JP2020088049A - Separator for solid electrolytic capacitor or hybrid electrolytic capacitor and solid electrolytic capacitor or hybrid electrolytic capacitor using the same - Google Patents

Abstract

An object of the present invention is to provide a separator for a solid electrolytic capacitor or a hybrid electrolytic capacitor that is excellent in electrolyte resistance, has a low resistance, and is capable of realizing a highly reliable solid electrolytic capacitor or hybrid electrolytic capacitor. be. SOLUTION: The fibrillated heat-resistant fiber, fibrillated cellulose, and non-fibrillated fiber are contained, and the non-fibrillated fiber has a resin having a melting point of 160°C or higher as a core component and a polyethylene as a sheath component. A separator for a solid electrolytic capacitor or a hybrid electrolytic capacitor, characterized in that it contains molded composite fibers and rayon fibers. [Selection figure] None

Description

The present invention relates to a solid electrolytic capacitor or a hybrid electrolytic capacitor separator (hereinafter, “solid electrolytic capacitor or hybrid electrolytic capacitor separator” may be abbreviated as “separator”), and a solid electrolytic capacitor or a hybrid electrolytic capacitor.

Recently, the performance of electronic devices such as personal computers (hereinafter, “personal computer” may be abbreviated as “personal computer”), home-use game machines, automobile electrical equipment, etc. has been remarkably improved, and at the same time, these electronic devices have been improved. There is also a strong demand for miniaturization of equipment. Therefore, there is an increasing need for miniaturization of components mounted on electronic circuit boards and the like used in these electronic devices.

“Solid electrolytic capacitor” is an aluminum electrolytic capacitor using a conductive polymer as a cathode material. Solid electrolytic capacitors have better ESR (equivalent series resistance) characteristics than aluminum electrolytic capacitors that use an electrolytic solution as a cathode material, so they can be miniaturized by reducing the number of members, and are used in personal computers and game consoles. Has been done.

Further, in personal computers and the like, there is a demand for higher speed and higher functionality of the CPU, and the operating frequency is further increasing. The conduction mechanism of the aluminum electrolytic capacitor using the electrolytic solution is ionic conduction, whereas the conduction mechanism of the solid electrolytic capacitor is electronic conduction, which shows high conductivity. In other words, since it has a good response to release the stored electrons, it has a low ESR characteristic and is advantageous as a capacitor used around the CPU in the power supply circuit.

In recent years, conductive polymer hybrid aluminum electrolytic capacitors using both a conductive polymer and an electrolytic solution as a cathode material have been put on the market by capacitor maker companies, and have low ESR characteristics and short circuit defects. It has also been used in automotive electrical equipment applications where it is essential to have a small amount. The "conductive polymer hybrid aluminum electrolytic capacitor" is also referred to as "hybrid electrolytic capacitor".

As a method for holding the conductive polymer that is the cathode material in the capacitor element, there are a method of polymerizing the conductive polymer in the capacitor element and a method of impregnating the capacitor element with the previously polymerized conductive polymer. is there.

When a conductive polymer is polymerized in the capacitor element, a solution containing a monomer and an oxidant (hereinafter, abbreviated as “polymerization solution”) is impregnated into the capacitor element, followed by heating and drying to polymerize the conductive polymer. A molecular layer is formed in the capacitor element.

When impregnating a conductive polymer that has been polymerized in advance, the capacitor element is impregnated with a suspension obtained by dispersing the conductive polymer in water (hereinafter abbreviated as “dispersion liquid”), and then heated and dried to make the conductive polymer conductive. A polymer layer is formed within the capacitor element.

In both cases of the polymerization liquid and the dispersion liquid, the heat resistance and chemical resistance of the fibers constituting the separator for the solid electrolytic capacitor or the hybrid electrolytic capacitor have become important.

So far, as a separator for a solid electrolytic capacitor, a solid electrolytic comprising a non-fibrillated organic fiber, a fibrillated polymer having a melting point or a thermal decomposition temperature of 250° C. or more, and a wet nonwoven fabric having a water absorption rate of 5 mm/min or more. A capacitor separator is disclosed (for example, see Patent Document 1).

However, the separator made of the wet-laid nonwoven fabric described in Patent Document 1 has polyethylene terephthalate having a melting point of 255° C. as the core and a polyester polyester having a melting point of 110° C. as the non-fibrillated organic fiber and a sheath having a melting point of 110° C. A core-sheath type composite fiber formed by arranging a phthalate copolymer) is used. Although this core-sheath type composite fiber is used as a binder fiber, it has an electrolytic solution resistance and can be sufficiently used under the conventional use environment. However, in the future, when a conductive polymer and an electrolytic solution are used together in a higher temperature atmosphere, especially for a hybrid electrolytic capacitor, the core-sheath type composite fiber deteriorates, which affects the life characteristics and reliability. I am concerned about this.

Japanese Patent No. 4163523

An object of the present invention is to provide a solid electrolytic capacitor or a separator for a hybrid electrolytic capacitor, which can realize a solid electrolytic capacitor or a hybrid electrolytic capacitor having excellent electrolytic solution resistance, low resistance, and high reliability.

As a result of earnest research to solve the above problems, the following inventions have been found.

(1) A fibrillated heat-resistant fiber, a fibrillated cellulose, and a non-fibrillated fiber are contained, and as the non-fibrillated fiber, a core-sheath type having a resin having a melting point of 160° C. or higher as a core component and polyethylene as a sheath component A separator for a solid electrolytic capacitor or a hybrid electrolytic capacitor, comprising a composite fiber and a rayon fiber.
(2) For the solid electrolytic capacitor or the hybrid electrolytic capacitor according to (1), wherein the rayon fiber has a fiber diameter of 9.5 μm or less and the content ratio of the rayon fiber to all fibers is 10% by mass or more and 35% by mass or less. Separator.
(3) A solid electrolytic capacitor or a hybrid electrolytic capacitor using the solid electrolytic capacitor or the separator for hybrid electrolytic capacitor as described in (1) or (2) above.

The solid electrolytic capacitor or the separator for hybrid electrolytic capacitor of the present invention is excellent in electrolytic solution resistance, and the solid electrolytic capacitor or hybrid electrolytic capacitor using the separator of the present invention can achieve the effect of low ESR.

The solid electrolytic capacitor or the separator for hybrid electrolytic capacitor of the present invention comprises fibrillated heat resistant fiber, fibrillated cellulose and non-fibrillated fiber, and as the non-fibrillated fiber, a resin having a melting point of 160° C. or higher is used as a core component. And a core-sheath type composite fiber containing polyethylene as a sheath component and rayon fiber.

The solid electrolytic capacitor is an aluminum electrolytic capacitor using a conductive polymer as a cathode material. The hybrid electrolytic capacitor is an aluminum electrolytic capacitor that uses both a conductive polymer and an electrolytic solution as a cathode material, and is also called a conductive polymer hybrid aluminum electrolytic capacitor. Examples of the conductive polymer used in the solid electrolytic capacitor or the hybrid electrolytic capacitor include polypyrrole, polythiophene, polyaniline, polyacetylene, and derivatives thereof.

The electrolytic solution used for the hybrid electrolytic capacitor is preferably an electrolytic solution containing a non-aqueous solvent and an organic salt. As the non-aqueous solvent, γ-butyrolactone, sulfolane, or a mixture thereof can be used. As the organic salt, an organic amine salt such as triethylamine borodisalicylate or a cyclic amidine salt can be used. The concentration of the organic salt in the non-aqueous solvent is not particularly limited and can be, for example, 5 to 50% by mass.

In the present invention, as the fibrillated heat resistant fiber, wholly aromatic polyamide, wholly aromatic polyester, polyimide, polyamideimide, polyetheretherketone, polyphenylene sulfide, polybenzimidazole, poly-p-phenylenebenzobisthiazole, poly- A fibrillated fiber made of a heat resistant resin such as p-phenylene benzobisoxazole or polytetrafluoroethylene is used. Among these, wholly aromatic polyamides, especially para- wholly aromatic polyamides, which are easily fibrillated and have high affinity with the electrolytic solution and the conductive polymer, are preferable.

In the present invention, the fibrillated heat-resistant fiber is a fiber mainly having very finely divided portions in a direction parallel to the fiber axis, at least a portion of which has a fiber diameter of 1 μm or less. Has an aspect ratio of length and width of 20/1 to 100000/1. Therefore, not only the number of fibers is very large, but also the aspect ratio is so large that fibrils are frequently entangled with each other and other fibers, and a dense nonwoven fabric with small pores can be formed. Therefore, a separator having excellent heat resistance can be obtained.

The modified freeness of the fibrillated heat-resistant fiber in the present invention is preferably 0 ml or more and less than 700 ml, more preferably 0 ml or more and less than 600 ml, and further preferably 0 ml or more and less than 450 ml. When the modified freeness is 700 ml or more, the fibrillation has not progressed so much, and there are many thick stem fibers. Therefore, the pore size tends to be large, and the distribution of the conductive polymer becomes nonuniform. The electrolyte retention may be deteriorated. On the other hand, when the modified freeness is less than 0 ml, fibrillation of the fibrillated heat-resistant fiber progresses too much, and the number of fine fibers joined with a certain amount of binder fiber increases, so that the tensile strength may decrease. is there. Fibrillation As the fibrillation of heat resistant fibers progresses, the modified freeness continues to decline. Then, even after the modified freeness reaches 0 ml, if the fibers are further fibrillated, the fibers pass through the mesh, and the modified freeness starts to rise. In the present invention, the state in which the modified freeness has started to rise backwards in this way is referred to as "the modified freeness is less than 0 ml".

In the present invention, the modified freeness refers to JIS P8121-2:2012 except that a 80 mesh wire net having a wire diameter of 0.14 mm and an opening of 0.18 mm is used as a sieving plate and the sample concentration is 0.1%. It is the value measured according to.

In the fibrillated heat resistant fiber, the mass weighted average fiber length is preferably 0.02 mm or more and 1.50 mm or less. The length-weighted average fiber length is preferably 0.02 mm or more and 1.00 mm or less. When the average fiber length is shorter than the preferred range, the fibrillated heat resistant fibers may fall off from the separator. If the average fiber length is longer than the preferred range, poor dispersion tends to occur, uneven basis weight may occur, the distribution of the conductive polymer may become nonuniform, and the retention of the electrolytic solution may deteriorate.

In the present invention, the mass-weighted average fiber length and the length-weighted average fiber length of the fibrillated heat-resistant fiber are measured by KajaaniFiberLabV3.5 (manufactured by Metso Automation Co.) using the weight-weighted average fiber length (Proj) mode. The average fiber length (L(w)) and the length-weighted average fiber length (L(l)).

The average fiber width of the fibrillated heat-resistant fiber is preferably 0.5 μm or more and 30.0 μm or less, more preferably 3.0 μm or more and 25.0 μm or less, and further preferably 5.0 μm or more and 20.0 μm or less. If the average fiber width exceeds 30.0 μm, the conductive polymer may have a non-uniform distribution, or the electrolyte retention may deteriorate. If the average fiber width is less than 0.5 μm, it may fall off from the separator, and the electrolyte retention may deteriorate.

In the present invention, the average fiber width of the fibrillated heat-resistant fiber is a fiber width measured using KajaaniFiberLabV3.5 (manufactured by Metso Automation).

The fibrillated heat-resistant fiber consists of a refiner, beater, mill, grinder, rotary homogenizer that gives shearing force by a high-speed rotating blade, inner blade of a high-speed rotating cylinder and fixed outer blade. High speed homogenizer of double cylinder type that generates shear force between them, ultrasonic crusher that atomizes by ultrasonic impact, gives a pressure difference of at least 20 MPa to the fiber suspension and passes it through a small-diameter orifice to increase the speed. It can be obtained by treating the fibers with a high-pressure homogenizer or the like that applies a shearing force or a cutting force to the fibers by colliding them and rapidly decelerating them.

The content of the fibrillated heat-resistant fiber is preferably 5% by mass or more and 70% by mass or less with respect to all the fiber components contained in the separator of the present invention. 15 mass% or more is more preferable, and 30 mass% or more is still more preferable. Further, it is more preferably 65% by mass or less, and further preferably 55% by mass or less. When the content of the fibrillated heat-resistant fiber is less than 5% by mass, the number of fibers is reduced, so that the fiber distribution is likely to be non-uniform, the conductive polymer film is likely to be non-uniformly formed, and the electrolytic solution is retained. Since the property is deteriorated, ESR and cycle characteristics are likely to deteriorate. On the other hand, when the content of the fibrillated heat resistant fiber exceeds 70% by mass, the tensile strength of the separator deteriorates and the productivity of the capacitor element decreases. Also, it becomes difficult to reduce the thickness.

Examples of the fibrillated cellulose in the present invention include solvent-spun cellulose, fibrillated non-wood fibers and non-wood pulp such as wood fibers and wood pulp, linters, lint, hemp, and soft cell fibers, and bacterial cellulose. The parenchyma fiber refers to a fiber which is insoluble in water and which has cellulose as a main component and is obtained by treating a portion mainly composed of parenchyma present in stems, leaves, roots, fruits, etc. of plants with alkali.

In the present invention, the average fiber diameter of the fibrillated cellulose is preferably 0.15 to 30 μm, more preferably 0.2 to 10 μm, further preferably 0.25 to 5 μm, and particularly preferably 0.1. 25 to 1 μm. The average fiber diameter is an average value of 40 fiber diameters obtained by measuring 40 fiber diameters randomly selected from the fibers forming the separator by observing the surface or cross section of the separator with a scanning electron microscope.

The length-weighted average fiber length of the fibrillated cellulose is preferably 0.2 mm or more and 3.0 mm or less, more preferably 0.2 mm or more and 2.0 mm or less, and 0.2 mm or more and 1.6 mm or less. Is more preferable. When the length-weighted average fiber length is 0.2 mm or more, it is possible to prevent an increase in the rate of falling out of the sieve net and flowing out into the wastewater during wet papermaking. In addition, when the length-weighted average fiber length is 3.0 mm or less, it is possible to prevent the fibers from being entangled and become lumped, and as a result, it is possible to prevent uneven thickness.

The length-weighted average fiber length of the fibrillated cellulose in the present invention is a length-weighted average fiber length (L(l)) measured in a projected fiber length (Proj) mode using KajaaniFiberLabV3.5 (manufactured by Metso Automation). ).

The effects of beating (fibrillation) include the fact that the fibers form a fine structure inside the separator to improve the liquid retaining property of the electrolytic solution and to reduce the pores. Further, a dense network structure is formed by the fibrillated heat resistant fiber, the non-fibrillated fiber and the fibrillated cellulose, the conductive polymer film is uniformly formed, and the separator having excellent electrolyte retention is easily obtained. ..

The content of fibrillated cellulose in the separator of the present invention is preferably 1 to 40% by mass, more preferably 5 to 20% by mass, and further preferably 5 to 10% by mass. If the content of fibrillated cellulose is less than 1% by mass, a sufficient network structure of the constituent fibers may not be obtained, and if it exceeds 40% by mass, the gap for forming the conductive polymer may be insufficient. Alternatively, the polymerization of the conductive polymer may be hindered and the ESR may be increased.

Fibrillation of fibrillated cellulose in the present invention, refiner, beater, mill, attritor, rotary homogenizer that gives a shearing force by a high-speed rotating blade, a high-speed rotating inner blade of the cylindrical and fixed outer blade High speed homogenizer of double cylinder type that generates shear force between them, ultrasonic crusher that atomizes by ultrasonic impact, gives a pressure difference of at least 20 MPa to the fiber suspension and passes it through a small-diameter orifice to increase the speed. It can be obtained by treating it with a high-pressure homogenizer or the like that applies shearing force or cutting force to the fiber by colliding it with sudden deceleration, but it is particularly preferable to treat with a high-pressure homogenizer because fine fibrils can be obtained. ..

In the present invention, the non-fibrillated fiber is characterized by containing a core-sheath type composite fiber having a resin having a melting point of 160° C. or higher as a core component and polyethylene as a sheath component, and rayon fiber. Hereinafter, unless otherwise specified, a “core-sheath composite fiber having a resin having a melting point of 160° C. or more as a core component and polyethylene as a sheath component” may be abbreviated as “core-sheath composite fiber”.

In the present invention, the content of the core-sheath type composite fiber is preferably 10 to 40% by mass, more preferably 15 to 35% by mass, and more preferably 20 to 20% with respect to the total fiber components contained in the separator. It is more preferably 30% by mass. When the separator contains the core-sheath type composite fiber, the bonding points are strengthened by melting the fibers, and the tensile strength of the separator is improved. Further, in the sheet-shaped separator, the fusion of the core-sheath type composite fibers present on the sheet surface also strengthens the adhesion on the sheet surface, and the effect of suppressing the fluff on the surface can be obtained. Further, as compared with other binder fibers, the core-sheath type composite fibers are more likely to uniformly entangle with the fibrillated heat-resistant fibers to form a network structure, and can be melted by applying heat to further increase the adhesive strength. It is possible to obtain a separator having a higher surface smoothness and an excellent denseness.

When the content of the core-sheath type composite fiber is less than 10% by mass, the number of bonding points between the fibers is reduced, and the effect of improving the tensile strength may be reduced. On the other hand, when the content of the core-sheath type composite fibers is more than 40% by mass, the number of bonding points between the core-sheath type composite fibers increases and the tensile strength becomes strong, but the separator surface is easily formed into a film and the conductive polymer Absorption may be deteriorated and the distribution of the conductive polymer may be non-uniform, which may deteriorate ESR.

In the present invention, the resin having a melting point of 160° C. or higher used as the core component of the core-sheath type composite fiber includes polyester, acrylic, polypropylene, wholly aromatic polyester, wholly aromatic polyesteramide, polyamide, semi-aromatic polyamide, wholly aromatic. Group polyamide, wholly aromatic polyether, wholly aromatic polycarbonate, polyimide, polyamideimide (PAI), polyetheretherketone (PEEK), polyphenylene sulfide (PPS), poly-p-phenylene benzobisoxazole (PBO), polybenzo Examples thereof include resins such as imidazole (PBI), polytetrafluoroethylene (PTFE), and ethylene-vinyl alcohol copolymer.

These core-sheath type composite fibers may be used alone or in combination of two or more kinds. Among these, as the core component, polyester, acrylic, polypropylene, wholly aromatic polyester, wholly aromatic polyesteramide, polyamide, semi-aromatic polyamide, and wholly aromatic polyamide are preferable, and polyester, acrylic and polypropylene are more preferable.

When the melting point of the resin used as the core component is 160° C. or higher, the shape of the core can be maintained. The melting point of the resin is more preferably 163° C. or higher. In the present invention, the melting point is a value measured according to JIS K7121:2012.

In the present invention, by incorporating a core-sheath type composite fiber using polyethylene as a sheath component, the conventional polyester has a chemical resistance to a polymerization liquid, a dispersion liquid or an electrolytic solution, and a conventional polyester having a melting point of 110° C. ( It was found that the effect of remarkably improving is obtained as compared with the core-sheath type composite fiber using a copolymer of polyethylene terephthalate and polyethylene isophthalate.

The melting point of polyethylene as the sheath component is preferably 115° C. or higher in terms of the effect of suppressing excessive film formation on the separator surface, and 140° C. or lower is effective in enhancing the adhesiveness of the core-sheath type composite fiber. It is preferable from the point.

The fiber diameter A of the core-sheath type composite fiber is preferably 16 μm or less, more preferably 5 to 15 μm, further preferably 7 to 14 μm, and particularly preferably 9 to 13 μm. When the fiber diameter A is less than 5 μm, the productivity of the fiber is reduced and the fiber becomes very expensive. In addition, the separator is easily formed into a film. On the other hand, as the fiber diameter A exceeds 16 μm and the fiber diameter A increases, the number of fibers per mass decreases, so that the bonded portion between the fibers may decrease and the tensile strength of the separator may decrease.

In the present invention, for the fiber diameter A, the cross-sectional area of 20 fibers randomly selected from the fibers forming the separator is measured by observing the cross section of the separator with a scanning electron microscope, and the cross-sectional shape of the fiber is a perfect circle. It is an average value of 20 fibers when the fiber diameter is calculated by assuming that In the present invention, the fiber diameter A of all the core-sheath type conjugate fibers is preferably 16 μm or less.

The volume ratio of the core component to the sheath component of the core-sheath type composite fiber (also referred to as "core-sheath ratio") is preferably 80/20 to 40/60, more preferably 70/30 to 50/50. The core component maintains the fiber shape even after heat is applied, and maintains the tensile strength of the fiber. The sheath component is melted or softened when heat is applied to heat bond the constituent fibers. The thermal bonding of the sheath component makes the separator more dense in which the voids between the constituent fibers are partially filled.

When the core-sheath ratio is more than 40/60, the constituent fibers are strongly heat-bonded to each other, but the proportion of the core component is too small, so that the single fiber strength of the core-sheath type composite fiber itself is lowered. .. In addition, when the amount of the sheath component is large, the absorptivity of the conductive polymer and the electrolytic solution is lowered due to the excessive reduction of the porosity of the separator, and the work efficiency of the capacitor production is lowered, or the ESR is deteriorated. There are cases. On the other hand, when the core-sheath ratio is larger than 80/20 and the core component is too much, the single fiber strength of the core-sheath type composite fiber itself becomes high, but the constituent fibers of the separator are not sufficiently heat-bonded. Therefore, the tensile strength is reduced due to insufficient heat bonding between the fibers. In addition, the inconvenience that the porosity increases due to the fact that the constituent fibers are not sufficiently dense may deteriorate the characteristics of the capacitor. Furthermore, when the core-sheath ratio is 70/30 to 50/50, it is possible to obtain a separator having high conductive polymer and electrolyte absorbability and retention and having high tensile strength.

In the present invention, as the non-fibrillated fiber other than the core-sheath type composite fiber, natural fiber, rayon fiber, solvent-spun cellulose fiber, polyolefin, polyester, aromatic polyester, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyamide , Aromatic polyamide, polyether sulfone, acrylic, polyvinyl chloride, polyvinylidene chloride, polyvinyl ether, polyvinyl ketone, polyether, polyvinyl alcohol, diene, polyurethane, phenol, melamine, furan, urea, aniline, unsaturated polyester, fluorine Examples include non-fibrillated short fibers made of synthetic resins such as silicone and derivatives thereof.

The non-fibrillated fiber other than the core-sheath type composite fiber may be a fiber made of a single resin (single fiber) or a composite fiber made of two or more kinds of resins. Further, the non-fibrillated fiber contained in the separator of the present invention may be of one type or a combination of two or more types. Examples of the composite fiber include core-sheath type, eccentric type, side-by-side type, sea-island type, orange type, and multiple bimetal type.

In the present invention, the content rate of the whole non-fibrillated fiber including the core-sheath type composite fiber is preferably 25 to 94% by mass, and 30 to 80% by mass with respect to the total fiber components contained in the separator. More preferably, it is more preferably 35 to 65 mass %. By containing the non-fibrillated fiber, the tensile strength and puncture strength of the separator can be increased. When the content of the whole non-fibrillated fiber is less than 25% by mass, the tensile strength of the separator may be low, and the productivity of the separator and the assembly productivity of the capacitor may be reduced. On the other hand, when the content of the whole non-fibrillated fiber exceeds 94% by mass, the content of the fibrillated heat-resistant fiber or fibrillated cellulose decreases, so that the absorptivity of the conductive polymer may deteriorate or the conductivity may decrease. Since the distribution of the polymer becomes non-uniform, the ESR may be deteriorated, or the electrolyte retention may be deteriorated, which may deteriorate the ESR.

In the present invention, rayon fiber is used as the non-fibrillated fiber other than the core-sheath type composite fiber. The effect of using rayon fibers is that the conductive polymer and the electrolytic solution are well absorbed, the ESR is good, and the electrolytic solution resistance is excellent.

The fiber diameter A of the rayon fiber used in the present invention is preferably 9.5 μm or less, more preferably 5 μm or more and 9 μm or less, still more preferably 5 μm or more and 8 μm or less. When the fiber diameter A of the rayon fiber exceeds 9.5 μm, the number of fibers in the thickness direction decreases, and it may not be possible to ensure the required denseness. In addition, the unevenness becomes large, the thickness unevenness occurs on the sheet surface, and the tensile strength and the surface strength of the separator are likely to decrease. The rayon fibers can be used even if the fiber diameter A is less than 5 μm, but the rayon fibers currently available have a fiber diameter A of 5 μm or more. The thinner the rayon fiber, the more difficult it becomes to manufacture stably, and the more expensive it becomes.

In the present invention, the content of rayon fibers is preferably 10% by mass or more and 35% by mass or less, more preferably 15% by mass or more and 30% by mass or less, and more preferably 20% by mass or more, based on the total fibers. It is more preferably 25 mass% or less. When the content is in the range of 10% by mass or more and 35% by mass or less, the absorbability of the conductive polymer or the electrolytic solution and the ESR tend to be good. In addition, a separator having excellent electrolytic solution resistance can be easily obtained. When the content exceeds 35% by mass, the required denseness cannot be ensured, the tensile strength of the separator becomes low, the tensile maintenance ratio after storage of the electrolytic solution decreases, and the production of the separator. And the assembly productivity of capacitors may decrease. On the other hand, when the content is less than 10% by mass, the absorption of the conductive polymer or the electrolytic solution may be deteriorated or the distribution of the conductive polymer may be non-uniform, so that the ESR may be deteriorated.

The fiber length of the rayon fiber is preferably 1 mm or more and 6 mm or less, more preferably 2 mm or more and 5 mm or less, and further preferably 3 mm or more and 4 mm or less. When the fiber length exceeds 6 mm, the formation may be poor and the denseness may be deteriorated. If the fiber length is less than 1 mm, the tensile strength of the separator may be low, and the separator may be damaged during handling or during assembly of the capacitor element.

The fineness of the non-fibrillated fiber other than the core-sheath type composite fiber and the rayon fiber is preferably 0.01 dtex or more and 0.6 dtex or less, and more preferably 0.02 dtex or more and 0.3 dtex or less. If the fineness exceeds 0.6 dtex, the number of fibers in the thickness direction decreases, so that the pore size distribution of the separator becomes wider, the absorption of the conductive polymer or the electrolytic solution decreases, and the ESR deteriorates. There are cases. On the other hand, when the fineness is less than 0.01 dtex, the fiber becomes very expensive, and stable production of the fiber becomes difficult, or when the separator is produced by a wet papermaking method, the dehydration property is lowered and the productivity of the separator is decreased. Of the conductive polymer or the electrolytic solution may be reduced, and the unevenness of the basis weight may be easily generated.

The fiber length of non-fibrillated fibers other than rayon fibers is preferably 1 mm or more and 10 mm or less, more preferably 1 mm or more and 5 mm or less. When the fiber length exceeds 10 mm, poor formation may occur. On the other hand, when the fiber length is less than 1 mm, the tensile strength of the separator may be low and the separator may be damaged in the electrode laminating step.

The thickness of the separator of the present invention is not particularly limited, but is preferably 20 μm or more, more preferably 30 μm or more, and further preferably 40 μm or more. Further, it is preferably 70 μm or less, more preferably 60 μm or less, still more preferably 50 μm or less. Even when the thickness of the separator is in the above range, in the separator of the present invention, the ESR can be suppressed to be low, and the tensile strength required in the electrode laminating step can be maintained. There is no loss of workability. If the thickness of the separator exceeds 70 μm, the ESR of the separator may become too high. Moreover, it may not be possible to increase the capacity of the capacitor. If the thickness of the separator is less than 20 μm, the strength of the separator becomes too weak and there is a risk of damage during handling of the separator or cutting into a narrow width.

The density of the separator of the present invention is preferably 0.20 g/cm ³ or more and 0.50 g/cm ³ or less, and more preferably 0.25 g/cm ³ or more and 0.40 g/cm ³ or less. If the density is less than 0.20 g/cm ³ , the strength of the separator may be too weak, and the separator may be damaged during handling or cutting. If it exceeds 0.50 g/cm ³ , the separator may be formed into a film. In some cases, the absorption rate and retention of the conductive polymer and the electrolytic solution are deteriorated, and the ESR and cycle characteristics are deteriorated.

The separator of the present invention is preferably a wet nonwoven fabric produced by a wet papermaking method. In the wet papermaking method, fibers are dispersed in water to form a uniform papermaking slurry, and this papermaking slurry is strained with a paper machine to produce a wet non-woven fabric. Examples of the paper machine include a cylinder paper machine, a fourdrinier paper machine, an inclined type paper machine, an inclined shortdrinier paper machine, and a combination machine thereof. In the step of producing a wet-laid nonwoven fabric, a hydroentangling treatment may be carried out if necessary. As a processing treatment of the wet-laid nonwoven fabric, heat treatment, calender treatment, thermal calender treatment, or the like may be performed.

The present invention will be described below with reference to examples, but the present invention is not limited to these examples. In the examples, all percentages (%) and parts are based on mass unless otherwise specified.

<Production of separator>
Example 1
Para-type wholly aromatic polyamide fiber (fineness: 2.5 dtex, fiber length: 3 mm) was dispersed in water to an initial concentration of 2.5% by mass, and a double disc refiner was used to create a clearance each time the pass was repeated. After repeatedly beating 15 times while narrowing, using a high-pressure homogenizer, modified freeness 350 ml, mass weighted average fiber length 1.30 mm, length weighted average fiber length 0.59 mm, fiber width 25.2 mm A fibrillated heat resistant fiber was obtained.

Cotton linter pulp was dispersed in water to a concentration of 2.5% by mass, and after being repeatedly treated 10 times with a double disc refiner while gradually narrowing the clearance, it was treated with a high pressure homogenizer to obtain an average fiber. Fibrillated cellulose having a diameter of 0.3 μm and a length weighted average fiber length of 0.22 mm was obtained.

50 parts of fibrillated heat-resistant fiber, 10 parts of fibrillated cellulose, 20 parts of rayon fiber having a fiber diameter of A8.3 μm, fiber length of 4 mm, fiber diameter of A11.8 μm, fiber length of 5 mm, core component being polyethylene terephthalate (melting point 265° C. ), 20 parts of a core-sheath type composite fiber (core-sheath ratio=50/50) whose sheath component is polyethylene (melting point 135° C.) is mixed together, disintegrated in water of a pulper, and uniformly stirred under agitation. A raw material slurry (0.5% concentration) was prepared. This raw material slurry was used to obtain a wet paper web using a cylinder paper machine, and was dried with a cylinder dryer having a surface temperature of 150° C., after which both sides of the sheet were heat-treated at 180° C. with a thermal calendar to obtain a basis weight of 17. A separator having a thickness of 5 g/m ² and a thickness of 52 μm was obtained.

Example 2
30 parts of fibrillated heat-resistant fiber used in Example 1, 5 parts of fibrillated cellulose used in Example 1, 35 parts of rayon fiber having a fiber diameter A of 8.3 μm and a fiber length of 4 mm, fiber diameter of A8.1 μm, fiber length 30 parts of 5 mm core-sheath type composite fiber (core-sheath ratio=50/50) in which the core component is polypropylene (melting point 165° C.) and the sheath component is polyethylene (melting point 135° C.) are mixed together in water of pulper. The mixture was disaggregated and stirred under stirring by an agitator to prepare a uniform raw material slurry (0.5% concentration). This raw material slurry was used to obtain a wet paper web using a cylinder paper machine, and was dried with a cylinder dryer having a surface temperature of 150° C., after which both sides of the sheet were heat-treated at 180° C. with a thermal calendar to obtain a basis weight of 17. A separator having a thickness of 0 g/m ² and a thickness of 54 μm was obtained.

Example 3
50 parts of fibrillated heat-resistant fiber used in Example 1, 10 parts of fibrillated cellulose used in Example 1, 20 parts of rayon fiber having a fiber diameter of A9.4 μm, fiber length of 5 mm, fiber diameter of A8.1 μm, fiber length 20 parts of 5 mm core-sheath type composite fiber (core-sheath ratio=50/50) in which the core component is polypropylene (melting point 165° C.) and the sheath component is polyethylene (melting point 135° C.) are mixed together in water of pulper. The mixture was disaggregated and stirred under stirring by an agitator to prepare a uniform raw material slurry (0.5% concentration). This raw material slurry was used to obtain a wet paper web using a cylinder paper machine, and was dried with a cylinder dryer having a surface temperature of 150° C., after which both sides of the sheet were heat-treated at 180° C. with a thermal calendar to obtain a basis weight of 17. A separator having a thickness of 3 μm/m ² and a thickness of 52 μm was obtained.

Example 4
50 parts of fibrillated heat-resistant fiber used in Example 1, 10 parts of fibrillated cellulose used in Example 1, 10 parts of rayon fiber with fiber diameter A 5.3 μm, fiber length 3 mm, fiber diameter A 11.8 μm, fiber length 5 mm of 30 parts of core-sheath type composite fiber (core-sheath ratio=50/50) having a core component of polyethylene terephthalate (melting point 265° C.) and a sheath component of polyethylene (melting point 135° C.) are mixed together, and the pulper in water is mixed. Was disaggregated and stirred under stirring by an agitator to prepare a uniform raw material slurry (0.5% concentration). This raw material slurry was used to obtain a wet paper web using a cylinder paper machine, and was dried with a cylinder dryer having a surface temperature of 150° C., after which both sides of the sheet were heat-treated at 180° C. with a thermal calendar to obtain a basis weight of 17. A separator having a thickness of 5 g/m ² and a thickness of 53 μm was obtained.

Example 5
50 parts of fibrillated heat-resistant fiber used in Example 1, 10 parts of fibrillated cellulose used in Example 1, 9 parts of rayon fiber having fiber diameter A5.3 μm, fiber length 3 mm, fiber diameter A11.8 μm, fiber length 5 mm of 31 parts of core-sheath type composite fibers (core-sheath ratio=50/50) having a core component of polyethylene terephthalate (melting point 265° C.) and a sheath component of polyethylene (melting point 135° C.) are mixed together, and the pulper in water is mixed. Was disaggregated and stirred under stirring by an agitator to prepare a uniform raw material slurry (0.5% concentration). This raw material slurry was used to obtain a wet paper web using a cylinder paper machine, and was dried with a cylinder dryer having a surface temperature of 150° C., after which both sides of the sheet were heat-treated at 180° C. with a thermal calendar to obtain a basis weight of 17. A separator having a thickness of 5 g/m ² and a thickness of 52 μm was obtained.

Example 6
30 parts of fibrillated heat-resistant fiber used in Example 1, 5 parts of fibrillated cellulose used in Example 1, 37 parts of rayon fiber having a fiber diameter A of 8.3 μm and a fiber length of 4 mm, fiber diameter A of 8.1 μm, fiber length 28 parts of 5 mm core-sheath type composite fiber (core-sheath ratio=50/50) having a core component of polypropylene (melting point 165° C.) and a sheath component of polyethylene (melting point 135° C.) were mixed together, and in a water of pulper. The mixture was disaggregated and stirred under stirring by an agitator to prepare a uniform raw material slurry (0.5% concentration). A wet paper web was obtained from this raw material slurry using a cylinder paper machine and dried with a cylinder dryer having a surface temperature of 150° C., after which both sides of the sheet were heat-treated at 180° C. with a thermal calender to obtain a basis weight of 17. A separator having a thickness of 0 g/m ² and a thickness of 54 μm was obtained.

Example 7
50 parts of fibrillated heat-resistant fiber used in Example 1, 10 parts of fibrillated cellulose used in Example 1, 20 parts of rayon fiber having a fiber diameter A of 9.7 μm and fiber length of 5 mm, fiber diameter of A8.1 μm, fiber length 20 parts of 5 mm core-sheath type composite fiber (core-sheath ratio=50/50) in which the core component is polypropylene (melting point 165° C.) and the sheath component is polyethylene (melting point 135° C.) are mixed together in water of pulper. The mixture was disaggregated and stirred under stirring by an agitator to prepare a uniform raw material slurry (0.5% concentration). This raw material slurry was used to obtain a wet paper web using a cylinder paper machine, and was dried with a cylinder dryer having a surface temperature of 150° C., after which both sides of the sheet were heat-treated at 180° C. with a thermal calendar to obtain a basis weight of 17. A separator having a thickness of ² g/m ² and a thickness of 53 μm was obtained.

Reference example 1
50 parts of fibrillated heat-resistant fiber used in Example 1, 10 parts of fibrillated cellulose used in Example 1, 20 parts of polyethylene terephthalate short fibers having a fiber diameter of A3.1 μm, fiber length of 3 mm, fiber diameter of A11.8 μm, 20 parts of a core-sheath type composite fiber (core-sheath ratio=50/50) having a fiber length of 5 mm and having a core component of polyethylene terephthalate (melting point 265° C.) and a sheath component of polyethylene (melting point 135° C.) are mixed together to obtain a pulper. Was disaggregated in water and stirred under an agitator to prepare a uniform raw material slurry (0.5% concentration). This raw material slurry was used to obtain a wet paper web using a cylinder paper machine, and was dried with a cylinder dryer having a surface temperature of 150° C., after which both sides of the sheet were heat-treated at 180° C. with a thermal calendar to obtain a basis weight of 17. A separator having a thickness of 5 g/m ² and a thickness of 50 μm was obtained.

Comparative Example 1
50 parts of fibrillated heat-resistant fiber used in Example 1, 10 parts of fibrillated cellulose used in Example 1, 20 parts of polyethylene terephthalate short fiber having a fiber diameter of A3.1 μm, fiber length of 3 mm, fiber diameter of A12.7 μm, 20 parts of a core-sheath type composite fiber (core-sheath ratio=50/50) having a fiber length of 5 mm and a core component of polyethylene terephthalate (melting point 255° C.) and a sheath component of polyethylene terephthalate/polyethylene isophthalate copolymer (melting point 110° C.) Were mixed together, disintegrated in water of pulper, and stirred under stirring by an agitator to prepare a uniform raw material slurry (0.5% concentration). A wet paper web was obtained from this raw material slurry using a cylinder paper machine and dried with a cylinder dryer having a surface temperature of 135° C., and thereafter, both sides of the sheet were heat-treated at 180° C. with a thermal calender to obtain a basis weight of 17. A separator having a thickness of 5 g/m ² and a thickness of 50 μm was obtained.

Comparative example 2
30 parts of fibrillated heat-resistant fiber used in Example 1, 5 parts of fibrillated cellulose used in Example 1, fiber diameter A 5.3 μm, 35 parts of polyethylene terephthalate short fiber having a fiber length of 3 mm, fiber diameter A 10.3 μm, 30 parts of a core-sheath type composite fiber (core-sheath ratio=50/50) having a fiber length of 5 mm and a core component of polyethylene terephthalate (melting point 255° C.) and a sheath component of polyethylene terephthalate/polyethylene isophthalate copolymer (melting point 110° C.) Were mixed together, disaggregated in water of pulper, and stirred under stirring by an agitator to prepare a uniform raw material slurry (0.5% concentration). This raw material slurry was used to obtain a wet paper web using a cylinder paper machine and was dried with a cylinder dryer having a surface temperature of 135° C., after which both sides of the sheet were heat-treated at 180° C. with a thermal calendar to obtain a basis weight of 17. A separator having a thickness of 0 g/m ² and a thickness of 50 μm was obtained.

The following physical properties were measured and evaluated for the solid electrolytic capacitors or the separators for hybrid electrolytic capacitors of Examples, Reference Examples and Comparative Examples, and the results are shown in Table 1.

<Basis weight of separator>
The basis weight of the separator was measured according to JIS P8124:2011.

<Separator thickness>
The thickness under a load of 5 N was measured using an outer micrometer specified in JIS B7502:2016.

<Water absorption of separator>
JIS C2300-2:2010 "Electrical Cellulose Paper-Part 2: Test Method" 22 According to the method specified in the B method of water absorption, a test piece has a width of 20 mm and a length of 200 mm. Three pieces were cut out, and fixed by immersing only the bottom end in 10 mm in ion-exchanged water, and the water absorption rate (mm/10 minutes) was defined as the height of the water sucked in for 10 minutes. It is considered that the higher the water absorption of the separator, the better the impregnation property of the conductive polymer polymerization liquid or dispersion liquid and the electrolytic solution.

<Mass maintenance rate of separator after storage of electrolyte>
The mass retention rate (%) of the separator after storage of the electrolytic solution is the mass W (g) when 5 test pieces each having a width of 50 mm and a length of 250 mm are sampled from each sample and brought into a water equilibrium state. After the measurement, it is immersed in γ-butyrolactone used as a non-aqueous solvent of the electrolytic solution and stored for 30 days in an atmosphere of 80±1°C. After that, the sample taken out was washed with water and dried, and the mass W ₂ (g) when it was brought to a water equilibrium state again was measured, and the mass retention rate after storage of the electrolytic solution was determined by the following formula. The average value of 5 sheets was used as a representative value.
Mass retention rate (%) of separator after storage of electrolytic solution=W ₂ /W×100

<Tensile strength retention rate of separator after storage of electrolyte>
The tensile strength T in the longitudinal direction of the separator before storage of the electrolytic solution was measured using a tabletop material testing machine (trade name: STA-1150, manufactured by Orientec Co., Ltd.) according to JIS P8113:2006. The size of the test piece was 250 mm in the longitudinal direction and 50 mm in width, the interval between the two grippers was 100 mm, and the pulling speed was 300 mm/min. 80 ± 1 ° C. of γ- butyrolactone and stored for 30 days, the mass retention rate of the separator using a specimen five measured similarly the vertical tensile strength were measured, a tensile after the electrolytic solution stored intensity T ₂ I asked. The tensile strength retention rate after storage of the electrolytic solution was determined by the following formula. The average value of 5 sheets was used as a representative value.
Tensile strength maintenance rate (%) of separator after storage of electrolytic solution=T ₂ /T×100

<Production of solid electrolytic capacitor>
The anode foil and the cathode foil that had been subjected to the etching treatment and the oxide film formation treatment were wound with the separators of the respective Examples, Reference Examples and Comparative Examples interposed therebetween so as not to come into contact with each other, to produce a capacitor element. The produced capacitor element was dried after the re-chemical conversion treatment. The capacitor element was impregnated with the conductive polymer dispersion and then heated and dried to form a conductive polymer. Next, the capacitor element was put in a predetermined case, the opening was sealed, and then aging was performed to obtain a solid electrolytic capacitor having a rated voltage of 35 V and a rated electrostatic capacity of 100 μF.

<Fabrication of hybrid electrolytic capacitor>
The anode foil and the cathode foil that had been subjected to the etching treatment and the oxide film formation treatment were wound with the separators of the respective Examples, Reference Examples and Comparative Examples interposed therebetween so as not to come into contact with each other, to produce a capacitor element. The produced capacitor element was dried after the re-chemical conversion treatment. The capacitor element was impregnated with the conductive polymer dispersion and then heated and dried to form a conductive polymer. Subsequently, the capacitor element was impregnated with a driving electrolytic solution, the capacitor element was put in a predetermined case, the opening was sealed, and then aging was performed to obtain a hybrid electrolytic capacitor having a rated voltage of 35 V and a rated electrostatic capacity of 150 μF.

<ESR measurement>
The ESR (equivalent series resistance) of the solid electrolytic capacitor and the hybrid electrolytic capacitor produced by the above method were measured by an LCR meter under the conditions of a temperature of 20° C. and a frequency of 100 kHz, and the results are shown in Table 2.

As shown in Table 1, the separators produced in Examples 1 to 4 contained fibrillated heat-resistant fibers, fibrillated cellulose, and non-fibrillated fibers, and as the non-fibrillated fibers, a resin having a melting point of 160° C. or higher was used. It contains a core-sheath type composite fiber having a core component and polyethylene as a sheath component, and rayon fiber having a fiber diameter of 9.5 μm or less. The separators of Examples 1 to 4 have excellent water absorption, a high mass retention rate and a high tensile strength retention rate when stored at high temperature (80±1° C.) in γ-butyrolactone, which is a non-aqueous solvent of the electrolytic solution, It had excellent electrolyte properties.

In the separators of Examples 5 and 6, the rayon fibers having a fiber diameter of 9.5 μm or less are less than 10% by mass and the rayon fibers are more than 35% by mass. In Example 5, a decrease in water absorption was observed as compared with Examples 1 to 4, and in Example 6 in which the content was more than 35% by mass, the fusion point between the polyethylene of the sheath component and the rayon fiber was loosened. Compared with Nos. 1 to 4, there was a tendency that the mass retention rate and the tensile strength retention rate after storage of the electrolytic solution tended to decrease.

The separator of Example 7 is a case where the rayon fiber having a fiber diameter of more than 9.5 μm is used, and compared with Example 3 using the rayon fiber having a fiber diameter of 9.5 μm or less, A decrease was observed, and the mass retention rate and the tensile retention rate after storage of the electrolytic solution tended to decrease.

The separator of Reference Example 1 contained, as non-fibrillated fibers, a core-sheath type composite fiber having a resin having a melting point of 160° C. or higher as a core component and polyethylene as a sheath component, and polyethylene terephthalate short fibers having a fiber diameter of 3.1 μm. In some cases, the water absorption was decreased, and the tensile strength after storage of the electrolytic solution was decreased.

The separators of Comparative Example 1 and Comparative Example 2 are cases where core-sheath type composite fibers having polyethylene terephthalate having a melting point of 255° C. as a core component and polyethylene terephthalate and polyethylene isophthalate copolymer as a sheath component are used as binder fibers. However, the electrolytic solution resistance was poor. In particular, the tensile strength retention rate after storage of the electrolytic solution was significantly reduced.

As shown in Table 2, the solid electrolytic capacitor and the hybrid electrolytic capacitor using a separator containing a core-sheath type composite fiber having a resin having a melting point of 160° C. or higher as a core component and polyethylene as a sheath component and rayon fiber have an ESR of Low and favorable results.

The solid electrolytic capacitor or the separator for hybrid electrolytic capacitor of the present invention can be suitably used for a solid electrolytic capacitor and a hybrid electrolytic capacitor.

Claims (3)

A core-sheath type composite fiber comprising fibrillated heat-resistant fiber, fibrillated cellulose and non-fibrillated fiber, wherein the non-fibrillated fiber comprises a resin having a melting point of 160° C. or higher as a core component and polyethylene as a sheath component. A separator for a solid electrolytic capacitor or a hybrid electrolytic capacitor, which comprises rayon fiber. The separator for a solid electrolytic capacitor or a hybrid electrolytic capacitor according to claim 1, wherein the rayon fiber has a fiber diameter of 9.5 μm or less, and the content ratio of the rayon fiber to all fibers is 10% by mass or more and 35% by mass or less. A solid electrolytic capacitor or a hybrid electrolytic capacitor comprising the solid electrolytic capacitor or the separator for hybrid electrolytic capacitor according to claim 1 or 2.