1. Field of the Invention
The present invention relates to method for manufacturing a liquid crystal display which includes a process of forming an orientation film for aligning liquid crystal material and a process of treating the liquid crystal, and a liquid crystal display manufactured by the method.
2. Description of Related Art
A conventional liquid crystal display can be produced in various sizes ranging from a subminiature size to a large size and diverse display patterns can be achieved. Liquid crystal displays have been widely applied to display devices. FIG. 1 shows an example of a liquid crystal display having a liquid crystal having a twist angle between 180.degree. and 270.degree.. As shown in FIG. 1, first and second transparent electrodes 13 and 14 are isolated from each other in parallel stripes and cross each other. The first and second electrodes 13 and 14 are located on the opposing surfaces of first and second transparent substrates 11 and 12, respectively. Orientation films 16 and 17 cover the transparent electrodes 13 and 14, respectively. Liquid crystal material 19 is injected between the orientation films 16 and 17, and the resultant structure is sealed by a sealant 18. Polarizing plates 21 and 22 are attached to the outer surfaces of the first and second transparent substrates 11 and 12, respectively, and the polarization directions of the polarizing plates 21 and 22 correspond to the twist angle of the liquid crystal 19.
The surfaces of the orientation films 16 and 17 are treated to orient the liquid crystal 19 in a predetermined direction. Here, treatment of the orientation films is an important factor in determining the pretilt angle of the orientation films. Preferably, the pretilt angle is large for an effective picture display.
Examples of orientation film treatment methods include: a rubbing method for rubbing the orientation films 16 and 17 in a predetermined direction using a cloth, a non-rubbing method including an SiO inclined angle deposition method, a figure transcription method and a light irradiation method using high-polymerization of light due to ultraviolet radiation. The rubbing method causes phase distortion and light dispersion since it is difficult to form fine and accurate orientation grooves on the orientation film. In particular, since the pretilt angle of the orientation film depends on the rubbing pressure, the rubbing pressure must be increased to obtain a large pretilt angle, and it is also difficult to obtain a uniform pretilt angle over the entire orientation film.
The light irradiation method, as an orientation treatment method performed by exposure to light and development of a photosensitive film coating the upper surface of the orientation film, can arbitrarily control the direction of orientation. However, in this type of non-rubbing method, there is a limit in improving the resolution of the picture since the orienting force is weak and the pretilt angle is not relatively large.
For example, a pretilt angle of 4 to 6.degree. is obtained by orienting polyimide (a high polymer compound) using the non-rubbing method. This pretilt angle is not within the normally acceptable range between 8.degree. and 10.degree.. Therefore, a reversely twisted domain where liquid crystal molecules are reversely twisted may be generated.
In order to solve the above problem, as disclosed in U.S. Pat. No. 5,464,669 issued to Kang et al. on Nov. 7, 1995, a method for forming a polyvinyl-4-fluorocinnamate (PVCN-F) film respectively on two opposing substrates and irradiating linearly-polarized UV rays having different energies on the respective PVCN-F films has been developed.
However, the PVCN-F polymer is relatively expensive, and since the pretilt angle depends on the difference in energies of linearly-polarized light, it is difficult to control the amount of light irradiation.