Abstract:
A glazing panel carrying a coating stack comprises in sequence at least: 
     a glass substrate 
     a base antireflective layer 
     an infra-red reflecting layer, and 
     a top antireflective layer 
     and is characterized in that at least one of the antireflective layers comprises at least one mixed oxide layer which comprises an oxide which is a mixture of Zn and at least one additional material X, in which the atomic ratio X/Zn is greater than or equal to 0.12 and in which X is one or more of the materials selected from the group comprising the elements of groups 2a, 3a, 5a, 4b, 5b, 6b of the periodic table. The glazing panel exhibits a combination of advantageous properties, particularly thermal stability.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to glazing panels and particularly, but not exclusively, to solar control glazing panels which are intended to undergo heat treatment following application of a solar control filter. 
     2. Discussion of Background 
     EP 233003A describes a glazing panel carrying a sputter coated optical filter having the structure: glass substrate/SnO2 base dielectric/first metallic barrier of Al, Ti, Zn, Zr or Ta/Ag/second metallic barrier of Al, Ti, Zn, Zr or Ta/SnO2 top dielectric. The optical filter is designed to block a significant portion of the incident radiation in the infra red portion of the spectrum whilst allowing passage of a significant portion of the incident radiation in the visible portion of the spectrum. In this way, the filter acts to reduce the heating effect of incident sunlight whilst allowing good visibility through the glazing and is particularly suitable for car windscreens. 
     In this type of structure, the Ag layer acts to reflect incident infra red radiation and in order to fulfil this role must be maintained as silver metal rather than silver oxide and must not be contaminated by adjacent layers. The dielectric layers which sandwich the Ag layer serve to reduce the reflection of the visible portion of the spectrum which the Ag layer would otherwise provoke. The second barrier serves to prevent oxidation of the Ag layer during sputtering of the overlying SnO2 dielectric layer in an oxidising atmosphere; this barrier is at least partially oxidised during this process. The main role of the first barrier is to prevent oxidation of the silver layer during heat treatment of the coating (e.g. during bending and/or tempering) of the glazing panel by being oxidised itself rather than allowing passage of oxygen to the Ag layer. This oxidation of the barrier during heat treatment provokes an increase in TL of the glazing panel. 
     EP 792847A discloses a heat treatable solar control glazing panel which is based on the same principle and has the structure: glass substrate/ZnO dielectric/Zn barrier/Ag/Zn barrier/ZnO dielectric/Zn barrier/Ag/Zn barrier/ZnO dielectric. The Zn barriers positioned below each of the Ag layers are intended to be oxidised completely during heat treatment and serve to protect the Ag layers from oxidation. As well known in the art, the structure of having two, spaced Ag layers rather than a single Ag layer increases the selectivity of the filter. 
     EP 275474 A discloses a heat treatable solar control panel having the structure: glass substrate/zinc stannate dielectric/Ti barrier/Ag/Ti barrier/zinc stannate dielectric. Ti barriers are generally favoured in this type of heat treatable structure due to their high affinity for oxygen and relative ease with which they can be oxidised to form titanium oxide. 
     SUMMARY OF THE INVENTION 
     The present invention provides a glazing panel. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 shows a glazing panel having the following sequential structure: 
     glass substrate  10 , 
     antireflective layer  11 , comprising antireflective layer  12  and barrier layer  14 , 
     infrared reflective layer  15 , 
     barrier layer  16 , 
     antireflective layer  17 , 
     barrier layer  18 , 
     infrared reflective layer  19 , 
     antireflective layer  21  comprising barrier layer  20  and antireflective layer  22 . 
    
    
     The antireflective layer is a layer composed of at least one member selected from the group consisting of oxides, nitrides and carbides and double compounds thereof. 
     As the oxide, for example, an oxide of at least one element selected from the group consisting of Zn, Ti, Sn, Si, Al, Ta or Zr may be mentioned. In addition, for example, zinc oxide containing Al, Ga, Si or Sn or indium oxide containing Sn may be mentioned. 
     As the nitride, a nitride of at least one element selected from the group consisting of Si, Al and B (a nitride (A)) or a mixture (inclusive of a double nitride) of a nitride of Zr or Ti with a nitride (A) may be mentioned. 
     As the double compound, SiO x C y , SiO x N y , SiAl x N y  or SiAl x O y N z  may be mentioned. The antireflective layer may be a single layer or a multiple layer. 
     Especially, a zinc oxide or a zinc oxide containing at least one element selected from the group consisting of Sn, Al, Cr, Ti, Si, B, Mg, In and Ga is preferable, because it makes it possible to stably form an adjacent infra-red reflecting layer with a high crystallinity. Especially, a zinc oxide containing Al and/or Ti is preferable. 
     The infra-red reflecting material is a material that has a reflectance higher than the reflectance of sodalime glass in the band of wavelength between 780 nm and 50 μm. 
     The infra-red reflecting layer is a layer composed of Ag only or a layer comprising Ag as the main component and an additional metal element (such as Pd, Au or Cu). When an additional metal element is contained, the content of the additional metal element is preferably from 0.3 to 10 at %, more preferably from 0.3 to 5 at %, based on the total of Ag and the additional metal element. If the content of an additional metal element is less than 0.3 at %, the effect of stabilizing Ag is small. Also, if the content of an additional metal element exceeds 10 at %, the effect of stabilizing Ag diminishes. Especially, Pd as the additional metal element can immobilize Ag atoms, namely depress the migration of Ag atoms and affords a layer which is excellent in stability and chemical resistance at high temperatures. As the Pd content increases, the rate of film formation tends to decrease, the visible light transmittance tends to lower, and the shielding selectivity between visible rays and near infrared rays tends to become poor. Therefore, the Pd content is preferred to be at most 5.0 at %, especially from 0.3 to 2.0 at %. 
     When the glass laminate of the present invention comprises more than one infra-red reflecting layer, each infra-red reflecting layer may have the same composition or a different composition. The infra-red reflecting layer may be a multiple layer comprising at least two laminated films, for example, a multiple layer composed of Ag and Pd. 
     In a glazing panel having a three layer type laminated coating, the thicknesses of the base antireflective layer, the infra-red layer and the top antireflective layer layer are preferably from 15 to 45 nm, from 9 to 16 nm (especially from 9 to 12 nm) and from 30 to 45 nm, respectively. A glazing panel comprising a colorless soda lime glass substrate of 2 mm thick and a three layer type laminated coating formed on the substrate has such representative optical properties as a luminous transmittance (TL) of about from 75 to 85% and an energetic transmittance (TE) of about from 50 to 70% after heat treatment. 
     In a glazing panel having a five layer type laminated coating, the thicknesses of the base antireflective layer, the infra-red layer the central antireflective layer, the infra-red layer and the top antireflective layer layer are preferably from 16 to 50 nm (especially from 20 to 45 nm), from 6.5 to 16 nm (especially from 6.5 to 12.5 nm), from 40 to 100 nm (especially from 45 to 90 nm), from 6.5 to 16 nm (especially from 6.5 to 12.5 nm) and from 16 to 50 nm (especially from 20 to 45 nm), respectively. A glazing panel comprising a colorless soda lime glass substrate of 2 mm thick and a five layer type laminated coating formed on the substrate has such representative optical properties as a luminous transmittance (TL) of about from 70 to 80% and an energetic transmittance (TE) of about from 40 to 50% after heat treatment. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Providing at least one of the antireflective layers comprising a mixture of Zn and one of the specified additional materials provides an advantageous combination of properties. The antireflective layer must not only carry out its principal role of preventing excessive reflection in the visible portion of the spectrum but must also for example, be compatible with the other layers in the coating stack, be mechanically and chemically resistant and be suited to production on an industrial scale. 
     Any suitable method or combination of methods may be used to deposit the coating layers. For example, evaporation (thermal or electron beam), liquid pyrolysis, chemical vapour deposition, vacuum deposition and sputtering, particularly magnetron sputtering, the latter being particularly preferred. Different layers of the coating stack may be deposited using different techniques. 
     The antireflective layer according to the present invention may provide an advantageous combination of: 
     thermal stability if the glazing panel is heated, for example during tempering and/or bending. Notably, use of the present invention may reduce degradation of the infra red reflecting layer when compared with comparable structures using, for example, known ZnO or SnO 2  antireflective layers. 
     ease and controllability of deposition: the antireflective layer according to the present invention may be deposited more easily and with more control than, for example, Al 2 O 3  or SiO 2 . Whilst Al 2 O 3  and SiO 2  show a good degree of thermal stability they are difficult to deposit using common sputtering techniques. 
     mechanical resistance: the antireflective layer according to the present invention may be used without prejudicing the mechanical resistance of the coating. In particular, it may perform well in pummel tests when the glazing panel is used in a laminated structure. 
     compatibility with Ag: crystallisation of the Ag layer affects its optical properties. A pure ZnO layer adjacent the Ag can lead to excessive crystallisation of the Ag and to problems of haze in the coating, particularly during heat treatment. However, where an antireflective layer does not consist of ZnO there may be insufficient recrystallisation of the Ag layers resulting in a level of infra red reflection and a level of electrical conductivity in the coating which are below the optimum obtainable. The present invention may be used to favour crystallisation to a sufficient degree to provide good infra red reflecting properties whilst avoiding excessive haze. In particular, it may provide a favourable crystallisation compared with an antireflective layer composed of TiO 2 . One possible explanation for this may be that the presence of the material X in the zinc oxide structure may reduce the crystal grain growth in the mixed oxide layer, especially perpendicular to the substrate. This may result in a less crystalline, more amorphous structure which reduces diffusion that might otherwise be likely to occur at crystal grain boundaries. 
     production cycle time: an oxide layer which is a mixture of Zn and at least one of the specified addition materials, particularly when the additional material is Ti, Ta, Zr, Nb, Bi or a mixture of these metals, will generally have a higher refractive index than antireflective layers of, for example, ZnO and SnO 2 , which are commonly used in similar structures and yet will be quicker to deposit than known antireflective layers having relatively high refractive indexes, for example, TiO 2 . Consequently, this may enable the production cycle time to be improved. 
     good selectivity: the higher refractive index may, in addition, facilitate an increase in the selectivity of the coating stack, particularly when the additional material is Ti, Ta, Zr, Nb, Bi or a mixture of these metals. 
     Use of the antireflective layer in accordance with the present invention as the or part of the top antireflective layer, particularly as a layer exposed to the atmosphere may provide good chemical and mechanical resistance. Furthermore, it may provide good compatibility with a laminating film, for example a pvb film, if the glazing panel is to be laminated to form, for example, a car windscreen or other laminated glazing panel. 
     The advantageous properties of the antireflective layer according to the present invention may not be obtainable if the atomic ratio X/Zn is below the specified minimum, for example, if the material X is present only in the form of an impurity or if the atomic ratio X/Zn is not sufficiently great. 
     The atomic ratio X/Zn may be less than about 5; it may be less that or equal to about 4 or to about 3. This may ensure a sufficient quantity of Zn in the antireflective layer to provide advantageous properties. 
     The advantageous combination of properties obtainable with the antireflective layer according to the present invention may be utilized in a coating stack having two, or indeed more than two, spaced infra-red reflecting layers. 
     Multiple spaced infra-red reflecting layers may be used to provide the glazing panel with a selectivity that is greater than 1.5 or 1.7. 
     Particularly advantageous properties may be obtained if additional material X consists 
     essentially of Ti 
     of Ti with one or more additional materials from the specified group of materials, for example, Ti and Al 
     essentially of Al 
     of Al with one or more additional materials from the specified group of materials. 
     The combination of properties that may be provided by the present invention have particular advantages in relation to heat treatable and heat treated glazing panels. Nevertheless, the invention may also be used in respect of glazings which are not heat treated. The term “heat treatable glazing panel” as used herein means that the glazing panel carrying the coating stack is adapted to undergo a bending and/or thermal tempering and/or thermal hardening operation and/or other heat treatment process without the haze of the so treated glazing panel exceeding 0.5, and preferably without the haze exceeding 0.3. The term “substantially haze free heat treated glazing panel” as used herein means a glazing panel carrying a coating stack which has been bent and/or thermally tempered and/or thermally hardened and has a haze that does not exceed 0.5 and which preferably does not exceed 0.3. 
     In the present invention, a glazing panel can be subjected to heat treatment for 1) bending, 2) tempering, 3) sintering of colored ceramic print or silver bus bar print, 4) vacuum sealing of vacuum double glazing and 5) calcination of a wet-coated low reflective coating or antiglare coating. For example, it is heated to a temperature of from 570 to 700° C. in the atmosphere for 1) bending or 2) tempering. 
     Arranging the thickness of the mixed oxide layer in accordance with the present invention to have a thickness of at least 50 Å may provide a sufficient quantity to have a worthwhile or noticeable effect. The geometrical thickness of the mixed oxide layer in accordance with the present invention may be at least 80 Å, 100 Å, 120 Å, 140 Å or 160 Å. 
     An oxide layer which is a mixture of Zn and at least one of the specified addition materials may be used to confer advantageous properties on one, more than one or preferably all of the antireflective layer in the coating stack. Use in all of the antireflective layers of the coating stack may simplify process control and ordering and storage of the necessary targets. Where more than one antireflective layers comprises an oxide layer which is a mixture of Zn and at least one of the specified addition materials, such oxide layers may have the same or substantially the same composition. 
     A particularly advantageous combination of the properties discussed above may be obtained when the atomic ratio X/Zn is within the range of about 0.12-1, preferably about 0.15-0.6 and more preferably about 0.2-0.5. 
     The oxide layer in accordance with the present invention may be compatible for use with and may be advantageously combined in one or more of the antireflective layers with a layer comprising a nitride of aluminium or a nitride of silicon or a mixture thereof. This may provide particularly good thermal stability, particularly when the combination is used in the base and/or the top antireflective layer. 
     The filter stack may comprise one or more barrier layers underlying and/or overlying the infra red reflecting layer, as is known in the art. Barriers of, for example, one or more of the following material may be used: Ti, Zn, Ta, Cr, “stainless steel”, Zr, Ni, NiCr, ZnTi NiTi and ZnAl. Such barriers may be deposited, for example, as metallic layers or as sub-oxides (i.e. partially oxidised layers). Alternatively, nitrided barrier layers may also be used. 
     One or more of such barrier layers may comprise the same materials as the mixed oxide layer, particularly the adjacent mixed oxide layer. This may facilitate management of targets and control of deposition conditions and in the latter case may prove good adhesion between the layers and thus good mechanical durability of the coating stack. 
     Heat treatment may provoke an increase in the TL of the glazing panel. Such an increase in TL may be advantageous in ensuring that TL is sufficiently high for the glazing panel to be used in a vehicle windscreen. TL may increase in absolute terms during heat treatment by, for example, greater than about 2.5%, greater than about 3%, greater than about 5%, greater than about 8% or greater than about 10%. 
     According to another aspect, the present invention provides a method of manufacturing a glazing panel. Such a method may be used to manufacture, for example, heat treated architectural glazing panels, vehicle glazings and particularly windscreens. 
     Examples of the present invention will now be described with reference to FIG. 1 which is a cross-section through a glazing panel prior to a bending and tempering operation (for ease of representation, the relative thicknesses of the glazing panel and coating layers are not shown to scale). 
     EXAMPLE 1 
     FIG. 1 shows a double Ag layer, heat treatable, coating layer deposited on a glass substrate by magnetron sputtering and having the following sequential structure: 
     
       
         
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Reference 
                 Geometrical 
                   
               
               
                   
                 number 
                 thickness 
                 Atomic ratios 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Glass substrate 
                 10 
                 2 
                 mm 
                   
               
               
                 Base dielectric 
                 11 
               
               
                 comprising: ZnTiOx 
                 12 
                 280 
                 Å 
                 Ti/Zn = 0.25 
               
               
                 ZnTiOy underlying barrier 
                 14 
                 15 
                 Å 
                 Ti/Zn =  2.5 
               
               
                 Ag 
                 15 
                 100 
                 Å 
               
               
                 Ti overlying barrier 
                 16 
                 20 
                 Å 
               
               
                 Central dielectric 
                 17 
                 680 
                 Å 
                 Ti/Zn = 0.25 
               
               
                 comprising ZnTiOx 
               
               
                 ZnTiOy underlying barrier 
                 18 
                 10 
                 Å 
                 Ti/Zn =  2.5 
               
               
                 Ag 
                 19 
                 100 
                 Å 
               
               
                 Ti overlying barrier 
                 20 
                 20 
                 Å 
               
               
                 Top dielectric 
                 21 
               
               
                 comprising ZnTiOx 
                 22 
                 240 
                 Å 
                 Ti/Zn = 0.25 
               
               
                   
               
             
          
         
       
     
     in which ZnTiOx is a mixed oxide containing Zn and Ti deposited in this example by reactively sputtering a target which is an alloy or mixture of Zn and Ti in the presence of oxygen. The ZnTiOy barriers are similarly deposited by sputtering a target which is an alloy or mixture of Zn and Ti in an argon rich oxygen containing atmosphere to deposit a barrier that is not fully oxidised. 
     Alternatively, a mixed oxide layer may be formed by sputtering a target which is a mixture of zinc oxide and an oxide of material X, particularly in an argon gas or argon rich oxygen containing atmosphere. 
     The oxidation state in each of the base, central and top ZnTiOx dielectric layers need not necessarily be the same. Similarly, the oxidation state in each of the ZnTiOy barriers need not be the same. Equally, the Ti//Zn ratio need not be the same for all of the layers; for example, the barrier layers may have a different Ti/Zn ratio to the antireflective dielectric layers and the antireflective dielectric layers may have different Ti/Zn ratios from each other. 
     Each overlying barrier protects its underlying silver layer from oxidation during sputter deposition of its overlying ZnTiOx oxide layer. Whilst further oxidation of these barriers layers may occur during deposition of their overlying oxide layers a portion of these barriers preferably remains in the form of an oxide that is not fully oxidised to provide a barrier for subsequent heat treatment of the glazing panel. 
     This particular glazing panel is intended for incorporation in a laminated vehicle windscreen and displays the following properties: 
     
       
         
               
               
               
               
             
           
               
                   
                   
               
               
                   
                   
                 Prior to heat 
                 Following heat 
               
               
                   
                   
                 treatment see Note 1   
                 treatment see Note 2   
               
               
                   
                 Property 
                 
                   below 
                 
                 
                   below 
                 
               
               
                   
                   
               
             
             
               
                   
                 TL (Illuminant A) 
                 64% 
                 77% 
               
               
                   
                 TE (System Moon 2) 
                 39% 
                 40% 
               
               
                   
                 haze 
                 0.1 
                 0.28 
               
               
                   
                 a* 
                 −12 (coated side) 
                 −3 (external) 
               
               
                   
                 b* 
                 +4 (coated side) 
                 −8 (external) 
               
               
                   
                 RE (System Moon 2) 
                 33% (coated side) 
                 34% (external) 
               
               
                   
                   
               
               
                   
                   Note 1 Measured for monolithic glazing panel with coating prior to heat treatment  
               
               
                   
                   Note 2 Measured following heat treatment at 650° C. for 10 minutes followed by bending and tempering, and lamination with clear 2 mm glass sheet and 0.76 mm clear pvb  
               
             
          
         
       
     
     Heat treatment preferably causes substantially complete oxidation of all of the barrier layers such that the structure of the coating stack after heat treatment is: 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Reference 
                 Geometrical 
                   
               
               
                   
                 number 
                 thickness 
                 Atomic ratios 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Glass substrate 
                 10 
                  2 mm 
                   
               
               
                 Base dielectric comprising: 
                 11 
               
               
                 ZnTiOx 
                 12 
                 280 Å 
                 Ti/Zn = 0.25 
               
               
                 ZnTiOx (oxidised underlying 
                 14 
                 22 Å-28 Å 
                 Ti/Zn =  2.5 
               
               
                 barrier) 
               
               
                 Ag 
                 15 
                 100 Å 
               
               
                 TiOx 
                 16 
                 30 Å-40 Å 
               
               
                 Central dielectric 
                 17 
                 680 Å 
                 Ti/Zn = 0.25 
               
               
                 comprising ZnTiOx 
               
               
                 ZnTiOx (oxidised underlying 
                 18 
                 15 Å-20 Å 
                 Ti/Zn =  2.5 
               
               
                 barrier) 
               
               
                 Ag 
                 19 
                 100 Å 
               
               
                 TiOx (oxidised overlying 
                 20 
                 30 Å-40 Å 
               
               
                 barrier) 
               
               
                 Top dielectric comprising: 
                 21 
               
               
                 ZnTiOx 
                 22 
                 240 Å 
                 Ti/Zn = 0.25 
               
               
                   
               
             
          
         
       
     
     The TiOx overlying barriers may be partially oxidised or may be fully oxidised to TiO2 depending upon the conditions of the heat treatment to which the glazing panel is subjected. 
     EXAMPLE 2 
     Example 2 is similar to Example 1, except that ZnAlOx is used in the antireflective layers. The coating stacks and properties of the Example are set out below: 
     
       
         
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Reference 
                 Geometrical 
                   
               
               
                   
                 number 
                 thickness 
                 Atomic ratios 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Glass substrate 
                 10 
                 2 
                 mm 
                   
               
               
                 Base dielectric 
                 11 
               
               
                 comprising: ZnAlOx 
                 12 
                 315 
                 Å 
                 Al/Zn = 0.4 
               
               
                 Ti underlying barrier 
                 14 
                 10 
                 Å 
               
               
                 Ag 
                 15 
                 100 
                 Å 
               
               
                 Ti overlying barrier 
                 16 
                 20 
                 Å 
               
               
                 Central dielectric 
                 17 
               
               
                 comprising ZnAlOx 
                   
                 760 
                 Å 
                 Al/Zn = 0.4 
               
               
                 Ti underlying barrier 
                 18 
                 8 
                 Å 
               
               
                 Ag 
                 19 
                 100 
                 Å 
               
               
                 Ti overlying barrier 
                 20 
                 20 
                 Å 
               
               
                 Top dielectric comprising: 
                 21 
                 270 
                 Å 
                 Al/Zn = 0.4 
               
               
                 ZnAlOx 
                 22 
               
               
                   
               
             
          
         
       
     
     in which ZnAlOx is a mixed oxide containing Zn and Al deposited in this example by reactively sputtering a target which is an alloy or mixture of Zn and Al in the presence of oxygen. The Ti barriers are deposited by sputtering a titanium target in a substantially inert, oxygen free atmosphere. 
     At least a portion of the overlying barriers  16 ,  20  is oxidised during deposition of their overlying oxide layers. Nevertheless, a portion of these barriers preferably remains in metallic form, or at least in the form of an oxide that is not fully oxidised to provide a barrier for subsequent heat treatment of the glazing panel. 
     This particular glazing panel is intended for incorporation in a laminated vehicle windscreen and displays the following properties: 
     
       
         
               
               
               
               
             
           
               
                   
                   
               
               
                   
                   
                 Prior to heat 
                 Following heat 
               
               
                   
                   
                 treatment see Note 1   
                 treatment see Note 2   
               
               
                   
                 Property 
                 
                   below 
                 
                 
                   below 
                 
               
               
                   
                   
               
             
             
               
                   
                 TL (Illuminant A) 
                 61% 
                 76% 
               
               
                   
                 TE (System Moon 2) 
                 36% 
                 43% 
               
               
                   
                 haze 
                 0.1 
                 0.29 
               
               
                   
                 a* 
                 −17 (coated side) 
                 −4 (external) 
               
               
                   
                 b* 
                 +6 (coated side) 
                 −9 (external) 
               
               
                   
                 RE (System Moon 2) 
                 30% (coated side) 
                 32% (external) 
               
               
                   
                   
               
               
                   
                   Note 1 Measured for monolithic glazing panel with coating prior to heat treatment  
               
               
                   
                   Note 2 Measured following heat treatment at 625° C. for 14 minutes followed by bending and tempering, and lamination with clear 2 mm glass sheet and 0.76 mm clear pvb  
               
             
          
         
       
     
     Heat treatment preferably causes substantially complete oxidation of all of the barrier layers such that the structure of the coating stack after heat treatment is: 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                   
               
               
                 Coating stack following heat treatment 
               
             
          
           
               
                   
                 Reference 
                 Geometrical 
                   
               
               
                   
                 number 
                 thickness 
                 Atomic ratios 
               
               
                   
                   
               
             
          
           
               
                 Glass substrate 
                 10 
                  2 mm 
                   
               
               
                 Base dielectric comprising: 
                 11 
               
               
                 ZnAlOx 
                 12 
                 315 Å 
                 Al/Zn = 0.4 
               
               
                 TiOx oxidised underlying 
                 14 
                 15 Å-20 Å 
               
               
                 barrier 
               
               
                 Ag 
                 15 
                 100 Å 
               
               
                 TiOx (oxidised overlying 
                 16 
                 30 Å-40 Å 
               
               
                 barrier) 
               
               
                 Central dielectric 
                 17 
               
               
                 comprising ZnAlOx 
                   
                 760 Å 
                 Al/Zn = 0.4 
               
               
                 TiOx (oxidised underlying 
                 18 
                 12 Å-15 Å 
               
               
                 barrier) 
               
               
                 Ag 
                 19 
                 100 Å 
               
               
                 TiOx (oxidised overlying 
                 20 
                 30 Å-40 Å 
               
               
                 barrier) 
               
               
                 Top dielectric comprising: 
                 21 
               
               
                 ZnAlOx 
                 22 
                 270 Å 
                 Al/Zn = 0.4 
               
               
                   
               
             
          
         
       
     
     In an alternative embodiment, the base dielectric layer of Example 2 may comprise a first layer of ZnAlOx having an atomic ratio Al/Zn of between 0.12 and 1, and an overlying layer of ZnAlOx having an atomic ratio Al/Zn which is less than that of the first layer, for example 0.1. 
     Additional layers may be introduced above, below or between the film stacking arrangement if desired without departing from the invention. 
     In addition to the advantageous optical properties that may be obtained, each of the examples provides a coating layer which may be electrically heated, for example, in an electrically heated car windscreen to provide a de-misting and/or de-frosting function with the addition of suitably placed electrical connectors. 
     The colour co-ordinates of the examples are particularly suited to car windscreens as they give a neutral or slightly blue appearance in reflection when the windscreen is mounted at an angle in the car body. For other applications, for example architectural applications, the colour in reflection may be adjusted as is known in the art by adjusting the thicknesses of the dielectric layers and/or silver layer(s). 
     The TL of the glazing panel may be adjusted to suit the desired application. For example 
     if the glazing panel is to be used as a windscreen for the European market, TL may be selected to be greater than 75% (as required by European regulations). 
     if the glazing panel is to be used as a windscreen for the US market, TL may be selected to be greater than 70% (as required by US regulations). 
     if the glazing panel is to be used as a vehicle front sidelight, TL may be adjusted to be greater than 70% (as required by European regulations). 
     if the glazing panel is to be used as a vehicle rear sidelight or a rear window for a vehicle, TL may be selected to be between about 30% and 70%. 
     Such adjustment of TL may be achieved, for example, 
     by adapting the thicknesses of the layers of the coating stack, in particular the thicknesses of the dielectric layers and/or the infra-red reflecting layer(s). 
     by combining the coating stack with a tinted glass substrate. 
     by combining the coating stack with a tinted pvb or other laminating layer. 
     Glossary 
     Unless otherwise indicated by the context, the terms listed below have the following meanings in this specification: 
     
       
         
               
               
               
             
           
               
                   
               
             
             
               
                 a* 
                   
                 colour co-ordinate measured on the CIELab scale at normal incidence 
               
               
                 Ag 
                 silver 
               
               
                 Al 
                 aluminium 
               
               
                 Al2O3 
                 aluminium 
               
               
                   
                 oxide 
               
               
                 AlN 
                 aluminium 
               
               
                   
                 nitride 
               
               
                 b* 
                   
                 colour co-ordinate measured on the CIELab scale at normal incidence 
               
               
                 Bi 
                 bismuth 
               
               
                 Cr 
                 chromium 
               
               
                 haze 
                   
                 the percentage of transmitted light which in passing through the specimen deviates 
               
               
                   
                   
                 from the incident beam by forward scattering, as measured in accordance with the 
               
               
                   
                   
                 ASTM Designation D 1003-61 (Reapproved 1988). 
               
               
                 infra red 
                   
                 a material that has a reflectance higher than the reflectance of sodalime glass in 
               
               
                 reflecting 
                   
                 the band of wavelenghts between 780 nm and 50 microns 
               
               
                 material 
               
               
                 Nb 
                 niobium 
               
               
                 NiCr 
                   
                 an alloy or mixture comprising nickel and chromium 
               
               
                 NiTi 
                   
                 an alloy or mixture comprising nickel and titanium 
               
               
                 RE 
                 energetic 
                 the solar flux (luminous and non-luminous) reflected from a substrate as a 
               
               
                   
                 reflection 
                 percentage of the incident solar flux 
               
               
                 selectivity 
                   
                 the ratio of the luminous transmittance to the solar factor i.e. TL/TE 
               
               
                 SiO2 
                 silicon oxide 
               
               
                 Si3N4 
                 silicon nitride 
               
               
                 SnO2 
                 tin oxide 
               
               
                 Ta 
                 tantalum 
               
               
                 TE 
                 energetic 
                 the solar flux (luminous and non-luminous) transmitted through a substrate as a 
               
               
                   
                 transmittance 
                 percentage of the incident solar flux 
               
               
                 Ti 
                 titanium 
               
               
                 TL 
                 luminous 
                 the luminous flux transmitted through a substrate as a percentage of the incident 
               
               
                   
                 transmittance 
                 luminous flux 
               
               
                 Zn 
                 zinc 
               
               
                 ZnAl 
                   
                 an alloy or mixture comprising zinc and aluminium 
               
               
                 ZnAlOx 
                   
                 a mixed oxide containing zinc and aluminium 
               
               
                 ZnAlOy 
                   
                 a partially oxidised mixture comprising zinc and aluminium 
               
               
                 ZnO 
                 zinc oxide 
               
               
                 ZnTi 
                   
                 an alloy or mixture comprising zinc and titanium 
               
               
                 ZnTiOx 
                   
                 a mixed oxide containing zinc and titanium 
               
               
                 ZnTiOy 
                   
                 a partially oxidised mixture comprising zinc and titanium 
               
               
                 Zr 
                 zirconium