Method of making photochromic glasses suitable for simultaneous heat treatment and shaping

Claim 1

A method for forming glass sheet from potentially photochromic glass and thereafter simultaneously shaping articles from said glass sheet and developing photochromic properties therein which comprises the steps of: (a) melting a batch for a glass consisting essentially, in weight percent on the oxide basis, of about 57.1-65.3% SiO 2 , 9.6-13.9% Al 2 O 3 , 12-22% B 2 O 3 , 1-3.5% Li 2 O, 3.7-12% Na 2 O, 0-5.8% K 2 O, 6-15% total of Li 2 O+Na 2 O+K 2 O, the molar ratio Li 2 O:Na 2 O +K 2 +K 2 O not exceeding 2:3, 0.15-0.7% PbO, 0.12-0.18% Ag, 0.2-1% Cl, 0.06-0.13% Br, 0-2.5% F, and 0.002-0.02% CuO, the Ag, Cl, and Br ranges representing values as analyzed in the glass; (b) adjusting the temperature of at least one region of the glass melt to provide a viscosity therein of about 10 4 -10 6 poises; (c) drawing the glass melt at a viscosity of about 10 4 -10 6 poises directly past platinum or platinum-clad refractory forming means to produce potentially photochromic drawn glass sheet of optical quality, said glass exhibiting good resistance to surface crystal growth in contact with platinum such that over a contact period of 30 days the growth of a crystalline layer will not exceed 10 microns in thickness; (d) cooling the glass sheet below the softening point of the glass and cutting articles of desired geometries therefrom; (e) edge supporting said articles on alveolated molds; and then (f) heating said articles at a temperature between about 610°-660° C. for a period of time sufficient to simultaneously sag the glass to a desired curvature into the concave portions of the alveolated molds, but not into contact with the inner surface of said molds, and develop photochromic properties in the glass.

Claim 2

A method for forming glass sheet from potentially photochromic glass and thereafter simultaneously shaping articles from said glass sheet and developing photochromic properties therein which comprises the steps of: (a) melting a batch for a glass consisting essentially, in weight percent on the oxide basis, of about 57.1-65.3% SiO 2 , 9.6-13.9% Al 2 O 3 , 12-22% B 2 O 3 , 1-3.5% Li 2 O, 3.7-12% Na 2 O, 0-5.8% K 2 O, 6-15% total of Li 2 O+Na 2 O+K 2 O, the molar ratio Li 2 O:Na 2 O +K 2 +K 2 O not exceeding 2:3, 0.15-0.7% PbO, 0.12-0.18% Ag, 0.2-1% Cl, 0.06-0.13% Br, 0-2.5% F, and 0.002-0.02% CuO, the Ag, Cl, and Br ranges representing values as analyzed in the glass; (b) adjusting the temperature of at least one region of the glass melt to provide a viscosity therein of about 10 4 -10 6 poises; (c) drawing the glass melt at a viscosity of about 10 4 -10 6 poises directly past platinum or platinum-clad refractory forming means to produce potentially photochromic drawn glass sheet of optical quality, said glass exhibiting good resistance to surface crystal growth in contact with platinum such that over a contact period of 30 days the growth of a crystalline layer will not exceed 10 microns in thickness; (d) cooling the glass sheet below the softening point of the glass and cutting articles of desired geometries therefrom; (e) edge supporting said articles on alveolated molds; and then (f) heating said articles at a temperature between about 610°-660° C. for a period of time sufficient to simultaneously sag the glass to a desired curvature into the concave portions of the alveolated molds, but not into contact with the inner surface of said molds, and develop photochromic properties in the glass.