A liquid crystal display device is widely used as a display device of a television, a personal computer, a PDA, or the like due to its thin thickness, light weight, and low power consumption. In particular, recently, the size of a liquid crystal display device has been rapidly increased as represented by a liquid crystal display device for a television. In order to increase the size, the multi-domain vertical alignment (MVA) mode is preferably used in which even a large-sized device having a wide viewing angle can be manufactured at a high yield. In the MVA mode, at the time a voltage is not applied to a liquid crystal layer, liquid crystal molecules are aligned perpendicular to a substrate surface. Therefore, a higher contrast ratio can be obtained than that of the twisted nematic (TN) mode of the related art.
In the MVA mode, the tilt direction of liquid crystal molecules is not regulated by an alignment film but is determined by the influence of a protrusion (rib) formed of an insulating material. Therefore, an alignment treatment for an alignment film is not necessary, and static electricity and dust caused by rubbing are not generated. Accordingly, a washing process and the like after the alignment treatment are not necessary. In addition, there is little variation in the initial tilt of liquid crystal molecules, which is effective for process simplification, yield improvement, and cost reduction.
However, in the MVA mode, although the alignment treatment is not necessary, it is necessary that an undercoat film corresponding to the alignment film be formed. Therefore, it is necessary to deal with the influence of the thickness nonuniformity of the undercoat film and the mixing of foreign materials on the alignment of liquid crystal molecules, and the production process and investment in plant and equipment are increased to form the undercoat film. In consideration of such circumstances, it is more preferable that the undercoat film be not provided.
On the other hand, recently, pre-tilt angle imparting techniques have attracted attention in which polymer components such as monomers and oligomers (hereinafter, abbreviated as “monomers and the like”) are mixed with liquid crystal to obtain a liquid crystal layer composition; the liquid crystal layer composition is sealed between substrates; and the monomers and the like are polymerized to form a polymer layer in a state where liquid crystal molecules are tilted by applying a voltage between the substrates (for example, refer to Patent Literatures 1 to 8). Due to the influence of such a polymer layer, the liquid crystal molecules have a predetermined pre-tilt angle after the voltage application is stopped. Therefore, the tilt direction of the liquid crystal molecules is maintained without an alignment film. Such monomers and the like are polymerized by heat or irradiation of light (for example, ultraviolet rays).