Thermal transfer printing with heat amplification

Abstract

Incorporation of certain thermally labile additives into thermal transfer printing ink formulations is found to cause considerable improvement in printing efficiency. The additives were specifically selected to be labile at temperatures just above the melting point of the inks, but undergo molecular transformation or decomposition in unimolecular processes accompanied by exothermicity and at the same time are stable in the ambient. During the printing cycle, the heat released due to thermally induced reactions of the additives is superimposed on the energy supplied by the printing head, with consequent reduction in the input power requirement. Thus, the process has been termed heat amplification. Among the various systems studied, p-azidobenzoic acid, 1,2,3-dicarboxyquadricyclane, 2, and 1,1′-azobis((N,N′-dimethylformamide), 3, were found to be most suitable for practical applications from the chemistry and toxicity considerations. When tested in the Ames mutagenicity assay, Compounds 1 and 2, as well as their corresponding thermal decomposition products, showed a negative response toward Salmonella typhimurium TA-100 and TA1535 with and without metabolic activation. Thermogravimetric analysis and differential scanning calorimetry show that these compounds undergo decomposition/structural changes at 189.9°, 178.3°, and 207.3°C, with enthalpies of 125, 68, and 32.3 KJ/mol, respectively.