Sakai Chemical Industry Co., Ltd.

Susumu Iwasaki

Shigefumi Kamisaka

Iwao Yamazaki

Tutomu Hatanaka

Seiji Matsumoto

Yoshihiko Nakane

Osamu Nagasawa

Tatsuo Takano

A process for producing microcrystalline barium ferrite platelets which comprises: forming an aqueous alkaline dispersion containing coprecipitates of hydroxides of barium ions, iron (III) ions, and optionally ions of a substituent element; heating the dispersion to a temperature of not less than 50.degree. C. and not more than the boiling point of the dispersion under an atmospheric pressure to convert the coprecipitates to precursors of the barium ferrite; calcining the precursors to provide microcrystalline barium ferrite platelets; the improvement comprising the step of adding a carbonating agent such as sodium carbonate to the aqueous alkaline dispersion before or after the heating of the aqueous dispersion to insolubilize water soluble barium ions therein, and the step of calcining the barium ferrite precursors in the presnece of sodium sulfate at temperatures of 700.degree.-900.degree. C., to provide microcrystalline barium ferrite platelets of about 0.03-0.1 .mu.m in average particle size and 2-5 in planarity ratio.

Process for producing microcrystalline barium ferrite platelets

A process of producing a spinel structure Ni/Zn ferrite-modified, Co/Ti-substituted microcrystalline barium ferrite platelets having an average particle size of 0.03-0.15 .mu.m, a temperature coefficient of coercive force of not more than +1 Oe/.degree. C., including small absolute values in negative region, and a saturated magnetization of not less than 56 emu/g, which comprises: forming substantially amorphous preecursors of Co/Ti-substituted barium ferrites; adding an aqueous solution of nickel salts to the dispersion of the precursors of Co/Ti-substituted barium ferrites, and subjecting the slurry to hydrothermal reaction, thereby to provide precursors of spinel structure nickel ferrite-modified, Co/Ti-substituted barium ferrites; depositing a water insoluble zinc compound on the precursors; and calcining the precursors in the presence of barium chloride, washing the calcined products to remove therefrom the barium chloride, and drying.

Process for producing microcrystalline Co/Ti-substituted barium ferrite

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

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Osaka, Japan

Susumu Iwasaki