Method of forming a thermoformable polypropylene foam sheet

• US 6,251,319 B1
• Filed: 04/30/1999
• Issued: 06/26/2001
• Est. Priority Date: 05/27/1998
• Status: Expired due to Fees

• Current Assignee: The Dow Chemical Company (Dow, Inc.)
• Original Assignee: The Dow Chemical Company (Dow, Inc.)
• Inventors: Christenson, Christopher P., Tusim, Martin H., Park, Chung P., Cornell, Martin C., Suh, Kyung W.
• Primary Examiner(s): Kuhns, Allan R.
• Application Number:
  US09/302,306
• Time in Patent Office: 788 Days
• Field of Search: 264/45.9, 264/50, 264/51, 264/53, 264/146, 264/DIG.5
• US Class Current: 264/45.9
• CPC Class Codes: B29C 43/00 Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor by liberation of internal stresses B29C61/006
• CPC Class Codes: B29C 44/22 consisting of at least two parts of chemically or physically different materials, e.g. having different densities
• CPC Class Codes: B29C 44/5654 Subdividing foamed articles to obtain particular surface properties, e.g. on multiple modules
• CPC Class Codes: B29C 48/001 Combinations of extrusion moulding with other shaping operations
• CPC Class Codes: B29C 48/0011 combined with compression moulding
• CPC Class Codes: B29C 48/0012 combined with shaping by internal pressure generated in the material, e.g. foaming
• CPC Class Codes: B29C 48/0017 combined with blow-moulding or thermoforming
• CPC Class Codes: B29C 48/0022 combined with cutting
• CPC Class Codes: B29C 48/05 Filamentary, e.g. strands
• CPC Class Codes: B29C 48/06 Rod-shaped
• CPC Class Codes: B29C 48/08 flexible, e.g. films
• CPC Class Codes: B29C 48/09 Articles with cross-sections having partially or fully enclosed cavities, e.g. pipes or channels
• CPC Class Codes: B29C 48/15 incorporating preformed parts or layers, e.g. extrusion moulding around inserts
• CPC Class Codes: B29K 2105/04 cellular or porous
• CPC Class Codes: B29K 2105/0854 in the form of a non-woven mat
• CPC Class Codes: B32B 2266/0257 Polyamide
• CPC Class Codes: B32B 2266/0264 Polyester
• CPC Class Codes: B32B 2305/30 Fillers, e.g. particles, powders, beads, flakes, spheres, chips
• CPC Class Codes: B32B 2323/10 Polypropylene
• CPC Class Codes: B32B 2605/00 Vehicles
• CPC Class Codes: B32B 27/065 : of foam
• CPC Class Codes: B32B 27/32 : comprising polyolefins comprising vinyl (co)polymers or acrylic (co)polymers B32B27/30
• CPC Class Codes: B32B 5/18 : characterised by features of a layer of foamed material
• CPC Class Codes: B32B 5/245 : another layer next to it being a foam layer
• CPC Class Codes: B32B 5/32 : at least two layers being foamed and next to each other
• CPC Class Codes: B60R 13/02 : Internal Trim mouldings ; Internal Ledges; Wall liners for passenger compartments; Roof liners B60R13/01 takes precedence ; padded linings for the vehicle interior B60R21/04; arrangements or adaptations of floor mats or carpets in vehicles B60N3/04; internal lining for trains B61D17/18
• CPC Class Codes: B60R 13/0225 : self supporting head liners
• CPC Class Codes: B60R 13/0815 : Acoustic or thermal insulation of passenger compartments wall or roof liners integrating the insulating function B60R13/02; insulating floor mats or carpets B60N3/04
• CPC Class Codes: C08J 2201/03 : Extrusion of the foamable blend
• CPC Class Codes: C08J 2203/06 : CO2, N2 or noble gases
• CPC Class Codes: C08J 2203/14 : Saturated hydrocarbons, e.g. butane; Unspecified hydrocarbons
• CPC Class Codes: C08J 2205/04 : characterised by the foam pores
• CPC Class Codes: C08J 2205/052 : Closed cells, i.e. more than 50% of the pores are closed
• CPC Class Codes: C08J 2323/12 : Polypropene
• CPC Class Codes: C08J 2423/06 : Polyethene
• CPC Class Codes: C08J 9/0061 : characterized by the use of several polymeric components
• CPC Class Codes: C08J 9/122 : Hydrogen, oxygen, CO2, nitrogen or noble gases
• CPC Class Codes: C08J 9/127 : Mixtures of organic and inorganic blowing agents
• CPC Class Codes: C08J 9/141 : Hydrocarbons
• CPC Class Codes: C08J 9/142 : Compounds containing oxygen but no halogen atom
• CPC Class Codes: Y10S 264/05 : Use of one or more blowing agents together

Abstract

A process for making a polymer foam sheet, which comprises (i) extruding through an annular extrusion die a foamable composition comprising at least one polypropylene polymer and at least one blowing agent, at a pressure, temperature, and extrusion rate sufficient to prevent foaming of the composition prior to exiting the die, under conditions sufficient to form a foam tube having a density of at least 16 kg/m³ and no greater than 200 kg/m³, an open cell content of less than 70 percent, a circumference of at least 1 meter, and a foam thickness of at least 2 mm and no greater than 25 mm, wherein the blowing agent is used in an amount of from 0.2 to 4.5 moles per kg of polymer, (ii) allowing the foam to cool to a temperature below the melt temperature of the polypropylene, and (iii) cutting the tube of foam along its radius to form a foam sheet, wherein at least 70 percent by weight of the polymer in such sheet is a polypropylene having a melt strength in the range of from 25 to 60 cN when measured at 190° C.

Claims

1. A process for making a polymer foam sheet, which comprises (i) extruding through an annular extrusion die a foamable composition comprising at least one polypropylene polymer and at least one blowing agent, at a pressure, temperature, and extrusion rate sufficient to prevent foaming of the composition prior to exiting the die, under conditions sufficient to form a foam tube having a density of at least 16 kg/m³ and no greater than 200 kg/m³, an open cell content of less than 70 percent, a circumference of at least 1 meter, and a foam thickness of at least 7 mm and no greater than 25 mm, wherein the blowing agent is used in an amount of from 0.2 to 4.5 moles per kg of polymer, (ii) allowing the foam to cool to a temperature below the melt temperature of the polypropylene, and (iii) cutting the tube of foam along its radius to form a foam sheet, wherein at least 70 percent by weight of the polymer in such sheet is a polypropylene having a melt strength in the range of from 25 to 60 cN when measured at 190°

C.

2. The process of claim 1 wherein the foam solids comprise at least 80 percent by weight of the polymer in such sheet is a polypropylene having a melt strength in the range of from 25 to 60 cN when measured at 190°

C.

3. The process of claim 1 wherein the foam has a density of least 32 kg/m³.

4. The process of claim 1 wherein the sheet has a width of at least 1.1 m.

5. The process of claim 1 wherein the sheet has a width of at least 1.1 m and a thickness of at least 8 mm.

6. The process of claim 1 wherein the sheet has a width of at least 1.2 m.

7. The process of claim 1 wherein the sheet has a width of at least 1.2 m.

8. The process of claim 1 wherein the sheet has a width of at least 1.2 m and a thickness of at least 8 mm.

9. The process of claim 1 wherein the blowing agent is isobutane.

10. The process of claim 1 wherein the blowing agent is a combination of an organic and an inorganic blowing agent.

11. The process of claim 1 wherein the organic blowing agent is selected from n-butane, isobutane, propane, and ethanol.

12. The process of claim 10 wherein the organic blowing agent is selected from n-butane, isobutane, propane, and ethanol.

13. The process of claim 10 wherein the inorganic blowing agent is selected from carbon dioxide, argon, water, and nitrogen.

14. The process of claim 1 wherein the blowing agent is an inorganic blowing agent, selected from carbon dioxide, argon, water, and nitrogen.

15. The process of claim 1 wherein the polypropylene has a melt flow rate of less than 10 dg/min.

16. The process of claim 1 wherein the foamable composition is co-extruded with a non-foamable molten polymer under conditions sufficient to form a sheet having foamed and non-foamed portions.

17. The process of claim 1 wherein the foam has an average cell size in the range of from 0.1 mm to 6.0 mm.

18. The process of claim 1 wherein the foam has an average cell size in the range of from 0.5 mm to 6.0 mm.

19. The process of claim 17 wherein the foam has an average cell size of at least 0.75 mm.

20. The process of claim 18 wherein the foam has an average cell size of at least 1.0 mm.

21. The process of claim 1 wherein at least 75 percent of the polymer in the sheet is a polypropylene having a melt strength in the range of from 25 to 60 cN when measured at 190°

C.

22. The process of claim 1 wherein at least 95 percent of the polymer in the sheet is a polypropylene having a melt strength in the range of from 25 to 60 cN when measured at 190°

C.

23. The process of claim 1 wherein the pressure of the foamable composition prior to extrusion is at least 3 MPa.

24. The process of claim 1 wherein the foam has an open cell content of less than 50 percent.