Reduction of mold release failure using directional solidification in large-area injection molding of micro shapes

Abstract

In reproducing large-area micro shape by injection molding, one of the biggest problem is that the difference of thermal contraction between the mold material and the resin causes a residual stress in the product, and it becomes difficult to release the product from the mold. In this paper, the authors propose a new method which is called ‘directional solidification method’ for solving the problem. The method can reduce the thermal contraction of the product and the releasing resistance by letting the resin solidify sequentially from one end of the cavity toward the another end. In order to realize the method, the authors developed a mold which can make a temperature gradient, and realized the directional solidification of the resin. Using the mold, we reproduced plate-shape products which has micro shapes on their surfaces under two molding conditions such as uniform temperature and temperature gradient. The experimental results showed that the resistance under temperature gradient was 12% lower than under uniform temperature. Through this experiment, it was confirmed that the directional solidification method improved releasability of the products with micro shapes on their surfaces.