Pigment dispersions with polymeric dispersants having pending chromophore groups

1. A pigment dispersion comprising:

a color pigment represented by formula (I):

and

a polymeric dispersant having, via a linking group covalently linked to its polymeric backbone, at least one pending chromophore group which has a molecular weight smaller than 95% of the molecular weight of the color pigment; wherein

R1 to R10 are independently selected from the group consisting of hydrogen, a halogen atom, a methyl group, an ethyl group, a methoxy group, an ethoxy group, —CF 3 , —COOH, —COOCH 3 , —SO 2 NH—C 6 H 5 , —CONH—C 6 H 5 , —CONH—C 6 H 5 —CONH 2 , and —CONH 2 ; and

the pigment dispersion is an inkjet ink and the pigment comprises 0.1 wt % to 20 wt % of the inkjet ink based on a total weight of the inkjet ink.

2. The pigment dispersion according to claim 1 , wherein the pending chromophore group is represented by formula (II):

wherein

one of L1, L2, or L3 is the linking group and is selected from the group consisting of an aliphatic group, a substituted aliphatic group, an unsaturated aliphatic group, and a substituted unsaturated aliphatic group;

L1, L2, and/or L3, if not representing the linking group, are independently selected from the group consisting of hydrogen, an alkyl group, an alkenyl group, an alkoxy group, a carboxylic acid group, an ester group, an acyl group, a nitro group, and a halogen;

AR1 and AR2 represent an aromatic group; and

n represents the integer 0 or 1.

3. The pigment dispersion according to claim 1 , wherein the pending chromophore group is represented by Formula (III):

wherein

one of R1 to R11 is the linking group forming a covalent bond with the polymeric backbone;

R1 to R11, if not representing the linking group, are independently selected from the group consisting of hydrogen, an alkyl group, an alkenyl group, an alkoxy group, an alcohol group, a carboxylic acid group, an ester group, an acyl group, a nitro group and a halogen; or

R7 and R8 may together form a heterocyclic ring.

4. The pigment dispersion according to claim 3 , wherein the heterocyclic ring formed by R7 and R8 is imidazolone or 2,3-dihydroxypyrazine.

5. The pigment dispersion according to claim 1 , wherein the linking group contains at least one atom selected from the group consisting of an oxygen atom, a nitrogen atom, and a sulphur atom.

6. The pigment dispersion according to claim 5 , wherein the linking group in unreacted form is represented by —O—CH 2 —CH 2 —OH.

7. The pigment dispersion according to claim 6 , wherein the pending chromophore group represented by formula (III) having an unreacted linking group is selected from the group consisting of:

8. The pigment dispersion according to claim 1 , wherein the color pigment is selected from the group consisting of C. I. Pigment Yellow 155 and C. I. Pigment Yellow 198.

9. The pigment dispersion according to claim 1 , wherein the polymeric backbone of the polymeric dispersant is a homopolymer.

10. The pigment dispersion according to claim 1 , wherein the pending chromophore group is present in the range of 1 to 30 percent based on the number of monomeric units of the polymeric dispersant.

11. The pigment dispersion according to claim 1 , wherein the polymeric dispersant has a number average molecular weight Mn between 500 and 30,000 and a polymeric dispersity PD smaller than 2.

12. The pigment dispersion according to claim 1 , wherein the inkjet ink is a curable inkjet ink.

13. A method for preparing the inkjet ink according to claim 1 , comprising the step of preparing the polymeric dispersant by copolymerizing a monomer already containing the pending chromophore group.

14. The pigment dispersion according to claim 1 , wherein the polymeric dispersant includes at least two chromophore groups.