Generation of pretilt angle in NLCs and EO characteristics of a photo-aligned TN-LCD with oblique non-polarized UV light irradiation on a polyimide surface

Abstract

We have investigated the generation of pretilt angle for a nematic liquid crystal (NLC) alignment in cells with oblique non-polarized ultraviolet (UV) light irradiation on polyimide (PI) surfaces. It was found that monodomain alignment of the NLC is obtained with an incident angle of 70 degrees and 75 degrees on the PI surface. It is considered that this alignment may be attributed to the anisotropic dispersion force due to photo-depolymerization of polymer on PI surfaces. Also, the generated NLC pretilt angles are all about 3 degrees at an incident angle of 70 degrees and 75 degrees for 1 h irradiation. Next, we observed that the voltage-transmittance characteristics for a photo-aligned twisted nematic (TN) LCD with an incident angle of 80 degrees on a PI surface were excellent. Also, we measured that the voltage-holding-ratio (VHR) of a photo-aligned TN-LCD is about 94%; it is almost same as obtained for rubbing-aligned TN-LCDs. Finally, the slow response time of photo-aligned TN-LCDs is attributable to their weak anchoring strength.