Konishiroku Photo Industry Co., Ltd.

Takeo Nishimura

Makoto Tomono

Goichi Yamakawa

Nobuo Takahashi

Shotaro Watanabe

An iron powder developer carrier for electrophotography having at least the outer surface thereof coated with iron oxide. The iron oxide has a particle size of 50 to 200.mu., an apparent density of 1.5 to 2.5 g/cm.sup.3 and a specific surface area of 0.01 to 0.3 m.sup.2 /g. A process for the preparation of iron powder developer carriers for electrophotography, which comprises the steps of subjecting a starting iron powder to a primary calcination treatment in an inert gas atmosphere without using a binder, pulverizing and classifying said calcination product to prepare an intermediate iron powder, reducing the intermediate iron powder in a reducing atmosphere and washing the intermediate iron powder, and subjecting the intermediate iron powder to an oxidizing calcination treatment.

Developing material for electrophotography, process for preparation

An iron powder developing carrier for developing an electrostatic latent image, a manufacturing method thereof, a developer containing said developing carrier and a method of forming a visible image by using said developer. Said iron powder developing carrier has the apparent density from 1.5 to 2.5. Said manufacturing method comprises the steps of sintering a raw iron powder having been ground to particles of not larger than 50 microns in diameter without using any binder agent at the temperature from 900.degree. to 1200.degree. C. to form an sintered body, grinding and classifying said sintered body into an intermediate iron powder having the particle diameter from 50 to 200 microns, then treating said intermediate iron powder to oxidize at the temperature from 280.degree. to 390.degree. C., and adjusting the resultant iron powder so as to have the apparent density from 1.5 to 2.5.

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Kawaguchi, Japan

Takeo Nishimura