| 摘要 |
PROBLEM TO BE SOLVED: To surely prevent soil on the back of a recording medium by applying a reverse transfer bias voltage, which is opposite in polarity to a transfer bias voltage, to areas other than a recording medium in the case a part of transferred toner image is present on an area of intermediate transfer body, that is other than the area corresponding to the recording medium. SOLUTION: Based on a signal from a paper detection sensor 58 or a cassette sensor, a CPU detects the size of a recording paper 26 in the carrying direction. Only in an area corresponding to the size of the recording paper 26 in the carrying direction, does the CPU apply a transfer bias voltage to a backup roll 25 via a transfer-bias-voltage-application high voltage power source 47. In an area where the recording paper 26 and a toner image mismatch occurs, it applies a reverse transfer bias voltage to the backup roll 25 via the transfer- bias-voltage-application high voltage power source. This prevents a toner image which protruded from the recording paper 26 from being transferred a secondary transfer roll 27. |
