| 摘要 |
PROBLEM TO BE SOLVED: To obtain an evaporable colorant having excellent heat stability and being desirable for use in an colorant evaporation type thermal recording system by purifying an evaporable colorant to a specified total chromium and titanium content. SOLUTION: This colorant has a total chromium and titanium content of 5,000 ppb or below, particularly, 100 ppb or below. The colorant 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 total chromium and titanium content of 5,000 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, re-precipitation utilizing a solvent, column chromatography or evaporation purification. Among them, chromatography, evaporation purification or the like is particularly effective. In particular, evaporation purification is advantageous in that it can be practiced without using any solvent. |
