Rheology improvers and pigment compositions having improved rheology

An 1-aminoanthraquinone, anthanthrone, anthrapyrimidine, quinacridone, diketopyrrolopyrrole, flavanthrone, indanthrone, isoindolinone, isoviolanthrone, perinone, pyranthrone or thioindigo pigment, mixed crystal or the solid solution therof, wherein the pigment, the mixed crystal or the solid solution has on its surface sulfonate groups of the formula (I),

• wherein
• R1 is methyl or ethyl,
• R2 is C6-C24alkyl, C6-C24alkenyl or C7-C24aralkyl,
• R3 and R4 are each independently of the other a chain consisting of 1, 2 or 3 members, each member independently of any other(s) being —(CH2)2O—, —(CH2)3O—, —CH(CH3)CH2O—, —CH2CH(CH3)O— or —CH2CH(CH2O—)O— and the chains being terminated by H, CH3, C2H5 or C(═O)CH3,
• m is a number from 0.3 to 1.0 and
• n is a number from 0 to (1.0−m).

An 1-aminoanthraquinone, anthanthrone, anthrapyrimidine, quinacridone, diketopyrrolopyrrole, flavanthrone, indanthrone, isoindolinone, isoviolanthrone, perinone, pyranthrone or thioindigo compound, which compound has one or more sulfonate groups of formula (I)

• wherein
• R1 is methyl or ethyl,
• R2 is C8-C24alkyl, C6-C24alkenyl or C7-C24aralkyl,
• R3 and R4 are each independently of the other a chain consisting of 1, 2 or 3 members, each member independently of any other(s) being —(CH2)2O—, —(CH2)3O—, —CH(CH3)CH2O—, —CH2CH(CH3)O— or —CH2CH(CH2O—)O— and the chains being terminated by H, CH3, C2H5 or C(═O)CH3,
• m is a number from 0.3 to 1.0 and
• n is a number from 0 to (1.0−m).