Patent GB-706779-A (GB)
Title: Electrophotographic duplicating machine
IPC: G03G15/30
Filed: 1951-03-05
Abstract: 706,779. Electrophotographic duplicating machines. BATTELLE DEVELOPMENT CORPORATION. March 5, 1951 [March 4, 1950], No. 5240/51. Class 98(2) [Also in Group XVI] The machine comprises a printing cylinder, a master plate wrapped on the outside of the cylinder, the plate having a conductive backing, a coating of photoconducting insulating material on the backing, and a master image of insulating and/or opaque material bonded to the coating, a corona discharge device adjacent the plate for charging the coating and the master image, a lamp for flooding the charged surface with light to discharge the coating and leave a charge only on the master image, a developer device for applying resin powder to the master image, a guiding device for directing a web of paper against and removing it from contact with the cylinder so that powder may be transferred from the master image to the paper and driving means for moving the web and cylinder in step whereby the cylinder carries the master image sequentially past the discharge device, paper-removing guide, the lamp, the developer device, and the paper-directing guide. The master image is preferably prepared by means of an electrophotographic plate comprising a conducting support as of aluminium or steel and a photoconducting insulating layer as of sulphur, anthracene, or amorphous selenium. The plate is uniformly charged in the dark as by passage beneath an electrode from which a corona discharge is made, the charged plate is exposed to the document to be duplicated in a photographic camera, enlarger, or contactprinting frame so that the charge is caused to leak away from the exposed areas, and the resulting electrostatic image is developed by dusting it with a powder, such as a fusible resin powder or asphalt, or a mixture of such a powder, which has been ball-milled with carbon black, with a coarser carrier material such as soya bean protein. The powder image so formed is bonded to the plate either by spraying it with a mist of a volatile solvent such as trichloroethylene and then evaporating off the solvent, or if the powder is fusible by heating the plate in an oven. Instead of an insulating developing powder a conducting powder may be used, providing it is opaque and so prevents discharge of the image areas of the plate when this is subsequently charged and exposed. Such a master plate made from a flexible electrophotographic plate 46 comprising an aluminium foil support and bearing an affixed powder image is secured with the affixed image outwards to a cylinder 26 rotatably supported at 27. A corona discharge electrode comprising parallel wires 66 with a protective earthed shield 67 is located adjacent the cylinder surface which is earthed and a paper strip 51 from a supply reel 50 is fed around the cylinder beneath the electrode and taken off over a roller 53 beltdriven from an electric motor 56. A developer unit comprising a container 35 having an adjustable door 38 adapted to flow developer powder over the cylinder, surplus powder being collected at 36, is removably mounted by lugs 43 engaging a bar 44, and tubular electric lamp 68 is arranged to illuminate the plate while a vacuum cleaner nozzle 69 removes surplus powder from the non-image areas of the plate. The lamp being switched on and the electrode 66 raised to its working potential, the motor 56 is started, rotating roller 53 to wind off the paper strip. The electrode 66 charges the plate 46 which is discharged in the non-image areas by the lamp 68, and the electrostatic image so formed is developed by the powder flowed over the cylinder at 37, the powder image so formed being transferred by corona discharge from the electrode 66 to the paper strip 51 to which the transferred powder image is bonded by heating elements 61 surrounding the roller 53 and if desired also embedded therein. The image-bearing paper strip may then be cut into sheets either automatically or manually. When no more copies are required, the image may be removed from the plate by rubbing with cotton swabs soaked in trichlorethylene, whereafter the plate is cleaned with ethanol. The principle on which the invention is based is described in the Specification with reference to a procedure disclosed in pages 993-996 of Volume 38, No. 12, of the Journal of the Optical Society of America.