Patent GB-679533-A (GB)
Title: Apparatus for producing photographs electrically
IPC: G03G15/22
Filed: 1947-07-31
Abstract: 679,533. Electrophotographic apparatus. BATTELLE DEVELOPMENT CORPORATION. July 31, 1947 [Nov. 16, 1940], No. 20758/47. Class 98 (ii). [Also in Group XVI] A machine for making electrophotographic copies by the process of Specification 672,767 is characterized by a plate with a layer of photo - conductive insulating material, an electrostatic charging device for the layer and devices for projecting a light image on to the layer, dusting the layer with a powder and transferring powder from the layer to a receiving sheet, and a device for moving the plate successively into co-operative relation with the charging projection, dusting and transfer devices. In the form shown a drum 25 is rotated by an electric motor through reduction gearing. It carries the conducting backing layer 23 with photo-conductive insulating coating 24 which is charged by the rotating brush or plush covered roller 32 which is discharged by contact with the metal rod 37. Transparent or translucent matter 90 for copying is fed into a shoot between plates 38, 39 from which it is released by removal of fingers controlled by a lever 44 operated by a cam on the drum shaft. The sheet 90 is held in contact with the insulating layer by an endless transparent belt 48, carried on rollers 46, 47, and exposure is effected by the lamp 52 controlled by a switch on the drum shaft. The sheet then falls into the space 92. The electrostatic image on the layer 24 passes over the trough 55 containing a brush 57, rotated by an electric motor, and dust which is agitated into a cloud by the brush to adhere to the image. A sheet 91 is fed between rollers 62, 63. The latter dips into a trough of water or a liquid which is adhesive or a solvent for the dust; the former is lowered into contact with the drum, by cams carried by the drum, during passage of the layer 24. The moistened sheet 91 is thus rolled on to the layer 24 and the dust image transferred to it. The sheet is then passed back between flat heating elements 73, 74 by which the dust, if resinous, is melted on to it. In a modification the sheet 91 is heated, instead of being wetted, before being rolled in contact with the drum. A brush 76, rotated by the same electric motor as the roller 32, cleans the layer 24 in readiness for the next exposure. A suction device may be provided to take away dust removed by the brush. The charging roller 32 may be replaced by a pair of rollers carrying an endless band with a plush outer surface in contact with the drum. A felt wick dipping in water may be provided to moisten, and remove electrostatic charges from, the surface of the band 48 as it leaves the drum. The heating elements 73, 74 are each divided into two parts, one to heat them quickly to attain cooking temperature, the other to maintain this temperature. Thermostatic control is provided, the switch controlling the electrical supply to the remainder of the machine which cannot be operated until working temperature is reached. The power supply also passes through a switch, which is opened by a cam on the drum shaft in the rest position of the machine. Another parallel switch is closed for a short period to start the machine, after which it runs to complete one cycle of operations. A modified machine is described for photographing objects or opaque originals. Two drums are provided with an endless belt running over them and carrying the photo-conductive insulating layer and its conducting support layer. The band is stopped and the object illuminated for exposure the duration of which is determined by a time switch. In this machine two dust troughs are provided for alternative use. After the dust image has been formed it can, instead of being transferred to paper, be heated to melt it on to the metal layer 23 and to evaporate the insulating layer (e.g. of anthracene). Lithographic and hectographic printing layers can be so prepared, using respectively resins which are wetted by ink and which contain alcohol soluble dye, which latter will transfer to paper wetted with alcohol. A metal sheet carrying a resin image may be used on the drum of the machine illustrated, without any light exposure step, to produce successive prints by charging the resin electrostatically. Since the resin is not photo-conductive a metallic backing carrying a photo-conductive layer and a resin image may be used to overprint said image on to prints of successive originals.