Liquid Crystal Alignment at Low Temperatures in Flexible Liquid Crystal Displays

We report on the pretilt angles of liquid crystals (LCs) at a low baking temperature (120°) and on the retardation values with a high birefringence and low cell gap, both of which showed significant improvement in their response time for flexible super twisted nematic cells. Three different types of polyimides (PIs) were used to control the pretilt angle from 9° up to about 40°. A low baking temperature for the PIs with alkyl side chains induced a high pretilt angle. The pretilt angles of the PI-A having alkyl chains and similar LC phases increased rapidly up to 40° after aging , while the pretilt angles of the PIs with normal alkyl chains decreased. Due to the high birefringence, a low cell gap, and a high pretilt in the flexible display, a fast response time (25% reduction) and low switching voltage (52.8% reduction) are demonstrated.