Industrial deinking of ink compositions

1. An ink composition comprising pigment particles and a stimulus responsive dispersing agent for dispersing said pigment in a protic polar solvent, which stimulus responsive dispersing agent comprises: an anchoring part for anchoring to a pigment particle,

a hydrophilic stabilization part for solvent stabilization of the pigment, and

a stimulus responsive part provided with a photolabile group, which stimulus responsive part initiates upon exposure to a stimulus being UV-light, decomposition of the stimulus responsive dispersing agent into a first agent comprising the anchoring part and into a second agent comprising the hydrophilic stabilization part,

wherein the photolabile group is a combination of a benzoyl-group and a polar group in the α-position to the carbonyl of the benzoyl-group, which combination corresponds to the structural formula XXa or XXb:

wherein

R 1 -R 8 are substituents or hydrogen;

at least one of R 1 -R 3 in formula (XXa) contains a heteroatom chosen from O and N bonded to the carbon atom in the α-position;

the stabilizing part and the anchoring parts are bonded to the shown stimulus responsive part on opposed sides of the said combination.

2. The ink composition according to claim 1 , wherein the photolabile group is selected from the group consisting of:

2-phenyl-2-hydroxy-1-phenylethanone moiety;

2-oxo-1,2-diphenylethyl formate moiety;

hydroxyacetophenone derivative;

alkylaminoacetophenone derivative;

benzyl ketal derivative

a benzoylphosphinoxide;

a benzoylphosphinate; and

a bisacyl- or bisbenzoyl phosphine oxide.

3. The ink composition according to claim 1 , wherein the anchoring part comprises an elongated chain with a chain length of at least 8.

4. The ink composition according to claim 3 , wherein the anchoring part comprises a polymer material.

5. The ink composition according to claim 4 , wherein the anchoring part is attached to the phenyl ring of the benzoyl group.

6. The ink composition according to claim 1 , wherein the hydrophilic stabilizing part comprises a polyalcohol group.

7. The ink composition according to claim 1 , wherein the hydrophilic stabilizing part comprises a polar group or a charged group.

8. The ink composition according to claim 7 , wherein the charged group is an acid anion.

9. The ink composition according to claim 1 , wherein at least one of R 1 and R 2 contains a phenyl-group.

10. The ink composition according to claim 9 , wherein said phenyl group is substituted with either the anchoring part or the stabilizing part.

11. The ink composition according to claim 1 , wherein the stimulus responsive dispersing agent comprises two or more stimulus responsive parts.

12. The ink composition as claimed in claim 1 , wherein the stimulus responsive part comprises a benzoine derivative comprising the structural formula (I) or (IV), wherein R 1 , R 2 are electron-donating groups, X comprises the hydrophilic stabilizing part and R 3 and/or R 4 form part of or comprise the anchoring part:

13. The ink composition as claimed in claim 1 , wherein the stimulus responsive part comprises a benzoine derivative comprising the structural formula (I) or (IV):

wherein R 1 ,R 2 are electron-donating groups, X comprises the anchoring part and R 3 and/or R 4 form part of or comprise the hydrophilic stabilizing part.

14. The ink composition as claimed in claim 1 , wherein the protic polar solvent is a solvent mixture of water and one or more alcohols.

15. The ink composition as claimed in claim 1 , wherein the photolabile group is a combination of a benzoyl-group and a polar group in the α-position to the carbonyl of the benzoyl-group according to the structural formula XXa:

wherein

R 1 -R 8 are substituents or hydrogen;

at least one of R 1 -R 3 contains a heteroatom chosen from O and N bonded to the carbon atom in the α-position;

the stabilizing part and the anchoring parts are bonded to the shown stimulus responsive part on opposed sides of the said combination.

16. The ink composition as claimed in claim 1 , wherein the photolabile group is a combination of a benzoyl-group and a polar group in the α-position to the carbonyl of the benzoyl-group according to the structural formula XXb:

wherein

R 1 -R 7 are substituents or hydrogen;

the stabilizing part and the anchoring parts are bonded to the shown stimulus responsive part on opposed sides of the said combination.

17. A method for printing the ink composition according to claim 1 , comprising printing said ink composition onto a substrate.

18. The method according to claim 17 , further comprising a step of decomposing the stimulus responsive dispersing agent into the first agent comprising the anchoring part, which is a hydrophobic moiety, and the second agent comprising the hydrophilic stabilization part.

19. The method according to claim 18 , wherein the printing comprises an application step and a drying step and wherein the decomposition step occurs (i) after application before drying of the ink composition (ii) after application and drying of the ink composition or (iii) wherein the decomposition step is initiated by exposure to irradiation upon start of the application step.

20. The method according to claim 17 , wherein the substrate is paper.

21. Paper with a print with the ink composition as claimed in claim 1 .

22. A method of industrial deinking of the paper as claimed in claim 21 during recycling of paper, wherein the ink is separated from paper pulp so as to obtain an uncolored white paper mass suitable for reuse.

23. The method as claimed in claim 22 , wherein a decomposition step of the stimulus responsive dispersing agent of the ink composition is carried out at a start of an industrial deinking process by applying UV-light as a stimulus.

24. The method as claimed in claim 22 , wherein the industrial deinking comprises the steps of:

mixing paper with water and detergent;

applying mechanical energy to make a paper pulp;

increasing a pH level of the paper pulp to between pH8-9;

floating the paper pulp, so as to separate an ink-containing foam from a pulp mixture; and

skimming away the ink-containing foam.