Patent Publication Number: US-2007098998-A1

Title: Diffusion sheet and manufacturing method thereof

Description:
RELATED APPLICATIONS  
      This application is a Continuation patent application of co-pending application Ser. No. 10/863,490, filed on 9 Jun. 2004 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a diffusion sheet structure in the direct type backlight module with anti-UV rays function and its manufacturing method, which especially points at a diffusion sheet in the backlight module applied to TFT-LCD TV. This invention explores a diffusion sheet with a ultra-violet rays absorption layer avoid yellow and pyrolysis phenomenon and finally to improve product quality and materials lifespan.  
      2. Description of the Prior Art  
      Since TFT-LCD has been invented, all kinds of colour monitor have been widely applied in the daily life, such as notebook, PC monitor, colour mobile phone, PDA, and LCD TV etc., which have accordingly replaced conventional display such as CRT, TN and STN. An example of TFT-LCD TV, TFT-LCD TV being accordingly accepted by the consumers is because of liquid crystal panel producing technology improvement, such as short response time, high resolution, and higher yield of large panel. Besides, higher brightness of backlight module is also one of the main factors.  
      The larger size of TFT-LCD TV requires more, the higher brightness of one requires more. Normally the brightness of TFT-LCD TV requires 800-1200 Cd/m 2 , moreover, the uniform backlight module technology through light guide panel by the traditional edge light source can not satisfy the requirements of TFT-LCD TV. Therefore, high brightness of direct type backlight source is occurred.  
      In order to enhance the brightness of TFT-LCD TV, it is necessary to increase the quantity of CCFL (Cold Cathode Fluorescent Lamp) and the edge light source is changed into direct type light source, shown as  FIG. 1 , which is a schematic diagram of the prior art of direct type backlight module. As  FIG. 1  shown, said direct type backlight module  1 ′ comprises of a reflector  10 ′, plural light source  20 ′ and a diffusion sheet  30 ′. In order to avoid lamp mark, the light guide panel is required to be replaced by diffusion sheet to uniformly disperse the brightness of light source. The thickness of diffusion sheet is controlled in a range of 2 to 3 mm, the thickness of relative light guide panel is a range of 3 to 12 mm which having a large capability of reducing materials cost and to achieve the purpose of weight. The present diffusion sheet is mainly composed of PMMA (Polymethyl Methacrylate), MS (MMA/Styrene Copolymer), PC (Polycarbonate), and COC (Cycle Olefin Copolymer). and adding light diffusion particles in the transparent substrate to achieve uniform light.  
      The main strength of diffusion sheet in the composition of PMMA is well optical transmittance and yellow-resistance, however, the water absorption ratio of PMMA is in a range of 0.3 to 0.4% which resulted in a defect of warp and bad dimensional stability on the large TV. The light transmittance of MS and PC is small 2 to 3% than PMMA, but MS and PC has good performance on high temperature resistance and dimensional stability. The main defect is that MS and PC under irradiation of UV rays result in the problem of yellow. If the diffusion sheet in the composition of PC is long time irradiated under CCFL, then the problems of yellow will occur and result in colour temperature and chromatic aberration of panel. This problem is the main reason why diffusion sheet with PC materials cannot be extensively applied.  
      Therefore, providing a novel diffusion sheet structure in the direct type backlight module with anti-UV rays function and its manufacturing method for the aforesaid problems can not only improve the defects of yellow of the conventional diffusion sheet which resulted in deviation, but also can be simplified the process. Based on the inventor engaging on the research and develop and sales experiences for the related products for many years, the inventor finally proposes a method to improve the aforementioned problems for diffusion sheet structure in the direct type backlight module with anti-UV rays function and its manufacturing method, according to his professional background.  
     SUMMARY OF THE INVENTION  
      The primary purpose of the present invention is to provide a diffusion sheet structure in the direct type backlight module with anti-UV rays function and its manufacturing method, which using a ultra-violet rays absorption layer sets on a diffusion layer to achieve insulating ultra-violet rays directly irradiated on the diffusion and to avoid yellow and pyrolysis phenomenon occurred on the diffusion sheet. Furthermore, to avoid the deviation caused from color temperature and chromaticity coordinate of TFT-LCD TV because of yellow diffusion sheet, then to achieve the purpose of improving product quality and materials lifespan.  
      In order to perform the aforementioned purposes, efficiency and characteristics of each, the present invention explores that diffusion sheet structure in the direct type backlight module with anti-UV rays function and its manufacturing method, which is a diffusion sheet in the backlight module applied to TFT-LCD TV, and plural layer of the diffusion sheet made by a method of a multi-layer co-extruder. The present invention advocates that while producing diffusion sheet, at least a ultra-violet rays absorption layer set on the surface of diffusion sheet at the same time to achieve insulating ultra-violet rays directly irradiated on the diffusion sheet and to avoid yellow and pyrolysis phenomenon occurred on the diffusion sheet. These results in avoiding the deviation caused from color temperature and chromaticity coordinate of TFT-LCD TV because of yellow diffusion sheet, then to achieve the purpose of improving product quality and materials lifespan. For manufacturing technology, it is mainly using a co-extruder to produce multi-layer structure of diffusion sheet which is based on the diffusion sheet that a substrate adding a light diffusion materials, and in a range of 10 to 500 μm thickness of sheet is co-extruded at least on one side of diffusion sheet at the same time, then adding a transparent resin of UV rays absorbent to form at least one side of UV rays absorbent on said diffusion sheet, therefore, at least one side of anti-UV rays of diffusion sheet is formed. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       FIG. 1  is an illustrated diagram of the direct type backlight module of the prior art;  
       FIG. 2  is a schematic diagram of the preferred embodiment of the present invention;  
       FIG. 2A  is a schematic diagram of another preferred embodiment of the present invention;  
       FIG. 3  is flowchart of the preferred embodiment of the present invention; and  
       FIG. 4  is a graphic of the preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      In order to clearly express and explore the feature characteristics and efficiency of the present invention for the committee of patent, the preferred embodiment and detailed description is as below.  
      In order to improve the yellow problems of the prior art which is resulted from UV rays for diffusion sheet of direct type backlight module that applied to TFT-LCD TV, the present invention proposes that setting a transparent substrate with a UV rays absorbent on the surface of diffusion sheet, the thickness of UV rays absorption can be controlled in a range of 1 to 200 μm. The present invention also proposes a process of co-extrusion While diffusion sheet is extruded by the main extruder, the sub-extruder extrudes UV rays absorption layer at the same time at least on one side of said diffusion sheet to achieve the effect of insulating UV rays directly irradiating on diffusion sheet to avoid yellow problem.  
       FIG. 2  is a schematic diagram of the preferred embodiment of the present invention that explores diffusion sheet structure of the direct type backlight module applying to TFT-LCD TV. As shown in  FIG. 2 , the present invention explores a structure of diffusion sheet of the direct type backlight module with anti-UV rays function. Said diffusion sheet  10  comprises at least a UV rays absorption layer  100  and a diffusion sheet  110 , wherein said UV rays absorption layer  100  is located at least one side of said diffusion sheet  110 , wherein said UV rays absorption layer  100  is a UV rays  200  to insulate UV rays directly irradiating on said diffusion sheet  10  to avoid the problems of yellow and pyrolysis occurred on diffusion sheet.  
      Wherein said UV rays absorption layer  100  comprises a resin  102  which is selected from a transparent acrylic resin and a UV rays absorbent, the thickness of said UV rays absorption layer  100  is in a range of 10 to 200 μm. Said diffusion sheet  110  comprises pural light diffusion particles  112  which is selected from one of organic and inorganic materials, such as acrylic resin, Titanium Dioxide (TiO 2 ), Silicon Dioxide (SiO 2 ), and Silicon and its particle size is in a range of 1˜50 μm. And a substrate  114  which is selected from one of acrylic resin, PMMA (Polymethyl Methacrylate), MS (MMA Styrene Copolymer), PC (Polycarbonate) and Cyclo Olefin Copolymer (COC).  
      Moreover,  FIG. 2A  is a schematic diagram of another preferred embodiment of the present invention that explores diffusion sheet structure. As shown in  FIG. 2 , the present invention explores that said diffusion sheet  10 , wherein said UV rays absorption layer  110  can be located on the top and bottom of said diffusion sheet  120 .  
       FIG. 3  is flowchart of the preferred embodiment of the present invention that explores a manufacturing process of diffusion sheet. As shown in  FIG. 3 , the present invention explores that a method of manufacturing diffusion sheet in the direct type backlight module with anti-UV rays comprising the steps of: 
      Step S 110 : extruding a diffusion layer by adding a plurality of light diffusion particles into a substrate and using a first extruder;     Step S 120 : extruding a ultra-violet rays absorption layer by adding a ultra-violet rays absorbent into a resin and using a second extruder;     Step S 130 : taking said ultra-violet rays absorption layer to touch at least one surface of said diffusion layer by a multi-layer T-die;     Step S 140 : co-extruding said diffusion layer and said ultra-violet rays absorption layer to form a plate structure of light diffusion sheet with anti-yellow and well dimensional stability.    
      Among step  110 , the content of said light diffusion particles is 10 percent of said substrate. Among step  120 , the increment of said UV rays absorbent is 1 to 5% of said resin.  
      Finally,  FIG. 4  is a graphic of the preferred embodiment of the present invention that explores diffusion sheet. As shown in  FIG. 4 , the present invention explores that steps of a diffusion sheet and its manufacturing method. Firstly, it is mainly using the first extruder  40  adding 10 percent of PMMA light diffusion particles  20  of PC resin  30  to extrude a diffusion sheet  50 . Secondly, it is using the second extruder  80  adding 1 to 5% of UV rays absorbent  60  of transparent resin layer  70  to extrude a UV rays absorption layer  90 . Thirdly, said UV rays absorption layer  90  is adhered on the top and bottom of diffusion layer  50  through multi-layer T-die  95 . Finally, said PC diffusion layer  50  and at least a UV rays absorption layer  90  co-extrude a diffusion sheet  98  with plate structure of yellow-resistance and well dimensional stability.  
      Therefore, the present invention is related to a diffusion sheet and its manufacturing method which a diffusion sheet of backlight module applied to TFT-LCD TV that using a method of multi-layer co-extrusion molding technology produces plural layer diffusion sheet. The present invention is that while producing diffusion sheet of direct type backlight module of TFT-LCD TV, at least a ultra-violet rays absorption layer set on the surface of diffusion sheet at the same time to achieve insulating ultra-violet rays directly irradiated on the diffusion and to avoid yellow and pyrolysis phenomenon occurred on the diffusion sheet. These results in avoiding the deviation caused from color temperature and chromaticity coordinate of TFT-LCD TV because of yellow diffusion sheet, then to achieve the purpose of improving product quality and materials lifespan.  
      While certain preferred embodiments of the present invention have been disclosed in detail, it is to be understood that various modifications may be adopted without departing from the spirit of the invention or scope of the following claims.