inner and outer peripheries.

Another object of the present invention is to provide a magnetic recording/reproducing device with high S/N and high resolution. Furthermore, another object of the present device is to provide a magnetic recording/reproducing device that has fewer malfunctions and is less likely to cause head crashes.

[Means to solve the problem]

In order to achieve the above object of the present invention, a binder for dispersing magnetic powder such as epoxy resin, phenol resin, vinyl resin, etc. is made into a powdered resin with a particle size of 20 μm or less, and this is prepared in advance with a BET value of 40 rrr/ After mechanically mixing thoroughly with ferromagnetic powder having a specific surface area of 100 g or more, an appropriate amount of solvent is added to swell the uniformly mixed powdered resin and kneaded under high shear stress. The resin powder is brought into a nearly molten state and uniformly kneaded with the ferromagnetic powder, and then kneaded in a ball mill as in the conventional method. Through the above steps, a magnetic paint having a tactoid structure in which ferromagnetic powder is uniformly dispersed can be obtained.

When a magnetic disk was manufactured by applying the magnetic paint produced in this way to a non-magnetic substrate and orienting it, the surface roughness before processing was very small, 0.015μIRa or less, and 5.25μIRa or less. It was possible to obtain a substantially uniform magnetic disk having a magnetic recording film thickness of 0.2 μm or less in inch disks, and the object of the present invention was fully achieved.

Furthermore, according to the present invention, the coating film thickness (film thickness before processing) is 0.
05μm, coating surface roughness (surface roughness before processing) 0.010μm
It is also possible to form an extremely thin magnetic layer of m Ra without any visible defects. Therefore, it has become possible to obtain a magnetic disk having a smooth thin film recording layer without performing a large amount of coating processing as in the past.

In the present invention, the coating film thickness before processing is as thin as 0.2 μm or less, and the coating surface roughness before processing is 0.0+, 5 μm Ra.
As it is small, it hardly requires any coating processing, and the amount of coating film processing is extremely small compared to conventional methods, making it difficult to get scratches. A magnetic recording/reproducing device can be produced.

[Effect]

When the amount of solvent in a magnetic paint increases, the agglomeration of the ferromagnetic powder progresses, making it impossible to apply a thin film and also deteriorating the surface roughness (smoothness). This also applies to the case of Japanese Patent Application Laid-Open No. 63-48612 mentioned above as the prior art. In this magnetic paint, the magnetic powder in the paint is randomly dispersed one by one, and although it is a fairly stable paint,
The limit of thin film coating is that the film thickness before processing is 0.2 μm. If the film is thinner than this, visual defects will appear on the coating surface. In addition, in the present invention, the ferromagnetic powder has a specific surface area of B
E
It was not possible to obtain a magnetic disk medium with a roughness of 0.03 μm or less on the processed front surface. On the other hand, magnetic paints in which magnetic powder forms a bundle of several tens of water magnetic powders, so-called tactoids, such as those described in Japanese Patent Publication No. 57-40566 and Japanese Patent Application Laid-Open No. 63-4422, In a paint in which ferromagnetic powder is dispersed in an epoxy resin, agglomeration of the ferromagnetic powder progresses significantly when the amount of solvent in the paint increases.

In order to knead ferromagnetic powder under high shear stress, a small amount of resin solution is usually added to mix the powder.

The solution to be added is locally absorbed by a portion of the ferromagnetic powder, making it difficult for the magnetic powder to become uniform, whereas solid/solid mixtures are much easier to mix uniformly. In the present invention, in order to sufficiently mix in advance a resin composition such as an epoxy resin finely pulverized to 20 μm or less and a ferromagnetic powder having a specific surface area of BET40rrF/g or more, the ferromagnetic powder and the resin composition are mixed in advance. This results in a uniformly mixed state. The resin powder is then swollen by the addition of a solvent, and the ferromagnetic powder is adsorbed and kneaded using it as a core, resulting in a magnetic paint with an even tactoid structure, resulting in extremely small surface roughness. It is believed that this makes it possible to form a thin magnetic film.

In the present invention, a powdered epoxy resin is used for dispersing ferromagnetic powder, but the smaller the fineness of the epoxy resin powder, and the larger the specific surface area of the ferromagnetic powder, the smaller the surface roughness. Thin film coating is possible. The fineness of the resin powder is 20 μm or less, more preferably 10 μm.
m or less, preferably 1 ferromagnetic powder has a BET value of 40rr?
It is desirable to have a specific surface area of 50 m/g or more, more preferably a BET value of 50 m/g or more.

The limit of thin film coating with these magnetic paints is 0.9
μm (Japanese Patent Publication No. 57-40566), 0.45 μm (Japanese Patent Publication No. 63-4422), and the roughness of the processed front surface is 0.030.
μmRa is the limit.

In the magnetic paint according to the present invention, even though the magnetic powder forms a tactoid structure in the paint, the agglomeration of the ferromagnetic powder does not proceed even if the amount of solvent in the paint is increased. Thin film coating is possible with rough surfaces. In addition, the peculiarity of the magnetic paint according to the present invention is that when the magnetic paint is spin-coated onto a magnetic disk disk, 1 the coating is normally thinner on the inner circumferential side of the magnetic disk disk and thicker on the outer circumferential side, creating a film thickness gradient. On the other hand, with the magnetic paint according to the present invention, there is almost no difference in film thickness between the inner and outer peripheries of a magnetic disk (5.25 inches) due to high-speed spin coating.

From the inner circumference to the outer circumference, the film thickness before processing is, for example, 0.
Formation of a uniform thin film of 0.05 μm, processing surface roughness of 0.01 μm
This is possible due to the high smoothness of mRa. This makes it possible to increase the resolution of the magnetic disk and reduce noise, and it is also possible to significantly shorten the coating processing time.

The most important problem with such ultra-thin magnetic disks is the reliability of the coating. Since the present invention is not a continuous medium but a coated medium, various coating methods such as adding reinforcing materials to the coating film, making the coating film porous, and impregnating it with a liquid lubricant, etc. Various measures can be taken to maintain membrane reliability. Among these, a particularly effective method is to add single-crystal alumina fine particles, diamond fine particles, etc. whose particle size is less than the film thickness before processing as a reinforcing material. Another method, as described in the examples, is to apply a two-layer coating, for example, as a base layer, a resin layer with a small amount of reinforcing material dispersed in a polymeric binder, and as an upper layer. It is also possible to form ultrathin magnetic layers according to the invention.

〔Example〕

An example of the present invention will be described below in more detail.

(Example 1) A plate-shaped epoxy resin was pulverized using a jet mill to obtain epoxy resin powder with a particle size of about 8.0 μm. 27.5 parts by weight of the above powdered epoxy resin and ferromagnetic powder (BET value 40r)
CO-adhered iron oxide powder (He7) with a specific surface area of ri'/g
700e)), 100 parts by weight and single crystal alumina 5
After thoroughly mixing the parts by weight, 10 parts by weight of cyclohexanone was added and further mixing was carried out in a kneader kneader.

Thereafter, 5 parts by weight of cyclohexanone was further added and crosstalk was performed under high shear stress.

Put the above mixture into a ball mill pot, add 160 parts by weight of a mixed solvent consisting of cyclohexanone and isophorone,
Ball mill kneading was performed for 3 days to disperse the ferromagnetic powder. Next, a solution of 27.5 parts by weight of phenol resin and 6 parts by weight of vinyl resin dissolved in 800 parts by weight of a mixed solvent consisting of cyclohexanone, isophorone, and dioxane was added to prepare a magnetic paint for a magnetic disk. next,
The above coating material was spin-coated onto a 5.25-inch aluminum substrate whose surface had been cleaned in advance, and magnetic field orientation was performed using a well-known method. The coated magnetic disk is 21
After baking at 0°C, coating film thickness and surface roughness were measured.

The film thickness of the obtained coating disc before processing was R38m and 0.
Even with R60+n+t+, Q was 20 μm. Moreover, the surface roughness before processing was 0.014 μm, and the Br/8m value in the Ra circumferential direction was 0.85. Note that no visual defects were observed on the coating surface.

(Example 2) 100 parts by weight of ferromagnetic powder (CO-coated iron oxide powder (He7700e) with a specific surface area of BET value 45 rrr/g), 3 parts by weight of single crystal alumina, and epoxy resin with a particle size of about 3.0 μm. After thoroughly mixing 27.5 parts by weight of fine powder, 10 parts by weight of cyclohexanone was added and further mixing was carried out in a kneader kneader. Thereafter, 5 parts by weight of cyclohexanone was added and crosstalk was performed under high shear stress.

Put the above mixture into a ball mill pot, add 160 parts by weight of a mixed solvent consisting of cyclohexanone and isophorone,
Ball mill kneading was performed for 3 days to disperse the ferromagnetic powder. Next, a solution of 12.5 parts by weight of phenol resin and 6 parts by weight of vinyl resin dissolved in 990 parts by weight of a mixed solvent consisting of cyclohexanone, isophorone, and dioxane was added to prepare a magnetic paint for a magnetic disk. Next, the above paint was spin-coated onto a 5.25-inch aluminum substrate whose surface had been previously cleaned, magnetic field orientation was performed using a well-known method, and after baking, the film thickness and surface roughness were measured. The film thickness of the obtained coating disc before processing is R38+
m and R60mm were both 0°10 μm. In addition, the surface roughness before processing is 0.012 μIRa, and B r in the circumferential direction.
/Bm value was 0.84. Note that no visual defects were observed on the coating surface.

(Example 3) 100 parts by weight of ferromagnetic powder (Co-coated iron oxide powder (He 7700e) with a specific surface area of BET value 50 rrr/g), 3 parts by weight of single crystal alumina, and epoxy resin with a particle size of 2.0 μm After thoroughly mixing 35 parts by weight of fine powder, 10 parts by weight of cyclohexanone was added, and cross-mixing was performed under high shear stress in a kneader kneader.

Put the above mixture into a ball mill pot, add 130 parts by weight of a mixed solvent consisting of cyclohexanone and isophorone,
Ball mill kneading was performed for 3 days to disperse the ferromagnetic powder. Next, a solution of 15 parts by weight of phenol resin and 3 parts by weight of vinyl resin dissolved in 14 parts by weight of a mixed solvent consisting of cyclohexanone, isophorone, and dioxane was added.
A magnetic paint for magnetic disks was prepared. Next, the above paint was spin-coated onto a 5.25-inch aluminum substrate whose surface had been previously cleaned, magnetic field orientation was performed using a well-known method, and after baking, the film thickness and surface roughness were measured. The film thickness of the obtained coating disc before processing was R38m,
Both R60mm and 0.07μm.

The surface roughness before processing was 0.011 μmRa. Also,
The B r /B m value was 0.86. Note that no visual defects were observed on the coating surface.

(Example 4) 100 parts by weight of ferromagnetic powder (Co-coated iron oxide powder (Hc77006) with a specific surface area of BET value 55 rrr/g), a trace amount of diamond fine particles, and epoxy resin fine powder with a particle size of about 2.0 μm After thoroughly mixing 40 parts by weight, 10 parts by weight of cyclohexanone was added and cross-talk was performed under high shear stress.

Put the above mixture into a ball millbot, add 130 parts by weight of a mixed solvent consisting of cyclohexanone and isophorone,
Ball mill kneading was performed for 3 days to disperse the ferromagnetic powder. Next, a solution of 20 parts by weight of phenolic resin and 6 parts by weight of vinyl resin dissolved in 1850 parts by weight of a mixed solvent consisting of cyclohexanone, isophorone, and dioxane was added.
A magnetic paint for magnetic disks was prepared. Next, the above paint was spin-coated onto a 5.25-inch aluminum substrate whose surface had been previously cleaned, magnetic field orientation was performed using a well-known method, and after baking, the film thickness and surface roughness were measured. The film thickness of the obtained coating disc before processing is R38ny
a and R60mw* were both 0.05 μm, and the surface roughness before processing was 0.010 μmRa. Also, B r in the circumferential direction
/Bm value was 0.85.

Note that no visual defects were observed on the coating surface.

As described above, the present invention has made it possible for the first time to form a smooth, ultra-thin magnetic coating film with low surface roughness.

As described in the examples, this technology is extremely easy to use not only to form a single layer of magnetic coating on a non-magnetic substrate, but also to form a multilayer coating of at least two or more layers on a non-magnetic substrate. be.

Furthermore, although continuous media such as sputtering, vapor deposition, and plating have excellent electromagnetic conversion characteristics, they are inferior to coating media in terms of reliability. ! ! The main reason for this is that while it is possible to contain reinforcing materials, lubricants, etc. in the coating film with a single cloth medium, this is not possible with a continuous medium. Therefore, by forming the ultra-thin magnetic layer of the present invention (having the same coercive force as the continuous medium) containing a small amount of reinforcing material such as diamond particles on the surface of the continuous medium, the reliability of the continuous medium can be improved. It is also possible to bring it up to the level of the application medium.

As the polymer binder for dispersing ferromagnetic powder used in the above examples of the present invention, epoxy resin phenol resin,
Vinyl resin is used, but other commonly used vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinyl acetate-vinyl alcohol copolymers, acrylonitrile-
Vinyl resins such as acrylic acid-2-hydroxyethyl methacrylate copolymer, rubber resins such as acrylonitrile-butadiene copolymer, cellulose resins such as nitrocellulose and acetylcellulose, epoxy resins such as phenoxy, urethane, Ordinary organic polymer compounds that have good binding properties for ferromagnetic powder can be used, such as urethane resins such as urethane prepolymers. Note that the vinyl resin used as the polymeric binder for dispersing ferromagnetic powder in the present invention includes polyvinyl butyral, polyvinyl formal, polyvinyl acetate, etc. Among these, it is particularly preferable to use polyvinyl butyral. .

In addition, as the ferromagnetic powder, CO-coated iron oxide powder is used in this example, but other materials with a BET value of 40rr are also used.
Iron oxide powder, metal powder, barium ferrite powder, iron carbide powder, etc. having a specific surface area of r/g or more can be used.

〔Effect of the invention〕

As described above in detail, the magnetic paint produced by the method of the present invention has a tactoid structure in which ferromagnetic powder is uniformly dispersed in the paint. When this is applied to a magnetic recording medium, for example, a magnetic disk using a 5.25-inch aluminum substrate, the surface roughness before processing is as low as 0.015 μmRa or less, and the inner and outer circumferences of the magnetic disk are It is possible to easily form a thin film having an extremely thin and uniform thickness of 0.2 μm or less by coating. For this reason, there is almost no need for coating processing, which has the effect of significantly reducing electrical defects caused by scratches and the like during coating processing. Also,
Disk noise can be expected to be reduced by about 30% or more, and an improvement in resolution can also be expected.

In carrying out the present invention, the kneader mixer used had a mixing capacity of IQ, a power of 2.2 KW, and 4) P, 800 g of ferromagnetic powder was charged, and the blade rotation speed was 3 Qr.
Crosstalk was carried out at pm. In this case at least 10 I)
dynes/a! Crosstalk occurs under the above-mentioned shear stress. In the present invention, in this way, 106 dynes/
It is important to perform the crosstalk under a shear stress of ci or more.

Claims (1)

[Claims] 1. A magnetic recording layer is formed by applying a magnetic paint in which ferromagnetic powder particles containing ferromagnetic powder particles or reinforcing material particles are dispersed in a polymeric binder onto a non-magnetic substrate. In the formed magnetic recording medium, the film thickness of the magnetic recording layer is 0.
A magnetic recording medium characterized by having a substantially uniform coating film of 2 μm or less. 2. The magnetic recording medium according to claim 1, wherein the magnetic coating film formed on the non-magnetic substrate before processing is a substantially uniform coating film having a thickness of 0.2 μm or less. 3. The thickness of the magnetic coating film formed on the non-magnetic substrate before processing is 0.3 μm or less, and the surface roughness of the magnetic coating film before processing is 0.015 μmRa or less. A magnetic recording medium according to claim 1. 4. In a magnetic recording medium having at least two coating films or magnetic recording layers on a non-magnetic substrate, at least one layer of the coating film or magnetic recording layer comprises ferromagnetic fine particles containing ferromagnetic powder fine particles or reinforcing material fine particles. A magnetic recording medium according to any one of claims 1 to 3, characterized in that the magnetic recording medium is a coating film comprising a polymeric binder dispersed in a polymeric binder. 5. The magnetic recording medium according to claims 1 to 4, wherein the magnetic recording medium is a magnetic disk. 6. A magnetic recording and reproducing apparatus comprising a magnetic recording medium according to claims 1 to 5 and a magnetic head for performing recording and reproducing on the magnetic recording medium. 7. In the method for producing a magnetic paint, which is a paint composition for forming a magnetic recording film of a magnetic recording medium according to claims 1 to 3, the specific surface area BE constituting the magnetic recording film is
When mixing ferromagnetic powder fine particles with a T value of 40 m^2/g or more and a resin composition that is a dispersion binder for the ferromagnetic powder, the resin composition is mixed into a fine powder of 20 μm or less in a solid state. The method includes the step of sufficiently mechanically mixing the ferromagnetic particles or the ferromagnetic particles including the reinforcing material particles and the resin composition made into a fine powder, and then kneading the mixture under high shear stress. A method for producing magnetic paint, characterized by: 8. The method for producing a magnetic paint according to claim 7, wherein the resin composition contains at least one of an epoxy resin, a phenol resin, and a vinyl resin. 9. Production of a magnetic paint according to claim 7, wherein the ferromagnetic fine particles are at least one of iron oxide powder, Co-coated iron oxide powder, metal powder, barium ferrite powder, and iron carbide powder. Method. 10. The above ferromagnetic fine particles have a specific surface area BET value of 40 m^
2/g or more iron oxide powder, Co-adhered iron oxide powder, metal powder,
The magnetic recording medium according to any one of claims 1 to 3, which is at least one of barium ferrite powder and iron carbide powder.