Abstract:
The invention provides a backlight module including: a light guiding plate having a first side surface and a second side surface; a plurality of light sources arranged along the second side surface of the light guiding plate; a quantum dot enhancement film (QDEF) disposed above the light guiding plate, wherein the QDEF includes a first edge adjacent to the first side surface and a second edge adjacent to the second side surface; and a frame disposed outside the light guiding plate, the frame having a first extension portion covering the first edge of the QDEF and a second extension portion covering the second edge of the QDEF, wherein a distance between an end of the first extending portion and the first edge of the QDEF is greater than a distance between an end of the second extension portion and the second edge of the QDEF.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a Continuation of pending U.S. patent application Ser. No. 14/456,175, filed Aug. 11, 2014 and entitled “Backlight Module and Display Device using the same” which claims priority of Taiwan Patent Application No. 102132146, filed on Sep. 6, 2013, the entirety of which is incorporated by reference herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Field of the Invention 
         [0003]    The present invention relates to a backlight module and a display device, and in particular to a backlight module and a display device capable of preventing blue light leaks from the edge of the display. 
         [0004]    Description of the Related Art 
         [0005]    To raise the color saturation of a liquid crystal display for better image quality, a manufacturer in this field has proposed an approach which applies a film called Quantum Dot Enhancement Film (QDEF) to a backlight module consisting of blue LEDs. Quantum dot enhancement film has a plurality of quantum dot phosphors of different sizes to convert the incident blue light to light having different wavelengths. Thereby, the spectrum of white light mixed from the light having different wavelengths is wider such that the color saturation of the display is higher. 
         [0006]    In the backlight module, four edges of the quantum dot enhancement film formed on the surface of a light guiding plate should keep a predetermined distance away from the frame surrounding the light guiding plate to prevent compressive deformation due to thermal expansion. However, a portion of blue light is emitted from the gap without passing through the quantum dot enhancement film such that the user could become conscious of blue light leaks from the four edges of the display. 
         [0007]    In view of this problem, the invention provides a backlight module and a display device reducing blue light leaks from the edges of the display for a better visual experience. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    A detailed description is given in the following embodiments with reference to the accompanying drawings. 
         [0009]    The invention provides a backlight module, including: a light guiding plate having a first side surface and a second side surface; a plurality of light sources arranged along the second side surface of the light guiding plate; an optical film disposed above the light guiding plate; a quantum dot enhancement film disposed between the light guiding plate and the optical film, wherein the quantum dot enhancement film comprises a first edge and a second edge, the first edge is adjacent to the first side surface of the light guiding plate, and the second edge is adjacent to the second side surface of the light guiding plate; and a frame disposed outside the light guiding plate, the frame having a first extension portion and a second extension portion, wherein the first extension portion covers the first edge of the quantum dot enhancement film, and the second extension portion covers the second edge of the quantum dot enhancement film, wherein a distance between an end of the first extending portion and the first edge of the quantum dot enhancement film is a first distance, a distance between an end of the second extension portion and the second edge of the quantum dot enhancement film is a second distance, and the second distance is greater than the first distance. 
         [0010]    In the above backlight module, the frame has a white surface faced to the quantum dot enhancement film or the light guiding plate. The at least one of the plurality of light sources is a blue LED. The optical film is a diffusion film or a brightness enhancement film. 
         [0011]    The above backlight module further includes: a printed circuit board disposed adjacent to the light guiding plate, the light guiding plate disposed between the printed circuit board and the quantum dot enhancement film. 
         [0012]    The above backlight module further includes: a reflection film having a third edge and a fourth edge, wherein the third edge is adjacent to the first side surface of the light guiding plate, and the fourth edge is adjacent to the second side surface of the light guiding plate, wherein the light guiding plate is disposed between the quantum dot enhancement film and the reflection film, the first edge of the quantum dot enhancement film and the second edge of the quantum dot enhancement film are opposite to each other, the third edge of the reflection film and the fourth edge of the reflection film are opposite to each other, a distance between the first edge and the second edge is a third distance, a distance between the third edge and the fourth edge is a fourth distance, and the third distance is greater than the fourth distance. 
         [0013]    The invention also provides a display device, including: a display panel; and a backlight module disposed adjacent to the display panel, the backlight module including: a light guiding plate having a first side surface and a second side surface; a plurality of light sources arranged along the second side surface of the light guiding plate; an optical film disposed above the light guiding plate; a quantum dot enhancement film disposed between the light guiding plate and the optical film, wherein the quantum dot enhancement film comprises a first edge and a second edge, the first edge is adjacent to the first side surface of the light guiding plate, and the second edge is adjacent to the second side surface of the light guiding plate; and a frame disposed outside the light guiding plate, the frame having a first extension portion and a second extension portion, wherein the first extension portion covers the first edge of the quantum dot enhancement film, and the second extension portion covers the second edge of the quantum dot enhancement film, wherein a distance between an end of the first extending portion and the first edge of the quantum dot enhancement film is a first distance, a distance between the end of the second extension portion and the second edge of the quantum dot enhancement film is a second distance, and the second distance is greater than the first distance. 
         [0014]    In the above display device, the frame has a white surface faced to the quantum dot enhancement film or the light guiding plate. At least one of the plurality of light sources is a blue LED. The optical film is a diffusion film or a brightness enhancement film. The backlight module further includes: a printed circuit board located adjacent to the light guiding plate, the light guiding plate disposed between the printed circuit board and the quantum dot enhancement film. 
         [0015]    The above display device further includes: a reflection film having a third edge and a fourth edge, wherein the third edge is adjacent to the first side surface of the light guiding plate, and the fourth edge is adjacent to the second side surface of the light guiding plate, wherein the light guiding plate is disposed between the quantum dot enhancement film and the reflection film, the first edge of the quantum dot enhancement film and the second edge of the quantum dot enhancement film are opposite to each other, the third edge of the reflection film and the fourth edge of the reflection film are opposite to each other, a distance between the first edge and the second edge is a third distance, a distance between the third edge and the fourth edge is a fourth distance, and the third distance is greater than the fourth distance. 
         [0016]    In the above display device, the display panel further includes: a first substrate and a first polarizer, wherein the first substrate is disposed between the first polarizer and the quantum dot enhancement film of the backlight module, a thickness of the first polarizer is a first thickness, a thickness of the quantum dot enhancement film is a second thickness, and the second thickness is greater than the first thickness. The display panel further includes: a second substrate and a second polarizer, wherein the second substrate is disposed between the first substrate and the quantum dot enhancement film of the backlight module, the second polarizer is disposed between the second substrate and the quantum dot enhancement film of the backlight module, a thickness of the second polarizer is a third thickness, and the second thickness is greater than the third thickness. In the above display device, the first polarizer has a fifth edge and a sixth edge, the fifth edge is adjacent to the first side surface of the light guiding plate, and the sixth edge is adjacent to the second side surface of the light guiding plate, the first polarizer covers the end of the first extension portion, the first polarizer covers the end of the second extension portion, a distance between the end of the first extending portion and the fifth edge of the first polarizer is a fourth distance, a distance between the end of the second extension portion and the sixth edge of the first polarizer is a fifth distance, and the fifth distance is greater than the fourth distance. 
         [0017]    According to the above backlight module and display device, blue light leaks from edges of the display can be prevented to improve the visual experience. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
           [0019]      FIG. 1  is a three-dimensional diagram showing a backlight module of a liquid crystal display; 
           [0020]      FIG. 2  is a section view of a conventional backlight module; 
           [0021]      FIG. 3  is a section view of a backlight module in accordance with Embodiment 1 of the invention; and 
           [0022]      FIG. 4  is a section view of a backlight module and a display panel in accordance with Embodiment 2 of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
         [0024]      FIG. 1  is a three-dimensional diagram showing a backlight module of a liquid crystal display. As shown in  FIG. 1 , basically three portions can be seen from the appearance of the backlight module  1 : a planar illuminant portion  10 , a frame portion  12 , and a housing portion  14 . The planar illuminant portion  10  emits planar light toward the +Z direction. The frame portion  12  surrounds the planar illuminant portion  10  to restrict the X-directional position and the Y-directional position of the planar illuminant portion  10 . The housing portion  14  contains the planar illuminant portion  10  and the frame portion  12 , and functions with the frame portion  12  to restrict the Z-directional position of the planar illuminant portion  10 . 
         [0025]      FIG. 2  is a section view of a conventional backlight module. When a convention backlight module is viewed from the A-A′ section of  FIG. 1 , as shown in  FIG. 2 , the backlight module  2  comprises an LED light source  21 , a light guiding plate  22 , an optical film assembly  23 , a ring-shaped frame  24 , a bezel  25 , a printed circuit board  26 , a fixation pad  27 , and a reflection film  28 . The LED light source  21 , the light guiding plate  22 , and the optical film assembly  23  correspond to the planar illuminant portion  10  shown in  FIG. 1 ; the ring-shaped frame  24  and the fixation pad  27  correspond to the frame portion  12  shown in  FIG. 1 ; and the bezel  25  correspond to the housing portion  14  shown in  FIG. 1 . 
         [0026]    The LED light source  21  comprises a plurality of blue light LED arranged along the Y direction, and emits blue light toward the −X direction. The light guiding plate  22  is a rectangular plane structure which guides the blue light emitted from the LED light source  21  and reflects the light repeatedly therein. The diffused light is then converted into uniform planar light and emitted from a first surface S along the +Z direction. The optical film assembly  23  is adhered on the first surface S of the light guiding plate  22 . The optical film assembly  23  comprises a bottom optical film  231 , and two upper optical films  232  layered above the bottom optical film  231 . The bottom optical film  231  is a quantum dot enhancement film for converting blue light into multiple-color-mixed-light which is close to white light. The two upper optical films  232  can be diffusion film, micro-lens brightness enhancement film, etc. 
         [0027]    The ring-shaped frame  24  has two sides extending along the Y direction to restrict the X-directional position of the LED light source  21  and the light guiding plate  22 , and the other sides extending along the X direction to restrict the Y-directional position of the LED light source  21  and the light guiding plate  22 . The ring-shaped frame  24  further has an extension portion  241  extending toward the +X direction. The bezel  2  has a “C” shaped cross section in the XZ plane to wrap the LED light source  21 , the light guiding plate  22 , and the ring-shaped frame  24  therein. The bottom surface of the bezel  25  further functions with the extension portion  241  to restrict the Z-directional position of the light guiding plate  22 . 
         [0028]    The printed circuit board  26  comprises a circuit for driving the LED light source  21 , and is adhered across the ring-shaped frame  24  and the light guiding plate  22 . The fixation pad  27  overlaps on the printed circuit board  26  to restrict the Z-directional position of the light guiding plate  22 . The extension portion  241  of the ring-shaped frame  24  and the +Z directional surface of the fixation pad  27  are further used as a platform to support and adhere the display panel (not shown) thereon. The reflection film  28  is adhered between the −Z-directional surface of the light guiding plate  22  and the +Z-directional surface of the bezel  25  for reflecting light to the +Z direction. 
         [0029]    When the structure shown in  FIG. 2  is assembled, the ring-shaped frame  24  and the fixation pad  27  are used to fix the light guiding plate and then the optical film assembly  23  is placed on the +Z directional surface of the light guiding plate  22 . A gap must be preserved between the optical film assembly  23  and the extension portion  241  of the ring-shaped frame  24 , and between the optical film assembly  23  and the fixation pad  27  to prevent compressive deformation due to thermal expansion. However, the gap causes blue light leaks. From  FIG. 2 , it can be seen that the regions of the light guiding plate  22  at the gap positions are not covered by any one of the extension portion  241 , the optical film assembly  23  and fixation pad  27 . Therefore, blue light not passing through the quantum dot enhancement film  331  will be seen by the human eye such that visual experience becomes worse. 
         [0030]      FIG. 3  is a section view of a backlight module in accordance with Embodiment 1 of the invention. When a backlight module in accordance with Embodiment 1 is viewed from the A-A′ section of  FIG. 1 , as shown in  FIG. 3 , the backlight module  3  comprises a LED light source  31 , a light guiding plate  32 , an optical film assembly  33 , a ring-shaped frame  34 , a bezel  35 , a printed circuit board  36 , a shielding pad  37 , and a reflection film  38 . 
         [0031]    The LED light source  31 , the light guiding plate  32 , the bezel  35 , and the reflection film  38  shown in  FIG. 3  are the same as the LED light source  21 , the light guiding plate  22 , the bezel  25 , and the reflection film  28  respectively. Detailed descriptions for those elements are omitted. 
         [0032]    In the structure shown in  FIG. 3 , the ring-shaped frame  34  has an extension portion  341  extending toward the +X direction and an extension portion  342  extending toward the −X direction. Although not shown in  FIG. 3 , the ring-shaped frame  34  also has an extension portion extending toward the +X direction and an extension portion extending toward the −X direction. The feature of Embodiment 1 of the invention is that the quantum dot enhancement film  331  which is the bottom optical film of the optical film assembly  33  extends toward the −X, +Y, and −Y directions more than the upper optical films  332 , such that the extension portion  341  can cover at least three edges of the quantum dot enhancement film  331 . At the side where the LED light source  31  is arranged, the extension portion  32  has to cover at least the LED light source  31 . Therefore, if the extension portion  32  further extends toward the −X direction, the extension portion  32  is difficult to form and the strength thereof could be reduced. In this regard, the extension portion  342  extends only to the edge of the light guiding plate  32 . Thus, the shielding pad  37  is added for further extending from the extension portion  342  toward the −X direction, which stretches across the gap between the optical film assembly  33  and the extension portion  342  and reaches the top of the optical film assembly  33 . On the other hand, in cases where the thickness of the backlight module is not increased, the printed circuit board  36  formed below the LED light source  31  can not only increase the possible thickness of the extension portion  342  to increase its strength but also shorten the distance between the quantum dot enhancement film  331  and the LED light source  31 . 
         [0033]    In this embodiment, the quantum dot enhancement film  331  extends to the bottom of the extension portion  341 . Therefore, the region of the light guiding plate  32  at the gap between the extension portion  341  and the optical film assembly  33  is at least coved by the quantum dot enhancement film  331 . The blue light emitted from the light guiding plate  32  must pass through at least the quantum dot enhancement film  331  and then be converted to multiple-color-mixed-light which is close to white light. When the display is watched, white light leaks are more acceptable than blue light leaks. At the side where the LED light source  31  is arranged, the shielding pad  37  covers the gap so the blue light doesn&#39;t leak from this edge. 
         [0034]      FIG. 4  is a section view of a backlight module and a display panel in accordance with Embodiment 2 of the invention. When a backlight module in accordance with Embodiment 2 is viewed from the A-A′ section of  FIG. 1 , as shown in  FIG. 4 , the backlight module  4  comprises an LED light source  41 , a light guiding plate  42 , an optical film assembly  43 , a ring-shaped frame  44 , a bezel  45 , a printed circuit board  46 , and a reflection film  48 . In comparison with  FIGS. 2 and 3 ,  FIG. 4  depicts a display panel  5  for showing the structure when the backlight module  4  and the display panel  5  are assembled. The display panel  5  comprises a lower substrate  51 , an upper substrate  52 , a lower polarizer  53 , and an upper polarizer  54 . The display panel  5  is placed on the +Z directional surfaces of the extension portions  441  and  442  of the ring-shaped frame  44 . 
         [0035]    The LED light source  41 , the light guiding plate  42 , the extension portion  441  of the ring-shaped frame  44 , the bezel  45 , the printed circuit board  46 , and the reflection film  48  in Embodiment 2 are the same as the LED light source  31 , the light guiding plate  32 , the extension portion  341  of the ring-shaped frame  34 , the bezel  35 , the printed circuit board  36 , and the reflection film  38  in Embodiment 1 respectively. Detailed descriptions for those elements are omitted. 
         [0036]    The difference between Embodiments 1 and 2 is that bottom optical film which is the quantum dot enhancement film  431  not only extends toward the −X, +Y and −Y directions but also toward the +X direction more the upper optical films  432 . The extension portion  442  of the ring-shaped frame  44  which extends toward the −X direction not only covers the LED light source  41  but also extends to the top of the quantum dot enhancement film  431 . Thereby, even at the side where the LED light source  41  is arranged, the region of the light guiding plate  42  at the gap between the extension portion  442  and the optical film assembly  43  is covered by at least the quantum dot enhancement film  431 . In this way the blue light emitted from the light guiding plate  42  must pass through at least the quantum dot enhancement film  431  and then be converted to multiple-color-mixed-light which is close to white light. 
         [0037]    Furthermore, the ring-shaped frame  34  in Embodiment 1 and ring-shaped frame  44  in Embodiment 2 can adopt a material with a white surface. With the white material having high reflectivity, the ring-shaped frame  34  or  44  reflects light incident to its surface to the quantum dot enhancement film  331  or  431 , which reduces the intensity of blue light to increase vision experience. 
         [0038]    According to Embodiment 1 and Embodiment 2, by extending only the quantum dot enhancement film which is at the lowest layer of the optical film assembly to the bottom of the extension portion of the ring-shaped frame, the invention prevents blue light leak from the edges of the display and improves vision experience. The entire optical film assembly is not required to extend to the bottom of the extension portion, so the extension portion of the ring-shaped frame doesn&#39;t have to be made extremely thin. The yield rate in the manufacturing process can be improved. 
         [0039]    While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.