FR3118769A1 - Process for obtaining laminated curved glazing - Google Patents

Abstract

The subject of the invention is a process for obtaining a curved laminated glazing in which (a) a first sheet of glass (10) is provided, coated with a stack of thin layers (12), then (b) , on part of the stack of thin layers (12), an enamel layer (14). Also deposited (c) on at least part of the stack of thin layers (12) and/or on at least part of the enamel layer (14), a sacrificial thermal homogenization layer (16), step c) being able to be carried out before or after step b). The stack of thin layers (12) located under the enamel layer (14) is completely dissolved by said enamel layer (14) and the sacrificial thermal homogenization layer (16) is at least partially eliminated at least after bending (d). After lamination (e) with an additional sheet of glass (20), the enamel layer (14) is turned towards a lamination spacer (30). Fig. 1

Description

Process for obtaining laminated curved glazing

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.

Laminated glazing is glazing in which two sheets of glass are adhesively bonded by means of a lamination insert. 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 burglary resistance or improved acoustic properties.

These glazings often include coatings of various types, intended to impart different properties.

Layers of enamel, generally black and opaque, are often deposited on part of the glazing, usually in the form of a peripheral band intended to conceal and protect against ultraviolet radiation the polymeric seals used to fix and position the glazing on the body bay. Enameled areas also conceal the attachment areas for the interior mirror and various connectors and sensors.

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 insert. The aesthetic appearance of the enamel layer seen from the outside of the vehicle is of particular importance for car manufacturers. 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 point glass, which under the effect of a baking heat treatment softens and adheres to the glass sheet. A mineral layer is thus formed, 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.

In the context of the manufacture of laminated glazing, the two sheets of glass of the glazing are often bent together, the sheet of glass intended to be positioned inside the vehicle generally being arranged above the other sheet of glass, who wears the enamel. In other processes, each sheet of glass is bent separately. In all cases, the enamel must have non-stick properties in order to prevent, during bending, any sticking between the two sheets of glass or between the glass sheet and the bending tools. To do this, glazes containing bismuth are usually used, i.e. obtained from glass frits containing bismuth oxide.

Coatings, generally in the form of stacks of thin layers, may also be present on one of the glass sheets of the laminated glazing. They may in particular be electrically conductive layers, which may provide two types of functionality. The electrically conductive layers can on the one hand, when current leads are provided, dissipate heat by Joule effect. These are then heating layers, useful for example for defrosting or demisting. These layers also have, through 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 insert.

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 glass sheet, and therefore on the same face of the glass sheet in question. so that these coatings are protected inside the laminated glazing.

It has however been observed that when a sheet of glass coated with a stack of thin layers had to be provided with an enamel layer, 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 notably 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 enamel. stacking, causing a significant drop in adhesion of the enamel, modifying its optical appearance (in particular the color on the glass side, that is to say on the side opposite to the enamel) and reducing its chemical resistance, in particular to acids.

Several solutions have been proposed to this problem.

It is possible to remove the stack of thin layers beforehand at the places where the enamel layer must be deposited, for example by means of abrasives, so that the enamel is deposited in direct contact with the glass sheet and avoid any adhesion problems between the enamel layer and the stack of thin layers. However, mechanical abrasion generates visible scratches, including on the enamel layer.

The application WO2014/133929, and before it the application WO0029346 proposed the idea of using for the enamel special glass frits capable during firing or pre-firing of dissolving the stack of thin layers to attach directly to glass. However, such enamels do not have good anti-adhesive properties, leading during bending to sticking of the two glass sheets together or to sticking of the glass sheet with the bending tools.

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

It has also been observed that the simultaneous presence, on the same sheet of glass, of an enamelled zone and electrically conductive layers could lead to undesirable deformation of the glass during heat treatments, in particular pre-firing. These deformations on line can affect the movement of the glass sheet on the conveyors and/or its gripping by robotic machines.

The object of the invention is to obviate these various disadvantages.

To this end, the subject of the invention is a process for obtaining a curved laminated glazing, in particular for the windshield or roof of a motor vehicle, comprising the following steps:
To. 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 depositing, on part of the surface of the stack of thin layers, a layer of enamel,
vs. a step of depositing, on at least part of the stack of thin layers and/or on at least part of the enamel layer, a sacrificial thermal homogenization layer, step c) being able to be carried out before or after step b), then
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 and the sacrificial thermal homogenization layer being at least partially eliminated at least at the end of this step, then
e. a step of laminating said first sheet of glass with an additional sheet of glass by means of a lamination insert, so that the enamel layer faces towards said insert.

The invention also relates to a curved laminated glazing, in particular for the 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 and a layer of enamel, said first sheet of glass being laminated with an additional glass sheet at the means of a lamination spacer, so that the enamel layer faces said spacer.

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 d), sometimes before, in direct contact with the glass sheet. The sacrificial layer of thermal homogenization makes it possible to avoid the appearance of the aforementioned deformations. The use of a sacrificial layer of thermal homogenization, when it is deposited on the enamel layer, also makes it possible to improve the aesthetics of the latter.

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

Step a

The first sheet of glass can be flat or curved. The first sheet of glass is generally flat when the stack of thin layers is deposited, then the enamel layer, and is then curved during step d. The first sheet of glass is therefore curved in the curved laminated glazing according to the invention.

The glass of the first glass sheet is typically a silico-soda-lime glass, but other glasses, for example borosilicates or aluminosilicates can also be used. The first sheet of glass is preferably obtained by floating, that is to say by a process consisting in pouring molten glass onto a bath of molten tin.

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

The first sheet of glass preferably has a thickness comprised in a range ranging 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.

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

The first sheet of glass 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.

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 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.

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.

By “contact”, we mean in this text a physical contact. The expression “based on” preferably means the fact that the layer in question comprises at least 50% by weight of the material considered, in particular 60%, even 70% and even 80% or 90%. The layer may even essentially consist or consist of this material. By “essentially consist”, it should be understood that the layer can comprise impurities without influence on its properties. The terms "oxide" or "nitride" do not necessarily mean that the oxides or nitrides are stoichiometric. They can indeed be under-stoichiometric, over-stoichiometric or stoichiometric.

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 layer based on a nitride is a layer based on silicon nitride, more particularly a layer consisting essentially of a silicon nitride. When the silicon nitride layer is deposited by sputtering, it generally contains aluminum, because it is customary to dope silicon targets with aluminum in order to accelerate the deposition rates.

The layer based on a nitride preferably has a physical thickness comprised in a range ranging from 2 to 100 nm, in particular from 5 to 80 nm.

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

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 layers of oxides or oxynitrides.

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

These layers are particularly appreciated for their low emissivity, which gives the glazing excellent thermal insulation properties. In the glazing fitted to land vehicles, in particular automobiles, railways, or even air or maritime vehicles, low-emission glazing makes it possible in hot weather to reflect part of the solar radiation outwards, and therefore to limit the heating of the passenger compartment of said vehicles, and if necessary to reduce air conditioning costs. Conversely, in cold weather, these glazings allow the heat to be retained within the passenger compartment, and therefore reduce the energy cost of heating. It is the same in the case of the glazing equipping the buildings.

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, in particular between 3 and 40 nm.

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

In order to protect the or each electroconductive 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.

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).

The stack of thin layers is preferably deposited by sputtering, in particular assisted by 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 from 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 scrolling the glass sheet under different targets, generally in a single device.

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

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

Step b

In the present text, the term "enamel composition" refers to the liquid composition which is used to deposit a layer of wet enamel during step b. The term "enamel layer" is used to qualify the layer at each stage of the process, both the wet layer (before pre-firing, if necessary before drying) and the final layer (after firing).

During step b, 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 include lead oxide.

The enamel composition generally also 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 eliminated during the pre-baking or the baking of the enamel. 'E-mail. The medium typically includes solvents, thinners, oils and/or resins.

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

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.

In order to ensure that there is no sticking during bending, the deposition of the enamel layer is preferably carried out by screen printing an enamel composition comprising 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.

“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 not be dissolved by the frit either. 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 glass frits with a high melting point or inorganic pigments (the latter being in particular called “complex inorganic color pigments” or CICPs).

It has been observed that the enamel composition must include a sufficient proportion of "large" refractory particles (therefore the size, also called diameter, is at least 20 µm) in order to prevent any sticking of the glass sheets between them. during bending or of the glass sheet with the bending tools. Due to their size, the large refractory particles create during bending a morphology in which the particles form peaks, the molten or softened glass frit gathering in the valleys. This size of 20 μm and more is much greater than that of the glass frit and the pigments conventionally used.

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%.

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 volume proportions mentioned above.

Another way to characterize the enamel composition, and to easily detect the presence of large particles, consists in measuring 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, in particular between 40 and 60 µm.

The enamel composition should not normally contain particles (refractory or not) with a diameter greater than 80 µm in order to allow deposition by screen printing. The presence of such particles can be determined by laser granulometry or using a Hegman gauge.

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 composition enamel to pass through the screen in areas where the screen meshes are not sealed, so as to form a layer of moist enamel. In order to ensure a homogeneous deposition of large refractory particles, the mesh size of the screen is preferably at least 40 μm, in particular at least 60 μm, or even at least 70 μm. A mesh opening that is too small will trap the particles and prevent their homogeneous deposition, while an opening that is too large leads to too high an enamel thickness which risks weakening the glass mechanically. The mesh opening is preferably at most 100 μm, in particular at most 80 μm.

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

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

Step c

The sacrificial thermal homogenization layer (also called sacrificial layer) makes it possible during bending or during any pre-firing, described in more detail below, to homogenize the temperature experienced in the different zones of the glass sheet. , those coated with enamel and those coated by stacking thin layers. The inventors were able to demonstrate that this layer also made it possible, when it is deposited on the enamel layer, to achieve darker shades, that is to say to reduce the value of L* after firing .

In a first embodiment, step c) is carried out after step b) and in step c) the sacrificial thermal homogenization layer is deposited on at least part of the enamel layer.

In this first mode, the sacrificial layer is preferably deposited on the entire glass sheet, therefore on the entire enamel layer and the stack of thin layers. Alternatively, the sacrificial layer may be deposited only on the enamel layer and on the zone of the stack of thin layers located close to the enamel layer. The sacrificial layer can also be deposited only on the enamel layer (on part or all).

In a second embodiment, step c) is carried out before step b) and in step c) the sacrificial thermal homogenization layer is deposited on a part (in particular on the part) of the stack of thin layers which is not intended to be covered by the enamel layer.

The sacrificial layer is preferably deposited by depositing a fluid, in particular liquid, composition. It can be deposited by all kinds of techniques, in particular by screen printing, by spraying, by roller, by curtain, by digital printing or even by pad printing.

The thickness of the sacrificial layer is preferably between 100 nm and 80 μm, in particular between 1 μm and 30 μm, or even between 5 μm and 20 μm.

The sacrificial thermal homogenization layer preferably comprises a resin and/or elements that absorb infrared radiation. It advantageously comprises a resin and elements that absorb infrared radiation.

Preferably, the sacrificial layer absorbs part of the infrared radiation. For this purpose, it advantageously comprises (as an element absorbing infrared radiation) pigments, in particular black pigments, or carbon black. The pigments preferably comprise one or more oxides chosen from chromium, copper, iron, manganese, cobalt and nickel oxides. Carbon black is preferred because of its ability to be further eliminated by combustion during pre-firing or bending.

The sacrificial layer can, alternatively or cumulatively, reflect part of the infrared radiation. It can then comprise pigments that reflect infrared radiation, in particular titanium dioxide pigments.

In order to facilitate the deposition of the sacrificial layer and so that it can withstand various manipulations or handling, for example conveying or contact with tools, the sacrificial layer preferably comprises a resin. The resin then acts as a binder making it possible to temporarily fix the sacrificial layer to the glass sheet. The resin also plays a role of thermal homogenization through its combustion during pre-curing or bending. The sacrificial layer can therefore be made of resin.

According to one embodiment, the sacrificial layer comprises a resin and refractory mineral compounds, for example pigments, or compounds liable to leave residues, and the complete elimination of the sacrificial layer is carried out after the bending step or after the pre-cooking step, in particular by washing and/or brushing.

According to another embodiment, the sacrificial layer comprises a resin and combustible mineral compounds, the elimination of the sacrificial layer being carried out simultaneously with the bending or with the pre-baking. In this case, the combustible compounds are eliminated by combustion during bending or pre-firing. By “combustible” minerals, it is in fact meant that these compounds are capable of burning during bending or pre-firing.

In both cases, the resin will generally be eliminated either during the bending, or if necessary, before the bending, by the pre-curing treatment.

The resin content in the sacrificial layer is preferably at least 10% by weight, or at least 20% and/or at most 60% by weight.

The resin can in particular be chosen from acrylic resins, epoxy resins, alkyd resins and polyurethane resins, alone or as a mixture, in aqueous or solvent phase. Copolymers of these different polymers can also be used. The resin can be in aqueous or solvent phase, with a dry extract content typically between 20 and 80%, in particular between 30 and 70% by weight.

The resin may be a resin that crosslinks under ultraviolet radiation, in particular based on (meth)acrylates and optionally on a photo-initiator; resin without solvent, or optionally in aqueous or solvent phase. The resin may not be cured if the glass sheet does not need to be handled between the application of the sacrificial layer and the bending or pre-baking heat treatment. Otherwise, it is preferable to provide a step of drying by ultraviolet radiation.

The resin can be a latex, that is to say in the form of an aqueous dispersion or emulsion. Drying can take place in air or in the oven, but the drying step can be omitted if the glass sheet does not need to be handled between the application of the sacrificial layer and the bending heat treatment or pre-cooking.

The resin can be a thermoplastic resin, for example a thermofusible resin (hot-melt) or a thermoplastic elastomer, for example an SEBS (polystyrene-b-poly(ethylene-butylene)-b-polystyrene) copolymer.

The resin may be the resin of an organic medium for enamel composition.

In a particularly preferred mode, the sacrificial layer comprises carbon black in an organic medium for enamel composition.

The sacrificial layer is at least partially eliminated at least at the end of the bending step, that is to say that at the end of the bending step at least part of the sacrificial layer does not exist more. It may even have been completely eliminated before the end of the bending step. It may also have been partially or totally eliminated before the start of the bending step, in particular in the case of pre-curing.

According to one embodiment, the method comprises a pre-baking step denoted c1, detailed below, and the sacrificial layer is at least partially eliminated during this pre-baking step. In the case where the sacrificial layer comprises a resin, the resin is for example totally eliminated during the pre-baking. The sacrificial layer can even be completely eliminated during this step, so that the sacrificial layer no longer exists at the start of the subsequent bending step.

According to another embodiment, the method does not include a pre-baking step and the sacrificial layer is then at least partially (or even totally) eliminated during the bending.

If the sacrificial layer has left residues, in particular mineral residues, at the end of the bending step, it is important to remove them, for example by washing, before the lamination step.

Step d

The 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.

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.

According to a second embodiment, the first glass sheet and the additional glass sheet are bent together, the enamel layer being turned towards said additional glass sheet. In this case, it is important to avoid any sticking between the two sheets of glass. The glass sheets can be kept at a distance by placing between them an intermediate powder providing a space of a few tens of micrometers, typically 20 to 50 μm. The intermediate powder is for example based on calcium carbonate and/or magnesium. During bending, 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.

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. As indicated above, it advantageously forms a band at the periphery of the first sheet of glass. In this way, the enamel layer is able to hide and protect joints, connectors and even sensors against ultraviolet radiation.

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

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

Optional pre-cooking step (c1)

The method preferably comprises, between step c) and step d) or, when step b) is carried out after step c), between step b) and step d), a step c1) pre-baking of the enamel layer during which the stack of thin layers located under the enamel layer is at least partially dissolved by said enamel layer and the sacrificial thermal homogenization layer is at least partially eliminated.

This step is particularly useful in the second embodiment described above, in which the first sheet of glass and the additional sheet of glass are bent together, the enamel layer being facing said additional sheet of glass.

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

Such a pre-baking makes it possible to eliminate the organic medium, or in general any organic component possibly present in the enamel layer.

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 glaze or stack, the stack may even be completely dissolved by the glaze layer during pre-firing. Alternatively, it may be only partially dissolved during the pre-firing, and it is then completely dissolved during the bending (step d).

Step e

The lamination step can be carried out by treatment in an autoclave, for example at temperatures of 110 to 160° C. and under a pressure ranging from 10 to 15 bars. Prior to the autoclave treatment, the air trapped between the glass sheets and the lamination insert can be eliminated by calendering or by depression.

As said previously, the additional sheet is preferably the inner sheet of the laminated glazing, that is to say 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.

The additional glass sheet can be made of silico-soda-lime glass, or even of borosilicate or aluminosilicate glass. It can be clear or tinted glass. Its thickness is preferably between 0.5 and 4 mm, in particular between 1 and 3 mm.

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 sheet of glass 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. The chemical reinforcement (also called "ion exchange") consists in bringing the surface of the glass into contact with a molten potassium salt (for example potassium nitrate), so as to reinforce the surface of the glass by exchanging ions of the glass (here sodium ions) by ions of greater ionic radius (here potassium ions). This ionic 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 implemented at a temperature ranging from 380 to 550° C., and for a duration ranging from 30 minutes to 3 hours. The chemical reinforcement 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.

According to another preferred embodiment, the additional glass sheet carries on the face opposite the face facing the lamination insert (preferably face 4, the additional sheet being the inner sheet) a stack of additional thin layers, in particular a stack with low emissivity, comprising a conductive transparent oxide, in particular indium tin oxide (ITO). The invention is also particularly useful for this type of configuration, for which it is tricky to arrange stacks of thin layers on both sides of the same sheet of glass (side 3 and 4). In this embodiment, the lamination insert 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.

As an example of this latter preferred embodiment, mention may be made of a domed laminated roof comprising, from outside 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 tinted PVB lamination spacer, and an additional sheet of tinted glass glass, carrying on face 4 a stack of low-emissivity thin layers, in particular based on ITO.

The lamination interlayer preferably comprises at least one sheet of polyvinylacetal, in particular of polyvinylbutyral (PVB).

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

The lamination insert can advantageously have sound absorption properties in order to absorb sounds of aerial or solid-borne origin. It may in particular consist for this purpose of three polymeric sheets, including two so-called outer PVB sheets framing an inner polymeric sheet, optionally made of PVB, of lower hardness than that of the outer sheets.

The lamination insert can also have thermal insulation properties, in particular for reflecting infrared radiation. It may for this purpose comprise a coating of thin layers with low emissivity, for example a coating comprising a thin layer of silver or an alternating coating of dielectric layers of different refractive indices, deposited on an internal PET sheet flanked by two external PVB sheets.

The thickness of the lamination insert is generally within a range ranging from 0.3 to 1.5 mm, in particular from 0.5 to 1 mm. The lamination insert 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 vision system, known as HUD ( head-up display).

Examples

The examples of embodiment which follow illustrate the invention in a non-limiting manner, in connection with FIGS. 1 and 2.

schematically illustrates an embodiment of the method according to the invention, in which step c) is carried out after step b).

schematically illustrates another embodiment of the method according to the invention, in which step c) is carried out before step b).

These figures represent a schematic section of part of the glass sheets and of the elements deposited on the glass sheets, near their periphery. The various elements are obviously not represented to scale, so as to be able to visualize them.

In the embodiment of the , step b) is carried out before step c). The first sheet of glass 10 coated with the stack of thin layers 12 is provided in step a), then part of the stack 12 is coated with a layer of enamel 14, in particular by screen printing (step b).

The glass sheet is then coated with a sacrificial thermal homogenization layer 16 (step c).

The assembly then undergoes pre-firing (step c1), which in the case shown, leads to partial dissolution of the stack 12 by the enamel 14 and the elimination of the sacrificial layer 16.

An additional sheet of glass 20, here provided with a stack of additional thin layers 22, is then placed on the first sheet of glass 10, the assembly then being bent (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.

As an alternative to this embodiment, the first glass sheet 10 is not bent with the additional glass sheet 20 and the pre-baking step c1 is not implemented.

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 insert 30. The diagram here shows each of the separate elements, in exploded view.

In the embodiment illustrated by the , step c) is implemented before step b). The sacrificial layer 16 is therefore deposited on the stack of thin layers 12, but only in the part (known as “clear of sight”) which will not be covered by the enamel layer 14 in step b) which follows.

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

The enamel composition included large refractory oxide particles having a size greater than 20 µm. The enamel layer was deposited using a screen with a mesh size of 71 µm.

The enamel was then dried (150°C, 1 to 2 minutes).

A sacrificial layer comprising 90% by weight of organic medium for enamel composition (Ferro 80 1026) and 10% by weight of carbon black particles was then deposited on one half of the enamel layer.

The whole was then pre-fired at temperatures ranging from 500 to 600°C.

After this pre-curing, the aesthetics, more particularly the black color seen from the "glass" side, was evaluated by measuring the clarity L* in reflection (illuminant D65, reference observer 10°).

In the areas where the sacrificial layer was deposited, the enamel had a lower L* value. For example, for a pre-bake temperature of 560°C, the value of L* was 5.0 in the zone where the sacrificial layer was present, and 7.5 in the zone where it was absent.

Claims (12)

Process for obtaining a curved laminated glazing, in particular for the windshield or roof of a motor vehicle, comprising the following steps:
To. the supply of 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 depositing, on part of the surface of the stack of thin layers (12), a layer of enamel (14),
vs. a step of depositing, on at least part of the stack of thin layers (12) and/or on at least part of the enamel layer (14), a sacrificial thermal homogenization layer (16) , it being possible for step c) to be carried out before or after step b), then
d. a step of bending the first sheet of glass (10), the stack of thin layers (12) located under the enamel layer (14) being completely dissolved by said enamel layer (14) at least from this step and the sacrificial thermal homogenization layer (16) being at least partially removed at least at the end of this step, then
e. a step of laminating said first sheet of glass (10) with an additional sheet of glass (20) by means of a lamination insert (30), so that the enamel layer (14) faces said insert (30). Method according to claim 1, such that the stack of thin layers (12) comprises at least one functional layer, in particular an electrically conductive functional layer. Process according to the preceding claim, 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 oxide and tin, doped tin oxides and doped zinc oxides. 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 on the periphery of the first sheet of glass (10). Method according to one of the preceding claims, in which the deposition of the enamel layer (14) is carried out by screen printing an enamel composition comprising 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. Method according to the preceding claim, in which the refractory particles are based on metal oxides or metals. Method according to one of the preceding claims, in which step c) is carried out after step b) and in which, in step c), the sacrificial thermal homogenization layer (16) is deposited on at least part of the enamel layer (14). Process according to one of Claims 1 to 6, in which step c) is carried out before step b) and in which, in step c), the sacrificial thermal homogenization layer (16) is deposited on a part of the stack of thin layers (12) which is not intended to be covered by the enamel layer (14). Method according to one of the preceding claims, in which the sacrificial thermal homogenization layer (16) comprises a resin and/or elements which absorb infrared radiation. Method according to one of the preceding claims, such as:
- the method comprises, between step c) and step d) or, when step b) is carried out after step c), between step b) and step d), a step c1 pre-baking of 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 the sacrificial thermal homogenization layer (16) is at least partially eliminated,
- in step d) the first glass sheet (10) and the additional glass sheet (20) are bent together, the enamel layer (14) facing said additional glass sheet (20). Method according to one of the preceding claims, in which the additional glass sheet (20) bears, on the face opposite the face facing the lamination insert (30), a stack of additional thin layers (22), in particular a low-emissivity stack comprising a conductive transparent oxide. Curved laminated glazing, in particular for the windshield or roof of a motor vehicle, obtained by the process of one of the preceding claims, comprising a first sheet of glass (10) coated on at least part of one of its faces with a stack of thin layers (12) and an enamel layer (14), said first glass sheet (10) being laminated with an additional glass sheet (20) by means of a lamination insert (30) , so that the enamel layer (14) faces said spacer (30).