Acrylic rubber composition and crosslinked rubber

Abstract

Provided is an acrylic rubber composition containing an acrylic rubber (A), an organic peroxide (B), a co-crosslinking agent (C), and a chalcogenide (D), the content of the organic peroxide (B) being 0.1-5 parts by weight per 100 parts by weight of the acrylic rubber (A), the content of the co-crosslinking agent (C) being 0.1-10 parts by weight per 100 parts by weight of the acrylic rubber (A), and the content of the chalcogenide (D) being 0.1-5 parts by weight per 100 parts by weight of the acrylic rubber (A). The content of the chalcogenide compound (D) is 0.05-3 parts by weight per 100 parts by weight of the acrylic rubber (A).

Description

Technical Field

[0001] This invention relates to acrylic rubber compositions and rubber crosslinkers. Background Technology

[0002] Acrylic rubber compositions are typically crosslinked as follows: as a primary crosslinking, heating at approximately 150°C to 190°C for several minutes to tens of minutes, followed by a secondary crosslinking process involving heating in air at 140°C to 200°C for several hours.

[0003] For example, Patent Document 1 discloses an acrylic rubber composition which is made by combining an organic peroxide and a bismaleimide compound as a vulcanizing agent in an acrylic rubber composed of 30-80% by weight of methoxyethyl acrylate, 70-20% by weight of alkyl acrylate and / or alkoxy-substituted alkyl acrylate (except for methoxyethyl acrylate), and 0-30% by weight of other copolymerizable monomers without crosslinking point groups.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent document 1: Japanese Patent Application Publication No. 5-214196. Summary of the Invention

[0007] The problem the invention aims to solve

[0008] From the perspectives of productivity, energy saving, and carbon neutrality of rubber crosslinking products, there is a desire for an acrylic rubber composition that can produce rubber crosslinking products with good physical properties through only one crosslinking process without the need for secondary crosslinking.

[0009] For example, in the aforementioned Patent Document 1, although the rubber composition is obtained through a single vulcanization process, it suffers from poor scorch stability. Generally speaking, if the scorch stability is poor, unexpected cross-linking reactions will begin during the storage of the acrylic rubber composition or during processing using the acrylic rubber composition, resulting in a rubber composition with poor storage stability and processability.

[0010] The present invention was made in view of the following actual situation, and its object is to provide an acrylic rubber composition that has sufficient crosslinking speed, good scorch stability, and can form a rubber crosslink with sufficient mechanical properties even without secondary crosslinking.

[0011] Solution for solving the problem

[0012] Through in-depth research, the inventors discovered that the above-mentioned objectives can be achieved by using an acrylic rubber composition containing acrylic rubber (A), organic peroxide (B), co-crosslinking agent (C), and sulfur compound (D) in a specific ratio, thus completing the present invention.

[0013] That is, according to the present invention, the following acrylic rubber composition and rubber crosslinker can be provided.

[0014] [1] An acrylic rubber composition comprising acrylic rubber (A), organic peroxide (B), co-crosslinking agent (C), and sulfide compound (D),

[0015] The content of the aforementioned organic peroxide (B) is 0.1 to 5 parts by weight relative to 100 parts by weight of the aforementioned acrylic rubber (A).

[0016] 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).

[0017] The content of the sulfur compound (D) is 0.05 to 3 parts by weight relative to 100 parts by weight of the acrylic rubber (A).

[0018] [2] The acrylic rubber composition according to [1], wherein the acrylic rubber (A) contains (meth)acrylate alkyl ester monomer units and / or (meth)acrylate alkoxyalkyl ester monomer units in a content ratio of 40 to 100% by weight.

[0019] [3] A rubber crosslinker formed by crosslinking the acrylic rubber composition described in [1] or [2].

[0020] [4] The rubber crosslinking material according to [3] is a hose material or a sealing material.

[0021] The effects of the invention

[0022] According to the present invention, an acrylic rubber composition can be provided that has sufficient crosslinking speed, good scorch stability, and can form a rubber crosslink with sufficient mechanical properties even without secondary crosslinking. Detailed Implementation

[0023] The acrylic rubber composition of the present invention contains acrylic rubber (A), organic peroxide (B), co-crosslinking agent (C), and sulfide compound (D).

[0024] The content of the aforementioned organic peroxide (B) is 0.1 to 5 parts by weight relative to 100 parts by weight of the aforementioned acrylic rubber (A).

[0025] 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).

[0026] The content of the sulfur compound (D) is 0.05 to 3 parts by weight relative to 100 parts by weight of the acrylic rubber (A).

[0027] The acrylic rubber composition of the present invention, by combining acrylic rubber (A), organic peroxide (B), co-crosslinking agent (C) and sulfide compound (D) in the specific amounts described above, exhibits sufficient crosslinking speed, good scorch stability, and can form a rubber crosslink with sufficient mechanical properties (specifically, tensile properties and hardness) even without secondary crosslinking.

[0028] <Acrylic Rubber (A)>

[0029] The acrylic rubber (A) used in this invention is not particularly limited as long as it contains (meth)acrylate monomer (meaning acrylate monomer and / or methacrylate monomer. Hereinafter, the description of "(meth)acrylate" is also understood to mean) units as the main component (e.g., more than 50% by weight of all monomer units in the acrylic rubber).

[0030] The (meth)acrylate monomers that form the main component of the acrylic rubber (A) used in this invention are not particularly limited, and examples include (meth)acrylate alkyl monomers and (meth)acrylate alkoxyalkyl monomers.

[0031] As the alkyl ester monomer of (meth)acrylate, there is no particular limitation, but it is preferred to be an ester of alkanol with (meth)acrylate having 1 to 12 carbon atoms (an alkyl ester of (meth)acrylate having 1 to 12 carbon atoms), more preferably an ester of alkanol with (meth)acrylate having 1 to 8 carbon atoms (an alkyl ester of (meth)acrylate having 1 to 8 carbon atoms), and even more preferably an ester of alkanol with (meth)acrylate having 2 to 6 carbon atoms (an alkyl ester of (meth)acrylate having 2 to 6 carbon atoms).

[0032] Specific examples of alkyl methacrylate monomers include: methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, and cyclohexyl methacrylate. Among these, ethyl methacrylate and n-butyl methacrylate are preferred, and ethyl acrylate and n-butyl acrylate are more preferred. These can be used alone or in combination of two or more.

[0033] For example, the acrylic rubber (A) used in this invention may contain both ethyl acrylate units and n-butyl acrylate units as (meth)acrylate alkyl ester monomer units. In this case, the weight ratio of the two monomer units [content of ethyl acrylate units: content of n-butyl acrylate units] is preferably 1:99 to 99:1, more preferably 10:90 to 90:10, further preferably 30:70 to 80:20, and particularly preferably 40:60 to 60:40.

[0034] The monomer for (meth)acrylate alkoxyalkyl esters is not particularly limited, but preferably is an ester of alkoxyalkyl alcohol with 2 to 12 carbon atoms and (meth)acrylate (a (meth)acrylate having 2 to 12 carbon atoms), more preferably is an ester of alkoxyalkyl alcohol with 2 to 8 carbon atoms and (meth)acrylate (a (meth)acrylate having 2 to 8 carbon atoms), and even more preferably is an ester of alkoxyalkyl alcohol with 2 to 6 carbon atoms and (meth)acrylate (a (meth)acrylate having 2 to 6 carbon atoms).

[0035] Specific examples of alkoxyalkyl ester monomers of (meth)acrylate include: methoxymethyl methacrylate, ethoxymethyl methacrylate, 2-methoxyethyl methacrylate, 2-ethoxyethyl methacrylate, 2-propoxyethyl methacrylate, 2-butoxyethyl methacrylate, 3-methoxypropyl methacrylate, and 4-methoxybutyl methacrylate. Among these, 2-ethoxyethyl methacrylate and 2-methoxyethyl methacrylate 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.

[0036] In all the monomer units constituting the acrylic rubber (A) used in this invention, the total content of (meth)acrylate alkyl monomer units and (meth)acrylate alkoxyalkyl monomer units is preferably 40% by weight or more, more preferably 60% by weight or more, further preferably 80% by weight or more, even more preferably 90% by weight or more, and particularly preferably 95% or more. By ensuring that the total content of (meth)acrylate alkyl monomer units and (meth)acrylate alkoxyalkyl monomer units is within the above-mentioned range, the mechanical properties of the obtained rubber crosslinked product will become more superior.

[0037] The acrylic rubber (A) used in this invention only needs to contain (meth)acrylate monomers as the main component in the molecule, but preferably contains at least (meth)acrylate alkyl monomer units.

[0038] When the acrylic rubber (A) used in this invention comprises (meth)acrylate alkyl ester monomer units and (meth)acrylate alkoxyalkyl ester monomer units, the weight ratio of the contents of the two monomer units [content of (meth)acrylate alkyl ester monomer units : content of (meth)acrylate alkoxyalkyl ester monomer units] is preferably 1:99 to 99:1, more preferably 40:60 to 98:2, even more preferably 60:40 to 95:5, and particularly preferably 70:30 to 85:15.

[0039] In addition to (meth)acrylate monomer units, the acrylic rubber (A) used in this invention may also contain carboxyl monomer units, epoxy monomer units, halogen monomer units, diene monomer units, etc.

[0040] There are no particular limitations on the carboxyl-containing monomers that form carboxyl-containing monomer units, but examples include α,β-ene unsaturated dicarboxylic acid monoester monomers, α,β-ene unsaturated monocarboxylic acids, and α,β-ene unsaturated dicarboxylic acids.

[0041] As a monomer for α,β-ene unsaturated dicarboxylic acid monoesters, monoesters of α,β-ene unsaturated dicarboxylic acids with 4 to 12 carbon atoms and alkanols with 1 to 12 carbon atoms are preferred; monoesters of α,β-ene unsaturated dicarboxylic acids with 4 to 6 carbon atoms and alkanols with 2 to 8 carbon atoms are more preferred; and monoesters of α,β-ene unsaturated dicarboxylic acids with 4 carbon atoms and alkanols with 2 to 6 carbon atoms are even more preferred.

[0042] Specific examples of α,β-ene-based unsaturated dicarboxylic acid monoester monomers include: monomethyl fumarate, monoethyl fumarate, monobutyl fumarate, monomethyl maleate, monoethyl maleate, and monobutyl maleate, etc., which are monoalkyl esters of butenedioic acid; monocyclopentyl fumarate, monocyclohexyl fumarate, monocyclohexenyl fumarate, monocyclopentyl maleate, monocyclohexenyl maleate, etc., which are butenedioic acid monoesters with alicyclic structures; monomethyl itaconic acid, monoethyl itaconic acid, monobutyl itaconic acid, and monocyclohexenyl itaconic acid, etc., which are itaconic acid monoesters; etc. These can be used alone or in combination of two or more. Furthermore, among the above monomers, dicarboxylic acids also include those existing in the form of anhydrides.

[0043] Specific examples of α,β-ene unsaturated monocarboxylic acids include acrylic acid, methacrylic acid, α-ethylacrylic acid, crotonic acid, and cinnamic acid.

[0044] Specific examples of α,β-ene unsaturated dicarboxylic acids include: fumaric acid, maleic acid, and other butenedioic acids; itaconic acid; citraconic acid; chloromaleic acid; etc. Additionally, those monomers existing in anhydride form are also included among the above-mentioned monomers.

[0045] Among these, α,β-ene unsaturated dicarboxylic acid monoester monomers are preferred, butadiene mono-chain alkyl esters and butadiene monoesters with alicyclic structures are more preferred, and monobutyl fumarate, monobutyl maleate, monocyclohexyl fumarate and monocyclohexyl maleate are even more preferred, with monobutyl fumarate being particularly preferred.

[0046] When the acrylic rubber (A) used in this invention contains carboxyl-containing monomer units, the content of the carboxyl-containing monomer units 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 keeping the content of the carboxyl-containing monomer units within the above range, it is possible to achieve a higher level of balance between scorch stability and the mechanical properties of the primary crosslinked product.

[0047] There are no particular limitations on the monomers that form the epoxy-containing monomer units, but examples include epoxy-containing (meth)acrylates and epoxy-containing ethers.

[0048] Specific examples of epoxy-containing (meth)acrylates include glycidyl (meth)acrylate.

[0049] Specific examples of epoxy-containing ethers include allyl glycidyl ether and vinyl glycidyl ether. Among these, glycidyl methacrylate and allyl glycidyl ether are preferred. These epoxy-containing monomers can be used alone or in combination of two or more.

[0050] When the acrylic rubber (A) used in this invention contains monomer units with epoxy groups, the content of the monomer units with epoxy groups 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 keeping the content of the monomer units with epoxy groups within the above range, it is possible to achieve a higher level of balance between crosslinking speed, scorch stability, and mechanical properties of the primary crosslinked product.

[0051] There are no particular limitations on the monomers that form monomeric units containing halogen atoms, but examples include: unsaturated alcohol esters of halogenated saturated carboxylic acids, alkyl esters of (meth)acrylate, alkyl esters of (meth)acrylate, alkyl (haloacetylcarbamoyl)acrylate, halogenated unsaturated ethers, halogenated unsaturated ketones, aromatic vinyl compounds containing halogenated methyl groups, halogenated unsaturated amides, and unsaturated monomers containing halogenated acetyl groups.

[0052] Specific examples of unsaturated alcohol esters containing halogenated saturated carboxylic acids include vinyl chloroacetate, vinyl 2-chloropropionate, and allyl chloroacetate.

[0053] Specific examples of (meth)acrylate haloalkyl esters include: methyl methacrylate, 1-chloroethyl methacrylate, 2-chloroethyl methacrylate, 1,2-dichloroethyl methacrylate, 2-chloropropyl methacrylate, 3-chloropropyl methacrylate, and 2,3-dichloropropyl methacrylate.

[0054] Specific examples of (meth)acrylate haloacyloxyalkyl esters include: 2-(chloroacetoxy)ethyl methacrylate, 2-(chloroacetoxy)propyl methacrylate, 3-(chloroacetoxy)propyl methacrylate, and 3-(hydroxychloroacetoxy)propyl methacrylate.

[0055] Specific examples of (meth)acrylate (haloacetylcarbamoyloxy) alkyl esters include 2-(chloroacetylcarbamoyloxy)ethyl methacrylate and 3-(chloroacetylcarbamoyloxy)propyl methacrylate.

[0056] Specific examples of halogenated unsaturated ethers include: chloromethyl vinyl ether, 2-chloroethyl vinyl ether, 3-chloropropyl vinyl ether, 2-chloroethyl allyl ether, and 3-chloropropyl allyl ether.

[0057] Specific examples of halogenated unsaturated ketones include 2-chloroethyl vinyl ketone, 3-chloropropyl vinyl ketone, and 2-chloroethyl allyl ketone.

[0058] Specific examples of aromatic vinyl compounds containing halogenated methyl groups include: p-chloromethylstyrene, m-chloromethylstyrene, o-chloromethylstyrene, and p-chloromethyl-α-methylstyrene.

[0059] Specific examples of halogen-containing unsaturated amides include N-chloromethyl (meth)acrylamide, etc.

[0060] Specific examples of unsaturated monomers containing halogenated acetyl groups include 3-(hydroxychloroacetoxy)propyl allyl ether and p-vinylbenzylchloroacetate.

[0061] Among these, unsaturated alcohol esters and halogenated unsaturated ethers containing halogenated saturated carboxylic acids are preferred, vinyl chloroacetate and 2-chloroethyl vinyl ether are more preferred, and vinyl chloroacetate is even more preferred. These monomers containing halogen atoms can be used alone or in combination of two or more.

[0062] When the acrylic rubber (A) used in this invention contains monomer units having halogen atoms, the content of monomer units having halogen atoms 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 keeping the content of monomer units having halogen atoms within the above range, it is possible to achieve a higher level of balance between crosslinking speed, scorch stability, and mechanical properties of the primary crosslinked product.

[0063] Diene monomers that form diene monomer units can be categorized as conjugated diene monomers and non-conjugated diene monomers.

[0064] Specific examples of conjugated diene monomers include 1,3-butadiene, isoprene, and piperylene.

[0065] Specific examples of non-conjugated diene monomers include: ethylidene norbornene, dicyclopentadiene, dicyclopentadienyl (meth)acrylate, and ethyl (meth)acrylate-2-dicyclopentadienyl.

[0066] The aforementioned carboxyl-containing monomers, epoxy-containing monomers, halogen-containing monomers, and diene monomers can be used alone or in combination of two or more.

[0067] In addition to the monomer units described above, the acrylic rubber (A) used in this invention may also have units capable of copolymerizing with other monomers. Such other copolymerizable monomers are not particularly limited, and examples include aromatic vinyl monomers, α,β-ene unsaturated nitrile monomers, acrylamide monomers, α,β-ene unsaturated dicarboxylic acid diester monomers, and other olefin monomers.

[0068] Examples of aromatic vinyl monomers include styrene, α-methylstyrene, and divinylbenzene.

[0069] Examples of α,β-olefinic unsaturated nitrile monomers include acrylonitrile and methacrylonitrile.

[0070] Examples of acrylamide monomers include acrylamide and methacrylamide.

[0071] Examples of α,β-ene unsaturated dicarboxylic acid diester monomers include: dialkyl maleate esters with alkyl groups having 1 to 18 carbon atoms, such as dimethyl maleate and di-n-butyl maleate; dialkyl fumarate esters with alkyl groups having 1 to 18 carbon atoms, such as dimethyl fumarate and di-n-butyl fumarate; dialkyl maleate esters with cycloalkyl groups having 4 to 16 carbon atoms, such as dicyclopentyl maleate and dicyclohexyl maleate; dialkyl fumarate esters with cycloalkyl groups having 4 to 16 carbon atoms, such as dicyclopentyl fumarate and dicyclohexyl fumarate; dialkyl itaconic acid esters with alkyl groups having 1 to 18 carbon atoms, such as dimethyl itaconic acid and di-n-butyl itaconic acid; dialkyl itaconic acid esters with cycloalkyl groups having 4 to 16 carbon atoms, such as dicyclohexyl itaconic acid; and so on.

[0072] Other olefin monomers include: ethylene, propylene, vinyl chloride, vinylidene chloride, vinyl acetate, ethyl vinyl ether, butyl vinyl ether, etc.

[0073] Other monomers capable of copolymerization can be used alone or in combination of two or more. In the monomer units constituting the acrylic rubber (A) used in this invention, the content of other monomer units capable of copolymerization is preferably 48.7% by weight or less, more preferably 28.5% by weight or less, further preferably 18.5% by weight or less, particularly preferably 13.5% by weight or less, and most preferably 8.0% by weight or less.

[0074] The acrylic rubber (A) used in this invention can be obtained by polymerizing the above-mentioned monomers. As the form of polymerization reaction, any of the following methods can be used: emulsion polymerization, suspension polymerization, bulk polymerization, and solution polymerization. However, from the perspective of ease of controlling the polymerization reaction, emulsion polymerization under normal pressure is preferred.

[0075] Emulsion polymerization can be batch, semi-batch, or continuous. Polymerization is typically carried out within a temperature range of 0–70°C, preferably 5–50°C. It is not necessary to supply all types and quantities of the monomers to the reaction site at the beginning of the reaction; factors such as copolymerization reactivity and reaction conversion rate can be considered, allowing for continuous or intermittent addition throughout the reaction time, or introduction in one go or in batches during or even later stages. Furthermore, the feed ratio of each monomer in the polymerization reaction can be adjusted according to the reactivity of each monomer. However, since polymerization reactions are mostly carried out almost quantitatively, this should be taken into account, and the feed ratio should be determined based on the monomer unit composition of the acrylic rubber (A) to be produced. After polymerization, solidification and drying yield solid acrylic rubber (A).

[0076] The Mooney viscosity (ML1+4, 100°C) of the acrylic rubber (A) used in this invention, manufactured in this way, is preferably 10 to 150, more preferably 10 to 80, further preferably 20 to 70, even more preferably 25 to 60, and particularly preferably 30 to 50.

[0077] The shape of the acrylic rubber (A) used in this invention is not particularly limited, and it can be any shape such as in a rubber package, sheet, or powder.

[0078] <Organic Peroxides (B)>

[0079] The acrylic rubber composition of the present invention contains 0.1 to 5 parts by weight of organic peroxide (B) relative to 100 parts by weight of acrylic rubber (A).

[0080] As for organic peroxide (B), any organic peroxide used as a crosslinking agent in the rubber industry is acceptable, without any particular limitation. Examples include dialkyl peroxides, diacyl peroxides, and peroxide esters.

[0081] Examples of dialkyl peroxides include: dicumyl peroxide, di-tert-butyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)-3-hexyne, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, and 1,3-bis(tert-butylperoxyisopropyl)benzene.

[0082] Examples of diacyl peroxides include benzoyl peroxide and isobutyryl peroxide.

[0083] Examples of peroxide esters include 2,5-dimethyl-2,5-bis(benzoyl peroxide)hexane and tert-butyl peroxide isopropyl carbonate.

[0084] Among these, dialkyl peroxides are preferred, and 1,3-bis(tert-butylperoxyisopropyl)benzene is more preferred.

[0085] In the acrylic rubber composition of the present invention, the content of organic peroxide (B) is 0.1 to 5 parts by weight relative to 100 parts by weight of acrylic rubber (A). When the content of organic peroxide (B) is too low, the crosslinking of the acrylic rubber composition cannot proceed sufficiently, and a rubber crosslinked product cannot be obtained. On the other hand, when the content of organic peroxide (B) is too high, the scorch stability and the mechanical properties of the primary crosslinked product become insufficient.

[0086] The content of organic peroxide (B) is not particularly limited as long as it is 0.1 to 5 parts by weight relative to 100 parts by weight of 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 keeping the content of organic peroxide (B) within the above range, it is possible to achieve a higher level of balance between crosslinking speed, scorch stability, and mechanical properties of the primary crosslinked product.

[0087] The acrylic rubber composition of the present invention may also contain a crosslinking agent other than organic peroxide (B), but its content is preferably 0.5 parts by weight or less, more preferably 0.1 parts by weight or less, relative to 100 parts by weight of acrylic rubber (A).

[0088] <Co-crosslinking agent (C)>

[0089] The acrylic rubber composition of the present invention contains 0.1 to 10 parts by weight of co-crosslinking agent (C) relative to 100 parts by weight of acrylic rubber (A).

[0090] As a co-crosslinking agent (C), there are no particular limitations, but low-molecular-weight or high-molecular-weight compounds having multiple unsaturated groups with free radical reactivity in the molecule are preferred. Examples include: polyfunctional vinyl compounds such as divinylbenzene and divinylnaphthalene; isocyanurates such as triallyl isocyanurate and trimethylallyl isocyanurate; cyanurates such as triallyl cyanurate; maleimides such as N,N'-m-phenylenebismaleimide and diphenylmethane-4,4'-bismaleimide; diallyl phthalate and diisophthalate. Allyl esters of polybasic acids such as allyl ester, diallyl maleate, diallyl fumarate, diallyl sebacate, and triallyl phosphate; diethylene glycol dielyl carbonate; allyl ethers such as ethylene glycol diallyl ether, triallyl ether of trimethylolpropane, and partial allyl ethers of pentaerythritol; allyl-modified resins such as allylated phenolic varnishes and allylated methyl phenolic resins; methacrylate compounds or acrylate compounds with 3 to 5 functional groups such as trimethylolpropane trimethacrylate and trimethylolpropane triacrylate; etc. These can be used alone or in combination.

[0091] Among these, isocyanurates, maleimides, allyl ethers, and methacrylates or acrylates having 3 to 5 functional groups are preferred, with triallyl isocyanurates, N,N'-m-phenylenebismaleimide, and trimethylolpropane trimethacrylate being more preferred.

[0092] In the acrylic rubber composition of the present invention, the content of the co-crosslinking agent (C) is 0.1 to 10 parts by weight relative to 100 parts by weight of acrylic rubber (A). When the content of the co-crosslinking agent (C) is too low, the crosslinking of the acrylic rubber composition cannot proceed sufficiently, and a rubber crosslinked product cannot be obtained. On the other hand, when the content of the co-crosslinking agent (C) is too high, the scorch stability and the mechanical properties of the primary crosslinked product become insufficient.

[0093] 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 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 keeping the content of the co-crosslinking agent (C) within the above range, it is possible to achieve a higher level of balance between crosslinking speed, scorch stability, and the mechanical properties of the primary crosslinked product.

[0094] <Chalcogenide Compounds (D)>

[0095] The acrylic rubber composition of the present invention contains 0.05 to 3 parts by weight of a sulfide compound (D) relative to 100 parts by weight of acrylic rubber (A).

[0096] In this invention, a sulfur compound (D) is incorporated into an acrylic rubber (A) in the amounts specified above, together with an organic peroxide (B) and a co-crosslinking agent (C).

[0097] In particular, through in-depth research, the inventors discovered that, in addition to the organic peroxide (B) and co-crosslinking agent (C), by using the aforementioned prescribed amount of sulfur compound (D), the reaction between acrylic rubber (A) and the organic peroxide (B) and co-crosslinking agent (C) can be suppressed. This suppresses unexpected crosslinking reactions in the acrylic rubber (A) and results in good scorch stability. Specifically, according to the present invention, by appropriately controlling the amount of sulfur compound (D), it is possible to achieve both good scorch stability and sufficient crosslinking speed.

[0098] Furthermore, based on the above, the inventors conducted further research and found that the rubber crosslinked product obtained by crosslinking the acrylic rubber composition having the above-described structure can possess sufficient mechanical properties. In particular, according to the inventors' understanding, when crosslinking acrylic rubber (A) using an organic peroxide (B) and a co-crosslinking agent (C) (i.e., without using a sulfide compound (D)), a reaction occurs simultaneously with the crosslinking reaction of acrylic rubber (A), causing the molecular backbone of acrylic rubber (A) to be cleaved by the organic peroxide (B). This results in a decrease in the molecular weight of acrylic rubber (A), leading to insufficient mechanical properties in the obtained rubber crosslinked product. The inventors conducted research on this issue and found that, in addition to the organic peroxide (B) and the co-crosslinking agent (C), by using the aforementioned specified amount of a sulfide compound (D), which acts on acrylic rubber (A) during the crosslinking reaction, the cleavage of the molecular backbone of acrylic rubber (A) can be effectively suppressed. This suppresses the decrease in the molecular weight of acrylic rubber (A), resulting in sufficient mechanical properties in the obtained rubber crosslinked product. In particular, according to the present invention, by adopting such a configuration, the mechanical properties of the obtained rubber crosslinked compound can be fully realized even without secondary crosslinking.

[0099] Examples of sulfur compounds (D) include: powdered sulfur, sulfur bloom, precipitated sulfur, colloidal sulfur, surface-treated sulfur, insoluble sulfur, etc.; sulfur chloride, sulfur dichloride, morpholine disulfide, alkylphenol disulfide, N,N'-dithiobis(hexahydro-2H-azacycloheptan-2-one), phosphorus-containing polysulfides, high-molecular-weight polysulfides, 2-(4'-morpholinyldithio)benzothiazole, phenothiazine, etc.; dithiocarbamic acids and their zinc salts, such as dibutyldithiocarbamic acid, di-2-ethylhexyldithiocarbamic acid, dicyclohexyldithiocarbamic acid, diphenyldithiocarbamic acid, dibenzyldithiocarbamic acid, etc.; thiuram compounds, such as tetramethylthiuram disulfide, tetraethylthiuram disulfide, and tetramethylthiuram monosulfide; etc. These can be used alone or in combination of two or more.

[0100] Among these, sulfur, phenothiazine, zinc dibutyldithiocarbamate, and tetramethylthiuram disulfide are preferred.

[0101] In the acrylic rubber composition of the present invention, the content of the sulfide compound (D) is 0.05 to 3 parts by weight relative to 100 parts by weight of acrylic rubber (A). When the content of the sulfide compound (D) is too low, the scorch stability and mechanical properties of the primary crosslinking of the acrylic rubber composition become insufficient. On the other hand, when the content of the sulfide compound (D) is too high, the acrylic rubber composition cannot be sufficiently crosslinked.

[0102] The content of the sulfide 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 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 keeping the content of the sulfide compound (D) within the above range, it is possible to achieve a higher level of balance between crosslinking speed, scorch stability, and mechanical properties of the primary crosslinked product.

[0103] <Other Ingredients>

[0104] The acrylic rubber composition of the present invention may also contain rubber other than acrylic rubber (A).

[0105] The rubbers that can be used in this invention, other than acrylic rubber (A), are not particularly limited, and 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, and polysiloxane-based elastomers. One of these can be used alone, or two or more can be used in combination.

[0106] The proportion of acrylic rubber (A) component in the rubber component of the acrylic rubber composition can be appropriately selected according to the intended use, but it is preferably 70% by weight or more, more preferably 90% by weight or more, further preferably 95% by weight or more, and particularly preferably 100% by weight (i.e., the rubber component of the acrylic rubber composition is substantially composed of only acrylic rubber (A) component).

[0107] The acrylic rubber composition of the present invention preferably contains fillers such as reinforcing fillers and non-reinforcing fillers.

[0108] Examples of reinforcing fillers include: furnace black, acetylene black, thermal cracking black, channel black, graphite, and other carbon blacks; wet-process silica, dry-process silica, colloidal silica, and other silicas; etc. Examples of non-reinforcing fillers include: quartz powder, diatomaceous earth and other clays, zinc oxide, basic magnesium carbonate, activated calcium carbonate, magnesium silicate, aluminum silicate, titanium dioxide, talc, aluminum sulfate, calcium sulfate, barium sulfate, etc. A single filler can be used, or two or more can be used in combination.

[0109] In the acrylic rubber composition of the present invention, the content of filler 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 acrylic rubber (A) in the acrylic rubber composition.

[0110] The acrylic rubber composition of the present invention may contain an antioxidant as needed. There are no particular limitations on the antioxidant, but examples include: phenolic antioxidants such as double-hindered phenol, semi-hindered phenol, less-hindered phenol, and phenolic antioxidants without hindered groups; phosphite antioxidants; thioester antioxidants; secondary amine antioxidants such as phenyl-α-naphthylamine, phenyl-β-naphthylamine, p-(p-toluenesulfonamide)-diphenylamine, 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, N,N-diphenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, and butyraldehyde-aniline condensate; imidazole antioxidants; quinoline antioxidants; hydroquinone antioxidants; and so on.

[0111] Antioxidants can be used alone or in combination of two or more. The content of antioxidants 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, relative to 100 parts by weight of the rubber component containing the copolymer rubber of the present invention.

[0112] Furthermore, in addition to the components described above, the acrylic rubber composition of the present invention can also be formulated with compounding agents commonly used in the rubber processing field. Examples of such compounding agents include: light stabilizers; plasticizers; softeners; processing aids; adhesives; lubricants; flame retardants; mildew inhibitors; antistatic agents; colorants; etc. The amount of these compounding agents is not particularly limited as long as it does not impair the purpose or effect of the present invention, and can be appropriately formulated to meet the desired formulation purpose.

[0113] The acrylic rubber composition of the present invention can be prepared by incorporating a crosslinking agent, a co-crosslinking agent, a sulfur compound, and other various compounding agents as needed into a rubber component containing acrylic rubber (A), mixing and kneading it using an open roller mill, a Banbury mixer, various kneaders, etc., and then further kneading it using a mixing roller.

[0114] There is no particular limitation on the order of combination of the components, but it is preferable to mix the components that are not easily reacted or decomposed by heat after they are fully mixed, and then mix them for a short time at a temperature that will not cause reaction or decomposition, as a crosslinking agent for the components that are easily reacted or decomposed by heat.

[0115] The minimum Mooney viscosity (Vm, 125°C) of the acrylic rubber composition of the present invention at 125°C is preferably 10 to 80, more preferably 20 to 70, and even more preferably 30 to 60.

[0116] <Rubber crosslinking>

[0117] The rubber crosslinked product of the present invention is formed by crosslinking the acrylic rubber composition of the present invention described above.

[0118] The rubber crosslinked compound of the present invention can be manufactured by using the acrylic rubber composition of the present invention, molding it with a molding machine corresponding to the desired shape, such as an extruder, injection molding machine, compressor, and roller, and then performing a crosslinking reaction by heating to fix the shape into a rubber crosslinked compound. In this case, crosslinking can be performed after pre-molding or simultaneously with molding. In addition, the molding temperature is usually 10 to 140°C, preferably 25 to 120°C.

[0119] The crosslinking temperature is typically 150–190°C, preferably 160–180°C, and the crosslinking time is typically 2–60 minutes, preferably 3–40 minutes. As for the heating method, appropriate methods for rubber crosslinking, such as pressing heating, steam heating, oven heating, and hot air heating, can be selected.

[0120] In the method for manufacturing the rubber crosslinked compound of the present invention, a rubber crosslinked compound with sufficient mechanical properties can be obtained even if only one crosslinking is performed. However, in addition to performing one crosslinking, a second crosslinking can also be performed. The second crosslinking is usually carried out in a heated air environment at 130 to 220°C for 1 to 48 hours.

[0121] From the viewpoints of productivity, energy conservation, and carbon neutrality, the rubber crosslinker of the present invention is preferably a primary crosslinker of the acrylic rubber composition of the present invention. For example, the rubber crosslinker of the present invention is preferably a primary crosslinker obtained by heating and crosslinking the acrylic rubber composition of the present invention at a temperature of 150°C to 190°C for 2 to 60 minutes.

[0122] The rubber crosslinking material of the present invention can be used as: sealing materials such as O-rings, gaskets, diaphragms, oil seals, shaft seals, bearing seals, mechanical seals, wellhead seals, seals for electrical / electronic equipment, and seals for air compression equipment; cylinder head gaskets installed at the connection between the cylinder block and cylinder head, rocker arm cover gaskets installed at the connection between the rocker arm cover and cylinder head, oil pan gaskets installed at the connection between the oil pan and the cylinder head or transmission housing, gaskets for fuel cell spacers installed between a pair of housings holding a unit battery having a positive electrode, an electrolyte plate, and a negative electrode, and gaskets for the top cover of a hard disk drive; cushioning materials, shock-absorbing materials; wire sheathing materials; industrial tapes; pipe materials; hose materials; belt materials; dust cover materials; sheet materials; etc. In particular, the rubber crosslinking material of the present invention is suitable for use as hose materials, sealing materials, etc.

[0123] Furthermore, the rubber crosslinked material of the present invention, as an extruded molded product and crosslinked product that can be used in automotive applications, is suitable for, for example: fuel oil system hoses such as fuel hoses, filler hoses, exhaust hoses, steam hoses, oil hoses, etc.; air system hoses such as turbo air hoses, transmission control hoses, etc.; and various hose materials such as radiator hoses, heater hoses, brake hoses, air conditioning hoses, etc.

[0124] Example

[0125] The present invention will now be described in detail with reference to examples, but the present invention is not limited to these examples. Furthermore, unless otherwise specified, "parts" are by weight. Additionally, various physical properties were measured as follows.

[0126] <Polymer Mooney viscosity (ML1+4, 100℃)>

[0127] The Mooney viscosity (polymer Mooney viscosity) of acrylic rubber (A) was determined at 100°C according to JIS K6300.

[0128] <Characteristics of scorching>

[0129] The Mooney scorch of the acrylic rubber composition was determined according to JIS K6300 at 125°C to obtain the minimum Mooney viscosity "Vm" and the Mooney scorch time "t5". The larger the Mooney scorch time "t5" value, the better the scorch stability.

[0130] <Crosslinkability Test>

[0131] For acrylic rubber compositions, a crosslinking test was conducted using a rubber vulcanization testing machine (Dynamic Modular Rheometer, MDR, manufactured by Alpha Technologies) at 170°C for 20 minutes. Then, based on the results of the crosslinking test, the minimum torque "ML", maximum torque "MH", and T90 were determined. Furthermore, "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 set to 100%. If the T90 value is within 15 minutes, it can be determined that the crosslinking speed is sufficient for practical application.

[0132] <Normal physical properties of rubber crosslinked products (primary crosslinked products)>

[0133] According to JIS K6251, dumbbell-shaped No. 3 test pieces were cut from sheet-like acrylic rubber crosslinked material (primary crosslinked material), and the tensile strength, elongation, and stress at 100% constant elongation of the obtained test pieces were measured. In addition, the hardness of the rubber crosslinked material was measured using a durometer (Type A) according to JIS K6253-3.

[0134] <Increase in tensile strength caused by secondary cross-linking>

[0135] A secondary crosslinked material was obtained by heating a sheet of acrylic rubber crosslinked material (primary crosslinked material) in an oven at 170°C for 4 hours. Test pieces were cut from the secondary crosslinked material according to JIS K6251, and the tensile strength of the obtained test pieces was measured. Then, the increase in tensile strength caused by the secondary crosslinking was calculated using the following formula.

[0136] The percentage increase in tensile strength caused by secondary crosslinking (%) = ("Tensile strength of the secondary crosslinked compound" - "Tensile strength of the primary crosslinked compound") / "Tensile strength of the primary crosslinked compound" × 100

[0137] If the increase in tensile strength caused by secondary crosslinking is less than 20%, it can be determined that the crosslinking reaction is sufficient even without secondary crosslinking.

[0138] <Synthesis Example 1 (Preparation of Acrylic Rubber (A-1))>

[0139] In a polymerization reactor equipped with a thermometer, a stirring device, a nitrogen inlet pipe, and a pressure reducing device, 200 parts of water, 3 parts of sodium lauryl sulfate, 98 parts of ethyl acrylate, and 2 parts of vinyl chloroacetate were added. After repeated degassing under reduced pressure and nitrogen replacement to thoroughly remove oxygen, 0.002 parts of sodium formaldehyde sulfoxylate and 0.005 parts of cumene hydroperoxide were added. Emulsion polymerization was initiated at ambient pressure and temperature and continued until the polymerization conversion reached 95%. The resulting emulsion polymer 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℃) of the obtained acrylic rubber (A-1) was 45, and the composition of acrylic rubber (A-1) was 98 wt% ethyl acrylate units and 2 wt% vinyl chloroacetate units.

[0140] <Synthesis Example 2 (Preparation of Acrylic Rubber (A-2))>

[0141] The amount of ethyl acrylate was changed from 98 parts to 48 parts, and 2 parts of monobutyl fumarate were added instead of 2 parts of vinyl chloroacetate. Furthermore, 50 parts of n-butyl acrylate were added. Otherwise, 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. The composition of acrylic rubber (A-2) was 48 wt% ethyl acrylate units, 50 wt% n-butyl acrylate units, and 2 wt% monobutyl fumarate units.

[0142] <Synthesis Example 3 (Preparation of Acrylic Rubber (A-3))>

[0143] 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, and 2 parts of allyl glycidyl ether was added instead of 2 parts of monobutyl fumarate. Furthermore, 27 parts of 2-methoxyethyl acrylate were added. Otherwise, acrylic rubber (A-3) was obtained in the same manner as in Synthesis Example 2. The Mooney viscosity (ML1+4, 100°C) of the obtained acrylic rubber (A-3) was 40. The composition of 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.

[0144] <Synthetic Example 4 (Preparation of Acrylic Rubber (A-4))>

[0145] The amount of ethyl acrylate was changed from 48 parts to 49 parts, and the amount of n-butyl acrylate was changed from 50 parts to 51 parts. No monobutyl fumarate was added. Otherwise, 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 acrylic rubber (A-4) was 49 wt% ethyl acrylate units and 51 wt% n-butyl acrylate units.

[0146] <Synthetic Example 5 (Preparation of Acrylic Rubber (A-5))>

[0147] The amount of ethyl acrylate was changed from 49 parts to 45 parts, and the amount of n-butyl acrylate was changed from 51 parts to 37 parts. Additionally, 18 parts of 2-methoxyethyl acrylate were added. Otherwise, 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. The composition of acrylic rubber (A-5) was 45 wt% ethyl acrylate units, 37 wt% n-butyl acrylate units, and 18 wt% 2-methoxyethyl acrylate units.

[0148] <Example 1>

[0149] (Preparation of acrylic rubber composition)

[0150] 100 parts of acrylic rubber (A-1), 60 parts of carbon black (trade name "Seast 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 Co., Ltd.), and 2 parts of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine (trade name "NOCRAC CD", manufactured by Ouchi Shinsei Chemical Co., Ltd., antioxidant) were mixed using a Banbury mixer. Then, 5.00 parts (2.00 parts based on organic peroxide purity) of 1,3-bis(tert-butylperoxyisopropyl)benzene (trade name "Vulcup 40KE", manufactured by Hercules, organic peroxide, 40% grade) and 2.00 parts of N,N'-m-phenylenebismaleimide (trade name "VULNOC") were added. An acrylic rubber composition was obtained by mixing 0.50 parts of sulfur (trade name "SULFAX PMC", manufactured by Ouchi Shinsei Chemical Industry Co., Ltd., a co-crosslinking agent) and 0.50 parts of sulfur (trade name "SULFAX PMC", manufactured by Tsurumi Chemical Industry Co., Ltd.) at 50°C using an open roller mill. The obtained acrylic rubber composition was then used to evaluate scorch characteristics and conduct crosslinking tests according to the methods described above. The results are shown in Table 1.

[0151] (Manufacturing of rubber crosslinks)

[0152] The acrylic rubber composition was molded and crosslinked at 10 MPa for 20 minutes at 170°C to obtain a sheet-like rubber crosslinked product (primary crosslinked product) measuring 15 cm × 15 cm × 2 mm. Using the obtained sheet-like rubber crosslinked product (primary crosslinked product), the normal physical properties (tensile strength, elongation, stress at 100% elongation, and hardness) and the increase in tensile strength due to secondary crosslinking were measured. The results are shown in Table 1.

[0153] <Examples 2-4>

[0154] Acrylic rubber (A-1) was replaced with acrylic rubber (A-2), acrylic rubber (A-3), and acrylic rubber (A-4), respectively. Otherwise, acrylic rubber compositions were obtained in the same manner as in Example 1, and evaluated in the same way. Then, rubber crosslinks were obtained in the same manner as in Example 1, except that the obtained acrylic rubber compositions were used, and evaluated in the same way. The results are shown in Table 1.

[0155] <Comparative Example 1>

[0156] Without the addition of sulfur, an acrylic rubber composition was obtained in the same manner as in Example 1, and evaluated in the same way. Then, except for using the obtained acrylic rubber composition, a rubber crosslinker was obtained in the same manner as in Example 1, and evaluated in the same way. The results are shown in Table 1.

[0157] <Comparative Examples 2-4>

[0158] Acrylic rubber (A-1) was replaced with acrylic rubber (A-2), acrylic rubber (A-3), and acrylic rubber (A-4), respectively. Otherwise, acrylic rubber compositions were obtained in the same manner as in Comparative Example 1, and were evaluated in the same way. Then, rubber crosslinks were obtained in the same manner as in Example 1, except that the obtained acrylic rubber compositions were used, and were evaluated in the same way. The results are shown in Table 1.

[0159] <Examples 5-7>

[0160] Acrylic rubber (A-5) was used instead of 100 parts of acrylic rubber (A-1), and the amount of sulfur was varied as described in Table 2. Otherwise, the acrylic rubber composition was obtained in the same manner as in Example 1, and evaluated in the same manner. Then, except for using the obtained acrylic rubber composition, the rubber crosslinks were obtained in the same manner as in Example 1, and evaluated in the same manner. The results are shown in Table 2.

[0161] <Example 8>

[0162] Using 2.00 parts of triallyl isocyanurate (trade name "TAIC", manufactured by Nippon Chemical Co., Ltd., co-crosslinking agent) instead of 2.00 parts of N,N'-m-phenylenebismaleimide, and using 1.00 parts of phenothiazine (trade name "TDP", manufactured by Kawaguchi Chemical Co., Ltd., sulfide compound) instead of 0.20 parts of sulfur, an acrylic rubber composition was obtained in the same manner as in Example 5, and evaluated in the same manner. Then, except using the obtained acrylic rubber composition, a rubber crosslinker was obtained in the same manner as in Example 5, and evaluated in the same manner. The results are shown in Table 2.

[0163] <Example 9>

[0164] Using 1.00 part of zinc dibutyldithiocarbamate (trade name "NOCCELER BZ", manufactured by Ouchi Shinsei Chemical Co., Ltd., a sulfide compound) instead of 1.00 part of phenothiazine, an acrylic rubber composition was obtained in the same manner as in Example 8, and evaluated in the same manner. Then, except using the obtained acrylic rubber composition, a rubber crosslink was obtained in the same manner as in Example 8, and evaluated in the same manner. The results are shown in Table 2.

[0165] <Example 10>

[0166] Using 2.00 parts of trimethylolpropane trimethacrylate (trade name "TMPT", manufactured by Shin-Nakamura Chemical Industry Co., Ltd., co-crosslinking agent) instead of 2.00 parts of N,N'-m-phenylenebismaleimide, and using 1.00 parts of tetramethylthiuram disulfide (trade name "TMTD", manufactured by Sanshin Chemical Industry Co., Ltd., sulfide compound) instead of 0.20 parts of sulfur, an acrylic rubber composition was obtained in the same manner as in Example 5, and evaluated in the same manner. Then, except using the obtained acrylic rubber composition, a rubber crosslinker was obtained in the same manner as in Example 5, and evaluated in the same manner. The results are shown in Table 2.

[0167] <Examples 11, 12>

[0168] As described in Table 2, the amount of N,N'-m-phenylenebismaleimide was varied, and the acrylic rubber composition was obtained and evaluated in the same manner as in Example 6. Then, except for using the obtained acrylic rubber composition, a rubber crosslink was obtained and evaluated in the same manner as in Example 6. The results are shown in Table 2.

[0169] <Examples 13 and 14>

[0170] As described in Table 2, the amount of 1,3-bis(tert-butylperoxyisopropyl)benzene was varied, and the acrylic rubber composition was obtained in the same manner as in Example 6, and evaluated in the same manner. Then, except that the obtained acrylic rubber composition was used, the rubber crosslinks were obtained in the same manner as in Example 6, and evaluated in the same manner. The results are shown in Table 2.

[0171] <Comparative Example 5>

[0172] Without N,N'-m-phenylenebismaleimide, an acrylic rubber composition was obtained in the same manner as in Example 6, and evaluated in the same way. Then, except for using the obtained acrylic rubber composition, a rubber crosslink was obtained in the same manner as in Example 6, and evaluated in the same way. The results are shown in Table 3.

[0173] <Comparative Example 6>

[0174] The amount of N,N'-m-phenylenebismaleimide was changed from 2.00 parts to 15.00 parts, and the acrylic rubber composition was obtained in the same manner as in Example 6, and evaluated in the same manner. Then, except for using the obtained acrylic rubber composition, rubber crosslinks were obtained in the same manner as in Example 6, and evaluated in the same manner. The results are shown in Table 3.

[0175] <Comparative Examples 7 and 8>

[0176] As described in Table 3, the amount of 1,3-bis(tert-butylperoxyisopropyl)benzene was varied, and the acrylic rubber composition was obtained in the same manner as in Example 6, and evaluated in the same manner. Then, except that the obtained acrylic rubber composition was used, the rubber crosslinks were obtained in the same manner as in Example 6, and evaluated in the same manner. The results are shown in Table 3.

[0177] <Comparative Example 9>

[0178] The amount of sulfur was changed from 0.50 parts to 5.00 parts, and the acrylic rubber composition was obtained in the same manner as in Example 6, and evaluated in the same way. Then, except that the obtained acrylic rubber composition was used, the rubber crosslinker was obtained in the same manner as in Example 6, and evaluated in the same way. The results are shown in Table 3.

[0179] [Table 1]

[0180]

[0181] [Table 2]

[0182]

[0183] [Table 3]

[0184]

[0185] As shown in Tables 1 and 2, acrylic rubber compositions containing acrylic rubber (A), organic peroxide (B), co-crosslinking agent (C) and sulfide compound (D) in specific proportions exhibit sufficient crosslinking speed, good scorch stability, and can form rubber crosslinks with sufficient mechanical properties even without secondary crosslinking (Examples 1-14).

[0186] On the other hand, when the acrylic rubber composition does not contain sulfur compounds (D), the resulting acrylic rubber composition has insufficient scorch stability and crosslinking, and the mechanical properties of the crosslinked rubber obtained from such acrylic rubber composition are poor (Comparative Examples 1-4).

[0187] Furthermore, when the acrylic rubber composition does not contain a co-crosslinking agent (C), or when the content of organic peroxide (B) is too low, or when the content of sulfur compounds (D) is too high, the crosslinking of the obtained acrylic rubber composition cannot be sufficiently carried out, and the rubber crosslinked product cannot be obtained (Comparative Examples 5, 7, 9).

[0188] Furthermore, when the content of organic peroxide (B) or co-crosslinking agent (C) in the acrylic rubber composition is too high, the scorch stability of the acrylic rubber composition is low, and consequently, the mechanical properties (especially elongation) of the rubber crosslinked product obtained from such acrylic rubber composition are poor (Comparative Examples 6 and 8).

Claims

1. An acrylic rubber composition comprising acrylic rubber (A), an organic peroxide (B), a co-crosslinking agent (C), and a sulfur compound (D), 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). The content of the sulfide compound (D) is 0.05 to 3 parts by weight relative to 100 parts by weight of the acrylic rubber (A).

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

3. A rubber crosslinker formed by crosslinking the acrylic rubber composition of claim 1 or 2.

4. The rubber crosslinking material according to claim 3, wherein it is a hose material or a sealing material.

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