To obtain an ink which can give an image having a high gloss and excellent resistance to smearing and water by using a dispersion of polymer particles containing an ionically modified pigment.

This ink comprises a dispersion of particles of an ionically modified polymer which is an ionomeric polyadduct or polycondensate containing a pigment and having, desirably, 4-180 milliequivalents/100 g of ionic groups or groups convertible thereinto. This is obtained by combining a dispersion of an ionically modified polymer obtained by reacting an NCO-containing prepolymer obtained from hexanediol/neopentyl glycol polyadipate and 1,6- diisocyanatohexane with sodium 2-aminoethyl-β-aminopropionate with a yellow pigment of the formula to form a pigment latex, adding an organic solvent such as diethylene glycol, a nonionic surfactant, and deionized water to the latex, and agitating the resulting mixture in an ultrasonic bath.