| 摘要 |
PROBLEM TO BE SOLVED: To obtain an ink excellent in dispersion stability, capable of suppressing the occurrence of clogging in a nozzle or a pen point and excellent in discharge stability by oxidizing a carbon black with ozone in the presence of water and specifying the value of the total acidic groups and active hydrogen content. SOLUTION: A carbon black is mixed with water and ozone is then introduced into the resultant mixture to carry out the oxidizing treatment of the carbon black. Thereby, the amount of the total acidic groups is regulated to >=0.5 μequ/m<2> and the active hydrogen content is regulated to <=2.0 mmol/g. Since an alkali metal and an alkaline earth metal in the carbon black are dissolved in water to deteriorate the oxidation efficiency of ozone, the contents thereof are preferably lower and <=1 wt.%. A carbon black having <=0.5 wt.% total content of sulfur and sulfur compounds expressed in terms of analytical value of the sulfur and <=1 extracted humic acid concentration expressed in terms of absorbance of an extracted liquid is preferably used. The amount of water is preferably (95:5) to (0.5:99.5) expressed in terms of weight ratio of carbon black to the water. The pH of the dispersion is preferably 2-10. |
