Process for preparing perylene-3,4,9,10-tetracarboxylic diimide in transparent pigment form

摘要

The present invention provides a process for preparing transparent perylimide pigments of the formula (I) in which u is a number from 0 to 8 and, if u>0, E is a chlorine or bromine atom and, where u>1, may be a combination thereof, which comprises wet-grinding a crude perylimide pigment in a liquid medium in a stirred ballmill operated at a power density of from 1.0 kW per liter of milling space and at a stirrer tip speed of more than 12 m/s under the action of grinding media having a diameter of less than or equal to 0.9 mm, and isolating the resulting pigment.