JPH0419688B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to a dielectric film in which a polymer of a five-membered heterocyclic compound such as pyrrole, thiophene, or furan is laminated as a composite layer with a polymer. Concerning improvements in the manufacturing method of solid electrolytic capacitors.

[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, their electrical properties are more stable than conventional electrolytic capacitors, and there is a risk of drying out and the need for a container that can withstand gas pressure. In addition to the advantage that there is no need to create a structure,
It is characterized by its long shelf life.

Furthermore, there are also advantages in that the capacitor can be easily miniaturized and formed into any desired 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 NOx gas is generated during the thermal decomposition. And Nox
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 disclosed in JP-A-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. things 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.

Examples of means for forming a polymer of a five-membered heterocyclic compound on a dielectric film include forming a polymer film by electrolytic oxidation reaction as disclosed in JP-A-61-2315, and JP-A-62-47109. There is a method of forming a polymer film by a gas phase polymerization method, as in the above publication. 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.

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.

[Problem to be solved by the invention]

As described above, the polymer film of a five-membered heterocyclic compound has excellent properties as a solid electrolyte, but solid electrolytic capacitors are subject to various mechanical shocks to the solid electrolyte layer during the manufacturing process, and this shock The polymer film may be damaged by this, resulting in deterioration of electrical properties such as leakage current. Furthermore, even after the product is completed, the electrical properties of the polymer film may deteriorate due to exposure to high temperatures during soldering.

The object of the present invention is to form a polymer film that has excellent resistance to such mechanical damage and deterioration factors such as heat, chemicals, and humidity.

[Means to solve the problem]

The present invention was made to solve this problem, and when a five-membered heterocyclic compound is formed on a dielectric film by vapor phase polymerization, an anion is added to the oxidizing agent applied or immersed on the dielectric film. By mixing polymers that do not contain groups and performing gas phase polymerization,
It has been discovered that by forming a mixed layer of the polymer and a five-membered heterocyclic compound, a film that meets the objectives of the present invention can be formed.

In the present invention, after adhering an oxidizing agent and a polymer containing no anionic group on a dielectric film, the surface thereof is coated with the following 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.) Furan, thiophene, pyrrole, or their derivatives, which are membered ring compounds, are laminated by gas phase polymerization to form a composite layer consisting of a polymer that does not contain the anion group and a polymer of a five-membered heterocyclic compound as a solid electrolyte layer. This is a manufacturing method characterized by:

In addition, in the present invention, as polymers not containing anionic groups forming the composite layer of the solid electrolyte, polyvinyl alcohol, polyacrylic acid, polyphosphoric acid, polyvinylpyridine, polyethyleneimine, cellulose, alginic acid, pectic acid, polyvinyl chloride,
It is also characterized by the use of a material selected from polystyrene, polyethylene oxide, or agar.

To illustrate a preferred example of the solid electrolytic capacitor obtained by the manufacturing method of the present invention, as shown in FIG. 1, an aluminum layer 1 and an Al ₂ O _Three porous dielectric layers 2 and a composite layer 3 of polymer and pyrrole polymer are laminated 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. Further, as a feature of the present invention, this oxidizing agent solution is used as a mixed solution in which a polymer having no anionic group is simultaneously blended.

It is desirable that the oxidizing agent used here has an oxidizing effect that promotes the polymerization of the five-membered heterocyclic compound, and is not harmful to the porous dielectric layer or the polymer to be mixed at the same time.

Examples of such oxidizing agents include FeCl ₃ , quinone, FeBr ₃ , Fe(NO ₃ ) ₃ , Fe ₂ (C ₂ O ₄ ) ₃ , Fe
(ClO ₄ ) ₃ , K ₃ Fe(CN) ₆ , (C ₅ H ₅ ) ₂ Fe ⁺ FeCl ₄ ^- ,
CuCl ₂ , CuBr ₂ , CuSO ₄ , Cu(NO ₃ ) ₂ ,
Examples include those selected from (NH ₄ ) ₂ S ₂ O ₈ , K ₂ S ₂ O ₈ , H ₂ O ₂ , HNO ₃ , PbO ₂ and diazonium salts.

In addition, the polymers used in the mixture here have the function of using the polymer matrix of this polymer as a site for the polymerization reaction to form a polymer film, so anions such as sulfone groups are used to promote the oxidation reaction. There is no need to include groups. Further, those having solubility in the solvent that dissolves the above-mentioned oxidizing agent are preferable.

Preferred examples of such polymers include polyvinyl alcohol, polyacrylic acid, polyphosphoric acid, polyvinylpyridine, polyethyleneimine, cellulose, alginic acid, pectic acid, polyvinyl chloride, polystyrene, polyethylene oxide, agar, and the like. Among these, polyvinyl alcohol is one of the most preferred because it has various advantages such as easy availability and selection of polymerization degree, and no adverse effects on electrolytic capacitors.

These polymers can be used alone or in combination of two or more.

In the present invention, the solvent used to dissolve the oxidizing agent and polymer is not particularly limited as long as it dissolves the oxidizing agent and polymer. Examples of this solvent include ethers such as diethyl ether and dimethyl ether, furans such as tetrahydrofuran, aliphatic nitriles such as acetonitrile and propionitrile, aliphatic ketones such as ethylacetone and propylacetone, nitromethane, nitroethane, etc. aliphatic nitro compounds, aromatic compounds such as xylene, benzene, and toluene, aliphatic compounds such as hexane, pentane, and heptane, alicyclic compounds such as cyclohexane and cyclopentane, and esters such as ethyl acetate, methyl acetate, and propyl acetate. compounds, alcohols such as methanol, ethanol, propanol, and butanol, dimethylformamide (acid amide), dimethyl sulfoxide, and water.

Particularly preferred among these solvents are water,
Alcohols or ethyl acetate.

In the method of the present invention, various known methods can be employed to coat the surface of the dielectric film with a solution of an oxidizing agent and a polymer dissolved in a solvent. This can be carried out by applying a solution of oxidizing agent or by immersing an electrode body on which a dielectric film is formed in an oxidizing agent solution.

A dielectric film coated with a solution of an oxidizing agent and polymer is either in a dry state, that is, after it has been removed, or in a state in which the solvent is not dry, that is, the solvent does not evaporate and is wet. A gas phase polymerization reaction is carried out.

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 and polymer coated on the dielectric material. By adjusting the concentration of molecules and the thickness of the coating, the desired polymer layer can be obtained.

The dielectric film contains aluminum oxide (Al ₂ O ₃ ) formed on the surface of the aluminum base material.
In addition to oxides of tartar, niobium, titanium, zirconium, etc. 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 a gas phase polymer of pyrrole is formed on a dielectric film, coating is performed by coating a mixture of an oxidizing agent and a polymer containing no anionic group on the dielectric film. In the polymer matrix, the oxidizing agent and the five-membered heterocyclic compound monomer vapor undergo a polymerization reaction and are incorporated into the polymer matrix to form a polymer film, resulting in a strong and adhesive polymer film. is obtained.

〔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 .

25 g of ferric chloride (FeCl ₃ ) and 1.6 g of polyvinyl alcohol (PVA) (degree of polymerization 300) were added to 100 g of water on the Al ₂ O ₃ porous dielectric oxide film on the surface of the aluminum substrate thus obtained. Apply a solution dissolved in.

Next, it was applied onto the Al ₂ O ₃ porous dielectric film.
While the FeCl ₃ and PVA-containing solution are wet, the aluminum foil is suspended in a sealed container containing a container containing a pyrrole monomer solution, and reacted at room temperature and pressure for 1 hour. - Obtaining an aluminum foil with a polypyrrole composite layer formed thereon.

The above was carried out using the apparatus shown in Figure 2, where 7 is an aluminum substrate having an Al ₂ O ₃ porous dielectric film coated with FeCl ₃ and PVA on the surface, and 8 is an aluminum substrate with a pyrrole monomer liquid. , 9 is 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 a PVA-polypyrrole composite membrane, and then dried for a day and night to form a solid electrolytic capacitor. Incidentally, a schematic structural diagram of this capacitor is as 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 4.1μF, tangent of loss angle (Tanδ)
was 2.0%, and the leakage current was 0.5μA (25V).

The electrical conductivity of the PVA-polypyrrole composite film was 1 s/cm.

Example 2 As an oxidizing agent and a polymer, 8 g of p-quinone and 1.5 g of polyvinyl chloride were mixed with 100 g of dimethylformamide.
The experiment was carried out under the same conditions as in Example 1, except that the solution was used. As a result, the capacitance of the obtained solid electrolytic capacitor was 4.0μF, the loss angle tangent (Tanδ) was 2.5%, and the leakage current was 0.7μA.
(25V).

Example 3 An experiment was conducted under the same conditions as in Example 1, except that 8 g of p-quinone and 1.5 g of polystyrene dissolved in 100 g of dimethyl ethyl ketone were used as the oxidizing agent and polymer. As a result, the capacitance of the obtained solid electrolytic capacitor was 4.0μF, the loss angle tangent (Tanδ) was 2.3%, and the leakage current was 0.3μA.
(25V).

Comparative Example 1 Using the same aluminum foil as that used in the above example, using only the same oxidizing agent as in Example 1, and using a solution excluding the polymer, applying the oxidizing agent solution on the dielectric film, Gas phase polymerization treatment was performed in a wet state. All other conditions were the same as in Example 1. The capacitance of the solid electrolytic capacitor of Comparative Example 1 obtained as a result was 4.2μF, and the tangent of the loss angle (Tanδ)
was 1.9%, and the leakage current was 7.2μA (25V).

Comparative Example 2 Using only the same oxidizing agent as in Example 2 above but excluding the polymer, the oxidizing agent solution was applied onto a dielectric film and subjected to vapor phase polymerization in a wet state. 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 was 4.1 μF, and the tangent of the loss angle (Tanδ)
was 2.3%, and the leakage current was 7.8μA (25V).

Comparative Example 3 Using only the same oxidizing agent as in Example 3 above but excluding the polymer, the oxidizing agent solution was applied onto the dielectric film, and after waiting for the surface to dry, gas phase polymerization was performed. I went to All other conditions are Example 3.
The same as The resulting solid electrolytic capacitor of Comparative Example 3 had a capacitance of 4.2 μF, a loss angle tangent (Tan δ) of 2.0%, and a leakage current of 6.5 μA (25 V).

From the above results, it is clear that when a solution containing an oxidizing agent and a polymer is applied during gas phase polymerization to perform a polymerization reaction with a five-membered heterocyclic compound as in the present invention, a solution containing no polymer is used. We were able to obtain superior characteristics in terms of both the loss angle tangent and leakage current compared to the previous model.

Further, the composite membrane formed by the method of the present invention has excellent mechanical strength, and even if it is mechanically damaged during the manufacturing process, there is little increase in leakage current, etc.

〔Effect of the invention〕

As described above, the method for producing a solid electrolytic capacitor of the present invention is effective in forming a polymer layer of an electrolytic capacitor using a polymer of a five-membered heterocyclic compound as a solid electrolyte, mechanically, thermally, and chemically. Since a stable, dense, and highly adhesive composite film can be formed, a solid electrolytic capacitor with low loss and low leakage current characteristics can be obtained.

Moreover, since the present invention is less susceptible to mechanical damage during the manufacturing of solid electrolytic capacitors, the manufacturing process can be easily managed and production efficiency can be increased. In addition, in this type of electrolytic capacitor, it is necessary to perform aging several times during the manufacturing process in order to repair the deterioration of the film, but according to the present invention, the film is strong and has excellent adhesion, so this aging process can be eliminated or significantly reduced.

In addition, a highly reliable solid electrolytic capacitor whose characteristics do not deteriorate when soldered to a board after commercialization can be provided.

[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 polymer-polypyrrole composite on a porous dielectric material. 1: Aluminum layer, 2: Al ₂ O ₃ porous dielectric layer, 3: Composite layer consisting of polymer and pyrrole polymer, 4: Silver paste, 5: Anode side lead wire,
6: Cathode side lead wire, 7: Aluminum substrate having Al ₂ O ₃ porous dielectric film, 8: Pyrrole monomer liquid, 9: Sealed container.

Claims (1)

[Claims] 1. After attaching an oxidizing agent and a polymer containing no anionic group to the dielectric film, the following general formula is applied to the surface of the dielectric film. (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.) Manufacture of a solid electrolytic capacitor, characterized in that a membered ring compound is laminated by gas phase polymerization to form a composite layer consisting of a polymer not containing an anion group and a polymer of a five-membered heterocyclic compound as a solid electrolyte layer. Law. 2 Polymers containing no anionic groups include polyvinyl alcohol, polyacrylic acid, polyphosphoric acid, polyvinylpyridine, polyethyleneimine, cellulose, alginic acid, pectic acid, polyvinyl chloride,
The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein the solid electrolytic capacitor is selected from polystyrene, polyethylene oxide, or agar.