Generation of Pretilt Angle of Liquid Crystals Aligned on Organic-Solvent-Soluble Polyimide Alignment Films for Active-Matrix TN-LCDs and its Mechanism Caused by the Micro-Surface Structure of Surfaces

Abstract

The increasing of pretilt angles of liquid crystals (LCs) in active-matrix twisted nematic liquid crystal displays (AM-TN-LCDs) is one of the most important subjects to achieve high contrast and defect-free AM-TN-LCDs. We have developed the new generation method of the pretilt angle by using newly synthesized organic-solvent-soluble polyimides (PIs) containing two types of diamine. These PIs are useful in the production process of AM-TN-LCDs due to their low temperature process, say 180°C. The maximum pretilt angle of 2.8° for an NLC, ZLI-1565, is obtained using the PI containing two types of diamine with a mole fraction of 50/50. This phenomenon can be explained on the basis of the micro-topography of the PI surfaces and, in particular, the obtained pretilt angles may be attributed to the relative bulkiness of diamines used in the PIs.