Tdk Corporation

Shigeru Takamatsu

Hitoshi Azegami

Kiyoto Fukushima

Yuji Ishihara

Eiji Kitaura

Masahiro Takizawa

Hideo Dobashi

A magnetic recording medium, comprising a plastic base coated with a magnetic layer of a ferromagnetic powder dispersed in a resin binder, contains in the magnetic layer .alpha.-Al.sub.2 O.sub.3 particles with an average particle size of 0.1 to 0.3 .mu.m as determined by electron microscopy in an amount of more than 0.5% but less than 15% by weight on the basis of the ferromagnetic powder weight. The .alpha.-Al.sub.2 O.sub.3 particles have an .alpha.-transformation rate of at least 50%. The powder is produced by an organic alumina process.

Magnetic recording medium

In a magnetic recording medium consisting of a base coated with a magnetic coating material, or a dispersion of magnetic particles in a resinous binder, the binder comprises a copolymer composed of vinyl chloride, a vinyl alkylcarboxylate, another monomer copolymerizable with vinyl chloride, and a saponified vinyl alkylcarboxylate and having an OH/CH absorption ratio according to the infrared absorption spectrum of 0.2 to 0.7, a polyurethane resin having in its molecule a --SO.sub.3 M group wherein M represents an alkali metal atom, and a polyurethane resin or polyester resin or both containing no --SO.sub.3 M group wherein M represents an alkali metal atom, and a polyisocyanate.

A magnetic recording medium comprising a plastic base of polyester film or the like having a magnetic coat formed on one side, the magnetic coat consisting of a dispersion of a ferromagnetic powder in a resin binder, characterized in that the magnetic coat contains a nonmagnetic composite oxide powder of a spinel structure in an amount of 0.5 to 15% by weight on the basis of the ferromagnetic powder weight. The composite oxide in powder form ranges in particle diameter from 0.1 to 0.7 .mu.m and has a Mohs hardness of not less than 5.

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Komoro, Japan

Shigeru Takamatsu