Verbesserungen an der oder fuer die Herstellung von Flachdruck-Offset-Platten

摘要

1,134,742. Printing plates. GESTETNER Ltd. 22 Nov., 1965 [23 Nov., 1964], No. 47601/64. Heading B6C. [Also in Divisions C3 and D2] An electrographic sheet comprises an electrically conductive sheet of impervious paper, an electrically conductive layer having a conductivity of 4 x 10-3 to 2 Î 10-4 mhos on one side of the paper, and on the conductive layer an outer layer of bitumen, which may contain up to 30% of carnauba wax. The paper may be made conductive by impregnation with an electrolyte, or by incorporating particles of carbon in it during manufacture. Its conductivity may be 1À6 x 10-5 to 2 x 10-6 mhos. The conductive layer may be of conductive particles dispersed in a film-forming binder. There may be a second conductive layer of lower conductivity, e.g. 1À4 Î 10-5 to 2 Î 10-6 mhos, on the side of the sheet opposite the first conductive layer. The conductivities are determined using two brass electrodes 1 cm. apart, each 1 cm. square, pressed on to the sheet and connected to a conductivity meter. Planographic plates are imaged by placing them with their hydrophilic faces in contact with the outer bitumen layer of the above electrographic sheet, and applying an electric discharge by stylus so that the bitumen layer is transferred where the image is to be formed. The electrographic sheet may be attached along one edge to a blank planographio plate, or to a flexible supporting sheet. Planographic plates are made by coating paper with one of the following: (I) sodium carboxymethylcellulose, glycerine and china clay, insolubilized with copper sulphate, aluminium sulphate, ferric chloride and chromium trioxide; (II) china clay, casein and dimethylolurea, followed by sodium alginate in aqueous butanol and insolubilized by zinc acetate in aqueous butanol; or (III) sodium carboxymethylcellulose, clay, copper sulphate, acetic acid, ammonium bichromate, and ferric chloride. The paper may be first coated on one or both sides with china clay and ammoniacal casein.