Cross-linked pigment dispersion based on polyurethane dispersants

1. An aqueous pigment dispersion comprising a colorant and a polyurethane dispersant, wherein said polyurethane dispersant is comprised of a polymer with:

(a) an aqueous dispersing moiety, wherein said dispersing moiety is pendant to the polymer backbone and terminal to the polymer chain, and said dispersing moiety is selected from the group consisting of —COOM, —OPO 3 M 2 , —PO 3 M 2 , —SO 3 M, —(CH 2 CHR 5 O) n —CH 3 , and mixtures thereof; and

(b) a cross-linkable moiety that is cross-linked with a cross-linking agent, wherein said cross-linkable moiety is pendent to the polymer backbone;

wherein the polyurethane dispersant comprises at least one compound of the general structure of Formula I:

wherein each X is independently —OPO 3 M 2 , —PO 3 M 2 , —SO 3 M or —(CH 2 CHR 5 O) n —CH 3 ;

each M is independently Na, K, Li, H or N(R 6 ) 4 ;

each Y is independently O, S or NR 4 ;

each W is independently N, O or S;

each R 1 is independently C 1 -C 20 alkyl, C 3 -C 20 substituted alkyl, C 6 -C 40 aryl or C 9 -C 40 substituted aryl;

R 2 is comprised of difunctional isocyanate reactants Z 1 and Z 2 , and a hydrophobic polyol Z 3 , wherein there is at least one Z 1 , at least one Z 2 and at least one Z 3 ;

each R 3 is independently C 1 -C 20 alkyl, C 3 -C 20 substituted alkyl or a straight bond, provided that when R 3 is a straight bond, X is —(CH 2 CHR 5 O) n —CH 3 ;

each R 4 is independently —R 3 —X, H, C 1 -C 20 alkyl or C 3 -C 20 substituted alkyl;

each R 5 is independently H or C 1 -C 12 alkyl;

each R 6 is independently H, C 1 -C 20 alkyl, C 7 -C 20 aralkyl or C 6 -C 40 aryl;

n is an integer from 2 to 30;

Z 1 is a difunctional isocyanate reactant substituted with an aqueous dispersing moiety;

Z 2 is a difunctional isocyanate reactant substituted with one or more cross-linkable moieties; and

Z 3 is a hydrophobic polyol with MW less than 3000.

2. The pigment dispersion of claim 1 , wherein the cross-linking agent is one or more members selected from the group consisting of epoxide, isocyanate, carbodiimide, N-methylol, oxazoline, silane, and mixtures thereof.

3. The pigment dispersion of claim 2 , wherein Z 1 is a diol substituted with the aqueous dispersing moiety.

4. The pigment dispersion of claim 3 , wherein Z 2 is a diol substituted with one or more cross-linkable moieties.

5. The pigment dispersion of claim 4 , wherein the aqueous dispersing moiety consists of one or more carboxyl groups.

6. The pigment dispersion of claim 5 , wherein the cross-linkable moiety consists of one or more carboxyl groups.

7. The pigment dispersion of claim 6 , wherein Y is NR 4 .

8. The pigment dispersion of claim 2 , wherein each X is —(CH 2 CHR 5 O) n —CH 3 .

9. The pigment dispersion of claim 8 , wherein Z 1 is a diol substituted with the aqueous dispersing moiety.

10. The pigment dispersion of claim 9 , wherein Z 2 is a diol substituted with one or more cross-linkable moieties.

11. The pigment dispersion of claim 2 , wherein each X is —SO 3 M.

12. The pigment dispersion of claim 11 , wherein Z 1 is a diol substituted with the aqueous dispersing moiety.

13. The pigment dispersion of claim 12 , wherein Z 2 is a diol substituted with one or more cross-linkable moieties.

14. The pigment dispersion of claim 2 , wherein each Y is NR 4 and each R 4 is —R 3 —X.

15. The pigment dispersion of claim 14 , wherein each W is O.

16. The pigment dispersion of claim 14 , wherein each W is N.

17. The pigment dispersion of claim 2 , wherein the mole ratio of the cross-linkable moiety to the cross-linking agent is from 15:1 to 1:1.5.

18. An aqueous ink jet ink comprising an aqueous ink vehicle and an aqueous pigment dispersion, wherein said aqueous pigment dispersion comprises a colorant and a polyurethane dispersant, wherein said polyurethane dispersant comprises a polymer with:

(a) an aqueous dispersing moiety, wherein said dispersing moiety is pendant to the polymer backbone and terminal to the polymer chain, and said dispersing moiety is selected from the group consisting of —COOM, —OPO 3 M 2 , —PO 3 M 2 , —SO 3 M, —(CH 2 CHR 5 O) n —CH 3 , and mixtures thereof; and

(b) a cross-linkable moiety that is cross-linked with a cross-linking agent, wherein said cross-linkable moiety is pendent to the polymer backbone;

wherein the polyurethane dispersant comprises at least one compound of the general structure of Formula I:

wherein each X is independently —OPO 3 M 2 , —PO 3 M 2 , —SO 3 M or —(CH 2 CHR 5 O) n —CH 3 ;

each M is independently Na, K, Li, H or N(R 6 ) 4 ;

each Y is independently O, S or NR 4 ;

each W is independently N, O or S;

each R 1 is independently C 1 -C 20 alkyl, C 3 -C 20 substituted alkyl, C 6 -C 40 aryl or C 9 -C 40 substituted aryl;

R 2 is comprised of difunctional isocyanate reactants Z 1 and Z 2 , and a hydrophobic polyol Z 3 , wherein there is at least one Z 1 , at least one Z 2 and at least one Z 3 ;

each R 3 is independently C 1 -C 20 alkyl, C 3 -C 20 substituted alkyl or a straight bond, provided that when R 3 is a straight bond, X is —(CH 2 CHR 5 O) n —CH 3 ;

each R 4 is independently —R 3 —X, H, C 1 -C 20 alkyl or C 3 -C 20 substituted alkyl;

each R 5 is independently H or C 1 -C 12 alkyl;

each R 6 is independently H, C 1 -C 20 alkyl, C 7 -C 20 aralkyl or C 6 -C 40 aryl;

n is an integer from 2 to 30;

Z 1 is a difunctional isocyanate reactant substituted with an aqueous dispersing moiety;

Z 2 is a difunctional isocyanate reactant substituted with one or more cross-linkable moieties; and

Z 3 is a hydrophobic polyol with MW less than 3000.

19. The ink of claim 18 , wherein Z 1 is a diol substituted with the aqueous dispersing moiety.

20. The ink of claim 19 , wherein Z 2 is a diol substituted with one or more cross-linkable moieties.