JP2609656B2 - Method for producing magnetic paint and magnetic recording medium and magnetic recording / reproducing apparatus using the same - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a magnetic recording medium, and more particularly to a method for producing a magnetic paint for forming a magnetic recording layer of a magnetic recording medium, and an electrical property and reliability using the same. A magnetic recording medium suitable for an excellent high-density magnetic disk and the like, and a magnetic recording / reproducing apparatus having the above-mentioned magnetic recording medium and a magnetic head for performing recording and reproduction on the magnetic recording medium.

[Conventional technology]

A conventional method for producing a magnetic recording medium by applying a magnetic paint in which a ferromagnetic powder is dispersed in a polymer binder containing an epoxy resin or the like to a non-magnetic substrate is disclosed in Japanese Patent Publication No. 55-816. Many have been proposed, including the beginning. Among them, a method of kneading and manufacturing a ferromagnetic powder together with a resin or the like is disclosed in JP-B-57-40566 and JP-A-56-100871. This is a method of producing a magnetic paint by kneading under a high shear stress together with a resin solution in which a ferromagnetic powder and an epoxy resin or the like are dissolved in cyclohexanone, and applying this to produce a magnetic recording technique. But,
In these prior arts, no consideration was given to sufficiently mixing the ferromagnetic powder with the epoxy resin as a binder for dispersion before kneading. Therefore, in the magnetic coatings obtained by these prior art methods, the kneading is carried out in a state where a small amount of the resin solution added during kneading is locally absorbed by a part of the ferromagnetic powder. It was extremely difficult to obtain a magnetic paint having a tactoid structure in which powders were uniformly dispersed in terms of kneading performance. Therefore, when a magnetic recording layer is formed using the magnetic paint according to the conventional method, it is impossible to form a thin film having a thickness of less than about 0.9 μm, and the surface roughness of the coated surface before processing is about 0.08. It was coarse with μmRa. And, as the recording density of the magnetic disk increases, the thinning of the coating film progresses, the amount of coating film processing must be increased, and an increase in the amount of coating film processing not only leads to an increase in processing time, There is a problem that an increase in the frequency of occurrence of scratches on the coating film surface causes an increase in electrical defects.

An increase in electrical defects causes a malfunction in the magnetic recording / reproducing apparatus. Further, scratches on the surface of the coating film also damage the surface of the magnetic head facing the disk, causing head crash.

[Problems to be solved by the invention]

The magnetic paint manufactured according to the above-described conventional technique has an insufficient dispersion of the magnetic powder in the magnetic paint, so that with this magnetic paint, it is practically impossible to form a thin film having a thickness of less than 0.9 μm, The surface roughness before processing was as coarse as about 0.08 μmRa. Further, in recent high-density magnetic disk drives, thin-film heads are used as magnetic heads, so that there is a problem that if the film thickness of the magnetic disk medium is large, signals cannot be sufficiently written. The magnetic disk medium is usually applied thin on the inner peripheral side and thicker on the outer peripheral side. Therefore, the above-described trouble in the thin film head usually occurs at the outer peripheral portion of the magnetic disk. As a countermeasure, it is necessary to make the thickness of the outer peripheral portion of the magnetic disk thinner, but at present, there is no other method than increasing the amount of coating on the outer peripheral portion than on the inner peripheral portion. As a result, an increase in coating film processing time and an increase in electrical defects due to generation of a large amount of scratches are caused.

An object of the present invention is to improve the state of dispersion of magnetic powder in a paint by improving the method for producing a magnetic paint. As a result, by reducing the surface roughness of the coated surface of the magnetic disk before processing, the S / N (signal / signal) of the magnetic disk medium is reduced.
Noise) ratio is to be improved, and the film thickness at the time of coating is set to 0.9 μm or less together with the inner and outer circumferences of the magnetic disk.

Another object of the present invention is to provide a magnetic recording / reproducing device and a magnetic recording device with high S / N and high resolution. Further, another object of the present apparatus is to reduce malfunctions,
An object of the present invention is to provide a magnetic recording / reproducing apparatus in which a crash hardly occurs.

[Means for solving the problem]

In order to achieve the above object of the present invention, the present inventors have conducted intensive studies, and as a result, conventionally, a bulk or plate-like epoxy resin, phenol resin, vinyl resin which is a binder for dispersing magnetic powders This is the particle size
Powder resin of 20μm or less
After sufficiently mechanically mixing with a ferromagnetic powder having a specific surface area of T value of 30 m ² / g or more, a suitable solvent is added to swell the uniformly mixed powdery resin, Kneading under shear stress, the resin powder is almost melted and uniformly kneaded with the ferromagnetic powder, and then, by performing ball mill kneading as before, the ferromagnetic powder is uniformly dispersed. It has been found that a magnetic paint having a tactoid structure can be obtained.
Then, using the magnetic paint manufactured in this manner, a magnetic disk was produced by applying the composition to a non-magnetic substrate and orienting it.The surface roughness before processing was extremely small at 0.030 μm Ra or less, and moreover, 5.25 inches. An almost uniform magnetic disk having a magnetic film thickness of 0.7 μm or less was obtained, and the object of the present invention was sufficiently achieved.

According to the present invention, a magnetic recording apparatus in which the coating film thickness is as thin as 0.7 μm or less and the processed film thickness is 0.3 μm or less, scratches are unlikely to occur, and therefore, malfunctions are reduced and head crash is unlikely to occur. Can be made.

[Action]

To knead ferromagnetic powder under high shear stress, usually
A small amount of resin solution is added and kneading is performed, but the added solution is locally absorbed by a part of the ferromagnetic powder, and the magnetic powder is hard to be in a uniform state. Are much easier to mix. In the present invention, a ferromagnetic powder having a non-surface area having a BET value of 30 m ² / g or more and a resin composition such as a finely ground epoxy resin having a particle size of 20 μm or less is sufficiently mixed in advance. And the resin composition are in a uniform mixed state. The subsequent addition of the solvent causes the resin particles to swell, and the ferromagnetic powder is adsorbed and kneaded with the nuclei as a nucleus, so that a magnetic paint having a uniform tactoid structure can be obtained. It is considered that a thin film can be formed.

Epoxy resin for dispersing the ferromagnetic powder in the present invention,
Phenolic resin, vinyl resin, and other powdery resins are used.The smaller the particle size of these resin powders and the larger the specific surface area of ferromagnetic powders, the more it is possible to apply thin films with smaller surface roughness. Become. The particle size of the resin powder is preferably 20 μm or less, and the ferromagnetic powder has a BET value of 30 m ² / g.
It is desirable to have the above specific surface area.

In general, when the amount of a solvent in a magnetic paint increases, agglomeration of the ferromagnetic powder proceeds, making it impossible to apply a thin film and reducing the surface roughness (smoothness). This tendency is due to the fact that the magnetic powder forms a tactoid in the paint, for example, as described in JP-B-57-40566 and JP-A-56-100871, which are conventional techniques. Is particularly remarkable in a coating material in which is dispersed in an epoxy resin solution. In the magnetic paint according to the present invention, despite the fact that the magnetic powder forms a tactoid structure in the paint, even if the amount of solvent in the paint is increased, the aggregation of the ferromagnetic powder does not proceed, so that the small It becomes possible to apply a thin film with surface roughness. Also, the specificity of the magnetic paint according to the present invention is that when the magnetic paint is spin-coated on a magnetic disk, the inner peripheral side of the magnetic disk is usually thinner and the outer peripheral side is thicker, resulting in a film thickness gradient. On the other hand, in the magnetic paint according to the present invention, by performing high-speed spin coating, there is almost no difference in the film thickness between the inner and outer circumferences of the magnetic disk (5.25 inch). Thus, for example, a uniform thin film of 0.5 μm can be formed. As a result, it is possible to increase the resolution of the magnetic disk, and the trouble at the time of writing with the thin-film head is eliminated. Further, the coating film processing time can be significantly reduced.

〔Example〕

Hereinafter, an embodiment of the present invention will be described in more detail.

Example 1 A plate-like epoxy resin was pulverized by a jet mill to obtain an epoxy resin powder having a particle size of about 8.0 μm. After thoroughly mixing 25 parts by weight of the above powdery epoxy resin, ferromagnetic powder (iron oxide powder (Hc7700e) having a specific surface area of 40 m ² / g BET value, Hc7700e), 100 parts by weight and 5 parts by weight of single crystal alumina And 10 parts by weight of cyclohexanone, and further mixed in a kneader kneader. Thereafter, 5 parts by weight of cyclohexanone was further added and kneaded under high shear stress for about 4 hours.

Put the kneaded material in a ball mill pot, added 140 parts by weight of a mixed solvent consisting of cyclohexanone and isophorone,
The ball mill was kneaded for 3 days to disperse the ferromagnetic powder. Next, a solution prepared by dissolving 25 parts by weight of a phenol resin and 6 parts by weight of a hinyl resin in 490 parts by weight of a mixed solvent composed of cyclohexanone / isophorone / dioxane was added to prepare a magnetic paint for a magnetic disk. Next, the above-mentioned paint was spin-coated on a 5.25 inch aluminum substrate whose surface had been cleaned in advance, and magnetic field orientation was performed by a known method. After baking the applied magnetic disk at 210 ° C., the coating thickness and surface roughness were measured.

The thickness of the obtained coated disc before processing is 0.50 at R38 mm.
μm and R60 mm were also 0.50 μm. The surface roughness before processing was 0.020 μmRa. After that, the coating film is processed by a well-known method, and the film thickness after the processing is R38mm and R60mm.
It was 0.30 μm.

This disk was subjected to electrical measurement using a metal-in-gap type head having a gap length of 0.3 μm. The measurement conditions were 26.25kFCI for the highest recording frequency and 6.5 for the lowest recording frequency.
It was 6 kFCI. The playback output and noise were measured, and the signal-to-noise ratio at the highest recording frequency was calculated as S / N, and the signal at the highest recording frequency was divided by the signal at the lowest recording frequency and expressed as a percentage. . The result is shown in FIG. The vertical axis is S / N, and the horizontal axis is resolution. In the following examples, the same measurement was performed for the comparative example, and the results are collectively shown in FIG.

Example 2 100 parts by weight of ferromagnetic powder (Co-coated iron oxide powder (Hc7700e) having a specific surface area of 45 m ² / g BET value), 5 parts by weight of single crystal alumina, and an epoxy resin having a particle size of about 3.0 μm After sufficiently mixing 25 parts by weight of the powder, 10 parts by weight of cyclohexanone was added, and further mixed in a kneader kneader. afterwards,
5 parts by weight of cyclohexanone was added and kneaded under high shear stress for about 4 hours.

Put the kneaded material in a ball mill pot, added 140 parts by weight of a mixed solvent consisting of cyclohexanone / isophorone,
Ball mill kneading was performed for 3 days to disperse the ferromagnetic powder. Next, a solution prepared by dissolving 25 parts by weight of a phenol resin and 6 parts by weight of a vinyl resin in 550 parts by weight of a mixed solvent composed of cyclohexanone / isophorone / dioxane was added to prepare a magnetic paint for a magnetic disk. Next, the above-mentioned paint was spin-coated on a 5.25 inch aluminum substrate whose surface had been cleaned in advance, magnetic field orientation was performed by a known method, and after baking, the coating thickness and surface roughness were measured. The film thickness of the obtained coated disc before processing is 0.40μ for both R38mm and R60mm.
m. No visual defects were observed on the coated surface.
After that, the coating film is processed by a well-known method, R38mm, R60
mm was 0.22 μm.

Example 3 100 parts by weight of ferromagnetic powder (iron oxide powder (Hc7700e) having a specific surface area of 50 m ² / g BET value) and 25 parts by weight of an epoxy resin powder having a particle size of about 2.0 μm were sufficiently mixed. Cyclohexanone 10
The mixture was added in parts by weight and further mixed in a kneader kneader. Thereafter, 5 parts by weight of cyclohexanone was added and kneaded under high shear stress for about 4 hours.

Put the kneaded material in a ball mill pot, added 165 parts by weight of a mixed solvent consisting of cyclohexanone / isophorone,
Ball mill kneading was performed for 3 days to disperse the ferromagnetic powder. Next, a solution prepared by dissolving 25 parts by weight of a phenol resin and 6 parts by weight of a vinyl resin in 600 parts by weight of a mixed solvent composed of cyclohexanone / isophorone / dioxane was added to prepare a magnetic paint for a magnetic disk. Next, the above-mentioned paint was spin-coated on a 5.25 inch aluminum substrate whose surface had been cleaned in advance, magnetic field orientation was performed by a known method, and after baking, the coating thickness and surface roughness were measured. The film thickness of the obtained coated disc before processing is 0.30 for both R38mm and R60mm.
μm, and the surface roughness before processing was 0.015 μmRa. afterwards,
Perform coating film processing by a well-known method.
It was 20 μm.

Example 4 An epoxy resin powder having a particle size of about 20 μm was prepared. 25 parts by weight of the above powdery epoxy resin and ferromagnetic powder (BET value 30 m ² / g
After sufficiently mixing 100 parts by weight of iron oxide powder (Hc3500e) having a specific surface area of 5% and 5 parts by weight of single-crystal alumina, 10 parts by weight of cyclohexanone was added and further mixed in a kneader kneader. Then, add cyclohexanone 5
The mixture was kneaded under high shear stress for about 4 hours with the addition of parts by weight.

Put the kneaded material in a ball mill pot, added a mixed solvent of cyclohexanone and isophorone 200 parts by weight,
The ball mill was kneaded for 3 days to disperse the ferromagnetic powder. Next, a solution prepared by dissolving 25 parts by weight of a phenol resin and 6 parts by weight of a vinyl resin in 400 parts by weight of a mixed solvent of cyclohexanone / isophorone / dioxane was added to prepare a magnetic paint for a magnetic disk. Next, the surface was previously cleaned, and the above-mentioned paint was spin-coated on a 5.25 inch aluminum substrate, and magnetic field orientation was performed by a known method. After baking the applied magnetic disk at 210 ° C., the coating thickness and surface roughness were measured. The film thickness of the obtained coated disk before processing was 0.6 μm at R38 mm and 0.7 μm at R60 mm. The surface roughness before processing was 0.030 μmRa. After that, perform coating film processing by a well-known method, R38 mm, R60 mm
Both were set to 0.30 μm.

Comparative Example 1 100 parts by weight of ferromagnetic powder (iron oxide powder (Hc3500e) having a specific surface area of 30 m ² / g BET value) and 5 parts by weight of single crystal alumina were charged into a kneader kneader and mixed. Then the epoxy resin
A solution in which 14 parts by weight of cyclohexanone was dissolved in 21 parts by weight was added, and mixing was continued. Further, a solution in which 6 parts by weight of an epoxy resin was dissolved in 9 parts by weight of cyclohexanone was added, and kneading was performed under high shear stress for about 4 hours.

The kneaded material was placed in a ball mill pot, and 5 parts by weight of an epoxy resin and 180 parts by weight of a mixed solvent composed of cyclohexanone and isophorone were added, and the mixture was kneaded with a ball mill for 5 days to disperse the ferromagnetic powder. Next, a solution prepared by dissolving 25 parts by weight of a phenol resin and 6 parts by weight of a vinyl resin in 350 parts by weight of a mixed solvent of cyclohexanone / isophorone / dioxane was added to prepare a magnetic paint for a magnetic disk.

Next, the coating material was spin-coated on a 5.25 inch aluminum substrate whose surface had been cleaned in advance, magnetic field orientation was performed by a well-known method, and baking was performed. Then, the coating film thickness and surface roughness were measured. The film thickness of the obtained coated disk before processing was 0.9 μm for R38 mm and 1.0 μm for R60 mm. The surface roughness before processing was 0.08 μmRa. After that, the coating film is processed by a well-known method, R38mm, 0.3μm, R60m
m and 0.35 μm.

(Comparative Example 2) 100 parts by weight of ferromagnetic powder (Co-coated iron oxide powder (Hc7700e) having a specific surface area of a BET value of 40 m ² / g) and 5 parts by weight of single crystal alumina were charged into a kneader kneader and mixed. did. Thereafter, a solution in which 14 parts by weight of an epoxy resin was dissolved in 21 parts by weight of cyclohexanone was added, and mixing was continued. Further, a solution in which 6 parts by weight of an epoxy resin was dissolved in 9 parts by weight of cyclohexanone was added, and kneading was performed under high shear stress for about 4 hours.

The kneaded material was placed in a ball mill pot, and 5 parts by weight of an epoxy resin and 180 parts by weight of a mixed solvent composed of cyclohexanone and isophorone were added, and the mixture was kneaded with a ball mill for 5 days to disperse the ferromagnetic powder. Next, a solution prepared by dissolving 25 parts by weight of a phenol resin and 6 parts by weight of a vinyl resin in 450 parts by weight of a mixed solvent of cyclohexanone / isophorone / dioxane was added to prepare a magnetic paint for a magnetic disk.

Next, the coating material was spin-coated on a 5.25 inch aluminum substrate whose surface had been cleaned in advance, magnetic field orientation was performed by a well-known method, and baking was performed. Then, the coating film thickness and surface roughness were measured. The film thickness of the obtained coated disk before processing was 0.4 μm for R38 mm and 0.7 μm for R60 mm. The surface roughness before processing was 0.23 μmRa.

(Comparative Example 3) A plate-like epoxy resin was pulverized with a mixer to a particle size of about 100.
A μm epoxy resin powder was obtained. After sufficiently mixing 25 parts by weight of the powdered epoxy resin, ferromagnetic powder (iron oxide powder (Hc3400e) having a specific surface area of 22 m ² / g BET value of 22 m ² / g), 100 parts by weight and 5 parts by weight of single crystal alumina, cyclohexanone 10 parts by weight were added and further mixed in a kneader kneader. Thereafter, 5 parts by weight of cyclohexanone was further added and kneaded under high shear stress for about 4 hours.

Put the kneaded material in a ball mill pot, added a mixed solvent of cyclohexanone and isophorone 200 parts by weight,
The ball mill was kneaded for 5 days to disperse the ferromagnetic powder. Next, a solution in which 25 parts by weight of a phenol resin and 6 parts by weight of a hinyl resin were dissolved in 280 parts by weight of a mixed solvent composed of cyclohexanone / isophorone / dioxane was added to prepare a magnetic coating material for a magnetic disk. Next, the above-mentioned paint was spin-coated on a 5.25 inch aluminum substrate whose surface had been cleaned in advance, and magnetic field orientation was performed by a known method. After baking the applied magnetic disk at 210 ° C., the coating thickness and surface roughness were measured.

The film thickness of the obtained coated disk before processing is 0.8μ at R38mm.
m, 0.9 μm for R60 mm. The surface roughness before processing is
It was 0.045 μmRa.

As the polymer binder for dispersing the ferromagnetic powder used in the above-described embodiments of the present invention, epoxy resin, phenol resin, and vinyl resin are used. Polymers, vinyl resins such as vinyl chloride-vinyl acetate-vinyl alcohol copolymer, acrylonitrile-acrylic acid-2-hydroxyethyl methacrylate copolymer, rubber resins such as acrylonitrile-butadiene copolymer, nitrocellulose, acetyl Ordinary organic high molecular compounds having good binding properties of ferromagnetic powder, such as cellulose resin such as cellulose, epoxy resin such as phenoxy, and urethane resin such as urethane and urethane prepolymer, can be used. In addition, as the vinyl resin used as the polymer binder for dispersing the ferromagnetic powder in the present invention, polyvinyl butyral, polyvinyl formal, polyvinyl acetate and the like can be mentioned, and among them, it is particularly preferable to use polyvinyl butyral .

In this embodiment, iron oxide powder and Co-coated iron oxide powder are used as the ferromagnetic powder.
Metal powder, barium ferrite powder, or the like having a specific surface area of 0 m ² / g or more can be used.

〔The invention's effect〕

As described in detail above, the magnetic paint manufactured by the method of the present invention can obtain a magnetic paint having a tactoid structure in which ferromagnetic powder is uniformly dispersed in the paint, and this is coated with a magnetic recording medium, for example, 14 inches. When applied to a magnetic disk using an aluminum substrate, the surface roughness before processing is 0.
The surface roughness is as small as 050μmRa or less, and the extremely thin and uniform thin film of 0.9μm or less on both the inner and outer circumferences of the magnetic disk can be easily formed by a coating method. Compared with this, the processing time can be reduced by half, and furthermore, there is an effect that voltage defects due to scratches during processing can be reduced by half. In addition, the noise of the magnetic disk can be expected to be reduced by about 30% and the output resolution can be improved. Further, since the thickness of the outer peripheral portion of the magnetic disk is small, it is possible to eliminate troubles when using the thin film head.

[Brief description of the drawings]

FIG. 1 is a diagram showing a comparison of the electrical characteristics of the magnetic disks of Example 1, Example 2, Example 3, Example 4, and Comparative Example 1 of the present invention.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasutaro Uesaka 1-280 Higashi Koikekubo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. (72) Inventor Masayuki Katsumoto 1-280 Higashi Koikekubo, Kokubunji-shi, Tokyo Hitachi, Ltd. (56) References JP-A-63-124221 (JP, A) JP-A-60-57527 (JP, A)

Claims (13)

(57) [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, comprising: a ferromagnetic powder constituting a magnetic recording film; and a dispersion binder of the ferromagnetic powder. When mixing with the resin composition, the resin composition is fine powder, the ferromagnetic powder or ferromagnetic powder containing a filler, and the fine powder resin composition, mechanically After sufficient mixing, the specific surface area BET value of the ferromagnetic powder in the method for producing a magnetic paint including a step of adding a solvent or a liquid dispersion binder and kneading under high shear stress is 30 m
^A method for producing a magnetic paint, characterized by being at least ² / g. 2. The method according to claim 1, wherein the ferromagnetic powder is at least one of iron oxide powder, Co-coated iron oxide powder, metal powder, and barium ferrite powder. Method. 3. The method according to claim 1, wherein the resin composition contains at least one of an epoxy resin, a phenol resin, and a vinyl resin. 4. The method according to claim 1, wherein the resin composition is a fine powder having an average particle size of 20 μm or less. 5. A magnetic recording medium produced by using a magnetic paint which is a paint composition for forming a magnetic recording film, comprising a ferromagnetic powder or a filler having a specific surface area BET value of 30 m ² / g or more. After the ferromagnetic powder containing and the finely divided resin composition which is a dispersion binder of the ferromagnetic powder are mechanically sufficiently mixed, a solvent is added and kneaded under high shear stress. Using a magnetic paint produced by a method including a step, a magnetic coating film is formed on a non-magnetic substrate, and the thickness of the magnetic coating film before processing is thin and almost uniform, and the surface roughness is small. A magnetic recording medium having a magnetic coating film. 6. The magnetic recording medium according to claim 5, wherein said ferromagnetic powder is at least one of iron oxide powder, Co-coated iron oxide powder, metal powder, and barium ferrite powder. 7. The magnetic recording medium according to claim 5, wherein said resin composition comprises at least one of an epoxy resin, a phenol resin and a vinyl resin. 8. The magnetic recording medium according to claim 5, wherein said resin composition is a fine powder having an average particle diameter of 20 μm or less. 9. The magnetic recording medium according to claim 5, wherein said magnetic recording medium is a magnetic disk. 10. The magnetic coating film before processing formed on the nonmagnetic substrate is a substantially uniform magnetic coating film having a thickness of 0.7 μm or less, and the surface roughness of the magnetic coating film is 0.03 μmRa or less. The magnetic recording medium according to claim 5, wherein 11. A magnetic head provided with a magnetic material having a saturation magnetic flux density of 4 kG or more at least near a magnetic gap.
A magnetic recording / reproducing apparatus, comprising: the magnetic recording medium according to claim 5 for performing recording and reproduction. 12. A magnetic recording / reproducing apparatus according to claim 11, wherein said magnetic material has a thickness of 5 μm or more. 13. The magnetic recording / reproducing apparatus according to claim 11, wherein said saturation magnetic flux density is 9 kG or more.