Abstract:
To provide a backlight having a positioning member that can prevent from coming off from metal frame and damaging a display panel even when used in a harsh environment such as undergoing sharp temperature changes. 
     A backlight unit comprises a light guiding module having a light source and a light guide plate; a resin frame having a recess formed by side walls and bottom surface thereof, and housing the light guiding module; and a metal frame fitted with the resin frame, having an opening in an upper surface thereof and the opening being located above the recess of the resin frame, and allowing to pass light from the light guiding module therethrough. The resin frame has a protrusion on the top surface of one of the side walls of the recess. The metal frame has a notch on the upper surface thereof so that the protrusion passes therethrough. The opening allows the light from the light guiding module to pass therethrough.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a backlight unit to be disposed on the back of a liquid display panel or the like. 
         [0003]    2. Description of the Related Art 
         [0004]    A backlight unit comprises a light guiding module (“flight guiding module” is also called “backlight”) and a resin flame which houses the backlight. The backlight unit is disposed on the back of a display panel, such as liquid crystal display, so that the light from the light guiding module is provided to a display area of the display panel. 
         [0005]    Japanese patent publication JP2000-75273A discloses a backlight unit comprising a metal frame provided on a display panel side of a resin frame, for the purpose of increasing the strength of the resin frame. The metal frame is formed substantially in a box shape. The upper flat surface (or plane) of the metal frame has an opening formed in an portion corresponding to a display area of the display panel so that light from a light guiding module can pass therethrough. 
         [0006]    By fitting the resin frame and the metal frame with each other, a structure having high strength against twisting around diagonal is achieved In addition, display panel positioning spacers formed from a resin are provided on corners of the metal frame, which makes it possible to align the display panel and the metal frame. 
         [0007]    In case the positioning spacers formed from resin are provided on the metal frame, however, the positioning spacers may come off from the metal frame during use in an environment that undergoes sharp temperature changes, due to impact and/or the difference in thermal expansion coefficient between different materials. 
         [0008]    In case positioning spacers formed from a metal are provided on the metal frame, on the other hand, the display panel may be damaged (e.g. scratched) by the positioning spacers formed from metal during manufacture and use, because metal is tend to be stiffer than the material used in the display panel. 
         [0009]    The present invention provides a backlight unit that can maintain high reliability, such as avoiding coming off a spacer and damaging a display panel by a spacer, even when used in a harsh environment such as undergoing sharp temperature changes. 
       SUMMARY OF THE INVENTION 
       [0010]    In order to achieve the object described above, a backlight unit of the present invention comprises a light guiding module having a light source and a light guide plate; a resin frame having a recess formed by side walls and bottom surface thereof, and housing the light guiding module; and a metal frame fitted with the resin frame, having an opening in an upper surface thereof and the opening being located above the recess of the resin frame, and allowing to pass light from the light guiding module therethrough, wherein the resin frame has a protrusion on the top surface of one of the side walls of the recess, the metal frame has a notch on the upper surface thereof so that the protrusion passes therethrough, and the opening allows the light from the light guiding module to pass therethrough. 
         [0011]    In an embodiment of the present invention, the resin frame has a second protrusion on the top surface of another side wall extending in different direction from that of said one of side walls and the metal frame has a second notch so that the second protrusion passes therethrough. 
         [0012]    In another embodiment of the present invention, the opening has substantially rectangular shape, the resin frame has four second protrusions on top surfaces of side walls thereof, each of the four protrusions is adjacent to a different corner of the resin frame and has a portion disposed outside of an extension of the shorter side that constitutes the opening in upper surface of the metal frame, and the metal has four second notches so that the four second protrusion passes therethrough. 
         [0013]    It is preferable that the opening has rounded corners of radius of curvature in a range from 0.3 to 2.3 mm. 
         [0014]    The present invention can provide a backlight unit that is capable of maintaining high reliability (e.g. avoiding coming off a positioning member and damaging a display panel by a spacer) even when used in a harsh environment. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1(   a ) is a schematic perspective view of the backlight unit according to one embodiment of the present invention, and  FIG. 1(   b ) is a schematic exploded perspective view of the backlight unit shown in  FIG. 1(   a ). 
           [0016]      FIG. 2  is a schematic perspective view of the backlight unit according to another embodiment of the present invention. 
           [0017]      FIG. 3  is a schematic perspective view of the backlight unit according to still another embodiment of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0018]    Embodiments of the light emitting apparatus of the present invention will now be described in detail. 
       First Embodiment 
       [0019]      FIG. 1(   a ) shows in a schematic perspective view of a backlight unit  10  according to the first embodiment of the invention viewed from the side of the flat surface thereof.  FIG. 1(   b ) shows a schematic exploded perspective view of backlight unit  10  viewed from the side of the flat surface thereof. The backlight unit  10  comprises a resin frame  11 , a light guiding module (also called a “backlight”)  12  and a metal frame  13 . Specifically, the backlight unit  10  comprises the light guiding module  12 , the resin frame  11  that has a recess  11   a  where the light guiding module  12  is housed, and the metal frame  13 , which is fitted with the resin frame  11 , having an opening (or window)  13   a  that covers the recess  11   a  of the resin frame  11  (i.e. the opening  13   a  is arranged on or above the recess  11   a ) and allows to the light from the light guiding module  12  to pass therethrough. The opening  13   a  is disposed on upper surface of the metal frame  13 . 
         [0020]    The resin frame  11  has protrusions  11   b  on a flat surface of the periphery of the recess  11   a  (i.e. the protrusions  11   b  are disposed on the top surface of a side wall of the resin flame  11  as described detail below). The resin frame  11  preferably has protrusion  11   c  on another flat surface of the periphery of the recess  11   a  (i.e. the protrusion  11   c  may be disposed on the top surface of another side wall of the resin flame  11 ) as shown in  FIGS. 1(   a ) and  1 ( b ). The metal frame  13  has notches  13   b  in the periphery flat surface of the opening  13   a  (i.e. in the upper surface of the metal frame  13  as descried detail below) where the protrusions  11   b  can pass through. In case the protrusion  11   c  is disposed, as shown in  FIGS. 1(   a ) and  1 ( b ), the metal frame  13  has a notch  13   c  in a side wall of the metal frame  13  where the protrusion  11   c  can pass through. 
         [0021]    The details of the resin frame  11 , the light guiding module  12  and the metal frame  13  are described as below. 
       Resin Frame  11   
       [0022]    The resin frame  11  of the first embodiment has the recess  11   a  constituted from a bottom surface (i.e. bottom plate) of substantially rectangular shape and side faces (i.e. four side walls) surrounding the bottom surface. The resin frame  11   a  has the protrusions  11   b  that protrude upwardly (i.e. parallel to the z axis direction in  FIGS. 1(   a ) and  1 ( b )) from the flat top surface of one of the side walls (periphery walls) of the recess  11   a  and are molded integrally with the side wall. The resin frame  11  preferably has the protrusions  11   c  that protrude upwardly (i.e. parallel to the z axis direction in  FIGS. 1(   a ) and  1 ( b )) from the flat top surface of another side walls of which extending direction is different form the that of the side wall on which protrusions  11   b  are formed. The protrusion  11   c  is also molded integrally with the side wall of recess  11   a . For the material to form the resin frame  11 , resins that include various light dispersants may be preferably used. Size and shape of the resin frame  11  may be selected in accordance to the size and shape of the light guiding module  12  to be housed therein. For the material to form the resin frame  11  it is preferable to use a resin that has high impact resistance and weatherability, particularly it is preferable to use polycarbonate resin. 
         [0023]    The protrusions  11   b ,  11   c  of the resin frame  11  pass through the notches  13   b ,  13   c  metal frame  13 , respectively and protrude from the metal frame  13  upwardly, thereby the protrusions  11   b ,  11   c  play the role of, positioning of the display panel to be disposed on the upper flat surface side of the metal frame  13  by contacting with the display panel, in addition to alignment with the metal frame  13  by fitting with the notches  13   b ,  13   c . The protrusions  11   b ,  11   c  with frame  11  can be prevented from the problems of coming off from metal frame  13  and damaging a display panel, which may be raised in conventional spacers as aforementioned, because protrusions  11   b ,  11   c  are made of resin and strongly bonded with the resin frame  11  by forming integrally with resin frame  11 . Furthermore, forming the positioning members, such as protrusions  11   b ,  11   c , integrally with the resin frame  11  improves the positioning accuracy and enables it to reduce the number of components. 
         [0024]    In the embodiment shown in  FIGS. 1(   a ) and ( b ), the protrusions  11   b  are provided at two positions on the top face of the side wall of the resin frame  11  (i.e. on the flat surface of a periphery) in the direction of shorter side of the recess  11   a  (i.e. the side wall extending in direction of the y axis in  FIG. 1(   b )). The number of the protrusions  11   b  may be one, however two or more is preferable. The protrusion  11   c  may be provided at one position on the top face of the side wall side wall of the resin frame  11  in the direction of longer side of the recess  11   a  (i.e. the side wall extending in direction of the y axis in  FIG. 1(   b )), and the protrusion  11   c  also protrudes outwardly (i.e. in the −x direction in  FIG. 1(   b )) from the outer surface (i.e. y-z plane) of the side wall. The protrusions  11   b  define the position of the display panel in the y axis direction of  FIG. 1(   b ) and The protrusions  11   c  defines the position of the display panel in the x axis direction of  FIG. 1(   b ). 
         [0025]    Therefore, this arrangement of the protrusions  11   b ,  11   c  results in the regulating the position of the display panel in two different directions on the upper surface of metal frame  13  where the display panel can slid two dimensionally, thereby the display panel can be disposed exactly in a desired position. 
         [0026]    The protrusion  11   c  is more preferably formed on the top surface of the side walls of the recess  11   a  which side wall adjoin to the side wall on which the protrusions  11   b  is formed, as shown in  FIGS. 1(   a ) and  1 ( b ) In this more preferred embodiment the protrusions  11   b  and the protrusion  11   c  are aligned in L letter shape thereby it become easier to adjust the position of the display panel. As aforementioned, these protrusions  11   b ,  11   c  protrude from the corresponding notches  13   b ,  13   c  of the metal frame  13 . It is preferable that the resin frame  11  has, on the bottom plate thereof, a hole (not shown) for the purpose of improving the dissipation of heat from the light guiding module  12  dispose therein. 
       Light Guiding Module  12   
       [0027]    The light guiding module  12  of this embodiment, housed in the recess  11   a  of the resin frame  11 , comprises light sources  12   a  and a light guide plate  12   c  that has a light receiving side face opposing the light sources  12   a  and lets the light from the light source  12   a  emerge from the flat surface. In a preferred embodiment, the light guiding module  12  further comprises a mounting board  12   b  whereon the light sources  12   a  are mounted and an optical sheet  12   d  laminated on the light guide plate  12   c  for optically controlling the light emerging from the light guide plate  12   c . In this embodiment, a metal plate  12   e  that is bent in L-letter shape may be disposed along the bottom surface and the side wall of the resin frame  11 , while a light reflecting sheet  12   f , the light guide plate  12   c  and the optical sheet  12   d  are formed successively on the flat surface of the metal plate  12   e , while the mounting board  12   b  whereon the light sources  12   a  are mounted is disposed on the inside of the side face of the metal plate  12   e . Constitution of the backlight of the present invention is not restricted to that described above, and various conventional light guiding modules (i.e. backlights) that have been used may be employed. 
         [0028]    The light source  12   a  of this embodiment refers to a light emitting member that is capable of introducing light into the light guide plate, including a semiconductor light emitting element such as light emitting diode and semiconductor laser, cold cathode tube or various combinations thereof. With regard to the relative arrangement between the light source  12   a  and light guide plate  12   c , this embodiment employs edge-light type where the light source  12   a  are opposing to the end face of the light guide plate  12   c , although the present invention is not limited to this constitution, and direct type (or direct light type) where the light source  12   a  are opposing to the bottom surface of the light guide plate  12   c  may also be employed. 
         [0029]    The mounting board  12   b  may be provided for the purpose of mounting the light sources and fastening them thereon, and has a wiring formed from a conductor for supplying power to the light sources  12   a . The mounting board  12   b  may preferably be constituted from a glass epoxy substrate, a flexible substrate or a metal member bonded by an insulating resin with electrically conductive pattern formed thereon from copper foil or the like. Alternatively, a board having high heat dissipating property may be formed with wiring formed via an insulating material on a metallic material such as aluminum or copper. The mounting board  12   b  is preferably disposed in close contact with a chassis such as metal plate  12   e  via a member having high heat conductivity such as heat dissipating sheet. 
         [0030]    The light guide plate  12   c  is a translucent member that is capable of guiding the light, that has been emitted by the light source  12   a  and entered through a part of one end face thereof, by making use of reflection inside thereof and emitting the light in a desired configuration through a predetermined light emitting surface. Therefore, the light guide plate  12   c  may have various shapes such as pointer of a meter or a plate that can be used as liquid crystal backlight in accordance to the desired shape of the light emitting surface. The light guide plate  12   c  has translucency in order to emit the light from the light source  12   a  efficiently through the light emitting surface. The light guide plate  12   c  may be formed from various materials such as epoxy resin, polycarbonate resin or glass. 
         [0031]    The optical sheet  12   d  of this embodiment is formed by laminating a diffuser sheet, a first prism lens sheet and a second prism lens sheet having prisms disposed in a direction different from that of the first prism lens sheet, placed one on another in this order from the side of the light guide plate  12   c . The diffuser sheet, the first prism lens sheet and the second prism lens sheet are formed in a shape that corresponds to the size and shape of the light emitting surface of the light guide plate  12   c . The optical sheet  12   d  is not limited to this constitution, and may be formed by placing those selected from among the diffuser sheet, the prism lens sheet and polarization sheet one on another. Number of the component sheets that constitute the optical sheet and the order of placing the component sheets may be adjusted in accordance to the optical property of the backlight unit. 
         [0032]    The light reflecting sheet  12   f  is preferably formed from a white PET (polyethylene terephthalate), or by coating the surface thereof with a metallic material, since high light reflectivity is required. The metal plate  12   e  is a member provided for the purpose of dissipating heat, generated by the light source  12   a  mounted on the inside, through the bottom of the resin frame  11 , and is formed preferably from aluminum. 
       Metal Frame  13   
       [0033]    The metal frame  13  of this embodiment has an upper plate (upper surface) and side walls (e.g. four side walls) to accommodate the resin frame  11  therein. That is, the metal frame  13  may cover the recess  11   a . The upper flat surface of the metal frame  13  has an opening (window)  13   a  through which light from the light guiding module  12  can pass. The opening  13   a  is generally rectangular shape corresponding to the shape of display area of the panel display and formed large enough that the light from the light guiding module  12  can be reached to entire display area of the display panel. The remaining portion of the upper flat surface of the metal frame  13  to be left after forming opening  13   a  (i.e. the portion in the upper flat surface where the opening  13  is not formed) forms a peripheral flat surface of the opening  13   a . Protrusions  13   b  through which the protrusions  11   b  of the resin frame  11  can pass are formed on the upper flat surface of metal  13   a  (i.e. periphery flat surface of the opening  13   a ). If the protrusion  11   c  is formed, the protrusion  13   c  through which the protrusion  11   c  of the resin frame  11  can pass is formed on the side wall of the metal frame  13 . 
         [0034]    The notches  13   b ,  13   c  may have any shape that accommodates the shape of the protrusions  11   b ,  11   c . In this embodiment, the notches  13   b , which are set to correspond to the protrusion  11   b  protruding from the upper surface of the side wall of resin frame  11 , are formed only in the upper surface of metal frame  13 . Since the notches  13   b  are not formed on the side wall of metal frame  13 , the metal frame  13  has higher strength against twisting around diagonal advantageously. As shown in the  FIGS. 1(   a ) and  1 ( b ) the notches  13   b  are hole disposed on the upper surface of the metal  13 . As used herein, the term “notch” includes any hole in which the protrusion can pass through. In the embodiment shown in  FIGS. 1(   a ) and  1 ( b ), the notch  13   c , which is set to correspond to the protrusion  11   c , is formed by cutting the side wall of metal frame  13 . By forming the notch  13   c  in the side wall of metal frame  13 , the protrusion  11   c  protruding outwardly from the outer surface of the side wall as well as protruding upwardly from the upper surface of the side wall of the resin frame  11  can pass through the notch  13 . The protrude  11   c  can be located in the outside of outer surface of the side wall of metal frame  13 , thereby the size of metal frame  13  can be reduced even if same size display panel is disposed on the metal frame  13 . In a preferred embodiment, the notch  13   c  also may be formed in a similar manner to the notch  13   b , i.e. the notch  13   c  formed only in the upper surface of metal frame  13  extending along the direction of the y axis in  FIG. 1(   b ). 
         [0035]    The metal frame  13  may be formed from a stainless steel that has high corrosion resistance. In the case of this embodiment where a plurality of light sources  12   a  that generate heat are mounted, in particular, it is preferable to use a ferrite-based stainless steel that has high heat conductivity. In this embodiment, a metal frame  13  formed from JIS (Japanese Industrial Standards):SUS430 with a thickness of 0.3 mm is used. 
         [0036]    The metal frame  13  and the resin frame  11  have shapes that can fit with each other. In this embodiment, the recess  11   d  may be provided in the side walls of the resin frame  11 , and the protrusion  13   d  may be provided on the side walls of the metal frame  13  to fit with the recess  11   d  for fastening as shown in  FIG. 1(   b ). The structure having the protrusion formed from a metal that has resilience is fitted in the recess  11   d  of resin such as that described above is less prone to wear of the protrusion, and is therefore more advantageous than the structure of fitting a protrusion formed from a resin into a recess of metal. There are no restrictions on the number and shape of the recesses  11   d  and the protrusions  13   d , as long as fitting of these members is prevented from becoming loose. 
       Second Embodiment 
       [0037]      FIG. 2  shows a backlight unit  20  according to the second embodiment of the invention. The backlight unit  20  has substantially the same constitution as the first embodiment, except that four protrusions  21   c  are provided and four notches  23   c  are disposed on a metal frame  23  so as to oppose the protrusions  21   c  as shown in  FIG. 2 . Each of the four protrusions  21   c  is adjacent to a different corner of a resin frame  21 . That is, each corner of the resin  21  in the second embodiment has a protrusion  21   c  which are adjacent to the corner (i.e. a protrusion  21   c  disposed on the corner or nearby the corner) and protrudes from a top surface of the resin frame  21 . In this arrangement of the four protrusions  21   c  where the four protrusions  21   c  are adjacent to different corners, the distance between the protrusions  21   c  are increased compared with the case where the four protrusions  21   c  are not adjacent to the corners (e.g. four protrusions  21   c  are disposed on the middle portions of side walls of the resin frame  12 ). In the preferred embodiment of backlight unit  20 , each of the four protrusions  21   c  has a portion which is disposed outside of an extension of the shorter edge of the opening  23   a  of the upper surface of a metal frame  23  (extension of edge of opening  23   a  in x direction in  FIG. 2 ) as shown in  FIG. 2 , so that the four protrusion  21   c  are certainly adjacent to each of the four corners of resin frame  23 . This also means that each of the four notches  23  has a portion which is disposed outside of an extension of the shorter edge of the opening  23   a . The four protrusions  21   c  of the backlight unit  20  result in the higher accuracy of the positioning of a display panel disposed on the backlight unit  20  because the number of the protrusions  21   c  is increased to four and the protrusion  21   c  of the backlight unit  20  have enough distance therebetween to obtain the higher accuracy. 
         [0038]    At least one (preferably two or more) of the four protrusions  21   c  extends in the direction of longer side of the recess  22  (i.e. in the direction of y axis in  FIG. 2 ), thereby the position of a display panel in the x axis direction of  FIG. 2  is defined. The rest of the four protrusions  21   c  may extend in different directions, such as in the x axis direction in  FIG. 2 . The protrusions  21   c  preferably protrude outwardly from the outer surface of the side wall of resin frame  21 , similar as the protrusion  11   c  in the backlight unit  10  according to the first embodiment of the invention. When the protrusions  21   c  protrude outwardly as mentioned, the notches  23   c  are formed by cutting side walls of a metal frame  23 , similar as the notch  13   c  of the backlight unit  10 , thereby the protrusions  21   c  can pass through the notches  23   c  and protrude upwardly from the upper surface of the metal frame  23 . In this preferred embodiment the notched  13   c  are formed in the portion of side wall of metal frame  23  adjacent to different corners of metal frame  23  because the protrusions  21   c  are adjacent to different corners of resin frame  21 . This constitution makes it possible to maintain higher strength to endure extraneous force acting on the metal frame  23  compared with the case where the notches  13  are formed in the middle portions of side walls of the metal frame  23 . 
       Third Embodiment 
       [0039]      FIG. 3  shows a backlight unit  30  according to the third embodiment of the invention. The backlight unit  30  has substantially the same constitution as the second embodiment, except that an opening  33   a  has rounded corners  33   e  of radius of curvature in a range from 0.3 to 2.3 mm, as shown in  FIG. 3 . By rounding of the corners of the opening  33   a , it is made possible to increase the strength of the metal frame  33  while maintaining the aperture area of the opening  33   a  required passing the light from a light guiding module. The rounding corners  33   e  may applied to only one or some of corners of the opening  33   e . However in a preferred embodiment all corners (i.e. four corners) of the opening  33   a  are the rounding corners  33   a . The rounding corners  33   e  may be applied to the corners of the opening  13   a  according to the first embodiment. 
         [0040]    The present invention is applicable to an onboard liquid crystal display apparatus and the like as a backlight unit that is resistant to vibration, low in profile, compact and consumes less power. 
         [0041]    This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2008-30092 under the Paris Convention, and, thus, the entire contents thereof are incorporated herein by reference.