Isoindoline pigment having improved low shear dispersibility

A process for the preparation of a novel pigment composition by thermal treatment of a dispersion of

• a pigment of formula ##STR4## at least one C.sub.2 -C.sub.16 alkylenedicarboxylic acid-di C.sub.1 -C.sub.12 alkyl ester:
• and
• at least one C.sub.12 -C.sub.12 fatty acid ester of polyhydroxy-C.sub.2 -C.sub.12 alkane;
• in an inert hydrophilic diluent, which comprises adding
• 1) at least one C.sub.2 -C.sub.16 alkylenedicarboxylic acid-di-C.sub.1-C.sub.12 alkyl ester, at the latest before the end of the thermal treatment;
• and
• 2) when its quantity is more then 0% by weight, at least one C.sub.12 -C.sub.24 fatty acid ester of polyhydroxy-C.sub.2 -C.sub.12 alkane, at the earliest after the start of the thermal treatment,
• whereby the addition of the C.sub.2 -C.sub.16 alkylenedicarboxylic acid-di-C.sub.1 -C.sub.12 alkyl ester is started before the addition of the C.sub.12 -C.sub.22 fatty acid ester of polyhydroxy-C.sub.2 -C.sub.12 alkane is started, and the amount of pigment of formula (I) is 70-95% by weight, the amount of C.sub.2 -C.sub.16 alkylenedicarboxylic acid-di-C.sub.1 -C.sub.12 alkyl ester is 5-15% by weight, and the amount of C.sub.12 -C.sub.24 fatty acid ester of polyhydroxy-C.sub.2 -C.sub.12 alkane is 0-15% by weight, each based on the total weight of pigment of formula (I), C.sub.2 -C.sub.16 alkylenedicarboxylic acid-di-C.sub.1 C.sub.12 alkyl-ester and C.sub.12 -C.sub.24 fatty acid ester of polyhydroxy-C.sub.2 -C.sub.12 alkane.