Selection of dispersants for the dispersion of C.I. Pigment Violet 23 in organic medium

The dispersion of the organic carbazole violet pigment (C.I. Pigment Violet 23) in organic solvent requires the use of dispersant additives. Three carboxylic dispersants have been investigated regarding this purpose. Their adsorption behaviour has been evaluated by means of adsorption isotherms and the molecular interactions taking place at the surface have been inferred from 13C NMR spectroscopy. The rheological behaviour of the dispersions has considerably been improved by the presence of the dispersants. In particular, the copolymer dispersant that adsorbs the most strongly reduces the suspension viscosity and allows to increase the pigment loading by 50% keeping the rheological properties. The consequences of deflocculation of the suspension on the colorimetric properties are an enhanced tinting strength and an improved colour stability.