The effects of the linearly polarized UV (LPUV) irradiation and thermal treatment of a photo-degradable polyimide (CBDA-ODA) alignment layer (AL) on its AL properties, liquid crystal (LC) alignment, and LCD characteristics have been investigated. The best quality of LC photo-alignment have been induced by the LPUVirradiation with much (about 5~10 times) less dosage than that generating the maximum anisotropy of the AL. A thermal treatment of the LPUV-irradiated AL has effectively removed the undesirable, low-M.W. fragments of the AL generated during the photo-decomposition and increased the stability of the AL, which has resulted in improvement of the LC alignment and the LCD property.

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For a cinnamate-branched alicyclic copolymer, we have investigated the effects of various LPUV exposure parameters on photoinduced LC alignment over it. The alignment induced at the optimal exposure conditions has shown excellent uniformity, a large LC order parameter and a good thermal stability, which is comparable to the rubbing-induced alignment.

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Abstract:The mechanical rubbing of a polyimide (PI) layer with a velvet cloth has been dominantly used to induce a uniform alignment of liquid crystal molecules in the manufacturing process of liquid crystal displays (LCDs). The rubbing process is affected by its process parameters and also by the nature and properties of the rubbing cloth used. We fabricated the rubbing cloths with various pile densities and different weaving structures and then investigated how the parameters were related to the effect of the cloth on the rubbing process and the properties of rubbed PI alignment layers (ALs). As the pile density increases at same rubbing process parameters, the degree of molecular orientation of the rubbed AL and its surface roughness increase with an increase of the contact area between the rubbing cloth and the AL surface. Furthermore, a more uniform rubbing is also achieved. The results in this work showed that higher pile density of the rubbing cloth induces a better rubbing effect, which is indeed more favorable to the LCD process. It was also observed that the weaving can exert some influence on the rubbing process.