| 摘要 |
PURPOSE:To obtain a sharp image free from background fog and high in gradation using a one-component developer, by applying a specified alternating electric field across the gap between an electrostatic image bearing plate thicker than a development layer and a developer bearing body. CONSTITUTION:An alternating electric field having <=1kHz frequency and max. and min. voltages Vmax and Vmin satisfying the conditions of expressionIand II when the image areas of an electrostatic image is positive in order to execute necessary control of transfer and retransfer of a toner to and from the image areas and the nonimage areas, thus permitting a sharp high-gradation image to be formed by jumping development with a one-component developer, and to be well reproduced and free of background fog. When the electrostatic image is negative, similar operation are executed. In these expressions, VD, VL are potentials of the image areas and the nonimage areas of the electrostatic image; Vth.f, Vth.r stand for threshold values of potential difference for transferring the toner to the electrostatic image forming face and the development layer face. |
