Process for processing expandable polymer particles and foam article thereof

• US 7,358,280 B2
• Filed: 08/10/2004
• Issued: 04/15/2008
• Est. Priority Date: 08/15/2003
• Status: Expired due to Fees

• Current Assignee: NOVA Chemicals (International) S.A. (NOVA Chemicals Holding GmbH)
• Original Assignee: NOVA Chemicals (International) S.A. (NOVA Chemicals Holding GmbH)
• Inventors: Metsaars, Alphonsus Catharina Gerardus, Teubert, Joachim, Bleijenberg, Karel Cornelis, Berghmans, Michel Florentine Jozef
• Primary Examiner(s): ZEMEL, IRINA SOPJIA
• Application Number:
  US10/915,141
• Publication Number:
  US 20050059747A1
• Time in Patent Office: 1,344 Days
• Field of Search: 521/56, 521/58, 521/60, 521/146
• US Class Current: 521/56
• 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 polymer particles which optionally contain a blowing agent, the steps consisting of:

a) in a pressurization unit, over-pressurizing said polymer particles with a high pressurized gas to create a high gas pressure inside said particles;

b) immediately transferring said particles to a pre-expander and pre-expanding said particles with a heating medium to form pre-expanded particles, and directing a flow of hot dry air onto said pre-expanded particles to dry said pre-expanded particles in the pre-expander while maintaining sufficient positive pressure in said pre-expanded particles which pressure is above atmospheric pressure and below the gas pressure in said particles as a result of step a);

c) without maturing said pre-expanded particles, immediately injecting said pre-expanded particles into a molding machine and molding said pre-expanded particles into a foam article using at least the residual gas pressure in said particles; and

after step b) and prior to step c), optionally transferring said pre-expanded particles of step b) directly from said pre-expander to a pressure silo to maintain the pressure in said pre-expanded particles.

2. The process of claim 1, wherein said gas in the over-pressuring 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 8000 kPa and said over-pressurizing occurs for about 15 to about 7200 minutes.

3. The process of claim 2, wherein said polymer is polystyrene and said gas has a temperature of about 90°

C. or less.

4. The process of claim 3, 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.

5. The process of claim 1, wherein said drying of said pre-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 pre-expanded particles for a time ranging from about 1 to about 900 seconds.

6. The 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.

7. The 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.

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

9. The 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, microwaves, high frequency radiation, and electromagnetic waves.

10. The 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.

11. The process of claim 10, wherein said polymer is polystyrene.

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

13. The process of claim 1, wherein said 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.

14. The process of claim 1, wherein said 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.

15. The process of claim 1, wherein said 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.

16. The process of claim 1, wherein said 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.