Image forming apparatus having improved image transfer characteristics

Abstract

By application of a voltage from a power source, a transfer roller carries out both transfers of (A) a first transfer for transferring a toner image on a photoreceptor to an intermediate transfer medium and (B) a second transfer for transferring overlapped color toner image on the intermediate transfer medium at once onto a recording sheet. A transfer voltage in accordance with, for example, a sheet thickness, as detected by sheet type detection of a sheet type detecting section is applied to the transfer roller in each stage. When the sheet type detecting section detects that the recording sheet is longer than a periphery of a fixing belt, a heater lamp is turned on in advance at any instant between a time when the recording sheet is brought into contact with the fixing roller and a time when the fixing roller completes one rotation, taking into consideration a time required for conduction of heat from the heater lamp to the fixing belt. As a result, it is possible to reduce ozone generated and make the device compact, and desirable transfer characteristics in accordance with a sheet type are obtained, thus realizing uniform fixing of an unfixed toner image onto the recording sheet, from the front end to the rear end.