JP2000138133A - Solid electrolytic capacitor and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid electrolytic capacitor having improved characteristic, and its manufacturing method. SOLUTION: A capacitor element is formed by winding an anode foil sheet and a cathode foil sheet together with a separator, and a reform operation is performed by dipping the capacitor element into ammonium dihydrogenphosphate aqueous solution for 5 to 120 minutes. Then, the capacitor element is dipped into the aqueous solution of an additive containing one or two or more kinds selected from borasic acid or borasic acid salt, mannitol, ammonium dihydrogenphosphate for 30 seconds to 5 minutes, and it is dried up at 60 to 120 deg.C for one minute to 5 hours. Subsequently, EDT or EDT solution is impregnated to the capacitor element, P-toluensulphone and a ferric of 30 to 50% impregnated, and heated up at 20 to 180 deg.C for 30 minutes or longer. Then, the surface of the capacitor element is coated with resin and an aging treatment is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid electrolytic capacitor and a method for manufacturing the same, and more particularly, to a solid electrolytic capacitor improved to improve withstand voltage characteristics and a method for manufacturing the same.

[0002]

2. Description of the Related Art In an electrolytic capacitor using a metal having a valve action such as tantalum or aluminum, a valve action metal as an anode-side counter electrode is formed into a shape of a sintered body or an etching foil to expand a dielectric material. By using such a structure, it is possible to obtain a large capacity with a small size. In particular, a solid electrolytic capacitor using a solid electrolyte as an electrolyte has characteristics that it is small, large-capacity, low equivalent series resistance, easy to chip, and suitable for surface mounting. It is indispensable for miniaturization, high performance, and low cost of electronic devices.

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

As a solid electrolyte used for a solid electrolytic capacitor, manganese dioxide, 7, 7, 8, 8-
A tetracyanoquinodimethane (TCNQ) complex is known, but recently, polyethylenedioxythiophene (hereinafter, referred to as PEDT), which has a slow reaction rate and excellent adhesion to an oxide film layer of an anode electrode, has been developed. There is a technique (Japanese Patent Laid-Open No. 2-15611) that has been focused on.

[0005] For example, a PED is used for a wound type capacitor element.
As shown in FIG. 6, a solid electrolytic capacitor of the type in which a solid electrolyte layer made of T is formed is formed as follows: formation → capacitor element formation → repair formation → impregnation of EDT and oxidizer → polymerization → insertion into an outer case → resin sealing → It is manufactured by a manufacturing process called aging. Below, about this manufacturing process,
A brief description will be given with reference to FIGS.

First, as shown in FIG. 8, the surface of the anode foil 1 made of a valve metal such as aluminum is roughened by electrochemical etching in an aqueous chloride solution to form a large number of etching pits 8. After formation, a voltage is applied in an aqueous solution of ammonium borate or the like to form oxide film layer 4 serving as a dielectric (chemical formation). Like the anode foil 1, the cathode foil 2 as shown in FIG. 7 is also made of a valve metal such as aluminum, but its surface is only subjected to etching. As shown in FIG. 7, lead wires 6 and 7 for connecting the respective electrodes to the outside are connected to the anode foil 1 and the cathode foil 2 by known means such as stitching and ultrasonic welding.

Next, the anode foil 1 having the oxide film layer 4 formed on the surface thereof as described above and the cathode foil 2 having only the etching pits 8 formed thereon are separated by a separator 3 as shown in FIG.
To form the capacitor element 10 and then perform repair formation. In the repair formation, the electrode foil is subjected to mechanical stress in the winding step, and when the oxide film is damaged due to cracks caused by the mechanical stress, the electrode foil is formed again in a chemical conversion solution, An oxide film is formed on the cracked portion to repair the damage.

Subsequently, the restoration-formed capacitor element 10 is replaced with 3,4-ethylenedioxythiophene (hereinafter referred to as E
This polymer solution is impregnated in the capacitor element 10 by immersion in a mixed solution (polymer solution) of an oxidant and an oxidizing agent. Alternatively, the capacitor element 10 is alternately immersed in the EDT and the oxidizing agent solution for impregnation. In either case,
After the capacitor element 10 is impregnated with EDT and an oxidizing agent, a polymerization reaction is performed to produce a solid electrolyte layer 5 made of PEDT as shown in FIG.

Thereafter, the capacitor element 10 is inserted into an outer case (not shown). Subsequently, a thermosetting resin such as an epoxy resin is adhered to the inside of the exterior case and thermally cured to cover the exterior of the capacitor element 10 with the exterior resin (resin sealing), thereby completing a solid electrolytic capacitor. If the resin sealing is performed in this manner, the oxide film layer 4 is damaged and the leakage current characteristics are deteriorated. Therefore, after the resin sealing, it is necessary to apply a voltage corresponding to the capacitor rated voltage and perform high-temperature aging. Thus, the oxide film layer 4 is repaired to improve the characteristics.

In the above manufacturing method, a dipping method is used as a method for impregnating the capacitor element with EDT and an oxidizing agent. However, a method of injecting the EDT and the oxidizing agent at a normal temperature by a syringe or the like (injection method). Can also be used.

The solid electrolytic capacitor using PEDT obtained in this way has the feature that the withstand voltage of the capacitor can be set higher than the formation voltage of the anode foil, so that it is small and large. A solid electrolytic capacitor having a capacity can be realized.

[0012]

However, even in a solid electrolytic capacitor using PEDT manufactured by the above-described method, the withstand voltage characteristic is not yet sufficient, and a leakage current characteristic outside the standard is generated. There was a problem. In addition, a capacitor having a high leakage current needs to be debugged at the time of shipping inspection, and the manufacturing efficiency has been extremely poor.

The present invention has been proposed to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide a solid electrolytic capacitor having improved withstand voltage characteristics and a method of manufacturing the same. It is in.

[0014]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have made intensive studies on a solid electrolytic capacitor capable of improving withstand voltage characteristics and a method of manufacturing the same, and as a result, completed the present invention. That is what led to it. That is, the present inventors have added various additives at various times during the manufacturing process of the solid electrolytic capacitor, and as a result of earnestly examining whether or not the withstand voltage characteristics are improved, boric acid or a salt thereof is obtained. , Mannite and ammonium dihydrogen phosphate gave good results.

As described above, it is considered that a good effect was obtained by adding an additive of boric acid or a salt thereof, mannite, and ammonium dihydrogen phosphate for the following reasons. That is, in the aging (re-chemical conversion) of the final manufacturing process, the damage of the oxide film received during the manufacturing is repaired. At this time, boric acid or its salt, mannitol, phosphoric acid, which is present in the capacitor element, is repaired. It is considered that an additive such as ammonium dihydrogen enhances the repairing action in the aging step, so that the withstand voltage characteristics are improved.

(Method for Manufacturing Solid Electrolytic Capacitor) Next, an example of a method for manufacturing a wound solid electrolytic capacitor according to the present invention will be described. That is, the anode foil is wound together with the cathode foil and the separator to form a capacitor element, and the capacitor element is immersed in an aqueous solution of ammonium dihydrogen phosphate for 5 to 120 minutes to perform repair formation. Next, the capacitor element is immersed in an aqueous solution of one or more additives selected from boric acid or a salt thereof, mannite, and ammonium dihydrogen phosphate for 30 seconds to 5 minutes, and then at 60 to 120 ° C. Dry for 1 minute to 5 hours. continue,
This capacitor element is impregnated with EDT or EDT solution,
Further, the mixture is impregnated with a 30 to 50% ferric paratoluenesulfonate butanol solution and heated at 20 to 180 ° C. for 30 minutes or more. Thereafter, the surface of the capacitor element is covered with a resin, and aging is performed. Here, as a method of impregnating the capacitor element with EDT and an oxidizing agent, an injection method of injecting a fixed amount at room temperature with a syringe or the like is used, but it is needless to say that an immersion method can be used.

Thus, the repair formation of the oxide film and the PED
By immersing the capacitor element in an aqueous solution of an additive and drying it between the step of forming T and these additives, these additives can be present in the vicinity of the oxide film. It is considered that a stable complex or the like is formed by bonding to the oxide film and the oxide film can be stabilized.

(Chemical solution for repair chemical formation) As a chemical solution for repair chemical formation, a chemical solution of phosphoric acid such as ammonium dihydrogen phosphate and diammonium hydrogen phosphate, a chemical solution of boric acid such as ammonium borate, An adipic acid-based chemical solution such as ammonium adipate can be used.
It is desirable to use ammonium dihydrogen phosphate. Also, the immersion time is desirably 5 to 120 minutes.

(Additives) Examples of boric acid or boric acid salts thereof include ammonium salts, amine salts, quaternary ammonium salts and quaternary ammonium salts of cyclic amidine compounds. The amount of boric acid or a salt thereof, mannitol, and ammonium dihydrogen phosphate is 0.1 to 10 wt%, more preferably 1 to 8 w%, based on water.
t%. If the amount is less than 0.1 wt%, the effect is small, and if it exceeds 10 wt%, the capacitance tends to decrease. It is considered that the reason why the capacitance is reduced when the added amount exceeds 10 wt% is that the amount of the additive existing on the surface of the oxide film is so large that the adhesion between the oxide film and PEDT is hindered. . Further, the temperature of the aqueous solution of boric acid or a salt thereof, mannite, ammonium dihydrogen phosphate is 10 to 60 ° C, the impregnation time is 30 seconds to 5 minutes, the drying temperature is 60 to 120 ° C, and the drying time is 1 minute to 1 hour. Five hours is desirable.

The above-mentioned boric acid or a salt thereof, mannitol and ammonium dihydrogen phosphate can be used not only as an aqueous solution but also by dissolving them in various solvents. Such solvents include protic polar solvents,
Aprotic polar solvents are mentioned. Examples of the protic polar solvent include monohydric alcohols (such as methanol and ethanol), polyhydric alcohols and oxyalcohol compounds (such as ethylene glycol, methyl cellosolve, and 1,3-butanediol). Examples of aprotic polar solvents include amides (N, N-dimethylformamide, N-ethylformamide, etc.), lactones (γ-butyrolactone, etc.), cyclic amides (N-methyl-2-pyrrolidone, etc.), Examples thereof include carbonates (such as propylene carbonate), nitriles (such as acetonitrile), and oxides (such as dimethyl sulfoxide).

(EDT, Oxidizing Agent) As the EDT to be impregnated in the capacitor element, an EDT monomer can be used, and the EDT and the volatile solvent are mixed in a ratio of 1: 1 to 1: 3.
Can 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, and nitrogen compounds such as acetonitrile. However, among them, methanol, ethanol, acetone and the like are preferable. As the oxidizing agent, ferric paratoluenesulfonate dissolved in butanol is used. In this case, the ratio between butanol and ferric paratoluenesulfonate may be arbitrary, but in the present invention, the ratio is 30 to
A 50% solution is used. The mixing ratio between EDT and oxidizing agent is preferably in the range of 1: 3 to 1: 6.

(Timing when additive is present in capacitor element) The present inventors have conducted various studies on the timing when the additive is present in the capacitor element. If so, it turned out to be good at any stage. Before the repair formation step, the additive present in the capacitor element dissolves in the chemical conversion solution during the repair formation, so that good results cannot be obtained.

That is, as described above,
It may be after the repair formation or after the step of forming the PEDT polymer layer. For example, the following (1) to
The method (5) can be considered. The method (1) corresponds to the above-described manufacturing method. In addition, the following (1) to (5)
Among the above methods, the method (1) in which the additive can be present in a good state on the oxide film is most preferable.

(1) After restoration formation: see FIG. 1 Chemical formation → capacitor element formation → repair formation → immersion in an additive solution → impregnation of EDT and oxidant → polymerization → insertion into outer case → resin sealing → aging 2) After forming the PEDT polymer layer ... see Fig. 2 Chemical formation → formation of capacitor element → restoration formation → impregnation of EDT and oxidant → polymerization → immersion in additive solution → insertion into outer case → resin sealing → aging The concentration, temperature, impregnation time, drying temperature, and drying time of the additive solution in this method are the same as the conditions described in the above section (additive).

(3) Included in the chemical solution for restoration chemical formation—see FIG. 3 Chemical formation → capacitor element formation → repair formation (containing additives in the chemical formation solution) → impregnation of EDT and oxidizing agent → polymerization → Insertion → resin sealing → aging In this method, a chemical conversion solution described in the above section (repair formation) can be used as a chemical conversion solution for repair formation, and the immersion time is also 5 to 120 minutes in the same manner as described above. Is desirable. The amount of the additive to be contained in the chemical conversion solution is 0.1 to 10% by weight, more preferably 1 to 8% by weight, based on the chemical conversion solution for restoration chemical formation.

(4) Contained in EDT or EDT solution—See FIG. 4 Chemical formation → capacitor element formation → repair formation → impregnation of EDT and oxidizing agent (containing additives in EDT or EDT solution) → polymerization → outer case Insertion → resin sealing → aging In this method, the amount of the additive contained in the EDT or the EDT solution is 0.1 to 10% by weight, more preferably 1 to 8% by weight, based on the EDT or the EDT solution. .

(5) Including additives in the oxidizing agent solution ... FIG.
See Chemical formation → Capacitor element formation → Restoration chemical formation → Impregnation of EDT and oxidizing agent (containing additives in oxidizing agent solution) → Polymerization → Insertion into outer case → Resin sealing → Aging In this method, oxidizing agent solution Is 0.1 to 10 wt%, more preferably 1 to 8 wt%, based on the oxidizing agent solution.

As described above, the additive is contained in water, a restoration chemical solution, EDT or an EDT solution, or an oxidizing agent solution, and after impregnating the capacitor element with this solution and drying, the additive is contained in the capacitor element. The concentration of this additive in these solutions can be from 0.1 to 10 wt%, more preferably from 1 to 8 w
t%.

[0029]

Hereinafter, the present invention will be described in more detail with reference to examples. In addition, the solid electrolytic capacitor according to the present invention was prepared as in the following Examples 1 to 9. As a conventional example, a solid electrolytic capacitor manufactured by a conventional method was used.

(Examples 1 to 9) An anode foil and a cathode foil each having an oxide film layer formed on the surface thereof were wound via a separator to form a capacitor element having an element shape of 4φ × 7L. Then, the capacitor element was immersed in an aqueous solution of ammonium dihydrogen phosphate for 40 minutes to perform repair formation.
Next, this capacitor element was immersed in an aqueous solution of an additive having the composition shown in Table 1 for 2 minutes.
Dried for hours. Subsequently, the capacitor element was impregnated with an EDT monomer by an injection method, further impregnated with a 40% ferric paratoluenesulfonate butanol solution as an oxidizing agent solution, and heated at 100 ° C. for 1 hour to obtain PEDT.
Was formed. After that, the surface of the solid electrolytic capacitor is covered with a resin, aging is performed,
A solid electrolytic capacitor was formed. The solid electrolytic capacitor has a rated voltage of 25 WV and a rated capacity of 6.8 μF.
It is.

(Conventional example) A solid electrolytic capacitor was formed according to the above-mentioned conventional technique. That is, a solid electrolytic capacitor was formed without adding any additives.

[Comparison Results] Table 1 shows the electrical characteristics of the solid electrolytic capacitors of Examples 1 to 9 obtained by the above-mentioned method and the conventional solid electrolytic capacitor.

[0033]

[Table 1]

As is apparent from Table 1, the maximum value of the leakage current of the conventional example is 5 × 10 ³ , which exceeds the standard value, and debugging of this capacitor is necessary. In contrast, in Examples 1 to 4 in which only boric acid was added, the maximum value of the leakage current was 3 × 10 to 3 × 10 ² ,
It decreased to 0.6 to 6% of the conventional example. In particular, Examples 2-4
, The maximum value of the leakage current is 3 × 10 to 7 × 10
And 0.6 to 1.4% of the conventional example. Also, the average value of the leakage current was 3 × 10 in the first embodiment, which was only reduced to 30% of the conventional example. However, in the second to fourth embodiments, the average value of the leakage current was 5 to 10. 7, which is significantly reduced to 5 to 7% of the conventional example.

From this, it was found that the leakage current was greatly reduced by immersing the capacitor element in an aqueous solution of boric acid as an additive after the capacitor element was repair-formed. In particular, when the added amount of boric acid was 1% or more, the effect was remarkable.

In Examples 7 to 9 in which only ammonium dihydrogen phosphate was added, the maximum value of the leakage current was 5
× 10 to 9 × 10, which is 1.0 to 1.8% of the conventional example. In particular, in Example 8, the maximum value of the leakage current was 5 × 10, which was significantly reduced to 1.0% of the conventional example.
The average value of the leakage current is 5 to 8, which is 5 to 8 of the conventional example.
It has dropped significantly to 8%. From this, it was found that the leakage current was significantly reduced by immersing the capacitor element in an aqueous solution of ammonium dihydrogen phosphate as an additive after the capacitor element was repair-formed. In particular,
When the amount of ammonium dihydrogen phosphate added was 1.25%, the effect was remarkable.

Next, in Examples 5 and 6 in which boric acid and mannite were added, the maximum value of the leakage current was 10 to 5 ×
10, which is 0.2 to 1% of the conventional example. In particular,
In Example 6, the maximum value of the leakage current was 10, which was significantly reduced to 0.2% of the conventional example. Further, the average value of the leakage current was 1 to 5, which was significantly reduced to 1 to 5% of the conventional example. From this, it was found that the leakage current was significantly reduced by immersing the capacitor element in a mixed solution of boric acid and mannite as an additive after the capacitor element was repair-formed. In particular, the amount of boric acid added is 1.2
The effect was remarkable when 5% and the amount of mannitol added were 2.5%.

Further, Example 1 in which only boric acid was added,
When compared with Example 5 in which mannite was added to the same amount of boric acid, the maximum value of the leakage current was reduced from 3 × 10 ² to 5 × 10. In addition, comparing Example 2 in which only boric acid was added and Example 6 in which mannite was added to the same amount of boric acid, the maximum value of the leakage current was reduced from 7 × 10 to 10. This proved that the case where boric acid and mannitol were added was more effective than the case where only boric acid was added. This result also suggests that the same effect as when only boric acid or ammonium dihydrogen phosphate is added can be obtained when only mannite is added.

Further, when the equivalent series resistance (ESR) was examined, the ESR of Example 1 was 0.070, which is almost the same as that of the conventional example.
Is 0.065 to 0.067, which is lower than the conventional example. From this, it was found that the ESR can be reduced when the added amount of boric acid is 1% or more.

As described above, in a solid electrolytic capacitor in which one or more additives selected from boric acid, mannitol and ammonium dihydrogen phosphate are present in the capacitor element, the withstand voltage is greatly improved. It became clear to do. Although not shown in Table 1, when the above-mentioned boric acid salt was examined, almost the same results were obtained.

[0041]

As described above, according to the present invention, one or more additives selected from boric acid or a salt thereof, mannite, and ammonium dihydrogen phosphate are added to a capacitor in a manufacturing process. By allowing the solid electrolytic capacitor to be present in the capacitor element at any time after the repair formation step and before the resin sealing step, the withstand voltage of the solid electrolytic capacitor can be significantly improved.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating an example of a manufacturing process of a solid electrolytic capacitor according to the present invention.

FIG. 2 is a flowchart showing an example of a manufacturing process of the solid electrolytic capacitor according to the present invention.

FIG. 3 is a flowchart illustrating an example of a manufacturing process of the solid electrolytic capacitor according to the present invention.

FIG. 4 is a flowchart illustrating an example of a manufacturing process of the solid electrolytic capacitor according to the present invention.

FIG. 5 is a flowchart showing an example of a manufacturing process of the solid electrolytic capacitor according to the present invention.

FIG. 6 is a flowchart showing an example of a manufacturing process of a conventional solid electrolytic capacitor.

FIG. 7 is an exploded perspective view showing an example of a capacitor element targeted by the present invention.

FIG. 8 is an enlarged sectional view showing an anode foil of the capacitor element of FIG. 7;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Anode foil 2 ... Cathode foil 3 ... Separator 4 ... Oxide film layer 5 ... Solid electrolyte layer 6, 7 ... Lead wire 8 ... Etching pit 10 ... Capacitor element

Claims (8)

[Claims] 1. A solid electrolytic capacitor comprising a capacitor element in which a bipolar electrode foil connected to an electrode lead-out means is wound via a separator and a solid electrolyte layer made of polyethylene dioxythiophene is formed between the bipolar electrode foils. The solid electrolytic capacitor according to claim 1, wherein one or more additives selected from boric acid or a salt thereof, mannite, and ammonium dihydrogen phosphate are present in the capacitor element. 2. The solid electrolytic capacitor according to claim 1, wherein the additive is introduced into the capacitor element as a solution. 3. The amount of the additive is 0.1 to 10% by weight based on the solvent.
3. The solid electrolytic capacitor according to item 1. 4. The solid electrolytic capacitor according to claim 2, wherein the solvent of the additive is water. 5. A step of forming a capacitor element by winding an anode foil together with a cathode foil and a separator; a step of performing repair formation on the capacitor element; and impregnating the capacitor element with ethylenedioxythiophene and an oxidizing agent. A step of forming a solid electrolyte layer made of polyethylene dioxythiophene, and a method of manufacturing a solid electrolytic capacitor having a step of sealing the capacitor element with a resin, from the step of performing the repair formation to the step of sealing with a resin A step of introducing one or two or more additives selected from boric acid or a salt thereof, mannitol, and ammonium dihydrogen phosphate in the capacitor element. Manufacturing method. 6. The step of introducing the additive includes impregnating the capacitor element with a solution containing one or more additives selected from boric acid or a salt thereof, mannitol, and ammonium dihydrogen phosphate. The method for manufacturing a solid electrolytic capacitor according to claim 5, wherein: 7. An additive concentration of a solution containing the additive,
The method for producing a solid electrolytic capacitor according to claim 6, wherein the content is 0.1 to 10 wt%. 8. The method according to claim 6, wherein the solvent of the additive is water.