Hydrogenated nitrile rubber

Abstract

Provided is a hydrogenated nitrile rubber with which, because of excellent viscosity characteristics (dispersibility) and stability of conductive material dispersions thereof when producing an electrode for an electrochemical element, the produced electrochemical element has excellent cycling characteristics and output characteristics, and excellent inhibition of cracks of electrode active material after cycle testing can be attained. This hydrogenated nitrile rubber comprises nitrile group-containing monomer units and conjugated diene monomer units and / or alkylene structural units, has a weight average molecular weight (Mw) in the range of 1,000-1,000,000 and an iodine value in the range of 0.1-100 mg / 100 mg, contains 2,2-methylenebis(4-methyl-6-tert-butylphenol) as an antioxidant, and has a calcium (Ca) content in the range of 1-2,500 ppm and a sodium (Na) content of 300 ppm or less.

Description

Hydrogenated Nitrile Rubber

[0001] The present invention relates to hydrogenated nitrile rubber and a method for producing the same, a bale made of hydrogenated nitrile rubber, a binder for a positive electrode obtained by dispersing or dissolving hydrogenated nitrile rubber or a hydrogenated nitrile rubber bale in a solvent, a positive electrode containing hydrogenated nitrile rubber, and a method for producing the same.

[0002] Electrochemical devices such as lithium ion secondary batteries, lithium ion capacitors, and electric double layer capacitors are small, lightweight, have high energy density, and can be repeatedly charged and discharged, and are therefore used in a wide range of applications. Therefore, in recent years, improvements in battery components such as electrodes have been investigated with the aim of further improving the performance of electrochemical devices.

[0003] Here, an electrode used in an electrochemical element typically includes a current collector and an electrode mixture layer formed on the current collector. This electrode mixture layer is formed, for example, by applying a slurry containing an electrode active material, a conductive material, a binder, etc., onto the current collector and then drying the applied slurry.

[0004] Therefore, in recent years, attempts have been made to improve the binder used in forming the electrode mixture layer in order to achieve further improvements in the performance of electrochemical elements. For example, a technology using a polymer containing a nitrile group-containing monomer unit as the binder has been investigated.

[0005] For example, Patent Document 1 (JP 2018-160421 A) discloses a binder composition that contains a polymer containing a conjugated diene monomer unit and / or an alkylene structural unit and a nitrile group-containing monomer unit, and an organic solvent, and that has a solution turbidity of 1 to 80 at a solid content concentration of 10% by mass and has an excellent balance between peel strength and secondary battery output characteristics. Specifically, nitrile rubber latex, obtained by emulsion polymerization of acrylonitrile and 1,3-butadiene, was added to a 1% by mass aqueous solution of calcium chloride to coagulate, washed with water, filtered, and then vacuum-dried to obtain nitrile rubber. The resulting nitrile rubber was then metathesized with a ruthenium-based Grubbs catalyst and ethylene as a coolefin, followed by hydrogenation using a rhodium-based Wilkinson catalyst with an iodine value of 5 mg / 100 mg as the endpoint. 0.2 parts of activated carbon with an average diameter of 15 μm was then added and stirred for 30 minutes to obtain a hydrogenated polymer with a calcium ion concentration of 1000 ppm and an iodine value of 5 mg / 100 mg. N-methylpyrrolidone (NMP) was then added, and water was evaporated under reduced pressure to obtain an NMP solution of the hydrogenated polymer with a solution turbidity of 20. Electrodes were fabricated using a binder composition consisting of 1.6 parts polyvinylidene fluoride (solution viscosity 5 kPa s) and 0.4 parts of the hydrogenated polymer as a binder composition. However, the binder composition obtained here has a problem that the stability of the conductive material dispersion is poor, making it difficult to prepare an electrochemical element electrode.

[0006] Patent Document 2 (Japanese Patent No. 6911985) discloses an electrochemical element having excellent rate characteristics and high-temperature storage stability, which includes a polymer containing α,β-ethylenically unsaturated nitrile monomer units and specific alkylene structural units, which has a volume average particle diameter D of 50 to 800 nm when subjected to dynamic light scattering measurement, and at least one peak detected in the range of 5 μm to 30 μm, and a conductive carbon material. Specifically, the element discloses copolymerizing acrylonitrile and 1,3-butadiene, adding dibutylhydroxytoluene (BHT) as an antioxidant, and then adding a 25% by mass aqueous solution of calcium chloride in an amount of 3 parts per 100 parts of the polymer to coagulate the polymer, passing 50 times the amount of ion-exchanged water through the polymer for washing, and then subjecting the polymer to a hydrogenation reaction using a palladium catalyst, followed by filtering off the palladium catalyst, to obtain polymers with iodine values ​​of 5 mg / 100 mg and 55 mg / 100 mg. However, it is desired that the polymer obtained here has further improvements in dispersibility in the dispersion of the dispersant, cycle characteristics of the electrochemical device, and suppression of cracking of the electrode active material after cycle testing.

[0007] On the other hand, Patent Document 3 (Japanese Patent No. 6,309,634) discloses hydrogenated nitrile rubber containing a specific phenolic antioxidant, which is useful for sealing materials, hose materials, transmission hoses, etc. in the automotive field. Specifically, an antioxidant of 2,2-methylenebis(4-methyl-6-tert-butylphenol) is added to an emulsion polymerization liquid obtained by emulsion polymerizing acrylonitrile and 1,3-butadiene, and the resulting mixture is coagulated with an aqueous sodium chloride solution or an aqueous magnesium chloride solution prepared with calcium ion-containing tap water. The resulting mixture is washed with calcium ion-containing tap water, mechanically dehydrated, and vacuum dried to obtain NBR. The resulting mixture is then hydrogenated in monochlorobenzene using a rhodium-based catalyst until the amount of remaining double bonds in the polymer reaches less than 1%, and a carboxyl group-containing water-soluble polymer, a 2% aqueous calcium chloride solution (0.15 parts by mass based on 100 parts by mass of hydrogenated nitrile rubber), and a dilute aqueous sodium hydroxide solution are continuously measured and added to the chlorobenzene solution after the reaction to coagulate the resulting hydrogenated nitrile rubber. However, even when the hydrogenated nitrile rubber obtained here was used as a binder for producing electrodes, the output characteristics and cycle characteristics were extremely poor, and cracking of the active material occurred after cycle testing, making it unsuitable as a binder for electrodes.

[0008] Patent Document 4 (WO 2007 / 049651) discloses a carboxyl group-containing nitrile rubber which provides a crosslinked product with low compression set and dynamic heat generation and has excellent processability, and which has an α,β-ethylenically unsaturated nitrile monomer unit content of 10 to 60% by weight, an iodine value of 120 or less, and a total amount of magnesium, calcium, and aluminum of 2,000 ppm or less. A specific carboxyl group-containing nitrile rubber is obtained by adding an aqueous magnesium sulfate solution to a latex of a nitrile group-containing saturated copolymer rubber obtained by emulsion polymerizing acrylonitrile, mono-n-butyl fumarate, and butadiene and then hydrogenating the copolymer with a palladium catalyst, coagulating the resulting mixture, filtering and washing with water three times, removing the aqueous magnesium sulfate solution contained in the rubber through a centrifuge, and vacuum drying at 60°C for 12 hours to obtain a nitrile rubber having a magnesium content of 1 to 2 ppm, a calcium content of 1 ppm, and an aluminum content of 1 ppm. However, there is a demand for a polymer suitable as a binder for a positive electrode, which has the stability of a conductive material dispersion and, when used in an electrochemical element, can improve the electrode peel strength and cracking of the active material layer after a cycle test.

[0009] Patent Document 5 (JP 2009-179686 A) discloses a method for recovering carboxyl group-containing nitrile rubber from a latex of carboxyl group-containing nitrile rubber, which uses an extruder having a rotatable screw disposed inside a barrel having at least a coagulation zone formed therein. Specifically, a latex of carboxyl group-containing nitrile rubber (acrylonitrile monomer units: 34 wt%, butadiene monomer units: 59 wt%, n-monobutyl maleate monomer units: 7 wt%, iodine value: 10, solids concentration: 10.8 wt%) obtained by emulsion polymerization in accordance with Patent Document 4 and an aqueous magnesium sulfate solution (coagulant concentration: 5 wt%) as a coagulation liquid are prepared, and coagulation, drainage, washing, dehydration, and drying are carried out using a screw-type extruder equipped with a coagulation zone, a drainage zone, a washing / dehydration zone, and a drying zone, whereby a sheet-like carboxyl group-containing nitrile rubber having a Mooney viscosity of 40 is recovered. However, there is a demand for a polymer suitable as a binder for a positive electrode, which has the stability of a conductive material dispersion and, when used in an electrochemical element, can improve the electrode peel strength and cracking of the active material layer after a cycle test.

[0010] Japanese Patent Publication No. 2018-160421 Japanese Patent No. 6911985 Japanese Patent No. 6309634 WO2007 / 049651 Japanese Patent Publication No. 2009-179686

[0011] The present invention has been made in view of the above circumstances, and has an object to provide a hydrogenated nitrile rubber which has excellent viscosity characteristics (dispersibility) and stability when a conductive material dispersion is used to produce an electrode for an electrochemical element, and which therefore has excellent cycle characteristics and output characteristics of the produced electrochemical element and is also excellent in suppressing cracking of the electrode active material after a cycle test, a method for producing the same, a bale made of hydrogenated nitrile rubber, a binder for a positive electrode formed by dispersing or dissolving hydrogenated nitrile rubber or hydrogenated nitrile rubber bale in a solvent, and a positive electrode which contains hydrogenated nitrile rubber and a method for producing the same.

[0012] The present inventors have conducted extensive research in view of the above-mentioned problems and have found that, by using a hydrogenated nitrile rubber, which contains a nitrile group-containing monomer unit and a conjugated diene monomer unit and / or an alkylene structural unit, has a specific amount of iodine value and weight-average molecular weight (Mw), contains a specific antioxidant, and has a specific Ca content and Na content, as a binder for a positive electrode, the viscosity characteristics and stability of a conductive material dispersion liquid can be excellent in the cycle characteristics and output characteristics of the produced electrochemical element, and the electrochemical element can also be excellent in the prevention of cracking of the electrode active material after a cycle test.

[0013] The present inventors have also found that the above properties are further improved by using, as a positive electrode binder, a hydrogenated nitrile rubber in which the contents of Rh, Ru, Pd, Mg, etc. in the hydrogenated nitrile rubber are further limited. The present inventors have also found that the above properties are further improved by using, as a positive electrode material, a hydrogenated nitrile rubber having a high bulk density, and in particular, the stability of the conductive material dispersion is remarkably improved.

[0014] The present inventors have also found that by using calcium chloride as a coagulant for the hydrogenated nitrile rubber veil, the electrode peeling characteristics of electrochemical elements such as lithium ion secondary batteries are superior to those when other coagulants are used, and deterioration of cycle characteristics and cracking of the active material layer after cycle testing can be prevented.

[0015] The present inventors have found that hydrogenated nitrile rubber, which is a polymer (nitrile rubber) obtained by emulsion polymerizing a nitrile group-containing monomer and a conjugated diene monomer and coagulating the polymer with calcium chloride, can increase the viscosity characteristics of a conductive material dispersion when the conductive material dispersion is prepared, and can also suppress cracking of the electrode active material in the resulting electrode after a cycle test, thereby significantly improving the cycle characteristics of an electrochemical element.

[0016] The present inventors have found that hydrogenated nitrile rubber is obtained by emulsion polymerizing a nitrile group-containing monomer and a conjugated diene monomer, followed by coagulation with calcium chloride of the emulsion polymerization liquid to which a specific antioxidant has been added, and then hydrogenating the polymer obtained. This hydrogenated nitrile rubber can significantly improve the viscosity characteristics and stability of a conductive material dispersion when used to prepare a conductive material dispersion, and can also suppress cracking of the electrode active material in the resulting electrode after a cycle test, thereby significantly improving the output characteristics and cycle characteristics of an electrochemical element.

[0017] The present inventors have found that hydrogenated nitrile rubber, which exhibits excellent viscosity characteristics and stability of the conductive material dispersion and is also excellent in the output characteristics and cycle characteristics of electrochemical devices and in suppressing cracking of the active material after cycle tests, can be easily produced by hydrogenating nitrile rubber containing a specific antioxidant. The present inventors have also found that such hydrogenated nitrile rubber can be easily obtained by emulsion polymerizing a monomer component containing a nitrile group-containing monomer and a conjugated diene monomer, adding the specific antioxidant, coagulating the emulsion polymerization liquid with an aqueous calcium chloride solution, thoroughly washing the resulting water-containing crumbs to obtain a polymer, subjecting the resulting polymer to metathesis with a Grubbs catalyst and a coolefin, and then hydrogenating it with a Wilkinson catalyst. The present inventors have also found that the Ca content in the hydrogenated nitrile rubber can be easily controlled by treating the hydrogenated nitrile rubber with an adsorbent such as activated carbon as necessary after the hydrogenation reaction, and that hydrogenated nitrile rubber with a high bulk density can be easily produced by drying the hydrogenated nitrile rubber by melt-kneading it under reduced pressure using a screw extruder.

[0018] The present inventors have also found that the effects of the present invention can be maintained by baling and maintaining the hydrogenated nitrile rubber of the present invention, and that by dispersing or dissolving the emulsion polymerization liquid of the present invention in N-methylpyrrolidone, it becomes a binder suitable for producing positive electrodes of electrochemical elements.

[0019] The present inventors have also found that the stability of a conductive material dispersion can be significantly improved by making the hydrogenated nitrile rubber bale contain a specific antioxidant, and that increasing the bulk density of the hydrogenated nitrile rubber bale and reducing the amount of air contained therein as much as possible further improves the stability of the dispersion with the conductive material, preventing cracking of the electrode active material and improving various properties of the electrochemical device. The present inventors speculate that the stability of the conductive material dispersion is deteriorated by the influence of oxygen radicals generated in the hydrogenated nitrile rubber, which react with and crosslink active sites on the surface of the electrode material, and that the absence of a specific antioxidant or air inside the bale effectively prevents the generation and reaction of these oxygen radicals. The present inventors have also found that a hydrogenated nitrile rubber bale with a high bulk density can be easily obtained by melt-kneading the bale under reduced pressure using a screw extruder, extruding it into a sheet, and then laminating the extruded hydrogenated nitrile rubber sheets.

[0020] The present inventors have completed the present invention based on these findings.

[0021] Thus, according to the present invention, there is provided a hydrogenated nitrile rubber which contains nitrile group-containing monomer units and conjugated diene monomer units and / or alkylene structural units, has a weight average molecular weight (Mw) in the range of 1,000 to 1,000,000, an iodine value in the range of 0.1 to 100 mg / 100 mg, contains 2,2-methylenebis(4-methyl-6-tert-butylphenol) as an antioxidant, has a calcium (Ca) content in the range of 1 to 2500 ppm, and has a sodium (Na) content of 300 ppm or less.

[0022] In the hydrogenated nitrile rubber of the present invention, the content of the antioxidant is preferably in the range of 0.001 to 3 mass %.

[0023] In the hydrogenated nitrile rubber of the present invention, it is further preferred that the rhodium (Rh) and / or ruthenium (Ru) content is 0.1 to 50 ppm, the palladium (Pd) content is 200 ppm or less, and the magnesium (Mg) content is 50 ppm or less.

[0024] In the hydrogenated nitrile rubber of the present invention, the bulk density is 0.8 g / cm３ It is preferable that this is equal to or greater than this.

[0025] Furthermore, in the hydrogenated nitrile rubber, it is preferable that the chlorine (Cl) content is in the range of 10 ppm or more and 3000 ppm or less, and the mass ratio (Ca / Cl) to the calcium (Ca) content is in the range of 0.1 to 4.

[0026] Furthermore, in the hydrogenated nitrile rubber, the total proportion of the nitrile group-containing monomer units and the conjugated diene monomer units and / or alkylene structural units in the hydrogenated nitrile rubber is preferably 97 mass % or more.

[0027] The hydrogenated nitrile rubber of the present invention is preferably one obtained by emulsion polymerizing a nitrile group-containing monomer and a conjugated diene monomer, coagulating the polymer with calcium chloride, and hydrogenating the resulting polymer.

[0028] The hydrogenated nitrile rubber of the present invention is preferably one obtained by emulsion polymerizing a nitrile group-containing monomer and a conjugated diene monomer, adding 2,2-methylenebis(4-methyl-6-tert-butylphenol) as an antioxidant, and then coagulating the polymer with calcium chloride, and hydrogenating the resulting polymer.

[0029] According to the present invention, there is also provided a method for producing the hydrogenated nitrile rubber, which comprises hydrogenating a nitrile rubber containing 2,2-methylenebis(4-methyl-6-tert-butylphenol) as an antioxidant.

[0030] According to the present invention, there is also provided a method for producing the above-mentioned hydrogenated nitrile rubber, which comprises: an emulsion polymerization step of emulsion-polymerizing a monomer component containing a nitrile group-containing monomer and a conjugated diene monomer to obtain an emulsion polymerization liquid; an antioxidant addition step of adding 2,2-methylenebis(4-methyl-6-tert-butylphenol) as an antioxidant to the emulsion polymerization liquid; a coagulation step of contacting the emulsion polymerization liquid to which the antioxidant has been added with calcium chloride to produce water-containing crumbs; a washing and drying step of washing and drying the water-containing crumbs to obtain a polymer; and a hydrogenation step of hydrogenating the polymer using a hydrogenation catalyst.

[0031] In the method for producing hydrogenated nitrile rubber of the present invention, the hydrogenation step preferably comprises subjecting the polymer to metathesis using a ruthenium-based catalyst and a coolefin, followed by hydrogenation using a rhodium-based catalyst.

[0032] In the method for producing hydrogenated nitrile rubber of the present invention, it is preferable to further provide a purification step of treating the hydrogenated nitrile rubber with an adsorbent after the hydrogenation step.

[0033] In the method for producing hydrogenated nitrile rubber of the present invention, it is preferable to dry the hydrogenated nitrile rubber using a screw extruder.

[0034] In the method for producing hydrogenated nitrile rubber of the present invention, the screw extruder is preferably equipped with a vacuum drying barrel.

[0035] According to the present invention, there is also provided a hydrogenated nitrile rubber bale obtained by baling the above hydrogenated nitrile rubber.

[0036] In the hydrogenated nitrile rubber bale of the present invention, the bulk density is 0.8 g / cm ３ It is preferable that this is equal to or greater than this.

[0037] The present invention also provides a binder for a positive electrode, which is obtained by dispersing or dissolving the hydrogenated nitrile rubber in N-methylpyrrolidone (NMP).

[0038] The present invention also provides a binder for a positive electrode, which is obtained by dispersing or dissolving the hydrogenated nitrile rubber veil in N-methylpyrrolidone (NMP).

[0039] The present invention also provides a positive electrode comprising a current collector and a positive electrode mixture layer containing a conductive material, a positive electrode active material, and a binder containing the hydrogenated nitrile rubber.

[0040] According to the present invention, there is further provided a method for producing a positive electrode, which includes a step of applying a positive electrode composite layer slurry obtained by mixing the above-mentioned positive electrode binder and a conductive material and then mixing the resultant with a positive electrode active material onto a current collector, and drying the resulting slurry.

[0041] According to the present invention, there are provided hydrogenated nitrile rubber which has excellent viscosity characteristics and stability and is therefore capable of suppressing cracking of the electrode active material after a cycle test of the produced electrochemical element and improving the cycle characteristics and output characteristics, a method for producing the same, a hydrogenated nitrile rubber bale made of hydrogenated nitrile rubber, a binder for a positive electrode formed by dispersing or dissolving hydrogenated nitrile rubber or hydrogenated nitrile rubber bale in a solvent, and a positive electrode comprising hydrogenated nitrile rubber and a method for producing the same.

[0042] Hereinafter, embodiments of the present invention will be described in detail.

[0043] The hydrogenated nitrile rubber of the present invention is characterized by comprising nitrile group-containing monomer units and conjugated diene monomer units and / or alkylene structural units, having a weight average molecular weight (Mw) in the range of 1,000 to 1,000,000, an iodine value of 0.1 to 100 mg / 100 mg, containing an antioxidant of 2,2-methylenebis(4-methyl-6-tert-butylphenol), and having a Ca content in the range of 1 to 2,500 ppm and a Na content of 300 ppm or less.

[0044] <Monomer Component> The hydrogenated nitrile rubber of the present invention contains a nitrile group-containing monomer unit and a conjugated diene monomer unit and / or an alkylene structural unit. Such hydrogenated nitrile rubber is a component that can function as a binder in an electrode mixture layer formed in an electrochemical element, holding an electrode active material and the like without causing it to detach from a current collector. Furthermore, such hydrogenated nitrile rubber can also function as a dispersant that can disperse a conductive material in a conductive material dispersion liquid containing a conductive material.

[0045] Specifically, the hydrogenated nitrile rubber may be a hydrogenated polymer obtained by hydrogenating a polymer containing conjugated diene monomer units and nitrile group-containing monomer units. When the polymer containing conjugated diene monomer units and nitrile group-containing monomer units is completely hydrogenated, the polymer becomes a polymer containing alkylene structural units and nitrile group-containing monomer units, and when the hydrogenation is partially carried out, the polymer becomes a polymer containing conjugated diene monomer units, alkylene structural units, and nitrile group-containing monomer units.

[0046] (Nitrile Group-Containing Monomer Unit) Examples of nitrile group-containing monomers that can form nitrile group-containing monomer units include α,β-ethylenically unsaturated nitrile monomers. Specifically, the α,β-ethylenically unsaturated nitrile monomer is not particularly limited as long as it is an α,β-ethylenically unsaturated compound having a nitrile group, and examples include acrylonitrile; α-halogenoacrylonitriles such as α-chloroacrylonitrile and α-bromoacrylonitrile; and α-alkylacrylonitriles such as methacrylonitrile and α-ethylacrylonitrile. Among these, acrylonitrile is preferred. One type of nitrile group-containing monomer may be used alone, or two or more types may be used in combination at any ratio.

[0047] The content of the nitrile group-containing monomer units in the hydrogenated nitrile rubber is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, and is preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less, based on 100% by mass of all repeating units in the hydrogenated nitrile rubber. If the content of the nitrile group-containing monomer units is within the above-mentioned range, the dispersion stability of the conductive material dispersion can be increased, and the peel strength of the obtained electrode can be further improved.

[0048] (Conjugated Diene Monomer Unit) Here, examples of the conjugated diene monomer capable of forming the conjugated diene monomer unit include conjugated diene compounds having 4 or more carbon atoms, such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, and 1,3-pentadiene. Of these, isoprene and 1,3-butadiene are preferred, and 1,3-butadiene is particularly preferred.

[0049] (Alkylene structural unit) Here, the alkylene structural unit is a unit represented by the general formula: -C ｎ H ２ｎ- [where n is an integer of 2 or greater]. The alkylene structural unit may be linear or branched, but from the viewpoint of reducing the resistance of the electrode and improving the rate characteristics of the electrochemical device, the alkylene structural unit is preferably linear, i.e., a linear alkylene structural unit. Furthermore, the alkylene structural unit preferably has 4 or more carbon atoms (i.e., n in the above general formula is an integer of 4 or greater).

[0050] The alkylene structural unit may be linear or branched, but is preferably a linear alkylene structural unit, and preferably has 4 or more carbon atoms (i.e., n in the general formula above is an integer of 4 or more).

[0051] The method for introducing alkylene structural units into a polymer is not particularly limited, and examples thereof include the following methods (1) and (2): (1) a method of preparing a polymer from a monomer composition containing a conjugated diene monomer and hydrogenating the polymer to convert the conjugated diene monomer units into alkylene structural units; and (2) a method of preparing a polymer from a monomer composition containing a 1-olefin monomer. Among these, method (1) is preferred because it allows for easy production of the polymer.

[0052] That is, the alkylene structural unit is preferably a structural unit obtained by hydrogenating a conjugated diene monomer unit (conjugated diene hydride unit), and more preferably a structural unit obtained by hydrogenating a 1,3-butadiene unit (1,3-butadiene hydride unit). Examples of the 1-olefin monomer include ethylene, propylene, 1-butene, and 1-hexene.

[0053] These conjugated diene monomers and 1-olefin monomers can be used alone or in combination of two or more.

[0054] The total content of the conjugated diene monomer units and the alkylene structural units in the hydrogenated nitrile rubber is preferably 50% by mass or more, more preferably 55% by mass or more, and particularly preferably 60% by mass or more, and is preferably 90% by mass or less, more preferably 85% by mass or less, and particularly preferably 80% by mass or less, when the total repeating units in the hydrogenated nitrile rubber (the total of the structural units and the monomer units) is taken as 100% by mass. If the total content of the conjugated diene monomer units and the alkylene structural units in the polymer is within the above range, the dispersion stability of the conductive material dispersion and the cycle characteristics of the electrochemical device can be improved.

[0055] When the hydrogenated nitrile rubber has only one of the content ratio of alkylene structural units and the content ratio of conjugated diene monomer units, it is preferable that the content ratio of the alkylene structural units and the conjugated diene monomer units satisfy the above range.

[0056] (Nitrile Group-Containing Monomer Units, Conjugated Diene Monomer Units, Alkylene Structural Units) The total proportion of the nitrile group-containing monomer units and the conjugated diene monomer units and / or alkylene structural units in the hydrogenated nitrile rubber of the present invention is not particularly limited, but when it is usually 80% by mass or more, preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 97% by mass or more, and most preferably 99% by mass or more, the dispersion stability of the conductive material dispersion and the cycle characteristics of the electrochemical device can be improved.

[0057] (Other repeating units) The other repeating units are not particularly limited, but examples thereof include aromatic vinyl monomer units, acidic group-containing monomer units, and (meth)acrylic acid ester monomer units. The hydrogenated nitrile rubber may contain one type of other repeating unit, or may contain two or more types of other repeating units. In the present invention, "(meth)acrylic" means acrylic and / or methacrylic.

[0058] Examples of aromatic vinyl monomers that can form aromatic vinyl monomer units include styrene, α-methylstyrene, p-t-butylstyrene, butoxystyrene, vinyltoluene, chlorostyrene, and vinylnaphthalene. The aromatic vinyl monomers may be used alone or in combination of two or more at any ratio. Among these, styrene is preferred.

[0059] Examples of the acidic group-containing monomer capable of forming the acidic group-containing monomer unit include a carboxylic acid group-containing monomer, a sulfonic acid group-containing monomer, and a phosphoric acid group-containing monomer. The acidic group-containing monomer may be used alone or in combination of two or more kinds in any ratio.

[0060] Examples of the carboxylic acid group-containing monomer include monocarboxylic acids and their derivatives, dicarboxylic acids and their acid anhydrides and their derivatives.

[0061] Examples of the monocarboxylic acid include acrylic acid, methacrylic acid, and crotonic acid.

[0062] Examples of the monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, and α-chloro-β-E-methoxyacrylic acid.

[0063] Examples of dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid.

[0064] Examples of dicarboxylic acid derivatives include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, and maleic acid monoesters such as nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, and fluoroalkyl maleate.

[0065] Examples of the acid anhydrides of dicarboxylic acids include maleic anhydride, acrylic anhydride, methyl maleic anhydride, and dimethyl maleic anhydride.

[0066] Furthermore, as the carboxylic acid group-containing monomer, an acid anhydride that generates a carboxylic acid group upon hydrolysis can also be used, among which acrylic acid and methacrylic acid are preferred as the carboxylic acid group-containing monomer.

[0067] Examples of sulfonic acid group-containing monomers include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth)allyl sulfonic acid, styrene sulfonic acid, (meth)acrylic acid-2-ethyl sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, etc. In the present invention, "(meth)allyl" means allyl and / or methallyl.

[0068] Examples of the phosphate group-containing monomer include 2-(meth)acryloyloxyethyl phosphate, methyl-2-(meth)acryloyloxyethyl phosphate, ethyl-(meth)acryloyloxyethyl phosphate, etc. In the present invention, "(meth)acryloyl" means acryloyl and / or methacryloyl.

[0069] Examples of (meth)acrylic acid ester monomers that can form (meth)acrylic acid ester monomer units include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, and stearyl acrylate. Acrylic acid alkyl esters include methacrylic acid alkyl esters such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, and stearyl methacrylate. The (meth)acrylic acid ester monomers may be used alone or in combination of two or more at any ratio.

[0070] The content of other repeating units in the hydrogenated nitrile rubber is preferably 0% by mass or more and 30% by mass or less, more preferably 0% by mass or more and 20% by mass or less, even more preferably 0% by mass or more and 10% by mass or less, and particularly preferably 0% by mass or more and 5% by mass or less, based on 100% by mass of all repeating units in the hydrogenated nitrile rubber.

[0071] <Hydrogenated Nitrile Rubber> The hydrogenated nitrile rubber of the present invention is characterized by containing the repeating unit described above, having specific amounts of weight average molecular weight (Mw) and iodine value, and containing specific amounts of Ca and Na and a specific antioxidant.

[0072] The weight average molecular weight (Mw) of the hydrogenated nitrile rubber of the present invention is in the range of 1,000 to 1,000,000, preferably 2,000 to 500,000, more preferably 4,000 to 400,000, and most preferably 5,000 to 250,000. If the weight average molecular weight (Mw) of the hydrogenated nitrile rubber is in this range, the dispersion stability of the conductive material dispersion can be improved and the peel strength of the obtained electrode can be increased, which is suitable.

[0073] The iodine value of the hydrogenated nitrile rubber of the present invention is in the range of 0.1 to 100 mg / 100 mg, preferably 1 to 80 mg / 100 mg, more preferably 1 to 60 mg / 100 mg, even more preferably 2 to 60 mg / 100 mg, particularly preferably 2 to 40 mg / 100 mg, and most preferably 2 to 25 mg / 100 mg. When the iodine value of the hydrogenated nitrile rubber is in this range, the viscosity characteristics of the conductive material dispersion, the peel strength of the electrode, and the output characteristics of the electrochemical element are suitably well balanced.

[0074] The Ca content of the hydrogenated nitrile rubber of the present invention is in the range of 1 to 2500 ppm, preferably 10 to 1500 ppm, more preferably 50 to 1000, even more preferably 100 to 800 ppm, and most preferably 200 to 500 ppm. The Ca content of the hydrogenated nitrile rubber is also usually 1 ppm or more, preferably 3 ppm or more, more preferably 5 ppm or more, and is alternatively preferred in the order of 10 ppm or more, 20 ppm or more, 30 ppm or more, 50 ppm or more, 70 ppm or more, 100 ppm or more, 150 ppm or more, 200 ppm or more, 250 ppm or more, and 300 ppm or more. The Ca content in the hydrogenated nitrile rubber is usually preferably 2000 ppm or less, 1500 ppm or less, 1200 ppm or less, 1000 ppm or less, 800 ppm or less, 700 ppm or less, 600 ppm or less, and 500 ppm or less, in that order. When the Ca content in the hydrogenated nitrile rubber is within this range, cracking of the electrode active material in the resulting electrode can be well suppressed and the peel strength of the electrode can be increased. Furthermore, when the Ca content in the hydrogenated nitrile rubber is within this range, the dispersion stability (viscosity characteristics) of the conductive material can be improved when a conductive material dispersion is prepared, and the cycle characteristics of the resulting electrochemical element and the effect of suppressing cracking of the electrode active material after a cycle test can be improved, which is preferable.

[0075] The Cl content in the hydrogenated nitrile rubber of the present invention is not particularly limited, but is usually 3000 ppm or less, preferably 2500 ppm or less, more preferably 2000 ppm or less, even more preferably 1500 ppm or less, and most preferably 1000 ppm or less. The lower limit of the Cl content in the hydrogenated nitrile rubber is not particularly limited, but is usually 0.5 ppm or more, preferably 1 ppm or more, and preferably 2.5 ppm or more, or is preferably 5 ppm or more, 10 ppm or more, 20 ppm or more, 30 ppm or more, 40 ppm or more, 50 ppm or more, 70 ppm or more, and 100 ppm or more, in that order. When the Cl content in the hydrogenated nitrile rubber is within this range, the viscosity characteristics of the conductive material dispersion liquid can be increased when a conductive material dispersion liquid of the hydrogenated nitrile rubber is prepared, and this is advantageous because it can suppress the cycle characteristics of the resulting electrochemical device and cracking of the electrode active material after a cycle test.

[0076] The mass ratio (Ca / Cl) of the Ca content to the Cl content in the hydrogenated nitrile rubber of the present invention is not particularly limited, but is usually in the range of 0.01 to 10, preferably 0.1 to 5, more preferably 0.1 to 4, even more preferably 0.2 to 4, particularly preferably 0.5 to 3, and most preferably 0.6 to 2.5. When the mass ratio of the Ca content to the Cl content in the hydrogenated nitrile rubber is in this range, the viscosity characteristics of the conductive material dispersion can be increased when the conductive material dispersion is prepared, and the cycle characteristics of the resulting electrochemical device and cracking of the electrode active material after a cycle test can be suppressed, which is preferable.

[0077] The Na content in the hydrogenated nitrile rubber of the present invention is 300 ppm or less, preferably 250 ppm or less, more preferably 100 ppm or less, even more preferably 75 ppm or less, and most preferably 50 ppm or less. When the Na content in the hydrogenated nitrile rubber is in this range, cracking of the active material in the electrode is suppressed and the cycle characteristics of the electrochemical device are improved, which is preferable.

[0078] The Rh and / or Ru content (total amount of Rh and Ru) in the hydrogenated nitrile rubber of the present invention is not particularly limited, but when it is in the range of usually 0.1 to 50 ppm, preferably 0.2 to 40 ppm, more preferably 0.5 to 25 ppm, even more preferably 1 to 25 ppm, and most preferably 1 to 15 ppm, cracking of the active material in the produced electrode can be suppressed, which is suitable.

[0079] The Pd content in the hydrogenated nitrile rubber of the present invention is not particularly limited, but is usually 200 ppm or less, preferably 100 ppm or less, more preferably 75 ppm or less, even more preferably 50 ppm or less, and most preferably 10 ppm or less. When the Pd content in the hydrogenated nitrile rubber is in this range, cracking of the active material in the electrode is suppressed and the cycle characteristics of the electrochemical device are improved, which is preferable.

[0080] The Mg content in the hydrogenated nitrile rubber of the present invention is not particularly limited, but is usually 50 ppm or less, preferably 30 ppm or less, more preferably 20 ppm or less, even more preferably 10 ppm or less, and most preferably 5 ppm or less. When the Mg content in the hydrogenated nitrile rubber is in this range, cracking of the active material in the electrode is suppressed and the cycle characteristics of the electrochemical element are improved, which is preferable.

[0081] The bulk density of the hydrogenated nitrile rubber of the present invention is not particularly limited, but is usually 0.6 g / cm ３ or more, preferably 0.7 g / cm ３ More preferably, 0.8 g / cm ３ More preferably, 0.85 g / cm ３ or more, most preferably 0.9 g / cm ３ The upper limit of the bulk density of the hydrogenated nitrile rubber is not particularly limited, but is usually 1.2 g / cm ３ or less, preferably 1.15 g / cm ３ or less, more preferably 1.1 g / cm ３ More preferably, 1.05 g / cm or less ３ Below, most preferably 1 g / cm ３ When the bulk density of the hydrogenated nitrile rubber is within this range, the effect of the phenolic antioxidant is highly enhanced, the stability of the conductive material dispersion is excellent, and the cycle characteristics of the electrochemical device and cracking of the active material after cycle testing are prevented. The bulk density of the hydrogenated nitrile rubber can be easily adjusted, for example, by drying with a screw extruder described below or by baling the hydrogenated nitrile rubber.

[0082] The hydrogenated nitrile rubber of the present invention is characterized by containing 2,2-methylenebis(4-methyl-6-tert-butylphenol) as an antioxidant.

[0083] The content of the antioxidant in the hydrogenated nitrile rubber is not particularly limited, but is usually in the range of 0.001 to 3 mass%, preferably 0.005 to 2 mass%, more preferably 0.01 to 1 mass%, even more preferably 0.03 to 0.7 mass%, and most preferably 0.05 to 0.5 mass%.

[0084] The hydrogenated nitrile rubber of the present invention may contain antioxidants other than the above-mentioned antioxidants, for example, other phenol-based antioxidants and amine-based antioxidants, within the range that does not impair the object of the present invention.

[0085] The hydrogenated nitrile rubber of the present invention is not particularly limited, but is preferably one obtained by emulsion polymerizing a nitrile group-containing monomer and a conjugated diene monomer, followed by coagulation with calcium chloride, followed by hydrogenation of the resulting polymer. When coagulating an emulsion polymerization solution to obtain a polymer, the size, shape, and properties of the resulting hydrous crumbs vary greatly depending on the type of coagulant used, and the residues of various secondary materials from the polymerization and coagulation processes that can be removed in subsequent washing and dehydration processes vary. It is impossible to verify all traces of these secondary materials and their reaction products, and these small residues affect various properties, particularly when used in electrochemical devices. Therefore, for electrochemical device applications, it is preferable to use calcium chloride as a coagulant and then hydrogenate the isolated polymer. Furthermore, among calcium (Ca) compounds, those using calcium chloride are preferred because they are easily removed in subsequent washing and purification processes, thereby reducing the residue in the hydrogenated nitrile rubber. Furthermore, hydrogenated nitrile rubber obtained by hydrogenating nitrile rubber obtained using calcium chloride as a coagulant is preferable because it has excellent electrode peeling properties for electrochemical elements such as lithium ion secondary batteries and is more effective in preventing deterioration of cycle characteristics and cracking of the active material layer after cycle testing than when other coagulants are used.

[0086] The hydrogenated nitrile rubber of the present invention is preferably one obtained by emulsion polymerizing a nitrile group-containing monomer and a conjugated diene monomer, coagulating the polymer with calcium chloride, and hydrogenating the resulting polymer.

[0087] The effect of the above specific antioxidant is far greater and more preferable when the hydrogenated nitrile rubber is produced by adding it to an emulsion polymerization solution obtained by emulsion polymerizing a nitrile group-containing monomer and a conjugated diene monomer, rather than mixing it with the hydrogenated nitrile rubber after production. Although it cannot be measured, this is thought to be because the specific 2,2-methylenebis(4-methyl-6-tert-butylphenol) antioxidant is uniformly dispersed in fine particles in the hydrogenated nitrile rubber obtained by coagulating the emulsion polymerization solution with calcium chloride, thereby exhibiting a high effect.

[0088] <Method for producing hydrogenated nitrile rubber> The method for producing the hydrogenated nitrile rubber of the present invention is not particularly limited, but for example, the hydrogenated nitrile rubber can be easily produced by hydrogenating a nitrile rubber containing 2,2-methylenebis(4-methyl-6-tert-butylphenol) as an antioxidant.

[0089] The hydrogenated nitrile rubber of the present invention can be easily produced by a process comprising: an emulsion polymerization step of emulsion-polymerizing a monomer component containing a nitrile group-containing monomer and a conjugated diene monomer to obtain an emulsion polymerization liquid; an antioxidant addition step of adding an antioxidant, 2,2-methylenebis(4-methyl-6-tert-butylphenol), to the emulsion polymerization liquid; a coagulation step of contacting the emulsion polymerization liquid to which the antioxidant has been added with calcium chloride to produce water-containing crumbs; a washing and drying step of washing and drying the water-containing crumbs to obtain a polymer; and a hydrogenation step of hydrogenating the polymer using a hydrogenation catalyst.

[0090] It is also preferable that the hydrogenation step involves subjecting a polymer to metathesis using the ruthenium-based catalyst and a coolefin, followed by hydrogenation using a rhodium-based catalyst, and that the hydrogenated nitrile rubber further be subjected to a purification step of treating it with an adsorbent after the hydrogenation step.

[0091] (Emulsion Polymerization Step) The emulsion polymerization step in the method for producing hydrogenated nitrile rubber of the present invention is a step of emulsion-polymerizing a monomer component containing a nitrile group-containing monomer and a conjugated diene monomer to obtain an emulsion polymerization liquid.

[0092] The monomer components used are the same as those described above, and the amounts used may be appropriately selected so as to obtain the monomer composition of the hydrogenated nitrile rubber.

[0093] The emulsifier used in emulsion polymerization is not particularly limited, but examples thereof include anionic emulsifiers, cationic emulsifiers, and nonionic emulsifiers, and preferably includes anionic emulsifiers.

[0094] The anionic emulsifier is not particularly limited, and examples thereof include salts of fatty acids such as myristic acid, palmitic acid, oleic acid, and linolenic acid; alkylbenzenesulfonates such as sodium dodecylbenzenesulfonate; sulfates such as sodium lauryl sulfate, phosphates such as polyoxyalkylene alkyl ether phosphates; and alkyl sulfosuccinates. Among these anionic emulsifiers, fatty acid salts and sulfates are preferred, and fatty acid salts are particularly preferred. Suitable sulfates include sodium lauryl sulfate, ammonium lauryl sulfate, sodium myristyl sulfate, sodium laureth sulfate, polyoxyethylene alkyl sulfate, and polyoxyethylene alkylaryl sulfate. Suitable fatty acid salts include potassium oleate, sodium oleate, and potassium palmitate, with potassium oleate being particularly preferred.

[0095] These emulsifiers can be used alone or in combination of two or more. The amount used is usually in the range of 0.01 to 10 parts by mass, preferably 0.1 to 5 parts by mass, and more preferably 1 to 3 parts by mass, per 100 parts by mass of the monomer component.

[0096] The method for mixing the monomer component, emulsifier, and water may be according to a conventional method, such as a method of stirring the monomer, emulsifier, and water using a stirrer such as a homogenizer or a disk turbine. The amount of water used is usually in the range of 10 to 750 parts by mass, preferably 50 to 500 parts by mass, and more preferably 100 to 400 parts by mass, per 100 parts by mass of the monomer component.

[0097] The polymerization catalyst used in emulsion polymerization is not particularly limited as long as it is one that is commonly used in emulsion polymerization. For example, a redox catalyst consisting of a radical generator and a reducing agent can be used.

[0098] Examples of the radical generator include peroxides and azo compounds, and preferably peroxides. As the peroxide, inorganic peroxides and organic peroxides can be used.

[0099] Examples of inorganic peroxides include sodium persulfate, potassium persulfate, hydrogen peroxide, and ammonium persulfate. Among these, potassium persulfate, hydrogen peroxide, and ammonium persulfate are preferred, with potassium persulfate being particularly preferred.

[0100] The organic peroxide is not particularly limited as long as it is a known peroxide used in emulsion polymerization, and examples thereof include 2,2-di(4,4-di-(t-butylperoxy)cyclohexyl)propane, 1-di-(t-hexylperoxy)cyclohexane, 1,1-di-(t-butylperoxy)cyclohexane, 4,4-di-(t-butylperoxy)n-butyl valerate, 2,2-di-(t-butylperoxy)butane, t-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, paramenthane hydroperoxide, and benzoyl peroxide. Examples of the peroxide include 1,1,3,3-tetraethylbutyl hydroperoxide, t-butylcumyl peroxide, di-t-butyl peroxide, di-t-hexyl peroxide, di(2-t-butylperoxyisopropyl)benzene, dicumyl peroxide, diisobutyryl peroxide, di(3,5,5-trimethylhexanoyl)peroxide, and dilauroyl peroxide. Of these, diisopropylbenzene hydroperoxide, cumene hydroperoxide, paramenthane hydroperoxide, and benzoyl peroxide are preferred.

[0101] These radical generators can be used alone or in combination of two or more kinds, and the amount used is usually in the range of 0.0001 to 5 parts by mass, preferably 0.0005 to 1 part by mass, and more preferably 0.001 to 0.5 parts by mass, per 100 parts by mass of the monomer component.

[0102] The amount of water used in the emulsion polymerization reaction may be only that used in the emulsification of the monomer components, but is adjusted to be in the range of usually 10 to 1,000 parts by mass, preferably 50 to 500 parts by mass, more preferably 80 to 400 parts by mass, and most preferably 100 to 300 parts by mass, per 100 parts by mass of the monomer components used in the polymerization.

[0103] The emulsion polymerization reaction may be carried out in accordance with a conventional method, and may be a batch, semi-batch, or continuous method. The polymerization temperature and polymerization time are not particularly limited and can be appropriately selected depending on the type of polymerization initiator used, etc. The polymerization temperature is usually in the range of 0 to 100°C, preferably 5 to 80°C, and more preferably 10 to 50°C, and the polymerization time is usually 0.5 to 100 hours, preferably 1 to 10 hours.

[0104] The polymerization conversion rate of the emulsion polymerization reaction is not particularly limited, but when it is usually 70% by mass or more, preferably 80% by mass or more, and more preferably 90% by mass or more, the hydrogenated nitrile rubber produced is excellent in strength characteristics and has no monomer odor, which is suitable. A polymerization terminator may be used to terminate the polymerization.

[0105] (Antiaging Agent Addition Step) The antioxidant addition step in the method for producing hydrogenated nitrile rubber of the present invention is characterized by adding 2,2-methylenebis(4-methyl-6-tert-butylphenol) compound as an antioxidant to the emulsion polymerization liquid after the emulsion polymerization.

[0106] The method of adding the antioxidant to the emulsion polymerization liquid is not particularly limited and may be any conventional method. For example, the antioxidant may be added as is or may be emulsified with an emulsifier before being added.

[0107] The amount of antioxidant used may be appropriately selected so as to achieve the content of antioxidant in the hydrogenated nitrile rubber of the present invention, and is usually in the range of 0.001 to 15 parts by mass, preferably 0.01 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, particularly preferably 0.3 to 3 parts by mass, and most preferably 0.5 to 2 parts by mass, per 100 parts by mass of the monomer component.

[0108] (Coagulation Step) In the method for producing hydrogenated nitrile rubber of the present invention, the coagulation step is a step in which the emulsion polymerization liquid to which the antioxidant has been added is brought into contact with calcium chloride to produce water-containing crumbs. In particular, using calcium chloride as a coagulant and setting the Ca content in the produced emulsion polymerization liquid within a specific range is preferable because it contributes to the dispersibility of the conductive material dispersion, greatly increases the peel strength of the produced electrode, and is also excellent in the cycle characteristics of the electrochemical device and in the effect of suppressing cracking of the electrode active material after a cycle test.

[0109] The solids concentration of the emulsion polymerization liquid used in the coagulation step is not particularly limited, but is usually adjusted to within the range of 5 to 50 mass %, preferably 10 to 45 mass %, and more preferably 20 to 40 mass %.

[0110] The calcium chloride used is usually used as an aqueous solution, and the coagulant concentration of the aqueous solution is usually in the range of 0.1 to 70 mass%, preferably 1 to 60 mass%, more preferably 5 to 50 mass%, and particularly preferably 10 to 30 mass%, which is suitable because the particle size of the generated hydrous crumbs can be uniformly concentrated in a specific region.

[0111] The temperature in the coagulation reaction is not particularly limited, but a temperature of 40°C or higher, preferably 40 to 90°C, more preferably 50 to 80°C, is suitable for producing uniform water-containing crumbs.

[0112] The method of contacting the emulsion polymerization liquid with the aqueous calcium chloride solution (coagulation liquid) is not particularly limited, and may be, for example, a method of adding the emulsion polymerization liquid to the coagulation liquid being stirred, or a method of adding the coagulation liquid to the emulsion polymerization liquid being stirred. However, the method of adding the coagulation liquid to the emulsion polymerization liquid being stirred is preferred because it can make the shape and diameter of the generated water-containing crumbs uniform and concentrate them, thereby significantly improving the efficiency of washing out the emulsifier and coagulation agent.

[0113] (Water-washing and drying step) The water-washing and drying step in the method for producing hydrogenated nitrile rubber of the present invention is a step of washing and drying the water-containing crumbs produced above to obtain a polymer.

[0114] The washing method is not particularly limited and may be a conventional method, but it is effective to wash the hydrous crumbs coagulated with the high concentration of calcium chloride with a large amount of water. The amount of water used is usually 10 to 500 times, preferably 25 to 250 times, more preferably 50 to 100 times, based on 100 parts by mass of the polymer.

[0115] The temperature of the water used for washing is not particularly limited, but it is preferable to use warm water, and washing efficiency can be significantly improved when the temperature is usually 40° C. or higher, preferably 40 to 100° C., more preferably 50 to 90° C., and most preferably 60 to 80° C. By setting the temperature of the washing water to the above lower limit or higher, the emulsifier and coagulant are released from the water-containing crumbs, and washing efficiency is further improved.

[0116] The washing time is not particularly limited, but is usually in the range of 1 to 120 minutes, preferably 2 to 60 minutes, and more preferably 3 to 30 minutes.

[0117] The washed hydrous crumbs may be dried in a conventional manner, for example, using a dryer such as a hot air dryer, a reduced pressure dryer, an expander dryer, a kneader dryer, or a screw extruder.

[0118] The moisture content of the dry rubber is less than 1% by weight, preferably 0.8% by weight or less, more preferably 0.6% by weight or less.

[0119] (Hydrogenation Step) The hydrogenation step in the method for producing hydrogenated nitrile rubber of the present invention is a step in which the above-obtained polymer (dry rubber) is hydrogenated using a hydrogenation catalyst, and can be easily carried out by subjecting the polymer (dry rubber) to metathesis using a ruthenium-based catalyst and a coolefin, followed by hydrogenation using a rhodium-based catalyst.

[0120] Metathesis Reaction The metathesis reaction can be carried out using the method described in Japanese Patent No. 4,509,792, for example.

[0121] As a catalyst for the metathesis reaction, known ruthenium-based catalysts can be used, among which Grubbs catalysts such as bis(tricyclohexylphosphine)benzylidene ruthenium dichloride and 1,3-bis(2,4,6-trimethylphenyl)-2-(imidazolidinylidene)(dichlorophenylmethylene)(tricyclohexylphosphine)ruthenium are preferred.

[0122] The metathesis reaction is carried out in the presence of a coolefin.

[0123] Examples of the coolefin include olefins having 2 to 16 carbon atoms, such as ethylene, isobutane, styrene, and 1-hexane, and functional group-containing unsaturated compounds, such as cis-2-butene-1,4-diol, 3-butene-1-amine, vinyltrimethoxysilane, methoxypolyalkylene glycol methacrylate, and 2-(methacryloyloxy)ethanesulfonic acid, with the functional group-containing unsaturated compounds being preferred.

[0124] The amount of coolefin used is usually in the range of 0.1 to 20 parts by mass, preferably 0.5 to 10 parts by mass, more preferably 1 to 5 parts by mass, per 100 parts by mass of the polymer.

[0125] The reaction can be carried out in a solvent that does not deactivate the catalyst or interfere with the reaction. Preferred solvents include, but are not limited to, dichloromethane, benzene, toluene, tetrahydrofuran, cyclohexane, monochlorobenzene (MCB), etc., and most preferably MCB. In some cases, the coolefin itself can act as the solvent, in which case no other solvent is required.

[0126] The polymer concentration in the metathesis reaction is not critical, but is usually in the range of 1 to 20% by weight, preferably 6 to 15% by weight.

[0127] The reaction solution in the metathesis reaction is usually stirred vigorously, for example, at a speed in the range of 200 to 1000 rpm, preferably 300 to 900 rpm, more preferably 500 to 800 rpm.

[0128] The temperature of the metathesis reaction is usually in the range of 20 to 140°C, preferably 60 to 120°C. The reaction time depends on many factors, such as the concentration of cement, the amount of catalyst used, and the reaction temperature, but is usually complete within 2 hours. The progress of the metathesis reaction can be monitored using standard analytical methods, such as GPC or solution viscosity.

[0129] Hydrogenation Reaction The hydrogenation reaction can be carried out by dissolving the polymer in a solvent and then adding a hydrogenation catalyst, but the hydrogenation reaction after the metathesis is preferably carried out in the same reaction vessel as that used for the metathesis reaction, by adding a hydrogenation catalyst to the vessel without isolating the metathesis product, and then carrying out hydrogenation treatment to produce hydrogenated nitrile rubber.

[0130] The solvent for the hydrogenation reaction may be either an aqueous solvent or an organic solvent, but is preferably an organic solvent. Suitable organic solvents include, for example, acetone, methyl ethyl ketone, ethyl acetate, tetrahydrofuran, 1,3-dioxane, benzene, toluene, methylene chloride, chloroform, monochlorobenzene (MCB), and dichlorobenzene. Among these, MCB is particularly suitable as it is a good solvent for both the nitrile group-containing nitrile rubber before hydrogenation and the hydrogenated nitrile rubber after hydrogenation.

[0131] The hydrogenation catalyst can be any method known in the art, without any particular limitations. For example, the method described in Japanese Patent No. 6309634 can be used, and in particular, Wilkinson's catalyst (PPh ３ ) ３ It is preferred to use known homogeneous hydrogenation catalysts such as RhCl. Also, the Grubbs catalyst is a dihydride complex (PR) which is itself an olefin hydrogenation catalyst in the presence of hydrogen. ３ ) ２ RuCl ２ H ２ The hydrogenation reaction can be carried out without adding the Wilkinson catalyst, but the hydrogenation rate tends to be slower.

[0132] The amount of the hydrogenation catalyst used may be appropriately selected depending on the purpose of use and the iodine value, but is usually in the range of 0.001 to 0.5 parts by mass, preferably 0.005 to 0.1 parts by mass, and more preferably 0.01 to 0.05 parts by mass, based on 100 parts by mass of the polymer before hydrogenation.

[0133] The hydrogenation reaction can use a co-catalyst as needed. Examples of the co-catalyst for the Wilkinson catalyst include phosphine, diphosphine, and triphenylphosphine, with triphenylphosphine being preferred. These co-catalysts can be used alone or in combination of two or more. The amount used is usually 0.01 to 15 parts by mass, preferably 0.1 to 10 parts by mass, and more preferably 0.5 to 5 parts by mass, based on 100 parts by mass of the polymer to be hydrogenated.

[0134] The polymer concentration in the hydrogenation reaction is not particularly limited as long as it is within a range in which the polymer can be dissolved, but is usually in the range of 1 to 30 mass %, preferably 5 to 25 mass %, more preferably 7 to 20 mass %.

[0135] The pressure of the hydrogenation reaction is not particularly limited, but is usually in the range of 0.1 to 30 MPa, preferably 1 to 20 MPa, and more preferably 5 to 15 MPa.

[0136] The hydrogenation reaction temperature is usually in the range of 30 to 200° C., preferably 50 to 170° C., more preferably 100 to 150° C. The reaction time is usually 1 to 50 hours, preferably 2 to 25 hours.

[0137] The hydrogenation reaction can be stopped once the desired hydrogenation level is reached by depressurizing or cooling the reactor. Residual hydrogen is typically removed with a nitrogen purge. The hydrogenation catalyst can also be removed prior to removal of the solvent and isolation of the hydrogenated nitrile rubber from the organic layer.

[0138] (Purification Step) In the method for producing hydrogenated nitrile rubber of the present invention, after the hydrogenation step, there is a step of performing an adsorbent treatment on the hydrogenated nitrile rubber, and the adsorbent treatment can be performed so that the calcium (Ca) content in the hydrogenated nitrile rubber becomes a value of 1 to 2500 ppm.

[0139] The adsorbent is not particularly limited, but examples thereof include activated carbon, ion exchange resin, and synthetic zeolite, with activated carbon being preferred.

[0140] The adsorbent treatment can be carried out by adding an adsorbent to a reaction liquid containing hydrogenated nitrile rubber after hydrogenation and mixing. There are no particular limitations on the amount of adsorbent added, but it is usually in the range of 0.001 to 1 part by mass, preferably 0.05 to 0.5 parts by mass, and more preferably 0.01 to 0.4 parts by mass per 100 parts by mass of hydrogenated nitrile rubber. The mixing temperature is usually room temperature to 80°C, preferably room temperature to 60°C, and the mixing time is usually 1 minute to 1 hour, preferably 20 to 40 minutes.

[0141] After the treatment with the adsorbent, the adsorbent is removed by filtration or decantation, and the filtrate is dried to obtain the hydrogenated nitrile rubber.

[0142] Examples of purification methods by filtration / decantation include (i) a method of filtering using a bag filter, cartridge filter, filter paper, membrane filter, or the like, after adding an adsorbent as necessary; (ii) a method of using a filter such as a leaf filter, filter press, candle filter, or drum filter to form a cake layer of a filter aid such as diatomaceous earth or perlite, and then allowing the filtrate to flow; and (iii) a method of removing the metal salt by centrifuging to settle the metal salt formed from the residue and metal ions during polymerization and then removing it from the bottom.

[0143] The hydrogenated nitrile rubber of the present invention can be obtained as a dried hydrogenated nitrile rubber by removing the solvent after the purification step.

[0144] <Drying Hydrogenated Nitrile Rubber Using a Screw Extruder> In drying hydrogenated nitrile rubber, drying using a screw extruder is preferred because it can remove internal air and increase bulk density. Specifically, the hydrogenated nitrile rubber-containing solution after the hydrogenation reaction or after the purification step following the hydrogenation reaction can be coagulated, and the resulting water-containing crumbs can be dried using a screw extruder. (Coagulation Step) The coagulation step for the hydrogenated nitrile rubber-containing filtrate obtained in the purification step from which impurities have been removed is not particularly limited, and a conventional method can be followed. Specific coagulation methods include contacting the filtrate with a coagulant or with a large amount of poor solvent, and preferably contacting the filtrate with a large amount of poor solvent. The poor solvent is not particularly limited, but methanol, water, steam, etc. are preferably used. The coagulation reaction may be selected as appropriate. For example, the coagulation reaction temperature is usually selected from the range of room temperature to 100°C, and the coagulation reaction time is selected from the range of several minutes to several hours.

[0145] The hydrous crumbs of the hydrogenated nitrile rubber produced in the coagulation reaction can be washed as needed. The washing method is not particularly limited and may be a conventional method, but washing with a large amount of water is efficient. The amount of water used is typically 10 to 500 times, preferably 25 to 250 times, and more preferably 50 to 100 times, the amount of water per 100 parts by mass of the polymer. The temperature of the water used for washing is not particularly limited, but it is preferable to use warm water. A temperature of typically 40°C or higher, preferably 40 to 100°C, more preferably 50 to 90°C, and most preferably 60 to 80°C, can significantly improve washing efficiency. By setting the temperature of the washing water at or above the lower limit, the emulsifier and coagulant are liberated from the hydrous crumbs, further improving washing efficiency.

[0146] After coagulation, or alternatively after washing, the wet crumbs can be isolated by filtration.

[0147] (Drying step) In the present invention, the hydrous crumbs of the hydrogenated nitrile rubber isolated above can be dried using a screw extruder. By melting and kneading the hydrogenated nitrile rubber under reduced pressure in the screw extruder and drying it, the air contained therein is removed to obtain a dried rubber (hydrogenated nitrile rubber) with a high bulk density, and when used as a positive electrode material, it is suitable because it has excellent dispersion stability with the conductive material and prevents peel strength of the electrochemical element electrode and cracking of the active material layer after cycle testing.

[0148] -Screw-type extruder-Dehydration in the dehydration barrel The dehydration of the hydrous crumbs is carried out in a dehydration barrel having a dehydration slit. The opening of the dehydration slit may be selected appropriately depending on the conditions of use, but a size in the range of usually 0.1 to 1 mm, preferably 0.2 to 0.6 mm, is suitable because it minimizes the loss of hydrous crumbs and enables efficient dehydration of the hydrous crumbs.

[0149] The number of dehydration barrels in the screw extruder is not particularly limited, but usually a plurality of barrels, preferably 2 to 10 barrels, more preferably 3 to 6 barrels, is suitable for efficiently dehydrating the tacky hydrogenated nitrile rubber.

[0150] The set temperature of the dehydration barrel is appropriately selected depending on the type of hydrogenated nitrile rubber, the ash content, the water content, the operating conditions, etc., but is usually in the range of 60 to 150°C, preferably 70 to 140°C, and more preferably 80 to 130°C. The set temperature of the dehydration barrel for dehydration in a drained state is usually 60 to 120°C, preferably 70 to 110°C, and more preferably 80 to 100°C. The set temperature of the dehydration barrel for drying in an exhausted steam state is usually in the range of 100 to 150°C, preferably 105 to 140°C, and more preferably 110 to 130°C.

[0151] The moisture content after dehydration, in which moisture is squeezed out from the hydrous crumb, is not particularly limited, but is usually 1 to 45% by mass, preferably 1 to 40% by mass, more preferably 5 to 35% by mass, and particularly preferably 10 to 35% by mass.

[0152] Drying of Drying Barrel Section The hydrous crumbs dehydrated in the dehydration barrel section are further dried in the drying barrel section under reduced pressure. The degree of reduced pressure in the drying barrel may be selected as appropriate, but a pressure of usually 1 to 50 kPa, preferably 2 to 30 kPa, more preferably 3 to 20 kPa is suitable because the hydrous crumbs can be dried efficiently. In addition, by extruding the molten hydrogenated nitrile rubber inside the drying barrel under reduced pressure, the air present inside is also removed, and a sheet-like hydrogenated nitrile rubber having a high bulk specific gravity can be produced, which is suitable.

[0153] The set temperature of the drying barrel may be appropriately selected, but when it is usually in the range of 100 to 250°C, preferably 110 to 200°C, more preferably 120 to 180°C, the hydrogenated nitrile rubber can be dried efficiently without discoloration or deterioration.

[0154] The number of drying barrels in a screw extruder is not particularly limited, but is usually multiple, preferably 2 to 10, and more preferably 3 to 8. When multiple drying barrels are used, the degree of reduced pressure may be similar for all drying barrels or may be different. When multiple drying barrels are used, the set temperatures may be similar for all drying barrels or may be different, but it is preferable to make the temperature of the discharge section (closer to the die) higher than the temperature of the introduction section (closer to the dehydration barrel) in order to increase drying efficiency.

[0155] The water content of the dried rubber after drying is usually less than 1% by mass, preferably 0.8% by mass or less, and more preferably 0.6% by mass or less.

[0156] Extrusion of hydrogenated nitrile rubber (die section) The hydrogenated nitrile rubber dehydrated and dried in the screw sections of the dehydration barrel and drying barrel is sent to a straightening die section having no screw. A breaker plate or a wire mesh may or may not be provided between the screw section and the die section.

[0157] The extruded hydrogenated nitrile rubber can be obtained in various shapes such as granules, columns, round rods, sheets, etc., depending on the shape of the die nozzle. However, it is preferable to extrude the hydrogenated nitrile rubber in a sheet shape using a substantially rectangular die, since this results in a dried rubber with less air entrapment, a large bulk density, and excellent storage stability.

[0158] The resin pressure in the die section is not particularly limited, but is usually in the range of 0.1 to 10 MPa, preferably 0.5 to 5 MPa, and more preferably 1 to 3 MPa, which is suitable for minimizing air entrainment and providing excellent productivity.

[0159] Screw-type extruder and operating conditions The screw length (L) of the screw-type extruder used may be appropriately selected depending on the purpose of use, but is usually in the range of 2000 to 15000 mm, preferably 2500 to 10000 mm, and more preferably 3000 to 7000 mm.

[0160] The screw diameter (D) of the screw extruder used may be appropriately selected depending on the intended use, but is usually in the range of 50 to 250 mm, preferably 70 to 200 mm, more preferably 80 to 160 mm.

[0161] The ratio (L / D) of the screw length (L) to the screw diameter (D) of the screw extruder used is not particularly limited, but is usually in the range of 10 to 150, preferably 15 to 100, more preferably 20 to 80, and particularly preferably 30 to 60, since this allows the moisture content of the dried rubber to be reduced to less than 1% by mass without causing a decrease in molecular weight or burning.

[0162] The rotation speed (N) of the screw extruder used may be appropriately selected depending on various conditions, but is usually 10 to 1000 rpm, preferably 30 to 800 rpm, more preferably 50 to 600 rpm, and most preferably 100 to 400 rpm.

[0163] The throughput (Q) of the screw extruder used is not particularly limited, but is usually in the range of 100 to 1500 kg / hr, preferably 120 to 1200 kg / hr, more preferably 150 to 1000 kg / hr, and most preferably 200 to 800 kg / hr.

[0164] The ratio (Q / N) of the extrusion rate (Q) to the rotation speed (N) of the screw extruder used is not particularly limited, but is usually in the range of 1 to 10, preferably 1 to 5, and more preferably 1 to 3.

[0165] Dried Rubber The shape of the dried rubber extruded from the screw extruder is not particularly limited, and examples thereof include crumbs, powder, rods, and sheets, with the sheet shape being particularly preferred.

[0166] <Hydrogenated Nitrile Rubber Bale> The hydrogenated nitrile rubber bale of the present invention can be produced by baling the dried hydrogenated nitrile rubber.

[0167] The hydrogenated nitrile rubber bale of the present invention is made of the hydrogenated nitrile rubber, and by bailing it, the effects of the hydrogenated nitrile rubber of the present invention can be maintained even during storage, which is preferable.Furthermore, since the bulk density of the hydrogenated nitrile rubber bale can be increased and it can be stored in a state where air is not present inside, the generation of oxygen radicals can be suppressed, which is preferable.

[0168] The shape of the hydrogenated nitrile rubber bale of the present invention is not particularly limited, but is usually a rectangular parallelepiped. The size is also not particularly limited, but the width is usually in the range of 100 to 800 mm, preferably 200 to 500 mm, more preferably 250 to 450 mm, the length is usually in the range of 300 to 1200 mm, preferably 400 to 1000 mm, more preferably 500 to 800 mm, and the height is usually in the range of 50 to 500 mm, preferably 100 to 300 mm, more preferably 150 to 250 mm.

[0169] The bulk density of the hydrogenated nitrile rubber bale of the present invention is not particularly limited, but is usually 0.6 g / cm ３ or more, preferably 0.7 g / cm ３ More preferably, 0.8 g / cm ３ More preferably, 0.85 g / cm ３ or more, most preferably 0.9 g / cm ３ The upper limit of the bulk density of the hydrogenated nitrile rubber bale is not particularly limited, but is usually 1.2 g / cm ３ or less, preferably 1.15 g / cm ３ or less, more preferably 1.1 g / cm ３ More preferably, 1.05 g / cm or less ３ Below, most preferably 1 g / cm ３When the bulk density of the hydrogenated nitrile rubber bale is within this range, the effect of the specific antioxidant is highly enhanced, the stability of the conductive material dispersion is excellent, and the cycle characteristics of the electrochemical device and cracking of the active material after cycle testing can be prevented.

[0170] The iodine value, Rh content, Ru content, Pd content, Ca content, Na content, Mg content, Cl content and Ca / Cl ratio of the hydrogenated nitrile rubber bale of the present invention are the same as those of the hydrogenated nitrile rubber.

[0171] The water content of the hydrogenated nitrile rubber bale of the present invention is not particularly limited, but is generally less than 1% by mass, preferably 0.8% by mass or less, and more preferably 0.6% by mass or less, which is suitable for excellent storage stability.

[0172] The Mooney viscosity (ML1+4, 100°C) of the hydrogenated nitrile rubber veil of the present invention is not particularly limited, but when it is in the range of usually 10 to 150, preferably 15 to 100, more preferably 20 to 80, the conductive material dispersibility and the peel strength at the electrode are well balanced, and this is suitable.

[0173] Baling of hydrogenated nitrile rubber can be carried out according to conventional methods. For example, the dried hydrogenated nitrile rubber can be placed in a baler and compressed. The compression pressure is selected appropriately depending on the intended use, but is usually in the range of 0.1 to 15 MPa, preferably 0.5 to 10 MPa, and more preferably 1 to 5 MPa. The compression time is not particularly limited, but is usually in the range of 1 to 60 seconds, preferably 5 to 50 seconds, and more preferably 10 to 40 seconds. Alternatively, dried rubber can be produced in sheet form and layered to form bales. Baling by layering sheets is easy to produce, produces bales with few bubbles (high bulk density), and is therefore preferable because of its excellent storage stability.

[0174] In the present invention, further, by laminating the sheet-like dried rubber (hydrogenated nitrile rubber) extruded from the screw-type extruder, a suitable hydrogenated nitrile rubber bale having a large bulk density can be easily produced.

[0175] <Positive Electrode Binder> The positive electrode binder of the present invention is obtained by dissolving or dispersing the hydrogenated nitrile rubber or the hydrogenated nitrile rubber bale in N-methylpyrrolidone (NMP), and is suitable as a material for producing a positive electrode of an electrochemical element. When the hydrogenated nitrile rubber bale is used as a positive electrode material, it is usually broken down into small pieces and dissolved or dispersed in a solvent.

[0176] The positive electrode binder of the present invention can be combined with other components as needed, in addition to hydrogenated nitrile rubber and NMP. Examples of other components include, but are not limited to, binders other than hydrogenated nitrile rubber (such as polyvinylidene fluoride and polyacrylate), reinforcing materials, leveling agents, viscosity modifiers, and electrolyte additives. These components are not particularly limited as long as they do not affect the battery reaction, and known components can be used. The positive electrode binder of the present invention may also contain a solvent other than NMP to the extent that the properties of the present invention are not impaired. These other components may be used alone, or two or more may be combined in any ratio.

[0177] The solid content of the binder for a positive electrode of the present invention is not particularly limited, but is usually in the range of 0.1 to 40 mass %, preferably 0.5 to 20 mass %, and more preferably 1 to 10 mass %.

[0178] The hydrogenated nitrile rubber, NMP, and other components used as needed may be mixed in a conventional manner.

[0179] <Electrode for electrochemical element> The positive electrode of the present invention is characterized by comprising a current collector and a positive electrode mixture layer containing a binder containing the hydrogenated nitrile rubber, a conductive material, and a positive electrode active material. The positive electrode can be produced by mixing the positive electrode binder and the conductive material, optionally adding a solvent, and then mixing the positive electrode active material to form a positive electrode mixture layer slurry, which is then applied onto the current collector and dried.

[0180] (Conductive Material) The conductive material is a component that functions to ensure electrical contact between electrode active materials. Carbonaceous materials can be suitably used as the conductive material. Examples of such carbonaceous materials include carbon black (e.g., acetylene black, Ketjen Black (registered trademark), furnace black, etc.), single-walled or multi-walled carbon nanotubes (multi-walled carbon nanotubes include cup-stacked types), carbon nanohorns, vapor-grown carbon fibers, milled carbon fibers obtained by calcining and then crushing polymer fibers, single-walled or multi-walled graphene, and carbon nonwoven fabric sheets obtained by calcining nonwoven fabrics made of polymer fibers. These materials may be used alone or in combination of two or more types in any ratio. Among these, carbon nanotubes (CNTs) are preferred from the viewpoint of forming good conductive paths.

[0181] When mixing the positive electrode binder of the present invention with the conductive material, the ratio of the conductive material to the positive electrode binder is not particularly limited. For example, the conductive material and the positive electrode binder may be mixed so that the resulting conductive material dispersion contains typically 1 to 100 parts by mass, preferably 5 to 50 parts by mass, and more preferably 10 to 30 parts by mass of hydrogenated nitrile rubber per 100 parts by mass of the conductive material. Furthermore, when mixing the positive electrode binder and the conductive material, NMP can be added as needed to adjust the viscosity.

[0182] The solid content concentration when the positive electrode binder of the present invention and a conductive material are mixed is usually 0.01% by mass or more, preferably 1.0% by mass or more, and more preferably 3.0% by mass or more, and the upper limit is usually 10.0% by mass or less, preferably 9.0% by mass or less, and more preferably 8.0% by mass or less. If the solid content concentration is equal to or higher than the lower limit, the coatability of the conductive material dispersion can be improved. Furthermore, if the solid content concentration is equal to or lower than the upper limit, the rate characteristics of the resulting electrochemical device can be improved.

[0183] The method for mixing the positive electrode binder of the present invention and the conductive material is not particularly limited, and for example, they can be mixed using a known mixing device.

[0184] (Positive Electrode Active Material) The positive electrode active material is not particularly limited, but when the electrochemical element is a lithium ion secondary battery, a metal oxide containing lithium (Li) can be used. The positive electrode active material is preferably a positive electrode active material containing at least one selected from the group consisting of cobalt (Co), nickel (Ni), manganese (Mn), and iron (Fe) in addition to lithium (Li). Such a positive electrode active material is preferably a lithium-containing cobalt oxide (LiCoO ２ ), lithium manganese oxide (LiMn ２ O ４ ), lithium-containing nickel oxide (LiNiO ２ ), Co—Ni—Mn lithium-containing composite oxide, Ni—Mn—Al lithium-containing composite oxide, Ni—Co—Al lithium-containing composite oxide, olivine-type lithium manganese phosphate (LiMnPO ４ ), olivine-type lithium iron phosphate (LiFePO ４ ), Li １＋ｘ Mn ２－ｘ O ４ (0<X<2) Lithium-excess spinel compound represented by Li[Ni ０．１７ Li ０．２ Co ０．０７ Mn ０．５６ ]O ２ , LiNi ０．５ Mn １．５ O ４ , Li[Ni ０．５ Co ０．２ Mn ０．３ ]O ２ The particle size of the positive electrode active material is not particularly limited and can be the same as that of a conventionally used electrode active material. The positive electrode active material may be used alone or in combination of two or more types in any ratio.

[0185] The positive electrode active material can be mixed with the positive electrode binder and conductive material to form a positive electrode composite layer slurry. The mixing method is not particularly limited and can be performed using a known mixing device. The amount of the positive electrode active material is not particularly limited and can be within a range that has been conventionally used.

[0186] <Electrode for electrochemical device> The positive electrode of the present invention can be obtained by applying the above-mentioned positive electrode mixture layer slurry onto a current collector and drying it. Since the positive electrode of the present invention has a positive electrode mixture layer formed from the above-mentioned positive electrode binder containing the hydrogenated nitrile rubber of the present invention, the positive electrode has excellent flexibility and is less likely to crack in the electrode active material.

[0187] (Current Collector) The current collector is made of a material that is electrically conductive and electrochemically durable. There are no particular limitations on the current collector, and known current collectors can be used. For example, a current collector made of aluminum or an aluminum alloy can be used as the current collector provided in the positive electrode of a lithium ion secondary battery. In this case, aluminum and an aluminum alloy may be used in combination, or different types of aluminum alloys may be used in combination. Aluminum and aluminum alloys are heat resistant and electrochemically stable, making them excellent current collector materials.

[0188] The method for producing the positive electrode of the present invention is not particularly limited. For example, the positive electrode of the present invention can be produced by applying the above-mentioned positive electrode composite layer slurry of the present invention to at least one surface of a current collector and drying the applied positive electrode composite layer to form a positive electrode composite layer. More specifically, the production method includes a step of applying the positive electrode composite layer slurry to at least one surface of a current collector (application step), and a step of drying the positive electrode composite layer slurry applied to at least one surface of the current collector to form a positive electrode composite layer on the current collector (drying step).

[0189] (Coating Step) The method for applying the positive electrode composite layer slurry onto the current collector is not particularly limited, and known methods can be used. Specifically, examples of the coating method include a doctor blade method, a dipping method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method. In this case, the electrode slurry may be applied to only one side of the current collector, or may be applied to both sides. The thickness of the slurry film on the current collector after application and before drying can be appropriately set depending on the thickness of the positive electrode composite layer obtained by drying.

[0190] (Drying step) The method for drying the positive electrode composite layer slurry on the current collector is not particularly limited and any known method can be used, for example, drying with warm air, hot air, or low-humidity air, vacuum drying, or drying by irradiation with infrared rays or electron beams, etc. By drying the positive electrode composite layer slurry on the current collector in this manner, a positive electrode composite layer can be formed on the current collector, and a positive electrode including the current collector and the positive electrode composite layer can be obtained.

[0191] After the drying step, the electrode mixture layer may be subjected to pressure treatment using a mold press, a roll press, etc. Pressure treatment allows the positive electrode mixture layer to be well adhered to the current collector.

[0192] Furthermore, when the positive electrode mixture layer contains a curable polymer, the polymer may be cured after the positive electrode mixture layer is formed.

[0193] <Electrochemical Device> An electrochemical device comprising the above-described positive electrode of the present invention has excellent cycle characteristics, and is preferably a lithium ion secondary battery in particular.

[0194] Hereinafter, the configuration of a lithium ion secondary battery will be described as an example of an electrochemical element. This lithium ion secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator, and the positive electrode is the electrode of the present invention.

[0195] (Negative Electrode) The negative electrode is not particularly limited, and any known electrode can be used.

[0196] (Electrolyte) As the electrolyte, an organic electrolyte solution in which a supporting electrolyte is dissolved in an organic solvent is usually used. As the supporting electrolyte, for example, a lithium salt is used. As the lithium salt, for example, LiPF ６ , LiAsF ６ , LiBF ４ , LiSbF ６ , LiAlCl ４ , LiClO ４ , C.F. ３ SO ３ Li, C ４ F ９ SO ３ Li, CF ３ COOLi, (CF ３ CO) ２ NLi, (CF３ SO ２ ) ２ NLi, (C ２ F ５ SO ２ Among them, LiPF is particularly preferred because it is easily soluble in solvents and shows a high degree of dissociation. ６ , LiClO ４ , C.F. ３ SO ３ Li is preferred, and LiPF ６ is particularly preferred. Note that one type of electrolyte may be used alone, or two or more types may be used in combination in any ratio. Generally, the lithium ion conductivity tends to increase as the supporting electrolyte with a higher degree of dissociation is used, so the lithium ion conductivity can be adjusted by the type of supporting electrolyte.

[0197] The organic solvent used in the electrolyte is not particularly limited as long as it can dissolve the supporting electrolyte. For example, carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), and methyl ethyl carbonate (EMC) are preferably used. esters such as γ-butyrolactone and methyl formate are also suitable. Ethers such as 1,2-dimethoxyethane and tetrahydrofuran are also suitable. Sulfur-containing compounds such as sulfolane and dimethyl sulfoxide are also suitable. Mixtures of these solvents may also be used. Among these, carbonates are preferred because they have a high dielectric constant and a wide stable potential range. A mixture of ethylene carbonate and diethyl carbonate is even more preferred.

[0198] The concentration of the electrolyte in the electrolytic solution can be adjusted appropriately, and is preferably 0.5 to 15 mass %, more preferably 2 to 13 mass %, and even more preferably 5 to 10 mass %. Known additives, such as vinylene carbonate, fluoroethylene carbonate, and ethyl methyl sulfone, may also be added to the electrolytic solution.

[0199] (Separator) The separator is not particularly limited, and for example, those described in JP 2012-204303 A can be used. Among these, a microporous film made of a polyolefin resin (polyethylene, polypropylene, polybutene, polyvinyl chloride) is preferred because it allows the thickness of the entire separator to be thin, thereby increasing the ratio of the electrode active material in the lithium ion secondary battery and increasing the capacity per volume.

[0200] (Method for Manufacturing Lithium-Ion Secondary Battery) The lithium-ion secondary battery according to the present invention can be manufactured, for example, by stacking a positive electrode and a negative electrode with a separator interposed therebetween, rolling or folding the resulting assembly as necessary according to the battery shape, placing it in a battery container, injecting an electrolyte into the battery container, and sealing it. To prevent internal pressure rise, overcharge / discharge, and the like in the secondary battery, a fuse, an overcurrent prevention element such as a PTC element, an expanded metal, a lead plate, or the like may be provided as necessary. The shape of the secondary battery may be any of a coin type, a button type, a sheet type, a cylindrical type, a rectangular type, a flat type, and the like.

[0201] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. In the following description, the units "%", "ppm" and "parts" that represent amounts are by mass unless otherwise specified.

[0202] Furthermore, in a polymer produced by copolymerizing a plurality of types of monomers, the ratio of a monomer unit formed by polymerizing a certain monomer in the polymer usually coincides with the ratio (feed ratio) of the certain monomer to all the monomers used in the polymerization of the polymer, unless otherwise specified. Furthermore, when the polymer is a hydrogenated polymer obtained by hydrogenating a polymer containing conjugated diene monomer units, the total content of unhydrogenated conjugated diene monomer units and alkylene structural units as hydrogenated conjugated diene monomer units in the hydrogenated polymer coincides with the ratio (feed ratio) of the conjugated diene monomer to all the monomers used in the polymerization of the polymer.

[0203] In the examples and comparative examples, various measurements and evaluations were carried out according to the following methods.

[0204] <Iodine Value> The iodine value of the hydrogenated nitrile rubber was measured in accordance with JIS K 6235.

[0205] <Weight-average molecular weight> The weight-average molecular weight (Mw) of the hydrogenated nitrile rubber was measured by gel permeation chromatography (GPC) using a 10 mM LiBr-dimethylformamide (DMF) solution under the following measurement conditions: Separation column: Shodex KD-806M (manufactured by Showa Denko K.K.) Detector: Differential refractometer detector RID-10A (manufactured by Shimadzu Corporation) Eluent flow rate: 0.3 mL / min Column temperature: 40°C Standard polymer: TSK standard polystyrene (manufactured by Tosoh Corporation)

[0206] <Metal Content> Approximately 0.5 g of hydrogenated nitrile rubber bale was collected and dissolved in approximately 5 mL of concentrated sulfuric acid. After carbonization on a heater, the mixture was incinerated in an electric furnace at 1000°C for approximately 3 hours. After cooling, approximately 2 mL of concentrated nitric acid was gradually added to the mixture for wet decomposition. After decomposition, the acid was concentrated and adjusted to a constant volume of 10 mL with ultrapure water. The metal ion concentration was measured using an ICP-MS (ICP-MS 7900, manufactured by Agilent). The metal ion concentration contained in the hydrogenated nitrile rubber was then calculated from the measured value. The metal ions measured were calcium ions, rhodium ions, ruthenium ions, palladium ions, iron ions, sodium ions, and magnesium ions.

[0207] <Chlorine Content> 1 g of hydrogenated nitrile rubber balls was dissolved in 150 ml of a mixed solution prepared by mixing methyl ethyl ketone and isopropanol at a volume ratio of 4:1, and 2% dilute sulfuric acid was further added to prepare a sample solution. This was then added dropwise with a 0.005 N aqueous solution of silver nitrate, and the chlorine content was calculated by potentiometric titration (using Hiranuma COMITE-101 or an equivalent product, silver supporting electrode AG-68 / silver reference electrode AM-44).

[0208] <Bulk specific gravity> A piece of approximately 2 cm x 3 cm x 0.2 cm was cut out from a hydrogenated nitrile rubber bale, and the bulk specific gravity (g / cm ３ ) was measured.

[0209] <Viscosity of Conductive Material Dispersion> The viscosity of the conductive material dispersion obtained in each Example and Comparative Example was measured for 120 seconds at a temperature of 25°C and a shear rate of 10 (1 / s) using a rheometer ("MCR302" manufactured by Anton Paar), and the average viscosity measured from 61 seconds to 120 seconds was evaluated according to the following criteria: A: 1 Pa s or less B: More than 1 Pa s and 5 Pa s or less C: More than 5 Pa s and 10 Pa s or less D: More than 10 Pa s

[0210] <Conductive material dispersion stability> After measuring the dispersion viscosity (η0) for the conductive material dispersions obtained in each Example and Comparative Example, the dispersion was stored in a sealed container at 25°C for 10 days. Thereafter, the dispersion viscosity was measured again (η1), and the viscosity change rate was calculated as follows to define the conductive material dispersion stability. Evaluation was performed according to the following criteria. Viscosity change rate Δη=η1 / η0×100 A: Viscosity change rate Δη was 90% or more and less than 110% B: Viscosity change rate Δη was 80% or more and less than 90%, or 110% or more and less than 120% C: Viscosity change rate Δη was 70% or more and less than 80%, or 120% or more and less than 130% D: Viscosity change rate Δη was 60% or more and less than 70%, or 130% or more and less than 140% E: Viscosity change rate Δη was less than 60%, or 140% or more

[0211] <Cycle Characteristics> After injecting the electrolyte, the lithium-ion secondary batteries prepared in the Examples and Comparative Examples were left standing at 25°C for 5 hours. Next, they were charged to a cell voltage of 3.65 V at 25°C using a constant current of 0.2 C, and then aged for 12 hours at 60°C. Then, they were discharged to a cell voltage of 3.00 V using a constant current of 0.2 C at 25°C. Subsequently, they were subjected to CC-CV charging (upper cell voltage 4.20 V) using a constant current of 0.2 C, and CC discharging to 3.00 V using a constant current of 0.2 C. This 0.2 C charge-discharge cycle was repeated three times. Next, 300 cycles of charge-discharge were performed at a charge-discharge rate of 1.0 C at a cell voltage of 4.20-3.00 V in a 45°C environment. The discharge capacity at the first cycle was defined as X1, and the discharge capacity at the 300th cycle as X2. Using the discharge capacities X1 and X2, the capacity retention rate = (X2 / X1) x 100 (%) was calculated and evaluated according to the following criteria. A larger capacity retention rate indicates that the lithium ion secondary battery has better cycle characteristics. A: Capacity retention rate is 85% or more B: Capacity retention rate is 80% or more but less than 85% C: Capacity retention rate is 75% or more but less than 80% D: Capacity retention rate is less than 75%

[0212] <Presence or absence of cracks in active material after cycling> The lithium ion secondary batteries produced in Examples and Comparative Examples were disassembled after the cycle test, and cross-sectional SEM images of the removed positive electrodes were observed at 1000x magnification. The number of cracks observed in the active material was evaluated as follows according to the number of cracks observed in the active material: A: Less than 2 cracked active material pieces B: 2 or more but less than 5 cracked active material pieces C: 5 or more but less than 9 cracked active material pieces D: 9 or more cracked active material pieces

[0213] <Output Characteristics> The output characteristics of the lithium-ion secondary batteries prepared in the Examples and Comparative Examples were evaluated by measuring the I-V resistance using the following method. As with the cycle characteristics, the lithium-ion secondary batteries were subjected to aging treatment and three charge / discharge cycles three times. They were then charged at 25°C until the charge rate reached 50% (i.e., until the charge capacity reached 350 mAh for a 700 mAh cell capacity). The resistance was measured using the following procedure: (1) Determine the voltage change ΔV(0.2) after 30 seconds of discharge using a 0.2 C constant current method (I0.2). (2) Charge the battery for 30 seconds using a 0.2 C constant current method. (3) Determine the voltage change ΔV(1.0) after 30 seconds of discharge using a 1.0 C constant current method (I1.0). I-V resistance (Ω) = {ΔV(1.0) - ΔV(0.2)} / (I1.0 - I0.2). Evaluation was performed based on the calculated I-V resistance values ​​as follows: A: 0.25Ω or less B: More than 0.25Ω and less than 0.30Ω C: More than 0.30Ω and less than 0.35 D: More than 0.35Ω

[0214] Example 1 <Production of Hydrogenated Nitrile Rubber> - Emulsion Polymerization Step to Washing and Drying Step - A reactor having an internal volume of 10 liters was charged with 100 parts of ion-exchanged water, 33 parts of acrylonitrile as an α,β-ethylenically unsaturated nitrile monomer, and 67 parts of 1,3-butadiene as a conjugated diene monomer, and 2 parts of potassium oleate as an emulsifier, 0.1 part of potassium phosphate as a stabilizer, and further, 0.3 parts of tert-dodecyl mercaptan (TDM) as a molecular weight modifier. Emulsion polymerization was carried out at a temperature of 5°C in the presence of 0.35 parts of potassium persulfate as a polymerization initiator, to copolymerize acrylonitrile and 1,3-butadiene.

[0215] When the polymerization conversion rate reached 89%, 0.2 parts of hydroxylamine sulfate per 100 parts of monomer was added to terminate the polymerization. Subsequently, the mixture was heated and subjected to steam distillation at about 90°C under reduced pressure to recover the residual monomer, and then 0.1 parts of 2,2-methylenebis(4-methyl-6-tert-butylphenol) (MBBP) as an antioxidant was added to obtain an emulsion polymerization liquid.

[0216] Calcium chloride (CaCl) was used as a coagulant in an amount of 3 parts per 100 parts of polymer solids in the resulting emulsion polymerization liquid. ２A 25% aqueous solution of 2,4-dimethylaminobenzoate (2,4-dimethylaminobenzoate) was added with stirring to coagulate the polymer in the emulsion polymerization solution. The polymer was then filtered, washed with ion-exchanged water in an amount 50 times the amount of the obtained polymer, and then dried at a temperature of 90° C. under reduced pressure to obtain a polymer.

[0217] - Hydrogenation Step I (Metathesis Reaction) - Next, 9 parts of the obtained polymer were dissolved in 141 parts of monochlorobenzene, a halogenated hydrocarbon, and the solution was charged into a reactor. The reactor was then heated to 80°C, and 2 L of a monochlorobenzene solution containing bis(tricyclohexylphosphine)benzylidene ruthenium dichloride as a Grubbs catalyst was added so that the amount of Grubbs catalyst relative to the polymer was 1,000 ppm. Then, 4.4 parts of cis-2-butene-1,4-diol as a coolefin was added per 100 parts of Precursor 1, and the metathesis reaction of the polymer was carried out at a stirring speed of 600 rpm. During the reaction, the temperature was maintained constant using a cooling coil connected to a temperature control device and a heat sensor.

[0218] - Hydrogenation step II (hydrogenation reaction) - After that, the inside of the reactor was pressurized with 0.7 MPa of H ２ The reactor was degassed three times at 100°C. The temperature of the reactor was then raised to 130°C, and 1 L of a monochlorobenzene solution containing a Wilkinson catalyst and triphenylphosphine was added to the reactor. The amount of Wilkinson catalyst was 0.03 parts and the amount of triphenylphosphine was 1 part per 100 parts of the polymer. The temperature was then raised to 138°C, and the polymer was hydrogenated under a hydrogen pressure (gauge pressure) of 8.4 MPa.

[0219] - Purification Step - After completion of the hydrogenation reaction, 0.2 parts of activated carbon with an average diameter of 15 μm was added to the reactor and stirred for 30 minutes to adjust the concentration of divalent or higher metal ions, including calcium ions. The mixture was then filtered through a filter with a pore size of 5 μm. The filtered solution was then heated and dried until the monochlorobenzene solvent concentration reached 50 ppm, and hydrogenated nitrile rubber A was isolated. The iodine value, weight average molecular weight, and metal content of the obtained hydrogenated nitrile rubber A were measured. The results are shown in Table 1. Furthermore, 20 parts (20 kg) of the isolated nitrile rubber A were loaded into a 300 × 650 × 300 mm baler and compacted at a pressure of 3 MPa for 30 seconds to obtain nitrile rubber bale A. When hydrogenated nitrile rubber bale A was subjected to the same measurements as hydrogenated nitrile rubber A, the measured values ​​were the same.

[0220] <Preparation of positive electrode binder> 920 parts of NMP was weighed into a 2 L vessel equipped with a stirring blade and heated to 80° C. Next, 80 parts of hydrogenated nitrile rubber A cut into pieces of about 1 cm square from the hydrogenated nitrile rubber bale A produced above was added and dissolved with continued stirring for 5 hours to prepare a positive electrode binder A with a solids concentration of 8%.

[0221] <Preparation of Conductive Material Dispersion> Multi-walled carbon nanotubes (BET specific surface area: 250 m) were used as the conductive material. ２ 5 parts of a 100% ethanol (1 / g), 12.5 parts (corresponding to 1 part as solids) of the positive electrode binder having a solids concentration of 8% obtained as described above, and 82.5 parts of NMP as an organic solvent were added, and the mixture was stirred using a disper (3000 rpm, 10 minutes). Thereafter, a bead mill ("LMZ015" manufactured by Ashizawa Fine Tech) using zirconia beads having a diameter of 1 mm was used to mix at a peripheral speed of 8 m / s for 1 hour to prepare a conductive material dispersion, and the viscosity of the dispersion was measured, and the results are shown in Table 1. The stability of the conductive material dispersion was also evaluated, and the results are shown in Table 1.

[0222] <Preparation of slurry for secondary battery positive electrode> A ternary active material (LiNi) having a layered structure was added as a positive electrode active material to the above-mentioned conductive material dispersion. ０．５ Co ０．２ Mn ０．３ O ２98.0 parts of 10 μm (average particle size), 1.0 part of polyvinylidene fluoride as a binder, 1.0 part of the conductive material dispersion (solid content equivalent), and NMP were added and mixed with a planetary mixer (60 rpm, 30 minutes) to prepare a positive electrode slurry. The amount of NMP added was adjusted so that the viscosity of the resulting positive electrode slurry (measured with a single cylindrical rotational viscometer in accordance with JIS Z8803:1991, temperature: 25°C, rotation speed: 60 rpm) was within the range of 4000 to 5000 mPa s.

[0223] <Preparation of Positive Electrode> An aluminum foil having a thickness of 20 μm was prepared as a current collector. The positive electrode slurry was applied to the aluminum foil using a comma coater so that the coating weight after drying was 20 mg / cm. ２ The coating was applied so that the density became 3.5 g / cm. The coating was dried at 120°C for 5 minutes and at 130°C for 5 minutes, and then heat-treated at 60°C for 10 hours to obtain a positive electrode blank. The positive electrode blank was rolled using a roll press to obtain a positive electrode blank having a density of 3.5 g / cm. ３ A sheet-shaped positive electrode was fabricated from the positive electrode mixture layer and aluminum foil. This sheet-shaped positive electrode was cut into a width of 4.8 cm and a length of 50 cm to prepare a positive electrode for a lithium ion secondary battery.

[0224] <Preparation of a negative electrode for a lithium ion secondary battery> 33 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 3.5 parts of itaconic acid as a carboxylic acid group-containing monomer, 63.5 parts of styrene as an aromatic vinyl monomer, 0.4 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water, and 0.5 parts of potassium persulfate as a polymerization initiator were placed in a 5 MPa pressure vessel equipped with a stirrer, and after thorough stirring, the mixture was heated to 50 ° C to initiate polymerization. When the polymerization conversion rate reached 96%, the mixture was cooled to terminate the polymerization reaction, yielding a mixture containing a particulate binder (styrene-butadiene copolymer). A 5% aqueous sodium hydroxide solution was added to the mixture to adjust the pH to 8, and unreacted monomer was removed by heated vacuum distillation. The mixture was then cooled to 30 ° C or below to obtain an aqueous dispersion containing a negative electrode binder.

[0225] Next, 48.75 parts of artificial graphite and 48.75 parts of natural graphite as negative electrode active materials, and 1 part of carboxymethyl cellulose as a thickener were added to a planetary mixer. The mixture was then diluted with ion-exchanged water to a solids concentration of 60%, and then kneaded for 60 minutes at a rotation speed of 45 rpm. Then, 1.5 parts (solids equivalent) of the aqueous dispersion containing the negative electrode binder obtained as described above was added, and the mixture was kneaded for 40 minutes at a rotation speed of 40 rpm. Then, ion-exchanged water was added to the mixture to a viscosity of 3000±500 mPa s (measured with a Brookfield viscometer at 25°C and 60 rpm), thereby preparing a negative electrode composite layer slurry.

[0226] Next, a copper foil having a thickness of 15 μm was prepared as a current collector. The negative electrode slurry was applied to both sides of the copper foil in a coated amount of 10 mg / cm after drying. ２ The negative electrode blank was rolled using a roll press to a density of 1.6 g / cm. ３ A sheet-shaped negative electrode was fabricated consisting of the negative electrode mixture layers (both sides) and copper foil. The sheet-shaped negative electrode was then cut into a piece 5.0 cm wide and 52 cm long to prepare a negative electrode for a lithium ion secondary battery.

[0227] <Fabrication of Lithium-Ion Secondary Battery> The fabricated lithium-ion secondary battery positive electrode and lithium-ion secondary battery negative electrode were arranged with the electrode mixture layers facing each other, and a 15 μm thick separator (a polyethylene microporous film) was interposed between them. The resulting wound body was then wound around a core with a diameter of 20 mm to obtain a wound body. The resulting wound body was then compressed in one direction at a speed of 10 mm / sec until it reached a thickness of 4.5 mm. The compressed wound body had an elliptical shape in plan view, and the ratio of its major axis to its minor axis (major axis / minor axis) was 7.7.

[0228] In addition, the electrolyte is LiPF with a concentration of 1.0 M. ６ A solution (solvent: a mixed solvent of ethylene carbonate (EC) / diethyl carbonate (DEC)=3 / 7 (volume ratio), additive: containing 2 vol % (solvent ratio) of vinylene carbonate) was prepared.

[0229] The compressed wound body was then housed in an aluminum laminate case together with 3.2 g of non-aqueous electrolyte. A nickel lead wire was connected to a predetermined location on the negative electrode, and an aluminum lead wire was connected to a predetermined location on the positive electrode. The opening of the case was then thermally sealed to obtain a lithium-ion secondary battery. This lithium-ion secondary battery was a pouch-shaped battery of a predetermined size capable of housing the wound body, and had a nominal capacity of 700 mAh.

[0230] The resulting lithium ion secondary battery was evaluated for output characteristics, cycle characteristics, and cracking of the electrode active material after cycling. The results are shown in Table 1.

[0231] (Example 2) Except for changing the amount of activated carbon used in the purification step to 0.5 parts, hydrogenated nitrile rubber B, hydrogenated nitrile rubber bale B, and positive electrode binder B were obtained in the same manner as in Example 1. Measurements and evaluations of hydrogenated nitrile rubber B were carried out, and the results are shown in Table 1.

[0232] (Example 3) Except for changing the amount of activated carbon used in the purification step to 0.08 parts, hydrogenated nitrile rubber C, hydrogenated nitrile rubber bale C, and positive electrode binder C were obtained in the same manner as in Example 1. Hydrogenated nitrile rubber C was measured and evaluated, and the results are shown in Table 1.

[0233] (Example 4) Hydrogenated nitrile rubber D, hydrogenated nitrile rubber bale D and positive electrode binder D were obtained in the same manner as in Example 1, except that the amount of activated carbon used in the purification step was changed to 0.07 parts. Hydrogenated nitrile rubber D was measured and evaluated, and the results are shown in Table 1.

[0234] (Example 5) Except for changing the amount of activated carbon used in the purification step to 0.05 parts, hydrogenated nitrile rubber E, hydrogenated nitrile rubber bale E and positive electrode binder E were obtained in the same manner as in Example 1. Hydrogenated nitrile rubber E was measured and evaluated, and the results are shown in Table 1.

[0235] (Example 6) Hydrogenated nitrile rubber F, hydrogenated nitrile rubber bale F and positive electrode binder F were obtained in the same manner as in Example 1, except that the amount of activated carbon used in the purification step was changed to 0.02 parts. Hydrogenated nitrile rubber F was measured and evaluated, and the results are shown in Table 1. (Comparative Example 1) Hydrogenated nitrile rubber G, hydrogenated nitrile rubber bale G and positive electrode binder G were obtained in the same manner as in Example 1, except that the amount of activated carbon used in the purification step was changed to 2 parts. Hydrogenated nitrile rubber G was measured and evaluated, and the results are shown in Table 1.

[0236] (Example 7) The amount of Grubbs catalyst in the metathesis reaction was changed to 4000 ppm, and the metathesis reaction was carried out without adding 1 L of a monochlorobenzene solution containing Wilkinson catalyst and triphenylphosphine to the reactor. The inside of the reactor was pressurized under H 2 of 0.7 MPa. ２ After degassing three times at 100° C., the temperature was raised to 140° C., and the hydrogenation reaction was carried out under a hydrogen pressure of 8.4 MPa. Except for this, hydrogenated nitrile rubber H, hydrogenated nitrile rubber bale H, and positive electrode binder H were obtained in the same manner as in Example 1. Hydrogenated nitrile rubber H was measured and evaluated, and the results are shown in Table 2.

[0237] (Example 8) Except for changing the amount of Grubbs catalyst in the metathesis reaction to 3000 ppm, hydrogenated nitrile rubber I, hydrogenated nitrile rubber bale I, and positive electrode binder I were obtained in the same manner as in Example 1. Hydrogenated nitrile rubber I was measured and evaluated, and the results are shown in Table 2.

[0238] (Example 9) Except for changing the amount of Grubbs catalyst in the metathesis reaction to 500 ppm, hydrogenated nitrile rubber J, hydrogenated nitrile rubber bale J, and positive electrode binder J were obtained in the same manner as in Example 1. Hydrogenated nitrile rubber J was measured and evaluated, and the results are shown in Table 2.

[0239] (Example 10) Hydrogenated nitrile rubber K, hydrogenated nitrile rubber bale K, and positive electrode binder K were obtained in the same manner as in Example 1, except that the amount of Grubbs catalyst in the metathesis reaction was changed to 400 ppm. Hydrogenated nitrile rubber K was measured and evaluated, and the results are shown in Table 2.

[0240] (Example 11) Except for changing the amount of Grubbs catalyst in the metathesis reaction to 200 ppm, hydrogenated nitrile rubber L, hydrogenated nitrile rubber bale L, and positive electrode binder L were obtained in the same manner as in Example 1. Hydrogenated nitrile rubber L was measured and evaluated, and the results are shown in Table 2.

[0241] Comparative Example 2 Except for not adding an antioxidant, hydrogenated nitrile rubber M, hydrogenated nitrile rubber bale M, and positive electrode binder M were obtained in the same manner as in Example 1. Measurements and evaluations of hydrogenated nitrile rubber M were carried out, and the results are shown in Table 2.

[0242] (Comparative Example 3) Hydrogenated nitrile rubber N, hydrogenated nitrile rubber bale N and positive electrode binder N were obtained in the same manner as in Example 1, except that the iodine value of the hydrogenated nitrile rubber in the hydrogenation reaction was stopped at 150. Hydrogenated nitrile rubber N was measured and evaluated, and the results are shown in Table 2.

[0243]

[0244]

[0245] From Tables 1 and 2, it can be seen that the hydrogenated nitrile rubbers A to F and H to L of the present invention contain nitrile group-containing monomer units and conjugated diene monomer units and / or alkylene structural units, have a weight average molecular weight (Mw) in the range of 1,000 to 1,000,000, an iodine value of 0.1 to 100 mg / 100 mg, contain an antioxidant of 2,2-methylenebis(4-methyl-6-tert-butylphenol), have a Ca content in the range of 1 to 2500 ppm and a Na content of 300 ppm or less, are excellent in viscosity characteristics and stability of the conductive material dispersion, and are excellent in all of the output characteristics, cycle characteristics, and effect of suppressing cracking of the electrode active material after a cycle test of an electrochemical element, and that the respective characteristics are well-balanced (comparison of Examples 1 to 11 with Comparative Examples 1 to 3).

[0246] With regard to the viscosity characteristics (dispersibility) of the conductive material dispersion, the hydrogenated nitrile rubbers A to F and H to K of the present invention are all excellent, but it is particularly evident that the viscosity correlates with the iodine value of the hydrogenated nitrile rubber, and as the iodine value increases, the viscosity of the conductive material dispersion increases and the dispersibility deteriorates (comparison with Examples 1, 7 to 11, and Comparative Example 2). It is also evident that the dispersibility of the conductive material dispersion is affected by the Ca content in the hydrogenated nitrile rubber, and when the Ca content becomes particularly high, the viscosity of the dispersion increases, deteriorating, albeit slightly (comparison with the viscosity change from Example 4 to Example 6 and Comparative Example 3). It is evident that the viscosity characteristics of the conductive material dispersion are excellent when the iodine value of the hydrogenated nitrile rubber is small and the Ca content in the hydrogenated nitrile rubber is small.

[0247] It is clear that the stability of the conductive material dispersion is greatly affected by the presence or absence of the specific antioxidant 2,2-methylenebis(4-methyl-6-tert-butylphenol), and is extremely deteriorated if it is not contained. It is also clear that it correlates with the iodine value of the hydrogenated nitrile rubber, and that the smaller the iodine value, the better (comparison between Example 11 and Comparative Examples 1 and 2 and other Examples and Comparative Examples).

[0248] It is clear that the output characteristics of the electrochemical element correlate with the iodine value of the hydrogenated nitrile rubber, and that a smaller iodine value is preferable (comparison between Examples 1 to 11 and Comparative Examples 1 to 3).

[0249] It is clear that the cycle characteristics of the electrochemical element are greatly affected by the amount of Ca in the hydrogenated nitrile rubber, and deteriorate when the amount is too large (comparison among Examples 1 to 6).

[0250] It can be seen that the suppression of cracking of the electrode active material after the cycle test of the electrochemical element correlates with the amount of Ca in the hydrogenated nitrile rubber, and tends to worsen as the amount decreases (particularly, comparison between Examples 3 to 6 and Comparative Example 3).

[0251] On the other hand, although not shown in the comparative examples of the present application, hydrogenated nitrile rubbers in which large amounts of Na content, Rh and / or Ru content, Pd content, and Mg content remain have poor cycle characteristics of electrochemical elements and cause cracking of the electrode active material after a cycle test. However, Tables 1 and 2 show that, as long as the contents of these metals are within the ranges of hydrogenated nitrile rubbers A to F and H to L of the present invention, they do not affect any of the properties such as the viscosity characteristics and stability of the conductive material dispersion, output characteristics, cycle characteristics, and the effect of suppressing cracking of the electrode active material after a cycle test.

[0252] Furthermore, from the main text of the Examples and Tables 1 and 2, it is understood that the novel hydrogenated nitrile rubbers A to F and H to L of the present invention can be produced by a combination of known methods, such as that [Mw] can be adjusted by the amount of catalyst in the metathesis reaction, that [iodine value] can be adjusted by the amount of hydrogenation catalyst, the molecular weight of the polymer after the metathesis reaction, and monitoring of the hydrogenation rate, that [Mg, Na] content can be adjusted without using any auxiliary materials that would cause problems in the production steps such as the emulsion polymerization step and the hydrogenation step, and that [Ca] used in the coagulant and [Ru, Rh] used in the hydrogenation catalyst can be adjusted by washing with water and treating with an adsorbent. (Comparative Example 4) Performance evaluation was carried out in the same manner as in Comparative Example 2, except that the positive electrode binder M in Comparative Example 2 was prepared by breaking down the hydrogenated nitrile rubber M before baling (a block of hydrogenated nitrile rubber obtained by directly drying a polymer-containing monochlorobenzene solution to remove the solvent) into small pieces and dissolving it in NMP, instead of the hydrogenated nitrile rubber bale M. The results were viscosity (dispersibility) evaluation: A, conductive material dispersion stability: E, output characteristics: A, cycle characteristics: A, and active material cracking after cycling: B. When hydrogenated nitrile rubber M (block) was used instead of hydrogenated nitrile rubber bale M, the conductive material dispersion stability deteriorated from D to E. This was because, when the bulk density of both was measured, the bulk density of hydrogenated nitrile rubber bale M was 0.7 to 0.75 g / cm ３ On the other hand, the bulk density of the hydrogenated nitrile rubber M is 0.5 to 0.6 g / cm ３ In other words, it is believed that because a large amount of air is contained within the hydrogenated nitrile rubber in block form with a low bulk density, oxygen radicals generated within the hydrogenated nitrile rubber react with the active points on the surface of the conductive material, causing crosslinking and worsening stability.

[0253] (Examples 12 to 17) A large amount of steam was introduced into the hydrogenated nitrile rubber-containing monochlorobenzene solution filtered after the purification steps of Examples 1 to 6 to isolate hydrous crumbs. The isolated hydrous crumbs were then dried using a screw-type extruder having a vacuum drying barrel and a substantially rectangular die under conditions that would not affect the properties of the hydrogenated nitrile rubber, and a sheet-like dried rubber (width 300 mm x thickness 30 mm) was extruded. After the extruded dried rubber sheet reached 50°C or below, it was cut to a predetermined length of 650 mm, and 10 sheets were stacked to obtain hydrogenated nitrile rubber bales O to T. When the bulk density of hydrogenated nitrile rubber bales O to T, from which internal air had been removed using the screw-type extruder, was measured, it was found that each had a bulk density of 0.85 g / cm. ３ This was a value far greater than the bulk density of 0.7 to 0.75 of the hydrogenated nitrile rubber bales A to F compressed at 3 MPa using the balers of Examples 1 to 6.

[0254] Using the prepared hydrogenated nitrile rubber bales O to T, positive electrode binders O to T were prepared and performance evaluations were conducted in the same manner as in Examples 1 to 6. Although the evaluation did not change the evaluation level, all performances were significantly superior to the results of Examples 1 to 6. In particular, the evaluation of conductive material dispersion stability was originally all rated "A." However, when hydrogenated nitrile rubber bales O to T with high bulk specific gravity (almost no internal air) were used, the viscosity change rate Δη was almost unchanged, reaching a value close to 100%. Furthermore, when the evaluation was performed on an average of five runs, the results were good with little variation. These results suggest that hydrogenated nitrile rubber bales O to T have little internal air and are less likely to generate oxygen radicals, which contributed to the stability of the conductive material dispersion. Incidentally, when crumb-like hydrogenated nitrile rubbers O to T are obtained by directly drying the water-containing crumbs before being fed into a screw-type extruder, the bulk specific gravity of each was 0.5 to 0.6 g / cm. ３ The range was.

[0255] The screw extruder used in Examples 12 to 17 was composed of one supply barrel, three dehydration barrels (first to third dehydration barrels), five drying barrels (first to fifth drying barrels), and a die section, and the operating conditions of the screw extruder were as follows:

[0256] Set temperatures of each barrel: First to third dehydration barrels: 90 to 120°C First to fifth drying barrels: 120 to 180°C Operating conditions: Diameter (D) of screw in barrel unit: 132 mm Total length (L) of screw in barrel unit: 4620 mm L / D: 35 Rotation speed of screw in barrel unit: 135 rpm Residence time: 100 seconds Degree of vacuum in drying barrel: 10 kPa Resin pressure in die: 2 MPa

[0257] In addition, the hydrogenated nitrile rubber bales O to T produced above were different from the hydrogenated nitrile rubber bales A to F produced in Examples 1 to 6 only in bulk specific gravity as a bale characteristic, but the molecular weight of the constituent hydrogenated nitrile rubber, iodine value, antioxidant content, chlorine content and various metal contents were the same.

[0258] According to the present invention, it is possible to provide a hydrogenated nitrile rubber and a method for producing the same, which can improve the viscosity characteristics and stability of a conductive material dispersion, prevent cracking of the active material in the electrode, and improve the cycle characteristics and output characteristics of an electrochemical device. According to the present invention, it is possible to provide a hydrogenated nitrile rubber bale, which can improve the viscosity characteristics and stability of a conductive material dispersion, prevent cracking of the active material in the electrode, and improve the cycle characteristics and output characteristics of an electrochemical device. According to the present invention, it is possible to provide a positive electrode binder, which can improve the viscosity characteristics and stability of a conductive material dispersion, prevent cracking of the active material in the electrode, and improve the cycle characteristics and output characteristics of an electrochemical device. Furthermore, according to the present invention, it is possible to provide a positive electrode for an electrochemical device, which has little cracking of the electrode active material and excellent cycle characteristics and output characteristics, and a method for producing the same.

Claims

1. A hydrogenated nitrile rubber which contains a nitrile group-containing monomer unit, a conjugated diene monomer unit and / or an alkylene structural unit, has a weight average molecular weight (Mw) in the range of 1,000 to 1,000,000, an iodine value in the range of 0.1 to 100 mg / 100 mg, contains 2,2-methylenebis(4-methyl-6-tert-butylphenol) as an antioxidant, has a calcium (Ca) content in the range of 1 to 2500 ppm, and has a sodium (Na) content of 300 ppm or less.

2. The hydrogenated nitrile rubber according to claim 1, wherein the content of the antioxidant is in the range of 0.001 to 3 mass %.

3. The hydrogenated nitrile rubber according to claim 1, further comprising a rhodium (Rh) and / or ruthenium (Ru) content of 0.1 to 50 ppm, a palladium (Pd) content of 200 ppm or less, and a magnesium (Mg) content of 50 ppm or less.

4. Bulk density is 0.8 g / cm ３ The hydrogenated nitrile rubber according to claim 1.

5. The hydrogenated nitrile rubber according to claim 4, further comprising a chlorine (Cl) content in the range of 10 ppm to 3,000 ppm, and a mass ratio (Ca / Cl) to the calcium (Ca) content in the range of 0.1 to 4.

6. The hydrogenated nitrile rubber according to claim 4, wherein the total ratio of the nitrile group-containing monomer units and the conjugated diene monomer units and / or alkylene structural units in the hydrogenated nitrile rubber is 97 mass % or more.

7. The hydrogenated nitrile rubber according to claim 1, which is prepared by emulsion polymerizing a nitrile group-containing monomer and a conjugated diene monomer, coagulating the polymer with calcium chloride, and hydrogenating the polymer.

8. The hydrogenated nitrile rubber according to claim 1, which is obtained by emulsion polymerizing a nitrile group-containing monomer and a conjugated diene monomer, adding 2,2-methylenebis(4-methyl-6-tert-butylphenol) as an antioxidant, coagulating the polymer with calcium chloride, and hydrogenating the polymer.

9. The method for producing hydrogenated nitrile rubber according to claim 1, which comprises hydrogenating a nitrile rubber containing 2,2-methylenebis(4-methyl-6-tert-butylphenol) as an antioxidant.

10. A method for producing hydrogenated nitrile rubber according to claim 1, comprising: an emulsion polymerization step of emulsion-polymerizing monomer components containing a nitrile group-containing monomer and a conjugated diene monomer to obtain an emulsion polymerization liquid; an antioxidant addition step of adding 2,2-methylenebis(4-methyl-6-tert-butylphenol) as an antioxidant to the emulsion polymerization liquid; a coagulation step of contacting the emulsion polymerization liquid to which the antioxidant has been added with calcium chloride to produce water-containing crumbs; a washing and drying step of washing and drying the water-containing crumbs to obtain a polymer; and a hydrogenation step of hydrogenating the polymer using a hydrogenation catalyst.

11. The method for producing hydrogenated nitrile rubber according to claim 10, wherein the hydrogenation step comprises subjecting the polymer to metathesis with a ruthenium catalyst and a coolefin, followed by hydrogenation with a rhodium catalyst.

12. The method for producing hydrogenated nitrile rubber according to claim 10, further comprising a purification step of subjecting the hydrogenated nitrile rubber to an adsorbent treatment after the hydrogenation step.

13. The method for producing hydrogenated nitrile rubber according to claim 8, wherein the hydrogenated nitrile rubber is dried using a screw-type extruder.

14. The method for producing hydrogenated nitrile rubber according to claim 13, wherein the screw-type extruder is equipped with a drying barrel under reduced pressure.

15. A hydrogenated nitrile rubber bale obtained by baling the hydrogenated nitrile rubber according to claim 1.

16. Bulk density is 0.8 g / cm ３ The hydrogenated nitrile rubber veil according to claim 15, 17. A positive electrode binder obtained by dispersing or dissolving the hydrogenated nitrile rubber according to claim 1 in N-methylpyrrolidone (NMP).

18. A positive electrode binder obtained by dispersing or dissolving the hydrogenated nitrile rubber veil according to claim 16 in N-methylpyrrolidone (NMP).

19. A positive electrode comprising a positive electrode mixture layer containing a conductive material, a positive electrode active material, and a binder containing the hydrogenated nitrile rubber according to claim 1, and a current collector.

20. A method for producing a positive electrode, comprising the steps of: mixing the positive electrode binder according to claim 17 with a conductive material, and then mixing the resultant with a positive electrode active material to obtain a positive electrode mixture layer slurry; coating the resulting slurry on a current collector; and drying the resulting mixture.

21. A method for producing a positive electrode, comprising the steps of: mixing the positive electrode binder according to claim 18 with a conductive material; and then mixing the resultant mixture with a positive electrode active material to obtain a positive electrode mixture layer slurry; coating the resulting slurry on a current collector; and drying the resulting mixture.

Images