A glass sheet coated with a stack of thin layers and an enamel layer

Abstract

The present invention is directed to a material comprising a glass sheet coated over at least a portion of one of its faces with a stack of thin layers, said stack being coated over at least a portion of its surface with a bismuth-free enamel layer, said enamel layer being coated with a non-stick layer.

Description

Technical Field

[0001] The present invention relates to the field of materials comprising a glass sheet coated with a stack of thin layers and an enamel layer. Such materials are particularly intended to be incorporated into curved laminated glazing for automotive applications, such as roofs or windshields.

Background Art

[0002] Laminated glazing is glazing in which two glass sheets are adhesively joined using an intermediate layer of the laminate. The intermediate layer, in particular, makes it possible to retain the glass fragments in the event of breakage, but also provides other functionalities, particularly from the viewpoints of durability against intrusion and improvement of acoustic properties.

[0003] These glazings often include various types of coatings aimed at imparting various properties.

[0004] An enamel layer, generally black and opaque, is often applied over part of the glazing in the form of a peripheral strip intended to hide the polymer seal that generally serves to fix and position the glazing in the body opening and to protect it from ultraviolet radiation. The enamel-coated zone also hides the fixing zone of the interior rearview mirror and various connectors and sensors.

[0005] In laminated glazing, these enamel layers are generally arranged on side 2, which is conventionally numbered from the side intended to be positioned outside the vehicle. Side 2 is thus the side in contact with the intermediate layer of the laminate. The aesthetic appearance of the enamel layer visible from outside the vehicle is of particular importance to automobile manufacturers. Enamel is generally obtained by firing a composition containing glass frit and pigments at temperatures above 500 °C. The glass frit consists of fine particles of glass with a low melting point, which soften under the influence of the firing heat treatment and adhere to the glass sheet. An inorganic layer is thus formed that adheres perfectly to the glass while retaining the pigment particles, has high chemical resistance and mechanical strength, and is generally opaque. The firing process is generally carried out simultaneously with the bending of the glass sheet.

[0006] In the context of the manufacture of laminated glazing, the two glass sheets of the glazing are curved together, and the glass sheet intended to be positioned inside the vehicle is generally placed on top of the other glass sheet, which has enamel. At that time, it is necessary for the enamel to have non-sticking properties in order to prevent any adhesion between the two glass sheets during bending. For this purpose, an enamel containing bismuth, i.e., an enamel obtained from a glass frit containing bismuth oxide, is usually used.

[0007] Coatings that are generally in the form of stacks of thin layers can also be present on one of the laminated glazing glass sheets. They can in particular be conductive layers, which can provide two types of functionality. On the one hand, when the supply of current is prepared, the conductive layer can dissipate heat by the Joule effect. It is then a heating layer, useful for example for defrosting or anti-fogging. On the other hand, these layers have solar control or low emissivity properties because they reflect infrared radiation. The layer is then highly valued for improving thermal comfort or for the energy savings brought about by the layer by reducing consumption for heating and air conditioning purposes. The stack of these layers is generally arranged on face 3 of the laminated glazing and thus also in contact with the intermediate layer of the laminate.

[0008] However, in certain cases, which will be described in detail later, it may be of interest to place the enamel layer and the stack of thin layers on the same glass sheet and thus on the same face of the glass sheet in question, so that these coatings are protected inside the laminated glazing.

[0009] However, when the glass sheet coated with a stack of thin layers has to be provided with an enamel layer containing bismuth (and thus non-stick), an unfavourable interaction was observed to occur between the stack and the enamel during bending, leading in particular to a deterioration of the aesthetic appearance of the enamel. In particular, when the stack contains at least one nitride layer, bubbles are created inside the enamel, near the interface between the enamel and the stack, inducing a significant decrease in the adhesion of the enamel, changing its optical appearance (especially the colour on the glass side, i.e. the side opposite the enamel), and reducing its chemical resistance, especially acid resistance.

[0010] A number of solutions have been proposed to this problem.

[0011] Since the enamel is applied in direct contact with the glass sheet and to avoid any adhesion problems between the enamel layer and the stack of thin layers, it is possible to pre-remove the stack of thin layers from the location where the enamel layer has to be applied, for example using an abrasive. However, mechanical polishing causes visible scratches, including on the enamel layer.

[0012] WO 2014 / 133929 proposes the idea of using a special glass frit for the enamel that can melt the stack of thin layers in order to be directly fixed to the glass during firing. Such a method is however costly.

[0013] Regarding WO 2019 / 106264, it is proposed to modify the stack of thin layers by adding an oxide layer between the stack and the enamel containing bismuth.

Prior Art Documents

Patent Documents

[0014]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0015] The object of the present invention is to propose a simpler and less costly solution to the above problems.

Means for Solving the Problems

[0016] For this purpose, the present invention is directed to a material comprising a glass sheet, which glass sheet is coated over at least a part of one of its faces with a stack of thin layers, said stack being coated over at least a part of its surface with an enamel layer that does not contain bismuth, said enamel layer being coated with a non-stick layer.

[0017] The present invention is also directed to a method for obtaining a material according to the present invention, said method comprising the following steps: - providing a glass sheet coated with a stack of thin layers over at least a part of one of its faces, then - depositing an enamel layer that does not contain bismuth over at least a part of the surface of the stack of thin layers, then - depositing a non-stick layer on said enamel layer.

[0018] The present invention is also directed, inter alia, to a curved laminated glazing for the windshield or roof of a motor vehicle, said curved laminated glazing comprising a material according to the present invention that is adhesively bonded to an additional glass sheet using an intermediate layer of the laminate, the enamel layer and the stack of thin layers being oriented towards the intermediate layer, in particular being on face 2 of the glazing.

[0019] The present invention finally relates to a method for obtaining a curved laminated glazing as defined above, said method comprising the following steps: - providing a material according to the present invention or a material obtained by the method mentioned above and an additional glass sheet, then - simultaneously bending the material and the additional glass sheet, then - laminating said material together with the additional glass sheet using an intermediate layer of the laminate, the enamel layer and the stack of thin layers being oriented towards the intermediate layer.

[0020] Unlike what is proposed in the above-mentioned International Publication No. 2014 / 133929, the stack of thin layers is not deteriorated by the application of enamel. The material according to the invention thus has, in succession, a stack of thin layers and then an enamel layer, the enamel layer not being in contact with the glass sheet.

[0021] The use of an enamel layer that does not contain bismuth makes it possible to avoid any unfavorable interaction during bending, in particular with a stack of thin layers that includes at least one nitride-based layer. However, these enamels do not make it possible to avoid the adhesion between two glass sheets during bending, so a non-sticking layer is arranged on top of the enamel layer.

[0022] The "non-sticking" layer means a layer that makes it possible to prevent two glass sheets from adhering to each other during bending.

[0023] The glass sheet can be flat or curved. The glass sheet is generally flat during the application of the stack of thin layers and then the application of the enamel layer, and then it is curved. The glass sheet is thus usually flat in the material (intermediate product) according to the invention and curved in the curved laminated glazing (final product) according to the invention.

[0024] The glass is typically soda-lime-silica glass, but other glasses, such as borosilicate glass or aluminosilicate glass, can also be used. The glass sheet is preferably obtained by the float process, that is to say by a process consisting of flowing molten glass onto a molten tin bath.

[0025] The glass sheet may be made of clear glass or may be made of colored glass, preferably colored glass such as green, gray, or blue. To do so, the chemical composition of the glass sheet advantageously includes iron oxide with a weight content of 0.5 to 2%. The chemical composition of the glass sheet may also contain other colorants such as cobalt oxide, chromium oxide, nickel oxide, erbium oxide, or selenium.

[0026] The glass sheet preferably has a thickness included in the range of 0.7 to 19 mm, especially 1 to 10 mm, particularly 2 to 6 mm, and more preferably 2 to 4 mm.

[0027] The lateral dimensions of the glass sheet should be adapted according to the dimensions of the laminated glazing for which the glass sheet is intended to be incorporated. The glass sheet preferably has an area of at least 1 m 2 .

[0028] The glass sheet is preferably coated with a stack of thin layers over at least 70%, especially at least 90%, and more preferably over the entire area of the surface of the glass sheet. In practice, certain zones may not be coated, especially for providing communication windows for passing waves.

[0029] The stack is preferably coated with an enamel layer over 2 to 25% of its area, especially 3 to 20%, and more preferably 5 to 15%. The enamel layer preferably includes a peripheral strip, i.e., a self - contained strip that extends inwardly from each point on the periphery of the glass sheet with a specific width, typically 1 to 20 cm.

[0030] The non - stick layer preferably coats the entire enamel layer. Advantageously, the non - stick layer coats only the enamel layer and does not exist in zones where the enamel layer is not coated.

[0031] The stack of thin layers preferably contacts a glass sheet. The enamel layer preferably contacts the stack of thin layers. The non-stick layer preferably contacts the enamel layer. In the present specification, the stack of thin layers, the enamel layer and the non-stick layer are collectively referred to as a "coating". The material according to the present invention is preferably composed of these coatings.

[0032] In the present specification, "contact" means physical contact. The expression "based on" preferably means that the layer in question contains at least 50% by weight, especially 60% by weight, more preferably 70% by weight, still more preferably 80% by weight or 90% by weight of the material under consideration. The layer can further consist essentially of this material or consist of this material. It should be understood that "consisting essentially of" means that the layer can contain impurities that do not affect its properties. The terms "oxide" or "nitride" do not necessarily mean that the oxide or nitride is stoichiometric. They can actually be sub-stoichiometric, super-stoichiometric or stoichiometric.

[0033] The stack preferably contains at least one nitride-based layer. The nitride is especially a nitride of at least one element selected from aluminum, silicon, zirconium, titanium. The nitride can contain nitrides of at least two or three of these elements, for example silicon and zirconium nitrides, or silicon and aluminum nitrides. Preferably, the nitride-based layer is a layer based on silicon nitride, more specifically a layer consisting essentially of silicon nitride. When a layer of silicon nitride is deposited by cathodic sputtering, the layer generally contains aluminum, because it is customary to dope the silicon target with aluminum to increase the deposition rate.

[0034] The nitride-based layer preferably has a physical thickness of 2 to 100 nm, especially 5 to 80 nm.

[0035] Nitride-based layers are commonly used in many stacks of thin layers because these layers have advantageous blocking properties in that they prevent the oxidation of other layers present in the stack, especially the functional layers described below.

[0036] The stack preferably includes at least one functional layer, especially a conductive functional layer. The functional layer is preferably included between two dielectric thin layers, and at least one of the dielectric thin layers is a nitride-based layer. Other possible dielectric layers are, for example, oxide layers or oxynitride layers.

[0037] At least one conductive functional layer is preferably selected from among the following: - Metal layers, especially made of silver or niobium and furthermore gold, and - Layers of transparent conductive oxides, especially selected from indium tin oxide, tin oxide doped (e.g., with fluorine or antimony), zinc oxide doped (e.g., with aluminum or gallium).

[0038] These layers are particularly highly regarded for the low emissivity of the layers, which confers excellent heat insulation properties to the glazing. In the glazing equipped on land vehicles, especially automobiles, railway vehicles, or also aircraft and ships, low-emissivity glazing makes it possible to reflect part of the solar radiation outward during hot times, and thus to limit the temperature rise in the passenger compartment of said vehicle, and also, where appropriate, to reduce the air conditioning costs. Conversely, during cold times, these glazings make it possible to retain the heat inside the passenger compartment and thus also to reduce the energy required for heating. The same applies to the glazing equipped in buildings.

[0039] According to a preferred embodiment, the stack of thin layers includes at least one, especially one, two or three, and even four silver layers. The physical thickness of the silver layer or, where appropriate, the total thickness of the silver layers is preferably 2 to 20 nm, especially 3 to 15 nm.

[0040] According to another preferred embodiment, the stack of thin layers includes at least one indium tin oxide layer. Its physical thickness is preferably 30 to 200 nm, especially 40 to 150 nm.

[0041] During the bending process, each of these layers (whether made of metal or based on a transparent conductive oxide) is preferably surrounded by at least two dielectric layers in order to protect the conductive thin layer or each conductive thin layer. The dielectric layer is preferably based on an oxide, nitride and / or oxynitride of at least one element selected from silicon, aluminum, titanium, zinc, zirconium, tin.

[0042] At least part of the stack of thin layers can be deposited by various known techniques, such as chemical vapor deposition (CVD) or, especially, by magnetically assisted, cathode sputtering (magnetron method).

[0043] The stack of thin layers is preferably deposited by magnetically assisted, cathode sputtering. In this method, a plasma is created under high vacuum near a target containing the chemical element to be deposited. The active species of the plasma collide with the target, separating the element, and the separated element is deposited on the glass sheet to form the desired thin layer. This method is called a "reactive" method when the layer consists of a material resulting from a chemical reaction between the element separated from the target and the gas contained in the plasma. A major advantage of this method is that, generally in just one and the same apparatus, by passing the glass sheet successively under different targets, a very complex stack of layers can be deposited on the same line.

[0044] The above stack has conductive and infrared reflection properties useful for providing a heating function (defrosting, anti-fogging) and / or a heat insulation function.

[0045] When the stack of thin layers is intended to provide a heating function, a supply of current must be provided. This can be, inter alia, silver paste strips applied by screen printing onto the stack of thin layers at two opposite edges of the glass sheet.

[0046] The enamel layer is preferably formed from a composition containing at least one pigment and at least one glass frit. The enamel layer preferably does not contain lead oxide.

[0047] The enamel composition generally contains an organic medium, which is intended to facilitate the application of the composition onto the substrate and its temporary adhesion to the substrate, which is removed during firing of the enamel. The medium typically includes solvents, diluents, oils and / or resins. As used herein, "enamel composition" is defined as the liquid composition used to deposit a wet enamel layer on a glass sheet. The term "enamel layer" is used to define the final layer after firing, while the term "wet enamel layer" is used to depict the enamel layer before firing.

[0048] The enamel layer is preferably applied by screen printing. To do so, a screen printing screen including a mesh with some blocked areas is placed on the glass sheet, then the enamel composition is placed on the screen, and then a squeegee is applied to push the enamel composition through the screen in the zones where the mesh of the screen is not blocked, forming a wet enamel layer.

[0049] The application of the enamel layer preferably includes a firing step at a temperature of preferably at least 600 °C, more preferably 650 °C, and at most 700 °C, during subsequent processing for bending the glass sheet.

[0050] The pigment preferably contains one or more oxides selected from oxides of chromium, copper, iron, manganese, cobalt, and nickel. It can be, for example, copper chromate and / or iron chromate.

[0051] In a preferred embodiment of the present invention, the enamel layer is based on zinc borosilicate.

[0052] More specifically, the enamel layer preferably has a chemical composition containing the following oxides, and their weight contents vary within the limiting ranges mentioned below: B2O3 2 - 20%, especially 4 - 10% SiO2 20 - 45%, especially 25 - 40% Bi2O3 0 ZnO 8 - 25%, especially 10 - 20%

[0053] The composition preferably contains at least one alkali metal oxide, especially potassium oxide with a content of at most 5% and / or sodium oxide with a content of 2 - 15%, especially 5 - 13%. The composition preferably contains titanium oxide (TiO2) with a content of 1 - 10%, especially 2 - 7%. The composition also includes a pigment, such as copper chromate. In this case, the typical contents of Cr2O3 and CuO are 8 - 20% and 3 - 12% respectively.

[0054] The chemical composition of the enamel can be determined by conventional chemical analysis methods, especially from the fired enamel. It is thus indeed the chemical composition of the fired enamel layer, not the chemical composition of the glass frit used for forming the enamel.

[0055] Preferably, the enamel layer is opaque and black. Its lightness L measured in reflection on the glass side* is preferably less than 5. As shown above, the enamel layer advantageously forms a strip at the periphery of the glass sheet. Thus, the enamel layer can hide seals, connection components, or also sensors and protect them from ultraviolet radiation.

[0056] The non-stick layer is preferably a layer or a sol-gel layer based on heat-resistant particles (especially pigments). The non-stick layer preferably does not contain bismuth, because it has been observed that the presence of bismuth can cause defects even if the non-stick layer is not in contact with a stack of thin layers.

[0057] Heat-resistant particles mean particles that do not change during bending.

[0058] The heat-resistant particles can be, for example, alumina particles. The heat-resistant particles can advantageously be pigments.

[0059] The pigment preferably contains one or more transition metal oxides, especially selected from oxides of chromium, copper, iron, manganese, cobalt, nickel and titanium.

[0060] Preferably the pigment is a titanium oxide pigment having excellent non-stick properties. (Although the enamel is generally black) these pigments are white, but these pigments do not change the appearance of the enamel visible from outside the vehicle. In the final laminated glazing, when additional glass sheets or the intermediate layer of the laminate are colored, the color provided by these pigments does not impair the aesthetics visible from inside the passenger compartment.

[0061] The pigment-based layer preferably contains at least 40% by weight, especially at least 60% by weight, and even more preferably at least 80% by weight of pigment.

[0062] According to a preferred embodiment, the non - sticking layer is composed of pigments. These pigments are fixed to the glass sheet thanks to the underlying enamel layer. That is, its softening during bending makes it possible to fix the pigments deposited thereon.

[0063] According to another embodiment, the non - sticking layer contains pigments and a vitreous binder. The vitreous binder does not contain bismuth and can be based on the same glass frit as the underlying enamel. In order to obtain non - sticking properties, the mass ratio of pigments in the non - sticking layer must be at least 40% by weight. A very simple means of obtaining this type of layer consists in adding a certain proportion of pigments to the same enamel composition as that used for the deposition of the underlying enamel layer.

[0064] According to yet another embodiment, the non - sticking layer is a sol - gel layer. A sol - gel layer means a layer obtained by the sol - gel process. The sol - gel layer is preferably based on silica.

[0065] The sol - gel process is a method in which a sol containing the precursor of the layer to be produced is deposited on the glass sheet by various means such as spray coating, curtain coating, flow coating, roll coating, screen printing, etc. Screen printing is preferred here because it easily allows the sol - gel layer to be deposited only on a part of the glass sheet, in this case the zone covered with enamel (and advantageously the whole of this zone).

[0066] The sol preferably contains an organometallic precursor of the layer to be produced, such as tetraethyl orthosilicate (TEOS). The layer is then generally dried and then annealed to increase the density of the layer. The annealing is preferably carried out during the same process as the firing of the enamel, and thus generally during the bending of the glass sheet.

[0067] The non-sticking layer preferably has a thickness of 5 to 100 μm (especially in the wet state). When the layer is based on heat-resistant particles, its thickness is preferably 10 to 100 μm, especially 12 to 30 μm. When the layer is a sol-gel layer, its thickness is preferably 5 to 20 μm.

[0068] Preferably, the enameling process and the non-sticking layer deposition process are carried out by screen printing.

[0069] When the non-sticking layer is composed of a pigment, the pigment is mixed in an organic medium, and the organic medium is then removed during bending or, in some cases, during possible pre-firing.

[0070] Following the enameling process, there is preferably a drying process at a temperature typically of 100 to 200 °C, after which the non-sticking layer is deposited.

[0071] When depositing a non-sticking layer based on heat-resistant particles by screen printing, the heat-resistant particles must have a size compatible with the screen used for screen printing. The particles preferably have a D90 of 5 to 40 μm. The particle size distribution here is a volume distribution and is determined, for example, by laser granulometry.

[0072] Following the non-sticking layer deposition process, there is preferably a pre-firing process at a temperature preferably of 150 to 600 °C. Such pre-firing makes it possible to remove the organic medium or, generally, any organic components that may be present in the layer.

[0073] The pre-firing process is usually carried out when using an enamel based on bismuth in order to develop the non-sticking properties of such an enamel by causing its partial crystallization. This process, however, must be carried out at a high temperature, typically at least 500 °C, while the pre-firing carried out within the scope of the present method can advantageously be carried out at a lower temperature.

[0074] In the case of curved laminated glazing, the material according to the invention is adhered and joined to an additional glass sheet using the intermediate layer of the laminate, and the coating is oriented towards the intermediate layer. The coating is preferably positioned on the face 2 of the glazing, i.e. on the face of the glass sheet which is oriented towards the intermediate layer of the laminate and which is intended to be positioned on the outside of the vehicle.

[0075] The bending can be carried out, inter alia, typically at a temperature of 550 to 650 °C, by gravity (the glass deforms under its own weight) or by pressing. The glass sheets are preferably held at a distance from each other by arranging between them an intermediate layer powder which typically ensures a space of some tens of micrometres, typically 20 to 50 μm. The intermediate layer powder is based, for example, on calcium carbonate and / or magnesium carbonate.

[0076] During the bending operation, the inner glass sheet (which is intended to be positioned inside the passenger compartment) is usually placed on top of the outer glass sheet. Thus, during the bending process, the additional glass sheet is placed on top of the material according to the invention.

[0077] The lamination process can be carried out, for example, by autoclaving at a temperature of 110 to 160 °C and a pressure of 10 to 15 bar. Prior to the autoclaving process, the air trapped between the glass sheet and the laminate intermediate layer can be removed by calendering or by negative pressure.

[0078] As mentioned above, the additional sheet is preferably the inner sheet of the laminated glazing which is intended to be positioned inside the passenger compartment of the vehicle, i.e. the sheet which is located on the concave side of the glazing. Thus, the coating is arranged on face 2 of the laminated glazing.

[0079] The additional glass sheet may be made of soda-lime-silica glass, or alternatively may also be made of borosilicate glass or aluminosilicate glass. The additional glass sheet may be made of clear glass or alternatively may also be made of colored glass. Its thickness is preferably from 0.5 to 4 mm, especially from 1 to 3 mm.

[0080] According to a preferred embodiment, the additional glass sheet has a thickness of from 0.5 to 1.2 mm. The additional glass sheet is especially preferably made of sodium aluminosilicate glass which is chemically strengthened. The additional glass sheet is preferably the inner sheet of the laminated glazing. The present invention is particularly useful for this type of configuration, for which it is difficult to arrange a 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) to exchange the ions of the glass (here sodium ions) with ions of a larger ionic radius (here potassium ions), thereby strengthening the surface of the glass. This ion exchange makes it possible to form a compressive stress at the surface of the glass and over a certain thickness. Preferably, the surface stress is at least 300 MPa, especially 400 MPa or even further 500 MPa and at most 700 MPa, and the thickness of the compression zone is at least 20 μm, typically from 20 to 50 μm. The stress profile can be determined in a known manner using a polarizing microscope equipped with a Babinet compensator. The chemical strengthening step is preferably carried out at a temperature of from 380 to 550 °C over a duration of from 30 minutes to 3 hours. Chemical strengthening is preferably carried out after bending but before the lamination step. The resulting glazing is preferably the front glass of a motor vehicle, especially a heated front glass.

[0081] According to another preferred embodiment, the additional glass sheet has, on the face opposite to the face directed towards the intermediate layer of the laminate (preferably face 4 and the additional sheet is the inner sheet), a stack of additional thin layers, in particular a low emissivity stack containing 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 place the stack of thin layers on two faces (faces 3 and 4) of the same glass sheet. In this embodiment, the intermediate layer of the laminate and / or the additional glass sheet are preferably colored, and the glass sheet having the coating may be made of clear glass. The resulting glazing is preferably the roof of a motor vehicle.

[0082] As an example of the immediately preceding preferred embodiment, a curved laminated roof can be cited which, from the outside of the vehicle, comprises a clear glass sheet coated on face 2 with a stack of thin layers containing at least one silver layer, then an enamel layer, then a non-stick layer, an intermediate layer of a colored PVB-based laminate, and an additional glass sheet made of colored glass having, on face 4, a stack of low emissivity thin layers based in particular on ITO.

[0083] The intermediate layer of the laminate preferably comprises at least one sheet of polyvinyl acetal, in particular a sheet of polyvinyl butyral (PVB).

[0084] The intermediate layer of the laminate may or may not be colored in order to adjust the optical or thermal properties of the glazing if necessary.

[0085] The intermediate layer of the laminate can advantageously have sound-absorbing properties for absorbing air-borne or solid-borne sound. For that purpose, the intermediate layer of the laminate can in particular consist of three polymer sheets, two of which, called outer sheets, are PVB sheets surrounding an inner polymer sheet having a lower hardness than the hardness of the outer sheets and which may in some cases be made of PVB.

[0086] The intermediate layer of the laminate can also have heat insulation properties, particularly infrared radiation reflection properties. For this purpose, the intermediate layer of the laminate can include a low-emissivity thin layer coating, such as a coating containing a thin layer of silver or a coating alternately containing dielectric layers of different refractive indices, which is applied onto a PET inner sheet surrounded by two PVB outer sheets.

[0087] The thickness of the intermediate layer of the laminate generally ranges from 0.3 to 1.5 mm, particularly within the range of 0.5 to 1 mm. The intermediate layer of the laminate can have a thickness that is thinner at the edge of the glazing than at the center of the glazing in order to avoid the formation of double images when using a head-up display system called HUD.

Embodiments for Carrying out the Invention

[0088] The following examples illustrate the present invention non - limitatively.

[0089] A 2.1 - mm - thick glass sheet pre - coated by cathodic sputtering with a stack of thin layers including two silver layers protected by a zinc oxide layer, a silicon nitride layer, and a blocking agent NiCr was coated by screen printing with an enamel layer having a wet thickness of 25 μm.

[0090] In an example according to the present invention, the enamel layer "E1" (an enamel commercialized under the reference number 144011 by Ferro) was based on a zinc borosilicate frit (free of bismuth) and a black pigment based on oxides of chromium and copper.

[0091] In a comparative example, the enamel layer "E2" (an enamel commercialized under the reference number DV173770 / N by Prince) was based on a zinc borosilicate bismuth frit and a black pigment based on oxides of chromium and copper.

[0092] Next, on top of the enamel layer, after drying at a temperature of 150°C, a non-stick layer with the following composition according to the example was applied by screen printing: -A1: A pigment of TiO2 in A1, with a wet thickness of approximately 10 μm, having a D50 of about 3 - 5 μm and a D90 of about 10 μm. -A2: A silica sol - gel in A2, with a wet thickness of approximately 7 μm, deposited from a solution commercialized under the reference number TLU0059B01 by Ferro Corporation. -A3: The enamel layer E2 in A3, with a wet thickness of 25 μm. -A4: A mixture of 80 wt% of enamel E1 and 20 wt% of a TiO2 pigment, with a wet thickness of 10 μm.

[0093] The glass sheet thus coated was then subjected to a pre - firing treatment at 570°C for 120 seconds.

[0094] Next, on top of the coated side of the glass sheet, an additional glass sheet made of colored glass with a thickness of 2.1 mm, coated in face 4 with a low - emissivity stack based on ITO, was placed. An intermediate layer powder based on calcium carbonate, ensuring a space of several tens of micrometers, was placed between the two glass sheets. The whole was then subjected to a heat treatment for bending at 600°C for 480 seconds.

[0095] Table 1 below summarizes the results obtained for each example (Comparative Examples C1 - C3 and Examples 1 - 3 according to the present invention), showing the properties of the enamel layer and (if present) the non - stick layer, as well as the results from the viewpoints of aesthetics and adhesion.

[0096] Aesthetics, more specifically the black color visible from face 1, is evaluated by measuring the lightness L in reflection * (D65 light source, standard observer of 10°). For adhesion, it is evaluated qualitatively by visual observation.

[0097]

Table 1

[0098] Comparative Examples C1 and C2 do not use a non-sticking layer. Comparative Example C1 shows that although the enamel containing bismuth does not bring about adhesion, it is not possible to obtain the desired black color tone due to the interaction between the enamel and the thin layer stack during bending. The enamel without bismuth in Comparative Example C2 makes it possible to reach the desired color tone, however, adhesion between the two glass sheets has been observed.

[0099] Comparative Example C3 uses a bismuth-free enamel in contact with the stack and a bismuth-containing enamel in contact with an additional glass sheet placed thereon. In that case, adhesion is avoided, however, the presence of the bismuth-containing enamel impairs the aesthetics even if it is not in contact with the thin layer stack.

[0100] Examples 1 to 3 according to the present invention show that using a non-sticking layer in combination with a bismuth-free enamel makes it possible to simultaneously obtain non-adhesion and a satisfactory aesthetics.

Claims

1. A material comprising a glass sheet, wherein at least a part of one of its surfaces is coated with a stack of thin layers, the stack is coated with an enamel layer containing no bismuth over at least a part of its surface, the enamel layer is coated with a non-stick layer, and the non-stick layer is a layer or sol-gel layer based on heat-resistant particles and contains no bismuth.

2. The material according to claim 1, wherein the stack of thin layers includes at least one layer based on a nitride of at least one element selected from among nitrides of aluminum, silicon, zirconium, and titanium.

3. The material according to claim 1 or 2, wherein the stack includes at least one functional layer, particularly a conductive functional layer.

4. The material according to claim 3, wherein at least one conductive functional layer is selected from among a metal layer made of silver or niobium, in particular, and a layer of a transparent conductive oxide selected from among indium tin oxide, doped tin oxide, and doped zinc oxide.

5. The material according to any one of claims 1 to 4, wherein the enamel layer is based on zinc borosilicate.

6. The material according to any one of claims 1 to 5, wherein the enamel layer is opaque, black, and forms a strip at the periphery of the glass sheet.

7. The material according to any one of claims 1 to 6, wherein the heat-resistant particles are pigments.

8. The material according to any one of claims 1 to 6, wherein the sol-gel layer is based on silica.

9. A curved laminated glazing, particularly for an automotive windshield or roof, adhered and joined to an additional glass sheet using an intermediate layer of the laminate, comprising the material according to any one of claims 1 to 8, wherein the enamel layer and the stack of thin layers face the intermediate layer, particularly on surface 2 of the glazing.

10. The curved laminated glazing according to claim 9, wherein the additional glass sheet has a thickness of 0.5 to 1.2 mm and is particularly made of chemically strengthened sodium aluminosilicate glass.

11. The curved laminated glazing according to claim 9, wherein an additional glass sheet has, on a surface opposite to the surface facing towards the intermediate layer of the laminate, a stack of additional thin layers, in particular a low-emissivity stack containing a transparent conductive oxide.

12. The following steps - providing a glass sheet coated with a stack of thin layers over at least a part of one of the surfaces, then - depositing an enamel layer containing no bismuth over at least a part of the surface of the stack of thin layers, then - depositing a non-stick layer on the enamel layer A method for obtaining a material according to any one of claims 1 to 8, comprising the steps.

13. The method according to claim 12, wherein the step of depositing the enamel layer and the step of depositing the non-stick layer are performed by screen printing.

14. The following steps - providing a material according to any one of claims 1 to 8 or a material obtained by the method according to claim 12 or 13 and an additional glass sheet, then - simultaneously bending the material and the additional glass sheet, then - laminating the material with the additional glass sheet using the intermediate layer, with the enamel layer and the stack of thin layers facing towards the intermediate layer of the laminate A method for obtaining a curved laminated glazing according to any one of claims 9 to 11, comprising the steps.

Images