Lexmark W820 Service Manual page 77

4025-XXX
4.
Transfer
As the paper travels between the BTR and the drum surface, the Bias Transfer Roll
(BTR) applies a positive charge to the back of the printing paper. This positive
charge transfers the negative charged toner image from the drum surface to the top
surface of the paper. The toner image is now on the paper and the paper is now
stuck to the drum surface, due to the relative electrical differences between the
negative electrical charge of the inner conductive layer of the drum and the positive
electrical charge of the paper.
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