Acrylic copolymer, compositions containing acrylic copolymer, products of crosslinked acrylic rubber, and methods for the production of acrylic copolymers.

Abstract

Invention details;

Description

Acrylic copolymer, acrylic copolymer-containing composition, crosslinked acrylic rubber, and method for producing acrylic copolymer

[0001] The present invention relates to an acrylic copolymer, an acrylic copolymer-containing composition and a crosslinked product thereof, and a method for producing the acrylic copolymer.

[0002] Generally, acrylic copolymers are polymers whose main raw material is alkyl (meth)acrylate ester, and are known as materials with excellent physical properties related to durability. They are widely used as industrial rubber materials such as engine gaskets, oil hoses, air hoses, and O-rings, as well as automotive rubber materials.

[0003] When acrylic copolymers are used as automotive rubber materials such as the above-mentioned hoses and gaskets, they are required to have excellent compression set in order to exhibit sufficient sealing performance. Furthermore, they must also have excellent processability so that they can be used in a variety of molding methods to form hoses, gaskets, etc., and they must also have sufficient mechanical strength as crosslinked products.

[0004] Generally, when low compression set and mechanical strength are required, a method of increasing the crosslink density is adopted. However, increasing the crosslink density leads to a trade-off in that the vulcanization rate increases and processability deteriorates.

[0005] In view of this situation, Patent Document 1 proposes an acrylic rubber vulcanizate that exhibits excellent low compression set during processing, which is an acrylic copolymer composition comprising an alkyl acrylate having an alkyl group of 1 to 8 carbon atoms, an alkoxy alkyl acrylate having an alkoxy group of 1 to 4 carbon atoms and an alkylene group of 1 to 4 carbon atoms, dicyclopentadiene, ethylidene norbornene and a dicyclopentenyl group-containing ester of an unsaturated carboxylic acid, an organic peroxide as a crosslinking agent, and a crosslinking aid having two or more (meth)acrylates.

[0006] Patent No. 5010663

[0007] In view of the above problems, the present invention aims to provide an acrylic copolymer that satisfies both processability and low compression set and further has sufficient mechanical strength, an acrylic copolymer-containing composition and a crosslinked product thereof, and a method for producing the acrylic copolymer.

[0008] The present inventors have conducted extensive research to achieve the above object, and have found that a composition using an acrylic copolymer in which a substituent derived from a polymerization initiator has been introduced into at least one or both ends of the polymer chain has excellent processability, and that a crosslinked product obtained by crosslinking this composition has excellent low compression set and mechanical strength, thereby completing the present invention. The above crosslinked product is also sometimes referred to as an "acrylic copolymer crosslinked product."

[0009] The aspects of the present invention are as follows: Item 1. An acrylic copolymer containing at least a structural unit derived from an alkyl acrylate ester, a structural unit derived from a crosslinkable monomer, and a structural unit derived from a polymerization initiator, and further satisfying the following conditions (A) and (B): (A) The structural unit derived from the polymerization initiator is a structural unit derived from a compound represented by the following formula (1) or (2): (n is a natural number, and 1≦n≦4) (B) The acrylic copolymer has a residual amount of monovalent metal ions of 30 ppm by mass or more and 5,000 ppm by mass or less, a residual amount of divalent or more metal ions of 300 ppm by mass or less, and a ratio of the residual amount of monovalent metal ions to the residual amount of divalent or more metal ions ([residual amount of monovalent metal ions] / [residual amount of divalent or more metal ions]) of 10 or more. Item 2. The acrylic copolymer according to Item 1, wherein, relative to 100% by mass of the acrylic copolymer, the content of structural units derived from an alkyl acrylate ester is 50% by mass to 99.8% by mass, the content of structural units derived from a crosslinkable monomer is 0.1 to 10% by mass, and the content of structural units derived from a polymerization initiator is 0.001 to 2% by mass. Item 3. The acrylic copolymer according to Item 1 or 2, wherein the content of structural units derived from an alkyl acrylate ester having an alkyl group having 1 to 3 carbon atoms is 0 to 100% by mass and / or the content of structural units derived from an alkyl acrylate ester having an alkyl group having 4 to 6 carbon atoms is 0 to 100% by mass, relative to 100% by mass of the structural units derived from the alkyl acrylate ester. Item 4. The acrylic copolymer according to any one of Items 1 to 3, wherein the structural units derived from a crosslinkable monomer are structural units derived from a crosslinkable monomer having a carboxyl group. Item 5. An acrylic copolymer-containing composition comprising the acrylic copolymer according to any one of Items 1 to 4 and at least a crosslinking agent. Item 6. A crosslinked acrylic rubber obtained by crosslinking the acrylic copolymer-containing composition according to Item 5. Item 7. A method for producing the acrylic copolymer according to any one of Items 1 to 4, comprising: an emulsion polymerization step of emulsion-polymerizing acrylic copolymer components containing at least an alkyl acrylate, a crosslinkable monomer, and a polymerization initiator having an alkyl group using an emulsifier to obtain an emulsion polymerization liquid; a salting-out step of salting out the emulsion polymerization liquid with 0.01 to 10 parts by mass of a monovalent metal salt per 100 parts by mass of the emulsion polymerization liquid to obtain hydrous crumbs; a water-washing step of washing the hydrous crumbs; and a drying step of drying the washed hydrous crumbs. Item 8. A method for producing an acrylic copolymer according to Item 7, wherein the monovalent metal salt is at least one selected from the group consisting of metal sulfates, metal acetates, and metal carbonates of sodium.

[0010] According to the present invention, it is possible to provide an acrylic copolymer, an acrylic copolymer-containing composition, an acrylic copolymer crosslinked product, and a method for producing an acrylic copolymer, which have both processability and low compression set and also have sufficient mechanical strength.

[0011] The acrylic copolymer of the present invention has a substituent derived from the polymerization initiator at at least one end or both ends of the polymer chain. More specifically, the acrylic copolymer of the present invention is an acrylic copolymer containing a structural unit derived from an alkyl acrylate ester, a structural unit derived from a crosslinkable monomer, and a structural unit derived from a polymerization initiator having an alkyl group (preferably a structural unit derived from a compound represented by the above formula (1) or (2)), and the copolymer has a substituent derived from the polymerization initiator at at least one end or both ends. This provides good processability. Furthermore, by controlling the type and amount of residual metal contained in the acrylic copolymer of the present invention within specific ranges, good low compression set properties can be obtained. The acrylic copolymer of the present invention has a substituent derived from the polymerization initiator at at least one end or both ends of the copolymer, and by controlling the type and amount of residual metal within specific ranges, an acrylic copolymer, an acrylic copolymer-containing composition, and an acrylic copolymer crosslinked product are provided that achieve both processability and low compression set and also have sufficient mechanical strength.

[0012] <Acrylic Copolymer> The acrylic copolymer of the present invention has a substituent derived from a polymerization initiator at at least one end or both ends of the polymer chain. More specifically, the acrylic copolymer of the present invention is an acrylic copolymer containing a structural unit derived from an alkyl acrylate ester, a structural unit derived from a crosslinkable monomer, and a structural unit derived from a polymerization initiator, and has a substituent derived from the polymerization initiator at at least one end or both ends (preferably one end) of the copolymer chain.

[0013] The structural units derived from alkyl acrylates preferably include structural units derived from alkyl acrylates having an alkyl group containing 1 to 3 carbon atoms and / or structural units derived from alkyl acrylates having an alkyl group containing 4 to 6 carbon atoms. The structural units derived from alkyl acrylates may be structural units derived from a single type of alkyl acrylate, or two or more types of alkyl acrylates.

[0014] Specific examples of alkyl acrylate esters having an alkyl group having 1 to 3 carbon atoms include methyl acrylate, ethyl acrylate, n-propyl acrylate, and isopropyl acrylate, with methyl acrylate and ethyl acrylate being preferred.

[0015] Specific examples of alkyl acrylates having an alkyl group having 4 to 6 carbon atoms include alkyl acrylates such as n-butyl acrylate, n-pentyl acrylate, and n-hexyl acrylate, with n-butyl acrylate being preferred.

[0016] The content of structural units derived from an alkyl acrylate ester having an alkyl group having 1 to 3 carbon atoms in 100% by mass of structural units derived from an alkyl acrylate ester is preferably 0% by mass to 100% by mass, and more specifically, the lower limit is preferably 0% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, particularly preferably 25% by mass or more, and most preferably 30% by mass or more, and the upper limit is preferably 100% by mass or less, more preferably 90% by mass or less, even more preferably 80% by mass or less, particularly preferably 70% by mass or less, and most preferably 60% by mass or less. In this specification, the notation "to" means at least the value before "to" and at most the value after "to"

[0017] Furthermore, the content of structural units derived from an alkyl acrylate ester having an alkyl group having 4 to 6 carbon atoms, relative to 100% by mass of structural units derived from an alkyl acrylate ester, is preferably 0% by mass to 100% by mass; more specifically, the lower limit is preferably 0% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, particularly preferably 30% by mass or more, and most preferably 40% by mass or more; and the upper limit is preferably 100% by mass or less, more preferably 90% by mass or less, even more preferably 80% by mass or less, particularly preferably 75% by mass or less, and most preferably 70% by mass or less.

[0018] In 100% by mass of the acrylic copolymer of the present invention, the content of structural units derived from alkyl acrylate esters is preferably 50% by mass to 99.8% by mass. More specifically, the lower limit is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, particularly preferably 80% by mass or more, and most preferably 90% by mass or more, and the upper limit is preferably 99.8% by mass or less, more preferably 99.5% by mass or less, and most preferably 99% by mass or less. This tends to more favorably achieve the desired effect. In this specification, the content of structural units derived from alkyl acrylate esters refers to the total content when multiple structural units are contained. The same applies to other structural units.

[0019] The structural unit derived from the crosslinkable monomer is not particularly limited as long as it has a crosslinking group capable of reacting with a crosslinking agent, and examples of the crosslinking group include a carboxyl group, an epoxy group, and a halogen group. The structural unit derived from the crosslinkable monomer can be used alone or in combination of two or more. Among these, a structural unit derived from a crosslinkable monomer having a carboxyl group as a crosslinking group is preferred.

[0020] Examples of structural units derived from crosslinkable monomers having a carboxyl group as a crosslinking group include structural units derived from ethylenically unsaturated monocarboxylic acids such as methacrylic acid, acrylic acid, crotonic acid, 2-pentenoic acid, and cinnamic acid; structural units derived from ethylenically unsaturated dicarboxylic acids such as fumaric acid, maleic acid, and itaconic acid; and structural units derived from ethylenically unsaturated dicarboxylic acid monoesters such as monoalkyl fumarates such as monomethyl fumarate, monoethyl fumarate, monopropyl fumarate, monobutyl fumarate, monohexyl fumarate, and monooctyl fumarate; monoalkyl maleates such as monomethyl maleate, monoethyl maleate, monopropyl maleate, monobutyl maleate, monopentyl maleate, and monodecyl maleate; and monoalkyl itaconic acid esters such as monomethyl itaconate, monoethyl itaconate, monopropyl itaconate, and monobutyl itaconate. These may be used alone or in combination of two or more types. A structural unit derived from an ethylenically unsaturated dicarboxylic acid monoester is preferred, a structural unit derived from a fumaric acid monoalkyl ester is more preferred, and a structural unit derived from a fumaric acid monoalkyl ester having an alkyl group having 1 to 4 carbon atoms is most preferred.

[0021] Examples of structural units derived from crosslinkable monomers having an epoxy group as a crosslinking group include structural units derived from epoxy group-containing alkyl acrylates such as glycidyl acrylate, structural units derived from epoxy group-containing styrenes such as p-vinylbenzyl glycidyl ether, and structural units derived from epoxy group-containing ethers such as allyl glycidyl ether and vinyl glycidyl ether, 3,4-epoxy-1-pentene, 3,4-epoxy-1-butene, 4,5-epoxy-2-pentene, 4-vinylcyclohexyl glycidyl ether, cyclohexenylmethyl glycidyl ether, 3,4-epoxy-1-vinylcyclohexene, and allylphenyl glycidyl ether. These may be used alone or in combination of two or more.

[0022] Examples of constituent units derived from crosslinkable monomers having a halogen group as a crosslinking group include constituent units derived from 2-chloroethyl vinyl ether, 2-chloroethyl acrylate, vinylbenzyl chloride, vinyl monochloroacetate, allyl chloroacetate, etc. These can be used alone or in combination of two or more.

[0023] The content of the structural unit derived from the crosslinkable monomer in 100% by mass of the acrylic copolymer of the present invention is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, even more preferably 0.5% by mass or more, and is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 2.5% by mass or less. This tends to more suitably obtain the effects.

[0024] The structural unit derived from the polymerization initiator is not particularly limited as long as it is a structural unit derived from a polymerization initiator represented by the following formula (1) or (2), and specific examples thereof preferably include peroxide-based polymerization initiators such as t-amyl hydroperoxide and di-t-amyl hydroperoxide. These polymerization initiators can be used alone or in combination of two or more. (n is a natural number, 1≦n≦4)

[0025] The number n is 1 to 4, but the upper limit is preferably 3 or less, more preferably 2 or less, and further preferably 1.

[0026] The content of the structural unit derived from the polymerization initiator (structural unit derived from the compound represented by the above formula (1) or (2)) in 100% by mass of the acrylic copolymer of the present invention is preferably 0.001 to 2.0% by mass, and more specifically, the lower limit is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, even more preferably 0.01% by mass or more, and particularly preferably 0.02% by mass or more, and the upper limit is preferably 2.0% by mass or less, more preferably 1.50% by mass or less, even more preferably 0.50% by mass or less, and particularly preferably 0.20% by mass or less. This tends to more favorably achieve the effects.

[0027] In the acrylic copolymer of the present invention, the total content of the constituent units derived from an alkyl acrylate ester, the constituent units derived from a crosslinkable monomer, and the constituent units derived from a polymerization initiator having an alkyl group (constituent units derived from the compound represented by the above formula (1) or (2)) is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, or may be 100% by mass, based on 100% by mass of the acrylic copolymer. This tends to more suitably achieve the effects.

[0028] Furthermore, the acrylic copolymer of the present invention may contain, as a constituent unit of the acrylic copolymer, a copolymerizable monomer other than the above-mentioned monomers, so long as it does not deviate from the spirit of the present invention. Examples of other monomers include alkoxyalkyl acrylate esters, ethylenically unsaturated nitrile monomers, acrylamide monomers, aromatic vinyl monomers, conjugated diene monomers, non-conjugated diene monomers, other olefin monomers, copolymerizable antioxidants, etc. These may be used alone or in combination of two or more.

[0029] Examples of alkoxyalkyl acrylates include alkyl acrylates such as methoxymethyl acrylate, methoxyethyl acrylate, ethoxymethyl acrylate, 2-ethoxyethyl acrylate, 2-propoxyethyl acrylate, 2-butoxyethyl acrylate, 2-methoxypropyl acrylate, 2-ethoxypropyl acrylate, 3-methoxypropyl acrylate, 3-ethoxypropyl acrylate, 4-methoxybutyl acrylate, and 4-ethoxybutyl acrylate, with 2-methoxyethyl acrylate being preferred. These may be used alone or in combination of two or more.

[0030] Examples of ethylenically unsaturated nitrile monomers include acrylonitrile, methacrylonitrile, α-methoxyacrylonitrile, vinylidene cyanide, etc. These may be used alone or in combination of two or more.

[0031] Examples of acrylamide monomers include acrylamide, methacrylamide, diacetone acrylamide, diacetone methacrylamide, N-butoxymethyl acrylamide, N-butoxymethyl methacrylamide, N-butoxyethyl acrylamide, N-butoxyethyl methacrylamide, N-methoxymethyl acrylamide, N-methoxymethyl methacrylamide, N-propoxymethyl acrylamide, N-propoxymethyl methacrylamide, N-methyl acrylamide, N-methyl methacrylamide, N,N-dimethyl acrylamide, N,N-dimethyl methacrylamide, N,N-diethyl acrylamide, N,N-diethyl methacrylamide, N-methylolacrylamide, N-methylol methacrylamide, ethacrylamide, crotonamide, cinnamic acid amide, maleindiamide, itacondiamide, methylmaleamide, methylitaconamide, maleinimide, itaconimide, etc. These can be used alone or in combination of two or more.

[0032] Examples of aromatic vinyl monomers include styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, o-ethylstyrene, p-ethylstyrene, α-fluorostyrene, p-trifluoromethylstyrene, p-methoxystyrene, p-aminostyrene, p-dimethylaminostyrene, p-acetoxystyrene, styrenesulfonic acid or a salt thereof, α-vinylnaphthalene, 1-vinylnaphthalene-4-sulfonic acid or a salt thereof, 2-vinylfluorene, 2-vinylpyridine, 4-vinylpyridine, divinylbenzene, diisopropenylbenzene, vinylbenzyl chloride, etc. These may be used alone or in combination of two or more.

[0033] Examples of conjugated diene monomers include 1,3-butadiene, 2-methyl-1,3-butadiene, 2-chloro-1,3-butadiene, 1,2-dichloro-1,3-butadiene, 2,3-dichloro-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-neopentyl-1,3-butadiene, 2-bromo-1,3-butadiene, 2-cyano-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, chloroprene, piperylene, etc. These can be used alone or in combination of two or more.

[0034] Examples of non-conjugated diene monomers include 1,4-pentadiene, 1,4-hexadiene, ethylidene norbornene, norbornadiene, dicyclopentadiene, etc. These may be used alone or in combination of two or more.

[0035] Other olefin-based monomers include, for example, esters such as dicyclopentadienyl acrylate, dicyclopentadienyl methacrylate, dicyclopentadienylethyl acrylate, dicyclopentadienylethyl methacrylate, ethylene, propylene, vinyl chloride, vinylidene chloride, 1,2-dichloroethylene, vinyl acetate, vinyl fluoride, vinylidene fluoride, 1,2-difluoroethylene, vinyl bromide, vinylidene bromide, 1,2-dibromoethylene, ethyl vinyl ether, butyl vinyl ether, etc. These may be used alone or in combination of two or more.

[0036] Examples of copolymerizable antioxidants include structural units derived from copolymerizable amine-based antioxidants such as N-(4-anilinophenyl)methacrylamide, N-(4-anilinophenyl)acrylamide, N-(4-anilinophenyl)maleimide, N-(4-p-toluidinylphenyl)maleimide, N-(4-anilino-1-naphthyl)maleimide, 4-hydroxyphenylmaleimide, and 3-hydroxyphenylmaleimide, as well as copolymerizable phenol-based antioxidants such as 2-tert-butyl-4-methyl-6-(2-hydroxy-3-tert-butyl-5-methylbenzyl)phenyl acrylate, 1'-hydroxy[2,2'-ethylidenebis[4,6-bis(1,1-dimethylpropyl)benzene]]-1-yl acrylate, hydroxycinnamic acid, ferulic acid, and allyl cresol. These can be used alone or in combination of two or more.

[0037] In the acrylic copolymer of the present invention, the content of the structural units can be determined by nuclear magnetic resonance spectroscopy of the obtained polymer.

[0038] <Method for producing acrylic copolymer> The acrylic copolymer of the present invention can be produced by polymerizing various monomers, and the monomers used may be commercially available products and are not particularly limited. The acrylic copolymer used in the present invention has a substituent derived from a polymerization initiator at at least one end or both ends of the polymer chain. For example, as described above, such an acrylic copolymer can be produced by polymerizing the acrylic copolymer using a polymerization initiator having an alkyl group (a compound represented by the above formula (1) or formula (2)) to obtain an acrylic copolymer having an alkyl group derived from the polymerization initiator at the polymerization initiation end of the polymer chain.

[0039] The production process for producing the acrylic copolymer of the present invention preferably comprises: an emulsion polymerization step of emulsion-polymerizing acrylic copolymer components containing at least an alkyl acrylate, a crosslinkable monomer, and a polymerization initiator having an alkyl group (a compound represented by the above formula (1) or (2)) using an emulsifier to obtain an emulsion polymerization liquid; a salting-out step of adding 0.01 to 10 parts by mass of a monovalent metal salt to 100 parts by mass of the emulsion polymerization liquid to perform salting-out to obtain hydrous crumbs; a water-washing step of washing the hydrous crumbs; and a drying step of drying the washed hydrous crumbs.

[0040] <Emulsion Polymerization Step> As the form of the polymerization reaction, any of emulsion polymerization, suspension polymerization, bulk polymerization, and solution polymerization can be used. However, from the viewpoint of ease of control of the polymerization reaction, it is preferable to use emulsion polymerization under normal pressure, which is generally used as a conventionally known method for producing acrylic copolymers.

[0041] In the case of emulsion polymerization, a conventional method may be used, and commonly used conventional polymerization initiators, emulsifiers, chain transfer agents, polymerization terminators, etc. Here, as for the polymerization initiator, as described above, it is preferable to use a polymerization initiator having an alkyl group (a compound represented by the above formula (1) or (2)).

[0042] The emulsifier used in the present invention is not particularly limited, and nonionic emulsifiers and anionic emulsifiers commonly used in emulsion polymerization methods can be used. Nonionic emulsifiers include, for example, polyoxyethylene alkyl ethers, polyoxyethylene alcohol ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene polycyclic phenyl ethers, polyoxyalkylene alkyl ethers, sorbitan fatty acid esters, polyoxyethylene fatty acid esters, and polyoxyethylene sorbitan fatty acid esters. Anionic emulsifiers include alkylbenzenesulfonates, alkyl sulfates, polyoxyethylene alkyl ether sulfates, polyoxyalkylene alkyl ether phosphates or their salts, fatty acid salts, and the like, and these may be used alone or in combination. Typical examples of anionic emulsifiers include sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, and triethanolamine dodecyl sulfate.

[0043] The amount of emulsifier used in the present invention may be any amount generally used in emulsion polymerization. Specifically, it is in the range of 0.01 to 10 parts by mass, preferably 0.03 to 7 parts by mass, and more preferably 0.05 to 5 parts by mass, per 100 parts by mass of the monomers constituting the acrylic copolymer. When a reactive surfactant is used as a monomer component, the addition of an emulsifier is not necessarily required.

[0044] The polymerization initiator used in the present invention is not particularly limited as long as it is a polymerization initiator represented by the following formula (1) or formula (2). Specific examples thereof preferably include peroxide polymerization initiators such as t-amyl hydroperoxide and di-t-amyl hydroperoxide. These polymerization initiators can be used alone or in combination of two or more. (n is a natural number, 1≦n≦4)

[0045] The number n is 1 to 4, but the upper limit is preferably 3 or less, more preferably 2 or less, and further preferably 1.

[0046] The amount of the polymerization initiator used in the present invention may be any amount generally used in emulsion polymerization, specifically, in the range of 0.001 to 2 parts by mass, preferably 0.005 to 1.50 parts by mass, and more preferably 0.01 to 0.5 parts by mass, per 100 parts by mass of the polymerizable monomers constituting the acrylic copolymer.

[0047] Furthermore, organic peroxides and inorganic peroxides used as polymerization initiators can be used as redox polymerization initiators by combining them with a reducing agent. The reducing agent to be used in combination is not particularly limited, but examples include compounds containing reduced metal ions such as ferrous sulfate and cuprous naphthenate, methane compounds such as sodium methanesulfonate, amine compounds such as dimethylaniline, ascorbic acid and its salts, and reducing inorganic salts such as alkali metal salts of sulfite and thiosulfate. These reducing agents can be used alone or in combination of two or more. The amount of reducing agent used is preferably 0.0003 to 10.0 parts by mass per 100 parts by mass of the monomers constituting the acrylic copolymer.

[0048] Specific examples of the chain transfer agent include alkyl mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, and n-stearyl mercaptan, xanthogen compounds such as 2,4-diphenyl-4-methyl-1-pentene, 2,4-diphenyl-4-methyl-2-pentene, dimethyl xanthogen disulfide, and diisopropyl xanthogen disulfide, and terpinolene, tetramethylthiuram disulfide, tetraethylthiuram disulfide, and tetramethylthiuram monosulfide. Examples of suitable chain transfer agents include thiuram compounds, phenolic compounds such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol, allyl compounds such as allyl alcohol, halogenated hydrocarbon compounds such as dichloromethane, dibromomethane and carbon tetrabromide, vinyl ethers such as α-benzyloxystyrene, α-benzyloxyacrylonitrile and α-benzyloxyacrylamide, triphenylethane, pentaphenylethane, acrolein, methacrolein, thioglycolic acid, thiomalic acid, and 2-ethylhexyl thioglycolate, and these may be used alone or in combination of two or more. The amount of these chain transfer agents is not particularly limited, but is typically 0 to 5 parts by mass per 100 parts by mass of the monomers constituting the acrylic copolymer.

[0049] Examples of polymerization terminators include hydroxylamine, hydroxylamine sulfate, diethylhydroxyamine, hydroxyamine sulfonic acid and its alkali metal salts, sodium dimethyldithiocarbamate, and quinone compounds such as hydroquinone. These may be used alone or in combination of two or more. The amount of polymerization terminator used is not particularly limited, but is typically 0 to 2 parts by mass per 100 parts by mass of the monomers constituting the acrylic copolymer. By using a polymerization terminator having an alkyl group and a functional group capable of reacting with radicals in the polymer chain as the polymerization terminator, an acrylic copolymer having an alkyl group at the polymerization termination terminal can be obtained.

[0050] Furthermore, the pH of the polymer obtained by the above method can be adjusted, if necessary, by using a base as a pH adjuster. Specific examples of bases include sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium bicarbonate, ammonia, inorganic ammonium compounds, and organic amine compounds. These may be used alone or in combination. The pH range is 1 to 11, preferably 1.5 to 10.5, and more preferably 2 to 10.

[0051] In addition, if necessary, polymerization auxiliary materials such as particle size adjusters, chelating agents, oxygen scavengers, etc. may be used. These may be used alone or in combination of two or more.

[0052] The emulsion polymerization may be carried out in a batch, semi-batch, or continuous manner. The polymerization time and temperature are not particularly limited. They can be appropriately selected depending on the type of polymerization initiator used, but generally, the polymerization temperature is 10°C to 100°C, and the polymerization time is 0.5 hours to 100 hours.

[0053] <Salting-out step> The method for recovering the water-containing crumbs from the emulsion polymerization liquid obtained by the above method (salting-out method) is not particularly limited, and a commonly used method can be adopted. One example is a method in which the emulsion polymerization liquid is continuously or batchwise fed to an aqueous solution containing a salting-out agent, and the water-containing crumbs are obtained by this operation.

[0054] The salting-out agent is not particularly limited, and monovalent to trivalent metal salts can be used. However, it is preferable to use monovalent metal salts. Specific examples include inorganic salts such as chlorides, sulfates, nitrates, and carbonates of lithium, sodium, potassium, and cesium, and organic salts such as acetates and phosphates. If divalent or higher metal salts (present as metal ions in the acrylic copolymer) remain in the acrylic copolymer, the divalent metal ions will inhibit the crosslinking reaction during the crosslinking reaction, which may adversely affect the low compression set. One or more salting-out agents may be used.

[0055] Specific examples of monovalent metal salts include metal chlorides such as lithium chloride, sodium chloride, potassium chloride, and cesium chloride; metal sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, and cesium sulfate; metal nitrates such as lithium nitrate, sodium nitrate, potassium nitrate, and cesium nitrate; metal carbonates such as lithium carbonate, sodium carbonate, potassium carbonate, and cesium carbonate; and metal acetates such as lithium acetate, sodium acetate, potassium acetate, and cesium acetate. Among these, sodium chloride, sodium sulfate, sodium nitrate, sodium carbonate, and sodium acetate are preferred, sodium sulfate and sodium nitrate are more preferred, and sodium sulfate is even more preferred. Furthermore, at least one selected from the group consisting of metal sulfates, metal acetates, and metal carbonates of sodium is also preferred. These can be used alone or in combination of two or more.

[0056] Furthermore, as described above, the divalent metal salt contained in the monovalent metal salt used as a salting-out agent remains in the acrylic copolymer, affecting the low compression set property. Therefore, the purity of the monovalent metal salt is preferably 99.0% or more, more preferably 99.5% or more, and may be 100%.

[0057] In the salting out step, the amount of monovalent metal salt added is preferably 0.01 to 10 parts by mass per 100 parts by mass of the emulsion polymerization liquid. More specifically, the lower limit is preferably 0.01 part by mass, more preferably 0.1 part by mass, and even more preferably 1 part by mass. The upper limit is preferably 10 parts by mass, more preferably 9.5 parts by mass, and even more preferably 9 parts by mass. By keeping the amount within these ranges, the amount of residual monovalent metal ions and residual divalent or higher metal ions contained in the acrylic copolymer after water washing can be appropriately controlled.

[0058] The residual amount of monovalent metal ions (preferably sodium ions) contained in the acrylic copolymer of the present invention is preferably within the range of 30 ppm by mass to 5000 ppm by mass, with the lower limit being more preferably 50 ppm by mass or more, even more preferably 100 ppm by mass or more, particularly preferably 150 ppm by mass or more, and most preferably 200 ppm by mass or more, and the upper limit being more preferably 4500 ppm by mass or less, even more preferably 4000 ppm by mass or less. If the amount falls outside these ranges, there is a possibility that the heat resistance and low compression set properties may be adversely affected.

[0059] The residual amount of divalent or higher metal ions (preferably the total of magnesium ions and calcium ions) contained in the acrylic copolymer of the present invention is preferably 300 ppm by mass or less, more preferably 200 ppm by mass or less, even more preferably 100 ppm by mass or less, particularly preferably 50 ppm by mass or less, and most preferably 10 ppm by mass or less.

[0060] Furthermore, in the acrylic copolymer of the present invention, the ratio of the residual amount of monovalent metal ions (preferably sodium ions) to the residual amount of divalent or more metal ions (preferably the sum of magnesium ions and calcium ions) ([residual amount of monovalent metal ions (preferably sodium ions)] / [residual amount of divalent or more metal ions (preferably the sum of magnesium ions and calcium ions)]) is preferably 10 or more, more preferably 50 or more, and even more preferably 100 or more. For example, if the residual amount of divalent or more metal ions is greater than the residual amount of monovalent metal ions, this may adversely affect low compression set, as described above. The upper limit of this ratio is not particularly limited, but is, for example, 10,000 or less. In this specification, the residual amount of metal ions in the acrylic copolymer is measured by the method described in the Examples.

[0061] The salting-out temperature is not particularly limited, but is generally 50° C. to 100° C., preferably in the range of 60° C. to 100° C. When the salting-out temperature is within the above range, it tends to be possible to more suitably control the type and amount of residual metals contained in the acrylic copolymer to fall within the range specified in the present application.

[0062] Furthermore, an antioxidant can be added during the salting-out step. Specific examples of the antioxidant include phenol-based antioxidants, amine-based antioxidants, phosphite-based antioxidants, and hindered amine-based antioxidants. These antioxidants may be used alone or in combination.

[0063] Furthermore, during the salting-out step, the pH can be adjusted as needed by using a base as a pH adjuster. Specific examples of bases include sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium bicarbonate, ammonia, inorganic ammonium compounds, and organic amine compounds. These may be used alone or in combination. The pH range is 1 to 11, preferably 2 to 10, and more preferably 4 to 8.

[0064] <Water Washing Step> The hydrous crumb obtained in the salting-out step is preferably washed with water to remove the salting-out agent. If water washing is not performed at all or is performed insufficiently, metal ion residues derived from the salting-out agent may adversely affect mechanical properties and may precipitate during the molding step. The hydrous crumb obtained in the salting-out step is preferably thoroughly washed with water to remove the salting-out agent so that the residual amount of monovalent metal ions in the acrylic copolymer is 30 ppm by mass or more and 5000 ppm by mass or less, the residual amount of divalent or more metal ions is 300 ppm by mass or less, and the ratio of the residual amount of monovalent metal ions to the residual amount of divalent or more metal ions ([residual amount of monovalent metal ions] / [residual amount of divalent or more metal ions]) is 10 or more. This tends to more suitably control the type and amount of residual metals contained in the acrylic copolymer within the specified range of the present application.

[0065] In the water washing, a method of mixing the water-containing crumbs with added water (batch method) or a method of continuously washing the crumbs while dehydrating the crumbs (continuous method) can be used. In either method, the temperature during the water washing is preferably 5 to 60°C, more preferably 10 to 50°C, and the mixing time is 1 to 60 minutes, more preferably 2 to 30 minutes.

[0066] When water washing is carried out batchwise, the amount of water to be added to the water-containing crumbs is not particularly limited, but from the viewpoint of being able to effectively reduce the amount of salting-out agent remaining in the finally obtained acrylic rubber, the amount of water per water washing is preferably 50 to 9,800 parts by mass, and more preferably 300 to 1,800 parts by mass, per 100 parts by mass of the acrylic copolymer component contained in the water-containing crumbs.

[0067] The number of times of water washing is not particularly limited, and for the purpose of reducing the amount of metal ions remaining in the acrylic copolymer due to the salting-out agent, it is preferably 2 to 8 times, more preferably 2 to 6 times. Note that, although the amount of metal ions remaining can be reduced as the number of times of water washing increases, the effect of removing the salting-out agent decreases with each increase in the number of times, and in addition, the increase in the number of steps increases the impact of reduced productivity, so it is preferable to keep the number of times of water washing within the above range.

[0068] Furthermore, when washing with water is performed continuously, the end of washing can be determined by measuring the electrical conductivity of the aqueous slurry mixture, and the electrical conductivity is preferably 12 mS / cm or less, more preferably 10 mS / cm or less, and even more preferably 8 mS / cm or less. By reducing the electrical conductivity to this level or less, the amount of metal ions remaining in the acrylic copolymer due to the salting-out agent can be sufficiently reduced.

[0069] The electrical conductivity of the slurry mixture was measured by placing the collected supernatant of the slurry mixture in a 110 mL sample bottle. The electrical conductivity of the supernatant collected in the 110 mL sample bottle at 23°C was measured using an AC two-electrode method. The electrical conductivity can be measured using a portable electrical conductivity meter ES-51 manufactured by Horiba, Ltd. and a waterproof general-purpose electrical conductivity cell 9382-10D manufactured by Horiba, Ltd.

[0070] <Drying step> The acrylic copolymer can be obtained by removing water from the water-containing crumbs after washing and drying. The drying method is not particularly limited, but is generally carried out using a flash dryer, a twin-screw extruder, a fluidized bed dryer, or the like. Furthermore, a dehydration step using a centrifuge or the like may be carried out before the drying step.

[0071] From the viewpoint of processability, the molecular weight range of the acrylic copolymer of the present invention produced in this manner, expressed as Mooney viscosity (ML1+4) at 100°C in the Mooney scorch test specified in JIS K 6300-1: 2013, is preferably 10 to 100, more preferably 15 to 90, and even more preferably 20 to 80. In this specification, the Mooney viscosity of the acrylic copolymer is a value measured by the method described in the examples.

[0072] The weight average molecular weight (Mw) of the acrylic copolymer of the present invention is preferably 100,000 to 8,000,000, more preferably 400,000 to 7,500,000, and even more preferably 800,000 to 7,000,000. This tends to make it possible to obtain the desired effect.

[0073] <Acrylic Copolymer-Containing Composition> The acrylic copolymer-containing composition of the present invention can be obtained by containing the above-described acrylic copolymer and at least a crosslinking agent.

[0074] As the crosslinking agent, a conventionally known crosslinking agent that is usually used for crosslinking rubber, such as a polyamine compound, a polyepoxy compound, a polyisocyanate compound, an aziridine compound, a sulfur compound, a metal soap, a basic metal oxide, and an organometallic halide, can be used. Among these, a polyamine compound can be preferably used.

[0075] Examples of the polyvalent amine compound include aliphatic polyvalent amine compounds such as hexamethylenediamine, hexamethylenediamine carbamate, and N,N'-dicinnamylidene-1,6-hexanediamine; and aromatic polyvalent amine compounds such as 4,4'-methylenedianiline, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-(m-phenylenediisopropylidene)dianiline, 4,4'-(p-phenylenediisopropylidene)dianiline, 2,2'-bis[4-(4-aminophenoxy)phenyl]propane, 4,4'-diaminobenzanilide, 4,4'-bis(4-aminophenoxy)biphenyl, m-xylylenediamine, p-xylylenediamine, 1,3,5-benzenetriamine, 1,3,5-benzenetriaminomethyl, and isophthalic acid dihydrazide. Of these, aliphatic polyamine compounds are preferred.

[0076] Examples of the polyfunctional epoxy compound include glycidyl ether type epoxy compounds such as phenol novolac type epoxy compounds, cresol novolac type epoxy compounds, cresol type epoxy compounds, bisphenol A type epoxy compounds, bisphenol F type epoxy compounds, brominated bisphenol A type epoxy compounds, brominated bisphenol F type epoxy compounds, and hydrogenated bisphenol A type epoxy compounds, as well as other polyfunctional epoxy compounds such as alicyclic epoxy compounds, glycidyl ester type epoxy compounds, glycidyl amine type epoxy compounds, and isocyanurate type epoxy compounds.

[0077] Examples of polyisocyanate compounds include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, 1,5-naphthylene diisocyanate, 1,3,6-hexamethylene triisocyanate, 1,6,11-undecane triisocyanate, and bicycloheptane triisocyanate.

[0078] Examples of the aziridine compound include tris-2,4,6-(1-aziridinyl)-1,3,5-triazine, tris[1-(2-methyl)aziridinyl]phosphinoxide, and hexa[1-(2-methyl)aziridinyl]triphosphatriazine.

[0079] Examples of sulfur compounds include sulfur, 4,4'-dithiomorpholine, tetramethylthiuram disulfide, and tetraethylthiuram disulfide.

[0080] Examples of basic metal oxides include zinc oxide, lead oxide, calcium oxide, and magnesium oxide.

[0081] The organic metal halide may be, for example, a dicyclopentadienyl metal dihalide, and the metal may be titanium, zirconium, or the like.

[0082] These crosslinking agents can be used alone or in combination of two or more. The amount of each crosslinking agent is 0.05 to 20 parts by mass, preferably 0.1 to 10 parts by mass, per 100 parts by mass of the acrylic copolymer of the present invention.

[0083] The acrylic copolymer-containing composition of the present invention may also contain any of other additives commonly used in the art, such as lubricants, antioxidants, light stabilizers, fillers, reinforcing agents, plasticizers, processing aids, pigments, colorants, crosslinking accelerators, crosslinking aids, crosslinking retarders, antistatic agents, foaming agents, etc. These may be used alone or in combination of two or more.

[0084] Examples of the reinforcing agent include carbon black, and the content thereof is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 30 parts by mass or more, relative to 100 parts by mass of the acrylic copolymer, and is preferably 120 parts by mass or less, and more preferably 100 parts by mass or less.

[0085] Examples of antioxidants include amine-based, phosphate-based, quinoline-based, cresol-based, phenol-based, and dithiocarbamate metal salts. In the present invention, it is preferable to use amine-based and phenol-based antioxidants. These antioxidants may be used alone or in combination of two or more.

[0086] Examples of amine-based antiaging agents include phenyl-α-naphthylamine, phenyl-β-naphthylamine, p-(p-toluenesulfonylamido)-diphenylamine, 4,4′-bis(α,α-dimethylbenzyl)diphenylamine, N,N-diphenyl-p-phenylenediamine, N-isopropyl-N′-phenyl-p-phenylenediamine, and butyraldehyde-aniline condensates.

[0087] Examples of phenolic antioxidants include 2,6-di-t-butyl-4-methylphenol, 2,6-di-t-butylphenol, butylhydroxyanisole, 2,6-di-t-butyl-α-dimethylamino-p-cresol, octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, styrenated phenol, 2,2'-methylene-bis(6-α-methyl-benzyl-p-cresol), 4,4'-methylenebis( 2,6-di-t-butylphenol), 2,2'-methylene-bis(4-methyl-6-t-butylphenol), 2,4-bis[(octylthio)methyl]-6-methylphenol, 2,2'-thiobis-(4-methyl-6-t-butylphenol), 4,4'-thiobis-(6-t-butyl-o-cresol), 2,6-di-t-butyl-4-(4,6-bis(octylthio)-1,3,5-triazin-2-ylamino)phenol, and the like.

[0088] The content of the antioxidant is preferably 0.1 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, and particularly preferably 0.3 to 3 parts by mass, relative to 100 parts by mass of the acrylic copolymer.

[0089] Examples of the crosslinking accelerator include guanidine compounds, amine compounds, thiourea compounds, thiazole compounds, sulfenamide compounds, thiuram compounds, and quaternary ammonium salts, and guanidine compounds and amine compounds are preferred. These may be used alone or in combination of two or more.

[0090] The content of the crosslinking accelerator is preferably 0.1 to 15 parts by mass, more preferably 0.1 to 10 parts by mass, and particularly preferably 0.1 to 5 parts by mass, relative to 100 parts by mass of the acrylic copolymer.

[0091] Furthermore, it is also possible to blend with rubbers, resins, etc. that are commonly used in the relevant technical field, as long as it does not deviate from the spirit of the present invention. Examples of commonly used rubbers that can be used in the present invention include butadiene rubber, styrene-butadiene rubber, isoprene rubber, natural rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene-isoprene rubber, ethylene-propylene-diene rubber, epichlorohydrin rubber, etc., and examples of resins that can be used in the present invention include PMMA (polymethyl methacrylate) resin, PS (polystyrene) resin, PUR (polyurethane) resin, PVC (polyvinyl chloride) resin, EVA (ethylene / vinyl acetate) resin, AS (styrene / acrylonitrile) resin, PE (polyethylene) resin, etc. These can be used alone or in combination of two or more.

[0092] The total amount of the rubber and resin is 50 parts by mass or less, preferably 10 parts by mass or less, and more preferably 5 parts by mass or less, per 100 parts by mass of the acrylic copolymer of the present invention.

[0093] From the viewpoint of processability, the extensional viscosity of the acrylic copolymer-containing composition of the present invention is preferably 100,000 to 3,000,000 Pa·s, more preferably 500,000 to 2,750,000 Pa·s, and even more preferably 750,000 to 2,500,000 Pa·s. In this specification, the extensional viscosity of the acrylic copolymer-containing composition is a value measured by the method described in the examples.

[0094] <Cross-linked acrylic copolymer (cross-linked acrylic rubber)> The cross-linked acrylic copolymer of the present invention can be obtained by cross-linking the above-mentioned acrylic copolymer-containing composition.

[0095] The acrylic copolymer-containing composition can be compounded to obtain the acrylic copolymer cross-linked product of the present invention using any means conventionally used in the field of rubber processing, such as an open roll, a Banbury mixer, or various kneaders. The compounding procedure can be performed using the usual procedure used in the field of rubber processing. For example, the compounding procedure can be performed by first kneading only the rubber, then adding compounding ingredients other than the cross-linking agent and cross-linking accelerator to prepare a kneaded compound A, and then adding the cross-linking agent and cross-linking accelerator to perform a kneaded compound B.

[0096] The acrylic copolymer cross-linked product of the present invention can be obtained by heating the acrylic copolymer-containing composition to a temperature of typically 100°C to 250°C to form an acrylic copolymer cross-linked product (acrylic rubber cross-linked product). The cross-linking time varies depending on the temperature, but is typically between 0.5 and 300 minutes. The cross-linking molding may involve integrally performing cross-linking and molding, or by reheating a previously molded acrylic copolymer-containing composition to form a cross-linked acrylic copolymer, or by first heating the cross-linked acrylic copolymer and then processing it for molding. Specific methods for cross-linking molding include compression molding using a mold, injection molding, heating using a steam can, an air bath, infrared radiation, or microwaves, among others.

[0097] The acrylic copolymer-containing composition of the present invention thus obtained has excellent roll processability during processing, and the crosslinked acrylic copolymer of the present invention has excellent normal state physical properties such as elongation at break and low compression set.

[0098] Therefore, taking advantage of the above-mentioned properties, the cross-linked acrylic copolymer (cross-linked acrylic rubber) of the present invention can be suitably used as various gaskets, such as O-rings, packings, diaphragms, oil seals, shaft seals, bearing seals, mechanical seals, wellhead seals, seals for electric and electronic equipment, seals for pneumatic equipment, cylinder head gaskets attached to the joint between a cylinder block and a cylinder head, rocker cover gaskets attached to the joint between a rocker cover and a cylinder head, oil pan gaskets attached to the joint between an oil pan and a cylinder block or a transmission case, fuel cell separator gaskets attached between a pair of housings sandwiching a unit cell having a positive electrode, an electrolyte plate, and a negative electrode, and gaskets for the top covers of hard disk drives.

[0099] The cross-linked acrylic copolymer of the present invention is also suitable for use as extrusion molded products and mold cross-linked products for automobile applications, for example, various hoses such as fuel oil hoses around fuel tanks, such as fuel hoses, filler neck hoses, vent hoses, vapor hoses and oil hoses, air hoses such as turbo air hoses and emission control hoses, radiator hoses, heater hoses, brake hoses and air conditioner hoses.

[0100] The present invention will be specifically described with reference to Examples and Comparative Examples. However, the present invention is not limited to these. In these Examples and Comparative Examples, the physical properties of the crosslinked acrylic copolymer obtained by producing an acrylic copolymer and crosslinking an acrylic copolymer-containing composition containing the obtained acrylic copolymer and a crosslinking agent were evaluated.

[0101] Example 1 (Production of Acrylic Copolymer) A polymerization reactor equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a pressure reducing device was charged with 200 parts by mass of water, 4.0 parts by mass of polyoxyalkylene alkyl ether phosphate ester, 138.0 parts by mass of ethyl acrylate, 256.0 parts by mass of n-butyl acrylate, and 6.0 parts by mass of monobutyl fumarate. Degassing under reduced pressure and nitrogen substitution were repeated to thoroughly remove oxygen, and then 0.001 parts by mass of ferrous sulfate, 0.1 parts by mass of sodium ascorbate, and 0.1 parts by mass of t-amyl hydroperoxide were added to initiate an emulsion polymerization reaction at normal pressure and room temperature. The reaction was continued until the polymerization conversion reached a predetermined value, and 0.0075 parts by mass of hydroquinone was added to terminate the polymerization. The resulting emulsion polymerization liquid was salted out at 70 to 80°C with a 10% by mass aqueous sodium sulfate solution so that the sodium sulfate concentration was 6 parts by mass per 100 parts by mass. The solution was then drained, and 120 parts of ion-exchanged water was added to wash the polymer with water. The resulting acrylic copolymer was washed three times and then dried to obtain a Mooney viscosity measurement, a residual metal ion measurement, and a capillary flow test according to the following evaluation methods. The results are shown in Tables 1 and 2.

[0102] <Mooney Viscosity Measurement (ML1+4, 100°C)> The Mooney viscosity (ML1+4) of the obtained acrylic copolymer was measured at a measurement temperature of 100°C using a Mooney Viscometer AM-3 manufactured by Toyo Seiki Seisakusho, in accordance with the Mooney viscosity test of JIS K6300-1:2013, a physical testing method for uncrosslinked rubber.

[0103] <Metal Ion Residual Amount Measurement> The amount of residual metal ions contained in the obtained acrylic copolymer was quantitatively measured using an ICP optical emission analyzer. Specifically, an ULTIMA2 instrument manufactured by HORIBA JOBIN YVON was used. Approximately 0.5 g of the sample was collected in a platinum crucible, pre-ashed using an electric heater, and then heated at 600°C in an electric furnace for 1 hour. Ultrapure water was added to the resulting residue and heated to dissolve various metals. The solution was then filled up in a measuring flask and the amount of residual metal ions was measured. Note that only sodium ions were detected as monovalent metal ions, and magnesium ions and calcium ions as divalent or higher metal ions, while other metal ions were below the detection limit.

[0104] (Production of Acrylic Copolymer Composition) 100 parts by mass of the acrylic copolymer obtained above, 60 parts by mass of carbon black (classification according to ASTM D1765: N550), 2 parts by mass of stearic acid (dispersant and softener for carbon black), and 2 parts by mass of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine (antiaging agent) were kneaded in a kneader at 120°C to obtain kneaded compound A. A capillary flow test was performed on the obtained kneaded compound A as described below. The results are shown in Table 2. Thereafter, 0.6 parts by mass of hexamethylenediamine carbamate (aliphatic diamine crosslinking agent) and 2 parts by mass of di-o-tolylguanidine (crosslinking accelerator) were added, and the mixture was kneaded with a kneading roll at room temperature to obtain kneaded compound B, which was used as an acrylic copolymer-containing composition. Using the obtained acrylic copolymer composition, normal state physical property tests and compression set tests were performed according to the methods described below. The results are shown in Tables 1 and 2.

[0105] <Capillary flow test (extensional viscosity measurement)> 100 parts by mass of the obtained acrylic copolymer was kneaded in a kneader with 60 parts by mass of carbon black (classification according to ASTM D1765: N550), 2 parts by mass of stearic acid, and 2 parts by mass of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine at 120°C. The mixture was then measured using an IMATEK Corporation capillary rheometer R6000 model, using a long die with a diameter of 1 mm and a length of 16 mm and a short die with a diameter of 1 mm and a length of 0.25 mm. The measurement temperature was 80°C, and the shear rate was decelerated in 11 steps from 1000 seconds to 10 seconds. The maximum extensional viscosity was measured at an extensional rate of 9 to 12 seconds. Note that although the optimal extensional rate varies depending on the molding method, it is generally performed in the high extensional rate range. Therefore, when compared under the same conditions, a lower viscosity indicates better processability.

[0106] <Normal State Physical Property Tests: 100% Modulus, Tensile Strength, Elongation, and Hardness> The above acrylic copolymer composition was molded into a sheet having a thickness of 2 to 2.5 mm, and the resulting uncrosslinked sheet was pressed at 180°C for 10 minutes and further heated in an air oven at 180°C for 12 hours to obtain a crosslinked acrylic rubber product. This crosslinked product was punched into a No. 3 dumbbell, and the 100% modulus, tensile strength, elongation, and hardness were measured. The 100% modulus, tensile strength, and elongation were tested in accordance with JIS K6251:2017 and evaluated using an AGS-5KNY manufactured by Shimadzu Corporation. The hardness was measured in accordance with JIS K6253:2012 using a hardness tester manufactured by Kobunshi Keiki Co., Ltd.

[0107] <Compression Set Test> The above acrylic copolymer composition was press-vulcanized at 170°C for 20 minutes using a mold for preparing a test piece, and then an O-ring test piece was obtained. Using the obtained O-ring test piece, measurements were performed under the implementation conditions of 175°C for 70 hours. If the rate of change after measurement is 30% or less, it can be said that the low compression set property is excellent. The measurement was performed in accordance with JIS K 6262:2013.

[0108] An acrylic copolymer was obtained in the same manner as in Example 1, except that the polymerization initiator, t-amyl hydroperoxide, was changed to di-t-amyl hydroperoxide. As in Example 1, Mooney viscosity measurement, metal ion residual amount measurement, normal state physical property test of the crosslinked acrylic copolymer, and compression set test were also carried out in the same manner. The results are shown in Table 1.

[0109] An acrylic copolymer was obtained in the same manner as in Example 1, except that the salting-out agent was changed from sodium sulfate to magnesium sulfate. As in Example 1, Mooney viscosity measurement, metal ion residual amount measurement, normal state physical property test of the acrylic copolymer crosslinked product, and compression set test were also carried out in the same manner. The results are shown in Table 1.

[0110] An acrylic copolymer was obtained in the same manner as in Example 1, except that the salting-out agent was changed from sodium sulfate to calcium chloride. As in Example 1, Mooney viscosity measurement, metal ion residual amount measurement, normal state physical property test of the crosslinked acrylic copolymer, and compression set test were also carried out in the same manner. The results are shown in Table 1.

[0111] An acrylic copolymer was obtained in the same manner as in Example 1, except that the amount of ethyl acrylate was changed to 394 parts by mass and the amount of butyl acrylate was changed to 0 parts by mass. As in Example 1, Mooney viscosity measurement, metal ion residual amount measurement, capillary flow test, normal state physical property test of the acrylic copolymer crosslinked product, and compression set test were also performed in the same manner. The results are shown in Table 2.

[0112] An acrylic copolymer was obtained in the same manner as in Example 1, except that ammonium persulfate was used instead of t-amyl hydroperoxide as the polymerization initiator. As in Example 1, Mooney viscosity measurement, metal ion residual amount measurement, capillary flow test, normal state physical property test of the acrylic copolymer crosslinked product, and compression set test were also carried out in the same manner. The results are shown in Table 2.

[0113] An acrylic copolymer was obtained in the same manner as in Example 1, except that the polymerization initiator, t-amyl hydroperoxide, was changed to hydrogen peroxide. As in Example 1, Mooney viscosity measurement, metal ion residual amount measurement, capillary flow test, normal state physical property test of the acrylic copolymer crosslinked product, and compression set test were also performed in the same manner, and the results are shown in Table 2.

[0114] An acrylic copolymer was obtained in the same manner as in Example 1, except that the polymerization initiator, t-amyl hydroperoxide, was changed to t-butyl hydroperoxide. Mooney viscosity measurement, metal ion residual amount measurement, capillary flow test, normal state physical property test of the acrylic copolymer crosslinked product, and compression set test were also carried out in the same manner as in Example 1, and the results are shown in Table 2.

[0115]

[0116]

[0117] As can be seen from Table 1, salting out using a monovalent metal salt improved compression set. Furthermore, as can be seen from Table 2, the acrylic copolymer using a polymerization initiator having a t-amyl group showed a lower elongational viscosity in the high elongation rate range than commonly used polymerization initiators, suggesting that this acrylic copolymer has improved processability.

[0118] The acrylic copolymer of the present invention can be widely used as a rubber product taking advantage of its excellent processability and low compression set. In particular, crosslinked products produced using the acrylic copolymer of the present invention are effective as industrial rubber materials such as oil seals, engine gaskets, oil hoses, air hoses, and O-rings, as well as automotive rubber materials, which require excellent processability and low compression set.

Claims

DEPCT691. Acrylic copolymers, which comprise at least a structural unit derived from an alkyl acrylate, a structural unit derived from a crosslinkable monomer, and a structural unit derived from a polymerization initiator, in which the acrylic copolymer meets the following conditions (A) and (B): (A) the structural unit derived from the polymerization initiator is a structural unit derived from a compound represented by the following formulas (1) or (2): (chemical formula)(1)(chemical formula)(2), where n represents a positive integer (natural number), and 1 is less than or equal to n is less than or equal to 4; and (B) the acrylic copolymer contains residual monovalent metal ions of 30 parts per million by mass or higher and 5000 parts per million by mass or lower, and higher than 300 parts per million by mass or higher divalent or valence metal ions than the residual.and the ratio of the amount of residual monovalent metal ions present to the amount of residual divalent or higher valence metal ions present ([amount of residual monovalent metal ions present] / [amount of residual divalent or higher valence metal ions present]) 10 or more.

2. Acrylic copolymers according to claim 1, where, per 100% by mass of acrylic copolymer, the amount of structural units derived from alkyl acrylate is 50 to 99.8% by mass, the amount of structural units derived from crosslinkable monomers is 0.1 to 10% by mass, and the amount The amount of structural units derived from the polymerization initiator is 0.001 to 2% by mass.

3. Acrylic copolymer pursuant to claim 1, where at least one of the following is as follows: the amount of structural units derived from alkyl acrylates with C1-C3 alkyl groups is 0 to 100% by mass per 100% by mass of structural units derived from alkyl acrylates; the amount of structural units derived from alkyl acrylates with C4-C6 alkyl groups is 0 to 100% by mass per 100% by mass of structural units derived from alkyl acrylates.

4. Acrylic copolymer pursuant to claim 1,where the crosslinked monomer structural unit is a crosslinked monomer structural unit containing a carboxyl group; 5. An acrylic copolymer composition, which includes an acrylic copolymer according to one of the claims 1 to 4 and at least a crosslinking agent; 6. A crosslinked acrylic rubber product obtained by crosslinking an acrylic copolymer composition according to claim 5; 7. A method for the production of an acrylic copolymer according to claim 1, which includes: the emulsion polymerization of an acrylic copolymer composition, which includes at least an alkyl acrylate, a crosslinked monomer, and an alkyl polymerization initiator.Using an emulsifying agent to obtain an emulsifying liquid; a salt displacement operation with 0.01 to 10 parts by mass of monovalent metal salts relative to 100 parts by mass of the emulsifying liquid to obtain aqueous crumbs; washing the aqueous crumbs with water; and drying the washed aqueous crumbs.

8. Method for the production of acrylic copolymers according to claim 7, where at least one of the monovalent metal salts is selected from the group consisting of metal sulfates, metal acetates, or metal carbonates of sodium;