Patent GB-1297519-A (GB)
Inventor: PRESSMAN GERALD L
IPC: G03G15/34
Filed: 1969-11-17
Abstract: 1297519 Electrographic processes ELECTROPRINT INC 17 Nov 1969 [15 Nov 1968] 56167/69 Heading G2H [Also in Division B6] A method of electrostatic image reproduction comprises. creating charge levels in accordance with the image to be reproduced of equal magnitude and opposite sign on respective sides of a perforate screen comprising an insulative layer, projecting  the charged particles towards the screen which  allows passage therethrough in accordance with the image and intercepting the particles which pass through the screen on to a receiving medium. The screen may comprise a wire mesh or an apertured metal plate Figs. 61a to 61i (not shown), with photo-conductive material thereon. The photo-conductive layer may be used on its own or in combination an insulating layer which may lie between the conductive layer and the photoconductive layer or either surround or be surrounded by the photo-conductive layer Figs 8a to 8c (not shown). In one embodiment using an apertured screen 43 Fig.7, the screen is simultaneously electrostatically charged and exposed to a visible image (left-hand part of the Figure 7) to give an imagewise electrostatic charge on the screen. Charged toner particles are propelled from a source 47 towards the screen 43 (right hand part of Figure 7) and a paper sheet 49 by a biassing voltage V 1  whilst the apertured screen 43 is maintained at a voltage V 2  which enhances or diminishes the electrostatic field of the imagewise charge thus allowing or preventing the passage of particle through the screen and onto the sheet 49 in an imagewise manner. In another embodiment Fig.6 (not shown) the screen is charged and then exposed imagewise in separate steps. An apparatus for cyclic reproduction, Fig.10 may incorporate the apertured screen 121. An image 132 is projected onto the screen through transparent electrode 134 and insulating material 165 whilst an electrostatic charge of either polarity is provided by circuit 136. The electrostatic image is developed at 140 by projecting marking particles from 141 through the screen 121 onto paper 145 using a biassing voltage provided by drum 150. The visible image on paper sheet 145 is fixed at 157. Marking particles remaining on the screen 121 are removed at 170. An enhancing field may be applied to the screen by a corona source 161. Other cyclic apparatus are disclosed wherein the photo-conductive or insulating layer takes the form of a cylinder and the image is projected thereon from within the cylinder Figs. 17 and 42 (not shown). In another apparatus Fig.41 (not shown) the insulating layer 165 is replaced by a photo-conductive layer (165"). A plurality of development stations may be used Fig.48 (not shown) particularly as a computer print-out in conjunction with a CRT display Fig. 49 and 50 (not shown). Other apparatus may use a charging stylus (601) Fig.51 (not shown) or an electrostatic typewriter (709) Fig.52 (not shown) to form the electrostatic image on the screen. In two embodiments Figs. 53 and 53 (not shown) two endless apertured screens are used and ions are projected towards the first screen bearing the electrostatic image so that ions passing through the first screen in an imagewise manner modulate the field on the second screen. Marking materials (931) may then be projected at the image on the second screen (925) to give a developed image or ions may be projected at the second screen (851) onto a sheet of paper (867) to give an electrostatic image thereon which is subsequently developed (871). The apertured screen may be charged in an imagewise manner by using a sheet comprising a conductive backing (251) and an insulating (253) or photo-conductive layer (263) and having on the surface of the layer the electrostatic image which is transferred to the screen Figs. 18 to 23 and 24 to 26 (not shown). The apertured screen 409 may be incorporated in a camera, Fig.44 against a photo-conductive layer 406 and exposed to an image through lens 403 and shutter 405. The screen 409 is removed and a visible image developed from it Fig.45 (not shown). In another camera Fig.46 (not shown) the electrostatic field is enhanced by a sequential operation of the shutter and lights (420) within the camera together with a reversal of the field across the screen. A photographic enlarger Figs. 55 to 58 (not shown) may also be made using the apertured screen.