JPH031505A - Ferromagnetic powder and magnetic recording medium using same - Google Patents

Abstract

PURPOSE:To sharply lower electric resistance of ferromagnetic powder of oxide, to lower electric resistance of the surface of a magnetic recording medium using it and to remarkably improve reliability, by forming coating on the surface of the powder. CONSTITUTION:An organic material is melted in a proper solvent, oxide ferromagnetic powder is dipped and dried to form a coating of an organic material on the ferromagnetic powder surface followed by being treated in inert gas under a high temperature 200 to 600 deg.C to decompose and carbonize the organic material while forming a carbon coating on the surface of ferromagnetic powder of oxide. A formation amount of the carbon coating is desirably in the range of 0.1 to 15wt.%. As the ferromagnetic powder of oxide, iron oxide magnetic powder, barium ferrite magnetic powder, chrome oxide magnetic powder as well as cobalt containing iron oxide magnetic powder are to be mentioned. A magnetic layer mainly containing aforesaid ferromagnetic powder and a binder is applied on a nonmagnetic supporter to obtain a magnetic recording medium.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to ferromagnetic powder for magnetic recording media, and more particularly to improving the electrical conductivity thereof.

[Conventional technology]

As a ferromagnetic powder for Shiki recording media, r -Fe2O3, C
Oxide-based ferromagnetic powders such as r02 are often used. These acid-based ferromagnetic powders have high electrical resistance, and in magnetic recording media using these ferromagnetic powders, the surface electrical resistance of the magnetic layer becomes significantly high. As a result, the surface of the magnetic layer becomes electrically charged due to friction, etc., causing dust to adhere to it, causing dropouts, or causing the recording media to stick to each other, or damage the recording media and the cover that protects them. It will stick and cause poor running.

As an antistatic measure, conductive substances are added to the magnetic layer, but this reduces the content of ferromagnetic powder in the magnetic recording medium, which affects the magnetic properties and electromagnetic conversion properties. Decline? cause. Other countermeasures include providing a conductive undercoat layer or using a support coated with a nonmagnetic metal, but these methods have the disadvantage of being expensive.

[Problem that the invention seeks to solve]

An object of the present invention is to solve the problem of high electrical resistance of oxide ferromagnetic powder, and thereby provide an excellent oxide ferromagnetic powder for magnetic recording media. As a result of various studies on methods for improving the electrical conductivity of oxide-based ferromagnetic powder without impairing its magnetic properties, it was found that forming a carbonaceous film on the surface of the ferromagnetic powder is effective. The inventors discovered that a magnetic recording medium using ferromagnetic powder having a coating can maintain the surface electrical resistance of the magnetic layer within a predetermined resistance value range, and at the same time, the electromagnetic conversion characteristics do not deteriorate, leading to the present invention. .

By using the carbonaceous film-forming oxide magnetic powder, the surface electrical resistance of the magnetic layer can reach a desired value without adding carbon black or the like to the magnetic layer.

Furthermore, in order to obtain a magnetic layer with lower surface electrical resistance, the objective can be achieved by adding less conductive material. Therefore, the resulting magnetic recording medium has an increased content of ferromagnetic powder, and the magnetic properties and electromagnetic conversion characteristics of the medium are improved.

The method for forming a carbonaceous film on the surface of oxide-based ferromagnetic powder is as follows:
Although not particularly limited, it can also be formed by the following method.

Organic substances such as methyl methacrylate, ethyl methacrylate, methyl acrylate, ethyl acrylate, ethyl crotonate, and ethyl crotonate are dissolved in an appropriate solvent, and oxide-based ferromagnetic powder is immersed in the solution. After drying and forming a film of organic substance on the surface of the ferromagnetic powder,
This ferromagnetic powder is treated in an inert gas at high temperatures of 200 to 600°C to decompose and carbonize organic substances.
There is a method in which a vapor of an organic substance such as benzene, toluene, xylene, naphthalene, benzoic acid, etc. is brought into contact with ferromagnetic powder, and then heated and carbonized in this state to form a carbonaceous film.

The amount of carbonaceous film formed is 0.1 to 15% by weight based on ferromagnetism.
, preferably in the range of 0.5 to 10% by weight.

If this amount is less than 0.1% by weight, the electrical conductivity of the ferromagnetic powder will not improve, and if it is more than 15% by weight, the amount of ferromagnetic powder will decrease, and when used in a magnetic recording medium, the magnetic properties and electromagnetic conversion properties of the medium will be reduced. decreases.

Examples of the oxide-based ferromagnetic powder used in the present invention include iron oxide magnetic powder, barium ferrite magnetic powder, chromium oxide magnetic powder, and cobalt-containing iron oxide magnetic powder.

Further, a magnetic recording medium using the carbonaceous film-forming oxide-based ferromagnetic powder can be manufactured by a conventional manufacturing method.

〔Example〕

Examples of the present invention will be described below.

Example 1 Toluene solution 51 containing 2% by weight of methyl methacrylate
Inside, coercive force 3400s, saturation magnetization 74.2smu/
j', average particle diameter 0.25 μm, average axial ratio 8 r −F
e. Disperse 50 (l) of 03 powder and add 10
Heated to 0°C. The mixture was heated until most of the toluene had evaporated and stirring was no longer possible, and the mixture was filtered and dried to completely evaporate the toluene. This magnetic powder was placed in a quartz boat and heated at 400°C in a tube furnace under argon gas.
A carbonaceous film was formed on the particle surface by heating for a period of time. The amount of carbonaceous coating was 560% by weight.

Example 2 In Example 1, treatment in a tube furnace, temperature 400"Q
A carbonaceous film was entirely formed on the surface of the ferromagnetic powder in the same manner as in Example 1 except that the temperature was changed to t-500°C.

Example 3 A carbonaceous film was formed on the surface of the ferromagnetic powder in the same manner as in Example 1, except that methyl acrylate was used instead of methyl methacrylate.

Example 4 In Example 1, barium ferrite powder (coercive force 5300 s,
Saturation magnetization60. Oemu/I, average particle diameter o, 07 μm
A carbonaceous film was formed on the surface of the ferromagnetic powder in the same manner as in Example 1, except that particles having an average particle thickness of 0.0085 μm were used.

Examples of magnetic recording media using carbonaceous film-formed ferromagnetism and comparative examples thereof will be described below.

Example 5 Carbonaceous film-forming γ-FeO powder obtained in Example 1 100 parts by weight Vinyl chloride-vinyl acetate-vinyl alcohol copolymer (VAGH manufactured by UCC Co., Ltd.) 14 //Polyurethane resin (manufactured by Dainippon Ink Co., Ltd., VAGH) Dex T-5201) 9 //
Polyincyanate compound 2 〃Methyl ethyl ketone 62 〃Toluene
62 Prepare a magnetic paint with the above composition, apply this paint on a polyester film with a thickness of 25 μm so that the thickness after drying is 4 μm, dry it, perform calendering treatment, and then cut it to a specified width. And magnetic chi 1? Created.

Example 6 Same as Example 5 except that the same amount of carbonaceous film-forming nocurium ferrite obtained in Example 4 was used instead of the magnetic powder obtained in Example 1 as the ferromagnetic powder. Magnetic tape gold was fabricated.

Comparative Example 1 In Example 5, a carbonaceous film was formed as a ferromagnetic powder.
A magnetic tape was produced in the same manner as in Example 5, except that the same amount of r -Fe,03 powder before the formation of the carbonaceous film as in Example 1 was used in place of the -Fa,03 powder.

Comparative Example 2 In Example 6, except that the same amount of barium ferrite powder before carbonaceous film formation as in Example 4 was used as the ferromagnetic powder,
A magnetic tape was produced in the same manner as in Example 6.

The electrical resistance of the ferromagnetic powders of Examples 1 to 4 was measured. The results are shown in Table 1.

Table 1 Regarding the magnetic tapes obtained in Example 5.6 and Comparative Example, the surface electrical resistance of the magnetic layer was measured. The results are shown in Table 2.

Table 2 [Effects of the invention] As explained above, by forming a carbonaceous film on the surface of the oxide-based ferromagnetic powder, the electrical resistance of the ferromagnetic powder is significantly reduced, and this ferromagnetic powder can be used. The surface electrical resistance of the magnetic recording medium is also reduced, and the reliability of the magnetic recording medium can be significantly improved.

Claims (3)

[Claims] (1) A ferromagnetic powder characterized by forming a carbonaceous film on the particle surface of an oxide-based magnetic powder. (2) The ferromagnetic powder according to claim (1), characterized in that the amount of carbonaceous coating is 0.1 to 15% by weight. (3) A magnetic recording medium comprising a magnetic layer mainly containing the ferromagnetic powder according to claim (1) or claim (2) and a binder coated on a non-magnetic support.