Patent Description:
Insulated glazing units are known comprising at least two spaced apart sheets of glass. One such type of insulated glazing unit comprises two sheets of glass spaced apart by perimeter seals and are conventionally known as double glazed units. <CIT> shows in <FIG> an insulated glazing unit with an external low emissivity coating comprising one layer of fluorine doped tin oxide and an anti-iridescence coating in between the low emissivity coating and a sheet of glazing material.

Another type of insulated glazing unit comprises two sheets of glass spaced apart by an evacuated space. Disposed in the evacuated space is a plurality of spacers to maintain a spacing of around <NUM> between the two sheets of glass. The periphery of the two glass sheets may be sealed with a solder glass, for example as described in <CIT> or an organic material as described in <CIT>. This type of insulated glazing unit is often referred to as a vacuum insulated glazing unit, or VIG. VIG's are also described in <CIT>, <CIT>, <CIT> and <CIT>.

It is also known that a VIG may be one pane of a double glazed unit, for example as described in <CIT>, <CIT> and <CIT>. The VIG is spaced apart from another pane, such as a glass sheet. This type of insulated glazing unit has an evacuated low pressure space and an air space (typically filled with an inert gas such as argon or krypton).

It is known that the external surfaces of insulated glazing units such as double glazing units may become fogged due to condensation forming on the outer surfaces. This is a consequence of the emission of heat from the outer glazing. For the surface of a double glazing unit facing the outside i.e. the outer surface, if insufficient heat flows from the internal space to the outer surface, as is the case with insulated glazing units with low U values, the temperature of the outside surface drops. When there is a sufficiently high relative external atmospheric humidity this leads to fogging i.e. condensation or frost deposition, as a result of the temperature of the outer surface falling below the dew point.

The present invention provides a vacuum insulated glazing unit having improved thermal performance.

Accordingly from a first aspect the present invention provides a vacuum insulated glazing unit with the features of claim <NUM>, a vacuum insulated glazing unit with the features of claim <NUM> and a vacuum insulated glazing unit with the features of claim <NUM>.

The provision of the low emissivity coating on the second major surface of the second sheet of glazing material reduces the U-value of the insulated glazing unit compared to the same insulated glazing unit without the low emissivity coating on the second major surface of the second sheet of glazing material.

Such an insulated glazing unit may be installed in a building. When installed in a building, it is preferred that the first major surface of the first sheet of glazing material faces the exterior of the building, and the second major surface of the second sheet of glazing material faces the interior of the building Alternatively, the insulated glazing unit may be installed in a building such that the first major surface of the first sheet of glazing material faces the interior of the building, and the second major surface of the second sheet of glazing material faces the exterior of the building. When the insulated glazing unit is configured such that the second major surface of the second sheet of glazing material faces the exterior of a building in which the insulated glazing unit is installed, the provision of a low emissivity coating on the second major surface of the second sheet of glazing material helps reduce the formation of condensation on the second major surface of the second sheet of glazing material because the temperature of the second sheet of glazing material may be raised.

According to the present invention as defined in any of the claims <NUM>-<NUM> the first sheet of glazing material is spaced apart from the second sheet of glazing material by less than <NUM>, preferably by <NUM> to <NUM>, more preferably by <NUM> to <NUM>.

Suitably an hermetic seal extending around the periphery of each the first and second sheets of glazing material joins the first sheet of glazing material to the second sheet of glazing material. The hermetic seal ensures the first space is maintained at suitably low pressure. The spacers disposed in the first space prevents the second major surface of the first sheet of glazing material coming into contact with the first major surface of the second sheet of glazing material.

It is to be understood within the context of the present invention that when a coating has a layer A on a layer B, this does not rule out the possibility of there being one or more other layers i.e. layers C, D, E etc in between layer A and layer B. Similarly, when a surface of a sheet of glazing material has a layer A' thereon, this does not rule out the possibility of there being one or more other layers i.e. layers B, C, D, E etc in between layer A and the surface of the sheet of glazing material.

For clarity, the first major surface of the first sheet of glazing material is also referred to as surface i of the insulated glazing unit. For clarity, the second major surface of the first sheet of glazing material is also referred to as surface ii of the insulated glazing unit. For clarity, the first major surface of the second sheet of glazing material is also referred to as surface iii of the insulated glazing unit. For clarity, the second major surface of the first sheet of glazing material is also referred to as surface iv of the insulated glazing unit.

Using this notation for referring to the major surfaces of the sheets of glazing material, and for the avoidance of doubt, a vacuum insulated glazing unit according to the first aspect of the present invention as defined in any of the claims <NUM>-<NUM> has a low emissivity coating on surface iv.

Again for the avoidance of doubt, depending upon the orientation of the insulated glazing unit when installed in a building or the like, surface i may face either the interior of the building or the exterior of the building.

As is conventional in the art, the surface of an insulated glazing unit configured to directly face the external environment of a structure in which the insulated glazing unit is installed is referred to as surface <NUM>. The surface opposite surface <NUM> is referred to as surface <NUM> i.e. surface <NUM> is one major surface of a glazing pane and surface <NUM> is the opposing major surface of the glazing pane. The surface of the insulating glazing unit opposite surface <NUM> is referred to as surface <NUM>. The surface opposite surface <NUM> is referred to as surface <NUM>, and so on for additional glazing panes. For example, for an insulated glazing unit having two spaced apart glazing panes i.e. glass, surface <NUM> of the insulated glazing unit faces the exterior of the structure in which the insulated glazing unit is installed and surface <NUM> faces the interior of the structure in which the insulated glazing unit is installed. In relation to the naming convention adopted in the present application, surface i or surface iv of the insulated glazing unit of the first aspect of the present invention may be surface <NUM>.

Preferably the geometric thickness of the at least one fluorine doped tin oxide layer of the low emissivity coating on surface iv is between <NUM> and <NUM>.

In some embodiments preferably the geometric thickness of the at least one fluorine doped tin oxide layer of the low emissivity coating on surface iv is between <NUM> and <NUM>, more preferably between <NUM> and <NUM>, even more preferably between <NUM> and <NUM>.

By having a thin layer of fluorine doped tin oxide the low emissivity coating is less susceptible to surface damage because the coating is less rough. In addition costs are reduced because less coating is required to achieve the anti-condensation properties. Furthermore the G value of the insulated glazing unit is higher compared to the same insulated glazing unit with a thicker layer of fluorine doped tin oxide.

In some embodiments preferably the geometric thickness of the at least one layer of fluorine doped tin oxide of the low emissivity coating on surface iv is between <NUM> and <NUM>, more preferably between <NUM> and <NUM>.

In some embodiments preferably the geometric thickness of the at least one fluorine doped tin oxide layer of the low emissivity coating on surface iv is between <NUM> and <NUM>, more preferably between <NUM> and <NUM>.

Preferably the first anti-iridescence layer comprises a first layer and a second layer, wherein the first layer of the first anti-iridescence layer has a higher refractive index than the second layer of the first anti-iridescence layer and the second layer of the first anti-iridescence layer is in between the first layer of the first anti-iridescence layer and the first low emissivity coating.

Preferably the first layer of the first anti-iridescence layer comprises tin oxide.

Preferably the second layer of the first anti-iridescence layer comprises silica.

Preferably the first layer of the first anti-iridescence layer has a geometric thickness of between <NUM> and <NUM>, preferably between <NUM> and <NUM>.

Preferably the second layer of the first anti-iridescence layer has a geometric thickness of between <NUM> and <NUM>, preferably between <NUM> and <NUM>.

Preferably there is a first haze reducing layer in between the second sheet of glazing material and the first anti-iridescence layer.

Preferably the first haze reducing layer comprises silica.

Preferably the geometric thickness of the first haze reducing layer is between <NUM> and <NUM>, more preferably between <NUM> and <NUM>.

In a vacuum insulating glazing unit according to the present invention as defined in claim <NUM> there is a low emissivity coating on surface iii.

Preferably there is an anti-iridescence coating in between the low emissivity coating on surface iii and the second sheet of glazing material.

The anti-iridescence coating in between the low emissivity coating on surface iii and the second sheet of glazing material has the same preferable features as described above in relation to the first anti-iridescence coating.

The low emissivity coating on surface iii comprises at least one fluorine doped tin oxide layer. The low emissivity coating on surface iii may additionally comprise one silver layer.

When the low emissivity coating on surface iii comprises at least one silver layer, preferably the geometric thickness of the at least one silver layer is between <NUM> and <NUM>.

Preferably the geometric thickness of the at least one fluorine doped tin oxide layer of the low emissivity coating on surface iii is between <NUM> and <NUM>.

In some embodiments preferably the geometric thickness of the at least one fluorine doped tin oxide layer of the low emissivity coating on surface iii is between <NUM> and <NUM>, more preferably between <NUM> and <NUM>, even more preferably between <NUM> and <NUM>.

In some embodiments preferably the geometric thickness of the at least one fluorine doped tin oxide layer of the low emissivity coating on surface iii is between <NUM> and <NUM>.

In some embodiments preferably the geometric thickness of the at least one layer of fluorine doped tin oxide of the low emissivity coating on surface iii is between <NUM> and <NUM>, more preferably between <NUM> and <NUM>.

In some embodiments preferably the geometric thickness of the at least one fluorine doped tin oxide layer of the low emissivity coating on surface iii is between <NUM> and <NUM>, more preferably between <NUM> and <NUM>.

When the low emissivity coating on surface iii comprises at least one fluorine doped tin oxide layer, preferably there is an anti-iridescence layer of SiCOx between the low emissivity coating on surface <NUM> and the second sheet of glazing material. Preferably the SiCOx layer has a geometric thickness between <NUM> and <NUM>.

In a vacuum insulating glazing unit according to the present invention as defined in claim <NUM> there is a low emissivity coating on surface ii.

Preferably there is an anti-iridescence coating in between the low emissivity coating on surface ii and the first sheet of glazing material.

The anti-iridescence coating in between the low emissivity coating on surface ii and the first sheet of glazing material has the same preferable features as described above in relation to the first anti-iridescence coating.

The low emissivity coating on surface ii comprises at least one fluorine doped tin oxide layer. The low emissivity coating on surface ii may additionally comprise one silver layer.

When the low emissivity coating on surface ii comprises at least one silver layer, preferably the geometric thickness of the at least one silver layer is between <NUM> and <NUM>.

Preferably the geometric thickness of the at least one fluorine doped tin oxide layer of the low emissivity coating on surface ii is between <NUM> and <NUM>. In some embodiments preferably the geometric thickness of the at least one fluorine doped tin oxide layer of the low emissivity coating on surface ii is between <NUM> and <NUM>, more preferably between <NUM> and <NUM>, even more preferably between <NUM> and <NUM>.

In some embodiments preferably the geometric thickness of the at least one fluorine doped tin oxide layer of the low emissivity coating on surface ii is between <NUM> and <NUM>.

In some embodiments preferably the geometric thickness of the at least one layer of fluorine doped tin oxide of the low emissivity coating on surface ii is between <NUM> and <NUM>, more preferably between <NUM> and <NUM>.

In some embodiments preferably the geometric thickness of the at least one fluorine doped tin oxide layer of the low emissivity coating on surface ii is between <NUM> and <NUM>, more preferably between <NUM> and <NUM>.

When the low emissivity coating on surface ii comprises at least one fluorine doped tin oxide layer, preferably there is an anti-iridescence layer of SiCOx between the low emissivity coating on surface ii and the first sheet of glazing material. Preferably the SiCOx layer has a geometric thickness between <NUM> and <NUM>.

In some embodiments there is a low emissivity coating on surface i.

When the insulated glazing unit is configured such that the first major surface of the first sheet of glazing material (i.e. surface i) faces the exterior of a building in which the insulated glazing unit is installed, the provision of a low emissivity coating on the first major surface of the first sheet of glazing material helps reduce the formation of condensation on the first major surface because the temperature of the first sheet of glazing material may be raised.

Preferably there is an anti-iridescence coating in between the low emissivity coating on surface i and the first sheet of glazing material.

The anti-iridescence coating in between the low emissivity coating on surface i and the first sheet of glazing material has the same preferable features as described above in relation to the first anti-iridescence coating.

In some embodiments there is a low emissivity coating on surface i comprising at least one layer of fluorine doped tin oxide.

Preferably the geometric thickness of the at least one fluorine doped tin oxide layer of the low emissivity coating on surface i is between <NUM> and <NUM>.

Preferably the geometric thickness of the at least one fluorine doped tin oxide layer of the low emissivity coating on surface i is between <NUM> and <NUM>, more preferably between <NUM> and <NUM>, even more preferably between <NUM> and <NUM>.

In some embodiments preferably the geometric thickness of the at least one fluorine doped tin oxide layer of the low emissivity coating on surface i is between <NUM> and <NUM>, more preferably between <NUM> and <NUM>.

Insulated glazing units according to the first aspect of the present invention have other preferable features.

In some embodiments there are no other layers on the low emissivity coating on surface iv.

In some embodiments, there is a layer of silica on the low emissivity coating on surface iv. Preferably the layer of silica on the low emissivity coating on surface iv has a geometric thickness of between <NUM> and <NUM>.

In some embodiments, there is a layer of titania on the low emissivity coating on surface iv. Preferably the layer of titania on the low emissivity coating on surface iv has a geometric thickness of between <NUM> and <NUM>.

In embodiments where there is a low emissivity coating on surface i, preferably there is a layer of silica on the low emissivity coating on surface i. Preferably the layer of silica on the low emissivity coating on surface i has a geometric thickness of between <NUM> and <NUM>.

In embodiments where there is a low emissivity coating on surface i, preferably there is a layer of titania on the low emissivity coating on surface i. Preferably the layer of titania on the low emissivity coating on surface i has a geometric thickness of between <NUM> and <NUM>.

In embodiments where there is a low emissivity coating on surface i, preferably there is no other layer on the low emissivity coating on surface i.

In some embodiments, there is an antireflection coating on the low emissivity coating on surface iv.

Preferably the antireflection coating on the low emissivity coating on surface iv comprises at least four layers.

Preferably the antireflection coating on the low emissivity coating on surface iv comprises in sequence, a first layer of tin oxide, a second layer of silica, a third layer of fluorine doped tin oxide and a fourth layer of silica, wherein the first layer of tin oxide is between the second layer of silica and the low emissivity coating on surface iv.

Preferably the first layer of tin oxide of the antireflection coating on the low emissivity coating on surface iv has a geometric thickness between <NUM> and <NUM>.

Preferably the second layer of silica of the antireflection coating on the low emissivity coating on surface iv has a geometric thickness between <NUM> and <NUM>.

Preferably the third layer of fluorine doped tin oxide of the antireflection coating on the low emissivity coating on surface iv has a geometric thickness between <NUM> and <NUM>.

Preferably the fourth layer of silica of the antireflection coating on the low emissivity coating on surface iv has a geometric thickness between <NUM> and <NUM>.

In embodiments where there is a low emissivity coating on surface i, preferably there is an antireflection coating on the low emissivity coating on surface i.

Preferably the antireflection coating on the low emissivity coating on surface i comprises at least four layers.

Preferably the antireflection coating on the low emissivity coating on surface i comprises in sequence, a first layer of tin oxide, a second layer of silica, a third layer of fluorine doped tin oxide and a fourth layer of silica, wherein the first layer of tin oxide is between the second layer of silica and the low emissivity coating on surface <NUM>.

Preferably the first layer of tin oxide of the antireflection coating on the low emissivity coating on surface i has a geometric thickness between <NUM> and <NUM>, more preferably between <NUM> and <NUM>.

Preferably the second layer of silica of the antireflection coating on the low emissivity coating on surface i has a geometric thickness between <NUM> and <NUM>, more preferably between <NUM> and <NUM>.

Preferably the third layer of fluorine doped tin oxide of the antireflection coating on the low emissivity coating on surface i has a geometric thickness between <NUM> and <NUM>, more preferably between <NUM> and <NUM>.

Preferably the fourth layer of silica of the antireflection coating on the low emissivity coating on surface i has a geometric thickness between <NUM> and <NUM>, more preferably between <NUM> and <NUM>.

In some embodiments the roughness of the low emissivity coating on surface iv is less than <NUM>, more preferably between <NUM> and <NUM>, even more preferably between <NUM> and <NUM>.

In embodiments where the is a low emissivity coating on surface i, preferably the roughness of the low emissivity coating on surface i is less than <NUM>, more preferably between <NUM> and <NUM>, even more preferably between <NUM> and <NUM>.

In the first aspect of the present invention as defined in claim <NUM> the vacuum insulated glazing unit comprises a third sheet of glazing material facing the first sheet of the glazing material and being separated therefrom by a second space, the third sheet of glazing material having a first major surface and a second major surface, wherein the insulated glazing unit is configured such that the second major surface of the third sheet of glazing material and the first major surface of the first sheet of glazing material (i.e. surface i) face the second space.

Preferably the second space is an air space.

Preferably the second space is filled with an inert gas such as argon or krypton.

Preferably the third sheet of glazing material is spaced from the first sheet of glazing material by more than <NUM>, preferably by <NUM> to <NUM>, more preferably by <NUM> to <NUM>.

Preferably the first major surface of the third sheet of glazing material has a low emissivity coating thereon.

The second major surface of the third sheet of glazing material has a low emissivity coating thereon. The low emissivity coating on the second major surface of the third sheet of glazing material comprises at least one layer of fluorine doped tin oxide.

Embodiments of the first aspect of the present invention having a third sheet of glazing material having a low emissivity coating on the first major surface of the third sheet of glazing material have other preferable features.

Preferably there is an anti-iridescence coating in between the low emissivity coating on the first major surface of the third sheet of glazing material and the third sheet of glazing material.

Preferably the anti-iridescence layer comprises a first layer and a second layer, wherein the first layer of the anti-iridescence layer has a higher refractive index than the second layer of the anti-iridescence layer and the second layer of the anti-iridescence layer is in between the first layer of the anti-iridescence layer and the low emissivity coating on the first major surface of the third sheet of glazing material.

Preferably the first layer of the anti-iridescence layer comprises tin oxide.

Preferably the second layer of the anti-iridescence layer comprises silica.

Preferably the first layer of the anti-iridescence layer has a geometric thickness of between <NUM> and <NUM>, preferably between <NUM> and <NUM>.

Preferably the second layer of the anti-iridescence layer has a geometric thickness of between <NUM> and <NUM>, preferably between <NUM> and <NUM>.

Preferably there is a haze reducing layer in between the third sheet of glazing material and the anti-iridescence coating on the first major surface of the third sheet of glazing material.

Preferably the haze reducing layer comprises silica.

Preferably the thickness of the haze reducing layer is between <NUM> and <NUM>, more preferably between <NUM> and <NUM>.

When the first major surface of the third sheet of glazing material has a low emissivity coating thereon, preferably the low emissivity coating on the first major surface of the third sheet of glazing material comprises at least one layer of fluorine doped tin oxide.

Preferably the geometric thickness of the at least one fluorine doped tin oxide layer of the low emissivity coating on the first major surface of the third sheet of glazing material is between <NUM> and <NUM>.

Preferably the geometric thickness of the at least one layer of fluorine doped tin oxide of the low emissivity coating on the first major surface of the third sheet of glazing material is between <NUM> and <NUM>, more preferably between <NUM> and <NUM>, even more preferably between <NUM> and <NUM>.

By having a thin layer of fluorine doped tin oxide the low emissivity coating on the first major surface of the third sheet of glazing material is less susceptible to surface damage because the coating is less rough. In addition costs are reduced because less coating is required to achieve the anti-condensation properties. Furthermore the G value of the insulated glazing unit is higher compared to the same insulated glazing unit with a thicker layer of fluorine doped tin oxide.

Preferably the geometric thickness of the at least one fluorine doped tin oxide layer of the low emissivity coating on the first major surface of the third sheet of glazing material is between <NUM> and <NUM>, more preferably between <NUM> and <NUM>.

Preferably there are no other layers on the low emissivity coating on the first major surface of the third sheet of glazing material.

Preferably there is a layer of silica on the low emissivity coating on the first major surface of the third sheet of glazing material. Preferably the layer of silica on the low emissivity coating on the first major surface of the third sheet of glazing material has a geometric thickness of between <NUM> and <NUM>.

Preferably there is a layer of titania on the low emissivity coating on the first major surface of the third sheet of glazing material. Preferably the layer of titania on the low emissivity coating on the first major surface of the third sheet of glazing material has a geometric thickness of between <NUM> and <NUM>.

Preferably there is an antireflection coating on the low emissivity coating on the first major surface of the third sheet of glazing material.

Preferably the antireflection coating on the low emissivity coating on the first major surface of the third sheet of glazing material comprises at least four layers.

Preferably the antireflection coating on the low emissivity coating on the first major surface of the third sheet of glazing material comprises in sequence, a first layer of tin oxide, a second layer of silica, a third layer of fluorine doped tin oxide and a fourth layer of silica, wherein the first layer of tin oxide is between the second layer of silica and the low emissivity coating on the first major surface if the third sheet of glazing material.

Preferably the first layer of tin oxide of the antireflection coating on the low emissivity coating on the first major surface of the third sheet of glazing material has a geometric thickness between <NUM> and <NUM>.

Preferably the second layer of silica of the antireflection coating on the low emissivity coating on the first major surface of the third sheet of glazing material has a geometric thickness between <NUM> and <NUM>.

Preferably the third layer of fluorine doped tin oxide of the antireflection coating on the low emissivity coating on the first major surface of the third sheet of glazing material has a geometric thickness between <NUM> and <NUM>.

Preferably the fourth layer of silica of the antireflection coating on the low emissivity coating on the first major surface of the third sheet of glazing material has a geometric thickness between <NUM> and <NUM>.

Embodiments of the first aspect of the present invention having a third sheet of glazing material having a low emissivity coating on the second major surface thereof have other preferable features.

Preferably there is an anti-iridescence coating in between the low emissivity coating on the second major surface of the third sheet of glazing material and the third sheet of glazing material.

Preferably the anti-iridescence layer comprises a first layer and a second layer, wherein the first layer of the anti-iridescence layer has a higher refractive index than the second layer of the anti-iridescence layer and the second layer of the anti-iridescence layer is in between the first layer of the anti-iridescence layer and the low emissivity coating on the second major surface of the third sheet of glazing material.

Preferably there is a haze reducing layer in between the third sheet of glazing material and the anti-iridescence coating on the second major surface of the third sheet of glazing material.

According to the present invention as defined in claim <NUM>, the low emissivity coating on the second major surface of the third sheet of glazing material comprises at least one layer of fluorine doped tin oxide.

Preferably the geometric thickness of the at least one fluorine doped tin oxide layer of the low emissivity coating on the second major surface of the third sheet of glazing material is between <NUM> and <NUM>.

Preferably the geometric thickness of the at least one layer of fluorine doped tin oxide of the low emissivity coating on the second major surface of the third sheet of glazing material is between <NUM> and <NUM>, more preferably between <NUM> and <NUM>, even more preferably between <NUM> and <NUM>.

By having a thin layer of fluorine doped tin oxide the low emissivity coating on the second major surface of the third sheet of glazing material is less susceptible to surface damage (for example when being transported or during assembly of the insulated glazing) because the coating is less rough. In addition costs are reduced because less coating is required to achieve the anti-condensation properties. Furthermore the G value of the insulated glazing unit is higher compared to the same insulated glazing unit with a thicker layer of fluorine doped tin oxide.

Preferably the geometric thickness of the at least one fluorine doped tin oxide layer of the low emissivity coating on the second major surface of the third sheet of glazing material is between <NUM> and <NUM>, more preferably between <NUM> and <NUM>.

In some embodiments preferably the geometric thickness of the at least one fluorine doped tin oxide layer of the low emissivity coating on the second major surface of the third sheet of glazing material is between <NUM> and <NUM>, more preferably between <NUM> and <NUM>.

Preferably there are no other layers on the low emissivity coating on the second major surface of the third sheet of glazing material.

Preferably there is a layer of silica on the low emissivity coating on the second major surface of the third sheet of glazing material. Preferably the layer of silica on the low emissivity coating on the second major surface of the third sheet of glazing material has a geometric thickness of between <NUM> and <NUM>.

Preferably there is a layer of titania on the low emissivity coating on the second major surface of the third sheet of glazing material. Preferably the layer of titania on the low emissivity coating on the second major surface of the third sheet of glazing material has a geometric thickness of between <NUM> and <NUM>.

From a second aspect not forming part of the present invention it is provided an insulated glazing unit comprising a first sheet of glazing material and a second sheet of glazing material, there being a first space between the first sheet of glazing material and the second sheet of glazing material, wherein the first sheet of glazing material has a first major surface and an opposing second major surface, and the second sheet of glazing material has a first major surface and an opposing second major surface, wherein the second major surface of the first sheet of glazing material and the first major surface of the second sheet of glazing material face the first space, wherein the first space is a low pressure space having a pressure less than atmospheric pressure, there being a plurality of spacers disposed in the first space, wherein the first major surface of the second sheet of glazing material and/or the second major surface of the first sheet of glazing material has a low emissivity coating thereon, the insulated glazing unit further comprising a third sheet of glazing material facing the first sheet of the glazing material and being separated therefrom by a second space, the third sheet of glazing material having a first major surface and a second major surface, wherein the second major surface of the third sheet of glazing material and the first major surface of the first sheet of glazing material face the second space, and wherein the second major surface of the third sheet of glazing material has a low emissivity coating thereon, characterised in that the first major surface of the third sheet of glazing material has a low emissivity coating thereon.

Suitably the first sheet of glazing material is spaced apart from the second sheet of glazing material by less than <NUM>, preferably by <NUM> to <NUM>, more preferably by <NUM> to <NUM>.

Preferably there is a low emissivity coating on the second major surface of the first sheet of glazing material comprising at least one silver layer and/or at least on fluorine doped tin oxide layer.

Preferably there is a low emissivity coating on the first major surface of the second sheet of glazing material comprising at least one silver layer and/or at least on fluorine doped tin oxide layer.

In some embodiments of the second aspect not forming part of the present invention the low emissivity coating on the first major surface of the third sheet of glazing material comprises at least one layer of fluorine doped tin oxide.

Preferably the geometric thickness of the at least one layer of fluorine doped tin oxide of the low emissivity coating on the first major surface of the third sheet of glazing material is between <NUM> and <NUM>.

In some embodiments of the geometric thickness of the at least one layer of fluorine doped tin oxide of the low emissivity coating on the first major surface of the third sheet of glazing material is between <NUM> and <NUM>.

In some embodiments the geometric thickness of the at least one layer of fluorine doped tin oxide of the low emissivity coating on the first major surface of the third sheet of glazing material is between <NUM> and <NUM>, more preferably between <NUM> and <NUM>.

In some embodiments the geometric thickness of the at least one layer of fluorine doped tin oxide of the low emissivity coating on the first major surface of the third sheet of glazing material is between <NUM> and <NUM>, preferably between <NUM> and <NUM>.

In some embodiments of the second aspect not forming part of the present invention there are no other layers on the low emissivity coating on the first major surface of the third sheet of glazing material.

In some embodiments of the second aspect not forming part of the present invention, there is a layer of silica on the low emissivity coating on the first major surface of the third sheet of glazing material. Preferably the layer of silica on the low emissivity coating on the first major surface of the third sheet of glazing material has a geometric thickness of between <NUM> and <NUM>.

In some embodiments of the second aspect not forming part of the present invention, there is a layer of titania on the low emissivity coating on the first major surface of the third sheet of glazing material. Preferably the layer of titania on the low emissivity coating on the first major surface of the third sheet of glazing material has a geometric thickness of between <NUM> and <NUM>.

In some embodiments of the second aspect not forming part of the present invention, there is an antireflection coating on the low emissivity coating on the first major surface of the third sheet of glazing material.

Preferably the first layer of tin oxide has a geometric thickness between <NUM> and <NUM>.

Preferably the second layer of silica has a geometric thickness between <NUM> and <NUM>.

Preferably the third layer of fluorine doped tin oxide has a geometric thickness between <NUM> and <NUM>.

Preferably the fourth layer of silica has a geometric thickness between <NUM> and <NUM>.

In some embodiments of the second aspect not forming part of the present invention, preferably there is a haze reducing layer in between the third sheet of glazing material and the anti-iridescence coating on the second major surface of the third sheet of glazing material.

In some embodiments of the second aspect not forming part of the present invention the low emissivity coating on the second major surface of the third sheet of glazing material comprises at least one layer of fluorine doped tin oxide.

Preferably the geometric thickness of the at least one layer of fluorine doped tin oxide of the low emissivity coating on the second major surface of the third sheet of glazing material is between <NUM> and <NUM>.

Preferably the geometric thickness of the at least one layer of fluorine doped tin oxide of the low emissivity coating on the second major surface of the third sheet of glazing material is between <NUM> and <NUM>, more preferably between <NUM> and <NUM>.

In some embodiments of the second aspect not forming part of the present invention there are no other layers on the low emissivity coating on the second major surface of the third sheet of glazing material.

In some embodiments, there is a layer of silica on the low emissivity coating on the second major surface of the third sheet of glazing material. Preferably the layer of silica on the low emissivity coating on the second major surface of the third sheet of glazing material has a geometric thickness of between <NUM> and <NUM>.

In some embodiments, there is a layer of titania on the low emissivity coating on the second major surface of the third sheet of glazing material. Preferably the layer of titania on the low emissivity coating on the second major surface of the third sheet of glazing material has a geometric thickness of between <NUM> and <NUM>.

Embodiments of the first aspect of the present invention and the second aspect not forming part of the present invention have other preferable features. These other preferable features may be may be used in any combination and with the first and/or second aspects of the present invention.

In the first aspect of the present invention and the second aspect not forming part of the present invention, suitable glazing material is glass, in particular soda-lime-silica glass or borosilicate glass. A typical soda-lime-silica glass composition is (by weight), SiO<NUM> <NUM> - <NUM> %; Al<NUM>O<NUM> <NUM> - <NUM> %; Na<NUM>O <NUM> - <NUM> %; K<NUM>O <NUM> - <NUM> %; MgO <NUM> - <NUM> %; CaO <NUM> - <NUM> %; SO3 <NUM> - <NUM> %; Fe<NUM>O<NUM> <NUM> - <NUM> %.

Preferably the sheets of glazing material used in the first aspect of the present invention and the second aspect not forming part of the present invention have a thickness between <NUM> and <NUM>, more preferably between <NUM> and <NUM>, even more preferably between <NUM> and <NUM>.

For a particular insulated glazing unit, the sheets of glazing material may have the same or different thickness.

For a particular insulated glazing unit, the sheets of glazing material may have the same or different glass composition.

An insulated glazing according to the first aspect of the present invention and the second aspect not forming part of the present invention may comprise more than three sheets of glazing material.

An insulated glazing according to the first aspect of the present invention and the second aspect not forming part of the present invention may comprise two or more low pressure spaces.

An insulated glazing according to the first aspect of the present invention and the second aspect not forming part of the present invention may comprise two or vacuum insulated glazing panels.

A glazing unit according to the first aspect of the present invention and the second aspect not forming part of the present invention may be used as a window in a building with the second major surface of the second sheet of glazing material facing the interior of the building.

Any of the coatings described herein may be deposited using known deposition techniques, such as atmospheric pressure chemical vapour deposition (APCVD) or sputtering. As is known in the art, oxide layers are typically deposited using APCVD. Silver layers may be deposited using known sputtering techniques.

In the context of the present invention U-values were determined in accordance with EN12898 and EN673.

In the context of the present invention roughness values were determined using an Atomic Force Microscope and defined in terms of parameters in accordance with ISO/DIS <NUM>-<NUM> (<NUM>).

Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings (not to scale), in which:.

<FIG> shows a schematic representation of part of an insulated glazing unit according to the first aspect of the present invention. In this particular example, the insulated glazing unit is a vacuum insulated glazing unit <NUM> (VIG). The manufacture of such a VIG is described, for example, in <CIT>.

The VIG <NUM> has a first sheet of glass <NUM> and a second sheet of glass <NUM>. The first sheet of glass <NUM> has a first major surface <NUM> and an opposing second major surface (not labelled in the figure). The second sheet of coated glass has a first major surface and an opposing second major surface (both not labelled in the figure).

Each sheet of glass <NUM>, <NUM> is a soda-lime-silica composition having been made using the float process. Each glass sheet <NUM>, <NUM> is <NUM> thick.

The first sheet of glass <NUM> is spaced apart from the second sheet of glass <NUM> by a plurality of stainless steel spacers <NUM> (only five of which are shown in <FIG>). The spacers maintain a space <NUM> between the two glass sheets <NUM>, <NUM>. The space <NUM> is a low pressure space, having been evacuated during construction of the VIG <NUM>. A peripheral seal <NUM> of solder glass or the like ensures the space <NUM> remains at low pressure i.e. the peripheral seal <NUM> is a hermetic seal.

On the second major surface of the first sheet of glass <NUM> is a low emissivity coating <NUM>. On the second major surface of the second sheet of glass <NUM> is a low emissivity coating <NUM>.

The VIG <NUM> is configured such that in use the first major surface <NUM> of the first sheet of coated glass <NUM> faces the exterior of the building in which the VIG <NUM> is installed, and the second major surface of the second sheet of coated glass <NUM> (and consequently the low emissivity coating <NUM>) faces the interior of the building in which the VIG is installed.

Using conventional naming nomenclature for the surfaces of the VIG, the first major surface <NUM> is surface <NUM> of the VIG, the second opposing major surface of the first sheet of glass <NUM> is surface <NUM> of the VIG, the first major surface of the second sheet of coated glass <NUM> is surface <NUM> of the VIG and the outer surface of the low emissivity coating <NUM> on the second major surface of the second glass sheet <NUM> is surface <NUM> of the VIG. The outer surface of the low emissivity coating <NUM> is labelled with the numeral <NUM> on <FIG>.

Using the notation adopted in the present application, first major surface <NUM> may correspond to surface i, in which case the second opposing major surface of glass sheet <NUM> corresponds to surface ii, the first major surface of the second sheet of coated glass <NUM> corresponds to surface iii (i.e. the surface of coated glass sheet <NUM> facing space <NUM>) and the opposing major surface of glass sheet <NUM> corresponds to surface iv.

The emissivity coating <NUM> comprises at least one layer of fluorine doped tin oxide that has been deposited on the glass surface using atmospheric chemical deposition. The low emissivity coating <NUM> may be the same as the low emissivity coating <NUM>. The low emissivity coating <NUM> may consist of an undercoat layer of SiCOx having a geometric thickness of <NUM> and a low emissivity layer, on the undercoat layer, of fluorine doped tin oxide (SnO<NUM>:F ) having a geometric thickness of <NUM> i.e. the glass sheet <NUM> with low emissivity coating <NUM> on the second major surface having a structure glass/SiCOx(<NUM>)/SnO<NUM>:F(<NUM>).

The low emissivity coating <NUM> is described in more detail with reference to <FIG>.

In another alternative to the embodiment shown in <FIG>, the orientation of the glazing is changed such that the first major surface <NUM> of the first sheet of coated glass <NUM> faces the interior of the building in which the VIG <NUM> is installed, and the second major surface of the second sheet of coated glass <NUM> (and consequently the low emissivity coating <NUM>) faces the exterior of the building in which the VIG is installed i.e. the low emissivity coating <NUM> faces the sun. When the VIG is configured this way, the low emissivity coating on the exterior facing major surface of the VIG may help reduce the formation of condensation thereon because the temperature of the sheet of glass <NUM> may be raised. In this alternative, the glass sheet <NUM> may be an uncoated sheet of glass.

In any of the alternative described above in relation to <FIG>, there may be a low emissivity coating on the first major surface of the glass sheet <NUM> i.e. the surface of the glass sheet <NUM> facing the space <NUM>.

<FIG> shows a schematic representation of part of another insulated glazing unit according to the first aspect of the present invention The insulated glazing unit is also a vacuum insulated glazing unit <NUM> (VIG).

The VIG <NUM> has a first sheet of glass <NUM> and a second sheet of glass <NUM>. The first sheet of glass <NUM> has a first major surface and an opposing second major surface (both not labelled in the figure). The second sheet of glass has a first major surface and an opposing second major surface (both not labelled in the figure).

Each sheet of glass <NUM>, <NUM> is a soda-lime-silica composition having been made using the float process. Each glass sheet <NUM>, <NUM> is <NUM> thick but may be <NUM> thick.

The first sheet of glass <NUM> is spaced apart from the second sheet of glass <NUM> by a plurality of stainless steel spacers <NUM> (only five of which are shown in <FIG>, the spacers <NUM> being the same at the spacers <NUM> in <FIG>). The spacers <NUM> maintain a space <NUM> between the two glass sheets <NUM>, <NUM>. The space <NUM> is a low pressure space, having been evacuated during construction of the VIG <NUM>. A peripheral seal <NUM> of solder glass or the like ensures the space <NUM> remains at low pressure i.e. the peripheral seal <NUM> is a hermetic seal.

On the first major surface of the first sheet of glass <NUM> is a low emissivity coating <NUM>. On the second major surface of the first sheet of glass <NUM> is a low emissivity coating <NUM>. On the second major surface of the second sheet of glass <NUM> is a low emissivity coating <NUM>.

The VIG <NUM> is configured such that in use the first major surface of the first sheet of coated glass <NUM> (and consequently the low emissivity coating <NUM>) faces the exterior of the building in which the VIG <NUM> is installed, and the second major surface of the second sheet of coated glass <NUM> (and consequently the low emissivity coating <NUM>) faces the interior of the building in which the VIG <NUM> is installed.

The low emissivity coating <NUM> comprises at least one layer of fluorine doped tin oxide that has been deposited on the glass surface using atmospheric chemical deposition, typically when the glass is produced by the float process. The low emissivity coating <NUM> may be the same as the low emissivity coating <NUM>. The low emissivity coating <NUM> may consist of an undercoat layer of SiCOx having a geometric thickness of <NUM> and a low emissivity layer, on the undercoat layer, of fluorine doped tin oxide having a geometric thickness of <NUM> i.e. the glass sheet <NUM> with low emissivity coating <NUM> on the second major surface thereof having a structure glass/SiCOx(<NUM>)/SnO<NUM>:F(<NUM>).

The low emissivity coatings <NUM> and <NUM> are described in more detail with reference to <FIG>.

<FIG> shows part of an insulated glazing unit <NUM>. The insulated glazing unit <NUM> comprises a sheet of <NUM> soda-lime-silica glass <NUM> having a low emissivity coating <NUM> on a major surface thereof and a VIG <NUM> as described with reference to <FIG>. Such an insulated glazing unit is typically referred to as a triple glazed insulated glazing unit because there are three sheets of glazing material and two spaces between the sheets.

The VIG <NUM> is spaced about <NUM> apart from the coated glass sheet by a metal spacer <NUM> and a perimeter seal <NUM> of polyurethane or the like, thereby creating a space <NUM>. The space <NUM> is an air space and may be filled with an inert gas such as argon or krypton.

The low emissivity coating <NUM> is on the major surface of the glass sheet <NUM> that faces the space <NUM>.

The insulated glazing unit <NUM> is configured such that in use, the uncoated surface of the glass sheet <NUM> faces the exterior of the building. This is referred to a surface <NUM>. The coated surface of the glass sheet <NUM> faces the air space <NUM> and is referred to as surface <NUM>. The surface of the glass sheet <NUM> of VIG <NUM> acing the air space <NUM> is referred to as surface <NUM>. The coated surface of glass sheet <NUM> of the VIG <NUM> facing the low pressure space <NUM> is referred to as surface <NUM>. The uncoated surface of the glass sheet <NUM> of the VIG <NUM> facing the low pressure space <NUM> is referred to as surface <NUM> and the coated surface of the glass sheet <NUM> of the VIG <NUM> is referred to as surface <NUM> and faces the interior of the building.

This is conventional nomenclature for naming the surfaces of a triple glazed insulated glazing unit.

The low emissivity coatings <NUM>, <NUM> and <NUM> on surface <NUM>, <NUM> and <NUM> respectively reduce the U-value of the insulated glazing unit <NUM>.

In a variant to the example shown in <FIG>, the sheet of glass <NUM> may be coated on both major surfaces with a low emissivity coating i.e. surface <NUM> has a low emissivity coating thereon.

In this variant, the low emissivity coating on surface <NUM> may be the same as the low emissivity coating <NUM>. It is preferred that the low emissivity coating on the major surface of glass sheet <NUM> facing the airspace comprises at least one fluorine doped tin oxide layer, and is preferably the same as low emissivity coating <NUM> described with reference to <FIG>. Preferably the low emissivity coating on surface <NUM> is the same as coating <NUM> described with reference to <FIG> and <FIG>. The provision of a low emissivity coating on surface <NUM> helps raise the temperature of glass sheet <NUM> thereby helping reduce the formation of condensation thereon.

In another variant to the insulated glazing shown in <FIG>, the positions of the sheet of glass <NUM> and the VIG <NUM> may be reversed.

<FIG> shows a schematic representation of another insulated glazing unit according to the first aspect of the present invention. In this particular example, the insulated glazing unit is a vacuum insulated glazing unit <NUM> (VIG) and is similar to the VIG <NUM> and VIG <NUM> described above.

The VIG <NUM> has a first sheet of glass <NUM> and a second sheet of glass <NUM>. The first sheet of glass <NUM> has a first major surface and an opposing second major surface (both not labelled in the figure). The second sheet of coated glass has a first major surface and an opposing second major surface (both not labelled in the figure).

The first sheet of glass <NUM> is spaced apart from the second sheet of glass <NUM> by a plurality of stainless steel spacers <NUM> (only five of which are shown in <FIG>). The spacers maintain a space <NUM> between the two glass sheets <NUM>, <NUM> of about <NUM>. The space <NUM> is a low pressure space, having been evacuated during construction of the VIG <NUM>. A peripheral seal <NUM> of solder glass or the like ensures the space <NUM> remains at low pressure i.e. the peripheral seal <NUM> is a hermetic seal.

The second major surface of glass sheet <NUM> faces the space <NUM>. The first major surface of the glass sheet <NUM> faces the space <NUM>.

Both major surfaces of glass sheet <NUM> are uncoated. On the first major surface of glass sheet <NUM> is a low emissivity coating <NUM>. On the second major surface of the glass sheet <NUM> is a low emissivity coating <NUM>.

The VIG <NUM> is configured such that in use the first major surface of the first sheet of glass <NUM> faces the exterior of the building in which the VIG <NUM> is installed, and the second major surface of the second sheet of glass <NUM> (and consequently the low emissivity coating <NUM>) faces the interior of the building in which the VIG <NUM> is installed.

The low emissivity coating <NUM> comprises at least one layer of fluorine doped tin oxide that has been deposited on the glass surface using atmospheric chemical deposition. The low emissivity coating <NUM> may be the same as the low emissivity coating <NUM>. The low emissivity coating <NUM> may consist of an undercoat layer of SiCOx having a geometric thickness of <NUM> and a low emissivity layer, on the undercoat layer, of fluorine doped tin oxide having a geometric thickness of <NUM> i.e. the glass sheet <NUM> with low emissivity coating <NUM> on the first major surface thereof having a structure glass/SiCOx(<NUM>)/SnO<NUM>:F(<NUM>).

In an alternative to the embodiment shown in <FIG>, the orientation of the VIG <NUM> may be reversed such that in use i.e. when installed in a building, the low emissivity coating <NUM> faces the exterior of the building and the uncoated major surface of the first glass sheet <NUM> not facing the space <NUM> faces the interior of the building in which the VIG is installed.

In another embodiment, and with reference to <FIG>, <FIG> and <FIG>, the VIG <NUM> of <FIG> may be replaced with the VIG <NUM> of <FIG> or the VIG <NUM> of <FIG>.

<FIG> shows a schematic representation of part of an insulated glazing unit <NUM> according to the second aspect not forming part of the present invention.

The insulated glazing unit <NUM> comprises a sheet of <NUM> thick soda-lime-silica glass <NUM> spaced <NUM> apart from a VIG <NUM> by a metal spacer <NUM> and a perimeter seal <NUM>. There is an air space <NUM> between the glass sheet <NUM> and the VIG <NUM>.

The glass sheet <NUM> has first and second opposing major surfaces. The second major surface of the glass sheet <NUM> faces the air space <NUM>. There is a low emissivity coating <NUM> on the first major surface of the glass sheet <NUM> and a low emissivity coating <NUM> on the second major surface of the glass sheet <NUM>.

The low emissivity coating <NUM> comprises a single layer of sputtered silver, but may comprise a double layer or triple layer of sputtered silver. Each silver layer may have a thickness between <NUM> and <NUM>. Examples of such coatings are described in <CIT> and <CIT>. Alternatively the low emissivity coating <NUM> comprises at least one layer of fluorine doped tin oxide that has been deposited on the glass surface using atmospheric chemical deposition. The low emissivity coating <NUM> may be the same as the low emissivity coating <NUM>. The low emissivity coating <NUM> may consist of an undercoat layer of SiCOx having a geometric thickness of <NUM> and a low emissivity layer, on the undercoat layer, of fluorine doped tin oxide having a geometric thickness of <NUM> i.e. the SiCOx layer being in contact with the glass surface, and the SnO<NUM>:F layer being on the SiCOx layer.

The VIG <NUM> comprises a first sheet of glass <NUM> and a second sheet of glass <NUM> spaced apart from each other by about <NUM> by a plurality of stainless steel spacers <NUM>. The spacers maintain a space <NUM> between the two glass sheets <NUM>, <NUM>. The space <NUM> is a low pressure space, having been evacuated during construction of the VIG <NUM>. A peripheral seal <NUM> of solder glass or the like ensures the space <NUM> remains at low pressure i.e. the peripheral seal <NUM> is a hermetic seal.

Glass sheet <NUM> has a first major surface facing the air space <NUM> and a second major surface facing the low pressure space <NUM>. On the second major surface of glass sheet <NUM> is a low emissivity coating <NUM>. The low emissivity coating may be the same as the low emissivity coating <NUM>.

Glass sheet <NUM> has a first major surface facing the low pressure space <NUM> and a second opposing major surface. Both major surfaces of the glass sheet <NUM> are uncoated.

In use, the second major surface of the glass sheet <NUM> faces the interior of the building in which the insulated glazing unit <NUM> is installed.

In <FIG> the additional low emissivity coating <NUM> on surface <NUM> helps raise the temperature of glass sheet <NUM> to reduce the formation of condensation thereon.

<FIG> shows a cross-sectional representation of a coated glass sheet useful as a pane in an insulated glazing according to either the first aspect of the present invention or the second aspect not forming part of the present invention.

With reference to <FIG>, a coated pane <NUM> comprising a sheet of <NUM> thick clear float glass <NUM> was coated with a coating structure <NUM> using atmospheric chemical vapour deposition in the float bath region of a float furnace, for example as described in <CIT>.

The composition of glass sheet <NUM> was a conventional clear float glass composition (soda-lime-silica glass) having an Fe<NUM>O<NUM> content of <NUM>% by weight, although in another embodiment the Fe<NUM>O<NUM> content was between <NUM>% by weight and <NUM>% by weight, typically about <NUM>% by weight. In another example a higher Fe<NUM>O<NUM> content float glass composition was used, having an Fe<NUM>O<NUM> content by weight of about <NUM>%.

The hot float glass ribbon was first coated with a layer <NUM> of SiO<NUM> having a geometric thickness of <NUM>. This layer <NUM> is a haze reducing layer such that a coated glass sheet has less haze than a coated glass sheet without this layer. Other such coatings may be used, for example Si<NUM>N<NUM>.

Next a layer <NUM> of SnO<NUM> having a geometric thickness of <NUM> was deposited on the SiO<NUM> layer. This layer forms part of the anti-iridescence coating structure. Next a layer <NUM> of SiO<NUM> having a geometric thickness of <NUM> was deposited on the SnO<NUM> layer <NUM>. The combination of the <NUM> layer of SnO<NUM> and <NUM> layer of SiO<NUM> is an anti-iridescence coating. The layer <NUM> is a first layer of the anti-iridescence coating and the layer <NUM> is a second layer of the anti-iridescence coating.

Finally a layer <NUM> of fluorine doped tin oxide (SnO<NUM>:F) was deposited on the <NUM> thick SiO<NUM> layer. The SnO<NUM>:F layer <NUM> had a geometric thickness of <NUM>.

The layers <NUM>, <NUM>, <NUM> and <NUM> form the coating structure <NUM>. The coating structure <NUM> is a low emissivity coating.

The coating structure <NUM> corresponds to the low emissivity coating <NUM> in <FIG>, the low emissivity coating <NUM> and/or the low emissivity coating <NUM> in <FIG>, the low emissivity coating <NUM> in <FIG> and the low emissivity coating <NUM> in <FIG>.

If the SnO<NUM>:F layer <NUM> is too thick, it has more of a tendency to be damaged, for example when being handled or cleaned. Consequently it is not necessary to use any additional coating layers on the low emissivity coating <NUM>. Other coating layers may be deposited on the low emissivity coating <NUM> although this increases costs and manufacturing complexity.

As the low emissivity SnO<NUM>:F layer <NUM> becomes thinner, the durability of the coating increases but the emissivity increases, which is not desirable. For the coated substrate shown in <FIG>, the emissivity of the coating is <NUM>.

The roughness of the SnO<NUM>:F layer was determined to be about <NUM>. The roughness may be measured using an Atomic Force Microscope and defined in terms of parameters in accordance with ISO/DIS <NUM>-<NUM> (<NUM>).

The same coating as described above was deposited onto a <NUM> thick sheet of low iron float glass (having <NUM>% by weight Fe<NUM>O<NUM>). The visible light transmission of this coated sheet was <NUM>%, calculated according to EN410(<NUM>)/<NUM> (CEN).

In an alternative to the coating structure <NUM> shown in <FIG>, there may be not be a layer <NUM> of SiO<NUM>, instead the layer <NUM> is in contact with the surface of the glass sheet <NUM>. In this embodiment the geometric thickness of the layer <NUM> of SnO<NUM> may be between <NUM> and <NUM> and the geometric thickness of the layer <NUM> of SiO<NUM> on the layer <NUM> may have a geometric thickness of between <NUM> and <NUM>. The layer <NUM> of fluorine doped tin oxide (SnO<NUM>:F) on the SiO<NUM> layer <NUM> may have a geometric thickness between <NUM> and <NUM>, typically about <NUM>. Alternatively the layer <NUM> of fluorine doped tin oxide (SnO<NUM>:F) on the SiO<NUM> layer <NUM> may have a geometric thickness greater than <NUM>, typically up to about <NUM> i.e. within the range <NUM>-<NUM>.

The coating structure <NUM> as described may be used as a low emissivity coating on one or more major surface of glazing material in accordance with the first aspect of the invention and the second aspect not forming part of the invention.

Claim 1:
A vacuum insulated glazing unit (<NUM>, <NUM>, <NUM>, <NUM>) comprising a first sheet of glazing material (<NUM>, <NUM>, <NUM>) and a second sheet of glazing material (<NUM>, <NUM>, <NUM>), there being a first space (<NUM>, <NUM>, <NUM>) between the first sheet of glazing material and the second sheet of glazing material, the first sheet of glazing material being spaced apart from the second sheet of glazing material by less than <NUM>; wherein the first sheet of glazing material has a first major surface (<NUM>) and an opposing second major surface, and the second sheet of glazing material has a first major surface and an opposing second major surface, wherein the second major surface of the first sheet of glazing material and the first major surface of the second sheet of glazing material face the first space, wherein the first space is a low pressure space having a pressure less than atmospheric pressure, there being a plurality of spacers (<NUM>) disposed in the first space,
characterised in that
the second major surface of the second sheet of glazing material has a low emissivity coating (<NUM>, <NUM>, <NUM>) thereon, the low emissivity coating comprising at least one layer of fluorine doped tin oxide (<NUM>) and there is a first anti-iridescence coating in between the low emissivity coating and the second sheet of glazing material,
wherein there is a low emissivity coating (<NUM>, <NUM>) on the second major surface of the first sheet of glazing material, the low emissivity coating (<NUM>, <NUM>) on the second major surface of the first sheet of glazing material comprising at least one layer of fluorine doped tin oxide.