Abstract:
An apparatus for manufacturing a light guide in a liquid crystal display and a manufacturing method thereof with a simplified mold structure. In the apparatus, an core material portion is fixed to a light guide molding stamper to constitute a molding device along with the stamper. A fixing member fixes the stamper to the core material portion. The molding device constitutes a mold for molding the light guide, along with a stationary core and a movable core. Accordingly, the stamper and the molding core are integrally formed and sealed, so that a mold structure can be simplified and stable manufacturing of the light guide can be provided.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a technique of fabricating a light guide used for a liquid crystal display, and more particularly to a light guide fabricating apparatus and a manufacturing method thereof having a simplified mold structure. 
     2. Description of the Related Art 
     Generally, a liquid crystal display (LCD) controls light transmissivity of liquid crystal cells arranged in a matrix pattern with the aid of a video signal applied thereto to display a picture corresponding to the video signal. To this end, the LCD includes a liquid crystal display panel having liquid crystal cells arranged in an active matrix which control an amount of light transmitted from the lower portion thereof; a backlight unit for emitting light from the lower portion of the liquid crystal display panel; red, green and blue color filters corresponding to each liquid crystal cell at the lower portion of the liquid crystal display panel; and a black matrix layer for defining pixels. The backlight unit functions to evenly emit white light from the rear side of the liquid crystal display panel, and consists of a light source, a light guide, a reflector and a diffuser, etc. for uniformly transmitting light emitted from the light source into the panel. 
     FIG. 1 shows a sectional structure of a conventional backlight unit provided at the lower portion of a liquid crystal display panel. Referring to FIG. 1, the backlight unit includes a backlight lamp  22  for generating white light, a prism light guide  4  for guiding light passing through a light input  20  from the backlight lamp  22 , a lamp housing  24  for mounting the backlight lamp  22  and reflecting light into the light guide  4 , a reflector  2  for reflecting light from the lower portion of the prism light guide  4  toward the upper portion thereof where the liquid crystal display panel is positioned, first and second diffusing films  6  and  12 , and first and second prism films  8  and  10  for controlling diffusion and transmission direction of the light passing through the prism light guide  4 . The light guide  4  is formed in a prism shape with an inclined lower surface as shown in FIG.  2  and allows light inputted from the backlight lamp  22  to smoothly progress toward the upper portion thereof. Light transmission, via the lower surface of the prism light guide  4 , toward the lower portion thereof is reflected upward by the reflector  2  provided at the lower portion of the light guide  4 . Light passing through the prism light guide  4  is uniformly diffused by means of the first diffusing film  6 . Light passing through the first diffusing film  6  is controlled to make its transmission direction perpendicular to the liquid crystal display panel at the first and second prism films  8  and  10 . Light passing through the first and second prism films  8  and  10  is incident on the liquid crystal display panel by way of the second diffusing film  12  again. 
     For instance, the lower surface of the prism light guide  4  is inclined and provided with minute grooves  26  having a uniform distance as shown in FIG.  2 . Such grooves  26  are referred to as “prism unevenness”, which smooths a diffusion of light as well and reduces light loss on a path where light is transmitted toward the upper portion of the light guide  4 . This increases the amount of light transmitted toward the liquid crystal display panel. Typically, the prism light guide  4  is made from an acryl such as PMMA, etc., and the grooves  26  are formed in an equal distance to have a pitch width of about 0.07 to 0.08 mm by a machine working. 
     The prism light guide  4  having the structure as mentioned above is, for example, fabricated by an injection-molding device  30  as shown in FIG.  3 . Referring to FIG. 3, the conventional light guide injection-molding device  30  consists of a stamper  32  for forming groves  26 , a stationary core  34  to which the stamper  32  is attached, a vacuum tube  36  and a vacuum device (not shown) for attaching the stamper  32  to the stationary core  34  by a vacuum force, a stamper fixing segment  38  provided at the side portion of the stationary core  34  to determine an attached position of the stamper  32 , a movable core  40  defining a mold  46  along with the stationary core  34 , and a stationary molding plate  42  and a movable molding plate  44  for fixing the stationary and movable cores  34  and  40  at the exterior thereof. The stationary core  34  has a thickness of about 20 mm while the stamper  32  has a thickness of about 0.1 to 0.4 mm. In the conventional art, a brass plate (which is easy to work by a grinding process) is preferably used to make the stamper  32 . Recently, a high-hardness nickel has been used because the relatively soft brass plate wears too easily, which affects mass production operation. However, since nickel is very hard, it is difficult to form the grooves  26  at an equal distance by a grinding process. In order to solve this problem, a nickel stamper  32  has been made by using a brass plate provided with the prism unevenness grooving as a master, then electroplating nickel on the surface of the brass plate provided with the prism unevenness grooving to a desired thickness. In manufacturing the stamper  32  according to the electroplating method, the stamper  32  has a thickness of about 0.1 to 0.4 mm because it is difficult to make a large plating thickness. 
     Hereinafter, a conventional method of fabricating the prism light guide  4  is described. First, a position of the stamper  32  to be attached to the stationary core  34  is determined by the stamper fixing segment  38 . The stamper  32  is then attached to the attached portion of the stationary core  34 . The portion of the stamper  32  attached to the stationary core  34  has a plurality of vacuum holes connected the vacuum tube  36 . The stamper  32  is attached to the stationary core  34  by a vacuum force provided by evacuating air through the vacuum tube  36 . Thereafter, a prism light guide material is injected into a space between the stationary core  40  and the stamper  32  and then injection-molded to be made into the prism light guide  4  having the prism unevenness grooves  26 . 
     The conventional injection-molding device has a structure in which the stamper  32  is separate from the core  34  of the mold  46 . The stamper  32  is temporarily attached to the stationary core  34  of the mold  46  by evacuating air through the vacuum holes provided at the attached portion of the stamper  32  to the stationary core  34 . Such a stamper fixing method is mainly used for a product that must be changed frequently. In conventional compact disc injection-molding device (as an example of another application), various kinds of discs must be formed so various kinds of stampers must be changed frequently. Thus, the stamper fixing method employing a vacuum system is used in which attachment and detachment of the appropriate stamper is easy. However, the prism light guide  4  in the LCD is mass produced and therefore does not require frequent attachment and detachment of the stamper until a life of the stamper  32  expires. Therefore, the above-mentioned stamper attaching method using a vacuum system is not available. The conventional injection-molding device  30  has a drawback because it requires an additional device for evacuating air and the attached portion of the stamper  32  to the stationary core  34  must be provided with a plurality of vacuum holes, so device  30  has complex structure and facilities. Also, the conventional injection-molding device  30  unstable attachment due to a deterioration of the vacuum force applied to the stamper  32 , its manufacturing becomes unstable. Furthermore, it is inconvenient because cleaning and fine surface grinding work, etc. on the attached portion of the stationary core  34  to the stamper  32  are required to provide an easy air evacuation and strengthen the vacuum force. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention provides an apparatus for manufacturing a light guide in a liquid crystal display and a manufacturing method thereof wherein a mold structure is simplified. 
     The present invention also provides an apparatus for manufacturing a light guide in a liquid crystal display and a manufacturing method thereof that are adapted to make a stable light guide molding work. 
     Therefore, a light guide fabricating apparatus according to one aspect of the present invention includes a stamper for molding a light guide; a core material portion with a desired thickness fixed to the stamper, to constitute an integral molding core; and a fixing member or structure for fixing the stamper to the core material portion, said integral-type molding device defining a mold for molding the light guide along with the stationary core and the movable core. 
     A method of manufacturing a light guide fabricating apparatus according to another aspect of the present invention includes fixing a light guide molding stamper to a core material portion having a desired thickness to form an integral mold core; and fixing the integral mold core to the stationary core and the movable core to define a mold. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other aspects of the present 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 section view showing a structure of a general backlight unit provided at the lower portion of a liquid crystal display panel; 
     FIG. 2 is a section view showing a detailed structure of the prism light guide in FIG. 1; 
     FIG. 3 is a section view showing a structure of a conventional injection-molding device used for fabricating the prism light guide; 
     FIG. 4 is a section view showing a structure of a light guide fabricating apparatus according to a first embodiment of the present invention; 
     FIG. 5A to FIG. 5E are section views for explaining a method of manufacturing a stamper-integrated mold core according to a first embodiment of the present invention; 
     FIG. 6 is a section view showing a structure of a light guide fabricating an apparatus for molding double-faced prism unevenness grooving having an integral mold structure according to the first embodiment of the present invention; and 
     FIG. 7 is a section view showing a structure of a light guide fabricating apparatus according to a second embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 4, a light guide fabricating apparatus according to a first embodiment of the present invention is shown. In the conventional light guide injection-molding device, a stamper for injection-molding the prism light guide is separate from a core. However, in a light guide injection-molding device according to the first embodiment of the present invention, the stamper is engaged to a core material portion having a desired thickness to be made into an integral mold. In order to form prism unevenness grooves having the same shape at the lower surface of a prism light guide  52 , the injection-molding device  50  includes a stamper  54  provided with prism unevenness grooves at a surface contacting an injected light guide material, a core material portion  58  to which the stamper  54  is attached by virtue of a nickel electroplate structure  56  on the surfaces of the stamper  54  and the core material portion  58 , a movable core  62  for fixing an integral molding device  60  in which the stamper  54  and the core inside material  58  are fixedly joined by nickel electroplating  56 , a stationary core  66  of a mold  64  provided along with the integral molding device  60  and the movable core  62 , and a stationary molding plate  68  and a movable molding plate  70  for fixing the stationary core  66  and the movable core  62 , respectively. The stamper  54  is formed about 0.3 to 0.4 mm thick by electroplating nickel on the surface of a brass plate master provided with prism unevenness grooves. The core material portion  58  to which the stamper  54  is attached uses the same metal (e.g., nickel) as the stamper  54  or a different metal (e.g., Prehardening steel) from the stamper  54 , and has a thickness of about 20 to 30 mm. 
     The prism light guide  52  is manufactured by injecting a substance such as acryl, etc. into a space between the integral molding device  60  fixed with the stamper  54  and the stationary core  66  under pressure. The light guide fabricating apparatus according to the present invention does not require additional complex facilities such as the conventional vacuum device, etc. because the stamper  54  and the core inside material  58  are mutually bonded to each other by virtue of the nickel electroplate  56  on the surface thereof. Accordingly, it is possible to provide a simplified mold structure as well as more stable manufacturing of the prism light guide  52  because the stamper  54  is always kept attached to the inside material portion  58 . 
     In a first embodiment of the present invention, a method of manufacturing the molding device  60  will be described with reference to FIGS. 5A to FIG.  5 E. First, as shown in FIG. 5A, prism unevenness grooves  82  are formed on the surface of a brass plate by a grinding process employing, for example, a bit  80  to prepare a master  84 . By a mechanical machining using the bit  80 , a pitch width P of the prism unevenness grooves  82  are formed at equal distances on the surface of the master  84 , from 0.07 to 0.08 mm. Next, as shown in FIG. 5B, the surface of the master  84  provided with the prism unevenness grooves  82  is electroplated with nickel to form a nickel electrotype  86 . Subsequently, as shown in FIG. 5C, the nickel electrotype  86  is separated from the master  84  to provide a nickel electrotype  86  having the prism unevenness grooves  82 . Then, the rear and side surfaces of the electrotype  86  are machined to complete the nickel stamper  54 . In this case, the stamper  54  has a thickness of about 0.3 to 0.4 mm. Finally, the manufactured stamper  54  is put on the core material portion  58  with a thickness of 20 to 30 mm to perform an electrotyping work for fixing the stamper  54  and the core material portion  58 . In other words, as shown in FIG. 5E, the surfaces of the stamper  54  and the core inside material portion  58  are electroplated with nickel to form a nickel sealing electroplate  56 . The core material portion  58  may be made from the same metal material (e.g., nickel) as the stamper  54  or a different metal material (e.g., Prehardening steel). Consequently, the integral-type molding device  69  in which the stamper  54  and the core material portion  58  are sealed together by the nickel electroplate  56  is completed. 
     Such a molding device also is applicable to a molding device for forming unevenness grooves at both sides of the prism light guide. In this case, groove-forming stampers  92  and  94  are provided at the upper and lower portions of the injection-molded prism light guide  90 , respectively, as shown in FIG.  6 . The stamper  92  for forming prism unevenness grooves on the lower surface of the prism light guide  90  is fixed to a core material portion  98  at the lower portion thereof by a nickel electroplate  96  similar to that in FIG. 4, to make molding device  106 . On the other hand, the upper stamper  94  for forming the prism unevenness grooves on the upper surface of the prism light guide  90  is fixed to an upper core material portion  102  by an upper nickel electroplate  100  to make an upper molding device  104 . A general core metal such as Prehardening steel is used as the lower and upper core material portions  98  and  102 . Since complex features such as an additional vacuum device for fixing the stampers are not required, the mold structure can be simplified. Also, because the lower stamper  92  or the upper stamper  94  is always fixed to the core material portions  98  and  102  by the nickel electroplates  96  and  100 , a stable injection-molding work can be made. 
     Referring to FIG. 7, a light guide fabricating apparatus according to a second embodiment of the present invention is shown. In a light guide injection-molding device according to the second embodiment of the present invention, a stamper is engaged with a core by bolt members to provide a mold. In order to form prism unevenness grooves on the lower surface of prism light guide  112 , the light guide injection-molding device  110  includes a stamper  114  provided with prism unevenness grooves on a surface contacting an injected light guide material, a molding core  116  to which the stamper  114  is attached, one or more bolts  118  for engaging the stamper  114  with the molding core  116 , a stationary core  126  constituting a mold  124  along with the integral-type molding device  120  made by engaging the stamper  114  and the molding core  116 , and a movable core  122 , and a stationary molding plate  128  and a movable molding plate  130  for fixing the stationary core  126  and the movable core  122  at the exterior thereof, respectively. The stamper  114  is manufactured by the nickel electroplating system using a brass plate master like the first embodiment. In the second embodiment, however, since bolt holes are formed in the stamper  114  to engage the stamper  114  and the molding core with bolts, the plated electrotype must have a middle thickness of about 6 to 12 mm. For the sake of bolt-engaging, the stamper  114  is put on the molding core  116  and a plurality of bolt-engaging holes are formed from the lower portion of the molding core  116  to a desired depth of the stamper  114  by a grinding process. Bolts  118  are then inserted into the holes to fix the stamper  114  to the molding core  116 . By this method, the mold structure can not only be simplified, but also the stamper  114  can also be stably fixed to the molding core  116 . The stamper-integrated mold structure employing the bolt-engagement system is also applicable to a double-faced unevenness-molding device for transcription-molding both sides of the prism light guide. In this case, the upper and lower stampers are fixed to the stationary and movable cores, respectively, by bolts to be integrally formed. 
     As described above according to the present invention, a light guide molding stamper is fixed to an core material portion by nickel electroplate or by bolt members and the like. Such a fixing method is advantageous because it is useful for mass production of a mold structure with a considerably simplified structure. In addition, fixing the stamper to the core material portion of the core as well as stable product manufacturing can be obtained. 
     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.