In this paper, weld line formation in injection molding is precisely studied with a high speed camera system and infrared thermography. In the filling stage of the injection molding process, polymer melt injected into the mold cavity is simultaneously cooled by the cold mold wall. As is generally known, viscosity of the polymeric material is a function of temperature and time. Therefore it is considered that weld line formation of molded products is not only governed by the melt flow condition during the filling stage, but also affected by the thermal history of the melt in the cavity. In this study, the flow condition and temperature distribution of the melt around an obstructive pin was visualized and measured with a high speed camera system and infrared thermography. Polystyrene was used as the molding material. In the experiment, transmission interference optics was used to visualize the melt flow with the camera system. The temperature distribution of the melt around the pin was measured with thermography. By using these equipment, the formation process of the weld line structure behind the pin and the effect of the molding conditions on the weld line shape were precisely investigated. As a result, it was clearly shown that the obstructive pin inserted in the mold cavity not only disturbed the melt flow condition, but also affected the temperature distribution within the melt. It was also found that the cross sectional shape of the V notch formed on the molded surface was governed by the temperature of the molded skin. It was experimentally confirmed that the size of the V notch was significantly reduced when the temperature of the skin was maintained above the glass transition temperature of the material.

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Injection compression molding process was applied to examine how controlled compression pressure can influence the crystallinity and light absorbance in poly (ethylene terephthalate) (PET). Several interesting results are obtained: (1) The crystallinity of molded parts was increased with increasing compression pressure in PET whereas it was decreased in PP. (2) It was possible to control the skin-core region and crystallinity in the core region by intentionally controlling the compression pressure during the solidification process. (3) The simulated crystallinity distributed in the thickness direction was in good agreement with experiment at various compression pressures. (4) Lambert-Beer's law was found to be applicable for the relationship between average crystallinity and light absorbance.

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We have developed the Ultrasonic Injection Molding (UIM) system as a precision injection molding technology, in which the ultrasonic vibration has been applied to injection molding. In general, a certain shape in minute scale is often transcribed on the surface of products in order to invest the polymer products with an optical function. In consideration of these applications, effectiveness of the UIM system for improving the degree of transcription of a minute shape (triangular pyramid of 70μm in height) was experimentally investigated in this paper under various mold temperature conditions. The results showed that the degree of transcription of the minute shape is improved markedly by the UIM system in comparison with the conventional molding at the same mold temperature, and that the mold temperature in UIM could be reduced about 20K in order to obtain the same transcription as in the conventional molding. The mechanism of the improvement of transcription in UIM could be attributed to the inertia force acting on the polymer melt due to ultrasonic vibration during the melt filling process. Namely, the inertia force due to ultrasonic vibration would stuff the resin into the minute part of mold surface. Furthermore the local heating of resin due to absorption of the ultrasonic vibration was considered to be another mechanism of the transcription improvement during the packing-holding process. Heating due to absorption of ultrasonic vibration, which is evident especially in the region between molten- and solidified-layers would result in reduction of deformation resistance of the solidified layer, and thus the transcription due to packing-holding pressure would be helped by the UIM.

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A high level cleanliness is required in polymer processing environments in order to obtain reliability in advanced applications for plastic components such as packages of electronic devices and optical elements. It is important to know contamination particle behavior during injection molding machine operations. From the view point of practical research, the actual movements of articles originating in the sliding elements of the machine were measured in the processing environment. Particle movements were theoretically analyzed using aerodynamics and numerical analysis methods of air turbulent flows and particle concentrations. Comparing these calculated results for particle concentration with those from particle number measurements, the proposed numerical analyses were confirmed to be effective for use in contamination control during polymer processing environments. Furthermore, it was suggested theoretically that heat convection around heated molds was closely related to movements of small sized particles, and was one of the important factors for realization of cleanliness in polymer processing environments.

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The shearing operation is the most important factor in the screw plastication process. In order to clarify the shearing operation along the screw axis, we developed an experimental screw and measurement system, for measuring the torque profiles in the axial direction of the screw. The experimental screw was divided into several segments along the axial length, and each segment had strain gauges attached to the inner-hole surface. Using this equipment, the torque profiles and torque deviation profiles in the axial direction of the screw were measured during the plastication of polypropylene. The validity of this method was also confirmed. The observed results corresponded exactly to the polymer melting behavior observed by dynamic visualization using a visual heating cylinder. In particular, the effects of the melting behavior, such as the variation of the solid-bed ratio, the break-up phenomena, and the change of the relative position between the screw and the area where melting starts on the transition of the screw torque profiles during the reciprocating plastication process were investigated. Further studies such as quantitative analyses of the plastication phenomena using different screw configurations by combining with the visualization technique are planned.

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In the injection molding of an optical disk, a precise minute pit pattern is transcribed from a nickel sheet stamper in 0.3mm thickness. Various defects or mis-transcriptions are sometimes generated, but the causes of these defects have not yet been completely clarified. Thus ideal molding conditions and optimum mold designs can not be precisely determined.
In this paper, the injection molding of an optical disk for a sample-servo-type application is performed by using an injection-compression molding system and the generation mechanism of transcription defects was studied. The following conclusions were obtained.: (1) Mis-transcriptions are classified into three types; multiple transcription errors, scratches in radial directions and scratches in other direction. Their occurrence is affected by the compression pressure holding time and mold temperature. (2) In the case of rather low mold temperatures, multiple transcription errors occur when the compression time is short, but scratches occur when the compression holding time is long. (3) A relative displacement of the polymer molding from the stamper cccurs when a cooling time is longer than 10s, which results in multiple transcription error.

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