Prediction of birefringence in plastics optical elements using 3D CAE for injection molding

Recent improvements of plastics optics performance and manufacturing technology of plastics lenses have resulted in rapid application of plastics optical elements. One of the factors in delaying the applications of the plastics optical elements is the existence of birefringence in plastics lenses. It gives us a challenge to resolve the problem so that the plastics optical elements can achieve much higher levels of performance. It is generally recognized that the mechanism of birefringence generation is relevant to the resin behaviors during the injection molding process. If this mechanism is fully understood by now analysis, it may be a great contribution to the fabrication of plastics optical elements. However, conventional two-dimensional now analysis on injection molding fails to grasp the phenomena of birefringence. In this paper, we have successfully identified some phenomena on injection molding that are closely related to the generation of birefringence. We analyzed the phenomena in details in filling, packing, and cooling processes during the injection molding process using three-dimensional CAE system, called 3D TIMON. The analyzed results were confirmed experimentally and they enabled us to predict the generation of birefringence by CAE analysis.