In order to clarify undesirable molding phenomena in injection molding, it is important to measure melt pressure distribution on the injection mold cavity in detail. In a previous paper, we reported a new method for measuring melt pressure distribution on the injection mold cavity surface using a mold with a pressure transmission pin array and tactile sensor. In this study, we attempted to measure the variation of melt pressure distribution when the injection rate and the holding pressure are changed. The results indicate phenomenon in which pressure remains near the gate in the cavity until the instant the mold is opened. This phenomenon is considered to be due to the extreme increase in melt density from the filling process through the pressure holding process and cooling process, which causes the melt to cool and solidify before it can shrink adequately. Furthermore, it was also found that there exists a close relation between the thickness distribution, residual pressure distribution and birefringence pattern of molded products.

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We derived the theoretical formulas for three mechanisms of devolatilization in a twin screw extruder. These are flash, surface refreshment and forced expansion. The method for flash devolatilization is based on the equation of equilibrium concentration which shows that volatiles break off from polymer when they are relieved from high pressure condition. For surface refreshment devolatilization, we applied Latinen's model to allow estimation of polymer behavior in the unfilled screw conveying condition. Forced expansion devolatilization is based on the expansion theory in which foams are generated under reduced pressure and volatiles are diffused on the exposed surface layer after mixing with the injected devolatilization agent. Based on these models, we developed the simulation software of twin-screw extrusion by the FAN method and it allows us to quantitatively estimate volatile concentration and polymer temperature with a high accuracy in the actual multi-vent extrusion process for LDPE + n-hexane.

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It is very important to estimate the neck formation and neck propagation behavior of plastic molded materials in the field of polymer processing. In a previous paper, to evaluate the results on the neck formation and neck propagation behavior for polybutylene terephthalate (PBT) molding in uniaxial tensile test, a numerical model based on the Finite Element Method (FEM) was developed. However, there are some difficulties in determining material properties. In order to overcome them, the authors developed the determination technique for the material properties from not only load-displacement behavior but also the strain distribution around the necked region analyzed by Digital Image Correlation (DIC). Then, it was confirmed that the numerical results under the calculated elasto-plastic constitutive law show good agreement with both experimental load-displacement behavior and strain distribution around the necked region.

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Injection molding is used in various fields. Surface properties are an important subject and there are many reports on them. From the viewpoints of cost and productivity, the injection molding of multi-cavity injection die is used widely. However, there is no report on the research of surface properties in these injection moldings.
In this study, we observed surface state and measured surface roughness for the injection molding with emboss form on the surface and compared with surface state about molding conditions. Moreover, we carried out the optimization of runner design in consideration of simultaneous filling using injection molding flow analysis and considered the influence of runner balance on the surface state. High mold temperature improves surface properties for the whole injection molding. Short filling time improves surface properties for the portions do not require much packing pressure. The optimized runner balance can realize uniform surface properties in multi cavity injection die.

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The CAE method for the injection molding process is now used in the plastic industry for the purpose of predicting warp problems. But the accuracy of this is not good enough for the mold designer. We have proposed a theoretical method to predict anisotropic property distribution for the thermal expansion coefficient in the thickness direction. It was found that there is a good relation between the thermal expansion and the molecular orientations, and also between the thermal expansion coefficient and the energy of shear rate.
It is important to know the growing process of the solidified layer during the injection molding, to obtain the accurate flow mode as key information for CAE technology.
In this paper, visualization experiments were conducted on the effects of molding conditions on solidified layer growth. The results made the following points clear.
1) The effects of resin temperature and mold temperature on solidified layer growth are low.
2) Solidified layer growth changes depending on resin flow velocity in cavity during the injection molding.
3) Growth rate of solidified layer is affected by shear heat resulting from distribution of resin flow velocity. Therefore it is important to predict the shear heat for predicting the growth rate of the solidified layer.

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