JPS58177523A - Manufacture of paint for magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a paint for a magnetic recording medium which has good dispersion efficiency and is not mixed with broken powder of a dispersive medium by stirring paint components for coating layer formation together with the dispersive medium having hollowed parts. CONSTITUTION:The dispersive medium is made of s surface material which has high breaking strength and large specific gravity and has the hollowed parts for decreasing the specific gravity substantially. Copper, SUS304, etc., are usable as its blank material and the hollowed parts are formed specially to hold about 3-7 specific gravity. The number and shapes of the hollow parts are not restricted as far as the specific gravity is obtained. This dispersive medium is used to mix and disperse the paint for a magnetic recording medium by convensional procedure. This method results in that no broken powder of the dispersive medium itself is contained and specially, when magnetic powder is used, the magnetic powder never break, obtaining the paint for the magnetic recording medium in an excellent dispersed state.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a coating material for magnetic recording media.

In recent years, the need for high-density recording media has increased, and therefore magnetic recording media are required to be made thinner. Therefore, at the same time as thinning the non-magnetic support of the recording medium,
It is also required to reduce the thickness of the coating film formed on the support. Therefore, it has become necessary to make the paint used to form the coating film more finely powdered than before. However, in the conventional paint manufacturing method, the main method was to disperse the paint in a vessel filled with glass beads, such as a vertical-lid or horizontal sand mill, using a high-speed rotating disk or pin. In this method, the strength of the glass beads used as the dispersion medium is weak, so if the number of revolutions of the blade that stirs the beads is increased in order to increase the dispersion efficiency, the beads will inevitably be crushed by the impact of the beads. This crushed bead powder causes dropout in the magnetic recording medium, and the thinner the magnetic recording medium is, the more serious the problem will be.

However, in order to prevent crushed bead powder from getting mixed into the paint, even if you use a metal object with a high specific gravity such as a steel ball to disperse and mix the paint, the problem of mixing in the crushed beads can be eliminated. However, other problems and inconveniences may arise. If a steel ball is used, the steel ball itself will not be crushed, but especially when mixing and dispersing magnetic powder, the magnetic powder itself will be destroyed by the impact of the steel ball and its coercive force will deteriorate. . Even if it were possible to suppress the occurrence of dropouts, magnetic recording media made using such magnetic paints would deteriorate in magnetic properties such as coercive force, squareness ratio, and transfer characteristics, making it difficult to use as high-density recording media. is inappropriate.

Therefore, the present invention provides a method for producing a paint for magnetic recording media that has good dispersion efficiency and does not contain crushed particles of the dispersion medium.

In the method according to the present invention, the dispersion medium is made of a material with high material breaking strength and high specific gravity, and is provided with a hollow portion to effectively lower the specific gravity. Materials that can be used include steel and 8US.
3Q4 or the like can be used, and in particular, a hollow portion may be formed so that the specific gravity is about 6 to 7. There is no limit to the number of hollows 1ts provided in the dispersion medium, and the hollows 1ts can be provided so as to have a predetermined specific gravity. Further, the shape of the cutout is not limited, and the dispersion medium can be, for example, cylindrical, a ball with a hole, or the like. Note that a dispersion medium having a hollow portion is easier to manufacture and more practical than a dispersion medium having a hollow portion.

The above-mentioned dispersion medium can be used to mix and disperse the coating material for magnetic recording media by a conventional method. That is, such a dispersion medium can be similarly applied to dispersion using rotating stirring disks or pins such as sand mills and attritors, as well as dispersion machines such as ball mills and vibration mills.

By the method of the present invention, it is possible to obtain a paint for magnetic recording media that does not contain crushed powder of the dispersion medium itself, and in particular, in the case of magnetic powder, does not destroy the magnetic powder and is in a good dispersed state. In the past, if magnetic chips 7 were made using such magnetic powder, it would be extremely useful as it would have fewer dropouts and would not deteriorate tape coercive force, ceramic ratio, or transfer characteristics.

The magnetic powder used in this invention is not particularly limited to those used in coated magnetic recording media, and examples include γ-Fe20B, Fe3O4
, i -Fe20B and Fe5 (iron oxide in the oxidation state intermediate between J4, containing Co r -k'e205 , containing 0 Co
) Iron oxide in an oxidation state intermediate between r -Fe2057Fe3O4, the above iron oxide further containing one or more Kinpo Motoki (transition metal element in %), the above iron oxide containing CO oxide or hydroxide Those with a coating layer mainly composed of substances, C
Oxide-based magnetic materials such as those formed by reducing the surface of rO2, CrO2 to form a Cr2O5 layer, or Fe, Co%
Metals such as Ni. Or Fe-Co alloy, Fe-Ni
alloy, Fe-Co-Ni alloy, Co-N1-P alloy,
Co-N1-Fe-B alloy, Fe-Ni-Zn alloy, F
Examples include ferromagnetic fine powders such as alloys such as e-Ma-Zn alloy and Fe-Co-N1-P alloy.

Magnetic paints also contain abrasives such as aluminum oxide, chromium oxide, and silicon oxide, antistatic agents such as carbon black, lubricants such as molybdenum disulfide, graphite, silicone oil, and olive oil, and dispersants such as lecithin. can do. In addition, examples of binders that can be used include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl propionate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-propion Iron-vinyl-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, acrylic ester - Vinylidene chloride copolymer, methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-styrene copolymer, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, acrylonitrile-butadiene-acrylic acid copolymer , acrylonitrile-butadiene-methacrylic acid copolymer, styrene-butadiene copolymer, formal resin, acetal resin, butyral resin, phenol resin, polyester resin, polyurethane resin, polyamide resin, urea resin, urea-formaldehyde resin, melamine resin, epoxy resin, alkyd resin, phenoxy resin, polyvinyl fluoride, or a mixture thereof.Furthermore, usable solvents include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, methanol, ethanol, etc. Alcohols, esters such as methyl acetate, ethyl acetate, butyl acetate, and ethyl butyrate, glycol ethers such as ethylene glycol monoethyl ether, ethylene glycol dimethyl ether dioxane, benzene,
Aromatic hydrocarbons such as toluene and xylene, hexane,
Examples include aliphatic hydrocarbons such as heptane.

The magnetic coating material obtained as described above is applied to a non-magnetic support according to a conventional coating method such as a doctor blade method or a gravure coating method to form a desired magnetic recording medium. Examples of the nonmagnetic support used include polyesters such as polyethylene terephthalate, polyolefins such as polypropylene, cellulose 111 conductors such as cellulose diacetate and cellulose triacetate, polycarbonate, polyvinyl chloride, polyimide,
Examples include polyamide, metals such as aluminum and copper, and paper.

The coatings obtained according to the invention can also be used in backcoat layers. This back coat layer is made by combining solid powders of carbon black, graphite, kaolin, barium sulfate, titanium oxide, silicon dioxide, talc, zinc oxide, etc. with a binder made of thermoplastic or thermosetting resin as described above. It is formed by dissolving it in the same organic solvent as mentioned above and applying it to the other side of the nonmagnetic support in the same manner as the magnetic layer.

Hereinafter, this invention will be explained in more detail with reference to Examples.

Example 1 A magnetic paint having the following composition was prepared.

Cr2O32PHF Lecithin 2 PH
P-butyl stearate i, 5
After pre-stirring about 3 kg of the above PHP composition, the material becomes 8U.
Cylindrical beads made of 8304 (bead diameter 2m+; length/diameter; 1.8U8 parts: void part -1:3; apparent 12Ff
= 3.0) to 6! A packed 61 volume Sand Mill I trowel steel rotating disc was rotated at 120 rpm for approximately 3 hours of mixing. This magnetic paint was applied to a 3-inch wide polyethylene terephthalate film to a thickness of 4 μm, and the film was slit to a 3-inch width to prepare a video magnetic tape.

Examples 2 to 9 Magnetic tapes were produced in the same manner as in Example 1 using the beads shown in the table below.

Comparative Examples 1 to 5 Magnetic tapes were produced in the same manner as in Example 1, except that beads shown in the table below were used.

The magnetostatic properties, electromagnetic conversion properties, and number of dropouts were measured for the magnetic tapes obtained in Examples 1 to 9 and Comparative Examples 1 to 5 described above. The results are also shown in the table below.

From the results shown in the above table, it can be seen that the magnetic tape using the magnetic paint obtained by the present invention uses beads made of a material with high breaking strength, so it is difficult to avoid broken glass powder such as glass beads as in the comparative example. Unfortunately, there were no dropouts caused by this. In addition, in this invention, a material with such high breaking strength is used, but since the beads are provided with hollow parts and have a lower specific gravity than ordinary steel ball beads, when steel ball beads are used, Since there is no destruction of the magnetic powder as seen in the above, and uniform mixing and dispersion can be obtained, it has excellent properties as a magnetic tape, such as electromagnetic conversion characteristics such as tape angle ratio and video S/N ratio.

Agent, warehouse l　Yoshio Tsuneko ! Toshiki Sugiura

Claims (1)

[Claims] (A method for producing a paint for a magnetic recording medium, which comprises stirring a paint component for forming a coating layer together with a dispersion medium having a cut-out portion.