Influence of different dispersants on the quality and stability of aqueous quinacridone magenta pigment dispersion for ink-jet applications

The stability of water-based pigment dispersions is a key factor in determining their utility in ink-jet applications, and the appropriate choice of dispersant plays a special role. Among the pigment formulations tested to date, literature data on magenta pigments are very limited. Thus, the goal of this work was to study the influence of the type and loading of dispersants on the quality and stability of quinacridone magenta pigment dispersions. Three different commercially available dispersants were tested: (1) a cationic styrene-maleic anhydride copolymer, (2) an anionic polyacrylate, and (3) a nonionic alkyl ethoxylate. Pigment and dispersing agents were analysed using the Fourier Transform–infrared method. The stability of pigment dispersions was determined by comparative studies of changes in the pigment particle size, viscosity, pH, filtration time, optical density and gloss during the accelerated ageing test. Moreover, Turbiscan AGS and LUMiFuge analysers were used for evaluations of the instability of the dispersions. The properties of each dispersing agent affected the performances of the different dispersants. The highest stability for the pigment formulations was provided using the nonionic dispersant (small particle size, < 60 nm; the lowest viscosity < 60 mPa·s at the optimal dispersant content; favourable results of the filtration test; the highest pigment dispersability, proven by optical density and gloss). The Turbiscan AGS and LUMiFuge results indicated that the stability of all tested quinacridone magenta pigment dispersions was excellent (Turbiscan Stability Index values below three, and no significant differences in transmission profiles, respectively). However, it was found that the measurement results were influenced by the viscosity of the formulations.