A Novel Polyimide Alignment Film Material for Mura Improvement of Liquid Crystal Display

In fringe field switching (FFS) displays, the polyimides (PI) normally possess no side-trains to guarantee the low pre-tilt (typically <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$&lt;0.2^{\circ}$</tex>), and the photolysis type under 254 nm linear polarized ultraviolet (UV) light is the dominant process. The photolysis product was removed during the subsequent oven processing at temperature exceeding <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$200{ }^{\circ} \mathrm{C}$</tex>. However, if the residues remain, they will adversely affect the liquid crystal alignment and the liquid will be disordered around the residues, causing light leakage in the dark state (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$L 0$</tex>) of the display panel, which is called crushed bright spot mura. In this paper, we addressed the issue of broken bright-point mura through three approaches. A novel polyimide incorporating a low-molecular-weight diamine was developed, the exposure dose of UV intensity was optimized, and post-UV baking time and temperature were increased. These efforts significantly mitigated the occurrence of crushed bright spot mura issue in FFS displays. Our work provides valuable insights for the liquid crystal display (LCD) industry in designing polyimide structures and achieving high-reliability in panel manufacturing.