Patent Publication Number: US-2022236471-A1

Title: Display device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation application of U.S. application Ser. No. 13/572,757, filed Aug. 13, 2012, the contents of which are incorporated herein by reference. 
     The present application claims priority from Japanese application JP 2011-177436 filed on Aug. 15, 2011, the contents of which are hereby incorporated by reference into this application. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a display device. 
     2. Description of the Related Art 
     In a display device including a side-light type backlight unit, light entering an end surface of a light guide plate travels inside the light guide plate and exits from a front surface of the light guide plate (Japanese Patent Application Laid-open No. 2009-276531). As a light source of the backlight unit, a light emitting diode (LED) is generally used. The LED is mounted on a flexible wiring board and is arranged so as to face the end surface of the light guide plate. Further, an optical sheet is arranged on the front surface of the light guide plate. 
     When the flexible wiring board is fixed to an end portion of the front surface of the light guide plate with a light-shielding double-sided tape, on the front surface side of the light guide plate, there is formed a gap from which the light guide plate is exposed between the light-shielding double-sided tape and the optical sheet. Light exiting from the gap does not pass through the optical sheet and enters a display panel from an end surface thereof. Therefore, when the display panel is obliquely viewed, the light of the LED may be directly observed, which causes a problem of display quality degradation. 
     SUMMARY OF THE INVENTION 
     The present invention has an object to provide a display device which is capable of blocking leakage light from a light guide plate to prevent quality degradation. 
     (1) According to an exemplary embodiment of the present invention, there is provided a display device, including: a display panel; and a backlight unit to be used as a planar light source of the display panel. The backlight unit includes: a light source having an emission region narrower than an emission region of the planar light source; a wiring board having the light source mounted thereon; a light guide plate having an end surface into which light from the light source enters, and a front surface from which the light exits; a light-shielding pressure-sensitive adhesive sheet for causing the wiring board to adhere to an end portion of the front surface of the light guide plate; and a light diffusion sheet which overlaps with the front surface of the light guide plate. The front surface of the light guide plate includes an effective region serving as the planar light source and a light entering region ranging from the end surface into which the light enters to the effective region. The wiring board and the light-shielding pressure-sensitive adhesive sheet each have a part positioned in the light entering region. The light diffusion sheet is arranged from the effective region to the light entering region, and at least an end portion thereof overlaps with the light-shielding pressure-sensitive adhesive sheet in the light entering region. On a side closer to the effective region with respect to the light-shielding pressure-sensitive adhesive sheet, the light entering region is covered with the light diffusion sheet without a gap. According to the exemplary embodiment of the present invention, the light diffusion sheet and the light-shielding pressure-sensitive adhesive sheet are provided in an overlapping manner without a gap. Therefore, the leakage light from the light guide plate can be blocked to prevent quality degradation. 
     (2) in the display device as described in Item (1), at least a part of the light-shielding pressure-sensitive adhesive sheet may be interposed between the wiring board and the light guide plate. 
     (3) In the display device as described in Item (1), the light-shielding pressure-sensitive adhesive sheet may adhere from a surface of the wiring board directed to a side opposite to the light guide plate to the front surface of the light guide plate. 
     (4) In the display device as described in item (2) or (3), the light-shielding pressure-sensitive adhesive sheet may include an overlapping portion with the wiring board, the light-shielding pressure-sensitive adhesive sheet extending off from the overlapping portion in a direction of the effective region, and overlapping with the light diffusion sheet outside the wiring board. 
     (5) In the display device as described in Item (4), the light-shielding pressure-sensitive adhesive sheet may overlap with the light diffusion sheet arranged on the light guide plate. 
     (6) In the display device as described in Item (4), the light diffusion sheet may overlap with the light-shielding pressure-sensitive adhesive sheet arranged on the light guide plate. 
     (7) In the display device as described in any one of Items (4) to (6), the light diffusion sheet may include a non-overlapping portion at which overlapping with the light-shielding pressure-sensitive adhesive sheet is avoided, and the display device may further include a light-shielding film which is formed so as to cross a boundary between the overlapping portion and the non-overlapping portion. 
     (8) In the display device as described in Item (2), the light diffusion sheet may be arranged so as to reach a surface of the wiring board directed on a side opposite to the light guide plate, and the light diffusion sheet may overlap with the light-shielding pressure-sensitive adhesive sheet through an intermediation of the wiring board. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is a sectional view illustrating a display device according to an embodiment to which the present invention is applied; 
         FIG. 2  is a sectional view illustrating a display device according to a first modified example of the embodiment; 
         FIG. 3  is a sectional view illustrating a display device according to a second modified example of the embodiment; 
         FIG. 4  is a sectional view illustrating a display device according to a third modified example of the embodiment; and 
         FIG. 5  is a sectional view illustrating a display device according to a fourth modified example of the embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, an embodiment of the present invention is described with reference to the drawings. 
       FIG. 1  is a sectional view illustrating a display device according to an embodiment to which the present invention is applied. The display device includes a display panel  10 . The display panel  10  is a light-shutter type display panel which controls passing and blocking of light to display an image. The display panel  10  illustrated in  FIG. 1  is a liquid crystal display panel, and includes a pair of substrates  12  and  14  made of glass and the like, liquid crystal (not shown) sandwiched between the substrates, and polarizing plates  18  arranged on outer sides of the pair of substrates  12  and  14 , respectively. 
     One substrate (lower substrate in FIG,  1 )  12  extends off from another substrate (upper substrate in  FIG. 1 )  14 . On a surface of the one substrate  12  on a side opposed to the another substrate  14  in a part which extends off from the another substrate  14 , there is mounted an integrated circuit chip  20  having a driver circuit embedded therein, for driving the liquid crystal. Further, a flexible wiring board  22  is fixed to the part on which the integrated circuit chip  20  is mounted. 
     The display device includes a backlight unit  24  which is used as a planar light source of the display panel  10 . The backlight unit  24  includes a light source  26 . The light source  26  is a point light source such as a light emitting diode (LED). The point light source has a narrower emission region than that of the planar light source. The light source  26  emits white light. 
     The light source  26  is mounted on a wiring board  28  such as a flexible printed circuit (FPC) board, and is electrically connected to a wiring pattern (not shown) on the wiring board  28 . The wiring board  28  is arranged so that the light source  26  is directed downward (to a side opposite to the display panel  10 ). The wiring board  28  includes a part which overlaps with the light source  26  and a part outside a region on which the light source  26  is mounted. The wiring board  28  is arranged so as to overlap with at least an end portion of the display panel  10 . Further, the wiring board  28  is arranged so as to overlap with the integrated circuit chip  20 . The wiring board  28  is opaque, but does not have a light-shielding property and transmits light. 
     The backlight unit  24  includes a light guide plate  30 . The light guide plate  30  is provided for converting the light of the light source  26  (point light source) into a planar light source to illuminate the display panel  10  with the planar light source. The light from the light source  26  enters an end surface of the light guide plate  30 . For the entrance of the light from the light source  26 , the end portion of the light guide plate  30  is arranged adjacent to the light source  26 . The wiring board  28  is positioned on the light source  26 , and an end portion of the wiring board  28  overlaps with the light guide plate  30 . The light source  26  and the light guide plate  30  may be provided in contact with each other, or a gap may be provided therebetween. Light exits in a planar shape from a front surface  32  of the light guide plate  30 . The front surface  32  of the light guide plate  30 , which performs planar emission, is opposed to the display panel  10 . The front surface  32  of the light guide plate  30  includes an effective region  34  as the planar light source, and a light entering region  36  ranging from the end surface, into which light enters, to the effective region  34 . 
     The backlight unit  24  includes a light diffusion sheet  38  which overlaps with the front surface  32  of the light guide plate  30 . The light diffusion sheet  38  is arranged on the light guide plate  30  (on a side closer to the display panel  10 ). The light diffusion sheet  38  is arranged in a range from the effective region  34  to the light entering region  36  of the light guide plate  30 . The light diffusion sheet  38  has a weak light diffusion action, and hence influence on light distribution can be weakened when light passes through the light diffusion sheet  38 . On the light diffusion sheet  38  (on a side closer to the display panel  10 ), a plurality of prism sheets  40  are arranged. When light passes through the prism sheets  40 , light is collected to the front side to increase the front brightness. The light diffusion sheet  38  and the prism sheets  40  are collectively called an optical sheet. Further, below the light guide plate  30  (on a side opposite to the display panel  10 ), a reflective sheet  42  is arranged. 
     The display device includes an inner frame  44 , and the backlight unit  24  is arranged inside the inner frame  44 . The inner frame  44  is a resin molded product, and is also called a mold. The inner frame  44  supports the display panel  10 . The display panel  10  is adhered to the inner frame  44  by a double-sided tape  46 . In the example illustrated in  FIG. 1 , a lower surface of a left end portion of the double-sided tape  46  is adhered to the inner frame  44 , and an upper surface of a right end portion of the double-sided tape  46  is adhered to the polarizing plate  18  of the display panel  10 . The double-sided tape  46  has a light-shielding property. The double-sided tape  46  covers the wiring board  28  having the light source  26  mounted thereon, and extends off from the wiring board  28 . Therefore, with the double-sided tape  46 , light emitted from the light source  26  to pass through the wiring board  28  and light leaked from a periphery of the wiring board  28  are blocked. Note that, the double-sided tape  46  is also adhered to the wiring board  28  and the prism sheet  40 . 
     The inner frame  44  surrounds and holds the light guide plate  30  and the light source  26 . The wiring board  28  having the light source  26  mounted thereon is adhered to the inner frame  44  with a double-sided tape  48 . Specifically, the wiring board  28  extends in mutual opposite directions from the region on which the light source  26  is mounted, and one end portion thereof is adhered to the inner frame  44  in an overlapped manner. The double-sided tape  48  is interposed between the wiring board  28  and the inner frame  44 . The double-sided tape  48  has a light-shielding property. The inner frame  44 , the backlight unit  24 , and the display panel  10  are housed in an outer frame  50 . 
     The backlight unit  24  includes a light-shielding pressure-sensitive adhesive sheet  52 . The light-shielding pressure-sensitive adhesive sheet  52  includes a light-shielding layer and a pressure-sensitive adhesive layer (both not shown). When the light-shielding layer is black, the light-shielding layer can absorb light to reduce light reflection. The pressure-sensitive adhesive layer is formed on both surfaces of the light-shielding layer. When the pressure-sensitive adhesive layer is an insulating member, the light-shielding layer may be a conductor. Further, the double-sided tape  48  and the light-shielding pressure-sensitive adhesive sheet  52  may be integrated with each other. 
     The light-shielding pressure-sensitive adhesive sheet  52  causes the wiring board  28  to adhere to an end portion of the front surface  32  of the light guide plate  30 . The wiring board  28  and the light-shielding pressure-sensitive adhesive sheet  52  each have a part positioned in the light entering region  36  of the light guide plate  30 . At least a part of the light-shielding pressure-sensitive adhesive sheet  52  is interposed between the wiring board  28  and the light guide plate  30 . The light-shielding pressure-sensitive adhesive sheet  52  includes an overlapping portion with respect to the wiring board  28 , and extends off from the overlapping portion in a direction of the effective region  34 . In the light entering region  36  of the light guide plate  30 , the light-shielding pressure-sensitive adhesive sheet  52  overlaps with the light diffusion sheet  38  outside the wiring board  28 . In the light entering region  36 , at least an end portion of the light diffusion sheet  38  overlaps with the light-shielding pressure-sensitive adhesive sheet  52 . On a side closer to the effective region  34  with respect to the light-shielding pressure-sensitive adhesive sheet  52 , the light entering region  36  is covered with the light diffusion sheet  38  without a gap. The light diffusion sheet  38  overlaps with the light-shielding pressure-sensitive adhesive sheet  52  arranged on the light guide plate  30 . 
     According to this embodiment, the light diffusion sheet  38  overlaps with the light-shielding pressure-sensitive adhesive sheet  52  without a gap, and hence it is possible to block the leakage light from the light guide plate  30  to prevent quality degradation. 
       FIG. 2  is a sectional view illustrating a display device according to a first modified example of the embodiment. In this example, the light diffusion sheet  38  includes an overlapping portion with the light-shielding pressure-sensitive adhesive sheet  52 , and a non-overlapping portion at which the overlapping is avoided. On the light diffusion sheet  38 , a light-shielding film  54  is formed so as to cross a boundary between the overlapping portion and the non-overlapping portion. The light-shielding film  54  may be formed by printing and the like. With the light-shielding film  54 , it is possible to prevent light leakage from the boundary between the overlapping portion and the non-overlapping portion. Other configurations correspond to the contents described in the above-mentioned embodiment. 
       FIG. 3  is a sectional view illustrating a display device according to a second modified example of the embodiment. In this example, the positions of the light diffusion sheet  38  and the light-shielding pressure-sensitive adhesive sheet  52  are inverted from those of the example of  FIG. 1 . That is, the light-shielding pressure-sensitive adhesive sheet  52  overlaps with the light diffusion sheet  38  arranged on the light guide plate  30 . Other configurations correspond to the contents described in the above-mentioned embodiment. 
       FIG. 4  is a sectional view illustrating a display device according to a third modified example of the embodiment. In this example, a light diffusion sheet  138  is arranged so as to reach a surface of the wiring board  28  which is directed to a side opposite to the light guide plate  30 . Specifically, the light diffusion sheet  138  extends from the effective region  34  to the light entering region  36  of the light guide plate  30  to run on the wiring board  28 . 
     The light diffusion sheet  138  overlaps with a light-shielding pressure-sensitive adhesive sheet  152  through an intermediation of the wiring board  28 . The light-shielding pressure-sensitive adhesive sheet  152  adheres to the wiring board  28  and the light guide plate  30 . The light-shielding pressure-sensitive adhesive sheet  152  is arranged only at a position at which the wiring board  28  overlaps with the light guide plate  30 , and does not directly adhere to the light diffusion sheet  138 . 
     A double-sided tape  146  which causes the display panel  10  to adhere to the inner frame  44  is positioned on the light diffusion sheet  138  on the wiring board  28 , As is understood through comparison to the example of HG.  1 , in the example of  FIG. 4 , the light diffusion sheet  138  serves as a spacer so that the double-sided tape  146  adheres to the display panel  10  even on the wiring board  28 . A surface of the double-sided tape  146  on a side opposite to the display panel  10  adheres to the light diffusion sheet  138 . That is, the double-sided tape  146  causes the display panel  10  and the light diffusion sheet  138  to adhere to each other. Other configurations correspond to the contents described in the above-mentioned embodiment. 
       FIG. 5  is a sectional view illustrating a display device according to a fourth modified example of the embodiment. In this example, a light-shielding pressure-sensitive adhesive sheet  252  adheres from the surface of the wiring board  28  directed to a side opposite to the light guide plate  30  to the front surface  32  of the light guide plate  30 . Further, the light-shielding pressure-sensitive adhesive sheet  252  covers the upper side of the light source  26 , and hence has an effect of blocking light passing through the wiring board  28 . 
     A double-sided tape  246  which causes the display panel  10  to adhere to the inner frame  44  is positioned on the light-shielding pressure-sensitive adhesive sheet  252  on the wiring board  28 . The light-shielding pressure-sensitive adhesive sheet  252  serves as a spacer so that the double-sided tape  246  adheres to the display panel  10 . A surface of the double-sided tape  246  on a side opposite to the display panel  10  adheres to the wiring board  28  and the light-shielding pressure-sensitive adhesive sheet  252 . Other configurations correspond to the contents described in the above-mentioned embodiment. Note that, for the overlapping of the light-shielding pressure-sensitive adhesive sheet  252  with the light diffusion sheet  38 , the light-shielding pressure-sensitive adhesive sheet  252  may be positioned above the light diffusion sheet  38 , or the light diffusion sheet  38  may be positioned above the light-shielding pressure-sensitive adhesive sheet  252 . 
     While there have been described what are at present considered to be certain embodiments of the invention, it will be understood that various modifications may be made thereto, and it is intended that the appended claims cover all such modifications as fall within the true spirit and scope of the invention.