| 摘要 |
PROBLEM TO BE SOLVED: To provide a C. I. Pigment Yellow 191 mixture containing β, γ, δor ε polymorph, or a mixture of two, three, or four of them, at least 10%, preferably 25%, more preferably 50%, most preferably 75%, and a method of its preparation. SOLUTION: These crystal polymorphs of β phase, γ phase, δ phase, and εphase are obtained by acting a solvent selected from the group consisting of diethylene glycol dimethyl ether, N-methyl pyrrolidone, dimethyl sulfoxide, ethylene glycol, dimethylacetamide, and dimethylformamide on a compound represented by formula (1), or a tautomer, cis/trans isomer, or tautomeric cis/ trans isomer, and reprecipitating it. |
