Process for producing 4,4'-Diamino-1,1'-dianthraquinonyl pigments

摘要

4,4'-Diamino-1,1'-dianthraquinonyl compounds which are obtained in a known manner and which are easy to agglomerate or aggregate owing mainly to their too fine particle size are conditioned by heating an aqueous suspension consisting essentially of the 4,4'-diamino-1,1'-dianthraquinonyl compound and water in the presence or absence of a mineral acid or an alkali. The thus obtained 4,4'-diamino-1,1'-dianthraquinonyl pigments are used in paints, printing inks, coloring of plastics and the like. The aqueous suspension is preferably prepared by desulfonating a 4,4'-diamino-1,1'-dianthraquinonyl-3,3'-disulfonic acid compound in a mineral acid such as sulfuric acid and then mixing the desulfonation reaction mixture with water or by once isolating the resulting 4,4'-diamino-1,1'-dianthraquinonyl compound and mixing the isolated compound with water.