To obtain an aqueous pigment dispersion in which carbon black contained exhibits excellent initial and long-term dispersibility and an excellent dispersion stability by using a surface-modified carbon black prepared by wet oxidation with a hypohalogenous acid and/or its salt and by specifying the concentration of a divalent metal cation in the dispersion.
The concentration of a divalent metal cation in the aquous pigment dispersion is adjusted to 100 ppm or lower, preferably 50 ppm or lower. Calcium, manganese, and copper ions, etc., are listed as the divalent metal cation. Preferably, the surface-modified carbon black has an average particle size of 300 nm or lower and its content in the dispersion is 1-30 wt.%. Sodium hypochlorite is preferable as the hypohalogenous acid (salt). The dispersion is prepared by finely dispersing carbon black in water, oxidizing the carbon black with a hypohalogenous acid (salt), and adjusting the concentration of a divalent metal cation in the dispersion to 100 ppm or lower.
YAGYU TATSUYA
MURAI NOBUYUKI
MATSUI MAKIKO
