Abstract: The present invention relates to [1] a water-based ink containing water-insoluble polymer particles (A), an organic solvent (B) and water, in which a polymer constituting the water-insoluble polymer particles (A) is in the form of a crosslinked polymer; the organic solvent (B) contains a polyhydric alcohol ether; and a rate of change in viscosity of the organic solvent (B) as calculated according to the formula (1) is not more than 140%, and [2] a printing method of printing characters or images on a printing medium using the water-based ink described in the above [1], in which a water absorption of the printing medium per a unit surface area thereof as measured by contacting the printing medium with pure water for 100 milliseconds is not less than 0 g/m2 and not more than 10 g/m2.

Abstract: The present invention relates to an ink-jet printing method using an apparatus including a printing means for ejecting a black ink to a printing substrate to print characters or images on the printing substrate, and a drying means disposed on a downstream side of a transportation direction of the printing substrate, in which the printing substrate is a label printing substrate; the black ink is a water-based composite black ink; the water-based composite black ink contains a composite black pigment containing carbon black, and a content of the carbon black in the composite black pigment is not more than 25% by mass; and the drying means is an infrared heater for heating the water-based composite black ink ejected onto the printing substrate to a temperature of not lower than 95° C. and not higher than 125° C.

Abstract: The present invention relates to [1] a water-based ink for ink-jet printing containing titanium oxide (A) and a pigment dispersant (B), in which the pigment dispersant (B) contains a constitutional unit derived from an anionic group-containing monomer (a) and a constitutional unit derived from a polyalkylene glycol (meth)acrylate (b); an average molar number of addition of an alkyleneoxide in the polyalkylene glycol (meth)acrylate (b) is from 15 to 100; an acid value of the pigment dispersant (B) is from 100 to 400 mgKOH/g; and a content of the pigment dispersant (B) in the water-based ink is from 0.3 to 18 parts by mass on the basis of 100 parts by mass of the titanium oxide (A), and [2] an ink-jet printing method of ejecting the water-based ink described in the above item [1] onto a printing medium using an ink-jet printing apparatus to print characters or images on the printing medium.