Monomer for solid electrolytic capacitor, the solid electrolytic capacitor, and manufacturing method

Abstract

To realize a solid electrolytic capacitor having a high withstand voltage.SOLUTION: A monomer for a solid electrolytic capacitor that produces a conductive polymer is a 3,4-ethylenedioxythiophene derivative, and ethylene glycol monomethyl ether or polyethylene glycol monomethyl ether is introduced into the 2-position of the ethylenedioxy skeleton of 3,4-ethylenedioxythiophene. The solid electrolytic capacitor includes an anode body and a cathode body in each of which a conductive polymer having the monomer for the solid electrolytic capacitor as a monomer unit is attached to a dielectric film. The solid electrolytic capacitor includes: a polymerization step of polymerizing a monomer for the solid electrolytic capacitor to produce a conductive polymer, and an element forming step of forming a capacitor element having the anode body, the cathode body, and the conductive polymer.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a solid electrolytic capacitor having a conductive polymer, a monomer constituting the conductive polymer, and a manufacturing method. [Background technology]

[0002] Capacitors are used in a variety of applications, including communications, industrial equipment, and automotive applications. For example, in automotive applications, capacitors are used in voltage systems of, for example, 12V, 24V, or 48V for engine start-up or electrical systems including an ECU (Electronic Control Unit). A power supply circuit is provided between the ECU and the battery to convert +12V DC voltage into the operating voltage of the ECU. The power supply circuit functions as a step-down switching regulator and includes a capacitor that absorbs input current fluctuations and a capacitor that smooths the output voltage.

[0003] Electrolytic capacitors have anodes and cathodes made of valve metals such as tantalum or aluminum. The anodes are enlarged by sintering the valve metal into a shape such as etched foil, and the enlarged surfaces are coated with a dielectric film by anodizing or other processes. An electrolyte is interposed between the anode and cathode, acting as a true cathode in close contact with the anode.

[0004] When the electrolyte is a liquid electrolyte, the liquid evaporates and dissipates over time, causing the capacitor to dry out. In contrast, when the electrolyte is a conductive polymer, the dry out phenomenon does not occur. Therefore, solid electrolytic capacitors incorporating such conductive polymers are attracting attention in fields where long-life components are required, such as communications, industrial equipment, and automotive applications.

[0005] A widely used conductive polymer is poly(3,4-ethylenedioxythiophene) (PEDOT), which has high conductivity. Poly(3,4-ethylenedioxythiophene) is typically doped with polystyrene sulfonate (PSS) to achieve high conductivity. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2021-64737 Summary of the Invention [Problem to be solved by the invention]

[0007] In technical fields such as communications, industrial equipment, and automotive applications, capacitors with long lifespans are required to balance the service life of the equipment. Furthermore, the safety factor of these devices is increasing year by year, and capacitors are sometimes required to withstand voltages several times the circuit voltage. Therefore, there is a demand for the development of new conductive polymer materials with withstand voltages exceeding that of PEDOT.

[0008] The present invention has been proposed to solve the above-mentioned problems, and its purpose is to realize a solid electrolytic capacitor with a high withstand voltage. To this end, the present invention provides a monomer for a solid electrolytic capacitor used to produce a conductive polymer for the solid electrolytic capacitor, a solid electrolytic capacitor made using this monomer, and a method for manufacturing this solid electrolytic capacitor. [Means for solving the problem]

[0009] In order to solve the above problems, the monomer for a solid electrolytic capacitor of this embodiment is a 3,4-ethylenedioxythiophene derivative represented by the following formula (Chemical Formula 1), in which R in the formula (Chemical Formula 1) has a structure represented by the following formula (Chemical Formula 2), and is used to produce a conductive polymer for a solid electrolytic capacitor.

[0010] [ka]

[0011] [ka]

[0012] The 3,4-ethylenedioxythiophene derivative may be such that n in formula (Chemical Formula 2) is 3 or more.

[0013] In order to solve the above-described problems, the solid electrolytic capacitor of the present embodiment includes a conductive polymer containing the monomer for a solid electrolytic capacitor as a monomer unit, an anode body having a dielectric coating with the conductive polymer attached to the dielectric coating, and a cathode body facing the anode body.

[0014] Furthermore, in order to solve the above-described problems, the method for manufacturing the solid electrolytic capacitor of the present embodiment may include a polymerization step of polymerizing the monomer for the solid electrolytic capacitor to produce a conductive polymer, and an element formation step of forming a capacitor element having an anode body, a cathode body, and the conductive polymer. [Effects of the Invention]

[0015] The withstand voltage of the solid electrolytic capacitor can be increased. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a graph showing measurement results of VI characteristics of an example and a comparative example. [Figure 2] 1 is a bar graph showing the withstand voltages of Examples and Comparative Examples. [Figure 3] 1 is a graph showing capacitance versus polymer species and oxidant species. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, a monomer for a solid electrolytic capacitor, a solid electrolytic capacitor, and a manufacturing method thereof according to embodiments of the present invention will be described. However, the present invention is not limited to the embodiments described below.

[0018] (monomer for solid electrolytic capacitors) A solid electrolytic capacitor is a passive element that obtains capacitance through the dielectric polarization of a dielectric film and stores and discharges electric charge through the capacitance. The solid electrolytic capacitor includes an anode body, a cathode body, a solid electrolyte layer, and a separator, each of which has a dielectric film formed on its surface. The anode body and the cathode body are arranged opposite each other, with the separator and the solid electrolyte layer interposed between them. The anode body and the cathode body are arranged in a stacked configuration, where they are alternately stacked with the separator sandwiched between them, or in a wound configuration, where they are wound with the separator sandwiched between them.

[0019] The solid electrolyte layer contains a conductive polymer. The conductive polymer is supported on a separator, adheres to a dielectric film formed on the surface of the anode body, and is arranged so as to connect the dielectric film and the cathode body, creating a conductive path and forming a true cathode. The conductive polymer is a conjugated polymer having π-conjugated double bonds and is produced using a monomer for solid electrolytic capacitors.

[0020] The monomer for a solid electrolytic capacitor is a 3,4-ethylenedioxythiophene derivative represented by the following formula (Chemical Formula 3), in which R has a structure represented by the following formula (Chemical Formula 4).

[0021] [ka]

[0022] [ka]

[0023] That is, this monomer for solid electrolytic capacitors is 3,4-ethylenedioxythiophene in which an ethylene glycol monomethyl ether repeating unit where n is 1 has been introduced at the second position of the ethylenedioxy skeleton, or 3,4-ethylenedioxythiophene in which a polyethylene glycol monomethyl ether repeating unit where n is 2 or more has been introduced.

[0024] Particularly preferably, the monomer for solid electrolytic capacitors is 3,4-ethylenedioxythiophene in which triethylene glycol monomethyl ether has been introduced at the 2-position of the ethylenedioxy skeleton, where n is 3, i.e., 2-{2-[2-(2-(2,3-dihydrothieno[3,4-b][1,4]dioxin-2-yl)methoxy)ethoxy]ethoxy}ethan-1-ol (hereinafter also referred to as EDOT-EG3), or 3,4-ethylenedioxythiophene in which polyethylene glycol monomethyl ether has been introduced at the 2-position of the ethylenedioxy skeleton, where n is 4 or more.

[0025] By incorporating a conductive polymer made from this solid electrolytic capacitor monomer into a solid electrolytic capacitor, the voltage resistance of the solid electrolytic capacitor is improved compared to when the conductive polymer monomer is EDOT. However, simply introducing an ethylene glycol monomethyl ether group into the second position of the ethylenedioxy skeleton does not achieve the same voltage resistance improvement effect as, for example, Bu-EDOT, which is said to increase the voltage resistance of solid electrolytic capacitors more than EDOT. Bu-EDOT is 3,4-ethylenedioxythiophene with a butyl group introduced into the second position of the ethylenedioxy skeleton.

[0026] However, when n = 3 in the above formula (Chemical Formula 4), i.e., when EDOT-EG3 with triethylene glycol monomethyl ether is used as a monomer for solid electrolytic capacitors, a conductive polymer is produced that far exceeds not only PEDOT but also Bu-PEDOT in the improvement of voltage resistance. This significant improvement in voltage resistance is unique to the above formula (Chemical Formula 4) when n is 3 or more.

[0027] Methods for producing conductive polymers using monomers for solid electrolytic capacitors include chemical oxidative polymerization and electrolytic oxidative polymerization. In chemical oxidative polymerization, a solution containing the monomer for solid electrolytic capacitors is mixed with an oxidizing agent to cause a polymerization reaction. In electrolytic oxidative polymerization, the monomer for solid electrolytic capacitors is mixed with a supporting electrolyte and the polymerization reaction is carried out in the electrolytic solution by a constant potential method, a constant current method, or a potential sweep method.

[0028] In the chemical oxidative polymerization, the oxidizing agent may be any known compound that releases a dopant. Examples of such oxidizing agents include trivalent iron salts such as iron(III) p-toluenesulfonate, iron(III) naphthalenesulfonate, and iron(III) anthraquinonesulfonate, and peroxodisulfates such as peroxodisulfate, ammonium peroxodisulfate, and sodium peroxodisulfate. A single compound may be used, or two or more compounds may be used. The polymerization temperature is not strictly limited, but is generally in the range of 10 to 200°C. The polymerization time is generally in the range of 10 minutes to 30 hours.

[0029] Preferably, the polymerization reaction is carried out using an iron-based oxidizing agent such as a trivalent iron salt as the oxidizing agent. The conductive polymer obtained by polymerizing this monomer for a solid electrolytic capacitor using an iron-based oxidizing agent not only improves the withstand voltage of the solid electrolytic capacitor but also improves the capacitance of the solid electrolytic capacitor, compared to when a non-iron-based oxidizing agent such as a peroxodisulfate is used.

[0030] In the electrolytic oxidation polymerization, the supporting electrolyte contains at least one compound selected from the group consisting of borodisalicylic acid and borodisalicylic acid salts. Examples of the salt include alkali metal salts such as lithium salt, sodium salt, and potassium salt, alkylammonium salts such as ammonium salt, ethylammonium salt, and butylammonium salt, dialkylammonium salts such as diethylammonium salt and dibutylammonium salt, trialkylammonium salts such as triethylammonium salt and tributylammonium salt, and tetraalkylammonium salts such as tetraethylammonium salt and tetrabutylammonium salt.

[0031] In the case of the constant potential method, a potential of 1.0 to 1.5 V relative to the reference electrode is suitable, and in the case of the constant current method, a potential of 1 to 10,000 μA / cm 2In the case of a potential sweep method, it is preferable to sweep the potential in the range of 0 to 1.5 V with respect to the reference electrode at a rate of 5 to 200 mV / sec. There is no strict limit to the polymerization temperature, but it is generally in the range of 10 to 60°C. The polymerization time is generally in the range of 10 minutes to 30 hours.

[0032] In chemical oxidation polymerization or electrolytic oxidation polymerization, the solvent to which the monomer for a solid electrolytic capacitor, oxidizing agent, or supporting electrolyte is added can be any solvent that can dissolve the desired amount of monomer and supporting electrolyte and does not adversely affect the electrolytic oxidation polymerization. Examples of solvents include water, methanol, ethanol, isopropanol, butanol, ethylene glycol, acetonitrile, butyronitrile, acetone, methyl ethyl ketone, tetrahydrofuran, 1,4-dioxane, γ-butyrolactone, methyl acetate, ethyl acetate, methyl benzoate, ethyl benzoate, ethylene carbonate, propylene carbonate, nitromethane, nitrobenzene, sulfolane, and dimethyl sulfolane. These solvents can be used alone or in combination.

[0033] This solid electrolytic capacitor monomer can be obtained by the following production method: For example, 3,4-ethylenedioxythiophene in which triethylene glycol monomethyl ether is introduced at the 2-position of the ethylenedioxy skeleton can be produced as follows.

[0034] First, triethylene glycol monochlorohydrin is reacted with 3,4-dihydro-2H-pyran under acidic conditions to protect the hydroxyl groups, and then iodinated by reaction with sodium iodide in acetone. Triethylene glycol monochlorohydrin is a precursor to the polyethylene glycol monomethyl ether moiety to be introduced into the ethylenedioxy skeleton. 3,4-ethylenedioxythiophene, in which methanol has been introduced into the ethylenedioxy skeleton, is heated and stirred in tetrahydrofuran in the presence of sodium hydride, and then the iodized precursor is added and reacted at room temperature. The resulting reaction product is deprotected under acidic conditions and purified to yield 3,4-ethylenedioxythiophene in which triethylene glycol monomethyl ether has been introduced into the 2-position of the ethylenedioxy skeleton.

[0035] (conductive polymer) The conductive polymer produced using this solid electrolytic capacitor monomer is doped with a dopant, thereby exhibiting high conductivity. Any known dopant can be used without any particular limitation. The dopant is doped into the conductive polymer by adding it to a polymerization solution together with the solid electrolytic capacitor monomer. During chemical oxidative polymerization, an oxidizing agent that releases the dopant may be used to dope the conductive polymer during polymerization. The dopant may be used alone or in combination of two or more types. Furthermore, a polymer or a monomer may be used.

[0036] Examples of dopants include inorganic acids such as polyanions, boric acid, nitric acid, and phosphoric acid, and organic acids such as acetic acid, oxalic acid, citric acid, tartaric acid, squaric acid, rhodizonic acid, croconic acid, salicylic acid, p-toluenesulfonic acid, 1,2-dihydroxy-3,5-benzenedisulfonic acid, methanesulfonic acid, trifluoromethanesulfonic acid, borodisalicylic acid, bisoxalateborate acid, sulfonylimide acid, dodecylbenzenesulfonic acid, propylnaphthalenesulfonic acid, and butylnaphthalenesulfonic acid.

[0037] Examples of polyanions include substituted or unsubstituted polyalkylenes, substituted or unsubstituted polyalkenylenes, substituted or unsubstituted polyimides, substituted or unsubstituted polyamides, and substituted or unsubstituted polyesters, and include polymers consisting only of structural units having anionic groups, and polymers consisting of structural units having anionic groups and structural units not having anionic groups.Specific examples of polyanions include polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallylsulfonic acid, polyacrylic sulfonic acid, polymethacrylic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, polyacrylic acid, polymethacrylic acid, and polymaleic acid.

[0038] The conductive polymer is formed in the capacitor element by a polymerization reaction while the capacitor element is immersed in a polymerization solution that produces the conductive polymer. The capacitor element is a laminate in which an anode body and a cathode body are stacked with a separator interposed therebetween.

[0039] (electrode foil) The anode and cathode bodies are elongated foils made of valve metals such as aluminum, tantalum, niobium, niobium oxide, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. The purity of the anode body is preferably 99.9% or higher, but impurities such as silicon, iron, copper, magnesium, and zinc may be included.

[0040] The anode body has a surface-expanding layer formed on one or both sides. The surface-expanding layer can be an etched layer formed by etching a foil, a sintered layer formed by sintering valve metal powder, or a vapor-deposited layer formed by vapor-depositing valve metal particles onto a foil. That is, the surface-expanding layer has a porous structure consisting of tunnel-like pits, spongy pits, or voids between densely packed powder or particles.

[0041] A tunnel-shaped etching pit is a hole dug in the foil thickness direction. This tunnel-shaped etching pit is typically formed by passing a direct current in an acidic aqueous solution containing halogen ions, such as hydrochloric acid. The tunnel-shaped etching pit can be further expanded by passing a direct current in an acidic aqueous solution containing nitric acid. A spongy etching pit is a sponge-like layer with a series of fine voids. This spongy etching pit is formed by passing an alternating current in an acidic aqueous solution containing halogen ions, such as hydrochloric acid.

[0042] The sintered layer is produced by obtaining a powder of a valve action metal of the same or different type as the foil by a milling method, atomization method, melt spinning method, rotating disk method, rotating electrode method, etc., forming a paste with a binder or solvent, applying it to the foil, drying it, and heating and sintering it in a vacuum or reducing atmosphere, etc. The atomization method may be any of water atomization method, gas atomization method, and water gas atomization method. The vapor deposition layer is produced by, for example, a resistance heating vapor deposition method or an electron beam heating vapor deposition method. This vapor deposition layer is formed by heating and evaporating a valve action metal of the same or different type as the foil by resistance heat or electron beam energy, and depositing the vapor of the valve action metal particles on the surface of the foil.

[0043] The purity of the valve metal in the cathode body is desirably 99% or more, but may contain impurities such as silicon, iron, copper, magnesium, zinc, etc. The cathode body may be a plain foil that is not surface-enlarged, or may be surface-enlarged by forming tunnel-shaped etching pits or spongy etching pits as necessary, or may be surface-enlarged by vapor-depositing or sintering particles of the valve metal.

[0044] The cathode body may also be a laminate of a metal layer and a carbon layer. The carbon layer of the cathode body is arranged facing the anode body. The carbon layer is formed in a paste form, and after a solid electrolyte layer is formed on the anode body, the carbon layer is applied on the solid electrolyte layer and cured by heating. The metal layer is, for example, a silver layer. The metal layer is formed in a paste form, and the silver layer is applied on the carbon layer and cured by heating.

[0045] The dielectric film formed on the surface of the anode body is the dielectric layer of the solid electrolytic capacitor. The dielectric film is formed on one or both sides of the anode body on which the surface expansion layer is formed. When the surface expansion layer is formed, the dielectric film is formed on the surface of the surface expansion layer along the irregularities of the surface expansion layer. The dielectric film is typically an oxide film formed on the surface of the surface expansion layer formed on the anode body, and if the anode body is made of aluminum, it is an aluminum oxide layer formed by oxidizing the surface of the surface expansion layer.

[0046] This dielectric film is formed by chemical conversion treatment. In the chemical conversion treatment, a voltage is applied in a chemical conversion solution until a desired withstand voltage is achieved. In the chemical conversion treatment for forming the dielectric film, it is preferable to form a dielectric film with a thickness of 1.1 to 1.5 nm in order to obtain a withstand voltage of 1 V. The chemical conversion solution is a solution that does not contain halogen ions, and examples thereof include phosphoric acid-based chemical conversion solutions such as ammonium dihydrogen phosphate, boric acid-based chemical conversion solutions such as ammonium borate, and adipic acid-based chemical conversion solutions such as ammonium adipate.

[0047] An oxide film of about 1 to 10 V may also be formed intentionally on the surface layer of the cathode body by chemical conversion treatment, or an oxide film may be formed naturally. The natural oxide film that naturally forms on the surface layer of the cathode body is formed by the cathode body reacting with oxygen in the air.

[0048] Furthermore, a conductive layer may be laminated on the cathode body. The conductive layer may contain primarily an inorganic substance or an inorganic compound. Examples of inorganic substances or inorganic compounds include titanium, zirconium, tantalum, niobium, nitrides or carbides of these, aluminum carbide, carbon materials, and composites or mixtures of these. Specific examples include a carbon layer, which is a conductive layer of a carbon material, a conductive layer of titanium nitride, a conductive layer of titanium carbide, a conductive layer made of a mixture of titanium and a carbon material, and a conductive layer made of a composite of aluminum carbide (Al4C3) and titanium oxide (TiO2).

[0049] The conductive layer containing a carbon material, i.e., the carbon layer, contains graphite, carbon black, or a mixture thereof as the carbon material. Examples of graphite include natural graphite, artificial graphite, and graphitized ketjen black. Examples of carbon black include ketjen black, acetylene black, channel black, and thermal black. In addition, the carbon layer may contain activated carbon, carbon nanohorn, or fibrous carbon as the carbon material. Activated carbon is derived from natural plant tissues such as coconut husks, synthetic resins such as phenol, and fossil fuels such as coal, coke, and pitch. Examples of fibrous carbon include carbon nanotubes (hereinafter referred to as CNTs) and carbon nanofibers (hereinafter referred to as CNFs). Activated carbon and fibrous carbon are preferred because they delocalize pi electrons and have a large specific surface area.

[0050] The cathode body may be a laminate of a metal layer and a carbon layer. The carbon layer of the cathode body is arranged facing the cathode body. The carbon layer is made into a paste form, and after a solid electrolyte layer containing a conductive polymer is formed on the anode body, the carbon layer is applied onto the electrolyte layer and cured by heating. The metal layer is, for example, a silver layer. The metal layer is made into a paste form and applied onto the carbon layer and cured by heating.

[0051] (separator) The separator may be made of cellulose such as kraft, Manila hemp, esparto, hemp, rayon, or a mixture thereof; polyester-based resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and derivatives thereof; polytetrafluoroethylene-based resins, polyvinylidene fluoride-based resins, vinylon-based resins; polyamide-based resins such as aliphatic polyamides, semi-aromatic polyamides, and wholly aromatic polyamides; polyimide-based resins, polyethylene resins, polypropylene resins, trimethylpentene resins, polyphenylene sulfide resins, acrylic resins, and polyvinyl alcohol resins; and these resins may be used alone or in combination.

[0052] The separator insulates the anode body from the cathode body and holds the conductive polymer between them. If the conductive polymer can be maintained between the anode body and the cathode body by itself and the anode body and the cathode body can be isolated from each other by the solid electrolyte so that they do not come into contact with each other, the separator may be omitted.

[0053] (Manufacturing method) A wound solid electrolytic capacitor is manufactured through an anode formation process, a cathode formation process, a winding process, an electrolyte formation process, and an assembly process. The anode formation process forms an anode body. The cathode formation process forms a cathode body. The winding process forms a capacitor element. The electrolyte formation process deposits a conductive polymer on at least the dielectric film of the anode body. The assembly process houses the capacitor element with the conductive polymer deposited in a case.

[0054] The anode formation process includes a surface enlargement process in which a surface enlargement layer is formed on the anode body, and a chemical conversion process in which a dielectric film is formed on the surface enlargement layer. The cathode formation process includes a surface enlargement process in which a surface enlargement layer is formed on the cathode body, as needed, and a chemical conversion process in which an oxide film is formed. The anode body and cathode body are cut to the desired width. External terminals are connected to the anode body and cathode body, respectively. The external terminals are electrically and mechanically connected to the anode body and cathode body by cold welding, ultrasonic welding, laser welding, or the like. The external terminals are conductors that protrude from the capacitor element and electrically connect the solid electrolytic capacitor to the mounting substrate.

[0055] Wound solid electrolytic capacitors use long anode and cathode bodies and a separator. In the winding process, the anode and cathode bodies are wound with the separator interposed between them to create a cylindrical capacitor element. The separator is overlapped so that one end protrudes beyond the other end of the anode and cathode bodies. The protruding separator is wound first so that the cylindrical core is aligned with the short sides of the anode and cathode bodies, creating a winding core. Then, using this winding core as a winding axis, the long sides of the anode and cathode bodies are rolled up to form the capacitor element.

[0056] The winding process may include a repair chemical formation process to repair bare valve metal portions exposed when the anode body and cathode body are cut to the desired width, as well as defects in the anode body and cathode body caused by physical stress such as winding. In the repair chemical formation process, a voltage is applied to the capacitor element in a chemical formation solution. Examples of chemical formation solutions include phosphoric acid-based solutions such as ammonium dihydrogen phosphate, boric acid-based solutions such as ammonium borate, adipic acid-based solutions such as ammonium adipate, and mixed solutions of boric acid and dicarboxylic acid such as citric acid. The repair chemical formation voltage is preferably 0.1 to 1.2 times the chemical formation voltage. A voltage application method in which a constant voltage is applied from the start of repair chemical formation, or a voltage application method in which the applied voltage is increased stepwise at regular intervals, may be appropriately selected.

[0057] Next, the electrolyte formation process includes a polymerization process and an attachment process. The electrolyte formation process may be performed by, for example, chemical oxidation polymerization or electrolytic oxidation polymerization. When the capacitor element is immersed in a polymerization solution to cause the polymerization reaction, the polymerization process and the attachment process are performed simultaneously.

[0058] In the assembly process, the capacitor element with the conductive polymer attached is housed in an outer case with one end closed and the other end open. The opening of the outer case is sealed with a sealing member. The outer case is made of aluminum, an aluminum alloy containing aluminum or manganese, or stainless steel. The sealing member is an elastic insulator such as a rubber plate, or a laminate of a hard substrate insulating plate such as a synthetic resin plate and an elastic insulator, which is crimped from the outside of the case and tightly adheres to the case. In the assembly process, after the capacitor element is sealed in the outer case, an aging process is performed. In the aging process, a DC voltage is applied to the solid electrolytic capacitor to repair defects in the dielectric coating and insulate the conductive polymer present in the defective parts of the dielectric coating, thereby improving the reliability of the solid electrolytic capacitor.

[0059] In a stacked solid electrolytic capacitor, a flat anode body is formed in the anode formation process, and an insulating resist layer is printed and dried on the area excluding the area that will become the anode, including the area where the anode-side external terminal will be connected later. That is, the insulating resist layer is printed in advance to prevent the conductive polymer from adhering to the area that will become the anode-side terminal.

[0060] After printing the insulating resist layer, the process moves to the electrolyte formation process. For the electrolyte formation process, chemical oxidation polymerization, for example, can be used, as in the case of wound-type solid electrolytic capacitors. The anode body with the printed insulating resist layer is immersed in a solution containing a monomer for solid electrolytic capacitors and a solution containing an oxidizer. Alternatively, the anode body with the printed insulating resist layer is immersed in a mixed solvent prepared by stirring and mixing the monomer for solid electrolytic capacitors and the oxidizer. Then, a polymerization reaction is carried out to attach a conductive polymer to the anode body.

[0061] The electrolyte formation process may be performed using electrolytic oxidation polymerization, as in the case of wound-type solid electrolytic capacitors. In electrolytic oxidation polymerization, an anode body with an insulating resist layer printed thereon is immersed in a solution containing a conductive polymer and a supporting electrolyte. Then, a polymerization reaction is performed to attach the conductive polymer to the anode body.

[0062] Next, the cathode formation process is carried out. In the cathode formation process, a carbon paste is printed on a solid electrolyte layer containing a conductive polymer using a screen printer or the like, and then dried. This drying process forms a carbon layer on the solid electrolyte layer. Furthermore, a metal paste such as silver paste is printed on the carbon layer and then dried. After this drying process, a silver layer is formed on the carbon layer. These carbon and silver layers correspond to the cathode body of the solid electrolytic capacitor.

[0063] After the cathode body is formed, the insulating resist layer is peeled off. The insulating resist layer may be peeled off by laser irradiation or mechanical peeling using a jig. The exposed portion is plated to complete the anode terminal.

[0064] The capacitor element thus fabricated can be flat-shaped without an exterior coating, or coated with a laminate film, for example. Alternatively, the capacitor element can be encapsulated by molding, dip-coating, or printing with a resin such as a heat-resistant resin or an insulating resin. Then, in the aging process, a DC voltage is applied to the solid electrolytic capacitor to repair defects in the dielectric film, etc. [Example]

[0065] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0066] Example 1 Solid electrolytic capacitors were fabricated in Example 1 and Comparative Examples 1 to 3. The solid electrolytic capacitors in Example 1 and Comparative Examples 1 to 3 had the same configuration except for the type of solid electrolytic capacitor monomer, and were fabricated by the same manufacturing method.

[0067] An aluminum foil was prepared as an anode body. A surface-expanding layer consisting of spongy pits was formed on both sides of the aluminum foil by AC etching. In the AC etching process, an AC current was passed through the aluminum foil in an aqueous solution containing hydrochloric acid. The surface-expanded anode body was then subjected to a chemical conversion treatment, and a dielectric film was formed along the irregularities of the surface-expanding layer. In the chemical conversion treatment process, the anode body was immersed in an ammonium adipate aqueous solution at 70°C, and the voltage applied to the anode body was raised to 39.6 V, after which the voltage was maintained for 30 minutes.

[0068] An aluminum foil with titanium carbide vapor-deposited on both sides was prepared as the cathode body. A mixed paper of fibrillated acrylic fiber and nylon fiber was used as the separator. One side of this separator was coated with polyvinyl alcohol. The cathode body was placed on the anode body with the separator interposed between them, and the laminate of the anode body, cathode body, and separator was wound to form a cylindrical capacitor element. The separator was placed with the polyvinyl alcohol-coated side facing the anode body.

[0069] The capacitor element is cylindrical, 6.3 mm in diameter and 5.8 mm in height, with a rated voltage of 16 WV and a rated capacitance of 100 μF. After winding, the capacitor element underwent a chemical restoration treatment. During the chemical restoration treatment, the capacitor element was immersed in an aqueous solution of ammonium dihydrogen phosphate at a temperature of 90°C, and a voltage of 42 V was applied while conducting a current density of 2 mA for 30 minutes. The capacitor element was then exposed to a temperature of 170°C for 60 minutes, after which it was dried.

[0070] After the repair chemical conversion, the process moved to the electrolyte formation process. In the electrolyte formation process, the polymerization process and the adhesion process were performed simultaneously. That is, in the electrolyte formation process, the capacitor element was impregnated with a polymerization liquid and subjected to chemical oxidative polymerization. First, 15 mg of a solid electrolytic capacitor monomer according to Examples 1 and 2 and Comparative Example 1 and 44 mg of an oxidizing agent were dispensed onto the capacitor element. The oxidizing agent was iron p-toluenesulfonate. Ethanol was used as the solvent.

[0071] After the capacitor element was impregnated with the solid electrolytic capacitor monomer and the oxidizing agent, the capacitor element was placed in a thermostatic chamber to initiate chemical oxidative polymerization. The temperature in the thermostatic chamber was maintained at 60°C for 30 minutes, then raised to 170°C and maintained there for 80 minutes. This produced conductive polymers in the capacitor element, each of which contained the solid electrolytic capacitor monomers according to Examples 1 and 2 and Comparative Example 1 as monomer units.

[0072] The monomer for a solid electrolytic capacitor used in Example 1 is represented by the following formula (5), and is 3,4-ethylenedioxythiophene (EDOT-EG3) in which triethylene glycol monomethyl ether is introduced at the 2-position of the ethylenedioxy skeleton. [ka]

[0073] The monomer for a solid electrolytic capacitor used in Comparative Example 1 was 3,4-ethylenedioxythiophene (hereinafter also referred to as EDOT) represented by the following formula (6). [ka]

[0074] The monomer for a solid electrolytic capacitor used in Comparative Example 2 is represented by the following formula (7), and is 3,4-ethylenedioxythiophene in which a butyl group is introduced at the 2-position of the ethylenedioxy skeleton (hereinafter also referred to as Bu-EDOT). [ka]

[0075] The monomer for a solid electrolytic capacitor used in Comparative Example 3 is represented by the following formula (8), and is 3,4-ethylenedioxythiophene in which ethylene glycol monomethyl ether is introduced at the 2-position of the ethylenedioxy skeleton (hereinafter also referred to as EDOT-EG1). [ka]

[0076] Moving on to the assembly process, a wound capacitor element consisting of a solid electrolyte layer containing each conductive polymer, an anode body, a cathode body, and a separator was housed in an aluminum exterior case, and the opening of the exterior case was sealed with a sealant. Note that external terminals had been connected to the anode body and the cathode body during the anode and cathode formation processes, and were extended from the sealant. Then, a voltage of 20.8 V was applied for 60 minutes in a temperature environment of 135°C, and the solid electrolytic capacitors of Example 1 and Comparative Examples 1 to 3 were subjected to an aging treatment.

[0077] The withstand voltage of the solid electrolytic capacitors of Example 1 and Comparative Examples 1 to 3 was measured. The voltage of the solid electrolytic capacitors placed at room temperature was increased from 0 V at intervals of 0.2 V every second. The current-voltage rise curve was examined, and the voltage (V) at which the current value reached 20 mA was taken as the withstand voltage. A source meter (KEITHLEY, 2410) was used to measure and record the withstand voltage.

[0078] The measurement results of the withstand voltage of the solid electrolytic capacitors of Example 1 and Comparative Examples 1 to 3 are shown in Figures 1 and 2. Figure 1 is a graph showing the measurement results of the VI characteristics of Example 1 and Comparative Examples 1 to 3. In Figure 1, the solid line represents Example 1, the dashed line represents Comparative Example 1, the two-dot chain line represents Comparative Example 2, and the one-dot chain line represents Comparative Example 3. Figure 2 is a bar graph showing the withstand voltage of Example 1 and Comparative Examples 1 to 3.

[0079] As shown in Figures 1 and 2, the withstand voltage of Example 1 using EDOT-EG3 was 50.1 V, the withstand voltage of Comparative Example 1 using EDOT was 34.3 V, the withstand voltage of Comparative Example 2 using Bu-EDOT was 39.7 V, and the withstand voltage of Comparative Example 3 using EDOT-EG1 was 36.9 V.

[0080] Comparing Comparative Example 1 and Comparative Example 3, when EDOT-EG1, in which ethylene glycol monomethyl ether with a repeating unit n of 1 is introduced at the second position of the ethylenedioxy skeleton, is used as a monomer for a solid electrolytic capacitor, the breakdown voltage of the solid electrolytic capacitor is increased compared to when EDOT is used as a monomer for a solid electrolytic capacitor.

[0081] However, when comparing Comparative Example 2 and Comparative Example 3, even if ethylene glycol monomethyl ether is introduced at the 2-position of the ethylenedioxy skeleton, it is not possible to increase the withstand voltage of the solid electrolytic capacitor, as can be achieved with Bu-EDOT, which has a butyl group introduced at the 2-position of the ethylenedioxy skeleton, as a monomer for solid electrolytic capacitors.

[0082] On the other hand, comparing Example 1 and Comparative Example 3, when EDOT-EG3, in which the repeating unit n is increased to 3 and triethylene glycol monomethyl ether is introduced at the second position of the ethylenedioxy skeleton, is used as a monomer for a solid electrolytic capacitor, the withstand voltage of the solid electrolytic capacitor suddenly rises. When this EDOT-EG3 is used as a monomer for a solid electrolytic capacitor, the withstand voltage of the solid electrolytic capacitor increases, far exceeding that of Bu-EDOT, which EDOT-EG1 could not surpass in terms of withstand voltage.

[0083] This confirmed that the voltage resistance of solid electrolytic capacitors can be improved by using 3,4-ethylenedioxythiophene (EDOT-EG3), in which triethylene glycol monomethyl ether, a repeating unit with n=3, introduced at the second position of the ethylenedioxy skeleton, as a monomer for solid electrolytic capacitors to produce conductive polymers.

[0084] Examples 2 and 3 Solid electrolytic capacitors of Examples 2 and 3 to Comparative Examples 4 to 7 were also fabricated. In the manufacturing process of Comparative Examples 4 and 5, 3,4-ethylenedioxythiophene (EDOT) represented by the above formula (6) was used as the monomer for the solid electrolytic capacitor, as in Comparative Example 1. In the manufacturing process of Comparative Examples 6 and 7, EDOT-EG1 represented by the above formula (8) in which ethylene glycol monomethyl ether was introduced at the 2-position of the ethylenedioxy skeleton was used as the monomer for the solid electrolytic capacitor, as in Comparative Example 3. In the manufacturing process of Examples 2 and 3, EDOT-EG3 represented by the above formula (5) in which triethylene glycol monomethyl ether was introduced at the 2-position of the ethylenedioxy skeleton was used as the monomer for the solid electrolytic capacitor, as in Example 1.

[0085] In addition, p-toluenesulfonic acid was used as the dopant in the production processes of Comparative Examples 4, 6, and 2. 2-naphthalenesulfonic acid diluted with an equal amount of water was used as the dopant in the production processes of Comparative Examples 5, 7, and 3. Iron-based iron(III) p-toluenesulfonate was used as the oxidizing agent for the polymerization reaction in the production processes of Comparative Examples 4, 6, and 2, and non-iron-based ammonium peroxodisulfate was used as the oxidizing agent for the polymerization reaction in the production processes of Comparative Examples 5, 7, and 3.

[0086] The solid electrolytic capacitors of Examples 2 and 3 and Comparative Examples 4 to 7 were manufactured as follows: Both sides of the anode body were masked with imide tape, leaving four circular exposed areas with a diameter of 10 mm on one side of the foil. 14.4 μL of dopant was dropped onto each of the four exposed areas, and the resulting material was dried at 60°C for 50 minutes.

[0087] Next, 14.4 μL of oxidizing agent was dropped onto each of the four exposed areas, followed by drying for 50 minutes in a 60°C environment. The oxidizing agents in Comparative Examples 4, 6, and 2 were mixed with 42 wt% of 1-butanol based on the total amount of the dropped solution. The oxidizing agents in Comparative Examples 5, 7, and 3 were mixed with 45 wt% of water based on the total amount of the dropped solution.

[0088] Next, 12 μL of a monomer for a solid electrolytic capacitor was dropped onto each of the four exposed areas. The monomer for a solid electrolytic capacitor in Comparative Example 4, Comparative Example 6, and Example 2 was mixed with 40 wt % of 1-butanol based on the total amount of the dropped solution. The monomer for a solid electrolytic capacitor in Comparative Example 5, Comparative Example 7, and Example 3 was mixed with 40 wt % of ethanol based on the total amount of the dropped solution.

[0089] After the dopant, oxidant, and monomer for solid electrolytic capacitors were dropped, a polymerization reaction was initiated, which was carried out by leaving the mixture at room temperature for 5 minutes, then at 60°C for 30 minutes, and finally at 180°C for 30 minutes.

[0090] After the polymerization reaction was completed, carbon paste to form the cathode body was applied to each of the four exposed areas and dried for 30 minutes in a temperature environment of 110°C. Silver paste was applied on top of the carbon layer, and copper foil to form the leader wire was attached, after which the silver paste was dried for 30 minutes in a temperature environment of 110°C.

[0091] The capacitance of the solid electrolytic capacitors of Examples 2 and 3 and Comparative Examples 4 to 7 was measured. The capacitance was measured using an LCR meter (Agilent ZM2376, manufactured by NF Corporation). The ambient temperature during measurement was 25°C, the AC signal level was a sine wave of 1.0 Vrms, and the measurement frequency was 120 Hz.

[0092] The measurement results of the capacitance are shown in Table 1 below. In Table 1, Cap is the capacitance. (Table 1) TIFF2025161749000010.tif91154

[0093] Based on Table 1 above, the capacitances of Examples 2 and 3 and Comparative Examples 4 to 7 are shown in the graph of Figure 3. In Figure 3, iron(III) p-toluenesulfonate is represented as an iron-based oxidant, and ammonium peroxodiate is represented as a non-iron-based oxidant.

[0094] As shown in Table 1 above and Figure 3, comparing Comparative Example 4 and Comparative Example 5, in which the solid electrolytic capacitor monomer is EDOT, the capacitance is improved when the oxidant is ammonium peroxodisulfate, a non-iron-based oxidant, and the capacitance is lower when the oxidant is iron-based oxidant, iron(III) p-toluenesulfonate.

[0095] In contrast, when Example 2 and Example 3, in which the solid electrolytic capacitor monomer is EDOT-EG3, are compared, the opposite results to those for EDOT are shown. That is, when the oxidant is ammonium peroxodioxane, a non-iron-based oxidant, the capacitance is low, and when the oxidant is iron-based oxidant iron(III) p-toluenesulfonate, the capacitance is improved.

[0096] From these results, it was confirmed that when a conductive polymer is polymerized using a monomer for a solid electrolytic capacitor, which is a 3,4-ethylenedioxythiophene derivative represented by the above formula (Chemical Formula 3), in which R in the formula (Chemical Formula 3) has a structure represented by the above formula (Chemical Formula 4), it is preferable to use an iron-based oxidizing agent, and that this not only improves the withstand voltage of the solid electrolytic capacitor but also improves the capacitance of the solid electrolytic capacitor.

Claims

1. It is a 3,4-ethylenedioxythiophene derivative represented by the following formula (Chemical Formula 1): R in the formula (Chemical Formula 1) has a structure represented by the following formula (Chemical Formula 2): Used to create conductive polymers for solid electrolytic capacitors, A monomer for solid electrolytic capacitors characterized by: 【Chemical 1】 【Chemistry 2】

2. The 3,4-ethylenedioxythiophene derivative is represented by the formula (Chemical Formula 2), in which n is 3 or more; 2. The monomer for a solid electrolytic capacitor according to claim 1,

3. A conductive polymer containing the monomer for a solid electrolytic capacitor according to claim 1 or 2 as a monomer unit; an anode body having a dielectric coating with the conductive polymer attached to the dielectric coating; a cathode body facing the anode body; To have A solid electrolytic capacitor characterized by:

4. a polymerization step of polymerizing the monomer for a solid electrolytic capacitor according to claim 1 or 2 to produce a conductive polymer; an element forming step of forming a capacitor element having an anode body, a cathode body, and the conductive polymer; containing, A method for manufacturing a solid electrolytic capacitor, comprising:

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