Solid electrolytic capacitor and method for producing solid electrolytic capacitor

Abstract

To provide a solid electrolytic capacitor that has a high withstand voltage.SOLUTION: A solid electrolytic capacitor includes: a porous anode body including a valve metal and a dielectric oxide film layer formed on a surface of the valve metal; and an electrolyte layer formed on a surface of the dielectric oxide film layer. The electrolyte layer includes: a first conductive polymer layer formed by chemical polymerization and in contact with the dielectric oxide film layer; a second conductive polymer layer formed by electrolytic polymerization and formed on a side opposite to the dielectric oxide film layer with respect to the first conductive polymer layer; and a barrier layer having conductivity and formed between the first conductive polymer layer and the second conductive polymer layer. The barrier layer prevents a conductive polymer layer from being formed by electrolytic polymerization in a region closer to the anode body than the barrier layer.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Solid electrolytic capacitors are used as small, high-capacity capacitors for use in electronic devices, etc. Patent Document 1 describes a method for producing a solid electrolytic capacitor with excellent capacitance (Cs) and equivalent series resistance (ESR) by forming a conductive polymer layer by electrolytic polymerization. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-89542 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, there has been a demand for capacitors that are small in size, have high capacitance, and also have high withstand voltage.

[0005] An object of the present disclosure is to provide a solid electrolytic capacitor having a high withstand voltage. [Means for solving the problem]

[0006] The solid electrolytic capacitor according to an embodiment of the present disclosure comprises: a porous anode body having a valve metal and a dielectric oxide film layer formed on the surface of the valve metal; an electrolyte layer formed on the surface of the dielectric oxide film layer, The electrolyte layer is a first conductive polymer layer formed by chemical polymerization and in contact with the dielectric oxide film layer; a second conductive polymer layer formed by electrolytic polymerization on the opposite side of the first conductive polymer layer from the dielectric oxide film layer; a barrier layer having conductivity formed between the first conductive polymer layer and the second conductive polymer layer, The barrier layer prevents a conductive polymer layer from being formed by electrolytic polymerization in a region closer to the anode body than the barrier layer.

[0007] A method for manufacturing a solid electrolytic capacitor according to an embodiment of the present disclosure includes: forming a first conductive polymer layer by chemical polymerization on the surface of a porous anode body having a valve metal and a dielectric oxide film layer formed on the surface of the valve metal; forming a conductive barrier layer on the first conductive polymer layer; and forming a second conductive polymer layer on the barrier layer by electrolytic polymerization. [Effects of the Invention]

[0008] According to the present disclosure, a solid electrolytic capacitor having a high withstand voltage can be provided. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view showing a solid electrolytic capacitor according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic cross-sectional view showing an electrolyte layer of the solid electrolytic capacitor according to an embodiment of the present disclosure. [Figure 3] FIG. 1 is a schematic cross-sectional view showing an electrolyte layer of a solid electrolytic capacitor according to a first conventional example. [Figure 4] FIG. 10 is a schematic cross-sectional view showing an electrolyte layer of a solid electrolytic capacitor according to a second conventional example. DETAILED DESCRIPTION OF THE INVENTION

[0010] Specific examples of the solid electrolytic capacitor and the method for manufacturing the solid electrolytic capacitor according to the present disclosure will be described below with reference to the drawings, but the present disclosure is not limited to these examples.

[0011] [Solid electrolytic capacitor configuration] Fig. 1 is a cross-sectional view showing a solid electrolytic capacitor 1 according to one embodiment of the present disclosure. As shown in Fig. 1, the solid electrolytic capacitor 1 includes an anode body 10, an electrolyte layer 20, and a cathode layer 30. The solid electrolytic capacitor 1 of this embodiment can be formed by sequentially stacking the electrolyte layer 20 and the cathode layer 30 on the anode body 10.

[0012] The anode body 10 is porous and includes a valve metal 11 and a dielectric oxide film layer 12 formed on the surface of the valve metal 11. The valve metal 11 is, for example, a sintered body containing valve metal particles, or a porous metal body that has been roughened to enlarge the surface. Examples of the valve metal 11 include at least one selected from the group consisting of aluminum, tantalum, niobium, tungsten, titanium, and zirconium, or alloys of these valve metals. Among these, at least one valve metal selected from the group consisting of aluminum, tantalum, and niobium is preferred.

[0013] The dielectric oxide film layer 12 is an oxide film formed by oxidizing the surface of the valve metal 11. Specifically, the dielectric oxide film layer 12 can be formed on the surface of the valve metal 11 by electrolytically oxidizing the valve metal 11 in an aqueous solution containing adipic acid, citric acid, phosphoric acid, or a salt thereof. The dielectric oxide film layer 12 is also formed in the pores of the anode body 10 by electrolytic oxidation. The thickness of the dielectric oxide film layer 12 can be adjusted appropriately by the voltage applied during electrolytic oxidation.

[0014] The electrolyte layer 20 is made of a solid electrolyte such as a conductive polymer. In this embodiment, the electrolyte layer 20 includes a first conductive polymer layer 21, a second conductive polymer layer 22, and a barrier layer 23 (see FIG. 2). The first conductive polymer layer 21 is formed on the surface of the dielectric oxide film layer 12. The second conductive polymer layer 22 is formed on the opposite side of the first conductive polymer layer 21 from the dielectric oxide film layer 12.

[0015] Examples of the conductive polymer constituting the first conductive polymer layer 21 or the second conductive polymer layer 22 include conductive polymers containing thiophene, aniline, pyrrole, or derivatives thereof as repeating units, and combinations of two or more of these. The conductive polymer may also be doped with a dopant having an anionic group or a salt thereof.

[0016] In the solid electrolytic capacitor 1 of this embodiment, the first conductive polymer layer 21 is formed by chemical polymerization. The second conductive polymer layer 22 is formed by electrolytic polymerization. The thickness of the first conductive polymer layer 21 is, for example, 1 nm or more and 300 μm or less. The thickness of the second conductive polymer layer 22 is, for example, 1 μm or more and 300 μm or less.

[0017] The barrier layer 23 is formed between the first conductive polymer layer 21 and the second conductive polymer layer 22. The barrier layer 23 is conductive and may be composed of a conductive polymer. The barrier layer 23 is formed by a method other than chemical polymerization or electrolytic polymerization, thereby distinguishing it from the first conductive polymer layer 21 and the second conductive polymer layer 22. The barrier layer 23 can be formed, for example, by applying and drying a conductive polymer dispersion or a conductive polymer solution. For example, a PEDOT / PSS dispersion, in which poly(3,4-ethylenedioxythiophene) (PEDOT) is doped with polystyrene sulfonate (PSS) as a dopant, can be used. Alternatively, a self-doped soluble conductive polymer solution, in which a π-conjugated polymer has an anionic group with dopant function, may be used. The barrier layer 23 prevents the formation of a conductive polymer layer by electrolytic polymerization in the region closer to the anode body 10 than the barrier layer 23. Details of the electrolyte layer 20 in this embodiment will be described later.

[0018] The cathode layer 30 is provided on the electrolyte layer 20. The cathode layer 30 may be configured, for example, of a carbon layer and a silver layer laminated on the carbon layer, but is not particularly limited to this. The cathode layer 30 is connected to a lead frame 60b. The cathode layer 30 is connected to the cathode-side lead frame 60b via a conductive adhesive 50, for example, as shown in FIG. 1.

[0019] The anode lead 40 is a lead for ensuring electrical connection between the anode body 10 and the outside. The anode lead 40 may be a metal wire embedded in the valve metal 11, for example, a metal wire of the same type as the valve metal. The anode lead 40 is connected to a lead frame 60a on the anode side. The anode lead 40 and the lead frame 60a are connected by welding, for example.

[0020] After connecting the anode lead 40 and the cathode layer 30 to the lead frames 60a and 60b, respectively, the exterior resin 70 is formed using a mold press or the like, thereby obtaining the solid electrolytic capacitor 1.

[0021] [Electrolyte layer formation method] Methods for forming the conductive polymer layer that constitutes the electrolyte layer 20 mainly include chemical polymerization, electrolytic polymerization, and coating and drying of a conductive polymer dispersion or solution. For each formation method, an overview of the method and the characteristics of the formed electrolyte layer are described below. In the following description, a conductive polymer layer formed by chemical polymerization may be referred to as a "chemically polymerized layer," and a conductive polymer layer formed by electrolytic polymerization may be referred to as an "electrolytically polymerized layer." Furthermore, the method of coating and drying a conductive polymer dispersion or solution may be referred to as "solution coating."

[0022] Chemical polymerization and electrolytic polymerization are methods of forming conductive polymers by immersing an object such as an anode in a monomer solution and polymerizing the monomer on the surface of the object (in situ polymerization). When a porous anode is immersed in a monomer solution, the monomer penetrates into the pores P of the anode, so both chemical polymerization and electrolytic polymerization make it possible to form an electrolyte layer inside the anode. Forming an electrolyte layer inside the anode increases the contact area between the dielectric oxide film layer and the electrolyte layer, resulting in a high-capacity capacitor.

[0023] In chemical polymerization, an object such as an anode is immersed in an oxidant solution and then dried to form oxidant crystals. The object is then immersed in a monomer solution, and the monomer and oxidant crystals are brought into contact, causing a polymerization reaction of the monomer to form a conductive polymer layer. The chemically polymerized layer tends to have relatively low uniformity as a film, and tends to have a three-dimensional shape with many irregularities and low density.

[0024] Electropolymerization utilizes an electrochemical reaction, where a current is passed through a solution containing a monomer and a supporting electrolyte to polymerize the monomer and produce a conductive polymer layer. The electropolymerized layer is highly uniform and dense as a film. Furthermore, the film obtained by electropolymerization has high dimensional stability, allowing the electrolyte layer to be formed uniformly even at the corners of the target object. Therefore, electropolymerization can be used to manufacture smaller capacitors. However, electropolymerization requires passing a current through the monomer solution, but it is difficult to pass a current through the dielectric oxide film layer, making it difficult to form an electropolymerized layer directly on the dielectric oxide film layer. Therefore, a method is used in which a conductive polymer layer is formed on the dielectric oxide film layer by chemical polymerization or solution coating before electropolymerization.

[0025] On the other hand, conductive polymer dispersions or conductive polymer solutions are less likely to penetrate into the pores of the anode body than monomer solutions. Therefore, when forming an electrolyte layer by solution coating, unlike chemical polymerization or electrolytic polymerization, it is difficult for the electrolyte layer to form inside the anode body. Also, while solution coating produces a highly uniform film, it is difficult to form an electrolyte layer at the corners of the object, unlike electrolytic polymerization. Therefore, to ensure that the electrolyte layer is formed at the corners, it is necessary to increase the thickness of the electrolyte layer, which is considered to be disadvantageous for miniaturizing capacitors.

[0026] [Detailed structure of the electrolyte layer] Next, the configuration of the electrolyte layer 20 in this embodiment will be described in more detail, in comparison with conventional examples. Fig. 2 shows the cross-sectional structure of the solid electrolytic capacitor 1 of this embodiment, Fig. 3 shows the cross-sectional structure of a solid electrolytic capacitor 101 according to a first conventional example, and Fig. 4 shows the cross-sectional structure of a solid electrolytic capacitor 201 according to a second conventional example. All of Figs. 2 to 4 show a porous structure consisting of a valve metal 11 and a dielectric oxide film layer 12 formed on the surface of the valve metal 11. Furthermore, Fig. 2 shows electrolyte layer 20, Fig. 3 shows electrolyte layer 120, and Fig. 4 shows electrolyte layer 220, respectively. All of Figs. 2 to 4 are enlarged cross-sectional views of the vicinity of the boundary between the anode body 10 and the electrolyte layers 20, 120, and 220.

[0027] (First conventional example) First, a description will be given of solid electrolytic capacitor 101 according to a first conventional example shown in Fig. 3. Electrolyte layer 120 of solid electrolytic capacitor 101 is made up of chemically polymerized layer 121 and electrolytically polymerized layer 122.

[0028] As described above, chemical polymerization forms a conductive polymer layer not only on the surface but also inside anode body 10. Therefore, in solid electrolytic capacitor 101 of the first conventional example, chemically polymerized layer 121 is also formed in hole P of anode body 10, as shown in FIG. 3. Furthermore, chemically polymerized layer 121 does not have high uniformity as a film. Therefore, as schematically shown in FIG. 3, even if chemically polymerized layer 121 is formed on dielectric oxide coating layer 12, dielectric oxide coating layer 12 is not completely covered by chemically polymerized layer 121 alone, and is left partially exposed.

[0029] In the first conventional example, chemically polymerized layer 121 is formed first, followed by electrolytically polymerized layer 122. In the case of electrolytic polymerization, as in the case of chemical polymerization, electrolytically polymerized layer 122 is formed not only on the surface of anode body 10 but also in holes P. Therefore, electrolytically polymerized layer 122 is formed partially overlapping chemically polymerized layer 121, and on the other hand, is formed directly on dielectric oxide film layer 12 in the portions where chemically polymerized layer 121 is not formed.

[0030] As shown in Figure 3, a dielectric oxide layer 12 is formed on the surface of a valve metal 11, but there are localized defect portions D where the dielectric oxide layer 12 is not present and the valve metal 11 is exposed. In the first conventional example, a conductive polymer layer (a chemically polymerized layer 121 or an electrolytically polymerized layer 122) can also be formed in the defect portion D present in the hole P shown in Figure 3. If a conductive polymer layer is formed in the defect portion D, current can flow through that portion without passing through the dielectric oxide layer 12, which may reduce the withstand voltage of the capacitor.

[0031] However, in the case of chemical polymerization, the formed chemically polymerized layer 121 is not highly uniform. Therefore, even if the chemically polymerized layer 121 is formed in the defect portion D, the chemically polymerized layer 121 formed in the defect portion D can be oxidized and insulated by subsequently performing a local chemical conversion treatment (e.g., application of a weak current) and thus a decrease in withstand voltage can be prevented. On the other hand, since the electrolytically polymerized layer 122 is more uniform than the chemically polymerized layer 121, it is difficult to perform a treatment to locally insulate the electrolytically polymerized layer 122 when the electrolytically polymerized layer 122 is formed in the defect portion D. As a result, as shown in FIG. 3, there are portions in the defect portion D where the electrolytically polymerized layer 122 and the valve metal 11 come into direct contact, leading to a decrease in withstand voltage. Therefore, it is difficult to obtain a high withstand voltage with a configuration having a combination of the chemically polymerized layer 121 and the electrolytically polymerized layer 122 as in the first conventional example.

[0032] (Second conventional example) Next, a description will be given of a solid electrolytic capacitor 201 according to a second conventional example shown in Fig. 4. The solid electrolytic capacitor 201 includes an electrolyte layer 220 formed by first forming a conductive polymer layer 223 on the surface of the anode body 10 by applying a solution, and then laminating a chemically polymerized layer 221 and an electrolytically polymerized layer 222 in this order.

[0033] In the solution coating process, the conductive polymer dispersion or conductive polymer solution does not enter the pores P of the anode body 10, and therefore, as shown in FIG. 4, a conductive polymer layer 223 is formed only on the surface of the anode body 10. Next, the chemically polymerized layer 221 and the electrolytically polymerized layer 222 are formed in sequence, but because the conductive polymer layer 223 is already formed, the monomer solution does not enter the interior of the pores P, and therefore a chemically polymerized layer or an electrolytically polymerized layer cannot be formed inside the pores P. Therefore, in a capacitor having the configuration of the second conventional example shown in FIG. 4, the contact area between the dielectric oxide film layer 12 and the electrolyte layer 220 is reduced, resulting in a decrease in capacitance and an increase in equivalent series resistance (ESR).

[0034] (Present embodiment) Next, a description will be given of a solid electrolytic capacitor 1 according to an embodiment of the present disclosure shown in Fig. 2. As shown in Fig. 2, the solid electrolytic capacitor 1 includes an electrolyte layer 20 including a first conductive polymer layer 21 (hereinafter referred to as chemically polymerized layer 21) formed by chemical polymerization, a second conductive polymer layer 22 (hereinafter referred to as electrolytically polymerized layer 22) formed by electrolytic polymerization, and a barrier layer 23 formed by solution application.

[0035] In this embodiment, chemically polymerized layer 21 is formed so as to fill hole P of anode body 10, similar to the first conventional example shown in FIG.

[0036] 3, solid electrolytic capacitor 1 of this embodiment is different from the first conventional example shown in Fig. 3 in that barrier layer 23 is formed after chemically polymerized layer 21 is formed and before electrolytically polymerized layer 22 is formed. As described above, the conductive polymer dispersion or conductive polymer solution does not enter pores P, and therefore barrier layer 23 formed by applying the solution is formed only on the surface of anode body 10 as shown in Fig. 2.

[0037] When electrolytically polymerized layer 22 is formed after barrier layer 23 is formed, the presence of barrier layer 23 prevents electrolytically polymerized layer 22 from being formed on the anode body 10 side of barrier layer 23. Therefore, electrolytically polymerized layer 22 is not formed in hole P of anode body 10, and formation of an electrolytically polymerized layer in defect portion D can be avoided.

[0038] The configuration of this embodiment prevents the formation of an electrolytically polymerized layer at the defect D, improving the withstand voltage of the capacitor compared to the first conventional example shown in FIG. 3. Furthermore, compared to the second conventional example shown in FIG. 4, the chemically polymerized layer 21 is formed at the hole P, resulting in a larger capacitance. Furthermore, the electrolytically polymerized layer 22 is formed on the barrier layer 23, which has a relatively flat surface, rather than on the chemically polymerized layer 21, which has many irregularities. This allows for a more uniform film with excellent dimensional accuracy, which is suitable for miniaturizing capacitors.

[0039] When the barrier layer 23 is formed by applying a conductive polymer dispersion, the particle size of the conductive polymer contained in the conductive polymer dispersion is preferably 5 nm or more. The particle size of the conductive polymer here refers to the d50 (median diameter) in the number distribution. The particle size of the conductive polymer can be measured using dynamic light scattering. There is no particular upper limit to the particle size of the conductive polymer, but it may be, for example, 100 nm or less. The particle size of the conductive polymer can be adjusted by, for example, the strength of the external force applied during the dispersion treatment of the conductive polymer dispersion, the polymerization temperature, the amount and speed of the oxidizing agent added, the stirring conditions, etc.

[0040] The barrier layer 23 preferably has a water absorption of 50% by mass or less over 24 hours in an atmosphere at a temperature of 85°C and a humidity of 85% RH. The low water absorption of the barrier layer 23 makes it less likely for the barrier layer 23 to swell or peel when immersed in an electropolymerization solution, thereby preventing a deterioration in ESR and an increase in size. Furthermore, the barrier layer 23 preferably has a contact angle with water of 10° or more. A water contact angle of 10°C or more provides sufficiently high hydrophobicity, preventing the barrier layer 23 from swelling or peeling when immersed in an electropolymerization solution. Methods for reducing the water absorption or increasing the water contact angle include, for example, using PEDOT (poly(3,4-ethylenedioxythiophene)) doped with PSS (poly(4-styrenesulfonic acid)) as the barrier layer 23 and reducing the proportion of the hydrophilic dopant PSS, using a hydrophobic anion having a long-chain alkyl group or a phenyl group as the dopant, or adding a hydrophobic binder resin to the dispersion. When a binder resin is added, examples of the resin to be added include fluorine-based resins, polyester resins, oxetane resins, polyurethane resins, polyimide resins, styrene-butadiene rubbers, melamine resins, silicon resins, alkyd resins, phenolic resins, epoxy resins, butyral resins, acrylic resins, and silicone resins. In the present disclosure, any of the above methods may be used to modify the properties of the barrier layer, such as the water absorption capacity and contact angle with water, or two or more methods may be combined. Note that the properties of the barrier layer 23, such as the water absorption capacity and contact angle with water, may be considered to be the same as the properties of a standalone film formed from the same material as the barrier layer 23, and there is no need to directly measure the properties of the barrier layer 23 incorporated into a capacitor.

[0041] The ratio of the area where the barrier layer 23 is formed to the area of ​​the surface of the anode body 10 where the electrolyte layer 20 is formed (hereinafter sometimes referred to as the "barrier layer coverage") is preferably 50% or more. The area of ​​the surface of the anode body here is not the actual surface area taking pores into account, but the area of ​​the surface when viewed as a simple shape such as a rectangular parallelepiped, ignoring the pores. Increasing the barrier layer coverage can more reliably prevent the formation of an electrolytic polymerization layer on the anode body 10 side. The barrier layer coverage is more preferably 80% or more, and most preferably 100%.

[0042] The first conductive polymer layer (chemically polymerized layer) 21 is preferably subjected to a primer treatment. The primer treatment can improve adhesion with the subsequently laminated barrier layer 23, thereby increasing the barrier layer coverage. The primer material is not particularly limited, but a polyvalent amine or a salt thereof can be used. More specifically, examples of the primer include 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane, 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane, 1,10-diaminodecane, and derivatives thereof. The primer treatment can be performed, for example, by immersing the chemically polymerized layer 21 in an aqueous amine solution such as those listed above, followed by drying.

[0043] It is preferable that the barrier layer 23 has a sufficiently low sheet resistance. Specifically, when the barrier layer 23 is formed by solution coating, it is preferable that the sheet resistance of the film obtained by coating and drying the conductive polymer dispersion or conductive polymer solution used to form the barrier layer 23 is 100 Ω / □ or less. If the sheet resistance of the barrier layer 23 is sufficiently low, it is possible to avoid poor formation of the electrolytic polymerization layer and an increase in ESR.

[0044] The thickness of barrier layer 23 is preferably 30 μm or less, more preferably 20 μm or less, and even more preferably 10 μm or less. When the thickness of the barrier layer is within the above range, an increase in ESR can be avoided while effectively preventing the formation of an electrolytic polymerization layer on the anode body 10 side. The lower limit of the thickness of barrier layer 23 is not particularly limited, but may be, for example, 0.1 μm or more, or 0.5 μm or more.

[0045] The solid electrolytic capacitor 1 includes, as the cathode layer 30, a carbon layer formed on the second conductive polymer layer 22 and a silver layer formed on the carbon layer, and the silver layer preferably has a surface roughness Ra of 3.0 μm or less. A flat silver layer provides high dimensional stability and facilitates miniaturization of the capacitor. The surface roughness Ra of the silver layer decreases as the surface of the electrolytic polymer layer 22 formed thereunder becomes flatter. Therefore, by adopting the configuration of the electrolyte layer 20 of the present disclosure, the surface roughness Ra of the silver layer can be easily kept within the above range.

[0046] Whether or not a finished capacitor has the configuration of the solid electrolytic capacitor of the present disclosure can be confirmed by disassembling the capacitor and observing and evaluating it. The finished capacitor may be, for example, a resin-molded capacitor. [Example]

[0047] The solid electrolytic capacitor of the present disclosure will be described in further detail below with reference to specific examples, but the present disclosure is not limited to these examples.

[0048] [Preparation of polymer film] First, in order to evaluate the properties of the conductive polymer layer used as the barrier layer of the solid electrolytic capacitor, a polymer film was produced independently using the conductive polymer dispersion liquid used to form the barrier layer.

[0049] (Experimental Example 1) Conductive polymer dispersion A was prepared by dispersing PEDOT / PSS (a conductive polymer composed of poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(4-styrenesulfonic acid) (PSS)), polyester resin (Plascoat® Z-687, manufactured by GOO Chemical Industry Co., Ltd.), and ethylene glycol in water. The particle size of the conductive polymer contained in the dispersion was measured by dynamic light scattering using a dynamic light scattering analyzer (ESLZ-1000ZS, manufactured by Otsuka Electronics Co., Ltd.) in accordance with JIS Z8828:2019. Conductive polymer dispersion A was diluted 50 times by weight with pure water, and measurements were performed using a quartz cell at a wavelength of 660 nm, a scattering angle of 15°, and a temperature of 25°C. The obtained data were analyzed using the cumulant method (Levenberg-Marquardt method) to calculate the particle size. The particle size of the conductive polymer here is the d50 (median diameter) in the number distribution.

[0050] Next, 1 ml of the conductive polymer dispersion A was dropped onto a glass plate and dried in a drying oven at 150° C. for 30 minutes to obtain a polymer film A.

[0051] <Water absorption amount> The resulting polymer film A was cut out and left in a thermo-hygrostat chamber at 85°C and 85% RH for 24 hours, then removed from the chamber and a test piece scraped off with a spatula. The resulting test piece was placed in a simultaneous thermogravimetry and differential thermal analyzer (Hitachi High-Tech Corporation, STA7200) and heated from 25°C to 150°C at a rate of 10°C / min, and the change in weight of the test piece was measured. The water absorption (%) was calculated from the weight of the test piece before heating and at 150°C using the following formula (1): Water absorption (%) = ((weight before heating) - (weight at 150°C)) / (weight at 150°C) × 100 Formula (1)

[0052] <Contact angle> 10 μL of pure water was dropped onto polymer film A obtained in the same manner as above, and the contact angle θ with respect to water was measured. Specifically, assuming that the planar shape of the water droplet on polymer film A was a perfect circle, the contact angle θ was calculated using the formula θ = 2 arctan(h / r) from the radius r of the perfect circle and the height h of the water droplet (θ / 2 method).

[0053] <Sheet resistance> 1 ml of conductive polymer dispersion A was applied to a glass plate to cover an area of ​​2.0 × 2.0 cm, and then dried in a drying oven at 150°C for 30 minutes to obtain polymer film A. The sheet resistance (Ω / □) of the obtained polymer film A was measured by the four-probe method using a resistivity meter (Loresta-GP MCP-T610, manufactured by Mitsubishi Chemical Corporation).

[0054] Table 1 shows the composition of conductive polymer dispersion A, and the results of measuring the particle size of the conductive polymer, water absorption, contact angle with water, and sheet resistance of polymer film A obtained from conductive polymer dispersion A.

[0055] (Experimental Examples 2 to 8) Conductive polymer dispersions B to G having compositions different from conductive polymer dispersion A were prepared, and the same operations and measurements were carried out as in Experimental Example 1. Furthermore, an aqueous solution of self-doped PEDOT dissolved in water was prepared as conductive polymer solution H, and the water absorption, contact angle, and sheet resistance were measured using the same methods as in Experimental Example 1. The compositions and evaluation results of each conductive polymer dispersion and conductive polymer solution are shown in Table 1.

[0056] [Table 1]

[0057] [Manufacturing of solid electrolytic capacitors] (Example 1) The solid electrolytic capacitor of Example 1 was manufactured by the following steps 1 to 6. (Step 1: Formation of capacitor element) First, tantalum fine powder with a specific charge of approximately 1,500,000 μFV / g was compressed using a powder press to obtain a roughly rectangular parallelepiped pressed body with a length of 2.5 mm, width of 1.5 mm, and thickness of 0.6 mm, and a tantalum wire with a diameter of 0.19 mm embedded therein. The longitudinal direction of the pressed body was along the longitudinal direction of the tantalum wire. The length of the tantalum wire protruding from the surface of the pressed body was 5.0 mm. The resulting pressed body was sintered at 1300°C in an inert gas to obtain a porous sintered body of tantalum fine powder. The resulting sintered body of tantalum fine powder, which served as a valve metal, was anodized at 15 V in an 85°C phosphoric acid aqueous solution to obtain a capacitor element (anode body) in which a dielectric oxide film layer made of tantalum oxide was formed on the entire surface of the sintered tantalum fine powder. In the following description, capacitor elements with some kind of layer or terminal formed on the surface may also be simply referred to as "capacitor elements."

[0058] (Step 2: Chemical polymerization) Next, the capacitor element obtained in step 1 was immersed in a methanol solution of ferric p-toluenesulfonate, an oxidant and dopant, for 10 minutes, then removed from the solution and dried at room temperature for 30 minutes (step 2-a). The capacitor element was then immersed in a thiophene derivative (3,4-ethylenedioxythiophene), a monomer, for 1 minute, removed from the solution, and left at room temperature for 30 minutes to polymerize the 3,4-ethylenedioxythiophene (step 2-b). The capacitor element was then immersed in ethanol to remove unreacted materials and oxidant residues (step 2-c). The polymerization process, including steps 2-a (adding the oxidant), 2-b (polymerizing 3,4-ethylenedioxythiophene), and 2-c (washing), was repeated a total of six times to obtain a capacitor element with a first conductive polymer layer (chemically polymerized layer) formed on its surface, consisting of poly(3,4-ethylenedioxythiophene) (PEDOT) doped with p-toluenesulfonic acid.

[0059] (Step 3: Formation of Barrier Layer) The capacitor element obtained in step 2 was immersed in conductive polymer dispersion liquid A for 1 minute, then removed and dried at 150° C. for 30 minutes, thereby obtaining a capacitor element in which a barrier layer was formed on the first conductive polymer layer.

[0060] (Step 4: Electrolytic polymerization) The capacitor element obtained in step 3 was immersed in a solution containing 3,4-ethylenedioxythiophene and organic sodium sulfonate, and a stainless steel wire (Φ1.0 mm) was placed in contact with the capacitor element as an external power supply terminal. A DC voltage of 3 V or less was applied to the power supply terminal side as the anode, and electropolymerization was performed. This resulted in a capacitor element in which a second conductive polymer layer (electropolymerized layer) was formed on the barrier layer.

[0061] (Step 5: Formation of cathode layer) The capacitor element obtained in step 4 was immersed in graphite paste for 1 minute, pulled out, and then dried at 120°C for 1 hour, thereby forming a carbon layer on the second conductive polymer layer. The capacitor element was then immersed in silver paste for 1 minute, pulled out, and then dried at 120°C for 1 hour, thereby forming a silver layer on the carbon layer. The laminated structure of the carbon layer and silver layer constitutes the cathode layer.

[0062] (Step 6: Attaching electrodes and molding) In the capacitor element obtained in step 5, the valve metal lead and the anode were connected by welding. The silver layer and the cathode were connected using a conductive adhesive. Finally, a resin coating was formed on the capacitor element using a mold press, yielding the solid electrolytic capacitor of Example 1.

[0063] (Examples 2 to 8) In step 3, the solid electrolytic capacitors of Examples 2 to 8 were obtained in the same manner as in Example 1, except that conductive polymer dispersions B to G and conductive polymer solution H were used, respectively, instead of conductive polymer dispersion A when forming the barrier layer.

[0064] (Example 9) The solid electrolytic capacitor of Example 9 was obtained in the same manner as in Example 1, except that in step 3, only about half of the capacitor element was immersed in conductive polymer dispersion A in order to change the barrier layer coverage.

[0065] (Example 10) After step 2 and before performing step 3, the capacitor element was immersed in a primer solution (a 5% by mass aqueous solution of 1,10-decanediamine) for 1 minute and dried at 125°C for 30 minutes to perform primer treatment, and the solid electrolytic capacitor of example 10 was obtained in the same manner as in example 1.

[0066] (Examples 11-14) In order to change the thickness of the barrier layer, the solid electrolytic capacitors of Examples 11 to 14 were obtained in the same manner as in Example 1, except that in Step 3, the number of repetitions of the step of immersing in conductive polymer dispersion A for 1 minute and the step of drying for 30 minutes was changed to 3 times, 5 times, 10 times, and 15 times, respectively.

[0067] (Example 15) A solid electrolytic capacitor of Example 15 was obtained in the same manner as in Example 1, except that step 3 was not performed and the barrier layer was not formed.

[0068] (Example 16) The solid electrolytic capacitor of Example 16 was obtained in the same manner as in Example 1, except that in step 2, steps 2-a to 2-c were repeated 10 times, and steps 3 and 4 were not performed, so that the barrier layer and the electrolytic polymerization layer were not formed.

[0069] The solid electrolytic capacitors of Examples 1 to 16 were evaluated for coverage, withstand voltage, equivalent series resistance (ESR), and surface roughness of the capacitor element.

[0070] <Coverage> After the barrier layer formation in step 3 was completed and before step 4 was performed, an optical microscope (Keyence VHX-5000) was used to photograph the appearance of the barrier layer on five surfaces of each capacitor element, excluding the surface where the tantalum wire protruded. The photographs were saved in bitmap format. The saved photographs were imported into spreadsheet software (Microsoft Excel) in binary data format, and pixel information of the image was extracted from the binary data. The pixel information was converted to grayscale using the brightness method. A histogram was created from the grayscale values, and a binarization threshold was determined using the mode method. The image was then binarized using the determined threshold, and the barrier layer-covered portion of the capacitor element was defined as black, and the uncovered portion was defined as white. The barrier layer coverage rate was calculated from the ratio of pixels determined as black to the external surface area of ​​the capacitor element. Note that the external surface area of ​​the capacitor element here does not refer to the actual surface area taking into account the pores of the porous capacitor element, but rather to the surface area when the capacitor element is viewed as a rectangular parallelepiped, ignoring the pores.

[0071] <Voltage resistance> Each capacitor was placed in a thermostatic chamber at 85°C, and the current value was measured when a DC voltage was applied while increasing the voltage at a rate of 1 V / sec. The voltage at which the current value exceeded 200 mA was defined as the withstand voltage (V).

[0072] <Equivalent series resistance (ESR)> The equivalent series resistance (ESR) of each capacitor was measured at 100 kHz using an LCR meter (4263B LCR METER, manufactured by Hewlett Packard).

[0073] <Surface roughness> After the silver layer was formed in step 6, the surface roughness of the capacitor element was measured before carrying out step 7. Specifically, a three-dimensional measuring machine (Keyence Corporation, VR-6100) was used to measure the line roughness at three different points on the surface of the capacitor element on which the silver layer was formed, and the surface line roughness Ra (μm) was calculated from the average of the three measurements.

[0074] Tables 2 and 3 show the evaluation results of the solid electrolytic capacitors of Examples 1 to 16.

[0075] [Table 2]

[0076] [Table 3]

[0077] In Tables 2 and 3, Examples 1, 2, and 5 to 13 are working examples, and Examples 3, 4, 15, and 16 are comparative examples. A comparison of Example 1 and Example 15 shows that the provision of a barrier layer improves the withstand voltage. Examples 1 to 3 and Examples 9 to 12 show that the withstand voltage improves as the coverage of the barrier layer increases. Examples 1 and 10 to 14 show that the equivalent series resistance decreases as the thickness of the barrier layer decreases.

[0078] In the case where a barrier layer with low hydrophobicity is formed as in Examples 3 and 4, the barrier layer swells, resulting in a deterioration in the surface roughness Ra, but in the case where a barrier layer is designed to have high hydrophobicity as in Examples 1, 2, 5, 6, and 7, swelling can be suppressed and the deterioration of surface roughness can be prevented. Here, means for increasing the hydrophobicity of the barrier layer include, but are not limited to, using a hydrophobic anion having a long-chain alkyl group or a phenyl group as a dopant, and adding a hydrophobic binder resin to the dispersion. [Explanation of symbols]

[0079] 1,101,201 Solid electrolytic capacitors 10 Anode body 11 Valve Metals 12 Dielectric oxide film layer 20,120,220 electrolyte layer 21,121,221 First conductive polymer layer (chemically polymerized layer) 22,122,222 Second conductive polymer layer (electrolytic polymer layer) 23 Barrier Layer 223 Conductive polymer layer 30 cathode layer 40 Anode lead 50 Conductive adhesive 60a, 60b Lead frame 70 Exterior resin

Claims

1. a porous anode body having a valve metal and a dielectric oxide film layer formed on the surface of the valve metal; an electrolyte layer formed on the surface of the dielectric oxide film layer, The electrolyte layer is a first conductive polymer layer formed by chemical polymerization and in contact with the dielectric oxide film layer; a second conductive polymer layer formed by electrolytic polymerization on the opposite side of the first conductive polymer layer from the dielectric oxide film layer; a barrier layer having conductivity formed between the first conductive polymer layer and the second conductive polymer layer, the barrier layer prevents a conductive polymer layer from being formed by electrolytic polymerization in a region closer to the anode body than the barrier layer. Solid electrolytic capacitor.

2. 2. The solid electrolytic capacitor according to claim 1, wherein the barrier layer is formed by applying a conductive polymer dispersion or a conductive polymer solution and drying it.

3. 3. The solid electrolytic capacitor according to claim 2, wherein the particle size d50 in the number distribution of the conductive polymer contained in the conductive polymer dispersion is 5 nm or more.

4. 3. The solid electrolytic capacitor according to claim 1, wherein the barrier layer has a water absorption of 50% by mass or less in an atmosphere at a temperature of 85° C. and a humidity of 85% RH for 24 hours.

5. 3. The solid electrolytic capacitor according to claim 1, wherein a ratio of an area where the barrier layer is formed to an area where the electrolyte layer is formed is 50% or more.

6. 3. The solid electrolytic capacitor according to claim 1, wherein the first conductive polymer layer is treated with a primer.

7. 3. The solid electrolytic capacitor according to claim 2, wherein the sheet resistance of a film obtained by coating and drying the conductive polymer dispersion or the conductive polymer solution used to form the barrier layer is 100 Ω / □ or less.

8. 3. The solid electrolytic capacitor according to claim 1, wherein the barrier layer has a thickness of 30 [mu]m or less.

9. a carbon layer formed on the second conductive polymer layer; and a silver layer formed on the carbon layer, 3. The solid electrolytic capacitor according to claim 1, wherein the silver layer has a surface roughness Ra of 3.0 μm or less.

10. forming a first conductive polymer layer by chemical polymerization on the surface of a porous anode body having a valve metal and a dielectric oxide film layer formed on the surface of the valve metal; forming a conductive barrier layer on the first conductive polymer layer; and forming a second conductive polymer layer on the barrier layer by electrolytic polymerization.

Images