Compositions: ceramic – Ceramic compositions – Glass compositions – compositions containing glass other than...
Reexamination Certificate
1996-10-30
2003-04-22
Group, Karl (Department: 1755)
Compositions: ceramic
Ceramic compositions
Glass compositions, compositions containing glass other than...
Reexamination Certificate
active
06551953
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to soda-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 ultraviolet wavelength range. This is desirable for the sake of reducing the rate at which the sun's rays deteriorate plastics and fabrics in applications such as automobiles. A particular objective of the invention is to permit glass of this 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:
SiO
2
66-75%
Na
2
O
10-20
CaO
5-15
MgO
0-5
Al
2
O
3
0-5
K
2
O
0-5
Other minor ingredients, including melting and refining aids such as SO
3
, may also appear in the glass composition. Small amounts of K
2
O, BaO or B
2
O
3
and other minor constituents 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 colorant in the category of glasses relevant to the present invention is iron, which is usually present in both the Fe
2
O
3
and FeO forms. As is conventional, the total amount of iron present in a glass is expressed herein as Fe
2
O
3
, 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 iron being about 0.25.
Recently, it has become important to maximize 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 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 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 glass described above are set forth below:
Light Green
Dark Green
Dark Green
Example A
Example B
Example C
Total Iron (wt. %)
0.521
0.803
0.728
FeO/Tot. Iron
0.268
0.284
0.291
LT
A
(%)
80.45
71.1
72.44
TSUV (%)
54.82
38.8
42.28
TSIR (%)
37.38
22.4
24.62
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 transmittance is not desirable because it would impermissibly lower the luminous (visible light) transmittance. Furthermore, the use of 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 titanium oxide in glass to reduce ultraviolet transmittance as disclosed in U.S. Pat. Nos. 2,860,059 and 5,077,133, and the following example is of a commercial product that takes this latter approach:
Example D
CeO
2
(wt. %)
0.60
TiO
2
(wt. %)
0.22
Total Iron (wt. %)
0.783
FeO/Tot. Iron
0.266
LT
A
(%)
72.5
TSUV (%)
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 objectives 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 (Fe
2
O
3
) to ensure the glass has at least a 70% 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 disclosure, except where noted, is based on a glass thickness of 3.9 millimeters (0.154 inch). Luminous transmittance (LT
A
) is measured using C.I.E. standard illuminant “A” over the wavelength range 380 to 770 nanometers at 10 nanometer intervals. Total solar ultraviolet transmittance (TSUV) is measured over the wavelength range 300 to 400 nanometers at 10 nanometer intervals. Total solar infrared transmittance (TSIR) is 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 {X
0
, X
1
, . . . , X
n
} where X
i
=a+(i×h). Generally, either the Rectangular Rule or the 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:
I=∫
a
b
f
(
X
)
dX
In the case of the Rectangular Rule, the constant value f(X
i
) is used as an approximation of f(X) on [X
i−1
,X
i
]. This yields a step-function approximation of f(x) on [a,b], and the numerical integration formula:
I
=
∑
i
=
1
n
f
(
X
i
)
×
h
For the Trapezoidal Rule, f(X) is approximated on [X
i−1
,X
i
] by a straight line passing through the graph of f at the end points. Thus, the interpolating function for f(X) is piecewise linear on [a,b] and the integration formula becomes:
I
=
[
f
(
X
o
)
+
2
∑
i
=
1
n
-
1
f
(
X
i
)
+
f
(
X
n
)
]
×
(
h
/
2
)
The transmittance data presented throughout this disclosure is based on the Trapezodial Rule.
SUMMARY OF THE INVENTION
The present invention provides a green tinted, ultraviolet absorbing, soda lime silica glass having a luminous transmittance of at least 70 percent and ultraviolet transmittance of no more than 38 percent at thickness ranging from 0.154 to 0.189 inches (3.9 to 4.9 mm). These properties are achieved in the present invention by using a colorant portion that is either (a) greater than 0.6 percent by weight total iron (expressed as Fe
2
O
3
) with a redox (FeO/total iron) of from 0.275 to less than 0.35 or (b) from greater than 0.6 to 0.85 percent by weight total iron with a redox of less than 0.35. It is preferred that the glass have a dominant wavelength of 495 to 535 nanometers.
REFERENCES:
patent: 4859637 (1989-08-01), Roberts
patent: 5240886 (1993-08-01), Gulotta et al.
patent: 0 297 404 (1989-01-01), None
patent: 0 321 297 (1989-06-01), None
patent: 57-106537 (1982-07-01), None
patent: 59-50045 (1984-03-01), None
Coloured Glasses, “Chapter VII. The Colours Produced by Iron”, published by The Society of Glass Technology, 1951, pp. 89-120.
Gulotta Joseph A.
Shelestak Larry J.
Group Karl
PPG Industries Ohio Inc.
Siminerio Andrew C.
Stachel Kenneth J.
LandOfFree
Ultraviolet absorbing green tinted glass does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Ultraviolet absorbing green tinted glass, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ultraviolet absorbing green tinted glass will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3042566