1. Field of Invention
The present invention relates to an optical crystal polymer film and, in particular, to a polymer film without cholesteric liquid crystal, a polymer film, and a reflective display module.
2. Related Art
After the progressive and development of flat panel display (FPD) devices, the FPD devices have gradually replaced the traditional CRT (Cathode Ray Tube) display devices because of their superior properties of lighter, thinner, low power consumption, and no irradiation. Moreover, the FPD devices are now applied to various kinds of electronic products. The cholesteric liquid crystal is a typical material used in the display technology such as the bi-stable display (e.g. electronic paper).
FIG. 1 is a schematic diagram showing the molecular arrangement of the cholesteric liquid crystal 11, which can be the chiral cholesteric liquid crystal or achiral cholesteric liquid crystal doped with chiral compounds. The cholesteric liquid crystal molecule typically has a chiral center. Thus, the liquid crystal molecules can be stacked in parallel and arranged in layers. The liquid crystal layers are in parallel to each other, and the liquid crystal molecules of each layer are aligned in the same direction. The lengthwise axle of the liquid crystal molecules is in parallel to the surface of the layer. In addition, the lengthwise axles of liquid crystal molecules in every adjacent two layers are regularly rotated with a certain angle, so that the stacked layers can form a spiral structure. When the stacked layers are totally rotated for 360 degrees, the direction the lengthwise axle of liquid crystal molecules comes back to the initial direction, which defines a pitch P. The liquid crystal molecules with the above-mentioned spiral structure can polarize the inputted light and then emit a light with a specific wavelength. In addition, the pitch can determine the wavelength of the strongest reflective light.
FIG. 2 and FIG. 3 are schematic diagrams showing the molecule arrangements of the cholesteric liquid crystal. As shown in FIG. 2, the cholesteric liquid crystal 11 is sandwiched between two glass substrates 12 and 13, a black absorption layer 14 is configured at the bottom. When the electronic field is not applied, the cholesteric liquid crystal 11 forms a planar texture. Since the spiral period (pitch) is roughly the same as the wavelength of light, the above-mentioned periodical structure can induce the Bragg reflection for the light of specific wavelength. The peak of the reflected light is λ=nP, wherein n is the average refractive index. In general, this reflection feature can be applied to the optical components and liquid crystal displays. FIG. 3 further illustrates the alignment of the focal-conic cholesteric liquid crystal.
Currently, the optical film with the Bragg reflection feature can be designed and manufactured with the cholesteric liquid crystal. For example, it may include the pure cholesteric liquid crystal film or the polymer film doped with the cholesteric liquid crystal.
In the polymer stabilized cholesteric liquid crystal, a few amount of monomer (less than 20%) can be added, so that the monomer can be distributed in the cholesteric liquid crystal, thereby forming the stabilized planar texture and achieving the Bragg reflection effect. However, the cholesteric liquid crystal is a very expensive material, so the manufacturing cost increases. This is the reason why the cholesteric liquid crystal can not be widely used.
Therefore, it is an important subject of the present invention to provide a novel polymer film, which has the photonic crystal structure without using the expansive cholesteric liquid crystal. Moreover, the polymer film may have the Bragg reflection effect without containing any of liquid crystal or fluid. Thus, the manufacturing cost thereof can be sufficiently reduced, and the application fields thereof can be broadened.