JPH01149224A - Production of magnetic coating compound and magnetic recording medium formed by using said compound - Google Patents

Abstract

PURPOSE:To improve the dispersibility of magnetic powder in a coating compd. and to improve the S/N of a magnetic disk medium by using fine powder of <=20mum for a resin compsn. CONSTITUTION:The resin compsn. such as epoxy resin ground as finely as <=20mum and ferromagnetic powder are previously sufficiently mixed to form the uniformly mixed state of the ferromagnetic powder and the resin compsn. A solvent is thereafter added to the mixture to swell the resin particles and to adsorb the ferromagnetic powder on the swollen particles as nuclei. Such mixture is kneaded and the magnetic coating compd. having a uniform tactoid structure is obtd. A thin magnetic film having extremely small surface roughness is thereby formed and the noises of a magnetic disk are decreased.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to magnetic recording media, and in particular to a method for producing a magnetic coating material that forms a magnetic recording layer of a magnetic recording medium, as well as electrical properties and reliability using the same. This invention relates to a magnetic recording medium suitable for excellent high-density magnetic disks.

(Prior art) A conventional method of manufacturing magnetic recording media by applying a magnetic paint in which ferromagnetic powder is dispersed in a polymeric binder containing an epoxy resin or the like onto a non-magnetic substrate is known from Japanese Patent Publication No. 55 -816
A number of proposals have been made, including in the Publication No. Among these, a method of manufacturing by kneading ferromagnetic powder with an epoxy resin or the like is disclosed in Japanese Patent Publication No. 40566/1982 and Japanese Patent Application Laid-open No. 100871/1983. This is a method in which ferromagnetic powder and an epoxy resin are mixed with a resin solution in cyclohexanone under high shear stress to create a magnetic paint, and this is applied to produce a magnetic recording medium. However, in these conventional techniques, no consideration was given to sufficiently mixing the ferromagnetic powder with the epoxy resin as a dispersion binder before cross-talking. Therefore, in the magnetic paints obtained by these conventional methods, the small amount of resin solution added at the time of kneading is locally absorbed into a part of the ferromagnetic powder, and thus the magnetic paint is It has been extremely difficult to obtain a magnetic paint with a tactoid structure in which powder is uniformly dispersed due to crosstalk performance. Therefore, when forming a magnetic recording layer using a magnetic paint by this conventional method, it is impossible to form a thin film with a thickness of less than approximately 0.9 μm, and the roughness of the coated surface is approximately 0.08μmRa
It was rough. As the recording density of magnetic disks increases, the coating film becomes thinner, making it necessary to increase the amount of coating film processing.Increasing the amount of coating film processing not only leads to an increase in processing time, but also A problem arises in that the frequency of scratches on the surface of the coating film increases, leading to an increase in electrical defects.

[Problem that the invention seeks to solve]

In the magnetic paint manufactured by the above-mentioned conventional technology, the magnetic powder in the magnetic paint was insufficiently dispersed, so it was virtually impossible to form a thin film with a thickness of less than 0.9 μm, and it was difficult to apply the magnetic paint. The roughness of the surface before processing is approximately 0.08μm
It was rough with Ra. Furthermore, since recent high recording density magnetic disk devices use thin film heads as magnetic heads, there is a problem that signals cannot be written sufficiently if the film thickness of the magnetic disk medium is large. Magnetic disk media are usually coated thinly on the inner circumferential side and thickly on the outer circumferential side. Therefore, the above-mentioned fold pull in the thin film head usually occurs at the outer periphery of the magnetic disk.

As a countermeasure to this, it is necessary to reduce the film thickness on the outer circumference of the magnetic disk, but at present there is no other way than to make the amount of coating on the outer circumference larger than on the inner circumference. the result,
This results in an increase in coating film processing time and an increase in electrical defects due to the occurrence of a large number of scratches.

An object of the present invention is to improve the dispersion state of magnetic powder in the paint by improving the method for producing magnetic paint. As a result, by reducing the surface roughness of the magnetic disk coating surface before processing, the S/N (signal/noise) ratio of the magnetic disk medium is improved, and the film thickness at the time of coating is reduced on both the inner and outer periphery of the magnetic disk. The purpose is to make it 0.9 μm or less.

[Means for solving problems]

In order to achieve the above object of the present invention, the present inventors have conducted extensive research and have found that conventional binders for dispersing magnetic powder, such as epoxy resins, phenolic resins, and vinyl resins in the form of lumps or plates, This was made into a powdered resin with a particle size of 20 μm or less using a pulverizing device such as a jet mill, and after mechanically mixing it thoroughly with ferromagnetic powder, an appropriate amount of Add a solvent to swell the uniformly mixed powdered resin, cross-wire it under high shear stress, bring the resin powder to a nearly molten state, and mix it uniformly with the ferromagnetic powder. It was discovered that a magnetic paint with a tactoid structure in which ferromagnetic powder is uniformly dispersed can be obtained by performing ball mill cross-fertilization as in the conventional method. When a magnetic disk was produced 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, less than 0.050 μm Ra. The coating thickness before processing from the inner circumference to the outer circumference of an 8.8-inch magnetic disk is 0.9
It is possible to obtain a nearly uniform magnetic disk of less than μm,
The object of the present invention could be fully achieved.

[Effect]

To cross-wire ferromagnetic powder under high shear stress, a small amount of resin solution is usually added to cross-wire, but the added solution is locally absorbed by a part of the ferromagnetic powder. Magnetic powder is difficult to be in a uniform state, and solids/solids are much easier to mix uniformly.6 In the present invention,
The ferromagnetic powder and the ferromagnetic powder are thoroughly mixed in advance with a resin composition such as an epoxy resin that has been finely ground to a size of 20 μm or less, so that the ferromagnetic powder and the resin composition are in a uniformly mixed state. Then, the resin particles are swollen by the subsequent addition of a solvent, and the ferromagnetic powder is adsorbed and kneaded using the ferromagnetic powder as a nucleus, resulting in a magnetic paint with a uniform tactoid structure.
It is believed that this makes it possible to form a magnetic thin film with extremely small surface roughness.

In the present invention, powdered resins such as epoxy resins, phenolic resins, and vinyl resins are used for dispersing ferromagnetic powders, and the smaller the particle size of these resin powders, the easier it is to apply a thin film with a smaller surface roughness. It becomes possible. Regarding the particle size of the resin powder, the smaller the particle size, the greater the effect.

In particular, it is desirable that the thickness be 20 μm or less. For example, when using epoxy resin, the surface roughness before processing of the magnetic disk obtained by applying the prepared magnetic paint is as shown in Figure 1.
When using epoxy resin powder with a particle size of 200 μm, 0
．． 045 μmRa, whereas when using epoxy resin powder with a particle size of 20 μm, it is 0.030 μmRa. In addition, the surface roughness before processing of the magnetic disk obtained by storing the prepared magnetic paint with vibration for 10 days and applying it to a non-magnetic substrate is as follows: While it is 0.070μmRa,
0.0 when using epoxy resin powder with a particle size of 20 μm.
040 μmRa, and 0.027 μmRa when using an epoxy resin with a particle size of 3 μm. by this,
As shown in FIG. 2, it is possible to reduce the noise of the magnetic disk.

Generally, when the amount of solvent in a magnetic paint increases, the aggregation of ferromagnetic powder progresses, making it impossible to apply a thin film and reducing surface roughness (smoothness). This tendency is related to magnetic paints in which magnetic powder forms tactoids in the paint, for example, the conventional techniques such as Japanese Patent Publication No. 57-40566 and Japanese Patent Application Laid-Open No. 56-10
This is particularly noticeable in paints in which ferromagnetic powder is dispersed in an epoxy resin solution, as described in Japanese Patent No. 0871. 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. Therefore, thin film coating with roughness is possible. In addition, the uniqueness of the magnetic paint according to the present invention is that when the magnetic paint is spin-coated onto a magnetic disk disk, it is normally applied thinly on the inner circumferential side of the magnetic disk disk and thickly 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 (8.8 inches) due to high-speed spin coating, and from the inner periphery to the outer periphery, there is no difference in film thickness before processing. It is possible to form a uniform thin film with a thickness of 1, for example, 0.4 μm. This makes it possible to increase the resolution of the magnetic disk, and eliminates problems when writing with a thin film head. It is also possible to significantly shorten the coating film processing time.

It has also been found that when the resin composition is pulverized with a jet mill to a particle size of 20 μm or less, the wettability of the magnetic paint is significantly improved. For epoxy resin, particle size is 40μm
When spin-coating magnetic paint using epoxy resin powder on a 14-inch aluminum substrate, the rotation speed is 20 Or
pm, the magnetic paint is repelled on the outer periphery of the aluminum substrate and cannot be applied. Rotation speed to 150
When the rpm is lowered, even the outer periphery of the aluminum substrate can be wetted and coating becomes possible.

On the other hand, when spin coating magnetic paint using epoxy resin powder with a particle size of 20 μm or less, the coating rotation speed is 20 μm or less.
Completely wet the outer periphery of the aluminum substrate with Orpm,
It has very good coating properties. This saves magnetic paint and shortens the time required for coating, which has an extremely large economic effect. In addition, as mentioned earlier, magnetic paint using epoxy resin powder with a particle size of 20 μm does not cause agglomeration of the magnetic powder, and the paint can be stored for a long period of time. It can be said that forming a fine powder of 20 μm or less is extremely effective.

〔Example〕

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

(Example 1) Epoxy resin powder having a particle size of about 10 μm was prepared using a jet mill. After thoroughly mixing 25 parts by weight of the powdered epoxy resin, 100 parts by weight of ferromagnetic powder and 10 parts by weight of single crystal alumina, 10 parts by weight of cyclohexanone was added and further mixing was carried out in a kneader mixer. Thereafter, 5 parts by weight of cyclohexanone was further added and crosstalk was performed under high shear stress for about 4 hours.

Put the above mixture into a ball mill pot, add 200 parts by weight of a mixed solvent consisting of cyclohexanone and isophorone,
Ball mill kneading was performed for 5 days to disperse the ferromagnetic powder. Next, add 25 parts by weight of phenolic resin and 6 parts by weight of vinyl resin.
Adding a solution in which parts by weight were dissolved in 350 parts by weight of a mixed solvent consisting of cyclohexanone, isophorone, and dioxane,
A magnetic paint for magnetic disks was prepared. Next, the above paint was dropped at 20 rpm onto an 8.8-inch aluminum substrate whose surface had been cleaned in advance, and the coating was heated at 1500 rpm.
After spin coating at m, magnetic field orientation was performed by a well-known method. After baking the coated magnetic disk at 210° C., the coating thickness and surface roughness were measured. The film thickness of the obtained coated disk before processing is 0 at the radius R65nv++ of the magnetic disk.
．． 41 μm, and 0.43 μm for R105nyn. The surface roughness before processing was 0.027 μmRa.

This magnetic paint was stored for 10 days by stirring, and then spin-coated, oriented, and baked on an aluminum substrate in the same manner as above. The film thickness of the obtained coating disc before processing is 0.38 pm for R65nwn, Q is 40 μm for R105 mm, and the surface roughness before processing is 0.030 μmRa.
Met. Even though this magnetic paint was stored for a long time, the magnetic powder hardly reagglomerated! ! The wettability of the Fl material was also excellent, and it was possible to apply it thinly and uniformly with small surface roughness.

(Example 2) Epoxy resin powder having a particle size of approximately 3 μm was prepared using a jet mill, and a magnetic paint and a magnetic disk were prepared in the same manner as in Example 1 using this powder. The film thickness of the obtained coated disk before processing is 0.40 at radius R65+am of the magnetic disk.
The length was 11 m, the radius was 105 mm, and the surface roughness before processing was 0.025 μm Ra.

In addition, after storing this magnetic paint for 10 days in the same manner as in Example 1, the film thickness of the prepared magnetic disk before processing was R65m and 0.
．． The surface roughness before machining was 0.027 μm Ra with a diameter of 38 μm and a radius of 105 mm. Even though this magnetic paint was stored for a long period of time, the magnetic powder hardly reagglomerated, the paint had excellent wettability, and could be applied thinly and uniformly with small surface roughness.

(Example 3) Epoxy resin powder with a particle size of 20 μm was prepared using a jet mill, and a magnetic paint and a magnetic disk were prepared in the same manner as in Example 1 using this powder. The film thickness of the obtained coated disk before processing is 0.4 when the radius of the magnetic disk is R65m5.
The surface roughness before processing was 2 μm, 0.43 μm in the R105 field, and 0.030 μm.

Furthermore, after storing this magnetic paint for 10 days in the same manner as in Example 1, the film thickness of the prepared magnetic disk before processing was R65+nm.
So 0.40. pm, 0.040μm at R105rrta
The roughness before processing was 0,040 μmRa.

Even though this magnetic paint was stored for a long period of time, the re-aggregation of the magnetic powder did not progress much, and the wettability of the paint was excellent, allowing it to be applied thinly and uniformly with minimal surface roughness.

(Comparative Example 1) Epoxy resin powder with a particle size of 40 μm was prepared using a jet mill, and a magnetic paint was prepared in the same manner as in Example 1 using this powder. Next, clean the surface in advance 8, 8
Apply the above paint on an inch aluminum substrate at 150 rpm.
After applying it dropwise at 1,500 rpm, magnetic field orientation was performed using a well-known method. After baking the coated magnetic disk at 210° C., the coating thickness and surface roughness were measured.

The film thickness of the obtained coated disk before processing is 0.45 μm when the radius of the magnetic disk is R65+nm, and 0.45 μm when the radius R is 105 nm.
The roughness before processing was 0.040 μm Ra.

Further, this magnetic paint was stored for 10 days in the same manner as in Example 1, and then applied, oriented, and baked in the same manner as above. The film thickness of the obtained coating disc before processing was R65wn and 0.42.
μm, R105nn was 0.48 μm, and the surface roughness before processing was 0.050 μm Ra. This magnetic paint had poor wettability, and when the paint was dropped at 200 rpm, the aluminum substrate repelled the paint, and in particular, the outer periphery of the magnetic disk was hardly wetted.

(Comparative Example 2) An epoxy resin powder having a particle size of approximately 40 μm was prepared using a mixer, and a magnetic paint and a magnetic disk were prepared in the same manner as in Comparative Example 1 using this powder. The film thickness of the obtained coated disk before processing is 0.48 μm at a magnetic disk radius of 65+m.
, R105+m is 0.50 μm, and the surface roughness before processing is 0.
It was 045 μmRa.

Further, after storing this magnetic paint for 10 days in the same manner as in Example 1, a magnetic disk was prepared in the same manner as in Comparative Example 1. The film thickness of this magnetic disk before processing is R65m and O-45pm.
p R105+nm was 0.50+mm, and the surface roughness before processing was 0.070 μm Ra. This magnetic paint had poor wettability, and when the paint was dropped at 20 rpm, the aluminum substrate repelled the paint, and in particular, the outer periphery of the magnetic disk was hardly wet. When this magnetic paint was stored for a long period of time, the magnetic powder reagglomerated and the surface roughness increased.

(Comparative Example 3) 100 parts by weight of ferromagnetic powder and 10 parts by weight of single crystal alumina were charged into a kneader and mixed. Thereafter, a solution of 14 parts by weight of epoxy resin dissolved in 21 parts by weight of cyclohexanone was added and mixing was continued. Further, a solution of 6 parts by weight of epoxy resin dissolved in 9 parts by weight of cyclohexanone was added, and crosstalk was performed under high shear stress for about 4 hours.

Put the above mixture into a ball mill pot and use epoxy resin 5
180 parts by weight of a mixed solvent consisting of cyclohexanone and isophorone were added and kneaded in a ball mill for 5 days to disperse the ferromagnetic powder.

Next, a solution prepared by dissolving 25 parts by weight of phenol liver fat and 6 parts by weight of vinyl resin in 350 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 at 150 rpm onto an 8.8-inch aluminum substrate whose surface had been cleaned in advance, and magnetic field orientation was performed using a well-known method. After baking, the paint film thickness and surface roughness were determined. 6 The film thickness of the obtained coated disk before processing is 65 mm in radius of the magnetic disk.
Agglomerates of magnetic powder were observed on the coated surface of the magnetic disk, which had a roughness of 0.50 μm at R105+mm and 0.75 μm at R105+mm, and a roughness of 0.18 amRa before processing.

As mentioned above, the particle size pulverized with a jet mill is 20
Resin powder with a particle diameter of μm or less is particularly effective.

To form a thin film, 1 magnetic paint containing a large amount of solvent is usually used, but magnetic powder is particularly likely to aggregate in such a paint. 6 Therefore, it is necessary to form a thin film with a small surface roughness and to It is very difficult to maintain it for a long time.

The present invention solves these problems by using resin powder with a particle size of 2 μm or less.

Epoxy resin was used as a polymeric binder for dispersing ferromagnetic powder in the above examples of the present invention.

Phenol resin and vinyl resin are used, but other
Commonly used vinyl resins such as vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, acrylonitrile-acrylic acid-2-hydroxyethyl methacrylate copolymer, acrylonitrile-butadiene copolymer Ordinary organic materials that have good binding properties for ferromagnetic powders, such as rubber resins such as polymers, fiber cord resins such as nitrocellulose and acetylcellulose, epoxy resins such as phenoxy, and urethane resins such as urethane and urethane prepolymers. A polymer compound can be used. In addition, examples of the vinyl resin used as the polymeric binder for dispersing ferromagnetic powder in the present invention include polyvinyl butyral, polyvinyl formal, polyvinyl acetate, etc. Among these, it is particularly preferable to use polyvinyl butyral. .

〔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. This magnetic paint has excellent wettability and has a long paint life. When this is applied to a magnetic recording medium, for example a magnetic disk using an 8.8 inch aluminum substrate, the surface roughness before processing is 0.
The surface roughness is very small, less than 0.050 μmRa, and it is possible to easily form a thin film with a uniform thickness of less than 0.9 μm on both the inner and outer circumferences of the magnetic disk by a coating method. Compared to the above, the machining time can be halved, and electrical defects caused by scratches during machining can also be halved. Also,
It is expected that the noise of the magnetic disk will be reduced by about 30%, and that the output resolution will also be improved. Furthermore, since the film thickness at the outer periphery of the magnetic disk is thin, troubles when using a thin film head can be eliminated.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the particle size of the resin powder and the surface roughness of the obtained magnetic disk before processing, and Figure 2 is a graph showing the relationship between the surface roughness of the magnetic disk before processing and magnetic disk noise. It is. 0, 口... Roughness of the processed front surface of the magnetic disk applied immediately after preparing the magnetic paint, ・, S... Represents the processed surface roughness of the magnetic disk applied 10 days after the preparation of the magnetic paint, o, ・
... Particle size, mouth, 1 of resin powder crushed by jet mill
...One of the resin powders crushed with a sand mill / ゛ Uji main life tree / lχ tachi L (, x >

Claims (1)

[Claims] 1. A method for producing a magnetic paint, which is a paint composition for forming a magnetic recording film of a magnetic recording medium, including ferromagnetic powder constituting the magnetic recording film and dispersion bonding of the ferromagnetic powder. When mixing the resin composition as a powder, the resin composition is made into a fine powder, and the ferromagnetic powder or the ferromagnetic powder containing a filler and the resin composition made into a fine powder are machined. 1. A method for producing a magnetic coating comprising the step of mixing the resin composition thoroughly and then kneading it under high shear stress, the method comprising turning the resin composition into a fine powder of 20 μm or less. 2. The method for producing a magnetic paint according to claim 1, wherein the resin composition contains at least one of epoxy resin, phenol resin, and vinyl resin. 3. The method for producing a magnetic paint according to claim 1, in which a jet mill is used to form the resin composition into a fine powder of 20 μm or less. 4. In a magnetic recording medium manufactured using a magnetic paint that is a paint composition for forming a magnetic recording film, ferromagnetic powder that constitutes the magnetic recording film and a resin that is a dispersion binder for the ferromagnetic powder When mixing with the resin composition, 20μ of the resin composition
The above-mentioned ferromagnetic powder or ferromagnetic powder containing a filler and the above-mentioned finely powdered resin composition are mechanically mixed sufficiently, and then kneaded under high shear stress. A magnetic paint film is formed on a non-magnetic substrate using a magnetic paint manufactured by a method including a step of A magnetic recording medium with a small magnetic coating. 5. The magnetic recording medium according to claim 4, wherein the resin composition comprises at least one of epoxy resin, phenol resin, and vinyl resin. 6. The magnetic recording medium according to claim 4 or 5, wherein the magnetic recording medium is a magnetic disk. 7. The magnetic coating film formed on the non-magnetic substrate before processing is a substantially uniform magnetic coating film with a film thickness of 0.9 μm or less, and the surface roughness of the magnetic coating film is 0.05 μmRa or less. A magnetic recording medium according to any one of claims 4 to 6.