The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Aug. 14, 2001
Filed:
Sep. 28, 1999
Walter R. Harfmann, Matthews, NC (US);
Genpak, L.L.C., Glens Falls, NY (US);
Abstract
A crystalline polymer resin, such as poly(ethylene terephthalate), is heated to melting. One or more blowing agents is selected wherein at least one of the blowing agents has a boiling point greater than the glass transition temperature for the resin and less than the forming temperature, such as the temperature of the mold used to form the useful article. The blowing agent(s) and resin are combined to create a mixture with a blowing agent concentration sufficient to produce a theoretical sheet foam density of less than 0.4 g/cm,. 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,. The extruded sheet is then cooled by direct contact with a cooling surface at a surface temperature 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,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,with a crystallinity of greater than 20%.