Process for obtaining glazing with electrically conductive patterns

Abstract

The invention relates to a method for obtaining a glazing provided with electroconductive patterns, 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 at the temperature at which the drops are ejected.

Description

Title of the invention: Method for obtaining glazing provided 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 over 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 electroconductive patterns is generally carried out by screen printing. To do this, a screen printing screen is used, some of the meshes of which are closed, and an electroconductive paste comprising metallic particles, often silver, is forced through the unclosed meshes of the screen, using a doctor blade. The electroconductive 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 certain drawbacks. First of all, it requires the use of a different screen for each model of motor vehicle. In addition, the limited lifespan of the screens means that they must be replaced periodically. Finally, it may happen, despite careful washing, that silver paste remains attached to the screens, leading on the one hand to losses of silver paste and on the other hand to defects on the glazing.

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

[0006] To this end, the invention relates to a method for obtaining glazing provided with electroconductive patterns, comprising printing on a sheet of glass, in a single pass, electroconductive 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 at the temperature at which the drops are ejected.

[0007] The invention also relates to glazing, in particular automotive glazing, obtained by this method, 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 layers of enamel 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 glazing, 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 made of soda-lime glass, but may be made of 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 electro-patterns. conductive. 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. Other metals are however 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 usually used, generally between 550 and 720°C, which correspond to the temperatures used for bending and / or tempering the glass. After softening, a vitreous or vitrocrystalline binder is thus obtained which is capable of fixing the metal particles to the glass.

[0017] The particles of the ink (frit and metal particles) have a volume particle size distribution such that the D90 is at most 2 pm, and even at most 1 pm. The particle size distribution can in particular be determined by laser particle size analysis. Fine particles make it possible to avoid clogging the nozzles of the print heads.

[0018] The ink also comprises an organic medium. The medium generally comprises a solvent. The solvent is preferably chosen from alcohols (for example 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 at least partially removed during a possible drying step, and in any case completely removed after 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" type technique. In such a technique, the print heads comprise nozzles through which drops of ink are projected locally 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, in particular 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 modifying the quantities of solvent and solid particles. Overall, the viscosity increases when the quantity of solvent decreases and the quantity of solid particles increases. The viscosity of the ink is measured at a shear rate of 100 s1. Since inks generally exhibit Newtonian behavior, the shear rate, however, 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 volume of the drops is between 60 and 200 pL, in particular between 80 and 180 pL. Such volumes make it possible to ensure good coalescence of the drops and therefore to obtain physical continuity of the deposited ink, even after a single pass. In contrast, the 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 electroconductive patterns would generally require at least two or three passes to obtain a continuous coating.

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

[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 as to be able to deposit over the entire glass sheet. Preferably, the print heads are arranged in a staggered pattern to ensure overlapping areas between two neighboring heads. As stated previously, 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 processes for manufacturing automotive glazing.

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

[0026] The printing step preferably comprises a drying step. Drying is carried out, for example, by means of infrared radiation. The 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] The soldering is in particular carried out using a solder alloy. The connector is typically metallic, in particular made of steel containing chromium. The solder alloy is preferably lead-free, in particular based on tin, silver and copper. The soldering is preferably carried out on a portion of the collector strips.

[0030] The thickness of the electroconductive patterns (final, therefore after bending) is preferably between 5 and 30 μm, in particular between 5 and 20 μm, or even between 10 and 3 pm.

[0031] The 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] The electrically conductive patterns are in particular antennas, collector strips, alarm wires and / or heating wires. The collector strips (also called "bus bars") are preferably located in the two opposite lateral parts of the glazing. The heating wires are preferably located mainly in the central part of the glazing, and extend parallel to the long edge of the glazing between the two collector strips. This is the case in particular for a rear window. The width of the heating wires is preferably between 0.1 and 1.0 mm, in particular between 0.2 and 0.8 mm.

[0033] In the case of a windshield, the electrically conductive patterns are in particular antennas. The electrically conductive patterns can also be heating wires providing local heating in the camera windows, for example for detecting the distance of the front vehicle.

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

[0035] [Fig-1] 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 for fixing 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 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, causing 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 approximately 100 nozzles, or Nitrox (Xaar) - which include between 1000 and 2000 nozzles.

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

Claims

Claims

1. 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 at the temperature at which the drops are ejected.

2. The method of claim 1, wherein the metal particles are silver particles.

3. Method according to one of the preceding claims, in which the weight content of metal particles in the ink is between 62 and 80%.

4. 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.

5. 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 and the volume of the drops is between 60 and 200 pL, in particular between 80 and 180 pL.

6. 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.

7. Method according to one of the preceding claims, in which the electrically conductive patterns (3, 5) comprise lines (3) and collector strips (5).

8. 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).

9. 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 part of the electrically conductive patterns.

10. Glazing, in particular automotive glazing, obtained by the method according to one of the preceding claims, comprising a glass sheet (1) provided with electrically conductive patterns (3, 5).

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