In electrophotography, an image copy can be obtained by developing electrostatically charged images formed on a photoreceptor with resin particles generally containing pigments (hereinafter "toners") to visualize the images, transferring the visual images onto a paper, and fixing the resulting images with a heated roll.
The photoreceptor then undergoes cleaning to again form electrostatically charged images thereon.
It is necessary that toners used for such electrostatic development have characteristics suitable for duplicating processes such as flowability, caking resistance, the ability to adequately fix images, electrical charging properties, and cleaning ability.
The addition of fine particles of inorganic substances such as silica, alumina or titania to toner composition has generally been performed, particularly to increase flowability and caking resistance among the above characteristics.
However, dispersibility of such fine particles of inorganic substances often depends upon the surface structure of the fine particles. When dispersibility is poor, satisfactory flowability and caking resistance cannot be obtained, cleaning is incomplete, toners firmly adhere on a photoreceptor, thereby forming black spots on image copies, and electrical charging properties of a developer decreases with passage of time.
Accordingly, the primary objects of the present invention are to solve the above described problems caused when inorganic fine particles are incorporated in toners.