Ultraviolet absorbing green tinted glass

;~ 2109059 ULTRAVIOLET ABSORBING GREEN TINTED GLASS BACKGROUND OF THE INVFNTION This invention relates to ~oda-lime-silica glass particularly suitable for controlling transmittance of solar radiation in window glazing applications.

The glass may be generally described as being green tinted, and is designed to have low heat transmittance and particularly enhanced absorption in the 10 ultraviolet wavelength range. This i8 desirable for the sake of reducing the rate at which the sun's rays deteriorate plasticR and fabrics in applications such as automobiles. A particular ob~ective of the invention is to permit glass of thi~ type to be made at a lower cost by reducing the amount of costly ingredients required.

Soda-lime-silica flat glass may be essentially characterized by the following composition on a weight percentage basis of the total glass:

SiO2 66 - 75% Na20 10 - 20 CaO 5 - 15 MgO O - 5 A1203 0 - 5 K20 0 - 5 Other minor ingredients, including melting and refining 25 aids such as S03, may also appear in the glass composition. Small amounts of K20, BaO or B203 and other minor constit~ents have also sometimes been included in flat glass and may be considered optional. To this base glass are added the coloring constituents that produce the transmittance properties of the glass. The primary 30 colorant in the category of glasses relevant to the present invention is iron, which is usually present in both the Fe203 and ~' - 2109~59 FeO forms. As is conventional, the total amount of iron present in a glass is expreæsed herein as Fe203, regardless of the form actually present. A typical green tinted automotive glass has about 0.5 percent by weight total iron, with the ratio of FeO to total 5 iron being about 0.25.

Recently, it has become important to ' i7.e the solar performance of automotive glazing. The use of larger glass areas and the elimination of CFC air conditioning coolants places a greater burden on the car interior and air conditioning systems. A 10 goal has been established to limit ultraviolet transmittance to no more than 38 percent in some automotive glass. At the same time, it is a requirement that glass in vision areas of automobiles have an luminious transmittance of at least 70 percent.

Two approaches have been followed to improve the solar 15 performance of the glass and meet these goals. In the first approach, high iron levels are used in the glass. The colorant composition and transmittance properties for examples of two commercial annealed products of this high iron, dark green tinted type along with an example of the conventional, light green tinted 20 glass described above are set forth below:

Light Green Dark Green Dark Green Example A Example B Example C 25 Total Iron (wt.%) 0.521 0.803 0.728 FeO/Tot.

Iron0.268 0.284 0.291 LTA (7) 80.45 71.1 72.44 TS W (%) 54.82 38.8 42.28 TSIR (70) 37.38 22.4 24.62 30 TSET (%) 57.85 44.5 46.92 Although Examples B and C show a reduction in ultraviolet transmittance, the percentage still exceeds the desired goal.

Merely increasing the amount of total iron to reduce the ultraviolet 35 transmittance is not desirable because it would impermissibly lower the luminous (visible light) transmittance. Furthermore, the use of - 21090~9 very high levels of iron can create problems in manufacturing the glass, such as shorter campaigns or the use of expensive electric boosting.

The second approach uses cerium oxide or cerium oxide plus 5 titanium oxide in glass to reduce ultraviolet transmittance as disclosed in U.S.

Patent Nos. 2,860,059 and 5,077,133, and the following example is of a commercial product that takes this latter approach:

Example D CeO2 (wt.%) 0.60 TiO2 (wt.%) 0.22 Total Iron (wt.%) 0.783 FeO/Tot.

Iron 0.266 15 LTA (%) 72.5 TS W (%) 31.8 TSIR (%) 23.7 TSET (%) 45.7 This glass exhibits the desired combination of low ultraviolet transmittance and high luminous transmittance, but the high cost of cerium sources substantially increases the cost of making this glass.

It would be desirable if these ob~ectives could be met without incurring such high raw material costs.

It has also been found that glasses made according to these two approaches darkens upon tempering and exposure to solar ultraviolet radiation.

This in turn lowers luminious transmittance.

It is therefore necessary to reduce the heat absorbing component (Fe203) to ensure the glass has at least a 70% 30 luminious transmittance after use.

For these reasons, it would be desirable to produce glasses with enhanced spectral properties but at lower cost and with reduced solarization.

The transmittance data provided above and throughout this 35 disclosure, except where noted, is based on a glass thickness of 3.9 millimeters (0.154 inch). Luminous transmittance (LTA) is measured - 2109059 using C.I.E. standard illuminant "A" over the wavelength range 380 to 770 nanometers at 10 nanometer intervals. Total solar ultraviolet transmittance (TS W ) is measured over the wavelength range 300 to 400 nanometers at 10 nanometer intervals. Total solsr 5 infrared transmittance (TSIR) i8 measured over the wavelength range 800 to 2100 nanometers at 50 nanometer intervals. Total solar energy transmittance (TSET) represents a computed value based on measured transmittances from 300 to 2100 nanometers at 50 nanometer intervals.

To determine this transmittance data, the transmittance values are integrated over the wavelength range [a,b]. This range is divided into n equal subintervals of length h by points {X0, Xl, . . ., Xn } where Xi = a + (i x h). Generally, either the Rectangular Rule or the 15 Trapezoidal Rule is used to compute the transmittance data. For each method, a different interpolating function is used to approximate the integrand f in each subinterval.

The sum of integrals of these interpolating functions provides an approximation of the integral:

b I = raf(X)dX In the case of the Rectangular Rule, the constant value f(Xi) is used as an approximation of f(X) on [Xi_l,Xi].

This yields 25 a step-function approximation of f(X) on [a,b], and the numerical integration formula:

~ f (Xi ) X h i=l For the Trapezoidal Rule, f(X) is approximated on [Xi_l,Xi] by a straight line passing through the graph of f at the end points. Thus, the interpolating function for f (X) is piecewise 35 linear on [a,b] and the integration formula becomes:

n-l I = [f(Xo)+2 ~ f(Xi) + f(Xn)] x (h/2) i=l - 2109059 -- 5 - The transmittance data presented throughout this disclosure is based on the Trapezodial Rule.

SUM~ARY OF THE INVENTION The present invention provides a green tinted, ultraviolet absorbing, soda lime silica glass that has luminous transmittance of at least 70 percent and ultraviolet transmittance of no more than 38 percent at thicknesses ranging from 0.154 to 0.189 inches (3.9 to 4.9 mm).

These properties are achieved in the present invention by 10 using a colorant that is less than 2.0 percent by weight TiO2 of the total glass composition, preferably 0.05 to 0.60 weight percent TiO2, greater than 0.60 percent by weight total iron (expressed as Fe203), preferably 0.6 to 0.95 weight percent total iron, ant a ratio of FeO/total iron (ferrous iron expressed as FeO divided by 15 the total iron expressed as Fe203) of less than 0.350, preferably 0.24 to 0.29.

The combination of iron and titanium oxide can actually increase the luminious transmittance, thereby allowing the maximum level of heat absorbing agent to be used and improve the overall solar performance of the glass.

The present invention also provides a method of producing green tinted, ultraviolet absorbing glass exhibiting ultraviolet transmittance no greater than 38 percent (300 to 400 nanometers) and luminous transmittance (illuminant A) of at least 70 percent at thicknesses ranging from 0.154 to 0.189.The method includes the 25 steps of melting and forming soda lime silica glass having a colorant portion consisting essentially of, on a weight percent basis, less than 2.0% TiO2, preferably 0.05 to 0.60 weight percent TiO2, and greater than 0.6% iron (expressed as Fe203), preferably 0.6 to 0.95 weight percent total iron, and a ratio of FeO/total iron 30 (ferrous iron expressed as FeO divided by the total iron expressed as Fe203) of less than 0.350, preferably 0.24 to 0.29, and tempering the glass to increase its luminous transmittance to a value greater than 70 percent.

DETAILED DESCRIPTION The base glass composition is not critical to the present - 2109059 -- 6 - invention and may consist of any conventional soda-lime-silica flat glass composition, which may be characterized by the ranges set forth above. Preferably, the base glass is one known by those of skill in the art to be producible in a continuous melting furnace 5 and formed into a flat sheet by the float proces6. A specific example of a base glass of the present invention can be seen in the following example which is Example A discussed earlier.

~ase Glass ~Ample A Composition Si02 72.67percent by weight Na20 13.76 CaO 8.71 MgO 3.84 A1203 0.14 K20 0.05 S03 0.214 Fe203 (total) 0.521 Additionally, traces of impurities may be present without significant effect on the glass. Melting and fining aids such as S03 are useful during production of the glass, but their residual 20 amounts in the glass can vary and have no significant effect on the properties of the glass product. K20 is present in this example as sn impurity, and its presence is not required, although it serves a function in the glass essentially equivalent to that of Na20. The batch mixture of raw materials from which the glass of Example 1 was 25 melted was as follows:

Sand 1000 parts by weight Soda ash 329 Limestone 71 Dolomite 242 Gypsum 19.65 Rouge 6.4 It is important to control the ratio of ferrous to total iron in order to get the required spectral properties. One of the ways to control this ratio of ferrous to total iron is by 35 selecting an amount of coal or other reducing agent to be included in the batch mixture. Instead of coal, various other sources of - 21090~9 carbon are known to serve as reducing agents during melting of glass.

Another means of control i8 by way of the rstio of air to fuel in the melting furnace. A higher air to fuel ratio produces conditions in the melting furnace that are more oxidizing, which, in 5 turn, leads to a lower ferrous to total iron ratio.

Specifying the oxidizing control measures depends upon the particular operating characteristics of a particular melting furnace.

In some cases, as with the base glass in Example A, it may be desirable to include no coal or other reducing agent in order to attain the proper glass 10 redox conditions required for the present invention.

It has been found that the spectral characteristics of soda lime silica glass change as a result of its subsequent use and processing.

More specifically, the glass tends to darken upon exposure to ultraviolet radiation, which in turn lowers LTA, TSW 15 and TSET.

This effect, referred to as solarization, is particularly significant in high iron (Fe203 > 0.6 wt.%) and cerium cont~n~ng glass.

In addition, it has been found that tempering also changes the glass's spectral characteristics.

As used herein, tempering mean6 heating the glass to above its annealing point temperature, 20 typically about 1000 to 1040F. (530 to 560C.) for soda lime silica glass, and quickly cooling it to rapidly drop the glass temperature through the annealing range to the glass annealing point temperature, which is typically about 925 to 970F. (496 to 521C.).

This operation induces compressive stresses in the outer 25 layers of the glass and tensile stresses in the center.

Referring to Table 1, Examples 1 through 3 are modifications of the base gla~s described in Example A which illustrates the benefits of using titanium oxide in the glass batch to lower ultraviolet transmittance as well as improve luminous 30 transmittance.

Table 1 illustrates the base glass modifications and the average spectral properties of the annealed glass based on six samples for each composition.

Table 2 shows the change in the percentages of the spectral properties of Examples 1, 2 and 3 due to solarization and tempering.

The results for Examples 1 and 2 are 35 based on actual production glass while ~xample 3 results are based on laboratory melts.

- 21090~9 -- 8 - Table 1 (0.154 inch reference thichness) Example 1 F~mple 2 F~ple 3 Fe2O3 (wt. %) 0.917 0.523 0.824 5 Redox 0.262 0.268 0.267 TiOz 0.017 0.325 0.40 LTA (%) 70.3 79.6 71.3 TS W (%) 37.0 48.3 36.6 TSIR (7O) 19.8 37.9 21.7 10 TSET (7O) 42.7 57.2 43.7 Table 2 (change in spectral property percentage) Example 1 LTA TS W TSIR TSET Tempering -0.4 -2.2 0 -0.3 Solarization -0.7 -0.80.4 -0.2 Total -1.1% -3.0% 0.4% -0.5% 20 Example 2 LT~ TSIR TSET Tempering -0.2 -1.50.2 0 Solarization -0.4 -0.80.5 0.1 Total -0.6% -2.3% 0.7% 0.1% Example 3 LTA TS W TSIR TSET Tempering 0.6 -3.40.4 0.6 Solarization =Q~_ -0,50.5 0 30 Total 0.2% -3.9% 0.9% 0.6% Referring to Table 1, although all three examples include TiO2, the 0.017 wt. % amount in Example 1 i8 merely a trace amount of titanium oxide resulting from impurities in the glass batch 35 materials. With respect to Examples 2 and 3, it can be seen that the addition of titanium oxide to both a typical soda lime silica 2109059 glass (Example 2) and a high iron glass (Example 3) reduces the ultraviolet transmittance by 12% and 33%, respectively when compared to the base gla6s composition (Example A). From this it is clear that titanium oxide or titanium oxide with additional iron (Fe203) 5 at levels disclosed herein may be used as an ultraviolet radiation absorber to reduce ultraviolet transmittance without the need of other additives.

Referring to Table 2, of particular significance is the effect the titanium oxide has on LTA after solarization and 10 tempering. In Example 1, the LTA dropped a total amount of 1.1%.

This means it would be expected that the LTA of 70.3% for the annealed glass would eventually drop to about 69.2% after tempering and exposure to ultraviolet radiation. It i8 noted that this LTA value is below the 70% level required under federal law. In Example 15 2, the LTA dropped 0.6% which i6 about half of the drop found in Example 1. In Example 3, the LTA actually increased 0.2%.

In comparing the individual effects of solarization and tempering on LTA, solarization reduced the LTA in Example 1 by 0.7% while the reduction in Examples 2 and 3 was only 0.4%. Tempering 20 reduced the LTA in Example 1 by 0.4% while the reduction in Example 2 was only 0.2%. In Example 3, tempering actually increased the LTA by 0.670 rather than decrease it as shown in Example 1. This reduced effect of solarization and tempering on LTA in Example 3 and the unexpected increase in luminous transmittance is particularly 25 significant when compared to Example 1 because, since both compositions have nearly the same high amount of total iron and comparable redox, this effect may be attributed mainly to the presence of titanium oxide. As a result, it is clear that the combination of iron and titanium oxide can actually increase the 30 LTA, thereby allowing the maximum amount of iron to be used and improve the overall solar performance of the glass.

Table 2 also indicates that the drop in TS W for Example 3 is greater than Example 1, with a 50% increase in the contribution due to tempering while the drop due to solarization is reduced.

35 This reduction in TS W is favorable since TS W is a spectral property that the glass compositions are attempting to reduce.

- 2109059 -- 10 - Again, since the iron content and redox for Examples 1 and 3 are comparable, the advantageous reduction in TS W is principally attributable to the pre6ence of titanium oxide in the glas6.

In the present invention, titanium oxide is used to enhance 5 the spectral properties of glass. More particularly, not only is it added to reduce TS W in annealed glass but also to further reduce the TS W as a result of tempering and solarization and improve the ultraviolet transmittance performance. In addition, the titanium oxide reduces the drop in LTA by inhibiting solarization and 10 tempering and in some instances, actually improves the LTA. As a result, glass compositions may be formulated with titanium oxide to provide spectral properties, and in particular LTA and TS W , that are borderline with respect to or do not meet desired specifications, with the expectation that solarization and tempering 15 of the glass will increase LTA and reduce TS W so that the glass meets the specifications.

Tables 3, 4, 5 and 6 illustrate examples of other gla6s compositions which include high iron along with titanium oxide and their spectral properties prior to solarization and tempering. The 20 spectral data for Tables 3 and 4 are based on laboratory melts at reference thicknesses of 0.154 inch (3.9 mm) and 0.189 inch (4.9 mm), respectively. The spectral data in Tables 5 and 6 was generated using a computer model which predicts the spectral properties of the glass based on the glass composition and redox.

Table 3 (at 0.154 inch thickness) Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 30 Fe203 (wt.%) 0.807 0.833 0.830 0.837 0.808 Redox 0.260 0.283 0.270 0.28 0.285 TiO2 (wt.%) 0.42 0.42 0.42 0.42 0.41 LTA (%) 72.3 72.6 71.1 70.9 71.2 TS W (%) 37.1 36.2 36.6 35.9 36.8 35 TSIR (%) 24.0 25.2 21.2 21.6 21.6 TSET (%) 45.4 46.1 43.3 43.4 43.6 21090~9 11 Table 4 (at 0.189 inch thickne6s) Ex. 9 Ex. 10Ex. 11Ex. 12 Ex. 13 5 Fe203 (wt.%) 0.729 0.7380.764 0.749 0.718 Redox 0.255 0.2740.251 0.254 0.265 TiO2 (wt.%) 0.41 0.42 0.47 0.52 0.42 LTA (%) 70.5 70.7 69.9 70.3 70.9 TS W (%) 34.3 35.4 33.1 32.2 35.7 10 TSIR (%) 21.0 20.6 20.0 21.3 20.3 TSET (%) 42.8 42.7 41.9 42.7 42.7 T~hle 5 (at 0.154 inch thickness) Ex. 14 Ex. 15Ex. 16 Ex. 17 Ex. 18 Fe203 (wt.%) 0.910 0.9300.845 0.925 0.807 Redox 0.268 0.2520.265 0.255 O.Z62 20 TiO2 (wt.%) 0.05 0.15 0.30 0.30 0.35 LTA (%) 70.5 70.7 71.7 70.6 72.6 TSW (%) 36.6 34.7 36.4 34.0 37.0 TSIR (%) 20.9 22.0 23.4 21.8 25.2 TSET (%) 43.1 43.7 45.0 43.4 46.3 T~hle 6 (at 0.189 inch thickness) Ex. 19 Ex. 20Ex. 21 Ex. 22 Ex. 23 Fe203 (wt.%) 0.700 0.7000.690 0.700 0.650 Redox 0.268 0.2720.265 0.265 0.280 TiO2 (wt.%) 0.05 0.15 0.30 0.35 0.40 LTA (%) 71.5 71.2 71.6 71.3 71.8 35 TS W (%) 37.g 37.1 35.9 37.1 36.7 TSIR (%) 22.6 22.1 23.3 22.9 23.4 TSET (~) 44.6 44.1 44.8 44.4 45.0 - 12 - 2109059 It is expected solarization and tempering will effect the glass compositions in Examples 4 through 23 in a manner similar to that shown for Example 3.

Based on the test results, it is believed that titanium 5 oxide, in an amount up to 2.0 weight percent of the glass batch may be used to reduce ultraviolet transmittance to a desired level, and in particular to a level not to exceed 38%.

The ultraviolet transmittance herein has been reported with reference to the wavelength range 300 to 400 nanometers.

Others 10 may use the range 300 to 390 nanometers for measuring ultraviolet.

The goal of a ; , ultraviolet transmittance of 38 percent for the present invention would be approximately equivalent to 31 percent if the range 300 to 390 nanometers is used. In addition, if the Rectangular Rule is used over the 300 to 390 nanometer range, 15 the goal of the ultraviolet transmittance would be approximately 34 percent.

The glass of the present invention has a distinctly green color. The color may be a matter of taste, and the specific color characteristics need not be considered critical to the present 20 invention, but the glasses that have been made in accordance with the invention have been characterized by excitation purity greater than 1 percent, usually from 2 to 4 percent, and d~ ;nflnt wavelength from 495 to 535 nanometers.

In the present invention, titanium was included in the 25 glass composition in the form of titanium oxide. It should be appreciated by those skilled in the art that titanium in forms other than TiO2, e.g. an elemental form, may be used in the batch composition but it will be converted to this oxide form within the ranges disclosed herein during the batch melting and refining 30 process.

The total solar energy transmittance (TSET) of the glass of the present invention is relatively low, thereby significantly reducing the amount of thermal energy that passes through a window glazed with the glass. Although not critical to the invention, the 35 TSET of the glasses of the present invention are generally lower than 45 percent.

2 LO90a9 - 13 The invention has been described with reference to specific embodiments, but it should be understood that variations and modifications that are known to those of skill in the art may be resorted to within the scope of the invention as defined by the 5 claims that follow.