Process and apparatus for producing gas pressurized foam particles

• US 4,804,507 A
• Filed: 04/25/1988
• Issued: 02/14/1989
• Est. Priority Date: 04/25/1988
• Status: Expired due to Fees

• Current Assignee: The Dow Chemical Company (Dow, Inc.)
• Original Assignee: The Dow Chemical Company (Dow, Inc.)
• Inventors: Rubens, Louis C., Chum, Stephen P.
• Primary Examiner(s): Anderson, Philip
• Application Number:
  US07/185,639
• Time in Patent Office: 295 Days
• Field of Search: 264/51, 264/50, 264/DIG. 5, 264/DIG. 15, 264/DIG. 18, 425/4 R
• US Class Current: 264/50
• CPC Class Codes: B29C 44/3461 Making or treating expandable particles
• CPC Class Codes: Y10S 264/05 Use of one or more blowing agents together
• CPC Class Codes: Y10S 264/15 Aging of foamed resin products
• CPC Class Codes: Y10S 264/18 Cross-linking a thermoplastic linear foam during molding

Abstract

Closed-cell foam particles are pressurized to produce particles useful in a process using secondary foaming to achieve a lower density foam. Closed-cell foam particles are initially compressed in a first stage compression tank and then transferred to a main gas pressurization tank. The main gas pressurization tank comprises multi-level shelves, each with a set of compartments. Charges of foam particles pass sequentially through the shelves while becoming fully pressurized. The multi-level shelves with means to move charges of foam particles from shelf to shelf are responsible for the closed cell foam particles becoming pressurized in an efficient manner.

Claims

1. A process for producing gas pressurized closed-cell foam particles suitable for secondary foaming to a lower density foam, comprising the steps of:

(a) charging closed cell foam particles to a first stage compression tank wherein the foam particles are subjected to a pressure of from about 10 psig to about 150 psig to compress said foam particles to about 30%-40% of their original volume at atmospheric pressure;

(b) transferring the pressurized foam particles to a main gas pressurization tank maintained under a pressure of from about 40 psig to about 100 psig and a temperature of from about 30°

C. to about 90°

C., said gas pressurization tank having multi-level shelves through which individual charges of compressed foam particles sequentially pass, each shelf holding a separate charge of foam particles from the first stage compression tank and further wherein each shelf has a plurality of compartments to prevent bridging and immobilization of the foam particles; and

(c) passing the foam particles from one shelf to the next in a first-in-first-out sequence, during which said foam particles partially recover their volume without exceeding the free volume in each of said plurality of compartments;

(d) discharging the foam particles from the last shelf level of the main gas pressurization tank, said foam particles having an internal pressure greater than atmospheric pressure and suitable for secondary foaming.

2. The process of claim 1 further comprising the steps of cooling the gas pressurized foam particles discharged from the main gas pressurization tank in a refrigerated decompression tank maintained at a pressure substantially equal to that found in the main gas pressurization tank and at a temperature of less than about -10°

C. and venting the refrigerated decompression tank to the atmosphere while maintaining the reduced temperature of the foam particles, said foam particles capable of being stored for a prolonged period without substantially reducing their secondary foaming capability.

3. The process of claim 2 wherein the pressure maintained in the first stage compression tank is substantially equal to the pressure maintained in the main gas pressurization tank.

4. The process of claim 3 wherein the main gas pressure tank in maintained at a pressure of from about 40 psig to about 100 psig and a temperature of from about 70°

C. to about 85°

C.

5. The process of claim 4 wherein the main gas pressurization tank has from four to eight shelves.

6. The process of claim 5 wherein the distance between shelves increases progressively towards a discharge end.

7. The process of claim 6 wherein each shelf has from four to eight compartments.

8. The process of claim 7 wherein the main gas pressurization tank has a shaft extending vertically through its center with a set of fixed discs and movable discs mounted on the shaft, said discs forming each shelf, further wherein each of the fixed discs has partition plates extending vertically therefrom and each of the movable discs has sweep plates extending vertically therefrom, said plates forming the compartments of each shelf.

9. The process of claim 8 further wherein each movable disc and fixed disc has an opening through which the foam particles pass when aligned.

10. The process of claim 1 wherein said foam particles are moistened under a nitrogen gas pressure in said first stage compression tank and said main gas pressurization tank.

11. A gas pressurization tank having multi-level shelves to hold separate charges of foam particles and alllow transfer of foam particle charges sequentially therethrough, comprising:

(a) a main tank with charge and discharge openings through which foam particles pass;

(b) multi-level shelves within the main tank characterized by having a series of at least four compartments at each shelf level with the compartment heights increasing at each shelf level from the charge opening to the discharge opening; and

(c) means for gravity transferring individual charges of foam particles in compartments found at each shelf level to compartments found at a lower shelf level.

12. The apparatus of claim 11 wherein a floor of each shelf level comprises a fixed disc which fits into the main tank with spaced openings arranged in a sequence and a movable disc with spaced openings arranged in a sequence positioned directly above the fixed disc such that when aligned the movable disc covers the openings in the fixed disc while rotation of the movable disc about its axis a set distance will cause alignment of the openings on the fixed disc with the openings in the movable disc to cause any foam particles within the compartments of the shelf level to drop to a shelf below.

13. The apparatus of claim 12 wherein each fixed disc at least four vertical partition plates extending therefrom to the next shelf level with an opening in the fixed disc between each partition plate.

14. The apparatus of claim 13 wherein each movable disc has a sweep plate extending vertically therefrom to the next shelf level with an opening in the movable disc between each sweep plate.

15. The apparatus of claim 14 wherein each shelf level has from four to eight compartments when the movable disc is revolved such that each of its sweep plates abuts the partition plates of the fixed disc.

16. The apparatus of claim 15 further comprising a shaft which extends vertically through the center of the tank with the movable discs mounted thereon.

17. The apparatus of claim 16 further comprising means to cause the movable discs to independently revolve until the opening in a movable disc is in alignment with the opening in the fixed disc.

18. The apparatus of claim 11 further comprising means to maintain the tank at a pressure of from about 40 psig to about 100 psig and a temperature of from about 30°

C. to about 90°

C.