Low-E matchable coated articles and methods of making same

[0002] This is a continuation-in-part (CIP) of commonly owned U.S. patent application Ser. No. 09/455,026, filed Dec. 6, 1999.

[0003] This invention relates to low-E coated articles that have approximately the same color characteristics as viewed by the naked eye both before and after heat treatment (e.g., thermal tempering), and corresponding methods. Such coated articles may be used in insulating glass (IG) units, windshields, and other suitable applications.

[0004] Solar control coating systems are known. For example, commonly owned U.S. Pat. No. 5,688,585 discloses a solar control coated article including: glass/Si₃N₄/NiCr/Si₃N₄. One object of the '585 patent is to provide a sputter coated layer system that after heat treatment is matchable colorwise with its non-heat treated counterpart. While the coating systems of the '585 patent are excellent for their intended purposes, they suffer from certain disadvantages. In particular, they tend to have rather high emissivity values (e.g., because no silver (Ag) layer is disclosed in the '585 patent).

[0005] Low-emissivity (low-E) coating systems are also known in the art. For example, commonly owned U.S. Pat. No. 5,376,455 discloses: glass/Si₃N₄/NiCr/Ag/NiCr/Si₃N₄. Low-E coating systems such as this are typically designed for maximum visible transmission. For this reason, the NiCr layers are made rather thin. This enables high transmission and low-E characteristics, but less than desirable solar control (e.g., shading coefficient) characteristics. Thus, the low-E coating system of the '455 patent is unfortunately not sufficiently color matchable after heat treatment with its non-heat treated counterpart, and lacks superior solar control characteristics such as shading coefficient (SC).

[0006] Accordingly, when it is desired to provide an insulating glass (IG) unit with both low emissivity (low-E) and solar control characteristics, it has often been necessary to combine the solar control coating of the '585 patent with the low-E coating of the '455 patent in a single IG unit. For example, the solar control coating of the '585 patent is placed on the #2 surface of the IG unit while the low-E coating of the '455 patent is placed on the #3 surface of the IG unit. The need for these two separate and distinct coatings in an IG unit is undesirable, for both cost and processing reasons.

[0007] The need for matchability (before heat treatment vs. after heat treatment) is also known. Glass substrates are often produced in large quantities and cut to size in order to fulfill the needs of a particular situation such as a new multi-window and door office building, vehicle windshield needs, etc. It is often desirable in such applications that some of the windows and/or doors be heat treated (i.e., tempered, heat strengthened or bent) while others need not be. Office buildings often employ IG units and/or laminates for safety and/or thermal control. It is desirable that the units and/or laminates which are heat treated substantially match their non-heat treated counterparts (e.g., with regard to color, reflectance, and/or the like, at least on the glass side) for architectural and/or aesthetic purposes. In addition, it is sometimes desirable that certain windows, doors, windshields, etc. be of a substantially neutral color, preferably tending to the blue-green side of the spectrum.

[0008] It has in the past been possible to achieve matchability in systems other than those of the aforesaid '585 patent, but only between two different layer systems, one of which is heat treated and the other is not. The necessity of developing and using two different layer systems to achieve matchability creates additional manufacturing expense and inventory needs which are undesirable.

[0009] U.S. Pat. Nos. 6,014,872 and 5,800,933 (see Example B) disclose a heat treatable low-E layer system including: glassTiO₂/Si₃N₄/NiCr/Ag/NiCr/Si₃N₄. Unfortunately, when heat treated this low-E layer system is not approximately matchable colorwise with its non-heat treated counterpart (as viewed from the glass side). This is because this low-E layer system has a ΔE_ab*(glass side) value of greater than 4.1 (i.e., for Example B, Δa*_Gis 1.49, Δb*_Gis 3.81, and ΔL* is not measured; using Equation (1) below then ΔE on the glass side must necessarily be greater than 4.1 and is probably much higher than that).

[0010] In view of the above, it will be apparent to those skilled in the art that there exists a need for a coating or layer system that could satisfy both solar control and low-E requirements (e.g., so a solar control coating and a separate low-E coating need not be used together on different surfaces of the same IG unit). In addition to and/or instead of the above need, there also exists a need in the art for a low-E coating or layer system which after heat treatment substantially matches in color and/or reflection (as viewed by a naked human eye from the glass side) its non-heat treated counterpart. In other words, there exists a need in the art for a low-E matchable coating or layering system.

[0011] It is a purpose of this invention to fulfill any and/or all of the above-listed needs, and/or other needs which will become more apparent to the skilled artisan once given the following disclosure.

[0012] An object of this invention is to provide a low-E coating or layer system that has good color stability with heat treatment.

[0013] Another object of this invention is to provide a low-E matchable coating or layering system.

[0014] Another object of this invention is to provide a coating or layer system that has improved IR reflectance characteristics relative to those of the coating systems described in U.S. Pat. No. 5,688,585.

[0015] Another object of this invention is to provide a coating or layer system that when heat treated is substantially matchable to its non-heat treated counterpart.

[0016] Another object of this invention is to fulfill one or more of the above-listed objects.

[0017] It has been surprisingly found that silver in rather substantial thicknesses may be employed while still achieving color stability with heat treatment (e.g., thermal tempering, bending, or heat strengthening). The layer systems of the invention may be utilized, for example, in the context of IG units, vehicle windows and windshields, or the like.

[0018] According to certain exemplary embodiments of this invention, one or more of the above-listed objects or needs is/are fulfilled by providing a coated article comprising:

[0019] a layer system supported by a glass substrate, said layer system comprising an infrared (IR) reflecting silver layer located between first and second dielectric layers; and

[0020] wherein said coated article has a ΔE*_abvalue (glass side) no greater than 3.0 (more preferably no greater than 2.5) after or due to heat treatment.

[0021] Further embodiments of this invention fulfill one or more of the above-listed needs or objects by providing a coated article comprising:

[0022] a substrate;

[0023] a layer system provided on the substrate, said layer system comprising from the glass outwardly, a first silicon nitride inclusive layer, a first Ni or NiCr inclusive layer, an IR reflecting metal layer, a second Ni or NiCr inclusive layer, and a second silicon nitride inclusive layer;

[0024] wherein each of said first and second Ni or NiCr inclusive layers is at least about 20 Å thick; and

[0025] wherein said coated article has a hemispherical emissivity (E_h) of no greater than 0.25 before heat treatment, a sheet resistance R_Sno greater than 20 ohms/square before heat treatment, and a ΔE*_abvalue (glass side) no greater than 2.5 after or due to heat treatment.

[0026] Other embodiments of this invention fulfill one or more of the above-listed needs or objects by providing a method of making a coated article, the method comprising:

[0027] depositing a layer system on a glass substrate, the layer system including an infrared (IR) reflecting metal layer located between first and second dielectric layers, wherein prior to heat treatment the glass substrate with the layer system thereon has a sheet resistance R_Sno greater than 20 ohms/square; and

[0028] heat treating the substrate with the layer system thereon so that due to said heat treating the resulting substrate with the layer system thereon has a ΔE*_abvalue (glass side) no greater than 2.5.

[0029] This invention will now be described with respect to certain embodiments thereof as illustrated in the following drawings, wherein:

[0030] FIG. 1 is a partial side cross sectional view of an embodiment of a layer system according to this invention.

[0031] FIG. 2 is a partial cross-sectional view of an IG unit as contemplated by this invention, in which the layer system of FIG. 1 may be used.

[0032] Certain embodiments of this invention provide a coating or layer system that may be used in applications such as IG units, vehicle windows, vehicle windshields, and other suitable applications. Certain embodiments of this invention provide a layer system that has excellent color stability (i.e., a low value of ΔE and/or a low value of Δa*; where Δ is indicative of change in view of heat treatment) with heat treatment (e.g., thermal tempering, bending, or thermal heat strengthening) both monolithically and in the context of dual pane environments such as IG units or windshields. Such heat treatments often necessitate heating the coated substrate to temperatures above 1100° F. (593° C.) and up to 1450° F. (788° C.) for a sufficient period of time to insure the end result (e.g., tempering, bending, and/or heat strengthening). Certain embodiments of this invention combine both (i) color stability with heat treatment, and (ii) the use of a silver layer for IR reflection. Certain embodiments of this invention combine (i) and (ii), along with (iii) color in the blue-green quadrant (i.e., third quadrant) of the color spectrum when applied to a clear and/or green glass substrate. Certain embodiments of this invention combine (i), (ii) and (iii), along with (iv) low-emissivity characteristics.

[0033] FIG. 1 is a side cross sectional view of a coated article according to an embodiment of this invention. The coated article includes substrate 1 (e.g., clear, green, bronze, or blue-green glass substrate from about 1.0 to 10.0 mm thick), first dielectric layer 3 (e.g., of or including silicon nitride (e.g., Si₃N₄), titanium dioxide, silicon oxide, silicon dioxide, silicon oxynitride, or zinc oxide), nickel (Ni) or nickel-chrome (NiCr) inclusive layer 5 (other oxidation resistant materials may be used instead of Ni or NiCr in alternative embodiments of this invention), IR reflecting silver (Ag) inclusive layer 7, nickel (Ni) or nickel-chrome (NiCr) inclusive layer 9 (other oxidation resistant materials may be used instead of Ni or NiCr in alternative embodiments of this invention), and second dielectric layer 11 (e.g., of or including silicon nitride (e.g., Si₃N₄), titanium dioxide, silicon oxide, silicon dioxide, silicon oxynitride, or zinc oxide). Other layer(s) below or above the illustrated coating system may also be provided. Thus, while the layer system is “on” or “supported by” substrate 1 (directly or indirectly), other layer(s) may be provided therebetween. Thus, for example, the layer system of FIG. 1 may be considered “on” the substrate 1 even though other layer(s) are provided therebetween.

[0034] IR reflecting Ag layer 7 is preferably Ag metal, although it is possible that some small amount of oxidation could occur with respect thereto. The same is true for Ni or NiCr layers 5 and 9. Thus, in certain preferred embodiments of this invention, layers 5, 7 and 9 are no more than about 25% oxidized, more preferably no more than about 10% oxidized, and most preferably no more than 1% oxidized. In certain preferred embodiments, layers 5 and/or 9 are of non-nitrided and nonoxidized nickel or nickel alloy (e.g., nichrome of, by weight percent, 80/20 nickel/chrome). An exemplary apparatus which may be used to form the layer coating systems of this invention is a conventional sputter coating system, such as the multichamber G-49 large area flat glass sputter coater produced by Airco, Inc.

[0035] In embodiments of this invention where layers 3 and 11 comprise Si₃N₄, a target including Si employed to form these layers may be admixed with up to 6-20% by weight aluminum or stainless steel (e.g. SS#316), with about this amount then appearing in the layers so formed. Moreover, while layers 5 and 9 may be metallic nickel, a nichrome preferably consisting essentially of, by weight about 80-90% Ni and 10-20% Cr, may be employed in certain preferred embodiments. Other metals may also be used in alternative embodiments. Moreover, while it is possible to employ certain other IR reflecting metals as layer 7, l such as gold or platinum in certain embodiments of this invention, layer 7 herein consists essentially of metallic silver in certain embodiments of this invention. An example of layers 5 and 9 includes not only SS-316 which consists essentially of 10% Ni and 90% other ingredients, mainly Fe and Cr, but Haynes 214 alloy as well, which by weight consists essentially of (as a nominal composition):

[0036] In other embodiments of this invention, coated articles may be as follows: glass/silicon nitride/nichrome/silver/nichrome/silver/nichrome/silicon nitride. In such embodiments, the respective silicon nitride, nichrome and/or silver layers may have thicknesses similar to those discussed for these material in other embodiments of this invention. Alternatively, certain layers may be thinner, for example as follows: glass/silicon nitride (40 Å)/nichrome(35 Å)/silver(50 Å)/nichrome(30 Å)/silver(50 Å)/nichrome(35 Å)/silicon nitride(261 Å). It is believed that these dual silver embodiments will experience color stability characteristics similar to those of the FIG. 1 embodiment as described herein. This embodiment may even experience better durability than the FIG. 1 embodiment in certain instances.

[0037] FIG. 2 illustrates the coating or layer system 22 of FIG. 1 (or of the aforesaid dual silver embodiment) being utilized on surface #2 of an IG window unit. In order to differentiate the “inside” of the IG unit from its “outside”, the sun 19 is schematically presented on the outside. The IG unit includes outside glass pane or sheet 21 and inside glass pane or sheet 23. These two glass substrates (e.g. float glass 2 mm to 8 mm thick) are sealed at their peripheral edges by a conventional sealant 25 and are provided with a conventional desiccant strip 27. The panes are then retained in a conventional window or door retaining frame (shown in partial schematic form). By sealing the peripheral edges of the glass sheets and replacing the air in chamber 30 with a gas such as argon, a typical, high insulating value IG unit is formed. Either inner wall 24 or 26 (or both) may be provided with a layer system (see FIG. 1) of this invention. In this illustrated embodiment of FIG. 2, inner wall 24 (i.e., surface #2) of outside glass sheet 21 has been provided with a sputter-coated layer system of FIG. 1 thereon.

[0038] Turning back to FIG. 1, while various thicknesses may be used consistent with one or more of the objects and/or needs discussed herein, according to certain exemplary embodiments of this invention, the preferred thicknesses and materials for the respective layers on the glass substrate 1 are as follows:

[0039] As can be seen from Table 1 above, the upper Ni or NiCr layer 9 has been substantially thickened relative to embodiments of the aforesaid '455 patent. These thicknesses are preferably met before and/or after any heat treatment. Moreover, the lower dielectric layer 3 has been thinned relative to the '455 patent. Surprisingly, it is believed that one or more of these changes results in the matchability or lower ΔE values (to be described below) associated with certain embodiments of this invention (i.e., improved stability with heat treatment). One or both of these changes may also be associated with improved durability experienced by certain embodiments of this invention. Also, it is noted that these embodiments represent a significant improvement over the '585 patent because the instant inventor has found a way to (i) use an Ag layer to reflect IR so as to achieve a low-E layer system, and at the same time (ii) have good stability with heat treatment (i.e., a low ΔE and/or Δa* value(s)). This combination of a low-E system with good stability with heat treatment is believed novel and inventive.

[0040] In certain exemplary embodiments, the stability with heat treatment results in substantial matchability between heat treated and non-heat treated versions of the coating or layer system. In other words, in monolithic and/or IG applications, in certain embodiments of this invention two glass substrates having the same coating system thereon (one heat treated after deposition and the other not heat treated) appear to the naked human eye to look substantially the same when viewed from the glass side of the product (i.e. looking through at least one substrate of glass before viewing the coating). In certain embodiments of this invention it has also been found that matchability (while achievable in monolithic applications) may even be improved in IG and/or laminate applications.

[0041] Thus, in certain embodiments, matchability is achieved monolithically. However, other embodiments only achieve matchability when used in a dual or multi-glass substrate structure such as an IG unit. While the precise reason for these latter embodiments may not be fully understood, it is believed that by using two or more glass substrates located in transmitting (and thus reflecting) relationship with one another, the reflection of visible light from the glass substrate opposite the viewed substrate tends to mask or cancel any difference in appearance between the heat treated, coated substrate being viewed when compared to its unheat treated counterpart. It is further believed that when the light transmittance of the coatings of this invention increase during heat treatment, this enhances the aforesaid masking affect, thus further canceling any difference. It, therefore, becomes an unexpected beneficial characteristic of certain embodiments of this invention due to this masking effect, that the heat treated coated substrate if employed monolithically, i.e. compared to itself when non-heat treated, need not be matchable in order to achieve matchability in the articles of this invention (but may be in certain embodiments). Thus, in certain embodiments, the ΔE of the monolithic (individual) substrate may be substantially higher than 2.5 and matchability still be achieved in the dual or multipane articles of this invention.

[0042] The values ΔE and Δa* are important in determining whether or not there is matchability, or substantial matchability, in the context of this invention. Color herein is described by reference to the conventional a*, b* values, which in certain embodiments of this invention are both negative in order to provide color in the desired substantially neutral color range tending to the blue-green quadrant. The term Δa* is simply indicative of how much color value a* changes due to heat treatment.

[0043] The term ΔE is well understood in the art and is reported, along with various techniques for determining it, in ASTM 2244-93 as well as being reported in Hunter et. al., The Measurement of Appearance,2^ndEd. Cptr. 9, page 162 et seq. [John Wiley & Sons, 1987]. As used in the art, ΔE is a way of adequately expressing the change (or lack thereof) in reflectance and/or transmittance (and thus color appearance, as well) in an article after or due to heat treatment. ΔE may be calculated by the “ab” technique, or by the Hunter technique (designated by employing a subscript “H”). Both are deemed useful, and equivalent for the purposes of this invention. For example, as reported in Hunter et. al. referenced above, the rectangular coordinate/scale technique (CIE LAB 1976) known as the L*, a*, b* scale may be used, wherein:

[0044] L* is (CIE 1976) lightness units

[0045] a* is (CIE 1976) red-green units

[0046] b* is (CIE 1976) yellow-blue units

[0047] and the distance ΔE between L*_oa*_ob*_oand L*₁a*₁b*₁is:

[0048] ΔE*_ab=[(ΔL*)²+(Δa*)²+(Δb*)²]^1/2  (1)

[0049] where:

[0050] ΔL*=L*₁−L*_o  (2)

[0051] Δa*=a*₁−a*_o  (3)

[0052] Δb*=b*₁−b*_o  (4)

[0053] where the subscript “o” represents the coating (coated article) before heat treatment and the subscript “1” represents the coating (coated article) after heat treatment; and the numbers employed (e.g., a*, b*, L) are those calculated by the aforesaid (CIE LAB 1976) L*, a*, b* coordinate technique. Thus, ΔE may be recited as ΔE*_aband vice versa. Also within the scope of this invention and the quantification of ΔE are the equivalent numbers if converted to those calculated by any other technique employing the same concept of ΔE as defined above.

[0054] In certain embodiments of this invention, layer systems herein provided on clear monolithic glass substrates have color as follows before heat treatment, as viewed from the glass side of the coated article (R_G%):

[0055] After heat treatment, in certain embodiments of this invention layer systems provided on clear monolithic glass substrates have color characteristics ΔE and Δa* as follows, when viewed from the glass (G) side (as opposed to the layer side) of the coated article:

[0056] Accordingly, coated articles according to certain embodiments of this invention have a ΔE*_abvalue (glass side) of no greater than 3.0, more preferably no greater than 2.5, and even more preferably no greater than 2.0; and have a Δa* value (glass side) of no greater than about 1.0, more preferably no greater than 0.8. When one or both of these are achieved, matchability may result. It is noted that b* values are not deemed as important as a* values, because a* changes are believed to be more noticeable to the naked human eye than are b* changes in certain instances.

[0057] The following four Example coated articles (each annealed and heat treated) were made in accordance with certain embodiments of this invention. For each of the four Examples, the layer system was: glass/Si₃N₄/NiCr/Ag/NiCr/Si₃N₄(e.g., see FIG. 1). For each of these Examples, the substrate was of substantially clear 5.6-6.0 mm thick soda-lime-silica glass. The coater/process setups for the four Examples were as follows.

[0058] With regard to Examples 1-2, they were made using a G-49 large area flat glass sputter coater produced by Airco, Inc., using line speed of 170 IPM, with coat zones 3-5 being used; where “*” means Al content of approximately 10% and gas (e.g., Ar, N₂) flow was measured in sccm units. All targets for Examples 1-2 were C-Mag targets, except that the targets used for depositing the Ag and NiCr layers (target #s 19-21) were planar. Moreover, in Examples 1-2 the first silicon nitride layer was deposited in coat zone 3 using AC power, the NiCr and Ag layers were deposited in coat zone 4 using DC power, and the overcoat silicon nitride layer was deposited in coat zone 5 using AC power. The coater was set up and ran as follows during the sputtering of Examples 1-2:

[0059] Examples 3-4 were made using a Leybold TG-1 sputter coater using line speed of 4 m/min.; where “*” again means aluminum (Al) target content of approximately 10% and gas (e.g., Ar, N₂) flow was measured in sccm units. Target #s 34, 42, 55 and 61 were 2 x C-Mag targets, target #s 44, 51 and 53 were planar targets, and target #65 was a Twin-Mag target. Pressure was measured in mTorr. The coater was set up and ran as follows during the sputtering of Examples 3-4:

[0060] After being sputtered onto a glass substrate as set forth above, Examples 1-4 were tested and were found to have the following characteristics monolithically (not in a IG unit), where the heat treatment was thermally tempering the monolithic product in a conventional tempering furnace at approximately 1265° F. for three minute cycles and quenching to room temperature (note: a* and b* color coordinate values are in accordance with CIE LAB 1976, Ill. C 10 degree observer technique):

[0061] Moreover, each of Examples 1-4 was found to be chemically and mechanically durable as these terms are defined below, both before and after heat treatment.

[0062] As can be seen from the above, each of Examples 1-4 had good matchability because, as viewed from the glass (G) side of the respective articles, ΔE*_abwas no greater than 2.5, and preferably no greater than 2.0; while Δa*_G(the absolute value thereof, as used herein) was no greater than 1.0, and preferably no greater than 0.8. These values (i.e., ΔE and Δa*) are important as measured from the glass (G) side of the coated article, as opposed to the film (F) side because viewers in most applications predominantly view the products from the glass sides thereof. With regard to matchability for example, Example 3 had the following values (viewed from the glass (G) side):

[0063] Thus, using the equation ΔE*_ab=[(ΔL*)²+(Δa*)²+(Δb*)²]^1/2, it can be determined that [(1.47)²+(0.36)²+(0.32)²]^1/2=(2.3929)^1/2=1.5=ΔE*_ab(glass side). This relatively low ΔE*_abvalue from the G side of the article indicates good matchability (before versus after heat treatment).

[0064] Each of the above-listed examples also had low-emissivity characteristics as shown by each of the above-listed Examples having a hemispherical emissivity (E_h) no greater than 0.25, and more preferably no greater than 0.20, before and/or after heat treatment (HT). Thicker Ag layers may also be used, which would provide lower emissivity and/or sheet resistance than those report here, in accordance with certain embodiments of this invention. Compare these low emissivity values to the hemispherical emissivity values of 0.48 to 0.73 in U.S. Pat. No. 5,688,585. Each of the aforesaid Examples 1-4 was also characterized by low sheet resistance values of R_Sno greater than 20 ohms/square, more preferably no greater than 15 ohms/square, and even more preferably no greater than about 12 ohms/square (before and/or after HT). Again, compare these low sheet resistance (R_S) values to the sheet resistance values of 89-269 ohms/square in U.S. Pat. No. 5,688,585. Accordingly, it can be seen that Examples 1-4 herein truly have low-E characteristics while at the same time surprisingly being able to achieve substantial matchability before versus after heat treatment.

[0065] Coated articles according to certain embodiments of this invention preferably have a visible transmittance (TY%) of no greater than about 60%, more preferably from about 40-60% before HT, and most preferably from about 48-58% before HT. Coated articles according to certain embodiments of this invention preferably have a visible transmittance (TY%) of from about 45-65% after HT, more preferably from about 50-60% after HT. In a similar manner, coated articles according to certain embodiments of this invention preferably have a shading coefficient (SC) of no greater than about 0.65 (before and/or after HT), more preferably from about 0.40 to 0.60 (before and/or after HT). Additionally, coated articles according to certain embodiments of this invention preferably have a glass side reflectance value (R_GY %) of at least 12%, and more preferably from 12-20% before HT and from about 11-19% after HT.

[0066] It can also be seen that according to certain preferred embodiments of this invention coated articles are characterized by an a*_Gvalue of from about 0.0 to −4.0, more preferably from about 0.0 to −2.5, before and/or after heat treatment. This enables coated articles according to certain embodiments of this invention to have a desirable neutral or blue-green color, especially when b*_Gis also negative.

[0067] The aforesaid characteristics may be measured at a glass substrate thickness of about 6 mm, or any other suitable substrate thickness from 1-10 mm. Moreover, it is noted that the units of Examples 1-4 may ultimately be utilized in the context of an IG unit, a windshield, window or the like.

[0068] Certain terms are prevalently used in the glass coating art, particularly when defining the properties and solar management characteristics of coated glass. Such terms are used herein in accordance with their well known meaning. For example, as used herein:

[0069] Intensity of reflected visible wavelength light, i.e. “reflectance” is defined by its percentage and is reported as R_XY (i.e. the Y value cited below in ASTM E-308-85), wherein “X” is either “G” for glass side or “F” for film side. “Glass side” (e.g. “G”) means, as viewed from the side of the glass substrate opposite that on which the coating resides, while “film side” (i.e. “F”) means, as viewed from the side of the glass substrate on which the coating resides.

[0070] Color characteristics are measured and reported herein using the CIE LAB 1976 a*, b* coordinates and scale (i.e. the CIE 1976 a*b* diagram). Other similar coordinates may be equivalently used such as by the subscript “h” to signify the conventional use of the Hunter method (or units) Ill. C, 10° observer, or the CIE LUV u*v* coordinates. These scales are defined herein according to ASTM D-2244-93 “Standard Test Method for Calculation of Color Differences From Instrumentally Measured Color Coordinates” Sep. 15, 1993 as augmented by ASTM E-308-85, Annual Book of ASTM Standards, Vol. 06.01 “Standard Method for Computing the Colors of Objects by 10 Using the CIE System” and/or as reported in IES LIGHTING HANDBOOK 1981 Reference Volume.

[0071] The terms “emissivity” and “transmittance” are well understood in the art and are used herein according to their well known meaning. Thus, for example, the term “transmittance” herein means solar transmittance, which is made up of visible light transmittance (TY), infrared energy transmittance, and ultraviolet light transmittance. Total solar energy transmittance (TS) is then usually characterized as a weighted average of these other values. With respect to these transmittances, visible transmittance, as reported herein, is characterized by the standard Illuminant C technique at 380-720 nm; infrared is 800-2100 nm; ultraviolet is 300-400 nm; and total solar is 300-2100 nm. For purposes of emissivity, however, a particular infrared range (i.e. 2,500-40,000 nm) is employed.

[0072] Visible transmittance can be measured using known, conventional techniques. For example, by using a spectrophotometer, such as a Beckman 5240 (Beckman Sci. Inst. Corp.), a spectral curve of transmission is obtained. Visible transmission is then calculated using the aforesaid ASTM 308/2244-93 methodology. A lesser number of wavelength points may be employed than prescribed, if desired. Another technique for measuring visible transmittance is to employ a spectrometer such as a commercially available Spectrogard spectrophotometer manufactured by Pacific Scientific Corporation. This device measures and reports visible transmittance directly. As reported and measured herein, visible transmittance (i.e. the Y value in the CIE tristimulus values, ASTM E-308-85) uses the Ill. C., 10 degree observer.

[0073] “Emissivity” (E) is a measure, or characteristic of both absorption and reflectance of light at given wavelengths. It is usually represented by the formula:

[0074] E=1−Reflectance_film

[0075] For architectural purposes, emissivity values become quite important in the so-called “mid-range”, sometimes also called the “far range” of the infrared spectrum, i.e. about 2,500-40,000 nm., for example, as specified by the WINDOW 4.1 program, LBL-35298 (1994) by Lawrence Berkeley Laboratories, as referenced below. The term “emissivity” as used herein, is thus used to refer to emissivity values measured in this infrared range as specified by the 1991 Proposed ASTM Standard for measuring infrared energy to calculate emittance, as proposed by the Primary Glass Manufacturers' Council and entitled “Test Method for Measuring and Calculating Emittance of Architectural Flat Glass Products Using Radiometric Measurements”. This Standard, and its provisions, are incorporated herein by reference. In this Standard, emissivity is reported as hemispherical emissivity (E_h) and normal emissivity (E_n).

[0076] The actual accumulation of data for measurement of such emissivity values is conventional and may be done by using, for example, a Beckman Model 4260 spectrophotometer with “VW” attachment (Beckman Scientific Inst. Corp.). This spectrophotometer measures reflectance versus wavelength, and from this, emissivity is calculated using the aforesaid 1991 Proposed ASTM Standard which has been incorporated herein by reference.

[0077] Another term employed herein is “sheet resistance”. Sheet resistance (R_S) is a well known term in the art and is used herein in accordance with its well known meaning. It is here reported in ohms per square units. Generally speaking, this term refers to the resistance in ohms for any square of a layer system on a glass substrate to an electric current passed through the layer system. Sheet resistance is an indication of how well the layer or layer system is reflecting infrared energy, and is thus often used along with emissivity as a measure of this characteristic. “Sheet resistance” may for example be conveniently measured by using a 4-point probe ohmmeter, such as a dispensable 4-point resistivity probe with a Magnetron Instruments Corp. head, Model M-800 produced by Signatone Corp. of Santa Clara, Calif.

[0078] “Chemical durability” or “chemically durable” is used herein synonymously with the term of art “chemically resistant” or “chemical stability”. Chemical durability is determined by boiling a 2″×S″ sample of a coated glass substrate in about 500 cc of 5% HCl for one hour (i.e. at about 220° F.). The sample is deemed to pass this test (and thus the layer system is “chemically resistant” or is deemed to be “chemically durable” or to have “chemical durability”) if the sample's layer system shows no visible discoloration or no pinholes greater than about 0.003″ in diameter after this one hour boil.

[0079] “Mechanical durabi1ility” as used herein is defined by the following tests. The test uses a Pacific Scientific Abrasion Tester (or equivalent) wherein a 2″×4″×1″ nylon brush is cyclically passed over the layer system in 500 cycles employing 150 gm of weight, applied to a 6″×17″ sample. In this test, if no substantial, noticeable scratches appear when viewed with the naked eye under visible light, the test is deemed passed, and the article is said to be “mechanically durable” or to have “mechanical durability”.

[0080] The terms “heat treatment” and “heat treating” as used herein mean heating the article to a temperature sufficient to enabling thermal tempering, bending, or heat strengthening of the glass inclusive article. This definition includes, for example, heating a coated article to a temperature of at least about 1100 degrees F. (e.g., to a temperature of from about 550 degrees C. to 900 degrees C.) for a sufficient period to enable tempering.

[0081] The term “U-value” (synonymous with “thermal transmittance”) is a term well understood in the art and is used herein according to this well known meaning. “U-value” herein is reported in terms of BTU/hr/ft²/OF, and may be determined according to the guarded hot box method as reported in, and according to ASTM designation: C236-89 (reapproved 1993).

[0082] The term “shading coefficient” is a term well understood in the art and is used herein according to its well known meaning. It is determined according to ASHPAE Standard 142 “Standard Method for Determining and Expressing the Heat Transfer and Total Optical Properties of Fenestration Products” by ASHPAE Standards Project Committee, SPC 142, September 1995.

[0083] Once given the above disclosure many other features, modifications and improvements will become apparent to the skilled artisan. Such other features, modifications and improvements are therefore considered to be a part of this invention, the scope of which is to be determined by the following claims: