JPH0222488B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention comprises a dielectric sheet carrying at least one contact switch in a contact control switchboard, the or each switch having a first contactable electrode on one side of the sheet. , in which second and third electrodes spaced apart from each other are attached to opposite sides of the sheet in a capacitive relationship with the first electrode. The three electrodes together form two capacitors connected in series. In use, an alternating current signal is applied to one of the second and third electrodes, while the other is connected to an output monitoring circuit. When the first electrode is touched with a finger, the signal passed to the input of the monitoring circuit is significantly reduced, and this reduction in signal is used to effect the switch. Such switches are used in many fields, for example as elevator control switches, household appliance switches (for example for cookers) and as switch banks, for example as telephone "touch dial" or computer input keyboards. For reliable opening and closing, such switches should have as high a capacitance as possible. The reason for this is that the signal applied to the electrode by the pulse generator should remain at the highest possible level when entering the detection circuit, taking into account the input impedance. The higher this level is, the easier it is for the threshold circuit built into the detection circuit to reject the noise signal. It may be mentioned that for some commercially available detection circuits developed specifically for the capacitive touch control switch system, the typical value to be achieved for the capacitance of this system is 3 pF. Particularly in the case of a panel with a series of switches, it is desirable for each switch to occupy a small area. This desire is to some extent contradictory to the requirement for a capacitance above a given threshold, since according to the well-known classical formula, the capacitance of a plate capacitor is proportional to its area. It is. According to the same equation, capacitance is inversely proportional to the thickness of the dielectric material. Thus, both the area of the switch and the thickness of the panel could be reduced while, of course, maintaining the same capacitance. It is also possible to influence the capacitance by the choice of dielectric material, but this is likely to be in clear conflict with other requirements. for example,
Natural dielectric materials such as mica are not suitable for high volume series production. Because plastic materials wear easily and are thin and generally flexible, touch control switch panels containing touchable electrodes deposited on plastic dielectric sheets can quickly wear to the point where they are no longer reliable in operation. . Ordinary soda lime glass can be used as a dielectric and is satisfactory for scratch resistance, but should be thick enough for impact resistance. This limits the ability to reduce the size of the switch while maintaining its capacitance above a certain threshold. It is an object of the present invention to remedy these drawbacks. According to the present invention, there is provided a touch control switch panel consisting of a dielectric sheet carrying at least one contact switch, the or each switch being mounted on one side of the sheet. one contactable electrode on the other side of the sheet;
second and third spaced apart electrodes are attached in a capacitive relationship to the first electrode, and the dielectric sheet is chemically hardened;
It is characterized in that at least one of the electrodes consists of a coating deposited on a sheet. The contact control switch panel according to the present invention is characterized by the fact that the glass dielectric has undergone a hardening process, so that the thickness of the glass sheet can be reduced, while its capacitance can be maintained at a sufficient level. It is more impact resistant than known panels. Preferably each electrode consists of a coating deposited on the sheet. Chemical hardening of glass is known per se.
The most prevalent type of quenching consists of exchanging alkali metal ions from the glass with alkali metal ions from the contact medium while heating the glass. This ion exchange occurs in the surface layer of the glass, which is several microns to tens of microns thick. In one operation, ion exchange is performed at a temperature high enough to cause stress relaxation within the glass;
The ions that enter the glass cause the coefficient of thermal expansion on the surface layer of the glass to decrease. As an example, lithium ions are replaced by sodium ions within the glass. Because high lithium glass has a low coefficient of expansion, compressive surface stresses are induced in the glass when the treated glass is cooled. In another operation, the ions in the glass surface are replaced by larger ions, and the ion exchange takes place at a temperature below the annealing point (corresponding to a viscosity of 10 ^13.2 poise), so that stress relaxation does not occur. do not have. In one example, potassium ions are substituted into the glass. For example, 470
It is carried out in a molten nitric acid solution kept at ℃. Since potassium ions are larger than sodium ions, compressive surface stress is again induced in the treated glass. Advantageously, the dielectric sheet is at most 3 mm thick, preferably at most 1.5 mm. A 1 mm thick hardened glass sheet is particularly suitable for use as the dielectric sheet. In a preferred embodiment of the present invention, the
Alternatively, the maximum dimension of the seat area occupied by a given switch is less than or equal to 30 mm; advantageously, such dimension is less than or equal to 25 mm. Preferably, the or a switch occupies an area of not more than 450mm ^{2 ;}
It is advantageous if: The various coating materials that can be used to make the electrodes include metals, conductive metal oxides, and conductive (or metal-containing) enamels. As far as the first contactable electrode is concerned, the coating consists of tin oxide or indium oxide and is preferably a conductive metal oxide coating containing a doping agent. Tin oxide is particularly preferred for its hardness, chemical stability and also for economic reasons. metals (especially tin)
The reason why oxides are preferable is as follows. It is extremely difficult, if not impossible, to chemically harden a glass sheet on which a coating has been deposited. Therefore, in practice, when practicing the invention, the sheet must be hardened before depositing the electrodes. If the hardened sheet is subsequently heated to a temperature at which any substantial stress relaxation can occur, much of the additional strength imparted to the glass is lost. Metal oxide coatings of sufficient hardness and conductivity can be easily deposited at lower temperatures. Of course, it would also be possible to make the first accessible electrode from a conductive (eg, silver-containing) enamel whose composition is chosen to have a relatively low melting point. However, in general, the lower the melting point of the enamel, the lower its hardness, and thus also its resistance to wear and corrosion. The abrasion resistance requirements for the second and third electrodes are not strong as they are not normally exposed to contact, and in fact the second and third electrodes are made of conductive enamel. Preferably, it is produced by deposition. There are some advantages to using a conductive enamel coating on the non-exposed surfaces of the switch panel. Firstly, the paste of enamel-forming components can be easily applied to the dielectric, for example by silk-screen printing techniques. Conductor leads for interconnection can also be deposited at the same time, if desired.
Second, enamel also facilitates semi-date connections. In some preferred embodiments of the invention, an opaque coating is deposited on the surface of the tempered glass sheet prior to depositing the electrodes or the like on the surface.
Such opaque coatings mask any electrical circuitry located behind the panel and are preferably applied to non-exposed surfaces thereof. If desired, such a coating may include a window associated with the switch followed by a light to indicate the status of the switch circuit. Preferably, a backing support is applied and bonded to the non-exposed side of the panel. This adds stiffness to the panel and makes it more resistant to bending. Advantageously, the backing support is a synthetic plastic material. Such a support may be molded into a panel, for example. In some embodiments of the invention, the support is a solid block, while in other embodiments of the invention, the support is multilocular.
For example, the support has a honeycomb structure. The support may also be an intumescent material, such as foam glass, or may be made of a printed circuit board. The present invention includes a method of making a contact control switch panel comprising a dielectric sheet carrying at least one contact switch, the or each switch having a first contact on one side of the sheet. a dielectric sheet and a second and third spaced apart electrode on the other side of the sheet in capacitive relationship with the first electrode; selected and subjected to a chemical quenching treatment at a high temperature, and at least one conductive coating is deposited on the quenched sheet to constitute one or more said electrodes, while the temperature of the sheet is lower than the annealing point (corresponding to a glass viscosity of 10 ^{to 13.2} poise),
It is characterized by substantially avoiding stress relaxation. This is a very simple method of forming a contact control switch panel according to the present invention, and avoids any difficulties that may occur when hardening the glass sheet after depositing the conductive coating (or the like). Preferably, the first accessible electrode is formed by depositing a metal oxide coating on the one side of the sheet. Advantageously, the metal oxide coating contains a doping agent to increase its electrical conductivity. Suitable doping agents include one or more of the following ions: antimony, arsenic, cadmium, chlorine, fluorine and tellurium. The metal oxide may be, for example, iridium oxide, but preferably tin oxide. In some embodiments of the invention, the oxide coating is made, for example, by pyrolysis of a metal salt that is sprayed in solution in an organic solvent onto the sheet. Examples of such solutions are dibutyltin diacetate in ethyl alcohol and dimethyl formamide.
It is preferable to use a solution of SnCl ₄ .5H ₂ O to which an arbitrary amount of acetic trifluoride is added to provide fluorine ions for doping. In other preferred embodiments, the oxide coating is sputtered. Various techniques may be used to limit the painting to the required area. According to a first preferred method, a mask is applied to the sheet by silk-screen printing, covering the areas that will not be painted in the finished panel, and the mask is removed after the conductive coating has been applied over the entire hardened sheet. This leaves the paint only on the necessary area. According to a second preferred method, an oxide coating is deposited over the entire surface of the hardened sheet. Then, an acid-resistant mask is applied by silk screen printing to mask the area of that or each electrode, and unnecessary paint is etched away. The second and third electrodes are preferably made by depositing conductive enamel onto the opposite sides of the glass sheet. Such conductive enamels are preferably deposited by applying an enamel paste to a hardened glass sheet and melting it in situ. Such enamel pastes are preferably applied by screen printing techniques.
Silver-containing enamels, especially of the organic type, are particularly suitable. Advantageously, the tempered glass sheet is opacified by applying a non-conductive opaque enamel coating, preferably on one of its faces. Such coating is advantageously carried out prior to the deposition of the second and third electrodes, preferably on non-exposed surfaces of the sheet. The first electrode is preferably deposited prior to the deposition of the second and third electrodes, and before the opaque enamel coating is applied. This avoids problems due to remelting of the enamel coating during deposition of the oxide coating. Preferably, a backing support is applied and bonded to the non-exposed side of the panel. Such a support may be, for example, a synthetic plastic material or may be made by molding the panels in situ. In some embodiments of the invention, one of the second and third electrodes may be shaped to surround at least a large portion of the periphery of the other. If possible,
The area of the interior of such electrodes shall be at least one quarter of the area of the exterior electrodes. Such an electrode arrangement provides an advantageous compromise with respect to the helix capacitance of the system, the change in capacitance when the first electrode is touched, and the amount of material that must be used to form the second and third electrodes. In this connection, we would like to draw your attention to our co-dated patent application no. On the other side are second and third electrodes in capacitive relationship with the first electrode, one of the second and third electrodes (hereinafter referred to as the "external electrode") , and others (hereafter referred to as "internal electrodes")
The electrode is characterized in that it is shaped so as to surround at least most of the periphery of the electrode, and that the ratio of the area of the internal electrode to the area of the external electrode is greater than 1:0.25. Preferred embodiments of the invention will now be described with reference to the accompanying drawings. 1 and 2, a sheet 1 of quenched soda-lime glass is coated with SnO ₂ on its upper or exposed surface.
A square first electrode 2 doped with is now attached. The first electrode is surrounded by a boundary 3, here indicated as the number "1", and carries an indicator 4 which serves to indicate the function to be carried out by the switch of which the electrode 2 is a part. The lower or non-exposed surface of the tempered glass sheet 1 is provided with an opaque, non-conductive enamel layer 5 having a window 6 in exact alignment with the indicia 4.
covered with. Second and third electrodes 7 and 8 are in capacitive relationship with the first electrode 2 on either side of the window 6 on the opaque enamel layer 5 on the non-exposed surface of the hardened glass sheet 1. is deposited. These electrodes are made of silver-containing enamel. 3 and 4 illustrate a contact control switch panel, generally indicated at 10, having a number of contact control switches S1 through S0 deposited on a hardened glass sheet 11. FIG. As described with reference to FIGS. 1 and 2, each switch includes a first contactable electrode 12 deposited on the exposed surface of the glass sheet 11, on which there is in turn a boundary 13. and reference index 14 are deposited. Each individual indicator 14 may, for example, consist of a reference numeral of the switch with which it is associated. An opacifying layer 15 of non-conductive material is deposited on the back side of the hardened glass sheet 11. This layer may be provided with windows, such as the windows 6 shown in FIGS. 1 and 2, if desired. Each switch also has a gap of 1
6, comprising second and third electrodes 17, 18, respectively, separated by 6. As seen in Figure 4, the third electrodes of the switches S1 to S0 are connected to a common AC power source, while the second electrodes of each switch S1 to S0 are connected to the output circuit.
Connected from OC1 to OC0. The second and third electrodes are suitably made of silver-containing material and can all be applied in one operation by silk printing techniques. Conductive wires connecting the electrodes to the AC power source and output circuit may be soldered to the electrodes, or
Alternatively, the printed conductor may be applied with the same or subsequent printing techniques. After making the necessary electrical connections, the backing support 19 is installed behind the panel. This serves to protect the second and third electrodes and their associated conductors from wear and corrosion during handling prior to installation, but their primary function is to protect the panel from its use. The purpose is to support against bending. To make a panel as shown in the figure, a glass sheet 1 or 11, e.g. soda-lime glass, of the desired thickness is polished and then quenched in any convenient manner, e.g. at 470° C. for a period of 8 hours.
The glass is immersed in a bath of molten potassium nitric acid maintained at a temperature of 100°C, displacing the sodium ions that were previously part of the glass and causing the potassium ions to diffuse into the surface layer. After quenching, wash the glass and attach it to the first electrode 2 or 12.
is deposited on one side of it. It is particularly suitable that the first electrode is formed from a metal oxide, for example _SnO2 . Such oxide coatings may be deposited by cathodic sputtering techniques, but it is preferred that such coatings be deposited by thermal decomposition of salts, for example by spraying methods and in solution in organic solvents.
Suitable solutions are dibutyltin diacetate in ethanol with a doping amount of ammonium difluoride or tin tetrachloride in dimethylformamide with a doping amount of acetic trifluoride. Such a solution is sprayed onto a tempered glass sheet heated to 450°C to form a uniform coating of the desired thickness, e.g. This can be used as a guideline for when to stop spraying. The coating thus formed is as abrasion resistant as glass. Alternatively, the coating may be deposited by pyrolyzing the salt in the vapor phase. The coating can also be obtained by dipping the hardened sheet in an alcoholic solution of a tin compound followed by a baking operation. Yet another possible method is to form the coating by depositing a tin organic compound-containing paste by silk printing and then hardening. After applying such a uniform coating, an acid-resistant mask is applied by silk printing over the area to be occupied by the electrodes 2 to 12, and the remaining area of the coating erodes away. Then, the front surface of the hardened glass is painted with a decorative material to form edges 3, 13 and indicators 4, 14. An optional step is to cover the back side of the hardened glass sheet with an opacifying layer 5 or 15. In both cases these coatings may be made of low-melting enamels.
However, preferably a synthetic plastic material is used that polymerizes in situ to form an opaque coating. For example, an epoxy-type lacquer whose polymerization temperature is 120° C. or less may be used. Then apply the second and third electrodes to the back of the panel. The second and third electrodes may be made of conductive enamel or lacquer when the polymerizable opacifying layer is not present; however, when the polymerizable opacifying layer is present, these electrodes are made from lacquer. These materials are applied in a silk printing fashion and heated to melt and vitrify the enamel or provide rapid hardening of the lacquer. In special cases, silver-containing lacquer
No. 4929 manufactured by Nemovrs was used for the second and third electrodes. After painting, the latsker was roasted at 100°C for 1 hour. Another Lutzker that may be used for the same purpose is Degussa Lutzker No. 245. Conductors may also be applied at the same silk printing step for any necessary electrical connections. but,
In order to keep the dimensions of the panel small, preferably the wire conductors are soldered to the second and third electrodes. This soldering is performed, for example, by applying a paste of solder and slacks to the electrodes and melting it with a jet of hot air. The composition of the solder used is Sn: 62%;
Pb: 36%; Ag: 2% is sufficient. When using a soldering iron, its temperature should be limited to 250°C. After making the necessary electrical wiring, the panel may be molded onto a backing support 19 to stiffen it (and protect the conductors on the back side). This may be done by polymerizing the fluid synthetic resin in situ. One suitable fluid medium is a resin with the following weight percent composition: PLEXIMON 705 or 706 98.6% monoterpene butyl maleate 0.2% benzoyl peroxide 0.1% triethyl phosphate 0.7% Rohm activator 17 (maleic naphthenate) ) 0.4% PLEXIMON 705 and 706™ are methyl methacrylate resins manufactured by Rohm. This resin composition polymerizes in 8 hours at temperatures between 20°C and 30°C. Another resin that may be used to form the backing support is Polyester
There are polyester resins such as "GTS". FIG. 5 depicts a variation of the embodiment shown in FIGS. 3 and 4, in which like elements are designated with the same reference numerals. As noted with reference to FIGS. 3 and 4, the switch panel, designated here at 20, consists of a hardened glass sheet 11 on which a plurality of switches, such as S4, S5, and S6, are formed. , these consist of a first accessible electrode 12, a lip 13 and an indicator 14, on which an opacifying layer 15 is deposited. Each switch includes second and third electrodes 22, 23 spaced apart by a gap 21, but these are not deposited on the opacifying layer 15 but on the printed circuit board 24. This disc is bonded to the opacifying layer 15 by an adhesive 25 and serves as a support for the glass sheet 11. Second and third electrodes 22, 23
Conveniently it is made of metallic copper deposit, as is known in the printed circuit process. The printed circuit board 24 has a plurality of holes 26.
are drilled through which the various second and third electrodes 22, 23 are connected by soldered wires at 28 to appropriate parts 29 of the printed circuit. FIG. 6 depicts a touch control switch similar to that shown in FIGS. 1-4. In FIG. 6, on the non-exposed surface of a sheet 61 of quenched soda-lime glass,
It has a rectangular shape and has a pair of electrodes (second and third electrodes) 62 and 63 separated by a gap 64. Together, the electrodes 62, 63 and the gap 64 between them occupy a square on the non-exposed surface of the sheet 61. A first electrode is deposited on the exposed surface of sheet 61. A portion of the boundary of the first electrode is shown at 65. The first electrode is square and exactly matches the square formed by the second and third electrodes. FIG. 7 depicts a circular contact control switch formed on a hardened glass sheet 71. FIG. Partially circular second and third electrodes 72, 73 separated by a diametrical gap 74 are deposited on the non-exposed surface of sheet 74. A circular first electrode, a portion of its periphery indicated at 75, is deposited on the exposed surface of the sheet 71 and is connected to the second and third electrodes 72, 73 between them. It corresponds exactly to the circle formed by gap 74. Figure 8 is a diagram of a contact control switch, in which:
The hardened glass sheet 81 is a square annular third electrode 8
A square second electrode 82 surrounded by 3 is attached.
The second and third electrodes are separated by a square annular gap 84. A first electrode (not shown) is on the other side of the sheet 81, and its boundary is a third electrode 83.
is deposited in exact alignment with the periphery of FIG. 9 depicts a contact control switch in which a hardened glass sheet 91 bears a circular second electrode 92 surrounded by an annular third electrode 93. The second and third electrodes are separated by an annular gap 94. On the other side of the sheet 91 a first electrode (not shown) is deposited with its boundaries precisely aligned with the periphery of the third electrode 93. Various special touch control switches are described herein by way of example. EXAMPLE (FIG. 6) A 1 mm thick glass sheet is hardened and a 12 mm square first electrode is deposited on one of its faces. This first electrode is made of doped tin oxide. 12×5mm each
Second and third electrodes 62, 63 having dimensions of are then formed on opposite sides of the glass sheet 61.
These electrodes are separated by 2 mm gaps 64 and are made of silver-containing enamel. The total area of the seat occupied by the switch is 144 mm ² . In the first variant, the hardened glass sheet 61 has a thickness of
2.8mm and in the second variant 4.9mm thick. EXAMPLE (FIG. 8) A 1 mm thick glass sheet 81 is hardened and a 12 mm square first electrode of doped tin oxide is deposited on one side. On the opposite side of the sheet are second and third electrodes 8.
2 and 83 in exact alignment with the first electrode. The second electrode 82 is 6 mm square, and a square annular gap 84 with a width of 1 mm connects the third electrode 82, which is a ring with a width of 2 mm.
separated from 3. The second and third electrodes are made of silver-containing enamel. The area of the helix switch is ^144mm2 . In the modification, the hardened glass sheet 81 has a thickness of 2.8 mm.
It is 4.9mm thick. Embodiment (FIG. 8) In a variation of the embodiment, the second electrode 82 has four
It is separated from a third electrode 83 having a width of 2 mm by a square annular gap 84 having a width of 2 mm. Such switches are formed on hardened glass having the following thicknesses: 1 mm, 2.8 mm, and
4.9mm, and the helix switch area is also ^144mm2 . EXAMPLE (FIG. 7) A glass sheet 71 with a thickness of 1 mm is hardened and a first circular electrode made of doped tin oxide with a diameter of 13.5 mm is deposited on one side. On the opposite side, part-circular second and third electrodes 72, 73 made of silver-containing enamel are deposited. These electrodes are separated by a 2 mm wide gap 74. The second and third electrodes, together with the gap separating them, occupy a circular area of diameter 13.5 mm, which corresponds exactly to the first electrode. The area of the helix switch is ^143mm2 . In the variant, the switch is 2.8mm thick and 4.9
Formed on mm-thick hardened glass. EXAMPLE (FIG. 9) A glass sheet 91 1 mm thick is hardened and a first circular electrode 13.5 mm in diameter made of doped tin oxide is deposited on one side. On the opposite side, in exact correspondence with the first electrode, second and third electrodes 92, 93 made of silver-containing enamel are deposited. The second electrode has a diameter of 7.5
An annular gap 94 occupying a circular area of mm and having a width of 1 mm.
from the third electrode, which is a 2 mm wide ring. The helix switch area is again
It is ^143mm2 . In deformation, the switch is 2.8mm and 4.9mm
Formed on thick hardened glass. Embodiment (FIG. 9) In a variation of the embodiment, the second electrode has a diameter
5.5 mm, and the annular gap 94 is 2 mm wide.
Again, the switch is formed on hardened glass of the following thicknesses: 1 mm, 2.8 mm, and 4.9 mm.
mm. Since these switches occupy similar heald areas, their capacitance when not touched and the change in their capacitance when touched can be directly compared as shown in the table below.

TABLE The active surface area column shows the percentage of the first electrode that corresponds exactly to one or the other of the second and third electrodes. The value of capacitance shown in this application is
Measured using the universal bridge WAYN KERR, model B224. Measurements were performed under normal atmospheric conditions. The capacitive switch system is arranged horizontally with the SnO ₂ coating on top. Standard connecting wires are connected by fixed terminal clamps to 5 mm long wires soldered to the second and third electrodes.

[Brief explanation of drawings]

FIG. 1 is a detailed perspective view of the touch control switch panel. FIG. 2 is a cross-section of a portion of the panel of FIG. FIG. 3 is a cutaway view of another embodiment of the panel. FIG. 4 is a bottom view of the panel of FIG.
FIG. 5 is a cutaway view of a third embodiment of the panel. Figures 6-9 are bottom plan views of the switch showing various arrangements of electrodes.

Claims (1)

[Scope of Claims] 1. A contact control switch panel consisting of a hardened dielectric glass sheet carrying at least one contact switch, the switch or each switch being connected to one side of the sheet. a first contactable electrode on the top and second and third mutually spaced electrodes on the opposite side of the sheet in capacitive relation to the first electrode. CLAIMS 1. A contact control switch panel in which at least one of the electrodes comprises a coating deposited on a sheet, the glass sheet being subjected to a chemical hardening treatment. 2. A panel according to claim 1, characterized in that each said electrode consists of a coating deposited on said sheet. 3. The panel according to claim 1 or 2, wherein the dielectric sheet has a thickness of at most 3 mm. 4. The panel according to claim 3, wherein the dielectric sheet has a maximum thickness of 1.5 mm. 5. A panel according to any one of claims 1 to 4, characterized in that the maximum dimension of the switch or the sheet area occupied by the switch is 30 mm or less. 6. Claim 5, characterized in that the maximum dimension of the seat area occupied by the switch or a certain switch is 25 mm or less.
Panel described in section. 7. A panel according to any one of claims 1 to 6, characterized in that the sheet area occupied by the switch or switches is 450 mm ² or less. 8. A panel according to claim 7, characterized in that the sheet area occupied by the switch or switches is 250 mm ² or less. 9. Claims characterized in that the or at least one first contactable electrode consists of an electrically conductive metal oxide coating made of tin oxide or indium oxide and containing a doping agent. A panel according to any one of the ranges 1 to 8. 10. A panel according to any one of claims 1 to 8, characterized in that a backing support is applied and bonded to the unexposed side of the panel. 11. A panel according to claim 10, characterized in that the backing support is a synthetic plastic material. 12. A panel according to claim 10 or 11, characterized in that the backing support comprises a printed circuit board. 13 consisting of a dielectric glass sheet carrying at least one contact switch, the or each switch having a first contactable electrode on one side of the sheet and a second contactable electrode on the opposite side of the sheet. a third spaced apart electrode attached in capacitive relationship to the first electrode, and at least one electrically conductive coating is deposited on the sheet to form one or more of the electrodes. In a method of manufacturing a contact switch panel, the glass sheet is subjected to a chemical quenching treatment at an elevated temperature, and the conductive coating is applied while the temperature of the sheet is below its annealing point to substantially avoid stress relaxation. is deposited on said tempered glass. 14 characterized in that the or at least one said first accessible electrode is formed by depositing a metal oxide coating on said one side of the sheet by pyrolysis of a metal salt. The method according to claim 13, wherein: 15. characterized in that a mask is silk-screen applied to the sheet, covering areas that will not be painted in the finished panel, and that the mask is removed after the conductive coating has been applied to the entire area of the hardened sheet. The method according to claim 13 or 14, wherein: 16. Any of claims 13 to 15, wherein the second and third electrodes are formed by depositing a conductive enamel on opposite sides of a glass sheet. The method described in paragraph (1). 17. Claims 14 to 16, characterized in that the first electrode is deposited on the sheet prior to the deposition of the second and third electrodes.
The method described in any one of the preceding paragraphs. 18. A method according to any one of claims 13 to 17, characterized in that a backing support is applied and bonded to the unexposed side of the panel.