Provide a foamable polymer composition containing: (i) a thermoplastic polymer matrix and a blowing agent (a) the thermoplastic polymer matrix containing a styrene acrylonitrile copolymer having a weight averaged molecular weight in a range of 90 000 to 150 000 and polymerized acrylonitrile concentration in a range of five to twenty weight percent relative to total polymer matrix weight; and (ii) a blowing agent containing water 1 1 1 2 tetrafluouroethane and at least one of difluoromethane and 1 1 difluoroethane; (b) cooling the foamable polymer composition to a foaming temperature; and (c) extruding the foamable polymer composition and allowing the blowing agent to expand the foamable polymer composition into a polymeric foam having an average vertical cell size in a range of 0.5 millimeters to 1.8 millimeters and a density in a range of 24 to 40 kilograms per cubic meter and a Normalized Roughness Quotient of 3.5 or less in a Milled Surface Test.
展开▼
