FORMULATION OF AN INVISIBLE INFRARED PRINTING INK

A new, invisible to the naked eye and infrared (IR) readable, ink form ulation based on silicon(IV) 2,3-naphthalocyanine bis(trihexylsilyloxi de) as colorant is described The ink formulation is based on absorptio n and reflection of light in the IR, in contrast to the currently empl oyed mechanism of excitation and fluorescence detection. The ink absor bs strongly at 790 nm and has highly transmitting characteristics in t he visible. A good contrast level was obtained with an illumination so urce emitting at 790 nm. The ink is stable, lightfast and applicable t o offset printing, and can also be extended to other printing techniqu es.