Light weight board of improved surface flatness and process for production thereof

• US 20030082346A1
• Filed: 10/27/2001
• Published: 05/01/2003
• Est. Priority Date: 10/27/2001
• Status: Active Grant

• Current Assignee: Inteplast Group Limited
• Original Assignee: Inteplast Group Limited
• Inventors: Yang, Haur Horng, Wu, Phillip C. L., Li, Jyh-Yao Raphael, Cheng, Yao
• Granted Patent: US 6,759,114 B2
• Time in Patent Office: Days
• US Class Current: 428/188
• CPC Class Codes: B29C 44/0461 by having different chemical compositions in different places, e.g. having different concentrations of foaming agent, feeding one composition after the other
• 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 44/348 by regulating the temperature and/or the pressure, e.g. suppression of foaming until the pressure is rapidly decreased
• CPC Class Codes: B29C 48/07 Flat, e.g. panels
• CPC Class Codes: B29C 48/08 flexible, e.g. films
• CPC Class Codes: B29C 48/11 comprising two or more partially or fully enclosed cavities, e.g. honeycomb-shaped
• CPC Class Codes: B29L 2031/60 Multitubular or multicompartmented articles, e.g. honeycomb
• CPC Class Codes: B32B 3/20 of hollow pieces, e.g. tubes; of pieces with channels or cavities
• CPC Class Codes: E04C 2/34 composed of two or more spaced sheet-like parts E04C2/32 takes precedence; spacers for cavity walls E04B2/44
• CPC Class Codes: E04C 2/543 Hollow multi-walled panels with integrated webs
• CPC Class Codes: Y10T 428/24661 Forming, or cooperating to form cells
• CPC Class Codes: Y10T 428/24744 Longitudinal or transverse tubular cavity or cell
• CPC Class Codes: Y10T 428/249971 Preformed hollow element-containing
• CPC Class Codes: Y10T 428/249976 Voids specified as closed

Abstract

An extruded hollow thermoplastic board, which includes a pair of flat and parallel sheets spaced apart and interconnected by extending ribs, generally has a plurality of depression bands in the areas where the flat sheets and extending ribs are joined. The bands, which negatively affect the surface flatness, are especially apparent for crystalline thermoplastic materials. A hollow thermoplastic board, which effectively reduces the depth of the depression bands by inclusion of locationally fixed gas pockets in the rib area during production, is disclosed in the present invention. The hollow thermoplastic board of the present invention substantially enhances the surface smoothness and is highly beneficial to applications such as printing, lamination and graphic art. The present invention also provides a method for production of the hollow thermoplastic boards of smooth surfaces.

Claims

1. A light weight hollow thermoplastic board, which comprises:

a first planar sheet;

a second planar sheet; and

,

a plurality of ribs, each of said ribs having a plurality of fixed gas pockets located therein;

wherein said first planar sheet and said second planar are spaced apart by and are interconnected by said ribs.

2. The light weight hollow thermoplastic board of claim 1 wherein said board is formed in an integral form.

3. The light weight hollow thermoplastic board of claim 1 wherein said ribs are positioned at right angles to said first planar sheet and said second planar sheet and create rectangular cross-sectioned passageways therebetween.

4. The light weight hollow thermoplastic board of claim 1 wherein said ribs are positioned at angles other than right angles to said first planar sheet and said second planar sheet and create trapezoidal cross-sectioned passageways therebetween.

5. The light weight hollow thermoplastic board of claim 1 wherein said ribs are arcuated and create cross-sectioned passageways therebetween selected from the group consisting of elliptical and circular.

6. The light weight hollow thermoplastic board of claim 1 wherein said ribs are u-shaped.

7. The light weight hollow thermoplastic board of claim 1 wherein said board is made of a thermoplastic polymer selected from the group consisting of olefins, styrenes, vinyl chlorides, acrylics, polycarbonates and ethylene terephthalates.

8. The light weight hollow thermoplastic board of claim 7 wherein said thermoplastic polymer is selected from the group consisting of polypropylenes, linear polyethylene, branched polyethylene and copolymers thereof.

9. A process for producing a light weight hollow thermoplastic board having a first planer sheet and a second planer sheet which are spaced apart by and interconnected by longitudinally extended ribs, which comprises:

extruding molten thermoplastic through an extruder having a die assembly with a die with a cavity having a cross-section corresponding to a desired external shape of a thermoplastic board and having mandrels within said cavity to create a soft board having a plurality of passageways and extended ribs between a first planer sheet and a second planer sheet, such that thermoplastic is extruded at a first planar sheet area, a second planar sheet area and a rib area;

introducing a blowing agent into thermoplastic being extruded at said rib area so as to create gas pockets in said thermoplastic being extruded at said rib area; and

,

advancing the resulting soft board to a sizer and cooler assembly to set the first dimensions of the soft board, to cool it to a rigid board and to establish a plurality of locationally fixed gas pockets in said extended ribs.

10. The process of claim 9 wherein said blowing agent is a physically introduced blowing gas.

11. The process of claim 10 wherein said blowing agent is introduced into said rib area thermoplastic at pressure above ambient pressure.

12. The process of claim 10 wherein said blowing agent is selected from the group consisting of carbon dioxide, nitrogen and inert gases.

13. The process of claim 9 wherein said blowing agent is a chemical blowing agent.

14. The process of claim 13 wherein there are separate thermoplastic feed hoppers for said sheet area and said rib area, and said blowing agent is introduced into said thermoplastic that is fed through said feed hopper for said rib area.

15. The process of claim 13 wherein said blowing agent is elected from the group consisting of organic blowing agents and inorganic blowing agents.

16. The process of claim 15 wherein blowing agent is an organic blowing agent selected from the group consisting of azodicarbonamide, N,N′

-dinitrosopentamethylene tetramine, N,N′

-dinitroso-N,N′

-dimethyl terephthal amide, benzene sulfonyl hydrazide, benzne-1,3-disulfohydrazide, and terephthalic azide.

17. The process of claim 15 wherein said blowing agent is added to thermoplastic for the rib area of extrusion in an amount of about 0.01 to about 5% based on total weight.

18. The process of claim 9 wherein said process further includes annealing said rigid board in an oven.

19. The process of claim 9 wherein said board is made of thermoplastic polymer selected from the groups consisting of olefins, styrenes, vinyl chlorides, acrylics, carbonates and ethylene terephthalates.

20. The process of claim 19 wherein said thermoplastic polymer is selected from the group consisting of the group consisting of polypropylenes, linear polyethylene, branched polyethylene and copolymers thereof.