Patent ID: 7994231

Claim:
A process for making closed cell polyamide foam comprising the steps of: (a) subjecting a polyamide resin to at least one inert gas at a pressure higher than atmospheric in order to drive gas into the resin, (a1) raising the temperature of the resin to or above its softening point, wherein steps (a) and (a1) can take place in any order or simultaneously, and (a2) lowering the pressure to a pressure higher than atmospheric pressure but lower than the pressure of step (a) and cooling the resin to below its softening point to result in a partially expanded polyamide resin, and (a3) heating the partially expanded polyamide resin to a temperature above its softening point under a pressure of gas, and then, (b) reducing the pressure whilst maintaining the temperature at or above the softening point of the resin, in order to expand the resin to result in closed cell polyamide foam.