Process for converting crude and/or coarsely crystalline perylenetetracarboxylic acid diimides to a pigmentary form

Claim 1

A process for converting an unpurified, non-pigmentary crystalline perylene-3,4,9,10-tetracarboxylic acid diimide of the formula: ##STR26## wherein A is phenyl which is unsubstituted or substituted by 1 to 3 substituents selected from the group consisting of C 1 -C 4 alkyl, C 1 -C 4 alkoxy, phenoxy, chlorine, bromine, fluorine, lower alkanoylamino, benzoylamino, carbonylaminophenyl and carbonylamino-C 1 -C 4 alkyl or phenylazo, or A is an unsaturated 5-membered or 6-membered ring containing 1 or 2 nitrogen atoms as sole hetero atoms which may be fused to a benzene ring, C 3 -C 6 alkyl, or C 2 -C 3 alkyl which is substituted by C 1 -C 4 alkoxy, phenyl, or C 2 -C 5 alkanoylamino, the two A groups being identical or different, to a pigmentary form, comprising: milling said unpurified, non-pigmentary perylene diimide in a high-speed stirred mill in the absence of a surfactant until it has been communited to a finely divided state required for pigmentary applications; and isolating said finely ground pigment.