Abstract:
In a display panel mounted on a display device, a configuration of mounting that realizes decrease in thickness and weight and exhibits high reliability as well. The display panel is provided with a screen, a plastic frame supporting at least part of the outer periphery of a surface light source device, and a metallic frame disposed on the outside of the plastic frame. On the plastic frame, bosses for fixing the display panel are formed. The metallic frame is furnished at the positions opposite the bosses with holes that allow insertion of screws for fixing the display panel. The display panel is fixed to the outer cover of the display device by causing the fixing screws to be fastened by screwing into the bosses formed on the plastic frame of the display panel.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a display panel provided with a screen such as a liquid crystal panel and a display device provided with a display panel and, more particularly, relates to an improvement in the structure for attaching the display panel to the display device. 
     2. Description of the Related Art 
     In recent years, as display devices for information equipment including personal computers and word processors and for video and imaging equipment including televisions, camcorders, and car navigation systems, liquid crystal devices having features of lightweight, small thickness, and low power consumption have been widely used. These liquid crystal display devices, with a view to realizing a bright display screen, mostly adopt a configuration having built in a lighting unit (surface lighting source device) directed to projecting an illuminating light from behind a liquid crystal panel. 
     The lighting units are classified by the location of a light source: an edge light type and a direct backlight type (or direct type). The edge light type is arranged in such a manner that light is introduced to the edge of a light guiding plate disposed on the opposite of a liquid crystal panel. The direct backlight is arranged in such a manner that a plurality of light tubes such as fluorescent radiation tubes are disposed below the liquid crystal panel, and a diffusing plate disposed between the light tubes and the liquid crystal panel. Of the two types, the edge light type is suitable for displays of portable electronics and laptop computers since a light source should be installed at a sidewall of a light guiding plate. 
     Incidentally, when the surface light source device of the aforementioned edge light type is to be assembled in the display panel, the surface light source device having a light guiding plate is required to be disposed behind the liquid crystal panel. Thus, in order to hold a light guiding plate and a sheet material, the surface light source device and the liquid crystal panel have been held by fitting a metallic frame into a plastic frame that supports the outer peripheral part of a light guiding plate. 
     The display panel of the structure described above is assembled into an outer cover (housing) for electronics such as a laptop computer. The display panel is ordinarily assembled with screws, for example, by embedding it in a plastic frame with metallic nuts or by fastening it with mounting screws to an outer cover whose metallic frame has screw threads (Refer to JP-A HEI 11-305209). 
     JP-A HEI 11-305209 discloses a mounting structure for retaining a liquid crystal display device from its side surfaces that has screw holes and screw threads on each side surfaces of the outer covers. The screw threads are burred by being pressed and the inside of the treads are tapped (refer to Paragraph 0013). 
     SUMMARY OF THE INVENTION 
     In recent years, in search of higher performance and in consideration of environmental protection, video equipment and office automation equipment have been manufactured more lightly and thinly. In line with the trend, the display devices and the display panels are also required to be manufactured as lightly and thinly as possible. As a result, in the structure of the display panel mentioned above, for example, the metallic frame is made of metal plate which is as thin as possible. 
     In this situation, an effort to thread on a metallic frame and use the screw threads as a female screw as contemplated by the invention disclosed in JP-A HEI 11-305209 results in failing to secure a sufficient number of screw threads and lacking in stable mounting. Insufficient screw threads might cause screw threads to be broken, for example when threads are repeatedly tightened at assembly and repairing processes. That contributes to quality problem. 
     This invention has been proposed in view of the technical difficulty mentioned above and is aimed at providing a display panel and a display device both of high quality level such that a mounting structure manifesting high reliability while allowing decrease of thickness and decrease of weight as well can be realized and the hindrance due to breakage of screw threads will not occur. 
     For the purpose of accomplishing the object mentioned above, this invention is directed to a display panel that is provided with a screen such as a liquid crystal panel, a plastic frame supporting at least part of the outer periphery of a surface light source device, and a metallic frame disposed on the outside of the plastic frame and is characterized by the plastic frame having a boss to fasten a screw that fastens the display panel to the plastic frame and as well having a hole disposed on the opposite of the boss on the metallic frame to insert the screw for fastening the display panel. 
     Then, the display device of this invention is provided with a display device mentioned above, and characterized by the fact that the display panel is assembled into the outer frame of the display device by fastening the plastic frame of the display panel to the outer frame with screws, and the screws are inserted from the holes of the outer cover into the bosses on the plastic frame. 
     The display panel of this invention has formed a female screw adapted to fasten a fixing screw to a plastic frame. The plastic frame is thicker than the metallic frame and, therefore, allows a sufficient number of screw threads to be formed therein even when the metallic frame is thin. When the plastic frame is fastened to the display pane with screw, therefore, stable mounting is realized and consequently the screw thread is prevented from being broken when threads are repeatedly tightened at assembly and repairing processes. 
     Particularly the female screw is integrally formed inside the boss, the tubular projection stuck out from the plastic frame, and the tubular projection is supported with an elastic piece. In doing so, the stress of tightening the screw that applies to the plastic frame can be suppressed and it prevents adverse effects on the display such as the liquid crystal panel supported by the plastic frame. Tightening screws can be more smoothly. 
     This invention is capable of securing the number of screw threads allowed to be formed in the female screw while realizing manufacture of the display panel in decreased thickness and weight and enabling the display panel to be stably mounted on the outer cover on the display device without breaking screw threads. It is, therefore, capable of providing a display panel and a display device both with high quality. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view illustrating an example of the structure of a display panel. 
         FIG. 2  is a schematic perspective view illustrating the display panel in an assembled state. 
         FIG. 3  is an exploded perspective view illustrating the display panel in a state mounted on the outer cover (housing) of a display device. 
         FIG. 4  is an enlarged perspective view illustrating the neighborhood of a female screw serving to fasten a fixing screw. 
         FIG. 5A  is a perspective view illustrating as partially broken the neighborhood of the female screw in accordance with an embodiment of the present invention.  FIG. 5B  is a perspective view illustrating as partially broken the neighborhood of the female screw in accordance with a conventional art. 
         FIG. 6  is a schematic cross section of an essential part, illustrating a boss formed on a plastic frame. 
         FIG. 7  is a schematic cross section of an essential part, illustrating another boss on a plastic frame. 
         FIG. 8  is a schematic cross section of an essential part, illustrating a case of causing a boss forming a female screw therein to be formed as separated from a plastic frame. 
         FIG. 9  is a schematic perspective view of an essential part, illustrating the plastic frame of  FIG. 8  as observed from a varied angle. 
         FIG. 10  is a schematic perspective view of an essential part, illustrating the supporting plate portion in an altered shape. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Now, the mode of embodying the display panel and the display device that are contemplated by this invention will be explained below by reference to the accompanying drawings. 
       FIG. 1  is an exploded view illustrating a display panel  1  (liquid crystal display panel) in which a surface light source is assembled. The display panel in the present mode of embodiment is provided, as illustrated in  FIG. 1 , with a liquid crystal panel  2  and a light source panel  3  and is enabled to retain these panels by the combination of a metallic frame  4  and a plastic frame  5 . 
     The liquid crystal panel  2  is built by having a liquid crystal material sealed in between an array substrate and a counter substrate. The array substrate has picture element electrodes and switching elements (thin-film transistors) formed in the shape of a matrix in conformity with display picture elements. On the array substrate, signal wires for sending electric signals to the picture element electrodes and signal wires for supplying the thin-film transistors, namely switching elements, with electric signals are disposed as mutually intersecting perpendicularly. On the other hand, the counter substrate has a counter electrode formed of a transparent electrode material (ITO, for example) on substantially the whole surface thereof so as to form color filter layers in conformity with the picture elements. Further, on the outer surfaces of the array substrate and the counter substrate mentioned above, the polarization plate and the polarization axe are orthogonally attached together. 
     To the liquid crystal panel  2  possessing the structure mentioned above, a circuit board for supplying the liquid crystal panel  2  with driving signals is electrically connected. The image display is accomplished by the switching elements being driven based on the driving signals from the circuit board. The region in which this image display is carried out constitutes a display region and the liquid crystal panel  2  mentioned above is fated to own the display region that has arrayed a plurality of display picture elements. 
     The light source panel  3  mentioned above is assembled as a backlight for the liquid crystal panel  2  and is provided with a light guiding plate  31  for irradiating from a light source to the back surface of the liquid crystal panel  2  and a reflecting sheet  32  disposed on the back surface side of this light guiding plate  31 . The light source is disposed along at least one side of the light guiding plate  31 . In the case of the present mode of embodiment, a light source circuit board  33  having loaded an LED light source is installed in the long side of the light guiding plate  31 . The light emitted from the LED light source is reflected directly or via the reflecting sheet  32  and guided to the light guiding plate  31 , passed through the light guiding plate  31 , and irradiated on the liquid crystal panel  2 . The liquid crystal panel  2  transmits the reflected light and eventually displays images such as irradiated images and characters in prescribed brightness. 
     The metallic frame  4  is made of such a metallic material as stainless steel and the plastic frame  5  is made of various plastic materials. The metallic frame  4  and the plastic frame  5  are respectively furnished with outer frames  41  and  51  disposed substantially perpendicularly to the main surfaces of the liquid crystal panel  2  and the light source panel  3 . These outer frames  41  and  51  serve to hold the outer peripheries respectively of the liquid crystal panel  2  and the light source panel  3 . The metallic frame  4  is provided in the top part thereof with a supporting part  42  overhung inward and this supporting part  42  is built to support the outer peripheral part of the upper surface of the liquid crystal panel  2 . The plastic frame  5  is similarly provided with a supporting part  52  that extending inwardly in the middle of the height of the plastic frame  5 , and the upper surface of the supporting part  52  supports the outer peripheral edge of the light source panel  3  from beneath The liquid crystal panel  2  and the light source panel  3  are supported by being sandwiched between the supporting part  42  of the metallic frame  4  and the supporting part  52  of the plastic frame  5 . 
       FIG. 2  shows the assembled display panel  1  in which the liquid crystal panel  2  and the light source panel  3  are supported by the so-called joint structure between the metallic frame  4  and the plastic frame  5 . 
     The display panel  1  mentioned above is assembled as a screen for a laptop computer, for example, and is used for displaying various information. In this instance, the display panel  1  is required to be fastened to the outer cover (housing) of the laptop computer. The display panel is generally fastened with screws. As illustrated in  FIG. 3 , for example, the display panel  1  is fastened to a laptop computer housing  11  by screwing fixing screws  13  through mounting holes  12   a  disposed on a supporting plate  12  on the laptop computer housing  11 .  FIG. 3  illustrates four portions are fastened with the fixing screws  13 , in particular, two portions each on the short side of the display panel  1 . 
     Prior to screwing the display panel  1 , it is necessary that female screw parts be formed at the positions corresponding to the mounting holes  12   a  in the supporting plate  12  of the display panel  1 . At this time, an effort to form female screws in the metallic frame  4  serving as an outer frame for the display panel  1  results in incurring difficulty in forming a sufficient number of screw threads and acquiring a stable mounting state when the metallic plate for the metallic frame  4  is thin. Screw threads might be broken when threads are repeatedly tightened at assembly and repairing processes. 
     The present mode of embodiment, therefore, contemplates forming female screw parts  53  in the outer frame  51  of the plastic frame  5  as illustrated in an enlarged state in  FIG. 4  and fastening the fixing screws  13  thereto by screwing. To be specific, recesses  57  having a prescribed width in the direction of wall thickness of the outer frame  51  are formed in the outer frame  51  of the plastic frame  5 , the recesses  57  are extended from bottom surfaces  58  of the recesses  57  toward the exterior of the outer frame  51  at the positions for fastening the fixing screws  13  by screwing in the recesses  57 , cylindrical bosses (tubular projections)  54  reaching substantially the same height as the outer surface of the outer frame  51  are formed as integrally implanted in the bottom surfaces  58  of the recesses  57 , and screw threads conforming to the fixing screws  13  are formed on the inner wall surfaces of the bosses  54  and used as the female screw parts  53 . 
     In conformity to female screws  53  on the plastic frame  5 , the metallic frame  4  should include circular holes  43  for allowing the fixing screws  31  to be inserted. While the holes  43  are formed in a size allowing the fixing screws  13  to be inserted, the diameter of the holes can be adjusted to be smaller than that of the head of the fixing screw  13 . 
       FIG. 5  illustrates the difference in sizes of screw threads when the female screws are formed in the plastic frame  5  and in the metallic frame  4 .  FIG. 5A  shows the female screws  53  that are formed in the plastic frame  5 , and  FIG. 5B  shows female screws  44  that are screw threads formed by squeezing the metallic frame  4 . 
     When the female screw  53  is formed in the outer frame  51  of the plastic frame  5  as illustrated in  FIG. 5A , the size D (the size of depth of the circular recess) allowing a screw thread to be formed in the female screw  53  can be arbitrarily set so long as it is smaller than the size of thickness of the outer frame  51 . To be specific, the size D mentioned above can be freely set in the range in which the cylindrical boss  54  avoids surpassing the outer surface of the outer frame  51 . Within this range, the size that allows formation of a sufficient number of screw threads conforming to the screw threads of the fixing screw  13  mentioned above can be set. The size D is not restricted by the thickness t of the metallic frame  4 . 
     When a female screw part  44  is formed in the metallic frame  4  as illustrated in  FIG. 5B , the size d that allows formation of screw threads is restricted by the thickness of the metallic frame  4 . Generally, the available number of screw threads that can be formed in the metallic frame  4  is determined by the height 1.5 to 2 times the thickness of the metallic frame  4 . When the thickness of the metallic frame  4  is 0.5 mm and the pitch of the fixing screws  13  is 0.4 mm, for example, the standard workable height will be 0.5 mm×2=1 mm and the available number of screw threads will be 1 mm÷0.4 mm=2.5 (threads). Though the minimum number of threads (two threads) that is generally required can be secured, virtually no allowance is granted. A further decrease of the thickness of the metallic frame  4  will be at a disadvantage for the sake of screwing because the available number of screw threads that can be formed is further decreased. 
     By forming in the plastic frame  5  the female screw parts  53  corresponding to the fixing screw  13  as described above, it is rendered possible to increase the number of formable screw threads and realize a stable state of mounting. Further, the possibility that the screw threads will be broken can be repressed even when the tying work is repeated during the operation of assembling and the operation of repairing, for example. 
     Incidentally, while the aforementioned female screw  53  may be obtained solely by forming a cylindrical recess in the outer frame  51  of the plastic frame  5 , it is more favorably obtained by forming a cylindrical projection (so-called boss) in the recess  57  of the outer frame  51  of the plastic frame  5  as mentioned above.  FIG. 6  is a schematic cross section of the essential part, showing the structure forming the boss  54  in the plastic frame  5  and the female screw  53  in the boss  54 . By adopting this structure, it is possible to suppress the stress applied to the plastic frame  5  during screwing, and maintain the strength of screwing. 
     The plastic frame  5 , as described formerly, plays a key role in sandwiching the liquid crystal panel  2  and the light source panel  3  with the metallic frame  4  and consequently holding them. When the boss  54  is integrally implanted in an independent form on the plastic frame and the female screw  53  is formed therein as described above, it is possible to suppress the stress applied to the plastic frame  5 , the liquid crystal panel  2  and the light source panel  3  during screwing and lead to prevent the display quality from decreasing. When the optical structural element is exposed to stress and consequently suffered to induce strain, it possibly entails such problems as degrading optical properties and lowering the quality level of display. When the boss  54  is integrally implanted in an independent form on the plastic frame and the female screw  53  is formed therein as described above, it is possible to suppress the stress applied to the plastic frame  5 , the liquid crystal panel  2  and the light source panel  3  during screwing and lead to prevent the display quality from decreasing. 
     When the boss  54  mentioned above has its leading edge formed as a minor diameter  54   a  conforming in size with the hole  43  of the metallic frame  4  and the plastic frame  5  and the metallic frame  4  are assembled in a form having the minor diameter part  54   a  inserted in the hole  43  mentioned above as illustrated in  FIG. 7 , the structure of screwing will be more stable. Further, since the hole  43  of the metallic frame  4  is made to fit the minor diameter  54   a  of the boss  54 , it incidentally functions as a means for locating the metallic frame  4 . 
     Then, for the purpose of further alleviating the stress generated during the course of screwing, the boss  54  mentioned above may be integrally formed in a state of being connected to a side face  59  of the outer frame  51  in the recess  57  of the plastic frame  5 . 
       FIG. 8  illustrates the case of having the cylindrically shaped boss  54  partly connected to the outer frame  51  of the plastic frame  5 . As illustrated in  FIG. 6  and  FIG. 7 , the boss  54  is integrally projected in the state of being implanted on the bottom surface  58  in the recess  57  of the outer frame  51  for the plastic frame  5 . In the present case, part of the outer wall surface of the boss  54  and part of the side face (inner wall surface)  59  in the recess  57  of the plastic frame  5  are integrally formed as connected with two sheet-like connecting parts  55 ,  56 . The boss, thus formed, is enabled to increase its mechanical strength and as well manifest an effect of alleviating the stress applied to the plastic frame  5  during the course of a screwing operation as compared with the case of merely forming the female screw in the plastic frame  5 . The boss  54  and the connecting parts  55  and  56  may be so constructed as to float from the bottom surface  58  of the recess  57  of the plastic frame  5 . Specifically, as illustrated in  FIG. 9 , a gap s is formed between the boss  54  and the bottom surface  58  in the recess  57  of the outer frame  51  of the plastic  5  and the boss  54  is made to assume the state of being supported as separated from the bottom surface  58  of the outer frame  51  with the two connecting parts  55  and  56 . The connecting parts  55  and  56  become to support elastically the boss  54  by utilizing the flexibility of resin and fulfill the role of alleviating the stress exerted during the operation of screwing the boss  54  and alleviating the stress propagated to the plastic frame  5 . 
     Separating the boss from the plastic frame  5  is only required modifications for molds of the plastic frame  5 . The outer frame  51 , the boss  54 , and the connecting parts  55  and  56  can be integrally molded in a hollow shape. 
       FIG. 10  illustrates the case of causing the one connecting part  56  of the connecting parts  55  and  56  that are jointly supporting the boss  54  to be altered in a shape snaking in the direction of the wall thickness of the plastic frame  5 . By altering the shape of the connecting part  56  in the snaking pattern, it is rendered possible to alleviate the stress effectively. The altered shape also can cope with a dimensional change caused by thermal expansion, for example. In this case, the alteration can be applied to either or both of the connecting parts  55  and  56 . 
     Since the display panel and the display device of this invention that have such structures as described above adopt a configuration of forming the boss  54  in the plastic frame  5  and then forming the female screw  53  in the boss  54 , they are able to improve the reliability of the female screw  53 . Following this invention, therefore, it is possible to improve the workability and the accuracy of assembly as well as reliability of the female screws, and consequently improve the product quality controlling the variation of product accuracy. It is further capable of realizing decrease of thickness and weight in the relevant products to the same degree as attained heretofore and realizing better quality level than attained heretofore.