US Patent 7135432 Direct thermographic materials with phenolic reducing agents

Non-photosensitive direct thermographic materials comprise a reducing agent that is a specific ortho-amino-phenol, para-amino-phenol, or hydroquinone compound. These compounds can reduce silver(I) ion to metallic silver to produce a dense black silver image under the short time and high temperature conditions that occur when using thermal print-heads during direct thermal printing. The materials are characterized by their calculated aqueous deprotonation and their calculated anion HOMO energies.