Solar control glazing may be used to control one or more of the following properties of a glazing panel: a) direct energy transmittance (DET) i. e. the proportion of the solar energy transmitted directly through a substrate as a percentage of the incident solar energy; b) solar factor (SF) i. e. the solar energy that is transmitted through a substrate (including the energy absorbed by the substrate and emitted by the substrate towards the interior) as a percentage of the incident solar energy; c) luminous transmittance (LT) i. e. the luminous flux transmitted through a substrate as a percentage of the incident luminous flux; d) luminous reflectance (RL) i. e. the luminous flux reflected from a substrate as a percentage of the incident luminous flux; e) selectivity i. e. the ratio of the luminous transmittance to the solar factor (LT/SF). f) purity (p) of the colour i. e. the excitation purity specified according to a linear scale on which a defined white light source has a purity of zero and the pure colour has a purity of 100%. The purity of the coated substrate is measured from the side opposite the coated side. g) dominant wavelength (D) i. e. the peak wavelength in the range transmitted or reflected by the substrate.

These and other properties of glazing panels as referred to herein are based on the standard definitions of the International Commission on Illumination-Commission Internationale de lEclairage ("CIE"). Unless otherwise stated, values herein are given with respect to standard CIE Illuminant C (which represents average daylight having a colour temperature of 6700°K) for a clear, approximately 6 mm thick glass substrate arranged as a single glazing sheet. The colour co-ordinates referred to herein are measured on the Hunter scale.

Solar control glazing usually consists of a glass substrate which carries a solar filter. One particular known type of solar filter consists of the following layers (in order): 1) a metal oxide layer 200A to 400A thick 2) an infra-red reflecting metal layer 50A to 200A thick 3) a barrier layer 4) a metal oxide layer 400A to 800A thick 5) an infra-red reflecting metal layer 50A to 200A thick 6) a barrier layer 7) a metal oxide layer 200A to 400A thick The thicknesses of the various layer can be varied over a wide range and the figures given above are merely to indicate a general order of magnitude.

In this structure: the infra-red reflecting metal layers are typically silver or a silver alloy; their principal role in the filter is to reflect solar energy in the infra- red portion of the spectrum whilst transmitting a significant portion of the incident visible light.

* the metal oxides layers may be, for example, tin oxide, zinc oxide, titanium oxide, bismuth oxide, tantalum oxide, indium oxide or mixtures thereof; their role in the filter is to reduce the amount of visible light reflected by the silver layers, to provide a physical protection for the silver layers and to prevent oxidation of the silver layers when exposed to the atmosphere. These layers are substantially non-absorbent. the principal role of each barrier is to prevent undesired oxidation of its immediately underlying silver layer, particularly when the overlying metal oxide layer is deposited by magnetron sputtering of a metal target in an oxidising atmosphere. They may be omitted entirely if the manufacturing process is such that the silver layers are not degraded during manufacture of the filter. The barriers are kept as thin as possible so as to have no effect, or only a negligible effect, upon the solar properties of the glazing. The barriers are typically metal, partially oxidised metal, or metal oxide layers. Where, for example, the barrier is sputter deposited metal and the overlying dielectric is a sputter deposited metal oxide, the metal barrier is oxidised throughout the majority of its thickness when the overlying metal oxide is deposited, thus protecting the silver layer from oxidation and forming an additional, thin dielectric layer.

Titanium, niobium, nickel chrome and zinc are commonly used as

barriers in this way. A thickness of perhaps lA or 2A may remain as unoxidised metal adjacent the underlying silver layer. In any case, the thickness and amount of oxidation of the barrier layer is controlled such that the residual absorption of the barrier layer in the visible portion of the spectrum is less than 2% and preferably less than 1%. The barrier layers may merge into their overlying dielectric layers. For example, if the barrier is titanium deposited in metallic form and the overlying antireflective layer is titanium dioxide deposited by sputtering a titanium target in an oxidising atmosphere then the barrier will be substantially oxidised during deposition of the antireflective layer. In this case there may not be a clearly discernible boundary between the barrier layer and the antireflective layer. The same is true if, for example, the barrier layer is a sputtered layer of titanium dioxide or sub-stoichiometric titanium dioxide with a titanium dioxide antireflective layer or if the barrier is metallic zinc with an overlying zinc oxide anti-reflective layer.

For some applications, particularly architectural applications in which relatively large glazing surfaces are used, it is desirable to provide glazing units, usually as double glazing units, which transmit a significant portion of the incident visible light (to provide good interior visibility with natural light) whilst preventing passage of a significant portion of the incident solar energy (to avoid overheating the interior). For example, it is desirable in certain applications to have a glazing sheet with a luminous transmittance in the order of 66% and a direct energy transmittance in the order of 38% or less. Such a glazing sheet can be assembled as a double glazing unit to provide a luminous transmittance in the order of 60% and a solar factor in the order of 30%. Such high selectivity glazing units, which have a selectivity greater than about 1.7 and preferably greater than about 1.8, can be considered to be a particular species of solar control panel.

As well as affecting the direct energy transmittance and the luminous transmittance of a glazing sheet, a solar filter must confer an aesthetically acceptable colour to the glazing and be both technically and economically feasible to produce on an industrial scale. Many solar glazing panels are produced by magnetron sputter deposition of the solar filter on a glass substrate. Development of a new coating installation requires considerable investment. Consequently, the ability to manufacture a new filter using existing plant with minimum modification and delay and the flexibility of being able to manufacture a range of different products using a single manufacturing installation is a significant advantage.

The filter structure described above may be used to produce a glazing pane having a luminous transmittance in the order of 70% with a direct energy transmittance of greater than 40%. The exact properties may be varied by changing the thicknesses and/or nature of the layers.

Increasing the thickness of the silver layers will, in general, increase the amount of incident radiation that is reflected by the filter and thus reduce both TL and DET. However, increasing the thickness of one or each of the silver layer to such an extent as to obtain a direct energy transmittance below about 40% results in the appearance of the glazing becoming undesirably metallic rather than substantially neutral. Indeed, it is for this reason that the structure described above uses two spaced silver layers rather than a single, thicker silver layer.

An alternative modification might be to add a third infra-red reflecting silver layer with overlying barrier and metal oxide layers to the double silver layer structure described above. This would require significant modification to existing coaters and/or add considerably to the process time and consequently to the cost of producing such a filter.

According to a first aspect, the present invention provides a solar control panel as defined in Claim 1.

Additional, optional features are defined in the dependent claims.

The substrate is preferably glass and the solar control coating may be deposited directly onto the substrate, preferably by sputtering which may be magnetically enhanced. Unless otherwise specified, one or more additional layers may be provided above and/or below and/or between the layers which are defined.

The nature and thicknesses of the layers making up the solar control coating may be chosen to produce one or more of: a) a combination of relatively low transmission of solar energy and relatively low reflection of visible light b) a substantially neutral colour in reflection and in transmission with colour purity values in the order of 1% c) good angular stability.

Angular stability, i. e. substantially constant reflected colour irrespective of the angle at which a glazing panel is viewed is particularly desirable for architectural application in which large glazing surfaces are used and may be improved by use of the additional absorbing layer of the present

invention, especially when this is positioned directly underneath an infra-red reflecting layer.

A glazing panel in accordance with the invention may have a selectivity greater than about 1.7, preferably greater than about 1.8.

The invention may be used to provide a glazing panel which is substantially neutral in reflection, in which case the colour purity may be less than 10%, or a glazing panel which is blue or bluish in reflection. In each case, this provides a glazing panel which is aesthetically acceptable, particularly for architectural applications. The dominant wavelength in reflection is preferably less than 510nm and is preferably greater than 465nm.

Depositing of the infra-red reflecting layer may be facilitated by depositing this on the additional absorbing layer, particularly when this is a metal or metal alloy layer.

The additional light absorbing layer may be titanium in metallic form. Titanium targets are commonly used in existing coating installations, particularly for depositing titanium barrier layers. Use of titanium as the additional light absorbing layer may provide the desired characteristics for this layer whilst, in addition, simplifying the production process. Alternatively, the additional light absorbing layer may comprise at least one material selected from the group consisting of (a) tin in metallic form, (b) chrome in metallic form, (c) an alloy of nickel and chrome in metallic form, (d) stainless steel in metallic form, (e) a nitride, (f) a nitride of stainless steel, (g) titanium nitride, (h) zirconium nitride, (i) a carbide.

The antireflective layers may comprise, for example, zinc oxide, tin oxide, titanium oxide or a mixed oxide of stainless steel. A particular advantage of a mixed oxide of stainless steel which may be used to increase the selectivity of the coating is its slight absorption in the blue portion of the visible spectrum. The human eye is not particularly sensitive to this portion of the spectrum so that absorbing radiation in this portion of the spectrum reduces the direct energy transmittance more than it reduces the luminous transmittance.

A suitable amount of absorption may be achieved by arranging for the additional absorbing layer to have a geometrical thickness of at least 5 nm. The additional absorbing layer may have a geometrical thickness of at least 10 nm.

One or more of the antireflective layers may comprise discrete layers of one or more oxides, for example a first layer of tin oxide and a second overlying layer of zinc oxide, a first layer of zinc oxide and a second

overlying layer of tin oxide, a first layer of zinc oxide a second overlying layer of tin oxide and a third overlying layer of zinc oxide. Such structures may increase the abrasion resistance of the coating.

One or more additional layers may be incorporated into the solar control coating. For example, an abrasive resistant overcoat of silicon oxide or titanium oxide may be provided. Alternatively or additionally, a primer layer, for example silicon oxide, may be provided directly adjacent to the substrate surface and/or beneath one or more of the infra-red reflecting layers.

The aspect of the invention defined in Claim 18 relates to enabling a new and particularly desirable set of optical properties to be obtained based on a commonly used general structure of a solar filter. This aspect of the invention may enable such properties to be obtained with little or no modification of common manufacturing equipment.

Non-limiting examples of the present invention will now be described: Example 1 A solar control panel produced by magnetron sputtering consists of the following sequential layers on a 6 mm thick glass substrate: * a first antireflective zinc oxide layer having a thickness of about 349A deposited by sputtering a zinc target in an oxidising atmosphere; * a first infra-red reflecting silver layer having a thickness of about 93A deposited by sputtering a silver target in an inert argon atmosphere; * a first barrier layer deposited by sputtering about a 30A thickness of titanium metal from a titanium target in an inert argon atmosphere substantially all of which is subsequently oxidised during deposition of the overlying antireflective layer so that the residual absorption of this barrier is less than about 1%; & a second antireflective zinc oxide layer having a thickness of about 849A deposited by sputtering a zinc target in an oxidising atmosphere; * an absorbing layer of metallic titanium having a thickness of about 12A deposited by sputtering a titanium target in an inert argon atmosphere; * a second infra-red reflecting silver layer having a thickness of about 170A deposited by sputtering a silver target in an inert argon atmosphere; * a second barrier layer deposited by sputtering about a 35A thickness of titanium metal from a titanium target in an inert argon

atmosphere substantially all of which is subsequently oxidised during deposition of the overlying antireflective layer so that the residual absorption of this barrier is less than about 1%; and * a third anti-reflective zinc oxide layer having a thickness of about 308A deposited by sputtering a zinc target in an oxidising atmosphere.

The properties of this glazing panel are luminous transmittance 65% direct energy transmittance 38% reflection of visible light 9.5% colour co-ordinates in reflection al =1. 1 b''=-12.7 dominant wavelength in reflection 476nm colour purity in reflection 21% dominant wavelength in transmission 509 nm colour purity in transmission 1.9 % A sealed double glazing unit comprising the glazing panel of Example 1 spaced 15mm from a 6 mm thick sheet of clear glass has the followingproperties: luminous transmittance 59 % solar factor 31 % reflection of visible light 13% a colour co-ordinates a*=-0.3 b*=-ll dominant wavelength in reflection 477 nm colour purity in reflection 18 % dominant wavelength in transmission 521 nm colour purity in transmission 1.7 % In accordance with standard practice, the solar control filter is arranged in position 2 in the double glazing unit i. e. at the interior of the glazing unit (to protect it from abrasion and exposure to the atmosphere) on the sheet of the glazing unit that is exposed to the exterior. This is also the case for the other examples given below.

The glazing of this example has a pleasant, blue appearance in reflection.

Example 2 By way of comparison, Example 2 relates to a solar control glazing panel which does not form part of the invention and which consists of the solar control glazing panel of Example 1 with the omission of the absorbent titanium layer.

This properties of this glazing panel are: luminous transmittance 73.5% direct energy transmittance 43.5% reflection of visible light 10.7% colour co-ordinates in reflection a*=-0.3 b*=-8.5 dominant wavelength in reflection 478nm colour purity in reflection 15% dominant wavelength in transmission 545 nm colour purity in transmission 6.5 % A sealed double glazing unit comprising the glazing panel of Example 2 spaced 15mm from a 6 mm thick sheet of clear glass has the followingproperties: luminous transmittance 65 % solar factor 35 % reflection of visible light 15 % colour co-ordinates a*==-l. l b*=-7 dominant wavelength in reflection 480 nm colour purity in reflection 12 % dominant wavelength in transmission 545 nm colour purity in transmission 2.7 % The luminous transmittance and solar factor of the double glazing unit using the glazing of Example 2 are higher than those of Example 1.

In addition, the Example 2 glazing is undesirably yellow in transmission.

Example 3 A solar control panel was produced by magnetron sputtering of the following sequential layers on a 6 mm thick glass substrate: * a first antireflective layer comprising a layer of zinc oxide having a thickness of about 197A deposited by sputtering a zinc target in an

oxidising atmosphere, a layer of mixed"stainless steel"oxide having a thickness of about 25A deposited by subsequently sputtering a stainless steel target in an oxidising atmosphere and a layer of zinc oxide having a thickness of about 58A deposited by subsequently sputtering a zinc target in an oxidising atmosphere; * a first infra-red reflecting silver layer having a thickness of about 157A deposited by sputtering a silver target in an inert argon atmosphere; * a first barrier layer deposited by sputtering about a 30A thickness of titanium metal from a titanium target in an inert argon atmosphere substantially all of which is subsequently oxidised during deposition of the overlying antireflective layer so that the residual absorption of this barrier is less than about 1%; * a second antireflective zinc oxide layer having a thickness of about 825A deposited by sputtering a zinc target in an oxidising atmosphere; * an absorbing layer of metallic titanium having a thickness of about 13A deposited by sputtering a titanium target in an inert argon atmosphere; * a second infra-red reflecting silver layer having a thickness of about 130A deposited by sputtering a silver target in an inert argon atmosphere; * a second barrier layer deposited by sputtering about a 30A thickness of titanium metal from a titanium target in an inert argon atmosphere substantially all of which is subsequently oxidised during deposition of the overlying antireflective layer so that the residual absorption of this barrier is less than about 1%; and * a third anti-reflective zinc oxide layer having a thickness of about 309A deposited by sputtering a zinc target in an oxidising atmosphere.

This glazing panel had the following properties: luminous transmittance 62% direct energy transmittance 35% reflection of visible light 12% colour co-ordinates in reflection a'=0.0 b*=-2.2 dominant wavelength in reflection 477nm colour purity in reflection 3.7% dominant wavelength in transmission 512 nm colour purity in transmission 3 %

A sealed double glazing unit comprising the glazing panel of Example 3 spaced 15mm from a 6 mm thick sheet of clear glass has the followingproperties: luminous transmittance 56 % solar factor 28 % reflection of visible light 15 % colour co-ordinates in reflection a*=--1 b l =-2.6 dominant wavelength in reflection 482 nm colour purity in reflection 5.3 % dominant wavelength in transmission 518 nm colour purity in transmission 1.6 % Example 3 shows a glazing having a particularly desirable luminous transmittance and solar factor for certain application which is substantially neutral in colour in both reflection and transmission.

Example 4 A solar control panel was produced by magnetron sputtering of the following sequential layers on a 6 mm thick glass substrate: * a first antireflective layer comprising a layer of zinc oxide having a thickness of about 321 A deposited by sputtering a zinc target in an oxidising atmosphere * an absorbing layer of metallic titanium having a thickness of about 30 A deposited by sputtering a titanium target in an inert argon atmosphere; * a first infra-red reflecting silver layer having a thickness of about 157A deposited by sputtering a silver target in an inert argon atmosphere; * a first barrier layer deposited by sputtering about a 30A thickness of titanium metal from a titanium target in an inert argon atmosphere substantially all of which is subsequently oxidised during deposition of the overlying antireflective layer so that the residual absorption of this barrier is less than about 1%; * a second antireflective comprising a layer of zinc oxide having a thickness of about 780 A deposited by sputtering a zinc target in an oxidising atmosphere;

* a second infra-red reflecting silver layer having a thickness of about 158 A deposited by sputtering a silver target in an inert argon atmosphere; * a second barrier layer deposited by sputtering about a 30A thickness of titanium metal from a titanium target in an inert argon atmosphere substantially all of which is subsequently oxidised during deposition of the overlying antireflective layer so that the residual absorption of this barrier is less than about 1%; and * a third anti-reflective zinc oxide layer having a thickness of about 330 A deposited by sputtering a zinc target in an oxidising atmosphere.

This glazing panel had the following properties: luminous transmittance 56% o direct energy transmittance 32% reflection of visible light 11% colour co-ordinates in reflection a,. 0 b*=-4 dominant wavelength in reflection 477nm colour purity in reflection 7 % dominant wavelength in transmission 485 nm colour purity in transmission 6 % A sealed double glazing unit comprising the glazing panel of Example 3 spaced 15mm from a 6 mm thick sheet of clear glass has the followingproperties: luminous transmittance 51 % solar factor 26 % reflection of visible light 13 % colour co-ordinates in reflection a*=-0.8 b*=-4.5 dominant wavelength in reflection 480 nm colour purity in reflection 8 % dominant wavelength in transmission 487 nm colour purity in transmission 6 %