JP4854009B2 - Solid electrolytic capacitor - Google Patents

Description

  The present invention relates to a solid electrolytic capacitor, and more particularly to a solid electrolytic capacitor using a conductive polymer layer as a solid electrolyte with improved reliability.

  In recent years, a dielectric oxide film layer is formed on a porous body of a valve metal such as aluminum by an anodic oxidation method, then a conductive polymer layer is formed on the oxide film layer, and this is used as a solid electrolyte. Capacitors have been developed, and the conductivity of solid electrolytes is 10 to 100 times higher than that of solid electrolytic capacitors using manganese dioxide as a solid electrolyte, and the equivalent series resistance (hereinafter referred to as ESR) can be lowered. Since the characteristics have been greatly improved, it has begun to be used in various electronic devices, particularly for high frequency noise absorption in small devices.

  Further, along with the high density mounting, there is an increasing demand for characteristics of the small size, large capacity and low ESR for this solid electrolytic capacitor.

  In order to synthesize a conductive polymer, 3,4-ethylenedioxythiophene (hereinafter referred to as EDT), pyrrole, aniline, or the like is used as a monomer. When this is used as a solid electrolyte of a capacitor, oxidation is performed. It was formed by chemical oxidation polymerization method (for example, Patent Document 1 etc.) in which a conductive polymer layer is formed by adding an agent and a dopant and reacting on an oxide film layer of a metal porous body, or by the chemical oxidation polymerization method A method of forming a thick conductive polymer layer by using an electropolymerization method with the conductive polymer layer as a base (for example, Patent Document 2) is mainly used. On the other hand, a solution of a soluble conductive polymer is prepared separately without polymerizing the metal porous body on the oxide film layer, and the porous body is impregnated with the polymer solution, followed by drying and coating. There is also a method of forming a conductive polymer layer directly on the oxide film layer (hereinafter referred to as a slurry polymer method) (for example, Patent Document 3).

  In order to actually form a conductive polymer on the anodic oxide film layer of a solid electrolytic capacitor, the surface is roughened (etched), and therefore, from the viewpoint of coverage, ESR, and reliability, When performing oxidative polymerization or the like, it is necessary to control the liquid concentration to form a conductive polymer layer up to the inside of the porous body in order to improve the liquid impregnation property. In addition, regarding the electrolytic polymerization method, it is necessary to correctly select voltage, application time, monomer concentration, solvent, etc., and to fill the details. Furthermore, impregnation is similarly required for the slurry polymer method.

  In order to meet recent demands for lowering ESR, it is necessary to improve the conductivity of the conductive polymer itself. However, regarding the lowering of ESR on the order of several mΩ, an anodized film layer, a chemically oxidized polymer film, and an electrolytic polymer film Alternatively, the adhesiveness of the slurry polymer film (film formed by the slurry polymer method) contributes to contact resistance, and thus has become an important factor. That is, the adhesion between the chemical oxidation polymer film that forms a conductive polymer layer by immersing alternately in the monomer solution and the oxidant / dopant solution ten times or more and the outer slurry polymer film formed thereon, or the inside It was necessary to improve the adhesion between the slurry polymer film formed on the outer side and the outer slurry polymer film. Further, in recent years, a roughening (etching) technique has been developed, so that the pit width becomes nano-order, and impregnation and adhesion are becoming increasingly important.

Japanese Patent No. 3040113 Japanese Patent Publication No. 03-61331 JP 2001-023437 A

  In order to form the conductive polymer layer on the valve action metal anodized film layer, there is the above-mentioned example, but considering the mass productivity, etc., it takes man-hours and costs for the placement of the reference electrode for the electrolytic polymerization method, Not suitable. In consideration of mass productivity, the best method is to apply a slurry polymer film directly on the anodized film layer to form a conductive polymer layer. However, anodization is sufficient to ensure sufficient coverage, ESR, and reliability. It is necessary to form the outer conductive polymer layer with the slurry polymer film after the inner conductive polymer layer is formed on the film layer using chemical oxidative polymerization or a solution of a low molecular weight soluble conductive polymer. is there.

  However, in the conventional method, the adhesion between the chemical oxidation polymer film and the slurry polymer film is poor, and when the reliability evaluation is performed, the chemical oxidation polymer film itself has a resistance value higher than that due to deterioration due to oxidation. Deterioration of ESR occurred due to an increase in the interface resistance between the polymer film and the slurry polymer film. Accordingly, an object of the present invention is to provide a solid electrolytic capacitor in which a conductive polymer layer is formed using a solution of a soluble conductive polymer, and the increase in ESR is suppressed even in reliability evaluation. is there.

The solid electrolytic capacitor of the present invention comprises an anodized film layer formed on the surface of a roughened aluminum substrate, and a conductive polymer layer formed on the anodized film layer, and the conductive polymer in the solid electrolytic capacitor of the layer with the solid electrolyte, the form the inside of the conductive polymer layer on the anodized film layer, aliphatic organic acid aqueous solution having a carboxylic acid group at least two, Fang aromatic sulfonic acid aqueous solution, Alternatively, after immersing and drying in a mixed aqueous solution of the aliphatic organic acid aqueous solution and the aromatic sulfonic acid aqueous solution, a solution of a soluble conductive polymer to which a glycol-based solvent is added is applied and dried to form an outer conductive polymer layer. Is formed.

  In addition, the concentration of the glycol solvent is preferably 1% by weight to 50% by weight, and the aliphatic organic acid is at least one selected from citric acid, adipic acid, dodecanoic acid, sebacic acid, maleic acid, and malonic acid. Preferably, the aromatic sulfonic acid is at least one selected from p-toluenesulfonic acid, dodecylbenzenesulfonic acid, naphthalenesulfonic acid, naphthalene disulfonic acid, and 1,3,6-naphthalenetrisulfonic acid. It is preferable that

  According to the present invention, an outer conductive polymer layer is formed on an inner conductive polymer layer using a solution of a soluble conductive polymer to which a glycol solvent is added, and the inner conductive polymer layer is formed. By improving the adhesion between the outer conductive polymer layer and the outer conductive polymer layer, the thermal degradation of ESR can be reduced, and a solid electrolytic capacitor excellent in reliability can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram for explaining a solid electrolytic capacitor according to an embodiment of the present invention. FIG. 1 (a) is a schematic sectional view, and FIG. 1 (b) is an enlarged sectional view of a portion A in FIG. It is. As shown in FIG. 1, anodic oxidation is performed by forming the surface of a flat aluminum substrate 1 roughened by etching or the like in an aqueous solution containing adipic acid, citric acid, phosphoric acid, or a salt thereof. The coating layer 2 is formed. After that, a resist strip 3 is provided for separating the anode portion 9 at the center and the cathode portions 10 at both ends. The resist strip 3 may be made of a thermosetting resin such as an epoxy resin, or a thermoplastic resin can serve its purpose. Thereafter, the inner conductive polymer layer 4 is formed on the anodized film layer 2 by chemical oxidative polymerization such as polypyrrole or by a slurry polymer method. After that, it is immersed in an aliphatic organic acid aqueous solution having at least two carboxylic acid groups, or an aromatic sulfonic acid aqueous solution, or a mixed aqueous solution of an aliphatic organic acid aqueous solution and an aromatic sulfonic acid aqueous solution, and then dried. The conductive polymer layer 5 is formed by applying and drying a solution of a soluble conductive polymer to which a glycol solvent is added. For example, after mixing and stirring EDT monomer and polystyrene sulfonic acid as a dopant in an aqueous solution as a solution of a soluble conductive polymer to which a glycol-based solvent is added, ammonium peroxodisulfate, potassium peroxodisulfate, etc. are added as oxidizing agents, and 24H to 72H (Time) After continuous stirring, the outer conductive polymer layer 5 is formed by applying and drying an additive containing 1 to 50 wt% of a glycol solvent as an additive. Thereafter, a graphite paste layer 6 and a silver paste layer 7 are sequentially formed to obtain a solid electrolytic capacitor having an anode portion 9 and a cathode portion 10.

  Examples of glycol solvents include ethylene glycol, 1,2-dimethoxyethane, 1,2-diethoxyethane, diethylene glycol, 2- (2-methoxyethoxy) ethanol, 2- (2-ethoxyethoxy) ethanol, and ethylene glycol monomethyl ether. Acetic acid ester, 2-ethoxyethyl acetate, diethylene glycol diacrylate, diethylene glycol monobutyl ether, dimethoxytetraethylene glycol, ethyl triglycol, 2-hydroxyethyl methacrylate, ethylene glycol formate, ethylene glycol acetate, carbitol acetate, butyl carbitol acetate , Polyethylene glycol, diethylene glycol monomethyl ether acetate, triethylene glycol monomethyl Examples include ether, ethylene glycol stearate, and polyethylene glycol stearate.

  Examples of the aliphatic organic acid include adipic acid, dodecanoic acid, sebacine (sebacin) acid, citric acid, maleic acid, and malonic acid. Examples of the aromatic sulfonic acid include p-toluenesulfonic acid, dodecylbenzenesulfonic acid, naphthalenesulfonic acid, naphthalene disulfonic acid, and 1,3,6-naphthalenetrisulfonic acid.

  In the present invention, as an example of a solid electrolytic capacitor in a broad sense, an example in which the cathode portion is formed at the center portion of the aluminum base and the anode portions are formed at both ends is shown. However, the conductive polymer layer is formed on the anodized film layer. And a solid electrolytic capacitor including one anode portion formed on one cathode portion and a portion other than the cathode portion.

  Examples will be described below.

Example 1
After forming a flat aluminum foil in an aqueous solution to form an anodized film layer, an inner conductive polymer layer made of polypyrrole was formed on the anodized film layer by chemical oxidative polymerization. Next, an organic acid and an aromatic sulfonic acid aqueous solution were prepared by sequentially immersing and drying in a citric acid 1 wt% aqueous solution, 1,3,6-naphthalene trisulfonic acid 1.5 wt% aqueous solution, and those not acid-treated. . (Hereinafter, described as having and without acid treatment) After mixing and stirring EDT monomer and polystyrene sulfonic acid as a dopant in an aqueous solution, ammonium peroxodisulfate is added as an oxidizing agent, and continuously stirred for 24H to 72H to obtain a slurry polymer solution. (Solution of soluble conductive polymer) A is synthesized. A slurry polymer solution B is obtained by adding 10 wt% of ethylene glycol thereto. This was coated on the inner conductive polymer layer, each of which was made of a chemical oxidation polymerized film, and dried to form the outer conductive polymer layer. A graphite paste layer and a silver paste layer were sequentially formed thereon to form a solid electrolytic capacitor, and then initial ESR [100 kHz] and ESR [100 kHz] after 125 ° C. and 300 H were measured. The results, that is, the ESR reliability evaluation results are shown in Table 1.

  From this result, there is no change in the initial ESR at any level, but the increase in ESR is large in the case where the glycol-based solvent is not added at high temperature (samples 1 and 3) and the case where the acid treatment is not performed (samples 1 and 2). It can be seen that the adhesion and contact resistance are deteriorated.

(Example 2)
0, 0.5, 1, 5, 10, 20, 30, 40, 50, 80 wt% of ethylene glycol was added to the slurry polymer liquid A used in Example 1, respectively, and an aqueous citric acid solution, 1, 3, 6-, respectively. An acid-treated solution with a naphthalene trisulfonic acid aqueous solution was prepared, and a graphite paste layer and a silver paste layer were sequentially formed thereon to form a solid electrolytic capacitor. Then, initial ESR [100 kHz], ESR after 125 ° C. and 300 H, [100 kHz] Was measured. The results, that is, the results of ethylene glycol addition concentration and ESR reliability evaluation are shown in Table 2.

  From this result, it is understood that the glycol solvent addition concentration is 1 wt% to 50 wt% (samples 13 to 19 are most effective in suppressing the increase in ESR at high temperatures.

(Example 3)
Before forming the outer conductive polymer layer with the slurry polymer liquid B used in Example 1, citric acid, adipic acid, dodecanoic acid, sebacine (sebacin) acid, maleic acid, malon are treated with an acid treatment as an organic acid aqueous solution. Acids each carried out in 3 wt% aqueous solution, p-toluenesulfonic acid (described as p-TS in the table), naphthalenesulfonic acid (described as NS in the table), naphthalene disulfonic acid (referred to as DNS in the table) as an aromatic sulfonic acid aqueous solution Description) 1,3,6-naphthalene trisulfonic acid (described as TNS in the table), dodecylbenzenesulfonic acid (described as DBS in the table), each carried out in a 1.5 wt aqueous solution, and further citric acid 3 wt%, 1, A solution prepared with a mixed aqueous solution of 3,6-naphthalenetrisulfonic acid 1.5 wt% and a solution not subjected to acid treatment were prepared. A phyto paste layer and a silver paste layer were sequentially formed to form a solid electrolytic capacitor, and then initial ESR (100 kHz) and ESR (100 kHz) after 125 ° C. and 300 H were measured. Table 3 shows a comparison result of the ESR change by the result, that is, the organic acid, the aromatic sulfonic acid, and the mixed aqueous solution during the acid treatment.

  From this result, the heat resistance of ESR is improved by immersing in an organic acid aqueous solution or aromatic sulfonic acid aqueous solution, but the most effective effect of the present invention is obtained by immersing in a mixed aqueous solution of organic acid and aromatic sulfonic acid. It turns out that this is the case.

The figure explaining the solid electrolytic capacitor by embodiment of this invention, Fig.1 (a) is a schematic cross section, FIG.1 (b) is an expanded sectional view of A part of Fig.1 (a).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Aluminum base | substrate 2 Anodized film layer 3 Resist strip | belt 4 Inner conductive polymer layer 5 Outer conductive polymer layer 6 Graphite paste layer 7 Silver paste layer 8 Resist printing part (epoxy resin printing part)
9 Anode 10 Cathode

Claims (4)

Solid electrolysis comprising an anodized film layer formed on the surface of a roughened aluminum substrate and a conductive polymer layer formed on the anodized film layer, wherein the conductive polymer layer is a solid electrolyte. in the capacitor, the forming the inner conductive polymer layer on the anodized film layer, aliphatic organic acid aqueous solution having a carboxylic acid group at least two, Fang aromatic sulfonic acid aqueous solution or the aliphatic organic acid aqueous solution, and A solid obtained by immersing and drying in a mixed aqueous solution of the aromatic sulfonic acid aqueous solution, applying a solution of a soluble conductive polymer added with a glycol solvent, and drying to form an outer conductive polymer layer Electrolytic capacitor.   2. The solid electrolytic capacitor according to claim 1, wherein the concentration of the glycol solvent is 1% by weight to 50% by weight.   3. The solid electrolytic capacitor according to claim 1, wherein the aliphatic organic acid is at least one selected from citric acid, adipic acid, dodecanoic acid, sebacic acid, maleic acid, and malonic acid. Electrolytic capacitor.   The solid electrolytic capacitor according to claim 1, wherein the aromatic sulfonic acid is p-toluenesulfonic acid, dodecylbenzenesulfonic acid, naphthalenesulfonic acid, naphthalene disulfonic acid, 1,3,6-naphthalene. A solid electrolytic capacitor characterized in that it is at least one selected from trisulfonic acid.

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