Preparation of ozone resistant printing plates

Claim 1

A process for improving the ozone resistance of the surface of relief flexographic printing plates wherein the reliefs are prepared by imagewise exposure with actinic radiation and liquid washout development of the unexposed areas of a layer of a photosensitive elastomeric composition comprising (1) at least 30% by weight of a block copolymer having (A) at least one solvent-soluble, thermoplastic nonelastomeric block having a glass transition temperature above 25° C. and a number average molecular weight of about 2,000 to 100,000; (B) an elastomeric polymeric mid-block having a glass transition temperature below 10° C. and a number average molecular weight of about 25,000 to 1,000,000; and (C) a polymer block taken from the group of nonelastomeric block (A) and a polymer block having a glass transition temperature in the range of -30° C. to +15° C. prepared by homopolymerization or copolymerization of aliphatic diene hydrocarbon of 4 to 5 carbon atoms or by random copolymerization of at least one aliphatic diene hydrocarbon of 4 or 5 carbon atoms with at least one styrene monomer of the formula CH 2 ═CRR', where R is hydrogen or methyl and R' is phenyl or C 1 to C 4 -alkyl-substituted phenyl; (2) at least 1% by weight of at least one addition polymerizable ethylenically unsaturated compound containing at least one terminal ethylenic group; and (3) a polymerization-effective amount of polymerization initiator activatable by actinic radiation, wherein after drying there is applied to the dry relief surface of the printing plate a solvent solution containing at least 1% by weight of a dithiocarbamate compound taken from the group consisting of nickel dialkyldithiocarbamate and zinc dialkyldithiocarbamate wherein alkyl is from 1 to 4 carbon atoms.