Method for preparing dry planographic plates with plasma

Abstract

The invention provides a novel planographic printing plate suitable for dry planographic printing without supply of dampening water and a method for the preparation thereof. The inventive printing plate has, on one surface of a base plate, a layer of an organopolysiloxane composed of the areas where fresh surface of the organopolysiloxane is exposed bare as the ink-repellent non-image areas and the areas where the surface of the organopolysiloxane layer has been subjected to the treatment with low temperature plasma to be oleophilic or ink-receptive as the image areas of the printing plate. According to the inventive method, the pattern-wise exposure of the organopolysiloxane layer to the plasma atmosphere is performed by first providing a pattern-wise layer of a plasma resistant protective resist layer on the organopolysiloxane layer followed by the plasma treatment and removal of the resist layer. In an improved embodiment of the invention, a layer of an abrasion-resistant ink-receptive material is provided on the organopolysiloxane layer in the plasma-treated areas so that the durability of the printing plate is remarkably improved. Further, incorporation of a metachromatic substance susceptible to plasma treatment, e.g. a dye subject to color change by the plasma treatment, in the organopolysiloxane or in an undercoating primer layer facilitates determination of the end point of the plasma treatment.