Nissin Chemical Industry Co., Ltd.

Tateo Ishida

Yoshiyuki Yasuhara

Kyoiti Imai

The magnetic coating composition of the invention comprises ferromagnetic particles having a specific surface area of at least 35 m.sup.2 /g dispersed in a resinous vehicle which is a polyvinyl chloride-based copolymeric resin composed of five types of monomeric moieties including (a) a moiety of vinyl chloride, (b) a moiety of vinyl alcohol, (c) a moiety of a vinyl carboxylate having from 6 to 20 carbon atoms in a unit, (d) a moiety of a vinyl or allyl monomer having a sul-fonic acid group or a sulfonic acid group in the form of a metal salt in the molecule, and (e) a moiety of a vinyl or allyl monomer having an epoxy group in the molecule. This vehicle resin is advantageous in respect of the dispersibility of the ferromagnetic particles to greatly facilitate the coating operation due to the relatively low viscosity of the coating composition as compared with conventional resins.

Magnetic recording medium and magnetic coating composition therefor

The invention provides a coating composition used for forming a magnetic layer on the surface of substrates to prepare magnetic recording media, e.g., recording tapes, of which the characteristic ingredient is a novel copolymeric resin. The copolymeric resin is a partial or complete saponification product of a copolymer obtained by the copolymerization of 4 types of comonomers in a spe-cified proportion including (1) vinyl chloride, (2) vinyl acetate, (3) a monomer having an ethylenically unsaturated polymerizable group and an epoxy group in the same molecule and (4) a monomer having an ethylenically unsaturated polymerizable group in the form of a sulfonic acid or a metal salt thereof. The vinyl acetate moiety is converted into a vinyl alcohol moiety partially or completely by the saponification. This copolymeric resin is advantageous in respect of the dispersibility of the ferromagnetic particles and the high crosslinkability which serves to improve the durability of the magnetic recording medium prepared by using the resin.

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Fukui, Japan

Tateo Ishida