In order to carry out a curing reaction analysis of epoxy resin used as electrical insulators, the authors have previously reported kinematic and viscoelastic analyses in parts I and II of this series of reports. The space between two concentric iron cylinders was filled with epoxy resin and the circumferential strain on the outer iron cylinder surface was measured in part II. The results of a finite element model gave good agreement with the results of measurements during gelation. However, the model results showed poor agreement before gelation, probably because of the assumption of full adhesion between the epoxy resin and iron cylinders. In order to improve the agreement, two new adhesion models have been proposed for the epoxy-resin interface.
1) One model assumes that full adhesion is immediately achieved when the epoxy resin begins to gel. The calculated circumferential strain changes on the outer iron cylinder surface do not give good agreement with experimental values after gel initiation.
2) The other model assumes that adhesion is gradually formed as the epoxy resin gels. The calculated circumferential strain changes agree very well with experimental values.
These results indicate that adhesion between the epoxy resin and the iron cylinders is gradually formed. The temperature distribution of the epoxy resin during the curing reaction changes little with time. The internal stresses in the epoxy resin goes up because adhesion increases during the gelation process.

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Following the previous study, the resin temperature distribution through the thickness of a cavity was directly measured using an integrated thermocouple sensor. The following conditions were controlled in this study: (1) resin temperature and mold temperature, (2) surface roughness conditions and (3) cavity thickness.
The conclusions of this present study are the following:
(1) When the (incoming) resin temperature was raised at a fixed mold temperature, no peak was observed in the temperature distribution. However, when the mold temperature was appropriately adjusted at constant (incoming) resin temperature, a peak in the temperature distribution could develop. This peak was relatively insensitive to changes in the mold temperature.
(2) Adjustment of the cavity surface properties from a satin surface finish to a mirror finish did not change the location of the temperature peak, but did alter the temperature distribution in the region between the temperature peak and the cavity wall.
(3) When the cavity thickness was changed, the temperature peak was found to occur at the same distance from the cavity wall. It was also confirmed that the temperature distribution was relatively flat from the peak to the cavity wall.
(4) The conclusions from the previous studies and the above results clarify that the following five factors cause the temperature peak phenomenon: (1) the crystallization temperature “Tc” or viscosity properties near the glass transition point “Tg”, (2) latent heat, (3) thermal conductivity, (4) resin temperature and (5) cavity thickness.

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The material properties within injection molded products may display a distribution or anisotropy due to the influence of the resin flow velocity distribution profile and the cooling rate during the injection molding process. As a result, the products may warp. From the standpoint of production efficiency, it is very important to predict such warpage prior to the injection molding process, and injection molding CAE tools are widely used at present to conduct warpage analyses.
Warpage analysis techniques currently available do not provide sufficient accuracy because they cannot predict the distribution of material properties that occurs in the interior of injection molded products. This is especially true for thick injection molded products, which display a large distribution of material properties across their thicknesses. As that distribution is thought to affect warpage substantially, the accuracy of the warpage analysis presumably declines even further.
In this research, a thick flat plate was injection molded from a medium density crystalline polyethylene material, and the distribution of the thermal expansion coefficient was measured along the thickness of the molded part. The molecular orientation ratio and crystallinity were also measured and their correlation was examined in order to investigate a method for predicting the thermal expansion coefficient distribution. The results revealed that the thermal expansion coefficient displayed a large variation and anisotropy in the thickness direction and that the distribution correlated with the crystallinity. Moreover, using the thermal expansion coefficient data obtained by these measurements, a material property database was created for use in conducting warpage analyses that take account of the distribution of material properties along the thickness of injection molded products. A multi-layer analysis model was then used in an effort to improve warpage analysis accuracy. The results indicated that warpage analysis accuracy was improved, which shows that a multi-layer model that takes account of the distribution of material properties is effective in conducting more accurate warpage analyses.

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As a packaging material, plastic film is widely used in daily life to protect merchandise while improving their marketing appeal. There are many cases when the plastic film packaging is formed into bags by heat sealing the edges. In order to discuss the properties of the heat-sealed portion of these plastic film bags, oriented polypropylene film OPP and cast polypropylene film (CPP) were heat-sealed, and the strength and crystalline structure of the heat sealed regions were investigated. The strength was obtained from peel tests according to JIS Z 1707 and from tensile tests for circular notched specimens. The crystalline structure was analyzed by differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FT-IR). The crystallinity of the heat-sealed part affected the tensile strength. When the crystallinity of OPP was high, the strength obtained from the tensile test for circular notched specimens was high, and the relation between crystallinity and the strength could be established.

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