Effects of Copolyester/Polycarbonate Blend Composition on the Thermal Diffusivity of Dye Transfer Printing Tadakazu Miyata, 1 Kanako Inaki, 1 Junko Morikawa, 2 Rahmat Satoto, 2 Toshimasa Hashimoto 2 1 Advanced Technology Research Laboratory, Oji Paper Co., Ltd., 1–10-6, Shinonome, Koto-ku, Tokyo 135-8558, Japan 2 Faculty of Engineering, Tokyo Institute of Technology, 2–12-1, O-okayama, Meguro-ku, Tokyo 152-8552, Japan Received 17 March 2003; accepted 24 September 2003 ABSTRACT: The effect of the blend composition on the thermal diffusivity for blends of a poly(ethylene-co-cyclo- hexane 1,4-dimethanol terephthalate) (PETG) and a bisphe- nol-A polycarbonate (PC) that have been used as base films for a thermal dye transfer (TDT) printing system was exam- ined. The inflection point in the thermal diffusivity mea- sured by temperature wave analysis almost matched the inflection point of storage modulus measured by dynamic mechanical analysis. This result implied that the tempera- ture dependence of thermal diffusivity related to the change in the microstructure of the PETG/PC blend. Furthermore, the correlation between the printing sensitivity and the ther- mal diffusivity at the actual thermal head temperature of TDT printing was found. The thermal diffusivity increased with increasing PC content, while the printing sensitivity decreased. The PETG/PC blend film suitable for the TDT printing base film could be obtained by adjusting the PC content in the blend. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 72–76, 2004 Key words: blends; polyesters; polycarbonates; thermal dif- fusivity; thermal dye transfer printing INTRODUCTION A thermal dye transfer (TDT) printing system is a color hard copy process that is capable of producing near photographic quality images. In this process, a thermal head is used to transfer a dye from a color ribbon onto a receiver paper, as illustrated schemati- cally in Figure 1. It has been commercially used as video printers. A TDT printing sheet requires both good printing sensitivity and good heat resistance. Many patents and some papers concerned with the factors that determine printing sensitivities have been published. 1–3 One of the most important physical properties that influences the printing sensitivity is the thermal diffusivity of a base film. The dependence of printing sensitivity on the thermal diffusivity has been examined using the finite element prediction meth- od. 4,5 From this prediction, greater decrease of thermal diffusivity is necessary to achieve better printing sen- sitivity. In recent years, blends of poly(ethylene-co-cyclohex- ane 1,4-dimethanol terephthalate) (PETG) and poly- carbonate (PC) have been used as the base film for a TDT printing sheet. PETG has a good processing prop- erty, but a low Tg and a low softening temperature. It has been attempted to improve the poor heat-resis- tance of PETG by blending it with PC. It is well known that the thermal diffusivity of poly- mer blends depends upon the composition and the miscibility. 6–8 The miscibility can be assessed by the location of a peak top temperature of loss tangent (tan) measured by dynamic mechanical analysis (DMA), which is the most useful transition point in blend investigations. 9 The miscibility of PETG/PC blends was investigated by DMA in many re- ports. 10 –14 However, the correlation between the ther- mal diffusivity and the blend composition of PETG/PC blends has not been examined yet. In this study, the relationship between the blend composition and printing sensitivity was examined as a function of thermal diffusivity. First, the effects of blend composition on the dynamic viscoelasticity of PETG/PC blends and thermal diffusivity were inves- tigated by DMA and “temperature wave analysis” (TWA) method, which was proposed by Hashimoto et al. 15–19 to measure the thermal diffusivity. And the correlation between the printing sensitivity and blend composition was discussed in the case of applying these blend polymers to base films of a TDT imaging system. EXPERIMENTAL Materials PETG copolyester (Eastar PETG 6763, Mn = 26,000) was supplied by Eastman Chemical Company. It con- sists of cyclohexane dimethanol, ethylene glycol, and terephthalic acid in a molar ratio of approximately 1 / Correspondence to: T. Miyata (tadakazu-miyata@ojipaper. co.jp Journal of Applied Polymer Science, Vol. 92, 72–76 (2004) © 2004 Wiley Periodicals, Inc.