Process and apparatus for extruding a low density elastomeric thermoplastic foam

A method of extruding a soft, low density elastomeric thermoplastic foam in a single screw extruder having a screw disposed in an extruder barrel, the method comprising the steps of:

• a) selecting a foamable thermoplastic elastomer having a Shore A hardness of approximately 65 or less and comprising a blend of a polyolefin resin and a vulcanized monoolefin copolymer rubber;
• b) feeding said thermoplastic elastomer into the extruder barrel;
• c) compressing and melting said thermoplastic elastomer within said extruder barrel;
• d) introducing a blowing agent into the melted resin early enough to permit extended mixing;
• e) preventing the backflow of said blowing agent;
• f) mixing the melted thermoplastic elastomer and the blowing agent for an extended period to obtain a uniform mixture;
• g) cooling the uniform mixture to a predetermined temperature;
• and
• h) forcing the uniform mixture through a die to form an extruded foam profile having a density of less than approximately 20 lbs/ft.sup.3.