Abstract:
A liquid crystal display comprises: first and second panels facing each other; a compensation film and a first polarizer disposed on the first panel, the compensation film having phase retardation characteristics; and a second polarizer having a supporting film disposed on the second panel, the supporting film having phase retardation characteristics. In alternative embodiments, a supporting film is used in place of the compensation film. The supporting film has retardation characteristics.

Description:
BACKGROUND OF THE INVENTION 
   1. Technical Field 
   The present disclosure relates to liquid crystal displays, more particularly, liquid crystal displays having polarizing or compensating films. 
   2. Discussion of the Related Art 
   A liquid crystal display (LCD) includes a pair of upper and lower panels, and a liquid crystal layer interposed therebetween for housing liquid crystals. The upper panel is provided with a common electrode and color filters; the lower panel is provided with pixel electrodes and thin film transistors (TFTs). The liquid crystals in the liquid crystal layer are subjected to an electric field generated between electrodes of the upper and lower panels. The variation of the field strength changes the molecular orientations of the liquid crystals and the changed molecular orientations in turn change the transmittance of light passing through the liquid crystal display such that desired images are obtained. 
   Light, an electromagnetic wave, oscillates in directions perpendicular to its moving direction. Generally, the oscillation of light is not confined or biased to a particular direction. Thus, polarizers are used to direct the transmitted light. Generally, polarizers are disposed exterior to the upper or lower panels such that the light transmitted through the liquid crystal layer is polarized. 
   A compensation film can also be interposed between the polarizer and the upper and lower panels to enhance viewing angle and/or color inversion features of an LCD. The compensation film retards or shifts one component of the light to convert the elliptically polarized light generated by the liquid crystal display cell into linear polarized light, which can be effectively polarized by the polarizer. 
   Typically, a polarizer and a compensation film are separately disposed in an LCD, by affixing to the panel. 
   SUMMARY OF INVENTION 
   According to an embodiment of the present disclosure, a liquid crystal display comprises: first and second panels facing each other; a compensation film and a first polarizer disposed on the first panel, the compensation film having phase retardation characteristics; and a second polarizer having a supporting film disposed on the second panel, the supporting film having phase retardation characteristics. 
   Preferably, the first polarizer includes a first supporting film and the phase retardation of the first supporting film combined with the compensation film ranges about 130 nm to about 160 nm in the vertical direction. The phase retardation of the second supporting film ranges about 0 nm to about 5 nm in the horizontal direction and about 100 nm to about 140 nm in the vertical direction. The phase retardation of the compensation film ranges about 40 nm to about 60 nm in the horizontal direction and about 80 nm to about 100 nm in the vertical direction, and the phase retardation of the first supporting film ranges about 0 nm to about 5 nm in the horizontal direction and about 50 nm to about 60 nm in the vertical direction. 
   Preferably, an elongation direction for the polarizing medium having zero value of phase retardation in the horizontal direction is the same direction with an absorption axis of the polarizer disposed on the first panel. The compensation film is laminated perpendicular to the elongation direction of the polarizing medium. 
   Preferably, a liquid crystal layer for housing liquid crystals interposed between the first and the second panels. The liquid crystals are aligned in a vertical alignment mode. The polarizers include a polarizing medium made of polyvinyl alcohol (PVA). The supporting films are made of triacetate cellulose (TAC) or cellulous acetate propionate (CAP). 
   According to another embodiment of the present disclosure, a liquid crystal display comprises: first and second panels facing each other; and a first polarizer having a first supporting film disposed on the first panel and a second polarizer having a second supporting film disposed on the second panel, wherein the supporting films disposed on the first panel and the second panel have phase retardation characteristics. 
   Preferably, phase retardation of the first supporting film ranges about 40 nm to about 60 nm in the horizontal direction and about 120 nm to about 160 nm in the vertical direction, and phase retardation of the second supporting film ranges about 0 nm to about 5 nm in the horizontal direction and about 100 nm to about 140 nm in the vertical direction. 
   Preferably, the phase retardation of the first and second supporting films ranges about 40 nm to about 60 nm in the horizontal direction and about 120 nm to about 160 nm in the vertical direction. 
   Preferably, the phase retardation of the first supporting film ranges about 50 nm to about 70 nm in the horizontal direction and about 210 nm to about 250 nm in the vertical direction, and the phase retardation of the second supporting film ranges about 0 nm to about 5 nm in the horizontal direction and about 50 nm to about 60 nm in the vertical direction. 
   According to still another embodiment of the present disclosure, a method of forming panels in a liquid crystal display device comprises: positioning first and second panels to face each other; disposing a first polarizer having a first supporting film on the first panel; and disposing a second polarizer having a second supporting film on the second panel, wherein the supporting films disposed on the first panel and the second panel have phase retardation characteristics. 
   According to another embodiment of the present disclosure, a method of forming panels in a liquid crystal display device comprises: positioning first and second panels to face each other; disposing a compensation film and a first polarizer on the first panel, the compensation film having phase retardation characteristics; and disposing a second polarizer having a supporting film on the second panel, the supporting film having phase retardation characteristics. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present disclosure will become more apparent by describing preferred embodiments thereof in detail with reference to the accompanying drawings, of which: 
       FIG. 1  is a sectional view of an LCD according to an embodiment of the present disclosure; 
       FIG. 2A  shows an elongation direction of a polarizing medium; 
       FIG. 2B  shows an elongation direction of a compensation film and a supporting film; 
       FIG. 3  is a sectional view of an LCD according to another embodiment of the present disclosure; 
       FIG. 4A  shows an elongation direction of a polarizing medium; 
       FIG. 4B  shows an elongation direction of a supporting film; 
       FIG. 5  is a sectional view of an LCD according to still another embodiment of the present disclosure; 
       FIG. 6A  shows an elongation direction of a polarizing medium; 
       FIG. 6B  shows an elongation direction of a supporting film; and 
       FIG. 7  is a sectional view of an LCD according to another embodiment of the present disclosure. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   The present disclosure will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the disclosure are shown. This disclosure may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. 
   The liquid crystal displays according to embodiments of the present invention will now be described with reference to the drawings. 
     FIG. 1  is a sectional view of an LCD according to an embodiment of the present disclosure. As shown in  FIG. 1 , an LCD includes a lower panel  110 , an upper panel  210 , and a liquid crystal layer  3  for housing liquid crystals interposed between the lower panel  110  and the upper panel  210 . The lower panel  110  includes a TFT array panel (not shown) and the upper panel  210  includes a color filter (not shown). Alignment layers (not shown) are disposed on the two panels to anchor the liquid crystals. Electrodes (not shown) for generating electric field are formed on the two panels. The liquid crystals are preferably aligned in vertical alignment (VA) mode. In VA mode, the molecules of liquid crystals are normally aligned at right angles to the panels, swinging through 90 degrees to lie parallel with the panels in the presence of the electric field. 
   A lower polarizer  12  is disposed under the lower panel  110 . The lower polarizer comprises a polarizing medium  12   b  interposed between two supporting films  12   a  and  12   c . As shown in  FIG. 1 , the supporting film  12   c  is positioned closer to the lower panel  110  as compared to the distance between the supporting film  12   a  and the lower panel  110 . 
   A compensation film  23  is disposed on the upper panel  210  and an upper polarizer  22  is disposed on the compensation film  23 . The upper polarizer  22  includes two supporting films  22   a  and  22   c  and a polarizing medium  22   b.    
   The supporting films  12   a,    12   c,    22   a,  and  22   c  are preferably made of tri-acetyl cellulous (TAC) or cellulous acetate propionate (CAP). The polarizing mediums  12   b  and  22   b  are preferably made of polyvinyl alcohol (PVA). 
   The compensation film  23  is preferably formed as a thin film made of a material having different values for Nx, Ny, and Nz. Nx denotes the refractive index in the direction of its major axis. Ny denotes the refractive index in the direction of its minor axis. Nz denotes the refractive index in the direction perpendicular to the major and minor axis. 
   Thin films such as the lower polarizer  12 , the compensation film  23 , and the upper polarizer  22  exhibit phase retardation characteristics which can be used for enhancing viewing angle and/or color inversion. Phase retardation of a thin film is calculated according to the following equations:
 
 Ro= ( Nx−Ny ) d 
 
   
     
       
         
           
             R 
             ′ 
           
           = 
           
             
               ( 
               
                 
                   
                     Nx 
                     + 
                     Ny 
                   
                   2 
                 
                 - 
                 Nz 
               
               ) 
             
             ⁢ 
             
                 
             
             ⁢ 
             d 
           
         
       
     
   
   Here, Ro denotes phase retardation in the horizontal direction. R′ denotes phase retardation in the vertical (thickness) direction. Small d denotes the thickness of the thin film. 
   According to an embodiment of the present disclosure, the supporting film  22   a  can be made with Ro which is about 0 nm to about 5 nm and R′ which ranges between about 50 nm and about 60 nm. The compensation film  23  on the upper panel  210  can be made with Ro ranging between about 40 nm and about 60 nm and R′ ranging between about 80 nm and about 100 nm. Thus, R′ of the thin film on the upper panel  210  in total ranges between about 130 nm and about 160 nm. 
   The supporting film  12   c  of the lower polarizer  12  can be made with Ro which is about 0 nm to about 5 nm and R′ ranges between about 100 nm and about 140 nm. Having such characteristics, the lower polarizer  12  increases phase retardation and additional compensation films are not necessary under the lower panel  110 . 
   Thus, the same overall effect as was achieved in conventional art using compensation film is achieved by the lower polarizer  12  without using compensation film. Although description of the above embodiment is directed to upper and lower polarizers, one ordinary skilled in the art can readily appreciate that the upper and lower panels and associated polarizers and films are interchangeable, without degradation in retardation characteristics. 
   Thin films of zero (0) Ro, i.e., thin films having no phase retardation in their horizontal direction, can be fabricated by lamination using a roll.  FIG. 2A  shows an elongation direction for the polarizing medium  22   b.    FIG. 2B  shows an elongation direction for the compensation film  23 . 
   As shown in  FIGS. 2A and 2B , an absorption axis B of the upper polarizer  22  along which the light vanishes is the same as an elongation direction A of the polarizing medium  22   b.  A polarization axis (not shown) of the upper polarizer  22  along which the light penetrates is perpendicular to the elongation direction A of the polarizing medium  22   b.  A phase retardation axis D of the compensation film  23  having non-zero value of Ro should be perpendicular to the absorption axis B of the upper polarizer  22 . Therefore, the compensation film  23  is preferably laminated in the direction C perpendicular to the elongation direction A of the polarizing medium  22   b.    
     FIG. 3  is a sectional view of an LCD according to another embodiment of the present disclosure. As shown in  FIG. 3 , an LCD includes a lower panel  110 , an upper panel  210 , and a liquid crystal layer  3  for housing liquid crystals interposed between the lower panel  110  and the upper panel  210 . The liquid crystals are preferably aligned in vertical alignment (VA) mode. A lower polarizer  12  is disposed on the lower panel  110 . The lower polarizer comprises a polarizing medium  12   b  interposed between two supporting films  12   a  and  12   c.  The upper polarizer  22  includes two supporting films  22   a  and  22   c  and a polarizing medium  22   b.    
   The supporting film  22   a  is preferably formed as a thin film made of a material having different values for Nx, Ny, and Nz. The supporting films  12   a,    12   c,  and  22   c  can be made of tri-acetyl cellulous (TAC) and the polarizing medium  12   b  and  22   b  can be made of poly-vinyl alcohol (PVA). The supporting film  22   a  can be made with Ro which ranges between about 40 nm and about 60 nm and R′ which ranges between about 120 nm and about 160 nm. The supporting film  12   c  can be made with Ro which is about 0 nm to about 5 nm and R′ which ranges between about 100 nm and about 140 nm. 
   The lower polarizer  12  increases phase retardation because the supporting film  12   c  has R′ ranging between about 100 nm and about 140 nm. The upper polarizer  22  increases phase retardation because the supporting film  22   a  has Ro ranging between 40 nm and 60 nm and R′ ranging between about 120 nm and about 160 nm. Thus, a compensation film is neither necessary under the lower panel  110  nor above the upper panel  210 . 
     FIG. 4A  shows the elongation direction for the polarizing medium  22   b.    FIG. 4B  shows the elongation direction for the supporting film  22   a.  As shown in  FIGS. 4A and 4B , an absorption axis B of the upper polarizer  22  along which the light vanishes is the same as an elongation direction A of the polarizing medium  22   b.  A polarization axis (not shown) of the upper polarizer  22  along which the light penetrates is perpendicular to the elongation direction A of the polarizing medium  22   b.    
   A phase retardation axis D of the supporting film  22   a  having non-zero value of Ro is the same as an elongation direction C of the supporting film  22   a.  The phase retardation axis of the supporting film  22   a  having non-zero value of Ro should be perpendicular to the absorption axis B of the upper polarizer  22 . The supporting film  22   a  can be laminated in the direction C perpendicular to the elongation direction A of the polarizing medium  22   b.    
   According to still another embodiment of the present disclosure as shown in  FIG. 5 , the supporting film  12   c  and the supporting film  22   a  are preferably formed as thin films made of a material having different values of Nx, Ny, and Nz. The supporting films  12   a  and  22   c  can be made of tri-acetyl cellulous (TAC) and the polarizing mediums  12   b  and  22   b  can be made of poly-vinyl alcohol (PVA). 
   Both the supporting film  12   c  and the supporting film  22   a  can be made with Ro which ranges between about 40 nm and about 60 nm and R′ which ranges between about 120 nm and about 160 nm. The lower polarizer  12  increases its phase retardation because the supporting film  12   c  has Ro ranging between about 40 nm and about 60 nm and R′ ranging between about 120 nm and about 160 nm. The upper polarizer  22  increases its phase retardation because the supporting film  22   a  has Ro ranging between about 40 nm and about 60 nm and R′ ranging between about 120 nm and about 160 nm. 
     FIG. 6A  shows the elongation direction for the polarizing medium  12   b  and the polarizing medium  22   b.    FIG. 6B  shows the elongation direction for the supporting film  22   a  and the supporting film  12   c.    
   As shown in  FIGS. 6A and 6B , an absorption axis B of the upper polarizer  22  along which the light vanishes is the same as an elongation direction A of the polarizing medium  22   b.  A polarization axis (not shown) of the upper polarizer  22  along which the light penetrates is perpendicular to the elongation direction A of the polarizing medium  22   b.  An absorption axis B of the lower polarizer  12  along which the light vanishes is the same as an elongation direction A of the polarizing medium  12   b.  A polarization axis (not shown) of the lower polarizer  12  along which the light penetrates is perpendicular to the elongation direction A of the polarizing medium  12   b.    
   A phase retardation axis D of the supporting film  22   a  having non-zero value of Ro is the same as an elongation direction C of the supporting film  22   a.  The phase retardation axis D of the supporting film  22   a  having non-zero value of Ro should be perpendicular to the absorption axis B of the upper polarizer  22 . A phase retardation axis D of the supporting film  12   c  having non-zero value of Ro is the same as an elongation direction C of the supporting film  12   c.  The phase retardation axis D of the supporting film  12   c  having a non-zero value should be perpendicular to the absorption axis B of the upper polarizer  22 . 
   The supporting film  22   a  can be laminated in the direction C perpendicular to the elongation direction A of the polarizing medium  22   b.  The supporting film  12   c  can be laminated in the direction C perpendicular to the elongation direction A of the polarizing medium  12   b.    
     FIG. 7  is a sectional view of an LCD according to still another embodiment of the present disclosure. As shown in  FIG. 7 , an LCD includes a lower panel, an upper panel  210 , and a liquid crystal layer  3  for housing liquid crystals interposed between the lower panel  110  and the upper panel  210 . The liquid crystals are preferably aligned in vertical alignment (VA) mode. A lower polarizer  12  is disposed on the lower panel  110 . The lower polarizer comprises a polarizer medium  12   b  interposed between two supporting films  12   a  and  12   c.  The upper polarizer  22  includes two supporting films  12   a  and  12   c.  The upper polarizer  22  includes two supporting films  22   a  and  22   c  and a polarizing medium  22   b.    
   The supporting film  22   a  is preferably formed as a thin film made of a material having different values for Nx, Ny, and Nz. The supporting films  12   a,    12   c,  and  22   c  can be made of tri-acetyl cellulous (TAC) and the polarizing medium  12   b  and  22   b  can be made of poly-vinyl alcohol (PVA). The supporting film  22   a  can be made with Ro which ranges between about 50 nm and about 70 nm and R′ which ranges between about 210 nm and about 250 nm. The supporting film  12   c  can be made with Ro which is about 0 nm to about 5 nm and R′ which ranges between about 50 nm and about 60 nm. 
   The lower polarizer  12  increases phase retardation because the supporting film  12   c  has R′ ranging between about 50 nm and about 60 nm. The upper polarizer  22  increases phase retardation because the supporting film  22   a  has Ro ranging between 50 nm and 70 nm and R′ ranging between about 100 nm and about 140 nm. Thus, a compensation film is neither necessary under the lower panel  110  nor above the upper panel  210 . 
   Elongation directions for the polarizing medium  22   b  and the supporting film  22   a  are the same with the embodiment described in connection with  FIGS. 4A and 4B . 
   Although preferred embodiments of the present disclosure have been described in detail hereinabove, it should be clearly understood that many variations and/or modifications of the basic inventive concept herein taught which may appear to those skilled in the present art will still fall within the spirit and scope of the present invention, as defined in the appended claims.