A method for obtaining a curved glazing unit with a stack of thin films and an enamel layer, comprising a step of partial removal of the stack.

Abstract

The invention relates to a method for obtaining curved glazing comprising (a) supplying a first sheet of glass (10), coated on at least part of one of its faces with a stack of thin films (12), (b) a step of removing said stack of thin films (12) in an area (13) referred to as the enameling zone, so as to achieve partial removal of said stack of thin films (12) in said enameling zone (13) by creating a plurality of ablated areas (16) distributed within said enameling zone, (c) a step of depositing, in the enameling zone, a layer of enamel (14) onto the surface of the stack of thin films (12), and then (d) a step of curving the first sheet of glass (10), the stack of thin films (12) located beneath the enamel layer (14) being completely dissolved by said enamel layer (14) at least at the end of this step.

Description

Title of the invention: Method for obtaining curved glazing provided with a stack of thin layers and a layer of enamel, comprising a step of partial ablation 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] The glazings are, for example, laminated glazings, 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.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 the laminated glazing. These may in particular be electrically conductive layers, which may provide two types of functionality. On the one hand, when current leads are provided, they 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. 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] 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. In the case of laminated glazing, the coatings will be protected inside the laminated glazing.

[0008] 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, 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 black shades often desired.

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

[0010] It is possible to remove the entire stack of thin layers beforehand 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 enameling, which are capable of dissolving the stack of thin layers during firing or pre-firing 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 method making it possible to achieve good optical, mechanical and chemical properties at lower cooking 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. the 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 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 enamel layer being completely dissolved by said enamel layer at least at the end of this step.

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

[0016] In this text, the stack of thin layers and the enamel layer are collectively referred to as “the coatings”.

[0017] Step a)

[0018] 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 glazing according to the invention.

[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 to say 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 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 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 glass sheet (and where appropriate of the additional glass sheet which will be discussed in the remainder of the text) are to be adapted according to those of the glazing (possibly laminated) 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.

[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 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 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] By "contact" is meant in the present text a physical contact. By the expression "based on" is preferably meant the fact that the layer in question comprises at least 50% by weight of the material considered, in particular 60%, or even 70% and even 80% or 90%. The layer may even essentially consist or consist of this material. By "essentially consist", it is to 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.

[0027] 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 silicon and zirconium nitride, or a silicon and aluminum nitride. Preferably, the nitride-based layer is a silicon nitride-based layer, more particularly a layer consisting essentially of a silicon nitride. When the silicon nitride layer is deposited by sputtering, it generally contains aluminum, since it is common practice to dope silicon targets with aluminum in order to accelerate deposition rates.

[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 the 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, 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).

[0032] 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.

[0033] According to a preferred embodiment, the stack of thin layers comprises at least one layer of silver, in particular one, two or three, or even four layers of silver. 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, especially 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 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).

[0037] The stack of thin layers is preferably deposited by cathode sputtering, in particular assisted by a magnetic field. In this method, 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 method 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 method lies in the possibility of depositing on the same line a very complex stack of layers 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 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.

[0040] Step b)

[0041] The (partial) ablation of step b) is preferably a laser ablation. A laser ablation is an ablation treatment which implements a treatment of the stack of thin layers by means of laser radiation. Other possible methods are mechanical etching (stripping, brushing) or chemical etching.

[0042] Ablation, particularly laser, makes it possible to achieve partial ablation of the stacking of thin layers in the enameling area. The enameling area is understood to mean the area intended to be enameled in step c). Step b) is not normally carried out in areas which 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 makes it possible, in the ablated areas, to completely remove the stacking of thin layers and therefore to restore the surface of bare glass.

[0044] Preferably, the ablated areas represent a total of 5 to 60%, in particular 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 allow the firing temperature required to dissolve the stack to be significantly reduced. Too large an area requires an unnecessarily long and expensive treatment. The ablated areas are preferably distributed uniformly in the area to be enameled.

[0045] The ablated zones 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 zones 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 zones, in particular between two neighboring points, is preferably between 50 and 600 μm. A greater density of small ablation zones makes it easier for the enamel to subsequently dissolve the stack. The ablated zones in the form of points are easily produced using a laser beam in the form of a spot moved opposite the glass sheet.The spot size allows you 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. Other lasers can however 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 surface of the glass. 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 lasers allow the distance between the ablated areas to be adjusted. The laser power is preferably between 10 and 100 W, particularly 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 even 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 stack of thin layers. The laser beam thus passes through the glass sheet before reaching the stack of thin layers. In such a configuration, the laser beam makes it possible to locally heat the interface between the glass and the stack, causing delamination of the latter. The laser radiation can alternatively be emitted from the same side as the face coated by the stack of thin layers. This alternative is, however, less preferred because it is more likely to damage the glass and generally leads to lower ablation quality.

[0050] Step cl

[0051] 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 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 to the latter, and which is removed where appropriate 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 enamel to be capable of dissolving 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 chosen from oxides of chromium, copper, iron, manganese, cobalt and nickel. Examples include 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] 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, zirconium or titanium oxide, or complex oxides such as high-melting glass frits or inorganic pigments (the latter being in particular 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 makes it possible to prevent the glass sheets from sticking together during bending, or the glass sheet from sticking with the bending tools. Due to their size, the 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.

[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 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.

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

[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 into 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 pm. 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, glass or glass-ceramic frits with a high melting point or inorganic pigments. The quantity of particles having at least one dimension greater than or equal to 30 pm 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 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 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 pm, in particular at most 80 pm.

[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 in particular be carried out by gravity (the glass deforming under its own weight) or by pressing, at temperatures typically ranging from 550 to 650°C.

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

[0071] According to a first embodiment, the two glass sheets (first glass sheet and additional glass sheet) are bent separately. In this case, it is important to avoid any sticking between the first glass sheet 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 curving, the inner glass sheet (intended to be positioned inside the passenger compartment) is normally placed above the outer glass sheet. Thus, during the curving 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 indicated previously, the enamel layer 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.

[0075] Optional pre-cooking step (cl)

[0076] The method preferably comprises, between step c) and step d), a step cl) 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, the enamel layer being turned towards the additional glass sheet.

[0078] The dissolution of the stack of thin layers 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 at the end of 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 the pre-firing, this total dissolution is obtained during the bending, which completes the firing of the enamel.

[0080] 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.

[0081] The pre-cooking 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 stack of thin layers 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 is facing 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 the autoclave treatment, the air trapped between the glass sheets and the lamination interlayer can be removed by calendering or by vacuum.

[0087] 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.

[0088] 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.

[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 reinforcement (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 pm. 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 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 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 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.

[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 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.

[0097] Examples

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

[0099] [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.

[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 zones 16 in the enameling zone 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 bending is not shown here. The diagram illustrates the fact that at the end of the bending, the enamel 14 has completely dissolved the underlying stack of thin layers 12.

[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] [Fig.2] 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 layers 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 under 70 pm wide spot shape. As noted earlier, the spots are not necessarily perfectly circular.

[0106] First series of examples

[0107] Clear glass sheets 2.1 mm thick, previously coated by sputtering with a stack of thin layers comprising three silver layers protected by zinc oxide layers, silicon nitride layers and NiCr blockers, were treated as previously described in connection with [Fig. 2]. The ablated areas were points whose largest dimension was about 70 pm, extending along lines spaced about 100 pm apart. The ablated areas represent a total of 20% of the surface area of ​​the enameling area.

[0108] The glass sheets were then partially coated by screen printing with enamel layers with a wet thickness of 25 μm. The deposition of the enamel layer was carried out by screen printing, then the enamel was dried (150°C, 1 to 2 minutes). The samples were then introduced into a temperature gradient oven for a period of 180 seconds in order to determine the firing temperature necessary 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. Furthermore, 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 series 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 enameled 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 series of examples

[0113] 900*650 mm2 primitives 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 strip. The glass sheets were curved by pressing in an industrial furnace, with a pressing tool temperature of 550°C. Eight glass sheets were made bricked and compared to 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

Claims

1. 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 glass sheet (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.

2. The method of claim 1, wherein the ablation step b) is a laser ablation step.

3. 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).

4. 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.

5. 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 of the enameling zone.

6. Method according to one of the preceding claims, in which the ablated zones (16) have at least one dimension between 5 and 500 pm, in particular between 10 and 200 pm.

7. Method according to one of claims 2 to 6, in which the laser (15) used in step b) emits radiation in a wavelength between 350 and 1100 nm.

8. Method according to one of claims 2 to 7, in which the laser (15) used in step b) is a pulsed laser, in particular chosen from nanosecond, picosecond and femtosecond lasers.

9. Method according to one of claims 2 to 8, such that in step b) the laser radiation is emitted from the side opposite the face coated by the stack of thin layers (12).

10. 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).

11. Method according to one of claims 3 to 10, such that: - the method comprises between step c) and step d) a step cl) 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).

12. Curved glazing, in particular for a windshield or roof of a motor vehicle, obtained by the method of one of the preceding claims, comprising a first glass sheet (10) coated on at least part of one of its faces with a stack of thin layers (12), said first glass sheet (10) being coated on part of its surface with an enamel layer (14), said first glass sheet (10) preferably being laminated with an additional glass sheet (20) by means of a lamination interlayer (30) and said enamel layer (14) being turned towards said lamination interlayer (30).

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