Process for surface treatment of flexographic printing plates containing butadiene/acrylonitrile copolymers

Claim 2

A process for providing improved solvent resistant surfaces of relief flexographic printing plates wherein the reliefs are prepared by imagewise exposure with actinic radiation and liquid development of the unexposed areas of a layer of a photosensitive, elastomeric composition comprising a high molecular weight butadiene/acrylonitrile copolymer having a number average molecular weight of 20,000 to 75,000, an acrylonitrile content of 10 to 50% by weight and a carboxyl content of 0 to 15% by weight and a nongaseous ethylenically unsaturated compound containing at least one terminal ethylenic group, the improvement, wherein after drying, the developed surface is, in either order, (1) postexposed to a source of actinic radiation, and (2) contacted with an aqueous solution having a free bromine concentration of 0.01 to 3.5% by weight for about 15 seconds to 20 minutes.

Claim 3

A process according to claim 1 wherein the printing plate is dipped into the aqueous bromine solution.

Claim 4

A process according to claim 1 or claim 2 wherein the aqueous bromine solution is prepared by mixing bromine or alkali bromate-bromide-acid mixture in water.

Claim 5

A process according to claim 1 or claim 2 wherein the flexographic printing plate is prepared by imagewise exposure and liquid development of a photosensitive, elastomeric element which comprises (A) a flexible support and (B) a layer of a photosensitive, elastomeric composition which comprises, based on the total weight of composition (a) 55 to 90% by weight of a high molecular weight butadiene/acrylonitrile copolymer having a number average molecular weight of 20,000 to 75,000, an acrylonitrile content of 10 to 50% by weight and a carboxyl content of 0 to 15% by weight, (b) 2 to 40% by weight of a nongaseous, ethylenically unsaturated compound containing at least one terminal ethylenic group, said compound being capable of forming a high polymer by free-radical initiated, chain-propagating addition polymerization and being compatible with polymer (a); (c) 0.001 to 10% by weight of an organic, radiation-sensitive, free-radical generating system, activatable by actinic radiation which initiates polymerization of the unsaturated compound; and (d) 0 to 15% by weight of a compatible plasticizer; and optionally between layers (A) and (B) a layer of an adhesive composition.

Claim 6

A process according to claim 1 wherein the developed surface is prepared by aqueous development and the bromine treatment is applied without the necessity of drying the developed surface.