Patent Publication Number: US-9842703-B2

Title: Aluminum electrolytic capacitor and rubber seal for same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation application of Ser. No. 14/387,619, filed on Sep. 24, 2014, which is National Phase of International Application No. PCT/JP2012/002919 filed Apr. 27, 2012. 
    
    
     TECHNICAL FIELD 
     The present invention relates to an aluminum electrolytic capacitor and, more particularly, to a technique for inserting a lead terminal through a terminal passage hole of a rubber seal without applying such an excessively large load as to deteriorate characteristics to a capacitor element. 
     BACKGROUND ART 
     Referring to a sectional view of  FIG. 11 , an aluminum electrolytic capacitor includes, as basic components, a capacitor element  1  including a pair of lead terminals  2 ,  2 . As shown in  FIG. 12 , the capacitor element  1  is formed by winding, via not-shown separator paper, in a spiral shape, an anode foil la and a cathode foil  1   b  made of aluminum material and having the lead terminals  2  attached thereto. 
     The capacitor element  1  is housed in an armor case  3  having a bottomed cylindrical shape together with a predetermined electrolytic substance. An opening section of the armor case  3  is sealed by a rubber seal  4 . Terminal passage holes  5 ,  5  are drilled in the rubber seal  4 . Respective distal end portions of the lead terminals  2 ,  2  are drawn out to the outside through the terminal passage holes  5 ,  5 . 
     Actually, the rubber seal  4  is housed in the armor case  3  together with the capacitor element  1  in a state in which the tip of the rubber seal  4  is attached to the lead terminals  2 ,  2  earlier. The rubber seal  4  is hermetically fixed in the opening section of the armor case  3  by caulking of a lateral reduction groove  3   a  of the armor case  3 , which is formed later, and an end edge  3   b  of the armor case  3 . 
     Usually, an aluminum case is used as the armor case  3 . Isobutylene-isoprene rubber or the like is used as the rubber seal  4 . Usually, non-aqueous or aqueous electrolyzed liquid is used as the electrolytic substance. However, a solid electrolyte is sometimes used. 
     As shown in  FIG. 12 , the lead terminal  2  includes a tab terminal  21  and an outside lead wire  22 . The tab terminal  21  is made of an aluminum material and includes a flat section  21   a  press-molded in a battledore shape and a round bar section  21   b.    
     The tab terminal  21  of this type can be obtained by cutting an aluminum round bar material at predetermined length and pressing one end side of the round bar material. The flat section  21   a  is attached to the anode foil la and the cathode foil lb by caulking needles, welding, or the like. 
     Usually, a copper-coated steel wire (CP wire) is used as the outside lead wire  22 . To improve solderability to a circuit board, the outside lead wire  22  includes a plated layer on the surface. In the case of Pb (lead) free, Sn 100% plating, Sn/Bi (0.5%) plating, or the like is mainly applied to the plated layer. 
     The outside lead wire  22  is smaller in diameter than the round bar section  21   b  of the tab terminal  21  and is welded to an end face of the round bar section  21   b . A welded section of the outside lead wire  22  is denoted by reference numeral  23 . 
     Incidentally, when the plated layer on the surface is the Sn  100 % plating, the plated layer other than the welded section  23  is stable. However, in the welded section  23 , Al, An, Cu, Fe, and the like are mixed. When the welded section  23  is exposed to the outside air, stress acts on an Sn layer because of hydration and oxidation reaction of Al. An Sn whisker (a whisker-like crystal substance)  23   a  intensely occurs and grows. 
     In the Sn/Bi (0.5%) plating, although the growth of the whisker is relaxed than that in the Sn 100%, the whisker also occurs. When the growth of the whisker is conspicuous, there is a risk that the whisker scatters on the circuit board and, in the worst case, shirt-circuits an electronic circuit. 
     Therefore, in order to suppress the occurrence of the whisker as much as possible and prevent the scattering of the whisker to the outside, in Patent Documents 1 and 2, as shown in  FIG. 13 , the applicant proposes to coaxially connect, as the terminal passage hole  5  of the rubber seal  4 , a large-diameter round bar mating hole  51 , in which the round bar section  21   b  of the tab terminal  21  is fit, and a small-diameter lead wire passage hole  52 , through which the outside lead wire  22  is inserted, and set a hole diameter φ 2  of the lead wire passage hole  52  smaller than an outer diameter  41  of the outside lead wire  22  (φ 2 &lt;φ 1 ) to shut off the welded section  23  from the outside air. 
     According to Patent Documents 1 and 2, the scattering to the outside of the whisker  23   a  that occurs in the welded section  23  is prevented. However, on the other hand, since the hole diameter φ 2  of the lead wire passage hole  52  is smaller than the outer diameter φ 1  of the outside lead wire  22  (φ&lt;φ 1 ), when the outside lead wire  22  is forcibly inserted through the lead wire passage hole  52 , excessively large stress is applied to the capacitor element  1 . Because of the excessive stress, the characteristics of the capacitor element  1  are sometimes deteriorated. 
     In order to solve this point, Patent Document 3 proposes to form, in the lead wire passage hole of the rubber seal, a funnel-shaped cylindrical body made of a thin film gradually reduced in diameter toward the outer side of the capacitor. 
     Patent Document 4 proposes to integrally form, in the lead wire passage hole of the rubber seal, a sealing plug body having a slit for inserting the lead terminal and draw out the lead terminal to the outside via the slit. 
     As a technique similar to Patent Document 4, Patent Document 5 proposes to integrally form, in the lead wire passage hole of the rubber seal, a sealing plug made of a thin wall for closing the passage hole and draw out the lead terminal to the outside piecing through the sealing plug. 
     CITATION LIST 
     Patent Documents 
     Patent Document 1: Japanese Patent Laid-Open No. 2006-295055 
     Patent Document 2: Japanese Patent Laid-Open No. 2008-10865 
     Patent Document 3: Japanese Patent Laid-Open No. 2008-251982 
     Patent Document 4: Japanese Patent Laid-Open No. 2009-212175 
     Patent Document 5: Japanese Patent Laid-Open No. 2010-161277 
     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, in the case of the invention described in Patent Document 3, there is a problem in that, because of a molding technique for the rubber seal, it is difficult to integrally form, in the rubber seal, the funnel-shaped cylindrical body made of the thin film gradually reduced in diameter toward the outer side of the capacitor and, even if the cylindrical body can be molded, reliability is poor because the periphery of the lead terminal is sealed by the funnel-shaped thin film portion. 
     In the invention described in Patent Document 4, the lead wire is drawn out to the outside via the slit of the sealing plug. In the invention described in Patent Document 5, the lead terminal is drawn out to the outside piercing through the sealing plug. Therefore, in both inventions, there is a problem in that it is difficult to surely seal the periphery of the lead terminal. 
     Therefore, it is an object of the present invention to insert the lead terminal through the terminal passage hole of the rubber seal without applying such an excessively large load as to deteriorate characteristics to the capacitor element and while keeping a state in which the lead terminal can be surely shut off from the outside air. 
     Means for Solving the Problems 
     In order to solve the problems, the present invention provides an aluminum electrolytic capacitor including: a capacitor element formed by winding, via a separator, an anode foil and a cathode foil both having lead terminals attached thereto; an armor case having a bottomed cylindrical shape in which the capacitor element is housed together with a predetermined electrolytic substance; and a rubber seal having a terminal passage hole for the lead terminals drilled therein and mounted on an opening section of the armor case, the lead terminal including a tab terminal having a flat section and a round bar section and an outside lead wire having a plated layer on the surface and welded to an end of the round bar section, the terminal passage hole of the rubber seal including a round bar mating hole, in which the round bar section of the tab terminal is fit, and a lead wire passage hole coaxial with the round bar mating hole and smaller in diameter than the round bar mating hole, the outside lead wire being inserted through the lead wire passage hole, and a hole diameter of the lead wire passage hole being smaller than an outer diameter of the outside lead wire, the outside lead wire being forcibly inserted through the lead wire passage hole to be drawn out to the outside of the armor case, and a welded section of the round bar section and the outside lead wire being shut off from the outside air, wherein 
     a conical guide surface gradually reduced in diameter is formed between the round bar mating hole and the lead wire passage hole in the terminal passage hole, the outside lead wire includes a lead wire body larger in diameter than the hole diameter of the lead wire passage hole and a passage guide part integrally connected to a distal end portion of the lead wire body, the passage guide part is formed to be gradually reduced in diameter from the lead wire body to be smaller in diameter than the hole diameter of the lead wire passage hole, and, in the passage guide part, a substantially conical sloped surface having a predetermined inclination angle is formed. 
     In the present invention, it is preferable that, when an inclination angle of the guide surface with respect to an imaginary plane X orthogonal to an axis Y passing the terminal passage hole is represented as θa and the inclination angle of the sloped surface is represented as θb, θa&lt;θb. 
     Preferably, at least the surface of the passage guide part of the outside lead wire and/or at least the inner surface of the lead wire passage hole of the rubber seal is coated with low-friction resin. 
     In this case, it is preferable that coating thickness of the low-friction resin is 0.3 to 1.5 μm. 
     As the low-friction resin, polyparaxylene or silicone oil emulsion is preferably adopted. 
     When the entire rubber seal is coated with the low-friction resin, the electrolytic substance in use may be either non-aqueous or aqueous electrolyzed liquid. 
     The present invention is suitable for an aluminum electrolytic capacitor in which lead-free tin plating is applied to the outside lead wire and a whisker tends to occur in a welded section of the outside lead wire. 
     According to a preferred form of the present invention, in preventing the electrolyzed liquid from being accumulated between the guide surface and the welded section, when an inclination angle of the welded section with respect to an imaginary plane X orthogonal to an axis Y passing the terminal passage hole is represented as θc, the guide surface includes an inclined surface having an angle substantially the same as the inclination angle θc. 
     As a more preferable form, with a boundary set in an intersection portion of an extended line of an outer diameter surface of the lead wire body and the guide surface in a state in which the lead wire body and the lead wire passage hole are set to be coaxial, the guide surface includes a first inclined surface inclined at an angle substantially the same as the inclination angle θc from the intersection portion to the inner surface of the round bar mating hole and a second inclined surface inclined at an angle smaller than the inclination angle θc from the intersection portion to the inner peripheral edge of the lead wire passage hole. 
     In preventing the electrolyzed liquid from being accumulated between the guide surface and the welded section, it is preferable that the lead terminals are fit in the terminal passage hole until the lower end of the welded section comes into contact with the intersection portion so that the first inclined surface substantially adheres to the welded section. 
     The present invention also includes a three-terminal type aluminum electrolytic capacitor including, besides the lead terminals respectively attached to the anode foil and the cathode foil, an electrically neutral dummy terminal not connected to the capacitor element, a dummy terminal passage hole for the dummy terminal being further drilled in the rubber seal and the dummy terminal and the dummy terminal passage holes being formed the same as the lead terminals and the terminal passage hole for the lead terminals. 
     The present invention also includes a rubber seal for an aluminum electrolytic capacitor including a terminal passage hole through which a lead terminal formed by welding an outside lead wire to an end of a round bar section included in a tab terminal, the terminal passage hole including a round bar mating hole in which the round bar section is fit and a lead wire passage hole coaxial with the round bar mating hole and smaller in diameter than the round bar mating hole, the outside lead wire being inserted through the lead wire passage hole, and a hole diameter of the lead wire passage hole being smaller than an outer diameter of the outside lead wire, and the outside lead wire being forcibly inserted through the lead wire passage hole such that a welded section of the round bar section and the outside lead wire is shut off from the outside air, wherein 
     a conical guide surface gradually reduced in diameter is formed between the round bar mating hole and the lead wire passage hole in the terminal passage hole and, when an inclination angle of the welded section with respect to an imaginary plane X orthogonal to an axis Y passing the terminal passage hole is represented as θc, the guide surface includes an inclined surface having an angle substantially the same as the inclination angle θc. 
     In the rubber seal, too, with a boundary set in an intersection portion of an extended line of an outer diameter surface of the outside lead wire and the guide surface in a state in which the outside lead wire and the lead wire passage hole are set to be coaxial, the guide surface includes a first inclined surface inclined at an angle substantially the same as the inclination angle θc from the intersection portion to the inner surface of the round bar mating hole and a second inclined surface inclined at an angle smaller than the inclination angle θc from the intersection portion to the inner peripheral edge of the lead wire passage hole. 
     It is preferable that at least the inside of the terminal passage hole is coated with low-friction resin at film thickness of 0.3 to 1.5 μm. 
     Advantages of the Invention 
     According to the present invention, the conical guide surface gradually reduced in diameter is formed between the round bar mating hole and the lead wire passage hole in the terminal passage hole, the passage guide part gradually reduced in diameter from the lead wire body to be smaller in diameter than the hole diameter of the lead wire passage hole is integrally formed on the distal end side of the outside lead wire, and the substantially conical sloped surface having the predetermined inclination angle is formed in the passage guide part. Therefore, it is possible to insert the lead terminal through the terminal passage hole of the rubber seal without applying such an excessively large load as to deteriorate characteristics to the capacitor element and while keeping a state in which the lead terminal is surely shut off from the outside air. 
     Therefore, in manufacturing the aluminum electrolytic capacitor in which the lead-free tin plating is applied to the outside lead wire, occurrence of a whisker in the welded section is suppressed as much as possible, and, even if the whisker occurs, in preventing scattering of the whisker to the outside, the hole diameter of the lead wire passage hole is set smaller than the outer diameter of the outside lead wire, the outside lead wire is forcibly inserted through the lead wire passage hole and drawn out to the outside of the armor case, and the welded section of the round bar section and the outside lead wire is shut off from the outside air, an yield rate of the manufacturing is improved and it is possible to further improve productivity. 
     When the inclination angle of the welded section with respect to the imaginary plane X orthogonal to the axis Y passing the terminal passage hole is represented as θc, the inclined surface having the angle substantially the same as the inclination angle θc is included in the guide surface. Therefore, an amount of the electrolyzed liquid accumulated between the guide surface and the welded section greatly decreases. It is possible to prevent a liquid leak of the electrolyzed liquid. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view separately showing an outside lead wire of a lead terminal and a terminal passage hole of a rubber seal included in an aluminum electrolytic capacitor of the present invention; 
         FIG. 2  is an enlarged sectional view showing a main part of  FIG. 1 ; 
         FIG. 3  is a schematic diagram showing a state in which the outside lead wire of the lead terminal is inserted through the terminal passage hole of the rubber seal; 
         FIGS. 4( a ), 4( b ), and 4( c )  are actual object photographs showing end shapes of the outside lead wire according to examples 1 to 3 of the present invention; 
         FIGS. 5( a ), 5( b ), 5( c ), 5( d ), and 5( e )  are actual object photographs showing end shapes of the outside lead wire as comparative examples 1 to 5; 
         FIG. 6  is a graph of examples 1 to 3 of the present invention and comparative examples 1 to 5 showing pressure applied to a capacitor element when the lead terminal is inserted; 
         FIG. 7  is a sectional view showing a state in which the outside lead wire of the lead terminal is inserted through the terminal passage hole of the rubber seal; 
         FIG. 8  is a sectional view of a terminal passage hole for explaining points to note in setting a guide surface of the terminal passage hole close to an inclination angle of a welded section; 
         FIG. 9  is a sectional view of the terminal passage hole showing a preferred embodiment for setting the guide surface of the terminal passage hole close to the inclination angle of the welded section; 
         FIG. 10( a )  is a plan view showing a rubber seal having three terminals including a dummy terminal and  FIG. 10( b )  is an A-A line enlarged sectional view of the rubber seal; 
         FIG. 11  is a schematic sectional view showing a basic configuration of the aluminum electrolytic capacitor; 
         FIG. 12  is a perspective view showing a state in which the lead terminal used in the aluminum electrolytic capacitor is attached to an electrode foil; and 
         FIG. 13  is an enlarged sectional view showing, as a conventional example, a dimensional relation between a terminal passage hole of a rubber seal and an outside lead wire of a lead terminal for which whisker measures are taken. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     Next, several embodiments of the present invention are explained with reference to  FIG. 1  to  FIG. 10( b ) . However, the present invention is not limited to the embodiments. Note that, in the embodiments, components that are the same as or may be regarded the same as the conventional example explained with reference to preceding  FIGS. 11 to 13  are denoted by the same reference numerals and signs. 
     In  FIG. 1  and  FIG. 2 , only a main part of the present invention is shown. However, referring to  FIG. 11  to  FIG. 13  as well, like the conventional example explained earlier, an aluminum electrolytic capacitor of the present invention includes, as basic components, the capacitor element  1  including the pair of lead terminals  2 ,  2 , the armor case  3 , and the rubber seal  4 . 
     As shown in  FIG. 12 , the capacitor element  1  is formed by winding, in a spiral shape, via not-shown separator paper, the anode foil  1   a  and the cathode foil lb made of the aluminum material having the lead terminal  2  attached thereto. 
     The capacitor element  1  is housed in the armor case  3  having the bottomed cylindrical shape made of the aluminum material together with the predetermined electrolytic substance. The opening section of the armor case  3  is sealed by the rubber seal  4 . The terminal passage holes  5 ,  5  are drilled in the rubber seal  4 . The respective distal end portions of the lead terminals  2 ,  2  are drawn out to the outside through the terminal passage holes  5 ,  5 . 
     Actually, the rubber seal  4  is housed in the armor case  3  together with the capacitor element  1  in a state in which the rubber seal  4  is attached to the lead terminals  2 ,  2  earlier. The rubber seal  4  is hermetically fixed in the opening section of the armor case  3  by caulking of the lateral reduction groove  3   a  of the armor case  3 , which is formed later, and the end edge  3   b  of the armor case  3 . 
     As the rubber seal  4 , preferably, a rubber material such as vulcanized IIR (isobutylene-isoprene rubber) or EPT (ethylene propylene rubber) is used. As the electrolytic substance, usually, non-aqueous or aqueous electrolyzed liquid is used. However, a solid electrolyte may be used. Usually, the capacitor element  1  is housed in the armor case  3  in a state in which the electrolyzed liquid is impregnated. 
     As shown in  FIG. 12 , the lead terminal  2  includes the tab terminal  21  and the outside lead wire  22 . The tab terminal  21  is made of the aluminum material and includes the flat section  21   a  press-molded in the battledore shape and the round bar section  21   b.    
     The tab terminal  21  of this type can be obtained by cutting an aluminum round bar material at predetermined length and pressing one end side of the round bar material. The flat section  21   a  is attached to the anode foil la and the cathode foil lb by caulking needles, welding, or the like. 
     Usually, a copper-coated steel wire (CP wire) is used as the outside lead wire  22 . To improve solderability to a circuit board, the outside lead wire  22  includes a plated layer on the surface. In the case of Pb (lead) free, Sn 100% plating, Sn/Bi (0.5%) plating, or the like is mainly applied to the plated layer. 
     As shown in  FIG. 1  as well, the outside lead wire  22  is smaller in diameter than the round bar section  21   b  of the tab terminal  21  and is welded to an end face of the round bar section  21   b . A welded section of the outside lead wire  22  is denoted by reference numeral  23 . 
     As explained above, when the plated layer on the surface is the Sn 100% plating, the plated layer other than the welded section  23  is stable. However, in the welded section  23 , Al, An, Cu, Fe, and the like are mixed. When the welded section  23  is exposed to the outside air, stress acts on an Sn layer because of hydration and oxidation reaction of Al. An Sn whisker (a whisker-like crystal substance)  23   a  intensely occurs and grows. 
     In the Sn/Bi (0.5%) plating, the growth of the whisker is relaxed than that in the Sn 100%, the whisker also occurs. When the growth of the whisker is conspicuous, there is a risk that the whisker scatters on the circuit board and, in the worst case, shirt-circuits an electronic circuit. 
     In order to suppress the occurrence of the whisker in the welded section  23  as much as possible and prevent the scattering of the whisker to the outside, in the present invention, as the terminal passage hole  5  of the rubber seal  4 , the large-diameter round bar mating hole  51 , in which the round bar section  21   b  of the tab terminal  21  is fit, and the small-diameter lead wire passage hole  52 , through which the outside lead wire  22  is inserted, are coaxially connected and the hole diameter φ 2  of the lead wire passage hole  52  is set smaller than the outer diameter φ 1  of the outside lead wire  22  (φ 2 &lt;φ 1 ) to shut off the welded section  23  from the outside air. However, in the present invention, a configuration explained below is adopted to make it possible to insert the outside lead wire  22  through the lead wire passage hole  52  of the rubber seal  4  without applying such an excessively large load as to deteriorate characteristics to the capacitor element  1  and while keeping a state in which the outside lead wire  22  is surely shut off from the outside air. 
     Referring to  FIG. 2 , according to the present invention, besides a lead wire body  221  having an outer diameter φ 1  larger than a hole diameter  42  of the lead wire passage hole  52 , the outside lead wire  22  integrally includes a passage guide part  222  to the lead wire passage hole  52  on the distal end portion side (in  FIG. 2 , the lower end side) of the lead wire body  221 . 
     Note that, in  FIG. 2 , a chain line drawn downward from the lead wire body  221  indicates the conventional outside lead wire not including the passage guide part  222 . 
     The passage guide part  222  is formed to be gradually reduced in diameter from the lead wire body  221  such that a distal end portion (in  FIG. 2 , a lower end portion)  222   a  thereof has a diameter φ 3  smaller than the hole diameter φ 2  of the lead wire passage hole  52  (φ 3 &lt;φ 2 ). 
     In this embodiment, the distal end portion  222   a  having the outer diameter φ 3  of the passage guide part  222  is formed substantially flat. However, a portion above the outer diameter φ 3  entering the lead wire passage hole  52  may be formed in an arcuate shape. 
     In the present invention, in the passage guide part  222 , a conical sloped surface  223  having a predetermined angle is formed in a portion from the distal end portion  222   a  having the outer diameter φ 3  to the lead wire body  221  having the outer diameter φ 1 . Consequently, when the outside lead wire  22  is inserted through the lead wire passage hole  52 , first, the sloped surface  223  of the passage guide part  222  comes into contact with the inner edge of the lead wire passage hole  52 . 
     On the rubber seal  4  side, as the terminal passage hole  5 , the round bar mating hole  51  having a hole diameter φ 4  (φ 1 &lt;φ 4 ), in which the round bar section  21   b  of the tab terminal  21  is fit closely, and the lead wire passage hole  52  having a hole diameter φ 2  (φ 3 &lt;φ 2 &lt;φ 1 ) are coaxially provided. However, in the present invention, a conical guide surface  53  gradually reduced in diameter from the round bar mating hole  51  side is formed between the round bar mating hole  51  and the lead wire passage hole  52 . Note that, when the outer diameter of the round bar section  21   b  is represented as φ 5 , the hole diameter φ 4  of the round bar mating hole  51  is slightly smaller than the outer diameter φ 5  of the round bar section  21   b  (φ 4 &lt;φ 5 ). 
     With the passage guide part  222  set as a distal end, the outside lead wire  22  is inserted through the lead wire passage hole  52  while expanding the lead wire passage hole  52 . In that case, in order to prevent a peak load from being applied to the capacitor element  1 , when an inclination angle of the guide surface  53  with respect to the imaginary plane X-X orthogonal to the axis Y-Y passing the terminal passage hole  5  is represented as θa and an inclination angle of the sloped surface  223  is represented as θb, it is preferable that θa&lt;θb. Note that a creeping distance of the sloped surface  223  is proportional to the inclination angle θb. 
     In improving insertability of the outside lead wire  22  through the lead wire passage hole  52 , it is also effective to coat the inner surface of the lead wire passage hole  52  and the surface of the guide surface  53  with low-friction resin such as polyparaxylene or silicone oil emulsion for improving slippage. 
     In this case, coating thickness of the low-friction resin is preferably 0.3 to 1.5 μm. Note that, if the film thickness is smaller than 0.3 μm, the slippage by the low-friction resin is not sufficiently displayed. On the other hand, it is undesirable if the film thickness exceeds 1.5 μm because the electrolyzed liquid is likely to leak from between the outside lead wire  22  and the lead wire passage hole  52 . The low-friction resin may be applied to the outside lead wire  22  side. 
     When lead-free tin plating is applied to the outside lead wire  22 , in suppressing the growth of the whisker  23   a  in the welded section  23 , it is preferable to form the guide surface  53  to adhere to the welded section  23   a.    
     As shown in  FIG. 3 , in a state in which the flat section  21   a  of the lead terminal  2  is firmly attached to the electrode foils  1   a  and  1   b  of the capacitor element  1  by, for example, the caulking needle, the lead terminal  2  is forcibly inserted into the lead wire passage hole  52  of the rubber seal  4  by a pressing force of a press head  60  applied from an upper part of the capacitor element  1 . Concerning examples 1 to 3 of the present invention shown in  FIGS. 4( a ), 4( b ) , and  4 ( c ) and comparative examples 1 to 5 shown in  FIGS. 5( a ), 5( b ), 5( c ), 5( d ) , and  5 ( e ), pressure applied to a caulking portion  21   c  of the lead terminal  2  was measured. Therefore, an example of the measurement is explained. 
     Note that, after the distal end portion of the outside lead wire  22  projects from the lead wire passage hole  52 , the pressing by the press head  60  is stopped. Instead, the lead terminal  2  is pulled by a not-shown pulling device. Therefore, the pressure applied to the caulking portion  21   c  of the lead terminal  2  is reduced to substantially 0. 
     In this example, in both of examples 1 to 3 of the present invention and comparative examples 1 to 5, a lead wire (a CP wire) having a diameter of φ 0 . 8  mm was used as the outside lead wire  22 . In both of examples 1 to 3 of the present invention and comparative examples 1 to 5, the hole diameter φ 2  of the lead wire passage hole  52  was set to 0.5 mm and the inclination angle θa of the guide surface  53  was set to 30°. 
     In example 1 of the present invention shown in  FIG. 4( a ) , the outer diameter φ 3  of the distal end portion  222   a  of the passage guide part  222  was set to 0.3 mm and the inclination angle θb of the sloped surface  223  was set to 45°. 
     In example 2 of the present invention shown in  FIG. 4( b ) , the outer diameter φ 3  of the distal end portion  222   a  of the passage guide part  222  was set to 0.3 mm and the inclination angle θb of the sloped surface  223  was set to 70°. 
     In example 3 of the present invention shown in  FIG. 4( c ) , the outer diameter φ 3  of the distal end portion  222   a  of the passage guide part  222  was set to 0.1 mm and the inclination angle θb of the sloped surface  223  was set to 70°. 
     In comparative example 1 shown in  FIG. 5( a ) , the passage guide part  222  was not formed and the lead wire having the diameter of φ 0 . 8  mm was directly used. Therefore, an end diameter of the lead wire was φ 0 . 8  mm and the inclination angle θb was 0°. 
     In comparative example 2 shown in  FIG. 5( b ) , the outer diameter φ 3  of the distal end portion  222   a  of the passage guide part  222  was set to 0.6 mm and the inclination angle θb of the sloped surface  223  was set to 60°. 
     In comparative example 3 shown in  FIG. 5( c ) , the outer diameter φ 3  of the distal end portion  222   a  of the passage guide part  222  was set to 0.2 mm and the inclination angle θb of the sloped surface  223  was set to 15°. 
     In comparative example 4 shown in  FIG. 5( d ) , the outer diameter φ 3  of the distal end portion  222   a  of the passage guide part  222  was set to 0.6 mm and the inclination angle θb of the sloped surface  223  was set to 60°. 
     In comparative example 5 shown in  FIG. 5( e ) , the outer diameter φ 3  of the distal end portion  222   a  of the passage guide part  222  was set to 0.6 mm and the inclination angle θb of the sloped surface  223  was set to 70°. 
     On the other hand, on the rubber seal  4  side, as explained above, the hole diameter φ 2  of the lead wire passage hole  52  is 0.5 mm. Besides, the hole diameter φ 4  of the round bar mating hole  51  is 1.9 mm, axial direction thickness T 1  of the lead wire passage hole  52  is 0.5 mm, height T 2  of the guide surface  53  viewed from the inner edge of the lead wire passage hole  52  is 0.4 mm, and a radial direction distance dl of the guide surface  53  is 0.7 mm. 
     Note that the rubber seal  4  is preferably a rubber material having Shore hardness equal to or higher than 80 that cause less scratches. In this example, a rubber material having Shore hardness of 84 was used as the rubber seal  4 . 
     In Table 1, pressure (gf) of the caulking portion  21   c  of the lead terminal  2  measured by a push-pull gauge in examples 1 to 3 of the present invention and comparative examples 1 to 5 is shown. In  FIG. 6 , a graph by measurement data of the pressure is shown. Note that a distance in Table 1 and the graph is set to 0 mm in a place immediately before the outside lead wire  22  collides with the lead wire passage hole  52 . 
     
       
         
           
               
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Moving 
                 Force (gf/push-pull gauge data) 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 distance 
                 Comparative 
                 Comparative 
                 Comparative 
                 Comparative 
                 Comparative 
                   
                   
                   
               
               
                 (mm) 
                 example 1 
                 example 2 
                 example 3 
                 example 4 
                 example 5 
                 Example 1 
                 Example 2 
                 Example 3 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 0.8 
                 250 
                 320 
                 320 
                 300 
                 350 
                 200 
                 140 
                 100 
               
               
                 1.2 
                 420 
                 420 
                 450 
                 420 
                 420 
                 210 
                 190 
                 120 
               
               
                 1.6 
                 530 
                 600 
                 500 
                 210 
                 270 
                 220 
                 220 
                 160 
               
               
                 1.8 
                 600 
                 600 
                 320 
                 210 
                 240 
                 240 
                 240 
                 170 
               
               
                 2.0 
                 700 
                 240 
                 240 
                 210 
                 240 
                 250 
                 240 
                 190 
               
               
                 2.2 
                 750 
                 240 
                 240 
                 210 
                 240 
                 250 
                 240 
                 210 
               
               
                 2.4 
                 110 
                 240 
                 240 
                 210 
                 240 
                 250 
                 240 
                 210 
               
               
                 3.2 
                 110 
                 240 
                 240 
                 210 
                 240 
                 250 
                 240 
                 210 
               
               
                   
               
            
           
         
       
     
     As it is seen from Table 1 and the graph, the peak pressure is 750 (gf) in comparative example 1, the peak pressure is 600 (gf) in comparative example 2, the peak pressure is 500 (gf) in comparative example 3, and the peak pressure is 420 (gf) in comparative example 4 and comparative example 5. The pressure is likely to deteriorate the characteristics of the capacitor element  1  when the lead wire is inserted through. 
     On the other hand, in examples 1 to 3 of the present invention, a peak of the pressure is hardly observed when the lead wire is inserted through. In examples 1 and 2 of the present invention, the pressure transitions at about 220 to 250 (gf). In examples 3 of the present invention, the pressure transitions at about 120 to 210 (gf). 
     Therefore, according to the present invention, it is possible to insert the lead terminal  2  through the terminal passage hole  5  of the rubber seal  4  without applying such an excessively large load as to deteriorate characteristics to the capacitor element  1  and while keeping a state in which the lead terminal  2  can be surely shut off from the outside air. Note that, in the case of example 3 of the present invention, it is likely that a product main body is hurt by a sharp-pointed shape of the distal end. Therefore, examples 1 and 2 of the present invention are considered to be most preferable. 
     Incidentally, as shown in  FIG. 1 , when an inclination angle of the welded section  23  with respect to the imaginary plane X-X is represented as θc, the inclination angle θc of the welded section  23  is generally about 60 to 70°, although depending on the outer diameter φ 5  of the round bar section  21   b  and the outer diameter φ 1  of the outside lead wire  22 . 
     Note that the actual surface of the welded section  23  includes fine unevenness. The inclination angle θc is an angle of a line connecting a lower end  23   a  and an upper end  23   b  of the welded section  23  (the lower end edge of the round bar section  21   b  ) with respect to the imaginary plane X-X. 
     On the other hand, when the inclination angle θa of the guide surface  53  is set to, for example, 30° as in the example explained above, as shown in  FIG. 7 , after the lead wire is inserted through, a gap G is formed between the guide surface  53  and the welded section  23 . Therefore, a problem explained below occurs. 
     As explained with reference to  FIG. 3 , the lead terminal  2  is inserted through the terminal passage hole  5  of the rubber seal  4  in a state in which the lead terminal  2  is attached to the capacitor element  1 . Since the electrolyzed liquid is impregnated in the capacitor element  1 , a part of the electrolyzed liquid collects in the gap G. Then, the electrolyzed liquid sometimes gradually leaks from a space between the outside lead wire  22  and the lead wire passage hole  52 . 
     This problem is solved by setting the inclination angel θa of the guide surface  53  close to the inclination angle θc of the welded section  23  to narrow the gap G. In that case, the following points need to be taken into account. 
     Referring to  FIG. 8 , when the outside lead wire  22  is inserted through the lead wire passage hole  52  as shown in  FIG. 7 , the lower end  23   a  of the welded section  23  collides with an intersection P of the guide surface  53  and the outer diameter surface of the outside lead wire  22 . Therefore, as indicated by an alternate long and two short dashes line, it is conceivable to form the guide surface  53  as an inclined surface having the inclination angle θc passing the intersection P. 
     However, if the guide surface  53  is formed as the inclined surface, the axial direction thickness T 1  of the lead wire passage hole  52  is shaved by Ta and reduced. Therefore, this is not preferable in hermetically sealing the outside lead wire  22  and reliability is spoiled. 
     Therefore, in the present invention, as shown in  FIG. 9 , with the intersection P set as a boundary, the guide surface  53  is divided into first and second two broken line-like inclined surfaces  53   a  and  53   b  having different inclination angles. 
     That is, the first inclined surface  53   a  is formed as an inclined surface inclined at an angle (e.g., about 60 to 70°) substantially the same as the inclination angle θc of the welded section  23  from the intersection P to the inner surface of the round bar mating hole  51 . On the other hand, the second inclined surface  53   b  is formed as an inclined surface inclined at an angle (e.g., about 30°) smaller than the inclination angle θc from the intersection P to the inner peripheral edge of the terminal passage hole  52 . 
     Consequently, it is possible to set the inclination angle of the guide surface  53  close to the inclination angle θc of the welded section  23  and narrow the gap G without reducing the axial direction thickness T 1  of the lead wire passage hole  52 , without hardly shifting an attachment height position of the tab terminal  21  to the rubber seal  4  upward in  FIG. 7 , and without spoiling a guidance effect of the passage guide part  222  of the outside lead wire  22  with respect to the lead wire passage hole  52 . 
     The present invention also includes a three-terminal type aluminum electrolytic capacitor including, as shown in  FIG. 10( a ) , besides the lead terminals  2 , 2  (see  FIGS. 11 and 12 ) respectively attached to the anode foil la and the cathode foil  1   b,  an electrically neutral dummy terminal  30  not connected to the capacitor element  1  is inserted through the rubber seal  4 . 
     The dummy terminal  30  is a terminal soldered to a not-shown circuit board together with the lead terminals  2 ,  2  solely to improve mounting stability. The dummy terminal  30  is different from the lead terminal  2  in that the dummy terminal  30  is larger in diameter than the lead terminal  2  and, as shown in  FIG. 10( b ) , the tab terminal  21  does not include the flat section  21   a  and includes only the round bar section  21   b.    
     That is, on one end side (in  FIG. 10( b ) , the lower end side) of the round bar section  21   b , the outside lead wire  22  is integrally attached via the welded section  23 . In this embodiment, on the other end side (in  FIG. 10( b ) , the upper end side) of the round bar section  21   b , a flange section  31  expanded in diameter is formed. 
     On the rubber seal  4  side, the terminal passage hole  5  formed by coaxially connecting the large-diameter round bar mating hole  51 , in which the round bar section  21   b  of the dummy terminal  30  is fit, and the small-diameter lead wire passage hole  52 , through which the outside lead wire  22  is inserted, is drilled. However, in this embodiment, a recess  54 , in which the flange section  31  is closely fit, is formed at the upper edge of the round bar mating hole  51 . 
     In the three-terminal type aluminum electrolytic capacitor, the hole diameter φ 2  of the lead wire passage hole  52  of the dummy terminal  30  is smaller than the outer diameter φ 1  of the outside lead wire  22  (φ 2 &lt;φ 1 ) to shut off the welded section  23  from the outside air. However, to make it possible to insert the outside lead wire  22  through the lead wire passage hole  52  of the rubber seal  4  without applying such an excessively large load as to deteriorate characteristics to the capacitor element  1  and while keeping a state in which the outside lead wire  22  can be surely shut off from the outside air, as in the lead terminal  2 , the passage guide part  222  having the sloped surface  223  is integrally formed at the distal end of the outside lead wire  22 . In the terminal passage hole  5 , the guide surface  53  for guiding the distal end of the outside lead wire  22  to the lead wire passage hole  52  is formed. 
     In order to further narrow the gap G (see  FIG. 7 ) between the welded section  23  in the dummy terminal  30  and the guide surface  53 , as explained with reference to  FIG. 9  above, the guide surface  53  may include the first inclined surface  53   a  inclined at an angle substantially the same as the inclination angle θc of the welded section  23  from the intersection P to the inner surface of the round bar mating hole  51  and the second inclined surface  53   b  inclined at an angle smaller than the inclination angle θc from the intersection P to the inner peripheral edge of the terminal passage hole  52 . 
     In this way, according to the present invention, in the three-terminal type aluminum electrolytic capacitor including the dummy terminal  30 , too, it is possible to insert the outside lead wire  22  through the lead wire passage hole  52  of the rubber seal  4  without applying such an excessively large load as to deteriorate characteristics to the capacitor element  1  and while keeping a state in which the outside lead wire  22  can be surely shut off from the outside air and it is possible to form the gap G between the welded section  23  and the guide surface  53  as narrow as possible. 
     DESCRIPTION OF SYMBOLS 
     
         
           1  Capacitor element 
           2  Lead terminal 
           3  Armor case 
           4  Rubber seal 
           5  Terminal passage hole 
           21  Tab terminal 
           21   a  Flat section 
           21   b  Round bar section 
           22  Outside lead wire 
           221  Lead wire body 
           222  Passage guide part 
           222   a  Distal end portion of the passage guide part 
           223  Sloped surface 
           23  Welded section 
           30  Dummy terminal 
           51  Round bar mating hole 
           52  Lead wire passage hole 
           53  Guide surface 
           53   a  First inclined surface 
           53   b  Second inclined surface 
         P Intersection