Patent ID: 7666558

Claim:
A method of forming an image, comprising: providing an image forming medium comprising: a substrate; and an imaging layer coated on or impregnated into said substrate, wherein the imaging layer comprises a photochromic polymer, optionally dispersed in a polymeric binder, the photochromic polymer comprising a polymer having at least one photochromic unit grafted therein; and heating the photochromic polymer to a temperature at or near a glass transition temperature or melting temperature of the photochromic polymer; and exposing the image forming medium to UV irradiation of a first wavelength in an imagewise manner for a time period ranging from about 10 milliseconds to about 5 minutes at an intensity ranging from about 0.1 mW/cm 2 to about 100 mW/cm 2 to form a visible image, wherein the polymer and the photochromic unit are selected so that: the imaging layer exhibits a reversible transition between a colorless state and a colored state in response to heat and light, and the imaging layer does not exhibit a transition from the colored state to colorless state when heated in the absence of light.