GB2190877A - Glazing panels - Google Patents

Description

GB 2 190 877 A 1

SPECIFICATION

Glazing panels This invention relates to a g lazing panel comprising at least two sheets of glass bonded together into a 5 laminate by i ntervening adhesive material in which at least one glass sheet bears an electrically conductive coating extending between at leasttwo electrodes. The invention also relates to a g lazing panel comprising a conductively coated g lass sheet.

Such glazing panels are occasionally used as part of an alarm system. The panels may be connected into an electrical circuit which includes means for monitoring the resistance of the coating and for souncing an alarm 10 if that resistance changes due for example to breakage of the g lass sheet bearing the coating.

Such circuits may be divided into two categories, so-called "al 1-ornothing " circu its, which require substantially complete opening of the circuit across the coating, and circuits which respond to any change in the resistance of the coati ng which is more than a preselected threshold val ue. Such threshold circuits tend to be rather complicated, because not only should they be able to respond to partial breakage of the coated 15 sheet, but they should also be proof against spu rious alarm sig nals due to resistance changes brought about by variations in the temperature of the g lazing panel on changes in the weather. "AI 1-or-nothing " circuits, since they simply respond to the presence or substantial absence of cu rrent f low across the coating can be very much simpler and therefore less expensive to manufacture and install.

In order for an "all-or-nothing " circuit to work, it wil 1 be appreciated that it is necessary for currentf low 20 throug h the coating to be substantially completely interrupted. It is not always easy to ensu re that this will be the case, especially where the coated g lass sheet is incorporated in a laminated glazing panel. If the glass sheets of the laminate are annealed, it is by no means certain that any cracks in the laminate will propagate all the way across it, with the result that for example a small hole could be cut i n the la minate to allow unauthorised access to an interior door or wi ndow handle wthout causing an alarm sig na 1. If the glass sheets 25 are tempered, crack propagation right across the lam inate is su bstantial ly ensu red, but the resulting glass fragments tend to be held together by the adhesive used to bond the laminate, with the result the breaking of the circu it through the coating is not reliable if only a small hole is made in the panel.

It is an object of this invention in its first aspect to provide a laminated g lazing panel which wil 1 a] low a substantially reliable interruption of the conductive coating on breakage and which is therefore particularly 30 suitable for use in conjunction with a relatively inexpensive alarm circuit, for example a circuit of the "a] 1-or-nothing " type.

According to the present invention, there is provided a g lazing panel comprising at least two sheets of glass bonded together i nto a laminate by intervening adhesive material in wh ich at least one g lass sheet bears an electrically conductive coating extending between at least two electrodes, cha racterised in that 35 su rface layers of at least two g lass said sheets are unequal ly stressed so that on breakage, one g lass sheet is caused to break into smal ler f ragments than another thereby to impart a cu rvature to the laminate, and in that said conductive coating is appi ied to a sheet face which will become convex on such breakage.

Because the coated sheet face wil 1 become convexly curved on breakage of the lam inate, separation of the coating at the junction between neighbouring fragments of the coated sheet when broken is ensured, so 40 giving a more reliable interruption of the conductive coating.

The deg ree of curvatu re which will be i mparted to the la minate on breakage is fou nd to depend on the way in which the individual glass sheets break, and this in tu rn depends on the extent to which their surfaces are stressed. In general the more highly stressed are the surfaces of a glass sheet, the g reater is the amount of energy which wil 1 be released on breakage of that sheet and which wi 11 accordingly be availa ble forthe 45 creation of new surfaces so implying that the sheet will break into a larger number of fragments, and into smaller frag ments. It is fou nd that i n a laminate of glass sheets whose su rf aces are u neq ually stressed, the sheet which is more stressed breaks into smal ler fragments a nd consequently the face of the other sheet which is directed towards that more hig hly stressed sheet tends to become convex. It is to be borne i n mind in this context that it is not on ly the absolute su rface stress which is i m portant, but also the depth to which the 50 su rface of the sheet is stressed. By way of example two g lass sheets of the same thickness, say 5m m, may be tempered to increase their su rf ace stress, one by a chemical tem peri ng techn iq ue and the other by a thermal tempering technique. By chemical tempering, the surface stress in the glass can be raised to a mean value of as much as 1 OOOMPa, but only over about 20Km at each face. By thermal tempering, the su rface stress in the glass can be raised to a mean val ue of, say, 130M Pa, over about one fifth of its thickness at each face. Taking 55 into accou nt the stress and the depth to wh ich the glass is stressed therefore, over a u nit area of the sheets, the amou nt of energy stored in the thermal ly tempered sheet is six to seven ti mes greater than is stored in the chemical ly tempered sheet. As a resu It, the thermal ly tempered sheet wil 1 tend to break into smal ler frag ments than the chem ical ly tempered sheet.

It is also to be noted that because one sheet is less high ly su rf ace stressed that another, it wi 11 tend to break 60 into larger f ragments. It is found that the presence of large f ragments i n the space occu pied by a 9 lazing panel tends to make access through that space more difficult.

In preferred embodiments of the invention, one glass sheet of the laminate is su rface stressed to impartto it a mechanical resistance which is at least 1.5 times, a nd preferably at least twice, that of another glass sheet of the laminate. The adoption of this preferred feature has several advantages. The more highly stressed 65 2 GB 2 190 877 A 2 sheet is thereby made more difficult to break in the first place, imparting additional security to the space enclosed. In the event of breakage, that sheet will tend to break into fragments which, because of the greater difference in stress between the sheets, will be relatively smaller so imparting a greater curvature to the laminate on breakage. It has been found that this greater curvature can be sufficient to ensure the propagation of cracks across the full width of the said other sheet. This is can be of value if the said other 5 sheet is a sheet of annealed glass. In the case of annealed glass, even breakage due to impact may not ordinarily be sufficient to ensure the propagation of cracks all the way across it, but the curvature imparted to such an annealed sheet which is laminated to a relatively highly stressed sheet as aforesaid will cause additional stress in the annealed sheet and can resu It in the reliable propagation of a crack from side to side thereof, and thus in reliable alarm signalling.

Advantageously, one glass sheet of the laminate is surface stressed to impart to it a mean compressive surface stress of at ieast65MPa. This promotes a high resistance to mechanical shock so making the sheet more difficuitto break, and ensures that when broken, the sheetwill fragment into small pieces.

Preferably, said coating is applied to a sheet face which is interior of the panel. This helps to protectthe coating against accidental damage for example due to over-enthusiatic cleaning, and against weathering. It 15 is also important in helping to prevent the coating from becoming covered with a film or droplets of moisture, for example due to rain or condensation. it is possible that such moisture would be able to form a conductive bridge, so preventing the generation of an alarm signal on breakage of the panel. Byway of example, such coating could be applied as an exterior coating of a laminate which is to be incorporated as one pane of a hollow glazing panel. It is preferred however that the coating should be applied to a sheetface 20 which is interior of the laminate, since this gives better protection against condensation and weathering, and also against damage during handling prior to installation.

Advantageously, at least one glass sheet is so shaped as to leave a marginal rebate in the laminate for accommodating a connector attached to each said electrode. This avoids the need to shape a frame forthe laminate in such away as to accommodate the connectors which will be required for installing the panel in an 25 alarm system.

It is preferred thatthe oreach such marginal rebate accommodates a said connector and isfilled with a non-conductive filler material. This gives a neat edge to the laminatewhich simplifies framing.

In some preferred embodiments of the invention, such laminate comprises a chemically tempered glass sheet and a thermally tempered glass sheet. Such tempered sheets can be very highlystressed in their 30 surfaces, so giving a very high resistanceto breakage. Also, because of those stresses, crack propagation all theway acrossthe sheets is ensured on breakage. In orderto ensure convexity of the coated sheetface on breakage,the coating could be applied tothatface of the thermally tempered sheetwhich will face awayfrom the chemically tempered sheet in the laminate, but it is preferred thatsaid coating is applied to a face of such chemically tempered sheetwhich faces such thermailytempered sheet. 35 In other preferred embodiments of the invention, such laminate comprises a thermally toughened glass sheetand a tempered glass sheet. The expression "thermally toughened" is used herein to denote glass which has been subjected to a thermal conditioning such as to inducetherein compressive surface stresses in the range 24MPa to 70MPa.

Such tempering can be effected by a chemical or a thermal treatment. It isto be noted here that chemically 40 tempered and thermally toughened glass sheets have rather better optical qualitythan dothermally tempered glass sheets. It appears that the thermal tempering processtendsto have a somewhat deleterious effect on the planeity of a glass sheetto which is is applied. However chemically tempered glass is more expensivethan thermally tempered glass.

Such a laminatewill not be so resistantto breakage as a laminate of the same thickness made using 45 tempered sheet as aforesaid, but it is less expensiveto manufacture and still give reliable interruption ofthe conductive coating. The coating could be applied to thatface of thetempered sheetwhich will faceaway from the toughened sheet, but it is preferred that said coating is applied to a face of such thermally toughened sheetwhich faces such tempered sheet.

In yet other embodiments of the invention, such laminate comprises an annealed glass sheet and a 50 tempered or thermally toughened glass sheet. Such a laminatewili not be so resistantto breakage asa laminate of the samethickness made using tempered sheets ortempered and thermally toughened sheets as aforesaid, but it is still less expensiveto manufacture and again can give reliable interruption of the conductive coating. The coating could be applied to thatface of thetempered ortoughened sheetwhichwill face awayfrom the annealed sheet, but it is preferred thatsaid coating is appliedto a face of such annealed 55 sheetwhich facessuch tempered ortoughened sheet.

The use of a thermally toughened glass sheetforthe purposes in view presents consderable advantages, and is itself believed to be new. Accordingly, in itssecond aspect, the present invention provides a glazing panel comprising a conductively coated glass sheet, characterised in that said conductive coating extends between at leasttwo electrodes and is applied to a face of a glass sheetwhich has been thermailytoughened. 60 Such a sheet has an increased mechanical resistance as compared with an annealed sheet, and crack propagation across itsfull extent is ensured on breakage, so giving a reliable alarm signal when connected into an alarm system. Such a sheet is also less expensiveto manufacturethan a tempered sheet, whether the tempering is effected thermally orchernically, and a simple sheetof thermally toughened glass isvery much less expensive to manufacture than a laminated glass pane. Such a panel therefore enables a basic degree of 65 3 GB 2 190 877 A 3 protectionto be afforded at lowcost, and can be used in conjunction with an alarm circuitofthe all-or-nothing" type, also of lowcost,to give a reliable alarm signal on breakage. Such athermally toughened, coated glasssheet mayof course be incorporated into a hollowgiazing panel togetherwith another glass sheet which may be thermally or chemically tempered if desired, in orderto giveadditional protection. This will of course be morecostly, but maystill be less expensive than the use of a laminated 5 pane.

In the most preferred embodiments of the invention, said electrodes are localised electrodes. The use of localised electrodes as opposed to bus strips which could extend along the full length of opposite side of the coated sheetface gives the advantage that circuit interruption is more likely to occurwith a relatively small crack across the panel. For example, if, as is preferred, such localised electrodes are located at substantially 10 diametrically opposed positions in the panel, then a diagonal breakage across a corner of the panel which carries such an electrode will cause interruption of an alarm circuit into which the panel is connected.

However if full length bus strips were to be used in such a situation, there would still be a current path unless the coated sheet was broken across the full width between the bus strips.

Advantageously, said conductively coated sheet is polygonal and said electrodes are deposited at each 15 corner of the conductively coated sheetface. This allows greater versatility in connecting the electrodes to an alarm circuit.

Preferably, said electrodes are constituted by deposits of conductive enamel. This may be an organic enamel, or an inorganic enamel, and it is preferably a silver containing enamel. Such enamels are simple and relatively inexpensiveto apply, and theycan provide a surfacewhich is easilywettable by molten solder, 20 which makes reliable connection to a connector particularly convenient.

In the most preferred embodiments of the invention, said coating is a coating of doped tin oxide. Dopecitin oxide coatings can easily be given an appropriate resistivity for the purposes in view, they can be applied in a relatively inexpensive way as compared for examplewith metallic coatings, and they can easily beformed so thatthey are hard and weather resistant. Such coatings can also have a high optical quality so thatthey do not 25 interfere with vision through the coated sheet.

The present invention extends to a panel as hereinbefore defined wherein said electrodes are connected into an electric circuit comprising means for maintaining a potential difference across said coating between said electrodes and signal means for generating a signal in response to a decrease in flow of currentthrough the coating to or below a predetermined value. 30 The present invention will now be described in greater detail with reference to the accompanying diagrammatic drawings in which Figure 1 is a cross sectional view of a laminated glazing panel Figure2 is a cross sectional view of a coated sheet of glass Figure 3 is a cross sectional view of a glazing panel incorporating a laminated pane 35 Figure 4 is a perspective view of a corner of the laminate of Figure 1, and Figures 5and 6 are diagrammatic views of two panels connected into electrical circuits for monitoring current flow through the conductive coating.

Figure 1 shows a laminate 1 comprising a first sheet of glass 2 which bears a conductive coating 3 and whose coated face is bonded to a second glass sheet 4 by an intervening layer of adhesive thermoplastics 40 material 5.

Figure 2 shows a single sheet of glass 6 bearing a conductive coating 7 which extends between electrodes8 located at opposite ends of the sheet 6.

Figure 3 shows a hollow glazing panel incorporating a laminated pane 9 comprising a first glass sheet 10 bonded via an intervening layer of thermoplastics adhesive material 11 to one face of a second glass sheet 12 45 whose otherface bears a conductive coati ng 13. The coated (13) face of the second glass sheet 12 is bonded by glue layers 14 to a marg inal spacer member 15 which is i n turn bonded to a thi rd g lass sheet 16.

Figure 4 shows a corner of the laminate 1 and illustrates how an electrode such as the electrode 8 of Figure 2 may be arranged as a localised electrode occu pying a corner of the coated glass sheet 2. In Fig u re 4, the second glass sheet 4 is bevel led 17 at its corner so as to leave a rebate 18 in the margin of the laminate 1 atthe 50 region of the electrode 8 in order to accommodate a connector 19 which may for exam pie be soldered to the electrode 8. After attachment of the connector 19, the rebate 18 may be filled u p with a non-conductive fil [er material, for example an epoxy resin. At least one other corner, preferably at least the diagonal ly opposite corner, of the laminate 1 is of similar construction.

Figure 5 il lustrates a conductively coated panel 1 bearing an electrode 8 at each of its four corners 55 connected into a monitoring circuit. One electrode is directly connected to earth, while the diagonally opposite electrode is connected to a battery and then via a resistor 20 and an induction coil 21, to earth. A typical panel may have a conductive coating with a resistance of 200 ohms, and it is suitable to use a 12 volt battery and a balancing resistor 20 also of 200 ohms. On breakage of the panel, its conductive coating wil 1 be ru ptured and its resistance will suddenly i ncrease to something of the order of 1 megoh m, with a consequent 60 suddent change in the current f]owing i n the circuit shown. The induction coil 21 can then operate to induce an alarm sig nal. If desired that coil may be replaced by a relay.

In Figure 6 a possible alternative circuit is shown in which one electrode of the panel is again connected directlyto earth. The opposite electrode is connected via a battery and a resistor 22 to an operational amplifier 23 arranged to deliver an alarm signal on change of current through the conductive coating of the 65 4 GB 2 190 877 A 4 panel 1.

Examples 1 to 3 These Examples are all constructed in accordance with Figures 1 and 4. In these Examples each of the glass sheets 2 and 4 is of float glass 6mm thick,the coating 3 is of doped tin oxide having a thickness of 750nm and 5 a resistivity of 20ohms persquare, and the adhesive material used was polyvinylbutyral 0.76mm thick. The following Table 1 shows various treatments applied to the glass sheets 2 and 4togetherwith mean compressive surface stresses induced thereby.

TABLE 1 10

Sheet2 Sheet4 EX. Treatment Stress MPa Treatment Stress MPa 1 Thermal toughening 60 Chemical tempering 550x32Km 2 Thermal toughening 60 Thermal tempering 130 15 3 Chemical tempering 600x32Rm Thermal tempering 130 Each of these panels is designed to be located with itsfirst, coated sheet 2 facing the exterior of an enclosure whose interior it is desired to protect. In each case it is found that if an attack on that first sheet 2 is sufficiently strong to destroythe integrity of the second sheet 4, which is more highly surface stressed dueto 20 the nature of thetreatments to which the sheets have been subjected, that second sheet4 will fragment and impart a convex curvature to the coated face of the first sheet. This curvature imparts additional stress to the first sheet 2 and is sufficientto ensure that it becomes broken from edge to edge if this has not already been done bythe initial attack. As a result of this, and because of the curvature imparted to the coated face, positive separation of the coating 3 is ensured so allowing for a reliable alarm signal to be delivered by a rathersimple 25 circuitto which the panel may be connected.

Example 4

The sheet illustrated in Figure 2 is a sheet of glasswhich has been thermally toughened to induce in ita mean compressive surface stress of 70MPa. 30 Examples 5 to 7 These Examples are all constructed in accordancewith Figure 3. In these Examples each of the glasssheets 10,12 and 16 is of drawn glass4mm thick,the coating 13 is of doped tin oxide having a thickness of 850nm and a resistivity of 25 ohms persquare, and the adhesive material 11 usedwas polyvinylbutyral 0.76mm 35 thick. Thefollowing Table 2 shows various treatments applied to the glass sheets 10 and 12 togetherwith mean compressive surface stresses induced thereby.

TABLE 2

40 Sheet10 Sheet12 Ex. Treatment Stress MPa Treatment Stress MPa Thermal toughening 65 Chemical tempering 60OX30Km 6 Thermal toughening 65 Thermal tempering 130 7 Chemical tempering 500x20Km Thermal tempering 130 45 In each case it is found that if an attack on the first sheet 10 is sufficiently strong to destroy the integrity of the second sheet 12, which is more highly surface stressed due to the nature of the treatments to which the sheets have been subjected, that second sheet 12 will fragment and impart a convex curvature to its coated face. 50 In variants of Examples 5 to 7, the laminated pane 9 of Figure 3 is replaced by a laminated pane 1 of any of Examples 1 to 3, or bythe thermally toughened and coated sheet 6 of Exampie4.

Claims (15)

1. 55 1. A glazing panel comprising at least two sheets of glass bonded together into a laminate by intervening adhesive material in which at least one glass sheet bears an electrically conductive coating extending between at least two electrodes, characterised in that surface layers of at least two said glass sheets are unequally stressed so that on breakage, one glass sheet is caused to break into smal lerf ragments than another therebyto impart a curvature to the laminate, and in that said conductive coating is applied to a sheet 60 face which will become convex on such breakage.
2. 2. A panel according to claim 1, wherein one glass sheet of the laminate is surface stressed to impartto it a mechanical resistance which is at least 1.5 times, and preferably at least twice, that of another glass sheet of the laminate.
3. 3. A panel according to claim 1 or2, wherein one glass sheet of the laminate is surface stressed to impart 65 GB 2 190 877 A 5 to ita mean compressive surfacestress of at least65MPa.
4. 4. A panel according to any preceding claim, wherein said coating is applied to a sheet face which is interior of the panel.
5. 5. A panel according to claim 4, wherein at least one glass sheet is so shaped as to leave a marginal rebate in the laminate for accommodating a connector attached to each said electrode. 5
6. 6. A panel according to claim 5, wherein the or each such marginal rebate accommodates a said connector and is filled with a non-conductive filler material.
7. 7. A panel according to any of claims 4 to 6, wherein such laminate comprises a chemical lytempered glass sheet and a thermally tempered glass sheet.
8. 8. A panel according to any of claims 4 to 6, wherein such laminate comprises a thermally toughened 10 glass sheet and a tempered glass sheet.
9. 9. A glazing panel comprising a conductively coated glass sheet, characterised in that said conductive coating extends between at least two electrodes and is applied to a face of a glass sheet which has been thermally toughened.
10. 10. A panel according to any preceding claim, wherein said electrodes are localised electrodes. 15
11. 11. A panel according to any preceding claim, wherein said electrodes are located at substantially diametrically opposed positions in the panel.
12. 12. A panel according to any preceding claim, wherein said conductively coated sheet is polygonal and said electrodes are deposited at each corner of the conductively coated sheet face.
13. 13. A panel according to any preceding claim, wherein said electrodes are constituted by deposits of 20 conductive enamel.
14. 14. A panel according to any preceding claim, wherein said coating is a coating of doped tin oxide.
15. 15. A panel according to any preceding claim, wherein said electrodes are connected into an electric circuit comprising means for maintaining a potential difference across said coating between said electrodes and signal means for generating a signal in response to a decrease in flow of current through the coating to or 25 below a predetermined value.

    Printed for Her Majesty's Stationery Office by Croydon Printing Company (11 K) Ltd, 10187, D8991685.

    Published by The Patent Office, 25 Southampton Buildings, London WC2A l AY, from which copies maybe obtained.

    i