Patent ID: 7211139

Claim:
A process for preparing a quinacridone pigment comprising: (a) grinding a crude quinacridone pigment in the presence of (i) an inorganic salt, (ii) an organic liquid in which the crude quinacridone pigment and salt are substantially insoluble, and (iii) a quinacridone pigment derivative in an amount less than 10 wt. % relative to the weight of the crude quinacridone pigment; (b) discharging the crude quinacridone pigment from step (a) into water, thereby attaining a water pigment mixture; (c) adding to the water pigment mixture of step (b), an acid in an amount sufficient to adjust the pH of the mixture to 1.5 or lower; and (d) isolating from the mixture a quinacridone pigment having a particle size ranging from 20 to 80 nm.