Abstract
In this study, we investigated the development of morphology during injection molding and the relationships between molding condition and morphology. Two types of spiral flow: “closed spiral flow” and “open spiral flow” were used in this study. The moldings with closed spiral flow pass through filling, packing and cooling stage, and the moldings with open spiral flow pass through only filling and cooling stage. The morphology and cavity pressure during molding of the two spiral flows were examined in order to establish the development of morphology. The molding condition was changed by cylinder temperature, mold temperature, and injection speed. The relationship between molding condition and variation of morphology was investigated. Three types of morphology were observed: a skin layer, a “microcrystalline layer”, and a spherulitic core. A transcrystal was observed at the end of the moldings and at low flow rates. The skin layer become thickr when the cylinder temperature and mold temperature were low. The extension of microcrystalline layer greatly depends on the flow time. Effects of the cylinder temperature, mold temperature, and injection pressure on crystallite sizes of spherulite cores were small.
