JPS5850005B2 - Jikikirokuyouji Seifun Matsuno Seizouhou - Google Patents

Description

[Detailed description of the invention] The present invention relates to improvements in magnetic powder for magnetic recording.

In recent years, with the demand for higher performance magnetic recording, recording elements using ferromagnetic iron oxide powder containing cobalt atoms have been developed.

Various proposals have been made regarding the production method of this type of magnetic powder, and the inventors have also proposed a method for producing acicular γ-Fe2.
We proposed a method in which a ferromagnetic iron oxide film containing cobalt atoms is epitaxially grown on the core crystal using 03 powder or Fe3O4 powder.

With this method, it is possible to easily produce ferromagnetic iron oxide containing cobalt atoms, which has a uniform needle-shaped particle size and stable magnetic properties. characteristics may not be fully demonstrated.

Commercially available ferromagnetic Fe3O4 and r-Fe203 powders are usually produced by thermally reducing goethite powder or by thermally oxidizing it after thermal reduction, but the ferromagnetic iron oxide powder obtained by these methods has good acicular shape. Although the particles have a uniform particle size distribution, a large number of relatively large pores are likely to be formed within the particles.

Therefore, when such porous ferromagnetic iron oxide powder is used as a nucleus crystal and a ferromagnetic iron oxide coating containing cobalt atoms, particularly a thin coating, is formed on the nucleus crystal, the pores remain in the particles. Easy to do.

When a magnetic coating material is prepared by kneading this magnetic powder having perforated pores with a binder, it is difficult to disperse the powder particles, and a substantial degree of filling cannot be achieved, making it difficult to obtain desired characteristics.

The present invention was made from this viewpoint, and Fe3O4
A magnetite (Fe304) layer, which is easy to grow epitaxially, is first formed on a ferromagnetic iron oxide powder such as The purpose is to obtain magnetic powder by epitaxially growing a magnetic iron oxide film.

To form a magnetite layer on a ferromagnetic iron oxide powder such as Fe3O4 or γ-Fe2O3, the iron oxide powder is dispersed in a ferrous salt solution such as ferrous chloride or ferrous sulfate;
This can be easily achieved by mixing an alkaline solution with this and allowing the oxidation reaction to occur in this mixed solution.

The alkaline concentration of the above-mentioned alkaline solution is sufficient as long as it causes precipitation of iron hydroxide in the mixed solution.

The surface properties of the magnetic powder particles obtained in this manner mainly depend on the amount of ferrous salt added to the iron oxide powder.
A preferable magnetite layer is formed by adding mol or more.

Next, in order to epitaxially grow a ferromagnetic iron oxide layer containing cobalt atoms on this magnetite layer, a metal salt solution containing an iron salt and a cobalt salt is mixed with an alkaline solution in which at least cobalt hydroxide is precipitated. This can be achieved by dispersing the above-mentioned nuclear crystal powder in a liquid and carrying out an oxidation reaction by blowing an oxidizing gas such as air into the solution or adding an oxidizing agent such as H2O2.

This growth is influenced by the alkaline concentration of the alkaline solution and the oxidation temperature, and the amount of alkali added is
When the molar equivalent ratio is 0.5 or more, the generation of new nuclei such as goethite is also suppressed, and as the oxidation temperature becomes higher than room temperature, it is further promoted.

The coercive force of the magnetic powder thus obtained is mainly determined by the content of cobalt atoms in the magnetic powder, and the coercive force increases as the content of cobalt atoms increases.

Next, embodiments according to the present invention will be described.

Example For a solution 31 with a concentration of 0.3 mol 11 ferrous sulfate, 1.
An 8 molar 11 concentration NaOH solution 31 is added to precipitate iron hydroxide.

In this solution, acicular γ-Fe203 powder (long axis approximately 0.3μ
, axial ratio of about 7, coercive force of about 300 oersted, saturation magnetic flux density of about 4350 gauss) was added to about 2251, and heated at 60℃3.
The oxidation reaction was carried out by blowing air at a rate of 31/min while stirring for a period of time, and magnetite (Fe
304) Precipitate crystals.

The ferromagnetic iron oxide powder obtained in this way has a coercive force of about 350 oersted and a saturation magnetic flux density of about 4400 Gauss, and although the particle size has increased slightly, the shape has hardly changed and the surface is smooth. It will be done.

Next, 15 oz of this magnetic powder was added to a metal salt solution in which 0.02 mol of ferrous sulfate and 1 mol of cobal sulfate (cobal sulfate) were dissolved in water 11, and a NaOH solution 11 with a concentration of 0.2 mol 11 was added to dissolve iron. and cobalt hydroxide were added to the precipitated solution, and an oxidation reaction was carried out by blowing air at a rate of 31/min while stirring at 60°C for 3 hours. grow.

After the reaction, the magnetic powder is thoroughly washed with water to remove the reaction solution, and then dried.

The magnetic powder thus obtained has a coercive force of approximately 40
The saturation magnetic flux density is 4300 Gauss.

Comparative Example In the example, a ferromagnetic iron oxide layer containing cobalt atoms was directly formed on the ferromagnetic iron oxide powder particles of the raw material without forming a magnetite layer.

Using the magnetic powder obtained in each example and comparative example, prepare a magnetic paint, apply this paint onto a base film to make a magnetic tape, and measure its square shape (Br/Bs) and sensitivity. did.

Incidentally, the following composition was used for the magnetic paint.

Magnetic powder 75 parts by weight Vinyl chloride vinyl acetate copolymer 25 〃DOP
5 〃Toluene-methylinbutylke) 200//n mixed solvent The following table shows the measurement results.As is clear from the results, the magnetic powder obtained by the method of the present invention has a
It can be seen that both the squareness and sensitivity are improved.

Claims (1)

[Claims] 1 Precipitate a magnetite layer on ferromagnetic iron oxide powder,
A magnetic powder for magnetic recording, characterized in that a ferromagnetic iron oxide layer containing cobalt atoms is deposited on the magnetite layer.