JPH0312027A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve corrosion resistance by using whisker particles as a ferromagnetic powder. CONSTITUTION:A magnetic layer comprising ferromagnetic powder dispersed in a binder is formed on a nonmagnetic supporting body. The ferromagnetic powder consists of whisker particles essentially comprising Fe, Co and Ni. Thereby, the layer has excellent corrosion resistance though it has large saturation magnetic flux density.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording medium using a novel magnetic material.

[Prior Art] Metal magnetic powder is characterized by having larger coercive force and saturation magnetization than iron oxide magnetic powder, and has been put into practical use as a magnetic powder suitable for high-density recording.

On the other hand, metal magnetic powder has the disadvantage that its surface is active and easily corroded, and attempts have been made to form an oxide film on the particle surface in order to solve this disadvantage. However, by forming such an oxide film,
Corrosion resistance has improved to some extent, but sufficient corrosion resistance has not yet been achieved. Therefore, if a medium using such metal magnetic powder is kept under high temperature and high humidity, a problem arises in that the magnetization decreases. Further, when the thickness of the oxide film is increased, the corrosion resistance is improved, but the saturation magnetization is significantly lowered, and the characteristic of metal magnetic powder, which is high saturation magnetization, is lost.

The present inventors investigated the cause of the poor corrosion resistance of such metal magnetic powders and found that in metal magnetic powders produced using conventional goethite as a starting material, vacancies generated during the dehydration and reduction processes of goethite The cause was found to be that the pores did not disappear completely and more or less vacancies remained in the metal magnetic powder.

In other words, even though the magnetic powder looks like a square, it was thought that the reason for the decrease in corrosion resistance is that the surface area increases due to the pores remaining in the powder.

[Problems to be Solved by the Invention] The present invention has been made to solve the above-mentioned problems, and by using a novel magnetic material without holes in the metal magnetic powder,
The purpose of the present invention is to provide a magnetic recording medium with excellent edibility.

[Structure and operation of the invention] This invention was made by the inventors to solve the above problem,
By using whisker particles mainly composed of iron, cobalt, and nickel as the metal magnetic powder, the edibility of the medium is significantly improved. In other words, unlike conventional metal magnetic powders, which are made by removing water and oxygen from goethite particles and reducing them to metal, whisker particles are single-crystal particles that have grown into needle-shaped crystals during the metal precipitation process. Therefore, there are no pores inside the particles.

Therefore, the present inventors have focused on the fact that there are no holes in whisker particles, and have been studying the use of these whisker particles as metal magnetic powder for magnetic recording. As a result, they discovered that by using whisker particles, it is possible to provide a magnetic recording medium with significantly superior corrosion resistance, leading to the present invention.

These whisker particles are produced using, for example, the following CVD method.

That is, carbonyl compounds and chlorides such as iron, cobalt, and nickel are heated and evaporated in an airtight container, and then introduced into a reduction furnace using nitrogen gas as a carrier gas. A mixed gas of nitrogen gas as a carrier gas and hydrogen gas as a reducing gas is flowed into the reduction furnace. Vapors of metal compounds are
While being reduced to metal in a reduction furnace, crystals grow in the direction of air flow in a mixed gas of nitrogen and hydrogen, producing rod-shaped particles.

As for the particle shape, it is preferable that the average length of the particles is 1 μm or less, and whisker particles of about 0.1 to 0.5 μm are usually used.

If the particle length is too large, noise in the medium will increase, and if the particle length is too small, the dispersibility in the medium will decrease, which is not preferable.

The shape of such particles can usually be controlled by changing the flow rate of the carrier gas or the reduction temperature.

It is also possible to control the shape of the particles by applying a magnetic field during reduction.

In addition, the coercive force is 3, which is usually used for magnetic recording media.
The coercive force, which is preferably controlled to about 00 to 20,000 e, is controlled by controlling the particle shape as described above, but it can also be controlled by changing the composition of the elements constituting the particles.

To manufacture the magnetic recording medium of the present invention, a magnetic paint is prepared by adding and mixing the above-mentioned whisker particles to an organic solvent together with a binder and various additives blended as necessary. A magnetic layer may be formed by applying it on a non-magnetic support such as a polyester film by any means and drying it.

[Example] Examples of the present invention will be described below.

Example As the metal magnetic powder, alloy whisker particles of iron and cobalt, made of Coercive Crab 14500e and having a saturation magnetization of 138.2 parts mu/g, were used. The whisker particles are acicular particles with an average particle length of about 0.4 μm. Using these particles, a magnetic paint was prepared with the following composition.

Magnetic particles 100 parts Vinyl chloride-vinyl acetate-10 parts vinyl alcohol copolymer (manufactured by UCC, VAG) Polyurethane resin 7 parts (manufactured by Dainippon Ink Chemical Co., Ltd., T5201) Trifunctional isocyanate compound 3 parts ( Manufactured by Nippon Polyurethane Co., Ltd., Coronat) Toluene
80 parts cyclohexanone 80 parts This magnetic paint was applied onto a base film so that the thickness of the magnetic layer after drying was 4 μm.

Comparative Example As a metal magnetic powder, instead of an alloy whisker of iron and cobalt, coercive crab 14200e, saturation magnetization: 128.6
A magnetic medium was produced in the same manner as in the example except that acicular particles mainly composed of iron, which were produced using conventional goethite as a starting material and had a particle length of 0.4 μm and a particle length of 0.4 μm, were used. .

[Effects of the Invention] Table 1 shows the results of examining the coercive force, saturation magnetic flux density, and corrosion resistance of the magnetic media obtained in Examples and Comparative Examples.
For corrosion resistance, the medium temperature is 60'C.

It is expressed as the percentage decrease in saturation magnetic flux density after being maintained in an atmosphere with 90% humidity for 7 days.

As is clear from the table, the medium of the present invention using whisker particles as the metal magnetic powder has a higher saturation magnetic flux density than the medium using metal magnetic powder produced by the conventional method. It exhibits excellent corrosion resistance.

Claims (1)

[Claims] (1) In a magnetic recording medium in which a magnetic layer in which ferromagnetic powder is dispersed in a binder is formed on a non-magnetic support, whisker particles mainly composed of iron, cobalt, and nickel are used as the ferromagnetic powder. A magnetic recording medium characterized by: