Abstract:
This illumination device is provided with light sources ( 15 ) arranged in one direction along a line or side-by-side, a light-guide plate ( 14 ) which guides light incident from an incidence surface ( 14   a ) on the side circumferential surface across from the light sources ( 15 ) and emits planar illumination light from an exit surface ( 14   b ) on the front surface, a chassis ( 13 ) which covers and supports the light sources ( 15 ) and the periphery of the light-guide plate ( 14 ), a scattering pattern ( 18 ) which is formed on the back surface ( 14   c ) of the light-guide plate ( 14 ), and positioning units ( 14   g ) which are provided jutting from the side peripheral surface of the light-guide plate ( 14 ) for positioning the light-guide plate ( 14 ) by fitting with the inner surface of the chassis ( 13 ), wherein the scattering pattern ( 18 ) is provided so as to extend on the positioning units ( 14   g ).

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an illumination device including a light guide plate, a display device using the same, and a television receiving device. 
       BACKGROUND ART 
       [0002]    Patent Document 1 discloses a conventional illumination device. This illumination device constitutes a backlight of a display device and has a light guide plate and light sources that are held in a chassis thereof. The light sources are composed of a plurality of LEDs and are provided side by side in one direction on a substrate. The light guide plate is formed in the shape of a thin plate rectangular in planar view and has, at one side circumferential surface thereof, an incidence surface opposed to the light sources. At a front surface of the light guide plate, an emission surface for emitting illumination light is formed. Furthermore, a reflection sheet is arranged on the side circumferential surface of the light guide plate in intimate contact therewith so as to avoid the light sources. 
         [0003]    Emission light emitted by the light sources enters the light guide plate from the incidence surface and is guided through the light guide plate. Light that has been guided through the light guide plate and entered the emission surface at an incidence angle smaller than a critical angle is emitted as illumination light from the emission surface. Furthermore, light that has reached the side circumferential surface of the light guide plate is reflected by the reflection sheet to be guided again through the light guide plate and then is emitted from the emission surface. 
         [0004]    Furthermore, Patent Document 2 discloses an illumination device including a light guide plate provided on its back surface with a scattering pattern. The scattering pattern is formed in the form of dots, and a multitude of such dots are formed so as to be dispersed on the back surface of the light guide plate. By the scattering pattern, light that has been guided through the light guide plate is reflected in a scattered manner at the back surface of the light guide plate in a direction toward an emission surface thereof. With this configuration, uniform illumination light is emitted from the emission surface, and light that reaches a side circumferential surface of the light guide plate is decreased, as a result of which the need for a reflection sheet can be eliminated. 
         [0005]    Furthermore, there is known an illumination device including a light guide plate that has, at a side circumferential surface thereof, a positioning portion provided in a projecting manner for the purpose of positioning and holding the light guide plate on a chassis.  FIG. 7  is a plan view showing a vicinity of the positioning portion of this light guide plate. A positioning portion  14   g  is provided in a projecting manner at, for example, each of two orthogonal ones of side circumferential surfaces of a light guide plate  14  and is used for positioning of the light guide plate  14  by being fitted into an inner surface of a chassis (not shown). 
         [0006]    Furthermore, a scattering pattern  18  in the form of dots provided on a back surface of the light guide plate  14  is provided to extend further to an outer circumference side beyond an emission region W for emitting illumination light so that uniform illumination light is emitted from the emission region W. 
       LIST OF CITATIONS 
     Patent Literature 
       [0007]    Patent Document 1: JP-A-2008-166200 (pages 4 to 5, FIG. 4) 
         [0008]    Patent Document 2: JP-A-2011-142086 (pages 5 to 16, FIG. 11) 
       SUMMARY OF THE INVENTION 
     Technical Problem 
       [0009]    According to the illumination device including the light guide plate  14  having the positioning portion  14   g,  however, light that, without the positioning portion  14   g,  would be totally reflected at the side circumferential surface of the light guide plate  14  as shown by an arrow Al is partly emitted via the positioning portion  14   g  as shown by an arrow A 2 . This has led to a problem that a luminance of illumination light in the emission region W is decreased in a vicinity of the positioning portion  14   g,  which results in the occurrence of luminance unevenness. 
         [0010]    With regard thereto, providing a reflection sheet on an outer surface of the positioning portion  14   g  can prevent luminance unevenness. This, however, leads to a problem that the cost of the illumination device is increased, and a reflection characteristic of the reflection sheet is deteriorated over time, which results in the occurrence of luminance unevenness. 
         [0011]    It is an object of the present invention to provide an illumination device that is capable of providing illumination light with a uniform luminance distribution, a display device using the same, and a television receiving device. 
       Solution To the Problem 
       [0012]    In order to achieve the above-described object, an illumination device according to the present invention includes a light source that is provided in side-by-side arrangement in one direction or provided to extend in one direction, a light guide plate that guides light that has entered from an incidence surface at a side circumferential surface thereof opposed to the light source and emits planar illumination light from an emission surface at a front surface thereof, a chassis that holds the light source and the light guide plate while covering a periphery of the light source and the light guide plate, a scattering pattern that is formed on a back surface of the light guide plate, and a positioning portion that is provided in a projecting manner at a side circumferential surface of the light guide plate and is used for positioning of the light guide plate by being fitted into an inner surface of the chassis. In the illumination device, the scattering pattern is provided to extend further onto the positioning portion. 
         [0013]    According to this configuration, the positioning portion of the light guide plate is fitted into the inner surface of the chassis, and thus positioning of the light guide plate is achieved. Light emitted from the light source enters the light guide plate from the incidence surface and is guided therethrough to be reflected in a scattered manner by the scattering pattern provided at the back surface, so that planar illumination light is emitted from an emission region of the emission surface at the front surface. Furthermore, guided light that has reached the positioning portion is reflected in a scattered manner by a portion of the scattering pattern which is provided on the positioning portion, and is guided in a direction toward the emission region. 
         [0014]    Furthermore, in the present invention, in the illumination device configured as above, a portion of the scattering pattern which lies on the positioning portion has density larger than density of a portion of the scattering pattern which lies on an emission region for emitting illumination light. According to this configuration, in the positioning portion, light reflected in a scattered manner in a direction toward the emission region is increased. 
         [0015]    Furthermore, in the present invention, in the illumination device configured as above, the positioning portion is formed at an opposed surface opposed to the incidence surface and both surfaces contiguous to the incidence surface, and the positioning portions at the surfaces contiguous to the incidence surface are disposed at locations closer to the incidence surface than to the opposed surface. 
         [0016]    Furthermore, in the present invention, in the illumination device configured as above, the scattering pattern is formed by printing. 
         [0017]    Furthermore, in the present invention, in the illumination device configured as above, the scattering pattern is formed by using a white ink. 
         [0018]    Furthermore, in the present invention, in the illumination device configured as above, the light source is a white light emitting diode. 
         [0019]    Furthermore, in the present invention, in the illumination device configured as above, the white light emitting diode includes a light emitting chip that emits blue light and a luminous body layer that is provided around the light emitting chip and has an emission peak in a yellow region. According to this configuration, there is emitted white light resulting from mixing of blue light emitted by the light emitting chip and yellow light emitted by the luminous body layer. 
         [0020]    Furthermore, in the present invention, in the illumination device configured as above, the white light emitting diode includes a light emitting chip that emits blue light and a luminous body layer that is provided around the light emitting chip and has an emission peak in each of a green region and a red region. According to this configuration, there is emitted white light resulting from mixing of blue light emitted by the light emitting chip and green light and red light emitted by the luminous body layer. 
         [0021]    Furthermore, in the present invention, in the illumination device configured as above, the white light emitting diode includes a first light emitting chip that emits blue light, a luminous body layer that is provided around the first light emitting chip and has an emission peak in a green region, and a second light emitting chip that emits red light. According to this configuration, there is emitted white light resulting from mixing of blue light emitted by the first light emitting chip, green light emitted by the luminous boy layer, and red light emitted by the second light emitting chip. 
         [0022]    Furthermore, in the present invention, in the illumination device configured as above, the white light emitting diode includes a first light emitting chip that emits blue light, a second light emitting chip that emits red light, and a third light emitting chip that emits green light. According to this configuration, there is emitted white light resulting from mixing of blue light emitted by the first light emitting chip, red light emitted by the second light emitting chip, and green light emitted by the third light emitting chip. 
         [0023]    Furthermore, in the present invention, in the illumination device configured as above, the white light emitting diode includes a light emitting chip that emits ultraviolet light and a luminous body layer that is provided around the light emitting chip and has an emission peak in each of a blue region, a green region, and a red region. According to this configuration, there is emitted white light resulting from mixing of blue light, green light, and red light emitted by the luminous body layer. 
         [0024]    Furthermore, a display device according to the present invention includes the illumination device configured as above and a display panel that is disposed so as to be opposed to the emission surface. 
         [0025]    Furthermore, in the present invention, in the display device configured as above, the display panel is a liquid crystal panel using liquid crystal. 
         [0026]    Furthermore, a television receiving device according to the present invention includes the display device configured as above. 
       Advantageous Effects of the Invention 
       [0027]    According to the present invention, the scattering pattern is provided to extend further onto the positioning portion provided in a projecting manner at the side circumferential surface of the light guide plate, and thus guided light that has reached the positioning portion is partly reflected in a scattered manner in a direction toward the emission region. With this configuration, light emitted sideways from the positioning portion is decreased, and thus decrease in luminance in the vicinity of the positioning portion is suppressed, so that illumination light with uniform luminance distribution can be provided. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0028]    [ FIG. 1 ] is an exploded perspective view showing a display device including an illumination device of a first embodiment of the present invention. 
           [0029]    [ FIG. 2 ] is a side sectional view showing the display device including the illumination device of the first embodiment of the present invention. 
           [0030]    [ FIG. 3 ] is a plan view showing the illumination device of the first embodiment of the present invention. 
           [0031]    [ FIG. 4 ] is a plan view showing a positioning portion of a light guide plate of the illumination device of the first embodiment of the present invention. 
           [0032]    [ FIG. 5 ] is a plan view showing a positioning portion of a light guide plate of an illumination device of a second embodiment of the present invention. 
           [0033]    [ FIG. 6 ] is a plan view showing a positioning portion of a light guide plate of an illumination device of a third embodiment of the present invention. 
           [0034]    [ FIG. 7 ] is a plan view showing a positioning portion of a light guide plate of a conventional illumination device. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0035]    Hereinafter, embodiments of the present invention will be described with reference to the appended drawings. For the sake of convenience of explanation, in each of the drawings, portions similar to those in the foregoing conventional example shown in  FIG. 7  are indicated by the same reference symbols.  FIG. 1  is an exploded perspective view showing a display device including an illumination device of a first embodiment. A display device  1  is to be incorporated in a television receiving device or the like, and includes a liquid crystal panel  2  and an illumination device  10  that constitutes a backlight and is arranged behind the liquid crystal panel  2 . The liquid crystal panel  2  is held to the illumination device  10  by a bezel  3  that covers a circumferential portion of a display surface  2   a  of the liquid crystal panel  2  at a front surface thereof. 
         [0036]    The illumination device  10  is configured as an edge light type in which a light source  15  (see  FIG. 2 ) is arranged so as to be opposed to an incidence surface  14   a  (see  FIG. 2 ) at one side circumferential surface of a light guide plate  14  that is rectangular in planar view. The illumination device  10  is covered by a chassis  11  composed of a back portion  12  on a back surface side and a front portion  13  on a front surface side. Furthermore, on an emission surface  14   b  (see  FIG. 2 ) of the light guide plate  14  at a front surface thereof, an optical sheet  16  such as a diffusion sheet is arranged. 
         [0037]      FIG. 2  shows a side sectional view of the display device  1 . The front portion  13  of the chassis  11  is made of a resin such as polycarbonate and covers a circumferential portion of the emission surface  14   b  of the light guide plate  14 . A back surface of the liquid crystal panel  2  is supported by the front portion  13 , and the liquid crystal panel  2  is held between the front portion  13  and the bezel  3 . 
         [0038]    The back portion  12  of the chassis  11  is made of a metal such as a steel plate, aluminum and the like or a resin such as polycarbonate, carbon fiber reinforced plastic (CFRP) and the like. The use of a resin to form the back portion  12  can achieve a weight reduction and thus is more preferable. The back portion  12  has a plurality of ribs  13   b  that are provided in a projecting manner to extend in a direction parallel to the incidence surface  14   a  of the light guide plate  14  and support a back surface  14   c  of the light guide plate  14 . With this configuration, the ribs  13   b  make line contact with the light guide plate  14 . The ribs  13   b  may be provided to extend in a direction orthogonal to the incidence surface  14   a  or may be formed so as to make point contact with the light guide plate  14 . 
         [0039]    The light guide plate  14  is formed of a thin plate rectangular in planar view, which is made of a transparent member such as acrylic, and guides light that has entered from the incidence surface  14   a.  A scattering pattern  18  for reflecting light in a scattered manner is provided on the back surface  14   c  of the light guide plate  14 . The light source  15  is formed of a white light emitting diode mounted on a substrate  15   a,  and a plurality of the light sources  15  are provided side by side in one direction along the incidence surface  14   a  of the light guide plate  14  at the one side circumferential surface thereof. The light source  15  may be formed in a linear shape and provided to extend in one direction along the incidence surface  14   a.    
         [0040]    The white light emitting diode forming the light source  15  has, for example, a light emitting chip that emits blue light and a luminous body layer that is provided around the light emitting chip and has an emission peak in a yellow region. With this configuration, there is emitted white light resulting from mixing of blue light emitted by the light emitting chip and yellow light emitted by the luminous body layer. The luminous body layer can be formed by containing a phosphor that performs wavelength conversion of blue light of the light emitting chip into yellow light. 
         [0041]    Here, the white light emitting diode may have a light emitting chip that emits blue light and a luminous body layer that is provided around the light emitting chip and has an emission peak in each of a green region and a red region. With this configuration, there is emitted white light resulting from mixing of blue light emitted by the light emitting chip and green light and red light emitted by the luminous body layer. The luminous body layer can be formed by containing phosphors that perform wavelength conversion of blue light of the light emitting chip into green light and red light, respectively. 
         [0042]    Also, the white light emitting diode may have a first light emitting chip that emits blue light, a luminous body layer that is provided around the first light emitting chip and has an emission peak in a green region, and a second light emitting chip that emits red light. With this configuration, there is emitted white light resulting from mixing of blue light emitted by the first light emitting chip, green light emitted by the luminous body layer, and red light emitted by the second light emitting chip. The luminous body layer can be formed by containing a phosphor that performs wavelength conversion of blue light of the first light emitting chip into green light. 
         [0043]    Furthermore, the white light emitting diode may have a first light emitting chip that emits blue light, a second light emitting chip that emits red light, and a third light emitting chip that emits green light. With this configuration, there is emitted white light resulting from mixing of blue light emitted by the first light emitting chip, red light emitted by the second light emitting chip, and green light emitted by the third light emitting chip. 
         [0044]    Furthermore, the white light emitting diode may have a light emitting chip that emits ultraviolet light and a luminous body layer that is provided around the light emitting chip and has an emission peak in each of a blue region, a green region, and a red region. With this configuration, there is emitted white light resulting from mixing of blue light, green light, and red light emitted by the luminous body layer. The luminous body layer can be formed by containing phosphors that perform wavelength conversion of ultraviolet light of the light emitting chip into blue light, green light, and red light, respectively. 
         [0045]      FIG. 3  shows a plan view of the illumination device  10 . The light guide plate  14  which is arranged on an inner side of the front portion  13  of the chassis  11  has a positioning portion  14   g  that is provided in a projecting manner at each of an opposed surface  14   e  opposed to the incidence surface  14   a  and both side surfaces  14   d  contiguous to the incidence surface  14   a.  The positioning portions  14   g  at both the side surfaces  14   d  are disposed at locations closer to the incidence surface  14   a  than to the opposed surface  14   e.    
         [0046]    On an inner circumferential surface of the front portion  13 , a plurality of ribs  13   a  into each of which the positioning portion  14   g  is to be fitted are provided in a projecting manner. The positioning portion  14   g  is fitted into each of the ribs  13   a,  and thus the light guide plate  14  is held in a state where positioning thereof is achieved in directions parallel to and perpendicular to the incidence surface  14   a,  respectively. A concave portion into which the positioning portion  14   g  is to be fitted may be provided by forming a concave on the inner circumferential surface of the front portion  13 . 
         [0047]    Since the circumferential portion of the emission surface  14   a  of the light guide plate  14  is covered by the front portion  13  (see  FIG. 2 ), the emission region W for emitting illumination light is formed on a side inward of an outer circumference. The liquid crystal panel  2  (see  FIG. 1 ) is illuminated with illumination light emitted from the emission region W. 
         [0048]      FIG. 4  is a plan view showing a detail of the positioning portion  14   g  of the light guide plate  14 . The scattering pattern  18  formed on the back surface  14   c  (see  FIG. 2 ) of the light guide plate  14  is formed in the form of, for example, white dots that are circular in planar view, and a multitude of such dots are disposed so as to be dispersed in a triangular lattice shape. The scattering pattern  18  may be disposed in a tetragonal lattice shape or in a random manner. The scattering pattern  18  can be formed by, for example, printing, by screen printing, ink-jet printing, or the like, a white ink in paste form containing a metal oxide on the back surface  14   c  of the light guide plate  14 . 
         [0049]    The scattering pattern  18  is not only provided in the emission region W but also provided to extend further to an outer circumference side beyond the emission region W and even further onto the positioning portion  14   g.  A scattering pattern  18   b  lying on the positioning portion  14   g  is disposed in a trapezoidal shape in planar view. In this case, the scattering pattern  18   b  lying on the positioning portion  14   g  is formed to have a dot diameter larger than that of a scattering pattern  18   a  lying on the emission region W. As a result, the scattering pattern  18   b  lying on the positioning portion  14   g  has density larger than density of the scattering pattern  18   a  lying on the emission region W. 
         [0050]    In the display device  1  configured as above, light emitted from the light source  15  enters the light guide plate  14  from the incidence surface  14   a  and is guided through the light guide plate  14 . Guided light that has reached the back surface  14   c  of the light guide plate  14  is reflected in a scattered manner by the scattering pattern  18 . With this configuration, light that enters the emission surface  14   b  at an incidence angle smaller than a critical angle is generated, so that planar illumination light is emitted from the emission region W of the emission surface  14   b.  The liquid crystal panel  2  is illuminated with the illumination light emitted from the emission region W, and thus an image is displayed on the display surface  2   a.    
         [0051]    Furthermore, since the scattering pattern  18  is provided to extend further to the outer circumference side beyond the emission region W, illumination light can be emitted such that it is uniform even at a circumferential edge of the emission region W. Moreover, since the scattering pattern  18   b  is provided on the positioning portion  14   g,  light that has been guided through the light guide plate  14  and reached the positioning portion  14   g  is reflected in a scattered manner by the scattering pattern  18   b.  With this configuration, reflection light reflected by the scattering pattern  18   b  is partly guided in a direction toward the emission region W, and thus light emitted sideways from the positioning portion  14   g  is decreased. 
         [0052]    According to this embodiment, the scattering pattern  18  is provided to extend further onto the positioning portion  14   g  provided in a projecting manner at the side circumferential surface of the light guide plate  14 , and thus guided light that has reached the positioning portion  14   g  is partly reflected in a scattered manner in the direction toward the emission region W. With this configuration, light emitted sideways from the positioning portion  14   g  is decreased, and thus decrease in luminance in the vicinity of the positioning portion  14   g  is suppressed, so that illumination light with a uniform luminance distribution can be provided. 
         [0053]    Furthermore, since the scattering pattern  18   b  lying on the positioning portion  14   g  has density larger than density of the scattering pattern  18   a  lying on the emission region W, in the positioning portion  14   g,  light reflected in a scattered manner in direction toward the emission region W can be increased. Thus, illumination light with a further uniform luminance distribution can be provided. 
         [0054]    Furthermore, the positioning portions  14   g  at both the side surfaces  14   d  contiguous to the incidence surface  14   a  are disposed at locations closer to the incidence surface  14   a  than to the opposed surface  14   e.  With this configuration, the light guide plate  14  can be further stably supported. In this case, it becomes easy for emission light emitted by those ones of the light sources  15  which are located at both end portions of the incidence surface  14   a  to reach the positioning portions  14   g  at both the side surfaces  14   d  disposed at locations close to the ones of the light sources  15 . Accordingly, with the scattering pattern  18  provided to extend further onto the positioning portion  14   g,  effect of decreasing light emitted sideways from the positioning portion  14   g  is enhanced. 
         [0055]    Furthermore, the scattering pattern  18  can be easily formed by printing a white ink. 
         [0056]    Furthermore, since the light source  15  is a white light emitting diode, the illumination device  10  constituting a backlight can be easily realized. 
         [0057]    Next,  FIG. 5  is a plan view showing a positioning portion  14   g  of a light guide plate  14  of an illumination device  10  of a second embodiment. For the sake of convenience of explanation, portions similar to those in the foregoing first embodiment shown in  FIGS. 1 to 4  are indicated by the same reference symbols. This embodiment is different from the first embodiment in how a scattering pattern  18   b  lying on the positioning portion  14   g  is disposed. Other portions are similar to those in the first embodiment. 
         [0058]    A scattering pattern  18  is provided to extend further onto the positioning portion  14   g,  and the scattering pattern  18   b  lying on the positioning portion  14   g  is disposed in a rectangular shape in planar view. In this case, the scattering pattern  18   b  lying on the positioning portion  14   g  is formed to have a dot diameter larger than that of a scattering pattern  18   a  lying on an emission region W. With this configuration, effects similar to those of the first embodiment can be obtained. 
         [0059]    Next,  FIG. 6  is a plan view showing a positioning portion  14   g  of a light guide plate  14  of an illumination device  10  of a third embodiment. For the sake of convenience of explanation, portions similar to those in the foregoing first embodiment shown in  FIGS. 1 to 4  are indicated by the same reference symbols. This embodiment is different from the first embodiment in how a scattering pattern  18   b  lying on the positioning portion  14   g  is disposed. Other portions are similar to those in the first embodiment. 
         [0060]    A scattering pattern  18  is provided to extend further onto the positioning portion  14   g,  and the scattering pattern  18   b  lying on the positioning portion  14   g  is disposed in a triangular shape in planar view. In this case, the scattering pattern  18   b  lying on the positioning portion  14   g  is formed to have a dot diameter larger than that of a scattering pattern  18   a  lying on an emission region W. With this configuration, effects similar to those of the first embodiment can be obtained. 
         [0061]    While in each of the first to third embodiments, the illumination device  10  is formed as a one-side light incidence type in which the light sources  15  are arranged along only one side of the light guide plate  14 , a two-side light incidence type also may be adopted in which the light sources  15  are arranged along opposed two sides of the light guide plate  14 . 
       INDUSTRIAL APPLICABILITY 
       [0062]    The present invention is applicable to display devices using an illumination device having a light guide plate, such as of a television receiving device, a display, and a mobile phone. 
       LIST OF REFERENCE SYMBOLS 
       [0063]      1  liquid crystal display device 
         [0064]      2  display panel 
         [0065]      3  bezel 
         [0066]      10  illumination device 
         [0067]      11  chassis 
         [0068]      12  back portion 
         [0069]      13  front portion 
         [0070]      13   a  rib 
         [0071]      14  light guide plate 
         [0072]      14   a  incidence surface 
         [0073]      14   b  emission surface 
         [0074]      14   c  back surface 
         [0075]      14   g  positioning portion 
         [0076]      15  light source 
         [0077]      16  optical sheet 
         [0078]      18 ,  18   a,    18   b  scattering pattern