Process for processing expandable polymer particles and foam article thereof

• US 20050059747A1
• Filed: 08/10/2004
• Published: 03/17/2005
• Est. Priority Date: 08/15/2003
• Status: Active Grant

• Current Assignee: NOVA Chemicals (International) S.A. (NOVA Chemicals Holding GmbH)
• Original Assignee: NOVA Chemicals (International) S.A. (NOVA Chemicals Holding GmbH)
• Inventors: Bleijenberg, Karel Cornelis, Berghmans, Michel Florentine Jozef, Metsaars, Alphonsus Catharina Gerardus, Teubert, Joachim
• Granted Patent: US 7,358,280 B2
• Time in Patent Office: Days
• US Class Current: 521/50
• CPC Class Codes: B29C 44/3426 Heating by introducing steam in the mould
• CPC Class Codes: B29C 44/3453 Feeding the blowing agent to solid plastic material
• CPC Class Codes: B29C 44/3461 Making or treating expandable particles
• CPC Class Codes: B29C 44/445 in the form of expandable granules, particles or beads
• CPC Class Codes: C08J 9/22 After-treatment of expandable particles; Forming foamed products
• CPC Class Codes: C08J 9/228 Forming foamed products
• CPC Class Codes: C08J 9/232 by sintering expandable particles

Abstract

Process for processing expandable polymer particles e.g. polystyrene (EPS) that eliminates the maturing step between the pre-expander and molding steps. The expandable particles are first over pressurized with gas, e.g. air, carbon dioxide, nitrogen, and mixtures thereof, at a pressure between 500 and 8000 kPa and a temperature between −20° C. and 130° C. for 15 to 7200 minutes to create a gas pressure in the particles. Using the gas pressure in the particles, pre-expanding the particles with a heating medium, e.g. steam at a temperature between 100° C. and 120° C. and at a pressure ranging above atmospheric pressure and below the gas pressure in said particles, i.e. 50 to 200 kPa for 5 to 120 seconds. The pre-expanded particles are air dried in the pre-expander while holding a positive pressure in the particles; are optionally transferred to a pressure silo; and then are transferred to a molding machine where the gas pressure in the particles is used to form a foam article.

Claims

1. A process for processing expandable polymer particles, comprising:

a) pressurizing said expandable polymer particles with a high pressurized gas to create a high gas pressure inside said particles;

b) pre-expanding said particles with a heating medium at a pressure ranging above atmospheric pressure and below the gas pressure in said particles as a result of step a) and drying the pre-expanded particles; and

c) immediately molding said particles into a foam article using at least the residual gas pressure in said particles.

2. A process of claim 1, wherein said drying of said pre-expanded particles in step b) occurs while said particles are kept under a pressure ranging above atmospheric pressure and below the gas pressure of step a).

3. A process of claim 1, wherein said gas in the pressurizing of said particles of step a) has a temperature ranging from about −

20°

to about 130°

C. and a pressure ranging from about 500 kPa to about 80000 kPa and said pressurizing occurs for about 15 to about 7200 minutes.

4. A process of claim 3, wherein said polymer is polystyrene and said gas has a temperature of about 90°

C. or less.

5. A process of claim 4 wherein said heating medium for said pre-expanding of said particles of step b) has a temperature ranging from about 100°

C. to about 120°

C. and a pressure ranging from about 50 kPa to about 200 kPa and is applied to said particles for a time ranging from about 5 to about 120 seconds.

6. A process of claim 2 wherein said drying of said expanded particles in step b) consists of an air flow having a temperature ranging from about 20°

to about 90°

C. and a pressure ranging from about 1 kPa to about 10 kPa and is applied to said particles for a time ranging from about 1 to about 900 seconds.

7. A process of claim 1 wherein said process further comprising:

after pre-expanding of said particles of step b) and prior to said molding of said particles of step c), transferring said particles to a pressure silo to maintain the pressure in said particles.

8. A process of claim 1 wherein in steps b) and c), the pressure in said particles is maintained at least at a pressure ranging from about 50 kPa to about 200 kPa.

9. A process of claim 1 wherein said pressurized gas in step a) is selected from the group consisting of air, nitrogen, carbon dioxide, and mixtures thereof.

10. A process of claim 1 wherein said pressurized gas in step a) is selected from the group consisting of air, carbon dioxide, and mixtures thereof.

11. A process of claim 1 wherein said heating medium in said step b) is selected from the group consisting of steam, hot air, hot water, radiant heat, micro-waves, high frequency radiation, and electromagnetic waves.

12. A process of claim 1 wherein said polymer is selected from the group consisting of polystyrene polyethylene, polypropylene, and an interpenetrating network of polyethylene and polymerized vinyl aromatic resins.

13. A process of claim 12 wherein said polymer is polystyrene.

14. A process of claim 1 wherein said expandable polymer particles contain a blowing agent selected from the group consisting of an inorganic blowing agent, an organic blowing agent, and mixtures thereof.

15. A process of claim 1 wherein said expandable polymer particles are polystyrene, are pre-nucleated, and contain an organic blowing agent in an amount less than 3 percent by weight based on the weight of the particles.

16. A process of claim 1 wherein said expandable polymer particles are pre-nucleated and contain an inorganic blowing agent selected from the group consisting of carbon dioxide, nitrogen, air, water, and mixtures thereof, and wherein said pressurized gas in step a) is selected from the group consisting of air, nitrogen, carbon dioxide, and mixtures thereof.

17. A process of claim 1 wherein said expandable particles are pre-nucleated and contain carbon dioxide as the blowing agent, and wherein the gas in step a) is selected from air and carbon dioxide.

18. A process of claim 1 wherein said expandable particles are comprised of solid polystyrene particles that are impregnated with carbon dioxide and then pre-nucleated, and wherein the pressurized gas in step a) is selected from air and carbon dioxide.

19. A foam article formed from the polymer particles processed according to the process of claim 1.

20. Particles processed according to steps a) and b) of the process of claim 1.

21. An apparatus for processing expandable polymer particles, comprising:

a pressurization unit for pressurizing said particles with a pressurized gas to create a gas pressure in said particles that is greater than the pressure outside said particles;

a pre-expander unit for applying a heating medium at a temperature ranging between about 100°

C. and 120°

C. and a pressure ranging above atmospheric pressure and below the gas pressure in the particles so that the residual gas pressure in the particles is used as the blowing agent and said pre-expander unit including drying means for drying said particles in said pressure ranging above atmospheric pressure and below the gas pressure in said particles until the particles are dry, and a molding unit for forming a foam article.

22. An apparatus of claim 21 wherein said pressurized gas in said pressurization unit is selected from the group consisting of air, nitrogen, carbon dioxide and mixtures thereof.

23. An apparatus of claim 21 wherein said pressurized gas in said pressurization unit is selected from the group consisting of air, carbon dioxide, and mixtures thereof.

24. An apparatus of claim 21 wherein said heating medium in said pre-expander unit is selected from the group consisting of steam, hot air, hot water, radiation, microwave, high frequency radiation, and electromagnetic radiation.