| 摘要 |
A crystalline polymer resin, e.g. pet, is heated to melting. A blowing agent and resin are mixed to produce a theoretical sheet foam density of less than 0.4 g/cm<3>. The mixture is cooled to a temperature approaching the freezing point of the mixture, and then extruded into a substantially uniform closed cell polymer foam sheet of density less than 0.4 g/cm<3>. The extruded sheet is then cooled by direct contact with a cooling surface below the glass transition temperature such that the blowing agent(s) condenses and the sheet has a density of greater than 0.4 g/cm<3> and a sheet crystallinity of less than 15 %. An article is then formed from the cooled sheet by applying heat such that the condensed blowing agent(s) vaporizes and the article crystallizes at a density of less than 0.4 g/cm<3> with a crystallinity of greater than 20 %.
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