射出成形品に生ずる物性値分布の予測手法の検討(2)

射出成形中の板厚方向の樹脂流速分布と分子配向度の関係

抄録

The prediction of anisotropy of the thermal expansion coefficient and its distribution in molded products is important to improve the accuracy of numerical simulation for product warpage.
We have previously proposed a prediction method whereby the molecular orientation of each layer of a molded product is found from the shear stress distribution produced by the resin flow velocity distribution during molding. The anisotropy of the thermal expansion coefficient and its distribution in the thickness direction are then predicted from the molecular orientation ratio distribution. When this method was used to examine the molecular orientation ratio and the anisotropy of the thermal expansion coefficient of a non-crystalline material, it was shown that a good correlation exists between the two.
The aim of the present research was to examine a method of predicting the molecular orientation ratio distribution in the thickness direction of a molded product, which is induced by resin flow. Detailed measurements were made of the resin flow velocity in the thickness direction of a molded product during the molding process using a visualization mold and the PIV method. The measured data were used to calculate the shear stress distribution, and a comparison was made with the molecular orientation ratio distribution of the molded product. The results made clear the following points.
(1) The maximum shear stress calculated from the resin flow velocity distribution was the smallest near the surface of the molded product and the shear stress increased toward the center of the product.
(2) The molecular orientation ratio of each layer of the molded product was determined by the impulse produced under the impact of shear stress during the molding process and correlated well with the tendency for shear stress to increase toward the center of the product.
These results indicate that the molecular orientation ratio can be predicted from the distribution of the resin flow velocity and that the thermal expansion coefficient, which shows a good correlation with the molecular orientation ratio, can be predicted from the resin flow velocity distribution.