# US 4,399,086 A · Process for manufacturing foamed plastic sheets > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 4,399,086 A - Document ID: US4399086A - Status: Granted - Kind: A - Application number: 06/236,638 - Filed: 1981-02-20 - Granted: 1983-08-16 - Earliest claimed: 1980-03-04 - Assignees: Swiss Aluminium Ltd. - Inventors: Juris Walter - Web page: https://patentgrep.com/patent/US4399086A ## CPC - B29C 44/505: {extruding the compound through a flat die (in general B29C48/03)} - B29C 44/56: After-treatment of articles, e.g. for altering the shape - B29L 2007/00: Flat articles, e.g. films or sheets (B29L2024/00 takes precedence) - Y10S 264/14: forming integral skin on a foamed product - B29C: SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING (making preforms B29B11/00; making laminated products by combining previously unconnected layers which become one product whose layers will remain together B32B37/00 - B32B41/00) - B29L: INDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES - Y10S: TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS ## Abstract The invention relates to a process for the continuous manufacture of foamed sheets of thermoplastic material having an extreme width to thickness ratio, small thickness tolerance, a uniform cell structure and, over the whole cross section on both sides of the sheet a thin, non-foamed outer skin. The plastic, which already contains the foaming agent is, on emerging from a wide-slit nozzle, allowed to foam freely without any restriction and cool. The sheet or strip formed in this manner is then heated locally at the surface and calibrated to final dimension. ## Claims ### Claim 1 A process for the continuous production of wide, thin, foamed thermoplastic sheets characterized by a uniform cell structure and a thin non-foamed outer skin comprising feeding a thermoplastic material containing a foaming agent through the nozzle of an extruder, allowing the extruded thermoplastic to foam freely in an unconfined space so as to allow for substantially complete foaming, cooling the freely substantially completely foamed extruded thermoplastic to a non-formable solid state, selectively heating the surface of the cooled freely substantially completely foamed extruded thermoplastic so that the outer zone of the freely foamed extruded thermoplastic is in a formable state while the core of the freely foamed extruded thermoplastic remains in a non-formable solid state and passing said selectively heated freely foamed extruded thermoplastic through a calibrating device so as to produce a foamed thermoplastic sheet of desired thickness having a thin non-foamed outer skin. ### Claim 2 (depends on 1) A process according to claim 1 wherein the outer zone comprises not more than 50% of the cross section of the cooled free foamed extruded thermoplastic. ### Claim 3 (depends on 1) A process according to claim 1 wherein the outer zone comprises from about 10-30% of the cross section of the cooled free foamed extruded thermoplastic. ### Claim 4 (depends on 1) A process according to claim 1 including the steps of providing a wide-slit nozzle for the extruder having a width of from about 1,000 mm to 2,000 mm and a height of from about 0.3 mm to 6.0 mm. ### Claim 5 (depends on 1) A process according to claim 1 including the steps of providing a wide-slit nozzle for the extruder having a width of from about 1,300 mm to 1,700 mm and a height of from about 0.3 mm to 4.0 mm. ### Claim 6 A process for the continuous production of wide, thin, foamed thermoplastic sheets characterized by a uniform cell structure and a thin non-foamed outer skin comprising providing an extruder having a wide-slit nozzle, feeding a thermoplastic material containing a foaming agent through said wide-slit nozzle of said extruder, allowing the extruded thermoplastic to foam freely in an unconfined space so as to allow for substantially complete foaming and cooling said freely foamed extruded thermoplastic in said unconfined space to a non-formable solid state, providing heating means for selectively heating the surface of the cooled freely foamed extruded thermoplastic so that the outer zone of the freely foamed extruded thermoplastic is in a formable state while the core of the freely foamed extruded thermoplastic remains in a non-formable state, providing a calibrating means for calibrating the freely foamed extruded thermoplastic to final thickness and passing said selectively heated freely foamed extruded thermoplastic through said calibrating means so as to produce a foamed thermoplastic sheet of desired thickness having a thin non-foamed outer skin. ### Claim 7 (depends on 6) A process according to claim 6 including the steps of locating said calibrating means immediately downstream of said heating means. ### Claim 8 (depends on 6) A process according to claim 6 wherein the outer zone comprises not more than 50% of the cross section of the cooled free foamed extruded thermoplastic. ### Claim 9 (depends on 6) A process according to claim 6 wherein the outer zone comprises from about 10-30% of the cross section of the cooled free foamed extruded thermoplastic. ### Claim 10 (depends on 6) A process according to claim 6 including the steps of providing a wide-slit nozzle for the extruder having a width of from about 1,000 mm to 2,000 mm and a height of from about 0.3 mm to 6.0 mm. ### Claim 11 (depends on 6) A process according to claim 6 including the steps of providing a wide-slit nozzle for the extruder having a width of from about 1,300 mm to 1,700 mm and a height of from about 0.3 mm to 4.0 mm. ### Claim 12 (depends on 6) A process according to claim 6 including the steps of providing a hot air heater. ### Claim 13 (depends on 6) A process according to claim 6 including the steps of providing an infra-red radiating heater. ### Claim 14 An extrusion apparatus for use in the continuous production of wide, thin, foamed thermoplastic sheets characterized by a uniform cell structure and a thin non-foamed outer skin comprising, in combination, a plastic extruder having a wide-slit nozzle, means defining an unconfined space adjacent to and downstream of said wide-slit nozzle for receiving the extruded thermoplastic material from said wide-slit nozzle wherein said thermoplastic material substantially completely foams and thereafter is cooled to a non-formable solid state, heating means adjacent to and downstream of said means defining an unconfined space for selectively heating the surface of the foamed extruded thermoplastic material and calibrating means downstream of said heating means for calibrating the foamed extruded thermoplastic material to final thickness so as to produce a foamed thermoplastic sheet of desired thickness having a thin non-foamed outer skin. ### Claim 15 (depends on 14) An extrusion apparatus according to claim 14 wherein said wide-slit nozzle has a width of from about 1,000 mm to 2,000 mm and a height of from about 0.3 mm to 6.0 mm. ### Claim 16 (depends on 14) An extrusion apparatus according to claim 14 wherein said wide-slit nozzle has a width of from about 1,300 mm to 1,700 mm and a height of from about 0.3 mm to 4.0 mm. ### Claim 17 (depends on 14) An extrusion apparatus according to claim 14 wherein said heating means is a hot air heater. ### Claim 18 (depends on 14) An extrusion apparatus according to claim 14 wherein said heating means is an infra-red radiating heater.