Dry presensitised plate for lithographic printing - has substrate coated with special photosensitive layer contg. water-soluble cpds. and polymerisable cpds. and a silicone rubber layer

摘要

Presensitised plates (I), for use in the prodn. of lithographic printing plate which do not require wetting with water, comprise a substrate coated with (IA) a photopolymerisable light-sensitive layer and (IB) a silicone rubber layer. Layer (IA) contains (i) a water-soluble cpd. with or without a polymerisable unsatd. gp. (ii) a cpd. with at least 2 polymerisable unsatd. gps. (iii) a water-insol. polymeric cpd. with film-forming properties and (iv) a photopolymerisation initiator, with wt. ratio (i):(ii) = 0.01-0.08. ADVANTAGE - Provides dry PS plates with excellent shade reproduction, even with long delay between the image-forming exposure and the removal of layer (IB) from the unexposed parts. (In prior arts systems, post-polymerisation occurs in the exposed parts and extends into the unexposed parts, making it difficult to remove the silicone rubber and preventing reproduction of half-tone points on the light areas).