Tdk Corporation

Kazuhiro Kuroda

Kazushi Tanaka

Hitoshi Azegami

Yasushi Ishikawa

Hideki Sasaki

Osamu Inoue

Yasufumi Takasugi

Tsunehiko Ikarashi

Kazunori Tamazaki

Masahide Kohno

Masashi Hayama

Hirokazu Kambe

Kenichiro Eguchi

Ryoichi Awano

In a magnetic recording medium comprising on a non-magnetic substrate a magnetic layer obtained by dispersing ferromagnetic powder in an electron beam-curable resin followed by electron beam curing or a backcoat layer obtained by curing an electron beam-curable resin with electron beams, a combination of an electron beam-curable vinyl chloride resin having a sulfur-containing polar group and an electron beam-curable urethane resin having a phosphorus-containing polar group is used as the electron beam-curable resin. This results in improvements in dispersibility, surface smoothness, and electromagnetic characteristics, as well as a lowering of error rate in high density digital recording. Storage property is good.

Magnetic recording medium

A magnetic layer of a magnetic recording medium comprising a magnetic powder dispersed in a binder resin contains a powder of Ti-containing Al.sub.2 O.sub.3. The magnetic recording medium may alterenatively incorporate the Ti-containing Al.sub.2 O.sub.3 powder in the back coating or in both the magnetic layer and the back coating. A superior running stability and a superior durability are attained.

A magnetic recording medium whose magnetic layer formed on a base comprises a magnetic powder and a binder which contains a tertiary amine and uses 1,4-cyclohexanedimethanol as a chain extender. The magnetic powder is preferably of CrO.sub.2. The medium is made by mixing and dispersing the magnetic powder in a binder which consists of a reaction product of (A) a polyester which is a reaction product of a diol selected from among ethylene glycol, propylene glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentadiol, and 1,6-hexanediol, and adipic acid, (B) a chain extender consisting of 1,4-cyclohexanedimethanol, (C) an aliphatic or aromatic diisocyanate in an amount substantially equal to the combined molar amount of the polyester and the chain extender, and (D) a tertiary amine, and applying the resulting magnetic coating material to a base.

A magnetic recording medium comprising a plastic base and a magnetic layer formed thereon by applying a dispersion of a ferromagnetic powder in a resin binder, the magnetic layer containing the ferromagnetic powder which has a BET specific surface area of at least 35 m.sup.2 /g and .alpha.-Al2O3 particles having a particle size not exceeding one half the mean particle diameter of the ferromagnetic powder and less than 0.1 .mu.m in diameter, the .alpha.-Al2O3 particles being added in an amount greater than 5% but less than 15% by weight on the basis of the weight of the ferromagnetic powder. The magnetic powder is a metallic magnetic powder containing iron as the major constituent. The .alpha.-Al2O3 particles are cube-shaped.

In a magnetic recording medium wherein a magnetic coating composition comprising a binder and a magnetic powder is applied to the surface of a substrate, the dispersion of magnetic powder in binder is improved for enhanced physical and electromagnetic properties by using a vinyl chloride/hydroxyl group-containing vinyl monomer/polar group-containing monomer copolymer or a vinyl chloride/vinyl acetate/hydroxyl group-containing vinyl monomer/polar group-containing monomer copolymer having not been subjected to saponification, the polar group-containing monomer preferably containing an epoxy group as an additional polar group. Electromagnetic properties are further improved with a metal magnetic powder having a BET value of up to 60 m.sup.2 /g and a pH value of at least 7.

A magnetic recording medium comprising a substrate and magnetic recording double-layers formed on the substrate, wherein the magnetic material of the magnetic recording under-layer is composed essentially of an alloy or metal magnetic powder having a specific surface area of at most 30 m.sup.2 /g as measured by BET method, and the magnetic material of the magnetic recording top-layer is composed essentially of an iron oxide or Co-adsorbed iron oxide powder having a specific surface area of at least 25 m.sup.2 /g as measured by BET method.

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Karuizawa, Japan

Kazuhiro Kuroda