Patent Publication Number: US-2006001041-A1

Title: Organic light emitting device

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      This invention relates to an organic light emitting device, more particularly to an organic light emitting device with at least one moisture absorbent around a light transmittable region of a cover.  
      2. Description of the Related Art  
       FIG. 1  illustrates a conventional organic light emitting device that includes a substrate  21 , an array of organic light emitting diodes (OLED)  22  mounted on the substrate  21 , and a cover  24  that covers sealingly the OLEDs  22  through a sealing band  23  so as to define a closed space  20  thereamong and so as to prevent oxygen and moisture from entering into the closed space  20 . A moisture absorbent  25  is disposed securely in a recess  241  in the cover  24 , which spans an area aligned with and covering the array of the OLEDs  22 , for absorbing moisture in the closed space  20  so as to prevent damage to the OLEDs  20  as a result of the presence of moisture in the closed space  20 .  
      Formation of the recess  241  in the cover  24  is normally conducted by sand blasting techniques or etching techniques. As a consequence, the transmittance of the cover  24  at the area where the recess  241  is formed is significantly decreased. Moreover, since the moisture absorbent  25  confronts the array of the OLEDs  22 , a portion of the light emitted by the OLEDs  22  is undesirably reflected by the moisture absorbent  25 .  
     SUMMARY OF THE INVENTION  
      The object of the present invention is to provide an organic light emitting device that is capable of overcoming the aforesaid drawbacks associated with the prior art.  
      According to this invention, an organic light emitting device comprises: a substrate having a diode-mounting region and a surrounding region around the diode-mounting region; an array of organic light emitting diodes mounted on the diode-mounting region of the substrate; a cover disposed over the organic light emitting diodes and having a light transmittable region corresponding to and confronting the diode-mounting region of the substrate, and an encompassing region around the light transmittable region and corresponding to and confronting the surrounding region of the substrate; an outer sealing band surrounding the organic light emitting diodes and connected sealingly to the encompassing region of the cover and the surrounding region of the substrate so as to cooperate with the substrate and the cover to define a closed space thereamong and so as to seal the organic light emitting diodes in the closed space; and an outer moisture absorbent disposed between the array of the organic light emitting diodes and the outer sealing band within the closed space for absorbing moisture in the closed space. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiments of the invention, with reference to the accompanying drawings, in which:  
       FIG. 1  is a schematic sectional view of a conventional organic light emitting device;  
       FIG. 2  is a schematic sectional view of the first preferred embodiment of an organic light emitting device according to this invention;  
       FIG. 3  is a schematic sectional view taken along lines III-III in  FIG. 2 ;  
       FIG. 4  is a schematic sectional view of the second preferred embodiment of the organic light emitting device according to this invention;  
       FIG. 5  is a schematic sectional view taken along lines V-V in  FIG. 4 ;  
       FIG. 6  is a schematic sectional view of the third preferred embodiment of this invention;  
       FIG. 7  is a schematic sectional view of the fourth preferred embodiment of the organic light emitting device according to this invention; and  
       FIG. 8  is a schematic sectional view taken along lines VIII-VIII in  FIG. 7 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Before the present invention is described in greater detail, it should be noted that same reference numerals have been used to denote like elements throughout the specification.  
       FIGS. 2 and 3  illustrate the first preferred embodiment of an organic light emitting device according to the present invention.  
      The organic light emitting device includes: a substrate  3  having a diode-mounting region  31  and a surrounding region  32  around the diode-mounting region  31 ; an array  4  of organic light emitting diodes  41  mounted on the diode-mounting region  31  of the substrate  3 ; a cover  6  disposed over the organic light emitting diodes  41  and having a light transmittable region  61  corresponding to and confronting the diode-mounting region  31  of the substrate  3 , and an encompassing region  62  around the light transmittable region  61  and corresponding to and confronting the surrounding region  32  of the substrate  3 ; an outer sealing band  51  surrounding the organic light emitting diodes  41  and connected sealingly to the encompassing region  62  of the cover  6  and the surrounding region  32  of the substrate  3  so as to cooperate with the substrate  3  and the cover  6  to define a closed space  8  thereamong and so as to seal the organic light emitting diodes  41  in the closed space  8 ; and an outer moisture absorbent  71  disposed between the array  4  of the organic light emitting diodes  41  and the outer sealing band  51  within the closed space  8  for absorbing moisture in the closed space  8 .  
      In this embodiment, the encompassing region  62  of the cover  6  is formed with an outer retaining groove  63  that surrounds the light transmittable region  61  of the cover  6 . The outer moisture absorbent  71  is mounted securely in and extends along the outer retaining groove  63 .  
       FIGS. 4 and 5  illustrate the second preferred embodiment of the organic light emitting device according to this invention. The organic light emitting device of this embodiment differs from the previous embodiment in that it further includes an inner sealing band  52  that surrounds the organic light emitting diodes  41 , that is disposed between the outer moisture absorbent  71  and the array  4  of the organic light emitting diodes  41 , and that is connected sealingly to the encompassing region  62  of the cover  6  and the surrounding region  32  of the substrate  3  so as to enhance the sealing effect of the closed space  8 .  
       FIG. 6  illustrate the third preferred embodiment of the organic light emitting device according to this invention. The organic light emitting device of this embodiment differs from the second preferred embodiment in that the inner sealing band  52  cooperates with the outer moisture absorbent  71  to define a first space  81  therebetween, cooperates with the array  4  of the organic light emitting diodes  41  to define a second space  82  therebetween, and is formed with a plurality of passages  521  in fluid communication with the first and second spaces  81 ,  82 .  
       FIGS. 7 and 8  illustrate the fourth preferred embodiment of the organic light emitting device according to this invention. The organic light emitting device of this embodiment differs from the second preferred embodiment in that the encompassing region  62  of the cover  6  is further formed with an inner retaining groove  64  surrounding the light transmittable region  61  of the cover  6  and disposed between the inner sealing band  52  and the array  4  of the organic light emitting diodes  41 . An inner moisture absorbent  72  is mounted securely in and extends along the inner retaining groove  64  in the cover  6  so as to enhance the absorbing of moisture in the closed space  8 .  
      Preferably, the inner and outer moisture absorbents  72 ,  71  are made from a material selected from the group consisting of CaO, BaO, CaCl 2 , CaH 2 , NaH, CaSO 4 , CaCO 3 , MgSO 4 , Na 2 SO 4 , Ca 2 SO 4 , and SrO.  
      Preferably, the cover  6  and the substrate  3  are made from a transparent material selected from the group consisting of glass and plastics.  
      Preferably, the inner and outer sealing bands  52 ,  51  are made from epoxy resin.  
      By positioning the outer moisture absorbent  71  at a position offset from the array  4  of the organic light emitting diodes  41 , the aforesaid drawbacks associated with the prior art can be eliminated.  
      While the present invention has been described in connection with what is considered the most practical and preferred embodiments, it is understood that this invention is not limited to the disclosed embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretations and equivalent arrangements.