PPG patents fluorescent colorants

Patent No. U.S. 7,384,694 B2
PPG Industries has been granted a patent for a multi-layer coating applied to a substrate wherein the coating reflects colored light and is comprised of an upper layer comprised of a resinous binder and colorants which emit fluorescent light when exposed to visible light; the colorants being selected from dyes and pigments that will not scatter light that mask fluorescent light; the colorants being present in the upper layer in amounts of 0.001 to 50 weight percent; and a lower layer comprising a resinous binder and light-absorbing particles, wherein the coating composition exposed to a first light level exhibits a first colored appearance that is dominated by absorbance of light by both of the colorants and the light-absorbing particles and wherein the coating composition exposed to a second light level of higher intensity than the first light level exhibits a second colored appearance dominated by fluorescent light emitted by the colorants, wherein the lower layer has a color value L* less than 40.