PRODUCTION OF FOAMED RESINS

• US 3,624,192 A
• Filed: 05/06/1968
• Issued: 11/30/1971
• Est. Priority Date: 05/19/1967
• Status: Expired due to Term

• Current Assignee: John Gerald Mccoy, William Rees Foster
• Original Assignee: John Gerald Mccoy, William Rees Foster
• Inventors: McCoy, John Gerald, Foster, William Rees
• Primary Examiner(s): Anderson, Philip E.
• Application Number:
  US04/726,857
• Time in Patent Office: 1,303 Days
• Field of Search: 264/51,53,48,177,237 18/12,5
• US Class Current: 264/51
• CPC Class Codes: B29C 44/468 in a plurality of parallel streams which unite during the foaming
• CPC Class Codes: B29C 44/505 extruding the compound through a flat die in general B29C48/03
• CPC Class Codes: B29L 2007/00 Flat articles, e.g. films or sheets B29L2024/00 takes precedence

Abstract

Die assemblies and processes for extruding a foamable thermoplastic polyvinylaromatic resin through a rectangular die orifice into a zone of lower pressure such that foaming of the resin occurs as it moves through the zone, said zone being defined by a pair of opposing concave surfaces maintained at a temperature lower than the extrusion temperature and curved so that they substantially conform to the corresponding surfaces of the freely expanding resin without exerting a substantial compressive force thereon. The die assemblies and processes are particularly useful for the production of low-density foamed boards having smooth surfaces.

Claims

1. A process for the production of foamed thermoplastic polyvinylaromatic resins having an improved surface finish which comprises extruding a foamable thermoplastic polyvinylaromatic resin through a rectangular die orifice into a zone of lower pressure such that foaming of the resin occurs as it moves through the zone, said zone being defined by a pair of opposing concave surfaces maintained at a temperature lower than the extrusion temperature and curved so that they substantially conform to the corresponding surfaces of the freely expanding resin whereby substantially no compressive force is exerted by said opposing concave surfaces upon said freely expanding resin.

2. The process of claim 1 wherein the resin is polystyrene.

3. The process of claim 1 wherein the die has a plurality of obstructions transversely distributed therein whereby substantial resistance to the flow of the foamable resin is provided and back pressure within the die is increased.

4. The process of claim 3 wherein the die has extending into it at its inlet end a plurality of separate channels communicating with a number of slits arranged in the form of a network at the outlet end of the die, each slit having a row of channels associated with it.

5. The process of claim 4 wherein each of at least the majority of the meshes of the slit network has a substantially central passage leading back from the front face of the die to the inlet end of the die and not communicating directly with the slits.

6. The process of claim 5 wherein grooves extending from the outlet end of each of at least the majority of the passages toward the outlet of its surrounding mesh of slits are provided in the front face of the die to assist in ensuring that a strand of foamed resin extruded from each passage substantially fills the space formed by the enveloping foamed resin issuing from the surrounding mesh of slits.

7. The process of claim 1 wherein the zone-defining surfaces have a concave curved cross section that conforms exactly to the corresponding surfaces of the freely expanding resin.

8. The process of claim 1 wherein the zone-defining surfaces have a concave cross section corresponding to an arc of a circle.

9. The process of claim 1 wherein the zone-defining surfaces reach their greatest distance apart where the foamed resin is completely expanded and thereafter extend parallel to each other.