Method for obtaining curved laminated glazing

Abstract

The invention relates to a method for obtaining curved laminated glazing, the method comprising: a) providing a first glass sheet (10) coated on one of its faces with a stack of thin films (12); b) depositing, on the stack of thin films, an additional layer of enamel (14) or ceramic digital ink; c) gravity bending the first glass sheet and an additional glass sheet (20), the two sheets being bent together such that the face of the first glass sheet that is free of the additional layer faces the additional sheet, and that the first glass sheet is placed on top of the additional glass sheet, the stack of thin films located under the additional layer being entirely dissolved by the additional layer at the latest by the end of this bending step; and d) laminating the first glass sheet with the additional glass sheet.

Description

Description Title of the invention: Method for obtaining curved laminated glazing Prior art

[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.

[0006] The firing step is generally carried out simultaneously with the bending of the glass. In the context of the manufacture of laminated glazing, the two sheets of glass of the glazing are conventionally bent together, the sheet of glass intended to be positioned inside the vehicle being arranged above (in the direction of gravity) the other sheet of glass which carries the enamel. More specifically, during bending, the enamel layer is located opposite the sheet of glass intended to be positioned inside the vehicle. It is therefore 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.

[0007] Coatings, generally in the form of stacks of thin layers, can also be present on one of the glass sheets of the laminated glazing. These can notably be electrically conductive layers, which can provide two types of functionality. On the one hand, when current leads are provided, electrically conductive layers can dissipate heat by 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 arranged 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. It has been observed, in particular when the stack contained at least one layer of nitride 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, that is to say on the side opposite the enamel) and reducing its chemical resistance, in particular to acids.

[0010] Several solutions have been proposed to this problem. For example, it has been considered to first remove the thin-film stack at the locations where the enamel layer is to be deposited, for example using 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.

[0011] Application WO2014 / 133929, and before it application WO00029346, proposed using special glass frits for enamelling, which, during firing or pre-firing, are capable of dissolving the stack of thin layers and attaching 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. More recently, application WO2022 / 153001 proposed a solution based on the use of an enamel capable of dissolving the stack of thin layers (principle of application WO2014 / 13392) and comprising refractory particles having a specific diameter so as to have improved non-stick properties. This solution is however not optimal because, in the context of large-scale mass production and with a high rate, it is particularly difficult to distribute the refractory particles homogeneously in the enamel layer.This results in two difficulties during the bending process: 1) certain areas of the enamel layer are deficient in refractory particles, so that the anti-sticking function is not correctly achieved, 2) certain areas of the enamel layer are too rich in refractory particles, which creates a risk of deterioration by friction of the glass sheet located opposite said enamel layer and intended to be positioned inside the vehicle. This deterioration is likely to lead to breakage when the glazing is integrated into a vehicle, or possibly after the integration has been carried out (e.g.: when the vehicle is moving). Statement of the invention

[0012] The present invention aims to remedy all or part of the drawbacks of the prior art, in particular those set out above, by proposing a solution which makes it possible to obtain laminated curved glazing so that during bending, on the one hand, the stack of thin layers dissolves so that an additional layer (e.g. enamel) deposited above the thin layers attaches directly to the glass, and, on the other hand, any risk of the two sheets of glass sticking together is eliminated. This results in more efficient manufacturing than that of laminated curved glazing of the state of the art, and therefore usable without constraints for large-scale series production.

[0013] For this purpose, and according to a first aspect, the invention relates to a method for obtaining laminated curved glazing, in particular for a motor vehicle windshield or roof, comprising: a) providing a first glass sheet, coated on at least part of one of its faces with a stack of thin layers, b) depositing, on part of the surface of the stack of thin layers, an additional layer of enamel or ceramic digital ink, c) gravity bending of the first glass sheet and an additional glass sheet with which said first glass sheet is intended to be laminated, the two sheets being bent together so that the face of the first glass sheet devoid of the additional layer is turned towards the additional sheet and the first glass sheet is placed above the additional glass sheet,the stack of thin layers located under the additional layer being completely dissolved by said additional layer at the latest at the end of this bending step, d) lamination of the first glass sheet with the additional glass sheet by means of a lamination interlayer, so that the additional layer is facing said interlayer.,

[0014] The invention also relates to laminated curved glazing, in particular for the windshield or roof of a motor vehicle, obtained by the production process according to the invention.

[0015] The laminated curved glazing according to the invention comprises a first sheet of glass and an additional sheet of glass assembled by means of a lamination interlayer, characterized in that the first sheet of glass is coated on at least part of one of its faces with a stack of thin layers and that an additional layer of enamel or ceramic digital ink is deposited on a part of the surface of the stack of thin layers, said additional layer being turned towards said interlayer, and in that the first glass sheet no longer comprises a stack of thin layers under the additional layer, said stack of thin layers located under the additional layer having been completely dissolved by said additional layer at the latest at the end of this bending step.

[0016] By convention and as indicated previously, the first glass sheet of the glazing comprises a face - called face 1 - intended to be positioned outside the vehicle and an opposite face - called face 2 - oriented towards the lamination interlayer (arranged between said first glass sheet and the additional glass sheet) and the additional glass sheet comprises a face - called face 3 - oriented towards the interlayer and a face - called face 4 - intended to be positioned inside the vehicle.

[0017] Advantageously, the face - called face 1 - of the first glass sheet of the glazing according to the invention is free of marks linked to the bending frame implemented during the gravity bending step (c). Indeed, said bending frame is in contact with the additional glass sheet (and not the first glass sheet of the glazing), more precisely face 3, during the gravity bending step (step c).

[0018] Advantageously, the glazing according to the invention is characterized by the fact that, where appropriate, the slight marks linked to the contact of the bending frame with the glass are carried by the face - called face 3 - of the additional glass sheet, thanks to which said marks are invisible in the glazing since said face 3 is oriented towards the lamination interlayer.

[0019] Advantageously, the value of the clarity L* in reflection characterizing the homogeneity of the black color seen from the face - called face 1 - of the first sheet of glass of the laminated curved glazing according to the invention is less than or equal to 6.0, preferably less than 5.0 and greater than 3.5, for example between 4 and 4.3.

[0020] Advantageously, the glazing according to the invention thus presents, in addition to the absence of marks on face 1, an improved aesthetic compared to glazing according to the state of the art due to the homogeneity of the black color.

[0021] Advantageously, the glazing according to the invention has better resistance than laminated glazing according to the prior art and this results from the fact that the glass sheet additional (face 3) - and no longer the first sheet of glass (face 1) - is in contact with the bending frame during step (c) of gravity bending.

[0022] Indeed, the direct contact between the bending frame and the glass influences the stresses in the thickness of the glass so that if this impacts the first sheet of glass in a glazing according to the prior art this is not the case in a glazing according to the invention in which the face 3 of the additional sheet of glass is the one which is in contact with said bending frame.

[0023] By comparison, the direct contact of the cooling frame causing cooling of the glass therefore no longer influences the stresses in the thickness of the glass and consequently the mechanical resistance of the first sheet of glass located on the outside and in particular its face 1. This is the reason why the glazing according to the invention has better resistance than a laminated glazing according to the prior art since the additional sheet of glass having been in contact with the bending frame is advantageously located inside the glazing.

[0024] This reduction in stresses in the thickness of the glass of said first sheet of glass then gives the glazing obtained a reinforcement of the edge stresses, which reinforcement is furthermore a distinctive technical characteristic of the glazing according to the invention and which is perfectly measurable for example with a gravel test (well known to the person skilled in the art) carried out on face 1 intended to be positioned outside the vehicle.

[0025] The dissolution of the thin-film stack by the additional layer makes it possible to avoid the aforementioned interactions. The constituent elements of the stack are dissolved in the additional layer, which is in direct contact with the glass sheet at the latest at the end of the bending step (step c).

[0026] Furthermore, and particularly advantageously, the relative arrangement of the sheets with respect to each other, during the bending step, is reversed in comparison with the configuration of the prior art. Thus, in the invention, and following the direction of gravity, the faces of the glass sheets are presented in the following order: face 2, face 1, face 4, face 3. In this way, any risk of sticking between the two glass sheets is eliminated. The manufacture of curved laminated glazing can therefore be envisaged independently of the capacity of the additional layer to achieve an absence of bonding, for example via the use of refractory particles.

[0027] In this text, the stack of thin layers and the additional layer are collectively referred to as “the coatings”.

[0028] Furthermore, it is considered in no way limiting for the remainder of the description that the additional layer is an enamel layer. It is important to note, however, that these provisions are not limiting of the invention, the additional layer may also correspond to a layer of ceramic digital ink, provided that the latter is capable of achieving, at the end of the bending process, the total dissolution of the functional layers on which it rests. Any ceramic digital ink having such properties and known to the person skilled in the art may be envisaged. The deposition of such an ink on a part of the surface of the stack of thin layers is also carried out according to any known printing technique.

[0029] Generally speaking, and unless otherwise stated, all of the aspects described from now on are applicable in a similar manner to the case of an additional layer corresponding to a layer of ceramic digital ink, any technical adjustments necessary for this adaptation being within the reach of the person skilled in the art.

[0030] Step a

[0031] 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.

[0032] 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.

[0033] The first glass sheet may be 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 include other coloring agents, such as cobalt oxide, chromium oxide, nickel oxide, erbium oxide, or selenium.

[0034] 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.

[0035] 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 in 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 m 2 .

[0036] 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 in fact not be coated in order in particular to provide communication windows allowing waves to pass through.

[0037] 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 strip, that is to say a strip closed on itself which, from each point of the periphery of the first glass sheet, extends towards the inside of the first glass sheet over a certain width, generally variable, typically between 1 and 20 cm.

[0038] 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.

[0039] 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 to be understood that the layer may include impurities without influence on its properties. The terms "oxide" or "nitride" do not necessarily mean that the oxides or nitrides are stoichiometric. They can in fact be sub-stoichiometric, super-stoichiometric or stoichiometric.

[0040] 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 cathode sputtering, it generally contains aluminum, since it is common practice to dope silicon targets with aluminum in order to accelerate deposition rates.

[0041] The nitride-based layer preferably has a physical thickness in a range from 2 to 100 nm, in particular from 5 to 80 nm.

[0042] 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.

[0043] 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.

[0044] At least one electrically conductive functional layer is advantageously chosen from: - metallic layers, particularly 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).

[0045] These layers are particularly appreciated for their low emissivity, which gives the glazing excellent thermal insulation properties. In glazing fitted to land vehicles, particularly cars, railways, or even In 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, this glazing helps retain heat within the passenger compartment, and therefore reduces the energy consumption of heating. The same is true for glazing used in buildings.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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).

[0050] 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 scrolling the glass sheet under different targets, generally in a single device.

[0051] The aforementioned stacks have electricity conduction and infrared reflection properties useful for providing a heating function (defrosting, demisting) and / or a thermal insulation function.

[0052] 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.

[0053] It should be noted that the stack of thin layers is not limited by the fact of comprising an electrically conductive layer. Generally speaking, any functional layer / combination of functional layers known to the person skilled in the art can be envisaged, the choice of a particular layer / combination of layers constituting only a variant of implementation of the invention. In particular, any functional layer capable of modifying the optical behavior (examples: anti-reflective glazing, reflective glazing used to reduce the solar factor), chemical behavior (examples: “self-cleaning” glazing, hydrophobic windows), electrical behavior (electrically conductive and transparent deposits) or even mechanical behavior (example: anti-scratch treatments) can be envisaged.

[0054] Step b

[0055] In addition to the functional layers described above, the first glass sheet comprises an enamel layer made from an enamel composition (this is the layer referred to above as the “additional layer”).

[0056] 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 pre-firing, and where appropriate before drying) and the final layer (after firing).

[0057] In step b, the enamel layer is preferably deposited from an enamel composition comprising at least one pigment, at least one glass frit.

[0058] In certain particular embodiments, the enamel composition further comprises refractory particles.

[0059] Alternatively, according to other embodiments, the enamel composition is a crystallizing enamel. No limitation is attached to the type of crystallizing enamel that can be used. For example, it may be a crystallizing enamel marketed under the name “TDF9801 AIR” by the company Vibrantz.

[0060] The enamel composition, like the enamel layer, preferably does not include lead oxide.

[0061] 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 thereto, and which is removed during the pre-firing or firing of the enamel. The medium typically comprises solvents, diluents, oils and / or resins.

[0062] The glass frit is capable of dissolving the underlying layer stack. Preferably, the glass frit is based on bismuth and zinc borosilicate. In order to make it more "aggressive" with respect to the layer stack, the bismuth and / or boron contents are preferably higher than those of the glass frits usually used.

[0063] 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.

[0064] As mentioned above, the enamel composition may comprise, in certain embodiments, refractory particles (the presence of refractory particles is not envisaged for the case where the additional layer corresponds to a ceramic digital ink). The term “refractory particles” means 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. The refractory particles are in particular based on metal oxides or metals. The metal oxides are in particular simple oxides, such as for example aluminum, titanium or zirconium oxide, or complex oxides such as high-melting glass frits or inorganic pigments (the latter being notably called “complex inorganic colored pigments” or CICP), in particular black inorganic pigments.

[0065] The enamel composition may, for example, include a sufficient proportion of "large" refractory particles (so the size, also called diameter, is at least 20 μm). This can in particular help prevent the glass sheet from sticking with one or more bending tools, such as a pressing frame. 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.

[0066] 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%.

[0067] Preferably, the enamel composition contains refractory particles whose diameter is at least 30 pm, in particular at least 40 pm, and even at least 50 pm, in the above-mentioned volume proportions.

[0068] Another way to characterize the composition of enamel, and 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).

[0069] When the enamel composition contains refractory particles, it does not contain particles (refractory or not) with a diameter greater than 80 pm to facilitate deposition by screen printing. The fineness of the enamel composition can thus be between 20 and 80 pm, in particular between 40 and 60 pm. The presence of such refractory particles can be determined by laser granulometry or using a Hegman gauge.

[0070] The refractory particles are preferably zirconia-based. Zirconia-based particles are understood to mean particles comprising at least 80% by weight, in particular 85% by weight, of zirconium oxide (ZrO2). The zirconia is preferably stabilized, in particular using yttrium. It may also contain sintering aid additives, in particular chosen from AI2O3, TiOz, ZnO, SiOz and mixtures thereof.

[0071] Preferably, the zirconia-based particles have a chemical composition comprising, in particular consisting of, the following constituents, in the following weight content ranges: - ZrO2: 83-97% - Y2 03: 2-8% - AI2 03: 0-3% - black pigments: 0-6%, especially 1-6%.

[0072] The zirconia-based particles are preferably calcined, in particular at a temperature between 1100 and 1500°C.

[0073] The zirconia-based particles preferably have a volume particle size distribution, determined by laser particle size analysis, such that the D10 is at least 20 pm, in particular between 30 and 45 pm, the D50 is between 40 and 52 pm and the D90 is at most 65 pm, in particular between 55 and 65 pm.

[0074] Refractory particles, especially those based on zirconia, may have a white / grey colour. In particular, the clarity L* in reflection is preferably less than 6, and even preferably less than 5. The colourimetric coordinate a* (respectively b*) is preferably between -2 and 0 (respectively between -1.5 and 1.5). The colourimetric parameters are determined in accordance with ISO 7724 (D65-10 0 ). To do this, the particles, particularly those based on zirconia, may contain pigments of suitable color, typically in a content of between 1 and 6% by weight.

[0075] The average sphericity of refractory particles, in particular refractory particles, is preferably greater than 0.60, in particular 0.70, or even 0.80 and even greater than 0.85. The sphericity of a particle corresponds to the ratio between the smallest Feret diameter and the largest Feret diameter. The average roundness of refractory particles is preferably greater than 0.6, in particular 0.7 and even 0.8 or 0.9. The average sphericity (or roundness) corresponds to the arithmetic mean of the sphericity (or roundness) of 50 to 200 particles. The roundness corresponds to 4.A / n.Lf 2 , Lf being the largest Feret diameter and A the projected area of ​​a particle. These different parameters, in particular the Feret diameters, are measured in particular by dynamic image analysis, for example using a Camsizer XT particle analyzer marketed by the Horiba company.

[0076] It was observed that the use of particles of suitable color, and / or spherical particles, without too many roughnesses, made it possible to improve the aesthetics of the enamel after firing, in particular reducing the blur visible in reflection from face 1 under strong illumination.

[0077] 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. The mesh opening of the screen is preferably at least 40 μm, in particular at least 60 μm, or even at least 70 μm, to improve the homogenization of the deposit. 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 pm, in particular at most 80 pm.

[0078] The thickness of the wet enamel layer is preferably between 15 and 40 pm, in particular between 20 and 30 pm.

[0079] 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.

[0080] Step c

[0081] Bending is carried out by gravity (the glass deforms under its own weight), at temperatures typically ranging from 550 to 650°C.

[0082] More specifically, the first sheet of glass (i.e. the sheet of glass bearing the enamel composition) and the additional sheet of glass (i.e. the sheet of glass intended to be positioned inside the passenger compartment) are bent together (gravity bending known as “pair-bending”).

[0083] The face of the first sheet of glass without the enamel layer (i.e. the face 1) is turned towards the additional sheet when bending, more particularly towards face 4 of the latter. In addition, the first sheet of glass is placed above the additional sheet of glass during bending.

[0084] In other words, during bending, it is face 3 of the additional sheet which rests in contact on the bending frame, face 2 of the first sheet of glass being exposed and not sandwiched between the two sheets of glass, unlike face 1.

[0085] It results in particular from these provisions, in addition to the advantages described above concerning the total elimination of the risk of sticking between the two sheets of glass, that the laminated curved glazing intended to be assembled is distinguished from those of the state of the art in that face 3 (and not face 1) bears slight marks linked to this state of rest on the bending frame.

[0086] Advantageously, the face 1 of the first glass sheet 10 of the glazing is free of marks linked to the bending frame since said bending frame is in contact with the additional glass sheet 20 during the bending step (c) by gravity.

[0087] 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 pm. The interlayer powder is, for example, based on calcium and / or magnesium carbonate.

[0088] 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. As indicated previously, it advantageously forms a band on the periphery of the first glass sheet. In this way, the enamel layer is capable of concealing and protecting against ultraviolet radiation joints, connection elements, or even sensors.

[0089] If the enamel layer has not already completely dissolved the stack of thin layers at the end of the pre-firing described below, this total dissolution is obtained during the bending, which completes the firing of the enamel.

[0090] Conventionally, firing is carried out in a tunnel-type oven. Such an oven is, for example, configured to perform radiant heating.

[0091] Alternatively, or in addition to such radiative heating, convective heating may be implemented. The fact that the heating comprises at least one The convective part advantageously reduces temperature contrasts at the glass level, and therefore in particular minimizes stresses in the glass sheets. This results in a reduction in the risk of glass breakage during the bending stage.

[0092] 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.

[0093] Optional pre-cooking step (bl)

[0094] The method preferably comprises, between step b) and step c), a step bl) 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.

[0095] As is well known, the furnace used during pre-firing forms a separate unit within the production line from the furnace used during bending. The furnace used during pre-firing uses at least convective heating to pre-fire the enameled glass. It should also be noted that the pre-firing here concerns only the first sheet of glass since it is the latter which carries the enamel layer.

[0096] The pre-baking step is preferably carried out at a temperature between 150 and 800°C, in particular between 500 and 700°C.

[0097] Such pre-firing allows the elimination of the organic medium, or, in general, any organic component possibly present in the enamel layer.

[0098] During pre-firing, the thin-film stack is 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).

[0099] Step d

[0100] 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 sheets of glass and the lamination interlayer can be removed by calendering or by vacuum.

[0101] 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.

[0102] 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.

[0103] The additional glass sheet may, for example, have a thickness of between 0.5 and 1.2 mm. The additional glass sheet is, in particular, made of sodium aluminosilicate glass, preferably chemically strengthened.

[0104] 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 compressive 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 then preferably a motor vehicle windshield, for example a heated windshield.

[0105] In certain embodiments, 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) a stack of layers additional thin films, including a low-emissivity stack, comprising a transparent conductive oxide, including 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 sides of the same glass sheet (sides 3 and 4). In these embodiments, 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 then preferably a motor vehicle roof.

[0106] As a more particular example of embodiment, mention may be made of a laminated curved roof comprising, from the exterior of the vehicle, a clear glass sheet coated on face 2 with a stack of thin layers comprising at least one layer of silver then a layer of enamel, a tinted PVB lamination interlayer, and an additional glass sheet of tinted glass, carrying on face 4 a stack of low-emissivity thin layers, in particular based on ITO.

[0107] The lamination interlayer preferably comprises at least one sheet of polyvinyl acetal, in particular polyvinyl butyral (PVB).

[0108] The lamination interlayer can be tinted or untinted in order to regulate the optical or thermal properties of the glazing if necessary.

[0109] 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.

[0110] 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. [YES] The thickness of the lamination interlayer is generally in the range from 0.3 to 1.5 mm, in particular from 0.5 to 1 mm. The lamination interlayer may have a thinner thickness on one edge of the glazing than at the other. center of the glazing to avoid the formation of a double image when using a head-up display (HUD) system.

[0112] Examples

[0113] The following exemplary embodiments illustrate the invention in a non-limiting manner, in connection with Figure 1.

[0114] [Fig.l] 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.

[0115] 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).

[0116] The assembly then undergoes pre-firing (step bl), which in the case shown, leads to a partial dissolution of the stack 12 by the enamel 14.

[0117] An additional glass sheet 20, here provided with an additional stack of thin layers 22, is then placed below the first glass sheet 10. The relative positions of the first glass sheet 10 and the additional glass sheet 20 for the implementation of gravity bending (step c, the force of gravity being symbolized by the arrow denoted "g") are illustrated in FIG. 1. The direction of orientation of gravity is also represented in FIG. 1 by means of an arrow referenced by the letter "g". Furthermore, and as illustrated in FIG. 1, the face 1 of the first glass sheet 10 (i.e. the face provided with the enamel 14) is exposed and not sandwiched between the two glass sheets 10, 20.

[0118] It is important to note that the view shown in Figure 1 is only that of the end of the glass sheet, so that the result of the bending (i.e. the curvature of the glass sheets 10, 20) is not shown here. That being said, the diagram illustrates in particular the fact that at the end of the bending, the enamel 14 has completely dissolved the underlying stack of thin layers 12.

[0119] Subsequently, in step d, the first glass sheet 10 coated with the thin layer stack 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.

[0120] The method implemented by the examples corresponds to the embodiment of Figure 1.

[0121] Glass sheets 2.1 mm thick, previously coated by sputtering with a thin-film stack comprising three silver layers protected by zinc oxide layers, silicon nitride layers and NiCr blockers, were screen-coated with enamel layers with a wet thickness of 25 μm.

[0122] The deposition of the enamel layer was carried out using a screen with a mesh opening of 68 pm.

[0123] The enamel was then dried (150°C, 1 to 2 minutes) and then pre-fired at a temperature between 630-660°C.

[0124] After pairing with an additional glass sheet made of soda-lime-silica glass provided on face 4 with a stack comprising a layer of ITO, the assembly was curved at a temperature above 600°C, for example reaching 650°C or even more, and this during a cycle whose duration is preferably between 300 and 500 seconds.

[0125] The inventors were thus able to verify that the relative arrangement of the glass sheets in relation to each other during bending advantageously eliminates the risk of sticking between them. These verifications were carried out during multiple tests, in particular using the TDF9693 FIR enamel marketed by the Vibrantz company.

[0126] Furthermore, after firing, the aesthetics, more particularly the homogeneity of the black color seen from face 1, was evaluated by measuring the L* clarity in reflection (illuminant D65, reference observer 10°). A value less than or equal to 6.0, preferably less than 5.0, is considered acceptable. Here again, excellent results could be achieved, in particular with the TDF9693 FIR enamel (obtaining an L* value between 4 and 4.3).

[0127] Advantageously, the value of the clarity L* in reflection characterizing the homogeneity of the black color seen from face 1 of the first sheet of glass 10 of the glazing is less than or equal to 6.0, preferably less than 5.0 and greater than 3.5, for example between 4 and 4.3.

[0128] The following table provides a summary of the results obtained during different tests carried out using TDF9693 FIR enamel.

[0129] In this table, the expression "reverse bending" (respectively the expression "standard bending") refers to the relative arrangement of the glass sheets with respect to each other as envisaged in the context of the present invention (respectively as envisaged in the state of the art).

[0130] Furthermore, regarding the homogeneity of the black color seen from side 1, a rating scale was used, in which the symbol "+" indicates a good result (L* value between 5 and 6) and the symbol "++" indicates an excellent result (L* value less than 5).

Claims

Claims

1. Method for obtaining laminated curved glazing, in particular for a motor vehicle windshield or roof, comprising: a) providing a first glass sheet (10), coated on at least part of one of its faces with a stack of thin layers (12), b) depositing, on part of the surface of the stack of thin layers (12), an additional layer of enamel (14) or ceramic digital ink, c) gravity bending of the first glass sheet (10) and an additional glass sheet (20) with which said first glass sheet (10) is intended to be laminated, the two sheets (10, 20) being bent together so that the face of the first glass sheet (10) devoid of the additional layer is turned towards the additional sheet (20) and the first glass sheet (10) is placed above the additional glass sheet (20),the stack of thin layers (12) located under the additional layer being completely dissolved by said additional layer at the latest at the end of this bending step, d) laminating the first glass sheet (10) with the additional glass sheet (20) by means of a laminating interlayer (30), so that the additional layer is facing said interlayer (30).,

2. Method according to claim 1, such that the stack of thin layers (12) comprises at least one functional layer, in particular an electrically conductive layer.

3. Method according to claim 2, in which the electroconductive functional layer is chosen from metallic layers, in particular silver or niobium, and layers of a transparent conductive oxide, in particular chosen from indium and tin oxide, doped tin oxides and doped zinc oxides.

4. Method according to one of the preceding claims, such that after step d), the additional layer is opaque, black in color, and forms a band at the periphery of the first glass sheet (10).

5. A method according to any preceding claim, wherein the additional layer is an enamel layer, the enamel composition comprising refractory particles having a diameter of at least 20 pm in a volume proportion of at least 0.5%, but no particles having a diameter greater than 80 pm.

6. A method according to claim 5, wherein the refractory particles are based on metal oxides or metals.

7. A method according to claim 6, wherein the metal oxides are simple oxides, such as aluminum, titanium or zirconium oxide, or complex oxides such as high melting point glass frits or inorganic pigments.

8. A method according to any one of claims 1 to 4, wherein the additional layer is an enamel layer, the enamel composition being a crystallizing enamel.

9. Method according to one of the preceding claims, in which the additional layer is an enamel layer, the deposition of the enamel layer (14) being carried out by screen printing using a screen printing screen having a mesh opening of at least 40 μm.

10. Method according to one of the preceding claims, said method comprising between step b) and step c) a step bl) of pre-baking the additional layer during which the stack of thin layers (12) located under the additional layer is at least partially dissolved by said additional layer.

11. Method according to one of the preceding claims, in which the additional glass sheet (20) has a thickness of between 0.5 and 1.2 mm, in particular is made of chemically reinforced sodium aluminosilicate glass.

12. Method according to one of the preceding claims, in which the additional glass sheet (20) carries, on the face opposite the face facing the lamination interlayer (30), an additional stack of thin layers (22), in particular a low-emissivity stack comprising a transparent conductive oxide.

13. A method according to any preceding claim, wherein step c) is carried out in an oven configured to perform radiative and / or convective heating.

14. Laminated curved glazing, in particular for a windshield or roof of a motor vehicle, obtained by the method of one of the preceding claims.

15. Laminated curved glazing according to claim 14 comprising a first sheet of glass and an additional sheet of glass assembled by means of a lamination interlayer, characterized in that the first sheet of glass is coated on at least part of one of its faces with a stack of thin layers and that an additional layer of enamel or ceramic digital ink is deposited on part of the surface of the stack of thin layers, said additional layer being turned towards said interlayer, and in that the first sheet of glass is devoid of a stack of thin layers under the additional layer.

16. Laminated curved glazing according to claim 14 or 15, in which the face of the first glass sheet (10) of the glazing is free of marks linked to the bending frame implemented during the gravity bending step (c).

17. Laminated curved glazing according to one of claims 14 to 16, in which the value of the clarity L* in reflection characterizing the homogeneity of the black color seen from the face of the first glass sheet (10) of the glazing is less than or equal to 6.0, preferably less than 5.0 and greater than 3.5, for example between 4 and

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