JPH0722068B2 - Capacitor manufacturing method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a capacitor in which a polyimide coating is formed on the surface of a porous conductor and used as a dielectric layer.

2. Description of the Related Art Film capacitors are usually manufactured by winding polyester or polypropylene film as a dielectric with metal such as aluminum foil, or by vacuum-depositing metal on one or both sides and then winding or laminating. There is.

Problems to be Solved by the Invention Generally, in order to obtain a large-capacity film capacitor, a plastic film obtained by vacuum-depositing metal on one side or both sides is used in a wound or laminated state, but the dielectric constant of the plastic film is It is as small as a few, and it is difficult to obtain a large-capacity film capacitor because there is a limit in thinning the film, and a practical use in a circuit is limited to several microfarads.

Since it is preferable to increase the surface area of the dielectric in order to obtain a large-capacity capacitor, it is preferable to make the surface of the conductor serving as an electrode porous and form the dielectric on the surface. Therefore, after roughening treatment like an etched aluminum foil, in order to form a polyimide on the surface of the conductor whose surface area has been enlarged, after dipping in a solution containing polyamic acid and sufficiently filling the pores with polyamic acid However, when heat-dehydrated to form a polyimide, all the pores were filled, and the expanded surface area could not be used effectively, and it was difficult to obtain the expected capacity.

On the other hand, with an electrolytic capacitor having a structure in which an oxide film is formed as a dielectric on the surface of a valve metal such as aluminum or tantalum, the oxide film can be made very thin, so a small capacitor with a large capacity can be obtained. Since the dielectric oxide film is fragile, it has many defects such as weakness against mechanical stress and impact, resulting in a large leakage current. Further, since the dielectric oxide film of the valve metal has a rectifying action, it is difficult to form a nonpolar capacitor.

The purpose of the present invention is to form a polyimide coating as a dielectric on the porous conductor surface, in a capacitor having a structure in which a counter electrode is formed on the polyimide coating, the porous conductor surface of the It is an object of the present invention to provide a method for producing a capacitor having a large capacity and excellent characteristics by forming a polyimide coating film having good followability according to the shape.

Means for Solving the Problems As a result of earnest research, the present inventors have invented a method for manufacturing a capacitor that can achieve the above object.

That is, in a method for producing a capacitor in which a derivative layer made of a polyimide coating is formed on the surface of a porous conductor, and a derivative layer serving as a counter electrode is further formed on the surface of the polyimide coating, a solution containing a polyamic acid salt is charged. The method for producing a capacitor is characterized in that a polyamic acid thin film is formed on a surface of a porous derivative by electrodeposition as a liquid to be deposited, and then a polyimide film is formed by heating and dehydrating the polyamic acid.

As the porous conductor, aluminum, tantalum, nickel, titanium, stainless steel, copper or carbon is preferable from the viewpoint of easy porosity, electric conductivity and stability. Further, as a method of making these conductors porous,
Examples include electrochemical etching, chemical etching using acid or alkali, roughening by ion beam or sputtering, roughening by sandblasting or surface grinding, and porosity by sintering fine conductor powder. However, the porous conductor of the present invention is not limited to these examples.

The polyamic acid salt used for electrodeposition is obtained by reacting a tetracarboxylic acid anhydride with a diamine to form a polyamic acid, and then adding a base dissolved in an organic solvent to partially or entirely dissolve the carboxyl group of the polyamic acid. I get it in harmony.

The tetracarboxylic acid anhydride is not particularly limited,
For example, compounds as shown in the following (1) to (6) can be used.

The dimian is not particularly limited, but for example, the following compounds (7) to (10) can be used (in the formula, X is O, CH ₂ , SO ₂ , C (CH ₃ ) ₂ , Represents C (CF ₃ ) ₂ .

Besides these, aliphatic diamines such as ethylenediamine and hexamethylenediamine can also be used.

The organic solvent is not particularly limited as long as it dissolves the polyamic acid used, N, N-dimethylacetamide, N, N-dimethylformamide, dimethoxyethane, N-methylpyrrolidone, N-methylcaprolactam, dimethyl sulfoxide. Highly polar solvents such as The base is not particularly limited, but inorganic hydroxides such as sodium hydroxide, inorganic basic salts such as sodium carbonate, alkylamines such as trimethylamine and triethylamine, nitrogen-containing heteroaromatics such as pyridine, quinoline and isoquinoline. There are compounds, etc.

The polyamic acid salt solution prepared as described above is used as the electrodeposition liquid as it is, or a poor solvent for the polyamic acid is appropriately added to form the electrodeposition liquid. The poor solvent for the polyamic acid used at this time varies depending on the polyamic acid used, but in general, alcohols such as methanol, ethanol, ethylene glycol, propylene glycol, and glycerin, ketones such as acetone, methyl ethyl ketone, cyclohexanone, benzene, and toluene. Aromatic hydrocarbons such as xylene, carbon tetrachloride, organic chlorine compounds such as chloroform, and organic nitrogen compounds such as nitromethane are used.

Next, in order to form a polyamic acid coating on the surface of the porous conductor, the porous conductor is immersed in the above electrodeposition solution as an anode, and a voltage of 1 to 300 V is applied between the outer cathode and the outer cathode. And electrodeposition.

In this way, the polyamic acid film formed on the surface of the porous conductor is heated and dehydrated to form a polyimide film.

As described above, after the polyimide coating film is formed on the porous conductor surface, the counter electrode is formed on the polyimide coating film. As a method of forming a counter electrode, a method of forming a counter electrode by providing a conductor layer made of a metal oxide such as indium tin oxide or manganese dioxide, a conductive paste using carbon, silver, gold, copper or the like, dipping or coating To form a conductor layer, a method of forming a conductor layer by solvent impregnation or solution coating of an organic conductive material such as TCNQ complex, conductive molecular film by chemical oxidative polymerization, conductive by electrolytic polymerization There is a method of forming a counter electrode by sequentially laminating conductive polymer films. Considering the adhesion to the polyimide coating, the conductivity, and the like, it is preferable to sequentially stack a conductive polymer film formed by chemical oxidative polymerization and a conductive polymer film formed by electrolytic polymerization to form a counter electrode. By using this method, a counter electrode corresponding to the surface shape of the polyimide coating can be formed, and even if the dielectric coating has a defect, the capacitor has a small leakage current.

A method for forming a counter electrode by sequentially stacking a conductive polymer film formed by chemical oxidative polymerization and a conductive polymer film formed by electrolytic polymerization on the polyimide coating will be described below.

After uniformly dispersing a solution containing at least 0.01 mol / l of a conductive polymer monomer on a polyimide coating formed on the surface of a porous conductor, 0.001 mol / l to 2 mol / l of an oxidizer was used.
The surface is made electrically conductive by forming a conductive polymer film chemically oxidized and polymerized by a method of contacting with a solution containing the same or, conversely, uniformly dispersing an oxidizing agent, and then contacting with a solution of a conductive polymer monomer.

Oxidizing agents used for chemical oxidative polymerization include halogens such as iodine, bromine and bromine iodide, arsenic pentafluoride, antimony pentafluoride, silicon tetrafluoride, phosphorus pentachloride, aluminum chloride, molybdenum chloride and other metal halides. , Sulfuric acid, nitric acid, fluorosulfuric acid, trifluoromethane sulfuric acid, chlorosulfuric acid and other protic acids, sulfur trioxide, nitrogen dioxide and other oxygen-containing compounds, sodium persulfate, persulfate such as ammonium persulfate, hydrogen peroxide, peracetic acid, etc. For example, peroxide.

Conductive polymers include polypyrrole, polythiophene,
Polyfuran is used, and from the viewpoint of stability, polypyrrole is particularly preferably used.

After that, in an electrolytic solution containing a supporting electrolyte 0.01 mol / l to 2 mol / l and a conductive polymer monomer 0.01 mol / l to 5 mol / l, electrolytic polymerization is performed using a conductive polymer film by chemical oxidative polymerization as an anode. A uniform electrolytically polymerized conductive polymer film is formed on the chemically oxidatively polymerized conductive polymer film.

In the supporting electrolyte used in the electropolymerization of the present invention, anions are halide anions such as hexafluoroline, hexafluoroarsenic and tetrafluoroboron, halogen anions such as iodine, bromine and chlorine, perchlorate anion, benzenesulfonic acid, It is a sulfonate anion such as alkylbenzene sulfonic acid, and the cation is an alkali metal cation such as lithium, potassium or sodium, or a quaternary ammonium cation such as ammonium or tetraalkylammonium. LiPF ₆ and LiAs as compounds
Examples include F ₆ , LiClO ₄ , LiBF ₄ , KI, NaPF ₆ , NaClO ₄ , sodium toluenesulfonate, and tetrabutylammonium toluenesulfonate.

After forming the counter electrode as described above, the lead of the counter electrode is taken out from a part of the counter electrode and sealed with a resin mold or an outer case to provide the capacitor of the present invention.

Effect In the method for producing a capacitor according to the present invention, a thin film polyimide film can be formed on the surface of a porous conductor according to the shape of the surface, so that the surface area can be effectively used and a small capacitor having a large capacity can be obtained. It is possible and it becomes a non-polar capacitor.

EXAMPLES Hereinafter, the present invention will be described in detail with reference to examples.

In addition, the part in an Example and a comparative example represents a weight part.

(Example 1) The surface of a high-purity aluminum foil was electrolytically etched to 50
After roughening the surface twice and cutting it to 10 mm x 3 mm, a lead was attached by caulking to obtain a metal electrode.

On the other hand, 3.3 parts of p-phenylenediamine (Compound 7) was added to N, N
-Dissolve in 90 parts of dimethylformide, add 6.7 parts of pyromellitic dianhydride (Compound 1) and react at room temperature for 12 hours to prepare a polyamic acid solution, then add trimethylamine
1.8 parts of the polyamic acid was added and reacted at 40 ° C. for 30 minutes to neutralize a part of the carboxyl groups of the polyamic acid to obtain a polyamic acid salt solution. To 60 parts of this solution, 40 parts of methanol was added to prepare an electrodeposition liquid.

The electrodeposition liquid was placed in a stainless steel container, and the roughened metal electrode was immersed to form an anode. A voltage of 150 V was applied for 3 minutes using the stainless steel container as a cathode, and a thin film of polyamic acid was applied to the surface of the metal electrode. Was formed. Next, the metal electrode was taken out of the container and heated at 250 ° C. for 2 hours to obtain an element having a polyimide coating formed on its surface.

This device was dipped in a 2 mol / l solution of pyrole / ethanol for 5 minutes and then dipped in a 0.5 mol / l ammonium persulfate aqueous solution for 5 minutes to form a polypyrrole film by chemical oxidative polymerization. Furthermore, this element was immersed in an acetonitrile solution containing 1 mol / l of pyrrole monomer and 1 mol / l of tetraethylammonium paratoluenesulfonate as a supporting electrolyte, and polypyrrole chemically oxidized and polymerized was used as an anode, and constant current electropolymerization was performed between it and an external electrode. (1mA / cm ² , 30 minutes)
A polypyrrole film was formed by electrolytic polymerization. This element was dipped in colloidal carbon, and a silver paste was further applied to form a conductive coating film, and a counter electrode was taken out from a part thereof to complete a capacitor. The characteristics of the obtained capacitor are shown in Table 1.

Example 2 A capacitor was completed according to Example 1 except that 40 parts of methanol was not added. The characteristics of the obtained capacitor are shown in Table 1.

(Examples 3 to 5) Instead of the aluminum etching foil in Example 1, a tantalum sintered body (Example 3) which was sintered to be 50 times porous, and a sponge nickel having an effective surface area of 30 times was used. (Example 4), sponge stainless steel with an effective surface area of 30 times (SU
S304) (Example 5) was used, but the procedure was the same as in Example 1. The characteristics of the obtained capacitor are shown in Table 1.

(Example 6) The procedure of Example 1 was repeated except that trimethylamine was added to the polyamic acid solution in Example 1 and then 40 parts of acetone was added instead of methanol. The characteristics of the obtained capacitor are shown in Table 1.

Example 7 In Example 1, 3.3 parts of p-phenylenediamine was added to 4,
Example 1 was repeated except that 4.0 parts of 4'-diaminodiphenyl ether (Compound 9) and 6.7 parts of pyromellitic dianhydride were replaced with 6.0 parts of biphenyltetracarboxylic dianhydride (Compound 2). The characteristics of the obtained capacitor are shown in Table 1.

EFFECTS OF THE INVENTION According to the method of the present invention, a thin polyimide film can be formed inside the pores of a porous conductor, so that an excellent capacitor having a small size, a large capacity, high heat resistance, and nonpolarity can be realized. Is.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location H01G 4/33 (72) Inventor Nobuyuki Kume 1006 Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Kenichi Hashizume, 2470, Handa, Shibukawa, Gunma, Japan Central Research Institute (72) Inventor, Hideo Yamamoto, 2470, Handa, Shibukawa, Gunma, Japan, Central Research Institute, Japan (72) Inventor, Isa Gongma 2470, Handa, Shibukawa, Gunma Japan Central Research Institute

Claims (4)

[Claims] 1. A method for producing a capacitor, comprising: forming a dielectric layer made of a polyimide coating on the surface of a porous conductor, and further forming a counter conductive layer on the surface of the polyimide coating; Electrodeposition using a solution containing a polyamic acid as the electrodeposition solution, after forming a thin film of polyamic acid on the surface of the porous conductor, a capacitor characterized by forming a polyimide coating by heating dehydration of the polyamic acid Manufacturing method. 2. The method for producing a capacitor according to claim 1, wherein a poor solvent for polyamic acid is added to an electrodeposition liquid containing a polyamic acid salt for electrodeposition. 3. The capacitor according to claim 1, wherein the conductor layer serving as a counter electrode is formed by sequentially laminating a conductive polymer film formed by chemical oxidative polymerization and a conductive polymer film formed by electrolytic polymerization. Manufacturing method. 4. The method for producing a capacitor according to claim 1, wherein the conductive polymer film is polypyrrole.