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Abstract

A process for converting a crude, coarsely crystalline perylene-3,4,9,10-tetracarboxylic acid diimide of the formula ##STR1## where A is unsubstituted or substituted phenyl, an unsaturated 5-membered or 6-membered heterocyclic ring which contains one or two nitrogen atoms and may be fused to a benzene nucleus, C.sub.3 -C.sub.6 -alkyl, or C.sub.2 -C.sub.3 -alkyl which is substituted by C.sub.1 -C.sub.4 -alkoxy, phenyl or C-acylamino, to a pigmentary form, wherein the crude pigment, in aqueous suspension, is comminuted in a high-speed mill in the absence of a surfactant. The pigments obtained give pure shade colorations of high to extremely high hiding power, and have a high tinctorial strength in white reductions.

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First Claim