Supersaturated solid solutions of photochromic materials in epoxies

Claim 1

A method of preparing a photochromic filter effective at room temperature consisting essentially of a. a photochromic material, the molecules of which have a polynuclear conjugated aromatic ring system, which system has a set of electronic energy levels such that at least one of said levels is metastable and characterized by having strongly-allowed transitions from the metastable level to higher electronic states whose energy spacings relative to the metastable state correspond to energies of photons capable of exciting a visual response in the retina of the human eye, namely whose wavelength is in the range of 4000 to 7500 Angstrom units, and which metastable energy level is populated by producing a redistribution of the electrons such that the electronic configuration peculiar to the ground state is altered to the electronic configuration characteristic of the metastable state when the ground state molecules are subjected to excitation by photons having energies greater than that corresponding to photons having a wavelength of about 6000 Angstroms, b. dispersed as a supersaturated solid solution at a concentration of about 5 X 10 5 to 1 X 10 2 moles per liter in a substantially optically transparent epoxy resin which shows a high transmittance in the ultraviolet region of 3000 to 4000 A., and is solid at room temperature and substantially free from uncombined oxygen and active centers capable of reacting with free radicals and biradicals, comprising: completely dissolving at least one such photochromic material in a volatile benzenoid solvent in such volume that said photochromic material is completely soluble therein, and also dissolving therein an epoxide component of a substantially transparent epoxy resin which shows a high transmittance in the ultraviolet region of 3000 to 4000 A., the volume of said solvent being such that said epoxide is also completely soluble therein evaporating said solvent by heat and reduced pressure, under conditions which avoid bumping and boiling, until the said solvent is removed thereby forming a supersaturated solution of said photochromic material in said epoxide, and before the photochromic material crystallizes from the epoxide, adding a hardener, mixing until homogeneous, placing between optically transparent layers through which gaseous oxygen does not diffuse, and holding under a curing cycle until the epoxide and hardener react, thereby forming a stable hard epoxy resin matrix layer in which the molecules of the photochromic material are locked in solid solution, and which is protected from atmospheric oxygen by said optically transparent layer through which gaseous oxygen does not diffuse on each side.

Claim 2

A method of preparing a photochromic filter effective at room temperature consisting essentially of a. a photochromic material, the molecules of which have a polynuclear conjugated aromatic ring system, which system has a set of electronic energy levels such that at least one of said levels is metastable and characterized by having strongly-allowed transitions from the metastable level to higher electronic states whose energy spacings relative to the metastable state correspond to energies of photons capable of exciting a visual response in the retina of the human eye, namely whose wavelength is in the range of 4000 to 7500 Angstrom units, and which metastable energy level is populated by producing a redistribution of the electrons such that the electronic configuration peculiar to the ground state is altered to the electronic configuration characteristic of the metastable state when the ground state molecules are subjected to excitation by photons having energies greater than that corresponding to photons having a wavelength of about 6000 Angstroms, b. dispersed as a supersaturated solid solution at a concentration of about 5 X 10 5 to 1 X 10 2 moles per liter in a substantially optically transparent epoxy resin which shows a high transmittance in the ultraviolet region of 3000 to 4000 A., and is solid at room temperature and substantially free from uncombined oxygen and active centers capable of reacting with free radicals and biradicals, comprising: completely dissolving at least one such photochromic material in a volatile benzenoid solvent in such volume that said photochromic material is completely soluble therein, and also dissolving therein an epoxide component of a substantially transparent epoxy resin which shows a high transmittance in the ultraviolet region of 3000 to 4000 A., the volume of said solvent being such that said epoxide is also completely soluble therein evaporating said solvent by heat and reduced pressure, under conditions which avoid bumping and boiling, until the said solvent is removed thereby forming a supersaturated solution of said photochromic material in said epoxide, and before the photochromic material crystallizes from the epoxide, adding a hardener, mixing until homogeneous, placing between optically transparent layers through which gaseous oxygen does not diffuse, and holding under a curing cycle until the epoxide and hardener react, thereby forming a stable hard epoxy resin matrix layer in which the molecules of the photochromic material are locked in solid solution, and which is protected from atmospheric oxygen by said optically transparent layer through which gaseous oxygen does not diffuse on each side.