Stable pigment dispersions

1. A pigment dispersion comprising:

a pigment and a block copolymer consisting of ionic aromatic monomeric units.

2. The pigment dispersion according to claim 1 , wherein the block copolymer contains at least 25 ionic aromatic monomeric units.

3. The pigment dispersion according to claim 1 , wherein the ionic aromatic monomeric units have a solubility of 10 mg/L or more at 25° C. in water with a pH>7.

4. The pigment dispersion according to claim 1 , wherein the ionic aromatic monomeric units 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.

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

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

7. The pigment dispersion according to claim 4 , wherein the ionic aromatic monomeric unit is a vinyl benzoic acid or a salt thereof.

8. The pigment dispersion according to claim 4 , wherein the ionic aromatic monomeric unit is styrenesulfonic acid or a salt thereof.

9. The pigment dispersion according to claim 8 , 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.

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

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

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

13. A pigment dispersion comprising:

a pigment and a block copolymer consisting of ionic aromatic monomeric units; wherein

the ionic aromatic monomeric units are represented by Formula (I):

wherein,

m=1;

n is 1 or an integer value greater than 1;

R represents hydrogen or methyl;

L is represented by —(C═O)—O—;

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.

14. The pigment dispersion according to claim 13 , wherein M + is selected from the group consisting of Na + , Li + , K + , NH 4 + , and quaternary amine.

15. A colored layer coated from a coating solution containing the pigment dispersion according to claim 13 .

16. An inkjet ink comprising the pigment dispersion according to claim 13 .

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

18. A process for preparing a pigment dispersion comprising the steps of:

a) synthesizing a block copolymer consisting of ionic aromatic monomeric units 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) using the synthesized block copolymer to prepare a pigment dispersion.

19. The process for preparing the pigment dispersion according to claim 18 , wherein the water-soluble reversible addition fragmentation chain transfer polymerization agent is 4-cyanopentanoic acid dithiobenzoate.

20. The process for preparing the pigment dispersion according to claim 18 , wherein the pigment dispersion is prepared by precipitation.