JP4462505B2 - Solid electrolytic capacitor - Google Patents

Description

  The present invention relates to a solid electrolytic capacitor having a good electrostatic capacity.

  Electrolytic capacitors that use metals with valve action such as tantalum, aluminum, niobium, etc., expand the dielectric by making the valve action metal as the anode-side counter electrode into the shape of a sintered body or etching foil, etc. Therefore, a large capacity can be obtained with a small size, so that 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, electronic information devices have been digitized, and the driving frequency of a microprocessor (MPU) which is the heart of these electronic information devices has been increased. Along with this, the power consumption has been increasing and the problem of reliability due to heat generation has become obvious. Therefore, the drive voltage has been reduced as a countermeasure.

  In order to reduce the drive voltage, a DC-DC converter called a voltage control module is widely used as a circuit for supplying highly accurate power to the microprocessor, and the output side capacitor is used to prevent a voltage drop. Many capacitors with low ESR are used. As the capacitor having such a low ESR characteristic, the solid electrolytic capacitor as described above has been put into practical use and widely used.

However, the increase in the driving frequency of the microprocessor is remarkable, and accordingly, the power consumption further increases. In order to cope with this, further increase in the power supplied from the capacitor to prevent the voltage drop is required. That is, it is necessary to be able to supply a large amount of power in a short time, and for this reason, a large capacity is required for the solid electrolytic capacitor.
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 solid electrolytic capacitor capable of improving the capacitance.

The present invention focuses on the relationship between the so-called appearance rate of capacitance and the adhesion between the dielectric oxide film and the solid electrolyte layer. In a solid electrolytic capacitor, the dendritic polymer having a siloxane skeleton on the dielectric oxide film A first polymer layer made of (hereinafter referred to as a dendritic polymer) and a second polymer made of a conductive polymer produced by a polymerization reaction of a polymerizable monomer and an oxidizing agent on the first polymer layer It is characterized by forming a layer.

  In the solid electrolytic capacitor, the first polymer may be bis (dimethylvinylsiloxy) methylsilane, tris (dimethylvinylsiloxy) silane, bis (dimethylallylsiloxy) methylsilane, or tris (dimethylallylsiloxy) silane. From a polymer in which more than one species are mixed, or a polymer in which bis (dimethylsiloxy) methylvinylsilane, tris (dimethylsiloxy) vinylsilane, bis (dimethylsiloxy) methylallylsilane, tris (dimethylsiloxy) allylsilane is used alone or in combination of two or more. It is characterized by being selected.

  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 a dendritic polymer on the dielectric oxide film, the dielectric oxide film and the second polymer layer which is a solid electrolyte Can be firmly adhered to each other through the first polymer layer.

That is, the first polymer layer has a dendritic 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 is made of a conductive polymer as a solid electrolyte layer. As a result, the capacity appearance rate can be improved.

  In general, the adhesion between a dielectric oxide film formed by anodization, which is a dielectric of a solid electrolytic capacitor, and a 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 caused by the difficulty.

Based on these findings, by using a specific branched polymer (dendritic polymer) , both the covalent bond with the hydroxyl group on the surface of the dielectric oxide film and the affinity with the conductive polymer are improved, and the capacity appearance rate is reduced. It has been found that it can be improved.

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 dendritic polymer , specifically, bis (dimethylvinylsiloxy) methylsilane, tris (dimethylvinylsiloxy) silane, bis (dimethylallylsiloxy) methylsilane, tris (dimethylallylsiloxy) silane alone or A polymer in which two or more types are mixed, or a polymer in which bis (dimethylsiloxy) methylvinylsilane, tris (dimethylsiloxy) vinylsilane, bis (dimethylsiloxy) methylallylsilane, tris (dimethylsiloxy) allylsilane is used alone or in combination of two or more types 5 wt% or less, preferably 0.01 to 3 wt%, more preferably 0.1 to 2 wt% of a branched polymer selected from hexane solution, and after lifting, the solvent was evaporated at 40 to 100 ° C. If the concentration is less than this range, the capacity improvement is not sufficient, 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 the 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.

Dendritic polymer
The dendritic polymer can be synthesized, for example, as follows. 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-tetramethyldisiloxanecomplex 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 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.

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.

  Further, 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, this capacitor element was dipped in a 0.01 wt% hexane solution of bis (dimethylvinylsiloxy) methylsilane and pulled up, 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 to form 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 dipped in a 0.1 wt% hexane solution of bis (dimethylvinylsiloxy) methylsilane 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 1.0 wt% hexane solution of bis (dimethylvinylsiloxy) methylsilane 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 a hexane solution of bis (dimethylvinylsiloxy) methylsilane.

  For each example and conventional example obtained by the above method, the electrostatic capacity was examined. The results shown in Table 1 were obtained.

  As is clear from Table 1, in the example, the capacitance increased by about 1.5 to 3.5 times and the ESR also decreased in comparison with the conventional example.

Claims (5)

A first polymer layer made of a dendritic polymer having a siloxane skeleton is formed on the dielectric oxide film, and the conductive material generated by a polymerization reaction between a polymerizable monomer and an oxidizing agent is formed on the first polymer layer. Solid electrolytic capacitor in which a second polymer layer made of a conductive polymer is formed.   A polymer in which the first polymer is bis (dimethylvinylsiloxy) methylsilane, tris (dimethylvinylsiloxy) silane, bis (dimethylallylsiloxy) methylsilane, tris (dimethylallylsiloxy) silane alone or in combination of two or more; Or bis (dimethylsiloxy) methylvinylsilane, tris (dimethylsiloxy) vinylsilane, bis (dimethylsiloxy) methylallylsilane, or tris (dimethylsiloxy) allylsilane alone or in a mixture of two or more. Solid electrolytic capacitor. The solid electrolytic capacitor according to claim 1 or 2, wherein the molecular weight of the first polymer is in the range of 1000 to 80000. 4. The solid electrolytic capacitor according to claim 1, wherein the dielectric oxide film is made of a valve metal oxide selected from aluminum, tantalum, and niobium. 5. 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.