Patent Publication Number: US-2011051070-A1

Title: Liquid crystal display device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese application JP 2009-193938 filed on Aug. 25, 2009, the content of which is hereby incorporated by reference into this application. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device which can improve mechanical strength of the liquid crystal display device where a first substrate (for example, a substrate on which color filters are formed) and a second substrate (for example, a substrate on which thin film transistors are formed) are arranged to face each other in an opposed manner and a liquid crystal layer is arranged between both substrates, and can ensure the stable electrical connection between lines formed on the substrate on which the thin film transistors are formed and the substrate on which the color filters are formed. 
     The liquid crystal display device has been popularly used in various kinds of equipments such as a mobile phone or personal digital assistant. Recently, to realize the reduction of thickness, the reduction of weight and bending (imparting of flexibility) of a display screen of a liquid crystal display device, a thin glass substrate or a resin substrate is used as a substrate material for forming the liquid crystal display device. 
     Further, as shown in JP-A-9-105918 (patent document 1) or the like, a lateral-electric-field liquid crystal display device is configured such that pixel electrodes and common electrodes are formed on a substrate side on which thin film transistors are formed, and an electric field is generated parallel to the substrate. In such a lateral electric field drive method, electrodes for driving liquid crystal molecules are not formed on a substrate on which color filters are formed. Accordingly, when a high potential such as static electricity is applied from the outside of a surface of a liquid crystal display panel, there arises a drawback that an abnormal display occurs. Accordingly, as disclosed in JP-A-9-105918, it is necessary to provide a conductive film to a surface of the substrate on which the color filters are formed opposite to a surface of the substrate which faces a substrate on which thin film transistors are formed in an opposed manner. 
       FIG. 9A  and  FIG. 9B  show one example of a liquid crystal display panel used in a conventional liquid crystal display device where a glass substrate (substrate SUB 1 ) on which color filters are formed and a glass substrate (substrate SUB 2 ) on which thin film transistors (hereinafter referred to as “TFTs”) are formed are arranged to face each other in an opposed manner, and a liquid crystal layer is formed between both substrates. Further, polarizers PO 1 , PO 2  are arranged on outer surfaces of both substrates. 
       FIG. 9A  is constituted of a plan view and a cross-sectional view of the liquid crystal display panel, and  FIG. 9B  is an enlarged view of a region surrounded by a dotted line “a”. As shown in the plan view of  FIG. 9A , an area (lateral length: B, longitudinal length: D) of the polarizer PO 1  is set smaller than an area (lateral length: A, longitudinal length: C) of the substrate SUB 1  (A&gt;B or C&gt;D). This area setting is made to enable the electrical grounding on a substrate SUB 1  side. That is, as shown in  FIG. 10A  and  FIG. 10B , by exposing a portion of the substrate SUB 1  from the polarizer PO 1 , it is possible to ensure a region where the electrical connection is established using a conductive paste BP. 
       FIG. 10A  and  FIG. 10B  show a mode in which flexible printed circuit board lines FPC (hereinafter referred to as “FPC lines”) are connected to the liquid crystal display panel shown in  FIG. 9 , wherein  FIG. 10A  is a perspective view and  FIG. 10B  is a cross-sectional view of an electrically connected portion. Lines CL for connection with the FPC lines are formed on the substrate SUB 2 . On a surface of the substrate SUB 1  on a side opposite to a surface of the substrate SUB 1  which faces the substrate SUB 2  in an opposed manner, a transparent conductive film CON made of ITO or the like is formed so as to impart conductivity to the surface. Further, the transparent conductive film CON and a grounding line out of the lines CL are electrically connected with each other using a conductive paste BP such as a silver paste. Symbol SE indicates a sealing member which is provided for sealing liquid crystal LC between both substrates. 
     SUMMARY OF THE INVENTION 
     In the conventional liquid crystal display device, although a thickness of the glass substrate is approximately 0.2 mm to 0.5 mm, there may be a case where the thickness of the glass substrate is decreased to 0.05 mm or less for realizing the reduction of thickness, the reduction of weight, bending of a display screen of the liquid crystal display device or the like. In such a case, at the time of forming a transparent conductive film on the substrate SUB 1  using an ITO vacuum sputtering method or a coating method of a conductive coating material or the like, there arises a drawback that the substrate SUB 1  is easily broken. 
     Further, by applying conductivity to the polarizer PO 1  instead of forming a transparent conductive film on the substrate SUB 1 , the liquid crystal display device is expected to take the similar countermeasure against static electricity. However, the polarization characteristic of the polarizer (polyvinyl alcoholic material) is generated by stretching the polarizer in a manufacturing step thereof and hence, the shrinkage of the polarizer is liable to occur with time. Accordingly, even when electrical grounding is applied to the polarizer using the conductive paste or the like, there arises a drawback that the defective connection between the conductive paste and the conductivity applied surface is liable to occur due to the shrinkage of the polarizer. 
     The present invention has been made to overcome the above-mentioned drawbacks, and it is an object of the present invention to provide a liquid crystal display device which can improve mechanical strength of the liquid crystal display device and, at the same time, can ensure the electrical connection between lines formed on a second substrate (a substrate on which thin film transistors are formed, for example) and a first substrate (a substrate on which color filters are formed, for example). 
     The display device according to the present invention has following technical features to overcome the above-mentioned drawbacks. 
     (1) The present invention is directed to a liquid crystal display device including: a first substrate and a second substrate which are arranged to face each other in an opposed manner; and a liquid crystal layer which is arranged between the first substrate and the second substrate, wherein the first substrate includes a resin substrate having conductivity and a polarizer, the polarizer is arranged on a surface of the resin substrate on a side opposite to a surface of the resin substrate which faces the second substrate in an opposed manner, a main surface of the resin substrate includes an exposure portion which exposes a portion of the main surface of the resin substrate from a main surface of the polarizer, a plurality of lines are formed on the second substrate, and the first substrate is electrically connected with at least one of the plurality of lines via the exposure portion. 
     (2) In the liquid crystal display device having the above-mentioned constitution (1), an area of the main surface of the polarizer is set smaller than an area of the main surface of the resin substrate. 
     (3) In the liquid crystal display device having the above-mentioned constitution (1), the resin substrate has a notched portion, and the exposure portion is formed on the notched portion. 
     (4) In the liquid crystal display device having the above-mentioned constitution (1), the resin substrate has a projecting portion which is formed in a projecting manner from the main surface of the polarizer, and the exposure portion is formed on the projecting portion. 
     (5) In the liquid crystal display device having any one of the above-mentioned constitutions (1) to (4), a conductive film is formed on a surface of the resin substrate on a side opposite to a surface of the resin substrate which faces the second substrate in an opposed manner. 
     (6) In the liquid crystal display device having any one of the above-mentioned constitutions (1) to (5), color filters are formed on the first substrate, and thin film transistors are formed on the second substrate. 
     (7) In the liquid crystal display device having any one of the above-mentioned constitutions (1) to (5), color filters and thin film transistors are formed on the second substrate. 
     (8) In the liquid crystal display device having any one of the above-mentioned constitutions (1) to (6), the first substrate includes a first glass substrate on which color filters are formed, and the resin substrate is arranged on a surface of the first glass substrate on a side opposite to a surface of the first glass substrate which faces the second substrate. 
     (9) In the liquid crystal display device having the above-mentioned constitution (8), a thickness of the first glass substrate is 0.05 mm or less. 
     (10) In the liquid crystal display device having any one of the above-mentioned constitutions (1) to (6), color filters are formed on the resin substrate. 
     (11) In the liquid crystal display device having any one of the above-mentioned constitutions (1) to (10), the second substrate includes a second glass substrate and a second resin substrate, thin film transistors are formed on the second glass substrate, and the second resin substrate is arranged on a surface of the second glass substrate on a side opposite to a surface of the second glass substrate which faces the first substrate. 
     (12) In the liquid crystal display device having the above-mentioned constitution (11), a thickness of the second glass substrate is 0.05 mm or less. 
     (13) In the liquid crystal display device having any one of the above-mentioned constitutions (1) to (10), a thickness of the second glass substrate is 0.05 mm or less. 
     (14) In the liquid crystal display device having any one of the above-mentioned constitutions (1) to (13), the liquid crystal display device includes a plurality of pixels, pixel electrodes which are formed for the plurality of respective pixels, and common electrodes which generate an electric field between the pixel electrodes and the common electrodes, and the pixel electrodes and the common electrodes are formed on the second substrate. 
     According to the present invention, the substrate on which color filters are formed is formed using the resin substrate and hence, it is possible to enhance the mechanical strength of the liquid crystal display device. Further, by imparting the conductivity to the resin substrate and by establishing the electrical connection at the portion of the resin substrate which is exposed from the polarizer, it is possible to ensure the stable electrical connection between the lines formed on the second substrate (for example, the substrate on which the thin film transistors are formed) and the first substrate (for example, the substrate on which the color filters are formed). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  and  FIG. 1B  are views for explaining a first embodiment of a liquid crystal display panel used in the liquid crystal display device of the present invention; 
         FIG. 2A  and  FIG. 2B  are views for explaining a mode of connection between the liquid crystal display panel shown in  FIG. 1  and FPC lines; 
         FIG. 3A  and  FIG. 3B  are views for explaining a second embodiment of a liquid crystal display panel used in the liquid crystal display device of the present invention; 
         FIG. 4A  and  FIG. 4B  are views for explaining a third embodiment of a liquid crystal display panel used in the liquid crystal display device of the present invention; 
         FIG. 5A  and  FIG. 5B  are views for explaining a fourth embodiment of a liquid crystal display panel used in the liquid crystal display device of the present invention; 
         FIG. 6A  and  FIG. 6B  are views for explaining a mode of connection between the liquid crystal display panel shown in  FIG. 5  and FPC lines; 
         FIG. 7A  and  FIG. 7B  are views for explaining a fifth embodiment of a liquid crystal display panel used in the liquid crystal display device of the present invention; 
         FIG. 8A  and  FIG. 8B  are views for explaining a mode of connection between the liquid crystal display panel shown in  FIG. 7  and FPC lines; 
         FIG. 9A  and  FIG. 9B  are views for explaining a liquid crystal display panel used in a conventional liquid crystal display device; and 
         FIG. 10A  and  FIG. 10B  are views for explaining a mode of connection between the conventional liquid crystal display panel shown in  FIG. 9  and FPC lines. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A liquid crystal display device according to the present invention is explained in detail hereinafter.  FIG. 1A  and  FIG. 1B  are views showing a first embodiment of a liquid crystal display panel used in a liquid crystal display device of the present invention. Further,  FIG. 2A  and  FIG. 2B  show a mode in which the liquid crystal display panel shown in  FIG. 1  and flexible printed circuit board lines (FPC lines) are connected to each other. 
     The liquid crystal display device of the present invention is characterized in that, in the liquid crystal display device where a substrate on which thin film transistors are formed and a substrate on which color filters are formed are arranged to face each other in an opposed manner, and a liquid crystal layer is arranged between both substrates, a resin substrate RE 1  to which conductivity is imparted is formed on a substrate side on which the color filters are formed, a polarizer Pal is formed on an outer surface (surface opposite to a liquid crystal layer) of the resin substrate, an area of the polarizer PO 1  is set smaller than an area of the outer surface of the resin substrate, and the electrical connection is made by making use of a portion of the outer surface of the resin substrate exposed from the polarizer. 
     In the first embodiment, with respect to the glass substrate (substrate SUB 1 ) on which the color filters are formed, the color filters are formed on a liquid-crystal-layer side (a surface side which faces the substrate SUB 2  in an opposed manner) of the glass substrate (substrate SUB 1 ), and the resin substrate RE 1  is adhered to a side opposite to the liquid crystal layer (a surface opposite to the surface which faces the substrate SUB 2  in an opposed manner) of the glass substrate (SUB 1 ). Further, the polarizer PO 1  is adhered to an outer surface of the resin substrate RE 1 . The substrate SUB 1  is a thin plate having a thickness of 0.05 mm or less, and the resin substrate RE 1  is provided for reinforcing the substrate SUB 1 . A thickness of the resin substrate RE 1  is approximately 0.1 mm. 
     The resin substrate RE 1  is formed by preferably using a heat resistant resin such as polyethylene naphthalate, a polyimide material or a polycarbonate material. Further, to prevent an abnormal display due to static electricity, conductivity is imparted to the resin substrate RE 1 . As a method for imparting conductivity, there has been known a method which forms a transparent conductive film made of ITO, polyaniline, polythiophene or the like on an outer surface of the resin substrate RE 1 , a method which uses a conductive material in a resin per se which constitutes the substrate, a method which adds a conductive material to the inside of a resin which constitutes the substrate or the like. 
     On the substrate SUB 2 , pixel electrodes and common electrodes which correspond to respective display pixels, thin film transistors which constitute switching elements for driving the electrodes and various lines such as signal lines, scanning lines and power supply lines are arranged. Particularly, in a lateral-electric-field liquid crystal display device, electric members such as the electrodes and the lines are concentrated on the substrate SUB 2  side, and the electric members are not provided to the substrate SUB 1  side at all and hence, the above-mentioned countermeasure to cope with static electricity is indispensable. 
     Also on the substrate SUB 2  side, in the same manner as the substrate SUB 1 , a thickness of the substrate SUB 2  per se is decreased, and a resin substrate RE 2  is provided for reinforcing the substrate SUB 2 . Further, a polarizer PO 2  can be adhered to an outer surface of the resin substrate RE 2 . Although a heat resistant resin may preferably be used as a material of the resin substrate RE 2  in the same manner as the resin substrate RE 1  on the substrate SUB 1  side, as described previously, electrodes, the lines and the like are arranged on the substrate SUB 2  side and hence, it is not particularly necessary to impart conductivity to the resin substrate RE 2 . 
     Liquid crystal LC is sealed between the substrate SUB 2  and the substrate SUB 1  using a sealing member SE as shown in  FIG. 2B . 
     Lines CL for connecting signal lines, scanning lines, electricity supply lines not shown in the drawing which are formed on the substrate SUB 2  with the outside of the liquid crystal display panel are formed on the substrate SUB 2 . Further, the lines CL also include a grounding line for the electrical connection with the substrate SUB 1 . 
     As shown in  FIG. 2A  and  FIG. 2B , FPC lines are connected to the liquid crystal display panel, and more particularly to the lines CL of the substrate SUB 2 . Further, the resin substrate RE 1  and the grounding line out of the lines CL are electrically connected with each other using a conductive paste BP such as a silver paste as shown in  FIG. 2A  and  FIG. 2B . 
     Next, the technical feature of the liquid crystal display device of the present invention is explained. That is, the constitution which makes an area of the polarizer PO 1  smaller than an area of the outer surface of the resin substrate RE 1  for establishing the electrical connection between the resin substrate RE 1  and the lines CL is explained.  FIG. 1A ,  FIG. 1B ,  FIG. 3A ,  FIG. 3B  and  FIG. 4A  and  FIG. 4B  show various embodiments.  FIG. 1A ,  FIG. 3A  and  FIG. 4A  are plan views and cross-sectional views of the liquid crystal display panel, and  FIG. 1B ,  FIG. 3B  and  FIG. 4B  are enlarged views showing a region indicated by a dotted line “a” in  FIG. 1A ,  FIG. 3A  and  FIG. 4A  which are cross-sectional views. 
     In the first embodiment shown in  FIG. 1A  and  FIG. 1B , an area (lateral length: B, longitudinal length: D) of a main surface of the polarizer PO 1  is set smaller than an area (lateral length: A, longitudinal length: C) of a main surface of the resin substrate RE 1  (A&gt;B or C&gt;D). 
     Further, in the second embodiment shown in  FIG. 3A  and  FIG. 3B , a notched portion  1  is formed in a portion of the polarizer PO 1  so as to expose a portion of the resin substrate RE 1 . 
     Further, in the third embodiment shown in  FIG. 4A  and  FIG. 4B , a portion of the resin substrate RE 1  is formed as a projection portion  2  which projects from the polarizer PO 1  in a tab shape so as to expose the portion of the resin substrate RE 1 . 
     In all of first to third embodiments, the glass substrate (substrate SUB 1 ) on which the color filters are formed and the glass substrate (substrate SUB 2 ) on which the thin film transistors are formed are used as an example. However, the above-mentioned constitution may be adopted as a method for exposing a portion of a resin substrate from a polarizer also in the constitution of various substrates described later in the same manner. 
       FIG. 5A ,  FIG. 5B ,  FIG. 6A  and  FIG. 6B  show a liquid crystal display device according to a fourth embodiment of the present invention. In the fourth embodiment, a resin substrate RE 3  is used as a substrate on which color filters are formed. By directly forming the color filters on the resin substrate RE 3 , it is unnecessary to use a glass substrate as a color-filter-side substrate thus realizing a further reduction of weight and the further bending of a display screen. 
     A polarizer PO 1  is formed on an outer surface of the resin substrate RE 3  and, in the same manner as the constitution shown in  FIG. 1 , an area of the polarizer PO 1  is set smaller than an area of the resin substrate RE 3 . As a material for forming the resin substrate RE 3 , a material substantially equal to the material for forming the resin substrate RE 1  of the first embodiment can be used. Further, in the same manner as the resin substrate RE 1  of the first embodiment, conductivity is imparted to the resin substrate RE 3 . 
     As shown in  FIG. 5A  and  FIG. 5B  or  FIG. 6A  and  FIG. 6B , with respect to a substrate side on which thin film transistors are formed, in the same manner as the first to third embodiments, the thin film transistors and the like are formed on a substrate SUB 2 , and a resin substrate RE 2  and a polarizer PO 2  are sequentially arranged on an outer surface of the substrate SUB 2 . As shown in  FIG. 6B , a space is defined between the substrate SUB 2  and the resin substrate RE 3 , and liquid crystal LC is sealed in the space using a sealing member SE. 
       FIG. 6A  and  FIG. 6B  show a mode in which a liquid crystal display panel shown in  FIG. 5  and FPC lines are connected to each other. The resin substrate RE 3  to which conductivity is imparted and a grounding line (included in the lines CL) on the substrate SUB 2  are electrically connected with each other using a conductive paste BP. 
       FIG. 7A ,  FIG. 7B ,  FIG. 8A  and  FIG. 8B  show a liquid crystal display device according to a fifth embodiment of the present invention. In the fifth embodiment, a resin substrate RE 3  is used as a substrate on which color filters are formed, and a resin substrate RE 4  is used as a substrate on which thin film transistors are formed. By directly forming the color filters, thin film transistors and the like on the resin substrate RE 3  or RE 4 , it is unnecessary to use a glass substrate as a substrate which constitutes the liquid crystal display panel thus realizing the further reduction of weight and the further bending of a display screen. 
     The color filters are formed on an inner surface (a surface which faces a liquid crystal layer in an opposed manner) of the resin substrate RE 3 , and thin film transistors and various electrodes and lines are formed on an inner surface of the resin substrate RE 4 . As a method of forming the thin film transistors and various electrodes and lines on the resin substrate RE 4 , for example, a method in which thin film transistors and various electrodes and lines are firstly formed on a glass substrate, and the thin film transistors and various electrodes and lines are transferred to the resin substrate RE 4  is named. Further, in the same manner as the first to fourth embodiments, conductivity is imparted to the resin substrate RE 3  and, as shown in  FIG. 8 , the resin substrate RE 3  is electrically connected with the lines CL formed on the resin substrate RE 4  using a conductive paste BP. 
     On outer surfaces of the respective resin substrates (RE 3 , RE 4 ), polarizers (PO 1 , PO 2 ) are formed. Particularly, an area of the polarizer PO 1  is set smaller than an area of an outer surface of the resin substrate RE 3 . 
     In the above-mentioned first to fifth embodiments, irrelevant to whether the substrate SUB 1 , SUB 2  is formed of the glass substrate or the resin substrate, the constitution where out of the pair of substrates, the thin film transistors and various electrodes and lines are formed on one substrate, and the color filters are formed on the other substrate is described. However, the present invention is also applicable to the constitution where color filters are also formed on one substrate together with the thin film transistors and various electrodes and lines and the resin substrate RE 1  or RE 3  to which conductivity is imparted is formed on the other substrate (so-called color filter-ON-TFT structure). 
     As has been explained heretofore, according to the present invention, it is possible to provide the liquid crystal display device which can improve the mechanical strength of the liquid crystal display device, and to ensure the stable electrical connection between the lines formed on the substrate on which the thin film transistors are formed and the substrate on which the color filters are formed. 
     While there have been described what are at present considered to be certain embodiments of the invention, it will be understood that various modifications may be made thereto, and it is intended that the appended claims cover all such modifications as fall within the true spirit and scope of the invention.