JPH0430409A - Manufacture of solid electrolytic capacitor - Google Patents

Abstract

PURPOSE:To obtain a solid electrolytic capacitor by a method wherein a valve metal, on the surface of which a dielectric layer and a conductive layer are provided sucessively, is dipped into an electrolytic polymerizing liquid, and electrode for electric polymerization and a second electrode for positional polymerization, which is separated from the above-mentioned electrode, are provided on the surface through the intermediary of insulating substance, and a polymerized film is formed on the surface by applying potential. CONSTITUTION:A conductive layer is provided on the surface of an oxide film of valve metal, an electrode for electrolytic polymerization is brought into contact with the above-mentioned conductive layer through the intermediary of electric insulating substance, electric potential is applied, and the conductive layer is coated with an electrolytic polymerization high molecule. As a result, when the electrode for polymerization is exfoliated after the electrolytic polymerization is finished, the electrolytic polymerization film is not exfoliated from the surface of the valve metal. Besides, when the electrolytic insulating material is relatively soft material, the hard metal-to metal contact of the valve metal and the electrolytic polymerizing electrode can be prevented, the damage of the oxide film can be prevented, and the manufacture of a solid electrolytic capacitor, having small leakage current and high withstand voltage, can be accomplished.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to solid electrolytic capacitors with excellent capacitor characteristics, especially frequency characteristics, and reliability characteristics under high temperature and high humidity conditions, particularly solid electrolytic capacitors using conductive polymers as the solid electrolyte. The present invention relates to a method for manufacturing a capacitor.

2. Description of the Related Art In recent years, with the digitalization of electrical equipment, capacitors are required to be small, large in capacity, and have low impedance in the high frequency range. Traditionally, capacitors used in the high frequency range include plastic capacitors, mica capacitors,
There are multilayer ceramic capacitors, but these capacitors have a large shape and are difficult to increase capacity. On the other hand, examples of large capacity capacitors include electrolytic capacitors such as aluminum dry electrolytic capacitors and aluminum or tantalum solid electrolytic capacitors. In these capacitors, the oxide film that serves as the dielectric material is extremely thin, making it possible to achieve large capacitance, but on the other hand, the oxide film is easily damaged, so it is necessary to provide an electrolyte between the cathode and the cathode to repair it. There is.

In aluminum dry capacitors, etched positive and negative electrode aluminum foils are wound through a separator.
The separator is impregnated with liquid electrolyte. This liquid electrolyte has ionic conductivity and high specific resistance, resulting in large losses and significantly inferior impedance frequency characteristics and temperature characteristics. In addition, liquid leakage, evaporation, etc. are unavoidable, resulting in a decrease in capacity and an increase in loss over time. In addition, tantalum solid electrolytic capacitors use manganese dioxide as the electrolyte, which improves the problems of temperature characteristics, capacity, loss, etc., but the relatively high specific resistance of manganese dioxide causes loss,
The impedance frequency characteristics are inferior compared to multilayer ceramic capacitors or film capacitors.

In contrast, recently, organic semiconductors with high conductivity and excellent anodic oxidation properties have been used as solid electrolytes instead of manganese dioxide. It has been proposed to use -tetracyanoquinodimethane complex salt (hereinafter abbreviated as "TCNQ salt").

Invention by the same applicant (Japanese Patent Publication No. 10777/1983) and invention by Shin Niwa (Japanese Patent Publication No. 176/1982)
As published in Publication No. 09), such TC
In aluminum solid electrolytic capacitors using NQ salt,
Frequency and temperature characteristics have been significantly improved, and low leakage current characteristics have been achieved. In addition, TCNQ salt has excellent thermal stability as an organic conductive material.
The high-temperature lifespan of the resulting capacitor is said to far exceed that of conventional dry electrolytic capacitors. Furthermore, in recent years,
By electrolytically polymerizing heterocyclic monomers such as pyrrole and thiophene using a supporting electrolyte, a highly conductive polymer containing the anion of the supporting electrolyte as a dopant is formed on the anode body, and this is a solid that is used as an electrolyte. Electrolytic capacitors have been proposed (JP-A-60-37114, JP-A-60-233017).

Problems to be Solved by the Invention However, according to the electrolytic polymerization method, polymers can be formed on the anode surface by electrolytic oxidation of monomers;
It has been difficult to form electrolytically polymerized polymers on the dielectric surface, which is insulated because it has an oxide film, without destroying the film.

Furthermore, even if the oxide film is partially destroyed and electropolymerization is performed, it is difficult to increase the growth rate and it takes a long time to cover the entire surface. Furthermore, if an electrolytic polymer film is grown from the oxidized film broken part provided in a part of the capacitor anode whose surface has been enlarged by etching etc., as described above, the growth will not reach the inside of the etch pin. It has been difficult to obtain a capacitor with a high capacity achievement rate.

On the other hand, it is not impossible to coat the valve metal surface with an electropolymerized polymer before forming an oxide film and then form an oxide film by anodic oxidation, but in this case, a chemical reaction is performed via the electrolyte polymer film. As a result, it has been difficult to obtain a capacitor with good characteristics due to deterioration of the electrolytically polymerized membrane and deterioration of its adhesion to the valve metal surface.

For this reason, an attempt has been made to form an electrolytically polymerized film by bringing a polymerization initiating electrode into contact with the surface of the valve metal having an oxide film from the outside, but in this case, the oxide film is removed by contact with the polymerization initiating electrode. There has been a problem in that leakage current characteristics and withstand voltage inevitably deteriorate due to damage or peeling of the polymer film when separating the polymerization initiating electrode after forming the polymer film. It is also possible to form an electrolytic polymer film by providing the electrolytic polymer electrode close to the valve metal, since the electrolytic polymer film grows from the electrolytic polymer electrode and comes into contact with the valve metal. When the electrolytically polymerized electrode is peeled off, part of the polymer film peels off from the valve metal, so an increase in leakage current and a decrease in withstand voltage were unavoidable.

In the case of etched capacitor anodes, in addition to this, it is difficult to form an electrolytic polymer film inside the etch pits, similar to when electrolytic polymerization is performed by destroying the oxide film, so the capacity achievement rate is reduced. It was difficult to realize a high capacitor.

The present invention solves the above problems, and provides a polymer coating that prevents damage to the oxide film, has excellent leakage current and withstand voltage characteristics, is easy to coat with electropolymerized polymer, has a high coverage rate, and has a high capacity and The purpose of this invention is to provide a manufacturing method that can realize a solid electrolytic capacitor with excellent loss.

Means for Solving the Problems The present invention achieves the above object, and its technical means is to provide a conductive layer on the surface of the valve metal on which an oxide film serving as a dielectric has been formed, and to immerse this in an electrolytic polymerization solution. , a potential is applied between a first electrode for electrolytic polymerization installed on the surface of the conductive layer via an electrically insulating material and a second electrode for electrolytic polymerization installed apart from the first electrode, and the electrolytic A polymer film is formed on a valve metal provided with an oxide film and a conductive layer. When an electrically insulating substance is provided on a part of the valve metal surface on which a dielectric layer and a conductive layer are sequentially formed, an electrolytic polymer film grows from the first electrode for electrolytic polymerization by applying a potential. Therefore, even if the electrode for electrolytic polymerization is provided close to the electrically insulating material, the same effect as when the electrode is brought into contact can be obtained.

Function The present invention provides a conductive layer on the surface of the oxide film of a valve metal having an oxide film, brings an electrode for electrolytic polymerization into contact with this conductive layer via an electrically insulating material, and applies a potential to achieve high electrolytic polymerization. It is designed to be coated with molecules.

This can prevent a part of the electropolymerized membrane from peeling off from the valve metal surface when the polymerization electrode is peeled off after the electrolytic polymerization is completed, thereby preventing short-circuit failures or an increase in leakage current. Furthermore, if the electrically insulating material is a relatively soft material such as a polymeric material, direct contact between the hard metals between the valve metal on which the oxide and conductive layer are formed and the electrode for electrolytic polymerization can be avoided. It also has the effect of preventing damage to the oxide film that serves as the dielectric.
A solid electrolytic capacitor with low leakage current and high withstand voltage can be realized. This is based on the fact newly discovered by the inventors that an electrolytic polymer film grows relatively easily on the surface of an electrically insulating material that has a relatively smooth surface.

By shortening the distance between the part covered with an electrically insulating material from the contact part of the electrode for electrolytic polymerization to the exposed part of the valve metal provided with the oxide film and conductive layer, it is practically possible to It is possible to form an electrolytically polymerized film on the entire surface in the same amount of time. If an electrically insulating material is placed on the front and back sides of the valve metal with an oxide film and a conductive layer formed on it, dividing it into two parts, and then placed above and below the surface of the electrolytic polymerization liquid, the surface of the valve metal can be etched by etching or other means. When the area is enlarged, it is possible to prevent the polymerization liquid from seeping up due to capillary action and making the boundary between the area where the electrolytically polymerized film is formed and the area where it is not unclear from becoming unclear. This makes it possible to reduce short-circuit failures or leakage currents that occur due to reasons different from those described above. By shortening the distance between the part covered with an electrically insulating material from the contact part of the electrode for electrolytic polymerization to the exposed part of the valve metal provided with the oxide film and conductive layer, it is practically possible to It is possible to form an electrolytically polymerized film on the entire surface in the same amount of time. Any electrically insulating material can be used as long as it does not substantially dissolve in the electrolytic polymerization solution, but polymeric materials are preferred because they have a particularly great effect on preventing damage to the oxide film formed on the valve metal surface. It is. Among polymer materials, condensation polymers are more preferable because they have a high growth rate of a polymer film, and among these, polyimide is particularly preferable because it also has excellent heat resistance. Any method can be used to interpose the electrically insulating material, and in addition to being attached to the surface of a valve metal on which an oxide film and a conductive layer have been formed, it can also be used by placing it on the surface of an electrode for electrolytic polymerization.

Since a conductive layer is provided on the oxide film, it is possible to easily grow electrolytic polymerization in the direction of the surface through this, and especially when using a valve metal that has been corrugated by etching, it is possible to easily grow electrolytic polymerization inside the etch pit. It is possible to form an electrolytically polymerized film up to 10%, and a capacitor with a high capacity achievement rate can be easily obtained.

Although any material can be used for the conductive layer, it is preferably used because a thin conductive layer can be formed inside the etch pits of the valve metal etched with pyrolytic manganese oxide. Although there is no limitation on the shape of the electrode, it is preferable to use one whose surface area has been expanded by etching or the like.

EXAMPLES Hereinafter, examples of the present invention will be described with reference to the drawings. 1st
The figure is a sectional view of a capacitor anode foil showing one embodiment of the invention to which a polymer film is attached. FIG. 2 is a sectional view showing one embodiment of an apparatus for performing electrolytic polymerization according to the present invention.

Example 1 As shown in Fig. 1, an 8 x 10 mm aluminum etched foil was used as the valve metal 6, an anode lead 7 was attached to this foil, and 35V was applied at about 70°C using a 3% ammonium adipate aqueous solution. Dielectric coating 6 by anodic oxidation
After forming, it is soaked in a 30% manganese nitrate aqueous solution and further
The anode was prepared by heating at 0° C. for 10 minutes and depositing pyrolyzed manganese oxide as a conductive layer 4 on the surface. As shown in FIG. 1, a polymer film 1 made of mica (polyimide film) having a width of 1 mm and a thickness of about 26 μm was attached to both sides of the anode foil. Thereafter, as shown in FIG. 2, a first electrode 2 made of stainless steel for electrolytic polymerization was brought into contact with the polymer film 1, and the electrode was made of pyrrole (0.3M), sodium p-toluenesulfonate (0.15M), and water. Electrolyte 8
A voltage of 3V was applied between the first electrode 2 for electrolytic polymerization and the second electrode 3 for electrolytic polymerization provided apart from each other to form an electrolytic polymerized membrane in which polypyrrole was doped with naphthalene sulfonate anions (Fig. (not shown) was formed on the conductive layer 4. 9 is an electrolytic polymerization tank. Table 1 shows the time required to coat the entire surface.

The first electrode 2 for electrolytic polymerization (Table 1) was removed, washed with water, and dried. Carbon paste and silver paste were applied onto the electrolytic polymerized membrane, and the cathode lead was taken out to complete a capacitor element. This was then externally sealed with epoxy resin to complete 10 capacitors.

Table 1 shows the average values of capacity, loss, leakage current, and breakdown voltage in 120H2 after aging at 13V. As is clear from the comparison with the results of Comparative Example 1.2, it was demonstrated that the capacitor according to the present invention has extremely excellent characteristics.

Comparative Example 1 Ten capacitors were produced in the same manner as in Example 1, except that the anode foil and the electrolytic polymerization electrode were brought into direct contact without providing manganese oxide or pasting mica pieces. A similar evaluation was conducted. The results are shown in Table 1. It was shown that it took an extremely long time to cover the entire surface with the electrolytic polymer film, and that the capacitance and loss of the obtained capacitor were significantly inferior to the capacitor obtained in Example 1. Furthermore, the leakage current and withstand voltage characteristics were also poor. is shown to be low. From the above, it is clear that the effect of the present invention is that a conductive layer is provided on the anode valve metal surface on which an oxide film is formed, and a polymer film is further interposed between the electrode for electrolytic polymerization and the anode covered with the electrolytic polymer film.

Note that a capacitor was also produced under the same conditions as in Example 1 except that the manganese oxide layer was not provided on the surface of the oxide film. In this case, the breakdown voltage and leakage current characteristics were the same as in Example 1, but the capacity and loss were inferior as in Comparative Example 1.

Note that a capacitor was also produced under the same conditions as in Example 1, except that the electrolytically polymerized electrode was brought into contact without using a mica piece.

In this case, the capacity and withstand voltage characteristics were the same as those of Example 1, but the leakage current and withstand voltage characteristics were the same as those of Comparative Example 1.
It was as inferior as in the case of .

Example 2 Ten capacitors were produced in the same manner as in Example 1, except that a piece of quartz glass of the same size was attached in place of the mica in Example 1, and the same evaluation as in Example 1 was performed. The result is the first
Shown in the table. It is clear that the capacity, loss, leakage current, and withstand voltage are superior to those of Comparative Example 1, and the effects of the present invention are verified.

Example 3 Ten capacitors were produced in the same manner as in Example 1, except that polyimide having a thickness of 26 μm was attached instead of mica in Example 1, and the same evaluation as in Example 1 was performed. The results are shown in Table 1. It is clear that the time required to cover the entire surface with the electropolymerized membrane is shorter than that of Example 1, and that the capacity, loss, leakage current, and withstand voltage are superior to those of Comparative Example 1, demonstrating that the effects of the present invention are Proven.

Example 4 Ten capacitors were produced in the same manner as in Example 1, except that polyester having a thickness of about 100 μm was attached instead of mica in Example 1, and the same evaluation as in Example 1 was performed. The results are shown in Table 1. It is clear that the capacity, loss, leakage current, and withstand voltage are superior to those of Comparative Example 1.
The effectiveness of the invention was demonstrated.

Example 6 Ten capacitors were produced in the same manner as in Example 1 except that a 25 μm thick polyphenylene sulfide film was attached instead of the mica in Example 1, and the same evaluation as in Example 1 was performed. The results are shown in Table 1. It is clear that the capacity, loss, leakage current, and withstand voltage are superior to those of Comparative Example 1, and the effects of the present invention are verified.

Example 6 Ten capacitors were produced in the same manner as in Example 1, except that a 26 μm thick polyamide film was attached instead of the mica in Example 1, and the same evaluation as in Example 1 was performed. The results are shown in Table 1. It is clear that the time required to cover the entire surface by electrolytic polymerization is shorter than in Example 1, and the capacity, loss, leakage current, and withstand voltage are superior to those in Comparative Example 1, demonstrating the effectiveness of the present invention. .

Example 10 capacitors were produced in the same manner as in Example 1, except that instead of contacting the electropolymerized electrodes of Example 1 on the mica, they were placed in close proximity to 1, 2, and 3, and the results were as follows. are shown in Table 1. The time required to cover the entire surface with the electrolytic polymer film tends to increase with the distance between the electrolytic polymer electrode and the mica, but when the time is 2 or less, substantially favorable results were obtained in terms of capacitor production. Note that the capacitor characteristics were excellent as in Example 1, regardless of the proximity distance of the electrolytically polymerized electrode.

Example 8 Sodium dodecyl sulfate (SDS), n
-butyl phosphate ester (NBP), sodium heptanobutylnaphthalene sulfonate (SMBN8), sodium lysopropylnaphthalene sulfonate (STIP)
1 in the same manner as in Example 1 except that NS) was used, respectively.
0 capacitors were produced and evaluated in the same manner as in Example 1.

The results are shown in Table 1. It is clear that the time required to cover the entire surface by electrolytic polymerization is almost the same as in Example 1, and the capacity, loss, leakage current, and withstand voltage are superior to those in Comparative Example 1, demonstrating the effectiveness of the present invention. .

Example 9 Ten pieces were prepared in the same manner as in Example 1, except that the monomer pyrrole in Example 1 was replaced with thiophene, the supporting electrolyte sodium p-toluenesulfonate was replaced with tetraethylammonium, and the solvent water was replaced with acetonitrile. A capacitor was manufactured and evaluated in the same manner as in Example 1. The results are shown in Table 1. It is clear that the time required to cover the entire surface by electrolytic polymerization is almost the same as in Example 1, and the capacity, loss, leakage current, and withstand voltage are superior to those in Comparative Example 1, demonstrating the effectiveness of the present invention. .

Example 1 After embossing, heat treatment at approximately 90°C using 10% phosphoric acid aqueous solution
Ten capacitors were produced in the same manner as in Example 1, except that a mental foil that had been anodized to which 35 V was applied was used, and the same evaluation as in Example 1 was performed. The results are shown in Table 1.

As is clear from the comparison with Comparative Example 2, the capacitor of this example was shown to be excellent in capacity, loss, leakage current, and withstand voltage characteristics, demonstrating the effects of the present invention.

Comparative Example 2 Without providing a manganese oxide layer and without attaching mica foil,
Ten capacitors were produced in the same manner as in Example 9, except that the anode foil and the electrode for electrolytic polymerization were brought into direct contact.
The same evaluation was conducted. The results are shown in Table 1. It was shown that it took an extremely long time to cover the entire surface with the electrolytic polymer film, and that the capacitance and loss of the obtained capacitor were significantly inferior to the capacitor obtained in Example 1. Furthermore, the leakage current and withstand voltage characteristics were also poor. is shown to be low. From the above, a conductive layer is provided on the anode valve metal surface on which an oxide film has been formed,
Furthermore, the effect of the present invention in which a polymer film is interposed between the electrode for electrolytic polymerization and the anode covered with the electrolytic polymerized membrane is clear.

Note that although the examples have described only the case where pyrolyzed manganese oxide is used as the conductive layer, the conductive layer may be formed using other conductive materials, and the present invention is not limited to this type.

In addition, in the example, only the case where the electrical insulating material of 1-width width was applied across the front and back sides of the electrode foil was described, but it may be applied only to one side, or it may not cover the entire width of the capacitor electrode. The present invention is not limited to the shape.

In addition, although only the case where the electrical insulating material with the thickness of 25-100 micrometers was used was described in the Example, the thickness other than this may be used, and the present invention is not limited to this thickness.

In addition, although the case where a film-shaped electrical insulating material was attached and used was described in the Example, it can also be formed using vapor deposition, sputtering, etc., and this invention is not limited to the formation method.

In addition, although the example uses pyrrole and thiophene, it is also possible to use those with derived substituents, and it is also possible to use a mixture of them, and the present invention is not limited to these types. Not done.

Effects of the Invention In short, the present invention provides a conductive layer on the surface of a valve metal on which an oxide film serving as a dielectric is formed, immerses this in an electrolytic polymerization solution, and installs it on the surface of the conductive layer via an electrically insulating material. A potential is applied between a first electrode for electrolytic polymerization and a second electrode for electrolytic polymerization installed apart from the first electrode to form an electrolytic polymer film on a conductive layer, and it is an electrically insulating film. Since the electrode for electrolytic polymerization is arranged with a material interposed between the electrodes, damage to the oxide film that serves as the dielectric and peeling of the electrolytic polymer film from the valve metal surface when the electrode is removed is prevented, reducing leakage current and withstand voltage. Provides solid electrolytic capacitors with excellent characteristics, etc., and because a conductive layer is provided on the surface of the capacitor electrode, coating with electrolytically polymerized polymer is easy and a polymer film with a high coverage rate can be obtained, and has excellent capacity and loss. It has the advantage of being able to

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a capacitor anode foil to which a polymer film is attached according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view showing an embodiment of an apparatus for electrolytic polymerization according to the present invention. DESCRIPTION OF SYMBOLS 1... Polymer film, 2... First electrode for electrolytic polymerization, 3... Second electrode for electrolytic polymerization, 4... Conductive layer, 5...
... Dielectric film, 6... Valve metal, 7... Anode lead, 8... Electrolyte solution for electrolytic polymerization, 9... Electrolytic polymerization tank. Name of agent: Patent attorney Shigetaka Awano and 1 other famous artist Figure 7 Anode lead

Claims (1)

[Scope of Claims] (1) For electrolytic polymerization, a valve metal having a dielectric layer and a conductive layer sequentially formed on its surface is immersed in an electrolytic polymerization solution, and an electrically insulating material is provided on the surface of the valve metal. A method for producing a solid electrolytic capacitor, comprising applying a potential between a first electrode and a second electrode for polymerization provided at a position separated from the first electrode to form a polymer film on the surface. . (2) The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein the electrically insulating material is a polymeric material. (3) An electrically insulating material is provided on a part of the valve metal surface on which a dielectric layer and a conductive layer are sequentially formed, and the first electrode for electrolytic polymerization is in contact with or near the electrically insulating material. 2. The method of manufacturing a solid electrolytic capacitor according to claim 1. (4) The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein the conductive layer is formed by immersing the valve metal on which the dielectric is formed in an aqueous manganese nitrate solution and then thermally decomposing the manganese nitrate at 200 to 400°C. (6) The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein the electrolytic polymerization solution comprises an electrolytically polymerizable monomer, a supporting electrolyte, and a solvent. (6) The method for producing a solid electrolytic capacitor according to claim 5, wherein the electrolytic monomer contains at least one of pyrrole, thiophene, or a derivative thereof. (7) The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein the valve metal is one selected from aluminum and tantalum.