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

Claim 1

A process for extruding a foamed product at high efficiency and with smoother surfaces at a given throughput and concentration of modifier comprising introducing a composition comprising 100 parts by weight of polyvinyl chloride or copolymers of vinyl chloride containing up to 20% by weight of other monovinylidine compounds, a blowing agent and about 1 to 25 parts by weight of a modifier system 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 substantially ungrafted 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 polymerized from a shell-forming monomer system comprised of, in major part, at least one C 1 to C 4 alkyl methacrylate, polymerized in the presence of, but substantially ungrafted to, a core polymerized from a monomer or monomer mixture comprising, in major part, at least one C 1 to C 8 alkyl acrylate; into a plasticating extruder and extruding said composition at a temperature of about 250°-400° F. through a die to foam said smoother surfaced product.