Patent Publication Number: US-2010110331-A1

Title: Optical film, backlight unit,  and liquid crystal display

Description:
This application claims the benefit of Korean Patent Application No. 10-2008-0109909 filed on Nov. 6, 2008 and No. 10-2008-0115000 filed on Nov. 19, 2008 the entire contents of which is incorporated by reference. 
     BACKGROUND 
     1. Field 
     Embodiments of the invention relate to an optical film, a backlight unit including the optical film, and a liquid crystal display including the backlight unit. 
     2. Description of the Related Art 
     A display field visually displays information of various electrical signals. In the display field, various kinds of flat panel displays having excellent characteristics such as thin profile, lightness in weight, and low power consumption have been introduced. Additionally, flat panel displays are replacing cathode ray tubes (CRT). 
     Examples of flat panel displays include a liquid crystal display (LCD), a plasma display panel (PDP), a field emission display (FED), and an electroluminescence display (ELD). The liquid crystal display is used as a display panel of notebooks, monitors of personal computers, and TV monitors because of a high contrast ratio and excellent display characteristics of a moving picture. 
     The liquid crystal display is considered as a light receiving display. The liquid crystal display includes a liquid crystal display panel that displays an image and a backlight unit that is positioned under the liquid crystal display panel to provide the liquid crystal display panel with light. 
     The backlight unit includes a light source and an optical sheet. The optical sheet includes a diffusion sheet, a prism, or a protective sheet. In the backlight unit, the optical sheet including a plurality of sheets may be used to diffuse and focus light produced by the light source. However, there may be limits to improvement in fabrication yield and improvement in a luminance of the backlight unit. 
     SUMMARY 
     Embodiments of the invention provide an optical film capable of improving a luminance and preventing generation of a bright line, a backlight unit including the optical film, and a liquid crystal display including the backlight unit. 
     In one aspect, there is an optical film comprising a base and a projection including a plurality of microlenses and a plurality of grooves positioned around the plurality of microlenses. 
     In another aspect, there is a back light unit comprising a light source and an optical film on the light source, the optical film including a base and a projection including a plurality of microlenses, a plurality of grooves positioned around the plurality of microlenses, and a remaining portion excluding the microlenses and the grooves from the projection, wherein a relationship P: 2W 1 +W 2  between the microlenses, the grooves, and the remaining portion is approximately 25:1 to 25:15, where P is a pitch of the microlenses, W 1  is a width of one of the grooves inside the pitch P of the microlenses, and W 2  is a width of the remaining portion inside the pitch P of the microlenses. 
     In still another aspect, there is a liquid crystal display comprising a light source, an optical film on the light source, the optical film including a base and a projection including a plurality of microlenses, a plurality of grooves positioned around the plurality of microlenses, and a remaining portion excluding the microlenses and the grooves from the projection, wherein a relationship P: 2W 1 +W 2  between the microlenses, the grooves, and the remaining portion is approximately 25:1 to 25:15, where P is a pitch of the microlenses, W 1  is a width of one of the grooves inside the pitch P of the microlenses, and W 2  is a width of the remaining portion inside the pitch P of the microlenses, and a liquid crystal display panel on the optical film. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings: 
         FIG. 1  illustrates an exemplary method of manufacturing an optical film according to an embodiment of the invention; 
         FIGS. 2 to 5  illustrate an optical film according to a first exemplary embodiment of the invention; 
         FIGS. 6 and 7  illustrate an optical film according to a second exemplary embodiment of the invention; 
         FIGS. 8 and 9  illustrate an optical film according to a third exemplary embodiment of the invention; 
         FIGS. 10 and 11  illustrate an optical film according to a fourth exemplary embodiment of the invention; 
         FIGS. 12 and 13  illustrate various structures of an optical film according to embodiments of the invention; 
         FIGS. 14 and 15  illustrate an exemplary configuration of a backlight unit according to an embodiment of the invention; 
         FIGS. 16 and 17  illustrate another exemplary configuration of a backlight unit according to an embodiment of the invention; and 
         FIGS. 18 and 19  illustrate an exemplary structure of a liquid crystal display according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail embodiments of the invention examples of which are illustrated in the accompanying drawings. 
       FIG. 1  illustrates an exemplary method of manufacturing an optical film according to an embodiment of the invention. 
     As shown in  FIG. 1 , a first resin  1  and a second resin  2  are coextruded. More specifically, an extrusion process is simultaneously performed on the first and second resins  1  and  2  by providing the first resin  1  to a first extruder  10  and providing the second resin  2  to a second extruder  20 . 
     A material of the first and second resins  1  and  2  may use polystyrene (PS), polyacrylate (PA), polymethylmethacrylate (PMMA), polycarbonate (PC), or polyethyleneterephthalate (PET). Other materials may be used. It may be preferable to use polycarbonate having a refractive index of 1.58 in consideration of optical application. 
     Each of the first and second resins  1  and  2  may use polycarbonate pellets. The pellets may be solidified particles of a predetermined material. Namely, the pellets may be not powders but large-sized particles. The pellets may be formed by mixing each of the first and second resins  1  and  2  with an additive such as an antioxidant and an UV additive. 
     Each of the first and second resins  1  and  2  may include diffusion particles. When the first and second resins  1  and  2  including the diffusion particles are used to manufacture an optical film, the first and second resins  1  and  2  may contribute to light diffusion of the optical film. 
     If the first and second resins  1  and  2  do not include the diffusion particles, an optical film according to a first exemplary embodiment of the invention described later may be manufactured. If the first and second resins  1  and  2  include the diffusion particles, an optical film according to a second exemplary embodiment of the invention described later may be manufactured. If only the first resin  1  includes the diffusion particles, an optical film according to a third exemplary embodiment of the invention described later may be manufactured. 
     The diffusion particles may be formed of at least one selected from the group consisting of silicon, polymethylmethacrylate (PMMA), and polycarbonate (PC). The diffusion particles may have a diameter of approximately 1 μm to 20 μm. Other materials and diameters may be used. 
     An inner temperate of each of the first and second extruders  10  and  20  is approximately 280 to 300° C. Therefore, if resin pellets are provided to each of the first and second extruders  10  and  20 , the resin pellets are melted inside the first and second extruders  10  and  20 , and then the first and second resins  1  and  2  are discharged through extrusion pipes  11  and  21  of the first and second extruders  10  and  20 . 
     The coextruded first and second resins  1  and  2  are simultaneously rolled using a first roll  30  having a first structured surface  31  and a second roll  40  having a second structured surface  41  to form an optical film  60  including a base  55  having a curved surface and a projection  56 . 
     More specifically, if the first and second resins  1  and  2  are extruded respectively through the extrusion pipes  11  and  21 , the first and second resins  1  and  2  are together extruded. 
     A surface temperature of each of the first and second rolls  30  and  40  is kept at approximately 90 to 100° C. The first and second resins  1  and  2  rolled between the first and second rolls  30  and  40  may be rapidly cooled and solidified. 
     The coextruded first and second resins  1  and  2  pass between the first and second rolls  30  and  40  and are rolled, and thus the optical film  60  including the base  55  and the projection  56  may be manufactured. 
     The first structured surface  31  of the first roll  30  may have a meandering wave pattern, and the second structured surface  41  of the second roll  40  may have a reversed shape of the microlens. 
     The surface of the second roll  40  may be coated with nickel (Ni) and then ceramic, and then the coated surface of the second roll  40  is processed using a laser to form the second structured surface  41  of the second roll  40 . More specifically, if a laser beam is irradiated to the surface of the second roll  40 , ceramic in a portion of the second roll  40 , to which the laser beam is irradiated, is melted and flows laterally. Hence, the surface of the second roll  40  has a reversed shape of the microlens. Because a melted form of ceramic remains in the surface of the second roll  40 , the microlens may have a predetermined surface roughness when the microlens is manufactured using the second roll  40  in a subsequent process. Hence, the optical film  60  rolled by the first and second rolls  30  and  40  may include a plurality of microlenses, the projection  56  having grooves positioned around the plurality of microlenses, and the base  55  having the curved surface. 
     One surface of the optical film  60  has a reversed shape of the first structured surface  31  of the first roll  30  and has a curved surface of a meandering wave pattern. Another surface of the optical film  60  has a reversed shape of the second structured surface  41  of the second roll  40  and has the microlens-shaped projection  56 . Accordingly, the optical film  60  including the base  55 , of which a lower surface is the curved surface, and the projection  56  may be formed. 
     On the other hand, the first structured surface  31  of the first roll  30  may be a flat surface. Hence, the one surface of the optical film  60  may be a flat surface. 
     Hereinafter, optical films manufactured by the exemplary method of manufacturing the optical film according to the embodiment of the invention illustrated in  FIG. 1  are described later. 
       FIGS. 2 to 5  illustrate an optical film according to a first exemplary embodiment of the invention. 
     As shown in  FIGS. 2 to 5 , an optical film  100  according to a first exemplary embodiment of the invention may include a base  110  and a projection  120  on the base  110 . The projection  120  may include a plurality of microlenses  121 , a plurality of grooves  122  positioned around the plurality of microlenses  121 , and a remaining portion  123  excluding the microlenses  121  and the grooves  122  from the projection  120 . 
     The base  110  may support the optical film  100  and transmit light coming from a light source. The base  110  may be formed of polystyrene (PS), polyacrylate (PA), polymethylmethacrylate (PMMA), polycarbonate (PC), or polyethyleneterephthalate (PET). Other materials may be used. It may be preferable to use polycarbonates having a refractive index of 1.58 in consideration of optical application. 
     A lower surface  111  of the base  110  may be a curved surface. The curved surface may have a regular or irregular pattern. On the other hand, as shown in  FIG. 3 , the lower surface  111  of the base  110  may be a flat surface. 
     The projection  120  on the base  110  may focus or diffuse light. The projection  120  may be formed of polystyrene (PS), polyacrylate (PA), polymethylmethacrylate (PMMA), polycarbonate (PC), or polyethyleneterephthalate (PET). Other materials may be used. It may be preferable to use polycarbonates having a refractive index of 1.58 in consideration of optical application. 
     The plurality of microlenses  121  may have an embossed form of a hemispherical shape. A diffusivity, a refractive index, a focusing level, etc. of the microlenses  121  may change depending on a size and a density of the microlenses  121 . Hence, a pitch P between the microlenses  121  may be approximately 25 μm to 75 μm. Diameters of the microlenses  121  may be uniform or non-uniform (i.e., the diameters may vary). Heights of the microlenses  121  may be uniform or non-uniform (i.e., the heights may vary). 
     The diameter of each of the microlenses  121  may be approximately 20 μm to 60 μm. The microlenses  121  may occupy 50% to 90% of a whole area of the projection  120 . A difference between the heights of the microlenses  121  may be equal to or less than approximately 5 μm. Other diameters, percentages, height differences may be used. 
     As described above, when the microlens  121  has the embossed form of the hemispherical shape, a portion of light from the outside (for example, from a bottom of the microlens  121 ) may be uniformly refracted from the hemispherical surface in an azimuth direction and then be transmitted by the microlens  121 . Because of this, a portion of light coming from the bottom of the microlens  121  may be uniformly diffused upward and may be focused. 
     An average surface roughness of each of the microlenses  121  may be approximately 0.3 μm to 1.5 μm. When the average surface roughness of the microlenses  121  is equal to or greater than 0.3 μm, a diffusion characteristic of the optical film  100  may be improved. When the average surface roughness of the microlenses  121  is equal to or less than 1.5 μm, a luminance characteristic of the optical film  100  may be improved. 
     The microlens  121 , the groove  122 , and the remaining portion  123  of the projection  120  are described in detail with reference to  FIG. 4 . 
     As shown in  FIG. 4 , the grooves  122  are positioned around the microlenses  121 . The grooves  122  may be formed during a fabrication of the optical film  100 . An average surface roughness of each of the grooves  122  may be approximately 0.1 μm to 3 μm. A width of each of the grooves  122  may be approximately 1 μm to 5 μm. Other average surface roughnesses or widths may be used. 
     The remaining portion  123  may be a remaining portion excluding the microlens  121  and the groove  122  from the projection  120 . The remaining portions  123  may have a uniform roughness. An average surface roughness of the remaining portions  123  may be approximately 0.1 μm to 3 μm. Other average surface roughnesses may be used. 
     As shown in  FIGS. 2 and 3 , a relationship P: 2W 1 +W 2  between the microlenses  121 , the grooves  122 , and the remaining portion  123  may be approximately 25:1 to 25:15, where P is a pitch of the microlenses  121 , W 1  is a width of one of the grooves  122  inside the pitch P of the microlenses  121 , and W 2  is a width of the remaining portion  123  inside the pitch P of the microlenses  121 . The pitch P is a distance between center points of the adjacent microlenses  121 . 
     When the relationship P: 2W 1 +W 2  is equal to or greater than 25:1, the diffusion characteristic of the optical film  100  may be improved because of an increase in a width of each of the grooves  122  and the remaining portion  123 . When the relationship P: 2W 1 +W 2  is equal to or less than 25:15, a reduction in the luminance characteristic of the optical film  100  resulting from the wide pitch P of the microlens  121  may be prevented. 
       FIG. 5  is a plane view schematically illustrating an optical film having the size of 100 μm×100 μm. 
     As shown in  FIG. 5 , in the optical film  100  according to the first exemplary embodiment of the invention, a ratio S 1 : (S 2 +S 3 ) of an area S 1  of the microlenses  121  to a sum of an area S 2  of the grooves  122  and an area S 3  of the remaining portion  123  may be approximately 20:11 to 20:50. The ratio S 1 : (S 2 +S 3 ) is obtained by changing the sum (S 2 +S 3 ) of areas from 11 to 50 in a state where the area S 1  of the microlenses  121  is fixed at 20. 
     When the ratio S 1 : (S 2 +S 3 ) is equal to or greater than 20:11, the diffusion characteristic of the optical film  100  may be improved because of an increase in the area S 2  of the grooves  122  and the area S 3  of the remaining portion  123 . When the ratio S 1 : (S 2 +S 3 ) is equal to or less than 20:50, a reduction in the luminance characteristic of the optical film  100  resulting from the large area S 2  of the grooves  122  and the large area S 3  of the remaining portion  123  may be prevented. 
     A ratio S 2 :S 3  of the area S 2  of the grooves  122  to the area S 3  of the remaining portion  123  may be approximately 1:1 to 1:6.25. When the ratio S 2 :S 3  is equal to or greater than 1:1, the diffusion characteristic of the optical film  100  may be improved because of an increase in the area S 3  of the remaining portion  123 . When the ratio S 2 :S 3  is equal to or less than 1:6.25, a reduction in the luminance characteristic of the optical film  100  resulting from the large area S 3  of the remaining portion  123  may be prevented. 
     As described above, in the optical film  100  according to the first exemplary embodiment of the invention, the base  110  may diffuse light from the light source under the base  110 , and light coming from the projection  120  may be focused and diffused. Hence, the luminance and the luminance uniformity of light may be simultaneously improved. 
       FIGS. 6 and 7  illustrate an optical film according to a second exemplary embodiment of the invention. 
     As shown in  FIGS. 6 and 7 , an optical film  200  according to a second exemplary embodiment of the invention may include a base  210  and a projection  220  on the base  210 . The projection  220  may include a plurality of microlenses  221 , a plurality of grooves  222  positioned around the plurality of microlenses  221 , and a remaining portion  223  excluding the microlenses  221  and the grooves  222  from the projection  220 . 
     A lower surface  211  of the base  210  may be a curved surface in the same manner as the first exemplary embodiment. The curved surface may have a regular or irregular pattern. On the other hand, as shown in  FIG. 7 , the lower surface  211  of the base  210  may be a flat surface. 
     An average surface roughness of each of the microlenses  221  may be approximately 0.3 μm to 1.5 μm. An average surface roughness of each of the grooves  222  may be approximately 0.1 μm to 3 μm. A width of each of the grooves  222  may be approximately 1 μm to 5 μm. Other average surface roughnesses or widths may be used. 
     In the same manner as the first exemplary embodiment, a relationship P: 2W 1 +W 2  between the microlenses  221 , the grooves  222 , and the remaining portion  223  may be approximately 25:1 to 25:15, where P is a pitch of the microlenses  221 , W 1  is a width of one of the grooves  222  inside the pitch P of the microlenses  221 , and W 2  is a width of the remaining portion  223  inside the pitch P of the microlenses  221 . The pitch P is a distance between center points of the adjacent microlenses  221 . 
     Further, a ratio S 1 : (S 2 +S 3 ) of an area S 1  of the microlenses  221  to a sum of an area S 2  of the grooves  222  and an area S 3  of the remaining portion  223  may be approximately 20:11 to 20:50. A ratio S 2 :S 3  of the area S 2  of the grooves  222  to the area S 3  of the remaining portion  223  may be approximately 1:1 to 1:6.25. 
     The base  210  and the projection  220  may include a plurality of diffusion particles  230 . The diffusion particles  230  may be formed of at least one selected from the group consisting of silicon, polymethylmethacrylate (PMMA), and polycarbonate (PC). The diffusion particles  230  may have a diameter of approximately 1 μm to 20 μm. The diffusion particles  230  may have the uniform or nonuniform size and may be uniformly or nonuniformly distributed in each of the base  210  and the projection  220 . The diffusion particles  230  may diffuse light from a light source to improve luminance uniformity. 
     Because the optical film  200  according to the second exemplary embodiment of the invention further includes the diffusion particles  230  unlike the optical film  100  according to the first exemplary embodiment of the invention, the diffusion characteristic of light may be further improved. 
       FIGS. 8 and 9  illustrate an optical film according to a third exemplary embodiment of the invention. 
     As shown in  FIGS. 8 and 9 , an optical film  300  according to a third exemplary embodiment of the invention may include a base  310  and a projection  320  on the base  310 . The projection  320  may include a plurality of microlenses  321 , a plurality of grooves  322  positioned around the plurality of microlenses  321 , and a remaining portion  323  excluding the microlenses  321  and the grooves  322  from the projection  320 . The base  310  may include a first base area  315  and a second base area  316  under the first base area  315 . 
     The second base area  316  may include a plurality of diffusion particles  330 . The diffusion particles  330  may be formed of at least one selected from the group consisting of silicon, polymethylmethacrylate (PMMA), and polycarbonate (PC). The diffusion particles  330  may have a diameter of approximately 1 μm to 20 μm. The diffusion particles  330  may have the uniform or nonuniform size and may be uniformly or nonuniformly distributed in the second base area  316 . The diffusion particles  330  may diffuse light from a light source to improve luminance uniformity. 
     The first base area  315  and the second base area  316  may be distinguished from each other depending on whether or not the diffusion particles  330  exist. The second base area  316  may occupy an area ranging from a bottom of the base  310  to an end of a diffusion particle  330  in an uppermost portion, and the first base area  315  may occupy an area ranging from the end of the diffusion particle  330  in the uppermost portion to a top of the base  310 . A ratio T 2 :T 1  of a thickness T 2  of the second base area  316  to a thickness T 1  of the optical film  300  may be approximately 1:5 to 1:20. 
     A lower surface  311  of the base  310  may be a curved surface. The curved surface may have a regular or irregular pattern. On the other hand, as shown in  FIG. 9 , the lower surface  311  of the base  310  may be a flat surface. 
     In the same manner as the first and second exemplary embodiments, an average surface roughness of each of the microlenses  321  may be approximately 0.3 μm to 1.5 μm. An average surface roughness of each of the grooves  322  may be approximately 0.1 μm to 3 μm. A width of each of the grooves  322  may be approximately 1 μm to 5 μm. Other average surface roughnesses or widths may be used. An average surface roughness of each of the remaining portion  323  may be approximately 0.1 μm to 3 μm. Other average surface roughnesses or widths may be used. 
     In the same manner as the first and second exemplary embodiments, a relationship P: 2W 1 +W 2  between the microlenses  321 , the grooves  322 , and the remaining portion  323  may be approximately 25:1 to 25:15, where P is a pitch of the microlenses  321 , W 1  is a width of one of the grooves  322  inside the pitch P of the microlenses  321 , and W 2  is a width of the remaining portion  323  inside the pitch P of the microlenses  321 . The pitch P is a distance between center points of the adjacent microlenses  321 . 
     Further, a ratio S 1 : (S 2 +S 3 ) of an area S 1  of the microlenses  321  to a sum of an area S 2  of the grooves  322  and an area S 3  of the remaining portion  323  may be approximately 20:11 to 20:50. A ratio S 2 :S 3  of the area S 2  of the grooves  322  to the area S 3  of the remaining portion  323  may be approximately 1:1 to 1:6.25. 
       FIGS. 10 and 11  illustrate an optical film according to a fourth exemplary embodiment of the invention. 
     As shown in  FIGS. 10 and 11 , an optical film  400  according to a fourth exemplary embodiment of the invention may include a base  410  and a projection  420  on the base  410 . The projection  420  may include a plurality of microlenses  421 , a plurality of grooves  422  positioned around the plurality of microlenses  421 , and a remaining portion  423  excluding the microlenses  421  and the grooves  422  from the projection  420 . The base  410  may include a first base area  415  and a second base area  416  under the first base area  415 . 
     The first base area  415  and the projection  420  may include a plurality of diffusion particles  430 . The diffusion particles  430  may be formed of at least one selected from the group consisting of silicon, polymethylmethacrylate (PMMA), and polycarbonates (PC). The diffusion particles  430  may have a diameter of approximately 1 μm to 20 μm. The diffusion particles  430  may have the uniform or nonuniform size and may be uniformly or nonuniformly distributed in each of the first base area  415  and the projection  420 . The diffusion particles  430  may diffuse light from a light source to improve luminance uniformity. 
     The first base area  415  and the second base area  416  may be distinguished from each other depending on whether or not the diffusion particles  430  exist. The first base area  415  may occupy an area ranging from a bottom of the projection  420  to an end of a diffusion particle  430  in a lowermost portion, and the second base area  416  may occupy an area ranging from the end of the diffusion particle  430  in the lowermost portion to a bottom of the base  410 . A ratio T 2 :T 1  of a thickness T 2  of the second base area  416  to a thickness T 1  of the optical film  400  may be approximately 1:5 to 1:20. 
     In the same manner as the first to third exemplary embodiments, a lower surface  411  of the base  410  may be a curved surface. The curved surface may have a regular or irregular pattern. On the other hand, as shown in  FIG. 11 , the lower surface  411  of the base  410  may be a flat surface. 
     An average surface roughness of each of the microlenses  421  may be approximately 0.3 μm to 1.5 μm. An average surface roughness of each of the grooves  422  may be approximately 0.1 μm to 3 μm. A width of each of the grooves  422  may be approximately 1 μm to 5 μm. Other average surface roughnesses or widths may be used. An average surface roughness of each of the remaining portion  423  may be approximately 0.1 μm to 3 μm. Other average surface roughnesses or widths may be used. 
     In the same manner as the first to third exemplary embodiments, a relationship P: 2W 1 +W 2  between the microlenses  421 , the grooves  422 , and the remaining portion  423  may be approximately 25:1 to 25:15, where P is a pitch of the microlenses  421 , W 1  is a width of one of the grooves  422  inside the pitch P of the microlenses  421 , and W 2  is a width of the remaining portion  423  inside the pitch P of the microlenses  421 . The pitch P is a distance between center points of the adjacent microlenses  421 . 
     Further, a ratio S 1 : (S 2 +S 3 ) of an area S 1  of the microlenses  421  to a sum of an area S 2  of the grooves  422  and an area S 3  of the remaining portion  423  may be approximately 20:11 to 20:50. A ratio S 2 :S 3  of the area S 2  of the grooves  422  to the area S 3  of the remaining portion  423  maybe approximately 1:1 to 1:6.25. 
     As shown in  FIGS. 12 and 13 , the microlenses  421  may have the uniform or nonuniform size. Other sizes may be used. 
     An experimental example measuring the diffusion and luminance characteristics according to the ratio P: 2W 1 +W 2  is described below. The following experimental example may be embodied in many different forms in the embodiments of the invention. Other experimental examples may be used. 
     EXPERIMENTAL EXAMPLE  
     First resin pellets containing polycarbonates resin and an additive were provided to a first extruder, and second resin pellets containing polycarbonates resin were provided to a second extruder. Hence, the first and second pellets were coextruded. 
     The first and second pellets were extruded using a first roll having a flat surface and a second roll having a reversed shape of a microlens. 11 samples of an optical film were manufactured by changing a width W 1  of each of grooves positioned around microlenses and a width W 2  of a remaining portion in a state a pitch P of the microlenses was fixed at 25 μm. More specifically, the 11 samples were manufactured by changing a value of (2W 1 +W 2 ) to 0.6, 1, 2, 4, 6, 8, 10, 12, 14, 15, and 16 in a state the pitch P of the microlenses was fixed at 25 μm. 
     Table 1 indicates a result evaluating diffusion and luminance characteristics of the 11 samples. In the following Table 1, ×, ∘, and represent bad, good, and excellent states of the characteristics, respectively. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Diffusion 
                 Luminance 
               
               
                 P:2W1 + W2 
                 characteristic 
                 characteristic 
               
               
                   
               
             
            
               
                  25:0.6 
                 X 
                 X 
               
               
                 25:1  
                 ◯ 
                 ◯ 
               
               
                 25:2  
                 ◯ 
                 ◯ 
               
               
                 25:4  
                 ◯ 
                 ◯ 
               
               
                 25:6  
                 ⊚ 
                 ◯ 
               
               
                 25:8  
                 ⊚ 
                 ◯ 
               
               
                 25:10 
                 ⊚ 
                 ◯ 
               
               
                 25:12 
                 ⊚ 
                 ◯ 
               
               
                 25:14 
                 ◯ 
                 ◯ 
               
               
                 25:15 
                 ◯ 
                 ◯ 
               
               
                 25:16 
                 ◯ 
                 X 
               
               
                   
               
            
           
         
       
     
     As indicated in Table 1, when a ratio P: 2W 1 +W 2  was equal to or greater than 25:1, the diffusion characteristic of the optical film may be improved. When a ratio P: 2W 1 +W 2  exceeded 25:15, the luminance characteristic of the optical film may be reduced. When the ratio P: 2W 1 +W 2  was 25:6 to 25:12, the diffusion characteristic of the optical film may be further improved. 
       FIGS. 14 and 15  are an exploded perspective view and a cross-sectional view illustrating a configuration of a backlight unit according to an exemplary embodiment of the invention. 
       FIG. 14  shows an edge type backlight unit including the optical film according to the exemplary embodiments of the invention. Since the optical film according to the exemplary embodiments of the invention is described above, a further description may be briefly made or may be entirely omitted. 
     As shown in  FIGS. 14 and 15 , a backlight unit  500  according to an exemplary embodiment of the invention may be included in a liquid crystal display and may provide light to a liquid crystal display panel included in the liquid crystal display. 
     The backlight unit  500  may include a light source  520  and an optical film  530 . The backlight unit  500  may further include a light guide  540  (or light guide plate), a reflector  550  (or reflector plate), a bottom cover  560 , and a mold frame  570 . 
     The light source  520  may produce light using a driving power received from outside and may emit the produced light. 
     The light source  520  may be positioned at one side of the light guide  540  along a long axis direction of the light guide  540 . The light source  520  may be positioned at both sides of the light guide  540 . Light from the light source  520  may be directly incident on the light guide  540 . Alternatively, the light from the light source  520  may be reflected by a light source housing  522  surrounding a portion of the light source  520 , for example, surrounding about ¾ of an outer circumferential surface of the light source  520 , and then the light may be incident on the light guide  540 . 
     The light source  520  may be one of a cold cathode fluorescent lamp (CCFL), a hot cathode fluorescent lamp (HCFL), an external electrode fluorescent lamp (EEFL), and a light emitting diode (LED). Other light sources may also be used. 
     The optical film  530  may be positioned on the light guide  540 . The optical film  530  may focus the light from the light source  520 . 
     The optical film according to the exemplary embodiments of the invention includes a base and a projection including a plurality of microlenses and a plurality of grooves positioned around the plurality of microlenses. Although it is not shown, the optical film may include a prism sheet or a protective sheet. 
     The light guide  540  may face the light source  520 . The light guide  540  may guide the light so as to emit the light from the light source  520  in an upward manner. 
     The reflector  550  may be positioned under the light guide  540 . The reflector  550  may reflect the light upward. The light may come from the light source  520  and then may be emitted downward via the light guide  540 . 
     The bottom cover  560  may include a bottom portion  562  and a side portion  564  extending from the bottom portion  562  to form a recipient space. The recipient space may receive the light source  520 , the optical film  530 , the light guide  540 , and the reflector  550 . 
     The mold frame  570  may be an approximately rectangular-shaped frame. The mold frame  570  may be fastened to the bottom cover  560  from an upper side of the bottom cover  560  in a top-down manner. 
       FIGS. 16 and 17  are an exploded perspective view and a cross-sectional view illustrating another configuration of a backlight unit according to an embodiment of the invention. 
       FIGS. 16 and 17  show a direct type backlight unit. Since a backlight unit shown in  FIGS. 16 and 17  may be substantially the same as the backlight unit shown in  FIGS. 14 and 15  (except a location of a light source and changes in components depending on location of the light source), a further description may be briefly made or may be entirely omitted. 
     As shown in  FIGS. 16 and 17 , a backlight unit  600  according to an embodiment of the invention may be included in a liquid crystal display and may provide light to a liquid crystal display panel included in the liquid crystal display. 
     The backlight unit  600  may include a light source  620  and an optical film  630 . The backlight unit  600  may further include a reflector  650  (or reflector plate), a bottom cover  660 , a mold frame  670 , and a diffusion plate  680  (or diffuser). 
     The light source  620  may be positioned under the diffusion plate  680 . Therefore, light from the light source  620  may be directly incident on the diffusion plate  680 . 
     The optical film  630  may be positioned on the diffusion plate  680 . The optical film  630  may focus the light from the light source  620 . 
     The optical film according to the exemplary embodiments of the invention includes a base and a projection including a plurality of microlenses and a plurality of grooves positioned around the plurality of microlenses. Although it is not shown, the optical film may include a prism sheet or a protective sheet. 
     The diffusion plate  680  may be positioned between the light source  620  and the optical film  630  and may diffuse the light from the light source  620  in an upward manner. A shape of the light source  620  underlying the diffusion plate  680  may not be seen from a top of the backlight unit  600  because of the diffusion plate  680 . The diffusion plate  680  may further diffuse the light from the light source  620 . 
       FIGS. 18 and 19  are an exploded perspective view and a cross-sectional view illustrating a configuration of a liquid crystal display according to an exemplary embodiment of the invention.  FIGS. 18 and 19  show a liquid crystal display including the backlight unit shown in  FIGS. 14 and 15 . However, the liquid crystal display shown in  FIGS. 18 and 19  may include the backlight unit shown in  FIGS. 16 and 17 . Since the backlight unit shown in  FIGS. 18 and 19  is described above with reference to  FIGS. 14 and 15 , a further description thereof will be briefly made or will be entirely omitted. 
     As shown in  FIGS. 18 and 19 , a liquid crystal display  700  according to an exemplary embodiment of the invention may display an image using electro-optical characteristics of liquid crystals. 
     The liquid crystal display  700  may include the backlight unit  710  and a liquid crystal display panel  810 . 
     The backlight unit  710  may be positioned under the liquid crystal display panel  810  and may provide light to the liquid crystal display panel  810 . The backlight unit  710  may include a light source  720  and an optical film  730 . The backlight unit  710  may further include a light guide  740  (or light guide plate), a reflector  750  (or reflector plate), a bottom cover  760 , and a mold frame  770 . 
     The liquid crystal display panel  810  may be positioned on the mold frame  770 . The liquid crystal display panel  810  may be fixed by a top cover  820  that is fastened to the bottom cover  760  in a top-down manner. 
     The liquid crystal display panel  810  may display an image using light provided by the light source  720  of the backlight unit  710 . 
     The liquid crystal display panel  810  may include a color filter substrate  812  and a thin film transistor substrate  814  that are opposite to each other with liquid crystals interposed between the color filter substrate  812  and the thin film transistor substrate  814 . 
     The color filter substrate  812  may achieve colors of an image displayed on the liquid crystal display panel  810 . 
     The color filter substrate  812  may include a color filter array of a thin film form on a substrate made of a transparent material, such as glass or plastic. For example, the color filter substrate  812  may include red, green, and blue color filters. An upper polarizing plate may be positioned on the color filter substrate  812 . 
     The thin film transistor substrate  814  may be electrically connected to a printed circuit board  718 , on which a plurality of circuit parts are mounted, through a driving film  716 . The thin film transistor substrate  814  may apply a driving voltage received from the printed circuit board  718  to the liquid crystals in response to a driving signal received from the printed circuit board  718 . 
     The thin film transistor substrate  814  may include a thin film transistor and a pixel electrode on another substrate formed of a transparent material, such as glass or plastic. A lower polarizing plate may be positioned under the thin film transistor substrate  814 . 
     As described above, because the optical film according to the exemplary embodiments of the invention is manufactured using an extruding method, mass production is possible and production yield may increase. 
     Furthermore, because the optical film according to the exemplary embodiments of the invention includes the base having the curved surface and the projection, the optical film can efficiently focus light. Accordingly, the luminance of light can be improved. 
     Furthermore, because the optical film according to the exemplary embodiments of the invention includes the diffusion particles, the bright line in which a luminance of a portion, in which a light source is positioned under the portion, is greater than other portions, can be prevented. Accordingly, the reliability of the optical film can be improved. 
     Any reference in this specification to “one embodiment,” “an embodiment,” “example embodiment,” etc., means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with any embodiment, it is submitted that it is within the purview of one skilled in the art to effect such feature, structure, or characteristic in connection with other ones of the embodiments. 
     Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.