GB772873A - Electrostatic image reproduction - Google Patents

Abstract

772,873. Transferring electrostatic images. BATTELLE DEVELOPMENT CORPORATION. May 21, 1954 [May 29, 1953], No. 15064/54. Class 98(2) An undeveloped electrostatic latent image such as one formed on a xerographic plate is transferred to an insulating receiving surface by placing said surface in close proximity (i.e. an air gap of 2-90 microns) to the image-carrying surface and applying an electric field between the surfaces. The insulating surface may then be removed and the image thereon developed or used for a further transfer of charge to obtain an image which is not laterally reversed. As shown a transfer sheet of insulating material 20 is laid on top of a xerographic plate comprising a photoconductive layer 22 carrying an electrostatic image and supported on a conductive backing 21. An electric field is applied by a corona discharge from a grid of fine wires 23 held at a potential of several thousand volts with respect to the earthed channel 24. a control grid 25 being held at some intermediate potential. This device is moved back and forth over the back of the insulating sheet 29. The charge applied may be either positive or negative. Alternatively, the field may be applied by a conductive rod or roller connected to a source of potential and moved across the back of sheet 29. The insulating sheet may be of cellulose acetate, ethyl cellulose, polystyrene, polyethylene or insulating paper (i.e. of low moisture content). It is preferred to use paper sized with an insulating resin, or impregnated with ethyl cellulose, polystyrene, cellulose nitrate or cellulose acetate or paper coated on one or both sides with such plastic materials. The insulating sheet is preferably precharged prior to laying it on the photoconductive layer, and this is done by laying it on an earthed metal plate and passing a high voltage ion source over it. Either the face or the back of the sheet may be precharged. Improved results are obtained in the transfer step if an additional sheet is laid over sheet 29. This additional sheet may be of insulating material such as paper, cellulose acetate or polystyrene, but it is preferably conducting, as of metal, in which case the field may be applied by connecting a source of potential between the two conducting backing sheets, and the field may then be maintained while the surfaces are being separated. After transfer, the sheets are preferably removed as a unit and the image developed with or without the backing sheet., In a further embodiment, first an insulating sheet and then a conducting sheet are laid over sheet 29 during transfer. The sheet 29 with its backing layers may be precharged as described above. The transferred image may be developed by using a powder/carrier developer which is fixed by heating, or by blowing a charged powder or ink across its surface. The theory of the transfer in the various cases is fully discussed. Specifications 672,767, 679,715, 696,515 and U.S.A. Specification 2,346,812 are referred to.