Process for the preparation of 4,10-dibromoanthanthrone pigment

A process for the preparation of 4, 10-dibromoanthanthrone pigment in transparent pigment form, which comprises first subjecting the crude 4, 10-dibromoanthanthrone pigment, which is in the coarsely crystalline state, to wet milling in an aqueous medium in a stirred ball mill which is operated at a power density of more than 2.5 kW per liter of milling space and at a peripheral stirrer speed of more than 12 m/s under the action of grinding media with a diameter of less than 1.0 mm, until the desired degree of fine division is reached (millbase suspension), and then isolating the resulting pigment in a conventional manner;

• or subjecting the prepigment obtained in the wet milling to a treatment at elevated temperature (finish) in an aqueous medium, and then isolating the pigment.

A process for the preparation of 4, 10-dibromoanthanthrone pigment in opaque pigment form, which comprises first subjecting the crude 4, 10-dibromoanthanthrone pigment, which is in the coarsely crystalline state, to wet milling in an aqueous medium in a stirred ball mill which is operated at a power density of more than 2.5 kW per liter of milling space and at a peripheral stirrer speed of more than 12 m/s under the action of grinding media with a diameter of less than 1.0 mm, until the desired degree of fine division is reached (millbase suspension, and then subjecting the prepigment obtained in the wet milling to a treatment at elevated temperature (finish) in an aqueous-organic medium or a liquid aromatic compound or in aqueous-organic medium at a temperature of up to 155.degree. C., and then isolating the pigment.