JP2567234B2 - Manufacturing method of solid electrolytic capacitor - Google Patents

Description

The present invention relates to a method for manufacturing a solid electrolytic capacitor in which a lead dioxide layer is laminated on a dielectric film.

(Problems to be Solved by Conventional Techniques and Inventions) Conventionally, instead of a wet ionic electrolyte used for an electrolytic capacitor, a dielectric metal oxide film, particularly a tantalum electrode (anode) surface is formed by oxidation. It is known that a semiconductor manganese dioxide (MnO ₂ ) layer called a solid electrolyte is formed on a tantalum oxide film, which has been commercialized.

Then, in the same manner, MnO ₂ is deposited on the dielectric metal oxide film.
Attempts have been made to use lead dioxide as the solid electrolyte instead of, but such early attempts were not yet commercially viable.

However, since lead dioxide has a remarkably high conductivity, it was expected to obtain a capacitor having excellent electrical and physical characteristics as compared with a capacitor having an MnO ₂ layer. It was not possible to make a practical capacitor successfully because there was no good way to form a layer of lead dioxide.

As one of the methods to solve such a point, when forming a lead dioxide layer on a capacitor, a divalent lead compound in an aqueous solution is oxidized, particularly by persulfate, to form lead dioxide. It has been proposed to utilize the reaction. According to this method, the conventional problems, in particular, the mechanical strength of the lead dioxide layer laminated on the dielectric oxide film is improved, and the lead dioxide layer can be easily formed. Is said to be obtained.

By the way, the dielectric of the solid electrolytic capacitor is generally made porous, and it is said that a film of lead dioxide is laminated on the porous dielectric to form a solid electrolytic capacitor. . Therefore, it is necessary that the aqueous solution containing the divalent lead compound and the oxidizing agent and the entire surface of the porous dielectric material are in contact with each other when the lead dioxide film is formed, and they are present on the porous dielectric surface. It is desired that the aqueous solution containing the divalent lead compound and the oxidizing agent penetrates into the inside of the fine pit.

However, the metal oxide film that is the porous dielectric film, especially the Al ₂ O ₃ film layer, has poor wettability with water, and therefore, when a lead dioxide film is to be laminated, the surface of the Al ₂ O ₃ film is the divalent lead. It has not been sufficiently contacted with an aqueous solution containing a compound and an oxidizing agent, especially persulfate, and as a result, it has been impossible to uniformly form a lead dioxide film on the dielectric film. The solid electrolytic capacitor manufactured in this manner is difficult to make into a uniform product, and its electrical characteristics and physical-mechanical characteristics are not always satisfactory.

In particular, since the inside of the fine pits existing on the porous dielectric film cannot fully contact the aqueous solution, the characteristics of the solid electrolytic capacitor that the dielectric layer is made porous and the lead dioxide layer is formed on it I couldn't make the most of it.

(Means for Solving Problems) As a result of earnest research in view of such problems, the present inventor has brought the dielectric film into contact with an aqueous solution containing a divalent lead compound and an oxidizing agent to form a film on the dielectric film. When a solid electrolytic capacitor is manufactured by stacking lead dioxide films, the dielectric film is previously immersed in a solution containing a surfactant, dried, and then contacted with an aqueous solution containing the divalent lead compound and oxidant. By doing so, they have found that such problems can be solved.

If such a method is adopted, the contact between the surface of the dielectric film and the aqueous solution will be good, and the precipitation of lead dioxide will be achieved even in the fine pits on the surface of the dielectric film, and the dielectric film and the lead dioxide film will be formed. Is excellent in adhesion, and the obtained solid electrolytic capacitor has excellent electrical characteristics and the like.

That is, the present invention provides a method for producing a solid electrolytic capacitor in which a dielectric metal oxide film on an anode foil is contacted with a solution containing a lead (II) compound and a persulfate to laminate a lead dioxide film. The method for producing a solid electrolytic capacitor is characterized in that the dielectric metal oxide film of the anode foil is previously dipped in a solution containing a surfactant, dried, and then performed.

The dielectric metal oxide film of the present invention is preferably formed by an ordinary method formed by anodizing the surface of the metal anode foil.

Furthermore, in contacting the dielectric film with a solution consisting of a divalent lead compound for oxidizing lead to lead dioxide and a persulfate, a lead (II) compound such as lead acetate and easily soluble silver is used. It is also preferable to manufacture a solid electrolytic capacitor by using an acidic solution containing a salt and a solution containing a persulfate selected from alkali metals and ammonium and laminating a lead dioxide film on the dielectric film.

The surfactant used in the present invention is not particularly limited as long as it enhances the contact property between the dielectric film and the solution in contact with the dielectric film.

As the surfactant used in the present invention, if the surfactant is added to the solution, it can penetrate the solution to the complex and very fine pits on the surface of the dielectric film. It is not particularly limited.

The surfactant used in the present invention is not particularly limited as long as it can improve the electrical properties and physical mechanical properties of the solid electrolytic capacitor manufactured using the same. Things can be used.

Examples of the surfactant that can be used in the present invention include water-soluble surfactants and oil-soluble surfactants,
A water-soluble surfactant can be used more preferably.

Examples of the water-soluble surfactant used here include an ionic surfactant and a nonionic surfactant, and further, the ionic surfactant includes a cationic surfactant, an anionic surfactant and Examples include zwitterionic surfactants.

In addition, examples of the surfactant that can be used in the present invention include polymer surfactants, organometallic surfactants, fluorine-based surfactants and reactive surfactants.

Preferably carboxylate as anionic surface active agent used herein, sulfonate, sulfate esters, phosphoric acid esters, are exemplified phosphonic acid salts, and more preferably the formula R-COO ^- carboxylate the formula R-SO ₃ ^- sulfonate, R-O · SO ₃ ^- sulfuric acid esters of the formula Phosphate ester of formula R Phosphonic acid ester (wherein R is an alkyl group)
And the like. Specific examples of these include fatty acid salts such as sodium laurate, sodium myristate, sodium palmitate, sodium stearate, potassium stearate, potassium palmitate, potassium myristate, potassium laurate, and alkylbenzene sulfonic acid. Salts such as those known as ABS and LAS, alkylnaphthalene sulfonates, alkyl sulfonates such as SAS, α-olefin sulfonates such as AOS, also α-sulfonated Fatty acid salt, N
-Methyl-N-oleyl taurine, for example known as Igepon T, petroleum sulfonates, alkyl sulphates, sulphated fats and oils such as sulphated castor oil, sulphated olive oil, polyoxyethylene alkyl ether sulphates, polyoxys Ethylene alkyl phenyl ether sulfate, polyoxyethylene styrenated phenyl ether sulfate, alkyl phosphate, polyoxyethylene alkyl ether phosphate, polyoxyethylene alkyl phenyl ether phosphate, naphthalene sulfonate formaldehyde condensation Things can be given.

Examples of the cationic surfactant used here include amine salts such as primary amine salts, secondary amine salts and tertiary amine salts, as well as quaternary ammonium salts, phosphonium salts and sulfonium salts. Salt and the like can be mentioned, more preferably (In the above formula, R is an alkyl group, and R _{1 to} R ₃ are alkyl groups which may be the same or different.) And the like. Specific examples of these include, for example, octylamine salt, dodecylethanolamine salt, N
-(Ethylstearic acid) -N-diethanolamine salt, trimethyldodecyl ammonium salt, N-hexa.
Dodecylpyridinium salt, lauryl isoquinolinium salt, dimethyl dodecyl phenylphosphonium salt,
Dodecyl benzyl methyl sulfonium salt is mentioned.

As the zwitterionic surfactant used here, those having a sulfonic acid group and an amine or ammonium base in the molecule, those having a sulfonic acid group and an amine or ammonium base in the molecule, and a sulfate ester group in the molecule Examples thereof include those having an amine or ammonium base, and more preferably (In the above formula, R is an alkyl group, R _{1 and} R ₂ are the same or different alkyl groups, and R ₃ is an alkylene group.) And the like. Specific examples of these include N-octadecyloxymethyl-N, N-dimethylbetaine and N-heptadecyl-N-ethyl-sulfobetaine.

Examples of the nonionic surfactant used here include the following.

_{R-COO-CH 2 -CH 2} -O-CH 2 - ... CH 2 -OH, R-COO-
_{C 6 H 11 O 4, R} -COO-C 12 H 21 O 10, R-CO · NH-R 1 -OH, _{R-CO- [O-CH 2} -CH 2 -CH 2] -OH, R-CO-N-
_{[O-CH 2 -CH 2]} n-OH, R- [O-CH 2 -CH 2] n-O
H, R-NH- [O- CH 2 -CH 2] n-OH, R-S- [O · C
_{H 2 -CH 2] n-OH} , _{H- [O-CH 2 -CH 2} -] n- in _{[O-CH 2 -CH 2]} n-OH ( above formula R is an alkyl group, R ₁ and R ₂ may be the same or different alkyl Specific examples of these are polyoxyethylene (n = 5) lauric acid ester, polyoxyethylene (n = 5) laurylamine, polyoxyethylene (n = 15) lauryl amide, and polyoxy. Ethylene (n
= 13) oleyl alcohol, polyoxyethylene (n =
8) Octylphenol, triethyl glycol monolauryl ether, hexaethylene glycol stearate, etc.

Further, the fluorine surfactant used here is a substitute for the hydrogen atom bonded to the carbon of the hydrophobic group of the above-mentioned anionic surfactant, cationic surfactant, zwitterionic surfactant and nonionic surfactant. In which a part or all of them are substituted with a fluorine atom.

Specific examples of these include perfluorobutanoate, [1-10] difluorodecanoate, perfluorooctylamine salt, and N-perfluoropentadecyl-N-ethylsulfobetaine.

Examples of the organometallic surfactant used here include Si, Ti, S in the main chain of the above-mentioned anionic surfactant, cationic surfactant, zwitterionic surfactant and nonionic surfactant.
Examples thereof include those having metals such as n, Zr and Ge.

Specific examples of these are, for example, 7-
(Triethylsilano) hexanoate, (BuO) ₃・ Ti [O
Ti (OBu) (OCOC ₁₇ H ₅₅ ) ₃ OTi (OBu) ₂ ] and the like.

In the present invention, the surfactant solution to be immersed in the dielectric film is not particularly limited as long as it has a concentration such that the solution can sufficiently contact and penetrate the surface of the dielectric film. Depending on the type, the nature of the dielectric film used and the type and concentration of the solute in the solution to be added, an optimum maximum value can be used.

Even if the concentration is low, the desired amount of surfactant can be retained on the dielectric film by dipping and drying the dielectric film several times.

The concentration can usually be effectively used even at a very low concentration, and may be a dilute solution of 10 ⁻⁵ mol /.

However, it is substantially meaningless to retain a larger amount of surfactant than necessary, and it is economically disadvantageous.

The concentration of the surfactant used is more preferably 0.05 Wt%
The concentration of the aqueous solution is 1.0 Wt%, particularly preferably about 0.1 Wt%.

The surfactant used in the present invention lowers the surface tension of water between the surface of the dielectric film and the aqueous solution to allow the aqueous solution to penetrate to the complex and very fine pits, resulting in the lead dioxide film. All of the above-mentioned surfactants can be used as long as the formation of the above is good.

A preferred specific example of the solid electrolytic capacitor obtained by the method of the present invention is shown schematically in FIG. 1. From the anode side to the cathode side, the aluminum layer 1, Al ₂ O ₃
Dielectric layer 2, lead dioxide layer 3, colloidal carbon layer 4,
The silver paste layer 5 is shown in the order of schematic diagrams. Further, an anode side lead wire 6 is connected to the aluminum layer 1 and a cathode side lead wire 7 is connected to the silver paste layer 5.

As the substrate of the dielectric film used in the method of the present invention, those whose oxides are known to be excellent dielectric materials are preferable, and not only aluminum but also tantalum, niobium, thiane, zircon. And so on. It is particularly preferable that the surface of the substrate is treated by etching or the like to make the surface porous. Any known method can be used essentially for making the substrate surface porous, but the etching method is more convenient and superior.
This etching method is performed by subjecting the metal foil to be the above-mentioned substrate to AC electrolytic etching in an acid aqueous solution, preferably hydrochloric acid aqueous solution. The aqueous acid solution that can be used in this case can be selected from known etching solutions.
Mineral acids such as sulfuric acid and hydrochloric acid are preferable as the acid. This etching process can also be performed by appropriately selecting arbitrary conditions depending on the degree to which the metal layer that is the substrate is made porous.

The first step of the method for manufacturing a solid electrolytic capacitor according to the present invention is equivalent to the step of forming an Al ₂ O ₃ dielectric layer 2 on an aluminum layer 1 as shown in the preferable structural schematic view of FIG. To do.

That is, a dielectric film is formed on the surface of the metal layer of the substrate obtained as described above. The dielectric film can be formed by oxidizing the surface of the metal layer of the substrate. Although various known methods can be adopted as the oxidation treatment method, an electrical oxidation method is preferable. This electrical oxidation method includes, for example, a voltage of 60
It is made by anodizing at -80 V, preferably 70 V.

Also, such anodization can be carried out in an electrolyte commonly used for suitable anodization containing citric acid, phosphoric acid or the like.

The conditions for this electrical oxidation may be any appropriate conditions depending on the thickness of the oxide film or the material of the metal layer of the substrate used. It is desirable to select it, for example,
It can be performed by adjusting the working voltage and the oxidation time.

The dielectric film thus formed is made of the metal oxide of the substrate used, and includes aluminum oxide (Al ₂ O ₃ ), Ta ₂ O ₅ , Nb ₂ O ₅ , TiO ₂ , and ZrO. ₂ etc.

Further, the dielectric film in the present invention is not limited to a normal film form, and may have any form as long as it can be used as a normal solid electrolytic capacitor, and is not necessarily a uniform film. It doesn't have to be. And the form of the film can be appropriately selected as required.

The next step of the method for manufacturing a solid electrolytic capacitor according to the present invention corresponds to the step of forming the lead dioxide layer 3 on the Al ₂ O ₃ dielectric layer 2 as shown in FIG. is there.

By the way, lead dioxide is produced by oxidizing a divalent lead compound in a solution, particularly in an aqueous solution, with a persulfate as shown in the following formula.

Pb ²⁺ ＋ S ₂ O ₈ ^2- ＋ 2H ₂ O ＋ PbO ₂ ↓ ＋ 2SO ₄ ² ＋ 4H ⁺ However, if such a reaction is carried out on the surface of the dielectric layer as it is, lead dioxide usually produced is hard to adhere to the surface. .

Further, the dielectric layer formed as described above has a problem that it is difficult to sufficiently contact the surface with the solution when the surface is contacted with the solution.

In most cases, the above-mentioned dielectric layer is formed by subjecting a film-forming metal to be a substrate to a porous treatment to increase its surface area, but its surface has complicated and fine pits.

Therefore, it is considered that the above-mentioned problem occurs because the solution does not penetrate to the entire surface of the derivative layer under the influence of the surface tension of the solution.

Further, the dielectric layer is composed of a metal oxide obtained by oxidizing the metal of the substrate, and such a metal oxide layer does not always have good contact with the solution. In particular,
The aluminum oxide film has poor wettability with water, and the surface of the aluminum oxide film cannot be satisfactorily treated when an aqueous solution which is commonly used is used. That is, it is not possible to form a lead oxide layer in every corner of the complex and fine pits on the surface of the film, and not only the electric characteristics of the obtained solid electrolytic capacitor are poor, but also the physical characteristics of the solid electrolytic capacitor are poor. The mechanical and mechanical properties are also poor.

In addition, in the solution used to form lead dioxide, in addition to solutes such as divalent lead compounds and persulfates,
Since the solute for adjusting the PH is added, the surface tension of the solution itself increases, and it becomes difficult for the solution to permeate to every corner of the surface of the dielectric layer that has complex and fine pits. .

However, according to the research conducted by the present inventor, such a problem is that the dielectric film is previously immersed in a solution containing a surfactant,
The solution can be solved all at once by drying and contacting the dielectric film having the surface active agent retained thereon with the solution.

That is, the surface of the dielectric film obtained above is treated by a conventional method with a lead (II) compound, for example, an acetic acid salt, and a persulfate selected from the group consisting of sodium persulfate, potassium persulfate, ammonium persulfate and the like. When contacting with a solution containing, the dielectric film is preliminarily selected from the anionic, cationic, amphoteric, nonionic, fluorine-based and organometallic surfactants, or one or more selected from the above-mentioned surfactants. By soaking in a solution containing a surfactant containing a combination of the above and drying, a lead dioxide film is effectively formed on the surface of the dielectric film.

In the present invention, the surfactant intervenes in the contact surface between the surface of the dielectric film and lead dioxide, which is the solid electrolyte, and adheres the dielectric film and the solid electrolyte. By dispersing or remaining in the solid electrolyte layer, the conductivity of the solid electrolyte layer is not affected and the strength of the solid electrolyte is not reduced.

The thickness of the lead dioxide film formed here is such that the surface of the dielectric film is subjected to repeated contact treatment until a lead dioxide layer having a desired thickness is obtained in the lead dioxide film forming solution, or the pH of the lead dioxide film forming solution is PH. By adjusting the formation rate of the lead dioxide layer and the thickness of the layer.

As a method of changing the pH of the lead dioxide film forming solution, for example, a weakly acidic or neutral solution is made alkaline. As a concrete method for making this alkaline side, ammonium hydroxide, sodium hydroxide,
It is possible to gradually add a solution of potassium hydroxide or the like so as to obtain a desired PH value, for example, 10 to 12, and particularly an optimum PH value of 10.3.

The thickness of the formed lead dioxide film can be selected by arbitrarily selecting the range required for a normal solid electrolytic capacitor.

Generally, it is considered desirable for a solid electrolytic capacitor to grow a film in the range of 4000 to 6000 angstroms.

Furthermore, as another method, (a) a solution containing a required persulfate selected from ammonium persulfate, sodium persulfate and potassium persulfate, and (b) a divalent lead compound,
For example, a solution containing lead acetate and an alkali selected from ammonium hydroxide, potassium hydroxide and sodium hydroxide may be mixed on the surface of the dielectric film.

In this case, the mixing treatment can be performed by adding and mixing the solution (b) to the solution (a).

The next step of the method for producing a solid electrolytic capacitor according to the present invention is, as shown in the preferred structural schematic diagram of FIG. 1, a cathode electrode layer (colloidal carbon layer 4 and silver paste layer 5) on a lead dioxide layer 3. (Composed of more).

There is no particular limitation on the cathode electrode layer as long as it is acceptable for use as a solid electrolytic capacitor, and various methods can be used.

Although the method of manufacturing a solid electrolytic capacitor using a foil mainly made of a film-forming metal has been described above, this method can also be used for manufacturing a solid electrolytic capacitor of another form.

For example, the present invention can be applied to the one using a solid electrolytic capacitor, winding, etc., which is created by printing such as forming a film form metal on a specific substrate by vapor deposition.

Those skilled in the art can easily recognize that the drawings and the description of the processes described above are provided for the understanding of the present invention and that various modifications can be made.

(Examples) The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

Example 1 A high-purity (99.99) aluminum foil is used as a substrate, and the surface of this aluminum foil is subjected to AC electrolytic etching in a hydrochloric acid aqueous solution to increase the surface area.

Next, after etching, wash it well, and anodize the surface of the etched aluminum foil at a voltage of about 90 V.
A dielectric oxide film of l ₂ O ₃ was formed. The capacitance of the obtained film was 28 μF / 10 cm ² (however, the measured value in a water bath). This was cut into a width of 6 mm and a length of 27 mm, and the anode side lead wire was connected.

Next, this is immersed in water containing 0.1 wt% of a nonionic surfactant (trade name of "Kao Amate"). After drying this, 1 mol / solution 20 g of acetate (Pb (OCOCH ₃ ) ₂ ) 3H ₂ O) and ammonium peroxodisulfate (NH ₄ ) ₂ S ₂ O ₈ ) 2
Immerse in a mixed solution of 20 mol / solution and react at 80 ° C for 20 minutes. By repeating this operation 2-3 times, a lead dioxide (PbO ₂ ) film is formed on the dielectric film.

Then, it is washed with water and dried at 130 ° C. for 1 hour to obtain an aluminum foil on which the lead dioxide film 3 and the Al ₂ O ₃ (porous) dielectric layer 2 are formed. Next, colloidal carbon 4 is applied to the surface of the lead dioxide layer 3, and a conductive paste "Dotite" in which silver powder is dispersed in an acrylic solvent is further applied.
"XA-167 (trade name)" (silver paste) 5 was applied on the surface and dried overnight and the cathode side lead wire 7 was connected to form a solid electrolytic capacitor. The structural schematic diagram of this capacitor is as shown in FIG.

Next, the electrical characteristics of the obtained solid electrolytic capacitor were measured.

As a result, the capacitance (C) of the solid electrolytic capacitor is
1.8μF, loss angle tangent (tan δ) is 4.7%, leakage current (L
C) was 0.3 μA (25V) *.

However, *: current value 3 minutes after applying 25 V. Comparative Example 1 The same aluminum foil as that used in Example 1 above was used, and an Al ₂ O ₃ dielectric oxide film was formed on the surface in the same manner as in Example 1 above. Was formed.

A lead dioxide layer was formed on the Al ₂ O ₃ dielectric coating surface of the aluminum foil by the same treatment as in Example 1 except that the dielectric coating was not treated with the surfactant-containing aqueous solution. This was made into a solid electrolytic capacitor in the same manner as in Example 1.

Then, when the electrical characteristics were measured in the same manner as in Example 1, the capacitance (C) was 1.5 μF and the loss angle (tan
δ) was 0.098 and the leakage current (LC) was 0.6 μA.

Example 2 The use of a high-magnification etched Al foil in which the electrostatic capacity of the Al ₂ O ₃ dielectric film on the surface was 59 μF / 10 cm ² (however, measured value in a water bath), and the fluorine-based surfactant was used. Experiments were performed in the same manner as in Example 1 except that the dielectric film was dipped and dried in an aqueous solution containing 0.1 wt% of the surfactant "Daikin Unitine (anionic)" (trade name). I went.

As a result, the electric characteristics of the obtained solid electrolytic capacitor were as follows: capacitance (C) 4.0 μF, tangent of loss angle (tan δ)
Was 6.8% and the leakage current (LC) was 0.4 μA (25V) *.

However, a current value 3 minutes after * 25 V was applied Comparative Example 2 The same high-magnification etched aluminum foil used in Example 2 was used.

A lead dioxide layer was formed on the surface of the aluminum foil in the same manner as in Example 1 except that the dielectric coating was not treated with the surfactant-containing aqueous solution. This was made into a solid electrolytic capacitor in the same manner as in Example 1.

Then, when the electrical characteristics were measured in the same manner as in Example 1, the capacitance (C) was 3.0 μF and the loss angle (tan
δ) was 0.120 and the leakage current (LC) was 1.9 μA.

From these results, the solid electrolytic capacitor obtained by the example method using the surfactant of the present invention has the capacitance increased to 1.2 times or more that of the solid electrolytic capacitor obtained by the comparative example method using no surfactant. You can see that

Also, the tangent (tan δ) of the loss angle and the leakage current (LC) are greatly reduced, and it can be seen that the electric characteristics of the solid electrolytic capacitor are very good.

(Effect of the Invention) As described in detail above, according to the method of the present invention,
Since lead dioxide is deposited and formed even in the fine pits of the dielectric layer, the adhesion between the dielectric and lead dioxide is also improved,
The obtained solid electrolytic capacitor using lead dioxide as an electrolyte has very excellent electrical characteristics.

In particular, it is easy to obtain an electrolytic capacitor in which the capacitance is remarkably increased and the tangent of the loss angle and the leakage current are greatly reduced.

[Brief description of drawings]

FIG. 1 shows a structural schematic diagram of a solid electrolytic capacitor obtained in an example of the present invention. 1: Aluminum layer, 2: Al ₂ O ₃ dielectric layer, 3: Lead dioxide layer, 4: Colloidal carbon layer, 5: Silver paste layer, 6: Anode side lead wire, 7: Cathode side lead wire

Claims (1)

(57) [Claims] 1. A method for producing a solid electrolytic capacitor, comprising laminating a lead dioxide film by bringing a solution containing a lead (II) compound and a persulfate into contact with a dielectric metal oxide film on an anode foil. The dielectric metal oxide film of the anode foil is immersed in a solution containing a surfactant in advance and dried, and then a solution containing the lead (II) compound and a persulfate is brought into contact with the solid electrolyte. Capacitor manufacturing method.