The present invention relates to toughenable coated substrates and to a process for the manufacture of same. More specifically, the invention relates to toughenable, coated glass substrates and to a process for preparing same in which one or more layers are applied to a coated substrate which is then toughened, by heat treatment, without significant damage to the coating layers on the substrate, and which demonstrate minimal internal and external reflection values. As a result of the toughenable coated glass substrate providing minimal internal and external reflection values, when placed in an insulated glazing unit (IGU), the IGU also exhibits minimal internal and external reflection values.

It is known to deposit layers or coatings on substrates such as glass for various purposes. For example, sol gel type deposition processes are disclosed in each of EP 1429997, DE 10146687, EP1328483 and US 6918957, wherein a silica sol is applied to the surface of a substrate and the substrate then heated at an elevated temperature to‘drive-off organic material, resulting in the production of a silica coating.

Other types of deposition processes include for example chemical vapour deposition (CVD), whereby a vapour of a precursor is directed towards the surface of a substrate, often at elevated temperature.

Processes for depositing conductive oxides such as indium tin oxide, doped tin oxide, doped zinc oxide and doped cadmium oxide are also known. These processes may include for example but are not limited to: chemical vapour deposition (CVD), flame pyrolysis, sputtering, or other types of physical vapour deposition.

Glass coatings which provide low emissivity and/or for solar control may be deposited by physical vapour deposition processes, for example, sputtering.

Sputtered low emissivity (low-e) and solar control coating stacks applied to a glass substrate are commonly made up of repeating sequences based on:

dielectric layer sequence / (Ag/ dielectric layer sequence) ¹¹ ,

with each of the n dielectrics layers possibly varying in thicknesses and/or composition. The value of n may be 1 or 2 and even 3 or 4. It is also known to coat both sides of glass substrates to produce glazing units for architectural glazing markets. Indeed, products are available which use the technologies described above to coat for instance, first one side of a glass substrate and then another. For example, NSG produce coated glass products in which one side of the glass substrate is coated with a self cleaning or anti-reflective coating, applied by chemical vapour deposition (CVD), and the other side of the glass substrate is coated with a physical vapour deposition (PVD) (sputtered) low emissivity coating.

Alternative products exist in which a low-emissivity coating is applied to each side of a glass substrate, but wherein one of the low-emissivity coatings is applied by chemical vapour deposition and the other low-emissivity coating is applied by sputtering.

However, thermally tempering or toughening, many coated glass products prepared using the technologies described above is difficult to achieve without damaging the coating layers, thereby leading to inferior products in terms of either a lack of colour uniformity or visual clarity.

In toughened or tempered glass, a glass substrate is processed by a controlled thermal or chemical treatment, to increase its strength compared with normal glass. The act of tempering or toughening places the outer surfaces of the glass substrate into compression and the inner body of the glass substrate into tension. When the toughened or tempered glass is broken, in contrast to glass plate (also known as annealed glass), the induced stresses cause the toughened glass to crumble into small granular chunks instead of splintering into jagged shards.

Coated glass panes which are toughened to impart safety properties and/or bent, are desirable for a large number of applications in both architectural and motor vehicle glazings. It is known that for thermally toughening and/or bending glass panes it is necessary to process the glass panes by a heat treatment at temperatures near or above the softening point of the glass used and then either to toughen them by rapid cooling or to bend them with the aid of bending means. The relevant temperature range for standard float glass of the soda lime silica type is typically about 580 - 690 °C, the glass panes being kept in this temperature range for several minutes before initiating the actual toughening and/or bending process. “Heat treatment”,“heat treated” and“heat treatable” in the following description and claims refer to thermal bending and/or toughening processes such as mentioned above and to other thermal processes during which a coated glass pane reaches temperatures in the range of about 580 - 690 °C for a period of several minutes, for example, for up to about 10 minutes. A coated glass pane is deemed to be heat treatable if it survives a heat treatment without significant damage, typical damages caused by heat treatments being high haze values, pinholes or spots.

However, heat treatment often leads to a change in colour or a loss of colour for coated glass substrates, with some known heat treatable coated glass panes showing significant and clearly noticeable modifications to their optical properties and particularly their reflection colour during and after heat treatment.

For instance, in US 9,919,960 B2 there is described a solar-control glazing consisting of a glass substrate bearing a multilayer stack, with at least one thin functional layer that reflects infrared radiation. However, there is no mention in this document of how to achieve a heat-treated coated glass substrate which demonstrates minimal internal and external reflection values. Likewise, in WO 2014/139755, there is described a glass panel comprising on at least one of the surfaces of a glass substrate, a multilayer stack including at least one solar radiation absorption layer, based on zirconium and chromium and dielectric coatings surrounding said solar radiation absorption layer.

US 2005/0196622 describes a coated article having two infrared reflecting layers in which an absorption layer of NiCr is located below the two infrared reflecting layers, and WO 2007/054655 describes a transparent substrate with a multilayer coating for use in manufacturing thermal insulation and/or solar protection glazing units.

Depositing a coating with two or more silver layers on a glass substrate with the required colour co-ordinates based on the CIE colour space whilst demonstrating low glass and coated side reflections is extremely challenging.

Indeed, it is especially difficult to obtain the above properties for a glass substrate when glass with solar control properties is also required. The present invention therefore seeks to address the above problems and provide a coated glass substrate which may be used as a solar control glazing and which not only demonstrates low external and internal reflections, but which additionally provides grey and/or neutral transmission and reflection colours.

That is, the present invention seeks to provide a heat treatable coating with single of multiple silver based layers on a glass substrate whilst retaining the desired a* and b* values in transmission and reflection without a costly increase in the number of coating layers deposited.

In addition, the present invention seeks to provide a coated glass substrate which may be used to provide a glazing with a high Selectivity value, (which is the ratio of light transmission (LT) to Total Solar Heat Transmission (TSHT)), and a low Total Solar Heat Transmission value.

Further, the present invention seeks to provide a coated glass substrate which exhibits a high level of solar control, using a metallic functional layer comprised for example of silver, and which provides a low shading coefficient, such as for example 25% or less.

It is preferred therefore that coated glass substrates prepared in accordance with the present invention may be used in an Insulated Glazing Unit (IGU) to provide a product with low internal and external reflections, that is, combined internal and external reflections in the Insulated Glazing Unit (IGU) of preferably 25% or less.

Consequently, a double glazing unit (DGU) prepared with a coated glass substrate according to the present invention will preferably achieve a Shading Coefficient of 25% or less (in which the Shading Coefficient (SC) relates to the Total Solar Heat Transmission (TSHT) value of a double glazed unit relative to the Total Solar Heat Transmission (TSHT) value for 3mm clear float glass).

The present invention further seeks to provide a coated glass substrate which meets the above optical requirements, and which may be fully toughened, that it, the glass substrates demonstrate low or minimal haze levels when the coating stacks are subjected to toughening furnace temperatures of between in the range of about 580 to 690 °C for a period of several minutes, for example, for up to about 10 minutes. In order to produce coating stacks with the properties required of the present invention in terms of colour neutrality and thermal stability, it is necessary for the location of the absorber in the stack design to be carefully chosen. In particular, the inventors have found that the choice of position of the absorber in the stack design greatly effects the external reflection values obtained when a coated glass substrate prepared in accordance with the present invention is incorporated into an insulated glazing unit (IGU).

Therefore, according to a first aspect of the present invention there is provided a toughenable coated float glass substrate, said float glass substrate comprising:

i) a first surface; and

ii) a second surface, wherein

the first surface of the glass substrate is coated with one or more layers applied by physical vapour deposition (PVD); said one or more layers applied by physical vapour deposition (PVD) comprising in sequence from the glass substrate:

a lower anti-reflection layer;

a functional metal layer;

a barrier layer; and

an upper anti -reflection layer;

wherein the barrier layer comprises NiCrOx and is in direct contact with the functional metal layer; and wherein

the one of more layers comprise one or more absorbing layer based on Ti, V, Cr, Fe, or W, Ni, Si, Nb, and alloys thereof and nitrides; and wherein

the coated float glass substrate exhibits combined internal (Rg Y) and external (Rc Y) reflection values of less than or equal to 22 after heat treatment.

Preferably, according to the CIE colour space the b* value according to the CIE colour is in the range 2 to -15 for both the first coated (Rc b*) surface and the second uncoated (Rg b*) surface for reflection and transmission.

Also, preferably according to the CIE colour space the a* value is in the range 2 to -10 for both the first coated (Rc a*) surface and the second uncoated (Rc a*) surface for reflection and transmission. Further the toughenable coated substrate according to the present invention preferably comprises a light transmission in the range 25 to 35%. More preferably the toughenable coated substrate according to present invention preferably comprises a light transmission in the range 27 to 33%. Even more preferably the toughenable coated substrate according to the present invention comprises a light transmission in the range 28 to 31%.

In a preferred embodiment of the coated glass substrate according to the present invention the one or more layers applied by physical vapour deposition (PVD) comprise two or more functional metal layer deposited in the following sequence from the glass substrate:

a lower anti -reflection layer comprising:

a first dielectric layer;

a first absorbing layer;

a second dielectric layer;

a first functional metal layer;

a barrier layer;

a central anti -reflection layer comprising;

a second functional metal layer;

a second barrier layer; and

an upper anti -reflection layer.

It is preferred that the toughenable coated substrate according to the present invention further comprises one or more absorbing layer in the central and /or upper anti -reflection layer, or alternatively, the toughenable coated substrate according to the present invention comprises one or more absorbing layer in the upper anti -reflection layer.

In relation to the present invention it is also preferred that the one or more absorbing layer in the lower anti -reflection layer, and central and/or upper anti -reflection layer is based on WNx; W; NiCr; NiCrOx; NiCrNx; NiSix; NiSixNy; FeSix and FeSixNy. Most preferably, the one or more absorbing layer in the lower anti-reflection layer, central and/or the upper anti -reflection layer is based on tungsten (W), tungsten nitride (WNx) or NiCr.

The coated glass substrates according to the present invention therefore comprise at least one absorber layer, to achieve the low internal and external reflections and a shading coefficient (SC) of 25% or less. That is, suitable absorbers for use in the present invention and which are able to achieve the required heat stability and colour neutrality comprise for example: WNx; W; NiCr; NiCrOx; NiCrNx; NiSix; NiSixNy; FeSix and FeSixNy

The one or more absorbing layer in the lower anti -reflection layer, preferably comprises a thickness in the range 3 to lOnm. In addition, the one or more absorbing layer in the central anti-reflection layer and/or the upper anti -reflection also preferably comprise a thickness in the range 3 to lOnm.

It is especially preferred in relation to the present invention that each functional metal layer comprises silver. The thickness of each functional metal layer is preferably in the range 5 to 15nm. More preferably, the thickness of each functional metal layer is preferably in the range 8 to 13nm.

For the toughenable coated substrate according to the present invention it is further preferred that the or each absorbing layer in the lower dielectric layer contacts at least one layer based on an (oxi)nitride of Si and/or an (oxi)nitride of A1 and/or alloys thereof.

More preferably, the or each absorbing layer in the lower dielectric layer is embedded between and/or contacts two layers based on an (oxi)nitride of Si and/or an (oxi)nitride of A1 and/or alloys thereof.

It is also especially preferred in relation to the present invention that the or each barrier layer is in direct contact with the or each functional metal layer and that each barrier layer preferably comprises NiCrOx or a NiCr metal alloy.

It is further especially preferred that when the barrier layer comprises a NiCr metal alloy, that the NiCr metal alloy is in direct contact with the first functional metal layer and that the lower anti -reflection layer comprises one or more absorber layer.

Also in relation to the present invention, the change in colour for transmission and or reflection after heat treatment (DE*) for each side of the coated substrate is less than 10%. More preferably, it is preferred that the change in colour for transmission and or reflection after heat treatment (DE*) for the coated substrate is less or equal to 8 or 7. Most preferably, it is preferred that the change in colour for transmission and or reflection after heat treatment (DE*) for the coated substrate is less or equal to 5.

Acccording to a second aspect of the present invention there is provided a process for preparing a coated toughenable float glass substrate according to the first aspect of the present invention comprising the steps of:

i) providing a float glass substrate with a first surface and a second surface;

ii) depositing by physical vapour deposition (PVD) one or more layers on the first surface of the substrate including at least one functional metal layer and at least one absorbing layer; and

iii) heat treating the coated glass substrate to toughen the glass without degrading the one or more layers deposited on the glass substrate.

According to a third aspect of the present invention there is provided the use of a toughenable coated float glass substrate according to the first aspect of the present invention in a glazing article.

According to a fourth aspect of the present invention there is provided the use of a toughenable coated float glass substrate according to the first aspect of the present invention in an insulated glazing unit.

In relation to the fourth aspect of the present invention the insulated glazing unit (IGU) preferably comprises a shading coefficient of less than or equal to 25%.

According to a fifth aspect of the present invention there is provided the use of a toughenable coated float glass substrate according to the first aspect of the present invention in an automotive motive glazing such as for example, windscreen, sidelight, rooflight or backlight.

It will be appreciated that all features relating to the first aspect of the present invention apply also in relation to the second, third and fourth aspects of the present invention.

Further details in relation to all aspects of the present invention are as follows. The lower anti -reflection layer may preferably comprise one or more base layer based on an (oxi)nitride of silicon, an (oxi)nitride of aluminium and/or alloys thereof. The one or more base layer based on an (oxi)nitride of silicon, an (oxi)nitride of aluminium and/or alloys thereof is preferably located between the glass substrate and the one of more absorbing layer based on Ti, V, Cr, Fe, or W, Ni, Si, Nb, and alloys thereof and nitrides. The lower anti -reflection layer preferably also comprises a layer based on an oxide of zinc (Zn) and tin (Sn) and/or an oxide of tin (Sn), and/or a top layer based on an oxide of zinc (Zn) or titanium.

For the coated glass substrate according to the present invention comprising a functional metal layer in the form of a silver-based functional layer, the lower anti -reflection layer may further comprise a separation layer. The separation may preferably be based on a metal oxide.

The separation layer may preferably have a thickness of at least 0.5 nm; or preferably from 0.5 to 6 nm; more preferably from 0.5 to 5 nm. The separation layer preferably provides protection during the deposition process and during a subsequent heat treatment. The separation layer is preferably either essentially fully oxidised immediately after deposition, or it oxidizes to an essentially fully oxidized layer during deposition of a subsequent oxide layer.

The separation layer based on a metal oxide preferably comprises a layer based on an oxide of: Ti, Zn, NiCr, InSn, Zr, A1 and/or Si.

The separation layer may further comprise one or more chemical elements chosen from at least one of the following elements: Ti, V, Mn, Co, Cu, Zn, Zr, Hf, Al, Nb, Ni, Cr, Mo, Ta, Si, or from an alloy based on at least one of these materials, used for instance as dopants or alloyants.

Preferably however, the separation layer based on a metal oxide does not include one or more other chemical elements.

In one preferred embodiment of the present invention, the separation layer is based on a metal oxide, which comprises an oxide of zinc (Zn) or an oxide of titanium.

Whilst the separation layer may be based on an oxide of titanium when the layer sequence comprises one silver-based functional layer, it may be preferred that when the layer sequence or stack comprises more than one silver-based functional layer that the separation layer is based on a layer of zinc.

In one preferred embodiment of the present invention, the separation layer is based on a metal oxide, which comprises an oxide of zinc (Zn).

Whether the lower anti -reflection layer preferably comprises three, four or more layers as described above will depend upon the number of silver-based functional layers present in the sequence.

The base layer based on an (oxi)nitride of silicon and/or an (oxi)nitride of aluminium and/or alloys thereof of the lower anti -reflection layer may preferably comprise a thickness of at least 5 nm. More preferably, the base layer based on an (oxi)nitride of silicon and/or an (oxi)nitride of aluminium and/or alloys thereof of the lower anti -reflection layer comprises a thickness of from 5 to 60 nm. Even more preferably the base layer based on an (oxi) nitride of silicon and/or an (oxi)nitride of aluminium and/or alloys thereof of the lower anti-reflection layer comprises a thickness of from: 10 to 50 nm; 12 to 45 nm; or 15 to 40 nm. Most preferably the base layer based on an (oxi)nitride of silicon and/or an (oxi)nitride of aluminium and/or alloys thereof of the lower anti -reflection layer comprises a thickness of from 15 to 30 nm. This base layer serves as a glass side diffusion barrier amongst other uses.

The term“(oxi)nitride of silicon” encompasses both silicon (Si) nitride (SiN _x ) and silicon (Si) oxinitride (SiO _x N _y ), whilst the term“(oxi)nitride of aluminium” encompasses both aluminium (Al) nitride (A1N _X ) and aluminium (Al) oxinitride (A10 _x N _y ). Silicon (Si) nitride, silicon (Si) oxinitride, aluminium (Al) nitride and aluminium (Al) oxinitride layers are preferably essentially stoichiometric (for example, in silicon nitride = S13N4, the value of x in SiN _x = 1.33) but may also be substoichiometric or even super-stoichiometric, as long as the heat treatability of the coating is not negatively affected thereby. One preferred composition of the base layer based on an (oxi)nitride of silicon and/or an (oxi)nitride of aluminium of the lower anti- reflection layer is an essentially stoichiometric mixed nitride SEoAhoN _x .

Layers of an (oxi)nitride of silicon and/or an (oxi)nitride of aluminium may be reactively sputtered from silicon (Si-) and/or aluminium (Al)-based targets respectively in a sputtering atmosphere containing nitrogen and argon. An oxygen content of the base layer based on an (oxi)nitride of silicon and/or an (oxi)nitride of aluminium may result from residual oxygen in the sputtering atmosphere or from a controlled content of added oxygen in said atmosphere. It is generally preferred if the oxygen content of the silicon (oxi)nitride and/or aluminium (oxi)nitride is significantly lower than its nitrogen content, that is, if the atomic ratio O/N in the layer is kept significantly below 1. It is most preferred to use Si nitride and/or aluminium nitride with negligible oxygen content for the base layer of the lower anti -reflection layer. This feature may be controlled by making sure that the refractive index of the layer does not differ significantly from the refractive index of an oxygen-free Si nitride and/or aluminium nitride layer.

It is within the scope of the invention to use mixed silicon (Si) and/or aluminium (Al) targets or to otherwise add metals or semiconductors to the silicon (Si) and/or aluminium (Al) component of this layer as long as the essential barrier and protection property of the base layer of the lower anti-reflection layer is not lost. For example, the aluminium (Al) with silicon (Si) targets may be mixed, other mixed targets not being excluded. Additional components may be typically present in amounts of from 10 to 15 weight %. Aluminium is usually present in mixed silicon targets in an amount of 10 weight %.

The layer based on an oxide of zinc (Zn) and tin (Sn) and/or an oxide of tin (Sn) of the lower anti -reflection layer preferably serves to improve stability during a heat treatment by providing a dense and thermally stable layer and contributing to reduce the haze after a heat treatment.

The layer based on an oxide of zinc (Zn) and tin (Sn) and/or an oxide of tin (Sn) of the lower anti -reflection layer may preferably have a thickness of at least 0.5 nm. Preferably the layer based on an oxide of zinc (Zn) and tin (Sn) and/or an oxide of tin (Sn) of the lower anti- reflection layer may have a thickness of from: 0.5 to 15 nm; or 2.0 to 14 nm; or 3 to 13 nm. Most preferably the layer based on an oxide of zinc (Zn) and tin (Sn) and/or an oxide of tin (Sn) of the lower anti -reflection layer may have a thickness of from 5 to 15 nm for a coated glass substrate with layer sequence comprising one silver-based functional layer. An upper thickness limit in the region of 15 nm is preferred due to optical interference conditions and by a reduction of heat treatability due to the resulting reduction in the thickness of the base layer that would be needed to maintain the optical interference boundary conditions for anti reflecting the functional layer. In an alternative embodiment in relation to the first aspect of the present invention, when the coated glass pane comprises more than one silver-based functional layer, the layer based on an oxide of zinc (Zn) and tin (Sn) and/or an oxide of tin (Sn) of the lower anti -reflection layer preferably has a thickness of at least 12 nm. More preferably, the layer based on an oxide of zinc (Zn) and tin (Sn) and/or an oxide of tin (Sn) of the lower anti -reflection layer preferably has a thickness of from 12nm to 20nm. Even more preferably, the layer based on an oxide of zinc (Zn) and tin (Sn) and/or an oxide of tin (Sn) of the lower anti -reflection layer preferably has a thickness of from 12nm to 16nm. However, most preferably, the layer based on an oxide of zinc (Zn) and tin (Sn) and/or an oxide of tin (Sn) of the lower anti-reflection layer preferably has a thickness of from 12nm to 14nm.

The layer based on an oxide of zinc (Zn) and tin (Sn) and/or an oxide of tin (Sn) of the lower anti-reflection layer is preferably located directly on a layer based on an (oxi)nitride of silicon and/or an (oxi)nitride of aluminium and/or alloys thereof.

The layer based on an oxide of zinc (Zn) and tin (Sn) (abbreviation: ZnSnO _x ) of the lower anti reflection layer may preferably comprise: 10 to 90 weight % zinc (Zn) and 90 to 10 weight % tin (Sn); more preferably about 40 to 60 weight % zinc (Zn) and about 40 to 60 weight % tin (Sn); even more preferably about 50 weight % each of zinc (Zn) and tin (Sn), in weight % of the total metal content of the layer. In some preferred embodiments the layer based on an oxide of zinc (Zn) and tin (Sn) of the lower anti -reflection layer may comprise: at most 18 weight % tin (Sn), more preferably at most 15 weight % tin (Sn), even more preferably at most 10 weight % tin (Sn). The layer based on an oxide of Zn and Sn may also preferably be deposited by reactive sputtering of a mixed ZnSn target in the presence of O2.

Preferably, the layer based on an oxide of zinc (Zn) and tin (Sn) and/or the top layer based on an oxide of zinc (Zn) or titanium are preferably located above the one or more absorbing layer in the lower anti -reflection layer.

Preferably the lower anti-reflection layer comprises two or more layers based on an (oxi)nitride of silicon, an (oxi)nitride of aluminium and/or alloys thereof. The two or more base layer based on an (oxi)nitride of silicon, an (oxi)nitride of aluminium and/or alloys are preferably located between the glass substrate and the layer based on an oxide of zinc (Zn) and tin (Sn) and/or an oxide of tin (Sn) in the lower anti-reflection layer. Alternatively, the two or more layers based on an (oxi)nitride of silicon, an (oxi)nitride of aluminium and/or alloys thereof may also be located in the central or upper antireflection layers, most preferably however, the two or more layers based on an (oxi)nitride of silicon, an (oxi)nitride of aluminium and/or alloys thereof are preferably located in the lower and/or upper antireflection layers.

It is most preferred that when the layer sequence comprises two or more silver based functional layers, that the lower anti -reflection layer comprises two or more layers of an (oxi)nitride of silicon and/or (oxi)nitride of aluminium and/or alloys thereof.

The top layer based on an oxide of zinc (Zn) in the lower anti -reflection layer primarily functions as a growth promoting layer for a subsequently deposited silver-based functional layer. The top layer based on an oxide of zinc (Zn) is optionally mixed with metals such as aluminium (Al) or tin (Sn) in an amount of up to about 10 weight % (weight % referring to the target metal content). A typical content of said metals such as aluminium (Al) or tin (Sn) is about 2 weight %, Aluminium (Al) being actually preferred. Zinc oxide (ZnO) and mixed zinc (Zn) oxides have proven very effective as a growth promoting layer and thereby assisting in achieving a low sheet resistance at a given thickness of the subsequently deposited silver-based functional layer. It is preferred if the top layer based on an oxide of zinc (Zn) of the lower anti- reflection layer is reactively sputtered from a zinc (Zn) target in the presence of oxygen (O2), or if it is deposited by sputtering, a ceramic target, for example based on ZnO:Al, in an atmosphere containing zero or only a small amount, that is, generally no more than about 5 volume %, of oxygen. The top layer of the lower anti -reflection layer based on an oxide of zinc (Zn) may preferably have a thickness of at least 2 nm. More preferably, the top layer of the lower anti -reflection layer based on an oxide of zinc (Zn) may preferably have a thickness of from 2 to 15 nm; or from 2.5 to 12 nm. Even more preferably the top layer of the lower anti- reflection layer based on an oxide of zinc (Zn) may preferably have a thickness of from 2.5 to 10 nm. Most preferably the top layer of the lower anti -reflection layer based on an oxide of zinc (Zn) has a thickness of from 2.5 to 8 nm.

The silver-based functional layer(s) preferably consists essentially of silver without any additive, as is normally the case in the area of low-emissivity and/or solar control coatings. It is, however, within the scope of the invention to modify the properties of the silver-based functional layer(s) by adding doping agents, alloy additives or the like or even adding very thin metal or metal compound layers, as long as the properties of the silver-based functional layer(s) necessary to function as highly light-transmitting and low light-absorbent IR-reflective layer(s), are not substantially impaired thereby.

The thickness of each silver-based functional layer is dominated by its technical purpose. For typical low-emissivity and/or solar control purposes the preferred layer thickness for a single silver-based layer may preferably be from: 5 to 20 nm; more preferably from 5 to 15 nm; even more preferably from 6 to 15 nm; even more preferably from 8 to 15 nm; most preferably from 8 to 14 nm. With such a layer thickness, light transmittance values of above 86 % and a normal emissivity below 0.05 after a heat treatment may be readily achieved in accordance with the present invention for single silver coatings. If better solar control properties are required, the thickness of the silver-based functional layer may be adequately increased, or several spaced functional layers may be provided as further explained below.

Preferably the top layer based on an oxide of zinc (Zn) in the lower anti -reflection layer is in direct contact with the silver-based functional layer. Preferably, the number of layers between the glass substrate and the silver-based functional layer consists of four layers, five layers or more layers of the lower anti-reflection layer described above.

While the invention relates to coated panes which comprise only one silver-based functional layer, it is preferably within the scope of the invention to apply the inventive concept to prepare low-emissivity and/or solar control coatings comprising two or more silver-based functional layers. When providing more than one silver-based functional layer, all of the silver-based functional layers are spaced apart by intervening dielectric layers, referred to herein collectively as “central anti -reflection layers”, to form a Fabry -Perot interference filter, whereby the optical properties of the low emissivity and/or solar control coating may be further optimized for the respective application.

Preferably, each silver-based functional layer is spaced apart from an adjacent silver-based functional layer by an intervening central anti -reflection layer. The intervening central anti- reflection layer(s) may comprise a combination of one or more of the following layers: a layer based on an (oxi)nitride of silicon and/or an (oxi)nitride of aluminium; a layer based on an oxide of Zn and Sn and/or an oxide of Sn; and a layer based on a metal oxide such as an oxide of Zn.

In some preferred embodiments each silver-based functional layer is spaced apart from an adjacent silver-based functional layer by an intervening central anti -reflection layer, wherein each central anti -reflection layer comprises at least, in sequence from the silver-based functional layer that is located nearest to the glass substrate, a layer based on an (oxi)nitride of silicon and/or an (oxi)nitride of aluminium; a layer based on an oxide of Zn and Sn and/or an oxide of Sn; and a layer based on a metal oxide such as an oxide of Zn.

The coated glass pane according to the present invention preferably comprises also a barrier layer. The barrier layer is preferably located in direct contact with the silver based functional layer.

The barrier layer may preferably be based on an oxide of Zn with a thickness of: at least 0.5nm, more preferably, the barrier layer is based on an oxide of Zn with a thickness of from 0.5 to 10 nm. Most preferably the barrier layer is based on an oxide of Zn with a thickness of from 1 to 10 nm.

It has been found that a superior protection of the silver-based functional layer during the deposition process and a high optical stability during a heat treatment may be achieved if the barrier layer comprises a layer of a mixed metal oxide sputtered from a mixed metal oxide target. When the barrier layer is based on an oxide of zinc (Zn), said oxide may be a mixed metal oxide such as ZnO:Al. Good results are particularly achieved if a layer based on ZnO: A1 is sputtered from a conductive ZnO:Al target. ZnO:Al may be deposited fully oxidized or such that it is slightly suboxidic.

In addition, it is possible when the barrier layer comprises a layer based on an oxide of zinc (Zn) for the barrier to actually comprise a number of zinc oxide layers such as layers based not only on a mixed metal oxide such as ZnO:Al, but also on an oxide of zinc (Zn) and tin (Sn). Suitable barrier layers may therefore be in the form of ZnO: Al, ZnSn0 ₄ , ZnO: Al. Such triple barrier arrangements may have a combined thickness of between 3 and 12nm. Further triple barrier arrangements may preferably be selected from the group consisting of the following combinations of layers in sequence from the silver-based functional layer: ZnO:Al/TiO _x /ZnO:Al, ZnO:Al/ZnSnO _x /ZnO:Al, TiO _x /ZnSnO _x /ZnO:Al, TiO _x /ZnO:Al/TiO _x , TiO _x /ZnSnO _x /TiO _x , and ZnO:Al/ZnSnO _x /TiO _x .

At least a portion of the barrier layer that is in direct contact with the silver-based functional layer is preferably deposited using non-reactive sputtering of an oxidic target to avoid silver damage.

In addition, and as an alternative to the barrier layer being based on an oxide of zinc (Zn), it has further been found that suitable protection of the silver-based functional layer during the deposition process and a high optical stability during heat treatment may be achieved also if the barrier layer comprises a mixed metal oxide based on Nickel (Ni) and Chromium, such as a layer of sub stoichiometric NiCrO _x . This is especially the case when the coated glass pane comprises two or more silver-based functional layers, however, the layer of substoichiometric NiCrO _x may also be used when the coated glass pane comprises a single silver-based functional layer.

Furthermore, it has been found that when the barrier layer comprises a Nickel (Ni) and Chromium (Cr) metal alloy, that is a layer of NiCr, that it is possible to attain low internal and external reflections, especially if the NiCr metal alloy layer is used in direct contact over the first silver and is combined with an absorber in the lower ant-reflection layer.

Therefore, for coated glass panes comprising two or more silver based functional layers (or even three or four silver layers) it is preferred that each silver-based functional layer is spaced apart from an adjacent silver-based functional layer by an intervening central anti -reflection layer, wherein each central anti -reflection layer comprises at least, in sequence from the silver- based functional layer that is located nearest to the glass substrate:

a layer based on a mixed metal oxide comprising nickel (Ni) and chromium; and/or a layer based on a mixed metal oxide based on zinc and aluminium, that is ZAO; and optionally, a layer based on an (oxi)nitride of silicon and/or an (oxi)nitride of aluminium; and/or

a layer based on an oxide of Zn and Sn; and/or

a layer based on a metal oxide such as an oxide of Zn. Also, in relation to the first aspect of the present invention the coated glass preferably comprises an upper anti -reflection layer. The upper anti -reflection layer may preferably comprise:

i) an uppermost barrier layer based on an oxide of nickel (Ni) and chromium or an oxide of zinc doped with aluminium (Al); and/or

ii) a layer based on an oxide of zinc (Zn) and tin (Sn), or a layer based on an oxide of zinc and aluminium, or a layer based on a nitride of tungsten or NiCr; and/or

iii) a layer based on an (oxi)nitride of silicon and/or an (oxi)nitride of aluminium; and/or iv) a layer based on an oxide of zinc (Zn) and tin (Sn).

The layer based on an oxide of Zn and Sn and/or an oxide of Sn in the upper anti -reflection layer may preferably have a thickness of at least l .Onm; more preferably at least 3 nm or 4 nm, or even at least 5 nm, but preferably at least 6 nm; more preferably at least 7nm. In addition, the layer based on an oxide of Zn and Sn and/or an oxide of Sn in the upper anti -reflection layer preferably has a thickness of 12 nm or less; most preferably at most 10 nm; and especially from 5 to 9 nm. These preferred thicknesses enable further ease of deposition and improvement in optical characteristics such as haze whilst retaining mechanical durability.

The layer based on an oxide of Zn in the upper anti -reflection layer may preferably have a thickness of at least 0.5 nm, more preferably at least 0.5 nm or 1 nm; or even at least 1.5 nm; but preferably less than 5 nm; more preferably 4 nm. These preferred thicknesses also enable further ease of deposition and improvement in optical characteristics such as haze whilst retaining mechanical durability.

Preferably the layers in the upper anti -reflection layer are based on essentially stoichiometric metal oxides. The use of barrier layers based on essentially stoichiometric metal oxides rather than metallic or less than 95% stoichiometric barrier layers leads to an extremely high optical stability of the coating during a heat treatment and effectively assists in keeping optical modifications during heat treatment small. Additionally, the use of layers based on essentially stoichiometric metal oxides provides benefits in terms of mechanical robustness.

In the context of the present invention the term“non-reactive sputtering” includes sputtering an oxidic target in a low oxygen atmosphere (that is with zero, or up to 5 % volume oxygen) to provide an essentially stoichiometric oxide. Also, in the context of the present invention, where a layer is said to be“based on” a particular material or materials, this means unless stated otherwise, the layer predominantly comprises said material or materials in an amount of at least 50 atomic %.

Where a layer is based on ZnSnO _x ,“ZnSnO _x ” means a mixed oxide of Zn and Sn as described and defined elsewhere in the description.

The layer in the upper anti -reflection layer based on an (oxi)nitride of aluminium or an (oxi)nitride of silicon may preferably comprise a thickness of at least 5 nm; preferably from 5 to 50 nm; more preferably from 10 to 45 nm; even more preferably from 10 to 40 nm; most preferably from 25 to 40 nm. Such thicknesses provide further improvement in terms of mechanical robustness of the coated pane. Said layer based on an (oxi)nitride of aluminium, an (oxi)nitride of silicon, may preferably be in direct contact with the layer based on an oxide of zinc (Zn) in the upper anti -reflection layer.

The layer based on an (oxi)nitride of aluminium, an (oxi)nitride of silicon, may comprise a major part of the upper anti -reflection layer and provide stability (better protection during heat treatments) and diffusion barrier properties. Said layer is preferably deposited as an A1 nitride and/or Si nitride layer by reactive sputtering of a Si, A1 or mixed SiAl target, for example, of a S190AI 10 target in a N2 containing atmosphere. The composition of the layer based on an (oxi)nitride of aluminium and/or an (oxi)nitride of silicon may be essentially stoichiometric Si ₉ oAlioN _x .

To minimize any light absorption in the coating and to reduce the light transmittance increase during heat treatment, all individual layers of the upper and lower anti -reflection layers are preferably deposited with an essentially stoichiometric composition.

To further optimize the optical properties of the coated pane the upper anti -reflection layers may comprise further partial layers consisting of suitable materials generally known for dielectric layers of low-e and/or solar control coatings, in particular chosen from one or more of the oxides of Sn, Ti, Zn, Nb, Ce, Hf, Ta, Zr, A1 and/or Si and/or of (oxi)nitrides of Si and/or A1 or combinations thereof. When adding such further partial layers it should however be verified that the heat treatability aimed at herein is not impaired thereby. It will be appreciated that any further layer may contain additives that modify its properties and/or facilitate its manufacture, for example, doping agents or reaction products of reactive sputtering gases. In the case of oxide based layers, nitrogen may be added to the sputtering atmosphere leading to the formation of oxinitrides rather than oxides, in the case of nitride based layers oxygen may be added to the sputtering atmosphere, also leading to the formation of oxinitrides rather than nitrides.

Care must be taken by performing a proper material, structure and thickness selection when adding any such further partial layer to the basic layer sequence of the inventive pane that the properties primarily aimed at, for example, a high thermal stability, are not significantly impaired thereby.

In addition, a feature of the coated glass panes according to the present invention is that the one or more layers preferably comprise one or more absorbing layers. The one or more absorbing layers may preferably be located in the lower anti -reflection layer and/or the central and /or upper anti -reflection layer, depending on the number of silver- based functional layers.

The at least one absorbing layer may comprise a layer based on Ti, V, Cr, Fe, or W, Ni Nb, and alloys thereof and nitrides. More preferably the at least one absorbing layer is based on tungsten (W), preferably tungsten nitride or nichrome NiCr.

It is most preferred that the at least one absorbing layer based on tungsten is located in the lower anti-reflection layer and/or the upper anti -reflection layer.

It is also preferred in relation to the present invention, that the at least one absorbing layer preferably contacts at least one layer based on an (oxi)nitride of Si and/or an (oxi)nitride of A1 and/or alloys thereof. More preferably the at least one absorbing layer is embedded between and contacts two layers based on an (oxi)nitride of Si and/or an (oxi)nitride of A1 and/or alloys thereof. This arrangement is beneficial in terms of exhibiting the lowest haze and having the potential to achieve the most neutral transmitted or reflected colours before and after heat treatment. Preferably the at least one absorbing layer contacts at least one layer based on a nitride of Al. More preferably the at least one absorbing layer is embedded between and contacts two layers based on a nitride of Al.

The absorbing layer based on tungsten, preferably in the form of tungsten nitride, WNx, in the lower and or upper anti -reflection layer may preferably have a thickness of at least 0.5 nm, more preferably at least 0.5 nm or 1 nm; or even at least 1.5 nm; but preferably 15 nm or less; more preferably 12 nm or less. These preferred thicknesses also enable further ease of deposition and improvement in optical characteristics such as haze whilst retaining mechanical durability.

It is therefore most preferred that in relation to the present invention the stack sequence for the coated glass substrate follows the sequence from the glass substrate:

Di la / Absorber 1 / Di lb / Ag 1 / Barrier 1 / Di 2 / Ag 2 / Barrier 2/ Absorber 2 / Di 3 or

Di la / Absorber 1 / Di lb / Ag 1 / Barrier 1 / Absorber 2 / Di 2/ Ag 2/ Barrier 2 / Di 3 where Di = dielectric layer and Ag = silver layer,

A preferred example of a stack sequence in relation to the present invention deposited in order from the glass substrate is preferably therefore:

SiNx (15)/ WNx (3)/ SiNx (10)/ZnSnOx (13)/ZnO (3)/ Ag (9.8) /NiCrOx (1)/ ZAO (7)/ AINx (36)/ ZnSnOx (ll)/ZnO (13)/ Ag (13.2)/ NiCrOx (1 )/ WNx (3.3) / AINx (40) / ZnSnOx (5) wherein SiNx, ZnSnOx, ZnO, ZAO and AINx are all dielectric materials, as will be discussed further in the experimental section below.

Embodiments of the present invention will now be described by way of example only with reference to the following examples. EXPERIMENTAL

A series of experiments were conducted to assess the impact of using one or more absorber layer in a layer stack sequence deposited on a float glass substrate in terms of transmission and internal and external reflection of the coated substrate.

Experiment 1 - Comparison of results for glass substrates coated with a layer sequence according to the present invention which includes at least one absorber layer.

A series of coating layers (referred to as a stack) were deposited onto a float glass substrate. The coating layers included at least one silver based low-emissivity coating. The series of layers are identified in Table 1.

The coating layers were deposited on a 4mm thick standard float glass pane with a light transmittance in the region of 88% using single or dual magnetrons equipped with MF-AC and/or DC magnetron (or pulsed DC) power supplies.

In Table 1 the materials are listed along with the geometrical thickness of each layer in nanometres in brackets. The coating layers are obtained as follows:

Layers of an oxide of zinc (Zn) and tin (Sn) were reactively sputtered from zinc-tin targets (weight ratio Zn : Sn approximately 50:50) in an argon/oxygen (Ar/Ch) sputter atmosphere. The ZnOx layers were sputtered from Al-doped Zn targets (aluminium (Al) content about 2 weight %) in an Ar/Ch sputter atmosphere.

The functional layers of essentially pure silver (Ag) were sputtered from silver targets in an Ar sputter atmosphere without any added oxygen and at a partial pressure of residual oxygen below 10 ^"5 mbar.

The layers of silicon nitride (SiN _x ) were reactively sputtered from mixed Si 90 Al 10 targets in an Argon/Nitrogen (Ar/N2) sputter atmosphere containing only residual oxygen.

The layers of nickel chromium nitride (NiCrNx) were reactively sputtered from nickel- chromium alloy targets (with approximately 80 weight % nickel (Ni) and 20 weight % chromium (Cr)) in and Ar/N2 sputtering atmosphere.

The layers of silicon oxide (SiOx) were sputtered from mixed SLoAho targets in an Argon/Oxygen (Ar/Ck). The layers of AIN were reactively sputtered from an A1 target in an Argon/Nitrogen (Ar/N2) sputter atmosphere containing only residual oxygen.

The layers of ZAO were sputtered from a ceramic ZnO:Al target (with an aluminium (Al) content in the region of 10 weight %) in an Ar/02 sputtering atmosphere.

The layers of NiCrOx were sputtered reactively from Nickel -Chromium alloy targets (with approximately 80 weight % nickel (Ni) and 20 weight % chromium (Cr)) in and Ar/0 ₂ sputtering atmosphere.

The layers of WNx were sputtered reactively from metallic W targets in an Ar/N2 sputtering atmosphere.

The coating stack layers were deposited using standard process conditions.

Table 1 - results for silver based low emissivity coating stacks applied to float glass sheets in the presence of at least one absorber layer.

Table 2 - results for silver based low emissivity coating stacks applied to a float glass sheet in the presence of one or more absorber layers.

Tables 1 and 2 provide details of the layer sequences for a comparative coated glass substrates and coated glass substrates according to the present invention.

The methodology used to collect the data in Tables 1 and 2 is set out below. For each example, the layers were deposited on a glass pane in the sequence shown starting with the layer at the top of each column. Table 3 provides details of the light transmission measurements recorded for the coatings of Comparative Examples 1, 2 3 and Examples 4 to 11 after heat treatment.

Heat treatability tests - immediately after deposition of the coatings to the glass substrate in each example in Tables 1 and 2, the coating stack parameters such as light transmittance (T _L ), colour co-ordinates and shading coefficient were measured for each coated glass substrate. That is, the coated glass substrates were heat treated in the region of 650 °C for 5 minutes.

The values stated for the change in percentage (%) light transmittance and reflectance upon heat treatment of the coated glass pane Examples in Table 3 were derived from measurements according to EN 410, the details of which are incorporated herein by reference.

Colour characteristics - the colour characteristics for each sample were measured and reported using the well-established CIE LAB L*, a*, b* coordinates (as described for example in paragraphs [0030] and [0031] of WO 2004/063111A1, incorporated herein by reference). The change in transmission colour upon heat treatment, T DE* = ((Aa*) ² + (Ab*) ² + (AL*) ² ) ^1/2 , wherein AL*, Aa* and Ab* are the differences of the colour values L*, a*, b* of the coated glass pane each before and after a heat treatment. DE* values of less than 10 are preferred for layer sequences with one silver-based functional layer, representing a low and practically non- noticeable colour modification caused by the heat treatment. For layer sequences comprising two or more silver-based functional layer, lower T DE* values provide an indication of the stability of the sequences; the lower the T DE* values the more superior the results and appearance of the coated glass pane.

Table 3 - Light transmission measurements recorded for the coatings of Comparative Examples 1. 2 3 and Examples 4 to 11 after heat treatment.

Table 3 illustrates the light transmission measurements recorded for the coatings of comparative Examples 1, 2 3 and Examples 4 to 11 after heat treatment, and Table 4 illustrates the colour measurements recorded according to the CIE colour system for the coatings of Comparative Examples 2 and 3 and Examples 4, 9, 10 and 11 when installed in an insulated glazing unit (IGU).

In Tables 3 and 4:

T a* and T b* represent the transmitted colour co-ordinates according to the CIE colour system.

Rg a* and Rg b* represent the colour co-ordinates according to the CIE colour system for the uncoated side of the glass substrate.

Rc a* and Rc b* represent the colour co-ordinates according to the CIE colour system for the coated side of the glass substrate.

Rg Y represents the reflection for the uncoated side of the glass substrate.

Rc Y represents the reflection for the coated side of the glass substrate.

** Shading Coefficient is a measure of the total amount of heat passing through the glass substrate (known as the total solar heat transmittance) compared with that through a single clear glass. The shading coefficient (SC) is derived by comparing the solar radiant heat transmission properties of any glass with a clear float glass having a total solar heat transmittance of 0.87 (that is, clear float glass about 4mm thick).

Experiment 2 - Comparison of insulated glazing units prepared with coated glass

substrates according to Comparative Examples 2 and 3 and Examples 4. 9. 10 and 11 according to the present invention which includes at least one absorber layer.

An insulated glazing unit (IGU) (1) as illustrated in Figure 1 was prepared using a 6mm glass sheet (2) with a coating (5) as described in either Comparative Example 2, Comparative Example 3 or Examples 4, 9, 10 or 11. That is, a 4mm thick float glass sheet (2) with a coating as detailed in Comparative Examples 2 or 3, or Examples 4, 9, 10 or 11 was assembled with a second 4 mm thick uncoated float glass sheet (3). The two sheets of glass (2, 3) were assembled such that the coated side (5) of the coated glass sheet (2) faced the interspace gap (8) (referred to as position two in a DGU when installed), that is, the coated glass sheet (5) is closer to the external environment than the uncoated glass sheet (3) to form a thermal insulation (or double) glazing unit. The glass sheets were positioned with an interspace distance of 16 mm between them and the interspace gap (8) was filled with a 90% argon gas and 10% air filling. The uncoated face (4) of the coated glass sheet (2) was therefore present at position 1, and the two uncoated faces (6) and (7) of the second glass sheet (3) were present at positions 3 and 4 respectively. The properties of the double glazing with the coating from each of Comparative Examples 2 and 3 and Example 4, 9, 10 or 11 at position 2, were measured in accordance with EN 410. The results are as provided in Table 4.

Table 4 illustrates the CIE colour system and light transmission values for a double glazing unit prepared with a heat treated coated glass substrate according to the present invention (Examples 4, 9, 10,11) and for two comparative heat treated coated glass substrates (Examples 2 and 3). It can be seen from the results that according to the present invention it is possible to produce a double glazing unit with a heat treated coated glass substrate according to the present invention with minimal internal and external reflections which also produces minimal internal and external reflection values for a double glazing unit (IGU).

Table 4 - Colour measurements recorded according to CIE colour system for the coatings of

Comparative Examples 2 and 3 and Examples 4. 9. 10.11 in an IGU.

It can be seen from the above results that it is possible to prepare coated glass substrates according to the present invention with a coating deposited by physical vapour deposition (PVD) (or sputtering) followed by heat treatment and toughening, which provide the required colour and solar control properties demanded by the glazing industry, and which are able to be incorporated into an insulated glazing unit and still retain the required colour and when viewed from either side of the glazing unit.

More specifically, the inventors have found that it is possible to produce toughenable coated glass substrates in which the internal and external reflections are minimized by using one or more stable absorber in combination with dielectric layers in a set order from the glass substrate. In addition, the inventors have surprisingly found that by using one or more stable absorber layer in combination with a series of dielectric layers in a coating for a glass substrate that it is possible to prepare an insulated glazing unit (IGU) again with minimal internal and external reflection whilst appearing neutral or grey for the transmitted colour .

As can be seen from the comparative date, simply incorporating a single absorber layer in the lowest dielectric layer closest to the glass substrate resulted in a glass substrate with undesirably high internal reflections, that is, combined internal reflections of the order of 25% or more when the glass substrate was used in an insulated glazing unit (IGU).

The inventors have therefore found that to achieve the required colour in transmission and also low internal and external reflections, it is most preferable to use a single absorber layer in the dielectric layer closest to the glass substrate and preferably also a second absorber layer in the stack design. Further, the inventors have found that it is preferable to position the second absorber layer above either the first and/or second silver based functional layer, and therefore in a middle or upper portion of the layer sequence, that is furthest from the glass substrate. The inventors have also found that low reflections may be achieved by using a NiCr metal alloy layer in contact with the first silver functional layer with a first absorber layer in the lower anti- reflection layer.

More preferably, the inventors have found that the second absorber layer is preferably positioned after a barrier layer (such as for example NiCrOx) in the middle or upper portion of the layer sequence. By such an arrangement the inventors found that it is possible to achieve a glass substrate with a preferred neutral or grey colouration and with low internal and external reflection values.

Consequently, the present invention demonstrates that it is possible to achieve optimised solar control properties in a PVD (or sputtered) deposited stack sequence using one or more absorber layers whilst retaining a grey or neutral colour in transmission for the coated glass substrate which when incorporated into an insulated glazing unit is able to achieve a shading coefficient of preferably 25% or less and a Selectivity (light transmission (LT) to Total Solar Heat Transmission (TSHT)) of preferably between 1.50 and 1.55.