Abstract:
An exemplary prism sheet consists of a transparent main body. The transparent main body includes a surface and a plurality of spherical micro-protrusions. The spherical micro-protrusions are integrally formed on the surface. A backlight module using the present prism sheet is also provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is related to five co-pending U.S. patent applications, which are: applications Ser. No. 11/933,439 and Ser. No. 11/933,441, filed on Nov. 1, 2007, and both entitled “PRISM SHEET AND LIQUID CRYSTAL DISPLAY DEVICE USING THE SAME”, application Ser. No. 11/946,860 and Ser. No. 11/946,862, filed on Nov. 29, 2007, and both entitled “PRISM SHEET AND LIQUID CRYSTAL DISPLAY DEVICE USING THE SAME”, and application Ser. No. [to be determined], with Attorney Docket No. U.S.15564, and entitled “PRISM SHEET AND LIQUID CRYSTAL DISPLAY DEVICE USING THE SAME”. In all these co-pending applications, the inventor is Shao-Han Chang. All of the co-pending applications have the same assignee as the present application. The disclosures of the above identified applications are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to prisms, and particularly to a prism sheet used in a backlight module. 
         [0004]    2. Discussion of the Related Art 
         [0005]    In a liquid crystal display device (LCD device), liquid crystal is a substance that does not illuminate light by itself. Instead, the liquid crystal relies on light received from a light source, in order that the liquid crystal can facilitate the display of information. In the case of a typical liquid crystal display device, a backlight module powered by electricity supplies the needed light. 
         [0006]      FIG. 6  is a typical backlight module  100  employing a typical prism sheet  10 . The backlight module  100  includes a housing  11  and a plurality of lamps  12  positioned in the housing  11 . The backlight module  100  further includes a light diffusion plate  13 , and a prism sheet  10  in that order. The prism sheet  10  includes a base layer  101  and a prism layer  103  formed on the base layer  101 . The prism layer  103  has a plurality of prism lenses  105  each having a triangular cross section. The prism lenses  105  are arranged regularly, and each extends along a direction parallel to one edge of the prism sheet  10 . In use, light emitted from the lamps  12  enters the prism sheet  10  after scattered in the diffusion plate  13 . The light is refracted and concentrated by the prism lenses  105  of the prism sheet  10 , and then the light finally propagates into the LCD panel. 
         [0007]    Generally, a method of manufacturing the prism sheet  10  includes the following steps. First, a melted ultraviolet-cured transparent resin is coated on the base layer  101 , and then the melted ultraviolet-cured transparent resin having triangular cross section is solidified to form the prism layer  103  having prism lenses  105 . This results in that the prism lenses  105  of the prism layer  103  are usually damaged or scratched due to their poor rigidity and mechanical strength. 
         [0008]    In order to protect the prism layer  103  of the prism sheet  10  in use, the backlight module  100  usually further includes an upper light diffusion film  14  disposed on the prism sheet  10 . Although the upper light diffusion film  14  and the prism sheet  10  are in contact with each other, a plurality of air pockets still exist at the boundaries between the light diffusion film  14  and the prism sheet  10 . When the backlight module  100  is in use, light passes through the air pockets, and some of the light undergoes total reflection at one or another of the corresponding boundaries. In addition, the upper light diffusion film  14  may absorb an amount of the light from the prism sheet  10 . As a result, a brightness of light illumination of the backlight module  100  is reduced. 
         [0009]    What is needed, therefore, is a new prism sheet and a backlight module using the prism sheet that can overcome the above-mentioned shortcomings. 
       SUMMARY 
       [0010]    In one aspect, a prism sheet according to a preferred embodiment consists of a transparent main body. The transparent main body includes a surface and a plurality of spherical micro-protrusions. The spherical micro-protrusions are integrally formed on the surface. 
         [0011]    In another aspect, a backlight module according to a preferred embodiment includes a plurality of lamps, a light diffusion plate and a prism sheet. The light diffusion plate is located above the lamps. The prism sheet is disposed on the light diffusion plate. The prism sheet is the same as described in a previous paragraph. 
         [0012]    Other advantages and novel features will become more apparent from the following detailed description of various embodiments, when taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present prism sheet and backlight module. Moreover, in the drawings, like reference numerals designate corresponding parts throughout several views, and all the views are schematic. 
           [0014]      FIG. 1  is a side, cross-sectional view of a backlight module using a prism sheet according to a first preferred embodiment of the present invention. 
           [0015]      FIG. 2  is an isometric view of the prism sheet of  FIG. 1 . 
           [0016]      FIG. 3  is a side, cross-sectional view of the prism sheet of  FIG. 2 , taken along line III-III thereof. 
           [0017]      FIG. 4  is a top plane view of a prism sheet according to a second preferred embodiment of the present invention. 
           [0018]      FIG. 5  is a top plane view of a prism sheet according to a third preferred embodiment of the present invention. 
           [0019]      FIG. 6  is a side, cross-sectional view of a conventional backlight module using a typical prism sheet. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0020]    Reference will now be made to the drawings to describe preferred embodiments of the present prism sheet and backlight module, in detail. 
         [0021]    Referring to  FIG. 1 , a backlight module  200  in accordance with a first preferred embodiment of the present invention is shown. The backlight module  200  includes a prism sheet  20 , a housing  21 , a plurality of lamps  22  and a light diffusion plate  23 . The lamps  22  are regularly aligned above a base of the housing  21 . The light diffusion plate  23  and the prism sheet  20  are stacked on the top of the housing  21  in that order. 
         [0022]    Referring to  FIGS. 2 and 3  together, the prism sheet  20  has a transparent main body. The transparent main body includes a light input surface  201 , a light output surface  203 , and a plurality of spherical micro-protrusions  205 . The light input surface  201  and the light output surface  203  are on opposite sides of the main body. The spherical micro-protrusions  205  are integrally formed on the light output surface  203  by injection molding technology. The prism sheet  20  is positioned on the light diffusion plate  23  such that the light input surface  201  is adjacent to the light diffusion plate  23  and the light output surface  203  faces away from the light diffusion plate  23 . 
         [0023]    In the first embodiment, the spherical micro-protrusions  205  are formed on the light output surface  203  of the prism sheet  20  in a regular matrix manner. Rows and columns of the spherical micro-protrusions  205  in the matrix are parallel to the edges of the prism sheet  20  (along an X-direction or a Y-direction) correspondingly. A pitch P between adjacent centers of the micro-protrusions  205  is configured to be in the range from about 0.025 millimeters to about 1.5 millimeters. A radius R of each spherical micro-protrusion  205  is in a range from about a quarter of the pitch P to about double of the pitch P. A depth H of the spherical micro-protrusion  205  relative to the light output surface  203  is in the range from about 0.01 millimeters to the radius R. In this embodiment, the depth H equals to the radius R. In an alternative embodiment, each spherical micro-protrusion  205  is a part of a hemisphere micro-protrusion  205 . 
         [0024]    The light input surface  201  can be either a planar surface or a rough surface. The spherical micro-protrusions  205  of the light output surface  203  are configured for converging the received light from the light output surface  203 . The thickness of the prism sheet  20  is preferably in a range from about 0.2 millimeters to about 2 millimeters. The prism sheet  20  can be made of transparent material selected from the group consisting of polycarbonate (PC), polymethyl methacrylate (PMMA), polystyrene (PS), copolymer of methylmethacrylate and styrene (MS), and any suitable combination thereof. 
         [0025]    Referring to  FIG. 1  again, the housing  21  is made of metal or plastic materials. An interior of the housing  21  is configured to be highly reflective. 
         [0026]    The lamps  22  can be point light sources such as light emitting diodes or linear light sources such as cold cathode fluorescent lamps. In this embodiment, the lamps are the cold cathode fluorescent lamps. 
         [0027]    In the backlight module  200 , the spherical protrusions  205  have curve side surfaces in all direction, thus when the light exiting the prism sheet  20  via the light output surface  203 , the light, from every direction, would converge by the spherical protrusions  205 . The spherical micro-protrusions  205  are integrally formed on the light output surface  203 , the materials of the spherical micro-protrusions  205  is same to that of the other portion of the prism sheet  20 . Therefore, a bonding strength between the spherical micro-protrusions  205  and the other portion of the prism sheet  20  is enhanced, and rigidity and mechanical strength of the prism sheet  20  would be improved. And thus the prism sheet  20  is not easy to be damaged or scratched. Furthermore, the spherical micro-protrusions  205  are integrally formed on the light output surface  203 , and there are no common interfaces in the prism sheet  20 . Thus there is little or no back reflection at common interfaces, and an efficiency of utilization of light is increased. In addition, it is easy to mass-produce the prism sheet  20  via the injection molding method. 
         [0028]    Referring to  FIG. 4 , a prism sheet  30  in accordance with a second preferred embodiment of the present invention is shown. The prism sheet  30  is similar in principle to the prism sheet  20 . However, spherical micro-protrusions  305  are aligned side by side on a light output surface  303  of the prism sheet  30  in rows. Adjacent spherical micro-protrusions  305  in each row adjoin each other. The spherical micro-protrusions  305  in any two adjacent rows are staggered relative to each other yet abut each other. Thus a matrix comprised of offset rows of the spherical micro-protrusions  305  is formed. In another words, a honeycomb pattern of the spherical micro-protrusions  305  is formed. 
         [0029]    Referring to  FIG. 5 , a prism sheet  40  according to a third embodiment is shown. The prism sheet  40  is similar in principle to the prism sheet  30  of the second embodiment. A plurality of spherical micro-protrusions  405  are formed on a light output surface  403  in a random manner. When the prism sheet  40  is used in a liquid crystal device, a random arrangement of the micro-protrusions  405  is different from that of pixels of a liquid crystal display panel. Thus moiré pattern interference effect caused by the prism sheet  40  and the pixel pitch of the liquid crystal display panel is kept minimal or eliminated. 
         [0030]    Finally, while various embodiments have been described and illustrated, the invention is not to be construed as being limited thereto. Various modifications can be made to the embodiments by those skilled in the art without departing from the true spirit and scope of the invention as defined by the appended claims.