Importance

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Abstract

The present invention provides an improved block copolymer composition for extruding films having excellent stress relaxation and increased retained tension or load at elevated temperatures, as well as a film cast from this composition. The composition is comprised of (a) 100 parts by weight of a mixture of two or more hydrogenated styrenic block copolymers (HSBC's) having at least two polystyrene end-blocks and a mid-block of a polymerized diene wherein at least 80 mol % of the residual unsaturation has been hydrogenated, wherein HSBC #1 has an apparent number average molecular weight between 35,000 and 90,000 and a polystyrene content between 15 and 40 percent by weight, wherein HSBC #2 has an apparent number average molecular weight between 95,000 and 150,000 and a polystyrene content between 15 and 40 percent by weight, wherein the ration w/w of HSBC #1 versus HSBC #2 is in the range of from 8:1 to 1:8, (b) from 10 to 50 parts by weight per 100 parts by weight of polymer (phr) of a a medium molecular weight polystyrene (2) or a mixture of a low molecular weight polystyrene (1) and a medium molecular weight polystyrene (2), wherein PS (1) has a molecular weight in the range of 500 to 4,000 and PS(2) has a molecular weight in the range of 20,000 to 150,000 and wherein PS(1) and PS(2) are used in a weight ratio of 1:5 to 5:1, (c) from 3 to 50 phr of a filler, and (d) from 30 to 70 phr of a softening agent.

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First Claim