Late-News Poster: Effect of the Surface Anisotropy of a Rubbed Polyimide Film on Liquid Crystal Alignment Properties

Morphological and molecular orientational anisotropies of a rubbed polyimide film, which is a general alignment layer in a mass production of the 42 '' IPS-mode LCD, were analyzed. The results of our AFM (Atomic Force Microscopy) and XRR (X-ray Reflectivity) measurements of rubbed polyimide surface didn't show any morphological anisotropy between parallel and perpendicular to a rubbing direction. On the other hand, orientational anisotropy of polyimide chains on their surface was observed by a NEXAFS (Near Edge X-ray Adsorption Fine Structure) analysis. The reason for this is that the hardness of a polyimide film and the rubbing process in LCD manufacturing were optimized to minimize a rubbing scratch, which deteriorates an image quality if any. From these results, we imply that only molecular orientation without any morphological anisotropy at the polyimide surface is enough to attain LC (Liquid Crystal) alignment ability for currently mass-produced IPS-mode LCD products. In order to reveal the effect of molecular anisotropy on LC alignment properties, we enhanced the orientational anisotropy of polyimide chains by changing their molecular structures. We then confirmed that the increase of the orientational anisotropy could improve contrast ratio of a 42 '' IPS-mode LCD TV.