Process for preparing linear unsubstituted -phase quinacridone pigments

摘要

Process for preparing linear unsubstituted -phase quinacridone pigments A process for preparing linear unsubstituted - phase quinacridone pigments or pigment preparations, which comprises P Pa) cyclizing 2,5-dianilinoterephthalic acid in polyphosphoric acid or polyphosphoric ester with a phosphorus pentoxide content of at least 84% by weight to form the quinacridone,P Pb) subsequently hydrolyzing this quinacridone with water or with an aqueous mineral acid solution, preferably orthophosphoric acid solution, at a temperature of at least 40 C., preferably from 60 to 105. degree. C., to form the crude quinacridone pigment which is predominantly in the -phase, PPc) then heating the crude - phase quinacridone pigment to a temperature between 120 and 200. degree. C. in the presence of a from 0.1 to 3% strength by weight, preferably from 0.2 to 2% strength by weight, inorganic base in water and alkali-stable organic solvents, for the change of phase into coarsely crystalline crude -phase pigment, andPPd) subjecting the coarsely crystalline crude -phase quinacridone pigment, for the fine division to form a pigment or prepigment, to dry or wet milling; and then isolating the resulting finely divided -phase pigment;P Pe) or subjecting the finely divided - phase prepigment obtained in d) to a finish treatment in the presence of solvents, and then isolating the pigment.