Black pigment dispersion

A dispersion which is useful for electrophoretic displays comprising

• α) a bis-oxodihydro-indolylene-benzodifuranone colourant of the formula I
• wherein Rl and R6 are each independently of the other H, CH3, CF3, F or Cl;
• R2, R3, R4, R5, R7, R8, R9 and R10 are each independently of all others H, halogen, R11, COOH, COOR11, COO−, CONH2, CONHR11, CONR11R12, CN, OH, OR11, OOCR11, OOCNH2, OOCNHR11, OOCNR11R12, NO2, NH2, NHR11, NR11R12, NHCOR12, NR11COR12N═CH2, N═CHR11, N═CR11R12, SH, SR11, SOR11, SO2R11, SO3R11, SO3H, SO3−, SO2NH2, SO2NHR11 or SO2NR11R12;
• and R2 and R3, R3 and R4, R4 and R5, R7 and R8, R8 and R9, and/or R9 and R10 can also be linked together by a direct bond or an O, S, NH or NR11 bridge;
• R11 and R12 are each independently of the other C1-C12 alkyl, C1-C12 cycloalkyl, C1-C12 alkenyl, C1-C12 cycloalkenyl or C1-C12 alkinyl, each of which is uninterrupted or interrupted by oxygen, NH, NR13 and/or sulfur in two or more fragments each comprising at least 2 C atoms, and each of which is also unsubstituted or substituted one or more times with COOH, COOR13, COO−, CONH2, CONHR13, CONR13R14, CN, oxo, OH, OR13, OOCR13, OOCNH2, OOCNHR13, OOCNR13R14, NR13, NH2, NHR13, , NR13R14, NHCOR14, NR13COR14, N═CH2, N═CHR13, N═CR13R14, SH, SR13, SOR13, SO2R13, SO3R13, SO3H, SO3−, SO2NH2, SO2NHR13, SO2NR13R14or halogen;
• or C7-C12 aralkyl, C1-C11 heteroaryl or C6-C12 aryl, each of which is unsubstituted or substituted one or more times with COOH, COOR13, COO−, CONH2, CONHR13, CONR13R14, CN, OH, OR13, OOCR13, OOCNH2, OOCNHR13, OOCNR13R14, NO2, NH2, NHR13, NR13R14, NHCOR14, NR13COR14, N═CH2, N═CHR13, N═CR13R14, SH, SR13, SOR13, SO2R13, SO3R13, SO3H, SO3−, SO2NH2, SO2NHR13, SO2NR13R14 or halogen;
• and each R13 or R14 is, independently of any other R13 or R14, C1-C6 alkyl, benzyl or phenyl, each of which is unsubstituted or substituted one or more times with substituents as defined above, with the proviso that the total number of atoms in any substituent of R13 and R14 is from 1 to 8;
• whereby pairs of substituents selected from the group consisting of all R13 and R14 can optionally be linked together by a direct bond or an O, S, NH or NR11 bridge so as to form rings,
• or a cis-trans isomer thereof or a salt of such colourant or isomer having a salt-forming group,
• β) a polymeric dispersant comprising modified poly(meth)acrylate polymers obtained by the process comprising the steps
• a1) polymerizing in a first step one or more ethylenically unsaturated monomers in the presence of at least one nitroxylether having the structural element of the formula
• wherein X represents a group having at least one carbon atom and is such that the free radical X● derived from X is capable of initiating polymerization;
• or
• a2) polymerizing in a first step one or more ethylenically unsaturated monomers in the presence of at least one stable free nitroxyl radical of the formula
• and a free radical initiator;
• wherein at least one monomer used in the steps a1) or a2) is a C1-C6 alkyl or hydroxy C1-C6 alkyl ester of acrylic or methacrylic acid;
• and a second step
• b) comprising the modification of the polymer or copolymer prepared under a1) or a2) by a transesterification reaction, an amidation, hydrolysis or anhydride modification or a combination thereof, and
• γ) a solvent which is suitable for dispersions used in electrophoretic displays.