In accordance with the advance in the display industry, a low driving voltage, high resolution, reduction in volume of the monitor, and flatness of the monitor are realized in a liquid crystal display field. Accordingly, demands for liquid crystal displays are significantly growing. In liquid crystal display technologies, it is essential to align liquid crystals in a desired direction.
In the related art, a contact-type rubbing process is used as a known process of aligning liquid crystals. The process includes applying a polymer film formed of a polymer such as polyimide on a substrate such as glass, and rubbing a surface of the resulting substrate using fibers such as nylon or polyester in a predetermined direction. However, in the contact-type rubbing process, fine dust may be generated or electrostatic discharge (ESD) may occur when the fibroid materials are rubbed with the polymer film and problems may occur during the production of liquid crystal panels due to the trouble of the process.
Recently, many studies have been made to produce an aligning layer using a novel contactless-type process in order to avoid the above problems of the contact-type rubbing process. Examples of the contactless-type process of producing the aligning layer include a photo alignment process, an energy beam alignment process, a vapor deposition alignment process, and an etching process using lithography. However, the contactless-type aligning layer is difficult to be commercialized due to low thermal stability and residual images as compared to the aligning layer produced using the contact-type rubbing. Particularly, in the case of the photoaligning layer, since thermal stability is significantly reduced and the residual images are maintained for a long time, the photoaligning layer cannot be commercially produced even though convenience of the process is assured.
With respect to improvement in thermal stability, Korean Patent No. 10-0357841 discloses novel linear and cyclic polymers or oligomers of coumarin and quinolinol derivatives having the photoreactive ethen group, and the use of the polymers or the oligomers as the liquid crystal aligning layer. However, the patent is problematic in that residual images are very easily formed due to a rod-shaped mesogen bonded to a main chain.
To avoid the above-mentioned problem regarding the residual images, Korean Patent No. 10-0258847 suggests a liquid crystal aligning layer that is mixed with a thermosetting resin or has a functional group capable of being thermally cured. However, the patent is problematic in that alignment and thermal stability are poor.