| 摘要 |
PROBLEM TO BE SOLVED: To provide an ink that gives sufficient optical density on both of a plain paper with high permeability and a plain paper with low permeability, and is further improved in resistance to bleeding and resistance to white blur.SOLUTION: The ink comprises a self-dispersion pigment, a surfactant, and a water-soluble organic solvent; and the ink has dynamic surface tension of, measured by a maximum bubble pressure method at 25°C, 46 mN/m or more at a life time of 50 msec, and 40 mN/m or less at a life time of 2,000 msec. The self-dispersion pigment includes a functional group containing a phosphonic acid group bonded to a particle surface, in which an amount of the functional groups introduced and bonded to the self-dispersion pigment is 0.33 mmol/g or less. The water-soluble organic solvent includes a water-soluble organic solvent (A); the water-soluble organic solvent (A) has a dissolution index of 0.8 or more with the surfactant; and the proportion of the water-soluble organic solvent (A) in the total content of the water-soluble organic solvent is 75 mass% or more. |
