GB1009509A - Improvements in electrophotography - Google Patents

Abstract

1,009,509. Electrophotographic processes. RANK-XEROX Ltd. April 17, 1962 [May 1, 1961], No. 14768/62. Heading G2H. An electrostatic image is formed from an image of non-uniform brightness, e.g. a PPI tubes, by non-uniformly charging a photoconductive layer in inverse relationship with the non-uniformity of brightness before exposure. In one embodiment, a corona discharge device 12, Fig. 1, is rotated by an angle 11. The device 12 has a conductor 17 within a shield 18 having a tapered slit 19, Fig. 3 (not shown). In other embodiments, Fig. 5 (not shown) conductor 17 is tapered, thus varying the charging current, the device 12 is curved towards the edge of the photoconductive layer Fig. 6 (not shown. In further embodiments, the conductor 17 is connected at its ends to a resistor 21, Fig. 7 (not shown), a grid 18, Fig. 8 (not shown) may replace shield 18, Fig. 1, or needles 23, Fig. 9 (not shown) are connected to tappings on a voltage divider 22. A fixed corona discharge, Fig. 10, has two interwound conductors 25, 26 fed by pulsed D. C., the pulses of one conductor being displaced 180 degrees with respect to the other. The device 12, Fig. 11, is mounted on a reversible worm 27, above a photoconductive layer supported in an inclined position. For producing continuous tone reproductions, a development electrode 29, Fig. 12 may be used in development. The electrode 29 comprises a graphite disc connected at its centre to a voltage dropping device. The thickness of the disc is tapered outwardly, such that the disc has the same potential across its surface as the corresponding background areas of an image to be developed. In another embodiment, concentric rings 36 Fig. 13 (not shown) are individually connected to tappings of a voltage divider 37. An endless band photoconductive member 38, Fig. 14, is charged over a circular area by device 39 so as to have a minimum potential at its centre and a higher potential at the periphery of that area. The charged area is exposed to a PPI tube and developed by cascading developer from a hopper 42. The developed image is transferred to a paper web 45 by corona discharge and the transferred image is fixed to the web 45. In another embodiment, a hexagonal drum 51 Fig. 15 (not shown) is intermittently driven by a motor 52 through charging, exposure, developing, transfer and cleaning stations.