US Patent 7211139 Process for preparing nanoscale quinacridone

This invention relates to a method for production of nanoscale size quinacridones through a wet-salt attrition process by combining a crude quinacridone pigment in the presence of (i) an inorganic salt, (ii) an organic liquid in which the quinacridone pigment and salt are substantially insoluble, and (iii) a quinacridone derivative in an amount less than 10 wt. % relative to the quinacridone pigment; discharging the ground quinacridone pigment into water; adding an acid to produce a solution pH of 1.5 or lower; and isolating the quinacridone pigment.