Novel polymer wide viewing angle compensation films for liquid crystal displays (LCDs)

We report on generating uniaxial negative birefringent compensation films, made of specifically designed polyimides. These polymers were synthesized via a polycondensation of dianhydride [such as 2,2'-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride] and 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl. The uniaxial negative birefringent (n(x) = n(y) > n(z)) polyimide substrates are achieved using a solution-casting method in conventional solvents, which exhibit the desirable optical phase retardation [(n(x) - n(z)) x d] values from 50 to 400 nm varying with the film thickness. In these polyimide films, the long chain rigid molecules adopt intrinsic planar orientation. In detail, the majority of phenylene-imide rings and phenylenes preferentially adopt nearly planar conformations parallel to the film substrate. In addition, these films also possess high transparency (or transmittance) and little color shift. The unique color dispersion curve indicates that this type of materials is very suitable for the applications in LCDs due to an excellent mimic for the retardation color dispersion curve with respect to LC molecules. Significantly low in-plane retardation (< 1 nm) allows this new technology based film to achieve sufficiently high contrast ratio while highly negative retardation dramatically suppresses the gray scale inversion to improve the viewing angle performance in a variety of new mode LCDs.