PREPARATION OF POLYMER FOAM AND PRODUCT

A method for producing a thermoplastic polymer extruded foam body having an average cell size of from 0.05 mm to 3.5 mm, a density of from 1.0 lbs/ft (16 kg/m ) to 5.0 lbs/ft (80 kg/cm ), a minimal cross- sectional thickness of 0.5 in (1.3 cm) and a minimal cross-sectional area of 8 in (52 cm ) comprises the steps of: heat plastifying the resin; introducing the plastified resin into a mixing device; introducing a blowing agent into the mixing device; maintaining a pressure in the mixing device at or above a pressure greater than an equilibrium vapor pressure of the blowing agent in the resin and blowing agent mixture; passing the mixture through a cooling device; passing the mixture through a die having a given die pressure greater than atmospheric pressure; maintaining a specific defined minimum critical pressure drop between the pressure at the inlet of the mixing device and the inlet of the die. Blowing agents useful in such process are disclosed as well polymer foam bodies made by the process and consistently having improved uniformity of surface quality.