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

Abstract

Provided are: an acrylic copolymer having both processability and low compression set properties and also having sufficient mechanical strength; a composition containing the acrylic copolymer; a crosslinked product of the composition; and a method for producing the acrylic copolymer. It is found that a composition using an acrylic copolymer having a substituent derived from a polymerization initiator introduced to at least one end or both ends of a polymer chain has excellent processability, and a crosslinked product obtained by crosslinking the composition has excellent low compression set properties and mechanical strength.

Description

Technical Field

[0001] This invention relates to acrylic copolymers, compositions containing acrylic copolymers and their crosslinks, and methods for manufacturing acrylic copolymers. Background Technology

[0002] Generally speaking, acrylic copolymers are polymers based on alkyl (meth)acrylates. They are known as materials with excellent properties related to durability and are widely used as industrial rubber materials such as engine gaskets, fuel hoses, air hoses, and O-rings, and / or automotive rubber materials.

[0003] When acrylic copolymers are used in automotive rubber materials such as hoses and / or gaskets as described above, excellent compression set is required to achieve adequate sealing performance. Furthermore, to mold hoses and / or gaskets, they need to be adaptable to various molding methods, thus requiring excellent processability, and as crosslinking materials, they need to possess sufficient mechanical strength.

[0004] Typically, when low compression set and mechanical strength are required, the method of increasing crosslinking density is adopted. However, this has the opposite property of increasing crosslinking density, which leads to faster vulcanization and worse processability.

[0005] In response to this situation, Patent Document 1 proposes an acrylic copolymer composition that, during processing, becomes an acrylic rubber vulcanizate with excellent low compression set. The acrylic copolymer composition comprises an acrylic copolymer and a crosslinking aid. The acrylic copolymer comprises alkyl acrylates having 1 to 8 carbon atoms, alkoxy acrylates having 1 to 4 carbon atoms and alkylene acrylates having 1 to 4 carbon atoms, dicyclopentadiene, ethylidene norbornene, and dicyclopentenyl esters of unsaturated carboxylic acids. The crosslinking aid comprises an organic peroxide as a crosslinking agent and two or more (meth)acrylates.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent No. 5010663 Summary of the Invention

[0009] The problem the invention aims to solve

[0010] In view of the above-mentioned issues, the object of the present invention is to provide acrylic copolymers that have both processability and low compression set, and thus sufficient mechanical strength, compositions containing acrylic copolymers and their crosslinks, as well as a method for manufacturing acrylic copolymers.

[0011] Solution for solving the problem

[0012] To achieve the above-mentioned objectives, the inventors conducted various studies and discovered that compositions using acrylic copolymers with substituents derived from polymerization initiators introduced at at least one end or both ends of the polymer chain exhibit excellent processability. Furthermore, crosslinked products formed from these compositions possess excellent low compression set and mechanical strength, thus completing the present invention. It should be noted that the aforementioned crosslinked products are sometimes referred to as "acrylic copolymer crosslinked products."

[0013] The present invention is described below.

[0014] Item 1 An acrylic copolymer comprising at least structural units derived from alkyl acrylates, structural units derived from crosslinking monomers and structural units derived from polymerization initiators, said acrylic copolymer also satisfying the following conditions (A) and (B).

[0015] (A) The structural unit derived from the polymerization initiator is derived from the structural unit of the compound represented by formula (1) or formula (2) below.

[0016]

[0017]

[0018] (n is a natural number, 1≤n≤4)

[0019] (B) The residual amount of monovalent metal ions in the acrylic copolymer is more than 30 ppm by mass and less than 5000 ppm by mass, the residual amount of divalent or higher metal ions is less than 300 ppm by mass, and the ratio of the residual amount of monovalent metal ions to the residual amount of divalent or higher metal ions ([residual amount of monovalent metal ions] / [residual amount of divalent or higher metal ions]) is more than 10.

[0020] Item 2 is the acrylic copolymer according to Item 1, wherein, relative to 100% by mass of the acrylic copolymer, the content of structural units derived from alkyl acrylates is 50% to 99.8% by mass, the content of structural units derived from crosslinking monomers is 0.1% to 10% by mass, and the content of structural units derived from polymerization initiators is 0.001% to 2% by mass.

[0021] Item 3 is an acrylic copolymer according to Item 1 or 2, wherein, relative to 100% by mass of the structural units derived from alkyl acrylates, the content of structural units derived from alkyl acrylates having 1 to 3 carbon atoms is 0 to 100% by mass and / or the content of structural units derived from alkyl acrylates having 4 to 6 carbon atoms is 0 to 100% by mass.

[0022] Item 4 is an acrylic copolymer according to any one of items 1 to 3, wherein the structural unit derived from the crosslinking monomer is a structural unit derived from a crosslinking monomer having a carboxyl group.

[0023] Item 5 A composition containing an acrylic copolymer, wherein the acrylic copolymer described in any one of Items 1 to 4 contains at least a crosslinking agent.

[0024] Item 6 is an acrylic rubber crosslinker, which is formed by crosslinking the composition containing the acrylic copolymer described in Item 5.

[0025] Item 7. A method for manufacturing an acrylic copolymer, which is the method for manufacturing an acrylic copolymer according to any one of Items 1 to 4, comprising:

[0026] In the emulsion polymerization process, an emulsifier is used to emulsion polymerize an acrylic copolymer component comprising at least an alkyl acrylate, a crosslinking monomer, and an alkyl polymerization initiator, thereby obtaining an emulsion polymer solution;

[0027] In the salting-out process, 0.01 to 10 parts by weight of a monovalent metal salt are used to salt out 100 parts by weight of the emulsion polymerization liquid to obtain water-containing particles;

[0028] The water washing process cleans the water-containing particles; and

[0029] The drying process involves drying the cleaned, water-containing granules.

[0030] Item 8 is the method for manufacturing an acrylic copolymer according to Item 7, wherein the monovalent metal salt is at least one selected from the group consisting of sodium sulfate, sodium acetate, and sodium carbonate.

[0031] The effects of the invention

[0032] According to the present invention, acrylic copolymers that combine processability and low compression set, and thus have sufficient mechanical strength, compositions containing acrylic copolymers, crosslinked acrylic copolymers, and methods for manufacturing acrylic copolymers can be provided. Detailed Implementation

[0033] The acrylic copolymers of the present invention have substituents derived from a polymerization initiator at at least one end or both ends of the polymer chain. More specifically, the acrylic copolymers of the present invention are acrylic copolymers comprising structural units derived from alkyl acrylates, structural units derived from crosslinking monomers, and structural units derived from alkyl-containing polymerization initiators (preferably structural units derived from compounds shown in formula (1) or (2) above), wherein the copolymer has substituents derived from a polymerization initiator at at least one end or both ends. This results in good processability. Furthermore, by keeping the type and amount of residual metals contained in the acrylic copolymers of the present invention within a specific range, good low compression set is achieved. In the acrylic copolymers of the present invention, by having substituents derived from a polymerization initiator at at least one end or both ends of the copolymer, and by keeping the type and amount of residual metals within a specific range, acrylic copolymers that balance processability and low compression set, and thus have sufficient mechanical strength, compositions containing acrylic copolymers, and crosslinked acrylic copolymers are provided.

[0034] <Acrylic copolymers>

[0035] The acrylic copolymers of the present invention have substituents derived from a polymerization initiator at at least one end or both ends of the polymer chain. More specifically, the acrylic copolymers of the present invention are acrylic copolymers comprising structural units derived from alkyl acrylates, structural units derived from crosslinking monomers, and structural units derived from a polymerization initiator, wherein the copolymer chain has substituents derived from a polymerization initiator at at least one end or both ends (preferably one end).

[0036] As structural units derived from the aforementioned alkyl acrylates, structural units derived from alkyl acrylates having 1 to 3 carbon atoms and / or structural units derived from alkyl acrylates having 4 to 6 carbon atoms are preferred. The structural units derived from alkyl acrylates may be structural units derived from a single or two or more alkyl acrylates.

[0037] Specific examples of alkyl acrylates 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.

[0038] Specific examples of alkyl acrylates 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.

[0039] Of the 100% by mass of structural units derived from alkyl acrylates, the content of structural units derived from alkyl acrylates having 1 to 3 carbon atoms is preferably 0% to 100% by mass. More specifically, as a lower limit, it is preferably 0% or more by mass, more preferably 10% or more by mass, further preferably 20% or more by mass, particularly preferably 25% or more by mass, and most preferably 30% or more by mass. As an upper limit, it is preferably 100% or less by mass, more preferably 90% or less by mass, further preferably 80% or less by mass, particularly preferably 70% or less by mass, and most preferably 60% or less by mass. It should be noted that in this specification, the expression "~" refers to a value above the value before "~" and a value below the value after "~".

[0040] Furthermore, of the 100% by mass of structural units derived from alkyl acrylates, the content of structural units derived from alkyl acrylates having 4 to 6 carbon atoms is preferably 0% to 100% by mass. More specifically, as a lower limit, it is preferably 0% or more by mass, more preferably 10% or more by mass, further preferably 20% or more by mass, particularly preferably 30% or more by mass, and most preferably 40% or more by mass. As an upper limit, it is preferably 100% or less by mass, more preferably 90% or less by mass, further preferably 80% or less by mass, particularly preferably 75% or less by mass, and most preferably 70% or less by mass.

[0041] In the acrylic copolymer of the present invention, the content of structural units derived from alkyl acrylates in 100% by mass is preferably 50% to 99.8% by mass. More specifically, as a lower limit, it is preferably 50% by mass or more, more preferably 60% by mass or more, further preferably 70% by mass or more, particularly preferably 80% by mass or more, and most preferably 90% by mass or more. As an upper limit, it is preferably 99.8% by mass or less, more preferably 99.5% by mass or less, and most preferably 99% by mass or less. Therefore, there is a tendency to obtain more suitable effects.

[0042] It should be noted that, in this specification, the content of structural units derived from alkyl acrylates refers to the total content when multiple structural units are present. The same applies to other structural units.

[0043] As for the structural units derived from the aforementioned crosslinking monomers, there are no particular limitations as long as they have a crosslinking group capable of reacting with the crosslinking agent. Examples of crosslinking groups include carboxyl groups, epoxy groups, and halogen groups. Structural units derived from crosslinking monomers can be used alone or in combination of two or more. Preferably, structural units derived from crosslinking monomers with a carboxyl group as the crosslinking group are used.

[0044] Structural units derived from crosslinking monomers with carboxyl groups as crosslinking groups include, for example, structural units derived from olefinic unsaturated monocarboxylic acids such as methacrylic acid, acrylic acid, crotonic acid, 2-pentenoic acid, and cinnamic acid; structural units derived from olefinic unsaturated dicarboxylic acids such as fumaric acid, maleic acid, and itaconic acid; and structural units derived from olefinic unsaturated dicarboxylic acid monoesters such as fumaric acid monomethyl ester, fumaric acid monoethyl ester, fumaric acid monopropyl ester, fumaric acid monobutyl ester, fumaric acid monohexyl ester, fumaric acid monooctyl ester, etc.; olefinic acid monoalkyl esters such as maleic acid monomethyl ester, maleic acid monoethyl ester, maleic acid monopropyl ester, maleic acid monobutyl ester, maleic acid monopentyl ester, maleic acid monodecyl ester, etc.; and olefinic acid monoalkyl esters such as itaconic acid monomethyl ester, itaconic acid monoethyl ester, itaconic acid monopropyl ester, itaconic acid monobutyl ester, etc. These can be used alone or in combination of two or more, preferably structural units derived from olefinic unsaturated dicarboxylic acid monoesters, more preferably structural units derived from monoalkyl fumarate esters, and most preferably structural units derived from monoalkyl fumarate esters having 1 to 4 carbon atoms.

[0045] Structural units derived from crosslinking monomers with epoxy groups as crosslinking groups include, for example, structural units derived from epoxy-containing alkyl acrylates such as glycidyl acrylate; structural units derived from epoxy-containing styrene such as p-vinylbenzyl glycidyl ether; and structural units derived from epoxy-containing ethers such as allyl glycidyl ether, vinyl glycidyl ether, 3,4-epoxy-1-pentene, 3,4-epoxy-1-butene, 4,5-epoxy-2-pentene, 4-vinylcyclohexyl glycidyl ether, cyclohexenyl methyl glycidyl ether, 3,4-epoxy-1-vinylcyclohexene, and allyl phenyl glycidyl ether. These units can be used alone or in combination of two or more.

[0046] Structural units derived from crosslinking monomers with halogen groups as crosslinking groups include, for example, structural units derived from 2-chloroethyl vinyl ether, 2-chloroethyl acrylate, p-chloromethylstyrene, vinyl monochloroacetate, allyl chloroacetate, etc. They can be used alone or in combination of two or more.

[0047] In the acrylic copolymer of the present invention, the content of structural units derived from crosslinking monomers in 100% by mass 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, preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 2.5% by mass or less. Therefore, there is a tendency to obtain more suitable effects.

[0048] As for the structural unit derived from the above-mentioned polymerization initiator, there is no particular limitation as long as it is derived from the structural unit of the polymerization initiator shown in formula (1) or formula (2) below. As a specific example, peroxide-based polymerization initiators such as tert-amyl hydroperoxide and di-tert-amyl hydroperoxide are preferred. These polymerization initiators can be used alone or in combination of two or more.

[0049]

[0050] (n is a natural number, 1≤n≤4)

[0051] n is 1 to 4, preferably 3 or less, more preferably 2 or less, and n is even more preferably 1.

[0052] In the acrylic copolymer of the present invention, the content of structural units derived from the polymerization initiator (derived from the structural units of the compounds shown in formula (1) or formula (2) above) in 100% by mass is preferably 0.001 to 2.0% by mass. More specifically, as a lower limit, it 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, particularly preferably 0.02% by mass or more. As an upper limit, it 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, particularly preferably 0.20% by mass or less. Thus, there is a tendency to obtain more suitable effects.

[0053] In the acrylic copolymer of the present invention, the total content of structural units derived from alkyl acrylates, structural units derived from crosslinking monomers, and structural units derived from polymerization initiators having alkyl groups (structural units derived from compounds shown in formula (1) or (2) above) in 100% by mass of the acrylic copolymer is preferably 70% by mass or more, more preferably 80% by mass or more, further preferably 90% by mass or more, particularly preferably 95% by mass or more, and may also be 100% by mass. Thus, there is a tendency to obtain more suitable effects.

[0054] Furthermore, the acrylic copolymers of the present invention may also contain copolymerizable monomers other than those described above as structural units of the acrylic copolymer, provided that they do not depart from the spirit of the invention. Examples of other monomers include alkoxyalkyl acrylates, olefinically unsaturated nitrile monomers, acrylamide monomers, aromatic vinyl monomers, conjugated diene monomers, non-conjugated diene monomers, other olefin monomers, and copolymerizable anti-aging agents. These monomers may be used alone or in combination of two or more.

[0055] Examples of alkyl acrylates include 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 can be used alone or in combination of two or more.

[0056] Examples of olefinically unsaturated nitrile monomers include acrylonitrile, methacrylonitrile, α-methoxyacrylonitrile, and dicyanide. They can be used alone or in combination of two or more.

[0057] Examples of acrylamide monomers include acrylamide, methacrylamide, diacetone acrylamide, diacetone methacrylamide, N-butoxymethylacrylamide, N-butoxymethylmethylacrylamide, N-butoxyethylacrylamide, N-methoxymethylacrylamide, N-methoxymethylmethylacrylamide, N-propoxymethylacrylamide, N-propoxymethylmethylacrylamide, N-methylacrylamide, N-methylmethylacrylamide, N,N-dimethylacrylamide, N,N-dimethylmethylacrylamide, N,N-diethylacrylamide, N,N-diethylacrylamide, N-hydroxymethylacrylamide, N-hydroxymethylmethylacrylamide, ethylacrylamide, crotonamide, cinnamamide, maleic anhydride, itaconitumamide, methylmaleamide, methylitaconitumamide, maleimide, itaconitumide, etc. They can be used alone or in combination of two or more.

[0058] 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, styrene sulfonic acid or its salts, α-vinylnaphthalene, 1-vinylnaphthalene-4-sulfonic acid or its salts, 2-vinylfluorene, 2-vinylpyridine, 4-vinylpyridine, divinylbenzene, diisopropylbenzene, and p-chloromethylstyrene. These can be used alone or in combination of two or more.

[0059] 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, and isoprene. They can be used alone or in combination of two or more.

[0060] Examples of non-conjugated diene monomers include 1,4-pentadiene, 1,4-hexadiene, ethylene norbornene, norbornene, and dicyclopentadiene. They can be used alone or in combination of two or more.

[0061] Other olefinic monomers include, for example, esters such as dicyclopentadienyl acrylate, dicyclopentadienyl methacrylate, ethyl dicyclopentadienyl acrylate, and ethyl dicyclopentadienyl 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; and butyl vinyl ether. These can be used alone or in combination of two or more.

[0062] Examples of copolymeric anti-aging agents include structural units derived from copolymeric amine anti-aging agents such as N-(4-anilinophenyl)methacrylamide, N-(4-anilinophenyl)acrylamide, N-(4-anilinophenyl)maleimide, N-(4-p-tolylphenyl)maleimide, N-(4-anilino-1-naphthyl)maleimide, 4-hydroxyphenylmaleimide, and 3-hydroxyphenylmaleimide; 2-tert-butyl-4-methyl-6-(2-hydroxy-3-tert-butyl-5-methylbenzyl)phenyl acrylate; 2-{1-[2-hydroxy-3,5-bis(2-methylbut-2-yl)phenyl]ethyl}-4,6-di(2-methylbut-2-yl)phenyl acrylate; hydroxycinnamic acid; ferulic acid; and allyl cresol. These can be used alone or in combination of two or more.

[0063] In the acrylic copolymers of the present invention, the content of their structural units can be determined by the nuclear magnetic resonance spectrum of the resulting polymer.

[0064] <Methods for manufacturing acrylic copolymers>

[0065] The acrylic copolymers of the present invention can be manufactured by polymerizing various monomers separately, and the monomers used can all be commercially available and are not particularly limited. The acrylic copolymers used in the present invention have substituents derived from the polymerization initiator at at least one end or both ends of the polymer chain. For such acrylic copolymers, for example, as described above, by polymerizing the acrylic copolymers using polymerization initiators having alkyl groups (compounds shown in formula (1) or formula (2) above), acrylic copolymers having alkyl groups derived from the polymerization initiation end of the polymer chain can be obtained.

[0066] As a manufacturing process for producing the acrylic copolymer of the present invention, a method for producing the acrylic copolymer comprising the following steps is preferred:

[0067] In the emulsion polymerization process, an emulsion polymer is carried out using an emulsifier on an acrylic copolymer component that contains at least an alkyl acrylate, a crosslinking monomer, and an alkyl polymerization initiator (a compound shown in formula (1) or formula (2) above), thereby obtaining an emulsion polymer solution;

[0068] In the salting-out process, 0.01 to 10 parts by weight of a monovalent metal salt are used to salt out 100 parts by weight of the emulsion polymerization liquid to obtain water-containing particles;

[0069] The water washing process cleans the water-containing particles; and

[0070] The drying process involves drying the cleaned, water-containing granules.

[0071] <Emulsion Polymerization Process>

[0072] As the form of polymerization reaction, any of the following methods can be used: emulsion polymerization, suspension polymerization, bulk polymerization, and solution polymerization. From the perspective of ease of controlling the polymerization reaction, emulsion polymerization under normal pressure, which is a conventionally known method for manufacturing acrylic copolymers, is preferred.

[0073] In the case of polymerization using emulsion polymerization, conventional methods can be used, and commonly used and previously known substances can be used for polymerization initiators, emulsifiers, chain transfer agents, polymerization terminators, etc. Here, regarding polymerization initiators, as mentioned above, polymerization initiators having alkyl groups (compounds shown in formula (1) or formula (2) above) are preferred.

[0074] The emulsifier used in this invention is not particularly limited, and nonionic and anionic emulsifiers commonly used in emulsion polymerization can be used. Examples of nonionic emulsifiers include polyoxyethylene alkyl ethers, polyoxyethylene alcohol ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene polycyclic phenyl ethers, polyoxyethylene alkylene ethers, sorbitan fatty acid esters, polyoxyethylene fatty acid esters, and polyoxyethylene sorbitan fatty acid esters. Examples of anionic emulsifiers include alkylbenzene sulfonates, alkyl sulfate salts, polyoxyethylene alkyl ether sulfate salts, polyoxyethylene alkyl ether phosphates or their salts, and fatty acid salts. One or more of these can be used. Representative examples of anionic emulsifiers include sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and triethanolamine dodecyl sulfate.

[0075] The amount of emulsifier used in this invention is only the amount commonly used in emulsion polymerization. Specifically, it is in the range of 0.01 parts by weight to 10 parts by weight relative to 100 parts by weight of the monomer constituting the acrylic copolymer, preferably 0.03 parts by weight to 7 parts by weight, and more preferably 0.05 parts by weight to 5 parts by weight. When using a reactive surfactant as a monomer component, it is not necessarily necessary to add an emulsifier.

[0076] The polymerization initiator used in this invention is not particularly limited as long as it is a polymerization initiator shown in formula (1) or formula (2) below. As a specific example, peroxide-based polymerization initiators such as tert-amyl hydroperoxide and di-tert-amyl hydroperoxide are preferred. These polymerization initiators can be used alone or in combination of two or more.

[0077]

[0078]

[0079] (n is a natural number, 1≤n≤4)

[0080] n is 1 to 4, preferably 3 or less, more preferably 2 or less, and n is even more preferably 1.

[0081] The amount of polymerization initiator used in this invention is only the amount commonly used in emulsion polymerization. Specifically, it is in the range of 0.001 parts by mass to 2 parts by mass relative to 100 parts by mass of the polymerizable monomer constituting the acrylic copolymer, preferably 0.005 parts by mass to 1.50 parts by mass, and more preferably 0.01 parts by mass to 0.5 parts by mass.

[0082] Furthermore, organic and inorganic peroxides, which serve as polymerization initiators, can be used as redox polymerization initiators in combination with reducing agents. There are no particular limitations on the reducing agents used in combination; examples include compounds containing metal ions in a reduced state, such as ferrous sulfate and cuprous naphthenate; methane compounds such as sodium methanesulfonate; amine compounds such as dimethylaniline; ascorbic acid and its salts; and inorganic salts with reducing properties, such as alkali metal salts of sulfurous acid 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 weight relative to 100 parts by weight of the monomer constituting the acrylic copolymer.

[0083] Chain transfer agents can be used as needed. Specific examples of chain transfer agents include alkyl thiols such as n-hexylthiol, n-octylthiol, tert-octylthiol, n-dodecylthiol, tert-dodecylthiol, and n-stearylthiol; xanthate compounds such as 2,4-diphenyl-4-methyl-1-pentene and 2,4-diphenyl-4-methyl-2-pentene; dimethyl disulfide xanthate and diisopropyl disulfide xanthate; terpinene; tetramethylthiuram disulfide; tetraethylthiuram disulfide; and tetramethylthiuram monosulfide. Thiuram compounds, phenolic compounds such as 2,6-di-tert-butyl-4-methylphenol and styrene-modified phenol, allyl compounds such as allyl alcohol, halogenated hydrocarbons such as dichloromethane, dibromomethane, and carbon tetrabromide, vinyl ethers such as α-benzyloxystyrene, α-benzyloxyacrylonitrile, and α-benzyloxyacrylamide, triphenylethane, pentaphenylethane, acrolein, methacrolein, mercaptoacetic acid, thiomalic acid, and 2-ethylhexyl mercaptoacetic acid, etc., may be used, one or more of them. The amount of these chain transfer agents is not particularly limited, and they are generally used in amounts of 0 to 5 parts by weight relative to 100 parts by weight of the monomers constituting the acrylic copolymer.

[0084] Examples of polymerization terminators include hydroxylamine, hydroxylamine sulfate, diethylhydroxylamine, hydroxylamine sulfonic acid and its alkali metal salts, sodium dimethyl dithiocarbamate, and quinone compounds such as hydroquinone. One or more of these can be used. The amount of polymerization terminator used is not particularly limited, but is generally 0 to 2 parts by mass relative to 100 parts by mass of the monomer constituting the acrylic copolymer. Here, by using a polymerization terminator having functional groups and alkyl groups capable of reacting with free radicals of the polymer chain, an acrylic copolymer with alkyl groups at the polymerization termination end can be obtained.

[0085] Furthermore, the polymer obtained by the above method can be used as a pH adjuster to adjust the pH as needed. Specific examples of alkalis include sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium bicarbonate, ammonia, inorganic ammonium compounds, organic amine compounds, etc. One or more of them can be used. The pH range is pH 1 to 11, preferably pH 1.5 to 10.5, and more preferably pH 2 to 10.

[0086] In addition, polymerization auxiliaries such as particle size modifiers, chelating agents, and oxygen scavengers can be used as needed. One or more of them can be used.

[0087] Emulsion polymerization can be carried out in any of the following types: batch, semi-batch, or continuous. There are no particular limitations on polymerization time and temperature. The polymerization can be appropriately selected based on factors such as the type of polymerization initiator used. Typically, the polymerization temperature is between 10°C and 100°C, and the polymerization time is between 0.5 hours and 100 hours.

[0088] <Salting process>

[0089] There are no particular limitations on the method for recovering aqueous particles from the emulsion polymerization solution obtained by the above method (salting-out method), and conventional methods can be used. As an example, a method can be described in which the emulsion polymerization solution is continuously or batchively fed into an aqueous solution containing a salting-out agent, thereby obtaining aqueous particles.

[0090] There are no particular limitations on the salting-out agent; monovalent to trivalent metal salts can be used, with monovalent metal salts being preferred. Specific examples include inorganic salts such as chlorides, sulfates, nitrates, and carbonates of lithium, sodium, potassium, and cesium, as well as organic salts such as acetates and phosphates. If divalent or higher metal salts (existing as metal ions in acrylic copolymers) remain in the acrylic copolymer, these divalent metal ions will hinder the crosslinking reaction, potentially negatively impacting low compression set. One or more salting-out agents can be used.

[0091] 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 salt 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.

[0092] In addition, as mentioned above, the presence of divalent metal salts in the monovalent metal salts used as salting-out agents in the acrylic copolymers can affect the low compression set. Therefore, the purity of the monovalent metal salt is preferably 99.0% or more, more preferably 99.5% or more, and can also be 100%.

[0093] In the salting-out process, the amount of monovalent metal salt added is preferably 0.01 to 10 parts by weight relative to 100 parts by weight of the emulsion polymerization solution. More specifically, as a lower limit, it is preferably 0.01 parts by weight, more preferably 0.1 parts by weight, and even more preferably 1 part by weight. Furthermore, as an upper limit, it is preferably 10 parts by weight, more preferably 9.5 parts by weight, and even more preferably 9 parts by weight. By falling within these ranges, the residual amount of monovalent metal ions and divalent or higher metal ions in the acrylic copolymer after washing can be appropriately managed.

[0094] The residual amount of monovalent metal ions (preferably sodium ions) in the acrylic copolymers of the present invention is preferably in 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, further preferably 100 ppm by mass or more, particularly preferably 150 ppm by mass or more, and most preferably 200 ppm by mass or more. The upper limit is more preferably 4500 ppm by mass or less, and further preferably 4000 ppm by mass or less. If the content is outside these ranges, it may adversely affect the heat resistance and / or low compression set.

[0095] The residual amount of divalent or higher metal ions (preferably the sum of magnesium 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.

[0096] Furthermore, in the acrylic copolymers of the present invention, the ratio of the residual amount of monovalent metal ions (preferably sodium ions) to the residual amount of divalent or higher metal ions (preferably the sum of magnesium and calcium ions) ([residual amount of monovalent metal ions (preferably sodium ions)] / [residual amount of divalent or higher metal ions (preferably the sum of magnesium 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 higher metal ions is greater than the residual amount of monovalent metal ions, as described above, it may have an adverse effect on low compression set. It should be noted that the upper limit of the above ratio is not particularly limited, for example, it is 10,000 or less.

[0097] In this specification, the residual amount of metal ions in acrylic copolymers is determined by the methods described in the examples.

[0098] The salting-out temperature is not particularly limited, but is typically between 50°C and 100°C, preferably between 60°C and 100°C. By keeping the salting-out temperature within the above range, there is a tendency to make the types and amounts of residual metals contained in the acrylic copolymer more appropriately within the specific range of this application.

[0099] Furthermore, anti-aging agents can be added during the salting-out process. Specific examples of anti-aging agents include phenolic antioxidants, amine antioxidants, phosphite antioxidants, and hindered amine antioxidants. One or more of these can be used.

[0100] Furthermore, in the salting-out process, an alkali can be used as a pH adjuster to adjust the pH as needed. Specific examples of alkalis include sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium bicarbonate, ammonia, inorganic ammonium compounds, and organic amine compounds. One or more of these can be used. The pH range is pH 1 to 11, preferably pH 2 to 10, and more preferably pH 4 to 8.

[0101] <Washing Process>

[0102] To remove the salting-out agent, it is preferable to wash the aqueous particles obtained in the salting-out process with water. If washing is not performed at all or is insufficient, residual metal ions from the salting-out agent may adversely affect mechanical properties and may precipitate during the molding process. To remove the salting-out agent, it is preferable to thoroughly wash the aqueous particles obtained in the salting-out process with water in a manner 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 higher 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 higher metal ions ([residual amount of monovalent metal ions] / [residual amount of divalent or higher metal ions]) is 10 or more. Therefore, there is a tendency to more appropriately control the types and amounts of residual metals contained in the acrylic copolymer within the specific range of this application.

[0103] In the washing process, the washing method can be carried out by mixing water with the water-containing particles (intermittent method) or by continuously washing while dehydrating (continuous method). Regardless of the method used, the washing temperature is preferably 5°C to 60°C, more preferably 10°C to 50°C, and the mixing time is 1 minute to 60 minutes, more preferably 2 minutes to 30 minutes.

[0104] When the washing is performed intermittently, there is no particular limitation on the amount of water added to the water-containing particles. From the viewpoint of effectively reducing the residual amount of salting-out agent in the final acrylic rubber, the amount of water for each wash is preferably 50 to 9,800 parts by mass relative to 100 parts by mass of the acrylic copolymer component contained in the water-containing particles, more preferably 300 to 1,800 parts by mass.

[0105] There is no particular limitation on the number of washes, but from the perspective of reducing the amount of metal ions remaining due to the salting-out agent in acrylic copolymers, 2 to 8 washes are preferred, and 2 to 6 washes are more preferred. It should be noted that while more washes can reduce the amount of metal ions remaining, the removal effect of the salting-out agent decreases with each increase in the number of washes, and the impact of reduced productivity will become greater due to the increase in the number of processes. Therefore, the number of washes is preferably set within the above range.

[0106] Furthermore, when performing continuous water washing, the standard for ending the water washing can be determined by measuring the conductivity of the aqueous solution of the slurry mixture. The 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 setting the conductivity to this level or below, the residual amount of metal ions caused by the salting-out agent in the acrylic copolymer is sufficiently reduced.

[0107] The conductivity of the slurry mixture was determined by placing the supernatant of the collected slurry mixture into a 110 mL sample vial. The conductivity of the supernatant collected in the 110 mL sample vial at 23°C was measured using an AC two-electrode method. Conductivity measurements could be performed using portable conductivity meters such as the ES-51 manufactured by Kuba Corporation and the waterproof general-purpose conductivity meter 9382-10D manufactured by Kuba Corporation.

[0108] <Drying Process>

[0109] Acrylic copolymers can be obtained by removing moisture from the water-containing granules after washing and drying. There are no particular limitations on the drying method; flash dryers, twin-screw extruders, and / or flow dryers are commonly used. Alternatively, a dehydration process using a centrifuge or similar device can be performed before the drying process.

[0110] From a processability point of view, the molecular weight range of the acrylic copolymer of the present invention thus manufactured, expressed as the Mooney viscosity (ML1+4) at 100°C in the Mooney scorch test as specified in JISK 6300-1:2013, is preferably 10 to 100, more preferably 15 to 90, and even more preferably 20 to 80.

[0111] In this specification, the Mooney viscosity of the acrylic copolymers is a value determined by the method described in the examples.

[0112] The weight-average molecular weight (Mw) of the acrylic copolymers 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. Therefore, there is a tendency to obtain more suitable results.

[0113] Compositions containing acrylic copolymers

[0114] The composition containing acrylic copolymer of the present invention can be obtained by containing the above-mentioned acrylic copolymer and at least a crosslinking agent.

[0115] As a crosslinking agent, conventionally known crosslinking agents commonly used in the crosslinking of rubber, such as polyamine compounds, polyepoxide compounds, polyisocyanate compounds, aziridine compounds, sulfur compounds, metal soaps, basic metal oxides, and organometallic halides, can be used. Among these, polyamine compounds are preferred.

[0116] Examples of polyamine compounds include, for instance, aliphatic polyamine compounds such as hexamethylenediamine, hexamethylenediamine carbamate, and N,N'-biscinnamaldehyde-1,6-hexanediamine, and / or aromatic polyamine compounds such as 4,4'-methylenediphenylamine, 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, 4,4'-diaminobenzoylaniline, 4,4'-bis(4-aminophenoxy)biphenyl, m-phenylenediamine, p-phenylenediamine, 1,3,5-triaminobenzene, 1,3,5-triaminomethylbenzene, and isophthalic acid dihydrazide. Aliphatic polyamine compounds are preferred.

[0117] Examples of multi-component epoxy compounds include phenolic varnish-type epoxy compounds, cresolic varnish-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, hydrogenated bisphenol A-type epoxy compounds, glycidyl ether-type epoxy compounds, alicyclic epoxy compounds, glycidyl ester-type epoxy compounds, glycidyl amine-type epoxy compounds, isocyanurate-type epoxy compounds, and other multi-component epoxy compounds.

[0118] Examples of polyisocyanate compounds include 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, terephthalic diisocyanate, isophthalic diisocyanate, 1,5-naphthalene diisocyanate, 1,3,6-hexamethylene triisocyanate, 1,6,11-undecane triisocyanate, and bicycloheptane triisocyanate.

[0119] Examples of aziridine compounds include tri-2,4,6-(1-aziridine)-1,3,5-triazine, tris[1-(2-methyl)aziridine]phosphine oxide, and hexa[1-(2-methyl)aziridine]triphosphatazine.

[0120] Examples of sulfur compounds include sulfur, 4,4'-dithiomorpholine and / or tetramethylthiuram disulfide, tetraethylthiuram disulfide, etc.

[0121] Examples of alkaline metal oxides include zinc oxide, lead oxide, calcium oxide, and magnesium oxide.

[0122] Examples of organometal halides include dicyclopentadienyl metal dihalides, and examples of metals include titanium and zirconium.

[0123] These crosslinking agents can be used alone or in combination of two or more. The amount of crosslinking agent is 0.05 to 20 parts by weight, preferably 0.1 to 10 parts by weight, relative to 100 parts by weight of the acrylic copolymer of the present invention.

[0124] Furthermore, the compositions of the present invention containing acrylic copolymers can be freely blended with other additives commonly used in this art, such as lubricants, anti-aging agents, light stabilizers, fillers, reinforcing agents, plasticizers, processing aids, pigments, colorants, crosslinking accelerators, crosslinking aids, crosslinking delay agents, antistatic agents, foaming agents, etc. They can be used alone or in combination of two or more.

[0125] Examples of reinforcing agents include carbon black, the content of which is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, further preferably 30 parts by mass or more, more preferably 120 parts by mass or less, and more preferably 100 parts by mass or less, relative to 100 parts by mass of the acrylic copolymer.

[0126] Examples of anti-aging agents include amine-based, phosphate-based, quinoline-based, cresol-based, phenol-based, and dithiocarbamate metal salts. In this invention, amine-based and phenol-based anti-aging agents are preferred. They can be used alone or in combination of two or more.

[0127] Examples of amine-based anti-aging agents include phenyl-α-naphthylamine, phenyl-β-naphthylamine, p-(p-toluenesulfonamide)-diphenylamine, 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, N,N-diphenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, and butyraldehyde-aniline condensate.

[0128] Examples of phenolic anti-aging agents include 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butylphenol, butylated hydroxyanisole, 2,6-di-tert-butyl-α-dimethylamino-p-cresol, octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, stylated phenol, 2,2'-methylenebis(6-α-methyl-benzyl-p-cresol), and 4,4'-methylenebis(2 Examples of phenols include 2,2'-methylene-bis(4-methyl-6-tert-butylphenol), 2,4-bis[(octylthio)methyl]-6-methylphenol, 2,2'-thiobis(4-methyl-6-tert-butylphenol), 4,4'-thiobis(6-tert-butyl-o-cresol), and 2,6-di-tert-butyl-4-(4,6-bis(octylthio)-1,3,5-triazine-2-ylamino)phenol.

[0129] The content of the anti-aging agent is preferably 0.1 to 10 parts by weight relative to 100 parts by weight of the acrylic copolymer, more preferably 0.1 to 5 parts by weight, and particularly preferably 0.3 to 3 parts by weight.

[0130] Examples of crosslinking promoters include guanidine compounds, amine compounds, thiourea compounds, thiazole compounds, sulfenamide compounds, thiuram compounds, and quaternary ammonium salts, with guanidine compounds and amine compounds being preferred. They can be used alone or in combination of two or more.

[0131] The content of the crosslinking accelerator is preferably 0.1 to 15 parts by weight relative to 100 parts by weight of the acrylic copolymer, more preferably 0.1 to 10 parts by weight, and particularly preferably 0.1 to 5 parts by weight.

[0132] Furthermore, without departing from the spirit of the present invention, it is also possible to mix it with rubbers, resins, etc., commonly used in this technical field. 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. Examples of resins 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.

[0133] The total amount of the above-mentioned rubber and resin is 50 parts by weight or less, preferably 10 parts by weight or less, and more preferably 5 parts by weight or less, relative to 100 parts by weight of the acrylic copolymer of the present invention.

[0134] From a processability point of view, the elongation viscosity of the composition containing acrylic copolymers 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.

[0135] In this specification, the elongation viscosity of compositions containing acrylic copolymers is a value determined by the method described in the examples.

[0136] <Acrylic copolymer crosslinks (acrylic rubber crosslinks)>

[0137] The acrylic copolymer crosslinked product of the present invention can be obtained by crosslinking the above-described composition containing acrylic copolymer.

[0138] As a compounding method for obtaining the acrylic copolymer crosslinked product of the present invention, any means conventionally used in the rubber processing field can be employed, such as open roller mills, Banbury mixers, various kneaders, etc. The compounding steps can be performed according to the usual procedures in the rubber processing field. For example, the following steps can be followed: first, only rubber is compounded; then, compound mixture A containing compounding agents other than crosslinking agents and crosslinking accelerators is prepared; and then compound mixture B containing crosslinking agents and crosslinking accelerators is performed.

[0139] The acrylic copolymer crosslinks of the present invention can be prepared by heating the above-mentioned composition containing acrylic copolymers to 100°C to 250°C to produce acrylic copolymer crosslinks (acrylic rubber crosslinks). The crosslinking time varies depending on the temperature, but is generally between 0.5 minutes and 300 minutes. Crosslinking molding can be performed integrally with crosslinking and molding, and / or by reheating the pre-molded composition containing acrylic copolymers to produce acrylic copolymer crosslinks, and by heating and then processing the acrylic copolymer crosslinks to form them. As a specific method of crosslinking molding, any method can be used, such as compression molding using a mold, injection molding, heating using a steam bath, air bath, infrared radiation, or microwave.

[0140] The composition containing acrylic copolymers obtained in this way has excellent roll processability during processing, and the crosslinked acrylic copolymers of the present invention have excellent normal physical properties such as elongation at break and low compression set.

[0141] Therefore, the acrylic copolymer crosslinker (acrylic rubber crosslinker) of the present invention effectively utilizes the above-mentioned characteristics and is suitable for use as O-rings, gaskets, diaphragms, oil seals, shaft seals, bearing seals, mechanical seals, wellhead seals, seals for electrical / electronic equipment, seals for pneumatic equipment, cylinder head gaskets installed at the connection between the cylinder block and the cylinder head, rocker arm cover gaskets installed at the connection between the rocker arm cover and the cylinder head, oil pan gaskets installed at the connection between the oil pan and the cylinder block or transmission housing, fuel cell separator gaskets installed between a pair of housings holding a unit cell having a positive electrode, an electrolyte plate and a negative electrode, and hard disk drive top cover gaskets, etc.

[0142] In addition, the acrylic copolymer crosslinking products of the present invention are suitable for use as extruded and molded crosslinking products in automotive applications, such as fuel hoses, fuel filler necks, exhaust hoses, vapor hoses, fuel transfer hoses, etc., fuel oil system hoses around fuel tanks, turbocharger intake hoses, emission control hoses, etc., radiator hoses, heater hoses, brake hoses, air conditioning hoses, and various other types of hoses.

[0143] Example

[0144] The present invention will be specifically described through examples and comparative examples. However, the present invention is not limited thereto. In these examples and comparative examples, the manufacture of acrylic copolymers and the physical properties of crosslinked acrylic copolymers obtained by crosslinking compositions containing acrylic copolymers and crosslinking agents were evaluated.

[0145] [Example 1]

[0146] (Manufacturing of acrylic copolymers)

[0147] In a polymerization reactor equipped with a thermometer, stirring device, nitrogen inlet pipe, and pressure reducing device, 200 parts by mass of water, 4.0 parts by mass of polyoxyalkylene ether phosphate, 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 were added. After repeated degassing using pressure reducing and nitrogen replacement to fully remove oxygen, 0.001 parts by mass of ferrous sulfate, 0.1 parts by mass of sodium ascorbate, and 0.1 parts by mass of tert-amyl hydrogen peroxide were added. The emulsion polymerization reaction was started at normal pressure and temperature and continued until the polymerization conversion rate reached the specified value. The polymerization was stopped by adding 0.0075 parts by mass of hydroquinone. Relative to 100 parts by mass of the resulting emulsion polymer, salting out was performed using a 10% sodium sulfate aqueous solution at 70-80°C, with the result being 6 parts by mass of sodium sulfate. The solution was then drained, and 120 parts by mass of deionized water were added to wash the polymer. This washing process was repeated three times, followed by drying to obtain an acrylic copolymer. The obtained acrylic copolymers were subjected to Mooney viscosity determination, metal ion residue determination, and capillary flow test according to the following evaluation methods. The results are shown in Tables 1 and 2.

[0148] <Mounney Viscosity Measurement (ML1+4, 100℃)>

[0149] Mooney viscosity test according to JIS K6300-1:2013 physical test method for uncrosslinked rubber, using Mooney Viscometer AM-3 manufactured by Toyo Seiki Co., Ltd., was performed on the obtained acrylic copolymer at a test temperature of 100°C (ML1+4).

[0150] <Determination of Metal Ion Residual Content>

[0151] The residual metal ions in the obtained acrylic copolymers were quantitatively determined using an ICP emission spectrometer. Specifically, using a HORIBA JOBIN YVON ULTIMA2 instrument, approximately 0.5 g of sample was collected in a platinum crucible, pre-ashed with an electric heater, and then heated at 600°C for 1 hour in an electric furnace. Ultrapure water was added to the resulting residue and heated to dissolve the various metals. After dilution to volume in a volumetric flask, the residual amounts of each metal ion were determined. It should be noted that only sodium ions were detected as monovalent metal ions, and only magnesium and calcium ions were detected as divalent or higher metal ions; other metal ions were below the detection limit.

[0152] (Preparation of acrylic copolymer compositions)

[0153] 100 parts by weight of the acrylic copolymer obtained above, 60 parts by weight of carbon black (based on ASTM D1765 classification; N550), 2 parts by weight of stearic acid (a dispersant and softener for carbon black), and 2 parts by weight of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine (an anti-aging agent) were kneaded at 120°C using a kneader to obtain compound A. Capillary flow tests were performed on the obtained compound A as described below. The results are shown in Table 2. Then, 0.6 parts by weight of hexamethylenediamine carbamate (an aliphatic diamine crosslinking agent) and 2 parts by weight of di-o-tolueneguanidine (a crosslinking accelerator) were added, and the mixture was kneaded at room temperature using a kneading roller to obtain compound B, which was used as the composition containing the acrylic copolymer. Using the obtained acrylic copolymer composition, normal physical properties and compression set tests were performed according to the methods described below. The results are shown in Tables 1 and 2.

[0154] <Capillary Flow Test (Elongation Viscosity Measurement)>

[0155] To obtain 100 parts by weight of the resulting acrylic copolymer, 60 parts by weight of carbon black (based on ASTM D1765 classification; N550), 2 parts by weight of stearic acid, and 2 parts by weight of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine were kneaded at 120°C using a kneader. For the mixture, an IMATEK R6000 capillary rheometer was used, employing a long die (1 mm diameter, 16 mm length) and a short die (1 mm diameter, 0.25 mm length). The measurement temperature was 80°C, and the shear rate was reduced from 1000 seconds to 10 seconds in 11 stages. The elongation rate was measured in 9–12 seconds. -1 The highest elongation viscosity at that time. Also, depending on the molding method, the optimal elongation speed varies, but it generally occurs in the high elongation speed range. Therefore, when comparing under the same conditions, it can be said that the lower viscosity has superior processability.

[0156] Routine physical property tests: 100% modulus, tensile strength, elongation, hardness.

[0157] The above-mentioned acrylic copolymer composition was formed into sheets with a thickness of 2-2.5 mm. The resulting uncrosslinked sheets were pressurized at 180°C for 10 minutes, and then heated in an air oven at 180°C for 12 hours to obtain an acrylic rubber crosslink. The crosslinked material was cut into No. 3 dumbbells, and its 100% modulus, tensile strength, elongation, and hardness were measured. The 100% modulus, tensile strength, and elongation were tested according to JIS K6251:2017 using an AGS-5KNY hardness tester manufactured by Shimadzu Corporation. The hardness was measured according to JIS K6253:2012 using a hardness tester manufactured by Polymer Instruments Co., Ltd.

[0158] <Compression Permanent Deformation Test>

[0159] The above-mentioned acrylic copolymer composition was vulcanized under pressure at 170°C for 20 minutes using a mold for test piece preparation, and then an O-ring test piece was obtained. The obtained O-ring test pieces were then tested under the conditions of 175°C for 70 hours. If the rate of change after testing is less than 30%, it can be said that the low compression set is excellent. The test was conducted according to JIS K6262:2013.

[0160] [Example 2]

[0161] The polymerization initiator was changed from tert-amyl hydrogen peroxide to di-tert-amyl hydrogen peroxide, and the process was otherwise carried out in the same manner as in Example 1 to obtain an acrylic copolymer. Mooney viscosity, metal ion residue, normal physical properties of the crosslinked acrylic copolymer, and compression set were performed in the same manner as in Example 1, and the results are shown in Table 1.

[0162] [Comparative Example 1]

[0163] Except for changing the salting-out agent from sodium sulfate to magnesium sulfate, the same method as in Example 1 was used to obtain the acrylic copolymer. Mooney viscosity, metal ion residue, normal physical properties of the crosslinked acrylic copolymer, and compression set were tested in the same manner as in Example 1, and the results are shown in Table 1.

[0164] [Comparative Example 2]

[0165] Except for changing the salting-out agent from sodium sulfate to calcium chloride, the same method as in Example 1 was used to obtain the acrylic copolymer. Mooney viscosity, metal ion residue, normal physical properties of the crosslinked acrylic copolymer, and compression set were performed in the same manner as in Example 1, and the results are shown in Table 1.

[0166] [Example 3]

[0167] Except for changing ethyl acrylate to 394 parts by mass and butyl acrylate to 0 parts by mass, the same method as in Example 1 was used to obtain the acrylic copolymer. Mooney viscosity measurement, metal ion residue measurement, capillary flow test, normal physical property test of the acrylic copolymer crosslinker, and compression set test were performed in the same manner as in Example 1, and the results are shown in Table 2.

[0168] [Comparative Example 3]

[0169] The polymerization initiator, tert-amyl hydrogen peroxide, was replaced with ammonium persulfate. Otherwise, the process was carried out in the same manner as in Example 1 to obtain the acrylic copolymer. Mooney viscosity, metal ion residue, capillary flow, normal physical properties of the crosslinked acrylic copolymer, and compression set were performed in the same manner as in Example 1, and the results are shown in Table 2.

[0170] [Comparative Example 4]

[0171] The polymerization initiator was changed from tert-amyl hydrogen peroxide to hydrogen peroxide, and otherwise the process was carried out in the same manner as in Example 1 to obtain an acrylic copolymer. Mooney viscosity, metal ion residue, capillary flow, normal physical properties of the crosslinked acrylic copolymer, and compression set were performed in the same manner as in Example 1, and the results are shown in Table 2.

[0172] [Comparative Example 5]

[0173] The polymerization initiator was changed from tert-amyl hydrogen peroxide to tert-butyl hydrogen peroxide, and the process was otherwise carried out in the same manner as in Example 1 to obtain an acrylic copolymer. Mooney viscosity, metal ion residue, capillary flow, normal physical properties of the crosslinked acrylic copolymer, and compression set were performed in the same manner as in Example 1, and the results are shown in Table 2.

[0174] [Table 1]

[0175]

[0176] [Table 2]

[0177]

[0178] According to Table 1, salting out with a monovalent metal salt improved compression set. Furthermore, Table 2 shows that acrylic copolymers using a tert-amyl polymerization initiator, compared to commonly used polymerization initiators, exhibited reduced elongation viscosity in the high elongation velocity region, resulting in further improved processability.

[0179] Industrial availability

[0180] The acrylic copolymers of this invention can be widely used as rubber products exhibiting excellent processability and low compressive strain. In particular, crosslinked products made using the acrylic copolymers of this invention are effective for industrial rubber materials and / or automotive rubber materials requiring excellent processability and low compressive strain, such as oil seals, engine gaskets, fuel hoses, gas hoses, and O-rings.

Claims

1. An acrylic copolymer comprising at least structural units derived from alkyl acrylates, structural units derived from crosslinking monomers, and structural units derived from polymerization initiators, said acrylic copolymer further satisfying conditions (A) and (B). (A) The structural unit derived from the polymerization initiator is derived from the structural unit of the compound represented by formula (1) or formula (2) below. in, n is a natural number, 1≤n≤4; (B) The residual amount of monovalent metal ions in the acrylic copolymer is more than 30 ppm by mass and less than 5000 ppm by mass, the residual amount of divalent or higher metal ions is less than 300 ppm by mass, and the ratio of the residual amount of monovalent metal ions to the residual amount of divalent or higher metal ions ([residual amount of monovalent metal ions] / [residual amount of divalent or higher metal ions]) is more than 10.

2. The acrylic copolymer according to claim 1, wherein, Relative to 100% by mass of the acrylic copolymer, the content of structural units derived from alkyl acrylates is 50% to 99.8% by mass, the content of structural units derived from crosslinking monomers is 0.1% to 10% by mass, and the content of structural units derived from polymerization initiators is 0.001% to 2% by mass.

3. The acrylic copolymer according to claim 1, wherein, The content of structural units derived from alkyl acrylates is 0-100% by mass relative to 100% by mass of the structural units derived from alkyl acrylates having 1 to 3 carbon atoms, and / or the content of structural units derived from alkyl acrylates having 4 to 6 carbon atoms is 0-100% by mass.

4. The acrylic copolymer according to claim 1, wherein, The structural units derived from crosslinking monomers are structural units derived from crosslinking monomers with carboxyl groups.

5. A composition containing an acrylic copolymer, wherein the acrylic copolymer according to any one of claims 1 to 4 contains at least a crosslinking agent.

6. An acrylic rubber crosslinker, which is formed by crosslinking the composition containing the acrylic copolymer as described in claim 5.

7. A method for manufacturing an acrylic copolymer, comprising the method for manufacturing an acrylic copolymer according to claim 1, wherein: In the emulsion polymerization process, an emulsifier is used to emulsion polymerize an acrylic copolymer component comprising at least an alkyl acrylate, a crosslinking monomer, and an alkyl polymerization initiator, thereby obtaining an emulsion polymer solution; In the salting-out process, 0.01 to 10 parts by weight of a monovalent metal salt are used to salt out 100 parts by weight of the emulsion polymerization liquid to obtain water-containing particles; The water washing process is used to clean the water-containing particles; and The drying process involves drying the cleaned, water-containing granules.

8. The method for manufacturing the acrylic copolymer according to claim 7, wherein, The monovalent metal salt is at least one selected from the group consisting of sodium sulfate, sodium acetate, and sodium carbonate.

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