GB2300133A

GB2300133A - Coated substrate having high luminous transmission, low solar factor and neutral aspect in reflection.

Info

Publication number: GB2300133A
Application number: GB9607822A
Authority: GB
Inventors: Jean-Michel Depauw; Karel Vandiest
Original assignee: Glaverbel Belgium SA
Current assignee: AGC Glass Europe SA
Priority date: 1995-04-27
Filing date: 1996-04-15
Publication date: 1996-10-30
Anticipated expiration: 2016-04-15
Also published as: GB2300133B; GB9508543D0; DE19616841A1; IT1285048B1; ITTO960305A0; NL1002945C2; SE9601504L; CH691593A5; ITTO960305A1; ES2119681A1; BE1009463A3; FR2733495B1; ES2119681B1; LU88748A1; JPH08304601A; NL1002945A1; SE9601504D0; DE19616841B4; FR2733495A1; SE513822C2

Description

- 1 2300133 COATED SUBSTRATE HAVING HIGH LUMINOUS TRANSMISSION, LOW SOLAR

FACTOR AND NEUTRAL ASPECT IN REFLECTION This invention relates to a coated substrate, in particular to a coated substrate having a high level of luminous transmission, a low solar factor and a neutral aspect in reflection.

Coated substrates find use in various fields for various purposes. Thus, for example, coated glass is used in low emissivity or solar screening panels, for use in buildings and vehicles.

In order to impart specific desired properties to the coated substrate the coating may include several layers, each of which satisfies particular requirements of the coating. The layer constituents and their thicknesses are usually narrowly defined to ensure the achievement of the specific requirements of the coated substrate as a whole.

United States patent 4985312 relates to a glass plate with a multilayer coating to impart heat reflecting properties to the plate. A base layer of indium-tin oxide or A1N is deposited on the plate, followed by alternately heat reflective layers of silver or copper with a thickness of 40 to 200 A (4 to 20 nm), barrier layers of metallic zinc with a thickness of 20 to 200 A, and protective layers of the same material as the base layer.

SCARLETS. DOC 4150 SCARLET 2 1278B EP-Bl-0277228 relates to a glass assembly concerned with transmitting light in the visible spectrum while blocking solar radiation outside the visible spectrum. Its assembly includes a glass substrate with, in sequence from the substrate, a stack of coating layers comprising a first layer of dielectric material, a second layer of reflective material, third and fourth layers of dielectric material, a fifth layer of reflective material and a sixth layer of dielectric material, whereby the Illuminant A transmission through the assembly is at least 70% and its total solar transmission is less than 55%-.

WO 90/05439 similarly relates to transparent glazing units having transparent coating stacks to reduce solar transmission and increase solar reflection. The coatings include electrically conducting components which permit optional heating of the glazing units. In its broadest aspect the claimed stack includes at least two layers of 80-180 A thick silver metal interposed between layers of dielectric material and further includes a transparent protective cover, whereby the glazing unit has an Illuminant A transmission of at least 70961, an Illuminant C reflectance not greater than 12.5%, a total solar reflectance of at least 29% and a total solar transmission not greater than 42%. The dielectric layers outside the silver layers are 200-500 A thick and the dielectric layers between the silver layers are 400-1500 thick.

The present invention relates to specific components, and to specifically selected ranges of thickness of layers, in a SCARLETB.DOC 4150 SCARLET coating stack to achieve the desired combination of a high level of luminous transmission, a low solar factor and a neutral aspect in reflection.

1278B For coated substrates to be used in windows for buildings or vehicles, it is desired that the product of which the coated substrate forms a part shall not pass too great a proportion of total incident solar radiation, i.e. in order that the interior of the building or vehicle shall not become overheated in sunny weather. The transmission of total incident solar radiation may be expressed in terms of the "solar factor" (Fs herein) As used herein, the expression "solar factor" denotes the sum of the energy directly transmitted and the energy which is absorbed and re-radiated on the side away from the energy source, and is a proportion of the total radiant energy incident on the coated substrate.

The solar factor data quoted herein are measured according to Document No. 20 of 1972 from C.I.E. (Commision Internationale de 1'Eclairage).

International patent application WO 93/19936 (CARDINAL I G COMPANY) discloses a coating for a transparent substrate which exhibits a neutral colour by transmission, through a wide range of angles of incidence of light. The coating employs a base coat adjacent to the transparent substrate having a thickness of no more than about 27.5 nm and may include two reflective metal layers having an intermediate layer of an anti-reflective metal oxide there-between and an outer antireflective layer of metal oxide over the second reflective metal layer. Such a multi-layer coated substrate yields a SCARLETB.DOC 4150 SCARLET 1278B luminous transmission of only 60t with a strong blue colour by reflection. It is however desirable for the coated substrate to have a high visible transmission, so that for example the occupants of a building can see out and sufficient light enters the building to enable the occupants to work without excessive use of artificial light. As used herein, the term "luminous transmission" (TLC herein) is to be taken to mean the luminous flux transmitted through the coated substrate as a percentage of the incident luminous flux expressed by the standard illuminant C (C.I.E.).

Commercially available solar screening products are glass sheets carrying a single or a multi-coating.

It is desired to provide coated substrates which are substantially neutral in reflection from the side opposite to the coated side (the "opposite" side as used herein), i.e. the purity of reflected colour is low. Low purity of colour has been found to be particularly difficult to achieve simultaneously with a low solar factor and a high level of luminous transmission. The purity of a colour is defined according to a linear scale where a defined white light source has a purity of zero and the pure colour has a purity of 100%. By the term "colour purity" as used herein, we mean excitation purity measured with illuminant C as defined in International Lighting Vocabulary, published by the International Commission on Illumination (CIE), 1987, pages 87 and 89. The "colour purity,, is measured from the opposite side of the product.

SCARLETB.DOC 4150 SCARLET - 5 - 1278B With coated substrates according to the prior art, there is a tendency for the dominant wavelength (XD) in reflection and the colour purity to change according to the angle of view and in particular for the coated substrates to have a pink aspect when viewed at 450 to the opposite surface.

It is an object of the present invention to provide a coated substrate having a high level of luminous transmission, a low solar factor and a neutral aspect in reflection.

We have discovered that this objective may be realised, and other advantages may be obtained, by a multi-coated substrate in which the coating layers are formed from specific materials and are present within specific thickness limits.

According to the invention there is provided a coated substrate having a high level of luminous transmission, a low solar factor and a neutral aspect in reflection, comprising a surface carrying the following coating layers in the order given:

(i) a first layer of transparent dielectric non-absorbent material adjacent the substrate having an optical thickness of between 60 and 75 nm; (ii) a first layer of silver or silver alloy having a geometric thickness of between 9 and 11 nm; (iii) a second layer of transparent dielectric non-absorbent material having an optical thickness of between 135 and nm; (iv) a second layer of silver or silver alloy having a geometric thickness of between 12 and 15 nm; SCARLETB.DOC 4150 SCARLET - 6 - 1278B (v) a third layer of transparent dielectric non-absorbent material having an optical thickness of between 45 and 65 nm, such that the coated substrate exhibits the following properties: a luminous transmission TLC greater than 70%, preferably at least 75%; a solar factor F. less than 479., preferably not more than 46%, most preferably not more than 45%; and a purity of colour in reflection normal to the opposite surface of not more than 129.-, preferably not more than 10%, most preferably not more than 99.-.

The quoted properties of the coated substrate are on the basis of a single sheet of ordinary clear soda-lime glass having a thickness of 6 mm observed from the face opposite to the coated face, i.e. from the glass side. In this respect it should be noted that the opposite face will usually be uncoated.

The relationship between the thicknesses of the various layers of nonabsorbent material and the optical properties of the coated substrate are not fully understood, but it is clear that the thickness of these layers is critical.

In a preferred embodiment of the invention, the layers have the following thicknesses:

(i) the first layer of non-absorbent material has an optical thickness of between 63 and 72 nm; (ii) the first layer of silver or silver alloy has a geometric thickness of between 9.5 and 10.5 nm; SCARLETB.DOC 4150 SCARLET - 7 - 1278B (iii) the second layer of non-absorbent material has an optical thickness of between 144 and 160 nm; (iv) the second layer of silver or silver alloy has a geometric thickness of between 13 and 14 nm; and (v) the third layer of non-absorbent material has an optical thickness of between 50 and 58 nm.

With the arrangement and thicknesses of coating layers defined and claimed herein the coated substrate has a high luminous transmission, a low solar factor and a neutral colour in reflection from the opposite side. Furthermore the stability of colour is high, that is to say that in the event of some limited variation in the thickness of one of the coatings (arising for example from a lack of uniformity of thickness between one point on the substrate to another), there is no significant variation in colour and that the colour is close to neutral when the angle of observation tends towards the normal to the opposite side.

On the other hand, the coated substrate according to the invention presents a colour in reflection when observed normal to the opposite surface which is aesthetically agreeable, without being either yellow or pink. When the purity of reflection is low, a tint of yellow or pink can be very noticeable. This colour remains aesthetically agreeable even when viewed at an angle to the surface, that is to say the reflected colour becomes neither yellow or pink as the angle of observation decreases. This is a very important factor when considering glazing panels incorporated in a large building. In fact the angle of observation of the facade of a SCARLETB. DOC 4150 SCARLET 1278B building, for example, is different when a stationary observer looks at the ground floor, an intermediate floor and the top floor of the building. If the glazing panels at the ground floor appear blue-green, while those at an intermediate floor appear pink, this change is quite noticeable. Similarly, if the observer were to move, the angle of observation would change but the colour should remain within the preferred aesthetic norms.

On the other hand this particular arrangement of layers allows one to obtain a low luminous reflection (RL herein) close to the luminous reflection obtained with an uncoated substrate.

In the coated substrates according to the invention, the nature and thicknesses of the coating layers may be such that the direct energy transmission TED (defined as the fraction of the solar energy which is transmitted through the coated substrate without change in wavelength) is preferably from 34% to 40%, advantageously from 36% to 39%.

The nature and thicknesses of the coating layers may be such that colour purity remains neutral when the angle of observation changes, in particular that the coated substrate exhibits a purity of colour in reflection at an angle of 450 to the opposite surface of less than 9%, most preferably less than 6%.

At an angle of 600 to the opposite surface (by convention the normal to the surface is taken as 00), the purity of reflected colour is preferably less than 1%.

SCARLETB.DOC 4150 SCARLET 9 - 1278B When the coated substrate is used in a simple glazing unit, constituted by a single coated sheet of clear glass having a thickness of 6 mm, the luminous transmission TLC is preferably between 70% and 81%, advantageously from 75% to 79-, the solar factor is preferably from 41% to 46% and the luminous reflection RL is preferably not more than 8%. The colour in reflection from the opposite side is neutral with a purity of preferably not more than 10%, preferably not more than 9%.

The dominant wavelength of reflection is preferably between 485 and 505 nm. Above this range a yellow colour is observed. Below this range, a pink colour is observed when the angle of observation changes. When the purity of colour in reflection normal to the opposite surface is at least 3%, it is easier to avoid the colour tending to pink when the angle of observation moves away from the normal, particularly if the dominant wavelength is at the lower end of the preferred range. In fact, when the purity is in the order of 1 - 2% and the dominant wavelength is less than 495 nm, the colour tends to pink as the angle of observation moves away from the normal, and this is particularly noticeable by the eye, in spite of the very low purity.

The metal layers comprise silver or a silver alloy, such as alloys of silver with platinum or palladium.

The coated substrate according to the invention may further comprise a layer of sacrificial material provided above (i.e. subsequently deposited) and in contact with each metal layer. The purpose of the layer of sacrificial material is to protect SCARLETB.DOC 4150 SCARLET - 10 - 1278B the silver or the silver alloy during deposition of the next nonabsorbent layer.

The coating layers are preferably applied by cathode sputtering. For reasons concerning the cathode sputtering process, each metal layer is coated with a thin layer of a sacrificial metal (a "barrier" layer) which becomes converted to the oxide during the coating process. This sacrificial metal is preferably titanium, although zinc, copper, a nickel/chromium alloy or aluminium may alternatively be used. A similar barrier layer may optionally be placed below each metal layer. The sacrificial material is preferably present in substantially fully oxidised condition, since the unoxidised material may have the effect of reducing luminous transmission. The sacrificial material becomes oxidised during the deposit of the next layer, when the next layer is deposited in a reactive (e.g. 0.) atmosphere. The term "sacrificial material" as used herein is intended to embrace not only the sacrificial metal as deposited on the silver or silver alloy layers, but also the oxide or partial oxide to which this sacrificial metal becomes converted during further processing. While these sacrificial layers provide improvement by protecting the silver layer against oxidation, improving chemical durability further by increasing the thickness of the sacrificial layers reduces the luminous transmission of the products. The thicknesses of the sacrificial material layers, if present, are therefore critical to the present invention.

SCARLETB.DOC 4150 SCARLET 1278B It is preferred that a first layer of sacrificial material (iia) having a geometric thickness of between 2.5 and 5 nm is provided between the first metal layer (ii) and the second non-absorbent layer (iii), and a second layer of sacrificial material (iva) having a geometric thickness of between 3 and 6 nm is provided between the second metal layer (iv) and the third non-absorbent layer (v).

If the next layer of non-absorbent material is a nitride (for example Si.N4) rather than an oxide, the layer is deposited in an atmosphere of nitrogen. In this case, one need not deposit a layer of sacrificial material over the silver or silver alloy layer before depositing the nitride in a nitrogen atmosphere.

The coating layers may be completed by a protective layer, such as a thin (3 nm geometric) layer of S'02, which protects the coating without significantly modifying the optical properties of the product (see British patent application No. 9417112.1 filed 24 August 1994 - Glaverbel). Otherwise the third non-absorbent layer will usually constitute an exposed layer.

Preferably, the optional thin exposed protective additional layer is selected from oxides, nitrides and oxynitrides of silicon. This layer provides the coated substrate with improved chemical and/or mechanical durability, while minimising any consequential changes in its optical properties. Advantageously, said exposed protective SCARLETB.DOC 4150 SCARLET - 12 - 1278B additional layer is S'02, most preferably having a thickness of from 2 to 5 nm (geometric).

Particularly where the thickness of the protective layer is low, the effect thereof on the optical properties of the product may be minimal.

The products according to the invention may usefully be employed in laminated glass structures. As glazing panels, the products may be installed in single or multi-glazed assemblies. The coated substrates may be used for a range of different purposes, such as glazing units of buildings, especially as double-glazing units and also windshields for vehicles, such as laminated glass structures.

A multiple glazing unit may comprise at least two sheets of transparent vitreous material positioned in face-to-face spaced apart relationship, having a gas space there-between delimited by a peripherally extending spacer, wherein at least one of the sheets is a coated substrate according to the present invention, with the coated surface directed towards the gas space.

A laminated glazing unit may comprise at least two sheets of transparent vitreous material secured to each other with the aid of an intervening film of polymer adhesive material, wherein at least one of the sheets is a coated substrate according to the present invention, with the coated surface directed towards the polymer adhesive.

SCARLETB.DOC 4150 SCARLET - 13 - 1278B In preferred embodiments of the invention where the coated substrate is incorporated in a double-glazed unit formed of two sheets of clear glass, each 6 mm in thickness, with an intervening space of 15 mm filled with argon, the luminous transmission TLC lies between 62% and 72%, advantageously between 6601 and 70%, the solar factor Fs lies between 34% and 40-0c, advantageously from 36% to 39%, the purity of colour in reflection normal to the opposite surface is not more than 8%, most preferably not more than 7% and the luminous reflection is not more than 12%. For the determination of the properties of such embodiments, the unit is considered as being installed with the coating in position 11211, (the opposite face being in position 111"), i.e. the coated substrate is positioned towards the exterior with the coated surface being directed towards is the internal gas space of the double-glazing unit.

The non-absorbent layers may be represented by a single non absorbent material such as zinc oxide, tin oxide or silicon nitride, a mixture or a complex of non-absorbent materials such as Zn2Sn04 or by a number of successive layers.

By the term "non-absorbent material,, used herein we mean materials which have a "refractive index" n(k) which is greater than, preferably substantially greater than the value of the "spectral absorption index" k(k) over the whole of the visible spectrum (380 to 780 nm). Definitions of refractive index and spectral absorption index can be found in International Lighting Vocabulary, published by the International Commission on Illumination (CIE), 1987, pages 127, 138 and 139. In particular, we have found advantage in SCARLETB.DOC 4150 SCARLET 12-78B choosing a material for which the refractive index n(k) is greater than 10 times the spectral absorption index k(k) over the wavelength range 380 to 780 nm. Most preferably, the material of the non- absorbent coating layers is selected from aluminium nitride, silicon nitride, stannic oxide, zinc oxide, zirconium oxide and mixtures thereof. It should be noted that silicon nitride is deposited using a cathode of silicon which has been doped, for example with aluminium, nickel, boron, phosphorus and/or tin, in order to facilitate the deposition process. As a result these dopant elements may be present in the non- absorbent material layer. Preferably, the nonabsorbent material has an index of refraction measured at 550 nm of between 1.85 and 2.2, advantageously between 1.9 and 2.1. Zinc oxide is a particularly preferred material due to its high deposit rate, its well adapted refractive index to the purpose of the invention and its beneficial effect on the passivation of the silver layer, but because of its relatively high porosity in thick coatings and its poor chemical resistance, it is preferred to split up the zinc oxide layer into two or more layers by another non-absorbent material, disposed there-between, such as for instance stannic oxide. Thus preferably, one or more of said layers of non-absorbent material are composite coating layers, that is a single layer containing two or more non-absorbent materials deposited simultaneously and/or successively. Advantageously, one or more of the said layers of non-absorbent material are formed alternately by zinc oxide and stannic oxide, such as ZnO/SnO./ZnO or ZnO/Sn02/ZnO/Sn02/Zno/... . etc.

SCARLETB.DOC 4150 SCARLET 1278B In some embodiments, such as for application in the field of vehicle windows, for example laminated windscreens, silicon nitride (S'3N4) is particularly preferred as the non-absorbent material, especially in view of its chemical durability. In this case, a sacrificial material layer is not really beneficial, and thus not necessarily required, between the silver layer and the non-absorbent layer deposited thereon.

It should be noted that, in the metal oxide or nitride non-absorbent material coating layer, it is not essential for the metal and the oxygen or nitrogen to be present in stoichiometric proportions.

Still further coating layers may be provided, but we have found that this may have the effect of reducing the luminous transmission. Only two or three metal layers are therefore preferred.

The substrate is preferably in the form of a sheet of vitreous material, such as glass or some other transparent rigid material.

Preferably, the substrate is clear glass, although the invention also extends to the use of coloured glass as the substrate, where the invention provides the advantage that the inherent colour of the substrate is not significantly modified by the coating.

The process for forming the products according to the invention may be carried out by introducing the substrate into SCARLETB.DOC 4150 SCARLET 16 - 1278B a processing chamber containing an appropriate magnetron sputtering source, and provided with entry and outlet gas-locks, a conveyor for the substrate, power sources, sputtering gas inlets and an evacuation outlet. The substrate is transported past the activated sputtering source and cold sputtered by an appropriate atmosphere (oxygen gas in the case of an oxide coating) to give the desired layer on the substrate. This process is repeated for each coating layer.

The invention will now be described in more detail, with reference to the following non-limiting examples.

EXAMPLE 1

A sheet of glass was introduced into a processing chamber containing a number of planar magnetron sputtering sources and provided with entry gaslocks, a conveyor for the substrate, power sources, sputtering gas inlets and an evacuation outlet. The deposition is achieved by the substrate being passed several time under the same cathodes. The on-line deposition apparatus comprises two deposition chambers and one entry lock. The first chamber is intended for the deposition of oxides (or nitrides) in a reactive atmosphere (oxygen or nitrogen) and comprises a number of cathodes provided with targets formed of zinc and tin, which are required for the deposition of the coating. The second chamber is intended for the deposition of metals in an inert atmosphere (Ar) and comprises a silver cathode and a titanium cathode. The substrate makes a number of return passages, under the cathodes activated as necessary, in order to obtain the SCARLETB.DOC 4150 SCARLET desired succession of coating layers. The pressure in each chamber was reduced to 0.3 Pa.

The coated properties: Substrate: Layer (i) Layer (ii) product had the following composition and optical 6 mm clear glass 35 nm zinc oxide 9.5 nm silver Layer (iia) 3 nm titanium Layer (iii) 75 nm zinc oxide Layer (iv) 13.5 nm silver Layer (iva) 5.5 = titanium Layer (v) 26 nm zinc oxide Sinq1e qlazinq shee 1278B Transmission (TLC) Solar factor (F,) Direct energy transmission (TED) Luminous reflection Purity of reflected colour (normal) Outside sheet of a double qlazinq uni Transmission (TLC) Solar factor (F,) Luminous reflection Dominant wavelength XD (normal) Purity of colour (normal) Dominant wavelength XD (4511) Purity of colour (450) SCARLETB.DOC 7 6 % 43. 5% 37% 7 - 89. 6.605 t:

490 = 6.3% 490 nm 4. 55-16 4150 SCARLET - 18 - 1278B EXAMPLE 2 is In a first variation of Example 1, the layers of zinc oxide are subdivided into ZnO/Sn02/ZnO layers according to the proportions 3/4 ZnO and 1/4 Sn02. The total thickness of these layers is proportionally reduced to take account of the difference between the index of refraction of ZnO (about 2.0) and Sn02 (about 1.9) in order to conserve the same optical thickness as the ZnO-only layers of Example 1. The observed properties are identical, but the coating is more resistant to corrosion.

EXAMPLES 3 & 4 In variants of Example 2, a thin (3 nm) protective coating of S'02 is deposited over the final coating layer without modifying the optical properties of the coated substrate, while providing an improved chemical and/or mechanical durability for the coated substrate in the case of both Examples 3 and 4, and while being fully compatible with the PVB (polyvinylbutyral) intermediate film in the case of Example 4.

EXAMPLES 5-9

In further variations of Example 1, coatings of the compositions shown in Table Al were applied to the glass substrate. In accordance with the definitions in the claims the quoted thicknesses of the ZnO layers are optical thicknesses and those for the Ag and Ti are geometric SCARLETB.DOC 4150 SCARLET - 19 - 12-78B thicknesses. To assist in comparing optical and geometric thicknesses it is mentioned here that the refractive index of ZnO is 2.0 and the refractive index of Ti02 is about 2.5 (optical thickness = geometric thickness x refractive index).

The coated product had the optical properties shown in Table A2. It will be seen that the coating stacks of the invention achieve highly effective combinations of light transmission, solar factor and colour purity. Perhaps most notable are the low solar factors, including one (Example 6) as low as 42%.

SCARLETB.DOC 4150 SCARLET Table A1

1278B Example Coating Layers (nm) ZnO Ag Ti znO Ag Ti 60 9 3 135 12 3 6 75 11 3 160 15 3 7 75 10 3 140 14 3 8 75 9.5 3 156 13.5 3 9 60 9.5 3 156 13.5 3 ZnO 40 55 50 56 56 Table A2

Example Single lazing Double GIa23ng TLC Fs %D Purity TLC Fs X-D ty (%) M (nm) (%) M M M 74 44.7 456 5 66 37.2 460 3.6 6 72 42 493 12 65 34.9 494 9 7 73.5 44 493 6 66 37.3 498 3.9 8 76 46 504 6 68 37 500 4 9 74 46 496 10 66 36 498 7 SCARLETB.DOC 4150 SCARLET

Claims

1. A coated substrate having a high level of luminous transmission, a low solar factor and a neutral aspect in reflection, comprising a surface carrying the following coating layers in the order given:

(i) a first layer of transparent dielectric non-absorbent material adjacent the substrate having an optical thickness of between 60 and 75 nm; (ii) a first layer of silver or silver alloy having a geometric thickness of between 9 and 11 nm; (iii) a second layer of transparent dielectric non-absorbent material having an optical thickness of between 135 and nm; (iv) a second layer of silver or silver alloy having a geometric thickness of between 12 and 15 nm; (v) a third layer of transparent dielectric non-absorbent material having an optical thickness of between 45 and 65 nm, such that the coated substrate exhibits the following properties:

luminous transmission TLC greater than 70 solar factor Fs less than 47 t; and a purity of colour in reflection normal to the opposite surface of not more than 12%.

1278B

2. A coated substrate according to claim 1, wherein the nature and thicknesses of the coating layers are such that the coated substrate exhibits a direct energy transmission TE,)of from 340-. to 40%.

SCARLETB.DOC 4 4150 SCARLET - 22 - 1278B

3. A coated substrate according to claim 1 or 2, wherein the nature and thicknesses of the coating layers are such that the luminous transmission TLC is not less than 75%.

4. A coated substrate according to any preceding claim, wherein the nature and thicknesses of the coating layers are such that the solar factor Fs is not more than 46t, preferably not more than 45t.

5. A coated substrate according to any preceding claim, wherein the nature and thicknesses of the coating layers are such that the purity of colour in reflection normal to the opposite surface is not more than 10%, preferably not more than 9%.

6. A coated substrate according to any preceding claim, wherein the nature and thicknesses of the coating layers are such that the purity of colour in reflection normal to the opposite surface is at least 3%.

7. A coated substrate according to any preceding claim, wherein the nature and thicknesses of the coating layers are such that the coated substrate exhibits a purity of colour in reflection at an angle of 450 to the opposite surface of not more than 9 t.

8. A coated substrate according to any preceding claim, wherein: (i) the first layer of non-absorbent material has an optical thickness of between 63 and 72 nm; SCARLETB.DOC 4150 SCARLET - 23 - 1278B (ii) the first layer of silver or silver alloy has a geometric thickness of between 9.5 and 10.5 nm; (iii) the second layer of non-absorbent material has an optical thickness of between 144 and 160 nm; (iv) the second layer of silver or silver alloy has a geometric thickness of between 13 and 14 nm; and (v) the third layer of non-absorbent material has an optical thickness of between 50 and 58 nm.

9. A coated substrate according to any preceding claim, further comprising a sacrificial material provided above and in contact with each metal layer.

10. A coated substrate according to claim 9, wherein the said sacrificial material is titanium.

11. A coated substrate according to claim 9 or 10, wherein the said sacrificial material is in a substantially fully oxidised condition.

12. A coated substrate according to any one of claims 9 to 11, comprising: (iia) a first layer of sacrificial material having a geometric thickness of between 2.5 and 5 nm, positioned between the first layer of silver or silver alloy and the second layer of non-absorbent material.

(iva) a second layer of sacrificial material having a geometric thickness of between 3 and 6 nm, positioned between the second layer of silver or silver alloy and the third layer of non-absorbent material.

SCARLETB.DOC 4150 SCARLET - 24 - 1278B

13. A coated substrate according to any preceding claim, wherein the said non-absorbent material is selected from zinc oxide, tin oxide, silicon nitride and mixtures thereof.

14. A coated substrate according to any preceding claim, wherein the said non-absorbent material has an index of refraction measured at 550 nm of between 1.85 and 2.2.

15. A coated substrate according to claim 14, wherein the said nonabsorbent material has an index of refraction measured at 550 nm of between 1.9 and 2.1.

16. A coated substrate according to any preceding claim, wherein one or more of the said layers of non-absorbent material are composite coating layers.

17. A coated substrate according to any preceding claim, wherein the dominant wavelength of reflection from the opposite surface lies between 485 and 505 nm.

18. A multiple glazing unit comprising at least two sheets of transparent vitreous material positioned in face-toface spaced apart relationship, having a gas space therebetween delimited by a peripherally extending spacer, characterised in that at least one of the said sheets is a coated substrate according to any one of claims 1 to 17, with the coated surface directed towards the said gas space.

SCARLETB.DOC 4150 SCARLET - 25 - 1278B

19. A multiple glazing unit according to claim 18, wherein the purity of colour in reflection normal to the opposite surface is not more than 8%, preferably not more than 7 %.

SCARLETB.DOC