Pre-sensitised dry lithographic printing plate with silicone rubber - contg. hydrogen siloxane, siloxane with unsatd. gp. and reactive cyclic siloxane

摘要

PS dry lithographic printing plates have a substrate, a light-sensitive layer and a silicone rubber layer. The novelty is that the silicone rubber layer is produced by applying a mixt of a polyvalent H-organopolysiloxane (I) with min 2 H-Si gps in the mol, a polysiloxane (II) with min 2 unsatd C-C linkages in the mol and an alkyl-substd reactive cyclic siloxane cpd (III) with epoxy gps and drying the coating. (III) is of formula (IIIA) R1 = (substd alkyl, including Me; R2 = a gamma-glycidyoxypropyl, beta-(epoxycyclohex-4-yl)ethyl or beta-methyl-beta-(glycidoxycarbonyl)ethyl gp; 1 = 0-3; m = 2-5; n = 1-4; (l + m + N) = 3-6. (I) is alpha, omega-bis( dimethyl hydrogensilyl)poly-dimethyl -siloxane, -poly(methyl-hydrogen) -siloxane or -poly(methyl-hydrogen) (dimethyl)siloxane copolymer; -siloxane or -poly(methyl-hydrogen) (dimethyl)siloxane copolymer. (II) is alpha, omega-bis(dimethyl-vinyl silyl)(dimethyl)siloxane, silicone resins contg gps with compsn (IIA) (CH2=CHMe2Si00.5)(Me3Si00.5)m(Si02)n (IIA); l/(m+n) = 0.05-0.5; and (l+m)/n = 0.5-1.5. The amts are 0.1-20 equiv unsatd C-C linkages in (II) and 20-0.5 equiv (III) per 10 equiv SiH gps in (I). The silicone rubber compsn also contains an addn reaction catalyst, pref Pt, Pt chloride, or olefin-coordinated Pt; a crosslinking inhibitor, consisting of organopolysiloxane contg vinyl gps or alcohols with C-C triple bonds; and an adhesion promoter, , silane or siloxane with hydrolysable functional gps and/or a filler. The silicone rubber layer is 0.5-5 microns thick. ADVANTAGE - The adhesion between the light-sensitive layer and silicone rubber layer varies little with time. The plate gives excellent image reproduction, has excellent printing durability and antiscratch properties and gives hardly any background contamination.