Patent ID: 7025817

Claim:
An ink, comprising water, a water-soluble coloring material having a molecular weight of 600 or less in a free acid form, at least two kinds of water-soluble organic solvents, and urea or a derivative thereof, wherein the ink satisfies conditions that: (1) the at least two kinds of water-soluble organic solvents show a vapor pressure lower than the vapor pressure of water at 25° C.; (2) when a comparison is made between a solubility of the water-soluble coloring material in each of the water-soluble organic solvents and a solubility of the water-soluble coloring material in water, the water-soluble organic solvents that satisfy the condition (1) include a water-soluble organic solvent A giving the solubility higher than the solubility in water and a water-soluble organic solvent B giving the solubility equal to or lower than the solubility in water; and (3) the solubility difference between the solubility of the water-soluble coloring material in the water-soluble organic solvent A and the solubility of the water-soluble coloring material in the water-soluble organic solvent B is 10% or more; and wherein the water-soluble coloring material is represented by the following general formula (I) in a free acid form: wherein m is an integer of 0 to 2, n is an integer of 0 to 1 where (m+n) is an integer of 1 or more.