Manufacturing method for solid electrolytic capacitors

Abstract

A method for manufacturing a solid electrolytic capacitor that can ensure sufficient long-term reliability and also can provide a sufficiently high initial capacitance. [Solution] A method for manufacturing a solid electrolytic capacitor (20) includes a first step of preparing a porous body (4) containing a valve action metal and having a dielectric layer (5) formed to cover at least a portion of the surface; a second step of irradiating plasma onto at least a portion of the surface of the porous body to introduce hydroxyl groups; and a third step of forming a first conductive polymer layer by applying a first dispersion liquid containing a first dispersion medium and particles of a second conductive polymer dispersed in the first dispersion medium to the surface of the porous body into which hydroxyl groups have been introduced.

Description

[Technical Field]

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

[0002] A solid electrolytic capacitor includes, for example, a capacitor element including an anode portion (anode body) and a cathode portion, and an exterior body that seals the capacitor element. The capacitor element includes, for example, a dielectric layer that covers at least a portion of the anode portion, a solid electrolyte layer that covers at least a portion of the dielectric layer, and a cathode extraction layer that covers at least a portion of the solid electrolyte layer. In the capacitor element, the cathode portion is formed, for example, by the solid electrolyte layer and the cathode extraction layer. In the capacitor element, the anode portion is formed, for example, as a porous body containing a valve metal.

[0003] Patent Document 1 discloses a method for manufacturing a solid electrolytic capacitor, the method comprising the steps of: fabricating a capacitor element having an anode body with an anode lead portion; and sequentially forming a dielectric coating layer, a cathode layer (corresponding to the solid electrolyte layer in the present application), and the cathode lead portion on the circumferential surface of the anode body excluding the anode lead portion; wherein the step of fabricating the capacitor element comprises the steps of forming the anode body with the anode lead portion, forming the dielectric coating layer, forming the cathode layer, forming the cathode lead portion, and performing a surface treatment by ultraviolet irradiation or plasma irradiation.

[0004] Patent Document 1 also discloses a method for manufacturing a solid electrolytic capacitor in which, after the step of forming the dielectric coating layer, a surface treatment step is performed by ultraviolet irradiation or plasma irradiation. In other words, it discloses treating the surface of the dielectric coating layer by ultraviolet irradiation or plasma irradiation. More specifically, it discloses roughening the surface of the dielectric coating layer by ultraviolet irradiation or plasma irradiation. Patent Document 1 also discloses that roughening improves the surface tension and wettability of the surface of the dielectric coating layer, thereby improving the adhesion of the cathode layer (solid electrolyte layer) to the dielectric coating layer. Patent Document 1 further discloses that improving the adhesion of the cathode layer to the dielectric coating layer can reduce the initial ESR of the solid electrolytic capacitor. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-238776 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when a solid electrolytic capacitor includes a capacitor element having a conductive polymer layer as a solid electrolyte layer, the reliability of the solid electrolytic capacitor may not be sufficiently ensured when the solid electrolytic capacitor is repeatedly charged and discharged. In other words, the long-term reliability of the solid electrolytic capacitor may not be sufficiently ensured. For example, when the solid electrolytic capacitor is repeatedly charged and discharged, the capacitance of the solid electrolytic capacitor after the repeated charging and discharging may be significantly reduced compared to the capacitance of the solid electrolytic capacitor before the repeated charging and discharging (i.e., the initial capacitance).

[0007] However, in any of the documents including Patent Document 1, sufficient consideration has not yet been given to ensuring the long-term reliability of solid electrolytic capacitors.

[0008] Furthermore, although Patent Document 1 considers lowering the initial ESR of a solid electrolytic capacitor by roughening the surface of the dielectric coating layer, it does not consider at all how to increase the initial capacitance of the solid electrolytic capacitor.

[0009] Therefore, an object of the present disclosure is to provide a method for manufacturing a solid electrolytic capacitor that can ensure sufficient long-term reliability and also can provide a sufficiently high initial capacitance. [Means for solving the problem]

[0010] One aspect of the present invention relates to a method for manufacturing a solid electrolytic capacitor, comprising: a first step of preparing a porous body containing a valve action metal and having a dielectric layer formed so as to cover at least a portion of the surface; a second step of irradiating at least a portion of the surface of the porous body with plasma to introduce hydroxyl groups; and a third step of applying a first dispersion liquid containing a first dispersion medium and particles of a first conductive polymer dispersed in the first dispersion medium to the surface of the porous body into which the hydroxyl groups have been introduced, thereby forming a first conductive polymer layer. [Effects of the Invention]

[0011] According to the present disclosure, it is possible to provide a method for manufacturing a solid electrolytic capacitor that can ensure sufficient long-term reliability and also can provide a sufficiently high initial capacitance. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a side cross-sectional view showing a configuration of a solid electrolytic capacitor according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0013] The following describes embodiments of the present disclosure using examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be used as examples, but other numerical values, materials, etc. may be applied as long as the effects of the present disclosure are obtained. Note that known components may be applied to components characteristic of the present disclosure. In this specification, when a "range between numerical value A and numerical value B" is mentioned, the range includes numerical value A and numerical value B.

[0014] In the following description, when lower and upper limits of numerical values ​​relating to specific physical properties, conditions, etc. are exemplified, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit is not equal to or greater than the upper limit. When multiple materials are exemplified, one of them can be selected and used alone, or two or more can be used in combination, unless otherwise specified.

[0015] The present disclosure encompasses any combination of two or more claims arbitrarily selected from the appended claims, i.e., any combination of two or more claims arbitrarily selected from the appended claims may be combined unless a technical contradiction arises.

[0016] (Solid Electrolytic Capacitor Manufacturing Method) A method for manufacturing a solid electrolytic capacitor according to an embodiment of the present disclosure includes a first step of preparing a porous body containing a valve action metal and having a dielectric layer formed so as to cover at least a portion of the surface; a second step of irradiating at least a portion of the surface of the porous body with plasma to introduce hydroxyl groups; and a third step of forming a first conductive polymer layer by applying a first dispersion liquid containing a first dispersion medium and particles of a first conductive polymer dispersed in the first dispersion medium to the surface of the porous body into which hydroxyl groups have been introduced.

[0017] In the method for manufacturing a solid electrolytic capacitor according to the embodiment of the present disclosure, it is important to irradiate plasma onto at least a portion of the surface of the porous body to introduce hydroxyl groups in the second step. The reason for this will be explained below.

[0018] The solid electrolytic capacitor includes, for example, a capacitor element and an exterior body that seals the capacitor element. The capacitor element includes, for example, a dielectric layer that covers at least a portion of the anode portion, a solid electrolyte layer that covers at least a portion of the dielectric layer, and a cathode extraction layer that covers at least a portion of the solid electrolyte layer. In the capacitor element, the anode portion is formed as, for example, a porous body containing a valve metal. Such a porous body is typically a sintered product obtained by sintering a compact of raw material particles (raw material powder) containing the valve metal.

[0019] In a solid electrolytic capacitor configured as described above, if the surface of the dielectric layer is embrittled and roughened by plasma irradiation, the adhesion of the solid electrolyte layer to the dielectric layer can be improved in the initial state. However, when the solid electrolytic capacitor is repeatedly charged and discharged, the capacitor element repeatedly heats and cools, which increases the frequency of thermal contraction in the dielectric layer. As a result, defects (e.g., cracks) occur on the surface of the embrittled dielectric layer, and the solid electrolyte layer is thought to peel off at these defects. The adverse effects of such surface roughening are thought to be particularly pronounced when charging and discharging are repeated rapidly and when the dielectric layer is thin (e.g., when the dielectric layer is 10 nm or less).

[0020] In addition, in a capacitor element in which the anode portion is formed as a porous body containing a valve metal, the dielectric layer covers the outer surface (main surface) of the porous body and is arranged along the inner wall surfaces of the multiple holes in the surface portion of the porous body, and the solid electrolyte layer is formed to cover at least a portion of the surface of the dielectric layer covering the outer surface of the porous body and at least a portion of the surface of the dielectric arranged on the inner wall surfaces of the multiple holes. To increase the initial capacitance of a solid electrolytic capacitor, it is desirable that the solid electrolyte layer be formed so as to sufficiently penetrate into the multiple holes. The surface portion refers to the portion of the porous body that is 0.1L or less away from the main surface in the thickness direction, where L is the thickness of the porous body.

[0021] In the method for manufacturing a solid electrolytic capacitor according to an embodiment of the present disclosure, as described above, in the second step, plasma is irradiated onto at least a portion of the surface of the porous body to introduce hydroxyl groups. More specifically, plasma is irradiated to an extent that does not embrittle the surface of the dielectric layer, thereby introducing hydroxyl groups into at least a portion of the surface of the dielectric layer. Therefore, even when the resulting solid electrolytic capacitor is repeatedly charged and discharged, defects (e.g., cracks) can be prevented from occurring on the surface of the dielectric layer. This prevents the solid electrolyte layer from peeling off from the surface of the dielectric layer, thereby ensuring sufficient long-term reliability of the solid electrolytic capacitor. For example, when the solid electrolytic capacitor is repeatedly charged and discharged, the capacitance of the solid electrolytic capacitor after repeated charging and discharging can be prevented from decreasing significantly compared to the capacitance of the solid electrolytic capacitor before repeated charging and discharging (i.e., initial).

[0022] Furthermore, in the method for manufacturing a solid electrolytic capacitor according to an embodiment of the present disclosure, as described above, hydroxyl groups are introduced into at least a portion of the surface of the dielectric layer in the porous body. That is, the hydrophilicity of at least a portion of the surface of the dielectric layer is enhanced. Here, water is typically used as the first dispersion medium for dispersing the particles of the first conductive polymer. Therefore, the contact angle of the first dispersion liquid (including the first dispersion medium) with the surface of the dielectric layer, which has been enhanced in hydrophilicity as described above, can be reduced. This allows the first conductive polymer layer to be formed in a state in which the first dispersion liquid has sufficiently penetrated into the interiors of the multiple pores. As a result, the initial capacitance of the solid electrolytic capacitor can be increased.

[0023] Hereinafter, each step of the method for manufacturing a solid electrolytic capacitor according to an embodiment of the present disclosure will be described.

[0024] (1st step) In the first step, a porous body is prepared that contains a valve metal and has a dielectric layer formed so as to cover at least a portion of the surface.

[0025] Examples of the valve metal include aluminum (Al), titanium (Ti), tantalum (Ta), niobium (Nb), zirconium (Zr), and hafnium (Hf).

[0026] The porous body may be, for example, a sintered product obtained by sintering a compact of raw material particles (raw material powder) containing a valve metal. The raw material particles may be particles of a valve metal, particles of an alloy containing a valve metal, or particles of a compound containing a valve metal. The raw material particles may be used alone or in combination of two or more types.

[0027] The porous body can be obtained, for example, by pressure-molding raw material particles into a predetermined shape to obtain a molded body, and then sintering the molded body. A rod-shaped anode wire may be disposed in the porous body with a portion of the anode wire embedded therein. In this case, a portion of the anode wire may be embedded in the porous body so as to pass through the center. When an anode wire is disposed in the porous body as described above, the raw material particles may be placed in a mold with the anode wire disposed in a predetermined position in the mold, and the raw material particles in the mold may then be pressure-molded to obtain a molded body. The obtained molded body may then be sintered to obtain a porous body with a portion of the anode wire embedded therein. The porous body typically has a rectangular parallelepiped shape.

[0028] The dielectric layer is formed to cover the outer surface (main surface) of the porous body, and also to conform to the inner wall surfaces of the multiple pores in the surface layer portion of the porous body. The dielectric layer can be formed by subjecting the porous body to a chemical conversion treatment to grow an oxide film on the outer surface and the inner wall surfaces of the multiple pores in the surface layer portion of the porous body. The chemical conversion treatment may be performed by immersing the porous body in a chemical conversion solution and anodizing the outer surface and the inner wall surfaces of the multiple pores in the surface layer portion of the porous body. An acid aqueous solution such as an aqueous phosphoric acid solution can be used as the chemical conversion solution. Alternatively, the porous body may be heated in an oxygen-containing atmosphere to oxidize the outer surface and the inner wall surfaces of the multiple pores in the surface layer portion of the porous body, thereby growing an oxide film on these surfaces.

[0029] The thickness of the dielectric layer may be 10 nm or less, 7 nm or less, or 5 nm or less. The lower limit of the thickness of the dielectric layer is typically 0.5 nm. As described above, repeated charge and discharge of a solid electrolytic capacitor increases the frequency of thermal contraction in the dielectric layer, which is thought to cause defects (e.g., cracks) in embrittled portions of the surface of the dielectric layer, leading to peeling of the solid electrolyte layer at the defective portions on the surface of the dielectric layer. Furthermore, when the thickness of the dielectric layer is as thin as 10 nm or less, defects occurring in the embrittled portions on the surface of the dielectric layer become significant, leading to significant peeling of the solid electrolyte layer. However, in the method for manufacturing a solid electrolytic capacitor according to an embodiment of the present disclosure, plasma is irradiated to a degree that does not embrittle the surface of the dielectric layer, thereby introducing hydroxyl groups into at least a portion of the surface of the dielectric layer. Therefore, even when the thickness of the dielectric layer in the resulting solid electrolytic capacitor is as thin as 10 nm or less, significant defects on the surface of the dielectric layer due to repeated charge and discharge can be sufficiently suppressed. This sufficiently suppresses significant peeling of the solid electrolyte layer.

[0030] (2nd process) In the second step, plasma is irradiated onto at least a portion of the surface of the porous body to introduce hydroxyl groups. The hydroxyl groups may be introduced as hydroxyl groups themselves or as hydroxyl groups in other substituents (e.g., carboxyl groups). Preferably, the hydroxyl groups are introduced not only into the dielectric layer formed on the outer surface of the porous body but also into the dielectric layer formed on the inner wall surfaces of the plurality of pores in the surface layer portion of the porous body. By introducing hydroxyl groups into the dielectric layer formed on the inner wall surfaces of the plurality of pores, the hydrophilicity of these dielectric layers is enhanced. Water is typically used as the first dispersion medium for dispersing the particles of the first conductive polymer. Therefore, the contact angle of the first dispersion liquid (including the first dispersion liquid) with the surface of the dielectric layer, whose hydrophilicity has been enhanced as described above, can be reduced. This allows the first conductive polymer layer to be formed in a state in which the first dispersion liquid has sufficiently penetrated into the interiors of the plurality of pores.

[0031] The plasma irradiation can be carried out using a plasma device equipped with a plasma generation chamber and a plasma nozzle for ejecting the plasma generated in the plasma generation chamber. Furthermore, the plasma irradiation to introduce hydroxyl groups as described above can be carried out by irradiating at least a part of the surface of the porous body with oxygen plasma.

[0032] Oxygen or air is used as the process gas for generating oxygen plasma. Plasma irradiation may be carried out under atmospheric pressure or under a pressure lower than atmospheric pressure (reduced pressure), but is preferably carried out under reduced pressure. When plasma irradiation is carried out under reduced pressure, the pressure is preferably 1000 Pa or less, more preferably 500 Pa or less, more preferably 200 Pa or less, and even more preferably 150 Pa or less. The lower limit of the pressure under reduced pressure is usually 10 Pa.

[0033] Plasma irradiation is preferably carried out so that Ra1-Ra0 (ΔRa) is 0.1 or less (ΔRa≦0.1), where Ra0 is the surface roughness Ra (arithmetic mean surface roughness) of the porous body before plasma irradiation and Ra1 is the surface roughness Ra of the porous body after plasma irradiation. This more sufficiently prevents the surface of the porous body from becoming rough due to plasma irradiation. Plasma irradiation is more preferably carried out so that ΔRa≦0.02, more preferably ΔRa≦0.01, and optimally so that ΔRa=0. The surface roughness Ra of the porous body can be obtained, for example, by measuring the surface roughness at any five points on the porous body using a VHX series manufactured by KEYENCE Corporation and arithmetically averaging these measured values.

[0034] When the plasma temperature is TP, the plasma irradiation is preferably carried out at TP≦80°C, more preferably at TP≦70°C, and even more preferably at TP≦60°C. The plasma irradiation may be carried out at 30°C≦TP or at 40°C≦TP. In other words, the plasma irradiation is preferably carried out using low-temperature plasma. By using low-temperature plasma, it is possible to sufficiently prevent the surface of the dielectric layer from becoming rough due to the plasma irradiation. The plasma temperature TP means the temperature at a position 10 mm from the plasma nozzle of the plasma device.

[0035] The plasma irradiation time is preferably 60 minutes or less, more preferably 30 minutes or less, and even more preferably 20 minutes or less. The plasma irradiation time may be 1 second or more, 1 minute or more, 5 minutes or more, or 10 minutes or more. By keeping the irradiation time within the above range, hydroxyl groups can be suitably introduced into the surface of the dielectric layer while sufficiently suppressing roughness of the surface of the dielectric layer.

[0036] The plasma irradiation intensity is preferably 1000 W or less, more preferably 800 W or less, and even more preferably 600 W or less. The plasma irradiation intensity may be 10 W or more, 100 W or more, or 200 W or more. When the irradiation intensity is within the above range, hydroxyl groups can be suitably introduced into the surface of the dielectric layer while sufficiently suppressing roughness of the surface of the dielectric layer.

[0037] When oxygen is used as the process gas, the flow rate (oxygen flow rate) of oxygen supplied to the plasma generation chamber is preferably 2000 mL / min or less, more preferably 1500 mL / min or less, and even more preferably 1200 mL / min or less. The oxygen flow rate may be 200 mL / min or more, 500 mL / min or more, or 800 mL / min or more. By keeping the oxygen flow rate within the above range, oxygen plasma can be suitably generated in the plasma device.

[0038] (3rd step) In the third step, a first conductive polymer layer is formed by applying a first dispersion liquid containing a first dispersion medium and particles of a first conductive polymer dispersed in the first dispersion medium to the surface of the porous body into which hydroxyl groups have been introduced.

[0039] The first dispersion liquid can be applied to the dielectric layer, for example, by immersing a plasma-irradiated porous body (hereinafter also referred to as the plasma-irradiated porous body) in the first dispersion liquid and then removing the plasma-irradiated porous body from the first dispersion liquid. The immersion time of the plasma-irradiated porous body is, for example, 10 to 120 seconds, and preferably 30 to 60 seconds. The plasma-irradiated porous body may be immersed in the first dispersion liquid once, or may be immersed two or more times. The porous body removed from the first dispersion liquid may be heated. The heating temperature is, for example, 100°C to 200°C, and preferably 140°C to 180°C.

[0040] The average particle diameter of the first conductive polymer particles is preferably 20 nm or less. The average particle diameter of the first conductive polymer particles may be less than 10 nm. The average particle diameter of the first conductive polymer particles is the median diameter in a volume-based distribution measured with a particle size measuring device using dynamic light scattering. When the average particle diameter of the first conductive polymer particles is within the above range, the first dispersion can be sufficiently penetrated into the multiple pores in the surface layer portion of the porous body.

[0041] The first conductive polymer is preferably soluble in the first dispersion medium. The first dispersion medium preferably has a hydroxyl group. An example of a first dispersion medium having a hydroxyl group is water. When the first dispersion medium has a hydroxyl group, the first conductive polymer is preferably a self-doping conductive polymer in order to increase solubility in the first dispersion medium. As described below, a self-doping conductive polymer has an anionic group such as a sulfo group, a carboxyl group, a phosphate group, or a phosphonate group in its structure, and such anionic group is hydrophilic. Therefore, when the first conductive polymer is a self-doping conductive polymer, solubility in a first dispersion medium having a hydroxyl group can be increased.

[0042] Furthermore, self-doping conductive polymers have relatively flexible polymer chains, randomly positioned functional groups such as anionic groups, and low polymer chain orientation and crystallinity. Therefore, self-doping conductive polymers are easier to dissolve in a dispersion medium or to disperse into fine particles in a dispersion medium than non-self-doping conductive polymers. Therefore, when the first conductive polymer is a self-doping conductive polymer, the viscosity of the first dispersion can be reduced, allowing the first dispersion to fully penetrate into the multiple pores in the surface layer of the porous body. This allows a first conductive polymer layer to be fully formed on the inner walls of the multiple pores.

[0043] A self-doping conductive polymer has, for example, a conjugated polymer skeleton and a functional group (e.g., an anionic group) covalently bonded directly or indirectly to the skeleton, where the functional group functions as a dopant.

[0044] Examples of the anionic group include a sulfo group, a carboxyl group, a phosphate group, and a phosphonic group. The self-doping conductive polymer may have one or more types of anionic groups, or may have two or more types. From the viewpoint of further increasing the conductivity of the self-doping conductive polymer, it is preferable that the self-doping conductive polymer has at least a sulfo group.

[0045] In the first conductive polymer layer, the anionic group of the self-doping conductive polymer may be contained in any form, such as an anion, free form, ester, or salt, or may be contained in a form that interacts with or is complexed with a component contained in the first conductive polymer layer. In this specification, all of these forms are simply referred to as anionic group.

[0046] Examples of conjugated polymers constituting the skeleton of self-doping conductive polymers include polymers having a basic skeleton of a π-conjugated polymer (such as polypyrrole, polythiophene, polyaniline, polyfuran, polyacetylene, polyphenylene, polyphenylenevinylene, polyacene, and polythiophenevinylene). The above polymers may contain at least one type of monomer unit constituting the basic skeleton. The above polymers also include homopolymers, copolymers of two or more types of monomers, and derivatives thereof (such as substituted products having substituents). For example, polythiophenes include poly(3,4-ethylenedioxythiophene). Self-doping conductive polymers have anionic groups in the skeleton of these conjugated polymers. The anionic groups may be introduced directly into the skeleton of the conjugated polymer or via a linking group. Preferred linking groups include polyvalent groups (divalent groups) containing an alkylene group. Examples of linking groups include aliphatic polyvalent groups (divalent groups) such as alkylene groups, -R 1 -XR 2 The group (X is an oxygen element or a sulfur element, R 1 and R 2 are the same or different alkylene groups.) The alkylene group contained in the linking group may have, for example, 1 or more and 10 or less, or may have 1 or more and 6 or less carbon atoms.

[0047] The conjugated polymer constituting the skeleton of the self-doping conductive polymer may be polypyrrole, polythiophene, or polyaniline. From the viewpoint of easily obtaining high conductivity, the self-doping conductive polymer preferably has a conjugated polymer skeleton containing a repeating structure of monomer units corresponding to a thiophene compound and an anionic group introduced into the skeleton.

[0048] The thiophene compound includes a compound having a thiophene ring and capable of forming a repeating structure of the corresponding monomer unit, which can be linked at the 2- and 5-positions of the thiophene ring to form a repeating structure of the monomer unit.

[0049] The thiophene compound may have a substituent at, for example, at least one of the 3- and 4-positions of the thiophene ring. The substituent at the 3-position and the substituent at the 4-position may be linked to form a ring fused to the thiophene ring. Examples of the thiophene compound include thiophenes which may have a substituent at, for example, the 3- and 4-positions, alkylenedioxythiophene compounds (C thiophenes such as ethylenedioxythiophene compounds), and the like. 2-4 Alkylenedioxythiophene compounds include compounds having a substituent on the alkylene group moiety.

[0050] Examples of the substituent include alkyl groups (C such as methyl and ethyl groups). 1-4 alkyl groups, alkoxy groups (methoxy groups, ethoxy groups, etc.) 1-4 Alkoxy groups, hydroxy groups, hydroxyalkyl groups (hydroxy C groups such as hydroxymethyl groups) 1-4 The thiophene ring (in the case of an alkylenedioxythiophene ring, at least one of the thiophene ring and the alkylene group) may have, as a substituent, the above-mentioned anionic group or a group containing an anionic group (for example, a sulfoalkyl group).

[0051] The self-doped conductive polymer may have a backbone of a conjugated polymer (such as PEDOT) containing at least a repeating structure of monomer units corresponding to a 3,4-ethylenedioxythiophene compound (such as 3,4-ethylenedioxythiophene (EDOT)). The backbone of the conjugated polymer containing a repeating structure of monomer units corresponding to EDOT may contain only monomer units corresponding to EDOT, or may contain monomer units corresponding to thiophene compounds other than EDOT.

[0052] The weight-average molecular weight (Mw) of the self-doping conductive polymer may be 1,000 or more and 1,000,000 or less, or 1,000 or more and 50,000 or less. The weight-average molecular weight (Mw) is a polystyrene-equivalent value measured by gel permeation chromatography (GPC). GPC is usually measured using a polystyrene gel column and water / methanol (volume ratio 8 / 2) as the mobile phase.

[0053] (4th step) In the fourth step, a second conductive polymer layer is formed by applying a second dispersion liquid containing a second dispersion medium and particles of the second conductive polymer dispersed in the second dispersion medium to at least a portion of the surface of the first conductive polymer layer. As the second dispersion medium, water or the like can be used, as with the first dispersion medium.

[0054] The second dispersion liquid can be applied to the first conductive polymer layer by, for example, immersing the porous body on which the first conductive polymer layer has been formed in the second dispersion liquid and then removing the porous body on which the first conductive polymer layer has been formed from the second dispersion liquid. The immersion time of the porous body on which the first conductive polymer layer has been formed is, for example, 10 to 120 seconds, and preferably 30 to 60 seconds. The porous body on which the first conductive polymer layer has been formed may be immersed in the second dispersion liquid once, or may be immersed two or more times. The porous body on which the first conductive polymer layer has been formed may be heated after being removed from the second dispersion liquid. The heating temperature is, for example, 100°C to 200°C, and preferably 140°C to 180°C.

[0055] The average particle size of the second conductive polymer particles is preferably larger than that of the first conductive polymer particles. In other words, the average particle size of the first conductive polymer particles is preferably smaller than that of the second conductive polymer particles. The second conductive polymer particles preferably have an average particle size of 100 nm or less, more preferably 50 nm or less, and even more preferably about 20 nm. By having the average particle size of the second conductive polymer particles larger than that of the first conductive polymer particles, the second conductive polymer layer can be formed thicker than the first conductive polymer layer. Furthermore, by having the average particle size of the second conductive polymer particles within the above-mentioned range, the second conductive polymer particles dispersed in the second dispersion can penetrate deeper into the multiple pores (fine pores) in the porous body. This can improve the initial capacitance and voltage resistance of the solid electrolytic capacitor. The particle size of the second conductive polymer particles is also the median diameter in a volume-based distribution measured using a particle size analyzer using dynamic light scattering.

[0056] The second conductive polymer is preferably a non-self-doping conductive polymer. As described above, self-doping conductive polymers are more easily dissolved in a dispersion medium or dispersed in the form of fine particles in a dispersion medium than non-self-doping conductive polymers. In other words, non-self-doping conductive polymers are less likely to dissolve in a dispersion medium or to be dispersed in the form of fine particles in a dispersion medium than self-doping conductive polymers. Therefore, the non-self-doping conductive polymer exhibits less variation in average particle size before and after dispersion in a dispersion medium. Therefore, when the second conductive polymer is a non-self-doping conductive polymer, it is easier to form the second conductive polymer layer thicker than the first conductive polymer layer. This allows the solid electrolytic capacitor to have improved initial capacitance and voltage resistance. Furthermore, as described above, in order to further reduce variation in the average particle size of the second conductive polymer, the second conductive polymer is preferably insoluble in the second dispersion medium. The second conductive polymer being insoluble in the second dispersion medium means that, when the average particle diameter of the second conductive polymer particles before being dispersed in the second dispersion medium is d0 and the average particle diameter of the second conductive polymer particles after being dispersed in the second dispersion medium is d1, the ratio of d1 to d0 (d1 / d0×100) is 90% or more.

[0057] The non-self-doping conductive polymer includes, for example, a conjugated polymer and a dopant. In the non-self-doping conductive polymer, the conjugated polymer is, for example, a non-self-doping conjugated polymer. For example, the non-self-doping conjugated polymer is, for example, a conjugated polymer having no anionic group.

[0058] Examples of conjugated polymers include the conjugated polymers (e.g., π-conjugated polymers) exemplified as the conjugated polymer constituting the backbone of the self-doping conductive polymer. One type of conjugated polymer may be used alone, or two or more types may be used in combination. From the viewpoint of improving the initial capacitance, voltage resistance, and heat resistance, the non-self-doping conductive polymer preferably contains a repeating structure of a monomer unit of a thiophene compound. Examples of thiophene compounds corresponding to such monomer units include the thiophene compounds described in the self-doping conductive polymer. The non-self-doping conductive polymer may contain at least a conjugated polymer (e.g., PEDOT) containing a repeating structure of a monomer unit corresponding to a 3,4-ethylenedioxythiophene compound (EDOT). The conjugated polymer containing a repeating structure of a monomer unit corresponding to EDOT may contain only a monomer unit corresponding to EDOT, or may contain a monomer unit corresponding to a thiophene compound other than EDOT.

[0059] The dopant may be at least one selected from the group consisting of anions and polyanions (polymer anions). Examples of anions include sulfate ions, nitrate ions, phosphate ions, borate ions, organic sulfonate ions, and carboxylate ions. Examples of dopants that generate sulfonate ions include p-toluenesulfonic acid and naphthalenesulfonic acid. Polymer anions may be used to improve heat resistance, reliability, and voltage resistance. Examples of polymer anions having sulfo groups include polymeric polysulfonic acids. Specific examples of polymer anions include polyvinylsulfonic acid, polystyrenesulfonic acid (PSS (including copolymers and substituted derivatives thereof)), polyallylsulfonic acid, polyacrylicsulfonic acid, polymethacrylicsulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprenesulfonic acid, polyestersulfonic acids (e.g., aromatic polyestersulfonic acids), and phenolsulfonic acid novolac resins. These dopants may be used alone or in combination of two or more, but the dopants are not limited to the specific examples given above.

[0060] In the non-self-doping conductive polymer, the amount of the dopant may be 10 parts by mass or more and 1000 parts by mass or less, or 20 parts by mass or more and 500 parts by mass or less, per 100 parts by mass of the conjugated polymer.

[0061] The method for manufacturing a solid electrolytic capacitor according to an embodiment of the present disclosure may include, after the fourth step, a fifth step of forming a third conductive polymer layer by applying a third dispersion liquid containing a third dispersion medium and particles of a third conductive polymer dispersed in the third dispersion medium to at least a portion of the surface of the second conductive polymer layer. The third dispersion medium may be water, as with the first dispersion medium. The third conductive polymer may be a non-self-doping conductive polymer, as with the second conductive polymer. The average particle size of the third conductive polymer particles is preferably larger than the average particle size of the second conductive polymer particles. By having the average particle size of the third conductive polymer particles larger than the average particle size of the second conductive polymer particles, the third conductive polymer layer can be formed thicker than the second conductive polymer layer. By providing a third conductive polymer layer that is thicker than the second conductive polymer layer, the initial capacitance and voltage resistance of the solid electrolytic capacitor can be further improved.

[0062] The method for manufacturing a solid electrolytic capacitor according to an embodiment of the present disclosure may include a sixth step of forming a cathode extraction layer on at least a portion of the surface of the second conductive polymer layer or the third conductive polymer layer after performing the fourth step or the fifth step. The cathode extraction layer may include, for example, a carbon layer formed on at least a portion of the surface of the second conductive polymer layer or the third conductive polymer layer, and a metal paste layer formed on at least a portion of the surface of the carbon layer. Therefore, the sixth step may include a first substep of forming a carbon layer by applying a fourth dispersion liquid in which graphite particles or the like are dispersed in water to at least a portion of the surface of the second conductive polymer layer or the third conductive polymer layer, and a second substep of forming a metal paste layer by applying a metal paste containing metal particles (e.g., silver particles) and a binder resin (e.g., epoxy resin) to at least a portion of the surface of the carbon layer. That is, a capacitor element may be obtained by performing the first to sixth steps.

[0063] The method for manufacturing a solid electrolytic capacitor according to an embodiment of the present disclosure may include a seventh step of electrically connecting an anode lead terminal and a cathode lead terminal to the capacitor element obtained by carrying out steps 1 to 6. In step 7, the anode lead terminal may be connected to an anode wire that is disposed with a portion of the anode lead terminal embedded in a porous body. In step 7, the cathode lead terminal may be connected to the cathode extraction layer by a conductive member (e.g., silver paste). The method for manufacturing a solid electrolytic capacitor according to an embodiment of the present disclosure may include an eighth step of covering, with an exterior body, the capacitor element to which the anode lead and cathode lead are electrically connected, in step 7. In step 8, the capacitor element may be covered with resin (e.g., epoxy resin) so that each of the anode lead terminal and the cathode lead terminal is partially exposed. That is, the exterior body may be a resin exterior body.

[0064] Hereinafter, the configuration of a solid electrolytic capacitor according to an embodiment of the present disclosure will be described with reference to the drawings.

[0065] 1, solid electrolytic capacitor 20 includes capacitor element 10, exterior housing 11 that seals capacitor element 10, and anode lead terminal 12 and cathode lead terminal 13 that are electrically connected to capacitor element 10. A portion of anode lead terminal 12 and a portion of cathode lead terminal 13 are exposed from exterior housing 11. The remaining portion of anode lead terminal 12, together with capacitor element 10, is covered by exterior housing 11.

[0066] Capacitor element 10 includes an anode portion 1, a solid electrolyte layer 2 formed on anode portion 1, and a cathode extraction layer 3 formed on solid electrolyte layer 2. In capacitor element 10, the solid electrolyte layer 2 and cathode extraction layer 3 form a cathode portion. Anode portion 1 includes a porous body 4 containing a valve metal and a dielectric layer 5 covering the porous body 4.

[0067] 1, the porous body 4 is a sintered body obtained by sintering a compact of raw material particles (raw material powder) containing a valve metal. Examples of the valve metal include aluminum (Al), titanium (Ti), tantalum (Ta), niobium (Nb), zirconium (Zr), and hafnium (Hf).

[0068] The porous body 4 has a substantially rectangular parallelepiped shape and six sides. A portion of the anode wire 6 is exposed from one side of the porous body 4. That is, the anode wire 6 has a first portion 6a that is embedded in the porous body 4 from one side thereof, and a second portion 6b that extends from the one side thereof. The second portion 6b is joined to the anode lead terminal 12 by welding or the like. In the example shown in FIG. 1 , the first portion 6a is embedded in the porous body 4 so as to pass through the center, but it may also be embedded in the porous body 4 so as not to pass through the center. The anode wire 6 may contain a valve metal.

[0069] The dielectric layer 5 is formed to cover at least a portion of the outer surface (main surface) of the porous body 4, and is also formed to fit along the inner wall surfaces of the pores in the surface layer portion of the porous body 4. In the example shown in FIG. 1, plasma is applied to introduce hydroxyl groups into at least a portion of the surface of the porous body 4. More specifically, hydroxyl groups are introduced into at least a portion of the surface of the dielectric layer 5 formed on the porous body 4. In addition, in the example shown in FIG. 1, when the surface roughness of the porous body 4 before plasma application is Ra0 and the surface roughness of the porous body 4 after plasma application is Ra1, ΔRa (Ra1 - Ra0) is 0.1 or less. In other words, the roughness of the surface of the porous body 4 caused by plasma application is further sufficiently suppressed.

[0070] The solid electrolyte layer 2 is disposed so as to cover at least a portion of the dielectric layer 5. In the example shown in Fig. 1, the solid electrolyte layer 2 is formed on the outer surface (main surface) of the porous body 4 with the dielectric layer 5 interposed therebetween, and is also formed along the inner wall surfaces of the plurality of pores in the surface layer portion of the porous body 4.

[0071] In the example shown in FIG. 1 , the solid electrolyte layer 2 has a first conductive polymer layer containing a first conductive polymer. The first conductive polymer layer is disposed so as to cover at least a portion of the dielectric layer 5. The first conductive polymer is preferably a self-doping conductive polymer. As described above, the first conductive polymer layer is formed by applying a first dispersion liquid containing a first dispersion medium and particles of the first conductive polymer dispersed in the first dispersion medium to the surface of the dielectric layer.

[0072] In the example shown in FIG. 1 , the solid electrolyte layer 2 includes a second conductive polymer layer covering at least a portion of the first conductive polymer layer. That is, the solid electrolyte layer 2 is configured as a laminate of the first conductive polymer layer and the second conductive polymer layer. The second conductive polymer layer includes a second conductive polymer. The second conductive polymer is preferably a non-self-doping conductive polymer. As described above, the second conductive polymer layer is formed by applying a second dispersion liquid containing a second dispersion medium and particles of the second conductive polymer dispersed in the second dispersion medium to the surface of the first conductive polymer layer. The solid electrolyte layer 2 may also include a third conductive polymer layer covering at least a portion of the second conductive polymer layer. The third conductive polymer layer preferably contains a non-self-doping conductive polymer having an average particle diameter larger than that of the second conductive polymer as the third conductive polymer. The third conductive polymer layer is formed by applying a third dispersion liquid containing a third dispersion medium and particles of the third conductive polymer dispersed in the third dispersion medium to the surface of the second conductive polymer.

[0073] The first conductive polymer layer and the second conductive polymer layer may contain additives as needed. The first conductive polymer layer may contain a known conductive material other than the first conductive polymer. The second conductive polymer layer may contain a known conductive material other than the second conductive polymer. Examples of such conductive materials include at least one selected from the group consisting of conductive inorganic materials such as manganese compounds (e.g., manganese dioxide) and TCNQ complex salts. Similarly to the first conductive polymer layer and the second conductive polymer layer, the third conductive polymer layer may also contain additives as needed, or may contain a known conductive material other than the third conductive polymer.

[0074] 1, cathode extraction layer 3 includes carbon layer 3a formed on solid electrolyte layer 2 and metal paste layer 3b formed on carbon layer 3a. Carbon layer 3a may be formed of a conductive carbon material such as graphite and a resin. Metal paste layer 3b may be formed of metal particles (e.g., silver particles) and a resin, or may be formed of a known silver paste.

[0075] Cathode extraction layer 3 is connected to cathode lead terminal 13 by conductive member 8. That is, cathode extraction layer 3 is electrically connected to cathode lead terminal 13. Conductive member 8 is made of a conductive material. Conductive member 8 may be formed using a material containing metal particles (for example, silver particles) and a resin, or may be formed using a known metal paste (for example, silver paste). The metal paste is heated to form conductive member 8. Note that conductive member 8 may be made of a plurality of conductive layers of different types.

[0076] The exterior body 11 is disposed around the capacitor element 10 so that the capacitor element 10 is not exposed on the surface of the solid electrolytic capacitor 20. Furthermore, the exterior body 11 insulates the anode lead terminal 12 from the cathode lead terminal 13. A known exterior resin used for solid electrolytic capacitors may be used for the exterior body 11. For example, the exterior body 11 may be formed using an insulating resin material used to seal the capacitor element. The exterior body 11 may be formed by placing the capacitor element in a mold, and then introducing an uncured thermosetting resin into the mold by transfer molding, compression molding, or the like, and curing the resin.

[0077] Examples of resins that can be used to form the exterior body 11 include epoxy resin, phenol resin, silicone resin, melamine resin, urea resin, alkyd resin, polyurethane resin, polyimide resin, and unsaturated polyester resin. The exterior body 11 may also contain materials other than resin (such as inorganic fillers).

[0078] A portion of cathode lead terminal 13 is exposed from exterior body 11 and is used as a cathode external terminal. The material of cathode lead terminal 13 may be any material that can be used as a cathode lead terminal material for solid electrolytic capacitors. For example, a known cathode lead terminal material used for solid electrolytic capacitors may be used. Cathode lead terminal 13 may be formed by processing a metal sheet (including a metal plate and a metal foil) made of a metal (such as copper or a copper alloy) using a known metal processing method.

[0079] A portion of the anode lead terminal 12 is exposed from the exterior package 11 and is used as an external anode terminal. The material of the anode lead terminal 12 may be any material that can be used as an anode lead terminal of a solid electrolytic capacitor. For example, a known anode lead terminal material used in solid electrolytic capacitors may be used. The anode lead terminal 12 may be formed by processing a metal sheet (including a metal plate and a metal foil) made of a metal (such as copper or a copper alloy) using a known metal processing method.

[0080] (Addendum) The above description discloses the following techniques. (Technology 1) A first step of preparing a porous body containing a valve metal and having a dielectric layer formed so as to cover at least a portion of the surface; a second step of irradiating plasma onto at least a portion of the surface of the porous body to introduce hydroxyl groups; and a third step of forming a first conductive polymer layer by applying a first dispersion liquid containing a first dispersion medium and particles of a first conductive polymer dispersed in the first dispersion medium to the surface of the porous body into which the hydroxyl groups have been introduced. A method for manufacturing a solid electrolytic capacitor. (Technology 2) When the surface roughness of the porous body before the plasma irradiation is Ra0 and the surface roughness of the porous body after the plasma irradiation is Ra1, Ra1-Ra0 is 0.1 μm or less. The method for manufacturing the solid electrolytic capacitor according to the first aspect of the present invention. (Technology 3) the first conductive polymer is soluble in the first dispersion medium; 2. A method for producing a solid electrolytic capacitor according to claim 1. (Technology 4) The first conductive polymer particles have an average particle size of 20 nm or less. 4. A method for manufacturing a solid electrolytic capacitor according to any one of techniques 1 to 3. (Technology 5) a fourth step of forming a second conductive polymer layer by applying a second dispersion liquid containing a second dispersion medium and particles of a second conductive polymer dispersed in the second dispersion medium to at least a part of the surface of the first conductive polymer layer; the second conductive polymer is insoluble in the second dispersion medium; 5. A method for manufacturing a solid electrolytic capacitor according to any one of techniques 1 to 4. (Technology 6) the average particle size of the particles of the first conductive polymer is smaller than the average particle size of the particles of the second conductive polymer; The method for manufacturing a solid electrolytic capacitor according to the fifth aspect of the present invention. [Example]

[0081] The present disclosure will be specifically described below based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0082] [Example 1] A capacitor element was fabricated as follows, and its characteristics were evaluated.

[0083] (1) Preparation of a porous body having a dielectric layer (first step) A tantalum sintered body (porous body) with a portion of an anode wire embedded therein was prepared as the anode body. The surface of this tantalum sintered body was anodized to form a dielectric layer containing tantalum oxide on the surface of the anode body. For the anodization, an aqueous solution of phosphoric acid (phosphoric acid concentration: 0.017% by mass) was used as the anodization solution, and the anodization temperature (liquid temperature of the anodization solution) was set to 30°C. The anodization voltage was increased from 0 V to 80 V over two hours and then held at 80 V for two hours.

[0084] (2) Plasma irradiation (second step) In the tantalum sintered body on which the dielectric layer was formed in the first step, plasma was irradiated to the region where the solid electrolyte layer was to be formed. The plasma irradiation was carried out using a plasma device equipped with a plasma generation chamber and a plasma nozzle that ejects the plasma generated in the plasma generation chamber. The plasma irradiation conditions were as shown in Table 1 below. The plasma temperature TP is the temperature at a position 10 mm from the plasma nozzle, the oxygen flow rate is the flow rate when oxygen is supplied to the plasma generation chamber, and the pressure is the pressure inside the plasma generation chamber.

[0085] [Table 1]

[0086] (3) Formation of the first conductive polymer layer (third step) A first dispersion liquid was prepared by dispersing particles of a self-doping polythiophene-based polymer in water. The concentration of the polythiophene-based polymer in the first dispersion liquid was 1 to 3% by mass. As the self-doping polythiophene-based polymer, PEDOT (weight average molecular weight (Mw) of approximately 10,000) having a sulfo group bonded to the PEDOT skeleton via a linking group containing a butylene group was used. The average particle diameter of the self-doping polythiophene-based polymer particles was several nm (less than 10 nm). The average particle diameter of the self-doping polythiophene-based polymer particles was measured according to the method described in the embodiment section above.

[0087] The plasma-treated tantalum sintered compact was immersed in the first dispersion for about 30 to 60 seconds, and then the tantalum sintered compact was pulled out of the first dispersion. After repeating this process twice, the tantalum sintered compact was heated (dried) at 140 to 180°C for 10 to 20 minutes to form a first conductive polymer layer.

[0088] (4) Formation of the second conductive polymer layer (fourth step) A second dispersion liquid was prepared by dispersing particles of a first non-self-doping conductive polymer (PSS-doped PEDOT) in water. The concentration of the first non-self-doping conductive polymer in the second dispersion liquid was 1 to 3 mass %. The average particle diameter of the first non-self-doping conductive polymer was 20 nm. The average particle diameter of the first non-self-doping conductive polymer was measured according to the method described in the above embodiment section.

[0089] The tantalum sintered compact on which the first conductive polymer layer was formed was immersed in the second dispersion for about 30 to 60 seconds, and then the tantalum sintered compact was pulled out of the second dispersion. After repeating this process three times, the tantalum sintered compact was heated (dried) at 140 to 180°C for 10 to 20 minutes to form a second conductive polymer layer on the first conductive polymer layer.

[0090] (5) Formation of the third conductive polymer layer A third dispersion liquid was prepared by dispersing particles of a second non-self-doping conductive polymer (PSS-doped PEDOT) in water. The concentration of the second non-self-doping conductive polymer in the third dispersion liquid was 1 to 3 mass %. The average particle diameter of the second non-self-doping conductive polymer particles was 200 nm. That is, the first non-self-doping conductive polymer particles and the second non-self-doping conductive polymer particles differed only in their average particle diameters. The average particle diameter of the second non-self-doping conductive polymer was measured according to the method described in the above embodiment section.

[0091] The tantalum sintered compact on which the second conductive polymer layer was formed was immersed in the third dispersion for about 30 to 60 seconds, and then the tantalum sintered compact was pulled out of the third dispersion. After repeating this process five times, the tantalum sintered compact was subjected to primary heating (primary drying) at 60 to 100°C for 10 to 20 minutes, and further to secondary heating (secondary drying) at 140 to 180°C for 10 to 20 minutes, thereby forming a third conductive polymer layer on the second conductive polymer.

[0092] (6) Formation of cathode extraction layer The tantalum sintered compact on which the third conductive polymer layer was formed was immersed in a fourth dispersion liquid in which graphite particles were dispersed in water, and then the tantalum sintered compact was pulled out of the fourth dispersion liquid. The tantalum sintered compact pulled out of the fourth dispersion liquid was then dried at 180°C for 10 to 30 minutes. This formed a carbon layer on the surface of the third conductive polymer layer.

[0093] Next, a silver paste containing silver particles and a binder resin (epoxy resin) was applied to the surface of the carbon layer, followed by drying at 60 to 80°C for 20 to 40 minutes (primary drying), and then drying at 180°C for 30 to 60 minutes (secondary drying) to harden the binder resin. This formed a metal particle-containing layer on the surface of the carbon layer. In this way, a cathode extraction layer having a carbon layer and a metal particle-containing layer was formed, thereby obtaining a capacitor element according to Example 1.

[0094] [Comparative Example 1] A capacitor element according to Comparative Example 1 was obtained in the same manner as in Example 1, except that plasma irradiation was not performed.

[0095] <Surface roughness and contact angle> The surface roughness Ra (arithmetic mean surface roughness, in μm) and contact angle θ (in degrees) were measured for the tantalum sintered compacts according to Example 1 and Comparative Example 1. The surface roughness Ra was measured using a VHX series manufactured by KEYENCE Corporation. The contact angle θ was measured using a contact angle meter (DMs-401) manufactured by KYOWA Corporation. The results are shown in Table 2 below. For each example, the contact angle θ of the tantalum sintered compact was measured at any five points on the surface of the tantalum sintered compact, and the obtained measured values ​​were taken as the arithmetic mean. The contact angle θ of the tantalum sintered compact is the contact angle with respect to water.

[0096] [Table 2]

[0097] It can be seen from Table 2 that the surface roughness Ra of the tantalum sintered compact according to Example 1 (the tantalum sintered compact after plasma irradiation) does not change from the surface roughness Ra of the tantalum sintered compact according to Comparative Example 1 (the tantalum sintered compact before plasma irradiation). It can also be seen from Table 2 that the contact angle θ of the tantalum sintered compact according to Example 1 is smaller than the contact angle θ of the tantalum sintered compact according to Comparative Example 1. That is, it can be seen that the hydrophilicity of the tantalum sintered compact according to Example 1 is enhanced. From these, it can be seen that hydroxyl groups can be introduced into the tantalum sintered compact according to Example 1 without roughening the surface.

[0098] <Adhesion> The tantalum sintered compacts according to Example 1 and Comparative Example 1 were evaluated for adhesion of the first conductive polymer layer to the dielectric layer. Adhesion was evaluated by conducting a peel test using the cross-cut method of JIS-K5600, and then calculating the peel rate PR (%) relative to the coating area of ​​the first conductive polymer layer before the test. Here, if the coating area of ​​the first conductive polymer layer before the test is S0 and the coating area of ​​the first conductive polymer layer after the test is S1, the peel rate PR can be calculated using the following formula: Peeling rate PR (%) = (S0-S1) / S0 x 100

[0099] The results of calculating the peeling rates PR for Example 1 and Comparative Example 1 are shown in Table 3 below.

[0100] [Table 3]

[0101] It can be seen from Table 3 that the tantalum sintered compact according to Example 1 has a smaller peeling rate PR than the tantalum sintered compact according to Comparative Example 1. This indicates that in Example 1, the introduction of hydroxyl groups into the dielectric layer improves the adhesion of the first conductive polymer layer to the dielectric layer.

[0102] <Initial capacitance> Using a four-terminal LCR meter, the initial capacitance C0 (unit: μF) of the capacitor elements according to Example 1 and Comparative Example 1 was measured in an environment of 20°C. Note that for each example, the initial capacitance C0 was the arithmetic average of the measurements for 30 capacitor elements. The measurement results of the initial capacitance C0 are shown in Table 4 below.

[0103] <Reliability evaluation> A charge-discharge test was carried out on the capacitor elements according to Example 1 and Comparative Example 1 under the following conditions, and then the capacitance C1 (unit: μF) after the charge-discharge test was measured.

[0104] <Charge / discharge test> ·Temperature: Normal temperature (25±2℃) Charging: After holding the voltage at 0V for 1 second, the voltage is increased to 50V and held there for 1 second. The voltage is increased from 0V to 50V in 0.6 seconds. Discharge: After holding the voltage at 50V for 1 second, the voltage is reduced to 0V and held there for 1 second. The voltage is reduced from 50V to 0V in 0.08 seconds. Number of cycles: 10K

[0105] The capacitance C1 was measured in the same manner as the capacitance C0. Then, for each example, the capacitance change rate CR (%) of the capacitance C1 relative to the capacitance C0 was calculated according to the following formula. This was used to evaluate the reliability of the capacitor elements of Example 1 and Comparative Example 1. The values ​​of the capacitance change rate CR for Example 1 and Comparative Example 1 are shown in Table 4 below. For each example, the capacitance change rate CR is the arithmetic average of the calculated values ​​for 30 capacitor elements. ·Capacitance change rate CR(%)=(C1-C0) / C0×100

[0106] [Table 4]

[0107] From Table 4, it can be seen that the initial capacitance C0 of the capacitor element according to Example 1 is higher than the initial capacitance C0 of the capacitor element according to Comparative Example 1. It can also be seen that the capacitance change rate CR of the capacitor element according to Example 1 is sufficiently lower than the capacitance change rate CR of the capacitor element according to Comparative Example 1. From this, it can be seen that by irradiating plasma onto at least a portion of the surface of the porous body to introduce hydroxyl groups, it is possible to ensure sufficient long-term reliability in a solid electrolytic capacitor, as well as to sufficiently increase the initial capacitance.

[0108] While the present invention has been described with respect to presently preferred embodiments, such disclosure should not be interpreted as limiting. Various variations 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 variations and modifications that do not depart from the true spirit and scope of the invention. [Industrial Applicability]

[0109] The method for manufacturing a solid electrolytic capacitor according to the present disclosure can be used in applications that require manufacturing a solid electrolytic capacitor that can not only ensure sufficient long-term reliability but also have a sufficiently high initial capacitance. [Explanation of symbols]

[0110] 1: anode part, 2: solid electrolyte layer, 3: cathode lead layer, 3a: carbon layer, 3b: metal paste layer, 4: porous body, 5: dielectric layer, 6: anode wire, 6a: first part, 6b: second part, 8: conductive member, 10: capacitor element, 11: exterior body, 12: anode lead terminal, 13: cathode lead terminal, 20: solid electrolytic capacitor

Claims

1. A first step of preparing a porous body containing a valve metal and having a dielectric layer formed so as to cover at least a portion of a surface thereof; a second step of irradiating plasma onto at least a portion of the surface of the porous body to introduce hydroxyl groups; and a third step of forming a first conductive polymer layer by applying a first dispersion liquid containing a first dispersion medium and particles of a first conductive polymer dispersed in the first dispersion medium to the surface of the porous body into which the hydroxyl groups have been introduced. A method for manufacturing a solid electrolytic capacitor.

2. When the surface roughness of the porous body before the plasma irradiation is Ra0 and the surface roughness of the porous body after the plasma irradiation is Ra1, Ra1-Ra0 is 0.1 μm or less. The method for manufacturing the solid electrolytic capacitor according to claim 1 .

3. the first conductive polymer is soluble in the first dispersion medium; The method for manufacturing the solid electrolytic capacitor according to claim 1 or 2.

4. the first conductive polymer particles have an average particle size of 20 nm or less; The method for manufacturing the solid electrolytic capacitor according to claim 1 or 2.

5. a fourth step of forming a second conductive polymer layer by applying a second dispersion liquid containing a second dispersion medium and particles of a second conductive polymer dispersed in the second dispersion medium to at least a part of the surface of the first conductive polymer layer; the second conductive polymer is insoluble in the second dispersion medium; The method for manufacturing the solid electrolytic capacitor according to claim 1 or 2.

6. the average particle size of the particles of the first conductive polymer is smaller than the average particle size of the particles of the second conductive polymer; The method for manufacturing the solid electrolytic capacitor according to claim 5 .

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