WO2025047950A1 - Hydrogenated nitrile rubber - Google Patents

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

The present invention relates to hydrogenated nitrile rubber and a method for producing the same, a veil made of hydrogenated nitrile rubber, a binder for positive electrodes formed by dispersing or dissolving hydrogenated nitrile rubber or a hydrogenated nitrile rubber veil in a solvent, a positive electrode containing hydrogenated nitrile rubber, and a method for producing the same.

Electrochemical elements 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, making them used in a wide range of applications. For this reason, in recent years, efforts have been made to improve battery components such as electrodes in order to further improve the performance of electrochemical elements.

The electrodes used in electrochemical elements typically include 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.

In recent years, therefore, attempts have been made to improve the binders used in forming the electrode mixture layers in order to achieve further improvements in the performance of electrochemical elements. For example, technology that uses polymers containing nitrile group-containing monomer units as binders is being investigated.

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 has a solution turbidity of 1 to 80 at a solids concentration of 10 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 is added to a 1% by mass calcium chloride aqueous solution to coagulate, washed with water, filtered, and then vacuum dried to obtain nitrile rubber, and the obtained nitrile rubber is subjected to metathesis with a ruthenium-based Grubbs catalyst and ethylene as a coolefin, and then hydrogenated with a rhodium-based Wilkinson catalyst with an iodine value of 5 mg/100 mg as the end point, and then 0.2 parts of activated carbon with an average diameter of 15 μm is 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. Then, N-methylpyrrolidone (NMP) is added, and water is evaporated under reduced pressure to obtain an NMP solution of the hydrogenated polymer with a solution turbidity of 20, and an electrode is produced using a binder composition consisting of 1.6 parts of 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 had poor stability in the conductive material dispersion, making it difficult to produce electrochemical element electrodes.

Patent Document 2 (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, and having a volume average particle diameter D of 50 to 800 nm when dynamic light scattering measurement is performed, and at least one peak detected in the range of 5 μm to 30 μm, and a conductive carbon material; specifically, acrylonitrile and 1,3-butadiene are copolymerized, dibutylhydroxytoluene (BHT) is added as an anti-aging agent, and then a 25% by mass aqueous solution of calcium chloride in an amount of 3 parts per 100 parts of polymer is added to coagulate, and 50 times the amount of ion-exchanged water is passed through to wash the polymer, and then a hydrogenation reaction is performed using a palladium catalyst, after which the palladium catalyst is filtered off to obtain polymers with iodine values of 5 mg/100 mg and 55 mg/100 mg. However, it is desirable to further improve the dispersibility of the dispersion liquid, the cycle characteristics of the electrochemical device, and the suppression of cracking of the electrode active material after cycle testing in the polymer obtained here.

On the other hand, Patent Document 3 (Patent No. 6309634) discloses hydrogenated nitrile rubber containing a specific phenol-based antioxidant useful for sealing materials, hose materials, transmission hoses, etc. in the automotive field. Specifically, after adding an antioxidant of 2,2-methylenebis(4-methyl-6-tert-butylphenol) to an emulsion polymerization liquid obtained by emulsion polymerization of acrylonitrile and 1,3-butadiene, the mixture is coagulated with an aqueous sodium chloride solution or an aqueous magnesium chloride solution prepared with calcium ion-containing tap water, washed with calcium ion-containing tap water, mechanically dehydrated, and vacuum dried to obtain NBR, which 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 then 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 mixture to obtain hydrogenated nitrile rubber. However, even when the hydrogenated nitrile rubber obtained here was used as a binder for electrode production, the output characteristics and cycle characteristics were extremely poor, and cracks in the active material occurred after cycle testing, making it unsuitable as a binder for electrodes.

Patent Document 4 (WO2007/049651) discloses a carboxyl group-containing nitrile rubber that has an α,β-ethylenically unsaturated nitrile monomer unit content of 10-60% by weight, an iodine value of 120 or less, and a total amount of magnesium, calcium, and aluminum of 2000 ppm or less, which gives a crosslinked product with small compression set and dynamic heat generation and is excellent in processability. 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 polymerization of acrylonitrile, mono n-butyl fumarate, and butadiene and then hydrogenating the rubber with a palladium catalyst, and after coagulation, filtering and washing with water are repeated three times, and the aqueous magnesium sulfate solution contained in the rubber is removed by centrifuging the rubber, followed by vacuum drying at 60°C for 12 hours to obtain a nitrile rubber with a magnesium content of 1-2 ppm, a calcium content of 1 ppm, and an aluminum content of 1 ppm. However, there is a demand for a polymer that is suitable as a binder for positive electrodes, 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 cycle testing.

Patent Document 5 (JP 2009-179686 A) discloses a method of recovering carboxyl group-containing nitrile rubber from a latex of carboxyl group-containing nitrile rubber, in which an extruder is used in which a screw is arranged inside a barrel in which at least a coagulation zone is formed and can be rotated. Specifically, a latex of carboxyl group-containing nitrile rubber obtained by emulsion polymerization according to Patent Document 4 (acrylonitrile monomer unit: 34% by weight, butadiene monomer unit: 59% by weight, n-monobutyl maleate monomer unit: 7% by weight, iodine value: 10, solids concentration: 10.8% by weight) and an aqueous magnesium sulfate solution (coagulant concentration: 5% by weight) are prepared as a coagulation liquid, and a screw-type extruder equipped with a coagulation zone, a drainage zone, a washing/dehydration zone, and a drying zone is used to perform coagulation, drainage, washing/dehydration, and drying, and a sheet-like carboxyl group-containing nitrile rubber with a Mooney viscosity of 40 is recovered. However, there is a demand for a polymer that is suitable as a binder for positive electrodes, 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 cycle testing.

JP 2018-160421 A Patent No. 6911985 Patent No. 6309634 WO2007/049651 publication JP 2009-179686 A

The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a hydrogenated nitrile rubber and a method for producing the same, which has excellent viscosity characteristics (dispersibility) and stability of the conductive material dispersion when producing electrodes for electrochemical elements, and therefore excellent cycle characteristics and output characteristics of the produced electrochemical elements, and also excellent in suppressing cracking of the electrode active material after cycle testing; a veil made of hydrogenated nitrile rubber; a binder for positive electrodes formed by dispersing or dissolving hydrogenated nitrile rubber or hydrogenated nitrile rubber veil in a solvent; and a positive electrode containing hydrogenated nitrile rubber and a method for producing the same.

The inventors conducted extensive research in light of the above problems and discovered that the use of hydrogenated nitrile rubber, which contains a nitrile group-containing monomer unit, a conjugated diene monomer unit and/or an alkylene structural unit, has a specific iodine value and weight-average molecular weight (Mw), contains a specific antioxidant, and has a specific Ca content and Na content, as a positive electrode binder results in excellent viscosity characteristics and stability of the conductive material dispersion in the manufacture of electrochemical elements, and is also excellent in the cycle characteristics and output characteristics of the manufactured electrochemical elements, and in the prevention of cracking of the electrode active material after cycle testing.

The inventors have also found that the above characteristics are further improved by using hydrogenated nitrile rubber in which the content of Rh, Ru, Pd, Mg, etc. in the hydrogenated nitrile rubber is further limited as a binder for the positive electrode. The inventors have also found that the above characteristics are further improved by using hydrogenated nitrile rubber with a high bulk density as a positive electrode material, and in particular, the stability of the conductive material dispersion is significantly improved.

The inventors have also discovered that by using calcium chloride as a coagulant for the hydrogenated nitrile rubber veil, the electrode peel 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.

The inventors have discovered 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 it with calcium chloride, can increase the viscosity characteristics of a conductive material dispersion when it is prepared, and can suppress cracking of the electrode active material in the resulting electrode after cycle testing, thereby significantly improving the cycle characteristics of an electrochemical element.

The inventors have discovered that hydrogenated nitrile rubber is obtained by emulsion polymerizing a nitrile group-containing monomer and a conjugated diene monomer, followed by adding a specific anti-aging agent to the emulsion polymerization liquid, and then coagulating the resulting emulsion polymerization liquid with calcium chloride, and that when this polymer is hydrogenated, it can significantly improve the viscosity characteristics and stability of a conductive material dispersion when it is prepared, and it can also suppress cracking of the electrode active material after cycle testing in the resulting electrode, significantly improving the output characteristics and cycle characteristics of an electrochemical element.

The present inventors have found that hydrogenated nitrile rubber, which has excellent viscosity characteristics and stability of the conductive material dispersion, and is also excellent in output characteristics and cycle characteristics of an electrochemical element, 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, coagulating the emulsion polymerization liquid to which a specific antioxidant has been added with an aqueous calcium chloride solution, thoroughly washing the resulting water-containing crumb to obtain a polymer, and then subjecting the resulting polymer to metathesis with a Grubbs catalyst and a coolefin, and then hydrogenating it with a Wilkinson catalyst. The 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-type extruder.

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

The inventors have also found that the stability of the conductive material dispersion liquid can be significantly improved by making the hydrogenated nitrile rubber veil contain a specific antioxidant, and that by increasing the bulk density of the hydrogenated nitrile rubber veil and reducing the amount of air contained therein as much as possible, the stability of the dispersion liquid with the conductive material can be further improved, preventing cracking of the electrode active material and improving various properties of the electrochemical element. The inventors presume that the stability of the conductive material dispersion liquid is deteriorated by the reaction and crosslinking with the active points on the surface of the electrode material due to the influence of oxygen radicals generated in the hydrogenated nitrile rubber, and that the absence of a specific antioxidant or air inside the veil works well against the generation and reaction of these oxygen radicals. The inventors have also found that a hydrogenated nitrile rubber veil with a high bulk density can be easily obtained by melt-kneading the hydrogenated nitrile rubber veil under reduced pressure using a screw-type extruder, extruding it into a sheet, and then laminating the extruded hydrogenated nitrile rubber sheets.

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

Thus, according to the present invention, there is provided a hydrogenated nitrile rubber that 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 anti-aging agent, has a calcium (Ca) content in the range of 1 to 2500 ppm, and has a sodium (Na) content of 300 ppm or less.

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%.

In the hydrogenated nitrile rubber of the present invention, it is further preferable 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.

In the hydrogenated nitrile rubber of the present invention, the bulk density is preferably 0.8 g/cm ³ or more.

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

Furthermore, in the hydrogenated nitrile rubber, 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 preferably 97 mass% or more.

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 then hydrogenating the resulting polymer.

In the hydrogenated nitrile rubber of the present invention, it is preferable to use a polymer 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 anti-aging agent, and then coagulating the polymer with calcium chloride, and then hydrogenating the resulting polymer.

The present invention also provides a method for producing the above-mentioned hydrogenated nitrile rubber, which comprises hydrogenating a nitrile rubber containing the antioxidant 2,2-methylenebis(4-methyl-6-tert-butylphenol).

According to the present invention, there is also provided an emulsion polymerization process for obtaining an emulsion polymerization liquid by emulsion polymerizing a monomer component including a nitrile group-containing monomer and a conjugated diene monomer;
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 containing the antioxidant with calcium chloride to produce a water-containing crumb;
a washing and drying step of washing and drying the water-containing crumbs to obtain a polymer;
a hydrogenation step of hydrogenating the polymer using a hydrogenation catalyst;
There is provided a method for producing the hydrogenated nitrile rubber, comprising:

In the method for producing hydrogenated nitrile rubber of the present invention, the hydrogenation step preferably involves subjecting the polymer to metathesis with a ruthenium catalyst and a coolefin, followed by hydrogenation with a rhodium catalyst.

In the method for producing hydrogenated nitrile rubber of the present invention, it is preferable to further provide a purification step in which the hydrogenated nitrile rubber is subjected to an adsorbent treatment after the hydrogenation step.

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

In the method for producing hydrogenated nitrile rubber of the present invention, it is preferable that the screw-type extruder is equipped with a reduced pressure drying barrel.

The present invention also provides a hydrogenated nitrile rubber bale obtained by baling the above hydrogenated nitrile rubber.

In the hydrogenated nitrile rubber bale of the present invention, it is preferable that the bulk density is 0.8 g/ ^cm3 or more.

According to the present invention, a binder for a positive electrode is also provided, which is prepared by dispersing or dissolving the hydrogenated nitrile rubber in N-methylpyrrolidone (NMP).

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

The present invention also provides 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, and a current collector.

The present invention further provides a method for producing a positive electrode, which includes a step of applying a positive electrode composite layer slurry obtained by mixing the positive electrode binder and conductive material and then mixing the positive electrode active material onto a current collector and drying the resulting mixture.

The present invention provides hydrogenated nitrile rubber and a manufacturing method thereof, which can suppress cracking of the electrode active material after cycle testing of the manufactured electrochemical element and improve cycle characteristics and output characteristics due to the excellent viscosity characteristics and stability of the conductive material dispersion liquid, hydrogenated nitrile rubber veil made of hydrogenated nitrile rubber, a positive electrode binder made by dispersing or dissolving hydrogenated nitrile rubber or hydrogenated nitrile rubber veil in a solvent, and a positive electrode containing hydrogenated nitrile rubber and a manufacturing method thereof.

The following describes in detail an embodiment of the present invention.

The hydrogenated nitrile rubber of the present invention 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, has an iodine value of 0.1 to 100 mg/100 mg, contains an antioxidant of 2,2-methylenebis(4-methyl-6-tert-butylphenol), has a Ca content in the range of 1 to 2500 ppm, and has a Na content of 300 ppm or less.

<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. The hydrogenated nitrile rubber is a component that can function as a binder that holds an electrode active material and the like from a current collector without causing the electrode active material to be detached from the current collector in an electrode mixture layer formed in an electrochemical element. The hydrogenated nitrile rubber can also function as a dispersant that can disperse a conductive material in a conductive material dispersion liquid that contains a conductive material.

Specifically, hydrogenated nitrile rubber can 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 contains alkylene structural units and nitrile group-containing monomer units, and when the hydrogenation is partially performed, the polymer contains conjugated diene monomer units, alkylene structural units, and nitrile group-containing monomer units.

(Nitrile Group-Containing Monomer Unit)
Examples of nitrile group-containing monomers capable of forming 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 thereof include acrylonitrile; α-halogenoacrylonitriles such as α-chloroacrylonitrile and α-bromoacrylonitrile; α-alkylacrylonitriles such as methacrylonitrile and α-ethylacrylonitrile; and the like. Among these, acrylonitrile is preferred. The nitrile group-containing monomer may be used alone or in combination of two or more kinds at any ratio.

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, even more preferably 20% by mass or more, preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less, assuming that the total repeating units in the hydrogenated nitrile rubber is 100% by mass. 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.

(Conjugated diene monomer units)
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. Among these, isoprene and 1,3-butadiene are preferred, and 1,3-butadiene is particularly preferred.

(Alkylene structural unit)
Here, the alkylene structural unit is a repeating unit composed only of an alkylene structure represented by the general formula: -C _n H _2n - [wherein n is an integer of 2 or more]. The alkylene structural unit may be linear or branched, but from the viewpoint of reducing the resistance of the electrode while improving the rate characteristics of the electrochemical device, the alkylene structural unit is preferably linear, i.e., a linear alkylene structural unit. In addition, 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 more).

The alkylene structural unit may be linear or branched, but it is preferable that the alkylene structural unit is linear, i.e., a linear alkylene structural unit. It is also preferable that the alkylene structural unit has 4 or more carbon atoms (i.e., n in the above general formula is an integer of 4 or more).

The method for introducing an alkylene structural unit into a polymer is not particularly limited, but may be, for example, the following method (1) or (2):
(1) A method of preparing a polymer from a monomer composition containing a conjugated diene monomer and converting the conjugated diene monomer unit into an alkylene structural unit by hydrogenating the polymer. (2) A method of preparing a polymer from a monomer composition containing a 1-olefin monomer. Among these, the method (1) is preferred because it is easy to produce the polymer.

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.

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

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, particularly preferably 60% by mass or more, preferably 90% by mass or less, more preferably 85% by mass or less, particularly preferably 80% by mass or less, when the total repeating units (the sum of the structural units and the monomer units) in the hydrogenated nitrile rubber 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 element can be improved.

In addition, when the hydrogenated nitrile rubber has only one of the content ratio of alkylene structural units and conjugated diene monomer units, it is preferable that the ratio satisfies the above range.

(nitrile group-containing monomer unit, conjugated diene monomer unit, alkylene structural unit)
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 of the present invention is not particularly limited, but when it is usually 80 mass % or more, preferably 90 mass % or more, more preferably 95 mass % or more, further preferably 97 mass % or more, and most preferably 99 mass % or more, the dispersion stability of the conductive material dispersion and the cycle characteristics of the electrochemical element can be improved.

(Other repeating units)
The other repeating units are not particularly limited, but may 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.

Aromatic vinyl monomers that can form aromatic vinyl monomer units include, for example, 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.

Examples of acidic group-containing monomers capable of forming acidic group-containing monomer units include carboxylic acid group-containing monomers, sulfonic acid group-containing monomers, and phosphoric acid group-containing monomers. Note that the acidic group-containing monomers may be used alone or in combination of two or more types in any ratio.

Carboxylic acid group-containing monomers include monocarboxylic acids and their derivatives, dicarboxylic acids and their acid anhydrides, and their derivatives.

Monocarboxylic acids include acrylic acid, methacrylic acid, and crotonic acid.

Monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic acid, etc.

Dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid.

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 maleates.

Examples of dicarboxylic acid anhydrides include maleic anhydride, acrylic anhydride, methyl maleic anhydride, and dimethyl maleic anhydride.

Also, as the carboxylic acid group-containing monomer, an acid anhydride that generates a carboxylic acid group by hydrolysis can be used. Among them, acrylic acid and methacrylic acid are preferred as the carboxylic acid group-containing monomer.

Examples of the sulfonic acid group-containing monomer 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, and 3-allyloxy-2-hydroxypropanesulfonic acid.
In the present invention, "(meth)allyl" means allyl and/or methallyl.

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

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, stearyl acrylate, etc. Acrylic acid alkyl esters: 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 kinds in any ratio.

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, with the total repeating units in the hydrogenated nitrile rubber being 100% by mass.

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

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, it is preferable because it can increase the dispersion stability of the conductive material dispersion liquid and also increase the peel strength of the resulting electrode.

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 highly balanced, which is preferable.

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 in the hydrogenated nitrile rubber is also usually 1 ppm or more, preferably 3 ppm or more, more preferably 5 ppm or more, or 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 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 in this range, cracking of the electrode active material in the resulting electrode can be effectively suppressed, and the peel strength of the electrode can be increased. In addition, when the Ca content in the hydrogenated nitrile rubber is in this range, the dispersion stability (viscosity characteristics) of the conductive material can be improved when a conductive material dispersion liquid is prepared, and the cycle characteristics of the resulting electrochemical element and the effect of suppressing cracking of the electrode active material after cycle testing can be improved, which is preferable.

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, preferably 2.5 ppm or more, or 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 are preferred in this order. When the Cl content in the hydrogenated nitrile rubber is in this range, when a conductive material dispersion of the hydrogenated nitrile rubber is prepared, the viscosity characteristics of the conductive material dispersion can be increased, and the cycle characteristics of the resulting electrochemical element and cracking of the electrode active material after cycle testing can be suppressed, which is preferable.

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 element and cracking of the electrode active material after cycle testing can be suppressed, which is preferable.

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 element are improved, which is preferable.

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 is usually in the range of 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, which is suitable for suppressing cracking of the active material in the produced electrode.

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 element are improved, which is preferable.

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.

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 or more, more preferably 0.8 g/cm ³ or more, even more preferably 0.85 g/cm ³ or more, and most preferably 0.9 g/cm ³ or more. 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 or less, even more preferably 1.05 g/cm ³ or less, and most preferably 1 g/cm ³ or less. When the bulk density of the hydrogenated nitrile rubber is within this range, the effect of the phenol-based antioxidant is highly enhanced, the stability of the conductive material dispersion is excellent, and the cycle characteristics of the electrochemical element and cracking of the active material after cycle testing can be prevented.
The bulk density of the hydrogenated nitrile rubber can be easily adjusted, for example, by drying with a screw-type extruder described below or by baling the hydrogenated nitrile rubber.

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

The content of the above-mentioned 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%.

The hydrogenated nitrile rubber of the present invention may contain antioxidants other than the above-mentioned antioxidants, such as other phenol-based antioxidants or amine-based antioxidants, to the extent that the object of the present invention is not impaired.

The hydrogenated nitrile rubber of the present invention is not particularly limited, but is preferably one obtained by emulsion polymerization of a nitrile group-containing monomer and a conjugated diene monomer, coagulating the polymer with calcium chloride, and hydrogenating the polymer. When the emulsion polymerization liquid is coagulated to obtain a polymer, the size, shape, and properties of the water-containing crumbs produced vary greatly depending on the type of coagulant used, and the residues of various secondary materials in the polymerization and coagulation processes that can be removed in the subsequent washing and dehydration processes vary. It is not possible to verify all trace residues of these secondary materials and their reactants, and especially when used in electrochemical elements, these slight residues affect various characteristics. For this reason, for electrochemical element applications, it is preferable to use calcium chloride as a coagulant and then hydrogenate the isolated polymer. Among calcium (Ca) compounds, those using calcium chloride are preferred because they are easily removed in the subsequent washing and purification processes, and therefore can reduce the residues in the hydrogenated nitrile rubber. In addition, hydrogenated nitrile rubber, which is made by hydrogenating nitrile rubber obtained using calcium chloride as a coagulant, is suitable because it has excellent electrode peeling properties for electrochemical elements such as lithium ion secondary batteries, and is more effective at preventing deterioration of cycle characteristics and cracking of the active material layer after cycle testing than when other coagulants are used.

The hydrogenated nitrile rubber of the present invention is preferably 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.

The effect of the specific antioxidant is much higher and more suitable for hydrogenated nitrile rubber produced by adding it to the emulsion polymerization liquid obtained by emulsion polymerization of a nitrile group-containing monomer and a conjugated diene monomer than when it is mixed with hydrogenated nitrile rubber after production. Although this cannot be measured, it is believed that this is because the specific 2,2-methylenebis(4-methyl-6-tert-butylphenol) antioxidant is finely and uniformly dispersed in the hydrogenated nitrile rubber obtained by coagulating the emulsion polymerization liquid in which it is uniformly dispersed with calcium chloride, thereby demonstrating its high effect.

<Method of 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.

The hydrogenated nitrile rubber of the present invention is produced by an emulsion polymerization process 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 in which the emulsion polymerization liquid containing the antioxidant is contacted with calcium chloride to produce a water-containing crumb;
a washing and drying step of washing and drying the wet crumbs to obtain a polymer;
a hydrogenation step of hydrogenating the polymer using a hydrogenation catalyst;
The composition can be easily produced by a method comprising the steps of:

Furthermore, it is preferable that the hydrogenation step involves subjecting the polymer to metathesis using the ruthenium catalyst and further a coolefin, followed by hydrogenation using a rhodium catalyst, and that a purification step is further provided after the hydrogenation step in which the hydrogenated nitrile rubber is subjected to an adsorbent treatment.

(Emulsion polymerization process)
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.

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

The emulsifier used in emulsion polymerization is not particularly limited, but examples include anionic emulsifiers, cationic emulsifiers, and nonionic emulsifiers, and preferably contains an anionic emulsifier.

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; alkylbenzene sulfonates such as sodium dodecylbenzene sulfonate; sulfate salts such as sodium lauryl sulfate, and phosphate salts such as polyoxyalkylene alkyl ether phosphate salts; and alkyl sulfosuccinates. Among these anionic emulsifiers, fatty acid salts and sulfate salts are preferred, and fatty acid salts are particularly preferred. Suitable sulfate salts include, for example, sodium lauryl sulfate, ammonium lauryl sulfate, sodium myristyl sulfate, sodium laureth sulfate, sodium polyoxyethylene alkyl sulfate, and sodium polyoxyethylene alkylaryl sulfate. Suitable fatty acid salts include, for example, potassium oleate, sodium oleate, and potassium palmitate, with potassium oleate being particularly preferred.

These emulsifiers can be used alone or in combination of two or more. The amount used is usually 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.

The monomer component, emulsifier, and water can be mixed in the usual manner, such as by stirring the monomer, emulsifier, and water using a stirrer such as a homogenizer or a disk turbine. The amount of water used is usually 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.

There are no particular limitations on the polymerization catalyst used in emulsion polymerization, so 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.

The radical generator may be, for example, a peroxide or an azo compound, with peroxide being preferred. As the peroxide, inorganic peroxides or organic peroxides may be used.

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.

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, benzoyl peroxide, etc. Side, 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, dilauroyl peroxide, etc. are included, and among these, diisopropylbenzene hydroperoxide, cumene hydroperoxide, paramenthane hydroperoxide, benzoyl peroxide, etc. are preferred.

These radical generators can be used alone or in combination of two or more types, 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.

The amount of water used in the emulsion polymerization reaction may be only that used during the emulsification of the monomer components, but is usually adjusted to be in the range of 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.

The emulsion polymerization reaction may be carried out in the usual manner, and may be batch, semi-batch, or continuous. The polymerization temperature and polymerization time are not particularly limited and may be appropriately selected depending on the type of polymerization initiator used. 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, and preferably 1 to 10 hours.

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 has excellent strength characteristics and is free of monomer odor, which is suitable. A polymerization terminator may be used to stop the polymerization.

(Anti-aging agent addition process)
The antioxidant addition step in the method for producing hydrogenated nitrile rubber of the present invention is characterized by adding a 2,2-methylenebis(4-methyl-6-tert-butylphenol) compound as an antioxidant to the emulsion polymerization liquid after the emulsion polymerization.

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.

The amount of antioxidant used may be appropriately selected so as to be the content of the antioxidant in the hydrogenated nitrile rubber of the present invention, but 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.

(Solidification process)
The coagulation step in the method for producing hydrogenated nitrile rubber of the present invention is a step in which the emulsion polymerization liquid containing the antioxidant is brought into contact with calcium chloride to produce water-containing crumbs. In particular, by using calcium chloride as a coagulant and setting the Ca content in the produced emulsion polymerization liquid within a specific range, it is preferable because it contributes to the dispersibility of the conductive material dispersion liquid, extremely increases the peel strength of the produced electrode, and is also excellent in the cycle characteristics of the electrochemical element and in the effect of suppressing cracking of the electrode active material after cycle testing.

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

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% by mass, preferably 1 to 60% by mass, more preferably 5 to 50% by mass, and particularly preferably 10 to 30% by mass, which is suitable for concentrating the particle size of the generated hydrous crumbs uniformly in a specific area.

There are no particular limitations on the temperature during the solidification reaction, but a temperature of 40°C or higher, preferably 40 to 90°C, and more preferably 50 to 80°C, is generally preferred to produce uniform hydrous crumbs.

There are no particular limitations on the contact between the emulsion polymerization liquid and the calcium chloride aqueous solution (coagulation liquid), but for example, either 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, is acceptable, but the method of adding the coagulation liquid to the emulsion polymerization liquid being stirred is preferable because it makes the shape and diameter of the water-containing crumbs that are generated uniform and concentrated, and significantly improves the washing efficiency of the emulsifier and coagulation agent.

(Washing and drying process)
The water washing and drying step in the process for producing hydrogenated nitrile rubber of the present invention is a step of washing and drying the water-containing crumbs produced as described above to obtain a polymer.

The washing method is not particularly limited and may be any ordinary 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, and more preferably 50 to 100 times, 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, which is usually 40°C or higher, preferably 40 to 100°C, more preferably 50 to 90°C, and most preferably 60 to 80°C, as this significantly improves the washing efficiency. By setting the temperature of the washing water at or above the lower limit, the emulsifier and coagulant are released from the water-containing crumbs, further improving the washing efficiency.

There are no particular limitations on the cleaning time, but it is usually in the range of 1 to 120 minutes, preferably 2 to 60 minutes, and more preferably 3 to 30 minutes.

The washed hydrous crumbs can be dried in the usual manner, for example, using a dryer such as a hot air dryer, a vacuum dryer, an expander dryer, a kneader type dryer, or a screw type extruder.

The moisture content of the dry rubber is less than 1% by mass, preferably 0.8% by mass or less, and more preferably 0.6% by mass or less.

(Hydrogenation step)
The hydrogenation step in the production method for 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, and then hydrogenating the polymer (dry rubber) using a rhodium-based catalyst.

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

　Any known ruthenium catalyst can be used as a catalyst for the metathesis reaction. Among them, it is preferable to use a Grubbs catalyst such as bis(tricyclohexylphosphine)benzylidene ruthenium dichloride or 1,3-bis(2,4,6-trimethylphenyl)-2-(imidazolidinylidene)(dichlorophenylmethylene)(tricyclohexylphosphine)ruthenium as a catalyst for the metathesis reaction.

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

Examples of coolefins 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 functional group-containing unsaturated compounds being preferred.

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, and more preferably 1 to 5 parts by mass, per 100 parts by mass of the polymer.

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

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.

The reaction solution in the metathesis reaction is usually stirred vigorously, for example, at 200 to 1000 rpm, preferably 300 to 900 rpm, and more preferably 500 to 800 rpm.

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 cement concentration, 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.

Hydrogenation reaction The hydrogenation reaction can be carried out by dissolving the polymer in a solvent and then adding a hydrogenation catalyst. However, the hydrogenation reaction after the above-mentioned metathesis is preferably carried out in the same reaction vessel as that 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.

The solvent for the hydrogenation reaction can 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.

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 it is particularly preferable to use a known homogeneous hydrogenation catalyst such as Wilkinson's catalyst ((PPh ₃ ) ₃ RhCl). In addition, the Grubbs catalyst is converted into a dihydride complex (PR ₃ ) ₂ RuCl ₂ H ₂ , which is itself an olefin hydrogenation catalyst, in the presence of hydrogen. The hydrogenation reaction can be carried out without adding the Wilkinson catalyst, but the hydrogenation rate tends to be slow.

The amount of 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, or 0.01 to 0.05 parts by mass, based on 100 parts by mass of the polymer before hydrogenation.

In the hydrogenation reaction, a cocatalyst can be used as necessary. Examples of cocatalysts for the Wilkinson catalyst include phosphine, diphosphine, and triphenylphosphine, with triphenylphosphine being preferred. These cocatalysts can be used alone or in combination of two or more types, and the amount used is usually in the range of 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.

The polymer concentration in the hydrogenation reaction is not particularly limited as long as the polymer is soluble, but is usually in the range of 1 to 30 mass%, preferably 5 to 25 mass%, and more preferably 7 to 20 mass%.

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.

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

The hydrogenation reaction can be stopped once the desired hydrogenation level has been reached by depressurizing or cooling the reactor. Residual hydrogen is usually 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.

(Refining process)
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.

Adsorbents are not particularly limited, but examples include activated carbon, ion exchange resins, and synthetic zeolites, with activated carbon being preferred.

The adsorbent treatment can be carried out by adding an adsorbent to the reaction liquid containing the 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 in the range of 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.

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

Refining methods by filtration and decantation include, for example, (i) a method of filtering using a bag filter, cartridge filter, filter paper, membrane filter, etc., after adding an adsorbent as necessary; (ii) a method of using a filter such as a leaf filter, filter press, candle filter, drum filter, etc., forming a cake layer of a filter aid such as diatomaceous earth or perlite, and then draining the filtrate; (iii) a method of removing the metal salts by sedimenting the metal salts formed by the residues and metal ions during polymerization using centrifugation and then removing them from the bottom; etc.

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

<Drying of hydrogenated nitrile rubber using a screw-type extruder>
In drying the hydrogenated nitrile rubber, drying with a screw-type extruder is preferable because it can remove the air contained therein and increase the bulk density. Specifically, the hydrogenated nitrile rubber-containing solution after the hydrogenation reaction or after the purification step after the hydrogenation reaction is solidified, and the resulting water-containing crumbs can be dried using a screw-type extruder.
(Solidification process)
The coagulation step of the filtrate containing hydrogenated nitrile rubber from which impurities have been removed and obtained in the above purification step is not particularly limited, and may be performed according to a conventional method. Specific coagulation methods include a method of contacting with a coagulant and a method of contacting with a large amount of poor solvent, and preferably a method of contacting with a large amount of poor solvent. There is no particular limit to the poor solvent, but methanol, water, steam, etc. are preferably used. The coagulation reaction may be appropriately selected, and for example, the coagulation reaction temperature is usually selected within the range of room temperature to 100°C, and the coagulation reaction time is appropriately selected within the range of several minutes to several hours.

The hydrous crumbs of hydrogenated nitrile rubber produced by the coagulation reaction can be washed as necessary. The washing method is not particularly limited and may be any conventional method, but washing with a large amount of water is efficient. The amount of water used is usually 10 to 500 times, preferably 25 to 250 times, and more preferably 50 to 100 times, 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, and it is usually preferable to use warm water at a temperature of 40°C or higher, preferably 40 to 100°C, more preferably 50 to 90°C, and most preferably 60 to 80°C, since this significantly increases the washing efficiency. By setting the temperature of the washing water at or above the lower limit, the emulsifier and coagulant are released from the hydrous crumbs, and the washing efficiency is further improved.

After coagulation or washing, the hydrous crumbs can be isolated by filtration.

(Drying process)
In the present invention, the hydrous crumb 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 present inside is removed to obtain a dry rubber (hydrogenated nitrile rubber) having a high bulk density. When used as a positive electrode material, it is suitable because it has excellent dispersion stability with the conductive material, and prevents the peel strength of the electrochemical element electrode and cracking of the active material layer after cycle testing.

-Screw type extruder-
The dehydration of the dehydrated hydrous crumbs in the dehydration barrel is carried out in a dehydration barrel having a dehydration slit. The opening of the dehydration slit may be appropriately selected depending on the conditions of use, but when it is in the range of usually 0.1 to 1 mm, preferably 0.2 to 0.6 mm, the loss of the hydrous crumbs is small and the hydrous crumbs can be efficiently dehydrated.

The number of dehydration barrels in a screw-type extruder is not particularly limited, but typically multiple barrels, preferably 2 to 10 barrels, and more preferably 3 to 6 barrels, are suitable for efficiently dehydrating the sticky hydrogenated nitrile rubber.

The set temperature of the dehydration barrel is selected appropriately 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 drainage state is usually in the range of 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 exhaust steam state is usually in the range of 100 to 150°C, preferably 105 to 140°C, and more preferably 110 to 130°C.

There are no particular limitations on the moisture content after dehydration, in which the moisture is squeezed out of the hydrous crumb, but it 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.

Drying in the drying barrel section The water-containing crumbs dehydrated in the above-mentioned 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 appropriately selected, but is usually 1 to 50 kPa, preferably 2 to 30 kPa, and more preferably 3 to 20 kPa, which is suitable for efficiently drying the water-containing crumbs. In addition, by extruding the molten hydrogenated nitrile rubber inside the drying barrel under reduced pressure, the air present therein is also removed, and a sheet-like hydrogenated nitrile rubber having a high bulk density can be produced, which is suitable.

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

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

The moisture 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.

Hydrogenated nitrile rubber extrusion (die section)
The hydrogenated nitrile rubber dehydrated and dried in the screw section of the dehydrating barrel and the drying barrel is sent to a screw-free straightening die section. A breaker plate or a wire mesh may or may not be provided between the screw section and the die section.

The hydrogenated nitrile rubber extruded can be produced in a variety of shapes, including granules, columns, rods, and sheets, depending on the shape of the die nozzle. However, using a roughly rectangular die shape to produce a sheet-like rubber is ideal, as it produces dried rubber with less air entrapment, a high bulk density, and excellent storage stability.

The resin pressure in the die section is not particularly limited, but a pressure in the range of 0.1 to 10 MPa, preferably 0.5 to 5 MPa, and more preferably 1 to 3 MPa is usually suitable as it reduces air entrapment and provides excellent productivity.

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.

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

The ratio (L/D) of the screw length (L) to the screw diameter (D) of the screw-type 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, which is suitable for reducing the moisture content to less than 1% by mass without causing a decrease in the molecular weight of the dried rubber or burning.

The rotation speed (N) of the screw-type extruder used may be selected appropriately depending on the 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.

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.

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.

The shape of the dried rubber extruded from the dried rubber screw-type extruder is not particularly limited, and examples thereof include crumb, powder, rod, and sheet shapes, with the sheet shape being particularly preferred.

<Hydrogenated nitrile rubber veil>
The hydrogenated nitrile rubber bale of the present invention can be produced by baling the above-mentioned dried hydrogenated nitrile rubber.

The hydrogenated nitrile rubber bale of the present invention is made of the hydrogenated nitrile rubber, and by baling it, the effect of the hydrogenated nitrile rubber of the present invention can be maintained even during storage, which is preferable. In addition, the bulk density of the hydrogenated nitrile rubber bale can be increased, allowing it to be stored without air being present, which is preferable because it also suppresses the generation of oxygen radicals.

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

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 or more, more preferably 0.8 g/cm ³ or more, even more preferably 0.85 g/cm ³ or more, and most preferably 0.9 g/cm ³ or more. 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 or less, even more preferably 1.05 g/cm ³ or less, and most preferably 1 g/cm ³ or less. When 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 element and cracking of the active material after cycle testing can be prevented.

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 veil of the present invention are the same as those of the hydrogenated nitrile rubber.

The moisture content of the hydrogenated nitrile rubber veil of the present invention is not particularly limited, but is generally excellent in storage stability and is suitable when it is less than 1% by mass, preferably 0.8% by mass or less, and more preferably 0.6% by mass or less.

The Mooney viscosity (ML1+4, 100°C) of the hydrogenated nitrile rubber veil of the present invention is not particularly limited, but is usually in the range of 10 to 150, preferably 15 to 100, and more preferably 20 to 80, which provides a high level of balance between the conductive material dispersibility and the peel strength at the electrode and is suitable.

The hydrogenated nitrile rubber can be baled in the usual manner, for example by putting the dried hydrogenated nitrile rubber into a baler and compressing it. 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 in sheet form can be made and layered to make bales. Baling by layering sheets is easy to manufacture, produces bales with few bubbles (high bulk density), and is suitable for excellent storage stability.

In the present invention, by stacking the sheet-like dried rubber (hydrogenated nitrile rubber) extruded from the screw-type extruder, a suitable hydrogenated nitrile rubber bale with a high bulk density can be easily produced.

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

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

The solid content of the positive electrode binder 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%.

The hydrogenated nitrile rubber, NMP, and other components used as necessary can be mixed in the usual manner.

<Electrodes for electrochemical elements>
The positive electrode of the present invention is characterized by comprising a positive electrode mixture layer containing a binder containing the hydrogenated nitrile rubber, a conductive material, and a positive electrode active material, and can be produced by mixing the positive electrode binder and the conductive material, optionally with 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.

(Conductive material)
The conductive material is a component that functions to ensure electrical contact between electrode active materials. As the conductive material, a carbonaceous material can be suitably used. Examples of such carbonaceous materials include carbon black (e.g., acetylene black, Ketjen Black (registered trademark), furnace black, etc.), single-layer or multi-layer carbon nanotubes (multi-layer carbon nanotubes include cup-stack type), carbon nanohorns, vapor-grown carbon fibers, milled carbon fibers obtained by crushing polymer fibers after baking, single-layer or multi-layer graphene, and carbon nonwoven fabric sheets obtained by baking nonwoven fabric made of polymer fibers. Note that these may be used alone or in combination of two or more types in any ratio. Among these, carbon nanotubes (CNTs) are preferable from the viewpoint of forming a good conductive path.

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. The conductive material and the positive electrode binder may be mixed, for example, in such a way 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 conductive material. In addition, when mixing the positive electrode binder and the conductive material, NMP can be added as necessary to adjust the viscosity.

The solids concentration when the positive electrode binder of the present invention is mixed with the conductive material is usually 0.01 mass% or more, preferably 1.0 mass% or more, and more preferably 3.0 mass% or more, and the upper limit is usually 10.0 mass% or less, preferably 9.0 mass% or less, and more preferably 8.0 mass% or less. If the solids concentration is equal to or greater than the lower limit, the coatability of the conductive material dispersion can be improved. Also, if the solids concentration is equal to or less than the upper limit, the rate characteristics of the resulting electrochemical element can be improved.

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.

(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). Examples of such positive electrode active materials include lithium-containing cobalt oxide (LiCoO ₂ ), lithium manganate (LiMn ₂ O ₄ ), lithium-containing nickel oxide (LiNiO ₂ ), lithium-containing composite oxides of Co—Ni—Mn, lithium-containing composite oxides of Ni—Mn—Al, lithium-containing composite oxides of Ni—Co—Al, olivine-type lithium manganese phosphate (LiMnPO ₄ ), olivine-type lithium iron phosphate (LiFePO ₄ ), lithium-excess spinel compounds represented by Li _1+x Mn _2-x O ₄ (0<x<2), 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 kinds in any ratio.

The positive electrode active material can be mixed with the mixture of 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 the range that has been conventionally used.

<Electrodes for electrochemical elements>
The positive electrode of the present invention can be obtained by applying the positive electrode mixture layer slurry onto a current collector and drying it. Since the positive electrode mixture layer of the positive electrode of the present invention is formed from the positive electrode binder containing the hydrogenated nitrile rubber of the present invention, the positive electrode of the present invention has excellent flexibility and is less susceptible to cracking of the electrode active material.

(Current collector)
The current collector is made of a material that is electrically conductive and electrochemically durable. The current collector is not particularly limited and any known current collector can be used. For example, a current collector made of aluminum or an aluminum alloy can be used as a 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 excellent current collector materials because they are heat resistant and electrochemically stable.

The method for manufacturing the positive electrode of the present invention is not particularly limited. For example, the positive electrode of the present invention can be manufactured 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 to form a positive electrode composite layer. More specifically, the manufacturing 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).

(Coating process)
The method of applying the positive electrode composite layer slurry onto the current collector is not particularly limited and any known method can be used. Specifically, the application method can be a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a brush coating method, or the like. 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 according to the thickness of the positive electrode composite layer obtained by drying.

(Drying process)
The method for drying the positive electrode mixture layer slurry on the current collector is not particularly limited and may be a known method, 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 mixture layer slurry on the current collector in this manner, a positive electrode mixture layer can be formed on the current collector, and a positive electrode including the current collector and the positive electrode mixture layer can be obtained.

After the drying step, the electrode mixture layer may be subjected to a pressure treatment using a die press or roll press. This pressure treatment allows the positive electrode mixture layer to adhere well to the current collector.

Furthermore, if the positive electrode composite layer contains a curable polymer, the polymer may be cured after the positive electrode composite layer is formed.

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

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.

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

(Electrolyte)
As the electrolyte, an organic electrolyte 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, _LiPF6 , LiAsF6, _{LiBF4 , LiSbF6} , _LiAlCl4 , LiClO4, _CF3SO3Li , _C4F9SO3Li , _CF3COOLi , ( _{CF3CO ) 2NLi} , _{( CF3SO2 ) 2NLi} , ( _C2F5SO2 )NLi _{, etc.} are listed. Among them, _LiPF6 , _LiClO4 , and _CF3SO3Li are preferred, and _LiPF6 is particularly preferred, because _they are easily dissolved in the solvent _and show a high degree _of dissociation. The electrolyte may be used alone or in any combination of two or more kinds in any ratio. Usually, the lithium ion conductivity tends to be higher when a supporting electrolyte with a higher degree of dissociation is used, so the lithium ion conductivity can be adjusted by the type of supporting electrolyte.

The organic solvent used in the electrolyte is not particularly limited as long as it can dissolve the supporting electrolyte, but examples of suitable organic solvents include carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), and methyl ethyl carbonate (EMC); esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; and sulfur-containing compounds such as sulfolane and dimethyl sulfoxide. A mixture of these solvents may also be used. Among these, it is preferable to use carbonates because they have a high dielectric constant and a wide stable potential range, and it is even more preferable to use a mixture of ethylene carbonate and diethyl carbonate.

The concentration of the electrolyte in the electrolyte solution can be adjusted as appropriate, and is preferably 0.5 to 15 mass%, more preferably 2 to 13 mass%, and even more preferably 5 to 10 mass%. In addition, known additives such as vinylene carbonate, fluoroethylene carbonate, and ethyl methyl sulfone may be added to the electrolyte solution.

(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, since it can reduce the thickness of the entire separator, thereby increasing the ratio of the electrode active material in the lithium ion secondary battery and increasing the capacity per volume.

(Method of manufacturing lithium ion secondary battery)
The lithium ion secondary battery according to the present invention can be produced, for example, by stacking a positive electrode and a negative electrode with a separator therebetween, wrapping or folding the stack according to the battery shape as necessary, placing the stack in a battery container, injecting an electrolyte into the battery container, and sealing the container. In order to prevent the occurrence of an internal pressure rise in the secondary battery, overcharging and overdischarging, etc., a fuse, an overcurrent prevention element such as a PTC element, an expanded metal, a lead plate, etc. may be provided as necessary. The shape of the secondary battery may be, for example, any of a coin type, a button type, a sheet type, a cylindrical type, a square type, a flat type, etc.

The present invention will be explained in detail below based on examples, but the present invention is not limited to these examples. In the following explanation, the amounts "%", "ppm" and "parts" are based on mass unless otherwise specified.

In addition, in a polymer produced by copolymerizing multiple types of monomers, the ratio of monomer units formed by polymerizing a certain monomer in the polymer usually coincides with the ratio (feed ratio) of that certain monomer to all monomers used in the polymerization of the polymer, unless otherwise specified. In addition, when a polymer is a hydrogenated polymer obtained by hydrogenating a polymer containing a conjugated diene monomer unit, the total content ratio 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 monomers used in the polymerization of the polymer.

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

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

<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)

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

<Chlorine content>
1 g of hydrogenated nitrile rubber veil was dissolved in 150 ml of a mixture of methyl ethyl ketone and isopropanol in a volume ratio of 4:1, and 2% dilute sulfuric acid was added to prepare a sample solution, which was then dripped with a 0.005 N aqueous solution of silver nitrate and the chlorine content was calculated by potentiometric titration (HIRANUMA COMITE-101 or equivalent, silver supporting electrode AG-68/silver reference electrode AM-44).

<Bulk density>
A piece measuring approximately 2 cm×3 cm×0.2 cm was cut out from the hydrogenated nitrile rubber bale, and the bulk density (g/cm ³ ) was measured using an automatic pycnometer (manufactured by Toyo Seiki Seisakusho, product name: "DSG-1").

<Viscosity of conductive material dispersion>
The conductive material dispersion obtained in each of the Examples and Comparative Examples was measured for viscosity 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). 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 less than 5 Pa・s C: More than 5 Pa・s and less than 10 Pa・s D: More than 10 Pa・s

<Stability of conductive material dispersion>
The conductive material dispersions obtained in each Example and Comparative Example were measured for viscosity (η0) and then stored in a sealed container at 25° C. for 10 days. The dispersion viscosity was then measured again (η1) and the viscosity change rate was calculated according to the following formula, which was used as 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 is 90% or more and less than 110%. B: Viscosity change rate Δη is 80% or more and less than 90%, or 110% or more and less than 120%. C: Viscosity change rate Δη is 70% or more and less than 80%, or 120% or more and less than 130%. D: Viscosity change rate Δη is 60% or more and less than 70%, or 130% or more and less than 140%. E: Viscosity change rate Δη is less than 60%, or 140% or more.

<Cycle characteristics>
The lithium ion secondary batteries prepared in the examples and comparative examples were left to stand at a temperature of 25°C for 5 hours after injecting the electrolyte. Next, the batteries were charged to a cell voltage of 3.65V at a constant current of 0.2C at a temperature of 25°C, and then aged at a temperature of 60°C for 12 hours. Then, the batteries were discharged to a cell voltage of 3.00V at a constant current of 0.2C at a temperature of 25°C. Then, the batteries were CC-CV charged (upper cell voltage 4.20V) at a constant current of 0.2C, and CC discharged to 3.00V at a constant current of 0.2C. This charge and discharge at 0.2C was repeated three times.
Next, 300 cycles of charge and discharge were performed at a cell voltage of 4.20-3.00 V and a charge and discharge rate of 1.0 C in an environment of 45° C. In this case, the discharge capacity of the first cycle was defined as X1, and the discharge capacity of the 300th cycle was defined as X2. Using the discharge capacity X1 and the discharge capacity X2, the capacity retention rate = (X2/X1) x 100 (%) was calculated and evaluated according to the following criteria. A larger value of the 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 and less than 85%. C: Capacity retention rate is 75% or more and less than 80%. D: Capacity retention rate is less than 75%.

<Whether or not the active material cracks after cycling>
The lithium ion secondary batteries produced in the 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.
A: Less than 2 pieces of broken active material B: 2 or more but less than 5 pieces of broken active material C: 5 or more but less than 9 pieces of broken active material D: 9 or more pieces of broken active material

<Output characteristics>
The output characteristics of the lithium ion secondary batteries produced in the Examples and Comparative Examples were evaluated by measuring the IV resistance by the following method.
As in the case of the cycle characteristics, the lithium-ion secondary battery that had been subjected to aging treatment and three cycles of charge and discharge was charged at a temperature of 25° C. until the charge rate reached 50% (i.e., until the charge capacity reached 350 mAh in the case of a cell capacity of 700 mAh), and the resistance value was measured according to the following procedure.
(1) Calculate the voltage change ΔV (0.2) when discharging for 30 seconds using a 0.2 C constant current method (I0.2).
(2) Charge at 0.2 C constant current for 30 seconds.
(3) Calculate the voltage change ΔV(1.0) when discharging for 30 seconds using a 1.0 C constant current method (I1.0).
IV resistance value (Ω) = {ΔV(1.0)-ΔV(0.2)}/(I1.0-I0.2)
According to the calculated IV resistance value, the evaluation was performed as follows.
A: 0.25 Ω or less B: More than 0.25 Ω and less than 0.30 Ω C: More than 0.30 Ω and less than 0.35 D: More than 0.35 Ω

Example 1
<Production of hydrogenated nitrile rubber>
- Emulsion polymerization process - Washing and drying process -
Into a reactor having an internal volume of 10 L, 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 were charged, and 2 parts of potassium oleate as an emulsifier, 0.1 parts of potassium phosphate as a stabilizer, and further, 0.3 parts of tert-dodecyl mercaptan (TDM) as a molecular weight regulator were added, and 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, thereby copolymerizing acrylonitrile and 1,3-butadiene.

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

A 25% aqueous solution of calcium chloride (CaCl ₂ ) was added as a coagulant in an amount of 3 parts per 100 parts of the polymer solid content in the obtained emulsion polymerization liquid while stirring, and the polymer in the emulsion polymerization liquid was coagulated. The polymer was then filtered, washed with 50 times the amount of ion-exchanged water relative to the obtained polymer, and dried under reduced pressure at a temperature of 90° C. to obtain a polymer.

-Hydrogenation step I (metaseism reaction)-
Next, 9 parts of the obtained polymer was dissolved in 141 parts of monochlorobenzene, which is a halogenated hydrocarbon, and the solution was charged into a reactor. Then, after the reactor was heated to 80° C., 2 L of a monochlorobenzene solution containing bis(tricyclohexylphosphine)benzylidene ruthenium dichloride as a Grubbs catalyst was added so that the amount of the Grubbs catalyst relative to the polymer was 1000 ppm. Then, 4.4 parts of cis-2-butene-1,4-diol as a coolefin was added relative to 100 parts of the precursor 1, and the polymer was subjected to a metathesis reaction at a stirring speed of 600 rpm. During the reaction, the temperature was kept constant using a cooling coil connected to a temperature control device and a heat sensor.

- Hydrogenation step II (hydrogenation reaction) -
Then, the inside of the reactor was degassed three times with 0.7 MPa _H2 while continuing stirring. Then, the temperature of the reactor was raised to 130°C, and 1 L of a monochlorobenzene solution containing Wilkinson's catalyst and triphenylphosphine was added to the reactor. The amount of Wilkinson's catalyst was 0.03 parts and the amount of triphenylphosphine was 1 part per 100 parts of the polymer. Then, the temperature was raised to 138°C, and the hydrogenation reaction of the polymer was carried out under the condition of a hydrogen pressure (gauge pressure) of 8.4 MPa.

-Refining process-
After the hydrogenation reaction was completed, 0.2 parts of activated carbon with an average diameter of 15 μm was added to the reactor and stirred for 30 minutes in order to adjust the concentration of divalent or higher metal ions including calcium ions. Then, the mixture was filtered through a filter with a pore size of 5 μm. The filtered solution was then heated and dried until the monochlorobenzene solvent was 50 ppm, and hydrogenated nitrile rubber A was isolated. The iodine value, weight average molecular weight, and metal content were measured using the obtained hydrogenated nitrile rubber A. The results are shown in Table 1. In addition, 20 parts (20 kg) of the isolated nitrile rubber A were filled into a 300×650×300 mm baler and pressed at a pressure of 3 MPa for 30 seconds to obtain nitrile rubber bale A. When the hydrogenated nitrile rubber bale A was measured in the same manner as hydrogenated nitrile rubber A, the measured values were the same.

<Preparation of Positive Electrode Binder>
920 parts of NMP was weighed out into a 2 L container 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 while continuing to stir for 5 hours, thereby preparing a positive electrode binder A with a solid content concentration of 8%.

<Preparation of Conductive Material Dispersion>
Five parts of multi-walled carbon nanotubes (BET specific surface area: 250 ^m2 /g) as a conductive material, 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), and then mixed at a peripheral speed of 8 m/s for 1 hour using a bead mill (manufactured by Ashizawa Finetech, "LMZ015") using zirconia beads having a diameter of 1 mm 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.

<Preparation of slurry for secondary battery positive electrode>
In the above-mentioned conductive material dispersion, 98.0 parts of a ternary active material ( _{LiNi0.5Co0.2Mn0.3O2} ) having a layered structure as a positive electrode active material (average particle size: _{10 μm} ), _1.0 parts of polyvinylidene fluoride as a binder, 1.0 parts of the above-mentioned conductive material dispersion (solid content equivalent amount), 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 obtained 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.

<Preparation of Positive Electrode>
A 20 μm thick aluminum foil was prepared as a current collector. The above positive electrode slurry was applied to the aluminum foil with a comma coater so that the weight per unit area after drying was 20 mg/cm ² , and then dried at 120° C. for 5 minutes and 130° C. for 5 minutes, and then heated at 60° C. for 10 hours to obtain a positive electrode raw sheet. This positive electrode raw sheet was rolled with a roll press to produce a sheet-shaped positive electrode consisting of a positive electrode composite layer with a density of 3.5 g/cm ³ and aluminum foil. This sheet-shaped positive electrode was cut to a width of 4.8 cm and a length of 50 cm to obtain a positive electrode for a lithium ion secondary battery.

<Preparation of negative electrode for lithium ion secondary battery>
In a 5 MPa pressure vessel equipped with a stirrer, 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 added, thoroughly stirred, and then heated to 50 ° C. to start polymerization. When the polymerization conversion rate reached 96%, the mixture was cooled to stop the polymerization reaction, and a mixture containing a particulate binder (styrene-butadiene copolymer) was obtained. After adjusting the pH to 8 by adding a 5% aqueous sodium hydroxide solution to the mixture, the unreacted monomer was removed by heating and vacuum distillation. The mixture was then cooled to 30 ° C. or less to obtain an aqueous dispersion containing a binder for the negative electrode.

Next, 48.75 parts of artificial graphite and 48.75 parts of natural graphite were added as negative electrode active materials, and 1 part of carboxymethyl cellulose was added as a thickener 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 of the aqueous dispersion containing the negative electrode binder obtained as described above was added in terms of solids, and kneaded for 40 minutes at a rotation speed of 40 rpm. Then, ion-exchanged water was added to obtain a viscosity of 3000±500 mPa·s (measured with a B-type viscometer at 25°C and 60 rpm), to prepare a slurry for the negative electrode composite layer.

Next, a copper foil having a thickness of 15 μm was prepared as a current collector. The above-mentioned negative electrode slurry was applied to both sides of the copper foil so that the coating amount after drying was 10 mg/cm ² , and then dried at 80 ° C for 5 minutes and at 120 ° C for 5 minutes to obtain a negative electrode raw sheet. This negative electrode raw sheet was rolled with a roll press to produce a sheet-shaped negative electrode consisting of a negative electrode composite layer (both sides) having a density of 1.6 g/cm ³ and copper foil. Then, the sheet-shaped negative electrode was cut to a width of 5.0 cm and a length of 52 cm to obtain a negative electrode for a lithium ion secondary battery.

<Preparation of Lithium-Ion Secondary Battery>
The positive electrode for lithium ion secondary battery and the negative electrode for lithium ion secondary battery thus prepared were arranged so that the electrode mixture layers faced each other, and a separator (a microporous film made of polyethylene) having a thickness of 15 μm was interposed between them, and the electrodes were wound using a core having a diameter of 20 mm to obtain a wound body. The wound body thus obtained was then compressed in one direction at a speed of 10 mm/sec until the thickness became 4.5 mm. The wound body after compression had an elliptical shape in a plan view, and the ratio of the major axis to the minor axis (major axis/minor axis) was 7.7.

In addition, a 1.0 M LiPF ₆ solution (solvent: a mixed solvent of ethylene carbonate (EC)/diethyl carbonate (DEC)=3/7 (volume ratio), additive: containing 2 vol% vinylene carbonate (solvent ratio)) was prepared as an electrolyte.

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

The resulting lithium-ion secondary batteries were evaluated for output characteristics, cycle characteristics, and cracking of the electrode active material after cycling. The results are shown in Table 1.

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 veil B and positive electrode binder B were obtained in the same manner as in Example 1. Hydrogenated nitrile rubber B was measured and evaluated, and the results are shown in Table 1.

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 veil 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.

Example 4
Except for changing the amount of activated carbon used in the purification step to 0.07 parts, hydrogenated nitrile rubber D, hydrogenated nitrile rubber veil D and positive electrode binder D were obtained in the same manner as in Example 1. Hydrogenated nitrile rubber D was measured and evaluated, and the results are shown in Table 1.

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 veil 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.

Example 6
Except for changing the amount of activated carbon used in the purification step to 0.02 parts, hydrogenated nitrile rubber F, hydrogenated nitrile rubber veil F and positive electrode binder F were obtained in the same manner as in Example 1. Hydrogenated nitrile rubber F was measured and evaluated, and the results are shown in Table 1.
(Comparative Example 1)
Except for changing the amount of activated carbon used in the purification step to 2 parts, hydrogenated nitrile rubber G, hydrogenated nitrile rubber veil G and positive electrode binder G were obtained in the same manner as in Example 1. Hydrogenated nitrile rubber G was measured and evaluated, and the results are shown in Table 1.

(Example 7)
The amount of Grubbs catalyst in the metathesis reaction was changed to 4000 ppm, and the metathesis reaction was performed without adding 1 L of a monochlorobenzene solution containing Wilkinson catalyst and triphenylphosphine to the reactor, and the inside of the reactor was degassed three times with 0.7 MPa _H2 , and the temperature was raised to 140°C, and the hydrogenation reaction was performed under the condition of a hydrogen pressure of 8.4 MPa. Hydrogenated nitrile rubber H, hydrogenated nitrile rubber veil H, and positive electrode binder H were obtained in the same manner as in Example 1. Measurement and evaluation of hydrogenated nitrile rubber H were performed, and the results are shown in Table 2.

(Example 8)
Except for changing the amount of Grubbs catalyst in the metathesis reaction to 3000 ppm, hydrogenated nitrile rubber I, hydrogenated nitrile rubber veil 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.

Example 9
Except for changing the amount of Grubbs catalyst in the metathesis reaction to 500 ppm, hydrogenated nitrile rubber J, hydrogenated nitrile rubber veil 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.

Example 10
Except for changing the amount of Grubbs catalyst in the metathesis reaction to 400 ppm, hydrogenated nitrile rubber K, hydrogenated nitrile rubber veil K and positive electrode binder K were obtained in the same manner as in Example 1. Hydrogenated nitrile rubber K was measured and evaluated, and the results are shown in Table 2.

(Example 11)
Except for changing the amount of Grubbs catalyst in the metathesis reaction to 200 ppm, hydrogenated nitrile rubber L, hydrogenated nitrile rubber veil 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.

(Comparative Example 2)
Except for not adding the antioxidant, the same procedure as in Example 1 was carried out to obtain hydrogenated nitrile rubber M, hydrogenated nitrile rubber veil M and positive electrode binder M. The hydrogenated nitrile rubber M was measured and evaluated, and the results are shown in Table 2.

(Comparative Example 3)
Hydrogenated nitrile rubber N, hydrogenated nitrile rubber veil 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.

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 the output characteristics, cycle characteristics, and effect of suppressing cracking of the electrode active material after cycle testing of the electrochemical element, and each characteristic is highly balanced (Comparison between Examples 1 to 11 and Comparative Examples 1 to 3).

The viscosity characteristics (dispersibility) of the conductive material dispersion liquid are excellent for the hydrogenated nitrile rubbers A to F and H to K of the present invention, but it is particularly evident that the viscosity of the conductive material dispersion liquid increases and dispersibility deteriorates as the iodine value of the hydrogenated nitrile rubber increases (comparison with Examples 1, 7 to 11, and Comparative Example 2). It is also evident that the dispersibility of the conductive material dispersion liquid is affected by the Ca content in the hydrogenated nitrile rubber, and that when the Ca content is particularly high, the viscosity of the dispersion liquid increases and deteriorates, 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 liquid are excellent when the iodine value of the hydrogenated nitrile rubber is small and the Ca content in the hydrogenated nitrile rubber is small.

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 it is clear that the absence of this agent results in a dramatic deterioration in the stability. It is also correlated with the iodine value of the hydrogenated nitrile rubber, and it is clear that the smaller the iodine value, the better (Comparison of Example 11 and Comparative Examples 1-2 with other Examples and Comparative Examples).

The output characteristics of the electrochemical element correlate with the iodine value of the hydrogenated nitrile rubber, and it can be seen that a smaller iodine value is preferable (comparison of Examples 1 to 11 and Comparative Examples 1 to 3).

The cycle characteristics of the electrochemical element are significantly affected by the amount of Ca in the hydrogenated nitrile rubber, and it can be seen that the characteristics deteriorate when the amount is too high (comparison of Examples 1 to 6).

The inhibition of cracking of the electrode active material after cycle testing of the electrochemical element correlates with the amount of Ca in the hydrogenated nitrile rubber, and tends to worsen as the amount decreases (particularly when comparing Examples 3 to 6 with Comparative Example 3).

On the other hand, although not shown in the comparative examples of this application, hydrogenated nitrile rubbers with large amounts of Na, Rh and/or Ru, Pd, and Mg remaining in them have poor cycle characteristics for electrochemical elements and can cause cracking of the electrode active material after cycle testing. However, from Tables 1 and 2, it can be seen that if 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 characteristics, 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 cycle testing.

Moreover, 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 for metathesis reaction, that [iodine value] can be adjusted by the amount of hydrogenation catalyst, the polymer molecular weight after metathesis reaction, and monitoring of hydrogenation rate, that [Mg, Na] content can be adjusted without using auxiliary materials that may be caused in the production stages such as emulsion polymerization process and hydrogenation process, 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)
The 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 dividing the hydrogenated nitrile rubber M (a block of hydrogenated nitrile rubber obtained by directly drying a polymer-containing monochlorobenzene solution to remove the solvent) before baling instead of the hydrogenated nitrile rubber veil M, and dissolving it in NMP. 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 veil M, the conductive material dispersion stability was deteriorated from D to E. This is because, when the bulk density of both was measured, the bulk density of the hydrogenated nitrile rubber veil M was 0.7 to 0.75 g/cm ³ , while the bulk density of the block of hydrogenated nitrile rubber M was 0.5 to 0.6 g/cm ³ . In other words, since a large amount of air is contained within a block of hydrogenated nitrile rubber with a low bulk density, it is believed that the oxygen radicals generated within the hydrogenated nitrile rubber react with the active points on the surface of the conductive material, causing crosslinking, thereby deteriorating stability.

(Examples 12 to 17)
A large amount of steam was introduced into the hydrogenated nitrile rubber-containing monochlorobenzene solution filtered after the purification process of Examples 1 to 6 to isolate hydrous crumbs. The isolated hydrous crumbs were then dried under conditions that would not affect the properties of the hydrogenated nitrile rubber using a screw-type extruder having a vacuum drying barrel and a substantially rectangular die section, 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 lower, 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 was measured, the hydrogenated nitrile rubber bales O to T from which the internal air had been removed using the screw-type extruder all had a bulk density of 0.85 g/cm ³ or more, which was much larger 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 baler of Examples 1 to 6.

When the prepared hydrogenated nitrile rubber veils O to T were used to adjust the positive electrode binders O to T in the same manner as in Examples 1 to 6 and the performance evaluation was performed, the evaluation level was not changed, but all of the performances were significantly higher than the results of Examples 1 to 6. In particular, the evaluation of the conductive material dispersion stability was originally all rated "A", but when hydrogenated nitrile rubber veils O to T with a large bulk density (almost no air inside) were used, the viscosity change rate Δη was almost unchanged, at a value close to 100%. In addition, when the evaluation was performed on the average of five times, the results were good with little variation. These are presumed to be due to the fact that the hydrogenated nitrile rubber veils O to T have little air inside and are less likely to generate oxygen radicals, which contributed to the stability of the conductive material dispersion. Incidentally, when the hydrous crumbs before being subjected to the screw-type extruder were directly dried to obtain crumb-like hydrogenated nitrile rubbers O to T, the bulk density was in the range of 0.5 to 0.6 g/cm ³ for each.

The screw-type 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-type extruder were as follows:

Set temperature for each barrel:
・First to third dehydration barrels: 90 to 120°C
First to fifth drying barrels: 120 to 180° C.
Operating conditions:
Diameter of the screw in the barrel unit (D): 132 mm
Total length of the screw in the barrel unit (L): 4620 mm
・L/D: 35
・Rotation speed of the screw in the barrel unit: 135 rpm
Residence time: 100 seconds Drying barrel vacuum level: 10 kPa
・Die resin pressure: 2 MPa

Furthermore, the hydrogenated nitrile rubber bales O-T produced above differ only in bulk density as a bale characteristic compared to the hydrogenated nitrile rubber bales A-F produced in Examples 1-6, but the molecular weight, iodine value, antioxidant content, chlorine content and various metal contents of the constituent hydrogenated nitrile rubber were unchanged.

According to the present invention, it is possible to provide a hydrogenated nitrile rubber and a production method thereof, which can improve the viscosity characteristics and stability of a conductive material dispersion liquid, prevent cracking of the active material in an electrode, and improve the cycle characteristics and output characteristics of an electrochemical element.
According to the present invention, it is possible to provide a hydrogenated nitrile rubber veil which can enhance the viscosity characteristics and stability of a conductive material dispersion, prevent cracking of the active material in an electrode, and improve the cycle characteristics and output characteristics of an electrochemical element.
According to the present invention, it is possible to provide a positive electrode binder that can enhance the viscosity characteristics and stability of a conductive material dispersion, prevent cracking of the active material in an electrode, and improve the cycle characteristics and output characteristics of an electrochemical element.
Furthermore, according to the present invention, it is possible to provide a positive electrode for an electrochemical element which is less susceptible to cracking of the electrode active material and has excellent cycle characteristics and output characteristics, and a method for producing the same.

Claims (21)

Hydrogenated nitrile rubber containing 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 and an iodine value in the range of 0.1 to 100 mg/100 mg, containing 2,2-methylenebis(4-methyl-6-tert-butylphenol) as an antioxidant, having a calcium (Ca) content in the range of 1 to 2500 ppm, and a sodium (Na) content of 300 ppm or less. The hydrogenated nitrile rubber according to claim 1, wherein the content of the antioxidant is in the range of 0.001 to 3 mass %. The hydrogenated nitrile rubber according to claim 1 further comprises 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. 2. The hydrogenated nitrile rubber according to claim 1, having a bulk density of 0.8 g/ ^cm3 or more. The hydrogenated nitrile rubber according to claim 4, further comprising a chlorine (Cl) content in the range of 10 ppm to 3000 ppm, and a mass ratio (Ca/Cl) to the calcium (Ca) content in the range of 0.1 to 4. 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% by mass or more. The hydrogenated nitrile rubber according to claim 1 is 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. The hydrogenated nitrile rubber according to claim 1 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 anti-aging agent, and then coagulating the polymer with calcium chloride, and hydrogenating the resulting polymer. The method for producing hydrogenated nitrile rubber according to claim 1, which comprises hydrogenating nitrile rubber containing the antioxidant 2,2-methylenebis(4-methyl-6-tert-butylphenol). an emulsion polymerization step of emulsion-polymerizing a monomer component including 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 containing the antioxidant with calcium chloride to produce a water-containing crumb;
a washing and drying step of washing and drying the water-containing crumbs to obtain a polymer;
a hydrogenation step of hydrogenating the polymer using a hydrogenation catalyst;
A method for producing the hydrogenated nitrile rubber according to claim 1, comprising: 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, and then hydrogenating the polymer with a rhodium catalyst. 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. The method for producing hydrogenated nitrile rubber according to claim 8, wherein the hydrogenated nitrile rubber is dried using a screw-type extruder. The method for producing hydrogenated nitrile rubber according to claim 13, wherein the screw-type extruder is equipped with a vacuum drying barrel. Hydrogenated nitrile rubber bale obtained by baling the hydrogenated nitrile rubber according to claim 1. The hydrogenated nitrile rubber veil according to claim 15, having a bulk density of 0.8 g/ ^cm3 or more. A positive electrode binder obtained by dispersing or dissolving the hydrogenated nitrile rubber according to claim 1 in N-methylpyrrolidone (NMP). A positive electrode binder obtained by dispersing or dissolving the hydrogenated nitrile rubber veil according to claim 16 in N-methylpyrrolidone (NMP). 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. A method for manufacturing a positive electrode comprising the steps of: mixing the positive electrode binder according to claim 17 with a conductive material, and then mixing the positive electrode active material to obtain a positive electrode composite layer slurry; coating the resulting slurry on a current collector; and drying the slurry. 20. 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 with a positive electrode active material to obtain a positive electrode mixture layer slurry; applying the resulting slurry onto a current collector; and drying the resulting slurry.