WO2024120712A1

WO2024120712A1 - Insulating multiple glazing including two low-emissivity coatings

Info

Publication number: WO2024120712A1
Application number: PCT/EP2023/080833
Authority: WO
Inventors: Stijn Mahieu; Valérie FARINA
Original assignee: Agc Glass Europe
Priority date: 2022-12-07
Filing date: 2023-11-06
Publication date: 2024-06-13

Abstract

The present invention concerns an insulating glazing unit, comprising n glass substrates separated by gas cavities, with n ≥ 2, the first substrate defining the outer wall of the glazing and the last substrate defining the inner wall of said glazing, said last substrate incorporating: on its outwards-facing face, a first low emissivity coating comprising at least one metallic functional layer and having a first emissivity value εn1, and, on its inwards-facing face, a second low emissivity coating comprising at least one functional layer of transparent conductive oxide (TCO) and having a first emissivity value εn2; and wherein a ratio of emissivity of the second low emissivity coating by the emissivity of the first low emissivity coating, εn2/εn1, is less than 42.

Description

Insulating Multiple Glazing including two low-emissivity coatings

Field of the invention

[0001]The invention relates to multiple glazings, in particular double glazing or triple glazing for the building sector, said glazing comprising a metallic functional layer that can act on solar radiation and/or infrared radiation.

Background of the invention

[0002] The invention more particularly relates to insulating glazing having a high solar factor, and therefore intended primarily for cold climates.

[0003] Such insulated glazings are intended to equip more particularly buildings, in particular to reduce heat loss in winter (so-called "low-emissive glazing") and maximize heat gain from sunlight.

[0004] In insulating glazings, or multiple glazing units, typically two or three glass sheets are kept apart by spacers, so as to define a cavity in between glass sheets filled with a gas which may comprise air, nitrogen, argon and/or krypton. The glass sheets are commonly also numbered, starting from the exterior, the glazing being positioned as intended in a building. The first glass sheet is the outermost glass sheet, the last glass sheet is the innermost glass sheet.

[0005] In a glazing, the glass sheet faces are conventionally numbered starting from the exterior. The expression “face 1” of the glazing is understood in the art to mean, the external face of the glazing unit, which face is intended to be positioned in contact with the exterior of the building, facing outwards. Face 2 is the face opposite face 1 , in other words the other face of the same glass pane, facing inwards. In a multiple glazing unit, comprising two or more glass panes, face 3 is the face of the second glass pane of the glazing unit that faces face 2 and faces outwards, and face 4 is the face opposite face 3 on the second glass pane and faces inwards, etc.

[0006]The thermal transfer coefficient U designates the amount of heat passing, i.e. heat loss, through the glazing and is an indicator for the thermal insulation performance of glazings. In insulating glazings, it is therefore sought to minimize heat loss from the inside to the outside, that is to minimize the coefficient U. The coefficient U is measured in the scope of the invention according to the conditions described in the international standard ISO 10292-1994.

[0007] Heat gain from sunlight may be evaluated using the solar factor SF or g. It is defined as the ratio between the energy entering the room through the glazing and the incident solar energy. The energy entering the room is the sum of the energy from the sun transmitted directly through the glazing and of the energy absorbed by the glazing that is re-emitted inwards. The solar factor SF is measured in the scope of the invention according to the conditions described in the international standard ISO 9050-2003.

[0008] In a known manner, an insulating glazing may be provided with low emissivity (low-E) coatings on one or more of its glass sheets. Low-E coatings reduce heat loss by reflecting infrared radiation from the heated interior back towards the interior of the building. Low-E coatings generally comprise a stack of layers and at least one infrared reflecting functional layer. The infrared reflecting functional layer may be a transparent conductive oxide layer, especially of the type ITO (mixed oxide of indium and tin) or SnO2:F (fluorine doped tin oxide). For higher insulating performance, a metallic functional layer is preferred, in particular a silver based layer. The latter kind of low-E coating generally comprises an alternating sequence of n metallic functional layers and n+1 dielectric or antireflective coatings and is deposited, for example, by means of vacuum deposition techniques such as magnetic field-assisted cathodic sputtering, more commonly referred to as "magnetron sputtering" or simply “sputtering”. Such low-E coatings are generally deposited faces in contact with a cavity of the multiple glazing to protect them from degradation.

[0009] The presence of a low-emissive coating also has the effect of lowering the solar factor and generally the higher the emissivity of a metallic functional layer based low-E coating, the lower its solar factor.

[0010] It has been proposed to provide double glazing units comprising a combination of two low-E coatings on different faces of a glazing. It is possible to further reduce the energy transmission factor and to obtain DGUs having a U = 1 , 1 , by having a first low-e coating comprising a silver layer deposited on the face 2 or face 3 of the double glazing, whose action is complemented by another low-e coating deposited on the face 4, comprising at least one layer of a transparent conductive oxide. [0011] While the presence of two low-E coatings on two different faces of a glazing may advantageously reduce the energy transmission coefficient U, the inventor(s) have found that it is also accompanied by a significant decrease in light transmittance and/or Solar Factor.

[0012]W02011/161204A1 discloses double glazings comprising at one glass sheet that has a set of low-e coating on each face, one face being coated by sputtering with a low-e coating comprising a silver functional layer that reflects infrared radiation. The other face’s low-e coating comprises a fluorine doped tin oxide layer deposited using gas phase pyrolysis. The disclosed glazings have a light transmittance of 62 percent (with 4 mm thick clear glass sheets), while a DGU with a single low-E layer reaches 70% of light transmittance. The U value was also found to be reduced.

[0013]W02012/131243A1 discloses a double glazing wherein the inner glazing is provided on its outwards facing side with a silver based low-E and on its inwards facing side with a TCO based lowE. The presence of a silicon oxide toplayer on the TCO provides a high solar factor. The disclosed glazings reach a U-value of 1 .0 Wm’²K’¹ and a solar factor of up to 63.2%.

[0014] Performances of thermal insulation and aesthetics are however still to be improved.

Summary of invention

[0015] It is an object of the present invention to provide for an insulating glazing unit having enhanced thermal insulation properties, while retaining a high solar factor and a reasonably low reflectance to the outside.

[0016]The present invention relates to an insulating glazing, comprising n glass substrates, with n > 2, separated by gas cavities, the first substrate defining the outer wall of the glazing and the last, n-th, substrate defining the inner wall of said glazing, said last substrate incorporating: a. on its outwards-facing face, a first low emissivity coating comprising at least one metallic functional layer and having a first emissivity value £_n1 , and, b. on its inwards-facing face a second low emissivity coating comprising at least one functional layer of transparent conductive oxide (TCO) and having a second emissivity value s_n2; wherein a ratio of emissivity of the second low emissivity coating by the emissivity of the first low emissivity coating (£_n2/£_n1 ) is less than 4.2.

[0017]The emissivity values £_n1 and £_n2 are evaluated on otherwise uncoated 4 mm thick clear glass samples.

[0018] Because of the particular combination of first and second low emissivity coatings and in particular because of the choice of different kind of functional layers for these low emissivity coatings, double glazing units may be obtained that provide the following advantages, with two 4 mm thick clear or preferably mid-iron sodalime glass sheets and a space between glass sheets of 15 mm filled to 90% with argon: a. a high solar factor SF, with SF > 65%, preferably SF > 68%, more preferably SF > 70%; b. an insulating property enabling a value U < 1.1 W/(m²K), preferably U < 1 .0 W/(m²K) to be reached; c. a low level of reflection measured on the external side of the building LRext < 11 %; d. a neutrality of tint in reflection, with preferred values in reflection measured on the external side of the building (LRext): -3 < a* < 3, advantageously -2 < a* < 2, and -12 < b* < -2, advantageously -10 < b* < -4.

[0019] Because of the particular combination of first and second low emissivity coatings and in particular because of the choice of different kind of functional layers for these low emissivity coatings, triple glazing units may be obtained that provide the following advantages, with three 4 mm thick clear or preferably mid-iron sodalime glass sheets and spaces between glass sheets of 14 to 18 mm filled to 90% with argon: a. a high solar factor SF, with SF > 56%, preferably SF > 58%, more preferably SF > 60%; b. an insulating property enabling a value U < 0.6 W/(m²K), preferably U < 0.5 W/(m²K) to be reached; c. a low level of reflection measured on the external side of the building LRext < 16%; d. a neutrality of tint in reflection, with preferred values in reflection measured on the external side of the building (LRext): -3 < a* < 3, advantageously -2 < a* < 2, and -12 < b* < -2, advantageously -10 < b* < -4

[0020] In triple glazing units, such values may in particular be obtained with a third low emissivity coating on face 2 or face 3, that is, on the inwards facing side of the first glass substrate or on the outwards facing side of the second substrate.

Brief description of drawings

[0021] FIG. 1 is a schematic cross-sectional view of a double glazing unit (DGU) according to an embodiment of the invention.

[0022] FIG. 2 is a schematic cross-sectional view of a triple glazing unit (TGU) according to an embodiment of the invention.

Description of embodiments

[0023] The following information is used in the present invention: a. light transmission (LT) is the percentage of incident light flux, illuminant D65/2°, transmitted by the glazing. b. light reflection (LR) is the percentage of incident light flux, illuminant D65/2°, reflected by the glazing. It may be measured on a single glazing from the layer side (LRc) or the substrate side (LRg). It may be measured on the external side of the building (LRext) or the internal side of the building or vehicle (LRint), in particular on a multiple glazing unit or a laminated glazing. c. energy transmission (ET) is the percentage of incident energy radiation transmitted by the glazing calculated in accordance with standard EN410. d. energy reflection (ER) is the percentage of incident energy radiation reflected by the glazing calculated in accordance with standard EN410. It may be measured on the external side of the building or vehicle (ERext) or the internal side of the building or vehicle (ERint). e. solar factor (SF or g) is the percentage of incident energy radiation that is directly transmitted by the glazing, on the one hand, and absorbed by this, then radiated in the opposite direction to the energy source in relation to the glazing. It is here calculated in accordance with standard EN410. f. the U value (coefficient k) and emissivity (s) are calculated in accordance with standards EN673 and ISO 10292. g. the CIELAB 1976 values (L*a*b*) are used to define the tints. They are measured with illuminant D65/10⁰. h. AE*=[(L*)²+(a*)²+(b*²)]1/2 represents the tint variation during the heat treatment, i.e. the difference between before and after heat treatment colours. i. the resistance per square (Rsq) ("sheet resistance"), expressed in ohms per square (£)/□), measures the electrical resistance of thin films.

[0024] When values are referred to as "in the range of between a and b", they may be equal to a or b.

[0025]As is well known in the art, multiple glazings comprise n glass substrates, numbered starting from the outside inwards. Once installed on a building, the 1 st substrate is destined to form the outer wall of the glazing, i.e. is in contact with the building exterior; the last or n-th substrate is destined to form the inner wall of the glazing, i.e. is in contact with the inside of the building. Most often, n=2 (double glazing) or n=3 (triple glazing).

[0026]The positioning of the stack of layers in a multiple glazing structure is given according to the classic sequential numbering of the faces of a glazing unit, face 1 being on the exterior of the building or vehicle and face 4 (in the case of a double glazing unit) or face 6 (in the case of a triple glazing unit) on the interior.

[0027] When referring to silicon nitride or silicon oxide layers herein, it should be understood that the layers may also incorporate a small quantity of aluminium, as is well-known in the art of magnetron sputtered coatings. Such aluminium is included as doping agent, generally in a quantity of 10 wt.% at most.

[0028] For the sake of clarity, when using terms like "below", "above", "lower", "upper", "first" or "last" herein, it is always in the context of a sequence of layers starting from the glass below, going upward, further away from the glass. Such sequences may comprise additional intermediate layers, in between the defined layers, except when a direct contact is specified.

[0029] The present invention relates to a glazing unit according to claim 1 and the dependent claims present preferred embodiments.

[0030] For the purposes of the present invention, the term "glass substrate" or simply “substrate” is intended to mean a single glass sheet or a set of bonded glass sheets, in particular two or more glass sheets, bonded together in a so-called laminated structure by a polymer sheet, in particular a polymer sheet of PVB (polyvinyl butyral) or EVA (ethyl vinyl acetate) according to techniques well known in the art.

[0031] In the scope of the present invention, a "coating" is a stack of at least two superimposed layers and a “film” is a part of a coating comprising one or more superimposed layers.

[0032] In the scope of the present invention, "contact" between layers means that no other intermediate layer is interposed between the two mentioned layers.

[0033] In the scope of the present invention, a “low emissivity coating” is considered any known coating in the field to reduce the normal emissivity s_n of a glass substrate. The term “emissivity” is understood to mean the normal emissivity at 283 K within the meaning of standard EN 12898:2019. In the low emissivity coatings of the present invention, the functional layers are the infrared reflecting layers, that are responsible for the low emissivity property.

[0034] Regarding layer composition, by the expression “based on” is meant in particular that a layer comprises at least 80%, or even 90% and even 95% by weight of the material considered.

[0035] The glass substrates of the present invention may independently be soda-lime- silicate glass, alumino-silicate glass, alkali-free glass, boro-silicate glass, etc. Preferably, the glass substrates of the invention are made of soda-lime glass or alumino-silicate glass. Advantageously, the glass substrate of the invention is a float glass pane. The term “float glass pane” is understood to mean a glass pane formed by the float process, which is well known in the art.

[0036] According to an embodiment of the invention, the glass pane has a composition comprising, in a content expressed in percentages of the total weight of the glass: SiO₂ 55 - 85%

AI2O3 0 - 30%

B2O3 0 - 20%

Na₂O 0 - 25%; preferably 5-20%

CaO 0 - 20%

MgO 0 - 15%

K₂O 0 - 20%

BaO 0 - 20%.

[0037] The preferred soda-lime glass substrates may independently be selected from clear glass substrates or low iron clear glass substrates (also referred to as extra clear glass substrates).

[0038] Clear glass substrates are considered herein having a composition comprising a total iron content (expressed in terms of Fe₂O3) ranging from 0.002 to 0.15 weight%, alternatively from 0.002 to 0.10 weight%, or from 0.002 to 0.08 weight%. Clear glass substrates are typically characterised by a light transmittance ranging from 89 to 90.3% (for a 4 mm sheet, at D65/2°).

[0039] In a preferred embodiment of the present invention, the total iron content, expressed in the form of Fe2O3, is less than or equal to 0.06 weight%, generally ranging from 0.002 to 0.06 weight%, for at least one, preferably for all of the glass substrates of the multiple glazing unit. With such a total iron content, it is possible to obtain a glass pane with high transmittance. Thereby high solar factors can be obtained, reaching at least 65%, 68%, even 70% in a double glazing and at least 56%, 58%, even 60% in a triple glazing.

[0040] In an advantageous embodiment of the present invention, the composition comprises a total iron (expressed in the form of Fe₂O3) content ranging from 0.02 to 0.06 weight%, as is considered typical for a mid-iron soda lime glass. Such a glass composition allows for high light transmission at reasonable cost. [0041] In an advantageous embodiment of the present invention, the composition comprises a total iron (expressed in the form of Fe2Os) content ranging from 0.002 to 0.02 weight%, as is considered typical in a low-iron soda lime glass. More advantageously, the composition comprises a total iron (expressed in the form of Fe2Os) content ranging from 0.002 to 0.015 weight%. Such low iron contents allow for the highest light transmission levels, though the raw materials necessary are generally more expensive.

[0042] Ideally, the glass composition does not comprise B2O3 (meaning that it is not intentionally added, but could be present as undesired impurities in very low amounts).

[0043]The glass substrates of the multiple glazing units according to the invention may independently have a thickness of from 0.1 to 25 mm. Advantageously, the glass substrates according to the invention independently have a thickness of from 1 to 12 mm, 2 to 12 mm, 3 to 12 mm, alternatively 2 to 7 mm, alternatively 3 to 6 mm.

[0044]The invention also relates to a multiple glazing unit wherein one or more glass substrates are heat strengthened or tempered.

[0045] In an advantageous embodiment of the present invention, at least the last glass susbtrate is heat strengthened or tempered. In particular, heat load induced mechanical stresses may be experienced by the last substrate bearing the first and second low emissivity coatings and the improved U value and SF value may lead to glass breakage due to heat accumulation when the last substrate is not heat strengthened or tempered.

[0046]The last substrate may be heat strengthened or tempered before being coated with any of the first and second low-emissivity coatings. Alternately, the last substrate is first coated with any one of the first or second low emissivity coatings, then tempered or heat strengthened, then coated with the other low emissivity coating. In an advantageous embodiment of the present invention, the last substrate is tempered after being coated with the first and the second low emissivity coatings.

[0047] The last substrate may also be chemically strengthened before being coated with any of the first and second low-emissivity coatings. [0048] In the scope of the present invention, the first low emissivity coating comprising at least one metallic functional layer comprises an alternating arrangement of n infrared reflecting metallic functional layers and n+1 dielectric films, with n > 1 , such that each functional layer is surrounded by dielectric films. In the scope of the present invention, a dielectric film may comprise one or more layers of dielectric material.

[0049] The first low emissivity coating may comprise one, two, or three infrared reflecting metallic functional layers. In particular, the infrared reflecting metallic functional layers’ material may be selected from silver or of silver-containing metal alloys or may essentially consist of silver. Alternatively, metallic functional layers may comprise gold or copper. In particular, the first low emissivity coating provides an otherwise uncoated clear glass substrate, for example having a thickness ranging from 4 to 12 mm, with a first normal emissivity s_n1 less than or equal to 0.07, preferably less than or equal to 0.06, and greater or equal to 0.01 .

[0050] Each infrared reflecting metallic functional layer of the first low emissivity coating is surrounded by two dielectric films, each comprising in general one or more dielectric layers. The dielectric layers may comprise or be based on nitrides, oxides or oxynitrides. In particular, the dielectrics may comprise or be based on nitrides, oxides or oxy nitrides of silicon, aluminium, tin, zinc, titanium, zirconium or niobium. Furthermore, the dielectric layers may comprise or be based on a mixture of two or more of the nitrides, oxides or oxy nitrides of silicon, aluminium, tin, zinc, titanium, zirconium or niobium.

[0051] Each infrared reflecting metallic functional layer of the first low emissivity coating may be in direct contact with one or two contact layers, for instance comprising zinc oxide, or comprising titanium, nickel, chromium, palladium, tungsten, or niobium or comprising oxides or sub-oxides of titanium, nickel, chromium, palladium, tungsten, or niobium or comprising nitrides or oxynitrides of titanium, nickel, chromium, palladium, tungsten, or niobium.

[0052]According to an embodiment of the present invention, one or more zinc oxide comprising contact layers, are doped with aluminium or gallium. Alternately one or more zinc oxide comprising contact layers comprise or are based on an oxide of zinc combined with at least two elements selected from the group comprising titanium, aluminium, indium, gallium, vanadium, molybdenum, magnesium, chromium, zirconium, copper, or silicon.

[0053]The first low emissivity coating may further comprise an absorber layer, for example inserted in a dielectric film or below or above a dielectric film. For the purpose of the present invention, an absorber layer comprises a material, for example metal or a metal nitride, having an extinction coefficient k at a wavelength in the range from 380 nm to 780 nm of at least 1.0 or even of at least 2.0. More details on absorbers are provided below. For increased light transmittance, the first low emissivity coating does preferably not comprise an absorbing layer inserted in a dielectric film or below or above a dielectric film.

[0054]The first low emissivity coating may also comprise an uppermost protective film for increased chemical and/or mechanical durability. The uppermost protective film may comprise a silicon nitride comprising layer and may further comprise, above and in contact with the silicon nitride based layer, a layer comprising an oxide of titanium and/or of zirconium.

[0055] In particular embodiments, the first low emissivity coating may have a normal emissivity s_n1 ranging of from 0.035 to 0.07, alternatively of from 0.035 to 0.065, preferably 0.045 to 0.060. The advantage of having such a first low emissivity is that the solar factor remains optimal. When the normal emissivity of the first low emissivity coating is lower than 0.030, and for example as low as from 0.010 to 0.025, the solar factor is negatively impacted and thus too low. The emissivity is adjusted mainly by the layer thickness of the metallic functional layer.

[0056]According to a preferred embodiment of the present invention, the first low emissivity coating preferably comprises one single infrared reflecting metallic functional layer surrounded by two dielectric films. Such coatings with one single infrared reflecting metallic functional layer surrounded by two dielectric films may easily achieve a normal emissivity s_n1 ranging of from 0.035 to 0.065, preferably 0.045 to 0.060, and is easily produced at reasonable cost. Such coatings also tend to have higher SF values than coatings with two or more infrared reflecting metallic functional layers.

[0057]The physical thickness of each infrared reflecting metallic functional layer of the first low emissivity coating may have a physical thickness of from 5 to 20 nm, alternatively of from 6 to 16 nm, alternatively of from 7 to 14 nm, alternatively of from 7 to 10 nm.

[0058] Here within thicknesses of layers are physical thicknesses in nm, unless otherwise indicated.

[0059] In a suitable embodiment, the first low emissivity coating comprising one single layer of infrared reflecting metallic functional layer, comprises in sequence starting from the substrate surface

(i) a first dielectric film, in direct contact with the substrate, which may comprise one or more layers made from an oxide, a nitride or an oxynitride material and having a thickness greater than 3 nm; such materials, which may have a refractive index ranging from 1.7 to 2.5, include but are not limited to silicon nitride, optionally doped with zirconium; titanium oxide; mixed titanium and zirconium oxide; zinc oxide; silicon oxide; mixed zinc tin oxide, in particular Z^SnCU;

(ii) a first contact layer based on zinc oxide or indium oxide with a thickness greater than 3 nm;

(iii) one single infrared reflecting metallic functional layer, in contact with the first and second contact layers;

(iv) a second contact layer based on metallic titanium, titanium oxide, titanium suboxide, zinc oxide, aluminium doped zinc oxide, zinctin oxide, with a thickness greater than 3 nm,

(v) a second dielectric film furthest away from the substrate which may comprise one or more layers made from an oxide, a nitride, or an oxynitride material and having a thickness greater than 3 nm; such materials, having a refractive index ranging from 1.7 to 2.5, include but are not limited to silicon nitride, optionally doped with zirconium; titanium oxide; mixed titanium and zirconium oxide; zinc oxide; silicon oxide; mixed zinc tin oxide, in particular Zn2SnO4;

(vi) optionally a protective top layer, such as a layer comprising mixed nitride of silicon and zirconium, or a mixed oxide of titanium and zirconium.

[0060] Here within, the refractive indexes are determined at a wavelength of 550 nm.

[0061] In preferred embodiments, the second dielectric film comprises, in sequence starting from the second contact layer: a layer made from an oxide other than silicon oxide with a thickness greater than 3 nm and a layer made from a silicon nitride or a silicon oxide with a thickness greater than 10 nm,

[0062] According to an embodiment of the present invention, the edges of the first low emissivity coating may be deleted, for example to ensure good adhesion of the inner glass pane to the spacers and/or to avoid deterioration of the coating.

[0063] According to an embodiment of the present invention, the second low emissivity coating comprising at least one functional layer of transparent conductive oxide (TCO) comprises a material selected from mixed indium tin oxide (ITO), in particular ITO with an ln2O3/SnO2 mass ratio of 90/10 or more, tin oxide doped with fluorine (SnO2:F), in particular doped with 0.5 to 2 atomic % of fluorine or tin oxide doped with antimony (Sb), aluminium-doped ZnO (AZO), gallium-doped ZnO (GZO), gallium and aluminium co-doped ZnO (AGZO), and niobium-doped titanium oxide (TiO2:Nb).

[0064] Advantageously the second low emissivity coating comprises a single functional layer of TCO.

[0065] In particular, the second low emissivity coating may provide a glass substrate, for example having a thickness of 4 mm, with a second normal emissivity s_n2 less than or equal to 0.40, preferably less than or equal to 0.30 or very advantageously less than or equal to 0.20. s_n2 may be larger or equal to 0.08. The emissivity is adjusted by the TCO material thickness and TCO material choice.

[0066] The total physical thickness of the at least one functional layer of TCO may range of from 100 to 550 nm, alternatively of from 150 to 500 nm, alternatively of from 200 to 490 nm.

[0067] According to an embodiment of the present invention, the second low emissivity coating further comprises in between the glass pane and at least one TCO functional layer, a layer comprising titanium oxide (layer H) which may have a refractive index of between 1 .7 and 2.5. Said layer H may have a physical thickness ranging of from 2 to 24 nm, alternatively of from 3 to 19 nm, alternatively of from 4 to 15 nm.

[0068] Said layer H may comprise titanium oxide or a mixed titanium zirconium oxide. Said layer H comprising titanium oxide improves the resistance to the heat treatment of the second low emissivity coating, i.e. avoids increase of emissivity upon heat treatment or tempering, such that the desired emissivity is effectively achieved, and that the quality of the coating is maintained over time. This even more if the layer comprising titanium oxide is in contact with the glass substrate, even more if the layer H is in direct contact with the at least one or single TCO layer.

[0069] In an embodiment of the present invention, the second low emissivity coating comprises a neutralizing undercoat between the substrate and the at least one TCO functional layer. The function of the neutralizing undercoat is to allow the neutralization of the color in reflection of the coated pane, i.e. to avoid interference colors in reflection, in particular for the thickness of the functional layer chosen. It is preferably in direct contact with the glass substrate. It is preferably in direct contact with at least one TCO, in particular with a single TCO.

[0070] In an embodiment of the present invention, the neutralizing undercoat of the second low emissivity coating is a single neutralization layer consisting essentially of silicon oxynitrides, such as SiOxNy, or silicon oxycarbides, such as SiOxCy, x being less than 2, the refractive index is advantageously in the range from 1 .65 to 1 .78, the thickness of this single layer preferably being between 55 and 95 nm. The “x” and “y” values are chosen to adjust the refractive index values. Alternatively, the single neutralization layer can be a mixed layer consisting essentially of Sn and Si oxides, the thickness of which is between 55 and 95 nm, advantageously between 60 and 90 nm and very advantageously between 70 and 90 nm.

[0071] In an embodiment of the present invention, the neutralizing undercoat of the second low emissivity coating is a double neutralization layer consisting of a first underlayer of a material having a higher refractive index than that of glass, such as TiO2, SnO2 or ZnO, or a mixture of ZnO and SnCh, coated with a second underlayer having a lower refractive index than the first underlayer. This second underlayer is for example a layer of a silicon oxide, silicon oxycarbide, such as SiOxCy, or silicon oxynitride, such as SiO_xN_y, x being less than or equal to 2. The thickness of the first underlayer layer is preferably between 5 nm and 15 nm when it is TiO2 and preferably between 15 nm and 35 nm when it is SnCh, ZnO, or a mixture of ZnO and SnO2. The thickness of the second underlayer is preferably between 15 nm and 40 nm when it is a silicon oxide, oxycarbide or oxynitride. Silicon oxide is optionally doped with aluminium or zirconium, with dopant level up to 15 % at most.

[0072] Double neutralization layer undercoats of a first underlayer of either TiO2 or SnO2 and a second underlayer based on silicon oxide are particularly preferred, as the resultant low emissivity coatings provide lower emissivity values after tempering. In this regard, a first underlayer of TiCh is even more preferred.

[0073]Additional layers may be deposited above the at least one TCO layer. According to an embodiment of the present invention, the second low emissivity coating comprises above all TCO layers, a coating R for improving chemical or mechanical resistance, R may therefore in particular comprise a silicon nitride comprising layer. Silicon nitride is optionally doped with aluminium up to 15 at %.

[0074] According to an embodiment of the present invention, the second low emissivity coating comprises a topmost layer, layer T. Layer T may in particular have a refractive index of between 1 .40 and 1 .68. Layer T may have a thickness in the range from 40 to 120 nm. Layer T may in particular comprise a single layer comprising silicon oxide or a double layer of two different sublayers T 1 and T2 each comprising silicon oxide. In both configurations, single or double layer T, a reduction of the visible light reflectance is obtained, thus increasing visible light transmission. That is, the last, i.e. topmost, layer in the second low emissivity coating interestingly reduces the reflection of visible light of the glazing, thus increasing visible light transmission. At least one of T1 or T2 may comprise mixed silicon zirconium oxide, preferably having a thickness of from 1 to 12 nm, imparting further mechanical and/or chemical resistance to the coating.

[0075] Exemplary embodiments of the second low emissivity coating’s layer sequences are shown in Table 1 , starting from the glass. The undercoats here are double neutralizing layer undercoats. [0076] Table 1

[0077]Additional intermediate layers may be inserted between these various layers without departing from the present invention. However, to maintain high transmittance, preferably the second low emissivity coating does not contain an absorber layer. Absorber layers may be layers having an extinction coefficient k above 0.1 in the visible wavelength range. Absorber layers may also have a, refractive index n above 1 in the visible wavelength range. Example thicknesses for absorber layers may range from 0.2 to 15 nm. Absorber layers may for example comprise or consist of NiCr, W, Nb, Pd, Si, Ti, or alloys based on Ni and/or Cr and/or W, or from TiN, CrN, WN, NbN, TaN, ZrN, NiCrN, or NiCrWN, or a mixture of these nitrides.

[0078]According to an advantageous embodiment of the present invention, the thicknesses of the one or more layers of the second low emissivity coating, other than the TCO functional layers, are chosen so as to make the color in reflection of the TCO-based insulating layer coated glass pane as neutral as possible, with CIELAB color coordinates a* and b* as close as possible to 0, preferably also when viewed from an angle.

[0079] According to an embodiment of the present invention, the second low emissivity coating is free of any metallic layer.

[0080]The optimal U value of the present multiple glazing unit may be achieved by specifically selecting the first and second low emissivity coatings, such that a ratio of emissivity of the second low emissivity coating by the emissivity of the first low emissivity coating (£_n2/£_n1 ) is less than 4.2, preferably comprised of from 1 .5 to 4.0, more preferably of 1.7 to 3.9. The U value depends not only on the coatings but also on the number of glass substrates and intermediate cavities. The optimal U value may be less than or equal to 1 .0 for a double glazing unit, and less than or equal to 0.6 for a triple glazing unit.

[0081]According to an embodiment of the present invention, the first glass substrate is free of any low emissivity coating on its second surface (face 2) of the insulating glazing unit. Thereby higher light transmittance may be obtained.

[0082]According to an embodiment of the present invention, the glass substrates other than the last glass substrate are free of any low emissivity coatings. In particular in double glazing units according to embodiments of the present invention, the first glass substrate may be free of any low emissivity coating.

[0083]A double glazing unit according to an embodiment of the present invention, combining on the last substrate the first and second low emissivity coatings, in particular with one gas cavity of 15 mm width filled with 90% Ar, in particular with both glass substrates being mid-iron or low-iron glass substrates, may reach enhanced thermal insulation properties with an optimal U value of less than or equal to 1.0, while retaining a high solar factor (SF) superior or equal to 65, even superior or equal to 70, and a reasonably low reflectance to the outside (Rout) of less than 11 %.

[0084]A triple glazing according to an embodiment of the present invention, may comprise on face 2 or 3 a third low emissivity coating. Any possible embodiment of the first low emissivity coating is also an available embodiment of the third low emissivity coating. Such a third low emissivity coating may further increase solar and thermal protection. The third low emissivity coating has a third emissivity value £n3.

[0085] In an embodiment of the present a ratio of emissivity of the second low emissivity coating by the emissivity of the third low emissivity coating (£_n2/£_n3) is less than 4.2, preferably £_n2/£_n3 ranges from 1 .5 to 4.0, more preferably from 1 .7 to 3.9.

[0086]A triple glazing unit according to an embodiment of the present invention, combining on the last substrate the first and second low emissivity coatings, in particular with two gas cavities of 15 mm width filled with 90% Ar, in particular with both glass substrates being mid-iron or low-iron glass substrates, may have enhanced thermal insulation properties with a U value of less than or equal to 0.6, while retaining a high solar factor (SF) superior or equal to 56, and a reasonably low reflectance to the outside (Rout) of less than 16%.

[0087] In the scope of the present invention, the first and second low emissivity coatings may be provided by various vacuum deposition methods or combinations thereof, including magnetron sputtering, LPCVD (low pressure chemical vapor deposition), plasma enhanced chemical vapor deposition (PECVD). Individual layers of the same coating may be provided by different deposition methods. Advantageously, the first low emissivity coating is deposited by magnetron sputtering.

[0088] In the scope of the present invention, the second low emissivity coating may also be, at least partly, deposited by chemical vapor deposition (CVD) in particular directly on a float line during the production of the last glass substrate. Such a process may deliver a more durable coating than other deposition methods at lower cost. In this case the TCO layer comprises preferably fluorine doped tin oxide SnO₂:F.

[0089] According to an embodiment of the present invention, the layer T of the second low emissivity coating is deposited by magnetron sputtering or PECVD, in particular while all other layers of this coating are deposited by CVD. Certain float lines may have limited space available for additional coatings as a large part of the float line needs to be dedicated to controlled cooling of the glass substrate.

[0090] In CVD or PECVD, a titanium oxide based layer may be provided using titanium tetraisopropoxide (TTIP) or TiCI4.

[0091] In CVD or PECVD, a tin based layer may be provided using monobutyl-tin- trichloride (MBTC) combined with a fluorine source such as trifluoroacetic acid (TFA), ammonium bifluoride (NF F.HF) or hydrofluoric acid (HF), for example. Other well-known tin precursors include, but are not limited to, dimethyltin dichloride, dibutyltin dichloride, tetramethyltin, tetrabutyltin, dioctyltin dichloride, dibutyltin diacetate and tin tetrachloride. Other fluorine sources include fluorine gas, hydrogen fluoride, nitrogen trifluoride, trifluoroacetic acid (CF3CO2H), bromo- trifluoromethane, difluoroethane and chlorodifluoromethane.

[0092] In CVD and PECVD, the precursors used to provide for the silicon oxide comprising layer may include silane, oxygen or CO2 and a carrier gas (N2).

[0093] In CVD and PECVD, aluminium precursors may include trimethylaluminium, alane, aluminium trichloride.

[0094] In an embodiment of the present invention, the second low emissivity coating may have a roughness Rq of at most 12 nm, at most 7 nm or even at most 5 nm. The roughness may be adjusted by the thickness of the TCO layer. The roughness may also be adjusted by adding a polishing step after the deposition of the coating as a whole or of at least the TCO layers of the coating. Particularly low roughness of Rq less than 2 nm may obtained when the whole second low emissivity coating is deposited by magnetron sputtering. Rq roughness is the root mean square average of the roughness profile ordinates defined according to ISO 4287. A lower roughness may decrease and/or simplify cleaning of the surface.

[0095] FIG. 1 is a schematical cross-section of a double glazing unit (DGU) according to an embodiment of the present invention. The DGU of Fig. 1 comprises two sheets of glass, a first substrate (101 ) and a second substrate (102). The two substrates are held apart by spacer (110), the assembly delimiting an enclosed space, or cavity, filled with an intermediate gas cavity (104).

[0096]The first substrate (101 ) defines the outer wall of the glazing, turned towards the outside (111 ), in contact with the outside (11 1 ), and the last substrate, that is the second substrate (102) defines the inner wall of the DGU glazing, in contact with the inside (112). The second (and last) substrate incorporates on the outwards-facing face (105), a first low emissivity coating (106) comprising at least one metallic functional layer and, on the inwards-facing face (107), a second low emissivity coating (108) comprising at least one functional layer of transparent conductive oxide.

[0097] FIG. 2 is a schematical cross-section of a triple glazing unit (TGU) according to an embodiment of the present invention. The TGU of Fig. 2 comprises three sheets of glass, a first substrate (201 ), a second substrate (202), and a last, third substrate (203). The three substrates are held apart by spacers (210a, 210b) respectively, the assembly delimiting two enclosed spaces, or cavities, filled a gas (204a, 204b).

[0098] The first substrate (201 ) defines the outer wall of the glazing, in contact with the outside (211 ) and the last substrate, that is the third substrate (203) defines the inner wall of the TGU glazing, in contact with the inside (212). The third (and last) substrate incorporates on the outwards-facing face, face 5 (205), a first low emissivity coating (206) comprising at least one metallic functional layer and on the inwards-facing face, face 6 (207) a second low emissivity coating (208) comprising at least one functional layer of transparent conductive oxide.

[0099] Optionally, a third low emissivity coating (213) comprising at least one metallic functional layer is present on the outwards facing face, face 3 (214) of the second glass substrate (202).

Examples

[0100] In all the examples below, the coatings are deposited on clear soda-lime glass substrates.

[0101]Table 2 summarizes the layer sequences, starting from the glass surface, of coatings A to D used in the different examples below. Layer thicknesses are indicated in brackets.

[0102] Table 2

Examples 1 and 2 - double glazing units

[0103] In the double glazings of Examples 1 and 2 below, first and second low emissivity coatings were deposited on face 3 and face 4. All glass substrates are normal clear soda lime glass float glass substrates of 4 mm thickness. The first glass substrate bears no coating. The glass substrates are held apart by spacers at a distance of 15 mm and the cavity between the two glass substrates is filled with an Ar/air 90/10 mixture.

[0104] In Examples 1 and 2, the first low emissivity coating is coating A.

[0105] Coating A provides an otherwise uncoated glass substate with an emissivity s_n1 of 0.048.

[0106] In Example 1 , the second low emissivity coating is coating B.

[0107] Coating B provides an otherwise uncoated glass substrate with an emissivity s_n2 of 0.12.

[0108] In Example 2, the second low emissivity coating is coating C. [0109] Coating C provides an otherwise uncoated glass substrate with an emissivity s_n2 of 0.12.

[0110] Here within, ZSO stands for Zn2SnO4, AZO stands for zinc oxide doped with aluminium in an approximate proportion of 2% by weight, SiN represents silicon nitride and TZO stands for a mixed oxide of titanium and zirconium with a TiO2/ZrO2 weight ratio of 65/35; SiZrOx stands for a mixed oxide of silicon and zirconium with an Zr/Si atomic ratio of 0.12.

[0111]The results reported in Table 3 show that the double glazing units equipped with the two low emissivity coatings according to the invention exhibit the better cumulative performance in terms of thermal transmittance U and solar factor > 65%, even > 68%, and even equal or more than 70%, while ensuring an acceptable exterior reflectance Rout of less than 10%.

[0112]Table 3 - double glazing units

[0113] Publication WO2011/161204A1 provided for a configuration 4, which is considered herein as Comparative example 1 , of a DGU of 2 glass sheets of 4 mm thickness held apart by spacers at a distance of 15 mm having the cavity between the two glass substrates filled with an Ar/air 90/10 mixture. The double glazing unit of configuration 4 of WO2011/161204A1 comprised a first low emissivity coating having a first emissivity £_n1 of 0.01 , on the outwards facing face of the last substrate, and a second low emissivity coating having a second emissivity s_n2 of 0.1 , on the inwards facing face of the last substrate, such that the ratio £_n2/£_n1 = 10. Such double glazing unit was found to demonstrate a U value of 0.9 W/(m²K), however at the detriment of a lower light transmission of 62%, a higher exterior reflectance of 21 % and a lower solar factor of 49%.

Examples 3 to 8 - triple glazing units

[0114] In triple glazings of examples 3 to 8 below, first and second low emissivity coatings were deposited on face 5 and face 6 respectively. All glass substrates are normal clear soda lime glass float glass substrates of 4 mm thickness. The first glass substrate bears no coating. The glass substrates are held apart by spacers at a distance of 16 mm from each other and the cavity between any two glass substrates is filled with an Ar/air 90/10 mixture.

[0115] In Examples 3, 4, 7 and 8, the first low emissivity coating is coating A.

[0116] In Examples 5 and 6, the first low emissivity coating is coating D.

[0117] Coating D provides an otherwise uncoated glass substate with an emissivity £_n1 of 0.072.

[0118] In Examples 3, 5, and 7, the second low emissivity coating is coating B described hereinabove. In examples 4, 6, and 8 the second low emissivity coating is coating C described hereinabove.

[0119] In addition to the first and second low emissivity coatings, the triple glazing units of Examples 3 to 8 bear a third low emissivity coating which is identical to the respective first low emissivity coating of each Example. For Examples 3 to 6 the third low emissivity coating is on face 2, for Examples 7 and 8 the third low emissivity coating is on face 3.

[0120] The results reported in Table 4 show that the triple glazing units equipped with the two low emissivity coatings according to the invention exhibit the better cumulative performance in terms of thermal transmittance U with values of 0.6 W/(m²K) and solar factor > 56%, even > 58%, and even equal or more than 59%, while ensuring an acceptable exterior reflectance of less than 18%, even less than 16%, and even less than 14% in some instances where the first and third low emissivity coatings have emissivities < 0.05.

[0121]Table 4 - triple glazing units

[0122] The U value may even be decreased further if the used glass sheets are kept further apart. For Examples 3 to 8, U may be of 0.5 with glass sheet distances of 18 mm, instead of 16 mm.

Claims

Claim 1 . Insulating glazing unit, comprising n glass substrates separated by gas cavities, with n >2, the first substrate defining the outer wall of the glazing and the last, n-th, substrate defining the inner wall of said glazing, said last substrate incorporating: a. on its outwards-facing face, a first low emissivity coating comprising at least one metallic functional layer and having a first emissivity value £_n1 , and, b. on its inwards-facing face, a second low emissivity coating comprising at least one functional layer of transparent conductive oxide (TCO) and having a second emissivity value s_n2; wherein a ratio of emissivity of the second low emissivity coating by the emissivity of the first low emissivity coating, £_n2/£_n1 , is less than 4.2.

Claim 2. Insulating glazing unit according to claim 1 , wherein the last substrate is heat strengthened or tempered.

Claim 3. Insulating glazing according to any one preceding claim, wherein the thickness of the at least one functional layer of transparent conductive oxide is comprised between 100 and 550 nm.

Claim 4. Insulating glazing according to any one preceding claim, wherein the thickness of the at least one metallic functional layer is comprised between 5 and 20 nm.

Claim 5. Insulating glazing according to any one preceding claim, wherein the at least one infrared reflecting metallic functional layer’s material is selected from silver or of silver-containing metal alloys, gold and copper.

Claim 6. Insulating glazing according to any one preceding claim, wherein the at least one functional layer of transparent conductive oxide comprises a material selected from mixed indium tin oxide, tin oxide doped with fluorine, tin oxide doped with antimony, aluminium-doped ZnO, gallium-doped ZnO, gallium and aluminium co-doped ZnO (AGZO), and niobium-doped titanium oxide.

Claim 7. Insulating glazing according to any one preceding claim, wherein £n1 < 0.07.

Claim 8. Insulating glazing according to any one preceding claim, wherein s_n2 < 0.40.

Claim 9. Insulating glazing according to any one preceding claim, wherein the first low emissivity coating comprises a single metallic functional layer.

Claim 10. Insulating glazing according to any one preceding claim, wherein the second low emissivity coating comprises a single functional layer of transparent conductive oxide.

Claim 11 . Insulating glazing according to any one preceding claim, wherein the second low emissivity coating comprises, in between the last substrate and at least one TCO functional layer, a layer comprising titanium oxide or a neutralizing undercoat.

Claim 12. Insulating glazing according to any one preceding claim, wherein the second low emissivity coating comprises above all TCO layers a coating R comprising a silicon nitride comprising layer.

Claim 13. Insulating glazing according to any one preceding claim, wherein the second low emissivity coating comprises a topmost layer, layer T selected from a. a single layer having a refractive index of between 1 .40 and 1 .68 and optionally a thickness in the range from 40 to 120 nm; and b. a double layer of two different sublayers T 1 and T2 each comprising silicon oxide.

Claim 14. Insulating glazing according to any one preceding claim, wherein n=3 and further comprising on face 2 or face 3 a third low emissivity wherein the third low emissivity coating comprises at least one metallic functional layer.

Claim 15. Insulating glazing according to claim 15, wherein a ratio of emissivity of the third low emissivity coating has a third emissivity value s_n3 and wherein the second low emissivity coating by the emissivity of the third low emissivity coating, £_n2/£_n3, is less than 4.2.