| 摘要 |
PROBLEM TO BE SOLVED: To provide an image forming apparatus enhancing remarkably transfer performance in a black monochrome mode, without impairing transfer performance in a full color mode. SOLUTION: In a black monochrome mode, an intermediary transfer belt 9 is separated from an upstream photosensitive drum 1K in a state in which a downstream photosensitive drum contacts the intermediary transfer belt 9. At this time, a stretching roller 15 is moved upwardly in interrelation with a contact-separation mechanism 30 to increase an angle of contactθ1 of the intermediary transfer belt 9 with the downstream photosensitive drum 1K compared with the case of a full-color mode. On the other hand, in the full-color mode, the stretching roller 15 is moved downwardly to be separated from an inner surface of the intermediary transfer belt 9. COPYRIGHT: (C)2009,JPO&INPIT
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