Abstract:
Disclosed are a side light-type backlight device with high brightness and excellent light use efficiency, a liquid crystal display device and a television receiver. The disclosed backlight device has a light guide plate that emits, from the top surface, light that entered from the side surface thereof, a substrate that is disposed at the side surface of the light guide plate and that has a plurality of LEDs emitting light from the top aligned thereon, and an outer case enclosing the light guide plate and the substrate. Of the plurality of LEDs, the end LEDs are provided with inclined sections such that the illumination direction of said end LEDs intersect with that of the other LEDs.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a side-lighting type backlight device that includes an LED light source and a light guide plate, a liquid crystal display device, and a television receiver. 
       BACKGROUND ART 
       [0002]    Conventional backlight devices that are used for liquid crystal display devices include a side-lighting type backlight device in which a light source is disposed so as to face the side surface of a light guide plate, a direct-lighting type backlight device in which a light source is disposed directly below a liquid crystal panel, and the like. The side-lighting type backlight device is used for small and medium-sized liquid crystal display devices and liquid crystal display devices that require thin-profile, in particular. The direct-lighting type backlight device is used for large monitors, televisions, and the like. In the past, the light source of these backlight devices was mainly made of cold-cathode fluorescent lamps (CCFL), but recently, in view of environmental issues, the CCFLs have been replaced by LEDs that use less power and contain no mercury. 
         [0003]    Patent Document 1 shown in  FIG. 8  is an example of the side-lighting type backlight device that uses LEDs as the light source thereof. Patent Document 1 describes a side-lighting type backlight device that has a plurality of light sources, in which four chip-type LEDs  9   a  to  9   d , for example, are provided on a light incident surface  71  of a light guide plate  7 . In light source facing portions of the light incident surface  71  (preferably two ends of the light incident surface  71 ), which face at least the chip-type LEDs  9   a  and  9   d  at the opposite ends, inclined surfaces  7   a  and  7   b  are formed, and with these inclined surfaces  7   a  and  7   b,  the chip-type LEDs  9   a  and  9   d  are disposed such that optical axes L 1  and L 2  thereof are directed toward the center of the light guide plate  7 . In Patent Document 1, with this configuration, light emitted from the respective light sources are distributed uniformly in the entire light guide plate, thereby providing the illuminating light with enhanced uniformity to a liquid crystal display element. 
         [0004]    Structures and types of a typical chip-type LED are explained with reference to  FIG. 9 . A chip-type LED  9  includes a semiconductor light-emitting element (not shown) that has an n-type semiconductor layer, a p-type semiconductor layer, and an active layer sandwiched therebetween and that is packaged in a package  15  and connecting terminals  16  (anode and cathode) that are used to connect the semiconductor light-emitting element to a circuit board, thereby supplying power, for example. Further, the package  15  has a light-emitting surface  14  where a lens that adjusts directional characteristics of illuminating light is provided. The chip-type LEDs are categorized into two types, a top-emitting type and a side-emitting type, depending on where the light-emitting surface  14  is located with respect to the package  15 . 
         [0005]    In the top-emitting type (top view type) shown in  FIG. 9(   a ), the light-emitting surface  14  is provided on the top surface of the package  15 , and light is emitted in a direction perpendicular to a mounting surface  91  that faces the connecting terminals  16 . The top-emitting type LED  9  has advantages such as higher brightness and longer life. Also, because the illumination direction is perpendicular to the mounting surface  91 , this type is mainly used for the direct-lighting type backlight device. Specifically, by disposing a substrate having the chip-type LED  9  mounted thereon below the bottom surface of the light guide plate  7  such that the mounting surface  91  becomes parallel with the light guide plate  7 , the light-emitting surface  14  of the chip-type LED  9  faces the light incident surface, which is the bottom surface, of the light guide plate  7 . 
         [0006]    On the other hand, in the side-emitting type (side view type) shown in  FIG. 9(   b ), the light-emitting surface  14  is provided on the side surface of the package  15 , and light is emitted in a direction parallel with the mounting surface  91 . Because Patent Document 1 and conventional side-lighting type backlight devices are configured such that light is emitted to the light incident surface  71  that is provided on the side surface of the light guide plate  7 , this side-emitting type LED  9  is employed therein. Specifically, by disposing a substrate having the side-emitting type LED  9  mounted thereon near the side surface of the light guide plate  7  such that the mounting surface  91  becomes parallel with the light guide plate  7 , the light-emitting surface  14  of the chip-type LED  9  faces the light incident surface provided on the side surface of the light guide plate  7 . With this side-emitting type LED  9 , when improving the uniformity of the illuminating light in the manner described in Patent Document 1 shown in  FIG. 8 , the light-emitting surfaces of the LEDs  9  can be easily arranged so as to face the inclined surfaces  7   a  and  7   b  of the light emitting surface  71  by turning the LEDs  9  horizontally on the substrate. 
       RELATED ART DOCUMENT 
     Patent Document 
       [0007]    Patent Document 1: Japanese Patent Application Laid-Open Publication No. 2004-177890 
       PROBLEMS TO BE SOLVED BY THE INVENTION 
       [0008]    However, because the side-emitting type LEDs  9  has lower brightness and shorter life as compared with the top-emitting type LEDs, the backlight device in Patent Document 1 and conventional side-lighting type backlight devices that typically employed the side-emitting type LEDs had a problem in terms of brightness and reliability. On the other hand, the top-emitting type LED  9  has higher brightness and longer life, however, it is difficult to adjust the illumination direction relative to the light guide plate  7 , and therefore, when the top-emitting type LED was used in the side-lighting type backlight device, it was not possible to achieve the uniform illuminating light. 
       SUMMARY OF THE INVENTION 
     Means for Solving the Problems 
       [0009]    A backlight device according to the present invention includes a light guide plate that emits, from a top surface, light that entered from a side surface, a substrate that is disposed on a side surface of the light guide plate and that has a plurality of top-emitting type LEDs arranged thereon, and an outer case that encloses the light guide plate and the substrate, wherein, of the plurality of LEDs, an LED at an end is provided with a tilting portion such that an illumination direction thereof intersect with that of other LEDs. 
       Effects of the Invention 
       [0010]    Because a top-emitting type LED that has high brightness and long life is used for the backlight device, and because the illumination direction of the LED at the end is made to intersect with that of other LEDs by the tilting portion, light emitted from the plurality of LEDs can be distributed efficiently over the entire light guide plate, thereby improving the brightness of the illuminating light for a liquid crystal panel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a perspective view for illustrating a backlight device and a liquid crystal display device according to Embodiment 1. 
           [0012]      FIG. 2  is an enlarged cross-sectional view for illustrating a configuration of a principal portion of the backlight device of Embodiment 1. 
           [0013]      FIG. 3  is a plan view for illustrating a configuration of a principal portion of the backlight device of Embodiment 1. 
           [0014]      FIG. 4   a  is an enlarged cross-sectional view for illustrating a tilting portion of a chip-type LED of Embodiment 1. 
           [0015]      FIG. 4   b  is an enlarged cross-sectional view for illustrating a tilting portion of a chip-type LED of Embodiment 1. 
           [0016]      FIG. 4   c  is an enlarged cross-sectional view for illustrating a tilting portion of a chip-type LED of Embodiment 1. 
           [0017]      FIG. 4   d  is an enlarged cross-sectional view for illustrating a tilting portion of a chip-type LED of Embodiment 1. 
           [0018]      FIG. 5  is a plan view for illustrating a configuration of a principal portion of a backlight device according to Embodiment 2. 
           [0019]      FIG. 6  is an enlarged cross-sectional view for illustrating a tilting portion of a chip-type LED according to Embodiment 2. 
           [0020]      FIG. 7  is a plan view for illustrating a modification example of the backlight device of Embodiment 2. 
           [0021]      FIG. 8  is a plan view of a conventional backlight device for a liquid crystal display element. 
           [0022]      FIG. 9   a  is a side view for illustrating chip-type LEDs of a top-emitting type and a side-emitting type. 
           [0023]      FIG. 9   b  is a side view for illustrating chip-type LEDs of a top-emitting type and a side-emitting type. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0024]    Below, preferred embodiments of a backlight device of the present invention and a liquid crystal display device using the same will be explained with reference to figures. In the descriptions below, an example in which the present invention is applied to a transmissive liquid crystal display device will be explained. 
       Embodiment 1 
       [0025]      FIG. 1  is a perspective view for illustrating a backlight device and a liquid crystal display device according to Embodiment 1 of the present invention. As shown in  FIG. 1 , in a liquid crystal display device  1 , a backlight device  2  and a liquid crystal panel  3  that receives light emitted from the backlight device  2  are formed as a single unit, thereby constituting the transmissive liquid crystal display device  1 . The liquid crystal display device  1  also includes a diffusion sheet  4 , a prism sheet  5 , and a polarizing sheet  6  disposed between the backlight device  2  and the liquid crystal panel  3 , for example, and with these optical sheets, the brightness of the light emitted from the backlight device  2  is made uniform, which improves the display performance of the liquid crystal panel  3 . 
         [0026]    The backlight device  2  is a side-lighting type backlight device in which light sources are provided on the side surface of a light guide plate  7 , and uses a plurality of top-emitting type LEDs  9  as the light source. When comparing the optical characteristics and electric characteristics of the top-emitting type LED  9  with those of side-emitting type LEDs, the average luminance is 20% higher, and the average life is 30% longer in the top-emitting type LED  9  under the same operation conditions. Also, the light illumination direction is a direction perpendicular to the mounting surface  91 . The actual illuminating light spreads in a prescribed manner (directional characteristics) from the center axis, which is the illumination direction. 
         [0027]      FIG. 2  is a cross-sectional view of the backlight device  2  of the present invention. The light guide plate  7  is formed in a rectangular shape by using a synthetic resin such as a transparent acrylic resin as a material, for example. A prescribed side surface thereof is a light incident surface  71 , and the top surface is a light emerging surface  72 . Below the light guide plate  7 , a reflective sheet  8  is disposed so as to efficiently reflect light from the light source toward the liquid crystal panel provided above. 
         [0028]    As shown in  FIGS. 1 and 2 , the top-emitting type LED  9  is mounted on a circuit board  10 , and is attached to a side wall surface  11   a  that is an end portion of an outer case (back bezel)  11  of the backlight device  2  folded upwardly at a right angle. The top-emitting type LED  9  is disposed such that the light-emitting surface  14  thereof faces the light incident surface  71  of the light guide plate  7 . 
         [0029]      FIG. 3  is a plan view of the backlight device  2  of the present invention. As shown in  FIGS. 1 to 3 , of a plurality ( 9   a  to  9   f ) of top-emitting type LEDs  9 , LEDs  9   a  and  9   f  at the ends are provided with tilting portions  12  that make the light-emitting surfaces  14  inclined such that the illumination direction intersects with that of other LEDs  9   b  to  9   e.    
         [0030]    As shown in  FIG. 3 , the LEDs  9   a  and  9   f  at the ends are provided with tilting portions  12  between the mounting surface  91  of the LEDs  9  and the respective circuit boards  10 , for example, and the respective light-emitting surfaces  14  of the LEDs  9  are thereby inclined inwardly relative to the light guide plate  7 . Thus, the LEDs  9  are disposed such that the illumination direction of the LED  9   a  at the end, for example, intersects with the illumination direction of the LED  9   b  adjacent thereto. 
         [0031]    By providing the tilting portion  12  in the manner described above, the illumination direction of the LED  9   a  at the end can be adjusted such that the entire light beam emitted therefrom, which spreads in a prescribed manner, is incident on the light guide plate  7 . Thus, at the end of the illumination area  13 , the illuminating light beams from the LED  9   a  and from the LED  9   b  are efficiently combined, thereby achieving uniform illumination. 
         [0032]      FIGS. 4(   a ) to  4 ( e ) are enlarged cross-sectional views showing examples of specific configurations of the tilting portions  12 . The tilt angle of the tilting portion  12  is appropriately set by taking into account the directional characteristics of the top-emitting type LED  9 , uneven brightness in the display region  13 , and the like. 
         [0033]    The tilting portion  12  shown in  FIG. 4(   a ) is formed by using different amounts of solder  18  between the two terminals (anode and cathode) in connecting the top-emitting type LED  9  to the circuit board  10  by the solder  18 . If the LED  9  has a strong directivity, and the emitted light thereof travels straight, for example, even when the tilt angle of the tilting portion  12  is small, the entire emitted light beam can be radiated to the display region  13  efficiently. When the tilt angle is small as described, by using a larger amount of the solder  18  in the anode side as compared with the cathode side in connecting the connecting terminals  16  of the LED  9  to the connecting terminals  17  of the circuit board  10 , for example, the chip-type LED  9  can be made declined from the anode side to the cathode side, and the tilting portion  12  can be formed in a simple manner. 
         [0034]    In the tilting portion  12  shown in  FIG. 4(   b ), the LED  9  is inclined by placing one of the two terminals of anode and cathode on a protrusion  19  that is formed on the circuit board  10  in connecting the terminal. The protrusion  19  is provided under the connecting terminal  17  of the circuit board  10 , which is connected to one of the two connecting terminals (anode and cathode)  16  of the LED  9 , and is made of laminated layers that constitute the circuit board  10  such as a wiring layer (metal material) and an insulating layer (resin material). With the tilting portion  12  using the protrusion  19 , because the height of the protrusion  19  can be adjusted by the total thickness of the layers such as the wiring layer and the insulating layer, the tilt angle of the tilting portion  12  can be set in a quantitative manner. 
         [0035]    In the tilting portion  12  shown in  FIG. 4(   c ), the LED  9  is inclined by combining the tilting portion  12  formed by the solder  18  and the tilting portion  12  formed by the protrusion  19 . The tilting portion  12  formed by combining the solder  18  and the protrusion  19  makes possible a larger tilt angle than a tilting portion that uses the solder  18  alone or the protrusion  19  alone. 
         [0036]    In the tilting portion  12  shown in  FIG. 4(   d ), the LED  9  is inclined along an inclination of a relay terminal  20  that is disposed between the circuit board  10  and the LED  9 . The relay terminal  20  is formed so as to have an inclined surface on the top surface, and includes a package made of a resin material, for example, and conductors  21  that are provided inside the package and that allow electricity to flow in the vertical direction. The end surfaces of the conductors  21  are respectively exposed from the inclined surface on the top and from the bottom surface, thereby providing connecting terminals  21   a  and  21   b.  By using this relay terminal  20 , and by connecting the connecting terminals  21   a  and  21   b  that are respectively exposed from the top surface and the bottom surface of the package to the connecting terminals  17  of the circuit board  10  and to the connecting terminals  16  of the LED  9 , the LED  9  can be made inclined along the inclined top surface of the relay terminal  20 . 
         [0037]    In the titling portion  12  using the relay terminal  20 , the tilt angle is set by the inclined shape of the package, and therefore, the inclination of the chip-type LED  9  can be set with a greater degree of freedom. Also, the inclination direction of the inclined surface can be freely set by the inclination direction of the package of the relay terminal  20 , regardless of the direction in which the two terminals (anode and cathode) in the chip-type LED  9  are connected. 
         [0038]    In Embodiment 1 of the present invention, the plurality of top-emitting type LEDs  9  that have higher luminance and longer life are used as the light source of the backlight device  2 , and by providing the tilting portion  12  between the mounting surface  91  and the circuit board  10  of the LED  9  at the end, the illumination direction of the LED at the end can be made to interest with the illumination direction of other LEDs, which allows the light emitted from the plurality of chip-type LEDs  9   a  to  9   f  to be distributed efficiently over the entire light guide plate. Therefore, in the backlight device of the present invention, the brightness of the light that illuminates the liquid crystal panel  3  can be made uniform, and the uneven brightness can be eliminated, thereby improving the brightness. Also, by using the backlight device of the present invention, a liquid crystal display device with excellent display quality can be provided. 
       Embodiment 2 
       [0039]      FIG. 5  is a plan view of the backlight device  2  according to Embodiment 2 of the present invention. This embodiment differs from Embodiment 1 above in a configuration of the tilting portion  12 , and because other configurations may be the same as those of Embodiment 1 above, the detailed descriptions thereof are omitted. 
         [0040]    In Embodiment 2, as shown in  FIG. 5 , one end of an outer case (back bezel)  11  of the backlight device  2  is folded toward the light incident surface  71  of the light guide plate  7  at a right angle so as to form a side wall surface  11   a . Further, incisions  11   b  are made from the outside to respective end portions of the side wall surface  11   a  where the LEDs  9   a  and  9   f  are disposed, and the portions of the side wall surface  11   a  with the incisions are bent inwardly toward the light guide plate  7  at a prescribed angle, thereby forming bent portions  11   c.  The tilting portions  12  are provided in this way. 
         [0041]      FIG. 6  is an enlarged cross-sectional view showing an example of the configuration of the tilting portion  12  according to Embodiment 2. As described above, the tilting portion  12  is provided by bending sections of the side wall surface  11   a,  in which the LEDs  9   a  and  9   f  at the ends are disposed, inwardly toward the light guide plate  7  so as to form the bent portions  11   c.  The top-emitting type LEDs  9  are connected to connecting terminals  17  of an FPC  22  having flexibility by solder  18 , for example, and are thereafter disposed on the side wall surface  11   a  by bonding the FPC  22  to the side wall surface  11   a  and the bent portions  11   c  such that the LED  9   a  at the end is positioned in the bent portion  11   c.    
         [0042]    The bent portions  11   c  may also be formed by bonding the FPC  22  having a plurality of LEDs  9  mounted thereon to the side wall surface  11   a  that has incisions in portions at the ends, and by thereafter bending the portions of the side wall surface  11   a  having the incisions together with the FPC  22  toward the center of the display region  13  at a prescribed angle, thereby making the LEDs  9   a  and  9   f  at the ends located in the bent portions  11   c  inclined. Alternatively, instead of using the FPC  22 , the LEDs  9  at the ends and the other LEDs  9  may be respectively mounted on different circuit boards  10 , and the different circuit boards  10  may be separately disposed on the side wall surface  11   a  and on the bent portions  11   c.    
         [0043]    In this embodiment, because the tilt angle of the tilting portion  12  is set by the bending angle of the bent portion  11   c  provided in the side wall surface  11   a  of the outer case  11 , the tilt angle of the LEDs  9   a  and  9   f  at the ends can be made greater. As shown in  FIG. 7 , for example, it is possible to bend the bent portions  11   c,  which are the tilting portions  12 , at 90° such that the illumination directions of the LEDs  9   a  and  9   f  at the ends intersect with the illumination direction of the other LEDs  9   b  to  9   e  at a right angle. 
         [0044]    In an area of the display region  13  near the light incident surface  71 , for example, uneven brightness with brighter areas and darker areas may occur in the arrangement direction of the LEDs  9   b  to  9   e  due to the illuminating light from the LEDs  9   b  to  9   e  adjacent to each other overlapping in some areas and not overlapping in the other areas. However, as described above, with the tilting portions  12 , the illumination directions of the LEDs  9   a  and  9   f  at the ends can be made to intersect with the illumination direction of the other LEDs  9   b  to  9   e  at a right angle, and the illuminating light from the LEDs  9   a  and  9   f  at the ends is thereby emitted in a direction that crosses the brighter and darker areas that cause uneven brightness. This way, the entire area with the uneven brightness is illuminated and becomes brighter, thereby suppressing the uneven brightness. 
         [0045]    In Embodiment 2, the bent portions  11   c,  which are the tilting portions  12 , are formed by using a portion of the outer case  11 . The outer case  11  is made of a metal plate and therefore dissipates heat effectively, and because heat generated by the LEDs  9  in emitting light is transmitted throughout the entire outer case  11 , and is dissipated effectively, the thermal deterioration of LEDs  9  can be prevented, allowing for a further improvement of life thereof. 
         [0046]    Embodiments 1 and 2 have been described above, however, the present invention is not limited to the embodiments above, and various modifications can be made without departing from the scope of the present invention. In the backlight device  2  of Embodiment 1 shown in  FIG. 3 , for example, it is also possible to form cut-out portions in the light incident surface  71  where it faces the LEDs  9   a  and  9   f  at the ends, which are inclined, such that the LEDs  9  and the light guide plate  7  can be made closer to each other and a frame portion can be thereby made narrower. 
         [0047]    Although the backlight device  2  shown in  FIGS. 5 and 7  is configured such that the light guide plate  7  and the LEDs  9  are disposed close to each other, thereby achieving the narrower frame, it is also possible to dispose the light guide plate  7  and the LEDs  9  so as to be further away from each other. When the distance between the light guide plate  7  and the LEDs  9  is increased, the frame portion becomes larger, but it becomes possible to suppress the uneven brightness with brighter and darker areas, which occurs near the light incident surface  71  of the light guide plate  7 . 
         [0048]    The tilting portions  12  described in Embodiments 1 and 2 may be provided for a plurality of LEDs  9  disposed at the end, respectively. In Embodiments shown in  FIGS. 3 and 5 , for example, the tilting portions  12  can also be provided for the LED  9   a  and the LED  9   b  in the end portion, respectively, such that the illumination directions thereof cross the illumination direction of the other LEDs  9   c  and  9   d  in the center, thereby achieving the further efficient light illumination. 
         [0049]    In the embodiment shown in  FIG. 5 , a single titling portion  12  may be provided for a plurality of LEDs  9  in the end portion. By disposing the LEDs  9   a  and  9   b  at the end on the same tilting portion  12 , for example, the illumination directions thereof can be made to cross the illumination direction of the other LEDs  9   c  and  9   d  in the center, thereby achieving the further efficient light illumination. 
       DESCRIPTIONS OF REFERENCE CHARACTERS 
       [0000]    
       
           1  liquid crystal display device 
           2  backlight device 
           3  liquid crystal panel 
           4  diffusion sheet 
           5  prism sheet 
           6  polarizing sheet 
           7  light guide plate 
           7   a,    7   b  cut-out portion 
           8  reflective sheet 
           9 ,  9   a,    9   b,    9   c,    9   d,    9   e,    9   f  chip-type LED 
           10  substrate 
           11  outer case 
           11   a  side wall surface 
           11   b  incision 
           11   c  bent portion 
           12  tilting portion 
           13  display region 
           14  light-emitting surface 
           15  package 
           16 ,  17  connecting terminal 
           18  solder 
           19  protrusion 
           20  relay terminal 
           21  conducting portion 
           22  FPC 
           71  light incident surface 
           72  light emerging face 
           91  mounting surface