Acrylic rubber composition and rubber crosslinked product

Abstract

The present invention provides an acrylic rubber composition which contains an acrylic rubber (A), an organic peroxide (B), a co-crosslinking agent (C), and a sulfur-based compound (D), wherein: the content of the organic peroxide (B) is 0.1-5 parts by weight with respect to 100 parts by weight of the acrylic rubber (A); the content of the co-crosslinking agent (C) is 0.1-10 parts by weight with respect to 100 parts by weight of the acrylic rubber (A); and the content of the sulfur-based compound (D) is 0.05-3 parts by weight with respect to 100 parts by weight of the acrylic rubber (A).

Description

Acrylic rubber composition and cross-linked rubber

[0001] The present invention relates to an acrylic rubber composition and a cross-linked rubber product.

[0002] The acrylic rubber composition is usually crosslinked by heating at about 150°C to 190°C for several minutes to several tens of minutes as primary crosslinking, and then heating in a heated air environment at 140°C to 200°C for several hours as secondary crosslinking.

[0003] For example, Patent Document 1 discloses an acrylic rubber composition comprising 30 to 80% by weight of methoxyethyl acrylate, 70 to 20% by weight of alkyl acrylate and / or alkoxy-substituted alkyl acrylate (excluding methoxyethyl acrylate), and 0 to 30% by weight of other monomers having no copolymerizable crosslinking point group, and further comprising an organic peroxide and a bismaleimide compound blended as a vulcanizing agent into the acrylic rubber.

[0004] Japanese Patent Application Publication No. 5-214196

[0005] From the viewpoints of productivity, energy saving, and carbon neutrality of cross-linked rubber products, there is a demand for an acrylic rubber composition that can produce cross-linked rubber products having good physical properties by primary cross-linking alone, without requiring secondary cross-linking.

[0006] For example, in the above-mentioned Patent Document 1, a cross-linked rubber product is obtained by primary vulcanization of an acrylic rubber composition, but there is a problem that the scorch stability is poor. Generally, when the scorch stability is poor, an unintended cross-linking reaction starts during storage of the acrylic rubber composition or when the acrylic rubber composition is used for processing, resulting in a rubber composition with poor storage stability and processability.

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an acrylic rubber composition which has a sufficient crosslinking rate, has good scorch stability, and is capable of giving a cross-linked rubber product having sufficient mechanical properties even without secondary crosslinking.

[0008] As a result of intensive research, the present inventors have found that the above object can be achieved by an acrylic rubber composition containing an acrylic rubber (A), an organic peroxide (B), a co-crosslinking agent (C), and a sulfur-based compound (D) in specific content ratios, and have thus completed the present invention.

[0009] That is, according to the present invention, the following acrylic rubber composition and cross-linked rubber product are provided. [1] An acrylic rubber composition containing an acrylic rubber (A), an organic peroxide (B), a co-crosslinking agent (C), and a sulfur-based compound (D), wherein the content of the organic peroxide (B) is 0.1 to 5 parts by weight per 100 parts by weight of the acrylic rubber (A), the content of the co-crosslinking agent (C) is 0.1 to 10 parts by weight per 100 parts by weight of the acrylic rubber (A), and the content of the sulfur-based compound (D) is 0.05 to 3 parts by weight per 100 parts by weight of the acrylic rubber (A). [2] The acrylic rubber composition according to [1], wherein the acrylic rubber (A) contains 40 to 100% by weight of (meth)acrylic acid alkyl ester and / or (meth)acrylic acid alkoxyalkyl ester monomer units. [3] A cross-linked rubber product obtained by cross-linking the acrylic rubber composition according to [1] or [2]. [4] The cross-linked rubber product according to [3], which is a hose material or a sealing material.

[0010] According to the present invention, it is possible to provide an acrylic rubber composition which has a sufficient crosslinking rate, has good scorch stability, and is capable of giving a cross-linked rubber product having sufficient mechanical properties even without secondary crosslinking.

[0011] The acrylic rubber composition of the present invention contains an acrylic rubber (A), an organic peroxide (B), a co-crosslinking agent (C), and a sulfur-based compound (D), wherein the content of the organic peroxide (B) is 0.1 to 5 parts by weight relative to 100 parts by weight of the acrylic rubber (A), the content of the co-crosslinking agent (C) is 0.1 to 10 parts by weight relative to 100 parts by weight of the acrylic rubber (A), and the content of the sulfur-based compound (D) is 0.05 to 3 parts by weight relative to 100 parts by weight of the acrylic rubber (A).

[0012] The acrylic rubber composition of the present invention contains the acrylic rubber (A), the organic peroxide (B), the co-crosslinking agent (C), and the sulfur-based compound (D) in the above-mentioned specific amounts in combination, and thereby can provide a cross-linked rubber product that has a sufficient cross-linking rate, good scorch stability, and sufficient mechanical properties (specifically, tensile properties and hardness) even without secondary cross-linking.

[0013] <Acrylic Rubber (A)> The acrylic rubber (A) used in the present invention is not particularly limited as long as it contains a (meth)acrylic acid ester monomer (meaning an acrylic acid ester monomer and / or a methacrylic acid ester monomer. Hereinafter, the term "(meth)acrylic" will be understood in the same way) unit as the main component (for example, 50% by weight or more of all monomer units in the acrylic rubber) in the molecule.

[0014] The (meth)acrylic acid ester monomer forming the (meth)acrylic acid ester monomer unit as the main component of the acrylic rubber (A) used in the present invention is not particularly limited, but examples thereof include (meth)acrylic acid alkyl ester monomers and (meth)acrylic acid alkoxyalkyl ester monomers.

[0015] The (meth)acrylic acid alkyl ester monomer is not particularly limited, but is preferably an ester of an alkanol having 1 to 12 carbon atoms and (meth)acrylic acid (a (meth)acrylic acid ester having an alkyl group having 1 to 12 carbon atoms), more preferably an ester of an alkanol having 1 to 8 carbon atoms and (meth)acrylic acid (a (meth)acrylic acid ester having an alkyl group having 1 to 8 carbon atoms), and even more preferably an ester of an alkanol having 2 to 6 carbon atoms and (meth)acrylic acid (a (meth)acrylic acid ester having an alkyl group having 2 to 6 carbon atoms).

[0016] Specific examples of the (meth)acrylic acid alkyl ester monomer include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and cyclohexyl (meth)acrylate. Among these, ethyl (meth)acrylate and n-butyl (meth)acrylate are preferred, and ethyl acrylate and n-butyl acrylate are more preferred. These can be used alone or in combination of two or more.

[0017] For example, the acrylic rubber (A) used in the present invention may contain both ethyl acrylate units and n-butyl acrylate units as (meth)acrylic acid alkyl ester monomer units. In this case, the weight ratio of the contents of both monomer units [ethyl acrylate unit content: n-butyl acrylate unit content] is preferably 1:99 to 99:1, more preferably 10:90 to 90:10, even more preferably 30:70 to 80:20, and particularly preferably 40:60 to 60:40.

[0018] The (meth)acrylic acid alkoxyalkyl ester monomer is not particularly limited, but is preferably an ester of an alkoxyalkyl alcohol having 2 to 12 carbon atoms and (meth)acrylic acid (a (meth)acrylic acid ester having an alkoxyalkyl group having 2 to 12 carbon atoms), more preferably an ester of an alkoxyalkyl alcohol having 2 to 8 carbon atoms and (meth)acrylic acid (a (meth)acrylic acid ester having an alkoxyalkyl group having 2 to 8 carbon atoms), and even more preferably an ester of an alkoxyalkyl alcohol having 2 to 6 carbon atoms and (meth)acrylic acid (a (meth)acrylic acid ester having an alkoxyalkyl group having 2 to 6 carbon atoms).

[0019] Specific examples of the (meth)acrylic acid alkoxyalkyl ester monomer include methoxymethyl (meth)acrylate, ethoxymethyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-propoxyethyl (meth)acrylate, 2-butoxyethyl (meth)acrylate, 3-methoxypropyl (meth)acrylate, and 4-methoxybutyl (meth)acrylate. Among these, 2-ethoxyethyl (meth)acrylate and 2-methoxyethyl (meth)acrylate are preferred, and 2-ethoxyethyl acrylate and 2-methoxyethyl acrylate are particularly preferred. These can be used alone or in combination of two or more.

[0020] The total content of (meth)acrylic acid alkyl ester monomer units and (meth)acrylic acid alkoxyalkyl ester monomer units in all monomer units constituting the acrylic rubber (A) used in the present invention is preferably 40% by weight or more, more preferably 60% by weight or more, even more preferably 80% by weight or more, particularly preferably 90% by weight or more, and particularly preferably 95% by weight or more. When the total content of (meth)acrylic acid alkyl ester monomer units and (meth)acrylic acid alkoxyalkyl ester monomer units is within the above range, the obtained cross-linked rubber product has even more excellent mechanical properties.

[0021] The acrylic rubber (A) used in the present invention may contain a (meth)acrylic acid ester monomer as a main component in the molecule, but preferably contains at least a (meth)acrylic acid alkyl ester monomer unit.

[0022] When the acrylic rubber (A) used in the present invention contains (meth)acrylic acid alkyl ester monomer units and (meth)acrylic acid alkoxyalkyl ester monomer units, the weight ratio of the contents of both monomer units [(meth)acrylic acid alkyl ester monomer unit content: (meth)acrylic acid alkoxyalkyl ester monomer unit content] is preferably 1:99 to 99:1, more preferably 40:60 to 98:2, still more preferably 60:40 to 95:5, and particularly preferably 70:30 to 85:15.

[0023] The acrylic rubber (A) used in the present invention may contain, in addition to (meth)acrylic acid ester monomer units, carboxyl group-containing monomer units, epoxy group-containing monomer units, halogen atom-containing monomer units, diene monomer units, etc.

[0024] The carboxyl group-containing monomer that forms the carboxyl group-containing monomer unit is not particularly limited, but examples thereof include an α,β-ethylenically unsaturated dicarboxylic acid monoester monomer, an α,β-ethylenically unsaturated monocarboxylic acid, and an α,β-ethylenically unsaturated dicarboxylic acid.

[0025] The α,β-ethylenically unsaturated dicarboxylic acid monoester monomer is preferably a monoester of an α,β-ethylenically unsaturated dicarboxylic acid having 4 to 12 carbon atoms and an alkanol having 1 to 12 carbon atoms, more preferably a monoester of an α,β-ethylenically unsaturated dicarboxylic acid having 4 to 6 carbon atoms and an alkanol having 2 to 8 carbon atoms, and even more preferably a monoester of an α,β-ethylenically unsaturated dicarboxylic acid having 4 carbon atoms and an alkanol having 2 to 6 carbon atoms.

[0026] Specific examples of α,β-ethylenically unsaturated dicarboxylic acid monoester monomers include butenedioic acid mono-chain alkyl esters such as monomethyl fumarate, monoethyl fumarate, mono-n-butyl fumarate, monomethyl maleate, monoethyl maleate, and mono-n-butyl maleate; butenedioic acid monoesters having an alicyclic structure such as monocyclopentyl fumarate, monocyclohexyl fumarate, monocyclohexenyl fumarate, monocyclopentyl maleate, monocyclohexyl maleate, and monocyclohexenyl maleate; and itaconic acid monoesters such as monomethyl itaconate, monoethyl itaconate, mono-n-butyl itaconate, and monocyclohexyl itaconate. These may be used alone or in combination of two or more. Among the above-mentioned monomers, the dicarboxylic acid may also exist as an anhydride. Specific examples of α,β-ethylenically unsaturated monocarboxylic acids include acrylic acid, methacrylic acid, α-ethylacrylic acid, crotonic acid, and cinnamic acid. Specific examples of α,β-ethylenically unsaturated dicarboxylic acids include butenedioic acids such as fumaric acid and maleic acid; itaconic acid; citraconic acid; and chloromaleic acid. The above-mentioned monomers also include those present as anhydrides. Among these, α,β-ethylenically unsaturated dicarboxylic acid monoester monomers are preferred, with butenedioic acid mono-chain alkyl esters and butenedioic acid monoesters having an alicyclic structure being more preferred, mono-n-butyl fumarate, mono-n-butyl maleate, monocyclohexyl fumarate, and monocyclohexyl maleate being even more preferred, and mono-n-butyl fumarate being particularly preferred.

[0027] When the acrylic rubber (A) used in the present invention contains a carboxyl group-containing monomer unit, the content of the carboxyl group-containing monomer unit is preferably 0.1 to 10% by weight, more preferably 0.5 to 7% by weight, even more preferably 0.5 to 5% by weight, and particularly preferably 1 to 3% by weight. By having the content of the carboxyl group-containing monomer unit within the above range, it is possible to achieve both scorch stability and mechanical properties of the primary crosslinked product at an even higher level.

[0028] The epoxy group-containing monomer that forms the epoxy group-containing monomer unit is not particularly limited, but examples thereof include epoxy group-containing (meth)acrylic acid esters and epoxy group-containing ethers.

[0029] Specific examples of epoxy group-containing (meth)acrylic acid esters include glycidyl (meth)acrylate. Specific examples of epoxy group-containing ethers include allyl glycidyl ether and vinyl glycidyl ether. Among these, glycidyl methacrylate and allyl glycidyl ether are preferred. These epoxy group-containing monomers can be used alone or in combination of two or more.

[0030] When the acrylic rubber (A) used in the present invention contains a monomer unit having an epoxy group, the content of the monomer unit having an epoxy group is preferably 0.1 to 10% by weight, more preferably 0.5 to 7% by weight, even more preferably 0.5 to 5% by weight, and particularly preferably 1 to 3% by weight. By having the content of the monomer unit having an epoxy group in the above range, it is possible to achieve all of the crosslinking rate, scorch stability, and mechanical properties of the primary crosslinked product at an even higher level.

[0031] The halogen atom-containing monomer that forms the halogen atom-containing monomer unit is not particularly limited, and examples thereof include unsaturated alcohol esters of halogen-containing saturated carboxylic acids, (meth)acrylic acid haloalkyl esters, (meth)acrylic acid haloacyloxyalkyl esters, (meth)acrylic acid (haloacetylcarbamoyloxy)alkyl esters, halogen-containing unsaturated ethers, halogen-containing unsaturated ketones, halomethyl group-containing aromatic vinyl compounds, halogen-containing unsaturated amides, and haloacetyl group-containing unsaturated monomers.

[0032] Specific examples of unsaturated alcohol esters of halogen-containing saturated carboxylic acids include vinyl monochloroacetate, vinyl 2-chloropropionate, and allyl chloroacetate. Specific examples of (meth)acrylic acid haloalkyl esters include chloromethyl (meth)acrylate, 1-chloroethyl (meth)acrylate, 2-chloroethyl (meth)acrylate, 1,2-dichloroethyl (meth)acrylate, 2-chloropropyl (meth)acrylate, 3-chloropropyl (meth)acrylate, and 2,3-dichloropropyl (meth)acrylate. Specific examples of (meth)acrylic acid haloacyloxyalkyl esters include 2-(chloroacetoxy)ethyl (meth)acrylate, 2-(chloroacetoxy)propyl (meth)acrylate, 3-(chloroacetoxy)propyl (meth)acrylate, and 3-(hydroxychloroacetoxy)propyl (meth)acrylate. Specific examples of (meth)acrylic acid (haloacetylcarbamoyloxy)alkyl esters include 2-(chloroacetylcarbamoyloxy)ethyl (meth)acrylate and 3-(chloroacetylcarbamoyloxy)propyl (meth)acrylate. Specific examples of halogen-containing unsaturated ethers include chloromethyl vinyl ether, 2-chloroethyl vinyl ether, 3-chloropropyl vinyl ether, 2-chloroethyl allyl ether, and 3-chloropropyl allyl ether. Specific examples of halogen-containing unsaturated ketones include 2-chloroethyl vinyl ketone, 3-chloropropyl vinyl ketone, and 2-chloroethyl allyl ketone. Specific examples of halomethyl group-containing aromatic vinyl compounds include p-chloromethylstyrene, m-chloromethylstyrene, o-chloromethylstyrene, and p-chloromethyl-α-methylstyrene. Specific examples of halogen-containing unsaturated amides include N-chloromethyl(meth)acrylamide. Specific examples of haloacetyl group-containing unsaturated monomers include 3-(hydroxychloroacetoxy)propyl allyl ether and p-vinylbenzyl chloroacetic acid ester.Among these, unsaturated alcohol esters of halogen-containing saturated carboxylic acids and halogen-containing unsaturated ethers are preferred, vinyl monochloroacetate and 2-chloroethyl vinyl ether are more preferred, and vinyl monochloroacetate is even more preferred. These halogen atom-containing monomers can be used alone or in combination of two or more.

[0033] When the acrylic rubber (A) used in the present invention contains a monomer unit having a halogen atom, the content of the monomer unit having a halogen atom is preferably 0.1 to 10% by weight, more preferably 0.5 to 7% by weight, even more preferably 0.5 to 5% by weight, and particularly preferably 1 to 3% by weight. By having the content of the monomer unit having a halogen atom in the above range, it is possible to achieve all of the crosslinking rate, scorch stability, and mechanical properties of the primary crosslinked product at an even higher level.

[0034] The diene monomer forming the diene monomer unit may be a conjugated diene monomer or a non-conjugated diene monomer.

[0035] Specific examples of conjugated diene monomers include 1,3-butadiene, isoprene, and piperylene. Specific examples of non-conjugated diene monomers include ethylidene norbornene, dicyclopentadiene, dicyclopentadienyl (meth)acrylate, and 2-dicyclopentadienylethyl (meth)acrylate.

[0036] The above-mentioned carboxyl group-containing monomers, epoxy group-containing monomers, halogen atom-containing monomers and diene monomers can be used either individually or in combination of two or more.

[0037] The acrylic rubber (A) used in the present invention may contain, in addition to the above-mentioned monomer units, units of other monomers copolymerizable therewith. Such copolymerizable other monomers are not particularly limited, but include aromatic vinyl monomers, α,β-ethylenically unsaturated nitrile monomers, acrylamide monomers, α,β-ethylenically unsaturated dicarboxylic acid diester monomers, other olefin monomers, etc.

[0038] Examples of aromatic vinyl monomers include styrene, α-methylstyrene, divinylbenzene, etc. Examples of α,β-ethylenically unsaturated nitrile monomers include acrylonitrile, methacrylonitrile, etc. Examples of acrylamide monomers include acrylamide, methacrylamide, etc. Examples of the α,β-ethylenically unsaturated dicarboxylic acid diester monomer include dialkyl maleates such as dimethyl maleate and di-n-butyl maleate, wherein the alkyl group has 1 to 18 carbon atoms; dialkyl fumarate esters such as dimethyl fumarate and di-n-butyl fumarate, wherein the alkyl group has 1 to 18 carbon atoms; dicycloalkyl maleates such as dicyclopentyl maleate and dicyclohexyl maleate, wherein the cycloalkyl group has 4 to 16 carbon atoms; dicycloalkyl fumarate esters such as dicyclopentyl fumarate and dicyclohexyl fumarate, wherein the cycloalkyl group has 4 to 16 carbon atoms; dialkyl itaconate esters such as dimethyl itaconate and di-n-butyl itaconate, wherein the alkyl group has 1 to 18 carbon atoms; and dicycloalkyl itaconate esters such as dicyclohexyl itaconate, wherein the cycloalkyl group has 4 to 16 carbon atoms. Other olefinic monomers include ethylene, propylene, vinyl chloride, vinylidene chloride, vinyl acetate, ethyl vinyl ether, and butyl vinyl ether.

[0039] The other copolymerizable monomers can be used alone or in combination of two or more. The content of the units of the other copolymerizable monomers in the monomer units constituting the acrylic rubber (A) used in the present invention is preferably 48.7% by weight or less, more preferably 28.5% by weight or less, even more preferably 18.5% by weight or less, particularly preferably 13.5% by weight or less, and most preferably 8.0% by weight or less.

[0040] The acrylic rubber (A) used in the present invention can be obtained by polymerizing the above-mentioned monomers. As the form of the polymerization reaction, any of emulsion polymerization, suspension polymerization, bulk polymerization, and solution polymerization can be used, but from the viewpoint of ease of control of the polymerization reaction, emulsion polymerization under normal pressure is preferred.

[0041] Emulsion polymerization may be performed batchwise, semi-batchwise, or continuously. Polymerization is typically carried out at a temperature ranging from 0 to 70°C, preferably from 5 to 50°C. The above-mentioned monomers do not necessarily need to be supplied in their entirety to the reaction site from the beginning of the reaction; they may be added continuously or intermittently throughout the reaction time, or may be introduced all at once or in portions during or after the reaction, taking into account factors such as copolymerization reactivity ratio and reaction conversion rate. The ratios of the monomers added in the polymerization reaction may be adjusted based on the reactivity of each monomer. However, because the polymerization reaction often proceeds nearly quantitatively, the ratios may be determined based on the monomer unit composition of the acrylic rubber (A) to be produced, taking these factors into consideration. After polymerization, solidification and drying are performed to obtain a solid acrylic rubber (A).

[0042] The Mooney viscosity (ML1+4, 100°C) (polymer Mooney) of the acrylic rubber (A) used in the present invention produced in this manner is preferably 10 to 150, more preferably 10 to 80, even more preferably 20 to 70, particularly preferably 25 to 60, and particularly preferably 30 to 50.

[0043] The shape of the acrylic rubber (A) used in the present invention is not particularly limited, and may be any of a veil, a sheet, a powder, or the like.

[0044] <Organic Peroxide (B)> The acrylic rubber composition of the present invention contains 0.1 to 5 parts by weight of the organic peroxide (B) based on 100 parts by weight of the acrylic rubber (A).

[0045] The organic peroxide (B) is not particularly limited as long as it is used as a crosslinking agent in the rubber industry, and examples thereof include dialkyl peroxides, diacyl peroxides, and peroxy esters.

[0046] Examples of dialkyl peroxides include dicumyl peroxide, di-t-butyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)-3-hexyne, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and 1,3-bis(t-butylperoxyisopropyl)benzene. Examples of diacyl peroxides include benzoyl peroxide and isobutyryl peroxide. Examples of peroxy esters include 2,5-dimethyl-2,5-bis(benzoylperoxy)hexane and t-butylperoxyisopropyl carbonate. Of these, dialkyl peroxides are preferred, and 1,3-bis(t-butylperoxyisopropyl)benzene is more preferred.

[0047] The content of the organic peroxide (B) in the acrylic rubber composition of the present invention is 0.1 to 5 parts by weight per 100 parts by weight of the acrylic rubber (A). If the content of the organic peroxide (B) is too low, the crosslinking of the acrylic rubber composition does not proceed sufficiently, making it impossible to obtain a crosslinked rubber product. On the other hand, if the content of the organic peroxide (B) is too high, the scorch stability and the mechanical properties of the primary crosslinked product become insufficient.

[0048] The content of the organic peroxide (B) is not particularly limited as long as it is 0.1 to 5 parts by weight per 100 parts by weight of the acrylic rubber (A), but is preferably 0.5 to 4.5 parts by weight, more preferably 1 to 4 parts by weight, and even more preferably 1.5 to 3 parts by weight. By setting the content of the organic peroxide (B) within the above range, it is possible to achieve all of the crosslinking rate, scorch stability, and mechanical properties of the primary crosslinked product at an even higher level.

[0049] The acrylic rubber composition of the present invention may contain a crosslinking agent other than the organic peroxide (B), but the content thereof is preferably 0.5 parts by weight or less, and more preferably 0.1 parts by weight or less, relative to 100 parts by weight of the acrylic rubber (A).

[0050] <Co-Crosslinking Agent (C)> The acrylic rubber composition of the present invention contains 0.1 to 10 parts by weight of the co-crosslinking agent (C) based on 100 parts by weight of the acrylic rubber (A).

[0051] The co-crosslinking agent (C) is not particularly limited, but is preferably a low-molecular-weight or high-molecular-weight compound having a plurality of radically reactive unsaturated groups in the molecule, and examples thereof include polyfunctional vinyl compounds such as divinylbenzene and divinylnaphthalene; isocyanurates such as triallyl isocyanurate and trimethallyl isocyanurate; cyanurates such as triallyl cyanurate; maleimides such as N,N'-m-phenylenedimaleimide and diphenylmethane-4,4'-bismaleimide; diallyl phthalate, diallyl isophthalate, diallyl maleate, and Examples of suitable amines include allyl esters of polyvalent acids such as allyl fumarate, diallyl sebacate, and triallyl phosphate; diethylene glycol bisallyl carbonate; allyl ethers such as ethylene glycol diallyl ether, triallyl ether of trimethylolpropane, and partial allyl ether of pentaerythritol; allyl-modified resins such as allylated novolak and allylated resole resin; and tri- to penta-functional methacrylate and acrylate compounds such as trimethylolpropane trimethacrylate and trimethylolpropane triacrylate. These may be used alone or in combination. Among these, isocyanurates, maleimides, allyl ethers, and tri- to penta-functional methacrylate and acrylate compounds are preferred, with triallyl isocyanurate, N,N'-m-phenylenedimaleimide, and trimethylolpropane trimethacrylate being more preferred.

[0052] The content of the co-crosslinking agent (C) in the acrylic rubber composition of the present invention is 0.1 to 10 parts by weight per 100 parts by weight of the acrylic rubber (A). If the content of the co-crosslinking agent (C) is too low, the crosslinking of the acrylic rubber composition does not proceed sufficiently, making it impossible to obtain a cross-linked rubber product. On the other hand, if the content of the co-crosslinking agent (C) is too high, the scorch stability and the mechanical properties of the primary cross-linked product become insufficient.

[0053] The content of the co-crosslinking agent (C) is not particularly limited as long as it is 0.1 to 10 parts by weight relative to 100 parts by weight of the acrylic rubber (A), but is preferably 0.2 to 8 parts by weight, more preferably 0.3 to 7 parts by weight, and even more preferably 0.5 to 5 parts by weight. By setting the content of the co-crosslinking agent (C) within the above range, it is possible to achieve all of the crosslinking rate, scorch stability, and mechanical properties of the primary crosslinked product at an even higher level.

[0054] <Sulfur-Based Compound (D)> The acrylic rubber composition of the present invention contains 0.05 to 3 parts by weight of a sulfur-based compound (D) based on 100 parts by weight of the acrylic rubber (A).

[0055] In the present invention, the sulfur-based compound (D) is blended with the acrylic rubber (A) in the above-mentioned predetermined amounts together with the organic peroxide (B) and the co-crosslinking agent (C). In particular, the present inventors conducted extensive research and found that by using the above-mentioned predetermined amount of sulfur-based compound (D) in addition to the organic peroxide (B) and the co-crosslinking agent (C), the reaction between the acrylic rubber (A) and the organic peroxide (B) and the co-crosslinking agent (C) can be suppressed, thereby preventing unintended crosslinking reactions of the acrylic rubber (A) and improving scorch stability. In particular, according to the present invention, by appropriately controlling the blending amount of the sulfur-based compound (D), it is possible to ensure a sufficient crosslinking rate while improving scorch stability. Furthermore, in addition to the above, the present inventors conducted extensive research and found that the cross-linked rubber obtained by crosslinking the acrylic rubber composition having the above-mentioned configuration can have sufficient mechanical properties. In particular, according to the findings of the present inventors, when crosslinking of acrylic rubber (A) is carried out using an organic peroxide (B) and a co-crosslinking agent (C) (i.e., without using a sulfur-based compound (D)), a reaction occurs in which the organic peroxide (B) severs the main chains of the molecules that form the acrylic rubber (A) as the crosslinking reaction of the acrylic rubber (A) progresses, resulting in a decrease in the molecular weight of the acrylic rubber (A) itself, and as a result, the mechanical properties of the resulting cross-linked rubber are insufficient. In response to this, the present inventors have conducted research and found that by using the above-mentioned predetermined amount of sulfur-based compound (D) in addition to the organic peroxide (B) and the co-crosslinking agent (C), the sulfur-based compound (D) acts on the acrylic rubber (A) during the cross-linking reaction, thereby effectively suppressing the severance of the main chains of the molecules that form the acrylic rubber (A), thereby suppressing a decrease in the molecular weight of the acrylic rubber (A) itself, and as a result, the mechanical properties of the resulting cross-linked rubber are sufficient. In particular, according to the present invention, by adopting such a configuration, the mechanical properties of the resulting cross-linked rubber are sufficient even without secondary cross-linking.

[0056] Examples of the sulfur-based compound (D) 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, N,N'-dithio-bis(hexahydro-2H-azepinone-2), phosphorus-containing polysulfides, polymeric polysulfides, 2-(4'-morpholinodithio)benzothiazole, and phenothiazine; dithiocarbamic acids such as dibutyldithiocarbamic acid, di-2-ethylhexyldithiocarbamic acid, dicyclohexyldithiocarbamic acid, diphenyldithiocarbamic acid, and dibenzyldithiocarbamic acid, and zinc salts thereof; and thiuram compounds such as tetramethylthiuram disulfide, tetraethylthiuram disulfide, and tetramethylthiuram monosulfide. These compounds may be used alone or in combination of two or more. Of these, sulfur, phenothiazine, zinc dibutyldithiocarbamate, and tetramethylthiuram disulfide are preferred.

[0057] The content of the sulfur-based compound (D) in the acrylic rubber composition of the present invention is 0.05 to 3 parts by weight per 100 parts by weight of the acrylic rubber (A). If the content of the sulfur-based compound (D) is too low, the scorch stability of the acrylic rubber composition and the mechanical properties of the primary crosslinked product become insufficient. On the other hand, if the content of the sulfur-based compound (D) is too high, the acrylic rubber composition cannot be sufficiently crosslinked.

[0058] The content of the sulfur-based compound (D) is not particularly limited as long as it is 0.05 to 3 parts by weight relative to 100 parts by weight of the acrylic rubber (A), but is preferably 0.06 to 2.5 parts by weight, more preferably 0.08 to 2.2 parts by weight, and even more preferably 0.1 to 2 parts by weight. By setting the content of the sulfur-based compound (D) within the above range, it is possible to achieve all of the crosslinking rate, scorch stability, and mechanical properties of the primary crosslinked product at an even higher level.

[0059] <Other Components> The acrylic rubber composition of the present invention may contain a rubber other than the acrylic rubber (A).

[0060] Rubbers other than the acrylic rubber (A) that can be used in the present invention are not particularly limited, but examples include natural rubber, polybutadiene rubber, polyisoprene rubber, styrene-butadiene rubber, acrylonitrile-butadiene rubber, silicone rubber, fluororubber, olefin-based elastomers, styrene-based elastomers, vinyl chloride-based elastomers, polyester-based elastomers, polyamide-based elastomers, polyurethane-based elastomers, polysiloxane-based elastomers, etc. These can be used alone or in combination of two or more.

[0061] The proportion of the acrylic rubber (A) component in the rubber component of the acrylic rubber composition may be selected appropriately depending on the intended use, but is preferably 70% by weight or more, more preferably 90% by weight or more, even more preferably 95% by weight or more, and particularly preferably 100% by weight (i.e., an embodiment in which the rubber component of the acrylic rubber composition consists essentially of the acrylic rubber (A) component).

[0062] The acrylic rubber composition of the present invention preferably contains a filler such as a reinforcing filler and a non-reinforcing filler.

[0063] Examples of reinforcing fillers include carbon blacks such as furnace black, acetylene black, thermal black, channel black, and graphite; and silicas such as wet silica, dry silica, and colloidal silica. Examples of non-reinforcing fillers include quartz powder, clays such as diatomaceous earth, zinc oxide, basic magnesium carbonate, activated calcium carbonate, magnesium silicate, aluminum silicate, titanium dioxide, talc, aluminum sulfate, calcium sulfate, and barium sulfate. The fillers can be used alone or in combination of two or more.

[0064] The content of the filler in the acrylic rubber composition of the present invention is not particularly limited, but is preferably 1 to 200 parts by weight, more preferably 10 to 150 parts by weight, and even more preferably 20 to 100 parts by weight, relative to 100 parts by weight of the rubber component containing the acrylic rubber (A) in the acrylic rubber composition.

[0065] The acrylic rubber composition of the present invention may contain an antioxidant as needed. The antioxidant is not particularly limited, but examples thereof include phenolic antioxidants such as doubly hindered phenolic antioxidants, semi-hindered phenolic antioxidants, less hindered phenolic antioxidants, and phenolic antioxidants having no hindered groups; phosphite ester antioxidants; sulfur ester antioxidants; secondary amine antioxidants such as phenyl-α-naphthylamine, phenyl-β-naphthylamine, p-(p-toluenesulfonylamido)-diphenylamine, 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, N,N-diphenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, and butyraldehyde-aniline condensates; imidazole antioxidants; quinoline antioxidants; and hydroquinone antioxidants.

[0066] The antioxidant may be used alone or in combination of two or more. The content of the antioxidant in the rubber composition of the present invention is not particularly limited, but is preferably 0.01 to 15 parts by weight, more preferably 0.05 to 10 parts by weight, and even more preferably 0.1 to 5 parts by weight, per 100 parts by weight of the rubber component containing the copolymer rubber of the present invention.

[0067] In addition to the above-mentioned components, the acrylic rubber composition of the present invention can also contain compounding agents commonly used in the field of rubber processing. Examples of such compounding agents include light stabilizers, plasticizers, softeners, processing aids, adhesives, slip agents, lubricants, flame retardants, mildew inhibitors, antistatic agents, colorants, etc. The amounts of these compounding agents to be added are not particularly limited as long as they do not impair the purpose and effects of the present invention, and can be appropriately added in amounts depending on the purpose of addition.

[0068] The acrylic rubber composition of the present invention can be prepared by blending a crosslinking agent, a co-crosslinking agent, a sulfur-based compound and various other compounding agents used as needed with a rubber component containing the acrylic rubber (A), mixing and kneading the mixture using an open roll, a Banbury mixer, various kneaders, or the like, and then further kneading the mixture using a kneading roll.

[0069] The order of mixing the components is not particularly limited, but it is preferable to thoroughly mix the components that are resistant to reaction or decomposition by heat, and then mix the crosslinking agent and other components that are resistant to reaction or decomposition by heat for a short period of time at a temperature at which they will not react or decompose.

[0070] The acrylic rubber composition of the present invention has a minimum Mooney viscosity at 125°C (Vm, 125°C) of preferably 10 to 80, more preferably 20 to 70, and even more preferably 30 to 60.

[0071] <Rubber Cross-Linked Product> The rubber cross-linked product of the present invention is obtained by cross-linking the above-described acrylic rubber composition of the present invention.

[0072] The cross-linked rubber product of the present invention can be produced by using the acrylic 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 rubber product. In this case, cross-linking may be carried out after molding in advance, or may be carried out simultaneously with molding. The molding temperature is usually 10 to 140°C, and preferably 25 to 120°C.

[0073] The crosslinking temperature is usually 150 to 190°C, preferably 160 to 180°C, and the crosslinking time is usually 2 to 60 minutes, preferably 3 to 40 minutes. The heating method may be appropriately selected from methods commonly used for crosslinking rubber, such as press heating, steam heating, oven heating, and hot air heating.

[0074] In the method for producing a cross-linked rubber product of the present invention, a cross-linked rubber product having sufficient mechanical properties can be obtained by only primary cross-linking, but secondary cross-linking may also be carried out in addition to the primary cross-linking. The secondary cross-linking is usually carried out in a heated air environment at 130 to 220°C for 1 to 48 hours.

[0075] From the viewpoints of productivity, energy saving, and carbon neutrality, the cross-linked rubber product of the present invention is preferably a primary cross-linked product of the acrylic rubber composition of the present invention. For example, the cross-linked rubber product of the present invention is preferably a primary cross-linked product obtained by thermally cross-linking the acrylic rubber composition of the present invention at a temperature of 150°C to 190°C for 2 to 60 minutes.

[0076] The cross-linked rubber product of the present invention can be used as sealing materials such as O-rings, packings, diaphragms, oil seals, shaft seals, bearing sheaths, mechanical seals, wellhead seals, seals for electric and electronic devices, and seals for air compressors; various gaskets such as cylinder head gaskets attached to the joint between a cylinder block and a cylinder head, rocker cover gaskets attached to the joint between a rocker cover and a cylinder head, oil pan gaskets attached to the joint between an oil pan and a cylinder head or a transmission case, gaskets for fuel cell separators attached between a pair of housings sandwiching a unit cell comprising a positive electrode, an electrolyte plate, and a negative electrode, and gaskets for the top covers of hard disk drives; cushioning materials, vibration-proofing materials; wire coating materials; industrial belts; tubing materials; hose materials; belt materials; boot materials; sheets; etc. In particular, the cross-linked rubber product of the present invention is preferably used for hose materials, sealing materials, etc.

[0077] The cross-linked rubber product of the present invention can also be suitably used as an extrusion molded product and a cross-linked product for automobile applications, for example, various hose materials such as fuel oil hoses for fuel tanks, such as fuel hoses, filler neck hoses, vent hoses, vapor hoses and oil hoses, air hoses, such as turbo air hoses and mission control hoses, radiator hoses, heater hoses, brake hoses and air conditioner hoses.

[0078] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. In addition, the "parts" below are based on weight unless otherwise specified. Various physical properties were measured as follows.

[0079] <Polymer Mooney Viscosity (ML1+4, 100°C)> The Mooney viscosity (polymer Mooney viscosity) of the acrylic rubber (A) was measured at a temperature of 100°C in accordance with JIS K6300.

[0080] <Scorch Properties> The Mooney scorch of the acrylic rubber composition was measured at a temperature of 125°C in accordance with JIS K6300, and the minimum Mooney viscosity "Vm" and Mooney scorch time "t5" were determined. The larger the Mooney scorch time "t5" value, the more excellent the scorch stability.

[0081] <Crosslinkability Test> A crosslinkability test was performed on the acrylic rubber composition using a rubber vulcanization tester (Moving Die Rheometer MDR, manufactured by Alpha Technologies) at 170°C for 20 minutes. From the results of the crosslinkability test, the minimum torque "ML", maximum torque "MH" and T90 were determined. Note that "T90" refers to the time required for the torque to increase by 90% from the minimum torque ML when "maximum torque MH - minimum torque ML" is taken as 100%, and if the T90 value is within 15 minutes, it can be determined that the crosslinking rate is sufficient for practical use.

[0082] <Normal state physical properties of cross-linked rubber product (primarily cross-linked product)> Dumbbell No. 3 shaped test pieces were cut out from the sheet-like acrylic rubber cross-linked product (primarily cross-linked product) in accordance with JIS K 6251, and the tensile strength, elongation, and 100% elongation stress of the obtained test pieces were measured. In addition, the hardness of the cross-linked rubber product was measured using a durometer hardness tester (Type A) in accordance with JIS K 6253-3.

[0083] <Percentage increase in tensile strength due to secondary crosslinking> A sheet-like acrylic rubber crosslinked product (primarily crosslinked product) was heated in an oven at 170°C for 4 hours to obtain a secondary crosslinked product. Test pieces were cut out from the secondary crosslinked product in accordance with JIS K6251, and the tensile strength of the obtained test pieces was measured. Then, the percent increase in tensile strength due to secondary crosslinking was calculated according to the following formula: Percentage increase in tensile strength due to secondary crosslinking (%) = ("tensile strength of secondary crosslinked product" - "tensile strength of primary crosslinked product") / "tensile strength of primary crosslinked product" x 100 If the percent increase in tensile strength due to secondary crosslinking is within 20%, it can be determined that the crosslinking reaction has progressed sufficiently, even without secondary crosslinking.

[0084] Synthesis Example 1 (Production of Acrylic Rubber (A-1)) A polymerization reactor equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a pressure reducing device was charged with 200 parts of water, 3 parts of sodium lauryl sulfate, 98 parts of ethyl acrylate, and 2 parts of vinyl monochloroacetate. Subsequently, degassing under reduced pressure and nitrogen substitution were repeated to thoroughly remove oxygen, and then 0.002 parts of sodium formaldehyde sulfoxylate and 0.005 parts of cumene hydroperoxide were added to initiate an emulsion polymerization reaction under normal pressure and temperature. The reaction was continued until the polymerization conversion rate reached 95%. The resulting emulsion polymerization liquid was coagulated with an aqueous magnesium sulfate solution, washed with water, and dried to obtain acrylic rubber (A-1). The Mooney viscosity (ML1+4, 100°C) of the resulting acrylic rubber (A-1) was 45, and the composition of the acrylic rubber (A-1) was 98% by weight of ethyl acrylate units and 2% by weight of vinyl monochloroacetate units.

[0085] Synthesis Example 2 (Production of Acrylic Rubber (A-2)) Except for changing the blending amount of ethyl acrylate from 98 parts to 48 parts, blending 2 parts of monobutyl fumarate instead of 2 parts of monochlorovinyl acetate, and further blending 50 parts of n-butyl acrylate, an acrylic rubber (A-2) was obtained in the same manner as in Synthesis Example 1. The Mooney viscosity (ML1+4, 100°C) of the obtained acrylic rubber (A-2) was 35, and the composition of the acrylic rubber (A-2) was 48% by weight of ethyl acrylate units, 50% by weight of n-butyl acrylate units, and 2% by weight of monobutyl fumarate units.

[0086] Synthesis Example 3 (Production of Acrylic Rubber (A-3)) An acrylic rubber (A-3) was obtained in the same manner as in Synthesis Example 2, except that the amount of ethyl acrylate was changed from 48 parts to 32 parts, the amount of n-butyl acrylate was changed from 50 parts to 39 parts, 2 parts of allyl glycidyl ether was blended in place of 2 parts of monobutyl fumarate, and 27 parts of 2-methoxyethyl acrylate was further blended. The Mooney viscosity (ML1+4, 100°C) of the obtained acrylic rubber (A-3) was 40, and the composition of the acrylic rubber (A-3) was 32 wt% ethyl acrylate units, 39 wt% n-butyl acrylate units, 27 wt% 2-methoxyethyl acrylate units, and 2 wt% allyl glycidyl ether units.

[0087] Synthesis Example 4 (Production of Acrylic Rubber (A-4)) Except for changing the blending amount of ethyl acrylate from 48 parts to 49 parts, the blending amount of n-butyl acrylate from 50 parts to 51 parts, and not blending monobutyl fumarate, an acrylic rubber (A-4) was obtained in the same manner as in Synthesis Example 2. The Mooney viscosity (ML1+4, 100°C) of the obtained acrylic rubber (A-4) was 38, and the composition of the acrylic rubber (A-4) was 49% by weight of ethyl acrylate units and 51% by weight of n-butyl acrylate units.

[0088] Synthesis Example 5 (Production of Acrylic Rubber (A-5)) Except for changing the blending amount of ethyl acrylate from 49 parts to 45 parts, the blending amount of n-butyl acrylate from 51 parts to 37 parts, and further blending 18 parts of 2-methoxyethyl acrylate, an acrylic rubber (A-5) was obtained in the same manner as in Synthesis Example 4. The Mooney viscosity (ML1+4, 100°C) of the obtained acrylic rubber (A-5) was 32, and the composition of the acrylic rubber (A-5) was 45% by weight of ethyl acrylate units, 37% by weight of n-butyl acrylate units, and 18% by weight of 2-methoxyethyl acrylate units.

[0089] Example 1 (Production of Acrylic Rubber Composition) 100 parts of acrylic rubber (A-1), 60 parts of carbon black (trade name "Seat SO", manufactured by Tokai Carbon Co., Ltd.), 2 parts of stearic acid (dispersant and softener for carbon black), 1 part of ester wax (trade name "Greg G-8205", manufactured by DIC Corporation), and 2 parts of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine (trade name "Nocrac CD", manufactured by Ouchi Shinko Chemical Industry Co., Ltd., antioxidant) were kneaded in a Banbury mixer, and then 5.00 parts (2.00 parts in terms of pure organic peroxide) of 1,3-bis(t-butylperoxyisopropyl)benzene (trade name "Vulcup40KE", manufactured by Hercules Chemicals, organic peroxide, 40% product), N,N'-m-phenylenedimaleimide (trade name "VULNOC 2.00 parts of "Sulfax PMC", manufactured by Ouchi Shinko Chemical Industry Co., Ltd., co-crosslinking agent) and 0.50 parts of sulfur (trade name "Sulfax PMC", manufactured by Tsurumi Chemical Industry Co., Ltd.) were added and kneaded with an open roll at 50°C to obtain an acrylic rubber composition. Using the obtained acrylic rubber composition, evaluation of scorch properties and crosslinkability tests were carried out according to the methods described above. The results are shown in Table 1.

[0090] (Production of Cross-Linked Rubber Product) The acrylic rubber composition was molded and cross-linked by pressing at 170°C for 20 minutes at 10 MPa to obtain a 15 cm x 15 cm x 2 mm sheet-shaped cross-linked rubber product (primary cross-linked product). Using the obtained sheet-shaped cross-linked rubber product (primary cross-linked product), normal state physical properties (tensile strength, elongation, stress at 100% elongation, hardness) and the rate of increase in tensile strength due to secondary cross-linking were measured. The results are shown in Table 1.

[0091] Examples 2 to 4 Acrylic rubber compositions were obtained in the same manner as in Example 1, except that acrylic rubber (A-2), acrylic rubber (A-3), and acrylic rubber (A-4) were used instead of acrylic rubber (A-1), and evaluations were similarly carried out. Then, cross-linked rubber products were obtained in the same manner as in Example 1, except that the obtained acrylic rubber compositions were used, and evaluations were similarly carried out. The results are shown in Table 1.

[0092] Comparative Example 1 An acrylic rubber composition was obtained in the same manner as in Example 1, except that sulfur was not blended, and evaluation was similarly carried out. Then, a cross-linked rubber product was obtained in the same manner as in Example 1, except that the obtained acrylic rubber composition was used, and evaluation was similarly carried out. The results are shown in Table 1.

[0093] Comparative Examples 2 to 4 Acrylic rubber compositions were obtained in the same manner as in Comparative Example 1, except that acrylic rubber (A-2), acrylic rubber (A-3), and acrylic rubber (A-4) were used instead of acrylic rubber (A-1), and evaluations were similarly carried out. Then, cross-linked rubber products were obtained in the same manner as in Example 1, except that the obtained acrylic rubber compositions were used, and evaluations were similarly carried out. The results are shown in Table 1.

[0094] Examples 5 to 7 Acrylic rubber compositions were obtained in the same manner as in Example 1, and evaluations were similarly carried out, except that acrylic rubber (A-5) was used instead of 100 parts of acrylic rubber (A-1), and the blending amount of sulfur was changed as shown in Table 2. Then, rubber cross-linked products were obtained in the same manner as in Example 1, and evaluations were similarly carried out, except that the obtained acrylic rubber compositions were used. The results are shown in Table 2.

[0095] Example 8 An acrylic rubber composition was obtained in the same manner as in Example 5, except that 2.00 parts of triallyl isocyanurate (trade name "TAIC", manufactured by Nippon Kasei Chemical Industry Co., Ltd., co-crosslinking agent) was used instead of 2.00 parts of N,N'-m-phenylenedimaleimide, and 1.00 parts of phenothiazine (trade name "TDP", manufactured by Kawaguchi Chemical Industry Co., Ltd., sulfur-based compound) was used instead of 0.20 parts of sulfur, and evaluation was similarly carried out. Then, a cross-linked rubber product was obtained in the same manner as in Example 5, except that the obtained acrylic rubber composition was used, and evaluation was similarly carried out. The results are shown in Table 2.

[0096] Example 9 An acrylic rubber composition was obtained in the same manner as in Example 8, except that 1.00 part of zinc dibutyldithiocarbamate (trade name "Noccela BZ", manufactured by Ouchi Shinko Chemical Industry Co., Ltd., a sulfur-based compound) was used instead of 1.00 part of phenothiazine, and evaluation was similarly carried out. Then, a cross-linked rubber product was obtained in the same manner as in Example 8, except that the obtained acrylic rubber composition was used, and evaluation was similarly carried out. The results are shown in Table 2.

[0097] Example 10 An acrylic rubber composition was obtained in the same manner as in Example 5, except that 2.00 parts of trimethylolpropane trimethacrylate (trade name "TMPT", manufactured by Shin-Nakamura Chemical Co., Ltd., co-crosslinking agent) was used instead of 2.00 parts of N,N'-m-phenylenedimaleimide, and 1.00 parts of tetramethylthiuram disulfide (trade name "TMTD", manufactured by Sanshin Chemical Industry Co., Ltd., sulfur-based compound) was used instead of 0.20 parts of sulfur, and evaluation was similarly carried out. Then, a cross-linked rubber product was obtained in the same manner as in Example 5, except that the obtained acrylic rubber composition was used, and evaluation was similarly carried out. The results are shown in Table 2.

[0098] Examples 11 and 12 Acrylic rubber compositions were obtained in the same manner as in Example 6, and evaluations were similarly carried out, except that the blending amount of N,N'-m-phenylenedimaleimide was changed as shown in Table 2. Then, except that the obtained acrylic rubber composition was used, a cross-linked rubber product was obtained in the same manner as in Example 6, and evaluations were similarly carried out. The results are shown in Table 2.

[0099] Examples 13 and 14 Acrylic rubber compositions were obtained in the same manner as in Example 6, and evaluations were similarly carried out, except that the blending amount of 1,3-bis(t-butylperoxyisopropyl)benzene was changed as shown in Table 2. Then, except that the obtained acrylic rubber composition was used, a cross-linked rubber product was obtained in the same manner as in Example 6, and evaluations were similarly carried out. The results are shown in Table 2.

[0100] Comparative Example 5 An acrylic rubber composition was obtained in the same manner as in Example 6, except that N,N'-m-phenylenedimaleimide was not blended, and evaluation was similarly carried out. Then, a cross-linked rubber product was obtained in the same manner as in Example 6, except that the obtained acrylic rubber composition was used, and evaluation was similarly carried out. The results are shown in Table 3.

[0101] Comparative Example 6 An acrylic rubber composition was obtained in the same manner as in Example 6, except that the amount of N,N'-m-phenylenedimaleimide blended was changed from 2.00 parts to 15.00 parts, and evaluation was similarly carried out. Then, a cross-linked rubber product was obtained in the same manner as in Example 6, except that the obtained acrylic rubber composition was used, and evaluation was similarly carried out. The results are shown in Table 3.

[0102] Comparative Examples 7 and 8 Acrylic rubber compositions were obtained in the same manner as in Example 6, except that the blending amount of 1,3-bis(t-butylperoxyisopropyl)benzene was changed as shown in Table 3, and evaluations were similarly carried out. Then, except that the obtained acrylic rubber composition was used, a cross-linked rubber product was obtained in the same manner as in Example 6, and evaluations were similarly carried out. The results are shown in Table 3.

[0103] Comparative Example 9 An acrylic rubber composition was obtained in the same manner as in Example 6, except that the blending amount of sulfur was changed from 0.50 parts to 5.00 parts, and evaluation was similarly carried out. Then, a cross-linked rubber product was obtained in the same manner as in Example 6, except that the obtained acrylic rubber composition was used, and evaluation was similarly carried out. The results are shown in Table 3.

[0104]

[0105]

[0106]

[0107] As shown in Tables 1 and 2, the acrylic rubber compositions containing the acrylic rubber (A), the organic peroxide (B), the co-crosslinking agent (C), and the sulfur-based compound (D) in specific content ratios had a sufficient crosslinking rate, good scorch stability, and were capable of giving cross-linked rubber products having sufficient mechanical properties even without secondary crosslinking (Examples 1 to 14).

[0108] On the other hand, when the acrylic rubber composition did not contain the sulfur-based compound (D), the resulting acrylic rubber composition had insufficient scorch stability and insufficient progress of crosslinking, and the cross-linked rubber product obtained from such an acrylic rubber composition had poor mechanical properties (Comparative Examples 1 to 4). Furthermore, when the acrylic rubber composition did not contain the co-crosslinking agent (C), or when the content of the organic peroxide (B) was too low, or when the content of the sulfur-based compound (D) was too high, the cross-linking of the resulting acrylic rubber composition did not progress sufficiently, and a cross-linked rubber product could not be obtained (Comparative Examples 5, 7, and 9). Furthermore, when the content of the organic peroxide (B) or the co-crosslinking agent (C) contained in the acrylic rubber composition was too high, the acrylic rubber composition had low scorch stability, and the cross-linked rubber product obtained from such an acrylic rubber composition had poor mechanical properties (elongation in particular) (Comparative Examples 6 and 8).

Claims

1. An acrylic rubber composition containing an acrylic rubber (A), an organic peroxide (B), a co-crosslinking agent (C), and a sulfur-based compound (D), wherein the content of the organic peroxide (B) is 0.1 to 5 parts by weight per 100 parts by weight of the acrylic rubber (A), the content of the co-crosslinking agent (C) is 0.1 to 10 parts by weight per 100 parts by weight of the acrylic rubber (A), and the content of the sulfur-based compound (D) is 0.05 to 3 parts by weight per 100 parts by weight of the acrylic rubber (A).

2. The acrylic rubber composition according to claim 1, wherein the acrylic rubber (A) contains 40 to 100% by weight of (meth)acrylic acid alkyl ester and / or (meth)acrylic acid alkoxyalkyl ester monomer units.

3. A cross-linked rubber product obtained by cross-linking the acrylic rubber composition according to claim 1 or 2.

4. The cross-linked rubber product according to claim 3, which is a hose material or a sealing material.

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