Flow-marks are known to occur due to inconsistent transcription with step-change portions for injection molding, in the step-change area and area opposite to it. It has been clarified that external defects such as these flow-marks are closely related to flow front behavior. The authors developed a rotary runner exchange system which is able to instantaneously switch between flow resins of two colors before the gate, and proposed a new visualization method which enables observation of the internal flow behavior. In this study, we focused on the asymmetric fountain flow behavior in the step-change portion in stepped cavity where cavity thickness changes from the thin part to thick part, and visualized the internal melt behavior near the stepped portion for GPPS. As a result, distribution of colored materials was seen corresponding to the generation of flow-marks at the side of the step-change portion. These colored materials were confirmed to be resins exposed to the outer surface of flow front by asymmetric diverging flow of high viscosity resins flowing near the skin layer of the step portion. And, this flow front was seen to contact the mold surface in the step-change portion, move as if sliding over it, and further elongate. Such flow behavior suggested that the rough surface of molded sample, which was formed by the above diverging flow, elongation, and sliding behavior, corresponded to the flow-mark generation area. This flow mark area spread down to the downstream side with increase in thickness of the thick cavity. This is because the position at which the flow front contacted the mold surface at the step-change portion was distant from the stepped corner. On the other hand, at the flat area opposite the step-change position, a large stagnant area was formed inside the flow front. The resin of shear flow area near skin layer in the thin part was found to ride onto this stagnant area, forming a pattern which turned back to the mold wall side.

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Degradation of ethylene-propylene-diene (EPDM) rubber seal used for supplying water system was investigated through nuclear magnetic resonance (NMR) spectroscopy and focused ion beam-scanning electron microscopy (FIB-SEM). The EPDM rubber practically was used for 3 years at 20-40°C in a city water system. The EPDM rubber before use was characterized by a solid state NMR spectrometer equipped with field gradient fast magic angle spinning (FG-MAS) probe. The change in surface morphology of the EPDM rubber after use was observed by SEM. The cross sectional depth image of the EPDM rubber was obtained by FIB-SEM, after cutting the EPDM rubber with the focused ion beam of Gallium. The distribution of metal ion in the cross section of the EPDM rubber was analyzed through energy dispersive x-ray spectroscopy (EDS). The degradation of the EPDM rubber was induced with the segregation of the metal ion such as Fe, Mg, and Si in the vicinity of the surface.

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In this study, a direct formation technique of the electrically conductive pattern was investigated on the surface of a polymeric material by using carbon dioxide laser irradiation. A small disk of molded polyacrylonitrile was used as a test specimen. The conditions of the laser irradiation required for both stabilization and carbonization processes of the polymeric material were determined by the thermal analysis of TG-DTA. A numerical simulation of temperature distribution around the laser irradiation point was performed to determine the conditions that can achieve the required temperature for the thermal treatment (stabilization and carbonization processes). The electrically conductive pattern of a straight shape having conductivity of 7.6 S/cm was formed by irradiating the laser to the sample surface that was stabilized in advance by the infrared furnace. However, the electrically conductive pattern could not be obtained because of a large quantity of decomposed gas generation, when the stabilization process was done by the laser irradiation. Therefore, the establishment of a method that can effectively remove decomposed gas from the polymeric material was indicated as an important issue to operate practically the present technique.

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