2. Technical Considerations and Prior Art Various dark tinted, infrared and ultraviolet radiation absorbing glass compositions are known in the art. The primary colorant in typical dark tinted automotive privacy glasses is iron, which is usually present in both the Fe203 and FeO forms. Some glasses use cobalt, selenium and, optionally, nickel in combination with iron to achieve a desired color and infrared and ultraviolet radiation, for example, as disclosed in U. S. Patent Nos. 4,873,206 to Jones; 5,278,108 to Cheng, et al.; 5,308,805 to Baker, et al.; 5,393,593 to Gulotta, et al.; 5,545,596 and 5,582,455 to Casariego, et al.; and European Patent application no. 0 705 800. Others also include chromium with this combination of colorants as disclosed in U. S. Patent Nos. 4,104,076 to Pons; 4,339,541 to Dela Ruye; 5,023,210 to Krumwiede, et al.; and 5,352,640 to Combes, et al.; European Patent application no. 0 536 049; French Patent No. 2,331,527 and Canadian Patent No. 2,148,954. Patents such as U. S.

Patent Nos. 5,521,128 and 5,346,867 to Jones, et al. and 5,411,922 to Jones

further includes manganese and/or titanium. Still, other glasses may include addition materials, such as disclosed in WO 96/00194, which teaches the inclusion of fluorine, zirconium, zinc, cerium, titanium and copper in the glass composition and requires that the sum of the alkaline earth oxides be less than 10 weight percent of the glass.

In producing infrared and ultraviolet radiation absorbing glasses, the relative amounts of iron and other additives must be closely monitored and controlled within an operating range to provide the desired color and spectral properties. It would be desirable to have a dark tinted bronze colored glass that may be used as a privacy glazing for vehicles to complement the bronze colored glasses available in automobiles and vans that exhibits superior solar performance properties and is compatible with commercial float glass manufacturing techniques.

SUMMARY OF THE INVENTION The present invention provides a bronze colored, infrared and ultraviolet absorbing glass composition having a luminous transmittance of up to 60 percent. The glass uses a standard soda-lime-silica glass base composition and additionally iron and selenium, and optionally cobalt, as infrared and ultraviolet radiation absorbing materials and colorants. The glass of the present invention has a luminous transmittance (LTA) of up to 60 percent and its color is characterized by a dominant wavelength in the range of 560 to 590 nanometers and an excitation purity of 12 to 75 percent at a thickness of 0.160 inches (4.06 millimeters).

In one embodiment of the invention, the glass composition of a bronze colored, infrared and ultraviolet radiation absorbing soda-lime-silica glass article includes a solar radiation absorbing and colorant portion consisting essentially of 0.7 to 2.2 percent by weight total iron, 0.15 to 0.5 percent by weight FeO, 3 to 100 PPM Se, and optionally up to 200 PPM CoO, and

preferably 1.1 to 1.4 percent by weight total iron, 0.24 to 0.36 percent by weight FeO, 20 to 45 PPM Se, and 0 to 70 PPM CoO.

DETAILED DESCRIPTION OF THE INVENTION The base glass of the present invention, that is, the major constituents of the glass without infrared or ultraviolet absorbing materials and/or colorants, which are an object of the present invention, is commercial soda- lime-silica glass typically characterized as follows: Weight Percent Si02 66 to 75 Na20 10 to 20 CaO 5 to 15 MgO 0 to 5 Ai203 0 to 5 K20 0 to 5 As used herein, all"weight percent (wt. %)" values are based on the total weight of the final glass composition.

To this base glass, the present invention adds infrared and ultraviolet radiation absorbing materials and colorants in the form of iron and selenium and optionally cobalt. As disclosed herein with respect to the glass compositions, iron is expressed in terms of Fe203 and FeO, selenium is expressed in terms of elemental Se, and cobalt is expressed in terms of CoO.

It should be appreciated that the glass compositions disclosed herein may include small amounts of other materials, for example, melting and refining aids, tramp materials or impurities. It should be further appreciated that in one embodiment of the invention, small amounts of additional materials may be included in the glass to provide the desired color characteristics and improve the solar performance of the glass, as will be discussed later in more detail.

The iron oxides in a glass composition perform several functions.

Ferric oxide, Fe203, is a strong ultraviolet radiation absorber and operates as a yellow colorant in the glass. Ferrous oxide, FeO, is a strong infrared radiation absorber and operates as a blue colorant. The total amount of iron present in the glasses disclosed herein is expressed in terms of Fe203 in accordance with standard analytical practice but that does not imply that all of the iron is actually in the form of Fe203. Likewise, the amount of iron in the ferrous state is reported as FeO, even though it may not actually be present in the glass as FeO. In order to reflect the relative amounts of ferrous and ferric iron in the glass compositions disclosed herein, the term"redox"shall mean the amount of iron in the ferrous state (expressed as FeO) divided by the amount of total iron (expressed as Fe203). Furthermore, unless stated otherwise, the term"total iron"in this specification shall mean total iron expressed in terms of Fe203 and the term"FeO"shall mean iron in the ferrous state expressed in terms of FeO.

Se is an ultraviolet absorbing colorant that imparts a pink or brown color to soda-lime-silica glass. Se may also absorb some infrared radiation and its use tends to reduce redox. CoO operates as a blue colorant and does not exhibit any appreciable infrared or ultraviolet radiation absorbing properties. A proper balance between the iron, i. e. ferric and ferrous oxides, selenium, and cobalt is required to obtain the desired bronze colored privacy glass with the desired spectral properties.

The glass of the present invention may be melted and refined in a continuous, large-scale, commercial glass melting operation and formed into flat glass sheets of varying thickness by the float process in which the molten glass is supported on a pool of molten metal, usually tin, as it assumes a ribbon shape and is cooled, in a manner well known in the art.

Although it is preferred that the glass disclosed herein be made using a conventional, overhead fired continuous melting operation, as is well known in

the art, the glass may also be produced using a multi-stage melting operation, as disclosed in U. S. Patent Nos. 4,381,934 to Kunkle, et al., 4,792,536 to Pecoraro, et al. and 4,886,539 to Cerutti, et al. If required, a stirring arrangement may be employed within the melting and/or forming stages of the glass production operation to homogenize the glass in order to produce glass of the highest optical quality.

Depending on the type of melting operation, sulfur may be added to the batch materials of a soda-lime-silica glass as a melting and refining aid.

Commercially produced float glass may include up to about 0.3 wt. % S03. In a glass composition that includes iron and sulfur, providing reducing conditions may create amber coloration which lowers luminous transmittance as discussed in U. S. Patent No. 4,792,536 to Pecoraro, et al. However, it is believed that the reducing conditions required to produce this coloration in float glass compositions of the type disclosed herein are limited to approximately the first 20 microns of the lower glass surface contacting the molten tin during the float forming operation, and to a lesser extent, to the exposed upper glass surface. Because of the glass'low sulfur content and the limited region of the glass in which any coloration could occur, depending on the particular soda-lime-silica-glass composition, sulfur in these surfaces essentially has no material effect on the glass color or spectral properties.

It should be appreciated that as a result of forming the glass on molten tin as discussed above, measurable amounts of tin oxide may migrate into surface portions of the glass on the side contacting the molten tin. Typically, a piece of float glass has an SnO2 concentration ranging from about 0.05 to 2 wt. % in about the first 25 microns below the surface of the glass that was in contact with the tin. Typical background levels of SnOz may be as high as 30 parts per million (PPM). It is believed that high tin concentrations in about the first 10 angstroms of the glass surface supported by the molten tin may

slightly increase the reflectivity of that glass surface; however, the overall impact on the glass properties is minimal.

Table 1 illustrates examples of experimental glass melts having glass compositions which embody the principles of the present invention. Similarly, Table 2 illustrates a series of computer modeled glass compositions embody- ing the principes of the present invention. The modeled compositions were generated by a glass color and spectral performance computer model developed by PPG Industries, Inc. Tables 1 and 2 list only the iron, selenium and cobalt portions of the examples. Analysis of selected experimental melts indicates that it is expected that the melts would most likely include up to about 15 PPM Cr203, up to about 40 PPM MnO2, and up to about 0.024 wt. percent Ti02. It is presumed that the Cr203, Mn02 and Ti02 entered the glass melts as part of the cullet. In addition, the modeled compositions were modeled to include up to about 9 PPM Cr203 and about 0.025 wt. % TiO2. It is believed that glass compositions of the instant invention produced by a commercial float process as discussed earlier may include these materials, but these levels of such materials are considered to be tramps levels which would not materially affect the color characteristics and spectral properties of the bronze glass of the present invention.

The spectral properties shown for Tables 1 and 2 are based on a reference thickness of 0.160 inches (4.06 mm). It should be appreciated that the spectral properties of the examples may be approximated at different thicknesses using the formulas disclosed in U. S. Patent No. 4,792,536.

With respect to the transmittance data provided in Table 1, the luminous transmittance (LTA) is measured using C. I. E. standard illuminant "A"with a 2° observer over the wavelength range of 380 to 770 nanometers.

Glass color, in terms of dominant wavelength and excitation purity, is measured using C. I. E. standard illuminant"C"with a 2° observer, following the procedures established in ASTM E308-90. The total solar ultraviolet

transmittance (TSUV) is measured over the wavelength range of 300 to 400 nanometers, total solar infrared transmittance (TSIR) is measured over the wavelength range of 720 to 2000 nanometers, and total solar energy transmittance (TSET) is measured over the wavelength range of 300 to 2000 nanometers. The TSUV, TSIR and TSET transmittance data are calculated using Parry Moon air mass 2.0 direct solar irradiance data and integrated using the Trapezoidal Rule, as is known in the art. The spectral properties presented in Table 2 are based on the same wavelength ranges and calculation procedures.

Sample Preparation The information provided in Table 1 is based on experimental laboratory melts having approximately the following batch components: cullet 239.74 gm sand 331.10 gm soda ash 108.27 gm limestone 28.14 gm dolomite 79.80 gm salt cake 2.32 gm Fe203 (total iron) as required Se as required Co304 as required The raw materials were adjusted to produce a final glass weight of 700 grams. Reducing agents were added as required to control redox. The cullet used in the melts (which formed approximately 30% of the melt) included up to 0.51 wt. % total iron, 0.055 wt. % Ti02 and 7 PPM Cr203. In preparing the melts, the ingredients were weighed out and mixed. A portion of the raw batch material was then placed in a silica crucible and heated to 2450°F (1343°C). When the batch material melted down, the remaining raw

materials were added to the crucible and the crucible was held at 2450°F (1343°C) for 30 minutes. The molten batch was then heated and held at temperatures of2500°F (1371°C), 2550°F (1399°C), 2600°F (1427°C) for 30 minutes, 30 minutes and 1 hour, respectively. Next, the molten glass was fritted in water, dried and reheated to 2650°F (1454°C) in a platinum crucible for two hours. The molten glass was then poured out of the crucible to form a slab and annealed. Samples were cut from the slab and ground and polished foranalysis.

The chemical analysis of the glass compositions (except for FeO) was determined using a RIGAKU 3370 X-ray fluorescence spectrophotometer.

The spectral characteristics of the glass were determined on annealed samples using a Perkin-Elmer Lambda 9 UVNIS/NIR spectrophotometer prior to tempering the glass or prolonge exposure to ultraviolet radiation, which will effect the spectral properties of the glass. The FeO content and redox was determined using the glass color and spectral performance computer model developed by PPG Industries, Inc.

The following is the approximate basic oxides of the experimental melts disclosed in Table 1 calculated based on the batch: Si02 72.1 wt. % Na20 13.6 wt. % CaO 8.8 wt. % MgO 3.8 wt. % Ai203 0.18 wt. % K20 0.057 wt. % It is expected that the basic oxide constituents of commercial soda-lime-silica glass compositions based on the experimental melts disclosed in Table 1 and the modeled compositions disclosed in Table 2 would be similar to those discussed earlier.

Table 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Ex. 9 Total iron (wt.%) 1.55 1.24 1.24 1.22 1.23 1.22 1.22 1.20 1.26 FeO (wt.%) 0.434 0.324 0.328 0.325 0.354 0.365 0.269 0.309 0.242 Model redox 0.280 0.262 0.265 0.266 0.287 0.299 0.220 0.257 0.192 Se(PPM) 44 45 49 40 34 28 30 37 31 CoO(PPM) 126 127 128 126 129 124 123 17 65 LTA(%) 13.76 17.39 18.21 19.70 20.06 22.11 25.04 31.72 32.36 TSUV(%) 4.27 6.57 7.07 8.32 9.47 11.23 11.00 9.26 10.10 TSIR(%) 6.42 11.81 11.81 11.74 10.18 9.51 16.81 13.31 19.75 TSET(%) 9.66 14.46 14.97 15.51 15.00 15.47 20.91 20.28 24.90 DW(nm) 579.4 580.3 580.2 578.5 578.0 572.8 576.9 580.4 577.5 Pe(%) 33.7 28.1 25.6 20.2 17.5 13.4 13.0 36.6 22.0 Ex. 10 Ex. 11 Ex. 12 Ex. 13 Ex. 14 Ex. 15 Ex. 16 Ex. 17 Ex. 18 Total iron (wt.%) 1.23 1.20 1.25 1.24 1.24 1.22 1.19 1.22 1.19 FeO (wt.%) 0.312 0.329 0.333 0.267 0.290 0.316 0.297 0.330 0.318 Model redox 0.254 0.274 0.266 0.215 0.234 0.258 0.250 0.271 0.267 Se(PPM) 37 21 17 23 20 22 18 19 16 CoO(PPM) 0 32 35 35 35 0 34 0 0 LTA(%) 33.96 35.93 37.48 37.96 38.54 40.31 40.35 43.20 47.62 TSUV(%) 9.15 14.15 14.70 12.95 14.33 13.56 16.07 15.65 18.27 TSIR(%) 13.12 11.82 11.70 17.10 14.95 12.87 14.31 11.90 12.73 TSET(%) 20.97 21.89 22.57 25.67 24.82 23.73 25.41 24.58 27.24 DW(nm) 579.3 575.1 572.7 576.5 574.8 577.0 573.8 574.7 573.5 Pe(%) 35.8 18.9 15.5 21.2 17.7 26.0 15.7 20.7 17.4 TABLE 2 Ex. 19 Ex. 20 Ex. 21 Ex. 22 Ex. 23 Ex. 24 Ex. 25 Ex. 26 Ex. 27 Total iron (wt.%) 0.72 0.72 .075 0.72 2.1 1.9 1.75 1.45 1.35 FeO (wt.%) 0.202 0.202 0.298 0.202 0.557 0.504 0.464 0.384 0.348 Model redox 0.280 0.280 0.397 0.280 0.265 0.265 0.265 0.265 0.258 Se(PPM) 61 52 93 52 24 24 24 24 35 CoO(PPM) 190 175 50 126 35 35 35 35 0 LTA(%) 10.74 13.21 13.64 16.70 26.52 28.29 29.69 32.74 33.79 TSUV(%) 5.43 6.78 3.98 6.83 4.52 5.43 6.24 8.34 6.86 TSIR(%) 24.60 24.69 14.09 24.87 3.41 4.51 5.59 8.69 10.66 TSET(%) 19.13 20.31 14.13 21.64 12.33 13.85 15.19 18.52 19.46 DW(nm) 589.5 588.9 590.0 586.9 570.1 571.3 572.2 574.3 580.7 Pe(%) 31.7 25.5 70.3 35.1 25.0 24.0 23.4 21.9 41.4 Ex. 28 Ex. 29 Ex. 30 Ex. 31 Ex. 32 Ex. 33 Ex. 34 Ex. 35 Total iron (wt.%) 1.32 1.15 1.06 0.95 1.2 1.2 1.1 0.9 FeO (wt.%) 0.350 0.305 0.281 0.252 0.462 0.434 0.284 0.293 Model redox 0.265 0.265 0.265 0.265 0.385 0.362 0.258 0.325 Se(PPM) 24 24 24 24 18 18 20 18 CoO(PPM) 35 35 35 35 6 6 0 10 LTA(%) 34.16 36.12 37.20 38.58 40.33 41.12 46.28 55.34 TSUV(%) 9.50 11.30 12.42 13.97 17.44 16.74 12.67 26.07 TSIR(%) 7.58 13.71 15.77 18.75 5.67 6.62 15.56 14.80 TSET(%) 20.32 23.10 24.81 27.17 20.01 20.85 27.74 32.54 DW(nm) 575.2 576.6 577.4 578.5 570.5 572.0 577.4 561.0 Pe(%) 21.3 20.5 20.1 14.0 12.9 14.6 26.2 6.0

Referring to Tables 1 and 2, the present invention provides a bronze colored glass having a standard soda-lime-silica glass base composition and addition iron and selenium, and optionally cobalt, as infrared and ultraviolet radiation absorbing materials and colorants and a luminous transmittance (LTA) of up to 60% and a color characterized by a dominant wavelength (DW) in the range of 560 to 590 nanometers (nm) and an excitation purity (Pe) of 12 to 75%. It is anticipated that the color of the glass may vary within the dominant wavelength range to provide a desired product. For example, as the dominant wavelength approaches 560 nanometers, the glass color may appear to be yellow green while as the dominant wavelength approaches 590 nanometers, the glass color may appear to be yellow orange. In addition, as the excitation purity gets smaller, the glass may appear to be more gray, while as the excitation purity increases, the color of the glass may appear more intense.

The redox ratio for the glass is maintained between 0.15 to 0.40, preferably between 0.18 to 0.30, more preferably between 0.24 to 0.29. The glass composition also has a TSUV of no greater than 40%, preferably no greater than 35%; a TSIR of no greater than 35%, preferably no greater than 30%; and a TSET of no greater than 40%, preferably no greater than 35%.

In one particular embodiment, the glass composition includes 0.7 to 2.2 wt. % total iron, preferably 1 to 1.6 wt. % total iron, and more preferably 1.1 to 1.4 wt. % total iron; 0.15 to 0.5 wt. % FeO, preferably 0.2 to 0.4 wt. % FeO, and more preferably 0.24 to 0.36 wt. % FeO; and 3 to 100 PPM Se, preferably 20 to 80 PPM Se, and more preferably 15 to 40 PPM Se. The glass has an LTA of up to 60% and a color characterized by a dominant wavelength of 571 to 590 nm, preferably 575 to 585 nm, and an excitation purity of 12 to 75%, preferably 15 to 35%, at a thickness of 0.16 inches (4.06 mm). As discussed earlier, cobalt may also be included in the glass

composition and more specifically, 0 to less than 100 PPM CoO, preferably 0 to 70 PPM CoO, and more preferably 20 to 50 PPM CoO.

The following are addition embodiments of the present invention which combine the same infrared and ultraviolet radiation absorbing materials and colorants discussed above to produce a glass having the desired color characteristics and spectral properties.

A glass composition which includes 0.7 to 1.35 wt. % total iron, 0.15 to 0.5 wt. % FeO, 3 to 100 PPM Se, and 0 to less than 100 PPM CoO, and has an LTA of up to 60% and a color characterized by a dominant wavelength of 560 to 590 nm and an excitation purity of 12 to 75%, at a thickness of 0.16 inches (4.06 mm).

A glass composition which includes 0.7 to 2.2 wt. % total iron, 0.15 to 0.5 wt. % FeO, 3 to 100 PPM Se, and 0 to less than 100 PPM CoO and has an LTA of 20 to 60% and a color characterized by a dominant wavelength of 560 to 590 nm and an excitation purity of 12 to 75%, at a thickness of 0.16 inches (4.06 mm).

A glass composition which includes 0.7 to 2.2 wt. % total iron, 0.15 to 0.5 wt. % FeO, 3 to 100 PPM Se, and 0 to 200 PPM CoO and has an LTA of up to 60% and a color characterized by a dominant wavelength of 571 to 590 nm and an excitation purity of 15 to 75%, at a thickness of 0.16 inches (4.06 mm).

A glass composition which includes 0.7 to 1.35 wt. % total iron, 0.15 to 0.5 wt. % FeO, 3 to 100 PPM Se, and 0 to 200 PPM CoO and has an LTA of up to 60% and a color characterized by a dominant wavelength of 560 to 590 nm and an excitation purity of 15 to 75%, at a thickness of 0.16 inches (4.06 mm).

A glass composition which includes 0.7 to 2.2 wt. % total iron, 0.15 to 0.5 wt. % FeO, 3 to 100 PPM Se, and 0 to 200 PPM CoO and has an LTA of 20 to 60% and a color characterized by a dominant wavelength of 560 to

590 nm and an excitation purity of 15 to 75%, at a thickness of 0.16 inches (4.06 mm).

A glass composition which includes 0.7 to 1.35 wt. % total iron, 0.15 to 0.5 wt. % FeO, 3 to 100 PPM Se, and 0 to less than 100 PPM CoO and has an LTA of 20 to 60% and a color characterized by a dominant wavelength of 571 to 590 nm and an excitation purity of 15 to 75%, at a thickness of 0.16 inches (4.06 mm).

It is expected that the spectral properties of the glass will change after tempering the glass and further upon prolonged exposure to ultraviolet radiation, commonly referred to as"solarization". In particular, it is estimated that tempering and solarization of the glass compositions disclosed herein may reduce LTA and TSIR by about 0.5 to 1%, reduce the TSUV by about 1 to 2%, and TSET by about 1 to 1.5%. As a result, in one embodiment of the invention, the glass has selected spectral properties that initially fall outside the desired ranges previously discussed but fall within the desired ranges after tempering and/or solarization.

Glass as disclosed herein and made by the float process typically ranges from a sheet thickness of about 1 millimeter to 10 millimeters.

For vehicle glazing applications, it is preferred that the glass sheets having a composition and spectral properties as disclosed herein have a thickness within the range of 0.126 to 0.197 inches (3.2 to 5 mm). It is anticipated that when using a single glass ply in the above thickness range, the glass will be tempered, e. g. for an automotive side or rear window.

It is also contemplated that the glass will have architectural applications and be used at thicknesses ranging from about 0.14 to 0.24 inches (3.6 to 6 mm).

When multiple plies are used for either automotive or architectural applications, it is anticipated that the glass plies will be annealed and

laminated together using a thermoplastic adhesive, such as polyvinyl butyral.

As discussed earlier, other materials may also be added to the glass compositions disclosed herein to further reduce infrared and ultraviolet radiation transmission and/or control glass color. In particular, it is contemplated that the following materials may be added to the iron and selenium, and optionally cobalt containing soda-lime-silica glass disclosed herein: Cr203 0 to 0.009 wt. % Ti02 0 to 0. 9 wt. % V205 0 to 0. 12 wt. % Mn02 0 to 1 wt. % Nd203 0 to 1 wt. % Sn02 0 to 2 wt. % ZnO 0 to 1 wt. % ! o MoO3 0 to 0.03 wt. % Ce02 0 to 2 wt. % NiO 0 to 0. 1 wt. % As should be appreciated, adjustments may have to be made to the basic iron and selenium, and optionally cobalt constituents to account for any coloring and/or redox affecting power of these addition materials.

Other variations as are known to those skilled in the art may be resorted to without departing from the scope of the invention as defined by the claims that follow.