Modifiers for PVC foam, process for extruding modified PVC foam and modified PVC foam compositions

Claim 1

A modifier system for extruding polyvinyl chloride foam comprising: a first core shell polymer having a hard shell polymerized from a shell-forming monomer system comprised of, in major part, at least one C 1 to C 4 alkyl methacrylate, having a molecular weight (M v ) above 1.5 million, polymerized in the presence of, but less than about 20% grafted to, a crosslinked core polymerized from a core-forming monomer system comprised of, in major part, C 2 to C 8 alkyl acrylate, and about 0.1 to 5 weight percent, based on C 2 to C 8 alkyl acrylate, of a glycol dimethacrylate crosslinking agent, the weight ratio of shell to core being about 40:60 to 75:25; and a second core-shell polymer having a shell polymer having an average molecular weight (M v ) of at least about 450,000 polymerized from a shell-forming monomer system comprised of, in major part, at least one C 1 to C 4 alkyl methacrylate, and polymerized in the presence of, but less than about 20% grafted to, a core polymer having an average molecular weight (M v ) of at least about 5,000 up to about 100,000 polymerized from a monomer or monomer mixture comprising, in major part, at least one C 1 to C 8 alkyl acrylate, the weight ratio of shell to core being about 60:40 to 0:100, wherein the weight ratio of the first core-shell polymer to the second core-shell polymer is about 20:1 to about 2:1.