GB2113699A

GB2113699A - Composite material

Info

Publication number: GB2113699A
Application number: GB08300894A
Authority: GB
Inventors: Frank Peter Wadeson
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-01-27
Filing date: 1983-01-13
Publication date: 1983-08-10
Also published as: GB2113699B; GB8300894D0

Abstract

A composite material comprises pieces of an expanded substance, such as polystyrene vermiculite or perlite, secured together by a flexible polyurethane material cured substantially in the absence of water. High performance packaging material may be formed from such a composite including precisely dimensioned, large polystyrene beads. A method of forming these composites is also disclosed.

Description

SPECIFICATION Composite material This invention relates to a composite material comprising pieces of an expanded substance bound together by an adhesive.

It is known to produce moulded articles by coating beads or kibbled pieces of expanded polystyrene with a polyurethane prepolymer and curing the resulting mixture under pressure with steam. The use of steam causes rapid polymerisation and results in short moiecules of polyurethane. The composite therefore has a comparatively weak structure.

According to a first aspect of the present invention a composite material comprises pieces of an expanded substance secured together by a flexible polyurethane material cured substantially in the absence of water.

The expanded substance may comprise polystyrene beads, pieces of vermiculite or pieces of perlite. Alternative substances may be used having the desirable properties of low density, resilience, low cost and optionally, good thermal insulation, fire resistance and water resistance. Use of beads of expanded polystyrene is especially preferred.

Preferably the expanded substance has the form of precisely dimensioned pieces such as beads each having a similar dimension. Composite materials in accordance with this preferred feature of the invention find application as high performance packaging materials. Use of irregularly dimensioned or kibbled pieces does not facilitate production of composites having predetermined and reproducible properties.

Preferably large pieces such as large beads having a diameter greater than 1 cm are employed since resilience of the composite is enhanced and hitherto unobtainable low density composites may be produced. Alternatively a precise mixture of large beads and smaller beads may be employed, the smaller beads serve to occupy the interstices between the larger beads.

Preferably a material in accordance with the invention comprises a cold-cured, flexible polyurethane, that is it may be cured at ambient temperatures.

It may be unnecessary to compress materials in accordance with this invention during their formation. Light compression such as tamping may be preferable to ensure that the composite adopts the shape of the mould, but compression is unnecessary to cause the pieces of expanded substance to bind together. The composite may therefore be tamped into position in a mould and may then be allowed to cure without compression. Use of expensive compression equipment is thereby avoided.

Materials in accordance with this invention may either comprise open interstices not occupied by the polyurethane or may be completely filled giving a harder product.

Polyurethane prepolymers which are preferred for use in accordance with this invention comprise pure methyl diphenyl diisocyanate. The latter material is less toxic than the commonly used toluene diisocyanate.

According to a second aspect of the present invention there is provided a method of forming a composite material comprising coating pieces of an expanded substance with a prepolymer and cure the prepolymer substantially in the absence of water to form a flexible polyurethane material. The curing may also be caused to occur at an ambient temperature.

The constituents of the composite may be mixed together using a worm screw or any other convenient means.

The method may further comprise use of a polyurethane prepolymerformulation which incorporates a catalyst. Any conventional polyurethane catalyst may be used, triethylene diamine being preferred.

Composite materials in accordance with this invention preferably comprise between 10% and 90% by weight of polystyrene and between 90% and 10% of polyurethane. More preferably the materials comprise between 30% and 50% by weight of polystyrene and between 70% and 50% of polyurethane.

Materials in accordance with this invention find many applications. Polystyrene/polyurethane composites are good shock absorbent packaging materials. Moulding of the materials may be carried out in cardboard boxes, wooden moulds, plastic moulds, hardboard moulds or in any other convenient container. Moulding may be performed in a container with an article to be packaged in situ.

Sheets or blocks of the material may be provided with surface layers of other materials such as foamed plastics, to provide a softer cushioning surface layer and to prevent loss of pieces of the expanded material. Alternatively surface layers of metal foil, paper or plastics film may be conveniently provided.

Composites in accordance with this invention may be easily cut with a hot wire. Intricate convoluted and recurved shapes may be produced by this means.

Materials in which the interstices between the pieces are filled with polyurethane may be used for car bumpers, boat fenders or for other applications in which it is necessary to withstand heavy shocks.

Such materials may have surface layers of rubber or of a hard elastomer.

Materials having open interstices may find use as a drainage medium for agricultural purposes or as a filter for water supplies.

Materials in accordance with the invention also find application as energy absorbent padding, for example in the interior of vehicles.

The formation of the composite at ambient tem- peratures may be exploited in formation of orthopaedic appliances such as seating. A patient may sit upon a bag containing the uncured material and remain there while curing takes place. The resultant structure would conform to the contours of the patient's body.

The invention is further described by means of Example.

Example 1 Polystyrene beads (21.25 g, 1 cm in diameter) were coated by stirring with a freshly prepared three component polyurethane elastomer formulation (Castomer E.S. 725, manufactured by Baxenden Chemical Co. Limited). The formulation comprised a first component "RES 1" (25.85 gm, a blend of polyols and catalysts with a viscosity of 6000 cps at 25"C), a second component "RES 2" (2.58 gm a chain extender having a viscosity of 1500 cps at 25"C) and a third component "ISO" (18.48 gm, an isocyanate terminated prepolymer with a viscosity of 1500 cps at 25"C). The mixture of beads and elastomer formulation was placed in a mould and allowed to stand under light compression for 3 hours at 20"C.

The resultant composite was a flexible mass which could be compressed to half of its size without causing permanent deformation.

Example 2 Example 1 was repeated with the polystyrene beads blown into a spray of the polyurethane formulation. The product exhibited similar properties.

Example 3 Example 1 was repeated with the addition of the catalyst, triethylamine diamine (0.5 g, DABCO DL33).

The resultant mixture set during the course of a few minutes. This formulation was found to be suitable for packaging of articles in situ.

Example 4 An alternative composition comprised polystyrene beads coated with a mixture containing Diprane 52 (100 parts w/w), Diprane C52 (167.3 parts w/w) and Diprane C (12.7 parts w/w). The mixture of beads and elastomer was placed in a mould and allowed to stand under light compression for 3 hours at 20"C.

The resultant composite was flexible and couid be compressed without permanent deformation.

Claims

1. A composite material comprising pieces of an expanded substance secured together by a flexible polyurethane material cured substantially in the absence of water.

2. A composite material as claimed in claim 1, wherein the expanded substance comprises polystyrene, vermiculite or perlite.

3. A composite material as claimed in claim 2, wherein the expanded substance comprises beads of expanded polystyrene.

4. A composite material as claimed in claim 3, comprising beads of expanded polystyrene each having a similar dimension.

5. A composite material as claimed in claim 4, comprising beads having a diameter greater than 1 cm.

6. A composite material as claimed in claim 3, comprising beads of two different sizes.

7. A composite material as claimed in any preceding claim, comprising a polyurethane material which has been cured at an ambient temperature.

8. A composite material as claimed in any preceding claim, wherein interstices between the pieces of expanded material are open to passage of air.

9. A composite material as claimed in any of claims 1 to 7, wherein interstices between the pieces of expanded material are filled with polyurethane.

10. A composite material as claimed in any of claims 3 to 9, comprising between 10% and 90% by weight of polystyrene and between 90% and 10% by weight of polyurethane.

11. A composite material as claimed in claim 10, comprising between 30% and 50% by weight of polystyrene and between 70% and 50% by weight of polyurethane.

12. A packaging material in accordance with any of claims 1 to 11.

13. A composite material as claimed in any of claims 1 to 11, comprising a surface layer of foamed plastics material, non-foamed plastics material, metal foil paper or rubber.

14. An orthopaedic appliance comprising composite material as claimed in any of claims 1 to 11 or 13.

15. A method of foaming a composite material comprising coating precisely dimension l pieces of an expanded substance with pieces of a prepolymer and curing the prepolymer substantially in the absence of water to form a flexible polyurethane material.

15. A method of foaming a composite material comprising coating pieces of an expanded substance with pieces of a prepolymer and curing the prepolymer substantially in the absence of water to form a flexible polyurethane material.

16. A method as claimed in claim 15, wherein the said substance comprises polystyrene, vermiculite or perlite.

17. A method as claimed in claim 16, wherein the said substance comprises beads of polystyrene.

18. A method as claimed in claim 17, wherein the beads each have a similar dimension.

19. A method as claimed in claim 18, wherein the beads have a diameter greater than 1 cm.

20. A method as claimed in any of claims 15 to 19, wherein the prepolymer is cured at an ambient temperature.

21. A method as claimed in any of claims 15 to 20 wherein the material is not compressed during curing.

22. A method as claimed in any of claims 15 to 21 ,wherein the prepolymer incorporates methyl phenyl diisocyanate.

23. A method as claimed in any of claims 15 to 22, wherein the prepolymer includes a catalyst.

24. A method as claimed in claim 23, wherein the catalyst comprises triethylamine diamine.

25. A composite material in accordance with claim 1 substantially as hereinbefore described.

26. A method in accordance with claim 15 substantially as hereinbefore described.

New claims or amendments to claims filed on 28 April 1983 Superseded claims 1 and 15 New or amended claims

1. A composite material comprising precisely dimensioned pieces of an expanded substance secured together by a flexible polyurethane material cured substantially in the absence of water.