JPS6286545A - Manufacture of magnetic paint - Google Patents

Abstract

PURPOSE:To efficiently disperse a magnetic paint by dispersing a mixture composed of a ferromagnetic powder, a coupling agent and a solvent after it is aged for the specified time after a mixing processing. CONSTITUTION:A magnetic paint forming material composed of the magnetic layer forming material of a magnetic recording medium and the solvent at least including the ferromagnetic powder and the linking agent are mixed, the mixture is adjusted, and next, after the mixture is aged at least for five hours, the mixture is dispersed, for example, by the sand grinder, etc. By such an operation, the dispersing property of the ferromagnetic powder, etc., is increased, and the dispersing process is efficiently executed. Especially, even at the time of using the fine particle ferromagnetic powder, the long period is not necessary, the satisfactory dispersion is obtained, and for such a reason, the damage of the ferromagnetic powder can be decreased at the dispersing process. Consequently, various characteristics such as the electromagnetic converting characteristics, etc., are satisfactorily held. When the time is sufficiently spent for the dispersion, the association body such as the secondary particles and the tertiary particles is decreased in the paint, and therefore, the uniformity and the surface smoothness of the magnetic layer formed by using these are satisfactory and the obtained magnetic recording media have the excellent electromagnetic converting characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing a magnetic coating material, and more particularly to a method for producing a magnetic coating material used for forming a magnetic layer of a magnetic recording medium.

[Background of the Invention and Prior Art] As a magnetic recording medium for computers, video, audio, etc., a magnetic paint in which a binder, ferromagnetic powder, and other additives are dispersed in a solvent is coated on a support and dried. A magnetic recording medium with a magnetic layer is used. The magnetic paint used to prepare the magnetic layer is usually prepared by mixing a magnetic layer forming material for a magnetic recording medium containing ferromagnetic powder and a binder with a solvent, or by mixing the binder and ferromagnetic powder with a solvent. After mixing this with the remaining ingredients, the resulting mixture undergoes a dispersion process in which granular ingredients such as ferromagnetic powder contained in an aggregated state are dispersed to a state close to that of primary particles. Manufactured.

Recently, with the practical use of 8mm video, for example, there has been a strong desire to develop magnetic recording media that can record at even higher density than conventional magnetic recording media. A method using ferromagnetic powder with high coercive force, such as powdered ferromagnetic metal fine powder, is being used.

However, when the ferromagnetic powder is made into fine particles, the dispersibility of the ferromagnetic powder tends to decrease when preparing a magnetic paint. Therefore, in magnetic paint containing finely divided ferromagnetic powder,
The ferromagnetic powder that has not been sufficiently dispersed in the magnetic coating material is present in a state where it is associated and forms secondary particles, tertiary particles, etc. Even if such a magnetic paint is used, it is not possible to prepare a magnetic layer having high electromagnetic conversion characteristics suitable for high-density recording.

In order to prepare a magnetic coating material in which particulate components such as ferromagnetic powder are well dispersed, it is conceivable to adopt a method of increasing the dispersion time. However, in the dispersion process, the ferromagnetic powder is exposed to harsh conditions such as high-speed stirring, so the ferromagnetic powder is damaged during the dispersion process, resulting in low f-electromagnetic characteristics of the resulting magnetic recording medium. becomes.

JP-A-59-117737 discloses that after a magnetic layer-forming agent is cross-dispersed, the coating is stabilized for 6 to 48 hours by standing still or by stirring with a propeller, and then filtered using a filter. An invention of a method for manufacturing a magnetic recording medium using a magnetic paint is disclosed.

The method disclosed in the above-mentioned publication is based on the phenomenon that the re-agglomeration of solid components after the cross line dispersion operation in the magnetic paint manufacturing process proceeds rapidly during several hours after the operation line r, and then becomes extremely slow. Based on this method, the method is intended to reduce the re-agglomeration of solid components after filtration by performing the filter filtration after the completion of the main re-agglomeration. That is, although this method may be effective in preventing reagglomeration after filtration, it cannot improve the dispersion efficiency in the dispersion process.

[Object of the Invention] An object of the present invention is to provide a new method for preparing a magnetic coating material for forming a magnetic layer of a magnetic recording medium.

Furthermore, the present invention improves the dispersion efficiency of the dispersion process commonly used when preparing magnetic paints.
In particular, the object of the present invention is to provide a method for producing magnetic particles that can obtain a well-dispersed magnetic paint even when finely divided ferromagnetic powder is used.

[Summary of the Invention] The present invention provides a method for preparing a mixture of a magnetic paint forming material consisting of a magnetic layer forming material for a magnetic recording medium containing at least a ferromagnetic powder and a binder, and a solvent, and a method of preparing a mixture of the obtained mixture. A method for producing a magnetic paint comprising an aging step of at least 5 hours for aging, and a dispersion step for dispersing the aged mixture.

[Effects of the Invention] According to the method of the present invention, the dispersibility of solid components such as ferromagnetic powder is significantly improved, so that the dispersion process can be carried out with high efficiency. Therefore, even when particularly finely divided ferromagnetic powder (for example, fine ferromagnetic metal powder) is used, it is possible to obtain a well-dispersed magnetic paint without making the dispersion process particularly long. .

In addition, the conventionally used iron oxide-based ferromagnetic powder (
For example, γ-ferrite, cobalt-containing ferrite)
In the dispersion, the time required for the dispersion process can be shortened compared to the time conventionally used, which has the advantage of reducing damage to the ferromagnetic powder during the dispersion process.

Therefore, by using the magnetic paint prepared by the method of the present invention, it is possible to produce a magnetic recording medium that has good two properties such as electromagnetic conversion properties. Furthermore, if the dispersion time is multiplied by nn to the same degree as conventional methods, the amount of aggregates such as secondary particles and tertiary particles in the resulting magnetic paint will be reduced. The uniformity and surface smoothness of the formed magnetic layer are significantly improved. That is, the magnetic recording medium thus obtained exhibits excellent electromagnetic conversion characteristics.

[Detailed Description of the Invention] The method for producing a magnetic coating material of the present invention includes a mixing step for preparing a mixture of a magnetic layer forming material and a solvent, and a dispersion step for dispersing this mixture. The main feature is that it includes a step of aging for a certain period of time.

In the method for producing a magnetic paint according to the present invention, first, a mixture of a binder, a magnetic layer forming material such as ferromagnetic powder, and a solvent is prepared.

The binder can be selected from conventional binders.

Examples of binders include vinyl chloride/vinyl acetate copolymers, vinyl chloride/vinyl acetate copolymers with vinyl alcohol, maleic acid and/or acrylic acid, vinyl chloride/vinylidene chloride copolymers, and vinyl chloride numbers. Cellulose derivatives such as acrylonitrile copolymers, ethylene-acetyl copolymers, nitrocellulose resins, acrylic resins, polyvinyl acetal resins, polyvinyl butyral resins, epoxy resins, phenoxy resins, polyurethane resins, and polycarbonate polyurethane resins. I can do it.

In particular, it is preferable to use a resin component with high hardness such as a vinyl chloride/vinyl acetate/maleic anhydride copolymer in combination with a resin with low hardness such as a polyurethane resin.

The blending ratio of the binder is usually 10 to 100 parts by weight (preferably 20 to 40 parts by weight) per 100 parts by weight of the ferromagnetic powder.

As the ferromagnetic powder, ferromagnetic powder commonly used in magnetic recording media can be used.

Examples of ferromagnetic powders include γ-Fe 20. Metal oxide-based ferromagnetic powder such as cobalt-containing γ-Fe 20
．． Examples include metal oxide-based ferromagnetic powders containing other components such as ferromagnetic metal powders containing iron, cobalt, or nickel.

The method for producing the magnetic coating material of the present invention is to produce a magnetic coating using a ferromagnetic metal fine powder having a specific surface a (S RET) of 42 m''/g or more (preferably h5rrf/g or more) among the above-mentioned ferromagnetic powders. It is particularly advantageous for use in the production of paints, since such fine ferromagnetic metal powders have particularly poor dispersibility.

As an example of this ferromagnetic metal fine powder, the metal content in the ferromagnetic metal fine powder is 75% or more, and the metal content is 8%.
0% by weight or more is at least one ferromagnetic metal or alloy (e.g., Fe, Co, Ni, Fe-Co, Fe-Ni
, Co-Ni, Co-N1-Fe), and other components (e.g., A, S,
i, Pb, Sc, Ti, V, Cr,
Mn, Cu, B, Y, Mo, Rh,
Pd, Ag, Sn, Sb, P, B
a, Ta, W, Re, Au, Hg
, S, Bi, La, Ce, Pr, Nd, Z
Mention may be made of alloys which may contain n, Te). Further, the ferromagnetic metal component E may contain a small amount of water, hydroxide, or oxide. The methods for producing these ferromagnetic metal fine powders are already known, and the ferromagnetic metal fine powders used in the present invention can also be manufactured according to these known methods.

There is no particular restriction on the shape of the ferromagnetic metal fine powder, but needle-like, granular, dice-like, rice-grain-like, and plate-like shapes are usually used. In particular, the present invention is advantageous when used in the production of magnetic paints using needle-shaped ferromagnetic metal fine powder. Since paint is generated, damage to the needle-shaped ferromagnetic metal fine powder caused by one-dispersion operation can be reduced.

In addition to the above binders and ferromagnetic powders, α-A 203
Solid components such as abrasives such as (hard inorganic particles) and granular antistatic agents such as carbon black can also be used.

The blending ratio of the abrasive is 1, which is usually 10 parts by weight or less per 100 parts by weight of the ferromagnetic metal fine powder. The abrasive used generally has an average particle diameter within the range of 0.1 to Igm.

In addition to the solid components listed in E, lubricants, antistatic agents, fillers, dispersants, and other materials commonly used in preparing magnetic paints can be blended.

As the solvent used in the present invention, those commonly used for preparing magnetic paints can be used.

Examples of such solvents include ketones (e.g. methyl ethyl ketone, cyclohexanone, diethyl ketone, methyl isobutyl ketone, acetone), ethers (e.g. diethyl ether, methyl ethyl ether, dioxane)
, esters (e.g., ethyl acetate, butyl acetate), aromatic solvents (e.g., toluene, xylene), alcohols (e.g., methanol, ethanol, propatool, butanol), etc. These can be used alone or in combination.

The amount of solvent is usually 30 to 3 parts per 100 parts by weight of ferromagnetic powder.
It is used within the range of 0.00 parts by weight.

As the mixing device, it is possible to use a device that is normally used as a mixing or kneading device when preparing a magnetic paint. Examples of mixing devices and kneading devices include a kneader, a Banbury mixer-1 high speed impeller disperser, and a dispersion machine.

Next, the mixing process of the present invention will be explained using as an example the preparation of a mixture of a magnetic layer forming material and a solvent using a kneader. First, - parts of the binder, ferromagnetic powder, and solvent are fed into a kneader and kneaded. A separately prepared abrasive and a solvent are added to the kneaded material discharged from the kneader. It is preferable to wash the kneader with a portion of the remaining solvent.
This cleaning liquid is also added to the above-mentioned kneaded material to form a mixture.

In the mixing process, a mixture of magnetic layer forming materials such as a binder and ferromagnetic powder and a solvent is obtained, but the solid components such as the ferromagnetic powder in the mixture are mostly in the state of multiple particles associated with each other. Usually, this mixing step does not lead to the release of the association.

In addition, by mixing solid components such as ferromagnetic powder and abrasive materials separately with a solvent, etc., and then mixing them all together, the dispersibility in the subsequent dispersion process will be improved and the mixing process will be improved. This is preferable because damage to the ferromagnetic powder can be prevented.

The mixture obtained as in Section L is then aged for a predetermined period of time or more. The aging time must be 5 hours or more. The aging time is preferably 10 hours or longer, and particularly preferably 48 hours or longer. Conventionally, it has been common to subject the mixture to a dispersion step immediately after mixing without aging the mixture.

Aging can be carried out by a method in which the mixture obtained in the above step is allowed to stand without stirring or the like. however,
When performing W1 stirring, which may be performed while stirring to an extent that can prevent sedimentation of solid components in the mixture,
It is preferable to set the stirring speed so that the maximum flow velocity of the mixture is 5 m/s or less. Although such low-speed stirring can prevent settling of particulate solid components in the mixture, low-speed stirring It does not have an active dispersion effect of releasing the association state of the particulate components contained in the particles and dispersing them in the state of primary particles.

It is not necessarily clear why the dispersibility of particulate components such as ferromagnetic powder (and abrasive material) contained in the mixture is improved by the aging step in the present invention, the step of aging the mixture of the magnetic layer forming material and the solvent. However, during the aging process, the binder and solvent are evenly distributed over the fine irregularities on the surface of the particles of ferromagnetic powder, abrasive, etc., so the affinity between the solvent, binder, etc. and granular components such as ferromagnetic powder is improved. It is surmised that this is to improve the performance.

The aging step is preferably carried out in a closed container to prevent the solvent in the mixture from dissipating due to evaporation or the like. Normally,
It is advantageous to use a stock tank or the like provided next to the mixing device for the magnetic layer forming material.

The thus aged mixture is first subjected to a dispersion step. This dispersion step releases the association of particulate components such as ferromagnetic powder in the mixture, and most of them are dispersed as primary particles.

The dispersion method can be carried out according to a conventional dispersion method. As examples of dispersion equipment used, mention may be made of ball mills, homomixers, sand mills, sand grinders, pebble mills, thoron mills, Szegvari attritors, high speed stone mills, high speed impact mills, high speed mixers and homogenizers.

The dispersion time can be appropriately set in consideration of various conditions such as the aging time, the type of dispersion device used, and the type of magnetic layer forming material.

~Generally, the gloss level of the magnetic layer surface obtained from magnetic paint is 1
Dispersion is performed so that the ratio is 15% or more.

Further, it is preferable to perform the dispersion so that the amount is 120% or more, and it is particularly preferable to perform the dispersion so that the amount is 130% or more.

For example, when a vinyl chloride-vinyl acetate-maleic anhydride copolymer and polyurethane are used as a binder, and a ferromagnetic metal fine powder with a specific surface area of 42d1g is used, the mixture is aged for 4 days after mixing. The dispersion time required to prepare a magnetic paint having the dispersibility necessary to obtain a magnetic paint with a reflectance of 115% using a sand grinder was about 45 minutes. On the other hand, according to a method that uses the same binder and ferromagnetic metal fine powder and immediately disperses it after mixing,
The dispersion time required to obtain magnetic layers with comparable reflectance was approximately 150 minutes.

The dispersed magnetic coating composition can be applied directly onto a support, but it is usually filtered using a filter, for example, a filter with a pore size in the range of 0.5 to 1.51 Lm.

The magnetic paint thus prepared is coated on a support and becomes a magnetic layer according to the usual magnetic recording medium manufacturing processes such as magnetic field orientation treatment, drying treatment, and surface smoothing treatment.

Next, Examples and Comparative Examples of the present invention will be described.

In addition, in the following examples, r part J is f unless otherwise specified.
Means 1 part by weight.

[Example 1] Ferromagnetic metal fine powder (composition: Fe-X1 alloy, average major axis length 20.2 m, specific surface area: 52.2 rrf/g, anti-magnetic crab 15300e) 300 parts vinyl chloride/vinyl acetate/ Maleic anhydride copolymer (manufactured by Nippon Zeon ■: 400X 110A, ffi degree: 400) 36 parts Polyurethane resin (manufactured by Nippon Polyurethane Corporation: N-2301) 36 parts Methyl ethyl ketone 150 parts After kneading for 60 minutes, the following ingredients were added and kneading was continued until the whole was homogeneous.

α-A pattern 20° (average particle size = 0.4 m) 15 parts methyl ethyl ketone 350 parts After kneading, the prepared mixture was left to stand in a closed container and aged for 6 hours.

After standing for 6 hours, dispersion was performed using a sand grinder.The dispersion times were 10 minutes, 20 minutes, 40 minutes, and 6 hours.
0 minutes, 80 minutes, 100 minutes, and 120 minutes, and after each time a sample of the magnetic paint was taken and deposited on a 5 inch wide, 20 ILm thick polyester support (3 mils).
75gm) Apply magnetic paint using a blade, dry it,
A magnetic layer was formed and the glossiness of its surface was measured.

The results are listed in Table 1.

[Example 2] A magnetic layer was formed in the same manner as in Example 1 except that the aging time was changed to 24 hours, and the glossiness of the surface thereof was measured.

The results are listed in Table 1.

[Example 3] A magnetic layer was formed in the same manner as in Example 1 except that the aging time was changed to 4 days, and the glossiness of the surface thereof was measured.

The results are shown in Table 1.

[Example 4] A magnetic layer was formed in the same manner as in Example 1 except that the aging time was changed to 14 days, and the glossiness of its surface was measured.

The results are shown in Table 1.

[Example 5] A magnetic layer was formed in the same manner as in Example 1 except that the aging time was changed to 34 days, and the glossiness of the surface thereof was measured.

The results are shown in Table 1.

[Comparative Example 1] A magnetic layer was formed in the same manner as in Example 1 except that the aging time was changed to 1 hour, and the glossiness of the surface thereof was measured.

The results are shown in Table 1.

[Comparative Example 2] A magnetic layer was formed in the same manner as in Example 1 except that dispersion was immediately carried out for 150 minutes without aging,
The surface gloss was measured and found to be 115%. Table 1 Dispersion time 10 20 40 80 80 100 1
20 Example 1 53 82 102 108 113
117 119 same 2 5? 82 105
112 119 123 125 same 3 5
8 85 101 122 128 131
133 same 4 88 91 115 12
4 130 133 134 same 5 88
93 117 128 132 138 13
8 Comparative Example 1 45 71 93 102 107 11
0 111 Note: Dispersion time is in minutes.

The results in Table 1 are shown as a graph in FIG.

The following can be seen from Table 1 and Figure 1.

The magnetic paint prepared according to the manufacturing method of the magnetic paint of the present invention has very good dispersibility, and the surface gloss of the normal magnetic layer reaches 115%, which is a preferable value. ) for 85 minutes, 2 (■) for 65 minutes, 3 (m) for 45 minutes, and 4 (IV
) required only 40 minutes of dispersion time, while 5(v) required only 38 minutes of dispersion time.

On the other hand, in Comparative Example 1 (VI), the gloss level reached only 111% even after 120 minutes of dispersion.

Furthermore, as shown in Comparative Example 2, the dispersion time required for the surface gloss of the magnetic layer coated with the magnetic paint, which was immediately dispersed without aging after mixing to reach 115%, was 150 minutes. .

[Brief explanation of drawings]

FIG. 1 is a graph showing variations in the glossiness of the surface of the magnetic layer formed when the dispersion time of the magnetic paints produced in Examples 1 to 5 and Comparative Example 1 varied.

Claims (1)

[Claims] 1. A mixing step of preparing a mixture of a magnetic paint forming material consisting of a magnetic layer forming material for a magnetic recording medium containing at least a ferromagnetic powder and a binder and a solvent, and aging of the obtained mixture. A method for producing a magnetic paint comprising an aging step for at least 5 hours for the aging process, and a dispersion step for dispersing the aged mixture. 2. The method for producing a magnetic paint according to claim 1, wherein the aging step is carried out for at least 10 hours. 3. The method for producing a magnetic paint according to claim 2, wherein the aging step is carried out for at least 48 hours. 4. The method for producing a magnetic paint according to claim 1, wherein the mixing step is carried out using a kneading device. 5. The method for producing a magnetic paint according to claim 1, wherein the aging step is carried out by allowing the mixture of magnetic paint forming materials to stand still. 6. Claim 1, characterized in that the aging step is carried out by leaving the mixture of magnetic paint forming materials while stirring to prevent the solid components in the mixture from settling. A method for manufacturing magnetic paint. 7. The method for producing a magnetic paint according to claim 1, wherein the ferromagnetic powder is a fine ferromagnetic metal powder having a specific surface area of 42 m^2/g or more. 8. The method for producing a magnetic paint according to claim 1, wherein the binder contains a vinyl chloride/vinyl acetate/maleic anhydride copolymer and a polyurethane resin.