Crystal Engineering of Pigments for Permanence

Abstract

Continuously improving demands upon the permanence of inkjet colorants have seen an increasing trend towards the use of pigments rather than dyes for applications such as outdoor signage printing. Appropriate selection of pigments for the formulation of YMC inks must be made to ensure that all components fade uniformly in order to preserve image colour quality for the longest possible duration. The permanence of a pigment can be influenced by control of the primary particle size distribution, which is well known to have a great bearing upon the resistance and coloristic properties. As primary particle size increases, a reduction in gloss, transparency and colour strength are observed, combined with an increase in permanence. Armed with this knowledge it is possible to “size engineer” pigment particles that will allow specific degrees of colour permanence to be achieved. Experimental work was carried out to manipulate the particle size of pigment Yellow 151 into small, medium and large size forms, which were then compared to one another in terms of permanence, gloss, opacity and colour strength. Physical reaction parameters used in synthesis were employed to control the pigment particle size. Small sized particles were synthesized by inducing rapid, homogeneous nucleation of the pigment. Large particles were formed by reducing the rate of nucleation followed by controlled crystal growth.