PRESSURE SENSITIVE ADHESIVE SHEETS AND COMPOSITIONS

1426497 Polymer blends as adhesives MINNESOTA MINING & MFG CO 12 Sept 1973 42929/73 Heading C3P A tacky, pressure-sensitive adhesive composition comprises (1) an A-B block copolymer with a number average molecular weight of at least 50,000 in which: the A block is thermoplastic and glassy and has a Tg above 75‹ C. as determined by torsion pendulum, a number average molecular weight of at least 15,000 and comprises 20-50 wt. per cent of the total block polymer molecular weight, and is polymerized from monomers having the group, and: the B block is elastomeric and amorphous at temperatures above - 20‹ C., has a Tg below -20‹ C. as determined by torsion pendulum, has a number average molecular weight of at least 35,000 and comprises 80-50 wt. per cent of the total block polymer molecular weight and is polymerized from conjugated dienes; and (2) 10-150 parts by wt. per 100 parts of the block copolymer, of at least one compatible tackifying resin. The A block may be polystyrene, poly-t-butyl styrene, poly-alphamethyl-styrene, poly-2-vinyl pyridine or polymethylmethacrylate. The B block may be polybutadiene, polyisoprene, and hydrogenated derivatives of these. Examples of tackifying resins are coal tar hydrocarbon resins, petroleum hydrocarbon polymers, polyterpenes, and condensation products of aromatic hydrocarbons with formaldehyde. A multiblock polymer may also be present, having two poly(vinyl aryl) end segments and a polydiene central segment.