GB2260512A

GB2260512A - Laminated window

Info

Publication number: GB2260512A
Application number: GB9121986A
Authority: GB
Inventors: Robert S Bruce; Pierre Chaussade
Original assignee: SULLY PRODUITS SPECIAUX; Triplex Aircraft and Special Products Ltd; Pilkington Aerospace Ltd
Current assignee: SULLY PRODUITS SPECIAUX; GKN Aerospace Transparency Systems Kings Norton Ltd
Priority date: 1991-10-16
Filing date: 1991-10-16
Publication date: 1993-04-21
Also published as: GB9121986D0

Abstract

A laminated window for use over a wide range of operating temperatures includes a layer of hard polyvinylbutyral (4, 6) and a layer of glass (2, 3), with an intermediate layer of a further interlayer material therebetween characterised by the inclusion of a separator (10, 11, 12, 13) between the said layer of glass and the hard polyvinylbutyral around the periphery thereof. <IMAGE>

Description

LAMINATED WINDOW The invention relates to windows incorporating a polyvinylbutyral interlayer and required to operate over a wide temperature range in service, and to a method of producing such windows.

Polyvinylbutyral is used as an interlayer material because of its strength and ability to absorb energy in the event of an impact on the window. Where high strength is required, for example in aircraft windows required to withstand bird impact, it is usual to use polyvinylbutyral containing no more than a small proportion (up to 25 typically about zOr) of plasticiser. Polyvinylbutyral containing up to 95,-'.' plasticiser is hereinafter referred to as "hard polyvinylbutyral".Unfortunately, such hard polyvinylbutyral tends to be insufficiently flexible at low teopert-tures, especially temperatures below 5"C, and it is thus common to use it in combination with other interlayer materials such as polyurethane, see for example UK patent specifications 1,529,109 and 2,134,445A.

UK patent 1,529,109 is concerned with the problem of "cold chipping" in aircraft windscreens. Cold chipping is likely to cccur when an interlayer of hard polyvinylbutyral is used in contact with an outer glass ply, or with a glass ply having an electroconductive coating on its inner surface for heating the window, in a windscreen required to operate over a wide range of temperature (say -65 C to +700C). It occurs as a result of differential contraction between the polyvinylbutyral and the glass resulting in the polyvinylbutyral plucking chips out of the glass surface around the periphery of the area common to the polyvinylbutyral and the glass.Previously, the problem had been solved in an anologous way using "soft polyvinylbutyral" containing moderate amounts of plasticiser (typically 30 to 40); such soft polyvinylbutyral is commonly used in architectural and automotive applications, has similar properties to polyurethane, and may similarly be used for this purpose. Other ways of protecting against cold chipping, when this is necessary, have involved the use of a separator e.g. release tape around the peripheral margin of the area of contact of the hard polyvinylbutyral and the glass, slightly inset within the polyvinylbutyral layer from the interfacial surface to reduce the force exerted by polyvinylbutyral on the glass.

An alternative use of layers of polyurethane is described in GB 2,134,445A, where a layer of polyurethane is used in combination with a layer of hard polyvinylbutyral to improve the impact resistance of a locomotive windscreen at the lower end of the temperature range in which it is required to operate. In this case, there is no cold chipping problem and the polyvinylbutyral is used in direct contact with outer glass ply, which may be electrically heated by a conductive coating on the inner surface thereof, over the whole area of the windscreen without precautions.This usage has been developed in a more recent application in which layers of polyurethane are used in a laminated aircraft windscreen having inner, outer and intermediate glass plies with hard polyvinylbutyral layers between them and layers of polyurethane between each polyvinylbutyral surface and the adjacent glass surface except the inner surface of the outer glass.

Whilst it may have been expected (from the teaching of UK patent 1,529,109) that such use would incidentally remove all risk of any cold chipping problems from the intermediate glass ply, the opposite has been found in practice. The risk of cold chipping appears to be exacerbated by inclusion of the polyurethane layer.

It has now been found that this detrimental effect may be avoided by inclusion of a separator between the hard polyvinylbutyral and the glass which can prevent inadvertent contact between the hard polyvinylbutyral and the glass.

Careful analysis and examination has shown that, without the separator, the polyvinylbutyral melts during lamination and flows to contact the glass. When a further interlayer material is located between the glass and the hard polyvinylbutyral, such further inter layer typically being a polyurethane layer, the contact with the glass of the flowed polyvinylbutyral is located beyond the edge of the further interlayer material. The resultant contact between glass and hard polyvinylbutyral, beyond the normal extent of contact between these layers, actually results in a cold chipping problem.

According to the present invention there is provided a laminated window for use over a wide range of operating temperatures including a layer of hard polyvinylbutyral and a layer of glass, with an intermediate layer of a further interplay material therebetween, characterised by the inclusion of a separator between the said layer of glass and the hard polyvinylbutyral around the periphery thereof.

Thus, the invention enables separation of the glass and the hard polyvinylbutyral even if or when the hard polyvinylbutyral has flowed during manufacture of the laminated window. The separator either acts as a physical barrier to prevent contact between the hard polyvinylbutyral and the glass if the hard polyvinylbutyral has run past the extent of the further interlayer material which is substantially the same size as the hard polyvinylbutyral or the separator consists of an extension of the further interlayer material so that such run past does not occur.

The separator is used to prevent any contact between the hard polyvinylbutyral and the glass during manufacture and use of the laminated window. For this purpose, the separator will generally extend beyond the edge of the hard polyvinylbutyral during lamination but may, if desired, subsequently be trimmed back so as not to extend beyond the hard polyvinylbutyral in the finished window.

The further interlayer material may be, for example, a polyurethane or a soft polyvinylebutyral, preferably with a higher proportion of plasticiser, for example a plasticiser content in the range 30 to 40% by weight.

In one preferred embodiment separator is located between the further interlayer and the hard polyvinylbutyral.

More preferably, the separator is in the form of a release tape with a first surface adhered to an adjacent interlayer surface and an opposed non-stick surface.

Preferably, a separator is provided between each hard polyvinylbutyral layer and further inter layer bonded to a glass layer around the periphery of said hard polyvinylbutyral layer and glass layer.

In another preferred embodiment the separator is located between the further interlayer and the glass.

Preferably, the separator comprises a first separator part which is located between the further interlayer and the glass and has first and second surfaces adhered to adjacent interlayer and glass surfaces respectively and a second separator part which extends beyond the periphery of the further interlayer.

Preferably, the separator comprises a tape having two adhesive faces or a gasket which has been deposited on the layer of glass.

Preferably, the gasket is a coating of a material having a sufficiently low modulus substantially to avoid promotion of cold chipping of the glass.

Preferably, the gasket has been deposited on the edge and the adjacent marginal portions of the face(s) of the layer of glass.

The gasket may comprise a layer of polyurethane which has been moulded onto the layer of glass; cast onto the layer of glass by dipping the layer of glass in liquid polyurethane; or sprayed onto the layer of glass.

Preferably, the layer of polyurethane has a thickness of from 0.1 to 0.7mm, more preferably from 0.1 to 0.2mm.

In another preferred embodiment, the separator and the further interlayer material comprise a single layer including an extending portion which extends beyond the periphery of the hard polyvinylbutyral.

Preferably, the extending portion extends at least about 5mm from the hard polyvinylbutyral.

In each embodiment the separator may extend around substantially the whole periphery of the hard polyvinylbutyral layer or the glass layer.

The invention also provides, in a further aspect, a method of producing a laminated window for use over a wide range of operating temperatures comprising a layer of glass, a layer of hard polyvinylbutyral and an intermediate layer of a further interlayer material characterised in that, during the step of laminating the said layers together, a separator is included between the said glass and the hard polyvinylbutyral extending beyond the edge of the hard polyvinylbutyral around the periphery thereof.

In one preferred embodiment the separator is located between the further interlayer and the hard polyvinylbutyral.

Preferably, the separator is in the form of a release tape with a first surface adhered to an adjacent interlayer surface and an opposed non-stick surface.

More preferably, the first surface is adhered to said further interlayer and said opposed non-stick surface faces the hard polyvinylbutyral layer.

Preferably, the separator where it extends beyond the peripheral edges of the adjacent layers is pressed against the face of the neighbouring glass during lamination.

Optionally, the portion of the separator extending beyond the peripheral edges of the adjacent layers is removed after lamination.

Preferably, a separator is used between each hard polyvinylbutyral layer and further interlayer bonded to a glass layer and extends beyond the periphery of said hard polyvinylbutyral layer.

Preferably, the separator comprises a first separator part which is located between the further inter layer and the glass and has first and second surfaces adhered to adjacent inter layer and glass surfaces respectively and a second separator part which extends beyond the periphery of the further interlayer.

The separator may comprise a tape having two adhesive faces or a gasket which is deposited on the layer of glass.

Preferably, the gasket is a coating of a material having a sufficiently low modulus so as substantially to avoid promotion of cold chipping of the glass.

Preferably, the gasket is deposited on the edge and the adjacent marginal portions of the face(s) of the layer of glass.

More preferably, the gasket comprises a layer of polyurethane which is moulded onto the layer of glass; cast onto the layer of glass by dipping the layer of glass in liquid polyurethane; or sprayed onto the layer of glass.

In another preferrred embodiment, the separator and the further interlayer material comprise a single layer including an extending portion which extends beyond the periphery of the hard polyvinylbutyral.

In any of the embodiments, the separator may extend around substantially the whole periphery of the hard polyvinylbutyral layer.

The separator is perferably in the form of a release tape, for example a polyester tape, which may have a first adhesive surface and an opposed non-stick surface, applied between the hard polyvinylbutyral and the further interlayer around the marginal periphery of said layers and extending sufficiently beyond the further interlayer to prevent-molten hard polyvinylbutyral running down onto the glass. The extension required will depend on a number of factors including the thickness of the further interlayer material, the thickness of hard polyvinylbutyral, the autoclaving time and temperature and the orientation of the laminate in the autoclave, but, when the further interlayer is thin, an extension of about 6 mm will usually be adequate.

It will be appreciated that, for best results, there is a separator between each hard polyvinylbutyral/further interlayer material interface adjacent a glass surface, and each separator preferably extends around s~st^^tia ly the whole periphery of the hard polyvinylbutyral layer. However, it should further be appreciated that it is also within the scope of the invention, and may offer some useful benefits, to include a separator between only one hard polyvinylbutyrallfurther interlayer material and it is not necessary (although desirable for best results) for that separator to extend around substantially the whole periphery of that interface.

The invention is illustrated but not limited by the following description with reference to the accompanying drawings in which: Figure 1 is a section through the edge of the components of a laminated windscreen after assembly together but before being fitted into the tooling used for autoclaving showing the use of separators in accordance with a first embodiment of the invention.

Figure 2 is a section, corresponding to Figure 2, through the edge of the assembly in the tooling used for autoclaving (tooling not shown), showing the disposition of the separators.

Figure 3 is a section, corresponding to Figures 1 and 2 through the edge of the assembly after autoclaving, removal from the tooling and trimming of the separators extending beyond the hard polyvinylbutyral layers.

Figure 4 is a section through a laminated window in accordance with a second embodiment of the present invention.

Figure 5 is a section through a laminated window in accordance with a third embodiment of the present invention.

Figure 6 is a section through a laminated window in accordance with a fourth embodiment of the present invention.

Referring particularly to Figure 1, an outer glass 1, with an electroconductive heating coating (not shown) on its inner surface, and two high strength structural glasses, intermediate glass 2 and inner glass 3, are assembled together with inter layers between them. Prior to assembly, the internal surfaces, i.e. surfaces of the glass to be laminated, are sprayed with silane primers in conventional manner. A hard polyvinylbutyral interlayer 4, made up of a plurality of pre-cut hard polyvinylbutyral sheets to provide the required thickness, and polyurethane inter layer 5 are provided between outer glass 1 and intermediate glass 2, with the polyvinylbutyral 4 in contact with the outer glass and the polyurethane 5 in contact with the outer surface of intermediate glass 2.A second hard polyvinylbutyral interlayer 6, again composed of a plurality of hard polyvinylbutyral sheets, sandwiched between polyurethane interlayers 7 and 8, is provided between intermediate glass 2 and inner glass 3.

Annular layers of soft polyvinylbutyral 9, 91 are inset in the peripheral margin of the hard polyvinylbutyral interlayer 4 on its face contacting the coated inner face of outer glass 1, the glass face in the laminate generally liable to cold chipping; a separator 10 is provided between layers 9 and 9 and effectively separates the hard polyvinylbutyral 4 from the glass in the important peripheral area where the outer glass 1 is liable to cold chip. The separator 10 is in the form of a tape, such as a polyester tape supplied by 3Ms as Part No 1601 with a silicone adhesive cn or. surface son an opposed non-stck surface.

In accordance with the invention, further separators, again in the form of a polyester tape with one adhesive surface and one non-stick surface, 11, 12 and ; are provided between interlayers 4 and 5, 6 and 7, and 6 and 8 respectively. In each of these latter cases, the tape forming the separator extends about 6 mm beyond the periphery of the adjacent polyurethane interlayer, and the tape is oriented with its adhesive face in contact with the adjacent polyurethane surface and its non-stick surface towards the adjacent polyvinylbutyral surface separating the polyurethane interlayer from the polyvinylbutyral layer.

When the assembly is enclosed in tooling, in order to control the shape of the window during the autoclaving process, the separators 11, 12 and 13, where they extend beyond the edge of the adjacent interlayers, are pressed down against the faces of the neighbouring glasses as shown in Figure 2. The whole assembly with tooling is placed in sealable wrapping which is evacuated and sealed; the wrapped assembly is then autoclaved at temperatures between 125"C and 1404C, and pressures between 100 psi and 200 psi (between 7 and 14 x 105 Pascal) in conventional manner.The assembly is then cooled and removed from the sealed wrapping, and the separators 11, 12 and 13 trimmed back to the edge of the adjacent polyurethane interlayers as shown in Figure 3, removing polyvinylbutyral which had melted during lamination and flowed down onto the surfaces of the separators contacting the glass.

In this way the invention avoids contact between hard polyvinylbutyral and glass occurring, as a result of the presence of the polyurethane interlayers, in a region beyond the normal area of contact between the interlayers and the glass in an area of glass (adjacent to or at its edge) which is most at risk of cold chipping.

A second embodiment of the present invention is illustrated in Figure 4 in which there is shown the edge of a laminated windscreen 20 which has substantially the same glass/hard polyvinylbutyral/polyurethane laminate construction as the first embodiment. The laminated windscreen 20 consists of an outer glass sheet 21 which is laminated to an intermediate glass sheet 22 by the combination of a relatively outward hard polyvinylbutyral layer 24 and a relatively inward polyurethane interlayer 25.

The intermediate glass sheet 22 is laminated to an inner glass sheet 23 by the combination of a relatively outward polyurethane interlayer 27, a central hard polyvinylbutyral layer 26 and relatively inward polyurethane interlayer 28.

These components of the laminate are similar to those illustrated in Figure 3. In this embodiment, separators are provided between the polyurethane interlayers 25, 27 and 28 and the respective glass sheets 22 and 23 to which they are laminated. Thus, a separator 29 is disposed between the polyurethane layer 25 and the intermediate glass ply 22, a separator 30 is disposed between the polyurethane layer 27 and the intermediate glass ply 22 and a separator 31 is provided between the polyurethane layer 28 and the inner glass ply 23.Each separator 29,30,31 has a first part 32,33,34 thereof which is disposed between the respective polyurethane interlayer 25,27,28 and glass sheet 22,23 laminate portion and has respective first and second surfaces adhered to the adjacent interlayer and glass surfaces and a second part 35,36,37 thereof which extends beyond the periphery of the respective polyurethane interlayer 25,27,28 so as to cover an otherwise unlaminated surface on a marginal portion of the glass sheet 22,23 in the region of the periphery of the glass sheet 22,23. The separator 29,30,31 acts to separate the respective glass sheet 22,23 from the hard polyvinylbutyral 24,26 even when the polyvinylbutyral 24,26 has flowed or run down beyond the edge of the respective polyurethane layer 25,27,28 which has substantially the same dimensions as the polyvinylbutyral sheet 24,26.

In the second embodiment, the separator 29,30,31 may comprise a polyester tape similar to that employed in the first embodiment but which is provided with two adhesive surfaces which are adhered to the polyvinylbutyral and glass surfaces. Alternatively, the separators 29,30,31 may comprise a gasket of polyurethane or silicone which has been deposited on the peripheral faces of the glass sheets 22,23.

The gasket is a coating which has a sufificently low modulus so as not to cause cold chipping to the class.

A third embodiment of the present invention is illustrated in Figure 5 which is a modification of the embodiment of Figure 4 wherein the separators 29,30,31 comprise gaskets of polyurethane or silicone. In this embodiment, a laminated window 40 comprises outer, intermediate, and inner glass sheets 41,42 and 43 which are laminated together with hard polyvinylbutyral layers 44 and 46 respectively and polyurethane interlayers 45,47,48.

Gaskets 49 and 50 of polyurethane are deposited over the periphery of the glass sheets 42 and 43 respectively so as to cover both the edges 51,52 and the marginial portions 53,54,55,56 of the surfaces of those glass sheets 42,43. The gasket 49 is dimensioned so as to have a first part 57 disposed between the polyurethane layer 45 and the intermediate glass sheet 42 at the marginal edge of the polyurethane layer 45 and in addition a second part 58 disposed between the polyurethane layer 47 and the intermediate glass sheet 42 at the marginal edge of the polyurethane layer 47 with the remainder of the gasket 49 extending over the marginal portions and edge of the glass sheet 42. The gasket 50 is dimensioned so that it has a part 59 which is disposed between the polyurethane layer 48 and the inner glass sheet 43 at the marginal edge of the polyurethane layer 48 with the remainder of the gasket 50 extending over the marginal portions and edge of the glass sheet 43. The polyurethane gaskets 49,50 may be formed by moulding polyurethane on the edges of the glass sheets and the marginal zones of the glass sheets. Alternatively, the polyurethane gasket may be formed by dipping the edges of the glass sheets in liquid polyurethane so as to cast the polyurethane gaskets onto the glass sheets. A further alternative arrangement, the polyurethane gaskets may be sprayed onto the edges and marginal zones of the glass sheets.In the second and third embodiments wherein a polyurethane gasket is employed, the thickness of the polyurethane must be above a threshold minimum value so as to prevent discontinuities in the polyurethane gasket.

Preferably, the polyurethane gasket has a thicknesss of from 0.1 to 0.7mm and more preferably the thickness is from 0.1 to 0.2mm.

A fourth embodiment of the present invention is illustrated in Figure 6. In this embodiment, a laminated window 60 comprises an outer glass sheet 61 laminated to an intermediate glass sheet 62 by the combination of a hard polyvinylbutyral layer 64 and a polyurethane inter layer 65 and the intermediate glass sheet 62 is laminated to an inner glass sheet 63 by the combination of a relatively outward polyurethane interlayer 67, a central hard polyvinylbutyral layer 66 and a relatively inward polyurethane interlayer 68.

Each polyurethane inter layer 65 and 68 is dimensioned so that it is substantially larger than the hard polyvinylbutyral layer to which it is laminated whereas in the preceding embodiments the hard polyvinylbutyral layers and the polyurethane inter layers have substantially the same dimensions. Each polyurethane interlayer 65,67 and 68 has a respective extending portion 69,70 and 71 which extends substantially beyond the respective edge 72,73 of the adjacent polyvinylbutyral layer 64,66. Each extending portion 69,70,71 acts, during lamination of the laminated windscreen, to prevent any hard polyvinylbutyral from contacting the glass and thus acts as a separator to separate the glass from undesired contact with any hard polyvinylbutyral. During the lamination process, the hard polyvinylbutyral can flow thereby to increase the size of the respective polyvinylbutyral layers 64,66. The extending portions 69,70 and 71 are dimensioned so as to prevent any such hard polyvinylbutyral from contacting the glass.

In all of the embodiments in the present invention, it is not necessary for the performance of the invention to trim back the separator layers and/or the polyurethane layers after the laminating process provided that the flow of polyvinylbutyral during laminating has not been such as to contact the glass. The separator and polyurethane layers generally are not detrimental to the adhesion of a silicon moulding real around the window edge. In addition,, such trimming can be difficult to achieve due to the thickness of the layers and the spaces between the layers and also trimmming could inadvertently cause undesirable scratching of the glass surface.

Claims

CLAIMS:

1. A laminated window for use over a wide range of operating temperatures including a layer of hard polyvinylbutyral and a layer of glass, with an intermediate layer of a further interlayer material therebetween, characterised by the inclusion of a separator between the said layer of glass and the hard polyvinylbutyral around the periphery thereof.

2. A laminated window for use over a wide range of operating temperatures including a layer of hard polyvinylbutyral and a layer of glass, with an intermediate layer of a further inter layer material therebetween, characterised by the inclusion of a separator between the said layer of glass and the hard polyvinylbutyral around the periphery thereof to prevent any contact between the hard polyvinylbutyral and the glass during manufacture or use of the laminated window.

3. A laminated window according to claim 1 or claim 2 wherein the further interlayer material is polyurethane.

4. A laminated window according to claim 1 or claim 2 wherein the further interlayer material is soft polyvinylbutyral.

5. A laminated window according to any one of claims 1 to wherein the separator is located between the further interlayer and the hard polyvinylbutyral.

6. A laminated window according to claim 5 in which the separator is in the form of a release tape with a first surface adhered to an adjacent interlayer surface and an opposed non-stick surface.

7. A laminated window according to claim 5 or claim 6 with a separator between each hard polyvinylbutyral layer and further interlayer bonded to a glass layer around the periphery of said hard polyvinylbutyral layer and glass layer.

8. A laminated window according to any one of claims 1 to 4 wherein the separator is located between the further interlayer and the glass.

9. A laminated window according to claim 8 wherein the separator comprises a first separator part which is located between the further inter layer and the glass and has first and second surfaces adhered to adjacent interlayer and glass surfaces respectively and a second separator part which extends beyond the periphery of the further interlayer.

10. A laminated window according to claim 9 wherein the separator comprises a tape having two adhesive faces.

11. A laminated window according to claim 9 wherein the separator comprises a gasket which has been deposited on the layer of glass.

12. A laminated window according to claim 11 wherein the gasket is a coating of a material having a sufficiently low modulus substantially to avoid promotion of cold chipping of the glass.

13. A laminated window according to claims 11 or 12 wherein the gasket has been deposited on the edge and the adjacent marginal portions of the face(s) of the layer of glass.

14. A laminated window according to claim 13 wherein the gasket comprises a layer of polyurethane which has been moulded onto the layer of glass; cast onto the layer of glass by dipping the layer of glass in liquid polyurethane; or sprayed onto the layer of glass.

15. A laminated window according to claim 14 wherein the layer of polyurethane has a thickness of from 0.1 to 0.7mm.

16. A laminated window according to claim 15 wherein the layer of polyurethane has a thickness of from 0.1 to 0.2mm.

17. A laminated window according to any one of claims 1 to 4 wherein the separator and the further interlayer material comprise a single layer including an extending portion which extends beyond the periphery of the hard polyvinylbutyral.

18. A laminated window according to claim 17 wherein the extending portion extends at least about 5mm from the hard polyvinylbutyral.

19. A laminated window according to any of the preceding claims wherein the separator extends around substantially the whole periphery of the hard polyvinylbutyral layer or the glass layer.

20. A laminated window substantially as hereinbefore described with reference to and as illustrated in Figure 3, Figure 4, Figure 5 or Figure 6.

21. A method producing a laminated window for use over a wide range of operating temperatures comprising a layer of glass, a layer of hard polyvinylbutyral and an intermediate layer of a further interlayer material characterised in that, during the step of laminating said layers together, a separator is included between the said glass and the hard polyvinylbutyral extending beyond the edge of the hard polyvinylbutyral around the periphery thereof.

22. A method according to claim 21 wherein the further interlayer material is polyurethane.

23. A method according to claim 21 wherein the further interlayer material is soft polyvinylbutyral.

24. A method according to any one of claims 21 to 23 wherein the separator is located between the further interlayer and the hard polyvinylbutyral.

25. A method according to claim 24 wherein the separator is in the form of a release tape with a first surface adhered to an adjacent interlayer surface and an opposed non-stick surface.

26. A method according to claim 25 wherein said first surface is adhered to said further interlayer and said opposed non-stick surface faces the hard polyvinylbutyral layer.

27. A method according to any one of claims 21 to 24 wherein the separator where it extends beyond the peripheral edges of the adjacent layers is pressed against the face of the neighbouring glass during lamination.

28. A method according to any of claims 21 to 27 wherein the portion of the separator extending beyond the peripheral edges of the adjacent layers is removed after lamination.

29. A method according to any of claims 21 to 28 wherein a separator is used between each hard polyvinylbutyral layer and further interlayer bonded to a glass layer and extends beyond the periphery of said hard polyvinylbutyral layer.

30. A method according to any one of claims 21 to 23 wherein the separator is located between the further interlayer and the glass.

31. A method according to claim 30 wherein the separator comprises a first separator part which is located between the further interlayer and the glass and has first and second surfaces adhered to adjacent interlayer and glass surfaces respectively and a second separator part which extends beyond the periphery of the further interlayer.

32. A method according to claim 31 wherein the separator comprises a tape having two adhesive faces.

33. A method according to claim 31 wherein the separator comprises a gasket which is deposited on the layer of glass.

34. A method according to claim 33 wherein the gasket is a coating of a material having a sufficiently low modulus so as substantially to avoid promotion of cold chipping of the glass.

35. A method according to claims 33 or 34 wherein the gasket is deposited on the edge and the adjacent marginal portions of the face(s) of the layer of glass.

36. A method according to claim 35 wherein the gasket comprises a layer of polyurethane which is moulded onto the layer of glass; cast onto the layer of glass by dipping the layer of glass in liquid polyurethane; or sprayed onto the layer of glass.

37. A method according to claim 36 wherein the layer of polyurethane has a thickness of from 0.1 to 0.7mm.

38. A method according to claim 37 wherein the layer of polyurethane has a thickness of from 0.1 to 0.2mm.

39. A method according to any one of claims 21 to 23 wherein the separator and the further inter layer material comprise a single layer including an extending portion which extends beyond the periphery of the hard polyvinylbutyral.

40. A method according to claim 39 wherein the extending portion extends at least about 5mm from the hard polyvinylbutyral.

41. A method according to any of claims 21 to 40 wherein the separator extends around substantially the whole periphery of the hard polyvinylbutyral layer.

42. A method of producing a laminated window for use over a wide range of operating temperatures comprising a layer of glass, a layer of hard polyvinylbutyral and an intermediate layer of a further interlayer material using a separator substantially as hereinbefore described with reference to, and as illustrated in, Figures 1 to 3, Figure 4, Figure 5 or Figure 6.

43. A laminated window for use over a wide range of oeprating temperatures produced by a method according to any of claims 21 to 42.