Organic conductor and electrolytic capacitor

Abstract

The present disclosure provides an organic conductor having excellent moisture resistance, and an electrolytic capacitor using the same. The organic conductor contains a conjugated polymer and a dopant. The dopant contains: a disulfonaphthalic acid compound having a naphthalene ring, two sulfo groups bonded to the naphthalene ring, and two carboxy groups, or an acid anhydride group thereof, bonded to the naphthalene ring; or an acid anhydride of the disulfonaphthalic acid compound.

Description

Organic conductors and electrolytic capacitors

[0001] The present disclosure relates to organic conductors and electrolytic capacitors.

[0002] Conjugated polymers such as polythiophene and polypyrrole exhibit conductivity when doped. Conjugated polymers with dopants are called conductive polymers or organic conductors. Self-doping organic conductors have also been developed in recent years. The performance of organic conductors can be controlled to some extent by selecting the type of conjugated polymer or additive (dopant, etc.). They are inexpensive and lightweight, making them suitable for use in a variety of electronic components. Proton-added compounds and electron-oxidized compounds are used as additive dopants.

[0003] For example, it has been proposed to add an organic sulfonic acid to the solid electrolyte layer of a solid electrolytic capacitor, and a naphthalene compound having a sulfo group, such as sulfonaphthoic acid, sulfonaphthalic acid, or disulfonaphthoic acid, may be used (Patent Documents 1 and 2).

[0004] International Publication No. 2019 / 131476 International Publication No. 2021 / 230013

[0005] When electronic devices using organic conductors are operated in a high-humidity environment, they may experience a decrease in capacitance and an increase in resistance. This is thought to be because, in a high-humidity environment, water molecules are adsorbed into the organic conductor, causing the dopant to be stripped from the conjugated polymer. Hereinafter, the stripping or desorption of the dopant from the conjugated polymer may be referred to as "dedoping."

[0006] A first aspect of the present disclosure relates to an organic conductor including a conjugated polymer and a dopant, wherein the dopant includes a disulfonaphthalic acid compound or an acid anhydride thereof having a naphthalene ring, two sulfo groups bonded to the naphthalene ring, and two carboxy groups or acid anhydride groups thereof bonded to the naphthalene ring.

[0007] A second aspect of the present disclosure relates to an electrolytic capacitor including an anode body having a dielectric layer on a surface thereof, and a solid electrolyte covering a portion of the dielectric layer, wherein the solid electrolyte includes the organic conductor described above.

[0008] It is possible to provide an organic conductor having excellent moisture resistance and an electrolytic capacitor using the same.

[0009] FIG. 1 is a cross-sectional schematic view of an electrolytic capacitor according to an embodiment of the present disclosure.

[0010] The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

[0011] Technique (1) The organic conductor of the present disclosure includes a conjugated polymer and a dopant. The dopant includes a disulfonaphthalic acid compound or an acid anhydride thereof having a naphthalene ring, two sulfo groups bonded to the naphthalene ring, and two carboxy groups or acid anhydride groups thereof bonded to the naphthalene ring. In this specification, an acid anhydride of a disulfonaphthalic acid compound (more specifically, an acid anhydride in which the two carboxy groups of a sulfonaphthalic acid compound form an acid anhydride group) may also be referred to as a disulfonaphthalic acid compound.

[0012] In the present disclosure, a disulfonaphthalic acid compound (including its acid anhydride) is used as a dopant. It is believed that the use of a disulfonaphthalic acid compound provides a stronger interaction or bonding strength with a conjugated polymer. Therefore, even if an organic conductor adsorbs water molecules in a high-humidity environment, dedoping is suppressed. A decrease in the conductivity of the organic conductor is suppressed. Even when the organic conductor is used in an electrolytic capacitor, high conductivity is maintained in a high-humidity environment, thereby suppressing an increase in the equivalent series resistance (ESR) of the electrolytic capacitor. The rate of change in ESR when an electrolytic capacitor is operated in a high-humidity environment is sometimes simply referred to as ΔESR hereinafter. Therefore, high reliability of the electrolytic capacitor can be ensured even when used in a high-humidity environment. Thus, by using the disulfonaphthalic acid compound as a dopant, excellent moisture resistance of the organic conductor can be ensured. The decrease in conductivity is particularly pronounced in a high-humidity environment at high temperatures. In the present disclosure, high conductivity of the organic conductor can be ensured even when the organic conductor is exposed to a high-temperature and high-humidity environment.

[0013] Disulfonaphthalic acid compounds have two sulfo groups and two carboxy groups or their acid anhydride groups on the naphthalene ring. Therefore, when disulfonaphthalic acid compounds (including acid anhydrides) are used as dopants in electrolytic capacitors, the two sulfo groups and two carboxy groups on the naphthalene ring are thought to easily interact with conjugated polymers. This is thought to reduce the ΔESR when the electrolytic capacitor is operated in a high-humidity environment. Disulfonaphthalic acid compounds have a greater ΔESR reduction effect than other sulfonaphthalenecarboxylic acid compounds (e.g., sulfonaphthoic acid, sulfonaphthalic acid, disulfonaphthoic acid, etc.). Therefore, disulfonaphthalic acid compounds are thought to interact more easily with conjugated polymers than other sulfonaphthalenecarboxylic acid compounds. The same effect can be obtained with the acid anhydrides of disulfonaphthalic acid compounds.

[0014] In the disulfonaphthalic acid compound used in the organic conductor and the organic conductor, the sulfo group is a free (-SO３ H) or anion (-SO ３ － ) or in the form of a salt. In organic conductors, the sulfo group may be contained in a form bonded to or interacting with a conjugated polymer. In electrolytic capacitors, the sulfo group may be contained in a form bonded to or interacting with other components contained in the electrolytic capacitor. In this specification, all of these forms of sulfo groups may be simply referred to as "sulfo group". Similarly, in disulfonaphthalic acid compounds used in organic conductors and organic conductors, the carboxy group may be in the form of a free (-COOH) or an anion (-COO － The two carboxy groups of the disulfonaphthalic acid compound may be present in the form of a single acid anhydride group. In organic conductors, the carboxy groups (including those formed by hydrolysis of acid anhydride groups) may be present in a form bonded to or interacting with a conjugated polymer. In electrolytic capacitors, the carboxy groups (including those formed by hydrolysis of acid anhydride groups) may be present in a form bonded to or interacting with other components of the electrolytic capacitor. In this specification, all of these forms of carboxy groups may be simply referred to as "carboxy groups." For example, a naphthalene compound having at least one sulfo group and at least one acid anhydride group formed by two carboxy groups is also included in the disulfonaphthalic acid compound of the present disclosure. The salt may be a salt of a sulfonic acid or carboxylic acid with either an organic base (such as an organic amine or organic ammonium) or an inorganic base (such as a metal hydroxide or ammonia).

[0015] The ΔESR when an electrolytic capacitor is operated in a high-humidity environment is evaluated by the ΔESR when an accelerated test is performed in a high-temperature, high-humidity environment. The ΔESR is, for example, the ESR before the accelerated test (initial) (= Z ０ ) and the ESR (= Z) after the accelerated test, ΔESR = (Z - Z ０ ) / Z ０The accelerated test is carried out by, for example, leaving the electrolytic capacitor in a high-temperature, high-humidity environment while applying the rated voltage.

[0016] In this specification, a high-humidity environment may have a relative humidity of 70% RH or higher, 80% RH or higher, or 85% RH or higher. The relative humidity of a high-humidity environment is 100% RH or lower. A high temperature in a high-temperature, high-humidity environment may be 40°C or higher, 60°C or higher, 80°C or higher, or 85°C or higher. A high temperature may be 280°C or lower. For example, in a reflow process in a substrate mounting process, an electrolytic capacitor is exposed to temperatures of 220°C or higher and 280°C or lower. Furthermore, electrolytic capacitors are sometimes used in high-temperature environments. In this specification, an accelerated test is performed at a high temperature, such as 85°C, in a high-humidity environment of 85% RH, and the moisture resistance of an organic conductor is evaluated based on the change in ESR (ΔESR) of an electrolytic capacitor using the organic conductor.

[0017] Technique (2) In the technique (1), the naphthalene ring has, for example, a first benzene ring and a second benzene ring fused with the first benzene ring. The disulfonaphthalic acid compound may include a disulfonaphthalic acid compound I in which, of the two sulfo groups and the two carboxy groups, two groups are bonded to the first benzene ring and the remaining two groups are bonded to the second benzene ring. By using the disulfonaphthalic acid compound I as a dopant, the ΔESR can be further reduced when the electrolytic capacitor is operated in a high-humidity environment. The disulfonaphthalic acid compound I is thought to interact more easily with conjugated polymers than other disulfonaphthalic acid compounds.

[0018] Technique (3) In the technique (2), for example, the first benzene ring has carbon atoms at positions 1 to 4 of the naphthalene ring, and the second benzene ring has carbon atoms at positions 5 to 8 of the naphthalene ring. The disulfonaphthalic acid compound I may include a disulfonaphthalic acid compound IA having the two groups at positions 1 and 3, positions 1 and 4, or positions 2 and 3 of the naphthalene ring, respectively, and the remaining two groups at positions 5 and 7, or positions 6 and 8 of the naphthalene ring, respectively. The disulfonaphthalic acid compound IA is included in the disulfonaphthalic acid compound I. By using the disulfonaphthalic acid compound IA as a dopant, the ΔESR can be further reduced when an electrolytic capacitor is operated in a high-humidity environment.

[0019] The carbon positions constituting the naphthalene ring are numbered as shown in the following formula (A): The 1st to 8th positions correspond to the numbers on the naphthalene ring below.

[0020]

[0021] Technique (4) In the technique (2) described above, for example, the first benzene ring has carbon atoms at positions 1 to 4 of the naphthalene ring, and the second benzene ring has carbon atoms at positions 5 to 8 of the naphthalene ring (see formula (A) above). The disulfonaphthalic acid compound I does not necessarily have the two sulfo groups at positions 1 and 2, positions 2 and 3, or positions 1 and 8 of the naphthalene ring simultaneously. Compared with a compound having two sulfo groups at such positions, a compound having two sulfo groups at other positions can further reduce ΔESR when used as a dopant in an electrolytic capacitor operated in a high-humidity environment.

[0022] Technique (5) In the technique (3), the disulfonaphthalic acid compound IA may include a disulfonaphthalic acid compound Ia having the two carboxy groups at the 1- and 4-positions, the 2- and 3-positions, or the 1- and 8-positions of the naphthalene ring, respectively. By using the disulfonaphthalic acid compound Ia as a dopant, the ΔESR can be further reduced when the electrolytic capacitor is operated in a high-humidity environment. The disulfonaphthalic acid compound Ia is included in both the disulfonaphthalic acid compound I and the disulfonaphthalic acid compound IA.

[0023] Technique (6): In any one of the techniques (1) to (5), the conjugated polymer may contain a monomer unit corresponding to a pyrrole compound. The disulfonaphthalic acid compound exhibits a relatively high bonding strength to such a conjugated polymer, and therefore, is likely to suppress undoping.

[0024] Technique (7) The present disclosure also encompasses an electrolytic capacitor. The electrolytic capacitor includes an anode body having a dielectric layer on its surface, and a solid electrolyte covering a portion of the dielectric layer. The solid electrolyte includes the organic conductor described in any one of Techniques (1) to (6) above. Because the organic conductor containing a disulfonaphthalic acid compound exhibits high moisture resistance, the ΔESR can be reduced when the electrolytic capacitor is operated in a high-humidity environment, compared to when other sulfonaphthalene carboxylic acid compounds are used as dopants.

[0025] The organic conductor and electrolytic capacitor of the present disclosure will be described in more detail below, including the above-mentioned techniques (1) to (7), with reference to the drawings as necessary. At least one of the above-mentioned techniques (1) to (7) may be combined with at least one of the elements described below, provided that no technical contradiction exists. Note that the drawings are schematic illustrations, and the ratios of the dimensions (e.g., thickness, length, width, height) of each component may differ from the actual ratios.

[0026] [Organic Conductor] The organic conductor of the present disclosure includes a conjugated polymer and a dopant. (Dopant) (Disulfonaphthalic Acid Compound) In the present disclosure, the dopant includes a disulfonaphthalic acid compound. The disulfonaphthalic acid compound has a naphthalene ring, two sulfo groups bonded to the naphthalene ring, and two carboxy groups bonded to the naphthalene ring. The high electron acceptor function of the disulfonaphthalic acid compound contributes to the high conductivity of the organic conductor. Furthermore, using a disulfonaphthalic acid compound as a dopant can suppress an increase in ΔESR when an electrolytic capacitor is operated in a high-humidity environment. This is thought to be because the disulfonaphthalic acid compound interacts or bonds more strongly with the conjugated polymer than other sulfonaphthalene carboxylic acid compounds, thereby suppressing undoping in a high-humidity environment.

[0027] The disulfonaphthalic acid compound may have a first substituent other than a sulfo group or a carboxy group on the naphthalene ring. Compounds having a first substituent are also encompassed in the disulfonaphthalic acid compound of the present disclosure. The first substituent may be an electron-donating group, an electron-withdrawing group other than a sulfo group or a carboxy group, or the like. However, from the viewpoints of easily exhibiting a higher electron acceptor function and easily coordinating to a conjugated polymer depending on the balance of the sulfo group and the carboxy group, a hydroxy group or an aliphatic hydrocarbon group is preferred as the first substituent. The carbon number of the aliphatic hydrocarbon group is, for example, 1 to 10, or may be 1 to 6 or 1 to 4. The aliphatic hydrocarbon group may be either saturated or unsaturated. Examples of the aliphatic hydrocarbon group include an alkyl group, an alkenyl group, an alkynyl group, and a dienyl group. Of these, an alkyl group is preferred. Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a hexyl group, an octyl group, and a 2-ethylhexyl group. The disulfonaphthalic acid compound may have one first substituent, or may have two or more first substituents. When the additive has two or more first substituents, at least two of the first substituents may be the same, or all of the first substituents may be different.

[0028] From the viewpoint that a higher electron acceptor function is likely to be exhibited due to the balance between the sulfo group and the carboxy group, it is also preferable that the disulfonaphthalic acid compound does not have a first substituent.

[0029] The naphthalene ring has a structure in which two benzene rings are fused. In this specification, the two benzene rings constituting the naphthalene ring may be referred to as the first benzene ring and the second benzene ring, respectively. The benzene ring having the carbon atoms at positions 1 to 4 of the naphthalene ring may be referred to as the first benzene ring, and the benzene ring having the carbon atoms at positions 5 to 8 of the naphthalene ring may be referred to as the second benzene ring. The positions of the carbon atoms in the naphthalene ring are shown in formula (A) as described above.

[0030] The positions of the sulfo group and the carboxy group are thought to affect the ΔESR when the electrolytic capacitor is operated in a high-humidity environment. From this perspective, the disulfonaphthalic acid compound preferably includes a disulfonaphthalic acid compound I in which, of the two sulfo groups and two carboxy groups, two groups are bonded to the first benzene ring and the remaining two groups are bonded to the second benzene ring. The disulfonaphthalic acid compound I is represented by the following formula (I). The disulfonaphthalic acid compound I also includes compounds in which the two carboxy groups form an acid anhydride group.

[0031] (In the formula, Y １ ~Y ４ Each of Y is a sulfo group or a carboxy group. １ ~Y ４ Two of them are sulfo groups and the remaining two are carboxy groups.)

[0032] The disulfonaphthalic acid compound I preferably contains a disulfonaphthalic acid compound IA (including an acid anhydride) having the above two groups at the 1- and 3-positions, the 1- and 4-positions, or the 2- and 3-positions, respectively, of the naphthalene ring, and the remaining two groups at the 5- and 7-positions, or the 6- and 8-positions, respectively, of the naphthalene ring. Furthermore, the disulfonaphthalic acid compound I preferably has two of the two sulfo groups and two carboxy groups at the m-positions on at least one of the first and second benzene rings. In these cases, the increase in ΔESR when the electrolytic capacitor is operated in a high-humidity environment can be further suppressed.

[0033] The disulfonaphthalic acid compound IA is represented, for example, by the following formula:

[0034] (In the formula, Y １ ~Y ４ Each of Y is a sulfo group or a carboxy group. １ ~Y ４ Two of the groups are sulfo groups and the remaining two are carboxy groups. １ ~Y ４ Depending on the type of compound (IA-c), compound (IA-d) may be the same as compound (IA-e), and compound (IA-f) may be the same as compound (IA-f).

[0035] In the disulfonaphthalic acid compound IA, when two carboxy groups are adjacent to each other, they may form one acid anhydride group. For example, when a disulfonaphthalic acid compound has carboxy groups at the 2- and 3-positions, the acid anhydride formed by these carboxy groups is included in the disulfonaphthalic acid compound IA. Furthermore, when a disulfonaphthalic acid compound has carboxy groups at the 1- and 8-positions, the acid anhydride formed by these carboxy groups is included in the disulfonaphthalic acid compound IA.

[0036] The disulfonaphthalic acid compound IA preferably includes a disulfonaphthalic acid compound Ia (including an acid anhydride) having two carboxy groups at the 1st and 4th positions, the 2nd and 3rd positions, or the 1st and 8th positions of the naphthalene ring. Use of the disulfonaphthalic acid compound Ia can further suppress an increase in ΔESR when the electrolytic capacitor is operated in a high-humidity environment.

[0037] Specific examples of the disulfonaphthalic acid compound Ia include compounds represented by the following formulas: From the viewpoint of further suppressing an increase in ΔESR, compounds represented by formula (Ia-b1), formula (Ia-b2), formula (Ia-c), formula (Ia-d), and formula (Ia-e) are preferred.

[0038]

[0039] The disulfonaphthalic acid compound also includes compounds having the above-mentioned first substituent in these formulas. Compounds having no first substituent and represented by these formulas are also preferred.

[0040] The organic conductor may contain one type of disulfonaphthalic acid compound or a combination of two or more types.

[0041] The dopant may include a dopant (second dopant) other than the disulfonaphthalic acid compound (first dopant). The second dopant may be a sulfonaphthalene carboxylic acid compound other than the first dopant, or may be other relatively low molecular weight anions, polymeric anions, etc. The organic conductor may include one type of second dopant or a combination of two or more types.

[0042] Examples of anions include sulfate ions, nitrate ions, phosphate ions, borate ions, organic sulfonate ions, and carboxylate ions. Compounds that generate these anions are used as the second dopant. Examples of dopants that generate sulfonate ions include aromatic sulfonic acid compounds (such as paratoluenesulfonic acid and naphthalenesulfonic acid).

[0043] Examples of polymeric anions include polyvinyl sulfonic acid, polystyrene sulfonic acid (PSS), polyallylsulfonic acid, polyacrylic sulfonic acid, polymethacrylic sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, polyester sulfonic acid (such as aromatic polyester sulfonic acid), phenolsulfonic acid novolac resin, and polyacrylic acid. The polymeric anion may be a polymer of a single monomer, a copolymer of two or more types of monomers, or a substituted product having a substituent.

[0044] However, these second dopants are merely examples and are not limited to these. The second dopants may be used alone or in combination of two or more.

[0045] The proportion of the disulfonaphthalic acid compound (first dopant) in the entire dopant of the organic conductor may be 50% by mass or more, 75% by mass or more, or 90% by mass or more. When the proportion of the disulfonaphthalic acid compound in the entire dopant is this high, it is advantageous for the disulfonaphthalic acid compound to further suppress an increase in ΔESR. The proportion of the disulfonaphthalic acid compound in the entire dopant of the organic conductor is 100% by mass or less. The dopant of the organic conductor may be composed solely of the disulfonaphthalic acid compound.

[0046] From the viewpoint of further suppressing an increase in ΔESR, the proportion of disulfonaphthalic acid compound I in the entire disulfonaphthalic acid compound may be 50% by mass or more, 75% by mass or more, or 90% by mass or more. The proportion of disulfonaphthalic acid compound I in the disulfonaphthalic acid compound is 100% by mass or less. The disulfonaphthalic acid compound may be composed solely of disulfonaphthalic acid compound I. From the same viewpoint, the proportion of disulfonaphthalic acid compound IA or disulfonaphthalic acid compound Ia in the disulfonaphthalic acid compound (or the total proportion of the compounds represented by each of formulas (Ia-b1), (Ia-b2), (Ia-c), (Ia-d), and (Ia-e)) may be selected from the above range. The disulfonaphthalic acid compound may be composed of only disulfonaphthalic acid compound IA or only disulfonaphthalic acid compound Ia (only compounds selected from the group consisting of compounds represented by formula (Ia-b1), formula (Ia-b2), formula (Ia-c), formula (Ia-d), and formula (Ia-e)).

[0047] Disulfonaphthalic acid compounds have a high bonding strength with conjugated polymers. The interaction energy of disulfonaphthalic acid compounds with conjugated polymers is preferably -15 kcal / mol or less, more preferably -19 kcal / mol or less, and can even be as low as -22 kcal / mol or less. The interaction energy between naphthalenesulfonic acid and polypyrrole is approximately -10 kcal / mol.

[0048] The interaction energy of a disulfonaphthalic acid compound with a conjugated polymer can be calculated by subtracting the potential energies of the disulfonaphthalic acid compound and the conjugated polymer when they exist alone from the potential energy of the complex of the disulfonaphthalic acid compound and the conjugated polymer. Each potential energy can be calculated from the Schrodinger equation using quantum chemistry calculation software (Gaussian09, manufactured by Gaussian).

[0049] A commercially available disulfonaphthalic acid compound may be used. The disulfonaphthalic acid compound may also be produced by a known method or a modified method thereof. For example, two sulfo groups may be introduced into a naphthalene compound having two carboxy groups (a naphthalic acid compound or its acid anhydride) by electrophilic substitution reaction using concentrated sulfuric acid, fuming sulfuric acid, chlorosulfuric acid, or the like. The carboxy groups may be protected with a protecting group, if necessary. Alternatively, the reaction mixture after the introduction of the sulfo groups may be neutralized to produce a salt, which may then be extracted with an organic solvent and converted into a proton by ion exchange, thereby recovering the sulfonaphthalic acid compound. Alternatively, the disulfonaphthalic acid compound may be produced by converting the amino group of a naphthalene compound having a sulfo group and an amino group into a carboxy group.

[0050] (Conjugated Polymer) The conjugated polymer may be any polymer that becomes a good conductor by the action of a dopant, and examples thereof include π-conjugated polymers and σ-conjugated polymers. The organic conductor may contain one type of conjugated polymer or two or more types of conjugated polymers.

[0051] Conjugated polymers include polymers having a basic skeleton such as polypyrrole, polythiophene, polyaniline, polyfuran, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, or polythiophene vinylene. These polymers include homopolymers, copolymers of two or more monomers, and derivatives thereof (e.g., substituted products having substituent groups). For example, polythiophenes include poly(3,4-ethylenedioxythiophene).

[0052] Among conjugated polymers, conjugated polymers containing a monomer unit corresponding to a pyrrole compound are preferred. Combining such a conjugated polymer with the first dopant mentioned above tends to achieve a higher bonding strength. Examples of pyrrole compounds include pyrrole, compounds in which an aliphatic ring or heterocycle is condensed with pyrrole, and substituted derivatives thereof (e.g., compounds having a substituent). Examples of the substituent include alkyl groups (including aminoalkyl groups and hydroxyalkyl groups), amino groups, substituted amino groups, alkoxy groups, hydroxy groups, mercapto groups, and halogen atoms. The pyrrole or condensed compound may contain one or more of these substituents. The conjugated polymer preferably has a repeating structure of a monomer unit corresponding to the pyrrole compound.

[0053] The weight average molecular weight (Mw) of the conjugated polymer is not particularly limited, but is, for example, 1,000 or more and 1,000,000 or less.

[0054] In this specification, the weight average molecular weight (Mw) is a value calculated as polystyrene as measured by gel permeation chromatography (GPC). GPC is usually performed using a polystyrene gel column and water / methanol (volume ratio 8 / 2) as the mobile phase.

[0055] The amount of the dopant is, for example, 0.1 parts by mass or more and 400 parts by mass or less, or may be 1 part by mass or more and 350 parts by mass or less, or may be 10 parts by mass or more and 300 parts by mass or less, relative to 100 parts by mass of the conjugated polymer.

[0056] Such organic conductors are highly reliable because they can suppress an increase in resistance even in high-humidity environments, making them suitable for use in a variety of electronic devices, particularly as solid electrolytes in electrolytic capacitors.

[0057] [Electrolytic Capacitor] The electrolytic capacitor includes an anode body having a dielectric layer on its surface and a solid electrolyte covering a portion of the dielectric layer. The solid electrolyte includes the organic conductor described above. The solid electrolyte constitutes a cathode portion of the electrolytic capacitor.

[0058] (Anode Body) The anode body can contain a valve metal, an alloy containing a valve metal, a compound containing a valve metal, or the like. These materials can be used alone or in combination of two or more. Examples of preferred valve metals include aluminum, tantalum, niobium, and titanium. Anode bodies with porous surfaces can be obtained by roughening the surface of a substrate (such as a foil-shaped or plate-shaped substrate) containing a valve metal, for example, by etching. The anode body can also be a compact of particles containing a valve metal, or a sintered body thereof. The sintered body has a porous structure.

[0059] (Dielectric Layer) The dielectric layer is formed by anodizing the valve metal on the surface of the anode body by chemical conversion treatment or the like. The dielectric layer is formed, for example, so as to cover at least a portion of the anode body. The dielectric layer is usually formed on the surface of the anode body. Since the dielectric layer is formed on the surface of a porous anode body, it is formed along the inner wall surfaces of holes and depressions (pits) on the surface of the anode body (including the inner wall surfaces of the holes).

[0060] The dielectric layer contains an oxide of the valve metal. For example, when tantalum is used as the valve metal, the dielectric layer contains Ta. ２ O ５ When aluminum is used as the valve metal, the dielectric layer contains Al ２ O ３ The dielectric layer is not limited to this, and may be a layer that functions as a dielectric.

[0061] (Cathode Section) The cathode section includes at least a solid electrolyte covering at least a part of the dielectric layer. The cathode section usually includes a solid electrolyte and a cathode extraction layer covering at least a part of the solid electrolyte.

[0062] (Solid Electrolyte) The solid electrolyte contains the organic conductor and is formed to cover the dielectric layer. The solid electrolyte does not necessarily have to cover the entire dielectric layer (entire surface). The solid electrolyte layer may be formed to cover at least a portion of the dielectric layer. In the electrolytic capacitor, the solid electrolyte may form a solid electrolyte layer.

[0063] The solid electrolyte may contain other additives, such as known additives other than dopants and known conductive materials other than organic conductors (e.g., conductive inorganic materials such as manganese dioxide).

[0064] The solid electrolyte can be formed, for example, by performing at least one of chemical polymerization and electrolytic polymerization of constituent monomers of a conjugated polymer on a dielectric layer in the presence of the additive. Alternatively, a solution in which the conjugated polymer and the additive are dissolved, or a dispersion in which the conjugated polymer and the additive are dispersed, can be brought into contact with the dielectric layer to form a solid electrolyte covering the dielectric layer. After the solution or dispersion is brought into contact with the dielectric layer, drying or heat treatment may be performed as necessary.

[0065] The solid electrolyte layer may be a single layer or may be composed of multiple layers. When the solid electrolyte layer is composed of multiple layers, the compositions of the layers (e.g., the type of conjugated polymer, the type of dopant or additive, and the ratio of each component) may be the same or different. If necessary, a layer for improving adhesion may be interposed between the dielectric layer and the solid electrolyte.

[0066] (Cathode Extraction Layer) The cathode extraction layer may include, for example, one or more conductive particle-containing layers, or may include a metal foil (cathode foil). The conductive particle-containing layer may include, for example, conductive particles (metal particles, conductive carbon particles, etc.) and a binder resin. The binder resin may be a thermoplastic resin or composition, or a curable resin composition. For example, the cathode extraction layer may be formed by a layer containing conductive carbon particles (e.g., a carbon layer) and a metal particle-containing layer covering the layer. The metal particles contained in the metal particle-containing layer may be formed of, for example, silver, copper, or an alloy thereof. The cathode extraction layer may be a metal foil coated with particles (e.g., non-metal particles such as carbon particles, metal particles, etc.). The configuration of the cathode extraction layer is not limited to these, and may also have a current-collecting function.

[0067] (Separator) When a metal foil is used for the cathode extraction layer, a separator may be disposed between the metal foil (cathode foil) and the anode body (e.g., anode foil). The separator is not particularly limited, and may be, for example, a nonwoven fabric containing fibers of cellulose, polyethylene terephthalate, vinylon, or polyamide (e.g., aliphatic polyamide, aromatic polyamide such as aramid). In this case, the separator may be impregnated with an organic conductor. In this case, the organic conductor is interposed between the anode foil having a dielectric layer and the cathode foil, and is in contact with each of the anode foil and the cathode foil.

[0068] (Other) For example, an electrolytic capacitor can be obtained by housing a capacitor element including an anode body and a cathode portion in a container or sealing it with an exterior body (such as a resin exterior body). The electrolytic capacitor may be either a chip type or a stacked type, or may be a wound type. The electrolytic capacitor may include at least one capacitor element, or may include two or more. The configuration of the capacitor element may be selected depending on the type of electrolytic capacitor. For example, the electrolytic capacitor may include a stack of two or more capacitor elements, or may include two or more wound-type capacitor elements. The configuration or number of capacitor elements may be selected depending on the type or application of the electrolytic capacitor.

[0069] In the capacitor element, one end of the cathode lead is electrically connected to the cathode extraction layer. One end of the anode lead is electrically connected to the anode body. The other end of the anode lead and the other end of the cathode lead are each drawn out from the exterior body or the container. The other end of each lead exposed from the exterior body or the container is used for soldering to a substrate on which the electrolytic capacitor is to be mounted. Each lead may be a lead wire or a lead frame. The container may have any shape as long as it can accommodate the capacitor element inside. The opening of the container is sealed, for example, with a sealing body while the capacitor element is housed inside.

[0070] FIG. 1 is a cross-sectional view schematically illustrating the structure of an electrolytic capacitor according to an embodiment of the present disclosure. As shown in FIG. 1 , the electrolytic capacitor 1 includes a capacitor element 2, a resin encapsulant 3 that encapsulates the capacitor element 2, and an anode terminal 4 and a cathode terminal 5, at least a portion of which is exposed outside the resin encapsulant 3. The anode terminal 4 and the cathode terminal 5 may be made of a metal such as copper or a copper alloy. The resin encapsulant 3 has a substantially rectangular parallelepiped outer shape, and the electrolytic capacitor 1 also has a substantially rectangular parallelepiped outer shape. The resin encapsulant 3 may be made of, for example, epoxy resin.

[0071] Capacitor element 2 includes an anode body 6, a dielectric layer 7 covering anode body 6, and a cathode portion 8 covering dielectric layer 7. Cathode portion 8 includes a solid electrolyte layer 9 covering dielectric layer 7, and a cathode extraction layer 10 covering solid electrolyte layer 9. Cathode extraction layer 10 has a carbon layer 11 and a metal particle-containing layer 12.

[0072] The anode body 6 includes a region facing the cathode portion 8 and a region not facing the cathode portion 8. Of the region of the anode body 6 not facing the cathode portion 8, an insulating separation layer 13 is formed in a strip-like shape on the surface of the anode body 6 in a portion adjacent to the cathode portion 8, thereby restricting contact between the cathode portion 8 and the anode body 6. Of the region of the anode body 6 not facing the cathode portion 8, another part is electrically connected to the anode terminal 4 by welding. The cathode terminal 5 is electrically connected to the cathode portion 8 via an adhesive layer 14 formed of a conductive adhesive.

[0073] The main surfaces 4S and 5S of the anode terminal 4 and the cathode terminal 5 are exposed from the same surface of the resin sealing material 3. These exposed surfaces are used for soldering to a substrate (not shown) on which the electrolytic capacitor 1 is to be mounted.

[0074] [Examples] Hereinafter, the present disclosure will be specifically described based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0075] Examples 1 to 3 (1) Synthesis of Disulfonaphthalic Acid Compound 3,6-Disulfo-1,8-naphthalic acid was produced from 1,8-naphthalic acid according to the following procedure. 0.17 mol of 1,8-naphthalic acid was added to 100 mL of fuming sulfuric acid (sulfur trioxide content: 30% by mass), and the resulting mixture was stirred at 130°C for 9 hours for sulfonation. The resulting reaction mixture was cooled to approximately -20°C using an ice bath. The cooled reaction mixture was diluted by pouring it onto ice made with ion-exchanged water.

[0076] The diluted mixture (first mixture) was neutralized by adding a 5 mol / L aqueous sodium hydroxide solution until the pH of the resulting mixture reached 9.

[0077] The neutralized mixture (second mixture) was vacuum dried at 80° C. to remove volatile components such as water, thereby obtaining a solid content containing a sulfonaphthalenecarboxylic acid compound.

[0078] The solid matter recovered above was subjected to an extraction treatment using methanol. More specifically, 2 L of methanol was added to the solid matter. The resulting mixture was heated to 45°C and then stirred for 10 minutes. The mixture was filtered, and the filtrate and the liquid obtained by washing the solid matter with methanol were combined and vacuum dried to recover the solid matter.

[0079] 10 g of the obtained solid was dissolved in 350 mL of ion-exchanged water. The obtained aqueous solution was purified by ion exchange. The ion exchange was carried out by filling a glass tube with a cation exchange resin that converts metal ions into protons and passing the aqueous solution through the cation exchange resin. The aqueous solution obtained by ion exchange was dried in vacuo to obtain 3,6-disulfo-1,8-naphthalic acid as a solid. 3,6-disulfo-1,8-naphthalic acid (A1) is a compound of the above formula (Ia-b1).

[0080] (2) Fabrication of Electrolytic Capacitor Electrolytic capacitor 1 shown in Fig. 1 was fabricated in the following manner, and its characteristics were evaluated. (a) Step of Preparing Anode Body 6 Anode body 6 was fabricated by roughening the surface of aluminum foil (thickness: 100 µm) as a substrate by etching.

[0081] (b) Step of forming dielectric layer 7 Anode body 6 was immersed in a phosphoric acid solution with a concentration of 0.3 mass % at a temperature of 70°C, and a direct current voltage of 70 V was applied for 20 minutes, thereby forming dielectric layer 7 containing aluminum oxide.

[0082] (c) Step of forming solid electrolyte layer 9 A solid electrolyte layer 9 containing polypyrrole and each of the additives (dopants) (A1) to (A3) as dopants was formed on the dielectric layer 7 by electrolytic polymerization according to the following procedure.

[0083] First, aqueous solutions containing pyrrole monomer and each of additives (A1) to (A3) were prepared. The pyrrole monomer concentration in the aqueous solution was 0.5 mol / L, and the additive concentration was 0.3 mol / L. Sulfuric acid was added to the aqueous solution to adjust the pH to 3.0.

[0084] Anode body 6 on which dielectric layer 7 was formed in (b) above and a counter electrode were immersed in the obtained aqueous solution, and electrolytic polymerization was performed at 25° C. and a polymerization voltage of 3 V, thereby forming solid electrolyte layer 9.

[0085] (d) Step of forming cathode extraction layer 10: A dispersion of graphite particles dispersed in water was applied to the surface of solid electrolyte layer 9 obtained in (c) above, and the applied dispersion was dried in the air to form carbon layer 11. Next, a silver paste containing silver particles and an epoxy resin was applied to the surface of carbon layer 11, and heated to form metal particle-containing layer 12. In this way, cathode extraction layer 10 composed of carbon layer 11 and metal particle-containing layer 12 was formed. In this way, capacitor element 2 was produced.

[0086] (e) Assembling the Electrolytic Capacitor The cathode extraction layer 10 of the capacitor element 2 obtained in (d) above was joined to one end of the cathode terminal 5 with a conductive adhesive. One end of the anode body 6 protruding from the capacitor element 2 was joined to one end of the anode terminal 4 by laser welding. Next, a resin sealing material 3 made of an insulating resin was formed around the periphery of the capacitor element 2. At this time, the other end of the anode terminal 4 and the other end of the cathode terminal 5 were extended from the resin sealing material 3. In this way, an electrolytic capacitor 1 with a rated voltage of 2 V and a capacitance of 30 μF was completed.

[0087] (3) Evaluation The following evaluations were made for the electrolytic capacitors or additives. (a) ΔESR The ESR of the electrolytic capacitors was evaluated before and after the accelerated test using the following procedure. In an environment of 20°C, the initial ESR (=Z ０ ) (mΩ) was measured. An accelerated test was performed by applying a rated voltage to the electrolytic capacitor for 125 hours in an environment of 85°C and 85% RH. After the accelerated test, the ESR (= Z) (mΩ) of the electrolytic capacitor was measured in an environment of 20°C using the same procedure as for the initial ESR. ΔESR = (Z - Z ０ ) / Z ０ The rate of change in a high humidity environment, ΔESR, was calculated by the above method.

[0088] (b) Interaction Energy The interaction energy between the additive and polypyrrole was calculated using the procedure described above.

[0089] Example 2 5,7-disulfo-1,4-naphthalic acid (A2) was produced in the same manner as in Example 1, except that 1,4-naphthalic acid was used instead of 1,8-naphthalic acid. Then, an electrolytic capacitor was produced and evaluated in the same manner as in Example 1, except that the resulting 5,7-disulfo-1,4-naphthalic acid was used as a dopant. 5,7-disulfo-1,4-naphthalic acid (A2) is a compound represented by the above formula (Ia-c).

[0090] Comparative Example 1 An electrolytic capacitor was produced and evaluated in the same manner as in Example 1, except that naphthalenesulfonic acid (B1) was used instead of compound (A1).

[0091] Comparative Examples 2 and 3 Electrolytic capacitors were produced and evaluated in the same manner as in Example 1, except that 3,6-disulfo-1-naphthoic acid (B2, Comparative Example 2) or 4,8-disulfo-2-naphthoic acid (B3, Comparative Example 3) was used instead of compound (A1). Compounds (B2) and (B3) were synthesized in the same manner as in Example 1 using 1-naphthoic acid or 2-naphthoic acid, respectively, as the raw material.

[0092] Example 3 5,7-disulfo-2,3-naphthalic acid (A3) was produced in the same manner as in Example 1, except that 2,3-naphthalic acid was used instead of 1,8-naphthalic acid. Then, an electrolytic capacitor was produced and evaluated in the same manner as in Example 1, except that the obtained 5,7-disulfo-2,3-naphthalic acid was used as a dopant. 5,7-disulfo-2,3-naphthalic acid (A3) is a compound represented by the above formula (Ia-e).

[0093] The evaluation results of the Examples and Comparative Examples are shown in Tables 1 and 2. In the tables, E1 to E3 represent Examples 1 to 3, respectively, and C1 to C3 represent Comparative Examples 1 to 3, respectively.

[0094]

[0095] As shown in Table 1, compounds E1 and E2, which use disulfonaphthalic acid compounds A1 and A2, show a significantly reduced increase in ESR change rate (ΔESR) under high humidity conditions compared to compounds C1, which uses naphthalenesulfonic acid, and compounds C2, which uses 3,6-disulfo-1-naphthoic acid B1. Compared to compounds C2, compounds E2 have a reduced ΔESR of 1 / 10 or less, and compounds E3 have a reduced ΔESR of 1 / 100 or less. Compounds A1, A2, and B1 all have a carboxy group at position 1 of the naphthalene ring.

[0096]

[0097] As shown in Table 2, E3, which uses disulfonaphthalic acid compound A3, exhibits a significantly reduced increase in the ESR change rate under high humidity conditions compared to C1, which uses naphthalenesulfonic acid, and C3, which uses 4,8-disulfo-2-naphthoic acid B3. Compared to C3, E3's ΔESR is reduced to 1 / 20 or less. Both compounds A3 and B3 have a carboxy group at the 2-position of the naphthalene ring.

[0098] The smaller the interaction energy between the additive and the conjugated polymer, the smaller the ΔESR. From this, it is thought that in E1 to E3, a high bonding strength was obtained between the additive and the conjugated polymer, which suppressed an increase in the resistance of the solid electrolyte layer even in a high-humidity environment, and therefore suppressed an increase in ΔESR.

[0099] While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention.

[0100] According to the present disclosure, an organic conductor having high moisture resistance can be provided. By using the organic conductor in various electronic devices such as electrolytic capacitors, the quality of the products can be stabilized even in high-humidity environments.

[0101] 1: Electrolytic capacitor 2: Capacitor element 3: Resin sealant 4: Anode terminal 4S: Main surface of anode terminal 5: Cathode terminal 5S: Main surface of cathode terminal 6: Anode body 7: Dielectric layer 8: Cathode portion 9: Solid electrolyte layer 10: Cathode extraction layer 11: Carbon layer 12: Metal particle-containing layer 13: Separation layer 14: Adhesive layer

Claims

1. An organic conductor comprising a conjugated polymer and a dopant, wherein the dopant comprises a disulfonaphthalic acid compound or an acid anhydride thereof having a naphthalene ring, two sulfo groups bonded to the naphthalene ring, and two carboxy groups or acid anhydride groups thereof bonded to the naphthalene ring.

2. The organic conductor according to claim 1, wherein the naphthalene ring has a first benzene ring and a second benzene ring condensed with the first benzene ring, and the disulfonaphthalic acid compound includes disulfonaphthalic acid compound I in which, of the two sulfo groups and the two carboxy groups, two groups are bonded to the first benzene ring and the remaining two groups are bonded to the second benzene ring.

3. The organic conductor according to claim 2, wherein the first benzene ring has carbon atoms at positions 1 to 4 of the naphthalene ring, the second benzene ring has carbon atoms at positions 5 to 8 of the naphthalene ring, and the disulfonaphthalic acid compound I includes disulfonaphthalic acid compound IA having the two groups at positions 1 and 3, 1 and 4, or 2 and 3 of the naphthalene ring, respectively, and the remaining two groups at positions 5 and 7, or 6 and 8 of the naphthalene ring, respectively.

4. The organic conductor according to claim 2, wherein the first benzene ring has carbon atoms at positions 1 to 4 of the naphthalene ring, the second benzene ring has carbon atoms at positions 5 to 8 of the naphthalene ring, and the disulfonaphthalic acid compound I does not simultaneously have the two sulfo groups at positions 1 and 2, positions 2 and 3, or positions 1 and 8 of the naphthalene ring.

5. The organic conductor according to claim 3, wherein the disulfonaphthalic acid compound IA includes a disulfonaphthalic acid compound Ia having the two carboxy groups at the 1- and 4-positions, the 2- and 3-positions, or the 1- and 8-positions of the naphthalene ring, respectively.

6. The organic conductor according to any one of claims 1 to 5, wherein the conjugated polymer contains a monomer unit corresponding to a pyrrole compound.

7. An electrolytic capacitor comprising an anode body having a dielectric layer on its surface, and a solid electrolyte covering a portion of the dielectric layer, wherein the solid electrolyte comprises the organic conductor according to any one of claims 1 to 5.

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