Process for Preparing a Planographic Printing Form

1,198,122. Planographic printing plates. GEVAERT-AGFA N.V. March 5, 1968 [March 6, 1967], No.10476/67. Headings G2H and G2M. Planographic printing plates are prepared by developing a latent electrostatic image on a recording layer containing an inorganic photo-conductor which can provide Zn ions to form a hydrophobic image deposit, and then treating the areas not bearing a hydrophobic deposit with an aqueous solution containing a polyamino compound comprising at least two non-aromatic amino groups, at least one of which is in salt or quaternized form. The polyamines may be polymers, may contain O and/or P atoms in the main chain, and/or may contain heterocyclic or other side groups; the polyamino compound may be applied in the plate wetting soln. or printing ink, and may be mixed with a hydrophilic colloid, preferably together with a hydrophilic precipitating or hardening agent, a hygroscopic compound (e. g. a polyol), a wetting agent, a swelling agent for the recording layer (e.g. acetone or methylethylketone), a C 1-3 alkanol to lower surface tension, an acid, Na 2 SO 3 as antioxidant, and a second hydrophilizing agent (e.g. phytic acid or a ferro- or ferri-cyanide). The recording layer may comprise ZnO in an insulating resin binder.