ELASTIC FILM GRADE THERMOPLASTIC POLYMER COMPOSITIONS HAVING IMPROVED ELASTIC PERFORMANCE
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.
1 . An elastic film grade thermoplastic polymer composition 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.
2 . The composition of claim 1 , wherein HSBC #1 is a polystyrene-polyethylene-butylene-polystyrene tri-block copolymer with an apparent number average molecular weight between 35,000 and 90,000, preferably between 50,000 and 80,000 and a polystyrene content (PSC) of 15 to 40 percent by weight, preferably of 20 to 35 percent by weight.
3 . The composition of claim 1 or 2 , wherein HSBC #2 is a polystyrene-polyethylene-butylene-polystyrene tri-block copolymer with an apparent number average molecular weight between 95,000 and 150,000, preferably between 100,000 and 135,000 and a polystyrene content (PSC) of 15 to 40 percent by weight, preferably of 20 to 35 percent by weight.
4 . The composition of any one of claims 1 to 3 , wherein a mixture of PS(1) and PS(2) is used.
5 . The composition of any one of claims 1 to 4 , wherein PS (1) has a molecular weight in the range of 500 to 4,000 and preferably in the range of 1,000 to 3,000.
6 . The composition of any one of claims 1 to 5 , wherein PS(2) has a molecular weight in the range of 100,000 to 150,000.
7 . The composition of any one of claims 1 to 6 , wherein PS(1) and PS(2) are presenting a weight ratio of 1:2 to 2:1.
8 . The composition of any one of claims 1 to 7 , wherein a filler is used selected from calcium carbonates, talc, and silicas.
9 . A film cast from an elastic film grade thermoplastic polymer composition as claimed in any one of claims 1 to 8 .