Reflective glazing comprising a chromium layer

Abstract

The invention relates to a reflective glazing capable of withstanding heat treatment, in particular annealing, bending and / or tempering, the glazing comprising a glass substrate and a stack of layers including a layer comprising silicon oxide having a thickness of between 15 and 35 nm, a metal layer based on chromium Cr having a thickness of between 45 and 65 nm, a layer comprising silicon nitride having a thickness of more than 20 nm and less than 30 nm and a layer consisting essentially of a metal chosen from titanium, zirconium, silicon or mixtures thereof, which metal has a thickness of more than 1 nm and less than 3 nm.

Description

Description Title: REFLECTIVE GLAZING COMPRISING A CHROMIUM LAYER. 5 The present invention relates to a glazing comprising a stack of layers of metallic appearance reflecting visible light and capable of withstanding heat treatments of the annealing, bending, thermal toughening type. Such a glazing comprises on a glass substrate a coating 10 comprising an essentially metallic layer reflecting a major part of the visible light, most often made of silver or alternatively another metal such as chromium. Most often this reflective layer is encapsulated in the stack by dielectric materials to protect it from corrosion. 15 Glazings coated with such a stack of layers having this fundamental structure are known in different embodiments.In other applications, for example for cladding walls or facades, for aesthetic reasons, the focus is more on the reflective properties of the layer stack. In many cases, a metallic-looking reflection is desired, but a reduced reflection with a very low light transmission is often preferred. Glazings with a high metallic reflection and a relatively low light transmission are therefore very decorative. In architecture, they are often used for cladding walls and facades (as glazing or facade paving) as mirror elements, as semi-transparent mirrors or as decorative glass plates. They can also be provided with an additional decorative print and are most often used in toughened and / or curved (bent) form.If they are used as monolithic glass panes, the surface layer is exposed without any protection to the atmosphere, so that it must have a particularly high resistance capacity to. atmospheric influences but also sufficient scratch resistance, which is essential in particular for cleaning operations. For safety reasons and / or to increase their bending and impact resistance, the 5 coated glass substrates intended for these applications are conventionally prestressed by thermal toughening, i.e. heated to a temperature above 500°C, 550°C or even 600°C and then very quickly cooled. The reflective thin-film stack described above must be able to overcome this thermal stress without damage. In particular, its aesthetic, optical, or even thermal or energy properties of coated glass glazing must not be affected by this.In particular, it is important that these glazings retain relatively neutral colors after such tempering, on the side 15 of the uncoated glass face (called the glass-side face) but also on the side of the stack of layers (called the stack-side face), that the chemical and physical resistance is sufficient to withstand external aggressions. Primarily, it is also essential that the tempering operations 20 do not result in the appearance of corrosion points (often called pinholes in the field.) The applicant company has already described, in publication EP 0 962 429 A1, a semi-transparent glazing with a light transmission of between 2 and 4% having a high thermal resistance 25. In the case of this known stack of layers, the dielectric base layer is composed of a material based on SiO2, Al2O. 3,of SiON, Si3N4 or AlN or a mixture of at least two of these materials. Among all these materials, it is indicated in paragraph

[0028] that the use of a base layer of silicon nitride is preferred because it protects the chromium layer better than another layer such as silicon oxide. The upper layer according to this publication can be based on silicon, silicon nitride or aluminum nitride. It is indicated in this publication that the thickness of this layer is between 2 and 20 nm, so as to limit the color in reflection of the glazing, in particular on the coating side. New glazings are now being sought with a light transmission significantly lower than that covered by EP 0962 429, and in particular less than 1%, or even less than 0.5%. To obtain such glazings, the applicant company has carried out a thickening of the chromium layer, on the basis of the stacks described in this publication. Such thickening leads to a reduction in light transmission but also to an increase in the visibility of defects such as corrosion points as described subsequently in the 10 examples.The invention thus aims to develop a glazing having a light reflection RL of the glass greater than 45% and preferably greater than 50% and a light transmission TL less than 1%, and preferably less than 0.5%, and comprising a stack of 15 reflective layers of metallic appearance, having high scratch and corrosion resistance and high thermal stability, such that it can withstand heat treatment at a temperature greater than 500°C, in particular toughening, bending or the like, without the appearance of corrosion points (pinholes) and whose coloring is substantially neutral in reflection on the glass side (a* and b* less than 5 in absolute value and if possible negative in the Lab system) and very little colored on the stack side (in particular a b* value less than or equal to 6 to avoid excessive yellow coloring), after said heat treatment.25 More particularly, the present invention relates to a reflective glazing capable of withstanding a heat treatment, in particular of the annealing, bending and / or tempering type, said glazing comprising a glass substrate and a stack of layers deposited on one of the faces 30 of said glass substrate, said stack successively comprising, from the surface of said substrate: - a layer comprising silicon oxide with a thickness of between 15 and 35 nm, - a metallic layer based on chromium Cr, with a thickness 35 of between 45 and 65 nm, - a layer comprising silicon nitride, with a thickness. greater than 20 nm and less than 30 nm, - a layer consisting essentially of a metal chosen from titanium, zirconium, silicon or their mixtures, with a thickness greater than 1 nm and less than 3 nm. 5 According to preferred but non-limiting embodiments of the present invention, which can of course, if necessary, be combined with each other: - The metal layer comprises more than 80% by weight of chromium, and preferably more than 90% by weight of chromium. 10 - The metal layer consists essentially of chromium. - The metal layer consists of an alloy of chromium with at least one other metal element, in which chromium represents more than 50% by weight of said alloy, said at least one element preferably being chosen from Al and / or Si. 15 - The metal layer consists of a CrAl alloy preferably comprising 20-25% by weight of Al, a CrSi alloy comprising 15 to 49% by weight of Si, or a CrAlSi alloy comprising 70-80% by weight of Cr.- The layer comprising silicon oxide has a thickness of between 21 and 29 nm. - The chromium-based metal layer has a thickness of between 50 and 60 nm. - The layer comprising silicon nitride has a thickness of between 21 and 28 nanometers, preferably between 21 and 25 nm. - The stack comprises only a single chromium-based layer. - The stack does not comprise silver or gold layers. - The stack does not comprise metal layers other than the chromium-based layer. 30 - The layer comprising silicon oxide is directly in contact with the surface of the glass substrate and directly in contact with the chromium-based layer. - The chromium-based layer is directly in contact with the layer comprising silicon nitride. 35 - The layer consisting essentially of titanium, zirconium or silicon is directly in contact with the layer comprising. silicon nitride. - The layer consisting essentially of titanium, zirconium or silicon is the last layer of the stack. - said stack only comprises the layer comprising silicon oxide, the chromium-based layer, the layer comprising silicon nitride and the layer consisting essentially of a metal chosen from titanium, zirconium, silicon or mixtures thereof. - The light transmission of said coated glazing is less than 1%, preferably less than 0.5%. - The light reflection of the uncoated side of the stack is greater than 45%, preferably greater than 50%. - The stack of layers is in the form of a discontinuous coating, of the decorative or screen type. - An opaque colored layer, in particular of the paint or enamel type, covers the areas of the glazing free from the stack. - Said glazing is annealed, curved and / or toughened. - said glazing is monolithic.20 The layer comprising silicon nitride mainly comprises silicon and nitrogen as main constituents. In particular, silicon and nitrogen together represent more than 50%, more than 60% or even more than 70% or even more than 80% of the atoms present in a layer, or even more than 90% of the atoms present in a layer. Preferably, said layers comprising silicon nitride are essentially composed of silicon and nitrogen and optionally of at least one element chosen from aluminum, boron or zirconium, preferably aluminum, apart from unavoidable impurities. Said layers comprising silicon nitride are in principle free of oxygen apart from unavoidable impurities, for example they comprise less than 5 mol% of elemental oxygen, in particular less than 1 mol% of elemental oxygen.Preferably, said layer has an N / Si ratio greater than 1.25 and are stoichiometric or substantially stoichiometric layers, preferably substantially stoichiometric. By "stoichiometric" is meant that the N / Si ratio is equal to 1.33. these silicon-based nitride layers, corresponding to the Si3N4 compound. By "substantially stoichiometric" is meant, for example, that the value measured for this Si3N4 compound differs by less than 5% from this theoretical value. 5 Indeed, it should be noted that the layers comprising silicon nitride according to the invention are obtained by a magnetron-assisted sputtering process from a metallic silicon target which may comprise a minor amount of another element such as aluminum and / or zirconium, for example around 8 atomic% of aluminum, in a reactive atmosphere containing nitrogen. In such a case, the N / Si ratio may vary substantially from the theoretical value 1.33 (= 4 / 3) (corresponding to the defined compound Si3N4) taking into account the stoichiometries of the defined compounds AlN and Si3N4.As an example, for a layer of silicon nitride comprising a little aluminum, obtained with the target described previously (8% aluminum), the N / Si ratio of the stoichiometric layer theoretically corresponds to a formulation: 92% (SiN1.33) / 8% (AlN) or an N / Si ratio of 1.41 (based on a theoretical formula 0.92 SiN1.33 0.08 AlN, or a ratio: N / Si 20 = [(0.92×1.33+0.08×1) / (0.92)] = 1.41). Similarly, the layer comprising silicon oxide mainly comprises silicon and oxygen as main constituents. In particular, silicon and oxygen together represent more than 50%, more than 60% or even more than 70% or even more than 25 80% of the atoms present in a layer, or even more than 90% of the atoms present in a layer.Preferably, said layers comprising silicon oxide are essentially composed of silicon and oxygen and optionally of at least one element chosen from aluminum, boron or zirconium, preferably aluminum, with the exception of unavoidable impurities. The layers comprising silicon oxide according to the invention are obtained by a magnetron-assisted cathode sputtering process from a metallic silicon target which may comprise a minor amount of another element such as aluminum and / or zirconium, for example around 8 atomic% of aluminum, in a reactive atmosphere containing oxygen. In particular, the silicon target is. same as that used to obtain the silicon nitride layer described above. The reflective functional layer is based on chromium. It is preferably composed essentially of chromium, or even 5 is composed of chromium, with the exception of unavoidable impurities. It can alternatively be based on an alloy comprising mainly chromium, in particular more than 50% chromium by weight, preferably more than 60% by weight, or even more than 70% by weight or even more than 80% by weight and very preferably more than 90% by weight of chromium. 10 This is in particular a binary chromium-aluminium alloy CrAl, with a mass content of 10% to 40% in aluminium, in particular 20 to 25% by weight of aluminium. It is also a chromium-silicon alloy, Cr-Si, with preferably at least 5 to 10% by weight of silicon, in particular between 5 and 49% by weight of silicon.It may also be a three-component alloy such as the Cr-Al-Si alloy, preferably comprising at least 60% by weight of chromium, in particular between 70 and 80% by weight of chromium. The upper layer of metal with a thickness greater than 1 nm and less than 3 nm consists essentially of a metal chosen from Ti, Zr, Si or their mixtures. Preferably, the thickness of this layer is between 1.5 nm and 2.5 nm. For example, the atomic sum of these three elements may represent more than 90%, or even more than 95% of the atoms in the layer (excluding oxygen). Preferably, the layer consists essentially of Ti. During a heating step such as quenching, bending or annealing, this layer is at least partially oxidized to the corresponding oxide. Thus, a layer of Ti is ultimately present in the stack in the form of TiOx, after quenching.The stacks of layers according to the invention make it possible to meet 30 to a large extent all the aforementioned requirements, the desired result being produced by the combined action of the different layers of the stack. The glazing according to the invention is constituted by a glass substrate on which the layers of the stack are deposited and is said to be 35 "bendable", and / or "toughenable", that is to say that they can undergo such a heat treatment without significant modification of their. appearance (in particular in terms of corrosion and colorimetry). The stacks of layers according to the invention are advantageously deposited on the glass substrates according to the known methods of reactive cathode sputtering assisted by a magnetic field 5 in industrial continuous coating installations. The coated glazings can then be subjected to a usual toughening process, without the stack of layers significantly losing its desired optical and aesthetic properties, in particular its colors in reflection. 10 After the deposition of the stack of layers according to the invention, an additional layer, for example a continuous color layer, in particular opaque, can be applied to the coated side, possibly for aesthetic purposes or to manufacture opaque glazings of the spandrel type. This layer can also be paint 15 or enamel, obtained by firing an enameling composition in a known manner.In this case, the firing operation can advantageously be linked to the operation of annealing, bending or tempering the glass substrate carrying the stack. The two operations can thus be concomitant. 20 The invention and its advantages are illustrated by the following examples: ^ Reference example (according to EP0962429) 25 The reference example is example 4 of the prior publication EP0962429 A1, which describes the following glazing: Glass - 15 nm Si3N4 - 35 nm Cr - 3 nm Si3N4 - 3 nm Ti, where the Ti is, after tempering, at least partially oxidized to titanium oxide TiOx. 30 Example 1 (comparative) In this example, a glazing identical to the reference example is synthesized but in which the thickness of the chromium layer is increased to 55 nm. 35 The conditions for depositing the stack are as follows:. On an industrial vacuum coating plant, 4 mm thick Planiclear™ clear float glass substrates are coated using a conventional magnetic field-assisted sputtering process to obtain the following layer stack: Glass - 15 nm Si3N4 - 55 nm Cr - 3 nm Si3N4 - 3 nm Ti The SiO2 layer is sputtered in DMS mode (Dual-Magnetron-Sputter mode), with two cathodes and an alternating current under a reactive atmosphere from a Si target with a working gas composed of Ar / O2, and the Si3N4 layer under a reactive atmosphere from a Si target with a working gas composed of Ar / N2, according to techniques well known in the field. The Cr layer is obtained by sputtering a target made of Cr in an atmosphere consisting of argon. The top Ti layer is obtained by sputtering a target made of Ti in an atmosphere made of argon.Example 2 (comparative) In this example, the thickness of the silicon nitride layer deposited above the chromium layer was increased: The procedure is the same as for example 1 to obtain the following glazing: Glass - 22 nm Si3N4 - 55 nm Cr - 23 nm Si3N4 – 2 nm Ti Example 3 (according to the invention) In this example, the procedure is the same as for example 1 to obtain the following glazing: Glass - 22 nm SiO2 - 55 nm Cr - 23 nm Si3N4 - 2 nm Ti Example 4 (comparative) In this example, the procedure is the same as for example 1 to obtain the following glazing: Glass - 22 nm SiO2- 55 nm Cr - 23 nm Si3N4- 3 nm Ti Example 5 ... proceed in the same way as for the example. 1 to obtain the following glazing: Glass - 22 nm SiO2 - 55 nm Cr - 23 nm Si3N4 - 1 nm Ti Example 6 (comparative) In this example, the procedure is the same as for example 1 to obtain the following glazing: Glass - 22 nm SiO2 - 55 nm Cr - 30 nm Si3N4 - 2 nm Ti Example 7 (comparative) In this example, the procedure is the same as for example 1 to obtain the following glazing: Glass - 22 nm SiO2 - 55 nm Cr - 23 nm Si3N4 The glazing thus coated is thermally toughened in an industrial toughening installation, by heating to a temperature of approximately 650°C and rapid cooling by blowing cold air using standard techniques.The glazings are then subjected to the following tests to determine their resistance to toughening and their potential use: - Optical quality: Measurement of the transmission of the coating system in the visible spectral region TL, of the reflection in the visible spectral region RL (according to illuminant D65) according to the ISO9050 (2003) standard. The a* and b* coordinates are determined in the colorimeter system (L, a*, b*) CIELAB. - Mechanical resistance: the scratch resistance of the coatings was measured using a SCRATCH HARDNESS TESTER 413 device supplied by the Erichsen company according to the following protocol: The sample is mounted on a rotary table (number of revolutions in the standard version: 5 min. -1). The test tool is attached to a load arm with an adjustable weight that allows the pressure of the tool to be adjusted to the sample (load range 0-10 N). The strength of the sample to this effect is visually assessed using the scratch track. The sample is considered suitable for sale if there is no no visible scratches with a load of 1 N and low visibility of scratches at 3 and 5 N. - Toughening corrosion test: the number of corrosion points is visually observed after toughening. 3 levels 5 of occurrence are defined: ++: very numerous corrosion points (pinholes) +: some visible corrosion points 0: no visible corrosion points 10 The results of the tests carried out for the evaluation of the properties of the layers are gathered in the following Table I, in which the results of the tests on the coated glazings after the toughening treatment are reported. [Table 1] Test Example Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 ) s R eee O *data EP0962429 NM: not measured The test results show that the stability of the stack, in particular its corrosion level and its colorimetry, is not affected by the thermal hardening treatment described above only for example 3 according to the invention, that is to say in which the thicknesses and materials used in the stack are selected according to the criteria defined above, and as reported in the claims which follow. In detail, it can be seen in the preceding table that the use of a layer of silicon oxide below the chromium layer is much more effective in preventing the appearance of corrosion points of the "pinholes" type. Without linking such a finding to any theory, it is possible that such defects were already present in example 4 of EP0962429 with a chromium thickness of 35 nm as described in the comparative example but were not visually detectable, due to a TL greater than 2%. Thus, comparative examples 1 and 2, which include a silicon nitride-based undercoat, exhibit such defects, unlike the layers whose undercoat is based on silicon oxide. Comparative example 1 shows in particular that the thickening of the chromium layer in the example according to EP 0962429 leads to the visual appearance of very many corrosion points, making such a product unsaleable. Comparative example 2 further shows that a thicker silicon nitride-based undercoat leads to a marked and undesirable yellow appearance of the glazing in reflection on the stack side (b* value much higher than 6).Examples 3 to 7, by comparison with Examples 1 and 2, unexpectedly show that the combination of an underlayer comprising silicon oxide and an overlayer comprising silicon nitride with a thickness greater than 20 nm makes it possible to effectively prevent the formation of said corrosion points. Comparative Examples 4 and 5 show the importance of selecting the thickness of the layer between 1 and 3 nm: thus a thickness of 3 nm leads to an undesirable marked yellow appearance of the glazing in reflection on the stack side, whereas a layer of 1 nm does not provide sufficient mechanical strength for the stack.Comparison of Comparative Example 7 with Example 3 according to the invention also shows that an additional metallic layer of Ti above the silicon nitride layer in the stack only very slightly modifies the b* value in reflection on the stack side, but only if its thickness does not reach 3 nanometers (Comparative Example 4). Comparative Example 6 shows that too great a thickness of the silicon nitride layer above the reflective chromium layer also leads to an undesirable marked yellow appearance of the glazing in reflection on the stack side (b* much higher than 6). The substrate provided with the stack of layers is preferably made of glass, and can be used as monolithic or incorporated glazing. in a laminated glazing or insulating multiple glazing structure. It can remain transparent or be opaque, and be continuous or have patterns. 5

Claims

Claims 1. Reflective glazing capable of withstanding heat treatment, in particular annealing, bending and / or tempering, said glazing comprising a glass substrate and a stack of layers deposited on one face of said glass substrate, said stack comprising successively, from the surface of said substrate: - a layer comprising silicon oxide of thickness between 15 and 35 nm, - a metallic layer based on chromium Cr, of thickness between 45 and 65 nm, - a layer comprising silicon nitride, of thickness greater than 20 nm and less than 30 nm, - a layer consisting essentially of a metal selected from titanium, zirconium, silicon or mixtures thereof, of thickness greater than 1 nm and less than 3 nm.

2. Glazing according to claim 1, in which the metallic layer consists essentially of chromium. 3.

1. Glazing according to claim 1, wherein the metallic layer is made of a chromium alloy with at least one other metallic element, wherein the chromium represents more than 0% by weight of said alloy, said at least one element being selected by reference from Al and / or Si.

4. Glazing according to claim 1, wherein the metallic layer is made of a CrAl alloy preferably comprising 0-25% by weight of Al, a CrSi alloy comprising 15-49% by weight of Si, or a CrAlSi alloy comprising 70-80% by weight of Cr.

5. Glazing according to any one of the preceding claims, wherein the layer comprising silicon oxide has a thickness of between 21 and 29 nm.

6. Glazing according to any one of the preceding claims, wherein the chromium-based metallic layer has a thickness of between 50 and 60 nm.

7. Glazing according to any one of the preceding claims in which the layer comprising silicon nitride has a. thickness between 21 and 28 nanometers, preferably between 21 and 25 nm.

8. Glazing according to any one of the preceding claims, wherein the stack comprises only a single chromium-based layer.

9. Glazing according to any one of the preceding claims, wherein the layer comprising silicon oxide is in direct contact with the surface of the glass substrate and in direct contact with the chromium-based layer.

10. Glazing according to any one of the preceding claims, wherein the chromium-based layer is in direct contact with the layer comprising silicon nitride.

11. Glazing according to any one of the preceding claims, wherein the layer consisting essentially of titanium, zirconium, or silicon is in direct contact with the layer comprising silicon nitride. 12.Glazing according to any one of the preceding claims, wherein the layer consisting essentially of titanium, zirconium, or silicon is the last layer of the stack.

13. Glazing according to any one of the preceding claims, wherein said stack comprises only the layer comprising silicon oxide, the chromium-based layer, the layer comprising silicon nitride, and the layer consisting essentially of a material selected from titanium, zirconium, silicon, or mixtures thereof.

14. Glazing according to any one of the preceding claims, wherein the light transmission is less than 1%, preferably less than 0.5%.

15. Glazing according to any one of the preceding claims, wherein the light reflection on the uncoated side of the stack is greater than 45%, preferably greater than 50%.

16. Glazing according to any one of the preceding claims, wherein the stack of layers is in the form of a continuous coating, of the decorative or patterned type. 17.Glazing according to the preceding claim, in which an opaque colour layer covers the areas of the glazing free from 'stacking'.

18. Glazing according to any one of the preceding claims, characterized in that it is annealed, curved, and / or tempered.

19. Glazing according to any one of the preceding claims, characterized in that it is monolithic. 5

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