Aging method for electrolytic capacitors

Abstract

This invention provides an aging method for electrolytic capacitors that allows for the simplification of the heating equipment without increasing the processing time during the aging process. [Solution] The electrolytic capacitor 1 consists of a capacitor element 11 impregnated with electrolyte housed in an outer case 12. The aging method involves applying a DC voltage to the electrolytic capacitor 1 and superimposing a ripple current onto the DC voltage applied to the electrolytic capacitor 1, thereby heating the electrolytic capacitor 1 with the ripple current.

Description

Technical Field

[0001] The present invention relates to an aging method for an electrolytic capacitor.

Background Art

[0002] When manufacturing an electrolytic capacitor, an aging treatment is performed to form a dielectric oxide film (hereinafter simply referred to as "oxide film") on the anode end surface and repair the damaged portion of the oxide film formed on the anode that was damaged during the manufacturing process. As a result, an increase in leakage current can be suppressed. Since a higher temperature is preferable for repairing the oxide film, the aging treatment is generally performed by applying a DC voltage to the electrolytic capacitor in a constant temperature bath maintained at a high temperature by a heater or the like. For example, Patent Document 1 discloses that an electrolytic capacitor conveyed into a heating device is heated by hot air, and a DC voltage is applied to perform aging processing.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the aging treatment of electrolytic capacitors, after the electrolytic capacitor to be subjected to the aging treatment is placed into a constant temperature bath maintained at a high temperature by a heater or the like, it takes time for the temperature of the electrolytic capacitor body to reach the aging execution temperature, which may lengthen the processing time in the aging step. Therefore, there is a demand for simplifying the apparatus without increasing the processing time.

[0005] Accordingly, an object of the present invention is to provide an aging method for an electrolytic capacitor that can simplify the heating apparatus without lengthening the processing time in the aging step.

Means for Solving the Problems

[0006] An electrolytic capacitor according to an embodiment of the present invention comprises a capacitor element impregnated with an electrolyte solution housed in an outer case, and the aging method involves applying a DC voltage to the electrolytic capacitor and superimposing a ripple current on the DC voltage applied to the electrolytic capacitor, thereby generating heat in the electrolytic capacitor.

[0007] According to the above configuration, the equipment for heating electrolytic capacitors can be simplified without increasing the processing time during the aging process.

[0008] In the aging method for an electrolytic capacitor according to an embodiment of the present invention, the effective value of the ripple current is 2 times or more and 5 times or less of the rated ripple current.

[0009] According to the above configuration, the time it takes for the electrolytic capacitor to stabilize (equilibrium) after reaching a predetermined temperature can be shortened.

[0010] The aging method for an electrolytic capacitor according to an embodiment of the present invention is such that the aging temperature is 40°C or higher and 70°C or lower.

[0011] With the above configuration, stable aging can be performed in a shorter time. [Effects of the Invention]

[0012] According to the present invention, the apparatus for heat-treating electrolytic capacitors can be simplified without increasing the processing time in the aging process. [Brief explanation of the drawing]

[0013] [Figure 1] This is a cross-sectional view showing the configuration of electrolytic capacitor 1. [Figure 2] This is a perspective view showing the capacitor element 11 of the electrolytic capacitor 1. [Modes for carrying out the invention]

[0014] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

[0015] Figure 1 shows an electrolytic capacitor 1 on which an aging method according to an embodiment of the present invention is performed. The electrolytic capacitor 1 has a capacitor element 11, an outer case 12, a sealing body 13, and lead tabs 14 and 15.

[0016] As shown in Figure 2, the capacitor element 11 consists of an anode foil (anodic aluminum foil) 14a and a cathode foil (cathode aluminum foil) 15b, which have been etched and subjected to dielectric oxide film formation, wound in a cylindrical shape via a separator 16, and secured with element fixing tape 21 (see Figure 1). This capacitor element 11 is housed in an outer case 12 (see Figure 1).

[0017] The outer case 12 is a bottomed cylindrical case. A sealing body 13 is fitted to the opening of the outer case 12, and the opening has a structure that is sealed by drawing. In this way, the sealing body 13 seals the opening of the outer case 12. For example, the sealing body 13 is an elastic material. More specifically, for example, the sealing body 13 is rubber. For example, the sealing body 13 may be natural rubber or synthetic rubber.

[0018] Lead tabs 14 and 15 are drawn out from the capacitor element 11. Lead wires 14b and 15b are welded to lead tabs 14 and 15, respectively. Lead wires 14b and 15b are formed to be thinner in diameter than lead tabs 14 and 15. Lead wires 14b and 15b are drawn out to the outside of the sealing body 13. At this time, lead tabs 14 and 15 are inserted into the sealing body 13. The insertion state of lead tabs 14 and 15 in the sealing body 13 will be described in detail later. The outer case 12 is covered by a sleeve 22 (see Figure 1).

[0019] The lead tab 14 is an anode-side lead tab connected to the anode foil 14a by a method such as crimping or welding. Further, the lead tab 15 is a cathode-side lead tab connected to the cathode foil 15a by a method such as crimping or welding.

[0020] The anode foil 14a (see FIG. 2) is a valve action metal having a dielectric oxide film formed on the surface thereof. Examples of the valve action metal include at least one selected from the group consisting of aluminum, tantalum, niobium, and titanium. The oxide film is formed, for example, by roughening the surface of the valve action metal foil by etching treatment, and then subjecting the resulting foil to chemical conversion treatment.

[0021] The cathode foil 15a is formed using a valve action metal. As the cathode foil 15a, for example, a foil obtained by roughening the surface of a valve action metal foil by etching treatment, or a foil obtained by subjecting the roughened foil to chemical conversion treatment is used. As the cathode foil 15a, a plain foil that is not subjected to etching treatment may be used. Further, a coated foil may be used in which a metal thin film containing at least one metal selected from the group consisting of titanium, nickel, titanium carbide, nickel carbide, titanium nitride, nickel nitride, titanium carbonitride, and nickel carbonitride is formed on the surface of the roughened foil or the plain foil. Alternatively, a coated foil in which a carbon thin film is formed on the surface of the roughened foil or the plain foil may be used.

[0022] The material of the separator 16 is not particularly limited. As the separator 16, for example, a material mainly composed of cellulose fibers may be used, or a mixed fiber in which chemical fibers are blended may be used. Examples of the chemical fibers include synthetic fibers such as polyester fibers, polyamide fibers, acrylic fibers, polyimide fibers, aramid fibers, and nylon fibers. The separator 16 holds an electrolytic solution. The electrolytic solution is not particularly limited. The electrolytic solution may contain, for example, a low-viscosity solvent and a low-volatility solvent, or may contain one of the low-viscosity solvent and the low-volatility solvent.

[0023] Next, a method for manufacturing the electrolytic capacitor 1 will be described.

[0024] First, a slitting process is performed to cut the anode foil 14a and cathode foil 15a (see Figure 2) to a predetermined width. At this time, the anode foil 14a that is cut is one that has undergone chemical conversion treatment. Then, a winding process is performed in which the anode foil 14a and cathode foil 15a are wound around a separator 16 to form a capacitor element 11. Lead tabs 14 and 15, to which lead wires 14b and 15b are welded, are connected to the anode foil 14a and cathode foil 15a used in the winding process. The capacitor element 11 is wound and secured with element-securing tape 21 (see Figure 1). Then, after the separator 16 is impregnated with electrolyte, the capacitor element 11 is housed in an outer case 12 (see Figure 1) covered with a sleeve 22. The opening of the outer case 12 is sealed with a sealing body 13.

[0025] Next, the capacitor element 11 undergoes an aging process. The aging process is performed to repair the cut edges of the capacitor element 11 and any oxide film that was damaged during its manufacture. The aging process is carried out by applying a DC voltage to the capacitor element 11 and superimposing a ripple current onto this DC voltage. In the aging process, it is common to perform a heat treatment on the capacitor element 11 in a container such as a constant temperature bath maintained at a high temperature by a heater, for example. In this embodiment, such a heat treatment is not performed, and instead, a ripple current is superimposed on the DC voltage applied to the capacitor element 11. This ripple current causes the capacitor element 11 to self-heat internally.

[0026] The frequency and RMS value of the ripple current may be determined based on the rated ripple current of the electrolytic capacitor 1. The rated ripple current is the RMS value (JIS C5101-1) of the maximum allowable AC current at a specified frequency to which the capacitor can be continuously applied at a specified temperature. Here, the RMS value of the ripple current may be obtained by multiplying the rated ripple current by a predetermined multiplier. The upper limit of this multiplier is preferably 5.5 times, and more preferably 4 times. The lower limit of this multiplier is preferably 2 times, and more preferably 3 times. The frequency and RMS value of the ripple current may also be determined based on the RMS voltage (Vms) of the ripple voltage generated by the ripple current.

[0027] Furthermore, the frequency and RMS value of the ripple current may be determined based on the temperature reached by the capacitor element 11 that is to be maintained during the aging process (aging temperature). The temperature of the capacitor element 11 may be measured directly or through the outer casing 12. In addition, the frequency and RMS value of the ripple current may be determined based on the self-temperature rise Δt due to the ripple current from the temperature in the atmosphere in which the aging process is performed to the temperature of the capacitor element 11 that is to be maintained during the aging process.

[0028] The self-temperature rise value Δt is calculated based on the following equation 1. Since coefficients such as the case surface area A are determined by the capacitor element 11 undergoing aging treatment, the frequency of the ripple current and the effective value of the ripple current are selected based on the self-temperature rise value Δt. The effective value of the ripple current is determined so that the sum of the ripple voltage generated by superimposing the ripple current and the DC voltage applied to the capacitor element 11 does not exceed the formation voltage of the anode foil 14a. The formation voltage is the voltage applied when forming an oxide film on the surface of the anode foil 14a by forming it before the slitting process. The upper limit of the temperature that the capacitor element 11 should reach during the aging process (aging temperature) is preferably 70°C. The lower limit of the temperature that the capacitor element 11 should reach during the aging process (aging temperature) is preferably 40°C.

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[0029] As described above, the electrolytic capacitor 1 of this embodiment consists of a capacitor element 11 impregnated with electrolyte housed in an outer case 12, and the aging method involves applying a DC voltage to the electrolytic capacitor 1 and superimposing a ripple current on the DC voltage applied to the electrolytic capacitor 1. The ripple current causes the electrolytic capacitor 1 to heat up.

[0030] This simplifies the equipment required for heating, such as heating the electrolytic capacitor 1 in a constant temperature chamber maintained at a high temperature by a heater or the like.

[0031] (Examples) Aging treatment (see Table 1) was performed on the comparative example (Comparative Example 1) and the examples (Examples 1-10), and the characteristics of each electrolytic capacitor were evaluated. The electrolytic capacitors used in the comparative example and examples (10 of each) had a rated voltage of 25V, a rated capacitance of 330μF, a rated ripple current of 0.6Arms (105℃ / 100kHz), and a product size of φ8×10L (mm). The upper limit specification for the leakage current of these electrolytic capacitors is 82.5μA, and products with a value below this are considered acceptable.

[0032] [Table 1]

[0033] As shown in Table 1, in Comparative Example 1, a conventional aging process was performed. In Comparative Example 1, after the capacitor temperature reached 85°C in a constant temperature bath heated to 85°C, a DC voltage of 28V was applied and the aging process was performed for 60 minutes. In Examples 1 to 10, a DC voltage of 25V was applied in an environment of 25°C. In Example 1, a ripple current of 120Hz, 0.30Arms was superimposed on the DC voltage of 25V and the aging process was performed for 60 minutes. In Example 2, a ripple current of 120Hz, 0.60Arms was superimposed on the DC voltage of 25V and the aging process was performed for 60 minutes. In Example 3, a ripple current of 120Hz, 0.90Arms was superimposed on the DC voltage of 25V and the aging process was performed for 60 minutes. In Example 4, a ripple current of 120Hz, 1.20Arms was superimposed on a DC voltage of 25V, and an aging process was performed for 60 minutes. In Example 5, a ripple current of 120Hz, 1.50Arms was superimposed on a DC voltage of 25V, and an aging process was performed for 60 minutes. In Example 6, a ripple current of 120Hz, 1.65Arms was superimposed on a DC voltage of 25V, and an aging process was performed for 60 minutes. In Example 7, a ripple current of 120Hz, 1.20Arms was superimposed on a DC voltage of 25V, and an aging process was performed for 30 minutes. In Example 8, a ripple current of 120Hz, 1.20Arms was superimposed on a DC voltage of 25V, and an aging process was performed for 45 minutes. In Example 9, a ripple current of 50Hz, 0.84Arms was superimposed on a DC voltage of 25V, and an aging process was performed for 60 minutes. Furthermore, the calculated self-temperature rise Δt is the same as in Example 4. In Example 10, a DC voltage of 25V was superimposed with a ripple current of 100kHz, 2.40Arms, and an aging process was performed for 60 minutes. Furthermore, the calculated self-temperature rise Δt is the same as in Examples 4 and 9.

[0034] Table 1 shows the frequency correction coefficients for the rated ripple current in the electrolytic capacitors used in Comparative Example 1 and Examples 1 to 10 of the present invention. The effective value of the ripple current in Examples 1 to 10 is obtained by multiplying the DC voltage by a frequency correction coefficient corresponding to the value of the ripple current frequency superimposed on the DC voltage. Table 1 shows the multiplier of the superimposed ripple current value to the rated ripple current at each ripple current frequency for Examples 1 to 10. For example, in the electrolytic capacitors used in the examples, when the superimposed ripple current frequency is 120 Hz, the frequency correction coefficient is 0.5, so the rated ripple current at this time is 0.6Arms × 0.5 = 0.3Arms. In Examples 1 to 8 in Table 1, the superimposed ripple current frequency is 120 Hz in all cases, and the effective value of the superimposed ripple current is shown as a multiple of 0.3Arms with respect to the rated ripple current. Also, when the superimposed ripple current frequencies are 50 Hz and 100 × 10 3 In the case of Hz, the rated ripple currents are 0.6Arms × 0.35 = 0.21Arms and 0.6Arms × 1 = 0.6Arms, respectively. In Examples 9 and 10 of Table 1, the effective value of the superimposed ripple current is four times the respective rated ripple current.

[0035] (Evaluation method) Leakage current was measured as a characteristic of the electrolytic capacitors after aging treatment. For Comparative Example 1 and Examples 1-10, the temperature reached by the electrolytic capacitors during aging (capacitor temperature) and the time it took to reach equilibrium at that temperature (temperature equilibrium time) were measured. The temperature of the electrolytic capacitors was measured on the bottom surface opposite the opening of the outer casing.

[0036] As shown in the evaluation results in Table 1, the leakage currents of Examples 1 to 10 were comparable to or within specifications of Comparative Example 1, demonstrating the effectiveness of superimposing a ripple current onto the DC voltage applied to electrolytic capacitor 1 during heating. It was confirmed that by superimposing a ripple current in addition to applying a DC voltage during the aging process, equivalent leakage current characteristics can be obtained in a shorter time than with conventional methods that use a heating device for aging.

[0037] Although embodiments and examples of the present invention have been described above, the present invention is not limited to the above embodiments and examples, and various modifications can be made without departing from the spirit of the invention. [Explanation of symbols]

[0038] 1: Electrolytic capacitor 11: Capacitor element 12: Outer case 13: Sealing body 14: Lead Tab 14a: Anode foil 14b: Lead wire 15: Lead Tab 15a: Cathode foil 15b: Lead wire 16: Separator 21: Element fixing tape 22: Sleeves

Claims

1. An electrolytic capacitor aging method comprising applying a DC voltage to an electrolytic capacitor, which consists of a capacitor element impregnated with an electrolyte solution housed in an outer case, A ripple current is superimposed on the DC voltage applied to the electrolytic capacitor. A method for aging electrolytic capacitors, characterized by the following features.

2. The effective value of the ripple current is between 2 and 5 times the rated ripple current. The aging method for an electrolytic capacitor according to claim 1.

3. The aging temperature is between 40°C and 70°C. A method for aging an electrolytic capacitor according to claim 1 or 2.

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