Stabilized photochromic materials

A photochromic plastic material comprising a plastic host having photochromic particles dispersed therein, said photochromic particles comprising silver halide crystals selected from the group consisting of silver chloride, silver bromide, silver iodide, and mixtures thereof, the dimensions of said crystals lying in the range between approximately 30 Angstroms and approximately 10,000 Angstroms, said crystals being capable of changing to a higher energy, light absorbing state when exposed to activating radiation, said crystals being coated with an inorganic nonoxide material to a coating volume less than 100 times the volume of the crystal, the coating being effective to protect said crystal from the adverse effects of halogen diffusion out of the crystal which occurs during photoactivation and host chemistry, the concentration of said silver halide crystals being from about 0.05 to about 10 percent of the photochromic plastic material.

A process for producing a photochromic particle suitable for incorporation into a plastic host to impart photochromic properties thereto, said process being characterized by the steps of:

• forming silver halide crystals the dimensions of which lie in the range between approximately 30 Angstroms and 10,000 Angstroms;
• and
• coating the surface of said crystals with a volume of material effective to render the particle impervious to diffusion of halogen produced during photoactivation and effective to protect the crystal from host chemistry, the coating step being effected by adding an acid to a dispersion of silver halide crystals, adding one of the group consisting of tetraethylorthosilicate and tetramethylorthosilicate, and evaporating the liquid phase of the dispersion.

A process for producing a photochromic particle suitable for incorporation into a plastic host to impart photochromic properties thereto, said process being characterized by the steps of:

• forming silver halide crystals the dimensions of which lie in the range between approximately 30 Angstroms and 10,000 Angstroms;
• and
• coating the surface of said crystals with a volume of material effective to render the particle impervious to diffusion of halogen produced during photoactivation and effective to protect the crystal from host chemistry, the coating step being effected by precipitating a titanium salt onto the surface of the crystal.

A process for producing a photochromic particle suitable for incorporation into a plastic host to impart photochromic properties thereto, said process being characterized by the steps of:

• forming silver halide crystals the dimensions of which lie in the range between approximately 30 Angstroms and 10,000 Angstroms;
• and
• coating the surface of said crystals with a volume of material effective to render the particle impervious to diffusion of halogen produced during photoactivation and effective to protect the crystal from host chemistry, the coating step being effected by cathodic sputtering in an atmosphere selected from the group consisting of oxygen, hydrogen sulfide, and nitrogen.

A process for producing a photochromic particle suitable for incorporation into a plastic host to impart photochromic properties thereto, said process being characterized by the steps of:

• forming silver halide crystals, the dimensions of which lie in the range between approximately 30 Angstroms and 10,000 Angstroms, the forming step being effected by precipitating said silver halide crystals by mixing a silver salt solution with a halide salt solution in the presence of a ripening inhibitor;
• and
• coating the surface of said crystal with a volume of material effective to render the particle impervious to diffusion of halogen produced during photoactivation and effective to protect the crystal from host chemistry.

A photochromic lens comprising an optically clear plastic host having photochromic particles dispersed therein, each of said photochromic particles comprising a silver halide crystal the dimensions of which lie in the range between approximately 30 Angstroms and 10,000 Angstroms, the silver halide being selected from the group consisting of silver chloride, silver bromide, silver iodide, and mixtures thereof, the crystals being capable of changing to a higher energy, light absorbing state when exposed to activating radiation, said crystals being coated with an inorganic non-oxide material to a coating volume less than about 100 times the volume of the crystal, the coating being effective to protect said crystal from the adverse effects of halogen diffusion out of the crystal which occurs during photoactivation and host chemistry, the concentration of said silver halide crystals in the host being between about 0.05 and 10 weight percent.