Seikei-Kakou

The effects of injection molding conditions on replication, birefringence and optical properties of microscopic V-groove structures in injection molded parts were examined for polycarbonate (PC) with different molecular weight. For optical properties, luminance and its distribution at the surface of the V-groove were measured. The micro-scale structure size was a continuous V-groove of 20μm in depth and 50μm in width. For injection molding conditions, melt temperature, mold temperature, injection velocity and holding pressure were varied at three levels. Birefringence decreased according as the degree of replication increased at higher melt temperature and higher mold temperature. This trend was more remarkable when higher molecular weight PC was used. It was found that the contrast value of luminance increased in proportion to higher degree of replication, but not significantly to birefringence.

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Warpage is a serious problem for box-shaped injection molded products. In this study, we experimentally manufactured a mold in which sheath thermo-couples are installed at each part, to measure in-mold temperature distribution for various patterns of cooling channels and core inserts made of several materials. Using the mold, we investigated the correlation between temperature distribution and warpage, and then obtained the following results;
(1) A clear correlation between warpage and temperature difference from the movable mold and stationary one was verified.
(2) The increase in temperature difference brought about higher warpage. Furthermore, the decrease in temperature difference caused the warpage reduction by 20-30% when the arrangement patterns of cooling channels were changed.

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This paper deals with a fundamental study on the weld structure of thin-wall injection molded polypropylene plates. Effects of the mold temperature and plate thickness on the weld characteristics were investigated. In the experiment, several measurements were performed; distribution of the optical retardation, specific latent heat for fusion, V notch depth and width, and tensile strength of the specimen. The results indicated that the fountain flow of the melt occurred in the filling stage even with a plate thickness of 0.3 mm. It was also shown that molecular orientation in the weld region was relatively low. Thermal property measurement showed that crystallinity of the molded specimen was affected not only by the mold wall temperature but also by the plate thickness. Mechanical strength reduction by the existence of the weld was experimentally confirmed through the tensile test, and it was shown that the thin-wall polypropylene plate molded at high mold temperature broke from the weld region under small strain.

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