CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation application of U.S. patent application Ser. No. 13/286,584 filed on Nov. 1, 2011, which claims priority to Korean Patent Application No. 10-2011-0060841 filed on Jun. 22, 2011 in the Korean Intellectual Property Office (KIPO), and all the benefits accruing therefrom under 35 U.S.C. §119, the contents of the prior applications being herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     (a) Field of the Invention 
     Embodiments of the present invention relate generally to flat panel displays. More specifically, embodiments of the present invention relate to a light guide plate for a backlight, and a manufacturing method therefor. 
     (b) Description of the Related Art 
     Much recent effort has focused on the development of various flat panel type display devices such as liquid crystal displays (LCDs), plasma display panel (PDPs), organic light emitting diode (OLED) displays, and the like. 
     The LCD has found widespread acceptance as a mobile flat panel display due to merits such as its excellent image quality, lightness, flatness, and low power consumption. As such, it has found uses in laptop computers, computer monitors, television displays, and the like. However, since the LCD panel itself does not emit light, a separate external light source is required in order to implement high-quality images. Accordingly, LCDs typically include a backlight unit that functions as a light source, supplying light to the liquid crystal panel, thereby projecting images. 
     The backlight unit typically includes a light source unit, a light guide plate, a reflector, and the like. The light generated from the light source unit is inputted to the light guide plate and the light is internally reflected, diffused, and refracted, and ultimately output to the liquid crystal panel. 
     The light guide plate is generally manufactured via an injection molding method. In the injection molding method, the entire light guide plate is injection-molded once so as to form fine optical patterns on the lower surface, or both upper and lower surfaces of the light guide plate. Additionally, light provided from the side is reflected or refracted by a shape of the optical pattern, and progresses toward the upper surface. 
     To improve the distribution and luminance of light, the light guide plate can be molded to include a pattern such as a lenticular shape. However, this increases the cost of the light guide plate. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and therefore it may contain information that is not in the prior art. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in an effort to provide a light guide plate for a backlight having an advantage of improving straightness (or the direction and distribution) of light, and a manufacturing method therefor. 
     An exemplary embodiment of the present invention provides a light guide plate for a backlight, including: a light source unit configured to generate light; a light guide plate positioned proximate to the light source unit and including an upper surface and a lower surface; and a light emission pattern configured to diffuse a portion of the light directed toward an image display panel, and a first straight pattern configured to channel the light along a direction substantially parallel to a direction of propagation of the light generated by the light source unit, both the light emission pattern and the first straight pattern being disposed on one of the upper surface and the lower surface of the light guide plate. The first straight pattern has peaks and valleys formed in alternating and repeating manner in a direction substantially perpendicular to a direction of propagation of the light generated by the light source unit. The light emission pattern and the first straight pattern are disposed at a same surface as the light guide plate. 
     A ratio of surface area of the light emission pattern to surface area of the first straight pattern may increase with increasing distance from the light source unit. 
     The first straight pattern may comprise a plurality of unit straight patterns, and the unit straight patterns of the first straight pattern may be arranged in a matrix form on one surface of the light guide plate. 
     Surface areas of the unit straight patterns may decrease with increasing distance from the light source unit. 
     The light emission pattern may comprise a plurality of unit light emission patterns, and the unit light emission patterns of the light emission pattern may be arranged in a matrix form on one surface of the light guide plate. 
     The surface of the light emission pattern and the surface of the first straight pattern may form a step. 
     The light guide plate for a backlight may further include a second straight pattern disposed on an opposite surface of the light guide plate from the surface on which the light emission pattern and the straight pattern are disposed. 
     The second straight pattern may have peaks and valleys formed in alternating and repeating manner in a direction perpendicular to a direction of propagation of the light generated by the light source unit. 
     Another exemplary embodiment of the present invention provides a manufacturing method of a light guide plate for a backlight, including: preparing a first substrate having a surface with an uneven profile and a second substrate having a surface with a repeating pattern of protrusions; forming a mold by pressing the first substrate onto a first surface of a photoresist, and pressing the second substrate onto a second surface of the photoresist; positioning a mask on one of the first substrate and the second substrate, and exposing the mold through the mask; forming a film master comprising surfaces with the uneven profile and the repeating pattern of protrusions, by developing the mold; and processing a light guide plate by an imprint method using the film master, so as to imprint the uneven profile and the repeating pattern of protrusions on the light guide plate, the imprinted uneven profile corresponding to a light emission pattern and the imprinted repeating pattern of protrusions corresponding to a straight pattern; wherein the light emission pattern and the straight pattern are disposed at a same surface as the light guide plate. 
     A ratio of surface area of the light emission pattern to surface area of the straight pattern may increase with increasing distance from the light source unit. 
     The first straight pattern may comprise a plurality of unit straight patterns, and the unit straight patterns of the first straight pattern may be arranged in a matrix form on one surface of the light guide plate. 
     Surface areas of the plurality of unit straight patterns may decrease with increasing distance from the light source unit. 
     The light emission pattern may comprise a plurality of unit light emission patterns, and the unit light emission patterns of the light emission pattern may be arranged in a matrix form on one surface of the light guide plate. 
     The surface of the light emission pattern and the surface of the first straight pattern may form a step. 
     The manufacturing method of a light guide plate for a backlight may further include forming a second straight pattern disposed on an opposite surface of the light guide plate from the surface on which the light emission pattern and the first straight pattern are disposed. 
     The second straight pattern may be formed by a screen printing method using an ink cured or curable by ultraviolet rays. 
     Yet another exemplary embodiment of the present invention provides a light guide plate for a backlight, including: a light source unit configured to generate light; a light guide plate positioned proximate to the light source unit and including an upper surface and a lower surface; a first straight pattern disposed on the upper surface of the light guide plate and configured to channel the light along a direction substantially parallel to a direction of propagation of the light generated by the light source unit; and a second straight pattern and a light emission pattern disposed on the lower surface of the light guide plate, the light emission pattern configured to diffuse a portion of the light directed toward the image display panel, and the second straight pattern configured to channel the light toward the image display panel. The first straight pattern and the second straight pattern each have peaks and valleys formed in alternating and repeating manner in a direction substantially perpendicular to a direction of propagation of the light generated by the light source unit, and the light emission pattern is disposed between adjacent second straight patterns and has peaks and valleys formed in alternating and repeating manner in a direction substantially parallel to a direction of propagation of the light generated by the light source unit. 
     Still another exemplary embodiment of the present invention provides a light guide plate for a backlight, including: a light source unit configured to generate light; a light guide plate positioned proximate to the light source unit and including an upper surface and a lower surface; a first straight pattern and a second straight pattern disposed on the upper surface and the lower surface of the light guide plate separately, each of the straight patterns configured to channel the light along a direction substantially parallel to a direction of propagation of the light generated by the light source unit; and a light emission pattern including a plurality of dots disposed on the second straight pattern and configured to diffuse a portion of the light directed toward the image display panel. The first straight pattern and the second straight pattern each have peaks and valleys formed in alternating and repeating manner in a direction substantially perpendicular to a direction of propagation of the light generated by the light source unit. Also, a pitch of the plurality of dots is at least three times a peak pitch of the second straight pattern in a direction substantially perpendicular to a direction of propagation of the light generated by the light source unit. 
     Still yet another exemplary embodiment of the present invention provides a method of manufacturing a light guide plate for a backlight, including: preparing a light source unit configured to generate light, and a light guide plate positioned proximate to the light source unit and including an upper surface and a lower surface; positioning a mask on the upper surface or the lower surface of the light guide plate; and forming a straight pattern and a light emission pattern at the same time by printing an ink curable by ultraviolet rays using the mask of the light guide plate. The straight pattern has peaks and valleys formed in alternating and repeating manner in a direction substantially perpendicular to a direction of propagation of the light generated by the light source unit. Also, the light emission pattern is disposed between adjacent straight patterns and has peaks and valleys formed in alternating and repeating manner in a direction substantially parallel to a direction of propagation of the light generated by the light source unit. 
     According to exemplary embodiments of the present invention, the manufacturing cost can be reduced by simultaneously forming a light emission pattern and a straight pattern on one surface of a light guide plate by using an imprint method. Also, uniformity of light from a planar light source inputted to a liquid crystal panel can be improved by improving the straightness of the light. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view illustrating a light guide plate for a backlight according to an exemplary embodiment of the present invention. 
         FIGS. 2 and 3  are cross-sectional views taken along a line II-II of  FIG. 1 . 
         FIG. 4  is a photograph illustrating a light emission pattern formed on one surface of the light guide plate of  FIG. 1 . 
         FIG. 5  is a photograph illustrating a straight pattern formed on one surface of the light guide plate of  FIG. 1 . 
         FIGS. 6 to 11  are cross-sectional views illustrating a method of manufacturing a light guide plate for a backlight according to another exemplary embodiment of the present invention. 
         FIG. 12  is a plan view illustrating a light guide plate for a backlight according to yet another exemplary embodiment of the present invention. 
         FIG. 13  is a plan view illustrating a light guide plate for a backlight according to still another exemplary embodiment of the present invention. 
         FIG. 14  is a perspective view illustrating a light guide plate for a backlight according to still yet another exemplary embodiment of the present invention. 
         FIGS. 15 and 16  are front views of a light guide plate viewed in the first direction of  FIG. 14 . 
         FIG. 17  is a perspective view illustrating a light guide plate for a backlight according to still yet another exemplary embodiment of the present invention. 
         FIG. 18  is a schematic diagram illustrating a method of manufacturing a light guide plate for a backlight according to still yet another exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. On the contrary, exemplary embodiments introduced herein are provided to make disclosed contents thorough and complete and sufficient transfer the spirit of the present invention to those skilled in the art. 
     In the drawings, the thickness of layers, films, panels, regions, etc., are exaggerated for clarity. It will be understood that when a layer is referred to as being “on” another layer or substrate, it can be directly on the other layer or intervening them may also be present. Like reference numerals designate like elements throughout the specification. 
       FIG. 1  is a plan view illustrating a light guide plate for a backlight according to an exemplary embodiment of the present invention.  FIGS. 2 and 3  are cross-sectional views taken along line II-II of  FIG. 1 .  FIG. 4  is a photograph illustrating a light emission pattern formed on one surface of the light guide plate of  FIG. 1 .  FIG. 5  is a photograph illustrating a straight pattern formed on one surface of the light guide plate of  FIG. 1 . 
     Referring to  FIGS. 1 and 2 , a light guide plate for a backlight according to an exemplary embodiment of the present invention includes a light source unit L and a light guide plate  200  adjacent to the light source unit L. 
     The light source unit L may be a side type backlight or a direct type backlight depending on the layout of the light source. The light source can utilize a fluorescent lamp, an LED element, or the like. 
     A light emission pattern  300  and a straight pattern  400  are disposed on one surface of the light guide plate  200 . 
     Depending on the relative positions of the light emission pattern  300  and light source unit L, the light emission pattern  300  reflects, diffuses, and/or refracts the light inputted to the light guide plate  200  from the light source unit L, so as to input or direct the light to a liquid crystal panel or other image display panel. Referring to  FIG. 4 , the light emission pattern  300  has an uneven surface. The light emission pattern  300  is formed on the same surface of the light guide plate  200  as the straight pattern  400 , but is not formed on the straight pattern  400 . That is, the light emission pattern  300  and the straight pattern  400  are disposed so as not to overlap with each other. 
     The straight pattern  400  allows light generated from the light source unit L to be channeled, or transmitted more directly to the light guide plate  200 , and to uniformly reach far away from the light source unit L. As shown in  FIG. 1 , the straight pattern  400  can include a plurality of unit straight patterns each having a dot shape and arranged in a matrix form on one surface of the light guide plate  200 . 
     The plurality of unit straight patterns may have a surface upon which peaks and valleys are repetitively formed along a direction which is substantially perpendicular to a leading direction LD of the light generated from the light source unit L.  FIG. 5  shows a prism shape as an example of the unit straight pattern shape. However, the unit straight pattern shape is not limited to a prism shape, and may be any shape, such as a semicircular shaped peak. 
     The surface area of the unit straight patterns decreases with increasing distance from the light source unit L in direction LD. Accordingly, portions of the light guide plate  200  closer to the light source unit L have more surface area devoted to the unit straight patterns and less devoted to the light emission pattern  300 , while portions of plate  200  farther from light source unit L have relatively less surface area devoted to the unit straight patterns and more to the light emission pattern  300 . In other words, the ratio of surface area of the light emission pattern  300  to surface area of the straight pattern  400  increases with increasing distance from the light source unit L. 
     As shown in  FIG. 2 , the light emission pattern  300  and the straight pattern  400  may have step differences in their heights. 
     As shown in  FIG. 3 , straight patterns may be additionally disposed on the opposite surface of the light guide plate  200  on which the light emission pattern  300  is located. This additional straight pattern may have a shape in which peaks and valleys are repetitively formed along a direction which is substantially perpendicular to the leading direction LD of the light generated from the light source unit L, like the straight pattern  400  described above. That is, the peaks and valleys repeat in alternating manner, to produce a repeating pattern of peaks followed by valleys. In order to distinguish the straight pattern  400  described above from the added straight pattern, the straight pattern described above is referred to as a first straight pattern  400 , and the added straight pattern is termed a second straight pattern  450 . 
       FIGS. 6 to 11  are cross-sectional views illustrating a manufacturing method of a light guide plate for a backlight according to another exemplary embodiment of the present invention. 
     Referring to  FIG. 6 , a first substrate  30  formed with uneven patterns (i.e. having a surface with an uneven profile), a second substrate  10  formed with a repeating arrangement of straight patterns such as a prism shape, and a photoresist  20  are prepared. 
     Referring to  FIG. 7 , the first substrate  30  and the second substrate  10  are pressed onto each surface of the photoresist  20 , and then exposed by using a mask. 
     Referring to  FIG. 8 , a mold configured by the first substrate  30 , the second substrate  10 , and the photoresist  20  is developed, and then the first substrate  30  is separated to form a film master  40 . The film master  40  includes a straight pattern X and a light emission pattern Y both facing the same direction (here, upward). 
     Referring to  FIG. 9 , a UV resin  50  is coated on the surface of the film master  40 . 
     Referring to  FIG. 10 , the film master  40  coated with the UV resin  50  is attached onto the light guide plate  200 , and the UV resin  50  is cured. 
     Referring to  FIG. 11 , the film master  40  is separated from the light guide plate  200  and a straight pattern X′ and a light emission pattern Y′ are formed on the same surface of the light guide plate  200 . 
     In this exemplary embodiment, the manufacturing cost can be reduced by simultaneously forming the light emission pattern and the straight pattern on the same surface of the light guide plate, via an imprint method. 
       FIG. 12  is a plan view illustrating a light guide plate for a backlight according to yet another exemplary embodiment of the present invention. 
     Referring to  FIG. 12 , a light guide plate has a shape similar to the exemplary embodiment described with reference to  FIGS. 1 and 2 . However, unlike the exemplary embodiment of  FIG. 1 , positions of a light emission pattern and a straight pattern are different from each other. 
     In the exemplary embodiment, a straight pattern  500  has a shape in which peaks and valleys are repetitively formed along a direction which is substantially perpendicular to a leading direction LD of the light generated from the light source unit L. However, unlike the exemplary embodiment of  FIG. 1 , a plurality of unit straight patterns are not formed. Instead, a light emission pattern  600  is formed to include a plurality of unit light emission patterns each having a dot shape and which are collectively arranged in a matrix form on one surface of the light guide plate. The size (or surface area) of the unit light emission patterns increases with increasing distance from unit L in the direction LD. Accordingly, the density of the unit light emission patterns increases as the density of light from unit L decreases, compensating for reduction in brightness, such that luminance in a planar light source inputted from the light guide plate to the liquid crystal panel may be more uniform. 
     The straight pattern  500  may be removed from a region at which the light emission pattern  600  is disposed. 
       FIG. 13  is a plan view illustrating a light guide plate for a backlight according to still another exemplary embodiment of the present invention. 
     In this exemplary embodiment, and similar to the exemplary embodiment of  FIG. 12 , a straight pattern  700  is formed, but a light emission pattern  800  is elongated in a leading direction LD of the light, rather than being arranged in a matrix configuration. In addition, the unit light emission patterns increases in width with increasing distance from unit L in direction LD. 
       FIG. 14  is a perspective view illustrating a light guide plate for a backlight according to still yet another exemplary embodiment of the present invention.  FIGS. 15 and 16  are front views of a light guide plate viewed in a first direction D1. The first direction D1 represents a direction in which light is inputted to a light guide plate  200  from a light source unit L. 
     Referring to  FIGS. 14 to 16 , a first straight pattern  210  is disposed on an upper surface of the light guide plate  200  and a second straight pattern  220  is disposed on a lower surface of the light guide plate  200 . The first straight pattern  210  and the second straight pattern  220  each have a shape in which peaks and valleys are repetitively formed along a direction perpendicular to the first direction D1. In  FIG. 14 , peak shapes of the straight patterns  210  and  220  are semicircular in cross section, but are not limited thereto and may be have various other shapes such as a prism shape or the like. 
     A dot-shaped light emission pattern  230  is disposed on the second straight pattern  220 . 
     In the exemplary embodiment, a peak pitch of the second straight pattern  220  (i.e. the distance between adjacent peaks of the second straight pattern  220 ) may be a half or less of a peak pitch of the first straight pattern  210  in a direction perpendicular to the first direction D1. A pitch of the dot-shaped light emission pattern  230  (i.e. the distance between centers of adjacent dot-shaped light emission patterns  230 ) may be at least three times the peak pitch of the second straight pattern  220 . If the pitch of the dot-shaped light emission pattern  230  is three times the peak pitch of the second straight pattern  220 , as shown in  FIG. 15 , the dot of the light emission pattern  230  may be formed at the valley of the second straight pattern  220 . Accordingly, a physical interference pattern may be generated between the second straight pattern  220  and the dots of the light emission pattern  230 . Therefore, in the light guide plate for a backlight according to the exemplary embodiment, the pitch of the dot-shaped light emission pattern  230  is at least three times the peak pitch of the second straight pattern  220 , such that the interference pattern can be prevented from being generated. 
       FIG. 17  is a perspective view illustrating a light guide plate for a backlight according to still yet another exemplary embodiment of the present invention. 
     Referring to  FIG. 17 , similar to the exemplary embodiment described in  FIG. 14 , a first straight pattern  210  is disposed on an upper surface of a light guide plate  200  and a second straight pattern  240  is disposed on a lower surface of the light guide plate  200 . The first straight pattern  210  and the second straight pattern  240  each have a shape in which peaks and valleys are repetitively formed along a direction perpendicular to a leading direction of the light generated from the light source unit. In the exemplary embodiment, a light emission pattern  250  is disposed between adjacent second straight patterns  240 , and has a shape in which peaks and valleys are repetitively formed along a direction parallel to a leading direction of the light generated from the light source unit. 
       FIG. 18  is a schematic diagram illustrating a method of manufacturing a light guide plate for a backlight according to still yet another exemplary embodiment of the present invention. 
     Referring to  FIG. 18 , a mask  260  is disposed on one surface of a light guide plate  200 , and then a pattern  280  is printed by a screen printing method. In this case, the ink used may be a material curable by ultraviolet rays (UV), and may be a low viscosity ink that forms a lens shape due to surface tension. Since ultraviolet ray (UV) curable ink is used, a light emission pattern may be formed on the light guide plate without using a separate optical scattering agent. In addition, like the exemplary embodiment of  FIG. 16 , the second straight pattern  240  and the light emission pattern  250  may be simultaneously formed on one surface of the light guide plate by using this screen printing method. 
     The straight pattern and the light emission pattern of the exemplary embodiments described above may be formed by using the screen printing method described in  FIG. 18 . 
     While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 
     DESCRIPTION OF SYMBOLS 
     
         
         
           
               200 : Light guide plate 
               230 ,  300 ,  600 ,  800 : Light emission pattern 
               210 ,  220 ,  240 ,  400 ,  450 ,  500 ,  700 : Straight pattern
A light guide plate for a backlight. The light guide plate includes: a light source unit for generating light; a light guide plate proximate to the light source unit and including an upper surface and a lower surface; and a light emission pattern configured to diffuse a portion of the light directed toward an image display panel, and a first straight pattern configured to channel the light along a direction substantially parallel to a direction of propagation of the light generated by the light source unit, both the light emission pattern and the first straight pattern being disposed on one of the upper surface and the lower surface of the light guide plate, in which the first straight pattern has peaks and valleys formed in alternating and repeating manner in a direction substantially perpendicular to a direction of propagation of the light generated by the light source unit.