GB852468A - Planographic printing plate - Google Patents

Abstract

852,468. Printing surfaces. TICKNER, A. (Columbia Ribbon & Carbon Manufacturing Co. Inc.) Jan. 14, 1957, No. 1422/57. Class 100(2) A process of making a planographic printing plate comprises applying to at least one side of a sheet of paper having sufficient wet strength to withstand printing stresses under moistened conditions a solution of a water soluble starch glycolate compressed in film forming concentration, drying the film to form a continuous coating of a water soluble starch glycolate and subsequently treating the coating to render it insoluble. The starch glycolate compound may be sodium or ammonium carboxymethyl starch, and the insolubilizing solution may be a solution of a salt or salts of a divalent or trivalent metal. Preferably the metal salts solution comprises 3 % by weight of copper sulphate, 1 % aluminium sulphate, ¢% ferric chloride, ¢% chromium trioxide, and 95 % water. The sodium or ammonium carboxymethyl starch is applied in solution at a concentration of 2% to 6% by weight. Mineral filler, such as china clay, is suspended in the starch glycolate solution and a small quantity of a plasticiser, such as glycerine, can be added to render the resulting film more pliable. Wet strength may be added to the paper foundation by the inclusion during manufacture of a urea-formaldehyde resin or a melamine-formaldehyde resin. The plate may be provided with an oleophilic image (a) prior to the application of the coating, (b) after the application of the water soluble starch glycolate compound but before it is rendered insoluble or (c) after the coating compound has been rendered insoluble. In the latter case the image may be formed photographically after coating the plate with a lightsensitive film. In an example, paper having a weight of about 60 lbs. per ream, and impregnated with a melamine-formaldehyde resin was coated with a composition made up of 3 parts by weight of sodium carboxymethyl starch, 150 parts water and 15 parts of china clay. The coating was dried and the coated paper then washed with a solution of 3% by weight of copper sulphate, 1 % aluminium sulphate, ¢% ferric chloride, ¢% chromium trioxide and 95% water. After drying and calendering the plate was coated on its rear surface with a 20% solution of polystyrene resin in ethyl acetate to form a water impervious film. The plate was then provided with a printing image.