Manufacturing method for electrolytic capacitors

Abstract

This invention provides an electrolytic capacitor that can easily form a uniform impregnation state of conductive polymer and reduce ESR, even if the shape of the electrolytic capacitor is large. [Solution] The method includes: a vacuum impregnation step of immersing the capacitor element in a conductive polymer dispersion in a reduced-pressure atmosphere of a predetermined vacuum degree and impregnating the separator with the conductive polymer dispersion; a pressurized atmosphere formation step of opening the reduced-pressure atmosphere to the atmosphere while the capacitor element remains immersed in the conductive polymer dispersion and further pressurizing it to a predetermined pressure; and a pressurized impregnation step of impregnating the separator of the capacitor element, which is immersed in the conductive polymer dispersion in the pressurized atmosphere, with the conductive polymer dispersion, and then opening it to the atmosphere.

Description

[[Technical Field]]

[0001] The present invention relates to a method for manufacturing an electrolytic capacitor. [[Background Art]]

[0002] As an electrolytic capacitor that is small in size, large in capacity and has a low ESR (equivalent series resistance), an electrolytic capacitor including an anode foil formed with a dielectric layer, a conductive polymer layer with high electrical conductivity formed to cover at least a part of the dielectric layer, and an electrolyte solution having a capability of repairing an anodic oxide film (a liquid that is composed of at least a solute and a solvent and has electrical conductivity with the capability of repairing an anodic oxide film) is regarded as promising as an in-vehicle electronic component. For example, Patent Document 1 describes a method for manufacturing an aluminum electrolytic capacitor, in which after a capacitor element is impregnated with a dispersion containing a conductive polymer, a polymer dopant, a base component and a solvent, part of the solvent is removed to form a conductive polymer layer. Further, Patent Document 2 describes that in order to obtain a low-ESR hybrid aluminum electrolytic capacitor, a conductive polymer layer is formed on the surface of an anode, the surface of a cathode and the surface of a separator, and then the respective materials are stacked and wound to manufacture the hybrid aluminum electrolytic capacitor. [[Prior Art Documents]] [[Patent Documents]]

[0003] [[Patent Document 1]] International Publication No. 2017 / 090241 [[Patent Document 2]] U.S. Patent No. 10777361 Specification [[Summary of the Invention]] [[Problem to be Solved by the Invention]]

[0004] However, in Patent Document 1, in order to achieve a low ESR, an SiO2 compound that becomes an impurity is required in addition to an excess amount of the conductive polymer, and as a result, there has been a problem that as the amount of impurities increases, the ESR of the element increases.

[0005] On the other hand, the method described in Patent Document 2 requires the pre-forming of conductive polymer layers on the anode surface, cathode surface, and separator surface. The conductive polymer layer is formed by coating a conductive polymer dispersion with a bar coater, and a large amount of conductive polymer dispersion is required to form a uniform conductive polymer layer. In addition, when anodes, cathodes, and separators with pre-formed conductive polymer layers are stacked and wound together, the electrical connections between the conductive polymer layers of the anode and separator, or between the cathode and separator, become uneven, and the distance between the anode and cathode increases. This increases the ESR of the hybrid aluminum electrolytic capacitor.

[0006] Here, hybrid aluminum electrolytic capacitors, in which a capacitor element with a conductive polymer layer is impregnated with an electrolyte, can provide electrolytic capacitors with low ESR. However, as hybrid aluminum electrolytic capacitors become larger, it has become a challenge to impregnate the conductive polymer uniformly into the interior of the element. In the manufacturing process of hybrid aluminum electrolytic capacitors, it is common to overlap and wind the electrode foil and separator and then vacuum impregnate them with a conductive polymer dispersion. However, as hybrid aluminum electrolytic capacitors become larger, the width of the electrode foil and separator also increases, so with the general vacuum impregnation method, the conductive polymer does not penetrate to the center of the element. The conductive polymer is unevenly distributed at one end and the other end in the width direction of the separator, and there is an unimpregnated area in the center, which hinders the reduction of ESR.

[0007] The present invention has been made in view of the above problems, and aims to provide a method for manufacturing an electrolytic capacitor that can easily form a uniform impregnation state of a conductive polymer and reduce ESR, even if the shape of the electrolytic capacitor is large. [Means for solving the problem]

[0008] The present invention relates to a method for manufacturing an electrolytic capacitor, comprising: a preparation step of preparing a capacitor element having an anode foil having an oxide film on its surface, a cathode foil, and a separator inserted between the anode foil and the cathode foil; a vacuum impregnation step of immersing the capacitor element in a conductive polymer dispersion in a reduced-pressure atmosphere of a predetermined vacuum degree and impregnating the separator with the conductive polymer dispersion; a pressurized atmosphere formation step of opening the reduced-pressure atmosphere to the atmosphere while the capacitor element remains immersed in the conductive polymer dispersion and further pressurizing it to a predetermined pressure; and a pressurized impregnation step of impregnating the separator of the capacitor element, which is immersed in the conductive polymer dispersion, with the conductive polymer dispersion in the pressurized atmosphere and then opening it to the atmosphere. [Effects of the Invention]

[0009] According to the present invention, even if the shape of the electrolytic capacitor is large, a uniform impregnation state of the conductive polymer can be easily formed, thereby reducing ESR. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a schematic diagram of an electrolytic capacitor according to an embodiment of the present invention. [Figure 2] Figure 2 is a cross-sectional view showing a portion of the cross-section passing through the axial center of a capacitor element (before impregnation with conductive polymer). [Figure 3] Figure 3 is a schematic cross-sectional view showing the impregnation state of the conductive polymer in a capacitor element. [Figure 4] Figure 4 schematically shows the results of confirming the formation state of the conductive polymer layer on the separator surface. [Figure 5] Figure 5 schematically shows the results of confirming the formation state of the conductive polymer layer on the separator surface of a conventional capacitor element that has undergone vacuum impregnation only. [Figure 6] Figure 6 shows the change in the impregnation state of the conductive polymer in the separator when vacuum impregnation is performed followed by pressure impregnation. [Figure 7]Figure 7 shows the impregnation process of a capacitor element with a conductive polymer. [Figure 8] Figure 8 is a flowchart showing the manufacturing process of electrolytic capacitors. [Figure 9] Figure 9 shows the change in the percentage of conductive polymer unimpregnated as the impregnation state of the separator is observed while the pressure is progressively increased. [Modes for carrying out the invention]

[0011] Embodiments of the present invention will be described below with reference to the drawings.

[0012] <Structure of an electrolytic capacitor> Figure 1 is a schematic diagram of an electrolytic capacitor 1 according to an embodiment of the present invention. As shown in Figure 1, the electrolytic capacitor 1 comprises a metal case 10 that functions as an outer casing, a capacitor element 20 installed in the metal case 10, and a sealing body 30. A wound type (cylindrical type) capacitor element 20 is preferably used, as it allows for good short-circuit path effect in electron transfer. However, a multilayer type capacitor element (prismatic type) in which anode foil and cathode foil are sequentially stacked with a separator in between may also be used. The following explanation will use a wound type electrolytic capacitor as an example.

[0013] The metal case 10 is a bottomed cylindrical aluminum case having an opening 11 at one end. In this embodiment, the metal case 10 is cylindrical as an example, but it may also be rectangular.

[0014] The capacitor element 20 comprises a pair of electrode foils. The pair of electrode foils are an anode foil 21 and a cathode foil 22. The capacitor element 20 is constructed by stacking and winding a separator 23, anode foil 21, separator 23, and cathode foil 22 in this order. The shape of the capacitor element 20 is made to substantially match the inner shape of the metal case 10. Therefore, the capacitor element 20 has a columnar shape.

[0015] As the anode foil 21 and the cathode foil 22, valve metals such as aluminum, tantalum, titanium and niobium, alloy foils thereof, vapor-deposited foils, and the like can be used. The entire surface of the anode foil 21 is covered with an oxide film. Accordingly, the anode foil 21 is insulated from other members. This oxide film functions as a dielectric, whereby the capacitor element 20 functions as a capacitor. On the surface of the cathode foil 22, an oxide film for coping with reverse voltage may be formed in addition to an oxide film formed by natural oxidation. Further, an inorganic material layer or a carbon layer may be formed on the surface of the cathode foil 22.

[0016] An anode lead terminal 23a is connected to the anode foil 21. A cathode lead terminal 23b is connected to the cathode foil 22.

[0017] The sealing body 30 is formed of a rubber sealing body having a pair of lead insertion holes 31a, 31b through which the anode lead terminal 23a and the cathode lead terminal 23b are inserted. The sealing body 30 is fitted into the opening 11 of the metal case 10, and is hermetically and firmly attached by a lateral constriction groove 12 formed along the outer periphery of the opening 11 by a caulking die or the like. There is no particular limitation on the rubber used for the sealing body 30, but butyl rubber having a low swelling rate with respect to a solvent of an electrolytic solution described later is preferably used. This makes it possible to reduce the influence of impurities extracted by ethylene glycol on capacitor characteristics when the electrolytic solution contains ethylene glycol. Specifically, butyl rubber having the characteristics that the swelling rate is less than 0.4 wt% even when immersed in an ethylene glycol solvent at 125° C. for 2000 hours or more, and the swelling rate is less than 2 wt% even when similarly immersed in a γ-butyrolactone solvent for 2000 hours or more is preferable.

[0018] The capacitor element 20 is impregnated with a conductive polymer. Examples of the conductive polymer include polythiophene, polypyrrole, polyaniline, polyacetylene, polyfuran, polyacetylene, polyparaphenylene, polyparaphenylene vinylene, polyacene, and polythiophene vinylene. The above-described conductive polymers may be used alone or in combination of two or more. Further, the above-described conductive polymer only needs to be a polymer containing at least 50% by mass or more of the basic monomer constituting the conductive polymer, such as thiophene, pyrrole, or the like, preferably contains 70% by mass or more, and more preferably contains 90% by mass. As the conductive polymer, poly(3,4-ethylenedioxythiophene) containing 3,4-ethylenedioxythiophene as a monomer unit can be suitably used.

[0019] The conductive polymer preferably contains a dopant. Examples of the dopant include polyvinylsulfonic acid, polystyrenesulfonic acid, polyallylsulfonic acid, polyacrylsulfonic acid, polymethacrylsulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprenesulfonic acid, and polyacrylic acid. The above-described dopants may be used alone or in combination of two or more.

[0020] Each separator 23 may be made of the same type of material or different materials. As the separator 23, for example, glass fiber, cellulose, rayon, polyethylene terephthalate, vinylon, aliphatic polyamide, and aromatic polyamide can be used. As the separator 23, a mixed paper composed of cellulose, rayon, and glass fiber can be suitably used.

[0021] The capacitor element 20 is impregnated with an electrolyte. While there are no limitations on the electrolyte as long as it is suitable for use in electrolytic capacitors, either a γ-butyllactone-based non-aqueous electrolyte or an ethylene glycol-based aqueous electrolyte can be used. Examples of solute components in the electrolyte include aliphatic carboxylic acids such as adipic acid, aromatic carboxylic acids such as phthalic acid, ammonia, amines such as triethylamine, and amidines such as tetramethylimidazolinium.

[0022] <Impregnation state of conductive polymer> Figure 2 is a cross-sectional view showing a portion of the cross-section passing through the axial center of the capacitor element 20 (before impregnation with conductive polymer). As shown in Figure 2, the anode foil 21 and cathode foil 22 are opposite each other via an insulating separator 23, and the separator 23 suppresses short circuits between the anode foil 21 and cathode foil 22. In the electrolytic capacitor 1 as a hybrid aluminum electrolytic capacitor, a conductive polymer layer is formed on the separator 23, the surface of the anode foil 21, and the surface of the cathode foil 22 by impregnating the separator 23 separating the anode foil 21 and cathode foil 22 with a conductive polymer dispersion and drying the dispersion medium. As a result, the electrolytic capacitor 1 can achieve low ESR.

[0023] Figure 3 is a schematic cross-sectional view showing the impregnation state of the conductive polymer 25 in the capacitor element 20. Figure 4 is a schematic diagram showing the results of confirming the formation state of the conductive polymer layer on the surface of the separator 23. Figures 3 and 4 show the results after vacuum impregnation followed by pressure impregnation.

[0024] As shown in Figures 3 and 4, when pressure impregnation is performed after vacuum impregnation, the conductive polymer 25 is impregnated almost uniformly from one end to the other in the width direction of the separator 23. The impregnation state of the conductive polymer on the surface of the anode foil 21 and the surface of the cathode foil 22 is the same as that of the separator 23. The capacitor element 20 is a large element with a width of 14.5 mm. Here, width or width direction refers to the direction perpendicular to the winding direction, i.e., the length direction, in the case of a wound type.

[0025] In this state of impregnation with conductive polymer, when considering the electron conduction path between the anode foil 21 and the cathode foil 22, the resistance is low across the entire surface where the conductive polymer layer is formed. In actual hybrid aluminum electrolytic capacitors, since the electrolyte is impregnated after the formation of the conductive polymer layer, the entire surface between the anode foil 21 and the cathode foil 22 is composed of a composite material of the conductive polymer layer and the electrolyte, resulting in a uniformly low resistance value in every part, thus reducing the ESR of the entire electrolytic capacitor element.

[0026] Figure 5 schematically shows the results of confirming the formation state of the conductive polymer layer on the surface of the separator 23 in a conventional capacitor element that underwent vacuum impregnation only. The separator 23 shown in Figure 5 is the same large element as in Figures 3 and 4, with a width of 14.5 mm. Conventionally, for capacitor elements 20 with a width of less than 6 mm, the conductive polymer could be impregnated to the center by vacuum impregnation alone. However, when vacuum impregnation alone is performed on a large capacitor element 20 with a width of 6 mm or more, the extension of the second impregnation region E2 to the center stops at a certain width, and a void region E10 is formed in the center where the conductive polymer film is not formed. As a result, the center is composed only of electrolyte, and since the conductivity of the conductive polymer layer is higher than that of the electrolyte, the center has high resistance even when the electrolyte is impregnated. Consequently, when vacuum impregnation alone is performed on a large capacitor element 20 of 6 mm or more, the center of the separator 23 has high resistance, and the ESR is high.

[0027] Figure 6 shows the change in the impregnation state of the conductive polymer 25 in the separator 23 when vacuum impregnation is performed followed by pressure impregnation. First, the capacitor element 20 is immersed in a conductive polymer dispersion contained in a predetermined container inside the chamber under a reduced pressure atmosphere. As a result, the capacitor element 20 and the conductive polymer dispersion come into contact, and as an initial impregnation, a first impregnation region E1 is formed at the upper and lower ends of the separator 23, similar to atmospheric pressure impregnation (Figure 6(a)). The reason for immersing the capacitor element 20 in a reduced pressure atmosphere is that, under atmospheric pressure, the impregnation rates of the conductive polymer and the solvent into the separator 23 are different. Once impregnation progresses to a certain extent, the solvent (e.g., water) from the conductive polymer solution reaches the central part of the separator 23 ahead of the conductive polymer, making it difficult for the conductive polymer to reach the central part of the separator 23 where the solvent has already filled.

[0028] Subsequently, as shown in Figure 6(b), vacuum impregnation proceeds, and a second impregnation region E2 is formed on the central side. This impregnation state in Figure 6(b) is the same as the impregnation state shown in Figure 5, where the conductive polymer does not reach the central side, and the impregnation process stops.

[0029] Subsequently, as shown in Figure 6(c), the capacitor element 20 is immersed in the conductive polymer dispersion while the chamber is pressurized, and the capacitor element 20 is pressurized and impregnated with the conductive polymer dispersion in a predetermined container. As a result, a third impregnation region E3 is formed from the second impregnation region E2 toward the center. During this pressurized impregnation, the conductive polymer dispersion pushes out the conductive polymer dispersion in the second impregnation region E2 toward the center, forming the third impregnation region E3 toward the center.

[0030] Furthermore, if the conductive polymer layer impregnates the entire separator 23 without any gaps, this impregnation treatment of conductive polymer can be applied not only to hybrid electrolytic capacitors impregnated with electrolyte, but also to solid electrolytic capacitors that are not impregnated with electrolyte.

[0031] <Impregnation process of conductive polymer> Figure 7 shows the process of impregnating a capacitor element with a conductive polymer. Figure 7 shows a vertical cross-section of the storage tank 90 installed in the chamber 9 and the capacitor element 20. The capacitor element 20 is immersed in a conductive polymer dispersion stored in the storage tank 90 so that the conductive polymer impregnates the separator 23.

[0032] The pressure control device 91 controls the pressure inside the chamber 9 using a pump (not shown) or the like. Specifically, the pressure control device 91 controls the vacuum level and pressurization level inside the chamber 9 according to the passage of time. The vacuum level and pressurization level are relative pressures when the atmospheric pressure around the chamber 9 is set to 0 kPa.

[0033] The pressure control device 91 executes the following processes in this order: depressurization S21, vacuum impregnation S22, atmospheric release S23, pressurization S24, pressurization impregnation S25, atmospheric release S26, and atmospheric retention S27. The processing times for depressurization S21, vacuum impregnation S22, atmospheric release S23, pressurization S24, pressurization impregnation S25, atmospheric release S26, and atmospheric retention S27 show the time change of pressure along with the depressurization time, vacuum impregnation time, atmospheric release time, pressurization time, pressurization impregnation time, atmospheric release time, and atmospheric retention time. The position of the capacitor element 20 relative to the storage tank 90 is also shown in accordance with each process.

[0034] Furthermore, the vacuum draining process S21 and the vacuum impregnation process S22 correspond to a vacuum impregnation process in which the capacitor element 20 is immersed in a conductive polymer dispersion in a vacuum atmosphere of a predetermined vacuum level, and the separator is impregnated with the conductive polymer. In addition, the atmospheric release process S23 and the pressurization process S24 correspond to a pressurized atmosphere formation process in which the vacuum atmosphere is released to the atmosphere while the capacitor element remains immersed in the conductive polymer dispersion, and then the atmosphere is further pressurized to a predetermined pressure level. Furthermore, the pressurized impregnation process S25, the atmospheric release process S26, and the atmospheric retention process S27 correspond to a pressurized impregnation process in which the separator of the capacitor element, which is immersed in the conductive polymer dispersion, is impregnated with the conductive polymer in a pressurized atmosphere, and then released to the atmosphere.

[0035] The vacuum extraction process S21 reduces the pressure inside the chamber 9 to a substantially vacuum state. For example, the vacuum inside the chamber 9 is reduced to -93 kPa. The vacuum extraction time is 60 seconds as an example. During the execution of the vacuum extraction process S21, the capacitor element 20 is held outside the conductive polymer dispersion inside the chamber 9. In other words, the capacitor element 20 is not immersed in the conductive polymer dispersion. Therefore, air is removed from inside the capacitor element 20 before it is immersed in the conductive polymer dispersion. This allows for smooth impregnation with the conductive polymer dispersion during the vacuum impregnation process.

[0036] The vacuum impregnation process S22 involves immersing the capacitor element 20 in a conductive polymer dispersion and maintaining a vacuum inside the chamber 9 for the duration of the vacuum impregnation time. In this process, the capacitor element 20 is completely immersed in the conductive polymer dispersion, and the conductive polymer impregnates the separator 23. This impregnation state is the same as that shown in Figure 6(b), and the impregnation does not reach the center of the separator 23. The vacuum impregnation time is, for example, 5 seconds.

[0037] Subsequently, in the atmospheric release treatment S23, the capacitor element 20 remains immersed in the conductive polymer dispersion, and the pressure inside the chamber 9 is returned to atmospheric pressure for the atmospheric release time. Then, in the pressurization treatment S24, the pressure is increased to a set pressure level, for example, 500 kPa, for the pressurization time. The capacitor element 20 remains immersed in the conductive polymer dispersion throughout the atmospheric release treatment S23 and the pressurization treatment S24.

[0038] Subsequently, during the pressure impregnation treatment S25, the pressure impregnation time and pressure level of 500 kPa are maintained, and during this time, the capacitor element 20 is impregnated with conductive polymer into the separator 23 by pressure impregnation. The impregnation state during this pressure impregnation treatment is the same as the impregnation state shown in Figure 6(c), and the conductive polymer is impregnated throughout the entire area of ​​the separator 23.

[0039] Subsequently, in the atmospheric release treatment S26, the capacitor element 20 remains immersed in the conductive polymer dispersion, and the pressure inside the chamber 9 is returned to atmospheric pressure for the atmospheric release time. Furthermore, in the atmospheric holding treatment S27, the capacitor element 20 remains immersed in the conductive polymer dispersion, and the pressure inside the chamber 9 is maintained at atmospheric pressure for the atmospheric pressure holding time. After this atmospheric holding time has elapsed, the capacitor element 20 is removed from the conductive polymer dispersion, and the impregnation treatment of the capacitor element 20 with conductive polymer is completed.

[0040] <Examples> The present invention will be described in more detail below with reference to examples.

[0041] (Example 1) In Example 1, a wound electrolytic capacitor (diameter 16 mm x length 21.5 mm (width = 14.5 mm)) was manufactured. The specific manufacturing method of this electrolytic capacitor is described below. Figure 8 is a flowchart of the manufacturing process of the electrolytic capacitor.

[0042] [Fabrication of capacitor elements] As shown in Figure 8, the capacitor element is first fabricated (step S11). Specifically, an anode lead terminal is connected to an anode foil with an oxide film formed on its surface. Then, a cathode lead terminal is connected to a cathode foil that has a conductive layer on its end face and has undergone a pretreatment to improve wettability. Subsequently, the separator, cathode foil, separator, and anode foil are laminated in this order, wound while wrapping the lead terminals, and the outer surface is fixed with winding tape to fabricate the capacitor element.

[0043] [Impregnation with conductive polymers] Next, the capacitor element was impregnated with a conductive polymer (step S12). Specifically, the capacitor element was immersed in a conductive polymer dispersion contained in a predetermined container under a reduced pressure atmosphere (-93kPa), and the vacuum impregnation time was set to 5 seconds. Next, while maintaining the capacitor element immersed in the conductive polymer dispersion, pressurization was started and a constant pressurized state (pressure level = 100kPa) was maintained. A pressurized impregnation time of 60 seconds was elapsed under this pressurized state, and then the capacitor element was removed from the conductive polymer dispersion, thereby impregnating the capacitor element with the conductive polymer dispersion. The capacitor element impregnated with the conductive polymer was dried in a drying oven at 150°C for 60 minutes to fix the conductive polymers in each layer together and form conductive paths.

[0044] [Impregnation with electrolyte solution] Next, the capacitor element was impregnated with an electrolyte (step S13). Specifically, a predetermined amount of electrolyte was impregnated into the capacitor element impregnated with a conductive polymer in a reduced-pressure atmosphere to fabricate an electrolytic capacitor that functions as a hybrid aluminum electrolytic capacitor. A commercially available electrolyte, ESE2 manufactured by Teika, was used.

[0045] [Capacitor element sealing] Next, the capacitor elements are sealed (step S14). That is, the capacitor elements impregnated with electrolyte are sealed to complete the electrolytic capacitor.

[0046] (Examples 2-11) The vacuum level, time to release to the atmosphere after vacuum impregnation, pressurized impregnation time, and time to release to the atmosphere after pressurized impregnation in Examples 2 to 11 were the same as in Example 1, with a vacuum level of -93 kPa, time to release to the atmosphere after vacuum impregnation of 24 seconds, pressurized impregnation time of 60 seconds, and time to release to the atmosphere after pressurized impregnation of 60 seconds.

[0047] The vacuum impregnation time for Examples 1-5 was 5 seconds, and the pressure levels were 100, 300, 500, 700, and 900 kPa, respectively. The vacuum impregnation time for Examples 6-8 was 30 seconds, and the pressure levels were 100, 300, and 500 kPa, respectively. The vacuum impregnation time for Examples 9-11 was 60 seconds, and the pressure levels were 100, 300, and 500 kPa, respectively.

[0048] (Comparative Example 1) For comparison with Examples 1-11, an electrolytic capacitor of Comparative Example 1 was fabricated using only vacuum impregnation. In Comparative Example 1, the vacuum level was set to -93kPa, the same as in Examples 1-11, during impregnation with the conductive polymer dispersion. The vacuum impregnation time was set to 30 seconds, the atmospheric release time was set to 24 seconds, and no subsequent pressurized impregnation was performed. Apart from this impregnation treatment with the conductive polymer dispersion, Comparative Example 1 was fabricated using the same process as in Examples 1-11.

[0049] <Characteristic analysis of the examples and comparative examples> The impregnation rate of conductive polymer and ESR were measured for the electrolytic capacitors obtained in each of Examples 1 to 11 and Comparative Example 1.

[0050] The conductive polymer impregnation rate is the percentage of the area of ​​the separator surface that is not impregnated with conductive polymer, obtained by disassembling the fabricated electrolytic capacitor.

[0051] ESR is the ESR value (initial ESR value) (mΩ) of an electrolytic capacitor at a frequency of 100kHz, measured using a 4-terminal LCR meter (manufactured by KEYSIGHT, model name E4980A).

[0052] <Impregnation conditions and analysis results of the examples and comparative examples> Table 1 shows the impregnation conditions and analysis results for Examples 1-11 and Comparative Example 1.

[0053] [Table 1]

[0054] The following was confirmed from the analysis results in Table 1. First, all of Examples 1 to 11, in which vacuum impregnation was followed by pressure impregnation, showed lower ESR compared to Comparative Example 1. This is understandable since the percentage of conductive polymer unimpregnated in all of Examples 1 to 11 was smaller than that of Comparative Example 1. Therefore, for large electrolytic capacitors with a width of 14.5 mm, ESR can be reduced by performing pressure impregnation after vacuum impregnation. In particular, the impregnation treatment of performing pressure impregnation after vacuum impregnation is useful for large electrolytic capacitors with a width of 6 mm or more.

[0055] Furthermore, in Examples 1 to 5, it was confirmed that as the pressure level increased, the percentage of unimpregnated conductive polymer within the capacitor element decreased, and the ESR also decreased. This means that, given the same vacuum impregnation time in the vacuum impregnation process, the percentage of unimpregnated conductive polymer in the separator can be reduced by setting a higher pressure level. As a result, by setting the pressure level in this way, the percentage of unimpregnated conductive polymer can be reliably brought close to zero.

[0056] Figure 9 shows the change in the percentage of unimpregnated conductive polymer in the separator as the pressure is progressively increased, based on observations of the impregnation state. Figure 9(a) corresponds to Comparative Example 1, and Figures 9(b), 9(d), and 9(f) correspond to Examples 1 to 3, respectively. Figure 9(c) shows the impregnation state set at a pressure of 200 kPa, which is intermediate between Example 1 and Example 2, and Figure 9(e) shows the impregnation state set at a pressure of 400 kPa, which is intermediate between Example 2 and Example 3.

[0057] The separator has a width of 14.5 mm. The maximum gap length in the region not impregnated with conductive polymer decreases as the pressure increases. When the pressure reaches 500 kPa, there are no regions in the separator that are not impregnated with conductive polymer, and the percentage of unimpregnated conductive polymer becomes 0.

[0058] On the other hand, comparing Examples 3, 8, and 11, it was confirmed that even with the same pressure of 500 kPa for pressure impregnation, shortening the vacuum impregnation time to 60 seconds, 30 seconds, and 5 seconds reduced the percentage of unimpregnated conductive polymer in the capacitor element, thereby lowering the ESR. This is thought to be because the shorter the time between vacuum impregnation and pressure impregnation, the more the conductive polymer dispersion is immersed in the element, thus reducing the ESR within the capacitor element.

[0059] Therefore, if the vacuum level in the vacuum impregnation process is the same and the pressure level in the pressure impregnation process is the same, it means that the vacuum impregnation time in the vacuum impregnation process can be shortened to reduce the percentage of the separator that remains unimpregnated with conductive polymer. As a result, by setting the vacuum impregnation time in this way, the percentage of the conductive polymer that remains unimpregnated can be reliably brought close to zero.

[0060] Furthermore, in the impregnation process that follows vacuum impregnation with pressure impregnation, it is preferable to set the vacuum level to -85 to -100 kPa, the vacuum impregnation time to 1 to 80 seconds, the atmospheric release time to 1 to 60 seconds, the pressure level to 1 to 1000 kPa, and the pressure impregnation time to 1 to 60 seconds.

[0061] Although embodiments and examples of the present invention have been described in detail above, the present invention is not limited to these specific embodiments or examples, and various modifications and changes are possible within the scope of the gist of the present invention as described in the claims. [Explanation of symbols]

[0062] 1 Electrolytic capacitor 9 Chambers 10 Metal Cases 11 Opening 12 Horizontal groove 20 Capacitor elements 21 Anode foil 22 Cathode Foil 23 Separator 23a Anode lead terminal 23b Cathode lead terminal 25 Conductive polymer 30 Sealing body 31a, 31b Lead insertion holes 90 Storage tanks 91 Pressure control device E1 First impregnation area E2 2nd impregnation area E3 Third impregnation area E10 void area

Claims

1. Preparation steps for preparing a capacitor element comprising an anode foil having an oxide film on its surface, a cathode foil, and a separator inserted between the anode foil and the cathode foil, A vacuum impregnation step in which the capacitor element is immersed in a conductive polymer dispersion in a reduced-pressure atmosphere at a predetermined vacuum level, and the separator is impregnated with the conductive polymer dispersion, A pressurized atmosphere formation step is performed by immersing the capacitor element in the conductive polymer dispersion, releasing the reduced pressure atmosphere to the atmosphere, and then pressurizing it to a predetermined pressure level to form a pressurized atmosphere. A pressurized impregnation step involves impregnating the separator of the capacitor element, which is immersed in the conductive polymer dispersion in the aforementioned pressurized atmosphere, with the conductive polymer dispersion, and then releasing it to the atmosphere. A method for manufacturing an electrolytic capacitor, characterized by including the following:

2. The aforementioned predetermined vacuum level is a relative pressure of -85 to -100 kPa when atmospheric pressure is set to 0 kPa. The impregnation time in the vacuum impregnation process is 1 to 80 seconds. The aforementioned predetermined pressure is a relative pressure of 1 to 1000 kPa when atmospheric pressure is set to 0 kPa. The impregnation time in the aforementioned pressurized impregnation process is 1 to 60 seconds. A method for manufacturing an electrolytic capacitor according to claim 1, characterized in that it is as described in the present invention.

3. The method for manufacturing an electrolytic capacitor according to claim 1 or 2, characterized in that the width of the separator of the capacitor element is 6 mm or more.

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