Method for obtaining curved glazing provided with a stack of thin layers and an enamel layer, comprising a step of partial ablation of the stack

Abstract

The subject of the invention is a method for obtaining curved glazing 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.) a step of ablating said stack of thin layers (12) in a zone (13) called enameling zone, so as to perform partial ablation of said stack of thin layers (12) in said enameling zone (13), thereby creating a plurality of ablated zones (16) distributed in said enameling zone, (c.) a step of depositing, in the enameling zone, an enamel layer (14) on the surface of the stack of thin layers (12), then (d.) a step of bending the first glass sheet (10), the stack of thin layers (12) located under the enamel layer (14) being totally dissolved by said enamel layer (14) at least at the end of this step.

Description

Method for obtaining curved glazing provided with a stack of thin layers and a layer of enamel, comprising a step of partial removal of the stack

[0001] The invention relates to the field of 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] Examples of glazing include laminated glazing, in which two sheets of glass are adhesively bonded together using a lamination interlayer. This interlayer not only retains 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 face 2, the faces being traditionally numbered starting from the face intended to be positioned on the outside of the vehicle. Face 2 is therefore a face 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 maintaining the pigment particles.The firing step is generally carried out simultaneously with the bending of the glass sheet.

[0006] Coatings, generally in the form of stacks of thin layers, may also be present, for example on one of the glass sheets of laminated glazing. These may in particular be electrically conductive layers, which can provide two types of functionality. On the one hand, when current leads are provided, they can dissipate heat by the Joule effect. These are then heating layers, useful for example for defrosting or demisting. On the other hand, these layers have solar control or low emissivity properties due to their reflection of infrared radiation. The layers are then appreciated for improving thermal comfort or for the energy savings they provide, by reducing consumption for heating or air conditioning. In the case of laminated glazing, these stacks of layers are generally arranged on face 3, therefore also in contact with the lamination interlayer.

[0007] 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. In the case of laminated glazing, the coatings will be protected inside the laminated glazing.

[0008] However, it has been observed that when a glass sheet coated with a stack of thin layers had to be provided with a layer of enamel, undesirable interactions could occur during bending between the stack and the enamel, leading in particular to a degradation of the aesthetic appearance of the enamel. In particular, it has been observed, in particular when the stack contained at least one nitride layer and the enamel contained bismuth, that bubbles were created within the enamel, near the interface between the latter and the stack, 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. As regards the optical appearance, it is difficult to achieve the often desired black shades.

[0009] Several solutions have been proposed to this problem.

[0010] It is possible to remove the entire thin-film stack in advance at the points where the enamel layer is to be deposited, for example by 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 WO0029346 proposed using special glass frits for enameling, which, during firing or pre-firing, are capable of dissolving the stack of thin layers and attaching directly to the glass. However, it turns out that the temperatures required for this dissolution are often high, which can lead to optical distortions of the glass sheet.

[0012] The invention aims to overcome these drawbacks by proposing a process making it possible to achieve good optical, mechanical and chemical properties at lower firing temperatures.

[0013] To this end, the invention relates to a method for obtaining curved glazing, in particular for a windshield or roof of a motor vehicle, comprising the following successive steps: a. providing a first sheet of glass, coated on at least part of one of its faces with a stack of thin layers, b. a step of ablation of said stack of thin layers in a zone called the enameling zone, so as to carry out a partial ablation of said stack of thin layers in said enameling zone by creating a plurality of ablated zones distributed in said enameling zone, c. a step of depositing, in the enameling zone, a layer of enamel on the surface of the stack of thin layers, d. a step of bending the first sheet of glass, the stack of thin layers located under the layer of enamel being completely dissolved by said layer of enamel at least at the end of this step.

[0014] The present description also relates to curved glazing, in particular for a windshield or roof of a motor vehicle, obtained (or capable of being obtained) by this process. This glazing comprises a first sheet of glass coated on at least part of one of its faces with a stack of thin layers, said first sheet of glass being coated on part of its surface with a layer of enamel, said first sheet of glass preferably being laminated with an additional sheet of glass by means of a lamination interlayer and said layer of enamel being turned towards said lamination interlayer.

[0015] The inventors were able to demonstrate that partial laser ablation made it possible, in the area intended to be subsequently enamelled, to facilitate the dissolution of the stack of thin layers by the enamel at a lower temperature.

[0016] In this text, the thin film stack and the enamel layer are collectively referred to as "the coatings".

[0017] Step a)

[0018] The first glass sheet can be flat or curved. The first glass sheet is generally flat at the time of deposition of the thin-film stack and then the enamel layer, and is then curved during step c. The first glass sheet is therefore curved in the final curved glazing.

[0019] 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.

[0020] The first glass sheet may be made of clear glass or tinted glass, preferably tinted glass, for example green, gray or blue. To achieve this, the chemical composition of the first glass sheet advantageously comprises iron oxide, in a weight content ranging from 0.5 to 2%. It may also comprise other coloring agents, such as for example cobalt oxide, chromium oxide, nickel oxide, erbium oxide, or selenium.

[0021] 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.

[0022] The lateral dimensions of the first sheet of glass (and where applicable of the additional sheet of glass which will be discussed later in the text) must be adapted according to those of the glazing (possibly laminated) into which it is intended to be integrated. The first sheet of glass (and / or the additional sheet of glass) preferably has a surface area of ​​at least 1 m².

[0023] The first glass sheet is preferably coated with the stack of thin layers over at least 70%, in particular over at least 90%, or even over the entire surface of the face of the glass sheet. Certain areas may not be coated in order in particular to provide communication windows allowing waves to pass through.

[0024] The stack is preferably coated with the enamel layer over 2 to 25%, in particular 3 to 20%, or even 5 to 15% of its surface. The enamel layer preferably comprises a peripheral band, that is to say a band closed on itself which, from each point of the periphery of the first sheet of glass, extends towards the inside of the first sheet of glass over a certain width, generally variable, typically between 1 and 20 cm depending on the zones of the final glazing.

[0025] 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.

[0026] In this text, the term "contact" means physical contact. The term "based on" preferably means that the layer in question comprises at least 50% by weight of the material in question, in particular 60%, or even 70%, and even 80% or 90%. The layer may even essentially consist of or consist of this material. By "essentially consist" it is meant that the layer may include impurities without influencing its properties. The terms "oxide" or "nitride" do not necessarily mean that the oxides or nitrides are stoichiometric. They may in fact be substoichiometric, superstoichiometric or stoichiometric.

[0027] 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.

[0028] The nitride-based layer preferably has a physical thickness in a range from 2 to 100 nm, in particular from 5 to 80 nm.

[0029] 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.

[0030] 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.

[0031] At least one electroconductive functional layer is advantageously chosen from:- metallic layers, in particular silver or niobium, or even gold, and- layers of a transparent conductive oxide, in particular chosen from indium and tin oxide, doped tin oxides (for example with fluorine or antimony) and doped zinc oxides (for example with aluminum or gallium).

[0032] These layers are particularly appreciated for their low emissivity, which gives the glazing excellent thermal insulation properties. In glazing used in land vehicles, particularly cars, railways, or even aircraft or maritime vehicles, low-emissivity glazing allows part of the solar radiation to be reflected outwards in hot weather, and therefore limits the heating of the passenger compartment of said vehicles, and where appropriate reduces air conditioning costs. Conversely, in cold weather, these glazings help to retain heat within the passenger compartment, and therefore reduce the energy effort required for heating. The same is true for glazing used in buildings.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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).

[0037] The stack of thin layers is preferably deposited by cathode sputtering, in particular assisted by a magnetic field. In this process, a plasma is created under a high vacuum in the vicinity of a target comprising the chemical elements to be deposited. The active species of the plasma, by bombarding the target, tear off said elements, which are deposited on the glass sheet, forming the desired thin layer. This process is called "reactive" when the layer is made of a material resulting from a chemical reaction between the elements torn off the target and the gas contained in the plasma. The major advantage of this process lies in the possibility of depositing a very complex stack of layers on the same line by successively moving the glass sheet under different targets, generally in a single device.

[0038] The aforementioned stacks have electricity conduction and infrared reflection properties useful for providing a heating function (defrosting, demisting) and / or a thermal insulation function.

[0039] 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.

[0040] Step b)

[0041] The (partial) ablation of step b) is preferably a laser ablation. A laser ablation is an ablation treatment that involves treating the thin-film stack using laser radiation. Other possible methods are mechanical (pickling, brushing) or chemical etching.

[0042] Ablation, particularly laser ablation, allows partial ablation of the stack of thin layers in the enameling zone. The term enameling zone means the area intended to be enameled during step c). Step b) is not normally carried out in areas that are not intended to be enameled. However, given industrial constraints, it may happen that there is not an exact match between the area where the ablation is carried out and the area where the enamel is deposited.

[0043] Ablation, particularly laser ablation, generally allows, in the ablated areas, the stacking of thin layers to be completely removed and therefore the surface of bare glass to be restored.

[0044] Preferably, the ablated areas represent a total of 5 to 60%, especially 10 to 30%, of the surface area of ​​the enameling area. This fraction is calculated by dividing the sum of the areas of the ablated areas by the surface area of ​​the enameling area. Too small an area does not significantly reduce the firing temperature required to dissolve the stack. Too large an area requires an unnecessarily long and expensive treatment. The ablated areas are preferably distributed evenly in the area to be enameled.

[0045] The ablated areas preferably have at least one dimension (and even advantageously two dimensions) between 5 and 500 µm, in particular between 10 and 200 µm, or even between 30 and 100 µm. The ablated areas are preferably in the form of points or lines. In the case of points, the dimensions indicated above preferably correspond to the diameter of the points (or to their largest dimensions, it being understood that the points do not necessarily have a perfectly circular shape). The distance between two neighboring ablated areas, in particular between two neighboring points, is preferably between 50 and 600 µm. A greater density of small ablation areas makes it easier for the enamel to subsequently dissolve the stack. The ablated areas in the form of points are easily produced using a laser beam in the form of a spot moved opposite the glass sheet. The size of the spot makes it possible to adjust the dimensions of the ablated areas.

[0046] The laser used in step b) preferably emits radiation in a wavelength between 300 and 1100 nm, in particular between 400 and 800 nm. These wavelengths are less likely to damage the glass because the latter absorbs little in this range. However, other lasers can be used, such as UV lasers (for example excimer lasers) or IR lasers. Whatever the wavelength, the laser can advantageously be a solid-state laser or a fiber laser.

[0047] The laser used in step b) is preferably a pulsed laser, in particular chosen from nanosecond, picosecond and femtosecond lasers. Ultra-short pulse lasers are preferred because they are less likely to damage the glass surface. The repetition rate is preferably between 100 and 1000 kHz, in particular between 200 and 500 kHz. The scanning speed and the repetition rate of the laser make it possible to adjust the distance between the ablated areas. The power of the laser is preferably between 10 and 100 W, in particular between 30 and 80 W.

[0048] Particularly suitable lasers are, for example, Nd:YAG or Nd:YVO4 lasers emitting at 1064 nm, advantageously frequency doubled (emitting at 532 nm) or frequency tripled (emitting at 355 nm), and in particular nanosecond or picosecond pulsed. Fiber lasers emitting at 1062 or 1030 nm have also proven suitable.

[0049] The laser radiation is preferably emitted from the side opposite the face coated by the thin-film stack. The laser beam thus passes through the glass sheet before reaching the thin-film stack. In such a configuration, the laser beam can locally heat the interface between the glass and the stack, resulting in delamination of the latter. Alternatively, the laser radiation can be emitted from the same side as the face coated by the thin-film stack. This alternative is, however, less preferred because it is more likely to damage the glass and generally leads to lower ablation quality.

[0050] Step c)

[0051] In this text, the term "enamel composition" refers to the liquid composition used to deposit a wet enamel layer during step b). The term "enamel layer" is used to describe the layer at each stage of the process, both the wet layer (before any pre-firing, and where appropriate before drying) and the final layer (after firing).

[0052] In step c), the enamel layer is preferably deposited from an enamel composition comprising at least one pigment and at least one glass frit. The enamel composition, like the enamel layer, preferably does not comprise lead oxide.

[0053] 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 if necessary during the pre-firing or firing of the enamel. The medium typically comprises solvents, diluents, oils and / or resins.

[0054] The glass frit is capable of dissolving the underlying layer stack. Preferably, the glass frit is based on bismuth and zinc borosilicate (or borate). In order for the glaze to be able to dissolve the thin layer stack during pre-firing or firing, the bismuth and / or boron contents are preferably higher than those of the glass frits usually used in order to make it more "aggressive" towards the layer stack and to reduce its glass transition temperature.

[0055] 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.

[0056] Advantageously, the enamel composition further comprises refractory particles having a diameter of at least 20 µm in a volume proportion of at least 0.5%, but no particles having a diameter greater than 80 µm.

[0057] Refractory particles are particles whose morphology is not significantly affected during bending. These particles must have a melting or softening temperature well above the temperatures experienced during bending, and must also not be dissolved by the frit. Refractory particles are notably based on metal oxides or metals. Metal oxides are notably simple oxides, such as for example aluminum, zirconium or titanium oxide, or complex oxides such as high-melting glass frits or inorganic pigments (the latter being notably called "complex inorganic colored pigments" or CICP).

[0058] The presence of a sufficient proportion of "large" refractory particles (whose size, also called diameter, is at least 20 µm) also helps prevent the glass sheets from sticking together during bending, or the glass sheet from sticking to the bending tools. Due to their size, large refractory particles create a morphology during bending in which the particles form peaks, with the molten or softened glass frit gathering in the valleys. This size of 20 µm and above is much larger than that of the glass frit and pigments conventionally used.

[0059] 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%.

[0060] Preferably, the enamel composition contains refractory particles with a diameter of at least 30 µm, in particular at least 40 µm, and even at least 50 µm, in the above-mentioned volume proportions.

[0061] Another way to easily detect the presence of large particles is to measure the fineness of the particles using a Hegman gauge (or fineness of grinding gauge). According to this method, the fineness of the enamel composition, measured using a Hegman gauge, is between 20 and 80 µm, particularly between 40 and 60 µm.

[0062] Preferably, the enamel composition does not contain particles (refractory or not) with a diameter greater than 80 µm in order to allow good deposition by screen printing. The presence of such particles can be determined by laser granulometry or using a Hegman gauge.

[0063] Rather than adding refractory particles to the enamel composition, it is possible to deposit, at least on the enamel layer, refractory particles based on oxides, carbides or metals, at least one dimension of which is greater than or equal to 30 µm. The refractory particles are, for example, based on oxides chosen from simple metal oxides, in particular aluminum, titanium or zirconium oxide, and complex oxides, in particular silicates, high-melting glass or glass-ceramic frits or inorganic pigments. The quantity of particles having at least one dimension greater than or equal to 30 µm is preferably at least 0.1 g / m², in particular at least 0.5 g / m². The refractory particles are preferably deposited in a mixture with elements absorbing infrared radiation, in particular chosen from a resin, pigments or carbon black.

[0064] The deposition of the enamel layer is preferably carried out by screen printing. To do this, a screen printing screen is placed on the glass sheet, which includes meshes, some of which are sealed, then the enamel composition is deposited on the screen, then a doctor blade is applied to force the enamel composition to pass through the screen in the areas where the meshes of the screen are not sealed, so as to form a layer of wet enamel. In order to ensure homogeneous deposition of large refractory particles, when the enamel composition contains them, the mesh opening of the screen is preferably at least 40 µm, in particular at least 60 µm, or even at least 70 µm. Too small a mesh opening will trap the particles and prevent their homogeneous deposition, while too large an opening leads to an excessively high enamel thickness which risks weakening the glass mechanically. The mesh opening is preferably at most 100 µm, in particular at most 80 µm.

[0065] Alternatively, the deposition of the enamel layer can be carried out by digital printing, for example by inkjet. This technique is however not suitable when the enamel composition contains large refractory particles as described above.

[0066] The thickness of the wet enamel layer is preferably between 15 and 40 µm, in particular between 20 and 30 µm.

[0067] Step c) 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.

[0068] Step d)

[0069] Bending can be carried out by gravity (the glass deforms under its own weight) or by pressing, at temperatures typically ranging from 550 to 650°C.

[0070] In the case of laminated glazing, several methods of implementation are possible.

[0071] According to a first embodiment, the two sheets of glass (first sheet of glass and additional sheet of glass) are bent separately. In this case, it is important to avoid any sticking between the first sheet of glass and the bending tools.

[0072] According to a second embodiment, the first glass sheet and the additional glass sheet are curved together, the enamel layer facing said additional glass sheet. In this case, it is important to avoid any sticking between the two glass sheets. The glass sheets can be kept apart by placing an interlayer powder between them ensuring a space of a few tens of micrometers, typically 20 to 50 µm. The interlayer powder is, for example, based on calcium and / or magnesium carbonate. During the bending process, the inner glass sheet (intended to be positioned inside the passenger compartment) is normally placed above the outer glass sheet. Thus, during the bending step, the additional glass sheet is placed above the first glass sheet.

[0073] Preferably, after step d), the enamel layer is opaque, black in color. Its clarity L* measured in reflection on the glass side is preferably less than 5. It has been observed that laser ablation makes it possible to reduce the value of the clarity L*, and therefore to obtain a deeper black enamel.

[0074] As previously indicated, the enamel layer advantageously forms a band on the periphery of the first sheet of glass. In this way, the enamel layer is able to conceal and protect against ultraviolet radiation joints, connection elements, or even sensors.

[0075] Optional pre-cooking step (c1)

[0076] The method preferably comprises, between step c) and step d), a step c1) 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.

[0077] This step is particularly useful in the second embodiment previously described, in which the first glass sheet and the additional glass sheet are curved together, with the enamel layer facing the additional glass sheet.

[0078] The dissolution of the thin-film stack by the enamel makes it possible to avoid the aforementioned interactions. The constituent elements of the stack are dissolved in the enamel layer, which is, at least after the bending step (step c), in direct contact with the glass sheet.

[0079] If the enamel layer has not already completely dissolved the stack of thin layers at the end of pre-firing, this total dissolution is obtained during bending, which completes the firing of the enamel.

[0080] 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.

[0081] The pre-baking step is preferably carried out at a temperature between 150 and 800°C, in particular between 500 and 700°C.

[0082] Such pre-firing makes it possible to eliminate the organic medium, or in general any organic component possibly present in the enamel layer.

[0083] During pre-firing, the thin-film stack is preferably 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 d).

[0084] Step e) (optional)

[0085] The method preferably comprises, after step d), a step e) of laminating the first glass sheet with an additional glass sheet by means of a laminating interlayer, so that the enamel layer faces said interlayer.

[0086] The lamination step can be carried out by autoclave treatment, for example at temperatures of 110 to 160°C and under a pressure of 10 to 15 bars. Prior to autoclave treatment, the air trapped between the glass sheets and the lamination interlayer can be removed by calendering or by vacuum.

[0087] 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.

[0088] 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.

[0089] According to a preferred embodiment, the additional glass sheet has a thickness of between 0.5 and 1.2 mm. The additional glass sheet is in particular made of sodium aluminosilicate glass, preferably chemically reinforced. The additional glass sheet is preferably the inner sheet of the laminated glazing. The invention is particularly useful for this type of configuration, for which it is difficult to arrange the stack of thin layers on face 3. Chemical strengthening (also called “ion exchange”) consists of bringing the surface of the glass into contact with a molten potassium salt (for example potassium nitrate), so as to strengthen the surface of the glass by exchanging ions of the glass (here sodium ions) with ions of larger ionic radius (here potassium ions). This ion exchange makes it possible to form compressive stresses on the surface of the glass and over a certain thickness.Preferably, the surface stress is at least 300 MPa, in particular 400 and even 500 MPa, and at most 700 MPa, and the thickness of the compression zone is at least 20 µm, typically between 20 and 50 µm. The stress profile can be determined in a known manner using a polarizing microscope equipped with a Babinet compensator. The chemical toughening step is preferably carried out at a temperature ranging from 380 to 550°C, and for a duration ranging from 30 minutes to 3 hours. The chemical strengthening is preferably carried out after the bending step but before the lamination step. The glazing obtained is preferably a motor vehicle windshield, in particular a heated windshield, the stack of thin layers serving to heat the windshield by the Joule effect.

[0090] According to another preferred embodiment, the additional glass sheet carries on the face opposite the face facing the lamination interlayer (preferably face 4, the additional sheet being the inner sheet) an additional stack of thin layers, in particular a low-emissivity stack, comprising a transparent conductive oxide, in particular indium tin oxide (ITO). The invention is also particularly useful for this type of configuration, for which it is difficult to arrange stacks of thin layers on both faces of the same glass sheet (faces 3 and 4). In this embodiment, the lamination interlayer and / or the additional glass sheet is preferably tinted, the glass sheet carrying the coatings possibly being made of clear glass. The glazing obtained is preferably a motor vehicle roof.

[0091] As an example of this latter preferred embodiment, mention may be made of a laminated curved roof comprising, from the outside of the vehicle, a sheet of clear glass coated on face 2 with a stack of thin layers comprising at least one layer of silver then a layer of enamel, a PVB lamination interlayer (preferably tinted), and an additional glass sheet of tinted glass, carrying on face 4 a stack of low-emissivity thin layers, in particular based on ITO.

[0092] The lamination interlayer preferably comprises at least one sheet of polyvinyl acetal, in particular polyvinyl butyral (PVB).

[0093] The lamination interlayer can be tinted or untinted in order to regulate the optical or thermal properties of the glazing if necessary.

[0094] 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.

[0095] 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.

[0096] The thickness of the lamination interlayer is generally in the range of 0.3 to 1.5 mm, in particular 0.5 to 1 mm. The lamination interlayer may have a thinner thickness on one edge of the glazing than in the center of the glazing in order to avoid the formation of a double image when using a head-up display (HUD) system.

[0097] Examples

[0098] The following exemplary embodiments illustrate the invention in a non-limiting manner, in connection with figures 1 and 2.

[0099] 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.

[0100] The first glass sheet 10 coated with the stack of thin layers 12 is provided in step a. A laser ablation treatment (step b) is then carried out using a laser 15, in order to create ablated areas 16 in the enameling area 13.

[0101] A part of the stack 12, in the enameling zone 13, is coated with a layer of enamel 14, in particular by screen printing (step c).

[0102] The assembly then undergoes pre-firing (step c1), which in the case shown, leads to a partial dissolution of the stack 12 by the enamel 14.

[0103] An additional glass sheet 20, here provided with an additional stack of thin layers 22, is then placed on the first glass sheet 10, the assembly then being curved (step d). The view shown being only that of the end of the glass sheet, the curving is not shown here. The diagram illustrates the fact that at the end of the curving, the enamel 14 has completely dissolved the underlying stack of thin layers 12.

[0104] In step e, the first glass sheet 10 coated with the stack of thin layers 12 and the enamel layer 14 and the additional glass sheet 20 coated with the additional stack 22 are assembled using the lamination interlayer 30. The diagram here represents each of the separate elements, in exploded view.

[0105] represents a scanning electron microscopy image. The black areas are ablated areas in the form of points obtained by irradiating, via the opposite face, a stack of thin films comprising three silver layers protected by zinc oxide layers, silicon nitride layers and NiCr blockers. The laser used was a 60 W picosecond pulsed Nd:YAG laser with a repetition rate of 400 kHz, emitting at 532 nm wavelength a beam in the form of a 70 µm wide spot. As previously indicated, the points are not necessarily perfectly circular.

[0106] First set of examples

[0107] Clear glass sheets 2.1 mm thick, previously sputter-coated with a thin-film stack comprising three silver layers protected by zinc oxide layers, silicon nitride layers and NiCr blockers, were treated as previously described in connection with the. The ablated areas were points with a largest dimension of about 70 µm, extending in lines spaced about 100 µm apart. The ablated areas represent a total of 20% of the surface area of ​​the enameling area.

[0108] The glass sheets were then partially screen-printed with enamel layers with a wet thickness of 25 µm. The enamel layer was deposited by screen printing, and the enamel was then dried (150°C, 1 to 2 minutes). The samples were then placed in a temperature gradient oven for 180 seconds to determine the firing temperature required to achieve an L* value (clarity measured in reflection on the glass side) of 5.

[0109] A clarity of 5 was obtained at a temperature of 615°C in the case of the samples according to the invention. In the absence of a partial ablation step, however, values ​​of 5 were only obtained at temperatures above 640°C. In addition, the value of b* (also in reflection on the glass side) was approximately -0.5 to -1, compared to -2 to -3 in the absence of partial ablation, indicating a purer black. The partial ablation step therefore makes it possible to reduce the firing temperature necessary to achieve a satisfactory optical appearance.

[0110] Second set of examples

[0111] Samples of 500*300 mm² were prepared in the same way as in the first series of examples, except that they were heated in a tempering furnace at 640°C for 180 seconds. The glazed area was in the form of a peripheral frame 75 mm wide. The color in reflection on the glass side for the samples according to the invention was L* = 3.9; a* = -0.25; b* = 0.25. In the absence of a partial ablation step, it was L*= 4.6; a*=-0.3; b* = 0.45. The partial ablation step therefore makes it easier to achieve deeper blacks.

[0112] Third set of examples

[0113] 900*650 mm² blanks were cut to form motor vehicle roofs. The ablation and enameling steps were carried out in the same way as for the previous examples. The enamel was deposited in the form of a peripheral band. The glass sheets were curved by pressing in an industrial furnace, with a pressing tool temperature of 550°C. Eight glass sheets were manufactured and compared with eight sheets that had not undergone laser ablation. The average value of L* for the glazings according to the invention was 5.5, compared to 6.2 for the comparative glazings.

Claims

Method for obtaining curved glazing, in particular for a windshield or roof of a motor vehicle, comprising the following successive steps: a. providing a first sheet of glass (10), coated on at least part of one of its faces with a stack of thin layers (12), b. a step of ablation of said stack of thin layers (12) in a zone (13) called the enameling zone, so as to carry out a partial ablation of said stack of thin layers (12) in said enameling zone (13) by creating a plurality of ablated zones (16) distributed in said enameling zone (13), c. a step of depositing, in the enameling zone (13), an enamel layer (14) on the surface of the stack of thin layers (12), d. a step of bending the first glass sheet (10), the stack of thin layers (12) located under the enamel layer (14) being completely dissolved by said enamel layer (14) at least at the end of this step. The method of claim 1, wherein the ablation step b) is a laser ablation step. Method according to one of the preceding claims, further comprising, after step d), a step e) of laminating said first glass sheet (10) with an additional glass sheet (20) by means of a laminating interlayer (30), so that the enamel layer (14) is facing said interlayer (30). Method according to one of the preceding claims, such that the stack of thin layers (12) comprises at least one functional layer, in particular an electroconductive functional layer chosen from metallic layers, in particular silver or niobium, and layers of a transparent conductive oxide. Method according to one of the preceding claims, in which the ablated zones (16) represent in total 5 to 60%, in particular 10 to 30%, of the surface area of ​​the enameling zone. Method according to one of the preceding claims, in which the ablated zones (16) have at least one dimension between 5 and 500 µm, in particular between 10 and 200 µm. Method according to one of the preceding claims, in which the ablated areas (16) are in the form of points or lines. Method according to one of the preceding claims, in which the distance between two neighboring ablated zones (16) is between 50 and 600 µm. Method according to one of claims 2 to 8, in which the laser (15) used in step b) emits radiation in a wavelength between 300 and 1100 nm, in particular between 400 and 800 nm. Method according to one of claims 2 to 9, in which the laser (15) used in step b) is a pulsed laser, in particular chosen from nanosecond, picosecond and femtosecond lasers. Method according to the preceding claim, in which the repetition rate of the laser (15) is between 100 and 1000 kHz, in particular between 200 and 500 kHz. Method according to one of claims 2 to 11, in which the power of the laser (15) is between 10 and 100 W, in particular between 30 and 80 W. Method according to one of claims 2 to 12, such that in step b) the laser radiation is emitted from the side opposite the face coated by the stack of thin layers (12). Method according to one of the preceding claims, such that after step d, the enamel layer (14) is opaque, black in color, and forms a band at the periphery of the first glass sheet (10). Method according to one of claims 3 to 14, such that:- the method comprises between step c) and step d) a step c1) of pre-firing the enamel layer (14) during which the stack of thin layers (12) located under the enamel layer (14) is at least partially dissolved by said enamel layer (14), and- in step d) the first glass sheet (10) and the additional glass sheet (20) are curved together, the enamel layer (14) being turned towards said additional glass sheet (20).

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