| 摘要 |
PROBLEM TO BE SOLVED: To obtain an ink excellent in dispersion stability, suppressing the occurrence of clogging in a nozzle or a pen point and excellent in discharge stability by removing sulfate ions from an aqueous dispersion of a carbon black and specifying the total acidic groups, the active hydrogen content of the carbon black, pH, etc., of a dispersion. SOLUTION: An aqueous dispersion of a carbon black is passed through an ion exchange resin, etc., to regulate the content of sulfate ions in the aqueous dispersion thereof to <=20 ppm or a carbon black with an ultralow content of sulfur is used to prepare a dispersion. The total acidic groups in the carbon black are regulated to >=3 μequ/m<2> to improve the dispersibility in an aqueous medium. The active hydrogen content in the carbon black is preferably <=2.0 mmol/g. Thereby, the carbon black is subjected to an oxidizing treatment in the presence of water. The pH of the aqueous dispersion of the carbon black is preferably regulated to 5-10. The content of the carbon black in the aqueous dispersion is preferably 0.5-50 wt.%. |
