Method for obtaining a glazing panel provided with electrically conductive patterns

Abstract

The invention relates to a method for obtaining a glazing panel provided with electrically conductive patterns, comprising single-pass printing, on a glass sheet (1), of electrically conductive patterns (3, 5) by means of a digital inkjet printing technique, the printing comprising ejecting drops of an ink which comprises a glass frit, metal particles and an organic medium, the content by weight of metal particles in the ink being greater than 60%, and the ink having a viscosity of between 30 and 500 mPa.s at a shear rate of 100 s-1 and at the temperature at which the drops are ejected.

Description

Process for obtaining glazing with electrically conductive patterns

[0001] The invention relates to the field of glazing, in particular to that of vehicle glazing, in particular automobiles. It relates more particularly to obtaining glazing provided with electrically conductive patterns.

[0002] It is known to print electroconductive tracks (also called electroconductive patterns) on glass sheets in order to obtain heated glazing. For example, rear windows of motor vehicles are commonly coated with electroconductive tracks, in the form of heating wires, which generally extend along the entire length of the glazing, and collector strips, intended for the supply of electric current and generally arranged on the lateral edges of the glazing. Such tracks or patterns allow the glazing to be defrosted and / or demisted.

[0003] The printing of electrically conductive patterns is generally carried out by screen printing. To do this, a screen printing screen with some of its meshes sealed is used, and an electrically conductive paste comprising metallic particles, often silver, is forced through the unsealed meshes of the screen using a doctor blade. The electrically conductive paste is generally very viscous (typically of the order of 30 Pa.s), and may contain large quantities of silver, typically 60 to 88% by weight, making it easy to achieve the desired electrical resistance ranges.

[0004] The screen printing technique does, however, have some drawbacks. First, it requires the use of a different screen for each vehicle model. In addition, the screens' limited lifespan requires them to be replaced periodically. Finally, despite careful washing, silver paste may remain attached to the screens, leading to losses of silver paste and defects in the glazing.

[0005] There is therefore a need for a printing process that overcomes these drawbacks and is notably more flexible and more economical, while still making it possible to obtain the desired properties for the final glazing.

[0006] To this end, the subject of the invention is a method for obtaining glazing provided with electrically conductive patterns, comprising printing on a sheet of glass, in a single pass, electrically conductive patterns by a digital printing technique of the inkjet type, said printing comprising the ejection of drops of an ink comprising a glass frit, metal particles and an organic medium, the weight content of metal particles in the ink being greater than 60%, and the ink having a viscosity of between 30 and 500 mPa.s for a shear rate of 100 s -1 and the temperature at which the drops are ejected.

[0007] The present application also describes a glazing, in particular an automotive glazing, obtained by this process, comprising a sheet of glass provided with electrically conductive patterns.

[0008] The inventors were able to demonstrate that it was possible to print the electroconductive patterns by inkjet in a single pass thanks to the use of a viscous ink containing large quantities of silver.

[0009] The inkjet printing technique has already been used to deposit enamel layers on glass sheets. For example, application EP3242915 discloses ceramic ink compositions suitable for inkjet printing, comprising a glass frit, pigment particles and an organic medium. These inks have a viscosity of 6 to 20 mPa.s, in order to be compatible with known print heads. The use of this ink makes it possible, for example, to print black enamels on automobile windows, from an enamel composition comprising a glass frit and black pigments. The inventors were, however, able to demonstrate that this process, although well suited to enamel printing, was, however, poorly suited to printing electrically conductive tracks.Since the content of solid particles (glass frit and silver particles) in the ink is limited to 80% and even more generally to 60%, the maximum weight quantity of silver particles that can be used in practice is less than 60%. It follows that several passes at the same location are necessary to achieve the desired electrical resistances, which increases the printing time compared to a single-layer application. For example, the inventors were able to demonstrate that with commercial electroconductive inks having a viscosity between 5 and 15 mPa.s, the electrical resistances necessary for the intended application required up to seven passes, which is not compatible with the industrial production rates of automotive glazing. The invention, on the contrary, makes it possible to print the electroconductive tracks in a single pass.

[0010] The glass sheet is typically soda-lime glass, but may be other types of glass, for example borosilicate or aluminosilicate. Its thickness is preferably between 0.7 and 6 mm, in particular between 1 and 4 mm. At least one dimension of the glass sheet is preferably at least 1 m. The glass sheet may be clear, or preferably tinted, for example green, gray or blue. To achieve this, the composition of the glass comprises colorants, in particular iron oxide, in a total weight content (expressed as Fe2O3) of between 0.05 and 1.5%, in particular between 0.1 and 1.0%.

[0011] The glass sheet is generally flat at the time of depositing the electrically conductive patterns. It is then preferably curved, normally during the heat treatment of baking the electrically conductive patterns. The final glazing is therefore preferably curved. The electrically conductive patterns are preferably arranged on the inner face of the glazing, intended to be placed inside the vehicle. In the case of curved glazing, the inner face is the concave face of the glazing.

[0012] The electrically conductive patterns preferably comprise collector lines and strips.

[0013] A portion of the electroconductive patterns is preferably deposited on an enamel coating. In particular, the method then comprises, before printing the electroconductive ink, a preliminary step of depositing and then drying a black enamel coating on the periphery of the glass sheet, on which a portion of the electroconductive patterns (in particular the collector strips) is deposited. Such a coating makes it possible to conceal and protect against ultraviolet radiation the seals used for positioning and mounting the glazing in the bodywork bay. The enamel coating also makes it possible to conceal the collector strips from the outside of the vehicle. The term "enamel" here encompasses various opaque materials, and includes in particular silicate paints. The enamel coating can be deposited by screen printing or, more preferably, by digital printing of the inkjet type.

[0014] Preferably, the metal particles are silver particles. However, other metals are possible, for example gold or copper.

[0015] The weight content of metal particles in the ink is preferably between 62 and 80%, in particular between 65 and 75%. The presence of metal particles, in particular silver, in large quantities, makes it possible to obtain particularly low resistivities, and therefore to achieve low electrical resistance without having to deposit patterns having a high thickness and / or width.

[0016] The glass frit preferably has a chemical composition of the bismuth and / or zinc borosilicate type. These compositions allow the frit to soften at the firing temperatures normally used, generally between 550 and 720°C, which correspond to the temperatures used for bending and / or tempering glass. After softening, a vitreous or vitrocrystalline binder is thus obtained, capable of fixing the metal particles to the glass.

[0017] The ink particles (frit and metal particles) have a volume particle size distribution such that the D90 is at most 2 µm, and even at most 1 µm. The particle size distribution can be determined by laser particle size analysis. Fine particles help prevent clogging of the print head nozzles.

[0018] The ink also comprises an organic medium. The medium generally comprises a solvent. The solvent is preferably selected from alcohols (e.g. ethanol, propanol or butanol), acetone, ethers, glycols, glycol ethers, esters and aromatic solvents (e.g. toluene or xylene). The organic medium may further comprise dispersants, rheology agents, surfactants and / or resins. The organic medium, which allows the formation of ink drops in which the glass frit and the metal particles are dispersed, is removed at least partially during a possible drying step, and in any event completely removed at the end of the baking of the ink, which generally takes place during the bending and / or tempering of the glass sheet.

[0019] The digital printing technique is preferably a "drop on demand" technique. In such a technique, the print heads include nozzles through which ink drops are locally projected onto the glass sheet. This technique is also called "drop on demand" (DOD) in English.

[0020] The viscosity of the ink is preferably between 50 and 400 mPa.s, especially between 100 and 350 mPa.s, or even between 150 and 300 mPa.s, or even between 180 and 250 mPa.s. The viscosity of the ink can be regulated by changing the amounts of solvent and solid particles. Overall, the viscosity increases when the amount of solvent decreases and the amount of solid particles increases. The viscosity of the ink is measured at a shear rate of 100 s -1. Since inks generally exhibit Newtonian behavior, the shear rate has little impact on the result. The viscosity of the ink is measured at the temperature at which the drops are ejected, i.e., the temperature to which the ink is brought before ejection, which depends on the printer used. In some embodiments, the ink is not heated by the printer, so the viscosity is measured at room temperature. In other embodiments, the ink is heated, for example to a temperature between 30 and 60°C, in particular between 40 and 50°C. In this case, the viscosity of the ink will be measured at this temperature. The viscosity can, for example, be measured using a cone-plate viscometer.

[0021] Preferably, the drop volume is between 60 and 200 pL, especially between 80 and 180 pL. Such volumes ensure good coalescence of the drops and therefore physical continuity of the deposited ink, even after a single pass. In contrast, inkjet printing processes used for depositing enamel on glass use drops having a volume of 10 to 60 pL, which in the case of depositing electrically conductive patterns would generally require at least two or three passes to obtain a continuous coating.

[0022] Print heads compatible with inks having the viscosity described above and capable of forming large volume drops are, for example, marketed under the names NovoJet by the company Quantica and Nitrox by the company Xaar.

[0023] Preferably, the printing is carried out by means of a printer comprising a plurality of print heads arranged in line over a length at least equal to the width of the glass sheet. Preferably, the glass sheet moves opposite the print heads, which are fixed. Alternatively, the glass sheet may be fixed and the print head support means may move opposite the glass sheet. This embodiment is, however, less preferred because it is less compatible with an industrial process in which the glass sheet is caused to move successively through different stations. Preferably, the print heads are therefore fixed. They are preferably arranged in a Y direction orthogonal to the X direction of movement of the glass sheet.

[0024] The print heads are preferably arranged on a support means so that they can be deposited over the entire glass sheet. Preferably, the print heads are arranged in a staggered pattern to ensure overlapping areas between two neighboring heads. As previously stated, the print heads are preferably fixed. Printing the electrically conductive patterns in a single pass using fixed print heads arranged opposite a moving glass sheet makes it possible to achieve printing speeds compatible with the rates of industrial automotive glazing manufacturing processes.

[0025] The number of print heads can be adjusted depending on the size of the patterns to be printed. It is preferably between 5 and 30, taking into account that the print heads allow printing widths between 50 and 200 mm.

[0026] The printing step preferably includes a drying step. Drying is carried out, for example, by means of infrared radiation. Drying temperatures preferably range from 120 to 180°C. The drying time is preferably between 30 seconds and 5 minutes, in particular between 1 minute and 2 minutes.

[0027] Preferably, the method further comprises, after the printing step, a step of bending the glass, then a step of soldering connectors onto a portion of the electrically conductive patterns.

[0028] Bending can be carried out, for example, by gravity (the glass deforms under its own weight) or by pressing, at temperatures typically ranging from 550 to 720°C. Bending can be followed by thermal tempering.

[0029] Soldering is performed in particular using a solder alloy. The connector is typically metallic, particularly steel containing chromium. The solder alloy is preferably lead-free, particularly based on tin, silver, and copper. Soldering is preferably performed on a portion of the collector strips.

[0030] The thickness of the electrically conductive patterns (final, therefore after bending) is preferably between 5 and 30 µm, in particular between 5 and 20 µm, or even between 10 and 15 µm.

[0031] Glazing is in particular a rear window of a motor vehicle, a side window of a motor vehicle or even a windshield of a motor vehicle.

[0032] Electrically conductive patterns include antennas, bus bars, alarm wires, and / or heating wires. The bus bars (also called bus bars) are preferably located in the two opposite side portions of the glazing. The heating wires are preferably located primarily in the central portion of the glazing, and extend parallel to the long edge of the glazing between the two bus bars. This is particularly the case for a rear window. The width of the heating wires is preferably between 0.1 and 1.0 mm, particularly between 0.2 and 0.8 mm.

[0033] In the case of a windshield, electrically conductive patterns include antennas. Electrically conductive patterns can also be heating wires that provide local heating in camera windows, for example, to detect the distance to the vehicle ahead.

[0034] In the case of side glazing, electrically conductive patterns include antennas or alarm wires.

[0035] illustrates in a schematic and non-limiting manner a method according to the invention.

[0036] The glass sheet 1, previously cut to the dimensions of the final glazing, for example a rear window of a motor vehicle, has been coated with an enamel coating 6 in the form of a peripheral strip. The enamel is for example black, but for greater readability of the figure only its outline is shown, in dotted lines. This peripheral coating 6, in particular intended to conceal and protect the polymer seals used to fix the glazing in the bodywork bay, has for example been deposited by inkjet printing and then dried.

[0037] The glass sheet 1 moves along the X direction, in the direction of movement indicated in the figure by an arrow. The means for supporting and conveying the glass sheet are not shown here. The glass sheet 1 moves opposite a fixed printer, of which only the means 9 for supporting the print heads 7 is shown. The printer obviously comprises other means not shown, such as ink reservoirs, means configured to bring the ink to the print heads (for example a pump) and control means (comprising for example a microprocessor, a memory card, sensors, etc.). The support means 9 extends along a Y direction, orthogonal to the direction of movement X of the glass sheet 1. The print heads are arranged in a line over a length greater than the width L of the glass sheet 1, the width being the largest dimension of the glass sheet 1 in the Y direction.

[0038] The print heads 7 are mounted on the support means 9 opposite the glass sheet 1. The print heads 7 are here arranged in a staggered pattern, on two lines parallel to each other and to the Y direction. This arrangement ensures overlap, so as to ensure that each point on the glass sheet can receive a drop of ink. Each print head 7 comprises a plurality of nozzles, for example between 50 and 2000 nozzles connected to an ink reservoir. The print heads 7 are preferably of the piezoelectric type. In this type of head, an electrical voltage applied to a piezoelectric membrane located near the nozzle makes it possible to deform the membrane and increase the pressure in the nozzle, resulting in the formation of a droplet and its ejection.As mentioned above, the print heads 7 are, for example, heads of the NovoJet type (Quantica GmbH) – which include around 100 nozzles, or Nitrox (Xaar) – which include between 1000 and 2000 nozzles.

[0039] In the part of the glass sheet 1 already printed (right part) two types of electrically conductive patterns are shown: a collector strip 5 and heating lines 3. The collector strip 5 is printed completely on the enamel coating 6, near the right side edge of the glass sheet 1. Another collector strip will be printed on the left side edge. The heating lines 3 start from the collector strip 5 and extend parallel to the X direction towards the left side edge of the glass sheet 1.

[0040] Other configurations are of course possible, for example the glass sheet can be rotated 90° relative to the printer, so that the heated lines are printed parallel to the Y direction. In this configuration, all print heads are used to print the lines.

Claims

Method for obtaining a glazing provided with electroconductive patterns (3, 5), comprising printing on a sheet of glass (1), in a single pass, electroconductive patterns (3, 5) by a digital printing technique of the inkjet type, said printing comprising the ejection of drops of an ink comprising a glass frit, metal particles and an organic medium, the weight content of metal particles in the ink being greater than 60%, and the ink having a viscosity of between 30 and 500 mPa.s for a shear rate of 100 s -1 and the temperature at which the drops are ejected. The method of claim 1, wherein the metal particles are silver particles. Method according to one of the preceding claims, in which the weight content of metal particles in the ink is between 62 and 80%, in particular between 65 and 75%. Method according to one of the preceding claims, in which the glass frit has a chemical composition of the bismuth and / or zinc borosilicate type. Method according to one of the preceding claims, in which the frit particles and the metal particles have a volume particle size distribution such that the D90 is at most 2 µm. Method according to one of the preceding claims, in which the digital printing technique of the inkjet type is a "drop on demand" type technique. Method according to the preceding claim, in which the volume of the drops is between 60 and 200 pL, in particular between 80 and 180 pL. Method according to one of the preceding claims, in which the ink has a viscosity of between 50 and 400 mPa.s, in particular between 100 and 350 mPa.s, for a shear rate of 100 s -1 and the temperature at which the drops are ejected. Method according to one of the preceding claims, in which the printing is carried out by means of a printer comprising a plurality of print heads (7) arranged in line over a length at least equal to the width (L) of the glass sheet (1), the glass sheet (1) moving opposite said print heads (7) which are fixed. Method according to the preceding claim, in which the glass sheet (1) moves opposite the print heads (7), said print heads (7) being fixed. Method according to one of the preceding claims, wherein the electrically conductive patterns (3, 5) comprise lines (3) and collector strips (5). Method according to one of the preceding claims, in which a part of the electrically conductive patterns (3, 5) is deposited on an enamel coating (6). Method according to one of the preceding claims, further comprising, after the printing step, a step of bending the glass, then a step of soldering connectors onto a portion of the electrically conductive patterns. Method according to the preceding claim, in which the thickness of the electrically conductive patterns after bending is between 5 and 30 µm, in particular between 5 and 20 µm. Method according to one of the preceding claims, in which the glazing is a rear window of a motor vehicle, a side window of a motor vehicle or a windshield of a motor vehicle, and the electrically conductive patterns (3, 5) are antennas, collector strips, alarm wires and / or heating wires.

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