Patent Publication Number: US-2007100092-A1

Title: High optical-performance resin compound

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a resin compound, particularly to a high optical-performance resin compound.  
      2. Description of the Related Art  
      At present, enhancing the light-emitting efficiency of LED is primarily via promoting the external quantum efficiency thereof, and the promotion of LED external quantum efficiency depends on the promotion of the internal quantum efficiency and light extraction efficiency thereof.  
      Light extraction efficiency refers to the photon number physically measured outside a light-emitting element after photons are created, absorbed, refracted, and reflected inside the light-emitting element. Owing to internal absorption, uneven current distribution, critical angle-induced loss, the outward-emitted light is only 4% of the light created by the light-emitting layer. In other words, much as the internal quantum efficiency of LED may be very high, the light that can be really received outside is still pretty little. Besides, the light color conversion loss of fluorescent material further reduces the light-emitting efficiency of LED.  
      At present, the methods of promoting the light extraction efficiency of LED can be divided into two technical domains; one is to utilize various fabrication technologies and chip designs to improve the light-emitting efficiency of LED, which primarily apply to the early-stage quadruple LED, and the focus thereof is to break through the limitation of critical angels; and the other one is to utilize improved packaging materials and packaging designs to promote the light-emitting efficiency of LED, including: high conversion efficiency fluorescent materials, high refractivity and high thermal conductivity packaging materials, improved optical designs of the packaging structures, and technologies of improving the evenness of fluorescent material coating. However, owing to the rectangular appearance of the conventional LED and the large difference between the refractive indices of LED and the packaging epoxy resin, most of the light created inside the LED chip can only be totally reflected inside the chip and can hardly be guided outward from the interior of the chip. Currently, the light-emitting efficiency of LED is improved via modifying the shape of the LED chips; however, the problem of total reflection still remains unsolved. Therefore, developing a packaging resin, which can enhance the light-emitting efficiency, is eagerly anticipated by the industry.  
      Accordingly, the present invention proposes a high optical-performance resin compound to overcome the problems of the conventional LED packaging resin.  
     SUMMARY OF THE INVENTION  
      The primary objective of the present invention is to provide a high optical-performance resin compound, wherein at least one kind of functional groups selected from the class consisting of sulfur atom, benzene ring and poly-benzene ring is added to the constituent of the resin, so that the resin not only has a high refractivity but also has a superior thermal stability.  
      The high optical-performance resin compound of the present invention comprises a resin material with the average molecular weight of 45˜25000, and 1˜120 portions (by weight) of a hardening agent is added to 100 portions (by weight) of the resin material; the backbone of the resin material or the hardening agent has at least one kind of functional groups selected from the class consisting of sulfur atom, benzene ring and poly-benzene ring.  
      To enable the objectives, technical contents, characteristics, and accomplishments of the present invention to be more easily understood, the embodiments of the present invention are to be described below in detail in cooperation with the attached drawings. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      The high optical-performance resin compound of the present invention utilizes a resin material and a hardening agent as the raw materials, and a functional group, which can enhance light-emitting efficiency, is added to one of them or both of them; the high optical-performance resin compound of the present invention is installed onto a light-emitting element via enveloping or printing in order to protect the light-emitting element and enhance the light-emitting efficiency thereof, wherein the light-emitting element may be a LED.  
      The high optical-performance resin compound of the present invention comprises a light-permeable resin material with the average molecular weight of 45˜25000, and 1˜120 portions (by weight) of a hardening agent is added to 100 portions (by weight) of the resin material, and the resin material reacts with the hardening agent at the temperature raging from 50 to 250° C. to obtain a thermosetting resin compound, wherein the backbone of the resin material or the hardening agent has at least one kind of functional groups selected from the class consisting of sulfur atom, benzene ring and poly-benzene ring.  
      The resin material may be the monomer of the epoxy resin having poly(bi)-thioether, or the prepolymer of the monomer of the epoxy resin having poly(bi)-thioether, or the derivative of the monomer of the epoxy resin having poly(bi)-thioethe, and the monomer of the epoxy resin with bi-thioether (EEW=216 g/eq.) is preferred.  
      The hardening agent may be selected from the following agent A, agent B and the combination of them: 
          A. MHHPA (Methylhexahydrophtalic anhydride) or MHHPA having substituents,     B. Polythiol, such as bi-thiol.        

      Further, a thermal stabilizing agent and an activator may also be added to the resin material; the thermal stabilizing agent can avoid the deterioration of the resin material during the curing process, and the activator can accelerate the reaction between the resin material and the hardening agent. The thermal stabilizing agent may be a phosphite-type one, and the activator may be an ammonium salt-type one.  
      After the description of the constituents of the high optical-performance resin compound of the present invention, the present invention is to be exemplified below with a specific formula so that the persons skilled in the art can understand, make and use the present invention according to the embodiments.  
      The efficacy of the present invention is demonstrated with a control experiment, and the constituents of the resin material of the control group (of the conventional technology) are shown in Table. 1.  
                           TABLE 1                                   Constituent   Weight (g)                                                        Resin material of   Epoxy resin   100           the control group   Hardening agent (MHHPA)   97               Ammonium salt activator   2               Phosphite thermal stabilizing   1               agent                      
 
      The constituents of the thermosetting resin compound of the present invention are shown in Table.2.  
                           TABLE 2                                   Constituent   Weight (g)                                                Resin compound of   Monomer of the epoxy resin with   100       the present invention   bi-thioether           Bi-thiol   30           Epoxy resin   20           Hardening agent (MHHPA)   16           Ammonium-salt activator   4           Phosphite thermal stabilizing   3           agent                  
 
      The resin material of the control group and the resin compound of the present invention are cast onto the LED semi-products to envelop LED chips according to the standard process of the LED packaging factory, and then the semi-products enveloped with the resin material of the control group and the resin compound of the present invention are cured at 160° C.  
      Next, the orthogonal-direction brightness of the cured LED products is measured with a brightness-test equipment, and the result is shown in Table.3.  
                       TABLE 3                           Resin compound of the   Resin material of the           present invention   control group       Test number   (m candela)   (m candela)                                            1   1147   667.1       2   903.7   728.0       3   882.9   759.6       4   1142.2   566.4       5   862.6   839.4       6   817.4   610.6       7   879.9   509.3       Average brightness   947.9   668.6                  
 
      It can be seen that the average brightness of the resin compound of the present invention is 41.78% higher than that of the resin material of the control group ((947.9−668.6)/668.6=41.78%).  
      In the present invention, at least one kind of functional groups selected from the class consisting of sulfur atom, benzene ring and poly-benzene ring is added to the constituents of the resin compound, so that the high optical-performance resin compound of the present invention not only has a high refractivity but also has a superior thermal stability. Therefore, the present invention can effectively overcome the problems of the conventional technologies.  
      Those embodiments described above are to clarify the present invention to enable the persons skilled in the art to understand, make and use the present invention; however, it is not intended to limit the scope of the present invention, and any equivalent modification and variation according to the spirit of the present invention is to be included within the scope of the claims of the present invention stated below.