Ricoh Company, Ltd.

Masaaki Nomura

Wasaburo Ohta

Koji Hirakura

Tsutomu Ishida

Tamio Ohhori

This invention provides an electrostatic copying method for forming multiple copies by repeating the process of developing an electrostatic latent image formed on an electrophotographic insulating material with a dry developer comprising electroscopic powder and carrier particles and the process of transferring the thus developed image onto a transfer sheet continuously without erasing said latent image, said carrier particles consisting of an essentially homogeneous ferromagnetic oxide having an apparent electric conductivity in the range of 10.sup.-11 -10.sup.-5 .OMEGA..sup.-1 cm.sup.-1, thereby rendering it possible to form multiple copies compared with the conventional copying methods.

Electrostatic copying method for forming multiple copies

An electrostatic image is formed on a rotating photoconductive drum and developed a number of times to form toner images which are transferred to respective copy sheets. The drum is rotated at a first speed for exposure and development of the first toner image and thereafter at a second higher speed for development of the subsequent toner images. A magnetic brush applies the toner substance to the drum, and is rotated at a third speed when the drum is rotated at the first speed and at a fourth speed which is higher than the third speed when the drum is rotated at the second speed, thereby applying more toner substance to the drum at the higher speed and maintaining the copy density constant. Alternatively or in combination, a bias voltage applied to the magnetic brush may be reduced at the higher drum speed, also resulting in the application of more toner substance to the drum.

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Tokyo, Japan

Masaaki Nomura