HK1032038B - Privacy glass - Google Patents

Description

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The invention relates to a tinted green colored soda-lime-silica glass with low light transmission which can be used as a privacy glass for vehicles, such as the side and rear windows of vans. As used herein, the term "green" refers to glass that includes a dominant wavelength of about 480-510nm and is characterized by a color of blue-green, yellow-green, or gray-green. In addition, the glass has lower infrared and ultraviolet radiation transmittance than typical green glass used in automobiles, and it can be matched to float glass manufacturing processes.

A variety of dark colored infrared and ultraviolet radiation absorbing glass compositions are known in the art. The primary colorant in typical dark colored automotive privacy glass is iron, which is usually present in both the ferric oxide and ferrous oxide forms. Some glasses employ cobalt, selenium and optionally nickel in combination with iron to further control infrared and ultraviolet radiation and color, as described, for example, in U.S. patent 4873206 to Jones, U.S. patent 5278108 to Cheng et al, U.S. patent 5308805 to Baker et al, U.S. patent 5393593 to Gulotta et al, U.S. patents 5545596 and 5582455 to Casariego et al, and european patent application 0705800. Still others include chromium in combination with colorants, such as those described in U.S. patent 4104076 to Pons, U.S. patent 4339541 to Dela Ruye, U.S. patent 5023210 to Krumwiede et al, and U.S. patent 5352640 to Combes et al, european patent application 0536049, french patent 2331527, and canadian patent 2148954. In addition, other glasses include additional materials, as described in WO96/00194, which states that fluorine, zirconium, zinc, cerium, titanium and copper are included in the glass composition and that the total amount of alkaline earth oxides is required to be less than 10% by weight of the glass.

In the manufacture of infrared and ultraviolet radiation absorbing glass, the relative amounts of iron and other added components must be closely monitored and controlled within an operating range to provide the desired color and spectral properties. There is a need for glasses having a dark green color that can be used as a privacy glass for vehicles, thereby supplementing the green glass with excellent solar properties typically used in automobiles and trucks, and that can be matched to industrial float glass manufacturing processes.

The present invention provides a green colored, infrared and ultraviolet absorbing glass having a luminous transmittance up to 60%. The glass uses a standard soda-lime-silica base glass and additionally iron, cobalt, chromium and titanium as infrared and ultraviolet radiation absorbing materials and colorants. The color of the glasses of the present invention is characterized by a dominant wavelength in the range of about 480-510nm, preferably about 490-525nm, and an excitation purity of no more than about 20%, preferably about 5-15%.

In one embodiment of the invention, the glass composition of a green colored, infrared and ultraviolet radiation absorbing soda-lime-silica glass article includes a solar radiation absorbing and colorant portion consisting essentially of about 0.90-2.0% total iron by weight, about 0.17-0.52% FeO by weight, about 40-150PPM CoO, about 250-800PPM Cr₂O₃And about 0.1-1% by weight TiO₂And (4) forming.

The base glass of the invention, i.e. the main component of the glass without infrared or ultraviolet absorbing materials and/or colorants, which is an object of the invention, is an industrial soda-lime-silica glass characterized in that:

by weight%

SiO₂ 66-75

Na₂O 10-20

CaO 5-15

MgO 0-5

Al₂O₃ 0-5

K₂O0-5 as used herein, all "wt%" values are based on the total weight of the final glass composition.

The present invention adds infrared and ultraviolet absorbing materials and colorants in the form of iron, cobalt, chromium, and titanium to the base glass. As used herein, iron is present as Fe₂O₃And FeO form, cobalt as CoO, chromium as Cr₂O₃Expressed as TiO, titanium₂And (4) showing. It should be understood that the glass compositions described herein may include minor amounts of other materials, such as melting and fining aids, trace materials, or impurities. It should also be understood that in one embodiment of the present invention, small amounts of additional materials may be included in the glass to improve the solar properties of the glass, as described in detail below.

Iron oxides in glass compositions have several functions. Fe₂O₃Is a strong ultraviolet radiation absorber and acts as a yellow colorant in the glass. Ferrous oxide FeO is a strong infrared radiation absorber and acts as a blue colorant. The total amount of iron in said glass being Fe according to standard analytical procedures₂O₃Meaning, but not necessarily, that all of the iron is actually Fe₂O₃Are present. The amount of iron, also in the ferrous state, is expressed as FeO, although it is not actually present in the glass as FeO. To reflect the relative amounts of ferrous and ferric iron in the glass composition, the term "redox" refers to the amount of iron in the ferrous state (expressed as FeO) divided by the total amount of iron (expressed as Fe)₂O₃Represented) of the same. In addition, unless otherwise specified, the present invention is not limited to the specific embodiments shown and describedThe term "total iron" in the specification means Fe₂O₃Expressed as total iron, the term "FeO" means iron in the ferrous state expressed as FeO.

The CoO functions as a blue colorant and a weak infrared radiation absorber in the glass. Cr (chromium) component₂O₃The glass composition can be made green. In addition, it is believed that chromium may also provide some ultraviolet radiation absorption. TiO 2₂Is an ultraviolet radiation absorber which imparts a yellow color to the glass composition. A suitable balance between the iron, i.e. ferric and ferrous oxides, chromium, cobalt and titanium content is required in order to obtain a green colored privacy glass with the desired optical properties.

The glass of the present invention can be melted and refined in a continuous, large-scale, industrial 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 the glass exists in the shape of a ribbon of glass and is cooled in a manner common in the art.

While the glass of the present invention is preferably made by a conventional continuous top-firing melting operation, as is well known in the art, the glass may also be made by a multi-stage melting operation, as described in U.S. Pat. No. 4381934 to Kunkle et al, U.S. Pat. No. 4792536 to Pecoraro et al, and U.S. Pat. No. 4886539 to Cerutti et al. If desired, stirring means may be provided at the melting and/or forming stages of the glass making operation to homogenize the glass so that the highest optical quality glass is produced.

Depending on the type of melting operation, sulfur may be added to the batch of soda-lime-silica glass as a melting and fining aid. Commercially produced float glass may contain up to about 0.3 wt.% SO₃. In glass compositions containing iron and sulfur, providing reducing conditions can produce a brown color that reduces light transmittance, as described in U.S. patent 4792536 to Pecoraro et al. It is believed that this occurs in the float glass compositions described hereinThe reducing conditions required for color are limited to about 20 microns on the lower surface of the glass that is in contact with the molten tin during the float forming operation and to a lesser extent to the exposed upper surface of the glass. Due to the lower sulfur content and the limited glass area where any coloration occurs, the sulfur in these surfaces does not have any substantial effect on the glass color or optical properties, depending on the particular soda-lime-silica glass composition.

It should be appreciated that as noted above, as a result of forming the glass on the molten tin, a measurable amount of tin oxide will migrate into the portion of the surface of the glass that is in contact with the molten tin. Typically, the tin dioxide concentration on the float glass is at least 0.05 to 2 weight percent in about 25 microns of the lower surface of the glass in contact with the tin. Typical background tin dioxide amounts may be as high as 30 Parts Per Million (PPM). It is believed that a higher tin concentration in about 10 microns of the glass surface supported by molten tin slightly increases the reflectivity of the glass surface, but the overall effect on the glass properties is small.

Table 1 shows an example of a test glass melt having a glass composition embodying the principles of the present invention. These experimental melts were analyzed to determine the presence of iron, cobalt, chromium and titanium. Similarly, table 2 shows a series of computer simulated glass compositions embodying the principles of the present invention. The composition model was generated by a glass color and performance computer model developed by PPG industries. The optical properties shown in tables 1 and 2 are based on a reference thickness of 0.160 inches (4.06 mm). It should be understood that the optical properties of these examples can be approximately calculated at different thicknesses using the formula described in us patent 4792536. Only the iron, cobalt, chromium and titanium portions of the examples are listed in the table.

For the transmittance data set forth in Table 1, the Light Transmittance (LTA) was measured using a C.I.E.standard light source "A" with a C.I.E. 2 degree observer, which was in the wavelength range of 380-770 nm. The color of the glass according to dominant wavelength and excitation purity was measured using c.i.e. standard illuminant "a" with a 2 degree observer, following the method described in astm e 308-90. The total solar ultraviolet Transmittance (TSUV) is measured in the wavelength range of 300-400nm, the total solar infrared Transmittance (TSIR) is measured in the wavelength range of 720-2000nm, and the Total Solar Energy Transmittance (TSET) is measured in the wavelength range of 300-2000 nm. The TSUV, TSIR and TSET transmittance data were calculated using Parry Moon air mass 2.0 direct solar irradiance data and integrated using the trapezoidal principle, as is known in the art. The optical properties reported in Table 2 are based on the same wavelength ranges and calculations.

Sample preparation

The information in table 1 is based on experimental melts having approximately the following batch compositions:

crushed glass 238.8 g

Sand 329.6 g

Soda ash 107.8 g

Limestone 28.0 g

Dolomite 79.4 g

Mirabilite 3.6 g

Fe₂O₃On demand

Co₃O₄On demand

Cr₂O₃On demand

TiO₂The raw materials were adjusted as necessary to give a final glass weight of 700 grams. Reducing agents are added as needed to control the redox ratio. The cullet used in the melt comprised 0.869 wt% total iron, 8PPMCr₂O₃And 0.218% by weight TiO₂. In the preparation of meltsWhen so desired, the components were weighed out and mixed. A portion of the feedstock was then placed in a quartz crucible and heated to 2450 degrees fahrenheit (1343 degrees celsius). When the batch materials were melted, the remaining materials were added to the crucible and the crucible was held at 2450 degrees Fahrenheit (1343 degrees Celsius) for 30 minutes. The molten batch was then heated and held at 2500 degrees Fahrenheit (1371 deg.C.), 2550 degrees Fahrenheit (1399 deg.C.), 2600 degrees Fahrenheit (1427 deg.C.) for 30 minutes, and 1 hour, respectively. The molten glass was then made into a frit in water, dried, and reheated to 2650 degrees Fahrenheit (1454 deg.C.) in a platinum crucible for 2 hours. The molten glass is then poured out of the crucible to form glass strands and annealed. Samples were cut from the glass strip and ground, polished, and analyzed.

The glass composition was chemically analyzed (except for FeO) using a RIGAKU 3370X-ray fluorescence spectrometer. The optical properties of the annealed sample glass were measured using a Perlin-Elmer Lambda 9 UV/VIS/NIR spectrometer and the glass was then tempered or exposed to UV radiation for a prolonged period of time as this would affect the optical properties of the glass. The FeO content and redox ratio were determined using a glass color and optical performance computer model developed by PPG industries, Inc.

The following are the basic oxides of the experimental melts described in Table 1, calculated from the batch formulations, which fall within the basic glass compositions of the invention described above.

SiO₂71.9% by weight

Na₂O13.8% by weight

CaO 8.7% by weight

MgO 3.8 wt%

Al₂O₃0.12% by weight

K₂O 0.037The% by weight of the base oxide constituents of the technical soda-lime-silica glass composition based on the experimental melt described in Table 1 and the model composition described in Table 2 are considered to be similar to those previously described.

TABLE 1

	Example 1	Example 2	Example 3	Example 4	Example 5	Example 6	Example 7	Example 8	Example 9	Example 10	Example 11	Example 12
													Total iron (wt.%)	1.031	1.031	1.036	1.039	1.046	1.053	1.061	1.072	1.132	1.142	1.153	1.222
FeO(wt.％)	0.301	0.301	0.278	0.300	0.176	0.242	0.188	0.238	0.374	0.295	0.234	0.240
													Model redox ratio	0.292	0.292	0.268	0.289	0.166	0.230	0.177	0.222	0.331	0.259	0.203	0.196
Cr2O3(PPM)	525	527	528	528	489	471	516	476	525	517	568	493
													CoO(PPM)	111	112	114	111	96	96	103	95	111	108	116	134
TiO2(wt.％)	0.182	0.181	0.183	0.183	0.290	0.237	0.302	0.236	0.249	0.247	0.247	0.339
													LTA(％)	39.31	39.54	39.85	38.96	45.87	44.01	44.17	43.25	36.72	38.78	40.00	38.58
TSUV(％)	29.44	29.76	29.45	29.51	26.33	27.44	25.76	26.20	25.03	24.02	24.40	20.36
													TSIR(％)	12.44	12.44	13.79	11.84	26.96	18.60	26.02	18.47	8.19	12.94	19.24	18.94
TSET(％)	25.54	25.66	26.53	25.07	35.53	30.48	34.29	30.00	21.74	25.16	28.97	27.43
													DW(nm)	490.91	490.83	491.02	490.8	496.1	493.5	495.6	494.2	491.8	493.0	493.8	494.5
Pe(％)	15.26	15.27	14.81	15.47	8.85	11.11	9.52	10.87	15.32	13.22	11.88	9.92

	Example 13	Example 14	Example 15	Example 16	Example 17	Example 18	Example 19	Example 20	Example 21	Example 22	Example 23	Example 24
													Total iron (wt.%)	1.227	1.242	1.256	1.261	1.299	1.300	1.304	1.304	1.305	1.305	1.306	1.309
FeO(wt.％)	0.314	0.303	0.291	0.295	0.213	0.255	0.237	0.317	0.197	0.321	0.327	0.335
													Model redox ratio	0.256	0.244	0.232	0.234	0.164	0.196	0.182	0.243	0.151	0.246	0.250	0.256
Cr2O3(PPM)	510	512	511	514	481	483	484	332	483	333	332	330
													CoO(PPM)	139	137	139	140	127	129	122	105	131	104	104	105
TiO2(wt.％)	0.344	0.345	0.345	0.345	0.314	0.314	0.316	0.314	0.318	0.314	0.314	0.3150
													LTA(％)	33.67	34.06	34.24	34.05	38.27	36.36	38.02	38.87	38.34	38.98	38.90	38.14
TSUV(％)	20.02	19.64	19.49	19.40	18.32	18.29	18.12	18.80	18.11	18.90	18.98	18.78
													TSTR(％)	11.55	12.37	13.31	12.99	21.36	16.60	18.44	11.92	23.46	11.58	11.29	10.66
TSET(％)	22.41	22.93	23.56	23.27	29.47	26.10	27.68	24.59	30.66	24.41	24.29	23.58
													DW(nm)	491.2	491.5	491.6	491.6	494.2	493.1	494.6	492.5	494.1	492.6	492.4	492.1
Pe(％)	15.79	15.21	14.93	15.04	11.13	12.70	11.17	15.51	11.08	12.42	12.53	13.16

TABLE 2

	Example 25	Example 26	Example 27	Example 28	Example 29	Example 30	Example 31	Example 32	Example 33	Example 34	Example 35	Example 36
													Total iron (wt.%)	1.450	1.500	1.540	1.540	1.650	1.650	1.700	1.850	1.850	1.900	1.900	2.000
FeO(wt.％)	0.371	0.384	0.396	0.394	0.422	0.422	0.435	0.473	0.473	0.486	0.486	0.512
													Model redox ratio	0.256	0.256	0.256	0.256	0.256	0.256	0.256	0.256	0.256	0.256	0.256	0.256
Cr2O3(PPM)	750	500	650	725	650	700	685	7000	7000	510	510	510
													CoO(PPM)	70	65	70	80	65	65	66	57	65	55	65	45
TiO2(wt.％)	0.825	0.500	0.715	0.705	0.750	1.0	0.585	0.800	0.800	1.0	0.500	1.0
													LTA(％)	38.22	41.07	38.31	36.267	37.87	37.26	37.03	36.52	35.46	37.89	36.83	38.29
TSUV(％)	15.13	16.12	14.60	14.54	13.28	12.42	13.29	11.21	11.20	10.44	11.81	9.70
													TSIR(％)	7.99	7.77	7.12	7.02	6.07	6.01	5.61	4.51	4.51	4.37	4.36	3.80
TSET(％)	20.36	21.87	20.02	19.17	19.03	18.56	18.41	17.18	16.87	17.77	17.71	17.34
													DW(nm)	522.0	509.6	516.15	513.8	519.9	525.3	518.2	527.6	523.2	525.1	511.7	530.7
Pe(％)	8.90	7.63	8.21	8.60	8.75	9.99	8.9	10.83	10.03	9.51	11.81	10.96

Referring to tables 1 and 2, the present invention provides a green colored glass having a standard soda-lime-silica glass base composition and added iron, cobalt, chromium and titanium as infrared and ultraviolet radiation absorbing materials and colorants and having a Luminous Transmittance (LTA) of no more than 60%, preferably 25 to 55%, and more preferably 30 to 50%. In the present invention, the color of the glass is preferably characterized by a Dominant Wavelength (DW) of about 480-510nm, preferably about 490-525nm, and an excitation purity (Pe) of no more than about 20%, preferably about 5-15%. The dominant wavelength of the glass is preferably in a narrower wavelength range depending on the desired color of the glass. For example, it is contemplated that various embodiments of the glass composition may have a dominant wavelength in the range of 490-505nm, 505-515nm, or 515-525nm when the desired color of the glass changes from a blue-green color to a yellow-green color, and in one particular embodiment the glass comprises about 0.9 to 2.0 wt.% total iron, preferably 0.9 to 1.5 wt.% total iron, more preferably 1 to 1.4 wt.% total iron, about 0.17 to 0.52 wt.% FeO, preferably about 0.20 to 0.40 wt.% FeO, more preferably about 0.24 to 0.35 wt.% FeO, about 40 to 150PPM CoO, preferably about 50 to 140PPM CoO, more preferably about 70 to 130PPM CoO, about 250-800 Cr₂O₃Preferably about 250-600PPM Cr₂O₃More preferably about 275-₂O₃And about 0.1 to 1 wt% TiO₂Preferably about 0.2 to 0.5% by weight TiO₂. The redox ratio of these glasses is maintained at about 0.15-0.35, preferably about 0.22-0.30, more preferably about 0.24-0.28. These glass compositions also have a TSUV of no more than about 35%, preferably no more than about 30%; no more than about 30%, preferably no more than about 20% TSIR; and no more than about 40%, preferably no more than about 35%, of TSET.

It is believed that the optical properties of the glass undergo some change after tempering of the glass and further prolonged exposure to uv radiation, known as solarization. In particular, it is believed that the tempering and solarization of the glass compositions described in the present invention will reduce LTA and TSIR by about 0.5-1%, TSUV by about 1-2%, and TSIR by about 0.5-1.5%. As a result, in one embodiment of the invention, the selected optical properties of the glass will initially fall outside the aforementioned ranges, but will fall within suitable ranges after tempering and/or solarization.

The glass described in the present invention and made by the float process is typically in the range of about 1mm to 10mm in sheet thickness.

For automotive glazing applications, it is preferred that the glass sheet having the composition and optical properties described have a thickness of 0.154 to 0.197 inches (3.9 to 5 mm). It is believed that when a single piece of glass is used, the glass should be tempered, for example for use in automotive side and rear glazings.

The glass is believed to be useful in construction and has a thickness of about 0.14 to 0.24 inches (3.6 to 6 mm).

Vanadium may be used to partially or fully replace chromium in the glass compositions of the present invention. More particularly, with V₂O₅The vanadium is shown to impart a yellow-green color to the glass and to absorb ultraviolet and infrared radiation at different valence states. It is believed that Cr in the range of about 250-600PPM as described above₂O₃Can be completely composed of about 0.1-0.32% by weight V₂O₅And (4) replacing.

As previously mentioned, other materials may also be added to the glass composition to further reduce infrared and ultraviolet radiation transmission and/or control glass color. Further, it is believed that the following materials may be added to the soda-lime-silica glass containing iron, cobalt, chromium and titanium:

MnO₂0 to 0.5% by weight

Nd₂O₃0 to 0.5% by weight

SnO₂0 to 2% by weight

0 to 0.5% by weight of ZnO

MoO₃0 to 0.015% by weight

CeO₂0 to 2% by weight

NiO 0-0.1 wt.% it should be understood that the base iron, cobalt, chromium and/or titanium composition may be adjusted for any coloring and/or reducing effect of these additional materials.

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

Claims (21)

1. A green colored, infrared and ultraviolet absorbing glass composition having a composition comprising the following base glass portions:

SiO₂66-75% by weight

Na₂O10-20% by weight

CaO 5-15% by weight

MgO 0-5 wt%

Al₂O₃0 to 5% by weight

K₂O0-5% by weight and a solar radiation absorbing and coloring part consisting of:

0.90-2.0% by weight of total iron

FeO 0.17-0.52 wt%

CoO 40-150PPM

Cr₂O₃ 250-800PPM

TiO₂0.1 to 1 weight percent of the glass has a Luminous Transmittance (LTA) of up to 60 percent at a thickness of 0.160 inches, wherein the weight percents are based on the total weight of the final glass composition.

2. The composition as in claim 1 wherein the total iron concentration is 0.9-1.5% by weight, the FeO concentration is 0.20-0.40% by weight, the CoO concentration is 50-140PPM, Cr₂O₃The concentration is 250-600 PPM.

3. The composition as in claim 2 wherein the total iron concentration is 1.0-1.4% by weight, the FeO concentration is 0.24-0.35% by weight, the CoO concentration is 70-130PPM, Cr₂O₃The concentration is 275-500PPM and TiO₂The concentration is 0.2-0.5% by weight.

4. The composition as in claim 3 wherein the glass has a Luminous Transmittance (LTA) of 25-55%, a total solar ultraviolet Transmittance (TSUV) of 35% or less, a total solar infrared Transmittance (TSIR) of 30% or less, a Total Solar Energy Transmittance (TSET) of 40% or less, and a color characterized by a dominant wavelength of 480-.

5. The composition as in claim 4 wherein the glass has a Luminous Transmittance (LTA) of 30 to 50 percent, a total solar ultraviolet Transmittance (TSUV) of 30 percent or less, a total solar infrared Transmittance (TSIR) of 20 percent or less, a Total Solar Energy Transmittance (TSET) of 35 percent or less and a color characterized by a dominant wavelength of 490-525nm and an excitation purity of 5 to 15 percent.

6. The composition of claim 1 wherein the glass has a redox of 0.15 to 0.35.

7. The composition of claim 6 wherein the glass has a redox of 0.22 to 0.30.

8. The composition as in claim 1 wherein the glass has a total solar ultraviolet Transmittance (TSUV) of 35 percent or less, a total solar infrared Transmittance (TSIR) of 30 percent or less and a Total Solar Energy Transmittance (TSET) of 40 percent or less.

9. The composition as in claim 8 wherein the glass has a total solar ultraviolet Transmittance (TSUV) of 30 percent or less, a total solar infrared Transmittance (TSIR) of 20 percent or less and a Total Solar Energy Transmittance (TSET) of 35 percent or less.

10. The composition as in claim 1 wherein the color of the glass is characterized by a dominant wavelength of 480-510nm and an excitation purity of no more than about 20 percent

11. The composition as in claim 7 wherein the color of the glass is characterized by a dominant wavelength of 490-525nm and an excitation purity of 5-15%.

12. The composition of claim 1 wherein the glass has a Luminous Transmittance (LTA) of 25 to 55 percent.

13. The composition of claim 12 wherein the glass has a Luminous Transmittance (LTA) of 30 to 50 percent.

14. A flat glass sheet formed by the float process from the glass composition recited in claim 1.

15. An automotive window formed from the flat glass sheet of claim 14.

16. A green colored, infrared and ultraviolet absorbing glass composition having a composition comprising the following base glass portions:

SiO₂66-75% by weight

Na₂O10-20% by weight

CaO 5-15% by weight

MgO 0-5 wt%

Al₂O₃0 to 5% by weight

K₂O0-5% by weight and a solar radiation absorbing and coloring part consisting of:

0.90-2.0% by weight of total iron

FeO 0.17-0.52 wt%

CoO 40-150PPM

Cr₂O₃ 250-800PPM

TiO₂0.1 to 1% by weight

V₂O₅0.1 to 0.32% by weight

MnO₂0 to 0.5% by weight

Nd₂O₃0 to 0.5% by weight

SnO₂0 to 2% by weight

0 to 0.5% by weight of ZnO

MoO₃0 to 0.015% by weight

CeO₂0 to 2% by weight

NiO 0-0.1 wt.% of the glass has a Luminous Transmittance (LTA) of up to 60%, wherein the weight percentages are based on the total weight of the final glass composition.

17. The composition as in claim 16 wherein the glass has a total solar ultraviolet Transmittance (TSUV) of 35 percent or less, a total solar infrared Transmittance (TSIR) of 30 percent or less and a Total Solar Energy Transmittance (TSET) of 40 percent or less.

18. The composition as in claim 16 wherein the color of the glass is characterized by a dominant wavelength of 480-510nm and an excitation purity of no more than 20 percent

19. The composition as in claim 16 wherein the glass has a total solar ultraviolet Transmittance (TSUV) of 30 percent or less, a total solar infrared Transmittance (TSIR) of 20 percent or less, a Total Solar Energy Transmittance (TSET) of 35 percent or less and the color of the glass is characterized by a dominant wavelength of 490-525nm and an excitation purity of 5-15 percent.

20. The composition as in claim 19 wherein the total iron concentration is 1.0-1.4% by weight, the FeO concentration is 0.24-0.35% by weight, the CoO concentration is 70-130PPM, Cr₂O₃The concentration is 275-500PPM and TiO₂The concentration is 0.2-0.5% by weight.

21. A flat glass sheet formed by the float process from the glass composition recited in claim 15.