Abstract:
A diffuser plate having a multi-aspheric structure comprises a plate and at least one aspheric microstructure. The plate is made of a transparent polymer. The plate is doped with a UV absorbent and several diffusion particles. The aspheric microstructure is formed on at least one surface of the plate. By the use of the aforesaid structure, the present invention can improve the conventional problems and provide the advantages including high light transmission rate, raised diffusion capability, improved brightness, and uniform light beams.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a diffuser plate having a multi-aspheric structure, and more particularly to a diffuser plate that utilizes a plate and at least one aspheric microstructure to provide many advantages including high light transmission rate, raised diffusion capability, improved brightness, and uniform light beams. 
       BACKGROUND OF THE INVENTION 
       [0002]    Generally speaking, a general diffuser plate is applied to a LCD monitor so as to allow a cold cathode fluorescent lamp (CCFL) of the LCD monitor to diffuse the light beams uniformly, thereby obtaining a uniform area light source. Referring to  FIG. 1  and  FIG. 2 , a diffuser plate is treated with two methods. In the first method, a diffuser plate  1 ′ is doped with diffusion particles  11 ′ so as to reflect, refract or scatter the light beams by the diffusion particles  11 ′. In the second method, a diffuser plate  1 ′ is doped with diffusion particles  11 ′ and a refraction structure  2 ′ is formed on the top of the diffuser plate  1 ′ so as to diffuse the light beams more uniformly. The second kind of diffuser plate provides better diffusion effect and is thus widely applied to the photonics industries. 
         [0003]    Referring to  FIG. 3 , a curve diagram is disclosed, wherein the curve line A indicates that no diffuser plate is utilized, and the curve line B indicates that the above-mentioned two methods are utilized. This diagram is related to the distribution of brightness, which is utilized usually for estimating the relationship between the relative brightness and the position of the backlight module and for estimating the brightness distribution of the backlight module along a longitudinal cross-section perpendicular to the lamp. The uniformity and brightness performance of the backlight module can be shown in this diagram. In the  FIG. 3 , the horizontal coordinate is the absolute coordinate of the backlight module. The vertical coordinate is the relative brightness after normalization. After comparison, the brightness distribution curve line A of the naked lamp shows that the relative brightness is changed significantly at different positions. It means that the brightness distribution of the backlight module is very poor when the human eyes look at different positions of the backlight module. It is apprehensible that the upper light beams of the lamp are allowed to enter the eyes directly, but the farther light beams can not be diffused to the dark region beside the lamp and the light beams can not be focused into the retinas of the eyes. As a result, almost every direct backlight module can not provide uniform brightness in the absence of an optical film. This backlight phenomenon of extreme non-uniform brightness is usually called as MURA defects. Therefore, a diffuser plate and a diffuser film are essential for the direct backlight module to improve the MURA defects caused by the non-uniform light source or lamp. Referring to the curve line B, this curve line B indicates that the relative brightness becomes very stable and uniform when the above-mentioned two methods are utilized. In other words, the diffuser plate can improve the brightness uniformity of the backlight plate obviously. However, the obtained brightness value may be decreased significantly because of the conservation of energy and the imperfect design. The brightness of the region exactly above the lamp is substantially higher than that of the center region between any two lamps. In particular, with the decrease of lamps in the 32 inches LCD TV, for example, from sixteen lamps to twelve lamps, the brightness and uniformity of the LCD monitor is further reduced, which further reduces the desire of the consumer for buying the LCD monitor. The lamp number of the existing backlight module of the LCD monitor is reduced for the purpose of reducing the production cost, which enlarges the distances among the lamps and makes the MURA defects become more serious. As a result, the diffuser plate and the diffuser film must be formed on the direct backlight module so as to uniform the brightness distribution of the backlight module. In other words, the general direct backlight module utilizes a diffuser plate and two diffuser films to reduce the MURA defects. The semi-sphere (or called as lenticular) refraction structure perhaps improves diffusion effect. But, the aberration usually exists in the semi-sphere microstructure. As a result, the diffusion angle of the light beam is so large that the human eyes can only sense partial brightness because the human eyes have limited filed of view. The addition of diffusion particles and the diffuser plate is unable to enter the retinas. In other words, the thickness of the backlight module must be increased to reduce the MURA defects. However, the increased thickness violates the purpose of forming thinner backlight module. As a result, in order to reduce the number of the lamp and the size and weight of the backlight module, a new design must be introduced into the diffuser plate so as to allow the light beams to enter the eyes and to maintain a certain amount of brightness and uniformity. 
       SUMMARY OF THE INVENTION 
       [0004]    It is a primary object of the present invention to form an aspheric structure on a plate for improving the brightness. In addition, the present invention discloses a multi-aspheric structure to avoid the non-uniformity of the single aspheric structure. 
         [0005]    In order to achieve the above-mentioned object, a diffuser plate having a multi-aspheric structure of the present invention comprises a plate and at least one aspheric microstructure. The plate is made of a transparent polymer and doped with a UV absorbent and several diffusion particles. The aspheric microstructure is formed on at least one surface of the plate and comprises a plurality of aspheric bars having at least one kind of arrangements. The aspheric bars have a curviform profile consisting of at least one curve line. By the use of the aforesaid structure, the present invention can improve the conventional problems and can provide the advantages including high light transmission rate, raised diffusion capability, improved brightness, and uniform light beams. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a side view showing a conventional diffuser plate doped with diffusion particles. 
           [0007]      FIG. 2  is an elevational diagram showing a surface structure of the conventional diffuser plate. 
           [0008]      FIG. 3  is a curve diagram showing the relative brightness and uniformity of the prior art. 
           [0009]      FIG. 4  is an elevational diagram showing the structure of a first preferred embodiment of the present invention. 
           [0010]      FIG. 5  is a side view showing the structure of a second preferred embodiment of the present invention. 
           [0011]      FIG. 6  is an elevational diagram showing the structure of a third preferred embodiment of the present invention. 
           [0012]      FIG. 7  is an elevational diagram showing the structure of a fourth preferred embodiment of the present invention. 
           [0013]      FIG. 8  is a side view showing the structure of a fifth preferred embodiment of the present invention. 
           [0014]      FIG. 9  is an elevational diagram showing the structure of a sixth preferred embodiment of the present invention. 
           [0015]      FIG. 10  is a side view showing the structure of a seventh preferred embodiment of the present invention. 
           [0016]      FIG. 11  is a curve diagram showing the comparison of the relative brightness and uniformity between the prior art and the seventh preferred embodiment of the present invention. 
           [0017]      FIG. 12  is a curve diagram showing the comparison of the relative brightness and uniformity between the prior art and the seventh preferred embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0018]    Referring to  FIG. 4 , a diffuser plate having a multi-aspheric structure in accordance with a first preferred embodiment of the present invention comprises a plate  1  and at least one aspheric microstructure  2 . The configuration of the aspheric microstructure  2  is determined by an aspheric equation mentioned in the traditional optics. 
         [0019]    The plate  1  is made of a transparent polymer selected from a group consisting of poly(methylmethacrylate) (PMMA), polycarbonate (PC), (methylmethacrylate)styrene (MS) and polystyrene (PS). The plate  1  is integrally formed by an extrusion process for forming a plurality of aspheric microstructures  2  on at least one surface of the plate  1 . In addition, the plate  1  has a UV absorbent  11  doped therein to prevent the direct UV light irradiation from causing the plate  1  to generate the phenomena of photoyellowing and cracking. In addition, the plate  1  has several diffusion particles  12  doped therein, wherein the diffusion particles  12  are made of a material selected from a group consisting of poly(methylmethacrylate) (PMMA), polycarbonate (PC), (methylmethacrylate)styrene (MS), polystyrene (PS), silica, silicon, melamine, calcium carbonate, Teflon, TiO 2  and SiO 2 . As a result, the phenomenon of optical diffusion occurs when the light passes through the diffusion particles  12 . 
         [0020]    The aspheric microstructure  2  is formed on at least one surface of aforesaid plate  1 . The aspheric microstructure  2  comprises at least one continuously arranged first aspheric bar  21 . The curviform profile of the first aspheric bar  21  comprises at least one curve line  211 . The curve line  211  is generally an aspheric curve line, a NURB curve line, a SPLINE curve line or a BEZIER curve line. The first aspheric bar  21  and the curve line  211  can be preferably designed in accordance with various light source arrangements of backlight module so that the backlight sources including line sources of CCFLs or point sources of LEDs that pass through the plate  1  and the aspheric microstructure  2  can be transformed into surface sources that have high brightness and uniformity for being applied to the panel. The first aspheric bar  21  can be extruded straightly along the curve line  211 . In accordance with requirement or processing limitation, the curve line  211  can be extruded wiggly in such as S shape to form the winding first aspheric bar  21 . In the practical processing, this microstructure bar can be carved out by a lathing machine, which has superfine cutting tools and is computer-controlled parameters. 
         [0021]    Referring to  FIG. 5 , a diffuser plate of a second preferred embodiment of the present invention has a configuration similar to that of the first preferred embodiment. The difference is that the aspheric microstructure  2  of the second preferred embodiment has several continuously arranged second aspheric bars  22 . Each second aspheric bar  22  comprises a first curve line  221 , a circular line  222 , and a straight line  223 . One end of the first curve line  221  is connected to one end of the circular line  222 . The other end of the circular line  222  is connected to one end of the straight line  223 . The other end of the straight line  223  is connected to one end of the first curve line  221  of another second aspheric bar  22 . In this preferred embodiment, the aspheric profile of the microstructure is constituted by several curve lines. This continuously arranged structure constitutes the aspheric microstructure  2  of the second preferred embodiment. 
         [0022]    Referring to  FIG. 6 , a diffuser plate of a third preferred embodiment of the present invention has a configuration similar to that of the first preferred embodiment. The difference is that the aspheric microstructure  2  of the third preferred embodiment has several third aspheric bars  23  and several parallel-arranged fourth aspheric bars  24  that adjacent to the third aspheric bars  23 . The third preferred embodiment is characterized by its regional arrangement. In other words, the aspheric structures that have the same shape are arranged in the same small region. The identical bars are distributed in the identical region. As a result, the aspheric microstructure  2  is constituted by various types of bars arranged in various regions. 
         [0023]    Referring to  FIG. 7 , a diffuser plate of a fourth preferred embodiment of the present invention has a configuration similar to that of the first preferred embodiment. The regional arrangement of the fourth preferred embodiment is different from that of the third preferred embodiment. In this fourth preferred embodiment, various types of structure are staggered with one other. In this fourth preferred embodiment, the aspheric microstructure  2  comprises several fifth aspheric bars  25  and several sixth aspheric bars  26 , wherein every sixth aspheric bar  26  is located between two adjacent sixth aspheric bars  26 . 
         [0024]    Referring to  FIG. 8 , a diffuser plate of a fifth preferred embodiment of the present invention has a configuration similar to that of the first preferred embodiment. The difference is that the aspheric microstructure  2  of the fifth preferred embodiment has several parallel-arranged seventh aspheric bars  27 , several adjacent-arranged eighth aspheric bars  28 , and an adjacent-arranged eighth aspheric bar  29 . 
         [0025]    Referring to  FIG. 9 , a diffuser plate of a sixth preferred embodiment of the present invention has a configuration similar to that of the first preferred embodiment. The difference is that the aspheric microstructure  2  of the sixth preferred embodiment has several parallel-arranged, gradually-changed tenth aspheric bars  2   a . The aspheric bars  2   a  that locate adjacent to each other have different shapes so as to prevent the problem of non-uniform brightness caused by significant difference between adjacent structures. By the use of the gradually-changed aspheric microstructure  2 , the brightness and uniformity can be increased effectively. 
         [0026]    Referring to  FIG. 10 , a diffuser plate of a seventh preferred embodiment of the present invention has a configuration similar to that of the first preferred embodiment. The difference is that the aspheric microstructure  2  of the seventh preferred embodiment has several parallel-arranged, gradually-changed eleventh aspheric bars  2   b  and several parallel arranged, gradually-changed twelfth aspheric bars  2   c . The eleventh aspheric bars  2   b  and the twelfth aspheric bars  2   c  are adjacent to one another and located regularly and continuously. Referring to  FIG. 10 , the curviform profiles of the aspheric bars  2   b  and  2   c  are changed from a smooth shape to a sharp shape. The seventh and sixth preferred embodiments adopt the structures that have gradually changed shapes. However, the aspheric shape of the seventh preferred embodiment is smoother than that of the sixth preferred embodiment. Therefore, the backlight module that utilizes the diffuser plate of the seventh preferred embodiment has smaller average brightness than the backlight module that utilizes the diffuser plate of the sixth preferred embodiment. On the contrary, the backlight module that utilizes the diffuser plate of the seventh preferred embodiment has more uniform visual angle and brightness than the backlight module that utilizes the diffuser plate of the sixth preferred embodiment. Referring to  FIG. 11 , the horizontal coordinate is the absolute position of the backlight module, and the vertical coordinate is the relative brightness after normalization. This figure shows the brightness distribution curve B of the conventional backlight module that utilizes the spherical reflection structure  2 ′ of the diffuser plate and the brightness distribution curve G of the diffuser plate of the seventh preferred embodiment. After comparison, the brightness distribution curve B shows that the spherical reflection structure  2 ′ has low brightness, and the brightness distribution curve G shows that the diffuser plate of the seventh preferred embodiment has high and uniform brightness. Compared with the conventional technology, the seventh preferred embodiment of the present invention increases the brightness by about 38%. 
         [0027]    In the above-mentioned seven preferred embodiments, the curviform profiles of the first aspheric bar  21  through the twelfth aspheric bar  2   c  are constituted by at least one lines. It is apparent that these lines can be constituted by aspheric lines, straight lines, NURB curve lines, SPLINE curve lines, BEZIER curve lines, and sphere lines, which are connected to form a compound asphere surface, such as the compound asphere microstructure of the second preferred embodiment shown in  FIG. 5 . The aspheric bars of the above-mentioned aspheric microstructure can be constituted by extending the curve lines from the straight lines. In addition, the aspheric microstructure can be constituted by extending the curve lines from the curve lines. 
         [0028]    It is worthy of mention that the shape and the distribution density of the aspheric microstructure  2  can be designed in accordance with the aspheric equation, Snell&#39;s law and the Fresnel equation. In addition, the distribution result of the brightness can be repeatedly calculated by optical procedure so as to provide the microstructure with optimum shape and distribution in accordance with the relative positions of the light sources and the various sizes of the backlight module. The size of the aspheric microstructure  2  is ranged from several tens micrometers to several hundreds micrometers. In the present invention, the structure width is ranged from about 20 micrometers to 780 micrometers. The practically shape of the diffuser plate may be changed slightly by the processing parameters and affected by the environment. In addition, the microstructure can be simplified to be partially composed of aspheric structures, straight structures or sphere structures according to the simplified route of CNC lathing machine and the reduced processing time. In addition, the microstructure is designed according to the injection molding processing or the extrusion materials so as to reduce the production cost. In the sixth and seventh preferred embodiments, the microstructures are provided with gradually changed shapes. It means that their structures are slightly different from each other so as to obtain optimum brightness and uniformity. But, the sixth and seventh preferred embodiments take longer processing time. As a result, the first through fifth preferred embodiments are disclosed to prevent the brightness value and the uniformity from being decreased significantly. For the purposes of simplifying the processing and procedure, the aspheric structures disclosed in these preferred embodiments are arranged at intervals or at different regions so that one or more aspheric structures that have different shapes can be distributed at the same small region or the aspheric structures that have the same shape can be arranged in the same small region. The aforesaid purposes and efficiency can be also achieved as long as the structures have proper sizes, shapes and arrangements. 
         [0029]    Referring to  FIG. 12 , a curve diagram is shown. The curve A shows the conventional brightness distribution of the naked lamp without the addition of any diffuser plate. The curve B shows the conventional brightness distribution of the sphere, pillar-shaped diffuser plate. The curves C, D, E, and F show the brightness distribution of other commercial samples of diffuser plate. The curve G shows the brightness distribution of the diffuser plate of the seventh preferred embodiment. After attaching these conventional diffuser plates and the diffuser plate of the seventh preferred embodiment that has the multi-aspheric structure to the backlight modules, a brightness measurement equipment (for example, model Topcon BM7-fast) is utilized to measure the final brightness and uniformity. The measurement result shows that the diffuser plate of the preferred embodiment has better brightness and uniformity than the conventional sphere diffuser plate and the flat-type diffuser plate that is only doped with different diffusion particles.