Nitrile group-containing copolymer rubber, rubber composition, and crosslinked rubber

Abstract

Provided is a nitrile group-containing copolymer rubber which contains an acrylonitrile unit (a), an α,β-ethylenically unsaturated nitrile monomer unit (b) excluding acrylonitrile, and a conjugated diene monomer unit (c), and which has an iodine value of 120 or less. In all monomer units, the contained proportion of the total of the acrylonitrile unit (a) and the α,β-ethylenically unsaturated nitrile monomer unit (b) excluding acrylonitrile is 1-50 wt%. The contained ratio of the acrylonitrile unit (a) and the α,β-ethylenically unsaturated nitrile monomer unit (b) excluding acrylonitrile as expressed in terms of the weight ratio 'contained amount of acrylonitrile unit (a): contained amount of: α,β-ethylenically unsaturated nitrile monomer unit (b) excluding acrylonitrile' is 10:90 to 90:10.

Description

Nitrile group-containing copolymer rubber, rubber composition and cross-linked rubber

[0001] The present invention relates to a nitrile group-containing copolymer rubber capable of giving a cross-linked rubber product excellent in heat resistance, oil resistance, and oil-induced hardening resistance in a heated environment (specifically, small changes in glass transition temperature and hardness when immersed in oil containing a polycyclic condensed aromatic compound in a heated environment), and to a rubber composition and a cross-linked rubber product obtained using such a nitrile group-containing copolymer rubber.

[0002] Saturated nitrile group-containing copolymer rubbers, typified by hydrogenated acrylonitrile-butadiene copolymer rubber, are superior in heat resistance, oil resistance, ozone resistance, etc. to general nitrile group-containing copolymer rubbers, such as acrylonitrile-butadiene copolymer rubber, which have many carbon-carbon unsaturated bonds in the main chain structure, and are therefore suitably used for rubber parts such as automotive seals, hoses, tubes, etc. Meanwhile, in recent years, automotive rubber parts are also required to have excellent oil resistance as well as excellent resistance to hardening in oil.

[0003] For example, Patent Document 1 discloses a nitrile rubber composition containing 100 parts by weight of a nitrile group-containing highly saturated copolymer rubber (A) containing 14% by weight or more but less than 21% by weight of α,β-ethylenically unsaturated nitrile monomer units and having an iodine value of 120 or less, 50 to 90 parts by weight of a filler (B), and 0 to 29.9 parts by weight of an adipate ester plasticizer and / or an ether ester plasticizer (C). The cross-linkable nitrile rubber composition disclosed in Patent Document 1 makes it possible to obtain a cross-linked rubber product having excellent oil-hardening resistance. On the other hand, rubber parts such as automotive seals, hoses, and tubes are often used in high-temperature environments. Therefore, from the perspective of being suitable for such applications, the rubber materials used for these rubber parts may be required to have excellent oil-hardening resistance in a heated environment, more specifically, excellent oil-hardening resistance after storage in a heated environment. In contrast, although Patent Document 1 examines oil resistance and resistance to hardening in oil, it does not examine resistance to hardening in oil under a heated environment.

[0004] International Publication No. 2017 / 047571

[0005] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a nitrile group-containing copolymer rubber which has good physical properties in normal state and is capable of giving a cross-linked rubber product which is excellent in heat resistance, oil resistance, and oil-induced hardening resistance in a heated environment (specifically, small changes in glass transition temperature and hardness when immersed in oil containing a polycyclic condensed aromatic compound after storage in a heated environment). Another object of the present invention is to provide a rubber composition and a cross-linked rubber product obtained using such a nitrile group-containing copolymer rubber.

[0006] As a result of intensive research into achieving the above object, the present inventors have found that the above object can be achieved by a nitrile group-containing copolymer rubber having an iodine value of 120 or less, which contains, as nitrile group-containing monomer units, acrylonitrile units and α,β-ethylenically unsaturated nitrile monomer units other than acrylonitrile in a predetermined content ratio, and have thereby completed the present invention.

[0007] That is, according to the present invention, there is provided a nitrile group-containing copolymer rubber which contains acrylonitrile units (a), α,β-ethylenically unsaturated nitrile monomer units other than acrylonitrile (b), and conjugated diene monomer units (c), and has an iodine value of 120 or less, wherein the total content of the acrylonitrile units (a) and the α,β-ethylenically unsaturated nitrile monomer units other than acrylonitrile (b) in all monomer units is 1 to 50% by weight, and the content ratio of the acrylonitrile units (a) to the α,β-ethylenically unsaturated nitrile monomer units other than acrylonitrile (b) is 10:90 to 90:10 in terms of the weight ratio of "content of acrylonitrile units (a) : content of α,β-ethylenically unsaturated nitrile monomer units other than acrylonitrile (b)". In the nitrile group-containing copolymer rubber of the present invention, the number of carbon atoms excluding cyano groups in the α,β-ethylenically unsaturated nitrile units other than acrylonitrile (b) is preferably 2 to 5. In the nitrile group-containing copolymer rubber of the present invention, the total content of the acrylonitrile units (a) and the α,β-ethylenically unsaturated nitrile monomer units other than acrylonitrile (b) in all monomer units is preferably 10 to 45% by weight. In the nitrile group-containing copolymer rubber of the present invention, the iodine value is preferably 80 or less. In the nitrile group-containing copolymer rubber of the present invention, the content ratio of the acrylonitrile units (a) to the α,β-ethylenically unsaturated nitrile monomer units other than acrylonitrile (b) is preferably 20:80 to 80:20 in terms of the weight ratio of "content of acrylonitrile units (a) : content of α,β-ethylenically unsaturated nitrile monomer units other than acrylonitrile (b)". In the nitrile group-containing copolymer rubber of the present invention, the content ratio of the acrylonitrile units (a) to the α,β-ethylenically unsaturated nitrile monomer units (b) other than acrylonitrile is preferably 25:75 to 75:25 in terms of the weight ratio of "content of acrylonitrile units (a):content of α,β-ethylenically unsaturated nitrile monomer units (b) other than acrylonitrile."In the nitrile group-containing copolymer rubber of the present invention, the content of the conjugated diene monomer units (c) is preferably 10 to 90% by weight.

[0008] According to the present invention, there is also provided a rubber composition obtained by blending the nitrile group-containing copolymer rubber of the present invention with a crosslinking agent. Furthermore, according to the present invention, there is also provided a crosslinked rubber obtained by crosslinking the rubber composition of the present invention.

[0009] According to the present invention, it is possible to provide a nitrile group-containing copolymer rubber which has good physical properties in normal state and is capable of giving a cross-linked rubber product which is excellent in heat resistance, oil resistance, and oil intermediate hardening resistance in a heated environment (specifically, small changes in glass transition temperature and hardness when immersed in oil containing a polycyclic fused aromatic compound after storage in a heated environment), as well as a rubber composition and a cross-linked rubber product obtained using such a nitrile group-containing copolymer rubber.

[0010] <Nitrile Group-Containing Copolymer Rubber> The nitrile group-containing copolymer rubber of the present invention is a nitrile group-containing copolymer rubber which contains acrylonitrile units (a), α,β-ethylenically unsaturated nitrile monomer units other than acrylonitrile (b), and conjugated diene monomer units (c), and has an iodine value of 120 or less, wherein the total content of the acrylonitrile units (a) and the α,β-ethylenically unsaturated nitrile monomer units other than acrylonitrile (b) in all monomer units is 1 to 50% by weight, and the content ratio of the acrylonitrile units (a) to the α,β-ethylenically unsaturated nitrile monomer units other than acrylonitrile (b) is 10:90 to 90:10 in terms of the weight ratio of "content of acrylonitrile units (a) : content of α,β-ethylenically unsaturated nitrile monomer units other than acrylonitrile (b)".

[0011] The nitrile group-containing copolymer rubber of the present invention contains, as nitrile group-containing monomer units, acrylonitrile units (a) and α,β-ethylenically unsaturated nitrile monomer units other than acrylonitrile (b). The α,β-ethylenically unsaturated nitrile monomer other than acrylonitrile constituting the α,β-ethylenically unsaturated nitrile monomer units other than acrylonitrile (b) is not limited as long as it is an α,β-ethylenically unsaturated compound (excluding acrylonitrile) having a nitrile group, and examples thereof include α-halogenoacrylonitriles such as α-chloroacrylonitrile and α-bromoacrylonitrile; and α-alkylacrylonitriles such as methacrylonitrile and ethacrylonitrile. Among these, α,β-ethylenically unsaturated compounds having 2 to 5 carbon atoms excluding cyano groups are preferred, α-alkylacrylonitriles are more preferred, and methacrylonitrile is particularly preferred. A plurality of these α,β-ethylenically unsaturated nitrile monomers other than acrylonitrile may be used in combination.

[0012] In the nitrile group-containing copolymer rubber of the present invention, the total content of the acrylonitrile units (a) and the α,β-ethylenically unsaturated nitrile monomer units (b) other than acrylonitrile is 1 to 50% by weight, preferably 10 to 45% by weight, more preferably 15 to 42% by weight, even more preferably 20 to 40% by weight, and particularly preferably 26 to 36% by weight. If the total content of the acrylonitrile units (a) and the α,β-ethylenically unsaturated nitrile monomer units (b) other than acrylonitrile is too low, the resulting cross-linked rubber may have poor oil resistance, whereas if it is too high, the oil resistance to cure in oil may be reduced.

[0013] In addition, the content ratio of the acrylonitrile units (a) to the α,β-ethylenically unsaturated nitrile monomer units (b) other than acrylonitrile in the nitrile group-containing copolymer rubber of the present invention, expressed as a weight ratio of "content of acrylonitrile units (a) : content of the α,β-ethylenically unsaturated nitrile monomer units (b) other than acrylonitrile", is 10:90 to 90:10, preferably 12:88 to 88:12, more preferably 15:85 to 85:15, still more preferably 20:80 to 80:20, still more preferably 25:75 to 75:25, and particularly preferably 30:70 to 60:40. If the content ratio of the acrylonitrile units (a) is too small, the obtained cross-linked rubber product will be inferior in tensile strength and oil resistance, whereas if the content ratio of the α,β-ethylenically unsaturated nitrile monomer units (b) other than acrylonitrile is too small, the obtained cross-linked rubber product will be inferior in oil resistance and oil-in-oil cure resistance in a heated environment.

[0014] The content of the acrylonitrile units (a) in the nitrile group-containing copolymer rubber of the present invention may be in the above-mentioned range in relation to the α,β-ethylenically unsaturated nitrile monomer units (b) other than acrylonitrile, and is preferably 1 to 45% by weight, more preferably 5 to 40% by weight, even more preferably 10 to 37.5% by weight, and particularly preferably 12 to 25% by weight, based on the total monomer units. The content of the α,β-ethylenically unsaturated nitrile monomer units (b) other than acrylonitrile in the nitrile group-containing copolymer rubber of the present invention may be in the above-mentioned range in relation to the acrylonitrile units (a), and is preferably 1 to 45% by weight, more preferably 5 to 40% by weight, even more preferably 10 to 37.5% by weight, and particularly preferably 12 to 25% by weight, based on the total monomer units. By setting the content of the acrylonitrile unit (a) and the content of the α,β-ethylenically unsaturated nitrile monomer unit (b) other than acrylonitrile within the above ranges, the obtained cross-linked rubber product can be made more excellent in heat resistance, oil resistance, and oil-in-heat cure resistance in a heated environment.

[0015] The conjugated diene monomer constituting the conjugated diene monomer unit (c) is preferably 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, or chloroprene, more preferably 1,3-butadiene or isoprene, and particularly preferably 1,3-butadiene. The conjugated diene monomer may be used alone or in combination of two or more types.

[0016] The content of the conjugated diene monomer units (c) (including hydrogenated portions) in the nitrile group-containing copolymer rubber of the present invention is preferably 10 to 90% by weight, more preferably 20 to 80% by weight, still more preferably 30 to 70% by weight, and particularly preferably 35 to 65% by weight, based on the total weight of the monomer units. By setting the content of the conjugated diene monomer units within the above range, the obtained cross-linked rubber product can be made excellent in rubber elasticity while maintaining good heat resistance and chemical resistance stability.

[0017] Furthermore, the nitrile group-containing copolymer rubber of the present invention preferably further contains a carboxyl group-containing monomer unit (d) in addition to the acrylonitrile unit (a), the α,β-ethylenically unsaturated nitrile monomer unit (b) other than acrylonitrile, and the conjugated diene monomer unit (c). By further containing the carboxyl group-containing monomer unit (d), a carboxyl group can be introduced into the nitrile group-containing copolymer rubber of the present invention.

[0018] The carboxyl group-containing monomer constituting the carboxyl group-containing monomer unit (d) is not particularly limited as long as it is a monomer having one or more unsubstituted (free) carboxyl groups that are not esterified, etc., and examples thereof include α,β-ethylenically unsaturated monocarboxylic acid monomers, α,β-ethylenically unsaturated polycarboxylic acid monomers, and α,β-ethylenically unsaturated dicarboxylic acid monoester monomers. The carboxyl group-containing monomer also includes 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 they form carboxyl groups by cleavage of the acid anhydride group after copolymerization.

[0019] Examples of the α,β-ethylenically unsaturated monocarboxylic acid monomer include acrylic acid, methacrylic acid, ethylacrylic acid, crotonic acid, and cinnamic acid.

[0020] Examples of the α,β-ethylenically unsaturated polycarboxylic acid monomer include butenedioic acids such as fumaric acid and maleic acid, itaconic acid, citraconic acid, mesaconic acid, glutaconic acid, allylmalonic acid, and teraconic acid. Examples of the anhydrides of α,β-unsaturated polycarboxylic acids include maleic anhydride, itaconic anhydride, and citraconic anhydride.

[0021] 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; monoalkyl fumarate esters such as monomethyl fumarate, monoethyl fumarate, monopropyl fumarate, and mono-n-butyl fumarate; monocycloalkyl fumarate esters such as monocyclopentyl fumarate, monocyclohexyl fumarate, and monocycloheptyl fumarate; monoalkylcycloalkyl fumarate esters such as monomethylcyclopentyl fumarate and monoethylcyclohexyl fumarate; monoalkyl citraconic acid esters such as monomethyl citraconic acid, monoethyl citraconic acid, monopropyl citraconic acid, and mono-n-butyl citraconic acid; monocycloalkyl citraconic acid esters such as monocyclopentyl citraconic acid, monocyclohexyl citraconic acid, and monocycloheptyl citraconic acid; monoalkyl citraconic acid cycloalkyl esters such as monomethylcyclopentyl citraconic acid and monoethylcyclohexyl citraconic acid; monoalkyl itaconic acid esters such as monomethyl itaconic acid, monoethyl itaconic acid, monopropyl itaconic acid, and mono-n-butyl itaconic acid; monocycloalkyl itaconic acid esters such as monocyclopentyl itaconic acid, monocyclohexyl itaconic acid, and monocycloheptyl itaconic acid; and monoalkyl itaconic acid cycloalkyl esters such as monomethylcyclopentyl itaconic acid and monoethylcyclohexyl itaconate.

[0022] The carboxyl group-containing monomer may be used alone or in combination of two or more kinds. Among these, α,β-ethylenically unsaturated monocarboxylic acid monomers are preferred, acrylic acid and methacrylic acid are more preferred, and methacrylic acid is particularly preferred, as these monomers will exhibit more pronounced effects of the present invention.

[0023] The content of the carboxyl group-containing monomer units (d) in the nitrile group-containing copolymer rubber of the present invention is preferably 0.1 to 10% by weight, more preferably 0.5 to 8% by weight, and even more preferably 1 to 5% by weight, based on the total monomer units. By setting the content of the carboxyl group-containing monomer units within the above range, the mechanical properties of the obtained cross-linked rubber can be made better.

[0024] The nitrile group-containing copolymer rubber of the present invention may contain α,β-ethylenically unsaturated monocarboxylic acid ester monomer units (e) in addition to the acrylonitrile units (a), the α,β-ethylenically unsaturated nitrile monomer units (b) other than acrylonitrile, the conjugated diene monomer units (c), and the carboxyl group-containing monomer units (d) contained as needed.

[0025] The α,β-ethylenically unsaturated monocarboxylic acid ester monomer constituting the α,β-ethylenically unsaturated monocarboxylic acid ester monomer unit (e) 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 or α,β-ethylenically unsaturated monocarboxylic acid alkoxyalkyl ester monomers are preferred, and α,β-ethylenically unsaturated monocarboxylic acid alkoxyalkyl ester monomers are more preferred. By incorporating the α,β-ethylenically unsaturated monocarboxylic acid ester monomer unit (e), the cold resistance of the resulting cross-linked rubber can be improved.

[0026] The alkyl ester monomer of α,β-ethylenically unsaturated monocarboxylic acid preferably has an alkyl group having 3 to 10 carbon atoms, more preferably an alkyl group having 3 to 8 carbon atoms, and even more preferably an alkyl group having 4 to 6 carbon atoms.

[0027] Specific examples of the α,β-ethylenically unsaturated monocarboxylic acid alkyl ester monomer 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; alkyl acrylate cycloalkyl ester monomers such as methylcyclopentyl acrylate, ethylcyclopentyl acrylate, and methylcyclohexyl acrylate; and methacrylates such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, n-pentyl methacrylate, and n-octyl methacrylate. Examples thereof include acrylic acid alkyl ester monomers; methacrylic acid cycloalkyl ester monomers such as cyclopentyl methacrylate, cyclohexyl methacrylate, and cyclopentyl methacrylate; methacrylic acid alkyl cycloalkyl ester monomers such as methylcyclopentyl methacrylate, ethylcyclopentyl methacrylate, and methylcyclohexyl methacrylate; crotonate alkyl ester monomers such as propyl crotonate, n-butyl crotonate, and 2-ethylhexyl crotonate; crotonate cycloalkyl ester monomers such as cyclopentyl crotonate, cyclohexyl crotonate, and cyclooctyl crotonate; and crotonate alkyl cycloalkyl ester monomers such as methylcyclopentyl crotonate and methylcyclohexyl crotonate.

[0028] Furthermore, as the α,β-ethylenically unsaturated monocarboxylic acid alkoxyalkyl ester monomer, those having an alkoxyalkyl group with 2 to 8 carbon atoms are preferred, those having an alkoxyalkyl group with 2 to 6 carbon atoms are more preferred, and those having an alkoxyalkyl group with 2 to 4 carbon atoms are even more preferred.

[0029] Specific examples of the α,β-ethylenically unsaturated monocarboxylic acid alkoxyalkyl ester monomer include alkoxyalkyl acrylate monomers such as methoxymethyl acrylate, methoxyethyl acrylate, methoxybutyl acrylate, ethoxymethyl acrylate, ethoxyethyl acrylate, ethoxypropyl acrylate, ethoxydodecyl acrylate, n-propoxyethyl acrylate, i-propoxyethyl acrylate, n-butoxyethyl acrylate, i-butoxyethyl acrylate, t-butoxyethyl acrylate, methoxypropyl acrylate, and methoxybutyl acrylate; alkoxyalkyl methacrylate monomers such as dimethyl methacrylate, methoxyethyl methacrylate, methoxybutyl methacrylate, ethoxymethyl methacrylate, ethoxyethyl methacrylate, ethoxypentyl methacrylate, n-propoxyethyl methacrylate, i-propoxyethyl methacrylate, n-butoxyethyl methacrylate, i-butoxyethyl methacrylate, t-butoxyethyl methacrylate, methoxypropyl methacrylate, methoxybutyl methacrylate, methoxy-polyethylene glycol (meth)acrylate, and methoxy-polyethylene glycol (meth)acrylate; and the like.

[0030] Among these α,β-ethylenically unsaturated monocarboxylic acid ester monomers, acrylic acid alkyl ester monomers and acrylic acid alkoxyalkyl ester monomers are preferred, n-butyl acrylate and methoxyethyl acrylate are more preferred, and methoxyethyl acrylate is particularly preferred, from the viewpoint of making the effects of the present invention more remarkable. Furthermore, these α,β-ethylenically unsaturated monocarboxylic acid ester monomers can also be used in combination of two or more kinds.

[0031] The content of the α,β-ethylenically unsaturated monocarboxylic acid ester monomer units in the nitrile group-containing copolymer rubber of the present invention is preferably 0 to 60% by weight, more preferably 0 to 50% by weight, even more preferably 0 to 40% by weight, and still more preferably 8 to 30% by weight, based on the total weight of the monomer units. By setting the content of the α,β-ethylenically unsaturated monocarboxylic acid ester monomer units within the above range, the cold resistance of the obtained cross-linked rubber can be more appropriately improved.

[0032] The nitrile group-containing copolymer rubber of the present invention may contain, in addition to the acrylonitrile units (a), the α,β-ethylenically unsaturated nitrile monomer units (b) other than acrylonitrile, the conjugated diene monomer units (c), and the carboxyl group-containing monomer units (d) and the α,β-ethylenically unsaturated monocarboxylic acid ester monomer units (e) which are contained as needed, units of other monomers copolymerizable with the monomers forming these units. Examples of such other monomers include α,β-ethylenically unsaturated monocarboxylic acid ester monomers other than those mentioned above, ethylene, α-olefin monomers, aromatic vinyl monomers, fluorine-containing vinyl monomers, copolymerizable antioxidants, etc.

[0033] Examples of the α,β-ethylenically unsaturated monocarboxylic acid ester monomer other than those mentioned above include (meth)acrylic acid esters having a cyanoalkyl group having 2 to 12 carbon atoms, such as α-cyanoethyl acrylate, α-cyanoethyl methacrylate, and cyanobutyl methacrylate; (meth)acrylic acid esters having a hydroxyalkyl group having 1 to 12 carbon atoms, such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and 2-hydroxyethyl methacrylate; and (meth)acrylic acid esters having a fluoroalkyl group having 1 to 12 carbon atoms, such as trifluoroethyl acrylate and tetrafluoropropyl methacrylate.

[0034] The α-olefin monomer preferably has 3 to 12 carbon atoms, and examples thereof include propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene.

[0035] Examples of the aromatic vinyl monomer include styrene, α-methylstyrene, and vinylpyridine.

[0036] Examples of the fluorine-containing vinyl monomer include fluoroethyl vinyl ether, fluoropropyl vinyl ether, o-trifluoromethylstyrene, vinyl pentafluorobenzoate, difluoroethylene, and tetrafluoroethylene.

[0037] 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, N-phenyl-4-(4-vinylbenzyloxy)aniline, and 4,4'-di-(α,α-dimethylbenzyl)diphenylamine.

[0038] A plurality of types of these copolymerizable other monomers may be used in combination. The content of the units of the other monomers is preferably 50% by weight or less, more preferably 40% by weight or less, and even more preferably 10% by weight or less, based on the total monomer units constituting the nitrile group-containing copolymer rubber.

[0039] The iodine value of the nitrile group-containing copolymer rubber of the present invention is not more than 120, preferably not more than 80, more preferably not more than 50, even more preferably not more than 30, particularly preferably not more than 20, and most preferably not more than 12. If the iodine value of the nitrile group-containing copolymer rubber is too high, the heat resistance and ozone resistance of the obtained cross-linked rubber may decrease.

[0040] The polymer Mooney viscosity (ML1+4, 100°C) of the nitrile group-containing copolymer rubber of the present invention is preferably 10 to 200, more preferably 15 to 150, still more preferably 15 to 100, and particularly preferably 30 to 80. By setting the polymer Mooney viscosity of the nitrile group-containing copolymer rubber within the above range, when a rubber composition is formed from the nitrile group-containing copolymer rubber, the mechanical properties of the resulting cross-linked rubber can be further improved while maintaining good processability of the rubber composition.

[0041] The method for producing the nitrile group-containing copolymer rubber of the present invention is not particularly limited, but it can be produced by copolymerizing the above-mentioned monomers and, if necessary, hydrogenating the carbon-carbon double bonds in the resulting copolymer. The polymerization method is not particularly limited, and known emulsion polymerization methods or solution polymerization methods may be used, but emulsion polymerization methods are preferred from the viewpoint of industrial productivity. During emulsion polymerization, commonly used polymerization auxiliary materials can be used in addition to an emulsifier, a polymerization initiator, and a molecular weight modifier.

[0042] The emulsifier is 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, oleic acid, and linolenic acid, alkylbenzenesulfonates such as sodium dodecylbenzenesulfonate, higher alcohol sulfates, and alkyl sulfosuccinates; and copolymerizable emulsifiers such as sulfoesters of α,β-unsaturated carboxylic acids, sulfate esters of α,β-unsaturated carboxylic acids, and sulfoalkylaryl ethers. The amount of emulsifier added is preferably 0.1 to 10 parts by weight, and more preferably 0.5 to 5 parts by weight, per 100 parts by weight of the monomers used in the polymerization.

[0043] The polymerization initiator is not particularly limited as long as it is a radical initiator, and examples thereof include inorganic peroxides such as potassium persulfate, sodium persulfate, ammonium persulfate, potassium perphosphate, and hydrogen peroxide; organic peroxides such as t-butyl peroxide, cumene hydroperoxide, p-menthane hydroperoxide, t-butylcumyl peroxide, acetyl peroxide, isobutyryl peroxide, octanoyl peroxide, dibenzoyl peroxide, 3,5,5-trimethylhexanoyl peroxide, and t-butylperoxyisobutyrate; and azo compounds such as azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, azobiscyclohexanecarbonitrile, and methyl azobisisobutyrate. These polymerization initiators can be used alone or in combination of two or more. Inorganic or organic peroxides are preferred as the polymerization initiator. When a peroxide is used as the polymerization initiator, it can also be used in combination with a reducing agent to form a redox polymerization initiator. The reducing agent is not particularly limited, but examples thereof include compounds containing reduced metal ions such as ferrous sulfate and cuprous naphthenate; sulfinates such as sodium hydroxymethanesulfinate; sulfites such as sodium sulfite, potassium sulfite, sodium hydrogen sulfite, aldehyde sodium hydrogen sulfite, and potassium hydrogen sulfite; etc. The amount of the polymerization initiator to be added is preferably 0.01 to 2 parts by weight based on 100 parts by weight of the monomers used in the polymerization.

[0044] The molecular weight modifier is not particularly limited, but examples thereof include mercaptans such as t-dodecyl mercaptan, n-dodecyl mercaptan, and octyl mercaptan; halogenated hydrocarbons such as carbon tetrachloride, methylene chloride, and methylene bromide; α-methylstyrene dimer; and sulfur-containing compounds such as tetraethylthiuram disulfide, dipentamethylenethiuram disulfide, and diisopropylxanthogen disulfide. These may be used alone or in combination of two or more.

[0045] Water is usually used as the medium for emulsion polymerization, and the amount of water is preferably 80 to 500 parts by weight, more preferably 80 to 300 parts by weight, per 100 parts by weight of the monomers used in the polymerization.

[0046] In emulsion polymerization, if necessary, it is possible to use additional polymerization auxiliary materials such as stabilizers, dispersants, pH adjusters, oxygen scavengers, particle size adjusters, etc. When these are used, the types and amounts used are not particularly limited.

[0047] The obtained copolymer may be hydrogenated (hydrogenation reaction) as needed. Hydrogenation may be carried out by a known method, such as an oil phase hydrogenation method in which the copolymer latex obtained by emulsion polymerization is coagulated and then hydrogenated in an oil phase, or an aqueous phase hydrogenation method in which the obtained copolymer latex is hydrogenated as is.

[0048] When hydrogenation is carried out by the oil phase hydrogenation method, preferably, the copolymer latex prepared by the above emulsion polymerization is dissolved in an organic solvent through salting out or coagulation with alcohol, filtration, drying, and then hydrogenation reaction (oil phase hydrogenation method) is carried out, and the obtained hydrogenated product is poured into a large amount of water, coagulated, filtration, and drying, thereby obtaining the nitrile group-containing copolymer rubber of the present invention.

[0049] For coagulation of the latex by salting out, known coagulants such as sodium chloride, calcium chloride, aluminum sulfate, etc. can be used. Furthermore, instead of coagulation by salting out, coagulation may be carried out using an alcohol such as methanol. The solvent for the oil phase hydrogenation method is not particularly limited as long as it is a liquid organic compound that dissolves the copolymer obtained by emulsion polymerization, but preferred examples include benzene, chlorobenzene, toluene, xylene, hexane, cyclohexane, tetrahydrofuran, methyl ethyl ketone, ethyl acetate, cyclohexanone, and acetone.

[0050] As the catalyst for the oil phase hydrogenation method, any known selective hydrogenation catalyst can be used without limitation, with palladium-based catalysts and rhodium-based catalysts being preferred, and palladium-based catalysts (such as palladium acetate, palladium chloride, and palladium hydroxide) being more preferred. Two or more of these may be used in combination, in which case it is preferable to use a palladium-based catalyst as the main active component. These catalysts are usually used by being supported on a carrier. Examples of carriers include silica, silica-alumina, alumina, diatomaceous earth, and activated carbon. The amount of catalyst used is preferably 10 to 5,000 ppm by weight, more preferably 100 to 3,000 ppm by weight, based on the copolymer.

[0051] Alternatively, when hydrogenation is carried out by aqueous phase hydrogenation, the copolymer latex prepared by the emulsion polymerization is preferably diluted with water as necessary and then subjected to hydrogenation reaction. The aqueous phase hydrogenation method includes a direct aqueous phase hydrogenation method in which hydrogen is supplied to a reaction system in the presence of a hydrogenation catalyst to carry out hydrogenation, and an indirect aqueous phase hydrogenation method in which hydrogenation is carried out by reduction in the presence of an oxidizing agent, a reducing agent, and an activator, and among these, the direct aqueous phase hydrogenation method is preferred.

[0052] In the aqueous phase direct hydrogenation method, the concentration of the copolymer in the aqueous phase (concentration in the latex state) is preferably 40% by weight or less to prevent aggregation. The hydrogenation catalyst is not particularly limited as long as it is a compound that is not easily decomposed by 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, dichloro(cyclooctadiene)palladium, dichloro(norbornadiene)palladium, and ammonium hexachloropalladate(IV); iodides such as palladium iodide; and palladium sulfate dihydrate. Among these, palladium salts of carboxylic acids, dichloro(norbornadiene)palladium, and ammonium hexachloropalladate(IV) are particularly preferred. The amount of hydrogenation catalyst used may be determined as appropriate, but is preferably 5 to 6,000 ppm by weight, more preferably 10 to 4,000 ppm by weight, based on the copolymer obtained by polymerization.

[0053] In the aqueous phase direct hydrogenation method, the hydrogenation catalyst in the latex is removed after the hydrogenation reaction is completed. For example, an adsorbent such as activated carbon or ion exchange resin is added to adsorb the hydrogenation catalyst under stirring, and then the latex is filtered or centrifuged. It is also possible to leave the hydrogenation catalyst in the latex without removing it.

[0054] In the aqueous layer direct hydrogenation method, the latex thus obtained after the hydrogenation reaction is subjected to salting out, coagulation with alcohol, filtration, drying, etc., to obtain the nitrile group-containing copolymer rubber of the present invention. In this case, the steps of filtration and drying following the coagulation can be carried out by known methods, respectively.

[0055] <Rubber Composition> The rubber composition of the present invention contains the above-described nitrile group-containing copolymer rubber of the present invention and a crosslinking agent.

[0056] The crosslinking agent is not particularly limited, but examples thereof include sulfur-based crosslinking agents, organic peroxide crosslinking agents, and polyamine-based crosslinking agents.

[0057] Examples of sulfur-based crosslinking agents include sulfur such as powdered sulfur, sulfur flowers, precipitated sulfur, colloidal sulfur, surface-treated sulfur, and insoluble sulfur; sulfur-containing compounds such as sulfur chloride, sulfur dichloride, morpholine disulfide, alkylphenol disulfide, dibenzothiazyl disulfide, N,N'-dithio-bis(hexahydro-2H-azenopine-2), phosphorus-containing polysulfides, and polymeric polysulfides; and sulfur-donating compounds such as tetramethylthiuram disulfide, selenium dimethyldithiocarbamate, and 2-(4'-morpholinodithio)benzothiazole. These may be used alone or in combination.

[0058] Examples of organic peroxide crosslinking agents include dicumyl peroxide, cumene hydroperoxide, t-butylcumyl peroxide, paramenthane hydroperoxide, di-t-butyl peroxide, 1,3-bis(t-butylperoxyisopropyl)benzene, 1,4-bis(t-butylperoxyisopropyl)benzene, 1,1-di-t-butylperoxy-3,3-trimethylcyclohexane, 4,4-bis-(t-butylperoxy)-n-butylvalerate, 2,5-dimethyl-2,5-di-t-butylperoxyhexane, 2,5-dimethyl-2,5-di-t-butylperoxyhexyne-3, 1,1-di-t-butylperoxy-3,5,5-trimethylcyclohexane, p-chlorobenzoyl peroxide, t-butylperoxyisopropyl carbonate, t-butylperoxybenzoate, etc. These may be used alone or in combination.

[0059] The polyamine-based crosslinking agent is not particularly limited as long as it is a compound having two or more amino groups or a compound that becomes a compound having two or more amino groups upon crosslinking. However, it is also preferred that the polyamine-based crosslinking agent is a compound in which multiple hydrogen atoms of an aliphatic hydrocarbon or aromatic hydrocarbon are converted into an amino group or a hydrazide structure (-CONHNH ２ wherein CO represents a carbonyl group.) and compounds which become such compounds upon crosslinking are preferred.

[0060] Specific examples of polyamine-based crosslinking agents include aliphatic polyamines such as hexamethylenediamine, hexamethylenediamine carbamate, N,N-dicinnamylidene-1,6-hexanediamine, tetramethylenepentamine, and hexamethylenediamine cinnamaldehyde adduct; 4,4-methylenedianiline, m-phenylenediamine, 4,4-diaminodiphenyl ether, 3,4-diaminodiphenyl ether, 4,4-(m-phenylenediisopropylidene)dianiline, 4,4-(p-phenylenediisopropylidene)dianiline, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 4,4-diaminobenzanilide, 4,4-bis(4-aminophenoxy)biphenyl, m-xylylenediamine, p-xylylenediamine, and 1,3,5-benzenetriamine. Aromatic polyamines: isophthalic dihydrazide, terephthalic dihydrazide, phthalic dihydrazide, 2,6-naphthalenedicarboxylic dihydrazide, naphthalene dihydrazide, oxalic dihydrazide, malonic dihydrazide, succinic dihydrazide, glutamic dihydrazide, adipic dihydrazide, pimelic dihydrazide, suberic dihydrazide, azelaic dihydrazide and polyhydrazides such as acetonedicarboxylic acid dihydrazide, sebacic acid dihydrazide, brassylic acid dihydrazide, dodecanedioic acid dihydrazide, acetonedicarboxylic acid dihydrazide, fumaric acid dihydrazide, maleic acid dihydrazide, itaconic acid dihydrazide, trimellitic acid dihydrazide, 1,3,5-benzenetricarboxylic acid dihydrazide, aconitic acid dihydrazide, and pyromellitic acid dihydrazide. Among these, aliphatic polyamines and aromatic polyamines are preferred, with hexamethylenediamine carbamate and 2,2-bis[4-(4-aminophenoxy)phenyl]propane being more preferred, and hexamethylenediamine carbamate being particularly preferred, in view of the ability to further enhance the effects of the present invention.

[0061] 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, relative to 100 parts by weight of the nitrile group-containing copolymer rubber. By setting the content of the crosslinking agent within the above range, the mechanical properties of the obtained crosslinked rubber can be made better.

[0062] Furthermore, the rubber composition of the present invention preferably contains a filler, since this can further improve the mechanical properties of the resulting cross-linked rubber. The filler is not particularly limited and may be any filler commonly used in the rubber field, and both organic and inorganic fillers can be used, but inorganic fillers are preferred because of their high compounding effect.

[0063] The inorganic filler may be any one that is commonly used in rubber compounding, and examples thereof include carbon black, silica, clay, alumina, aluminum hydroxide, magnesium oxide, magnesium hydroxide, calcium oxide, calcium hydroxide, aluminum magnesium oxide, titanium oxide, kaolin, pyrophyllite, bentonite, talc, attapulgite, magnesium calcium silicate, aluminum silicate, magnesium silicate, calcium silicate, and crystalline aluminosilicate. Among these, carbon black, silica, and clay are preferably used, and silica and clay are more preferred, with silica being particularly preferred, from the viewpoint that the obtained cross-linked rubber product can have excellent oil resistance during hardening in a heated environment. The inorganic fillers may be used alone or in combination of two or more types.

[0064] The carbon black may be any of those commonly used in rubber compounding, such as furnace black, acetylene black, thermal black, channel black, and graphite.

[0065] Examples of silica include, but are not limited to, natural silica such as quartz powder and silica stone powder; synthetic silica such as silicic anhydride (silica gel, aerosil, etc.) and silicic acid hydrate; and among these, synthetic silica is preferred.

[0066] The clay is not particularly limited as long as it is a natural mineral whose main component is hydrated aluminum silicate, and examples thereof include montmorillonite, pyrophyllite, kaolinite, halloysite, and sericite.

[0067] The inorganic filler may be one that has been subjected to a coupling treatment with a silane coupling agent, an aluminum-based coupling agent, a titanium-based coupling agent, or the like, or a surface modification treatment with a higher fatty acid or a metal salt thereof, a higher fatty acid derivative such as an ester or amide, a surfactant, etc. In this case, the inorganic filler may be one that has been subjected to a surface modification treatment in advance, or a mode may be adopted in which a surface modifier such as a coupling treatment is compounded with the inorganic filler when preparing the rubber composition, thereby performing a surface modification treatment on the inorganic filler.

[0068] The silane coupling agent is not particularly limited, but examples thereof include sulfur-containing silane coupling agents such as γ-mercaptopropyltrimethoxysilane, mercaptomethyltrimethoxysilane, mercaptomethyltriethoxysilane, bis(3-triethoxysilylpropyl)tetrasulfane, and bis(3-triethoxysilylpropyl)disulfane; γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, mercaptomethyltriethoxysilane, bis(3-triethoxysilylpropyl)tetrasulfane, and bis(3-triethoxysilylpropyl)disulfane; epoxy group-containing silane coupling agents such as N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, N-phenyl-3-aminopropyl amino group-containing silane coupling agents such as γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltris(β-methoxyethoxy)silane, γ-methacryloxypropylmethyldimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, γ-methacryloxypropyltriethoxysilane, and γ-acryloxypropyltrimethoxysilane; (meth)acryloxy group-containing silane coupling agents such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(β-methacryloxypropyltris(β-methoxyethoxy)silane, γ-methacryloxypropylmethyldimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, γ-methacryloxypropyltriethoxysilane, and γ-acryloxypropyltrimethoxysilane; vinyl group-containing silane coupling agents such as vinyltrichlorosilane, vinyltriacetoxysilane, etc.; chloropropyl group-containing silane coupling agents such as 3-chloropropyltrimethoxysilane; isocyanate group-containing silane coupling agents such as 3-isocyanatepropyltriethoxysilane; styryl group-containing silane coupling agents such as p-styryltrimethoxysilane; ureido group-containing silane coupling agents such as 3-ureidopropyltriethoxysilane; allyl group-containing silane coupling agents such as diallyldimethylsilane;Examples of suitable coupling agents include alkoxy group-containing silane coupling agents such as tetraethoxysilane, phenyl group-containing silane coupling agents such as diphenyldimethoxysilane, fluoro group-containing silane coupling agents such as trifluoropropyltrimethoxysilane, and alkyl group-containing silane coupling agents such as isobutyltrimethoxysilane and cyclohexylmethyldimethoxysilane. Examples of suitable coupling agents include acetoalkoxyaluminum diisopropylate, aluminum diisopropoxymonoethylacetoacetate, aluminum trisethylacetoacetate, and aluminum trisacetylacetonate. Examples of titanate coupling agents include isopropyl triisostearoyl titanate, isopropyl tris(dioctyl pyrophosphate) titanate, isopropyl tri(N-aminoethyl-aminoethyl) titanate, tetraoctyl bis(ditridecyl phosphite) titanate, tetra(2,2-diallyloxymethyl-1-butyl)bis(ditridecyl)phosphite titanate, bis(dioctyl pyrophosphate)oxyacetate titanate, bis(dioctyl pyrophosphate)ethylene titanate, tetraisopropyl bis(dioctyl phosphite) titanate, and isopropyl triisostearoyl titanate. These may be used alone or in combination of two or more.

[0069] The content of the inorganic filler in the rubber composition of the present invention is not particularly limited, but is preferably 1 to 200 parts by weight, more preferably 5 to 150 parts by weight, even more preferably 10 to 100 parts by weight, and particularly preferably 20 to 50 parts by weight, relative to 100 parts by weight of the nitrile group-containing copolymer rubber. By setting the content of the inorganic filler within the above range, the obtained cross-linked rubber product can be made to have excellent oil resistance during cure in a heated environment.

[0070] In addition to the above, the rubber composition of the present invention may contain compounding agents commonly used in the rubber field, for example, metal oxides such as zinc oxide and magnesium oxide, metal salts of α,β-ethylenically unsaturated carboxylic acids such as zinc methacrylate and zinc acrylate, plasticizers, co-crosslinking agents, crosslinking aids, crosslinking retarders, antioxidants, antioxidants, light stabilizers, scorch inhibitors such as primary amines, activators such as diethylene glycol, processing aids, slip agents, adhesives, lubricants, flame retardants, antifungal agents, acid acceptors, antistatic agents, pigments, foaming agents, etc. The amount of these compounding agents to be added is not particularly limited as long as it does not impair the purpose and effects of the present invention, and they may be added in amounts appropriate to the purpose of addition.

[0071] Furthermore, the rubber composition of the present invention may contain rubbers other than the above-described nitrile group-containing copolymer rubber of the present invention, provided that the effects of the present invention are not impaired. Examples of rubbers other than the nitrile group-containing copolymer rubber of the present invention include acrylic rubber, ethylene-acrylic acid copolymer rubber, fluororubber, styrene-butadiene copolymer rubber, polybutadiene rubber, ethylene-propylene copolymer rubber, ethylene-propylene-diene terpolymer rubber, epichlorohydrin rubber, urethane rubber, chloroprene rubber, silicone rubber, fluorosilicone rubber, chlorosulfonated polyethylene rubber, natural rubber, and polyisoprene rubber. When a rubber other than the nitrile group-containing copolymer rubber of the present invention is contained, the amount of the rubber contained therein is preferably 30 parts by weight or less, more preferably 20 parts by weight or less, and particularly preferably 10 parts by weight or less, per 100 parts by weight of the nitrile group-containing copolymer rubber of the present invention.

[0072] The rubber composition of the present invention is prepared by mixing the above-mentioned components preferably in a non-aqueous system. There is no limitation on the method for preparing the rubber composition of the present invention, but it can usually be prepared by first kneading the components excluding the crosslinking agent and heat-unstable components (for example, crosslinking aid) in a mixer such as a Banbury mixer, an intermixer, or a kneader, then transferring to a roll or the like, adding the crosslinking agent and heat-unstable components, and secondly kneading.

[0073] <Rubber Cross-Linked Product> The rubber cross-linked product of the present invention is obtained by cross-linking the above-described cross-linkable nitrile rubber composition of the present invention. The rubber cross-linked product of the present invention can be produced by using the cross-linkable nitrile rubber composition of the present invention, molding it into a desired shape using a molding machine such as an extruder, injection molding machine, compressor, or roll, and heating it to cause a cross-linking reaction, thereby fixing the shape as a cross-linked product. In this case, cross-linking may be carried out after molding in advance, or simultaneously with molding. The molding temperature is usually 10 to 200°C, preferably 25 to 120°C. The cross-linking temperature is usually 100 to 200°C, preferably 130 to 190°C, and the cross-linking time is usually 1 minute to 24 hours, preferably 2 minutes to 1 hour.

[0074] Depending on the shape, size, etc. of the cross-linked product, even if the surface is cross-linked, the inside may not be sufficiently cross-linked, so secondary cross-linking may be carried out by further heating. As the heating method, a general method used for cross-linking rubber, such as press heating, steam heating, oven heating, or hot air heating, may be appropriately selected.

[0075] The cross-linked rubber product of the present invention obtained in this manner is obtained using the rubber composition of the present invention described above, and has good physical properties in normal state, and is excellent in heat resistance, oil resistance, and oil-in-oil hardening resistance in a heated environment (specifically, small changes in glass transition temperature and hardness when immersed in oil containing a polycyclic condensed aromatic compound after storage in a heated environment). In particular, according to the present invention, with regard to oil-in-oil hardening resistance in a heated environment, even when the product is immersed in oil containing a polycyclic condensed aromatic compound after storage in a heated environment, in which oil-in-oil hardening is likely to occur relatively significantly, the occurrence of oil hardening can be effectively suppressed.

[0076] Therefore, by making use of these properties, the cross-linked rubber of the present invention can be used in a wide range of applications, including O-rings, packings, diaphragms, oil seals, shaft seals, bearing seals, wellhead seals, shock absorber seals, seals for pneumatic equipment, seals for sealing fluorocarbons or fluorohydrocarbons or carbon dioxide used in the cooling devices of air conditioners and compressors for refrigeration units of air conditioners, seals for sealing supercritical carbon dioxide or subcritical carbon dioxide used as a cleaning medium in precision cleaning, seals for rolling devices (rolling bearings, automotive hub units, automotive water pumps, linear guide devices, ball screws, etc.), valves and valve seats, BOP (Blow Out Pump), etc. various sealing materials such as intake manifold gaskets attached to the joint between the intake manifold and the cylinder head, cylinder head gaskets attached to the joint between the cylinder block and the cylinder head, rocker cover gaskets attached to the joint between the rocker cover and the cylinder head, oil pan gaskets attached to the joint between the oil pan and the cylinder block or the transmission case, gaskets for fuel cell separators attached between a pair of housings sandwiching a unit cell having a positive electrode, an electrolyte plate and a negative electrode, gaskets for the top cover of hard disk drives, and various other gaskets; printing rolls, steelmaking rolls, papermaking rolls, industrial rolls, office rolls, etc. various rolls such as rolls for machines; various belts such as flat belts (film core flat belts, cord flat belts, laminated flat belts, single-piece flat belts, etc.), V-belts (wrapped V-belts, raw edge V-belts, etc.), V-ribbed belts (single V-ribbed belts, double V-ribbed belts, wrapped V-ribbed belts, rubber-backed V-ribbed belts, upper cog V-ribbed belts, etc.), CVT belts, timing belts, toothed belts, conveyor belts; various hoses such as fuel hoses, turbo air hoses, oil hoses, radiator hoses, heater hoses, water hoses, vacuum brake hoses, control hoses, air conditioner hoses, brake hoses, power steering hoses, air hoses, marine hoses, risers, flow lines, etc.;The cross-linked rubber product of the present invention can be used in a wide range of applications, including various boots such as CVJ boots, propeller shaft boots, constant velocity joint boots, and rack and pinion boots; damping rubber parts such as cushioning materials, dynamic dampers, rubber couplings, air springs, vibration isolators, and clutch facings; dust covers, automotive interior materials, friction materials, tires, coated cables, shoe soles, electromagnetic wave shields, adhesives such as adhesives for flexible printed circuit boards, fuel cell separators, and the electronics field. In particular, the cross-linked rubber product of the present invention has excellent oil resistance to intermediate cure in a heated environment (specifically, small changes in glass transition temperature and hardness when immersed in oil containing a polycyclic fused aromatic compound after storage in a heated environment), and is therefore particularly suitable for use in applications where it is used in contact with fuel oil containing a polycyclic aromatic compound in a high-temperature environment.

[0077] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. In the following, "parts" are by weight unless otherwise specified. The methods for testing or evaluating physical properties and characteristics are as follows.

[0078] <Rubber Composition> The content ratio of each monomer unit constituting the nitrile group-containing copolymer rubber was measured by the following method. That is, the content ratio of methacrylic acid units was calculated by adding 100 mL of 2-butanone to 0.2 g of a 2 mm square nitrile group-containing copolymer rubber and stirring for 16 hours, then adding 20 mL of ethanol and 10 mL of water, and titrating with thymolphthalein as an indicator at room temperature with a 0.02 N aqueous ethanol solution of potassium hydroxide while stirring to determine the number of moles of carboxyl groups per 100 g of nitrile group-containing copolymer rubber, and converting the determined number of moles to the amount of methacrylic acid units. The content ratios of 1,3-butadiene units and saturated butadiene units were calculated by measuring the iodine value (according to JIS K 6235:2006) of the nitrile group-containing copolymer rubber before and after the hydrogenation reaction. The content ratios of methacrylonitrile units and acrylonitrile units were calculated by measuring the nitrogen content in the nitrile group-containing copolymer rubber by Dumas method and identifying the methacrylonitrile units and acrylonitrile units by pyrolysis gas chromatography in accordance with JIS K6451-1: 2016. The content ratio of 2-methoxyethyl acrylate units was calculated from the content ratios of methacrylic acid units, 1,3-butadiene units, saturated butadiene units, methacrylonitrile units, and acrylonitrile units determined above.

[0079] <Iodine Value> The iodine value of the nitrile group-containing copolymer rubber was measured in accordance with JIS K 6235:2006.

[0080] <Mooney Viscosity (Polymer Mooney)> The Mooney viscosity (polymer Mooney) of the nitrile group-containing copolymer rubber was measured in accordance with JIS K6300:2013 (unit: [ML1+4, 100°C]).

[0081] <Normal State Physical Properties (Tensile Strength, Elongation, Hardness)> The rubber composition was placed in a mold measuring 15 cm in length, 15 cm in width, and 0.2 cm in depth, and press-molded at 170°C for 20 minutes while applying a pressure of 10 MPa to obtain a sheet-like cross-linked rubber product. The obtained cross-linked rubber product was then transferred to a gear oven and subjected to secondary cross-linking at 170°C for 4 hours, and the obtained cross-linked rubber product was punched out with a JIS No. 3 dumbbell to prepare a test specimen. The obtained test specimens were then used to measure the tensile strength and elongation at break of the cross-linked rubber product in accordance with JIS K6251:2017, and the hardness of the cross-linked rubber product using a durometer hardness tester (Type A) in accordance with JIS K6253:2012.

[0082] <Heat Resistance Test> A heat resistance test was carried out in accordance with JIS K6257:2017 using a sheet-like cross-linked product obtained in the same manner as in the evaluation of the normal physical properties described above. Specifically, the obtained sheet-like cross-linked rubber product was held in a Geer oven under conditions of a temperature of 150°C for 504 hours, and then the tensile strength and elongation at break were measured in the same manner as in the normal physical properties described above, and the rate of change in tensile strength and the elongation after the heat resistance test were determined. The larger the value of the rate of change in tensile strength and the larger the elongation after the heat resistance test, the more excellent the heat resistance can be judged to be. The rate of change in tensile strength was calculated according to the following formula: Rate of change in tensile strength (%) = {(tensile strength after heat resistance test - tensile strength before heat resistance test) / tensile strength before heat resistance test} x 100

[0083] <Oil Resistance Test (IRM903)> Using a sheet-like cross-linked product obtained in the same manner as in the evaluation of the normal physical properties described above, an oil resistance test was performed in accordance with JIS K6258:2016 by immersing the product in test lubricating oil No. 3 (product name "IRM903", manufactured by Japan Sun Oil Co., Ltd.) at a temperature of 150°C for 504 hours. The volume of the cross-linked rubber product before and after immersion in the test lubricating oil was measured to calculate the volume change rate after the oil resistance test, and the elongation at break was measured in the same manner as in the normal physical properties described above to determine the elongation after the oil resistance test. The smaller the volume change rate after the oil resistance test, and the greater the elongation after the oil resistance test, the more excellent the oil resistance can be determined. The volume change rate after the oil resistance test was calculated according to the following formula: Volume change rate after oil resistance test (%) = {(volume after oil resistance test - volume before oil resistance test) / volume before oil resistance test} x 100

[0084] <Fuel Oil Resistance Test> Using a sheet-like cross-linked product obtained in the same manner as in the evaluation of the normal physical properties described above, a fuel oil resistance test was carried out in accordance with JIS K6258:2016 by immersing the obtained sheet-like cross-linked rubber product in a test fuel oil (Fuel B:ethanol=74:26 (volume ratio) (Fuel B is a mixture of isooctane:toluene=70:30 (volume ratio))) adjusted to 150°C for 168 hours. Then, for the cross-linked rubber product that had been subjected to the fuel oil resistance test, the tensile strength and elongation at break were measured in the same manner as in the normal physical properties described above, and the rate of change in tensile strength and the elongation after the fuel oil resistance test were determined. It can be determined that the larger the value of the rate of change in tensile strength and the greater the elongation after the fuel oil resistance test, the more excellent the oil resistance (fuel oil resistance). The rate of change in tensile strength was calculated according to the following formula. Change rate of tensile strength (%)={(tensile strength after fuel oil resistance test−tensile strength before fuel oil resistance test) / tensile strength before fuel oil resistance test}×100

[0085] <Oil Resistance Hardening Test in a Heated Environment (Changes in Glass Transition Temperature and Hardness Upon Immersion in a Fuel Oil Containing a Polycyclic Polycyclic Aromatic Compound)> A phenanthrene-containing test fuel oil was prepared by dissolving 10% by weight of phenanthrene in a mixture of Fuel C (a mixture of isooctane:toluene = 50:50 (volume ratio)) and ethanol (Fuel C:ethanol = 80:20 (volume ratio)). Furthermore, the glass transition temperature was measured using a sheet-like cross-linked product obtained in the same manner as in the evaluation of the normal physical properties described above. The glass transition temperature was measured in accordance with JIS K7121:2012 using a heat-flux differential scanning calorimeter (device: X-DSC7000, manufactured by SII Nanotechnologies Inc.) at a heating rate of 20°C / min. Then, using the sheet-like cross-linked product, in accordance with JIS K6257:2017, it was heated by being held in a gear oven at a temperature of 150°C for 504 hours, and then the heated cross-linked rubber product was immersed in the phenanthrene-containing test fuel oil prepared above at 60°C for 70 hours. Thereafter, the cross-linked rubber product was removed from the phenanthrene-containing test fuel oil, dried at 120°C for 3 hours, and further left to stand at room temperature for 24 hours. Thereafter, the glass transition temperature was measured in the same manner as above, and the hardness was measured in the same manner as the normal physical properties above, and the change in glass transition temperature and the change in hardness were determined according to the following formula. It can be determined that the smaller the change in glass transition temperature and the smaller the change in hardness, the better the oil resistance to intermediate cure in a heated environment. Change in glass transition temperature (°C) = glass transition temperature after oil resistance intermediate cure test - glass transition temperature before oil resistance intermediate cure test Change in hardness = hardness after oil resistance intermediate cure test - hardness before oil resistance intermediate cure test

[0086] Example 1: A metal bottle was charged with 180 parts ion-exchanged water, 25 parts of a 10 wt% aqueous solution of sodium dodecylbenzenesulfonate, 7 parts of methacrylonitrile, 21 parts of acrylonitrile, 30 parts of 2-methoxyethyl acrylate, 2 parts of methacrylic acid, and 0.5 parts of t-dodecyl mercaptan (molecular weight modifier), in that order. The gas inside was replaced with nitrogen three times, and then 40 parts of 1,3-butadiene was added. The metal bottle was kept at 5°C, and 0.1 parts of cumene hydroperoxide (polymerization initiator), a reducing agent, and an appropriate amount of a chelating agent were added. The polymerization reaction was carried out for 16 hours while rotating the metal bottle. The polymerization reaction was terminated by adding 0.1 parts of a 1 wt% aqueous solution of hydroquinone (polymerization terminator), and the residual monomer was removed using a rotary evaporator at 60°C to obtain a copolymer rubber latex (solids concentration: approximately 30 wt%).

[0087] Then, the copolymer rubber latex obtained above and a palladium catalyst (a solution obtained by mixing an aqueous solution of 1 wt % palladium chloride with an equal weight of ion-exchanged water) were added to an autoclave so that the palladium content relative to the dry weight of the copolymer rubber would be 3,500 ppm by weight, and a hydrogenation reaction was carried out at a hydrogen pressure of 3.0 MPa and a temperature of 50°C for 7 hours, thereby obtaining a latex of nitrile group-containing copolymer rubber (A-1).

[0088] Next, a double volume of methanol was added to the obtained latex to coagulate it, and then vacuum dried at 60°C for 12 hours to obtain a nitrile group-containing copolymer rubber (A-1). The composition of each monomer unit of the obtained nitrile group-containing copolymer rubber (A-1) was 8% by weight of methacrylonitrile units, 21% by weight of acrylonitrile units, 22% by weight of 2-methoxyethyl acrylate units, 2.1% by weight of methacrylic acid units, and 46.9% by weight of 1,3-butadiene units (including hydrogenated portions), and the iodine value was 8 and the polymer Mooney viscosity [ML1+4, 100°C] was 60.

[0089] Then, 100 parts of the obtained nitrile group-containing copolymer rubber (A-1) was mixed with 30 parts of silica (trade name "Carplex 1120", manufactured by Evonik Corporation), 5 parts of tri-2-ethylhexyl trimellitate (trade name "Adeka Cizer C-8", manufactured by ADEKA Corporation, plasticizer), and 1 part of polyoxyethylene alkyl ether phosphate ester (trade name "Phosphanol RL210 (manufactured by Toho Chemical Industry Co., Ltd., emulsifier), 1 part of stearic acid, 1.5 parts of 4,4'-di-(α,α-dimethylbenzyl)diphenylamine (trade name "Nocrac CD" (manufactured by Ouchi Shinko Chemical Industry Co., Ltd., antioxidant), 1.5 parts of a zinc salt of 2-mercaptobenzimidazole (trade name "Nocrac MBZ" (manufactured by Ouchi Shinko Chemical Industry Co., Ltd., antioxidant), 1.5 parts of a silane coupling agent (trade name "Silanogran HVS" (manufactured by Kettlitz Corporation), and 7 parts of zinc diacrylate (trade name "Dymalink 633" (manufactured by Cray Valley)) were blended and mixed at 50°C for 5 minutes. Next, the obtained mixture was transferred to a roll at 50°C, and 10 parts of 1,3-bis(t-butylperoxyisopropyl)benzene (trade name "Vulcup 40KE", manufactured by Hercules Pharmaceuticals, organic peroxide crosslinking agent, 40% product) was blended and kneaded to obtain a rubber composition.

[0090] The rubber compositions thus obtained were used to measure their normal physical properties (tensile strength, elongation, and hardness) and to carry out heat resistance tests, oil resistance tests (IRM903), fuel oil resistance tests, and oil cure resistance tests in a heated environment, according to the methods described above. The results are shown in Table 1.

[0091] Examples 2 to 4 Nitrile group-containing copolymer rubbers (A-2), (A-3), and (A-4) were obtained in the same manner as in Example 1, except that the amounts of methacrylonitrile, acrylonitrile, 2-methoxyethyl acrylate, methacrylic acid, and 1,3-butadiene used were changed to the amounts shown in Table 1. Rubber compositions were prepared in the same manner and evaluated in the same manner. The results are shown in Table 1. The monomer compositions, iodine values, and polymer Mooney viscosities [ML1+4, 100°C] of the nitrile group-containing copolymer rubbers (A-2), (A-3), and (A-4) were as shown in Table 1.

[0092] Examples 5 to 7 Nitrile group-containing copolymer rubbers (A-5), (A-6), and (A-7) were obtained in the same manner as in Example 1, except that the amounts of methacrylonitrile, acrylonitrile, methacrylic acid, and 1,3-butadiene used were as shown in Table 1, and 2-methoxyethyl acrylate was not used. Rubber compositions were prepared in the same manner, and evaluations were similarly carried out. The results are shown in Table 1. The monomer compositions, iodine values, and polymer Mooney viscosities [ML1+4, 100°C] of the nitrile group-containing copolymer rubbers (A-5), (A-6), and (A-7) were as shown in Table 1.

[0093] Example 8 A nitrile group-containing copolymer rubber (A-8) was obtained in the same manner as in Example 1, except that the amounts of methacrylonitrile, acrylonitrile, and 1,3-butadiene used were as shown in Table 1, and methacrylic acid and 2-methoxyethyl acrylate were not used. A rubber composition was prepared in the same manner, and evaluations were similarly carried out. The results are shown in Table 1. The monomer composition, iodine value, and polymer Mooney viscosity [ML1+4, 100°C] of the nitrile group-containing copolymer rubber (A-8) were as shown in Table 1.

[0094] Comparative Example 1 A nitrile group-containing copolymer rubber (A'-9) was obtained in the same manner as in Example 1, except that the amounts of methacrylonitrile, 2-methoxyethyl acrylate, methacrylic acid, and 1,3-butadiene used were as shown in Table 1, and acrylonitrile was not used. A rubber composition was prepared in the same manner, and evaluations were similarly carried out. The results are shown in Table 1. The monomer composition, iodine value, and polymer Mooney viscosity [ML1+4, 100°C] of the nitrile group-containing copolymer rubber (A'-9) were as shown in Table 1.

[0095] Comparative Example 2 A nitrile group-containing copolymer rubber (A'-10) was obtained in the same manner as in Example 1, except that the amounts of acrylonitrile, 2-methoxyethyl acrylate, methacrylic acid, and 1,3-butadiene used were as shown in Table 1, and methacrylonitrile was not used. A rubber composition was prepared in the same manner, and evaluations were similarly carried out. The results are shown in Table 1. The monomer composition, iodine value, and polymer Mooney viscosity [ML1+4, 100°C] of the nitrile group-containing copolymer rubber (A'-10) were as shown in Table 1.

[0096] Comparative Examples 3 and 4 Nitrile group-containing copolymer rubbers (A'-11) and (A'-12) were obtained in the same manner as in Example 1, except that the amounts of methacrylonitrile, acrylonitrile, 2-methoxyethyl acrylate, methacrylic acid, and 1,3-butadiene used were changed to the amounts shown in Table 1. Rubber compositions were prepared in the same manner and evaluated in the same manner. The results are shown in Table 1. The monomer compositions, iodine values, and polymer Mooney viscosities [ML1+4, 100°C] of the nitrile group-containing copolymer rubbers (A'-11) and (A'-12) were as shown in Table 1.

[0097] Comparative Example 5 A nitrile group-containing copolymer rubber (A'-13) was obtained in the same manner as in Example 1, except that the amounts of acrylonitrile and 1,3-butadiene used were as shown in Table 1, and 2-methoxyethyl acrylate, methacrylonitrile, and methacrylic acid were not used. A rubber composition was prepared in the same manner, and evaluations were similarly carried out. The results are shown in Table 1. The monomer composition, iodine value, and polymer Mooney viscosity [ML1+4, 100°C] of the nitrile group-containing copolymer rubber (A'-13) were as shown in Table 1.

[0098]

[0099] As shown in Table 1, according to a nitrile group-containing copolymer rubber which contains acrylonitrile units (a), α,β-ethylenically unsaturated nitrile monomer units (b) other than acrylonitrile, and conjugated diene monomer units (c), has an iodine value of 120 or less, and the content ratio of the acrylonitrile units (a) to the α,β-ethylenically unsaturated nitrile monomer units (b) other than acrylonitrile is within a specific range, the cross-linked rubber obtained using this has good physical properties at normal state, has excellent heat resistance, and exhibits excellent oil resistance both when the test lubricating oil IRM903 is used and when a fuel oil is used, and is also excellent in oil intermediate cure resistance in a heated environment (specifically, there is little change in glass transition temperature and hardness when the rubber is immersed in an oil containing a polycyclic condensed aromatic compound after storage in a heated environment) (Examples 1 to 8).

[0100] On the other hand, when the nitrile group-containing copolymer rubber did not contain acrylonitrile units (a), the cross-linked rubber obtained using this had low tensile strength in normal conditions, a large rate of volume change when immersed in test lubricating oil IRM903, insufficient oil resistance, and furthermore, after storage in a heated environment, a large change in hardness when immersed in oil containing a polycyclic condensed aromatic compound, indicating poor oil-hardening resistance in a heated environment (Comparative Example 1). Furthermore, when the nitrile group-containing copolymer rubber did not contain α,β-ethylenically unsaturated nitrile monomer units (b) other than acrylonitrile, or when the amount of α,β-ethylenically unsaturated nitrile monomer units (b) other than acrylonitrile was too small, the cross-linked rubber obtained using this had particularly large changes in glass transition temperature and hardness when immersed in oil containing a polycyclic condensed aromatic compound after storage in a heated environment, indicating particularly poor oil-hardening resistance in a heated environment (Comparative Examples 2, 4, and 5). When the amount of acrylonitrile units (a) in the nitrile group-containing copolymer rubber was too small, the cross-linked rubber obtained using the same had low tensile strength in normal state, and also had a large volume change rate when immersed in test lubricating oil IRM903, resulting in insufficient oil resistance (Comparative Example 3).

Claims

1. A nitrile group-containing copolymer rubber containing acrylonitrile units (a), α,β-ethylenically unsaturated nitrile monomer units (b) other than acrylonitrile, and conjugated diene monomer units (c), and having an iodine value of 120 or less, wherein the total content of the acrylonitrile units (a) and the α,β-ethylenically unsaturated nitrile monomer units (b) other than acrylonitrile in all monomer units is 1 to 50% by weight, and the content ratio of the acrylonitrile units (a) to the α,β-ethylenically unsaturated nitrile monomer units (b) other than acrylonitrile is a weight ratio of "content of acrylonitrile units (a): content of α,β-ethylenically unsaturated nitrile monomer units (b) other than acrylonitrile" of 10:90 to 90:

10. The nitrile group-containing copolymer rubber.

2. The nitrile group-containing copolymer rubber according to claim 1, wherein the carbon number excluding the cyano group in the α,β-ethylenically unsaturated nitrile monomer other than acrylonitrile, which constitutes the α,β-ethylenically unsaturated nitrile monomer units (b) other than acrylonitrile, is 2 to 5.

3. The nitrile group-containing copolymer rubber according to claim 1 or 2, wherein the total content of the acrylonitrile units (a) and the α,β-ethylenically unsaturated nitrile monomer units (b) other than acrylonitrile in all monomer units is 10 to 45% by weight.

4. The nitrile group-containing copolymer rubber according to claim 1 or 2, wherein the iodine value is 80 or less.

5. The nitrile group-containing copolymer rubber according to claim 1 or 2, wherein the content ratio of the acrylonitrile units (a) to the α,β-ethylenically unsaturated nitrile monomer units (b) other than acrylonitrile is a weight ratio of "content of acrylonitrile units (a): content of α,β-ethylenically unsaturated nitrile monomer units (b) other than acrylonitrile" of 20:80 to 80:

20.

6. The nitrile group-containing copolymer rubber according to claim 1 or 2, wherein the content ratio of the acrylonitrile units (a) to the α,β-ethylenically unsaturated nitrile monomer units (b) other than acrylonitrile is a weight ratio of "content of acrylonitrile units (a): content of α,β-ethylenically unsaturated nitrile monomer units (b) other than acrylonitrile" of 25:75 to 75:

25.

7. The nitrile group-containing copolymer rubber according to claim 1 or 2, wherein the content of the conjugated diene monomer unit (c) is 10 to 90% by weight.

8. A rubber composition obtained by blending a crosslinking agent with the nitrile group-containing copolymer rubber according to claim 1 or 2.

9. A rubber crosslinked product obtained by crosslinking the rubber composition according to claim 8.