Silver-free polarizing photochromic glasses
AssigneeCorning Glass Works
InventorsThomas P. Seward, III, Paul A. Tick
Life of this patent
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Abstract
Silver-free photochromic glasses capable of reversibly changing from the clear nonpolarizing state to the darkened polarizing state are provided by heating a photochromic alkali boroaluminosilicate base glass containing copper and/or cadmium halides to a working temperature and elongating the glass to modify the photochromic particles therein.
Claims9
A method of making a photochromic glass article capable of reversibly changing from a clear, nonpolarizing state to a darkened, polarizing state which comprises the steps of:
- a. providing a potentially photochromic glass article comprising, in weight percent, 40-75% SiO.sub.2, 4-26% Al.sub.2 O.sub.3, 4-26% B.sub.2 O.sub.3, 4-30% total of at least one alkali metal oxide selected in amounts not exceeding the indicated proportions from the group consisting of up to 8% Li.sub.2 O, up to 15% Na.sub.2 O, up to 20% K.sub.2 O, up to 25% Rb.sub.2 O, and up to 30% Cs.sub.2 O, 0.1-10% total of at least one metal oxide selected from the group consisting of CuO and CdO, and 0.1-6% total of at least one halogen selected from the group consisting of Cl, Br, and I, the sum of these constituents totalling at least about 75% by weight of the glass;
- b. heating the glass article to a temperature in the range of about 500.degree.-900.degree.C. for a time sufficient to cause the development therein of second-phase droplets having an average size in the range of about 100-1000A;
- c. adjusting the temperature of the glass article to obtain a glass viscosity in the range of about 10.sup.7 -10.sup.9 poises;
- d. elongating the glass article to a length at which the second phase droplets therein exhibit aspect ratios in the range of about 2:1 to about 5:1;
- and
- e. cooling the glass article to a temperature below the annealing point thereof.
A method of making a photochromic glass article capable of reversibly changing from a clear nonpolarizing state to a darkened polarizing state which comprises the steps of:
- a. providing a potentially photochromic glass article comprising, in weight percent, 40-75% SiO.sub.2, 4-26% Al.sub.2 O.sub.3, 4-26% B.sub.2 O.sub.3, 4-30% total of at least one alkali metal oxide selected in amounts not exceeding the indicated proportions from the group consisting of up to 8% Li.sub.2 O, up to 15% Na.sub.2 O, up to 20% K.sub.2 O, up to 25% Rb.sub.2 O, and up to 30% Cs.sub.2 O, 0.1-10% total of at least one metal oxide selected from the group consisting of CuO and CdO, and 0.1-6% total of at least one halogen selected from the group consisting of Cl, Br, and I, the sum of these constituents totalling at least about 75% by weight of the glass;
- b. heating the glass article to a temperature range in which the glass viscosity thereof is in the range of about 10.sup.7 -10.sup.9 poises and maintaining the glass article in that temperature range for a time sufficient to cause the development therein of second-phase droplets having an average size in the range of about 100-1000A;
- while simultaneously
- c. elongating the glass article to a length at which the second phase droplets developing therein exhibit aspect ratios in the range of about 2:1 to about 5:1;
- and
- d. cooling the glass article to a temperature below the annealing point thereof.
A photochromic polarizing glass article capable of reversibly changing from the clear nonpolarizing state to a darkened polarizing state which has a composition comprising, in weight percent, 40-75% SiO.sub.2, 4-26% Al.sub.2 O.sub.3, 4-26% B.sub.2 O.sub.3, 4-30% total of at least one alkali metal oxide selected in amounts not exceeding the indicated proportions from the group consisting of up to 8% Li.sub.2 O, up to 15% Na.sub.2 O, up to 20% K.sub.2 O, up to 25% Rb.sub.2 O and up to 30% Cs.sub.2 O, 0.1-10% total of at least one metal oxide selected from the group consisting of CuO and CdO, and 0.1-6% total of at least one halogen selected from the group consisting of Cl, Br, and I, the sum of these constituents totalling at least about 75% by weight of the glass.
Dependencies are inferred from the claim text.