Abstract:
A reference electrode is disclosed. The reference electrode is developed by spreading an aqueous KCl gelling agar solid gel/poly(vinyl chloride)carboxylated (PVC—COOH) double layer on a screen-printing Ag/AgCl electrode body. Such polymer double layer can maintain ion concentration and keep stable chemical capacitance potential during measurement. The reference electrode of the present invention provides fast response time and high stability for major ions detection measurements in a wide range.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to reference electrodes. 
         [0003]    2. Description of the Prior Art 
         [0004]    Propelled by the advances in technology and human need, electrical and chemical measuring elements are becoming smaller. As such, manufacturing methods and tools are being developed and improved on to meet the needs for ever smaller elements. 
         [0005]    Currently, reference electrodes are primarily made of glass or ceramic enclosing an electrolyte solution. However, due to the bulk size of the material such as glass or ceramic, the resulting reference electrodes cannot be reduced beyond a certain limit. Moreover, problems such as challenging manufacturing processes, fragile structure and high cost still exist. 
       SUMMARY OF THE INVENTION 
       [0006]    In view of the prior art and the needs of the related industries, the present invention provides a reference electrode that solves the abovementioned shortcomings of the conventional. 
         [0007]    One objective of the present invention is to provide a reference electrode, which is a layered structure that may include an insulating substrate, a conductive layer, an electrode layer, a solid electrolytic layer, a polymer protective film, an anti-oxidation layer and an insulating layer. More particularly, the solid electrolytic layer is solidified on the electrode layer by mixing an agar gel and an electrolyte solution under a high temperature. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention, and together with the description serve to explain the principles of the disclosure. In the drawings: 
           [0009]      FIG. 1  is a flowchart illustrating a method for manufacturing a reference electrode according to one embodiment of the present invention; and 
           [0010]      FIGS. 2A and 2B  are schematic diagrams depicting the structure of a reference electrode according to one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0011]    The present invention is directed to a reference electrode. Detailed steps and constituents are given below to assist in the understanding the present invention. Obviously, the implementations of the present invention are not limited to the specific details known by those skilled in the art of reference electrode. On the other hand, well-known steps or constituents are not described in details in order not to unnecessarily limit the present invention. Detailed embodiments of the present invention will be provided as follow. However, apart from these detailed descriptions, the present invention may be generally applied to other embodiments, and the scope of the present invention is thus limited only by the appended claims. 
         [0012]    The present invention proposes a reference electrode, which includes an insulating substrate, a conductive layer on the insulating substrate, an electrode layer on the conductive layer, a solid electrolytic layer on the electrode layer, a PVC—COOH protective film on the solid electrolytic layer, an anti-oxidation layer around the periphery of the conductive layer, an insulating layer around the periphery of the anti-oxidation layer. The solid electrolytic layer is formed by solidifying an electrolyte solution on the electrode layer using an agar gel. 
         [0013]    Referring to  FIG. 1 , a schematic diagram depicting a method of constructing a reference electrode according to the above embodiment is shown. First, in step  110 , a conductive layer is formed on a substrate. In step  120 , an electrode layer is then formed on the above conductive layer. In step  130 , a solid electrolytic layer is formed on the electrode layer. Then, in step  140 , an anti-oxidation layer is formed on the portion of the conductive layer not covered by the electrode layer. In step  150 , an insulating layer is formed at the periphery of the anti-oxidation layer. Finally, in step  160 , a polymer protective film is formed on the solid electrolytic layer. 
         [0014]    In addition, the step of forming a solid electrolytic layer further includes the following steps. In step  132 , an agar gel powder is mixed with an electrolyte solution to form a mixture. Then, in step  134 , the mixture is stirred under high temperature. Finally, in step  136 , the mixture is cooled and thus solidified on the electrode layer at a low temperature. The above high temperature may be in a range between about 100° C. and about 150° C., while the low temperature may be in a range between about 0° C. and about 40° C. 
         [0015]    Next, referring to  FIGS. 2A and 2B , schematic diagrams depicting the reference electrode constructed according to the above embodiment are shown. The reference electrode includes an insulating substrate  210 , a conductive layer  220 , an electrode layer  230 , a solid electrolytic layer  240 , a polymer protective film  250 , an anti-oxidation layer  260  and an insulating layer  270 , wherein the solid electrolytic layer  240  is solidified on the electrode layer  230  by mixing an agar gel and an electrolyte solution under a high temperature.  FIG. 2A  is a cross-sectional view of the reference electrode, while  FIG. 2B  is a front cross-sectional view of the same reference electrode along X axis. 
         [0016]    As shown in  FIG. 2A , the electrode layer  230  is formed on a portion of the conductive layer  220 . The anti-oxidation layer  260  is formed on the conductive layer  220  not covered by the electrode layer  230 , so as to prevent oxidation of the electrode layer. The electrode layer  230  having an area of 8 mm×3 mm is preferred. Further, the conductive layer  220  may be connected with a line conductor for passing signals measured by the reference electrode. In addition, the insulating layer  270  may be formed on the conductive layer  220  to cover the sides of the electrode layer  230  and the solid electrolytic layer  240 . 
         [0017]    The polymer protective film  250  may be one selected from PVC—COOH, polycarbonate, polyester, polyether, polyamide, polyurethane, polyimide, poly (vinyl chloride) (PVC), polyethylene or a combination thereof. Since PVC—COOH has a stronger polarity than traditional PVC materials, thus when the reference electrode is immersed into a test solution, a PVC—COOH protective film can attract more electrolytes in the test solution. In addition, due to high permeability of the PVC—COOH protective film, reaction time between the electrolytes and the solid electrolytic layer can be greatly reduced, thereby enhancing response time of the reference electrode. Furthermore, the PVC—COOH protective film is better at keeping moisture than traditional PVC materials, such that it gives the solid electrolytic layer a better protection and a more stable ion concentration at the surface of the electrode layer, thereby achieving a more ideal reference electrode. Compared to a traditional reference electrode that employs electrolyte solution, the reference electrode proposed by present invention not only provides a fast response time and stable output voltage, but can be easily manufactured and miniaturized at a cheaper cost. 
         [0018]    The substrate can be an insulating material selected from polycarbonate, polyester, polyether, polyamide, polyurethane, polyimide, poly (vinyl chloride) (PVC), glass, glass fiber, ceramic, PET or a combination thereof. In addition, the electrolyte solution can be a saturated potassium chloride solution, wherein the weight ratio of the agar gel powder and the saturated potassium chloride solution is 4%:96%. 
         [0019]    In a preferred embodiment of the present invention, the electrode layer includes silver (Ag) and silver chloride (AgCl) with a mix ratio of 1:2. Ag/AgCl is baked on the conductive layer at a temperature range of about 40° C. to 120° C. The conductive layer can be a silver paste or ITO (Indium Tin Oxide) film to enhance conduction. The anti-oxidation layer enclosing the periphery of the silver paste can be a conductive carbon paste, which enhances electrical conduction while preventing the silver paste from oxidation due to exposure. The conductive layer, the electrode layer, the anti-oxidation layer and the insulating layer can for example be formed by screen printing technique. In addition, the insulating layer could comprise UV curing gel to avoid that the test solution and the solid electrolytic layer contact to each other directly, and could fix the solid electrolytic layer more strongly for providing against the damage from external force. 
         [0020]    The foregoing description is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obvious modifications or variations are possible in light of the above teachings. In this regard, the embodiment or embodiments discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the inventions as determined by the appended claims when interpreted in accordance with the breath to which they are fairly and legally entitled. 
         [0021]    It is understood that several modifications, changes, and substitutions are intended in the foregoing disclosure and in some instances some features of the invention will be employed without a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.