FR2598970A1 - GLAZINGS COMPRISING A GLASS SHEET THAT HAS A CONDUCTIVE COATING - Google Patents

Abstract

THE INVENTION RELATES TO A GLASS INCLUDING A LAMINATED PANEL 1 HAVING AT LEAST TWO SHEETS OF GLASS 2, 4 SOLIDARIZED BY AN INTERMEDIATE ADHESIVE MATERIAL 5. A SHEET OF GLASS AT LEAST 2 CARRIES A COATING CONDUCTING ELECTRICITY 3 EXTENDING BETWEEN AT LEAST TWO ELECTRODES 8. THE SURFACE LAYERS OF AT LEAST TWO OF SAID SHEETS OF GLASS ARE THE SITUATION OF UNEQUAL STRAINS SO THAT AT THE RUPTURE, ONE OF THE SHEETS OF GLASS BREAKS INTO FRAGMENTS SMALLER THAN ANOTHER WHEN CONFIRMING AS WELL AS A BEND TO THE LAMINATED PANEL. THE CONDUCTIVE COATING 3 IS APPLIED TO A SHEET FACE WHICH BECOMES CONVEX WHEN SUCH A BREAKAGE. THE INVENTION APPLIES IN PARTICULAR TO WINDOWS USED IN AN ALARM SYSTEM.

Description

1. The present invention relates to a glazing unit comprising at least two

  glass sheets secured together as a laminated panel by means of an intermediate adhesive material, wherein at least one glass sheet carries an electrically conductive coating extending between at least two electrodes . Inveiintion also relates to a glazing unit comprising a

  glass sheet with a conductive coating.

  Such glazings are occasionally used as components of an alarm system. Glazing

  may be connected in an electrical circuit which comprises means for controlling the resistance of the coating and for setting an alarm if the resistance varies due to, for example, breaking of the glass sheet 15 bearing the coating.

  Such circuits can be classified into two categories, so-called "all or nothing" circuits, which require a substantially complete opening of the circuit through the coating, and circuits that respond to any variation in the resistance of the coating greater than one value. predetermined threshold. Such threshold circuits tend to be quite complicated because they must not only be able to respond to a partial breakage of the sheet bearing the coating, but they must also be tested against accidental alarm signals due to

  variations in resistance generated by changes in glazing temperature due to climate change.

  "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 hence less expensive to manufacture and install. Note that, for an "all or nothing" circuit to operate, it is necessary that the current flowing through the

  coating is substantially completely interrupted.

  It is not always easy to ensure that this is the case, especially when the glass sheet bearing 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 propagate all over, and as a result, for example, a small opening may be cut in the laminated panel to allow unauthorized access to an inside handle of a door or window without causing an alarm signal. If the glass sheets are soaked, the propagation of cracks over the entire laminated panel is substantially ensured, but the glass fragments produced tend to be held together by the adhesive used to join the laminated panel, and as a result, the breakage of the circuit through the coating is not certain if a small aperture only

is practiced 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 breakage of the conductive coating during its fracture and which is therefore particularly suitable for use in a relatively inexpensive alarm circuit. , for example a circuit of the

typc "all or nothing" ..

  The present invention relates to a glazing unit 25 comprising at least two glass sheets joined together in the form of a laminated panel by means of intermediate adhesive material, in which at least one glass sheet carries a conductive coating electricity extending between at least two electrodes, characterized in that the surface layers of at least two said sheets of glass are the seat of unequal stresses so that at break, one of the glass sheets is breaks into fragments smaller than another thereby conferring a curvature on the laminated panel, and that said conductive coating is applied to a sheet face

  which becomes convex during such a break.

  Because the face of the leaf bearing the

  fi. 3. will be convexly curved when breaking the laminated panel, the separation of the coating will be ensured at the junction between neighboring fragments of the sheet bearing 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 that will be imparted to the laminated panel upon its break depends upon the manner in which the glass sheets break individually, which, in turn, depends on the magnitude of the stresses on which their surfaces are exposed. headquarters. In general, the higher the stresses in the surface of a glass sheet, the greater the amount of energy released at breakage of that 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 glass. another leaf which is directed towards the one whose stresses are higher tends to become convex. It will be appreciated in this context that not only is the absolute surface stress important, but also the depth of the sheet layer is the seat of these constraints. By way of example, two glass sheets of the same thickness, for example 5 mm, can be quenched to increase their surface stresses, one by a chemical quenching treatment and the other by a heat quenching treatment. By the way

  chemical, the surface stress in the glass can be increased up to an average value as high as 1000MPa, but only about 20pm for each face.

  By thermal quenching, the surface stress in the glass can be increased to an average value of eg 130 MPa, about one-fifth of its thickness for each face. Taking into account the stress and the 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 toughened sheet is six to seven times higher than that stored in the chemically quenched sheet. As a result, the thermally toughened sheet will break into fragments smaller than the

chemically toughened sheet.

  It will also be appreciated 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 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 strength which is at least 1.5 times, and preferably at least twice, that of another glass sheet 20 of the laminated panel. The adoption of this preferred feature has several advantages. The higher the stress on a sheet, the more difficult it is to break it in the first place, giving additional security and space to protect. In case of breakage, this sheet tends to break into fragments which, because of the greater difference in stress between the sheets, will be relatively smaller in imparting greater curvature to the laminated panel upon its breakage. It has been found that this larger curvature may be sufficient to ensure the propagation of cracks over the entire width of the other sheet. This may be advantageous if the other sheet is an annealed glass sheet. In the case of annealed glass, even the burst 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 relatively high stress sheet as previously stated will cause additional stress in the annealed sheet. This may result in 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 glass sheet of the laminated panel is the seat of a mean compressive surface stress of at least 65 MPa. This promotes a high resistance to mechanical shock by making the sheet 10 more difficult to break, and ensures that when it is

  broken, it will break up into small pieces.

  Preferably, the coating is applied to a sheet face which is inside the panel. This helps to protect the coating against accidental deterioration, for example due to aggressive cleaning and aging. This feature is also important because it helps to prevent the coating from becoming covered with film or moisture droplets, for example due to rain or condensation. It is possible that such a humidity is capable of forming a conductive bridge, thereby avoiding the generation of an alarm signal at break of the glazing. By way of example, such a coating can be applied as an outer coating of a laminated panel which should constitute one of the panels of a hollow glazing unit. We

  However, it is preferred 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 deterioration during handling prior to placement.

  Advantageously, at least one glass sheet is shaped so as to leave the laminated panel a marginal rabbet for receiving a connector attached to each of said electrodes. This avoids the need to conform a frame for the laminated panel to receive the connectors necessary for the incorporation of the

panel in an alarm system.

  6. It is preferred 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

  laminated panel, which simplifies assembly.

  In some preferred embodiments of the invention, the laminated panel comprises a chemically toughened glass sheet and a thermally tempered glass sheet. The surfaces of such quenched sheets can be subjected to very high stresses, giving a very high resistance to breakage. In addition,

  Because of these constraints, the propagation of cracks in the trravers of the leaves is ensured during the rupture. In order to ensure the convexity of the face of the sheet carrying the coating upon breakage, the coating can be applied to the face of the thermally quenched sheet which does not face the sheet quenched chemically in the panel laminated. It is preferred, however, that the coating be carried by the face of the chemically toughened sheet that faces the thermally tempered sheet.

  In other preferred embodiments of the invention, the laminated panel comprises a thermally hardened glass sheet and a tempered glass sheet. The term "thermally cured" is used herein to describe glass which has been subjected to thermal conditioning of

  in order to induce superficial compressive stresses within the range of values 24MPa & 70MPa.

  Such quenching can be carried out chemically or thermally. It should be noted here that thermally toughened and tempered glass sheets have an optical quality superior to that of thermally toughened glass sheets. It appears that the thermal quenching 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 tempered glass.

  Such a laminated panel will not be as resistant

  7. at the same time as a laminated panel of the same thickness made with soaked sheets as described above, but it is less expensive to manufacture and provides a more reliable interruption of the conductive coating. The coating may be applied to the face of the quenched sheet that does not face the cured sheet, but it is preferred that it be applied to the surface of the cured sheet

  thermally that faces the soaked sheet.

  In other embodiments of the invention, such a laminated panel comprises an annealed glass sheet and a tempered or thermally hardened glass sheet. Such a laminated panel will not be as fracture resistant as a laminate panel of the same thickness made by hardened sheets or tempered and thermally hardened sheets as described above, but is less expensive. to manufacture and can also provide a certain interruption of the conductive coating. The coating may be applied to the face of the quenched or cured sheet that does not face the annealed sheet, but it is preferred that it be applied to the face of the sheet.

  annealed facing the hardened or hardened sheet.

  The use of thermally hardened 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 having 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. Such a sheet has a higher mechanical strength than an annealed sheet and, at break, crack propagation is ensured over its entire extent, thus providing reliable generation of an alarm signal when connected in a alarm system. Such a sheet is also less expensive to manufacture than

  quenched sheet, whether quenching is carried out thermally or chemically. A simple sheet of heat-hardened glass

  8. It 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 a low price, and can be used together with an "all or nothing" alarm circuit, also inexpensive, to give the break a reliable alarm signal. Such a thermally hardened, coated glass sheet may of course be incorporated into a hollow glazing with another glass sheet which may be tempered thermally or chemically if desired, to provide additional protection. This will obviously be more expensive, but nevertheless less expensive than the use of a laminated panel. In preferred embodiments of the invention, said electrodes are localized electrodes. The use of localized electrodes, as opposed to omnibus strips which would extend the entire length of the opposite sides of the sheet face bearing the coating, provides the advantage that the interruption of the 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 substantially opposite diametrically opposite points of the panel, a diagonal break across a corner of the panel which carries such an electrode will cause the 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 bearing the coating is broken, through the entire length of the strip.

  the width between the bus bands.

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

  connection of the electrodes in an alarm circuit.

  Preferably, the said electrodes are constituted

  9. killed with conductive enamel layers. Organic enamel or inorganic enamel can be used. It will preferably be an enamel containing silver. The application of such enamels is simple and relatively inexpensive, and they can provide a surface that is easily wettable by molten solder, giving a reliable connection.

to a suitable connector.

  In the preferred embodiments of the invention, said coating is a doped tin oxide coating. Oxide coatings can easily be imparted

  of tin doped resistivity appropriate to the aims pursued.

  They can be deposited relatively inexpensively as compared, for example, with metal coatings. And they can easily be formed so that they are hard and weather resistant.

  Such coatings may also have a high optical quality, so that they do not interfere with

  vision through the leaf bearing the coating.

  The present invention extends to a panel as described above wherein 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 a laminated glazing unit; Figure 2 is a sectional view of a coated glass sheet; Figure 3 is a sectional view of a double pane incorporating a laminated panel; FIG. 4 is a perspective view of a corner of the laminated glazing unit of FIG. 1, and 10. FIGS. 5 and 6 are schematic views of two panels connected in electrical circuits for

  check the current flowing through the conductive coating.

  FIG. 1 represents a laminated glazing unit 15 comprising a first glass sheet 2 which carries a conductive coating 3 and whose face bearing the coating is secured to a second sheet of glass 4 by means of an intermediate layer S of thermoplastic adhesive material . FIG. 2 shows a single sheet of glass 6 carrying a conductive coating 7 which extends between electrodes 8 disposed at opposite ends of the sheet 6. FIG. 3 shows a hollow glazing incorporating a laminated panel 9 comprising a first sheet 10 of glass secured by means of an intermediate layer 11 of thermoplastic adhesive material & a face of a second glass sheet 12, the other side of which carries a conductive coating 13. The face carrying the coating 13 of the second sheet of glass 12 is secured by adhesive layers 14 to a spacer 15 which, in turn, is

  secured to a third sheet of glass 16.

  FIG. 4 represents a corner of the laminated glazing

  1 and illustrates how an electrode such as the electrode 8 of FIG. 2 can be disposed 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 provide 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 may for example be welded & electrode 8.

  After fixing the connector 19, the rabbet 18 may be filled by means of a non-conductive filler, 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 an 11.

  conductive coating and an electrode 8 disposed in each of its four coinls, connected in a control circuit.

  One of the electrodes is directly connected to the ground, while the diametrically opposite electrode is connected to a battery and then, via a resistor 20 and an induction coil 21, to ground. A typical panel may have a conductive coating having a resistance of 200 ohms, and a 12 volt battery and a 200 ohm compensation resistor should be used as well. At the break of the panel, its conductive coating will be broken and its resistance will increase abruptly to a value of the order of 1 megohm, with a sudden sudden 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 electrode. the opposite is connected via a battery and a resistor 22 to an operational amplifier 23 for providing 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 in accordance with FIGS. 1 and 4. In these examples, each of the glass sheets 2 and 4 is a 6mm thick float glass sheet. 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 superficial compressive stresses they induce.

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12.

TABLE 1

SHEET 2 SHEET 4

  Ex. Treatment Contr. MPa Treatment Contr. MPa 1 Hardened. therm. 60 Chemical temp. 550x32pm 2 Hardened. therm. 60 Heat tempering 130 3 Quenching chlm. 600x32pm Heat tempering Each of these panels is designed so as to be placed with its first sheet 2, bearing the coating, facing the outside of an enclosure whose interior it is desired to protect. In each case, it is found 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 submitted, this second sheet 4 will fragment and

  will confer a convex curvature on the face of the first sheet bearing the coating. This curvature induces additional stress in the first sheet and is sufficient to ensure its break in part if it has not already occurred during the initial attack. As a result of the foregoing, and because of the curvature imparted to the face bearing 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 to which the panel can be connected.

EXAMPLE 4

  The sheet illustrated in Figure 2 is a sheet

  of glass which has undergone heat hardening treatment so as to induce a mean compressive surface stress of 70 MPa.

EXAMPLES 5 TO 7

  These examples are all constructed according to Figure 3. In these examples, each of the glass sheets 10, 12 and 16 is a 4mm thick drawn glass sheet. The coating 13, consisting of dopant tin oxide, has a thickness of 850 nm and a resistivity of 25 ohms per square. The adhesive material 11 used is polyvinyl butyral 13, 0.76 mm 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.

that they induce.

TABLE 2

SHEET 10 SHEET 12

  Ex. Treatment Contr. MPa Treatment Contr. MPa Hardened. therm. 65 Chemical temp. 600x30pm 6 Hardened. therm. 65 Heat tempering 130 7 Chemical temp. 500x2Opm Heat tempering In each case, it is found 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 are subjected. have been

  subject, this second sheet 12 will fragment and confer a convex curvature on its face bearing the coating.

  In 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 the examples 1 to 3, or by the sheet 6 of

  Example 4, heat-cured and coated.

14.

Claims (15)

  Glazing comprising at least two sheets of glass joined together in the form of a laminated panel by means of intermediate adhesive material, in which at least one glass sheet carries an electrically conductive coating; extending between at least two electrodes, characterized in that the surface layers of at least two said sheets of glass are the seat of unequal stresses so that at break, one of the glass sheets breaks into smaller fragments than another thus conferring a curvature laminated panel, and in that said conductive coating is applied on a sheet face which becomes convex during such a break. 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 strength which is at least 1.5 times, and preferably at least twice , that of another glass sheet 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 a medium superficial contrast 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   leaf face that is inside the panel.   5. Glazing according to claim 4, characterized   in that at least one glass sheet is shaped so as to leave the laminated panel with a marginal rabbet for receiving 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 filling material non-conductive.   7. Glazing according to one of claims 4 & 6,   Characterized in that the laminated panel comprises a chemically tempered glass sheet and a glass sheet thermally toughened.   8. Glazing according to one of claims 4 to 6,   characterized in that the laminated panel comprises a thermally hardened glass sheet and a tempered glass sheet. 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 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 disposed at points of the panel which are substantially diametrically opposed.   12. Glazing according to one of claims 1 & 11,   characterized in that said sheet bearing a conductive coating is polygonal and in that the electrodes are deposited at each corner of the sheet face carrying the conductive coating.   13. Vitrace according to one of claims 1 to 12,   characterized in that said electrodes are constituted layers of enamel conductive.   14. Glazing according to one of claims 1 to 13,   characterized in that said coating is a doped tin oxide coating.   15. Glazing according to one of claims 1 & 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 intensity current flowing through the coating to or 16.   below a predetermined threshold value.