Liquid toner dispersion and use thereof

1. A liquid toner dispersion provided with marking particles comprising a pigment and a resin, said dispersion comprising a nonpolar organic solvent and a hyper-dispersant comprising a graft copolymer provided with an anchor group comprising an amine-functionalised polymer, wherein the amine-functionalised polymer has 3-25 binding sites in the form of nitrogen atoms, onto which at least one stabilising group is grafted, wherein the amine-functionalised polymer has an weight-average molecular weight of in the range of 100-1000 g/mol, wherein said stabilising group comprises an oligomer of hydroxylated fatty acids, of which a carboxylic acid group is coupled to a binding site of the amine-functionalised polymer and wherein the graft copolymer has a weight-average molecular weight in the range of 1500-40,000 g/mol.

2. The liquid toner dispersion of claim 1 , wherein the graft copolymer has a weight-average molecular weight in the range of 2000-20,000 g/mol.

3. The liquid toner dispersion as claimed in claim 1 , wherein the at least one stabilising group is coupled to an amine-group of the anchor group so as to constitute an amide-linkage.

4. The liquid toner dispersion as claimed in claim 1 , wherein the amine-functionalised polymer has a weight-average molecular weight of less than 500 g/mol.

5. The liquid toner dispersion as claimed in claim 1 , wherein the amine-functionalised copolymer is linear.

6. The liquid toner dispersion as claimed in claim 1 , wherein the amine-functionalised polymer is chosen from the group of polyethyleneimine and polyallylamine.

7. The liquid toner dispersion as claimed in claim 1 , wherein the amine-functionalised polymer has a degree of polymerisation of at most 20.

8. The liquid toner dispersion as claimed in claim 7 , wherein the amine-functionalised polymer has a degree of polymerisation in the range of 5-10.

9. The liquid toner dispersion as claimed in claim 1 , wherein at least one of the fatty acid compound species grafted as a stabilising group has a molecular weight in the range of 1200-3500 g/mol.

10. The liquid toner dispersion as claimed in claim 9 , wherein the copolymer contains in addition to the hydroxylated fatty acid oligomer a hydroxylated fatty acid species with a molecular weight that is lower than 1200 g/mol, wherein a carboxylic group of the hydroxylated fatty acid species is coupled to a binding site of the amine-functionalized polymer.

11. The liquid toner dispersion as claimed in claim 1 , wherein the degree of substitution of the binding sites is in the range of 10-66%.

12. The liquid toner dispersion as claimed in claim 11 , wherein the degree of substitution of the binding sites is in the range of 10-50%.

13. A method of preparing a liquid toner dispersion comprising the steps of:

preparing an amine functionalised polymer with a weight-average molecular weight in the range of 100-1000 g/mol, said amine functionalized polymer having 3-25 binding sites in the form of nitrogen atoms;

grafting an oligomer of hydroxylated fatty acids onto the amine-functionalised polymer, therewith obtaining a hyper-dispersant, wherein a carboxylic acid group of said oligomer is coupled to a binding site of the amine-functionalized polymer, wherein the graft copolymer has a weight-average molecular weight in the range of 1500-40,000 g/mol; and

mixing the hyper-dispersant with a nonpolar organic solvent and marking particles.

14. The method as claimed in claim 13 , wherein the grafting comprises a first step, wherein a salt of the hydroxylated fatty acid oligomer and the amine-functionalised polymer is formed, and a second step, wherein the salt is converted into the polymer.

15. The method as claimed in claim 14 , wherein the conversion of the salt is incomplete.

16. A method of digitally printing a liquid toner dispersion, wherein use is made of a first member that rotates and is in rotational contact with a further member during printing, which printing method comprises the steps of:

charging a liquid toner dispersion as claimed in claim 1 to facilitate transfer thereof from the first member to the further member;

transferring the charged liquid toner dispersion from a surface of the first member via the at least one further member to a substrate, wherein excess liquid toner dispersion remains present on the first member after said transfer, and wherein the liquid toner dispersion is fused to obtain a fused film on the substrate, and;

removing, at least substantially, the excess liquid toner dispersion from the surface of the first member by means of a removal device.

17. The liquid toner dispersion as claimed in claim 1 , wherein the graft copolymer has a weight-average molecular weight in the range of 2500-10,000 g/mol.

18. The liquid toner dispersion as claimed in claim 10 , wherein the second hydroxylated fatty acid species has a degree of polymerisation of 1-3.

19. The liquid toner dispersion as claimed in claim 1 , wherein the oligomer of hydroxylated fatty acids is based on a hydroxylated fatty acid monomer with a chain length of 12-24.