Water-based ink composition, ink set and image forming method

1. A water-based ink composition comprising:

a water-based medium,

a colored particle containing a pigment and a water-insoluble polymer dispersant, and

a self-dispersing polymer particle containing a hydrophilic constituent unit, and a hydrophobic constituent unit derived from alicyclic (meth)acrylate, wherein

in the self-dispersing polymer particle, the content of the constituent unit derived from a styrene-based monomer is 10% by mass or less, the self-dispersing polymer particle is present in a form containing substantially no pigment, and the acid value (KOH mg/g) of the self-dispersing polymer is 25 to 100.

2. The water-based ink composition of claim 1 , wherein the self-dispersing polymer particle is a self-dispersing polymer particle in which the number of carbon atoms of an alicyclic hydrocarbon part of the alicyclic (meth)acrylate is 5 to 20.

3. The water-based ink composition of claim 1 , wherein the self-dispersing polymer particle is a self-dispersing polymer particle in which the content of the constituent unit derived from alicyclic (meth)acrylate is 20% by mass to 90% by mass in the polymer.

4. The water-based ink composition of claim 1 , wherein the self-dispersing polymer particle further comprises a constituent unit derived from (meth)acrylate having a chain alkyl group having 1 to 8 carbon atoms as a hydrophobic constituent unit.

5. The water-based ink composition of claim 1 , wherein the self-dispersing polymer particle comprises a constituent unit having a carboxy group as the hydrophilic constituent unit.

6. The water-based ink composition of claim 1 , wherein the average particle diameter of the self-dispersing polymer particle is 5 nm to 60 nm.

7. The water-based ink composition of claim 1 , wherein the water-based ink composition is an ink for inkjet recording.

8. The water-based ink composition of claim 1 , wherein in the self-dispersing polymer particle, the content of the constituent unit derived from the styrene-based monomer is 5% by mass or less.

9. The water-based ink composition of claim 1 , wherein in the self-dispersing polymer particle, the content of the constituent unit derived from the styrene-based monomer is 0% by mass or less.

10. The water-based ink composition of claim 1 , wherein the water-based medium contains a water-soluble solvent having a solubility parameter (SP value) of 27.5 or less at 90% by mass or more based on the entire water-soluble solvent, and at least one kind of compound represented by the following structure formula (1),

wherein l, m and n are each independently an integer of 1 or more, and represents l+m+n=3 to 15, AO represents ethyleneoxy (EO) and/or propyleneoxy (PO), and each AO in the (AO) l , (AO) m and (AO) n may be each the same or different.

11. The water-based ink composition of claim 1 , wherein the self-dispersing polymer particle is a self-dispersing polymer particle in which the alicyclic (meth)acrylate is at least one of dicyclic (meth)acrylate or tri- or higher cyclic (meth)acrylate.

12. The water-based ink composition of claim 11 , wherein the self-dispersing polymer particle is a self-dispersing polymer particle in which the alicyclic (meth)acrylate is at least one selected from isobornyl (meth)acrylate, adamantyl (meth)acrylate, or dicyclopentanyl (meth)acrylate.

13. An ink set comprising the water-based ink composition as defined in claim 1 .

14. A method for forming an image, comprising using the water-based ink composition as defined in claim 1 , or an ink set comprising the water-based ink composition as defined in claim 1 to impart the water-based ink composition to a recording medium.