1. Field of the Invention
The present invention relates to a method of making a phase difference film, more particularly to a method of making a phase difference film having two orientation directions.
2. Description of the Related Art
Three dimensional (3D) displays can be classified into glasses-type 3D displays and glasses-free-type 3D displays. Although the glasses-free-type 3D displays do not require the use of glasses for viewing images on the 3D displays, they have disadvantages, such as low resolution, low brightness, and a narrow viewing angle, which are difficult to solve.
The glasses used for viewing images on the glasses-type 3D displays provide a wide viewing angle. Among the aforementioned glasses, polarized glasses are more popular due to their low manufacturing costs and light weight. In addition, the polarized glasses can improve upon the flicker problem that shutter glasses have.
The polarized glasses use a film having a patterned polarizer or a phase difference film for changing the polarization directions of the left and right eye images before providing the left and right eye images to the left and right eyes of the viewer, thereby creating a 3D image viewing effect.
European Patent No. EP 0887667 discloses a method of making a patterned retarder (which can also be called as a phase difference film). The method involves plural rubbings of an alignment layer to form an aligning pattern having different orientation directions on the alignment layer. However, there exists an electrostatic problem during the rubbing operation (due to generation of charged particles). In addition, the method requires the use of complicated photolithography techniques, which involve an extraordinarily high precision operation and can result in a poor yield problem.
Other conventional methods of making a phase difference film include one that uses photo alignment techniques. In this method, two patterned hard masks (quartz masks) are used for shielding different regions of a liquid crystal material layer during two consecutive irradiating operations that use two different polarized lights, respectively. Although the method can overcome the aforementioned electrostatic problem, it requires the use of the hard masks, which hinders the use of the roll to roll processing in the manufacturing of the phase difference film and which has a light scattering problem that results in a need to incorporate a parallel light source for obtaining a precise structural pattern on the liquid crystal material layer. The method has disadvantages, such as having high manufacturing costs and hard to irradiate a large size liquid crystal material layer and to achieve mass production.