Stable pigment dispersions

1. A pigment dispersion comprising:

a pigment with at least one carboxylic acid group; and

a block copolymer; wherein monomeric units of the block copolymer consist of:

aromatic monomeric units A having at least one carboxylic acid group or a salt thereof; and

aromatic monomeric units B having at least one sulfonic acid group or a salt thereof.

2. The pigment dispersion according to claim 1 , wherein said block copolymer includes at least 25 monomeric units.

3. The pigment dispersion according to claim 1 , wherein the aromatic monomeric units A include at least one carboxylic acid group or a salt thereof and the aromatic monomeric units B include at least one sulfonic acid group or a salt thereof are represented by Formula (I):

wherein,

m=0 or 1;

n is 1 or an integer value greater than 1;

R represents hydrogen or methyl;

L represents a linking group containing at least one atom selected from the group consisting of C, O, and S;

Ar represents an aromatic group or a heteroaromatic group;

X is selected from the group consisting of COOH, COO − M + , SO 3 H, and SO 3 − M + ; and

M + represents a cation.

4. The pigment dispersion according to claim 3 , wherein m=1 and the linking group L is represented by —(C═O)—O—.

5. An inkjet ink comprising the pigment dispersion according to claim 4 .

6. The inkjet ink according to claim 5 , wherein the inkjet ink is a radiation curable inkjet ink.

7. The pigment dispersion according to claim 3 , wherein M 30 is selected from the group consisting of Na + , Li + , K + , NH 4 + , and quaternary amine.

8. An inkjet ink comprising the pigment dispersion according to claim 7 .

9. The pigment dispersion according to claim 3 , wherein the aromatic monomeric unit A including at least one carboxylic acid group or a salt thereof is vinyl benzoic acid or a salt thereof.

10. An inkjet ink comprising the pigment dispersion according to claim 9 .

11. The inkjet ink according to claim 10 , wherein the inkjet ink is a radiation curable inkjet ink.

12. The pigment dispersion according to claim 3 , wherein the aromatic monomeric unit B including at least one sulfonic acid group or a salt thereof is styrenesulfonic acid or a salt thereof.

13. The pigment dispersion according to claim 12 , wherein the styrenesulfonic acid or a salt thereof is selected from the group consisting of 4-styrenesulfonic acid, sodium 4-styrenesulfonate, potassium 4-styrenesulfonate, and ammonium 4-styrenesulfonate.

14. An inkjet ink comprising the pigment dispersion according to claim 12 .

15. The inkjet ink according to claim 14 , wherein the inkjet ink is a radiation curable inkjet ink.

16. An inkjet ink comprising the pigment dispersion according to claim 1 .

17. The inkjet ink according to claim 16 , wherein the inkjet ink is a radiation curable inkjet ink.

18. A colored layer coated from a coating solution comprising the pigment dispersion according to claim 1 .

19. A process for preparing a pigment dispersion as defined by claim 1 , comprising the steps of:

a) synthesizing a block copolymer consisting of aromatic monomeric units A and aromatic monomeric units B by reversible addition fragmentation chain transfer polymerization performed in an aqueous medium with a water-soluble reversible addition fragmentation chain transfer polymerization agent; and

b) dispersing at least one pigment with the synthesized block copolymer; wherein the aromatic monomeric units A have at least one carboxylic acid group or a salt thereof;

the aromatic monomeric units B have at least on sulfonic acid group or a salt thereof; and

the pigment is a pigment with at least one carboxylic acid group.

20. The process for preparing the pigment dispersion according to claim 19 , wherein the water-soluble reversible addition fragmentation chain transfer polymerization agent is 4-cyanopentanoic acid dithiobenzoate.

21. The process for preparing the pigment dispersion according to claim 20 , wherein the pigment dispersion is prepared by precipitation.