To provide a developing unit, in which a developer on a developing sleeve has stable and adequate electric charges even in repetitive development and gives a uniform high-grade image free of streaks and unevenness, and free of lowering of image density or occurrence of a ghost.
In the developing unit with a developer vessel 3 housing a developer 4 and a developer support 8 for forming and supporting a thin layer of the developer housed in the developer vessel on the surface and feeding the developer to a developing region, the developer is a negative-charge type developer having at least toner particles and an inorganic fine powder, the toner particles contain at least a bonding resin and a colorant, the weight average particle diameter of the toner is 5-12 μm, and the circularity of toner particles having ≥3 μm have been controlled. The developer support has at least a substrate 6 and an electrically conductive coating layer 7, which coats the substrate. The layer 7 contains at least a bonding resin and electrically conductive fine particles and a nitrogen-containing heterocyclic compound dispersed in the bonding resin.
GOSEKI YASUHIDE
SHIMAMURA MASAYOSHI
OKAMOTO NAOKI
FUJISHIMA KENJI
SAIKI KAZUNORI
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