JP2005286251A - Solid-state electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid-state electrolytic capacitor which can improve voltage resistance and shows excellent static electricity capacitance. <P>SOLUTION: On a dielectric material oxide film, a first polymer layer formed in the branching structure having the siloxane framework where at least any of hydroxyl group, dihydroxyl group, and epoxy group is substituted at the end thereof is formed. Moreover, a second polymer layer formed of a conductive polymer generated by polymerization between a polymeric monomer and an oxidizing agent is formed on this first polymer layer. The first polymer layer is formed in the branching structure having the siloxane framework and shows effective common coupling with the hydroxyl group at the surface of the dielectric material oxide film. In addition, this first polymer layer can improve voltage resistance by repairing the dielectric material oxide film through the supply of water content to the dielectric material oxide film from the hydroxyl group at the end thereof. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a solid electrolytic capacitor capable of improving withstand voltage.

  An electrolytic capacitor using a metal having a valve action such as tantalum or aluminum is obtained by expanding the dielectric by making the valve action metal as the anode-side counter electrode into the shape of a sintered body or an etching foil. Since it is small and a large capacity can be obtained, it is widely used. In particular, a solid electrolytic capacitor using a solid electrolyte as an electrolyte has features such as small size, large capacity, low equivalent series resistance, easy to chip, and suitable for surface mounting. It is indispensable for miniaturization, high functionality and low cost of electronic equipment.

  In this type of solid electrolytic capacitor, as a small-sized and large-capacity application, an anode foil and a cathode foil made of a valve metal such as aluminum are generally wound with a separator interposed therebetween to form a capacitor element. It is impregnated with a driving electrolyte, and has a sealed structure in which a capacitor element is housed in a metal case such as aluminum or a case made of synthetic resin. As the anode material, aluminum, tantalum, niobium, titanium and the like are used, and as the cathode material, the same kind of metal as the anode material is used.

  As solid electrolytes used for solid electrolytic capacitors, manganese dioxide and 7,7,8,8-tetracyanoquinodimethane (TCNQ) complexes are known. There is a technique (see Patent Document 1) that focuses on a conductive polymer such as polyethylenedioxythiophene (hereinafter referred to as PEDT) having excellent adhesion to an oxide film layer of an electrode.

  A solid electrolytic capacitor of a type in which a solid electrolyte layer made of a conductive polymer such as PEDT is formed on such a wound capacitor element is manufactured as follows. First, the surface of the anode foil made of valve action metal such as aluminum is roughened by electrochemical etching treatment in an aqueous chloride solution to form many etching pits, and then in an aqueous solution such as ammonium borate. A voltage is applied to form an oxide film layer serving as a dielectric (chemical conversion). Similar to the anode foil, the cathode foil is made of a valve metal such as aluminum, but the surface is only subjected to etching treatment.

Thus, the anode foil having the oxide film layer formed on the surface and the cathode foil having only the etching pits are wound through a separator to form a capacitor element. Subsequently, a polymerizable monomer such as 3,4-ethylenedioxythiophene (hereinafter referred to as EDT) and an oxidizer solution are respectively discharged into the capacitor element subjected to restoration conversion, or immersed in a mixed solution of the two. The polymerization reaction is promoted in the capacitor element, and a solid electrolyte layer made of a conductive polymer such as PEDT is generated. Thereafter, the capacitor element is housed in a bottomed cylindrical outer case, and the opening of the case is sealed with a sealing rubber to produce a solid electrolytic capacitor.
JP-A-2-15611

  By the way, in recent years, the solid electrolytic capacitor as described above has been used for in-vehicle use. Usually, the driving voltage of the on-vehicle circuit is 12V, and the solid electrolytic capacitor is required to have a high withstand voltage of 25V.

  Conventionally, the following method has been used to obtain such a high withstand voltage product. That is, the breakdown voltage has been improved by increasing the foil Vfs up to 16 WV, but it has been difficult to improve the breakdown voltage at 20 W or more because short-circuits frequently occur depending on the shape depending on the foil Vfs. Thus, as a result of studying this point, the present inventors have estimated that this is due to the attack of the oxidizing agent on the foil and the limit of the polymer pressure resistance itself (about 20 V on average). Therefore, we succeeded in commercializing 20W and 25W by changing the mixing ratio of the monomer and oxidant and improving the separator.

However, even if the above method is used, it has been difficult to realize 30 W and 35 W, for which development requirements are increasing in recent years.
Such a problem occurs not only when EDT is used as the polymerizable monomer but also when other thiophene derivatives, pyrrole, aniline, and the like are used.

  The present invention has been proposed to solve the above-described problems of the prior art, and an object of the present invention is to provide a method of manufacturing a solid electrolytic capacitor capable of improving the breakdown voltage.

  The present invention pays attention to the fact that a specific polymer supplies water from a terminal hydroxyl group. In a solid electrolytic capacitor, a dielectric oxide film has a branched structure having a siloxane skeleton, and has a hydroxyl group and dihydroxy at the terminal. And forming a first polymer layer made of a polymer substituted with at least one of an alkyl group and an epoxy group (hereinafter referred to as a branched polymer derivative), and a polymerization reaction between a polymerizable monomer and an oxidizing agent on the first polymer layer. The second polymer layer made of a conductive polymer produced by the above is formed.

  In the solid electrolytic capacitor, the first polymer is a dendritic polymer.

  In the solid electrolytic capacitor, the first polymer may be bis (dimethylvinylsiloxy) methylsilane, tris (dimethylvinylsiloxy) silane, bis (dimethylallylsiloxy) methylsilane, tris (dimethylallylsiloxy) silane alone, or Polymers in which two or more types are mixed, bis (dimethylsiloxy) methylvinylsilane, tris (dimethylsiloxy) vinylsilane, bis (dimethylsiloxy) methylallylsilane, tris (dimethylsiloxy) allylsilane alone or in combination of two or more types It is characterized in that at least one of a hydroxyl group, a dihydroxyl group and an epoxy group is substituted at the terminal of the polymer selected from

  In the solid electrolytic capacitor, the molecular weight of the first polymer is in the range of 1000 to 80000.

  In the solid electrolytic capacitor, the dielectric oxide film is an oxide of a valve metal selected from aluminum, tantalum, and niobium, and the dielectric oxide film is a foil-shaped valve metal, a plate-shaped valve metal, It is characterized in that it is formed on any surface layer of a powder sintered body.

  In the solid electrolytic capacitor, it is preferable that the polymerizable monomer is a thiophene derivative and the thiophene derivative is 3,4-ethylenedioxythiophene.

  As described above, according to the present invention, by forming the first polymer layer made of the branched polymer derivative on the dielectric oxide film, the dielectric oxide film and the second polymer layer that is a solid electrolyte Can be firmly adhered to the dielectric oxide film through the first polymer layer, and water is supplied to the dielectric oxide film from the terminal hydroxyl group of the branched polymer derivative, particularly on the dielectric oxide film side, The breakdown voltage is improved by repairing the dielectric oxide film.

  That is, the first polymer layer is composed of a branched structure having a siloxane skeleton, and therefore, the first polymer layer is efficiently covalently bonded to the hydroxyl group on the surface of the dielectric oxide film, and the second polymer layer composed of a conductive polymer as a solid electrolyte layer. Affinity is improved, and as a result, the capacity appearance rate is improved, and the dielectric oxide film is repaired with moisture supplied from the hydroxyl group, thereby improving the withstand voltage.

  In general, it is said that solid electrolytic capacitors are less self-healing than non-solid electrolytic capacitors. For this reason, it is necessary to take a large conversion voltage / rated voltage ratio. Normally, the formation voltage / rated voltage ratio is about 1.2 to 2 in the case of non-solid aluminum electrolytic capacitors, whereas it is 1.5 to 5 in solid electrolytic capacitors, and this tendency becomes stronger as the rated voltage increases. Become. Therefore, the maximum voltage of the solid electrolytic capacitor is realized only up to about 25V.

  In addition, the adhesion between the dielectric oxide film formed by anodizing, which is a dielectric of a solid electrolytic capacitor, and the conductive polymer is not necessarily strong. The cause is that when the conductive polymer is formed on the dielectric oxide film by chemical polymerization, the oxidizing agent used corrodes the dielectric oxide film, or hydroxyl groups on various metal oxide surfaces that are dielectric oxide films. Is considered to be due to poor affinity with the conductive polymer.

  Normally, when a conductive polymer is formed on a dielectric oxide film formed by anodic oxidation on a valve metal such as etched aluminum, the rate of appearance of the capacity (measured in the capacity / liquid appearing in the conductive polymer) Capacity) is only about 50-80%.

  So far, coating methods such as silane coupling agents, polyvinyl alcohol, and other surfactants have been used to protect or modify the dielectric oxide film, although some capacity appearance rate effects are recognized. , No significant improvement has been seen.

  The molecular structure of normal silane coupling agents, polyvinyl alcohol, and other surfactants is linear or similar, and is distributed almost in parallel to the surface of the dielectric oxide film to modify the surface. This is thought to be due to the difficulty.

  Based on these findings, the use of a specific branched polymer derivative improves both the covalent bond with the hydroxyl group on the surface of the dielectric oxide film and the affinity with the conductive polymer, thereby improving the capacity appearance rate. In addition, moisture is supplied to the dielectric oxide film from the terminal hydroxyl group arranged on the dielectric oxide film side of the branched polymer derivative, and the dielectric oxide film is repaired to improve the breakdown voltage.

Manufacturing Method of Solid Electrolytic Capacitor The manufacturing method of the solid electrolytic capacitor according to the present invention is as follows. That is, an anode foil and a cathode foil having an oxide film layer formed on the surface thereof are wound through a separator to form a capacitor element, and this capacitor element is subjected to restoration conversion.

  Thereafter, this capacitor element is a branched polymer derivative, specifically, bis (dimethylvinylsiloxy) methylsilane, tris (dimethylvinylsiloxy) silane, bis (dimethylallylsiloxy) methylsilane, tris (dimethylallylsiloxy) silane alone, Or a polymer that is a mixture of two or more, bis (dimethylsiloxy) methylvinylsilane, tris (dimethylsiloxy) vinylsilane, bis (dimethylsiloxy) methylallylsilane, tris (dimethylsiloxy) allylsilane alone, or a mixture of two or more 10 wt% or less, preferably 0.01 to 7 wt%, more preferably 10% by weight or less of the branched polymer derivative in which at least one of hydroxyl group, dihydroxyl group, and epoxy group is substituted at the terminal of the polymer selected from the combination. Properly is immersed in 0.3～6Wt% hexane solution, after pulling up, the solvent was evaporated at 40 to 100 ° C.. If the concentration is less than this range, the breakdown voltage is not sufficiently improved, and if it exceeds this range, the capacitance decreases.

  Subsequently, the capacitor element is immersed in a mixed solution of a polymerizable monomer and an oxidizing agent, and a polymerization reaction of a conductive polymer is generated in the capacitor element to form a solid electrolyte layer. And this capacitor | condenser element is accommodated in an exterior case, an opening edge part is sealed with sealing rubber | gum, and a solid electrolytic capacitor is formed.

Branched polymer A branched polymer is compoundable as follows, for example. That is, after a 100 ml three-necked flask equipped with a reflux tube was purged with nitrogen, 2.49 g (0.01 mol) of bis (dimethylvinylsiloxy) methylsilane (1) was dissolved in 50 ml of THF in this flask. Add a few drops of Karstedt catalyst (platinum (0) -1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex 0.1M in xylene) and heat to reflux until the Si-H group disappears completely in the IR spectrum. And cooled to room temperature. After removing the low boiling point solvent and the like with an evaporator, the product was dropped into acetonitrile to obtain a colorless viscous liquid polymer. The yield was 92%. As a result of GPC content measurement using polystyrene as a standard and THF as a developing solvent, the weight average molecular weight was 4,700.

Branched polymer derivative In the branched polymer derivative, at least one of a hydroxyl group, a dihydroxyl group, and an epoxy group is substituted at the terminal, and these may be all or selectively substituted.

EDT and Oxidizing Agent When EDT is used as the polymerizable monomer, EDT monomer can be used as EDT impregnated in the capacitor element, but the volume ratio of EDT and volatile solvent is 1: 0 to 1: 3. A mixed monomer solution can also be used.
Examples of the volatile solvent include hydrocarbons such as pentane, ethers such as tetrahydrofuran, esters such as ethyl formate, ketones such as acetone, alcohols such as methanol, nitrogen compounds such as acetonitrile, and the like. Of these, methanol, ethanol, acetone and the like are preferable.

  As the oxidizing agent, an aqueous solution of ferric paratoluenesulfonate, periodic acid or iodic acid dissolved in ethanol can be used, and the concentration of the oxidizing agent with respect to the solvent is preferably 40 to 65 wt%, and 45 to 57 wt%. % Is more preferable. The higher the oxidant concentration in the solvent, the lower the ESR. As the oxidant solvent, the volatile solvent used in the monomer solution can be used, and ethanol is particularly preferable. Ethanol is suitable as the oxidant solvent because it is easy to evaporate due to its low vapor pressure and the remaining amount is small.

Chemical conversion liquid for restoration chemical conversion Chemical liquid for restoration chemical conversion includes phosphoric acid-based chemical liquids such as ammonium dihydrogen phosphate and diammonium hydrogen phosphate, boric acid-based chemical liquids such as ammonium borate, and ammonium adipate. An adipic acid-based chemical conversion solution can be used, and among these, it is desirable to use ammonium dihydrogen phosphate. The immersion time is preferably 5 to 120 minutes.

Other polymerizable monomers The polymerizable monomers used in the present invention include thiophene derivatives other than EDT, aniline, pyrrole, furan, acetylene or derivatives thereof other than the above EDT, and are oxidatively polymerized with a predetermined oxidizing agent. Any conductive polymer can be applied. As the thiophene derivative, one having the following structural formula can be used.

  Subsequently, the present invention will be described in more detail based on examples and conventional examples manufactured as follows.

An electrode lead means was connected to the anode foil and the cathode foil having an oxide film layer formed on the surface, and both electrode foils were wound through a separator to form a capacitor element. And this capacitor | condenser element was immersed in ammonium dihydrogen phosphate aqueous solution for 40 minutes, and restoration | restoration conversion was performed. Thereafter, the capacitor element was dipped in a 0.05 wt% hexane solution of a derivative in which a hydroxyl group was substituted at the terminal of bis (dimethylvinylsiloxy) methylsilane, and then the solvent was removed by heat treatment.
Subsequently, a 40 wt% butanol solution of EDT and ferric p-toluenesulfonate is poured into a predetermined container so that the weight ratio thereof is 1: 3 to prepare a mixed solution, and the capacitor element is mixed as described above. The capacitor element was impregnated with EDT and an oxidizing agent by dipping in the solution for 10 seconds. Then, this capacitor element was left in a constant temperature bath at 120 ° C. for 1 hour to cause a polymerization reaction of PEDT in the capacitor element, thereby forming a solid electrolyte layer. Then, this capacitor | condenser element was accommodated in the bottomed cylindrical aluminum case, and it sealed with sealing rubber | gum, and formed the solid electrolytic capacitor.

  The capacitor element was immersed in a 0.5 wt% hexane solution of the above bis (dimethylvinylsiloxy) methylsilane derivative and pulled up, and then the solvent was removed by heat treatment. Otherwise, a solid electrolytic capacitor was prepared under the same conditions and steps as in Example 1.

  The capacitor element was dipped in a 5.0 wt% hexane solution of the above bis (dimethylvinylsiloxy) methylsilane derivative and pulled up, and then the solvent was removed by heat treatment. Otherwise, a solid electrolytic capacitor was prepared under the same conditions and steps as in Example 1.

Conventional Example A solid electrolytic capacitor was produced under the same conditions and steps as in Example 1 without immersing the capacitor element in the hexane solution of the bis (dimethylvinylsiloxy) methylsilane derivative.

  For each example and conventional example obtained by the above method, the withstand voltage and capacitance were examined. The results shown in Table 1 were obtained.

  As is apparent from Table 1, in the embodiment, the capacitance increases by about 1.5 times to 3.5 times as compared with the conventional example, and the breakdown voltage is improved by 3% to 30%. It was seen. Furthermore, a significant improvement is seen in the leakage current, and it is understood that the dielectric oxide film is repaired.

Claims (6)

  On the dielectric oxide film, a first polymer layer made of a polymer having a branched structure having a siloxane skeleton and having a terminal substituted with at least one of a hydroxyl group, a dihydroxyl group, and an epoxy group is formed. A solid electrolytic capacitor in which a second polymer layer made of a conductive polymer produced by a polymerization reaction of a polymerizable monomer and an oxidizing agent is formed on a polymer layer.   The solid electrolytic capacitor according to claim 1, wherein the first polymer is a dendritic polymer.   A polymer in which the first polymer is bis (dimethylvinylsiloxy) methylsilane, tris (dimethylvinylsiloxy) silane, bis (dimethylallylsiloxy) methylsilane, tris (dimethylallylsiloxy) silane, or a mixture of two or more. , Bis (dimethylsiloxy) methylvinylsilane, tris (dimethylsiloxy) vinylsilane, bis (dimethylsiloxy) methylallylsilane, tris (dimethylsiloxy) allylsilane alone, or a polymer selected from a mixture of two or more at the end of the polymer 3. The solid electrolytic capacitor according to claim 1, wherein at least any one of a hydroxyl group, a dihydroxyl group, and an epoxy group is substituted.   The solid electrolytic capacitor according to claim 1, wherein the molecular weight of the first polymer is in the range of 1000 to 80000.   5. The solid electrolytic capacitor according to claim 1, wherein the dielectric oxide film is made of an oxide of a valve metal selected from aluminum, tantalum, and niobium.   6. The solid electrolytic capacitor according to claim 1, wherein the dielectric oxide film is formed on a surface layer of any one of a foil-shaped valve metal, a plate-shaped valve metal, and a powder sintered body.