Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
     The disclosure of Japanese Patent Application No. 2007-3979 filed on Jan. 12, 2007 including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates to a liquid crystal display module, and more particularly to a miniaturized liquid crystal display module such as a mobile phone. 
     2. Description of Related Art 
     Currently, a small-sized liquid crystal display panel having a size of approximately 2 inches to 4 inches has been used as a mobile phone. The mobile phone includes a liquid crystal display module which is constituted of a liquid crystal display panel and a backlight device arranged on a back surface of the liquid crystal display panel, and a casing for storing the liquid crystal display module. 
     Here, although there is no direct relationship with the invention, patent document 1 (JP-A-11 (1999)-305228) discloses a technique for fixing a reflection sheet using a double-sided adhesive tape. 
     SUMMARY 
       FIG. 5  is a perspective view showing the constitution of a conventional liquid crystal display module. 
     A liquid crystal display panel is constituted by overlapping a TFT substrate  11  and a color filter substrate  12  (hereinafter, referred to as a CF substrate) with a liquid crystal layer sandwiched therebetween. Further, on a portion of the TFT substrate  11  where the TFT substrate  11  and the CF substrate  12  do not overlap each other, a driver chip  13  for controlling driving of the liquid crystal display panel is formed. Further, for supplying signals to the driver chip  13 , one end of a flexible printed circuit board  15  is arranged on the portion of the TFT substrate  11  where the TFT substrate  11  and the CF substrate  12  do not overlap each other. Further, a polarizer  14  is arranged on the CF substrate  12 , and a polarizer is also arranged on the TFT substrate  11 . 
     The liquid crystal display panel is arranged on an upper side of a frame-shaped mold frame  16 . Further, on a lower side of the mold frame  16 , optical sheets such as an upper diffusion sheet, an upper prism sheet, a lower prism sheet and a lower diffusion sheet not shown in the drawing, a light guide plate  17 , and a reflection sheet  19  are arranged in a state that these optical sheets, the light guide plate  17  and the reflection sheet  19  are sandwiched between a portion of the other end of the flexible printed circuit board  15  described above and the mold frame  16 . Here, on the other end of the flexible printed circuit board  15 , a light source  18  such as an LED is arranged to face a side surface of the light guide plate  17  in an opposed manner. 
       FIG. 6  is a view showing a cross-sectional constitution of the conventional liquid crystal display module taken along a line A-A′ in  FIG. 5 .  FIG. 6  shows a state that the liquid crystal display module shown in  FIG. 5  is stored in a space defined by an upper frame  21  and a lower frame  22 . Further,  FIG. 7  is a view showing a cross-sectional constitution of the conventional liquid crystal display module taken along a line B-B′ in  FIG. 5 .  FIG. 7  shows a state that the liquid crystal display module shown in  FIG. 5  is stored in the space defined by the upper frame  21  and the lower frame  22  in the same manner as  FIG. 6 . 
     As shown in  FIG. 6 , the other end of the flexible printed circuit board  15  is arranged to overlap a portion of the reflection sheet  19 . Further, as shown in  FIG. 7 , to the other end of the flexible printed circuit board  15 , a pushing pressure is applied from below by the lower frame  22  made of metal, for example. It has been found that, due to such a pushing pressure, the other end of the flexible printed circuit board  15  is brought into contact with the reflection sheet  19 , and as a result, the reflection sheet  19  is deflected thus generating display irregularities. 
     The invention has been made to overcome such drawbacks, and it is an object of the invention to provide a liquid crystal display module which can prevent the generation of display irregularities even when the liquid crystal display module having a relatively large display screen is stored in a casing having a relatively small storing space. 
     According to one aspect of the invention, there is provided a liquid crystal display module which includes a liquid crystal display panel and a backlight device arranged on a back surface of the liquid crystal display panel, wherein the backlight device is constituted of a light guide plate and a reflection sheet which is arranged on a back surface of the light guide plate, the liquid crystal display module includes a flexible printed circuit board having one end thereof mounted on the liquid crystal display panel and the other end thereof formed on a back side of the reflection sheet in an overlapping manner, and an insulation sheet arranged between the other end of the flexible printed circuit board and the reflection sheet. 
     Due to such a constitution, it is possible to provide a liquid crystal display module which can prevent the generation of display irregularities. 
     Further, in the liquid crystal display module, the insulation sheet has a thickness thereof set to a value not less than 20 μm and not more than 50 μm. Here, with respect to the thickness of the insulation sheet, when the thickness is set to a value not less than 30 μm and not more than 50 μm, it is possible to further expect the above-mentioned advantageous effect of the invention. The thickness of the insulation sheet is preferably set to a value not less than 35 μm and not more than 45 μm. 
     Further, in the liquid crystal display module, the other end of the flexible printed circuit board overlaps a portion of the reflection sheet, and the insulation sheet is arranged on the reflection sheet in a state that the insulation sheet gets over the other end of the flexible printed circuit board. 
     Further, in the liquid crystal display module, the insulation sheet is arranged on the reflection sheet in a state that the insulation sheet gets over the other end of the flexible printed circuit board by at least 10 mm or more. 
     It is considerable that the insulation sheet of the invention is preferably made of a material having a smooth surface such as polyethylene terephthalate sheet (PET sheet), for example. 
     Here, in the above-mentioned liquid crystal display module, the light source is arranged on the other end of the flexible printed circuit board, and the light source faces one side surface of the light guide plate in an opposed manner. Further, in the liquid crystal display module, optical sheets such as an upper diffusion sheet, an upper prism sheet, a lower prism sheet and a lower diffusion sheet are arranged between the light guide plate and the liquid crystal display panel. 
     According to the invention, it is possible to provide a liquid crystal display module which can prevent the generation of display irregularities. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view showing the constitution of a liquid crystal display module  10  according to the invention; 
         FIG. 2  is a view showing the cross-sectional constitution of the liquid crystal display module of the invention taken along a line A-A′ in  FIG. 1 , and showing a state that the liquid crystal display module is stored in a space defined by an upper frame  21  and a lower frame  22 ; 
         FIG. 3  is a view showing the conventional cross-sectional constitution of the liquid crystal display module taken along a line B-B′ in  FIG. 1 , and showing a state that the liquid crystal display module is stored in a space defined by an upper frame  21  and a lower frame  22 ; 
         FIG. 4  is a view showing the constitution of an insulation sheet of the invention; 
         FIG. 5  is a perspective view showing the constitution of a conventional liquid crystal display module; 
         FIG. 6  is a view showing the cross-sectional constitution of the conventional liquid crystal display module taken along a line A-A′ in  FIG. 5 , and showing a state that the conventional liquid crystal display module is stored in a space defined by an upper frame  21  and a lower frame  22 ; and 
         FIG. 7  is a view showing the cross-sectional constitution of the conventional liquid crystal display module taken along a line B-B′ in  FIG. 5 , and showing a state that the conventional liquid crystal display module is stored in the space defined by the upper frame  21  and the lower frame  22 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows the constitution of a liquid crystal display module  10  according to the invention. 
     A liquid crystal display panel is constituted by overlapping a TFT substrate  11  and a color filter substrate  12  (hereinafter, referred to as a CF substrate  12 ) formed of an insulative transparent substrate such as a glass substrate, a plastic substrate or the like, for example, with a liquid crystal layer sandwiched therebetween. Further, on a portion of the TFT substrate  11  where the TFT substrate  11  and the CF substrate  12  do not overlap each other, a driver chip  13  for controlling driving of the liquid crystal display panel is formed. Further, for supplying signals to the driver chip  13 , one end of a flexible printed circuit board  15  is arranged on the portion of the TFT substrate  11  where the TFT substrate  11  and the CF substrate  12  do not overlap each other. Further, a polarizer  14  is arranged on the CF substrate  12 , and a polarizer is also arranged on the TFT substrate  11 . Here, for arranging the driver chip  13  on the TFT substrate  11 , the CF substrate  12  is made smaller than the TFT substrate  11 . It is needless to say that when the driver chip is arranged on the CF substrate  12 , the CF substrate  12  is made larger than the TFT substrate  11  in size. 
     The liquid crystal display panel is arranged on an upper side of a frame-shaped mold frame  16 . Further, on a lower side of the mold frame  16 , optical sheets such as an upper diffusion sheet, an upper prism sheet, a lower prism sheet and a lower diffusion sheet not shown in the drawing, a light guide plate  17 , and a reflection sheet  19  are arranged in a state that these optical sheets, the light guide plate  17  and the reflection sheet  19  are sandwiched between a portion of the other end of the flexible printed circuit board  15  described above and the mold frame  16 . Here, on the other end of the flexible printed circuit board  15 , a light source  18  such as an LED is arranged to face a side surface of the light guide plate  17  in an opposed manner. 
     The light guide plate  17  is arranged in a state that one side surface of the light guide plate  17  faces the light source  18  in an opposed manner, and the light guide plate  17  is stored in the mold frame  16  on a side opposite to a side of the mold frame  16  in which the liquid crystal display panel is stored. Further, the reflection sheet  19  arranged below the light guide plate  17  is adhered to the mold frame  16  using an adhesive agent applied to a periphery of the reflection sheet  19 . 
       FIG. 2  shows the cross-sectional constitution of the liquid crystal display module of the invention taken along a line A-A′ in  FIG. 1 .  FIG. 2  shows a state that the liquid crystal display module shown in  FIG. 1  is stored in a space defined by an upper frame  21  and a lower frame  22 . Further,  FIG. 3  shows the cross-sectional constitution of the conventional liquid crystal display module taken along a line B-B′ in  FIG. 1 .  FIG. 3  also shows a state that the liquid crystal display module shown in  FIG. 1  is stored in the space defined by the upper frame  21  and the lower frame  22  in the same manner as  FIG. 2 . 
     As shown in  FIG. 2 , in the invention, the other end of the flexible printed circuit board  15  (a portion of the flexible printed circuit board  15  on which the light source  18  is arranged and which is arranged on a bottom surface of the lower frame  22 ) is configured to overlap a portion of the reflection sheet  19  having a length L 3  and, further, an insulation sheet  20  is arranged between the other end of the flexible printed circuit board  15  and the reflection sheet  19 . 
       FIG. 3  is the cross-sectional view taken along the line B-B′ in  FIG. 1  of the liquid crystal display module. As shown in  FIG. 3 , the other end of the flexible printed circuit board  15  is not brought into contact with the reflection sheet  19  directly but is brought into contact with the insulation sheet  20 . By arranging such an insulation sheet  20 , a pushing pressure applied to the reflection sheet  19  from the flexible printed circuit board  15  is alleviated or reduced and hence, it is possible to provide a liquid crystal display module having no display irregularities. 
     The insulation sheet  20  of the invention is explained in detail in conjunction with  FIG. 4 . 
       FIG. 4  is a view showing the technique feature of the invention.  FIG. 4  shows a state that the other end of the flexible printed circuit board  15  and the insulation sheet  20  arranged on the other end of the flexible printed circuit board  15 . 
     The insulation sheet  20  may be formed of a member having a smooth surface such as a polyethylene terephthalate (PET) sheet, for example. To acquire an advantageous effect of the invention, that is, to satisfy a demand for the reduction of thickness of a liquid crystal display module in general, it is confirmed necessary to set a thickness t 1  of the insulation sheet  20  to a value not less than 35 μm and not more than 45 μm to provide a liquid crystal display module having no display irregularities while satisfying the demand for the reduction of thickness. Here, by setting the thickness t 1  to a value not less than 30 μm, it is possible to expect the advantageous effects of the invention to a considerable extent. Further, even when the thickness t 1  is set to a value not less than 20 μm, it is possible to expect the above-mentioned advantageous effect that the display irregularities can be reduced to some extent. However, when the thickness t 1  is set to a value less than 20 μm, that is, the thickness t 1  becomes excessively small, the insulation sheet  20  no more plays a role of alleviating the pressure applied from the flexible printed circuit board  15  and hence, it is necessary to set the thickness t 1  to 20 μm at minimum. Here, the larger the thickness t 1  of the insulation sheet  20 , the pressure applied from the flexible printed circuit board  15  can be alleviated more. However, the increase of the thickness t 1  of the insulation sheet  20  is contrary to a demand for the reduction of thickness of the liquid crystal display module in general and hence, it is desirable to set the thickness t 1  to the value not more than 40 μm. The thickness t 1  of the insulation sheet  20  may be set to a value equal to or less than 60 μm at maximum. 
     Next, the insulation sheet  20  is arranged for alleviating the pressure applied to the reflection sheet  19  from the flexible printed circuit board  15  and hence, it is considered necessary to overlap the insulation sheet  20  to the other end of the flexible printed circuit board  15  (overlapping portion indicated by symbol L 1  in  FIG. 4 ) where the pressure is most remarkably applied. In the invention, although the insulation sheet  20  may be fixed by an adhesive agent or the like, to take a demand for the simple constitution and the role of the insulation sheet  20  to alleviate the pressure applied from the flexible printed circuit bard  15  into consideration, it is more preferable to freely insert the insulation sheet  20  between the flexible printed circuit board  15  and the reflective sheet  19  instead of fixing the insulation sheet  20  using an adhesive agent or the like. Accordingly, it is preferable that the insulation sheet  20  extends to the reflection sheet  19  in a state that the insulation sheet  20  gets over the other end of the flexible printed circuit board  15 . That is, the insulation sheet  20  is preferably arranged on the reflection sheet  19  in a state that the insulation sheet  20  gets over the flexible printed circuit board  15  by at least not less than 10 mm (L 4 ≧10 mm). Here, provided that a length L 2  of the insulation sheet  20  satisfies the relationship of L 2 ≧L 4 /2 with respect to a storing length L 4  of the insulation sheet  20  in the mold frame  16 , there is no possibility that the insulation sheet  20  is removed even when the insulation sheet  20  is freely held.

Technology Category: 3