Abstract:
A diffusion plate assembly includes a diffusion plate made from transparent material. Pluralities of bar-type patterns are disposed on the emission surface of the diffusion plate. The outline of these patterns has a first curve and a second curve. The protruding direction of the first curve and the second curve are inversed. The second curve is an arc whose radius curvature is between 0.05 mm and 0.3 mm.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a diffusion plate and a diffusion plate assembly and particularly to a diffusion plate that has a plurality of bar-type patterns on an emission surface and a diffusion plate assembly including the diffusion plate. 
   2. Description of the Prior Art 
   In recent years, the traditional cathode ray tube display (commonly called CRT display) has been gradually replaced by a liquid crystal display (LCD). The main reason is that the LCD releases far less radiation than the CRT display. Moreover, the production cost of the LCD dropped significantly in the recent years. In general, the LCD includes a backlight module and a liquid crystal panel. The backlight module mainly aims to provide a light source for the LCD. 
   The backlight module generally includes a diffusion plate which contains multiple light diffusion particles made from a transparent polymer to diffuse light generated by cold cathode fluorescent lamps (CCFLs) to reduce impact on display quality resulting from illumination shade generated by the CCFLs. Without the diffusion plate, the display surface will have visible bright and dark strips. In the earlier time, the diffusion plate is a plane structure. As technology advances, the diffusion plate with patterns formed on the emission surface has been developed to further improve the display quality. 
   Refer to  FIG. 1  for a conventional diffusion plate  100  which has a plurality of patterns  120  formed on an emission surface  110 . When light  10  passes through the patterns  120 , its travel direction changes, hence, reducing impact on display quality caused by the illumination shade generated by the CCFLs. The patterns  120  usually are formed in are shapes protruding outwards. Hence, light passing through the patterns  120  converges first at a focal point  120 P before diffusing. As a result, its diffusion effect is not desirable. 
   How to make the diffusion plate to fully generate desired diffusion effect is an issue remained to be resolved in the industry. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a diffusion plate and a diffusion plate assembly to improve luminous uniformity and display quality. 
   The diffusion plate according to the invention is made from transparent material and has an emission surface formed with a plurality of bar-type patterns. The patterns have a first curve and a second curve that protrude in opposite directions. The second curve is an arc formed at a radius curvature between 0.05 mm and 0.3 mm. 
   In one aspect, the patterns of the diffusion plate are formed at a vertical length less than ½ of the width. In one embodiment of the invention, the ratio of the vertical length and width is 1:2.4. 
   In another aspect, the patterns protrude outwards, but also may be indented inwards, to become concave troughs. 
   In yet another aspect, the diffusion plate may be made from materials selected from the group consisting of Polymethyl Methacrylate (PMMA), Polycarbonate (PC), Polystyrene (PS), Methyl Methacrylate Styrene (MS), Polypropene (PP), Polythylene (PE), and Polythylene terephthalate (PET). 
   In yet another aspect, the second curve has a radius curvature of 0.1 mm. 
   In yet another aspect, the diffusion plate of the invention is mainly made from a transparent polymer material with an emission surface formed with a plurality of bar-type patterns. The patterns have a first curve and a triangle that protrude in opposite directions. The triangle has a vertex angle between 90 and 120 degrees. 
   In yet another aspect, the invention also provides a diffusion plate assembly which includes a first diffusion plate and a second diffusion plate. The first diffusion plate is located above the second diffusion plate and has an emission surface formed with a first pattern consisting of a plurality of bars. The first pattern has a first curve and a second curve that protrude in opposite directions. The second curve is an arc formed at a radius curvature between 0.05 mm and 0.3 mm. The second diffusion plate has a light incident surface formed with a plurality of second patterns. 
   In one aspect, the first pattern of the diffusion plate assembly is formed at a vertical length less than ½ of the width. 
   In another aspect, the second pattern of the diffusion plate assembly is a prism structure with a vertex angle between 60 and 90 degrees. 
   As the diffusion plate of the invention has the first curve and second curve formed with the patterns that protrude in the opposite directions, light passing through the first curve and light passing through the second curve diffuse in different fashions. Hence, luminous distribution on the display surface is more desirable. For a LCD equipped with the diffusion plate of the invention, the display quality also improves. 
   The foregoing, as well as additional objects, features and advantages of the invention, will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic view of a conventional diffusion plate with patterns formed on the emission surface. 
       FIG. 2A  is a perspective view of a first embodiment of the diffusion plate of the invention. 
       FIG. 2B  is a side view of the first embodiment of the diffusion plate of the invention. 
       FIG. 3  is a schematic view of another diffusion plate for comparing with the first embodiment. 
       FIG. 4A  is a perspective view of a second embodiment of the diffusion plate of the invention. 
       FIG. 4B  is a side view of the second embodiment of the diffusion plate of the invention. 
       FIG. 5  is a schematic view of yet another diffusion plate for comparing with the second embodiment. 
       FIG. 6  is a schematic view of a diffusion plate assembly. 
       FIG. 7A  is a perspective view of a third embodiment of the diffusion plate of the invention. 
       FIG. 7B  is a side view of the third embodiment of the diffusion plate of the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Please refer to  FIGS. 2A and 2B  for a first embodiment of the diffusion plate of the invention. The diffusion plate  200  has an emission surface  202  which has a plurality of bar-type patterns  210  formed thereon. The patterns  210  are a protruding structure directing outwards. The patterns  210  have a vertical length H less than ½ of the width L. The patterns  210  consist of a first curve  212  and a second curve  214  that protrude in opposite directions. Namely, the first curve  212  protrudes in an outward direction, while the second curve  214  is indented inwards. In this embodiment, the second curve  214  is an arc formed at a radius curvature between 0.05 mm and 0.3 mm. 
   The diffusion plate  200  is made from transparent material, such as polymers, preferably having a penetration rate greater than 75%. The material for the diffusion plate  200  may be selected from the group consisting of Polymethyl Methacrylate (PMMA), Polycarbonate (PC), Polystyrene (PS), Methyl Methacrylate Styrene (MS), Polypropene (PP), Polythylene (PE) and Polythylene terephthalate (PET). 
   Referring to  FIG. 2B , when light  10  passes through the first curve  212 , it substantially converges at a focal point  212 P and, then, diffuses. However, the light  10  passing through the second curve  214  directly diffuses outwards. Hence, the light  10  passing through the patterns  210  diffuses in two different fashions. Refer to  FIG. 3  for a comparison with the first embodiment. Another diffusion plate  200 ′ also has patterns  210 ′, but they have only a first curve  212 ′ protruding outward without the indented second curve  214 . Hence, when the light  10  passes though the patterns  210 ′, it substantially converges inwards at a focal point  212 P′, then diffuses. 
   Comparing  FIG. 2B  with  FIG. 3 , when the light  10  passes through the patterns  210 , two different types of diffusion take place, and a more desirable diffusion effect is generated. Hence, it is less likely to generate bright and dark strips on the display surface. As a result, the LCD equipped with the diffusion plate  200  has an improved display quality. 
   Refer to  FIGS. 4A and 4B  for a second embodiment of the diffusion plate of the invention. A diffusion plate  300  has an emission surface  302  with a plurality of bar-type patterns  310  formed thereon. The patterns  310  are concaves indented inwards and have a vertical length H′ less than ½ of the width L′. In the embodiment, the ratio of the vertical length and width is 1:2.4. The patterns  310  consist of a first curve  312  and a second curve  314  that protrude in opposite directions. Namely, the first curve  312  is indented inwards, while the second curve  314  protrudes outwards. In this embodiment, the second curve  314  is an arc formed at a radius curvature between 0.05 mm and 0.3 mm. 
   Also referring to  FIG. 4B , when the light  10  passes through the first curve  312 , it diffuses outwards. However, the light  10  passing through the second curved  314  converges at a focal point  314 P and, then, diffuses. Thus, two types of diffusion take place when the light  10  passes through the patterns  310 . Refer to  FIG. 5  for comparing with the second embodiment. Yet another diffusion plate  300 ′ also has patterns  310 ′. However, they differ from the patterns  310  by having only a first curve  312 ′ that is indented inwards without the second curve  314  that protrudes outwards. Hence, the light  10  passing through the patterns  310 ′ diffuses outwards. 
   Comparing  FIG. 4B  with  FIG. 5 , after the light  10  has passed though the pattern  310 , two types of diffusion take places and a more desirable diffusion effect can be achieved. Thus, a LCD equipped with the diffusion plate  300  has an improved display quality. 
   In practice, the diffusion plates depicted in the first and second embodiments can be in coupled with other diffusion plates. For instance, the diffusion plate  200  can be coupled with a second diffusion plate  400  to form a diffusion plate assembly  20  (referring to  FIG. 6 ). The second diffusion plate  400  is located beneath the diffusion plate  200 . As the diffusion plate  200  has been discussed previously, it is omitted herein. The second diffusion plate  400  has a light incident surface  402  which has a plurality of second patterns  410  formed thereon. The second patterns  410  are a prism structure with a vertex angle between 60 and 90 degrees. In this embodiment, the second patterns  410  are formed to cross the patterns  210  at a normal angle. Namely, the second patterns  410  are laid  90  degrees from the patterns  210 . As the second patterns  410  can alter the light travel path, the total diffusion effect of the diffusion plate assembly  20  improves even more. Of course, to those skilled in the art, the second patterns  410  can also be formed in other shapes, such as semi-spherical or the like. In addition, the second patterns  410  may also be parallel with the patterns  210 , or differ at other angles. 
   The diffusion plate assembly  20  previously discussed has been tested through optical simulations. The diffusion plate assembly  20  is projected by one set of lights  10 . The second curve  214  of the diffusion plate  200  has a radius curvature of 0.1 mm. The uniformity obtained is 1.03. The uniformity is the brightness ratio of the most brightness spot and the most dark spot on the emission surface  202 . 
   Next, the diffusion plate  200  in the diffusion plate assembly  20  is replaced by another the diffusion plate  300  shown in  FIG. 4B , with the radius curvature of the second curve  314  of the diffusion plate  300  set at 0.1 mm. Then, the optical simulation is executed again. The resulting uniformity is 1.01. 
   Next, the diffusion plate  200  of the diffusion plate assembly  20  is replaced by another diffusion plate  200 ′ shown in  FIG. 3 . Then, the optical simulation is done again. The resulting uniformity is 1.1. 
   The optical simulation results indicate that the diffusion plate of the invention can achieve an improved uniformity. For a LCD equipped with the diffusion plate of the invention, its display quality improves. 
   Of course, to those skilled in the art, the second curve  314  may be changed to other shapes besides a curve. The following shows another embodiment. Refer to  FIGS. 7A and 7B  for a third embodiment of the diffusion plate of the invention. The diffusion plate  500  is made from polymers and has an emission surface  502  with a plurality of bar-type patterns  510  formed thereon. The patterns  510  have a first curve  512  and a triangle  514  protruding in opposite directions. Namely, the vertex angle θ of the triangle  514  is between 90 and 120 degrees. The patterns  510  have a vertical length H′ less than ½ of the width L′. Although the patterns  510  in the third embodiment protrude outwards, to those skilled in the art, they also can be formed by indenting inwards. 
   In the embodiments previously discussed, the patterns are formed at the same size. However, to those skilled in the art, they also can be formed in different sizes and laid in a staggered fashion. 
   Moreover, in the embodiments set forth above, the patterns of the diffusion plate are adjacent to one another. To those skilled in the art, they also may be spaced from one another at a selected distance. In the foregoing embodiments, while the vertical length H is less than ½ of the width, in practice, the vertical length H may also be greater than or equal to ½ of the width L. 
   While the preferred embodiments of the invention have been set forth for the purpose of disclosure, modifications of the disclosed embodiments of the invention as well as other embodiments thereof may occur to those skilled in the art. Accordingly, the appended claims are intended to cover all embodiments which do not depart from the spirit and scope of the invention.