Rotational moulding process

• US 6,180,203 B1
• Filed: 10/14/1998
• Issued: 01/30/2001
• Est. Priority Date: 04/09/1997
• Status: Expired due to Fees

• Current Assignee: Linpac Mouldings Limited (Strategic Value Partners LLC)
• Original Assignee: Linpac Mouldings Limited (Strategic Value Partners LLC)
• Inventors: Unkles, Peter J.
• Primary Examiner(s): Kuhns, Allan R.
• Application Number:
  US09/171,237
• Time in Patent Office: 839 Days
• Field of Search: 264/45.7, 264/310, 264/311, 264/911, 264/920, 264/54, 264/45.3, 428/71, 428/304.4, 428/313.3, 428/316.6, 428/903.3, 404/25, 108/51.11
• US Class Current: 428/71
• CPC Class Codes: B29C 41/003 characterised by the choice of material
• CPC Class Codes: B29C 41/04 Rotational or centrifugal casting, i.e. coating the inside of a mould by rotating the mould
• CPC Class Codes: B29C 41/20 incorporating preformed parts or layers, e.g. moulding inserts or for coating articles
• CPC Class Codes: B29C 44/043 using a rotating mould
• CPC Class Codes: B29C 44/445 in the form of expandable granules, particles or beads
• CPC Class Codes: B29K 2105/251 Particles, powder or granules expandable particles B29K2105/046
• CPC Class Codes: B29K 2105/26 Scrap or recycled material
• CPC Class Codes: B32B 1/00 Layered products having a non-planar shape
• CPC Class Codes: B32B 2250/04 4 layers
• CPC Class Codes: B32B 2250/242 All polymers belonging to those covered by group B32B27/32
• CPC Class Codes: B32B 2250/40 Symmetrical or sandwich layers, e.g. ABA, ABCBA, ABCCBA
• CPC Class Codes: B32B 2266/025 Polyolefin vinyl or acrylic copolymers B32B2266/0221, B32B2266/0242
• CPC Class Codes: B32B 2272/00 Resin or rubber layer comprising scrap, waste or recycling material
• CPC Class Codes: B32B 2307/4026 within the layer by addition of a colorant, e.g. pigments, dyes
• CPC Class Codes: B32B 2307/41 Opaque
• 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 3/085 spaced apart pieces on the surface of a layer
• CPC Class Codes: B32B 5/20 foamed in situ
• CPC Class Codes: B32B 5/32 at least two layers being foamed and next to each other
• CPC Class Codes: B32B 7/027 : Thermal properties
• CPC Class Codes: Y10S 264/911 : Recycling consumer used articles or products
• CPC Class Codes: Y10T 428/233 : Foamed or expanded material encased
• CPC Class Codes: Y10T 428/249953 : Composite having voids in a component [e.g., porous, cellular, etc.]
• CPC Class Codes: Y10T 428/249971 : Preformed hollow element-containing
• CPC Class Codes: Y10T 428/249981 : Plural void-containing components

Abstract

A method for rotational molding of articles, including the step of rotationally molding a mixture of particulate plastics material comprising at least one thermoplastics material having a first particle size and a second thermoplastics material having a larger particle size wherein, in use, said first thermoplastic material fuses to form an outer skin and subsequently said second thermoplastics material fuses to form an inner skin bonded to the outer skin of a resultant molded article. The method may also include the step of incorporating a quantity of rollable molded reinforcing elements in the mold with said first and second thermoplastics materials, wherein the reinforcing elements are located in a spaced array thereby forming bridges between opposed inner skin surfaces as they expand. Articles, such as a shipping pallet, rotationally molded using the method are also disclosed.

Claims

1. A method for rotational moulding of articles, comprising the steps of:

(a) rotationally moulding a mixture of particulate plastic material including at least one thermoplastic material having a first particle size and a second thermoplastic material comprised of a reclaimed plastic material and having a larger particle size;

said second thermoplastic material having a melt temperature higher than the melt temperature of the first thermoplastic material, said first thermoplastic material being homopolymeric, and said second thermoplastic material being a mixture of polymeric species;

(b) wherein, in use, said first thermoplastic material fuses to form an outer skin and subsequently said second thermoplastic material fuses to form an inner skin bonded to the outer skin of a resultant moulded article.

2. A method for rotational moulding of articles as claimed in claim 1, wherein the second thermoplastic material includes a quantity of thermosetting polymeric material.

3. A method for rotational moulding of articles as claimed in claim 1, wherein the second thermoplastic material includes a quantity of foaming agent.

4. A method for rotational moulding of articles as claimed in claim 3, wherein the foaming agent has a decomposition temperature greater than the melt temperature of the second thermoplastic material.

5. A method for rotational moulding of articles as claimed in claim 1, wherein the second thermoplastic material includes a quantity of filler material.

6. A method for rotational moulding of articles as claimed in claim 1, wherein particles of the second thermoplastic material include an adhesion resistant coating to reduce adhesion between the second thermoplastic material and the first thermoplastic material during the fusing of the outer skin.

7. A method for rotational moulding of articles, comprising the steps of:

(a) rotationally moulding a mixture of particulate plastic material including at least one thermoplastic material having a first particle size and a second thermoplastic material comprised of reclaimed plastics material and having a larger particle size, said second thermoplastic material having a melt temperature higher than the melt temperature of the first thermoplastic material, said first thermoplastic material being homopolymeric, and said second thermoplastic material being a mixture of polymeric species; and

(b) incorporating a quantity of rollable moulded reinforcing elements in the mold with said first and second thermoplastic material;

(c) wherein, in use, said first thermoplastic material fuses to form an outer skin and subsequently said second thermoplastic material fuses to form an inner skin bonded to the outer skin of a resultant moulded article and wherein the reinforcing elements are located in a spaced array thereby forming bridges between opposed inner skin surfaces as they expand.

8. A method for rotational moulding of articles as claimed in claim 7, wherein the reinforcing elements are larger than the particle size of the second thermoplastic material.

9. A method for rotational moulding of articles as claimed in claim 7, wherein the reinforcing elements are mechanically engaged between the opposed inner skin surfaces.

10. A method for rotational moulding of articles as claimed in claim 8, wherein the reinforcing elements are at least partially fused to said opposed inner skin surfaces.

11. A method for rotational moudling of articles as claimed in claim 7, wherein the reinforcing elements include an adhesion resistant coating to reduce adhesion between the reinforcing elements and the first and second thermoplastic material during the fusing of said skins.

12. A method for rotational moulding of articles as claimed in claim 7, wherein the reinforcing elements include an adhesion resistant additive to reduce adhesion between the reinforcing elements and the first and second thermoplastic material during the fusing of said skins.

13. A method for rotational moulding of articles as claimed in claim 7, wherein the reinforcing elements are comprised of plastic material.

14. A method for rotational moulding of articles as claimed in claim 7, wherein the reinforcing elements are comprised of ceramic material.

15. A rotationally moulded article of manufacture comprising an outer skin and an inner skin which article is manufactured using the rotational moulding method claimed in claim 7.

16. A rotationally moulded article of manufacture comprising an outer skin and an inner skin which article is manufactured using the rotational moulding method claimed in claim 7.

17. A rotationally moulded article of manufacture, comprising a shipping pallet, manhole cover, tank lid, or utility pit cover, said article comprising an outer skin, an inner skin and a quantity of rollable moulded reinforcing elements forming bridges between opposed inner skin surfaces when manufactured using the rotational moulding method claimed in claim 7.