System for forming low-density polymer foam article

Apparatus for forming a closed cell crystalline polymer foam article, comprising:

• means for heating a crystalline polymer resin to a melt temperature such that the resin melts;
• means for combining one or more blowing agents selected, together with the resin to create a mixture, wherein a concentration of the one or more blowing agents in the mixture is sufficient to produce a theoretical sheet foam density of less than 0.4 g/cm3, and wherein at least one of the one or more blowing agents has a boiling point greater than a glass transition temperature for the resin and less than or equal to a forming temperature;
• means for cooling the mixture to a temperature approaching a freezing temperature for the mixture;
• means for extruding a closed cell polymer foam sheet of density less than 0.4 g/cm3 from the cooled mixture;
• means for cooling the extruded polymer foam sheet by direct contact with a cooling surface at a surface temperature below the glass transition temperature, wherein the one or more blowing agents condense in response to the cooling and the polymer foam sheet has a density of greater than 0.4 g/cm3;
• and
• means for forming the cooled polymer foam sheet into an article, comprising means for applying heat, wherein the condensed one or more blowing agents vaporize and the article crystallizes at a density of less than 0.4 g/cm3 in response to the heat.