Sakai Chemical Industry Co., Ltd.

Hitachi Maxell, Limited

Seiji Matsumoto

Kiyoshi Fukai

Tadashi Koga

Haruo Andoh

Hajime Uno

Susumu Iwasaki

Yasuo Araki

Hideji Yamamoto

Tatsuo Takano

Shinya Nakatani

Shigeharu Higuchi

Osamu Nagasawa

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 method of producing single crystalline, acicular .alpha.-ferric oxide particles of narrow particle size distribution is provided. The method comprises heating an aqueous suspension of ferric hydroxide at temperatures of 100.degree.-250.degree. C. at an alkaline pH in the presence both a water soluble organic or inorganic compound capable of forming complexes with iron as a growth regulating agent and .alpha.-ferric oxide seed crystals of minor axes not larger than 0.4 microns in average in amounts of 0.1-25 mole % in terms of the Fe content thereof in relation to the ferric hydroxide.

Method of producing single crystalline, acicular .alpha.-ferric oxide

A method of producing cobalt-modified magnetic particles is provided. The method comprises heating an aqueous suspension of ferric hydroxide at temperatures of 100.degree.-250.degree. C. at an alkaline pH in the presence of a water soluble organic or inorganic compound capable of forming complexes with iron as a growth regulating agent, and preferably also in the presence of .alpha.-ferric oxide seed crystals of minor axes not larger than 0.4 microns in average in amounts of 0.1-25 mole % in terms of the Fe content thereof in relation to the ferric hydroxide, converting the obtained .alpha.-ferric oxide into .gamma.-ferric oxide by reduction thereof followed by oxidation, maintaining an aqueous suspension of the .gamma.-ferric oxide at temperatures of 30.degree.-50.degree. C. at an alkaline pH in the presence of ferrous hydroxide and cobaltous hydroxide in amounts of 0.5-50 mole %, respectively, in relation to the Fe content of the .gamma.-ferric oxide in the suspension for a length of time sufficient to modify the .gamma.-ferric oxide particles.

Method of producing cobalt-modified magnetic particles

An improved method for manufacturing a magnet paper sheet which comprises: thoroughly mixing about 70-90 parts by weight of magnetoplumbite barium ferrite powder and/or magnetoplumbite strontium ferrite powder essentially consisting of particles of primary particle size of about 0.1-2 microns and of secondary particle size smaller than about 20 microns, an anionic synthetic latex containing about 1-10 parts by weight in dry weight of a synthetic rubber and/or a synthetic resin such as SBR, NBR, polyvinyl acetate and polyacrylate, about 2-10 weight % of a cationic organic polymer electrolyte such as polyamine and polyethyleneimine based on the amount of the synthetic rubber and/or resin, and more than about 5 parts by weight of pulp fibers together into a slurry; forming the slurry into a paper sheet; and magnetizing the paper sheet.

Magnet paper sheet and a method for manufacturing the same

Single crystalline, acicular ferric oxide particles are produced by maintaining an aqueous suspension of ferric hydroxide at an elevated temperature at an alkaline pH in the presence of an organic phosphonic acid compound or a hydroxycarboxylic acid compound as a growth-regulating agent.

Production of acicular ferric oxide

Single crystalline, ferrite particles are obtained by the thermal reaction of ferric oxyhydroxide, ferric hydroxide, porous ferric oxide made therefrom or ferric oxide having a particle size less than 0.8.mu. with a strontium or barium compound such as the oxide, hydroxide, the carbonate or the carboxylate in the presence of a small amount of a metal chloride flux such as strontium chloride or barium chloride. The resulting particles have a well-defined, hexagonal plate configuration and are particularly adapted for the production of anisotropic magnets.

Production of single crystalline ferrite particles

Single crystalline ferrite particles are obtained by the thermal reaction of ferric oxyhydroxide, ferric hydroxide, porous ferric oxide made therefrom or ferric oxide having a particle size less than 0.8.mu. with a strontium or barium compound such as the oxide hydroxide, the carbonate or the carboxylate in the presence of a small amount of a metal chloride flux such as strontium chloride or barium chloride. The resulting particles have a well-defined, hexagonal plate configuration and are particularly adapted for the production of anisotropic magnets.

Growing community of inventors

Sakai, Japan

Seiji Matsumoto