Patent Publication Number: US-2011051248-A1

Title: Hybrid Optical Film

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention generally relates to a hybrid optical film. More particularly, this invention relates to a hybrid optical film for a backlight module of a liquid crystal display. 
     2. Description of the Prior Art 
     Recently, liquid crystal displays are widely used in many display devices such as televisions, computers, laptops, monitors, cell phones, digital cameras, etc. 
     Since liquid crystal does not emit light itself, a backlight module is needed to provide light. Therefore, a backlight module having a uniform light and sufficient brightness is pursued. 
     As shown in  FIG. 1A , a conventional backlight module  90  includes a combination of optical films  80  and a light source module  700 . The light source module  700  includes a light source  710 , a light guide plate  730 , a reflector  750  and a shell  770 . The combination of optical films  80  includes a diffusion film  81  and a brightness enhancement film  82  for increasing the uniformity of the light distribution and the brightness of the backlight module  90 . As shown in  FIG. 1B , the diffusion film  81  generally includes a base layer  400  having a plurality of diffusion structures  310  disposed on its surface for enhancing the uniformity of the light distribution of the backlight module. The brightness enhancement film  82  is also called a prism sheet, wherein prism structures  500  are formed on the surface of the base layer  400 . By means of the prism structures  500 , light can be used and recycled in a more efficient way to increase the brightness of the backlight module. 
     Regarding to the conventional backlight module  90 , though the uniformity of the light distribution and the brightness are respectively increased by the diffusion film  81  and the brightness enhancement film  82 , the backlight module  90  demands larger space and requires a complicated assembly process because the diffusion film  81  and the brightness enhancement film  82  are individually disposed. Therefore, replacing the diffusion film  81  and the brightness enhancement film  82  with one single optical film is proposed. As shown in  FIG. 1C , a plurality of diffusion structures  310  and prism structures  500  are respectively disposed on opposite faces of the base layer  400 . The plurality of diffusion structures  310  are embossed toward the light source module  700 . Although this design simplifies the assembly process, the brightness of the backlight module  90  is decreased because the refractive index of the diffusion structures  310  is smaller than the refractive index of the base layer  400  and the diffusion structures  310  are embossed toward the light source module  700 . Therefore, it is necessary for the optical film having the diffusion structures  310  and the prism structures  500  to be improved. 
     SUMMARY 
     It is an object of the present invention to provide a hybrid optical film for enhancing the brightness of a backlight module. 
     It is another object of the present invention to provide a hybrid optical film for simplifying the manufacturing process of a backlight module. 
     The hybrid optical film includes a first layer, a second layer, and a plurality of diffusion structures. The hybrid optical film further includes a base layer, wherein the second layer is disposed on the base layer. The base layer is preferably made of polyethylene terephthalate. The hybrid optical film further includes a prism structure layer disposed on a face of the base layer opposite to the second layer. 
     The first layer has a light entering face and a first refractive index. The second layer has a second refractive index and is disposed on a face of the first layer opposite to the light entering face, wherein the second refractive index is lower than the first refractive index. The plurality of diffusion structures are disposed on the interface of the first layer and the second layer. The diffusion structure has a third refractive index, wherein the third refractive index is between the first refractive index and the second refractive index and is selectively equal to the first refractive index and the second refractive index. 
     The plurality of diffusion structures are spheres, wherein the lower parts of the spheres are embedded into the first layer, the upper parts of the spheres are embedded into the second layer, the third refractive index is smaller than the first refractive index and is larger than the second refractive index. The diameter of the sphere is between 50 μm and 80 μm. The plurality of diffusion structures are embossed hemispheres embedded into the second layer, wherein the third refractive index is equal to the first refractive index. The diameter of the hemisphere is between 50 μm and 80 μm. The plurality of diffusion structures are embossed hemispheres embedded into the first layer, wherein the third refractive index is equal to the second refractive index. The diameter of the hemisphere is between 50 μm and 80 μm. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded view of a conventional backlight module; 
         FIG. 1B  is a cross-sectional view of a conventional backlight module; 
         FIG. 1C  is a cross-sectional view of another conventional backlight module; 
         FIG. 2  is a schematic view of a preferred embodiment of the present invention; and 
         FIGS. 3-5  are schematic views showing different embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The hybrid optical film of the present invention is for use with a backlight module. In an embodiment shown in  FIG. 2 , a hybrid optical film  800  and a light source module  700  form a backlight module  900 . The light source module  700  can include a light source, a light guide plate, a reflector, and a shell. The light source is preferably a light emitting diode. In other embodiments, however, the light source can be other types of light emitting device such as a cold cathode fluorescent lamp. In other embodiments, the light guide plate can be omitted. 
     As shown in  FIG. 2 , the hybrid optical film  800  includes a first layer  100 , a second layer  200 , and a plurality of diffusion structures  310 . The first layer  100  has a light entering face  101  and a first refractive index. The second layer  200  has a second refractive index and is disposed on a face of the first layer  100  opposite to the light entering face  101 , wherein the second refractive index is lower than the first refractive index. More particularly, the second layer  200  and the first layer  100  are disposed on the light source module  700  from the top to the bottom, wherein the light entering face  101  of the first layer  100  faces the light source module  700 . 
     The plurality of diffusion structures  310  are disposed on the interface of the first layer  100  and the second layer  200 . More particularly, a partial surface of the diffusion structure  310  is connected to the first layer  100 , while the other partial surface of the diffusion structure  310  is connected to the second layer  200 . The plurality of diffusion structures  310  are distributed between the first layer  100  and the second layer  200  and form a diffusion layer  300 . The diffusion structure  310  has a third refractive index which is between the first refractive index and the second refractive index and is selectively equal to the first refractive index or the second refractive index. Because the diffusion structure  310  can refract the light emitted by the light source module  700 , the hybrid optical film  800  of the present invention can increase the uniformity of the light distribution of the backlight module  900  by having the plurality of diffusion structures. 
     In an embodiment, the hybrid optical film  800  further includes a base layer  400 , wherein the second layer  200  is disposed on the base layer  400 . The base layer  400  can be selected from a group consisting of polyethylene terephthalate (PET), poly-methyl methacrylate (PMMA), poly-carbonate (PC), poly-styrene (PS), and a combination thereof as well as a transparent material such as glass. More particularly, the base layer  400  can be used as a base substrate for the second layer  200  to attach thereon. In an embodiment, the plurality of diffusion structures  310  are mixed with the raw material of the second layer  200  in advance and then spread on the base layer  400  by brushing, scrapping, spin coating, spraying, and etc. After the second layer  200  is formed, the first layer  100  is spread on the second layer  200  by brushing, scrapping, spin coating, spraying, etc. In other embodiments, however, the manufacturing method and the steps can be modified in accordance with the actual requirements. 
     The hybrid optical film  800  further includes a prism structure layer  500  disposed on a face of the base layer  400  opposite to the second layer  200 . The function of the prism structure layer  500  is to increase the light efficiency, wherein the angle, the size, the distribution, and the structure of the prism structures can be modified in accordance with the actual requirements. More specifically, comparing with the diffusion layer  81  and the brightness enhancement film  82  shown in  FIG. 1B  which are individually disposed as the conventional combination of optical films  80 , the hybrid optical film  800  of the present invention simultaneously includes the prism structure layer  500  and the diffusion layer  300  formed by the plurality of diffusion structures  310 . In other words, the diffusion layer  81  and the brightness enhancement film  82  in the prior art can be replaced by one hybrid optical film  800  of the present invention to simplify the manufacturing process of the backlight module  900 . Moreover, because the third refractive index of the diffusion structure  310  is between the first refractive index and the second refractive index and is selectively equal to the first refractive index or the second refractive index, that means that the light emitted by the light source module  700  sequentially passes through the first layer  100 , the diffusion layer  300 , and the second layer  200  with decreasing refractive index, the light can maintain concentrated when passing through the diffusion layer  300  and the brightness of the backlight module  900  will not be significantly degraded. Therefore, the hybrid optical film  800  can enhance the brightness of the backlight module  900  by means of the prism structure layer  500 , and the brightness enhancement effect is not diminished due to the disposition of the diffusion structures  310   
     The configuration of the diffusion structure  310  is further described below. As the embodiment shown in  FIG. 2 , the plurality of diffusion structures  310  are spheres, wherein the lower parts of the spheres are embedded into the first layer  100 , while the upper parts of the spheres are embedded into the second layer  200 . In this case, the third refractive index is preferably smaller than the first refractive index and is larger than the second refractive index. That is, the lower hemispheres of the spheres are preferably embedded into the first layer  100 , and the upper hemispheres of the spheres are embedded into the second layer  200 . The diameter of the sphere is preferably between 50 μm and 80 μm. In an embodiment, the plurality of diffusion structures  310  are mixed with the raw material of the second layer  200  in advance and are then spread on the base layer  400  by brushing, scrapping, spin coating, spraying, and etc. After the second layer  200  is formed, the first layer  100  is spread on the second layer  200  by brushing, scrapping, spin coating, spraying, and etc. In other embodiments, however, the manufacturing method and the steps can be modified in accordance with the actual requirements. 
     In a different embodiment shown in  FIG. 3 , the plurality of diffusion structures  310  are embossed hemispheres, which are embedded into the second layer  200 . In this case, the third refractive index of the diffusion structure  310  is preferably equal to the first refractive index of the first layer  100 . The diameter of the hemisphere is preferably between 50 μm and 80 μm. More particularly, the plurality of diffusion structures  310  and the first layer  100  can be integrally formed into a single piece, wherein the plurality of diffusion structures  310  are embossed hemispheres and embedded into the second layer  200  from the first layer  100 . Besides, the plurality of diffusion structures  310  can be embossed hemispheres attached on the surface of the first layer  100  by scrapping, spraying, printing, and etc. after the first layer  100  is formed and are embedded into the second layer  200 . In addition, a plurality of hemisphere cavities can be formed on the second layer  200  in advance, then the raw material of the first layer  100  is spread on the second layer  200  by brushing, scrapping, spin coating, spraying, and etc. Therefore, the diffusion structures  310  are spontaneously formed as hemispheres in the plurality of hemisphere cavities on the second layer  200 . In other embodiments, however, the manufacturing method and the steps can be modified in accordance with the actual requirements. 
     In a different embodiment shown in  FIG. 4 , the plurality of diffusion structures  310  are embossed hemispheres which are embedded into the first layer  100 . In this case, the third refractive index of the diffusion structure  310  is equal to the second refractive index of the second layer  200 . The diameter of the hemisphere is preferably between 50 μm and 80 μm. More particularly, the plurality of diffusion structures  310  and the second layer  200  can be integrally formed into a single piece, wherein the plurality of diffusion structures  310  are embossed hemispheres and embedded into the first layer  100  from the second layer  200 . Besides, the plurality of diffusion structures  310  can be embossed hemispheres attached on the surface of the second layer  200  by scrapping, spraying, printing, and etc. after the second layer  200  is formed and are embedded into the first layer  100 . In addition, a plurality of hemisphere cavities can be formed on the first layer  100  in advance, then the raw material of the second layer  200  is spread on the first layer  100  by brushing, scrapping, spin coating, spraying, and etc, wherein the diffusion structures  310  are spontaneously formed as hemispheres in the plurality of hemisphere cavities on the first layer  100 . In other embodiments, however, the manufacturing method and the steps can be modified in accordance with the actual requirements. 
     In a different embodiment shown in  FIG. 5 , the hybrid optical film  800  of the present invention includes a base layer  400 , a first layer  100 , and a diffusion layer  300 . The first layer  100  has a first refractive index and is disposed on the bottom side of the base layer  400 . The diffusion layer  300  consists of a plurality of hemispheres acting as diffusion structures  310  disposed on the interface of the first layer  100  and the base layer  400 , wherein the hemisphere has a second refractive index smaller than the first refractive index, and the hemispheres are embossed and embedded into the first layer  100 . The diameter of the hemisphere is preferably between 50 μm and 80 μm. More particularly, the plurality of diffusion structures  310  and the base layer  400  can be integrally formed into a single piece using the same or different materials, wherein the plurality of diffusion structures  310  are embossed hemispheres and embedded into the first layer  100  from the base layer  400 . Besides, the plurality of diffusion structures  310  can be embossed hemispheres attached on the surface of the base layer  400  by scrapping, spraying, printing, and etc. after the base layer  400  is formed and are embedded into the first layer  100 . In addition, a plurality of hemisphere cavities can be formed on the first layer  100  in advance, then the raw material of the diffusion structures  310  is spread on the first layer  100  by brushing, scrapping, spin coating, spraying, and etc. Therefore, the diffusion structures  310  are spontaneously formed as hemispheres in the plurality of hemisphere cavities on the first layer  100 . In other words, the embodiment shown in  FIG. 5  is similar to the embodiment shown in  FIG. 4  but without the second layer  200 . Therefore, the thickness of the hybrid optical film  800  can be further decreased. 
     Although the preferred embodiments of the present invention have been described herein, the above description is merely illustrative. Further modification of the invention herein disclosed will occur to those skilled in the respective arts and all such modifications are deemed to be within the scope of the invention as defined by the appended claims.