| 摘要 |
PROBLEM TO BE SOLVED: To obtain the subject excellent pigment excellent in initial dispersibility and long-term dispersibility to water or organic solvents and hardly causing aggregation of pigment particles by treating particle surface of an organic pigment with sulfur trioxide complex by a specific method. SOLUTION: An organic pigment (preferably having 10-0.05μm particle diameter) is dispersed into a basic solvent forming a complex with sulfur trioxide and sulfur trioxide is added thereto to treat particle surface of the organic pigment. For example, N,N-dimethylformamide, dioxane, pyridine, etc., can be used as the basic solvent. When the pigment is an insoluble or slightly soluble solvent having no reactivity with sulfur trioxide, the solvent can combinedly used with the basic solvent. A solvent capable of combinedly using with the basic solvent includes e.g. sulfolane or N-methylpyrrolidone.
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