Method and apparatus for the extrusion of foamable thermoplastic materials

Claim 1

In a process for the preparation of synthetic resinous thermoplastic foam, the steps of the method comprising providing a heat plastified synthetic resinous thermoplastic extrudable foamable composition, extruding the composition through an extrusion orifice into a shaping channel of lower pressure, said channel having internal walls, the channel having a cross-sectional configuration generally corresponding to the shape of the product desired, the extrudable composition expanding to generally fill said channel and contact said channel walls at a location adjacent a discharge opening thereof and withdrawing the foamed product from said channel at the discharge opening remote from the extrusion orifice, the improvement which comprises providing within said channel, at a location adjacent to the die, a gas under pressure, the gas pressure being sufficient to regulate the shape of the expanding composition at a location between the die and a location where the expanding composition contacts said channel walls.