With its excellent color and tone reproduction, thermal dye transfer printing produces continuous-tone color images that rival silver halide photography. However, conventional thermal dye transfer images fade easily when subjected to light or heat. To solve this problem, we have studied a chelate compound system and have found that certain sets of azo dyes and transition metal cationproviding compounds produce dye-metal complexes, or “chelate compounds”, that provide exceptionally high image stability.
Takao Abe, Shigeru Mano, Yorihiro Yamaya, Atsushi Tomotake, "Termal Dye Transfer Printing with Chelate Compounds" in Journal of Imaging Science and Technology, 1999, pp 339 - 344, https://doi.org/10.2352/J.ImagingSci.Technol.1999.43.4.art00005