Dependence of the birefringence of polystyrene film on the stretching conditions.

We investigated the dependence of the birefringence of polystyrene (PS) film with a negative optical birefringence on the stretching conditions. We varied the stretching ratio (SR), stretching speed (SS), and stretching temperature (ST), and measured the inplane birefringence and the N coefficient of the PS film. The inplane birefringence was increased with greater SR and SS but decreased with greater ST. The N coefficient of the stretched PS film was around zero and showed similar dependence on the stretching conditions like inplane birefringence.