Coated acicular fine particulate materials, processes for prepar

Details Coated acicular fine particulate materials, processes for prepar Coated acicular fine particulate materials, processes for prepar

1994-10-18

1996-09-03

Bonner, Melissa

Compositions

Magnetic

252 6257, 252 6259, 252 6255, 428403, C04B 3500

Patent

active

055520723

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to coated acicular fine particulate materials, processes for preparing the materials, and magnetic coating compositions and magnetic recording media containing the material.


BACKGROUND ART

Presently, magnetic recording media are commercially available which have various magnetic characteristics. Higher recording densities are the properties required of magnetic media of the next generation. Magnetic powders of higher coercive force are required to fulfill this requirement. The coercive force of magnetic powders is dependent largely on magnetic shape anisotropy attributable to their shape and magnetic crystalline anisotropy attributable to their magnetic energy. The present invention relates to a method of giving an improved coercive force by enhanced shape anisotropy. More particularly, the invention relates to a method of obtaining a high coercive force by using fine particles having a great axial ratio and utilizing the shape thereof for preparing a magnetic powder which is excellent in acicular properties.
Fine particles having an increased axial ratio generally deform and sinter under a thermal load during preparation, encountering difficulty in achieving the contemplated purpose.
Conventionally, fine particles are coated with aluminum, silica or like sintering preventing agent and are thereby prevented from deforming or sintering (e.g., U.S. Pat. No. 4,956,220). However, particulate materials, when in the form of fine particles, are liable to sinter during reaction and therefore require a large amount of sintering preventing agent, which increases the amount of nonmagnetic component and hampers the reduction reaction to result in the drawback of impaired magnetic characteristics.
An object of the present invention is to provide an acicular fine particulate material which is prepared by a promoted reduction reaction while being effectively prevented from sintering and which consequently affords magnetic recording media having a high recording density, and to provide a process for preparing the particulate material, and magnetic coating compositions and magnetic recording media containing the material.


DISCLOSURE OF THE INVENTION

The present invention provides an acicular fine particulate material which is coated with a compound containing at least one element selected from among elements of Groups III and IV of the Periodic Table in Periods 5 and 6, the acicular fine particulate material being one of (i) an acicular fine particulate material containing iron carbide, (ii) an acicular fine particulate material containing iron carbide, metallic iron and carbon, and (iii) an acicular fine particulate metallic iron containing carbon. The invention also provides a process for preparing the coated acicular fine particulate material, and magnetic coating compositions and magnetic recording media containing the particulate material.
The acicular fine particulate material of the present invention is characterized in that the material is coated with a compound containing at least one element selected from among those in Groups III and IV of the Periodic Table in Periods 5 and 6 (hereinafter referred to merely as "Group III or IV elements"). The Periodic Table hereinafter referred to is based on the table in conformity with the classification of subgroups prescribed by IUPAC in 1970.
The acicular fine particulate material of the present invention is (i) an acicular fine particulate material containing iron carbide, (ii) an acicular fine particulate material containing iron carbide, metallic iron and carbon, or (iii) an acicular fine particulate metallic iron containing carbon.
The acicular fine particulate material (i) containing iron carbide is described in detail in JP-B-43683/1989 and has the features of being higher in coercive force and saturation magnetization than conventional iron oxide magnetic powders and excellent in corrosion resistance. Such iron carbide is prepared, for example, by (a) contacting with heating a reducing agent containing no carbon a

REFERENCES:
patent: 4668414 (1987-05-01), Okamura et al.

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