We have designed and synthesized various diphenylether diazonium salts to produce a new fixable red-color-forming diazonium salt. The 4′-n-butyl-4-diazodiphenylether hexafluorophosphate (DED-PF6) obtained forms a vivid red color azo-dye, can be decomposed by 310-nm UV light, and shows good thermal stability. Combined with another commercially available diazonium salt, fixable black-red dual-color thermal recording (DCTR) was achieved. In red printing, the DCTR media allows additional recording and, when necessary, can be fixed by 310-nm UV light exposure. The DCTR is composed of only a single recording layer, which simplifies the manufacturing process compared to multi-layered recording media. DCTR also simplifies the printer mechanism, because it is not necessary to change the temperature of the thermal head between black printing and red printing; simply adding a fixing lamp to a conventional thermal printer is enough for DCTR.
Takeshi Koyano, Katsuaki Kaifu, Fumio Nakagawa, Takahiro Ootomo, Sadao Sone, Masanaka Shibusawa, Haruo Kimura, "Dual Color Direct Thermal Recording Using Diphenylether Diazonium Salt" in Journal of Imaging Science and Technology, 1998, pp 445 - 449, https://doi.org/10.2352/J.ImagingSci.Technol.1998.42.5.art00014