We proposed a new technique for stirring polymer melt in a mold by acoustic streaming to prevent formation of weldlines in injection molding process. We have demonstrated the generation of the acoustic streaming in high viscosity polymer melt. We radiated ultrasound in a disk-shaped mold to induce the acoustic streaming in the thickness direction of the mold. The acoustic streaming in the polymer melt was examined by observing, after cooling, the displacements of tracers in the cross section of the molded product. We have succeeded in generating the acoustic streaming in the polymer melt of 11000Pa·s in the mold. The acoustic streaming was, however, strongly affected by reflected waves from the surface of the melt. We have found that the acoustic streaming can be efficiently generated in the mold if the interference with the reflected waves are decreased by using a tone-burst ultrasound.

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The shrinkage degree ξ of polymer products must be considered when the molds are at the stage of designing. On the calculation of ξ, the descending temperature ΔT of polymer products after molding process and α (the coefficient of thermal expansion) are necessary.
It was found that α has the typical distributions at the various layers along the machine direction (MD) and the traverse direction (TD), especially under HDPE melts flow in the dies. Consequently, α distributions should be predicted for estimation of accurate ξ of HDPE products. In this study, we have investigated the experimental data of HDPE α distributions under extrusion process and calculated the strain distributions by polymer melts flow analysis using finite element method. The following results were obtained.
(1) The measured data of α (MD) distributions correspond to the strain distributions which generate along the flow direction within the inner and the outer die.
(2) The measured data of α (TD) distributions correspond to the strain distributions which generate along the θ direction within the inner and the outer die.
(3) The measured data of α distributions in this study showed the correlation between the strain distributions much better than the shear stress distributions.

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Transient elongational viscosity λ of supercooled isotactic polypropylene (iso-PP) was measured under constant strain rate γ. In addition to the rapid increase due to entanglement which is commonly observed in polymer melts, λ in the supercooled state showed another (much more rapid) increase due to crystallization. In the case of low strain rate, the time τ at which this increase of λ started was independent of γ. Under high strain rate, on the other hand, τ was inversely proportional to γ. This means that there is a critical strain (crystallization strain) γ_c at which crystallization starts. γ_c was about 3.7 in this study.

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In injection molding process, the molten resin flows speedy into the thin cavity and this causes high shear stress condition. In addition, the resin is rapidly cooled and solidified from the surface of the molded even if the molten resin flows in the cavity. It was reported that these phenomena result in the layered structure of the molded.
In this paper, the cross-sectional polarizing microphotograph of injection molded plates were analyzed for various molding condition so as to examine the effect of molding condition on the layered structure. In order to clarify the generating mechanism of layered structure, the observed layered structures were correlated with the solidified layer thickening process during injection molding and time dependence of maximum shear stress, which were obtained by the injection molding simulation. As a result, it was shown that the maximum shear stress occurred between the solid and liquid layers drastically changes when the thickening rate of the solidified layer changes discontinuously, and that the depth of the boundaries among the layers is in accordance with the depth at where the maximum shear stress changes drastically. These two facts enable us to conclude that the generation of the layered structure is dominated both by the changes of solidified layer thickening and by the maximum shear stress between the solid and liquid layers.

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Change of orientation distribution of whiskers in polystyrene-potassium titanate whisker composite melts under uniaxial elongational flow was studied by using wide angle X-ray diffraction. The orientation distribution had a single peak in the flow direction at all elongational strain rates, and the peak monotonously became sharp as elongational strain increased. The distribution was found to be strongly dependent on strain. These experimental results were compared with prediction of Jeffery theory. Although Jeffery theory does not take account of interaction among fillers, we found that tendency of the theory resembles to that of the orientation distribution under elongational flow even in high concentration systems.

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The objective of this research is the observation of fiber orientation for the whole of injection moldings, not a local observation. In this method, a remarkable point is using a degradation of the UV light level exposed. PPS/GF composite was exposed to accelerator weathering test about 400 hours. In this treatment, the surface was degraded, and fibers appeared on the surface. The phenomenon was observed on the whole surface of it. The fiber orientation of surface layer were observed using a optical-microscope. In this process, as a degradation of the surface of UV exposed was using, it is not under the effect of any plastics or any shapes. As there are no need of cutting or polishing for sample preparation, we can observe the fiber orientation of a curved surface, edge of a corner.

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For the analysis of the fiber orientation mechanism, it is very important to observe the dynamic behavior of fibers inside an injection mold. We have proposed a visual observation method utilizing a new Glass-Inserted Mold, in which two parallel glass blocks are fitted in the opposite faces of the injection cavity, across from each other. Using this method, we have attempted to directly observe the fiber orientation behavior during the cavity filling process of polystyrene with low fiber concentration of 0.1-0.2wt%. The results obtained through the visual analysis are summarized below.
(1) The back-lighting method utilizing Glass-Inserted Mold and Ni-coated tracer fibers is effective for the dynamic observation of the fiber orientation process.
(2) Based on the comparison between the analysis of molded products and VTR images, it has been confirmed that seven different orientation layers are obviously formed along the cavity thickness during the filling process under several molding conditions.
(3) The fibers in the frozen region are subjected to large extensional flow during the fountain flow process. In terms of the orthogonal layers, this frozen region can be classified into two fiber orientation layers: Skin layers-I and -II. As cavity thickness increases, the fibers in Skin layer-I tend to be strongly oriented towards the flow direction.
(4) In the flowing region, the fiber orientation angle is subjected to the influence of velocity profile along the cavity thickness. Core layer, in which most of the fibers are oriented perpendicular towards the flow direction, corresponds to a flat velocity region around the cavity thickness center. Intermediate layer, in which a considerable number of fibers are oriented towards the flow direction, corresponds to the steep velocity region appearing on both sides of the core layer.

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