JPS63207117A - Manufacture of solid electrolytic capacitor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a solid electrolytic capacitor that has excellent stability at high temperatures.

[Prior Art] In general, solid electrolytic capacitor elements are made by forming an oxide film layer on an anode substrate made of a valve metal, forming a semiconductor layer such as manganese dioxide as a counter electrode on the outer surface of this oxide film layer, and then forming a semiconductor layer made of manganese dioxide or the like as a counter electrode. A conductive layer such as paste is formed to reduce contact resistance.

[Problems to be Solved by the Invention] However, the above-mentioned solid electrolytic capacitor has a drawback in that the loss factor increases over time when a high temperature long-term life test is performed.

As a result of intensive research aimed at solving the above problems, the present inventors discovered that high temperature stability can be improved by first cleaning the semiconductor layer and then variously changing the components of the conductor layer.

The present invention was made based on the above discovery, and an object of the present invention is to provide a method for manufacturing a solid electrolytic capacitor whose high temperature stability does not deteriorate over a long period of time.

[Means for Solving the Problems] The present invention has been made to achieve the above object, and its gist is to provide a dielectric oxide film and a semiconductor layer on the surface of an anode substrate made of a metal having a valve action. , a method for manufacturing a solid electrolytic capacitor comprising sequentially forming conductive layers, after cleaning the surface of the semiconductor layer, forming a paste layer containing metal oxide powder and metal powder as main components as the conductive layer. A method for manufacturing a solid electrolytic capacitor comprising the steps of: cleaning the surface of the semiconductor layer, and then preparing a powder mixture containing a metal powder as the conductor and a metal oxide powder forming the semiconductor layer and with another compound. A method of manufacturing a solid electrolytic capacitor includes a step of forming a paste layer containing as a main component.

[Specific Structure and Effects of the Invention] The method for manufacturing a solid electrolytic capacitor of the present invention will be described below.

As the valve metal substrate used as the anode of the solid electrolytic capacitor of the present invention, any metal having a valve action can be used, such as aluminum, tantalum, niobium, titanium, and alloys using these as substrates.

The oxide film layer on the surface of the anode substrate may be an oxide layer of the anode substrate itself provided on the surface layer of the anode substrate, or another dielectric oxide layer provided on the surface of the anode substrate. However, it is particularly desirable that the layer be made of an oxide of the anode valve metal itself. In either case, a conventionally known method such as an anodization method using an electrolytic solution can be used to provide the oxide layer.

Although there are no particular limitations on the composition and manufacturing method of the semiconductor layer used in the present invention, in order to improve the performance of the capacitor, lead dioxide or lead dioxide and lead sulfate are used as main components, and conventionally known chemical precipitation methods are used. , or preferably by an electrochemical deposition method.

Examples of the chemical precipitation method include a method of chemical precipitation from a reaction mother liquor containing a lead-containing compound and an oxidizing agent.

Examples of lead-containing compounds include those in which a lead atom has a coordinate bond or an ionic bond with a chelate-forming compound such as oxine, acetylacetone, pyromeconic acid, salicylic acid, alizarin, polyvinyl acetate, porphyrin compounds, crown compounds, and cryptate compounds. lead-containing compounds,
Lead citrate, lead acetate, basic lead acetate, lead chloride, lead bromide,
Examples include lead perchlorate, lead chlorate, lead sulfamate, silicon hexafluoride chain, lead bromate, lead borofluoride, lead acetate hydrate, lead nitrate, and the like. These lead-containing compounds are appropriately selected depending on the solvent used for the reaction mother liquor.

Water or organic solvents are used as solvents.

Two or more types of lead-containing compounds may be used in combination.

The concentration of the lead-containing compound in the reaction mother liquor is within the range of 0.05 mol/g from the concentration giving saturation solubility, preferably within the range of 0.1 mol/Ω from the concentration giving saturation solubility, and more Preferably from the concentration giving saturation solubility to 0
It is in the range of 65 mol/g.

If the concentration of the lead-containing compound in the reaction mother liquor is less than 0.05 mol/g, a solid electrolytic capacitor with good performance cannot be obtained. Further, if the concentration of the lead-containing compound in the reaction mother liquor exceeds the saturation solubility, no merit can be observed by adding an increased amount.

Examples of the oxidizing agent include quinone, chloranil, pyridine-N-oxide, dimethyl sulfoxide, chromic acid, potassium permanganate, selenium oxide, mercury acetate,
Examples include vanadium oxide, sodium chlorate, ferric chloride, hydrogen peroxide, mustard powder, and benzoyl peroxide.

These oxidizing agents may be appropriately selected depending on the solvent used for the reaction mother liquor. Further, two or more oxidizing agents may be used in combination.

The amount of oxidizing agent used is 0.1 of the molar amount of lead-containing compound used.
It is preferably within the range of ~5 times the mole.

If the usage ratio of the oxidizing agent is more than 5 times the molar amount of the lead compound used, there is no cost advantage, and 0, 1
If the amount is less than twice the mole, a solid electrolytic capacitor with good performance cannot be obtained.

As a method for forming a semiconductor layer containing lead dioxide as a main component, for example, a reaction mother liquor is prepared by mixing a solution containing a lead-containing compound and a solution containing an oxidizing agent, and then the above-mentioned oxide film is added to the reaction mother liquor. A method of chemically depositing the anode by immersing the anode substrate therein can be mentioned.

On the other hand, examples of electrochemical deposition methods include the method previously proposed by the present inventors in which lead dioxide is deposited by electrolytic oxidation in an electrolytic solution containing a high concentration of lead-containing compounds. No. 81-26952).

Further, if the semiconductor layer is composed of a layer whose main components are lead dioxide, which plays the role of a semiconductor, and lead sulfate, which is an insulating material, the leakage current value of the capacitor can be reduced by adding lead sulfate. On the other hand, the present invention has found that although the addition of lead sulfate lowers the electrical conductivity of the semiconductor layer and increases the loss factor, it maintains and exhibits a high level of performance compared to conventional solid electrolytic capacitors. It was done. Therefore, when the semiconductor layer is composed of a mixture of lead dioxide and lead sulfate, good capacitor performance can be maintained over a wide range of compositions, such as 10 parts by weight or more of lead dioxide and less than 100 parts by weight of lead sulfate and 90 parts by weight or less of lead sulfate. However, preferably 80 to 50 parts by weight of lead sulfate to 20 to 50 parts by weight of lead dioxide.
A good balance between the leakage current value and the loss coefficient value can be achieved in a range of 75 to 65 parts by weight of lead sulfate to 50 parts by weight, more preferably 25 to 35 parts by weight of lead dioxide. If the amount of lead dioxide is less than 10 parts by weight, conductivity will be poor, resulting in a large loss factor and insufficient capacity.

A semiconductor layer containing lead dioxide and lead sulfate as main components can be formed by chemical precipitation using, for example, an aqueous solution containing lead ions and persulfate ions as a reaction mother liquid. Additionally, a suitable oxidizing agent that does not contain persulfate ions may be added.

The lead ion concentration in the mother liquor is 0.05 mol/Ω from the concentration that gives saturated solubility, preferably 0.1 mol/Ω from the concentration that gives saturated solubility, more preferably 0.5 mol/Ω from the concentration that gives saturated solubility. It is within the range of Ω. If the concentration of lead ions is higher than the saturation solubility, there is no benefit from adding an increased amount. In addition, the concentration of lead ions is 0.05 mol/
If it is lower than Ω, the lead ions in the mother liquor are too thin, so there is a problem that the number of applications must be increased.

On the other hand, the concentration of persulfate ions in the mother liquor is within the range of 5 to 0.05 in molar ratio to lead ions. If the concentration of persulfate ions is more than 5 in molar ratio to lead ions, unreacted persulfate ions remain, resulting in high costs, and the concentration of persulfate ions is 0.05 in molar ratio to lead ions. If the amount is less, unreacted lead ions remain and the conductivity deteriorates, which is not preferable.

Compounds that provide lead ion species include, for example, lead citrate, lead perchlorate, lead nitrate, lead acetate, basic lead acetate, lead chlorate, lead sulfamate, silicon hexafluoride chain, lead bromate, and chloride. Examples include lead and lead bromide. Two or more of these compounds providing lead ion species may be used in combination.

On the other hand, examples of compounds that provide persulfate ion species include potassium persulfate, sodium persulfate, ammonium persulfate, and the like. Two or more of these compounds that provide persulfate ion species may be used in combination.

In addition, examples of oxidizing agents include hydrogen peroxide, calcium hypochlorite, calcium chlorite, calcium chlorate,
Examples include calcium perchlorate.

Next, the surface of the semiconductor layer formed as described above is cleaned by ultrasonic cleaning.

The medium used for ultrasonic cleaning is water or an organic solvent such as alcohol. In addition, regarding the output, temperature, ultrasonic cleaning time, etc. when performing ultrasonic cleaning,
Since it varies depending on the type of anode substrate used, the type and composition of the semiconductor layer formed, etc., it is determined by preliminary experiments conducted in advance. Additionally, in addition to ultrasonic cleaning, cleaning the surface of the semiconductor layer may include cleaning with an organic solvent such as ethyl alcohol or methyl alcohol, or cleaning with water. The effect of ultrasonic cleaning is even better.

Next, in the present invention, the conductor layer provided on the ultrasonically cleaned semiconductor layer is a paste layer mainly composed of metal oxide powder and metal powder, and in particular, the semiconductor layer is used as the metal oxide powder. It is desirable to use metal oxides that form. Further, the conductive layer provided in the semiconductor layer-1 may be a paste layer mainly composed of a mixed powder of the metal oxide forming the semiconductor layer and other compounds, and metal powder. Examples of metal oxides include manganese dioxide, tin dioxide, tungsten dioxide, lead dioxide, -copper oxide, -zinc oxide, -nickel oxide, -cobalt oxide, titanium dioxide, iron sesquioxide, barium titanate, tantalum oxide, and trioxide. Examples include vanadium dioxide and tungsten trioxide, and lead dioxide is particularly desirable from the viewpoint of good conductivity. In addition, as metal powder,
For example, silver powder, gold powder, palladium powder, copper powder, nickel powder,
Examples include silver-copper alloy powder, silver-nickel alloy powder, silver-coated copper powder, silver-coated nickel powder, silver-coated carbon powder, and alloy powders thereof.

The metal powder is preferably flaky or coral-shaped in order to improve the conductivity of the conductive paste, but it may also be in the shape of a normal sphere or a shape similar to a sphere.

In addition, the content ratio of the metal oxide powder or the mixture powder of metal oxide and other compounds in the paste to the metal powder in the paste must be within the range of 1/6 to 6 times the weight of the metal powder. is preferred.

If the ratio of metal oxide powder or a mixture of metal oxide and other compounds is less than 1/6 times that of metal powder, the high temperature stability of the produced solid electrolytic capacitor may become insufficient.
Furthermore, if the amount exceeds 6 times that of the metal powder, the conductivity may become insufficient.

The effect of the above-mentioned mixed powder of metal powder and metal oxide powder or metal oxide and other compound is estimated as follows. That is, compared to the conductivity of metal powder, the conductivity of metal oxide powder or a mixture of metal oxide and other compounds is 1/100 to 1
/1000, but when the metal powder is dispersed in the paste together with the metal powder, the conductivity is not significantly impaired compared to when the metal powder alone is dispersed. On the other hand, regarding high temperature stability, the paste, which is an organic polymer material, has a large coefficient of thermal expansion, and it is considered important to keep this coefficient small in order to avoid thermal stress. Alternatively, a mixed powder of a metal oxide and another compound has the effect of reducing the coefficient of thermal expansion.

Pastes whose main components are metal oxides and metal powders, or pastes whose main components are mixed powders of metal oxides and other compounds are, for example, pastes whose main components are lead dioxide and metal powders, or whose semiconductor layer is mainly lead dioxide. When the layer is a layer containing lead dioxide, it is obtained by mixing lead dioxide, a lead-based compound as an insulator, such as lead sulfate, and metal powder with a suitable resin or olibomer and a solvent.

As the resin or oligomer, a resin or oligomer used in a known conductive paste is used,
Examples include acrylic resin, alkyd resin, fluororesin, vinyl resin, silicone resin, epoxy resin, urethane resin, novolak, resol, and the like. However, as a matter of course, it is not limited to these. Further, the solvent used may be any known solvent as long as it dissolves these resins or oligomers.

When the resin or oligomer is liquid, it is not necessary to use a solvent. Furthermore, in the case of a thermosetting resin or oligomer, a known curing agent may be added, or a liquid containing a curing agent may be prepared separately and mixed at the time of use.

The proportion of metal powder and metal oxide or mixed powder containing metal powder and metal oxide (hereinafter collectively referred to as powder) in the paste is 35 to 95% by weight, particularly 55 to 95% by weight.
5% by weight is preferred. If the proportion of powder is less than 35% by weight, the conductivity of the paste will be insufficient, and if it exceeds 95% by weight, the adhesiveness of the paste will be insufficient, both of which will deteriorate the performance of the solid electrolytic capacitor.

The solid electrolytic capacitor of the present invention configured as described above can be made of, for example, a resin mold, a resin case, a metal exterior case,
It can be made into a general-purpose capacitor product for various uses by resin dipping and laminate film exterior.

[Example] Hereinafter, the present invention will be explained by showing Examples and Comparative Examples.

Example 1 An aluminum foil having a length of 2 cm and a width of 0.5 cm was used as an anode, and after the surface of the foil was electrochemically etched using alternating current, an anode terminal was caulked to the etched aluminum foil to connect the anode terminal. Next, an oxide film of alumina was formed by electrochemical treatment in an aqueous solution of boric acid and ammonium borate to obtain etched aluminum chemical foil for low pressure (approximately 1.0 μF/cJ). Next, the chemically formed foil was immersed in a 1 mol/g aqueous solution of lead acetate trihydrate, and a diluted aqueous solution of hydrogen peroxide in an amount of 0.5 times the mole of lead acetate trihydrate was added. After being left for 1 hour, the lead dioxide layer deposited on the chemically formed foil was ultrasonically cleaned in water for 3 minutes, and then dried under reduced pressure at 120°C. Furthermore, using butyl acetate as a solvent, 32 parts by weight of silver powder (hereinafter referred to as parts),
It was immersed in a paste consisting of 60 parts of lead dioxide and 8 parts of urethane resin, pulled up, and then dried at 100°C. After connecting the cathode with the paste described above, the capacitor was sealed with resin to produce a solid electrolytic capacitor.

Example 2 The same chemically formed foil as in Example 1, except for the anode terminal, was placed in a mixed solution (reaction mother liquor) of an aqueous solution of 2.4 mol/ρ of lead acetate trihydrate and an aqueous solution of 4 mol/ρ of ammonium persulfate. Soak,
The reaction was carried out at 80°C for 30 minutes, and the semiconductor layer formed on the dielectric oxide film layer consisting of lead dioxide and lead sulfate was ultrasonically cleaned in water for 3 minutes, and then dried under reduced pressure at 120°C. The generated semiconductor layer consists of lead dioxide and lead sulfate, with lead dioxide being about 25%
It was confirmed by mass spectrometry, X-ray analysis, and infrared spectroscopy that the content was % by weight.

Next, a paste consisting of 30 parts of silver powder, 60 parts of lead dioxide, and 10 parts of acrylic resin was applied onto the semiconductor layer and dried, and then the cathode was taken out in the same manner as in Example 1 and sealed with resin to produce a solid electrolytic capacitor. did.

Example 3 A semiconductor layer was produced in the same manner as in Example 2, except that 0.05 mol/g of hydrogen peroxide solution was further added to the reaction mother liquor during semiconductor formation in Example 2. The semiconductor layer at this time is
It was confirmed that the composition was composed of lead dioxide and lead sulfate, and that lead dioxide contained approximately 50% by weight.

Furthermore, silver powder 25
A solid electrolytic capacitor was produced in the same manner as in Example 2.

Example 4 After forming a semiconductor layer consisting of lead dioxide and lead sulfate in the same manner as described in Example 2, it was subjected to sonic cleaning in water for 3 minutes. It was confirmed that about 25% by weight of lead dioxide was contained.

A paste consisting of 30 parts of silver powder, 50 parts of lead dioxide, 10 parts of lead sulfate, and 10 parts of acrylic resin was applied onto this semiconductor layer, and after drying, the cathode was taken out in the same manner as in Example 1, sealed with resin, and solidified. An electrolytic capacitor was manufactured.

Comparative Example 1 In Example 1, the lead dioxide content in the paste was eliminated, and silver powder 92
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that a conductive layer was formed using 8 parts of the urethane resin.

Comparative Example 2 A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the semiconductor layer was not cleaned with ultrasonic waves.

Table 1 shows the characteristic values of the solid electrolytic capacitors manufactured in Examples 1 to 4 and Comparative Examples 1.2.

Table 1 [Effects of the Invention] As described above, according to the method for manufacturing a solid electrolytic capacitor according to the present invention, the surface of the formed semiconductor layer is cleaned, and then metal oxide powder or metal oxide powder is , a process of forming a paste layer mainly composed of metal powder and metal powder as a conductor layer, or a process of forming a conductor layer containing metal powder and metal oxide powder forming a semiconductor layer, and further containing other compounds and a mixture powder thereof. Solid electrolytic capacitors have extremely excellent high temperature stability due to the synergistic effect of combining the process of cleaning the surface of the semiconductor layer and the process of forming a paste layer on the conductor layer. can be manufactured.

Claims (11)

[Claims] 1. In a method for manufacturing a solid electrolytic capacitor, in which a dielectric oxide film, a semiconductor layer, and a conductive layer are sequentially formed on the surface of an anode substrate made of a metal having valve action, after cleaning the surface of the semiconductor layer, A method for manufacturing a solid electrolytic capacitor, comprising the step of forming a paste layer containing metal oxide powder and metal powder as main components as a body layer. 2. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein the semiconductor layer is a layer containing lead dioxide as a main component. 3. 2. The method of manufacturing a solid electrolytic capacitor according to claim 1, wherein the semiconductor layer is a layer containing lead dioxide and lead sulfate as main components. 4. The method for manufacturing a solid electrolytic capacitor according to any one of claims 1 to 3, wherein the metal oxide powder is lead dioxide powder. 5. The method for manufacturing a solid electrolytic capacitor according to any one of claims 1 to 4, wherein the surface of the semiconductor layer is cleaned with ultrasonic waves. 6. In a method for manufacturing a solid electrolytic capacitor, in which a dielectric oxide film, a semiconductor layer, and a conductive layer are sequentially formed on the surface of an anode substrate made of a metal having valve action, after cleaning the surface of the semiconductor layer, A solid electrolytic capacitor comprising a step of forming a paste layer containing a metal powder and a metal oxide powder forming the semiconductor layer as a body layer, and a paste layer containing a mixture powder with other compounds as a main component. Production method. 7. 7. The method of manufacturing a solid electrolytic capacitor according to claim 6, wherein the semiconductor layer is a layer containing lead dioxide as a main component. 8. 7. The method of manufacturing a solid electrolytic capacitor according to claim 6, wherein the semiconductor layer is a layer containing lead dioxide and lead sulfate as main components. 9. The method for manufacturing a solid electrolytic capacitor according to any one of claims 6 to 8, wherein the metal oxide powder is lead dioxide powder. 10. 10. The method for manufacturing a solid electrolytic capacitor according to claim 6, wherein the mixed powder with other compounds contains lead dioxide and lead sulfate as main components. 11. The method for manufacturing a solid electrolytic capacitor according to any one of claims 6 to 10, wherein the surface of the semiconductor layer is cleaned with ultrasonic waves.