JPS60217529A - Magnetic powder for magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a medium for high-density recording having a high squareness ratio and good surface smoothness by providing thinly and uniformly an aluminum oxide film on the surface of magnetic powder which is planar and has the axis of easy magnetization in the direction perpendicular to the plate plane thereby improving dispersibility of said powder in a binder. CONSTITUTION:The aluminum oxide film is formed uniformly on the surface of the magnetic powder within a 0.1-2.0wt% range by the weight in terms of atomic weight of Al/magnetic powder by such a method consisting in suspending the hexagonal ferritic magnetic powder such as, for example, barium ferrite, strontium ferrite which is planar and has the axis of easy magnetization in the direction perpendicular to the plate plane into an aq. alkali soln., adding an aq. aluminum sulfate soln. and neutralizing the same by the gaseous CO2 blown thereto under stirring. The magnetic layer dispersed uniformly with such magnetic powder in the binder is formed. The magnetic powder treated in such a way has good dispersibility and the magnetic recording medium which is excellent in both of the electromagnetic conversion characteristic and surface smoothness is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a plate-shaped magnetic powder having an axis of easy magnetization perpendicular to the plate surface and suitable for use in magnetic recording media suitable for high-density recording.

[Background technology]

Generally, acicular magnetic powder is used as magnetic powder for magnetic recording media, and magnetic properties are improved by orienting this acicular magnetic powder in the in-plane longitudinal direction of a magnetic layer such as a magnetic tape. . However, in this way, when acicular magnetic powder is oriented in the longitudinal direction and the magnetization component in the longitudinal direction is utilized, when attempting to increase the density of magnetic recording, the demagnetizing field within the magnetic recording medium increases. However, there are limits to the improvement of recording density.

For this reason, in recent years, a perpendicular magnetic recording method has been adopted that uses plate-shaped hexagonal ferrite magnetic powder that has an axis of easy magnetization perpendicular to the plate surface and utilizes the magnetization component in the perpendicular direction. Efforts are being made to increase the density of However, the conventionally used input crystalline ferrite magnetic powder has the property that the powder particles tend to magnetically agglomerate with each other, and furthermore, because the particle shape is tabular, the tabular particles are piled up in parallel. They tend to form aggregates, resulting in poor dispersibility in the binder resin, making it difficult to sufficiently improve magnetic properties or electromagnetic conversion properties.

Therefore, as a method to eliminate such drawbacks, the dispersibility in the binder resin was improved by attaching 5t02 to the particle surface of the macrogonal ferrite magnetic powder (Japanese Patent Application Laid-open No. 57-56904). Attempts have been made to
Since the i02 particles cannot be sufficiently uniformly deposited, the adsorption amount of the binder resin is not so large, and the dispersibility in the binder resin cannot be sufficiently improved.

[Purpose of the invention]

The present invention solves these problems and provides a magnetic powder that has good dispersibility in a binder resin, is plate-shaped and has an axis of easy magnetization perpendicular to the plate surface, and is suitable for high-density recording. This purpose was achieved by forming an aluminum oxide coating on the surface of the magnetic powder particles, which are plate-shaped and have an axis of easy magnetization perpendicular to the plate surface.

[Summary of the invention]

This invention is characterized in that a dense and uniform aluminum oxide coating is provided on the particle surface of a magnetic powder that is plate-shaped and has an axis of easy magnetization perpendicular to the plate surface. When a uniform aluminum coating is provided on the particle surface, the agglomeration of the plate-shaped magnetic powder, which has an axis of easy magnetization perpendicular to the plate surface, is effectively suppressed, and a large amount of binder resin is adsorbed. Become. Therefore, when a magnetic recording medium is manufactured using this type of magnetic powder, the dispersibility of this type of magnetic powder in the binder resin is improved, the surface smoothness of the magnetic layer is also improved, and the magnetic properties or A magnetic recording medium with sufficiently improved electromagnetic conversion characteristics and suitable for high-density recording can be obtained.

In this invention, the aluminum oxide film formed on the particle surface of the magnetic powder, which is plate-shaped and has an easy axis of magnetization perpendicular to the plate surface, is plate-shaped and has an easy magnetization axis perpendicular to the plate surface. After dispersing the magnetic powder containing aluminum in an alkaline aqueous solution, an aqueous solution of an aluminum compound is added, and the liquid is neutralized by blowing carbon dioxide gas or adding acid to form a plate in a direction perpendicular to the plate surface. It is formed by precipitating an aluminum compound on the surface of magnetic powder particles with an easy magnetization axis of The magnetic powder 91 is well adhered to the surface of the particles having an easy axis of magnetization in the perpendicular direction.

The aluminum compounds used to form the aluminum oxide film include aluminum sulfate,
Water-soluble salts such as aluminum nitrate, aluminum chloride, and water-soluble aluminates such as sodium aluminate are preferably used. A uniform aluminum oxide coating is applied to the surface of magnetic powder particles that are plate-shaped and have an axis of easy magnetization perpendicular to the plate surface. The amount of adhesion is preferably within the range of 0.1 to 20% by weight in terms of atomic weight ratio of AI/magnetic powder; if it is too small, the dispersibility in the binder resin will not be sufficiently improved, and if it is too large. This makes it unsuitable as a magnetic powder for magnetic recording media.

When dispersing a plate-shaped magnetic powder with an axis of easy magnetization perpendicular to the plate surface in an alkali or aqueous solution, commonly used alkalis such as caustic soda and caustic potash are preferably used. The pH is preferably within the range of 10 to 14 since aluminum hydroxide is soluble in alkali.

In addition, a plate-shaped magnetic powder having an axis of easy magnetization perpendicular to the plate surface is dispersed in an alkaline aqueous solution, and then an aqueous solution of an aluminum compound is added thereto, and then neutralization is performed by blowing carbon dioxide gas. Alternatively, it is preferable to neutralize the PI by adding an acid such as hydrochloric acid, sulfuric acid, nitric acid, or carbonic acid until the PI becomes 8 or less.

Examples of the magnetic powder that is plate-shaped and has an axis of easy magnetization perpendicular to the plate surface include hexagonal ferrite magnetic powder such as barium ferrite magnetic powder, strontium ferrite magnetic powder, and lead ferrite magnetic powder. .

As described above, the magnetic powder, which is plate-shaped and has an axis of easy magnetization perpendicular to the plate surface with an aluminum oxide coating on the surface of the powder particles, can effectively suppress agglomeration, and can also absorb a large amount of binder resin. As a result, when a magnetic recording medium is manufactured using this type of magnetic powder, the surface smoothness of the magnetic layer is also good, and the magnetic properties or electromagnetic conversion properties are improved. A magnetic recording medium that is sufficiently improved and suitable for high-density recording can be obtained.

〔Example〕

Next, embodiments of the invention will be described.

Example 1 1 mole of ferric chloride, barium chloride! /8 mol, 1/3 o mol of cobalt chloride dissolved in 1β water, 1
0 mol of caustic soda was added to an aqueous solution of caustic soda and stirred. Next, this suspension was left to stand for one day, then placed in an autoclave and heated to react at 300° C. for 2 hours. After washing, dehydrating, and drying the reactive component, it was heat-treated in air at 8°0°C for 2 hours until the average particle size was 0.15.
μ, coercive force is 101 oersted, saturation magnetization is 5
Barium ferrite particles of 4.1 emu/g were obtained.

100 g of these barium ferrite particles were suspended in an alkaline aqueous solution 21 with a pH of 13 or higher and stirred for 30 minutes using a homomixer. Then, 30.2 ml of a 1 mol/β aluminum sulfate aqueous solution was added to the stirred solution while stirring, and the mixture was further stirred. While doing so, carbon dioxide gas was blown into the solution to neutralize it until the pH of the solution became 8 or higher, and an aluminum hydroxide film was deposited on the surface of the barium ferrite particles. Wash this suspension with water,
After filtering and drying, aluminum oxide (A120
3) Barium ferrite magnetic powder with a coating formed thereon was obtained. The coercive force of the obtained barium ferrite magnetic powder is 10
The saturation magnetization amount was 52.5 emu/g at 10 oersted. Further, as a result of chemical analysis, the amount of aluminum oxide deposited was A1/13aFe1201. The atomic weight ratio was 1.5% by weight. Using the barium ferrite magnetic powder thus obtained, --- Barium ferrite magnetic powder 100 parts by weight VAGH (
USA [J, (:, manufactured by Company C, salt 9 vinylide-vinyl acetate-vinyl alcohol copolymer) Bandesox T-52509 (manufactured by Dainippon Ink Co., Ltd., urethane elastomer) Coronate Nippon Polyurec 4.5 Made by company,
A magnetic paint was prepared by mixing and dispersing a composition consisting of 85% cyclohexanone and 85% methyl ethyl ketone (trifunctional low molecular weight isocyanate compound) in a ball mill for 3 days. This magnetic paint is applied onto a polyester film with a thickness of 13 μm to a dry thickness of 3.5 μm, dried to form a magnetic layer, treated with a microcalender, cut into predetermined shapes, and attached to a magnetic tape. It was.

Example 2 In the surface treatment of barium ferrite magnetic powder in Example 1, the amount of aluminum sulfate aqueous solution used was 30.
Example 1 except that the ml was changed from 2 ml to 154.0 ml.
The barium ferrite magnetic powder was surface-treated in the same manner as above, and the coercive force was 1010 oersted, the saturation magnetization was 46.8 emu / g, and the amount of aluminum oxide deposited was A 1 / B a Fe 12019 in terms of atoms. Barium ferrite magnetic powder having a weight ratio of 8.2% by weight was obtained, and a magnetic tape was obtained.

Example 3 In the surface treatment of barium ferrite magnetic powder in Example 1, the amount of aluminum sulfate aqueous solution used was 30.
Example 1 except that the ml was changed from 2 ml to 287.0 ml.
The barium ferrite magnetic powder was surface-treated in the same manner as above, and the coercive force was 1010 oersted, the saturation magnetization was 41.8 emu/g, and the amount of aluminum oxide deposited was 15.
A 1% by weight barium ferrite magnetic powder was obtained, and a magnetic tape was obtained.

Comparative Example 1 Produced in the same manner as Example 1 with an average particle diameter of 0.15
μ, coercive force is 1010 oersted, saturation magnetization is 5
100g of barium ferrite particles of 4.1emu/g
is suspended in pure water 21, and in this suspension, particles with an average particle size of 0
．． A solution in which 1 g of 5i02 particles of 0.013 μm were suspended in 500 cc' of pure water was added while stirring. After stirring for 2 hours, the precipitate was dried with a spray dryer, and the coercive force was 1010 oersted and the saturation magnetization was 53. ,．
6'emu 7g, 5i02 /BaFe
Barium ferrite magnetic powder was obtained with an atomic weight ratio of +20 tg and 0.93% by weight of barium ferrite magnetic powder attached to the particle surface. Next, a magnetic tape was produced in the same manner as in Example 1, except that the same amount of this treated magnetic powder was used in place of the barium ferrite magnetic powder used in the magnetic coating composition of Example 1.

Regarding the magnetic tapes obtained in each example and comparative example,
The squareness ratio and surface roughness of the magnetic layer were measured. The surface roughness of the magnetic layer was determined by measuring the center line average roughness using a stylus type surface roughness meter manufactured by Tokyo Seimitsu Co., Ltd. at a cutoff of 0.08 mm.

The table below shows the results.

〔Effect of the invention〕

As is clear from the table above, the magnetic tapes obtained in each example had a higher squareness ratio and lower surface roughness than the magnetic tape obtained in Comparative Example 1. The magnetic powder obtained in the form of a plate and having an axis of easy magnetization in the direction perpendicular to the plate surface has sufficiently improved dispersibility in the binder resin, and the magnetic recording medium obtained using this powder has an angular It can be seen that the type ratio is high and the surface smoothness of the magnetic layer is good, making it suitable for high-density recording.

Claims (1)

[Claims] 1. Magnetic powder for magnetic recording media, characterized in that it is plate-shaped and has an axis of easy magnetization perpendicular to the plate surface, and an aluminum oxide coating is provided on the particle surface.