Nippon Aerosil Co., Ltd.

Akira Inoue

Hirokuni Shirono

Eiji Komai

Takeyoshi Shibasaki

Hideaki Tashiro

Masanobu Kaneeda

Provided is a surface-modified metal oxide powder obtained by treating a surface of a metal oxide powder, wherein a ratio (A/B) of an initial triboelectrostatic charge amount (A) at a time of one minute after dispersion of the surface-modified metal oxide powder into a ferrite carrier to a triboelectrostatic charge amount (B) after a lapse of 30 additional minutes is from 1.0 to 2.0, and the triboelectrostatic charge amount (B) is from &#x2212;300 to +300 &#x3bc;C/g. The surface-modified metal oxide powder has a weaker charging property and a better stability over time of a triboelectrostatic charge amount than a conventional one; and thus, when this powder is used as an external additive, various properties including flowability and electrical charging can be stabilized, and in addition, problems such as fogging and image deterioration can be drastically remedied without significantly deteriorating characteristics as a developer and the like.

Surface-modified metal oxide powder and process for producing same

Firstly, a powder matrix is kept in a fluent state, said powder matrix consisting of a first oxide having an absorbed water amount of 0.1 to 50%, an averaged particle diameter of 0.005 to 0.5 &mgr;m and a surface hydroxyl group number of 0.1 to 25 &mgr;mol/m . Then, one or both of a halide and an alkoxide including metal or semi-metal identical with or different from the metal or semi-metal constituting said first oxide is allowed to contact with said powder matrix kept in the fluent state, by means of an inert carrier gas, and then they are heated at a temperature of from 25 to 800&deg; C., to thereby coat said powder matrix by a coating layer consisting of a second oxide. Further, a reaction by-product consisting of one or both of a hydrogen halide or an alcohol generated by said contacting is heated at a temperature of from 200 to 1000&deg; C. within the inert carrier gas to thereby eliminate the reaction by-product.

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Mie, Japan

Akira Inoue