Method for producing microcellular foamed plastic material with smooth integral skin

A method for continuously producing foamed plastic material with integral unmodified laminar skin, comprising the steps of:

• (1) delivering molten gas-impregnated plastic material from an extruder to an extrusion die under sufficient pressure to prevent foaming of said material,
• (2) maintaining the gas-impregnated material within said extrusion die under sufficient pressure to prevent foaming while cooling such material to below its atmospheric foaming temperature prior to its extrusion from said extrusion die,
• (3) extending said gas-impregnated material from said die at below its atmospheric foaming temperature,
• (4) conveying said material below its atmospheric foaming temperature along a degassing path beyond said die for allowing gas with which said material was impregnated to partially diffuse out of said material, and
• (5) reheating said material, after said gas has diffused out of surface regions of said material but while at least some gas remains in core regions thereof, to a temperature above said atmospheric foaming temperature to initiate foaming.

A method for continuously producing foamed plastic material with integral unmodified laminar skin, comprising the steps of;

• (1) delivering molten gas-impregnated plastic material from an extruder to an extrusion die under sufficient pressure to prevent foaming of said material,
• (2) maintaining said gas-impregnated plastic within said extrusion die under sufficient pressure to prevent foaming of said material,
• (3) extending said material from said extrusion die into an environment at substantially atmospheric pressure while said material is above its atmospheric foaming temperature,
• (4) cooling said material rapidly to below its atmospheric foaming temperature before said material has been exposed to substantially atmospheric pressure long enough to undergo significant foaming,
• (5) conveying said material below its atmospheric foaming temperature along a degassing path beyond said die for allowing gas with which said material was impregnated to partially diffuse out of said material, and
• (6) reheating said material, after said gas has diffused out of surface regions of said material but while at least some gas remains in core regions thereof, to a temperature above said atmospheric foaming temperature to initiate foaming.