GLAZING PANEL

Abstract: A glazing panel carrying a coating stack comprises in sequence at least: a glass substrate, a base antireflective layer, an underlying barrier layer, an infra-red reflecting layer, an overlying barrier layer, and a top antireflective layer in which the underlying barrier layer comprises a mixture of Zn and at least one additional material X, in which the atomic ratio X/Zn in the underlying barrier layer is greater than or equal to 0.03 and in which X is one or more of the materials selected from the group comprising the materials of Groups (3a, 3b, 4a, 5a, 5b, 6b, 7b) of the periodic table. This provides an advantageous combination of properties, particularly thermal stability when such a glazing panel is bent and/or tempered.

Description: Glazinσ 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/ SnO 2 base dielectric/ first metallic barrier of Al, Ti, Zn, Zr or Ta / Ag / second metallic barrier of Al, Ti, Zn, Zr or Ta / SnO 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 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 SnO 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 layer 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. SUBSTITUTE SHEET (RULE 2 ) Providing the underlying barrier as a mixture of Zn and one of the specified additional materials provides an advantageous combination of properties. The underlying barrier must not only carry out its principal role of protecting the Ag layer from undesirable oxidation during heat treatment 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 underlying barrier according to the present invention may provide an advantageous combination of: • thermal resistance in protecting its overlying Ag layer from degradation if the glazing panel is heated, for example during tempering and/or bending. Notably, tolerance to variations in a heating cycle to which the glazing panel is subjected may be greater than that obtainable with, for example, known Ti or Zn underlying barriers. • mechanical resistance: the underlying barrier may have greater adherence to an adjacent Ag layer than, for example, an Al barrier. This may be so even when the underlying barrier contains Al. • compatibility with Ag: crystallisation of the Ag layer affects its optical properties. A pure Zn or ZnO layer underlying the Ag can lead to excessive crystallisation of the Ag and to problems of haze in the coating, particularly if the coating is subjected to heat treatment. This may be controlled or alleviated using the present invention whilst still favouring crystallisation to a sufficient degree to provide good infra red reflecting properties. The advantageous properties of the underlying barrier layer may not be obtainable if the atomic ratio X/Zn is below the specified minimum, for example, if the material X is present in the Zn in the form of an impurity. 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 underlying barrier to provide advantageous properties. The underlying barrier is preferably deposited in the form of a metal or sub-oxide and serves not only to block passage of oxygen to the Ag layer but also diffusion of light ions, notably Na, from the glass substrate to the Ag layer. It must thus fulfil additional function to an overlying barrier and, consequently, different factors must be considered in its selection. Particularly good results may be obtainable if X is one or more of the materials selected from the group consisting of Al, Ti, Hf, Sb, Nb, Ta, and Zr. The thickness of the underlying barrier may be greater than about 5 A; preferably greater than about 10 A; this may provide a noticeable improvement in the properties of the coating if subjected to heat treatment. The thickness of the underlying barrier may be: less than or equal to about 50 A, particularly if X is Ti; less than or equal to about 40 A, particularly if the atomic ratio X/Zn is less than or equal to about 3; less than or equal to about 30 A, particularly if the atomic ratio X/Zn is less than or equal to about 1; less than or equal to about 25 A, particularly if X is Al. These thicknesses may confer suitable levels of stability on the coating if it is heat treated. Nevertheless, the optimum thickness will be influenced by the exact composition of the underlying barrier layer, the deposition conditions of the underlying barrier layer, the optical properties of the glazing panel being sought and the heat treatment regime (if any) to which the glazing panel is subjected. 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 in 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 underlying barrier layer of the invention may be utilised in a coating stack having two, or indeed more than two, spaced infra-red reflecting layers. Each infra-red reflecting layers may have an underlying barrier layer and in such cases at least one, and preferably all of the underlying barrier layers comprise the defined materials. 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. The invention thus has particular advantages in relation to heat treatable and heat treated glazing panels but 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 or 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 antiglare 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. The combination of Zn and Al in the underlying barrier layer may provide an advantageous combination of the properties discussed above, particularly when the atomic ratio Al/Zn is in the range 0.03 to 0.3 and preferably in the range 0.05 to 0.15. The atomic ratio Al/Zn may be less than about 1. An advantageous combination of properties may also be obtained with a combination of Zn and Ti in the underlying barrier layer, particularly when the atomic ratio Ti/Zn is in the range 1 to 10, preferably 1.5 to 6 and more preferably 2 to 5. Where the coating has more than one underlying barrier layer, these may have the same or substantially the same composition. This may simplify process control and ordering and storage of the necessary targets. A combination of the underlying barrier comprising Zn with additional material X and the dielectric layer adjacent to the underlying barrier also comprising Zn with the same additional material X may facilitate control of the oxidation of the underlying barrier during heat treatment of the glazing panel. Use of the same or similar material as the underlying barrier for the overlying barrier may facilitate control of oxidation of both barriers during heat treatment. This may be particularly so when one or more of the adjacent dielectric layers comprises a similar material. Use of similar materials for more than one layer of the coating stack may facilitate control of the process used to deposit the different layers by allowing similar conditions to be used for different coatings. Furthermore, use of targets of the same composition for depositing more than one layer of the coating may facilitate storage and ordering of such targets on an industrial scale. It may also provide good adhesion between the coating layers and thus good mechanical durability. According to another aspect, the present invention provides a method of manufacturing a glazing panel as defined in Claim 14. Such a method may be used to manufacture, for example, heat treated architectural glazing panel, 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 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 ZnAlOy barriers are similarly deposited by sputtering a target which is an alloy or mixture of Zn and Al 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 aluminium oxide, particularly in an argon gas or argon rich oxygen containing atmosphere. The oxidation state in each of the base, central and top ZnAlOx dielectric layers need not necessarily be the same. Similarly, the oxidation state in each of the ZnAlOy barriers need not be the same. Equally, the Al/Zn ratio need not be the same for all of the layers; for example, the barrier layers may have a different Al/Zn ratio to the antireflective dielectric layers and the antireflective dielectric layers may have different Al/Zn ratios from each other. Each overlying barrier protects its underlying silver layer from oxidation during sputter deposition of its overlying ZnAlOx 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 AIN (partially oxidised) layers may comprise a mixture of AIN and Al 2 0 3 , the AIN being partially oxidised during the heat treatment process. The barrier layers are not necessarily completely oxidised and their thickness will depend to a certain extent upon their degree of oxidation. 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 ZnAl barriers are similarly deposited by sputtering a target which is an alloy or mixture of Zn and Al 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: 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: 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 electtically 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 if a slightly green appearance is desired for a windscreen or in the case of architectural applications for which a different colour is desired, the colour in reflection may be adjusted as is known in the art by adjusting the thicknesses of the dielectric layers and/or the infra red reflecting 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 materials. 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 underlying barrier layer an infra-red reflecting layer an overlying barrier layer, and a top antireflective layer characterised in that the underlying barrier layer comprises a mixture of Zn and at least one additional material X, in which the atomic ratio X/Zn in the underlying barrier layer is greater than or equal to 0.03 and in which X is one or more of the materials selected from the group comprising the materials of Groups 3a, 3b, 4a, 4b, 5a, 5b, 6b, 7b 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 underlying barrier layer an infra-red reflecting layer an overlying barrier layer, a central antireflective layer an underlying barrier layer an infra-red reflecting layer an overlying barrier layer, a top antireflective layer characterised in that at least one of the underlying barrier layers comprises a mixture of Zn and at least one additional material X, in which the atomic ratio X/Zn in the underlying barrier layer is greater than or equal to 0.03 and in which X is one or more of the materials selected from the group comprising the materials of Groups 3a, 3b, 4a, 4b, 5a, 5b, 6b, 7b of the periodic table. 3. A glazing panel in accordance with claim 1 or claim 2, in which the glazing panel is a heat treatable or substantially haze free heat treated glazing panel. 4. A glazing panel in accordance with any one of claims 1 to 3, in which the or at least one of the underlying barrier layers comprises a mixture of Zn and Al having an atomic ratio Al/Zn of at least 0.03. 5. A glazing panel in accordance with Claim 4, in which the or at least one of the underlying barrier layers comprises a mixture of Zn and Al having an atomic ratio Al/Zn within the range 0.03 to 0.3. 6. A glazing panel in accordance with any one of claims 1 to 3, in which the or at least one of the underlying barrier layers comprises a mixture of Zn and Ti having an atomic ratio Ti/Zn of at least 0.03. 7. A glazing panel in accordance with claim 6, in which the or at least one of the underlying barrier layers comprises a mixture of Zn and Ti having an atomic ratio Ti/Zn within the range 1 to 10. 8. A glazing panel in accordance with any preceding claim, in which the atomic ratio X/Zn is less than or equal to 5. 9. A glazing panel in accordance with any preceding claim, in which the or at least one of the underlying barrier layers is deposited as a metal or in a form which is substantially metallic. 10. A glazing panel in accordance with any preceding claim, in which the or at least one of the underlying barrier layers has a geometrical thickness greater than or equal to 2 A and less than or equal to 50 A. 11. A glazing panel in accordance with any preceding claim, in which at least one of the antireflective layers comprises a layer of an oxide comprising a mixture of Zn and the additional material X of the or one of the underlying barrier layers. 12. A glazing panel in accordance with Claim 11, in which at least one of the antireflective layers comprises an oxide comprising a mixture of Zn and the additional material X with an atomic ratio X/Zn which is substantially the same as the atomic ratio X/Zn of the or one of the underlying barrier layers. 13. A glazing panel in accordance with any preceding claim, in which at least one overlying barrier comprises a mixture of Zn and one or more of an additional material selected from Groups 3a, 3b, 4a, 4b, 5a, 5b, 6b, 7b of the periodic table. 14. 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