GB1017682A - Improvements in xerography - Google Patents

Abstract

1,017,682. Electrophotographic processes. RANK XEROX Ltd. June 12,1962 [June 12, 1961], No. 36254/65. Divided out of 1,017,681. Heading G2H. A method of forming a zerographic reproduction of a pattern of light and shadow comprises forming on a xerographic plate a half-tone image charge pattern and electrostatically depositing finely divided toner particles of opposite polarity on the charge pattern, whereby particles of one polarity deposit on charged image areas and the particles of the other polarity deposits in areas immediately adjacent thereto. A suitable developer composition including toner particles of opposite polarity is described in Specification 1,017,681. A half-tone charge pattern may be produced as described in Specification 1,017,683, Fig. 2, 3, and 4 (all not shown) represent the charge pattern and development with toners of opposite polarity using a coarse, fine and very fine half-tone pattern respectively. A charged plate 10, Fig. 5A, is exposed through a half-tone screen 20 to uniform illumination, thereby producing a charge density pattern, Fig. 5B, on the surface of the plate 10. The plate is then exposed to a light pattern, e.g. a step wedge 21 Fig. 5C (not shown), whereby a charge density pattern Fig. 5D (not shown) is produced. Which upon upon development is a positive-positive reproduction. If desired, the exposure to a light pattern may precede exposure through the half-tone screen. In a modified method negative-positive reproduction, Fig. 6, the half-tone screen 20 is placed above the step wedge transparency 21 and a single exposure is made. Toners of contrasting colour may be used for development. Instead of using a half-tone screen, a xerographic plate having non-photo-sensitive areas may be used. For example, a plate may be formed by printing a pattern of insulating plastic on top of a photoconductive layer. The developed image may be electrostatically transferred to a sheet 17, Fig. 1D, of paper by recharging the deposited toner particles to a single polarity and by reversing the polarity of power supply 14 so effecting transfer to the sheet 17. Alternatively, transfer may be effected by an adhesive method. The transferred image is fixed in each case after transfer.