| 摘要 |
PURPOSE:To secure a dark part potential sufficiently even when a discharging current is reduced by providing an opening which is <=1/2 as large as the back surface of a conductive shield to the back surface, and grounding the shield through a varistor which has a less varistor value than the potential of the dark part on a photosensitive body. CONSTITUTION:When a discharge wire 31 is impressed with a high voltage from a high-voltage power source 16, the surface of the photosensitive drum 1 is electrostatically charged by corona discharging. At this time, a corona wind flows is apt to flow to a lower-potential side, so the shield 32 is grounded through the varistor 33 so as to obtain a necessary dark part potential with a less corona current while flowing out the corona wind to the back surface opening (b). In this case, the opening width l1 of the back surface of the shield 32 is preferably about >=1/2 as large as the width L of the electrifier and the varistor value should be less than the drak part potential because the corona wind flows to the photosensitive drum with a lower potential when the varistor value is larger than the dark part potential on the photosensitive drum 2. |
