Manufacturing method for electrode foil for electrolytic capacitor, manufacturing method for electrolytic capacitor, and power supply device

Abstract

This method for manufacturing an electrode foil for an electrolytic capacitor involves an etching step in which an AC current is applied to a metal foil in an etching solution and an electrode foil having a porous part in the surface is obtained. The aforementioned AC current includes at least two mutually different waveforms.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing an electrode foil for an electrolytic capacitor, a method for manufacturing an electrolytic capacitor, and a power supply device. [Background technology]

[0002] An electrolytic capacitor includes a capacitor element. A metal foil containing a valve metal is used as the anode of the capacitor element. To increase the capacitance of the capacitor element, all or part of the main surface of the metal foil is etched. The etching is performed by applying an alternating current to the metal foil in an etching solution.

[0003] Patent Documents 1 and 2 propose that, for an alternating current that repeats a single waveform, the waveform be configured to have a specific shape. Specifically, Patent Document 1 proposes that the alternating current include two half-waves in each positive and negative half cycle, where any one or all of the waveform, amplitude, and application time are the same or different, and that a rest period is provided between each half-wave, where the amplitude is zero or a minute current is applied to the positive or negative side at up to 1 / 15 of the maximum amplitude. Patent Document 2 proposes that the waveform in the positive half cycle include a portion that drops significantly from the peak and a portion that remains constant or rises or falls gradually from immediately after the drop to the end of the half cycle. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 7-235456 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-123552 Summary of the Invention [Problem to be solved by the invention]

[0005] When an alternating current is applied to a metal foil, an anodic reaction that dissolves the surface of the metal foil to form pits and a cathodic reaction that forms a thin protective film on the surface of the metal foil and inhibits dissolution of the surface occur alternately. The thickness of the protective film is non-uniform, and when an alternating current with a repeating waveform is applied, pits tend to form locally in areas where the protective film is thin, making it difficult to form pits uniformly on the metal foil surface. In Patent Documents 1 and 2, an alternating current with a repeating waveform is applied, making it difficult to form pits uniformly. [Means for solving the problem]

[0006] One aspect of the present invention relates to a method for producing an electrode foil for an electrolytic capacitor, comprising an etching step of applying an alternating current to a metal foil in an etching solution to obtain an electrode foil having a porous portion on its surface, wherein the alternating current has at least two different waveforms.

[0007] Another aspect of the present invention relates to a method for manufacturing an electrolytic capacitor, including the steps of the above-mentioned method for manufacturing an electrode foil for an electrolytic capacitor, covering the porous portion with a dielectric layer, and covering at least a portion of the dielectric layer with a solid electrolyte layer.

[0008] Yet another aspect of the present invention relates to a power supply device that applies an alternating current to a metal foil in an etching solution during a metal foil etching process, the power supply device including an output unit that outputs the alternating current, wherein the alternating current includes at least two types of waveforms that are different from each other. [Effects of the Invention]

[0009] According to the present invention, good etching pits can be formed in the metal foil. [Brief explanation of the drawings]

[0010] [Figure 1] 10 is a graph showing a case where the AC current is a sine wave. [Figure 2] 10 is a graph showing a case where the AC current is a triangular wave. [Figure 3]1 is a graph showing an example of the waveform of an AC current in an electrolytic etching step in a method for producing an electrode foil for an electrolytic capacitor according to one embodiment of the present invention. [Figure 4] 10 is a graph showing another example of the waveform of an AC current in the electrolytic etching step in the method for producing an electrode foil for an electrolytic capacitor according to one embodiment of the present invention. [Figure 5] 10 is a graph showing yet another example of the waveform of an AC current in the electrolytic etching step in the method for producing an electrode foil for an electrolytic capacitor according to one embodiment of the present invention. [Figure 6] 1 is an explanatory diagram schematically illustrating a power supply device according to an embodiment of the present invention. [Figure 7] 7 is a graph showing an example of first waveform data stored in a waveform storage unit of FIG. 6. [Figure 8] 7 is a graph showing an example of second waveform data stored in the modulation storage unit of FIG. 6. [Figure 9] 7 is a graph showing another example of second waveform data stored in the modulation storage unit of FIG. 6. [Figure 10] 7 is a graph showing yet another example of second waveform data stored in the modulation storage unit of FIG. 6. [Figure 11] FIG. 2 is an explanatory diagram schematically illustrating an example of an etching apparatus used in an etching step. [Figure 12] 1 is a cross-sectional view schematically showing a capacitor element according to one embodiment of the present invention. [Figure 13] 1 is a cross-sectional view schematically showing an electrolytic capacitor according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

[0012] [Method of manufacturing electrode foil for electrolytic capacitors] A method for producing an electrode foil according to one embodiment of the present invention includes an etching step of applying an alternating current to a metal foil in an etching solution to obtain an electrode foil having a porous portion on its surface. The alternating current has at least two different waveforms. Here, different waveforms refer to different wave shapes and / or sizes.

[0013] By applying an AC current having at least two different waveforms to the metal foil, the origins of pit formation on the surface of the metal foil can be dispersed, and localized pit formation in areas where the protective coating is thin can be suppressed, resulting in more uniform formation of pits on the surface of the metal foil.

[0014] In the current density profile over time, one waveform has a period Tw and a fluctuation width, and includes a positive half period and a negative half period. The shape of the positive half period and the shape of the negative half period may be point-symmetric with each other. The fluctuation width corresponds to the sum of the maximum current density value in the positive half period and the maximum current density value (absolute value) in the negative half period. The maximum current density values ​​present in the positive and negative half periods may be the same value. Examples of the wave shape include a sine wave as shown in FIG. 1, a triangular wave as shown in FIG. 2, and a rectangular wave. In FIGS. 1 and 2, Im represents the maximum current density value, and Tw represents the period. In this case, 2×Im corresponds to the fluctuation width, and Im corresponds to the amplitude.

[0015] The at least two types of waveforms may have different fluctuation amplitudes and / or periods. The at least two types of waveforms may have different maximum current density values ​​in the positive half cycle and / or the negative half cycle.

[0016] Furthermore, at least two types of waveforms may have the same fluctuation amplitude and period but different shapes, for example, the timing at which the current density reaches its maximum in one period may be different.

[0017] The alternating current is a modulated wave including at least two different waveforms, and the modulated wave may be repeated at a predetermined period Tm. The period Tm of the modulated wave is preferably the sum of the periods Tw of a plurality of waves (e.g., 2 to 400). When the wave period Tw is constant, the period Tm is preferably an integer multiple of the period Tw, and may be, for example, 2 to 400 times the period Tw, or 2 to 100 times the period Tw.

[0018] The modulation wave may have a fluctuation width that changes periodically. The maximum value of the current density may be changed, for example, in a sine wave, a triangular wave, or a sawtooth wave, as shown in Figs. 3 to 5 described later. In this case, the period Tm of the modulation wave may be constant, and the fluctuation width may change periodically. In this case, from the viewpoint of efficiently forming etching pits, the maximum value A of the fluctuation width may be set to 0.05. max The minimum fluctuation range A min Ratio of: A min / A max may be 0.5 or more, 0.6 or more, or 0.7 or more. min / A max A may be 0.99 or less, 0.97 or less, or 0.9 or less. min / A max For the range of min / A max Any combination of upper and lower limits may be used. For example, A min / A max may be 0.5 or more and 0.99 or less, 0.5 or more and 0.97 or less, 0.6 or more and 0.97 or less, or 0.7 or more and 0.97 or less. The maximum value of the current density is, for example, 5 A / cm 2 If the pit is large, the maximum value of the current density may be 3 A / cm 2 It may be the following:

[0019] Furthermore, the period Tw of the modulated wave may change periodically. The frequency (1 / Tw) is preferably, for example, 3 Hz or more and 65 Hz or less.

[0020] Here, FIGS. 3 to 5 are graphs each showing an example of a modulated wave of an alternating current in the electrolytic etching step in the method for producing an electrode foil for an electrolytic capacitor according to one embodiment of the present invention. In the graphs of Figures 3 to 5, the vertical axis represents current density. The modulated waves of Figures 3 to 5 are obtained by combining the first waveform data shown in Figure 7 with the second waveform data of Figures 8 to 10. The current density on the vertical axis of Figures 3 to 5 is expressed as a relative value when the maximum value of the current density of the first waveform data of Figure 7 is set to 1. The horizontal axis represents time (seconds), for example, the time from the start of etching.

[0021] The AC currents shown in Figures 3 to 5 are triangular waves, with a constant period Tw and a periodic change in the fluctuation width. The AC current in Figure 3 includes eight different waveforms, with the maximum value of the current density varying sinusoidally, and Tm being eight times Tw. In the AC current in Figure 3, the maximum value A of the fluctuation width max The minimum fluctuation range A min Ratio of: A min / A max is approximately 0.55.

[0022] The AC current in Figure 4 contains two types of waveforms with different fluctuation widths, and the maximum value of the current density changes in a triangular wave shape, with Tm being twice as large as Tw. max The minimum fluctuation range A min Ratio of: A min / A max is approximately 0.77.

[0023] The AC current in Figure 5 contains three types of waveforms with different fluctuation widths, and the maximum value of the current density changes in a sawtooth waveform, with Tm being three times Tw. max The minimum fluctuation range A min Ratio of: A min / A max is approximately 0.77.

[0024] Although a triangular wave is shown in Figs. 3 to 5, a wave other than a triangular wave, such as a sine wave, may also be used. In the AC currents shown in Figs. 3 to 5, the types of waveforms are not limited to the above numbers. Tm / Tw is not limited to the above numerical values. Tm / Tw is preferably 2 or more and 100 or less, and more preferably 2 or more and 80 or less. 1 / Tm is preferably 0.2 Hz or more and 100 Hz or less, and more preferably 0.5 Hz or more and 50 Hz or less. In Figs. 3 to 5, the frequency (1 / Tw) is approximately 24 Hz, but is not limited to this. The frequency (1 / Tw) is, for example, 4 Hz or more and 60 Hz or less, and preferably 5 Hz or more and 55 Hz or less. A min / A max is not limited to the above values. In the case of the modulated wave in Figure 3, A min / A max may be 0.55 or more and 0.99 or less, or may be 0.6 or more and 0.97 or less. In the case of the modulated wave of FIGS. 4 and 5, A min / A max may be 0.6 or more and 0.99 or less, or may be 0.7 or more and 0.97 or less.

[0025] (etching process) The metal foil is etched by passing the AC current between the metal foil and the electrode in an etching solution, with the electrode facing at least one of the main surfaces of the metal foil. The etching may be performed on only one or both main surfaces of the metal foil. The current density of the AC current and the etching time are not particularly limited and may be set appropriately depending on the thickness of the electrode foil, the desired depth of the etching pit, etc.

[0026] The average current density of the AC current applied in the etching step may be constant. In this case, the average current density of the AC current is, for example, 0.05 A / cm. 2 More than 1.7A / cm 2 less than or equal to 0.08 A / cm 2 More than 1.2A / cm 2The average current density is calculated by dividing the integrated value of the current density by time in the profile of the current density over time. When the period Tm of the modulated wave is constant, the integrated value of the current density over the period Tm is calculated and then divided by Tm. For example, in the case of the sine wave in Figure 1 (where the maximum current density is Im), the average current density is (2 / π) x Im. In the case of the triangular wave in Figure 2 (where the maximum current density is Im), the average current density is 1 / 2 x Im.

[0027] In the etching step, etching of the metal foil may be performed intermittently. In other words, the electrolytic etching step preferably has an electroless time. This promotes the diffusion of metal ions derived from the metal foil generated in the etching pit, making it easier to improve etching efficiency. The electroless time is, for example, the time required for the metal foil to move between electrodes when there are multiple electrodes, or the time required for the metal foil to move between etching tanks when there are multiple etching tanks.

[0028] The electroless period may also be a cleaning step for cleaning the metal foil. It is preferable to use pure water (ion-exchanged water) for cleaning the metal foil. This is because impurities are removed, making it easier for the metal ions to diffuse. The cleaning step may be performed during etching.

[0029] (metal foil) The metal foil contains a valve metal such as titanium, tantalum, aluminum, or niobium. The metal foil contains one or more of the above valve metals. The metal foil may contain the above valve metal in the form of an alloy or an intermetallic compound. The thickness of the metal foil is not particularly limited. The thickness of the metal foil is, for example, 10 μm or more and 300 μm or less. When the metal foil is used as an anode foil, the thickness of the metal foil is preferably 60 μm or more and 250 μm or less. When the metal foil is used as a cathode foil, the thickness of the metal foil is preferably 10 μm or more and 80 μm or less.

[0030] (etchant) The etching solution may be a known etching solution used in electrolytic etching. Examples of the etching solution include an aqueous solution containing sulfuric acid, nitric acid, phosphoric acid, and / or oxalic acid and hydrochloric acid. The aqueous solution may contain various additives such as a chelating agent. The concentrations of hydrochloric acid and other acids in the etching solution and the temperature are not particularly limited and may be appropriately set depending on the desired shape of the etching pit and the performance of the capacitor. The concentration of hydrochloric acid in the etching solution is, for example, 1 mol / L or more and 10 mol / L or less. The concentration of other acids in the etching solution is, for example, 0.01 mol / L or more and 1 mol / L or less. The temperature of the etching solution during the electrolytic etching process is not particularly limited and is, for example, 5°C or more and 60°C or less.

[0031] [Power supply] A power supply device according to one embodiment of the present invention relates to a power supply device that applies an alternating current to a metal foil in an etching solution during a metal foil etching process, and is equipped with an output unit that outputs the alternating current, and the alternating current includes at least two different types of waveforms.

[0032] Here, FIG. 6 is a diagram showing a schematic configuration of an example of a power supply device that outputs alternating current. 6 includes a waveform memory unit 201 that stores first waveform data of a first AC current, a modulation memory unit 202 that stores second waveform data that modulates the first waveform data, a synthesis unit 203 that synthesizes the first waveform data and the second waveform data, and an output unit 204 that outputs the AC current as a modulated wave based on the synthesized data synthesized by the synthesis unit 203. The second waveform data is data that indicates the degree to which the current density (maximum value), fluctuation width, period, etc. are modulated relative to the first waveform data.

[0033] The waveform storage unit 201 stores, for example, the first waveform data of the first AC current shown in Fig. 7. Fig. 7 shows waveform data that repeats a constant triangular wave. In the graph shown in Fig. 7, the vertical axis represents current density, which is expressed as a relative value with the maximum current density value being 1. The horizontal axis represents time (seconds).

[0034] The modulation storage unit 202 stores, for example, the second waveform data shown in Figures 8 to 10. In the graphs shown in Figures 8 to 10, the horizontal axis represents time (seconds), and the vertical axis represents modulation degree, which indicates the degree to which the current density of the first waveform data in Figure 7 is modulated.

[0035] When using the second waveform data shown in FIG. 8, if the current density of the first waveform data at any time is I and the modulation index is f, the modulated current density is I×(1+a×f). The modulation index varies sinusoidally between -1 and 1. a is a coefficient, which is set, for example, within the range of 0.01 to 0.3. When the modulation index f is 0, the current density is the same as the current density in FIG. 7. When the modulation index f is 1 and the coefficient a is 0.3, the current density (absolute value) is 30% larger than that of the first waveform data in FIG. 7. When the modulation index f is -1 and the coefficient a is 0.3, the current density (absolute value) is 30% smaller than that of the first waveform data in FIG. 7. When the coefficient a is 0.3, the modulated wave in FIG. 3 is obtained.

[0036] When using the second waveform data shown in FIGS. 9 and 10, if the current density of the first waveform data is I and the modulation index is f at any time, the modulated current density is I × (1 + a × |f|). The modulation index varies between 0 and 1 during the positive half cycle, and between -1 and 0 during the negative half cycle. a is a coefficient, set, for example, within the range of 0.01 to 0.3. When the modulation index f is 0, the current density is the same as the current density in FIG. 7. When the modulation index f is 1 and the coefficient a is 0.3 during the positive half cycle, the current density is 30% higher than the current density of the first waveform data (positive half cycle) in FIG. 7. When the modulation index f is -1 and the coefficient a is 0.3 during the negative half cycle, the current density (absolute value) is 30% higher than the current density (absolute value) of the first waveform data (negative half cycle) in FIG. 7. When the coefficient a is 0.3, the modulated waves shown in FIGS. 4 and 5 are obtained.

[0037] When the first waveform data shown in Fig. 7 and the second waveform data (coefficient a = 0.3) shown in Fig. 8 are combined, the AC current is output as the modulated wave shown in Fig. 3. When the first waveform data shown in Fig. 7 and the second waveform data (coefficient a = 0.3) shown in Fig. 9 are combined, the AC current is output as the modulated wave shown in Fig. 4. When the first waveform data shown in Fig. 7 and the second waveform data (coefficient a = 0.3) shown in Fig. 10 are combined, the AC current is output as the modulated wave shown in Fig. 5.

[0038] The fluctuation range of the modulated wave changes periodically, and the maximum fluctuation range A max The minimum fluctuation range A min Ratio of: A min / A max may be within the above range, and may be 0.5 or more and 0.97 or less. In this case, good etching pits can be efficiently formed.

[0039] In FIG. 6, the waveform storage unit and the modulation storage unit are provided inside the power supply device, but they may also be provided outside the power supply device.

[0040] The power supply device may also include a synthesizer that synthesizes first waveform data of a first AC current and second waveform data of a second AC current having a waveform different from that of the first AC current, and an output unit that outputs an AC current as a modulated wave based on the synthesized data synthesized by the synthesizer. The first AC current and the second AC current may have different periods or different periods and fluctuation ranges, for example. The power supply device may also include a storage unit that stores the waveform data of the first AC current and the second AC current. The storage unit may be provided external to the power supply device.

[0041] [Etching equipment] 11 is an explanatory diagram schematically illustrating an example of an etching apparatus used in the etching step. The etching apparatus 20 includes an etching tank 23 that holds an etching solution, a plurality of transport rolls 25 that transport the metal foil 10, a pair of electrodes 22 that face the metal foil 10, and an AC power supply 24 that applies current to the electrodes 22. The AC power supply 24 uses the above-mentioned power supply device (e.g., power supply device 200). The metal foil 10 moves within the etching tank 23 while being transported via the plurality of transport rolls 25. The metal foil 10 is etched while facing the electrode 22 in the etching tank 23. This results in the electrode foil 11.

[0042] FIG. 11 shows a case where etching is performed on a long metal foil, but the present invention is not limited to this. For example, etching may be performed on a metal foil having a certain area that is left stationary. Also, FIG. 11 shows the use of a pair of electrodes, but the present invention is not limited to this. For example, etching may be performed by placing the metal foil opposite one electrode and connecting the electrode and the metal foil to an AC power source. Furthermore, there may be multiple etching tanks. One etching tank may have two or more pairs of electrodes.

[0043] The etching apparatus may also include multiple power supply devices. For example, the etching apparatus may include multiple etching tanks, each connected to a power supply device. In this case, it is sufficient that at least one of the multiple power supply devices outputs an AC current as a modulated wave, and it is preferable that 20% or more of the multiple power supply devices output an AC current as a modulated wave. For example, if a power supply device is connected to each of 10 or more etching tanks, it is preferable that two or more power supply devices output an AC current as a modulated wave.

[0044] [Manufacturing method of electrolytic capacitors] A method for manufacturing an electrolytic capacitor according to one embodiment of the present invention includes the step (etching step) included in the method for manufacturing an electrode foil for an electrolytic capacitor described above, a step of covering the porous portion with a dielectric layer, and a step of covering at least a portion of the dielectric layer with a solid electrolyte layer.

[0045] (Dielectric layer forming process) The dielectric layer may contain an oxide of a valve metal. For example, when aluminum is used as the valve metal, the dielectric layer may contain Al2O3. The dielectric layer is formed, for example, by anodizing the surface of the anode body (the above-mentioned electrode foil) using a chemical conversion treatment or the like. However, the dielectric layer is not limited to this, and may be any layer that functions as a dielectric. The dielectric layer may be formed so as to cover at least a portion of the surface of the anode body. The dielectric layer is formed along the inner wall surfaces of the holes and depressions (pits) in the porous portion of the electrode foil.

[0046] (Solid electrolyte layer formation process) The solid electrolyte layer includes, for example, a manganese compound or a conductive polymer. A solid electrolyte layer including a conductive polymer can be formed, for example, by chemically polymerizing and / or electrolytically polymerizing a raw material monomer on a dielectric layer. Alternatively, the solid electrolyte layer can be formed by applying a solution in which a conductive polymer is dissolved or a dispersion in which a conductive polymer is dispersed to the dielectric layer. Examples of conductive polymers that can be used include polypyrrole, polyaniline, polythiophene, polyacetylene, and derivatives thereof. The solid electrolyte layer may include a dopant such as polystyrene sulfonic acid in addition to the conductive polymer. The solid electrolyte layer may further include additives as needed.

[0047] (Cathode extraction layer formation process) The method for manufacturing an electrolytic capacitor may further include a step of covering the solid electrolyte layer with a cathode extraction layer. In this manner, a capacitor element may be formed that includes an electrode foil, a dielectric layer, a solid electrolyte layer, and a cathode extraction layer. The cathode extraction layer may be formed so as to cover at least a portion of the solid electrolyte layer, or may be formed so as to cover the entire surface of the solid electrolyte layer. The cathode extraction layer may include, for example, a carbon layer and a metal (e.g., silver) paste layer formed on the surface of the carbon layer. The carbon layer is made of a composition containing a conductive carbon material such as graphite. The metal paste layer is made of a composition containing silver particles and a resin. The configuration of the cathode extraction layer is not limited thereto, and may be any configuration that has a current collecting function.

[0048] 12 is a cross-sectional view schematically illustrating a capacitor element according to this embodiment. Capacitor element 110 is sheet-shaped. Anode portion 110a is composed of electrode foil (anode body) 11. Cathode portion 110b includes anode body 11, dielectric layer 12, and cathode layer 13. Cathode layer 13 includes solid electrolyte layer 13a and cathode extraction layer 13b.

[0049] [Electrolytic capacitor] The capacitor element constitutes an electrolytic capacitor. The electrolytic capacitor may include a plurality of capacitor elements. In the electrolytic capacitor, the plurality of capacitor elements may be stacked. The number of stacked capacitor elements is not particularly limited, and may be, for example, 2 or more and 20 or less.

[0050] The anode portions of the stacked capacitor elements are joined together by welding and / or crimping, etc., and are electrically connected. An anode lead terminal is joined to the anode portion of at least one capacitor element. The multiple anode portions are crimped together, for example, by a bent anode lead terminal. The anode portions and the anode lead terminal may further be laser-welded. This improves the connection reliability between the multiple anode portions and between the anode portions and the anode lead terminal.

[0051] The cathode portions of the stacked capacitor elements are also electrically connected to each other. A cathode lead terminal is bonded to the cathode layer of at least one capacitor element. The cathode lead terminal is bonded to the cathode layer via, for example, a conductive adhesive.

[0052] The capacitor element is sealed with an insulating material so that at least a portion of the anode lead terminal and the cathode lead terminal are exposed. Examples of insulating materials include cured thermosetting resins and engineering plastics. Examples of thermosetting resins include epoxy resins, phenolic resins, silicone resins, melamine resins, urea resins, alkyd resins, polyurethanes, and unsaturated polyesters. Examples of engineering plastics include general-purpose engineering plastics and super engineering plastics. Examples of engineering plastics include polyimides and polyamideimides.

[0053] 13 is a cross-sectional view schematically illustrating an electrolytic capacitor according to this embodiment. The electrolytic capacitor 100 includes one or more capacitor elements 110, an anode lead terminal 120A joined to an anode portion 110a of the capacitor element 110, a cathode lead terminal 120B joined to a cathode portion 110b, and an insulating material 130 that seals the capacitor elements.

[0054] In this embodiment, an electrolytic capacitor using a solid electrolyte and having a capacitor element sealed with an insulating material has been described, but the present invention is not limited thereto. The electrode foil according to this embodiment can be applied to, for example, an electrolytic capacitor including a capacitor element in which an anode and a cathode formed by strip-shaped electrode foil are wound with a separator interposed therebetween, and an electrolytic solution. In this case, the electrode foil according to this embodiment is used for at least one of the anode and the cathode. In particular, the electrode foil according to this embodiment is preferably used for a large-capacity stacked electrolytic capacitor or an anode of a wound electrolytic capacitor. When an electrolytic capacitor includes multiple capacitor elements, each capacitor element may be wound.

[0055] [Example] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0056] Examples 1 to 3 An aluminum foil having a thickness of 100 μm and a purity of 99.98% was prepared and pretreated by immersing it in an aqueous solution of phosphoric acid with a concentration of 1.0 mass % at 90° C. for 60 seconds.

[0057] Next, electrolytic etching was performed as follows using an etching apparatus as shown in Fig. 11. An aqueous solution containing 5 mass% hydrochloric acid, 2 mass% aluminum chloride, 0.1 mass% sulfuric acid, 0.5 mass% phosphoric acid, and 0.2 mass% nitric acid was used as the etching solution, and the solution temperature was set to 35°C. The etching time was 5 minutes.

[0058] The power supply device shown in Figure 6 was used as the AC power supply. The first waveform data and second waveform data (coefficient a = 0.3) were combined and AC current was output as a modulated wave. The waveform data shown in Table 1 was used for the first waveform data and second waveform data, and the modulated wave shown in Table 1 was obtained.

[0059] [Table 1]

[0060] The etching time was 2 minutes. The frequency (1 / Tw) of the AC current was approximately 24 Hz. The average current density of the AC current was kept constant at 0.2 A / cm. 2 It was decided.

[0061] An aluminum foil was immersed in a 60°C aqueous solution containing 10% by mass of sulfuric acid for 60 seconds, and then heat-treated at 250°C for 120 seconds to produce an electrode foil for an electrolytic capacitor. Furthermore, a dielectric layer containing aluminum oxide (Al2O3) was formed on the surface of the electrode foil by anodization.

[0062] Comparative Example 1 An electrode foil was obtained in the same manner as in Example 1, except that the first waveform data and the second waveform data were not combined and the first AC current of the first waveform data was output as is. A dielectric layer containing aluminum oxide (Al2O3) was formed on the surface of the electrode foil by anodization.

[0063] The capacitance of the electrode foils (anode bodies) having a dielectric layer on the surface of Examples 1 to 3 and Comparative Example 1 was measured based on the test method for electrode foils for aluminum electrolytic capacitors (when the foil type was anode formed foil for medium to high voltage) of the Electronic Industries Association of Japan (EIAJ) standard RC-2364A. As a result, it was confirmed that the capacitance of Examples 1 to 3 was increased by about 15% compared to Comparative Example 1.

[0064] While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention. [Industrial Applicability]

[0065] The electrode foil produced by the method according to the present invention can achieve high capacitance and can therefore be used in capacitors for a variety of applications. [Explanation of symbols]

[0066] 200: Power supply 201: Waveform storage section 202: Modulation memory unit 203: Synthesis section 204: Output section 20: Etching equipment 22: Electrode 23: Etching tank 24: AC power supply 25: Transport roll 10: Metal foil 11: Electrode foil (anode body) 100: Electrolytic capacitor 110: Capacitor element 110a: Anode part 110b: Cathode part 12: Dielectric layer 13: Cathode layer 13a: Solid electrolyte layer 13b: Cathode extraction layer 120A: Anode lead terminal 120B: Cathode lead terminal 130: Insulating materials

Claims

1. The method includes an etching step of applying an alternating current to a metal foil in an etching solution to obtain an electrode foil having a porous portion on the surface thereof, the alternating current includes at least two different waveforms; the at least two types of waveforms differ from each other in at least one of fluctuation width and period; the AC current is a modulated wave including the at least two types of waveforms, The modulated wave is repeated at a predetermined cycle, The fluctuation width of the modulated wave changes periodically, The method for producing an electrode foil for an electrolytic capacitor, wherein the ratio of the minimum value A min of the fluctuation range to the maximum value A max of the fluctuation range, A min / A max , is 0.5 or more and 0.97 or less.

2. The method for producing an electrode foil for an electrolytic capacitor according to claim 1 includes the steps of: covering the porous portion with a dielectric layer; covering at least a portion of the dielectric layer with a solid electrolyte layer; A method for manufacturing an electrolytic capacitor, comprising:

3. A power supply device that applies an alternating current to a metal foil in an etching solution in a metal foil etching process, a waveform storage unit that stores first waveform data of the first AC current; a modulation storage unit that stores second waveform data that modulates the first waveform data; a synthesis unit that synthesizes the first waveform data and the second waveform data; an output unit that outputs the AC current as a modulated wave based on the combined data combined by the combining unit, the alternating current includes at least two different waveforms; The fluctuation width of the modulated wave changes periodically, A power supply device, wherein the ratio of the minimum value A min of the fluctuation range to the maximum value A max of the fluctuation range: A min / A max is 0.5 or more and 0.97 or less.

4. A power supply device as described in claim 3, wherein the synthesis unit synthesizes first waveform data of a first AC current and second waveform data of a second AC current having a waveform different from that of the first AC current.

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