Patent Publication Number: US-2007115693-A1

Title: Backlight module having light guide plate with positioning member for positioning optical films

Description:
FIELD OF THE INVENTION  
      The present invention relates to backlight modules typically used for liquid crystal display (LCD) devices, and especially to a backlight module having a light guide plate with a positioning member for positioning one or more optical films thereon.  
     BACKGROUND  
      Liquid crystal displays are commonly used as display devices for compact electronic apparatuses, because they not only provide good quality images with little power but also are very thin. The liquid crystal in a liquid crystal display does not emit any light itself. The liquid crystal has to be lighted by a light source so as to clearly and sharply display text and images. Thus, a backlight module is generally needed for a liquid crystal display.  
       FIG. 6  is a schematic, exploded, isometric view of a conventional backlight module. The backlight module  1  includes a top frame  11 , a prism film  12 , a diffusion film  13 , a light guide plate  14 , a cold cathode fluorescent lamp (CCFL)  15 , a lamp cover  16 , a reflective film  17 , and a bottom frame  18 .  
      The prism film  12  and the diffusion film  13  are optical films. The prism film  12  includes two opposite protrusions  121 . The diffusion film  13  includes two opposite protrusions  131 , corresponding in position to the protrusions  121  of the prism film  12 . The light guide plate  14  includes an elongate light incident surface  141 . The CCFL  15  is elongate, and is disposed adjacent the light incident surface  141 . The lamp cover  16  is elongate, and covers the CCFL  15 . The top frame  11  engages with the bottom frame  18  to form a space. The space contains the reflective film  17 , the light guide plate  14 , the diffusion film  13 , and the prism film  12 , in that order from bottom to top:  
      Also referring to  FIGS. 7 and 8 , the protrusions  121  and  131  of the prism film  12  and diffusion film  13  are contained in corresponding cutout portions (not labeled) of the bottom frame  18 . Thereby, the optical films  12  and  13  are retained on the light guide plate  14  in the bottom frame  18 . However, the protrusions  121  and  131  are not necessarily snugly received in the cutout portions. The optical films  12  and  13  are liable to shift in the bottom frame  18 . The backlight module  1  may become loose and unstable, and this may impair the performance of the backlight module  1 .  
      Accordingly, what is needed is a backlight module that can overcome the above-described deficiencies.  
     SUMMARY  
      An exemplary backlight module includes a light guide plate having a light incident surface and a light output surface adjacent to the incident surface; a light source disposed adjacent to the light incident surface; and at least one optical film. The light output surface of the light guide plate includes positioning member for positioning the at least one optical film.  
      Other advantages and novel features will become more apparent from the following detailed description of preferred embodiments when taken in conjunction with the accompanying drawings. In the drawings, all the views are schematic.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is an exploded, isometric view of a backlight module according to a first embodiment of the present invention.  
       FIG. 2  is an assembled view of a light guide plate, a CCFL, and a reflective film of the backlight module of  FIG. 1 .  
       FIG. 3  is an assembled view of the light guide plate, the CCFL, the reflective film, and a bottom frame of the backlight module of  FIG. 1 .  
       FIG. 4  is an assembled view of the backlight module of  FIG. 1 .  
       FIG. 5  is an isometric view of a light guide plate of a backlight module according to a second embodiment of the present invention.  
       FIG. 6  is an exploded, isometric view of a conventional backlight module.  
       FIG. 7  is an assembled view of the backlight module of  FIG. 6 .  
       FIG. 8  is an enlarged view of a circled portion VIII of  FIG. 7 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
      Reference will now be made to the drawings to describe the preferred embodiments in detail.  
       FIG. 1  is an exploded, isometric view of a backlight module  2  according to a first embodiment of the present invention. The backlight module  2  includes a plastic frame  21 , a prism film  22 , a diffusion film  23 , a light guide plate  24 , a light source  25 , a reflective film  27 , and an metal frame  28  arranged generally in that order from top to bottom. The prism film  22  and the diffusion film  23  are optical films. The light source  25  may be a cold cathode fluorescent lamp (CCFL). The metal frame  28  can be made of aluminum, metal, or any other suitable metal or alloy.  
      The light guide plate  24  includes a light incident surface  241 , a light output surface  242  generally adjacent to the light incident surface  241 , a bottom surface  243  opposite to the light output surface  242 , and three side surfaces  244  adjacent to the bottom surface  243 . A plurality of flanges  245  is formed at edge portions of the light output surface  242 . In the illustrated embodiment, there are four flanges  245 , which are joined end-to-end to cooperatively form a four-sided closed structure. A horizontal step portion  246  is formed between the light incident surface  241  and the flange  245  adjacent to the light incident surface  241 . An outmost vertical surface of each of the other three flanges  245  forms a part of the corresponding adjacent side surface  244 . The flanges  245  are integrally formed with the light guide plate  24 , and cooperate with the light output surface  242  to form a shallow space (not labeled) therebetween. The reflective film  27  includes a first crease  271 , and a second crease  272  parallel to the first crease  271 .  
      Also referring to  FIGS. 2-4 , when the backlight module  2  is assembled, the light source  25  is positioned adjacent to the light incident surface  241  of the light guide plate  24 . The reflective film  27  is attached to the bottom surface  243  of the light guide plate  24 , and is perpendicularly folded along the first and second creases  271  and  272  to form a cover that covers three sides of the light source  25 . A distal edge of the reflective film  27  is fixed to the step portion  246 . The reflective film  27 , light guide plate  24 , and light source  25  are received in the metal frame  28 . The diffusion film  23  and the prism film  22  are received in the shallow space formed by the flanges  245  and the light output surface  242 . Finally, the plastic frame  21  is engaged with the metal frame  28  to thereby fix the above-described components therein. Thus, assembly of the backlight module  2  is completed.  
      The flanges  246  can firmly fix the diffusion film  23  and the prism film  22  on the light output surface  242  of the light guide plate  24 . Therefore the backlight module  2  having the optical films  22 ,  23  can be mechanically stable and operate properly. Furthermore, the distal edge of the reflective film  27  is fixed to the step  246  formed between the light incident surface  241  and the adjacent flange  246 . Therefore there is no need for a light source cover, which lowers the cost and the weight of the backlight module  2 .  
       FIG. 5  is an isometric view of a light guide plate of a backlight module according to a second embodiment of the present invention. The light guide plate  54  has a structure similar to that of the light guide plate  24 . However, the light guide plate  54  includes four L-shaped flanges  545  disposed at four comers (not labeled) of a light output surface  542  thereof. A horizontal step portion  546  is formed between a light incident surface  541  of the light guide plate  54  and two of the flanges  545  adjacent to the light incident surface  541 . An outmost vertical surface of each of portions of the flanges  545  adjacent to three side surfaces  544  of the light guide plate  54  forms a part of the corresponding adjacent side surface  544 .  
      In alternative embodiments, only one optical film may be employed, or three or more optical films may be employed.  
      It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention.