Abstract:
A backlight module includes a light source, a light guide plate for guiding light from the light source, and a brightness enhancement film having a plurality of spherical surface microlenses for gathering light from the light guide plate. In contrast to traditional prism sheets, the brightness enhancement film having the plurality of spherical surface microlenses have better efficiency of light-gathering.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a backlight module used in a liquid crystal display, and more particularly, to a backlight module with a brightness enhancement film having a plurality of spherical surface microlenses. 
   2. Description of the Related Art 
   A backlight module is a key component of a liquid crystal display (LCD). The purpose of the backlight module is to provide a sufficient-brightness and an even-distribution light surface to the LCD panel. Because the LCD is widely used in various electronic products such as a monitor, a notebook computer, a digital camera, and a projector, the demand for the backlight module has increased tremendously. 
   Please refer to  FIG. 1 , which shows a prior art of a backlight module  20 . The backlight module  20  comprises a light source  22  (such as a cold cathode fluorescent lamp, a hot cathode fluorescent lamp, a light emitting diode), a light guide plate  26 , a reflector  24  disposed at a side of the light guide plate  26 , a diffusion sheet  28 , and prism sheets  30  and  32 . The reflector  24  is used for reflecting light from the light source  22  toward the light guide plate  26 . Then the light guide plate  26  guides light emitted from the light source  22  and light reflected from the reflector  24  as uniform planar light. Through the light-distributing of the diffusion sheet  28  and light-gathering of the prism sheets  30  and  32 , the light is fed into an LCD panel. The prism sheets  30  and  32  are formed by hardening an acrylic resin on a polyester film with a thickness of 125-μm by means of exposure under high energy UV light. The conventional prism sheets  30  and  32  are served as bar-alignment triangle prisms in characteristics of a vertex angle of substantial 90 degrees with an interval of 50 μm within each other. The prism sheets  30  and  32  can concentrate scatter light from the light guide plate  26  upward with substantial ±35 degrees with respect to a direction of an on-axis. Nevertheless, as shown in  FIG. 1 , the prism sheet  30  only concentrate light constituent of Y-axis upward, and the prism sheet  32  only concentrate light constituent of X-axis upward. Therefore, utilizing only a single prism sheet can enhance the brightness by 1.6 times, while, for better light-gathering quality, utilizing two prism sheets  30  and  32  with their prism alignments thereon being vertical to each other can enhance the brightness by 2 times or more. In other words, scatter light is gathered by means of prisms on the prism sheets  30  and  32 , therefore boosting the brightness of the LCD display by 2 times. In this manner, for the LCD display described above, power consumption is lowered and a life span of batteries is lengthened. 
   Consequently, using a single prism sheet fails to provide sufficient brightness, while using two prism sheets may result in more photo-energy consumption. Besides, using two prism sheets may induce higher cost for the backlight module as a result. 
   SUMMARY OF THE INVENTION 
   An objective of the present invention is to provide a backlight module comprising a brightness enhancement film with a plurality of spherical surface microlenses in lieu of a backlight module having two conventional prism sheets to solve the problem existing in prior art. 
   Briefly summarized, the invention provides a backlight module comprising a light source, a light guide plate for guiding light from the light source, and a brightness enhancement film comprising a plurality of spherical surface microlenses for gathering light from the light guide plate. 
   It is an advantage of the present invention that using one brightness enhancement film with a plurality of spherical surface microlenses thereon in lieu of the conventional structure of two prism sheets. The scatter light from the light guide plate can be concentrated toward a direction of an on-axis by the spherical surface microlenses, solving the conventional defect of needing to use two prism sheets to concentrate light. 
   The disclosed inventions will be described with references to the accompanying drawings, which show important example embodiments of the inventions and are incorporated in the specification hereof by related references. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a conventional backlight module. 
       FIG. 2  shows a backlight module according to an embodiment of the present invention. 
       FIG. 3  is an enlarged view of a first embodiment of the brightness enhancement film depicted in  FIG. 2 . 
       FIG. 4  is a side view of the first embodiment of the brightness enhancement film depicted in  FIG. 2 . 
       FIG. 5  is an enlarged view of a second embodiment of the brightness enhancement film depicted in  FIG. 2 . 
       FIG. 6  is a side view of the second embodiment of the brightness enhancement film depicted in  FIG. 2 . 
       FIG. 7  is an enlarged view of a third embodiment of the brightness enhancement film depicted in  FIG. 2 . 
       FIG. 8  is a side view of the third embodiment of the brightness enhancement film depicted in  FIG. 2 . 
       FIG. 9  is a schematic illustration showing light passing through a brightness enhancement film and a light guide plate. 
       FIGS. 10A-10I  illustrate a flow forming the brightness enhancement film according to the present invention. 
       FIG. 11  shows an appearance of the first photoresist and the second photoresist to be heated after a period of time. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Please refer to  FIG. 2 , which shows a backlight module  50  in accordance with the present invention. The backlight module  50  comprises a light source  52  (such as a cold cathode fluorescent lamp, a hot cathode fluorescent lamp, a light emitting diode), a light guide plate  56 , a reflector  54  disposed at a side of the light guide plate  56 , and a brightness enhancement film  60 . The reflector  54  is used for reflecting light from the light source  52  toward the light guide plate  56 . The light guide plate  56  guides light emitted from the light source  52  and light reflected from the reflector  54  and distributes the light as a uniform planar light source. Through the light-distributing of the diffusion sheet  58  and light-gathering of the brightness enhancement film  60 , the light is fed into an LCD panel. In  FIG. 2 , the diffusion sheet  58  is preferably disposed between the brightness enhancement film  60  and the light guild plate  56 . In other embodiments, either disposing the diffusion sheet  58  over the brightness enhancement film  60 , or no diffusion sheet arrangement is also allowed. 
   Please refer to  FIG. 3  to  FIG. 8 .  FIG. 3  and  FIG. 4 , respectively, are an enlarged view and a side view of a first embodiment of the brightness enhancement film  60  depicted in  FIG. 2 . The brightness enhancement film  60  comprises a plurality of spherical surface microlenses  62   a  and a plurality of carriers  64   a . Each spherical surface microlens  62   a  is disposed on corresponding one of the plurality of carriers  64   a . Each of the plurality of carriers  64   a  is closely disposed with each other. The plurality of carriers  64   a  are substantially shaped as triangles. 
     FIG. 5  and  FIG. 6 , respectively, are an enlarged view and a side view of a second embodiment of the brightness enhancement film  60  depicted in  FIG. 2 . The brightness enhancement film  60  comprises a plurality of spherical surface microlenses  62   b  and a plurality of carriers  64   b . Each spherical surface microlens  62   b  is disposed on corresponding one of the plurality of carriers  64   b . Each of the plurality of carriers  64   b  is closely disposed with each other. The plurality of carriers  64   b  are substantially shaped as rectangles. 
     FIG. 7  and  FIG. 8 , respectively, are an enlarged view and a side view of a third embodiment of the brightness enhancement film  60  depicted in  FIG. 2 . The brightness enhancement film  60  comprises a plurality of spherical surface microlenses  62   c  and a plurality of carriers  64   c . Each spherical surface microlen  62   c  is disposed on corresponding one of the plurality of carriers  64   c . Each of the plurality of carriers  64   c  is closely disposed with each other. The plurality of carriers  64   c  are substantially shaped as hexagons. 
   A resolution for better light-gathering performance is to increase a thickness of the carriers  64   a ,  64   b  or  64   c , or cushioning the carriers  64   a ,  64   b  or  64   c  with another carrier to obtain a higher ratio of height and width (h/w) of the brightness enhancement film  60 . 
   Referring to  FIG. 9 , the spherical surface microlenses  62  can refract any light constituents from the light guide plate  56  upward. 
   Please refer to  FIGS. 10A-10I , which illustrate a flow of forming the brightness enhancement film according to the present invention. First of all, as shown in  FIG. 10A , a first photoresist  210  (e.g. Az9260) is spread on a substrate  200  in a spin-coating manner. Next, a second photoresist  220  (e.g. AZ4620) is also spread evenly on the first photoresist  210  in a spin-coating manner. It is appreciated that melting point of the first photoresist  210  should be higher than that of the second photoresist  220 . Then, as shown in  FIG. 10B , etching the first photoresist  210  and the second photoresist  220  are performed to form an array pattern. As can be seen in  FIG. 10C , in a process of reflowing the first photoresist  210  and the second photoresist  220 , due to the fact that the melting point of the first photoresist  210  is higher than that of the second photoresist  220 , it happens that the first photoresist  210  is not completely melted but the second photoresist  220  has already melted. In doing so, the melted second photoresist  220  forms a half-sphere due to surface tension as the first photoresist  210  does not melt completely. As shown in  FIG. 10D , sputtering a nickel film  230  on the first photoresist  210  and the second photoresist  220  is executed after cooling the photoresists  210  and  220 . 
   Next, electroplating a Ni—Co film  240  on the nickel film  230  and sputtering an Au film  250  on the Ni—Co film  240  are illustrated in  FIG. 10E . Furthermore, the first photoresist  210  and the second photoresist  220 , covering with metal films  230 ,  240 ,  250 , are electroformed to form a cast  260 , as shown in  FIGS. 10F and 10G  Finally, a metal mold  270  is obtained by re-electroforming the cast  260 . Accordingly, a mass production of the brightness enhancement film  60  with a plurality of spherical surface microlenses is possible by injecting plastic material  280  such as polyester or polycarbonate into the metal mold  270 , as shown in  FIGS. 10H and 10I . 
   Preferably, spherical surface microlens  62   a ,  62   b , and  62   c  are substantially shaped as spheres. However, in real process of forming the metal mold  270 , the appearance of the melted second photoresist  220 , due to incomplete melt of the first photoresist  210 , is as shown in  FIG. 11 , rather than a half-sphere. As a result, the appearance of the spherical surface microlenses of the brightness enhancement film  60  made by the metal mold  270  is similar to the appearance shown in  FIG. 11 . 
   In contrast to prior art, the present inventive backlight module uses a brightness enhancement film with a plurality of spherical surface microlenses thereon in lieu of the conventional structure of two prism sheets. The scatter light from the light guide plate can be concentrated toward a direction of an on-axis by the spherical surface microlenses, solving the defect of the use of two prism sheets. In addition, the present inventive brightness enhancement film has the function of light-gathering and light-distributing. Since the light only passes through a single brightness enhancement film, photo energy consumption is reduced. Therefore, the use of the present inventive brightness enhancement film not only lowers costs, but also reduces power consumption. 
   The present invention has been described with references to certain preferred and alternative embodiments which are intended to be exemplary only and not limiting to the full scope of the present invention as set forth in the appended claims.