Patent GB-971611-A (GB)
Title: Improvements in or relating to methods for use in the preparation of printing master sheets and printing therefrom
IPC: B41M1/42
Filed: 1962-11-15
Abstract: 971,611. Printing surfaces and processes. W. RITZERFELD, and G. RITZERFELD. Nov. 15, 1962 [Dec. 15, 1961], No. 43234/62. Heading B6C In a method for the preparation of a printing master sheet and printing therefrom, a printing master sheet, which on its side to be printed from has a surface or layer which is electrostatically neutral or which can be electrostatically charged, is provided with a printing image by pressure transfer or impact transfer of regions, corresponding to printing image regions, of a layer of a transfer sheet or ribbon placed in contact with the said sheet side, an electrostatically chargeable material being contained in the layer, the printing image regions being then electrostatically charged and thereafter developed by the application thereto of a developing medium, the developed printing image being mechanically, electrostatically, or chemically transferred on to a sheet to be printed and thermally, chemically, or mechanically fixed thereon. In the printing apparatus of Fig. 5 a printing under sheet 10 of aluminium or zinc foil is fixed on a printing drum 8 by a device 9. The conductive surface 11 of the sheet 10 is poorly electrostatically chargeable but the printing image regions 12-pressure transferred from the transfer sheet-although not conductive are chargeable, being of powdered polystyrol embedded in non-conductive waxes, fats or oils such as paraffin, paraffin oil or petroleum jelly. On rotation of the drum a device 14 electrostatically charges the sheet 10 of which the regions 12 retain the charge. The image is developed with powder 16 whilst passing the chamber 15. Thereafter the printing procedure follows. In another arrangement, Fig. 6, the master sheet has a conductive base 17, which is poorly chargeable, and has image regions 18 transferred from the transfer layer which are electrically conductive. Accordingly an insulating intermediate layer 19 is carried therewith from the transfer layer sheet during inscription, so that on electrostatic charging by the device 14 the charge can flow away from the sheet 17 but not from the insulated regions 18. The transfer layer in this embodiment may consist of solid or liquid fatty acids and waxes high acid number-such as synthetic waxesin which metal salts or oxides are embedded. The non-conductive layer 19 may be paraffin. When using a conductive printing master sheet surfaces of, e.g. arsenic sulphdie, a non-conductive support material for the surface, e.g. paraffinated paper or polyethylene foil, should be used. Sheet 20, Fig. 7, supports conductive and electrostatically chargeable image regions 21 these being separated from the sheet by insulating layer 22. A positive charging chamber 23 of plus 20,000 volts, an earthing conductor 24, and a negative charging chamber 25 of minus 10,000 volts are provided. The sheet 20 is of aluminium foil, the layer 22 is of paraffin and metallic oxide is embedded in the layer of the transfer sheet. If the chargeable material, e.g. synthetic resin, is embedded in non-conductive material then layer 22 may be omitted. In Fig. 8, a non-conductive sheet 26 of hard rubber with a non-conductive layer 27 of hard rubber carries the non-conductive image regions 28 of embedded glass powder and a friction device 29 is provided for charging the layer 27 and regions 28 in opposition to each other. In yet another embodiment a non- conductive sheet 30, Fig. 9, with a conductive, or alternately non-conductive, layer 31 is provided with non-conductive image regions 32. Charging devices 33 and 34 are provided for subjecting the master sheet to respective charges of minus 6000 and plus 8000 volts. In this case zinc or other metal oxides may be used as master sheet material or surface, which can be strongly charged in the negative sense but poorly in the positive one. In the apparatus of Fig. 10 a non-conductive sheet 35 has a conductive or non-conductive layer 36 and non- conductive printing image regions 37 are provided therein. A charging chamber 38 effects negative charging of 12000 volts whilst a charging chamber 39 positively charges at 14000 volts. The developing powder in this case is positively charged. A metallic surface, e.g. aluminium, may be used in this apparatus as the master sheet surface, metallic oxide, e.g. zinc oxide, being embedded in the transfer layer as chargeable material. The master sheet material may alternatively comprise acetate foil supported by a base of paraffinated paper. For developing medium, glass powder, synthetic resin powder, or mixtures thereof, or glass with synthetic resin-coated developing media may be used. The medium may also be in liquid form and rolled on or sprayed. The medium may contain a dye component or reactor which itself is non-staining or only slightly staining the other dye components or component or reactor being provided in the moistening or fixing liquid for the sheets to be printed or in or on the paper to be printed, and/or worked into the layer transfer sheet. The developing medium may contain a dye component &c. the due reaction being caused by long wavelength radiation provided for the purposes of fixing, and possibly also by the provision of dye components or reactors in the moistening or fixing liquid when such is used. The medium may contain an alcohol-soluble dye, e.g. triphenylmethane dye, the moistening of the sheets to be printed being effected by an alcohol-containing solvent, and the paper to be printed being electrostatically charged in a sense opposite to that of the image layer regions of the master sheet. The layer transfer sheets or ribbons used should contain an electrostatically chargeable material which is embedded, for example in finely-divided form, in a layer comprising waxes, fats or oils. As electrostatic material, synthetic resins such as polystyrol, glass powder, hard rubber or expoxy resin may be used. Specification 971,612 is referred to.