| 摘要 |
PROBLEM TO BE SOLVED: To obtain an evaporable colorant having excellent heat stability and being desirable for use in a colorant evaporation type thermal recording system by purifying an evaporable colorant to a specified or lower lead content. SOLUTION: This colorant has a lead content of 50 ppb or below. The colorant is desirably has a nonionic structure and is exemplified by a methine colorant, an azomethine colorant, an azo colorant, a quinophthalone colorant, a coumarin colorant, an anthraquinone colorant or a fused polycyclic colorant. The colorant having a lead content of 50 ppb or below is produced by subjecting a colorant synthesized by a usual method to an advanced purification process such as recrystallization utilizing a solvent, a reprecipitation utilizing a solvent, column chromatography or evaporation purification and suitably selecting, for example, temperatures, pressures, atmospheres, solvents, and other conditions. Among the purification processes, column chromatography, evaporation purification, etc., are particularly effective. |
