Nitrile rubber composition and rubber crosslinking

Abstract

To provide a nitrile rubber composition capable of giving a rubber crosslinked product having low hardness and excellent tensile strength.SOLUTION: The nitrile rubber composition contains an oil-extended nitrile rubber, a plasticizer for compounding, and a filler. The oil-extended nitrile rubber contains a nitrile rubber component and a rubber additive plasticizer. The content ratio of the rubber additive plasticizer in the oil-extended nitrile rubber is 15 pts.wt. or more based on 100 pts.wt. of the nitrile rubber component of the oil-extended nitrile rubber.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a nitrile rubber composition, and more particularly, to a nitrile rubber composition capable of providing a rubber crosslinked product having a low hardness and excellent tensile strength, and a rubber crosslinked product obtained using such a nitrile rubber composition.

Background Art

[0002] Conventionally, nitrile rubber (acrylonitrile-butadiene copolymer rubber) is known as a rubber having excellent oil resistance, and its vulcanizate is mainly used as a material for various rubber products around industrial and automotive oils such as hoses, belts, gaskets, packings, seals, and rolls.

[0003] As such a nitrile rubber composition, for example, Patent Document 1 discloses a nitrile rubber composition comprising acrylonitrile-butadiene rubber, silica, an ether ester plasticizer, and a crosslinking agent. According to the nitrile rubber composition described in Patent Document 1, a rubber crosslinked product having excellent cold resistance and heat resistance, small compression set, and excellent oil resistance has been obtained.

[0004] Here, for the rubber crosslinked product of nitrile rubber, in addition to oil resistance, it is required to have a low hardness depending on its use. However, in the nitrile rubber composition described in Patent Document 1, there is a problem that when the content of the plasticizer is increased to reduce the hardness of the rubber crosslinked product, the tensile strength of the obtained rubber crosslinked product may decrease.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] This invention has been made in view of the above circumstances, and aims to provide a nitrile rubber composition that can provide a rubber crosslinked material with low hardness and excellent tensile strength, and a rubber crosslinked material obtained using such a nitrile rubber composition. [Means for solving the problem]

[0007] As a result of diligent research to achieve the above objective, the present inventors have discovered that the above objective can be achieved by using a nitrile rubber composition containing oil-extracted nitrile rubber containing a specific amount of rubber-additive plasticizer, a compounding plasticizer, and a filler, and have completed the present invention.

[0008] In other words, the present invention provides a nitrile rubber composition comprising an oil-expandable nitrile rubber, a compounding plasticizer, and a filler, wherein the oil-expandable nitrile rubber comprises a nitrile rubber component and a rubber-adding plasticizer, and the content ratio of the rubber-adding plasticizer in the oil-expandable nitrile rubber is 15 parts by weight or more per 100 parts by weight of the nitrile rubber component in the oil-expandable nitrile rubber.

[0009] In the nitrile rubber composition of the present invention, it is preferable that the rubber-added plasticizer is an adipic acid ether ester-based plasticizer.

[0010] In the nitrile rubber composition of the present invention, it is preferable that the total content ratio of the rubber additive plasticizer and the compounding plasticizer in the nitrile rubber composition is 18 parts by weight or more per 100 parts by weight of the nitrile rubber component in the oil-extracted nitrile rubber.

[0011] In the nitrile rubber composition of the present invention, it is preferable that the nitrile rubber component in the oil-spread nitrile rubber is a copolymer of acrylonitrile, butadiene, and isoprene.

[0012] Furthermore, according to the present invention, a crosslinked rubber product is provided which is obtained by crosslinking the nitrile rubber composition and which has a hardness of 50 or less as measured by a durometer hardness test. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a nitrile rubber composition that can give a rubber crosslinked material with low hardness and excellent tensile strength. [Modes for carrying out the invention]

[0014] <Nitrile rubber composition> The nitrile rubber composition of the present invention contains oil-expanded nitrile rubber, a compounding plasticizer, and a filler.

[0015] <Oil-applied nitrile rubber> Oil-applied nitrile rubber contains nitrile rubber components and rubber-additive plasticizers. The nitrile rubber component contains α,β-ethylenically unsaturated nitrile monomer units and conjugated diene monomer units.

[0016] The α,β-ethylenically unsaturated nitrile monomers that form the α,β-ethylenically unsaturated nitrile monomer units are not particularly limited, but any ethylenically unsaturated compound having a nitrile group and preferably 3 to 18 carbon atoms can be used. Examples of such α,β-ethylenically unsaturated nitrile monomers include acrylonitrile; α-halogenoacrylonitriles such as α-chloroacrylonitrile and α-bromoacrylonitrile; and α-alkylacrylonitriles such as methacrylonitrile and ethacrylonitrile. Among these, acrylonitrile and methacrylonitrile are preferred, and acrylonitrile is particularly preferred. These α,β-ethylenically unsaturated nitrile monomers may be used individually or in combination of two or more.

[0017] The content of α,β-ethylenically unsaturated nitrile monomer units in the nitrile rubber component of the oil-expandable nitrile rubber is 15 to 48% by weight, preferably 20 to 45% by weight, more preferably 25 to 40% by weight, and particularly preferably 30 to 40% by weight, relative to the total monomer units. If the content of α,β-ethylenically unsaturated nitrile monomer units is too low, the oil resistance of the resulting rubber crosslinked product will decrease. On the other hand, if the content of α,β-ethylenically unsaturated nitrile monomer units is too high, the affinity between the oil-expandable nitrile rubber and the plasticizer used in the compounding will deteriorate, and there is a risk that the plasticizer used in the compounding will leach to the surface (bleed) from the resulting rubber composition or rubber crosslinked product.

[0018] The conjugated diene monomers that form the conjugated diene monomer units are not particularly limited, but conjugated diene monomers having 4 to 6 carbon atoms, such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, and chloroprene, are preferred, 1,3-butadiene and isoprene are more preferred, and a combination of 1,3-butadiene or 1,3-butadiene and isoprene is even more preferred, as a nitrile rubber composition with even better shape retention can be obtained, making the combination of 1,3-butadiene and isoprene particularly preferred. These conjugated diene monomers may be used individually or in combination of two or more.

[0019] When 1,3-butadiene and isoprene are used in combination to form conjugated diene monomer units, the weight ratio of 1,3-butadiene units to isoprene units (1,3-butadiene units / isoprene units) is preferably 50 / 50 to 90 / 10, more preferably 60 / 40 to 90 / 10, and particularly preferably 70 / 30 to 85 / 15.

[0020] In the nitrile rubber component contained in the oil-extended nitrile rubber, the content of the conjugated diene monomer unit is preferably 45 to 85% by weight, more preferably 55 to 80% by weight, and particularly preferably 60 to 75% by weight, based on all monomer units. By setting the content of the conjugated diene monomer unit within the above range, the resulting rubber crosslinked product can have excellent mechanical properties while maintaining good rubber elasticity.

[0021] The nitrile rubber component contained in the oil-extended nitrile rubber may contain units of other monomers copolymerizable with the monomers forming these monomer units, in addition to the α,β-ethylenically unsaturated nitrile monomer unit and the conjugated diene monomer unit.

[0022] Examples of such other monomers include α-olefin monomers, non-conjugated diene monomers, aromatic vinyl monomers, α,β-ethylenically unsaturated monocarboxylic acids and their esters, α,β-ethylenically unsaturated polycarboxylic acids and their monoesters, polyesters and anhydrides, crosslinkable monomers, fluorine-containing vinyl monomers, copolymerizable antioxidants, and the like.

[0023] The α-olefin monomer preferably has 2 to 12 carbon atoms, and examples include ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, and the like.

[0024] The non-conjugated diene monomer preferably has 5 to 12 carbon atoms, and examples include 1,4-pentadiene, 1,4-hexadiene, vinyl norbornene, dicyclopentadiene, and the like.

[0025] Examples of the aromatic vinyl monomer include styrene, α-methylstyrene, vinyl pyridine, and the like.

[0026] Examples of the α,β-ethylenically unsaturated monocarboxylic acid preferably include acrylic acid, methacrylic acid, crotonic acid, cinnamic acid, and the like. Examples of α,β-ethylenically unsaturated monocarboxylic acid esters include (meth)acrylic acid esters having C1-C18 alkyl groups such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, n-dodecyl acrylate, methyl methacrylate, and ethyl methacrylate (abbreviations for "methacrylic acid ester and acrylic acid ester"; the same applies hereinafter); methoxymethyl acrylate, methoxyethyl acrylate, ethoxypropyl acrylate, methoxybutyl acrylate, ethoxidedodecyl acrylate, methoxyethyl methacrylate, methoxybutyl methacrylate, and ethoxypentyl methacrylate. Examples include (meth)acrylic acid esters having alkoxyalkyl groups with 2 to 18 carbon atoms; (meth)acrylic acid esters having cyanoalkyl groups with 2 to 12 carbon atoms, such as α-cyanoethyl acrylate, α-cyanoethyl methacrylate, and cyanobutyl methacrylate; (meth)acrylic acid esters having hydroxyalkyl groups with 1 to 12 carbon atoms, such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and 2-hydroxyethyl methacrylate; and (meth)acrylic acid esters having fluoroalkyl groups with 1 to 12 carbon atoms, such as trifluoroethyl acrylate and tetrafluoropropyl methacrylate.

[0027] Examples of α,β-ethylenically unsaturated polycarboxylic acids include maleic acid, fumaric acid, and itaconic acid. Examples of α,β-ethylenically unsaturated polycarboxylic acid monoesters 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 fumarates such as monomethyl fumarate, monoethyl fumarate, monopropyl fumarate, and mono-n-butyl fumarate; monocycloalkyl fumarates such as monocyclopentyl fumarate, monocyclohexyl fumarate, and monocycloheptyl fumarate; and monoalkylcycloalkyl fumarates such as monomethylcyclopentyl fumarate and monoethylcyclohexyl fumarate. Examples include: monoalkyl citraconate esters such as monomethyl citraconate, monoethyl citraconate, monopropyl citraconate, and mono-n-butyl citraconate; monocycloalkyl citraconate esters such as monocyclopentyl citraconate, monocyclohexyl citraconate, and monocycloheptyl citraconate; monoalkylcycloalkyl citraconate esters such as monomethylcyclopentyl citraconate and monoethylcyclohexyl citraconate; monoalkyl itaconate esters such as monomethyl itaconate, monoethyl itaconate, monopropyl itaconate, and mono-n-butyl itaconate; monocycloalkyl itaconate esters such as monocyclopentyl itaconate, monocyclohexyl itaconate, and monocycloheptyl itaconate; and monoalkylcycloalkyl itaconate esters such as monomethylcyclopentyl itaconate and monoethylcyclohexyl itaconate. Examples of α,β-ethylenically unsaturated polycarboxylic acid polyesters include dimethyl maleate, di-n-butyl maleate, dimethyl fumarate, di-n-butyl fumarate, dimethyl itaconate, and di-n-butyl itaconate. Examples of α,β-ethylenically unsaturated polycarboxylic acid anhydrides include maleic anhydride and itaconic anhydride.

[0028] Examples of crosslinkable monomers include polyfunctional ethylenically unsaturated monomers such as divinyl compounds like divinylbenzene; di(meth)acrylic acid esters such as ethylenedi(meth)acrylate, diethylene glycol di(meth)acrylate, and polyethylene glycol di(meth)acrylate; and trimethacrylic acid esters such as trimethylolpropanetri(meth)acrylate; as well as self-crosslinkable monomers such as N-methylol(meth)acrylamide and N,N'-dimethylol(meth)acrylamide.

[0029] Examples of fluorine-containing vinyl monomers include fluoroethyl vinyl ether, fluoropropyl vinyl ether, o-trifluoromethylstyrene, vinyl pentafluorobenzoate, difluoroethylene, and tetrafluoroethylene.

[0030] 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.

[0031] Multiple types of these copolymerizable monomers may be used in combination. The content of other monomer units in the nitrile rubber component contained in the oil-spread nitrile rubber is preferably 20% by weight or less, more preferably 10% by weight or less, and particularly preferably 5% by weight or less, relative to the total monomer units.

[0032] The oil-expandable nitrile rubber used in the present invention contains a rubber-additive plasticizer that has been added in advance to the above-mentioned nitrile rubber component. That is, the oil-expandable nitrile rubber used in the present invention is an oil-expandable rubber that contains a rubber-additive plasticizer as an oil-expanding oil. The rubber-additive plasticizer can be any plasticizer that is commonly used for rubber and is not particularly limited, but it is preferably an ester compound of a dicarboxylic acid and an ether-bonded alcohol. Since the oil-expandable nitrile rubber contains an ester compound of a dicarboxylic acid and an ether-bonded alcohol as a rubber-additive plasticizer that has been added in advance, the nitrile rubber composition of the present invention can produce a rubber crosslinked product that has low hardness and excellent tensile strength.

[0033] Examples of dicarboxylic acids that form ester compounds include those represented by the following general formula (1). HOOCRCOOH (1) (In the formula, R represents an alkylene group with 2 to 10 carbon atoms, and COOH represents a carboxyl group.)

[0034] In formula (1), R may be a linear or branched alkylene group, but a linear alkylene group is preferred. The number of carbon atoms in the alkylene group is preferably 2 to 10, and more preferably 4 to 8.

[0035] Examples of dicarboxylic acids that form ester compounds include succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebatic acid, with adipic acid being preferred among them.

[0036] A monohydric alcohol is preferred as the ether-bonded alcohol that forms the ester compound. The number of carbon atoms in the ether-bonded alcohol is preferably 4 to 10, more preferably 6 to 8. The number of ether bonds contained in the ether-bonded alcohol is preferably 1 to 4, more preferably 1 to 2.

[0037] As the ester compound, any compound obtained by combining a dicarboxylic acid and an ether-bonded alcohol can be used. Typically, monoester compounds and diester compounds are used, but diester compounds are preferred. As the ester compound, adipic acid ether ester compounds are preferably used. That is, as the rubber-added plasticizer, adipic acid ether ester-based plasticizers are preferably used.

[0038] The content of rubber-additive plasticizer in the oil-extracted nitrile rubber is 15 parts by weight or more per 100 parts by weight of the nitrile rubber component. The upper limit of the content of rubber-additive plasticizer in the oil-extracted nitrile rubber is not particularly limited, but is preferably 100 parts by weight or less, more preferably 50 parts by weight or less, and even more preferably 40 parts by weight or less. If the content of rubber-additive plasticizer is too low, the processability (ease of mixing of additives) of the resulting nitrile rubber composition will be poor, resulting in poor moldability of the resulting nitrile rubber composition and poor tensile stress of the resulting rubber crosslinked product. On the other hand, if the content of rubber-additive plasticizer is too high, the shape retention of the resulting nitrile rubber composition will be poor.

[0039] The Mooney viscosity (ML1+4, 100°C) of the oil-spread nitrile rubber is preferably 10 to 200, more preferably 20 to 150, and even more preferably 40 to 100. By setting the Mooney viscosity of the oil-spread nitrile rubber within the above range, a nitrile rubber composition can be obtained that provides a rubber crosslinked product with good normal physical properties.

[0040] <Plasticizers for compounding> The nitrile rubber composition of the present invention contains a compounding plasticizer and a filler in the oil-expanded nitrile rubber described above. That is, the nitrile rubber composition of the present invention is obtained by further compounding a compounding plasticizer in addition to the rubber additive plasticizer contained in the oil-expanded nitrile rubber described above, and then compounding a filler therein.

[0041] The plasticizer used in the compounding process can be any plasticizer commonly used for rubber, and is not particularly limited, but it is preferably an ester compound of a dicarboxylic acid and an ether-bonded alcohol. The ester compound of a dicarboxylic acid and an ether-bonded alcohol used as the plasticizer can be the same as those exemplified above as ester compounds of dicarboxylic acid and ether-bonded alcohol used as rubber additive plasticizers.

[0042] The content of the plasticizer in the nitrile rubber composition of the present invention is not particularly limited, but is preferably 3 parts by weight or more, more preferably 10 parts by weight or more, and even more preferably 20 parts by weight or more, based on 100 parts by weight of the nitrile rubber component contained in the oil-extracted nitrile rubber.

[0043] The total content of rubber additive plasticizers and compounding plasticizers contained in the nitrile rubber composition of the present invention is 18 parts by weight or more, preferably 30 parts by weight or more, and more preferably 45 parts by weight or more, per 100 parts by weight of nitrile rubber components contained in the oil-extracted nitrile rubber. The upper limit of the total content of rubber additive plasticizers and compounding plasticizers is not particularly limited, but is preferably 110 parts by weight or less, more preferably 85 parts by weight or less, and even more preferably 70 parts by weight or less, per 100 parts by weight of nitrile rubber components contained in the oil-extracted nitrile rubber.

[0044] <Filler> Furthermore, the nitrile rubber composition of the present invention contains a filler in addition to the oil-expandable nitrile rubber and compounding plasticizer described above. Any filler commonly used in the rubber field may be used as the filler, and there are no particular limitations. Both organic and inorganic fillers can be used, but inorganic fillers are preferred due to their superior compounding effect.

[0045] The inorganic filler can be any one commonly used for compounding rubber, such as carbon black, silica, clay, alumina, aluminum hydroxide, magnesium oxide, magnesium hydroxide, calcium oxide, calcium hydroxide, aluminum magnesium oxide, titanium dioxide, 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 preferred, and silica is more preferred. The inorganic filler can be used individually or in combination of multiple types.

[0046] Any carbon black commonly used for rubber compounding will suffice, such as furnace black, acetylene black, thermal black, channel black, and graphite.

[0047] Examples of silica include natural silica such as quartz powder and silica powder; and synthetic silica such as anhydrous silicic acid (silica gel, aerosil, etc.) and hydrated silicic acid; among these, synthetic silica is preferred. Furthermore, these silicas may be surface-treated with coupling agents or the like.

[0048] Clay can be any natural mineral whose main component is hydrated aluminum silicate, and is not particularly limited, but examples include montmorillonite, pyrophyllite, kaolinite, halloysite, and sericite.

[0049] The amount of filler in the nitrile rubber composition of the present invention is preferably 1 to 200 parts by weight, more preferably 15 to 150 parts by weight, and particularly preferably 30 to 100 parts by weight, per 100 parts by weight of the nitrile rubber component contained in the oil-extracted nitrile rubber.

[0050] Furthermore, in addition to oil-expanded nitrile rubber, compounding plasticizers, and plasticizers, the nitrile rubber composition of the present invention may also contain compounding agents commonly used in the rubber field, such as fillers like calcium carbonate, talc, and clay; metal oxides like zinc oxide and magnesium oxide; α,β-ethylenically unsaturated carboxylate metal salts like zinc methacrylate and zinc acrylate; co-crosslinking agents, crosslinking aids, crosslinking retarders, antioxidants, light stabilizers, scorch inhibitors like primary amines, activators like diethylene glycol, coupling agents, processing aids, lubricants, adhesives, flammable agents, fungicides, acid acceptors, antistatic agents, pigments, and foaming agents. The amounts of these compounding agents are not particularly limited as long as they do not hinder the objectives and effects of the present invention, and can be added in amounts appropriate to the purpose of compounding.

[0051] <Rubber other than oil-treated nitrile rubber> The nitrile rubber composition of the present invention may also contain rubbers other than the oil-expanded nitrile rubber described above. Examples of such rubbers include non-oil-expanded nitrile rubber that does not contain plasticizers, acrylic rubber, ethylene-acrylic acid copolymer rubber, styrene-butadiene copolymer rubber, polybutadiene rubber, ethylene-propylene copolymer rubber, ethylene-propylene-diene ternary copolymer rubber, epichlorohydrin rubber, fluororubber, urethane rubber, chloroprene rubber, silicone rubber, natural rubber, and polyisoprene rubber.

[0052] When a rubber other than oil-extracted nitrile rubber is blended, the amount of the rubber other than oil-extracted nitrile rubber in the nitrile rubber composition is preferably 230 parts by weight or less, more preferably 100 parts by weight or less, and even more preferably 65 parts by weight or less, per 100 parts by weight of the nitrile rubber component contained in the oil-extracted nitrile rubber.

[0053] When compounding rubbers other than oil-extracted nitrile rubber, the content of the compounding plasticizer in the nitrile rubber composition is not particularly limited, but is preferably 10 parts by weight or more, more preferably 20 parts by weight or more, based on 100 parts by weight of the total rubber components contained in the oil-extracted nitrile rubber and rubbers other than oil-extracted nitrile rubber.

[0054] When compounding rubber other than oil-extracted nitrile rubber, the total content of rubber additive plasticizers and compounding plasticizers in the nitrile rubber composition is 18 parts by weight or more, preferably 30 parts by weight or more, and more preferably 45 parts by weight or more, based on 100 parts by weight of the total rubber components contained in the oil-extracted nitrile rubber and rubber other than oil-extracted nitrile rubber. The upper limit of the total content of rubber additive plasticizers and compounding plasticizers is not particularly limited, but is preferably 110 parts by weight or less, more preferably 85 parts by weight or less, and even more preferably 70 parts by weight or less, based on 100 parts by weight of the nitrile rubber components contained in the oil-extracted nitrile rubber.

[0055] The nitrile rubber composition of the present invention is prepared by mixing the above-mentioned components, preferably in a non-aqueous system. There are no limitations on the method of preparing the nitrile rubber composition of the present invention, but it can usually be prepared by kneading the components, excluding the crosslinking agent and heat-unstable components, in a mixer such as a Banbury mixer, intermixer, or kneader. Kneading is usually carried out at a temperature of 10 to 200°C, preferably 30 to 180°C, for 1 minute to 1 hour, preferably 1 minute to 30 minutes.

[0056] <Rubber Crosslinked Products> The rubber crosslinked product of the present invention is obtained by crosslinking the nitrile rubber composition of the present invention described above. The crosslinked rubber product of the present invention can be manufactured by using a crosslinkable rubber composition obtained by transferring the nitrile rubber composition of the present invention to an open roll or the like, adding a crosslinking agent and heat-unstable components, molding it using a molding machine corresponding to the desired shape, such as an extruder, injection molding machine, compressor, or roll, and then heating it to carry out a crosslinking reaction and fix the shape as a crosslinked product. Mixing is usually carried out at a temperature of 10 to 90°C, preferably 20 to 60°C, for 1 minute to 1 hour, preferably 1 minute to 30 minutes. In this case, crosslinking may be performed either after pre-molding or simultaneously with molding. The molding temperature is usually 10 to 200°C, preferably 25 to 120°C. The crosslinking temperature is usually 100 to 200°C, preferably 130 to 190°C, and the crosslinking time is usually 1 minute to 24 hours, preferably 2 minutes to 1 hour.

[0057] The crosslinkable rubber composition obtained by kneading the nitrile rubber and crosslinking agent of the present invention has a compound Mooney viscosity (ML1+4, 100°C) preferably of 5 to 80, more preferably of 10 to 60, and even more preferably of 15 to 40. By setting the compound Mooney viscosity of the crosslinkable rubber composition within the above range, good normal physical properties can be obtained.

[0058] The crosslinking agent is not particularly limited and includes sulfur-based crosslinking agents and organic peroxide-based crosslinking agents. However, if the nitrile rubber component contained in the oil-spread nitrile rubber has monomer units having carboxyl groups, a polyamine-based crosslinking agent can also be used. Among the crosslinking agents, sulfur-based crosslinking agents are preferred because they allow for various crosslinking molding methods.

[0059] Examples of sulfur-based crosslinking agents include sulfur such as powdered sulfur, sulfurous salt, 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 polysulfide, and high molecular weight polysulfides; and sulfur-donating compounds such as tetramethylthiuram disulfide, selenium dimethyldithiocarbamate, and 2-(4'-morpholinodithio)benzothiazole. These can be used individually or in combination.

[0060] Examples of organic peroxide-based crosslinking agents include dicumyl peroxide, cumene hydroperoxide, t-butylcumyl peroxide, paramentane 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-butyl-peroxy)-n-butyl valerate, 2,5-dimethyl-2,5-di-t-butylperoxyhexane, 2,5-dimethyl-2,5-di-t-butylperoxyhexyn-3, 1,1-di-t-butylperoxy-3,5,5-trimethylcyclohexane, p-chlorobenzoyl peroxide, t-butylperoxyisopropyl carbonate, and t-butylperoxybenzoate. These can be used individually or in combination.

[0061] The polyamine 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 when crosslinked. However, compounds in which multiple hydrogen atoms of aliphatic hydrocarbons or aromatic hydrocarbons are substituted with amino groups or hydrazide structures (structures represented by -CONHNH2, where CO represents a carbonyl group), and compounds that become such a compound when crosslinked are preferred. Specific examples include aliphatic polyhydric amines such as hexamethylenediamine, hexamethylenediamine carbamate, tetramethylenepentamine, hexamethylenediamine cinnamaldehyde adduct, and hexamethylenediamine dibenzoate salt; aromatic polyhydric amines such as 2,2-bis{4-(4-aminophenoxy)phenyl}propane, 4,4'-methylenedianiline, m-phenylenediamine, p-phenylenediamine, and 4,4'-methylenebis(o-chloroaniline); and compounds having two or more hydrazide structures, such as isophthalic acid dihydrazide, adipic acid dihydrazide, and sebacate acid dihydrazide. These can be used individually or in combination.

[0062] The amount of crosslinking agent in the nitrile rubber composition of the present invention is not particularly limited, but is preferably 0.1 to 10 parts by weight, more preferably 0.2 to 5 parts by weight, per 100 parts by weight of the nitrile rubber component contained in the oil-spread nitrile rubber.

[0063] When using a sulfur-based crosslinking agent, it is preferable to use a crosslinking aid such as zinc oxide, guanidine-based crosslinking accelerator, thiazole-based crosslinking accelerator, thiram-based crosslinking accelerator, or dithiocarbamate-based crosslinking accelerator in combination.

[0064] Furthermore, when using an organic peroxide-based crosslinking agent, it is preferable to use triallyl cyanurate, trimethylolpropane trimethacrylate, N,N'-m-phenylene bismaleimide, etc., as crosslinking aids in combination.

[0065] Furthermore, when using a polyamine-based crosslinking agent, it is preferable to use a basic crosslinking accelerator in combination, such as a compound represented by the following general formula (2), a basic crosslinking accelerator having a cyclic amidine structure, a guanidine-based basic crosslinking accelerator, or an aldehyde-amine-based basic crosslinking accelerator, as a crosslinking aid. R 1 -NH-R 2 (2) (In the above general formula (2), R 1 and R 2 Each of these is independently an alkyl group having 1 to 12 carbon atoms, which may have substituents, or a cycloalkyl group having 5 to 12 carbon atoms, which may have substituents.

[0066] Crosslinking aids may be used alone, or multiple types may be used in combination. They may also be dispersed in clay, calcium carbonate, silica, etc., to improve processability. The amount of crosslinking aid used is not particularly limited and should be determined according to the application of the rubber crosslinked product, the required performance, the type of crosslinking agent, and the type of crosslinking aid.

[0067] Furthermore, depending on the shape and size of the crosslinked material, even if the surface is crosslinked, the interior may not be sufficiently crosslinked. In such cases, further heating may be performed to carry out secondary crosslinking. For heating, you can appropriately select from common methods used for crosslinking rubber, such as press heating, steam heating, oven heating, and hot air heating.

[0068] The rubber crosslinked product of the present invention obtained in this manner is obtained by crosslinking the nitrile rubber composition of the present invention described above, and therefore has low hardness while exhibiting excellent tensile strength.

[0069] Therefore, the rubber crosslinked material of the present invention utilizes these properties to create seals for O-rings, packings, diaphragms, oil seals, shaft seals, bearing seals, well head seals, shock absorber seals, coolant seals and oil coolant seals for sealing coolants such as long-life coolant (LLC), seals for pneumatic equipment, seals for sealing fluorocarbons or fluorohydrocarbons or carbon dioxide used in cooling devices of air conditioners and compressors for refrigeration units of air conditioning systems, seals for sealing supercritical or subcritical carbon dioxide used as cleaning media in precision cleaning, seals for rolling devices (rolling bearings, automotive hub units, automotive water pumps, linear guide devices and ball screws, etc.), valves and valve seats, and BOP (Blow Out) seals. Various sealing materials such as Preventer, Platter; intake manifold gaskets installed at the joint between the intake manifold and cylinder head, cylinder head gaskets installed at the joint between the cylinder block and cylinder head, rocker cover gaskets installed at the joint between the rocker cover and cylinder head, oil pan gaskets installed at the joint between the oil pan and cylinder block or transmission case, fuel cell separator gaskets installed between a pair of housings that sandwich a unit cell equipped with a positive electrode, electrolyte plate and negative electrode, and various gaskets such as top cover gaskets for hard disk drives; printing rolls, steelmaking rolls, papermaking rolls, industrial rolls, office rolls Various types of rolls such as machine rolls; flat belts (film core flat belts, corded flat belts, laminated flat belts, single 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, cog-topped V-ribbed belts, etc.), CVT belts, timing belts, toothed belts, conveyor belts, and other types of belts; various types of hoses such as fuel hoses, turbo air hoses, oil hoses, radiator hoses, heater hoses, water hoses, vacuum brake hoses, control hoses, air conditioning hoses, brake hoses, power steering hoses, air hoses, marine hoses, risers, flow lines, and other types of hoses;It 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 dampers, and clutch facings; dust covers, automotive interior components, tires, coated cables, shoe soles, electromagnetic shielding, adhesives for flexible printed circuit boards, fuel cell separators, and electronics. Among these, it is particularly suitable for use in rolls, belts, and hoses. [Examples]

[0070] The present invention will be specifically described below with reference to examples and comparative examples. Unless otherwise specified, "parts" herein refer to weight. The tests and evaluations were conducted as follows.

[0071] <Normal physical properties (tensile strength, elongation, hardness)> A crosslinkable rubber composition was obtained by kneading a nitrile rubber composition with a crosslinking agent. This 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 150°C for 60 minutes under a press pressure of 10 MPa to obtain a sheet-like crosslinked rubber material. Next, test specimens were prepared by punching out the obtained sheet-like crosslinked rubber material with a JIS No. 3 dumbbell. The tensile strength and elongation at break of the crosslinked rubber material were then measured using the obtained test specimens in accordance with JIS K6251:2017. In addition, the hardness of the crosslinked rubber material was measured using a durometer hardness tester (Type A) in accordance with JIS K6253-3.

[0072] <Example 1> To 100 parts of oil-applied nitrile rubber (product name "Nipol DN230", manufactured by Nippon Zeon Co., Ltd., acrylonitrile unit content: 29% by weight, adipate ether ester plasticizer content: 17% by weight), 1 part stearic acid, 5 parts zinc oxide, 35 parts silica (product name "Carplex #1120", manufactured by Evonik, inorganic filler), 8 parts titanium dioxide (product name "TITONE A-110", manufactured by Sakai Chemical Industry Co., Ltd.), 25 parts compounding plasticizer (product name "ADEKA Sizer RS-107", manufactured by ADEKA Corporation), 0.5 parts silane coupling agent (product name "A-189", manufactured by Momentive Corporation), and 1 part 2,2,4-trimethyl-1,2-dihydroquinoline polymer (product name "Nocrac 224", manufactured by Ouchi Shinko Chemical Industry Co., Ltd., antioxidant) were mixed and kneaded. Next, the resulting mixture was transferred to a roll at 50°C, and 0.5 parts of powdered sulfur (325 mesh), 1.5 parts of tetramethylthiuram disulfide (trade name "Noxellar TT", manufactured by Ouchi Shinko Chemical Industry Co., Ltd., vulcanization accelerator), and 1.5 parts of N-cyclohexyl-2-benzothiazolyl sulfenamide (trade name "Noxellar CZ", manufactured by Ouchi Shinko Chemical Industry Co., Ltd., vulcanization accelerator) were added and kneaded. Using the resulting crosslinkable rubber composition, the normal physical properties (tensile strength, elongation, and hardness) were measured according to the method described above. The results are shown in Table 1.

[0073] <Example 2> Nitrile rubber compositions were obtained and evaluated in the same manner as in Example 1, except that the content of powdered sulfur was changed to 1.5 parts, and 0.25 parts of 1,3-diphenylguanidine (trade name "Noxellar D", manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) and 1.5 parts of dibenzothiazyl disulfide (trade name "Noxellar DM", manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) were used as vulcanization accelerators. The results are shown in Table 1.

[0074] <Comparative Example 1> A nitrile rubber composition was obtained in the same manner as in Example 1, except that nitrile rubber (product name "Nipol 3350", manufactured by Nippon Zeon Co., Ltd., acrylonitrile unit content: 33% by weight, no plasticizer) was used instead of oil-expanded nitrile rubber (Nipol DN230), the content of the compounding plasticizer was changed to 50 parts, and the content of other compounding agents was changed to the amounts shown in Table 1. Then, a crosslinkable rubber composition was obtained in the same manner as in Example 1, except that the amounts of powdered sulfur and crosslinking accelerator were changed to the amounts shown in Table 1, and evaluated in the same manner. The results are shown in Table 1.

[0075] <Comparative Example 2> Nitrile rubber compositions were obtained in the same manner as in Example 2, except that nitrile rubber (product name "Nipol 3350", manufactured by Nippon Zeon Co., Ltd., acrylonitrile unit content: 33% by weight, no plasticizer) was used instead of oil-expanded nitrile rubber (Nipol DN230), the content of the compounding plasticizer was changed to 50 parts, and the content of other compounding agents was changed to the amounts shown in Table 1. Then, crosslinkable rubber compositions were obtained in the same manner as in Example 2, except that the amounts of powdered sulfur and crosslinking accelerator were changed to the amounts shown in Table 1, and evaluated in the same manner. The results are shown in Table 1.

[0076] [Table 1]

[0077] <Evaluation of the Examples and Comparative Examples> As shown in Table 1, a nitrile rubber composition comprising oil-expanded nitrile rubber, a compounding plasticizer, and a filler, wherein the content of the rubber additive plasticizer contained in the oil-expanded nitrile rubber is 15 parts by weight or more per 100 parts by weight of the nitrile rubber component, made it possible to obtain a rubber crosslinked product with low hardness while exhibiting excellent tensile strength and elongation (Examples 1 and 2). On the other hand, when nitrile rubber without plasticizers was used instead of oil-extracted nitrile rubber, the resulting crosslinked rubber product exhibited inferior tensile strength and elongation (Comparative Examples 1 and 2).

[0078] <Examples 3-49> Nitrile rubber compositions were obtained using the formulations shown in Tables 2-6, and sheet-like crosslinked rubber products were obtained in the same manner as the evaluation of normal physical properties described above. In Examples 3 to 49, the nitrile rubber and compounding agent shown in each table were mixed in the amounts shown in each table and mixed at 50°C. The resulting nitrile rubber composition was then transferred to a roll at 50°C and kneaded with the crosslinking agent and crosslinking accelerator shown in each table. Since the nitrile rubber compositions of Examples 3 to 49 also contain oil-expanded nitrile rubber, a compounding plasticizer, and a filler, the resulting crosslinked rubber product is considered to have low hardness while exhibiting excellent tensile strength and elongation, similar to Example 1.

[0079] The rubbers and compounding agents shown in each table are as follows: • Nipol DN230: Oil-applied nitrile rubber (product name "Nipol DN230", manufactured by Nippon Zeon Co., Ltd., acrylonitrile unit content: 29% by weight, adipate ether ester plasticizer content: 17% by weight) • Nipol DN3350: Nitrile rubber (product name "Nipol 3350", manufactured by Nippon Zeon Co., Ltd., acrylonitrile unit content: 33% by weight, no plasticizers) • Seest S: Carbon Black (Product name "Seest S", manufactured by Tokai Carbon Co., Ltd., inorganic filler) • Seest SO: Carbon Black (Product name "Seest SO", manufactured by Tokai Carbon Co., Ltd., inorganic filler) • Nipsil VN3: Silica (Product name "Nipsil VN3", manufactured by Tosoh Silica Co., Ltd., BET specific surface area: 200 m²) 2 / g) • Calcium carbonate (product name "Silver W", manufactured by Shiraishi Calcium Co., Ltd., inorganic filler) • Crown Clay: Clay (product name "ST-CROWN", manufactured by Shiraishi Calcium Co., Ltd., inorganic filler) • Titanium dioxide (product name "TITONE A-110", manufactured by Sakai Chemical Industry Co., Ltd., inorganic filler) • ADEKA Sizer RS-107: Plasticizer (Product name "ADEKA Sizer RS-107", manufactured by ADEKA Corporation) • A-189: Silane coupling agent (product name "A-189", manufactured by Momentive) • A-172: Silane coupling agent (product name "A-172", manufactured by Momentive) • Nocrac 224: 2,2,4-trimethyl-1,2-dihydroquinoline polymer (product name "Nocrac 224", manufactured by Ouchi Shinko Chemical Industry Co., Ltd., anti-aging agent) • Noxellar D: 1,3-diphenylguanidine (product name "Noxellar D", manufactured by Ouchi Shinko Chemical Industry Co., Ltd., vulcanization accelerator) • Noxellar DM: Dibenzothiazyl disulfide (product name "Noxellar DM", manufactured by Ouchi Shinko Chemical Industry Co., Ltd., vulcanization accelerator) • Noxellar TT: Tetramethylthiuram disulfide (product name "Noxellar TT", manufactured by Ouchi Shinko Chemical Industry Co., Ltd., vulcanization accelerator) 1.5 parts • Noxellar CZ: N-cyclohexyl-2-benzothiazolyl sulfenamide (product name "Noxellar CZ", manufactured by Ouchi Shinko Chemical Industry Co., Ltd., vulcanization accelerator) • Perkmill D-40: Dicumyl peroxide (product name "Perkmill D-40", manufactured by NOF Corporation, peroxide crosslinking agent) • TMPT: Trimethylolpropane trimethacrylate (product name "TMPT", manufactured by Shin-Nakamura Chemical Co., Ltd., crosslinking agent)

[0080] [Table 2]

[0081] [Table 3]

[0082] [Table 4]

[0083] [Table 5]

[0084] Table 6

Claims

1. A nitrile rubber composition comprising oil-applied nitrile rubber, a compounding plasticizer, and a filler, The oil-applied nitrile rubber comprises a nitrile rubber component and a rubber-adding plasticizer. The content ratio of the rubber-added plasticizer in the oil-expanded nitrile rubber is 15 parts by weight or more per 100 parts by weight of the nitrile rubber component in the oil-expanded nitrile rubber. A nitrile rubber composition in which the rubber additive plasticizer is an adipic acid ether ester type plasticizer.

2. The nitrile rubber composition according to claim 1, wherein the total content ratio of the rubber additive plasticizer and the compounding plasticizer in the nitrile rubber composition is 18 parts by weight or more per 100 parts by weight of the nitrile rubber component in the oil-spread nitrile rubber.

3. The nitrile rubber composition according to claim 1 or 2, wherein the nitrile rubber component in the oil-spread nitrile rubber is a copolymer of acrylonitrile, butadiene, and isoprene.

4. A rubber crosslinked product obtained by crosslinking a nitrile rubber composition according to any one of claims 1 to 3, A cross-linked rubber material having a hardness of 50 or less as measured by a durometer hardness test.

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