Patent Publication Number: US-7907231-B2

Title: Liquid crystal display apparatus and method for grounding liquid crystal display apparatus

Description:
The present Application is a Divisional Application of U.S. patent application Ser. No. 11/902,912, filed on Sep. 26, 2007. 
    
    
     RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese patent application No. 2006-262221, filed on Sep. 27, 2006, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a liquid crystal display apparatus and a method for grounding the liquid crystal display apparatus. 
     2. Description of the Related Art 
     Generally, a liquid crystal display apparatus includes a liquid crystal display panel, a backlight unit and a chassis (case). The backlight unit is arranged at a back face of the liquid crystal display panel. The liquid crystal display apparatus includes a structure in which the liquid crystal display panel integrated with the backlight unit is installed in a metallic frame (i.e. the chassis). 
     The liquid crystal display panel includes a liquid crystal driving circuit substrate, an opposite substrate, a sealing member and a liquid crystal material. The liquid crystal driving circuit substrate and the opposite substrate are oppositely arranged with a gap therebetween which is formed by the sealing member. The liquid crystal material is disposed in the gap to form the liquid crystal display panel. The liquid crystal driving circuit substrate includes a liquid crystal driving circuit on a surface thereof (the inner surface) which contacts the liquid crystal material. 
     Some opposite substrates of the liquid crystal display panels do not include a conductor on surfaces thereof. That is, such opposite substrate is not connected electrically anywhere and consequently, is in an electrically floating state. For example, a liquid crystal display apparatus of a normally black mode type according to IPS (In-Plane Switching) method includes the opposite substrate above mentioned. 
     A polarizing plate including a conductor on a surface thereof thereon is attached to a surface of the opposite substrate in the electrically floating state in order to discharge an electric charge (i.e. static electricity) on the opposite substrate. The opposite substrate is grounded (GND) when the conductor mounted on the surface of the polarizing plate contacts the metallic frame. 
     In such liquid crystal display panel, the polarizing plate at the opposite substrate side is smaller than an external shape of the liquid crystal display panel. Therefore, the conductor for grounding is pressed physically by the metallic frame against the polarizing plate arranged on a surface of the liquid crystal display panel. As a result, a stress is applied to the liquid crystal display panel, and consequently, the stress causes an uneven image on a screen. 
     Methods for grounding from the surface of the polarizing plate at the opposite substrate side according to a related art will be described in  FIG. 3  to  FIG. 7 . Japanese Patent Application Laid-Open No. 2004-355035 (Japanese Patent Application No. 2004-270865) discloses a liquid crystal display apparatus having a structure for grounding the opposite substrate mentioned above.  FIG. 3  is a cross sectional view showing the disclosed liquid crystal display apparatus.  FIG. 4  is a cross sectional view showing a structure of the polarizing plate shown in  FIG. 3 .  FIG. 5  is a fragmentary cross sectional view showing details of the liquid crystal display panel shown in  FIG. 3 . 
     The liquid crystal display apparatus shown in  FIG. 3  includes a liquid crystal material  11 , an upper polarizing plate  13   b , a conductor  16   a , a metallic frame  180 , a lower polarizing plate  15   a , a backlight unit  19  and a printed wiring board  21 . The conductor  16   a  includes, for example, a conductive rubber and forms electrical connection between the upper polarizing plate  13   b  and the metallic frame  180 . 
     As shown in  FIG. 4 , the upper polarizing plate  13   b  includes a three-layered structure having an optical polarizing layer  131 , a conductive layer  132  and an antireflection layer  133 . Both-sided adhesive tapes formed on both sides of the conductor  16   a  bond the upper polarizing plate  13   b  and the conductor  16   a  and bond the metallic frame  180  and the conductor  16   a . The conductive layer  132  is, for example, an ITO (Indium Tin Oxide) film formed with the sputtering method. A film made of SiO2 is formed as the antireflection layer  133  on the surface of the conductive layer  132  for protection thereof. 
     An opposite substrate  12  and an opposite substrate side polarizing plate  13   a  shown in  FIG. 5  correspond to the upper polarizing plate  13   b  shown in  FIG. 3 . A liquid crystal driving circuit substrate  14  and a liquid crystal driving circuit side polarizing plate  15   b  shown in  FIG. 5  correspond to the lower polarizing plate  15   a  shown in  FIG. 3 . The liquid crystal display panel has a structure that the liquid crystal driving circuit substrate  14  and the opposite substrate  12  are oppositely arranged with a predetermined gap and are sealed by a sealing member  17 . The liquid crystal material  11  is disposed in the gap therebetween. The polarizing plate  13   a  at the opposite substrate side is adhered to a front surface (i.e. a display surface side) of the liquid crystal display panel. The polarizing plate  15   a  at the liquid crystal driving circuit side is adhered to a rear surface of the liquid crystal display panel. 
     According to the structure shown in  FIG. 5 , when the metallic frame  180  presses the conductor  16   a  against the polarizing plate  13   a  at the opposite substrate side arranged on the surface of the liquid crystal display panel, an electrical grounding is secured. However, stress is applied to the liquid crystal display panel, and consequently, an uneven image on a screen due to the stress is generated. If the stress is made so small that the uneven images do not occur, the electric resistance between the polarizing plate  13   a  at the surface of the opposite substrate side and the metallic frame  180  via the conductor  16   a  becomes large. As a result, the electric charge can not be discharged sufficiently. 
       FIG. 6  is a fragmentary cross sectional view showing other liquid crystal display apparatus disclosed in Japanese Patent Application Laid-Open No. 2004-355035. According to the disclosed structure, the metallic frame  180  and the polarizing plate  13   a  at the opposite substrate side are connected electrically each other through a conductive tape  20 , instead of the conductor  16   a . In this case, since the conductive tape  20  is adhered to the surface of the polarizing plate  13   a  at the opposite substrate side, the electric charge can be discharged to the metallic frame  180  without the stress originated with the metallic frame  180  which is applied to the surface of the liquid crystal display panel. However, according to the structure, when the liquid crystal display panel and the backlight unit  19  are installed in the metallic frame  180 , it becomes necessary to perform a step for adhering the conductive tape  20  which is an extra process. As a result, production cost of the liquid crystal display apparatus increases due to the additive step in the assembly process of the apparatus. 
       FIG. 7  is a fragmentary cross sectional view showing further other liquid crystal display apparatus disclosed in Japanese Patent Application Laid-Open No. 2004-355035. According to the apparatus, a conductive tape  20   a  is used. Here, the conductive tape  20   a  is adhered to a metal part  22  of the backlight unit  19  instead of the metallic frame  180 . Accordingly, the apparatus includes the same difficulty as the apparatus shown in  FIG. 6 . 
     SUMMARY OF THE INVENTION 
     The present invention has been proposed in view of the above mentioned circumstances. The object of the present invention is to provide a liquid crystal display apparatus in which a stress is not applied to a liquid crystal display panel and an uneven image does not occur, even if a strong contact is made on a surface of a polarizing plate for connection to the ground, and to provide a method for grounding the liquid crystal display apparatus. 
     The present invention provides a liquid crystal display apparatus, including: a liquid crystal display panel; a polarizing plate which is processed to be conductive and is attached to a surface of the liquid crystal display panel; and a conductive frame, wherein the polarizing plate includes a projecting area which projects outward from the edge of the liquid crystal display panel, and wherein the conductive frame presses the projecting area of the polarizing plate in order to ground the polarizing plate. 
     Further, the present invention provides a method for grounding a liquid crystal display apparatus including a liquid crystal display panel, a polarizing plate which is processed to be conductive, and a conductive frame, the method including: attaching the polarizing plate to a surface of the liquid crystal display panel so that the polarizing plate includes a projecting area which projects outward from the edge of the liquid crystal display panel; and grounding the polarizing plate through the conductive frame which presses a surface of the projecting area of the polarizing plate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary features and advantages of the present invention will become apparent from the following detailed description when taken with the accompanying drawings in which: 
         FIG. 1  is a fragmentary cross sectional view showing a first exemplary embodiment of the present invention. 
         FIG. 2  is a fragmentary cross sectional view showing a second exemplary embodiment of the present invention. 
         FIG. 3  is a cross sectional view showing a related art of a liquid crystal display apparatus. 
         FIG. 4  is a cross sectional view showing a structure of the polarizing plate shown in  FIG. 3 . 
         FIG. 5  is a fragmentary cross sectional view showing details of the liquid crystal display panel shown in  FIG. 3 . 
         FIG. 6  is a fragmentary cross sectional view showing other related art of the liquid crystal display apparatus. 
         FIG. 7  is a fragmentary cross sectional view showing further other related art of the liquid crystal display apparatus. 
     
    
    
     DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     Exemplary embodiments of the present invention will now be described in detail in accordance with the accompanying drawings. 
     First Exemplary Embodiment 
       FIG. 1  is a cross sectional view of a part of a liquid crystal display apparatus according to a first exemplary embodiment of the present invention. As shown in  FIG. 1 , the liquid crystal display apparatus according to the embodiment includes a liquid crystal material  11 , an opposite substrate  12 , a polarizing plate  13  at an opposite substrate side, a liquid crystal driving circuit substrate  14 , a polarizing plate  15  at a liquid crystal driving circuit side, a conductor  16 , a sealing member  17 , a metallic frame  18  and a backlight unit  19 . 
     The liquid crystal driving circuit substrate  14  and the opposite substrate  12  are oppositely disposed each other by the sealing member  17  so that a gap is formed therebetween. The liquid crystal material  11  is put into the gap to form the liquid crystal display panel. A liquid crystal driving circuit is mounted on an inner surface of the liquid crystal driving circuit substrate  14 , which contacts the liquid crystal material  11 . The opposite substrate  12  does not include a conductive layer over a surface thereof and then is electrically floated. Since the opposite substrate  12  tends to be influenced by an electric charge (i.e. static electricity), the polarizing plate  13  at the opposite substrate side whose surface includes a conductive layer is attached or adhered to an outer surface of the opposite substrate  12 . 
     In the exemplary embodiment, the polarizing plate  13  at the opposite substrate side is larger than an external shape of the liquid crystal display panel (that is, the size of the external shape of the opposite substrate  12  and the liquid crystal driving circuit substrate  14 ). That is, when the polarizing plate  13  at the opposite substrate side is attached or adhered to a surface of the opposite substrate  12 , a part of the polarizing plate  13  projects outward from the edge of the liquid crystal display panel (i.e., a projecting area). Moreover, the surface of the projecting area of the polarizing plate  13 , which is processed to be conductive, is electrically connected to the metallic frame  18  via the conductor  16 . As a result, the opposite substrate  12  is grounded (GND) via the metallic frame  18  and an electric charge thereon are discharged. Further, the polarizing plate  15  at the liquid crystal driving circuit side is attached to an outer surface of the liquid crystal driving circuit substrate  14 . 
     The exemplary embodiment includes following features compared with the related art shown in  FIG. 3  to  FIG. 7 . 
     (1) the polarizing plate  13  at the opposite substrate side includes a part or area which projects outward from the edge of the external shape of the liquid crystal display panel. 
     (2) the electric connection to the ground is secured through the projecting area or part of the polarizing plate  13  which is pressed physically via the conductor  16  by the metallic frame  18 . 
     There are many methods to connect electrically to the surface of the polarizing plate  13  at the opposite substrate side for grounding. However, when the conductor  16  is pressed to the polarizing plate  13 , the stress due to the press is applied to the opposite substrate  12  which is one of elements of the display panel. Consequently, uneven image is generated on a screen. In particular, in the liquid crystal display apparatus of a normally black mode type according to IPS (In-Plane Switching) method, a white spot as unevenness occurs on a black screen. The unevenness on a screen may be generated by a small stress. If the stress to the polarizing plate  13  at the opposite substrate side is reduced in order to avoid generation of the unevenness on a screen, the electric connection to the ground becomes insufficient. 
     According to the exemplary embodiment, a part of the polarizing plate  13  at the opposite substrate side projects outward from the edge of the liquid crystal display panel. Moreover, the conductor  16  for grounding presses the projecting area of the polarizing plate  13  which is located on an upper part of the backlight unit  19 . Accordingly, although the stress is applied to the projecting area of the polarizing plate  13  at the opposite substrate side, the stress is not applied to the screen (i.e. the opposite substrate  12 ) of the liquid crystal display panel. Accordingly, it is possible to display an excellent image without the unevenness, since the liquid crystal display panel is free from stress and the electric connection for grounding can be secured sufficiently. 
     Next, a method for manufacturing the liquid crystal display apparatus shown in  FIG. 1  will be described. First, the liquid crystal driving circuit substrate  14  and the opposite substrate  12  are oppositely disposed, via the sealing member  17 , with a predetermined gap therebetween. The gap is filled with the liquid crystal material  11  and is sealed by the sealing member  17  to form the liquid crystal display panel. Next, the polarizing plate  13  is attached to an outer surface of the opposite substrate  12  in the display panel. Also, the polarizing plate  15  is attached to an outer surface of the liquid crystal driving circuit substrate  14 . An outer surface of the polarizing plate  13 , which does not contact the opposite substrate  12 , is processed to be conductive so that an electric charge on the display panel can be discharged. The process for forming conductivity may include a method of vapor deposition of conductor, such as transparent metal, on the polarizing plate  13 , and a method of applying transparent resin including metallic fillers to the polarizing plate  13 . 
     When the liquid crystal display apparatus is assembled, the conductor  16  is mounted on the metallic frame  18  so that the conductor  16  can connect the conductive projecting area of the polarizing plate  13 . The polarizing plate  13  and the metallic frame  18  are electrically connected and fixed each other via the conductor  16 , for example, with a double-faced adhesive tape, an adhesive or the like, each of which is electrically conductive. As a result, electric connection between the polarizing plate  13  and the metallic frame  18  which is connected to the ground (GND) can be secured. The metallic frame  18  can be made of metal such as stainless steel. The conductor  16  can be metallic spring, electrically conductive rubber or the like. Further, the metallic frame  18  may be made of material other than metal. That is, a conductive frame whose conductivity can secure the electric connection to the ground may be employed as the substitution of the metallic frame  18 . 
     Second Exemplary Embodiment 
     Next, a second exemplary embodiment of the present invention will be described with reference to drawings.  FIG. 2  is a cross sectional view of a part of a liquid crystal display apparatus according to the second exemplary embodiment of the present invention. The conductor  16  shown in  FIG. 1  is not used in  FIG. 2 . In  FIG. 2 , a metallic frame  18   a  includes an elastic contact part  18   b  which is formed to be convex toward the projecting area of the polarizing plate  13  through processing the metallic frame  18   a . The contact part  18   b  touches and presses the projecting area of the polarizing plate  13  to make electric contact therewith. The contact part  18   b  of the metallic frame  18   a  can be processed with various methods such as bending work and press work. 
     Electric connection between the metallic frame  18   a  and the polarizing plate  13  can be formed by strong contact between the contact part  18   b  and the projecting area of the polarizing plate  13 . Moreover, uneven image on a screen due to stress applied to the liquid crystal display panel is not generated, because the stress is not applied to the panel. Further, the metallic frame  18   a  according to the exemplary embodiment may be made of a conductive frame other than metal. A number of components and cost thereof can be reduced in the second embodiment, compared with the first embodiment, since it is unnecessary to use the conductor  16  mounted on the metallic frame  18   a.    
     As described above, according to the exemplary embodiments of the present invention, the part of the polarizing plate which is adhered to the surface of the liquid crystal display panel projects outward from the external shape of the display panel. The projecting area of the polarizing plate  13  is pressed from the conductive frame to make electric contact for grounding. Therefore, uneven image on a screen is not generated, since no stress is applied to the liquid crystal display panel even though the conductive frame strongly presses the polarizing plate to make electric contact for grounding. 
     The previous description of embodiments is provided to enable a person skilled in the art to make and use the present invention. Moreover, various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles and specific examples defined herein may be applied to other embodiments without the use of inventive faculty. Therefore, the present invention is not intended to be limited to the embodiments described herein but is to be accorded the widest scope as defined by the limitations of the claims and equivalents. 
     Further, it is noted that the inventor&#39;s intent is to retain all equivalents of the claimed invention even if the claims are amended during prosecution.