Abstract:
An electronic device includes a first substrate made of thin plastic sheet; a second substrate made of thin plastic sheet opposing the first substrate; a chamber formed between portions of the first and second substrates; and a sealing structure configured to seal the chamber at the interface between the first and second substrates, wherein the sealing structure surrounds the chamber and comprises a recess formed in one of the substrates and a protrusion formed on the other of the substrates, the protrusion engaging the recess.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This non-provisional patent application claims priority under 35 U.S.C. §119(a) from Patent Application No. 200910104842.0 filed in The People&#39;s Republic of China on Jan. 7, 2009. 
       FIELD OF THE INVENTION 
       [0002]    This invention relates to an electronic device and in particular, to a sealing structure of an electrophoretic display. 
       BACKGROUND OF THE INVENTION 
       [0003]    An electrophoretic display (EPD) is a non-emissive device based on the electrophoresis phenomenon of charged pigment particles suspended in a dielectric solvent. The display usually comprises two substrates with electrodes placed opposing each other and separated by spacers. An electrophoretic fluid composed of a colored solvent with charged pigment particles dispersed therein is enclosed between the two electrodes. One of the electrodes on the viewing side is usually transparent. When a voltage difference is applied across the two electrodes, the pigment particles migrate to one side causing either the color of the pigment particles or the color of the solvent to be seen from the viewing side. 
         [0004]    Known displays use an intermediate adhesive layer disposed between peripheries of the two substrates for sealing the electrophoretic fluid chambers. However, the adhesive layer is subject to aging and hardens losing its flexibility and may peel off from the substrates after being used for a long period, especially when used in environment with high temperature or subject to direct sunlight. 
       SUMMARY OF THE INVENTION 
       [0005]    Hence there is a desire for an improved EPD which can solve the above mentioned problem. 
         [0006]    Accordingly, in one aspect thereof, the present invention provides an electronic device comprising: a first substrate made of thin plastic sheet; a second substrate made of thin plastic sheet opposing the first substrate; a sealed chamber formed between portions of the first and second substrates; and a sealing structure configured to seal the chamber being formed at the interface between the first and second substrates, wherein the sealing structure surrounds the chamber and comprises a recess formed in one of the substrates and a protrusion formed on the other of the substrates, the protrusion being engaged in the recess. 
         [0007]    Preferably, the electronic device further comprises two opposing electrodes attached to inner surfaces of the first and second substrates respectively, the chamber being formed between the two electrodes. 
         [0008]    Preferably, the electronic device is an electrophoretic display, a plurality of microcapsules is received in the chamber and sandwiched between the electrodes, one of the substrates and a corresponding electrode attached thereon being made of transparent material. 
         [0009]    Preferably, the microcapsules are bonded to each other by a binder. 
         [0010]    Preferably, each of the microcapsules contains a dispersion comprising electrophoretic particles dispersed in a dispersion medium. 
         [0011]    Preferably, the protrusion comprises a rib, and the recess comprises a groove. 
         [0012]    Preferably, the rib and groove both have continuous configurations to thereby completely surround the chamber. 
         [0013]    Preferably, the rib is comprised of discontinuous sections, gaps between the sections are sealed with adhesive layer. 
         [0014]    Preferably, the sealing structure further comprises an adhesive layer spread at the interface. 
         [0015]    Preferably, there are at least one additional spaced sealing structure arranged in the radial direction of the chamber to thereby provide multiple seals for the chamber. 
         [0016]    Preferably, the protrusion comprises a plurality of bumps and the recess comprises a plurality of cavities. 
         [0017]    Preferably, the protrusion is a press fit in the recess. 
         [0018]    Preferably, the protrusion is secured in the recess by ultrasonic welding. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    A preferred embodiment of the invention will now be described, by way of example only, with reference to the single figure of the accompanying drawings, in which: 
           [0020]      FIG. 1  is a cross sectional view of an electrophoretic display in accordance with the preferred embodiment of the present invention. 
           [0021]    Dimensions of components and features shown in the figure are generally chosen for convenience and clarity of presentation and are not necessarily shown to scale. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]    The technical problem to be solved, the technical solution and the beneficial effects of the present invention are best understood from the following detailed description with reference to the accompanying figure and embodiments. It is to be understood that, the specific embodiments described here are merely examples to explain the invention and are not intended to limit the present invention. 
         [0023]    Referring to  FIG. 1 , an electrophoretic display  10  according to the preferred embodiment of the present invention comprises a first substrate  20 , a second substrate  30  opposing the first substrate  20 , and a display unit  40  disposed between the first and second substrates  20 ,  30 . The first and second substrates  20 ,  30  may be made of thin plastic sheet. 
         [0024]    The first substrate  20  is located close the viewing side and therefore made of transparent material. Preferably, the first substrate  20  is made of PET, PEN, PES, PC, or PE etc. A portion of the first substrate  20  corresponding to the display unit  40  is spaced from the second substrate  30  to thereby form a chamber therebetween. The display unit  40  is disposed in the chamber. The second substrate  30  may be made of transparent material or nontransparent material. Thus, in addition to PET, PEN, PES, PC, or PE, the second substrate  30  may be made of PI, PVC, PS or PP etc. 
         [0025]    At least one sealing structure is formed at the interface of the first and second substrates  20 ,  30 , surrounding the display unit  40 . The sealing structure surrounds the chamber and comprises a recess formed at one of the substrates and a protrusion formed from the other of the substrates, the protrusion is secured in the recess. As shown in  FIG. 1 , the sealing structure may comprise a groove  32  formed in a surface of the second substrate  30  facing the first substrate  20 , a rib  22  formed on a surface of the first substrate  20  facing the second substrate  30 . The rib  22  is secured in the groove  32 , to thereby form the sealing structure. 
         [0026]    A method to form the sealing structure will now be described in detail. A rib  22  is formed at the periphery of a surface of the first substrate  20  facing the second substrate  30  by punching, pressing, rolling or other ways. The periphery of the first substrate  20  is engaged with the periphery of the second substrate  30  using a hot press. The periphery of the second substrate  30  corresponding to the rib  22  of the first substrate is deformed to form a groove  32 . The rib  22  is pressed into the groove  32 . 
         [0027]    Alternatively, both the rib  22  and the groove  32  may be pre-formed before engagement. In another method the rib and groove may be formed together at the same time in a single step, whereby when the first substrate is overlaying the second substrate, a ridge is pressed from one substrate into the other to form the groove and to join the two substrates together. Additional mechanical connection means may be used to fix the rib  22  in the groove  32 . For example, ultrasonic welding may be used to fix the rib  22  in the groove  32 . 
         [0028]    Alternatively, the positions of the rib  22  and groove  32  may be exchanged. 
         [0029]    Preferably, an additional adhesive layer may be disposed at the interface between the first and second substrates  20 ,  30  before the rib  22  is fixed in the groove  32 . 
         [0030]    The rib  22  and groove  32  may have a continuous ring configuration, completely surrounding the display unit  40 . Alternatively, the rib  22  and groove  32  may be composed of several discontinuous sections, mostly but not completely surrounding the display unit  40 . An adhesive layer may be used to seal any gaps between adjacent sections. 
         [0031]    The protrusion  22  of the sealing structure is not limited to a rib. For example, the protrusion  22  may comprises a plurality of discrete bumps, and the recess  32  may comprise a plurality of discrete holes or cavities corresponding to the bumps. 
         [0032]    The display unit  40  comprises a first electrode  42  disposed at the inner surface of the first substrate  20 , a second electrode  44  disposed at the inner surface of the second substrate  30 , and an electrophoretic layer  46  disposed between the first and second electrodes  42 ,  44 . 
         [0033]    The electrodes  42 ,  44  may be made of ITO (Indium-Tin Oxide). The first electrode  42  is made of transparent material. 
         [0034]    The electrophoretic layer  46  comprises a plurality of microcapsules. The microcapsules are sandwiched between the electrodes  42 ,  44  and bonded to each other by a binder. In each of the microcapsules is sealed a dispersion comprising electrophoretic particles dispersed in a dispersion medium in advance by a micro capsulation technique. When a voltage difference is imposed between the two electrodes  42 ,  44 , the particles migrate closer one of the electrodes  42 ,  44  causing either the color of the particles or the color of the dispersion medium to be seen from the viewing side. 
         [0035]    Alternatively, each microcapsule may enclose therein two kinds of charged particles of different colors, for example, one kind of particle is made of TiO 2  in white and the other kind of particle is made of black carbon. When a voltage difference is applied between the two electrodes  42 ,  44 , the black particles migrate closer the first electrode  42  causing the color of the black particles to be seen from the viewing side. 
         [0036]    Alternatively, the sealing structure of the present invention may also be used to seal a chamber formed between two thin plastic sheets of other electric devices. 
         [0037]    In the description and claims of the present application, each of the verbs “comprise”, “include”, “contain” and “have”, and variations thereof, are used in an inclusive sense, to specify the presence of the stated item but not to exclude the presence of additional items. 
         [0038]    Although the invention is described with reference to one or more preferred embodiments, it should be appreciated by those skilled in the art that various modifications are possible. Therefore, the scope of the invention is to be determined by reference to the claims that follow.