Impact modifier combination for aromatic polyesters

Abstract

An improved toughened blend of an aromatic polyester with from 5 to 20 phr of an impact modifier, which impact modifier is a blend of (a) 80 to 85 weight percent of a core/shell impact modifier having a polybutadiene core and at least one shell formed from methyl methacrylate and styrene; and (b) 15 to 20 weight percent of a linear copolymer which contains from 50 to 85 parts of units derived from ethylene, from 5 to 40 parts of units derived from (meth)acrylic esters, and from 2 to 10 parts of a copolymerizable monomer containing an epoxy group. The toughened blend exhibits higher impact strength than would be calculated for the blend using a linear relationship based on values of notched Izod for two blends, each containing only one of the impact modifiers at an equal use level.

Description

Claims

1. A toughened blend consisting essentially of an aromatic polyester with from 5 to 20 parts, per 100 parts of polyester, of an impact modifier, which impact modifier is a blend of

(a) 80 to 85 weight percent of a core/shell impact modifier having

(1) from 70 to 90 parts of a core of a rubber which is a homopolymer of butyl acrylate or 2-ethylhexyl acrylate or a copolymer of butyl acrylate and/or 2-ethylhexyl acrylate with up to about 30% of at least one other copolymerized vinyl monomer;

(2) at least one shell, which one shell is a homopolymer of methyl methacrylate or a copolymer which contains a majority of units derived from either methyl methacrylate or styrene; and

(b) 15 to 20 weight percent of a linear copolymer which contains from 50 to 85 parts of units derived from ethylene, from 5 to 40 parts of units derived from a C.sub.1 -C.sub.8 ester of (meth)acrylic acid, and from 2 to 10 parts of a copolymerizable monomer containing an epoxy group,

wherein the blend contains essentially no polycarbonate,

and wherein the toughened blend exhibits higher impact strength, as measured by a notched Izod test, and a lower melt pressure to achieve acceptable molding, than would be calculated for the blend using a linear relationship based on values of notched Izod or for melt pressure to achieve adequate molding for two blends, each containing only one of the impact modifiers at an equal use level.

2. The composition of claim 1 wherein the polyester is poly(butylene terephthalate).

3. The composition of claim 1 wherein the rubber or at least one shell further contains units derived from a multi-unsaturated monomer.

4. The composition of claim 1 wherein the C.sub.1 -C.sub.8 ester of (meth)acrylic acid of the linear copolymer is ethyl acrylate.

5. The composition of claim 1 wherein the copolymerizable monomer containing an epoxy group of the linear copolymer is glycidyl methacrylate.