Patent Publication Number: US-9904100-B2

Title: Method of manufacturing a liquid crystal display device with antistatic polarizing layer

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of U.S. patent application Ser. No. 14/532,708 filed on Nov. 4, 2014, which claims the benefit of Korean Patent Application No. 10-2013- 0134382 filed on Nov. 6, 2013, both of which are hereby incorporated by reference as if fully set forth herein. 
    
    
     BACKGROUND 
     Field of the Disclosure 
     Embodiments of the present invention relate to a liquid crystal display (LCD) device, and more particularly, to a polarizing plate formed on a lower substrate or an upper substrate of an LCD device. 
     Discussion of the Related Art 
     A liquid crystal display (LCD) device is advantageous in that it enables low power consumption and portability. Due to these advantages, the LCD device is widely used in various fields, for example, notebook computer, monitor, spacecraft, aircraft, and etc. 
     The LCD device may include a lower substrate, an upper substrate, and a liquid crystal layer between the lower and upper substrates. As an electric field is applied to the LCD device, liquid crystal molecules of the liquid crystal layer are aligned so that a light transmittance is controlled, and thus an image is displayed on the LCD device. 
     Hereinafter, a related art LCD device will be described with reference to the accompanying drawings. 
       FIG. 1  is a cross sectional view illustrating the related art LCD device. 
     As shown in  FIG. 1 , the related art LCD device may include an upper substrate  10 , a lower substrate  20 , a liquid crystal layer  30 , an antistatic layer (static-electricity prevention layer)  40 , an upper polarizing plate  50 , and a lower polarizing plate  60 . 
     Although not shown, a light shielding layer for prevention of light leakage is provided on one surface of the upper substrate  10 , and more particularly, a lower surface of the upper substrate  10  facing the lower substrate  20 . Also, a color filter layer for a color realization is provided in a region between each light shielding layer. 
     Although not shown, a thin film transistor functioning as a switching device is formed on one surface of the lower substrate  20 , and more particularly, an upper surface of the lower substrate  20  facing the upper substrate  10 . Also, a pixel electrode is formed and connected with the thin film transistor, and a common electrode is arranged in parallel to the pixel electrode, wherein both the pixel and common electrodes are provided to form an electric field. 
     The liquid crystal layer  30  is formed between the upper substrate  10  and the lower substrate  20 , and an alignment direction of the liquid crystal layer  30  is controlled by the electric field formed through the use of pixel and common electrodes. 
     The antistatic layer (static-electricity prevention layer)  40  is formed on an upper surface of the upper substrate  10 . The antistatic layer  40  is provided to prevent static electricity from being generated for a manufacturing process. In more detail, as described above, the light shielding layer and the color filter layer are formed on the lower surface of the upper substrate  10 . For a process of forming these layers such as the light shielding layer and the color filter layer, the static electricity may be generated on the upper substrate  10  due to a contact with a plurality of processing and transferring apparatuses. In order to remove the static electricity, the antistatic layer  40  is formed of a conductive material, for example, Indium Tin Oxide (ITO), on the upper surface of the upper substrate  10 . 
     The upper polarizing plate  50  is formed on an upper surface of the antistatic layer  40 . The upper polarizing plate  50  may include an upper polarizer  51  having a predetermined optical axis, a first upper protection film  53  formed on one surface of the upper polarizer  51 , a second upper protection film  55  formed on the other surface of the upper polarizer  51 , and an upper adhesive  57  formed on a lower surface of the second upper protection film  55  so as to adhere the antistatic layer  40  and the upper polarizing plate  50  to each other. The upper polarizer  51  is manufactured by dyeing PVA (polyvinyl alcohol) with iodine. Since PVA is very weak in moisture, the first and second upper protection films  53  and  55  are respectively attached to both surfaces of the upper polarizer  51 . 
     The lower polarizing plate  60  is formed on a lower surface of the lower substrate  20 . The lower polarizing plate  60  may include a lower polarizer  61  having a predetermined optical axis, a first lower protection film  63  formed on one surface of the lower polarizer  61 , a second lower protection film  65  formed on the other surface of the lower polarizer  61 , and a lower adhesive  67  formed on an upper surface of the second lower protection film  65  so as to adhere the lower substrate  20  and the lower polarizing plate  60  to each other. In the same manner as the upper polarizer  51 , the lower polarizer  61  is also manufactured by dyeing PVA (polyvinyl alcohol) with iodine. In order to overcome the PVA weakness related with moisture, the first and second lower protection films  63  and  65  are respectively attached to both surfaces of the lower polarizer  61 . 
     However, the related art LCD device may have the following disadvantages. 
     A transmission wavelength for each of the upper polarizer  51  and the lower polarizer  61  may be optimized by complementary-color processes after dyeing PVA with iodine and stretching. However, it is very difficult to control the process of optimizing the transmission wavelength. Also, the upper polarizer  51  and the lower polarizer  61  may shrink due to a restoring force. In addition, a thinness of the LCD device has a limitation due the first and second upper protection films  53  and  55  and the first and second lower protection films  63  and  65 . 
     Also, the antistatic layer  40 , which is formed of ITO, may corrode due to the iodine included in the upper polarizer  51 . 
     SUMMARY 
     Accordingly, embodiments of the present invention are directed to an LCD device and a method of manufacturing the same that substantially obviates one or more problems due to limitations and disadvantages of the related art. 
     An aspect of embodiments of the present invention is directed to provide an LCD device with a polarizing plate which facilitates to control a manufacturing process, to prevent a problem related with shrinkage, to decrease a thickness of the LCD device, and also to overcome a problem related to corrosion of the antistatic layer. 
     Additional advantages and features of embodiments of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of embodiments of the invention. The objectives and other advantages of embodiments of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     To achieve these and other advantages and in accordance with the purpose of embodiments of the invention, as embodied and broadly described herein, there is provided an LCD device that may include first and second substrates, a liquid crystal layer between the first and second substrates, and a first polarizing layer on the first substrate, wherein the first polarizing layer includes a plurality of carbon nanotubes aligned in a first direction. 
     In another aspect of embodiments of the present invention, there is provided a method of manufacturing a liquid crystal display device that may include preparing first and second substrates, forming a first polarizing layer on the first substrate, and bonding the first and second substrates to each other while forming a liquid crystal layer between the first and second substrates, wherein the process of forming the first polarizing layer that may include preparing a carbon nanotube dispersion, coating the carbon nanotube dispersion onto the first substrate, and aligning a plurality of carbon nanotubes in a first direction. 
     In one embodiment, a liquid crystal display device comprises a first substrate, a second substrate, and a liquid crystal layer between the first substrate and the second substrate. A first polarizing layer is on the first substrate. A conductive element is connected to the first polarizing layer and also grounded to an external case for static removal. 
     It is to be understood that both the foregoing general description and the following detailed description of embodiments of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of embodiments of the invention. In the drawings: 
         FIG. 1  is a cross sectional view illustrating a related art LCD device; 
         FIG. 2  is a cross sectional view illustrating an LCD device according to one embodiment of the present invention; 
         FIG. 3  is a plane view illustrating a first polarizing layer according to one embodiment of the present invention; 
         FIGS. 4A and 4B  are cross sectional views illustrating a method for grounding the first polarizing layer according to various embodiments of the present invention; 
         FIG. 5  is a cross sectional view illustrating an LCD device according to another embodiment of the present invention; 
         FIG. 6  is a cross sectional view illustrating an LCD device according to another embodiment of the present invention; 
         FIGS. 7A to 7D  are cross sectional views illustrating a method of manufacturing the LCD device according to one embodiment of the present invention; and 
         FIGS. 8A to 8C  illustrate a method of forming the first polarizing layer according to one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to the exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
     During the description of the embodiments of the present invention, the following details about the terms used should be understood. 
     If a first element is positioned “on or above” a second element, it should be understood that the first and second elements may be brought into direct contact with each other, or a third element may be interposed between the first and second elements. 
     Also, terms such as “the first” or “the second”, do not describe the order of corresponding elements. These terms are simply meant to distinguish between any one element from other elements. 
     Hereinafter, an LCD device according to the embodiments of the present invention will be described with reference to the accompanying drawings. 
       FIG. 2  is a cross sectional view illustrating an LCD device according to one embodiment of the present invention. 
     As shown in  FIG. 2 , the LCD device according to one embodiment of the present invention may include first and second substrates  100  and  200  overlapping or facing each other, a liquid crystal layer  300  formed between the first and second substrates  100  and  200 , a first polarizing layer  400  formed on the first substrate  100 , and a second polarizing layer  500  formed on the second substrate  200 . 
     Although not shown, a backlight is provided under the second substrate  200 . The light emitted from the backlight passes through the second substrate  200 , the liquid crystal layer  300  and the first substrate  100 , to thereby display an image. Accordingly, the first substrate  100  corresponds to an upper substrate on which the image is displayed, and the second substrate  200  corresponds to a lower substrate on which the image is not displayed. 
     On one surface of the first substrate  100 , and more particularly, a lower surface of the first substrate  100  which faces the second substrate  200 , there are a light shielding layer  110  and a color filter layer  120 . 
     The light shielding layer  110  is provided to prevent the light from leaking in other regions except pixel regions, wherein the light shielding layer  110  is formed in a matrix configuration. 
     The color filter layer  120  is provided between each pattern of the matrix configuration for the light shielding layer  110 , wherein the color filter layer  120  includes red (R), green (G) and blue (B) color filters. 
     Although not shown, an overcoating layer for planarization of the substrate may be additionally provided on the color filter layer  120 . 
     On one surface of the second substrate  200 , and more particularly, an upper surface of the second substrate  200  which faces the first substrate  100 , there are a thin film transistor layer  210 , a pixel electrode  220  and a common electrode  230 . 
     In the thin film transistor layer  210 , although not shown, there are gate and data lines crossing each other to define the pixel region, and a thin film transistor functioning as a switching device at a crossing region of the gate and data lines. A detailed structure of each of the gate line, the data line and the thin film transistor may be changed to various shapes generally known to those in the art. 
     The pixel electrode  220  and the common electrode  230  are formed on the thin film transistor layer  210 . The pixel electrode  220  is electrically connected with the thin film transistor in each of the pixel regions. The common electrode  230  is arranged in parallel to the pixel electrode  220 . Accordingly, a horizontal electric field is generated between the pixel electrode  220  and the common electrode  230 , whereby an alignment of the liquid crystal layer  300  is driven by the horizontal electric field, to thereby realize an In-Plane Switching (IPS) LCD device. The pixel electrode  220  and the common electrode  230  may be formed in the same layer, but not necessarily. That is, the pixel electrode  220  and the common electrode  230  may be formed at the different layers. Although not shown, any one of the pixel electrode  220  and the common electrode  230  may be provided with a slit inside and formed on an insulating layer, and the other electrode may be provided in a plate structure and formed under the insulating layer, to thereby realize a Fringe-Field Switching (FFS) LCD device. 
     According to one embodiment of the present invention, both the pixel electrode  220  and the common electrode  230  are formed on the upper surface of the second substrate  200 . As a result, there is a need for removing static electricity from the upper surface of the first substrate  100 . 
     The first polarizing layer  400  is formed on the other surface of the first substrate  100 , and more particularly, an upper surface of the first substrate  100  which does not face towards (i.e. faces away from) the second substrate  200 . 
     The first polarizing layer  400  having the predetermined optical axis is formed of a material layer with conductivity. That is, according to the present invention, the first polarizing layer  400  serves a polarizing function and a static-electricity prevention function. Accordingly, there is no additional need for the antistatic layer of the related art on the upper surface of the first substrate  100 . 
     The first polarizing layer  400  serving the above functions may include carbon nanotubes. 
       FIG. 3  is a plane view illustrating the first polarizing layer  400  according to one embodiment of the present invention. 
     As shown in  FIG. 3 , the first polarizing layer  400  according to one embodiment of the present invention may include the plurality of carbon nanotubes  401  on the upper surface of the first substrate  100 . 
     The carbon nanotube  401  is obtained by round rolling a graphite layer of a plate shape. According to the shape of graphite layer, the carbon nanotube  401  may have properties of a conductor such as metal. Thus, if the plurality of carbon nanotubes  401  are densely concentrated on the first substrate  100 , they may function as an antistatic layer (static-electricity prevention layer). 
     The carbon nanotube  401  generally has better properties than ITO. In detail, electric conductivity of the carbon nanotube  401  is higher than that of ITO, and as a result the carbon nanotube  401  enables a stable electricity flow. While a sheet resistance value of ITO is 1×10 2 (Ω/cm2), a sheet resistance value of carbon nanotube is 10 −4 ˜10 −5 (Ω/cm2), that is, the sheet resistance value of carbon nanotube  401  is lower than the sheet resistance value of ITO. In addition, the carbon nanotube  401  is stronger than steel. Also the carbon nanotube  401  has good elasticity and is more flexible than ITO or inorganic material. Accordingly, as compared with ITO, the carbon nanotube  401  may be more readily applied to a flexible LCD device. 
     The carbon nanotube  401  which is applicable to the present invention may be various kinds of carbon nanotube having high conductivity, for example, SWNT(Single-walled Carbon Nanotube), DWNT(Double-walled Carbon Nanotube), MWNT(Multi-walled Carbon Nanotube), or Rope NT(Rope Carbon Nanotube). 
     Also, the carbon nanotubes  401  have properties of absorbing light components which are incident in its alignment direction. Thus, if the carbon nanotubes  401  are aligned in a constant direction, the carbon nanotubes  401  may function as a polarizer. For example, as shown in  FIG. 3 , if the plurality of carbon nanotubes  401  are aligned in a first direction, and more particularly, a horizontal direction, light components vibrating in the horizontal direction are absorbed in the carbon nanotubes  401 , and light components vibrating in a vertical direction pass through the carbon nanotubes  401 . That is, the carbon nanotubes  401  may function as the polarizer of the LCD device according to the present invention. 
     According to one embodiment of the present invention, the first polarizing layer  400  including the plurality of carbon nanotubes  401  aligned in the direction is applied to the LCD device so that the additional antistatic layer is unnecessary. Compared with the related art, it is simpler and easier to manufacture and maintain the first polarizing layer  400 , and furthermore it is possible to decrease the thickness of the LCD device. As will be seen from the following manufacturing process to be described, unlike the related art, there is no need for to perform a stretching process on the polarizing layer  400  as there is no shrinkage of the first polarizing layer  400 . 
     Referring once again to  FIG. 2 , the second polarizing layer  500  is formed on the other surface of the second substrate  200 , and more particularly, a lower surface of the second substrate  200  which does not face towards the first substrate  100 . 
     The second polarizing layer  500  has an optical axis which is different from the optical axis of the first polarizing layer  400 . Unlike the first polarizing layer  400 , it is unnecessary to provide the second polarizing layer  500  of conductive material layer. Accordingly, the second polarizing layer  500  may be formed of a polarizing plate, above as the related art. That is, the second polarizing layer  500  may include a polarizer having a predetermined optical axis, lower and upper protection films respectively formed on lower and upper surfaces of the polarizer, and an adhesive formed on an upper surface of the upper protection film. In this case, the polarizer may be manufactured by dyeing PVA (polyvinyl alcohol) with iodine. 
     However, it is not limited to the above structure. In a similar way to the first polarizing layer  400 , the second polarizing layer  500  may include a plurality of carbon nanotubes. In this case, the plurality of carbon nanotubes included in the second polarizing layer  500  may be aligned in a direction being perpendicular to that of the carbon nanotubes included in the first polarizing layer  400 . 
     The first polarizing layer  400  which functions as the aforementioned antistatic layer may be grounded as described with reference to  FIGS. 4A and 4B . 
       FIGS. 4A and 4B  are cross sectional views illustrating a method of grounding the first polarizing layer according to various embodiments of the present invention. 
     As shown in  FIG. 4A , after connecting a ground tape  600   a  with the first polarizing layer  400 , the ground tape  600   a  may be grounded to an external case (not shown). 
     As shown in  FIG. 4B , after connecting a silver (Ag) dot  600   b  with the first polarizing layer  400 , the silver (Ag) dot  600   b  may be grounded to an external case (not shown). Both the ground tape  600   a  and silver dot  600   b  are examples of electrically conductive elements that provide a static removal path from the first polarizing layer  400  to ground. 
       FIG. 5  is a cross sectional view illustrating an LCD device according to another embodiment of the present invention. Except for a change in position of a first polarizing layer  400 , the LCD device of  FIG. 5  is identical in structure to the above LCD device of  FIG. 2 . Accordingly, wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts, and a detailed description for the same parts will be omitted. 
     In the LCD device shown in  FIG. 2 , the first polarizing layer  400  is formed on the upper surface of the first substrate  100  which does not face towards the second substrate  200 . 
     However, in case of the LCD device shown in  FIG. 5 , the first polarizing layer  400  is formed on a lower surface of a first substrate  100  facing towards a second substrate  200 . In more detail, the first polarizing layer  400  is formed between the first substrate  100  and a light shielding layer  110 , and between the first substrate  100  and a color filter layer  120 . 
     If the first polarizing layer  400  is formed on the lower surface of the first substrate  100 , as shown in  FIG. 5 , a ground tape (not shown) is attached to the first polarizing layer  400 , and the ground tape is extended outside a sealant (not shown) for bonding both substrates  100  and  200  and is then grounded to an external case (not shown). 
       FIG. 6  is a cross sectional view illustrating an LCD device according to another embodiment of the present invention, which relates to a COT (Color on TFT) structure in which a color filter layer  120  is formed on a thin film transistor layer  210 . 
     In case of the COT structure shown in  FIG. 6 , only first polarizing layer  400  is formed on a first substrate  100 , whereby the first substrate  100  is simplified in its structure and manufacturing process. 
     In a detailed description for the LCD device of  FIG. 6 , the first polarizing layer  400  is formed on an upper surface of the first substrate  100 . In the same manner as the above embodiment, the first polarizing layer  400  may include a plurality of carbon nanotubes aligned in a first direction. Alternatively, the first polarizing layer  400  may be formed on a lower surface of the first substrate  100 . 
     On an upper surface of a second substrate  200  facing towards the first substrate  100 , there are a thin film transistor layer  210 , a color filter layer  120  on the thin film transistor layer  210 , and pixel and common electrodes  220  and  230  on the color filter layer  120 . Also, a second polarizing layer  500  is formed on the lower surface of the first substrate  100 . Then, a liquid crystal layer  300  is formed between the first substrate  100  and the second substrate  200 . 
       FIGS. 7A to 7D  are cross sectional views illustrating a method of manufacturing the LCD device according to one embodiment of the present invention, which relate to the method of manufacturing the LCD device shown in  FIG. 2 . 
     First, as shown in  FIG. 7A , the light shielding layer  110  is formed in the matrix configuration on the lower surface of the first substrate  100 , and the color filter layer  120  is formed between each pattern of the matrix configuration of the light shielding layer  110 . 
     Then, as shown in  FIG. 7B , the first polarizing layer  400  is formed on the upper surface of the first substrate  100 . A method of forming the first polarizing layer  400  will be described in detail with reference to  FIGS. 8A to 8C . 
     As shown in  FIG. 8A , a carbon nanotube dispersion  410  is prepared. The carbon nanotube dispersion  410  may be prepared by filling a container  700  with fluid  402 , supplying the plurality of carbon nanotubes  401  to the container  700  filled with fluid  402 , and dispersing the carbon nanotubes  401 . The carbon nanotubes bond together so that it is necessary to carry out the process of mixing the fluid  402  and uniformly dispersing the plurality of carbon nanotubes inside the fluid  402 . 
     The fluid  402  may use at least one selected from a group including Polyvinyl alcohol (PVA), Gelatin, Dichloroethene (DCE), Dimethylformamide (DMF) and Trade name Triton X- 100of nonionic surfactant, but not limited to these materials. 
     Preferably, the carbon nanotubes  401  are included within a range of 1% by weight to 50% by weight in the entire carbon nanotube dispersion  410 . If the carbon nanotubes  401  are less than 1% by weight, both polarizing and antistatic functions may be deteriorated. Meanwhile, if the carbon nanotubes  401  are more than 50% by weight, the carbon nanotubes  401  may be bonded together, which causes difficulties in alignment process. 
     In order to realize smooth dispersion and alignment of the carbon nanotubes  401 , it is preferable that a length of carbon nanotube  401  be not more than 200 μm, but not limited to this length. Also, in order to enhance a degree of dispersion of the carbon nanotubes  401  degree, it is possible to apply a functional group to the surface of carbon nanotube  401 . 
     The process of dispersing the carbon nanotubes  401  in the fluid  402  may be carried out by ultrasonic treatment or an ultracentrifugation process. 
     After that, as shown in  FIG. 8B , the carbon nanotube dispersion  410  is coated onto the upper surface of the first substrate  100 . After the coating process, the carbon nanotube dispersion  410  is dried to remove the fluid  402 . 
     Then, as shown in  FIG. 8C , an electric field is formed by one pair of electrodes  800   a  and  800   b , whereby the plurality of carbon nanotubes  401  are aligned in the first direction, thereby forming the first polarizing layer  400  including the plurality of carbon nanotubes  401  aligned in the first direction. 
     As shown in  FIG. 7C , the thin film transistor layer  210  is formed on the upper surface of the second substrate  200 , and the pixel and common electrodes  220  and  230  are formed on the thin film transistor layer  210 . 
     Also, the second polarizing layer  500  is formed on the lower surface of the second substrate  200 . According to the above method described with reference to  FIGS. 8A to 8C , the second polarizing layer  500  may be formed by aligning the plurality of carbon nanotubes in the second direction, but not necessarily. The second polarizing layer  500  may include the polarizer, the lower and upper protection films respectively formed on the lower and upper surfaces of the polarizer, and the adhesive formed on the upper surface of the upper protection film. The second polarizing layer  500  may be attached to the lower surface of the second substrate  200 . In this case, the second polarizing layer  500  may be attached after bonding the first and second substrates  100  and  200  to each other. 
     As shown in  FIG. 7D , while the liquid crystal layer  300  is formed between the first substrate  100  and the second substrate  200 , the first and second substrates  100  and  200  are bonded to each other. 
     This process may be carried out by bonding the first and second substrates  100  and  200  to each other through the use of sealant and injecting liquid crystal via an injection hole provided in the sealant. In another way, this process may be carried out by dispensing liquid crystal onto any one of the first and second substrates  100  and  200  and bonding the first and second substrates  100  and  200  to each other through the use of sealant. 
     Although not shown, the method of manufacturing the LCD device shown in  FIGS. 5 and 6  may include the process of forming the first polarizing layer  400  on the lower or upper surface of the first substrate  100  in accordance with the above method described with reference to  FIGS. 8A to 8C , and the process of forming the other elements included in the LCD device may use the various methods generally known to those in the art. 
     According to one embodiment of the present invention, the first polarizing layer  400  including the plurality of carbon nanotubes  401  arranged in the first direction is formed on the first substrate  100  so that the additional antistatic layer is unnecessary. Also, unlike the related art, there is no need for to perform a stretching process on the polarizing layer  400  as there is no shrinkage of the first polarizing layer  400 . In addition, as compared with the related art, it is simple and easy to manufacture and maintain the first polarizing layer  400 , and furthermore it is possible to make the LCD device thinner. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventions. 
     Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.