Effects of Photoinitiators on Nonpolarized Ultraviolet Light Orientated Polyimide Alignment Films

In order to improve the photosensitivity of OD-HAB6-CA polyimide alignment film and reduce the irradiation time under nonpolarized ultraviolet light (NPUVL), three types of photoinitiators, benzophenone (BP), 1-hydroxycyclohexyl phenyl ketone (184), and 2,4,6-trimethylbenzoyl-diphenyl phosphine oxide (TPO), are doped into the OD-HAB6-CA film. The results show that when the irradiation time and addition amount are the same, the photosensitivity of the OD-HAB6-CA alignment film containing 184 is higher than that of the other two. When the content of 184 is 1 mol equivalent of OD-HAB6-CA, the OD-HAB6-CA alignment film can induce the uniform alignment of liquid crystals (LCs) after only 4 min of NPUVL exposure. In addition, after the addition of photoinitiators, the alignment films still had good surface properties and thermal stability. Furthermore, the pretilt angle of the LC cells does not change after the addition of photoinitiators, and it remains at about 0.5°.