FIELD

This disclosure relates to a molding composition comprising a free-flowing elastomeric block copolymer.

BACKGROUND

Thermoplastic elastomers are used in molding composition comprising polypropylene and/or polypropylene random copolymers. Some HSBC shows a high cohesive strength, resulting in pellets, granulate or crumb of the composition agglomerate forming large clumps of granules, when the product is kept on stock, for example when stacked up in sacks, bags, Gaylords, cartons, or kept in a silo. It is even possible that an entire sack, bag, Gaylord, carton, or silo is filled with a mass of pellets or granules all or virtually all agglomerated into a single mass. Once the granulate agglomerates together, it has to be broken up with force to transport the pellets or granulate into the feed opening of relevant processing equipment such as a mixer or an extruder. U.S. Pat. No. 5,837,769 provides a free-flowing elastomer powder with the addition of “significant amounts” of a plasticizing oil.

There is a need for improved free-flowing HSBC compositions with solid flow characteristics, and molding compositions comprising free-flowing HSBC compositions for molding applications with improved properties including low haze.

SUMMARY

In one aspect, a composition is provided, comprising: a) 70-95 wt. % of a polyolefin polymer selected from polypropylene homopolymers, polypropylene copolymers, polypropylene impact copolymers, and mixtures thereof; and b) 5 to 30 wt. % of a free-flowing styrenic block copolymer (“FFSBC”). In embodiments, the composition consists essentially of: a) 70-95 wt. % of a polyolefin polymer selected from polypropylene homopolymers, polypropylene copolymers, polypropylene impact copolymers, and mixtures thereof; and b) 5 to 30 wt. % of a free-flowing styrenic block copolymer (“FFSBC”). The FFSBC is a styrenic block copolymer (SBC) coated with a functional dusting agent having a maximum particle size of 100 microns in an amount of up to 2 wt. % (based on the total weight of the SBC). The functional dusting agent is selected from modified sorbitols, benzoic acid salts, substituted benzoic acid salts, dicarboxylate metal salts, hexahydrophthalic acid metal salts, phenylphosphonic acid salts, phosphate ester salts, glycerolate salts, norbornane carboxylic acid salts, diamides, trisamides and derivatives thereof, tetramides, pine rosin derivatives, acetals and derivatives thereof, di-acetal derivatives, 2,6-naphthalene dicarboxamides, polyvinylcyclohexanes and combinations thereof. The coated SBC is free-flowing, requiring less than 400 lbs/ft2to break in a blocking test.

In another aspect, a process for making an article from the above molding composition is disclosed. The process comprises (i) providing the SBC described above, (ii) dry blending the SBC with a polyolefin to form a dry blended composition having 5-30 wt. % of the SBC and 70-95 wt. % of the polyolefin, (iii) forming an article from the dry-blended composition. In embodiments, the process consists essentially of: (i) providing the SBC described above, (ii) dry blending the SBC with a polyolefin to form a dry blended composition having 5-30 wt. % of the SBC and 70-95 wt. % of the polyolefin, (iii) forming an article from the dry-blended composition. The article has a notched Izod impact strength of 42 J/m or higher, measured at 23° C. in accordance with ASTM D256, and a haze value, measured according to ASTM D1003, of 95% or lower. The article may be formed by any of injection molding, extrusion, extrusion blow molding, rotational molding, thermal forming, and injection blow molding.

