Rubber composition and crosslinked product

Abstract

To improve the elongation at break of a cured product of a rubber composition.SOLUTION: There is provided a rubber composition which comprises at least one rubber selected from an acrylic rubber and an ethylene-vinyl acetate rubber, an organic peroxide, a cocrosslinking agent having a plurality of ethylenically unsaturated bonds and a phenothiazine-based compound.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a rubber composition and a crosslinked product. [Background technology]

[0002] Cross-linked acrylic rubber has excellent physical properties such as heat resistance, oil resistance, and mechanical properties, and is therefore used, for example, as a material for hoses and sealing parts in automobile engine compartments. One known method for cross-linking acrylic rubber is to cross-link acrylic rubber with a peroxide. For example, Patent Document 1 discloses a rubber composition containing acrylic rubber, a specific maleimide compound, a specific phenothiazine compound, and a peroxide, which is capable of exhibiting good physical properties even with primary vulcanization alone. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-174217 Summary of the Invention [Problem to be solved by the invention]

[0004] According to the investigations of the present inventors, there is still room for improvement in the elongation at break of a cross-linked product of a rubber composition. Therefore, one aspect of the present invention aims to improve the elongation at break of a cross-linked product of a rubber composition. [Means for solving the problem]

[0005] In Patent Document 1, a maleimide compound is used as a so-called co-crosslinking agent, but the present inventors have found that by using a co-crosslinking agent having an ethylenically unsaturated bond, the elongation at break of the crosslinked product of the rubber composition can be improved compared to when a maleimide compound is used.

[0006] The present invention includes the following aspects. [1] A rubber composition comprising at least one rubber selected from acrylic rubber and ethylene-vinyl acetate rubber, an organic peroxide, a co-crosslinking agent having multiple ethylenically unsaturated bonds, and a phenothiazine-based compound. [2] A rubber composition comprising a rubber containing at least one monomer unit selected from the group consisting of (meth)acrylic acid ester, vinyl acetate, and ethylene, an organic peroxide, a co-crosslinking agent having multiple ethylenically unsaturated bonds, and a phenothiazine-based compound. [3] The rubber composition according to [1] or [2], wherein the co-crosslinking agent comprises at least one selected from the group consisting of (poly)alkylene glycol di(meth)acrylate and trimethylolpropane tri(meth)acrylate. [4] The rubber composition according to any one of [1] to [3], wherein the co-crosslinking agent contains a compound represented by the following formula (1): [ka] [In the formula, R 1 and R 2 each independently represents a hydrogen atom or a methyl group, and m represents an integer of 1 to 3. [5] The rubber composition according to any one of [1] to [4], wherein the molar ratio of the ethylenically unsaturated bonds in the co-crosslinking agent to the OO bonds in the organic peroxide is 0.5 or more and 3.0 or less. [6] The rubber composition according to [1], wherein the rubber is an acrylic rubber containing a (meth)acrylic acid ester and a carboxylic acid vinyl ester as monomer units. [7] The rubber composition according to any one of [1] to [6], which is used as a rubber composition for a seal or a hose. [8] A crosslinked product of the rubber composition according to any one of [1] to [7]. [9] The cross-linked product according to [8], which is used as a seal or a hose. [Effects of the Invention]

[0007] According to one aspect of the present invention, the elongation at break of a cross-linked product of the rubber composition can be improved. According to another aspect of the present invention, the tensile strength at break of a cross-linked product of the rubber composition can also be improved. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited to the embodiments.

[0009] One embodiment of the present invention is a rubber composition containing at least one rubber selected from acrylic rubber and ethylene-vinyl acetate rubber, an organic peroxide, a co-crosslinking agent having multiple ethylenically unsaturated bonds, and a phenothiazine-based compound.

[0010] The acrylic rubber contains a (meth)acrylic acid ester as a monomer unit. The (meth)acrylic acid ester includes at least one selected from the group consisting of a (meth)acrylic acid alkyl ester and a (meth)acrylic acid alkoxyalkyl ester. In this specification, the term "(meth)acrylic acid ester" is used to encompass both an acrylic acid ester and the corresponding methacrylic acid ester. Similarly, the term "(meth)acrylic acid alkyl ester" is used to encompass both an acrylic acid alkyl ester and the corresponding methacrylic acid alkyl ester, and the term "(meth)acrylic acid alkoxyalkyl ester" is used to encompass both an acrylic acid alkoxyalkyl ester and the corresponding methacrylic acid alkoxyalkyl ester.

[0011] The (meth)acrylic acid ester preferably includes a (meth)acrylic acid alkyl ester. The alkyl group in the (meth)acrylic acid alkyl ester may be linear or branched. The number of carbon atoms in the alkyl group in the (meth)acrylic acid alkyl ester may be 1 or more and 16 or less.

[0012] The content of the (meth)acrylic acid alkyl ester may be 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, or 50% by mass or more, and may be 90% by mass or less, 80% by mass or less, 70% by mass or less, or 60% by mass or less, based on the total amount of monomer units in the acrylic rubber.

[0013] The (meth)acrylic acid alkyl ester preferably includes an acrylic acid alkyl ester. The alkyl group in the acrylic acid alkyl ester may be linear or branched. The number of carbon atoms in the alkyl group in the acrylic acid alkyl ester may be 1 or more and 16 or less. Specific examples of the acrylic acid alkyl ester include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-pentyl acrylate, isoamyl acrylate, n-hexyl acrylate, 2-methylpentyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, hexadecyl acrylate, 1-adamantyl acrylate, and cyclohexyl acrylate. These acrylic acid alkyl esters may be used alone or in combination of two or more.

[0014] The content of the acrylic acid alkyl ester may be 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, or 50% by mass or more, and may be 90% by mass or less, 80% by mass or less, 70% by mass or less, or 60% by mass or less, based on the total amount of monomer units in the acrylic rubber.

[0015] From the viewpoint of further improving the oil resistance of the cross-linked product of the acrylic rubber, the alkyl acrylate preferably contains an alkyl acrylate having an alkyl group having 3 or less carbon atoms (first alkyl acrylate ester). In addition to the first alkyl acrylate ester, the alkyl acrylate may further contain an alkyl acrylate having an alkyl group having 4 or more carbon atoms (second alkyl acrylate ester).

[0016] The number of carbon atoms in the alkyl group in the first alkyl acrylate may be 1 or more, or 2 or less. The first alkyl acrylate is preferably methyl acrylate or ethyl acrylate. The number of carbon atoms in the alkyl group in the second alkyl acrylate may be 8 or less, 6 or less, or 5 or less, or may be 4. The second alkyl acrylate is preferably n-butyl acrylate.

[0017] The content of the first alkyl acrylate may be 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, or 50% by mass or more, and may be 90% by mass or less, 80% by mass or less, 70% by mass or less, or 60% by mass or less, based on the total amount of monomer units in the acrylic rubber.

[0018] The content of the second alkyl acrylate may be 5% by mass or more, 10% by mass or more, or 20% by mass or more, and may be 60% by mass or less, 50% by mass or less, or 40% by mass or less, based on the total amount of monomer units in the acrylic rubber.

[0019] The (meth)acrylic acid alkyl ester may further contain a methacrylic acid alkyl ester. The alkyl group in the methacrylic acid alkyl ester may be linear or branched. The number of carbon atoms in the alkyl group in the methacrylic acid alkyl ester may be 1 or more or 4 or less, preferably 2 or more or 3 or more, and may be 3. Specific examples of the methacrylic acid alkyl ester include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, and isobutyl methacrylate. These methacrylic acid alkyl esters may be used alone or in combination of two or more. The methacrylic acid alkyl ester is preferably n-butyl methacrylate.

[0020] The content of the alkyl methacrylate ester may be 5% by mass or more, 7% by mass or more, or 10% by mass or more, and may be 30% by mass or less, 20% by mass or less, or 15% by mass or less, based on the total amount of monomer units in the acrylic rubber.

[0021] (Meth)acrylic acid alkoxyalkyl ester is an alkoxyalkyl group (-R a -OR b a group represented by R a represents an alkylene group, and R b represents an alkyl group). a ) and alkyl groups (R b The alkylene group (R) in the (meth)acrylic acid alkoxyalkyl ester may be linear or branched. a The number of carbon atoms in the alkyl group (R ) may be 1 or more, or 2 or more, and may be 4 or less, or 3 or less. b ) may have 1 or more carbon atoms, and may have 4 or less, 3 or less, or 2 or less carbon atoms.

[0022] Specific examples of (meth)acrylic acid alkoxyalkyl esters include 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-(n-propoxy)ethyl (meth)acrylate, 2-(n-butoxy)ethyl (meth)acrylate, 3-methoxypropyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate, 2-(n-propoxy)propyl (meth)acrylate, and 2-(n-butoxy)propyl acrylate. These (meth)acrylic acid alkoxyalkyl esters may be used alone or in combination of two or more.

[0023] The content of the (meth)acrylic acid alkoxyalkyl ester may be 5% by mass or more, 10% by mass or more, or 15% by mass or more, and may be 50% by mass or less, 40% by mass or less, or 30% by mass or less, based on the total amount of monomer units in the acrylic rubber.

[0024] In one embodiment, the acrylic rubber may contain the above-mentioned (meth)acrylic acid ester and vinyl carboxylate ester as monomer units. Specific examples of the vinyl carboxylate ester include vinyl acetate, vinyl neodecanoate, vinyl laurate, vinyl propionate, vinyl butyrate, vinyl caproate, vinyl caprylate, vinyl caprate, vinyl octylate, and vinyl pivalate. The vinyl carboxylate ester preferably contains at least one selected from the group consisting of vinyl acetate, vinyl neodecanoate, and vinyl laurate, and more preferably contains vinyl acetate.

[0025] The content of the vinyl carboxylic acid ester may be 15% by mass or more, 20% by mass or more, or 25% by mass or more, and may be 70% by mass or less, 60% by mass or less, or 50% by mass or less, based on the total amount of monomer units in the acrylic rubber.

[0026] The acrylic rubber may further include ethylene as a monomer unit. In one embodiment, the acrylic rubber may further include ethylene as a monomer unit in addition to a (meth)acrylic acid ester and a vinyl carboxylate ester. In another embodiment, the acrylic rubber may include a (meth)acrylic acid ester and at least one selected from the group consisting of ethylene and vinyl acetate as monomer units. The ethylene content may be 5% by mass or more, 8% by mass or more, or 10% by mass or more, and 50% by mass or less, 40% by mass or less, 30% by mass or less, 20% by mass or less, 15% by mass or less, or 12% by mass or less, based on the total amount of monomer units in the acrylic rubber.

[0027] The acrylic rubber may further contain a crosslinking group as a monomer unit. The crosslinking group is a monomer that is copolymerizable with the above-mentioned monomers and has a crosslinkable group that forms a crosslinking group (also referred to as a crosslinking point). The crosslinking group has a polymerizable carbon-carbon double bond, such as an acryloyl group, a methacryloyl group, an allyl group, a methallyl group, a vinyl group, or an alkenylene group. Examples of the crosslinking group include a carboxyl group, an epoxy group, and an active chlorine group. The crosslinking group may have one or more of these functional groups. In this specification, a monomer that can be classified as both a (meth)acrylic acid ester and a crosslinking group monomer is classified as a crosslinking group monomer.

[0028] Examples of crosslinkable monomers having a carboxyl group as a crosslinkable group include acrylic acid, methacrylic acid, crotonic acid, 2-pentenoic acid, maleic acid, fumaric acid, itaconic acid, monoalkyl fumarate, and monoalkyl maleate.

[0029] Examples of cross-linking monomers having an epoxy group as a cross-linkable group include glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, and methallyl glycidyl ether.

[0030] Examples of crosslinkable monomers having an active chlorine group as a crosslinkable group include 2-chloroethyl vinyl ether, 2-chloroethyl acrylate, vinylbenzyl chloride, vinyl chloroacetate, and allyl chloroacetate.

[0031] The content of the crosslinking monomer may be 0.5% by mass or more, 1% by mass or more, or 2% by mass or more, and may be 8% by mass or less, 6% by mass or less, or 4% by mass or less, based on the total amount of monomer units in the acrylic rubber.

[0032] The acrylic rubber may contain, as a monomer unit, other monomers copolymerizable with the above-mentioned monomers, such as alkyl vinyl ketone, vinyl ether, allyl ether, vinyl aromatic compound, vinyl nitrile, dialkyl maleate, dialkyl fumarate, dialkyl itaconic acid ester, dialkyl citraconic acid ester, dialkyl mesaconic acid ester, dialkyl 2-pentenedioate, and dialkyl acetylenedicarboxylic acid ester.

[0033] The acrylic rubber can be obtained by copolymerizing the above-mentioned monomers by a known polymerization method such as emulsion polymerization, suspension polymerization, solution polymerization, or bulk polymerization, preferably by suspension polymerization.

[0034] Ethylene-vinyl acetate rubber contains ethylene and vinyl acetate as monomer units. Ethylene-vinyl acetate rubber may contain only ethylene and vinyl acetate as monomer units, or may further contain other monomers in addition to ethylene and vinyl acetate. However, in this specification, rubber containing (meth)acrylic acid ester as a monomer unit in addition to ethylene and vinyl acetate is classified as acrylic rubber.

[0035] Other monomers include, for example, vinyl chloride, vinyl propionate, vinyl versatate, acrylic acid, methacrylic acid, maleic acid, itaconic acid, N-vinylpyrrolidone, styrene, acrylonitrile, (meth)acrylamide, triallyl cyanurate, and triallyl isocyanurate.

[0036] The ethylene content may be 5% by mass or more, 10% by mass or more, or 15% by mass or more, and may be 40% by mass or less, 35% by mass or less, or 30% by mass or less, based on the total amount of monomer units in the ethylene-vinyl acetate rubber.

[0037] The content of vinyl acetate may be 40% by mass or more, 45% by mass or more, or 50% by mass or more, and may be 95% by mass or less, 90% by mass or less, or 90% by mass or less, based on the total amount of monomer units in the ethylene-vinyl acetate rubber.

[0038] When the ethylene-vinyl acetate rubber further contains other monomers as monomer units, the content of the other monomers may be 0.5% by mass or more, 1% by mass or more, or 3% by mass or more, and may be 20% by mass or less, 15% by mass or less, or 10% by mass or less, based on the total amount of monomer units in the ethylene-vinyl acetate rubber.

[0039] The rubber content may be 50% by mass or more, 55% by mass or more, or 60% by mass or more, and 80% by mass or less, 75% by mass or less, or 70% by mass or less, based on the total amount of the rubber composition.

[0040] In another embodiment, the rubber composition may contain a rubber containing at least one monomer unit selected from the group consisting of (meth)acrylic acid esters, vinyl acetate, and ethylene, an organic peroxide, a co-crosslinking agent having multiple ethylenically unsaturated bonds, and a phenothiazine-based compound. Specific examples of the rubber containing at least one monomer unit selected from the group consisting of (meth)acrylic acid esters, vinyl acetate, and ethylene include the above-mentioned acrylic rubber and ethylene-vinyl acetate rubber.

[0041] The organic peroxide may be an organic peroxide commonly used for crosslinking rubber. Specific examples of the organic peroxide include dicumyl peroxide, benzoyl peroxide, 1,1-bis(t-butylperoxy)-3,5,5-trimethylcyclohexane, diisobutyryl peroxide, cumyl peroxyneodecanoate, di-n-propyl peroxydicarbonate, diisopropyl peroxydicarbonate, di-sec-butyl peroxydicarbonate, 1,1,3,3-tetramethylbutyl peroxyneodecanoate, di(4-t-butylcyclohexyl)peroxydicarbonate, Di(2-ethylhexyl) peroxydicarbonate, t-hexyl peroxyneodecanoate, t-butyl peroxyneodecanoate, t-butyl peroxyneoheptanoate, t-hexyl peroxypivalate, t-butyl peroxypivalate, di(3,5,5-trimethylhexanoyl) peroxide, dilauroyl peroxide, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, disuccinic acid peroxide, 2,5-dimethyl-2,5-di(2-ethylhexanoyl) (peroxy)hexane, t-hexylperoxy-2-ethylhexanoate, di(4-methylbenzoyl) peroxide, t-butylperoxy-2-ethylhexanoate, di(3-methylbenzoyl) peroxide, benzoyl(3-methylbenzoyl) peroxide, dibenzoyl peroxide, 1,1-di(t-butylperoxy)-2-methylcyclohexane, 1,1-di(t-hexylperoxy)-3,3,5-trimethylcyclohexane, 1,1-di(t-hexylperoxy)cyclohexa , 1,1-di(t-butylperoxy)cyclohexane, 2,2-di(4,4-di-(t-butylperoxy)cyclohexyl)propane, t-hexylperoxyisopropyl monocarbonate, t-butylperoxymaleic acid, t-butylperoxy-3,5,5-trimethylhexanoate, t-butylperoxylaurate, t-butylperoxyisopropyl monocarbonate, t-butylperoxy 2-ethylhexyl monocarbonate, t-hexylperoxybenzoate, 2,5-dimethyl-2,Examples of peroxyl groups include 5-di(benzoylperoxy)hexane, t-butyl peroxyacetate, 2,2-di-(t-butylperoxy)butane, t-butyl peroxybenzoate, n-butyl-4,4-di-(t-butylperoxy)valerate, 1,4-bis[(t-butylperoxy)isopropyl]benzene, butyl 4,4-bis[(t-butyl)peroxy]pentanoate, di-t-hexyl peroxide, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane, t-butyl-α-cumyl peroxide, di-t-butyl peroxide, p-menthane hydroperoxide, 2,5-bis(t-butylperoxy)-2,5-dimethyl-3-hexyne, diisopropylbenzene hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, cumene hydroperoxide, and t-butyl hydroperoxide. The organic peroxide may include at least one selected from the group consisting of dicumyl peroxide, 1,4-bis[(t-butylperoxy)isopropyl]benzene, and 4,4-bis[(t-butyl)peroxy]butyl pentanoate.

[0042] The content of the organic peroxide may be 1 part by mass or more, 3 parts by mass or more, 5 parts by mass or more, 6 parts by mass or more, or 7 parts by mass or more, and may be 20 parts by mass or less, 18 parts by mass or less, 16 parts by mass or less, or 15 parts by mass or less, per 100 parts by mass of rubber.

[0043] The co-crosslinking agent has a plurality of ethylenically unsaturated bonds, which are represented by the following formula (E): [ka]

[0044] The co-crosslinking agent may have a plurality of (meth)acryloyl groups or vinyl groups as groups having an ethylenically unsaturated bond. In this specification, the term "(meth)acryloyl group" is used to encompass both an acryloyl group and its corresponding (meth)acryloyl group. The number of ethylenically unsaturated bonds ((meth)acryloyl groups or vinyl groups) in the co-crosslinking agent may be 2 or more, 6 or less, 5 or less, 4 or less, or 3 or less, or may be 2 or 3.

[0045] The co-crosslinking agent having multiple (meth)acryloyl groups may be at least one selected from the group consisting of (poly)alkylene glycol di(meth)acrylate and trimethylolpropane tri(meth)acrylate. In this specification, the term "(poly)alkylene glycol di(meth)acrylate" is used to encompass both monoalkylene glycol di(meth)acrylate and polyalkylene glycol di(meth)acrylate.

[0046] The number of carbon atoms in the alkylene group in the (poly)alkylene glycol di(meth)acrylate may be 1 or more or 2 or more, and may be 4 or less or 3 or less, or may be 2 or 3, or may be 2. The number of alkylene groups (repeating number) in the (poly)alkylene glycol di(meth)acrylate may be 1 or more, and may be 3 or less or 2 or less.

[0047] The (poly)alkylene glycol di(meth)acrylate is preferably represented by the following formula (1): That is, the co-crosslinking agent preferably contains a compound represented by the following formula (1). [ka] In the formula, R 1 and R 2 each independently represents a hydrogen atom or a methyl group, and m represents an integer of 1 or greater. m may be an integer of 1 to 3, or may be 1 or 2, or may be 1.

[0048] Examples of the co-crosslinking agent having a plurality of vinyl groups include triallyl cyanurate and triallyl isocyanurate.

[0049] The content of the co-crosslinking agent may be 0.5 parts by mass or more, 1 part by mass or more, or 1.5 parts by mass or more, and may be 10 parts by mass or less, 8 parts by mass or less, or 6 parts by mass or less, per 100 parts by mass of rubber.

[0050] The molar ratio (C=C bond / OO bond) of ethylenically unsaturated group bonds (C=C bonds) in the crosslinking agent to OO bonds in the organic peroxide in the rubber composition may be 0.50 or more, preferably 0.60 or more, 0.70 or more, 0.80 or more, or 0.90 or more, from the viewpoint of further improving the elongation at break of the crosslinked product, and may be 3.3 or less, 3.2 or less, 3.1 or less, or 3.0 or less, and preferably 2.8 or less, 2.6 or less, 2.4 or less, 2.2 or less, or 2.0 or less.

[0051] The phenothiazine compound is a compound having a phenothiazine skeleton represented by the following formula (2). [ka]

[0052] The phenothiazine-based compound may be phenothiazine, or may be a substituted phenothiazine in which at least one of the 10-position (N-position) and the 2-position of phenothiazine is substituted. In the rubber composition of this embodiment, the radical trapping function of the phenothiazine-based compound is utilized to control the crosslinking reaction caused by the organic peroxide. Therefore, the substituted phenothiazine also has the same radical trapping ability as (unsubstituted) phenothiazine, and can be used in the same way as (unsubstituted) phenothiazine.

[0053] Specific examples of substituted phenothiazines include 2-chlorophenothiazine, 2-chlorophenothiazine-10-carbonyl chloride, 2-(trifluoromethyl)phenothiazine, 2-bromophenothiazine, N-methylphenothiazine, N-ethylphenothiazine, Nn-butylphenothiazine, N-cyclohexylphenothiazine, N-adamantylphenothiazine, N-vinylphenothiazine, N-(1-chloro)vinylphenothiazine, N-vinyl-2-phenylphenothiazine, N-phenylphenothiazine, N-benzylphenothiazine, 2-acetylphenothiazine, 2-carboxylphenothiazine, 2-toluylphenothiazine, and 2-naphthylphenothiazine.

[0054] The amount of the phenothiazine compound may be 0.1 parts by mass or more, 0.2 parts by mass or more, 0.3 parts by mass or more, 0.4 parts by mass or more, 0.5 parts by mass or more, more than 0.5 parts by mass, or 0.6 parts by mass or more, and may be 5 parts by mass or less, 4 parts by mass or less, 3 parts by mass or less, or 2 parts by mass or less, per 100 parts by mass of rubber.

[0055] From the viewpoint of improving the tensile strength at break of the crosslinked product as well as the elongation at break of the crosslinked product, the molar ratio of NH bonds in the phenothiazine compound to OO bonds in the organic peroxide in the rubber composition (NH bonds / OO bonds) may be 0.05 or more, preferably 0.07 or more, 0.09 or more, or 0.11 or more, more preferably 0.13 or more, more than 0.13, 0.14 or more, or 0.15 or more, and preferably 0.35 or less, more preferably 0.33 or less, 0.31 or less, or 0.29 or less, and even more preferably 0.27 or less. Note that when the N-position of the phenothiazine compound is substituted, the above NH bond refers to an N-substituent bond.

[0056] The rubber composition may further contain a radical trapping agent other than the phenothiazine-based compound. Examples of the radical trapping agent include 2-mercaptobenzimidazole, trimethylthiourea, triethylthiourea, tributylthiourea, dimethylthiourea, diethylthiourea, dibutylthiourea, diphenylguanidine, di-o-tolylguanidine, 2-imidazolinethione, 2-mercaptobenzothiazole, 2-(methylthio)benzothiazole, 2-methylbenzothiazole, 5-methoxy-2-methylbenzothiazole, 2-aminobenzothiazole, and 2-amino-4-methylbenzothiazole. 2-mercaptobenzothiazole, 2-amino-6-methylbenzothiazole, 2-amino-4-methoxybenzothiazole, 2-amino-6-methoxybenzothiazole, 4-methyl-2-mercaptobenzothiazole, 2,5-dimethylbenzothiazole, 2,6-dimethylbenzothiazole, 2-mercapto-5-methoxybenzothiazole, 2-mercapto-6-nitrobenzothiazole, 6-amino-2-mercaptobenzothiazole, and 2-amino-6-ethoxybenzothiazole.

[0057] The content of the radical trapping agent may be 0.1 parts by mass or more, 0.3 parts by mass or more, or 0.5 parts by mass or more, and may be 5 parts by mass or less, 3 parts by mass or less, or 1 part by mass or less, per 100 parts by mass of rubber.

[0058] The rubber composition may further contain a filler (reinforcing agent). Examples of fillers include carbon black, silica, talc, and calcium carbonate. The amount of filler may be 20 parts by mass or more, 30 parts by mass or more, or 40 parts by mass or more, and 100 parts by mass or less, 80 parts by mass or less, or 60 parts by mass or less, per 100 parts by mass of rubber.

[0059] The rubber composition may further contain a lubricant. Examples of lubricants include liquid paraffin, stearic acid, stearamide, zinc fatty acid, fatty acid ester, and organosilicone. The amount of lubricant may be 0.1 parts by mass or more, 0.5 parts by mass or more, or 0.7 parts by mass or more, and 10 parts by mass or less, 5 parts by mass or less, or 3 parts by mass or less, per 100 parts by mass of rubber.

[0060] The rubber composition may further contain an antioxidant. Examples of the antioxidant include amine-based antioxidants and phenol-based antioxidants. The content of the antioxidant may be 0.1 parts by mass or more, 0.2 parts by mass or more, or 0.3 parts by mass or more, and may be 5 parts by mass or less, 3 parts by mass or less, or 1 part by mass or less, per 100 parts by mass of rubber.

[0061] The rubber composition may further contain a release agent. Examples of the release agent include a phosphate ester and a mixture of a fatty acid, a fatty acid ester, an amine, and a wetting agent. The amount of the release agent may be 0.1 parts by mass or more, 0.2 parts by mass or more, or 0.3 parts by mass or more, and 5 parts by mass or less, 3 parts by mass or less, or 1 part by mass or less, per 100 parts by mass of rubber.

[0062] The above-mentioned Patent Document 1 discloses that the desired effect can be obtained by using 1 to 10 parts by mass of a maleimide compound represented by the following formula (X) relative to 100 parts by mass of acrylic rubber. [ka] In the formula, R 11 represents a hydrogen atom, an alkyl group (having 1 to 17 carbon atoms), a substituted alkyl group, an aryl group, a substituted aryl group, or a hydroxyl group, and R 12 represents a hydrogen atom, an alkyl group (having 1 to 17 carbon atoms), a substituted alkyl group, or an aryl group, and R 13 represents a hydrogen atom, an alkyl group (having 1 to 17 carbon atoms), a substituted alkyl group, or an aryl group.

[0063] In contrast, a rubber composition according to one embodiment does not contain a maleimide compound. A rubber composition according to another embodiment does not contain a maleimide compound represented by formula (X). A rubber composition according to another embodiment is not a rubber composition containing 1 to 10 parts by mass of a maleimide compound relative to 100 parts by mass of acrylic rubber. A rubber composition according to another embodiment is not a rubber composition containing 1 to 10 parts by mass of a maleimide compound represented by formula (X) relative to 100 parts by mass of acrylic rubber.

[0064] The rubber composition described above can be kneaded at a temperature below the temperature at which the crosslinking reaction by peroxide proceeds, and then heated at a predetermined temperature to obtain a crosslinked product (primary crosslinked product or secondary crosslinked product). Another embodiment of the present invention is a crosslinked product (primary crosslinked product or secondary crosslinked product) of the rubber composition described above.

[0065] The heating conditions for crosslinking can be set appropriately. The heating temperature may be 100°C or higher and 200°C or lower. The heating time may be 5 minutes or longer and 10 hours or shorter. As the heating method, methods used for crosslinking rubber, such as hot press heating, steam heating, and oven heating, can be used.

[0066] The apparatus for kneading, molding, and crosslinking the rubber composition and the apparatus for kneading and molding the crosslinked product of the rubber composition can be any apparatus commonly used for rubber compositions, such as a roll, kneader, Banbury mixer, internal mixer, or twin-screw extruder.

[0067] The rubber composition described above is suitably used as a rubber composition for seals (also referred to as sealing members) or hoses (also referred to as hose members). The rubber composition can also be used as a rubber composition for vibration-isolating rubber (also referred to as vibration-isolating rubber members) or wire-coating rubber (also referred to as wire-coating rubber members). A cross-linked product of the rubber composition described above is suitably used as a seal or hose. That is, another embodiment of the present invention is a seal or hose containing the cross-linked product. The cross-linked product can also be used as vibration-isolating rubber or wire-coating rubber. That is, another embodiment of the present invention is a vibration-isolating rubber containing the cross-linked product. Examples of hoses (hose members) include rubber hoses. Examples of seals (sealing members) include gaskets and packings. These components may consist solely of a cross-linked product of the rubber composition, or may include the cross-linked product in addition to other components.

[0068] Specific examples of hoses (hose members) include transmission oil cooler hoses, engine oil cooler hoses, air duct hoses, turbo intercooler hoses, hot air hoses, radiator hoses, power steering hoses, fuel system hoses, drain system hoses, etc. The hose member may have a reinforcing yarn or wire in an intermediate layer or the outermost layer of the hose.

[0069] Specific examples of seals (sealing members) include engine head cover gaskets, oil pan gaskets, oil seals, lip seal packings, O-rings, transmission seal gaskets, crankshafts, camshaft seal gaskets, valve stems, power steering seals, belt cover seals, boot materials for constant velocity joints, and rack and pinion boot materials.

[0070] Specific examples of anti-vibration rubber (anti-vibration rubber member) include a damper pulley, a center support cushion, and a suspension bush. [Example]

[0071] The present invention will be explained in more detail below based on examples, but the present invention is not limited to these examples.

[0072] (Example 1-1) (Preparation of Rubber Composition) 100 parts by mass of acrylic rubber (G1) having a monomer composition of ethyl acrylate / n-butyl acrylate / vinyl acetate / ethylene = 35 / 18 / 35 / 12 (mass ratio), 8 parts by mass of organic peroxide containing 1,4-bis[(t-butylperoxy)isopropyl]benzene (NOF Corporation "Perbutyl P-40" (concentration 40%)), 3 parts by mass of trimethylolpropane trimethacrylate ("TMPT", co-crosslinking agent), 0.5 parts by mass of phenothiazine, filler (carbon black A rubber composition was obtained by kneading 50 parts by mass of a lubricant (stearic acid, manufactured by Tokai Carbon Co., Ltd., "SEAST SO"), 1 part by mass of a lubricant (stearic acid, manufactured by Kao Corporation, "Lunac S-90"), 0.5 parts by mass of an antioxidant (4,4'-bis(α,α-dimethylbenzyl)diphenylamine, manufactured by Addivant, "Nauguard 445"), and 0.5 parts by mass of a release agent (a mixture of fatty acid, fatty acid ester, amine, and wetting agent, manufactured by Axel, "Moldwiz INT-21G") using an 8-inch open roll.

[0073] (Preparation of cross-linked product) Each rubber composition obtained was cut into a 2.4 mm thick sheet and then heated and pressed at 170°C and 4 MPa for 20 minutes using a press vulcanizer to obtain a primary crosslinked product of the rubber composition. Subsequently, the primary crosslinked product was heated in a gear oven at 170°C for 4 hours to obtain a secondary crosslinked product of the rubber composition.

[0074] (Measurement of elongation at break and tensile strength at break) The elongation at break Eb and tensile strength at break Tb of the secondary cross-linked product were measured using a dumbbell No. 3 according to JIS K6251:2017. The results are shown in Table 1.

[0075] (Comparative Example 1-1) Preparation of a rubber composition, production of a crosslinked product, and measurement of elongation at break and tensile strength at break were carried out in the same manner as in Example 1-1, except that N,N'-m-phenylenedimaleimide ("Valnoc PM" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) was used instead of TMPT as the co-crosslinking agent. Valnoc PM was used so that the TMPT in Example 1-1 and the Valnoc PM in Comparative Example 1-1 were in equimolar amounts.

[0076] (Examples 1-2 and Comparative Examples 1-2) In Example 1-2 and Comparative Example 1-2, preparation of rubber compositions, production of crosslinked products, and measurement of elongation at break and tensile strength at break were carried out in the same manner as in Example 1-1 and Comparative Example 1-1, except that an organic peroxide containing dicumyl peroxide (NOF Corp.'s "Percumyl D-40" (concentration 40%)) was used instead of Perbutyl P-40. Percumyl D-40 was used so that the Perbutyl P-40 in Example 1-1 and Comparative Example 1-1 and the Percumyl D-40 in Example 1-2 and Comparative Example 1-2 were equimolar.

[0077] [Table 1]

[0078] (Examples 1-3 and Comparative Examples 1-3) In Example 1-3 and Comparative Example 1-3, the preparation of rubber compositions, the production of crosslinked products, and the measurement of elongation at break and tensile strength at break were carried out in the same manner as in Example 1-1 and Comparative Example 1-1, except that an organic peroxide containing butyl 4,4-bis[(t-butyl)peroxy]pentanoate (NOF Corp.'s "Perhexa V-40" (40% concentration)) was used instead of Perbutyl P-40. Perhexa V-40 was used so that the amounts of Perbutyl P-40 in Example 1-1 and Comparative Example 1-1 and Perhexa V-40 in Example 1-3 and Comparative Example 1-3 were equimolar.

[0079] (Examples 1-4 and Comparative Examples 1-4, Examples 1-5 and Comparative Examples 1-5) Preparation of rubber compositions, production of cross-linked products, and measurement of elongation at break and tensile strength at break were carried out in the same manner as in Example 1-3 or Comparative Example 1-3, except that the content of TMPT, the content of Valnoc PM, or the content of Perhexa V-40 was changed as shown in Table 2.

[0080] [Table 2]

[0081] Example 2-1 (Preparation of Rubber Composition) A rubber composition was prepared in the same manner as in Example 1-1, except that acrylic rubber (G2) having a monomer composition of ethyl acrylate / n-butyl acrylate / vinyl acetate / ethylene = 35 / 18 / 35 / 12 (mass ratio) was used instead of acrylic rubber (G1), and 1.8 parts by mass of ethylene glycol dimethacrylate (EGDMA) was used instead of 3 parts by mass of TMPT as the co-crosslinking agent. Table 3 shows the molar ratio of ethylenically unsaturated bonds in the co-crosslinking agent to OO bonds in the organic peroxide in the rubber composition (C=C bonds / OO bonds), and the molar ratio of NH bonds in phenothiazine to OO bonds in the organic peroxide in the rubber composition (NH bonds / OO bonds).

[0082] (Preparation of cross-linked product) The obtained rubber composition was cut into a 2.4 mm thick sheet, and then heated and pressed at 170°C and 4 MPa for 20 minutes using a press vulcanizer to obtain a primary crosslinked product of the rubber composition. Subsequently, the primary crosslinked product was heated in a gear oven at 160°C for 4 hours to obtain a secondary crosslinked product of the rubber composition.

[0083] (Measurement of elongation at break and tensile strength at break) According to JIS K6251:2017, the elongation at break Eb and tensile strength at break Tb of the secondary cross-linked product were measured using a dumbbell No. 3. The results are shown in Table 3.

[0084] (Examples 2-2 and 2-3) Except for changing the content of phenothiazine as shown in Table 3, preparation of rubber compositions, production of crosslinked products, and measurement of elongation at break and tensile strength at break were carried out in the same manner as in Example 2-1.

[0085] [Table 3]

[0086] (Example 3-1) (Preparation of Rubber Composition) A rubber composition was prepared in the same manner as in Example 2-3, except that acrylic rubber (G3) having a monomer composition of ethyl acrylate / n-butyl acrylate / vinyl acetate / ethylene = 35 / 18 / 35 / 12 (mass ratio) was used instead of acrylic rubber (G2), and 2.2 parts by mass of triallyl cyanurate (TAC) was used instead of 1.8 parts by mass of EGDMA as the co-crosslinking agent. Table 4 shows the molar ratio of ethylenically unsaturated bonds in the co-crosslinking agent to OO bonds in the organic peroxide in the rubber composition (C=C bonds / OO bonds), and the molar ratio of NH bonds in phenothiazine to OO bonds in the organic peroxide in the rubber composition (NH bonds / OO bonds).

[0087] (Preparation of cross-linked product) The obtained rubber composition was cut into a 2.4 mm thick sheet, and then heated and pressed at 170°C and 4 MPa for 20 minutes using a press vulcanizer to obtain a primary crosslinked product of the rubber composition. Subsequently, the primary crosslinked product was heated in a gear oven at 160°C for 4 hours to obtain a secondary crosslinked product of the rubber composition.

[0088] (Measurement of elongation at break and tensile strength at break) According to JIS K6251:2017, the elongation at break Eb and tensile strength at break Tb of the secondary cross-linked product were measured using a dumbbell No. 3. The results are shown in Table 4.

[0089] (Examples 3-2 to 3-5) Except for changing the contents of organic peroxide and phenothiazine as shown in Table 4, the preparation of rubber compositions, the production of cross-linked products, and the measurement of elongation at break and tensile strength at break were carried out in the same manner as in Example 3-1.

[0090] (Comparative Example 3-1) Preparation of a rubber composition, production of a crosslinked product, and measurement of elongation at break and tensile strength at break were carried out in the same manner as in Example 3-1, except that phenothiazine or a co-crosslinking agent was not used.

[0091] [Table 4]

[0092] Example 4-1 (Preparation of Rubber Composition) A rubber composition was prepared in the same manner as in Example 1-1, except that acrylic rubber (G4) having a monomer composition of methyl acrylate / n-butyl acrylate / vinyl acetate = 20 / 40 / 40 (mass ratio) was used instead of acrylic rubber (G1), and 0.5 parts by mass of a lubricant (stearic acid amide, "Amide AP-1" manufactured by Mitsubishi Chemical Corporation) was further compounded. Table 5 shows the molar ratio of ethylenically unsaturated bonds in the co-crosslinking agent to OO bonds in the organic peroxide in the rubber composition (C=C bonds / OO bonds), and the molar ratio of NH bonds in phenothiazine to OO bonds in the organic peroxide in the rubber composition (NH bonds / OO bonds).

[0093] (Preparation of cross-linked product) The obtained rubber composition was cut into a 2.4 mm thick sheet, and then heated and pressed at 170°C and 4 MPa for 20 minutes using a press vulcanizer to obtain a primary crosslinked product of the rubber composition. Subsequently, the primary crosslinked product was heated in a gear oven at 160°C for 4 hours to obtain a secondary crosslinked product of the rubber composition.

[0094] (Measurement of elongation at break and tensile strength at break) According to JIS K6251:2017, the elongation at break Eb and tensile strength at break Tb of the secondary cross-linked product were measured using a dumbbell No. 3. The results are shown in Table 5.

[0095] (Examples 4-2 and 4-3) Except for changing the content of phenothiazine as shown in Table 5, preparation of rubber compositions, production of crosslinked products, and measurement of elongation at break and tensile strength at break were carried out in the same manner as in Example 4-1.

[0096] (Comparative Example 4-1) Preparation of a rubber composition, production of a crosslinked product, and measurement of elongation at break and tensile strength at break were carried out in the same manner as in Example 4-1, except that phenothiazine or a co-crosslinking agent was not used.

[0097] [Table 5]

[0098] (Example 5-1) (Preparation of Rubber Composition) A rubber composition was prepared in the same manner as in Example 2-1, except that an acrylic rubber (G5) having a monomer composition of methyl acrylate / n-butyl acrylate / vinyl acetate / ethylene = 21 / 42 / 27 / 10 (mass ratio) was used instead of the acrylic rubber (G2).

[0099] (Preparation of cross-linked product) The obtained rubber composition was cut into a 2.4 mm thick sheet, and then heated and pressed at 170°C and 4 MPa for 20 minutes using a press vulcanizer to obtain a primary crosslinked product of the rubber composition. Subsequently, the primary crosslinked product was heated in a gear oven at 160°C for 4 hours to obtain a secondary crosslinked product of the rubber composition.

[0100] (Measurement of elongation at break and tensile strength at break) According to JIS K6251:2017, the elongation at break Eb and tensile strength at break Tb of the secondary cross-linked product were measured using a dumbbell No. 3. The results are shown in Table 6.

[0101] (Examples 5-2 and 5-3) Except for further compounding trimethylthiourea in the amount shown in Table 6, preparation of a rubber composition, production of a crosslinked product, and measurement of elongation at break and tensile strength at break were carried out in the same manner as in Example 5-1.

[0102] [Table 6]

[0103] Example 6-1 (Preparation of Rubber Composition) A rubber composition was prepared in the same manner as in Example 5-1, except that an acrylic rubber (G6) having a monomer composition of ethyl acrylate / n-butyl acrylate / vinyl acetate / ethylene = 26 / 26 / 36 / 12 (mass ratio) was used instead of the acrylic rubber (G5).

[0104] (Preparation of cross-linked product) The obtained rubber composition was cut into a 2.4 mm thick sheet, and then heated and pressed at 170°C and 4 MPa for 20 minutes using a press vulcanizer to obtain a primary crosslinked product of the rubber composition. Subsequently, the primary crosslinked product was heated in a gear oven at 160°C for 4 hours to obtain a secondary crosslinked product of the rubber composition.

[0105] (Measurement of elongation at break and tensile strength at break) According to JIS K6251:2017, the elongation at break Eb and tensile strength at break Tb of the secondary cross-linked product were measured using a dumbbell No. 3. The results are shown in Table 7.

[0106] (Example 6-2) Preparation of a rubber composition, production of a crosslinked product, and measurement of elongation at break and tensile strength at break were carried out in the same manner as in Example 6-1, except that 0.5 parts by mass of trimethylthiourea was further compounded.

[0107] (Example 6-3) Preparation of a rubber composition, production of a crosslinked product, and measurement of elongation at break and tensile strength at break were carried out in the same manner as in Example 6-1, except that 0.5 parts by mass of 2-mercaptobenzimidazole was further compounded.

[0108] [Table 7]

[0109] Example 7-1 (Preparation of Rubber Composition) A rubber composition was prepared in the same manner as in Example 1-1, except that an ethylene-vinyl acetate rubber (G7) having a monomer composition of vinyl acetate / ethylene = 70 / 30 (mass ratio) was used instead of the acrylic rubber (G1), and 40 parts by mass of a filler (carbon black, "Seat SO" manufactured by Tokai Carbon Co., Ltd.) was used. Table 8 shows the molar ratio of ethylenically unsaturated bonds in the co-crosslinking agent to OO bonds in the organic peroxide in the rubber composition (C=C bonds / OO bonds), and the molar ratio of NH bonds in the phenothiazine to OO bonds in the organic peroxide in the rubber composition (NH bonds / OO bonds).

[0110] (Preparation of cross-linked product) The obtained rubber composition was cut into a 2.4 mm thick sheet, and then heated and pressed at 170°C and 4 MPa for 20 minutes using a press vulcanizer to obtain a primary crosslinked product of the rubber composition. Subsequently, the primary crosslinked product was heated in a gear oven at 170°C for 4 hours to obtain a secondary crosslinked product of the rubber composition.

[0111] (Measurement of elongation at break and tensile strength at break) According to JIS K6251:2017, the elongation at break Eb and tensile strength at break Tb of the secondary cross-linked product were measured using a dumbbell No. 3. The results are shown in Table 8.

[0112] (Example 7-2) Except for changing the content of phenothiazine as shown in Table 8, preparation of rubber compositions, production of crosslinked products, and measurement of elongation at break and tensile strength at break were carried out in the same manner as in Example 7-1.

[0113] [Table 8]

[0114] (Example 8-1) (Preparation of Rubber Composition) A rubber composition was prepared in the same manner as in Example 1-1, except that acrylic rubber (G8) having a monomer composition of ethyl acrylate / n-butyl acrylate / n-butyl methacrylate / methoxyethyl acrylate / ethylene = 24 / 39 / 10 / 24 / 3 (mass ratio) was used instead of acrylic rubber (G1), and 3 parts by mass of ethylene glycol dimethacrylate was used instead of 3 parts by mass of trimethylolpropane trimethacrylate as the co-crosslinking agent. Table 9 shows the molar ratio of ethylenically unsaturated bonds in the co-crosslinking agent to OO bonds in the organic peroxide in the rubber composition (C=C bonds / OO bonds), and the molar ratio of NH bonds in phenothiazine to OO bonds in the organic peroxide in the rubber composition (NH bonds / OO bonds).

[0115] (Preparation of cross-linked product) The obtained rubber composition was cut into a 2.4 mm thick sheet, and then heated and pressed at 170°C and 4 MPa for 20 minutes using a press vulcanizer to obtain a primary crosslinked product of the rubber composition. Subsequently, the primary crosslinked product was heated in a gear oven at 160°C for 4 hours to obtain a secondary crosslinked product of the rubber composition.

[0116] (Measurement of elongation at break and tensile strength at break) According to JIS K6251:2017, the elongation at break Eb and tensile strength at break Tb of the secondary crosslinked product were measured using a dumbbell No. 3. The results are shown in Table 9.

[0117] (Example 8-2) Except for changing the content of phenothiazine as shown in Table 9, preparation of rubber compositions, production of crosslinked products, and measurement of elongation at break and tensile strength at break were carried out in the same manner as in Example 8-1.

[0118] [Table 9]

[0119] (Example 9-1) (Preparation of Rubber Composition) A rubber composition was prepared in the same manner as in Example 8-2, except that acrylic rubber (G3) having a monomer composition of methyl acrylate / n-butyl acrylate / vinyl acetate / ethylene = 19 / 56 / 19 / 6 (mass ratio) was used instead of acrylic rubber (G8), and 0.5 parts by mass of a lubricant (stearic acid amide, "Amide AP-1" manufactured by Mitsubishi Chemical Corporation) was further compounded. Table 10 shows the molar ratio of NH bonds in phenothiazine to OO bonds in peroxide in the rubber composition (NH bonds / OO bonds).

[0120] (Scorch time measurement) The scorch time MLt5 of the rubber composition obtained was measured at 125°C in accordance with JIS K6300:2013. The results are shown in Table 10.

[0121] (Preparation of cross-linked product) The obtained rubber composition was cut into a 2.4 mm thick sheet, and then heated and pressed at 170°C and 4 MPa for 20 minutes using a press vulcanizer to obtain a primary crosslinked product of the rubber composition. Subsequently, the primary crosslinked product was heated in a gear oven at 160°C for 4 hours to obtain a secondary crosslinked product of the rubber composition.

[0122] (Measurement of tensile strength and elongation at break) According to JIS K6251:2017, the tensile strength at break Tb and elongation at break Eb of the secondary cross-linked product were measured using a dumbbell No. 3. The results are shown in Table 10.

[0123] (Examples 9-2 to 9-5) Except for changing the peroxide content and the phenothiazine content as shown in Table 10, the preparation of rubber compositions, the production of crosslinked products, and the respective measurements were carried out in the same manner as in Example 9-1.

[0124]

Table 10

Claims

1. at least one rubber selected from acrylic rubber and ethylene vinyl acetate rubber; an organic peroxide; a co-crosslinking agent having a plurality of ethylenically unsaturated bonds; a phenothiazine compound; A rubber composition comprising:

2. a rubber containing, as a monomer unit, at least one selected from the group consisting of (meth)acrylic acid ester, vinyl acetate, and ethylene; an organic peroxide; a co-crosslinking agent having a plurality of ethylenically unsaturated bonds; a phenothiazine compound; A rubber composition comprising:

3. The rubber composition according to claim 1 or 2, wherein the co-crosslinking agent comprises at least one selected from the group consisting of (poly)alkylene glycol di(meth)acrylate and trimethylolpropane tri(meth)acrylate.

4. The rubber composition according to claim 1 or 2, wherein the co-crosslinking agent comprises a compound represented by the following formula (1): 【Chemical 1】 [In the formula, R １ and R ２ each independently represents a hydrogen atom or a methyl group, and m represents an integer of 1 to 3.

5. 3. The rubber composition according to claim 1, wherein a molar ratio of ethylenically unsaturated bonds in the co-crosslinking agent to O-O bonds in the organic peroxide is 0.5 or more and 3.0 or less.

6. The rubber composition according to claim 1, wherein the rubber is an acrylic rubber containing a (meth)acrylic acid ester and a carboxylic acid vinyl ester as monomer units.

7. The rubber composition according to claim 1 or 2, which is used as a rubber composition for a seal or a hose.

8. A crosslinked product of the rubber composition according to claim 1 or 2.

9. The cross-linked product according to claim 8, which is used as a seal or a hose.

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