Ultraviolet absorbing photochromic glass of low silver content

• US 4,549,894 A
• Filed: 06/06/1984
• Issued: 10/29/1985
• Est. Priority Date: 06/06/1984
• Status: Expired due to Fees

• Current Assignee: Corning Glass Works Inc. (Corning Incorporated)
• Original Assignee: Corning Glass Works Inc. (Corning Incorporated)
• Inventors: Morgan, David W., Hares, George B., Morse, David L., Araujo, Roger J., Kerko, David J.
• Primary Examiner(s): Schor, Kenneth M.
• Application Number:
  US06/617,908
• Time in Patent Office: 510 Days
• Field of Search: 65/30.11, 501/13, 350/354, 351/162
• US Class Current: 65/30.11
• CPC Class Codes: C03C 3/091 containing aluminium
• CPC Class Codes: C03C 4/06 for phototropic or photochromic glass

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 ______________________________________

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.

2. A method according to claim 1 wherein said CeO₂ ranges about 0.1-0.4% and said Sb₂ O₃ and/or As₂ O₃ ranges about 0.15-0.5%.

3. A method according to claim 1 wherein said glass also contains up to 0.25% PbO.

4. A method according to claim 1 wherein said glass also contains up to 10% total of at least one of the following oxides in the indicated proportions of up to 5% La₂ O₃, up to 5% ZrO₂, and up to 3% TiO₂.