Simulating Stress Relaxation Effects for Sequential Biaxial Stretching of Optical Films in a Tenter

Control of the sequential orientation (tenter) process for optical films is one of the most important factors in developing the retardation films which are needed for large sized liquid crystal displays (LCD). Analysis to predict the thickness distributions and bowing phenomenon during the tentering process is performed by finite element analysis (FEA). In addition, this study provides a new calculation method to predict the optical axes of stretched films from elastoplastic FEA results. The optical axes have two components. One is a stress-dependent term and the other is a strain-dependent term. To predict the molecular orientation, time-dependent effects are concerned with both. Moreover, polymer relaxation processes are examined. The FEA and optical property calculation are independent in the methods. This method enables one to easily calculate optical axes of films during the tentering process without a change of the conventional FEA calculation process.