JP4360277B2 - Electrolytic capacitor and manufacturing method thereof - Google Patents

Description

  The present invention relates to an electrolytic capacitor used in various electronic devices and a method for manufacturing the same.

  With the increase in the frequency of electronic devices, there is a demand for a large-capacity electrolytic capacitor that is excellent in equivalent series resistance (hereinafter referred to as ESR) characteristics in the high-frequency region even in an electrolytic capacitor that is an electronic component. Recently, in order to reduce the ESR in this high frequency region, solid electrolytic capacitors using a solid electrolyte such as a conductive polymer with high electrical conductivity have been studied, and in response to the demand for larger capacity. For example, a solid electrolytic capacitor in which a conductive polymer is filled in a capacitor element having a winding structure in which an anode foil and a cathode foil are wound with a separator interposed therebetween has been commercialized.

  In order to avoid contact between the anode foil and the cathode foil, it is essential to interpose a separator in the wound solid electrolytic capacitor. As this separator, an electrolytic capacitor using a conventional driving electrolyte as an electrolyte can be used. The capacitor paper is wound using so-called electrolytic paper made of Manila hemp or kraft paper, and this electrolytic paper is carbonized by heating or the like (hereinafter referred to as carbonized paper), glass fiber nonwoven fabric or vinylon, What has synthetic fiber nonwoven fabrics, such as polyester and polyamide, as a main component is used.

  In addition, the conductive polymer used in the solid electrolyte is represented by a method in which 3,4-ethylenedioxythiophene is polymerized with ferric p-toluenesulfonate. It acts as an oxidant, and the anion component is a poly 3,4-ethylenedioxythiophene chemically oxidatively polymerized by an oxidant and dopant agent acting as a dopant, and chlorinated by pyrrole monomer as an oxidant and dopant agent. Polypyrrole chemically oxidized and polymerized with ferric iron or persulfate is known.

On the other hand, a wound-type electrolytic capacitor using both a solid electrolyte made of a conductive polymer and a driving electrolyte as a cathode lead material has been proposed. As this wound-type electrolytic capacitor, manila paper or kraft is used. Separator paper such as paper, or porous film or synthetic fiber nonwoven fabric separator is made conductive with a conductive polymer chemically polymerized with persulfate as an oxidant and dopant, and this conductive separator and driving electrolyte are used. There have been proposed electrolytic capacitors (for example, Patent Documents 1 and 2), electrolytic capacitors in which a wound capacitor element is impregnated with a conductive polymer and a driving electrolyte (for example, Patent Document 3).
JP-A-1-90517 JP-A-7-249543 Japanese Patent Laid-Open No. 11-186110

  However, in the above conventional wound solid electrolytic capacitor, it is difficult to construct a capacitor with a high withstand voltage because it uses a solid electrolyte such as a conductive polymer with poor repairability of the dielectric oxide film. Only a maximum voltage of about 25 to 32 V can be obtained, and even within this rated voltage range, sudden increase of leakage current or generation of dielectric oxide film defects may occur during use. Since a short circuit failure occurs, there is an inconvenience that the failure rate must be calculated and used.

  In addition, there is a problem that the short-circuit rate during aging is also high in the manufacturing process of the solid electrolytic capacitor, and the manufacturing defect rate is significantly higher than that of the electrolytic capacitor using the driving electrolytic solution. Although there is a tendency to be improved by the use of high density separators or separators having high heat resistance (for example, separators mainly made of polyester resin or aramid resin), conventional electrolytic capacitors using only a driving electrolyte When compared, it is not enough.

  For the purpose of improving these problems, electrolytic capacitors using both a solid electrolyte made of a conductive polymer and a driving electrolyte as a cathode lead material have been proposed. Because it is composed of a conductive polymer that is chemically oxidatively polymerized using persulfate such as ammonium persulfate as an oxidant and dopant agent, persulfate ions that function as dopants can be easily dedoped and eluted into the drive electrolyte. In addition, the conductivity of the conductive polymer is remarkably lowered by dedoping, the thermal stability when the electrolytic capacitor is constructed is poor, and there is a problem that the change with time of ESR in the high frequency region is large.

  In addition, chemical oxidation polymerization of 3,4-ethylenedioxythiophene and the like is performed using a transition metal oxidant / dopant that has an oxidation-reduction action of metal ions such as ferric p-toluenesulfonate which is difficult to be dedoped. There is also known a method for obtaining a solid electrolytic capacitor. However, when an electrolytic capacitor is configured by impregnating a capacitor element of this configuration with a driving electrolyte, residual metal ion components are electrochemically contained in the driving electrolyte. When there is a problem such as dissolution-deposition caused by the reaction, increasing the leakage current of the electrolytic capacitor, and even if the solid electrolytic capacitor is configured without impregnating this driving electrolyte, it is used in a high humidity atmosphere The remaining metal ion component is dissolved and precipitated by an electrochemical reaction in water due to the influence of moisture entering from the sealing portion, and the solid electrolytic capacitor There is a problem, such as increasing the leakage current of the capacitor.

  SUMMARY OF THE INVENTION It is an object of the present invention to provide a low ESR electrolytic capacitor having a high withstand voltage and excellent leakage current stability, and a method for manufacturing the same, in order to solve such conventional problems.

  In order to solve the above problems, the present invention comprises a capacitor element formed by winding an anode foil etched to form a dielectric oxide film and an etched cathode foil with a conductive separator interposed therebetween, In an electrolytic capacitor in which the capacitor element is housed in a metal case together with a driving electrolyte, the conductive separator is made conductive by forming a conductive polymer on a nonwoven fabric separator base material by gas phase polymerization, and The conductivity of the surface layer on at least the surface in contact with the anode foil is smaller than the conductivity of the inner layer.

  In addition, as a method of manufacturing this electrolytic capacitor, a capacitor element is formed by winding an anode foil and a cathode foil with a conductive separator interposed therebetween, and the capacitor element is impregnated with a driving electrolytic solution to form a metal case. And the step of forming the conductive separator impregnates a separator base material made of nonwoven fabric with an oxidant solution, and subsequently the separator base material in a monomer vapor of a conductive polymer. After conducting vapor phase polymerization to attach the conductive polymer to the separator base material, and then cleaning and drying it, surface treatment is performed to make the conductivity of the surface layer of the separator base material smaller than that of the inner layer. It is what I do.

  As described above, according to the present invention, the withstand voltage of the surface layer of the separator is increased by making the conductivity of the surface layer of the conductive separator smaller than that of the inner layer. Since the rate is high, a low ESR electrolytic capacitor can be obtained.

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

  FIG. 1 is a partial cross-sectional perspective view showing the structure of an electrolytic capacitor according to an embodiment of the present invention. In FIG. 1, 9 indicates a capacitor element, and the capacitor element 9 is roughened by etching. An anode foil 1 made of an aluminum foil on which a dielectric oxide film is formed by anodizing treatment, and a cathode foil 2 obtained by etching at least the aluminum foil, and at least a non-transition metal oxidant and an organic acid compound are included in between. It is constituted by winding with a conductive separator 3 coated with a conductive polymer formed by chemical oxidative polymerization of a polymerization monomer in a solution.

  4 and 5 are anode leads and cathode leads for external lead connected to the anode foil 1 and the cathode foil 2, respectively, and 7 is a bottomed cylindrical aluminum housing the capacitor element 9 together with a driving electrolyte not shown. The metal case 6 is a sealing member that has a hole through which the anode lead 4 and the cathode lead 5 are inserted to seal the opening of the metal case 7, and 8 has a hole through which the anode lead 4 and the cathode lead 5 are inserted. A seat plate made of an insulating resin mounted on the side of the sealing member 6, and is a surface mount type by folding the anode lead 4 and the cathode lead 5 along a groove provided on the outer surface of the seat plate 8. This is an electrolytic capacitor.

  The capacitor element 9 may be configured to be impregnated with a driving electrolyte solution in a step before sealing. Although FIG. 1 shows a surface mount type electrolytic capacitor, the present invention is not limited to the surface mount type, and an electrolytic capacitor having a configuration without the seat plate 8 may be used.

  Next, specific examples of the present invention will be described.

(Example 1)
A separator base material (base material thickness 50 μm, weight 25 g / m ² ) made of nonwoven fabric obtained by a spunbond method using aromatic polyamide resin mainly composed of polyparaphenylene terephthalamide as ammonium persulfate It was immersed in a mixed solvent of water and ethanol (hereinafter referred to as oxidizer solution A) containing 2-naphthalenesulfonic acid (concentration 5 wt%) which is an organic acid compound (concentration 3 wt%). At this time, the impregnation amount of the oxidizing agent solution A was 15 mg / cm ² . The separator impregnated with the oxidant solution A was placed on the tank containing the pyrrole monomer so that the separator impregnated with the oxidant solution A did not come into contact with the pyrrole monomer. Kept. After leaving for 5 minutes, the separator was taken out, and the base material of the separator coated with polypyrrole was washed in warm water at 60 ° C. for 5 minutes, and then dried at 105 ° C. to obtain a separator (hereinafter referred to as separator A and To do).

  When the electrical conductivity of this separator A was measured by a four-terminal method (measuring instrument: Loresta manufactured by Mitsubishi Chemical Corporation), the electrical conductivity was 3.5 S / cm.

  Furthermore, this separator A was heat-treated at a temperature of 220 ° C. for 5 minutes (hereinafter, this heat-treated separator is referred to as separator A2). When the conductivity of the surface layer of the separator A2 was measured by the four-terminal method (same as above), the conductivity was 3.0 S / cm.

In order to confirm the polymerization reaction, 1 cm ^{2 of the} separator A was cut finely, immersed in 10 ml of pure water, subjected to ultrasonic cleaning for 30 minutes, and then filtered with an ion chromatography analyzer. When the anion component in the liquid was qualitatively determined, 1-naphthalene sulfonate ion was detected in addition to sulfate ion (derived from ammonium persulfate).

  This result is that 1-naphthalenesulfonic acid, which is an organic acid ion, was detected by dissolving it by ultrasonic cleaning treatment. Therefore, the oxidant solution immersion-gas phase polymerization-water washing-drying treatment was repeated. It can be considered that it was confirmed that polypyrrole, which is a conductive polymer, was doped with 1-naphthalenesulfonic acid, which is an organic acid ion.

  Next, an anode foil made of an aluminum foil having a dielectric oxide film (formation voltage of 35 V) formed by roughening the surface by etching and then anodizing, and a cathode foil obtained by etching the aluminum foil, A capacitor element was obtained by winding with the separator A interposed. This capacitor element had a capacitance of 450 μF at a frequency of 120 Hz in a 10 wt% ethylene glycol solution of ammonium adipate.

  Subsequently, the capacitor element contains mono (triethylamine) = phthalate (concentration 25% by weight), p-nitrobenzoic acid (concentration 0.5% by weight), monobutyl phosphate (concentration 0.5% by weight). The γ-butyrolactone solution (hereinafter referred to as “driving electrolyte A”) was immersed under reduced pressure conditions (−700 mmHg), and the gaps of the capacitor elements were impregnated with the driving electrolyte A.

  Next, after inserting this capacitor element into a metal case made of bottomed cylindrical aluminum, a sealing member made of resin vulcanized butyl rubber (30 parts of butyl rubber polymer, 20 parts of carbon, 50 inorganic fillers) in the opening of this metal case. And sealing member hardness: 70 IRHD (international rubber hardness unit)), and then the end of the metal case is sealed by curling treatment, and both the lead and anode foils, respectively, are led out. The lead was passed through a seat plate made of polyphenylene sulfide, and the lead portion was bent flat to fix the seat plate.

  Finally, aging was performed by continuously applying a DC voltage of 30 V for 1 h (atmosphere temperature: 105 ° C.) to produce a surface mount type electrolytic capacitor (size: diameter 10 mm × height 10 mm).

(Example 2)
In Example 1 above, after the separator base material was immersed in the oxidant solution A, both ends of the separator base material were sandwiched between rollers of silicon rubber, and the amount of the oxidant solution A impregnated into the separator base material was determined by the length of the separator. The separator made uniform with 18 mg / cm ² with respect to the direction, and the separator impregnated with the oxidant solution A was placed on the tank containing the pyrrole monomer so that the separator impregnated with the oxidant solution A did not come into contact with the pyrrole monomer. The system was sealed and the ambient temperature was kept at 35 ° C. After leaving for 3 minutes, the separator was taken out, and the substrate of the separator coated with polypyrrole was washed by spraying room temperature pure water for 1 minute, and then dried at 105 ° C. to obtain a separator (hereinafter referred to as the separator). B). When the conductivity of the separator B was measured by the four probe method (same as above), the conductivity was 2.9 S / cm.

  Further, the separator B was immersed in an aqueous solution of sodium hydroxide pH = 12 for 5 minutes, and then washed by spraying pure for 1 minute, and then dried at 105 ° C. to obtain a separator (hereinafter referred to as separator B2). To do). When the conductivity of the surface layer of the separator B2 was measured by the four-terminal method (same as above), the conductivity was 2.5 S / cm.

  An electrolytic capacitor was produced in the same manner as in Example 1 except for the above.

(Example 3)
Separator base material (base material thickness 50 μm, weighing 25 g / m ² ) made of nonwoven fabric obtained by spunbonding using terephthalic resin mainly composed of polyethylene terephthalate as ammonium persulfate (concentration 10% by weight) And an aqueous solution containing 2-naphthalenesulfonic acid (concentration 3% by weight) which is an organic acid compound (hereinafter referred to as oxidant solution B). At this time, the impregnation amount of the oxidizing agent solution B was 20 mg / cm ² . The separator impregnated with the oxidant solution B is placed on the tank containing the pyrrole monomer with the pyrrole monomer liquid surface and the separator impregnated with the oxidant solution B at a distance of 3 cm, and the system is sealed and the atmosphere The temperature was kept at 35 ° C. After leaving for 3 minutes, the separator was taken out, and the base material of the separator coated with polypyrrole was washed in warm water at 70 ° C. for 3 minutes and then dried at 105 ° C. to obtain a separator (hereinafter referred to as separator C). To do). When the conductivity of the separator C was measured by the four probe method (same as above), the conductivity was 1.5 S / cm.

  Furthermore, this separator C was heat-treated at a temperature of 230 ° C. for 3 minutes (hereinafter, this heat-treated separator is referred to as a separator C2). When the conductivity of the surface layer of the separator C2 was measured by the four probe method (same as above), the conductivity was 1.2 S / cm.

  An electrolytic capacitor was produced in the same manner as in Example 1 except for the above.

(Example 4)
In Example 1 above, instead of the driving electrolyte A, mono (1,2,3,4-tetramethylimidazolinium) = phthalate (concentration 30 wt%), p-nitrobenzoic acid (concentration 0) 0.5% by weight) and a γ-butyrolactone solution containing monobutyl phosphate (concentration 0.5% by weight) (hereinafter referred to as drive electrolyte B). An electrolytic capacitor was produced.

(Example 5)
In Example 1 above, instead of the driving electrolyte A, mono (ethyldimethylmethylamine) = phthalate (concentration: 26 wt%), p-nitrophenol (concentration: 0.5 wt%), monobutyl phosphate ( 80 parts of γ-butyrolactone containing 0.5% by weight), hypophosphorous acid (0.1% by weight), boric acid (0.2% by weight), mannitol (0.2% by weight), An electrolytic capacitor was produced in the same manner as in Example 1 except that a mixed solution of 20 parts of ethylene glycol (hereinafter referred to as driving electrolyte C) was used.

(Example 6)
In Example 1 above, an electrolytic capacitor was obtained in the same manner as in Example 1 except that a separator was obtained using 2,3-ethylenedioxythiophene monomer instead of pyrrole monomer (hereinafter referred to as Separator D). Was made. When the conductivity of the separator D was measured by the four-terminal method (same as above), the conductivity was 2.3 S / cm.

  Further, the separator D was immersed in ammonia water pH = 11 for 10 minutes, then immersed in pure water for 5 minutes for cleaning, and then dried at 105 ° C. to obtain a separator (hereinafter referred to as separator D2). To do). When the conductivity of the surface layer of the separator D2 was measured by the four-terminal method (same as above), the conductivity was 2.2 S / cm.

  An electrolytic capacitor was produced in the same manner as in Example 1 except for the above.

(Comparative Example 1)
In Example 1 above, instead of the polymerization solution A, pyrrole (concentration 0.5 wt%) and 1-naphthalenesulfonic acid ferric acid (concentration 5 wt%) and p-nitrophenol which are transition metal salts of organic acids A chemical that utilizes the oxidation action of trivalent iron ions on its surface by immersing and lifting the separator substrate in an aqueous solution containing 0.1% by weight (hereinafter referred to as polymerization solution D). Polypyrrole to be a conductive polymer was formed by oxidative polymerization. The base material of the separator covered with polypyrrole was washed with water and dried at 70 ° C., and this operation was repeated three times to obtain a separator (hereinafter referred to as separator E) in the same manner as in Example 1 above. An electrolytic capacitor was produced. When the conductivity of the separator E was measured by the four probe method (same as above), the conductivity was 1.0 S / cm.

Further, in order to confirm the polymerization reaction, the iron concentration in the filtrate after 1 cm ^{2 of the} separator E was cut finely and immersed in 10 ml of pure water and subjected to ultrasonic cleaning for 30 minutes. When quantified with an atomic absorption spectrometer, 320 ppm of iron was detected. Furthermore, when the anion component in the filtrate was qualitatively analyzed with an ion chromatograph, 1-naphthalene sulfonate ion was detected in addition to sulfate ion (derived from ammonium persulfate). It was confirmed that polypyrrole, which is a molecule, is doped with 1-naphthalenesulfonic acid, which is an organic acid ion.

(Comparative Example 2)
In Example 1 above, instead of the polymerization solution A, an aqueous solution containing pyrrole (concentration 0.5% by weight), ammonium persulfate (concentration 3% by weight), and sulfuric acid (concentration 5% by weight) as an inorganic acid (hereinafter, This was used as a polymerization solution E), and the base material of the separator was dipped and pulled up, thereby forming polypyrrole as a conductive polymer on the surface by chemical oxidative polymerization utilizing the oxidizing action of ammonium persulfate. The base material of the separator coated with polypyrrole was washed with water and dried at 70 ° C., and the same procedure as in Example 1 was performed except that this operation was repeated three times (hereinafter referred to as separator F). An electrolytic capacitor was produced. When the conductivity of the separator F was measured by the four probe method (same as above), the conductivity was 1.0 S / cm.

Further, in order to confirm the polymerization reaction, the iron concentration in the filtrate after 1 cm ^{2 of the} separator F was finely cut and immersed in 10 ml of pure water and subjected to ultrasonic cleaning for 30 minutes. Iron was not detected as determined by an atomic absorption spectrometer. Furthermore, when the anion component in the filtrate was qualitatively analyzed with an ion chromatography analyzer, anions other than sulfate ions (derived from ammonium persulfate and sulfuric acid) were not detected. From this result, it was confirmed that there was no doped component other than sulfuric acid, which is an inorganic acid, in polypyrrole, which is a conductive polymer.

(Comparative Example 3)
An electrolytic capacitor in the same manner as in Example 1 except that the separator base material was 100% Manila hemp fiber (thickness 50 μm, weighed 20 g / m ² ) (hereinafter referred to as separator G). Was made. When the conductivity of the separator G was measured by the four probe method (same as above), the conductivity was as low as 0.12 S / cm and the mechanical strength was also weak.

(Comparative Example 4)
An electrolytic capacitor was produced in the same manner as in Example 1 except that the separator base material was not coated with a conductive polymer.

(Comparative Example 5)
An anode foil made of an aluminum foil having a dielectric oxide film (formation voltage 38 V) formed by roughening the surface by etching and then anodizing, and a cathode foil obtained by etching the aluminum foil, and polyparaphenylene between them Winding through a separator base material (base material thickness 50 μm, weighing 25 g / m ² ) made of nonwoven fabric obtained by spunbond method using aromatic aramid resin mainly composed of terephthalamide as raw material As a result, a capacitor element was obtained. This capacitor element had a capacitance of 450 μF at a frequency of 120 Hz in a 10 wt% ethylene glycol solution of ammonium adipate.

  This capacitor element includes 1 part of 3,4-ethylenedioxythiophene as a heterocyclic polymerizable monomer, 2 parts of p-toluenesulfonic acid ferric salt as an oxidizing agent, and 4 parts of n-butanol as a polymerization solution. After being pulled up by being immersed in the polymerization solution, poly 3,4-ethylenedioxythiophene, which is a conductive polymer, was formed between the electrode foils by chemical oxidative polymerization by leaving it at 85 ° C. for 60 minutes.

  Next, after the capacitor element is inserted into a metal case, a sealing member made of resin vulcanized butyl rubber (30 parts butyl rubber polymer, 20 parts carbon, 50 parts inorganic filler, sealing member hardness: 70IRHD (international rubber hardness unit)) is disposed, and then the opening end of the metal case is sealed by curling treatment, and both leads led out from the anode foil and the cathode foil are made of polyphenylene sulfide seat plate Then, the lead portion was bent flat to produce a surface mount type electrolytic capacitor.

  Finally, aging was performed by applying a DC voltage of 30 V continuously for 1 h (atmosphere temperature 105 ° C.), but the total number (100) of the tested electrolytic capacitors could be short-circuited and exhibit normal electrical characteristics. An electrolytic capacitor could not be obtained.

  About the electrolytic capacitors of Examples 1 to 7 and Comparative Examples 1 to 5 of the present invention produced as described above, the capacitance (measurement frequency 120 Hz), ESR (measurement frequency 100 kHz), leakage current (after applying the rated voltage 16V) (Table 1) shows the results of comparing the ESR and leakage current after performing a 500-h rated voltage 16V application test in a temperature atmosphere of 125 ° C. . Note that the number of tests was 100, and the ESR and leakage current values after the capacitance, ESR, leakage current, and rated voltage application tests were shown as average values for samples excluding short-circuited products. .

  As is clear from Table 1, the electrolytic capacitors of Examples 1 to 6 of the present invention are conductive polymers (separator conductivity: 1. 2 to 3.0 S / cm), compared with the case where the separator not coated with the conductive polymer shown in Comparative Example 4 is used (conductivity of the driving electrolyte: 5 mS / cm). Since the resistance value between the electrodes can be lowered, the ESR in the high frequency region can be further lowered.

  Compared with the case where separator E (residual iron: 320 ppm) coated with a conductive polymer using an iron salt-based oxidizing agent of transition metal shown in Comparative Example 1 is used, Even in a coexisting atmosphere, there are few problems such as an increase in leakage current due to dissolution and precipitation of transition metals and shorting during aging, and as a result, an electrolytic capacitor having a high withstand voltage and excellent leakage current stability can be obtained. it can.

  Compared with the case of using separator F (only inorganic acid is doped) coated with a conductive polymer using ammonium persulfate and sulfuric acid, which are inorganic acids, as dopant components, shown in Comparative Example 2, the dedoping reaction is performed. Therefore, it is difficult to cause a decrease in the conductivity of the conductive polymer due to, so that the rate of change of ESR after a 500 h test at 125 ° C. is small, and the surface mount type electrolytic capacitor is highly reliable.

  Using the separators F and A2 of Comparative Example 2 and Example 1 alone, the rate of decrease in conductivity when subjected to a heat treatment at 125 ° C. for 100 hours in a nitrogen atmosphere was measured. As a result, the separator F of Comparative Example 2 was removed. Although it was -60% with respect to the initial conductivity due to the influence of the doping, since the separator A2 of Example 1 is less likely to be undoped, the decrease rate of the conductivity is only -5%, and the heat resistance is high. It was confirmed to be a conductive polymer.

  In addition, the electrolytic capacitors of Examples 1 to 6 of the present invention are made of polypyrrole or poly3, which is a conductive polymer, using polyethylene terephthalate and an aromatic polyamide non-woven fabric as a separator base material coated with a conductive polymer. Since 4-ethylenedioxythiophene or the like can be strongly adhered and adhered onto the fiber by chemical oxidative polymerization, when the 100% Manila hemp fiber shown in Comparative Example 3 is used (separator conductivity: 0. 0). 12S / cm), the resistance value between the electrodes can be lowered, so that the ESR in the high frequency region can be further lowered, and the problem such as separation between the separator substrate and the conductive polymer is caused. As a result, the rate of change in ESR after a test at 120 ° C. for 500 hours is small, and the surface mount type electrolytic capacitor is highly reliable.

  In addition, the electrolytic capacitors of Examples 1 to 6 of the present invention cover the surface of the separator with a conductive polymer formed by chemical oxidative polymerization and contain a driving electrolytic solution, so that the dielectric oxide film is repaired. Compared to the case of using only a conductive polymer with poor repairability of the dielectric oxide film shown in Comparative Example 5 due to its excellent property, there are problems such as an increase in leakage current due to insufficient withstand voltage and a short circuit during aging. As a result, an electrolytic capacitor having a high withstand voltage and excellent leakage current stability can be formed.

  In addition, when poly 3,4-ethylenedioxythiophene is used as the conductive polymer covering the base material of the separator (Example 7), the conductivity associated with the breakage of the polymer chain due to oxidative degradation of the conductive polymer itself. Therefore, the ESR change in the high frequency region after the reflow treatment and the high temperature test is further reduced, and the reliability of the surface mount type electrolytic capacitor is further improved.

  The base material of the separator contains at least one selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, nylon, aromatic polyamide, polyimide, polyamideimide, polyetherimide, rayon, and vitreous. Due to the configuration of the non-woven fabric, the adhesion and adhesion between the solid electrolyte made of a chemically polymerizable conductive polymer such as polypyrrole and poly3,4-ethylenedioxythiophene and the base material of the non-woven fabric separator are very good. The ESR in the high frequency region can be further reduced.

  Moreover, the base material of the nonwoven fabric separator is different from the nonwoven fabric made from other synthetic resin materials by the thermal bonding method or mechanical entanglement method without using an adhesive for bonding fibers between the sheets. Since it can be made into a sheet and has a high melting point, even under soldering mounting conditions exceeding 250 ° C., it is difficult for the separator fiber to be cut or ESR increased due to thermal shrinkage of the resin, and it has low solder heat resistance. An electrolytic capacitor of ESR can be obtained.

  Among these nonwoven fabrics, nonwoven fabrics containing polyethylene terephthalate, polybutylene terephthalate, nylon, aromatic polyamide, polyimide, and polyamideimide obtained by the spunbond method or wet papermaking method are nonwoven fabrics obtained by the dry meltblowing method. Since the tensile strength is higher than that of the capacitor, the comparison with the same thickness and the same weight is preferable because the frequency of the separator breakage due to the winding of the capacitor element is reduced and the occurrence rate of the short circuit is reduced.

The thickness of the base material of the nonwoven fabric separator is preferably 100 μm or less, and the weight is preferably in the range of 10 to 60 g / m ² . By setting this range, it is possible to secure a tensile strength sufficient to withstand the breakage of the separator when the capacitor element is wound. Therefore, even a capacitor element having a small diameter has a large capacity per unit volume and a gap between the anode foil and the cathode foil. An electrolytic capacitor with low resistance and low ESR in a high frequency region can be obtained.

If the weight of the separator substrate is less than 10 g / m ^2, it is not preferable because the separator breaks frequently during winding, and if the weight exceeds 60 g / m ² , the ESR in the high frequency region increases, which is not preferable.

  In addition, the separator substrate is subjected to a dipping treatment in a solution when the conductive polymer is formed by chemical oxidative polymerization, so that the entanglement between the fibers is loosened. Since it is often thicker than the thickness, it is preferable that the thickness increase is 70 μm or less in consideration of the thickness increase.

  In addition, a nonwoven fabric obtained by mixing the base material of the nonwoven fabric separator and so-called cellulose fibers such as manila hemp and kraft fibers can also be used. In this case, the cellulose fiber content is 80% or less. desirable. When the content of the cellulose fiber exceeds 80%, the adhesiveness / adhesive effect cannot be sufficiently obtained, and the ESR in the high frequency region is deteriorated.

  In addition, as a surface treatment for making the conductivity of the surface layer of the separator base material smaller than that of the inner layer, the conductive polymer of the separator surface layer is oxidized and deteriorated by heat treatment in the range of 200 to 250 ° C. Since the electric conductivity is smaller than that of the inner layer and the withstand voltage of the separator surface layer is increased, the withstand voltage is high, and the electric conductivity of the inner layer of the separator is high, so that a low ESR electrolytic capacitor can be obtained.

  When the heat treatment temperature is lower than 200 ° C., oxygen deterioration is delayed, and when it exceeds 250 ° C., the conductivity decreases not only to the separator surface layer but also to the inner layer of the separator. preferable.

  Further, as the surface treatment, by immersing in a solution having pH = 8 or more, de-doping from the conductive polymer occurs in the alkaline liquid, and the conductivity of the separator surface layer becomes smaller than that of the inner layer, so that the separator surface layer Since the withstand voltage is high, the withstand voltage is high, and the conductivity of the inner layer of the separator is high, so that a low ESR electrolytic capacitor can be obtained.

  When the pH of the above solution is 8 or less, de-doping hardly occurs because it approaches the neutral region, and at pH = 14, not only the separator surface layer but also the inner layer of the separator occurs because of the strong alkaline solution. Therefore, pH = 9-13 is preferable.

Further, in the step of forming the conductive separator, the amount of the oxidizing agent attached to the separator substrate is set to 20 mg / cm ² or less per unit area of the separator, so that excess oxidizing agent remains during the chemical oxidative polymerization. The persulfate ion functioning as a dopant is not easily dedoped and eluted into the driving electrolyte, and the conductivity of the conductive polymer is not significantly reduced by dedoping. It is possible to obtain an electrolytic capacitor having high heat resistance, high leakage current stability and stable ESR in a high frequency region.

  Also, by controlling the amount of the oxidant attached to the separator base material by using a roller, the amount of the oxidant attached to the separator base material can be kept constant. Stable conductivity with respect to the direction can be obtained, and persulfate ions functioning as a dopant can be easily dedoped and eluted into the driving electrolyte, or the conductivity of the conductive polymer can be reduced by dedoping. It is possible to obtain an electrolytic capacitor having a high heat resistance that has a high withstand voltage, an excellent leakage current stability, and a stable ESR in a high frequency region without being significantly reduced.

  Also, if the atmospheric temperature for vapor phase polymerization is too low, the conductive polymer monomer cannot be vaporized, and if the temperature exceeds 50 ° C., the separator to which the oxidant solution is attached is made highly conductive. When exposed to molecular monomer vapors, the oxidant solution dries out, making it impossible to obtain a stable conductivity. By setting the ambient temperature in the range of 0 to 50 ° C., a stable separator conductivity can be obtained. Can be obtained.

  In addition, if the time for performing the above gas phase polymerization is 1 minute or less, the reaction is not sufficiently completed and stable conductivity cannot be obtained. However, by setting the time to 1 minute or more, stable separator conductivity can be obtained. It can be obtained.

  Further, in the step of forming the conductive separator, vapor phase polymerization is performed with vapor obtained by volatilizing the monomer solution, so that the separator to which the oxidant solution is attached does not come into contact with the monomer solution. Thus, a stable separator conductivity can be obtained without mixing the oxidant solution.

  Further, when the distance between the separator substrate immersed in the oxidizing agent in the gas phase polymerization and the liquid surface of the monomer solution is 0.5 cm or less, the separator comes into contact with the monomer solution, and is 10 cm or more. Since the high electrical conductivity cannot be obtained because the monomer vapor concentration of the conductive polymer is low, the distance between the separator substrate immersed in the oxidizing agent and the liquid level of the monomer solution is set to a range of 0.5 to 10 cm. Thus, a stable separator conductivity can be obtained.

  Further, in the step of forming the conductive separator, excess oxidant in the gas phase polymerization can be removed by washing with water and / or alcohol after the gas phase polymerization. There is no surplus oxidant remaining during the polymerization, and the persulfate ion functioning as a dopant is easily dedoped and eluted into the driving electrolyte, or the conductivity of the conductive polymer is remarkably reduced by dedoping. It is possible to obtain an electrolytic capacitor having high heat resistance, high withstand voltage, excellent leakage current stability and stable ESR in a high frequency region without being reduced.

  The excess oxidant cannot be removed when the cleaning time is 30 seconds or less, and sufficient cleaning is possible when the cleaning time is 1 hour or longer, so no further cleaning is necessary. By setting the cleaning time in the range of 30 seconds to 1 hour, excess oxidant does not remain during the chemical oxidative polymerization, and the persulfate ion functioning as a dopant can be easily dedoped to drive electrolyte. And high conductivity with high withstand voltage, excellent leakage current stability, stable ESR in high frequency region A capacitor can be obtained.

  Further, if the temperature at the time of washing is 10 ° C. or less, the amount of excess oxidant that dissolves is reduced, so that the excess oxidant cannot be removed, and the washing temperature is 80 ° C. or more. In some cases, since the temperature is high, the evaporation of the cleaning liquid increases and cleaning cannot be performed. Therefore, by setting the cleaning temperature in the range of 10 to 80 ° C., excess oxidant is generated during the chemical oxidative polymerization. The persulfate ion that functions as a dopant is not easily dedoped and eluted into the driving electrolyte, and the conductivity of the conductive polymer is not significantly reduced by dedoping. Therefore, it is possible to obtain an electrolytic capacitor having high heat resistance, excellent leakage current stability, stable ESR in a high frequency region, and high heat resistance.

  In the above embodiment, the structure and the manufacturing method in which the withstand voltage of the surface layer of the separator is increased by performing a surface treatment that makes the conductivity of the surface layer of the separator substrate smaller than that of the inner layer are taken as an example. Although described, the present invention is not limited to this, and a high resistance material is applied to or coated on the surface of the separator substrate, or a material having a conductivity smaller than that of the separator substrate is used. The same effect can be obtained even in a configuration in which the separator is laminated.

  The electrolytic capacitor according to the present invention and the manufacturing method thereof have a higher withstand voltage of the separator surface layer by making the conductivity of the surface layer of the conductive separator smaller than that of the inner layer, have a high withstand voltage, and have excellent leakage current stability. It has an exceptional effect that an electrolytic capacitor having a stable ESR in a high frequency region and having a high heat resistance can be obtained, and is optimal for use in a field where excellent ESR characteristics are required in the high frequency region.

The fragmentary sectional perspective view which showed the structure of the electrolytic capacitor by one embodiment of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Anode foil 2 Cathode foil 3 Separator 4 Anode lead 5 Cathode lead 6 Sealing member 7 Metal case 8 Seat plate 9 Capacitor element

Claims (14)

A capacitor element formed by winding an anode foil etched with a dielectric oxide film and an etched cathode foil with a conductive separator interposed therebetween, and the capacitor element together with a driving electrolyte and a metal case In the electrolytic capacitor housed in the inside, the conductive separator is made conductive by forming a conductive polymer on a nonwoven fabric separator base material by gas phase polymerization, and at least a surface layer on a surface in contact with the anode foil. An electrolytic capacitor having a conductivity smaller than that of the inner layer. The base material of the separator made of nonwoven fabric contains at least one selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, nylon, aromatic polyamide, polyimide, polyamideimide, polyetherimide, rayon, and glassy material. The electrolytic capacitor according to claim 1, which is a capacitor. Between the step of forming a conductive separator provided with conductivity by attaching a conductive polymer to the separator substrate, and the anode foil and the etched cathode foil formed by etching to form a dielectric oxide film between them A step of forming a capacitor element by winding with the conductive separator interposed therebetween, and a step of impregnating the capacitor element with a driving electrolyte and storing the capacitor element in a metal case. In the forming step, a separator base material made of nonwoven fabric is impregnated with an oxidant solution, and then this separator base material is vapor-phase polymerized in a monomer vapor of the conductive polymer to form the conductive polymer into the separator base material. After attaching and subsequently washing and drying, surface treatment is performed to make the conductivity of the surface layer of the separator base material smaller than that of the inner layer. Method of manufacturing an electrolytic capacitor. The method for producing an electrolytic capacitor according to claim 3, wherein the surface treatment for making the conductivity of the surface layer of the separator substrate smaller than that of the inner layer is heat-treated in a range of 200 to 250 ° C. The method for producing an electrolytic capacitor according to claim 3, wherein the surface treatment for making the surface layer of the separator substrate smaller than the inner layer is immersed in a solution having a pH of 8 or more. The method for producing an electrolytic capacitor according to claim 3, wherein in the step of forming the conductive separator, the amount of the oxidizing agent attached to the separator substrate is 20 mg / cm ² or less per unit area of the separator. The method for producing an electrolytic capacitor according to claim 6, wherein the amount of the oxidizing agent attached to the separator substrate is controlled by the pressure using a roller. The method for producing an electrolytic capacitor according to claim 3, wherein in the step of forming the conductive separator, the gas phase polymerization is performed by vapor obtained by volatilizing the monomer solution. The method for producing an electrolytic capacitor according to claim 8, wherein in the step of forming the conductive separator, the atmospheric temperature for performing the gas phase polymerization is set in a range of 0 to 50 ° C. The method for producing an electrolytic capacitor according to claim 8, wherein in the step of forming the conductive separator, the time for performing the gas phase polymerization is 1 minute or more. The method for producing an electrolytic capacitor according to claim 8, wherein the distance between the separator substrate impregnated with the oxidizing agent and the liquid level of the monomer solution in the gas phase polymerization is in the range of 0.5 cm to 10 cm. The method for producing an electrolytic capacitor according to claim 3, wherein in the step of forming the conductive separator, washing after the gas phase polymerization is performed by washing with water and / or washing with alcohol. The method for producing an electrolytic capacitor according to claim 12, wherein the cleaning time is in the range of 30 seconds to 1 hour. The manufacturing method of the electrolytic capacitor of Claim 12 which made the washing | cleaning temperature the range of 10-80 degreeC.

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