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Prediction of Molecular Orientation in Film Stretching Processes

The molecular orientation of plastic optical films was examined in this study. The target is to develop a method of predicting retardation and optic axes. In this study, we propose a mechanism for the molecular orientation, and a calculation method for these parameters. The method has two assumptions. One is that the retardation is proportional to the input energy going into the film, the other is that the retardation decreases owing to the successive relaxation effect. The increment vectors of an index ellipsoid and the total index were introduced to describe the molecular orientation behavior. These definitions enable us to relate finite element analysis (FEA) results of film stretching to the assumptions. The uniaxial stretching process is focused to examine the method of predicting the retardation. Although the method can also be used to predict optic axes, this issue will be discussed in a succeeding report. The results had good agreement with the experimental results. The method is potentially useful in predicting the optical properties of films in commercialized stretching processes, for example, the tenter stretching process.