JP2015060868A - Method of manufacturing separator for capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a separator for a capacitor capable of reducing the fault occurrence ratio and the internal short circuit occurrence ratio during manufacturing of the capacitor by improving surface strength of the separator in the method of manufacturing the separator for the capacitor by a wet papermaking method.SOLUTION: In a method of manufacturing a separator for a capacitor by a wet papermaking method, nonwoven fabric in a wet state made of two or more nonwoven fabric layers containing a fibrillated spinning cellulose fiber and a synthetic short fiber as an essential component is dried by a drying device formed by combining a Yankee dryer and a hot air hood, and percentage content of the synthetic short fiber in the nonwoven fabric layer in contact with the Yankee dryer is lower than that in the outermost layer not in contact with the Yankee dryer.

Description

  The present invention relates to a method for manufacturing a capacitor separator.

  A capacitor, which is a kind of electrochemical element, has a large electric capacity and has high stability against repeated charge and discharge, and is therefore widely used in applications such as a power supply used in vehicles and electrical equipment. Conventionally, as a capacitor separator (hereinafter, sometimes referred to as “separator”), a paper separator mainly composed of a beaten product of solvent-spun cellulose fiber or regenerated cellulose fiber has been used (for example, Patent Document 1). To 3). In order to follow the recent reduction in size and weight of electronic components, capacitors are also becoming smaller and lighter, and thin film separators are required. However, in the conventional paper separator, if the thickness is reduced, pinholes are easily formed, so that an internal short circuit is likely to occur, the strength is reduced, and handling is inconvenient. Therefore, a separator using a combination of fibrillated solvent-spun cellulose fibers and synthetic short fibers has been proposed (see, for example, Patent Document 3). A separator composed of two or more nonwoven layers is also described. However, a combination of fibrillated solvent-spun cellulose fibers and synthetic short fibers is used to form two or more layers of nonwoven fabric wetted by a wet papermaking method, and dried with a drying device consisting of a Yankee dryer and a hot air hood to produce a nonwoven fabric. In this case, the surface of the non-woven fabric is disturbed due to poor peeling at the contact surface between the Yankee dryer and the non-woven fabric, and the surface strength is likely to decrease. There was a problem that the defect occurrence rate and the internal short-circuit occurrence rate increased.

JP-A-5-267103 JP-A-11-168033 JP 2000-3834 A

  An object of the present invention is a method for producing a separator for a capacitor comprising two or more nonwoven fabric layers containing a fibrillated solvent-spun cellulose fiber and a synthetic short fiber, which improves the surface strength of the separator, An object of the present invention is to provide a method of manufacturing a capacitor separator having a low defect occurrence rate and an internal short-circuit occurrence rate.

  As a result of intensive studies to solve the above problems, the following means have been found and the present invention has been achieved.

  In a method for producing a capacitor separator by a wet papermaking method, a wet nonwoven fabric composed of two or more nonwoven fabric layers containing fibrillated solvent-spun cellulose fibers and synthetic short fibers as essential components, a Yankee dryer and a hot air hood A method for producing a capacitor separator, characterized in that the content of the synthetic short fibers in the non-woven fabric layer that is dried with a combined drying device and is in contact with the Yankee dryer is lower than the outermost layer that is not in contact with the Yankee dryer.

  According to the present invention, in a method for producing a capacitor separator by a wet papermaking method, a wet nonwoven fabric composed of two or more nonwoven fabric layers containing fibrillated solvent-spun cellulose fibers and synthetic short fibers as essential components, Nonwoven fabric that comes in contact with the Yankee dryer because the content of the synthetic short fibers in the nonwoven fabric layer that is dried with a drying device that combines the Yankee dryer and hot air hood and is in contact with the Yankee dryer is lower than the outermost layer that does not contact the Yankee dryer. The bond strength of hydrogenated fibrillated solvent-spun cellulose fibers in the layer is increased and the surface strength is improved, so that fluffing during peeling from the Yankee dryer can be reduced and scratch resistance can be improved. Suppresses fuzz during transportation during capacitor manufacturing, and the rate of defects is low. It is possible to obtain a low separator for capacitors of parts shorted incidence.

It is a figure which shows the process of winding, after drying the nonwoven fabric of a wet state with the drying apparatus which combined the Yankee dryer and the hot air hood.

  The solvent-spun cellulose fiber means a cellulose fiber obtained by dissolving and spinning directly in an organic solvent without passing through a cellulose derivative. In the present invention, solvent-spun cellulose fibers fibrillated by beating treatment are used. In the present invention, the beating degree of solvent-spun cellulose fiber is expressed by modified freeness.

  The modified freeness is a value measured in accordance with JIS P8121, except that an 80 mesh wire net 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 mass%. That is.

  The fibrillated solvent-spun cellulose fiber preferably has a modified freeness of 0 to 400 ml. The modified drainage degree of the fibrillated solvent-spun cellulose fiber is more preferably 0 to 300 ml, and further preferably 0 to 250 ml. If the modified drainage is more than 400 ml, the capacitor separator may be insufficiently dense and the internal short circuit defect rate may be increased.

  In order to obtain fibrillated solvent-spun cellulose fibers, solvent-spun cellulose short fibers are dispersed in water at an appropriate concentration, and this is subjected to shear force by a refiner, beater, mill, milling device, and high-speed rotary blade. Rotating blade type homogenizer, double cylindrical high speed homogenizer that generates shearing force between a cylindrical inner blade that rotates at high speed and a fixed outer blade, ultrasonic crusher that is refined by ultrasonic impact, high pressure It may be beaten by adjusting the conditions such as the shape of the blade, the flow rate, the number of treatments, the treatment speed, and the treatment concentration through a homogenizer.

  The length-weighted average fiber length of the fibrillated solvent-spun cellulose fiber is preferably 0.2 to 2.0 mm, more preferably 0.4 to 1.8 mm, and even more preferably 0.5 to 1.5 mm. When the length-weighted average fiber length is shorter than 0.2 mm, there are cases where the ratio of falling out of the screen and outflowing into the drainage during wet papermaking increases, or fluffing may occur due to rubbing. The fibers may be twisted and become lumps.

  In the present invention, the length-weighted average fiber length of the fibrillated solvent-spun cellulose fiber is determined by the JAPAN TAPPI paper pulp test method no. According to No. 52 “Paper and Pulp Fiber Length Test Method (Optical Automatic Measurement Method)”, measurement was performed using Kajaani Fiber Lab V3.5 (manufactured by Metso Automation).

  In Kajaani Fiber Lab V3.5 (manufactured by Metso Automation), for each fiber passing through the detection unit, the total true length (L) of the bent fiber and the shortest length (l) of both ends of the bent fiber are determined. Can be measured. The “length-weighted average fiber length” is an average fiber length obtained by measuring and calculating the shortest length (l) of both ends of the bent fiber.

  In the present invention, the capacitor separator preferably contains synthetic short fibers and fibrillated solvent-spun cellulose as essential components, and the entire nonwoven fabric layer contains 60 to 90% by mass of fibrillated solvent-spun cellulose fibers. . The content of the fibrillated solvent-spun cellulose fiber in the nonwoven fabric layer that comes into contact with the Yankee dryer is preferably 70 to 95% by mass, and more preferably 80 to 95% by mass. On the other hand, the content of the fibrillated solvent-spun cellulose in the outermost layer not in contact with the Yankee dryer is preferably 50 to 85% by mass, and more preferably 65 to 80% by mass. If the content of fibrillated solvent-spun cellulose fibers in the whole nonwoven fabric is less than 60% by mass, the separator may be insufficiently dense and the internal short-circuit defect rate may be high. May become weak and papermaking properties may deteriorate.

  As synthetic short fibers in the present invention, polyolefin, polyester, acrylic, wholly aromatic polyester, wholly aromatic polyester amide, aliphatic polyamide, semi-aromatic polyamide, wholly aromatic polyamide, wholly aromatic polyether, wholly aromatic polycarbonate, Polyimide, polyamideimide (PAI), polyetheretherketone (PEEK), polyphenylene sulfide (PPS), poly-p-phenylenebenzobisoxazole (PBO), polybenzimidazole (PBI), polytetrafluoroethylene (PTFE), ethylene -A single fiber or a composite fiber made of a resin such as a vinyl alcohol copolymer, or a fibrillated product thereof may be contained alone or in a combination of two or more. Moreover, you may contain what divided | segmented various split type composite fibers. Among these, polyolefin, polyester, acrylic, wholly aromatic polyester, wholly aromatic polyester amide, aliphatic polyamide, semi-aromatic polyamide, and wholly aromatic polyamide are preferable, and polyester and acrylic are more preferable.

  The average fiber diameter of the synthetic short fiber in the present invention is preferably from 0.1 to 20 μm, more preferably from 0.1 to 15 μm, further preferably from 0.1 to 10 μm. If the average fiber diameter is less than 0.1 μm, the fibers may be too thin and fall off from the separator. If the average fiber diameter is greater than 20 μm, it may be difficult to reduce the thickness of the separator.

  The average fiber diameter in the present invention is an average value of 100 fibers randomly selected by measuring the fiber diameter of fibers forming the separator from a scanning electron micrograph of the separator.

  1-15 mm is preferable, as for the fiber length of the synthetic short fiber in this invention, 2-10 mm is more preferable, and 3-5 mm is further more preferable. If the fiber length is shorter than 1 mm, it may fall off from the separator, and if it is longer than 15 mm, the fiber may be tangled and become lumpy, resulting in uneven thickness.

  In the present invention, the capacitor separator contains fibrillated solvent-spun cellulose and synthetic short fibers as essential components, and preferably contains 10 to 40% by mass of synthetic short fibers in the whole nonwoven fabric layer. The content of the synthetic short fibers in the nonwoven fabric layer in contact with the Yankee dryer is preferably 3 to 30% by mass, and more preferably 5 to 20% by mass. On the other hand, the content of the synthetic short fibers in the outermost layer not in contact with the Yankee dryer is preferably 10 to 40% by mass, and more preferably 20 to 30% by mass. If the content of the synthetic short fibers in the whole nonwoven fabric is less than 10% by mass, the strength of the wet paper may be weakened and the papermaking property may be deteriorated. If the content is more than 40% by mass, the denseness is insufficient and the internal short circuit failure rate. May be higher.

  In the present invention, the capacitor separator may contain fibers other than fibrillated solvent-spun cellulose and synthetic short fibers. Examples thereof include natural cellulose fibers, pulped and fibrillated natural cellulose fibers, solvent-spun cellulose short fibers, and inorganic fibers. The modified freeness of natural cellulose pulp or fibrillation is preferably 0 to 400 ml. Examples of the inorganic fiber include glass fiber, alumina fiber, silica fiber, alumina / silica fiber, zirconia fiber, rock wool and the like.

The basis weight of the separator for the capacitor in the present invention is preferably 5.0~25.0g / ^{m 2,} more preferably ^{7.0~20.0g / m 2, 7.0~18.0g / m} 2 and more preferable. If it is less than 5.0 g / m ² , sufficient mechanical strength may not be obtained, or the insulation between the positive electrode and the negative electrode may be insufficient and the internal short-circuit failure rate may increase. m and greater than ^2, there is a case where thinning of the separator for the capacitor becomes difficult.

  The thickness of the capacitor separator in the present invention is preferably 10.0 to 50.0 μm, more preferably 12.0 to 45.0 μm, and further preferably 15.0 to 40.0 μm. If the thickness is less than 10.0 μm, sufficient mechanical strength may not be obtained, or the insulation between the positive electrode and the negative electrode may be insufficient and the internal short circuit defect rate may be increased. If it is thicker than 50.0 μm, it may be difficult to reduce the thickness of the capacitor separator.

  In the manufacturing method of the capacitor separator of the present invention, a wet papermaking method using a combination papermaking machine formed by combining the same type or different types of papermaking nets in a circular net, a long net, a short net, and an inclined short net. A separator can be produced by combining two or more non-woven fabric layers and drying the non-woven fabric in a wet state by a drying device combining a Yankee dryer and a hot air hood. In addition to the fiber raw material, if necessary, a dispersing agent, a thickener, an inorganic filler, an organic filler, an antifoaming agent, and the like are added to the papermaking slurry, and the solid content is about 5 to 0.001% by mass. A papermaking slurry is prepared to a concentration. The papermaking slurry is further diluted to a predetermined concentration to perform wet papermaking. The capacitor separator obtained by the wet papermaking method is subjected to calendering, thermal calendering, heat treatment and the like, if necessary.

  The capacitor in the present invention means an electric double layer capacitor, a lithium ion capacitor, a hybrid capacitor, or a redox capacitor. In the electric double layer capacitor, an electric double layer is formed at the interface between the electrode and the electrolytic solution to store electricity. As the electrode active material, carbon materials such as activated carbon, carbon black, carbon aerogel, carbon nanotube, and non-porous carbon are mainly used. As an electrolytic solution, an aqueous solution in which an ion dissociable salt is dissolved, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, acetonitrile, γ-butyrolactone, dimethylformamide, tetrahydrofuran, dimethoxyethane, dimethoxymethane, sulfolane, dimethyl sulfoxide, Examples include, but are not limited to, those obtained by dissolving an ion dissociable salt in an organic solvent such as ethylene glycol, propylene glycol, methyl cellosolve, and mixed solvents thereof, and ionic liquids (solid molten salts). is not.

In the lithium ion capacitor, the negative electrode active material is a material capable of reversibly supporting lithium ions, and the positive electrode active material is a material capable of reversibly supporting lithium ions and / or anions. This is a capacitor in which lithium ions are supported. Examples of the negative electrode active material include graphite, non-graphitizable carbon, polyacene organic semiconductor, lithium titanate, and the like. Examples of the positive electrode active material include conductive polymers such as polypyrrole, polythiophene, polyaniline, and polyacetylene, activated carbon, and polyacene organic semiconductor. As the electrolytic solution, an aprotic organic solvent of a lithium salt is used. Examples of the lithium salt include LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiPF ₆ , and Li (C ₂ F ₅ SO ₂ ) N. Examples of the aprotic organic solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, acetonitrile, γ-butyrolactone, dimethylformamide, tetrahydrofuran, dimethoxyethane, dimethoxymethane, sulfolane, dimethyl sulfoxide, ethylene glycol, propylene glycol, and methyl. Cellsolve and mixed solvents thereof may be mentioned.

A hybrid capacitor is a capacitor in which the reaction mechanism or electrode material of the positive electrode and the negative electrode are different. For example, the negative electrode is an oxidation-reduction reaction, and the positive electrode is an electric double layer reaction. Examples of the negative electrode active material of the hybrid capacitor include activated carbon, graphite, hard carbon, polyacene, metal oxides such as Li ₄ Ti ₅ O ₁₂ , and n-type conductive polymers. Examples of the positive electrode active material include activated carbon, MnO ₂ , LiCoO ₂ , metal oxides such as ruthenium oxide, graphite, and a p-type conductive polymer.

A redox capacitor has a storage and discharge mechanism that uses all or part of oxidation / reduction of an electrode active material, adsorption / desorption of ions on the electrode surface, and charge / discharge in an electric double layer. Examples of electrode active materials for redox capacitors include metal oxides such as ruthenium oxide, iridium oxide, titanium oxide, zirconium oxide, nickel oxide, vanadium oxide, tungsten oxide, manganese oxide, and cobalt oxide, and composites of these metal oxides. Hydrates of these metal oxides, composites of these metal oxides and carbon materials, molybdenum nitride, composites of molybdenum nitride and metal oxides, graphite or Li ₄ Ti ₅ O capable of intercalating lithium ions ₁₂ , lithium metal oxides such as LiFePO ₄ , polypyrrole, polyaniline, polythiophene, polyacene, derivatives thereof, polyfluorene derivatives, polyquinoxaline derivatives, polyindoles, cyclic indole polymers, 1,5-diaminoanthraquinone, 1,4- Benzoki Non-, graphite and a complex of these quinone compounds, and metal complex polymers are exemplified. As an electrolytic solution, an aqueous solution in which an ion dissociable salt is dissolved, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, acetonitrile, γ-butyrolactone, dimethylformamide, tetrahydrofuran, dimethoxyethane, dimethoxymethane, sulfolane, dimethyl sulfoxide, Examples include, but are not limited to, those obtained by dissolving an ion dissociable salt in an organic solvent such as ethylene glycol, propylene glycol, methyl cellosolve, and mixed solvents thereof, and ionic liquids (solid molten salts). is not.

  The present invention will be described in more detail with reference to FIG. 1, but the present invention is not limited to the following examples.

<Fiber A1>
Using a refiner, a solvent-spun cellulose short fiber having an average fiber diameter of 12 μm and a fiber length of 4 mm is beaten to produce a fibrillated solvent-spun cellulose fiber having an average fiber length of 0.45 mm and a modified freeness of 0 ml. A1.

<Fiber A2>
Using a refiner, a solvent-spun cellulose short fiber having an average fiber diameter of 12 μm and a fiber length of 4 mm is beaten to produce a fibrillated solvent-spun cellulose fiber having an average fiber length of 0.75 mm and a modified freeness of 240 ml. A2.

<Fiber A3>
Using a refiner, a solvent-spun cellulose short fiber having an average fiber diameter of 12 μm and a fiber length of 4 mm is beaten to produce a fibrillated solvent-spun cellulose fiber having an average fiber length of 0.85 mm and a modified freeness of 280 ml. A3.

<Fiber A4>
Using a refiner, a solvent-spun cellulose short fiber having an average fiber diameter of 12 μm and a fiber length of 4 mm was beaten, and a fibrillated solvent-spun cellulose fiber having an average fiber length of 1.15 mm and a modified freeness of 380 ml was designated as fiber A4. .

<Fiber A5>
Using a refiner, solvent-spun cellulose short fibers having an average fiber diameter of 12 μm and a fiber length of 4 mm were beaten, and the fibrillated solvent-spun cellulose fibers having an average fiber length of 1.45 mm and a modified freeness of 450 ml were designated as fiber A5. .

<Synthetic short fiber B1>
Polyethylene terephthalate fiber having an average fiber diameter of 3 μm and a fiber length of 3 mm was designated as synthetic short fiber B1.

<Synthetic short fiber B2>
An acrylic fiber having an average fiber diameter of 4 μm and a fiber length of 3 mm was designated as synthetic short fiber B2.

<Synthetic short fiber B3>
An aliphatic polyamide fiber having an average fiber diameter of 7 μm and a fiber length of 5 mm was designated as synthetic short fiber B3.

<Microfibrillated natural cellulose fiber C1>
The linter was treated using a high-pressure homogenizer to produce microfibrillated natural cellulose fiber C1 having a modified freeness of 0 ml.

  A papermaking slurry was prepared according to the raw materials and blending amounts shown in Table 1.

<Separator>
Example 1
A slant / circular net combination paper machine is prepared by preparing slurry S1 containing 90 parts by mass of fiber A1, 10 parts by mass of synthetic short fiber B1, and slurry S2 containing 75 parts by mass of fiber A1 and 25 parts by mass of synthetic short fiber B1. The slurry S1 is set on the inclined side, the slurry S2 is set on the circular mesh side, the basis weight ratio between the inclined side and the circular mesh side is set to 50:50, and a wet nonwoven fabric 3 composed of two nonwoven fabric layers is formed. As shown in FIG. 1, the nonwoven fabric 4 is dried by a drying device combining the Yankee dryer 1 and the hot air hood 2, and the dried nonwoven fabric 4 is wound up through the guide roll 5 and the guide roll 6 to obtain a nonwoven fabric winding-up 7. It was. The temperature of the Yankee dryer 1 and the temperature of the hot air blown by the hot air hood 2 were 110 ° C. In this paper machine, the inclined side of the nonwoven fabric is a nonwoven fabric layer in contact with the Yankee dryer 1, and the circular mesh side is the outermost layer not in contact with the Yankee dryer 1 because the hot air from the hot air hood 2 hits it. The arrow in FIG. 1 has shown the conveyance direction of the nonwoven fabric. A separator was produced by subjecting the nonwoven fabric thus obtained to supercalendering at room temperature.

(Example 2)
A slurry S3 containing 90 parts by mass of fiber A2 and 10 parts by mass of synthetic short fiber B1 and a slurry S4 containing 75 parts by mass of fiber A2 and 25 parts by mass of synthetic short fiber B1 were prepared. A separator was produced in the same manner as in Example 1 except that S4 was on the circular mesh side.

(Example 3)
A slurry S5 containing 90 parts by mass of the fiber A3, 10 parts by mass of the synthetic short fiber B1, and a slurry S6 containing 75 parts by mass of the fiber A3 and 25 parts by mass of the synthetic short fiber B1 are prepared. A separator was produced in the same manner as in Example 1 except that S6 was changed to the circular mesh side.

Example 4
A slurry S7 containing 90 parts by mass of fiber A4, 10 parts by mass of synthetic short fiber B1 and a slurry S8 containing 75 parts by mass of fiber A4 and 25 parts by mass of synthetic short fiber B1 are prepared. A separator was produced in the same manner as in Example 1 except that S8 was on the circular mesh side.

(Example 5)
A slurry S9 containing 90 parts by mass of the fiber A5, 10 parts by mass of the synthetic short fiber B1, and a slurry S10 containing 75 parts by mass of the fiber A5 and 25 parts by mass of the synthetic short fiber B1 were prepared. A separator was produced in the same manner as in Example 1 except that S10 was changed to the circular mesh side.

(Example 6)
85 parts by mass of fiber A2, 10 parts by mass of synthetic short fiber B1, 5 parts by mass of microfibrillated natural cellulose fiber C1, and 70 parts by mass of fiber A2 and 25 parts by mass of synthetic short fiber B1, microfibrils A separator was prepared in the same manner as in Example 1 except that a slurry S12 containing 5 parts by mass of modified natural cellulose fiber C1 was prepared, and that the slurry S11 was inclined and the slurry S12 was circular.

(Example 7)
85 parts by mass of fiber A2, 10 parts by mass of synthetic short fiber B2, 5 parts by mass of microfibrillated natural cellulose fiber C1, and 70 parts by mass of fiber A2 and 25 parts by mass of synthetic short fiber B2, microfibril A separator was prepared in the same manner as in Example 1 except that a slurry S14 containing 5 parts by mass of modified natural cellulose fiber C1 was prepared, and that the slurry S13 was the inclined side and the slurry S14 was the circular mesh side.

(Example 8)
A slurry S15 containing 95 parts by mass of fiber A2 and 5 parts by mass of synthetic short fiber B2 and a slurry S16 containing 70 parts by mass of fiber A2 and 30 parts by mass of synthetic short fiber B2 were prepared. A separator was produced in the same manner as in Example 1 except that S16 was changed to the circular mesh side.

Example 9
A slurry S17 containing 85 parts by mass of fiber A3, 15 parts by mass of synthetic short fiber B3, and a slurry S18 containing 65 parts by mass of fiber A3 and 35 parts by mass of synthetic short fiber B3 are prepared. A separator was produced in the same manner as in Example 1 except that S18 was on the circular mesh side.

(Example 10)
A slurry S19 containing 95 parts by mass of fiber A3 and 5 parts by mass of synthetic short fiber B1, a slurry S20 containing 80 parts by mass of fiber A3 and 20 parts by mass of synthetic short fiber B1, and 70 parts by mass of fiber A3. A slurry S21 containing 30 parts by mass of the short fiber B1 is prepared, and using a slant / circular / circular net combination paper machine, the slurry S19 is slanted to be a non-woven fabric layer in contact with the Yankee dryer 1, and the slurry S20 is intermediate Layered circular mesh side, Slurry S21 is the outermost circular layer side not in contact with the Yankee dryer 1, each basis weight ratio is set to 40:30:30, wet nonwoven fabric composed of three nonwoven fabric layers 3 and dried with a drying device combining the Yankee dryer 1 and the hot air hood 2 as shown in FIG. Wound through the guide rolls 6, to give the winding 7 of the nonwoven fabric. The temperature of the Yankee dryer 1 and the temperature of the hot air blown by the hot air hood 2 were 110 ° C. A separator was produced by subjecting the nonwoven fabric thus obtained to supercalendering at room temperature.

(Example 11)
A slurry S5 containing 90 parts by mass of fiber A3 and 10 parts by mass of synthetic short fiber B1, and a slurry S6 containing 75 parts by mass of fiber A3 and 25 parts by mass of synthetic short fiber B1 were prepared. Using a combination paper machine, slurry S5 is set to the first layer of the circular mesh side, slurry S6 is set to the second layer of the circular mesh side, and the basis weight ratio is set to 50:50. A wet nonwoven fabric 3 is formed, and as shown in FIG. 1, the nonwoven fabric 4 is dried by a drying device combining the Yankee dryer 1 and the hot air hood 2, and the dried nonwoven fabric 4 is wound through the guide roll 5 and the guide roll 6. The nonwoven fabric wound up 7 was obtained. The temperature of the Yankee dryer 1 and the temperature of the hot air blown by the hot air hood 2 were 110 ° C. In this paper machine, the first layer of the circular mesh side is a non-woven fabric layer in contact with the Yankee dryer 1, and the second layer of the circular mesh side is the outermost layer not in contact with the Yankee dryer 1 due to the hot air from the hot air hood 2. A separator was produced by subjecting the obtained nonwoven fabric to a supercalender treatment at room temperature.

(Example 12)
A slurry S15 containing 95 parts by mass of fiber A2 and 5 parts by mass of synthetic short fiber B2 and a slurry S16 containing 70 parts by mass of fiber A2 and 30 parts by mass of synthetic short fiber B2 were prepared. Using a combination paper machine, a separator was produced in the same manner as in Example 11 except that the slurry S15 was on the first-layer side and the slurry S16 was on the second-layer side.

(Example 13)
Slurry S5 containing 90 parts by mass of fiber A3 and 10 parts by mass of synthetic short fiber B1 and slurry S6 containing 75 parts by mass of fiber A3 and 25 parts by mass of synthetic short fiber B1 were prepared. Using a machine, the slurry S5 is the first layer inclined side, the slurry S6 is the second layer inclined side, and the respective basis weight ratios are set to 50:50. As shown in FIG. 1, the nonwoven fabric 3 is formed and dried with a drying device combining the Yankee dryer 1 and the hot air hood 2, and the dried nonwoven fabric 4 is wound up through the guide roll 5 and the guide roll 6, Winding 7 was obtained. The temperature of the Yankee dryer 1 and the temperature of the hot air blown by the hot air hood 2 were 110 ° C. In this paper machine, the inclined side of the first layer is a non-woven fabric layer in contact with the Yankee dryer 1, and the inclined side of the second layer is the outermost layer not in contact with the Yankee dryer 1 due to the hot air of the hot air hood 2 hitting it. A separator was produced by subjecting the nonwoven fabric thus obtained to supercalendering at room temperature.

(Example 14)
Slurry S25 containing 85 parts by mass of fiber A2 and 15 parts by mass of synthetic short fiber B3, and slurry S22 containing 75 parts by mass of fiber A2 and 25 parts by mass of synthetic short fiber B3 were prepared, and a slanted / inclined combination papermaking A separator was prepared in the same manner as in Example 13 except that the slurry S25 was the first layer inclined side and the slurry S22 was the second layer inclined side.

(Example 15)
Slurry S22 containing 75 parts by mass of fiber A2 and 25 parts by mass of synthetic short fiber B3, and slurry S23 containing 60 parts by mass of fiber A2 and 40 parts by mass of synthetic short fiber B3 were prepared, and a slanted / inclined combination papermaking A separator was prepared in the same manner as in Example 13 except that the slurry S22 was the inclined side of the first layer and the slurry S23 was the inclined side of the second layer.

(Example 16)
Slurry S24 containing 97 parts by mass of fiber A2 and 3 parts by mass of synthetic short fiber B3, and slurry S25 containing 85 parts by mass of fiber A2 and 15 parts by mass of synthetic short fiber B3 were prepared, and a slanted / inclined combination papermaking A separator was produced in the same manner as in Example 13 except that the slurry S24 was the first layer inclined side and the slurry S25 was the second layer inclined side.

(Comparative Example 1)
A slurry S26 containing 70 parts by mass of fiber A3, 30 parts by mass of synthetic short fiber B3, and a slurry S17 containing 85 parts by mass of fiber A3 and 15 parts by mass of synthetic short fiber B3 are prepared. A separator was produced in the same manner as in Example 1 except that S17 was on the circular mesh side.

(Comparative Example 2)
A slurry S18 containing 65 parts by mass of fiber A3, 35 parts by mass of synthetic short fiber B3 and a slurry S27 containing 80 parts by mass of fiber A3 and 20 parts by mass of synthetic short fiber B3 are prepared, and slurry S18 is the first layer. A separator was produced in the same manner as in Example 13, except that the slant side of the slurry S27 was changed to the slant side of the second layer.

(Comparative Example 3)
A slurry S28 containing 60 parts by mass of the fiber A3 and 40 parts by mass of the synthetic short fiber B3 was prepared, except that both the first layer and the second layer were the same slurry S28. A separator was produced in the same manner as in Example 11.

(Comparative Example 4)
A slurry S28 containing 60 parts by mass of fiber A3 and 40 parts by mass of synthetic short fiber B3 is prepared, and a wet single-layer nonwoven fabric 3 is formed using a circular net paper machine, as shown in FIG. The non-woven fabric 4 was dried by a drying device combining the Yankee dryer 1 and the hot-air hood 2, and the dried non-woven fabric 4 was wound through the guide roll 5 and the guide roll 6 to obtain a non-woven fabric winding 7. The temperature of the Yankee dryer 1 and the temperature of the hot air blown by the hot air hood 2 were 110 ° C. A separator was produced by subjecting the nonwoven fabric thus obtained to supercalendering at room temperature.

[Separator basis weight]
The basis weight of the separator was measured according to JIS P 8124, and the results are shown in Table 2.

[Separator thickness]
The thickness of the separator was measured according to JIS P 8118, and the results are shown in Table 2.

[Surface strength of separator]
The surface strength of the separator was evaluated by fiber dropping and fluffing by an abrasion test. For each separator, 10 sheet samples each having a width of 25 mm and a length of 250 mm were prepared. Next, the produced sheet sample is set in a Gakushin friction fastness tester (trade name: AB-301, manufactured by Tester Sangyo Co., Ltd.), and a test cloth (100% cotton black cloth, Billiken Moss (registered trademark)). Was set on the wear jig, the wear jig was mounted on the separator, and the test was performed by reciprocating 5 times at a speed of 30 reciprocations per minute at a distance of 120 mm with the weight (1.96 N) applied. In each sample, the test was performed five times for each of the nonwoven fabric layer side (Yankee dryer surface side) in contact with the Yankee dryer and the outermost layer side (hot air hood surface side) not in contact with the Yankee dryer. After the test was completed, the test portion (25 mm square) of the test cloth was captured with a scanner, binarization processing was performed, and the ratio of the number of pixels of the white image to the total number of pixels was calculated. The smaller the ratio of the white image, the less the separator fibers fall off and the fuzz is preferable. The results were evaluated according to the following criteria.

A: The ratio of the number of pixels of the white image to the total number of pixels by binarization processing is less than 1%.
○: The ratio of the number of pixels of the white image to the total number of pixels by the binarization processing is 1% or more and less than 2%.
Δ: The ratio of the number of pixels of the white image to the total number of pixels by the binarization process is 2% or more and less than 4%.
X: The ratio of the number of pixels of the white image to the total number of pixels by binarization processing is 4% or more.

<Electric double layer capacitor>
[Production of electrode for electric double layer capacitor]
10 parts by mass of polyvinylidene fluoride is dissolved in 90 parts by mass of N-methyl-2-pyrrolidone, and 80 parts by mass of powdered activated carbon having an average particle size of 5.0 μm and a specific surface area of 2000 m ² / g starting from a phenol resin. Then, 10 parts by mass of acetylene black having an average particle diameter of 200 nm and 300 parts by mass of N-methyl-2-pyrrolidone were added and mixed sufficiently with a mixing stirrer to obtain an electrode slurry. After applying the electrode slurry to an aluminum foil current collector having a thickness of 30 μm whose surface has been etched with hydrochloric acid using an applicator and drying, press treatment is performed using a roll press apparatus, and an electric current having a thickness of 150 μm is obtained. An electrode for a double layer capacitor was produced.

[Production of electric double layer capacitor]
(Examples 1-16, Comparative Examples 1-4)
After winding the pair of polarizable electrodes prepared as described above through the separators of Examples 1 to 16 and Comparative Examples 1 to 4, and storing them in an aluminum case, and heating them at 150 ° C. for 10 hours in vacuum Then, an electrolytic solution was injected into an aluminum case, and the injection port was sealed to produce electric double layer capacitors of Examples 1 to 16 and Comparative Examples 1 to 4. As the electrolytic solution, a solution obtained by dissolving tetraethylammonium tetrafluoroborate in propylene carbonate so as to be 1.5 mol / l was used.

[Defect occurrence rate]
When the electric double layer capacitor was manufactured as described above, the ratio of the failure to normally manufacture the electric double layer capacitor due to fuzz, winding deviation, or the like is shown in Table 2 as the defect occurrence rate.

[Internal short-circuit failure rate]
Using the electric double layer capacitors of Examples and Comparative Examples, the internal short-circuit failure rate was calculated when the constant current charge / discharge was repeated 500 cycles at a charge / discharge voltage range of 0 to 2.7 V and a charge / discharge current of 200 mA. It was shown to.

  From the results of Examples 1 to 16 shown in Table 2, in the method for producing a capacitor separator by a wet papermaking method, from two or more non-woven fabric layers containing fibrillated solvent-spun cellulose fibers and synthetic short fibers as essential components The wet nonwoven fabric is dried with a drying device that combines a Yankee dryer and hot air hood, and the content of synthetic short fibers in the nonwoven fabric layer in contact with the Yankee dryer is higher than the content in the outermost layer not in contact with the Yankee dryer. By being low, the surface strength of the nonwoven fabric layer in contact with the Yankee dryer is improved, the wear resistance is good, the occurrence rate of defects at the time of producing an electric double layer capacitor can be reduced, and the internal short circuit defect rate can also be reduced.

  Comparing Examples 1 to 5, Examples 1 to 4 in which the modified freeness of the fibrillated solvent-spun cellulose is in a preferable range are superior to Example 5 in surface strength, defect occurrence rate, and internal short circuit failure. The rate is also low. Among them, Examples 1 and 2 are particularly excellent because the modified freeness is in the optimum range.

  When Example 3 and Example 9 are compared, the synthetic short fiber B1 is more preferable as the synthetic short fiber than the synthetic short fiber B3, and the surface strength of Example 3 is superior and the defect occurrence rate is higher. Also, the internal short circuit defect rate is low and excellent. Moreover, when Example 8 and Example 14 are compared, the synthetic short fiber B2 is more preferable as the synthetic short fiber than the synthetic short fiber B3, and the surface strength of Example 8 is superior and poor. The occurrence rate and internal short-circuit failure rate are also low and excellent.

  When comparing Examples 14 to 16, the fibrillated solvent-spun cellulose content in the non-woven fabric layer in contact with the Yankee dryer was outside the preferred range, and the fibrillated in the non-woven fabric layer in contact with the Yankee dryer was compared to Example 16. Example 15 in which the content of the solvent-spun cellulose is within a preferable range is superior in that the defective rate is low. Example 14 in which the content of fibrillated solvent-spun cellulose and synthetic staple fiber in the nonwoven fabric layer in contact with the Yankee dryer and in the outermost layer not in contact with the Yankee dryer is in a more preferable range, respectively, is worse than Example 15. The incidence is low and excellent.

  On the other hand, from the results of Comparative Examples 1 to 4, when the conditions of the present invention are not satisfied, the surface strength of the nonwoven fabric layer that is in contact with the Yankee dryer is low, the incidence of defects during the production of the electric double layer capacitor is high, and internal short circuit The incidence was also high. In Comparative Examples 1 and 2, the content of the synthetic short fibers in the non-woven fabric layer that is in contact with the Yankee dryer is higher than the content of the synthetic short fibers in the outermost layer that is not in contact with the Yankee dryer. The content of the synthetic short fibers in the non-woven fabric layer in contact with the dryer is the same as the content of the synthetic short fibers in the outermost layer not in contact with the Yankee dryer, and does not satisfy the conditions of the present invention. The surface strength of the non-woven fabric layer in contact was low, and the defect occurrence rate was high.

  Comparative Example 4 is a separator made of a single-layer nonwoven fabric, does not satisfy the conditions of the present invention, has a poor surface strength on the surface in contact with the Yankee dryer, has a high defect occurrence rate, and is a single layer. Combined with this, the internal short circuit failure rate was high.

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

DESCRIPTION OF SYMBOLS 1 Yankee dryer 2 Hot air hood 3 Wet nonwoven fabric 4 Dry nonwoven fabric 5 Guide roll 6 Guide roll 7 Winding of nonwoven fabric

Claims (1)

  In a method for producing a capacitor separator by a wet papermaking method, a wet nonwoven fabric composed of two or more nonwoven fabric layers containing fibrillated solvent-spun cellulose fibers and synthetic short fibers as essential components, a Yankee dryer and a hot air hood A method for producing a capacitor separator, characterized in that the content of the synthetic short fibers in the non-woven fabric layer that is dried with a combined drying device and is in contact with the Yankee dryer is lower than the outermost layer that is not in contact with the Yankee dryer.

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