Method for producing nitrile rubber

Abstract

The present invention provides a method for producing nitrile rubber, wherein the method comprises continuously supplying nitrile rubber latex and a coagulant to an extruder having a screw disposed inside a barrel so as to be freely rotatable, thereby recovering nitrile rubber from the nitrile rubber latex. In the method for producing nitrile rubber, the nitrile rubber latex is supplied to the extruder in a state where the nitrile rubber latex contains a hindered phenol-based antioxidant having a molecular weight of 300 to 3000 in a ratio of 0.1 to 3 parts by weight per 100 parts by weight of the nitrile rubber.

Description

Technical Field

[0001] The present invention relates to a method for producing nitrile rubber using an extruder in which a screw is freely rotatably disposed within a barrel. More specifically, the present invention relates to a method for producing nitrile rubber that effectively suppresses contamination of the extruder and molds used during molding, and that produces nitrile rubber with excellent processability. Background Art

[0002] Typically, polymer recovery from a polymer latex obtained through emulsion polymerization is performed by first adding a coagulant, such as an acid or an aqueous solution of an inorganic salt, to the polymer latex in a coagulation tank, coagulating the latex while stirring. The polymer pellets obtained from this coagulation operation are then introduced into a dehydration device, such as a centrifugal dehydrator or a press, for dehydration, and then introduced into a drying device, such as a belt dryer, a flash dryer, or an extrusion dryer, for drying. Furthermore, a granulator or baler is typically connected downstream of the drying device. In many cases, the dried polymer is ultimately processed into pellets, bales, or sheets for commercialization.

[0003] However, the method of using these dehydration and drying devices to recover polymers from polymer latex has many problems in terms of increasing the number of steps, increasing the equipment cost of the coagulation tank and accompanying equipment, and increasing the installation space.

[0004] To address this problem, Patent Document 1, for example, attempts to supply nitrile rubber latex and a coagulant directly into a screw extruder to perform coagulation, dehydration, and drying within the extruder. However, the method described in Patent Document 1 suffers from problems such as high contamination of the extruder used for coagulation, dehydration, and drying (particularly, high contamination of the extruder exhaust port), insufficient productivity, and insufficient processability of the resulting nitrile rubber.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2011-12142. Summary of the Invention

[0008] Problems to be solved by the invention

[0009] The present invention has been made in view of such actual circumstances, and an object of the present invention is to provide a method for producing nitrile rubber, in which, in an extruder in which a screw is freely rotatably arranged inside a barrel and recovers nitrile rubber from nitrile rubber latex, the method can effectively suppress contamination of the extruder and contamination of the mold used during molding, and can produce nitrile rubber with excellent processability.

[0010] Solutions for solving problems

[0011] The present inventors have conducted intensive studies to achieve the above-mentioned objectives and have found that, when recovering nitrile rubber from the nitrile rubber latex, the nitrile rubber latex and a coagulant are continuously supplied to an extruder having a screw disposed inside a barrel so as to be freely rotatable. The nitrile rubber latex is supplied to the extruder in a state where a specific amount of a hindered phenol-based age resister having a molecular weight of 300 to 3000 is contained in the nitrile rubber latex. This has led to the completion of the present invention.

[0012] That is, according to the present invention, there is provided a method for producing nitrile rubber, wherein the method comprises continuously supplying nitrile rubber latex and a coagulant to an extruder in which a screw is freely rotatably arranged inside a barrel, thereby recovering nitrile rubber from the nitrile rubber latex.

[0013] In the method for producing nitrile rubber, the nitrile rubber latex is supplied to the extruder in a state where the nitrile rubber latex contains 0.1 to 3 parts by weight of a hindered phenol antioxidant having a molecular weight of 300 to 3000 per 100 parts by weight of the nitrile rubber.

[0014] In the production method of the present invention, the maximum value of the chemiluminescence intensity of the nitrile rubber discharged from the extruder and recovered from the nitrile rubber latex measured in accordance with JIS K7351:2018 is preferably 2,000 to 25,000 counts / second.

[0015] In the production method of the present invention, it is preferred that the nitrile rubber contains 5 to 60% by weight of α,β-ethylenically unsaturated nitrile monomer units, and the iodine value of the nitrile rubber is 120 or less.

[0016] In the production method of the present invention, the ratio Q / N [kg / (hr·rpm)] of the supply rate Q [kg / hr] of the nitrile rubber to the extruder to the rotation speed N [rpm] of the screw of the extruder is preferably 0.22 kg / (hr·rpm) or less.

[0017] In the production method of the present invention, when adding the hindered phenol-based antioxidant to the nitrile rubber latex, it is preferred that the hindered phenol-based antioxidant be added to the nitrile rubber latex in the form of an emulsion.

[0018] Effects of the Invention

[0019] According to the present invention, a method for producing nitrile rubber using an extruder in which a screw is freely rotatably arranged inside a barrel can be provided, which can effectively suppress the occurrence of contamination of the extruder and the occurrence of contamination of the mold used for molding, and can produce nitrile rubber with excellent processability. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram showing an extruder used in the nitrile rubber recovery method according to the first embodiment of the present invention.

[0021] Figure 2 Schematic diagram showing the screw arranged inside the extruder.

[0022] Figure 3 for Figure 2 Schematic diagram of a partial truncation of the screw.

[0023] Figure 4 For the Figure 1 The IV-IV line and Figure 2 Cross-sectional view along line IV-IV.

[0024] Figure 5 For the Figure 1 The V-V line and Figure 2 Cross-sectional view along line V-V. DETAILED DESCRIPTION

[0025] The method for producing nitrile rubber of the present invention is a method for producing nitrile rubber by continuously supplying nitrile rubber latex and a coagulant to an extruder in which a screw is freely rotatably arranged inside a barrel, thereby recovering nitrile rubber from the nitrile rubber latex.

[0026] In the method for producing nitrile rubber, the nitrile rubber latex is supplied to the extruder in a state where the nitrile rubber latex contains 0.1 to 3 parts by weight of a hindered phenol antioxidant having a molecular weight of 300 to 3000 per 100 parts by weight of the nitrile rubber.

[0027] <Nitrile rubber>

[0028] First, the nitrile rubber used in the present invention will be described.

[0029] The nitrile rubber used in the present invention is not particularly limited, and examples thereof include copolymers obtained by copolymerizing an α,β-ethylenically unsaturated nitrile monomer, a conjugated diene monomer, and, if necessary, other monomers copolymerizable with these.

[0030] The α,β-ethylenically unsaturated nitrile monomer is not limited as long as it is an α,β-ethylenically unsaturated compound having a nitrile group. Examples include acrylonitrile; α-halogenated acrylonitriles such as α-chloroacrylonitrile and α-bromoacrylonitrile; and α-alkylacrylonitriles such as methacrylonitrile. Acrylonitrile is preferred. The α,β-ethylenically unsaturated nitrile monomer may be used alone or in combination of multiple types.

[0031] The content of α,β-ethylenically unsaturated nitrile monomer units in the nitrile rubber used in the present invention is preferably 5 to 60% by weight, more preferably 8 to 55% by weight, even more preferably 10 to 50% by weight, and even more preferably 15 to 25% by weight. By adjusting the content of α,β-ethylenically unsaturated nitrile monomer units within this range, a well-balanced oil resistance and cold resistance can be achieved in the cross-linked rubber.

[0032] As the conjugated diene monomer, a conjugated diene monomer having 4 to 6 carbon atoms, such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, and chloroprene, is more preferred, 1,3-butadiene and isoprene are more preferred, and 1,3-butadiene is particularly preferred. These may be used alone or in combination of two or more.

[0033] The content of conjugated diene monomer units (including saturated butadiene units) in the nitrile rubber used in the present invention is preferably 10 to 89.9% by weight, more preferably 15 to 81.5% by weight, further preferably 20 to 74% by weight, and even more preferably 32.5 to 59.5% by weight. By adjusting the content of conjugated diene monomer units within the above range, the cross-linked rubber can have excellent oil resistance, heat aging resistance, and chemical stability, and can also appropriately improve rubber elasticity.

[0034] The nitrile rubber used in the present invention is preferably a nitrile rubber copolymerized with a carboxyl group-containing monomer in addition to an α,β-ethylenically unsaturated nitrile monomer and a conjugated diene monomer. The copolymerization of the carboxyl group-containing monomer can improve the compression set resistance of the cross-linked rubber.

[0035] The carboxyl group-containing monomer is not particularly limited as long as it is copolymerizable with the α,β-ethylenically unsaturated nitrile monomer and has one or more unsubstituted (free) carboxyl groups that are not esterified or the like.

[0036] Examples of carboxyl group-containing monomers include α,β-ethylenically unsaturated monocarboxylic acid monomers, α,β-ethylenically unsaturated polycarboxylic acid monomers, and α,β-ethylenically unsaturated dicarboxylic acid monoester monomers. Carboxyl group-containing monomers also include monomers in which the carboxyl groups of these monomers form carboxylates. Furthermore, anhydrides of α,β-ethylenically unsaturated polycarboxylic acids can also be used as carboxyl group-containing monomers because the anhydride groups cleave after copolymerization to form carboxyl groups.

[0037] Examples of the α,β-ethylenically unsaturated monocarboxylic acid monomer include acrylic acid, methacrylic acid, ethacrylic acid, crotonic acid, and cinnamic acid.

[0038] Examples of α,β-ethylenically unsaturated polycarboxylic acid monomers include fumaric acid, maleic acid, and other butylated acids; itaconic acid; citraconic acid; mesaconic acid; glutaconic acid; allylmalonic acid; and rutaconic acid. Examples of α,β-unsaturated polycarboxylic acid anhydrides include maleic anhydride, itaconic anhydride, and citraconic anhydride.

[0039] Examples of the α,β-ethylenically unsaturated dicarboxylic acid monoester monomer include: monoalkyl maleates such as monomethyl maleate, monoethyl maleate, monopropyl maleate, and mono-n-butyl maleate; monocycloalkyl maleates such as monocyclopentyl maleate, monocyclohexyl maleate, and monocycloheptyl maleate; monoalkylcycloalkyl maleates such as monomethylcyclopentyl maleate and monoethylcyclohexyl maleate; monoalkylfumarates such as monomethylfumarate, monoethylfumarate, monopropylfumarate, and mono-n-butylfumarate; monocycloalkyl fumarates such as monocyclopentyl fumarate, monocyclohexyl fumarate, and monocycloheptyl fumarate; monomethylcyclopentyl fumarate and monoethylcyclohexyl fumarate. fumaric acid monoalkylcycloalkyl esters; citraconic acid monomethyl ester, citraconic acid monoethyl ester, citraconic acid monopropyl ester, citraconic acid mono-n-butyl ester; citraconic acid monocycloalkyl esters such as citraconic acid monocyclopentyl ester, citraconic acid monocyclohexyl ester, citraconic acid monocycloheptyl ester; citraconic acid monoalkylcycloalkyl esters such as citraconic acid monomethyl cyclopentyl ester, citraconic acid monoethyl cyclohexyl ester; itaconic acid monoalkyl esters such as monomethyl itaconate, monoethyl itaconate, monopropyl itaconate, mono-n-butyl itaconate; itaconic acid monocycloalkyl esters such as monocyclopentyl itaconate, monocyclohexyl itaconate, monocycloheptyl itaconate; itaconic acid monoalkylcycloalkyl esters such as monomethyl itaconate, monoethyl itaconate, etc.

[0040] The carboxyl group-containing monomer may be used alone or in combination. Among these, α,β-ethylenically unsaturated dicarboxylic acid monoester monomers are preferred, α,β-ethylenically unsaturated dicarboxylic acid monoalkyl ester monomers are more preferred, maleic acid monoalkyl esters are further preferred, and mono-n-butyl maleate is particularly preferred. The alkyl group of these alkyl esters preferably has 2 to 8 carbon atoms.

[0041] The content of the carboxyl group-containing monomer units in the nitrile rubber used in the present invention is preferably 0.1 to 20% by weight, more preferably 0.5 to 15% by weight, even more preferably 1 to 10% by weight, and even more preferably 2.5 to 7.5% by weight. By adjusting the content of the carboxyl group-containing monomer units within the above range, the mechanical properties and compression set resistance of the resulting cross-linked rubber can be further improved.

[0042] Furthermore, from the viewpoint of further improving cold resistance, the nitrile rubber used in the present invention is preferably one obtained by copolymerizing an α,β-ethylenically unsaturated monocarboxylic acid ester monomer in addition to an α,β-ethylenically unsaturated nitrile monomer, a conjugated diene monomer, and, if necessary, a carboxyl group-containing monomer.

[0043] The α,β-ethylenically unsaturated monocarboxylic acid ester monomer is not particularly limited, and examples thereof include α,β-ethylenically unsaturated monocarboxylic acid alkyl ester monomers, α,β-ethylenically unsaturated monocarboxylic acid alkoxyalkyl ester monomers, α,β-ethylenically unsaturated monocarboxylic acid aminoalkyl ester monomers, α,β-ethylenically unsaturated monocarboxylic acid hydroxyalkyl ester monomers, and α,β-ethylenically unsaturated monocarboxylic acid fluoroalkyl ester monomers. Among these, α,β-ethylenically unsaturated monocarboxylic acid alkyl ester monomers and α,β-ethylenically unsaturated monocarboxylic acid alkoxyalkyl ester monomers are preferred.

[0044] The alkyl ester monomer of an α,β-ethylenically unsaturated monocarboxylic acid is preferably a monomer having an alkyl group having 3 to 10 carbon atoms, more preferably a monomer having an alkyl group having 3 to 8 carbon atoms, and still more preferably a monomer having an alkyl group having 4 to 6 carbon atoms.

[0045] Specific examples of the α,β-ethylenically unsaturated monocarboxylic acid alkyl ester monomers include: alkyl acrylate monomers such as methyl acrylate, ethyl acrylate, propyl acrylate, isobutyl acrylate, n-butyl acrylate, n-pentyl acrylate, 2-ethylhexyl acrylate, and n-dodecyl acrylate; cycloalkyl acrylate monomers such as cyclopentyl acrylate and cyclohexyl acrylate; alkylcycloalkyl acrylate monomers such as methylcyclopentyl acrylate, ethylcyclopentyl acrylate, and methylcyclohexyl acrylate; methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, and n-pentyl methacrylate. , octyl methacrylate and other methacrylic acid alkyl ester monomers; methacrylic acid cyclopentyl ester monomers, such as cyclohexyl methacrylate, cyclopentyl methacrylate and other methacrylic acid cycloalkyl ester monomers; methacrylic acid alkyl cycloalkyl ester monomers, such as methylcyclopentyl methacrylate, ethylcyclopentyl methacrylate, methylcyclohexyl methacrylate; crotonate alkyl ester monomers, such as propyl crotonate, n-butyl crotonate, 2-ethylhexyl crotonate; crotonate cycloalkyl ester monomers, such as cyclopentyl crotonate, cyclohexyl crotonate, cyclooctyl crotonate; crotonate alkyl cycloalkyl ester monomers, such as methylcyclopentyl crotonate, methylcyclohexyl crotonate, etc.

[0046] Furthermore, as the α,β-ethylenically unsaturated monocarboxylic acid alkoxyalkyl ester monomer, a monomer having an alkoxyalkyl group having 2 to 8 carbon atoms as the alkoxyalkyl group is preferred, a monomer having an alkoxyalkyl group having 2 to 6 carbon atoms as the alkoxyalkyl group is more preferred, and a monomer having an alkoxyalkyl group having 2 to 4 carbon atoms as the alkoxyalkyl group is further preferred.

[0047] Specific examples of the α,β-ethylenically unsaturated monocarboxylic acid alkoxyalkyl ester monomers include: alkoxyalkyl acrylate monomers such as methoxymethyl acrylate, methoxyethyl acrylate, methoxybutyl acrylate, ethoxymethyl acrylate, ethoxyethyl acrylate, ethoxypropyl acrylate, ethoxydodecyl acrylate, n-propoxyethyl acrylate, isopropoxyethyl acrylate, n-butoxyethyl acrylate, isobutoxyethyl acrylate, tert-butoxyethyl acrylate, methoxypropyl acrylate, and methoxybutyl acrylate; and alkoxyalkyl methacrylate monomers such as methoxymethyl methacrylate, methoxyethyl methacrylate, methoxybutyl methacrylate, ethoxymethyl methacrylate, ethoxyethyl methacrylate, ethoxypentyl methacrylate, n-propoxyethyl methacrylate, isopropoxyethyl methacrylate, n-butoxyethyl methacrylate, isobutoxyethyl methacrylate, tert-butoxyethyl methacrylate, methoxypropyl methacrylate, and methoxybutyl methacrylate.

[0048] Among these α,β-ethylenically unsaturated monocarboxylic acid ester monomers, alkyl acrylate monomers and alkoxyalkyl acrylate monomers are preferred, and n-butyl acrylate and methoxyethyl acrylate are more preferred.

[0049] The α,β-ethylenically unsaturated monocarboxylic acid ester monomer may be used alone or in combination of two or more. The content of the α,β-ethylenically unsaturated monocarboxylic acid ester monomer units in the nitrile rubber used in the present invention is preferably 5 to 60% by weight, more preferably 10 to 55% by weight, even more preferably 15 to 50% by weight, and even more preferably 23 to 35% by weight. By adjusting the content of the α,β-ethylenically unsaturated monocarboxylic acid ester monomer units within the above range, the cold resistance of the resulting cross-linked rubber can be further appropriately improved.

[0050] Furthermore, the nitrile rubber used in the present invention may be a nitrile rubber obtained by copolymerizing, in addition to an α,β-ethylenically unsaturated nitrile monomer, a conjugated diene monomer, a carboxyl group-containing monomer, and an α,β-ethylenically unsaturated monocarboxylic acid ester monomer, other monomers copolymerizable with these monomers. Examples of such other monomers include an α,β-ethylenically unsaturated monocarboxylic acid ester monomer (excluding the aforementioned monomers), ethylene, an α-olefin monomer, an aromatic vinyl monomer, a fluorine-containing vinyl monomer, and a copolymerizable antioxidant.

[0051] Examples of the α,β-ethylenically unsaturated monocarboxylic acid ester monomer include (meth)acrylates having a cyanoalkyl group having 2 to 12 carbon atoms, such as α-cyanoethyl acrylate, α-cyanoethyl methacrylate, and cyanobutyl methacrylate; (meth)acrylates having a hydroxyalkyl group having 1 to 12 carbon atoms, such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and 2-hydroxyethyl methacrylate; and (meth)acrylates having a fluoroalkyl group having 1 to 12 carbon atoms, such as trifluoroethyl acrylate and tetrafluoropropyl methacrylate.

[0052] As the α-olefin monomer, a monomer having 3 to 12 carbon atoms is preferable, and examples thereof include propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene.

[0053] Examples of the aromatic vinyl monomer include styrene, α-methylstyrene, and vinylpyridine.

[0054] Examples of the fluorine-containing vinyl monomer include fluoroethyl vinyl ether, fluoropropyl vinyl ether, o-trifluoromethylstyrene, vinyl pentafluorobenzoate, difluoroethylene, and tetrafluoroethylene.

[0055] Examples of copolymerizable antioxidants include N-(4-anilinophenyl)acrylamide, N-(4-anilinophenyl)methacrylamide, N-(4-anilinophenyl)cinnamamide, N-(4-anilinophenyl)crotonamide, N-phenyl-4-(3-vinylbenzyloxy)aniline, and N-phenyl-4-(4-vinylbenzyloxy)aniline.

[0056] These other copolymerizable monomers may be used alone or in combination. The content of these other monomer units in the nitrile rubber used in the present invention is preferably 30% by weight or less, more preferably 15% by weight or less, and even more preferably 5% by weight or less.

[0057] The iodine value of the nitrile rubber used in the present invention is preferably 120 or less, more preferably 50 or less, even more preferably 20 or less, and even more preferably 10 or less. By setting the iodine value to be within the above range of 120 or less, the heat resistance and ozone resistance of the resulting cross-linked rubber can be further improved.

[0058] The Mooney viscosity [ML1+4 (100° C.)] of the nitrile rubber used in the present invention is preferably 5 to 200, more preferably 10 to 100, and even more preferably 15 to 80.

[0059] As the polymerization method for polymerizing the nitrile rubber used in the present invention, there is no particular limitation. For example, from the perspective of convenience, it is preferred to copolymerize α,β-ethylenically unsaturated nitrile monomers, conjugated diene monomers, and carboxyl-containing monomers that can be added as needed and other monomers that can copolymerize with these. As the polymerization method, any of the well-known emulsion polymerization method and solution polymerization method can also be used, but from the viewpoint of easily controlling the polymerization reaction, the emulsion polymerization method is preferred. According to the emulsion polymerization method, the nitrile rubber can be obtained in the form of a latex formed by dispersing the nitrile rubber in an aqueous medium, that is, in the form of a latex of the nitrile rubber.

[0060] In the emulsion polymerization, in addition to an emulsifier, a polymerization initiator, and a molecular weight regulator, commonly used polymerization auxiliary materials can also be used.

[0061] Emulsifiers are not particularly limited, but examples thereof include nonionic emulsifiers such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenol ethers, polyoxyethylene alkyl esters, and polyoxyethylene sorbitan alkyl esters; anionic emulsifiers such as salts of fatty acids such as myristic acid, palmitic acid, stearic acid, oleic acid, and linolenic acid, alkylbenzenesulfonates such as sodium dodecylbenzenesulfonate, polycondensates of naphthalenesulfonates and formalin, higher alcohol sulfates, and alkylsulfosuccinates; and copolymeric emulsifiers such as sulfonic acid esters of α,β-unsaturated carboxylic acids, sulfates of α,β-unsaturated carboxylic acids, and sulfoalkylaryl ethers. The amount of the emulsifier added is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 5 parts by weight, per 100 parts by weight of the monomers used for polymerization.

[0062] As a polymerization initiator, there is no particular limitation as long as it is a free radical initiator, and examples thereof include: inorganic peroxides such as potassium persulfate, sodium persulfate, ammonium persulfate, potassium superphosphate, and hydrogen peroxide; organic peroxides such as tert-butyl peroxide, cumene hydroperoxide, tert-butyl peroxide, tert-butyl cumyl peroxide, acetyl peroxide, isobutyryl peroxide, octanoyl peroxide, dibenzoyl peroxide, 3,5,5-trimethylhexanoyl peroxide, tert-butyl peroxyisobutyrate, and dicumyl peroxide; and azo compounds such as azobisisobutyronitrile, azobis(2,4-dimethylvaleronitrile), azobis(cyclohexanecarbonitrile), and methyl azobisisobutyrate. These polymerization initiators can be used alone or in combination of two or more. As a polymerization initiator, an inorganic or organic peroxide is preferred. When a peroxide is used as a polymerization initiator, it can also be combined with a reducing agent such as sodium bisulfite or ferrous sulfate to be used as a redox polymerization initiator. The amount of the polymerization initiator added is preferably 0.01 to 2 parts by weight relative to 100 parts by weight of the monomers used for polymerization.

[0063] The molecular weight modifier is not particularly limited, but includes: mercaptans such as tert-dodecyl mercaptan, n-dodecyl mercaptan, and octyl mercaptan; halogenated hydrocarbons such as carbon tetrachloride, dichloromethane, and dibromomethane; α-methylstyrene dimer; and sulfur-containing compounds such as tetraethylthiuram disulfide, dipentamethylenethiuram disulfide, and diisopropylxanthate disulfide. These can be used alone or in combination of two or more. Among these, mercaptans are preferred, with tert-dodecyl mercaptan being more preferred. The amount of the molecular weight modifier added is preferably 0.1 to 5 parts by weight per 100 parts by weight of the monomers used for polymerization.

[0064] Water is usually used as a medium for emulsion polymerization. The amount of water is preferably 80 to 500 parts by weight, more preferably 80 to 300 parts by weight, based on 100 parts by weight of the monomers used for polymerization.

[0065] During emulsion polymerization, polymerization auxiliary materials such as stabilizers, dispersants, pH adjusters, deoxidizers, and particle size adjusters may be used as needed. When these are used, their types and amounts are not particularly limited.

[0066] Furthermore, the obtained copolymer may be hydrogenated (hydrogenation reaction) as needed. Hydrogenation can be carried out by a known method, including: an oil layer hydrogenation method in which the latex of the copolymer obtained by emulsion polymerization is coagulated and then hydrogenated in an oil layer; an aqueous layer hydrogenation method in which the latex of the obtained copolymer is directly hydrogenated, etc. However, in the present invention, from the perspective of simplifying the manufacturing process, the aqueous layer hydrogenation method is preferably used. According to the aqueous layer hydrogenation method, nitrile rubber can be obtained in the form of a latex formed by dispersing nitrile rubber in an aqueous medium, that is, in the form of a nitrile rubber latex (an aqueous dispersion of nitrile rubber formed by dispersing nitrile rubber particles in water).

[0067] When hydrogenation is performed by aqueous hydrogenation, it is preferred to dilute the copolymer latex prepared by the above-mentioned emulsion polymerization with water as needed and then perform the hydrogenation reaction. Examples of aqueous hydrogenation methods include direct aqueous hydrogenation methods, in which hydrogen is supplied to a reaction system in the presence of a hydrogenation catalyst, and indirect aqueous hydrogenation methods, in which hydrogen is reduced in the presence of an oxidizing agent, a reducing agent, and an activating agent. Of these, direct aqueous hydrogenation methods are preferred.

[0068] The hydrogenation catalyst is not particularly limited as long as it is a compound that is not easily decomposed in water. Specific examples of palladium catalysts include palladium salts of carboxylic acids such as formic acid, propionic acid, lauric acid, succinic acid, oleic acid, and phthalic acid; palladium chlorides such as palladium chloride, palladium dichloro(cyclooctadiene), palladium dichloro(norbornadiene), and ammonium hexachloropalladate(IV); iodides such as palladium iodide; palladium nitrate; and palladium sulfate dihydrate. Among these, palladium salts of carboxylic acids, palladium dichloro(norbornadiene), and ammonium hexachloropalladate(IV) palladium chloride and palladium nitrate are particularly preferred. As hydrogenation catalysts, in addition to palladium catalysts containing palladium as the metal, ruthenium catalysts, rhodium catalysts, osmium catalysts, iridium catalysts, and platinum catalysts can also be used. The amount of metal (e.g., palladium) used in the hydrogenation catalyst can be appropriately determined, but is preferably 5 to 20,000 ppm by weight, and more preferably 10 to 15,000 ppm by weight, relative to the copolymer obtained by polymerization.

[0069] In the aqueous direct hydrogenation method, the hydrogenation catalyst in the latex can be removed after the hydrogenation reaction is completed. This method can be, for example, a step of adding an adsorbent such as activated carbon or ion exchange resin to adsorb the hydrogenation catalyst under stirring, or a step of forming a complex of the hydrogenation catalyst using an oxidizing agent, a reducing agent, and a complexing agent, followed by centrifugation and / or filtration of the latex. Alternatively, the hydrogenation catalyst may remain in the latex without removal.

[0070] <Method for producing nitrile rubber>

[0071] Next, a method for producing nitrile rubber by recovering nitrile rubber (solid nitrile rubber) from the nitrile rubber latex (aqueous dispersion of nitrile rubber) obtained as described above will be described. Figure 1 The case of the extruder 1 shown is described as an example, but the present invention is not particularly limited to the use of Figure 1 The method of the extruder 1 is shown.

[0072] like Figure 1 As shown, the extruder 1 includes a drive unit 2 and a single barrel 3 composed of 18 divided barrel segments 31 to 48. Inside the barrel 3, a coagulation zone 100, a drainage zone 102, a washing and dehydration zone 104, and a drying zone 106 are formed in order from the upstream side to the downstream side of the barrel 3.

[0073] The coagulation zone 100 is where nitrile rubber latex is brought into contact with a coagulant to coagulate the polymer, forming a pelletized nitrile rubber slurry (pellet slurry). The drainage zone 102 is where the liquid (slurry) produced after the nitrile rubber coagulation is separated from the pellet slurry and drained, forming water-containing pellets. The washing and dehydration zone 104 is where the water-containing pellets are washed, the washing water removed from the washed pellets, and then drained. The drying zone 106 is where the dehydrated pellets are dried.

[0074] exist Figure 1 In the extruder 1 shown, the interior of the barrel blocks 31 to 36 corresponds to the coagulation zone 100, the interior of the barrel block 37 corresponds to the drainage zone 102, the interior of the barrel blocks 38 to 41 corresponds to the cleaning and dehydration zone 104, and the interior of the barrel blocks 42 to 48 corresponds to the drying zone 106. The number of barrel blocks can be set to an optimal number according to the composition of the nitrile rubber to be processed, and is not limited to Figure 1 The method shown.

[0075] The barrel block 32, which forms part of the coagulation zone 100, is provided with a feed port 320 (not shown) for supplying nitrile rubber latex, a feed port 321 (not shown) for supplying a coagulant, and a feed port 322 (not shown) for supplying water vapor. Furthermore, the barrel block 37, which forms part of the drainage zone 102, is provided with a discharge slit 370 for discharging the slurry separated from the aqueous slurry of coagulated nitrile rubber. Furthermore, the barrel block 38, which forms part of the cleaning and dehydration zone 104, is provided with a wash water feed port 380 for receiving wash water, and the barrel block 39 is provided with a drain slit 390 for discharging the wash water to the outside. The barrel blocks 43, 46, and 47, which form part of the drying zone 106, are provided with exhaust ports 430, 460, and 470, respectively, for degassing.

[0076] Figure 2 Schematic diagram showing the screw disposed inside the extruder 1. The barrel 3 is provided with Figure 2 In order to drive the screw 5, a screw rod 5 is connected to the base end thereof. Figure 1 ) in the motor drive unit, thereby the screw 5 can be kept free to rotate and drive. The shape of the screw 5 is not particularly limited, for example, it can be appropriately combined with a variety of screw structures of the screw block and the kneading disk to form.

[0077] In the extruder 1, the screw 5 has different screw structures in the regions corresponding to the above-mentioned regions 100, 102, 104, and 106 formed inside the barrel 3. Figure 3 for Figure 2 Schematic diagram of a partial cutaway of the screw. Figure 3 As shown, the screw 5 is composed of a screw block 50 and a kneading disk 52. In addition, Figure 3 This is a diagram showing an example of a combination of a screw block 50 and a kneading disk 52, and the present invention is not particularly limited to this example. Figure 3 Combination shown.

[0078] like Figure 2 As shown, when the length of the screw 5 is L (mm) and the outer diameter of the screw 5 is Da (mm), L / Da is preferably 30 to 100, more preferably 40 to 80. In addition, the outer diameter Da of the screw 5 is determined by the ridge 50A of the screw block 50 constituting the screw (see Figure 3 ) is defined by its diameter when viewed from the axial direction.

[0079] In addition, if Figure 4 As shown, in the extruder 1, two such screws 5 are used to make a twin-screw extruder with parallel shaft cores and mutually meshed. Figure 4 For the Figure 1 The IV-IV line and Figure 2 The cross-sectional view of line IV-IV, Figure 4 The cross-sectional view shown is a cross-sectional view of the screw block 50 portion of the extruder 1, which is a cross-sectional view of the valley portion 50B. Figure 4 As shown, the two screws 5, 5 are of a biaxially intermeshing type, in which the ridges 50A of the solidification screw segments 50 of one screw 5 mesh with the valleys 50B of the solidification screw segments 50 of the other screw 5, and the valleys 50B of the solidification screw segments 50 of one screw 5 mesh with the ridges 50A of the solidification screw segments 50 of the other screw 5. The biaxially intermeshing type improves mixing properties in the respective regions 100, 102, 104, and 106. The two screws 5 can rotate in either the same or opposite directions, but preferably rotate in the same direction for self-cleaning performance.

[0080] like Figure 4 As shown in FIG. 1 , when the outer diameter of the screw block 50 is Da (mm) and the minor diameter of the valley portion 50B of the screw block 50 is Di (mm), Da / Di is preferably in the range of 1.2 to 2.5, more preferably in the range of 1.4 to 2.0, and even more preferably in the range of 1.5 to 1.8. By setting Da / Di in such a range, the recovery rate and production rate (the amount of dried nitrile rubber obtained per unit time) can be improved without increasing the size of the equipment.

[0081] In addition, if Figure 4 As shown, the minor diameter Di of the valley portion 50B is the diameter of the deepest portion of the valley portion 50B, i.e., the portion having a depth Di' (mm), as viewed in the axial direction. Specifically, the minor diameter Di of the valley portion 50B can be calculated from the outer diameter Da and the deepest portion of the valley portion 50B, i.e., the depth Di', by the equation Di = Da - Di' × 2.

[0082] The kneading disc 52 has a cross-sectional shape such as a pseudo-ellipse, an ellipse, or a truncated triangle and a certain thickness, and is fixed and used in the following manner: the symmetry axis of the cross-sectional shape of the kneading disc 52 is shifted by a predetermined angle each time and multiple discs are stacked, and the screw axis is aligned with the rotation center axis of the cross-sectional shape. Figure 5 For the Figure 1 The V-V line and Figure 2 The cross-sectional view of line V-V, Figure 5 The cross-sectional view shown is a cross-sectional view of the kneading disk 52 portion of the extruder 1. Figure 3 、 Figure 5, a configuration is shown in which the kneading discs 52 have a pseudo-elliptical cross-sectional shape and are stacked in a stack of five discs at a 45-degree angle. However, the kneading discs 52 are not particularly limited to this configuration. By combining multiple kneading discs 52 at a predetermined angle, a forward kneading disc, a neutral kneading disc, or a reverse kneading disc can be formed. A forward kneading disc is a kneading disc that has a forward conveying capability by staggering the phases of multiple kneading discs 52 in the forward direction (e.g., staggering by 45° or 60° at a time). A reverse kneading disc is a kneading disc that has a reverse conveying capability by staggering the phases of multiple kneading discs 52 in the reverse direction (e.g., staggering by 270° at a time). A neutral kneading disc is a kneading disc that has no conveying capability by staggering multiple kneading discs 52 by 90° and forming the discs parallel to the axial direction.

[0083] In addition, Figure 3 、 Figure 5 In the embodiment, the kneading disk 52 has a pseudo-elliptical cross-section. A pseudo-elliptical shape is defined as a shape where the ends of the major diameter of an ellipse are cut with arcs centered at the center of rotation of the shape. An elliptical shape is defined as a shape where the ends of a parallel band are cut with arcs centered at the center of rotation of the shape. Furthermore, a truncated triangle shape is defined as a shape where the portion of an equilateral triangle containing each vertex is cut with arcs centered at the center of rotation of the shape. In either case, the kneading disk 52 is positioned so that a predetermined clearance of approximately 0.1 to 5 mm is maintained between the ends of each disk and the inner wall surface 3a of the barrel 3. In the case of an elliptical or truncated triangle shape, the sides can be concave, drum-shaped, or triangularly coiled.

[0084] Furthermore, a die head 4 is connected to the downstream side of the barrel block 48. This die head 4 is used to extrude the nitrile rubber, which has been solidified, dehydrated, and dried within the barrel 3, into a desired shape, for example, a sheet. Furthermore, a wire mesh is typically provided upstream of the discharge port of the die head 4 to capture impurities and the like.

[0085] Next, a method for recovering nitrile rubber from nitrile rubber latex using such an extruder 1 will be described.

[0086] First, nitrile rubber latex is supplied to coagulation zone 100 from a pipe connected to feed port 320, a coagulant is supplied to coagulation zone 100 from a pipe connected to feed port 321, and water vapor is supplied to coagulation zone 100 from a pipe connected to feed port 322. The coagulant is not particularly limited, but from the perspective of ensuring sufficient processability of the resulting nitrile rubber, a monovalent or divalent metal salt is preferably used. Specific examples of the coagulant include calcium chloride, magnesium chloride, sodium chloride, magnesium sulfate, and barium chloride, with sodium chloride being particularly preferred.

[0087] In the present invention, when the nitrile rubber latex is fed into the extruder 1, a hindered phenol-based antioxidant having a molecular weight of 300 to 3000 is added to the nitrile rubber latex before it is fed into the extruder 1. This allows the nitrile rubber latex to contain the hindered phenol-based antioxidant and is fed into the extruder 1 in the state containing the hindered phenol-based antioxidant.

[0088] Specifically, a hindered phenol-based antioxidant having a molecular weight of 300 to 3000 is added to the nitrile rubber latex before it is fed into the extruder 1 at a ratio of 0.1 to 3 parts by weight per 100 parts by weight of the nitrile rubber contained in the nitrile rubber latex. The hindered phenol-based antioxidant is then fed into the extruder 1 in the presence of the added hindered phenol-based antioxidant. According to the present invention, the hindered phenol-based antioxidant having a molecular weight of 300 to 3000 is preliminarily added to the nitrile rubber latex before it is fed into the extruder 1. The hindered phenol-based antioxidant is then fed into the extruder 1 together with the coagulant, thereby recovering the nitrile rubber from the nitrile rubber latex. This specific amount of hindered phenol-based antioxidant effectively suppresses contamination of the extruder 1 and of the mold used for molding, thereby improving the processability of the resulting nitrile rubber (particularly, processability when a crosslinking agent, etc., is added to form a rubber composition).

[0089] The hindered phenol antioxidant is not particularly limited as long as it is a compound having a phenol structure and having bulky groups (such as tert-butyl and octylthiomethyl) at two ortho positions of the OH group (phenolic hydroxyl group) constituting the phenol structure, and having a molecular weight of 300 to 3000; or a compound having a phenol structure and having a bulky group (such as tert-butyl and octylthiomethyl) at one of the two ortho positions of the OH group (phenolic hydroxyl group) constituting the phenol structure and a methyl group at the other, and having a molecular weight of 300 to 3000. Examples thereof include 4,6-bis(octylthiomethyl)-o-cresol, 2,2'-methylenebis(4- methyl-6-tert-butylphenol), 2,2'-methylenebis(4-ethyl-6-tert-butylphenol), n-octadecyl-3-(3',5'-di-tert-butyl-4'-hydroxyphenyl) propionate, 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-s-triazine-2,4,6-(1H,3H,5H)-trione, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], N,N-hexamethylenebis(3,5-di-tert-butyl-4-hydroxy-hydrocinnamic acid), tris(3,5-di-tert-butyl-4-hydroxybenzyl) isocyanurate, etc. The molecular weight of the hindered phenol antioxidant is in the range of 300 to 3000, preferably 400 to 2000, more preferably 400 to 1200, further preferably 400 to 1000, and even more preferably 400 to 600. By setting the molecular weight of the hindered phenol antioxidant within the above-specified range, the occurrence of contamination of the extruder can be effectively suppressed, and nitrile rubber with excellent processability can be produced.

[0090] The amount of the hindered phenol-based antioxidant with a molecular weight of 300 to 3000 added to the nitrile rubber latex before being fed into the extruder 1 is 0.1 to 3 parts by weight, preferably 0.3 to 2.5 parts by weight, more preferably 0.5 to 2.0 parts by weight, further preferably 0.7 to 2.0 parts by weight, and even more preferably 0.7 to 1.6 parts by weight relative to 100 parts by weight of the nitrile rubber latex. When the amount of the hindered phenol-based antioxidant with a molecular weight of 300 to 3000 is too small, the processability of the resulting nitrile rubber will deteriorate. Alternatively, when the amount of the hindered phenol-based antioxidant with a molecular weight of 300 to 3000 is too large, when the resulting nitrile rubber is molded (or when cross-linking is performed simultaneously with molding), contamination will occur on the mold used for molding, and productivity will deteriorate.

[0091] Furthermore, when antioxidants other than hindered phenol-based antioxidants with a molecular weight of 300 to 3000 are used, contamination may occur on the extruder 1, more specifically, on the vents 430, 460, and 470 of the extruder 1, resulting in reduced productivity. In particular, when contamination occurs on the vents 430, 460, and 470 of the extruder 1, there is a risk that the contamination may enter the extruder 1 and contaminate the nitrile rubber. Therefore, to prevent such contamination of the nitrile rubber, frequent removal of the contamination from the vents 430, 460, and 470 of the extruder 1 is required, resulting in reduced productivity.

[0092] The method of pre-adding a hindered phenol-based antioxidant having a molecular weight of 300 to 3000 to the nitrile rubber latex before being fed into the extruder 1 is not particularly limited. The hindered phenol-based antioxidant can be added directly to the nitrile rubber latex. However, from the viewpoint of being able to more appropriately suppress the occurrence of contamination of the mold used during molding, it is preferred to emulsify the hindered phenol-based antioxidant in water and add it in the form of an emulsion.

[0093] When adding a hindered phenol-based antioxidant having a molecular weight of 300 to 3000 in an emulsion state to the nitrile rubber latex before being fed into the extruder 1, it is preferred to use an emulsifier to form the emulsion. The emulsifier is not particularly limited and can be appropriately selected depending on the type of hindered phenol-based antioxidant used. For example, an emulsifier used in the emulsion polymerization of the nitrile rubber described above can be used.

[0094] The content ratio of the hindered phenol-based antioxidant with a molecular weight of 300 to 3000 in the emulsion when the latex of the nitrile rubber before being fed into the extruder 1 is added in the form of an emulsion is not particularly limited. From the viewpoint of further improving the effect of adding in the form of an emulsion, it is preferably 1 to 70 weight %, more preferably 5 to 60 weight %, further preferably 10 to 50 weight %, and even more preferably 15 to 25 weight %.

[0095] In addition, the amount of coagulant supplied from the feed port 321 is preferably 0.5 to 200 parts by weight, more preferably 1 to 95 parts by weight, and even more preferably 45 to 75 parts by weight relative to 100 parts by weight of the nitrile rubber latex. By setting the supply amount of the coagulant to the above range, the nitrile rubber can be fully coagulated, the uncoagulated components can be reduced, and the yield can be improved. In addition, the coagulant can be dissolved in water or the like and supplied from the feed port 321 in the form of a coagulant liquid. The concentration of the coagulant in the coagulant liquid in this case is not particularly limited, but is preferably about 1 to 35% by weight, more preferably 15 to 25% by weight, relative to the entire coagulant liquid.

[0096] The nitrile rubber latex, coagulant, and water vapor supplied to the coagulation zone 100 come into contact with each other due to the rotation of the screw 5. The nitrile rubber coagulates and forms pellets with a diameter of approximately 5 to 30 mm, which are suspended in water to form a slurry (pellet slurry) with a pellet concentration of approximately 5 to 30% by weight. The temperature within the coagulation zone 100 is preferably 10 to 100°C, more preferably 45 to 90°C. By setting the temperature of the coagulation zone 100 within this range, the nitrile rubber can be effectively and fully coagulated, the uncoagulated components can be reduced, and the yield can be improved.

[0097] The pellet slurry obtained in the coagulation area 100 is transported to the drainage area 102 by the rotation of the screw 5. In the drainage area 102, the high concentration of coagulant contained in the pellet slurry is discharged from the slit 370 provided in the barrel block 37 in the form of slurry, and the pellets are obtained in a hydrated state containing about 40 to 70% by weight of water.

[0098] The pellets, which are in a moist state, obtained in the drainage zone 102 are transported to the washing and dehydration zone 104 by the rotation of the screw 5. In the washing and dehydration zone 104, washing water is introduced from the washing water inlet 380 provided in the barrel block 38. The washing water and the pellets are mixed to wash the pellets, and then dehydrated. The wastewater after washing is discharged from the slit 390 provided in the barrel block 39.

[0099] The screw structure of the screw 5 in the portion corresponding to the wash water inlet 380 of the barrel block 38 constituting the washing and dehydration zone 104 (i.e., the screw structure of the screw 5 at the outlet of the wash water inlet 380) is composed of multiple kneading discs 52. By having the screw structure of the portion corresponding to the wash water inlet 380 comprised of multiple kneading discs 52, the wash water supplied from the wash water inlet 380 can be supplied at an elevated pressure, thereby improving the washing efficiency. Furthermore, this can appropriately reduce the sodium content (derived from the coagulant, etc.) and the combined content of calcium, magnesium, and aluminum in the recovered nitrile rubber, thereby improving the water resistance of the resulting nitrile rubber.

[0100] In particular, by configuring the portion of the screw 5 corresponding to the wash water inlet 380 with multiple kneading discs 52, the presence of the multiple kneading discs 52 and the presence of the pellets kneaded by the multiple kneading discs 52 reduces the spatial volume of this portion. This suppresses the diffusion of the wash water supplied from the wash water inlet 380 within the barrel block 38 (or makes it difficult to secure a flow path), thereby increasing the pressure of the supplied wash water. Furthermore, when configuring the portion corresponding to the wash water inlet 380 with multiple kneading discs 52, the disc structure is not particularly limited; however, a forward kneading disc, a neutral kneading disc, or a reverse kneading disc is preferred, and a combination of these is also possible.

[0101] In addition, in the present invention, it is sufficient that the portion of the screw 5 corresponding to the cleaning water feed port 380 is composed of a plurality of kneading disks 52. However, from the perspective of more appropriately increasing the water pressure of the supplied cleaning water, it is preferred that the screw structure of the screw 5 in the barrel 38 having the cleaning water feed port 380 is a structure in which the proportion of the kneading disks 52 (the proportion in the length direction) is 30 to 100%, and more preferably a structure in which the proportion of the kneading disks 52 is 60 to 100%. By having such a structure, the cleaning efficiency of the pellets in the cleaning and dehydration area 104 can be further improved.

[0102] In addition, the proportion of the kneading disk 52 in the screw 5 in the entire cleaning and dehydration area 104 (the proportion in the longitudinal direction) is not particularly limited. From the perspective of improving the dehydration efficiency in addition to improving the cleaning efficiency, it is preferably 5 to 85%, and more preferably 10 to 80%.

[0103] The supply rate of the washing water supplied from the washing water inlet 380 is not particularly limited, but is preferably 30 to 600 L / hr, more preferably 70 to 500 L / hr. Furthermore, the amount of washing water supplied from the washing water inlet 380 is preferably 25 to 1000 parts by weight, more preferably 50 to 900 parts by weight, relative to 100 parts by weight of the nitrile rubber. By setting the washing water supply rate and the amount of washing water within the above ranges, the washing effect in the washing / dehydration zone 104 can be further improved, thereby further effectively reducing the sodium content derived from the coagulant, etc., and the total content of calcium, magnesium, and aluminum in the recovered nitrile rubber. Furthermore, the temperature of the washing water is not particularly limited, but is preferably 10 to 90°C, more preferably 40 to 80°C.

[0104] In the area before the wash water feed port 380 in the washing / dehydration zone 104, the barrel block temperature is preferably 40 to 100°C, more preferably 50 to 95°C. Furthermore, in the area after the wash water feed port 380, the barrel block temperature is preferably 80 to 200°C, more preferably 90 to 180°C. Furthermore, in the washing / dehydration zone 104, pellets containing approximately 2 to 20% by weight of water can be obtained after washing.

[0105] Next, the pellets obtained in the cleaning and dehydration area 104 are transported to the drying area 106 by the rotation of the screw 5. The pellets transported to the drying area 106 are plasticized and kneaded by the rotation of the screw 5 to form a melt, and are transported to the downstream side while generating heat and increasing in temperature. Then, when the melt reaches the exhaust ports 430, 460, and 470 provided in the barrel blocks 43, 46, and 47, the water contained in the melt is separated and vaporized in order to release the pressure. The separated and vaporized water (steam) is discharged to the outside through the exhaust pipe (omitted in the figure). The temperature inside the drying area 106 is preferably 90 to 200°C, and more preferably 100 to 180°C. In addition, the internal pressure (pressure at the die head) is approximately 1000 to 13000 kPa (G: gauge pressure). In addition, the drying area 106 can also be decompressed.

[0106] The pellets from which moisture has been separated after passing through the drying area 106 are transported to the outlet side by the screw 5 and introduced into the die head 4 in a state of containing substantially almost no moisture (moisture content is less than 1.0 weight %). Here, after being discharged in the form of sheets, for example, they are introduced into a slicer (not shown) and cut into appropriate lengths.

[0107] By carrying out the above-described process, nitrile rubber can be recovered from the nitrile rubber latex.

[0108] In the present invention, when the amount of nitrile rubber supplied to the feed port 320 of the extruder 1 per unit time (the amount of nitrile rubber recovered by the extruder 1 per unit time) is Q [kg / hr] and the rotational speed of the screw 5 is N [rpm], Q / N [kg / (hr·rpm)] is preferably 0.22 kg / (hr·rpm) or less, more preferably 0.21 kg / (hr·rpm) or less, and even more preferably 0.16 to 0.20 kg / (hr·rpm). The rotational speed N of the screw 5 is the rotational speed [rpm] of the screw 5 when it rotates within the barrel 3 of the extruder 1 for one minute. By setting Q / N within the above range, the amount of volatile components such as water contained in the recovered nitrile rubber can be effectively reduced even at relatively high production rates (throughput), thereby effectively suppressing problems such as interference with crosslinking due to residual volatile components such as water. As a result, when a cross-linked rubber product is produced, a cross-linked rubber product having excellent mechanical strength can be produced. The amount of volatile components such as water contained in the recovered nitrile rubber is preferably 0.7% by weight or less, more preferably 0.5% by weight or less.

[0109] The maximum chemiluminescence intensity of the recovered nitrile rubber measured in accordance with JIS K7351:2018 is preferably 2,000 to 25,000 counts / second, more preferably 3,000 to 20,000 counts / second, further preferably 5,000 to 20,000 counts / second, and particularly preferably 6,000 to 15,000 counts / second. By setting the maximum chemiluminescence intensity within the above range, the processability of the recovered nitrile rubber (particularly the processability when a crosslinking agent is added to form a rubber composition) can be further appropriately improved. Furthermore, the maximum chemiluminescence intensity can be measured, for example, by cutting a 1 cm square and 2 mm thick sample of the nitrile rubber with a razor and using this as a measurement sample using a chemiluminescence analyzer at a measurement temperature of 170°C and a N2 gas flow rate of 150 ml / min, in accordance with JIS K7351:2018 (High-sensitivity measurement method for weak luminescence containing peroxides in plastics) for a measurement time of 600 seconds. In addition, as a method for making the maximum value of the chemiluminescence intensity within the above-mentioned range, for example, there can be cited: a method of adjusting the type and amount of a hindered phenol-based antioxidant with a molecular weight of 300 to 3000 pre-added to the nitrile rubber latex before being fed into the extruder 1; a method of adjusting the structure of the screw 5 of the extruder 1, the rotation speed of the screw 5 of the extruder 1, the temperature of the drying area 106 of the extruder 1, etc.

[0110] <Rubber Composition>

[0111] And, the nitrile rubber manufactured as described above can be used as a rubber composition by, for example, mixing a cross-linking agent. As the cross-linking agent, there is no particular limitation, and sulfur cross-linking agents, organic peroxide cross-linking agents or polyamine cross-linking agents can be enumerated. Among these, when the nitrile rubber manufactured as described above is a carboxyl-containing nitrile rubber, polyamine cross-linking agents are preferred.

[0112] As a polyamine cross-linking agent, there is no particular limitation as long as it is a compound having two or more amino groups or a cross-linking agent that becomes a compound having two or more amino groups when cross-linked. Preferably, it is a compound in which multiple hydrogen atoms of an aliphatic hydrocarbon or an aromatic hydrocarbon are replaced by an amino group or a hydrazide structure (a structure represented by -CONHNH2, CO represents a carbonyl group) and a compound that becomes the form of such a compound when cross-linked.

[0113] Specific examples of the polyamine crosslinking agent include: aliphatic polyamines such as hexamethylenediamine, hexamethylenediamine carbamate, N,N-biscinnamaldehyde acetal-1,6-hexanediamine, tetramethylenepentamine, and hexamethylenediamine cinnamaldehyde adducts; 4,4-methylenedianiline, m-phenylenediamine, 4,4-diaminodiphenyl ether, 3,4-diaminodiphenyl ether, 4,4-(m-phenylenediisopropylidene)diphenylamine, 4,4-(p-phenylenediisopropylidene)diphenylamine, 2,2-bis[4,4-(4-aminophenoxy)phenyl]propane, 4,4-diaminobenzanilide, 4,4-bis(4-aminophenoxy)biphenyl, m-phenylenediamine, p-phenylenediamine, Aromatic polyamines such as benzyldiamine and 1,3,5-triaminobenzene; polyhydrazides such as isophthalic acid dihydrazide, terephthalic acid dihydrazide, phthalic acid dihydrazide, 2,6-naphthalene dihydrazide, naphthoic acid dihydrazide, oxalic acid dihydrazide, malonic acid dihydrazide, succinic acid dihydrazide, glutamic acid dihydrazide, adipic acid dihydrazide, pimelic acid dihydrazide, suberic acid dihydrazide, azelaic acid dihydrazide, sebacic acid dihydrazide, tridecanedioic acid dihydrazide, dodecanedioic acid dihydrazide, acetone dicarboxylic acid dihydrazide, fumaric acid dihydrazide, maleic acid dihydrazide, itaconic acid dihydrazide, trimellitic acid dihydrazide, 1,3,5-phenyltricarboxylic acid dihydrazide, aconitic acid dihydrazide, and pyromellitic acid dihydrazide. Among these, from the viewpoint of further remarkable effects of the present invention, aliphatic polyamines and aromatic polyamines are preferred, hexamethylenediamine carbamate and 2,2-bis[4-(4-aminophenoxy)phenyl]propane are more preferred, and hexamethylenediamine carbamate is particularly preferred.

[0114] The content of the crosslinking agent in the rubber composition of the present invention is not particularly limited, but is preferably 0.1 to 20 parts by weight, more preferably 0.2 to 15 parts by weight, and even more preferably 0.5 to 10 parts by weight per 100 parts by weight of the nitrile rubber.

[0115] In addition to the crosslinking agent, the rubber composition of the present invention may also contain compounding agents commonly used in the rubber field, such as fillers; metal oxides such as zinc oxide and magnesium oxide; α,β-ethylenically unsaturated carboxylic acid metal salts such as zinc methacrylate and zinc acrylate; crosslinking accelerators; co-crosslinking agents; crosslinking aids; crosslinking retarders; antioxidants; antioxidants; light stabilizers; scorch retarders such as primary amines; activators such as diethylene glycol; silane coupling agents; plasticizers; processing aids; lubricants; adhesives; lubricants; flame retardants; mildew inhibitors; acid neutralizers; antistatic agents; pigments; foaming agents, etc. The amounts of these compounding agents are not particularly limited, as long as they do not impair the objects and effects of the present invention, and may be added in amounts appropriate to the purpose of the compounding.

[0116] Furthermore, the rubber composition of the present invention may also contain rubbers other than nitrile rubber.

[0117] <Rubber cross-linked product>

[0118] Furthermore, the rubber composition can be cross-linked to produce a cross-linked rubber.

[0119] The cross-linked rubber product of the present invention can be produced by forming the rubber composition of the present invention into a desired shape using a molding machine such as an extruder, injection molding machine, compressor, or roller, and then heating the composition to cause a cross-linking reaction, thereby fixing the shape and producing the cross-linked product. In this case, cross-linking can be performed after pre-molding or simultaneously with molding. The molding temperature is generally 10 to 200°C, preferably 25 to 120°C. The cross-linking temperature is generally 100 to 200°C, preferably 130 to 190°C, and the cross-linking time is generally 1 minute to 24 hours, preferably 2 minutes to 1 hour.

[0120] In addition, depending on the shape and size of the cross-linked product, there may be cases where the surface is cross-linked but the interior is not fully cross-linked, so further heating can be performed to perform secondary cross-linking. As the heating method, a general method that can be used for cross-linking rubber, such as press heating, steam heating, oven heating, hot air heating, etc., can be appropriately selected.

[0121] The cross-linked rubber of the present invention is obtained by using a rubber composition containing the nitrile rubber of the present invention. The cross-linked rubber of the present invention can be used, for example, in O-rings, packings, spacers, oil seals, shaft seals, bearing seals, wellhead seals, shock absorber seals, coolant seals for sealing coolants such as long-life coolant (LLC), oil coolant seals, air compressor seals, cooling devices for air conditioners, seals for sealing freon, fluorocarbon, or carbon dioxide for refrigerator compressors of air conditioners, seals for sealing supercritical carbon dioxide or subcritical carbon dioxide as a cleaning medium for precision cleaning, seals for rotating devices (rolling bearings, automotive hub units, automotive water pumps, linear guides, ball screws, etc.), valves and valve seats, BOP (Blow Out Preventer, blowout preventer), discs and other sealing materials; intake manifold gaskets installed at the connection between the intake manifold and the cylinder head, cylinder head gaskets installed at the connection between the cylinder block and the cylinder head, rocker cover gaskets installed at the connection between the rocker cover and the cylinder head, oil pan gaskets installed at the connection between the oil pan and the cylinder block or the transmission case, fuel cell spacer gaskets installed between a pair of housings that sandwich a battery cell having a positive electrode, an electrolyte plate and a negative electrode, gaskets for the top cover of a hard disk drive, and other gaskets; various rollers such as printing rollers, ironmaking rollers, papermaking rollers, industrial rollers, and office equipment rollers; flat belts (film core flat belts, cord flat belts, etc.); belts), laminated flat belts, single-piece flat belts, etc.), V-belts (covered V-belts, cut-edge V-belts, etc.), V-ribbed belts (single V-ribbed belts, double V-ribbed belts, covered V-ribbed belts, back-rubber V-ribbed belts, top-tooth V-ribbed belts, etc.), CVT belts, timing belts, toothed belts, conveyor belts, etc.; various pipes such as fuel pipes, turbocharger pipes, oil pipes, radiator pipes, heater pipes, water pipes, vacuum hoses, control pipes, air conditioning pipes, brake pipes, power steering pipes, air pipes, offshore oil pipes, risers, flow pipes, CVJ protective covers, screw shaft protective covers, constant velocity joint protective covers, rack and pinion transmissions (rack andpinion) protective covers; damping material rubber parts such as cushioning materials, dynamic dampers, rubber couplings, air suspensions, shockproof materials, clutch lining materials; dust covers, automotive interior parts, friction materials, tires, coated cables, shoe soles, electromagnetic wave shielding bodies, adhesives such as adhesives for flexible printed circuit boards, fuel cell spacers, and in addition, can be used in a wide range of applications such as the electronics field.

[0122] Example

[0123] Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. In addition, "parts" in each example are based on weight unless otherwise specified.

[0124] Various physical properties were evaluated by the following methods.

[0125] [Content ratio of each monomer unit constituting hydrogenated nitrile rubber]

[0126] The content ratio of mono-n-butyl maleate units was calculated by the following method: 100 mL of 2-butanone was added to 0.2 g of a 2 mm square of hydrogenated nitrile rubber, and after stirring for 16 hours, 20 mL of ethanol and 10 mL of water were added. While stirring at room temperature, titration was performed using a 0.02 N aqueous ethanol solution of potassium hydroxide and thymolphthalein as an indicator to determine the molar number of carboxyl groups per 100 g of hydrogenated nitrile rubber. The determined molar number was converted into the amount of mono-n-butyl maleate units.

[0127] The content ratio of the 1,3-butadiene unit and the saturated butadiene unit was calculated by measuring the iodine value before and after the hydrogenation reaction using hydrogenated nitrile rubber (according to K6235:2006).

[0128] The content ratio of acrylonitrile units was calculated by measuring the nitrogen content in the hydrogenated nitrile rubber by the Kjeldahl method in accordance with JIS K6451-2:2016.

[0129] The content ratio of the n-butyl acrylate unit was calculated as the remaining component relative to the above-mentioned respective monomer units.

[0130] [Mooney viscosity of hydrogenated nitrile rubber]

[0131] The Mooney viscosity of the hydrogenated nitrile rubber (polymer Mooney, ML1+4, 100° C.) was measured at 100° C. in accordance with JIS K6300-1:2013.

[0132] [Mooney viscosity of rubber composition]

[0133] The Mooney viscosity of the rubber composition (composite Mooney, ML1+4, 100° C.) was measured at 100° C. in accordance with JIS K6300-1:2013.

[0134] [Maximum value of chemiluminescence intensity of hydrogenated nitrile rubber]

[0135] The recovered hydrogenated nitrile rubber was cut into 1 cm squares with a thickness of 2 mm using a razor. These samples were used as measurement samples. The chemiluminescence intensity of the samples was measured using a chemiluminescence analyzer (manufactured by Tohoku Electronics Industry Co., Ltd., trade name "CLA-FS4") at a measurement temperature of 170°C and a N2 gas flow rate of 150 ml / min, in accordance with JIS K7351:2018 (High-sensitivity determination of weak luminescence from peroxides contained in plastics) for a measurement time of 600 seconds. The maximum chemiluminescence intensity within the measurement time was then determined based on the measurement results.

[0136] [Volatile content of hydrogenated nitrile rubber]

[0137] The volatile content of hydrogenated nitrile rubber was measured in accordance with JIS K6238-1:2009 (oven method A). The hydrogenated nitrile rubber was dried at 105°C ± 5°C for 1 hour and then allowed to cool in a desiccator. The volatile content (weight %) was calculated from the weight difference before and after drying: [(rubber weight before drying - rubber weight after drying) / (rubber weight before drying)] × 100.

[0138] [Extruder contamination]

[0139] After the hydrogenated nitrile rubber latex (L1) was coagulated, cleaned, dehydrated, and dried using the extruder 1 for 6 consecutive hours, the contamination (the condition of the contamination of the vent caused by adhered rubber, compounding agents, etc.) of the vent 430 of the extruder 1 was visually judged and evaluated according to the following criteria.

[0140] ◎: No pollution

[0141] ○: Slightly polluted

[0142] △: Obviously contaminated

[0143] ×: Severe pollution

[0144] [Mold contamination]

[0145] The mold contamination evaluation method is as follows. First, a test piece of about 150 mm long, about 80 mm wide, and about 2 mm thick is prepared from the uncrosslinked rubber composition and clamped in a sheet mold of 150 mm × 80 mm × 2 mm. Next, the test piece is subjected to five cycles of 180°C and 100 kg / cm 3 The mold surface contamination during the press crosslinking (the condition of mold contamination caused by adhered rubber, compounding ingredients, etc.) was visually determined and evaluated according to the following criteria.

[0146] ◎: No pollution

[0147] ○: Slightly polluted

[0148] △: Obviously contaminated

[0149] ×: Severe pollution

[0150] [Production Example 1: Production of Hydrogenated Nitrile Rubber Latex (L1)]

[0151] To a metal bottle were added 180 parts of ion-exchanged water, 25 parts of a 10% by weight aqueous solution of sodium dodecylbenzenesulfonate, 5 parts of a 10% sodium salt of a naphthalenesulfonic acid formalin condensate, 20.4 parts of acrylonitrile, 5 parts of mono-n-butyl maleate, 35.2 parts of n-butyl acrylate, and 0.75 parts of tert-dodecylmercaptan (molecular weight modifier). After the atmosphere was replaced with nitrogen three times, 39.4 parts of 1,3-butadiene was added. The metal bottle was maintained at 10°C, and 0.1 parts of cumene hydroperoxide (polymerization initiator) and appropriate amounts of a reducing agent, a chelating agent, and a builder were added. The polymerization reaction was continued with stirring. When the polymerization conversion reached 80%, the polymerization reaction was terminated by adding 4 parts of a 2.5% by weight aqueous solution of 2,2,6,6-tetramethylpiperidinyl-1-oxyl radical (polymerization terminator). Next, the remaining monomers were removed at a water temperature of 60° C. to obtain a nitrile rubber latex (X1) (solid content concentration: 28% by weight).

[0152] In addition to the above, an aqueous solution of sodium chloride containing 2 times the molar equivalent of the Pd metal in the palladium chloride was added to palladium chloride (the weight ratio of the Pd metal in the palladium chloride to the nitrile rubber in the latex was 2800 ppm by weight) to prepare a palladium aqueous solution. Subsequently, polyvinylpyrrolidone having a weight-average molecular weight of 5000 was added to 300 parts of the obtained palladium aqueous solution in an amount 5 times the weight ratio of the Pd metal in the palladium chloride, and an aqueous potassium hydroxide solution was further added to prepare a catalyst aqueous solution having a pH of 12.0.

[0153] Next, the nitrile rubber latex (X1) obtained above and the catalyst aqueous solution prepared above were added to an autoclave so that the palladium content relative to the dry weight of the rubber contained in the nitrile rubber latex (X1) obtained above became 2800 ppm by weight, and hydrogenation was carried out at a hydrogen pressure of 3 MPa and a temperature of 50°C for 6 hours to obtain a hydrogenated nitrile rubber latex (L1) (solid content concentration: 13.5% by weight). The composition of the hydrogenated nitrile rubber contained in the obtained hydrogenated nitrile rubber latex (L1) was 20.5% by weight of acrylonitrile units, 45.5% by weight of 1,3-butadiene units (including saturated portions), 5.0% by weight of mono-n-butyl maleate units, and 29% by weight of n-butyl acrylate units, and the iodine value was 7.

[0154] [Example 1]

[0155] To the hydrogenated nitrile rubber latex (L1) obtained in Production Example 1, 0.8 parts of 4,6-bis(octylthiomethyl)-o-cresol (manufactured by BASF Japan, trade name "Irganox 1520L", molecular weight: 424.8) was added as an emulsion dispersed in 1.5 parts of a 20 wt % aqueous solution of sodium alkylbenzene sulfonate, relative to 100 parts by weight of the solid content in the latex, thereby preparing a latex to which a hindered phenol antioxidant was added (solid content concentration: 13.5 wt %).

[0156] Next, the latex to which the hindered phenol antioxidant prepared above was added was adjusted to pH 3.6 with a sulfuric acid aqueous solution (solid content concentration: 13.5 wt%), and then a sodium chloride aqueous solution (concentration: 25 wt%) and water vapor were used as a coagulation liquid to form a slurry. Figure 1 The extruder 1 shown coagulates, washes, dehydrates, and dries the hydrogenated nitrile rubber latex (L1), thereby recovering the solid hydrogenated nitrile rubber.

[0157] As the extruder 1, a twin-shaft intermeshing screw extruder rotating in the same direction is used in the following state: two screws (cylinder diameter = 47 mm, L / Da = 63) 5,5 are arranged in parallel in the barrel 3, and these screws 5,5 are driven to rotate in the same direction, and the ridge of one screw is meshed with the valley of the other screw, and the valley of one screw is meshed with the ridge of the other screw.

[0158] In addition, the axial screw length L1 of the area corresponding to the coagulation area 100 is 931 mm, the axial screw length L2 of the area corresponding to the drainage area 102 is 161 mm, the axial screw length L3 of the area corresponding to the cleaning and dehydration area 104 is 678 mm, and the axial screw length L4 of the area corresponding to the drying area 106 is set to 1058 mm.

[0159] In Example 1, the following screw structures were used as two screws 5, 5, and the set temperatures of the barrel blocks were: barrel blocks 31-39: 90°C, barrel blocks 40-43: 130-140°C, and barrel blocks 44-48: 120-130°C.

[0160] The screw structure of barrel block 38 is "BAAAAC"

[0161] Screw structure of barrel block 40 "DDDDAA"

[0162] Furthermore, "A" indicates a forward kneading disc, "B" indicates a neutral kneading disc, "C" indicates a reverse kneading disc, and "D" indicates a full-flight screw. Specifically, the screw structure in the portion corresponding to the wash water feed port 380 is composed of multiple kneading discs, and the proportion of the screw kneading discs in the barrel block 38 (the proportion in the longitudinal direction) is 100%.

[0163] Then, hydrogenated nitrile rubber latex (L1) adjusted to a pH of 3.6 was continuously supplied from feed port 320 provided in barrel block 32 of the extruder 1 having such a structure at a rate of 370 kg / hr (50 kg / hr in terms of hydrogenated nitrile rubber). Simultaneously, sodium chloride aqueous solution (coagulant concentration: 25 wt%) was continuously supplied from feed port 321 provided in barrel block 32 at a rate of 120 kg / hr, and steam was continuously supplied from feed port 322 provided in barrel block 32 at a pressure of 0.35 MPa and a rate of 80 kg / hr. Specifically, the concentration of the coagulant relative to the total amount of the slurry (amount of sodium chloride / amount of slurry formed from the total amount supplied) when passing through feed port 321 was set to 5.8 wt%, and the amount of sodium chloride was set to 60 parts per 100 parts of hydrogenated nitrile rubber. Simultaneously, wash water at 60°C was continuously supplied at a rate of 350 L / hr from a wash water inlet 380 provided in the barrel block 38. The extruder 1 was operated at a screw speed of 280 rpm, thereby continuously coagulating, washing, dehydrating, and drying the hydrogenated nitrile rubber latex (L1). Solid hydrogenated nitrile rubber was continuously recovered at a rate of 48 kg / hr. The water pressure of the wash water supplied from the wash water inlet 380 provided in the barrel block 38 was measured using a water pressure gauge provided near the wash water inlet 380 and was found to be 4.0 MPa. Furthermore, in Example 1, Q (hydrogenated nitrile rubber supply rate) / N (screw speed) = 0.18.

[0164] Next, the above-described method was used to evaluate the contamination of the exhaust port 430 during the recovery operation of the hydrogenated nitrile rubber using the extruder 1. The Mooney viscosity (polymer Mooney), the maximum chemiluminescence intensity, and the amount of volatile components of the recovered hydrogenated nitrile rubber were measured. The results are shown in Table 1.

[0165] Next, using a Banbury mixer, 100 parts of MT carbon (manufactured by Kenkabo Co., Ltd., trade name "Thermax MT", Thermal Black), 20 parts of tri(2-ethylhexyl) trimellitate (manufactured by Adecco Co., Ltd., trade name "ADK CIZER C-8", plasticizer), 1.5 parts of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine (manufactured by Ouchi Shinko Chemical Co., Ltd., trade name "NOCRAC CD", antioxidant), 1 part of stearic acid, and 1 part of polyoxyethylene alkyl ether phosphate (manufactured by Toho Chemical Co., Ltd., trade name "Phosphanol RL210", processing aid) were added to 100 parts of the recovered hydrogenated nitrile rubber, and mixed at 50°C for 5 minutes. Then, the obtained mixture was transferred to a roller at 50°C, and 4 parts of a mixture of a dicyclohexylamine salt of ethylene glycol and a long-chain alcohol (manufactured by Ouchi Shinko Chemical Industry Co., Ltd., trade name "NOC Master EGS", composed of 80% by weight of a dicyclohexylamine salt of ethylene glycol and 20% by weight of a long-chain alcohol (1-tetradecanol, 1-hexadecanol, 1-octadecanol), a basic crosslinking accelerator) and 2.2 parts of hexamethylenediamine carbamate (manufactured by DuPont Dow Elastomers, trade name "Diak #1", a polyamine crosslinking agent belonging to the aliphatic polyamine class) were added and kneaded to obtain a rubber composition.

[0166] The obtained rubber composition was then used to measure Mooney viscosity (composite Mooney) and evaluate mold contamination properties according to the above-mentioned methods.

[0167] [Example 2]

[0168] When adding 4,6-bis(octylthiomethyl)-o-cresol as a hindered phenol antioxidant to the hydrogenated nitrile rubber latex (L1) obtained in Example 1, it was not added in the form of an emulsion but directly. Except for this, a latex (solid content concentration: 13.5% by weight) with the addition of the hindered phenol antioxidant was obtained in the same manner as in Example 1. Then, using the obtained latex with the addition of the hindered phenol antioxidant, after adjusting the pH to 3.6 using an aqueous sulfuric acid solution (solid content concentration: 13.5% by weight), the hydrogenated nitrile rubber latex (L1) was coagulated, washed, dehydrated and dried in the same manner as in Example 1, thereby continuously recovering the solid hydrogenated nitrile rubber at a rate of 48 kg / hr. In addition, the recovered hydrogenated nitrile rubber was evaluated in the same manner as in Example 1, and a rubber composition was prepared in the same manner as in Example 1 and evaluated in the same manner. The results are shown in Table 1.

[0169] [Example 3]

[0170] To the hydrogenated nitrile rubber latex (L1) obtained in Production Example 1, an emulsion of 4,6-bis(octylthiomethyl)-o-cresol prepared in the same manner as in Example 1 was added so that the amount of 4,6-bis(octylthiomethyl)-o-cresol as a hindered phenol antioxidant was 1.5 parts per 100 parts of the solid content in the latex. A latex (solid content concentration: 13.5 wt%) with the hindered phenol antioxidant added was obtained in the same manner as in Example 1. The latex with the hindered phenol antioxidant added was then adjusted to pH 3.6 using an aqueous sulfuric acid solution (solid content concentration: 13.5 wt%). The hydrogenated nitrile rubber latex (L1) was coagulated, washed, dehydrated, and dried in the same manner as in Example 1, and solid hydrogenated nitrile rubber was continuously recovered at a rate of 48 kg / hr. The recovered hydrogenated nitrile rubber was evaluated in the same manner as in Example 1, and a rubber composition was prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0171] [Example 4]

[0172] To the hydrogenated nitrile rubber latex (L1) obtained in Production Example 1, an emulsion of 4,6-bis(octylthiomethyl)-o-cresol prepared in the same manner as in Example 1 was added so that the amount of 4,6-bis(octylthiomethyl)-o-cresol as a hindered phenol antioxidant was 2.2 parts per 100 parts of the solid content in the latex. A latex (solid content concentration: 13.5 wt%) with the hindered phenol antioxidant added was obtained in the same manner as in Example 1. The obtained latex with the hindered phenol antioxidant added was then adjusted to pH 3.6 using an aqueous sulfuric acid solution (solid content concentration: 13.5 wt%). The hydrogenated nitrile rubber latex (L1) was coagulated, washed, dehydrated, and dried in the same manner as in Example 1, and solid hydrogenated nitrile rubber was continuously recovered at a rate of 48 kg / hr. The recovered hydrogenated nitrile rubber was evaluated in the same manner as in Example 1, and a rubber composition was prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0173] [Example 5]

[0174] To the hydrogenated nitrile rubber latex (L1) obtained in Production Example 1, an emulsion of 4,6-bis(octylthiomethyl)-o-cresol prepared in the same manner as in Example 1 was added so that the amount of 4,6-bis(octylthiomethyl)-o-cresol as a hindered phenol antioxidant was 0.3 parts per 100 parts of the solid content in the latex. A latex (solid content concentration: 13.5 wt%) with the hindered phenol antioxidant added was obtained in the same manner as in Example 1. The obtained latex with the hindered phenol antioxidant added was then adjusted to pH 3.6 using an aqueous sulfuric acid solution (solid content concentration: 13.5 wt%). The hydrogenated nitrile rubber latex (L1) was coagulated, washed, dehydrated, and dried in the same manner as in Example 1, and solid hydrogenated nitrile rubber was continuously recovered at a rate of 48 kg / hr. The recovered hydrogenated nitrile rubber was evaluated in the same manner as in Example 1, and a rubber composition was prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0175] [Example 6]

[0176] To the hydrogenated nitrile rubber latex (L1) obtained in Production Example 1, 0.8 parts of pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (manufactured by BASF Japan, trade name "Irganox 1010", molecular weight: 1177.6) was added as an emulsion dispersed in 1.5 parts of a 20% by weight aqueous solution of sodium alkylbenzenesulfonate per 100 parts by weight of the solid content of the latex, thereby preparing a latex to which the hindered phenol antioxidant was added (solid content concentration: 13.5% by weight). The obtained latex to which the hindered phenol antioxidant was added was then adjusted to pH 3.6 using an aqueous sulfuric acid solution (solid content concentration: 13.5% by weight). The hydrogenated nitrile rubber latex (L1) was coagulated, washed, dehydrated, and dried in the same manner as in Example 1, and solid hydrogenated nitrile rubber was continuously recovered at a rate of 48 kg / hr. Furthermore, the recovered hydrogenated nitrile rubber was used and evaluated in the same manner as in Example 1. A rubber composition was also prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0177] [Example 7]

[0178] The hydrogenated nitrile rubber latex (L1) was coagulated, washed, dehydrated, and dried in the same manner as in Example 1, using the latex to which the hindered phenol antioxidant was added, obtained in the same manner as in Example 1. Solid hydrogenated nitrile rubber was continuously recovered at a rate of 48 kg / hr, except that the screw speed of extruder 1 was changed to 330 rpm (i.e., Q / N = 0.15). Furthermore, the recovered hydrogenated nitrile rubber was evaluated in the same manner as in Example 1, and a rubber composition was prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0179] [Comparative Example 1]

[0180] The hydrogenated nitrile rubber latex (L1) obtained in Production Example 1 was used without adding a hindered phenol-based antioxidant. After adjusting the pH to 3.6 with an aqueous sulfuric acid solution (solids concentration: 13.5 wt%), the hydrogenated nitrile rubber latex (L1) was coagulated, washed, dehydrated, and dried in the same manner as in Example 1. Solid hydrogenated nitrile rubber was continuously recovered at a rate of 48 kg / hr. The recovered hydrogenated nitrile rubber was evaluated in the same manner as in Example 1. A rubber composition was also prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0181] [Comparative Example 2]

[0182] To the hydrogenated nitrile rubber latex (L1) obtained in Production Example 1, 0.6 parts of 2,5-di-tert-amylhydroquinone (molecular weight: 250.4) as a polyphenol antioxidant was added in the form of an emulsion dispersed in 1.25 parts of a 20% by weight aqueous solution of sodium alkylbenzenesulfonate relative to 100 parts by weight of the solid content in the latex, thereby preparing a latex to which a polyphenol antioxidant was added (solid content concentration: 13.5% by weight). Then, using the obtained latex to which the polyphenol antioxidant was added, after adjusting the pH to 3.6 using an aqueous sulfuric acid solution (solid content concentration: 13.5% by weight), the supply rate of the hydrogenated nitrile rubber latex was changed to 326 kg / hr (44 kg / hr in terms of hydrogenated nitrile rubber conversion), and the screw speed of the extruder 1 was changed to 200 rpm (i.e., Q / N=0.22). Otherwise, the hydrogenated nitrile rubber latex (L1) was coagulated, washed, dehydrated, and dried in the same manner as in Example 1, thereby continuously recovering solid hydrogenated nitrile rubber at a rate of 42 kg / hr. Furthermore, the recovered hydrogenated nitrile rubber was evaluated in the same manner as in Example 1, and a rubber composition was prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0183] [Comparative Example 3]

[0184] When adding 2,5-di-tert-amylhydroquinone as a polyphenol antioxidant to the hydrogenated nitrile rubber latex (L1) obtained in Manufacturing Example 1, it was not added directly in the state of an emulsion. In addition, a latex (solid content concentration: 13.5 weight %) to which a polyphenol antioxidant was added was obtained in the same manner as in Comparative Example 2. Then, using the obtained latex to which a polyphenol antioxidant was added, after adjusting to pH=3.6 using an aqueous solution of sulfuric acid (solid content concentration: 13.5 weight %), the coagulation, cleaning, dehydration and drying of the hydrogenated nitrile rubber latex (L1) were carried out in the same manner as in Comparative Example 2, thereby continuously recovering solid hydrogenated nitrile rubber at a rate of 42 kg / hr. In addition, using the recovered hydrogenated nitrile rubber, the same evaluation as in Example 1 was performed, and a rubber composition was prepared in the same manner as in Example 1 and evaluated in the same manner. The results are shown in Table 1.

[0185] [Comparative Example 4]

[0186] A latex (solids concentration: 13.5 wt%) containing a hindered phenol antioxidant was obtained in the same manner as in Example 1, except that an emulsion of 4,6-bis(octylthiomethyl)-o-cresol prepared in the same manner as in Example 1 was added to the hydrogenated nitrile rubber latex (L1) obtained in Production Example 1 so that the amount of 4,6-bis(octylthiomethyl)-o-cresol added as a hindered phenol antioxidant was 4.0 parts relative to 100 parts of the solids content in the latex. The latex (L1) containing a hindered phenol antioxidant was adjusted to pH 3.6 using an aqueous sulfuric acid solution (solids concentration: 13.5 wt%) and the screw speed of the extruder 1 was changed to 200 rpm (i.e., Q / N = 0.25). The hydrogenated nitrile rubber latex (L1) was coagulated, washed, dehydrated, and dried in the same manner as in Example 1, thereby continuously recovering solid hydrogenated nitrile rubber at a rate of 48 kg / hr. Furthermore, the recovered hydrogenated nitrile rubber was used and evaluated in the same manner as in Example 1. A rubber composition was also prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0187] [Comparative Example 5]

[0188] To the hydrogenated nitrile rubber latex (L1) obtained in Production Example 1, 0.6 parts of 2,6-di-tert-butyl-4-methylphenol (manufactured by Ouchi Shinko Chemical Industry Co., Ltd., trade name "NOCRAC 200," molecular weight: 220.4) as a monophenolic antioxidant was directly added relative to 100 parts by weight of the solid content in the latex, thereby preparing a latex to which the monophenolic antioxidant was added (solid content concentration: 13.5 wt%). The resulting latex to which the monophenolic antioxidant was added was then adjusted to pH = 3.6 using an aqueous sulfuric acid solution (solid content concentration: 13.5 wt%) and the screw speed of the extruder 1 was changed to 200 rpm (i.e., Q / N = 0.25). The hydrogenated nitrile rubber latex (L1) was coagulated, washed, dehydrated, and dried in the same manner as in Example 1, thereby continuously recovering solid hydrogenated nitrile rubber at a rate of 48 kg / hr. Furthermore, the recovered hydrogenated nitrile rubber was used and evaluated in the same manner as in Example 1. A rubber composition was also prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0189] [Table 1]

[0190]

[0191] As shown in Table 1, when a hindered phenol-based antioxidant having a molecular weight of 300 to 3000 is added to a hydrogenated nitrile rubber latex at a ratio of 0.1 to 3 parts per 100 parts by weight of the hydrogenated nitrile rubber in the latex and the hydrogenated nitrile rubber is supplied to an extruder and a solid hydrogenated nitrile rubber is recovered from the hydrogenated nitrile rubber latex, contamination of the extruder can be suppressed, the Mooney viscosity (composite Mooney) when the rubber composition is prepared is low, and processability is excellent. Furthermore, contamination of the mold during molding and cross-linking can be effectively suppressed (Examples 1 to 7).

[0192] On the other hand, when hydrogenated nitrile rubber latex was supplied to an extruder without adding a hindered phenol antioxidant having a molecular weight of 300 to 3000, the Mooney viscosity (composite Mooney) of the resulting rubber composition was high and processability was poor (Comparative Example 1).

[0193] When an antioxidant other than the hindered phenol antioxidant with a molecular weight of 300 to 3000 was used instead of the hindered phenol antioxidant with a molecular weight of 300 to 3000, contamination of the extruder occurred, resulting in poor productivity (Comparative Examples 2, 3, and 5).

[0194] Furthermore, when the amount of the hindered phenol-based antioxidant having a molecular weight of 300 to 3000 is excessive, mold contamination occurs during molding and cross-linking, resulting in poor productivity (Comparative Example 4).

Claims

1. A method for producing nitrile rubber, comprising: continuously feeding nitrile rubber latex and a coagulant to an extruder having a screw disposed inside a barrel so as to be freely rotatable, thereby recovering nitrile rubber from the nitrile rubber latex; In the method for producing nitrile rubber, the nitrile rubber latex is supplied to the extruder in a state where the nitrile rubber latex contains a hindered phenol-based antioxidant having a molecular weight of 300 to 3000 in a ratio of 0.1 to 3 parts by weight relative to 100 parts by weight of the nitrile rubber. When the hindered phenol-based antioxidant is added to the nitrile rubber latex, the hindered phenol-based antioxidant is added to the nitrile rubber latex in the form of an emulsion.

2. The method for producing nitrile rubber according to claim 1, wherein The maximum value of the chemiluminescence intensity of the nitrile rubber discharged from the extruder and recovered from the nitrile rubber latex measured in accordance with JIS K7351:2018 is 2000 to 25000 counts / second.

3. The method for producing nitrile rubber according to claim 1 or 2, wherein: The nitrile rubber contains 5 to 60 weight percent of α,β-ethylenically unsaturated nitrile monomer units, and the iodine value of the nitrile rubber is 120 or less.

4. The method for producing nitrile rubber according to claim 1 or 2, wherein The ratio Q / N [kg / (hr·rpm)] of the supply rate Q [kg / hr] of the nitrile rubber to the extruder to the rotation speed N [rpm] of the screw of the extruder is 0.22 kg / (hr·rpm) or less.

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