Developing device for an image forming apparatus

摘要

In a developing device for an image forming apparatus, a developing roller has dielectric portions and conductive portions distributed regularly or irregularly over the surface thereof. The surfaces of the dielectric portions are smaller in height than the surfaces of the conductive portions. The difference in height is greater than one-half of the volumetric mean particle size of a toner. A charge opposite in polarity to a charge to be deposited on the toner is deposited on the dielectric portions. The dielectric portions, or recesses, each has a width more than three times as great as the volumetric mean particle size of the toner and a depth less than five times the volumetric particle size. The dielectric portions may be greater in height than the conductive portions and may be implemented as spiral grooves inclined more than 30 degrees relative to the axis of rotation of the developing roller. The developing roller may be moved at a higher linear velocity than a photoconductive drum.