Abstract
The thermal dye transfer color ink, which is developed to have same sensitivity as the commercially used thermal recording paper for G-II type facsimile, is composed of dyes such as SOT-Blue 2, -Red 2G and -Yellow 5 with suitable binder polymers. However, the light fastness of these dyes are class 3 for Blue 2, class 4 for Yellow 5, and class 5 for Red 2G, respectively. Thus, it was necessary to improve the light fastness of these dyes, especially, for -Blue 2.
It have been known that the prevention of decolaration of dye is carried out either by the charge transfer complex or the enclosure compound of dyes. For none polar binder polymer such as PMMA, in which the dye is dissolved rather than dispersed, it is not possible to form CT-complexes and, therefor, improvement of light fastness is not observed. For polar binder polymer such as PVA, in which the dye and electron-acceptor particles are dispersed rather than dissolved, it was necessary to add electron-acceptor in amount of as large as 50% to form complexes. As regard to the formation of enclosure compound, the size of dye molecule is too large for cyclodexitrin to enclose the dye molecule, and, accordingly, the improvement in light fasness was not so remarkable.
