Oki OKIPAGE 10i Service Manual page 34

(3) Exposure
Light emitted by the LED head irradiates the image drum surface. The surface potential of the irradiated
portion of the image drum drops, forming an electrostatic latent image associated with the image signal.
The image drum is coated with an underlayer (UL), a carrier generation layer (CGL), and carrier transfer
layer (CTL) on aluminum base. The organic photo conductor layer (OPC), comprising CTL and CGL, is
about 20 mm thick.
The image roller surface is charged to about -750 V by the contact charge of the charge roller.
When the light from the LED head irradiates the image drum surface, the light energy generates positive
and negative carriers in the CGL. The positive carriers are moved to the CTL by an electrical field acting
on the image drum. Likewise, the negative carriers flow into the aluminum layer (ground).
The positive carriers moved to the CTL combine with the negative charges on the image drum surface
accumulated by the contact charge of the charge roller, lowering the potential on the image drum surface.
The resultant drop in the potential of the irradiated portion of the image drum surface forms an
electrostatic latent image on it. The irradiated portion of the image drum surface is kept to about -100 V.