FIG. 13 is a sectional view illustrating the structure of a conventional capacitor. Capacitor element 20 is contained in case 22, which is made of aluminum and has a closed-end cylinder-shape, along with an electrolyte (not shown). The upper and lower end surfaces of capacitor element 20 have positive and negative electrodes extracted therefrom. Metal plate 21 is connected to one of the electrodes of capacitor element 20. One end of rod-shaped core material 24 disposed at the central portion of capacitor element 20 has flat-shaped terminal 24A for external connection. Core material 24 and metal plate 21 are electrically connected with each other. Meanwhile, the inner bottom surface of case 22 is connected to the other electrode of capacitor element 20. Flat-shaped terminal 25 for external connection is joined to the outer surface of case 22. The inner bottom surface of case 22 is provided with projection 22A. Insulating member 26 insulates core material 24 from case 22.
Insulative sealing plate 23 seals the opening of case 22. Sealing plate 23 is provided with hole 32 through which core material 24 pierces and hole 33 through which an electrolyte is injected. O-ring 29 is incorporated into sealing plate 23 around hole 32 to seal the space between core material 24 and sealing plate 23. Block 27 made of a rubber-like elastic insulating member is combined with cap 28, and blocks hole 33, thereby forming a pressure-regulating valve. Sealing rubber 30 disposed at the top peripheral surface of sealing plate 23 is compressed by forming curled part 22B that is the opening end of case 22 curled, to seal the space between case 22 and sealing plate 23. In a capacitor thus structured, case 22 functions as a collecting terminal. Such a capacitor is disclosed in Patent document 1, for example.
However, to decrease in size and to increase in capacitance of the above-described conventional capacitor, sealing plate 23 decreases in size as the external diameter of case 22 decreases. Consequently, it is extremely difficult to provide hole 33 and a pressure-regulating valve (for allowing an internal gas to escape outward when the pressure inside the capacitor rises to a given value or higher) on shrunk sealing plate 23 from the viewpoint of space. Concretely, a capacitor with such a structure becomes difficult to produce if the external diameter of case 22 is 20 mm or smaller.
Patent document 1: Japanese Patent Unexamined Publication No. 2000-315632