| 摘要 |
Process for the preparation of opaque 1,4-diketopyrrolo-[3,4-c]pyrroles of the formula <IMAGE> (I) wherein one of R1 and R2 is hydrogen, halogen or C1-C4-alkyl and other is hydrogen, which process essentially consists of milling the pigment in an alcohol and in the presence of a base at a temperature below 50 DEG C., the resulting product being a highly crystalline readily dispersable diketopyrrolopyrrole pigment having outstanding color strength, purity of shade and saturation.
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