Patent Publication Number: US-2021165266-A1

Title: Liquid crystal display device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese Patent Application JP 2019-218689 filed on Dec. 3, 2019, the content of which is hereby incorporated by reference into this application. 
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates to a liquid crystal display device having narrow picture frame which is suitable to a smart phone or tablet display and so forth. 
     (2) Description of the Related Art 
     In the liquid crystal display device, a TFT substrate, on which the thin film transistors (TFT) and the pixel electrodes are arranged in matrix, and the counter substrate oppose to each other; the liquid crystal layer is sandwiched between the TFT substrate and the counter substrate. A transmittance of light is controlled in each of the pixels, thus, images are formed. Since the liquid crystal display device is flat and light, it is used in various fields. 
     Specifically, in the small or medium sized liquid crystal display devices, a larger screen size is required while keeping the outer size of the display panel constant; consequently, so called picture frame of the screen becomes narrower. On the other hand, since a liquid crystal display panel is not a self-luminescent device, a back light is necessary. Therefore, the back light is also necessary to have narrow peripheral frame. 
     Patent document 1 and patent document 2 disclose the structure of the liquid crystal display device of narrow picture frame in which the liquid crystal display panel and the back light are interconnected with plate shaped component or resin without using the resin mold. 
     On the other hand, the outer surface of the substrate of the liquid crystal display panel is sometimes required to be kept in reference potential. Patent document 3 discloses to connect the terminal of the reference voltage to the conductive film formed on the bottom of liquid crystal display panel by filling the conductive resin in the cut out of the outer frame which surrounds the liquid crystal display panel. 
     Patent document 1: Japanese patent application laid open No. 2019-82523 
     Patent document 2: Japanese patent application laid open No. 2014-126685 
     Patent document 3: Japanese patent application laid open No. 2010-204331 
     SUMMARY OF THE INVENTION 
     When the picture frame of the liquid crystal display device is required to be narrow, the peripheral frame of the back light also must be narrow. In conventional back light, the light source, the light guide, the diffusing sheet, the prism sheet, the reflection sheet and so forth are installed in the resin mold. Then, the resin mold and the liquid crystal display panel are assembled with the black adhesive tape. Considering a mechanical strength of the resin mold, however, it is difficult to make narrow the frame width of the resin mold; consequently, there is a limit to attain a narrow frame back light with the resin mold. 
     On the other hand, in the liquid crystal display device of IPS (In Plane Switching) mode, the inside of the liquid crystal display panel is shielded by covering the surface of the counter substrate with the conductive film, and then a reference potential is applied to the conductive film. Conventionally, the voltage supplying pad formed in the terminal area of the TFT substrate and the conductive film of the surface of the counter substrate are interconnected with the conductive paste. However, according to the picture frame becomes narrower, it has become difficult to provide a space for the voltage suppling pad because enough area cannot be provided in the terminal area. 
     The purpose of the present invention is to realize the structure for supplying reference potential to the surface of the counter substrate without using the reference voltage supplying pad, and thus to realize the liquid crystal display device of narrow picture frame. 
     The present invention solves the above explained problems; the concrete measures are as follows. 
     (1) A liquid crystal display device including: a liquid crystal display panel and a back light, in which 
     the liquid crystal display panel includes a first substrate, on which wirings and pixels are formed, a first polarizing film adhered to the first substrate, a second substrate opposing to the first substrate, and a second polarizing plate adhered to the second substrate, 
     the second substrate and the second polarizing plate are mutually adhered by a conductive adhesive, 
     the back light includes a metal component, 
     the back light and the liquid crystal display panel are fixed by a conductive resin formed on a side surface of the metal component and a side surface of the liquid crystal display panel, and 
     the conductive resin electrically connects with the conductive adhesive. 
     (2) A liquid crystal display device including: a liquid crystal display panel and a back light, in which 
     the liquid crystal display panel includes a first substrate, on which wirings and pixels are formed, a first polarizing film adhered to the first substrate, a second substrate opposing to the first substrate, and a second polarizing plate adhered to the second substrate, 
     a transparent conductive film is formed on a surface of the second substrate to which the second polarizing plate is adhered, 
     the back light includes a metal component, 
     the back light and the liquid crystal display panel are fixed by a conductive resin formed on a side surface of the metal component and a side surface of the liquid crystal display panel, and 
     the conductive resin electrically connects with the transparent conductive film. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view of the liquid crystal display device when the present invention is not used; 
         FIG. 2  is a cross sectional view of  FIG. 1  along the line A-A; 
         FIG. 3  is a cross sectional view of  FIG. 1  along the line B-B; 
         FIG. 4  is a plan view of embodiment 1 of the present invention; 
         FIG. 5  is a schematic diagram of a coating process of the conductive resin; 
         FIG. 6  is a cross sectional view of  FIG. 4  along the line C-C; 
         FIG. 7  is a plan view of embodiment 2 of the present invention; 
         FIG. 8  is a cross sectional view of embodiment 3 of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention is explained in the following embodiments in detail. 
     Embodiment 1 
       FIG. 1  is a plane view of the liquid crystal display device in which the present invention is to be applied. In  FIG. 1 , the TFT substrate  100  and the counter substrate  200  are mutually adhered by the sealing material  160 ; the liquid crystal is sealed in the inner side from the sealing material. The upper polarizing plate  202  is adhered on the upper surface of the counter substrate  200 . The display area  80  is formed where the TFT substrate  100  and the counter substrate  200  overlap. 
     In the display area  80  of  FIG. 1 , the scan signal lines  81  extend in lateral direction (x direction) and are arranged in longitudinal direction (y direction); the video signal lines  82  extend in longitudinal direction and are arranged in lateral direction. The pixel  83  is formed in the area surrounded by the scan signal lines  81  and the video signal lines  82 . 
     The TFT substrate  100  is made larger than the counter substrate  200 ; the terminal area  90  is formed where the TFT substrate  100  does not overlap the counter substrate  200 . The driver IC  70  to drive the liquid crystal display device is installed on the terminal area  90 ; the flexible wiring substrate  60  connects to the terminal area  90  to supply the power and the signals to the liquid crystal display device. The back light  500  is set behind the liquid crystal display panel although it is not depicted in  FIG. 1 . 
     In  FIG. 1 , the cover glass  300  is adhered through the transparent adhesive on the upper polarizing film  202 , which is formed on the liquid crystal display panel. A transparent resin plate may be used instead of the cover glass  300 ; however, it is also referred to as the cover glass  300  in this specification for convenience. In  FIG. 1 , since the cover glass  300  is transparent, the liquid crystal display panel is seen through the cover glass  300 . The cover glass  300  is made larger than the liquid crystal display panel. In  FIG. 1 , in the side of the terminal area  90 , the flexible wiring substrate  60  extends outwardly than the outer edge of the cover glass  300 ; however, the flexible wiring substrate  60  is ultimately bent and set beneath the cover glass  300 . 
       FIG. 2  is a comparative example of the cross sectional view along the line A-A in  FIG. 1 , in which each of the components of the back light  500  are installed in the resin mold  560 . In  FIG. 2 , the cover glass  300  is adhered on the liquid crystal display panel  400  through the transparent adhesive  310 . Herein after, the assembly of the TFT substrate  100 , the lower polarizing plate  102 , the counter substrate  200  and the upper polarizing plate  202  is referred to as the liquid crystal display panel  400 . The back light  500  is set below the liquid crystal display panel  400 ; the liquid crystal display panel  400  is adhered to the back light  500  through the black adhesive tape  570  formed on the upper surface of the resin mold  560 . 
     In  FIG. 2 , the cover glass  300  is thickest, and is e.g. 0.5 to 0.7 mm thickness. By the way,  FIG. 2  is a model for explanation, which is different from the figure of the real product; it is the same for  FIG. 1  and other figures. The cover glass  300  and the liquid crystal display panel  400 , concretely the upper polarizing plate  202  of the liquid crystal display panel  400 , are mutually adhered by the transparent adhesive  310  of the acrylic resin base. 
     In  FIG. 2 , the TFT substrate  100 , in which the scan signal lines, the pixels and so forth are formed, adheres to the counter substrate  200 . The liquid crystal  150  is sandwiched between the TFT substrate  100  and the counter substrate  200 ; the TFT substrate  100  and the counter substrate  200  adhere to each other through the seal material  160 . 
     In  FIG. 2 , the lower polarizing plate  102  is adhered to the lower surface of the TFT substrate  100  through the adhesive  101 ; the upper polarizing plate  202  is adhered to the upper substrate  200  through the conductive adhesive  201 . Each a thickness of the upper polarizing plate  202  and a thickness of the lower polarizing plate  102  is e.g. 100 microns; each a thickness of the adhesive  101  for the polarizing plate and a thickness of the conductive adhesive  201  is e.g. 30 microns. 
     Since the electrode is not formed on the counter substrate  200  in the IPS mode liquid crystal display device, the conductive film is formed on the surface of the counter substrate  200 , opposing side to the cover glass  300 , and apply the reference potential to the conductive film to form a shield in order to prevent invasion of noise from outside. In  FIG. 2 , since the conductive adhesive  201  is formed on all the surface of the counter substrate  200 , it can work as a shield of the liquid crystal display panel  400 . For this purpose, a reference potential must be applied to the conductive adhesive  201 ; thus, conventionally, the structures shown in  FIG. 1  and  FIG. 3  are adopted as will be explained later. 
     The back light  500  is set behind the liquid crystal display panel  400 . The elements of the back light  500  are set in the resin mold  560 . The LEDs are used as a light source, however, the LEDs do not exist at the position of  FIG. 2 ; thus, the LEDs are omitted from the figure. By the way, the LEDs are generally set at the side of the terminal area  90  of  FIG. 1  in the back light  500 . 
     In  FIG. 2 , the reflection sheet  540  is set at the lower surface of the light guide  510 . The reflection sheet  540  reflects the light from the light guide  510  in the direction to the liquid crystal display panel  400 . The light guide  510 , which has a thickness of e.g. 200 microns, is thickest among the back light components. 
     The optical sheet group is set on the light guide  510 . The optical sheet group includes the diffusing sheet  520  and the prism sheet  530 . Although one diffusing sheet  520  and one prism sheet  530  are described in  FIG. 2 , there are several variations for the optical sheet group in the actual devices. For example, instead to the structure of  FIG. 2 , the structure of the optical sheet group can have four sheets of the lower diffusing sheet, lower prism sheet, upper prism sheet and the upper diffusing sheet stacked in this order on the light guide  510 . The optical sheets  520  and  530  can extend on the shoulder of the resin mold  560  and fixed to the resin mold  560  through the adhesive. A thickness of each of the optical sheets  520  and  530  is approximately 50 microns. 
     In  FIG. 2 , the liquid crystal display panel  400  is fixed on the upper surface of the resin mold  560  through e.g. the black adhesive tape  570 . A width wm1 of approximately 300 microns is necessary for the top of the resin mold  560  to securely fix the liquid crystal display panel  400  to the resin mold  560 . Further, a width wm 2  of approximately 600 microns is necessary for the resin mold  560  to securely fix the optical sheets  520  and  530  to the resin mold  560 . The black adhesive tape  570  is used for light shading. A thickness of the black adhesive tape  570  is e.g. 30 microns. 
     In  FIG. 2 , when an edge of the effective area of the back light  500  coincides to the edge of the light guide  510 , the frame width of the back light  500  is wb. The frame width wb is relatively large because the resin mold  560  exists. In  FIG. 2 , a light shielding structure is not formed on the side of the TFT substrate  100  and the counter substrate  200 , which constitutes the liquid crystal display panel  400 ; however, if the light shielding structure is formed on those sides, the frame width wb of the back light  500  becomes yet larger. 
       FIG. 3  is a cross sectional view of  FIG. 1  along the line B-B, which is a cross sectional view of conventional structure to supply the reference potential to the conductive adhesive  201  of the upper polarizing plate  202 , which can work as a shield. The cover glass and back light are omitted in  FIG. 3 . In  FIG. 3 , the TFT substrate  100  and the counter substrate  200  are mutually adhered by the seal material  160 , the liquid crystal  150  is sandwiched between the TFT substrate  100  and the counter substrate  200 . The voltage supplying pad  50  to supply the reference potential is formed on the terminal area where the TFT substrate  100  does not overlap the counter substrate  200 ; the voltage supplying pad  50  is connected to the flexible wiring substrate  60  through the reference voltage supplying wiring  55 . 
     In  FIG. 3 , the reference voltage supplying pad  50  and the conductive adhesive  201  electrically connect through the conductive paste  40 . Since the conductive paste  40  is a fluid of big viscosity before drying, it can flexibly deform its shape and be in close contact with the side surface of the conductive adhesive  201 . A resin dispersed with metal particles is mostly used as the conductive paste  40 ; the most popular one is a silver paste, which uses silver particles. 
     The area of the terminal area  90 , however, is also needed to be smaller according to the picture frame becoming narrower. Accordingly, for example, the driver IC  70  tends to be installed on the flexible wiring substrate  60 , not on the terminal area  90 . In addition, it becomes difficult to provide the space for the voltage supplying pad  50 , the voltage supplying wiring  55  and the coating area for the conductive paste  40  in the terminal area  90 . Consequently, it becomes an important problem how to supply the reference voltage to the conductive adhesive  201  of the upper polarizing plate  202 . 
       FIG. 4  is a plan view of the present invention. In  FIG. 4 , which is a counter structure of  FIG. 1 , the cover glass  300  is disposed on the upper polarizing plate  202  of the liquid crystal display panel  400 ; the back light  500  is set behind the liquid crystal display panel  400 . The structure of the liquid crystal display panel  400  is the same as explained in  FIG. 1 ; cover glass  300  is also the same as explained in  FIG. 2 . 
     Comparing with the structure of  FIG. 1 , the structure of  FIG. 4  has narrower width in the terminal area  90 ; the voltage supplying pad, the conductive paste and so forth are not formed on the terminal area  90 ; the driver IC is not installed on the terminal area  90  but installed on the flexible wiring substrate  60 . The liquid crystal display panel  400  and the back light  500 , which is set behind the liquid crystal display panel  400 , are fixed by coating the conductive resin  10  on the side surfaces of the liquid crystal display panel  400  and the back light  500 . The reference potential is supplied to the counter substrate  200  of the liquid crystal display panel  400  through the conductive resin  10 . In the meantime, when black conductive resin  10  is used, a leak of light from the sides of the liquid crystal display panel  400  and the back light  500  can be prevented. 
     The conductive resin  10  is a so called hot-melt adhesive, which is a thermoplastic resin that liquidizes when it is heated at a temperature of 90 to 100 centigrade. As depicted in  FIG. 5 , the conductive resin  10  is heated in a so called hot gun  600 , which has a heater in it, and is simultaneously coated on the side surfaces of the liquid crystal display panel  400  and the side surface of the back light  500 . Although there are several types of conductive resin  10 , the current embodiment uses the resin that is cured by absorbing moisture in the air. 
     The viscosity of the conductive resin  10  when it is coated is 2000 to 10000 mPa·s (milli Pascal·sec), more favorably, 2000 to 10000 mPa·s at 100 centigrade. Workability decreases when viscosity is too high. When the viscosity is too low, there is a chance the conductive resin  10  intrudes into a space in the back light  500  through a gap between the liquid crystal display panel  400  and the back light  500 . 
       FIG. 6  is a cross sectional view of  FIG. 4  along the line C-c. In  FIG. 6 , the structure of the liquid crystal display panel  400  and the cover glass  300  are the same as explained in  FIG. 2 . The feature of  FIG. 6  is the structure of back light  500  and the means to fix the liquid crystal display panel  400  and the back light  500 . In  FIG. 6 , the light guide  510 , the diffusing sheet  520 , prism sheet  530  and so forth are set in the metal frame  550  made of e.g. stainless steel. Since metal frame  550  provides a good strength and a good walkability, a thickness of the frame can be as less as 0.1 to 0.15 mm. In addition, since the frame  550  is formed as box like, it is easy to secure a mechanical strength. By the way, even the metal frame  550  works as the reflection sheet in  FIG. 6 , an independent reflection sheet can be set under the light guide  510 . 
     In  FIG. 6 , the conductive resin  10  is set on the side surface of the metal frame  550  and the side surface of the liquid crystal display panel  400  to fix the metal frame  550  and the liquid crystal display panel  400 . In the meantime, a predetermined gap g is formed between the lower polarizing plate  102  of the liquid crystal display panel  400  and the optical sheet group, e.g. the prism sheet  530  of the back light  500 , to prevent a generation of so called Newton ring; this gap g is also maintained by the conductive resin  10 . A thickness th of the conductive resin  10  is e.g. 0.15 to 0.3 mm. 
     Since the structure of  FIG. 6  does not use the resin mold, the picture frame width wb of the back light can be made substantially narrower; in other words, it is because, in the structure of  FIG. 6 , a thickness of the conductive resin  10  can be made as thin as approximately 0.2 mm and a thickness of the metal frame  550  can be made as thin as approximately 0.15 mm, in concretely. 
     In  FIG. 6 , the conductive adhesive  201 , which adheres the counter substrate  200  to the upper polarizing film  202  and also works as a shield, electrically connects with the metal frame  550 , which is supplied with reference potential, through the conductive resin  10 . Therefore, the voltage supplying pad  50  and so forth can be eliminated from the terminal area  90 . 
     The conductive resin  10  connects with the side surface of the conductive adhesive  201 , which has a thickness of 30 microns. Since the conductive resin  10  is a fluid of high viscosity when it is coated by the dispenser, it can flexibly contact the side surface of the thin conductive adhesive  201 . In addition, since the conductive resin  10  is coated all around the side surface of the liquid crystal display panel  400 , the conductive resin  10  and the conductive adhesive  201  can be electrically connected securely. 
     In  FIG. 6 , the side surface of the upper polarizing plate  202  and the conductive adhesive  201  and the side surface of the counter substrate  200  are flush with each other; however, even if an edge of the side surface of the upper polarizing plate  202  and the conductive adhesive  201  protrudes from the side surface of the counter substrate  200  or recedes from the side surface of the counter substrate  200 , the conductive resin  10  can cover those recess and protrusion and connect with the conductive adhesive  201  flexibly before it is cured by absorbing moisture in the air. Such function is the same when the conductive adhesive  10  is not moisture set resin, but it is thermoset resin or ultra violet ray set resin and so forth. 
     The conductive resin  10  is that the fine conductive particles are dispersed in the base resin as: EVA based, polyolefin based, synthetic rubber based, adhesive polymer based (polyethylene based or nylon based) or so forth. If the carbon, as graphite, is used as the conductive fine particles, the conductive resin  10  can be made black; therefore, conductive resin  10  can be also used as a light shading material on the side surfaces of the liquid crystal display panel  400  and the back light  500 . 
     In  FIG. 6 , many wirings are formed on the TFT substrate  100 ; those wrings, however, should not reach to the edge of the TFT substrate  100  to prevent those wirings are being short by the conductive resin  10 . In  FIG. 6 , the adhesive  101 , which adheres the TFT substrate  100  to the lower polarizing plate  101 , is not necessary to be conductive; however, when the TFT substrate  100  is necessary to be shielded from some reasons, the conductive adhesive  201  can be used. 
     As described above, according to embodiment 1, the voltage supplying pad  50  or the conductive paste  40  to supply the reference potential to the conductive film for shielding formed on the counter substrate  200  can be eliminated from the terminal area  90 ; thus, the liquid crystal display device of narrow picture frame can be realized. 
     Embodiment 2 
       FIG. 7  is a plan view of embodiment 2 of the present invention.  FIG. 7  differs from  FIG. 4  in that the conductive resin  10  is formed only on the side surfaces of the long sides of the liquid crystal panel  400  and the back light  500 , and the conductive resin  10  is not formed on the side surfaces of the short sides. The cross sectional view of  FIG. 7  along the line D-D is the same as  FIG. 6 . The cross sectional view of  FIG. 7  along the line E-E differs from  FIG. 7  only in that the conductive resin  10  is substituted by the non-conductive resin  20 . 
     In the short sides of the liquid crystal display panel  400 , specifically at the side the terminal area  90  is formed, many terminals are formed at the edge of the TFT substrate  100 ; and the flexible wiring substrate  60  connects to the terminals. Therefore, if the conductive resin  10  exists near the terminals of the TFT substrate  100 , there is a chance that the terminals are shorted. 
     The structure of  FIG. 7  can avoid this problem because the conductive resin  10  is formed only on long sides of the liquid crystal display panel  400  and the back light  500 ; and the non-conductive resin  20  is formed on the short sides. The enough contact area between the conductive adhesive  201  of the upper polarizing plate  202  and the conductive resin  10  can be secured even only at the long sides, thus, the reliability can be maintained. 
     Since the counter substrate  200  does not exist at the side of terminal area of the TFT substrate  100 , the reference potential cannot be supplied from terminal area  90  to the upper side of the counter substrate  200 . Therefore, it is not necessary to form the conductive resin  10  at the side of the terminal area  90 . 
     In  FIG. 7 , the conductive resin  10  is formed only at the long sides; however, the conductive resin  10  can be formed at the short side opposite to the side of the terminal area  90 . In addition, according to a layout of wirings formed on the TFT substrate  100 , the conductive resin  10  can be formed only on one side of the short sides or long sides of the liquid crystal display panel  400  and the back light  500 . 
     Embodiment 3 
       FIG. 8  is a cross sectional view of embodiment 3 of the present invention.  FIG. 8  is different from  FIG. 6  in that the conductive transparent conductive film  205  as e.g. ITO (Indium Tin Oxide) is formed on the surface of the counter substrate  200  to shield the liquid crystal display panel  400 . The transparent conductive film  205  is formed e.g. by sputtering. In this case, the adhesive  101  that adheres the upper polarizing plate  202  to the counter substrate  200  needs not to be conductive. 
     In the structure of  FIG. 8 , the conductive resin  10 , which connects with the metal frame  550 , connects with the transparent conductive film  205  formed on the surface of counter substrate  200 . The transparent conductive film  205  is made thin as 100 nm so that the transmittance is not substantially decreased. In  FIG. 8 , the upper polarizing plate  202  is made slightly smaller than the counter substrate; consequently, the edge of the upper polarizing plate  202  slightly recedes from the edge of the counter substrate  200  by a distance d. 
     Since the conductive resin  10  is a fluid of high viscosity when it is coated, it can flexibly intrude into this slight distance d, and can contact the transparent conductive film  205 ; thus, connection between the transparent conductive film  205  and the metal frame  550  can be attained. 
     Other structure of  FIG. 8  is the same as  FIG. 6 . In the meantime, even  FIG. 8  uses the non-conductive resin  101  for adhesion between the counter substrate  200  and the upper polarizing film  202 , the conductive adhesive  201  can be used as in the structure of  FIG. 6  if necessary. In addition, as shown in  FIG. 7  and so forth, the conductive resin  10  can be formed only at the long sides of the liquid crystal display panel  400  and the back light  500  as explained in embodiment 2. 
     As described above, the present invention can be applied in any cases as e.g. the shielding conductive film on the surface is conductive adhesive  201 , which adheres the upper polarizing plate  202  to the counter substrate  200  or the transparent conductive film  205  of e.g. ITO formed on the surface of the counter substrate  200 .