Injection molding thermoset interpolymers of ethylene-propylene and product thereof

Claim 1

A process for preparing an injection-molded thermoset composition which comprises: (a) mixing an interpolymer comprising ethylene and propylene, said interpolymer having an ethylene content in the range of about 62 to about 80 weight percent of ethylene and a crystalline content in the range of about 10 to 25 weight percent with from 50 to 150 parts by weight, per hundred parts by weight of interpolymer, of a low density polyethylene having a melt index in the range of 2 to 40 and 50 to 150 parts by weight, per hundred parts by weight of interpolymer, of a reinforcing carbon black having a nitrogen surface area of about 30 to 100 M 2 /gram at a temperature above the crystalline melting temperature of the polyethylene thereby preparing a first mixture; (b) cooling said first mixture to a temperature below 130° C.; (c) adding to said first mixture from 0.5 to 5 parts by weight, per hundred parts by weight of interpolymer, of one or more polyfunctional vinylic or allylic monomer and from 1 to 10 parts by weight, per hundred parts by weight of interpolymer, of an organic peroxide comprising one or more peroxide moieties in the molecule having the following structure: ##STR3## wherein R and R' are independently selected from the group consisting of C 1 to C 8 alkyl radicals said peroxide having a half-life when measured in low density polyethylene in excess of 5 hours at 130° C. and less than 1 minute at 230° C.; (d) admixing and fluxing said first mixture and said additives to a composition while maintaining the temperature below 130° C. the composition being flowable below 130° C.; (e) introducing the mixed and fluxed composition into the mold of an injection molding machine; (f) curing said composition to the crosslinked, thermoset state in the mold of said injection molding machine at a temperature of about 175° C. to about 230° C. for about 1 minute to about 10 minutes; and (g) obtaining from said mold a thermoset composition having a flexural modulus of about 20,000 to about 30,000 psi at room temperature.