Process for obtaining curved laminated glazing

Abstract

Method for obtaining curved laminated glazing The invention relates to a method for obtaining curved laminated glazing comprising: a) providing a first glass sheet (10) coated on one of its faces with a stack of thin layers (12), b) depositing, on the stack of thin layers, an additional layer of enamel (14) or ceramic digital ink, c) gravity bending of the first glass sheet and an additional glass sheet (20), 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. Figure 1.,

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 glazing is glazing in which two sheets of glass are adhesively bonded by means of a lamination interlayer. The latter makes it possible in particular to retain shards of glass in the event of breakage, but also provides other functionalities, in particular in terms of resistance to burglary or improvement of acoustic properties.

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

[0004] Layers of enamel, generally black and opaque, are often deposited on part of the glazing, usually in the form of a peripheral strip intended to conceal and protect against ultraviolet radiation the polymeric seals used for fixing and positioning the glazing on the bodywork bay. Enameled 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 face 2, the faces being traditionally numbered from the face intended to be positioned outside the vehicle. Face 2 is therefore a face in contact with the lamination interlayer. The aesthetic appearance of the enamel layer seen from outside 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 is composed of fine particles of a glass with a low melting point, 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 maintaining 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 particularly Specifically, during bending, the enamel layer is located opposite the glass sheet 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, 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. The electrically conductive layers can, on the one hand, when current leads are provided, dissipate heat by the Joule effect. These are then heating layers, useful for example for defrosting or demisting. These layers also have, due to their reflection of infrared radiation, solar control or low emissivity properties. 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] It may however be interesting, in certain cases which will be detailed later, to arrange 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] It has, however, 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, 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. Thus, it has been envisaged to first remove the stack of thin layers at the locations 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 stack of thin layers. However, mechanical abrasion generates visible scratches, including at the level of the enamel layer.

[0011] Application WO2014 / 133929, and before it application WO0029346, proposed using special glass frits for enamel which, during the firing or pre-firing, to dissolve the stack of thin layers to 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.

[0012] 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

[0013] The present invention aims to overcome 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 glazings 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 glazings of the state of the art, and therefore usable without constraints for large-scale mass production.

[0014] To this end, and according to a first aspect, the invention relates to a method for obtaining laminated curved glazing, in particular for a windshield or roof of a motor vehicle, comprising: (a) a supply of a first sheet of glass, coated on at least part of one of its faces with a stack of thin layers, (b) a deposit, on a part of the surface of the stack of thin layers, of 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) laminating the first glass sheet with the additional glass sheet by means of a laminating interlayer, such that the additional layer faces towards said interlayer.

[0015] The invention also relates to a laminated curved glazing, in particular for a windshield or roof of a motor vehicle, obtained by the production method according to the invention.

[0016] The dissolution of the stack of thin layers 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, at the latest at the end of the bending step (step c), in direct contact with the glass sheet.

[0017] 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 sticking, for example via the use of refractory particles.

[0018] In the present text, the stack of thin layers and the additional layer are collectively referred to as “the coatings”.

[0019] 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 portion of the surface of the stack of thin layers is also carried out according to any known printing technique.

[0020] 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.

[0021] Step a

[0022] 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.

[0023] 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 to say by a process consisting of pouring molten glass onto a bath of molten tin.

[0024] The first glass sheet may be made of clear glass or tinted glass, preferably tinted glass, for example green, gray or blue. To do 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 cobalt oxide, chromium oxide, nickel oxide, erbium oxide, or selenium.

[0025] 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.

[0026] The lateral dimensions of the first glass sheet (and of the additional glass sheet) are to be adapted according to those of the laminated glazing into which it is intended to be integrated. The first glass sheet (and / or the additional glass sheet) preferably has a surface area of ​​at least 1 m2.

[0027] 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 the waves to pass through.

[0028] 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, ty- sting between 1 and 20 cm.

[0029] 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.

[0030] In the present text, the term "contact" means physical contact. The expression "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 of", it should be understood that the layer may comprise impurities without influence on its properties. The terms "oxide" or "nitride" do not necessarily mean that the oxides or nitrides are stoichiometric. They may in fact be sub-stoichiometric, super-stoichiometric or stoichiometric.

[0031] The stack preferably comprises at least one layer based on a nitride. 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 nitride of silicon and zirconium, or a nitride of silicon and aluminum. Preferably, the layer based on a nitride is a layer based on silicon nitride, more particularly a layer consisting essentially of a silicon nitride. When the layer of silicon nitride is deposited by cathode sputtering it generally contains aluminum, since it is customary to dope silicon targets with aluminum in order to accelerate the deposition rates.

[0032] The nitride-based layer preferably has a physical thickness in a range from 2 to 100 nm, in particular from 5 to 80 nm.

[0033] Nitride-based layers are commonly used in many thin-film stacks because they have advantageous blocking properties, in that they prevent the oxidation of other layers present in the stack, in particular functional layers which will be described below.

[0034] 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.

[0035] 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 oxide indium and tin, doped tin oxides (e.g. with fluorine or antimony) and doped zinc oxides (e.g. with aluminum or gallium).

[0036] These layers are particularly appreciated for their low emissivity, which gives the glazing excellent thermal insulation properties. In glazing fitted to land vehicles, particularly automobiles, 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 allow the heat to be retained within the passenger compartment, and consequently reduces the energy effort required for heating. The same is true in the case of glazing fitted to buildings.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] At least part of the stack of thin layers can be deposited by various known techniques, for example by chemical vapor deposition (CVD), or by cathode sputtering, in particular assisted by a magnetic field (magnetron process).

[0041] 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 on the same line a very complex stack of layers by successively scroll the glass sheet under different targets, generally in a single device.

[0042] The aforementioned stacks have electricity conduction and infrared reflection properties useful for providing a heating function (defrosting, demisting) and / or a thermal insulation function.

[0043] When the stack of thin layers is intended to provide a heating function, current leads must be provided. These may in particular be strips of silver paste deposited by screen printing on the stack of thin layers, at two opposite edges of the glass sheet.

[0044] 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.

[0045] Step b

[0046] 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”).

[0047] In the present text, the term "enamel composition" refers to the liquid composition which is used to deposit a wet enamel layer during step b. The term "enamel layer" is used to describe the layer at each step of the process, both the wet layer (before pre-firing, and where appropriate before drying) and the final layer (after firing).

[0048] During step b, the enamel layer is preferably deposited from an enamel composition comprising at least one pigment, at least one glass frit.

[0049] In certain particular embodiments, the enamel composition further comprises refractory particles.

[0050] 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.

[0051] The enamel composition, like the enamel layer, preferably does not comprise lead oxide.

[0052] 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.

[0053] 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.

[0054] The pigments preferably comprise one or more oxides chosen from chromium, copper, iron, manganese, cobalt and nickel oxides. These may be, for example, copper and / or iron chromates.

[0055] 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.Metal oxides include simple oxides, such as aluminum, titanium or zirconium oxide, or complex oxides such as high-melting glass frits or inorganic pigments (the latter being referred to in particular as "complex inorganic colored pigments" or CICP), including black inorganic pigments.

[0056] The enamel composition may, for example, comprise a sufficient proportion of “large” refractory particles (so the size, also called diameter, is at least 20 μm). This may in particular help to 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 more is much larger than that of the glass frit and pigments conventionally used.

[0057] 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%.

[0058] Preferably, the enamel composition contains refractory particles whose diameter is at least 30 μm, in particular at least 40 μm, and even at least 50 μm, in the above-mentioned volume proportions.

[0059] Another way to characterize the enamel composition, and to easily detect the presence of large particles, consists of measuring the fineness of the particles using a Hegman gauge (or grinding fineness gauge).

[0060] When the enamel composition comprises refractory particles, it does not contain particles (refractory or not) with a diameter greater than 80 μm to facilitate deposition by screen printing. The fineness of the enamel composition can thus be between 20 and 80 μm, in particular between 40 and 60 μm. The presence of such refractory particles can be determined by laser granulometry or using a Hegman gauge.

[0061] The refractory particles are preferably based on zirconia. By zirconia-based particles is meant 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 Al2O3, TiO2, ZnO, SiO2 and mixtures thereof.

[0062] 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% - A12 03: 0-3% - black pigments: 0-6%, especially 1-6%.

[0063] The zirconia-based particles are preferably calcined, in particular at a temperature between 1100 and 1500°C.

[0064] 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.

[0065] The refractory particles, in particular 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 standard ISO 7724 (D65-100). To this end, the particles, in particular based on zirconia, may contain pigments of suitable colour, typically in a content of between 1 and 6% by weight.

[0066] The average sphericity of the refractory particles, in particular the 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 the 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 / JZ.LP, Lf being the largest Feret diameter and A the projected area of ​​a particle. These different parameters, in particular the Féret diameters, are measured by dynamic image analysis, for example using a Camsizer XT particle analyzer marketed by the Horiba company.

[0067] It has been observed that the use of particles of suitable color, and / or spherical particles, without too many roughnesses, makes 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.

[0068] The deposition of the enamel layer is carried out by screen printing. To do this, a screen printing screen is placed on the glass sheet, which comprises meshes, some of which are closed, then the enamel composition is deposited on the screen, then a doctor blade is applied in order to force the enamel composition to pass through the screen in the areas where the meshes of the screen are not closed, 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 weakening the glass mechanically. The mesh opening is preferably at most 100 pm, in particular at most 80 pm.

[0069] The thickness of the wet enamel layer is preferably between 15 and 40 μm, in particular between 20 and 30 μm.

[0070] 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.

[0071] Step c

[0072] Bending is carried out by gravity (the glass deforms under its own weight), at temperatures typically ranging from 550 to 650°C.

[0073] More particularly, the first glass sheet (i.e. the glass sheet bearing the enamel composition) and the additional glass sheet (i.e. the glass sheet intended to be positioned inside the passenger compartment) are curved together. (gravity bending known as “pair bending” in English).

[0074] The face of the first glass sheet without the enamel layer (i.e. face 1) is turned towards the additional sheet during bending, more particularly towards face 4 of the latter. In addition, the first glass sheet is placed above the additional glass sheet during bending.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] Conventionally, cooking is carried out in a tunnel-type oven. Such an oven is, for example, configured to carry out radiative heating.

[0081] Alternatively, or in addition to such radiative heating, convective heating may be implemented. The fact that the heating comprises at least one convective part advantageously makes it possible to reduce the temperature contrasts at the level of the glass, and therefore in particular to minimize the stresses in the glass sheets. This results in a reduction in the risk of breakage of the glass during the bending step.

[0082] The total dissolution of the stack of thin layers can be observed in particular by electron microscopy. Electrical measurements, in particular of square resistance, also make it possible to observe the dissolution of the stack.

[0083] Optional pre-cooking step (b I )

[0084] 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.

[0085] As is known, the furnace used during pre-baking forms, within the production line, a unit separate from that of the furnace used during bending. The furnace used during pre-baking uses at least convective heating in order to pre-bake the enameled glass. It should also be noted that the pre-baking here concerns only the first sheet of glass since it is the latter which carries the enamel layer.

[0086] The pre-cooking step is preferably carried out at a temperature between 150 and 800°C, in particular between 500 and 700°C.

[0087] Such pre-firing makes it possible to eliminate the organic medium, or, in general, any organic component possibly present in the enamel layer.

[0088] During pre-firing, the stack of thin layers is at least partially dissolved by the enamel layer. Depending on the temperature used and the type of enamel or stack, the stack may even be completely dissolved by the enamel layer during pre-firing. Alternatively, it may only be partially dissolved during pre-firing, and is then completely dissolved during bending (step c).

[0089] Step d

[0090] 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 the autoclave treatment, the air trapped between the glass sheets and the lamination interlayer can be removed by calendering or by vacuum.

[0091] As stated previously, 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.

[0092] The additional glass sheet may be made of soda-lime-silica glass, or of borosilicate or aluminosilicate glass. It may be made of clear or tinted glass. Its thickness is preferably between 0.5 and 4 mm, in particular between 1 and 3 mm.

[0093] 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 reinforced.

[0094] 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 reinforcement (also called “ion exchange”) consists of bringing the surface of the glass into contact with a molten potassium salt (for example potassium nitrate), way of strengthening the surface of the glass by exchanging glass ions (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.

[0095] 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) 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 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.

[0096] As a more particular example of embodiment, mention may be made of a laminated curved roof comprising, from the outside 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.

[0097] The lamination interlayer preferably comprises at least one sheet of polyvinyl acetal, in particular polyvinyl butyral (PVB).

[0098] The lamination interlayer can be tinted or untinted in order to regulate the optical or thermal properties of the glazing if necessary.

[0099] The lamination interlayer may advantageously have sound absorption properties in order to absorb sounds of airborne or solid-borne origin. It may 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.

[0100] 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.

[0101] The thickness of the lamination interlayer is generally in a range from 0.3 to 1.5 mm, in particular from 0.5 to 1 mm. The lamination interlayer may have a lower 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.

[0102] Examples

[0103] The following exemplary embodiments illustrate the invention in a non-limiting manner, in connection with [Fig.l].

[0104] [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.

[0105] 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).

[0106] 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.

[0107] 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.l]. The direction of orientation of gravity is also represented in [Fig.l] by means of an arrow referenced by the letter "g". Furthermore, and as illustrated in [Fig.l], 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.

[0108] It is important to note that the view shown in [Fig.l] 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.

[0109] Subsequently, 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.

[0110] The method implemented by the examples corresponds to the embodiment of [Fig.l].

[0111] 2.1 mm thick glass sheets, previously spray-coated Cathodic layers of 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.

[0112] The deposition of the enamel layer was carried out using a screen with a mesh opening of 68 μm.

[0113] The enamel was then dried (150°C, 1 to 2 minutes) and then pre-fired at a temperature between 630-660°C.

[0114] 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.

[0115] The inventors were thus able to verify that the relative arrangement of the glass sheets with respect 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 company Vibrantz.

[0116] In addition, after firing, the aesthetics, more particularly the homogeneity of the black color seen from face 1, was evaluated by measuring the clarity L* 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 of between 4 and 4.3).

[0117] The following table provides a summary of the results obtained during different tests carried out using TDF9693 FIR enamel. Examples Color homogeneity Bonding of glass sheets 1. Reverse bending TDF9693 with refractory particles + No bonding 2. Standard bending TDF9693 with refractory particles + Bonding in some corners 3. Reverse bending TDF9693 without refractory particles ++ No bonding 4. Standard bending TDF9693 without refractory particles ++ Complete bonding

[0118] 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).

[0119] Furthermore, with regard to the homogeneity of the black colour 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 windshield or roof of a motor vehicle, 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, an additional layer of enamel (14) or ceramic digital ink, c) gravity bending of the first glass sheet and an additional glass sheet (20) 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) laminating the first glass sheet with the additional glass sheet by means of a laminating interlayer (30), so that the additional layer is facing said interlayer.,

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.

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