Abstract:
A liquid crystal device includes a pair of substrates with at least one liquid crystal cell therebetween, filled with a mixture of an alignment solution and liquid crystal molecules. The liquid crystal molecules are exposed to UV rays and a first voltage is applied to the pair of substrates to form a polymer network in each of the liquid crystal cells. Thus, the liquid crystal molecules achieve a bend state without transiting from a splay state. Further, a method of aligning the liquid crystal molecules is provided.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure relates to liquid crystal display, and particularly to a liquid crystal display device and method of aligning liquid crystal molecules utilized by the device. 
         [0003]    2. Discussion of the Related Art 
         [0004]    Liquid crystal display (LCD) devices have come into widespread use in recent years because of their advantages such as thinner profile and lower power consumption. To enhance response time and expand viewing angle, optically compensated bend-mode liquid crystal displays (OCB-LCD) have been developed. 
         [0005]    However, it takes a relatively long period for liquid crystal molecules between a pair of substrates of the OCB-LCD device to reach a bend state so as to begin operation. Initially, the liquid crystal molecules are in a splay state when no voltage is applied. With application of voltage, the liquid crystal molecules transit from the splay state to an asymmetric splay state, then to the bend state when the voltage reaches a bend level. 
         [0006]    Therefore, a method of aligning liquid crystal molecules and liquid crystal display utilizing the method are desired. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    Many aspects of the disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, the emphasis instead being placed upon clearly illustrating the principles of the disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
           [0008]      FIG. 1  is a partially schematic view of an embodiment of a liquid crystal device; 
           [0009]      FIGS. 2A through 2E  are schematic views illustrating alignment transitions of liquid crystal molecules of the liquid crystal device of  FIG. 1 ; 
           [0010]      FIG. 3  is a schematic view of the liquid crystal device of  FIG. 1 ; 
           [0011]      FIG. 4  shows a relationship between the applied voltage, the light efficiency of the transmissive area and the reflective area of the liquid crystal device of  FIG. 1 ; and 
           [0012]      FIG. 5  shows a method of aligning liquid crystal molecules according to the disclosure. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0013]      FIG. 1  schematically shows a liquid crystal device  10  including a first substrate  20 , a second substrate  30 , a liquid crystal layer forming by a plurality of liquid crystal cells  40 , and a driving circuit  50 . The second substrate  30  has a second surface  31   a  opposite to a first surface  21   a  of the first substrate  20 . Each of the liquid crystal cells  40  includes a transmissive area  41   a  and a reflective area  41   b.    
         [0014]    The first substrate  20  successively forms a first electrode  22  and a first alignment film  24  on the first surface  21   a.  The second substrate  30  successively forms a second electrode  32  and a second alignment film  34  on the second surface  31   a.  The liquid crystal cells  40  are arranged between the first alignment film  24  and the second alignment film  34 , and are configured (structured and arranged) for being filled with a plurality of liquid crystal molecules  42 . 
         [0015]    In this embodiment, the first electrode  22  and the second electrode  32  are indium tin oxide (ITO) glass, and the first electrode  22  and the second electrode  32  are polyimide (PI) film. It is to be noted that rubbing directions of the PI films are parallel. 
         [0016]      FIGS. 2A through 2E  are schematic views illustrating the alignment transitions of the liquid crystal molecules  42 . An alignment solution is provided, including two kinds of monomers  44   a,    44   b  mixed together. The monomers  44   a,    44   b  include a side-chain polymer  44   a  and a photo-curable polymer  44   b.  The ratio of the side-chain polymer  44   a  to the photo-curable polymer  44   b  is approximately 1:2 to 1:3. As shown in  FIG. 2A , the transmissive area  41   a  and the reflective area  41   b  of the liquid crystal cells  40  are filled with a mixture of the alignment solution and the liquid crystal molecules  42 . Here, the weight percentage of the alignment solution of the mixture is approximately 3% to 7%. 
         [0017]    Also referring to  FIG. 2B , the driving circuit  50  applies a first voltage to the first substrate  20  and the second substrate  30 . In the embodiment, the first voltage is an alternating current voltage, approximately 5V to 9V. The first voltage generates a vertical electronic field between the first electrode  22  and the second electrode  32 , vertically aligning the liquid crystal molecules  42 . It is to be noted that the side-chain polymer  44   a  and the photo-curable polymer  44   b  are not affected by the vertical electronic field, but the alignment of the side-chain polymer  44   a  will be pulled up by the liquid crystal molecules  42 . 
         [0018]    In addition, ultra-violet (UV) light source  11  irradiates liquid crystal cells  40  when the first voltage is applied to the first substrate  20  and the second substrate  30 . As shown in  FIG. 2B , a mask  55  is provided between the transmissive area  41   a  and the UV light source  11 . The mask  55  is removed after a first time period, and the transmissive area  41   a  and the reflective area  41   b  are simultaneously irradiated by UV light source  11  for a second time period. 
         [0019]    In this embodiment, the UV rays have a uniform wavelength of about 254 nanometers (nm), about 302 nm, and about 365 nm. Alternatively, the UV light can have wavelengths of about 400 nm or less. Understandably, the alignment of the side-chain polymer  44   a  is affected by the time period during which the side-chain polymer  44   a  is exposed to the UV light source  11 . In other words, the angle between the side-chain polymer  44   a  and the first and second alignments film  24 ,  34  is close to approximately 90 degrees (°) when the side-chain polymer  44   a  has been exposed to the UV light source  11  for a sufficient period. At the same time, the photo-curable polymer  44   b  is substantially parallel to the first and second alignment films  24 ,  34  for exposure to the UV light source  11 . The alignment of the side-chain polymer  44   a  and the photo-curable polymer  44   b  are shown in  FIG. 2C . Thus, the side-chain polymer  44   a  and the photo-curable polymer  44   b  cooperatively form a polymer network to control a pretilt angle of the liquid crystal molecules  42 . 
         [0020]    In the embodiment, the pretilt angle of the liquid crystal molecules  42  of the transmissive area  41   a  is controlled within approximately 54° to 60°. After removing the applied voltage and the UV light source  11 , as shown in  FIG. 2D , the liquid crystal molecules  42  are in a bend state as expected. The pretilt angle of the liquid crystal molecules  42  of the reflective area  41   b  is controlled within approximately 65° to 70°. Thus, the pretilt angle of the liquid crystal molecules  42  of the reflective area  41   b  exceeds the pretilt angle of the liquid crystal molecules  42  of the transmissive area  41   a.    
         [0021]    A second voltage is applied to the first substrate  20  and the second substrate  30  when the liquid crystal molecules  42  are in the bend state. An initial value of the second voltage is approximately 0V. The second voltage is then gradually increased until reaching a saturated voltage (Vsat). Finally, the alignment of the liquid crystal molecules  42  is as shown in  FIG. 2E . 
         [0022]      FIG. 3  is a schematic view of the liquid crystal device  10 , which includes, in addition to the first substrate  20 , the second substrate  30  and the liquid crystal cells  40  as described, a first quarter-wavelength (¼λ) plate  72 , a first polarizing plate  82 , a second ¼λ plate  70 , a second polarizing plate  80  and a back-light plate  90 . The first ¼λ plate  72  and the first polarizing plate  82  are successively arranged in a second surface  21   b  of the first substrate  20 . The second ¼λ plate  70 , the second polarizing plate  80 , and the back-light plate  90  are successively arranged in the first surface  31   b  of the second substrate  30 . In addition, the liquid crystal device  10  also includes a reflector  60  arranged between the second ¼λ plate  70  and the reflective area  41   b.    
         [0023]    Here, the saturated voltage is approximately 6V (as shown in  FIG. 4 ). Thus, the operating voltage of the liquid crystal device  10  is approximately 0 to 6V after the liquid crystal device  10  is turned on. 
         [0024]      FIG. 5  is a flowchart illustrating a method for manufacturing a liquid crystal device  10  according to the disclosure. In block S 2 , an alignment solution including two kinds of monomers is generated. In block S 4 , the liquid crystal cells  40  are filled with a mixture of the alignment solution and the liquid crystal molecules  42 . In block S 6 , a first voltage is applied to the liquid crystal cells  40  and the UV light source  11  irradiates the liquid crystal cells  40  until the polymer network is formed. It is to be noted that a mask  55  is provided between the UV light source  11  and the transmissive area  41   a  for a first time period. After the time period, the mask  55  is removed and the transmissive area  41   a  and the reflective area  41   b  are simultaneously exposed to the UV light source  11 . In block S 8 , the UV light source  11  and the first voltage are turned off. At this time, the liquid crystal molecules  42  are in a bend state. 
         [0025]    In block S 10 , a second voltage is applied to the liquid crystal cells  40 . The initial value of the second voltage is approximately 0V. In block S 12 , the second voltage is then gradually increased until reaching a saturated voltage (Vsat). 
         [0026]    It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention.