Simultaneous retardation compensation during bending of plastic film coated with a polymer layer of opposite birefringence.
We proposed a method of eliminating the bending-induced retardation of a plastic film by coating it with a polymer layer with an opposite birefringence. We coated a polystyrene (PS) or a poly(methyl methacrylate) (PMMA) layer on a polycarbonate (PC) plastic film. The bare PC film is composed of main-chain-type polymers and showed an increase in retardation with bending. The main-chains of the PC polymer are reoriented along the circular arc direction during bending, resulting in a positive birefringence. In contrast, the 11 wt. % PS-coated and the 19 wt. % PMMA-coated PC films showed minimal change in the retardation regardless of the radius of curvature. The PS and the PMMA polymers are of the side-chain-type, and the side-chains were aligned perpendicular to the circular arc direction during bending, resulting in a negative birefringence. Consequently, the bending-induced retardation of the PC film can be compensated by the PS or the PMMA layer during bending of the film. This method of compensating for the bending-induced retardation of the plastic film can be useful for flexible display applications.
Evaluation of curving characteristics of flexible liquid crystal displays fabricated using polycarbonate substrates
The improvement of the contrast ratio of flexible liquid crystal displays (LCDs) fabricated using plastic substrates in a curved state is an important problem to achieve high-quality flexible LCDs. In this study, we evaluated the distributions of in-plane phase retardation and slow axis direction of polycarbonate substrates and the effects of curvature on the electro-optical properties of flexible LCDs. As a result, we clarified that the polycarbonate substrates have high uniformity in the in-plane phase retardation and slow axis direction, and that the change in the phase retardation of the polycarbonate substrate caused by the curvature deformation has a small effect on the electro-optical characteristics of flexible LCDs. We successfully achieved a high contrast ratio of by fabricating the device using polycarbonate substrates. This result indicates that it is possible to realize high-quality images in flexible LCDs fabricated using polycarbonate substrates even in the curved state.
Achromatic optical compensation using dispersion of uniaxial films for elimination of off-axis light leakage in a liquid crystal cell.
We propose an achromatic optical-compensation method using uniaxial films to eliminate the off-axis light leakage at the dark state in a homogeneously aligned liquid crystal cell. Three uniaxial films with different dispersion characteristics are used so that they can compensate each other to achieve achromatic effective phase retardation at off-axis. The retardation values are optimized with the aid of the Poincaré sphere and through numerical research. A contrast ratio of higher than 2000∶1 is predicted over the entire ±60° viewing cone for a homogeneously aligned LC cell with zero pretilt angle.