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] A first impregnation region E1, a second impregnation region E2, and a third impregnation region E3 are formed in layers on the separator 23 of the capacitor element 20, sequentially from the upper and lower ends in the width direction toward the center, and the relative density of the conductive polymer in the third impregnation region E3 formed in the center is smaller than that of the first impregnation region E1 and larger than that of the second impregnation region E2.

Description

[Technical Field]

[0001] The present invention relates to an electrolytic capacitor. [Background Art]

[0002] As an electrolytic capacitor that is compact, has large capacity and low ESR (equivalent series resistance), an electrolytic capacitor comprising 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 electrolytic solution capable of repairing anodized films (a liquid composed of at least a solute and a solvent, having electrical conductivity and the capability of repairing anodized films) is regarded as promising as an in-vehicle electronic component. For example, Patent Document 1 describes a method for producing an aluminum electrolytic capacitor, in which a separator is brought into contact with a conductive polymer dispersion in advance, and dried to remove the solvent, thereby forming a conductive polymer layer. Further, Patent Document 2 describes a method for achieving uniformization of the conductive polymer layer by adhering polystyrene sulfonic acid to the capacitor before forming the conductive polymer layer. [Prior Art Documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Unexamined Patent Publication No. 2016-171257 [Patent Document 2] Japanese Unexamined Patent Publication No. 2017-37950 [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] Here, in the impregnation step of forming the conductive polymer layer, the conductive polymer dispersion penetrates from the end portions of the element toward the inside thereof, so it tends to deposit at the end portions and hardly penetrates into the interior, resulting in non-uniform conductive polymer layers on the surfaces of the separator and the electrode foil. In particular, when the electrolytic capacitor has a large shape and a large width between the end portions of the element, there has been a problem that the conductive polymer layer is less likely to be formed in the central portion in the width direction.

[0005] Therefore, Patent Document 1 proposes a method of using a separator in which a polymer layer is formed by first contacting the separator with a conductive polymer dispersion and then drying it. However, in the method described in Patent Document 1, when the separator and electrode foil are stacked and wound together, the proportion of the conductive polymer layer impregnated in the separator that adheres to the electrode foil is low, resulting in a weak interaction between the conductive polymer layer impregnated in the separator and the electrode foil, which limits the reduction of ESR.

[0006] Furthermore, Patent Document 2 proposes a method for homogenizing capacitors by pre-applying polystyrene sulfonic acid to them. However, this method requires drying after impregnation to attach the polystyrene sulfonic acid to the capacitors, which inevitably increases the number of steps involved. In addition, it necessitates the addition of new materials, which may lead to increased lead time, increased costs, or deterioration of product characteristics.

[0007] This invention has been made in view of the above problems, and aims to provide an electrolytic capacitor that can reduce ESR even when the shape of the electrolytic capacitor is large. [Means for solving the problem]

[0008] The electrolytic capacitor according to the present invention comprises 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, and a conductive polymer impregnated in the capacitor element, wherein a first impregnation region, a second impregnation region, and a third impregnation region are formed in layers on the separator of the capacitor element, sequentially from both ends in the width direction toward the center, and the relative density of the conductive polymer in the third impregnation region formed in the center is smaller than that of the first impregnation region and larger than that of the second impregnation region. Herein, width or width direction refers to, for example, the winding direction in the case of a wound type, that is, the direction perpendicular to the length direction. [Effects of the Invention]

[0009] According to the present invention, ESR can be reduced even if the shape of the electrolytic capacitor is large. [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. [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 cathode foil 22, valve metals such as aluminum, tantalum, titanium, and niobium, as well as alloy foils and vapor-deposited foils, can be used. The anode foil 21 is covered with an oxide film over its entire surface. Therefore, the anode foil 21 is insulated from other components. This oxide film functions as a dielectric, allowing the capacitor element 20 to function as a capacitor. In addition to the oxide film formed by natural oxidation, an oxide film for reverse voltage protection may be formed on the surface of the cathode foil 22. Furthermore, an inorganic material layer or a carbon layer may be formed on the surface of the cathode foil 22.

[0016] Anode lead terminal 23a is connected to anode foil 21. Cathode lead terminal 23b is connected to cathode foil 22.

[0017] The sealing body 30 is a rubber sealing body having a pair of lead insertion holes 31a and 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 airtightly and firmly attached by a horizontal drawing groove 12 formed along the outer periphery of the opening 11 with 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 the solvent of the 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 preferred.

[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-mentioned conductive polymers may be used alone or in combination of two or more. Further, the above-mentioned conductive polymer may be any polymer containing at least 50% by mass or more of the basic monomer constituting the conductive polymer, for example, thiophene, pyrrole, etc., those containing 70% by mass or more are preferred, and those containing 90% by mass are more preferred. 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 dopants described above may be used alone or in combination of two or more thereof.

[0020] Each of the separators 23 may be made of the same type of material or different materials. For the separator 23, for example, glass fiber, cellulose, rayon, polyethylene terephthalate, vinylon, aliphatic polyamide, or 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 electrolytic solution. The electrolytic solution is not limited as long as it can be used for electrolytic capacitors, and both γ-butyrolactone-based non-aqueous electrolytic solutions and ethylene glycol-based aqueous electrolytic solutions can be used. Examples of solute components contained in the electrolytic solution include aliphatic carboxylic acids such as adipic acid, aromatic carboxylic acids such as phthalic acid, amines such as ammonia and triethylamine, and amidines such as tetramethylimidazolinium.

[0022] <Impregnation State of Conductive Polymer> Figure 2 is a cross-sectional view showing a part of a cross-section passing through the axial center of the capacitor element 20 (before impregnation with the conductive polymer). As shown in Figure 2, the anode foil 21 and the cathode foil 21 have a structure facing each other with an insulating separator 23 interposed therebetween, and the separator 23 suppresses a short circuit between the anode foil 21 and the cathode foil 22. The electrolytic capacitor 1, which is a hybrid aluminum electrolytic capacitor, forms a conductive polymer layer 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 the cathode foil 22 with a conductive polymer dispersion and drying the dispersion medium. Thereby, 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.

[0025] The impregnation state of the separator 23 is such that the conductive polymer 25 is impregnated in layers on the surfaces of the anode foil 21 and cathode foil 22, sequentially from both ends in the width direction toward the center, forming a first impregnation region E1, a second impregnation region E2, and a third impregnation region E3. The relative density of the conductive polymer 25 in the third impregnation region E3 formed in the center is smaller than that of the first impregnation region E1 and larger than that of the second impregnation region E2. Furthermore, the third impregnation region E3 on one end and the third impregnation region E3 on the other end are in contact in the center, and there are no unimpregnated regions between each third impregnation region E3. Even if there are unimpregnated regions, if the distance between the third impregnation region E3 on one end and the third impregnation region E3 on the other end is less than 5% of the width of the separator, it is equivalent to having no unimpregnated regions.

[0026] 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.

[0027] In particular, the density of the conductive polymer 25 in the third impregnation region E3 in the central part is greater than that of the second impregnation region E2 which occupies most of the peripheral part, resulting in lower resistance in the central part compared to the peripheral part. As a result, for example, the responsiveness to high-frequency currents can be increased.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] Subsequently, as shown in Figure 6(c), the capacitor element 20 is immersed in the conductive polymer dispersion while the chamber is pressurized, causing the capacitor element 20 to be pressurized and impregnated with the conductive polymer dispersion in a predetermined container. This forms a third impregnation region E3 from the second impregnation region E2 toward the center. During this pressurized impregnation, the conductive polymer dispersion pushes the conductive polymer dispersion from the second impregnation region E2 toward the center, forming the third impregnation region E3 toward the center. As a result, the density of the conductive polymer in the third impregnation region E3 becomes greater than the density of the conductive polymer in the second impregnation region E2, resulting in a higher density of conductive polymer in the center. The impregnation state in Figure 6(c) is the same as the impregnation state shown in Figures 3 and 4.

[0032] 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.

[0033] <Examples> The present invention will be described in more detail below with reference to examples.

[0034] (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.

[0035] [Fabrication of capacitor elements] First, an anode lead terminal was connected to an anode foil with an oxide film formed on its surface. Then, a cathode lead terminal was connected to a cathode foil that had a conductive layer on its end face and had undergone a pretreatment to improve its wettability. Subsequently, the separator, cathode foil, separator, and anode foil were laminated in this order, wound around the lead terminals, and the outer surface was secured with winding tape to fabricate a capacitor element.

[0036] [Impregnation with conductive polymers] In a reduced-pressure atmosphere (-93kPa), a capacitor element was immersed in a conductive polymer dispersion contained in a predetermined container, and the vacuum impregnation time was set to 30 seconds. Next, while maintaining the capacitor element immersed in the conductive polymer dispersion, pressurization was started and a constant pressurized state (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 conductive polymer was dried in a drying oven at 150°C for 60 minutes to fix the conductive polymer layers together and form conductive paths.

[0037] [Impregnation with electrolyte solution] An electrolytic capacitor functioning as a hybrid aluminum electrolytic capacitor was fabricated by impregnating this capacitor element with a predetermined amount of electrolyte in a reduced-pressure atmosphere. ESE2, a commercially available electrolyte manufactured by Teika, was used.

[0038] [Capacitor element sealing] The electrolytic capacitor was completed by sealing the capacitor element impregnated with electrolyte.

[0039] (Example 2) Example 2 uses the same impregnation conditions as Example 1, but with a pressure of 500 kPa. All other conditions are the same as in Example 1.

[0040] (Example 3) Example 3 uses the same impregnation conditions as Example 1, but with a pressure of 900 kPa. All other conditions are the same as in Example 1.

[0041] (Comparative Example 1) To compare with Examples 1-3, an electrolytic capacitor of Comparative Example 1 was fabricated with a different impregnation treatment. In Comparative Example 1, the atmospheric pressure impregnation time with the conductive polymer dispersion was set to 30 seconds, and no subsequent pressurized impregnation was performed. Except for this impregnation treatment with the conductive polymer dispersion, the electrolytic capacitor of Comparative Example 1 was fabricated using the same procedures as in Examples 1-3.

[0042] (Comparative Example 2) To compare with Examples 1-3, an electrolytic capacitor of Comparative Example 2 was fabricated with a different impregnation treatment. In Comparative Example 2, the vacuum impregnation time with the conductive polymer dispersion was set to 30 seconds, and subsequent pressure impregnation was omitted. Except for this impregnation treatment with the conductive polymer dispersion, the electrolytic capacitor of Comparative Example 2 was fabricated using the same procedures as in Examples 1-3.

[0043] (Comparative Example 3) To compare with Examples 1-3, an electrolytic capacitor of Comparative Example 3 was fabricated with a different impregnation treatment. In Comparative Example 3, vacuum impregnation was not performed during the impregnation of the conductive polymer dispersion. Instead, the pressure was set to 500 kPa, and the pressure impregnation time was allowed to last for 60 seconds. After that, the capacitor element was removed from the conductive polymer dispersion, thereby impregnating the capacitor element with the conductive polymer dispersion. Except for this impregnation treatment of the conductive polymer dispersion, the electrolytic capacitor of Comparative Example 3 was fabricated using the same procedures as in Examples 1-3.

[0044] (Comparative Example 4) To compare with Examples 1-3, an electrolytic capacitor of Comparative Example 4 was fabricated with a different impregnation treatment. In Comparative Example 4, the pressure was set to 500 kPa during impregnation with the conductive polymer dispersion, and the pressure impregnation time was 60 seconds. Then, while maintaining the state in which the capacitor element was immersed in the conductive polymer dispersion, the vacuum was set to -93 kPa, and vacuum impregnation was performed for a time of 30 seconds. After that, the capacitor element was removed from the conductive polymer dispersion, allowing the conductive polymer dispersion to penetrate into the capacitor element. Except for this impregnation treatment with the conductive polymer dispersion, the electrolytic capacitor of Comparative Example 4 was fabricated using the same procedures as in Examples 1-3.

[0045] <Characteristic analysis of the examples and comparative examples> For the electrolytic capacitors obtained in each of Examples 1-3 and Comparative Examples 1-4, the following were measured: the percentage of unimpregnated conductive polymer, ESR, number of impregnated layers, relative density of the impregnated layers, width of each impregnated layer, presence or absence of voids in the separator, and width ratio of the impregnated layers (E3 / (E1+E2)).

[0046] The impregnation rate of conductive polymer is the percentage of the area of ​​the separator surface that is not impregnated with conductive polymer, obtained by disassembling the capacitor element of the fabricated electrolytic capacitor.

[0047] 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).

[0048] The number of impregnation layers is the number of layers in the impregnation region E3 on the separator surface, i.e., the first impregnation region E1, the second impregnation region E2, and the third impregnation region E3. The relative density order of the impregnation layers is the density order relative to the first impregnation region E1, the second impregnation region E2, and the third impregnation region E3. The width of each impregnation layer is the average width of the first impregnation region E1 and the second impregnation region E2. The presence or absence of voids within the separator is the presence or absence of void region E10. The width ratio of the impregnation layers is the ratio of the width of the third impregnation region E3 to the width obtained by adding the width of the second impregnation region E2 to the width of the first impregnation region E1.

[0049] <Impregnation conditions and analysis results of the examples and comparative examples> The impregnation conditions and analysis results for Examples 1-3 and Comparative Examples 1-4 are shown in Tables 1 and 2.

[0050] [Table 1]

[0051] [Table 2]

[0052] The following was confirmed from the analysis results in Tables 1 and 2. First, Examples 1-3, which underwent pressure impregnation after vacuum impregnation, were able to obtain a lower ESR compared to all of Comparative Examples 1-4.

[0053] Furthermore, in Examples 1-3, it was confirmed that the unimpregnated conductive polymer rate decreased as the pressure level increased, and that the ESR corresponded to the unimpregnated conductive polymer rate.

[0054] Furthermore, the relative density order of the impregnation layers in Examples 1 to 3, when the impregnation layers extending from the upper and lower ends of the separator and electrode foil towards the center are designated as the first impregnation region E1, the second impregnation region E2, and the third impregnation region E3, is in the order of first impregnation region E1 > third impregnation region E3 > second impregnation region E2. It was confirmed that the width of the impregnation layer is narrowest in the first impregnation region E1. As a result, the second impregnation region E2 and the third impregnation region E3, which have relatively wide impregnation layers, occupy the majority of the impregnation region. Moreover, the density of the third impregnation region E3 in the central part is higher than the density of the second impregnation region E2. This indicates that the third impregnation region E3 has low resistance in the central part and greatly contributes to low ESR.

[0055] Furthermore, in Examples 1-3, the width ratio is 1 / 2 or more, which also indicates that the third impregnation region E3 in the central part contributes significantly to the reduction of ESR.

[0056] Furthermore, in Examples 1 to 3, the width of the impregnated layer is in the order of second impregnation region E2 > third impregnation region E3 > first impregnation region E1 when the pressure is low (Example 1), but when the pressure is high (Examples 2 and 3), it becomes third impregnation region E3 > second impregnation region E2 > first impregnation region E1. This means that the width of the third impregnation region E3 widens as the pressure increases. In Examples 2 and 3, there is no change in the width of the third impregnation region E3, because at the pressure level of Example 2, the third impregnation regions E3 from both ends come into contact in the center, making the gap between each third impregnation region E3 zero, and the width cannot be widened any further. Therefore, in larger electrolytic capacitors, the width of the capacitor element becomes even larger, so it is thought that the width of the third impregnation region E3 will widen. In other words, the width of the third impregnation region E3 can be widened by increasing the pressure, and even in large electrolytic capacitors with a wider width, the unimpregnated rate of conductive polymer can be made zero. Furthermore, even when there is a gap between the third impregnation regions E3 as in Example 1, the third impregnation region E3 is located towards the central part and the gap is small, which contributes to reducing ESR and results in a low ESR.

[0057] In Comparative Example 1, since neither vacuum impregnation nor pressure impregnation was performed, the rate of unimpregnated conductive polymer is high.

[0058] Furthermore, in Comparative Example 2, where only vacuum impregnation was performed, and Comparative Example 3, where only pressure impregnation was performed, the rate of unimpregnated conductive polymer was reduced somewhat, but still not as high as in Examples 1 to 3. Also, in terms of relative density of the impregnated layers, the conductive polymer impregnated layers on the separator and electrode foil surfaces consist of two layers, with the first impregnation region E1 > second impregnation region E2, indicating that the density of the conductive polymer in the central part is lower.

[0059] Furthermore, Comparative Example 4 involved both vacuum impregnation and pressure impregnation, but in this case, vacuum impregnation was performed after pressure impregnation. In Comparative Example 4, the effect of vacuum impregnation after pressure impregnation was almost negligible, and the reduction in the unimpregnated rate of conductive polymer was limited. In addition, although there were three conductive polymer impregnation layers, the density order was first impregnation region E1 > second impregnation region E2 > third impregnation region E3, which differed from the density order of Examples 1-3, and it was confirmed that the density was lower in the central part.

[0060] 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]

[0061] 1 Electrolytic capacitor 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 terminals 25 Conductive polymer 30 Sealing body 31a, 31b Lead insertion holes E1 First impregnation area E2 2nd impregnation area E3 Third impregnation area E10 Void Domain

Claims

1. 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, The conductive polymer impregnated in the capacitor element, It has, An electrolytic capacitor characterized in that, with respect to the separator of the capacitor element, a first impregnation region, a second impregnation region, and a third impregnation region are formed in layers, with a conductive polymer sequentially impregnated from both ends in the width direction toward the center, and the relative density of the conductive polymer in the third impregnation region formed in the center is smaller than that of the first impregnation region and larger than that of the second impregnation region.

2. The electrolytic capacitor according to claim 1, wherein there is an unimpregnated region between the third impregnated region on one end in the width direction and the third impregnated region on the other end, and the distance between the third impregnated region on one end and the third impregnated region on the other end is less than 5% of the width of the separator.

3. The electrolytic capacitor according to claim 2, characterized in that the third impregnation region on one end in the width direction and the third impregnation region on the other end are in contact at the central portion, and the unimpregnated region is 0.

4. The electrolytic capacitor according to claim 1, characterized in that the ratio of the width of the third impregnation region to the width obtained by adding the width of the second impregnation region to the width of the first impregnation region is 1 / 2 or more.

5. The electrolytic capacitor according to any one of claims 1 to 4, characterized in that the width of the separator of the capacitor element is 6 mm or more.

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