Sub-ambient pressure morphology control process for use in molding extruded polymer foams, and parts produced therefrom

A method of sub-ambient pressure processing of blow-molding polymer foams and skin-over-foam sandwich panels comprising the steps of:

• extruding a piece of parison from a polymer material;
• inflating the parison and offer a degree of internal cooling to begin forming an internal skin;
• forming an in-mold vacuum and gently draw the polymer material tightly to a mold surface;
• applying an internally applied pressure relative to the vacuum level maintained at the surface of the mold;
• maintaining said mold for a pre-determined hold time under vent vacuum and pre-blow to establish a part definition and inner and outer skins;
• applying a vacuum at a predefined level to the cavity interior sufficient to expand a warm foam core;
• regulating a vacuum inside the cavity interior for a pre-determined period to achieve a desired foam expansion;
• venting the cavity interior to relieve the vacuum;
• applying positive pressure to the cavity interior;
• turning off both positive pressure and in-mold vent vacuum;
• extracting the part from the mold.