Extrusion of foamable plastic materials

Claim 1

A process for producing an extruded plastic material product comprising the steps of extruding a thermoplastic material with an expanding agent therein through a die outlet, said thermoplastic material being selected from the group consisting of (A) styrene homo and copolymers and styrene derivatives substituted on the ring or in the alpha position, as well as mixtures of said polymers or copolymers with one or more elastomeric compounds, (B) acrylic homo and copolymers, (C) vinyl chloride homo and copolymers, and mixtures thereof with oNe or more elastomeric compounds, (D) polyolefins, (E) polyamides, (F) polyurethanes, (G), cellulose derivatives, (H) straight chain polyesters, (I) acetal homo and copolymers, (J) polycarbonates, (K) polyethers and (L) polyvinyl ethers and polyvinyl esters, the extruded material having an external surface thereon, feeding the extruded material through an elongated shaper immediately adjacent to the die outlet, the shaper having an internal surface defining a channel, said channel having an inlet and an outlet and said channel inlet circumscribing said die outlet, said shaper channel inlet and said die outlet each having a first side, and a second side opposite said first side, the shaper channel inlet and the die outlet being in close proximity along substantially the entire length of said first side of said shaper inlet and the corresponding side of said die outlet, said second side of the die outlet being substantially removed from the corresponding second side of the shaper inlet within said circumscribed area of said shaper along substantially the entire length of said second sides, thereby to provide for substantially unrestricted expansion of the plastic material extruded through the die within said circumscribing area of the shaper, the external surface of the material extruded through the die outlet immediately making contact with the internal surface of the shaper channel along substantially the entire length of said first side of said shaper inlet, and the channel outlet cross-section being substantially that of the product desired, cooling rapidly the external part adjacent the external surface of the extruded material along substantially the entire length of said first side of said external surface below the solidification point of the material immediately upon being fed into the shaper channel to form a thick skin of higher density along said first side of said external surface, thereby forming a continuous area of thick skin along the external surface of the extruded material adjacent said first side and imparting sufficient mechanical strength to the extruded product in the shaper to permit it to be pulled through the shaper, expanding the extruded material from said continuous area of thick skin towards said second side to substantially fill the channel and forming a continuous surface area substantially free of such a thick skin on the extruded material adjacent said second side of the shaper channel, and pulling the extruded product through the shaper.