| 摘要 |
PURPOSE: To shorten a cleaning time of a transfer roller performed at the time of forward rotation and backward rotation, by applying transfer bias whose polarity is the same as the polarity of the toner after the last transfer material of a series of the image forming operation is allowed to pass the transfer position, then the bias having the reverse polarity before the first transfer material is allowed to pass there. CONSTITUTION: An electrostatic latent image is formed by performing optical write-in corresponding to the image information by exposure means 3 consisting of laser beams. When the formed electrostatic latent image is allowed to pass a developing unit 4, the toner electrified to have the negative polarity is made stuck on the latent image part by application of the reverse polarity developing bias inside the developing unit by a power source 22, and the toner is formed on the photoreceptor. While, the transfer roller 5 is allowed to hold the transfer material P in press contact with the photoreceptor 1 side, and the toner image on the photoreceptor 1 is transferred to the transfer material side by the effect of electrostatic force generated by the bias having polarity opposite to that of the toner, applied from a power source 21. In such a manner, the necessary time for cleaning is shortened, by selectively applying the cleaning bias to the transfer roller 5. |
