GLASS PANE COATED WITH A STACK OF THIN LAYERS AND A LAYER OF ENAMEL

Description

[0001] The invention relates to the field of materials comprising a glass sheet coated with a stack of thin layers. Such materials are intended to form or be incorporated into building glazing or into parts of household appliances, such as oven doors.

[0002] Thin-film stacks confer various properties to materials, for example optical properties (reflective or anti-reflective layers), energy properties (solar control and / or low-emissivity layers) or even electrical conduction properties (used for example for heated glazing).

[0003] Glass sheets are sometimes coated, on at least part of their surface, with a layer of enamel. An enamel is a mineral material formed from a composition comprising at least one pigment and at least one glass frit. A glass frit consists of fine particles of a low-melting glass, which, under the effect of a heat treatment of firing, 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 retaining the pigment particles. Enamel layers can have a decorative or aesthetic function, but also a protective one.

[0004] Enamel layers can, for example, be deposited on the periphery of glass sheets used in oven doors to camouflage certain areas of the oven. Low-emissivity layers are sometimes placed under the enamel layer to reduce heat exchange with the outside of the oven. In the construction industry, there are also glazings called "spanels," used for building facades, in which the glass sheet is entirely covered with a colored and decorative layer of enamel. Solar control layers are sometimes placed under the enamel layer to limit the heating of the building under the effect of solar radiation. Enamel layers can also be used to create a certain design, by depositing the enamel in the form of any patterns, for example in applications on facades, partitions, shower walls, etc.The purpose of WO 96 / 41773 A1 is to prepare, for printing glass surfaces, printing pastes to be baked having a wider field of application and being able to use a greater variety of components, in particular with regard to the possibility of using less stable colored pigments.

[0005] The inventors were able to demonstrate that in the case of using enamels containing zinc and less than 5% by weight of bismuth oxide deposited on stacks of thin layers, the visual appearance of the enamel could depend strongly on the firing temperature. Typically, whether in the case of enameling bare glass or glass coated with a stack of thin layers, there is a minimum firing temperature necessary to obtain good firing of the enamel and a good visual appearance in reflection. For bare glass, the range of possible firing temperatures is wide, in the sense that an increase in the firing temperature of 50 or 100°C beyond this minimum firing temperature does not substantially modify the appearance in reflection of the enamel.On the other hand, in the case of glass coated with a stack of thin layers, a sometimes minimal increase in the firing temperature compared to the minimum firing temperature can lead to a change in the reflected appearance. The range of possible firing temperatures, called ΔT, is then reduced. Thus, it has been observed that for stacks whose last layer (or one of the last layers) was based on silicon nitride, the ΔT range could be as low as 5 or 10°C.

[0006] Low ΔT ranges are detrimental from an industrial production point of view because obtaining products with a uniform color requires the use of firing equipment capable of heating the glass sheet very uniformly. Even with high-performance equipment, the edges of the glass sheet often experience slightly higher temperatures than the center, which can lead to color heterogeneities. Finally, in the case of stacks of layers with low emissivity, the areas without enamel are heated mainly by convection while the areas covered with enamel are heated by convection and radiation. The areas close to the areas without enamel therefore experience lower temperatures than the others. It is therefore very difficult in the case of low ΔT ranges to industrially obtain perfectly homogeneous glass sheets in terms of visual appearance.

[0007] The invention aims to solve these problems by proposing stacks for which the ΔT range is high, making it possible to reduce industrial production costs.

[0008] To this end, the invention relates to a material comprising a glass sheet coated on at least part of one of its faces with a stack of thin layers, as in claim 1.

[0009] The invention also relates to a method for manufacturing a material according to the invention, comprising the deposition of a stack of thin layers on at least part of one face of a glass sheet, then the deposition, on at least part of the surface of said stack, of a layer of enamel comprising zinc and less than 5% by weight of bismuth oxide.

[0010] The material according to the invention has, in a superimposed manner, a stack of thin layers then a layer of enamel, the latter not being in contact with the glass sheet. The presence of a contact layer makes it possible to increase the ΔT range and therefore the visual homogeneity of the material.

[0011] The glass sheet is preferably flat, particularly when the material is intended for building glazing or furnace doors, but it can also be curved. In the latter case, the glass sheet is generally flat at the time of deposition of the stack of thin layers and then of the enamel layer, and can then be curved. The glass is typically a soda-lime-silica glass, but other glasses, for example borosilicates or aluminosilicates, can also be used. The 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. The glass sheet can be mechanically reinforced, in particular hardened or thermally tempered.To do this, the glass sheet is heated to a temperature of approximately 600°C or above, a treatment which can lead to bending of the glass if desired, and then cooled rapidly to create compressive stresses on its surface. The enamel is preferably fired during this heat treatment. The glass sheet may be clear or tinted, for example green, blue, gray or bronze. The glass sheet preferably has a thickness in the range of 0.7 to 19 mm, in particular 1 to 10 mm, particularly 2 to 6 mm, or even 2 to 4 mm.

[0012] The glass sheet is preferably coated with the stack of thin layers on at least 70%, in particular 80%, or even on the entire surface of the first face. Depending on the applications, the stack can be coated with the enamel layer on at least 80%, or even 90% of its surface (case of spandrels), or on at most 40%, in particular 30% and even 20%, or even 15% of its surface, often at the periphery of the glass sheet (case of oven doors, or even glazing incorporating a Marie-Louise). In the case of enameled patterns intended to confer a certain design, this figure is typically between 5 and 80%.

[0013] In this text, the term "contact" means physical contact. The term "based on" preferably means that the layer in question comprises at least 50% by weight of the material in question, in particular 60%, or even 70%, and even 80% or 90%. The layer may even essentially consist of or consist of this material. By "essentially consist" it is meant that the layer may include impurities without influencing its properties. The terms "oxide" or "nitride" do not necessarily mean that the oxides or nitrides are stoichiometric. They may in fact be substoichiometric, superstoichiometric or stoichiometric.

[0014] Preferably, the contact layer comprises an oxide of at least one element selected from aluminum, silicon, titanium, zinc, zirconium, tin. The contact layer may comprise an oxide of at least two or three of these elements, for example an oxide of zinc and tin, or an oxide of silicon and aluminum.

[0015] The contact layer is advantageously a silicon oxide-based layer, more particularly a layer consisting essentially of silicon oxide. When the silicon oxide layer is deposited by sputtering, it generally contains aluminum, since it is customary to dope silicon targets with aluminum in order to accelerate deposition rates.

[0016] The contact layer is preferably obtained by sputtering or by a sol-gel process. More details on these processes are given in the rest of the text.

[0017] The contact layer preferably has a physical thickness of at least 10 nm, in particular 20 nm, 30 nm, 40 nm, or even 50 nm and even 80 or 100 nm, or even 150 or 200 nm. This thickness is preferably at most 2 µm, in particular 1 µm, or even 500 nm and even 100 nm. Increasing the thickness of the contact layer is favorable to obtaining high ΔT ranges.

[0018] The stack preferably comprises at least one layer based on a nitride.

[0019] The at least one nitride-based layer preferably comprises 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.

[0020] The at least one nitride-based layer preferably has a physical thickness in a range from 2 to 100 nm, in particular from 5 to 80 nm, or even from 20 to 50 nm.

[0021] 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. The inventors were however able to demonstrate that the presence of these layers, in particular near the enamel layer, was detrimental to obtaining high ΔT ranges. The invention is therefore particularly useful for stacks containing this type of layer.

[0022] Preferably, at least one nitride-based layer is in contact with the contact layer, or less than 5 nm away from the contact layer. The advantages of the invention are even more evident for these stacks.

[0023] The stack preferably comprises at least one functional layer, in particular an electrically conductive, solar control, or low-emissivity 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.

[0024] At least one functional layer is advantageously chosen from: metallic layers, in particular made of silver or niobium, 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), and layers based on niobium nitride.

[0025] These coatings are particularly appreciated for their low emissivity or their ability to filter solar radiation, which gives the glazing excellent thermal insulation properties. In hot weather, low-emissivity glazing allows some of the solar radiation to be reflected outwards, and therefore limits the heating of the interior of homes, and if necessary reduces air conditioning costs. Conversely, in cold weather, these glazings help to retain heat inside the home, and therefore reduce the energy effort of heating. In the case of oven doors, low-emissivity coatings reduce heat emissions outside the oven, thus increasing its efficiency while limiting the risk of burns for users.

[0026] According to one embodiment of the invention, the stack of thin layers preferably 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. This layer is advantageously between two layers based on nitride, in particular silicon nitride. The contact layer is preferably based on silicon oxide.

[0027] According to another embodiment of the invention, the stack of thin layers comprises at least one layer of silver, in particular one, two or three layers of silver. The total physical thickness of silver is preferably between 3 and 30 nm, in particular between 5 and 20 nm. The or each layer of silver is preferably surrounded by dielectric layers, some of which are based on nitride, in particular silicon nitride.

[0028] According to another embodiment of the invention, the stack of thin layers comprises a layer of niobium or niobium nitride. The functional layer is preferably surrounded by dielectric layers, some of which are based on nitride, in particular silicon nitride.

[0029] Alternatively, the stack may not include a functional layer. The stack may thus, for example, include a succession of thin layers, none of which, individually, provides a particular function, but which together make it possible to obtain optical effects, in particular by means of multiple interferences. These may, for example, be anti-reflective stacks or, conversely, reflective stacks.

[0030] At least part of the thin-film stack can be deposited by various known techniques, for example by chemical vapor deposition (CVD), or by cathode sputtering, in particular assisted by a magnetic field (magnetron process).

[0031] According to one embodiment, the entire stack of thin layers (including the contact layer) is 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 a very complex stack of layers on the same line by successively moving the glass sheet under different targets, generally in a single device.

[0032] According to another embodiment, the entire stack of thin layers, with the exception of the contact layer, is deposited by sputtering, in particular assisted by a magnetic field. In this case, the contact layer is preferably deposited by a sol-gel process. In the latter process, a sol containing precursors of the layer to be produced is deposited on the glass sheet by various means, such as spraying, curtain, laminar coating, roller, screen printing, etc. The sol preferably contains organometallic precursors of the layer to be produced, for example tetraethyl orthosilicate (TEOS). The layer is then dried and then annealed in order to densify it. This process makes it possible to obtain thicker contact layers than by the sputtering process. The physical thickness of the contact layer can thus be at least 100 nm, in particular 200 nm and even 500 nm, or even 1 µm and more.

[0033] The enamel layer is preferably formed from a composition comprising at least one pigment and at least one zinc borosilicate glass frit. The enamel layer does not comprise lead oxide. The weight content of bismuth oxide in the enamel layer is advantageously at most 4%, in particular 3%, or even 2%, and even 1%. It is preferably zero.

[0034] 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 during the firing of the enamel. The medium typically comprises solvents, diluents, oils and / or resins. In this text, the term "enamel composition" refers to the liquid composition which is used to deposit, on the glass sheet, a layer of wet enamel. The term "enamel layer" is used to describe the final layer, after firing, while the term "wet enamel layer" is used to describe the layer of enamel before firing.

[0035] The enamel layer is preferably deposited by screen printing. To do this, a screen printing screen is placed on the glass sheet, which includes meshes, some of which are sealed, then the enamel composition is deposited on the screen, then a doctor blade is applied to force the enamel composition through the screen in the areas where the meshes of the screen are not sealed, so as to form a wet enamel layer.

[0036] The deposition of the enamel layer comprises a firing step, preferably at a temperature of at least 600 and even 650°C, and at most 700°C, preferably during a bending and / or tempering treatment of the glass sheet.

[0037] 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.

[0038] Preferably, the enamel layer is opaque, black or gray in color. However, any other color is possible: white, red, blue, green, yellow, etc. The enamel layer can cover the entire surface of the glass sheet, or be placed on the periphery of the glass sheet.

[0039] The invention also relates to glazing, in particular a sill, or a door for a household appliance comprising at least one material as described above.

[0040] The glazing is preferably a building glazing. It may in particular be a sill, a part of a facade, a partition, a shower screen, comprising a stack of thin layers conferring low emissivity and / or solar control properties or specific optical effects. The enamel may cover the entire glazing (case of the sill) or only a part, either to conceal and / or protect elements located behind the glazing, or to create a design.

[0041] The material according to the invention can be laminated to another glass sheet by means of a lamination interlayer, in particular made of polyvinyl butyral (PVB). The stack of thin layers is then preferably on the side of the interlayer. In this case, the use of a silica-based contact layer is particularly advantageous because silica has the same refractive index as PVB, so that it has no impact on the optics of the final material.

[0042] The appliance door is preferably an oven door or a refrigeration appliance door (positive or negative cold).

[0043] The oven door preferably comprises at least one outer glass, close to the user, and one inner glass, close to the interior of the oven. In this case, the material according to the invention may be an inner glass, in particular coated with a low-emissivity stack, or an outer glass, in particular coated with a stack providing optical effects, for example a reflective stack.

[0044] The refrigeration device door may in particular be single glazing or multiple glazing, in particular double glazing. The material according to the invention, integrated into this door, is preferably coated with a low-emissivity stack.

[0045] The following exemplary embodiments illustrate the invention in a non-limiting manner. Comparative example 1

[0046] In this comparative example, a sheet of clear soda-lime glass was screen-coated with a layer of black enamel. The enamel, based on zinc borosilicate, comprises (by weight) 8% B 2 O 3 , 32% SiO 2 , 17% ZnO, 4% TiO 2 , 2% Al 2 O 3 , 22% Cr 2 O 3 and 12% CuO. The composition of the enamel is free of bismuth oxide.

[0047] The ΔT range was then evaluated as follows. A sample was placed in a gradient furnace so as to fire the enamel at a different temperature depending on the area of the sample. A measurement of the L* clarity in non-specular reflection as a function of the area allowed the amplitude of the ΔT range to be evaluated.

[0048] The ΔT range is greater than 50°C. An L* value less than 5 (characteristic of a black color) is obtained. Comparative example 2

[0049] Comparative example 2 differs from the previous one in that the sheet of clear soda-lime glass was previously coated by magnetron sputtering with a stack of low-emissivity thin layers consisting, from the glass, of the following layers: SiN x (40 nm) / NiCr (1 nm) / Ag (7 nm) / NiCr (0.5 nm) / SiN x (40 nm) / TiZrO x (3 nm).

[0050] The enamel layer was therefore deposited in contact with this stack of thin layers.

[0051] In this case the ΔT range was only 5°C. L* values of 7 were obtained, characteristic of a less deep black than in the case of comparative example 1. Example 1

[0052] Example 1 differs from Comparative Example 2 in that a sol-gel deposited silica contact layer was deposited on the thin-film stack. The contact layer was deposited by screen printing and its thickness was 100 nm.

[0053] The ΔT range was at least 15°C. L* values of 5 were obtained. Example 2

[0054] In contrast to Example 1, the silica contact layer was deposited by magnetron sputtering of an aluminum-doped silicon target in a reactive plasma containing argon and oxygen. The thickness of the contact layer was 30 nm.

[0055] The ΔT range was at least 20°C. L* values of 5 were obtained.

[0056] Similar results were obtained with contact layer thicknesses of 50 and 70 nm. Example 3

[0057] In this example, the clear soda-lime glass sheet was previously coated by magnetron sputtering with a stack of thin solar control layers made up, from the glass, of the following layers: SiN x (10 nm) / Nb (30 nm) / SiN x (30 nm).

[0058] The silica contact layer was deposited by magnetron sputtering of an aluminum-doped silicon target in a reactive plasma containing argon and oxygen. The thickness of the contact layer was 10 or 30 nm depending on the tests.

[0059] The ΔT range was at least 20°C in all cases. L* values of 5 were obtained.

[0060] The use of a contact layer therefore made it possible to increase the range of usable cooking temperatures and to achieve deeper black shades.

Claims

1. A material comprising a glass sheet coated on at least part of one of its faces with a stack of thin layers, said stack being coated on at least part of its surface with an enamel layer comprising zinc and less than 5% by weight of bismuth oxide and not comprising lead oxide, said stack further comprising, in contact with the enamel layer, a layer, called contact layer, which is based on an oxide, the physical thickness of said contact layer being at least 5 nm.

2. The material as claimed in claim 1, wherein the contact layer comprises an oxide of at least one element selected from aluminum, silicon, titanium, zinc, zirconium, tin, in particular is a silicon oxide-based layer.

3. The material as claimed in one of the preceding claims, wherein the contact layer is obtained by sputtering or by a sol-gel process.

4. The material as claimed in one of the preceding claims, wherein the stack of thin layers comprises at least one layer based on a nitride, in particular a nitride of at least one element selected from aluminum, silicon, zirconium, titanium.

5. The material as claimed in the preceding claim, wherein at least one nitride-based layer is in contact with the contact layer or at a distance of less than 5 nm from the contact layer.

6. The material as claimed in one of the preceding claims, wherein the contact layer has a physical thickness of at least 10 nm, in particular of at least 20 nm.

7. The material as claimed in one of the preceding claims, such that the stack comprises at least one functional layer, in particular an electrically conductive, solar control, or low-emissivity functional layer.

8. The material as claimed in the preceding claim, wherein at least one functional layer is selected from metallic layers, in particular of silver or niobium, layers of a transparent conductive oxide, in particular selected from indium-tin oxide, doped tin oxides and doped zinc oxides, and layers based on niobium nitride.

9. The material as claimed in one of the preceding claims, such that the enamel layer is formed from a composition comprising at least one pigment and at least one zinc borosilicate glass frit.

10. The material as claimed in one of the preceding claims, such that the enamel layer is opaque, in particular of a black or gray color, and covers the entire surface of the glass sheet, or is placed on the periphery of the glass sheet.

11. A glazing, in particular a spandrel glass, or a door of a household appliance comprising at least one material as claimed in one of the preceding claims.

12. A process for manufacturing a material as claimed in one of claims 1 to 10, comprising the deposition of a stack of thin layers on at least part of one face of a glass sheet, and then the deposition on at least part of the surface of said stack of an enamel layer comprising zinc and less than 5% by weight of bismuth oxide.

13. The process as claimed in the preceding claim, wherein at least part of the stack of thin layers is deposited by sputtering.

14. The process as claimed in one of claims 12 and 13, wherein the deposition of the enamel layer comprises a firing step at a temperature of at least 600°C, in particular during a bending and / or tempering treatment of the glass sheet.