Flexographic printing plates containing blended adhesives

Claim 1

A photosensitive flexographic element which consists essentially of (A) a flexible support, (B) a layer of a photosensitive, elastomeric composition which consists essentially of, based on the total weight of composition (1) 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, (2) 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 highr polymer by free-radical initiated, chain-propagating addition polymerization and being compatible with polymer (1); (3) 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, optionally (4) thermal addition polymerization inhibitor, (5) antioxidant, (6) antiozonant, (7) immiscible, polymeric or nonpolymeric organic or inorganic fillers or reinforcing agents which are essentially transparent at the wavelengths used for exposure, and (8) compatible plasticizer; (C) optionally a thin, hard flexible solvent soluble layer, and (D) optionally a removable cover sheet; and between layers (A) and (B) a layer of an adhesive composition which provides an adhesion value for the photosensitive layer (B) to the support (A) of at least 3 lbs/inch (53.57 kg/m) and consists essentially of a blend of at least two polymers taken from the group consisting of (i) polyester resin which is a condensation polymer of ethylene glycol, terephthalic acid, isophthalic acid and azelaic acid in a molar ratio of about 6:2:1:3 the resin having a number average molecular weight of about 19,000 and a weight average molecular weight of about 37,000, 0 to 78% by weight based on the total weight of resin in the adhesive composition; (ii) polyurethane resin which is a crystalline, thermoplastic resin having a Brookfield viscosity of 100-1200 using 5% by weight solids in methyl ethyl ketone and a Brookfield spindle #3 at 12 rpm, and an adhesive activation temperature in the range of 54° to 63° C., 0 to 78% by weight based on the total weight of resin in the adhesive composition, (iii) polyamide which is a thermoplastic dimer acid polyamide resin having a Ball and Ring softening point of 132°-145° C., a viscosity at 210° C. of 40 to 60 poises, % elongation determined by ASTM D-1708 of 130 at -18° C., 560 at 24° C. and 100 at 60° C., tensile break determined by ASTM D-1708 of 4000 psi at -18° C., 450 psi at 24° C. and 170 psi at 60° C., 0 to 94% by weight based on the total weight of resin in the adhesive composition, and (iv) polyamide which is a thermoplastic dimer acid polyamide resin having a Ball and Ring softening point of 150°-160° C., a viscosity at 210° C. of 28 to 38 poises, % elongation determined by ASTM D-1708 of 350 at -18° C., 250 at 24° C. and 40 at 60° C., tensile break determined by ASTM D-1708 of 2200 psi at -18° C., 360 psi at 24° C. and 50 psi at 60° C., 0 to 97% by weight based on the total weight of resin in the adhesive composition with the proviso that when a blend of two polymers is present in the adhesive composition the percentage ranges are for the blend: (i) 23% to 77% and (ii) 77% to 23%, (i) 7% to 77% and (iii) 93% to 23%, (i) 3% to 70% and (iv) 97% to 30%, (ii) 7% to 72% and (iii) 93% to 28%, (ii) 10% to 60% and (iv) 90% to 40%, and (iii) 25 to 75% and (iv) 75% to 25%.