Method for fabricating an aluminum electrolytic capacitor device

Abstract: An aluminum electrolytic capacitor has a large cylindrical hole (6) in a core portion thereof. The anode and cathode foils and electrolyte-containing papers (3) are rolled with less tension for an initial predetermined number of turns than for the later turns. Instead of forming the hole large, a core portion is formed by rolling the electrolyte-containing papers (3) and either the anode foil (1 or 2) or the cathode foil (1 or 2), or neither of them.

Description: Field of the Invention The present invention relates to a method for fabricating an aluminum electrolytic capacitor as defined by the precharacterizing part of claim 1 and known from the GB-A-1 100 707. Description of the Related Art A conventional aluminum electrolytic capacitor is small in size but large in capacitance since its capacitance per unit area is significantly large. To meet the demand for down-sized electronic circuit component parts, the size of the aluminum electrolytic capacitor is further reduced and the capacitance thereof is further increased. As shown in Fig. 1, the diameter of a cylindrical hole of the core portion of a capacitor device is normally 3 to 6 mm. If such an aluminum electrolytic capacitor is subjected to abnormal stress, such as overvoltage, formation current locally flows into a portion where an anode foil and a cathode foil are not parallel. Such formation current causes an exothermic reaction, which causes the electrolyte to evaporate. Thus, gas pressure increases, generating force to expand the capacitor device outward and inward. Since the outside of the device is fastened by a tape, the electrode foils in an outer portion are not substantially affected. However, the electrode foils close to the core cylindrical hole are buckled toward the core hole by the increased pressure, causing a short circuit between the electrodes. In some cases, a spark caused by the short circuit ignites the electrolyte, and the capacitor burns. SUMMARY OF THE INVENTION The present invention is intended to solve the above problems of the conventional art. It is an object of the present invention to provide a method of making an aluminum electrolytic capacitor so as to avoid the incidence of short circuits between the anode and cathode foils caused by abnormal stress is prevented. Said method should also allow the fabrication of an aluminum electrolytic capacitor being suitable as a smoothing member in a switching power circuit. These objects are attained by the characterizing part of claim 1. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1(1) illustrates a conventional aluminum electrolytic capacitor, showing the diameter 1 of a core cylindrical hole thereof. Fig. 1(2) illustrates how an anode foil, a cathode foil and electrolyte-containing papers are rolled to form the conventional aluminum electrolytic capacitor shown in Fig. 1 (1) . Fig. 2 illustrates internal states of the aluminum electrolytic capacitor shown in Fig. 1 before and after application of overvoltage. Fig. 3 is a perspective view of another aluminum electrolytic capacitor. Fig. 4 is a top plan view of the aluminum electrolytic capacitor shown in Fig. 3. Fig. 5 illustrates internal states of the aluminum electrolytic capacitor shown in Fig. 3 before and after application of overvoltage. Fig. 6 is a perspective view of an aluminum electrolytic capacitor according to one embodiment of the present invention. Figs. 7(1) and 7(2) illustrate a portion of the aluminum electrolytic capacitor shown in Fig. 6, including no electrode foil. Figs. 8(1) and 8(2) illustrate another example of the portion including no electrode foil. Fig. 9 illustrates a switching circuit employing an aluminum electrolytic capacitor as shown in Fig. 3 or 6. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Fig. 3, an aluminum electrolytic capacitor comprises: an anode foil 1 and a cathode foil 2 separated by electrolyte-containing papers 3 which are rolled together to form a rolled capacitor ; a tape 7 provided around the outside periphery of the rolled capacitor device so as to fasten the rolled device; an anode lead terminal 4 and a cathode lead terminal 5 which are lead out from the anode and cathode foils 1 and 2, respectively. A core hole 6 is formed by removing a core rod around which the electrode foils 1, 2 and the papers 3 are rolled. Fig. 4 is a top plan view of the capacitor shown in Fig. 3. The core hole has a diameter , for example, of 7 mm, which is larger than that of a conventional aluminum electrolytic capacitor. The electrode foils 1, 2 and the papers 3 are rolled with smaller tension for a predetermined number of turns from the beginning, for example, five turns. Since the core hole of the aluminum electrolytic capacitor has a larger diameter  than the core hole of the conventional electrolytic capacitor, and since a portion adjacent to the core hole is formed by rolling the electrode foils and papers with smaller tension than in the other portion, the incidence of buckling and a short circuit is reduced. If the capacitor is subjected to abnormal stress, such as overvoltage, the buckling stress caused on the electrode foils (the anode and cathode foils 1, 2) in the portion adjacent to the core hole is substantially small. The foils 1, 2 therein bend toward the core hole, as shown in Fig. 5, absorbing the force caused therein. Thus, buckling or a short circuit is unlikely to occur. According to this embodiment, since the diameter of the core hole is 7 mm or greater, and since a portion adjacent to the core hole is formed by rolling the electrode foils and papers with smaller tension than in the other portion, the buckling force per unit area of the foils caused by abnormal stress, such as overvoltage, is substantially reduced, and the foils bend and wrinkle. Thus, the foils hardly ever buckle or break. The incidence of a short circuit between the electrodes and burning of the capacitor is substantially reduced. An embodiment of the present invention will be described below with reference to Figs. 6 to 8. Referring to Fig. 6, an aluminum electrolytic capacitor device comprises: an anode foil 1 and a cathode foil 2 separated by electrolyte-containing papers 3 which are rolled together to form a rolled capacitor ; a tape 7 provided around the outside periphery of the rolled capacitor device so as to fasten the rolled device; an anode lead terminal 4 and a cathode lead terminal 5 which are led out from the anode and cathode foils 1 and 2, respectively. A core hole 6 is formed by removing a core rod around which the electrode foils 1, 2 and the papers 3 are rolled. While, according to the conventional art, the electrode foils 1, 2 and the electrolyte-containing papers 3 are rolled together from the beginning, according to this embodiment, a portion adjacent to the core hole 6 does not contain both of the electrode foils 1 and 2. For example, as shown in Figs. 7(1) and 7(2), the papers 3 and the cathode foil 2 are rolled forming the core hole having a diameter 1 (3 to 6 mm) the same as in the conventional art until a roll having a diameter 2 is obtained. Then, the anode foil 1 is rolled together with the electrolyte-containing papers 3 and the cathode foil 2. Since the portion adjacent to the core hole does not contain the anode foil 1, buckling of the anode foil 1 hardly occurs even if the capacitor is subjected to abnormal stress, such as overvoltage. Thus, a short circuit between the electrodes and burning of the capacitor are substantially unlikely to occur. Alternatively, as shown in Figs. 8(1) and 8(2), the rolled portion up to the diameter 2 may be formed by solely using the electrolyte-containing papers 3. Then, the anode and cathode foils 1, 2 are rolled together with the electrolyte-containing papers 3. In addition, the electrode foils 1, 2 and the electrolyte-containing papers 3 may be rolled with reduced tension for a predetermined number of turns immediately outside the turn of the diameter 2. As described above, according to this embodiment, since a portion adjacent to the core hole does not contain both of the electrodes, the incidence of a short circuit and burning of the capacitor caused by abnormal stress, such as overvoltage, is substantially reduced. Fig. 9 illustrates a switching power circuit connected to a single-phase three-wire input power source for office machines, such as a copying machine, a facsimile or a laser beam printer, which employs an aluminum electrolytic capacitor as shown in Fig. 6. The switching power circuit is connected to the single-phase three-wire input power source and comprises a source-protecting means (a fuse) 12, a line filter circuit 13, a rectifier 14, an aluminum electrolytic capacitor 15 according to the present invention, a switching control circuit 16, a power transformer 17 and a smoothing circuit 18 connected to a load circuit of the secondary side. The aluminum electrolytic capacitor device 15 smooths the output of the rectifier 14. The aluminum electrolytic capacitor device 15 can be thus used since it has a large capacitance. Normally, DC voltage of 140 V is applied to an aluminum electrolytic capacitor device in a switching power circuit. If the neutral conductor of the single-phase three-wire input power source breaks, overvoltage 2½ to 2 times as high as the above-mentioned voltage level is applied to the aluminum electrolytic capacitor. Even if such a high voltage is applied, the aluminum electrolytic capacitor device according to the present invention hardly ignites.

Claims: A method for fabricating an aluminum electrolytic capacitor in form of a rolled unit comprising a cylindrical hollow core (6) by rolling an anode foil (1), a cathode foil (2) and electrolyte-containing papers (3) separating the anode and cathode foils, wherein the rolled unit has a portion adjacent the core (6) formed by rolling said electrolyte-containing paper (3) alone or only together with either one of the anode and cathode foils (1, 2) between a first diameter ( 1 ) position of the core (6) and a second, larger diameter ( 2 ), characterized in that following the formation of said portion, the anode foil (1), cathode foil (2) and the electrolyte-containing papers (3) are rolled with reduced tension for a predetermined number of turns immediately outside the turn of the second diameter ( 2 ), so as to prevent short circuits between the anode and cathode foils (1, 2) caused by abnormal stress. A method according to claim 1, wherein said core-adjacent portion, including said hollow core (6), is formed with a diameter as great as 7 mm or greater.

Inventors: FUJIWARA YOSHICHIKA, UCHIDA HIROSHI, WATABE TOSHINORI, FUJIWARA, YOSHICHIKA, UCHIDA, HIROSHI, WATABE, TOSHINORI, Fujiwara, Yoshichika, c/o Canon Kabushiki Kaisha, Uchida, Hiroshi, c/o Canon Kabushiki Kaisha, Watabe, Toshinori, c/o Canon Kabushiki Kaisha
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1992
Main classification: H01G2
IPC codes: H01G9