Image forming apparatus

Abstract

An image forming apparatus of the present invention is of the type causing a toner image transferred by primary transfer to again move via a primary image transfer region before secondary transfer. The apparatus includes an image carrier for carrying the toner image to be transferred by the primary transfer. An intermediate image transfer body transfers the toner image transferred thereto by the primary transfer to a recording medium by secondary transfer. The intermediate image transfer body forms the primary image transfer region in contact with the image carrier. A charge depositing device applies a bias to the primary image transfer region to thereby form an electric field for the primary transfer. When the intermediate image transfer body again conveys the toner image via the primary image transfer region while running idle, an electric field forming device forms an electric field weaker than an electric field assigned to the primary transfer in the primary image transfer region. A controller variably controls, in accordance with the surface potential of the image carrier, a bias for forming the electric field during idle run. The apparatus reduces or fully obviates the reverse charging of toner during the idle run of the intermediate image transfer body and insures high quality images even with thick sheets or OHP (OverHead Projector) sheets.