Abstract: A method for preparing an organic pigment dispersion, such as a flush pigment or ink product, comprises steps of introducing into a twin screw extruder a stable, water-borne pigment dispersion, an organic medium, and a destabilizing agent; mixing together the stable, water-borne pigment dispersion, the organic medium, and the destabilizing agent to produce a pigment flush phase and a water phase; and removing at least a part of the water phase. A twin-screw extruder for carrying out the flushing method has an addition and flushing zone, a water removal zone, and a zone for rinsing the crude organic pigment dispersion or flush with water and removing the rinse water. Additional materials may be added to form a finished pigmented product such as an ink product, masterbatch, or toner.

Abstract: A pigment is synthesized in an aqueous medium and the pigment dispersion is purified by ultrafiltration or microfiltration. In particular, an aqueous pigment dispersion having a very small average particle size and a narrow particle size distribution may be prepared by the steps of (a) synthesizing a pigment in an aqueous medium and (b) removing an impurity such as a dissolved synthesis by-product or unreacted starting material through cross flow filtration using a membrane having an average pore diameter of from about 3 nanometers to about 3000 nanometers to produce a purified aqueous pigment dispersion.