Phenolic Polymer-Based Color Developers for Thermal Papers: Synthesis, Characterization, and Applications

The demand for urgently replacing the problematic 4,4'-(propane-2,2-diyl)diphenol (BPA) color developer in thermal papers is increasing recently. In order to develop alternative color developer materials to BPA, novolac-type polymeric developer materials that not only exhibit excellent color-developing performance but also are difficult to be absorbed by the human skin were introduced. The target novolac polymers, BPAEP-FN, were synthesized by copolymerizing BPA and 4-ethylphenol monomer with various ratios. Among the prepared BPAEP-FN polymers, the BPAEP-FN_64 polymer showed highly improved static sensitivity as compared to a simple BPA-novolac polymer that contained no 4-ethylphenol at all. Moreover, it is possible to effectively adjust the static sensitivity of BPAEP-FN_64 thermal papers by using sensitizers such as diphenyl sulfone and 4-benzylbiphenyl and we are able to obtain static sensitivity similar to that of BPA thermal papers. In particular, BPAEP-FN_64 thermal papers showed superior durability to BPA thermal papers under harsh thermal conditions of the external environment.