Abstract:
A backlight unit having a polarization film for performing the function of a reflective polarization film, wherein the backlight unit includes a light source, an optical film and a polarization film. The light source emits a light having a certain wavelength, the optical film is located proximate to the light source to transmit the light outputted from the light guiding plate in a certain direction, and the polarization film is located proximate to the optical film. Here, the polarization film has a UV curing resin and lines disposed on the UV curing resin, and polarizes the light transmitted from the optical film. The backlight unit manufactures the polarization film by using an UV curing resin and a metal substance, and thus the manufacture period of the polarization film may be reduced enabling the polarization film to be manufactured in great quantities.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a backlight unit and a method of manufacturing a polarization film employed in the same. More particularly, the present invention relates to a backlight unit having a polarization film for performing the function of a reflective polarization film and a method of manufacturing the polarization film employed in the same. 
     2. Description of the Related Art 
     A Liquid crystal display (hereinafter, referred to as “LCD”) displays an image using change of the transmissivity of liquid crystals in LCD. The LCD is not a self light-emitting device, and so includes a backlight unit (hereinafter, referred to as “BLU”) for providing a light to a panel located over the BLU. 
       FIG. 1A  is a sectional view illustrating the BLU employed in the LCD. 
     In  FIG. 1A , the BLU  100  is driven by edge-light method, and includes a light source unit  110 , a light guiding plate  120 , a reflector  130 , an optical film  140  and a reflective polarization film  148 . 
     The light source unit  110  has at least one cold cathode fluorescent lamp (hereinafter, referred to as “CCFL”)  112  and a light source reflector  114 . 
     The CCFL  112  emits a linear light having a certain wavelength. 
     A light emitted from the CCFL  112  is reflected by the light source reflector  114  made up of reflective substance and the reflector  130 , and then the reflected light is diffused through the whole of the light guiding plate  120  as shown in  FIG. 1A . 
     The optical film  140  includes a diffuser  142 , a prism sheet  144  and a protection sheet  146 . 
     The diffuser  142  diffuses or condenses light transmitted from the light guiding plate  120  to maintain constantly the brightness of the BLU  100  and increase the view angle of the LCD. 
     The prism sheet  144  condenses light transmitted from the diffuser  142  in a direction of the panel so that the brightness of the light transmitted from the BLU  100  to the panel is enhanced. 
     The protection sheet  146  is located over the prism sheet  144  in order to prevent the prism sheet  144  from dust, etc, and increases the view angle of the LCD narrowed by the prism sheet  144 . 
     Only some of a light provided from the BLU  100  is transmitted through the panel (not shown). For example, P wave of the light provided from the BLU  100  is transmitted through the panel, and S wave of the light is absorbed by the panel. Accordingly, the reflective polarization film  148  is employed in the BLU  100  so as to use the S wave absorbed by the panel. 
     The reflective polarization film  148  reflects S wave of a light diffused by the protection sheet  146  in the direction of the light guiding plate  120 , and provides P wave of the light to the panel. 
     The S wave reflected by the reflective polarization film  148  is again reflected by the light guiding plate  120  or the reflector  130 . As a result, the reflected S wave is changed into light including P wave and S wave. 
     The changed light is again incident to the reflective polarization film  148  through the diffuser  142 , the prism sheet  144  and the protection sheet  146 . 
     The BLU  100  enhances the efficiency of the light by using the above described method. 
     Hereinafter, the reflective polarization film  148  will be described in detail. 
     The reflective polarization film  148  included in the BLU  100  employs a thin multi-layered reflective polarization film formed by depositing transparent substances having different refractive index. Here, a representative reflective polarization film  148  is DBEF (dual brightness enhancement film) of 3M Company. However, the thin multi-layered reflective polarization film is not good in the transmission efficiency for a particular wavelength and also is not good in the reflection efficiency for other wavelength. Accordingly, the following reflective polarization film shown in  FIG. 1B  has been developed so as to enhance the polarization characteristics of the thin multi-layered reflective polarization film. 
       FIG. 1B  is a perspective view illustrating a reflective polarization film employed in the BLU of  FIG. 1A . 
     In  FIG. 1B , a reflective polarization film  148  employed in the BLU  100  as a wire grid polarization film is manufactured by forming fine metal patterns  152  on a transparent substrate  150 . Here, the metal patterns  152  are formed by forming a metal thin film on the transparent substrate  150 , and then irradiating a polarized laser beam on the metal thin film. This is disclosed in Korean application number 2005-40544. 
     In the above reflective polarization film  148 , the interval of the metal patterns  152  should be formed finely so that the reflective polarization film  148  performs desired polarization function. However, it is difficult to form accurately the metal patterns  152  on the transparent substrate  150 , and so a process of manufacturing one reflective polarization film  148  has to be long. Accordingly, it is difficult to manufacture in great quantities the reflective polarization film  148 . 
     SUMMARY OF THE INVENTION 
     It is a feature of the present invention to provide a backlight unit having a polarization film for functioning reflective polarization film by using UV curing resin and metal substance and a method of manufacturing the polarization film. 
     In addition, it is another feature of the present invention to provide a method of manufacturing a polarization film employed in a backlight unit capable of manufacturing in great quantities the polarization film and reducing a manufacture period of the polarization film. 
     A backlight unit according to one embodiment of the present invention includes a light source, an optical film and a polarization film. The light source emits a light having a certain wavelength. The optical film is located proximate to the light source to transmit the light outputted from the light source in a certain direction. The polarization film is located proximate to the optical film. Here, the polarization film has a UV curing resin and lines disposed on the UV curing resin, and polarize the light transmitted from the optical film. 
     A display apparatus according to one embodiment of the present invention includes a light source, an optical film, a polarization film and a panel. The light source emits a light having a certain wavelength. The optical film is located proximate to the light source to transmit the light emitted from the light source. The polarization film is located proximate to the optical film to transmit some of the light from the optical film. The panel displays an image by using the light transmitted through the polarization film. The polarization film includes a transparent film, a UV curing resin formed on the transparent film, and a plurality of metal lines disposed on the UV curing resin. 
     A method of manufacturing a polarization film according to one embodiment of the present invention includes applying a UV curing resin on a transparent film; disposing a film in which pattern is formed at a location corresponding to the lines on the UV curing resin; irradiating ultraviolet rays on the film for a certain period of time; removing the irradiated film to form a layer having a predetermined pattern on the transparent film; and applying a metal substance onto the layer to form a plurality of lines on the layer. 
     As described above, a backlight unit and a method of manufacturing a polarization film in the same according to one embodiment of the present invention manufacture the polarization film by using UV curing resin and metal substance, and thus the manufacture period of the polarization film may be reduced. Accordingly, the polarization film may be manufactured in great quantities. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present invention will become readily apparent by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: 
         FIG. 1A  is a sectional view illustrating the BLU in the LCD; 
         FIG. 1B  is a perspective view illustrating a reflective polarization film employed in the BLU of  FIG. 1A ; 
         FIG. 2  is a sectional view illustrating a liquid crystal display employing a backlight unit according to one embodiment of the present invention; 
         FIG. 3A  to  FIG. 3C  are sectional views illustrating the backlight unit according to one embodiment of the present invention; 
         FIG. 4A  to  FIG. 4D  are sectional views a process of manufacturing the polarization film according to one embodiment of the present invention; and 
         FIG. 4E  and  FIG. 4F  are sectional and perspective views illustrating the polarization film manufactured by the process in  FIG. 4A  to  FIG. 4D . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, the preferred embodiments of the present invention will be explained in more detail with reference to the accompanying drawings. 
       FIG. 2  is a sectional view illustrating a liquid crystal display employing a backlight unit according to one embodiment of the present invention.  FIG. 3A  to  FIG. 3C  are sectional views illustrating the backlight unit according to one embodiment of the present invention. 
     In  FIG. 2 , the liquid crystal display (hereinafter, referred to as “LCD”) includes a LCD panel  200  and a backlight unit (hereinafter, referred to as “BLU”)  202 . 
     The LCD panel  200  includes a lower polarization film  204 , an upper polarization film  206 , a lower glass substrate  208 , an upper glass substrate  210 , a color filter  212 , a black matrix  214 , a pixel electrode  216 , a common electrode  218 , a liquid crystal layer  220  and a TFT array  222 . 
     The color filter  212  includes sub-color filters corresponding to red, green and blue light. 
     The TFT array  222  as switching device switches the pixel electrode  216 . 
     The common electrode  218  provides commonly a certain voltage to the color filter  212 . 
     The pixel electrode  216  provides certain voltages to the red sub-color filter, the green sub-color filter and the blue sub-color filter. 
     The pixel electrode  216  and the common electrode  218  array liquid crystals included in the liquid crystal layer  220  in accordance with the voltages. 
     The liquid crystal layer  220  includes the liquid crystals, wherein the liquid crystals are arrayed depending on voltage difference of the pixel electrode  216  and the common electrode  218 . As a result, a light transmitted from the backlight unit  202  is incident to the color filter  212  through the disposed liquid crystals. 
     The BLU  202  is located under the LCD panel  200 , and provides a light, e.g. white light to the LCD panel  200 . 
     The BLU  202  includes an edge-light type BLU where light source is located at side of a light guiding plate, and a direct-lighting type BLU where light source is located under a LCD panel. This will be described in detail with reference to the accompanying  FIG. 3A  to  FIG. 3C . 
     In  FIG. 3A , the BLU  202  as edge-light type BLU includes a light source unit  300 , a light guiding plate  310 , a reflector  320 , an optical film  330  and a polarization film  338 . 
     The light source unit  300  is located at side of the BLU  202 , and includes at least one light source  302 , e.g. cold cathode fluorescent lamp (hereinafter, referred to as “CCFL”) and a light source reflector  304 . Here, the light source  302  is not limited to the CCFL corresponding to linear light. 
     For example, point light source such as light emitting diode (LED), etc. as the light source  302  may be employed. For another example, surface light source such as external electrode fluorescent lamp (EEFL) may be employed. Here, when the EEFL is employed as the light source  302 , the BLU  202  may not include a light guiding plate because the EEFL emits a surface light. 
     Hereinafter, the light source  302  will be assumed as the CCFL for convenience of the description. 
     The CCFL  302  provides a very bright white light, and does not emit heat. 
     The light source reflector  304  packages the CCFL  302 , and reflects a light emitted from the CCFL  302  so that the light is incident into side of the light guiding plate  310 . Here, the light source reflector  304  is made up of substance having high reflectivity. In addition, the surface of the light source reflector  304  may be coated with silver (Ag). 
     The reflector  320  is located under the light guiding plate  310 , and reflects a light leaked from the light guiding plate  310  in a direction of the light guiding plate  310 . This reflector  320  is manufactured by coating silver (Ag) on a basic substance made up of aluminum (Al), etc. Here, a process of manufacturing the reflector  320  may further include titanium coating process so as to prevent the reflector  320  from heat. 
     The light guiding plate  310  is designed to totally reflect a light incident from the light source unit  300  above a critical angle as shown in  FIG. 3A , and is made up of transparent acryl resin such as poly methyl methacrylate (PMMA). 
     In addition, the light guiding plate  310  transmits the light incident from the light source unit  300  in a direction of the LCD panel  200 . 
     The optical film  330  includes a diffuser  332 , a prism sheet  334  and a protection sheet  336 . 
     The diffuser  332  diffuses or condenses a light transmitted from the light guiding plate  310  in accordance with the angle between the light transmitted from the light guiding plate  310  and normal of the light guiding plate  310 . 
     The prism sheet  334  condenses some of the light diffused or condensed by the diffuser  332  in a direction of the protection sheet  336 . 
     Optionally, the protection sheet  336  may be located over the prism sheet  334 , and protects the prism sheet  334  from dust, etc. In addition, the protection sheet  336  diffuses light condensed by the prism sheet  334  to increase the view angle of the LCD narrowed by the prism sheet  334 . 
     The polarization film  338  reflects a part of the light diffused by the protection sheet  336  in a direction of the light guiding plate  310  using metal patterns formed thereon, and provides the other light to the LCD panel  200 . For example, the polarization film  338  provides P wave of the light transmitted through the prism sheet  334  or the protection sheet  336  to the LCD panel  200 , and reflects S wave of the light in a direction of the light guiding plate  310 . 
     The S wave reflected by the polarization film  338  is again reflected by the light guiding plate  310  or the reflector  320 , and so the S wave reflected by the polarization film  338  is changed into a light including P wave and S wave. 
     Subsequently, the changed light is again incident to the polarization film  338  through the diffuser  332 , the prism sheet  334  and optionally the protection sheet  336 . In this case, P wave of the changed light is transmitted to the LCD panel  200  through the polarization film  338 , and S wave of the changed light is reflected in a direction of the light guiding plate  310  by the polarization film  338 . 
     Then, the reflected light is again reflected by the light guiding plate  310  or the reflector  320 , and so the reflected light is changed into a light including P wave and S wave. 
     The BLU  202  enhances the efficiency of a light by repeating the above process. 
     In the BLU  202  according to another embodiment of the present invention, the metal patterns formed on the polarization film  338  may be located toward the light guiding plate  310  as shown in  FIG. 3B . 
     The BLU  202  according to still another embodiment of the present invention may not include the protection sheet  336 . 
     In  FIG. 3C , the BLU  202  as direct-lighting type BLU includes a light source unit  350 , a transparent acryl plate  360 , an optical film  370  and a polarization film  378 .The optical film  370  includes a diffuser  372 , a prism sheet  374  and a protection sheet  376 . 
     Since elements of the present invention except the light source unit  350  and the transparent acryl plate  360  is the same as in the BLU in  FIG. 3A  and  FIG. 3B , any further description concerning to the same elements will be omitted. 
     The light source unit  350  includes a plurality of light sources  352  and a light source reflector  354 . 
     The light source reflector  354  packages the light sources  352 , and reflects a light emitted from the light sources  352  in a direction of the optical film  370 . Here, the light source reflector  354  is made up of substance having high reflectivity. In addition, the surface of the light source reflector  354  may be coated with silver (Ag). 
     The transparent acryl plate  360  transmits a light outputted from the light source unit  350 , and preferably is made up of PMMA. Here, a pattern or no pattern is formed on the transparent acryl plate  360 . 
     Hereinafter, a process of driving the LCD will be described in detail. 
     Now referring to  FIG. 2 , the BLU  202  provides a light to the LCD panel  200 . 
     Subsequently, the TFT array  222  switches the pixel electrode  216 . 
     Then, a certain voltage is provided to the pixel electrode  216  and the common electrode  218 , and so the liquid crystals included in the liquid crystal layer  220  are disposed depending on the voltage. 
     The light provided from the BLU  202  is transmitted through the liquid crystal layer  220  and the color filter  212 , and so an image is displayed on the LCD panel  200 . Here, one red sub-color filter, one green sub-color filter and one blue sub-color filter form one pixel. 
     Hereinafter, a method of manufacturing the polarization film  338  employed in the BLU  202  will be described in detail. 
       FIG. 4A  to  FIG. 4D  are sectional views a process of manufacturing the polarization film according to one embodiment of the present invention.  FIG. 4E  and  FIG. 4F  are sectional view and perspective view illustrating the polarization film manufactured by the process in  FIG. 4A  to  FIG. 4D . 
     As shown in  FIG. 4A , UV curing resin  410  is applied on a transparent film  400 . Here, the transparent film  400  is polyethylene terephthalate (PET) film, and the UV curing resin  410  is high polymer blend including a certain component reacting to ultraviolet rays (UV). On the other hand, the transparent film  400  is not limited to PET film. 
     Subsequently, a film  420  where a plurality of lines  424  having constant interval are formed is adhered or disposed on the UV curing resin  410  as shown in  FIG. 4B . Here, the lines  424  are made up of substance through which UV is not transmitted. Numeral  422  designates a UV transmitted parts of the film  420 . 
     Then, UV emitted from the UV lamp is irradiated on the film  420  as shown in  FIG. 4C . In this case, the UV curing resin  410  is cured by reacting to UV. Here, a plurality of first parts  414  corresponding to the lines  424  of the UV curing resin  410  are not cured because UV is not transmitted through the lines  424 . However, a plurality of second parts  412  of the UV curing resin  410  are cured by UV because UV is transmitted through the second parts  422  of the film  420 . 
     Subsequently, the film  420  adhered on the UV curing resin  410  is removed as shown in  FIG. 4D . 
     Then, metal substance  430  is applied on the UV curing resin  410 . In this case, metal having high reflectivity, for example, aluminum (Al), chromium (Cr) and silver (Ag), etc is used as the metal substance  430 . Of course, the metal substance  430  is not limited to the above metals. Accordingly, the metal substance  430  is not adhered on a cured part of the UV curing resin  410 , but is adhered on the other part of the UV curing resin  410  as shown in  FIG. 4E  and  FIG. 4F . As a result, a plurality of lines having constant interval are formed on the UV curing resin  410 . In other words, the polarization film  338  is manufactured. 
     The polarization film  338  according to one embodiment of the present invention performs the same function as a reflective polarization film described in Related Art when the interval of the lines is less than half wavelength of visible rays, i.e. about 100 nm to 350 nm. Preferably, the interval of the lines is about 120 mn. 
     In the above description, the metal substance  430  is applied on the UV curing resin  410  in thin film type as shown in  FIG. 4D . However, the metal substance  430  may be applied on the UV curing resin  410  in powder type. 
     From the preferred embodiments for the present invention, it is noted that modifications and variations can be made by a person skilled in the art in light of the above teachings. Therefore, it should be understood that changes may be made for a particular embodiment of the present invention within the scope and the spirit of the present invention outlined by the appended claims.