JP2017168696A - Separator for solid electrolytic capacitor and solid electrolytic capacitor using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator capable of realizing a solid electrolytic capacitor having a low short-circuit defect rate and a low ESR, and a solid electrolytic capacitor using the same.SOLUTION: Provided are the separator for a solid electrolytic capacitor and the solid electrolytic capacitor using the same. The separator for a solid electrolytic capacitor includes: a cellulose substrate mainly composed of solvent-spun cellulose fibers having a modified freeness of 75 to 250 ml and a length-weighted average fiber length of 0.80 to 1.80 mm; and a coating layer containing an inorganic filler provided on at least one surface of the separator substrate.SELECTED DRAWING: None

Description

  The present invention relates to a solid electrolytic capacitor separator and a solid electrolytic capacitor using the same.

  In a solid electrolytic capacitor using a conductive polymer such as polypyrrole or polythiophene as a solid electrolyte, a foil-like anode electrode and a cathode electrode are wound through a separator to form a winding element. By conducting the polymerization by impregnating the separator with a polymer solution of a conductive polymer, or impregnating the separator with a conductive polymer dispersion, a conductive polymer film that covers the separator is formed. Conventionally, as a separator of a solid electrolytic capacitor, a paper separator mainly composed of a beaten product of cellulose fibers such as natural cellulose fibers such as esparto and hemp pulp, solvent-spun cellulose fibers, and regenerated cellulose fibers has been used (for example, Patent Document 1). The cellulose fibers in these paper separators react with an oxidant used when polymerizing the conductive polymer to inhibit the polymerization of the conductive polymer, so that carbonization is performed in advance so as not to inhibit the polymerization. The For this reason, the carbon separator may be thermally shrunk or become brittle, so that burrs of the electrode may easily penetrate the separator, resulting in a high short-circuit defect rate.

  Therefore, as a solid electrolytic capacitor separator, a separator using a nonwoven fabric mainly composed of synthetic fibers (for example, see Patent Document 2) is disclosed. In the separator of Patent Document 2, the binder fiber is easy to form a film, the conductivity of the conductive polymer is deteriorated, and the equivalent series resistance (hereinafter sometimes abbreviated as “ESR”) of the solid electrolytic capacitor is increased. There was a problem.

JP 2002-15955 A Japanese Patent No. 3319501

  The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a separator capable of realizing a solid electrolytic capacitor having a low short-circuit defect rate and a low ESR, and a solid electrolytic capacitor using the separator.

  The present inventor has found the following invention as means for solving the above problems.

(1) A cellulose base material mainly composed of solvent-spun cellulose fibers having a modified freeness of 75 to 250 ml defined below and a length-weighted average fiber length of 0.80 to 1.80 mm; The separator for solid electrolytic capacitors which has a coating layer containing the inorganic filler provided in the at least one surface of the said cellulose base material.

Modified freeness: Freeness measured in accordance with JIS P8121, except that an 80-mesh wire mesh having a wire diameter of 0.14 mm and an aperture of 0.18 mm was used as the sieve plate, and the sample concentration was 0.1%.

(2) A solid electrolytic capacitor using the solid electrolytic capacitor separator according to (1).

  According to the present invention, by using a cellulose base material mainly composed of solvent-spun cellulose fibers having a modified freeness of 75 to 250 ml and a length-weighted average fiber length of 0.80 to 1.80 mm. A coating layer containing an inorganic filler provided on at least one surface of the cellulose substrate is uniformly formed on the substrate surface. Since the strength of the separator after carbonization can be increased by the coating layer containing the inorganic filler, the short-circuit defect rate of the solid electrolytic capacitor can be reduced. Moreover, since the cellulose base material does not contain the binder fiber which is easy to form a film, it is excellent in the absorbability of the polymerization liquid of the conductive polymer, and the ESR of the solid electrolytic capacitor can be lowered.

  In the present invention, the expression “separator” means a solid electrolytic capacitor separator. In the present invention, when “predetermined solvent-spun cellulose fiber” is described, “solvent spinning having a modified freeness of 75 to 250 ml and a length-weighted average fiber length of 0.80 to 1.80 mm”. It means “cellulose fiber”.

<Solid electrolytic capacitor>
The solid electrolytic capacitor in the present invention refers to a solid electrolytic capacitor using a functional polymer having conductivity (conductive polymer) as an electrolyte. Examples of the functional polymer having conductivity include polypyrrole, polythiophene, polyaniline, polyacetylene, polyacene, and derivatives thereof. The solid electrolytic capacitor in the present invention may be a combination of these functional polymers and an electrolytic solution. As the electrolytic solution, an aqueous solution in which an ion dissociable salt is dissolved, propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), acetonitrile (AN), γ-butyrolactone (BL ), Dimethylformamide (DMF), tetrahydrofuran (THF), dimethoxyethane (DME), dimethoxymethane (DMM), sulfolane (SL), dimethyl sulfoxide (DMSO), ethylene glycol, propylene glycol, etc. Although what melt | dissolved salt, an ionic liquid (solid molten salt), etc. are mentioned, It is not limited to these.

<Separator for solid electrolytic capacitor>
In the present invention, the solvent-spun cellulose fiber means a cellulose fiber obtained by directly dissolving and spinning in an organic solvent without passing through a cellulose derivative. In JIS L0204-2, the term “Lyocell” is used as the name of this fiber. In the present invention, solvent-spun cellulose fibers having a modified freeness of 75 to 250 ml and a length-weighted average fiber length of 0.80 to 1.80 mm are used. If the modified freeness is less than 75 ml or the length-weighted average fiber length is less than 0.80 mm, fibers are taken into the papermaking network and cannot be transferred to the felt. A problem occurs. When the modified freeness is more than 250 ml or the length weighted average fiber length is more than 1.80 mm, it is difficult to reduce the thickness of the separator, resulting in a problem of occurrence of coating layer spots.

  The modified freeness of the solvent-spun cellulose fiber is more preferably 90 to 220 ml, further preferably 90 to 175 ml. The length weighted average fiber length is more preferably 0.90 to 1.60 mm, and further preferably 0.90 to 1.30 mm. The fiber length distribution of a given solvent-spun cellulose fiber may have one peak or two or more peaks.

  The modified freeness in the present invention is that a wire mesh (made by PULP AND PAPER RESEARCH INSTITUTE OF CANADA) having a wire diameter of 0.14 mm and an aperture of 0.18 mm is used as a sieve plate, and the sample concentration is 0.1%. The freeness measured in accordance with JIS P8121. The reason why the modified freeness is adopted in the present invention is that the Canadian standard freeness specified in JIS P8121 is around several tens to 0 ml and the difference in the freeness cannot be discriminated any more. This is because the fiber length is shortened by beating, and the pulp sample slips through the holes in the sieve plate used in the Canadian standard freeness measurement, and the precise freeness is measured. This is because it is possible to clarify the beating degree of the sample that cannot be performed.

  The length-weighted average fiber length can be measured by using a commercially available fiber length measuring instrument that is obtained by using polarization characteristics obtained by applying laser light to the fiber. In the present invention, the projected fiber length was measured using Kajaani Fiber Lab V3.5 (manufactured by Metso Automation). “Length-weighted average fiber length” of solvent-spun cellulose fiber means “length-weighted average fiber length” measured and calculated according to the above.

  In the present invention, a predetermined solvent-spun cellulose fiber is fixed to a refiner, a beater, a beat refiner, a mill, an attritor, a rotary blade homogenizer that applies a shearing force by a high-speed rotary blade, and a cylindrical inner blade that rotates at high speed. Double-cylindrical high-speed homogenizer that generates shearing force between the outer blades, ultrasonic crusher that is refined by ultrasonic impact, high-pressure homogenizer, etc., through the blade shape, sample concentration, flow rate, and processing It is manufactured by adjusting conditions such as the number of times and processing speed.

  In the present invention, the cellulose substrate is mainly composed of a predetermined solvent-spun cellulose fiber. In the present invention, the “main body” means that the content of a predetermined solvent-spun cellulose fiber is 80% by mass or more. Moreover, the cellulose base material may contain cellulose fibers other than a predetermined solvent-spun cellulose fiber. For example, solvent-spun cellulose or regenerated cellulose short fibers or fibrillated products, natural cellulose fibers, natural cellulose fiber pulped products or fibrillated products may be contained.

  In the present invention, the cellulose substrate is produced by a papermaking method. Specifically, the fiber is dispersed in water to form a uniform slurry, and this slurry is rolled up by a paper machine. You may add chemical | medical agents, such as a dispersing aid, an antifoamer, a thickener, a flocculant, a paper strength enhancer, and a release agent, to a slurry as needed. Examples of the paper machine include a paper machine that independently uses a paper net such as a circular net, a long net, an inclined type, and an inclined short net, and a composite paper machine that combines a plurality of these paper nets.

In the present invention, the basis weight of the cellulosic substrate is preferably 6.5~17.0g / ^{m 2,} more preferably ^{7.0~16.0g / m 2, 8.0~15.0g / m} 2 is Further preferred. Exceeds 17.0 g / ^{m 2,} there is a case where the thickness of the separator is increased, is less than 6.5 g / ^{m 2,} may be difficult to obtain sufficient strength. The basis weight is measured based on the method defined in JIS P 8124 (paper and paperboard—basis weight measurement method).

  In the present invention, the cellulose substrate may be calendered as necessary after paper making to adjust the thickness. The calendar process may be performed at room temperature or may be performed by heating. The thickness is preferably 10 to 31 μm, more preferably 10 to 27 μm, and still more preferably 10 to 22 μm. If the thickness is less than 10 μm, sufficient strength may not be obtained. If the thickness is more than 31 μm, the thickness of the separator may increase. In addition, thickness means the value measured based on the method prescribed | regulated to JISB7502, ie, the value measured with the outside micrometer at the time of 5N load.

  The separator of the present invention has a cellulose base material mainly composed of a predetermined solvent-spun cellulose fiber and a coating layer containing an inorganic filler provided on at least one surface of the cellulose base material. Examples of inorganic fillers include calcium carbonate, sodium carbonate, alumina, gibbsite, boehmite, magnesium oxide, magnesium hydroxide, silica, titanium oxide, barium titanate, zirconium oxide, and other inorganic oxides, inorganic hydroxides, aluminum nitride, and nitride. Examples thereof include inorganic nitrides such as silicon, aluminum compounds, zeolites, and mica. Among these, alumina, boehmite, magnesium oxide, and magnesium hydroxide are preferable. The shape of the inorganic filler may be any of a spherical shape, a substantially spherical shape, a plate shape, a rectangular parallelepiped shape, a star shape, a scale shape, and an indefinite shape.

  The average particle size of the inorganic filler is preferably from 0.1 to 3.0 μm, more preferably from 0.3 to 2.5 μm, still more preferably from 0.5 to 2.0 μm. If it is less than 0.1 μm, the inorganic filler tends to penetrate into the cellulose substrate, and it becomes difficult to form a uniform coating layer on the substrate surface, which may cause a short circuit. If it exceeds 3.0 μm, it may be difficult to reduce the thickness of the separator or ESR may be increased.

  The average particle diameter in the present invention is a volume average particle diameter (D50) obtained from a particle size distribution measurement by a laser diffraction method.

  In the present invention, in addition to the inorganic filler, the coating layer containing the inorganic filler contains an inorganic or organic binder that is electrochemically stable and stable with respect to the electrolytic solution and can adhere the inorganic filler to the cellulose substrate. Is preferred.

  Examples of the organic binder include polyvinylidene fluoride (PVdF) and derivatives thereof, meta-type or para-type aromatic polyamide resins, polyimide resins such as aromatic polyimide, polysulfone resins, and ethylene-vinyl acetate copolymers (particularly, Copolymer of 20 to 35 mol% vinyl acetate), ethylene-acrylate copolymer, fluorine resin, styrene butadiene rubber (SBR) resin, carboxymethyl cellulose, hydroxyethyl cellulose, polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, polyurethane Examples thereof include, but are not limited to, resins and epoxy resins. Moreover, these binders may be used individually by 1 type, and may use 2 or more types together.

  As the inorganic binder, for example, generally called a silane coupling agent, a 3-glycidyloxytrimethoxysilane, methacryloyloxypropyltrimethylsilane, which chemically bonds an inorganic oxide and an organic compound through a dehydration or dealcoholization reaction or the like. A mixture of a silicon compound having an organic functional group such as methoxysilane or 3-aminopropyltriethoxysilane and an inorganic oxide sol such as silica or zirconium oxide is preferable because of excellent adhesion strength and heat resistance. Is not limited to this.

  In this invention, 85-99 mass% is preferable, as for content of the inorganic filler in the coating layer containing an inorganic filler, 87-99 mass% is more preferable, and 90-99 mass% is further more preferable. If it exceeds 99% by mass, the strength of the coating layer containing the inorganic filler may be weakened, and if it is less than 85% by mass, the internal resistance may be increased.

  In this invention, the coating layer containing an inorganic filler is obtained by the method of applying the coating liquid containing an inorganic filler to a cellulose base material.

  The medium for preparing the coating liquid containing the inorganic filler is not particularly limited as long as it can uniformly dissolve or disperse the binder and the inorganic filler. For example, aromatic hydrocarbons such as toluene, ethers such as tetrahydrofuran, etc. , Ketones such as methyl ethyl ketone, alcohols such as isopropanol, N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide, dimethyl sulfoxide, water and the like as necessary Can be used. Moreover, you may mix and use these media as needed.

  As a method of coating a coating liquid containing an inorganic filler on a cellulose substrate, for example, various coating methods such as blade, rod, reverse roll, lip, die, curtain, air knife, flexo, screen, offset, gravure, Various printing methods such as inkjet, transfer methods such as roll transfer and film transfer, pulling methods such as dipping, and the like can be selected and used as necessary. At the time of coating, the cellulose base material and the process paper may be stacked and applied, and the process paper may be peeled off after drying.

The coating amount of the coating layer containing an inorganic filler (bone dry) is preferably from 1.5~14.0g / ^{m 2,} more preferably 3.0~13.0g / ^{m 2,} 5.0~12.0g / M ² is more preferable. Exceeds 14.0 g / ^{m 2,} there is a case where the thickness of the separator is increased, is less than 1.5 g / ^{m 2,} there is a case where short circuit occurs.

The basis weight of the separator for a solid electrolytic capacitor of the present invention is preferably 8.0~31.0g / ^{m 2,} more preferably ^{10.0~29.0g / m 2, 13.0~27.0g / m} 2 Is more preferable. Exceeds 31.0 g / ^{m 2,} may ESR increases, is less than 8.0 g / ^{m 2,} and if the short circuit is likely to occur, it may be obtained sufficient strength is difficult .

  The thickness of the separator for a solid electrolytic capacitor of the present invention is preferably 11 to 40 μm, more preferably 11 to 35 μm, and still more preferably 11 to 30 μm. If it exceeds 40 μm, the thickness of the separator becomes too thick and ESR may be increased. If it is less than 11 μm, short-circuiting is likely to occur or sufficient strength may be difficult to obtain. .

  EXAMPLES Hereinafter, although an Example demonstrates this invention in more detail, this invention is not limited to an Example.

  Table 1 shows the modified freeness, length-weighted average fiber length, and Canadian standard freeness of the solvent-spun cellulose fibers F1 to F5, f1, and f2 used in Examples and Comparative Examples. The Canadian standard freeness was measured in accordance with JIS P8121. Moreover, the length weighted average fiber length and Canadian standard freeness of the Manila hemp pulp P1 used by the comparative example were shown. F1 to F5, f1, and f2 were produced using solvent-spun cellulose fibers (fineness: 1.7 dtex, fiber length: 4 mm, manufactured by Coatles Co., Ltd.), beating using a double disc refiner, and changing the beating time. P1 was also produced by beating using a double disc refiner.

  Table 2 shows the papermaking slurries used in Examples and Comparative Examples. The “mixing ratio” symbol in Table 2 corresponds to the “symbol” in Table 1.

<Cellulose base materials 1 to 5, 7>
Slurries 1 to 5 and 7 were prepared using a pulper, fed to a long paper machine to make paper, and dried with a 150 ° C. Yankee dryer. After papermaking, the thickness was adjusted by calendar treatment to prepare cellulose substrates 1 to 5 and 7.

<Cellulose base material 6>
A paper strength enhancer (trade name: Polystron (registered trademark) 1250, manufactured by Arakawa Chemical Co., Ltd.) is added to the slurry 6 at 2% by mass with respect to the solvent-spun cellulose fiber, and the mixture is stirred for a predetermined time and fed to the Nagaami paper machine The paper was made and dried with a Yankee dryer at 150 ° C. After papermaking, the thickness was adjusted by calendering to prepare a cellulose substrate 6.

<Cellulose base material 8>
Slurry 8 was prepared using a pulper, and the paper was made by feeding it to a long paper machine. However, many fibers were taken on the paper web, and the transfer of the wet paper to the felt became unstable and stable. Could not make paper.

<Cellulose base material 9>
A paper strength enhancer (trade name: Polystron (registered trademark) 1250, manufactured by Arakawa Chemical Co., Ltd.) was added to slurry 9 by 2% by mass with respect to Manila hemp pulp, stirred for a predetermined time, and fed to a long paper machine. Paper was made and dried with a Yankee dryer at 150 ° C. After papermaking, the thickness was adjusted by calendering to prepare a cellulose substrate 9.

<Preparation of coating liquid a1>
To 100 parts by weight of boehmite having an average particle size of 0.5 μm dispersed in 150 parts by weight of water, 75 parts by weight of a 2% by weight aqueous solution of carboxymethylcellulose sodium salt having a viscosity of 200 mPa · s at 25 ° C. Add and stir and mix, add and stir and mix 10 parts of a carboxy-modified styrene-butadiene copolymer resin emulsion (solid content concentration 50 mass%) with a glass transition point of -18 ° C. and a volume average particle size of 0.2 μm, and finally adjust Water was added to adjust the solid content concentration to 25% by mass to prepare a coating liquid a1.

<Preparation of coating liquid a2>
100 mass parts of magnesium hydroxide having an average particle size of 1.0 μm dispersed in 150 mass parts of water, 75 mass of a 2 mass% aqueous solution of carboxymethyl cellulose having a viscosity of 200 mPa · s of a 1 mass% aqueous solution at 25 ° C. Parts are added and stirred, and 10 parts by weight of a carboxy-modified styrene-butadiene copolymer resin emulsion (solid content concentration 50% by weight) having a glass transition point of -18 ° C. and a volume average particle size of 0.2 μm is added and stirred. Finally, adjusted water was added to adjust the solid content concentration to 25% by mass to prepare a coating liquid a2.

<Separator for solid electrolytic capacitor>
Example 1
After the cellulose base material 1 and the process paper are overlaid, the coating liquid a1 is coated and dried on the cellulose base material 1 with a die coater so that the coating amount (absolute dryness) is 14.0 g / m ^2. The process paper was peeled off to provide a coating layer, and the solid electrolytic capacitor separator of Example 1 shown in Table 4 was obtained.

(Example 2)
After the cellulose substrate 2 and the process paper are overlaid and the coating liquid a1 is coated and dried on the cellulose substrate 2 with a die coater so that the coating amount (absolutely dry) is 12.0 g / m ^2. The process paper was peeled off to provide a coating layer, and a solid electrolytic capacitor separator of Example 2 shown in Table 4 was obtained.

(Example 3)
After the cellulose base material 3 and the process paper are stacked, the coating liquid a1 is coated and dried on the cellulose base material 3 with a die coater so that the coating amount (absolutely dry) is 7.5 g / m ^2. The process paper was peeled off to provide a coating layer to obtain a solid electrolytic capacitor separator of Example 3 shown in Table 4.

Example 4
After the cellulose base material 4 and the process paper are stacked, the coating liquid a1 is coated and dried on the cellulose base material 4 with a die coater so that the coating amount (absolutely dry) is 3.0 g / m ^2. The process paper was peeled off to provide a coating layer to obtain a solid electrolytic capacitor separator of Example 4 shown in Table 4.

(Example 5)
After the cellulose base material 5 and the process paper are stacked, the coating liquid a1 is coated and dried on the cellulose base material 5 with a die coater so that the coating amount (absolutely dry) is 1.5 g / m ^2. The process paper was peeled off to provide a coating layer, and a solid electrolytic capacitor separator of Example 5 shown in Table 4 was obtained.

(Example 6)
After the cellulose substrate 6 and the process paper are overlaid, the coating liquid a2 is coated and dried on the cellulose substrate 6 with a die coater so that the coating amount (absolutely dry) is 6.9 g / m ^2. The process paper was peeled off to provide a coating layer, and a solid electrolytic capacitor separator of Example 6 shown in Table 4 was obtained.

(Example 7)
After the cellulose base material 3 and the process paper are overlaid and the coating liquid a2 is coated and dried on the cellulose base material 3 with a die coater so that the coating amount (absolutely dry) is 3.5 g / m ^2. The process paper was peeled off to provide a coating layer. Then, it overlaps with process paper so that the uncoated surface of the cellulose base material 3 may become an outer side, and the coating amount (absolute dryness) is 3 with a die coater on the uncoated surface of the cellulose base material 3. After coating and drying so as to be 0.5 g / m ² , the process paper was peeled off to provide a coating layer, and a solid electrolytic capacitor separator of Example 7 shown in Table 4 was obtained.

(Comparative Example 1)
After the cellulose base material 7 and the process paper are overlaid, the coating liquid a1 is coated and dried on the cellulose base material 7 with a die coater so that the coating amount (absolute dryness) is 10.0 g / m ^2. The process paper was peeled off to provide a coating layer, and a solid electrolytic capacitor separator of Comparative Example 1 shown in Table 4 was obtained.

(Comparative Example 2)
Since the cellulose base material 8 could not be produced, the solid electrolytic capacitor separator of Comparative Example 2 could not be produced.

(Comparative Example 3)
After the cellulose base material 9 and the process paper are stacked, the coating liquid a2 is coated and dried on the cellulose base material 9 with a die coater so that the coating amount (absolutely dry) is 6.9 g / m ^2. The process paper was peeled off to provide a coating layer, and a solid electrolytic capacitor separator of Comparative Example 3 shown in Table 4 was obtained.

(Comparative Example 4)
Slurry 10 was prepared using a pulper, fed to a long paper machine, paper-made, and dried with a Yankee dryer at 150 ° C. After paper making, calendar treatment was performed to adjust the thickness, and a solid electrolytic capacitor separator of Comparative Example 4 was produced.

<Production of solid electrolytic capacitor>
An aluminum foil with a dielectric film formed after etching the surface was roughened for the anode, and an aluminum foil without a dielectric film was used for the cathode. A solid electrolytic capacitor separator is placed between the anode and the cathode, wound using the anode, cathode, and solid electrolyte capacitor separators of the examples and comparative examples slitted to a predetermined width in advance. A rotating element was produced. At this time, in the case of a separator in which a coating layer containing an inorganic filler layer was provided on one side of the cellulose base material, the coating layer side was the cathode side. After heating the winding element of the solid electrolytic capacitor at 230 ° C. for 2 hours to carbonize the separator, the element was subjected to 3,4-ethylenedioxythiophene: iron (III) p-toluenesulfonate: n-butyl alcohol = It was immersed in a solution mixed at a mass ratio of 34:33:33 and heat-treated at 200 ° C. for 5 minutes to polymerize polythiophene to obtain a solid electrolytic capacitor element. Next, the solid electrolytic capacitor element was housed in a cylindrical case to produce solid electrolytic capacitors of Examples and Comparative Examples.

  The separators for solid electrolytic capacitors of Examples and Comparative Examples and solid electrolytic capacitors using the same were evaluated as follows, and the results are shown in Table 4.

[Short defect rate]
The presence or absence of conduction of the solid electrolytic capacitors of Examples and Comparative Examples was confirmed with a tester. 10 solid electrolytic capacitors were tested. If the number of conducting capacitors was 0, “◯” was indicated, 1 was indicated by “Δ”, and 2 or more were indicated by “X”.

[ESR]
The ESR of the solid electrolytic capacitors of Examples and Comparative Examples was measured using an LCR meter under the conditions of 20 ° C. and 100 kHz, and 10 average values were obtained. The ESR is represented by “◯” when it is less than 27 mΩ, “Δ” when it is 27 mΩ or more and less than 30 mΩ, and “X” when it is 30 mΩ or more.

  As shown in Table 4, the separators for solid electrolytic capacitors produced in Examples 1 to 7 have a modified drainage of 75 to 250 ml and a length weighted average fiber length of 0.80 to 1.80 mm. Because it has a cellulose substrate mainly composed of a certain solvent-spun cellulose fiber and a coating layer containing an inorganic filler provided on at least one surface of the cellulose substrate, the short-circuit defect rate is low, and the ESR is low. A solid electrolytic capacitor was obtained.

  On the other hand, the separator for a solid electrolytic capacitor produced in Comparative Example 1 has a modified drainage of solvent-spun cellulose fiber, which is the main component of the cellulose substrate, of more than 250 ml, and a length-weighted average fiber length of more than 1.80 mm. Therefore, the cellulose base material was unevenly formed, and the coating layer containing the inorganic filler was not uniformly formed on the surface of the base material, so that the short-circuit defect rate was increased.

  In Comparative Example 2, since the modified freeness of the solvent-spun cellulose fiber was less than 75 ml and the length-weighted average fiber length was less than 0.80 mm, many fibers were taken into the papermaking network, and the felt of wet paper As a result, transfer to the paper became unstable, paper could not be stably produced, and the cellulose substrate 8 could not be produced.

  In Comparative Example 3, since the predetermined solvent-spun cellulose fiber was not included, the cellulose base material was unevenly formed, and the layer containing the inorganic filler was not uniform, so the short defect rate was high. In addition, the gaps in the separator were easily closed, and the ESR was high.

  The solid electrolytic capacitor separator produced in Comparative Example 4 had a high short-circuit defect rate because there was no coating layer containing an inorganic filler.

  Since the separator for solid electrolytic capacitors produced in Example 1 had a slightly higher basis weight and a slightly thicker thickness, the ESR was slightly higher than the separators of Examples 2-7.

  The solid electrolytic capacitor separator produced in Example 5 had a slightly lower basis weight and a slightly thinner thickness, so that the short-circuit defect rate was slightly higher than those of Examples 1-4, 6, and 7.

  As an application example of the present invention, a solid electrolytic capacitor separator is suitable.

Claims (2)

A cellulose substrate mainly composed of solvent-spun cellulose fibers having a modified freeness of 75 to 250 ml and a length-weighted average fiber length of 0.80 to 1.80 mm as defined below; The separator for solid electrolytic capacitors which has a coating layer containing the inorganic filler provided in the at least one surface of the material.
Modified freeness: Freeness measured in accordance with JIS P8121, except that an 80-mesh wire mesh having a wire diameter of 0.14 mm and an aperture of 0.18 mm was used as the sieve plate, and the sample concentration was 0.1%.   A solid electrolytic capacitor using the separator for a solid electrolytic capacitor according to claim 1.