JP6908503B2 - Electrolytic capacitor - Google Patents

Description

The present invention relates to an electrolytic capacitor using an alloy of Ti and Zr as an anode, forming a dielectric film made of an oxide by anodizing, and using a liquid or solid electrolyte.

Conventionally, an electrolytic capacitor uses a valve acting metal as an anode, and an oxide film of the valve acting metal is formed as a dielectric on the surface of the anode by an electrolytic oxidation method or the like. As the valve action metal, aluminum, tantalum, niobium, titanium, zirconium and the like are known. In particular, in recent years, there has been a demand for even higher capacities of capacitors, and the use of titanium, which has a high relative permittivity of the oxide film, is being studied.

However, the electrolytic capacitor produced by electrolytically oxidizing titanium has a problem that the leakage current is large as compared with the conventional practical electrolytic capacitors such as aluminum and tantalum.

In order to prevent deterioration of the leakage current characteristic, Patent Document 1 discloses an electrolytic capacitor using an anode substrate alloyed by adding zircon to titanium. Zircon shows the most leakage current reduction effect in the range of 3 to 10 wt%, and it is said that practically preferable characteristics can be obtained up to about 50 wt%.

Patent Document 1 is a liquid electrolytic capacitor manufactured by impregnating an anode substrate with an electrolytic solution, but Patent Documents 2 and 3 describe a solid electrolytic capacitor, particularly as an anode of a solid electrolytic capacitor containing a conductive polymer as an electrolyte. It is proposed to use an alloy consisting of titanium and zirconium. According to Patent Document 2, a dielectric having a small leakage current can be obtained by suppressing the crystallization of the dielectric by adding a small amount of carbon atoms and stabilizing the amorphous structure. In Patent Document 3, a solid electrolytic capacitor having a large capacitance and a small leakage current is defined by setting the relationship between the composition ratio of titanium and zirconium of the anode and the film thickness of the dielectric (anodic oxide film) within a specific range. Is provided.

Special Publication No. 43-18012 Japanese Unexamined Patent Publication No. 2015-207689 Japanese Unexamined Patent Publication No. 2016-082126

When an electrolytic capacitor, particularly a solid electrolytic capacitor, is formed by using an alloy of a valve acting metal, particularly an anode composed of an alloy of titanium and zirconium, the present inventors disperse the leakage current even if the composition of the alloy is constant. I got the finding. Therefore, an object of the present invention is to provide an electrolytic capacitor using an anode made of an alloy of a valve acting metal, which has a low leakage current and suppressed variation.

That is, the present invention is an electrolytic capacitor containing an alloy composed of titanium and zirconium as an anode, an oxide film obtained by anodizing the anode as a dielectric, and an electrolyte, and iron in the alloy of the anode. The present invention relates to an electrolytic capacitor, characterized in that the total concentration of nickel and chromium is 100 ppm or less.

According to the present invention, by setting the total concentration of iron, nickel, and chromium contained in the alloy of titanium and zirconium to 100 ppm or less, an electrolytic capacitor having little variation in alloy composition and excellent leakage current characteristics is provided. be able to.

It is the schematic sectional drawing of the solid electrolytic capacitor which concerns on one Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to this embodiment.

An oxide film, which is a dielectric, is formed on the surface of the anode by performing anodizing treatment in an electrolytic solution using an alloy composed of titanium (Ti) and zirconium (Zr) as an anode. An electrolyte layer is formed on this.
In the present invention, titanium having an excellent relative permittivity of the oxide film is selected from the valve acting metals, and the alloy of titanium and zirconium of the same family reduces the abundance ratio of impurities such as iron to form the alloy composition. It was found that there is little variation and excellent leakage current characteristics can be achieved.

The alloy composed of Ti and Zr constituting the anode body is alloyed by mixing each elemental metal in a predetermined ratio. In the process of alloying, iron, nickel, and chromium (hereinafter referred to as iron-based metals) contained in the single metal are concentrated and separated, and the total amount of iron-based metals in the alloy is larger than the total amount of iron-based metals in the single metal. May decrease. However, the iron-based metal contained in the elemental metal contains at least 100 ppm or more of iron in the industrially obtained 2N5 (purity of about 99.5%) material, and even if alloyed using such a material, it may be alloyed. The total amount of iron-based metal is not reduced to 100 ppm or less. Therefore, in the present invention, an alloy ingot containing high-purity titanium and high-purity zirconium of 3N (purity 99.9%) or more, preferably 4N (purity 99.99%) or more is produced, and the obtained alloy ingot is iron-based. A method of producing an anode body by powdering it without being contaminated with metal, forming it under pressure, and then heat-treating it under high vacuum and high temperature is preferable. In addition, in this specification, high-purity titanium and high-purity zirconium refer to those having a total amount of iron-based metals of less than 100 ppm. The method for producing high-purity titanium and high-purity zirconium is not particularly specified, but for example, an iodide thermal decomposition method, a molten salt electrolysis purification method, a hydrogen plasma melting method, an electron beam melting method and the like can be used. The higher the purity of the raw material metal, the higher the price and the higher the cost of the anode or electrolytic capacitor. In the present invention, the total concentration of iron-based metals as an alloy may be 100 ppm or less. Therefore, if one of Ti and Zr is a high-purity product, the other is not a high-purity product depending on the composition ratio (iron concentration is 100 ppm). It can also be combined with the above). As a result, it is possible to suppress an increase in the manufacturing cost of the anode body. Further, in order to prevent iron-based metal contamination in the manufacturing process, it is possible to avoid mixing in contact with an apparatus mainly containing iron-based metal. Since an ultra-high purity product of 6N (purity 99.99999%) can contain up to 1 ppm of iron in the standard, the lower limit of the total amount of iron-based metals in the present invention is defined as 1 ppm for convenience. The lower limit of 1 ppm may be equal to or lower than the detection limit of the measuring device actually used.
The total amount of iron-based metal in the Ti—Zr alloy as the anode is more preferably 50 ppm or less.

The amount of iron-based metal in the alloy can be measured, for example, by ICP (radio frequency inductively coupled plasma) emission spectroscopy. ICP emission spectroscopic analysis is very sensitive and, in theory, the lower limit of detection may be 10 ppb or less for most elements. The device actually used may be any device capable of measuring on the order of ppm. For example, it can be confirmed that the detection lower limit is 100 ppm or less, particularly 50 ppm or less, which is specified even in an apparatus of 10 ppm. The measurement is carried out by dissolving the alloy in an appropriate acid to prepare a solution, introducing it into plasma in an atomized state, and causing it to emit light by excitation.
The iron-based metal in the alloy has the highest iron content, and the iron content may be the total amount of the iron-based metal.

Since Ti and Zr are homologous elements and become a solid solution at all rates, there is an advantage that a uniform alloy can be obtained with an arbitrary composition. However, when Zr has an atomic ratio of 20% or more, the leakage current becomes low after the electrolyte layer is formed, and the capacitor characteristics. Becomes good. Further, when the atomic ratio of Zr is 90% or less, the capacitance shows a better value than that of an electrolytic capacitor using Ta as an anode. Further, when the atomic ratio of Zr is 20% or more and 70% or less, the dielectric obtained by anodizing has an amorphous structure, which is more preferable because the heat resistance characteristics of the capacitor are improved. That is, the anode according to the present invention is preferably an alloy in which the atomic ratio of titanium and zirconium is 80:20 to 10:90 in Ti: Zr, and Ti: Zr is 80:20 to 30:70. Is more preferable.

The obtained alloy mass is crushed into a powder as described above, the powder is pressure-molded into a predetermined anode shape, and then heat-treated under high vacuum and high temperature to prepare an anode. The anode is a sintered body of alloy powder and is porous. Hereinafter, it is also referred to as a porous sintered body.
A known crusher can be used for pulverizing the alloy ingot, and an apparatus using a crushing medium such as a ball mill or a bead mill can be mentioned. _{In order to suppress contamination of iron-based metals, it is preferable to use, for example, a tank made of zirconia (ZrO 2} ) or a crushing medium having a hardness higher than that of the Ti—Zr alloy for these crushers. The particle size of the obtained powder is not particularly limited, but is preferably 100 μm or less, and preferably 10 μm or less. Further, pulverization to nanoparticles is not necessary, and pulverization to submicrons (0.1 μm: 100 nm) is sufficient.
In the high-temperature heat treatment for producing a porous sintered body, iron is concentrated at the grain boundary portion when the heat treatment is performed at a temperature equal to or higher than the transformation temperature of the titanium-zirconium alloy. However, if the iron-based metal concentration in the alloy is 100 ppm or less as in the present invention, segregation of iron into grain boundaries is reduced. As a result, the destruction of the oxide film formed by anodization is suppressed, a homogeneous oxide film without defects can be formed, and the leakage current of the electrolytic capacitor is improved.
Furthermore, it was found that the difference in affinity between titanium or zirconium and iron reduces the microscopic variation of the titanium-zirconium alloy when the concentration of iron in the alloy is less than 100 ppm. As a result, variations in the capacitance of the electrolytic capacitor are suppressed. In the present invention, the difference between the maximum value and the minimum value of the titanium composition ratio in the titanium-zirconium alloy (anode) is preferably 10 percentage points (ppt) or less, and more preferably 5 ppt or less. The composition ratio can be regarded as an overall composition ratio by measuring at any five points.
It has been confirmed that the same effect can be obtained for iron-based metals (nickel, chromium) other than iron contained in the alloy.

As the alloy composed of Ti and Zr constituting the anode body, those produced by an arc melting method, a sputtering method, a mechanical alloy method or the like can be used in addition to the above powder sintering method. The shape of the anode may be any known shape such as a plate shape, a foil shape, or a linear shape. Further, an alloy film made of Ti and Zr may be formed on an appropriate substrate. The anode body formed by the sintering method is advantageous for electrolytic capacitors having fine pores, a large surface area, and a high capacitance required.

[Dielectric]
The dielectric is composed of an oxide film formed by anodizing. The film thickness of the dielectric is appropriately determined so as to obtain a desired capacitance, but when a conductive polymer is used as the electrolyte, the leakage current after forming the electrolyte layer is 5 nm or more and 1000 nm or less. Will be low. The film thickness of the oxide film is determined by the anodizing treatment voltage and the composition of the anode. When the atomic ratio of Zr is 20% or more, the anodizing treatment voltage is 3 V or more and 500 V or less. The film thickness can be adjusted to 5 nm or more and 1000 nm or less by processing for several hours. The thinner the film thickness of the dielectric, the higher the capacitance, and the thicker the film thickness, the higher the voltage that can be used. Therefore, it can be appropriately selected from the above range according to the performance required for the electrolytic capacitor.
Further, a known electrolytic solution can be used for the anodizing treatment. For example, an aqueous solution containing phosphoric acid, nitric acid, boric acid, citric acid, or a sodium salt or ammonium salt thereof, or a non-aqueous solution can be used.

[Electrolyte layer]
A known electrolyte can be used for the electrolyte layer. Specifically, an electrolytic solution containing an electrolyte such as carboxylic acid or amine and composed of a solvent such as glycol or ether, a solid electrolyte composed of a conductive polymer such as manganese dioxide or polythiophene or polypyrrole, or a composite thereof is used. be able to. Among these, when a solid electrolyte made of a conductive polymer is contained, the leakage current of the electrolytic capacitor becomes lower, which is preferable.
As the conductive polymer formed on the dielectric composed of the oxide film, one or more selected from polypyrrole, polythiophene, polyaniline, polysilane, or derivatives thereof can be used. As a method for forming the electrolyte layer containing the conductive polymer, a chemical oxidation polymerization method, an electrolytic polymerization method, a dispersion liquid or a solution coating and drying method and the like can be applied. The electrolyte layer may contain a dopant that causes the conductive polymer to exhibit conductivity, and may further contain a binder, if necessary. Examples of the dopant include anionic dopants, and polyacid anions are particularly preferable. Examples of the binder include acrylic resin, urethane resin, epoxy resin, phenol resin, silicon resin, polyester resin, polyolefin resin, water-soluble resin such as polyvinyl alcohol and saccharides.

FIG. 1 shows a schematic cross-sectional view showing the structure of the solid electrolytic capacitor according to the present embodiment. This solid electrolytic capacitor has a structure in which the dielectric layer 2 and the electrolyte layer 3 are formed in this order on the anode body 1. A graphite layer 4 and a silver layer 5 are formed on the outer periphery of the electrolyte layer 3 to form a cathode, which is further connected to an electrode 7 serving as a connection terminal to the outside via a conductive adhesive 6. Further, a metal lead 8 made of a valve acting metal similar to that of the anode conductor 1 is provided on the surface of the anode conductor 1 on which the electrolyte layer 3 is not formed, and the metal lead 8 is an electrode of a connection terminal different from the cathode. It is connected to 7. Further, the whole is covered with an insulating exterior resin 9 such as an epoxy resin, and an electrolytic capacitor is formed.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples.

<Example 1>
As a raw material, high-purity titanium (Ti) produced by the iodide pyrolysis method and high-purity zirconium (Zr) produced by the iodide pyrolysis method are weighed at an atomic ratio of 40:60 and then melted by arc button. An alloy ingot was prepared by the method. The total amount of iron-based metals in both the produced high-purity titanium and high-purity zirconium was less than 100 ppm. This alloy mass was made into an alloy powder having an average particle size (D50) = 2 μm by using a ball mill and a bead mill of a zirconia tank. The obtained alloy powder was filled in a mold and pressure-molded to prepare a molded body having an outer diameter of 2.2 mm × 1.7 mm × 1.2 mm. Next, this molded body was sintered in a high temperature vacuum at 800 ° C. to obtain a porous sintered body. At this time, when the concentration contained in the porous sintered body was analyzed by ICP emission spectroscopy, the iron concentration and the total concentration of iron, nickel, and chromium were all less than 10 ppm. Table 1 shows the results of composition analysis of the porous sintered body with a transmission electron microscope. The composition analysis was performed at any 5 points of the obtained porous sintered body, and the difference (percent point: ppt) between the maximum value and the minimum value of the titanium composition ratio was described. Using the obtained porous sintered body as an anode, an electrolytic solution containing 0.05% by mass of phosphoric acid, 50% by mass of ethylene glycol and water is used to perform anodizing treatment at 25 ° C. for 2 hours at 100 V. To form an oxide film which is a dielectric. Subsequently, a dispersion liquid of polythiophene, which is a conductive polymer, was applied onto the oxide film, and then the solvent was dried to form an electrolyte layer. Further, a graphite paste and a silver paste were applied and cured to form a cathode extraction layer to obtain a solid electrolytic capacitor. A DC voltage of 5 V was applied to the obtained solid electrolytic capacitor, and the leakage current after 5 minutes was measured. The results are shown in Table 1.

<Example 2>
Porous by the same method as in Example 1 except that unrefined titanium sponge (total amount of iron-based metal: about 300 ppm) and high-purity zirconium prepared by the iodide pyrolysis method as in Example 1 were used as raw materials. A sintered body was obtained. At this time, when the concentration contained in the porous sintered body was analyzed by ICP emission spectroscopy, the iron concentration and the total concentration of iron, nickel, and chromium were all 50 ppm. Table 1 shows the results of composition analysis of the porous sintered body with a transmission electron microscope. Using the obtained porous sintered body as an anode body, a solid electrolytic capacitor was obtained by the same method as in Example 1. A DC voltage of 5 V was applied to the obtained solid electrolytic capacitor, and the leakage current after 5 minutes was measured. The results are shown in Table 1.

<Example 3>
Porous by the same method as in Example 1 except that high-purity titanium prepared by the iodide pyrolysis method and unrefined zirconium sponge (total amount of iron-based metal: about 500 ppm) were used as raw materials. A sintered body was obtained. At this time, when the concentration contained in the porous sintered body was analyzed by ICP emission spectroscopy, the iron concentration and the total concentration of iron, nickel, and chromium were all 90 ppm. Table 1 shows the results of composition analysis of the porous sintered body with a transmission electron microscope. Using the obtained porous sintered body as an anode body, a solid electrolytic capacitor was obtained by the same method as in Example 1. A DC voltage of 5 V was applied to the obtained solid electrolytic capacitor, and the leakage current after 5 minutes was measured. The results are shown in Table 1.

<Comparative example 1>
A porous sintered body was obtained by the same method as in Example 1 except that the unrefined titanium sponge used in Example 2 and the unrefined zirconium sponge used in Example 3 were used as raw materials. At this time, when the concentration contained in the porous sintered body was analyzed by ICP emission spectroscopy, the iron concentration and the total concentration of iron, nickel, and chromium were all 140 ppm. Table 1 shows the results of composition analysis of the porous sintered body with a transmission electron microscope. Using the obtained porous sintered body as an anode body, a solid electrolytic capacitor was obtained by the same method as in Example 1. A DC voltage of 5 V was applied to the obtained solid electrolytic capacitor, and the leakage current after 5 minutes was measured. The results are shown in Table 1.

<Comparative example 2>
A porous sintered body was obtained by the same method as in Example 1 except that a ball mill and a bead mill in a stainless steel tank were used. At this time, when the concentration contained in the porous sintered body was analyzed by ICP emission spectroscopy, the iron concentration was 80 ppm, and the total concentration of iron, nickel and chromium was 110 ppm. Table 1 shows the results of composition analysis of the porous sintered body with a transmission electron microscope. Using the obtained porous sintered body as an anode body, a solid electrolytic capacitor was obtained by the same method as in Example 1. A DC voltage of 5 V was applied to the obtained solid electrolytic capacitor, and the leakage current after 5 minutes was measured. The results are shown in Table 1.

From Table 1, when the total concentration of iron-based metals (iron, nickel, chromium) in the anode is 100 ppm or less, the composition variation in the anode is reduced and the leakage current of the electrolytic capacitor is reduced. Was found to be low.

1: Anode body (TiZr alloy)
2: Dielectric layer 3: Electrolyte layer (conductive polymer)
4: Graphite layer 5: Silver layer 6: Conductive adhesive 7: Electrode 8: Metal reed 9: Exterior resin

Claims (7)

An electrolytic capacitor containing an alloy composed of titanium and zirconium as an anode, an oxide film obtained by anodizing the anode as a dielectric, and an electrolyte, and the total amount of iron, nickel, and chromium in the alloy of the anode. der concentration 100ppm following is, the anode body is an electrolytic capacitor, characterized in that the difference between the maximum and minimum values of the titanium composition ratio measured at any five points is less than 10 percentage points. The electrolytic capacitor according to claim 1, wherein the anode is a porous body. The electrolytic capacitor according to claim 1 or 2 , wherein the electrolyte is a solid electrolyte. The electrolytic capacitor according to claim 3 , wherein the solid electrolyte contains a conductive polymer. The method for manufacturing an electrolytic capacitor according to any one of claims 1 to 4 , wherein a step of mixing a single titanium and a single zirconium to obtain an alloyed alloy ingot, and a step of crushing the alloy ingot to produce a powder. A method for producing an electrolytic capacitor, which comprises a step of obtaining the powder and a step of vacuum-sintering the powder to obtain a porous anode. The method for producing an electrolytic capacitor according to claim 5 , wherein one of the simple substance titanium and the simple substance zirconium is a high-purity product having a total concentration of iron, nickel and chromium of less than 100 ppm, and the other is a material having a total amount of more than 100 ppm. .. The method for manufacturing an electrolytic capacitor according to claim 5 or 6 , wherein the step of obtaining the powder is a powder of the alloy ingot using an apparatus that does not come into contact with an iron-based metal.

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