JP2002075789A - Solid electrolyte capacitor sheathed with laminated sheet and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a large-sized flat p late laminated solid electrolyte capacitor, having superior high-frequency characteristics, high withstand voltage, moisture resistance and a high capacity, and to provide a method for manufacturing the same. SOLUTION: The solid electrolyte capacitor, having a solid electrolyte layer formed by laminating a cathode foil 2 and an anode foil 1 via a separator 3 and polymerizing a 3,4-ethylenedioxythiophene by an oxidizer under a pressurized state by heating between both the foils, is sealed with a laminated sheet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a large flat solid electrolytic capacitor encapsulated in a laminate sheet and a method of manufacturing the same, and more particularly to a solid electrolytic capacitor using a conductive organic solid electrolyte.

2. Description of the Related Art An electrolytic capacitor is formed by forming an oxide film layer serving as a dielectric on the surface of an anode electrode made of a valve metal such as tantalum and aluminum and having fine holes and etching pits. Is drawn out.

[0002] The extraction of the electrode from the oxide film layer is performed by a conductive electrolyte layer. Therefore, in the electrolytic capacitor, the electrolyte layer serves as a true cathode. For example, in an aluminum electrolytic capacitor, a liquid electrolyte is used as a true electrode, and a cathode electrode merely serves to electrically connect the liquid electrolyte layer to an external terminal.

[0003] An electrolyte layer functioning as a true cathode is required to have adhesion, denseness, uniformity, and the like with an oxide film layer.
In particular, the adhesion in the fine holes of the anode electrode and the inside of the etching pits has a great effect on the electrical characteristics, and a number of electrolyte layers have been proposed.

[0004] A solid electrolytic capacitor uses a solid electrolyte having conductivity instead of a liquid electrolyte layer lacking impedance characteristics in a high-frequency region because it has ion conductivity. ,
7,8,8-Tetracyanoquinodimethane (TCNQ) complexes are known.

A solid electrolyte layer made of manganese dioxide is
An anode element made of a sintered body of tantalum is immersed in an aqueous solution of manganese nitrate, and is produced by thermal decomposition at a temperature of about 300 to 400 ° C. In a capacitor using such a solid electrolyte layer, the oxide film layer is easily damaged at the time of thermal decomposition of manganese nitrate, and therefore, a tendency for the leakage current to increase is observed. Further, since the specific resistance of manganese dioxide itself is high, it is also difficult to obtain sufficiently satisfactory characteristics in impedance characteristics. In addition, since the lead wire is damaged by the heat treatment, it is necessary to separately provide an external terminal for connection as a later process.

As a solid electrolytic capacitor using a TCNQ complex, one disclosed in Japanese Patent Application Laid-Open No. 58-191414 is known. An electrolyte layer is formed. This TCNQ complex has high conductivity and can obtain good results in frequency characteristics and temperature characteristics.

However, since the TCNQ complex has a property of being transferred to an insulator in a short time after melting, it is difficult to control the temperature during the manufacturing process of the capacitor. Furthermore, since the TCNQ complex itself lacks heat resistance, when mounted on a printed circuit board, remarkable fluctuations in characteristics due to solder heat are observed.

[0008] In order to solve the problems of the manganese dioxide and the TCNQ complex, it has been attempted to use a conductive polymer such as polypyrrole as a solid electrolyte layer.

A conductive polymer represented by polypyrrole is mainly produced by a chemical oxidation polymerization method (chemical polymerization) or an electrolytic oxidation polymerization method (electrolytic polymerization). However, it was difficult to form a strong film densely by chemical polymerization. On the other hand, in the electrolytic polymerization, it is necessary to apply a voltage to an object to form a film, and it is difficult to apply the voltage to an anode electrode for an electrolytic capacitor having an oxide film layer as an insulator formed on the surface. Therefore, on the surface of the oxide film layer, a conductive pre-coat layer, for example, a pre-coat layer of a conductive polymer film chemically polymerized using an oxidizing agent is formed in advance, and then an electrolyte layer by electrolytic polymerization using the pre-coat layer as an electrode. There has been proposed a method of forming the film (Japanese Patent Laid-Open No. 63-1).
No. 73313, JP-A-63-158829:
Manganese dioxide is used as the precoat layer).

However, in the case of electrolytic polymerization, the step of forming the precoat layer is required in advance, which complicates the manufacturing process. In addition, the solid electrolyte is placed near the external electrode for polymerization disposed on the surface of the anode electrode to be coated. Since the layer is formed, it is very difficult to continuously form a conductive polymer film having a uniform thickness over a wide range.

Therefore, a foil-like anode electrode and a cathode electrode are
Winding through a separator to form a so-called winding type capacitor element, this capacitor element is impregnated with a monomer solution such as pyrrole and an oxidizing agent, and an electrolyte layer consisting of a conductive polymer film formed only by chemical polymerization Has been attempted.

Such a wound-type capacitor element is well known for an aluminum electrolytic capacitor. By holding a conductive polymer layer with a separator, the complexity of electrolytic polymerization is avoided, and the surface area is also large. It was expected that the capacity would be expanded by the foil-like electrode.

However, when a capacitor element is impregnated with a mixed solution obtained by mixing a monomer solution and an oxidizing agent, a solid electrolyte layer is not formed inside the capacitor element, and the expected electrical characteristics cannot be obtained. There was found.

Therefore, a method of separately impregnating the monomer solution and the oxidizing agent and a method of lowering the polymerization reaction temperature have been tried, and a solid electrolytic capacitor having some good electric characteristics has been obtained. However, there remains a problem that the impedance is not high enough and the impedance becomes high. The cause is that in the above method, the solid electrolyte layer generated near the end of the capacitor element hinders the penetration of the solution into the inside of the capacitor element, and as a result, it has not been possible to form a dense and uniform solid electrolyte layer It was considered possible. In addition, when the polymerization reaction temperature is lowered, strict temperature control is required, and the production apparatus becomes complicated, resulting in a problem that the product cost is increased.

The present inventors have repeatedly studied various conductive polymers, and focused on polyethylene dioxythiophene, which has a slow reaction rate and excellent adhesion to the oxide film layer of the anode electrode ( As a result, a capacitor element in which an anode electrode foil and a cathode electrode foil are wound through a separator is impregnated with 3,4-ethylenedioxythiophene and an oxidizing agent. We have applied for an invention characterized in that polyethylene dioxythiophene, which is a solid electrolyte, is generated inside a capacitor element by a chemical polymerization reaction of the monomer and an oxidizing agent which proceeds slowly (Japanese Patent Application No. 8-131374). According to the present invention, it is possible to generate a solid electrolyte layer made of a dense and uniform conductive polymer inside a spirally wound capacitor element, utilizing the fact that the polymerization reaction rate of polyethylene dioxythiophene is slow. Thus, a solid electrolytic capacitor having excellent electric characteristics and a relatively high capacity was obtained.

[0016]

However, all of the electrolytic capacitor elements having the above-mentioned structure are required to have high withstand voltage, high capacitance and flattening due to the recent advancement of the functions of the circuit, and are more excellent. It has not been able to meet the demand for having high frequency characteristics. For example, in the case of a wound-type capacitor element, it is necessary to increase the number of windings in order to satisfy a high capacity requirement, but it is difficult to store it compactly because of its cylindrical shape.

Furthermore, when the capacitor element is of a wound type, there is a suggestion that the force for closing the coil contributes to the adhesion between the electrodes of the two electrodes and the solid electrolyte layer. It is difficult to make the tightening force for winding and closing the separator uniform, and it is also difficult to adjust this tightening force. For this reason, the efficiency of adhesion is not improved, and sufficient capacitance has not been obtained.

At present, in a multilayer solid electrolytic capacitor, it has not been possible to simultaneously satisfy all the requirements for high capacity, high withstand voltage, flattening, and excellent high frequency characteristics. The cause is that when the thickness of the dielectric film of the anode foil is increased to satisfy the high withstand voltage requirement, the obtained capacitance is reduced. In order to compensate for the capacitance, it is necessary to increase the area of the dielectric film of the anode foil. Therefore, if the shape of the multilayer capacitor is simply enlarged to satisfy this high capacity requirement, the solid electrolyte layer generated near the end of the capacitor element will hinder the penetration of the solution into the capacitor element, Cannot be sufficiently penetrated uniformly. As a result, a dense and uniform solid electrolyte layer cannot be formed, and it becomes difficult to adhere both electrode foils to the conductive polymer, which causes a problem that a sufficient capacitance cannot be obtained.

An object of the present invention is to solve the above-mentioned problems, to improve impedance characteristics, to provide high withstand voltage and high frequency characteristics, to have a large capacitance, and to easily store a large-sized laminated solid. An electrolytic capacitor and a method for manufacturing the same are provided.

[0020]

The above object is achieved by laminating a cathode electrode foil and an anode electrode foil having a dielectric oxide film formed on the surface thereof via a separator, and forming a 3,4-ethylenedioxythiophene monomer on the separator. And an oxidizing agent, and heated under pressure to polymerize and form the monomer and sealed in a laminate sheet, having high withstand voltage, high capacitance, and excellent high frequency characteristics. Achieved by large flat solid electrolytic capacitors.

In this electrolytic capacitor, a cathode electrode foil and an anode electrode foil having a dielectric oxide film formed on the surface thereof are laminated via a separator, and a 3,4-ethylenedioxythiophene monomer, an oxidizing agent and , And polymerized by heating under pressure to polymerize the monomer, and sealed in a laminate sheet bag.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The anode electrode foil may be made of any valve metal such as aluminum or tantalum, but aluminum is usually used. On the surface of the anode electrode foil, a voltage is applied in an aqueous solution of ammonium borate or the like to form an oxide film layer serving as a dielectric.

The cathode electrode foil may be any material as long as it can electrically connect the lead wire and the electrolyte. In one embodiment of the present invention, aluminum or the like is used. It is preferable to form a titanium nitride film on the surface of the cathode electrode foil because the capacitance increases.

Lead wires for connecting the respective electrodes to the outside are connected to the anode electrode foil and the cathode electrode foil by known means such as stitching and ultrasonic welding. The lead wire is made of aluminum or the like, and is composed of a connection portion with the anode electrode foil and the cathode electrode foil and an external connection portion that performs an electrical connection with the outside, and is led out from an end of the laminated capacitor element.

The anode electrode foil and the cathode electrode foil are subjected to repair formation in a chemical conversion solution and then immersed in a boric acid aqueous solution in order to repair a damaged portion or a cut surface of the film received in the processing step. This stabilizes the oxide film and increases the high withstand voltage.

Although a glass separator is usually used as the separator, as another embodiment, electrolytic paper used for a general electrolytic capacitor can be used. In other words, synthetic fibers, those made by mixing these,
Further, a nonwoven fabric obtained by mixing synthetic fibers and fibers for electrolytic paper or glass fibers can be used. Examples of the synthetic fiber include vinylon fiber, polyester fiber, nylon fiber, rayon fiber and the like. Furthermore, a synthetic resin porous separator can be used. Examples of these synthetic resins include polyamide, polyimide, and aramid. In addition, the said separator is 10-300.
The thickness is 0 μm, preferably 20 to 1500 μm. When a thickness in this range is used, a stable equivalent series resistance can be obtained.

The dimensions of the cathode electrode foil and the anode electrode foil are arbitrary depending on the specifications of the solid electrolytic capacitor to be manufactured. However, the dimensions are such that 3,4-ethylenedioxythiophene and the oxidizing agent penetrate into the center of the lamination. I just need. The separator may have a slightly larger width depending on the dimensions of the cathode electrode foil and the anode electrode foil. In order to obtain the capacitor having the performance of the present invention, the vertical and horizontal dimensions of the cathode electrode foil and the anode electrode foil are usually 10 mm or more, preferably 20 mm or more, and typically 25 to 50 mm.

The capacitor element is preferably formed by laminating a separator between the cathode electrode foil and the anode electrode foil.

By impregnating the capacitor element with 3,4-ethylenedioxythiophene and an oxidizing agent, the 3,4-ethylenedioxythiophene and the oxidizing agent penetrate into the inside of the capacitor element, and Process and mild chemical polymerization reaction that occurs appropriately after infiltration
A polymer of ethylenedioxythiophene, that is, a solid electrolyte layer is formed inside a capacitor element while being held by a separator.

3,4-ethylenedioxythiophene is
It can be obtained by a known production method disclosed in JP-A-2-15611 and the like. Further, the above-mentioned polymer of 3,4-ethylenedioxythiophene is poly3,4-ethylenedioxythiophene polymerized to an extent that it becomes a solid at normal temperature.

As the oxidizing agent, a solution in which ferric p-toluenesulfonate, which is an iron salt of aromatic sulfonic acid, is dissolved in a butanol solvent is used. As the solvent in the oxidizing agent, a normal organic solvent such as alcohols such as ethanol and butanol can be used.

As a method of impregnating the capacitor element with 3,4-ethylenedioxythiophene and an oxidizing agent, not only a method of immersing the capacitor element in a liquid in which 3,4-ethylenedioxythiophene and the oxidizing agent are mixed in advance, but also
As another embodiment, a method of immersing a capacitor element immersed in 3,4-ethylenedioxythiophene in an oxidizing agent, and a method of immersing a capacitor element immersed in an oxidizing agent in 3,4-ethylenedioxythiophene, Moreover,
A method is also possible in which the immersion operation is replaced by ejection of a solution from a syringe.

The temperature condition during the polymerization is preferably from 20 to 180 ° C. When the polymerization temperature is 20 ° C. or lower, the formation of 3,4-ethylenedioxythiophene does not proceed well, and the capacitance decreases and the equivalent series resistance increases. At a temperature higher than 180 ° C., the decomposition of 3,4-ethylenedioxythiophene occurs, the capacitance decreases, and the equivalent series resistance increases. That is, excellent high-frequency characteristics cannot be obtained.

The pressure condition during the polymerization is 30 to 1000 kg /
cm², Especially 100-600kg / cm ²Is preferred. 30
kg / cm²If the pressure is less than the produced polymer and electrode foil
Does not progress well, reducing capacitance and equivalent
The series resistance increases. 1000kg / cm²Than
Even at high pressure, the monomer and oxidizer between the electrode foils
As the amount decreases, the amount of polymer formed decreases, and
The series resistance increases. In other words, excellent high-frequency characteristics
I can't get it.

The solid electrolyte layer is obtained by advancing the polymerization reaction for 30 minutes or more under the above polymerization conditions. The reaction time of this polymerization reaction is preferably 30 minutes or more at which the polymerization reaction can be completely completed.

After the formation of the solid electrolyte layer by the polymerization reaction, the oxide film is repaired, that is, reformed. This step is carried out by applying a formation voltage in the presence of moisture absorbed from the air by the oxidizing agent remaining after the polymerization. At this time, even if an anode foil formed at a high voltage is used, the anode foil can be re-formed at a high voltage, so that a high withstand voltage can be achieved.

The laminate sheet used for the exterior is usually a sheet in which a metal foil and a synthetic resin are laminated. Aluminum foil is usually used as the metal foil. Examples of the synthetic resin include polypropylene (PP), polyethylene terephthalate (PET), polyphenylene sulfide,
Polyimide, polyester, polyvinyl chloride and the like are used. In the case of the exterior, a solid electrolytic capacitor is inserted into a bag formed of a laminate sheet in a state where the lead wires protrude out of the bag, and the opening is thermocompression-bonded by melting a synthetic resin to seal and seal.

According to the above embodiment, high withstand voltage of 50 V or more, high capacitance of 20 μF or more, and 5 to 10
A large flat solid electrolytic capacitor having excellent high-frequency characteristics with an equivalent series resistance of 100 mΩ or less at 00 kHz can be obtained.

[0039]

Next, a method of manufacturing a solid electrolytic capacitor according to the present invention and a solid electrolytic capacitor obtained by the method will be specifically described with reference to the drawings.

[0040]Example 1  FIG. 1 shows a solid electrolytic capacitor of the present invention, in which an anode electrode foil 1
And the cathode electrode foil 2 has a vertical dimension of 30 mm and a horizontal dimension of 40 mm.
mm of aluminum foil.

The anode electrode foil 1 was subjected to a chemical conversion treatment on its surface to form an oxide film layer 4 made of aluminum oxide on the surface. The surface of the cathode electrode foil 2 was subjected to the same chemical treatment as that of the anode electrode foil 1, and then a titanium nitride film was formed by a cathode arc plasma deposition method. In order to repair the damaged portion or cut surface of the bipolar foil received in the processing step, the oxide film is formed again by performing repair formation in an aqueous solution of ammonium phosphate, and further boric acid for stabilizing the oxide film. It was immersed in an aqueous solution.

A glass separator 3 having a thickness of 100 μm, a vertical dimension of 35 mm and a horizontal dimension of 90 mm is sandwiched between the cathode electrode foil 2 and the anode electrode 1 and laminated.
I got Note that lead wires 6 and 7 were electrically connected to the anode electrode foil 1 and the cathode electrode foil 2 of the capacitor element 10 in advance, respectively, and protruded from the end of the capacitor element 10.

The capacitor element 10 having the above configuration was impregnated with 3,4-ethylenedioxythiophene and an oxidizing agent. The oxidizing agent was p-
These mixed solutions were prepared using ferric toluenesulfonate.

The impregnation was performed by a method in which the capacitor element 10 was immersed in an impregnation tank containing a fixed amount of the mixed solution. Next, the capacitor element 10 impregnated with the mixed solution was pulled up from the impregnation tank, and was pressed under a pressure of 400 kg / cm ² for 1 hour.
Under heating at 50 ° C., a polymer by a polymerization reaction, that is, a solid electrolyte layer 5 was formed for 2 hours.

Further, when left at normal temperature, the oxidizing agent remaining in the solid electrolyte layer after the polymerization absorbed moisture in the air, and the repair of the anodic oxide film, that is, re-chemical formation proceeded by the moisture. After this step, the capacitor element is inserted into the bag body 11 of a laminated sheet (a sheet in which PET, aluminum foil, PET, and PP are laminated), and the opening is thermocompression-bonded by melting PP to be sealed and packaged ( FIG. 2), a series of manufacturing steps is completed.

[0046]Test example  Next, the electrical characteristics of the solid electrolytic capacitor of Example 1 are described.
Was measured. Prepare 10 samples each, each sample
Were measured for the initial electrical characteristics and the average value was determined.
(Initial characteristics). Further, the sample of Example 1 was heated to 70 ° C.
After leaving for 500 hours at 95% RH,
The average of the properties was determined (moisture resistance). The result is displayed
It is shown in FIG. The first embodiment shown in Table 1 has a rated voltage of 5
0 V and a rated capacitance of 20 μF.

[0047]

[Table 1]

As is apparent from the results, the solid electrolytic capacitor of Example 1 is less deteriorated by humidity. This indicates that the solid electrolytic capacitor was sealed with a bag of a laminate sheet, thereby keeping the solid electrolytic capacitor at low humidity and improving the moisture resistance.

[0049]

The polymerization of the 3,4-ethylenedioxythiophene monomer used in the present invention proceeds gently. Therefore, after the monomer and the oxidizing agent have sufficiently penetrated into the inside of the large-sized flat plate capacitor element, the polymerization reaction proceeds. The reaction is completed.
As a result, a dense and uniform solid electrolyte layer is satisfactorily formed, and the adhesion between the oxide film on the anode electrode foil and the solid electrolyte layer is increased, so that the capacitance increases and the equivalent series resistance value decreases. That is, a solid electrolytic capacitor having high capacitance and excellent high-frequency characteristics can be obtained. Further, in the withstand voltage characteristics, the characteristics of the polymer of 3,4-ethylenedioxythiophene itself are remarkably improved as compared with a conventional solid electrolytic capacitor using a conductive polymer for a solid electrolyte layer.

In the present invention, the polymer is produced under pressure during the polymerization reaction, so that the adhesion between the oxide film layer on the anode electrode foil and the solid electrolyte layer is significantly improved. In addition,
In the present invention, as a method for applying the pressure, a method is employed in which the pressure is sandwiched from both sides of the laminate. For this reason,
It has become possible to uniformly press the anode electrode foil and the cathode electrode foil via the separator. By using this method,
It has become possible to arbitrarily set the strength of the pressure to the most preferable condition. As a result, optimal pressurizing conditions can be created to promote the polymerization reaction, and the efficiency of increasing the adhesion between the oxide film layer on the anode electrode foil and the solid electrolyte layer is high.

Since the solid electrolytic capacitor packaged by the method of the present invention uses a laminate sheet, it can be kept thin. On the other hand, in the case of encapsulating with a resin or encasing with a metal case, the thickness becomes large, and a thin, low-profile solid electrolytic capacitor as in the present invention cannot be realized. Further, when the package is covered with a laminate sheet, the moisture resistance may decrease, but the capacitor element used in the present invention has good moisture resistance. As described above, the combination of the capacitor element of the present invention and the method of the exterior enables a low-profile electrolytic capacitor.

Further, by adopting a method of laminating the elements having the constitution of the present invention, the capacitance can be increased, and a desired capacitance can be obtained. In the solid electrolytic capacitor of the present invention, since the thicknesses of the electrode foil and the separator are thin, the solid electrolytic capacitor can be kept thin even if the above lamination is repeated.

The solid electrolytic capacitor of the present invention obtained by the above-described method has a high capacity requirement and a high withstand voltage requirement, a flattening requirement, that is, a demand for a thin and low profile, and an excellent requirement for the recent high performance of the circuit. In response to demands for high frequency characteristics, it has excellent high frequency characteristics, high withstand voltage and high capacitance, and can be stored compactly in automotive applications. It became.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view of a capacitor element used in the present invention.

FIG. 2 is a perspective view in which a capacitor used in the present invention is laminated and sealed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Anode electrode foil 2 Cathode electrode foil 3 Separator 5 Solid electrolyte layer 6, 7 Lead wire 10 Capacitor element 11 Laminate bag

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) H01G 9/05 G 9/24 E

Claims (5)

[Claims] 1. A cathode electrode foil and an anode electrode foil having a dielectric oxide film formed on the surface thereof are laminated via a separator, and the separator is impregnated with a 3,4-ethylenedioxythiophene monomer and an oxidizing agent. , Formed by heating under pressure to polymerize the monomer and sealed in a laminate sheet,
Large solid electrolytic capacitors with high withstand voltage, high capacitance, and excellent high frequency characteristics. 2. The pressure at the time of pressurization is 30 to 1000 kg / c.
The solid electrolytic capacitor according to claim 1, characterized in that the m ^2. 3. A high voltage resistance of not less than 50 V, a high capacitance of not less than 20 μF, and excellent high frequency characteristics having an equivalent series resistance of 100 mΩ or less at 5 to 1000 KHz. The solid electrolytic capacitor as described. 4. A cathode electrode foil and an anode electrode foil having a dielectric oxide film formed on the surface thereof are laminated via a separator, and the separator is impregnated with a 3,4-ethylenedioxythiophene monomer and an oxidizing agent. 2. The method for producing a solid electrolytic capacitor according to claim 1, wherein the monomer is polymerized by heating under pressure, and is sealed in a bag body of a laminate sheet. 5. The pressure at the time of pressurization is 30 to 1000 kg / c.
The method for producing a solid electrolytic capacitor according to claim 4, characterized in that the m ^2.