Neutral solar control stack

Abstract

Solar control glazing comprising a glass substrate and a stack of PVD layers comprising two silver layers for the reflection of part of infrared light and one absorbing layer decreasing the light transmittance. Dielectric and protective layers are associated to adjust the optical properties and also to bring some improved durability regarding mechanical and chemical robustness. Such kind of solar control glazing are destinated to be incorporated in insulating glazing unit (IGU) or in laminated assembly, where the silver comprising stack is facing the inside of IGU or laminated assembly.

Description

Neutral solar control stackTechnical Field.

[0001] The present invention relates to the field of solar control glazing comprising a glass substrate and a stack of PVD layers. The multilayers stack comprises two silver layers for the reflection of part of infrared light and one absorbing layer decreasing the light transmittance. To those functional layers, some dielectric layers are associated to adjust the optical properties and also to bring some improved durability regarding mechanical and chemical robustness. Such kind of solar control glazing are destinated to be incorporated in insulating glazing unit (IGU) or in laminated assembly, where the silver comprising stack is facing the inside of IGU or laminated assembly.Background Art

[0002] When the interior of a vehicle or a building is exposed to a great amount of solar energy, it can be requested to limit the amount of thermal energy penetrating inside through the glazing, to avoid overheating to a huge extend of the inside. The answer of glass manufacturer in that field has been so great that the demand of customer is more and more detailed. Today one must be able to manufacture a glazing that has a defined visible light transmittance, as well as the in and out reflectances. The specifications also include a defined colour in transmission and reflection. More over the glazing must be heat treatable at high temperature, durable against mechanical and chemical attack and above that, the glazing must be self-matchable, meaning that the colour in transmission and reflection, before and after heat treatment, should remain almost constant. Finally in term of optical quality, there is an increasing demand for a colour in reflection which is independent of the viewing angle. For each demand, the glass manufacturer must then find the corresponding stack of layers and this can sometimes request some new research and new concept to be found. Most of these properties are antagonistic and the man skilled in the art must be able to play together with a lot of parameters.

[0003] To avoid overheating, one must decrease the amount of solar energy passing through the window. This is currently done thanks to light reflecting and / or absorbing layers.Typically, this allows to decrease the light transmittance to a value below 50% and to have a solar factor below 30%. Such low transmittance and solar factor are challenging the possibility to keep a low external reflectance, while having a too high external reflectance may be a problematic issue.

[0004] A huge amount of literature describes a lot of potential issues and a lot of potential solutions and both (issues and solutions) are currently very well known. The inventive step today in that field mainly resides in the combination of characteristics in a complicated way in order to get specified result. And because so many parameters may be combined, new combinations still can give unexpected results.

[0005] A low-e stack comprising one or more silver layer is thus common knowledge. Each silver layer is protected by being embedded in other layers. Those other layers play different roles as for example sacrificial layer, antireflective layer, barrier layer, seed layer, interference layer and so on. The man of the art is an expert to choose one or another layer seeking a particular effect. Amongst those layers, unavoidable dielectric layers are playing a very important role thanks to their particular characteristics, as for example, their refractive index, potential redox, crystal structure. In this text, speaking of a dielectric layer will refers to a particular single layer and speaking of dielectric film will refers to a single or a group of dielectric layers surrounding the silver layers.

[0006] Silicon nitride (SiN) is known to be a very stable dielectric quite inert on a chemical point of view, even during treatment at high temperature (above 600°C). The very low affinity of SiN for oxygen or water makes it particularly suitable as barrier for both molecules. SiN is often used as a protection or a barrier in the last dielectric of a low-e stack. It can also be used as a barrier to block alkaline ion migration when located closer to the glass substrate. Silicon nitride has a refractive index of about 2 or higher and may contribute to the interferential result of dielectrics in the overall stack.

[0007] Zinc oxide (ZnO) is particularly known as a wetting layer, under and contacting the silver layer, to improve the crystallinity of the silver layer and, as a result, decrease the emissivity of the low-e stack. ZnO may also play a role of stabilising the silver layer, avoiding migration of some particles, it may be disposed under and / or above the silver layer and is advantageously deposited under all silver layers of the stack(EP084965A1). Zinc oxide may also sometimes appears as a dielectric layer in the stack. Most of the time, zinc oxide is not a pure stoichiometric compound but rather a doped oxide, with aluminium for example as doping element. Zinc oxide based layer may deposited in a reactive sputtering process from a metallic target under an oxygen atmosphere or may be deposited from a ceramic target under an inert atmosphere.

[0008] Zinc stannate (ZSO), as dielectric, is known as improving the durability of the stack. For example EP803481A2 discloses that the zinc stannate film is chemically more stable than ZnO and that it is thermally resistant. It is an amorphous material with good adhesion properties. The presence of such a layer may help to have less pinholes and lower haze after heat treatment. In the rest of the disclosure, speaking of a tin based oxide dielectric layer includes any dielectric layer comprising tin oxide as basic part, meaning at least 40% weight of tin oxide in the dielectric.

[0009] Herein Contact layers are the layers that are in contact with the silver layer. Such kind of layers have important and particular role to play in a low-e stack. First of all they protect the silver by being a barrier against possible oxidation during heat treatment or during deposition of further layers. Such contact layers also act as barrier against migration of other element from the stack or the glass into the functional layer and finally they may also play a role as barrier for the migration of the silver element. Besides this protection, the contact layer under the silver may play a role of improving the physical state of silver during deposition (for example with a better crystallisation) which result in a lower emissivity. As mentioned above, zinc oxide is an excellent contact barrier for different reasons.

[0010] Besides the dielectrics and contact layers, a solar control stack may include a solar radiation absorbing layer (ABS). This is mainly used to decrease the light transmittance without using a coloured glass substrate and to have a better chance to manage the other optical properties. Said solar radiation absorbing layer may be a metal, a nitride, an oxide or mixture of those. Most of the time, such kind of layer is thin, generally the thickness is below 10 nm, and it may be located in different places related to the silver layers. In a first approach, the absorbing layer is contacting at least one silver layer and plays then a double role of absorption and contact layer. The absorbing layer can be oxidized during the heat treatment and thiswill impact the optical properties. In a second approach, the absorbing layer is not contacting a silver layer and is embedded within 2 dielectric layers. Most of the time, both dielectric layers surrounding the absorbing layer, are silicon nitride. In this second approach, the absorbing layer may be located below both silver layers, between both silver layers or above both silver layers. Any combination of the different approaches is also possible. The choice or combination of the different possibilities impacts both durability and optical properties. For example W02009032032A1 discloses that NiCr as absorbing layer is positioned between the 2 silver layers of the stack to avoid a colour change while observing from a 10° or a 45° viewing angle. W02002048065A1 discloses that TiN as absorbing layer, at a similar place, allows to decrease the visible light transmittance and also to have a lower external reflectance (e.a. below 20%) but is responsible for a reddish colouration under a viewing angle of 45 and 60°. W02005091864A1 discloses that locating NiCr absorbing layer in the first dielectric makes it possible to tune the visible light transmittance by adjusting its thickness. W02008036188A1 explains that the absorbing layer embedded within 2 silicon nitride layers must be very thin (2-3 nm) to keep a neutral coloration from different viewing angles.

[0011] It would not be possible to mention all possible relative positions of the different layers in such stacks because lot of possibilities have been already disclosed and each time claiming some particular effect. Amongst all possible combinations, we have particularly considered two of existing ones.

[0012] EP646551A1 discloses the following low-e arrangement “SiN / NiCr / Ag / NiCr / SiN” which proves to be particularly chemically resistant while allowing a good visible light transmittance together with a low emissivity. This particular arrangement (arrangement A) has intrinsically two absorbing layers contacting the silver layer. A correct choice of layers thickness makes this arrangement particularly heat resistant and matchable with untreated counterpart. This particular arrangement has already been the subject of different patents in the field of heat treatable low-e stacks and still today proves to be an excellent arrangement largely used for stack that must face a high temperature treatment. Such kind of heat treatable stack can, for example, has a visible light transmittance of 76-78% for a normal emissivity of0.12 after heat treatment and a visible light transmittance of 70-73% for a normal emissivity of 0.16 before heat treatment (EP646551).

[0013] Beside the previous presented arrangement, another one is the following: “ZSO / ZnO / Ag / ZnO / ZSO”, as disclosed in W02000037384A1. Such arrangement (arrangement B) without metal contact layer, uses a zinc oxide ceramic cathode to deposit a non-sacrificial zinc oxide contact layer above the silver. This particular contact layer remains almost constant during the heat treatment step. Silver and ceramic cathodes may be sputtered in the same zone, since both deposition are performed under an inert atmosphere. More over use of a zinc stannate dielectric with the zinc oxide has the advantage that both oxides have a similar refracting index and as a consequence, the zinc oxide layer may be quite thin. Such arrangement may also be heat treated with the advantage that no major change will occur in the layer nature. This arrangement allows to reach visible light transmittance of nearly 80% for an emissivity below 0.06.

[0014] As presented above most useful dielectric layers are a nitride or an oxide of metal or semimetal. Each arrangement (A and B) are such that silver is better protected from oxygen during deposition process and further treatments. In the arrangement A, no oxygen is needed and in the arrangement B, oxygen is not required for the upward contact layer deposition which can be done with a ceramic target.

[0015] All those features and characteristics have already been combined in a lot of different arrangements with different targets as heat treatable low light transmission, different coloration, high visible transmission, and whatever was requested. Nevertheless the existing possible combinations do not allow to have a glazing with the following combined characteristics: a very low visible light transmittance and by the same way keeping a low external reflectance, a very good selectivity and an aesthetic such that the colour remains neutral from a 10° up to a 75° viewing angle.Object of the invention

[0016] The objective of this invention is to propose a new type of combination that has never been proposed: combination of arrangement A and arrangement B with an absorbing layer. In this particular invention, the absorbing layer is located below both silver layers. This new combination permits to have a low to very low visiblelight transmittance, a low reflectance in both direction, a good selectivity and a neutral colour in external reflectance which remains stable whatever the viewing angle is, between 10° to 75°. This new combination is thus a double silver low-e, incorporating at least one absorbing layer. This new combination is chemically and mechanically robust and is heat treatable.Summary of invention

[0017] This invention is seeking to build a low-emissive glazing with a visible light transmittance smaller than 40% while both internal and external reflectance are kept below 20%, preferably below 18% and more preferably below 15%, and even more preferably below 13%. The low visible transmittance is reached thanks to an absorbing layer. As another requirement, the glazing of the invention has a neutral aspect in external reflection, more particularly, a light grey aesthetic on the external side. The particular layers arrangement has also the advantage to avoid a reddish coloration in reflection. Finally the glazing of the invention is chemically and mechanically resistant and heat treatable. The glazing of the invention is conform to the norm EN 1096-3 (2012). Durability is also evaluated with the test defined in the norm 1096-2 (2012) but the conditions are adapted for a class C glass quality.

[0018] This invention is a combination of both arrangements A and B presented above and the combination incorporates an absorbing layer. More particularly, this invention is a low-e stack comprising not more and not less than 2 silver layers, the first silver layer being closest to the glass substrate and in an arrangement A configuration, the second silver layer deposited above the first silver layer, in an arrangement B configuration.

[0019] According to the invention, the stack comprises at least one absorbing layer which does not contact one of the silver layers and which is located below both silver layers. This particular disposition allows to keep a low external reflectance. Indeed a big part of the visible light is absorbed before having a chance to be reflected by the silver layer. To protect the absorbing layer, one silicon nitride layer is deposited under the absorbing layer and another silicon nitride layer is deposited above theabsorbing layer, in other words, the absorbing layer is surrounded by 2 silicon nitride layers.

[0020] The particular combination of the invention has the following advantages. The presence of the absorbing layer allows to reach a very low visible transmittance without increasing the reflectance in a too large extend. More particularly, it is possible to reach a light transmittance below 40%, even below 30% and keeping the external reflectance below 20%, preferably below 18% and more preferably below 15%, and even more preferably below 13%. Moreover, the particular combination of the invention results in a very good aesthetic and shows a true light grey appearance in external reflection.

[0021] The inventors have also observed that inversing both arrangements A and B (B closer to the glass substrate), with the absorbing layer below both silver layers, does not allow to reach the same optical performance. A low visible transmittance can result in a higher reflectance and / or aesthetic is not as good (less neutral in transmission and reflection) . Namely the external colour in reflection is changing more when changing the viewing angle.

[0022] The colour characteristics of the glazing of the invention is assessed through its CIE LAB parameters. To be as neutral as possible, a* and b* in external reflectance should both be close to zero. More particularly, a* value in external reflectance is comprised between -3 and 3 and more preferably between -2 and 2. The b* value in external reflectance is comprised between -6 and 0.

[0023] According a very important aspect of this invention, the colour in external reflection is quite stable whatever the viewing angle is. The absolute difference in the a* colour parameter in external reflectance measured at 10° and at any other orientation up to 75° is strictly smaller 2.5, preferably strictly smaller than 2.0 and more preferably strictly smaller than 1.5. The absolute difference in the b* colour parameter in external reflectance measured at 10° and at any other orientation up to 75° is strictly smaller than 2.0, preferably strictly smaller than 1.5 and more preferably strictly smaller than 1.2.

[0024] In the meaning of the invention, the absorbing layer is made of an absorbent material and by absorbent material, we hereby mean a material that is characterized by anextinction coefficient which is greater than 0.5 at a wavelength equal to 589 nm. The nature and roles of an absorbing layer (ABS) are also explained in paragraph 10.

[0025] According to the invention, the absorbing layer has a thickness which is at least 1 nm, preferably at least 3 nm and which is at most 10 nm, preferably 8 nm. The thickness is chosen in relation with the desired final visible transmittance.

[0026] According to a particular embodiment of the invention, the absorbing layer is a titanium nitride based layer.

[0027] According to a particular embodiment of the invention, the first silver layer, located above the absorbing layer is in direct contact, under and above, with nickel chromium (NiCr) based protective barriers (see arrangement A). Such a barrier has proven to allow a heat treatment without affecting the optical properties of the coated article.

[0028] According to the invention, the thickness of the first silver layer is at least 6 nm, preferably at least 8 nm and is at most 12 nm, preferably at most 10 nm. The thickness of the nickel chromium based layers contacting the first silver layer and disposed under the first silver layer (referenced as ei) is at least 0.5 nm, preferably at least 1.0 nm and at most 5.0 nm, preferably at most 3.5 nm. The thickness of the nickel chromium based layers contacting the first silver layer and disposed above the first silver layer (thickness referenced here as ez) is at least 0.5 nm, preferably at least 1.0 nm and at most 10.0 nm, preferably at most 8.0 nm.

[0029] According to the invention, the ratio ez I ei allows to adjust reflection levels (both external and internal). Indeed the inventor have found that preferably the relation between both thicknesses (§2 / ei) should be comprised between 0.6 and 7 and preferably between 0.8 and 6. This ratio is also advantageously fixed to ensure low colour shift during tempering. Increasing this ratio results in higher value of the external reflectance and a lower value of the internal reflectance.

[0030] According to the invention, the first silver layer is part of an arrangement A and is thus deposited between two silicon nitride based dielectric layers. The absorbing layer of the invention is inserted in the SiN layer below the first silver layer: SiN / ABS / SiN. The thickness of the first silicon nitride layer, closer to the glass substrate and under the absorbing layer is at least 15 nm, preferably at least 25 nm and is at most 60 nm, preferably at most 50 nm.

[0031] According to the invention the silicon nitride located above the absorbing layer and under the first silver layer has a thickness which is at least 15 nm, preferably at least 25 nm and at most 40 nm, preferably at most 30 nm.

[0032] According to the invention the silicon nitride layer located between both silver layer is at least 35 nm, preferably at least 40 nm and at most 65 nm, preferably at most 60 nm.

[0033] According to the invention, the second silver layer has a thickness which is at least 8 nm, preferably at least 12 nm and at most 18 nm, preferably at most 16 nm. Advantageously, the thickness of the second silver layer is greater than the thickness of the first silver layer. More particularly, the ratio between second and first silver layer is comprised between 1.4 to 3.0.

[0034] According to the invention, the second silver layer is in direct contact, under and above, with a zinc oxide based layer (see arrangement B). The zinc oxide based layer deposited under the second silver layer is a wetting layer allowing a better silver crystallisation resulting in a lower sheet resistance and a lower emissivity. The zinc oxide based layer deposited above the second silver layer is a barrier. Both zinc oxide layers deposited under and above the second silver layer have a thickness which is at least 2 nm, preferably at least 4 nm and which is at most 12 nm, preferably at most 10 nm.

[0035] According to the invention the second silver layer is part of an arrangement B. In this particular arrangement the silver layer is surrounded by tin oxide based dielectric layers. Advantageously the tin oxide based layers are zinc stannate.

[0036] According to the invention, the tin oxide based layer deposited under the second silver layer and below the zinc oxide, has a thickness which is at least 15 nm, preferably at least 20 nm and at most 40 nm, preferably at most 35 nm. More particularly, the cumulative thickness of dielectric layers located between both silver layers (D2), including all dielectric layers whatever the function thereof is, is comprised between 65 and 90 nm.

[0037] According to the invention, the tin oxide based layer deposited above the second silver layer has a thickness which is at least 10 nm and at most 20 nm, preferably at most 15 nm.

[0038] According to the invention, it has been found that supplementary layers are advantageously deposited above both arrangements A and B to improve the chemical and mechanical durability of the stack. More particularly a supplementary silicon nitride layer, known for its stability and protecting effect, is used as a good protection against oxygen, namely during heat treatment and a metal oxide top layer (here named top coat) is deposited as a mechanical top protection layer above the supplementary silicon nitride layer. The top coat is a metal oxide comprising a metal or a mixture of metals selected from titanium, zirconium, hafnium and silicon. More particularly, the top coat is a titanium zirconium oxide layer. Both layers together are forming a protecting film that makes the stack even more resistant.

[0039] According to the invention, the supplementary silicon nitride layer deposited above the second silver layer has a thickness which is at least 5 nm, preferably at least 8 nm and at most 18 nm, preferably at most 15 nm and the top coat has a thickness which is at least 1 nm, preferably at least 2 nm and at most 8 nm, preferably at most 6 nm.

[0040] According to the invention the cumulative thickness of all the dielectric layers above the second silver layer (D3), whatever the function thereof is (meaning even a barrier), is comprised between 30 and 40 nm, preferably between 32 and 38 nm.

[0041] The coated glazing of the invention is particularly convenient to be used in the assembly as a laminate or an isolating glazing unit, after a heat treatment has been performed. Heat treatment and assembly are part of common knowledge and will not be discussed further. Also in a known way, the sides of glass substrates of an assembly are numbered as Pl to P4, Pl being the most external side. In a particular embodiment of the invention, the coated side of the glazing of the invention corresponds to the P2 position. In an alternative embodiment the coating of the invention may be disposed at the P3 position.

[0042] The double glazing unit incorporating the coated glazing of the invention is characterized by a solar factor smaller than 25%, preferably smaller than 20% and more preferably smaller than 18%. The isolation performance are characterized by a thermal coefficient U that is at most equal to 1.6 W / m2.K and preferably at most equal to 1.5 W / m2.K. The shading coefficient is at most equal to 30%, preferably at most 26% and more preferably at most 22%. The external reflectance is at most18%, preferably at most 15% and more preferably at most 13% and the internal reflectance is at most equal to 20%, preferably at most 18%.

[0043] The glazing of this invention will undergo a heat treatment. Such kind of process is very well known and may involve any sequences the man in the art is used to do. According to a particular embodiment, the glass sheet is heated to a temperature comprised between 670 and 720°C for a time of 5 to 10 minutes, followed by a rapid cooling. After the treatment, no traces nor scratches are observed and the haze is also acceptable. If requested, the heat treatment may be performed together with a bending process.

[0044] Both monolithic and double gazing unit or laminates have been assessed for their durability and all pass the tests to fulfil the requirements of EN 1096-3 and EN 1096-2 adapted for class C coated glass.Brief description of drawings

[0045] This and other aspects of the present invention will now be described with reference to details discussed below. The following description and drawings are illustrative of the disclosure and are not to be construed as limiting the disclosure. The drawings are not to scale and should not be considered as a limitation of the invention.

[0046] Fig. l is a schematic representation of the stack of the invention.

[0047] Fig.2 illustrates a double glazing unit incorporating the stack of the invention

[0048] The meaning of the reference is given here below:(1) glass(2), (4), (8), (14) SiN based layers(3) abosorbing layer(5), (7) NiCr based layer(6), (11) silver layers(9), (13) tin oxide based layers(10), (12) zinc oxide based layers(15) metal oxide top layerDescription

[0049] Definitions- As used herein, the term comprising or comprise, are to be construed as being inclusive and open ended, and not exclusive. Specifically, when used in the specification and claims, the terms "comprises" and "comprising" and variations thereof mean the specified features, steps or components are included. These terms are not to be interpreted to exclude the presence of other features, steps or components.- For the sake of clarity, when using terms like “under”, "below", "above", "lower", "upper", "first" or "last" herein, it is always in the context of a sequence of layers starting from the glass below, going upward, further away from the glass. Such sequences may comprise additional intermediate layers, in between the defined layers, except when a direct contact is specified.- Without further precision, thicknesses are geometrical thicknesses.- Unless otherwise defined, all technical and scientific terms used herein are intended to have the same meaning as commonly understood to one of ordinary skill in the art- For the invention, the glass may be any type of inorganic glass with any possible thickness. More particularly and preferably, the glass is a silica soda lime glass which may be clear, extra clear or tinted. More particularly, the glass has a thickness comprised between 2 and 10 mm.

[0050] The different dielectric layers that are used in this disclosure are represented by letters. In order to avoid any confusion, for the entirety of this disclosure, we here define those letters:SiN: silicon nitride means a dielectric layer based on SislS . The real stoichiometry may vary, depending namely from the nitrogen ratio during the deposition. Other elements may be present, as for example, aluminium.- TiN: Titanium nitride is also a dielectric layer but will be consider as an absorbing layer thanks to its extinction coefficient (> 0.5 at 589 nm).- ZSO: is a tin oxide based dielectric layer containing a certain amount of zinc oxide. Its exact stoichiometry or composition is not a critical feature for thisinvention. In the example of this invention, the ZSO is the zinc stannate (Zn2SnO4).- ZnO: represent the zinc oxide based layer. For the rest of the text, zinc oxide may be pure zinc oxide, aluminium zinc oxide or other doped zinc oxide and may be in a particular crystallized state or not.- TZO: represent a titanium zirconium mixed oxide. It is an example of a hard mechanical resistant layer. Different ratios are possible and the oxide may contain other elements, as for example, hafnium. The exact composition is not an essential characteristic of this invention. For the examples, the cathode chosen of this invention was an alloy containing a 65 / 35 weight ratio of titanium / zirconium.Speaking about a particular material-based layer means that the layer content at least 40 percent weight of that material.- What we call the second dielectric (D2) is the stack of dielectric layers disposed between the 2 silver layers, that is at least “..SiN / ZSO / ZnO..”- What we call the third dielectric (D3) is the stack of dielectric layers disposed above the second silver layer, that is at least “..ZnO / ZSO / SiN / MeOx”.- NiCr designates a nickel chromium based layer.

[0051] It is quite common to use the term low-e to designate a glass which has a coating incorporating at least one silver layer and to speak of solar control when an absorbing mean is used to decrease the amount of solar energy passing through the window. For this disclosure both terms apply and may be used.

[0052] As used herein, the extinction coefficient k(k) is the value measured at a wavelength of 589 nm.

[0053] The optical performances, namely the light transmittance or reflectance, the shading coefficient, the solar factor (SF) are determined according to the norm EN 410 - 201 IE (illuminant D65, 2°). The solar factor is the total energy transmitted.The colour characteristics (L*, a*, b*) are also measured with a D65 illuminant but at a solid observer angle of from 10° (CIELAB system).Particularly for the invention, the colour coordinates in external reflection a* and b*, are measured at a solid observer angle of from 10° up to 75°. If the smallest value for a* or b* are called a* (min) and b* (min) and the biggest value for a* and b* arecalled a* (max) and b* (max), then the absolute difference for both coordinates are calculated as | a* (min) - a* (max) | and |b* (min) - b* (max) | .

[0054] The thermal performance as the emissivity (e) and the U value are calculated in accordance with standards EN673 and ISO 10292.

[0055] The chemical durability is determined according to the norm EN 1096-2 (2012) (condensation duration is 3 days and neutral salt spray duration is 2 days) and the norm 1096-3 (2012).

[0056] The mechanical durability is assessed according to the norm EN1096-2 (2012) where the abrasion resistance consists of 500 strokes.

[0057] One can add that all methods to measure optical and thermal performances and methods to measure chemical and mechanical durability are methods that are well known and currently used by the man skilled in the art.Description of embodiments / examples

[0058] The invention will be illustrated by some examples but one must understand that those examples are by no way limiting the scope of the invention.

[0059] In a first approach, the system CODE Theiss has been used to detect the impact of the different layers and select the correct thickness ranges in order to find how this special arrangement could allow to obtain the targeted results. Simulations mainly focused on the exterior aesthetic (true grey appearance in reflection) for a very small visible light transmittance and external reflectance, with low shading coefficient, and more particularly the colour in external reflectance and the stability of the colour in external reflectance whatever the viewing angle is. The table 1 summarizes the thicknesses that have been optimized for the different layers of the double silver stack of the invention. All the thicknesses are geometrical thicknesses and are given in nm.

[0060] Table 1

[0061] The inventors have also found that for the aesthetic of the glazing, the thicknesses of the two SiN surrounding the absorbing layer, the thicknesses of both dielectric films D2 and D3 and also the thickness of the second silver layer have a particular impact, namely on the colour stability in external reflection, measured at different viewing angle.

[0062] The particular arrangement of the invention is also characterized by a very low internal reflectance, which was a specification in order to avoid a mirror effect from an interior point of view.

[0063] Other arrangements that have been tested failed to give equivalent results regarding the complete scope (optical and thermal performances). For example, the inventors have tried to reverse arrangement A and B keeping the absorbing layer below both silver layers:SiN / TiN / SiN / ZSO / ZnO / Ag / ZnO / ZSO / SiN / NiCr / Ag / NiCr / SiN / TZO This alternative results in a poorer aesthetic. More particularly, this is difficult to obtain a neutral coloration in transmission and / or in reflection while keeping low levels of transmission and / or reflection.

[0064] In a second steps, some real samples have been produced to confirm the optical and thermal properties and to check the durability of the stack.

[0065] Deposition of dielectric and silver layers is performed following known methods. After current preparation process, the glass has been installed in a PVD coating unit and the different layers are successively sputtered.

[0066] Some samples are detailed in the table 2. The position of the glass substrate is given in order to avoid any confusion. The glass substrate used for the examples is a 6 mm thick soda-lime clear glass. The thicknesses of the layers are given in nm. All the samples have been produced by PVD in a known way.

[0067] Table 2

[0068] The optical properties of the 3 examples of the table 2 have been measured and are given in the table 3. The measures have been made on a Perkin Elmer instrument in a known way, on a monolithic glass.

[0069] Table 3

[0070] The three samples have also been tested for the chemical and mechanical durability, before (BB) and after (AB) heat treatment and all results fulfil the specifications of the norms for the tests defined above.

[0071] Finally, for 3 examples, the coated glass has been tempered and mounted to form an IGU assembly in a known way and corresponding to a [6-16 (air)-6] DV. For those particular examples, the coated stack is placed in the P2 position. The second glass is a 6 mm soda-lime clear glass spaced from the coated glass by a distance of 16 mm filled with air. Performances of the IGU are given in the table 4, the reference of the examples correspond to the monolithic glass from table 2.

[0072] Table 4

Claims

ClaimsClaim 1. A coated article including a coating supported by a glass substrate, the coating comprising first and second infrared reflecting layers comprising silver and one absorbing layer wherein- the first silver layer is closest to the glass substrate,- the first silver layer is protected by two nickel chromium based layers in direct contact with said first silver layer, one nickel chromium based layer deposited under said first silver layer and one nickel chromium based layer deposited above said first silver layer,- the second silver layer is protected by two zinc oxide based layers in direct contact with said second silver layer, one zinc oxide based layer deposited under said second silver layer and one zinc oxide based layer deposited above said second silver layer,- the absorbing layer is deposited under the two silver layers- said absorbing layer is surrounded by two silicon nitride layers.Claim 2. The coated article of claim 1 wherein said first silver layer is deposited between two silicon nitride based dielectric layers and said second silver layer is deposited between two tin oxide based dielectric layers.Claim 3. The coated article of any previous claims wherein the absorbing layer has a thickness of at least 1 nm, preferably at least 3 nm and which is at most 10 nm, preferably 8 nm.Claim 4. The coated article of any previous claims wherein the absorbing layer is a titanium nitride based layer.Claim 5. The coated article of any previous claims wherein the first silver layer has a thickness which is at least 6 nm, preferably at least 8 nm and which is at most 12 nm, preferably at most 10 nm.Claim 6. The coated article of any previous claims wherein the nickel chromium based layers in direct contact and under said first silver layer has a thickness which is at least 0.5 nm, preferably at least 1.0 nm and at most 5.0 nm, preferably at most 3.5 nm.Claim 7. The coated article of any previous claims wherein the nickel chromium based layers in direct contact and above said first silver layer has a thickness which is at least 0.5 nm, preferably at least 1.0 nm and at most 10.0 nm, preferably at most 8.0 nm.Claim 8. The coated article of any previous claims wherein the silicon nitride layer, closer to the glass substrate and under the absorbing layer has a thickness of at least 15 nm, preferably at least 25 nm and of at most 60 nm, preferably at most 50 nm.Claim 9. The coated article of any previous claims wherein the silicon nitride located above the absorbing layer and under the first silver layer has a thickness which is at least 15 nm, preferably at least 25 nm and at most 40 nm, preferably at most 30 nm.Claim 10. The coated article of any previous claims wherein the relation between the thickness of the nickel chromium layer above the first silver layer and the thickness of the nickel chromium layer under the first silver layer is comprised between 0.6 and 7.Claim 11. The coated article of any previous claims wherein the silicon nitride located between both silver layer is at least 35 nm, preferably at least 40 nm and at most 65 nm, preferably at most 60 nm.Claim 12. The coated article of any previous claims wherein the second silver layer has a thickness which is at least 8 nm, preferably at least 12 nm and at most 18 nm, preferably at most 16 nm.Claim 13. The coated article of any previous claim wherein the second silver layer is thicker than the first silver layer.Claim 14. The coated article of any previous claim wherein the ratio between second and first silver layer is comprised between 1.4 to 3.0.Claim 15. The coated article of any previous claims wherein the two zinc oxide based layers in direct contact with said second silver layer have a thickness which is at least 2 nm, preferably at least 4 nm and which is at most 12 nm, preferably at most 10 nm.Claim 16. The coated article of any previous claim wherein the tin oxide based dielectric layers located between first and second silver layers has a thickness which is least 15 nm, preferably at least 20 nm and at most 40 nm, preferably at most 35 nm.Claim 17. The coated article of any previous claim wherein the total thickness of the dielectric film located between both silver layers is comprised between 65 and 95 nm.Claim 18. The coated article of any previous claim wherein the tin oxide based dielectric layers located above both silver layers has a thickness which is at least 10 nm and at most 20 nm, preferably at most 15 nm.Claim 19. The coated article of any previous claim wherein a supplementary silicon nitride based layer is deposited above the tin oxide based dielectric layers located aboveboth silver layers and has a thickness which is at least 5 nm, preferably at least 8 nm and at most 18 nm, preferably at most 15 nm.Claim 20. The coated article of any previous claims wherein a metal oxide top coat layer is deposited above the supplementary silicon nitride based layer, the metal being selected from titanium, zirconium, hafnium, silicon or mixture thereof and has a thickness which is at least 1 nm, preferably at least 2 nm and at most 8 nm, preferably at most 6 nm.Claim 21. The coated article of any previous claim wherein the metal oxide top coat layer is a titanium zirconium oxide layer and has a thickness which is at least 1 nm, preferably at least 2 nm and at most 8 nm, preferably at most 6 nm.Claim 22. The coated article of any previous claim wherein the cumulative thickness of all the dielectric layers above the second silver layer is comprised between 20 and 50 nm, preferably between 30 and 40 nm.Claim 23. The coated article of any previous claim wherein the following layers are deposited on the glass substrate: a first silicon nitride layer, a titanium nitride absorbing layer, a second silicon nitride layer, a first nickel chromium based layer, a first silver layer, a second nickel chromium based layer, a silicon nitride layer, a zinc stannate layer, a zinc oxide based layer, a second silver layer, a zinc oxide based layer, a zinc stannate layer, a supplementary silicon nitride layer, a titanium zirconium oxide layer.Claim 24. The coated article of any previous claim wherein the colour in external reflectance has a a* parameter comprised between -3 and 3, more preferably between -2 and 2 and a b* parameter comprised between -6 and 0.Claim 25. The coated article of any previous claim wherein the absolute difference in the a* colour parameter in external reflectance measured at 10° and at any other orientation up to 75° is strictly smaller than 2.5, preferably strictly smaller than 2.0 and more preferably strictly smaller than 1.5.Claim 26. The coated article of any previous claim wherein the absolute difference in the b* colour parameter in external reflectance measured at 10° and at any other orientation up to 75° is strictly smaller than 2.0, preferably strictly smaller than 1.5 and more preferably strictly smaller than 1.2.Claim 27. The coated article of any previous claim wherein the visible light transmittance is at most 40%.Claim 28. The coated article of any previous claim wherein the external reflectance is at most 20%, preferably at most 18%, more preferably at most 15%, and still more preferably at most 13%.Claim 29. The coated article of any previous claim which is the first glass substrate of an insulating glazing unit and characterized in that the stack is located at the P2 position.Claim 30. The insulating glazing unit of the previous claim characterized in that the external reflectance is at most 18%, preferably at most 15% and more preferably at most 13% and the internal reflectance is at most 20%, preferably at most 18%.Claim 31. The insulating glazing unit of any of the claims 29 to 30 characterized in that the shading coefficient is at most equal to 30%, preferably at most 26% and more preferably at most 22%.Claim 32. The insulating glazing unit of any of the claims 29 to 31 characterized in that the thermal coefficient U is at most equal to 1.6 W / m2.K and preferably at most equal to 1.5 W / m2.K.

Images