How to obtain curved laminated glazing

Abstract

The present invention relates to a method for obtaining curved laminated glazing, in particular for the windshield or roof of a motor vehicle. The method comprises the application (b) of an enamel layer (14) on a stack of thin layers (12) applied on a first glass sheet (10), and the application (c) of heat-resistant particles (16) based on oxides, metals or carbides, having at least one dimension greater than 30 μm, on at least the enamel layer (14). The stack of thin layers (12) is completely fused by the enamel layer (14) after a bending step (d) that is carried out before the lamination (e) of the first glass sheet (10) with an additional glass sheet (20) using a laminate interlayer 30.

Description

[Technical Field]

[0001] The present invention relates to the field of curved laminated glazing for motor vehicles, for example for roofs or windshields, comprising a glass sheet coated with a stack of thin layers and an enamel layer. [Background technology]

[0002] Laminated glazing is glazing in which two glass sheets are adhesively joined together by means of a laminate interlayer, which makes it possible, in particular, to contain the glass shards in case of breakage, but also provides other functionalities, in particular in terms of resistance to intrusion and improved acoustic properties.

[0003] These glazings often include various types of coatings intended to impart different properties.

[0004] A layer of enamel, generally black and opaque, is applied over a portion of the glazing, often in the form of a peripheral strip intended to conceal and protect from ultraviolet radiation a polymer seal that helps secure and position the glazing in the opening in the vehicle body. The enameled area also conceals the interior rearview mirror fastening area and various connectors and sensors.

[0005] In laminated glazing, these enamel layers are generally arranged on side 2, which is conventionally numbered starting with the side intended to be positioned on the exterior of the vehicle. Side 2 is therefore the side in contact with the laminate interlayer. The aesthetic appearance of the enamel layer visible from the exterior of the vehicle is of particular importance to automobile manufacturers. Enamel is generally obtained by firing a composition containing glass frit and pigment at temperatures above 500°C. The glass frit, made of glass particles with a low melting point, softens and adheres to the glass sheet under the influence of the firing heat treatment. A generally opaque, inorganic layer with high chemical resistance and mechanical strength is thus formed, which adheres perfectly to the glass while retaining the pigment particles. The firing process is generally carried out simultaneously with the bending of the glass sheet.

[0006] In the context of laminated glazing production, two glass sheets of the glazing are bent together, and the glass sheet intended for placement inside the vehicle is generally placed on top of the other glass sheet, which has an enamel. To prevent any adhesion between the two glass sheets during the bending process, the enamel must then have anti-stick properties. To achieve this, bismuth-containing enamels, i.e. enamels obtained from glass frits containing bismuth oxide, are usually used.

[0007] Coatings, typically in the form of a stack of thin layers, can also be present on one of the glass sheets of the laminated glazing. These can be, among other things, electrically conductive layers, which can provide two types of functionality. On the one hand, electrically conductive layers can dissipate heat via the Joule effect when an electric current is applied. They are then heating layers, useful for defrosting and defogging, for example. On the other hand, these layers have solar control or low-emissivity properties because they reflect infrared radiation. The layers are then valued for their improved thermal comfort or for the energy savings they bring by reducing consumption for heating and air conditioning purposes. These layer stacks are typically located on face 3 of the laminated glazing and are therefore in contact with the laminate's interlayer.

[0008] However, in certain cases, which will be explained in more detail later, it may be of interest to arrange the enamel layer and the stack of thin layers on the same glass sheet, and thus on the same side of the glass sheet in question, so that these coatings are protected on the inside of the laminated glazing.

[0009] However, when a glass sheet coated with a stack of thin layers must be provided with an enamel layer, it has been observed that unfavorable interactions can occur between the stack and the enamel during bending, leading in particular to a deterioration in the aesthetic appearance of the enamel. In particular, when the stack comprises at least one nitride layer and the enamel contains bismuth, it has been observed that bubbles are produced inside the enamel, near the interface between the enamel and the stack, which induces a significant decrease in the adhesion of the enamel, alters its optical appearance (in particular the color of the glass side, i.e., the side opposite the enamel), and reduces its chemical resistance, in particular its resistance to acids.

[0010] Several solutions have been proposed to this problem.

[0011] Since the enamel is applied in direct contact with the glass sheet and to avoid any adhesion problems between the enamel layer and the stack of thin layers, it is possible to previously remove the stack of thin layers from the areas where the enamel layer must be applied, for example by using an abrasive. Mechanical abrasion, however, causes visible scratches, including at the enamel layer.

[0012] WO 2014 / 133929 and the earlier WO 00 / 29346 proposed the idea of ​​using special glass frits for the enamel, which can fuse a stack of thin layers to be fixed directly to the glass during firing or pre-firing. However, such enamels do not have good anti-stick properties and result in adhesion of two glass sheets to each other during bending.

[0013] WO 2019 / 106264 proposes modifying the thin-layer stack by adding an oxide layer between the stack and the bismuth-containing enamel, but such a modification is not always possible. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] International Publication No. 2014 / 133929 [Patent Document 2] International Publication No. 00 / 29346 [Patent Document 3] International Publication No. 2019 / 106264 Summary of the Invention [Problem to be solved by the invention]

[0015] The present invention aims to overcome these problems. [Means for solving the problem]

[0016] To that end, the present invention is directed to a method for obtaining a curved laminated glazing, in particular for a windshield or roof of a motor vehicle, which method comprises the following steps: a. providing a first glass sheet coated with a stack of thin layers over at least a portion of one of its faces; b. depositing an enamel layer over a portion of the surface of the stack of thin layers; c. depositing at least said enamel layer with refractory particles based on oxides, carbides or metals, having at least one dimension of 30 μm or more; d. bending the first glass sheet simultaneously with an additional glass sheet, the enamel layer facing the additional glass sheet; e. laminating the first glass sheet with an additional glass sheet using a laminate interlayer, the enamel layer facing the interlayer; Including, The method further includes a step of pre-firing the enamel layer, during which the stack of thin layers located below the enamel layer is at least partially dissolved by the enamel layer, the pre-firing step being a step called b1 carried out between steps b and c or a step called c1 carried out between steps c and d, and the stack of thin layers located below the enamel layer is completely dissolved by the enamel layer at least after step d.

[0017] The invention also relates to a curved laminated glazing, in particular for a windshield or roof of a motor vehicle, obtained or obtainable by this method.

[0018] The dissolution of the stack of thin layers by the enamel makes it possible to avoid the above-mentioned interactions: the components of the stack remain dissolved in the enamel layer, which, at least after the bending step (step d), is in direct contact with the glass sheet. As for the use of heat-resistant particles (deposited in step c), this makes it possible to avoid any adhesion between the two glass sheets during bending.

[0019] Within this specification, the stack of thin layers and the enamel layer are collectively defined as the "coating."

[0020] [Step a] The first glass sheet may be flat or curved. It is generally flat during the application of the stack of thin layers and then the application of the enamel layer, and is then curved during step d. The first glass sheet is therefore curved in the curved laminated glazing according to the invention.

[0021] The glass of the first glass sheet is typically soda-lime-silica glass, but other glasses, such as borosilicate and aluminosilicate glasses, can also be used. The first glass sheet is preferably obtained by the float process, i.e., by a process consisting of pouring molten glass onto a bath of molten tin.

[0022] The first glass sheet may be clear or tinted, preferably green, gray, or blue. To this end, the chemical composition of the first glass sheet advantageously includes iron oxide in a weight content of 0.5 to 2%. The chemical composition of the first glass sheet may also contain other colorants, such as cobalt oxide, chromium oxide, nickel oxide, erbium oxide, or selenium.

[0023] The first glass sheet preferably has a thickness comprised in the range of 0.7 to 19 mm, in particular 1 to 10 mm, in particular 2 to 6 mm, even more particularly 2 to 4 mm.

[0024] The lateral dimensions of the first glass sheet (and any additional glass sheets) should be adapted according to the dimensions of the laminated glazing in which they are intended to be incorporated. The first glass sheet (and / or any additional glass sheets) preferably has a width of at least 1 mm. 2 It has an area of

[0025] The first glass sheet is preferably coated with the stack of thin layers over at least 70%, in particular over at least 90%, or even over the entire area of ​​the face of the glass sheet, although certain areas may in fact be left uncoated in order to specifically provide communication windows for the passage of waves.

[0026] The stack is preferably coated with an enamel layer over 2 to 40%, in particular 3 to 30%, and even more preferably 5 to 20% of its area. The enamel layer preferably comprises a peripheral strip, i.e. a self-contained strip extending from each point of the peripheral edge of the first glass sheet towards the inside of the first glass sheet, with a specific width, typically 1 to 20 cm.

[0027] The stack of thin layers is preferably in contact with the glass sheet. The enamel layer is preferably in contact with the stack of thin layers during its application.

[0028] "Contact" herein means physical contact. The expression "based on" preferably means that the layer in question comprises at least 50% by weight, in particular 60% by weight, even 70% by weight, or even 80% or 90% by weight of the material under consideration. The layer can also essentially consist of or consist of this material. By "essentially consist," it should be understood that the layer may contain impurities that do not affect its properties. The terms "oxide" or "nitride" do not necessarily mean that the oxide or nitride is stoichiometric; they may in fact be substoichiometric, superstoichiometric, or stoichiometric.

[0029] The stack preferably includes at least one nitride-based layer. The nitride is, in particular, a nitride of at least one element selected from aluminum, silicon, zirconium, and titanium. The nitride may include nitrides of at least two or three of these elements, such as nitrides of silicon and zirconium, or nitrides of silicon and aluminum. Preferably, the nitride-based layer is a silicon nitride-based layer, more specifically a layer essentially consisting of silicon nitride. When a silicon nitride layer is deposited by cathode sputtering, it generally contains aluminum, since it is customary to dope silicon targets with aluminum to increase the deposition rate.

[0030] The nitride-based layer preferably has a physical thickness comprised within the range of 2 to 100 nm, in particular 5 to 80 nm.

[0031] Nitride-based layers are commonly used in many thin layer stacks because these layers have advantageous blocking properties in the sense that they prevent oxidation of other layers present in the stack, especially the functional layers that will be described below.

[0032] The stack preferably comprises at least one functional layer, in particular an electrically conductive functional layer. The functional layer is preferably comprised between two thin dielectric layers, at least one of which is a nitride-based layer. Other possible dielectric layers are, for example, oxide or oxynitride layers.

[0033] The at least one electrically conductive functional layer is advantageously chosen from: a metal layer, in particular made of silver or niobium or even gold, and a layer of transparent conductive oxide, chosen in particular from among indium tin oxide, tin oxide doped (for example with fluorine or antimony), zinc oxide doped (for example with aluminum or gallium).

[0034] These layers are particularly valued for their low emissivity, which endows the glazing with excellent thermal insulation properties. In glazings installed in land vehicles, especially automobiles, rail vehicles, but also aircraft and ships, low-emissivity glazing allows a portion of the solar radiation to be reflected to the outside in hot weather, thus limiting the temperature rise in the vehicle's interior and, where appropriate, reducing air conditioning costs. Conversely, in cold weather, these glazings allow the heat to be retained inside the interior of the vehicle, thereby reducing the energy required for heating. The same is true for glazings installed in buildings.

[0035] According to a preferred embodiment, the stack of thin layers comprises at least one silver layer, in particular one, two or three, or even four silver layers. The physical thickness of the silver layer or, where appropriate, the total thickness of the silver layers is preferably 2 to 20 nm, in particular 3 to 15 nm.

[0036] According to another preferred embodiment, the stack of thin layers comprises at least one layer of indium tin oxide, the physical thickness of which is preferably between 30 and 200 nm, in particular between 40 and 150 nm.

[0037] In order to protect the or each thin conductive layer (whether metallic or based on transparent conductive oxides) during the bending process, each of these layers is preferably surrounded by at least two dielectric layers, preferably based on oxides, nitrides and / or oxynitrides of at least one element chosen from silicon, aluminum, titanium, zinc, zirconium and tin.

[0038] At least part of the stack of thin layers can be deposited by various known techniques, for example by chemical vapor deposition (CVD) or by cathodic sputtering (magnetron method), especially with magnetic field assistance.

[0039] The stack of thin layers is preferably deposited by cathodic sputtering, particularly with magnetic field assistance. In this method, a plasma is created under high vacuum near a target containing the chemical elements to be deposited. Active species of the plasma bombard the target, detaching the elements, which are then deposited on the glass sheet to form the desired thin layer. This method is called a "reactive" method when the layer consists of a material resulting from a chemical reaction between the elements detached from the target and the gases contained in the plasma. A major advantage of this method is that very complex stacks of layers can be deposited on the same line by passing the glass sheet under various targets one after the other, typically in a single and identical device.

[0040] The stacks described above have conductive and infrared reflective properties that are useful for providing heating (defrosting, de-fogging) and / or thermal insulation functions.

[0041] When the stack of thin layers is intended to provide a heating function, an electric current supply must be provided, which can in particular be strips made of silver paste that are applied by screen printing onto the stack of thin layers at two opposite edges of the glass sheet.

[0042] [Step b] During step b, the enamel layer is preferably applied from a composition containing at least one pigment and at least one glass frit. The enamel layer preferably does not contain lead oxide.

[0043] Enamel compositions generally also contain an organic medium intended to facilitate application of the composition onto a substrate and its temporary adhesion to the substrate, which is removed upon pre-firing or firing of the enamel. The medium typically includes solvents, diluents, oils and / or resins.

[0044] The pigment preferably contains one or more oxides selected from the oxides of chromium, copper, iron, manganese, cobalt, nickel. It may be, by way of example, copper chromate and / or iron chromate.

[0045] Preferably, the glass frit is based on bismuth borosilicate, or even zinc bismuth borosilicate, and the bismuth and / or boron content is preferably higher than that of commonly used glass frits, in order to make the glass frit more "aggressive" towards the layer stack and to promote dissolution of the layer stack.

[0046] The enamel layer is preferably applied by screen printing by placing a screen printing screen containing a partially blocked mesh on the glass sheet, then placing the enamel composition on the screen, and then applying a squeegee to force the enamel composition through the screen in the areas where the mesh is not blocked to form a wet enamel layer.

[0047] The thickness of the wet enamel layer is preferably between 10 μm and 30 μm.

[0048] In this specification, "enamel composition" is defined as the liquid composition used to apply the wet enamel layer during step b. The term "enamel layer" is used to define the layer at each step of the method, whether it is a wet layer (before pre-firing and drying if necessary) or a final layer (after firing).

[0049] Step b is preferably immediately followed by a drying step, the drying step being aimed at removing at least a portion of the solvent contained in the enamel composition. Such drying is typically carried out at a temperature of 120° C. to 180° C. Such drying is carried out before step c (deposition of the heat-resistant particles) and, if necessary, before step b1 (pre-firing, if carried out before deposition of the heat-resistant particles).

[0050] [Process c] By heat-resistant particles is meant particles that are not altered during bending (step d).

[0051] The refractory particles may be based on oxides, carbides or metals.

[0052] The oxides are chosen in particular from among the single metal oxides, such as, for example, the oxide of aluminium, the oxide of titanium or also the oxide of zirconium, and composite oxides.

[0053] The complex oxides are selected in particular from silicates, glass or glass ceramic frits with high melting points (typically above 750°C) or also inorganic pigments. The pigments are, for example, solid solutions of transition metal oxides (such as chromium, iron, etc.). They are especially called "complex oxide pigments" or CICPs.

[0054] The metal is selected from, for example, tungsten, titanium, molybdenum and heat-resistant steel.

[0055] The silicates are especially alkaline earth silicates (such as magnesium silicate) or aluminum silicate.

[0056] The heat-resistant particles have at least one dimension of 30 μm or more, particularly 40 μm or more or 50 μm or more, or even 60 μm or more or 70 μm or more. The heat-resistant particles can even have at least one dimension of 100 μm or more, particularly 200 μm or more. The particles can be approximately spherical, in which case the relevant dimension is the diameter. The particles can also be, for example, fibrous, elongated, and have a length-to-diameter ratio of more than 3, or even more than 10. In this case, the diameter can be less than 100 μm, or even less than 50 μm, but the length is 100 μm or more, or even 200 μm or more, or 500 μm or more.

[0057] It has been found that if the particles are too small, adhesion cannot be avoided during the bending process. The chemical properties of the particles are also important to avoid defects during bending. In conventional bending methods, glass sheets are held apart by interlayer powders placed between them, which provide a gap of several tens of micrometers, typically 20 to 50 μm. The interlayer powders are, for example, based on calcium carbonate and / or magnesium carbonate. Although very fine (approximately 5 μm), they can form agglomerates with a size exceeding 10 μm. However, such carbonate-based powders have proven ineffective in this invention because, in addition to not preventing adhesion, they also react with the enamel during firing, ultimately giving it a gray tint.

[0058] The refractory particles are deposited on at least the enamel layer either after pre-firing of the enamel (step b1) or before pre-firing of the enamel (step c1).

[0059] The heat-resistant particles may be deposited only on the enamel layer, or alternatively, the heat-resistant particles may be deposited on the enamel layer and on regions of the first glass sheet near the enamel layer, or even over the entire surface of the glass sheet.

[0060] The amount of particles having at least one dimension greater than or equal to 30 μm (or greater than or equal to the preferred values ​​above) is preferably at least 0.1 g / m 2 , in particular at least 0.5 g / m 2 The amount is advantageously at most 10 g / m 2 is.

[0061] The heat-resistant particles may be applied alone. Alternatively, they may be applied in a mixture with elements that absorb infrared radiation. These absorbing elements can be organic or inorganic. These elements allow for uniform temperature distribution in various regions of the glass sheet during pre-firing (step c1), thus avoiding defects, such as optical distortion, in the glass regions located near the enamel. This effect is greatest when the absorbing elements are applied over the entire surface of the glass sheet, or at least in the region of the first glass sheet near the enamel layer. Alternatively, the absorbing elements may be applied only on the enamel layer. In this case, it has been observed that the enamel takes on a darker hue. The absorbing elements may be resins, which will burn during the pre-firing step (c1). They may also be absorbing particles, such as pigments or carbon black. Carbon black is particularly preferred due to its ability to be removed by combustion during pre-firing.

[0062] The heat-resistant particles can be applied by any means. According to one embodiment, the particles are applied by spraying or, more particularly, by sprinkling using a mesh. This typical example is particularly suitable when the particles are applied alone. This typical example also allows for the application of large particles. When the heat-resistant particles are applied as a mixture with an absorbent element as described above, the mixture can be applied by screen printing. In this case, the heat-resistant particles preferably have a size of less than 60 μm so as not to block the holes in the screen printing screen. In a preferred embodiment, step c involves the application by screen printing of a mixture comprising an organic medium, heat-resistant particles, and an absorbent element, in particular carbon black. This technique allows, for example, the application of the absorbent element over the entire surface of the glass sheet (when striving to equalize the temperature experienced by various areas of the glass sheet) or only on the enamel layer (which allows for a darker black shade for the enamel layer).

[0063] According to one embodiment, the refractory particles are deposited directly on the enamel layer.

[0064] [Step b2] According to another embodiment, the method includes, between steps b and c, and if necessary between steps b1 and c, step b2 of applying an adhesive layer capable of fixing the heat-resistant particles on the enamel layer only on the enamel layer.

[0065] The adhesive layer makes it possible to temporarily fix the heat-resistant particles to the enamel layer, and only to the enamel layer. The adhesive layer preferably covers the entire enamel layer.

[0066] The thickness of the adhesive layer is preferably 5 μm to 25 μm.

[0067] The adhesive layer may also include an absorbent element as defined above.

[0068] The method preferably comprises a step c2 after step c (particle deposition) and before step d (bending), of removing, especially by blowing air, any heat-resistant particles other than those fixed by the adhesive layer. Particles deposited on the coating or on any non-coated areas of the first glass sheet during step c are then removed before the bending step. In this way, any damage, such as scratches, to the coating or glass by particles is avoided.

[0069] When pre-firing of the enamel layer (step c1) is carried out between steps c and d, step c2 is usually carried out before this step c1.

[0070] The adhesive layer is preferably organic based so that it can be removed either during step d (bending) or during step c1 (pre-baking, if this is carried out after deposition of the particles).

[0071] The adhesive layer is preferably applied by screen printing of a composition comprising an organic medium and / or a resin and / or an organic adhesive.

[0072] The adhesive layer is preferably dried after deposition of the particles (step c) and, if necessary, before step c2.

[0073] The method preferably comprises a step d1 between step d (bending) and step e (lamination) of removing at least part of, or even the entire, the heat-resistant particles, making it possible to prevent them from being present in the laminated glazing. Removal can be carried out, inter alia, by blowing or washing.

[0074] [Pre-baking process (b1 or c1)] The pre-baking step is preferably carried out at a temperature between 150°C and 700°C, in particular between 550°C and 680°C.

[0075] Such a pre-baking makes it possible to remove the organic medium, or in general any organic components possibly present in the enamel layer. If the pre-baking is carried out after the application of the adhesive layer, it also often makes it possible to remove this adhesive layer.

[0076] During pre-firing, the stack of thin layers is at least partially melted by the enamel layer. Depending on the temperature used and the type of enamel or stack, the stack can even be completely melted by the enamel layer during pre-firing. Alternatively, the stack can only be partially melted during pre-firing, in which case the stack is completely melted during bending (step d).

[0077] According to one embodiment, a pre-firing step is carried out between step b (deposition of the enamel layer) and step c (deposition of the refractory particles). The pre-firing step is then called step b1.

[0078] Preferably, the method of the present invention then comprises, in order, step a, then step b (application of an enamel layer, preferably by screen printing), then optionally a step of drying the enamel layer, then step b1 (pre-firing), then optionally step b2 of applying an adhesive layer (preferably by screen printing), then step c of applying heat-resistant particles, then optionally a step of drying the adhesive layer, then optionally step c2 of removing heat-resistant particles other than those fixed by the adhesive layer, then bending step d, then optionally step d1 of removing the heat-resistant particles, and finally laminating step e.

[0079] According to another embodiment, the pre-firing step is carried out between step c (deposition of heat-resistant particles) and step d (bending). The pre-firing step is then called step c1.

[0080] Preferably, the method of the present invention then comprises, in order, step a, then step b (application of an enamel layer, preferably by screen printing), then optionally a step of drying the enamel layer, then optionally step b2 of applying an adhesive layer (preferably by screen printing), then step c of applying heat-resistant particles, then optionally a step of drying the adhesive layer, then optionally step c2 of removing heat-resistant particles other than those fixed by the adhesive layer, then step c1 (pre-firing), then step d of bending, then optionally step d1 of removing the heat-resistant particles, and finally step e of laminating.

[0081] [Step d] Bending can be carried out inter alia by gravity (the glass deforms under its own weight) or by pressing, typically at temperatures between 550 and 650°C.

[0082] The glass sheets can be held apart by placing an interlayer powder between them, which ensures a gap of several tens of micrometers, typically 20-50 μm, and is based on, for example, calcium carbonate and / or magnesium carbonate.

[0083] During bending, the inner glass sheet (intended to be positioned inside the vehicle cabin) is typically placed over the outer glass sheet, and thus, during the bending process, the additional glass sheet is placed over the first glass sheet.

[0084] Preferably, after step d, the enamel layer is opaque and has a black tint. Its lightness L measured in reflection on the glass side * is preferably less than 5. As indicated above, the enamel layer advantageously forms a strip at the periphery of the first glass sheet, which can thus conceal and protect the seals, connecting components and / or sensors from ultraviolet radiation.

[0085] If the enamel layer has not yet completely melted the stack of thin layers after pre-firing, this complete melting is achieved during the bending process, which completes the firing of the enamel.

[0086] The complete dissolution of the layer can be observed by electron microscopy, inter alia, by a colorimetric coordinate a close to 0, in any case less than 5. * and b * This results in a more neutral specular color.

[0087] [Process e] The lamination step can be carried out by autoclaving, for example at a temperature of 110-160°C and a pressure of 10-15 bar. Prior to autoclaving, air trapped between the glass sheets and the laminate interlayer can be removed by calendering or by negative pressure.

[0088] As mentioned above, the additional sheet is preferably the inner sheet of a laminated glazing intended to be positioned inside the passenger compartment of a vehicle, i.e. the sheet located on the concave side of the glazing. The coating is therefore arranged on face 2 of the laminated glazing.

[0089] The additional glass sheet may be made of soda-lime-silica glass, or alternatively borosilicate or aluminosilicate glass. The additional glass sheet may be made of clear glass or tinted glass. Its thickness is preferably 0.5 to 4 mm, in particular 1 to 3 mm.

[0090] According to a preferred embodiment, the additional glass sheet has a thickness of 0.5 to 1.2 mm. The additional glass sheet is made of sodium aluminosilicate glass, preferably chemically strengthened. The additional glass sheet is preferably the inner sheet of the laminated glazing. The present invention is particularly useful for this type of construction, where it is difficult to arrange a stack of thin layers on surface 3. Chemical strengthening (also called "ion exchange") consists in strengthening the surface of the glass by contacting the surface with dissolved potassium salts (e.g., potassium nitrate) and exchanging the glass ions (here, sodium ions) for ions of a larger ionic radius (here, potassium ions). This ion exchange allows compressive stresses to form at the surface and throughout the thickness of the glass. Preferably, the surface stress is at least 300 MPa, in particular 400 MPa or even 500 MPa and up to 700 MPa, and the thickness of the compressed zone is at least 20 μm, typically 20 to 50 μm. The stress profile can be determined in a known manner using a polarizing microscope equipped with a Babinet compensator. The chemical strengthening step is preferably carried out at a temperature of 380-550°C for a duration of 30 minutes to 3 hours. The chemical strengthening preferably takes place after the bending step but before the lamination step. The resulting glazing is preferably an automobile windshield, in particular a heated windshield.

[0091] According to another preferred embodiment, the additional glass sheet has, on its side of the laminate opposite to the side facing the interlayer (preferably side 4, the additional sheet being the inner sheet), a stack of additional thin layers, in particular a low-emissivity stack containing a transparent conductive oxide, in particular indium tin oxide (ITO). The invention is also particularly useful for this type of configuration, where it is difficult to arrange stacks of thin layers on both sides (sides 3 and 4) of the same glass sheet. In this embodiment, the interlayer and / or the additional glass sheet of the laminate are preferably tinted, and the glass sheet with the coating may be made of clear glass. The resulting glazing is preferably a car roof.

[0092] As an example of the immediately preceding preferred embodiment, one may cite a curved laminated roof comprising, from the outside of the vehicle, a clear glass sheet coated on face 2 with a stack of thin layers including at least one silver layer, followed by an enamel layer, an intermediate layer of a laminate made of tinted PVB, and an additional glass sheet made of tinted glass on face 4 with a stack of thin layers of low emissivity, in particular based on ITO.

[0093] The intermediate layer of the laminate preferably comprises at least one sheet of polyvinyl acetal, especially a sheet of polyvinyl butyral (PVB).

[0094] The interlayers of the laminate may or may not be tinted to adjust the optical or thermal properties of the glazing if required.

[0095] The intermediate layer of the laminate can advantageously have sound-absorbing properties for absorbing airborne or solid-borne sound, and for that purpose can consist in particular of three polymeric sheets, of which two PVB sheets, called outer sheets, surround an inner polymeric sheet, possibly made of PVB, of lower hardness than the outer sheets.

[0096] The interlayer of the laminate can also have thermal insulating properties, particularly infrared radiation reflecting properties, and for that purpose can comprise a low emissivity thin coating, for example a coating comprising a thin layer of silver or a coating comprising alternating dielectric layers of different refractive index, applied to an inner PET sheet surrounded by two outer PVB sheets.

[0097] The thickness of the laminate interlayer is generally within a range of 0.3 to 1.5 mm, in particular 0.5 to 1 mm. The laminate interlayer may have a smaller thickness at the edge of the glazing than at the center of the glazing, in order to avoid the formation of double images when using a head-up display system (HUD).

[0098] [Example] The following examples illustrate the invention in a non-limiting manner in conjunction with the following Figures 1 to 4. [Brief explanation of the drawings]

[0099] [Figure 1] 1 shows a schematic representation of an embodiment of the method according to the invention; [Figure 2] 2 shows a schematic representation of another embodiment of the method according to the invention; [Figure 3] 2 shows a schematic representation of another embodiment of the method according to the invention; [Figure 4] 2 shows a schematic representation of another embodiment of the method according to the invention; DETAILED DESCRIPTION OF THE INVENTION

[0100] These figures are cross-sectional views of a glass sheet and some of the components deposited on the glass sheet near its periphery, the various components obviously not being drawn to scale so that they can be visually identified.

[0101] A first glass sheet 10 coated with a stack 12 of thin layers is provided in step a, then part of the stack 12 is coated with an enamel layer 14 (step b), notably by screen printing.

[0102] In the embodiment of FIGS. 1 and 3, the whole is then subjected to a pre-firing (step b1), which in the case shown leads to a partial dissolution of the stack 12 by the enamel 14.

[0103] In the embodiment of FIG. 1, refractory particles 16 are then deposited onto the enamel layer 14 and stack 12 (step c).

[0104] An additional glass sheet 20, now provided with an additional stack of laminae 22, is then placed on top of the first glass sheet 10 and the whole is then bent (step d). The illustration shown shows only the edges of the glass sheets, the curvature is not shown here. The illustration shows that after bending, the enamel 14 has completely dissolved the underlying stack of laminae 12.

[0105] In step e, the first glass sheet 10 coated with the stack of thin layers 12 and the enamel layer 14 and the additional glass sheet 20 coated with the additional stack 22 are combined using the laminate interlayer 30. The figure now shows each of the separate components in an exploded view. The particles 16 were previously removed during step d1, not shown.

[0106] The embodiment of FIG. 2 differs from the embodiment of FIG. 1 in that a pre-firing step (step c1) is performed after the step c of attaching the heat-resistant particles 16 and before the bending step d.

[0107] 3 and 4 add step b2 of applying the adhesive layer 18 and step c2 of removing the heat-resistant particles 16 other than the heat-resistant particles fixed to the enamel layer 14. Thus, during step c, the particles 16 applied on the enamel layer 14 are fixed to the enamel layer 14, and during the bending step d, only the particles 16 fixed to the enamel layer 14 remain.

[0108] The embodiment of FIG. 4 differs from the embodiment of FIG. 3 in that a pre-firing step (step c1) is performed after the step c of attaching the heat-resistant particles 16 and before the bending step d.

[0109] Example 1 The method carried out according to Example 1 corresponds to the embodiment of FIG.

[0110] A 2.1 mm thick glass sheet, pre-coated by cathodic sputtering with a stack of thin layers including two silver layers protected by a zinc oxide layer, a silicon nitride layer and the blocking agent NiCr, was then coated by screen printing with a 25 μm wet thickness enamel layer.

[0111] After drying (150°C, 1-2 minutes) and then pre-firing at 630°C, the particles were dispersed over the entire surface of the first glass sheet and especially on the pre-fired enamel layer.

[0112] These particles were based on magnesium silicate and were obtained by milling fibers marketed under the reference Isofrax® 1260 C. The particles obtained had a diameter of less than 50 μm and a length of at least 1 mm.

[0113] After pairing with an additional glass sheet made of soda-lime-silica with a stack including an ITO layer on side 4, the whole was bent for 350 to 500 seconds at over 600°C. After cleaning to remove any heat-resistant particles, the two glass sheets were laminated together using an interlayer made of PVB.

[0114] After firing, the aesthetics, more specifically the black color visible from face 1, is the brightness L * (D65 illuminant, 10° standard observer). A value of less than 5 is considered acceptable. Adhesion was assessed qualitatively by visual observation.

[0115] L * The value of was less than 4.8 for bending temperatures above 628° C. and 3.6 for bending temperatures above 651° C. No adhesion was observed up to a bending temperature of 651° C.

[0116] Example 2 The method carried out according to Example 2 corresponds to the embodiment of FIG.

[0117] In step b2, a resin (medium Ferro 80-007) was applied by screen printing onto the enamel layer with a wet thickness of 10 to 15 μm. The adhesive layer thus obtained was then dried at 150° C. for 1 to 2 minutes to remove the solvent. The heat-resistant particles not fixed to the enamel by the adhesive layer were then removed by blowing air. The other steps were carried out in the same way as in Example 1.

[0118] In terms of aesthetics and absence of adhesion, the same results were obtained as for Example 1. However, unlike Example 1, no scratches were observed on the stack of thin layers.

[0119] Example 3 The method carried out according to Example 3 corresponds to the embodiment of Figure 4. The only difference compared to Example 2 is the order of steps: the particles are deposited on a layer of enamel that has only been dried, and the pre-firing is carried out immediately before bending.

[0120] In terms of aesthetics and lack of adhesion, the same results were obtained as for Example 2. Also, unlike Example 1, no scratches were observed on the stack of thin layers.

[0121] Comparative Example C1 In this comparative example, in comparison with Example 1, the deposition of refractory particles was replaced by the deposition by screen printing of 25 μm of bismuth-containing enamel with non-stick properties.

[0122] However, adhesion was observed, and furthermore, L * The value of was greater than 5 for all bending temperatures considered.

[0123] Comparative Example C2 In this comparative example, in comparison with Example 1, the deposition of refractory particles has been replaced by the deposition of black pigment having a size of less than 20 μm.

[0124] Although no adhesion was observed, L * The value of was at least 12.4 (observed for a bending temperature of 650°C).

[0125] Comparative Example C3 In this comparative example, in comparison with Example 1, the deposition of heat-resistant particles has been replaced by a deposition of white pigment having a size of less than 20 μm.

[0126] Although no adhesion was observed, L * The value of was at least 20.

[0127] Comparative example C4 In this comparative example, in comparison with Example 1, the deposition of refractory particles was replaced by the deposition by screen printing of a silica sol-gel layer (Ferro product TLU0059).

[0128] The aesthetics were satisfactory (L * <5, especially for the bending temperature of 654°C 3.3), adhesion was observed.

[0129] Comparative example C5 In this comparative example, in comparison with Example 1, the deposition of refractory particles was replaced by the deposition by screen printing of an alkali silicate-based solution which additionally contained a black pigment.

[0130] L * The value of was 16 for a bending temperature of 650° C., and transfer of the silicate layer onto the additional glass sheet was observed.

[0131] Comparative example C6 In this comparative example, in comparison with Example 1, the deposition of the refractory particles was replaced by the deposition by screen printing of 25 μm of a bismuth-containing enamel known for its non-stick properties and commercialized by the company Ferro under the reference 14316. Unlike Example 1, a second pre-firing treatment was carried out after the deposition of this enamel.

[0132] However, adhesion was observed, and furthermore, L * The value of was 8.9 for a bending temperature of 650°C. [Explanation of symbols]

[0133] 10 First Glass Sheet 12 Thin Layer Stack 14 Enamel layer 16 Heat-resistant particles 18 Adhesive layer 20 additional glass sheets 22 additional thin layer stacks 30 Intermediate layer of laminate

Claims

1. A method for obtaining curved laminated glazing, comprising the following steps: a. providing a first glass sheet (10) coated over at least a portion of one of its faces with a stack of thin layers (12); b. depositing an enamel layer (14) over a portion of the surface of the stack of thin layers (12); c) depositing at least said enamel layer (14) with refractory particles (16) based on oxides, carbides or metals, having at least one dimension of 30 μm or greater; d. bending the first glass sheet (10) simultaneously with an additional glass sheet (20), with the enamel layer (14) facing said additional glass sheet (20); e. laminating the first glass sheet (10) with an additional glass sheet (20) using a laminate interlayer (30), with the enamel layer (14) facing the interlayer (30); Including, The method further comprises a step of pre-firing the enamel layer (14), during which the stack of thin layers (12) located below the enamel layer (14) is at least partially dissolved by the enamel layer (14), the pre-firing step being a step called b1 carried out between steps b and c or a step called c1 carried out between steps c and d, and the stack of thin layers (12) located below the enamel layer (14) is completely dissolved by the enamel layer (14) at least after step d.

2. 2. The method of claim 1, wherein the stack of thin layers (12) comprises at least one functional layer selected from among a metal layer and a layer of a transparent conductive oxide.

3. 3. The method according to claim 1 or 2, wherein after step d, the enamel layer (14) is opaque, has a black tint and forms a strip at the periphery of the first glass sheet (10).

4. 4. The method according to claim 1, wherein the refractory particles (16) are based on an oxide selected from the group consisting of single metal oxides and composite oxides.

5. The method of claim 4, wherein the single metal oxide is an oxide of aluminum, an oxide of titanium or an oxide of zirconium.

6. A method according to claim 4 or 5, wherein the complex oxide is a silicate, a glass frit or glass ceramic frit having a high melting point, or an inorganic pigment.

7. 7. The method of any one of claims 1 to 6, wherein the refractory particles (16) have at least one dimension greater than or equal to 40 μm.

8. 8. The method of any one of claims 1 to 7, wherein the refractory particles (16) are elongated in shape and have a length / diameter ratio greater than 3.

9. 9. The method of any one of claims 1 to 8, wherein the amount of particles having at least one dimension greater than or equal to 30 [mu]m is at least 0.1 g / m<2>.

10. 10. The method according to any one of claims 1 to 9, wherein the heat-resistant particles (16) are applied in a mixture with an element that absorbs infrared radiation.

11. The method of claim 10, wherein the element that absorbs infrared radiation is selected from the group consisting of a resin, a pigment, and carbon black.

12. 12. The method of any one of claims 1 to 11, wherein heat-resistant particles (16) are deposited on the enamel layer (14) and on a region of the first glass sheet (10) near the enamel layer (14).

13. 13. The method according to claim 1, further comprising, between steps b and c, and if necessary between steps b1 and c, a step b2 of applying an adhesive layer (18) capable of fixing the heat-resistant particles (16) on the enamel layer (14) only on the enamel layer (14).

14. The method according to claim 13, further comprising the step c2 of removing the heat-resistant particles (16) other than those fixed by the adhesive layer (18) after step c and before step d.

15. 15. The method according to any one of claims 1 to 14, further comprising a step d1 between steps d and e of removing refractory particles (16).

16. The method according to any one of the preceding claims, wherein the additional glass sheet (20) has a thickness of 0.5 to 1.2 mm.

17. 16. The method according to any one of claims 1 to 15, wherein the additional glass sheet (20) has a stack of additional thin layers (22) on the side opposite to the side facing the interlayer (30) of the laminate.

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