| abstract |
The present invention provides a process for producing thermoplastic foam, including: (a) melting a thermoplastic polymer to produce a polymer melt; (b) introducing a carbon dioxide blowing agent into the polymer melt; (c) adding to the polymer melt one or more additives selected from the group consisting of (1) polysiloxane, and (2) mineral oil; and (d) extruding and foaming the melted polymer melt, blowing agent, and one or more additives to produce thermoplastic foam. The resultant thermoplastic foam can be thermoformed into various foamed articles, such as foam packaging trays. The quality of foams made from a carbon dioxide blowing agent, and particularly 100 % carbon dioxide, has been found to be substantially improved by adding one or more of the foregoing additives, i.e., polysiloxane, mineral oil and, optionally, polyolefin to the polymer melt during the extrusion and foaming process. Such foams have far less ruptured cells, surface cracks and corrugation than comparable foams made with a carbon dioxide blowing agent but which lack the additives of the present invention. |