JPH0419693B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a solid electrolytic capacitor in which a polymer layer of a five-membered heterocyclic compound such as pyrrole, thiophene, or furan is laminated on a dielectric film. It relates to a method of laminating layers.

[Conventional technology]

It has long been known that the characteristics of electrolytic capacitors are largely dependent on the electrolyte used therein.

The reason for this is that the electrolyte functions as a true cathode in contact with the oxide film on the surface of the electrode, which serves as a dielectric, and also has the function of repairing the extremely thin dielectric oxide film, and the properties of the electrolyte directly affect the electrolytic capacitor. This is because it affects the characteristics.

The properties required for the electrolyte are as follows:
It must not corrode the chemical conversion film, isolation paper, case, etc., it must have high electrical conductivity, it must be stable against temperature changes, the electrolyte itself must be stable and difficult to change, and it must be porous dielectric. For example, it must not damage body membranes.

Among electrolytic capacitors, solid electrolytic capacitors are characterized by using MnO ₂ solid semiconductor (solid electrolyte) instead of using electrolyte, electrolytic paste, etc. as the electrolyte.

By using such a solid electrolyte,
Solid electrolytic capacitors have been able to eliminate most of the problems caused by the electrolyte of conventional electrolytic capacitors. Because these solid electrolytic capacitors are made from solid, non-volatile inorganic materials,
In addition to the advantages that the electrical characteristics are more stable than conventional electrolytic capacitors, there is no need to worry about drying out, and there is no need for a container structure that can withstand gas pressure.
It is characterized by its long shelf life.

Furthermore, there are also advantages in that the capacitor can be miniaturized and easily formed into an arbitrary shape.

As described above, solid electrolytic capacitors have excellent characteristics, but when forming the MnO ₂ solid electrolyte used thereon on a porous dielectric film, it is necessary to After soaking in manganese nitrate (Mn( _NO3 ) ₂ ) solution, pyrolysis (200 ~
300℃) is adopted.

Then, on the MnO ₂ solid electrolyte layer thus formed on the porous dielectric film, a thin carbon film layer (graphite layer) is formed using a dispersion of graphite fine powder. This graphite layer serves as a medium for leading the cathode side of the capacitor to the outside, but this graphite layer also improves the contact between the electrode and the MnO ₂ solid electrolyte layer, and also provides mechanical support in the subsequent manufacturing process. It also plays a role in mitigating thermal shock.

However, in the process of creating this MnO ₂ electrolyte layer, Mn(NO ₃ ) ₂ must be thermally decomposed, and NO _x gas is generated during the thermal decomposition. And NO _X
The problem arises that the porous dielectric coating is damaged by the action of the gas.

Once the porous dielectric film is damaged in this way, the electrolytic capacitor will suffer from various problems such as a decrease in its withstand voltage, an increase in leakage current, or progress in the deterioration of the porous dielectric film. A problem arises. Further, the necessity of forming a graphite layer on the MnO ₂ solid electrolyte layer not only complicates the manufacturing process of solid electrolytic capacitors but also poses problems in terms of product quality.

By the way, in order to solve these conventional problems, attention has been paid to conductive polymers as a new solid electrolyte. For example, as described in Japanese Patent Application Laid-Open No. 60-37114, a polymer of a five-membered heterocyclic compound such as polythiophene, polypyrrole, or polyfuran is doped with an appropriate dopant to impart desired conductivity. are being considered.

These solid electrolytes have superior conductivity compared to conventional metal oxide electrolytes, and they do not generate gas or undergo high-temperature treatment that degrades the dielectric film when forming the electrolyte layer. It is attracting attention as a material that can provide electrolytic capacitors with unique characteristics.

As means for forming a polymer of a five-membered heterocyclic compound on a dielectric film, for example, a method of forming a polymer film by electrolytic oxidation reaction as disclosed in JP-A-61-2315, and a method as described in JP-A-62-47109 As disclosed in the publication, there is a method in which a polymer film is formed by a gas phase polymerization method. As described above, there are various methods for polymerizing five-membered heterocyclic compounds, but those using gas phase polymerization have advantages such as good adhesion to the dielectric film and low leakage current. This is one of the promising means of formation.

[Problem to be solved by the invention]

In the conventional gas phase polymerization method, for example,
According to Publication No. 47109, an oxidizing agent solution is applied onto a dielectric film, the solvent is removed by evaporation, etc., and then brought into contact with a gas of a five-membered heterocyclic compound in a container to form an oxidizer solution on the dielectric film. A gas phase polymerized film was formed.

In the formation of such a gas phase polymerized film, the present invention aims to obtain a polymeric film that has better adhesion than conventional ones and also has excellent electrical properties such as leakage current.

[Means to solve the problem]

The present invention has been made to solve these problems, and when a five-membered heterocyclic compound is formed on a dielectric film by vapor phase polymerization, the solvent of the oxidizing agent applied or immersed on the dielectric film is It has been discovered that a more excellent film can be formed by allowing it to remain during gas phase polymerization.

That is, the present invention uses an oxidizing agent applied to the surface of a dielectric film and a general formula (In the formula, X represents a substituent selected from the group consisting of NR ₃ , S, O, and Se, and R ₁ , R ₂ , and R ₃ represent hydrogen, an alkyl group, or an aryl group.) In a method for producing a solid electrolytic capacitor in which a polymerized layer is formed on the surface of a dielectric film by reacting member ring compounds such as pyrrole, thiophene, furan, etc. or their derivatives by gas phase polymerization, the oxidizing agent is water, This is a method for manufacturing solid electrolytic capacitors in which a dielectric film is coated or dipped in a solution state dissolved in a solvent consisting of alcohols or ethyl acetate, and gas phase polymerization is performed with the solvent remaining.

To illustrate a preferred example of a solid electrolytic capacitor obtained by the manufacturing method of the present invention, as shown in FIG.
An aluminum layer 1, an Al ₂ O ₃ dielectric layer 2, and a pyrrole polymer layer 3 are stacked in this order. Further, a silver paste layer 4 is formed on the cathode extraction side, and a cathode side lead wire 6 is connected to this silver paste 4.

The polymer formed in the present invention is formed from a five-membered heterocyclic compound by vapor phase polymerization, and the vapor phase polymerization involves exposing the anode member on which the dielectric film is formed to the vapor of the five-membered heterocyclic compound. This method forms a polymer film directly on the surface.

In this case, an oxidizing agent dissolved in a suitable solvent is present on the dielectric film. At this time, the gas phase polymerization reaction is carried out in a state in which the solvent remains without being removed as in the conventional method. The remaining solvent at this time acts as a catalyst for the reaction between the oxidizing agent and the five-membered heterocyclic compound vapor,
Forms a dense polymer film.

Particularly preferred solvents are selected from water, alcohols such as ethanol, methanol, propanol, butanol, or ethyl acetate.

In addition, oxidizing agents are those that dissolve in these solvents,
Any material can be selected as long as it does not deteriorate or adversely affect the dielectric film. Specific examples of such things include FeCl ₃ ,
( _NH4 ) _{2S2O8 ,} quinone, _FeBr3 , Fe( _NO3 ) _{3 , Fe2}
( _C2O4 ) ₃ , Fe _{( ClO4} ) ₃ , _K3Fe (CN) ₆ ,
(C ₅ H ₅ ) ₂ Fe ⁺ FeCl ₄ ^- , CuCl ₂ , CuBr ₂ , CuSO ₄ ,
Examples include Cu(NO ₃ ) ₂ , K ₂ S ₂ O ₈ , H ₂ O ₂ and HNO ₃ .

In the method of the present invention, various known methods can be used to coat the surface of the dielectric film with an oxidizing agent solution dissolved in a solvent, but it is preferable to apply the solution on the dielectric surface. Alternatively, it can be carried out by immersing an electrode body on which a dielectric film is formed in an oxidizing agent solution.

The dielectric film coated with the oxidizing agent solution undergoes a gas phase polymerization reaction while the oxidizing agent solution is not dry, that is, the solvent is not evaporated and the dielectric film is wet. The atmosphere for gas phase polymerization of the five-membered heterocyclic compound can be created by placing the five-membered heterocyclic compound solution in a sealed container. Alternatively, it can be produced by forcibly producing a saturated vapor of a five-membered heterocyclic compound and introducing it into a closed container.

In the method of the present invention, the thickness of the five-membered heterocyclic compound polymer depends on the concentration and thickness of the oxidizing agent coated on the dielectric. By adjusting the thickness, a desired polymer layer can be obtained.

Additionally, as the oxidizing agent undergoes gas phase polymerization with the solvent remaining, the solvents water, alcohols, and ethyl acetate act as if they were catalysts in the polymerization reaction between the pyrrole gas and the oxidizing agent. As a result, a dense polymer film with good adhesion can be formed on the dielectric film.

The dielectric film contains aluminum oxide (Al ₂ O ₃ ), which is oxidized on the surface of the aluminum base material, as well as tantalum, niobium, titanium,
Examples include oxides such as zirconium. There are various methods for forming these oxide films, but taking aluminum as an example, electrochemical oxidation, that is, anodic oxidation, is generally used in an electrolytic solution using aluminum as an anode.

Furthermore, the surface on which the dielectric oxide film is to be formed may be roughened in advance to make it porous to increase the surface area. Various methods can be selected for increasing the surface area, but a common method is to electrochemically etch the surface of a foil-like base material in a solution such as an aqueous solution of hydrochloric acid. .

[Effect]

In the method of the present invention, when forming a gas phase polymer of pyrrole on a dielectric film, if the gas phase polymerization is performed with the solvent of the oxidizing agent coated on the dielectric film remaining, the solvent In the polymerization reaction between pyrrole gas and an oxidizing agent, water, alcohols, methyl acetate, etc. can act as a catalyst to promote polymer formation and form a dense and strong polymer layer.

〔Example〕

The present invention will be specifically explained below with reference to Examples, but the present invention is not limited to these Examples.

Example 1 High purity 3cm x 2.5cm (purity 99.99
%), the surface of this aluminum foil is subjected to AC electrolytic etching in an aqueous hydrochloric acid solution to enlarge the surface area.

After etching, the substrate was thoroughly washed, and the surface of the etched aluminum foil was anodized at a voltage of about 70 V to form a porous dielectric oxide film of Al ₂ O ₃ .

_{FeCl 3 4}
Apply a solution of g dissolved in 10 c.c. of ethyl acetate.

Next, it was applied onto the Al ₂ O ₃ porous dielectric film.
While wet with the FeCl ₃ -containing solution, the aluminum foil was suspended in a closed container containing a container containing a pyrrole monomer solution.
The reaction is carried out for a period of time to obtain an aluminum foil on which a deep black-purple pyrrole polymer layer is formed.

The above was carried out using _the apparatus shown in Fig. 2.
An aluminum substrate having an Al ₂ O ₃ porous dielectric film, 8 a pyrrole monomer liquid, and 9 a closed container.

After that, conductive paste "Dotite XA-167" (product name) made by dispersing silver powder in acrylic solvent
was applied to the surface of the pyrrole polymer layer, and then dried for a day and night to form a solid electrolytic capacitor. In addition,
A schematic structural diagram of this capacitor is shown in FIG.

Next, in order to examine the electrical characteristics of the obtained solid electrolytic capacitor, an anode lead wire 5 was connected to the back surface of the aluminum foil, and a cathode lead wire 6 was connected to the silver paste 4 on the front surface, and between them. The characteristics were measured electrically. As a result, the capacitance of the solid electrolytic capacitor is 2.05μF, tangent of loss angle (Tanδ)
was 1.5%, and the leakage current was 0.2μA (25V).

The electrical conductivity of the above pyrrole polymer layer is
It was 1.5s/cm.

Example 2 An experiment was conducted under the same conditions as in Example 1, except that 5.6 g of (NH ₄ ) ₂ S ₂ O ₈ dissolved in 10 cc of water was used as the oxidizing agent. As a result, the capacitance of the obtained solid electrolytic capacitor was 2.02μF, the loss angle tangent (Tanδ) was 1.5%, and the leakage current was 0.3μA (25V).
It was hot.

Example 3 2.7g of p-quinone was added to ethanol as an oxidizing agent.
Example 1 except that the solution was dissolved in 10c.c.
The experiment was conducted under the same conditions. As a result, the capacitance of the solid electrolytic capacitor obtained was 2.02μF,
The tangent of the loss angle (Tanδ) is 1.8%, and the leakage current is
It was 0.3μA (25V).

Comparative Example 1 Using the same aluminum foil as that used in the above example and using the same oxidizing agent solution as in Example 1, after coating the oxidizing agent solution on the dielectric film, wait for the surface to dry, Gas phase polymerization treatment was performed. All other conditions were the same as in Example 1. The resulting solid electrolytic capacitor of Comparative Example 1 had a capacitance of 1.84 μF, a loss angle tangent (Tan δ) of 1.8%, and a leakage current of 0.3 μA (25 V).

Comparative Example 2 Using the same oxidizing agent solution as in Example 2 above, the oxidizing agent solution was applied onto the dielectric film, and after waiting for the surface to dry, a gas phase polymerization treatment was performed. All other conditions were the same as in Example 2. The capacitance of the solid electrolytic capacitor of Comparative Example 2 obtained as a result is
It was 1.71μF, the loss angle tangent (Tanδ) was 2.1%, and the leakage current was 0.5μA (25V).

Comparative Example 3 Using the same oxidizing agent solution as in Example 3 above, the oxidizing agent solution was applied onto the dielectric film, and after waiting for the surface to dry, a gas phase polymerization treatment was performed. All other conditions were the same as in Example 3. The capacitance of the solid electrolytic capacitor of Comparative Example 3 obtained as a result is
It was 1.65μF, the loss angle tangent (Tanδ) was 5.3%, and the leakage current was 0.6μA (25V).

From the above results, when the oxidizing agent solution is polymerized with a hetero5-membered ring compound in a state where the solvent remains during gas phase polymerization as in the present invention, the capacitance, loss angle tangent, and leakage current Regarding any of the
We were able to obtain excellent characteristics.

〔Effect of the invention〕

As described above, the method for manufacturing a solid electrolytic capacitor of the present invention enables the formation of a dense polymer film with good adhesion when forming a polymer layer of an electrolytic capacitor using a polymer of a five-membered heterocyclic compound as a solid electrolyte. Therefore, a solid electrolytic capacitor with low loss and low leakage current characteristics can be obtained.

Moreover, the present invention does not require the addition of any new process.
Rather, the gas phase polymerization reaction treatment can be performed immediately after coating with the oxidizing agent solution, and the production efficiency is also excellent.

[Brief explanation of drawings]

FIG. 1 is a schematic structural diagram of a solid electrolytic capacitor according to an embodiment of the present invention, and FIG. 2 is a schematic diagram of an apparatus for laminating a pyrrole polymer on a porous dielectric material. 1: aluminum layer, 2: Al ₂ O ₃ porous dielectric layer, 3: pyrrole polymer layer, 4: silver paste,
5: Anode side lead wire, 6: Cathode side lead wire, 7:
Aluminum substrate with Al ₂ O ₃ porous dielectric film, 8: Pyrrole monomer liquid, 9: Sealed container.

Claims (1)

[Claims] 1. An oxidizing agent applied or immersed on the surface of a dielectric film, and a general formula (In the formula, X represents a substituent selected from the group consisting of NR ₃ , S, O, and Se, and R ₁ , R ₂ , and R ₃ represent hydrogen, an alkyl group, or an aryl group.) A method for manufacturing a solid electrolytic capacitor in which a polymerized layer is formed on a dielectric film by reacting with a member ring compound by gas phase polymerization, wherein the oxidizing agent is dissolved in water, alcohol, or ethyl acetate to form a dielectric capacitor in a solution state. A method for producing a solid electrolytic capacitor, which is characterized by applying or dipping the solution onto the surface of a body film, and performing gas phase polymerization while the solution remains.