Electrographic reproduction method

1,140,831. Discharge printing. GEVAERTAGFA N.V. 25 Oct., 1966 [24 Jan., 1966], No. 3175/66. Heading B6C. An original is copied on a prepared copy sheet by irradiating the superposed documents with charge carriers emanating from a corona discharge unit. The prepared copy sheet comprises an aluminium coated paper base covered with a layer of a dyed semi-conductive material such as zinc-oxide, whilst the originals comprise an image-wise differentation in terms of electrical conductivity and/or electrical capacity. Examples of such originals are screen printing masters, planographic plates having a difference in conductivity between the printing and non- printing areas, relief images having electrically conductive relief parts, printed circuits and originals having conductive ink-markings, e.g. a very high carbon black content. Originals having metallized image markings and magnetic image markings may also be used. Dyes which may be used comprise quinone-imine dyes, diphenylamine, leucotriaryl - methane dyes, leucoxanthene dyes and leuco acridine dyes. The semi-conductive substance, which is preferably porous in structure, is preferably dispersed in an insulating binder such as polyvinylacetate, copolymers of vinylacetate and vinyl laurate and/or vinylstearate, polymethylmethacrylates, alkyd resins and silicon resins- In operation the semi-conductive material is positioned with its support on a conductive plate connected to the positive pole of a 6000 V. D.C. source, the negative pole of which is connected with the wires of a corona discharge unit. A graphic original comprising a paper printed with an ink containing carbon black is placed with its non-printed side upon the semiconductive layer. The corona wires are progressively moved all over the printed side of the original to subject the latter to a corona discharge current of 20ÁA for one minute. Owing to the bleaching effect of the corona discharge a pink positive legible image is obtained. The Specification also describes two further embodiments in which (a) an etched zinc letterpress plate original is used and (b) a metal screen printing master is employed as the original.