Hitachi Maxell, Limited

Sakai Chemical Industry Co., Ltd.

Haruo Andoh

Susumu Kitaoka

Jozo Shimizu

Satoru Yamaguchi

Junichi Hirata

Kozaburoh Satoh

Akira Kato

Toshinobu Sueyoshi

Seiji Matsumoto

Fumio Togawa

Toshihiko Tanabe

Hikaru Ishida

A magnetic recording medium which comprises a first magnetic layer on a base and a second magnetic layer thereon, the first magnetic layer containing magnetic particles having an average particle length (long axis diameter) of 0.4 to 0.7 .mu., the second magnetic layer containing magnetic particles having an average particle length (long axis diameter) of 0.25 to 0.35 .mu., the coercive force of which being 370 to 460 oersteds, and the ratio of coercive force of the upper or second layer to that of the lower or first magnetic layer being 1.05/l to 1.5/l. The magnetic recording medium has excellent sensitivity and frequency characteristics at entire frequency bands with less noise.

Magnetic recording medium

Cobalt-containing iron oxide magnetic particles having a high coercive force and a small surface electrical resistance which are useful as a recording element for a magnetic recording medium, and a method for the preparation of the same comprising reducing acicular .gamma.-Fe.sub.2 O.sub.3 particles in a reducing gas or liquid until the iron oxide reaches an intermediate oxidation state between .gamma.-Fe.sub.2 O.sub.3 and Fe.sub.3 O.sub.4, dispersing the resulting iron oxide particles into an aqueous solution containing a cobalt salt and optionally a ferrous salt and an alkali of one equivalent or more to the metal salt(s), and heating the mixture at a temperature of higher than room temperature up to a boiling point of the mixture under an atmospheric condition such that the divalent iron is substantially not oxidized. The cobalt is thereby predominantly incorporated into the most outer layer of the acicular iron oxide particles.

Cobalt-containing iron oxide magnetic particles and method for the

Method for preparing cobalt-containing iron oxide magnetic particles

A magnetic recording medium comprising a nonmagnetic support and a magnetic layer provided thereon is disclosed. The magnetic layer comprises a magnetic recording element and a binder, wherein the magnetic recording element mainly comprises acicular gamma-Fe.sub.2 O.sub.3 particles having an average porosity of not more than 5% by volume, a specific surface area of 24 to 30 m.sup.2 /g and the X-ray diffraction intensity at the face (210) to that at the face (311) of not more than 5%. The magnetic recording medium has improved electromagnetic conversion characteristics such as sensitivity and noise.

Magnetic recording medium and magnetic particles therefor

A magnetic recording medium which comprises a first magnetic layer on a base and a second magnetic layer over the first magnetic layer, the second magnetic layer containing magnetic particles having an average particle length (long axis diameter) of not more than 0.35.mu. , with a coercive force of from 660 to 760 oersteds, and the ratio of the coercive force of the upper or second magnetic layer to that of the lower or first magnetic layer being 1.1/1 to 1.6/1. The resulting magnetic recording medium has excellent sensitivity and frequency characteristics over the entire frequency bands with less noise.

An improved magnetic recording medium is disclosed, particularly a magnetic tape suitable for sound recording and video recording, which comprises as a recording element a mixture of cobalt-containing iron oxide magnetic particles consisting essentially of ferromagnetic iron oxide particles containing cobalt and optionally a divalent iron in the most outer layer thereof, and .gamma.-ferric oxide particles in the ratio of 10:90 to 50:50 by weight, said mixture of cobalt-containing iron oxide magnetic particles and .gamma.-ferric oxide particles being applied to a substrate (e.g. a polyester film) with a binding agent. The magnetic recording medium has excellent electromagnetic transducing properties and improved charging properties and is useful for conventional magnetic recording apparatus used at normal position with high sensitivity in wide range of frequency.

A magnetic recording medium which comprises a base and a magnetic layer of a magnetic coating composition comprising magnetic particles and a binder provided on said base, characterized in that the magnetic coating composition further comprises a dialkylsulfosuccinate.

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Suita, Japan

Haruo Andoh