GB2352998A

GB2352998A - Laminated window

Info

Publication number: GB2352998A
Application number: GB9918426A
Authority: GB
Inventors: Michael Lyon
Original assignee: Pilkington PLC
Current assignee: Pilkington Group Ltd
Priority date: 1999-08-05
Filing date: 1999-08-05
Publication date: 2001-02-14
Also published as: GB9918426D0

Abstract

A window 1 is laminated from at least two plies 21,22 of glazing material and at least one ply 27 of interlayer material, the window including an opaque ink band 20 on an internal face 24,25 of one of the plies of glazing material. A first further material 6 other than interlayer material overlies the ink band, and a second further material 23 is incorporated between the first material and the ink band so as to prevent contact with the ink band. This measure avoids a non-uniform appearance of the ink band. The first material may be a busbar 6 for an electric heating circuit, and the second material may be a further piece of interlayer material 23. The window may be intended for a vehicle.

Description

2352998 Laminated Window The present invention relates to a laminated

window, and more particularly to such a window having an opaque band adjacent its periphery for the purpose of obscuring vision through that portion of the window. Such windows are used for vehicles, e.g. as windscreens or rear windows. The invention also relates to a method of producing such windows, in which the various constituent plies are superimposed on each other to form an assembly, which is then laminated by application of heat and pressure. The laminated window may be electrically heated.

Laminated vehicle windows generally comprise at least two plies of glazing material (which may be glass in any of the usual forms, i.e. annealed, toughened, semi-toughened, tinted, clear, coated, etc.) with at least one ply of interlayer material extending between the plies of glazing material. However, more complex constructions are known. These may, for instance, include further plies of materials such as glass and polycarbonate to confer resistance to bullets, or further plies of interlayer carrying infra-red reflective coatings or antenna wires, or a combination of these.

It is known to provide an electrically heated laminated window heated by a resistive heating means extending over at least part of the window, with current collectors in the form of busbars making electrical connection between the heating means and a voltage supply. Such busbars generally extend adjacent the periphery of the window so that they do not interfere with vision. It is further known to provide an opaque band adjacent the periphery of the window for obscuration purposes, e.g. to obscure the busbars from external view, and/or, for a vehicle window, to obscure the part of the bodywork on which the window is mounted. Where the window is secured in position by adhesive, the "obscuration band" (as it is generally termed) fulfills the further function of protecting the adhesive from light, especially its ultra-violet component. Obscuration bands are generally screen-printed onto a flat sheet of glass in a black ceramic ink, which is dried and then fired during bending of the sheet at an elevated temperature. This sheet is then used as one of the plies which are assembled in the appropriate order, de-aired and laminated in known fashion at elevated temperature and pressure, e.g. in an autoclave.

2 However, it has been found that when the plies are assembled such that a further material is in direct contact with the ink of the obscuration band, the latter acquires a nonuniform appearance after lamination. The further material may, for example, be a busbar as described above. Where the obscuration band is black in colour, the non-uniform appearance generally takes the form of an apparent lightening of the band over the area of contact between the busbar and the band, to give a grey appearance in that area. While the difference in shade may be extremely small in absolute terms, if it is noticeable to the eye, it is considered unattractive from an aesthetic aspect. As the appearance of vehicles (particularly cars) is considered important, windows which are thus affected are unacceptable to the vehicle manufacturer, and hence unsaleable. The most obvious explanation of the problem, which was put forward by several personnel involved in attempting to alleviate the problem, is simply to assume that the ink is not sufficiently opaque, so that the busbar (which is normally tinned copper strip, i.e. it has a silvery appearance) shows through the ink. However, the present inventors did not agree, and conducted trials to test this explanation. Sample windows made with blackened busbar strip still displayed an apparent grey area over the busbar. Furthermore, when a window made with standard busbar of silver colour was delaminated, and the busbar removed from the obscuration band, the apparent grey colour remained. It is therefore to be deduced that a permanent colour change in fact occurs in the ink of the obscuration band. The cause of the:colour change is as yet unknown; certainly, attempts to avoid the problem by reformulating the inks used for the obscuration band have not been successful.

The present inventors have now realised that the apparently grey discolouration may be produced (or may also be produced) as a result of darkening of the ink around the busbar strip, instead of lightening of the ink in contact with the busbar. Furthermore, it was also the present inventors who realised that the problem is not limited to instances where it is a busbar that is in contact with the ink; it would appear that the presence of any material in contact with any part of the area of ink gives rise to correspondingly non-uniform shades of ink after lamination. Certainly, experiments with a variety of common materials indicated this to be the case.

3 Surprisingly, the inventors have also discovered that the problem may be satisfactorily alleviated by introducing yet a further material into the assembly before larnination.

According to the present invention there is provided a. laminated window laminated from at least two plies of glazing material and at least one ply of interlayer material extending between the plies of glazing material, the window including an opaque ink band provided on an internal face of one of the plies of glazing material and extending adjacent at least part of the periphery of that ply, wherein a first further material other than interlayer material is adjacent part of the ink band and overlies it, and a second further material is incorporated between the first material and the ink band, the second material being of sufficient extent to cover the first material and thereby prevent it contacting the ink band.

The invention is particularly advantageous for alleviating the nonuniform appearance of an obscuration band in an electrically heated window, wherein the window includes electrical heating means extending over an area between the plies of glazing material, and wherein the first further material comprises an electrically conductive material serving as a busbar for the electrical heating means.

Preferably the second further material is a piece of interlayer material, especially polyvinylbutyral (commonly referred to as "PVB" for short).

According to a second embodiment of the invention, the further ply may be in the form of a mask matching the shape of the opaque band, and large enough to prevent contact between the ply of interlayer material and all of the opaque band.

In the second embodiment, the second further material is preferably an impermeable material, for it may be the case that the non-uniforn-lity of shade of the obscuration band is linked to chemicals present in the PVB.

The present invention also provides a method of producing a laminated window comprising inner and outer plies of glass, at least one ply of interlayer material extending between the plies of glass, an opaque ink band on an internal face of one of the plies of glass, and a first further material other than interlayer material adjacent part of the ink band and overlying it, the method comprising the steps of- 4 - printing a band of ink onto a glass sheet which will form the outer ply of the window, heating the sheet to an elevated temperature so as to fire the ink to form an opaque obscuration band, and then cooling the sheet, - assembling the plies by superimposing them so that the first further material faces the ink band, while incorporating a second further material between the first material and the ink band, the second material being of sufficient extent to cover the first material and thereby prevent it contacting the ink band, - laminating the assembly of plies by application of heat and pressure to bond the plies together.

Advantageously, the ply of interlayer material deforms during lamination so as to accommodate at least part of the thickness of at least the second further material.

When the method is being used to produce laminated vehicle windows (e.g. windscreens or rear windows), the glass sheets are normally curved. In one processing route two glass sheets forming the inner and outer plies of the window are heated together to an elevated temperature, one superimposed on the other, and bent together to form a nesting pair. Alternatively, the sheets may be heated and press bent as individual, separate sheets.

The invention will now be fiirther described by way of the following specific embodiments, which are given by way of illustration and not of limitation, and with reference to the accompanying drawings in which:Fig. I is a plan view of a window according to the invention; Fig. 2 is a fragmentary sectional view, greatly enlarged, taken along the line II-II; Fig. 3 is a sectional view taken along the line 111-111; Fig. 4 shows a second embodiment of the invention, the view corresponding to that of Fig. 2.

Fig. 5 is an exploded sectional view taken in a similar direction to Fig. 3.

Referring to Figure 1, there is shown a laminated window 1, which is electrically heated by a resistant area heating means 2. Heating means 2 may be a transparent conductive film or an array of fine, closely spaced wires, as is known in the art. The heating means is connected to an external voltage supply (not shown) by busbars 6,7,8,9 which terminate in leads 18 with connectors 19. The busbars constitute the first further material in this example of the invention, and extend adjacent the periphery 10 of the window.

As may be seen from Fig. 3, the laminated window comprises an outer glass ply 21, an inner glass ply 22 ("inner" and "outer" are with reference to the orientation of the window when installed in a vehicle) and a fullsize ply of interlayer material 27, i.e. one matching the plies of glass in size.

Fig. 2 shows a greatly enlarged sectional view of a small part of the margin of the window of Fig. 1. Part of the inner ply 22, outer ply 2 1, interlayer ply 27, and busbar 6 are visible. An obscuration band 20 (not shown in Figs. I and 3 for clarity) of opaque screenprinted ink is provided on the inward-facing face 24 of the outer glass ply 21, extending adjacent its periphery 16.

The ink is a ceramic ink, and when the two glass plies are bent together as a superimposed pair to obtain matching curvatures, particular ink formulations are preferred which have a reduced tendency to stick to the adjacent ply during bending. Such formulations are known from EP-A-535 474 (corresponding to US 5,443,669), and comprise a glass frit, a ceramic pigment, and an inorganic binder, all mixed with an organic oil such as terpineol. to allow the ink to be screen printed. It is preferred that the inorganic binder be a silica gel, e.g. a commercially available silicic acid binder. A metallic alcohol compound may be added to the inorganic binder.

Other ceramic inks may also be used, e.g. when the glass plies are bent by press bending as individual sheets. For example, a commonly-used family of inks comprises a lead-based (e.g. lead borosilicate) frit, a heavy metal pigment (e.g. in the form of an oxide such as a spinel, e.g. copper chromite), an organic binder (e.g. ethyl cellulose) and an organic oil as before. Another family of inks comprises lead-free frits with slight crystallising properties and a reactive enamel, to reduce sticking tendencies. It may be that all ceramic inks are susceptible to the problem of non-uniform shade of colour described above, when used with a material other than interlayer in contact with the ink.

6 Still referring to Fig. 2, a second further material in the form of a ply 23 of material is provided between the busbar and the opaque obscuration band. In this embodiment the further ply 23 is a piece of PVB interlayer material large enough to cover the busbar 6.

As is well known, PVB interlayer is widely used in the automotive glass industry in the manufacture of laminated safety glass, and is available from large, well-known companies such as Dupont, Sekisui and Solutia in thicknesses of 0.76 mm and 0.38 mm. As an alternative to a strip of PVB, a strip of polyurethane ("PU") interlayer material may be used.

At the time of the work from which the invention derives, concern existed that the presence of a further strip of material, which together with the obscuration band and the busbar adds locally to the total thickness of the window, would cause weakening of the window. It is noted in this connection that windows used in vehicles must pass various safety tests, including resistance to breakage. There is a danger that a local increase in the thickness of the materials positioned between the inner and outer plies of glass will cause a corresponding localised change in the curvature of the glass plies, leading to the creation of tensile stresses which greatly facilitate crack propagation. Surprisingly, this is not found to be the case. Measurements of the total thickness of the laminated window show that the increase in total thickness in the area of the second further material is less than the thickness of the second further material itself before its incorporation into the window. In other words, some yielding or deformation of the materials (in particular of the interlayer material) occurs, probably during lamination, so as to accommodate at least part of the thickness of at least the second further material. This accommodation is thought to result from flowing of the PVB interlayer when at an elevated temperature during autoclaving.

Even though the PVB interlayer material appears to flow during autoclaving to accommodate items such as busbar 6 and further ply 23, it is nevertheless preferable to use thinner PVB for ply 23 than for principal ply 27. The smallest thickness of PVB which is generally commercially available is 0.38 mm. However, it is possible to prepare PVB of lesser thickness than 0.38 mm by stretching PVB at an elevated temperature to prevent it returning to its previous thickness (i.e. stretching it beyond its elastic limit without tearing it). In this way, PVB of 0.2 mm may be prepared and used as the second further material.

7 PU interlayer is available in even smaller thicknesses, e.g. 0. 15 mm. It should be noted that in Fig. 2 the thickness of the interlayer 27, busbar 6, further piece of interlayer 23 and obscuration band 20 have all been exaggerated for clarity relative to the glass plies 21,22.

It is possible to use a further ply of interlayer material which is the same size and shape as ply 27. However, where an array of heating wires is used to heat the window, this may give rise to optical distortion when the current is switched on, owing to changes in refractive index due to varying temperature increases.

Fig. 4 shows an alternative embodiment in which the further ply 28 is at least large enough to act as a mask for the whole of the opaque band 20, preventing contact with the interlayer material 27. The mask matches the opaque band in shape and extent, and may be composed of a thin plastics material, e.g. polyurethene. 'Me material should adhere to the adjacent plies to avoid compromising the integrity of the laminated window.

If the further ply does not extend beyond the obscuration band 20, i.e. it is not visible from inside or outside the vehicle, it need not be transparent, and any thin, durable, relatively inert sheet material, serving as a barrier, will be satisfactory.

Figure 5 is an exploded view of an assembly 30 of plies used to manufacture a laminated window according to the invention. The method of manufacture includes screen printing a band of ceramic ink of the type described above onto a glass sheet. This sheet has previously been cut to the appropriate size and shape to form a blank for the outer ply 21 of the window. The ink band is printed on the inward-facing face 24 of ply 21, and dried. Normally, a laminated window for vehicular use is curved, which requires at least two glass plies of matching curvature so that they laminate together without gaps or air bubbles remaining between the plies. In this case, a further glass blank, which will form inner ply 22, is placed upon the blank for outer ply 21 and the two sheets are heated to an elevated temperature at which the glass softens so that the sheets bend together to form a pair of plies with matching curvature. The elevated temperature also fires the ink to form an opaque, durable, obscuration band. After cooling, the plies are separated, e.g. by removing the upper one (i.e. inner ply 22). The inner ply 22 is turned over so that the convex face 25, which will face towards the exterior after installation in the vehicle, is uppermost. A full-size ply 27 of interlayer material is laid on the inner ply 22. In the 8 example of an electrically heated window, one of the plies carries the heating means. Busbars 6, 7, 8, 9 (busbars 8, 9 are not shown in Fig. 5) are located in the appropriate position on the interlayer, and may be tacked in position by local application of heat. Known suitable measures are taken to ensure electrical contact with the heating means; these vary depending on whether the heating element comprises an array of wires or an electroconductive coating. Strips 23 Pf PVB are positioned on top of the busbars, so that the latter will not be in contact with the ink of the obscuration band when the final ply 21 is added. In the second embodiment, in which a mask 28 is used instead of strips 23, this is positioned on the interlayer so as to cover the margin thereof and thereby prevent contact with the ink of the obscuration band.

In some cases, the window will incorporate further plies of interlayer having further functional items associated with them, e.g. antenna wires, or solar control coatings, and such further plies will be included in the assembly under the principal interlayer ply 27. Any electrical connections required are made before the item concerned is covered by the next ply. Finally, the outer glass ply 21 is in turn laid on top of the interlayer ply 27, busbars and PVB strips 23. The ply 27 of interlayer material is normally oversize initially, and then trimmed to size in one or two stages.

The assembly 30 of plies is then de-aired in known fashion, e.g. by application of vacuum around the edges, and laminated in an autoclave at elevated temperature and pressure.

By use of the invention, a uniformly dark obscuration band of attractive appearance is obtained, even when there is a variety of differing materials behind the band, between it and the first full-size ply of interlayer.

Claims

Claims

1. A window laminated from at least two plies of glazing material and at least one ply of interlayer material extending between the plies of glazing material, the window including an opaque ink band provided on an internal face of one of the plies of glazing material and extending adjacent at least part of the periphery of that ply, wherein a first further material other than interlayer material is adjacent part of the ink band and overlies it, and a second further material is incorporated between the first material and the ink band, the second material being of sufficient extent to cover the first material and thereby prevent it contacting the ink band.

2. A window as claimed in claim 1, including electrical heating means extending over an area between the plies of glazing material, wherein the first further material comprises an electrically conductive material serving as a busbar for the electrical heating means.

3. A window as claimed in claim I or claim 2, wherein the second further material is a piece of interlayer material, preferably polyvinylbutyral4. A window as claimed in claim 3, wherein the thickness of the interlayer is less than 0.38 nun.

5. A window as claimed in claim I or claim 2, wherein the second further material is in the form of a mask matching the shape and extent of the opaque band, and large enough to prevent contact between the ply of interlayer material and all of the opaque band.

6. A window as claimed in claim I or claim 2, wherein the second further material is impermeable.

7. A window as claimed in any preceding claim, wherein the increase in the total thickness of the window in the area of the second further material is less than the thickness of the second further material itself before its incorporation into the window.

8. An electrically heated window laminated from at least two plies of glazing material and at least one ply of interlayer material extending between the plies of glazing material, the window including a resistant area beating means extending over an area between the plies of glazing material, an opaque band provided on an internal face of one of the plies of glazing material and extending adjacent at least part of the periphery of that ply, at least one busbar positioned between the opaque band and the at least one ply of interlayer material, wherein a further ply of material is provided between the busbar and the opaque band.

9. A laminated window substantially as herein described with reference to and as illustrated in Figures 1, 2, 3 and 5 or Figures 1, 3 and 4 of the accompanying drawings.

10. A method of producing a laminated window comprising inner and outer plies of glass, at least one ply of interlayer material extending between the plies of glass, an opaque Ink band on an internal face of one of the plies of glass, and a first further material other than interlayer material adjacent part of the ink band and overlying it, the method comprising the steps of- - printing a band of ink onto a glass sheet which will form the outer ply of the window, - heating the sheet to an elevated temperature so as to fire the ink to form an opaque obscuration band, and then cooling the sheet, - assembling the plies by superimposing them so that the first further material faces the ink band, while incorporating a second further material between the first material and the ink band, the second material being of sufficient extent to cover the first material and thereby prevent it contacting the ink band, laminating the assembly of plies by application of heat and pressure to bond the plies together.

11. A method as claimed in claim 10, wherein the ply of interlayer material deforms during lamination so as to accommodate at least part of the thickness of at least the second further material.

12. A method as claimed in claim 10 or claim 11, wherein two glass sheets forming the inner and outer plies of the window are heated together to an elevated temperature, one superimposed on the other, and bent together to form a nesting pair.

13. A method as claimed in claim 10 or claim 11, wherein the glass sheets forming the inner and outer plies of the window are heated and individually press bent.

14. A method as claimed in any one of claim 10 to claim 13, wherein one of the plies carries an electrical heating means extending over the ply, and the first further material is a conductive material forming a busbar for supplying electric current to the heating means.

15. A method of producing a laminated window substantially as herein described with reference to and as illustrated in the accompanying drawings.