JP5695475B2 - Electrolytic capacitor separator and electrolytic capacitor using the same - Google Patents

Description

  The present invention relates to an electrolytic capacitor separator and an electrolytic capacitor.

  Conventionally, as an electrolytic capacitor separator using an electrolytic solution, a paper separator in which a paper strength enhancer is attached to paper mainly composed of hemp pulp or esparto pulp (for example, see Patent Documents 1 to 3), regenerated cellulose A paper separator made of a fiber beating raw material and natural pulp (see, for example, Patent Document 4) is used. Moreover, the separator containing the chemical fiber with little thermal deterioration in electrolyte solution is disclosed (for example, refer patent document 5). These separators have a problem that, when the thickness is reduced in order to lower the ESR, the piercing strength is weakened, so that the burr at the edge portion of the electrode foil is likely to penetrate and the short-circuit defect rate is increased. It was.

JP 2001-267182 A Japanese Patent Application Laid-Open No. 2004-200395 JP 2004-228600 A Japanese Patent No. 3466206 JP 2002-367863 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide an electrolytic capacitor separator that has an appropriate density even if it is thin, and an electrolytic capacitor that has a low short-circuit defect rate and low ESR and has a small ESR variation. is there.

  In the present invention, as a result of diligent research in order to solve this problem, solvent-spun cellulose fibers comprising a wet non-woven fabric containing, as essential components, short acrylic fibers and solvent-spun cellulose fibers that are beaten. The separator for an electrolytic capacitor having a modified freeness of 0 to 400 ml defined below and a length-weighted average fiber length of 0.20 to 2.00 mm has an appropriate denseness even if it is thin. In addition, the electrolytic capacitor equipped with the separator has been found to be excellent in low short-circuit defect rate and ESR, and have small variations in ESR.

  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%.

  The separator for an electrolytic capacitor of the present invention is composed of a wet non-woven fabric containing, as an essential component, short acrylic fibers and beaten solvent-spun cellulose fibers, and the modified freeness of the beaten solvent-spun cellulose fibers is 0 to 0. 400ml and length-weighted average fiber length is 0.20 to 2.00mm, so the pores of the separator are uniformly formed, have moderate density, and there are no parts where the fibers are extremely sparse The penetration of the burr of the electrode foil can be prevented. Therefore, the electrolytic capacitor including the separator is excellent in that the short-circuit defect rate and the ESR are low, and the variation in the ESR is small.

A graph showing the relationship between Canadian standard freeness and modified freeness (freeness measured according to JIS P8121 except that the sample concentration is 0.03%) of the solvent-spun cellulose fiber that is beaten It is. Modified drainage of solvent-spun cellulose fiber formed by beating (conforming to JIS P8121, except that 80-mesh wire mesh with a wire diameter of 0.14 mm and mesh size of 0.18 mm was used as the sieve plate and the sample concentration was 0.1%. It is an example of the graph showing the modified drainage degree measured in this way. Modified drainage of solvent-spun cellulose fibers used in the examples of the present invention (80-mesh wire mesh having a wire diameter of 0.14 mm and an aperture of 0.18 mm was used as a sieve plate, and the sample concentration was 0.1%. It is the graph showing the modified drainage degree measured based on JIS P8121 except having made it. It is a fiber length distribution histogram of solvent-spun cellulose fiber [I] beaten. It is a fiber length distribution histogram of solvent-spun cellulose fiber [II] obtained by beating. In the fiber length distribution histogram of the solvent-spun cellulose fibers [I] and [II] that are beaten, a graph of the ratio of fibers having a fiber length of every 0.05 mm between 1.00 and 2.00 mm and an approximate line FIG. It is an example of the fiber length distribution histogram of solvent-spun cellulose fiber [i] beaten having a maximum frequency peak between 0.00 and 1.00 mm. It is an example of the fiber length distribution histogram of solvent-spun cellulose fiber [ii] formed by beating having a peak between 1.50 and 3.50 mm in addition to the maximum frequency peak.

  In the present invention, the expression “separator” means an electrolytic capacitor separator.

  The acrylic short fiber in the present invention has a fiber length of 1 to 10 mm, and preferably 1 to 6 mm. When the fiber length is less than 1 mm, the puncture strength of the separator may be insufficient. When the fiber length is longer than 10 mm, the fibers may come together and the formation may be uneven. The fineness of the acrylic short fibers is preferably 0.05 to 1.0 dtex. If the fineness is less than 0.05 dtex, the puncture strength of the separator may be insufficient, and if it is greater than 1.0 dtex, the separator may have excessively high porosity or uneven thickness. Acrylic in the present invention is composed of a polymer of 100% acrylonitrile, and acrylonitrile is copolymerized with (meth) acrylic acid derivatives such as acrylic acid, methacrylic acid, acrylic acid ester, methacrylic acid ester, and vinyl acetate. It refers to what you let me. Acrylic short fibers are excellent in resistance to electrolyte. The separator of this invention becomes strong in puncture strength by containing an acrylic short fiber.

  The modified freeness in the present invention means that either the sample concentration or the sieve plate, or both the sample concentration and the sieve plate are changed with respect to the Canadian standard freeness measurement method defined in JIS P8121. Means the freeness measured. So far, the relationship between Canadian standard freeness and modified freeness of natural cellulose fibers such as conifer wood pulp, hardwood wood pulp, hemp pulp and esparto pulp has been reported. The relationship between Canadian standard freeness of spun cellulose fibers and modified freeness was not clear. In the present invention, the solvent-spun cellulose fiber was refined using a refiner, and the Canadian standard freeness and modified freeness were measured for each degree of refinement. It has been found that it is different from the drainage behavior of natural cellulose fibers disclosed in JP 2000-331663 A.

  FIG. 1 shows the relationship between Canadian standard freeness and modified freeness of solvent-spun cellulose fibers obtained by beating. In FIG. 1, the standard freeness means the Canadian standard freeness of JIS P8121. The modified freeness means the freeness measured in accordance with JIS P8121, except that the sample concentration is 0.03%. The horizontal axis in FIG. 1 indicates the length-weighted average fiber length, and the degree of miniaturization progresses toward the right. The Canadian standard freeness is 0.5 ml with a length-weighted average fiber length of 0.72 mm, but the shorter the length-weighted average fiber length is 0.55 mm or less, the greater the freeness. Yes. On the other hand, the modified freeness increases as the degree of refinement progresses. This drainage behavior is the drainage behavior of natural cellulose fibers disclosed in JP 2000-331663 A, that is, the Canadian standard freeness and modified freeness decrease as the degree of refinement progresses. The drainage behavior is quite different.

  The reason why the degree of freezing increases as the degree of refinement increases is that the length-weighted average fiber length of the solvent-spun cellulose fibers that are beaten as the refinement progresses, and the sample concentration is particularly low. In this case, since the entanglement between the fibers is reduced and the fiber network is hardly formed, the solvent-spun cellulose fiber itself that has been beaten passes through the holes in the sieve plate. That is, in the case of the solvent-spun cellulose fiber that has been refined, an accurate freeness cannot be measured by the measuring method of JIS P8121. In more detail, natural cellulose fibers are in a state where many fine fibrils are torn apart from the trunk of the fiber as the degree of refinement progresses, so fibers tend to be entangled with each other via fibrils, and a fiber network is easily formed. On the other hand, the solvent-spun cellulose fiber is easily finely divided in parallel to the long axis of the fiber by the refining treatment, and the uniformity of the fiber diameter in each fiber after division is high, so that the average fiber length becomes shorter. It is considered that the fibers do not easily entangle with each other and it is difficult to form a fiber network.

  In view of this, in the present invention, investigations were carried out to measure the exact freeness of solvent-spun cellulose fibers formed by beating. FIG. 2 shows an example of modified freeness measured by changing both the sample concentration and the sieve plate. That is, the modified freeness measured by using an 80-mesh wire net instead of the sieve plate specified in JIS P8121, and setting the sample concentration to 0.1%. The wire diameter of 80 mesh was 0.14 mm in diameter, and a wire mesh (manufactured by PULP AND PAPER RESEARCH INSTITUTE OF CANADA) having an opening of 0.18 mm was used. As can be seen from FIG. 2, the freeness decreases as the degree of refinement progresses, and the removal of the solvent-spun cellulose fiber formed by beating is suppressed, and the freeness can be measured more accurately. Recognize. Hereinafter, the modified freeness in the present invention is based on 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%. It means the measured modified freeness, and is simply expressed as “modified dryness” unless otherwise specified.

  The fiber length and the fiber length distribution histogram of the solvent-spun cellulose fiber that has been beaten can be determined using the polarization characteristics obtained by applying laser light to the fiber, and measured using a commercially available fiber length measuring instrument. Can do. In the present invention, JAPAN TAPPI paper pulp test method no. It was measured using Kajaani Fiber Lab V3.5 (manufactured by Metso Automation) according to 52 “Fiber length test method for paper and pulp (automatic optical measurement method)”. The “fiber length”, “average fiber length” and “fiber length distribution” of the solvent-spun cellulose fibers beaten are the “length-weighted fiber length” and “length-weighted average fiber length” measured and calculated according to the above. ”And“ length-weighted fiber length distribution ”.

  In addition, the length-weighted average fiber length can be adjusted in any way within the range of 0 to 400 ml of modified freeness by changing the conditions for refinement. Even so, solvent-spun cellulose fibers formed by beating different length-weighted average fiber lengths can be produced. FIG. 3 shows the modified freeness of solvent-spun cellulose fibers used in Examples 9 to 20 of the present invention.

  Solvent-spun cellulose fibers having a modified freeness of 0 to 400 ml and a length-weighted average fiber length of 0.20 to 2.00 mm have a narrow fiber diameter and high uniformity. It is possible to prevent the unevenness of the electrolyte in the separator. The solvent-spun cellulose fiber of the present invention preferably has a modified freeness of 0 to 300 ml, more preferably 0 to 250 ml. When the modified freeness exceeds 400 ml, the refinement process is insufficient, the fiber division does not proceed sufficiently, and the proportion of the original thick fiber diameter remains large, so a large through hole is made in the separator. The burrs at the edge portions of the electrode foil are likely to penetrate and the short-circuit defect rate is increased. The solvent-spun cellulose fiber of the present invention preferably has a length weighted average fiber length of 0.40 to 1.80 mm, and more preferably 0.50 to 1.50 mm. When the thickness is less than 0.20 mm, the drainage becomes worse, the papermaking property becomes worse, the fiber gap becomes narrower, and the ESR of the electrolytic capacitor becomes higher. If it exceeds 2.00 mm, miniaturization is insufficient, the ratio of thick fiber diameter increases, large through-holes are likely to open in the separator, fiber kinking occurs, texture and thickness variations occur, and ESR variations occur. Becomes larger. The length-weighted average fiber length of the solvent-spun cellulose fiber in the present invention can be measured by using a commercially available fiber length measuring instrument that is obtained by utilizing polarization characteristics obtained by applying laser light to the fiber.

  Furthermore, in the present invention, in a solvent-spun cellulose fiber having a modified freeness of 0 to 400 ml and a length-weighted average fiber length of 0.20 to 2.00 mm, a fiber length distribution histogram is obtained. As a result of detailed examination, when the first fiber length distribution described below is obtained, the effect of improving the liquid absorption is obtained, and when it has the second fiber length distribution, both the liquid absorption and the ion mobility are achieved. It was found that it is more preferable since the effect of the above is obtained.

  In the solvent-spun cellulose fiber that is beaten, the preferred first fiber length distribution has a maximum frequency peak between 0.00 and 1.00 mm in the fiber length distribution histogram, and a fiber length of 1.00 mm or more. The ratio of the fiber having 10% or more. It has been found that the solvent-spun cellulose fiber formed by such beating has good liquid absorbency. Moreover, when the inclination of the ratio of the fiber having a fiber length of every 0.05 mm between 1.00 and 2.00 mm is −3.0 or more and −0.5 or less, the liquid absorption is more excellent, It has been found that it is more preferable.

  FIG. 4 and FIG. 5 are fiber length distribution histograms of solvent-spun cellulose fibers formed by beating, fibers having a maximum frequency peak between 0.00 and 1.00 mm and having a fiber length of 1.00 mm or more. Is 10% or more. In terms of liquid absorbency, more preferably, in the fiber length distribution histogram, the ratio of fibers having a maximum frequency peak between 0.30 and 0.70 mm and having a fiber length of 1.00 mm or more is 12% or more. However, it is sufficient if it is about 50%.

  In the fiber length distribution histogram of solvent-spun cellulose fibers formed by beating, the slope of the ratio of fibers having a fiber length of 0.05 mm between 1.00 and 2.00 mm is −3.0 or more and −0.5 or less. -2.5 or more and -0.8 or less are more preferable, and -2.0 or more and -1.0 or less are more preferable. When the inclination is smaller than −3.0, the fiber gap is narrowed and the liquid absorbency may be lowered. On the other hand, when the inclination exceeds −0.5, the separator is unsatisfactory and ESR variation may increase. As shown in FIGS. 4 and 5, “large inclination” means a state in which the fiber length distribution of the solvent-spun cellulose fiber formed by beating is wide. “Slight inclination” is a state in which the fiber length distribution of the solvent-spun cellulose fibers formed by beating is narrow and the fiber lengths are more uniform. Note that the slope of the solvent-spun cellulose fiber [I] in FIG. 4 is -2.9, and the slope of the solvent-spun cellulose fiber [II] in FIG. 5 is -0.6. is there.

  In addition, "the inclination of the ratio of the fiber having a fiber length of every 0.05 mm between 1.00 and 2.00 mm" is 0. 0 between 1.00 and 2.00 mm as shown in FIG. For the value of the proportion of fibers having a fiber length of every 05 mm, an approximate straight line is calculated by the method of least squares, and the inclination of the obtained approximate straight line is meant.

  In the solvent-spun cellulose fiber formed by beating, the preferred second fiber length distribution has a maximum frequency peak between 0.00 and 1.00 mm in the fiber length distribution histogram of the solvent-spun cellulose fiber formed by beating. The ratio of fibers having a fiber length of 1.00 mm or more is 50% or more. The solvent-spun cellulose fiber thus beaten does not have a too narrow or too wide fiber gap, and can achieve both liquid absorbency and ion mobility of the electrolytic solution. Moreover, when it has a peak between 1.50 and 3.50 mm other than a maximum frequency peak, since a liquid absorptivity improves rather than the solvent spinning cellulose fiber which does not have such a peak, it is preferable.

  FIG. 7 is a fiber length distribution histogram of the solvent-spun cellulose fiber formed by beating, and the ratio of fibers having a maximum frequency peak between 0.00 and 1.00 mm and having a fiber length of 1.00 mm or more. 50% or more. In terms of not inhibiting ion migration in the electrolyte, the fiber length distribution histogram has a maximum frequency peak between 0.30 and 0.70 mm, and the percentage of fibers having a fiber length of 1.00 mm or more is 55%. More preferably. A higher proportion of fibers having a fiber length of 1.00 mm or more is desirable, but about 75% is sufficient.

  In the fiber length distribution histogram of the solvent-spun cellulose fiber that is beaten, it is more preferable to have a peak between 1.50 and 3.50 mm in addition to the above maximum frequency peak, as shown in FIG. It is more preferable to have a peak between .75 and 3.25 mm, and it is particularly preferable to have a peak between 1.90 and 3.00 mm. Having a peak in this range is preferable because the liquid absorbency is further improved. When the fiber length of the peak is shorter than 1.50 mm, the liquid absorbability may be deteriorated. On the other hand, if the thickness exceeds 3.50 mm, lumps may be generated, resulting in uneven thickness, and the separator may be unsatisfactory, or the fiber gap may become too wide, resulting in poor liquid absorbency.

  In order to obtain a solvent-spun cellulose fiber having a modified freeness of 0 to 400 ml and a length-weighted average fiber length of 0.20 to 2.00 mm, the solvent-spun cellulose short fibers are dispersed in water at an appropriate concentration. , A refiner, a beater, a mill, a grinding device, a rotary blade homogenizer that applies a shearing force by a high-speed rotating blade, a shearing force is generated between a cylindrical inner blade that rotates at high speed and a fixed outer blade It passes through a double-cylindrical high-speed homogenizer, an ultrasonic crusher that is miniaturized by impact by ultrasonic waves, a high-pressure homogenizer, etc., and adjusts the conditions such as blade shape, sample concentration, flow rate, number of treatments, treatment speed, etc. What is necessary is just to process.

  The total content of the short acrylic fiber and the solvent-spun cellulose fiber in the separator of the present invention is preferably 40 to 100% by mass. If it is less than 40% by mass, the puncture strength may be insufficient, the ESR of the electrolytic capacitor equipped with the separator may be high, or the ESR may be highly variable. The ratio of the short acrylic fiber and the solvent-spun cellulose fiber having a modified freeness of 0 to 400 ml in the separator of the present invention is preferably from 1: 9 to 8: 1, more preferably from 3:17 to 3: 1. . When the ratio of the acrylic short fibers is less than 1: 9, the puncture strength of the separator may be insufficient, and when it is more than 8: 1, it may be difficult to reduce the thickness of the separator or ESR may be increased.

  The separator of the present invention may contain short fibers other than solvent-spun cellulose fibers having acrylic short fibers, modified freeness of 0 to 400 ml, and length-weighted average fiber lengths of 0.20 to 2.00 mm. For example, short fibers and fibrils made of polyamide, short fibers of solvent-spun cellulose and regenerated cellulose, natural cellulose fibers, pulped and fibrillated products of natural cellulose fibers, solvent-spun cellulose fibers having a modified freeness of more than 400 ml, glass, Inorganic fibers made of alumina, silica and the like.

  The polyamide may be an aliphatic polyamide, an aromatic polyamide, or a wholly aromatic polyamide, but a wholly aromatic polyamide having excellent heat resistance is preferred. The short fiber of polyamide, solvent-spun cellulose or regenerated cellulose preferably has a fiber length of 1 to 10 mm, more preferably 1 to 6 mm. If the fiber length is less than 1 mm, it may be easy to fall off from the separator, and if it is longer than 10 mm, the fibers may come together and the formation may become uneven. The fineness of the short fibers of polyamide, solvent-spun cellulose and regenerated cellulose is preferably 0.01 to 2.0 dtex. If it is less than 0.01 dtex, the strength of the fiber itself is weak and the separator may break easily. If it is thicker than 2.0 dtex, it may be difficult to reduce the thickness of the separator.

  The natural cellulose fiber pulped product or fibrillated product preferably has a modified freeness of 0 to 400 ml. When the modified freeness exceeds 400 ml, the ratio of the thick fiber diameter increases, and the thickness unevenness is likely to occur in the separator. The average fiber diameter of the inorganic fibers is preferably 0.1 to 10.0 μm, and more preferably 0.1 to 3.0 μm. If the average fiber diameter is less than 0.1 μm, the inorganic fibers are likely to be broken, so that they may be easily detached from the separator, and if it is thicker than 10.0 μm, it may be difficult to reduce the thickness of the separator. The average fiber length of the inorganic fibers is preferably 0.1 to 10.0 mm, and more preferably 0.1 to 5.0 mm. If the average fiber length is less than 0.1 mm, the inorganic fibers may easily fall off from the separator, and if it is longer than 10.0 mm, the texture and thickness of the separator may be likely to be uneven.

  The porosity of the separator of the present invention is preferably 60.0 to 86.0%, and more preferably 62.0 to 80.0%. The porosity means a value obtained by dividing the value obtained by subtracting the density of the separator from the specific gravity of the separator by the specific gravity of the separator and multiplying by 100. The specific gravity of the separator is calculated from the specific gravity and ratio of the fibers constituting the separator. If the porosity is less than 60.0%, the electrolytic solution retainability may be deteriorated or the ESR of the electrolytic capacitor may be increased. If the porosity is larger than 86.0%, the short-circuit defect rate may increase or the ESR variation may increase.

  In order to adjust the porosity of the separator of the present invention, the density of the separator may be adjusted so as to obtain a desired porosity based on the specific gravity of the separator. When the content of thick fibers is increased, the density of the separator is reduced and the porosity is increased. When the thickness is reduced by calendering to increase the density of the separator, the porosity decreases. Increasing the content of fibers with a high specific gravity tends to increase the porosity.

  The separator of the present invention can be produced by a wet papermaking method. One layer may be used, or two or more layers may be combined. Specifically, a slurry in which a predetermined fiber is dispersed at a predetermined concentration is prepared, and a circular paper machine, a long paper machine, an inclined paper machine, a short paper machine, an inclined short paper machine, and a combination thereof are combined. What is necessary is just to make wet papermaking using either of the paper machines. After wet papermaking, heat treatment, calendering, thermal calendering, etc. are performed as necessary.

  The separator of the present invention preferably has a thickness of 15 to 100 μm, more preferably 20 to 60 μm. If the thickness is less than 15 μm, it may be broken during handling or processing, or a hole may be formed. If it is thicker than 100 μm, the ESR of the electrolytic capacitor may increase.

  The separator of the present invention preferably has a Gurley air permeability of 0.01 to 5.00 s / 100 ml, and more preferably 0.10 to 3.00 s / 100 ml. The Gurley air permeability is measured according to JIS P8117. If the Gurley air permeability is less than 0.01 s / 100 ml, burrs on the edge of the electrode foil are likely to penetrate, and the short-circuit failure rate of the electrolytic capacitor increases, and the deviation of the ESR occurs due to the uneven electrolyte in the separator. May become larger. If it is larger than 5.00 s / 100 ml, the ESR of the electrolytic capacitor may increase.

  The separator of the present invention preferably has an average puncture strength of 0.40 N or more, and more preferably 0.50 N or more. If the average piercing strength is less than 0.40 N, the short-circuit defect rate may be increased due to damage to the separator or the opening of the electrolytic capacitor. The piercing strength means a maximum load until a metal rod having a diameter of 1 mm is lowered at a constant speed perpendicular to the separator and the metal rod penetrates the separator. The average puncture strength is the average value obtained by measuring the puncture strength at any five or more locations of the separator sample.

  The electrolytic capacitor in the present invention uses a valve metal having an insulating oxide film formed on the surface of an aluminum foil as an anode, and uses an aluminum foil without an oxide film as a cathode. It refers to a structure in which an electrolyte is disposed between them.

  Examples of the electrolyte medium include water, ethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, ethylene glycol phenyl ether, methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, Acetone alcohol, benzyl alcohol, amyl alcohol, glycerin, γ-butyrolactone, α-acetyl-γ-butyrolactone, β-butyrolactone, N-methylformamide, N, N-dimethylformamide, N-ethylformamide, N, N-diethylformamide N-methylacetamide, N, N-dimethylacetamide, N-ethylacetamide, N, N-diethylacetoamide , Hexamethylphosphoric amide, acetonitrile, acrylonitrile, adiponitrile, 3-methoxypropionitrile, N-methyl-2-oxazolidinone, 3,5-dimethyl-2-oxazolidinone, ethylene carbonate, propylene carbonate, dimethyl sulfone, ethylmethyl Sulfone, diethylsulfone, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane and the like can be mentioned, and these solvents are used alone or as a mixed solvent, and ethylene glycol or γ-butyrolactone is preferable.

  Examples of the electrolyte of the electrolytic solution include boric acid, succinic acid, adipic acid, pimelic acid, maleic acid, benzoic acid, phthalic acid, salicylic acid, suberic acid, azelaic acid, sebacic acid, undecanoic acid, 2-methyl azelaic acid, 1,6 -Decanedicarboxylic acid, 5,6-decanedicarboxylic acid, salts of these acids (e.g. ammonium adipate, ammonium hydrogen maleate dimethylamine, 2-butyloctanedioic acid ammonia, hydrogen phthalate 1-ethyl-2,3- Dimethyl imidazolium, etc.), tetramethylammonium hydroxide, ethylmethylamine, diethylamine, trimethylamine, diethylmethylamine, ethyldimethylamine, triethylamine, tetramethylammonium, triethylmethylammonium, tetraethylammonium, carbon number 1-11 Alkyl group or quaternized imidazole compound arylalkyl group, benzimidazole compounds, alicyclic amidine compound and the like are used.

EXAMPLES Hereinafter, although an Example demonstrates this invention in more detail, this invention is not limited to an Example. Examples 1 to 8, 13, 18 to 20, 24, and 29 to 31 are reference examples.
<< Examples 1-8, Comparative Examples 1-3 >>
[Physical properties of solvent-spun cellulose fiber formed by beating]
About solvent-spun cellulose fiber that is beaten
(1) Modified freeness measured in accordance with JIS P8121, except that an 80-mesh wire mesh with 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%. Law Freeness "
(2) Length-weighted average fiber length: “Average fiber length”
Is shown in Table 3. In addition, the solvent-spun cellulose fiber in each state formed by beating is produced by processing a non-beaten solvent-spun cellulose short fiber (fineness: 1.7 dtex, fiber length: 6 mm, manufactured by Coatles) using a double disc refiner. did.

  Table 1 shows fibers used in Examples and Comparative Examples of the present invention. A1 to A11 mean solvent-spun cellulose fibers formed by beating, and a non-beaten solvent-spun cellulose short fiber (fineness: 1.7 dtex, fiber length: 6 mm, manufactured by Coatles Co., Ltd.) is processed using a double disc refiner. Produced. B1 is acrylic short fiber having a fineness of 0.1 dtex and a fiber length of 3 mm (trade name: Bonnell (registered trademark) manufactured by Mitsubishi Rayon), and B2 is an acrylic short fiber having a fineness of 0.4 dtex and a fiber length of 5 mm (made by Mitsubishi Rayon, product name). : Bonnell (registered trademark)), B3 means an acrylic short fiber (manufactured by Mitsubishi Rayon, trade name: Bonnell (registered trademark)) having a fineness of 1.0 dtex and a fiber length of 5 mm. B4 means solvent-spun cellulose short fibers (Lyocell (registered trademark) short fibers, fineness 1.7 dtex, fiber length 6 mm)). C1 means fibrillated linter fiber. The specific gravity of solvent-spun cellulose fibers, solvent-spun cellulose short fibers, and linter fibers with various modified freeness values was 1.50. The specific gravity of the acrylic short fiber was 1.17. In Table 2, the fiber which comprises the slurry corresponding to Examples 1-8 of this invention and Comparative Examples 1-3, and a compounding rate were shown. The fiber symbols in Table 2 correspond to the symbols in Table 1.

Example 1
After fiber B2 was dispersed in water with a pulper, fiber A1 was added and stirred for a predetermined time to prepare slurry 1. This was diluted to a predetermined concentration, fed to a circular paper machine and wet-made, and dried at a Yankee dryer temperature of 120 ° C. to produce the separator of Example 1.

Examples 2-7
Similarly to the preparation of slurry 1, acrylic short fibers were dispersed in water with a pulper, and then solvent-spun cellulose fibers formed by beating were added and stirred for a predetermined time to prepare slurries 2-7. Slurries 2 to 7 were diluted to a predetermined concentration, and wet papermaking was performed in the same manner as in Example 1 to prepare separators of Examples 2 to 7.

Example 8
After the fiber C1 was dispersed in water with a pulper, the fiber B1 was added and stirred for a predetermined time, and further the fiber A8 was added and stirred for a predetermined time to prepare slurry 8. This was diluted to a predetermined concentration, and wet papermaking was carried out in the same manner as in Example 1 to produce the separator of Example 8.

(Comparative Example 1)
After fiber B2 was dispersed in water with a pulper, fiber A9 was added and stirred for a predetermined time to prepare slurry 9. This was diluted to a predetermined concentration, fed to a circular paper machine, wet-made, and dried at a Yankee dryer temperature of 120 ° C., to produce a separator of Comparative Example 1.

(Comparative Examples 2 and 3)
In the same manner as in the slurry 9, the acrylic short fibers were dispersed in water with a pulper, and then the solvent-spun cellulose fibers formed by beating were added and stirred for a predetermined time to prepare slurries 10 and 11. Slurries 10 and 11 were diluted to a predetermined concentration, sent to a circular paper machine, and wet papermaking to produce separators of Comparative Examples 2 and 3.

  The separators of Examples 1 to 8 and Comparative Examples 1 to 3 were evaluated by the following test methods, and the results are shown in Table 3.

<Thickness>
The thickness of the separator was measured according to JIS P8118.

<Density>
The density of the separator was measured according to JIS P8124.

<Porosity>
The porosity of the separator was calculated by dividing the value obtained by subtracting the density of the separator from the specific gravity of the separator by the specific gravity of the separator and multiplying by 100.

<Gurley air permeability>
Using a Gurley permeability meter having a circular hole with an outer diameter of 28.6 mm, the time required for 100 ml of air to pass through the separator was measured at any five or more locations per sample, and the average value was obtained.

<Liquid absorption>
A sample in which the separator was cut to a width of 20 mm and a length of 150 mm was prepared. At this time, the direction cut to a length of 150 mm was the CD direction, that is, the direction perpendicular to the winding length direction of the separator winding (width direction). The bottom 10 mm of the separator sample is immersed and fixed in an electrolyte solution dissolved in γ-butyrolactone so that the concentration of 1,2,3,4-tetramethylimidazolinium phthalate is 30% by mass. The suction height was measured after standing for a minute. The higher the wicking height, the better.

<Electrolytic capacitor>
Using an aluminum foil formed by chemical conversion etching on the anode and an unformed etching aluminum foil on the cathode, the separators of Examples 1 to 8 and Comparative Examples 1 to 3 are respectively wound between them to produce a winding element. did. An electrolytic solution in which γ-butyrolactone was dissolved so that the concentration of 1,2,3,4-tetramethylimidazolinium phthalate was 30% by mass was injected into the winding element and sealed. Electrolytic capacitors 1 to 8 and Comparative Examples 1 to 3 were produced.

  The electrolytic capacitors of Examples 1 to 8 and Comparative Examples 1 to 3 were evaluated by the following test methods, and the results are shown in Table 4.

<ESR>
The ESR of the electrolytic capacitor was measured using an LCR meter at a frequency of 20 ° C. and 1 kHz, and an average value of 1000 capacitors was calculated.

<Variation>
The standard deviation of ESR of the electrolytic capacitor was used as an index of variation. The smaller the standard deviation value, the smaller the variation and the better.

<Short defective rate>
A winding element was produced by sandwiching the separators of Examples and Comparative Examples between the anode and the cathode, and the presence or absence of conduction between both electrodes was confirmed by a tester without impregnating the electrolyte. The ratio of the conductive winding element in the 1000 winding elements was defined as a short-circuit defect rate.

  The separators of Examples 1 to 8 are made of a wet nonwoven fabric containing, as essential components, acrylic short fibers and beaten solvent-spun cellulose fibers, and the modified freeness of solvent-spun cellulose fibers is 0 to 0. Since it was 400 ml and the length weighted average fiber length was 0.20 to 2.00 mm, the electrolyte solution was excellent in liquid absorbency. The electrolytic capacitors provided with the separators of Examples 1 to 8 were excellent because the short-circuit defect rate and ESR were low, and the variation in ESR was small.

  The separator of Comparative Example 1 contains short acrylic fibers and solvent-spun cellulose fibers formed by beating, but since the length-weighted average fiber length of solvent-spun cellulose fibers is less than 0.20 mm, the fiber gap is narrow, The liquid absorption was poor. The electrolytic capacitor provided with the separator of Comparative Example 1 had a small short-circuit defect rate and a small variation in ESR, but had a high ESR.

  The separator of Comparative Example 2 contains short acrylic fiber and solvent-spun cellulose fiber formed by beating, but since the length-weighted average fiber length of solvent-spun cellulose fiber exceeds 2.00 mm, the fiber diameter is large. Many solvent-spun cellulose fibers were mixed, surface smoothness was poor, and liquid absorbency was poor. Moreover, since the through-hole of the separator became large and the burr | flash of the electrode foil became easy to penetrate, the electrolytic capacitor provided with the separator of the comparative example 2 had a somewhat high short defect rate. Further, the ESR was high and the variation of the ESR was large.

  The separator of Comparative Example 3 contains acrylic short fibers and beaten solvent-spun cellulose fibers, but the modified freeness of the solvent-spun cellulose fibers exceeds 400 ml, and the length-weighted average fiber length is 2 Since it was longer than 0.000 mm, many solvent-spun cellulose fibers having a large fiber diameter were mixed, surface smoothness was poor, and liquid absorbency was poor. Moreover, since the through-hole of the separator became large and the burr of the electrode foil easily penetrated, the electrolytic capacitor equipped with the separator of Comparative Example 3 had a high short-circuit defect rate, a high ESR, and a large variation in ESR.

<< Examples 9 to 20 >>
[Physical properties of solvent-spun cellulose fiber formed by beating]
About solvent-spun cellulose fiber that is beaten
(1) Fiber length of maximum frequency peak in fiber length distribution histogram: “Fiber length of maximum frequency peak”
(2) Ratio of fibers having a fiber length of 1.00 mm or more: “fiber ratio of 1.00 mm or more”
(3) In the fiber length distribution histogram, the slope of the proportion of fibers having a fiber length of every 0.05 mm between 1.00 and 2.00 mm: “ratio of the proportion”
(4) Length-weighted average fiber length: “Average fiber length”
(5) Modified freeness measured according to JIS P8121, except that an 80-mesh wire mesh with 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%. Law Freeness "
Is shown in Table 5. Solvent-spun cellulose fibers A12 to A23 that are beaten are produced by treating unspun solvent-spun cellulose short fibers (fineness: 1.7 dtex, fiber length: 6 mm, manufactured by Coatles Co., Ltd.) using a double disc refiner. did.

  Slurries 12 to 23 shown in Table 6 were prepared in the same manner as slurry 1 or 8. The fiber symbols in Table 6 correspond to the symbols in Table 1 and Table 5. Slurries corresponding to Examples 9 to 20 were fed to a circular paper machine and subjected to wet papermaking, and dried at a Yankee dryer temperature of 120 ° C. to produce separators of Examples 9 to 20. The separator was evaluated in the same manner as in Example 1, and the evaluation results are shown in Table 7.

  Using the separators produced in Examples 9 to 20, an electrolytic capacitor was produced in the same manner as in Example 1. The electrolytic capacitor was evaluated in the same manner as in Example 1, and the results of the evaluation are shown in Table 8. .

  The separators produced in Examples 9 to 18 consist of a wet nonwoven fabric containing solvent-spun cellulose fibers beaten with acrylic short fibers as an essential component, and the modified freeness of solvent-spun cellulose fibers beaten is 0. In a fiber length distribution histogram of solvent-spun cellulose fibers formed by beating at a weight-weighted average fiber length of 0.20 to 2.00 mm at ˜400 ml, a maximum frequency peak between 0.00 and 1.00 mm The ratio of the fibers having a fiber length of 1.00 mm or more was 10% or more, and thus the electrolyte solution was excellent in liquid absorbency. The electrolytic capacitors comprising the separators produced in Examples 9 to 18 were excellent with a short-circuit defect rate and low ESR, small variations in ESR.

  The separator produced in Example 19 does not have a maximum frequency peak between 0.00 and 1.00 mm in the fiber length distribution histogram of the solvent-spun cellulose fiber formed by beating, so that the fiber gap is narrow and the liquid absorption The properties were inferior to those of Examples 9-18.

  In the separator produced in Example 20, the ratio of fibers having a fiber length of 1.00 mm or more is less than 10% in the fiber length distribution histogram of solvent-spun cellulose fibers formed by beating, so that the fiber gap is narrow and the absorption is small. The liquid property was inferior to Examples 9-18.

  The separators produced in Examples 9 to 12 and 14 to 17 are fibers having a fiber length of every 0.05 mm between 1.00 and 2.00 mm in a fiber length distribution histogram of solvent-spun cellulose fibers formed by beating. Since the slope of the ratio was -3.0 or more and -0.5 or less, the liquid absorption was more excellent.

  In the separator produced in Example 13, in the fiber length distribution histogram of the solvent-spun cellulose fiber formed by beating, the slope of the ratio of fibers having a fiber length of every 0.05 mm between 1.00 and 2.00 mm is − Since it was a minus side from 3.0, the fiber gap was narrow, and the liquid absorbency was inferior to Examples 9-12 and 14-17.

  In the separator produced in Example 18, in the fiber length distribution histogram of solvent-spun cellulose fibers formed by beating, the slope of the ratio of fibers having a fiber length of every 0.05 mm between 1.00 and 2.00 mm is − Since it is a plus side from 0.5, liquid absorbency was inferior to Examples 9-12 and 14-17.

<< Examples 21-31 >>
[Physical properties of solvent-spun cellulose fiber formed by beating]
About solvent-spun cellulose fiber that is beaten
(1) Ratio of fibers having a fiber length of 1.00 mm or more: “Fiber ratio of 1.00 mm or more”
(2) Fiber length of maximum frequency peak in fiber length distribution histogram: “Fiber length of maximum frequency peak”
(3) Fiber length of peaks other than the maximum frequency peak: “fiber length of second peak”
(4) Length-weighted average fiber length: “Average fiber length”
(5) Freeness measured in accordance with JIS P8121, except that an 80-mesh wire mesh with 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%. Water level "
Is shown in Table 9. The solvent-spun cellulose fibers A 24 to A 34 that have been beaten are processed by using a double disc refiner with solvent-spun cellulose single fibers that have not been beaten (fineness 1.7 dtex, fiber length 6 mm, manufactured by Coatles). Made.

Slurries 24 to 34 shown in Table 10 were prepared in the same manner as slurry 1 or 8. The fiber symbols in Table 10 correspond to the symbols in Table 1 and Table 9. Slurries corresponding to Examples 21 to 31 were fed to a circular paper machine and subjected to wet papermaking, and dried at a Yankee dryer temperature of 120 ° C. to produce separators of Examples 21 to 31. The separator was evaluated in the same manner as in Example 1, and the results of the evaluation are shown in Table 11.

  Using the separators produced in Examples 21-31, electrolytic capacitors were produced in the same manner as in Example 1. The electrolytic capacitors were evaluated in the same manner as in Example 1, and the results of the evaluation are shown in Table 12. It was.

  The separators produced in Examples 21 to 29 are made of a wet nonwoven fabric containing acrylic short fibers and beaten solvent-spun cellulose fibers as essential components, and have a modified freeness of solvent-spun cellulose fibers that are beaten. In the fiber length distribution histogram of solvent-spun cellulose fibers beaten with 0 to 400 ml and length-weighted average fiber length of 0.20 to 2.00 mm, the maximum frequency between 0.00 and 1.00 mm Since the ratio of the fiber having a peak and a fiber length of 1.00 mm or more is 50% or more, the liquid-absorbing property of the electrolytic solution was excellent. The electrolytic capacitors comprising the separators produced in Examples 21 to 29 were excellent because the short-circuit defect rate and ESR were low, and the variation in ESR was small.

  In the separator produced in Example 30, the maximum frequency peak exceeds 1.00 mm in the fiber length distribution histogram of the solvent-spun cellulose fiber formed by beating, so that the fiber gap is wide and the liquid absorbency is in Examples 21 to 21. It was inferior to 29. The electrolytic capacitor comprising the separator had a low short-circuit defect rate, but had a higher ESR than Examples 21 to 29 and a large variation in ESR.

  The separator produced in Example 31 has a narrow fiber gap because the ratio of fibers having a fiber length of 1.00 mm or more is less than 10% in the fiber length distribution histogram of solvent-spun cellulose fibers formed by beating. The liquid property was inferior to Examples 21-29. The electrolytic capacitor comprising the separator had a small ESR variation and a low short-circuit defect rate, but the ESR was higher than those of Examples 21-29.

  The separators produced in Examples 21 to 23 and 25 to 28 have a peak between 1.50 and 3.50 mm in addition to the maximum frequency peak in the fiber length distribution histogram of solvent-spun cellulose fibers formed by beating, It was more excellent in liquid absorbency.

  In the separator produced in Example 24, since the second peak of the solvent-spun cellulose fiber formed by beating is less than 1.50 mm, the fiber gap is slightly narrower, and the liquid absorption is higher than those in Examples 21 to 23 and 25 to 28. Slightly inferior. Therefore, ESR of the electrolytic capacitor comprising the separator was slightly inferior to those of Examples 21 to 23 and 25 to 28.

  In the separator produced in Example 29, since the second peak of the solvent-spun cellulose fiber formed by beating exceeds 3.50 mm, the fiber gap is wide and the liquid absorbency is higher than those of Examples 21 to 23 and 25 to 28. It was inferior. Although the short-circuit defect rate of the electrolytic capacitor comprising the separator was low, the variations in ESR and ESR were inferior to those of Examples 21 to 28.

  The present invention is applicable to an electrolytic capacitor.

Claims (2)

A wet non-woven fabric containing, as an essential component, short acrylic fiber and beaten solvent-spun cellulose fiber, and a modified freeness of solvent-spun cellulose fiber as defined below is 0 to 400 ml, and , Ri length weighted average fiber length of 0.20~2.00mm der,
A modified solvent-spun cellulose fiber having a modified freeness of 0 to 400 ml and a length-weighted average fiber length of 0.20 to 2.00 mm is represented by the following first fiber length distribution or second separator for electrolytic capacitors that have a fiber length distribution.
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%.
First fiber length distribution: In a fiber length distribution histogram of solvent-spun cellulose fibers formed by beating, fibers having a maximum frequency peak between 0.00 and 1.00 mm and having a fiber length of 1.00 mm or more The ratio is 10% or more and 51% or less, and the slope of the ratio of fibers having a fiber length of 0.05 mm between 1.00 and 2.00 mm is −3.0 or more and −0.5 or less.
Second fiber length distribution: In the fiber length distribution histogram of the solvent-spun cellulose fiber formed by beating, the maximum frequency peak is between 0.00 and 1.00 mm, and the fiber length is 1.00 mm or more. The ratio is 50% or more and 70% or less, and has a peak between 1.50 and 3.50 mm in addition to the maximum frequency peak. An electrolytic capacitor comprising the electrolytic capacitor separator according to claim 1.

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