Presensitised lithographic printing with minimised edge peel plate - has silicone rubber layer obtd. from mixt. of alkenyl-substd. polysiloxane(s) with different mol.wt. cured with hydrido-polysiloxane

摘要

PS dry lithographic printing plate has a substrate with light-sensitive coat (I) covered by a silicone rubber layer (II), obtd. by addn. cure of: (a) a basic polymer mixt. of 50-95 (wt.)% polysiloxane (IIIA) and 5-50% polysiloxane (IIIB) contg. at least 2 Si-bound alkenyl gps./ml. and gps. of the formula -(Si(R1)(R2)-O)k (III) and (b) a hydridopolysiloxane of the formula R1-Si(R4)2-O-(SiH(R4)-O)m-(Si(R4)2-O)n-Si)R4)2-R3 (IV) (where R1-2 are at least 70% Me, rest (ar)alkyl, aryl, vinyl or halohydrocarbyl; k is 100-500 in (IIIA) and k is 700-10000 in (IIIB); R3 is H or Me; R4 is at least 70% Me, rest (ar)alkyl, aryl or vinyl; and m + n is 4-100 and n/m is 0-1). The (IIIA):(IIIB) ratio is 70:30 to 90:10; and the amt. of (IV) 4-15 equiv. Si-H gps./equiv. unsatd. C-C gps. in (III). (II) pref. also contains a siloxane of the formula (R5)3-SiO-(Si(R5)2-O)p-(Si(R6)(R7)-O)q-Si(R5)3 (V) where R5 is 1-4C alkyl; R6-7 are a substd.) aromatic gp. or one of R6-7 = (substd.) alkyl; p/q is 99/1 to 10/90). (II) has a thickness of 0.5-5 g/m2. It has a protective coating produced by laminating with a transparent, opt. oriented and/or matted polyethylene, polypropylene, PVC, PVDC, PVA, PET or 'Cellophane' (RTM) film or by coating with one of these polymers. (I) contains a monomer, oligomer or macromonomer with photopolymerisable ethylenically unsatd. gp(s)., a film-forming polymer and photopolymerisation initiator. ADVANTAGE - (II) does not peel off as a result of loss of sensitivity caused by pressure changes at the edge of the original film during evacuation. The plate has good resistance to background soiling during printing and gives large editions.