GB2117776A

GB2117776A - Silicate-containing polyisocyanate-expanded polymer composite

Info

Publication number: GB2117776A
Application number: GB08301626A
Authority: GB
Inventors: Frank Peter Wadeson
Original assignee: EPSILON DEV Ltd
Current assignee: EPSILON DEV Ltd
Priority date: 1982-01-23
Filing date: 1983-01-21
Publication date: 1983-10-19
Also published as: GB8301626D0

Abstract

Composites comprise a major proportion of pieces of expanded polymer, e.g. polystyrene, a polyolefine, polybutadiene, polyisoprene or polytetrafluoroethylene, secured together by an adhesive comprising a non-foamed polyisocyanate formed from one or more isocyanate prepolymers and an aqueous alkali metal silicate solution, a proportion of said prepolymers incorporating non-ionic hydrophilic groups. Use of polystyrene is preferred. The composites are characterised by rigidity, good insulating properties economy of manufacture and fire resistance.

Description

SPECIFICATION Silicate-containing polyisocyanate-polyalkene composite This invention relates to a composite material comprising pieces of expanded polyalkene bound together by means of an adhesive comprising polyisocyanate and aqueous silicate. Synthetic resins comprising polyisocyanates and aqueous silicate are disclosed in U.K. Patent Specification No.

1421894.

According to the present invention a composite material comprises a major proportion of pieces of expanded polyalkene secured together by an adhesive comprising a non-foamed polyisocyanate formed from one or more isocyanate prepolymers and an aqueous alkalai metal silicate solution, a proportion of said prepolymers incorporating nonionic hydrophilic groups.

The polyalkene may comprise a polymer of any one or more alkenes, including polystyrene, polyethylene, polypropylene, polybutadiene, polyisoprene, polytetrafluoroethylene and copolymers thereof. Polystyrene is particularly preferred.

The pieces of polyalkene are preferably in the form of beads although non-spherical pieces such as granules, spirals or other shapes may be employed.

Preferably the polyalkene occupies not less than half of the volume of the composite. The polyalkene is therefore present in a greater proportion than it would be if it was used as a filler.

The polyalkene pieces are preferably at least partially coated with the adhesive, forming a composite in which interstices between the pieces are not occupied. The composite may have some of the properties of an open-celled foam. Production of composite does not have the difficulties inherent in foam production which arise due to uneven foaming and poor reproducibility.

The proportion of the space between the pieces of expanded polyalkene which is occupied by polyisocyanate adhesive governs the density of the resultant composite. When a dense product is required for constructional purposes, a large amount of adhesive is employed. Preferably not more than 50% of the space between the pieces is occupied by the adhesive.

Expanded polystyrene beads have a density of between 8 to 40kgm-3, usuaily approximately 16 kgm-3. Use of sufficient adhesive to fully occupy the interstices between the beads results in a composite having a density of roughly 320 kgm-3. Use of expanded polystyrene beads at a density of 16 kgm-3 with sufficient adhesive to produce a composite having a density of 170 kgm-3would result in the composite having approximately half of the space between the beads occupied by adhesive.

Composites which are particularly preferred in accordance with this invention comprise polystyrene beads at a density of 8 to 40 kgm-3 secured together by adhesive as hereinbefore defined, the composite having a density not greater than 170 kgm-3.

Composite materials preferred for use as insulating material comprise a density of polystyrene of 16 kgm-3 together with sufficient adhesive to securely bind the beads.

Composite materials preferred for use as packag ing material comprises a density of polystyrene of 32 kgm-3 together with adhesive at a density of 48 to 64 kgm-3 of adhesive or less.

Composite materials preferred for use as constructional panels comprise a similar density of polystyrene but between 64 to 80 kgm-3 of adhesive.

Hitherto block of expanded polystyrene have been manufactured by compacting and fusing beads of the foamed polymer by the influence of steam. It has only been possible to compact and fuse beads below a certain maximum size by use of such a process.

The present invention provides a means of overcoming this difficulty.

The aqueous alkali metal silicate solution may comprise the solution sold commercially as "waterglass". Preferred aqueous alkali metal silicate solutions have an average viscosity at 20"C of the order of 4000 Centipoises. Solutions which are very viscous are difficult to mix into a reaction mixture and excessively dilute solutions have the drawback that excess water must usually be removed from the product by evaporation. Preferred solution have a mean molecular ration of SiO2/M2O of 2 (where M is the alkali metal). The mean total solids may comprise between 42% and 55% of the weight of the solution and preferably represent between 46% and 50% of the weight of the solution. Preferably sodium containing silicate solutions are used.

The polyisocyanate is preferably prepared from a mixture of isocyanate prepolymers which contains isocyanate prepolymers incorporating non-ionic hydrophilic groups, the latter being in the proportion of between 1% and 99% by weight of the total prepolymers. More preferably the isocyanate prepolymers incorporating non-ionic hydrophilic groups comprise between 40% and 60% by weight of the total prepolymers.

The most preferred prepolymers mixture incorporates 50% by weight of non-ionic hydrophilic isocyanate prepolymer.

Many isocyanate prepolymers including prepolymers incorporating non-ionic hydrophilic groups are known from the prior art. Prepolymers which may be incorporated in the present invention may be prepared by conventional methods, for example those disclosed at page 4 line 102 to page 5 line 88 of U.K. Patent Specification No. 1421894.

Catalysts may be employed to prepare adhesives in accordance with the present invention. They may be known catalysts for example those disclosed at lines 9 to 61 of page 10 of U.K. Patent Specification No.1421894.

Surface active compounds may also be used as catalysts. These may include sodium alkyl sulphates such as sodium lauryl sulphate, for example Empicol ESB 3, Empicol BSO 3 manufactured by Albright and Wilson Limited, sodium alkyl ether sulphates such as sodium lauryl ether sulphate. for example Empimin KSN 70, Empimin DSM 30 and Empimin KSM 27 manufactured by Al bright and Wilson Limited; aqueous alkyl betaines, for example Empigen BB manufactured by Albright and Wilson Limited; alkyl amido propyl dimethyl amine betaine, for Example Empigen BT manufactured by Albright and Wilson Limited.

The catalysts are generally used in quantities of between 0.0001 and 10% by weight, based on the quantity of the prepolymers.

Composite materials in accordance with this invention possess many advantages. They are effective thermal insulators and have rigid and fire resistant structures which do not melt. The composites are also economical to manufacture, particularly since constructional panels constructed therefrom do not require provision of battening or other supports. The composites are also electrically conductive float in water and may be porous to water.

Fire resistance is an important property since fine expanded polystyrene melts and burns very easily.

The surfaces of materials in accordance with the invention do not burn but char forming afire resistant carbon-siiica coatings. Fire resistance increased with the proportion of adhesive and with increasing proportions of silicate.

Inert fillers may be included in composites in accordance with this invention.

The fillers may be selected from any of these commonly used, for example, those disclosed at page 14 lines 24-65 of U.K. Patent Specification No.

1421894.

Barytes is a particularly advantageous filler, having the advantage of imparting radiation absorbing properties to the composite. Barium or lead containing fillers such as barytes, lead powder or lead oxide find application in formation of constructional panels for use as screens for X-rays or other types of ionising radiation. Barytes filler for example may partially replace the silicate used in the composite, for example a composite may contain 1 part of isocyanate, 1 part silicate and 1.25 parts of barytes.

Laminations, for example of metal foil or sheet hardboard, glass, reinforced polyester, asbestos, cement sheet or any other convenient material, may be applied to the surface of a composite material constructed in accordance with the invention. It may not be necessary to apply additional adhesive to secure such a lamination.

The expanded polyalkene may be coated with the adhesive by blowing the pieces through a spray of the adhesive. The pieces may then be compressed for 15 minutes or less to form the composite material. Heavy compression is unnecessary. Mixing may also be performed in a wormscrew apparatus.

An application of composites in accordance with this invention particularly including expanded polystyrene is for construction of panels for temporary buildings. Such buildings may be of the kind used as site huts for building workers or emergency accommodation or factory built modular houses. The panels may be constructed by injection of an uncured composite comprising the adhesive and polystyrene beads into the cavities between inner and outer skins of the panels. The skins may be composed of wood, for example plywood. Adhesion of the composite to the skins strengthens the panels and makes it unnecessary to provide battens between the skins. The thicknesses of the skins may also be reduced. The fire resistant properties of the composite serve to increase the fire resistance of the panels. Thermal insulation and rigidity are also enhanced.

The following Examples illustrate the invention.

Example 1 Polystyrene beads (85gm) were coated with a mixture of sodium silicate (129.59,50% w/w solids, molecular ratio of SiO2/Na2O = 2.07, viscosity = 4000 Centipoises), 4,4'-diphenylmethane diisocyanate (28.89) and hydrophilic group containing isocyanate, prepolymer (Isocyanate 2401, Bayer Chemicals 28.8g) The mixture was placed under light compression in a mould for 15 minutes, the resultant material was removed and the latter allowed to stand for 3 days before testing. The resultant material was found to have a density of 46.9kgm-3 and aflexural strength of 152 KNm-2. The hardness was determined by measuring the force required to compress a 5cm cube of the material by 10%, the result being 15900 kgm-2.Theflexural strength was determined in accordance with BSS 4370 the result being 150 KNm-2. The Kvalue measured in accordance with BS 874-1973 Appendix C, was 0.0405 W m-1 OK-1 > Different proportions of the same materials and the same procedure were used in the following Examples.

Example 2 Polystyrene beads (859), were coated with a mixture of isocyanate prepolymer (39.19), 4,4'- diphenylmethane diisocyanate (39.19), and sodium silicate (176.19). The resultant material was found to have a density of 59.3Kgm-3.

Example 3 Polystyrene beads (859), were coated with a mixture of isocyanate prepolymer (48.99), 4,4'- diphenylmethane diisocyanate (48.99), and sodium silicate (220.19). The resultant material was found to have a density of 70.0kgm-3.

Example 4 Polystyrene beads (85g) were coated with a mixture of isocyanate prepolymer (58.79), 4,4'- diphenylmethane diisocyanate (58.79), and sodium silicate (264.29). The resultant material was found to have a density of 79.5kgm-3. The hardness of the resultant material determined as described in Example 1 was 20500 kgm-2. The fiexural strength was 270KN m-2 and the K value was 0.046 Wm-1 K-1.

Example 5 Polystyrene beads (859), were coated with a mixture of isocyanate prepolymer (78.09), 4,4'- diphenylmethane diisocyanate (78.0g), and sodium silicate (351.39). The resultant material was found to haveadensityof104.1 kgm-3.

Example 6 Polystyrene beads (85g), were coated with a mixture of isocyanate prepolymer (1209), 4,4'- diphenylmethane diisocyanate (1209), and sodium silicate (5409). the resultant material was found to have a density of 149kgm-3.

Example 7 Polystyrene beads (859) were coated with a mixture of isocyanate prepolymer (1689),4,4'- diphenylmethane diisocyanate (756g). The resultant material was found to have a density of 207kgm-3.

Example 8 Polystyrene beads (85g), were coated with a mixture of isocyanate prepolymer (227g), 4,4'- diphenylmethane diisocyanate (2279). and sodium silicate (1021g). The resultant material was found to have a density of 274kgm-3.

Example 9 Polystyrene beads (85g), were coated with a mixture of isocyanate prepolymers (2729), 4,4'- diphenylmethane diisocyanate (2729), and sodium silicate (1225g). The resultant material was found to have a density of 330kgm-3.

Example 10 Polystyrene beads (11 0g) were coated with a mixture of isocyanate prepolymer (309), 4,4'- diphenylmethane diiscyanate (309), and sodium silicate (135 g). The resultant material was found to have a density of 53 kgm-3 Example 11 Polystyrene beads (859), were coated with a mixture of isocyanate prepolymer (25.49), 4,4'- diphenylmethane diisocyanate (25.49), and sodium silicate (203.59). The resultant material was found to have a density of 58.3kgm-3.

Example 12 Polystyrene beads (859), were coated with a mixture of isocyanate prepolymer (509, Desmodur VL, Bayer Chemicals) 4,4'-diphenylmethane diiso cyanate (50g, Desmodur 2401, Bayer Chemicals), sodium silicate (100g, "125", Crossfield Chemicals, Warrington) and barytes (170g, J. Alcock Ltd.) The resultant material was found to have a density of 88.1 kgm-3. The material exhibited a flexural strength (BSS 4370) of 361 KNm-2 and a hardness as hereinbefore defined of 25000 kgm-2.

Materials produced in accordance with these Examples were tested for flame and heat resistance.

Specimens in accordance with each Example were heated for 2 minutes with the blue tip of a bunsen burner flame after which the flame was removed.

Dripping did not occur with any of the heated materials. Materials having a density less than 80kgm-3 were penetrated to a considerable depth by the flame and continued to burn for less than 30 seconds after removal of the flame. The denser materials did not burn after removal of the flame and those materials having a density in excess of 270kgm-3 were not penetrated by the flame.

Specimens of the materials were placed on a hot plate and the temperature of the latter was raised to 300"C during a period of 5 hours. A control sample of expanded polystyrene melted completely. The materials in accordance with the invention did not melt but were superficially charred.

Specimens in accordance with the invention were found to lose up to 10% oftheirweight upon heating in an oven for 5 hours at 50"C. No shrinkage of the specimens occurred.

Claims

1. A composite comprising a major proportion of pieces of expanded polyalkene secured together by an adhesive comprising a non-foamed polyisocyanate formed from one or more isocyanate prepolymers and an aqueous alkali metal silicate solution, a proportion of said prepolymers incorporating nonionic hydrophilic groups.

2. A composite as claimed in claim 1, wherein the alkali metal silicate solution has an average viscosity at 20"C of 4000 centipoises.

3. A composite as claimed in claim 1 or 2, wherein the alkali metal silicate solution has a mean molecular ratio of SiO2/M2O (where M is the alkali metal) of 2.

4. A composite as claimed in any preceding claim, wherein the mean total solids of the alkali metal silicate solution comprises 42% to 55% by weight of the said solution.

5. A composite as claimed in claim 4, wherein the said mean total solids comprises 46% to 50% by weight of the metal silicate solution.

6. A composite as claimed in any preceding claim, comprising sodium silicate solution.

7. A composite as claimed in any preceding claim, wherein the proportion of prepolymer incorporating non-ionic hydrophilic groups comprises 1% to 99% by weight of the prepolymers.

8. A composite as claimed in Claim 7, wherein the proportion of prepolymer incorporating nonionic hydrophilic groups comprises 40% to 60% by weight of the total prepolymers.

9. A composite as claimed in claim 8, wherein the proportion of prepolymer incorporating nonionic hydrophilic groups comprises 50% by weight of the total prepolymers.

10. A composite as claimed in any preceding claim, wherein the prepolymer incorporating nonionic hydrophilic groups is derived from a mono- or polyhydroxyl polyether.

11. A composite as claimed in claim 10, wherein the polyether is mixed with a polyhydric alcohol having a molecular weight below 400.

12. A composite as claimed in any preceding claim, wherein the prepolymer comprises one or more polyisocyanates selected from tolylene-2,4diisocyanate, tolylene-2,6-diisocyanate, polyphenylpolymethylene polyisocyanate, or modified polyisocyanates containing carbodiimide groups, urethane groups, allophanate groups, isocyanurate groups, urea groups or biuret groups.

13. A composite as claimed in any of claims 10 to 12, wherein the polyether contains terminal OH groups and which has been derived from a mono, di or trihydroxy alcohol and ethylene oxide and/or propylene oxide.

14. A composite as claimed in claim 13, including a monofunctional polyether derived from monohydric alcohol having a molecular weight of from 32 to 300 and ethylene oxide.

15. A composite as claimed in any preceding claim, wherein the adhesive includes a catalyst comprising a tertiary amine.

16. A composite as claimed in any preceding claim, wherein the adhesive includes a catalyst selected from: a silaamine, a tetraalkylammonium hydroxide, alkali metal hydroxide, alkali metal phenoxide, alkali metal alkoxide or hexahydrotriazine.

17. A composite as claimed in any preceding claim, wherein the adhesive includes a catalyst comprising an organic tin compound.

18. A composite as claimed in any preceding claim wherein the adhesive includes a catalyst comprising a surface active compound.

19. A composite as claimed in claim 18, including sodium alkyl sulphate, sodium alkyl ether or aqueous alkyl betaine.

20. A composite as claimed in any of claims 15 to 19, wherein the adhesive comprises between 0.0001% and 10% by weight of catalyst based on the quantity of prepolymer.

21. A composite as claimed in any preceding claim, wherein the polyalkene is selected from polystyrene, polyethene, polypropylene, polybuty lene, polybutadiene, polyisoprene, polytetraf- luoroethylene or copolymers thereof.

22. A composite as claimed in claim 21, wherein the polyalkene is polystyrene.

23. A composite comprising beads of a polyalkene material and an adhesive as claimed in any preceding claim.

24. A composite as claimed in any preceding claim, comprising not less than 50% by voiume of polyalkene.

25. A composite as claimed in any preceding claim, wherein interstices between said pieces are not occupied by said adhesive.

26. A composite as claimed in claim 25, wherein not more than 50% of the space between the pieces is filled by said adhesive.

27. A composite as claimed in claim 26, comprising a density of polystyrene of 8 to 40 kgm-3 and of adhesive of not more than 170 kgm-3.

28. A composite as claimed in any preceding claim, including a filler comprising barytes.

29. A composite as claimed in any preceding claim, having a lamination applied to the surface thereof.

30. A composite as claimed in claim 29, wherein the lamination comprises metal foil, metal sheet, hardboard, glass, reinforced polyester, asbestos cement sheeting.

31. A packing material comprising a composite as claimed in preceding claims.

32. A packing material as claimed in claim 31, having a density of polystyrene of 16 kgm-3 and a density of adhesive of not more than 64 kgm-3.

33. A packing material as claimed in claim 32, having a density of adhesive of not more than 48 kgm-3.

34. A constructional panel comprising a composite as claimed in any preceding claim.

35. A panel as claimed in claim 34, having a density of polystyrene of 32 kgm-3 and a density of adhesive of between 64 and 80 kgm-3.

36. An insulating material comprising a composite as claimed in any preceding claim.

37. A building comprising panels incorporating a composite as claimed in claims 34 or 35.

38. A composite as claimed in claim 1 substantially as hereinbefore described.

39. A composite as claimed in claim 38 substantially as described in any of the Examples.