JP2000173862A - Electrolytic capacitor separator and electrolytic capacitor provided therewith - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrolytic capacitor separator which is low in impedance, excellent in low-temperature characteristics, and high in lifetime characteristics and an electrolytic capacitor provided therewith. SOLUTION: A separator includes fibers fixed by binder that is soluble in electrolyte. An electrolytic capacitor is provided with electrolyte that contains organic solvent and water as solvent, the concentration of water contained in the solvent is 20 to 80 wt.% of all the solvent, the organic solvent contains one or more solvents selected out of proton and non-proton solvents, and the organic solvent contains also one or more elements selected out of carboxylic acid or carboxylate and inorganic acid or its salt as electrolyte and a separator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a separator for an electrolytic capacitor having low impedance, excellent low-temperature characteristics and good life characteristics, and an electrolytic capacitor using the separator.

[0002]

2. Description of the Related Art Generally, an electrolytic capacitor is formed by etching a high-purity aluminum foil to increase its surface area and anodizing the surface to make it dielectric, and an etched cathode foil facing the anode foil. And a separator (electrolytic paper, separator paper, etc.) interposed therebetween, and the wound element is impregnated with an electrolytic solution and sealed in a case.

In these conventional aluminum electrolytic capacitors, since the electrolytic solution is impregnated in the electrolytic paper, the impedance characteristics of the capacitor tend to be high. In order to improve the impedance characteristics, means for lowering the resistance of the electrolytic solution itself, thinning the electrolytic paper, or reducing the density have been studied.

However, when the resistance value of the electrolytic solution is reduced, the reactivity between the aluminum foil and the electrolytic solution is increased and the life characteristics are deteriorated. On the other hand, if the separator (electrolytic paper) is simply thinned or the density is lowered, The tensile strength is reduced, the shape retention is reduced, and problems such as breakage during the manufacturing process such as winding of a capacitor and a reduction in productivity are caused. As a result, problems such as an increase in the short-circuit defect rate occur.

[0005] Further, using cellulose fibers such as wood kraft pulp, softwood wood pulp, and manila hemp pulp, the hydrogen bond between fibers and the entanglement of fiber fibrils are used to improve the tensile strength and improve the shape retention. As a result, attempts have been made to reduce the thickness of the separator (electrolytic paper). However, even in such a case, the density of the separator has to be increased in order to further improve the impedance characteristics so as to satisfy the required performance. If the thickness is reduced and the thickness is reduced, the same problem as described above occurs, so that there is a limit.

[0006] Means for increasing the tensile strength by mixing thermoplastic fibers such as polyethylene fiber, polypropylene fiber, nylon fiber and the like in the raw material, and then fusing the thermoplastic fibers are known. In addition to fibers, viscose rayon fiber, polypropylene fiber, polyimide fiber, artificial fiber such as aramid fiber or synthetic fiber, glass fiber, blending strong fiber such as inorganic fiber such as alumina silica fiber, while ensuring the strength, Low density, thin,
In addition, attempts have been made to obtain a separator (electrolytic paper) having a high porosity. However, for example, when a thermoplastic fiber is used, it becomes a film under high-temperature conditions, which sometimes fills the voids. Further, for example, chlorine generated in the reaction and production process of synthetic fibers remains mixed with synthetic fibers, and particularly when Al is used for an electrode, it promotes corrosion and causes new problems, and the processing process is complicated. There are drawbacks such as being able to bring about. Further, technical problems such as the inability to obtain a homogenous and stable separator (electrolytic paper) and the difficulty in obtaining a sufficient gap to activate the movement of ions by the above-mentioned known means are difficult. There are also drawbacks such as high raw material costs.

Further, starch, vegetable gum, semi-synthetic polymer, synthetic polymer, etc. are added to a raw material suspension during the manufacturing process, which is a general means of increasing the tensile strength of paper, and fixed on the fiber surface layer. Even the known means of increasing the bond strength between the fibers cannot meet the stringent requirements for lower ESR (equivalent series resistance), i.e. lower impedance.

Further, the separator (electrolytic paper) as described above
On the other hand, in such an electrolytic capacitor, the characteristics of the electrolytic solution play a major role in determining the performance of the electrolytic capacitor.

Particularly, with the recent miniaturization of electrolytic capacitors, anode foils or cathode foils having a high etching magnification have been used and the resistivity of the capacitor body has been increased. As the electrolytic solution, an electrolyte having a small resistivity (specific resistance) and a high conductivity is always required.

In the conventional electrolytic solution, ethylene glycol is used as a main solvent, water (1% by weight to 30% by weight) is added thereto, and an ammonium salt of a carboxylic acid such as adipic acid or benzoic acid is dissolved as an electrolyte. There is something.

The electrolyte using ammonium carboxylate as the electrolyte has a remarkably low specific resistance of 300 to 400 Ωcm as compared with the conventional electrolyte using boric acid as the electrolyte.

However, in the case of using this ammonium carboxylate, even if various measures are taken, it is limited that its specific resistance is reduced to about 80 Ωcm.

That is, the specific resistance of the electrolytic solution can be lowered by increasing the amount of solute and increasing the amount of water added to another solvent such as ethylene glycol. When the concentration is more than 30% by weight, the electrolytic solution reacts with the electrode foil at a high temperature to generate gas and raises the internal pressure of the electrolytic capacitor.

On the other hand, the performance required for capacitors mounted and used in various electronic and electric products such as computers and audios, and various vehicles is becoming more severe. Maintaining low-impedance characteristics in a low-temperature region is indispensable.
At 0 ° C.), a low-temperature characteristic value represented by a | Z | ratio (impedance ratio) is strongly required. Furthermore, when a large amount of water is used in combination as a solvent component, problems such as freezing occur.

As described above, in the prior art, the specific resistance could be reduced to about 80 Ωcm by adding about 30% by weight of water at the maximum, but the specific resistance could not be reduced further. It was difficult to use in a wide temperature range from 105 ° C to -40 ° C.

[0016]

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrolytic capacitor having low impedance, excellent low-temperature characteristics, good life characteristics, improved short-circuit failure rate, and improved productivity. An object of the present invention is to provide a separator for an electrolytic capacitor used for the same.

[0017]

SUMMARY OF THE INVENTION The present invention provides a separator for an electrolytic capacitor, including a fiber fixed with a binder soluble in an electrolytic solution, for achieving the above object.

By configuring the separator disposed between the metal foils of aluminum or the like constituting the electrodes as described above, in the manufacturing process, the binder can fix the fibers and maintain sufficient strength. It is possible to prevent the occurrence of paper breakage in the element winding step and improve the winding productivity. Further, through this, the localization and uneven distribution of the fibers can be prevented even in the form of an element, so that it is possible to reduce the short-circuit failure rate while realizing low impedance by promoting thinning.

Further, when considering the function,
In the process of winding the separator between the electrodes, molding, impregnating the element with the electrolyte, and packaging the case, the binder that effectively functions to maintain strength, etc., after packaging, the temperature, time, electrolyte components and binder After a time that can be determined by preparing a combination of the above, the intermolecular spacing is expanded by the action of the solvent of the electrolytic solution. It is considered that the binder polymer in that state weakens the bond between the cellulose fibers and increases the voids.

The present invention also relates to a separator for an electrolytic capacitor containing fibers fixed with a binder soluble in an electrolytic solution, wherein the water concentration of the electrolytic solution solvent containing an organic solvent and water is 2%.
0 to 80% by weight. It is possible to utilize the decrease in specific resistance, which is an excellent characteristic of an electrolytic solution using a solvent containing high-concentration water, and to achieve the same effects as the separator.

Further, according to the present invention, in each of the above inventions, the density of the separator (measured at the time of forming the separator) is 0.1.
It is set to 5 g / cm ³ or less. That is, when the separator density is 0.5 g / cm ³ or less, the density of the cellulose fiber is 1.5 g / cm ³ , so the porosity of the separator セ パ レ ー タ [1- (separator density / cellulose density)]
× 100%｝ is 67% or more, and the increased void space contains the electrolyte sufficiently. Therefore, according to the above configuration, the strength (1.1 kg / 15
mm or more), the impedance can be lowered by minimizing the separator density in the electrolytic capacitor.

Further, in the present invention, various ionic and nonionic binders are used as the binder in each of the above-mentioned inventions. Among them, particularly, water-soluble binders such as polyvinyl alcohol, polyacrylamide and polyacrylic acid are used. Those using a polymer have excellent capacitor characteristics.

Further, the present invention includes the separator according to each of the above-mentioned inventions, comprising an organic solvent and water as a solvent for the electrolytic solution,
The water concentration in the organic solvent is 20 to 80% by weight of the total solvent,
The organic capacitor is an electrolytic capacitor including at least one selected from among protic and aprotic solvents.

Further, the present invention includes the separator according to each of the above-mentioned inventions, and comprises an organic solvent and water as a solvent for the electrolytic solution.
The water concentration in the organic solvent is 20 to 80% by weight of the total solvent,
The organic solvent includes at least one selected from among protic and aprotic solvents, and as an electrolyte of the electrolytic solution, at least one selected from carboxylic acids or salts thereof and inorganic acids or salts thereof. An electrolytic capacitor including the above.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The separator of the present invention preferably uses cellulose fibers such as wood kraft pulp, softwood wood pulp, manila hemp pulp, and sisal hemp as a fiber material.

In consideration of strength, low density, etc., other fiber materials, vinylon binder fibers, polyethylene fibers, polypropylene fibers, thermoplastic fibers such as nylon fibers, etc. are mixed and paper-made, and then the thermoplastic fibers are fused. Means for increasing the tensile strength are known, and, in addition to natural vegetable fibers, viscose rayon fibers, polypropylene fibers, polyimide fibers, synthetic fibers such as aramid fibers, glass fibers,
Incorporating inorganic fiber such as alumina silica fiber, low density,
And it is attempted to obtain paper with high porosity,
As explained in the section of the prior art, various problems occur when blending synthetic fibers, so that it is not advisable to use a large amount.

It is most preferable to use at least one kind of natural plant fiber which has few problems as described above and is compatible with water which is a solvent component of the electrolytic solution.

The electrolytic paper can be produced by a conventional papermaking method. For example, a conventionally used papermaking machine such as a netting machine having one or two or more netting bat portions of the above fiber material is used. The paper is made.

The binder can be mixed with the fiber material in advance at the time of papermaking, but it is not preferable because it requires an extra material and complicates steps such as a drying step.
Preferably, after drying the electrolytic paper after papermaking, the binder is impregnated to fix the fibers.

The amount of impregnation may be determined according to the strength at the time of production and the required characteristics of the electrolytic capacitor after production. The amount of impregnation is about 0.05% to 5.0% by weight based on the dry electrolytic paper. is there. The tensile strength of electrolytic paper is 1.1kg / 15mm
The above is one guide. Although the thickness of the electrolytic paper can be appropriately selected, it is usually about 40 to 60 μm.

The density of the electrolytic paper is 0.5 g / cm ³ or less of what is desired, 0.20~0.35g / cm ^3, it is also possible further to less than 0.20 g / cm ^3, low Desirable for impedance formation.

The binder can be used as long as it is soluble in the solvent component of the electrolytic solution. In particular, when water and an organic solvent are used as the solvent component of the electrolytic solution, water is used in an amount of 20 to 80%.
%, Preferably 30-80%, most preferably 45%
When it is contained in an amount of up to 80% by weight, various starches, carboxymethylcellulose, various gums and the like can be used, but the strength, the holding stability, the shape holding property, the ease of handling, and the fiber form in the electrolytic solution can be improved. Water-soluble polymers such as polyvinyl alcohol, polyacrylamide, and polyacrylic acid are excellent from the viewpoint of securing maintainability and low impedance characteristics. The amount of the binder varies depending on the type thereof, but is 0.1 to 1 with respect to 100 weight of the separator.
0 parts by weight, preferably about 0.5 to 5 parts by weight.

Electrolytic paper fixed with a binder (isolation paper)
According to a conventional method, a high-purity aluminum foil is etched, the surface thereof is anodized, and the surface is wound between an etched aluminum cathode foil facing the anode foil. The element is impregnated with an electrolytic solution, accommodated in an aluminum case, and sealed with an elastic sealing member to obtain an electrolytic capacitor.

The electrolyte to be impregnated is another feature of the present invention.

A conventional electrolytic solution comprises ethylene glycol as a main solvent, water (1% by weight to 30% by weight) added thereto,
In many cases, ammonium carboxylate such as adipic acid or benzoic acid is dissolved as an electrolyte.

As already described in the embodiments of the present invention, even in the case where ammonium carboxylate is used as the electrolyte, its specific resistance is limited to about 80 Ωcm.

However, the electrolyte solution contains an organic solvent and water as a solvent, and the water concentration in the organic solvent is adjusted to 20 to 8
0% by weight, and the organic solvent contains at least one selected from the group consisting of protic and aprotic solvents;
Moreover, the separator according to the present invention is configured to include the organic solvent and water as a solvent of the electrolytic solution, and the water concentration in the organic solvent is set to 20 to 80% by weight of the total solvent. Comprising at least one selected from solvents of a system and an aprotic solvent, and having, as an electrolyte of the electrolytic solution, at least one or more selected from carboxylic acids or salts thereof and inorganic acids or salts thereof, By obtaining an electrolytic capacitor, an electrolytic capacitor having low impedance, excellent low-temperature characteristics, and good life characteristics can be obtained.

As the organic solvent, a protic solvent and an aprotic solvent can be used. As an example of a typical protic solvent, an alcohol compound can be mentioned.

Specific examples of the alcohol compound include monohydric alcohols such as ethyl alcohol, propyl alcohol and butyl alcohol, dihydric alcohols (glycols) such as ethylene glycol, diethylene glycol, triethylene glycol and propylene glycol, and trihydric alcohols such as glycerin. Valent alcohols can be mentioned.

Examples of the aprotic solvents include intramolecular polarized compounds such as lactone compounds represented by γ-butyrolactone. As the organic solvent, at least one selected from a protic solvent and an aprotic solvent can be used. A plurality of proton solvents may be used,
A plurality of types of aprotic solvents may be used, or a mixed system of a protic solvent and an aprotic solvent may be used.

As described above, the solvent in the electrolytic solution of the present invention is a mixture of an organic solvent and water. In the present invention,
The use of such a mixed solvent lowers the freezing point of the solvent, thereby improving the impedance characteristics of the electrolyte at low temperatures, and has good low-temperature characteristics indicated by a low impedance ratio between low and normal temperatures. Can be realized. The content of water in the electrolyte is preferably from 20 to 80% by weight, and the remainder is an organic solvent. Whether the water content is less than 20% by weight or more than 80% by weight,
The degree of freezing point drop of the electrolytic solution becomes insufficient, and it becomes difficult to obtain good low-temperature characteristics of the electrolytic capacitor. A more preferred amount of water in the solvent is 30-80% by weight;
Most preferred is 45-80% by weight.

As the electrolyte in the electrolytic solution, one or more selected from carboxylic acids, salts of carboxylic acids, inorganic acids and salts of inorganic acids can be used. Those usable as carboxylic acids include monocarboxylic acids represented by formic acid, acetic acid, propionic acid, butyric acid, p-nitrobenzoic acid, salicylic acid and benzoic acid, malonic acid, succinic acid, glutaric acid, adipic acid, fumaric acid. Acid, maleic acid,
It includes dicarboxylic acids typified by phthalic acid and azelaic acid. For example, carboxylic acids having a functional group such as an OH group such as citric acid and oxybutyric acid can be used.

Those usable as inorganic acids include phosphoric acid, phosphorous acid, hypophosphorous acid, boric acid, sulfamic acid and the like. As salts of carboxylic acids or inorganic acids, ammonium salts, sodium salts, potassium salts, as well as amine salts, alkyl ammonium salts and the like can be used,
Of these, ammonium salts are more preferably used. Further, when an inorganic acid or a salt thereof is used as an electrolyte, it is expected that the freezing point of the electrolytic solution is lowered, and therefore, it is considered that this contributes to further improvement of the low temperature characteristics of the electrolytic solution.

The amount of the electrolyte used in the electrolytic solution of the present invention depends on the characteristics required for the electrolytic solution, the type of solvent used,
What is necessary is just to determine suitably according to conditions, such as the kind of electrolyte used.

As an additive, one or more selected from gluconic acid, lactone of gluconic acid, a chelating agent, 2-hydroxybenzyl alcohol, L-glutamic acid diacetate or a salt thereof, a nitro compound, and a saccharide are used. can do. The optimal amount of these additives is determined according to the combination of the additives and the composition of the electrolytic solution. Since the amount added at this time is determined by the characteristics of the added substance, the amount may be about several percent by weight or less of the electrolytic solution, or 1 percent by weight or less. By combining these additives, it is possible to avoid the reaction with the electrode at a high temperature, reduce the specific resistance at a low temperature, and improve the life of the capacitor.

For example, when gluconic acid or a lactone of gluconic acid is added, even if the amount of water used in the solvent in the electrolytic solution is 30% by weight or more in the solvent, the gas based on the reaction between the electrolytic solution and the electrode at a high temperature is used. Can be avoided and the specific resistance can be reduced. Further, by adding the chelate compound, the life of the electrode foil can be extended by suppressing the hydration reaction of the electrode foil. In addition, the same kind of effect can be obtained by adding 2-hydroxybenzyl alcohol, L-glutamic acid diacetic acid or a salt thereof, a nitro compound, or a saccharide. By adding these plural components in combination, a synergistic effect in improving the characteristics of the electrolytic capacitor can be achieved.

Examples of the nitro compound include at least one nitro compound selected from the group consisting of nitrophenol, nitrobenzoic acid, nitroacetophenone and nitroanisole.

As the chelating compounds, ethylenediaminetetraacetic acid (EDTA), trans-1,2-diaminocyclohexane-N, N, N ', N'-tetraacetic acid monohydrate (CyDTA), dihydroxyethylglycine (DHE)
G), ethylenediaminetetrakis (methylenephosphonic acid) (EDTPO), diethylenetriamine-N, N,
N ', N ", N" -pentaacetic acid (DTPA), diaminopropanoltetraacetic acid (DPTA-OH), ethylenediaminediacetic acid (EDDA), ethylenediamine-N, N'-bis (methylenephosphonic acid) hemihydrate Things (EDDP
O), glycol ether diamine tetraacetic acid (GEDT)
A) and the like.

Examples of the saccharide include glucose, fructose, xylose, and galactose.

In addition to these additives, additives commonly used in the field of aluminum electrolytic capacitors or other electrolytic capacitors may be further added.

[0051]

Examples (Examples 1 to 4 and Comparative Examples 1 and 2) Examples of the present invention will be described below. Ethylene glycol 4
5% by weight, 40% by weight of water, ammonium adipate 1
4.4% by weight, ethylenediaminetetraacetic acid 0.5% by weight,
The point that 0.1% by weight of D-gluconic acid-δ-lactone is used as the electrolyte and the point that the separator (electrolytic paper) is made of cellulosic fiber is common to the examples and comparative examples. A conventional cellulose-based separator that does not use a binder that dissolves in a solvent (only the density was changed in Conventional Examples 1 and 2) and the binder shown in the table (the amount of the binder used was 100% by weight in each example) The initial characteristics of the capacitor were compared using the cellulosic separator of the present invention (Examples 1 and 2 and Examples 3 and 4 in which the density was changed) using 2 parts by weight of the present invention. In addition, the low temperature (-
40 ° C.) and the impedance at normal temperature (20 ° C.).
Z | ratio) were measured at 120 Hz and 100 kHz. Impedance and E.C. S. R and (equivalent series resistance) are values at a measurement temperature of 25 ° C. Table 1 shows the measurement results.

[0052]

[Table 1]

No difference was found in the separator density between Comparative Example 1 and Examples 1 and 2 and between Comparative Example 2 and Examples 3 and 4 in Table 1, and almost no difference was found in the initial capacitor capacity. No difference is observed.

However, when tan δ is compared with that of the same density, the tan δ is smaller than that of the comparative example and is superior in impedance characteristics. Although the separators of Examples 1 and 2 have a higher density than the separator of Comparative Example 2, the initial tan δ, the impedance, and the E.C. S. R. Is small. It can be said that the strength can be sufficiently maintained during the manufacturing process, and that excellent characteristics can be obtained after mounting, that is, a product having good life characteristics can be obtained.

Among them, those using polyvinyl alcohol and polyacrylamide as the binders of Examples 3 and 4 have low separator density, low initial impedance and low E.C. S. R. Is extremely small, indicating that the initial characteristics of the capacitor are excellent. There is no substantial difference in the initial leakage current between the comparative examples and the examples.

Further, in the capacitor using the electrolytic solution of the present invention, the Z ratio was found to be small.
It can be seen that the Z ratio at a high frequency of kHz is suppressed smaller than that of the comparative example. This indicates that the electrolytic capacitor using the electrolytic solution of the present invention exhibits good low-temperature characteristics over a wide frequency range.

The composition of the electrolytic solution which exhibits particularly excellent electrolytic capacitor characteristics in combination with the separator of the present invention is shown in Table 2 below as a composition example together with a conventional example.

[0058]

[Table 2]

[Table 3]

As preferred examples of the composition in the present invention, a solvent obtained by combining an organic solvent and a large amount of water, and at least one or more electrolytes selected from the group consisting of a carboxylic acid or a salt thereof and an inorganic acid and a salt thereof are used as an electrolyte. Examples were given in which various basic components were combined with various additive components capable of obtaining an excellent additive effect. Composition Examples 1 and 2
Are examples in which gluconolactone and a chelate compound are combined as additives (in the case of this combination, usually 0.01 to 3% by weight in the electrolyte is preferable), and composition examples 3 and 4.
Is an example in which gluconolactone and a saccharide are combined (in the case of this combination, 0.01 to 5% by weight is usually preferable in the electrolytic solution), and composition examples 5 and 6 show gluconolactone and glutamic acid diacetate, respectively. And gluconolactone and hydroxybenzyl alcohol (in the case of these combinations, usually 0.01 to 5
% By weight is preferred. ), Composition Examples 7 and 8 are examples in which gluconolactone and a nitro compound are combined (in this combination, usually 0.01 to 3% by weight in the electrolyte is preferable).
It is.

[0060]

As described above, by using the separator according to the present invention and the electrolytic capacitor composed of the separator and the specific electrolytic solution, it is possible to obtain an electrolytic capacitor having low impedance, excellent low-temperature characteristics and good life characteristics.

Although the present invention has been described in detail with reference to the preferred embodiments, the present invention is not limited to these embodiments, and many modifications can be made without departing from the spirit of the invention. Of course.

Claims (6)

[Claims] 1. A separator for an electrolytic capacitor, comprising fibers fixed with a binder soluble in an electrolytic solution. 2. The separator for an electrolytic capacitor according to claim 1, wherein the water concentration of the electrolyte solvent containing the organic solvent and water is 20 to 80% by weight. 3. The separator according to claim 1, wherein the density of the separator is 0.5 g / cm ³ or less. 4. A binder comprising polyvinyl alcohol,
The separator according to claim 1, which is a water-soluble polymer such as polyacrylamide and polyacrylic acid. 5. An electrolytic solution containing an organic solvent and water as a solvent, wherein the water concentration in the organic solvent is 20 to 80% by weight of the total solvent, and the organic solvent is a solvent of a protic or aprotic solvent. Claims 1 or more including one or more selected from
An electrolytic capacitor comprising the separator according to 4. 6. An electrolytic solution containing an organic solvent and water as a solvent, wherein the water concentration in the organic solvent is 20 to 80% by weight of the total solvent, and the organic solvent is a solvent of a protic or aprotic solvent. And at least one selected from carboxylic acids or salts thereof and inorganic acids or salts thereof as an electrolyte of the electrolytic solution. Including, electrolytic capacitors.