Some characteristics of pigments that affect the kinetics of fading of prints made from water-based liquid ink formulations

A series of inks has been formulated that, when printed, give different fading profiles on exposure to Xenon Arc light. Such prints were designed to form the basis of a replacement for the ISO Blue Wool Scale, which is defined by BS EN ISO 105:B02. The effect of the crystal form of the titanium dioxide that was employed in the inks was investigated. It was shown that the anatase crystal form of titanium dioxide has a greater influence, than the rutile crystal form of titanium dioxide, on accelerating the fading of prints made from such inks. There is an optimum amount of titanium dioxide that should be added to such formulations, to protect the print from fading on exposure to xenon arc light. This situation was observed for both the rutile crystal form of titanium dioxide and the anatase crystal form of titanium dioxide. The effect of the particle size, of Pigment Blue 61, on fading was also evaluated. It has been shown that for a given mass of the blue pigment in a water-based ink, the lightfastness of subsequent prints increased for inks containing Pigment Blue 61 samples that contained smaller particle sized species.