Image forming apparatus employing a reversal developing system.

摘要

An image-forming apparatus employing a reversal developing system and using a photosensitive material (10) capable of being charged into both positive and negative polarities and further using a transfer roller (14) made of an electrically conducting sponge rubber. The photosensitive material (10) and the transfer roller (4) are press-contacted to each other with a suitable force, and a DC voltage is applied to the transfer roller (4), the DC voltage having a polarity opposite to the polarity of the potential created by the main charger (11) and having a value larger than a charge start voltage of the photosensitive material (10) but being so set that the potential on the surface of the photosensitive material (10) after discharge is not larger than 50 V in an absolute value. This apparatus permits a toner image formed on the surface of the photosensitive material (10) to be transferred at a high efficiency and enables the photosensitive material (10) to be uniformly charged in a next cycle of forming image.