JP2656578B2 - Manufacturing method of magnetic recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a magnetic recording medium having excellent electrical characteristics.

[Conventional technology]

A general method of producing a magnetic paint for forming a magnetic recording film of a magnetic recording medium is to knead and mix a ferromagnetic powder, a binder resin, and a solvent, and finally dilute the mixture to a required concentration. For example, JP-A-56-100871 and JP-B-57-4056
No. 6 discloses a method of manufacturing a magnetic recording medium including a step of kneading a ferromagnetic powder together with a solution of cyclohexanone such as an epoxy resin under a high shear stress using a kneader. By these kneading techniques, the ferromagnetic powder can be coated with a resin to enhance the dispersibility of the ferromagnetic powder in an organic solvent or a solution of the resin in an organic solvent. In order to prevent agglomeration of the ferromagnetic powder and enhance dispersibility, various improvements have been made in manufacturing methods and materials, and a powdered epoxy resin disclosed in JP-A-63-4422 is used. The method is one of them. By these methods, the dispersion of the ferromagnetic powder in the magnetic paint is improved, and a magnetic recording medium with low noise and high recording density is manufactured using the ferromagnetic powder.

[Problems to be solved by the invention]

In the above prior art, the surface roughness of the surface of the magnetic recording medium is not sufficiently considered, and a component of a surface roughness called a waviness having a large irregularity wavelength and a small surface roughness having a small irregularity wavelength are used. Without examining the components separately, a mixed value of the two was examined. Therefore, the magnetic recording medium according to the prior art described above has a problem that a component of a large undulation having a large wavelength of the irregularities is large, and the floating of the magnetic head is unstable.

Conventionally, surface roughness was measured for all surface roughnesses of wavelengths of 0.8 mm or less, but among surface roughnesses of wavelengths of 0.8 mm or less, surface roughness of wavelengths exceeding 0.08 mm It is a waviness component and is preferably studied separately from surface roughness at a wavelength of 0.08 mm or less.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of manufacturing a magnetic recording medium having low noise, high recording density, and a large surface roughness with a small wavelength.

[Means for solving the problem]

In order to achieve the above object, a method for producing a magnetic recording medium according to the present invention comprises applying a magnetic paint in which a ferromagnetic powder is dispersed in a solution of a resin as a binder onto a substrate to form a coating film. When forming and heat curing the coating film to form a magnetic recording film,
On the surface of the ferromagnetic powder in the magnetic coating, surface area 1 m ² per 1mg
At least 2 mg or less of the above resin is adsorbed.

In order to achieve the above object, a method for manufacturing a magnetic recording medium of the present invention is characterized in that a magnetic paint in which a ferromagnetic powder is dispersed in a solution of a resin as a binder is applied on a substrate. When a film is formed and the coating is thermally cured to form a magnetic recording film, the thickness of the ferromagnetic powder in the magnetic paint must be 50 mm or more.
An adsorption layer comprising the above resin and a solvent of 150 ° or less is provided.

In the magnetic paint used in the present invention, it is preferable to use the binder resin in the range of 0.2 to 1 part by weight based on 1 part by weight of the ferromagnetic powder. As the resin, for example, one kind or two or more kinds of epoxy resin, phenol resin, vinyl resin, acrylic resin, methacrylic resin, urethane resin and the like can be used. Here, the vinyl resin may be a homopolymer such as polyvinyl butyral, polyvinyl formal, or polyvinyl acetate, or a copolymer such as vinyl chloride-vinyl acetate copolymer or vinyl chloride-vinyl acetate-vinyl alcohol. Good. Further, the urethane-based resin has a broad meaning including urethane, urethane prepolymer and the like. The same applies to other resins.

Magnetic paints are usually diluted by solvents, 50-300 mPa
・ Applied to the substrate with a viscosity of about S. The formed coating film is magnetically oriented as necessary, and is thermally cured at a temperature not lower than the curing temperature of the resin but not higher than the decomposition temperature, for example, in the range of 200 to 250 ° C., depending on the resin used.

The magnetic paint used in the present invention, in addition to the ferromagnetic powder,
A reinforcing material such as alumina, zirconium oxide, and silicon carbide may be contained. These reinforcing materials are preferably added in the range of 1 to 20% by weight based on the magnetic powder.

Examples of the ferromagnetic powder include iron oxide powder, Co-coated iron oxide powder, iron carbide powder, metal powder, and barium ferrite powder.

[Action]

When the ferromagnetic powder is dispersed in a solvent as it is, aggregation occurs. Therefore, usually adsorb resin etc. on the surface,
Aggregation is prevented by the three-dimensional repulsion. Therefore, it is necessary to adsorb a certain amount or more of resin on the surface of the ferromagnetic powder. However, if the amount of the adsorbed resin is too large, entanglement between the resins occurs, and another type of aggregation occurs.
When the concentration is high, a structure is formed in the magnetic paint, and the viscosity may be so high that it is unsuitable for application.

The amount of adsorbed resin should be 1 mg or more per ² m2 of ferromagnetic powder surface area ² m
g or less, the thickness of the adsorption layer is approximately 50
~ 150〜. This value is based on Farbe und Lack, 76 (197
0), measured by the method described on page 656.

In general, the ferromagnetic powder used for the magnetic recording medium has a minor axis diameter of 200 to 500 mm in the case of acicular powder, and in the case of plate-like powder,
The thickness is about 50-200mm. Therefore, the thickness of the adsorbed resin film is almost the same order as the size of the ferromagnetic powder, and has a sufficient effect to prevent agglomeration, and at the same time, unnecessary entanglement of the resin occurs, causing undulation on the coated surface. It is thought that it does not reach.

〔Example〕

 Examples of the present invention will be described below.

(Examples 1 to 5) 100 parts by weight of a ferromagnetic powder (acicular γ-Fe ₂ O ₃ .BET surface area 22 m ² / g) and 25 parts by weight of an epoxy resin were charged into a kneader kneader and mixed, and then cyclohexanone 15 was added. Add ~ 20 parts by weight and add 4
Kneaded for hours. Put the kneaded material in a ball mill pot,
After adding 200 parts by weight of a mixed solvent composed of cyclohexanone, isophorone and dioxane and performing ball mill kneading for 5 days, a solution obtained by dissolving 25 parts by weight of a phenol resin and 6 parts by weight of a vinyl resin in 300 parts by weight of the above mixed solvent was added. A magnetic paint was prepared.

The magnetic paint was centrifuged to measure the resin concentration in the supernatant, and the amount of resin adsorbed on the ferromagnetic powder was determined. Details are as shown in Table 1.

Next, the above magnetic paint was spin-coated on an 8.8-inch diameter aluminum substrate whose surface had been cleaned in advance, and after a magnetic field orientation was performed by a known method, the coating film was heated and cured, and the surface roughness was measured. The values of the surface roughness are also shown in Table 1.

(Example 6) Ferromagnetic powder (acicular γ-Fe ₂ O ₃ , BET surface area 22 m ² / g) 100
Parts by weight and 25 parts by weight of the epoxy resin were charged into a kneader kneader and mixed, then 10 parts by weight of cyclohexanone was added, and the mixture was kneaded for 4 hours while cooling by flowing water along the outer wall of the container of the kneader. The kneaded material was used as a magnetic paint in the same manner as in Examples 1 to 5 to prepare a magnetic disk. Resin adsorption amount to the ferromagnetic powder in the 1.5 mg / m ^2, components of the following wavelengths 0.8mm working front roughness of the magnetic disk 0.040MyumRa, 0.8mm or less components than the wavelength 0.08mm is 0.019μmRa met Was.

Example 7 100 parts by weight of a ferromagnetic powder (acicular γ-Fe ₂ O ₃ , BET surface area 22 m ² / g) and 25 parts by weight of an epoxy resin were charged into a heating kneader kneader and mixed, and then cyclohexanone 25 was added. Parts by weight were added and kneaded for 4 hours. After heat-treating the above kneaded material at 100 ° C. for 2 hours, a magnetic paint was prepared in the same manner as in Examples 1 to 5 to prepare a magnetic disk. The amount of resin adsorbed on ferromagnetic powder is 1.
At 7 mg / m ² , the component having a wavelength of 0.8 mm or less of the processing front surface roughness of the magnetic disk was 0.043 μmRa, and the component having a wavelength of 0.08 mm or more and 0.8 mm or less was 0.023 μmRa.

(Examples 8 to 10) 100 parts by weight of ferromagnetic powder (hexagonal barium ferrite powder, BET surface area 30 m ² / g) and 25 parts by weight of an epoxy resin were charged into a kneader kneader and mixed, and then cyclohexanone 10 to 13 was added.
Parts by weight were added and kneaded for 4 hours. Example 1
In the same manner as in Examples 1 to 5, magnetic coating materials were used to prepare magnetic disks. Details are shown in Table 2.

(Comparative Examples 1 to 4) 100 parts by weight of ferromagnetic powder (acicular γ-Fe ₂ O ₃ , BET surface area 22 m ² / g) and 25 parts by weight of an epoxy resin were charged into a kneader kneader, mixed, and then mixed with cyclohexanone. Was added and kneaded for 4 hours. The kneaded material was used as a magnetic paint in the same manner as in Examples 1 to 5 to prepare a magnetic disk. Details are as shown in Table 3.

Comparative Example 5 100 parts by weight of a ferromagnetic powder, 25 parts by weight of an epoxy resin, and 200 parts by weight of a mixed solvent composed of cyclohexanone, isophorone, and dioxane were put into a ball mill pot and kneaded with a ball mill for 5 days. Next, a solution prepared by dissolving 25 parts by weight of a phenol resin and 6 parts by weight of a vinyl resin in 300 parts by weight of the above mixed solvent was added to prepare a magnetic paint. The amount of resin adsorbed on the ferromagnetic powder in the magnetic paint was 0.5 mg / m ² , and the roughness of the processed front surface of the magnetic disk produced using this in the same manner as in Examples 1 to 5 was 0.062 μm Ra. Was.

Comparative Examples 6 to 9 100 parts by weight of ferromagnetic powder (hexagonal barium ferrite powder, BET surface area 30 m ² / g) and 25 parts by weight of an epoxy resin were charged into a kneader kneader and mixed, and then cyclohexanone was added to Comparative Example 6. 15 parts by weight, Comparative Example 7 6 parts by weight, Comparative Examples 8 and 9
5 parts by weight and kneaded for 4 hours. The kneaded material was used as a magnetic paint in the same manner as in Examples 1 to 5 to prepare a magnetic disk. Details are shown in Table 4.

(Comparative Example 10) A plate-like epoxy resin was pulverized with a mixer to a particle size of about 200.
A μm epoxy resin powder was obtained. 25 parts by weight of the above powdery epoxy resin, 100 parts by weight of ferromagnetic powder and single crystal alumina 1
After sufficiently mixing 0 parts by weight, 10 parts by weight of cyclohexanone was 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 vinyl resin were dissolved in 280 parts by weight of a mixed solvent composed of cyclohexanone / isophorone / dioxane was added to prepare a magnetic paint for a magnetic disk. The resin adsorption amount of the ferromagnetic powder of this paint was 2.4 mg / m ² . Next, the paint was spin-coated at 1000 rpm on a 14-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 surface roughness was measured.

The component having a wavelength of 0.8 mm or less of the surface roughness of the obtained coated disk before processing was 0.045 μmRa, and the component having a wavelength of 0.08 mm or more and 0.8 mm or less was 0.030 μmRa.

(Comparative Example 11) An epoxy resin powder having a particle size of about 20 µm was prepared. After sufficiently mixing 25 parts by weight of the powdery epoxy resin, 100 parts by weight of ferromagnetic powder and 10 parts by weight of single-crystal alumina, 6 parts by weight of cyclohexanone was added and further mixed in a kneader kneader. Thereafter, 3 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 vinyl resin were dissolved in 280 parts by weight of a mixed solvent composed of cyclohexanone / isophorone / dioxane was added to prepare a magnetic paint for a magnetic disk. The resin adsorption amount of the ferromagnetic powder of this paint was 2.9 mg / m ² . Next, the paint was spin-coated at 1000 rpm on a 14-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 component of 0.8 mm or less of the surface roughness of the obtained coated disk before processing is 0.030 μmR.
a, the component of 0.08 to 0.8 mm was 0.026 μmRa.

FIG. 1 shows the relationship between the resin adsorption amount and the processing front surface roughness (wavelength <0.8 mm) of a part of the above Examples and Comparative Examples, and FIG. 1 also shows the resin adsorption amount and the processing front surface roughness (0.08 mm <wavelength <0.8 mm). mm) is shown in FIG. In the figure, black circles indicate Examples 1 to
7, open circles are Examples 8 to 10, black triangles are Comparative Examples 1 to 5,
Open triangles represent Comparative Examples 6 to 9.

As can be seen from the figure, both the component having a surface roughness of 0.8 mm or less and the component having a wavelength of 0.8 mm or less and 0.08 mm or more are excellent between 1 and ² mg / m ² of resin adsorption.

FIG. 3 shows that the magnetic disk with reduced surface roughness has low noise.

In the above embodiments of the present invention, an epoxy resin is used as the resin, but the same applies to phenol resins, vinyl resins, and the like. In addition, the same standard can be applied to the type of ferromagnetic powder regardless of the composition, manufacturing method, and shape. For example, γ-Fe ₂ O synthesized from goethite
₃ powder, hydrothermally synthesized γ-Fe ₂ O ₃ powder, hexagonal barium ferrite powder, metal powder and the like. Further, the present invention can be applied to a case where the sizes of the particles of the ferromagnetic powder are different.

〔The invention's effect〕

As described above, according to the present invention, the type of ferromagnetic powder,
A magnetic paint with excellent dispersibility can be obtained regardless of the shape and size. By using this magnetic paint, a magnetic recording medium suitable for high-density recording with low surface roughness, low noise before processing Can be produced.

[Brief description of the drawings]

FIG. 1 shows the BET surface area 1 of the ferromagnetic powder in the magnetic paint.
graph showing the resin adsorption amount per m ^2, the relationship between the working front roughness of the magnetic disk manufactured by using the magnetic coating material,
Fig. 2 shows the resin adsorption amount and surface roughness wavelength of 0.08mm or less.
FIG. 3 is a graph showing the relationship between the processed front surface roughness of the magnetic disk and the magnetic disk noise. ●: values of Examples 1 to 7 ○: values of Examples 8 to 10 ▲: values of Comparative Examples 1 to 5 △: values of Comparative Examples 6 to 9

Claims (4)

(57) [Claims] 1. A coating film is formed by applying a magnetic coating material in which at least a ferromagnetic powder is dispersed in a solution of a resin as a binder of the ferromagnetic powder on a substrate to form a coating film. In the method for producing a magnetic recording medium which cures to form a magnetic recording film, the ferromagnetic powder in the magnetic paint has a surface area of 1 m ²
A method for producing a magnetic recording medium, wherein 1 mg or more and 2 mg or less of the above resin are adsorbed per unit. 2. The method according to claim 1, wherein the resin contains at least an epoxy resin and a phenol resin. 3. A coating film is formed by applying a magnetic coating material in which at least a ferromagnetic powder is dispersed in a resin solution as a binder of the ferromagnetic powder on a substrate to form a coating film. In the method of manufacturing a magnetic recording medium that forms a magnetic recording film by curing, the ferromagnetic powder in the magnetic paint has, on its surface, an adsorption layer made of the resin and solvent having a thickness of 50 to 150 mm. A method for manufacturing a magnetic recording medium, comprising: 4. A method according to claim 3, wherein said resin contains at least an epoxy resin and a phenol resin.