JPS61191521A - Production of ferromagnetic iron powder - Google Patents

Abstract

PURPOSE:To increase the dispersion properties and the orientative properties or the like in a magnetic coat of the magnetic recording medium in case of immersing the ferromagnetic iron powder in an organic solvent and oxidizing the surface of the powder to produce the stable ferromagnetic iron powder by washing the powder with an organic solvent after the oxidation. CONSTITUTION:The ferromagnetic iron powder is produced by such a method that the hydrated iron oxide is dehydrated, calcined and reduced and thereafter the obtained ferromagnetic iron powder is immersed into an organic solvent such as benzene and toluene to prevent the spontaneous ignition or the like and the surface is slowly oxidized to stabilize a gas contg. oxygen. The aimed ferromagnetic iron powder is obtained by washing it successively with the organic solvent and removing the oxidized product (e.g. benzoic acid and cresol) of the organic solvent adhered on the surface of the ferromagnetic powder. This ferromagnetic iron powder is preferably used as the magnetic material of the magnetic recording medium for the high-density recording.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing ferromagnetic iron powder used as magnetic powder for magnetic recording.

(Prior Art) A needle-shaped ferromagnetic iron powder is generally known as a magnetic material for a magnetic recording medium for high-density recording.

This ferromagnetic iron powder is hydrated iron oxide (FeOOH), I!
f! It is obtained by heating, dehydrating, and reducing iron oxide or cobalt-containing iron oxide.

The ferromagnetic iron powder obtained in this way is very active because it is fine and easily reacts with oxygen in the atmosphere during use. Therefore, in order to provide chemical stability against oxidation, combustion, etc. in the atmosphere, and corrosion resistance such as rust prevention, surface stabilization is performed to form an IC film on the surface, that is, a non-WJJ film. Processing is done.

As a stabilization treatment method for such ferromagnetic iron powder, the ferromagnetic iron powder is immersed in an organic solvent such as toluene, a gas containing oxygen is introduced, and the surface of the magnetic iron powder is gradually oxidized and stabilized. There is. Alternatively, ferromagnetic iron powder is immersed in an organic solvent, and the organic solvent is evaporated and removed, so that contact with an inert gas containing an oxidizing gas is gradually carried out from the liquid phase to the gas phase. and so on.

The ferromagnetic iron powder after surface stabilization is mixed with an organic solvent and a binder and applied as a magnetic coating onto a support such as a polyester film or an aluminum plate to form a magnetic recording medium. In the production of magnetic recording media, the preparation of this magnetic paint is the most difficult, and the characteristics of the magnetic recording medium vary greatly depending on the coating conditions.

Although it is an important coating condition, it is difficult to achieve reproducibility with ferromagnetic iron powder using conventional methods, and the optimum coating conditions must be determined by actually setting the coating conditions each time the magnetic powder is changed. There are disadvantages such as the need to conduct a large number of exploratory tests.

As a result of various investigations into the reasons why reproducibility could not be achieved,
During the oxidation stabilization treatment, if the surface of the ferromagnetic iron powder is contaminated, that is, if the oxidation reaction is performed in the presence of an organic solvent, the organic solvent will be oxidized and this oxidation product will cause the ferromagnetic iron powder to become contaminated. I learned the fact that it is attached to the surface. this is,
In the system without iron powder, the organic solvent is not oxidized, but since the iron powder is very active, it is speculated that the iron powder acted as a catalyst.

Therefore, the type of organic brew produced depends on the type of organic solvent used and the oxidation conditions.

The amount will be different. It has been found that this surface-adhering organic oxide causes a difference in compatibility between the ferromagnetic iron powder, organic solvent, and binder when preparing magnetic paint, and is a major cause of the inability to obtain reproducibility.

[Problem that the invention seeks to solve]

An object of the present invention is to provide a method for producing ferromagnetic iron powder with excellent dispersibility and orientation in a magnetic coating film of a magnetic recording medium with good reproducibility.

[Means for solving problems]

The gist of the present invention is a method for producing ferromagnetic iron powder, which involves immersing ferromagnetic iron powder in an organic solvent, then fermenting the surface of the powder, and then washing it with the organic solvent.The details thereof will be explained below. .

The ferromagnetic iron powder of the present invention is an aggregate of acicular fine particles having a length of several μm or less. This ferromagnetic iron powder may contain, for example, cobalt, nickel, silicon, chromium, silver, tin, titanium, aluminum, etc. as additive elements.

Although various methods can be used for manufacturing, a method in which hydrated iron oxide is dehydrated in a gas phase, calcined, and reduced is suitable.

Ferromagnetic iron powder immediately after reduction will spontaneously ignite if taken out into the air, so it should be handled by immersing it in an organic solvent.

Desirable organic solvents include aromatic hydrocarbons such as benzene, toluene, and xylene, ketones such as methyl isobutyl ketone and cyclohexanone, esters such as butyl acetate, cyclohexane, methanol, dimethylformamide, and dioxane.

The method of oxidizing the surface of ferromagnetic iron powder immersed in an organic solvent involves introducing a gas containing oxygen into the ferromagnetic iron powder suspended in an organic solvent, gradually oxidizing the surface of the magnetic powder, and
Preferred methods include a stabilization method, or a method in which ferromagnetic iron powder is immersed in an organic solvent, and then the organic solvent is removed by evaporation, and the contact with the butyric gas is gradually brought into the gas phase from the liquid phase. It is.

The type and amount of the organic oxide produced vary depending on the conditions of this oxidation reaction and the type of organic solvent used. To give one example,
When toluene, the most common organic solvent, is used, an oxygen-containing gas is supplied to a suspension of magnetic powder, and the oxidation reaction is carried out at a temperature of 90°C, toluene compounds such as benzoic acid and cresol diphenylmethane are produced.

Washing is performed with an organic solvent to remove these organic oxides. Examples of organic solvents for cleaning include aromatic hydrocarbons such as benzene, toluene, and xylene, ketones such as methyl isobutyl ketone and cyclohexanone, esters such as butyl acetate, and cyclohexane. -F, methanol, dimethylformamide, dioxane, halogenated carbons such as chloroform, dichloromethane, and ethers can be used.

The ferromagnetic iron powder after washing is used as a magnetic coating or after surface treatment with a polymer compound or a silane coupling agent, and a magnetic recording medium is manufactured.

Hereinafter, the present invention will be explained in detail with reference to Examples and Comparative Examples.

Example 1 N1 and Sl are each 6% by weight based on XFe.

Acicular α-Ha^ containing 55% by weight was hydrogen reduced at 430°C for 5 hours.

The reduced iron powder was immersed in toluene and heated to 60°C for 1 hour while stirring to form a 509/l iron powder suspension. Oxidation stabilization treatment was performed by supplying a gas containing 0% oxygen and then supplying a gas containing 5% oxygen at a temperature of 90° C. for 2 hours.

Thereafter, the gas was turned off, the reactor was cooled to room temperature, the reactor was taken out, the toluene was removed, and the reactor was washed with fresh toluene. 2-methyl-diphenylmethane was detected in toluene after washing.

Example 2 Ni, Si, and Al were each 6% by weight based on IFe.

Acicular α-h^ containing 3% by weight and 5% by weight of α was treated under the same conditions as in Example 1 to produce ferromagnetic iron powder.

After the oxidative stabilization treatment, it was washed with ethanol.

2-methyldi7-dylmethane, cresol, and benzoic acid were detected in the ethanol after washing.

Comparative Example 1 Ferromagnetic iron powder was produced under the same conditions as in Example 1, except that washing with toluene after oxidative stabilization was omitted.

Comparative Example 2 Ferromagnetic iron powder was produced under the same conditions as in Example 2, except that washing with ethanol after oxidative stabilization was omitted.

Using these ferromagnetic iron powders according to the examples and comparative examples of the present invention, an oriented sheet was manufactured according to the following composition and method, and its magnetic property values, coercive force (Ha), residual magnetic flux density (Br), squareness ratio ( Table 1 shows the results of measuring Ra).

The magnetic paint for producing the oriented sheet is ferromagnetic iron powder, 100 parts by weight, vinyl chloride, vinyl acetate copolymer, 25 #lecithin.
A composition of 1.5 r toluene, 95 l, methyl ethyl ketone, and 95 y was mixed and dispersed in a paint shaker for 48 hours to prepare a composition.

As is clear from the above table, the oriented sheet (Example 1.2) obtained using the ferromagnetic iron powder obtained in the present invention was
Compared to the oriented sheet obtained using ferromagnetic iron powder obtained by the conventional method (Comparative Example 1.2), Br and Rs are higher, which indicates that the sheet obtained by the method of the present invention has higher Br and Rs. It can be seen that the ferromagnetic iron powder has excellent dispersibility and orientation.

Claims (1)

[Claims] (1) Production of ferromagnetic iron powder characterized by immersing ferromagnetic iron powder in an organic solvent, then oxidizing the surface of the powder to produce ferromagnetic iron powder, and washing with the organic solvent after oxidation. Law.