Abstract:
In a conductive sheet using a metal nanofiber, metal migration in a visible conductive pattern is eliminated. Also, the intervals of the conductive portion (separate sheet terminal) are shortened. On a substrate ( 26 ) is a conductive sheet ( 10 ), formed from a transparent conductive pattern ( 11 ) and a visible conductive pattern ( 16 ). The transparent conductive pattern comprises a first nanofiber layer ( 12 ) that is a layer including a metal nanofiber, and a first heat-insulating layer ( 29 ) adjacent to the first nanofiber layer. The visible conductive pattern ( 16 ) forms an underlayer pattern from a second nanofiber layer ( 17 ) that is a layer including a metal nanofiber, and a second heat-insulating layer ( 27 ) adjacent to the second nanofiber layer; and a top-layer pattern comprising a paste layer ( 18 ) that is a layer including a metal paste laminated on the underlayer pattern. The second heat-insulating layer ( 27 ) is a conductive sheet that is a layer including a metal nanofiber cut to a minimum size. The visible conductive pattern ( 16 ) forms a water-shielding layer ( 21 ) on the underlayer pattern, and forms the top-layer pattern on the water-shielding layer.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a conductive sheet used for devices, such as, but not limited to, touch panels, and a method for fabricating the same. 
       BACKGROUND ART 
       [0002]    In the conventional technology, there has been proposed a conductive sheet fabricated by disposing a certain pattern of layer containing an electrically conductive nanofiber, specifically a metal nanofiber, on a substrate of resins, glasses and the like (for example, those disclosed in Patent literature 1). 
         [0003]      FIG. 8(   a ) is a plan view of a conventional conductive sheet.  FIG. 8(   b ) is a magnified cross-sectional view of the conductive sheet taken along the plane indicated by the arrow 76 in  FIG. 8(   a ). The conductive sheet  110  has a terminal part  131   a,  which contains discrete terminals  132   a,    132   b  and  132   c,  on its periphery. 
         [0004]    The terminal part  131   a  is formed of a conventional visible conductor pattern  116  that comprises a bottom pattern formed by disposing second nanofiber layers  17  on a substrate  26  and a top pattern formed by disposing paste layers  18  on the bottom pattern. 
         [0005]    The second nanofiber layers  17  contain, for example, silver nanofiber, and the paste layers  18  contain, for example, silver paste. The paste layers  18  on the second nanofiber layers complement the function of the second nanofiber layers constituting the terminal part  131   a  in order to increase the electric conductivity (decrease the electric resistance) of the terminal part  131   a.  The visible conductor pattern (of the terminal part  131   a ) formed on the periphery of the conductive sheet  110  does not influence on the design or handling of a touch panel to which the conductive sheet  110  is incorporated, because the periphery of the conductive sheet  110  incorporated in a touch panel is covered with the flame of the touch panel. 
         [0006]    Second thermally-formed insulator layers  127  are disposed between adjacent second nanofiber layers  17 , and prevent short circuit between the second nanofiber layers  17 . The second thermally-formed insulator layers  127  do not have electrical conductivity as the metal nanofiber in the layers is divided into fine particles by irradiation processing. 
         [0007]    A flexible printed circuit is connected to the terminal part  131   a  by means of, for example, an anisotropic conductive adhesive. 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         PTL 1: Japanese patent publication laid open 2010-140859 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0009]    A conventional conductive sheet has a terminal part at which second nanofiber layers functioning as conductors are disposed alternately with second thermally-formed insulator layers that make the second nanofiber layers spaced apart in a short distance. Although the second thermally-formed insulator layers do not have electrical conductivity, the layers contain finely-divided metal nanofiber that may ionize during a long-term use of the conductive sheet. Ionized metal nanofiber causes metal migration at the terminal part of the conductive sheet and may lead to short circuit between discrete terminals. 
         [0010]    At the terminal part of a conventional conductive sheet connected with a flexible printed circuit, second thermally-formed insulator layers directly contact an anisotropic conductive adhesive used for the connection. The direct contact between the anisotropic conductive adhesive and second thermally-formed insulator layers generates a small electric current flowing between discrete terminals at the terminal part through the anisotropic conductive adhesive and finely-divided metal nanofiber in the second thermally-formed insulator layers so as to decrease the insulation resistance between the discrete terminals. The decreased insulation resistance may lead to short circuit between the discrete terminals. 
         [0011]    The distance between the discrete terminals at the terminal part of a conventional conductive sheet, for example, the distance between the terminals  132   a  and  132   b,  needs to be enlarged to some extent, though the enlargement disturbs miniaturization of a flexible printed circuit to be connected with the conductive sheet. One of the reasons of such enlargement is prevention of metal migration that is accelerated by smaller distance between discrete terminals. Another reason of the enlarged distance between discrete terminals is making a space for misalignment of the paste layer patterns which should be printed correctly on the patterns of the second nanofiber layers. 
         [0012]    The problems to be solved by the present invention are elimination of metal migration in a visible conductor pattern of a conductive sheet containing metal nanofiber, decreasing the distance between conductors (discrete terminals of a conductive sheet), and providing a method for fabricating such conductive sheet. 
       Solution to Problem 
       [0013]    A conductive sheet of the present invention comprises: a transparent conductor pattern comprising a first nanofiber layer containing metal nanofiber and a first thermally-formed insulator layer abutting the first nanofiber layer; and a visible conductor pattern comprising a bottom pattern formed of a second nanofiber layer containing metal nanofiber and a second thermally-formed insulator layer containing finely-divided metal nanofiber and abutting the second nanofiber layer, and a top pattern comprising a paste layer containing metal paste and disposed over the bottom pattern, said visible conductor pattern containing a waterproof layer that is formed on said bottom pattern so as to cover the bottom pattern, and said top pattern being formed on said waterproof layer. 
         [0014]    A conductive sheet according to one preferable embodiment of the present invention may employ silver nanofiber for said metal nanofiber and silver paste for said metal paste. 
         [0015]    A conductive sheet according to another preferable embodiment of the present invention may have a conductor wire comprising said visible conductor pattern. 
         [0016]    A conductive sheet with wiring of the present invention comprises a conductive sheet of the present invention and a flexible printed circuit, wherein said conductive sheet has a terminal part comprising said visible conductor pattern and being electrically connected to a joining terminal of the flexible printed circuit. 
         [0017]    A touch panel of the present invention comprises a conductive sheet with wiring of the present invention as an electrode thereof. 
         [0018]    A method for fabricating the conductive sheet of the present invention includes a process for fabricating said visible conductor pattern comprising the following steps of: 
         [0000]    (a) disposing a second nanofiber layer containing metal nanofiber on a substrate;
 
(b) disposing a waterproof layer on the second nanofiber layer disposed in the step (a);
 
(c) disposing a paste layer containing metal paste on the waterproof layer disposed in the step (b); and
 
(d) forming said bottom pattern and top pattern by irradiating the layers of the second nanofiber layer, waterproof layer and paste layer on the substrate completed in the step (c) from above the paste layer to cut the metal nanofiber in the second nanofiber layer and burn out the metal paste in the paste layer.
 
         [0019]    The present invention, preferable embodiments of the present invention and the elements contained therein can be combined as far as possible to work the invention. 
       Advantageous Effects of Invention 
       [0020]    The conductive sheet of the present invention includes, in addition to other elements of the invention, a bottom pattern comprising a second nanofiber layer and a second thermally-formed insulator layer, and also a waterproof layer covering the bottom pattern to prevent moisture intrusion into the second nanofiber layer and second thermally-formed insulator layer thereby minimizing metal migration. Thus the conductive sheet of the present invention has improved durability with minimum short circuit due to metal migration. The conductive sheet of the present invention enables smaller distance between visible conductor patterns and reduced sizes of the conductive sheet and a device to which the conductive sheet is incorporated. 
         [0021]    The conductive sheet with wiring of the present invention is durable and the conductive sheet and the wiring, i.e., a flexible printed circuit, have reduced-size terminal parts, owing to the conductive sheet of the present invention employed. 
         [0022]    The touch panel of the present invention is durable and has a reduced-size connector to a circuit, owing to the conductive sheet with wiring of the present invention incorporated therein. 
         [0023]    The method for fabricating the conductive sheet of the present invention includes, in addition to other elements of the present invention, the steps of layering the second nanofiber layer, waterproof layer and paste layer, and irradiating simultaneously the second nanofiber layer and the paste layer to form the visible conductor pattern so as to readily and efficiently fabricate waterproof layer. Thus the method is advantageous for fabricating a conductive sheet having visible conductor patterns spaced apart in a small distance and causing no metal migration. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0024]      FIG. 1  is an exploded diagram of a touch panel of the present invention. 
           [0025]      FIG. 2  is an illustrative diagram of a conductive sheet, where (a) is a plan view, (b) is a magnified cross-sectional view taken along the plane indicated by the arrow  73  in (a), and (c) is another cross-sectional view taken along the plane indicated by the arrow  75  in (a). 
           [0026]      FIG. 3  is an exploded diagram of a conductive sheet. 
           [0027]      FIG. 4  is a magnified cross-sectional view of a conductive sheet showing the contact between a paste layer  18  and a second nanofiber layer  17 . 
           [0028]      FIG. 5  is an illustrative diagram showing a process for fabricating a visible conductor pattern of a conductive sheet. 
           [0029]      FIG. 6  is a plan view of a conductive sheet model  81  of Experiment  1 . 
           [0030]      FIG. 7  is a plan view of a conductive sheet model  98  of Experiment  2 . 
           [0031]      FIG. 8  is an illustrative diagram of a conventional conductive sheet, where (a) is a plan view, and (b) is a magnified cross-sectional view taken along the plane indicated by the arrow  76  in (a). 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0032]    The conductive sheet, conductive sheet with wiring, capacitive touch panel, and the method for fabricating the conductive sheet of the present invention will be further described referring to the figures. Some of the figures are schematically drawn with magnification of some elements for readily understanding the present invention. Thus some of the dimensions of or dimensional ratios between the elements may be different from that of the actual conductive sheets or devices. The dimensions, materials, shapes and relative positions of the members and parts described in the working examples of the present invention merely explain the present invention and do not intend to restrict the scope of the present invention unless otherwise specified. The numbers used as the signs may collectively represent parts, and alphabetical letters are sometimes added to such numbers for representing each of such parts. 
         [0033]      FIG. 1  is an exploded diagram of a touch panel  1  that is fabricated by layering a second detector conductive sheet  10   b,  first detector conductive sheet  10   a,  and protective film  61  in the order on a display panel  63 . The display panel  63  is a liquid crystal display, though other known types of display may be employed for the display panel  63  without restriction. 
         [0034]    The second detector conductive sheet  10   b  includes a transparent conductor pattern  11   b.  The transparent conductor pattern  11   b  includes three rectangular electrodes arranged along the longer side of the second detector conductive sheet  10   b.  A conductor wire  33   b  is routed from each of the three electrodes to the terminal part  31   b  of the sheet. The terminal part  31   b  comprises a visible conductor pattern  16   b.  In the present invention and this description, “transparent” refers to a property of a material allowing light to pass through and “visible” refers to a property of a material absorbing visible light. 
         [0035]    The first detector conductive sheet  10   a  includes a transparent conductor pattern  11   a.  The transparent conductor pattern  11   a  includes three rectangular electrodes arranged along the shorter side of the first detector conductive sheet  10   a.  A conductor wire  33   a  is routed from each of the three electrodes to the terminal part  31   a  of the sheet. The terminal part  31   a  comprises a visible conductor pattern  16   a.    
         [0036]    The electrodes and control circuit of the touch panel are connected via flexible printed circuits (hereinafter referred to as FPC)  41   a  and  41   b.  The terminals  42   a  and  42   b  each at the respective end of the FPCs  41   a  and  41   b  are respectively connected to the terminal parts  31   a  and  31   b  of the conductive sheets. The FPCs  41   a  and  41   b  are adhered respectively to the terminal parts  31   a  and  31   b  with an anisotropic conductive adhesive. Cutouts  62  were made at the areas of the protective film  61  and the first detector conductive sheet  10   a  corresponding to the positions for adhering the FPCs to the terminal parts of the conductive sheets so as to readily connect the FPCs and the conductive sheets. The FPCs  41  are formed into a strip, and  FIG. 1  shows only the outline of the terminal parts  42  of the FPCs  41 . 
         [0037]    A known system can be employed for the control system of the touch panel, for example, capacitive sensing. The diagrammatic representation of a control circuit is omitted. 
         [0038]      FIG. 2  is an illustrative diagram of a conductive sheet  10 , and  FIG. 2(   a ) is a plan view of the conductive sheet  10 .  FIG. 2(   b ) is a magnified cross-sectional view taken along the plane indicated by the arrow  73  in  FIG. 2(   a ), and  FIG. 2(   c ) is a cross-sectional view taken along the plane indicated by the arrow  75  in  FIG. 2(   a ).  FIG. 3  is an exploded diagram of the conductive sheet. 
         [0039]    A terminal part  31   a  is made at the periphery of the conductive sheet  10 . Transparent electrodes  111 ,  112  and  113  are disposed at the center of the conductive sheet  10 . The three transparent electrodes  111 ,  112  and  113  are rectangular and arranged along the shorter side of the conductive sheet  10 . The three transparent electrodes  111 ,  112  and  113  are formed of the transparent conductor pattern. 
         [0040]    The transparent electrodes  111 ,  112  and  113  are respectively connected to discrete terminals  32   a,    32   b  and  32   c  via conductor wire  33 . The terminal part  31   a  of the conductive sheet is formed of the visible conductor pattern  16 . The conductor wire  33  may be formed of either the transparent conductor pattern or visible conductor pattern. 
         [0041]    The structure of the visible conductor pattern will be described by referring to  FIG. 2(   b ) and  FIG. 3 . The visible conductor pattern  16  comprises three layers. The first layer includes second nanofiber layers  17  and second thermally-formed insulator layers  27  disposed on a substrate  26 . The second nanofiber layers  17  and the second thermally-formed insulator layers  27  abut each other on the same plane. The second nanofiber layers  17  constitute a bottom pattern having a certain planar shape. 
         [0042]    The second layer is a waterproof layer  21  disposed on the second nanofiber layers  17  and the second thermally-formed insulator layers  27 . Paste layers  18  and insulation gaps  28  are formed on the waterproof layer  21 . 
         [0043]    The waterproof layer  21  covers the bottom pattern, and the third layer is the paste layers  18  formed on the waterproof layer  21 . The paste layers  18  constitute the top pattern that has the same planar shape as that of the bottom pattern. The parts abutting the paste layers  18  on the same plane are insulation gaps  28  which are actually voids.  FIG. 2(   b ) shows three paste layers  18  separated apart by the insulation gaps  28 . 
         [0044]    The paste layers  18  of the conductive sheet of the present invention need not always be disposed into the same planar shape as that of the bottom pattern. The paste layers  18  of the conductive sheet of the present invention independently function as a conductor without depending on the second nanofiber layers  17 . Thus the top pattern may be formed into a different planar shape from that of the bottom pattern. 
         [0045]    The top pattern and bottom pattern of a conventional conductive sheet cooperate to function as conductors by supplementing the other&#39;s conductive performance. Therefore the top pattern is required to be disposed into the same planar shape as that of the bottom pattern as far as possible. Difference in the planar shape between the upper and bottom patterns increases the area constituted by the paste layer  18  and nanofiber layer  17  to increase the width of the terminal part of the conductive sheet so as to increase the area of the terminal part on the conductive sheet. 
         [0046]    The conductive sheet of the present invention includes a waterproof layer  21  disposed between the lower and top patterns. The paste layers  18  alone function as conductors if the second nanofiber layers  17  and paste layers  18  contact at an area where the waterproof layer is not disposed. In this case, the top pattern may be disposed into a different shape from that of the bottom pattern. 
         [0047]    The transparent conductor pattern will be described by referring to  FIG. 2(   c ) and  FIG. 3 . The transparent conductor pattern  11  comprises first nanofiber layers  12  and first thermally-formed insulator layers  29  disposed on the substrate  26 . The first nanofiber layers  12  are formed into a certain planar shape to constitute the transparent electrode mentioned above, and abut the first thermally-formed insulator layers  29  on the same plane. The visible conductor pattern  16  and the transparent conductor pattern  11  are disposed on the same plane. 
         [0048]    The waterproof layer  21  prevents water intrusion into the bottom pattern. Ideally the waterproof layer  21  should cover the whole surface of the bottom pattern, in other words, the waterproof layer  21  should extend beyond the outline of the bottom pattern to some extent. 
         [0049]    However, the waterproof layer  21  prevents not only water intrusion but also electric conduction, and the waterproof layer  21  covering the bottom pattern prevents electric conduction between the paste layers  18  and the second nanofiber layers  17 . It is preferable to make the waterproof layer  21  cover the bottom pattern except the area where the paste layers  18  and the second nanofiber layers  17  directly contact to each other. 
         [0050]      FIG. 4  is a magnified cross-sectional view of the conductive sheet showing the direct contact between a paste layer  18  and a second nanofiber layer  17 . The outline of the waterproof layer  21  shown in  FIG. 4  draws back to the inside the outline of the second nanofiber layer  17  to allow a part of the second nanofiber layer  17  to come out. The paste layer  18  extends beyond the outline of the waterproof layer  21  to directly contact the second nanofiber layer  17 . The inside mentioned here means an area surrounded by an outline and the outside mentioned here means the area beyond an outline. 
         [0051]    Metal migration occurs under a condition where (1) moisture and (2) electric potential difference exist. The visible conductor pattern of the present invention does not cause metal migration owing to the waterproof layer included therein that prevents water intrusion into the second nanofiber layers and the second thermally-formed insulator layers. 
         [0052]    The process for fabricating the visible conductor pattern will be described.  FIG. 5  is an illustrative diagram showing a process for fabricating a visible conductor pattern. The process enables, for example, fabrication of the conductor wire of a conductive sheet. 
         [0053]    At first, a second nanofiber layer  17  containing metal nanofiber is disposed on a substrate  26  as shown in  FIG. 5(   a ). Then a waterproof layer  21  is disposed on the second nanofiber layer  17  as shown in  FIG. 5(   b ), and a paste layer  18  is disposed on the waterproof layer  21  as shown in  FIG. 5(   c ). 
         [0054]    Then the second nanofiber layer  17 , waterproof layer  21  and paste layer  18  on the substrate is irradiated with a laser  51  from above the paste layer  18 . The irradiation cuts metal nanofiber in the second nanofiber layer, partially removes the paste layer  18  to form the lower and top patterns, and thereby fabricates a visible conductor pattern. 
         [0055]    The process for fabricating a visible conductor pattern mentioned above enables fabrication of a conductive sheet having a transparent conductor pattern and a visible conductor pattern as described below. 
         [0056]    A first nanofiber layer and a second nanofiber layer are simultaneously formed at the step shown in  FIG. 5(   a ). The first nanofiber layer  12  can be formed at any area on the substrate  26  except the area where the second nanofiber  17  is formed. The first and second nanofiber layers are formed of the same material and into the same thickness simultaneously in the same operation. 
         [0057]    Then layers are added on the visible conductor pattern  16 , in other words, on the second nanofiber layer  17 , as shown in  FIG. 5(   b ) and  FIG. 5(   c ). At the step in  FIG. 5(   d ), the second thermally-formed insulator layers  27  are formed by irradiation, and the first thermally-formed insulator layers  29  are simultaneously formed by irradiating the transparent conductor pattern  11 , in other words, the first nanofiber layer  12 . Thus a conductive sheet having a transparent conductor pattern and a visible conductor pattern is fabricated in the process mentioned above. 
         [0058]    YAG laser is an example of lasers and irradiates beam with a spot size of several tens micrometer. The wavelength for the irradiation with YAG laser should range from 1200 nm to 350 nm, preferably from 1100 nm to 400 nm. Irradiation within the wavelength range does not burn the waterproof layer and substrate to make them remain after irradiation, and generates only a small quantity of heat which does not burn out the conductive sheet. 
         [0059]    Irradiation applies a proper amount of energy (heat) to metal nanofiber. The energy cuts the metal nanofiber, and simultaneously burns and removes some part of the paste layer. Other sources of radiation may be employed for the irradiation. 
         [0060]    The waterproof layer  21  should be transparent, because a transparent waterproof layer  21  survives the irradiation as it transmits the energy of radiation. On the contrary, opaque waterproof layer absorbs the energy of radiation and is consequently burnt by YAG laser. 
         [0061]    The materials for the waterproof layer include acrylic resins, vinyl chloride resins, polyurethane resins, epoxy resins, melamine resins and the like. Of those resins, polyurethane resins, epoxy resins and melamine resins are preferable for their transparency and waterproof performance. The waterproof layer can be formed by gravure coating, roller coating, comma coating, gravure printing, screen printing, offset printing and the like. 
         [0062]    The thickness of the waterproof layer should range from 1 μm to 30 μm, preferably from 5 μm to 20 μm. A waterproof layer having a thickness of at least 1 μm minimizes metal migration. A waterproof layer having a thickness at most 30 μm allows a protective film  61  attached on the conductive sheet to fit the bump formed by the waterproof layer and paste layer along the outline of the waterproof layer, and thus prevents void formation between the conductive sheet and the protective film to prevent poor appearance of resultant conductive sheet due to the void. 
         [0063]    In addition, the thickness of the waterproof layer  21  should be less than 10 times thickness of the paste layer  18 , preferably less than 4 times thickness. A waterproof layer  21  having such thickness prevents crack formation at the contact between the second nanofiber layers  17  and paste layers  18  along the outline of the waterproof layer  21 . 
         [0064]    The second nanofiber layers  17  comprise a metal nanofiber and a binder resin, such as acrylic, polyester, polyurethane and polyvinyl chloride resins and the like. The second nanofiber layers  17  can be formed by means of a versatile printing method such as gravure printing, offset printing, screen printing and the like, or coating with a slot die coater. 
         [0065]    The metal nanofiber includes the nanofibers of gold, silver, platinum, copper, palladium and the like. Those metal nanofibers are manufactured by applying an energized needle tip to a nanofiber precursor prepared by coating a support comprising, for example, a zirconium phosphate compound, with a metal ion such as gold, silver, platinum, copper and palladium ions and the like. Of those metal nanofibers, silver nanofiber is preferable for its high electrical conductivity, lower cost and translucency. The silver nanofiber should have a diameter ranging from 10 nm to 100 nm and a length ranging from 1 μm to 200 μm. 
         [0066]    The thickness of the second nanofiber layers  17  can be selected within the range from several tens nanometers to several hundred nanometers, and a second nanofiber layer having such thickness has sufficient strength and is soft enough to be readily processed. 
         [0067]    The materials and fabrication method for the first nanofiber layers  12  are the same as that for the second nanofiber layers  17 . 
         [0068]    The second thermally-formed insulator layers  27  comprise a metal nanofiber and a binder resin, for which acrylic, polyester, polyurethane and polyvinyl chloride resins and the like can be employed. 
         [0069]    The metal nanofiber constituting the second thermally-formed insulator layers  27  has dimensions ranging from 1/10 to 1/1000 of the dimensions of the metal nanofiber constituting the first and second metal nanofiber layers. The strands of the metal nanofiber constituting the second thermally-formed insulator layers  27  exist independently of each other in the layers to decrease the electric conductivity of the second thermally-formed insulator layers  27 . On the contrary, the strands of the metal nanofiber constituting the first nanofiber layer tangle, and similarly the strands of the metal nanofiber constituting the second nanofiber layer tangle. 
         [0070]    The second thermally-formed insulator layers  27  are fabricated in the following process. At first, a material being the same as that for the second nanofiber layer is disposed on a substrate by means of a versatile printing method such as gravure printing, offset printing, screen printing and the like, or coating with a slot die coater, and the disposed layer is then irradiated with a device such as YAG laser to heat the metal nanofiber in the layer. 
         [0071]    The thickness of the second thermally-formed insulator layer  27   s  is the same as that of the first nanofiber layer and the second metal nanofiber layer. 
         [0072]    The paste layers  18  comprise metal particles and a binder resin, for which acrylic, polyester, polyurethane and polyvinyl chloride resins and the like are employed. Of metal particles, silver is the most preferable for its good electrical conductivity and low cost. The paste layer has a thickness ranging from 1 μm to 30 μm, and is formed by gravure coating, roller coating, comma coating, gravure printing, screen printing, offset printing and the like. 
         [0073]    The materials for the substrate  26  include films of acrylic, polycarbonate, polyester, polybutylene terephthalate, polypropylene, polyamide, polyurethane, polyvinyl chloride and polyvinyl fluoride resins and the like, and glasses. The thickness of the substrate  26  can be selected within the range from 5 μm to 800 μm. A substrate having such thickness has sufficient strength and is soft enough to be readily processed. 
         [0074]    The visible conductor pattern having a waterproof layer mentioned above is applicable not only for forming a terminal part of a conductive sheet but also for forming conductor wire. Conductor wire comprising a visible conductor pattern having a waterproof layer enables decreased area of the rim of a conductive sheet without a risk of metal migration. 
       EXAMPLE 
       [0075]    Experiment 1 
         [0076]    A conductive sheet model  81  of Experiment 1 was fabricated as described below. The conductive sheet model  81  provides Example 1. 
         [0077]    A 50-μm thick biaxially-oriented polyethylene terephthalate film was employed for the substrate. A silver nanofiber material (ClearOhm®, produced by Cambrios Technologies Corp.) was disposed on the whole surface of the substrate to form a metal nanofiber layer. 
         [0078]    Then a polyurethane resin was disposed on the metal nanofiber layer to form a 15-μm thick waterproof layer.  FIG. 6  is a plan view of the conductive sheet model  81 . The waterproof layer was not formed on the electrode regions  82   a  and  82   b.  As shown in  FIG. 6 , the two electrode regions,  82   a  and  82   b,  were respectively formed at the opposite ends of the sheet. Each of the electrode regions  82   a  and  82   b  has a dimension of 10 mm by 30 mm, and the linear distance between the two electrode regions was 80 mm. 
         [0079]    Then the electrode regions  82   a  and  82   b  were covered with silver paste (DW-114L-1, produced by Toyobo Co., Ltd.) 5 μm thick to form electrodes. 
         [0080]    Then the metal nanofiber layer was etched into comb-shaped pattern with a YAG laser to form a thermally-formed insulator line  83 . The comb teeth of the comb-shaped pattern were arranged in 5 mm intervals (indicated by the arrow  84 ) and the width of each comb tooth (indicated by the arrow  85 ) was 5 mm. The width of the thermally-formed insulator line  83  was 0.1 mm. The conductive sheet model of Example 1 was fabricated in the process mentioned above. The silver nanofiber material, epoxy resin and silver paste were disposed on the substrate with a gravure printing machine. The wave length of the YAG laser employed was 1064 μm. 
       Examples 2 and 3, and Comparative Examples 1 and 2  
       [0081]    Conductive sheet models were fabricated according to the method of Example 1 except that different thickness and resins were employed for waterproof layers. In addition, the conductive sheet model of Comparative example 1 does not have a waterproof layer. 
         [0082]    Metal migration prevention performance of Examples 1 to 3 and Comparative examples 1 and 2 
         [0083]    The models of Examples 1 to 3 and Comparative examples 1 and 2 were tested in the following procedure. Both electrodes of a conductive sheet model were connected to power source to be energized with 20 V, and the time until the sheet model short-circuits was measured. The measurement was carried out at 60° C. and 95% RH (Relative Humidity). The result is shown in Table 1. 
         [0000]    
       
         
               
               
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 Waterproof layer 
                 Testing 
               
             
          
           
               
                   
                   
                 Thickness 
                 Time until short circuit 
               
               
                   
                 Material 
                 (μm) 
                 (min) 
               
               
                   
                   
               
             
          
           
               
                 Example 1 
                 Polyurethane 
                 6.7 
                 180 
               
               
                 Example 2 
                 Polyurethane 
                 15 
                 300 
               
               
                 Example 3 
                 Polyurethane 
                 27 
                 560 
               
               
                 Comparative 
                 None 
                 — 
                 5 
               
               
                 example 1 
               
               
                 Comparative 
                 Low-density 
                 15 
                 30 
               
               
                 example 2 
                 polyester 
               
               
                   
                 resin 
               
               
                   
               
             
          
         
       
     
         [0084]    Experiment 2 
         [0085]    A conductive sheet model  98  of Experiment 2 was fabricated as follows. The conductive sheet model  98  provides Example 4. 
         [0086]    A 50-μm thick biaxially-oriented polyethylene terephthalate film was employed for the substrate. A silver nanofiber material (ClearOhm®, produced by Cambrios Technologies Corp.) was disposed on the whole surface of the substrate to form a metal nanofiber layer. 
         [0087]      FIG. 7  is a plan view of the conductive sheet model  98 . On the metal nanofiber layer, a polyurethane resin was disposed to form two waterproof layers  86  and  87 . The waterproof layers  86  and  87  were formed into 15-μm thick rectangles of 20 mm (indicated by the arrow  94 ) by 50 mm (indicated by the arrow  95 ) separated apart in a distance of 1 mm (indicated by the arrow  96 ). The waterproof layer was not formed at the periphery of the substrate and at the electrode regions  88 ,  89  and  90 . 
         [0088]    The electrode regions were formed into rectangles of 0.1 mm by 21 mm, and 10 mm out of the 21 mm overlapped the waterproof layer  87  (indicated by the arrow  97 ). Silver paste (DW - 114L-1, produced by Toyobo Ld.) was disposed 5 μm thick to cover the electrode regions  88 ,  89  and  90  to form electrodes. 
       Example 5 and Comparative Examples 3, 4 and 5   
       [0089]    Conductive sheet models were fabricated according to the method of Example 4 except that different thickness and resins were employed for waterproof layers. 
         [0090]    Crack generation of Examples 4 and 5 and Comparative examples 3, 4 and 5 
         [0091]    The models of Examples 4 and 5 and Comparative examples 3, 4 and 5 were tested in the following procedure. 
         [0092]    The electric resistance of the electrodes of each conductive sheet model was measured. The electric resistance was measured between the points  91   a  and  91   b,  between the points  92   a  and  92   b  and between the points  93   a  and  93   b.  The three resistance values were calculated into an arithmetic mean, which was defined to be the initial resistance. 
         [0093]    Then each conductive sheet model was wound on an 8-mm diameter cylinder and unwound repeatedly 10 times. After the experiment, the electric resistance of the sheet model was measured in the same manner as that for the initial resistance. The electric resistance was measured between the points  91   a  and  91   b,  between the points  92   a  and  92   b  and between the points  93   a  and  93   b.  The three resistance values were calculated into an arithmetic mean, which was defined to be the resistance after the experiment. 
         [0094]    The ratio of the resistance after the experiment to the initial resistance was calculated by the following expression. 
         [0095]    R/R 0 =Resistance after the experiment (R)/Initial resistance (R 0 ) 
         [0096]    Based on the values of R/R 0  mentioned above, crack generation in the electrodes of each model was classified by the following criteria and shown in Table 2. 
         [0097]    ◯: 1≦R/R 0 &lt;1.1 
         [0098]    Δ: 1.1≦R/R 0 &lt;1.2 
         [0099]    ×: 1.2≦R/R 0    
         [0000]    
       
         
               
               
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
             
             
               
                   
                   
               
               
                   
                   
                 Testing 
               
               
                   
                 Waterproof layer 
                 Crack 
               
             
          
           
               
                   
                 Material 
                 Thickness (μm) 
                 generation 
               
               
                   
                   
               
             
          
           
               
                 Example 4 
                 Polyurethane 
                 15 
                 ◯ 
               
               
                 Example 5 
                 Polyurethane 
                 6.7 
                 ◯ 
               
               
                 Comparative example 3 
                 Polyurethane 
                 27 
                 Δ 
               
               
                 Comparative example 4 
                 Polyurethane 
                 35 
                 Δ 
               
               
                 Comparative example 5 
                 Polyurethane 
                 50 
                 X 
               
               
                   
               
             
          
         
       
     
         [0100]    Cracks were generated at the contact between the electrode (silver paste layer) and silver nanofiber layer along the outline of the waterproof layer. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           1  Touch panel 
           10  Conductive sheet 
           10   a  First detector conductive sheet 
           10   b  Second detector conductive sheet 
           11  Transparent conductor pattern 
           12  First nanofiber layer 
           16  Visible conductor pattern 
           17  Second nanofiber layer 
           18  Paste layer 
           21  Waterproof layer 
           26  Substrate 
           27  Second thermally-formed insulator layer 
           28  Insulation gap 
           29  First thermally-formed insulator layer 
           31 ,  31   a,    31   b  Terminal part of a conductive sheet 
           32   a,    32   b,    32   c  Discrete terminals 
           33 ,  33   a,    33   b  Conductor wire 
           41   a,    41   b  Flexible printed circuit 
           42  Terminal part of the circuit 
           51  Laser 
           61  Protective film 
           62  Cutout 
           63  Display panel 
           81  Conductive sheet model 
           82   a,    82   b  Electrode regions 
           83  Thermally-formed insulator line 
           86 ,  87  Waterproof layer 
           88 ,  89 ,  90  Electrode region 
           98  Conductive sheet model 
           110  Conventional conductive sheet 
           116  Conventional visible conductor pattern