Acrylic rubber composition, crosslinked rubber product, hose material, sealing material, pipe material, belt material, and dust cover material

Abstract

Provided is an acrylic rubber composition which contains a predetermined amount of a predetermined acrylic rubber (A), a predetermined polyamine crosslinking agent (B), and a predetermined crosslinking retarder (C), and wherein the relationship among the crosslinking point equivalent [a], the crosslinking agent amine equivalent [b], and the crosslinking retarder amine equivalent [c] satisfies formula (1) and formula (2), and wherein the crosslinking point equivalent [a], the crosslinking agent amine equivalent [b], and the crosslinking retarder amine equivalent [c] satisfy formula (1) and formula (2), and the crosslinking point equivalent [a], the crosslinking agent amine equivalent [b], and the crosslinking retarder amine equivalent [c] satisfy formula (1) and formula (2). Formula (1): 10 mephr < = crosslinking point equivalent [a] < = 25 mephr Formula (2): 2 < = (crosslinking point equivalent [a]-crosslinking retarder amine equivalent [c]) / crosslinking agent amine equivalent [b] < = 4.

Description

Technical Field

[0001] The present invention relates to an acrylic rubber composition, a rubber crosslinked product, a hose material, a sealing material, a cube material, a strip material, and a dust cover material. Background Art

[0002] As a method for crosslinking an acrylic rubber composition, the following method is generally employed: as a primary crosslinking, after heating at about 150°C to 190°C for several minutes to several tens of minutes, as a secondary crosslinking, heating is performed for several hours in a heated air environment at 140°C to 200°C (Patent Document 1).

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2009-084514. Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] From the viewpoints of productivity of the rubber crosslinked product, energy saving, and carbon neutrality, an acrylic rubber composition is desired which can produce a rubber crosslinked product having good physical properties only by primary crosslinking without secondary crosslinking.

[0008] The present invention has been completed in view of such circumstances, and an object thereof is to provide an acrylic rubber composition having good scorch stability and capable of forming a rubber crosslinked product having sufficient mechanical properties without secondary crosslinking.

[0009] Means for Solving the Problems

[0010] The present inventors conducted intensive studies and found that the above object can be achieved by an acrylic rubber composition containing a specified acrylic rubber (A), a polyamine-based crosslinking agent (B), and a crosslinking retarder (C) in specified amounts and satisfying the relationships of the crosslink point equivalent [a], the crosslinking agent amine equivalent [b], and the crosslinking retarder amine equivalent [c] with formulas (1) and (2), thereby completing the present invention.

[0011] That is, according to the present invention, the following acrylic rubber composition, rubber crosslinked product, hose material, sealing material, tube material, strip material, and dust cover material can be provided.

[0012] [1] An acrylic rubber composition containing an acrylic rubber (A), a polyamine crosslinking agent (B), and a crosslinking retarder (C), wherein the acrylic rubber (A) contains (meth)acrylic acid alkyl ester monomer units and / or (meth)acrylic acid alkoxyalkyl ester monomer units, and also contains carboxyl group-containing monomer units. The content of the polyamine crosslinking agent (B) is 0.4 to 1.6 parts by weight relative to 100 parts by weight of the acrylic rubber (A), and the content of the crosslinking retarder (C) is 0.4 to 1.5 parts by weight relative to 100 parts by weight of the acrylic rubber (A). The relationship among the crosslink point equivalent [a] (mephr), the crosslinking agent amine equivalent [b] (mephr), and the crosslinking retarder amine equivalent [c] (mephr) satisfies the following formula (1) and the following formula (2).

[0013] Formula (1): 10 mephr ≤ crosslink point equivalent [a] ≤ 25 mephr

[0014] Formula (2): 2 ≤ (crosslink point equivalent [a] - crosslinking retarder amine equivalent [c]) / crosslinking agent amine equivalent [b] ≤ 4

[0015] [2] The acrylic rubber composition according to [1], wherein the polyamine crosslinking agent (B) is a diamine compound.

[0016] [3] The acrylic rubber composition according to [1] or [2], wherein the polyamine crosslinking agent (B) is an aromatic polyamine compound.

[0017] [4] The acrylic rubber composition according to any one of [1] to [3], wherein the crosslinking retarder (C) is a monoamine-based crosslinking retarder.

[0018] [5] The acrylic rubber composition according to any one of [1] to [4], wherein the acrylic rubber composition further contains a filler.

[0019] [6] A rubber crosslinked product obtained by crosslinking the acrylic rubber composition according to any one of [1] to [5].

[0020] [7] A hose material, a sealing material, a pipe material, a strip material, or a dust cover material composed of the rubber crosslinked product according to [6].

[0021] Advantages of the Invention

[0022] According to the present invention, an acrylic rubber composition can be provided, which has good scorch stability and can form a rubber crosslinked product with sufficient mechanical properties without secondary crosslinking. Detailed Embodiments

[0023] The acrylic rubber composition of the present invention contains an acrylic rubber (A), a polyamine-based crosslinking agent (B), and a crosslinking retarder (C). The above acrylic rubber (A) contains (meth)acrylic acid alkyl ester monomer units and / or (meth)acrylic acid alkoxyalkyl ester monomer units, and carboxyl group-containing monomer units. The content of the above polyamine-based crosslinking agent (B) is 0.4 to 1.6 parts by weight relative to 100 parts by weight of the above acrylic rubber (A), and the content of the above crosslinking retarder (C) is 0.4 to 1.5 parts by weight relative to 100 parts by weight of the above acrylic rubber (A). The relationship among the crosslink point equivalent [a] (mephr), the crosslinking agent amine equivalent [b] (mephr), and the crosslinking retarder amine equivalent [c] (mephr) satisfies the following formula (1) and the following formula (2).

[0024] Formula (1): 10 mephr ≤ crosslink point equivalent [a] ≤ 25 mephr

[0025] Formula (2): 2 ≤ (crosslink point equivalent [a] - crosslinking retarder amine equivalent [c]) / crosslinking agent amine equivalent [b] ≤ 4

[0026] The acrylic rubber composition of the present invention not only contains the above specific acrylic rubber (A), amine-based crosslinking agent (B), and crosslinking retarder (C) in the above respective specific amounts, but is also adjusted so that the relationship among the crosslink point equivalent [a] (mephr), the crosslinking agent amine equivalent [b] (mephr), and the crosslinking retarder amine equivalent [c] (mephr) satisfies Formula (1) and Formula (2). By having such a composition, the acrylic rubber composition of the present invention has good scorch stability and can form a rubber crosslinked product having sufficient mechanical properties (specifically, tensile properties, tensile properties after aging, and compression set resistance) without secondary crosslinking.

[0027] <Acrylic Rubber (A)>

[0028] The acrylic rubber (A) used in the present invention contains (meth)acrylic acid alkyl ester monomer units and / or (meth)acrylic acid alkoxyalkyl ester monomer units, and also contains carboxyl group-containing monomer units.

[0029] The acrylic rubber (A) used in the present invention contains at least one (meth)acrylic acid ester monomer unit selected from (meth)acrylic acid alkyl ester monomer units and (meth)acrylic acid alkoxyalkyl ester monomer units.

[0030] In addition, (meth)acrylic acid alkyl ester means acrylic acid alkyl ester and / or methacrylic acid alkyl ester, and (meth)acrylic acid alkoxyalkyl ester means acrylic acid alkoxyalkyl ester and / or methacrylic acid alkoxyalkyl ester. Hereinafter, the description of "(meth)acrylic acid" can be understood in the same way.

[0031] The (meth)acrylic acid alkyl ester monomer for forming a (meth)acrylic acid alkyl ester monomer unit is not particularly limited, and an ester of an alkanol having 1 to 12 carbon atoms and (meth)acrylic acid (a (meth)acrylic acid ester having an alkyl group having 1 to 12 carbon atoms) is preferred, an ester of an alkanol having 1 to 8 carbon atoms and (meth)acrylic acid (a (meth)acrylic acid ester having an alkyl group having 1 to 8 carbon atoms) is more preferred, and an ester of an alkanol having 2 to 6 carbon atoms and (meth)acrylic acid (a (meth)acrylic acid ester having an alkyl group having 2 to 6 carbon atoms) is further preferred.

[0032] Specific examples of the (meth)acrylic acid alkyl ester monomer include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, and the like. Among these, ethyl (meth)acrylate and n-butyl (meth)acrylate are preferred, and ethyl acrylate and n-butyl acrylate are more preferred. These can be used alone or in combination of two or more.

[0033] For example, the acrylic rubber (A) used in the present invention may contain both an ethyl acrylate unit and an n-butyl acrylate unit as the (meth)acrylic acid alkyl ester monomer unit. In this case, the weight ratio of the contents of the two monomer units [content of ethyl acrylate unit: content of n-butyl acrylate unit] is preferably 1:99 to 99:1, more preferably 10:90 to 90:10, further preferably 20:30 to 85:15, and particularly preferably 30:70 to 80:20.

[0034] The (meth)acrylic acid alkoxyalkyl ester monomer for forming a (meth)acrylic acid alkoxyalkyl ester monomer unit is not particularly limited, and an ester of an alkoxyalkyl alcohol having 2 to 12 carbon atoms and (meth)acrylic acid (a (meth)acrylic acid ester having an alkoxyalkyl group having 2 to 12 carbon atoms) is preferred, an ester of an alkoxyalkyl alcohol having 2 to 8 carbon atoms and (meth)acrylic acid (a (meth)acrylic acid ester having an alkoxyalkyl group having 2 to 8 carbon atoms) is more preferred, and an ester of an alkoxyalkyl alcohol having 2 to 6 carbon atoms and (meth)acrylic acid (a (meth)acrylic acid ester having an alkoxyalkyl group having 2 to 6 carbon atoms) is further preferred.

[0035] Specific examples of the (meth)acrylic acid alkoxyalkyl ester monomer include methoxy methyl (meth)acrylate, ethoxy methyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-propoxyethyl (meth)acrylate, 2-butoxyethyl (meth)acrylate, 3-methoxypropyl (meth)acrylate, 4-methoxybutyl (meth)acrylate, and the like. Among these, 2-ethoxyethyl (meth)acrylate and 2-methoxyethyl (meth)acrylate are preferred, and 2-ethoxyethyl acrylate and 2-methoxyethyl acrylate are particularly preferred. These can be used alone or in combination of two or more.

[0036] In all monomer units of the acrylic rubber (A) used in the present invention, the total content of the (meth)acrylic acid alkyl ester monomer unit and the (meth)acrylic acid alkoxyalkyl ester monomer unit is preferably 50 to 98.7% by weight, more preferably 70 to 98.7% by weight, still more preferably 80 to 98.6% by weight, particularly preferably 85 to 98.5% by weight, and most preferably 90 to 98% by weight. By making the content of the (meth)acrylate monomer unit within the above range, the mechanical properties of the obtained rubber crosslinking product will become more excellent.

[0037] The acrylic rubber (A) used in the present invention may contain only either the (meth)acrylic acid alkyl ester monomer unit or the (meth)acrylic acid alkoxyalkyl ester monomer unit, or may contain both. The acrylic rubber (A) used in the present invention preferably contains at least the (meth)acrylic acid alkyl ester monomer unit.

[0038] When the acrylic rubber (A) used in the present invention contains the (meth)acrylic acid alkyl ester monomer unit, its content in all monomer units constituting the acrylic rubber (A) is preferably 1 to 98.7% by weight, more preferably 1 to 98.6% by weight, still more preferably 5 to 98.5% by weight, and particularly preferably 5 to 98% by weight.

[0039] When the acrylic rubber (A) used in the present invention contains the (meth)acrylic acid alkoxyalkyl ester monomer unit, its content in all monomer units constituting the acrylic rubber (A) is preferably 1 to 70% by weight, more preferably 1 to 60% by weight, still more preferably 2 to 60% by weight, and particularly preferably 3 to 50% by weight.

[0040] When the acrylic rubber (A) used in the present invention contains (meth)acrylic acid alkyl ester monomer units and (meth)acrylic acid alkoxyalkyl ester monomer units, the weight ratio of the contents of the two monomer units [(content of (meth)acrylic acid alkyl ester monomer units ∶ content of (meth)acrylic acid alkoxyalkyl ester monomer units)] is preferably 1∶99 to 99∶1, more preferably 50∶50 to 98∶2, and still more preferably 80∶20 to 95∶5.

[0041] The acrylic rubber (A) used in the present invention contains a carboxyl group-containing monomer unit in addition to (meth)acrylic acid alkyl ester monomer units and / or (meth)acrylic acid alkoxyalkyl ester monomer units.

[0042] The carboxyl group-containing monomer that forms the carboxyl group-containing monomer unit is not particularly limited, and examples thereof include α,β-ethylenically unsaturated dicarboxylic acid monoester monomers, α,β-ethylenically unsaturated monocarboxylic acids, and α,β-ethylenically unsaturated dicarboxylic acids.

[0043] As the α,β-ethylenically unsaturated dicarboxylic acid monoester monomer, a monoester of an α,β-ethylenically unsaturated dicarboxylic acid having 4 to 12 carbon atoms and an alkanol having 1 to 12 carbon atoms is preferred, a monoester of an α,β-ethylenically unsaturated dicarboxylic acid having 4 to 6 carbon atoms and an alkanol having 2 to 8 carbon atoms is more preferred, and a monoester of an α,β-ethylenically unsaturated dicarboxylic acid having 4 carbon atoms and an alkanol having 2 to 6 carbon atoms is still more preferred.

[0044] Specific examples of the α,β-ethylenically unsaturated dicarboxylic acid monoester monomer include: monomethyl fumarate, monoethyl fumarate, monon-butyl fumarate, monomethyl maleate, monoethyl maleate, monon-butyl maleate and other maleic acid mono-chain alkyl esters; monocyclopentyl fumarate, monocyclohexyl fumarate, monocyclohexenyl fumarate, monocyclopentyl maleate, monocyclohexyl maleate, monocyclohexenyl maleate and other maleic acid monoesters having an alicyclic structure; monomethyl itaconate, monoethyl itaconate, monon-butyl itaconate, monocyclohexyl itaconate and other itaconic acid monoesters. These can be used alone or in combination of two or more. In addition, among the above monomers, the dicarboxylic acid also includes monomers present as acid anhydrides.

[0045] Specific examples of the α,β-ethylenically unsaturated monocarboxylic acid include acrylic acid, methacrylic acid, α-ethylacrylic acid, crotonic acid, and cinnamic acid.

[0046] Specific examples of the α,β-ethylenically unsaturated dicarboxylic acid include: fumaric acid, maleic acid and other maleic acids; itaconic acid; citraconic acid; chloromaleic acid and the like. In addition, the above monomers also include monomers present as acid anhydrides.

[0047] Among these, α,β-ethylenically unsaturated dicarboxylic acid monoester monomers are preferred, and monoalkyl maleates and maleic acid monoesters having an alicyclic structure are more preferred. Further preferred are monobutyl fumarate, monobutyl maleate, monocyclohexyl fumarate, and monocyclohexyl maleate, and particularly preferred is monobutyl fumarate.

[0048] The acrylic rubber (A) used in the present invention has carboxyl groups as crosslinking points by containing carboxyl group-containing monomer units.

[0049] The crosslinking point equivalent [a] (mephr) in the acrylic rubber (A) used in the present invention satisfies the following formula (1):

[0050] Formula (1): 10 mephr ≤ crosslinking point equivalent [a] ≤ 25 mephr.

[0051] In the present invention, the crosslinking point equivalent [a] (mephr) represents 1000 times the equivalent (ephr) of the crosslinking points in 100 parts by weight of the acrylic rubber (A). In addition, the unit is mephr (milliequivalent per hundred rubber). For example, when the monomer units having crosslinking points in the acrylic rubber (A) are composed only of monomer units having one carboxyl group such as α,β-ethylenically unsaturated dicarboxylic acid monoester monomer units and / or monocarboxylic acid monomer units, the crosslinking point equivalent [a] is equal to 1000 times the equivalent (ephr) of the monomer units having one carboxyl group in 100 parts by weight of the acrylic rubber (A).

[0052] When the crosslinking point equivalent [a] is too small, it is difficult to form a primary crosslinked product having sufficient mechanical properties. On the other hand, when the crosslinking point equivalent [a] is too large, it is difficult to manufacture the acrylic rubber (A). In addition, it is also difficult to balance scorch stability and the mechanical properties of the primary crosslinked product.

[0053] The crosslinking point equivalent [a] is not particularly limited as long as it is 10 mephr or more and 25 mephr or less, preferably 11 to 22 mephr, more preferably 12 to 20 mephr, further preferably 12.5 to 18 mephr, and particularly preferably 12.5 to 16 mephr. By making the crosslinking point equivalent [a] within the above preferred range, it is possible to balance scorch stability and the mechanical properties of the primary crosslinked product at a higher level.

[0054] The content of the carboxyl group-containing monomer unit in all monomer units of the acrylic rubber (A) used in the present invention is not particularly limited as long as the crosslinking point equivalent [a] is within the above range, and is preferably 1.3 to 7.5% by weight, more preferably 1.5 to 5.0% by weight, still more preferably 1.7 to 4.0% by weight, particularly preferably 1.9 to 3.5% by weight, and most preferably 2.0 to 3.0% by weight. By making the content of the carboxyl group-containing monomer unit within the above range, scorch stability and the mechanical properties of the primary crosslinked product can be balanced at a higher level.

[0055] The acrylic rubber (A) used in the present invention preferably contains an α,β-ethylenically unsaturated dicarboxylic acid monoester monomer unit as the carboxyl group-containing monomer unit. In this case, in the acrylic rubber (A) used in the present invention, the weight ratio of the α,β-ethylenically unsaturated dicarboxylic acid monoester monomer unit to the content of the carboxyl group-containing monomer unit [content of α,β-ethylenically unsaturated dicarboxylic acid monoester monomer unit / content of carboxyl group-containing monomer unit] is preferably 50 to 100% by weight, more preferably 70 to 100% by weight, still more preferably 90 to 100% by weight. In one embodiment of the present invention, the acrylic rubber (A) may contain only the α,β-ethylenically unsaturated dicarboxylic acid monoester monomer unit as the carboxyl group-containing monomer unit. That is, the above weight ratio may be substantially 100% by weight.

[0056] In addition to the above monomer units, the acrylic rubber (A) used in the present invention may also have units of other monomers that can copolymerize with them. As such other copolymerizable monomers, there is no particular limitation, and examples include conjugated diene monomers, non-conjugated diene monomers, aromatic vinyl monomers, α,β-ethylenically unsaturated nitrile monomers, acrylamide-based monomers, α,β-ethylenically unsaturated dicarboxylic acid diester monomers, and other olefin-based monomers.

[0057] Examples of the conjugated diene monomer include 1,3-butadiene, isoprene, and piperylene.

[0058] Examples of the non-conjugated diene monomer include ethylidene norbornene, dicyclopentadiene, (meth)acrylic dicyclopentadiene ester, and (meth)acrylic-2-dicyclopentadienyl ethyl ester.

[0059] Examples of the aromatic vinyl monomer include styrene, α-methylstyrene, and divinylbenzene.

[0060] Examples of the α,β-ethylenically unsaturated nitrile monomer include acrylonitrile and methacrylonitrile.

[0061] Examples of the acrylamide-based monomer include acrylamide and methacrylamide.

[0062] Examples of the α,β-ethylenically unsaturated dicarboxylic acid diester monomers include: dialkyl maleates such as dimethyl maleate and di-n-butyl maleate, where the alkyl group has 1 to 18 carbon atoms; dialkyl fumarates such as dimethyl fumarate and di-n-butyl fumarate, where the alkyl group has 1 to 18 carbon atoms; dicycloalkyl maleates such as dicyclopentyl maleate and dicyclohexyl maleate, where the cycloalkyl group has 4 to 16 carbon atoms; dicycloalkyl fumarates such as dicyclopentyl fumarate and dicyclohexyl fumarate, where the cycloalkyl group has 4 to 16 carbon atoms; dialkyl itaconates such as dimethyl itaconate and di-n-butyl itaconate, where the alkyl group has 1 to 18 carbon atoms; dicycloalkyl itaconates such as dicyclohexyl itaconate, where the cycloalkyl group has 4 to 16 carbon atoms, and the like.

[0063] Examples of other olefin monomers include ethylene, propylene, vinyl chloride, vinylidene chloride, vinyl acetate, ethyl vinyl ether, butyl vinyl ether, and the like.

[0064] Other monomers capable of copolymerization can be used alone or in combination of two or more. In the monomer units of the acrylic rubber (A) used in the present invention, the content of the units of other monomers 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.

[0065] The acrylic rubber (A) used in the present invention can be obtained by polymerizing the above monomers. As the polymerization reaction method, any of emulsion polymerization, suspension polymerization, bulk polymerization, and solution polymerization can be used. From the aspect of controlling the ease of the polymerization reaction, etc., emulsion polymerization under normal pressure is preferably used.

[0066] The emulsion polymerization can be any of batch, semi-batch, and continuous types. The polymerization is usually carried out in the temperature range of 0 to 70 °C, preferably 5 to 50 °C. Regarding the above monomers, it is not necessary to supply all types and all amounts of monomers to the reaction at the start of the reaction. Considering the copolymerization reactivity ratio, reaction conversion rate, etc., they can be added continuously or intermittently throughout the reaction time, or added all at once or in batches in the middle or the latter half. In addition, the addition ratio of each monomer in the polymerization reaction can be adjusted according to the reactivity of each monomer. However, since the polymerization reaction mostly proceeds almost quantitatively, the addition ratio can be determined according to the monomer unit composition of the acrylic rubber (A) to be produced, taking such circumstances into account. After polymerization, through coagulation and drying, solid acrylic rubber (A) can be obtained.

[0067] The shape of the acrylic rubber (A) used in the present invention is not particularly limited and can be any of rubber bale shape, sheet shape, powder shape, etc.

[0068] <Polyamine crosslinking agent (B)>

[0069] The acrylic rubber composition of the present invention contains 0.4 to 1.6 parts by weight of a polyamine crosslinking agent (B) relative to 100 parts by weight of the acrylic rubber (A).

[0070] The polyamine crosslinking agent (B) is not particularly limited as long as it is a compound having two or more amino groups or a compound that will become a form having two or more amino groups during crosslinking. Examples of the polyamine crosslinking agent (B) include aliphatic polyamine compounds and their carbonates, and aromatic polyamine compounds.

[0071] Examples of the aliphatic polyamine compound and its carbonate are not particularly limited, and examples include hexamethylenediamine, hexamethylenediamine carbamate, and N,N'-dicyclohexylidene-1,6-hexanediamine. Among these, hexamethylenediamine carbamate is preferred.

[0072] Examples of the aromatic polyamine compound are not particularly limited, and examples include 4,4'-methylenedianiline, p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-(m-phenylene diisopropylidene)diphenylamine, 4,4'-(p-phenylene diisopropylidene)diphenylamine, 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), 4,4'-diaminobenzanilide, 4,4'-bis(4-aminophenoxy)biphenyl, m-xylylenediamine, p-xylylenediamine, and 1,3,5-benzenetriamine. Among these, 2,2'-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) is preferred.

[0073] Among the above, as the polyamine crosslinking agent (B), a diamine compound, that is, a compound having two amino groups or a compound that will become a form having two amino groups during crosslinking, is preferred. In addition, as the polyamine crosslinking agent (B), an aromatic polyamine compound is preferred, and an aromatic diamine compound is more preferred.

[0074] The content of the polyamine crosslinking agent (B) in the acrylic rubber composition of the present invention is 0.4 to 1.6 parts by weight relative to 100 parts by weight of the acrylic rubber (A). If the content of the polyamine crosslinking agent (B) is too much or too little, it will be difficult to balance the scorch stability and the mechanical properties of the primary crosslinked product.

[0075] The content of the polyamine-based crosslinking agent (B) is not particularly limited as long as it is 0.4 to 1.6 parts by weight relative to 100 parts by weight of the acrylic rubber (A), preferably 0.6 to 1.2 parts by weight, and more preferably 0.75 to 1.1 parts by weight. By making the content of the polyamine-based crosslinking agent (B) within the above range, scorch stability and the mechanical properties of the primary crosslinked product can be balanced at a higher level.

[0076] The acrylic rubber composition of the present invention may contain a crosslinking agent other than the polyamine-based crosslinking agent (B), and its content is preferably 0.5 parts by weight or less, and more preferably 0.1 parts by weight or less relative to 100 parts by weight of the acrylic rubber (A).

[0077] <Crosslinking retarder (C)>

[0078] The acrylic rubber composition of the present invention further contains 0.4 to 1.5 parts by weight of a crosslinking retarder (C) relative to 100 parts by weight of the acrylic rubber (A).

[0079] The crosslinking retarder (C) is preferably a monoamine-based crosslinking retarder, and more preferably a primary monoamine compound. The primary monoamine compound is a compound in which one hydrogen atom of ammonia is substituted by a hydrocarbon group, and examples include aliphatic primary monoamines, alicyclic primary monoamines, aromatic primary monoamines, amino alcohols, aminooxy compounds, etc. Among these, aliphatic primary monoamines are preferred, and aliphatic primary monoamines having 8 to 20 carbon atoms are particularly more preferred. In addition, when an aromatic polyamine compound as the polyamine-based crosslinking agent (B) and an aliphatic primary monoamine as the crosslinking retarder (C) are used in combination, the scorch stability becomes very good.

[0080] Examples of the aliphatic primary monoamine include methylamine, ethylamine, propylamine, allylamine, isopropylamine, n-butylamine, tert-butylamine, sec-butylamine, hexylamine, heptylamine, octylamine, nonylamine, decylamine, undecylamine, dodecylamine, tridecylamine, tetradecylamine, pentadecylamine, hexadecylamine, 2-ethylhexylamine, octadecylamine, cis-9-octadeceneamine, nonadecylamine, etc. Among these, aliphatic primary monoamines having 8 to 20 carbon atoms such as octylamine, decylamine, dodecylamine, tetradecylamine, hexadecylamine, octadecylamine, cis-9-octadeceneamine, nonadecylamine, etc. are preferred.

[0081] Examples of the alicyclic primary monoamine include cyclopropylamine, cyclobutylamine, cyclopentylamine, cyclohexylamine, etc.

[0082] Examples of the aromatic primary monoamine include aniline, o-toluidine, m-toluidine, benzylamine, α-naphthylamine, β-naphthylamine, etc.

[0083] Examples of the amino alcohol include aminoethanol, aminopropanol, D,L-aminopropanol, 2-aminobutanol, 2-amino-2-methylpropanol, 2-amino-2-hydroxymethyl-1,3-propanediol, 2-amino-2-methylpropane-1,3-diol, 2-amino-2-ethyl-1,3-propanediol, 1-chloro-3-aminopropan-2-ol, 3-amino-1,2-propanediol, 2-amino-1,3-propanediol and other amino alcohols.

[0084] Examples of the aminooxy compound include 3-methoxypropylamine, 3-ethoxypropylamine and the like.

[0085] The content of the crosslinking retarder (C) in the acrylic rubber composition of the present invention is 0.4 to 1.5 parts by weight relative to 100 parts by weight of the acrylic rubber (A). If the content of the crosslinking retarder (C) is too much or too little, it will be difficult to balance the scorch stability and the mechanical properties of the primary crosslinked product.

[0086] As long as the content of the crosslinking retarder (C) is 0.4 to 1.5 parts by weight relative to 100 parts by weight of the acrylic rubber (A), there is no particular limitation, and it is preferably 0.6 to 1.25 parts by weight, more preferably 0.7 to 1.1 parts by weight. By making the content of the crosslinking retarder (C) within the above range, the scorch stability and the mechanical properties of the primary crosslinked product can be balanced at a higher level.

[0087] <Formula (2)>

[0088] The relationship among the crosslinking point equivalent [a] (mephr), the crosslinking agent amine equivalent [b] (mephr) and the crosslinking retarder amine equivalent [c] (mephr) in the acrylic rubber composition of the present invention satisfies the following formula (2).

[0089] Formula (2): 2 ≤ (crosslinking point equivalent [a] - crosslinking retarder amine equivalent [c]) / crosslinking agent amine equivalent [b] ≤ 4

[0090] In the present invention, the crosslinking agent amine equivalent [b] (mephr) represents 1000 times the amino equivalent (ephr) of the polyamine-based crosslinking agent (B) relative to 100 parts by weight of the acrylic rubber (A). For example, when the polyamine-based crosslinking agent (B) is a diamine compound, the crosslinking agent amine equivalent [b] is equal to 2000 times the number of moles of the polyamine-based crosslinking agent (B) relative to 100 parts by weight of the acrylic rubber (A). In addition, when the polyamine-based crosslinking agent (B) is a compound that will become a compound having two or more amino groups during crosslinking, the amino equivalent of the polyamine-based crosslinking agent (B) represents the amino equivalent during crosslinking.

[0091] In the present invention, the crosslinking retarder amine equivalent [c] (mephr) represents 1000 times the amino equivalent (ephr) of the crosslinking retarder (C) with respect to 100 parts by weight of the acrylic rubber (A). For example, when the crosslinking retarder (C) is a monoamine-based crosslinking retarder, the crosslinking retarder amine equivalent [c] is equal to 1000 times the molar number (ephr) of the molecule of the crosslinking retarder (C) with respect to 100 parts by weight of the acrylic rubber (A).

[0092] The value of (crosslinking point equivalent [a] - crosslinking retarder amine equivalent [c]) / crosslinking agent amine equivalent [b] in formula (2) (hereinafter, sometimes referred to as "K value") is 2 or more and 4 or less. If the K value is too small or too large, it will be difficult to balance the scorch stability and the mechanical properties of the primary crosslinked product.

[0093] As long as the K value is 2 or more and 4 or less, it is not particularly limited, preferably 2 or more and 3.75 or less, more preferably 2.125 or more and 3.5 or less, and further preferably 2.25 or more and 3.25 or less. By making the K value within the above range, the scorch stability and the mechanical properties of the primary crosslinked product can be balanced at a higher level.

[0094] <Other components>

[0095] In addition, the acrylic rubber composition of the present invention preferably contains a crosslinking accelerator.

[0096] As the crosslinking accelerator, guanidine compounds, diazabicycloalkene compounds, imidazole compounds, quaternary salts, tertiary phosphine compounds, aliphatic primary secondary amine compounds, and aliphatic primary tertiary amine compounds, etc. can be used. These basic crosslinking accelerators can be used alone or in combination of two or more.

[0097] Specific examples of guanidine compounds include 1,3-ditolylguanidine, 1,3-diphenylguanidine, etc. Specific examples of diazabicycloalkene compounds include 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5-diazabicyclo[4.3.0]non-5-ene, etc. Specific examples of imidazole compounds include 2-methylimidazole, 2-phenylimidazole, etc. Specific examples of quaternary salts include tetra-n-butylammonium bromide, octadecyltri-n-butylammonium bromide, etc. Specific examples of tertiary phosphine compounds include triphenylphosphine, tri-p-tolylphosphine, etc.

[0098] An aliphatic primary secondary amine compound is a compound in which two hydrogen atoms of ammonia are replaced by aliphatic hydrocarbon groups. The aliphatic hydrocarbon group replacing the hydrogen atom is preferably an aliphatic hydrocarbon group having 1 to 30 carbon atoms. Specific examples of the aliphatic primary secondary amine compound include dialkylmonoamine compounds such as dimethylamine, diethylamine, dipropylamine, diallylamine, diisopropylamine, di-n-butylamine, di-tert-butylamine, di-sec-butylamine, dihexylamine, diheptylamine, dioctylamine, dinonylamine, didecylamine, di(undecyl)amine, di(dodecyl)amine, di(tridecyl)amine, di(tetradecyl)amine, di(pentadecyl)amine, di(hexadecyl)amine, di-2-ethylhexylamine, and di(octadecyl)amine.

[0099] An aliphatic primary tertiary amine compound is a compound in which all three hydrogen atoms of ammonia are replaced by aliphatic hydrocarbon groups. The aliphatic hydrocarbon group replacing the hydrogen atom is preferably an aliphatic hydrocarbon group having 1 to 30 carbon atoms. Specific examples of the aliphatic primary tertiary amine compound include trialkylmonoamines such as trimethylamine, triethylamine, tripropylamine, triallylamine, triisopropylamine, tri-n-butylamine, tri-tert-butylamine, tri-sec-butylamine, trihexylamine, triheptylamine, trioctylamine, trinonylamine, tridecylamine, tri(undecyl)amine, and tri(dodecyl)amine.

[0100] Among these, guanidine compounds, diazabicycloene compounds, and aliphatic primary secondary amine compounds are preferred, guanidine compounds and diazabicycloene compounds are more preferred, and 1,3-di-o-tolylguanidine and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) are further preferred.

[0101] The content of the crosslinking accelerator in the acrylic rubber composition of the present invention is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 6 parts by weight, and further preferably 1 to 4 parts by weight based on 100 parts by weight of the acrylic rubber (A). By making the content of the crosslinking accelerator within the above range, scorch stability and the mechanical properties of the primary crosslinked product can be balanced at a higher level.

[0102] The acrylic rubber composition of the present invention may also contain a rubber other than the acrylic rubber (A).

[0103] The rubber other than the acrylic rubber (A) that can be used in the present invention is not particularly limited, and examples include acrylic rubbers other than the acrylic rubber (A) used in the present invention, natural rubber, polybutadiene rubber, polyisoprene rubber, styrene-butadiene rubber, acrylonitrile-butadiene rubber, silicone rubber, fluororubber, olefin-based elastomers, styrene-based elastomers, vinyl chloride-based elastomers, polyester-based elastomers, polyamide-based elastomers, polyurethane-based elastomers, polysiloxane-based elastomers, etc. These can be used alone or in combination of two or more.

[0104] The proportion of the acrylic rubber (A) component in the rubber component of the acrylic rubber composition may be appropriately selected according to the intended use, preferably 70% by weight or more, more preferably 90% by weight or more, still more preferably 95% by weight or more, and particularly preferably 100% by weight (that is, the rubber component of the acrylic rubber composition is substantially composed only of the acrylic rubber (A) component).

[0105] The acrylic rubber composition of the present invention preferably contains fillers such as reinforcing fillers and non-reinforcing fillers.

[0106] Examples of the reinforcing filler include carbon blacks such as furnace black, acetylene black, thermal black, channel black, and graphite; and silicas such as wet silica, dry silica, and colloidal silica. In addition, examples of the non-reinforcing filler include clay such as quartz powder and diatomaceous earth, zinc oxide, basic magnesium carbonate, activated calcium carbonate, magnesium silicate, aluminum silicate, titanium dioxide, talc, aluminum sulfate, calcium sulfate, and barium sulfate. The fillers can be used alone or in combination of two or more.

[0107] The content of the filler in the acrylic rubber composition of the present invention is not particularly limited, and is preferably 1 to 200 parts by weight, more preferably 10 to 150 parts by weight, still more preferably 20 to 100 parts by weight, relative to 100 parts by weight of the rubber component containing the acrylic rubber (A) in the acrylic rubber composition.

[0108] The acrylic rubber composition of the present invention may contain an antioxidant as needed. There is no particular limitation on the antioxidant, and examples thereof include phenolic antioxidants such as bis-hindered phenol-based antioxidants, semi-hindered phenol-based antioxidants, less hindered phenol-based antioxidants, and phenol-based antioxidants without a hindered group; phosphite-based antioxidants; thioester-based antioxidants; secondary amine-based antioxidants such as phenyl-α-naphthylamine, phenyl-β-naphthylamine, p-(p-toluenesulfonylamino) diphenylamine, 4,4'-bis(α,α-dimethylbenzyl) diphenylamine, N,N-diphenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, and butyraldehyde-aniline condensate; imidazole-based antioxidants; quinoline-based antioxidants; and hydroquinone-based antioxidants.

[0109] The antioxidants can be used alone or in combination of two or more. The content of the antioxidant in the rubber composition of the present invention is not particularly limited, and is preferably 0.01 to 15 parts by weight, more preferably 0.05 to 10 parts by weight, still 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.

[0110] In addition to the above components, the acrylic rubber composition of the present invention can also be compounded with compounding agents commonly used in the rubber processing field. Examples of such compounding agents include: light stabilizers; plasticizers; softeners; processing aids; adhesives; slip agents; lubricants; flame retardants; mildew-proof agents; antistatic agents; colorants, etc. The compounding amounts of these compounding agents are not particularly limited as long as they do not hinder the objects and effects of the present invention, and can be appropriately compounded in amounts corresponding to the compounding purposes.

[0111] The acrylic rubber composition of the present invention can be prepared by the following method: compounding a crosslinking agent, a crosslinking retarder, and various other compounding agents used as needed into a rubber component containing acrylic rubber (A), and mixing and kneading through an open roll, a Banbury mixer, various kneaders, etc., and then further kneading using a kneading roll, etc., thereby preparing.

[0112] There is no particular limitation on the compounding order of each component. It is preferred to first fully mix the components that are not easily reactive and decomposed by heat, and then mix the crosslinking agent, etc., which are components that are easily reactive and decomposed by heat, at a temperature that is not likely to cause reaction and decomposition for a short time.

[0113] The Mooney viscosity (ML1+4, 100 °C) of the acrylic rubber composition of the present invention is preferably 10 to 80, more preferably 20 to 70, and further preferably 30 to 60.

[0114] <Rubber crosslinked product>

[0115] The rubber crosslinked product of the present invention is obtained by crosslinking the above acrylic rubber composition of the present invention.

[0116] The rubber crosslinked product of the present invention can be manufactured by the following method: using the acrylic rubber composition of the present invention, forming through a molding machine corresponding to the desired shape, such as an extruder, an injection molding machine, a compressor, and a roll, etc., and performing a crosslinking reaction by heating to fix the shape to form a rubber crosslinked product. In this case, crosslinking can be carried out after pre-forming, or crosslinking can be carried out simultaneously with forming. In addition, the molding temperature is usually 10 to 140 °C, preferably 25 to 120 °C.

[0117] The crosslinking temperature is usually 150 to 190 °C, preferably 160 to 180 °C, and the crosslinking time is usually 2 to 60 minutes, preferably 3 to 40 minutes. As the heating method, as long as methods such as press heating, steam heating, oven heating, and hot air heating that can be used for rubber crosslinking are appropriately selected.

[0118] In the manufacturing method of the rubber crosslinked product of the present invention, it is not necessarily required to perform secondary crosslinking, but secondary crosslinking can also be carried out. Secondary crosslinking is usually carried out in a heated air environment of 130 to 220 °C for 1 to 48 hours.

[0119] From the viewpoints of productivity, energy conservation, and carbon neutrality, the rubber crosslinked product of the present invention is preferably a primary crosslinked product of the acrylic rubber composition of the present invention. For example, the rubber crosslinked product of the present invention is preferably a primary crosslinked product formed 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.

[0120] The rubber crosslinked product of the present invention is preferably 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, seals for air compression equipment, etc.; various gaskets such as a cylinder head gasket installed at the connection part between a cylinder block and a cylinder head, a rocker cover gasket installed at the connection part between a rocker cover and a cylinder head, an oil pan gasket installed at the connection part between an oil pan and a cylinder head or a transmission case, a gasket for a fuel cell spacer installed between a pair of outer casings sandwiching a unit cell having a positive electrode, an electrolyte plate, and a negative electrode, a gasket for a top cover of a hard disk drive, etc.; cushioning materials, shockproof materials; wire coating materials; industrial belts; pipe and hose materials; strip materials; dust cover materials; sheet materials, etc.

[0121] In addition, the rubber crosslinked product of the present invention, as an extruded molded product and a crosslinked product that can be used for automotive applications, is preferably used for, for example, fuel oil system hoses such as fuel hoses, fuel filler neck hoses, exhaust hoses, vapor hoses, oil hoses, etc. for fuel tanks; air system hoses such as turbocharged air hoses, transmission control hoses, etc.; various hose materials such as radiator hoses, heater hoses, brake hoses, air conditioning hoses, etc.

[0122] Examples

[0123] Hereinafter, the present invention will be described in detail by way of examples, but the present invention is not limited to these examples. In addition, unless otherwise specified, "parts" hereinafter are based on weight. In addition, various physical properties are measured as follows.

[0124] <Crosslinking point equivalent>

[0125] The crosslinking point equivalent [a] in the acrylic rubber is calculated by dissolving a rubber sample in acetone and performing potentiometric titration with a potassium hydroxide solution.

[0126] <Mooney scorch time [t5]>

[0127] The Mooney scorch time [t5] of the acrylic rubber composition is measured in accordance with JIS K6300 under the condition that the temperature is 125°C. If the Mooney scorch time [t5] is 15 minutes or more, it can be judged that the scorch stability is good.

[0128] <Maximum torque [MH]>

[0129] The crosslinkability test of the acrylic rubber composition was carried out using a rubber vulcanization testing machine (Moving Die Rheometer MDR, manufactured by Alpha Technology Co., Ltd.) under the conditions of 170 °C and 20 minutes. Then, the maximum torque [MH] was measured according to the results of the crosslinkability test.

[0130] <Normal physical properties of acrylic rubber crosslink (primary crosslink)>

[0131] According to JIS K6251, test pieces were cut from the sheet-like acrylic rubber crosslink (primary crosslink), and the tensile strength, elongation at break, and 100% elongation stress of the obtained test pieces were measured. If the 100% elongation stress is 3 or more, it can be judged that the rubber crosslink has sufficient mechanical properties.

[0132] <Physical properties of acrylic rubber crosslink (primary crosslink) after heating>

[0133] For the sheet-like acrylic rubber crosslink (primary crosslink), an air heating aging test was carried out at 175 °C for 72 hours according to JIS K6257. Then, according to JIS K6251, test pieces were cut from the acrylic rubber crosslink after the air heating aging test, and the tensile strength and elongation at break of the obtained test pieces were measured.

[0134] <Compression set [CS] of acrylic rubber crosslink (primary crosslink)>

[0135] Using a cylindrical acrylic rubber crosslink (primary crosslink), the compression set [CS] under the compression conditions of a compression ratio of 25%, 175 °C, and 72 hours was determined according to JIS K6262.

[0136] <Increase ratio of 100% elongation stress due to secondary crosslinking>

[0137] The sheet-like acrylic rubber crosslink (primary crosslink) was heated in an oven at 170 °C for 4 hours to obtain a secondary crosslink. According to JIS K6251, test pieces were cut from the secondary crosslink, and the 100% elongation stress of the obtained test pieces was measured. Then, according to the following formula, the increase ratio of the 100% elongation stress due to secondary crosslinking was calculated.

[0138] Increase ratio of 100% elongation stress due to secondary crosslinking (%) = (100% elongation stress of secondary crosslink - 100% elongation stress of primary crosslink) / 100% elongation stress of primary crosslink × 100

[0139] The smaller the increase ratio of the 100% elongation stress due to secondary crosslinking, the better the crosslinking reaction caused by the primary crosslinking can be judged.

[0140] <Example 1>

[0141] (Manufacture of acrylic rubber)

[0142] 200 parts of water, 3 parts of sodium lauryl sulfate, 48.00 parts of ethyl acrylate, 48.00 parts of n-butyl acrylate, and 4 parts of monon-butyl fumarate were added to a polymerization reactor equipped with a thermometer, a stirring device, a nitrogen inlet tube, and a decompression device. Then, degassing under reduced pressure and nitrogen replacement were repeatedly carried out to thoroughly remove oxygen. Then, 0.002 parts of sodium formaldehyde sulfoxylate and 0.005 parts of cumene hydroperoxide were added, and an emulsion polymerization reaction was initiated at normal pressure and room temperature and continued until the polymerization conversion reached 95%. For the obtained emulsion polymerization liquid, it was coagulated with an aqueous magnesium sulfate solution, washed with water, and dried to obtain acrylic rubber (ACM-1). The content ratio of the monon-butyl fumarate unit in the obtained acrylic rubber (ACM-1) was 3.25% by weight. In addition, for the acrylic rubber (ACM-1), the crosslinking point equivalent [a] was measured according to the above method, and the result was 18.90 mephr.

[0143] (Manufacture of acrylic rubber composition)

[0144] 100 parts of acrylic rubber (ACM-1), 60 parts of carbon black (trade name “SeastSO”, manufactured by Tokai Carbon Co., Ltd.), 2 parts of stearic acid (a dispersant and softening agent for carbon black), 1 part of an ester wax (trade name “Greg G-8205”, manufactured by DIC Corporation), 0.95 parts of octadecylamine (LipoMin 18D, manufactured by Lion Specialty Chemical Co., Ltd., a monoamine-based crosslinking retarder), and 2 parts of 4,4′-bis(α,α-dimethylbenzyl)diphenylamine (an antioxidant) were kneaded with a Banbury mixer, and then 0.90 parts of BAPP (2,2′-bis[4-(4-aminophenoxy)phenyl]propane, a polyamine-based crosslinking agent (diamine)) and 2.00 parts of crosslinking accelerator 1 (trade name “NOCCELER DT”, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., 1,3-di-o-tolylguanidine) were added, and kneading was carried out with an open roll at 50 °C to obtain an acrylic rubber composition. Using the obtained acrylic rubber composition, the Mooney scorch time [t5] and the maximum torque [MH] were measured according to the above method. The results are shown in Table 1.

[0145] In addition, the crosslinking agent amine equivalent [b] of the acrylic rubber composition was 4.38 mephr, and the crosslinking retarder amine equivalent [c] was 3.52 mephr. Furthermore, using these values, the value of (crosslinking point equivalent [a] - crosslinking retarder amine equivalent [c]) / crosslinking agent amine equivalent [b] (i.e., the K value) was calculated, and the result was 3.51.

[0146] (Manufacture of acrylic rubber crosslinked product)

[0147] The acrylic rubber composition was molded and crosslinked by pressing at 10 MPa at 170 °C for 20 minutes to obtain a sheet-like acrylic rubber crosslinked product (primary crosslinked product) of 15 cm × 15 cm × 2 mm. Using the obtained sheet-like acrylic rubber crosslinked product (primary crosslinked product), the physical properties at normal temperature, the physical properties after heating, and the increase ratio of the 100% elongation stress due to secondary crosslinking were measured. The results are shown in Table 1. In addition, a cylindrical acrylic rubber crosslinked product (primary crosslinked product) with a diameter of 29 mm and a thickness of 12.5 mm was produced by pressing and crosslinking the acrylic rubber composition at 10 MPa at 170 °C for 20 minutes, and the compression set [CS] was measured. The results are shown in Table 1.

[0148] <Examples 2 to 7, Comparative Examples 1 to 12>

[0149] (Manufacture of acrylic rubber)

[0150] Using the monomers described in Tables 1 to 3 in the amounts described in Tables 1 to 3 to replace 48.00 parts of ethyl acrylate, 48.00 parts of n-butyl acrylate, and 4 parts of monon-butyl fumarate, and otherwise proceeding in the same manner as in Example 1, acrylic rubber was obtained. The content ratio of the monon-butyl fumarate unit in the obtained acrylic rubber is shown in Tables 1 to 3. In addition, for the acrylic rubber, the crosslinking point equivalent [a] was measured according to the above method, and the results are shown in Tables 1 to 3.

[0151] (Manufacture of acrylic rubber composition)

[0152] Using the acrylic rubber obtained above to replace the acrylic rubber (ACM-1), and changing the amounts of octadecylamine (crosslinking retarder) and BAPP (amine-based crosslinking agent), as well as the type and amount of the crosslinking accelerator as shown in Tables 1 to 3, and otherwise proceeding in the same manner as in Example 1, an acrylic rubber composition was obtained. In addition, in Example 7 and Comparative Example 3, Crosslinking Accelerator 2 (trade name "Rhenogran XLA-60", manufactured by Rhein Chemie, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) 60% (including the part that has become the zinc dialkyl diphosphate salt of DBU), acrylic polymer, and dispersant 40%) was used. The obtained acrylic rubber composition was measured in the same manner as in Example 1. The results are shown in Tables 1 to 3. In addition, for the acrylic rubber composition, the crosslinking agent amine equivalent [b], the crosslinking retarder amine equivalent [c], and the K value in formula (1) were calculated, and the results are shown in Tables 1 to 3.

[0153] <Comparative Example 13>

[0154] Into a polymerization reactor equipped with a thermometer, a stirring device, a nitrogen inlet tube, and a decompression device, 200 parts of water, 3 parts of sodium lauryl sulfate, 64.10 parts of ethyl acrylate, 21.90 parts of n-butyl acrylate, 7.50 parts of methoxyethyl acrylate, and 6.50 parts of monon-butyl fumarate were added. Then, degassing under reduced pressure and nitrogen replacement were repeatedly carried out to sufficiently remove oxygen. Then, 0.002 parts of sodium formaldehyde sulfoxylate and 0.005 parts of cumene hydroperoxide were added, and an emulsion polymerization reaction was initiated at normal pressure and room temperature. The reaction was continued until the polymerization conversion reached 95%. As a result, a large amount of coagulation occurred during the emulsion polymerization, and the desired acrylic rubber was not obtained. In addition, for the obtained emulsion polymerization liquid, it was coagulated with an aqueous magnesium sulfate solution, washed with water, and dried. For the obtained coagulum, the content ratio of the monon-butyl fumarate unit was determined, and the result was 5.10% by weight. In addition, the crosslinking point equivalent [a] was measured according to the above method, and the result was 29.65 mephr.

[0155] [Table 1]

[0156] Table 1

[0157]

[0158] [Table 2]

[0159] Table 2

[0160] [Table 3]

[0161] Table 3

[0162]

[0163] As shown in Table 1, an acrylic rubber composition containing a specified acrylic rubber (A), a polyamine-based crosslinking agent (B), and a crosslinking retarder (C) in specified amounts, and having the relationship between the crosslinking point equivalent [a], the crosslinking agent amine equivalent [b], and the crosslinking retarder amine equivalent [c] satisfying Formula (1) and Formula (2) has a scorch time (t5) of 15 minutes or more, has good scorch stability (processing stability), and can form a rubber crosslinked product having sufficient mechanical properties without secondary crosslinking (Examples 1 to 7).

[0164] On the other hand, when the content of the polyamine-based crosslinking agent (B) or the crosslinking retarder (C) relative to 100 parts by weight of the acrylic rubber (A) is outside the specified range, the scorch time (t5) becomes short, or the tensile properties or compression set resistance of the obtained primary crosslinked product deteriorates, and it is impossible to balance the scorch stability and the mechanical properties of the primary crosslinked product (Comparative Examples 1, 3 to 6).

[0165] Further, even when the contents of the polyamine-based crosslinking agent (B) and the crosslinking retarder (C) relative to 100 parts by weight of the acrylic rubber (A) are within the specified ranges, when the K value is outside the specified range, the scorch time (t5) becomes shorter, or the tensile properties or compression set resistance of the obtained primary crosslinked product deteriorates, and it is impossible to balance the scorch stability and the mechanical properties of the primary crosslinked product (Comparative Examples 2 and 7 to 12).

Claims

1. An acrylic rubber composition containing an acrylic rubber (A), a polyamine-based crosslinking agent (B), and a crosslinking retarder (C). The acrylic rubber (A) contains (meth)acrylic acid alkyl ester monomer units and / or (meth)acrylic acid alkoxyalkyl ester monomer units, and also contains carboxyl group-containing monomer units. The content of the polyamine-based crosslinking agent (B) is 0.4 to 1.6 parts by weight relative to 100 parts by weight of the acrylic rubber (A). The content of the crosslinking retarder (C) is 0.4 to 1.5 parts by weight relative to 100 parts by weight of the acrylic rubber (A). The relationship among the crosslink point equivalent [a] (mephr), the crosslinking agent amine equivalent [b] (mephr), and the crosslinking retarder amine equivalent [c] (mephr) satisfies the following formula (1) and the following formula (2). Formula (1): 10 mephr ≤ crosslink point equivalent [a] ≤ 25 mephr Formula (2): 2 ≤ (crosslink point equivalent [a] - crosslinking retarder amine equivalent [c]) / crosslinking agent amine equivalent [b] ≤ 4.

2. The acrylic rubber composition according to claim 1, wherein The polyamine-based crosslinking agent (B) is a diamine compound.

3. The acrylic rubber composition according to claim 1 or 2, wherein The polyamine-based crosslinking agent (B) is an aromatic polyamine compound.

4. The acrylic rubber composition according to any one of claims 1 to 3, wherein The crosslinking retarder (C) is a monoamine-based crosslinking retarder.

5. The acrylic rubber composition according to any one of claims 1 to 4, wherein The acrylic rubber composition further contains a filler.

6. A rubber crosslinked product obtained by crosslinking the acrylic rubber composition according to any one of claims 1 to 5.

7. A hose material, a sealing material, a pipe material, a strip material, or a dust cover material composed of the rubber crosslinked product according to claim 6.

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