Rubber composition for electrolytic capacitor sealing bodies

Abstract

To provide a rubber composition that can improve the low permeability and swelling resistance of a sealing body to electrolyte components such as γ-butyrolactone contained in the electrolyte of an electrolytic capacitor, while maintaining the excellent sealing properties of the sealing body. [Solution] A rubber composition for electrolytic capacitor sealing body containing rubber and cellulose nanofibers is provided.

Description

[Technical Field]

[0001] This disclosure relates to a rubber composition for electrolytic capacitor sealing bodies. [Background technology]

[0002] Patent Document 1 states that the specific surface area is 5 to 20 m². 2 A sealing body for electrolytic capacitors is described, comprising a rubber material to which flattened fine particles of / g are added. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2008-251980 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] The object of this disclosure is to provide a rubber composition that can improve the low permeability and swelling resistance of a sealing body to electrolyte components such as γ-butyrolactone contained in the electrolyte of an electrolytic capacitor, while maintaining the excellent sealing properties of the sealing body. [Means for solving the problem]

[0005] According to this disclosure, a rubber composition for electrolytic capacitor sealing bodies containing rubber and cellulose nanofibers is provided. [Effects of the Invention]

[0006] According to this disclosure, it is possible to provide a rubber composition that can improve the low permeability and swelling resistance of a sealing body to electrolyte components such as γ-butyrolactone contained in the electrolyte of an electrolytic capacitor, while maintaining the excellent sealing properties of the sealing body. [Modes for carrying out the invention]

[0007] The following describes specific embodiments of this disclosure in detail, but this disclosure is not limited to the embodiments described below.

[0008] Generally, electrolytic capacitors are constructed by impregnating a capacitor element, which consists of an aluminum anode foil, a cathode foil, and an insulating separator wound around it, with an electrolyte solution, housing it in a cylindrical cup-shaped aluminum case, and sealing the opening of this case with a sealing element. In such electrolytic capacitors, the lead wires drawn from the capacitor element are led to the outside through through holes in the sealing element, and the outer case is crimped in this state to maintain the seal. To maintain the seal between the outer case, lead wires, and the sealing element, rubber is generally used for the sealing element.

[0009] Patent Document 1 describes that ethylene propylene polymer (EPDM), isobutylene isoprene rubber (IIR: commonly known as butyl rubber), and butadiene styrene rubber (SBR) have been used as sealing rubbers for electrolytic capacitors where sealing properties and heat resistance are required. However, it states that at high temperatures, when these rubbers alone are used as sealing bodies, moisture from the outside air may enter the outer casing, or conversely, the internal electrolyte may evaporate to the outside, making it difficult to maintain the lifespan reliability of the capacitor. Patent Document 1 proposes adding flattened fine particles such as talc and mica to the rubber to solve the above problems.

[0010] However, there is a need for new methods that can improve the low permeability and swelling resistance of the sealing body to electrolyte components such as γ-butyrolactone contained in the electrolyte of the electrolytic capacitor, while maintaining the excellent sealing properties of the sealing body.

[0011] In other words, the present disclosure provides a rubber composition for forming a sealing body used in sealing an electrolytic capacitor, the rubber composition containing rubber and cellulose nanofibers.

[0012] The following provides a detailed description of each component of the rubber composition.

[0013] (Rubber) The rubber composition of the present disclosure contains rubber.

[0014] As the rubber, at least one selected from ethylene propylene rubber, butadiene styrene rubber, isobutylene isoprene rubber (IIR, butyl rubber), and fluororubber is preferable because it can further improve the low permeability and swelling resistance of the sealing body to electrolyte components such as γ-butyrolactone without impairing the excellent sealing property of the sealing body. Ethylene propylene rubber, isobutylene isoprene rubber, and fluororubber are more preferable, and fluororubber is even more preferable. Examples of ethylene propylene rubber include ethylene propylene rubber (EPR) and ethylene propylene diene rubber (EPDM).

[0015] In one embodiment, the rubber composition contains fluororubber. By using a rubber composition containing fluororubber, a sealing body excellent in compression set resistance at high temperature, low permeability, and swelling resistance to electrolyte components such as γ-butyrolactone contained in the electrolyte of an electrolytic capacitor can be obtained.

[0016] The fluororubber is an amorphous fluoropolymer. "Amorphous" means that the magnitude of the melting peak (ΔH) appearing in the differential scanning calorimetry [DSC] (heating rate 10 °C / min) or differential thermal analysis [DTA] (heating rate 10 °C / min) of the fluoropolymer is 4.5 J / g or less. The fluororubber exhibits elastomer characteristics by crosslinking. The elastomer characteristics mean the property that the polymer can be stretched and can retain its original length when the force required to stretch the polymer is no longer applied.

[0017] The fluorine content of fluororubber is preferably 61 to 73% by mass, more preferably 63% by mass or more, even more preferably 65% ​​by mass or more, still more preferably 67% by mass or more, particularly preferably 69% by mass or more, and more preferably 73% by mass or less, from the viewpoint of balancing low permeability, swelling resistance, and cost. 19 The composition of fluororubber can be calculated from the composition measured by 1F-NMR.

[0018] Partially fluorinated rubber is preferred as the fluororubber. In this disclosure, partially fluorinated rubber is a fluoropolymer containing fluoromonomer units, having a perfluoromonomer unit content of less than 90 mol% relative to the total polymerization units, having a glass transition temperature of 20°C or lower, and having a melting peak (ΔH) size of 4.5 J / g or lower.

[0019] The fluororubber is more preferably at least one selected from the group consisting of vinylidene fluoride (VdF) / hexafluoropropylene (HFP) copolymer, VdF / HFP / tetrafluoroethylene (TFE) copolymer, TFE / propylene copolymer, TFE / propylene / VdF copolymer, ethylene / HFP copolymer, ethylene / HFP / VdF copolymer, ethylene / HFP / TFE copolymer, VdF / TFE / perfluoro(alkyl vinyl ether) (PAVE) copolymer, VdF / 2,3,3,3-tetrafluoropropylene copolymer, and VdF / chlorotrifluoroethylene (CTFE) copolymer. Among these, fluororubber made of copolymers containing VdF units is even more preferred.

[0020] This section describes fluororubber made from copolymers containing the vinylidene fluoride (VdF) units described above (hereinafter also referred to as "VdF-based fluororubber"). VdF-based fluororubber is a fluororubber that contains polymerization units derived from at least VdF.

[0021] As the copolymer containing VdF units, it is preferably a copolymer containing polymerization units derived from VdF units and fluorine-containing ethylenic monomers (excluding VdF units). The copolymer containing VdF units preferably further contains polymerization units derived from monomers copolymerizable with VdF and fluorine-containing ethylenic monomers.

[0022] As the copolymer containing VdF units, it preferably contains 30 to 85 mol% of VdF units and 70 to 15 mol% of polymerization units derived from fluorine-containing ethylenic monomers, and more preferably contains 30 to 80 mol% of VdF units and 70 to 20 mol% of polymerization units derived from fluorine-containing ethylenic monomers. The amount of polymerization units derived from monomers copolymerizable with VdF and fluorine-containing ethylenic monomers is preferably 0 to 10 mol% based on the total amount of polymerization units derived from VdF units and fluorine-containing ethylenic monomers.

[0023] Examples of the fluorine-containing ethylenic monomer include tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoro(alkyl vinyl ether) (PAVE), fluoroalkyl vinyl ether, chlorotrifluoroethylene (CTFE), trifluoroethylene, trifluoropropylene, pentafluoropropylene, trifluorobutene, tetrafluoroisobutene, hexafluoroisobutene, vinyl fluoride, general formula: CHX 1 =CX 2 Rf 1 (wherein X 1 and X 2 one is H and the other is F, and Rf 1 is a linear or branched fluoroalkyl group having 1 to 12 carbon atoms.) represented by the fluoromonomer, general formula: CH2=CH-(CF2) n -X 3 (wherein X 3∫ is H or F, and n is an integer from 3 to 10. Examples of fluorine-containing monomers include fluoromonomers represented by ∫, ∫, and monomers that provide crosslinking sites. Among these, at least one selected from the group consisting of TFE, HFP, PAVE, CTFE, and 2,3,3,3-tetrafluoropropylene is preferred, and at least one selected from the group consisting of TFE, HFP, and PAVE is more preferred.

[0024] The above PAVE is a general formula: CF2=CFO(CF2CFX 4 O) p -(CF2CF2CF2O) q -Rf 2 (In the formula, X 4 represents F or CF3, and Rf 2 represents a perfluoroalkyl group with 1 to 5 carbon atoms. p represents an integer from 0 to 5, and q represents an integer from 0 to 5. ), and the general formula: CFX=CXOCF2OR 1 (In the formula, X represents the same or different H, F, or CF3, and R represents the same or different H, F, or CF3.) 1 This represents a linear or branched fluoroalkyl group having 1 to 6 carbon atoms, which may contain 1 to 2 atoms selected from the group consisting of H, Cl, Br, and I, or a cyclic fluoroalkyl group having 5 or 6 carbon atoms, which may contain 1 to 2 atoms selected from the group consisting of H, Cl, Br, and I.) At least one selected from the group consisting of is preferred.

[0025] As the PAVE mentioned above, perfluoro(methyl vinyl ether) or perfluoro(propyl vinyl ether) is more preferred, and perfluoro(methyl vinyl ether) is even more preferred. These can be used individually or in any combination.

[0026] Examples of monomers copolymerizable with VdF and fluorine-containing ethylenic monomers include non-fluorinated monomers such as ethylene, propylene, and alkyl vinyl ethers.

[0027] Specifically, one or more copolymers containing such VdF units are preferred, such as VdF / HFP copolymer, VdF / HFP / TFE copolymer, VdF / CTFE copolymer, VdF / CTFE / TFE copolymer, VdF / PAVE copolymer, VdF / TFE / PAVE copolymer, VdF / HFP / PAVE copolymer, VdF / HFP / TFE / PAVE copolymer, and VdF / 2,3,3,3-tetrafluoropropylene copolymer. Among these copolymers containing VdF units, at least one copolymer selected from the group consisting of VdF / HFP copolymer and VdF / HFP / TFE copolymer is particularly preferred in terms of heat resistance, non-stick properties, and flexibility.

[0028] The VdF / HFP copolymer is preferably one in which the molar ratio of VdF / HFP is 45-85 / 55-15, more preferably 50-80 / 50-20, and even more preferably 60-80 / 40-20.

[0029] As the VdF / HFP / TFE copolymer, a VdF / HFP / TFE molar ratio of 40-80 / 10-35 / 10-35 is preferred.

[0030] As the VdF / PAVE copolymer, one with a VdF / PAVE molar ratio of 65-90 / 10-35 is preferred.

[0031] As the VdF / TFE / PAVE copolymer, a VdF / TFE / PAVE molar ratio of 40-80 / 3-40 / 15-35 is preferred.

[0032] As the VdF / HFP / PAVE copolymer, a VdF / HFP / PAVE molar ratio of 65-90 / 3-25 / 3-25 is preferred.

[0033] The VdF / HFP / TFE / PAVE copolymer is preferably one in which the molar ratio of VdF / HFP / TFE / PAVE is 40-90 / 0-25 / 0-40 / 3-35, and more preferably 40-80 / 3-25 / 3-40 / 3-25.

[0034] The VdF / 2,3,3,3-tetrafluoropropylene copolymer is preferably one in which the molar ratio of VdF / 2,3,3,3-tetrafluoropropylene is 45-85 / 55-15, more preferably 50-80 / 50-20, and even more preferably 60-80 / 40-20.

[0035] The above-mentioned fluororubber may also preferably consist of a copolymer containing polymerization units derived from monomers that provide crosslinking sites. Examples of monomers that provide crosslinking sites include iodine-containing monomers such as perfluoro(6,6-dihydro-6-iodo-3-oxa-1-hexene) and perfluoro(5-iodo-3-oxa-1-pentene) as described in Japanese Patent Publication No. 5-63482 and Japanese Patent Application Publication No. 7-316234, bromine-containing monomers as described in Japanese Patent Publication No. 4-505341, cyano group-containing monomers, carboxyl group-containing monomers, and alkoxycarbonyl group-containing monomers as described in Japanese Patent Publication No. 4-505345 and Japanese Patent Publication No. 5-500070.

[0036] The above-mentioned fluororubber may be obtained by using a chain transfer agent during polymerization. Bromine compounds or iodine compounds may be used as the chain transfer agent. An example of a polymerization method using bromine compounds or iodine compounds is a method in which emulsion polymerization is carried out in an aqueous medium under pressurized conditions in the presence of a bromine compound or iodine compound, in a substantially oxygen-free environment (iodine transfer polymerization method). A typical example of a bromine compound or iodine compound used is, for example, a general formula: R 2 I x Br y (In the formula, x and y are integers from 0 to 2, and satisfy 1 ≤ x + y ≤ 2, R 2Examples of compounds represented by a saturated or unsaturated fluorohydrocarbon group or chlorofluorohydrocarbon group having 1 to 16 carbon atoms, or a hydrocarbon group having 1 to 3 carbon atoms (which may contain an oxygen atom). By using a bromine compound or an iodine compound, iodine or bromine is introduced into the polymer and functions as a crosslinking point.

[0037] Examples of the above-mentioned fluororubbers include peroxide-crosslinkable fluororubbers, polyol-crosslinkable fluororubbers, and polyamine-crosslinkable fluororubbers. Peroxide-crosslinkable fluororubbers and polyol-crosslinkable fluororubbers are preferred among the above-mentioned fluororubbers.

[0038] The peroxide-crosslinkable fluororubber described above is not particularly limited and may be any fluororubber having peroxide-crosslinkable parts. The peroxide-crosslinkable parts described above are not particularly limited and may include, for example, iodine atoms, bromine atoms, etc. When the fluororubber contains iodine atoms, the iodine content is preferably 0.001 to 10% by mass, more preferably 0.01% by mass or more, preferably 0.1% by mass or more, and more preferably 5% by mass or less.

[0039] The polyol-crosslinkable fluororubber described above is not particularly limited and can be any fluororubber having polyol-crosslinkable moieties. The polyol-crosslinkable moieties described above are not particularly limited and can include, for example, moieties having vinylidene fluoride (VdF) units. A method for introducing the crosslinkable moieties is to copolymerize monomers that provide the crosslinkable moieties during the polymerization of the fluororubber.

[0040] The Mooney viscosity (ML1+10(121°C)) of fluororubber at 121°C is preferably 2 or higher, more preferably 5 or higher, even more preferably 10 or higher, preferably 200 or lower, more preferably 120 or lower, even more preferably 100 or lower, and particularly preferably 80 or lower. The Mooney viscosity is measured in accordance with ASTM-D1646-15 and JIS K6300-1:2013.

[0041] (Cellulose nanofiber) Cellulose nanofibers are fine fibers made from cellulose. Either unmodified cellulose nanofibers or modified cellulose nanofibers made from modified cellulose may be used.

[0042] Modified cellulose is obtained by modifying cellulose. Examples of modified cellulose include carboxylated cellulose, carboxymethylated cellulose, cationized cellulose, and esterified cellulose. Carboxymethylated cellulose is distinguished from carboxymethyl cellulose in that at least a portion of it retains its fibrous shape when dispersed in water. The maintenance of the fibrous shape in the aqueous dispersion can be confirmed by observing the aqueous dispersion with an electron microscope.

[0043] The average fiber diameter of cellulose nanofibers may be between 3 nm and 10 μm, or between 3 and 500 nm. The average fiber diameter of cellulose nanofibers can be calculated by measuring the fiber diameter of 10 fibers using a scanning electron microscope (SEM), atomic force microscope (AFM), or transmission electron microscope (TEM), and averaging the measured values.

[0044] The aspect ratio (average fiber length / average fiber diameter) of cellulose nanofibers is preferably 50 to 1000. The average fiber diameter and average fiber length of cellulose nanofibers can be calculated by measuring the fiber diameter and fiber length of 10 fibers using a scanning electron microscope (SEM), atomic force microscope (AFM), or transmission electron microscope (TEM), and averaging the measured values.

[0045] In this disclosure, cellulose nanofibers obtained by known manufacturing methods can be used. When compounding with rubber, cellulose nanofiber powder may be compounded with the rubber, or an aqueous dispersion of cellulose nanofibers may be compounded with the rubber. Alternatively, a rubber composition may be prepared by preparing an aqueous dispersion containing rubber and cellulose nanofibers and co-coagulating the rubber and cellulose nanofibers in the aqueous dispersion.

[0046] The cellulose nanofiber content is preferably 1 to 50 parts by mass, more preferably 2 parts by mass or more, even more preferably 3 parts by mass or more, even more preferably 5 parts by mass or more, more preferably 40 parts by mass or less, and even more preferably 30 parts by mass or less, per 100 parts by mass of rubber. By setting the cellulose nanofiber content within the above range, the low permeability and swelling resistance of the sealing body to electrolyte components such as γ-butyrolactone can be further improved without impairing the excellent sealing performance of the sealing body.

[0047] (Crosslinking agent) In one embodiment, the rubber composition contains a crosslinking agent. The type of crosslinking agent is not particularly limited and can be appropriately selected depending on the type of rubber and the melt-mixing conditions.

[0048] Any of the following can be used as crosslinking agents: sulfur-based crosslinking agents, quinone dioxime-based crosslinking agents, polyamine-based crosslinking agents, polyol-based crosslinking agents, peroxide-based crosslinking agents, imidazole-based crosslinking agents, triazine-based crosslinking agents, oxazole-based crosslinking agents, or thiazole-based crosslinking agents, and may be used alone or in combination.

[0049] In one embodiment, the rubber composition contains at least one selected from the group consisting of sulfur-based crosslinking agents, quinone dioxime-based crosslinking agents, polyol-based crosslinking agents, and peroxide-based crosslinking agents. In one embodiment, the rubber composition contains at least one selected from the group consisting of sulfur-based crosslinking agents and peroxide-based crosslinking agents. In one embodiment, the rubber composition contains at least one selected from the group consisting of peroxide-based crosslinking agents.

[0050] Examples of sulfur-based crosslinking agents include powdered sulfur, precipitated sulfur, colloidal sulfur, surface-treated sulfur, insoluble sulfur, sulfur chloride, sulfur dichloride, disulfide compounds, and polysulfide compounds.

[0051] The rubber composition may contain a crosslinking accelerator along with a sulfur-based crosslinking agent. Examples of crosslinking accelerators include thiram-based accelerators and dithiocarbamate-based accelerators.

[0052] Examples of quinone dioxime crosslinking agents include p-quinone dioxime and p-p'-dibenzoylquinone dioxime.

[0053] The rubber composition may contain an oxidizing agent (activator) along with a quinone dioxime crosslinking agent. Examples of oxidizing agents include lead peroxide (PbO2, Pb3O4) and dibenzothiazyl disulfide (MBTS).

[0054] As polyol-based crosslinking agents, for example, polyhydroxy compounds, and in particular polyhydroxy aromatic compounds, are preferably used due to their excellent heat resistance.

[0055] Examples of polyhydroxyaromatic compounds include 2,2-bis(4-hydroxyphenyl)propane (hereinafter referred to as bisphenol A), 2,2-bis(4-hydroxyphenyl)perfluoropropane (hereinafter referred to as bisphenol AF), 1,3-dihydroxybenzene, 1,7-dihydroxynaphthalene, 2,7-dihydroxynaphthalene, 1,6-dihydroxynaphthalene, 4,4'-dihydroxydiphenyl, 4,4'-dihydroxystilbene, 2,6-dihydroxyanthracene, hydroquinone, and catechin. Examples include chol, 2,2-bis(4-hydroxyphenyl)butane (hereinafter referred to as bisphenol B), 4,4-bis(4-hydroxyphenyl)valeric acid, 2,2-bis(4-hydroxyphenyl)tetrafluorodichloropropane, 4,4'-dihydroxydiphenyl sulfone, 4,4'-dihydroxydiphenyl ketone, tri(4-hydroxyphenyl)methane, 3,3',5,5'-tetrachlorobisphenol A, 3,3',5,5'-tetrabromobisphenol A, and diaminobisphenol AF. These polyhydroxy aromatic compounds may also be alkali metal salts, alkaline earth metal salts, etc. Among these, polyhydroxy compounds are preferred, polyhydroxy aromatic compounds are more preferred due to their excellent heat resistance, and bisphenol AF is even more preferred.

[0056] The rubber composition may contain a crosslinking aid along with the polyol-based crosslinking agent. Using a crosslinking aid can accelerate the crosslinking reaction by promoting the formation of intramolecular double bonds in the dehydrofluoric acid reaction of the fluororubber main chain.

[0057] Onium compounds are generally used as crosslinking aids. The onium compounds are not particularly limited and include, for example, ammonium compounds such as quaternary ammonium salts, phosphonium compounds such as quaternary phosphonium salts, oxonium compounds, sulfonium compounds, cyclic amines, and monofunctional amine compounds. Among these, quaternary ammonium salts or quaternary phosphonium salts are preferred, and 8-benzyl-1,8-diazabicyclo[5,4,0]-7-undecenium chloride (DBU-B) or benzyltriphenylphosphonium chloride (BTPPC) are more preferred.

[0058] As peroxide-based crosslinking agents, organic peroxides that can readily generate peroxy radicals in the presence of heat or an oxidation-reduction system are preferably used.

[0059] Examples of peroxide-based crosslinking agents include 1,1-bis(t-butylperoxy)-3,5,5-trimethylcyclohexane, 2,5-dimethylhexane-2,5-dihydroperoxide, di-t-butylperoxide, t-butylcumylperoxide, dicumylperoxide, α,α-bis(t-butylperoxy)-p-diisopropylbenzene, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di(t-butylperoxy)-hexyne-3, benzoylperoxide, t-butylperoxybenzene, t-butylperoxymaleic acid, and t-butylperoxyisopropyl carbonate. Among these, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane is preferred.

[0060] The rubber composition may contain a crosslinking aid along with a peroxide-based crosslinking agent. Examples of crosslinking aids include triallyl cyanurate and triallyl isocyanurate (TAIC).

[0061] The crosslinking agent content is preferably 0.05 to 10 parts by mass, more preferably 0.1 to 10 parts by mass, even more preferably 0.3 to 7 parts by mass, and particularly preferably 1 to 5 parts by mass, per 100 parts by mass of rubber.

[0062] The crosslinking agent content is preferably 0.1 to 20 parts by mass, more preferably 0.1 to 10 parts by mass, even more preferably 0.2 to 10 parts by mass, and particularly preferably 0.3 to 5 parts by mass, per 100 parts by mass of rubber.

[0063] (Other ingredients) In one embodiment, the rubber composition contains various additives such as fillers (carbon black, bituminous coal, barium sulfate, diatomaceous earth, calcined clay, talc, wollastonite, carbon nanotubes, etc.), processing aids (wax, etc.), plasticizers, colorants, stabilizers, tackifiers (coumarone resin, coumarone-indene resin, etc.), release agents, conductivity enhancers, thermal conductivity enhancers, surface non-tackeners, flexibility enhancers, heat resistance improvers, flame retardants, foaming agents, and antioxidants described in International Publication No. 2012 / 023485.

[0064] Examples of fillers (excluding cellulose nanofibers) include metal oxides such as titanium dioxide and aluminum oxide; metal hydroxides such as magnesium hydroxide and aluminum hydroxide; carbonates such as magnesium carbonate, aluminum carbonate, calcium carbonate, and barium carbonate; silicates such as magnesium silicate, calcium silicate, and aluminum silicate; sulfates such as aluminum sulfate, calcium sulfate, and barium sulfate; metal sulfides such as molybdenum disulfide, iron sulfide, and copper sulfide; diatomaceous earth, asbestos, lithopone (zinc sulfide / barium sulfide), graphite, carbon fluoride, calcium fluoride, coke, quartz powder, talc, mica powder, wollastonite, carbon fiber, aramid fiber, various whiskers, glass fiber, organic reinforcing agents, organic fillers, polytetrafluoroethylene, fluorine-containing thermoplastic resins, mica, silica, Celite, and clay.

[0065] As carbon black, thermal carbon black and furnace carbon black are preferred, and MT carbon black, FT carbon black, and SRF carbon black are more preferred. When carbon black with a relatively large particle size, such as MT carbon black or FT carbon black, is blended, a molded article with excellent compression set characteristics can be obtained, while when carbon black with a fine particle size is blended, a molded article with excellent strength and elongation can be obtained. By blending different grades in combination, the above characteristics can be balanced.

[0066] The content of fillers such as carbon black is not particularly limited, but is preferably 0 to 300 parts by mass, more preferably 1 to 150 parts by mass, even more preferably 2 to 100 parts by mass, and particularly preferably 2 to 75 parts by mass per 100 parts by mass of rubber.

[0067] Rubber compositions can be produced by mixing rubber, cellulose nanofibers, and other desired materials using an open roll mixer, Banbury mixer, kneader, etc. Alternatively, they can be prepared by using a closed mixer or by co-coagulation from emulsion mixing. Crosslinking agents, additives, etc., may be added as desired.

[0068] (Molded body) Various molded articles can be obtained by molding a rubber composition. A molded article obtained from a rubber composition is also one of the present disclosures. Preferably, the molded article of the present disclosure is obtained by crosslinking the above rubber composition.

[0069] The molding can be carried out by conventionally known methods, such as compression molding, injection molding, extrusion molding, and calendering. Alternatively, the material may be dissolved in a solvent and molded by dip molding, coating, or other methods.

[0070] When obtaining various molded articles from a rubber composition, a crosslinking process may be performed. The crosslinking conditions vary depending on the molding method and the shape of the molded article. When the rubber composition contains fluororubber, the crosslinking conditions are, for example, in the range of a few seconds to 180 minutes at 100 to 200°C. Secondary crosslinking may also be performed to stabilize the physical properties of the crosslinked article. When the rubber composition contains fluororubber, the secondary crosslinking conditions are, for example, about 30 minutes to 30 hours at 150 to 300°C.

[0071] (Electrolytic capacitor sealing material) Molded articles obtained by molding the rubber composition exhibit excellent sealing properties and show excellent low permeability and swelling resistance to electrolyte components such as γ-butyrolactone contained in the electrolyte of an electrolytic capacitor. Therefore, the above-described rubber composition can be suitably used as a material for forming electrolytic capacitor sealing bodies. This disclosure also relates to the use of the above-described rubber composition for forming sealing bodies that suppress the reduction of the electrolyte containing γ-butyrolactone sealed in an electrolytic capacitor.

[0072] The electrolytic capacitor sealing bodies obtained from the rubber compositions described above exhibit excellent sealing properties, as well as low permeability to electrolyte components such as γ-butyrolactone and excellent swelling resistance. In particular, electrolytic capacitor sealing bodies obtained from rubber compositions containing fluororubber exhibit excellent resistance to compression set at high temperatures, as well as low permeability to electrolyte components such as γ-butyrolactone contained in the electrolyte of electrolytic capacitors and excellent swelling resistance.

[0073] The electrolytic capacitor sealing body of this disclosure may be composed of a molded body obtained by crosslinking the rubber composition described above, in whole or in part. For example, the electrolytic capacitor sealing body of this disclosure may be a sealing body composed solely of a molded body obtained by crosslinking the rubber composition described above, or a sealing body composed of a molded body obtained by crosslinking the rubber composition described above and a resin film integrated together. Examples of resins that form the resin film include phenolic resin, polyethylene naphthalate, polyphenylene sulfide, polyethersulfone, polyetherimide, polyetheretherketone, polyimide, ethylenetetrafluoroethylene, tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene / hexafluoropropylene copolymer, polychlorotrifluoroethylene, and polytetrafluoroethylene.

[0074] The electrolytic capacitor sealing body of this disclosure exhibits excellent low permeability to γ-butyrolactone contained in the electrolyte of the electrolytic capacitor and excellent resistance to swelling. Therefore, in electrolytic capacitors equipped with the electrolytic capacitor sealing body of this disclosure, the electrolyte is less likely to decrease, even when the electrolyte contains γ-butyrolactone. Consequently, electrolytic capacitors equipped with the electrolytic capacitor sealing body of this disclosure have a long lifespan.

[0075] In one embodiment, the electrolytic capacitor comprises a capacitor element impregnated with an electrolyte, an outer casing housing the capacitor element, a sealing body that seals the opening of the outer casing, and a lead terminal that penetrates the sealing body and protrudes from the outer casing to the outside. By using an electrolytic capacitor sealing body obtained by crosslinking the above-mentioned rubber composition as the sealing body, the electrolyte can be made less likely to decrease even when the electrolyte contains γ-butyrolactone.

[0076] Although embodiments have been described above, it should be understood that various modifications to the form and details are possible without departing from the spirit and scope of the claims.

[0077] <1> According to the first aspect of this disclosure, A rubber composition for electrolytic capacitor sealing bodies containing rubber and cellulose nanofibers is provided. <2> According to the second aspect of this disclosure, A rubber composition for electrolytic capacitor sealing is provided, wherein the rubber is at least one selected from ethylene propylene rubber, butadiene styrene rubber, isobutylene isoprene rubber, and fluororubber. <3> According to the third aspect of this disclosure, A rubber composition for electrolytic capacitor sealing is provided, wherein the cellulose nanofiber content is 1 to 50 parts by mass per 100 parts by mass of the rubber, according to a first or second view. <4> According to the fourth aspect of this disclosure, An electrolytic capacitor sealing body obtained from a rubber composition for electrolytic capacitor sealing bodies according to any of the first to third aspects is provided. [Examples]

[0078] Next, embodiments of the present disclosure will be described with reference to examples, but the present disclosure is not limited to such embodiments.

[0079] Each value in the examples was measured by the following method.

[0080] <Fluorine content> 19 The composition of fluororubber was calculated from the composition measured by 1F-NMR.

[0081] <Moony viscosity> Measurements were taken in accordance with ASTM D1646-15 and JIS K6300-1:2013. The measurement temperature was 121°C.

[0082] <Crosslinking properties> Regarding the rubber composition, at the time of primary crosslinking, using a vulcanization tester (MDR H2030 manufactured by EM and C Co., Ltd.), the crosslinking curve was obtained at the temperature described in the table, and from the change in torque, the minimum torque (ML), maximum torque (MH), crosslinking induction time (T10), intermediate crosslinking time (T50), and optimum crosslinking time (T90) were determined.

[0083] <Normal physical properties> Using a 2 mm thick molded body, with a tensile tester (Tensilon RTG - 1310 manufactured by A&D Company Limited), in accordance with JIS K6251 - 1:2015, under the condition of 500 mm / min, using a dumbbell No. 6, the 100% tensile stress (TS) and elongation (EL) at 23 °C were measured.

[0084] <Hardness (Shore A)> Using three stacked 2 mm thick molded bodies, with a Type A durometer, in accordance with JIS K6253 - 3:2012, the hardness (3 - second value, HS(3sec)) was measured.

[0085] <Specific gravity> Using a 2 mm thick and 20 mm square molded body, with an automatic specific gravity meter (High - precision type DMA - 220H manufactured by Shin Koden Co., Ltd.), the measurement was carried out in accordance with JIS K6268:1998.

[0086] <Compression set> Using the rubber compositions prepared in the examples and comparative examples, molded bodies (small - sized test pieces for compression set measurement (P - 24, O - ring)) were produced. Using the obtained test pieces, in accordance with Method A of JIS K6262:2013, the measurement was carried out at a compression rate of 25%, a test temperature of 200 °C, and a test time of 70 hours.

[0087] <γ - Butyrolactone immersion test> Samples were prepared from molded bodies obtained in the examples and comparative examples. Samples, whose mass and specific gravity had been measured beforehand using an automatic hydrometer (Shinko Denshi Co., Ltd., high-precision type DMA-220H), were immersed in a 100 ml glass container with a lid containing 50 ml of γ-butyrolactone. After 70 hours in a constant temperature device (60°C), the samples were removed and their mass and specific gravity were measured again using the automatic hydrometer. The volume of the sample before and after the test (volume = mass ÷ specific gravity) was calculated, and the rate of change in the volume of the sample before and after the immersion test was determined using the following formula. Volume change rate (%) = (Sample volume after test - Sample volume before test) × 100 / Sample volume before test

[0088] <γ-butyrolactone permeation test> A stainless steel container with a volume of 70 mL (opening area 1.26 × 10 -3 m 2 A 0.5 mm thick sheet-like molded body was prepared by adding 20 mL of γ-butyrolactone to a container and sealing it. An electronic balance (GX-603AWP, A&D Corporation) was used to weigh the test specimen. The specimen was placed in a constant temperature device (60°C) with the γ-butyrolactone in contact with the liquid, and its weight was measured. The permeability coefficient was determined using the following formula when the weight loss per unit time became constant.

[0089]

number

[0090] The following materials were used in the examples and comparative examples. Rubber: Ternary peroxide crosslinked fluororubber (VdF / HFP / TFE copolymer, fluorine content = 70% by mass, Mooney viscosity ML1 + 10 (121℃) = 21)

[0091] Carbon Black: Cancarb Thermax N990 Crosslinking agent: Triallyl isocyanurate (TAIC, manufactured by Mitsubishi Chemical Corporation) Crosslinking agent: 2,5-Dimethyl-2,5-di(t-butylperoxy)hexane (Perhexa 25B, manufactured by NOF Corporation)

[0092] Cellulose nanofibers Sugino Machine Co., Ltd. Binfis FMa-UNDP Median diameter: 5-10 μm Degree of polymerization: 200 Fiber length: extremely short Moisture content: 4~8% by mass

[0093] Example 1 To 100 parts by mass of fluororubber, 3 parts by mass of triallyl isocyanurate, 1 part by mass of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and 20 parts by mass of carbon black were mixed, and then 10 parts by mass of cellulose nanofiber was added. The mixture was then kneaded on a roll by a conventional method to prepare a rubber composition.

[0094] The obtained rubber composition was crosslinked by pressing it under the molding conditions described in Table 1 to obtain various molded articles. Various physical properties were measured for the obtained molded articles. The results are shown in Table 1.

[0095] Example 2 and Comparative Example 1 Except for changing the formulation as shown in Table 1, rubber compositions were prepared in the same manner as in Example 1, and various molded articles were obtained. The results are shown in Table 1.

[0096] [Table 1]

Claims

1. A rubber composition for electrolytic capacitor sealing bodies containing rubber and cellulose nanofibers.

2. The rubber composition for electrolytic capacitor sealing body according to claim 1, wherein the rubber is at least one selected from ethylene propylene rubber, butadiene styrene rubber, isobutylene isoprene rubber, and fluororubber.

3. The rubber composition for electrolytic capacitor sealing body according to claim 1 or 2, wherein the content of the cellulose nanofiber is 1 to 50 parts by mass per 100 parts by mass of the rubber.

4. An electrolytic capacitor sealing body obtained from the rubber composition for electrolytic capacitor sealing bodies described in claim 1 or 2.

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