| abstract |
A high-reliability invisible ink printing system is provided which generates high-definition, lightfast images that are easily read or otherwise detected using far red, infrared, and/or ultraviolet light. The inks contain an uncomplexed invisible metal phthalocyanine far red/infrared fluorophore (optimally chloroaluminum [III] phthalocyanine tetrasulfonic acid or salts thereof). An ultraviolet fluorophore can also be included. The inks are invisible to the unaided eye. However, when exposed to far red or infrared light (wavelength=about 650-715 nm) they will fluoresce at a wavelength of about 670-720 nm. If an ultraviolet fluorophore is employed, the inks can also be detected by applying ultraviolet light (wavelength=about 250-380 nm) which results in fluorescent emission at a wavelength of about 400-650 nm. The inks are well suited for delivery using inkjet technology to efficiently form invisible images. |