Process for manufacturing pigments

摘要

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.