Ultraviolet absorbing photochromic glass of low silver content
First Claim
1. A method for producing a photochromic glass article that, in cross section of <
- 2 mm but >
1.3 mm, will transmit less than 0.2% of radiations having wavelengths between 290-315 nm, can be chemically strengthened to pass the strength standards mandated by the FDA, and at 20°
-25°
C. will exhibit a darkened luminous transmittance below 35% and a fading rate such that after five minutes the luminous transmittance will be at least 1.75 times that of the darkened transmittance, which method comprises the steps of;
(a) melting a batch for a glass consisting essentially, expressed in terms of weight percent on the oxide basis, of
space="preserve" listing-type="tabular">______________________________________ SiO.sub.2 55-61 CeO.sub.2 0.1-1 B.sub.2 O.sub.3 18-21 Ag >
0.1-<
0.2 Al.sub.2 O.sub.3 5-11 CuO 0.003-0.015 Li.sub.2 O 1.5-3 Cl 0.2-0.6 Na.sub.2 O 2-5 Br 0.05-0.2 K.sub.2 O 4.5-8 Sb.sub.2 O.sub.3 and/or As.sub.2 O.sub.3 0.1-1.5 ______________________________________ wherein the amount of Sb2 O3 and/or As2 O3 is at least 75% of the amount of CeO2 present;
(b) cooling said melt and simultaneously forming a glass article of a desired geometry therefrom; and
thereafter(c) heating said glass article to a temperature between about 650°
-675°
C. for a sufficient period of time to cause the growth of silver halide crystallites therein whereby said photochromic glass article is provided which, at 20°
-25°
C., will exhibit a darkened luminous transmittance below 35% and a fading rate such that after five minutes the luminous transmittance will be at least 1.75 times that of the darkened transmittance.
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Accused Products
Abstract
There is disclosed a method of producing a photochromic glass having a reduced transmittance for ultraviolet radiation while having substantially unimpaired photochromic properties. The method comprises providing a combination of 0.1-1.0% CeO2 and 0.1-1.5% Sb2 O3 and/or As2 O3 as part of the glass composition. In an embodiment utilizing minimal silver content, the glass article in thicknesses of 1.3 to 2.0 mm. can be chemically strengthened to surpass the impact specification imposed by the Federal Food and Drug Administration for eyewear, will transmit less than 0.2% of radiation having wavelengths between 290-315 nm, and will demonstrate a darkened luminous transmittance at 20°-25° C. below 35% and a fading rate such that after five minutes the luminous transmittance will be at least 1.75 times that of the darkened transmittance. These glasses consist essentially of:
______________________________________
SiO2 55-61 Ag >0.1-<0.2 B2 O3 18-21 Cl 0.2-0.6 Al2 O3 5-11 Br 0.05-0.2 Li2 O 1.5-3 CuO 0.003-0.015 Na2 O 2-5 CeO2 0.1-1.0 K2 O 4.5-8 Sb2 O3 0.1-1.5 ______________________________________
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Citations
4 Claims
-
1. A method for producing a photochromic glass article that, in cross section of <
- 2 mm but >
1.3 mm, will transmit less than 0.2% of radiations having wavelengths between 290-315 nm, can be chemically strengthened to pass the strength standards mandated by the FDA, and at 20°
-25°
C. will exhibit a darkened luminous transmittance below 35% and a fading rate such that after five minutes the luminous transmittance will be at least 1.75 times that of the darkened transmittance, which method comprises the steps of;(a) melting a batch for a glass consisting essentially, expressed in terms of weight percent on the oxide basis, of
space="preserve" listing-type="tabular">______________________________________ SiO.sub.2 55-61 CeO.sub.2 0.1-1 B.sub.2 O.sub.3 18-21 Ag >
0.1-<
0.2 Al.sub.2 O.sub.3 5-11 CuO 0.003-0.015 Li.sub.2 O 1.5-3 Cl 0.2-0.6 Na.sub.2 O 2-5 Br 0.05-0.2 K.sub.2 O 4.5-8 Sb.sub.2 O.sub.3 and/or As.sub.2 O.sub.3 0.1-1.5 ______________________________________wherein the amount of Sb2 O3 and/or As2 O3 is at least 75% of the amount of CeO2 present; (b) cooling said melt and simultaneously forming a glass article of a desired geometry therefrom; and
thereafter(c) heating said glass article to a temperature between about 650°
-675°
C. for a sufficient period of time to cause the growth of silver halide crystallites therein whereby said photochromic glass article is provided which, at 20°
-25°
C., will exhibit a darkened luminous transmittance below 35% and a fading rate such that after five minutes the luminous transmittance will be at least 1.75 times that of the darkened transmittance. - View Dependent Claims (2, 3, 4)
- 2 mm but >
Specification