Clear ink composition, ink set, and method for producing inkjet record

1. A clear ink composition comprising water, a cationic resin and fine polymer particles, but no colorant, wherein the fine polymer particles form an emulsion in the clear ink composition and have an average particle diameter of 70 nm or less, and, wherein the fine polymer particles comprise a copolymer obtained by polymerizing an ethylenic unsaturated carboxylic acid monomer and another monomer copolymerizable therewith, in the presence of a copolymerizable surfactant or a water-soluble macromolecular compound containing alcoholic hydroxyl groups.

2. The clear ink composition according to claim 1 , wherein the glass transition temperature Tg, measured according to JIS K6900, of the fine polymer particles is 70° C. or less.

3. The clear ink composition according to claim 1 , wherein the pH of the copolymer is adjusted with the aid of a base.

4. The clear ink composition according to claim 3 , wherein the base is an inorganic base.

5. The clear ink composition according to claim 4 , wherein the inorganic base is an alkali metal hydroxide or alkaline-earth metal hydroxide.

6. The clear ink composition according to claim 1 , wherein the acid value of the copolymer is 40 or less.

7. The clear ink composition according to claim 1 , wherein the water-soluble macromolecular compound containing alcoholic hydroxyl groups is a vinyl alcohol polymer.

8. The clear ink composition according to claim 1 , wherein the ethylenic unsaturated carboxylic acid monomer is acrylic acid or methacrylic acid.

9. The clear ink composition according to claim 1 , wherein the other monomer copolymerizable with the ethylenic unsaturated carboxylic acid monomer is an ethylenic unsaturated carboxylic acid ester monomer.

10. The clear ink composition according to claim 1 , wherein the weight-average molecular weight (Mw) of the fine polymer particles is between 1000 and 1,000,000, inclusive.

11. The clear ink composition according to claim 1 , wherein the weight-average molecular weight (Mw) of the fine polymer particles is between 800 and 20,000, inclusive.

12. The clear ink composition according to claim 1 , wherein the pH of the fine polymer particles is between 8 and 11, inclusive.

13. The clear ink composition according to claim 1 , wherein the pH of the fine polymer particles is between 9 and 10, inclusive.

14. The clear ink composition according to claim 1 , wherein the turbidity of the fine polymer particles is 30 mg/L or less.

15. The clear ink composition according to claim 1 , wherein the minimum film formation temperature (MFT) of the fine polymer particles is 20° C. or less.

16. The clear ink composition according to claim 1 , wherein the content of the fine polymer particles in the clear ink composition is between 0.1 wt % and 5.0 wt %, inclusive.

17. A clear ink composition comprising water, a cationic resin and fine polymer particles, but no colorant, wherein the fine polymer particles form an emulsion in the clear ink composition and have an average particle diameter of 70 nm or less, and, wherein the fine polymer particles are fine polymer particles comprising a polymer that contains sulfonic acid groups.

18. The clear ink composition according to claim 17 , wherein the polymer that contains sulfonic acid groups is a polymer containing diene-based sulfonic acid groups and/or a polymer that contains non-diene sulfonic acid groups.

19. The clear ink composition according to claim 18 , wherein the polymer that contains non-diene sulfonic acid groups is a polymer containing acrylic sulfonic acid groups.

20. The clear ink composition according to claim 17 , wherein the acid value of the fine polymer particles is 100 or greater.

21. The clear ink composition according to claim 17 , wherein the weight-average molecular weight (Mw) of the fine polymer particles is between 8,000 and 20,000, inclusive, and the glass transition temperature (Tg; measured according to JIS K6900) is between 5° C. and 50° C., inclusive.

22. The clear ink composition according to claim 17 , wherein the minimum film formation temperature (MFT) of the fine polymer particles is 20° C. or less.

23. The clear ink composition according to claim 17 , wherein the content of the fine polymer particles in the clear ink composition is between 0.1 wt % and 5.0 wt %, inclusive.

24. The clear ink composition according to claim 1 or 17 , wherein the cationic resin is a resin that contains amino groups.

25. The clear ink composition according to claim 1 or 17 , wherein the cationic resin is polyethyleneimine.

26. The clear ink composition according to claim 25 , wherein the polyethyleneimine is a macromolecule containing at least one type of repeating units expressed by General Formula (1)

wherein R is hydrogen, an optionally substituted alkyl group, an optionally substituted aryl group, an optionally substituted pyridyl group, an optionally substituted alkylamino group, or an optionally substituted hydrazino group.

27. The clear ink composition according to claim 25 , wherein the weight-average molecular weight (Mw) of the polyethyleneimine is 100,000 or less.

28. The ink composition according to claim 1 or 17 , wherein the cationic resin is a polymer of a single monomer or a copolymer of a plurality of monomers comprising at least one compound selected from the group consisting of dimethylaminoethyl methacrylate (DM), methacryloyloxyethyl trimethylammonium chloride (DMC), methacryloyloxyethyl benzyl dimethylammonium chloride (DMBC), dimethylaminoethyl acrylate (DA), acryloyloxyethyl trimethylammonium chloride (DMQ), acryloyloxyethyl benzyl dimethylammonium chloride (DABC), dimethylaminopropyl acrylamide (DMAPAA), and acrylamidopropyl trimethylammonium chloride (DMAPAAQ).

29. The clear ink composition according to claim 1 or 17 , wherein the content of the cationic resin in the clear ink composition is between 0.1 wt % and 30.0 wt %, inclusive.

30. The clear ink composition according to claim 1 or 17 , further comprising an acetylene glycol compound, acetylene alcohol compound, or polysiloxane compound as a surfactant.

31. The clear ink composition according to claim 1 or 17 , wherein the surface tension is between 15 dyn/cm and 45 dyn/cm, inclusive.

32. The clear ink composition according to claim 1 or 17 , further comprising a glycol ether compound or alkyl diol compound.

33. The clear ink composition according to claim 32 , wherein the glycol ether compound is triethylene glycol monobutyl ether.

34. The clear ink composition according to claim 32 , wherein the alkyl diol compound is 1,2-hexanediol.

35. The clear ink composition according to claim 1 or 17 , further comprising a polyhydric alcohol compound.

36. The clear ink composition according to claim 35 , wherein the polyhydric alcohol compound is glycerol or ethylene glycol.

37. The clear ink composition according to claim 1 or 17 , used for inkjet recording.

38. An ink cartridge containing the clear ink composition according to claim 1 or 17 .

39. An ink set, comprising the clear ink composition according to claim 1 or 17 ; and at least a yellow ink composition, a magenta ink composition, and a cyan ink composition.

40. The ink set according to claim 39 , further comprising a red ink composition whose hue angle is the hue angle of a mixed color of the yellow ink composition and magenta ink composition.

41. The ink set according to claim 39 , further comprising a violet ink composition whose hue angle is the hue angle of a mixed color of the magenta ink composition and cyan ink composition.

42. The ink set according to claim 39 , further comprising a black ink composition.

43. A method for producing an inkjet record, comprising depositing the clear ink composition according to claim 1 or 17 , and a colorant-containing color ink composition on a recording medium to form a record.

44. The method for producing an inkjet record according to claim 43 , comprising ejecting the clear ink composition and the colorant-containing color ink composition during the same process.

45. The method for producing an inkjet record according to claim 43 , comprising depositing the clear ink composition such that, in portions in which the duty of the color ink composition on the recording medium is equal to or less than the target duty value, the sum of the duty value of the color ink composition and the duty value of the clear ink composition is equal to or greater than the target duty value.

46. The method for producing an inkjet record according to claim 45 , wherein the target duty value is 40%.

47. The method for producing an inkjet record according to claim 43 , comprising depositing the clear ink composition in the regions of a recording medium surface at a constant duty value irrespective of the duties of the color ink composition on the recording medium.

48. The method for producing an inkjet record according to claim 43 , comprising depositing the clear ink composition in the regions of a recording medium surface at a constant duty value of 20% or less irrespective of the duties of the color ink composition on the recording medium.

49. A record, on which recording is performed by the method for producing an inkjet record according to claim 43 .