FR3096471A1 - Colored mirror - Google Patents

Abstract

The subject of the invention is a specular mirror comprising a glass substrate coated on one of its faces, successively from said glass substrate, with a stack of thin layers, with a reflective layer of silver deposited by silver plating and then d 'a paint layer, characterized in that said stack of thin layers does not include 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 2.2 to 2.6 and an extinction coefficient k ranging from 0.02 to 0.06.

Description

Description Title of the invention: Colored mirror

The invention relates to the field of mirrors.

It relates more particularly to specular mirrors, in which a user can admire himself. Such mirrors are for example arranged inside dwellings, for example in bathrooms, or are used as elements of pieces of furniture (doors cupboard...) or decoration.

These mirrors generally comprise a glass substrate coated on face 2 (the face opposite that facing the user) with a reflective silver layer, which is 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 has the function of protecting the silver layer against corrosion.

The object of the invention is to provide a mirror having a golden hue in reflection.

To this end, the invention relates to a specular mirror comprising a glass substrate coated on one of its faces, successively from said glass substrate, with a stack of thin layers. of a reflective layer of silver deposited by silvering then of a layer of paint, characterized in that the 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 2.2 to 2.6 and an extinction coefficient k ranging from 0.02 to 0.06.

Another object of the invention is a process for obtaining the aforementioned mirror, comprising a step of depositing the stack of thin layers on a substrate. of glass, then a step of depositing, by areenture, the reflective layer of silver on said stack of thin layers, then a step of depositing the layer of liquid paint on said layer of silver, then a step of drying said layer of liquid paint.

[0005] By the expression “coated”, it is meant that the layer which coats the substrate or another layer is deposited above said substrate or this other layer, but not necessarily in contact with them.

When a first layer is placed “on top” of a second layer, it is meant that the first layer is farther from the substrate than the second layer.

[0006] The expression "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 layer based on silicon nitride advantageously comprises at least 80%, even 90% of silicon nitride.

When it is deposited by magnetic field-assisted sputtering, it advantageously comprises a small amount of aluminum, because the doping of a silicon target with aluminum makes it possible to accelerate the deposition of the layer.

The stoichiometry of the silicon nitride layer is not prejudged here.

[0007] Preferably, the stack of thin layers is in contact with the glass substrate and the reflective silver layer.

The mirror then preferably consists of the glass substrate, the stack of thin layers, the reflective silver layer and the paint layer.

The paint layer is normally in contact with the reflective silver layer.

[0008] The concept of contact does not however exclude the presence of surface treatments conventionally used in the silver plating process.

It is in fact advantageous to treat the surface on 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.

[0009] The thin layer dc stack does not include a metal layer, whether continuous or discontinuous.

It has indeed been observed that the metallic layers give a darker and less bright appearance, drawing more towards bronze.

[0010] The dc thin layer stack preferably comprises a single layer based on dc silicon nitride.

[0011] The glass substrate is preferably a flat substrate.

The thickness of the glass substrate is preferably within a range ranging from 1 to 19 mm, in particular from 2 to 12 mm and even from 3 to 9 mm.

The glass is preferably a silico-soda-lime glass, but other types of glass such as borosilicates or aluminosilicates can be used.

The glass is preferably obtained by floating.

The glass is preferably colorless.

It preferably comprises an iron content by weight, expressed as Fe20-,, of between 0.01 and 0.20%, in particular between 0.04 and 0.12%.

[0013] The reflective layer of silver is deposited by silver plating.

By silver plating is meant the method conventionally used for the manufacture of mirrors, and comprising the liquid deposition of a silver salt and a reducing agent.

The reflective silver layer preferably has a physical thickness ranging from 50 to 200 nm, in particular from 50 to 100 nm.

[0015] The mirror is preferably “copper-free”, in the sense that the reflective silver layer is not covered by a copper layer.

[0016] In the mirror, the layer of paint is generally obtained by drying a liquid paint deposited on the substrate.

Throughout this text, the term paint "will be used to qualify the paint in the dry state, while the term liquid paint" will be used to qualify the paint in the liquid state, intended to be deposited on the substrate. . 3

The liquid paint is preferably water-based or solvent-free.

By “aqueous base” is meant that the liquid paint comprises less than 10%, in particular 5% by weight of organic solvent, or even does not comprise organic solvents.

The weight percentage of dry extract of the liquid paint is preferably at least 50%, or even 60%, in particular from 60 to 70% in the case of water-based liquid paints.

It can 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 is preferably chosen from acrylic resins, polyurethane resins, epoxy resins and alkyd resins.

At least one mineral filler is advantageously chosen from zinc oxide, barium sulphate, zinc phosphates, in particular zinc orthophosphate, talc, calcium carbonate, mica, titanium oxide, carbon black and mixtures thereof.

The mineral fillers make it possible to improve the corrosion resistance of the silver layer and/or to obtain 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 further comprise various additives, such as antifoaming agents, biocides or surfactants.

The layer of liquid paint is preferably applied with a curtain, by spraying or by roller.

It can be deposited in several passes.

The drying step is preferably carried out in an oven, at a temperature of between 50 and 250°C, in particular between 100 and 200°C.

The drying time is preferably 2 to 60 minutes, especially 5 to 30 minutes.

The drying step is preferably preceded by a pre-drying step at a lower temperature, in particular between 30 and 60° C. for 5 to 60 minutes.

[0021] The layer of paint (after drying) preferably has a thickness of between 40 and 350 μm, in particular between 70 and 300 μm, or even between 100 and 250 μm.

[0022] The stack of thin layers is preferably deposited by cathode sputtering assisted by a magnetic field.

Other techniques are however possible, for example chemical vapor deposition (CVD) techniques.

The stack of thin layers advantageously comprises, in contact with the reflective layer of silver, an adhesion layer of metal oxide.

This layer, intended to improve the adhesion and the wetting of the silver layer during the deposition by silvering, is preferably made of titanium oxide.

Other oxides such as zinc and/or tin oxides are also well suited.

[0024] The titanium oxide adhesion layer is preferably deposited by magnetic field-assisted sputtering using a titanium oxide ceramic target, preferably without adding oxygen to the plasma or with an addition in small amount.

The adhesion layer preferably has a physical thickness ranging from 2 to 20 nm, in particular from 3 to 10 nm.

The stack of thin layers preferably consists of two thin layers.

The stack of thin layers is in this case constituted, successively from the glass substrate, of a layer based on silicon nitride (advantageously in contact with the glass substrate), then of an adhesion layer ( advantageously in contact with the reflective layer of silver).

The thickness of the layer based on silicon nitride influences the color obtained in reflection.

It is thus possible to vary the coordinate L" in reflection and to obtain more or less intense tints.

[0028] The physical thickness of the layer based on silicon nitride (in the case of a stack comprising only a single layer of this type), or the sum of the physical thicknesses of each layer based on silicon nitride (in the case of a stack comprising several of these layers), is preferably within a range ranging from 10 to 200 nm, in particular from 30 to 120 nm, or even from 50 to 100 nm.

It was observed that the higher thicknesses gave more sustained hues.

The color in reflection is also influenced by the optical properties of the layer based on silicon nitride, in particular by its extinction coefficient.

The layer based on silicon nitride has, at a wavelength of 550 nm, a refractive index n ranging from 2.2 to 2.6, preferably from 2.3 to 2.5, and a coefficient d extinction k ranging from 0.02 to 0.6, preferably from 0.03 to 0.3.

The extinction coefficient corresponds to the imaginary part of the complex refractive index.

These parameters can be measured in known manner by ellipsometry.

[0031] Such values can be obtained by depositing the layer based on silicon nitride by reactive sputtering assisted by magnetic field, thanks to 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 depositing layers based on silicon nitride.

Under usual conditions, the flow rates of nitrogen and argon are substantially equal, and give refractive indices of the order of 2.1 and extinction coefficients of the order of 0.

By reducing the nitrogen flow, for example so as to have a nitrogen flow approximately three times lower than the argon flow, the aforementioned ranges of values can be obtained.

The volume ratio between the proportion of nitrogen and the proportion of argon in the plasma gas is preferably between 10/90 and 35/65, in particular between 20/80 and 30/70.

The mirror according to the invention preferably has the following colorimetric coordinates in reflection: L* ranging from 60 to 90, in particular from 70 to 88, or even from 75 to 85, a* ranging from -2 to 10, in particular from -2 to 5, or even from -2 to 2, b* ranging from 30 to 70, in particular from 40 to 65, or even from 50 to 60.

The colon metric coordinates are calculated from a reflection spectrum between 380 and 780 nm, taking into account the D65 illuminant and the CIE-1964 reference observer (10n).

The light reflection of the mirror (also taking into account the illuminant D65 and the CIE-1964 reference observer (10n)) is preferably at least 50%, in particular 60%.

The light transmission is zero due to the presence of the paint layer, which is opaque.

The mirror preferably has good corrosion resistance.

Typically, edge corrosion is at most 1.5 mm, even 1.2 mm and even 1.0 mm after a 120 hour CASS test according to ISO 9227:2012.

The CASS test is a cupro-acetic salt spray resistance test.

The invention is illustrated by the following non-limiting example.

[0036] A clear glass substrate marketed by the Applicant under the trade reference Planicicar was coated with a stack of thin layers by cathode sputtering assisted by a magnetic field (magnetron process).

[0037] The stack consists successively of: - a layer of silicon nitride comprising 8% by weight of aluminium, and having a physical thickness of 80 nm, deposited using a silicon and aluminum target , under a flow of plasma gas comprising 26% by volume of nitrogen and 74% by volume of argon, then, - an adhesion layer of titanium oxide with a physical thickness of 5 nm, deposited using of a sub-stoichiometric titanium oxide ceramic target, in the absence of oxygen in the plasma.

[0038] The values of n and k at 550 nm from the silicon nitride layer are 2.42 and 0.09 respectively.

The substrate provided with this stack was then coated with a reflective layer of silver by a silvering process.

The thickness of the silver layer is 70 nm.

In known manner, the silver layer was then coated with a layer of paint.

[0040] The colorimetric coordinates in reflection of the mirror obtained (illuminant D65 and CIE-1964 reference observer) are as follows: U=83.8, a*=−0.9 and Wt=56.4.

The color in reflection is golden. 6

Claims (1)

CLAIMS[Claim I] Specular mirror comprising a glass substrate coated on one of its faces, successively from said glass substrate, with a stack of thin layers, with a reflective layer of silver deposited by silvering then with a layer of paint, 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 2.2 to 2.6 and an extinction coefficient k ranging from 0.02 to 0.06. [Claim 2] Mirror according to claim 1, in which the stack of thin layers is in contact with the glass substrate and the reflective layer of silver. [Claim 3] Mirror according to one of the preceding claims, in which the layer of paint is in contact with the reflective layer of silver. [Claim 4] Mirror according to one of the preceding claims, in which the reflective layer of silver has a physical thickness ranging from 50 to 200 nm. [Claim 5] Mirror according to one of the preceding claims, in which the stack of thin layers comprises, in contact with the reflective layer of silver, an adhesion layer of metal oxide, in particular of titanium oxide. [Claim 6] Mirror according to one of the preceding claims, in which the physical thickness of the layer based on silicon nitride, or the sum of the physical thicknesses of each layer based on silicon nitride, is included in a range ranging from 10 to 200 nm. [Claim 7] Mirror according to one of the preceding claims, in which the stack of thin layers consists of two thin layers [Claim 8] Mirror according to one of the preceding claims, which has the following colorimetric coordinates in reflection : L* ranging from 60 to 90, a* ranging from -2 to 10, b* ranging from 30 to 70. [Claim 9] Process for obtaining a mirror according to one of the preceding claims, comprising a step of depositing the stack of thin layers on a glass substrate, then a step of depositing, by silvering, the reflective layer of silver on said stack of thin layers. then a step of depositing a layer of liquid paint on said layer of silver, then a step of drying said layer of liquid paint. 7 [Claim 10] Process according to the preceding claim, in which the stack of thin layers is deposited by sputtering assisted by a magnetic field.