GB2325429A

GB2325429A - Solder bonding to glass

Info

Publication number: GB2325429A
Application number: GB9710399A
Authority: GB
Inventors: Anthony Richard Holland
Original assignee: Triplex Safety Glass Co
Current assignee: Pilkington Automotive Ltd
Priority date: 1997-05-22
Filing date: 1997-05-22
Publication date: 1998-11-25
Also published as: GB9710399D0

Abstract

A non-current carrying metallic mechanical element 30, 50, 61 is bonded to a glazing element 1, by solder 33, the glazing element being locally provided with a metal-containing layer 21. The mechanical element may be a means 30, for mounting an item on the glazing, or a part of a larger mechanism or assembly, e.g. a window lift mechanism, or a means such as a clip to assist during installation of the glazing in an aperture. The glazing may be a vehicle window. A preferred mounting means is in the form of a generally flat bracket 30 which allows the glazings to be packed tightly for transport to a vehicle assembly factory.

Description

A Glazing with a Mechanical Element Bonded Thereto The present invention relates to a glazing with a mechanical element bonded to it. The mechanical element may take a wide variety of forms; for instance it may be a means for mounting an item, such as an item of equipment, on the glazing; or it may be part of a larger mechanism or assembly, such as a window-opening mechanism; or it may be a means such as a clip or lug which assists during installation of the glazing in an aperture. The glazing may, but need not, be for a vehicle window such as a rear window, door window or other side window, windscreen or rooflight.

The bonding of elements to glazings has long presented difficulty, because the transparent materials of which glazings are composed, such as glass, do not lend themselves to the securing of fixings. Drilling of the glazing to accept a fixing means, such as a bolt, which passes through the resulting hole in the glazing, is frequently unacceptable because it weakens the glazing. Furthermore the hole requires sealing and the risk of leaks is ever present.

The manufacturers of glazings have therefore frequently resorted to bonding a mechanical element to a glazing, generally by means of an adhesive. However, this is not entirely satisfactory either, for the number of adhesives which are suitable for bonding to transparent glazing materials is small, and such adhesives tend to be expensive. Furthermore, some adhesives include aggressive chemicals requiring special handling in the factory, and may create environmental problems, while others require considerable time to set, often with the application of heat and/or pressure, thereby complicating the manufacturing process.

The strength and durability of the bond provided by adhesives also leaves something to be desired. Such adhesive bonds have been found in practice to be susceptible to extremes of heat and/or humidity. For example, while many adhesives provide a bond to glass which can withstand service temperatures of up to 1 lOQC, some vehicle manufacturers are now specifying that the bond must withstand temperatures up to 120QC or even 1309C, and 95% relative humidity. Such temperatures may be reached, for example, in vehicles parked in the sun in hot countries, and no adhesive has been found which gives satisfactory performance when subject to such high temperatures. Adhesives are also poor at accommodating the stresses caused by differential thermal expansion of the glazing material and the element being bonded, and at coping with vibration in service.

It is known to solder two components together where an electrically conducting joint is required. For instance, in the automotive industry, it is known to solder connectors to the busbars of resistive heating elements for the rear windows of vehicles. Furthermore, it is known from US 5,272,602 to provide a window with a lamp, and to integrate the electrical connections to the lamp with the mechanical fixings, so as to facilitate electrical connection of the lamp and eliminate the use of lengths of cable. According to the teaching of this document, a nut or a domed bracket is soldered to an electrically conductive pattern which is provided on the window. There is however no suggestion of how to improve bonding techniques where the element bonded is not used to pass an electric current.

A need therefore exists for a way of bonding elements to a glazing, which does not suffer from the disadvantages outlined above. It has now been realised that it is advantageous to solder a non-current-carrying mechanical element to a glazing, despite the traditional restrictions of soldering to the electrical, electronic and plumbing fields, and despite the apparent unsuitability of a glazing for soldering.

According to the present invention there is provided a glazing to which a non-currentcarrying metallic mechanical element is bonded, wherein the glazing is provided locally with a metal-containing layer, and the mechanical element is bonded to the glazing by soldering it to the metal-containing layer.

A solder bond attaching a mechanical element to a glazing is frequently better able to withstand high temperatures and high humidity than an adhesive bond. It will be appreciated that a glazing for a window which is exposed to the sun or rain, for example a vehicle window, may be subjected to such extreme conditions in service. The use of a solder bond therefore often proves to be more reliable in practice.

A wide range of solders is available, and it is important to ensure that the solidus (or melting point for a eutectic composition) of the solder is not below the maximum predicted temperature that will be encountered. Preferably, the solder used to bond the mechanical element to the glazing is one which melts within the range from l509C to 2809C, more preferably from 1 65 -C to 2359C. The well-known tin-lead family of solder compositions is suitable; these melt in the range from 1839C to 277 C. Another suitable solder consists of 25% tin, 62% lead, 10% bismuth and 3% silver.

The non-current-carrying metallic mechanical element may take a variety of forms. For instance, when installing a glazing in an aperture, various locating devices such as lugs, clips, or spacers are frequently used, and in some situations, especially in vehicular glazing, it is preferable if the locating device is provided already bonded to the glazing, as this facilitates assembly. Vehicular glazings are nowadays frequently adhesively bonded into a corresponding aperture in the vehicle body, and clips are often used to retain the glazing in position until the adhesive sets. Again, it is advantageous if the clips are provided already bonded to the glazing.

Another form of mechanical element is one which constitutes part of a larger mechanism or assembly. For instance, various constituent components of a window lift mechanism and/or a door locking mechanism (especially in vehicles) may be attached to a glazing.

A further category of mechanical element comprises a mounting means for another item, such an item of equipment which is to be mounted on a glazing. Generally, a glazing onto which an item is to be mounted will be manufactured in one factory, or part of a factory, and then transported to a different factory, or part of a factory, for further assembly, such as the actual mounting of the item itself onto the glazing. This is for example the case when the glazing is for a vehicle, since vehicle glazings are normally manufactured in a different factory to that in which the vehicle is assembled. It is therefore desirable to pack glazings as densely as possible for transport to the different factory, or part of a factory, to minimise transport costs.

According to an especially advantageous embodiment of the invention therefore, a glazing is provided wherein the mounting means includes a generally flat retaining bracket for a stud, and the bracket is constructed and arranged to allow the stud to be inserted in the bracket after the bracket has been soldered to the glazing. The use of a generally flat retaining bracket, wherein the stud need only be inserted after transport of the glazing to the different factory, or part of a factory, allows a greater packing density of the glazings to be achieved than if the studs were attached to the glazing before transport. Of course, where transport and/or packing density is not a consideration, the stud may be soldered directly to the glazing, or more precisely, directly to the metal-containing layer on the glazing. (In this specification, unless the context indicates otherwise, references to attaching or securing an element directly to the glazing are to be understood as including attaching or securing it directly to the metalcontaining layer).

The metal-containing layer is, naturally, one that is suitable for soldering to, and normally, a local area of the glazing is provided with a coating of the layer at a position at which a mounting means is to be provided. The layer is in effect provided as one or more patches on the glazing. Preferably, the layer is composed of a metal-containing ink, especially a silver-containing ink. The layer may be formed by printing, especially by screen-printing with a printing screen. It is well known to print an array of conducting lines onto glazings for vehicles to serve as a resistive heating element to demist or de-ice the glazing. Normally such a glazing is used for the rear window (or "backlight") of the vehicle, and it is especially advantageous, in terms of process efficiency during manufacture, to print the patches of silver containing ink for attaching the mounting means with the same printing screen as the resistive heating element, preferably in the same printing step, i.e. in effect at the same time.

Many different types of item may be mounted onto a glazing with the mounting means of the invention, provided that they are not too heavy, e.g. lamps, mirrors, alarms, sensors, handles, hinges, catches, or even lightweight loudspeakers, and a particularly useful application of the invention is to mount an additional stop lamp on a vehicle rear window. Such a lamp is sometimes referred as a high-mounted stop lamp.

The invention also provides a method of bonding a non-current-carrying metallic mechanical element to a glazing, comprising providing the glazing locally with a metal containing layer, and soldering the mechanical element to the layer.

in a preferred version of the method, the mechanical element is a mounting means for mounting an item onto the glazing, and the mounting means includes a generally flat retaining bracket for a stud, the method further comprising inserting the stud in the bracket after the bracket has been soldered to the glazing.

The invention will now be further described by way of the following specific embodimentc, which are given by way of illustration and not of limitation, and with reference to the accompanying drawings in which: Fig 1 shows a vehicle glazing which is provided with a resistive heating element and an additional stop lamp; Fig 2 is a similar view of the glazing, but showing it without the stop lamp; Fig 3 is a greatly enlarged view of a portion of the glazing, showing a mechanical element in the form of part of a mounting means, itself in the form of a generally flat retaining bracket; Fig 4 is a cross-section of Fig 3 taken on line IV-IV, but additionally showing a stud inserted in the bracket; Fig 5 shows a different embodiment of mounting means, in which a stud is soldered directly to the glazing; Fig 6 shows a glazing having a different form of mechanical element, namely a door glass clip which constitutes part of a window lift mechanism.

Several elements are common to more than one of the figures, and like reference numerals denote like elements.

Referring to Fig 1, a glazing 1 is shown which may be used for the rear window of a vehicle. The glazing, which is normally but not necessarily of tempered glass, is provided with a resistive heating element 2 in the form of an array of conducting lines 3 extending between spaced opposed busbars 4, and an additional stop lamp (a high-mounted stop lamp) generally designated 5, which is mounted on the glazing 1. The stop lamp 5 includes a housing 6 and a light source 7, which may be of any conventional type, e.g. a series of bulbs or light-emitting diodes, the exact type being unimportant to the invention. The housing 6 of the stop lamp 5 is mounted on the glazing by mounting means which are not shown in detail in Fig 1, but the location of which is indicated by reference numeral 8. Normally a glazing of this type is also provided with an opaque border 9 (known in the industry as an obscuration band) around its periphery, which is preferably extended to obscure the housing 6 of the stop lamp 5 from external view. However, the obscuration band 9 is represented in Fig 1 merely by indicating its inner edge with a dashed line, since otherwise the housing 6 would, strictly speaking, not be visible. Naturally, an aperture is provided in the obscuration band which corresponds in shape and position to the light source 7.

Fig 2 shows a similar view of the glazing to Fig 1, but without the additional stop lamp 5, and without the obscuration band 9. However, the outline of the lamp is shown for reference by a dashed line 20. A localised metal-containing layer, to which the mounting means is soldered, is shown in the form of two rectangular patches 21. Normally, of course, these patches are hidden from external view by the obscuration band.

As indicated above, the patches are preferably composed of an ink containing fine silver particles which is fired onto the glazing. Generally, the glazing is bent and tempered in the course of its manufacture, and the heat of the bending process fires the ink. However, if the glazing is of flat and annealed glass, a heating step is needed to fire the ink, or alternatively an ink which sets by a different mechanism may be used. Other means of providing the metalcontaining layer may be used, providing that the layer bonds securely to the glass, and also providing that the metal content is high enough, and the layer thick enough, for solder to bond to it strongly enough to support the item which is to be mounted on the glazing.

When the glazing includes other areas of the same ink for other purposes, as in the illustrated case where a resisting heating element 2 is provided, it is preferable to deposit all the desired areas of ink in one process step. Screen-printing is a preferred technique for depositing the conductors and busbars of the resistive heating element, and it is a simple matter to modify the screen to print the two patches 21 in the same printing step. However, when the glazing is not provided with any other areas of metal-containing layer, it may be simplest to paint patches onto the glazing where they are required, or to locally coat the glazing in some other manner.

When screen-printing is used to deposit the patches of metal-containing ink onto the glazing, solderability can be improved by increasing the thickness of the ink. Preferably the grade of printing screen and emulsion are selected to increase the thickness of the print It is also advantageous to use the technique described in EP 281 351 to thicken the patches of metal-containing ink which are printed, without incurring the expense of separately printing a second layer of ink on top of a first layer.

Fig 3 shows a localised area (i.e. a patch) of metal-containing layer greatly enlarged and denoted by reference numeral 21. In this embodiment, the non-current-carrying metallic mechnical element is a mounting means including a generally flat retaining bracket 30 which is soldered to patch 21. The bracket includes a slot 31 for a stud, and the bracket is constructed and arranged to allow the stud to be inserted in the bracket after the bracket has been soldered to the glazing. Although the stud itself is not shown in Fig 3, its location is indicated by dashed line 32. The bracket 30 is soldered to the patch 21 by blobs (i.e. small rounded spots) of solder 33, four blobs being preferable, i.e. one in the vicinity of each corner of the bracket.

Although it is possible to use a continuous layer of solder over all of the periphery of the bracket 30, an arrangement of discrete blobs is preferable because it is better able to accommodate stresses, such as those caused by differential thermal expansion. The bracket 30 has a slightly raised portion which is better shown in Fig 4 and is described below.

Fig 4 shows a cross-section of Fig 3 on line IV-IV, but with the stud 40 added. Part of glazing 1 is shown in cross-section, with patch 21 of metal-containing layer on one face of the glazing. When an obscuration band is present, in cross-section it will normally extend between the patch and the glazing, so as to hide the patch from external view. In other words, the patch is printed or otherwise deposited on the obscuration band. Between the generally flat retaining bracket 30 and the patch 21 is the layer of solder 33 attaching the bracket to the patch. The solder should be chosen to have a melting point (or melting range, in the case of non-eutectic compositions) that is above the maximum temperature expected to be encountered in service, but not so high that attachment of the mechanical element in the factory becomes a problem, nor so high that the temperature required to melt the solder damages the glazing.

Since some vehicle manufacturers specify temperature durability of 1309C for the bond which attaches the mechanical element to the glazing, and it is known that the tensile strength and shear strength of a solder falls off as it approaches its melting point, a suitable range of melting temperatures is from l50QC to 2804C. A suitable family of solders is the tin-lead family which has members melting in the range from 183- C to 2779C, for instance,60/40 Sn/Pb solder has a solidus of 1839C and a liquidus of 187QC. The presence of bismuth in a solder improves its ability to wet the surface to be soldered, and so another preferred solder consists of 25% tin, 62% lead, 10% bismuth and 3% silver. This has a solidus of 1619C and a liquidus of 2309C.

The solder bond is capable of bonding mechanical elements to a glazing more strongly than an adhesive. Although it is preferred to obscure the metal-containing layer (e.g. silver patch 21) from external view by means of an obscuration band as described above, for the attainment of the greatest overall strength, the metal-containing layer should be applied direct to the glazing.

It can be seen from Fig 4 why the bracket 30 is described as only "generally" flat, for it is preferably not absolutely flat. In fact a preferred design comprises a flat peripheral portion 42, and a raised flat central portion 43 which includes the slot 31, the raised portion 43 being joined to the peripheral portion 42 by a sloping portion 44. These portions are also indicated in Fig 3, although their form is not so apparent in plan view.

Preferably the peripheral portion 42 of the bracket is provided in known fashion with pips or dimples to maintain a minimum separation between the peripheral portion and the glazing, thereby providing a space for the solder 33. This alleviates the problem of solder being squeezed out from underneath the foot during soldering, which is both unsightly and weakens the bond.

The bracket 30 may be composed of any metal which lends itself to soldering, tinned copper or brass being preferred. Preferably the bracket is supplied with the blobs of solder already applied to the peripheral portion 42, i.e. it is presoldered, because this makes soldering the bracket to the patch more accurate and rapid. Similarly, it is preferable for the bracket to be supplied with a coating of flux on the peripheral portion.

Also shown in Fig 4 is the stud 40 which comprises a shank or stem 45, which is normally threaded, and a flat base or head 46. The base 46 of the stud is selected to be of appropriate size and thickness for it to slide under the raised flat portion 43 of bracket 30, the shank 45 entering the slot 31 at the same time. Preferably the base 46 is a snug fit in the bracket 30, so that the stud is held captive in the bracket until a nut or equivalent fixing element is threaded onto the shank and tightened.

In an alternative design of the bracket 30 (not illustrated), the flat peripheral portion 42 no longer extends along the longer side of the bracket. The flat peripheral portion 42 is separated into two "feet" and the raised flat central portion 43 extends from one long side of the bracket to the other, conferring a bridged form to the bracket.

Fig 5 shows a second embodiment of the invention in which a stud 50 is soldered directly to the glazing 1, or more precisely, the base 51 of the stud is soldered directly to the patch 21 of metal-containing layer, i.e. the retaining bracket is dispensed with. Again, the shank 52 of the stud may be threaded or otherwise adopted to receiving a corresponding securing element such as a nut to secure the lamp or other item on the studs. The base 51 of the stud may be provided with pips or dimples as described above in relation to the bracket, and likewise may be made from the same materials pretreated in the same way. Furthermore, the base 51 may also be of bridged form.

The advantage of the first (Figs 3 and 4) embodiment may be seen by comparing Figs 4 and 5. In Fig 4, the thickness, or height, of the bracket 30 is indicated by arrow H. This is the amount by which the thickness of the glazing is increased when the bracket 30 is soldered to it.

The corresponding thickness or height of the glazing of Fig 5 is denoted by arrow J. As mentioned earlier, the glazing is generally manufactured in one factory (the "glass plant") and transported to another factory (e.g. a vehicle assembly plant) for the next assembly step such as installing the glazing in a vehicle. Since the stud 40 need only be inserted into the bracket after the glazing has been transported to the vehicle assembly plant, the number of glazings which can be transported in one container, pallet, stillage, rack or other transport package (i.e.

the packing density) is governed, inter alia, by the thickness of the glazings as packed.

Clearly, the thickness H (Fig 4) of the bracket 30 is much less than corresponding thickness J of the stud 50 of Fig 5, allowing a greater packing density to be achieved with the first (Fig 4) embodiment Preferably, thickness H is less than 10 mm, more preferably it is less than 5 mm, and in an especially slim version it is less than 3 mm; The latter figure allowing virtually the same packing density to be achieved as with plain glazings to which no brackets have been attached. Furthermore, it will be appreciated that if inadvertent contact is made between one glazing and another during handling, the raised portion 43 of the generally flat retainer bracket 30 is far less likely to cause scratching or other damage than the protruding tip of stud 50. The slim design of bracket is also advantageous in that it facilitates the use of automatic soldering machines for the step of soldering the bracket to the glazing; the brackets 30 are easily packed into a magazine of such a machine, whereas the studs 50 are not, owing to their bulk and shape.

Fig 6 shows a vehicular door glass 60 to which a mechanical element in the form of a door glass clip 61 has been attached by soldering. Preferably the upper part of the clip is in the form of a channel 62 and either the side(s) or base of the channel may be soldered to the glass. At least the part of the clip to be soldered is composed of a solderable metal. Again, a localised metal-containing layer in the form of silver patches 63 has been applied to the glazing in the area to be soldered. The door glass clips are thereby bonded to the glass more securely than is possible with adhesives. The remainder of the door glass lift mechanism is connected to the door glass clips, e.g. by tapped holes 64, and is conventional.

The invention as described above allows product specifications set by vehicle manufacturers to be met more reliably and cost-effectively than the prior art technique of bonding a mounting means to a glazing with an adhesive, especially where high temperature durability is required.

In all the above versions of the invention, the mechanical element, though at least partly made of metal to enable it to be soldered, does not carry an electric current in normal service.

The soldered bond is therefore employed solely for its mechanical properties, and not, as is usually the case, for its properties of electrical conduction.

Claims

1. A glazing to which a non-current-carrying metallic mechanical element is bonded, wherein the glazing is provided locally with a metalcontaining layer, and the mechanical element is bonded to the glazing by soldering it to the metal-containing layer.

2. A glazing as claimed in claim l, wherein the mechanical element is bonded to the glazing by a solder which melts within the temperature range from 1509C to 280QC.

3. A glazing as claimed in claim 2, wherein the solder melts within the temperature range from l to 235QC.

4. A glazing as claimed in claim 2, wherein the solder is a tin-lead solder which melts within the temperature range from 1839C to 2779C.

5. A glazing as claimed in claim 2, wherein the solder consists of 25% tin, 62% lead, 10% bismuth and 3% silver.

6. A glazing as claimed in any preceding claim, wherein the mechanical element is a mounting means for mounting an item onto the glazing.

7. A glazing as claimed in any one of claims l to 5, wherein the mechanical element is part of a larger mechanism or assembly.

8. A glazing as claimed in any one of claims 1 to 5, wherein the mechanical element is a locating or retaining device which assists during installation of the glazing in an aperture.

9. A glazing as claimed in claim 6, wherein the mounting means includes a generally flat retaining bracket for a stud, and the bracket is constructed and arranged to allow the stud to be inserted in the bracket after the bracket has been soldered to the glazing.

10. A glazing as claimed in claim 9, wherein the bracket is less than 10 mm thick

11. A glazing as claimed in claim l(), wherein the bracket is less than 5 mm thick

12. A glazing as claimed in claim 11, wherein the bracket is less than 3 mm thick,

13. A glazing as claimed in claim 6 or in any one of claims 9 to 12, wherein the item to be mounted is an additional stop lamp.

14. A glazing as claimed in any preceding claim, wherein the metal-containing layer is provided in the form of a silver-containing ink, which is screen-printed onto the glazing with a printing screen.

15. A glazing as claimed in claim 14, wherein the glazing also includes a resistive heating element, which is also screen-printed on the glazing using the same printing screen.

16. A glazing substantially as herein described with reference to and as illustrated in Figures 1 to 4 or Figures 1, 2 and 5, or Figure 6 of the accompanying drawings.

17. A method of bonding a non-current-carrying metallic mechanical element to a glazing, comprising providing the glazing locally with a metalcontaining layer, and soldering the mechanical element to the layer.

18. A method as claimed in claim 17, wherein the mechanical element is a mounting means for mounting an item onto the glazing, and the mounting means includes a generally flat retaining bracket for a stud, the method further comprising inserting the stud in the bracket after the bracket has been soldered to the glazing.

19. A method as claimed in claim 17 or claim 18, comprising the step of screen-printing the metal-containing layer onto the glazing, the metal-containing layer being in the form of a silver-containing ink.

20. A method as claimed in claim 17 or claim 18, comprising painting the metalcontaining layer onto the glazing.

21. A method as claimed in claim 19, comprising screen-printing a resistive heating element onto the glazing in the same screen-printing step.

22. A method of bonding a non-current-carrying mechanical element to a glazing substantially as herein described with reference to and as illustrated in the accompanying drawings.