Colored mirror

Abstract

The invention relates to a specular mirror comprising a clear glass substrate coated on one of its faces, successively from said glass substrate, with a stack of thin layers, a reflective silver layer deposited by silvering and then a paint layer, characterized in that said stack of thin layers does not comprise a metallic layer and comprises at least one layer based on silicon nitride having, at a wavelength of 550 nm, a refractive index n ranging from 2.7 to 3.6 and an extinction coefficient k greater than 0.20.

Description

[0001]Description Title: Colored Mirror The invention relates to the field of mirrors. It concerns more particularly specular mirrors, in which a user can see their reflection. Such mirrors are, for example, placed inside dwellings, for example in bathrooms, or are used as elements of furniture (closet doors, etc.) or decoration. These mirrors generally comprise a glass substrate coated on face 2 (the face opposite the one facing the user) with a reflective layer of silver, which is itself coated with a layer of paint. The paint has an optical function, that of preventing any visibility through the mirror by blocking the passage of light rays transmitted through the silver layer. The paint also serves to protect the silver layer against corrosion. The aim of the invention is to provide a mirror with a gray reflection.It is known to use colored gray glass throughout for the manufacture of mirrors with integrated reflections. In this case, the desired gray coloration is obtained by adding one or more coloring agents, each containing at least one metallic element, to a standard glass composition. However, the use of such metallic elements or compounds in glass compositions presents several drawbacks from an industrial standpoint. Such mirrors are difficult and expensive to produce, and their manufacturing processes are polluting.Therefore, the invention relates to a specular mirror comprising a clear glass substrate coated on one of its faces, successively from said glass substrate, with a stack of thin films, a reflective silver coating deposited by silver plating and then a layer of paint, characterized in that said stack of thin films does not include a metallic layer and includes at least one silicon nitride-based layer having, at a wavelength of 550 nm, a refractive index n ranging from 2.7 to 3.6, in particular from 3.0 to 3.5 and an extinction coefficient k greater than 0.20, in particular from 0.20 to 0.50.The invention also relates to a method for obtaining the aforementioned mirror, comprising a step of depositing the stack of thin films onto a clear glass substrate, then a step of depositing, by silvering, the reflective silver coating onto said stack of thin films, then a step of depositing the liquid paint layer onto said silver layer, and finally a step of drying said liquid paint layer. The term "coated" means that the coating covering the substrate or another layer is deposited on top of said substrate or that other layer, but not necessarily in contact with them. When a first layer is placed "on top" of a second layer, it is understood that the first layer is further from the substrate than the second layer.The term "based on" generally means that the layer comprises at least 50% by weight of the compound in question, in particular at least 60%, and even 70% or 80%, or even 90% by weight of the compound in question. The silicon nitride-based layer advantageously comprises at least 80%, or even 90%, silicon nitride. When deposited by magnetic field-assisted sputtering, it advantageously comprises a small amount of aluminum, since doping a silicon target with aluminum accelerates the deposition of the layer. The stoichiometry of the silicon nitride layer is not specified here. Preferably, the stack of thin films is in contact with the glass substrate and the silver reflective layer. The mirror is then preferably made up of the glass substrate, the stacking of thin layers, the reflective silver layer and the paint layer.The paint layer is normally in contact with the reflective silver layer. However, the concept of contact does not preclude the presence of surface treatments commonly used in the silvering process. It is indeed advantageous to treat the surface onto which the silver will be deposited with a solution containing tin and palladium chlorides. These treatments can form extremely thin layers detectable only by advanced analytical techniques. The thin-film stack does not include a metallic layer, whether continuous or discontinuous. The thin-film stack preferably comprises a single layer based on silicon nitride. The glass substrate is preferably a flat substrate. The thickness of the glass substrate is preferably in the range of 1 to 19 mm, particularly 2 to 12 mm and even 3 to 9 mm. The glass according to the invention is a clear glass.The glass is preferably a soda-lime silicate glass, but other types of glass such as borosilicates or aluminosilicates may be used. The glass is preferably obtained by flotation. Clear glass is defined as colorless glass, including diamond glass. The reflective silver layer is deposited by silvering. Silvering is defined as the process classically used for the manufacture of mirrors, comprising the liquid deposition of a silver salt and a silver-conducing agent. The reflective silver layer preferably has a physical thickness ranging from 50 to 200 nm, particularly from 50 to 100 nm, or even from 60 to 90 nm. The mirror is preferably "copper-free," in the sense that the reflective silver layer is not covered by a copper layer. According to the invention, a layer of paint is deposited over the reflective silver layer.A paint layer is defined as a layer comprising at least one resin and at least one mineral filler, including at least one pigment. The paint layer is preferably obtained by depositing a liquid paint composition, generally comprising a solvent in addition to the resin and mineral fillers, and then drying the resulting layer. Throughout this text, the term "paint" will be used to refer to paint in its dry state, while the term "liquid paint" will be used to refer to paint in its liquid state, intended to be deposited on the substrate above the reflective silver layer. Drying this layer involves the evaporation of a large portion of the solvent. In some cases, when the paint is to be cross-linked, the paint layer must also be baked. We then distinguish between drying, in which solvents evaporate, the resin not having started to crosslink, and cooking, in which the resin crosslinks.According to another embodiment, the liquid paint is preferably water-based or solvent-free. "Water-based" means that the liquid paint contains less than 10%, and in particular less than 5% by weight, of organic solvent, or even no organic solvent at all. The weight percentage of dry extract in the liquid paint is preferably at least 50%, or even at least 60%, and in particular 60% to 70% in the case of water-based liquid paints. It may be 100% in the case of solvent-free liquid paint. The paint layer preferably comprises at least one resin and at least one mineral filler, including at least one pigment. At least one resin in the paint layer is preferably selected from acrylic resins, polyurethane resins, epoxy resins, and alkyd resins. Liquid paint is preferably based on an aqueous dispersion of an epoxy resin crosslinked with melamine.In the case of mirrors, such a paint has proven effective in protecting the underlying silver layer against corrosion. At least one mineral filler in the paint layer is advantageously chosen from zinc oxide, barium sulfate, zinc phosphates, particularly zinc orthophosphate, talc, calcium carbonate, mica, titanium dioxide, carbon black, and mixtures thereof. The mineral fillers improve the corrosion resistance of the silver layer and / or provide the desired opacity or tint. The paint layer preferably does not contain lead. The paint layer preferably comprises 20 to 50% by weight of resins and 30 to 80% by weight of mineral fillers. The paint layer may also contain various additives, such as antifoaming agents, biocides, or iodine agents. The liquid paint layer is preferably applied with a curtain, by spraying, or with a roller. It can be applied in several coats.The drying stage is preferably carried out in an oven at a temperature between 50 and 250°C, particularly between 100 and 200°C. The drying time is preferably 2 to 60 minutes, particularly 5 to 30 minutes. The drying stage is preferably preceded by a pre-drying stage at a lower temperature, particularly between 30 and 60°C for 5 to 60 minutes. The paint layer (after drying) preferably has a thickness in the range of 20 to 100 µm, particularly 30 to 80 µm, or even 40 to 70 µm. Greater thicknesses may be necessary where corrosion protection properties are required. This refers to the thickness of the layer in the final product. The paint layer can also be coated with a resin-based chip-retaining layer. The application of this resin-based chip-retaining layer can be achieved by depositing an aqueous dispersion of the resin.Such an aqueous dispersion is also called "tex." The chip retention layer is preferably made of resin. The resin is preferably polyurethane. The chip retention layer is then advantageously obtained by depositing an aqueous polyurethane dispersion. In the aqueous dispersion, particularly of polyurethane, the weight percentage of dry extract is preferably between 20 and 50%. Since such a resin layer does not require crosslinking, simple drying is sufficient. The advantages of such a resin choice are numerous. On the one hand, these resins withstand high temperatures, which is useful when the paint layer needs to be baked or completed later. On the other hand, these resins exhibit high elongation at break and low adhesion to the paint, which gives them good chip retention properties.The chip-retaining layer is preferably deposited directly onto the paint layer (i.e., in direct contact with it). The resin layer thickness is preferably between 20 and 60 µm, particularly between 25 and 40 µm. Thicknesses that are too small do not allow for the desired chip-retaining properties. This affects the layer thickness in the final product. The thin-film stack is preferably deposited by magnetic field-assisted sputtering. However, other techniques are possible, for example, chemical vapor deposition (CVD). The thin-film stack advantageously includes, in contact with the reflective silver layer, a metal oxide adhesion layer. This layer, intended to improve the adhesion and wetting of the silver layer during silver plating, is preferably made of titanium oxide.Other oxides such as zinc and / or tin oxides are also well suited. The titanium oxide adhesion layer is preferably deposited by magnetic field-assisted sputtering using a titanium oxide ceramic target, preferably without the addition of oxygen to the plasma or with only a small amount added. The adhesion layer preferably has a physical thickness ranging from 1 to 20 nm, particularly from 3 to 10 nm, and even more preferably from 3 to 5 nm. The thin-film stack preferably consists of two thin films. In this case, the thin-film stack consists, successively from the glass substrate, of a silicon nitride-based layer (advantageously in contact with the glass substrate), and then of an adhesion layer (advantageously in contact with the reflective silver layer). The thickness of the silicon nitride-based layer influences the color obtained in reflection.It is thus possible to vary the L* coordinate in reflection and obtain more or less intense colors. The physical thickness of the silicon nitride layer (in the case of a stack comprising only one such layer), or the sum of the physical thicknesses of each silicon nitride layer (in the case of a stack comprising several such layers), is preferably within a range of 30 to 80 nm, particularly 40 to 50 nm, or even 40 to 45 nm. It has been observed that greater thicknesses produce more intense colors, characterized by higher a* and b* values ​​in reflection. The reflected color is also influenced by the optical properties of the silicon nitride layer, particularly its extinction coefficient.The silicon nitride-based layer exhibits, at a wavelength of 550 nm, a refractive index n ranging from 2.7 to 3.6, preferably from 3.0 to 3.5, and an extinction coefficient k greater than 0.20, preferably ranging from 0.20 to 0.50. The extinction coefficient corresponds to the imaginary part of the complex refractive index. These parameters can be measured using known methods by arellipsometry. Such values ​​can be obtained by depositing the silicon nitride-based layer by magnetic field-assisted reactive sputtering, through a judicious choice of the proportion of nitrogen in the plasma, more particularly by reducing the proportion of nitrogen compared to the usual conditions for deposition of silicon nitride-based layers. Under typical conditions, the nitrogen and argon flow rates are approximately equal, and can give refractive indices between 1.9 and 2.2 and extinction coefficients on the order of 0.By reducing the nitrogen flow rate, for example to approximately three to five times lower than the argon flow rate, the aforementioned value ranges can be obtained. The volume ratio between the proportion of nitrogen and the proportion of argon in the plasma gas is preferably between 5 / 95 and 25 / 75, particularly between 6 / 94 and 15 / 85, or even between 7 / 93 and 11 / 89. Also, in the context of the deposition of the silicon nitride-based layer by magnetically assisted reactive sputtering, it has been observed that the deposition pressure during the deposition of the silicon nitride-based layer also influences the reflective appearance of the mirror. Higher pressure allows for greyer tints, characterized in particular by higher b* values. Conversely, lower pressure results in a* values ​​that may be too high compared to b* values, the resulting tint tending more towards pinkish-orange.The deposition pressure during the deposition of the silicon nitride-based layer is preferably between 0.1 and 1.5 Pa, in particular between 0.3 and 1.2 Pa, or even between 0.4 and 1.0 Pa. The mirror according to the invention preferably has the following colorimetric reflection coordinates: L* ranging from 60 to 80, in particular from 60 to 72, or even from 66 to 70, a* ranging from -2 to 3, and even from -1 to 2, in particular from -0.5 to 1.2, b* ranging from -3 to 5, and even from -2 to 2, or even from -1 to 1. The colorimetric coordinates are calculated from a reflection spectrum between 380 and 780 nm, taking into account the illuminant D65 and the CIE-1964 reference observer (10°). The light reflection of the mirror (also taking into account the illuminant D65 and the CIE-1964 reference observer (10°)) is preferably at least 30% and preferably between 31% and 45%. The light transmission is zero due to the presence of the opaque paint layer.The mirror preferably exhibits good corrosion resistance. The invention is illustrated by the following non-limiting examples. Example 1 A clear glass substrate marketed by the Applicant under the trade name Planicle ar has been coated with a stack of thin films by magnetic field-assisted sputtering (magnetron process). The stacking consists successively of: - a silicon nitride layer comprising 8% by weight of aluminium, and having a physical thickness of 43 nm, deposited using a silicon and aluminium target, under a flow of plasma gas comprising 9.1% by volume of nitrogen and 90.9% by volume of argon, under a pressure of 0.8 Pa, then, - an adhesion layer of titanium oxide with a physical thickness of 5 nm, deposited using a substoichiometric titanium oxide ceramic target, in the absence of oxygen in the plasma.The values ​​of n and k at 550 nm for the silicon nitride layer are 3.18 and 0.35, respectively. The substrate of this layer was then coated with a reflective silver layer by a silver plating process. The thickness of the silver layer is 70 nm. In a known manner, the silver layer was then coated with a layer of paint. The reflected colorimetric coordinates of the obtained mirror (illuminant D65 and reference observer CIE-1964) are as follows: L* = 66.4, a* = -0.8, and b* = 0.7. The reflected color is gray. Examples 2 to 10 In these examples, compared to example 1, at least one parameter has been varied, chosen from among the physical thickness of the silicon nitride layer, the deposition pressure, the percentage of nitrogen in the plasma gas and the thickness of the titanium oxide adhesion layer. All other conditions of example 1 are unchanged.Table 1 below indicates for each example: the thickness of the silicon nitride layer, denoted e and expressed in nm, - the deposition pressure, denoted P and expressed in Pa, - the percentage of nitrogen in the plasma gas, denoted N2 and expressed in %, - the physical thickness of the titanium oxide layer, denoted test and expressed in nm, - the light reflection, denoted RL, expressed in %, - the values ​​of L*, a*, b*. [Table 1]

Claims

Claims 1. A specular mirror comprising a clear glass substrate coated on one of its faces, successively from said glass substrate, with a stack of thin films, a reflective silver layer deposited by silver genture, and then a paint layer, characterized in that said stack of thin films does not comprise a chemmetallic layer and comprises at least one silicon nitride-based layer having, at a wavelength of 550 nm, a refractive index n ranging from 2.7 to 3.6 and an extinction coefficient k greater than 0.

20.

2. A mirror according to claim 1, in which the stack of thin films is in contact with the glass substrate and the reflective silver layer.

3. A mirror according to any one of the preceding claims, in which the paint layer is in contact with the reflective silver layer.

4. Mirror according to any one of the preceding claims, wherein the stacking of thin layers comprises a single layer based on silicon nitride. 5.A mirror according to any one of the preceding claims, wherein the reflective silver layer has a physical thickness ranging from 50 to 200 nm.

6. A mirror according to any one of the preceding claims, wherein the stack of thin layers comprises, in contact with the reflective silver layer, an adhesion layer of metal oxide, in particular titanium oxide.

7. A mirror according to the preceding claim, wherein the adhesion layer has a physical thickness ranging from 1 to 20 nm, in particular from 3 to 10 nm.

8. A mirror according to any one of the preceding claims, wherein the physical thickness of the silicon nitride-based layer, or the sum of the physical thicknesses of each silicon nitride-based layer, is included in a range from 30 to 80 nm, in particular from 40 to 50 nm, or even from 40 to 45 nm.

9. A mirror according to any one of the preceding claims, wherein the thin-film stack consists of two thin films.

10. A mirror according to any one of the preceding claims, wherein the silicon nitride-based layer has, at a wavelength of 550 nm, a refractive index ranging from 3.0 to 3.5 and / or an extinction coefficient κ ranging from 0.20 to 0.

50.

11. Mirror according to one of the preceding claims, which has the following colorimetric coordinates in reflections: L* ranging from 60 to 80, in particular from 60 to 72, a* ranging from -2 to 3, in particular from -1 to 2, b* ranging from -3 to 5, in particular from -2 to 2. 12.A mirror according to any one of the preceding claims, having a light reflectance of at least 30%, preferably between 31% and 45%.

13. A method for obtaining a mirror according to any one of the preceding claims, comprising a step of depositing the stack of thin films onto a clear glass substrate, then a step of depositing, by silver plating, the reflective silver coating onto said stack of thin films, then a step of depositing a layer of liquid paint onto said silver layer, and then a step of drying said liquid paint layer.

14. A method according to the preceding claim, wherein the stack of thin films is deposited by magnetic field-assisted sputtering.

15. A method according to the preceding claim, wherein the silicon nitride-based layer is deposited by magnetic field-assisted reactive sputtering in a plasma gas such that the volume ratio between the proportion of nitrogen and the proportion of argon ion in the plasma gas is between 5 / 95 and 25 / 75, in particular between 6 / 94 and 15 / 85.

16. A method according to claim 14 or 15, wherein the deposition pressure during the deposition of the silicon nitride-based layer is between 0.1 and 1.5 Pa, in particular between 0.3 and 1.2 Pa.