GLAZING PANEL

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 characterised 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: Glazing Panel 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. EP 233003A describes a glazing panel carrying a sputter coated optical filter having the structure: glass substrate/ Sn0 2 base dielectric/ first metallic barrier of Al, Ti, Zn, Zr or Ta / Ag / second metallic barrier of Al, Ti, Zn, Zr or Ta / Sn0 2 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; in order to fulfil this role it 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 Sn0 2 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. According to one aspect, the present invention provides a glazing panel as defined in Claim 1. 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 Sn0 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, A1 2 0 3 or Si0 2 . Whilst A1 2 0 3 and Si0 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 Ti0 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 Sn0 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, Ti0 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 10; it may be less that or equal to about 5 or to about 4 or to about 3. This may ensure a sufficient quantity of Zn in the antireflective layer to provide advantageous properties. The infra red reflecting material may be silver or a silver alloy, for example an alloy of silver containing one or more of Pd, Au, and Cu as an additional material. Such an additional material may be present in the silver alloy in an atomic ratio based on the total amount of silver and additional metal of 0.3 to 10%, preferably 0.3 to 5% and more particularly, especially where the additional material is Pd 0.3 to 2%. One or more of the antireflective layers may comprise an oxide, a nitride, a carbide or a mixture thereof. For example, the antireflective layer may comprise: • an oxide of one or more of Zn, Ti, Sn, Si, Al, Ta or Zr; an oxide of zinc containing Al, Ga, Si or Sn or an oxide of indium containing Sn; • a nitride of one or more of Si, Al and B or a mixture (including a double nitride) of a nitride of Zr or Ti with one of the aforementioned nitrides; • a double compound, for example, SiOxCy, SiOxNy, SiAlxNy or SiAlxOyNz. The antireflective layer may be a single layer or it may comprise two or more layers having different compositions. An oxide of zinc, preferably a zinc oxide containing at least one of Sn, Cr, Si, B, Mg, In, Ga and preferably Al and/or Ti is particularly preferred as use of these materials may facilitate stable formation of an adjacent infra red reflecting layer with a high crystallinity. As defined in Claim 2, the advantageous combination of properties obtainable with the antireflective layer according to the present invention may be utilised 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/or subject to another heat treatment process after deposition of the coating stack and has a haze that does not exceed 0.5 and which preferably does not exceed 0.3. Such heat treatment processes may involve heating or exposing the glazing carrying the coating stack to a temperature greater than about 560 °C, for example, between 560 °C and 700°C in the atmosphere. Other such heat treatment processes may be sintering of a ceramic or enamel material, vacuum sealing of a double glazing unit and calcination of a wet-coated low reflective coating or anti- glare coating. The heat treatment process, especially when this is a bending and/or thermal tempering and/or thermal hardening operation, may be carried out at a temperature of at least, 600 °C for at least 10 minutes, 12 minutes, or 15 minutes , at least 620 °C for at least 10 minutes, 12 minutes, or 15 minutes, or at least 640 °C for at least 10 minutes, 12 minutes, or 15 minutes. Arranging the thickness of the mixed oxide layer in accordance with the present invention to have a thickness of at least 50 A 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 A , 100 A , 120 A, 140 A or 160 A. 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 as defined in Claim 15. 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: 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: 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 2mm glass sheet and 0.76mm 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: The TiOx overlying barriers may be partially oxidised or may be fully oxidised to Ti02 depending upon the conditions of the heat treatment to which the glazing panel is subjected. Example 2 Example 2 is similar to Example 1, save that ZnAlOx is used in the antireflective layers. The coating stacks and properties of the Example are set out below: 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 dis la s the followin roperties: 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 0.76mm 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: 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:

Claims: Claims 1. A glazing panel carrying a coating stack comprising in sequence at least : a glass substrate a base antireflective layer an infra-red reflecting layer, and a top antireflective layer characterised 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. 2. A glazing panel in accordance with Claim 1 comprising in sequence at least: a glass substrate a base antireflective layer an infra-red reflecting layer a central antireflective layer an infra-red reflecting layer a top antireflective layer characterised 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. 3. A glazing panel in accordance with Claim 1 or Claim 2, in which X is one or more of the materials selected from the group comprising Ti and Al. 4. A glazing panel in accordance with any preceding claim, in which the glazing panel is a heat treatable or substantially haze free heat treated glazing panel. 5. A glazing panel in accordance with any preceding claim, in which the at least one mixed oxide layer has a geometrical thickness greater than or equal to 50 A. 6. A glazing panel in accordance with any preceding claim, in which each of the base antireflective layer and the top antireflective layer 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. 7. A glazing panel in accordance with any one of claims 2 to 6, in which the central antireflective layer 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. 8. A glazing panel in accordance with any preceding claim, in which the atomic ratio X/Zn of the mixed oxide layer is within the range 0.12-1. 9. A glazing panel in accordance with any preceding claim, in which the atomic ratio X/Zn of the mixed oxide layer is within the range 0.15-0.6. 10. A glazing panel in accordance with any preceding claim, in which the atomic ratio X/Zn of the mixed oxide layer is within the range 0.2-0.5. 11. A glazing panel in accordance with any preceding claim, in which the base antireflective layer comprises a layer adjacent to the substrate comprising a nitride of aluminium or a nitride of silicon or a mixture thereof and an overlying layer comprising the mixed oxide layer. 12. A glazing panel in accordance with any preceding claim, in which the top antireflective layer comprises the mixed oxide and an overlying layer comprising a nitride of aluminium or a nitride of silicon or a mixture thereof. 13. A glazing panel in accordance with any preceding claim, in which the glazing panel is a heat treatable or substantially haze free heat treated glazing panel and in which heat treatment of the heat treatable glazing panel to form the substantially haze free heat treated glazing panel provokes an increase of the value of TL of the glazing panel of at least 2.5%. 14. A glazing panel in accordance with any preceding claim, in which the atomic ratio X/Zn is less than or equal to 5. 15. A method of manufacturing a glazing panel having a haze of less than about 0.5 comprising the step of subjecting a glazing panel in accordance with any preceding claim to a heat treatment process at at least 570 °C.

Inventors: AOMINE NOBUTAKA, DECROUPET DANIEL, EBISAWA JUNICHI, NODA KAZUYOSHI, TAKEDA SATOSHI, AOMINE, NOBUTAKA, DECROUPET, DANIEL, EBISAWA, JUNICHI, NODA, KAZUYOSHI, TAKEDA, SATOSHI
Applicants: GLAVERBEL
Application year: 1999
Main classification: C03C17
IPC codes: B32B9, B32B17, C03C17, C23C14