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.

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The photoresponse of surface potential decay by the pulse illumination for the double layered organic photoreceptor was investigated. The decay curve by the light pulse depends on the transportation of charge carrier transport layer (CTL) and charge carrier generation layer (CGL), and injection from CGL to CTL The decay curve was separated into two parts. One is a straight decay part (A) after the light pulse is exposed. And, another is a gradual decay part (B) afterwards. Part (A) is formed by the packet movement of the carrier in CTL. Therefore, the decay depends on the velocity of the carrier and the amount of the carrier respectively. The velocity is controlled by the drift mobility of CTL. Mainly the voltage drop depends on the amount of the carrier of the boundary side in neighborhood of CTL and the carrier injection from CGL to CTL. In part (B) the decay is limited to the carrier tranportation of CGL and the carrier injection from CGL to CTL.

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Thickening a photoconductive layer in photoreceptors, we prepared a-Si:H photoreceptors with the high charging Potential (1090 V at 0.27 &mu:C/cm²) and the photosensitivity (1/E₅₀ = 10 cm²/μJ at 700 nm). These photoreceptors including carrier generation layer deposited by low deposition rate (2.5 μm/h) on a photoconductive layer deposited by high deposition rate (6.0 μm/h) show the great improvement of residual potential in the wavelength of 500 to 650 nm. The a-Si:H films using the carrier generation layer have lower hydrogen contents, smaller amounts of SiH₂ bonding, and narrower optical band gap than the a-Si:H using the other photoconductive layer. Also, these films show low defect densities as a result of ESR signal and decay properties of photocurrent.

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We have developed new phenolic compounds containing sulfur atoms used for the color-developers of the leuco-type thermosensitive papers.
The most valuable color-developer is a di-phenol which combines two 4-mercaptophenols with an alkylene group containing ether radicals.
The themosensitive paper using this color-developer has extremely high themosensitivity and high stability of the developed image.
In this paper, we report (1) Theoretical relationship between the thermosensitivity of the themosensitive paper and the ionization potensial of the color-developers and (2) Consideration to the reason why the colordevelopers with sulfur atoms having high-themosensitivity.

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