Method for obtaining an assembly glass provided with a conductive pattern

Abstract

This invention relates to a method for obtaining an assembled glass with conductive patterns, comprising printing conductive patterns (3,5) on a glass sheet (1) in a single pass using digital inkjet printing technology, wherein the printing comprises ejecting ink droplets, the ink comprising glass frit, metal particles and an organic medium, wherein the weight content of the metal particles in the ink is greater than 60%, and the ink is applied within 100 s. ‑1 At the shear rate and the temperature of the ejected droplets, the viscosity of the ink is 30 to 500 mPa·s.

Description

[0001] This invention relates to the field of assembly glass, particularly vehicle assembly glass, especially automotive assembly glass. More specifically, this invention relates to obtaining assembly glass with conductive patterns.

[0002] It is known to print conductive paths (also known as conductive patterns) on glass sheets to produce heatable assembly glass. For example, the rear window of a motor vehicle is typically coated with conductive paths in the form of heating wires, which usually extend along the entire length of the assembly glass, as well as busbars for supplying current, which are typically arranged on the side edges of the assembly glass. Such paths or patterns enable the assembly glass to defrost and / or defog.

[0003] Conductive patterns are typically printed using screen printing. This is achieved by using a screen printing stencil (with some of its mesh openings closed) and a squeegee to force a conductive paste containing metal particles (usually silver) through the unclosed mesh openings of the stencil. The conductive paste typically has a high viscosity (typically about 30 Pa·s) and can contain a significant amount of silver, usually 60 to 88% by weight, making it easy to achieve the desired resistance range.

[0004] However, screen printing technology does have its drawbacks. First, different screens are required for each vehicle model. Furthermore, the limited lifespan of the screens means they must be replaced periodically. Finally, despite careful cleaning, silver paste can still adhere to the screen, leading to paste loss and defects in the assembled glass.

[0005] Therefore, there is a need for a printing method that overcomes these drawbacks, and is particularly flexible and economical, while still achieving the desired properties of the final assembled glass.

[0006] Therefore, the present invention relates to a method for obtaining an assembled glass having a conductive pattern, comprising printing the conductive pattern on a glass sheet in a single pass using digital inkjet printing technology, wherein the printing comprises ejecting ink droplets, the ink comprising glass frit, metal particles, and an organic medium, wherein the weight content of the metal particles in the ink is greater than 60%, and the conductive pattern is applied within 100 s. -1 At the shear rate and the temperature of the ejected droplets, the viscosity of the ink is 30 to 500 mPa·s.

[0007] This application also describes an assembly glass, particularly automotive assembly glass, obtained by this method, comprising a glass sheet having a conductive pattern.

[0008] The inventors were able to demonstrate that conductive patterns can be printed using a viscous ink containing a large amount of silver through single-pass inkjet printing.

[0009] Inkjet printing technology has been used to deposit enamel layers on glass sheets. For example, EP3242915 describes ceramic ink compositions suitable for inkjet printing, comprising glass frit, pigment particles, and an organic medium. These inks have a viscosity of 6 to 20 mPa·s to ensure compatibility with known printheads. Using such inks, for example, black enamel can be printed on automotive glass using an enamel composition comprising glass frit and black pigment. However, the inventors have been able to demonstrate that this method, well-suited for enamel printing, is less suitable for printing conductive paths. Because the content of solid particles (glass frit and silver particles) in the ink is limited to 80%, and even more typically to 60%, the maximum weight amount of silver particles usable in practice is less than 60%. As a result, multiple passes are required at the same location to achieve the desired resistance, which increases printing time compared to a single coating application. For example, the inventors have been able to demonstrate that using commercially available conductive inks with a viscosity of 5 to 15 mPa·s, the required resistance for a target application requires up to seven passes, which is incompatible with the industrial production rates of automotive glass. In contrast, the present invention allows for the printing of conductive paths in a single pass.

[0010] Typically, the glass sheet is made of soda-lime glass, but it can also be made of other types of glass, such as borosilicate or aluminosilicate. Its thickness is preferably 0.7 to 6 mm, particularly 1 to 4 mm. At least one dimension of the glass sheet is preferably at least 1 μm. The assembled glass can be transparent, or preferably colored, such as green, gray, or blue. For this purpose, the glass composition contains a colorant, particularly iron oxide, at a total weight content (expressed as Fe2O3) of 0.05 to 1.5%, particularly 0.1 to 1.0%.

[0011] Typically, the glass sheet is flat when the conductive pattern is deposited. Preferably, it is then bent, usually during the heat treatment curing of the conductive pattern. Preferably, the finished assembly glass will then be bent. The conductive pattern is preferably arranged on the inner surface of the assembly glass, which is intended to be arranged inside the carrier. In the case of bending the assembly glass, the inner surface is a concave surface of the assembly glass.

[0012] The conductive pattern preferably includes lines and busbars.

[0013] A portion of the conductive pattern is preferably deposited on an enamel coating. Specifically, the method then includes a preliminary step before printing conductive ink, in which a portion of the conductive pattern (particularly the busbar) is deposited on the edge of the glass sheet and then dried. This coating allows for the concealment of seals used to position and mount the assembly glass in window openings within the vehicle body, and protects them from ultraviolet radiation. The enamel coating also allows the busbar to be concealed from the outside of the vehicle. The term "enamel" herein encompasses a range of opaque materials, particularly silicate lacquer. The enamel coating can be deposited by screen printing or, more preferably, by digital inkjet printing.

[0014] Preferably, the metal particles are silver particles. Other metals are also possible, such as gold or copper.

[0015] The weight content of metal particles in the ink is preferably 62 to 80%, particularly 65 to 75%. The presence of a large number of metal particles (especially silver) makes it possible to achieve particularly low resistivity, and thus low resistance, without depositing patterns of large thickness and / or width.

[0016] The glass frit preferably has a borosilicate-type chemical composition containing bismuth and / or zinc. These compositions soften the glass frit at commonly used curing temperatures (typically between 550 and 720°C), corresponding to the temperatures used for bending and / or tempering glass. After softening, a vitreous or glassy binder is obtained that can adhere metal particles to the glass.

[0017] The volumetric particle size distribution of the ink particles (glass and metal particles) results in a D90 of at most 2 µm, and even at most 1 µm. This particle size distribution can be determined specifically through laser particle size analysis. Fine particles prevent printhead nozzle clogging.

[0018] The ink also contains an organic medium. The medium typically contains 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 also contain dispersants, rheology modifiers, surfactants, and / or resins. The organic medium allows the formation of ink droplets in which glass frit and metal particles are dispersed, which are at least partially removed during possible drying steps and, in any case, completely removed at the end of ink curing, which typically occurs during the bending and / or tempering of the glass sheet.

[0019] Digital printing technology is preferably a "drop-on-demand" (DOD) technology. In this technology, the printhead includes nozzles through which ink droplets are locally ejected onto a glass sheet. This technology is also known as DOD.

[0020] The ink viscosity is preferably 50 to 400 mPa·s, particularly 100 to 350 mPa·s, or even 150 to 300 mPa·s, or even 180 to 250 mPa·s. Ink viscosity can be controlled by varying the amounts of solvent and solid particles. Generally, viscosity increases with decreasing solvent content and increasing solid particle content. The ink viscosity at 100 s⁻¹... -1 The viscosity is measured at the shear rate. Ink typically exhibits Newtonian behavior, so the shear rate has little effect on the results. Ink viscosity is measured at the temperature of the ejected droplets, i.e., the temperature to which the ink is heated 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, particularly between 40 and 50°C. In this case, the ink viscosity is measured at this temperature. For example, a cone-plate viscometer can be used to measure the viscosity.

[0021] Preferably, the droplet volume is 60 to 200 pL, particularly 80 to 180 pL. This volume ensures good droplet coalescence and thus ensures the physical continuity of the deposited ink, even after a single pass. In contrast, inkjet printing methods for depositing enamel on glass use droplets with volumes of 10 to 60 pL, which typically require at least two or three passes to obtain a continuous coating when depositing conductive patterns.

[0022] Printheads that are compatible with inks of the aforementioned viscosity and capable of forming large-volume droplets are, for example, sold by Quantica under the name NovoJet and by Xaar under the name Nitrox.

[0023] Preferably, printing is performed using a printer comprising multiple printheads arranged in a line along a length at least equal to the width of the glass sheet. Preferably, the glass sheet travels relative to the printheads, which are fixed. Alternatively, the glass sheet may be fixed, and the printhead support may be movable relative to the glass sheet. However, this embodiment is less preferred because it is less compatible with industrial methods where the glass sheet passes sequentially through different stations. Therefore, the printheads are preferably fixed. They are preferably arranged in the Y direction, perpendicular to the X direction of travel of the glass sheet.

[0024] Preferably, the printheads are arranged on a support device to allow deposition onto the entire glass sheet. Preferably, the printheads are staggered to ensure overlap between adjacent heads. As previously mentioned, the printheads are preferably fixed. By using fixed printheads positioned opposite the moving glass sheet to print conductive patterns in a single pass, printing speeds compatible with the production rates of industrial automotive assembly glass methods can be achieved.

[0025] The number of printheads can be adjusted based on the size of the pattern to be printed. It is preferably 5 to 30, considering that the printheads can print widths of 50 to 200 mm.

[0026] The printing process preferably includes a drying step. Drying is carried out, for example, using infrared radiation. The drying temperature is preferably 120 to 180°C. The drying time is preferably 30 seconds to 5 minutes, particularly 1 to 2 minutes.

[0027] Preferably, the method further includes a step of bending the glass after the printing step, followed by a step of soldering a connector onto a portion of the conductive pattern.

[0028] Bending can be done specifically using gravity (e.g., glass deforms under its own weight) or by pressing, at temperatures typically between 550 and 720°C. After bending, heat tempering can be performed.

[0029] Soldering is performed using a welding alloy. Connectors are typically metallic, particularly made of chromium-containing steel. The welding alloy is preferably lead-free, and particularly based on tin, silver, and copper. Soldering is preferably performed on a portion of the busbar.

[0030] The thickness of the conductive pattern (finally, and therefore after bending) is preferably 5 to 30 µm, particularly 5 to 20 µm, or even 10 to 15 µm.

[0031] Glass is installed, especially in the rear window, side window, or even the windshield of motor vehicles.

[0032] Conductive patterns, particularly antennas, busbars, alarm wires, and / or heating wires. Busbars are preferably located on two opposite sides of the assembled glass. Heating wires are preferably located primarily in the central portion of the assembled glass and extend parallel to the long edge of the assembled glass between the two busbars. This is especially true for rear windows. The width of the heating wires is preferably 0.1 to 1.0 mm, particularly 0.2 to 0.8 mm.

[0033] In the case of windshields, conductive patterns are particularly important for antennas. Conductive patterns can also be heating wires to ensure localized heating within the camera window, for example, for detecting distance to vehicles ahead.

[0034] When side windows are fitted with glass, conductive patterns are particularly important for antennas or alarm lines.

[0035] [ Figure 1 The method according to the invention is shown in an illustrative and non-limiting manner.

[0036] The glass sheet 1, previously cut to the final size for assembly (e.g., the rear window of a motor vehicle), has been coated with an enamel coating 6 in the form of an outer band. The enamel is, for example, black, but for the sake of readability, only its outline is shown, indicated by dashed lines. This outer coating 6 is specifically designed to conceal and protect the polymer seals used to secure the assembly glass to the window opening in the vehicle body, which have been deposited, for example, by inkjet printing and then dried.

[0037] The glass sheet 1 travels in the X direction, along the direction of travel indicated by the arrow in the figure. The means for supporting and conveying the glass sheet are not shown here. The glass sheet 1 travels relative to the stationary printer, with only the support device 9 for the printhead 7 shown. The printer, of course, includes other means not shown, such as an ink reservoir, means configured to feed ink to the printhead (e.g., a pump), and control means (e.g., including a microprocessor, memory card, sensors, etc.). The support device 9 extends in the Y direction, perpendicular to the X direction of travel of the glass sheet 1. The printheads are arranged in a line along a length greater than the width L of the glass sheet 1, the width being the maximum dimension of the glass sheet 1 in the Y direction.

[0038] Printhead 7 is mounted on support 9, opposite glass sheet 1. Here, printheads 7 are staggered, forming two parallel lines parallel to each other and parallel to the Y direction. This arrangement ensures overlap, allowing each point on the glass sheet to receive ink droplets. Each printhead 7 includes multiple nozzles, for example, 50 to 2000 nozzles connected to an ink reservoir. Printhead 7 is preferably piezoelectric. In this type of head, a voltage applied to a piezoelectric diaphragm located near the nozzle deforms the diaphragm and increases the pressure in the nozzle, causing droplet formation and ejection. As previously mentioned, printhead 7 is, for example, a NovoJet (Quantica GmbH) type head including approximately 100 nozzles, or a Nitrox (Xaar) type head including 1000 to 2000 nozzles.

[0039] The printed portion (right side) of the glass sheet 1 is characterized by two types of conductive patterns: busbars 5 and heating lines 3. Busbars 5 are printed entirely on the enamel coating 6, near the right edge of the glass sheet 1. Another busbar will be printed on the left edge. The heating line 3 starts from the busbar 5 and extends parallel to the X direction toward the left edge of the glass sheet 1.

[0040] Of course, other configurations are also possible; for example, the glass sheet can be rotated 90° relative to the printer, so that the heating lines are printed parallel to the Y direction. In this configuration, all printheads are used for printing lines.

Claims

1. A method for obtaining an assembled glass having conductive patterns (3,5) disposed thereon, comprising printing the conductive patterns (3,5) on a glass sheet (1) in a single pass using digital inkjet printing technology, said printing comprising ejecting ink droplets, said ink comprising glass frit, metal particles and an organic medium, said ink having a weight content of more than 60% of the metal particles, and wherein the metal particles in said ink have a content greater than 60% by weight, and wherein the ink has a content of more ... -1 At the shear rate and the temperature of the ejected droplets, the viscosity of the ink is 30 to 500 mPa·s.

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

3. The method according to any one of the preceding claims, wherein the weight content of the metal particles in the ink is 62 to 80%, particularly 65 to 75%.

4. The method according to any one of the preceding claims, wherein the glass frit has a chemical composition of bismuth and / or zinc borosilicate type.

5. The method according to any one of the preceding claims, wherein the volumetric particle size distribution of the glass frit particles and the metal particles is such that D90 is at most 2 µm.

6. The method according to any one of the preceding claims, wherein the digital inkjet printing technology is an "on-demand dripping" technology.

7. The method according to the preceding claims, wherein the droplet volume is 60 to 200 pL, particularly 80 to 180 pL.

8. The method according to any one of the preceding claims, wherein in 100 s -1 At the shear rate and the temperature of the ejected droplets, the viscosity of the ink is 50 to 400 mPa·s, particularly 100 to 350 mPa·s.

9. The method according to any one of the preceding claims, wherein the printing is performed by a printer comprising a plurality of printheads (7) arranged in a row along a length at least equal to the width (L) of the glass sheet (1), the glass sheet (1) running relative to the printheads (7), the printheads (7) being fixed.

10. The method according to the preceding claims, wherein the glass sheet (1) operates relative to the print head (7), and the print head (7) is fixed.

11. The method according to any one of the preceding claims, wherein the conductive pattern (3, 5) comprises a line (3) and a busbar (5).

12. The method according to any one of the preceding claims, wherein a portion of the conductive pattern (3,5) is deposited on the enamel coating (6).

13. The method according to any one of the preceding claims further includes a step of bending the glass after the printing step, followed by a step of soldering a connector onto a portion of the conductive pattern.

14. The method according to the preceding claim, wherein the thickness of the conductive pattern after bending is 5 to 30 µm, particularly 5 to 20 µm.

15. The method according to any one of the preceding claims, wherein the mounting glass is a rear window of a motor vehicle, a side window mounting glass of a motor vehicle, or even a windshield of a motor vehicle, and the conductive pattern (3,5) is an antenna, a busbar, an alarm wire, and / or a heating wire.

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