LU86892A1 - GLAZING COMPRISING A SHEET OF GLASS THAT HAS A CONDUCTIVE COATING - Google Patents

Description

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The present invention relates to a glazing unit comprising at least two sheets of glass secured to one another in the form of a laminated panel by means of intermediate adhesive material, in which at least one sheet of glass carries a conductive coating. electricity extending between at least two electrodes. The invention also relates to a glazing unit comprising a glass sheet carrying a conductive coating.

Such glazing is occasionally used as components of an alarm system. The glazing units can be connected in an electrical circuit which comprises means for monitoring the resistance of the coating and for setting off an alarm if the resistance varies due, for example, to the rupture of the sheet of glass carrying the coating.

Such circuits can be classified into two categories, circuits called "all or nothing", which require a substantially complete opening of the circuit through the coating, and circuits which prevent any variation in the resistance of the coating greater than a predetermined threshold value. Such threshold circuits tend to be relatively complicated because they must not only be able to respond to a partial rupture of the sheet carrying the coating, but they must also be resistant to accidental alarm signals due to variations of the resistance generated by variations in the temperature of the glazing due to climatic changes.

The "all or nothing" circuits, since they simply respond to the presence or substantial absence of current flowing through the coating, can be much simpler and therefore less expensive to manufacture and install.

Note that, for an "all or nothing" circuit 35 to work, it is necessary that the current flowing through the coating be substantially completely interrupted. It is not always easy to ensure that this is the - 1 l 2.

case, especially when the glass sheet carrying the coating is incorporated in a laminated glazing. If the glass sheets of the laminated panel are annealed, it is by no means certain that cracks in the laminated panel will spread over its entirety, and as a result, for example, a small opening can be cut in the laminated panel to allow unauthorized access to an interior door or window handle without causing an alarm signal. If the glass sheets are toughened the propagation of cracks over the whole of the laminated panel is substantially ensured, but the glass fragments produced tend to be held together by the adhesive used to secure the laminated panel, and it follows that the rupture of the circuit through the coating-15 is not certain if only a small opening is made in the panel.

One of the objects of the present invention in its first aspect is to provide a laminated glazing which allows a substantially certain rupture of the conductive coating during its fracture and which is therefore particularly suitable for its use in a relatively alarm circuit. inexpensive, for example an "all or nothing" type circuit.

The present invention relates to a glazing unit 25 comprising at least two sheets of glass secured to one another in the form of a laminated panel by means of intermediate adhesive material, in which at least one sheet of glass carries a conductive coating electricity extending between at least two electrodes, character-ized in that the surface layers of at least two said sheets of glass are the seat of unequal stresses so that at rupture, one of the sheets of glass breaks into smaller fragments than another, thereby imparting curvature to the laminated panel, and in that said conductive coating is applied to a sheet face which becomes convex upon such rupture.

Because the side of the sheet bearing the coating 3.

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tement will be curved convexly during the rupture of the laminated panel, the separation of the coating will be ensured at the junction between neighboring fragments of the sheet carrying the coating when it is broken. This promotes a more certain interruption of the conductive coating.

It has been found that the degree of curvature which will be imparted to the laminated panel upon breaking depends on how the glass sheets break individually, which, in turn, depends on the extent of the stresses on their surfaces are headquarters. In general, the higher the stresses in the surface of a glass sheet, the greater the amount of energy released at the breaking of this sheet. This energy will thus be available to create a new surface, which implies that the sheet will break into a larger number of smaller fragments. It has been found that in a laminated panel whose surfaces of the glass sheets which constitute it are the seat of unequal stresses, the sheet with the highest stresses breaks into smaller fragments and, consequently, the face of the The other sheet which is directed towards the one with the higher stresses tends to become convex. It will be appreciated in this context that it is not only the absolute surface stress which is important, but also the depth of the layer of the sheet which is the seat of these constraints. For example, two sheets of glass of the same thickness, 5 mm for example, can be toughened to increase their surface stresses, one by a chemical toughening treatment and the other by a thermal toughening treatment. By chemical toughening, the surface stress in the glass can be increased to an average value as high as lOOOMPa, but only about 20pm for each side. By thermal toughening, the surface stress in the glass can be increased to an average value of, for example, 130 MPa, over about a fifth of its thickness for each face. Taking into account the constraint and the - i ί 4.

depth of the layer which is the seat of these constraints, per unit area of the sheets, the amount of energy stored in the thermally quenched sheet is six to seven times greater than that stored in the chemically quenched sheet. As a result, the thermally quenched sheet will break into smaller fragments than the chemically quenched sheet.

It will also be noted that, since one of the sheets of the laminated panel is the seat of lower stresses than another, it will tend to break into larger fragments. It has been found that the presence of larger fragments in the space occupied by a glazing tends to make access through this space more difficult.

In preferred embodiments of the invention, a sheet of glass of the laminated panel is the seat of a surface stress giving it a mechanical resistance which is at least 1.5 times, and preferably at least twice, that of another glass sheet 20 of the laminated panel. Adopting this preferred feature has several advantages. The more a sheet is the seat of high stresses, the more difficult it is to break it in the first place, which gives additional security to the space that we want to protect. In the event of rupture, this sheet tends to break into fragments which, due to the greater difference in stresses between the sheets, will be relatively smaller by imparting greater curvature to the laminated panel upon rupture. It has been found that this greater curvature may be sufficient to ensure the propagation of the cracks over the entire width of the other sheet. This can be advantageous if the other sheet is an annealed glass sheet. In the case of annealed glass, even the fracture due to impact may not normally be sufficient to insure the propagation of cracks. But the curvature imparted to such an annealed sheet which is laminated with a sheet with relatively high stresses as has been J "5.

said previously will cause additional stress in the annealed sheet. This could result in the more certain propagation of a crack from one edge to the other of the sheet and thus, the more reliable generation of an alarm signal. .

Advantageously, a sheet of glass of the laminated panel is the seat of an average surface stress in compression of at least 65 MPa. This promotes high resistance to mechanical shock by making the sheet 10 more difficult to break, and ensures that, when broken, it will fragment into small pieces.

Preferably, the coating is applied to a sheet face which is inside the panel. This contributes to protecting the coating against accidental deterioration, for example due to overly vigorous cleaning, and against aging. This characteristic is also important because it helps 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 humidity is capable of forming a conductive bridge, thus avoiding the generation of an alarm signal when the glazing breaks. By way of example, such a coating can be applied in the form of an external coating of a laminated panel which must constitute one of the panels of a hollow glazing. It is preferred, however, that the coating be applied to a sheet face which is internal to the laminated panel, since this provides better protection against condensation and aging, as well as against deterioration during handling before placement.

Advantageously, at least one glass sheet is shaped so as to leave a marginal rebate for the laminated panel intended to receive a connector attached to each of said electrodes. This avoids the need to frame a frame for the laminated panel so as to receive the connectors necessary for incorporating the panel into an alarm system.

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We. prefers that the or each such marginal rebate receives a said connector and is filled with a non-conductive filler. This provides a clean edge to the laminated panel, which simplifies mounting.

In certain preferred embodiments of the invention, the laminated panel comprises a sheet of chemically toughened glass and a sheet of thermally toughened glass. The surfaces of such toughened sheets can be the site of very high stresses, giving a very high resistance to breakage. In addition, due to these constraints, the propagation of cracks through the sheets is ensured during rupture. In order to ensure the convexity of the face of the sheet carrying the coating upon rupture, the coating can be applied to the face of the thermally quenched sheet which does not face the sheet chemically quenched in the laminated panel . It is preferred, however, that the coating be carried by the face of the chemically quenched sheet which faces the thermally quenched sheet.

In other preferred embodiments of the invention, the laminated panel comprises a sheet of thermally hardened glass and a sheet of tempered glass. The term "thermally hardened" is used herein to describe glass which has been subjected to thermal conditioning so as to induce therein compressive stresses included in the range of values 24MPa to 70MPa.

Such quenching can be carried out chemically or thermally. It will be noted here that sheets of chemically toughened and thermally toughened glass have a higher optical quality than sheets of thermally toughened glass. It appears that the thermal tempering process tends to have a somewhat detrimental effect on the flatness of a glass sheet to which it is applied. However, chemically toughened glass is more expensive than thermally toughened glass.

Such a laminated panel will not be as strong

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both at break than a laminated panel of the same thickness produced by means of toughened sheets as described above, but it is less expensive to manufacture and provides a more reliable interruption of the conductive coating. The coating can be applied to the side of the hardened sheet which does not face the hardened sheet, but it is preferred that it is applied to the side of the thermally hardened sheet which faces the hardened sheet.

In other embodiments of the invention, such a laminated panel comprises an annealed glass sheet and a toughened or thermally toughened glass sheet. Such a laminated panel will not be as resistant to breakage as a laminated panel of the same thickness produced by means of toughened sheets or toughened and thermally hardened sheets as described above, but it is less expensive. to manufacture and can also provide a definite interruption of the conductive coating. The coating can be applied to the side of the quenched or cured sheet which does not face the annealed sheet, but it is preferred that it be applied to the side of the annealed sheet which faces the quenched or cured sheet.

The use of a thermally cured glass sheet for the intended purpose has considerable advantages, and it is believed that this is new in itself. Therefore, in its second aspect, the present invention relates to a glazing unit comprising a glass sheet carrying a conductive coating, characterized in that said conductive coating extends between at least two electrodes and is applied to one face of a sheet of glass which has been thermally hardened. Such a sheet has a higher mechanical resistance than an annealed sheet and, at break, the propagation of cracks is ensured over its entire extent, thus obtaining the reliable generation of an alarm signal when it is connected in a alarm system. Such a sheet is also less expensive to manufacture than a quenched sheet, whether the quenching is carried out thermally or chemically. A single sheet of thermally hardened glass> * 8.

is much less expensive to manufacture than a laminated glass panel. For this reason, such a panel makes it possible to offer a certain level of protection at low cost, and can be used in conjunction with an alarm circuit of the all-or-nothing type, also inexpensive, to give the rupture a reliable alarm signal. Such a thermally cured, coated glass sheet can of course be incorporated into hollow glazing with another glass sheet which can be thermally or chemically toughened if desired, in order to provide additional protection. This will obviously be more expensive, but nevertheless less expensive than the use of a laminated panel.

In the preferred embodiments of the invention, said electrodes are localized electrodes. The use of localized electrodes, as opposed to bus strips which extend over the entire length of the opposite sides of the sheet face carrying the coating, provides the advantage that the interruption of circuit 20 is more certain. to occur with a relatively small crack across the panel. For example, if, as is preferred, said electrodes are disposed at locations on the panel which are substantially diametrically opposed, a diagonal break through a corner of the panel which carries such an electrode will cause interruption an alarm circuit in which the panel is connected. On the other hand, if full length bus strips are used in such a situation, there may still be a path for the current, even if the sheet 30 carrying the coating is broken, across the entire width between the bus strips.

Advantageously, said sheet carrying a conductive coating is polygonal and the electrodes are deposited at each corner of the sheet face carrying the conductive coating. This allows greater flexibility in connection of the electrodes in an alarm circuit.

Preferably, said electrodes are made up of * * * 9.

killed with layers of conductive enamel. You can use an organic enamel or an inorganic enamel. It will preferably be an enamel containing silver. The application of such enamels is simple and relatively inexpensive, and they can provide a surface which is easily wettable by molten solder, which gives a reliable connection to a suitable connector.

In the preferred embodiments of the invention, said coating is a doped tin oxide coating. It is easy to give doped tin oxide coatings a resistivity suitable for the purposes pursued. They can be deposited relatively inexpensively by comparison, for example, with metallic coatings. And they can easily be formed so that they are hard and weather resistant. Such coatings can also have a high optical quality, so that they do not interfere with vision through the sheet carrying the coating.

The present invention extends to a panel as described above in which said electrodes are connected in an electrical circuit comprising means for maintaining a potential difference across said coating between said electrodes and signaling means to generate a signal in response to a decrease in the intensity of the current flowing through the coating up to or below a predetermined threshold value.

The present invention will now be described in more detail with reference to the accompanying schematic drawings in which Figure 1 is a sectional view of laminated glazing;

Figure 2 is a sectional view of a glass sheet having a coating;

Figure 3 is a sectional view of double glazing incorporating a laminated panel;

FIG. 4 is a perspective view of a corner of the laminated glazing of FIG. 1, and

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Figures 5 and 6 are schematic views of two panels connected in electrical circuits to control the current flowing through the conductive coating.

Figure 1 shows a laminated glazing 1 5 comprising a first glass sheet 2 which carries a conductive coating 3 and whose face carrying the coating is secured to a second glass sheet 4 by means of an intermediate layer 5 of thermoplastic adhesive material .

FIG. 2 represents a simple sheet of glass 6 carrying a conductive coating 7 which extends between electrodes 8 arranged at the opposite ends of the sheet 6.

FIG. 3 represents a hollow glazing incorporating a laminated panel 9 comprising a first sheet of glass 10 secured by means of an intermediate layer 11 of thermoplastic adhesive material to one side of a second sheet of glass 12 the other side of which carries a conductive coating 13. The surface carrying the coating 13 of the second glass sheet 12 is secured by layers of adhesive 14 to a spacer 15 which, in turn, is secured to a third glass sheet 16.

FIG. 4 shows a corner of the laminated glazing 1 and illustrates how an electrode such as the electrode 8 of FIG. 2 can be arranged in the form of a localized electrode occupying a corner of the glass sheet 2 carrying the coating. In FIG. 4, the second glass sheet 4 is cut obliquely at its corner so as to form a rebate 18 in the edge of the laminated panel 1 30 in the region of the electrode 8 in order to receive a connector 19 which can for example be welded to the electrode 8. After fixing the connector 19, the rebate 18 can be filled by means of a non-conductive filling material, for example an epoxy resin. At least one other corner, preferably at least the diametrically opposite corner, of the laminated panel 1 is of similar construction.

FIG. 5 illustrates a panel 1, carrying a

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conductive coating and an electrode 8 arranged in each of its four corners, connected in a control circuit. One of the electrodes is directly connected to ground, while the diametrically opposite electrode is connected 5 to a battery and then, via a resistor 20 and an induction coil 21, to ground. The characteristic panel may have a conductive coating having a resistance of 200 ohms, and a 12-volt battery and a compensation resistance 20 of 200 ohms should also be used. When the panel breaks, its conductive coating will be broken and its resistance will suddenly increase to a value of the order of 1 megohm, with a sudden significant change in the current flowing through the circuit shown. The induction coil 21 can then operate to induce an alarm signal.

FIG. 6 represents a possible variant of the circuit in which an electrode of the panel is again connected directly to ground. The opposite electrode is connected via a battery and a resistor 22 to an operational amplifier 23 intended to deliver an alarm signal in response to a change in the current flowing through the conductive coating of the panel 1.

EXAMPLES 1 TO 3

These examples are all constructed according to FIGS. 1 and 4. In these examples, each of the glass sheets 2 and 4 is a float glass sheet 6 mm thick. The coating 3, consisting of doped tin oxide, has a thickness of 750 nm and a resistivity of 20 ohms per square. The adhesive material used is polyvinyl butyral 0.76 mm thick. The following table 1 shows different treatments applied to the glass sheets 2 and 4 as well as the average surface stresses in compression which they induce.

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TABLE 1 SHEET 2 SHEET 4

Ex. Processing Contr. MPa Treatment Contr. MPa 1 Hardened, therm. 60 Chemical quenching. 550x32pm 5 2 Hardened, therm. 60 Therm quench. 130 3 Chemical quenching. 600x32pm Tempering therm. 130

Each of these panels is designed so as to be placed with its first sheet 2, carrying the covering, facing the outside of an enclosure from which it is desired to protect the interior. It is found in each case that if an attack on this first sheet 2 is strong enough to destroy the integrity of the second sheet 4, which is the seat of higher surface stresses due to the nature of the treatments to which the sheets 15 have been subjected, this second sheet 4 will fragment and give a convex curvature to the face of the first sheet carrying the coating. This curvature induces an additional stress in the first sheet and is sufficient to ensure that it breaks right through if it has not already occurred during the initial attack. As a result of the above, and due to the curvature imparted to the face carrying the coating, the positive separation of the coating 3 is ensured, which allows the certain generation of an alarm signal by a fairly simple circuit 25 at which the panel can be connected.

EXAMPLE 4

The sheet illustrated in FIG. 2 is a glass sheet which has undergone a thermal hardening treatment so as to induce therein an average surface stress 30 in compression of 70 MPa.

EXAMPLES 5 TO 7

These examples are all constructed according to FIG. 3. In these examples, each of the glass sheets 10, 12 and 16 is a sheet of drawn glass 4 mm thick. The coating 13, consisting of doped tin oxide, has a thickness of 850 nm and a resistivity of 25 ohms per square. The adhesive material 11 used is polyvinyl butyral of * ► * 13.

* 0.76mm thick. The following table 2 shows different treatments applied to the glass sheets 10 and 12 as well as the average surface stresses in compression which they induce.

5 TABLE 2 SHEET 10 SHEET 12

Ex. Processing Contr. MPa Treatment Contr. MPa 5 Hardened, therm. 65 Chemical quenching. 600x30pm 6 Hardened, therm. 65 Therm quench. 130 10 7 Quenching chem. 500x20pm Tempering therm. 130

It is found in each case that if an attack on this first sheet 10 is strong enough to destroy the integrity of the second sheet 12, which is the seat of higher surface stresses due to the nature of the treatments to which the sheets have been subjected, this second sheet 12 will fragment and give a convex curvature to its face carrying the coating.

As a variant of examples 5 to 7, the laminated panel 9 of FIG. 3 is replaced by a laminated panel 20 1 of each of examples there 3, or by the sheet 6 of example 4, thermally hardened and bearing a coating.

Claims (15)

1. Glazing comprising at least two sheets of glass joined to each other in the form of a laminated panel by means of intermediate adhesive material, in which at least one sheet of glass carries an electrically conductive coating 5 'extending between at least two electrodes, characterized in that the surface layers of at least two said glass sheets are the seat of unequal stresses so that at break, one of the glass sheets breaks into smaller fragments than another, thereby imparting curvature to the laminated panel, and in that said conductive coating is applied to a sheet face which becomes convex upon such rupture. 2. Glazing according to claim 1, characterized in that a glass sheet of the laminated panel is the seat of a surface stress giving it a mechanical resistance which is at least 1.5 times, and preferably at least twice , that of another sheet of glass from the laminated panel. 3. Glazing according to one of claims 1 or 2, characterized in that a glass sheet of the laminated panel is the seat of an average surface stress in compression of at least 65MPa. 4. Glazing according to one of claims 1 to 3, characterized in that the coating is applied to a sheet face which is inside the panel. 5. Glazing according to claim 4, characterized in that at least one sheet of glass is shaped so as to leave a marginal rebate on the laminated panel intended to receive a connector attached to each of said electrodes. 6. Glazing according to claim 5, characterized in that the or each such marginal rebate receives a said connector and is filled with a non-conductive filling material. 7. Glazing according to one of claims 4 to 6, -, X 15. * characterized in that the laminated panel comprises a sheet of chemically toughened glass and a sheet of thermally toughened glass. 8. Glazing according to one of claims 4 to 6, 5 characterized in that the laminated panel comprises a sheet of thermally hardened glass and a sheet of tempered glass. 9. Glazing comprising a glass sheet carrying a conductive coating, characterized in that said conductive coating extends between at least two electrodes and is applied to one side of a glass sheet which has been thermally hardened. 10. Glazing according to one of claims 1 to 9, characterized in that said electrodes are localized electrodes. 11. Glazing according to one of claims 1 to 10, characterized in that said electrodes are arranged at locations on the panel which are substantially diametrically opposite. 12. Glazing according to one of claims 1 to 11, characterized in that said sheet carrying a conductive coating is polygonal and in that the electrodes are deposited at each corner of the sheet face carrying the conductive coating. 13. Glazing according to one of claims 12 there, characterized in that said electrodes consist of layers of conductive enamel. 14. Glazing according to one of claims 1 to 13, characterized in that said coating is a coating of doped tin oxide. 15. Glazing according to one of claims 1 to 14, characterized in that said electrodes are connected in an electrical circuit comprising means for maintaining a potential difference across said coating between said electrodes and signaling means for generating a signal in response to a decrease in the intensity of the current flowing through the coating to or 16. - fi »below a predetermined threshold value.