Patent Abstract:
A liquid crystal display module is disclosed that has an optical sheet supported by a main support. In the module, the optical sheet is secured to a main support through a first securing point close to one corner at one side and secured to the main support through a second securing point close to each corner at the opposing side. In this liquid crystal display module, deformations in the optical sheet caused by applied heat from the light source is reduced or eliminated.

Full Description:
The present invention claims the benefit of Korean Patent Application No. 2003-16458 filed in Korea on Mar. 17, 2003, which is hereby incorporated by reference for all purposes as if fully set forth herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a liquid crystal display module, and more particularly to a liquid crystal display module that has a heat resistant structure. 
     2. Description of the Related Art 
     Generally, a liquid crystal display (LCD) includes a liquid crystal display module, driving circuitry for driving the liquid crystal display module, and a case. 
     The liquid crystal display module consists of a liquid crystal display panel having liquid crystal cells arranged in a matrix between two glass substrates, and a backlight unit for irradiating light onto the liquid crystal display panel. The liquid crystal display module is arranged with optical sheets for directing light vertically from the backlight unit toward the liquid crystal display panel. 
     In such liquid crystal display panel, the backlight unit and the optical sheets must be engaged with each other in an integral shape so as to prevent light loss, and protected from damage caused by an external impact. To this end, there are provided a case for the LCD enclosing the back light unit and the optical sheets including the edge of the liquid crystal display panel. 
     Referring to  FIG. 1 , the conventional liquid crystal display module includes a main support  14 , a backlight unit and a liquid crystal display panel  6  disposed at the inside of the main support  14 , a guide panel  30  arranged on the main support  14  to support the liquid crystal display panel  6  and secure optical sheets  8  of the backlight unit, and a case top  2  for enclosing the edge of the liquid crystal display panel  6  and the side surface of the main support  14 . 
     The liquid crystal display panel  6  is comprised of an upper substrate  3  and a lower substrate  5 . A liquid crystal is injected between the upper substrate  3  and the lower substrate  5 , and the liquid crystal display panel  6  is provided with a spacer (not shown) for constantly keeping a gap between the upper substrate  3  and the lower substrate  5 . The upper substrate  3  of the liquid crystal display panel  6  is provided with a color filter, a common electrode and a black matrix, etc. Signal wiring such as data line and a gate line, etc. (not shown) is formed at the lower substrate  5  of the liquid crystal display panel  6 , and a thin film transistor (TFT) is formed at an intersection between the data line and the gate line. The TFT switches a data signal to be transmitted from the data line into the liquid crystal cell in response to a scanning pulse (i.e., a gate pulse) from the gate line. A pixel electrode is formed at a pixel area between the data line and the gate line. One side of the liquid crystal display panel  6  is provided with data and gate pad areas connected to the data lines and the gate lines, respectively. A data tape carrier package mounted with a data driver integrated circuit (not shown) for applying a data signal to the data lines is attached onto the data pad area. Further, a gate tape carrier package mounted with a gate driver integrated circuit (not shown) for applying a scanning pulse (i.e., a gate pulse) to the gate lines is attached onto the gate pad area. 
     An upper polarizing sheet  4   a  is attached onto the upper substrate  3  of the liquid crystal display panel  6  while a lower polarizing sheet  4   b  is attached onto of the rear side of the lower substrate  5  of the liquid crystal display panel  6 . 
     The main support  14  is the product of a mold, the inner sidewall surface of which is molded into a stepped coverage face. The inner bottom layer of the main support  14  is mounted with a backlight unit including a reflective sheet  12 , a light guide plate  10 , a plurality of optical sheets  8  and a lamp housing (not shown). The upper surface of the main support  14  is provided with a protrusion protruded perpendicularly. 
     The backlight unit includes a lamp  22 , a lamp housing (not shown) for enclosing the lamp, a light guide plate  10  for progressing a light inputted from the lamp  22  into the liquid crystal display panel  6 , a reflective sheet  12  arranged at the rear side of the light guide plate  10 , and a plurality of optical sheets  8  disposed on the light guide plate  10 . 
     Light generated from the lamp  22  is incident, via an incidence face of the light guide plate  10 , into the light guide plate  10 . The lamp housing reflects light from the lamp  22  into an incidence face of the light guide plate  10 . 
     The reflective sheet  12  reflects light incident thereto through the rear side of the light guide plate  10  into the light guide plate  10 , thereby reducing light loss. In other words, if light from the lamp  22  is incident to the light guide plate  10 , then light having progressed into the lower surface and the side surface of the light guide plate  10  is reflected by the reflective sheet  12  to thereby be redirected toward the front side thereof. 
     The plurality of optical sheets  8  vertically raise light outputted from the light guide plate  10  to thereby improve the light efficiency. To this end, diffusing sheets are provided for diffusing light outputted from the light guide plate  10  into the entire area, and two prism sheets for redirecting the angle of the light diffused by the diffusing sheets vertically with respect to the liquid crystal display panel  6 . Thus, light outputted from the light guide plate  10  is incident, via the diffusing sheets and then the plurality of optical sheets  8 , to the liquid crystal display panel  6 . 
     As shown in  FIG. 2  to  FIG. 4 , the optical sheets  8  are provided with ears  16   a ,  16   b  and  16   c  extending into each side surface thereof, each of which is provided with a hole  18 . Each hole  18  of the ears  16   a ,  16   b  and  16   c  is inserted into the protrusion  20  of the main support  14 . By such an assembly structure of the holes  18  and the protrusions  20 , the optical sheets  8  are secured to the main support  14 . 
     The guide panel  30  supports the liquid crystal display panel  6 , and is fixed on the upper surface of the main support  14  to secure the optical sheets  8 . To this end, the side surface of the guide panel  30  is provided with a securing part for securing the liquid crystal display panel  6 , and the rear surface is provided with a protrusion hole  32  into which the protrusion  20  of the main support  14  is inserted. 
     The case top  2  is prepared into a square band shape having a plane part and a side part, each of which is bent perpendicularly. The case top  2  encloses the edge of the liquid crystal display panel  6  and the guide panel  30  engaged to the main support  14 . 
     In an assembling method of the liquid crystal display module, the reflective sheet  12  and the light guide plate  10  are sequentially disposed on the main support  14 . Then, the optical sheets  8  are inserted into the protrusion  20  of the main support  14 . In other words, the holes  18  defined at the ears  16   a ,  16   b  and  16   c  of the optical sheets  8  are inserted into the protrusion  20  of the main support  14 . 
     Subsequently, the guide panel  30  is engaged with the protrusion  20  of the main support  14  to which the optical sheets are secured. In other words, the protrusion hole  32  defined at the rear surface of the guide panel  30  is inserted into the protrusion  20  of the main support  14 . Thus, the guide panel  30  is inserted into the protrusion  20  of the main support  14  to thereby pressurize and secure the optical sheets  8 . 
     After the optical sheets  8  and the guide panel  30  are assembled to the main support  14 , the liquid crystal display panel  6  is loaded onto the securing part of the guide panel  30 . Then, as shown in  FIG. 1 , the case top  2  is assembled to enclose the edge of the liquid crystal display panel  6  secured to the guide panel  30 , the side surface of the guide panel  30  and the side surface of the main support  14 . 
     In order to secure the optical sheets  8 , a pair of upper and lower ears  16   a  and  16   b  are defined at one side of the optical sheets  8 , and one ear  16   c  is defined at the middle portion of a side opposed to the one side provided with the upper and lower ears  16   a  and  16   b . Each ear  16   a ,  16   b  and  16   c  is provided with a hole  18  for engaging it to the protrusion  20  of the main support  14 . 
     Each hole  18  defined at the ears  16   a ,  16   b  and  16   c  of the optical sheets  8  is inserted into the protrusion  20  of the main support  14  to be secured into the main support  14 . 
     Consequently, the guide panel  30  is secured to the protrusion  20  of the main support  14  into which the optical sheets  8  have been inserted and secured. In other words, the protrusion hole  32  defined at the rear surface of the guide panel  30  is inserted into the protrusion  20  of the main support  14 . Thus, the guide panel  30  is inserted into the protrusion  20  of the main support  14  to thereby pressurize and secure the optical sheets  8 . 
     The optical sheets  8  of the liquid crystal display module are especially susceptible to heat from the lamp (which, although not shown, is disposed in the lower left hand corner of  FIG. 4 ). The optical sheets  8  expand in two directions, a machine direction (MD) axis and a transverse direction (TD) axis, when heat is applied to them. 
     A thermal expansion coefficient in the MD axis of a general optical sheet is 3.8×10 −4  Cm 2 /° C. while a thermal expansion coefficient in the TD axis thereof is 2.7×10 −4  Cm 2 /° C. A ratio of a thermal expansion coefficient in the MD axis to a thermal expansion coefficient in the TD axis of such an optical sheet must be less than two to be relatively stable when heat is applied. Nevertheless, because of the disparity between the thermal expansion coefficients, a wrinkle  17  (i.e. deformation) occurs in the optical sheet to some extent when heat is applied. 
     Moreover, when a high light-convergence optical sheet such as a dual brightness enhancement film (DBEF) sheet is used, the thermal expansion coefficient of the optical sheet is increased due to an expansion process that occurs in the course of the assembling process. A thermal expansion coefficient in the MD axis of the DBEF sheet is 8.1×10 −5  Cm 2 /° C. while a thermal expansion coefficient in the TD axis thereof is 1.5×10 −5  Cm 2 /° C. As mentioned above, a ratio of a thermal expansion coefficient in the MD axis to that in the TD axis of the DBEF sheet is more than five. If heat is applied to such a DBEF film by the lamp, a wrinkle appears at the optical sheet  8 . Particularly, since a middle portion of the optical sheet  8  that has a large difference between the thermal expansion coefficients is secured by means of the hole  16   c  and the protrusion  20 , a sizeable wrinkle appears in the optical sheet  8 . 
     SUMMARY OF THE INVENTION 
     Accordingly, embodiments of the present invention provide a liquid crystal display module that is less susceptible to heat and decreases or eliminates deformation caused by applied heat. 
     In one embodiment of the invention, a liquid crystal display module according to an embodiment of the present invention includes a main support and an optical sheet secured onto the main support. The optical sheet is secured to the main support through a first securing point close to one corner of a first side of the optical sheet and secured to the main support through a second and third securing points close to corners of a second side of the optical sheet opposing the first side of the optical sheet. 
     In the liquid crystal display module, the main support may include a plurality of protrusions, the protrusions disposed at the first, second and third securing points. In this case, the optical sheet may include a plurality of holes into which the protrusions are inserted and further the optical sheet may include a plurality of ears, the ears provided with the holes and protruding toward an outside of the optical sheet. 
     The liquid crystal display including the protrusions may further include a guide panel for securing the optical sheets at the upper portion thereof. In this case, the guide panel may include a hole into which the protrusion is inserted case. 
     The liquid crystal display module may further include a liquid crystal display panel supported by the main support and a light guide plate and a reflective sheet supported by the main support at the lower portion of the optical sheet. 
     The number of the securing points on the first side of the optical sheet may be different from the number of securing points on the second side of the optical sheet. 
     The optical sheet may have a partially different thermal expansion coefficient. 
     The optical sheet may include a dual brightness enhancement film (DBEF). 
     One or more of the securing points may be positioned at a region less than 1/10 of the entire length of the optical sheet. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other advantages of the invention will be apparent from the following detailed description of the embodiments of the present invention with reference to the accompanying drawings, in which: 
         FIG. 1  is a schematic section view showing a structure of a conventional liquid crystal display module; 
         FIG. 2  is a plan view of the optical sheet shown in  FIG. 1 ; 
         FIG. 3  is a section view of the optical sheet taken along the I–I′ line in  FIG. 1 ; 
         FIG. 4  is a perspective view of the optical sheet shown in  FIG. 1 ; 
         FIG. 5  is a schematic section view showing a structure of a liquid crystal display module according to an embodiment of the present invention; 
         FIG. 6  is a plan view of the optical sheet shown in  FIG. 5 ; 
         FIG. 7  is a section view of the optical sheet taken along the I–I′ line in  FIG. 5 ; and 
         FIG. 8  is a perspective view of the optical sheet shown in  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIG. 5  to  FIG. 8 , a liquid crystal display module according to an embodiment of the present invention includes a main support  114 , a backlight unit and a liquid crystal display panel  106  disposed at the inside of the main support  114 , a guide panel  130  arranged on the main support  114  to support the liquid crystal display panel  106  and secure optical sheets  108  of the backlight unit, and a case top  102  for enclosing the edge of the liquid crystal display panel  106  and the side surface of the main support  114 . 
     The liquid crystal display panel  106  is comprised of an upper substrate  103  and a lower substrate  105 . A liquid crystal is injected between the upper substrate  103  and the lower substrate  105 , and the liquid crystal display panel  106  is provided with a spacer (not shown) for constantly keeping a gap between the upper substrate  103  and the lower substrate  105 . The upper substrate  103  of the liquid crystal display panel  106  is provided with a color filter, a common electrode and a black matrix, etc. Signal wiring such as data line and a gate line, etc. (not shown) is formed at the lower substrate  105  of the liquid crystal display panel  106 , and a thin film transistor (TFT) is formed at an intersection between the data line and the gate line. The TFT switches a data signal to be transmitted from the data line into the liquid crystal cell in response to a scanning pulse (i.e., a gate pulse) from the gate line. A pixel electrode is formed at a pixel area between the data line and the gate line. One side of the liquid crystal display panel  106  is provided with data and gate pad areas connected to the data lines and the gate lines, respectively. A data tape carrier package mounted with a data driver integrated circuit (not shown) for applying a data signal to the data lines is attached onto the data pad area. Further, a gate tape carrier package mounted with a gate driver integrated circuit (not shown) for applying a scanning pulse (i.e., a gate pulse) to the gate lines is attached onto the gate pad area. 
     An upper polarizing sheet  104   a  is attached onto the upper substrate  103  of the liquid crystal display panel  106  while a lower polarizing sheet  104   b  is attached onto the rear side of the lower substrate  105  of the liquid crystal display panel  106 . 
     The main support  114  is a product formed from a mold, the inner sidewall surface of which is molded into a stepped coverage face. The inner bottom layer of the main support  114  is mounted with a backlight unit including a light guide plate  110  integral with a reflective sheet  112 , a plurality of optical sheets  108  and a lamp housing (not shown). The upper surface of the main support  114  is provided with a perpendicular protrusion  120 . 
     The backlight unit includes a lamp  122 , a lamp housing (not shown) for enclosing the lamp, a light guide plate  110  for directing light inputted from the lamp into the liquid crystal display panel  106 , a reflective sheet  112  arranged at the rear side of the light guide plate  110 , and a plurality of optical sheets  108  disposed on the light guide plate  110 . 
     Light generated from the lamp  122  is incident, via an incidence face of the light guide plate  110 , into the light guide plate  110 . The lamp housing reflects light from the lamp  122  into an incidence face of the light guide plate  110 . 
     The reflective sheet  112  re-reflects light incident thereto through the rear side of the light guide plate  110  into the light guide plate  110 , thereby reducing light loss. In other words, if light from the lamp  122  is incident to the light guide plate  110 , then light having progressed into the lower surface and the side surface of the light guide plate  110  is reflected by the reflective sheet  112  to thereby be reflected toward the front side thereof. 
     The plurality of optical sheets  108  vertically direct light outputted from the light guide plate  110  to thereby improve the light efficiency. To this end, diffusing sheets are provided for diffusing light outputted from the light guide plate  110  into the entire area, and two prism sheets for vertically directing the angle of the light diffused by the diffusing sheets with respect to the liquid crystal display panel  106 . Thus, light outputted from the light guide plate  110  is incident, via the diffusing sheets and then the plurality of optical sheets  108 , to the liquid crystal display panel  106 . 
     As shown in  FIG. 6  to  FIG. 8 , the optical sheets  8  are provided with ears  116   a ,  116   b  and  116   c  extending into each side surface thereof, each of which is provided with a hole  118 . Each hole  118  of the ears  116   a ,  116   b  and  116   c  is inserted into the protrusion  120  of the main support  114 . By such an assembly structure of the holes  118  and the protrusions  120 , the optical sheets  108  are secured to the main support  114 . 
     The guide panel  130  supports the liquid crystal display panel  106 , and is fixed on the upper surface of the main support  114  to secure the optical sheets  108 . To this end, the side surface of the guide panel  130  is provided with a securing part for securing the liquid crystal display panel  106 , and the rear surface is provided with a protrusion hole  132  into which the protrusion  120  of the main support  114  is inserted. 
     The case top  102  is prepared into a square band shape having a plane part and a side part, each of which is bent perpendicularly. The case top  102  encloses the edge of the liquid crystal display panel  106  and the guide panel  130  engaged to the main support  114 . 
     In an assembling method of the liquid crystal display module, the reflective sheet  112  and the light guide plate  110  are sequentially disposed on the main support  114 . Then, the optical sheets  108  are inserted into the protrusion  120  of the main support  114 . In other words, the holes  118  defined at the ears  116   a ,  116   b  and  116   c  of the optical sheets  108  are inserted into the protrusion  120  of the main support  114 . 
     Subsequently, the guide panel  130  is engaged with the protrusion  120  of the main support  114  to which the optical sheets  108  are secured. In other words, the protrusion hole  132  defined at the rear surface of the guide panel  130  is inserted into the protrusion  120  of the main support  114 . Thus, the guide panel  130  is inserted into the protrusion  120  of the main support  114  to thereby pressurize and secure the optical sheets  108 . 
     After the optical sheets  108  and the guide panel  130  are assembled to the main support  114 , the liquid crystal display panel  106  is loaded onto the securing part of the guide panel  130 . Then, as shown in  FIG. 5 , the case top  102  is assembled to enclose the edge of the liquid crystal display panel  106  secured to the guide panel  130 , the side surface of the guide panel  130  and the side surface of the main support  114 . 
     As above, the optical sheets  108  in the liquid crystal display module expand in two directions: a machine direction (MD) axis and a transverse direction (TD) axis when heat is applied to the optical sheets  108 . 
     A ratio of a thermal expansion coefficient in the MD axis to a thermal expansion coefficient in the TD axis of a general optical sheet is less than two. 
     However, when a high light-convergence optical sheet such as a dual brightness enhancement film (DBEF) sheet is used, a thermal expansion coefficient of the optical sheet is increased due to an expansion process in the course of the assembling process. Thus, a ratio of a thermal expansion coefficient in the MD axis to that in the TD axis of the DBEF sheet is more than five. 
     In the embodiment of the present invention, in order to secure the optical sheets  108 , one side of the optical sheets  108  are provided with a pair of upper and lower ears  116   a  and  116   b , and a side of the optical sheets  108  opposing the side provided with a pair of upper and lower ears  116   a  and  116   b  is provided with an ear  116   a  at the upper portion of a traverse direction (TD) axis. The thermal expansion coefficient in the traverse direction (TD) axis is smaller than in the machine direction (MD) axis. 
     Each ear  116   a ,  116   b  and  116   c  is provided with a hole  118  for engaging with the protrusion  120  of the main support  114 . The hole  120  defined at each ear  116   a ,  116   b  and  116   c  of the optical sheets  108  is positioned at a region less than 1/10 of the entire length of the optical sheet  108  from the end of the optical sheet  108  as indicated in the following equation:
 
 D≦A/ 10  (1)
 
     (wherein D represents a position of the hole and A represents entire length of the optical sheet) 
     The hole  118  defined at each ear  116   a ,  116   b  and  116   c  of the optical sheets  108  is inserted into the protrusion  120  of the main support  114  to thereby secure the optical sheets  108 . 
     Subsequently, the guide panel  130  is secured to the protrusion  120  of the main support  114  into which the optical sheets  108  have been inserted and secured. In other words, a protrusion hole  132  defined at the rear surface of the guide panel  130  is inserted into the protrusion  120  of the main support  114 . Thus, the guide panel  130  is inserted into the protrusion  120  of the main support  114  to thereby pressurize and secure the optical sheets  108 . 
     As described above, a liquid crystal display module according to the present invention defines the ear  116   c  at the upper portion of the TD axis than the MD axis. This reduces or prevents a wrinkle caused by applied heat due to the difference in thermal expansion coefficients between the MD axis and the TD axis of the optical sheet. 
     Although the present invention has been explained by the embodiments shown in the drawings described above, it should be understood to the ordinary skilled person in the art that the invention is not limited to the embodiments, but rather that various changes or modifications thereof are possible without departing from the spirit of the invention. Accordingly, the scope of the invention shall be determined only by the appended claims and their equivalents.

Technology Classification (CPC): 6