Silver-free polarizing photochromic glasses

Claim 1

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 2 , 4-26% Al 2 O 3 , 4-26% B 2 O 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 2 O, up to 15% Na 2 O, up to 20% K 2 O, up to 25% Rb 2 O, and up to 30% Cs 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°-900°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 7 -10 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.

Claim 2

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 2 , 4-26% Al 2 O 3 , 4-26% B 2 O 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 2 O, up to 15% Na 2 O, up to 20% K 2 O, up to 25% Rb 2 O, and up to 30% Cs 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°-900°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 7 -10 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.

Claim 5

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 2 , 4-26% Al 2 O 3 , 4-26% B 2 O 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 2 O, up to 15% Na 2 O, up to 20% K 2 O, up to 25% Rb 2 O, and up to 30% Cs 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 7 -10 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.

Claim 6

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 2 , 4-26% Al 2 O 3 , 4-26% B 2 O 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 2 O, up to 15% Na 2 O, up to 20% K 2 O, up to 25% Rb 2 O, and up to 30% Cs 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 7 -10 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.