Wettability and Dispersion of Phthalocyanine Blue Pigment and Evaluation of Its Effect on Printing Quality

Abstract

In this chapter, we investigated the wettability and dispersion of phthalocyanine blue pigment in water-based solution, and qualitatively evaluated its effect on printing quality. First, we measured the contact angle between the phthalocyanine blue pigment and water, determined the sizes and size distributions of the pigment particles, and then mixed the pigment with resin and additives to produce water-based ink and determine the dispersion of the ink. We then made a proof on coated paper and measured its printing density, glossiness and smoothness. We produced several ink samples by adding different amounts of dispersant, determined the dispersion of these ink samples again, and then made printing samples of these inks and measured the resulting printing density, glossiness, and smoothness properties of the samples. We found there was a large contact angle between the phthalocyanine blue pigment and water droplets (72.6°). Untreated phthalocyanine blue pigment has poor dispersion in aqueous ink, and the dispersion of the ink could be greatly improved by adding dispersant. The samples printed with inks containing different amounts of dispersant all had higher printing density than the untreated proof, and the glossiness and smoothness of these samples were also greatly improved. Thus, we consider that an organic pigment such as phthalocyanine blue pigment, which has poor wettability, cannot be used in aqueous ink directly unless it has been properly treated. Using a dispersant is an efficient way to improve dispersion, but the optimum dosage must be determined experimentally. Good wettability and dispersion improve the optical and other printing properties of ink.