Patent Publication Number: US-2016230299-A1

Title: Drum electrode, method for producing drum electrode, plating device, method for producing resin molded body, and method for producing metal porous body

Description:
TECHNICAL FIELD 
     The present invention relates to a drum electrode which is used for plating the surface of a resin molded body having a three-dimensional network structure with a metal in a plating tank. The invention further relates to a method for producing the drum electrode, and a plating device, a method for producing a resin molded body, and a method for producing a metal porous body, each using the drum electrode. 
     BACKGROUND ART 
     In recent years, metal porous bodies having a three-dimensional network structure have been widely used in electrodes of batteries, various filters, catalyst carriers, and the like. A metal porous body is generally obtained by imparting electrical conductivity to the surface of a resin molded body having a three-dimensional network structure, such as foamed urethane or foamed melamine, electroplating the surface of the resin molded body with a metal, and then removing the resin molded body by heat treatment or the like. 
     In the case where a resin molded body to which electrical conductivity has been imparted has a high electrical resistance, in order to efficiently perform electroplating with a metal, it is preferable to feed power to the resin molded body in a plating solution using a drum electrode. However, in the case of a resin molded body having a three-dimensional network structure, a plating solution passes through interconnected pores of the resin molded body. Therefore, when a drum electrode whose entire surface is electrically conductive is used, a metal is electrodeposited not only on the resin molded body, but also on the surface of the drum electrode. Consequently, current efficiency is decreased, and furthermore, since it is difficult to remove the metal electrodeposited on the surface of the drum electrode, it becomes necessary to periodically replace the drum electrode. 
     Accordingly, metal electroplating is performed on the surface of a resin molded body having a three-dimensional network structure, for example, using a device shown in  FIG. 8 . In  FIG. 8 , reference sign  80  denotes a device for producing a metal porous body, reference sign  81  denotes a drum electrode serving as a cathode, reference sign  82  denotes a projection made of an electrically conductive material formed on the drum electrode  81 , reference sign  83  denotes an anode, reference sign  84  denotes a plating tank, reference sign  85  denotes a plating solution contained in the plating tank  84 , and reference sign W denotes a long resin molded body (work) having a three-dimensional network structure to which electrical conductivity has been imparted and which is to be plated. 
     The drum electrode  81  is immersed, at the lower portion thereof, in the plating solution  85  and rotates at the same velocity as the conveying velocity of the work W. The portion other than the projections  82  made of the electrically conductive material has an insulating property. During plating, the projections  82  penetrate into pores of the work W which is a porous body, and metal plating is performed in the vicinity of the projections  82 . Therefore, it is possible to sufficiently plate the work W including the inside thereof while avoiding electrodeposition of the metal on the surface of the drum electrode  81 . 
     A drum electrode used in such a device for producing a metal porous body is described, for example, in Japanese Unexamined Patent Application Publication No. 1-255686 (Patent Literature 1) or Japanese Unexamined Patent Application Publication No. 2013-007069 (Patent Literature 2). 
     CITATION LIST 
     Patent Literature 
     PTL 1: Japanese Unexamined Patent Application Publication No. 1-255686 
     PTL 2: Japanese Unexamined Patent Application Publication No. 2013-007069 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the existing drum electrode described above, while preventing electrodeposition of a metal on the surface of the drum electrode, it is possible to electrodeposit the metal uniformly on the surface of a resin molded body having a three-dimensional network structure. However, there is room for improvement from the viewpoint that the method for producing the drum electrode itself is complicated and costly and that it takes a lot of time and trouble to perform a cutting process in order to adjust the height of electrically conductive projections on which the metal has been electrodeposited during the operation. 
     Accordingly, it is an object to provide a drum electrode with which a metal can be electrodeposited on the surface of a long base material in a plating tank, which can be produced by an easy method, and in which the maintenance during the operation is easy; and a method for producing the same. It is another object to provide a plating device, a method for producing a resin molded body, and a production method, each using such a drum electrode. 
     Solution to Problem 
     In order to solve the problem described above, a drum electrode according to an embodiment of the present invention employs the following structure: 
     (1) That is, a drum electrode according to an embodiment of the present invention is a drum electrode for a device configured to plate a surface of a long base material having electrical conductivity with a metal, the drum electrode including a power feeding layer, an insulating layer which covers a surface of the power feeding layer, and a projecting electrode which projects from the surface of the insulating layer and is electrically connected to the power feeding layer, in which the projecting electrode is provided linearly in the circumferential direction of the drum electrode. 
     Advantageous Effects of Invention 
     According to the embodiment described above, it is possible to provide a drum electrode with which a metal can be electrodeposited on the surface of a long base material in a plating tank, which can be produced by an easy method, and in which the maintenance during the operation is easy; and a method for producing the same. It is also possible to provide a plating device, a method for producing a resin molded body, and a method for producing a metal porous body, each using such a drum electrode. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic view showing an example of a structure of a drum electrode according to the present invention. 
         FIG. 2  is a schematic view showing an example of a process for producing a drum electrode according to the present invention. 
         FIG. 3  is a schematic view showing an example of a structure of a ring-shaped insulating disk having a through-hole in the center thereof. 
         FIG. 4  is an enlarged cross-sectional view schematically showing a surface portion of an example of a drum electrode according to the present invention. 
         FIG. 5  is an enlarged cross-sectional view schematically showing a surface portion of another example of a drum electrode according to the present invention. 
         FIG. 6  is an enlarged cross-sectional view schematically showing a surface portion of a drum electrode in Example 2. 
         FIG. 7  is an enlarged cross-sectional view schematically showing a surface portion of a drum electrode in Example 3. 
         FIG. 8  is a schematic view showing an example of an existing device for producing a metal porous body. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First, contents of embodiments of the present invention are enumerated and described. 
     (1) A drum electrode according to an embodiment of the present invention is a drum electrode for a device configured to plate a surface of a long base material having electrical conductivity with a metal, the drum electrode including a power feeding layer, an insulating layer which covers a surface of the power feeding layer, and a projecting electrode which projects from the surface of the insulating layer and is electrically connected to the power feeding layer, in which the projecting electrode is provided linearly in the circumferential direction of the drum electrode. 
     When the drum electrode described in the item (1) is used, by feeding power to the long base material in a plating tank, a metal can be electrodeposited on the surface of the base material. Furthermore, as a result of thorough studies by the present inventors, it has been found that by providing a projecting electrode, which is linearly shaped in the circumferential direction, on the surface of the drum electrode, it is possible to perform electroplating with a metal with sufficient uniformity on a long base material in a plating tank. 
     That is, by using the structure described in the item (1), it is possible to electrodeposit a metal on the surface of a long base material in a plating tank, and it is possible to provide a drum electrode which can be produced by an easy method, and in which the maintenance during the operation is easy. 
     In the drum electrode according to the embodiment of the present invention, the expression “the projecting electrode is provided linearly” covers both the case of a continuous linear shape extending in the circumferential direction and the case of a discontinuous linear shape with a notch being formed partially. Furthermore, the projecting electrode is not necessarily completely parallel to the circumferential direction, but may be inclined at an angle of 60° or less and formed in a helical shape. 
     (2) Furthermore, in the drum electrode according to the embodiment of the present invention, preferably, the height of the projecting electrode varies with the location of the projecting electrode on the drum electrode. 
     As will be described later, in the drum electrode according to the embodiment of the present invention, depending on the maintenance method during use, the height of the projecting electrode may vary with the location of the projecting electrode. Even such a drum electrode can be suitably used for metal plating on the surface of the base material. Therefore, during use of the drum electrode, the number of maintenance methods to choose from increases. 
     (3) Furthermore, in the drum electrode according to the embodiment of the present invention, the base material is preferably a resin molded body having a three-dimensional network structure. 
     The drum electrode according to the embodiment of the present invention can also be suitably used for a long base material having a low electrical resistance, such as a copper plate. However, in the case where the base material is a resin molded body having a three-dimensional network structure, a higher effect can be achieved. For example, in the case where the base material is a resin molded body having a three-dimensional network structure that has undergone electrical conduction treatment by application of carbon, because of its high electrical resistance, the plating voltage increases in the existing drum electrode, and there is a possibility that the resin which is the base material will be burned off. Furthermore, it is difficult to form a plating film uniformly on the central portion in the thickness direction of the resin molded body or a surface opposite the surface in contact with the drum electrode. In contrast, in the drum electrode according to the embodiment of the present invention, since a projecting electrode is provided linearly in the circumferential direction, plating can be performed directly in a liquid, and therefore, the resistance of the base material can be decreased. Furthermore, it is possible to form a plating film uniformly even on the inside of the porous portion of the resin molded body. 
     Hereinafter, the resin molded body having a three-dimensional network structure may also be simply referred to as a resin molded body. 
     (4) A method for producing a drum electrode according to an embodiment of the present invention includes a step of covering a surface of a columnar power feeding layer with an insulating layer, a step of partially removing the surface of the insulating layer linearly in the circumferential direction so as to expose the surface of the power feeding layer, and a step of plating the linearly exposed surface of the power feeding layer with a metal to form a projecting electrode so as to be higher than the surface of the insulating layer. 
     (5) A method for producing a drum electrode according to another embodiment of the present invention includes a step of alternately stacking ring-shaped insulating disks and ring-shaped metal disks, each having a through-hole in the center thereof, to form a cylindrical shape; and a step of inserting a columnar power feeding member into the through-holes of the insulating disks and the metal disks, followed by fixing. 
     By using the method for producing a drum electrode described in the item (4) or (5), it is possible to easily produce the drum electrode according to the embodiment of the present invention described in the item (1). 
     (6) A plating device according to an embodiment of the present invention is configured to plate a surface of a long base material, to which electrical conductivity has been imparted, with a metal using a drum electrode provided in a plating tank, in which the drum electrode is the drum electrode described in any one of the items (1) to (3). 
     The plating device described in the item (6) uses the drum electrode described in the item (1) or (2). Therefore, excessive maintenance is not required compared with the existing plating device, and it is possible to easily produce a resin structure having a metal plating film on the surface thereof. 
     (7) A method for producing a resin structure according to an embodiment of the present invention includes a step of imparting electrical conductivity to a surface of a long base material made of a resin, and a step of plating the surface of the base material with a metal using a drum electrode provided in a plating tank to obtain a resin structure having a metal plating film on the surface thereof, in which the drum electrode is the drum electrode described in the item (1) or (2). 
     (8) A method for producing a metal porous body according to an embodiment of the present invention includes a step of imparting electrical conductivity to a surface of a resin molded body having a three-dimensional network structure, a step of plating the surface of the resin molded body with a metal using a drum electrode provided in a plating tank to obtain a resin structure, and a step of removing the resin molded body from the resin structure to obtain a metal porous body, in which the drum electrode is the drum electrode described in the item (1) or (2). 
     In the method for producing a resin structure described in the item (7) and the method for producing a metal porous body described in the item (8), since the drum electrode described in any one of the items (1) to (3) is used, the cost required for producing the drum electrode can be reduced, and it is possible to more inexpensively provide a resin structure or a metal porous body. Furthermore, since the drum electrode can be relatively easily maintained, the burden of control during the operation can be reduced, and it is possible to more easily provide a resin structure or a metal porous body. 
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE PRESENT INVENTION 
     Specific examples of a drum electrode and the like according to the embodiments of the present invention will be described below. It is intended that the scope of the present invention is not limited to the examples, but is determined by appended claims, and includes all variations of the equivalent meanings and ranges to the claims. 
     &lt;Drum Electrode&gt; 
     A drum electrode according to an embodiment of the present invention is a drum electrode for a device configured to plate a surface of a long base material having electrical conductivity with a metal. As shown in  FIG. 1 , the drum electrode includes a power feeding layer  11 , an insulating layer  12 , and projecting electrodes  13 . The insulating layer  12  covers the surface of the power feeding layer  11 , and the projecting electrodes  13  are formed so as to project from the surface of the insulating layer  12  and are electrically connected to the power feeding layer  11 . The projecting electrodes  13  are formed linearly in the circumferential direction of the drum electrode  1 . 
     The power feeding layer  11  is not particularly limited as long as it is electrically conductive, and various metals can be suitably used. Furthermore, the power feeding layer  11  may have a single-layer structure or a layered structure including two or more layers. That is, even when another electrical conductive material is disposed on the surface of the power feeding layer  11  serving as the center of the drum electrode  1 , it is acceptable as long as the individual layers sufficiently adhere to each other such that the layers do not move relatively and are electrically connected to each other. In the case where the degree of adhesion between the layers is low, the rotary drive is not sufficiently transmitted when the drum electrode  1  is rotated. Therefore, the degree of adhesion between the layers is preferably high. 
     The insulating layer  12  has an insulating property and is stable to a plating solution with which it is in contact in a plating tank where the drum electrode  1  is placed. For example, a resin, such as an epoxy resin, a silicon resin, or a fluororesin, can be suitably used as the insulating layer. In the case where the surface of the resin molded body is aluminum plated, the fluororesin is particularly preferable among the resins described above. Furthermore, an anodic oxide film formed on the surface of the power feeding layer  11  can also be suitably used. 
     The projecting electrode  13  is not particularly limited as long as it is electrically conductive, and various metal materials can be suitably used, but the projecting electrode  13  is preferably made of the same metal as the metal to be plated on the surface of the base material. Specifically, for example, a projecting electrode made of nickel is suitably used for nickel plating, and a projecting electrode made of aluminum is suitably used for aluminum plating. 
     In  FIG. 1 , the projecting electrodes  13  are each continuously formed linearly parallel to the circumferential direction of the drum electrode  1 . Accordingly, in the drum electrode  1 , the insulating layers  12  and the projecting electrodes  13  are alternately arranged. Furthermore, in a drum electrode according to the embodiment of the present invention, the projecting electrodes  13  may be continuously formed in the circumferential direction in a closed state, or the projecting electrodes  13  may be discontinuous with a notch being formed partially. In the case where a notch exists on a projecting electrode  13 , the length of the notch is preferably as small as possible, and is preferably smaller than the length of the continuous portion of the projecting electrode. 
     Furthermore, the projecting electrodes  13  may be formed parallel to the circumferential direction or may be formed with some inclination with respect to the circumferential direction. In the case where a continuous, linear projecting electrode has an inclination with respect to the circumferential direction, the projecting electrode  13  is formed in a helical shape on the surface of the drum electrode  1 . The angle between the projecting electrode  13  and the circumferential direction is preferably as small as possible, and is preferably 60° or less. 
     By increasing the width of the insulating layer  12  relative to the width of the projecting electrode  13 , current efficiency can be increased. On the other hand, for example, in the case where the base material is one such as a resin molded body that has undergone electrical conduction treatment by application of carbon, which has a large electrical resistance, the covering power of metal plating tends to be decreased. Furthermore, when the width of the insulating layer  12  is decreased relative to the width of the projecting electrode  13 , electrical resistance decreases, and the covering power of metal plating on the base material can be increased, but current efficiency tends to be decreased. 
     Therefore, taking the above-mentioned points into consideration, the width of the insulating layer  12  and the width of the projecting electrode  13  may be appropriately set depending on the material and thickness of the base material to be plated with a metal, the type of metal used for plating, or the like. For example in the case where aluminum plating is performed in a molten salt on a foamed urethane resin to which electrical conductivity has been imparted, by alternately arranging insulating layers  12  with a width of about 4 to 12 mm and projecting electrodes  13  with a width of about 1 to 4 mm, electroplating can be performed satisfactorily. 
     The projecting electrode  13  needs to project from the surface of the insulating layer  12 . The reason for this is that when the drum electrode  1  and the base material are brought into contact with each other, the projecting electrode  13  is in contact with the base material without fail so that power feeding can be performed. In particular, in the case where the base material is one such as a resin molded body having a three-dimensional network structure to which electrical conductivity has been imparted, which has a large electrical resistance and in which it is difficult to form a plating film uniformly even on the inside of the porous portion thereof, it is necessary to bring the projecting electrode  13  and the base material into contact with each other sufficiently. The projecting height of the projecting electrode  13  from the insulating layer  12  is not particularly limited, but is preferably more than 0 mm to about 2 mm, more preferably about 0.2 to 1.5 mm, and still more preferably about 0.5 to 1 mm. In this case, the projecting electrode  13  can be sufficiently brought into contact with the base material. 
     When the projecting electrode is lower than the insulating layer, since the surface of the base material and the projecting electrode are not in contact with each other, it is not possible to electroplate the surface of the base material with a metal. However, since the drum electrode according to the embodiment of the present invention is provided in a plating tank filled with a plating solution, when the plating solution and the projecting electrode are in contact with each other during the operation, the metal starts to be electrodeposited on the surface of the projecting electrode to increase the height of the projecting electrode, and as a result, the projecting electrode projects from the surface of the insulating layer. In such a state, since the projecting electrode and the base material come into contact with each other, power feeding becomes possible, and it is possible to electroplate the surface of the base material with the metal. 
     As described above, in the drum electrode according to the embodiment of the present invention, since the metal is electrodeposited on the surface of the projecting electrode during use, the height of the projecting electrode increases relative to the insulating layer. Therefore, when the drum electrode according to the embodiment of the present invention is used, preferably, a cutting bit is provided at a predetermined position from the surface of the insulating layer. Thereby, even when the metal is electrodeposited on the projecting electrode to increase the height of the projecting electrode, if the height of the projecting electrode exceeds the predetermined level, the excess portion will be cut by the bit, thus preventing the projecting electrode from excessively projecting. 
     The cutting bit may be provided on the upper side of the drum electrode (the side opposite to the plating tank). Furthermore, a cutting bit may be provided and fixed on the upper side of each projecting electrode. Alternatively, a plurality of cutting bits may be provided on the upper side of the drum electrode so as to be movable in a direction orthogonal to the circumferential direction. In the case where the cutting bits move in a direction orthogonal to the circumferential direction, the height of the projecting electrodes from the surface of the insulating layer does not become uniform. Even in such a state, it is possible to form a plating film uniformly on the surface of the base material. 
     Furthermore, the surface of the projecting electrode is preferably rough, rather than smooth, because good interlocking with the base material can be achieved. The method for roughening the surface of the projecting electrode is not particularly limited, and any method that forms appropriate irregularities may be used. In this case, the surface roughness may be on the order of micrometers (μm). Examples of the method for roughening the surface of the projecting electrode include a method in which the surface is polished with a coarse file, a method in which a thin plating film is formed, an etching method, and a method in which dissolution is performed using an acid or alkali. Furthermore, in the case where a metal is electrodeposited on the surface of the projecting electrode to roughen the surface, the roughened state can be used as it is. 
     As the base material, any long base material whose surface is to be plated with a metal may be used. Examples thereof include a resin sheet to which electrical conductivity has been imparted by application of carbon or the like. As the resin sheet, for example, a vinyl chloride sheet or the like may be used. 
     Furthermore, as described above, in the case where the base material is a resin molded body having a three-dimensional network structure, the performance of the drum electrode according to the embodiment of the present invention is highly exhibited. 
     As the resin molded body having a three-dimensional network structure, for example, a foamed resin molded body produced using polyurethane, a melamine resin, or the like can be used. Although expressed as the foamed resin molded body, a resin molded body having any shape can be selected as long as it has continuous pores (interconnected pores). For example, a body having a nonwoven fabric-like shape in which resin fibers, such as polypropylene or polyethylene, are entangled with each other can be used instead of the foamed resin molded body. 
     Furthermore, the type of metal used for plating is not particularly limited, and can be appropriately selected according to the intended purpose of the surface treatment of the base material. Examples thereof include aluminum, copper, nickel, zinc, tin, chromium, silver, and gold. 
     By using the drum electrode according to the embodiment of the present invention, even in the case where the base material is a resin molded body having a three-dimensional network structure, it is possible to electrodeposit a metal uniformly on the surface of the base material in a plating tank. As will be described later, the drum electrode itself can be produced by an easy method, and moreover, the burden of maintenance during use can be reduced. 
     &lt;Method for Producing Drum Electrode&gt; 
     (Production Method According to Embodiment 1) 
     The drum electrode according to the embodiment of the present invention described above can be produced by a method for producing a drum electrode, which includes a step of covering a surface of a columnar power feeding layer with an insulating layer (insulating layer formation step), a step of partially removing the surface of the insulating layer linearly in the circumferential direction so as to expose the surface of the power feeding layer (insulating layer partial removal step), and a step of plating the linearly exposed surface of the power feeding layer with a metal to form a projecting electrode so as to be higher than the surface of the insulating layer (projecting electrode formation step). 
     [Insulating Layer Formation Step] 
     First, a columnar, electrically conductive material serving as a power feeding layer is prepared. As described above, the material for the power feeding layer is not particularly limited as long as it is electrically conductive, and various metals can be suitably used. Furthermore, the power feeding layer may have a single-layer structure or a layered structure including two or more layers. 
     Subsequently, the columnar power feeding layer is entirely coated by disposing an insulating layer on the surface thereof. The insulating layer may be formed with a large thickness when the diameter of the power feeding layer is small relative to the diameter of the drum electrode to be produced. The insulating layer may be formed with a small thickness when the power feeding layer includes a plurality of layers and the diameter of the power feeding layer is close to the diameter of the drum electrode. 
     As described above, the insulating layer has an insulating property and is stable to a plating solution with which it is in contact in a plating tank where the drum electrode is placed. For example, the insulating layer can be formed by a method in which an insulating resin is used, a method in which an anodic oxide film is formed on the surface of the power feeding layer, or the like. 
     [Insulating Layer Partial Removal Step] 
     By undergoing the step described above, the entire surface of the power feeding layer is coated with the insulating layer. A groove is formed in a portion of the surface of the insulating layer in which a projecting electrode is to be formed. The insulating layer is removed until the groove reaches the surface of the power feeding layer located under the insulating layer. 
     In this step, by forming a plurality of grooves, each groove being continuously formed parallel to the circumferential direction, it is possible to produce a drum electrode in which insulating layers and projecting electrodes are alternately arranged. Furthermore, when each groove is not completely continuous in the circumferential direction and a portion without the groove is provided, it is possible to form a projecting electrode having a notch partially formed therein. Furthermore, when a groove is continuously formed at a certain angle (60° or less) with respect to the column direction, it is possible to form a projecting electrode which projects helically on the surface of the drum electrode. 
     [Projecting Electrode Formation Step] 
     A projecting electrode is formed on the exposed portion of the surface of the power feeding layer in which the groove has been formed in the insulating layer as described above. The projecting electrode is not particularly limited as long as it is electrically conductive, and various metal materials can be suitably used. Furthermore, as described above, the projecting electrode is preferably made of the same metal as the metal to be plated on the base material. 
     The method for forming the projecting electrode is not particularly limited. For example, the projecting electrode can be formed by plating the exposed portion of the surface of the power feeding layer with a metal. The plating method may be non-electrolytic plating or electrolytic plating. The plating is stopped when the metal plating that has started to grow on the exposed portion of the surface of the power feeding layer projects from the surface of the insulating layer. 
     (Production Method According to Embodiment 2) 
     The drum electrode according to the embodiment of the present invention described above can also be produced by a method for producing a drum electrode, which includes a step of alternately stacking ring-shaped insulating disks and ring-shaped metal disks, each having a through-hole in the center thereof, to form a cylindrical shape; and a step of inserting a columnar power feeding member into the through-holes of the insulating disks and the metal disks, followed by fixing. 
     In this method, as shown in  FIG. 2 , ring-shaped insulating disks  22  having a through-hole in the center thereof and ring-shaped metal disks  23  having a through-hole in the center thereof are produced and alternately arranged in a concentric fashion to form a cylindrical shape. A columnar power feeding member is inserted into the through-holes in the center and fixed firmly. 
     The insulating disks  22  and the metal disks  23  can be fixed together, for example, by fastening with bolts, application of an adhesive, or the like. Furthermore, fixing with the power feeding member which has been inserted into the through-hole can be performed in the same manner using bolts or an electrically conductive adhesive. 
     The diameter of the metal disk  23  is preferably larger than the diameter of the insulating disk  22 . However, even in the case where the diameter of the metal disk  23  is equal to or smaller than the diameter of the insulating disk  22 , after the power feeding member has been inserted, as in the method described above, the surface of the metal disk  23  may be plated with a metal. 
     Since the insulating disk  22  serves as the insulating layer described above, a material having an insulating property and is stable to a plating solution with which it is in contact in a plating tank where the drum electrode is placed can be used for the insulating disk  22 . 
     Since the metal disk  23  serves as the projecting electrode described above, the material for the metal disk  23  is not particularly limited as long as it is electrically conductive, and various metal materials can be suitably used. Preferably, the metal is the same as the metal to be plated on the base material. 
     As described above, the power feeding layer is not particularly limited as long as it is electrically conductive, and various metals can be suitably used. Furthermore, the power feeding layer may have a single-layer structure or a layered structure including two or more layers. 
     Furthermore, the insulating disk  22  may be a single ring-shaped disk or a disk formed by combining a plurality of plates. For example, the insulating disk  22  may be formed by combining a plurality of divided sectoral insulating disks (insulating layers)  32  as shown in  FIG. 3 . However, in the case where sectoral ones are used, joints must be welded or the like so that no voids are formed. When the joint portion has a void, the plating solution enters the void, and plating grows in the void. Therefore, a conductive portion that is continuous in a direction orthogonal to the circumferential direction is formed on the surface of the drum electrode. When such a conductive portion that is continuous in a direction orthogonal to the circumferential direction is formed, the current concentrates on the conductive portion, which may cause problems. For example, in the case where the base material is a resin molded body, the base material may be burned off. 
     In such a manner, the drum electrode according to the embodiment of the present invention can be produced. In accordance with these methods, it is possible to produce the drum electrode very easily compared with the existing drum electrode. 
       FIGS. 4 and 5  are each an enlarged cross-sectional view of a drum electrode obtained by the method described above.  FIG. 4  shows an example in which a power feeding layer is formed by stacking a plurality of layers, the surface portion thereof is covered with an insulating layer  42 , grooves are provided in the insulating layer  42 , and projecting electrodes  43  are formed in the grooves. Furthermore,  FIG. 5  shows an example in which the drum electrode is produced by alternately arranging insulating disks  52  and metal disks  53 , followed by fixing. 
     &lt;Plating Device&gt; 
     A plating device according to an embodiment of the present invention is configured to plate a surface of a long base material, to which electrical conductivity has been imparted, with a metal using a drum electrode provided in a plating tank, in which the drum electrode is the drum electrode according to the present invention described above. 
     The plating device according to the embodiment of the present invention can have the same basic structure as that of the existing device, for example, shown in  FIG. 8 , as long as the drum electrode according to the embodiment of the present invention is used. That is, the plating device has a structure in which, in a plating tank filled with a plating solution, the drum electrode according to the embodiment of the present invention is provided as a cathode and a metal for plating is provided as an anode. Furthermore, as described above, preferably, a cutting bit is provided on the upper side of the plating device so that it is possible to partially cut the projecting electrode on which the metal has been electrodeposited and whose height has been increased during the operation. 
     &lt;Method for Producing Resin Structure&gt; 
     A method for producing a resin structure according to an embodiment of the present invention includes a step of imparting electrical conductivity to a long base material made of a resin, and a step of plating a surface of the base material with a metal using a drum electrode provided in a plating tank to obtain a resin structure having a metal plating film on the surface thereof, in which the drum electrode is the drum electrode according to the embodiment of the present invention described above. 
     In the method for producing a resin structure according to the embodiment of the present invention, as long as the drum electrode according to the embodiment of the present invention is used as the drum electrode, the other steps can be performed as in the existing method for producing a resin structure. 
     Furthermore, any long base material made of a resin can be used as the base material as long as the surface thereof is to be plated with a metal as described above. As the method for imparting electrical conductivity to the surface of the base material, for example, a method may be used in which carbon powder formed into a paste is applied to the surface of the base material. 
     &lt;Method for Producing Metal Porous Body&gt; 
     A method for producing a metal porous body according to an embodiment of the present invention includes a step of imparting electrical conductivity to a resin molded body having a three-dimensional network structure, a step of plating a surface of the resin molded body with a metal using a drum electrode provided in a plating tank to obtain a resin structure, and a step of removing the resin molded body from the resin structure to obtain a metal porous body, in which the drum electrode is the drum electrode according to the embodiment of the present invention described above. In the method for producing a metal porous body according to the embodiment of the present invention, as long as the drum electrode according to the embodiment of the present invention is used as the drum electrode, the other steps can be performed as in the existing method for producing a resin structure. 
     As the resin molded body having a three-dimensional network structure serving as the base material, as described above, a foamed resin molded body can be suitably used. In addition, it is also possible to suitably use a body having a nonwoven fabric-like shape in which resin fibers are entangled with each other, and a resin molded body in any shape having continuous pores. 
     Furthermore, the method for imparting electrical conductivity to the resin molded body is not particularly limited. When the drum electrode according to the embodiment of the present invention is used, it is possible to perform electroplating satisfactorily even on a base material having a relatively large resistance, such as the one obtained by application of carbon. The method of application of carbon is not particularly limited, and a known method can be employed. 
     EXAMPLES 
     The present invention will be described in more detail below on the basis of examples. However, the examples are merely illustrative and the drum electrode and the like of the present invention are not limited thereto. It is intended that the scope of the present invention is determined by appended claims, and includes all variations of the equivalent meanings and ranges to the claims. 
     Example 1 
     &lt;Production of Drum Electrode  1 &gt; 
     24 Disks made of aluminum with a thickness of 1 mm and a diameter of 200 mm were prepared, and a through-hole with a diameter of 40 mm was formed in the center of each of the disks. 
     25 Insulating disks made of vinyl chloride with a thickness of 4 mm and a diameter of 199 mm were prepared, and a through-hole with a diameter of 40 mm was formed in the center of each of the disks. 
     The disks made of aluminum and the insulating disks were alternately arranged and fixed firmly with bolts. A power feeding layer made of titanium with a diameter of 39 mm and a length of 250 mm was inserted into the through-hole portion in the center, and fixed firmly with a jig. Thus, a drum electrode  1  was obtained, in which linear projecting electrodes continuously extending in the circumferential direction with a width of 1 mm were formed at an interval of 4 mm. 
     The projecting electrodes of the drum electrode  1  thus obtained were subjected to aluminum plating treatment in order to roughen the surfaces thereof. 
     &lt;Production of Metal Porous Body  1 &gt; 
     (Base Material) 
     As a base material, foamed urethane with a thickness of 1 mm, a porosity of 95% by volume, and a number of pores (cells) per inch of about 50 was prepared. By immersing the foamed urethane in a carbon suspension, followed by drying, electrical conductivity was imparted thereto. The carbon suspension contained 17% by mass of graphite and carbon black and 7% by mass of a resin binder, and further contained a penetrating agent and an anti-foaming agent. The particle size of the carbon black was 0.5 μm. 
     (Structure of Device for Producing Metal Porous Body) 
     As a plating solution, a molten salt was prepared by mixing aluminum chloride (AlCl 3 ) and 1-ethyl-3-methylimidazolium chloride (EMIC) at a mixing ratio of 2:1 (in terms of molar ratio), and a plating tank was filled with the plating solution. 
     In the plating tank, an aluminum electrode was placed as an anode, and the drum electrode  1  produced as described above was placed as a cathode. 
     (Production of Metal Porous Body) 
     The foamed urethane to which electrical conductivity had been imparted as prepared above was supplied as a base material to the device for producing a metal porous body having the structure described above, and aluminum electroplating was performed. Thereby, a metal porous body  1  was produced. The conveying velocity of the base material was set at 17 mm/min, and the applied current density was set at 8 A/dm 2 . 
     Furthermore, a cutting bit was provided on the upper side of the drum electrode  1  so as to be configured to appropriately cut aluminum electrodeposited on the surfaces of the projecting electrodes. The cutting bit was placed at a distance of 1 mm from the surface of the insulating layer and was moved in a reciprocating manner in a direction orthogonal to the circumferential direction. 
     Example 2 
     &lt;Production of Drum Electrode  2 &gt; 
     A drum made of aluminum with a diameter of 200 mm was prepared, and 24 linear projections extending continuously in the circumferential direction were formed at an interval of 4 mm. The width of the projections was set at 1 mm, and the height of the projections was set at 1.5 mm. 
     The entire surface of the aluminum drum was coated with a fluororesin (ETFE) with a thickness of 0.6 mm. Since the fluororesin layer was also formed on the surfaces of the projections, the surface coated with the fluororesin was scraped until the surfaces of the projections were exposed. Aluminum plating was grown with a thickness of 0.5 mm on the surfaces of the projections (aluminum) exposed from the surface of the fluororesin. Thus, a drum electrode  2  was obtained, in which linear projecting electrodes  63  continuously extending in the circumferential direction with a width of 1 mm were formed at an interval of 4 mm.  FIG. 6  is an enlarged cross-sectional view of a surface portion of the drum electrode  2 . In  FIG. 6 , reference sign  62  denotes the insulating layer made of the fluororesin. 
     &lt;Production of Metal Porous Body  2 &gt; 
     A metal porous body  2  was produced as in Example 1 except that the drum electrode  2  was used instead of the drum electrode  1  in the production of the metal porous body  1  in Example 1. 
     Example 3 
     &lt;Production of Drum Electrode  3 &gt; 
     A drum made of aluminum with a diameter of 200 mm was prepared, and by subjecting the surface thereof to anodic oxide coating treatment, an anodic oxide film of aluminum was formed. The thickness of the anodic oxide film of aluminum was about 10 μm. 
     On the surface of the drum on which the anodic oxide film had been formed, 24 grooves continuously extending in the circumferential direction were formed at an interval of 4 mm. The width of the grooves was set at 1 mm, and the depth of the grooves was set at 0.5 mm. By subjecting the surface of the drum to aluminum plating treatment, aluminum plating was grown in the grooves. Aluminum plating was formed so as to project from the surface of the anodic oxide film by 0.5 mm. Thus, a drum electrode  3  was obtained, in which linear projecting electrodes  73  continuously extending in the circumferential direction with a width of 1 mm were formed at an interval of 4 mm.  FIG. 7  is an enlarged cross-sectional view of a surface portion of the drum electrode  3 . In  FIG. 7 , reference sign  72  denotes anodic oxide coating serving as an insulating layer. 
     &lt;Production of Metal Porous Body  3 &gt; 
     A metal porous body  3  was produced as in Example 1 except that the drum electrode  3  was used instead of the drum electrode  1  in the production of the metal porous body  1  in Example 1. 
     Example 4 
     &lt;Production of Drum Electrode  4 &gt; 
     A drum electrode  4  was produced as in Example 1 except that the width of the projecting electrodes was set at 2 mm and the width of the insulating layer portion was set at 4 mm in the production of the drum electrode  1  in Example 1. 
     &lt;Production of Metal Porous Body  4 &gt; 
     A metal porous body  4  was produced as in Example 1 except that the drum electrode  4  was used instead of the drum electrode  1  in the production of the metal porous body  1  in Example 1. 
     Example 5 
     &lt;Production of Drum Electrode  5 &gt; 
     A drum electrode  5  was produced as in Example 1 except that the width of the projecting electrodes was set at 2 mm and the width of the insulating layer portion was set at 8 mm in the production of the drum electrode  1  in Example 1. 
     &lt;Production of Metal Porous Body  5 &gt; 
     A metal porous body  5  was produced as in Example 1 except that the drum electrode  5  was used instead of the drum electrode  1  in the production of the metal porous body  1  in Example 1. 
     Example 6 
     &lt;Production of Drum Electrode  6 &gt; 
     24 Disks made of copper with a thickness of 1 mm and a diameter of 200 mm were prepared, and a through-hole with a diameter of 40 mm was formed in the center of each of the disks. 
     25 Insulating disks made of vinyl chloride with a thickness of 4 mm and a diameter of 199 mm were prepared, and a through-hole with a diameter of 40 mm was formed in the center of each of the disks. 
     The disks made of copper and the insulating disks prepared as described above were alternately arranged and fixed firmly with bolts. A power feeding layer made of titanium with a diameter of 39 mm and a length of 250 mm was inserted into the through-hole portion in the center, and fixed firmly with a jig. Thus, a drum electrode  6  was obtained, in which linear projecting electrodes continuously extending in the circumferential direction with a width of 1 mm were formed at an interval of 4 mm. 
     &lt;Production of Metal Porous Body  6 &gt; 
     A metal porous body  6  was produced as in Example 1 except that a copper plating solution was used as a plating solution instead of the aluminum plating solution, a copper electrode was used as the anode instead of the aluminum electrode, and the drum electrode  6  was used instead of the drum electrode  1  in the production of the metal porous body  1  in Example 1. The copper plating solution used was composed of 70 g/L of copper sulfate and 200 g/L of sulfuric acid. 
     Example 7 
     &lt;Production of Drum Electrode  7 &gt; 
     A drum electrode  7  was produced as in Example 6 except that insulating disks with a width of 9 mm were used in the production of the drum electrode  6  in Example 6. 
     &lt;Production of Metal Porous Body  7 &gt; 
     A metal porous body  7  was produced as in Example 6 except that the drum electrode  7  was used instead of the drum electrode  6  in the production of the metal porous body  6  in Example 6. 
     [Evaluation of Metal Porous Bodies] 
     In the metal porous bodies produced in Examples 1 to 7, it was confirmed that aluminum or copper was satisfactorily plated on the surface of the foamed urethane. The variation in the coating weight of aluminum or copper in the width direction was within ±15% of the targeted coating weight. 
     REFERENCE SIGNS LIST 
       1  drum electrode 
       11  power feeding layer 
       12 ,  42 ,  62 ,  72  insulating layer 
       13 ,  43 ,  63 ,  73  projecting electrode 
       22 ,  52  insulating disk (insulating layer) 
       23 ,  53  metal disk (projecting electrode) 
       32  divided insulating disk (insulating layer) 
       81  existing drum electrode 
       82  projection 
       83  anode 
       84  plating tank 
       85  plating solution