Concerning PBT (Poly butylene terephthalate) film with three kinds of crystallization induction time, the effect of the crystallization induction time on temperature dependence of storage modulus was investigated. The storage modulus above glass transition temperature ca. 40℃ was inclined to decrease seriously as the crystallization induction time was higher. The size of crystal and its deviation, which are influenced by the crystallization induction time, were seriously related to temperature dependence of storage modulus. Storage modulus of PBT molded under exposed temperature in use depended on the crystallization induction time.

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The dimensional accuracy of a molded product is an important element that determines qualities of parts and the development for high accuracy work has been researched. The new process "Precision injection molding by the cooling rate control" has been proposed to decrease the mold shrinkage ratio and to improve the dimension accuracy of molded products in this study. This method improved the crystallization of a resin while keeping pressure and holding the mold temperature after injection at a given mold temperature (i. e. initial mold temperature). Afterwards, leave a part of the molded product that requires high accuracy in the mold and cool it locally and rapidly. In this report, the shrinkage characteristics and the crystallinity were investigated when cylindrical parts were molded with polyphenylene sulfide (PPS). The results showed that the mold shrinkage ratio at rapid cooling is smaller compared to the ratio at normal cooling, and the rapid cooling method showed the improvement in the circularity of molded products, however the lower crystallinity and the water-pressure strength reduction were not caused. Therefore, this molding method was effective to improve the accuracy of molded products without the reduction in physical properties of PPS. On the other hand, the effect of the rapid cooling was limited in the case where the initial mold temperature is higher than the glass transition temperature (Tg), that is, Tg seems to have influence on the shrinkage characteristics of the product. The clarification of the mechanism should be solved in the future.

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