Color image forming apparatus and belt unit and image forming unit thereof

摘要

The average friction factor between the contact surfaces of a drive roller and an intermediate transfer belt is set to not more than 0.45 and not less than 0.1, and before the primary transfer of the toner image of the last color is finished, a cleaning blade is separated from or comes into contact with the intermediate transfer belt with the drive roller as a backup member. The peripheral length of a photoconductor is greater by not more than 10% than the value obtained by dividing the length on a transfer member necessary for a predetermined image length by an integer n which is not less than 3 and not more than 9, and the ratio between the numbers of rotations of the transfer member and the photoconductor is 1:n.