Effect of Ammonium Salt of Styrene‐Maleate Copolymer on the Rheology of Quinacridone Red Pigment Dispersion

Abstract

The rheological properties of quinacridone pigment dispersion with ammonium salt of styrene‐maleate (SMA) copolymer (SMA‐NH4) as a dispersant were measured at 25°C. The effects of the SMA‐NH4 concentration, pH, and ionic strength of the system on the rheology of concentrated quinacridone pigment dispersion (in aqueous medium) were studied. All of the experimental results were correlated with the Herschel–Bulkley model. The estimated values of yield stress, τy, and model parameters such as the consistency coefficient, K, and the flow characteristic exponential, n, could reflect the variation of the surface charges of pigment particles, interactions between particles and the structure of dispersion. The flow curve of the quinacridone pigment dispersion without SMA‐NH4 showed a pseudoplastic character, while the flow curve of the quinacridone pigment dispersion with SMA‐NH4 copolymer showed a nearly Newtonian behavior. The rheological properties of aqueous quinacridone pigment dispersion with SMA‐NH4 were strongly affected by both pH and ionic strength.