METHOD FOR PRODUCING A CURVED LAMINATED GLAZING

Abstract

The invention relates to a method for obtaining curved laminated glazing, comprising: (a) supplying a first glass sheet (10), at least part of one of the faces of said sheet being covered with a thin-film stack (12); and, subsequently, (b) depositing an enamel layer (14) on part of the surface of the thin-film stack (12), by screen printing an enamel composition comprising 1 to 15 wt.-% zinc oxide particles having a volumetric particle size distribution such that the d90 value is at most 5 μm. After lamination (d) with an additional glass sheet (20), the enamel layer (14) faces a lamination interlayer (30).

Description

Process for obtaining laminated curved glazing

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

[0002] Laminated glass is a type of glass in which two sheets of glass are adhesively bonded together using a lamination interlayer. This interlayer not only helps retain shards of glass in the event of breakage, but also provides other features, particularly in terms of burglary resistance and improved acoustic properties.

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

[0004] Layers of enamel, usually black and opaque, are often applied to part of the glazing, usually in the form of a peripheral strip intended to conceal and protect from ultraviolet radiation the polymer seals used to fix and position the glazing on the bodywork opening. Enamelled areas also conceal the fixing areas of the interior rearview mirror and various connectors and sensors.

[0005] In laminated glazing, these enamel layers are generally arranged on side 2, the sides being traditionally numbered starting from the side intended to be positioned on the outside of the vehicle. Side 2 is therefore a side in contact with the lamination interlayer. The aesthetic appearance of the enamel layer seen from the outside of the vehicle is of particular importance for car manufacturers. The enamel is generally obtained by firing above 500°C a composition comprising a glass frit and pigments. A glass frit consists of fine particles of a low-melting glass, which under the effect of a firing heat treatment softens and adheres to the glass sheet. This forms a mineral layer, generally opaque, with high chemical and mechanical resistance, adhering perfectly to the glass while retaining the pigment particles.The firing step is generally carried out simultaneously with the bending of the glass sheet.

[0006] In the context of laminated glazing manufacturing, the two sheets of glass in the glazing are often bent together, with the sheet of glass intended to be positioned inside the vehicle generally being placed on top of the other sheet of glass, which carries the enamel. In other processes, each sheet of glass is bent separately. In all cases, it is necessary for the enamel to have non-stick properties in order to prevent, during bending, any sticking between the two sheets of glass or between the glass sheet and the bending tools. To achieve this, enamels containing bismuth are usually used, i.e. obtained from glass frits containing bismuth oxide.

[0007] Coatings, generally in the form of stacks of thin layers, may also be present on one of the glass sheets of the laminated glazing. These may in particular be electrically conductive layers, which can provide two types of functionality. On the one hand, when current leads are provided, the electrically conductive layers can dissipate heat by the Joule effect. These are then heating layers, useful for example for defrosting or demisting. On the other hand, these layers have solar control or low emissivity properties due to their reflection of infrared radiation. The layers are then appreciated for improving thermal comfort or for the energy savings they provide, by reducing consumption for heating or air conditioning. These stacks of layers are generally placed on face 3 of the laminated glazing, therefore also in contact with the lamination interlayer.

[0008] However, it may be interesting, in certain cases which will be detailed later, to place the enamel layer and the stack of thin layers on the same sheet of glass, and therefore on the same face of the sheet of glass in question so that these coatings are protected inside the laminated glazing.

[0009] However, it has been observed that when a glass sheet coated with a stack of thin layers had to be provided with a layer of enamel, undesirable interactions could occur during bending between the stack and the enamel, leading in particular to a degradation of the aesthetic appearance of the enamel. In particular, it has been observed, in particular when the stack contained at least one nitride layer and the enamel contained bismuth, that bubbles were created within the enamel, near the interface between the latter and the stack, causing a significant drop in adhesion of the enamel, modifying its optical appearance (in particular the color on the glass side, i.e. on the side opposite the enamel) and reducing its chemical resistance, in particular to acids.

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

[0011] It is possible to remove the thin-film stack in advance at the points where the enamel layer is to be deposited, for example by means of abrasives, so that the enamel is deposited in direct contact with the glass sheet and to avoid any adhesion problems between the enamel layer and the thin-film stack. However, mechanical abrasion generates visible scratches, including at the level of the enamel layer.

[0012] Application WO2014 / 133929 and before it application WO0029346 proposed the idea of ​​using special glass frits for enameling, which during firing or pre-firing can dissolve the stack of thin layers and attach directly to the glass. However, such enamels do not have good non-stick properties, causing the two sheets of glass to stick together during bending.

[0013] Application WO 2019 / 106264 proposes modifying the stack of thin layers by adding an oxide layer between the stack and the enamel comprising bismuth. However, it is not always possible to make such a modification.

[0014] The invention aims to overcome these drawbacks.

[0015] For this purpose, the invention relates to a method for obtaining laminated curved glazing, in particular for a motor vehicle windshield or roof, comprising the following successive steps: a. providing a first sheet of glass, coated on at least part of one of its faces with a stack of thin layers, b. a step of depositing, on part of the surface of the stack of thin layers, a layer of enamel, the deposition being carried out by screen printing an enamel composition comprising from 1 to 15% by weight of zinc oxide particles having a volume particle size distribution such that the d90 is at most 5 µm, c. a step of bending the first sheet of glass, the stack of thin layers located under the enamel layer being completely dissolved by said enamel layer at least at the end of this step, then d.a step of laminating said first glass sheet with an additional glass sheet by means of a laminating interlayer, so that the enamel layer faces said interlayer.

[0016] The invention also relates to a laminated curved glazing, in particular for a windshield or roof of a motor vehicle, obtained or capable of being obtained by this method. This glazing comprises a first glass sheet coated on at least part of one of its faces with a stack of thin layers coated on part of its surface with a layer of enamel comprising zinc oxide particles having a volume particle size distribution such that the d90 is at most 5 µm, said first glass sheet being laminated with an additional glass sheet by means of a lamination interlayer, said enamel layer facing said lamination interlayer.

[0017] The use of zinc oxide particles reduces the mechanical embrittlement of the glass by the enamel and improves the optical properties of the enamel, while reducing the risk of sticking during bending, either between the two sheets of glass or between the glass sheet and the bending tools, depending on the bending process used.

[0018] In this text, the thin-film stack and the enamel layer are collectively referred to as "the coatings". Step a

[0019] The first glass sheet may be flat or curved. The first glass sheet is generally flat at the time of deposition of the stack of thin layers and then of the enamel layer, and is then curved during step c. The first glass sheet is therefore curved in the curved laminated glazing according to the invention.

[0020] The glass of the first glass sheet is typically a soda-lime-silica glass, but other glasses, for example borosilicates or aluminosilicates, may also be used. The first glass sheet is preferably obtained by floatation, that is, by a process consisting of pouring molten glass onto a bath of molten tin.

[0021] The first glass sheet may be made of clear glass or tinted glass, preferably tinted glass, for example green, gray or blue. To achieve this, the chemical composition of the first glass sheet advantageously comprises iron oxide, in a weight content ranging from 0.5 to 2%. It may also comprise other coloring agents, such as for example cobalt oxide, chromium oxide, nickel oxide, erbium oxide, or selenium.

[0022] The first glass sheet preferably has a thickness in a range from 0.7 to 19 mm, in particular from 1 to 10 mm, particularly from 2 to 6 mm, or even from 2 to 4 mm.

[0023] The lateral dimensions of the first sheet of glass (and the additional sheet of glass) must be adapted according to those of the laminated glazing into which it is intended to be integrated. The first sheet of glass (and / or the additional sheet of glass) preferably has a surface area of ​​at least 1 m².

[0024] 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 surface of the face of the glass sheet. Certain areas may not be coated in order in particular to provide communication windows allowing waves to pass through.

[0025] The stack is preferably coated with the enamel layer over 2 to 25%, in particular 3 to 20%, or even 5 to 15% of its surface. The enamel layer preferably comprises a peripheral band, that is to say a band closed on itself which, from each point of the periphery of the first sheet of glass, extends towards the inside of the first sheet of glass over a certain width, generally variable, typically between 1 and 20 cm depending on the zones of the final glazing.

[0026] The stack of thin layers is preferably in contact with the glass sheet. During its deposition, the enamel layer is preferably in contact with the stack of thin layers.

[0027] In this text, the term "contact" means physical contact. The term "based on" preferably means that the layer in question comprises at least 50% by weight of the material in question, in particular 60%, or even 70%, and even 80% or 90%. The layer may even essentially consist of or consist of this material. By "essentially consist" it is meant that the layer may include impurities without influencing its properties. The terms "oxide" or "nitride" do not necessarily mean that the oxides or nitrides are stoichiometric. They may in fact be substoichiometric, superstoichiometric or stoichiometric.

[0028] The stack preferably comprises at least one nitride-based layer. The nitride is in particular a nitride of at least one element chosen from aluminum, silicon, zirconium, titanium. It may comprise a nitride of at least two or three of these elements, for example a silicon and zirconium nitride, or a silicon and aluminum nitride. Preferably, the nitride-based layer is a silicon nitride-based layer, more particularly a layer consisting essentially of a silicon nitride. When the silicon nitride layer is deposited by sputtering, it generally contains aluminum, since it is common practice to dope silicon targets with aluminum in order to accelerate deposition rates.

[0029] The nitride-based layer preferably has a physical thickness in a range from 2 to 100 nm, in particular from 5 to 80 nm.

[0030] Nitride-based layers are commonly used in many thin-film stacks because they have advantageous blocking properties, in that they prevent oxidation of other layers present in the stack, in particular functional layers which will be described below.

[0031] 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.

[0032] At least one electroconductive functional layer is advantageously chosen from:- metallic layers, in particular silver or niobium, or even gold, and- layers of a transparent conductive oxide, in particular chosen from indium and tin oxide, doped tin oxides (for example with fluorine or antimony) and doped zinc oxides (for example with aluminum or gallium).

[0033] These layers are particularly appreciated for their low emissivity, which gives the glazing excellent thermal insulation properties. In glazing used in land vehicles, particularly cars, railways, or even aircraft or maritime vehicles, low-emissivity glazing allows part of the solar radiation to be reflected outwards in hot weather, and therefore limits the heating of the passenger compartment of said vehicles, and where appropriate reduces air conditioning costs. Conversely, in cold weather, these glazings help to retain heat within the passenger compartment, and therefore reduce the energy effort required for heating. The same is true for glazing used in buildings.

[0034] 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 sum of the thicknesses of the silver layers is preferably between 2 and 50 nm, in particular between 3 and 40 nm.

[0035] According to another preferred embodiment, the stack of thin layers comprises at least one layer of indium and tin oxide. Its physical thickness is preferably between 30 and 200 nm, in particular between 40 and 150 nm.

[0036] In order to protect the or each electrically conductive thin layer (whether metallic or based on transparent conductive oxide) during the bending step, each of these layers is preferably framed by at least two dielectric layers. The dielectric layers are preferably based on oxide, nitride and / or oxynitride of at least one element chosen from silicon, aluminum, titanium, zinc, zirconium and tin.

[0037] At least part of the thin-film stack can be deposited by various known techniques, for example by chemical vapor deposition (CVD), or by cathode sputtering, in particular assisted by a magnetic field (magnetron process).

[0038] The stack of thin layers is preferably deposited by cathode sputtering, in particular assisted by a magnetic field. In this process, a plasma is created under a high vacuum in the vicinity of a target comprising the chemical elements to be deposited. The active species of the plasma, by bombarding the target, tear off said elements, which are deposited on the glass sheet, forming the desired thin layer. This process is called "reactive" when the layer is made of a material resulting from a chemical reaction between the elements torn off the target and the gas contained in the plasma. The major advantage of this process lies in the possibility of depositing a very complex stack of layers on the same line by successively moving the glass sheet under different targets, generally in a single device.

[0039] The aforementioned stacks have electricity conduction and infrared reflection properties useful for providing a heating function (defrosting, demisting) and / or a thermal insulation function.

[0040] When the stack of thin layers is intended to provide a heating function, current leads must be provided. These may include strips of silver paste deposited by screen printing on the stack of thin layers, at two opposite edges of the glass sheet. Step b

[0041] In this text, the term "enamel composition" refers to the liquid composition used to deposit a wet enamel layer during step b. The term "enamel layer" is used to describe the layer at each stage of the process, both the wet layer (before any pre-firing, and where appropriate before drying) and the final layer (after firing).

[0042] In step b, the enamel layer is preferably deposited from an enamel composition comprising at least one pigment, at least one glass frit and the zinc oxide particles. The enamel composition, like the enamel layer, preferably does not comprise lead oxide.

[0043] The enamel composition generally further comprises an organic medium, intended to facilitate the application of the composition to the substrate as well as its temporary adhesion to the latter, and which is removed during the pre-firing or firing of the enamel, if necessary. The medium typically comprises solvents, diluents, oils and / or resins.

[0044] The glass frit is capable of dissolving the underlying layer stack. Preferably, the glass frit is based on bismuth and zinc borosilicate (or borate). When it is desired that the glaze be capable of dissolving the thin layer stack during pre-firing or firing, as described in more detail later in the text, the bismuth and / or boron contents are preferably higher than those of the glass frits usually used in order to make it more "aggressive" towards the layer stack.

[0045] The pigments preferably comprise one or more oxides selected from chromium, copper, iron, manganese, cobalt and nickel oxides. These may be, for example, copper and / or iron chromates.

[0046] "Zinc oxide particles" means particles consisting or consisting essentially of zinc oxide (impurities may be present). This term therefore does not cover glass frit particles, which may contain zinc oxide in its composition.

[0047] By "d90" we conventionally mean the value such that 90% of the particles (by volume) have a size smaller than this value. The volume size distribution of the particles is preferably determined by laser granulometry.

[0048] Preferably, the zinc oxide particles have a volume particle size distribution such that the d90 is at most 3 µm, in particular at most 1 µm.

[0049] Preferably, the zinc oxide particles have a volume particle size distribution such that the d50 is between 200 and 900 nm, in particular between 300 and 800 nm.

[0050] The content of zinc oxide particles in the enamel composition is preferably between 2 and 10% by weight, in particular between 3 and 8% by weight.

[0051] Advantageously, the enamel composition further comprises refractory particles having a diameter of at least 20 µm in a volume proportion of at least 0.5%, but no particles having a diameter greater than 80 µm.

[0052] Refractory particles are particles whose morphology is not significantly affected during bending. These particles must have a melting or softening temperature well above the temperatures experienced during bending, and must also not be dissolved by the frit. Refractory particles are notably based on metal oxides or metals. Metal oxides are notably simple oxides, such as for example aluminum, zirconium or titanium oxide, or complex oxides such as high-melting glass frits or inorganic pigments (the latter being notably called "complex inorganic colored pigments" or CICP).

[0053] The presence of a sufficient proportion of "large" refractory particles (so the size, also called diameter, is at least 20 µm) also helps prevent the glass sheets from sticking together during bending, or the glass sheet from sticking with the bending tools. Due to their size, large refractory particles create a morphology during bending in which the particles form peaks, with the molten or softened glass frit gathering in the valleys. This size of 20 µm and above is much larger than that of the glass frit and pigments conventionally used.

[0054] The volume proportion of refractory particles having a size (or diameter) of 20 µm and more is preferably determined by laser granulometry. This proportion is at least 0.5% and preferably at least 1%, in particular at least 2% and even at least 3%.

[0055] Preferably, the enamel composition contains refractory particles with a diameter of at least 30 µm, in particular at least 40 µm, and even at least 50 µm, in the above-mentioned volume proportions.

[0056] Another way to easily detect the presence of large particles is to measure the fineness of the particles using a Hegman gauge (or fineness of grinding gauge). According to this method, the fineness of the enamel composition, measured using a Hegman gauge, is between 20 and 80 µm, particularly between 40 and 60 µm.

[0057] Preferably, the enamel composition does not contain particles (refractory or not) with a diameter greater than 80 µm in order to allow good deposition by screen printing. The presence of such particles can be determined by laser granulometry or using a Hegman gauge.

[0058] The enamel layer is deposited by screen printing. To do this, a screen printing screen is placed on the glass sheet, which includes meshes, some of which are sealed. The enamel composition is then deposited on the screen, and a doctor blade is then applied to force the enamel composition through the screen in the areas where the meshes of the screen are not sealed, so as to form a wet enamel layer. In order to ensure homogeneous deposition of large refractory particles, when the enamel composition contains them, the mesh opening of the screen is preferably at least 40 µm, in particular at least 60 µm, or even at least 70 µm. Too small a mesh opening will trap the particles and prevent their homogeneous deposition, while too large an opening leads to an excessively high enamel thickness which risks mechanically weakening the glass. The mesh opening is preferably at most 100 µm, in particular at most 80 µm.

[0059] The thickness of the wet enamel layer is preferably between 15 and 40 µm, in particular between 20 and 30 µm.

[0060] Step b is preferably immediately followed by a drying step, intended to remove at least part of the solvent contained in the enamel composition. Such drying is typically carried out at a temperature between 120 and 180°C. Step c

[0061] Bending can be carried out by gravity (the glass deforms under its own weight) or by pressing, at temperatures typically ranging from 550 to 650°C.

[0062] According to a first embodiment, the two sheets of glass (first sheet of glass and additional sheet of glass) are bent separately. In this case, it is important to avoid any sticking between the first sheet of glass and the bending tools.

[0063] According to a second embodiment, the first glass sheet and the additional glass sheet are curved together, the enamel layer facing said additional glass sheet. In this case, it is important to avoid any sticking between the two glass sheets. The glass sheets can be kept apart by placing an interlayer powder between them ensuring a space of a few tens of micrometers, typically 20 to 50 µm. The interlayer powder is, for example, based on calcium and / or magnesium carbonate. During the bending process, the inner glass sheet (intended to be positioned inside the passenger compartment) is normally placed above the outer glass sheet. Thus, during the bending step, the additional glass sheet is placed above the first glass sheet.

[0064] Preferably, after step c, the enamel layer is opaque, black in color. Its clarity L* measured in reflection on the glass side is preferably less than 5. It has been observed that the addition of zinc oxide particles makes it possible to reduce the value of the clarity L*, and therefore to obtain a deeper black enamel.

[0065] As previously indicated, the enamel layer advantageously forms a band on the periphery of the first sheet of glass. In this way, the enamel layer is able to conceal and protect against ultraviolet radiation joints, connection elements, or even sensors. Optional pre-cooking step (b1)

[0066] The method preferably comprises, between step b) and step c), a step b1) of pre-firing the enamel layer during which the stack of thin layers located under the enamel layer is at least partially dissolved by said enamel layer.

[0067] This step is particularly useful in the second embodiment previously described, in which the first glass sheet and the additional glass sheet are curved together, with the enamel layer facing the additional glass sheet.

[0068] The dissolution of the thin-film stack by the enamel makes it possible to avoid the aforementioned interactions. The constituent elements of the stack are dissolved in the enamel layer, which is, at least after the bending step (step c), in direct contact with the glass sheet.

[0069] If the enamel layer has not already completely dissolved the stack of thin layers at the end of pre-firing, this total dissolution is obtained during bending, which completes the firing of the enamel.

[0070] The complete dissolution of the thin-film stack can be observed by electron microscopy. Electrical measurements, particularly of square resistance, also make it possible to observe the dissolution of the stack.

[0071] The pre-baking step is preferably carried out at a temperature between 150 and 800°C, in particular between 500 and 700°C.

[0072] Such pre-firing makes it possible to eliminate the organic medium, or in general any organic component possibly present in the enamel layer.

[0073] During pre-firing, the thin-film stack is preferably at least partially dissolved by the glaze layer. Depending on the temperature used and the type of glaze or stack, the stack may even be completely dissolved by the glaze layer during pre-firing. Alternatively, it may only be partially dissolved during pre-firing, and is then completely dissolved during bending (step c). Step d

[0074] The lamination step can be carried out by autoclave treatment, for example at temperatures of 110 to 160°C and under a pressure of 10 to 15 bars. Prior to autoclave treatment, the air trapped between the glass sheets and the lamination interlayer can be removed by calendering or by vacuum.

[0075] As previously stated, the additional sheet is preferably the inner sheet of the laminated glazing, i.e. the sheet located on the concave side of the glazing, intended to be positioned inside the passenger compartment of the vehicle. In this way, the coatings are arranged on face 2 of the laminated glazing.

[0076] The additional glass sheet can be made of soda-lime-silica glass, or borosilicate or aluminosilicate glass. It can be clear or tinted glass. Its thickness is preferably between 0.5 and 4 mm, especially between 1 and 3 mm.

[0077] According to a preferred embodiment, the additional glass sheet has a thickness of between 0.5 and 1.2 mm. The additional glass sheet is in particular made of sodium aluminosilicate glass, preferably chemically reinforced. The additional glass sheet is preferably the inner sheet of the laminated glazing. The invention is particularly useful for this type of configuration, for which it is difficult to arrange the stack of thin layers on face 3. Chemical strengthening (also called “ion exchange”) consists of bringing the surface of the glass into contact with a molten potassium salt (for example potassium nitrate), so as to strengthen the surface of the glass by exchanging ions of the glass (here sodium ions) with ions of larger ionic radius (here potassium ions). This ion exchange makes it possible to form compressive stresses on the surface of the glass and over a certain thickness.Preferably, the surface stress is at least 300 MPa, in particular 400 and even 500 MPa, and at most 700 MPa, and the thickness of the compression zone is at least 20 µm, typically between 20 and 50 µm. The stress profile can be determined in a known manner using a polarizing microscope equipped with a Babinet compensator. The chemical toughening step is preferably carried out at a temperature ranging from 380 to 550°C, and for a duration ranging from 30 minutes to 3 hours. The chemical strengthening is preferably carried out after the bending step but before the lamination step. The glazing obtained is preferably a motor vehicle windshield, in particular a heated windshield.

[0078] According to another preferred embodiment, the additional glass sheet carries on the face opposite the face facing the lamination interlayer (preferably face 4, the additional sheet being the inner sheet) an additional stack of thin layers, in particular a low-emissivity stack, comprising a transparent conductive oxide, in particular indium tin oxide (ITO). The invention is also particularly useful for this type of configuration, for which it is difficult to arrange stacks of thin layers on both faces of the same glass sheet (faces 3 and 4). In this embodiment, the lamination interlayer and / or the additional glass sheet is preferably tinted, the glass sheet carrying the coatings possibly being made of clear glass. The glazing obtained is preferably a motor vehicle roof.

[0079] As an example of this latter preferred embodiment, mention may be made of a laminated curved roof comprising, from the outside of the vehicle, a sheet of clear glass coated on face 2 with a stack of thin layers comprising at least one layer of silver then a layer of enamel, a PVB lamination interlayer (preferably tinted), and an additional glass sheet of tinted glass, carrying on face 4 a stack of low-emissivity thin layers, in particular based on ITO.

[0080] The lamination interlayer preferably comprises at least one sheet of polyvinyl acetal, in particular polyvinyl butyral (PVB).

[0081] The lamination interlayer can be tinted or untinted in order to regulate the optical or thermal properties of the glazing if necessary.

[0082] The lamination interlayer can advantageously have sound absorption properties in order to absorb sounds of airborne or solid-borne origin. It can in particular be made for this purpose of three polymeric sheets, including two so-called external PVB sheets framing an internal polymeric sheet, possibly made of PVB, of lower hardness than that of the external sheets.

[0083] The lamination interlayer may also have thermal insulation properties, in particular infrared radiation reflection. For this purpose, it may comprise a coating of low-emissivity thin layers, for example a coating comprising a thin layer of silver or a coating alternating dielectric layers of different refractive indices, deposited on an internal PET sheet framed by two external PVB sheets.

[0084] The thickness of the lamination interlayer is generally in the range of 0.3 to 1.5 mm, in particular 0.5 to 1 mm. The lamination interlayer may have a thinner thickness on one edge of the glazing than in the center of the glazing in order to avoid the formation of a double image when using a head-up display (HUD) system. Examples

[0085] The following exemplary embodiments illustrate the invention in a non-limiting manner, in connection with the.

[0086] schematically illustrates an embodiment of the method according to the invention. It represents a schematic section of a part of the glass sheets and the elements deposited on the glass sheets, near their periphery. The various elements are obviously not shown to scale, so as to be able to visualize them.

[0087] The first glass sheet 10 coated with the stack of thin layers 12 is provided in step a, then a part of the stack 12 is coated with a layer of enamel 14, in particular by screen printing (step b).

[0088] The assembly then undergoes pre-firing (step b1), which in the case shown, leads to a partial dissolution of the stack 12 by the enamel 14.

[0089] An additional glass sheet 20, here provided with an additional stack of thin layers 22, is then placed on the first glass sheet 10, the assembly then being curved (step c). The view shown being only that of the end of the glass sheet, the bending is not shown here. The diagram illustrates the fact that at the end of the bending, the enamel 14 has completely dissolved the underlying stack of thin layers 12.

[0090] In step d, 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 assembled using the lamination interlayer 30. The diagram here represents each of the separate elements, in exploded view. First set of examples

[0091] The method implemented in the first series of examples corresponds to the embodiment of the.

[0092] Clear glass sheets 2.1 mm thick, previously sputter-coated with a thin-film stack comprising three silver layers protected by zinc oxide layers, silicon nitride layers and NiCr blockers, were partially screen-coated with 25 µm wet-thick enamel layers.

[0093] The enamel composition included, in addition to the glass frit, black pigments and the medium, 5% by weight of large refractory oxide particles having a size greater than 20 µm. In a first example according to the invention, 5% by weight of ZnO particles (D90 < 1 µm) were further added to the enamel composition.

[0094] The enamel layer was deposited by screen printing, then the enamel was dried (150°C, 1 to 2 minutes) before being pre-fired at approximately 650-680°C.

[0095] After pairing with an additional glass sheet made of tinted soda-lime-silica glass provided on face 4 with a stack comprising a layer of ITO, the assembly was curved at more than 600°C for 350 to 500 seconds.

[0096] After firing, the aesthetics, more particularly the black color seen from face 1, was evaluated by measuring the clarity L* in reflection (illuminant D65, reference observer 10°).

[0097] In the case of the example according to the invention, the L* value obtained was on average 4.5, compared to 5.1 for the comparative example (without ZnO particles). The comparative example also showed a slight blur in reflection, unlike the example according to the invention.

[0098] For the comparative example, approximately 25% of the glasses broke at the corners during bending, with sticking observed, as well as transfer of the enamel to the opposite glass. However, no breakage was observed for the example according to the invention.

[0099] The laminated glazing units were also subjected to 3-point bending tests. For the comparative example, the breaking force was 128 N, compared to 172 N for the example according to the invention. The values ​​given are average values ​​for a sample of 20 glazing units. Second set of examples

[0100] The examples in this second series of examples differ from those in the first series in that the bending of the two sheets of glass was carried out separately, by pressing at a temperature of 610-630°C.

[0101] As in the first series, the enamel composition included, in addition to the glass frit, black pigments and the medium, 5% by weight of large refractory oxide particles having a size greater than 20 µm. In a second example according to the invention, 5% by weight of ZnO particles (D90 < 1 µm) were further added to the enamel composition. A third example according to the invention contained 10% by weight of such particles.

[0102] In the case of the comparative example (without ZnO particles), sticking of the glass to the bending tool was observed. This was not the case in the case of the examples according to the invention.

Claims

A method for obtaining curved laminated glazing, particularly for windshields or motor vehicle roofs, comprising the following successive steps: a. supplying a first sheet of glass (10), coated on at least part of one of its faces with a stack of thin films (12), b. a step of depositing, on a part of the surface of the stack of thin films (12), a layer of enamel (14), the deposit being carried out by screen printing of an enamel composition comprising from 1 to 15% by weight of zinc oxide particles having a volume particle size distribution such that the d90 is at most 5 µm, c. a step of curving the first sheet of glass (10), the stack of thin films (12) located under the enamel layer (14) being totally dissolved by said enamel layer (14) at least at the end of this step, then d.a step of laminating said first sheet of glass (10) with an additional sheet of glass (20) by means of a laminating interlayer (30), so that the enamel layer (14) is turned towards said interlayer (30). A method according to claim 1, wherein the stacking of thin films (12) comprises at least one functional layer, in particular an electrically conductive functional layer. Method according to the preceding claim, wherein the electro-conductive functional layer is selected from metallic layers, in particular silver or niobium, and layers of a transparent conductive oxide, in particular selected from indium tin oxide, doped tin oxides and doped zinc oxides. A method according to any one of the preceding claims, such that after step c, the enamel layer (14) is opaque, black in color, and forms a band around the periphery of the first sheet of glass (10). A process according to any one of the preceding claims, wherein the zinc oxide particles have a volume particle size distribution such that d90 is at most 1 µm. A process according to any one of the preceding claims, wherein the zinc oxide particles have a volume particle size distribution such that the d50 is between 200 and 900 nm, in particular between 300 and 800 nm. A process according to any one of the preceding claims, wherein the zinc oxide particle content in the enamel composition is between 2 and 10% by weight, in particular between 3 and 8% by weight. A method according to any one of the preceding claims, wherein the enamel composition further comprises refractory particles having a diameter of at least 20 µm in a volume proportion of at least 0.5%, but no particles having a diameter greater than 80 µm. A process according to the preceding claim, wherein the refractory particles are based on metal oxides or metals. A method according to any one of the preceding claims, wherein the deposition of the enamel layer (14) is carried out by screen printing using a screen printing screen having a mesh opening of at least 40 µm. A method according to any one of the preceding claims, such that: - the method comprises between step b) and step c) a step b1) of pre-firing the enamel layer (14) during which the stack of thin layers (12) located under the enamel layer (14) is at least partially dissolved by said enamel layer (14), and - in step c) the first sheet of glass (10) and the additional sheet of glass (20) are curved together, the enamel layer (14) being turned towards said additional sheet of glass (20). A method according to any one of the preceding claims, wherein the additional glass sheet (20) carries, on the face opposite the face turned towards the lamination interlayer (30), an additional stack of thin films (22), in particular a low-emissivity stack comprising a transparent conductive oxide. Curved laminated glazing, in particular for windshields or roofs of motor vehicles, obtained by the process of one of the preceding claims, comprising a first sheet of glass (10) coated on at least a part of one of its faces with a stack of thin films (12), said first sheet of glass (10) being coated on a part of its surface with a layer of enamel (14) comprising zinc oxide particles having a volume particle size distribution such that the d90 is at most 5 µm, said first sheet of glass (10) being laminated with an additional sheet of glass (20) by means of a lamination interlayer (30), said enamel layer (14) being turned towards said lamination interlayer (30).