TOUGHENABLE COATED SUBSTRATE

Abstract

The present invention relates to a toughenable coated float glass substrate, a method of preparing same and the use thereof, said float glass substrate comprising a first surface and a second surface, wherein the first surface comprises one or more layers applied by chemical vapour deposition (CVD) and the second surface comprises one or more layers applied by physical vapour deposition (PVD); and wherein said one or more layers applied by physical vapour deposition (PVD) includes at least one functional metal layer; and wherein the second surface further comprises a protective layer applied in direct contact with the second surface; and wherein the coated float glass substrate exhibits a transmission b* colour value according to the CIE colour space of less than or equal to 3 and an external reflection b* of less than or equal to −5.

Claims

1.-23. (canceled)

24. A toughenable coated float glass substrate, said float glass substrate comprising: i) a first surface; and ii) a second surface, wherein the first surface comprises one or more layers applied by chemical vapour deposition (CVD) and the second surface comprises one or more layers applied by physical vapour deposition (PVD); and wherein said one or more layers applied by physical vapour deposition (PVD) includes at least one functional metal layer; and wherein the second surface further comprises a protective layer applied in direct contact with the second surface; and wherein the coated float glass substrate exhibits a transmission b* colour value according to the CIE colour space of less than or equal to 3 and an external reflection b* of less than or equal to −5.

25. The toughenable coated substrate according to claim 24, wherein the protective layer comprises a layer of silicon oxide (SiOx), wherein x is in the range 1.5 to 2.0.

26. The toughenable coated substrate according to claim 24, wherein according to the CIE colour space b* and a* are negative with respect to external reflection.

27. The toughenable coated substrate according to claim 24, wherein the protective layer is applied by physical vapour deposition (PVD).

28. The toughenable coated substrate according to claim 24, wherein the thickness of the protective layer is in the range 10 to 100 nm.

29. The toughenable coated substrate according to claim 24, wherein the thickness of the protective layer is in the range 30 to 70 nm.

30. The toughenable coated substrate according to claim 24, wherein the second surface of the float glass contacted molten tin during manufacture and wherein the first surface of the float glass contacted a bath atmosphere comprising nitrogen and hydrogen during manufacture.

31. The toughenable coated substrate according to claim 24, wherein the one or more layers applied by chemical vapour deposition (CVD) to the first surface of the glass substrate comprise one or more doped or undoped oxide layers selected from: silicon oxide (SiO.sub.2), tin oxide (SnO.sub.2), fluorine doped tin oxide (SnO.sub.2:F), titanium oxide (TiO.sub.2) and antimony doped tin oxide (SnO.sub.2:Sb).

32. The toughenable coated substrate according to claim 24, wherein the functional metal layer comprises silver.

33. The toughenable coated substrate according to claim 24, wherein the change in colour for transmission after heat treatment (ΔE*) for the coated substrate is less than or equal to 10.

34. The toughenable coated substrate according to claim 24, wherein the change in colour for reflection after heat treatment (ΔE*) for each side of the coated substrate is less than or equal to 10.

35. The toughenable coated substrate according to claim 24, wherein the said one or more layers applied by physical vapour deposition (PVD) includes at least one absorbing layer based on Ti, V, Cr, Fe, or W, Ni Nb, and alloys thereof and nitrides.

36. The toughenable coated substrate according to claim 35, wherein the at least one absorbing layer comprises tungsten (W), preferably tungsten nitride.

37. The process for preparing a dual coated toughenable float glass substrate according to claim 24, comprising the steps of: i) providing a float glass substrate with a first surface and a second surface, wherein the second surface of the glass substrates contacts molten tin during manufacture and the first surface contacts a bath atmosphere comprising nitrogen and hydrogen during manufacture; ii) depositing by chemical vapour deposition (CVD) one or more layers on the first surface of the substrate; iii) depositing by physical vapour deposition (PVD) one or more layers on the second surface of the substrate; iv) depositing by physical vapour deposition (PVD), a protective layer directly on the glass substrate prior to depositing the one or more layers on the second surface, wherein the protective layer comprises a thickness of between 10 nm and 100 nm; and v) heat treating the coated glass substrate to toughen the glass without degrading the one or more layers deposited on each side of the substrate.

38. The process according to claim 37, wherein the protective layer comprises a layer of silicon oxide (SiOx), wherein x is between 1.5 and 2.0.

39. The process according to claim 37, wherein the one or more layers deposited by physical vapour deposition (PVD) on the second surface of the substrate comprises a functional metal layer.

40. The process according to claim 39, wherein the functional metal layer comprises silver.

41. The process according to claim 37, wherein the protective layer is deposited to a thickness in the range of 30 nm and 70 nm.

42. The process according to claim 37, wherein the one or more layers applied by chemical vapour deposition (CVD) to the first surface of the substrate comprise one or more layers selected from: silicon oxide (SiO.sub.2), tin oxide (SnO.sub.2), fluorine doped tin oxide (SnO.sub.2:F), titanium oxide (TiO.sub.2) and antimony doped tin oxide (SnO.sub.2:Sb).

43. The process according to claim 37, wherein the physical vapour deposition (PVD) layer applied to the second surface of the substrate is applied after application of the one or more layers on the first surface of the substrate.

Description

EXPERIMENTAL

[0140] A series of experiments were conducted to assess the impact of providing a silicon oxide (SiO.sub.x) underlayer to the uncoated tin side of a sheet of float glass. After the silicon oxide layer had been applied to the ‘tin’ side of the float glass substrate, additional coating layers were applied atop the silicon oxide layer, the additional coating layers included at least one silver-based layer. In addition, the ‘air’ side of the float glass sheet was coated with a series of coating layers also.

Experiment 1—Comparison of Results for Glass Substrates Coated with a Silver-Based Low-Emissivity Coating in the Presence and Absence of a Silicon Oxide (SiO.SUB.2.) Undercoat Layer Applied to the Tin Side of the Glass Substrate

[0141] A silicon oxide (SiOx) undercoat layer was deposited onto the tin side of a float glass substrate prior to deposition of a series of coating layers (referred to as a stack); the coating layers including at least one silver based low-emissivity coating. The series of layers are identified in Table 1.

[0142] The silicon oxide (SiOx) layer and the additional coating layers were deposited on a 6 mm thick standard float glass pane with a light transmittance in the region of 88% using, single or dual magnetrons equipped with MF-AC and/or DC (or pulsed DC) power supplies.

[0143] In Table 1 the materials are listed along with the geometrical thickness of each layer in nanometres in brackets. The coating layers are obtained as follows:

[0144] Layers of an oxide of zinc (Zn) and tin (Sn) were reactively sputtered from zinc-tin targets (weight ratio Zn:Sn approximately 50:50) in an argon/oxygen (Ar/O.sub.2) sputter atmosphere.

[0145] Layers of titanium oxide (TiO.sub.x) layers were deposited from metallic titanium (Ti) targets in an argon/oxygen (Ar/O.sub.2) sputter atmosphere.

[0146] The ZnOx layers were sputtered from Al-doped Zn targets (aluminium (Al) content about 2 weight %) in an Ar/O.sub.2 sputter atmosphere.

[0147] The functional layers of essentially pure silver (Ag) were sputtered from silver targets in an Ar sputter atmosphere without any added oxygen and at a partial pressure of residual oxygen below 10.sup.−5 mbar.

[0148] The layers of silicon nitride (SiN.sub.x) were reactively sputtered from mixed Si.sub.90Al.sub.10 targets in an Argon/Nitrogen (Ar/N.sub.2) sputter atmosphere containing only residual oxygen.

[0149] The layers of silicon oxide (SiOx) were sputtered from mixed Si.sub.90Al.sub.10 targets in an Argon/Oxygen (Ar/O.sub.2).

[0150] The layers of AlN were reactively sputtered from an Al target in an Argon/Nitrogen (Ar/N.sub.2) sputter atmosphere containing only residual oxygen.

[0151] The layers of ZAO were sputtered from a ceramic ZnO:Al target (with an aluminium (Al) content in the region of 10 weight %) in an Ar/O.sub.2 sputtering atmosphere.

[0152] The layers of NiCrOx were sputtered reactively from Nickel-Chromium alloy targets (with approximately 80 weight % nickel (Ni) and 20 weight % chromium (Cr)) in and Ar/O.sub.2 sputtering atmosphere.

[0153] The layers of WNx were sputtered reactively from metallic W targets in an Ar/N.sub.2 sputtering atmosphere.

[0154] The coating stack layers were deposited using standard process conditions.

TABLE-US-00001 TABLE 1 results for silver based low emissivity coating stacks applied to float glass sheets in the presence and absence of a silicon oxide SiO.sub.2 underlayer. Comparative Comparative Example 1, Example 2 silver based Example 1 silver based Example 2 coating stack silver based coating stack Silver based (1) with coating stack (2) with coating stack no SiO.sub.2 (1) plus SiOx no SiO.sub.2 (2) plus SiOx underlayer underlayer underlayer underlayer Glass Glass Glass Glass — SiOx (30) — SiOx (30) SiNx (25.5) SiNx (25.5) SiNx (18) SiNx (18.0) ZnSnOx ZnSnOx (3.5) ZnSnOx (13) ZnSnOx (3.5) (13.0) TiOx (2.5) TiOx (2.5) — — ZnOx (5) ZnOx (5) ZnOx (3) ZnOx (3) Ag (14.3) Ag (14.3) Ag (8.6) Ag (8.6) ZAO (2) ZAO (2) NiCrOx (1) NiCrOx (1) ZnSnOx (2) ZnSnOx (2) — — ZAO (4) ZAO (4) ZAO (7) ZAO (7) AlNx (6) AlNx (6) AlNx (50.5) AlNx (50.5) WNx (2.1) WNx (2.1) — — AlNx (25.5) AlNx (25.5) — — ZnSnOx (7) ZnSnOx (7) ZnSnOx (11) ZnSnOx (11) — — ZnOx (13) ZnOx (13) — — Ag (17.3) Ag (17.3) — — NiCrOx (1) NiCrOx (1) — — ZAO (4) ZAO (4) — — AlNx (21.5) AlNx (21.5) — — ZnSnOx (7) ZnSnOx (7) T.sub.L AD 58.5 60.6 63.2 61.9 ΔT.sub.L 1.2 1.4 7.6 7.6 Rs AD 2.86 2.97 1.92 2.01 (ohm/sq) Rs HT 2.04 2.02 1.28 1.33 (ohm/sq) ΔRs −0.82 −0.95 −0.64 −0.68 (ohm/sq) T ΔE* 1.0 1.0 4.4 4.2 Oil-rub 0 0 0 0 Hazescan 79 42 76 46 R.sub.Film 8.8 8.7 11.7 12.3 R.sub.Glass 23.2 22.3 15.4 16.4 ΔR.sub.Film 0.8 1.1 2.5 2.5 ΔR.sub.Glass 0.2 0.0 0.3 0.2

[0155] Tables 1, 2a, 2b and 3 provide details of the layer sequences for comparative coated glass panes and coated glass panes according to the present invention along with the results of each stack tested for:

[0156] haze scan, oil rub test value, T.sub.L%—percentage (%) light transmittance value for the glass substrate before heat treatment, ΔT.sub.L—the change in percentage (%) light transmittance upon heat treatment, Rs AD—sheet resistance before heat treatment,

[0157] Rs HT—sheet resistance after heat treatment, Δ Rs (ohm/square)—change is heat resistance, and T ΔE*—which is a measure of the change in transmitted colour upon heat treatment.

[0158] The methodology used to collect the data in Tables 1, 2a, 2b and 3 is set out below. For each example, the layers were deposited on to a glass pane in the sequence shown starting with the layer at the top of each column.

[0159] Oil rub test—an oil rub test serves to simulate the influence of cutting oils used for cutting glass panes on the mechanical robustness of a coating. Coated glass panes that do not withstand an oil rub test are difficult to process and are unsuitable for most practical applications. The coated samples defined in Table 1 (and 2) were rubbed using a felt pad with an area 1.2×1.2 cm soaked in microscope oil of refractive index 1.52 (1.515 to 1.517). The samples are subjected to 500 cycles with a 1,000 g load at a speed of 37 cycles per minute. The oil rubbed samples were then evaluated using an internal evaluation system on a perfectness scale of 0 (perfect, no damage) to 9 (part of coating stack completely removed). A score of 6 or less is preferred.

[0160] Heat treatability tests—immediately after deposition of the coatings to the glass substrate in each example in Tables 1, 2a, 2b and 3, the coating stack parameters (such as sheet resistance (Rs), light transmittance (T.sub.L), haze scan, and colour co-ordinates were measured for each coated glass substrate. The coated glass substrates were then heat treated in the region of 650° C. for 5 minutes 30 seconds. Thereafter, the haze scan value, sheet resistance (Rs), percentage light transmittance and reflectance of both surfaces (T.sub.L, R.sub.Film, R.sub.Glass) and colour coordinates were again measured and the change in light transmittance and reflectance from both sides (ΔT.sub.L, ΔR.sub.Film, ΔR.sub.Glass), and the change in colour upon heat treatment (ΔE*), calculated therefrom.

[0161] The values stated for the change in percentage (%) light transmittance and reflectance upon heat treatment of the coated glass pane Examples in Tables 1 and 3 were derived from measurements according to EN 410, the details of which are incorporated herein by reference.

[0162] Sheet Resistance/Change in sheet resistance for examples—sheet resistance measurements were made using a NAGY SRM-12. This device utilises an inductor to generate eddy currents in a 100 mm×100 mm coated sample. This produces a measurable magnetic field, the magnitude of which is related to the resistivity of the sample. With this method the sheet resistance can be calculated. The instrument was used to measure the sheet resistance of samples before and after heat treatment at 650° C. for 5 minutes, 30 seconds.

[0163] Colour characteristics—the colour characteristics for each of sample 1 to 14 were measured and reported using the well-established CIE LAB L*, a*, b* coordinates (as described for example in paragraphs [0030] and [0031] of WO 2004/063111A1, incorporated herein by reference). The change in transmission colour upon heat treatment, T ΔE*=((Δa*).sup.2+(Δb*).sup.2+(ΔL*).sup.2).sup.1/2, wherein ΔL*, Δa* and Δb* are the differences of the colour values L*, a*, b* of the coated glass pane each before and after a heat treatment. ΔE* values of less than 3 (for example 2 or 2.5) are preferred for layer sequences with one silver-based functional layer, representing a low and practically non-noticeable colour modification caused by the heat treatment. For layer sequences comprising two or more silver-based functional layer, lower T ΔE* values provide an indication of the stability of the sequences; the lower the T ΔE* values the more superior the results and appearance of the coated glass pane.

[0164] Haze scan—A haze scoring system was applied to each example. The quality assessment evaluation system described hereinafter was also used to more clearly distinguish the visual quality of coatings under bright light conditions; properties that are not fully reflected by standard haze values measured in accordance with ASTM D 1003-61.

[0165] The evaluation system considers the more macroscopic effect of visible faults in the coating which cause local colour variations where the coating is damaged or imperfect (haze scan in Table 1). This assessment analyses the light levels in images of heat-treated samples taken using fixed lighting conditions and geometries.

[0166] To generate the images used to calculate haze scan values, samples are placed inside a black box, 30 cm away from the camera lens. Samples are illuminated using a standard 1200 lumen light with a brightness between 2400 and 2800 Lux, as measured at the samples position. The sample is then photographed using a standard aperture size and exposure length. The greyscale of each pixel in the resulting image is then recorded, with a value of 0 representing black and 255 representing white. Statistical analysis of these values is undertaken to give an overall assessment of the haze of the sample, referred to herein as the haze scan value. The lower the haze scan value recorded, the more superior the results.

Experiment 2a and 2b—Comparison of Glass Substrates Coated with a Silver Based Low-Emissivity coating in the Presence of Varying Thicknesses of a Silicon Oxide (SiO.SUB.2.) Undercoat Layer

[0167] In experiments 2a and 2b, various thicknesses of a layer of silicon oxide (SiOx) undercoat layer were deposited on a float glass substrate prior to deposition of each of the silver based low-emissivity coating stacks detailed in Table 1 for examples 1 and 2. That is, the silicon oxide undercoat layer was applied to the tin side of a float glass substrate before deposition of the silver based low-emissivity coating stack of example 1 listed in Table 1.

[0168] The silicon oxide (SiOx) layers were deposited on the tin side of a series of 6mm float glass substrates at thicknesses of 7.5 mm (example 1 only), 15 nm, 30 nm and 60 nm.

[0169] Tables 2a and 2b include details of the haze scan results and mean distribution values for the silver based low-emissivity coatings detailed in examples 1 and 2 in Table 1 respectively, applied to float glass sheets in the presence of varying thickness of SiO.sub.2 underlayer.

TABLE-US-00002 TABLE 2a Haze scan Example Example details values 4 6 mm float glass with no SiO.sub.2 coating layer 79 and a Ag based low-emissivity coating of comparative example 1 on the glass tin side 5 6 mm float glass with 7.5 nm SiO.sub.2 coating 63 layer on glass tin side followed by the deposition of the Ag based low-emissivity coating of example 1 also on the glass tin side 6 6 mm float glass with 15 nm SiO.sub.2 coating 50 layer on glass tin side followed by the deposition of the Ag based low-emissivity coating of example 1 also on the glass tin side 7 6 mm float glass with 30 nm SiO.sub.2 coating 42 layer on glass tin side followed by the deposition of the Ag based low-emissivity coating of example 1 also on the glass tin side 8 6 mm float glass with 60 nm SiO.sub.2 coating 40 layer on glass tin side followed by the deposition of the Ag based low-emissivity coating of example 1 also on the glass tin side

[0170] In each of examples 4 to 8 a pyrolytic silica/titania based coating was applied to the glass air side.

TABLE-US-00003 TABLE 2b Haze scan Example Example details values 3 6 mm float glass with no coating on glass tin side 19.2 and a pyrolytic silica/titania based coating on the glass air side 9 6 mm float glass with no SiO.sub.2 coating layer on the 75.6 glass tin side and with the Ag based low-emissivity coating of comparative example 2 deposited on the glass tin side 10 6 mm float glass with 15 nm SiO.sub.2 coating layer on 61.0 glass tin side followed by the deposition of the Ag based low-emissivity coating of example 2 also on the glass tin side 11 6 mm float glass with 30 nm SiO.sub.2 coating layer on 45.6 glass tin side followed by the deposition of the Ag based low-emissivity coating of example 2 also on the glass tin side 12 6 mm float glass with 60 nm SiO.sub.2 coating layer on 47.0 glass tin side followed by the deposition of the Ag based low-emissivity coating of example 2 also on the glass tin side

[0171] In each of examples 9 to 12 a pyrolytic silica/titania based coating was applied to the glass air side.

[0172] As can be seen from Tables 2a and 2b, improved haze scan results were obtained when the silicon oxide (SiO2) layer was applied to the float glass substrate in a thickness range of 30 to 60 nm. The haze scan measurements were recorded as described above in which a haze scoring system is applied to each of the examples in Tables 2a and 2b using a photographic methodology which analyses an image taken of each sample and then expresses the observed data as a “mean haze” value.

[0173] Photographs demonstrating the benefit of including a silicon oxide (SiOx) underlayer are provided in FIGS. 1 and 2.

Experiment 3—Comparison of a Float Glass Substrate Coated with a Silicon Oxide (SiO.SUB.2.) Underlayer and a Silicon Nitride-Based Layer Versus Float Glass Substrates Coated with a Silicon Nitride Base Layer Only

[0174] A further advantage related to the use of silicon oxide underlayer (SiOx) as a protective coating layer applied to the tin side of a float glass substrate and located between the glass substrate and further layers including at least one sputter deposited metal layer is that, the refractive index of the silicon oxide (SiOx) underlayer (1.54) is very close to that of the glass substrate (1.51). Consequently, the required optical properties provided by for example a subsequent low-emissivity and solar control coating is largely maintained with only small changes to the appearance of the coated glass pane being observed. This is illustrated by a comparison of a coating with variants of the same coating including either 50 nm of SiOx as a protective layer (Example 14) and also, the same coating whereby the base SiNx layer thickness is increased by 50 nm (Example 15). Details of the layer sequences are provided in Table 3.

TABLE-US-00004 TABLE 3 Example 14 Comparative Stack with Example 13 SiNx base Example 15 Stack with layer and Stack with SiNx base 50 nm SiOx thicker layer only underlayer SiNx layer Air side CVD coating CVD coating CVD coating Glass Glass Glass Tin Side — SiOx (50) — SiNx (18) SiNx (18) SiNx (68) ZnSnOx (13) ZnSnOx (13) ZnSnOx (13) ZnOx (3) ZnOx (3) ZnOx (3) Ag (8.6) Ag (8.6) Ag (8.6) NiCrOx (1) NiCrOx (1) NiCrOx (1) ZAO (7) ZAO (7) ZAO (7) AlNx (51) AlNx (51) AlNx (51) ZnSnOx (11) ZnSnOx (11) ZnSnOx (11) ZnOx (13) ZnOx (13) ZnOx (13) Ag (17.3) Ag (17.3) Ag (17.3) NiCrOx (1) NiCrOx (1) NiCrOx (1) ZAO (4) ZAO (4) ZAO (4) AlNx (22) AlNx (22) AlNx (22) ZnSnOx (7) ZnSnOx (7) ZnSnOx (7) T.sub.L 63.7 63.2 59.7 ΔT.sub.L 8.3 7.3 8.8 T ΔE* 4.7 4.5 5.5 R.sub.Film 13.4 14.5 16.8 R.sub.Glass 15.8 16.8 21.5 ΔR.sub.Film 3.3 2.2 1.5 ΔR.sub.Glass 0.2 1.0 −1.2

[0175] A comparison of the CIE L*, a* and b* values measured for examples 13, 14 and 15 described in Table 3 with a pyrolytic (CVD) coating on the ‘air’ side of the float glass substrate and a low-emissivity coating deposited on the tin side, both before and following heat treatment at 650° C. for 5 minutes, are provided in Tables 4 and 5.

[0176] That is, the change in transmission colour upon heat treatment was measured, T ΔE*=((Δa*).sup.2+(Δb*).sup.2+(ΔL*).sup.2).sup.1/2, wherein ΔL*, Δa* and Δb* are the differences of the colour values L*, a*, b* of the coated glass pane each before and after a heat treatment. ΔE* values of less than 3 (for example 2 or 2.5) are preferred for layer sequences with one silver-based functional layer, representing a low and practically non-noticeable colour modification caused by the heat treatment. For layer sequences comprising two or more silver-based functional layer, lower T ΔE* values provide an indication of the stability of the sequences; the lower the T ΔE* values the more superior the results and appearance of the coated glass pane.

[0177] From Tables 4 and 5 it can be seen that in relation to Example 14, it is possible to obtain toughening of a coated substrate according to the present invention whilst achieving acceptable colour changes after heat treatment. In contrast, comparative Example 15, is not as resilient to toughening and the increased thickness of the SiNx layer leads to unacceptable yellowing of the coating in relation to the colour of the coated glass substrate when viewed in transmission.

[0178] Tables 6 and 7 illustrate the difference in the CIE L*, a* and b* values measured for each side of float glass Examples 14 and 15 described above, compared with the values recorded for comparative example 13, which has no modification to the layer thicknesses and has no SiOx protection layer present.

[0179] In addition, it can be seen from Tables 6 and 7 that whilst the presence of a SiN.sub.3 layer offers some improvement in the imperfections observed when the stack of Example 15 is deposited on the tin side of a float glass substrate and heat treated, using such a coating layer, especially when a thicker layer is deposited, results in a change to the observed colour of the float glass both before and after heat treatment, rendering a glass substrate coated with such a layer undesirable in terms of colour and aesthetic appearance.

TABLE-US-00005 TABLE 4 provides the colour measurements recorded for the coatings of Examples 13, 14 and 15 before heat treatment. MEASUREMENTS FOR COATED FLOAT GLASS AS DEPOSITED (BEFORE HEAT TREATMENT) Transmission ‘Tin’ Side Reflection ‘Air’ Side Reflection Y L* a* b* Y L* a* b* Y L* a* b* Comparative Side 1 - CVD coating 63.67 83.79 −6.18 1.13 13.41 43.37 6.94 −4.37 15.75 46.65 1.17 −14.59 Example 13 on air side Side 2 - coating of c.example 13 on tin side Example 14 Side 1 - CVD coating 63.20 83.55 −5.80 0.08 14.52 44.96 6.57 −0.60 16.78 47.98 −0.51 −11.29 on air side Side 2 - coating of example 14 on tin side Comparative Side 1 - CVD coating 59.69 81.67 −3.00 10.11 16.83 48.04 −14.01 −16.37 21.45 53.44 −6.98 −24.08 Example 15 on air side Side 2 - coating of c.example 15 on tin side

TABLE-US-00006 TABLE 5 provides the colour measurements recorded for the coatings of Examples 13, 14 and 15 after heat treatment. MEASUREMENTS FOR COATED GLASS AS DEPOSITED (AFTER HEAT TREATMENT) Transmission ‘Tin’ Side Reflection ‘Air’ Side Reflection Y L* a* b* Y L* a* b* Y L* a* b* Comparative Side 1 - CVD coating 71.96 87.95 −5.11 2.92 15.05 45.7 5.91 −5.96 15.96 46.92 2.91 −12.49 Example 13 on air side Side 2 - coating of c.example 13 on tin side Example 14 Side 1 - CVD coating 70.51 87.24 −4.52 2.29 16.65 47.82 4.64 −2.84 17.79 49.24 1.07 −9.30 on air side Side 2 - coating of example 14 on tin side Comparative Side 1 - CVD coating 68.50 86.26 −1.77 12.93 18.26 49.81 −8.80 −21.18 20.26 52.13 −5.25 −25.11 Example 15 on air side Side 2 - coating of c.example 15 on tin side

TABLE-US-00007 TABLE 6 Difference in colour to comparative Example 13 before heat treatment. Transmission ‘Tin’ Side Reflection ‘Air’ Side Reflection Y L* a* b* Y L* a* b* Y L* a* b* Example 14 Side 1, CVD coating −0.47 −0.24 0.38 −1.05 1.11 1.59 −0.37 3.77 1.03 1.33 −1.68 3.30 on air side Side 2, coating of example 14 on tin side Comparative Side 1, CVD coating −12.27 −6.28 2.11 7.19 3.42 4.67 −20.95 −12.00 5.70 6.79 −8.15 −9.49 Example 15 on air side Side 2, coating of example 15 on tin side

TABLE-US-00008 TABLE 7 Difference in colour to comparative Example 13 after heat treatment. Transmission ‘Tin’ Side Reflection ‘Air’ Side Reflection Y L* a* b* Y L* a* b* Y L* a* b* Example 14 Side 1, CVD coating −1.45 −0.71 0.59 −0.63 1.60 2.12 −1.27 3.12 1.83 2.32 −1.84 3.19 on air side Side 2, coating of example 14 on tin side Comparative Side 1, CVD coating 4.83 2.47 4.41 11.8 3.21 4.11 −14.71 −15.22 4.30 5.21 −8.16 −12.62 Example 15 on air side Side 2, coating of example 15 on tin side

TABLE-US-00009 TABLE 8 Summary of the changes in CIE lab measurements recorded for Example 15, 16 and 17 after heat treatment. Transmission ‘Tin’ Side Reflection ‘Air’ Side Reflection ΔL* Δa* Δb* ΔE* ΔL* Δa* Δb* ΔE* ΔL* Δa* Δb* ΔE* Comparative Tin side 4.16 1.07 1.79 4.65 2.33 −1.03 −1.59 3.00 0.27 1.74 2.1 2.74 Example 15 Example 16 Tin side 3.69 1.28 2.21 4.49 2.86 −1.93 −2.24 4.11 1.26 1.58 1.99 2.84 Comparative Tin side 4.59 1.23 2.82 5.53 1.77 5.21 −4.81 7.31 −1.31 1.73 −1.03 2.40 Example 17

[0180] It can be seen from the results in Tables 6 and 7 that only a minor difference of 5 units or less is observed for the values of L*, a* or b* for comparative Example 13 compared with Example 14, with the additional layer of SiOx as a protection layer.

[0181] In contrast, a comparison of the values for L*, a* or b* for Example 14 compared with comparative Example 15, with a thicker base SiNx layer, revealed differences of up to 29.89 units.

[0182] An additional benefit highlighted by the results of Table 8 is that the change in the values of L*, a*, b* and ΔE for comparative Examples 13, 15 and Example 14 following heat treatment to 650° C. for 5 minutes, is very small for Example 14 with the SiOx protection layer. Additionally, the measured values for Example 14 were closer to those of Example 13 (the un-modified stack) in contrast to the values obtained for Example 15 (stack with a thicker SiNx layer).

[0183] For the results provided in summary Table 8, indicating the change in values observed for the coated glass substrates after heat treatment, changes in the recorded values for ΔE* for the transmission and reflection on the coated glass of less than 10 are preferred. Values observed for the coated glass substrates after heat treatment, changes in the recorded values for ΔE* for the transmission and reflection on the coated glass of less than 5 are highly preferred.

Experiment 4—Inclusion of a Visible Light Absorbing Layer

[0184] In another embodiment of the present invention, the inclusion of a visible light absorbing layer (for example Tungsten nitride, WNx) in the lower antireflection layer of the coating stack was investigated. It was found by the inventors that by including a visible light absorbing layer in the lower antireflection layer of the coating stack, that an additional benefit may be achieved, namely that of shifting the transmitted colour value to a substantially more negative b* value (that is, the value for blue colour in transmission) whilst maintaining negative b* values in reflection for both faces of the coated glass pane.

[0185] This is especially desirable when producing double sided coatings wherein the first coating applied for example by CVD comprises materials that are reflective in the blue region of the visible spectrum, since the CVD coating has the effect of increasing the resultant transmission b* value of the coated article and therefore providing the coated glass pane a yellowish appearance in transmission. That is, the inventors have found that it is possible to avoid the appearance of yellowing of the coating by adding a visible light absorbing layer such as tungsten nitride, WNx in the lower antireflection layer of the coating sequence.

[0186] Another benefit of the additional visible light absorbing layer is that the reflected colour on both faces of the coated pane are significantly blue in all cases that is the value of b* is −15 or lower. Even more beneficial is the fact that the reflected colours all display a negative value of a*.

[0187] A series of coatings were deposited onto the tin side of a float glass pane as described in Table 9, with a pyrolytic (CVD) coating on the air side of the float glass pane. The pyrolytic (CVD) coating is a silicon and titanium-based coating available under the tradename Pilkington Activ™. (examples 1 and 2 included for comparison) The beneficial effect on colour observed for the as deposited values are illustrated in Table 10 and the post heat treatment values in Table 11.

TABLE-US-00010 TABLE 9 Comparative Comparative Example Example Example Example 16 Example 17 23 24 25 Air side CVD CVD CVD CVD CVD coating coating coating coating coating Tin side Glass Glass Glass Glass Glass SiOx SiOx SiOx SiOx SiOx 60 60 50  60   60   SiNx SiNx SiNx SiNx SiNx 18 26 21  19.5  19.5  — — WNx WNx WNx — — 3 4.2 3.1 — — SiNx SiNx SiNx — — 19  16.5  11   ZnSnOx ZnSnOx ZnSnOx ZnSnOx ZnSnOx 13 13 13  13   13   ZnOx ZnOx ZnOx ZnOx ZnOx  3  3 5 3   3   Ag Ag Ag Ag Ag   8.6   7.6  12.9 9.4 8.9 NiCrOx NiCrOx NiCrOx NiCrOx NiCrOx  1   0.9 1 0.5 0.5 AZO AZO AZO AZO AZO  7  7 3 6   6   AlNx AlNx AlNx AlNx AlNx 51   50.1 24  15.5  15.5  ZnSnOx ZnSnOx ZnSnOx ZnSnOx ZnSnOx 11 11 11  11   11   ZnOx ZnOx ZnOx ZnOx ZnOx 13 16 5 8.5 8.5 Ag Ag Ag Ag Ag   17.3   16.7  11.9 11.2  11.8  NiCrOx NiCrOx NiCrOx NiCrOx NiCrOx  1  1 1 1   1   — WNx WNx WNx WNx — 16 3 6.5 4.2 AZO — AlNx AlNx AlNx  4 —  37.5 32   33.5  ZnSnOx ZnSnOx ZnSnOx ZnSnOx ZnSnOx  7  9 5 9   9  

TABLE-US-00011 TABLE 10 CIE LAB COLOUR MEASUREMENTS FOR EXAMPLES 16 TO 20 BEFORE HEAT TREATMENT Transmission ‘Tin’ Side Reflection ‘Air’ Side Reflection Y L a* b* Y L a* b* Y L a* b* Example 16 63.2 83.55 −5.80 0.08 14.52 44.96 6.57 −0.60 16.78 47.98 −0.51 −11.29 (comparative) Example 17 45.34 73.12 −3.61 0.88 19.48 51.24 −0.35 13.39 20.4 52.28 −4.39 −9.83 (comparative) Example 18 16.99 48.25 2.52 −9.65 10.68 39.04 −13.50 −9.90 23.16 55.24 −5.81 −18.47 Example 19 18.29 49.84 1.00 −7.62 6.85 31.44 −12.52 −15.63 20.35 52.23 −3.77 −21.24 Example 20 25.67 57.72 0.24 −2.67 11.42 40.28 −8.426 −14.74 19.50 51.27 −1.84 −19.23

TABLE-US-00012 TABLE 11 CIE LAB COLOUR MEASUREMENTS FOR EXAMPLES 16 TO 20 AFTER HEAT TREATMENT Transmission ‘Tin’ Side Reflection ‘Air’ Side Reflection Y L a* b* Y L a* b* Y L a* b* Example 16 70.51 87.24 −4.52 2.29 16.65 47.82 4.64 −2.84 17.79 49.24 1.07 −9.30 (comparative) Example 17 49.56 75.80 −2.45 1.57 20.25 52.12 −1.20 15.36 20.05 51.89 −3.30 −8.58 (comparative) Example 18 19.44 51.19 3.02 −10.6 13.99 44.22 −12.90 −7.09 23.89 55.98 −5.90 −19.01 Example 19 20.40 52.28 1.27 −7.6 8.12 34.21 −11.44 −15.01 20.28 52.14 −3.32 −22.45 Example 20 28.91 60.71 0.38 −2.51 13.45 43.43 −7.26 −13.41 19.71 51.5 −1.43 −19.92

[0188] It can be seen from the above discussion and results that a key advantage of the present invention is that it enables the production of glass sheets provided with a combination of chemical vapour deposition (CVD) and physical vapour deposition (PVD) or sputtered coating layers applied to opposing faces of float glass sheets which may be subsequently heat treated or toughened.

[0189] A further benefit provided by the present invention is that it maximises the advantages derived from both types of deposition methods applied to glass substrates. For instance, self-cleaning coatings deposited by for example CVD, may be applied to one side of the glass sheet, as these have been shown to display much higher levels of photoactivity than purely sputtered counterparts, whilst, silver-based low-emissivity (low-e) coating, which is known to have lower haze, sheet-resistance and greater selectivity for low-e/solar control purposes, may be deposited on the second side of the glass substrate, which has superior performance to a low-e coating deposited by CVD.

[0190] Whilst coated glass products do exist which take advantage of multiple technologies, in contrast to the present invention such products cannot be thermally tempered.

[0191] Also, even though products exist which do use multiple technologies to produce coatings and which may be toughened or annealed, the selectivity of such products is limited, and the performance of the products poor as the coatings do not include a silver layer.

[0192] By combining technologies in a single dual coated glass pane according to the present invention, in which sputtered coatings are deposited on the tin side of a float glass substrate (that is, the lower surface during formation and annealing of the float glass ribbon) and a CVD coating layers is deposited on the atmosphere (or air/gas) side of the float glass (upper surface during formation and annealing of the float glass ribbon inside the float bath), the present invention avoids the limitation of normal practice which is only to sputter deposit onto the atmosphere side of the glass substrate (as this side does not come into contact with rollers during the manufacture of the glass substrate and which may lead to marks and imperfections on the sputtered coatings), whilst maintaining high quality sputtered coatings,

[0193] The present invention therefore overcomes problems associated with the previous production of such products and which leads to damage of the sputtered coatings after thermal tempering or caused by contact with various types of rollers used in the float glass manufacturing process, particularly in the lehr, and which often only becomes apparent upon toughening, being demonstrated by an improvement in the hazescan values of at least 25%.

[0194] Alternative methods exist whereby a thermally toughened glass pane with for example a CVD coating present on one face and a sputtered, silver containing coating present on the second face of the substrate could be produced. One example of this is would be to thermally toughen cut-size plates of CVD coated glass and to subsequently deposit a silver based PVD coating onto the opposite face of the already cut to size and toughened glass however the disadvantages of such an approach are numerous and include inefficient utilisation of the PVD coating equipment, additional labour to manually load the cut-size plates onto the equipment and additional complexity to the supply chain increasing both cost and time taken to produce the toughened plate provided with a CVD coating on one surface and a silver based PVD coating on the opposite face.

[0195] A second alternative method of producing such an end-product could be to laminate together two toughened coated glass panes, one of which is provided with a CVD coating on one face and the other provided with a silver based PVD coating on one face. Such a laminated glass pane allows the processor to avoid deposition of a toughenable coating on the tin side of the glass substrate. However, this approach dramatically increases the cost to produce the final glass pane and requires the producer to hold stock of two separate products which must be processed separately and then laminated together.

[0196] The present invention avoids both of the difficult scenarios described above and allows the production of a thermally toughened glass pane provided with a CVD coating on one surface of the glass substrate and a silver based PVD coating on the second face of the glass substrate in the most efficient and cost-effective manner.

[0197] As the refractive index of the SiOx protective layer described by the present invention is close to that of the glass substrate, this affords a further benefit to the invention in that the inclusion of said protective layer makes only a small difference to the appearance of the coated glass pane, particularly when viewed in transmission and even more particularly in terms of the transmitted b*. If alternative materials such as SiNx are used (which have a refractive index higher than that of the SiOx protective layer described by the invention) then the appearance of the coated glass pane is much changed and often, this is in the form of very high values for transmission b* of over 10 units. This gives the coated glass pane a yellowish appearance when viewed in transmission which is aesthetically unappealing. In contrast, a similar product produced with an equivalent thickness of SiOx used as a protective layer according to the present invention not only exhibits superior toughening performance (that is lower haze) but also has substantially lower values of transmission b* of below 10 units, more preferably below 8 units and even more preferably below 6 units, which is aesthetically more pleasing to the ob server.

[0198] A further benefit of the present invention is that as well as providing the benefits described above, the invention also maintains a pleasing appearance when viewed in reflection, in particular the air side reflection (that is the reflection of the surface provided with a CVD coating which would be outermost when constructed into an insulating glazing unit). Monolithic panes produced according to the invention typically have air side reflection a* values in the range 10 to −10 units, more preferably between 7 and −10 units and even more preferably between 5 and −10 units. At the same time the values recorded for air side reflection b* are typically negative (that is blue in appearance) and preferably in the range of 0 to −30 units, more preferably in the range −2 to −27 units and even more preferably in the range −4 to −25 units.