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 whilst retaining a desired negative value for b* according to the CIE colour space in transmission and in reflection.

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/di electric 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 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.

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 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. Indeed, it can be extremely difficult to deposit a heat treatable coating with two or more silver layers on a glass substrate whilst retaining an appreciably negative b* value (that is greater than 4 units) in transmission, film side reflection and glass side reflection simultaneously without the cost of additional coating layers.

In the float glass process, a continuous strip of molten glass is poured from a furnace onto a large shallow bath of molten metal to form a float glass ribbon. Tin is usually used as the molten metal. The glass floats on the tin and as the glass cools, it spreads out to form a flat surface. Rollers are used across the top of the glass, to pull or stretch the glass to the required thickness of glass sheet. The surface of the glass sheet which is in contact with the tin during production is traditionally known as the‘tin’ side of the glass sheet or substrate. The opposite surface of the glass sheet which is in contact with an atmosphere of hydrogen and nitrogen generated in the bath is traditionally known as the‘air’ side.

When glass of the required colour is required, it is commonplace to add a colourant to the molten glass during the float glass production process to produce glass of the required colouration. Unfortunately, colourants are difficult to use, and are readily dispersed. Consequently, it is difficult to control the spread of colourant once introduced into a manufacturing facility. However, the greatest difficulty posed by using colourants in a float glass manufacturing facility is that once introduced into the molten glass, removal of the colourant to a sufficient extent to allow manufacture of non-coloured glass is time consuming and costly process, leading to excessive waste glass being generated in an attempt to ensure all traces of the colourant are removed.

The present invention therefore seeks to address the above problems and provide a glass substrate which avoids the need to use colourants in float glass manufacturing, instead providing coatings which enable the required colouration to be achieved. In addition, the present invention seeks to provide a coated glass substrate of the required colour which is able to withstand heat treatment, and which may therefore be toughened without damage and thereby not only meet the required aesthetic appearance of the coated glass but also deliver the properties required of coated glass substrates for both the architectural and automotive industries. Furthermore, the present invention seeks to provide a toughened and coated glass substrate which appears to an observer to be of the same colour when viewed from each side of the glass substrate.

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

at least a first surface of the coated glass substrate is coated with one or more layers applied by physical vapour deposition (PVD); and wherein

said one or more layers applied by physical vapour deposition (PVD) includes at least one functional metal layer; and

at least one absorbing layer based on Ti, V, Cr, Fe, or W, Ni Nb, and alloys thereof and nitrides; and wherein

the second surface further comprises at least one protective layer applied in direct contact with the second surface of the glass substrate before deposition of the one or more layers applied by physical vapour deposition (PVD), and wherein the coated float glass substrate exhibits a transmission colour value according to the CIE colour space of less than or equal to 3 and a glass side reflection of less than or equal to -4.

Preferably, for the toughenable coated substrate according to the first aspect of the present invention, the protective layer comprises a layer of silicon oxide (SiOx), wherein x is in the range 1.5 and 2.0.

According to the CIE colour space, the toughenable coated substrate according to the present invention preferably comprises a b* and a* value which are both negative with respect to external reflection. That is, the b* value is in the blue region of the CIE colour space and the a* value is in the green region of the CIE colour space.

Also, in relation to the first aspect of the present invention the protective layer is preferably applied by physical vapour deposition (PVD).

Preferably, the thickness of the protective layer is in the range 10 to lOOnm. More preferably the thickness of the protective layer is in the range 15 to 80nm. Even more preferably the thickness of the protective layer is in the range 30 to 70nm. Most preferably however, the thickness of the protective layer is in the range of 40 to 70 nm. Alternatively, the thickness of the protective layer may be in the range of 30 to 60nm, or even, 40 to 60nm.

It is preferred in relation to the first aspect of the present invention that for the toughenable coated substrate the second surface of the float glass contacted molten tin during manufacture and the first surface of the float glass contacted a bath atmosphere of nitrogen and hydrogen during manufacture.

Preferably, the one or more layers applied to the first surface of the toughenable coated substrate by physical vapour deposition (PVD) comprises a functional metal layer. It is preferred that the functional metal comprises silver.

In addition, in relation to the toughenable coated substrate according to the present invention, the one or more layers applied by physical vapour deposition (PVD) preferably includes at least one absorbing layer based on Ti, V, Cr, Fe, or W, Ni Nb, and alloys thereof and nitrides. Most preferably, the at least one absorbing layer comprises tungsten (W), preferably tungsten nitride.

Further in relation to the toughenable coated substrate according to the first aspect of the present invention, it is preferred that the change in colour for transmission after heat treatment (DE*) for the coated substrate is less than or equal to 10. More preferably, it is preferred that the change in colour for transmission 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 after heat treatment (DE*) for the coated substrate is less or equal to 5.

In addition, in relation to the toughenable coated substrate according to the first aspect of the present invention, it is preferred that the change in colour for reflection after heat treatment (DE*) for each side of the coated substrate is less than or equal to 10. More preferably, it is preferred that the change in colour for reflection after heat treatment (DE*) for each side of the coated substrate is less than or equal to 8 or 7. Most preferably, the change in colour for reflection after heat treatment (DE*) for each side of the coated substrate is less than or equal It is preferred that for the coated glass substrate according to present invention, the sequence of one or more layers applied above the protective layer of SiOx comprises in order from the SiOx layer:

a lower anti -reflection layer;

a silver-based functional layer;

a barrier layer; and

an upper anti -reflection layer.

Alternatively, for the coated glass substrate according to present invention, the sequence of one or more layers applied above the protective layer of SiOx comprises in order from the SiOx layer:

a lower anti -reflection layer;

a first silver-based functional layer;

a barrier layer ;

a central anti -reflection layer;

a second silver-based functional layer; and

an upper anti -reflection layer.

Also in relation to the present invention it is preferred that the absorbing layer is present in at least one of the anti -reflection layers. Alternatively, the absorbing layer is preferably present in more than one of the anti -reflection layers.

It is most referred in relation to the present invention that the at least one absorbing layer comprises tungsten (W), preferably tungsten nitride.

In addition, it is preferred that for the toughenable coated substrate according to the present invention that the or each absorbing layer contacts at least one layer based on an (oxi)nitride of Si and/or an (oxi)nitride of A1 and/or alloys thereof located in one or more of the anti- reflection layers.

Alternatively, it is preferred that for the toughenable coated substrate according to the present invention that the at least one absorbing 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 located in one or more of the anti -reflection layers. In an especially preferred embodiment of the toughenable coated substrate according to the present invention, each absorbing layer present in the coating preferably 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.

The or each absorbing layer based on tungsten preferably has a thickness in the range 0.5 nm to lOnm. Most preferably, the or each absorbing layer based on tungsten preferably has a thickness in the range 0.5 nm to 5nm.

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

i) providing a float glass substrate with a first surface and a second surface, wherein the first surface of the float glass substrate contacts a bath atmosphere of nitrogen and hydrogen during manufacture and the second surface of the float glass substrate contacts molten tin during manufacture;

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

iii) depositing by physical vapour deposition (PVD), a protective layer directly on the glass substrate prior to depositing the one or more layers on the second surface, wherein the protective layer comprises a thickness of between lOnm and lOOnm; and

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

In relation to the second aspect of the present invention it is preferred that the protective layer comprises a layer of silicon oxide (SiOx), wherein x is in the range 1.5 and 2.0.

In addition, for the one or more functional metal layers deposited by physical vapour deposition (PVD) on the first surface of the substrate, it is preferred that the functional metal layer comprises silver.

Also, in relation to the second aspect of the present invention it is preferred if the protective layer is deposited to a thickness of from 30nm and 70nm. Preferably, the thickness of the protective layer is deposited in the range 10 to lOOnm. More preferably the thickness of the protective layer is deposited in the range 15 to 80nm. Even more preferably the thickness of the protective layer is deposited in the range 30 to 70nm. Most preferably however, the thickness of the protective layer is deposited in the range of 40 to 70 nm. Alternatively, the thickness of the protective layer may be deposited in the range of 30 to 60nm, or even, 50 to 60nm.

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 article.

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 glazing such as for example, windscreen, sidelight, rooflight or backlight.

In the coated glass substrates according to the present invention with a protective layer of SiOx applied to the‘air’ side of the glass substrate, the coating stack preferably comprises the following sequence in order from the SiOx layer when the coating stack comprises a single silver-based functional layer: a lower anti -reflection layer; a silver-based functional layer; a barrier layer; and an upper anti-reflection layer.

Alternatively, when the coated glass substrates according to the present invention with a protective layer of SiOx applied to the‘air’ side of the glass substrate, comprises two silver layers, the coating stack preferably comprises the following sequence in order from the SiOx layer: a lower anti-reflection layer; a first silver-based functional layer; a barrier layer; a central anti-reflection layer; a second silver-based functional layer; and an upper anti -reflection layer.

In relation to the coating sequence used on the coated glass substrate according to the present invention, the lower anti-reflection layer may preferably comprise in sequence from the protective silicon oxide SiOx layer, a layer based on an oxide of zinc (Zn) and tin (Sn) and/or an oxide of tin (Sn); and a top layer based on an oxide of Zn.

The lower anti -reflection layer may also 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 protective silicon oxide SiOx layer 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.

Therefore, in an embodiment of the present invention the coated glass pane preferably comprises a base layer based on an (oxi)nitride of silicon and/or an (oxi)nitride of aluminium and/or alloys thereof located between the protective silicon oxide (SiOx) layer and the layer based on an oxide of zinc (Zn) and tin (Sn) and/or an oxide of tin (Sn). That is, the lower anti reflection layer may comprise three layers.

For the coated glass substrate comprising 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 and/or an (oxi)nitride of silicon and/or an (oxi)nitride of aluminium and/or alloys thereof.

In addition, 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; even more preferably from 0.5 to 4 nm; most preferably from 0.5 to 3 nm. These preferred thicknesses enable further improvement in haze upon heat treatment. 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.

When the separation layer is based on a metal oxide said separation layer may preferably comprise a layer based on an oxide of: Ti, Zn, NiCr, InSn, Zr, A1 and/or Si.

When the separation layer is preferably based on a metal oxide, it may be deposited using non reactive sputtering from a ceramic target based on for example a slightly substoichiometric titanium oxide, for example a TiOi.98 target, as an essentially stoichiometric or as a slightly substoichiometric oxide, by reactive sputtering of a target based on Ti in the presence of O2, or by depositing a thin layer based on Ti which is then oxidised. In the context of the present invention, an“essentially stoichiometric oxide” means an oxide that is at least 95% but at most 100% stoichiometric, whilst a“slightly substoichiometric oxide” means an oxide that is at least 95% but less than 100% stoichiometric. The use of TiOx as a separation layer is especially preferred when the coating sequence comprises a single silver-based functional layer.

In addition to the metal oxide and/or (oxi)nitride of silicon and/or (oxi)nitride of aluminium and/or alloys thereof upon which it is based, 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 and/or (oxi)nitride of silicon and/or (oxi)nitride of aluminium 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) and/or an oxide of titanium.

In another preferred embodiment of the present invention, the separation layer is based on a metal oxide, which comprises an oxide of titanium.

In addition, it is preferred that when the separation layer is based on a metal oxide and the metal oxide is based on titanium oxide, that the titanium oxide has a preferred thickness of from 0.5 to 3nm.

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; 15 to 45 nm; or 20 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 25 to 35 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 0.5 to 13 nm; or 1 to 12 nm. In addition, 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: 1 to 7 nm; or 2 to 6 nm; or 3 to 6 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 3 to 5 nm for a coated glass pane with layer sequence comprising a single silver-based functional layer. An upper thickness limit in the region of 8 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.

Whilst the separation layer may be preferably based on an oxide of titanium when the layer sequence comprises one silver-based functional layer, it may also be preferred that when the layer sequence or stack comprises more than one silver-based functional layer that the layer sequence comprises two or more separation layers in the lower anti -reflection layer.

Preferably the two or more separation layers are 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 protective silicon oxide SiOx layer 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 separation 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 separation 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.

In addition to the metal oxide and/or (oxi)nitride of silicon and/or (oxi)nitride of aluminium and/or alloys thereof upon which it is based, the separation layer may further include one or more other 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 and/or (oxi)nitride of silicon and/or (oxi)nitride of aluminium does not include one or more other chemical elements.

In an alternative embodiment of the present invention, the separation layer may be based on a metal oxide, which comprises an oxide of zinc (Zn) and/or an oxide of titanium or an oxide of titanium.

In addition, it is preferred that when the separation layer is based on a metal oxide and that the metal oxide is based on titanium oxide, that the titanium oxide has a preferred thickness of from 0.5 to 3nm.

However, it is preferred that when the layer sequence comprises two or more silver based functional layers, and the separation layer is based on one or more layers of an (oxi)nitride of silicon and/or (oxi)nitride of aluminium and/or alloys thereof, that the lower anti -reflection layer preferably comprises two or more layers based on one an (oxi)nitride of silicon and/or (oxi)nitride of aluminium and/or alloys thereof,

Alternatively, when the layer sequence comprises one silver based functional layers, the separation layer is preferably based on one or more layers of an on an oxide of titanium.

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 3 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 3 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 3 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 layers between the glass substrate and the silver-based functional layer may consist of three layers, four 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 substoichiometric 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.

Therefore, for coated glass panes comprising two or more silver based functional layers (or even 3 or 4 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 an oxide of 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 preferably comprises:

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; 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 1.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 SboAlio target in a N ₂ 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 SboAhoN _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, the coated glass panes according to the present invention 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 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.

In addition, it is 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 less than 10 nm; more preferably 8 nm. These preferred thicknesses also enable further ease of deposition and improvement in optical characteristics such as haze whilst retaining mechanical durability.

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.

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 a tungsten nitride absorber (WNx) layer in a layer stack sequence deposited on a float glass substrate in terms of the film and glass side reflection of the substrate.

Experiment 1 - Comparison of results for glass substrates coated with a layer sequence which includes tungsten nitride (WNx) as an 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 silicon oxide (SiOx) layer and the additional coating layers were deposited on a 6mm 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/02 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 w Al io targets in an Argon/Nitrogen (Ar/Ni) 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 SLoAl m targets in an Argon/Oxygen (Ar/CL).

The layers of AINx were reactively sputtered from an Al target in an Argon/Nitrogen (Ar/Ni) 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 emissivitv coating stacks applied to atmosphere on side of float glass sheets in the presence of at least two tungsten nitride absorber layers.

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

Table 2 provides details of the colour measurements recorded according to the CIE colour space for the coatings of comparative example 1 and examples 1, 2 and 3 before heat treatment, whilst, Table 3 details the colour measurements recorded according to the CIE colour space for the coatings of comparative example 1 and examples 1, 2 and 3 after heat treatment.

Table 4 provides details a summary of the changes in the CIE colour space measurements for examples 2 and 3 after heat treatment.

In Table 4, DE* - is a measure of the change in transmitted colour upon heat treatment.

The methodology used to collect the data in Table 1 is set out below. For each example, the layers were deposited on to a glass pane in the sequence shown starting with the layer at the top of each column. Heat treatability tests - immediately after deposition of the coatings to the glass substrate in each example in Table 1, the coating stack colour co-ordinates were measured for each coated glass substrate. The coated glass substrates were then heat treated in the region of 650 °C for 5 minutes 30 seconds. Thereafter, percentage light transmittance and reflectance of both surfaces (coated‘film’ and uncoated‘glass’) and colour coordinates were again measured and the change in light transmittance and the change in colour upon heat treatment (DE*) calculated.

The values stated for the change in percentage (%) light transmittance and reflectance upon heat treatment of the coated glass pane Examples detailed in Table 1 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 3 (for example 2 or 2.5) 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 4 illustrates the difference in the CIE colour system values L*, a* and b* measured for each side of the coated float glass. It can be seen from the results that it is possible to obtain toughening of the coated substrate whilst obtaining acceptable colour changes after heat treatment. Table 2 - Colour measurements recorded according to CIE colour system for the coatings of comparative Example 1 and Examples 1. 2. and 3 before heat treatment.

Table 3 - Colour measurements recorded according to CIE colour system for the coatings of comparative Example 1 and Examples 1. 2. and 3 after heat treatment.

Table 4 - Summary of the changes in CIE lab system colour measurements recorded for Examples 2 and 3 after heat treatment.

For the results provided in Table 4, changes in the values observed for the coated glass substrates after heat treatment, that is, for the recorded values for DE for the transmission and reflection on the coated glass, values of less than 10 are preferred. Indeed, for coated glass substrates after heat treatment, changes in the recorded values for DE for the transmission and reflection on the coated glass of less than 5 are highly preferred.

It can be seen from the results that in accordance with the present invention, coated glass substrates are provided with good solar control properties and a blue appearance when viewed in both transmission and reflection. In particular, the transmitted b* value is less than 0 (that is, a negative value for b*), more preferably less than -2 and even more preferably less than - 3. It is especially preferred that the value for transmitted a* is also in the range of -10 to 5 units, more preferably -8 to 4 units and especially between -7 and 3 units.

It is also preferable that the appearance of the coated glass is also blue when viewed in reflection, particularly when viewed from the uncoated surface of the coated glass pane (herein referred to as the‘glass’ side reflection). It is preferable that the value for reflected b* on the ‘glass’ side of the substrate has a negative value, more preferably has a value of less than -5 and most preferably that it has a value of less than -8. It is also desirable that the value for reflected a* on the‘glass’ side of the substrate fall in the range of -10 to 5 units, more preferably -10 to 2 and even more preferably -10 to 0, that is the value of a* is negative.

Due to the low light transmission required to provide effective solar control, it is often necessary to temper the glass substrate to avoid thermal breakage when installed into a building, it is therefore important that the coated glass is able to withstand the thermal tempering process whilst retaining an aesthetic appearance. It is therefore preferable that the value for DE is less than 10 with respect to transmission and reflection from both sides of the substrate, even more preferably the value of DE is less than 7 and most preferably the value of DE is less than 5.

Accordingly, the results demonstrate that the present invention provides a solar control coated glass substrate which is substantially blue in colour both in transmission and reflection. More specifically, the present invention provides a solar control coating stack which exhibits colour co-ordinates which are significantly negative in b* (that is blue) and of similar value. As a result, the coated glass substrates prepared in accordance with the present invention are able to be used in place of glass tinted with a colourant to achieve the same blue (b* value), whilst providing superior properties in terms of emissivity, and a solar heat gain co-efficient (SHGC) of less than 0.3 when assembled into an insulated glazing unit (IGU).

Additionally, the coated glass substrates of the present invention may be applied to the air side of a glass substrate already provided with a coating present on the tin side of the glass substrate, thereby increasing the flexibility of production facilities.