Flexible, low density thermoplastic foams and methods for lowering the density and increasing the flexibility of thermoplastic foams

Abstract

A flexible, low density thermoplastic foam and a method for lowering the density and increasing the flexibility of a thermoplastic foam having a melting temperature and being either amorphous with a softening temperature or semicrystalline with a glass transition temperature. The method comprises the steps of (a) decreasing the pressure on the thermoplastic foam to a subatmospheric pressure, further providing that while the thermoplastic foam is under the subatmospheric pressure, the thermoplastic foam is also at a temperature in the range of less than the melting temperature and greater than the softening temperature if the thermoplastic foam is amorphous, or greater than the glass transition temperature if the thermoplastic foam is semicrystalline, whereby the thermoplastic foam expands; (b) then exposing the thermoplastic foam to a superatmospheric pressure and a secondary expansion gas for a sufficient amount of time to allow the secondary blowing gas to permeate into the thermoplastic foam; and (c) then releasing the superatmospheric pressure on the thermoplastic foam whereby the thermoplastic foam expands. With this method, it is possible to produce thermoplastic foams having densities as low as 0.008 grams/cc. Also included in this invention are insulations made from these low density foams.