JP7394728B2 - Manufacturing method of electrolytic capacitor and electrolytic capacitor - Google Patents

Description

The present invention relates to a method for manufacturing an electrolytic capacitor and an electrolytic capacitor, particularly a method for manufacturing a hybrid aluminum electrolytic capacitor using a conductive polymer and an electrolyte in combination, and a hybrid aluminum electrolytic capacitor.

Conventionally, electrolytic capacitors are manufactured by forming an oxide film layer as a dielectric material on the surface of an anode electrode that is made of a valve metal such as aluminum, tantalum, or niobium and has etched pits or micropores. It is constructed by forming an electrolyte layer and drawing out the electrodes.
Since the electrolyte layer formed in this manner is a true cathode and has a great influence on the electrical characteristics of an electrolytic capacitor, various methods have been proposed to form the electrolyte layer.

Among these, solid electrolytic capacitors use an electronically conductive solid electrolyte instead of an ionically conductive liquid electrolyte in order to improve impedance characteristics in a high frequency range. For example, a solid electrolyte layer may be formed by using a 7,7,8,8-tetracyanoquinodimethane (TCNQ) complex as the solid electrolyte, melting the TCNQ complex with heat, and dipping and coating the anode electrode. , those using conductive polymers such as polyethylene dioxythiophene (PEDOT) as solid electrolytes are known. There are two methods for forming conductive polymers: one is to form a conductive polymer by chemical polymerization or electrolytic polymerization on an anode electrode using a monomer and a dopant, and the other is to form a conductive polymer by chemical polymerization or electrolytic polymerization on an anode electrode, or to form a conductive polymer using a dispersion or conductive polymer dispersed in a solvent. A known method is to immerse and apply a conductive polymer solution in which a conductive polymer is dissolved to an anode electrode, and then remove the solvent.

By the way, in order to reduce the leakage current (LC) of such a solid electrolytic capacitor, it is possible to reduce the leakage current (LC) by applying a predetermined voltage between both electrodes of the electrolytic capacitor for an appropriate time under predetermined conditions. Generally, an aging process is performed, and for example, in Patent Document 1 below, in order to eliminate in advance solid electrolytic capacitors whose leakage current increases when left at room temperature after aging, A method for manufacturing a solid electrolytic capacitor is disclosed, which is characterized in that the capacitor is left at 150° C. for 1 to 5 minutes, then the leakage current is measured, and those whose leakage current exceeds a specified value are rejected as defective products.

In addition, in recent years, hybrid capacitors (hereinafter referred to as "hybrid capacitors") that use conductive polymers and electrolytes as electrolytes have been used in fields such as automobiles. Also when forming a polymer layer, a dispersion liquid or a conductive polymer solution in which a conductive polymer is dispersed in water is used.
However, when a dispersion liquid or a conductive polymer solution is impregnated into an element to which a sealing rubber is not attached, the conductive polymer may creep upward and adhere to the round bar portion of the lead terminal. This is because the conductive polymer will penetrate even if the depth of immersion of the element in the dispersion liquid or conductive polymer solution is made shallow, and the adhesion of the conductive polymer to the round bar part can be completely suppressed. It is not possible. After being impregnated with a dispersion liquid or a conductive polymer solution, the conductive polymer is dried at high temperature to solidify the conductive polymer, but it is difficult to remove the solidified conductive polymer from the round bar, and it is difficult to remove leakage current. There was a problem in that it was difficult to reduce.

Patent No. 4720074

An object of the present invention is to solve the above-mentioned problems in the prior art and provide an electrolytic capacitor, particularly a hybrid aluminum electrolytic capacitor, with small fluctuations in leakage current (LC) before and after reflow, and a method for manufacturing the same. shall be.
As a result of various studies, the inventors of the present invention found that the upper surface of the wound element (the lead terminal side of the capacitor element formed by winding) was placed in a polyglycerin solution before the conductive polymer was completely solidified. The present invention was completed based on the discovery that leakage current can be improved by immersing the lead terminal above the circular plane (see reference numeral 5 in FIG. 2), that is, up to the round bar portion of the lead terminal.

The method for manufacturing an electrolytic capacitor of the present invention that can solve the above problems involves manufacturing a wound element by winding an anode foil and a cathode foil connected to lead terminals for external extraction electrodes via a separator. Winding element manufacturing process,
a chemical conversion treatment step of chemically treating the cut cross section of the anode foil and the attachment portion to the lead terminal of the wound element;
The wound element after the chemical conversion treatment is immersed in a dispersion of a conductive polymer dispersed in water or a conductive polymer solution to form a conductive polymer layer made of the conductive polymer to form a capacitor element. A conductive polymer formation process to produce;
a sealing step of storing the capacitor element and the electrolyte in a bottomed cylindrical metal case and sealing the opening of the metal case;
In a method for manufacturing an electrolytic capacitor, the method includes an aging treatment step,
In the conductive polymer forming step, after drying the wound element after being immersed in the dispersion liquid or the conductive polymer solution, the wound element is placed in a polyglycerin solution with the upper surface of the wound element being lower than the upper surface of the wound element. The method is characterized in that after being immersed up to the upper lead terminal, it is taken out from the polyglycerin solution and dried to form the conductive polymer layer.

Further, the present invention is a method for manufacturing an electrolytic capacitor having the above characteristics, wherein the polyglycerin solution uses ethanol, ethylene glycol, diethylene glycol, or a mixture thereof as a solvent.

Further, the present invention provides a method for manufacturing an electrolytic capacitor having the above characteristics, wherein the polyglycerin solution uses ethylene glycol as a solvent and has a polyglycerin concentration of 1 to 30% by weight. .

Further, in the present invention, the lead terminal for an externally drawn electrode comprises a flat part obtained by processing one of the round bar parts and a lead wire welded to the other of the round bar parts, and an anode foil and an anode foil connected to the flat part of the lead terminal. In an electrolytic capacitor comprising a wound element in which a cathode foil is wound through a separator, and a conductive polymer and an electrolyte held in the separator, the round bar portion of the lead terminal is coated with a polyglycerin coating. It is characterized by having.

Further, in the electrolytic capacitor having the above-mentioned characteristics, the present invention provides that the outer periphery of the wound element is located above the lower end of the wound element when the lead terminal extraction direction of the wound element is set upward. The winding element is characterized in that 1/3 to 2/3 of the height of the wound element is covered with the conductive polymer.

According to the present invention, an electrolytic capacitor, particularly a hybrid aluminum electrolytic capacitor, with less LC fluctuation before and after reflow can be manufactured.

FIG. 1 is a perspective view of main parts of an electrolytic capacitor according to an embodiment of the present invention. FIG. 2 is an exploded perspective view of the capacitor element shown in FIG. 1. FIG. 1 is an external view of a capacitor element according to an example of the present invention.

Hereinafter, preferred embodiments of an electrolytic capacitor (hybrid capacitor) manufactured by the manufacturing method of the present invention will be described with reference to the drawings.
The hybrid capacitor 1 illustrated in FIG. 1 includes a metal case 2, a capacitor element 3 housed in the metal case 2, and a sealing member 4 that seals the opening of the metal case 2. This is the top surface of element 3.

As shown in FIG. 2, the capacitor element 3 is formed by winding an anode foil (anode) 11 and a cathode foil (cathode) 12 into a cylindrical shape with a separator 13 in between, and is made of resin attached to the outer peripheral surface. The tape 14 is used to secure the winding.

The anode foil 11 is a foil made of a valve metal such as aluminum and has a dielectric oxide film formed on its surface. The derivative oxide film is formed by subjecting a valve metal foil whose surface has been roughened by etching to a chemical conversion treatment.

The cathode foil 12 is also formed using a valve metal foil such as aluminum, and the surface thereof is roughened by etching treatment (roughened foil). As the cathode foil 12, a plain foil without any other etching treatment can be used, and the surface of the roughened foil or plain foil may be coated with titanium, nickel, their carbides, nitrides, carbonitrides, or mixtures thereof. A thin metal film, a coated foil with a thin carbon film formed thereon, and a chemically formed foil with a dielectric oxide film formed thereon can also be used.

Flat parts of lead terminals (not shown) are connected to the anode foil 11 and the cathode foil 12, respectively. The anode foil 11 and the cathode foil 12 are connected to a lead terminal 21 and a lead terminal 22, respectively, via the flat portions of the lead terminals. As shown in FIG. 1, the lead terminals 21 and 22 are drawn out through holes 31 and 32 formed in the sealing member 4.
The separator 13 shown in FIG. 2 holds a conductive polymer and an electrolyte.

Next, a manufacturing method of the present invention for manufacturing an electrolytic capacitor having the above-described structure will be explained.
First, prepare an anode foil and a cathode foil cut to a predetermined width, connect lead terminals for external extraction electrodes to the anode foil and cathode foil, and wind the anode foil and cathode foil through a separator. By doing so, a wound element is manufactured (winding element manufacturing process).
The anode foil used in this case is made of a valve metal on which a dielectric oxide film is formed, and examples of the valve metal used for the anode foil include aluminum, tantalum, niobium, and the like. Further, the dielectric oxide film on the surface of the anode foil is formed by subjecting the surface of the valve metal to etching treatment and chemical oxidation treatment. On the other hand, the cathode foil is generally made of an aluminum foil on which carbide particles or titanium particles are held, or an aluminum foil whose surface has been etched, but is not limited thereto. Further, the separator used when producing the wound element is generally made mainly of cellulose fibers, but it may also be a mixed fiber separator mixed with chemical fibers or a synthetic fiber separator. Examples of the chemical fibers include synthetic fibers such as polyester fibers, polyamide fibers, acrylic fibers, polyimide fibers, aramid fibers, and nylon fibers.

Next, a so-called chemical conversion treatment is performed to repair the cut end of the anode foil in the wound element or the dielectric oxide film that was damaged during the attachment of the lead terminal (chemical conversion process). As the chemical conversion liquid used for this chemical conversion treatment, a chemical conversion liquid in which a solute of an organic acid salt having a carboxylic acid group or an inorganic acid salt such as phosphoric acid is dissolved in an organic solvent or an inorganic solvent can be used. At this time, use a chemical solution (e.g., phosphoric acid chemical solution or boric acid chemical solution) in which a solute mainly composed of ammonium adipate is dissolved in an aqueous solvent and the concentration is adjusted to 0.1 to 2.0% by weight. is preferable, and the first chemical conversion treatment is performed by applying a voltage similar to the chemical conversion voltage value of the dielectric oxide film.
Thereafter, heat treatment is applied, and a final chemical conversion is performed using a chemical conversion liquid in which a solute mainly composed of phosphoric acid is dissolved in an aqueous solvent and the concentration is adjusted to 0.1 to 0.5% by weight. In the present invention, a tough dielectric oxide film is formed by repeating this chemical formation and heat treatment process, and the heat treatment performed here is generally performed at a temperature range of 300°C or less for several minutes to several tens of minutes. .

Next, a conductive polymer layer, which is the cathode layer of a hybrid capacitor, is formed on the wound element that has been subjected to the above chemical conversion treatment to produce a capacitor element, but the method for forming the conductive polymer layer is limited. For example, the wound element after chemical conversion treatment is immersed in a dispersion of a conductive polymer in water, or a conductive polymer solution in which a conductive polymer is dissolved in a solvent is used. After the wound element after the chemical conversion treatment is immersed, the wound element is pulled up, the solvent is removed, and a conductive polymer layer is formed within the element (conductive polymer formation step). At this time, the immersion depth when impregnating the above-mentioned wound element in the dispersion liquid or conductive polymer solution is equal to the height of the wound element in the axial direction (hereinafter simply referred to as "wound element height"). It is preferable to set it to 1/3 to 2/3. That is, when the direction in which the lead terminals of the wound element are pulled out is set upward, the outer periphery of the tape is covered with conductive polymer from the lower end of the wound element to 1/3 to 2/3 of the height of the wound element. Impregnate it so that it is soaked. For drying to remove the solvent from the wound element, drying for a long time at about room temperature or drying under reduced pressure may be used.
Note that if the depth of immersion of the wound element in the dispersion liquid or conductive polymer solution is less than 1/3 of the height of the wound element, the formation of the conductive polymer inside the wound element will be insufficient. If it exceeds /3, the amount of conductive polymer adhering to the lead terminal increases, so that the effects of immersion in a polyglycerin solution and polyglycerin coating, which will be described later, cannot be sufficiently obtained. Further, the outer periphery of the wound element is a tape, and a conductive polymer is formed on the outer periphery of the wound element up to the position where the wound element is immersed in the dispersion liquid or the conductive polymer solution with respect to the tape surface.
In the present invention, the conductive polymer used when forming the conductive polymer layer includes polyethylenedioxythiophene/polystyrene sulfonic acid polymer (PEDOT-PSS), self-doped polyethylenedioxythiophene, polypyrrole, Examples include, but are not limited to, polyaniline.

In the manufacturing method of the present invention, after impregnating the wound element after chemical conversion treatment with a conductive polymer and before heating, the wound element to which the conductive polymer has adhered is impregnated with the conductive polymer. The wound element is immersed in the glycerin solution to a position above the upper surface thereof, and the round bar portion of the lead terminal is coated with the solution. At this time, at least ⅓ of the round bar portion from the top surface of the wound element, preferably the entire round bar portion, is immersed in the polyglycerin solution. If the immersion position of the round bar portion of the lead terminal is less than 1/3, the effect of reducing leakage current is small, and if the lead wire is immersed beyond the round bar portion, manufacturing equipment may be contaminated.

Thereafter, the capacitor element is taken out of the polyglycerin solution and heated at a temperature of 150 to 210° C. to completely solidify the conductive polymer and form a polyglycerin coating on the conductive polymer layer and the round rod portion. The polyglycerin used in the polyglycerin solution preferably has a weight average molecular weight of 100 to 1,000, more preferably a polyglycerin in the range of 200 to 400.
Examples of the solvent used in the polyglycerin solution include ethanol, ethylene glycol (EG), and diethylene glycol, but it is preferable to use ethylene glycol, which can adjust the orientation of the conductive polymer. A solvent (eg, polyalkylene glycol, etc.) that does not adversely affect the conductive polymer may be added to the polyglycerin solution. The concentration of the polyglycerin solution is preferably 1 to 30% by weight, more preferably 3 to 20% by weight, particularly preferably 5 to 15% by weight.
In the present invention, the conductive polymer attached to the round bar part of the lead terminal can be removed by providing a step of immersing the round bar part of the lead terminal above the top surface of the capacitor element in the polyglycerin solution. In addition, since a polyglycerin film is formed, it is thought that stabilization of leakage current before and after reflow can be achieved.

In the present invention, the capacitor element on which the conductive polymer layer is formed as described above is impregnated with an electrolytic solution. The electrolytic solution used in this case is generally a solution containing a solute and a stabilizer, and preferably has a boiling point of 180° C. or higher and a specific resistance of 1 kΩ·cm or higher.
Solvents in the above electrolyte include water, ethylene glycol, ethylene glycol monomethyl ether, 1,5-pentanediol, γ-butyrolactone, γ-valerolactone, N-methylformamide, sulfolane, etc., and solutes include: Examples include boric acid, adipic acid, maleic acid, benzoic acid, phthalic acid, salicylic acid, ricinoleic acid, phosphorous acid, dibutylamine, triethylamine, etc., and the solute concentration in the electrolyte is 0.5 to 15.0% by weight. It is preferably 1 to 11% by weight, and more preferably 1 to 11% by weight.

In the manufacturing method of the present invention, a capacitor element impregnated with the electrolytic solution described above is housed in a cylindrical metal case with a bottom, a sealing member for sealing the opening of the metal case is attached, and the capacitor element is impregnated with the electrolytic solution. The opening is sealed by curling (sealing process). At this time, the sealing member is made of elastic rubber (for example, butyl rubber, etc.) and has a through hole through which the external lead terminal passes. Note that the capacitor element and the electrolyte may be housed in a metal case, and the capacitor element may be impregnated with the electrolyte within the metal case.
Next, a rated voltage is applied to the capacitor under a temperature condition below the upper limit temperature of the category, and an aging treatment is performed (aging treatment step), thereby completing a hybrid aluminum electrolytic capacitor.
The hybrid capacitor obtained by carrying out the above process has achieved a reduction in leakage current, and has a characteristic that fluctuations in leakage current before and after reflow are small.
The present invention will be described in more detail below based on Examples, but the present invention is not limited to these Examples.

[Example: Example of manufacturing a hybrid aluminum electrolytic capacitor using the manufacturing method of the present invention]
The anode foil is prepared by roughening aluminum foil by etching and then chemical conversion treatment to form a dielectric oxide film, and the cathode foil is prepared by roughening the surface by etching. An ordinary cellulose fiber separator was used as a separator.
Then, the flat parts (formed of aluminum) of lead terminals for external extraction electrodes are connected to the anode foil and cathode foil cut to a predetermined width, respectively, and wound by winding them through the separator. The device was fabricated.

Next, the solute is dissolved in an aqueous solvent mainly containing ammonium adipate to prepare a chemical liquid with a concentration of 1% by weight, and this chemical liquid is applied to the wound element to adjust the chemical formation voltage value of the dielectric oxide film. A similar voltage was applied to perform the first chemical conversion treatment. Thereafter, a heat treatment (200° C., 30 minutes) was added, and a final chemical conversion was performed using a chemical conversion solution in which a solute mainly composed of phosphoric acid was dissolved in a water solvent and the concentration was adjusted to 0.2% by weight. By repeating this chemical formation and heat treatment process, a dielectric oxide film was formed.
Thereafter, the wound element after the chemical conversion treatment was immersed in a dispersion containing PEDOT/PSS under reduced pressure for 15 minutes so that the immersion depth was approximately 1/2 of the height of the wound element, and the dispersion was After the wound element was pulled up from the substrate, it was dried at 90° C. or lower. The dispersion liquid permeates inside the wound element and is retained up to the upper surface of the wound element, forming a conductive polymer. Since the corner is large, it is formed only up to the immersion position of the wound element.

Then, a polyglycerin solution is prepared by mixing 10% polyglycerin (PG, weight average molecular weight: 300) in ethylene glycol, and the wound element to which the conductive polymer is attached is placed in this solution. The polyglycerin solution was immersed so that the part above the top surface and the entire round bar part of the lead terminal was immersed, so that the polyglycerin solution adhered to the round bar part of the lead terminal of the wound element (soaking time: 1 minutes). Furthermore, although the conductive polymer attached to the surface of the round bar part of the lead terminal is removed by immersion in the polyglycerin solution, the conductive polymer formed on the tape surface is not removed much.
Thereafter, the wound element was pulled up and dried at 160°C to form a conductive polymer layer, thereby producing a capacitor element.

Thereafter, the capacitor element obtained above and a predetermined amount of electrolyte solution (solvent: 1,5-pentanediol and γ-valerolactone, solute: ricinoleic acid, phosphorous acid, dibutylamine, solute concentration: 10.5%) was housed in a bottomed cylindrical metal case, a sealing member (made of butyl rubber) for sealing the opening of the metal case was attached, and the opening of the metal case was sealed by curling. Subsequently, a predetermined voltage was applied to the capacitor under a temperature condition of 125° C., which is the upper limit temperature of the category, and an aging treatment (125° C., 1 hour) was performed to produce 50 hybrid aluminum electrolytic capacitors (products of the present invention). The hybrid capacitor manufactured in this example has a size of 10 mm in diameter x 10 mm in length, a rated voltage of 35 V, and a rated capacitance of 270 μF.

[Comparative example: When the wound element is immersed up to 1/2 of the height in polyglycerin solution]
Same as Example 1, except that the depth of immersion in the polyglycerin solution in the Example was set to about 1/2 of the height of the wound element, and the liquid level was not intentionally raised. Then, 50 hybrid aluminum electrolytic capacitors (comparative product) were manufactured. The size, rated voltage, and rated capacitance of the hybrid capacitor manufactured in this comparative example are the same as those in the example.

[Comparison of electrical characteristics before and after reflow]
Regarding the electrolytic capacitor manufactured in the above example and the electrolytic capacitor manufactured in the above comparative example, the electrical characteristics before reflow (after aging) and after reflow, that is, the capacitance (Cap) at a frequency of 120 Hz and the loss angle The tangent (tan δ), the equivalent series resistance (ESR) at a frequency of 100 kHz, and the leakage current (LC) after applying the rated voltage for 2 minutes were measured and compared.
The results are shown in Table 1 below. In addition to the maximum value (MAX), minimum value (MIN), and average value (AVE) of n=50 measured values, Table 1 also includes the rate of change in capacitance (ΔCap), rate of change in equivalent series resistance. is also shown.

From the results in Table 1 above, it can be seen that when a wound element with a conductive polymer attached to it is immersed in a polyglycerin solution up to the round bar part of the lead terminal to form a polyglycerin film on the round bar part, there is a difference between before and after reflow. It was confirmed that fluctuations in leakage current (LC) can be stabilized.

In the examples, PEDOT/PSS was used as the conductive polymer, but the same effect can be obtained by using other conductive polymers such as self-doped polyethylenedioxythiophene, polypyrrole, polyaniline, etc. .

According to the manufacturing method of the present invention, the wound element before completely solidifying the conductive polymer is immersed in a polyglycerin solution up to the portion above the upper surface of the element, that is, the round bar portion of the lead terminal. As a result, leakage current can be improved, and this manufacturing method is useful for manufacturing electrolytic capacitors, particularly conductive polymer hybrid aluminum electrolytic capacitors.

1 Hybrid capacitor 2 Metal case (exterior case)
3 Capacitor element 4 Sealing member 5 Top surface of capacitor element 11 Anode foil (anode)
12 Cathode foil (cathode)
13 Separator 14 Tape 15 Conductive polymer 21, 22 Lead terminal 23 Round bar part 31, 32 Hole

Claims (5)

a wound element manufacturing step of manufacturing a wound element by winding an anode foil and a cathode foil to which lead terminals for external extraction electrodes are connected via a separator;
a chemical conversion treatment step of chemically treating the cut cross section of the anode foil and the attachment portion to the lead terminal of the wound element;
The wound element after the chemical conversion treatment is immersed in a dispersion of a conductive polymer dispersed in water or a conductive polymer solution to form a conductive polymer layer made of the conductive polymer to form a capacitor element. A conductive polymer formation process to produce;
a sealing step of storing the capacitor element and the electrolyte in a bottomed cylindrical metal case and sealing the opening of the metal case;
In a method for manufacturing an electrolytic capacitor, the method includes an aging treatment step,
In the conductive polymer forming step, after drying the wound element after immersing it in the dispersion or conductive polymer solution, and before completely solidifying the conductive polymer, the wound element is coated with polyester. The round bar part of the lead terminal above the top surface of the wound element is immersed in the glycerin solution , and the conductive polymer adhering to the round bar part is removed , and then removed from the polyglycerin solution. A method for manufacturing an electrolytic capacitor , comprising drying to completely solidify the conductive polymer to form the conductive polymer layer. 2. The method for manufacturing an electrolytic capacitor according to claim 1, wherein the polyglycerin solution uses ethanol, ethylene glycol, diethylene glycol, or a mixture of two or more solvents of ethanol, ethylene glycol, and diethylene glycol as a solvent. 3. The method for manufacturing an electrolytic capacitor according to claim 1, wherein the polyglycerin solution uses ethylene glycol as a solvent and has a polyglycerin concentration of 1 to 30% by weight. The lead terminal for the external extraction electrode consists of a flat part made from one round bar part and a lead wire welded to the other round bar part, and the anode foil and cathode foil connected to the flat part of the lead terminal are separated by a separator. An electrolytic capacitor comprising a wound element wound through the separator, a conductive polymer held by the separator, and an electrolytic solution,
An electrolytic capacitor characterized in that the round rod portion of the lead terminal does not have a conductive polymer layer and is covered with a polyglycerin film . The outer periphery of the winding element extends from 1/3 to 2/3 of the height of the winding element above the lower end of the winding element, when the lead terminal drawing direction of the winding element is set upward. The electrolytic capacitor according to claim 4, wherein the electrolytic capacitor is covered with the conductive polymer.

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