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.
Elimination of light leakage over the entire viewing cone in a homogeneously-aligned liquid crystal cell.
We propose an optical compensation scheme that uses uniaxial films for perfect elimination of light leakage over the entire viewing cone in a homogeneously-aligned liquid crystal cell. Uniaxial films with different dispersion characteristics are used so that they can compensate one another to achieve achromatic optical compensation. Owing to the rotational symmetry of the polarization change on the S(2)-S(3) plane of the Poincaré sphere, we can eliminate the light leakage at all azimuth angles. The contrast ratio of the proposed configuration for white light is higher than 3000:1 at a polar angle of ± 85°, irrespective of the azimuth angle.
Optically Compensated In‐Plane‐Switching‐Mode TFT‐LCD Panel
An optically compensated in‐plane‐switching‐mode TFT‐LCD panel was developed. The panel has an optical compensation film between a liquid crystal layer and a polarizer, and shows a significantly high‐contrast viewing angle, good gray‐scale capability, small color shift, and a large tolerance for cell gap non‐uniformity compared with a conventional in‐plane‐switching‐mode LCD.