Thermoplastic elastomeric blends having enhanced surface appearance
Disclosed is a thermoplastic elastomer blend with reduced surface defects comprising a high flow, propylene-based resin, about 0.01 to 15 weight percent of a processability modifier component, and about 1 to 50 weight percent of an ethylene-based toughening component. The blend may also contain compatibilizers, additives, and mineral fillers.
1 . A thermoplastic elastomeric composition comprising:
a high flow, propylene-based resin having a melt flow rate of at least about 20 dg/min, measured at 230° C. and 2.16 kg, present in an amount sufficient to increase a rigidity of the composition;
an ethylene-based toughening component, with a weight average molecular weight of at least about 95,000 to 1,000,000 which is present in an amount sufficient to increase the impact strength of the composition and which comprises one or more ethylenic elastomers including one or more copolymers of ethylene and at least one other monomer which comprises one or more unsaturated organic acids or their derivatives, or one or more C 3 to C 20 alpha-olefins with an optional diene; and
about 0.01 to 15 weight percent of a processability modifier component with the following characteristics:
(a) a melt flow rate from about 0.001 to 4 dg/min, measured at 230° C. and 2.16 kg; and
(b) a weight average molecular weight of about 150,000 to less than 800,000.
2 . The composition of claim 1 , which comprises about 5 to 95 weight percent of the high flow, propylene-based resin and about 1 to 50 weight percent of an ethylene-based toughening component.
3 . The composition of claim 1 , comprises about 15 to 75 weight percent of the high flow, propylene-based resin, about 7 to 38 weight percent of the ethylene-based toughening component, and about 1 to 9 weight percent of the processability modifier component.
4 . The composition of claim 1 , wherein the high flow, propylene-based resin has a weight average molecular weight that is less than that of the processability modifier component.
5 . The composition of claim 1 , wherein the high flow, propylene-based resin comprises homopolymers of propylene, copolymers of at least about 50 weight percent propylene and at least one other C 2 to C 20 alpha-olefin, or mixtures thereof.
6 . The composition of claim 1 , wherein the high flow, propylene-based resin comprises a copolymer of at least about 70 weight percent propylene and a C 2 to C 20 alpha-olefin that comprises ethylene, 1-butene, 1-pentene, 1-hexene, methyl-1-butene, methyl-1-pentene, 1-octene, 1-decene, or a combination thereof.
7 . The composition of claim 1 , wherein the high flow, propylene-based resin has a melt flow rate of about 25 to 800 dg/min.
8 . The composition of claim 1 , wherein the high flow, propylene-based resin has a crystallinity of at least about 30 percent.
9 . The composition of claim 1 , wherein the ethylene-based toughening component comprises:
one or more ethylenic elastomers including one or more copolymers of ethylene with at least one other monomer chosen from C 3 to C 20 alpha-olefins, unsaturated organic acids and their derivatives; or
terpolymers of ethylene, a C 3 to C 20 alpha-olefin, and a nonconjugated diene monomer, or combinations thereof.
10 . The composition of claim 1 , wherein the ethylene-based toughening component comprises a copolymer of ethylene with at least one other C 3 to C 20 alpha-olefin monomer that comprises propylene, octene, butene, hexene, or a combination thereof.
11 . The composition of claim 1 , wherein the ethylene-based toughening component is substantially amorphous, has a Mooney viscosity of at least about 5, and has a weight average molecular weight of at least about 100,000 to 700,000.
12 . The composition of claim 1 , wherein the ethylene-based toughening component has a melt index of no more than about 5 dg/min and a density from about 0.80 to 0.91 g/cm 3 .
13 . The composition of claim 1 , wherein the ethylene-based toughening component comprises copolymers that are linear, substantially linear, random, blocky, or branched, or a combination thereof and that are substantially free of crosslinking.
14 . The composition of claim 1 , wherein the processability modifier component comprises homopolymers of propylene, copolymers of at least about 70 weight percent propylene and at least one other C 2 to C 20 alpha-olefin, or mixtures thereof.
15 . The composition of claim 1 , wherein the processability modifier component has a melt flow rate of greater than about 0.001 dg/min and less than about 1 dg/min, a weight average molecular weight (M w ) of about 200,000 to 700,000, and a density of about 0.85 to 0.936 g/cm 3 .
16 . The composition of claim 1 , further comprising about 1 to 15 weight percent of a styrenic compatibilizer.
17 . The composition of claim 1 , further comprising about 1 to 40 weight percent of at least one mineral filler.
18 . A molded article comprising the composition of claim 1 .
19 . An automotive component comprising the composition of claim 1 .
20 . A method of minimizing or avoiding visible surface defects on a molded article which comprises:
providing a thermoplastic elastomer composition comprising a high flow, propylene-based resin having a melt flow rate of at least about 20 dg/min, measured at 230° C. and 2.16 kg, present in an amount sufficient to increase a rigidity of the composition; an ethylene-based toughening component, with a weight average molecular weight of at least about 95,000, present in an amount sufficient to increase the impact strength of the composition; and about 0.01 to 15 weight percent of a processability modifier component with the following characteristics: (a) a melt flow rate from about 0.001 to 4 dg/min, measured at 230° C. and 2.16 kg; and (b) a weight average molecular weight of about 150,000 to less than 800,000; and
molding the composition to obtain an article having a reduced amount of surface defects compared to conventional molded compositions.