HP Color LaserJet 8500 Service Manual - Page 147

Developing block The black toner used in the printer is magnetic single-component toner composed of magnetite and resin. The color toner is nonmagnetic single-component toner composed of resin. The toners are given a negative charge when they rub against the developing cylinder and the blade. 4. Development The developing cylinder is biased to create a potential difference with the imaging drum. This bias consists of AC and DC components. The AC component breaks the toner free from the developing cylinder, creating a toner cloud. The DC component drives the toner particles to the imaged region on the imaging drum. The three color cartridges are brought into contact with the imaging drum when the carousel rotates. The black toner cartridge is set separately, and is always in contact with the imaging drum. When the area on the imaging drum exposed by the laser beam nears the developing cylinder, the charged toner particles move from the developer to the image surface because of the potential differences between the developing cylinder and the exposed imaging drum. Figure 28. EN Black toner cartridge (left) and color toner cartridge (right) development Image formation 145