成形加工

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Poly (ethylene terephthalate) (PET) foam was produced with a batch-wise method using carbon dioxide and nitrogen as physical blowing agents. Saturation pressure and temperature dependence of the foam structure was investigated. Solubility of the gases in PET and crystallinity of the PET induced by gas sorption were also investigated. PET foamed with CO₂ at 323K and pressures higher than 10MPa had very fine cell structure (cell number density of 10¹²cm^-3 and average cell diameter of 0.4μm). On the other hand, pressure dependence of the cell structure foamed with N₂ was similar to results of amorphous polystyrene foam, whose cell structure became fine with increasing pressure. Volumetric expansivity of the PET+CO₂ system rapidly decreased with increasing pressure, whereas that of the PET+N₂ system gradually increased with increasing pressure. Cell structure foamed with CO₂ became coarse with increasing saturation temperature. In the case of N₂, saturation temperature dependence of cell structure was not observed at higher than 400K regardless of the solubility increase. These results suggested that cell structure and volumetric expansivity related not only to crystallinity but also to crystalline structure.

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In general, warpage of injection molded parts is greatly affected by part design and molding conditions. Since the mechanisms of warpage are complicated, the ability to predict and avoid warpage is very difficult and has not yet been established. When parts are designed in 3-D, it is especially difficult to predict and take effective counter measures against warpage.
In this study, numerical warpage analysis and molding tests of plastic parts with large radii of curvature were carried out. Warpage for several patterns of molding parameters were compared for analysis and actual molding tests. Our results show that the amount of warpage predictd by the analysis was larger than that in the actual molding for all molding parameters tested. The differences between analytical and actual warpages correlated with initial warpage, which occurred just after the molded part was taken out from the tool.

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Theoretical and experimental studies on the dynamics of water-quenched air gap melt spinning were performed. The calculated spinning tension in the air region increases rapidly with decreasing air gap length. In particular, in the case of air gap lengths less than 2cm, high spinning tension can be obtained. It might be thought that high spinning tension during the spinning process leads to high molecular orientation of super fibers such as Aramid fibers. The maximum deformation rate in spinning processes with narrow air gaps appears at the boundary between air and water, which may be also related to the development of high molecular orientation.
Draw resonance experiments were performed using air gap melt spinning on Poly (ethylene terephthalate). With decreasing air gap length, the draw resonance instability was suppressed. This might be related to the results of numerical simulation in which larger Weissenberg numbers in the draw resonance analysis for the Maxwell fluid model and higher spinning tension in the air in the case of short air gap lengths lead to the stabilization of the spinning process.

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