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

摘要

A desulfonation reaction mixture of 4,4'-diamino-1,1'-dianthraquinonyl-3,3'-disulfonic acid obtainable in a conventional manner is mixed in the form of an aqueous acid suspension with a surface active agent, followed by filtration, whereby filterability and flowability of the produced 4,4'-diamino-1,1'-dianthraquinonyl pigment are efficiently improved.