WO2015150820A1

WO2015150820A1 - A polished coated glazing and a method of manufacturing the same

Info

Publication number: WO2015150820A1
Application number: PCT/GB2015/051036
Authority: WO
Inventors: David Lawrence Bamber; Simon James Hurst
Original assignee: Pilkington Group Limited
Priority date: 2014-04-04
Filing date: 2015-04-02
Publication date: 2015-10-08
Also published as: GB201406177D0

Abstract

The invention concerns a polished coated glazing, comprising a coating on a substrate. The coating comprises a first coating layer and a silica overcoat layer, the silica overcoat forming an exposed surface, wherein the silica overcoat layer is polished such that Sa is less than 15 nm. A method of manufacturing said glazing comprises the steps of providing a substrate, depositing a low emissivity coating, depositing a silica overcoat layer to form an exposed surface of the glazing and polishing the silica overcoat layer so as to reduce roughness Sa to less than 15 nm. Another embodiment of the invention is a polished coated glazing, comprising a coating on a substrate, such that the coating forms an exposed surface of the glazing, wherein the coating comprises a polished silica layer, having an arithmetical mean surface roughness, Sa, of less than 15 nm. Further embodiments include a laminated glazing and an insulating glazing unit. To achieve a desired level of planarization of an exposed surface of a glazing requires less polishing time with a silica layer forming the exposed surface according to the invention, than a non-silica layer.

Description

A Polished Coated Glazing and a Method of manufacturing the same

The invention relates to a polished coated glazing. The invention further relates to a method of manufacturing a polished coated glazing.

It is common for coatings to be provided on substrates, for example, float glass substrates, to impart specific properties or characteristics. Such coatings may be "hard" on-line coatings deposited pyrolytically onto the surface of float glass during its formation by a chemical vapour deposition (CVD) process, or "soft" off-line sputtered coatings which are deposited, for example by use of a magnetic sputtering technique under vacuum conditions. An example of an on-line coated glass is the applicant's low emissivity fluorine doped tin oxide coated glass known under the trade mark

K GLASS™. On-line coatings tend to have relatively rough surfaces after deposition. Although the coatings are quite hard and durable, the inherent roughness means that they can be quite easily marked or scuffed when deposited on an exposed surface of a glazing. When marked, the damage is obvious to the eye. Such marking is unacceptable to customers and so the coated side of the glass may be subjected to a polishing process (planarization), to reduce the microscopic rugosity of the coated surface and so reduce the risk of damage.

Planarization can be achieved by polishing the surface of the coating through the combined action of brushing and the application of abrasive slurry, for example, as described in W098/56725. However, care must be taken to choose suitable polishing conditions so as not to damage the active coating layer. Therefore, typically, brushes are used which have a minimal abrasive effect to avoid polishing away the active layer.

It is an object of the present invention to provide an improved polished coated glazing.

According to an aspect of the present invention there is provided a coated glazing comprising at least one substrate and a coating, the coating comprising a first coating layer, and a silica overcoat layer, the silica overcoat layer forming at least a part of an exposed surface of the glazing, wherein the silica overcoat layer is polished such that said layer has an arithmetical mean surface roughness, Sa, of less than 15nm. Most preferably, the silica overcoat layer is polished such that said layer has an arithmetical mean surface roughness, Sa, of less than 5nm. The silica overcoat layer is preferably polished such that said layer has an arithmetical mean surface roughness, Sa, of between 0.5nm and 2nm.

Preferably, the polished silica overcoat layer forms substantially the whole of the exposed surface of the glazing.

Preferably, the silica overcoat layer (Si0₂) has a geometric thickness of between substantially 5nm and 200nm, preferably between 10nm and 100nm, preferably between 20nm and 50nm, preferably between 25nm and 40nm, most preferably between 30nm and 35nm. The silica overcoat layer may be made from any suitable silica precursor. Preferably, the precursor comprises a silane precursor material, for example, as described in WO2013124634.

Preferably, the first coating layer is a low emissivity layer. Preferably, the low emissivity layer comprises a doped metal oxide. Most preferably, the doped metal oxide is fluorine doped tin oxide (Sn0₂:F). Most preferably, the silica overcoat layer is deposited directly over the low emissivity layer.

The doping of the metal oxide contributes to the coated glazing of the invention having an emissivity value of preferably less than 0.5, most preferably less than 0.4. The value of emissivity is measured according to EN 12898 (a published standard of the European Association of Flat Glass Manufacturers). The emissivity of a particular coating refers to the tendency of that coating to radiate energy. Thus a low emissivity coating is a poor thermal radiator (compared to a blackbody entity, which is a perfect radiator and is defined as having an emissivity of unity).

Preferably, the low emissivity layer has a geometric thickness of between substantially 50nm and 1 μηι, preferably between 150nm and 850nm. In a first preferred embodiment, the low emissivity layer has a thickness of approximately 350nm. In an alternative second preferred embodiment, the low emissivity layer has a thickness of approximately 800nm. Preferably, a colour suppression coating is provided on the substrate. Preferably, the colour suppression coating comprises a first tin oxide suppression layer having a thickness of preferably between 15nm to 35nm, most preferably 25nm; and a first silicon dioxide suppression layer having a thickness of preferably between 15nm to 35nm, most preferably 25nm. Preferably, said colour suppression coating is deposited directly over the substrate.

Preferably, the low emissivity layer is deposited directly over the colour suppression coating. Preferably, the polished silica overcoat layer is deposited directly over the low emissivity layer. When the substrate is a monolithic substrate, said substrate comprises a surface #1 and a surface #2. Surface #2 is that surface of the substrate which faces the interior of a building or vehicle cabin. Preferably, the exposed surface is surface #2. The polished silica overcoat is preferably deposited on surface #2. The polished silica overcoat may be deposited on surface #1 and/or surface #2.

Preferably, the at least one substrate is a ply of glass, preferably a float or rolled glass. The or each ply may be clear glass, preferably having greater than 70% visible light transmission (measured with llluminant A). Preferably, the or each ply has a geometric thickness of preferably from 2 to 10 mm, preferably between 3 to 4mm. The substrate may be a low-iron float glass, for example, having an iron content of 0.015% w/w or lower.

The glass used in the glazing of the present invention may be flat or it may be curved, and, in addition it may be toughened, for example by thermal or chemical tempering. When the glass is subjected to a heat treatment process, for example tempering or bending, this may be before or after deposition of the low emissivity coating.

Preferably, the coated glazing is a vehicle glazing. The vehicle glazing may be a laminated glazing. If the glazing is a vehicle roof-light, it preferably comprises a first and a second ply of clear glass, preferably having a tinted interlayer, preferably a tinted PVB interlayer.

The glazing may be a monolithic glazing, preferably comprising a tinted ply made by the applicant under the trade mark EZKOOL™ or more preferably GALAXSEE™. The glazing may be a vehicle window glazing. The or each substrate may be a ply of tinted glass, preferably having a visible light transmission of less than 85% at 3.15mm. The coated glazing may be for a building, for example a glazing for a window. The substrate may be manufactured from polymeric material.

In a further aspect, the invention provides a method of manufacturing a polished, coated glazing comprising the following steps:

(a) Providing a substrate;

(b) Directly or indirectly depositing a low emissivity layer on to the substrate;

(c) Directly or indirectly depositing a silica overcoat layer on the low emissivity layer such that said silica layer forms an exposed surface of the glazing;

(d) Polishing the silica overcoat layer so as to reduce the arithmetical mean surface roughness, Sa, to less than 15nm.

Most preferably, the silica overcoat layer is polished so as to reduce the arithmetical mean surface roughness, Sa, to less than 5nm.

Most preferably, the low emissivity layer comprises a fluorine doped tin oxide as hereinbefore described in relation to the coated glazing.

Preferably, less than 200nm of silica is deposited in step (c), preferably less than 100nm. Preferably, less than 50nm of silica is deposited in step (c). Most preferably, between 25nm to 35nm of silica is deposited in step (c).

Preferably, step (b) and preferably step (c) are carried out using a chemical vapour deposition process (CVD). Usually the CVD step is carried out at atmospheric pressure. Preferably, step (d) takes place remote from step (c), most preferably in an off-line polishing process. Preferably, when the coated glazing is a vehicle glazing, the polishing step (d) occurs before the glazing has been through a bending step.

Preferably, the silica overcoat layer is polished with at least one, preferably a plurality or polishing brushes, for example, those described in W098/56725 the teachings of which are hereby incorporated by reference. Preferably, the or each polishing brush has an axis of rotation transverse to the surface of the glazing. Preferably, the or each brush has a rotational speed of less than l OOOrpm, preferably between 500 and 600rpm, most preferably 550rpm. Preferably the bristles of the or each brush have a diameter in the range 0.1 to 1 mm, preferably 0.2 to 0.8 mm and more preferably 0.2 to 0.6 mm. Preferably, the length of the bristles of the or each brush are in the range 5 to 50 mm, more preferably 10 to 45 mm and most preferably 20 to 40 mm.

Preferably, the polishing step (d) uses a liquid polishing medium or slurry, preferably an aqueous polishing medium, preferably including an abrasive suspension. Preferably, the abrasive includes metal oxide abrasives, for example, alumina. The or each brush may be impregnated with a medium, for example, with silicon carbide or aluminium oxide. Preferably, the silica overcoat layer is polished for less than approximately 5 minutes, preferably less than 2 minutes. In a preferred embodiment, the silica overcoat is polished for approximately 1 minute, preferably using a "hard" brush of the type V3107 or V3109 manufactured by Botech Finishing Tools. Preferably, the polished silica overcoat has an arithmetical mean surface roughness of between 0.5nm and 2nm. Preferably, the final silica overcoat layer arithmetical mean surface roughness is less than the initial silica overcoat layer arithmetical mean surface roughness by between 5% and 90%. Preferably the final roughness is between 10% and 80% lower than the initial roughness. Preferably the final roughness is 60% lower than the initial roughness.

In a further aspect, the invention provides a laminated glazing comprising at least a first ply and a second ply with an interlayer therebetween, the first ply having a coating deposited thereon, the coating comprising a first coating layer, and a silica overcoat layer, the silica overcoat layer forming at least a part of an exposed surface of the glazing, wherein the silica overcoat layer is polished such that said layer has an arithmetical mean surface roughness, Sa, of less than 15nm, most preferably less than 5nm. The glazing may comprise a plurality of plies. Preferably, the laminated glazing is a laminated vehicle glazing.

Preferably, the first coating layer is a low emissivity layer as hereinbefore described in relation to the coated glazing. Preferably, the polished silica overcoat layer forms substantially the whole of the exposed surface of the glazing and preferably has a geometric thickness as hereinbefore described in relation to the coated glazing. Conventionally, the surfaces of a laminated glazing are referred to as "surface #1", "surface #2", "surface #3" and "surface #4" wherein surface #4 is understood to be that surface of the glazing which faces the interior of a vehicle cabin. Most preferably, the coating is provided on surface #4 of the glazing. The coating may be provided on surface #2 and/or surface #3 and/or surface #4. Preferably, the first ply and/or the second ply is a tinted or clear glazing.

The sheet of interlayer material is often a sheet of transparent plastic, for example polyvinylbutyral or such other suitable laminating material, and is ordinarily provided in a thickness of 0.76 mm. Alternatively, the sheet of interlayer material may be tinted to have an optimum visible light transmission of 35 % or less, preferably 18 % or less. Furthermore, the sheet of interlayer material may absorb infra-red radiation, for example when it comprises tin-doped indium oxide. By describing a sheet of interlayer material as being "infra-red absorbing" it is meant that when such a sheet (in 0.76 mm thickness) is interleaved between two pieces of clear glass (each of 2.1 mm thickness), the resulting laminate has a selectivity greater than 0.5 and preferably greater than 1 , where the "selectivity" is calculated by dividing the percentage visible light transmission by the percentage total energy, i.e. LT_A / TE, each measured for the laminate. In a further aspect, the invention provides an insulated glazed unit comprising at least a first and a second substrate, and a coating, the coating comprising a first coating layer, and a silica overcoat layer, the silica overcoat layer forming at least part of an exposed surface of the or each said substrate, wherein the silica overcoat layer is polished such that said layer has an arithmetical mean surface roughness, Sa, of less than 15nm, most preferably less than 5nm.

The coating may be deposited on a surface of the or each substrate which faces into the cavity of the unit. Preferably, the first coating layer is a low emissivity layer as hereinbefore described in relation to the coated glazing. Preferably, the polished silica overcoat layer forms substantially the whole of the exposed surface of the glazing and preferably has a geometric thickness as hereinbefore described in relation to the coated glazing. According to a further aspect of the present invention there is provided a coated glazing comprising at least one substrate and a coating deposited directly on top of the substrate such that the coating forms at least a part of an exposed surface of the glazing, wherein the coating is a polished silica layer having an arithmetical mean surface roughness, Sa, of less than 15nm. Most preferably, the coating is a polished silica layer having an arithmetical mean surface roughness, Sa, of less than 5nm.

Preferably, the polished silica overcoat layer forms substantially the whole of the exposed surface of the glazing and preferably has a geometric thickness as hereinbefore described in relation to the coated glazing. All of the features described herein may be combined with any one of the above aspects, in any combination.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, wherein:

Figure 1 shows a schematic sectional side view of a glazing according to the invention;

Figure 2 shows a schematic sectional side view of an alternative glazing according to the invention;

Figure 3 shows a schematic sectional side view of a laminated glazing according to the invention;

Figure 4 shows a schematic sectional side view of a double glazed unit according to the invention;

Figure 5 shows a schematic sectional side view of a further embodiment of a glazing according to the invention; Figure 6 shows a schematic sectional side view of a further embodiment of a laminated glazing according to the invention;

Figure 7 shows a schematic sectional side view of a further embodiment of a double glazed unit according to the invention; Figure 8a illustrates brush displacement with applied load for a Medium (V3106) type brush;

Figure 8b illustrates brush displacement with applied load for a Hard (V3107) type brush;

Figure 9a shows a Scanning Electron Microscope (SEM) image of a coated glass surface without a silica topcoat, in a First Trial, before polishing; Figure 9b shows a Scanning Electron Microscope (SEM) image of a coated glass surface without a silica topcoat, in a First Trial, after polishing;

Figure 9c illustrates the distribution of heights of the polished versus unpolished sample of the sample of Figures 9a and 9b;

Figure 10a shows a Scanning Electron Microscope (SEM) image of a coated glass surface with a silica topcoat, in a First Trial, before polishing;

Figure 10b shows a Scanning Electron Microscope (SEM) image of a coated glass surface with a silica topcoat, in a First Trial, after polishing;

Figure 10c illustrates the distribution of heights of the polished versus unpolished sample of Figures 10a and 10b; Figure 1 1a shows a Scanning Electron Microscope (SEM) image of a coated glass surface without a silica topcoat, in a Second Trial, before polishing;

Figure 1 1 b shows a Scanning Electron Microscope (SEM) image of a coated glass surface without a silica topcoat, in a Second Trial, after polishing;

Figure 11 c illustrates the distribution of heights of the polished versus unpolished sample of Figures 1 1a and 11 b;

Figure 12a shows a Scanning Electron Microscope (SEM) image of a coated glass surface with a silica topcoat, in a Second Trial, before polishing; Figure 12b shows a Scanning Electron Microscope (SEM) image of a coated glass surface with a silica topcoat, in a Second Trial, after polishing;

Figure 12c illustrates the distribution of heights of the polished versus unpolished sample of Figures 12a and 12b;

Figure 13a shows a Scanning Electron Microscope (SEM) image of a coated glass surface with a silica topcoat in a Third Trial before polishing; Figure 13b shows a Scanning Electron Microscope (SEM) image of a first region of a coated glass surface with a silica topcoat in a Third Trial before polishing using a secondary electron (SE) detector;

Figure 13c shows a Scanning Electron Microscope (SEM) image of a first region of a coated glass surface with a silica topcoat in a Third Trial before polishing using a back- scattered electron (BSE) detector;

Figure 13d shows a Scanning Electron Microscope (SEM) image of a second region of a coated glass surface with a silica topcoat in a Third Trial before polishing using a secondary electron (SE) detector;

Figure 13e shows a Scanning Electron Microscope (SEM) image of a second region of a coated glass surface with a silica topcoat in a Third Trial before polishing using a back-scattered electron (BSE) detector;

Figure 14a shows a Scanning Electron Microscope (SEM) image of a coated glass surface with a silica topcoat in a Third Trial after polishing;

Figure 14b shows a Scanning Electron Microscope (SEM) image of a first region of a coated glass surface with a silica topcoat in a Third Trial after polishing using a secondary electron (SE) detector;

Figure 14c shows a Scanning Electron Microscope (SEM) image of a first region of a coated glass surface with a silica topcoat in a Third Trial after polishing using a back- scattered electron (BSE) detector; Figure 14d shows a Scanning Electron Microscope (SEM) image of a second region of a coated glass surface with a silica topcoat in a Third Trial after polishing using a secondary electron (SE) detector;

Figure 14e shows a Scanning Electron Microscope (SEM) image of a second region of a coated glass surface with a silica topcoat in a Third Trial after polishing using a back- scattered electron (BSE) detector; and

Figure 14f illustrates the distribution of heights of the polished versus unpolished samples of the Third Trial.

Figure 1 shows a glazing 2 according to the invention. The glazing 2 is a monolithic glazing comprising a substrate 4 having a first surface 6 and a second surface 8 (surface #2). A coating 10 is deposited directly on to surface #2 so as to form an exposed surface of the glazing 2. The coating is a silica overcoat layer which is polished so as to have an arithmetical mean surface roughness, Sa, of less than 5nm as will be described in further detail below.

Figure 2 shows an alternative glazing 20 having a substrate 24. A coating 30 is deposited on the second surface 28 thereof. The coating 30 comprises a first layer 32 and a second layer 34. The first layer 32 is a low emissivity layer, particularly a fluorine doped tin oxide (Sn0₂:F) layer. The second layer 34 is a polished silica overcoat layer having an arithmetical mean surface roughness, Sa, of less than 5nm. The second layer 34 forms an exposed surface of the glazing 20. An embodiment of the invention is shown in Figure 3 which shows a laminated vehicle glazing 50 comprising a first ply 52, a second ply 54, and an interlayer 56 therebetween. Said plies are clear glass and the interlayer is a tinted PVB. The surfaces of the plies are commonly known to the skilled person as "surface #1", "surface #2", "surface #3", and "surface #4" wherein surface #4 is that surface which faces the interior of the cabin and is shown in the figure labelled 58. A coating is provided on surface #4. The coating comprises a first layer 62 of a low emissivity material, preferably Sn0₂:F, and a second layer 64 being an exposed layer which is a polished silica overcoat having an arithmetical mean surface roughness, Sa, of less than 5nm. Figure 4 shows an insulated glazed unit 70 having a first ply 72, a second ply 74 and a spacer 76 therebetween. A coating 78 is provided on surface #4 (80) of the glazing unit 70. The coating 78 comprises a first layer 82 being a low emissivity layer of preferably Sn0₂:F, and an outermost second layer 84 which is a polished silica overcoat layer having an arithmetical mean surface roughness, Sa, of less than 5nm. .

Figures 5 to 7 show an alternative coating 100 on a monolithic, laminated and insulated glazing respectively. The coating 100 comprises an outermost polished silica overcoat layer 1 14 of substantially between 25nm to 35nm thickness which is deposited directly on top of a Sn0₂:F layer 112 of substantially 340nm thickness.

The Sn0₂:F layer 1 12 may alternatively be of substantially 800nm thickness.

The Sn0₂:F layer 1 12 layer is deposited directly on top of a colour suppression layer comprising silicon dioxide 1 16 of approximately 25nm thickness and tin oxide layer 118 of substantially 25nm thickness.

Experimental

Three comparative polishing trials were undertaken to investigate the polishing conditions necessary to achieve a polished silica overcoat layer having an arithmetical mean surface roughness, Sa, of less than 5nm. In all cases the glass substrate was a 3.15mm thick float glass and all coatings were deposited on to the substrate by CVD during a float glass production process. Polishing took place in an offline process. During polishing, the brush was lowered until contact was just made with the exposed coating layer, such that the tips of the brush bristles were providing the majority of the contact between brush and coating.

Coated glazing A: Glass substrate having coating 100 without the silica overcoat layer. This is referred to below as "TEC15".

Coated glazing B: Glass substrate having coating 100 with a silica topcoat, referred to below as "TEC15+silica overcoat".

Different polishing brushes were used in the trials as indicated in Tables 1 a and 1 b. A polishing slurry was optionally used in some trials as shown; the polishing slurry was "Acepol AL" alumina slurry by Aachener Chemische Werke, diluted to 10%. In some trials, the polishing brush was impregnated with an abrasive as indicated.

Table 1a

The Medium (V3106) and Hard (V3107) brush type were tested to provide data in relation to the terms "Medium" and "Hard". Compression testing of the brush heads was undertaken to find displacement when a downwardly acting load (N) was applied to the brush head. An Instron 5500R universal mechanical tester with a 1 kN load cell attached at a crosshead displacement rate of 2mm/min was used. The compressive load was applied to the brush head via a flat plate and both load and crosshead displacement data were recorded at 1 N intervals until a displacement of 1 mm was achieved, the test was repeated 5 times (Run 1-5) for each of the brush heads.

The results are shown in Figures 8a and 8b. It is clear from the figures, that more force is required to displace the bristles of the "Hard" brush. The results are shown in tabulated form below in Table 1 b.

Table 1 b Results

First Polishing Trial

Table 3

Third Polishing Trial

Table 4 Durability Testing

Polished and unpolished samples of both TEC15 and TEC15 with silica overcoat were submitted for durability testing. The tests included Condensation (in accordance with British Standard EN 1096-2:2012 Annex B), Abrasion (in accordance with British Standard EN1096-2:2012 Annex E), Salt spray (in accordance with British Standard EN1096-2:2012 Annex D), and 35°C/75%RH (internal standard). Table 5 below shows the results of the Condensation testing:

Table 5

Table 6 below shows the results of the Abrasion testing:

Table 7 Table 8 below shows the results of the 35°C/75%RH testing:

Table 8

It was thought that some of the above tests would result in the silica overcoat being degraded. Although this was the case with unpolished silica overcoat samples, there is clear evidence that polishing significantly improves the performance in the above tests.

In summary, the durability results showed the following,

· Condensation - polished silica topcoat sample passed unlike the unpolished silica sample.

• Abrasion -only silica polished samples passed the test

Salt spray - silica topcoat showed no visual changes when compared to the silica unpolished sample.

· 35/75 - silica polished samples showed minimal degradation compared to unpolished samples.

SEM Analysis

In a scanning electron microscope a collimated beam of energetic electrons is scanned across the surface of a specimen, which is held under vacuum. The primary electron beam interacts with the specimen to produce secondary electrons (SE), backscattered electrons (BSE) and X-rays. The electrons are captured and displayed on a monitor, which is synchronised with the scanning of the beam. The result is a real time image of the surface under investigation, which can reveal topography (SE) and atomic number contrast (BSE). It should be noted that in the BSE mode of imaging brightness is directly proportional to average atomic number. The X-rays are analysed using energy dispersive spectroscopy (EDS). This gives elemental information only (boron to uranium), with a detection limit typically 0.1 to 0.2 %. The sampling depth is typically about 1 micron. Specimens were taken from samples of glazing A and B (as defined on page 1 1) from all trials and analysed using scanning electron microscopy (SEM) to determine how the coating structure had been altered on samples with and without a silica overcoat by the different polishing conditions. The specimens were mounted onto aluminium stubs in cross section and ultrasonically cleaned in methanol for 10 seconds. The cleaned specimens were coated with a thin layer of platinum (which provides a uniform conductive surface) prior to examination using the scanning electron microscope. Images were captured at an instrument magnification of 50,000x using both 80° and 90° specimen tilt. The images were taken using the secondary electron imaging mode, using a beam energy of 30kV. The instrument used was a XL30 FEG, manufactured by Philip, known as a Philips XL-30 FEG. Results of First Polishing Trial

Figures 9a and 9b are images of a TEC15 sample (without a silica overcoat) before and after polishing for 2mins respectively with a standard brush type. Each image was captured using a specimen tilt of 80°. Figure 9a shows the rounded peaks of the coating crystals 302 before polishing. In Figure 9b, after polishing with a standard brush type, the surface is shown to have been smoothed to a small degree. This is represented most clearly in Figure 9c which illustrates the shift in height distribution between the unpolished sample 305 and the polished sample 307 indicating that polishing has removed the larger peaks of the TEC 15 coating from the surface resulting in a mean height of approximately 40nm. The standard brush appears to have removes larger peaks in the coating.

Figures 10a and 10b are images of a TEC15+silica overcoat before and after polishing for 2mins respectively with the standard brush. Each image was captured using a specimen tilt of 80°. Figure 10a shows the plurality of rounded peaks of the silica overcoat crystals 309 before polishing. In Figure 10b, after polishing with the standard brush type, the larger of the rounded peaks appear slightly smoother 31 1. This finding is supported by Figure 10c which shows a drop in the number of large peaks in the polished sample 315; the distribution of the unpolished sample having a mean height around 60nm is much broader than the polished sample 315 having a narrower distribution with a mean height distribution of approximately 60nm.

Results of Second Polishing Trial

Figures 11 a and 1 1 b are images of a TEC15 sample (without a silica overcoat) before and after polishing for 1 min with a medium brush hardness (V3106) and using a slurry. Each image was captured using a specimen tilt of 80°.

Figure 1 1a shows the rounded peaks of the coating crystals 317 before polishing. In Figure 1 1 b, after polishing with the medium brush type, the surface is shown to have been smoothed 319. This is represented most clearly in Figure 1 1 c which illustrates the shift in height distribution between the unpolished sample 321 and the polished sample 323 indicating that polishing has removed the larger peaks from the coating surface.

Figures 12a and 12b are images of a TEC15+silica overcoat before and after polishing for 1 min respectively. Each image was captured using a specimen tilt of 80°. Figure 12a shows the plurality of rounded peaks of the silica overcoat crystals 325 before polishing. In Figure 12b, after polishing with the medium brush (V3106) type, the larger of the rounded peaks appear smoother 327. Figure 12c shows a shift in the distribution of large peaks from the unpolished sample 329 to the polished sample 331. The distribution of the polished sample 329 is narrow, indicating that the polishing process has removed a portion of the larger coating crystals. Figure 12c can be compared to Figure 10c as both have the same coating stack. It is clear that polishing with the medium brush results in a much narrower size distribution with the sample height mean of the polished sample being approximately 20nm less using the medium brush as that produced using the standard brush type.

Results of Third Polishing Trial

Figures 13a-e relate to TEC15+silica overcoat before polishing for 1 min with the hard (V3109) type brush with slurry. Figure 13a shows an SEM image captured using a specimen tilt of 80°. The figure shows a plurality of rounded peaks of the silica overcoat crystals 333. Although the silica overcoat has modified the TEC surface, there is still a significant variation of depth in the surface of this unpolished sample.

Figures 13b-e were taken at 90° specimen tilt. Two images from each region were captured; the first image in each group of two was captured using the secondary electron (SE) detector (which shows topography); the second image in each group showed the same region captured using the back-scattered electron (BSE) detector (which shows average atomic number differences). The 90° tilt images showed that the coating stack of the unpolished sample was 437 - 445nm thick. The BSE images of the unpolished specimen (Figures 13c and 13e) did not show any regions where the peak of a large TEC coating crystal was at the surface. The silica layer was a more consistent thickness at typically 31 - 39nm but there were some larger TEC crystals with a thinner silica overcoat layer of 16 - 23nm thickness.

Figures 14a-e relate to TEC15+silica overcoat after polishing for 1 min with the hard (V3109) type brush with slurry. Figure 14a shows the flattened peaks of the coating crystals 335 of the polished sample. There was very little variation of depth in the surface of the sample. This polished coating stack was 410 - 413nm thick. Therefore, the polishing process had removed approximately 24 - 35nm from the total stack.

The black arrows in the BSE images of the polished sample (Figures 14c and 14e) showed regions where the peak of a larger TEC coating crystal was at the surface (no silica overlayer), in other regions there was a thin layer of silica over the TEC material ranging from 12nm thick or less in some regions up to 66nm thick in a "valley".

Figure 14f shows the shift in height distribution between the unpolished sample 333 versus polished samples using hard brush types V3107 (reference 335) and V3109 (reference 337). This figure can be compared with corresponding polished silica samples of Figures 10c and 13c. It is clear that polishing using the "hard" brush type of Third Trial results in a much narrower size distribution and a mean height much smaller than that achieved using the standard and medium brushes. Further, the data shows that there was a much larger variation of depth in the surface of the unpolished sample compared to the polished sample. Additionally, the polishing process had removed approximately a 24nm - 35nm thickness of material from the polished sample. The SEMs show a silica layer remains over at least part of the exposed surface. It was noted that the silica layer at the surface of the polished sample varied greatly in thickness generally from 12nm or less up to 23nm. However it was at zero where the peak of a large TEC coating crystal was at the surface and up to 66nm thick in a "valley". The silica layer on the unpolished sample had a more consistent thickness at 31 nm - 39nm but there were some regions with larger TEC coating crystals where the silica layer was 16nm - 23nm thick.

The results show the surprising finding that it is easier to polish a silica overcoat sample than a non-silica overcoat sample. "Easier" generally means that polishing provides a smoother surface for silica overcoat products than for non-silica overcoat products (for identical polishing methods and polishing times); polishing times can be reduced for silica overcoat products than non-silica overcoat products (to achieve a desired level of planarisation); moderate amounts of polishing can provide significant planarisation without the complete removal of the silica overcoat (ie. a significant amount of planarised silica overcoat remains after moderate polishing).

It has been surprisingly found that a silica overcoat layer can be polished without completely polishing away said layer. The invention highlights that there may be advantages in polishing silica overcoat products when compared to non-silica overcoat products. Further, polishing can improve weathering performance and/or corrosion resistance, especially in the case of silica overcoat products that might previously be more prone to attack than non-silica overcoat products. The invention is not limited to automotive laminated glazing and would be equally applicable to monolithic glazing including glazing for architectural purposes. For example, the glazing may be a double glazed unit.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. A coated glazing comprising at least one substrate and a coating, the coating comprising a first coating layer, and a silica overcoat layer, the silica overcoat layer forming at least a part of an exposed surface of the glazing, wherein the silica overcoat layer is polished such that said layer has an arithmetical mean surface roughness, Sa, of less than 15nm.

2. A coated glazing as claimed in claim 1 , wherein the silica overcoat layer is polished such that said layer has an arithmetical mean surface roughness, Sa, of less than 5nm.

3. A coated glazing as claimed in claim 1 or 2, wherein the polished silica overcoat layer forms substantially the whole of the exposed surface of the glazing.

4. A coated glazing as claimed in any one of the preceding claims, wherein the silica overcoat layer has a geometric thickness of between substantially 5nm and 200nm.

5. A coated glazing as claimed in claim 4, wherein the silica overcoat layer has a geometric thickness of between 25nm and 35nm.

6. A coated glazing as claimed in any one of the preceding claims, wherein the first coating layer is a low emissivity layer.

7. A coated glazing as claimed in claim 6, wherein the low emissivity layer comprises a doped tin oxide, preferably, fluorine doped tin oxide (Sn0₂:F).

8. A coated glazing as claimed in any one of the preceding claims wherein the silica overcoat layer is deposited directly over the low emissivity layer.

9. A coated glazing as claimed in any one of the preceding claims, wherein the low emissivity layer has a geometric thickness of between substantially 50nm and 1 μηι.

10. A coated glazing as claimed in claim 9, wherein the low emissivity layer has a geometric thickness of approximately 350nm.

1 1. A coated glazing as claimed in claim 9, wherein the low emissivity layer has a geometric thickness of approximately 800nm

12. A coated glazing as claimed in any one of the preceding claims, wherein a colour suppression coating is provided on the substrate.

13. A method of manufacturing a polished, coated glazing comprising the following steps:

(a) Providing a substrate;

(c) Directly or indirectly depositing a silica overcoat layer on the low emissivity layer such that said silica overcoat layer forms at least part of an exposed surface of the glazing;

14. A method as claimed in claim 13 wherein less than 200nm of silica is deposited in step (c).

15. A method as claimed in any claim 13 or 14, wherein step (b) and preferably step (c) are carried out using a chemical vapour deposition process (CVD).

16. A method as claimed in any one of claims 13 to 15, wherein step (d) takes place remote from steps (b) and/or (c).

17. A method as claimed in any one of claims 13 to 16, wherein when the coated glazing is a vehicle glazing, the polishing step (d) occurs before the glazing has been through a bending step.

18. A method as claimed in any one of claims 13 to 17, wherein the silica overcoat layer forms substantially the whole of the exposed surface of the glazing.

19. A method as claimed in any one of claims 13 to 18, wherein the polishing step (d) uses a liquid polishing medium having an abrasive suspension of alumina.

20. A method as claimed in any one of claims 13 to 19, wherein the silica overcoat layer is polished for less than approximately 2 minutes.

21. A laminated glazing comprising at least a first ply and a second ply with an interlayer therebetween, the first ply having a coating deposited thereon, the coating comprising a first coating layer, and a silica overcoat layer, the silica overcoat layer forming at least a part of an exposed surface of the glazing, wherein the silica overcoat layer is polished such that said layer has an arithmetical mean surface roughness, Sa, of less than 15nm.

22. A laminated glazing as claimed in claim 21 wherein the first coating layer is a low emissivity layer, preferably a fluorine doped tin oxide layer.

23. A laminated glazing as claimed in claims 21 or 22, wherein the coating is provided on surface #4 of the glazing.

24. A laminated glazing as claimed in any one claims 21 to 23, wherein the glazing is a laminated vehicle glazing.

25. An insulated glazed unit comprising at least a first and a second substrate, and a coating, the coating comprising a first coating layer, and a silica overcoat layer, the silica overcoat layer forming at least part of an exposed surface of the or each said substrate, wherein the silica overcoat layer is polished such that said layer has an arithmetical mean surface roughness, Sa, of less than 15nm.

26. A coated glazing comprising at least one substrate and a coating deposited directly on top of the substrate such that the coating forms at least a part of an exposed surface of the glazing, wherein the coating consists of a polished silica layer having an arithmetical mean surface roughness, Sa, of less than 15nm.

27. A glazing as claimed in any one of the preceding claims, wherein the at least one substrate is a ply of glass, preferably having greater than 70% visible light transmission (measured with llluminant A).

28. A glazing substantially as hereinbefore described with reference to any one of the accompanying drawings.