PROCESS FOR THE PREPARATION OF PURE ORGANIC PIGMENTS

A process for preparing very pure copper phthalocyanine pigments of the alpha -modification, wherein substituted or unsubstituted copper phthalocyanines having different degrees of purity are converted into copper phthalocyanine salts capable of being isolated, with the aid of suitable acids which dissolve the impurities contained in the dyestuff, wherein these salts are separated from the acid, the copper phthalocyanines of the alpha -modification are set free in a pure form from the copper phthalocyanine salts by the action of water and wherein the isolated copper phthalocyanine is subject in an aqueous suspension to a mechanical fine division. This process yields copper phthalocyanines of the alpha -modification in a very pure form without causing problems with respect to the waste water.