Title of Invention	GLASS ARTICLE HAVING A ZINC OXIDE COATING AND METHOD FOR MAKING SAME
Abstract	A multi-layer thin film having as a primary component, a coating of highly doped zinc oxide, and optionally, a color suppression underlayer and a protective metal oxide overcoat. The film stack is preferably deposited on a transparent substrate by atmospheric chemical vapor deposition. The film stack exhibits a desirable combination of properties including high visible light transmittance, relatively low solar energy transmittance, low emissivity, and high solar selectivity.

Title of Invention

GLASS ARTICLE HAVING A ZINC OXIDE COATING AND METHOD FOR MAKING SAME

Abstract

A multi-layer thin film having as a primary component, a coating of highly doped zinc oxide, and optionally, a color suppression underlayer and a protective metal oxide overcoat. The film stack is preferably deposited on a transparent substrate by atmospheric chemical vapor deposition. The film stack exhibits a desirable combination of properties including high visible light transmittance, relatively low solar energy transmittance, low emissivity, and high solar selectivity.

Full Text	GLASS ARTICLE HAVING A ZINC OXIDE COATING AND METHOD FOR MAKING SAME BACKGROUND OF THE INVENTION This invention relates to a highly doped zinc oxide coated glass article exhibiting high visible light transmittance with low total solar energy transmittance. Coatings on architectural glass are commonly utilized to provide specific energy absorption and light transmittance properties. Additionally, coatings provide desired reflective or spectral properties that are aesthetically pleasing. The coated articles are often used singularly or in combination with other coated articles to form a glazing or window unit. Coated glass articles may be produced "on-line" by continuously coating a glass substrate while it Is being manufactured in a process known in the art as the "float glass process." Additionally, coated glass articles are produced "off-line" through a sputtering process. The former process involves casting glass onto a molten tin bath which is suitably enclosed, thereafter transferring the glass, after it is sufficiently cooled, to lift out rolls which are aligned with the bath, and finally cooling the glass as it advances across the rolls, initially through a lehr, and thereafter, while exposed to the ambient atmosphere. A non-oxidizing atmosphere is maintained in the float portion of the process, while the glass is In contact with the molten tin bath, to prevent oxidation of tin. An oxidizing atmosphere is maintained in the lehr. In general, the coatings are applied onto the glass substrate in the float bath of the float bath process. However, coatings may also be applied onto the substrate in the lehr. The attributes of the resulting coated glass substrate are dependent upon the specific coatings applied during the float glass process or an off-line sputtering process. The coating compositions and thicknesses impart energy absorption and light transmittance properties within the coated article while also affecting the spectral properties. Desired attributes may be obtainable by adjusting the compositions or thicknesses of the coating layer or layers. However, adjustments to enhance a specific property can adversely impact other transmittance or spectral properties of the coated glass article. Obtaining desired spectral properties is often difficult when trying to combine specific energy absorption and light transmittance properties in a coated glass article. It is also difficult to obtain useful film thicknesses as the available deposition time in on-line processes is mere seconds, as the continuous glass ribbon is moving at a speed of several hundred inches per minute. Deposition of zinc oxide coatings is known from the patent literature. U.S. Patent No. 4,751,149 describes a method of applying a zinc oxide coating to substrate at a low temperature by using a mixture of an organozinc compound and water carried in an inert gas. The resulting zinc oxide film is said to have relatively low resistivity which can be varied by addition of a Group III element. U.S. Patent no. 4.990, 286 describes zinc oxy-fluoride films produced by CVD from vapor mixtures of zinc, oxygen and fluorine-containing compounds. Electrical conductivity of the film is said to be increased by substituting fluorine from some of the oxygen in the zinc oxide. The resulting films are said to be transparent, electrically conductive and infrared reflecting. U.S. Patent No. 6,071,561 describes a method of depositing fluorine- doped zinc oxide films utilizing vaporized precursor compounds such as a chelate of dialkylzinc, more specifically utilizing an amine chelate, an oxygen source and a fluorine source. The coatings produced are said to be electrically conductive, IR reflective, UV absorbing and free of carbon. U.S. Patent No. 6,416,814 describes the utilization of ligated compounds of tin, titanium and zinc as CVD precursor compounds to form metal oxide coatings on heated substrates. U.S. Patent No. 6,858,306 describes a glass substrate having disposed thereon a multi-layer coating of an antimony doped tin oxide, and a coating of fluorine doped tin oxide. The glass substrate so coated exhibits low emittance and high solar selectivity, thus providing improved heat rejection in summer and heat retention in winter while still permitting the transmittance of a relatively high degree_of visible light. Deposition of highly doped zinc oxide has been reported in the scientific literature for use in, for example, solar cells. Some examples of such articles follow: Park et al. report deposition of highly doped ZnO films via pulsed laser deposition (see Japanese Journal of Applied Physics. Vol. 44, No. 11,2205, pp. 88027-31). Using aluminum as the dopant, samples with an electron concentration of 1.25 x 1021cm-3. and an electron mobility of 37.6 cm2N-s were said to have been produced. The investigators state that doped zinc oxide films can be used as transparent contacts in solar cells, laser diodes, ultra- violet lasers, thin film resistors, flat panel displays, and organic light-emitting diodes. Similarly, Singh et al. (Journal of Indian Institute of Science, Vol. 81, Sept-Oct 2001. pp. 527-533) describe deposition of highly doped ZnO by pulsed laser ablation. Using a zinc oxide target doped with 2% aluminum oxide, ZnO:AI samples with an electron concentration of 1.5 x 1021cm-3 and an electron mobility of 29 cm'3 /V-s were said to have been produced. Das and Ray deposited aluminum doped zinc oxide films by rf- magnetron sputtering, the films obtained were said to exhibit an electron concentration of 2.3 x 1021 cm'3. (Journal of Physics P: Applied Physics. Vol. 36, 2003. pp. 152-5.) Finally, Choiet al. deposited gallium doped zinc oxide by rf-magnetron sputtering and claims to have produced films exhibiting an electron concentration of 1.5 x 1021 cm3. (Thin Solid Films. Vol. 192-4, 1990, pp. 712- 720.) It would be advantageous to provide a coated glass article having a neutral tint that rejects solar energy in the summer and provides a low U value for the winter. A solar reducing glazing with a low emittance, and a low total solar energy transmittance, would significantly improve energy costs in buildings and homes while providing a desirable neutral tint. It would also be advantageous to provide a solar reducing glazing that has a neutral color in reflectance, a low emittance, a high visible light transmittance, and a low total solar energy transmittance. The use of such a neutral colored article in architectural glazings would permit the transmission of a high degree of visible light while rejecting a significant amount of near infrared energy. Furthermore, the low emittance characteristic of the glazing would minimize any indirect heat gain from absorption. SUMMARY OF THE INVENTION In accordance with the invention, there is provided a novel glass article useful for producing coated, heat reducing glass for architectural windows. The coated article includes a glass substrate having a coating of a highly doped zinc oxide deposited over the glass substrate and optionally, a protective overcoat deposited on and adhering to the surface of the coating of doped zinc oxide deposited on the heated glass substrate. Such protective overcoat may comprise any suitably durable thin film having a compatible refractive index. Examples of such protective overcoats are undoped tin oxide, silica and titanium oxide. Such protective overcoat may, optionally, be doped to render same electrically conductive. For example, tin oxide may be doped with fluorine. The coated glass article of the invention has a selectivity of 26 or more, preferably 33 or more, the selectivity being defined as the difference between visible light transmittance (llluminant C) and total solar energy transmittance. integrated with an air mass 1.5. The coating stack, when applied to a clear glass substrate having a nominal 6 mm thickness, has a visible light transmittance of 69% or more and a preferred total solar energy transmittance of less than 41%. Preferably, the coated glass article includes an iridescence-suppressing intertayer deposited between the heated glass substrate and the coating of doped zinc oxide. These coatings are such as to provide a neutral color in transmittance and reflectance when applied to a clear glass substrate. The doped zinc oxide coating in the coated glass article of the invention provides for the absorption of solar energy. While this includes the absorption of some visible light, the doped zinc oxide coating is relatively selective, absorbing more near infrared energy than visible light. The doped zinc coating thus reduces the total solar energy transmittance of the coated glass article of the invention. A method of forming the coated glass article of the present invention is also disclosed. While atmospheric chemical vapor deposition is the preferred method of deposition, other methods may be utilized. BRIEF DESCRIPTION OF THE DRAWINGS The above, as well as other advantages of the present invention, will become readily apparent to those skilled in the art from the following detailed description when considered in the light of the accompanying drawings in which: Fig. 1 is a schematic view, in vertical section, of an apparatus for practicing the float glass process, which includes four gas distributors suitably positioned in the float bath to apply coatings onto the glass substrate in accordance with the invention; Fig. 2 is a broken sectional view of a coated glass article according to the invention; and Fig. 3 is a diagram of an architectural glazing in accordance with the present invention, wherein the coated glass article is shown in an insulated glass unit as an outboard lite with the multilayer coating of the invention facing the interior. DETAILED DESCRIPTION OF THE INVENTION In accordance with the invention, a coated glass article having a multilayered coating of a highly doped zinc oxide layer over which an optional protective overcoat of, for example, a substantially undoped tin oxide layer is applied, provides an article which exhibits a low emittance, a high visible light transmittance, and a reduced total solar energy transmittance. The coated glass article is especially suitable for use in architectural glazings and windows. However, the coated glass article of the present invention may also be suitable for other applications, such as vehicle windows. The highly doped zinc oxide coating also lowers the emissivity of the coated glass article of the invention to less than 0.15, and preferably to less than 0.10. As part of an insulating glass unit, the low emittance value provides a winter time U-value of less than 0.34, and preferably less than 0.32. In addition, it has surprisingly been determined that the solar selectivity of the film stack described is more than twice that of previously known multilayer coatings having otherwise similar solar control properties. Preferably, tin oxide or other metal oxide coating is utilized to form an overcoat to protect the somewhat mechanically and chemically fragile zinc oxide coating. The protective overcoat may slightly increase the emissivity of the coating stack. In order to minimize emissivity changes, the thickness of the protective layer is preferably less than 1000 A. Alternatively, a protective layer consisting of tin oxide having a thickness greater than 1000 A could be doped with fluorine, niobium, or tantalum to achieve the desired emissivity. The specific coating stack on the glass substrate provides a neutral colored article having a high visible light transmittance, a reduced total solar energy transmittance, and a low emittance. The use of the inventive article in architectural glazings results in a glazing that rejects solar energy in the summer and provides a low U-value for the winter. Preferably, the coated glass article includes an iridescence-suppressing interlayer deposited between the glass substrate and the coating of doped zinc oxide. The coatings are such as to provide a neutral color in transmittance and reflectance when applied to a clear glass substrate. Fig. 2 illustrates the coated glass article of the invention, indicated generally by reference numeral 35, comprising a glass substrate 36 and a multilayered coating 37 adhered to one surface thereof. In the preferred embodiment illustrated, the multilayered coating comprises an iridescence- suppressing interlayer 38, a coating of doped zinc oxide 41, and a protective outer coating 42, for example, an undoped or fluorine doped tin oxide. In the embodiment illustrated, the iridescence-suppressing interlayer 38 is specifically comprised of a tin oxide coating 39 and a silicon dioxide coating 40. For most applications it will be preferred that the doped zinc oxide coating 41 in the coated glass article of the invention provides especially for the absorption of solar energy. While this includes the absorption of some visible light, the doped zinc oxide coating is relatively selective, absorbing more near infrared energy than visible light. The doped zinc oxide coating thus reduces the total solar energy transmittance of the coated glass article of the invention. The highly doped zinc oxide coating 41 includes a molar ratio of dopant to zinc of between about 0.1 % and 5%. Preferably, the molar ratio of dopant to zinc is between about 1% and 3%. The molar ratio will vary depending on the dopant selected from one or more of aluminum, gallium, indium and boron. Aluminum and gallium are preferred dopants. The doped zinc oxide coating 41 preferably has a free electron concentration of greater than 1.0 x 1021 cm-3, and more preferably has a free electron concentration greater than or equal to 1.5 x 1021 cm-3. The doped zinc oxide coating 41 is preferably deposited at a thickness of from about 1600 to about 9000 Angstroms, and preferably from about 1800 to about 5200 Angstroms. The most preferred coating thickness will depend on the free electron concentration in the zinc oxide coating as well as the glass thickness. As the thickness of the zinc oxide coating, doped with one or more of the previously noted dopants in the indicated molar ratio range, is increased above 9000 Angstroms, the absorption of visible light increases to the point that the visible light transmittance becomes undesirably low. However, as the thickness of the zinc oxide coating, doped in the indicated molar ratio range, is decreased below 1600 Angstroms, the total solar energy transmission becomes undesirably high The highly doped zinc oxide coating 41 lowers the emissivity of the coated glass article of the invention to less than 0.15, and preferably to less than 0.10. As part of an insulating glass unit, a sheet of glass coated with doped zinc oxide held in a spaced apart relationship from an uncoated sheet of clear glass by a frame member, the low emittance value provides a winter time U-value of less than 0.34, and preferably less than 0.32. In addition, it has surprisingly been determined that in accordance with the invention, the insulating glass unit exhibits solar selectivity greater than or equal to 28, and preferably greater than or equal to 33. The optional tin oxide overcoat 42 is preferably applied at a thickness of less than 1000 Angstroms, and even more preferably at a thickness from about 200 to about 250 Angstroms. The iridescence-suppressing interlayer 38 of the coating stack on the glass substrate 36 provides a means to reflect and refract light to interfere with the observance of iridescence. The layer specifically eliminates iridescence so that the coated article may, if desired, be neutral colored in both reflectance and transmittance. Furthermore, the interlayer suppresses the observance of off angle colors. Indescence-suppressing coatings are conventionally known within the art. For example, U.S. Patent Nos. 4,187,336, 4,419,386, and 4,206,252, each herein incorporated by reference, describe coating techniques suitable for suppressing interference colors. Single layer, multiple layer, or gradient layer color suppression coatings are suitable for use with the present invention. In the two component interlayer 38 illustrated in Fig. 2, which is the preferred type of iridescence-suppressing interiayer for use in the practice of the present Invention, the coating 39 deposited onto and adhering to the glass substrate has a high refractive index in the visible spectrum and is preferably tin oxide. The second coating 40, having a low refractive index, is deposited on and adheres to the first coating of the interiayer, and is preferably silicon dioxide. Generally, each coating has a thickness selected such that the interiayer forms a combined total optical thickness of about 1/6th to about 1/12th of a 500 nm design wavelength. Various deposition methods may be suitable to deposit the desired zinc oxide film stack, for example, various sputtering techniques. Chemical vapor deposition (CVD) is a preferred method of deposition. Atmospheric pressure chemical vapor deposition (APCVD) is particularly preferred. The glass substrates suitable for use In preparing the coated glass article according to the present invention may include any of the conventional glass compositions known in the art as useful for the preparation of architectural glazings. The preferred substrate is a clear float glass ribbon wherein the coatings of the present invention are applied in the heated zone of the float glass process where temperatures are in the range of 500-700°C. Additionally, tinted glass substrates may be suitable for applying the multilayered stack of the invention. However, certain tinted glass substrates may impact the spectral and energy transmittance properties of the invention. The specific coating stack on the glass substrate provides a coated glass article having a high visible light transmittance, a reduced total solar energy transmittance, and a low emittance. The coated glass article of the invention has a selectivity of 28 or more, the selectivity being defined as the difference between visible light transmittance (liluminant C) and a total solar energy transmittance, integrated with an air mass 1.5, on a clear glass substrate at a nominal 3 mm thickness. The selectivity is preferably 33 or more, with a preferred visible light transmittance of 73% or more and a preferred total solar energy transmittance of less than 41 %. The emittance of the present inventive article is less than 0.15, and preferably less than 0.10. Emittance or emissivity is a measure of both absorption and reflectance of light at given wavelengths. It is usually represented by the formula: Emissivity = 1- reflectance of the coating. The term emissivity is used to refer to emissivity values measured in the infrared range by ASTM standards. Emissivity is measured using radiometric measurements and is reported as hemispherical emissivity (eh) and normal emissivity. The use of the inventive article in architectural glazings results in a glazing that rejects solar energy in the summer and provides a low U value for the winter. The multilayered coatings of the present invention result in a coated glass article preferably exhibiting neutral color in both reflectance and transmittance. The color is defined by the composition and thickness of the various layers of the stack. In order to most effectively achieve color neutrality, it may be desirable to vary the thickness of the tin oxide and silica layers of the iridescence- suppressing interlayer between 150 Angstroms and 350 Angstroms. It is also important that, with respect to the subject invention, color neutrality is not strictly defined by mathematical limits, but also as perceived by the human eye in viewing the reflective color and the transmitted color. The coatings of the present Invention are preferably applied "on-line" onto the glass substrate by chemical vapor deposition during the glass manufacturing process. Fig. 1 illustrates an apparatus, indicated generally at 10, useful for the on-line production of the coated glass article of the present invention, comprising a float section 11, a lehr 12, and a cooling section 13. The float section 11 has a bottom 14 which contains a molten tin bath 15, a roof 16, sidewalls (not shown), and end walls 17, which together form a seal such that there is provided an enclosed zone 18, wherein a non-oxidizing atmosphere is maintained, as hereinafter described in greater detail, to prevent oxidation of the tin bath 15. During operation of the apparatus 10, molten glass 19 is cast onto a hearth 20, and flows therefrom under a metering wall 21, then downwardly onto the surface of the tin bath 15. from which it is removed by lift- out rolls 22 and conveyed through the lehr 12. and thereafter through the cooling section 13. A non-oxidizing atmosphere is maintained in the float section 11 by introducing a suitable gas, such as for example one composed of 99 percent by volume nitrogen and 1 percent by volume hydrogen, into the zone 18, through conduits 23 which are operably connected to a manifold 24. The non-oxidizing gas is introduced into the zone 18 from the conduits 23 at a rate sufficient to compensate for losses of the gas (some of the non-oxidizing atmosphere leaves the zone 18 by flowing under the end walls 17), and to maintain a slight positive pressure, conveniently about 0.001 to about 0.01 atmospheres above ambient pressure. The tin bath 15 and the enclosed zone 18 are heated by radiant heat directed downwardly from heaters 25. The heat zone 18 is generally maintained at a temperature of about 500-700°C. The atmosphere in the lehr 12 is typically air, and the cooling section 13 is not enclosed. Ambient air is blown onto the glass by fans 26. The apparatus 10 also includes gas distributors 27, 28, 29 and 30 located in the float zone 11. The desired precursor mixtures for the individual coatings are supplied to the respective gas distributors, which in turn direct the precursor mixtures to the hot surface of the glass ribbon. The precursors react at the glass surface to form the desired coatings. The coated glass article of the invention is ideally suited for use in architectural glazings. For example, the coated glass article may be utilized in an insulated glass unit. Thus, the coated glass article of the present invention is illustrated in Fig. 3 as an outboard lite 45 in an insulated glass unit 43 suitable for installation into a building structure. The insulated glass unit 43 also includes an inboard lite 53 made of a glass article and maintained in a spaced apart relationship from the outboard lite 45 by a frame (not shown) in the known manner. The glass substrate 45 of the present invention is positioned facing the exterior of the structure. The multilayered coating 49 of the present invention faces the interior with an air space 51 separating the outboard lite 45 from the inboard lite 53. When the protective overcoat is formed of fluorine doped tin oxide, the low emittance provided by the fluorine doped tin oxide improves the performance of the coated glass article in the summer and winter. The radiation energy, a component of the indirect gain from the glass to the building interior, is reduced under summer conditions with a low emittance coating. This is noticed as a reduction in the total solar heat transmittance (TSHT). TSHT is defined as including solar energy transmitted directly through the glass, and the solar energy absorbed by the glass, and subsequently convected and thermally radiated inwardly. Further, solar heat gain coefficient (SHGC) is defined as the ratio of total solar heat gain through the glass relative to the incident solar radiation. The major improvement in performance, however, occurs under winter conditions where the U-value of the glazing structure is reduced significantly with a low emittance coating. The U-value or the overall heat transfer coefficient is inversely proportional to the thermal resistance of the structure. A lower U-value means a reduction in heat loss through the glass from the interior to the exterior, resulting in savings in energy costs. Thus, the low emittance of the coated glass article, when combined with the surprisingly selective solar absorption of the multilayer stack provides improved heat rejection in summer and heat retention in winter. The resulting insulated glass unit, utilizing the coated glass article of the present invention, exhibits specific transmittance and spectral properties. The low emittance of surface 49 (Fig. 3) results in a U-value of less than 0.34 and preferably less than 0.32. The total solar heat transmittance of the unit is less than 41%. The insulated glass unit also exhibits a visible light transmittance (Illuminant C) of 62% or more. The insulated glass unit preferably exhibits a neutral color in both reflectance and transmittance. The following examples, which constitute the best mode presently contemplated for practicing the invention, are presented solely for the purpose of further Illustrating and disclosing the present invention, and are not to be construed as a limitation on the invention. PREDICTIVE EXAMPLES 1-15 and 16-23 A float glass process is used to produce a float glass ribbon having a thickness of 6mm. During the production of the float glass ribbon, the specified coatings are modeled to be consecutively applied onto the glass substrate in the float bath through conventional chemical vapor deposition methods at the thicknesses (in Angstroms) indicated in Table 1. The precursor mixture for the various tin oxide coatings Includes dimethyl tin dichloride, oxygen, water, and helium as a carrier gas. The precursor mixture for the silicon dioxide coating includes monosilane, ethylene, and oxygen and a carrier gas. The precursor mixture for the doped zinc oxide includes a Zn precursor such as diethyl zinc (DEZ), an oxygen source such as IPA (isopropanol), and a suitable aluminum precursor, for example, diethylaluminum chloride. Alternatively, a suitable gallium precursor could be substituted for the aluminum precursor. The resulting doped zinc oxide layer has a dopant concentration of about 2 atomic percent Al or Ga. The visible light transmittance (TVis), total solar energy transmittance (Tsol) and the solar selectivity (Tvis - Tsal) were calculated for the resulting coated glass article in each example. Tvis and TSOl, for the noted examples, are for a monolithic glazing, i.e., a single glass sheet. The results are also shown in Table I. Examples 16-23 were modeled on much the same basis as Examples 1- 15. except that Examples 16-23 represent an Insulated glass unit, as elsewhere defined herein, formed from two sheets of glass. The inventive coating stack was projected to be located on the so-called #2 surface; that is, on the major surface of the outboard glass sheet which faces the air space between the two glass sheets. The gap between the glass sheets was 12mm, and the space was filled with air. The electrical and optical properties of conductive materials can be characterized by NB, the concentration of free electrons in the material, and µ, the mobility of free electrons in the material. The solar selectivity of the coating stacks described herein depends primarily on the concentration of free electrons in the doped ZnO layer. As shown by Examples 2-4 in Table 1, the required solar selectivity can be achieved by using highly doped zinc oxide, where "highly-doped" refers to an electron concentration greater than 1.0 x 1021 electrons/cm3. By comparison, Example 1 shows that doped ZnO having an electron concentration of only 1.0 x 1021 electrons/cm3 results in a TviS (69%) that just meets the target value (>69%). The solar selectivity of the coating stacks described herein also depends on the electron mobility in the doped ZnO layer. As shown by Examples 3 and 6-8 in Table 1, the required solar selectivity can be achieved by using highly doped zinc oxide with an electron mobility in the range of 15-100 cm2N-s. By way of comparison. Example 5 shows that doped ZnO with an electron mobility of 10 results in a Tvis (69%) that just meets the target value (269%). Examples 9 and 10 demonstrate that a thin protective overcoat, on the order of 200-300A of, for example SnO2 or SiO2, does not substantially alter the solar performance of the film stack. Tvis and TSOl remain above the desired levels of 69% and only slightly greater than 40%, respectively. Example 11 demonstrates that a thicker doped overcoat (3000A fluorine doped tin oxide) does not seem to adversely affect the solar performance of the film stack, as both TviS and Tsol are within the targeted levels of > 69% and type modeled in Example 11 may provide lower emissivity and more nearly neutral color. Example 12 shows that undertayers beside SiO2, for example SnO2, may be utilized in the subject film stack while maintaining desired levels of Tvis and Tsol. Examples 13-15 show utilization of optional multi-layer color suppression interlayers which provide desired neutral color of transmitted light while, once again, maintaining desired levels of Tvis and Tsol. Table 2 shows the results of modeling of Insulated glass (IG) units, the structure of which has been previously described herein. The solar performance of the subject IG units consistently exhibit properties at, or above, desired levels, in particular, Tvis >62%, solar heat gain coefficient (SHGC) >0.40 and U-value of the doped zinc oxide coating. Emissivity is also, generally, less than 0.2, and for some examples, PREDICTIVE EXAMPLES 24-31 and 32-35 Examples 24-31, as shown in Table 3. were modeled utilizing Input parameters substantially similar to Examples 1-15. The substrate thickness was 3mm rather than 6mm, however. Similarly, Examples 32-35 were modeled as IG units substantially similar to those modeled In Examples 16-23. The thickness of both sheets of glass was, however, 3mm and the gap therebetween was 6mm, rather than 12mm. As can be observed from reviewing Table 3, with silmilar thicknesses of highly doped zinc oxide on thinner glass, it is still possible to maintain a Tsol of 40, and a solar selectivity >28, although the preferred solar selectivity of 33 is more difficult to achieve. Examples 32-35, displayed in Table 4, demonstrate that it is also possible to meet the desired solar performance levels for an IG unit utilizing 3mm glass, namely Tvis >62, SHGC >0.40 and U-value In accordance with the provisions of the patent statutes, the present invention has been described in what is considered to represent its preferred embodiment. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit and scope. For example, other coating methods, such as sputtering, may also be utilized to form the solar control coating of the present invention. What is claimed is: 1. A coated glass article comprising: a glass substrate; a coating of highly doped zinc oxide deposited over the glass substrate; and optionally, a protective metal oxide coating deposited over the zinc oxide coating; wherein the thickness of the coatings is selected so that the coated glass article exhibits a difference between visible light transmittance (llluminant C) and total solar energy transmittance, integrated with an air mass 1.5 on a clear glass substrate having a nominal 6 mm thickness, to provide a solar selectivity of 28 or more. 2. The coated glass article defined in claim 1, wherein the solar selectivity of the highly doped zinc oxide coating is 33 or more. 3. The coated glass article defined in claim 1, wherein the doped zinc oxide coating has been deposited at a temperature of 500°-700°C. 4. The coated glass article defined in claim 1, wherein a color suppression interlayer is deposited between the glass substrate and the coating of doped zinc oxide. 5. The coated glass article defined in claim 1, wherein a protective overcoat is deposited over the coating of highly doped zinc oxide, the overcoat comprised of a metal oxide selected from the group consisting of tin oxide, silicon dioxide, aluminum oxide, titanium dioxide, niobium oxide, and zirconium oxide. 6. The coated glass article defined in claim 5, wherein the protective overcoat is doped. 2. 7. The coated glass article defined in claim 1, wherein the doped zinc oxide coating has a thickness of > 1600A and 8. The coated glass article defined in claim 1, wherein the protective overcoat has a thickness of 1000 A or less. 9. The coated glass article defined in claim 1, wherein the protective overcoat has a thickness of 250 A or less. 10. The coated glass article defined in claim 1, wherein the electron concentration of the doped zinc oxide layer is > 1.0 x 1021 electrons/cm3. 11. The coated glass article defined in claim 1, exhibiting an emittance of 0.15 or less. 12. The coated glass article defined in claim 1, wherein the dopant of the zinc oxide coating is at least one chosen from the group consisting of aluminum, gallium, indium and boron. 13. The coated glass article defined in claim 1, wherein the visible light transmittance of the coated glass article is > 69%. 14. The coated glass article defined in claim 1, wherein the visible light transmittance of the coated glass article is > 73%. 15. The coated glass article defined in claim 1, wherein the total solar energy transmittance of the coated glass article is 10 16. An insulated glass unit comprising: at least first and second sheets of glass in parallel spaced apart relationship, each of the at least first and second glass sheets having first and second major surfaces, with each glass sheet having one major surface facing the space between the at least first and second glass sheets; and at least one of such major surfaces having a coating of highly doped zinc oxfde deposited thereover; the insulated glass unit exhibiting a visible light transmittance >60%, a U-value of 0.29 or greater and hemispherical emissivity 17. A coated glass article comprising: a glass substrate; a coating of highly doped zinc oxide deposited over the glass substrate; and a protective metal oxide coating deposited over the highly doped zinc oxide coating, the zinc oxide coating having an electron concentration >1.0 x 1021 electrons (cm'3) and an electron mobility of 10 cm2N-s more. 18. A method of forming a coated glass article comprising: providing a moving, heated glass ribbon; and depositing a coating of a highly doped zinc oxide over the moving, heated glass ribbon at a temperature of 500-700°C; wherein the doped zinc oxide coating is deposited at a thickness so that the coated glass article exhibits a difference between visible light transmittance (llluminant C) and total solar energy transmittance, integrated with air mass 1.5 on a clear glass substrate having a nominal 3mm thickness, to provide a selectivity of 28 or more. 19. The method defined in claim 18, wherein a color suppression coating is deposited between the glass substrate and the coating of highly doped zinc oxide. A multi-layer thin film having as a primary component, a coating of highly doped zinc oxide, and optionally, a color suppression underlayer and a protective metal oxide overcoat. The film stack is preferably deposited on a transparent substrate by atmospheric chemical vapor deposition. The film stack exhibits a desirable combination of properties including high visible light transmittance, relatively low solar energy transmittance, low emissivity, and high solar selectivity.

Full Text

GLASS ARTICLE HAVING A ZINC OXIDE COATING
AND METHOD FOR MAKING SAME
BACKGROUND OF THE INVENTION
This invention relates to a highly doped zinc oxide coated glass article
exhibiting high visible light transmittance with low total solar energy
transmittance.
Coatings on architectural glass are commonly utilized to provide specific
energy absorption and light transmittance properties. Additionally, coatings
provide desired reflective or spectral properties that are aesthetically pleasing.
The coated articles are often used singularly or in combination with other
coated articles to form a glazing or window unit.
Coated glass articles may be produced "on-line" by continuously coating
a glass substrate while it Is being manufactured in a process known in the art
as the "float glass process." Additionally, coated glass articles are produced
"off-line" through a sputtering process. The former process involves casting
glass onto a molten tin bath which is suitably enclosed, thereafter transferring
the glass, after it is sufficiently cooled, to lift out rolls which are aligned with the
bath, and finally cooling the glass as it advances across the rolls, initially
through a lehr, and thereafter, while exposed to the ambient atmosphere. A
non-oxidizing atmosphere is maintained in the float portion of the process,
while the glass is In contact with the molten tin bath, to prevent oxidation of tin.
An oxidizing atmosphere is maintained in the lehr. In general, the coatings are
applied onto the glass substrate in the float bath of the float bath process.
However, coatings may also be applied onto the substrate in the lehr.
The attributes of the resulting coated glass substrate are dependent
upon the specific coatings applied during the float glass process or an off-line
sputtering process. The coating compositions and thicknesses impart energy
absorption and light transmittance properties within the coated article while also
affecting the spectral properties. Desired attributes may be obtainable by
adjusting the compositions or thicknesses of the coating layer or layers.
However, adjustments to enhance a specific property can adversely impact
other transmittance or spectral properties of the coated glass article. Obtaining

desired spectral properties is often difficult when trying to combine specific
energy absorption and light transmittance properties in a coated glass article. It
is also difficult to obtain useful film thicknesses as the available deposition time
in on-line processes is mere seconds, as the continuous glass ribbon is moving
at a speed of several hundred inches per minute.
Deposition of zinc oxide coatings is known from the patent literature.
U.S. Patent No. 4,751,149 describes a method of applying a zinc oxide
coating to substrate at a low temperature by using a mixture of an organozinc
compound and water carried in an inert gas. The resulting zinc oxide film is
said to have relatively low resistivity which can be varied by addition of a Group
III element.
U.S. Patent no. 4.990, 286 describes zinc oxy-fluoride films produced by
CVD from vapor mixtures of zinc, oxygen and fluorine-containing compounds.
Electrical conductivity of the film is said to be increased by substituting fluorine
from some of the oxygen in the zinc oxide. The resulting films are said to be
transparent, electrically conductive and infrared reflecting.
U.S. Patent No. 6,071,561 describes a method of depositing fluorine-
doped zinc oxide films utilizing vaporized precursor compounds such as a
chelate of dialkylzinc, more specifically utilizing an amine chelate, an oxygen
source and a fluorine source. The coatings produced are said to be electrically
conductive, IR reflective, UV absorbing and free of carbon.
U.S. Patent No. 6,416,814 describes the utilization of ligated compounds
of tin, titanium and zinc as CVD precursor compounds to form metal oxide
coatings on heated substrates.
U.S. Patent No. 6,858,306 describes a glass substrate having disposed
thereon a multi-layer coating of an antimony doped tin oxide, and a coating of
fluorine doped tin oxide. The glass substrate so coated exhibits low emittance
and high solar selectivity, thus providing improved heat rejection in summer
and heat retention in winter while still permitting the transmittance of a relatively
high degree_of visible light.
Deposition of highly doped zinc oxide has been reported in the scientific
literature for use in, for example, solar cells. Some examples of such articles
follow:

Park et al. report deposition of highly doped ZnO films via pulsed laser
deposition (see Japanese Journal of Applied Physics. Vol. 44, No. 11,2205, pp.
88027-31). Using aluminum as the dopant, samples with an electron
concentration of 1.25 x 1021cm-3. and an electron mobility of 37.6 cm2N-s were
said to have been produced. The investigators state that doped zinc oxide
films can be used as transparent contacts in solar cells, laser diodes, ultra-
violet lasers, thin film resistors, flat panel displays, and organic light-emitting
diodes.
Similarly, Singh et al. (Journal of Indian Institute of Science, Vol. 81,
Sept-Oct 2001. pp. 527-533) describe deposition of highly doped ZnO by
pulsed laser ablation. Using a zinc oxide target doped with 2% aluminum
oxide, ZnO:AI samples with an electron concentration of 1.5 x 1021cm-3 and an
electron mobility of 29 cm'3 /V-s were said to have been produced.
Das and Ray deposited aluminum doped zinc oxide films by rf-
magnetron sputtering, the films obtained were said to exhibit an electron
concentration of 2.3 x 1021 cm'3. (Journal of Physics P: Applied Physics. Vol.
36, 2003. pp. 152-5.)
Finally, Choiet al. deposited gallium doped zinc oxide by rf-magnetron
sputtering and claims to have produced films exhibiting an electron
concentration of 1.5 x 1021 cm3. (Thin Solid Films. Vol. 192-4, 1990, pp. 712-
720.)
It would be advantageous to provide a coated glass article having a
neutral tint that rejects solar energy in the summer and provides a low U value
for the winter. A solar reducing glazing with a low emittance, and a low total
solar energy transmittance, would significantly improve energy costs in
buildings and homes while providing a desirable neutral tint.
It would also be advantageous to provide a solar reducing glazing that
has a neutral color in reflectance, a low emittance, a high visible light
transmittance, and a low total solar energy transmittance. The use of such a
neutral colored article in architectural glazings would permit the transmission of
a high degree of visible light while rejecting a significant amount of near
infrared energy. Furthermore, the low emittance characteristic of the glazing
would minimize any indirect heat gain from absorption.

SUMMARY OF THE INVENTION
In accordance with the invention, there is provided a novel glass article
useful for producing coated, heat reducing glass for architectural windows. The
coated article includes a glass substrate having a coating of a highly doped
zinc oxide deposited over the glass substrate and optionally, a protective
overcoat deposited on and adhering to the surface of the coating of doped zinc
oxide deposited on the heated glass substrate. Such protective overcoat may
comprise any suitably durable thin film having a compatible refractive index.
Examples of such protective overcoats are undoped tin oxide, silica and
titanium oxide. Such protective overcoat may, optionally, be doped to render
same electrically conductive. For example, tin oxide may be doped with
fluorine.
The coated glass article of the invention has a selectivity of 26 or more,
preferably 33 or more, the selectivity being defined as the difference between
visible light transmittance (llluminant C) and total solar energy transmittance.
integrated with an air mass 1.5. The coating stack, when applied to a clear
glass substrate having a nominal 6 mm thickness, has a visible light
transmittance of 69% or more and a preferred total solar energy transmittance
of less than 41%.
Preferably, the coated glass article includes an iridescence-suppressing
intertayer deposited between the heated glass substrate and the coating of
doped zinc oxide. These coatings are such as to provide a neutral color in
transmittance and reflectance when applied to a clear glass substrate.
The doped zinc oxide coating in the coated glass article of the invention
provides for the absorption of solar energy. While this includes the absorption
of some visible light, the doped zinc oxide coating is relatively selective,
absorbing more near infrared energy than visible light. The doped zinc coating
thus reduces the total solar energy transmittance of the coated glass article of
the invention.
A method of forming the coated glass article of the present invention is
also disclosed. While atmospheric chemical vapor deposition is the preferred
method of deposition, other methods may be utilized.

BRIEF DESCRIPTION OF THE DRAWINGS
The above, as well as other advantages of the present invention, will
become readily apparent to those skilled in the art from the following detailed
description when considered in the light of the accompanying drawings in
which:
Fig. 1 is a schematic view, in vertical section, of an apparatus for
practicing the float glass process, which includes four gas distributors suitably
positioned in the float bath to apply coatings onto the glass substrate in
accordance with the invention;
Fig. 2 is a broken sectional view of a coated glass article according to
the invention; and
Fig. 3 is a diagram of an architectural glazing in accordance with the
present invention, wherein the coated glass article is shown in an insulated
glass unit as an outboard lite with the multilayer coating of the invention facing
the interior.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with the invention, a coated glass article having a
multilayered coating of a highly doped zinc oxide layer over which an optional
protective overcoat of, for example, a substantially undoped tin oxide layer is
applied, provides an article which exhibits a low emittance, a high visible light
transmittance, and a reduced total solar energy transmittance. The coated
glass article is especially suitable for use in architectural glazings and windows.
However, the coated glass article of the present invention may also be suitable
for other applications, such as vehicle windows.
The highly doped zinc oxide coating also lowers the emissivity of the
coated glass article of the invention to less than 0.15, and preferably to less
than 0.10. As part of an insulating glass unit, the low emittance value provides
a winter time U-value of less than 0.34, and preferably less than 0.32. In
addition, it has surprisingly been determined that the solar selectivity of the film
stack described is more than twice that of previously known multilayer coatings
having otherwise similar solar control properties.

Preferably, tin oxide or other metal oxide coating is utilized to form an
overcoat to protect the somewhat mechanically and chemically fragile zinc
oxide coating. The protective overcoat may slightly increase the emissivity of
the coating stack. In order to minimize emissivity changes, the thickness of the
protective layer is preferably less than 1000 A. Alternatively, a protective layer
consisting of tin oxide having a thickness greater than 1000 A could be doped
with fluorine, niobium, or tantalum to achieve the desired emissivity.
The specific coating stack on the glass substrate provides a neutral
colored article having a high visible light transmittance, a reduced total solar
energy transmittance, and a low emittance. The use of the inventive article in
architectural glazings results in a glazing that rejects solar energy in the
summer and provides a low U-value for the winter.
Preferably, the coated glass article includes an iridescence-suppressing
interlayer deposited between the glass substrate and the coating of doped zinc
oxide. The coatings are such as to provide a neutral color in transmittance and
reflectance when applied to a clear glass substrate.
Fig. 2 illustrates the coated glass article of the invention, indicated
generally by reference numeral 35, comprising a glass substrate 36 and a
multilayered coating 37 adhered to one surface thereof. In the preferred
embodiment illustrated, the multilayered coating comprises an iridescence-
suppressing interlayer 38, a coating of doped zinc oxide 41, and a protective
outer coating 42, for example, an undoped or fluorine doped tin oxide. In the
embodiment illustrated, the iridescence-suppressing interlayer 38 is specifically
comprised of a tin oxide coating 39 and a silicon dioxide coating 40.
For most applications it will be preferred that the doped zinc oxide
coating 41 in the coated glass article of the invention provides especially for the
absorption of solar energy. While this includes the absorption of some visible
light, the doped zinc oxide coating is relatively selective, absorbing more near
infrared energy than visible light. The doped zinc oxide coating thus reduces
the total solar energy transmittance of the coated glass article of the invention.
The highly doped zinc oxide coating 41 includes a molar ratio of dopant
to zinc of between about 0.1 % and 5%. Preferably, the molar ratio of dopant to
zinc is between about 1% and 3%. The molar ratio will vary depending on the

dopant selected from one or more of aluminum, gallium, indium and boron.
Aluminum and gallium are preferred dopants. The doped zinc oxide coating 41
preferably has a free electron concentration of greater than 1.0 x 1021 cm-3, and
more preferably has a free electron concentration greater than or equal to 1.5 x
1021 cm-3. The doped zinc oxide coating 41 is preferably deposited at a
thickness of from about 1600 to about 9000 Angstroms, and preferably from
about 1800 to about 5200 Angstroms. The most preferred coating thickness
will depend on the free electron concentration in the zinc oxide coating as well
as the glass thickness. As the thickness of the zinc oxide coating, doped with
one or more of the previously noted dopants in the indicated molar ratio range,
is increased above 9000 Angstroms, the absorption of visible light increases to
the point that the visible light transmittance becomes undesirably low.
However, as the thickness of the zinc oxide coating, doped in the indicated
molar ratio range, is decreased below 1600 Angstroms, the total solar energy
transmission becomes undesirably high
The highly doped zinc oxide coating 41 lowers the emissivity of the
coated glass article of the invention to less than 0.15, and preferably to less
than 0.10. As part of an insulating glass unit, a sheet of glass coated with
doped zinc oxide held in a spaced apart relationship from an uncoated sheet of
clear glass by a frame member, the low emittance value provides a winter time
U-value of less than 0.34, and preferably less than 0.32. In addition, it has
surprisingly been determined that in accordance with the invention, the
insulating glass unit exhibits solar selectivity greater than or equal to 28, and
preferably greater than or equal to 33.
The optional tin oxide overcoat 42 is preferably applied at a thickness of
less than 1000 Angstroms, and even more preferably at a thickness from about
200 to about 250 Angstroms.
The iridescence-suppressing interlayer 38 of the coating stack on the
glass substrate 36 provides a means to reflect and refract light to interfere with
the observance of iridescence. The layer specifically eliminates iridescence so
that the coated article may, if desired, be neutral colored in both reflectance
and transmittance. Furthermore, the interlayer suppresses the observance of
off angle colors. Indescence-suppressing coatings are conventionally known

within the art. For example, U.S. Patent Nos. 4,187,336, 4,419,386, and
4,206,252, each herein incorporated by reference, describe coating techniques
suitable for suppressing interference colors. Single layer, multiple layer, or
gradient layer color suppression coatings are suitable for use with the present
invention.
In the two component interlayer 38 illustrated in Fig. 2, which is the
preferred type of iridescence-suppressing interiayer for use in the practice of
the present Invention, the coating 39 deposited onto and adhering to the glass
substrate has a high refractive index in the visible spectrum and is preferably
tin oxide. The second coating 40, having a low refractive index, is deposited on
and adheres to the first coating of the interiayer, and is preferably silicon
dioxide. Generally, each coating has a thickness selected such that the
interiayer forms a combined total optical thickness of about 1/6th to about 1/12th
of a 500 nm design wavelength.
Various deposition methods may be suitable to deposit the desired zinc
oxide film stack, for example, various sputtering techniques. Chemical vapor
deposition (CVD) is a preferred method of deposition. Atmospheric pressure
chemical vapor deposition (APCVD) is particularly preferred.
The glass substrates suitable for use In preparing the coated glass
article according to the present invention may include any of the conventional
glass compositions known in the art as useful for the preparation of
architectural glazings. The preferred substrate is a clear float glass ribbon
wherein the coatings of the present invention are applied in the heated zone of
the float glass process where temperatures are in the range of 500-700°C.
Additionally, tinted glass substrates may be suitable for applying the
multilayered stack of the invention. However, certain tinted glass substrates
may impact the spectral and energy transmittance properties of the invention.
The specific coating stack on the glass substrate provides a coated
glass article having a high visible light transmittance, a reduced total solar
energy transmittance, and a low emittance. The coated glass article of the
invention has a selectivity of 28 or more, the selectivity being defined as the
difference between visible light transmittance (liluminant C) and a total solar
energy transmittance, integrated with an air mass 1.5, on a clear glass

substrate at a nominal 3 mm thickness. The selectivity is preferably 33 or
more, with a preferred visible light transmittance of 73% or more and a
preferred total solar energy transmittance of less than 41 %. The emittance of
the present inventive article is less than 0.15, and preferably less than 0.10.
Emittance or emissivity is a measure of both absorption and reflectance of light
at given wavelengths. It is usually represented by the formula: Emissivity = 1-
reflectance of the coating. The term emissivity is used to refer to emissivity
values measured in the infrared range by ASTM standards. Emissivity is
measured using radiometric measurements and is reported as hemispherical
emissivity (eh) and normal emissivity. The use of the inventive article in
architectural glazings results in a glazing that rejects solar energy in the
summer and provides a low U value for the winter.
The multilayered coatings of the present invention result in a coated
glass article preferably exhibiting neutral color in both reflectance and
transmittance. The color is defined by the composition and thickness of the
various layers of the stack.
In order to most effectively achieve color neutrality, it may be desirable
to vary the thickness of the tin oxide and silica layers of the iridescence-
suppressing interlayer between 150 Angstroms and 350 Angstroms. It is also
important that, with respect to the subject invention, color neutrality is not
strictly defined by mathematical limits, but also as perceived by the human eye
in viewing the reflective color and the transmitted color.
The coatings of the present Invention are preferably applied "on-line"
onto the glass substrate by chemical vapor deposition during the glass
manufacturing process. Fig. 1 illustrates an apparatus, indicated generally at
10, useful for the on-line production of the coated glass article of the present
invention, comprising a float section 11, a lehr 12, and a cooling section 13.
The float section 11 has a bottom 14 which contains a molten tin bath 15, a roof
16, sidewalls (not shown), and end walls 17, which together form a seal such
that there is provided an enclosed zone 18, wherein a non-oxidizing
atmosphere is maintained, as hereinafter described in greater detail, to prevent
oxidation of the tin bath 15. During operation of the apparatus 10, molten glass
19 is cast onto a hearth 20, and flows therefrom under a metering wall 21, then

downwardly onto the surface of the tin bath 15. from which it is removed by lift-
out rolls 22 and conveyed through the lehr 12. and thereafter through the
cooling section 13.
A non-oxidizing atmosphere is maintained in the float section 11 by
introducing a suitable gas, such as for example one composed of 99 percent by
volume nitrogen and 1 percent by volume hydrogen, into the zone 18, through
conduits 23 which are operably connected to a manifold 24. The non-oxidizing
gas is introduced into the zone 18 from the conduits 23 at a rate sufficient to
compensate for losses of the gas (some of the non-oxidizing atmosphere
leaves the zone 18 by flowing under the end walls 17), and to maintain a slight
positive pressure, conveniently about 0.001 to about 0.01 atmospheres above
ambient pressure. The tin bath 15 and the enclosed zone 18 are heated by
radiant heat directed downwardly from heaters 25. The heat zone 18 is
generally maintained at a temperature of about 500-700°C. The atmosphere in
the lehr 12 is typically air, and the cooling section 13 is not enclosed. Ambient
air is blown onto the glass by fans 26.
The apparatus 10 also includes gas distributors 27, 28, 29 and 30
located in the float zone 11. The desired precursor mixtures for the individual
coatings are supplied to the respective gas distributors, which in turn direct the
precursor mixtures to the hot surface of the glass ribbon. The precursors react
at the glass surface to form the desired coatings.
The coated glass article of the invention is ideally suited for use in
architectural glazings. For example, the coated glass article may be utilized in
an insulated glass unit. Thus, the coated glass article of the present invention
is illustrated in Fig. 3 as an outboard lite 45 in an insulated glass unit 43
suitable for installation into a building structure. The insulated glass unit 43
also includes an inboard lite 53 made of a glass article and maintained in a
spaced apart relationship from the outboard lite 45 by a frame (not shown) in
the known manner. The glass substrate 45 of the present invention is
positioned facing the exterior of the structure. The multilayered coating 49 of
the present invention faces the interior with an air space 51 separating the
outboard lite 45 from the inboard lite 53.

When the protective overcoat is formed of fluorine doped tin oxide, the
low emittance provided by the fluorine doped tin oxide improves the
performance of the coated glass article in the summer and winter. The
radiation energy, a component of the indirect gain from the glass to the building
interior, is reduced under summer conditions with a low emittance coating.
This is noticed as a reduction in the total solar heat transmittance (TSHT).
TSHT is defined as including solar energy transmitted directly through the
glass, and the solar energy absorbed by the glass, and subsequently
convected and thermally radiated inwardly. Further, solar heat gain coefficient
(SHGC) is defined as the ratio of total solar heat gain through the glass relative
to the incident solar radiation. The major improvement in performance,
however, occurs under winter conditions where the U-value of the glazing
structure is reduced significantly with a low emittance coating. The U-value or
the overall heat transfer coefficient is inversely proportional to the thermal
resistance of the structure. A lower U-value means a reduction in heat loss
through the glass from the interior to the exterior, resulting in savings in energy
costs.
Thus, the low emittance of the coated glass article, when combined with
the surprisingly selective solar absorption of the multilayer stack provides
improved heat rejection in summer and heat retention in winter.
The resulting insulated glass unit, utilizing the coated glass article of the
present invention, exhibits specific transmittance and spectral properties. The
low emittance of surface 49 (Fig. 3) results in a U-value of less than 0.34 and
preferably less than 0.32. The total solar heat transmittance of the unit is less
than 41%. The insulated glass unit also exhibits a visible light transmittance
(Illuminant C) of 62% or more.
The insulated glass unit preferably exhibits a neutral color in both
reflectance and transmittance.
The following examples, which constitute the best mode presently
contemplated for practicing the invention, are presented solely for the purpose
of further Illustrating and disclosing the present invention, and are not to be
construed as a limitation on the invention.

PREDICTIVE EXAMPLES 1-15 and 16-23
A float glass process is used to produce a float glass ribbon having a
thickness of 6mm. During the production of the float glass ribbon, the specified
coatings are modeled to be consecutively applied onto the glass substrate in
the float bath through conventional chemical vapor deposition methods at the
thicknesses (in Angstroms) indicated in Table 1. The precursor mixture for the
various tin oxide coatings Includes dimethyl tin dichloride, oxygen, water, and
helium as a carrier gas. The precursor mixture for the silicon dioxide coating
includes monosilane, ethylene, and oxygen and a carrier gas. The precursor
mixture for the doped zinc oxide includes a Zn precursor such as diethyl zinc
(DEZ), an oxygen source such as IPA (isopropanol), and a suitable aluminum
precursor, for example, diethylaluminum chloride. Alternatively, a suitable
gallium precursor could be substituted for the aluminum precursor. The
resulting doped zinc oxide layer has a dopant concentration of about 2 atomic
percent Al or Ga.
The visible light transmittance (TVis), total solar energy transmittance
(Tsol) and the solar selectivity (Tvis - Tsal) were calculated for the resulting
coated glass article in each example. Tvis and TSOl, for the noted examples, are
for a monolithic glazing, i.e., a single glass sheet. The results are also shown
in Table I.

Examples 16-23 were modeled on much the same basis as Examples 1-
15. except that Examples 16-23 represent an Insulated glass unit, as elsewhere
defined herein, formed from two sheets of glass. The inventive coating stack
was projected to be located on the so-called #2 surface; that is, on the major
surface of the outboard glass sheet which faces the air space between the two
glass sheets. The gap between the glass sheets was 12mm, and the space
was filled with air.
The electrical and optical properties of conductive materials can be
characterized by NB, the concentration of free electrons in the material, and µ,
the mobility of free electrons in the material. The solar selectivity of the coating
stacks described herein depends primarily on the concentration of free
electrons in the doped ZnO layer. As shown by Examples 2-4 in Table 1, the
required solar selectivity can be achieved by using highly doped zinc oxide,
where "highly-doped" refers to an electron concentration greater than 1.0 x 1021
electrons/cm3. By comparison, Example 1 shows that doped ZnO having an
electron concentration of only 1.0 x 1021 electrons/cm3 results in a TviS (69%)
that just meets the target value (>69%). The solar selectivity of the coating
stacks described herein also depends on the electron mobility in the doped
ZnO layer. As shown by Examples 3 and 6-8 in Table 1, the required solar
selectivity can be achieved by using highly doped zinc oxide with an electron
mobility in the range of 15-100 cm2N-s. By way of comparison. Example 5
shows that doped ZnO with an electron mobility of 10 results in a Tvis (69%) that
just meets the target value (269%).
Examples 9 and 10 demonstrate that a thin protective overcoat, on the
order of 200-300A of, for example SnO2 or SiO2, does not substantially alter the
solar performance of the film stack. Tvis and TSOl remain above the desired
levels of 69% and only slightly greater than 40%, respectively.
Example 11 demonstrates that a thicker doped overcoat (3000A fluorine
doped tin oxide) does not seem to adversely affect the solar performance of the
film stack, as both TviS and Tsol are within the targeted levels of > 69% and
type modeled in Example 11 may provide lower emissivity and more nearly
neutral color.

Example 12 shows that undertayers beside SiO2, for example SnO2,
may be utilized in the subject film stack while maintaining desired levels of Tvis
and Tsol. Examples 13-15 show utilization of optional multi-layer color
suppression interlayers which provide desired neutral color of transmitted light
while, once again, maintaining desired levels of Tvis and Tsol.
Table 2 shows the results of modeling of Insulated glass (IG) units, the
structure of which has been previously described herein. The solar
performance of the subject IG units consistently exhibit properties at, or above,
desired levels, in particular, Tvis >62%, solar heat gain coefficient (SHGC)
>0.40 and U-value of the doped zinc oxide coating. Emissivity is also, generally, less than 0.2,
and for some examples,

PREDICTIVE EXAMPLES 24-31 and 32-35
Examples 24-31, as shown in Table 3. were modeled utilizing Input
parameters substantially similar to Examples 1-15. The substrate thickness
was 3mm rather than 6mm, however.
Similarly, Examples 32-35 were modeled as IG units substantially similar
to those modeled In Examples 16-23. The thickness of both sheets of glass
was, however, 3mm and the gap therebetween was 6mm, rather than 12mm.

As can be observed from reviewing Table 3, with silmilar thicknesses of
highly doped zinc oxide on thinner glass, it is still possible to maintain a Tsol of
40, and a solar selectivity >28, although the preferred solar selectivity of 33 is
more difficult to achieve.
Examples 32-35, displayed in Table 4, demonstrate that it is also
possible to meet the desired solar performance levels for an IG unit utilizing
3mm glass, namely Tvis >62, SHGC >0.40 and U-value In accordance with the provisions of the patent statutes, the present
invention has been described in what is considered to represent its preferred
embodiment. However, it should be noted that the invention can be practiced
otherwise than as specifically illustrated and described without departing from
its spirit and scope. For example, other coating methods, such as sputtering,
may also be utilized to form the solar control coating of the present invention.

What is claimed is:
1. A coated glass article comprising:
a glass substrate;
a coating of highly doped zinc oxide deposited over the glass
substrate; and
optionally, a protective metal oxide coating deposited over the
zinc oxide coating;
wherein the thickness of the coatings is selected so that the
coated glass article exhibits a difference between visible light transmittance
(llluminant C) and total solar energy transmittance, integrated with an air mass
1.5 on a clear glass substrate having a nominal 6 mm thickness, to provide a
solar selectivity of 28 or more.
2. The coated glass article defined in claim 1, wherein the solar
selectivity of the highly doped zinc oxide coating is 33 or more.
3. The coated glass article defined in claim 1, wherein the doped
zinc oxide coating has been deposited at a temperature of 500°-700°C.
4. The coated glass article defined in claim 1, wherein a color
suppression interlayer is deposited between the glass substrate and the
coating of doped zinc oxide.
5. The coated glass article defined in claim 1, wherein a protective
overcoat is deposited over the coating of highly doped zinc oxide, the overcoat
comprised of a metal oxide selected from the group consisting of tin oxide,
silicon dioxide, aluminum oxide, titanium dioxide, niobium oxide, and zirconium
oxide.
6. The coated glass article defined in claim 5, wherein the protective
overcoat is doped.
2.
7. The coated glass article defined in claim 1, wherein the doped
zinc oxide coating has a thickness of > 1600A and 8. The coated glass article defined in claim 1, wherein the protective
overcoat has a thickness of 1000 A or less.
9. The coated glass article defined in claim 1, wherein the protective
overcoat has a thickness of 250 A or less.
10. The coated glass article defined in claim 1, wherein the electron
concentration of the doped zinc oxide layer is > 1.0 x 1021 electrons/cm3.
11. The coated glass article defined in claim 1, exhibiting an
emittance of 0.15 or less.
12. The coated glass article defined in claim 1, wherein the dopant of
the zinc oxide coating is at least one chosen from the group consisting of
aluminum, gallium, indium and boron.
13. The coated glass article defined in claim 1, wherein the visible
light transmittance of the coated glass article is > 69%.
14. The coated glass article defined in claim 1, wherein the visible
light transmittance of the coated glass article is > 73%.
15. The coated glass article defined in claim 1, wherein the total solar
energy transmittance of the coated glass article is

10

16. An insulated glass unit comprising:
at least first and second sheets of glass in parallel spaced apart
relationship, each of the at least first and second glass sheets having first and
second major surfaces, with each glass sheet having one major surface facing
the space between the at least first and second glass sheets; and at least one
of such major surfaces having a coating of highly doped zinc oxfde deposited
thereover;
the insulated glass unit exhibiting a visible light transmittance
>60%, a U-value of 0.29 or greater and hemispherical emissivity 17. A coated glass article comprising:
a glass substrate;
a coating of highly doped zinc oxide deposited over the glass
substrate; and
a protective metal oxide coating deposited over the highly doped
zinc oxide coating, the zinc oxide coating having an electron concentration >1.0
x 1021 electrons (cm'3) and an electron mobility of 10 cm2N-s more.
18. A method of forming a coated glass article comprising:
providing a moving, heated glass ribbon; and
depositing a coating of a highly doped zinc oxide over the moving,
heated glass ribbon at a temperature of 500-700°C;
wherein the doped zinc oxide coating is deposited at a thickness
so that the coated glass article exhibits a difference between visible light
transmittance (llluminant C) and total solar energy transmittance, integrated
with air mass 1.5 on a clear glass substrate having a nominal 3mm thickness,
to provide a selectivity of 28 or more.
19. The method defined in claim 18, wherein a color suppression
coating is deposited between the glass substrate and the coating of highly
doped zinc oxide.

A multi-layer thin film having as a primary component, a coating of highly
doped zinc oxide, and optionally, a color suppression underlayer and a
protective metal oxide overcoat. The film stack is preferably deposited on a
transparent substrate by atmospheric chemical vapor deposition. The film stack
exhibits a desirable combination of properties including high visible light
transmittance, relatively low solar energy transmittance, low emissivity, and
high solar selectivity.

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Patent Number

272310

Indian Patent Application Number

5082/KOLNP/2008

PG Journal Number

14/2016

Publication Date

01-Apr-2016

Grant Date

29-Mar-2016

Date of Filing

15-Dec-2008

Name of Patentee

ARKEMA, INC.

Applicant Address

2000 MARKET STREET, PHILADELPHIA, PA

Inventors:

#	Inventor's Name	Inventor's Address
1	VARANASI, SRIKANTH	2119 EVERGREEN ROAD #4, OTTAWA HILLS, OH 43606
2	STRICKLER, DVID, A.	2647 BARRINGTON DRIVE, TOLEDO, OH 43606

PCT International Classification Number

C03C 17/245

PCT International Application Number

PCT/US2007/013133

PCT International Filing date

2007-06-04

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	60/811,048	2006-06-05	U.S.A.