Refractive index-corrected copper-cadmium halide photochromic glasses
AssigneeCorning Glass Works
InventorsRoger J. Araujo, Paul A. Tick
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Abstract
Alkali boroaluminosilicate glass compositions providing refractive index-corrected copper-cadmium halide photochromic glasses of optical quality, particularly useful for making ophthalmic lenses, are described. Ion-exchange-strengthenable glasses exhibiting good chemical durability and a satisfactory liquidus-viscosity relationship in combination with good photochromic properties and the required refractive index are also provided.
Claims4
A refractive index-corrected copper-cadmium halide photochromic glass having a composition, in weight percent, of about 45-56% SiO.sub.2, 14.5-21% B.sub.2 O.sub.3, 9.0-15% Al.sub.2 O.sub.3, 1.4-2.4% Li.sub.2 O, 2-12% Na.sub.2 O, 0-6.0% MgO, 0-3.5% BaO, 0-2.5% TiO.sub.2, 0-1.4% ZrO.sub.2, 0-1.5% La.sub.2 O.sub.3, at least 8% total of refractive index-correcting oxides MgO+BaO+TiO.sub.2 +ZrO.sub.2 +La.sub.2 O.sub.3, 0.1-0.5% Cuo, 0.3-1.5% CdO, 0.3-0.9% Cl, 0-0.6% SnO, and 0-2% F, said glass having:
- (a) a refractive index (n.sub.D) in the range of about 1.52-1.54;
- (b) chemical durability characterized by freedom from visible surface attack following a 10-minute exposure to 10% (wt.) HCl at 25.degree. C.;
- (c) a viscosity of at least 3000 poises at the liquidus temperature thereof;
- (d) photochromic properties which provide, in 2 mm. thickness, a transmittance not exceeding about 55% in the fully darkened state and fading of at least 12 percentage points of transmittance in a 5-minute fading interval from the fully darkened state;
- said glass being chemically strengthenable by sodium-for-lithium ion-exchange to provide a modulus of rupture strength of at least about 35,000 psi with an ion-exchange layer depth of at least about 3 mils, and (l) being essentially free of Ag, PbO and ZnO.
Dependencies are inferred from the claim text.