FR3081460A1 - GLAZING COMPRISING SILVER BASED ELECTROCONDUCTIVE TRAPS - Google Patents

Abstract

The invention relates to a glazing unit (1) having at least one transparent zone (3) and at least one opaque zone (4), said glazing unit (1) comprising a glass sheet (2) coated on one of its electroconductive track surfaces. (5) based on silver in at least one transparent zone (3) and at least one opaque zone (4), said electroconductive tracks (5) located in the at least one transparent zone (3) being covered on their upper surface (50) and on their lateral edges (51) by transparent protective tracks (6) based on an oxide.

Description

Description

Title of the invention: Glazing comprising electroconductive tracks based on silver [0001] The invention relates to the field of glazing. It relates more particularly to glazing, in particular for motor vehicles, comprising electrically conductive tracks.

Electrically conductive tracks, such as heating wires present in glazing for motor vehicles, are made from a conductive paste, such as for example a silver paste screen-printed on a sheet of glass, and are connected to a power supply system via connectors soldered to the conductive paste. These tracks are often present on the rear glasses of motor vehicles.

It appeared that the optical appearance of such silver-based tracks could deteriorate in certain environments. The polluted air of certain large cities, in particular in Asia and South America, and in particular because of high sulfur contents, can lead to a tarnishing of the tracks, which become progressively grayish then iridescent.

To solve this problem, the invention relates to a glazing unit having at least one transparent area and at least one opaque area, said glazing unit comprising a sheet of glass coated on one of its surfaces of electrically conductive tracks based on silver. in at least one transparent zone and at least one opaque zone, said electrically conductive tracks located in the at least one transparent zone being covered on their upper surface and on their lateral edges by transparent protective tracks based on an oxide.

The invention also relates to a process for obtaining glazing according to the invention. This process includes the following successive steps:

- A step of depositing electroconductive tracks by screen printing of silver paste on the surface of a glass sheet, then [0007] - a step of depositing transparent protective tracks based on an oxide by screen printing of a sol-gel solution, then [0008] - a step of cooking said electroconductive and protective tracks.

[0009] The glass sheet is typically made of soda-lime-silica glass, but may be made of other types of glass, for example borosilicate or aluminosilicate. It can be clear, or preferably tinted, for example in green, gray or blue. The light transmission (within the meaning of ISO 9050) of the glass sheet is preferably between 15 and 80%, in particular between 30 and 70%. The thickness of the glass sheet is preferably between 1 and 10 mm, in particular between 2 and 6 mm. The glass sheet generally has an area ranging from 1 to 3 m ² .

In the glazing according to the invention the glass sheet is preferably curved. However, it is preferably flat when the electrically conductive tracks and the protective tracks are deposited. After depositing these tracks, in particular by screen printing, the glass sheet can undergo various treatments conventionally implemented in the field of automobile glazing manufacturing, such as bending and / or tempering treatments, intended to impart shape and the desired mechanical resistance, and simultaneously baking the electrically conductive and protective tracks.

By "opaque area" means an area in which the light transmission factor (within the meaning of ISO 9050) is at most 5%, especially 2% and even 1%, or even is zero. The opaque areas are preferably located at least on the periphery of the glazing. The opaque areas preferably represent at most 40%, in particular 30%, and even 20%, of the surface of the glazing. They preferably comprise an opaque mineral layer, in particular an enamel layer. The opaque zones then make it possible to protect against ultraviolet radiation the polymeric seals used for positioning and fixing the glazing on the bodywork bay of the motor vehicle. They also make it possible to conceal said seals as well as other elements located on the glazing, such as for example the electrical connections or the collector strips, intended to collect the electricity. An enamel is a mineral layer formed by baking an enamel composition comprising a glass frit, in particular bismuth borosilicate glass, and pigments. The enamel is preferably a black enamel.

By "transparent area" means an area in which the light transmission factor (within the meaning of ISO 9050) is at least 15%, in particular 20% and even 30 or 40%, even 50% or 60% or 70%, measured in places without electrically conductive tracks. The light transmission factor is generally at most 90%, especially 80%. The transparent zone is generally located in the central zone of the glazing. It preferably represents at least 60%, in particular 70% and even 80%, of the surface of the glazing.

The electrically conductive tracks preferably occupy between 1 and 20%, in particular between 2 and 10%, of the surface of the glazing.

The electrically conductive tracks preferably include heating wires located at least in a transparent area of the glazing and collector strips (also called "bus bars") located in an opaque area of the glazing. The collector strips are generally located parallel to the height of the glazing, on the lateral edges, and are electrically supplied so as to circulate the electric current in the heating wires, to which they are connected. The heating wires generally extend in the direction of the width of the glazing, between two collecting strips. The heating wires preferably have a width (in the plane of the glazing) ranging from 0.1 to 1 mm, in particular from 0.25 to 0.7 mm. The heating wires preferably have, in the final glazing, therefore after baking, a thickness (according to a glazing normal) ranging from 2 to 30 μm, in particular from 2 to 20 μm.

The electrically conductive tracks are preferably deposited by screen printing with a silver paste.

The silver paste preferably comprises, in the wet state, between 60 and 98% silver by weight. The silver content by weight is preferably at most 90%, especially 80% and even 75%. It is preferably within a range ranging from 66 to 75%, in particular from 68 to 70%. Low silver contents are particularly suitable for lead-free solder alloys. The rest typically includes glass frit as well as an organic medium, the latter being removed during cooking.

A screen printing process comprises depositing, in particular using a doctor blade, a pasty liquid on a substrate through the meshes of a screen printing screen. The screen meshes are closed in the part corresponding to the areas of the substrate which must remain bare, so that the dough can pass through the screen only in the areas to be printed, according to a predefined pattern. The selective filling of the meshes is therefore made according to the negative of the pattern to be printed. This selective obturation is generally carried out by application to the screen of a photocrosslinkable resin and then by exposure, by means of ultraviolet radiation, of the parts of the screen to be closed. Selective exposure is, for example, carried out using a slide comprising a transparent support, typically made of polyester, coated with an opaque ultraviolet ink deposited according to the pattern to be printed. The mesh of the screen is chosen according to the viscosity and the surface tension of the dough as well as according to the thickness of the desired tracks. The screens used for the screen printing of electrically conductive tracks preferably comprise 77 wires per cm for a wire diameter of 48 pm or 77 wires per cm for a wire diameter of 55 pm, or alternatively 90 wires per cm for a wire diameter 48 pm.

Protective tracks cover the upper surface and the lateral edges of the electrically conductive tracks located in the transparent area. The visible electrically conductive tracks are therefore completely protected from the environment: their lower surface is in contact with the glass sheet and the parts likely to be in contact with the environment, namely the upper surface (parallel to the glass sheet ) and the lateral edges (in the direction of the thickness of the tracks, substantially along a normal to the glass sheet) are covered by the protective tracks.

According to a preferred embodiment, only the electrically conductive tracks located in a transparent area of the glazing are covered by the protective tracks. The electrically conductive tracks located in the opaque areas of the glazing are in fact not visible so that their tarnishing is not annoying from an aesthetic point of view. Alternatively, at least part, or even all, of the electrically conductive tracks (therefore including those located in an opaque zone) are covered by the protective tracks.

The thickness of the protective tracks is preferably within a range from 0.1 to 5 μm, in particular from 0.2 to 3 μm. Thin thicknesses have proven to be sufficient to prevent tarnishing of the silver-based tracks. In addition, high thicknesses increase the visibility of the protective tracks, which is detrimental to the aesthetics of the glazing.

The protective tracks are transparent and are based on an oxide. The protective tracks are preferably colorless. The light transmission factor, within the meaning of ISO 9050, of the material constituting the protective tracks is preferably at least 90% for a thickness of 1 mm. The term "based on" means that the material constituting the protective tracks preferably contains at least 50% by weight of an oxide. This content is even preferably at least 60%, especially 70% and even 80% or 90%, or even 95 or 99%. The material may in particular consist of an oxide.

The transparent tracks are preferably based on an oxide of at least one element chosen from silicon, titanium, zirconium, tin. Tracks based on or even made of silicon oxide are preferred. Silicon oxide indeed combines several advantages, namely a high transparency, a low reflection and an absence of color which makes the protective tracks totally invisible to the user, as well as a great ability to resist sulfur pollution.

The protective tracks are preferably deposited by screen printing of a solgel solution.

By sol-gel solution means a solution, preferably aqueous, containing precursors of the material forming the protective tracks. Said precursors preferably comprise organometallic compounds of said material and / or nanoparticles of said material and / or the products of chemical reactions liable to occur between said organometallic compounds and other constituents of the solution, for example water. Organometallic compounds are in fact liable to undergo hydrolysis and / or condensation reactions during the formation of the solution, therefore before application.

The screen used for the screen printing step of the protective tracks has a pattern close to that of the screen used for the screen printing step of the electrically conductive tracks. In the case where the protective tracks cover only the electroconductive tracks located in the transparent areas of the glazing, the screen meshes corresponding to the opaque areas are however closed. In addition, in order to ensure complete covering of the electrically conductive tracks, including their lateral edges, the width of the patterns is slightly greater than those of the patterns of the screen printing screen of the electrically conductive tracks. Generally, the protective tracks will have a smaller thickness than that of the electrically conductive tracks. The screen printing screen of the protective tracks will therefore have a higher number of threads per centimeter, for example 120 threads / cm, and therefore a smaller mesh.

The glazing according to the invention is preferably a rear window of a motor vehicle.

The method according to the invention preferably comprises a drying step at the end of each track deposition step. The drying is preferably carried out at a temperature between 100 and 200 ° C.

The baking step of the electrically conductive and protective tracks the baking step is preferably carried out simultaneously with bending of the glass sheet. The cooking temperature is preferably between 600 and 800 ° C, especially between 620 and 750 ° C.

The accompanying drawings illustrate the invention.

[Fig.l] is a representation of glazing according to the invention.

[Fig.2] is a schematic sectional representation of a glazing according to the invention, in part of the transparent area.

The glazing 1 is a rear window of a motor vehicle. It comprises a glass sheet 2 and has a central transparent zone 3 and a peripheral opaque zone 4, the opaque zone 4 comprising, deposited on the glass sheet 2 a layer of black enamel. The glazing 1 further comprises electrically conductive tracks located in the opaque zone 4, and not visible, as well as electrically conductive stations 5, located in the transparent zone 3, in the form of heating wires. The heating wires 5 extend here in the width of the glazing and are for example deposited by screen printing with a silver paste. In the opaque part 4, the heating wires are electrically connected to other electrically conductive tracks, in this case non-visible collecting strips, situated on the lateral edges of the glazing 1, and which are for example also deposited by screen printing of a silver paste. Transparent protective tracks 6 protect, in the transparent zone 3 of the glazing 1, the heating wires 5, by covering both their upper surface 50 and their lateral edges 51. The protective tracks 6 are for example made of silica and deposited by screen printing d 'a sol-gel solution.

The following examples illustrate the invention without limitation.

In a comparative example, a sheet of glass 4.85 mm thick was coated by screen printing with silver electroconductive tracks. To do this, a silver paste containing 80% silver was screen printed in known manner using a screen containing 77 threads / cm and then dried at 150 ° C for 2 minutes. The silver paste was then baked at 710 ° C for 3 minutes.

The example according to the invention differs from the comparative example in that protective tracks have been deposited on the silver-based electroconductive tracks. The protective tracks were deposited by screen printing of a sol-gel solution containing silica precursors using a screen containing 120 threads / cm, then dried at 150 ° C for 2 minutes.

The tarnish resistance was measured as follows: in a desiccator containing 500 ml of demineralized water is placed a cup containing 10 g of sulfur flower. The samples to be studied are introduced vertically into the desiccator, the latter then being hermetically sealed and then placed at a temperature of 70 ° C. for 2 days. The optical appearance of the samples is then assessed qualitatively.

In the case of the comparative example, the tracks had stains as well as an iridescent appearance characterized by an aspect in reflection ranging from orange to brown. In the case of the example according to the invention, however, the tracks have a uniform gray appearance.

Claims (1)

claims [Claim 1] Glazing (1) having at least one transparent zone (3) and at least one opaque zone (4), said glazing (1) comprising a glass sheet (2) coated on one of its surfaces with electrically conductive tracks (5) based silver in at least one transparent zone (3) and at least one opaque zone (4), said electrically conductive tracks (5) located in the at least one transparent zone (3) being covered on their upper surface (50) and on their lateral edges (51) by transparent protective tracks (6) based on an oxide. [Claim 2] Glazing (1) according to claim 1, in which the electrically conductive tracks comprise heating wires (5) located at least in a transparent zone (3) of the glazing and collector strips located in an opaque zone (4) of the glazing. [Claim 3] Glazing (1) according to one of the preceding claims, such that the electrically conductive tracks (5) are deposited by screen printing with a silver paste. [Claim 4] Glazing (1) according to one of the preceding claims, such that the protective tracks (6) are based on an oxide of at least one element chosen from silicon, titanium, zirconium, tin. [Claim 5] Glazing (1) according to one of the preceding claims, such that the protective tracks (6) are deposited by screen printing of a sol-gel solution. [Claim 6] Glazing (1) according to one of the preceding claims, in which the opaque zones (4) are located at least on the periphery of the glazing and comprise an opaque mineral layer, in particular a layer of enamel. [Claim 7] Glazing (1) according to one of the preceding claims, which is a rear window of a motor vehicle. [Claim 8] Method for obtaining a glazing unit (1) according to one of the preceding claims, comprising the following successive steps: - a step of depositing electroconductive tracks (5) by screen printing of silver paste on the surface of a glass sheet (2), then - a step of depositing transparent protective tracks (6) based on an oxide by screen printing of a sol-gel solution, then - A cooking step of said electroconductive (5) and protective (6) tracks. [Claim 9] Method according to claim 8, comprising a drying step at the end of each track deposition step (5, 6). [Claim 10] Method according to either of Claims 8 and 9, in which the baking step is carried out simultaneously with bending of the glass sheet.