Acrylic rubber, rubber compositions, and rubber crosslinked products

Abstract

This acrylic rubber contains: at least one type of cross-linkable group-containing monomer unit selected from the group consisting of carboxyl group-containing monomer units, halogen atom-containing monomer units, and epoxy group-containing monomer units; and (meth)acrylamide monomer units, wherein the content of the (meth)acrylamide monomer units is 0.2-17.5 wt% of all monomer units.

Description

[Technical Field]

[0001] The present invention relates to acrylic rubber, rubber compositions, and rubber crosslinked products, and more particularly to acrylic rubber that can provide rubber crosslinked products with excellent processability and excellent elongation at break and tensile strength, and to rubber compositions and rubber crosslinked products obtained using such acrylic rubber. [Background technology]

[0002] Acrylic rubber is a polymer whose main components are units derived from (meth)acrylic acid ester monomers, such as alkyl (meth)acrylate monomers and alkoxyalkyl (meth)acrylate monomers. It is generally known as a rubber with excellent heat resistance, oil resistance, and ozone resistance, and is widely used in fields such as automobiles.

[0003] Such acrylic rubber is typically produced by emulsion polymerization of monomer components mainly consisting of (meth)acrylic acid ester monomers, such as alkyl (meth)acrylate monomers or alkoxyalkyl (meth)acrylate monomers, adding a coagulant to the resulting emulsion polymerization solution to solidify it, and then drying the resulting hydrated crumb (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 7-145291 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, conventional acrylic rubbers, such as the acrylic rubber described in Patent Document 1, tend to stick to the roll when various compounding agents are added using a roll, resulting in insufficient processability when processing with a roll.

[0006] This invention has been made in view of the above circumstances, and aims to provide acrylic rubber that has excellent processability and can provide a rubber crosslinked product with excellent elongation at break and tensile strength, a rubber composition obtained using such acrylic rubber, and a rubber crosslinked product. [Means for solving the problem]

[0007] As a result of diligent research to achieve the above objective, the inventors have discovered that the above objective can be achieved in an acrylic rubber containing at least one crosslinkable group-containing monomer unit selected from the group consisting of carboxyl group-containing monomer units, halogen atom-containing monomer units, and epoxy group-containing monomer units, and (meth)acrylamide monomer units, by setting the content of the (meth)acrylamide monomer unit in the total monomer units to 0.2 to 17.5% by weight, thereby completing the present invention.

[0008] In other words, the present invention provides an acrylic rubber containing at least one crosslinkable group-containing monomer unit selected from the group consisting of carboxyl group-containing monomer units, halogen atom-containing monomer units, and epoxy group-containing monomer units, and (meth)acrylamide monomer units, wherein the content of the (meth)acrylamide monomer units in the total monomer units is 0.2 to 17.5% by weight. In the acrylic rubber of the present invention, it is preferable that the content of the (meth)acrylamide monomer unit in the total monomer unit is 1 to 15% by weight. In the acrylic rubber of the present invention, it is preferable that the crosslinkable group-containing monomer unit is the carboxyl group-containing monomer unit.

[0009] According to the present invention, a rubber composition is provided that contains a rubber component including the acrylic rubber described above and a crosslinking agent. Furthermore, according to the present invention, a crosslinked rubber product is provided, which is obtained by crosslinking the rubber composition described above. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide acrylic rubber that has excellent processability and can yield a rubber crosslinked product with excellent elongation at break and tensile strength, a rubber composition obtained using such acrylic rubber, and a rubber crosslinked product. [Modes for carrying out the invention]

[0011] <Acrylic rubber> The acrylic rubber of the present invention is an acrylic rubber containing at least one crosslinkable group-containing monomer unit selected from the group consisting of carboxyl group-containing monomer units, halogen atom-containing monomer units, and epoxy group-containing monomer units, and (meth)acrylamide monomer units, wherein the content of the (meth)acrylamide monomer units in the total monomer units is in the range of 0.2 to 17.5% by weight.

[0012] The acrylic rubber of the present invention is a rubbery polymer that contains (meth)acrylic acid ester monomers [meaning acrylic acid ester monomers and / or methacrylic acid ester monomers; hereinafter the same applies to methyl (meth)acrylate] units as the main component (preferably 30% by weight or more of the total monomer units constituting the acrylic rubber) in its molecule.

[0013] The (meth)acrylic acid ester monomers that form the (meth)acrylic acid ester monomer units, which are the main components of the acrylic rubber of the present invention, are not particularly limited, but examples include alkyl (meth)acrylic acid ester monomers and alkoxyalkyl (meth)acrylic acid ester monomers.

[0014] The alkyl (meth)acrylate monomer is not particularly limited, but an ester of an alkanol having 1 to 12 carbon atoms and (meth)acrylic acid (a (meth)acrylic acid ester having an alkyl group having 1 to 12 carbon atoms) is preferred, an ester of an alkanol having 1 to 8 carbon atoms and (meth)acrylic acid (a (meth)acrylic acid ester having an alkyl group having 1 to 8 carbon atoms) is more preferred, and an ester of an alkanol having 2 to 6 carbon atoms and (meth)acrylic acid (a (meth)acrylic acid ester having an alkyl group having 2 to 6 carbon atoms) is even more preferred.

[0015] Specific examples of alkyl (meth)acrylate monomers include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and cyclohexyl (meth)acrylate. Among these, ethyl (meth)acrylate and n-butyl (meth)acrylate are preferred, and ethyl acrylate and n-butyl acrylate are more preferred. These can be used individually or in combination of two or more. In particular, it is preferable to use ethyl acrylate and n-butyl acrylate in combination, and the weight ratio of "ethyl acrylate units: n-butyl acrylate units" is preferably 20:80 to 80:20, and more preferably 40:60 to 60:40.

[0016] (Meth)acrylic acid alkoxyalkyl ester monomers are not particularly limited, but esters of alkoxyalkyl alcohols having 2 to 12 carbon atoms and (meth)acrylic acid ((meth)acrylic acid esters having an alkoxyalkyl group having 2 to 12 carbon atoms) are preferred, esters of alkoxyalkyl alcohols having 2 to 8 carbon atoms and (meth)acrylic acid ((meth)acrylic acid esters having an alkoxyalkyl group having 2 to 8 carbon atoms) are more preferred, and esters of alkoxyalkyl alcohols having 2 to 6 carbon atoms and (meth)acrylic acid ((meth)acrylic acid esters having an alkoxyalkyl group having 2 to 6 carbon atoms) are even more preferred.

[0017] Specific examples of the (meth)acrylic acid alkoxyalkyl ester monomer include methoxymethyl (meth)acrylate, ethoxymethyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-propoxyethyl (meth)acrylate, 2-butoxyethyl (meth)acrylate, 3-methoxypropyl (meth)acrylate, and 4-methoxybutyl (meth)acrylate. Among these, 2-ethoxyethyl (meth)acrylate and 2-methoxyethyl (meth)acrylate are preferred, and 2-ethoxyethyl acrylate and 2-methoxyethyl acrylate are particularly preferred. These can be used alone or in combination of two or more.

[0018] The content of the (meth)acrylic acid ester monomer unit in all monomer units constituting the acrylic rubber of the present invention is preferably 50% by weight or more, more preferably 60% by weight or more, still more preferably 70 to 99.79% by weight, even more preferably 80 to 99.5% by weight, and particularly preferably 90 to 99% by weight. If the content of the (meth)acrylic acid ester monomer unit is too small, the weather resistance, heat resistance, and oil resistance of the obtained rubber crosslinked product may decrease.

[0019] The acrylic rubber of the present invention contains, in addition to (meth)acrylate monomer units, at least one crosslinkable group-containing monomer unit selected from the group consisting of carboxyl group-containing monomer units, halogen atom-containing monomer units, and epoxy group-containing monomer units. From the viewpoint of crosslinkability, carboxyl group-containing monomer units and halogen atom-containing monomer units are preferred as the crosslinkable group-containing monomer units, and carboxyl group-containing monomer units are more preferred.

[0020] The carboxyl group-containing monomer that forms the carboxyl group-containing monomer unit may be any monomer having a carboxyl group and is not particularly limited. For example, α,β-ethylenically unsaturated monocarboxylic acids, α,β-ethylenically unsaturated dicarboxylic acids, and α,β-ethylenically unsaturated dicarboxylic acid monoesters can be mentioned. By using an α,β-ethylenically unsaturated carboxylic acid monomer, the acrylic rubber can be made into a carboxyl group-containing acrylic rubber having a carboxyl group as a crosslinking point, thereby further enhancing the compression set resistance when it is made into a rubber crosslinked product.

[0021] The α,β-ethylenically unsaturated monocarboxylic acid is not particularly limited, but an α,β-ethylenically unsaturated monocarboxylic acid having 3 to 12 carbon atoms is preferred. Specific examples thereof include acrylic acid, methacrylic acid, α-ethylacrylic acid, crotonic acid, and cinnamic acid. The α,β-ethylenically unsaturated dicarboxylic acid is not particularly limited, but an α,β-ethylenically unsaturated dicarboxylic acid having 4 to 12 carbon atoms is preferred. Specific examples thereof include butenedioic acids such as fumaric acid and maleic acid; itaconic acid; citraconic acid; chloromaleic acid; and the like. The α,β-ethylenically unsaturated dicarboxylic acid monoester is not particularly limited, but a monoester of an α,β-ethylenically unsaturated dicarboxylic acid having 4 to 12 carbon atoms and an alkanol having 1 to 12 carbon atoms is preferred, a monoester of an α,β-ethylenically unsaturated dicarboxylic acid having 4 to 6 carbon atoms and an alkanol having 2 to 8 carbon atoms is more preferred, and a monoester of butensionic acid having 4 carbon atoms and an alkanol having 2 to 6 carbon atoms is even more preferred. Specific examples of α,β-ethylenically unsaturated dicarboxylic acid monoesters include monochain alkyl esters of butendionate such as monomethyl fumarate, monoethyl fumarate, mono-n-butyl fumarate, monomethyl maleate, monoethyl maleate, and mono-n-butyl maleate; monocyclic butendionate monoesters having an alicyclic structure such as monocyclopentyl fumarate, monocyclohexyl fumarate, monocyclohexenyl fumarate, monocyclopentyl maleate, monocyclohexyl maleate, and monocyclohexenyl maleate; and monoesters of itaconic acid such as monomethyl itaconicate, monoethyl itaconicate, mono-n-butyl itaconicate, and monocyclohexyl itaconicate.

[0022] Among these, α,β-ethylenically unsaturated dicarboxylic acid monoesters are preferred, but butendionate monochain alkyl esters or butendionate monoesters having an alicyclic structure are more preferred, mono-n-butyl fumarate, mono-n-butyl maleate, monocyclohexyl fumarate, and monocyclohexyl maleate are even more preferred, and mono-n-butyl fumarate is particularly preferred. These α,β-ethylenically unsaturated carboxylic acid monomers can be used individually or in combination of two or more. Note that among the above monomers, dicarboxylic acids also exist as anhydrides.

[0023] The halogen atom-containing monomers that form halogen atom-containing monomer units are not particularly limited, but examples include unsaturated alcohol esters of halogen-containing saturated carboxylic acids, (meth)acrylate haloalkyl esters, (meth)acrylate haloacyloxyalkyl esters, (meth)acrylate (haloacetylcarbamoyloxy)alkyl esters, halogen-containing unsaturated ethers, halogen-containing unsaturated ketones, halomethyl group-containing aromatic vinyl compounds, halogen-containing unsaturated amides, and haloacetyl group-containing unsaturated monomers. It is preferable that the monomer containing a halogen atom contains a chlorine atom as the halogen atom.

[0024] Specific examples of unsaturated alcohol esters of halogen-containing saturated carboxylic acids include vinyl monochloroacetate, vinyl 2-chloropropionate, and allyl chloroacetate. Specific examples of (meth)acrylate haloalkyl esters include chloromethyl (meth)acrylate, 1-chloroethyl (meth)acrylate, 2-chloroethyl (meth)acrylate, 1,2-dichloroethyl (meth)acrylate, 2-chloropropyl (meth)acrylate, 3-chloropropyl (meth)acrylate, and 2,3-dichloropropyl (meth)acrylate. Specific examples of (meth)acrylate haloasiloxyalkyl esters include 2-(chloroacetoxy)ethyl (meth)acrylate, 2-(chloroacetoxy)propyl (meth)acrylate, 3-(chloroacetoxy)propyl (meth)acrylate, and 3-(hydroxychloroacetoxy)propyl (meth)acrylate. Specific examples of (meth)acrylate (haloacetylcarbamoyloxy)alkyl esters include 2-(chloroacetylcarbamoyloxy)ethyl (meth)acrylate and 3-(chloroacetylcarbamoyloxy)propyl (meth)acrylate.

[0025] Specific examples of halogen-containing unsaturated ethers include chloromethyl vinyl ether, 2-chloroethyl vinyl ether, 3-chloropropyl vinyl ether, 2-chloroethyl allyl ether, and 3-chloropropyl allyl ether. Specific examples of halogen-containing unsaturated ketones include 2-chloroethyl vinyl ketone, 3-chloropropyl vinyl ketone, and 2-chloroethyl allyl ketone. Specific examples of halomethyl group-containing aromatic vinyl compounds include p-chloromethylstyrene, m-chloromethylstyrene, o-chloromethylstyrene, and p-chloromethyl-α-methylstyrene.

[0026] Specific examples of halogen-containing unsaturated amides include N-chloromethyl(meth)acrylamide. Specific examples of haloacetyl group-containing unsaturated monomers include 3-(hydroxychloroacetoxy)propyl allyl ether and p-vinylbenzylchloroacetic acid.

[0027] These halogen atom-containing monomers can be used individually or in combination of two or more. Among these halogen atom-containing monomers, unsaturated alcohol esters of halogen-containing saturated carboxylic acids are preferred, and vinyl monochloroacetate is more preferred.

[0028] The epoxy group-containing monomers that form epoxy group-containing monomer units are not particularly limited, but examples include epoxy group-containing (meth)acrylic acid esters such as glycidyl (meth)acrylate; epoxy group-containing ethers such as allyl glycidyl ether and vinyl glycidyl ether; and the like. These epoxy group-containing monomers can be used individually or in combination of two or more. Among these epoxy group-containing monomers, epoxy group-containing (meth)acrylic acid esters are preferred, and glycidyl methacrylate is more preferred.

[0029] The content of crosslinkable group-containing monomer units in the total monomer units constituting the acrylic rubber of the present invention is preferably 0.01% by weight or more, more preferably 0.01 to 20% by weight, even more preferably 0.1 to 10% by weight, even more preferably 0.5 to 5% by weight, and particularly preferably 1 to 3% by weight. By setting the content of crosslinkable group-containing monomer units within the above range, the resulting crosslinked rubber can be made to have excellent tensile strength and elongation at break while more appropriately improving resistance to compression set.

[0030] The acrylic rubber of the present invention contains (meth)acrylamide monomer units in addition to (meth)acrylic acid ester monomer units as the main component and the crosslinkable group-containing monomer units described above. Either acrylamide or methacrylamide can be used as the (meth)acrylamide monomer, but acrylamide is preferred. Furthermore, acrylamide and methacrylamide may be used in combination.

[0031] The content of (meth)acrylamide monomer units in the total monomer units constituting the acrylic rubber of the present invention is 0.2 to 17.5% by weight, preferably 1 to 15% by weight, and more preferably 2 to 10% by weight. By setting the content of (meth)acrylamide monomer units within the above range, it is possible to improve the processability of the acrylic rubber composition while maintaining good tensile strength and elongation at break of the resulting crosslinked rubber product. If the content of (meth)acrylamide monomer units is less than the above range, or if the acrylic rubber does not contain any (meth)acrylamide monomer units, adhesion to the roll surface occurs when kneaded with a roll, resulting in poor processability, and the resulting crosslinked rubber product will have poor elongation at break and tensile strength. Conversely, if the content of (meth)acrylamide monomer units is more than the above range, the polymer becomes water-soluble, making it difficult to recover the acrylic rubber by solidification and resulting in poor water resistance.

[0032] Furthermore, the acrylic rubber of the present invention may have, in addition to (meth)acrylic acid ester monomer units, crosslinkable group-containing monomer units, and (meth)acrylamide monomer units, other monomer units copolymerizable with these. Examples of such copolymerizable monomers are not particularly limited, but include aromatic vinyl monomers, α,β-ethylenically unsaturated nitrile monomers, α,β-ethylenically unsaturated dicarboxylic acid diester monomers, diene monomers, unconjugated diene monomers, and other olefin monomers.

[0033] Examples of aromatic vinyl monomers include styrene, α-methylstyrene, and divinylbenzene.

[0034] Examples of α,β-ethylenically unsaturated nitrile monomers include acrylonitrile and methacrylonitrile. Examples of α,β-ethylenically unsaturated dicarboxylic acid diester monomers include dialkyl maleate esters such as dimethyl maleate and di-n-butyl maleate, where the alkyl group has 1 to 18 carbon atoms; dialkyl fumarate esters such as dimethyl fumarate and di-n-butyl fumarate, where the alkyl group has 1 to 18 carbon atoms; dicycloalkyl maleate esters such as dicyclopentyl maleate and dicyclohexyl maleate, where the cycloalkyl group has 4 to 16 carbon atoms; dicycloalkyl fumarate esters such as dicyclopentyl fumarate and dicyclohexyl fumarate, where the cycloalkyl group has 4 to 16 carbon atoms; dialkyl itaconate esters such as dimethyl itaconate and di-n-butyl itaconate, where the alkyl group has 1 to 18 carbon atoms; and dicycloalkyl itaconate esters such as dicyclohexyl itaconate, where the cycloalkyl group has 4 to 16 carbon atoms. Other olefin monomers include ethylene, propylene, vinyl chloride, vinylidene chloride, vinyl acetate, ethyl vinyl ether, and butyl vinyl ether.

[0035] Examples of diene monomers include conjugated diene monomers and unconjugated diene monomers. Specific examples of conjugated diene monomers include 1,3-butadiene, isoprene, and piperine. Specific examples of non-conjugated diene monomers include ethylidene norbornene, dicyclopentadiene, dicyclopentadienyl (meth)acrylate, and 2-dicyclopentadienylethyl (meth)acrylate.

[0036] Among these copolymerizable monomers, styrene, acrylonitrile, methacrylonitrile, ethylene, and vinyl acetate are preferred, with acrylonitrile, methacrylonitrile, and ethylene being more preferred.

[0037] Other copolymerizable monomers can be used individually or in combination of two or more. The content of these copolymerizable monomer units in the monomer units constituting the acrylic rubber of the present invention is preferably 49.9% by weight or less, more preferably 29.9% by weight or less, even more preferably 15% by weight or less, even more preferably 9% by weight or less, and particularly preferably 4.5% by weight or less.

[0038] Furthermore, if the acrylic rubber of the present invention contains other copolymerizable monomer units, the content thereof may be within the above range, but in particular, if it contains ethylene units, the content of ethylene units in the monomer units constituting the acrylic rubber of the present invention is preferably 9% by weight or less, and more preferably 4.5% by weight or less. Similarly, if the acrylic rubber of the present invention contains acrylonitrile units or methacrylonitrile units, the total content of acrylonitrile units and methacrylonitrile units is preferably 9% by weight or less, and more preferably 4.5% by weight or less.

[0039] The acrylic rubber of the present invention preferably contains a phenolic antioxidant as an anti-aging agent. The phenolic antioxidant can be any compound having a phenolic structure (i.e., a structure having a benzene ring and an OH group bonded to the benzene ring), and is not particularly limited. Examples of phenolic antioxidants include double-hindered phenolic antioxidants, semi-hindered phenolic antioxidants, less-hindered phenolic antioxidants, and phenolic antioxidants without a hindered group.

[0040] Double-hindered phenolic antioxidants are phenolic compounds in which both the 2nd and 6th positions (i.e., the two ortho positions) of the OH group (phenolic hydroxyl group) constituting the phenolic structure are hindered groups. The hindered group can be any bulky group and is not particularly limited, but examples include substituents with four or more carbon atoms. Specific examples of hindered groups include tertiary alkyl groups such as t-butyl, t-pentyl, and t-hexyl groups; secondary alkyl groups such as sec-butyl and sec-pentyl groups; branched primary alkyl groups such as i-butyl and i-pentyl groups; cycloalkyl groups such as cyclohexyl and cyclopentyl groups; and alkyl groups in which alkylthio groups are substituted so that the total number of carbon atoms is four or more, such as octylthio and octylthiomethyl groups.

[0041] Specific examples of double-hindered phenol-based antioxidants include pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (e.g., trade name "Irganox 1010", manufactured by BASF), 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl) isocyanurate (e.g., trade name "Irganox 3114", manufactured by BASF), 2,4,6-tris(4-hydroxy-3,5-di-tert-butylbenzyl) mesitylene (e.g., trade name "Irganox 1330", manufactured by BASF), and 6-(4-hydroxy-3,5-di-tert-butylanilino)-2,4-bis(octylthio)-1,3,5-triazine (e.g., trade name "Irganox 565 (manufactured by BASF), 2,2'-thiodiethylbis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (for example, trade name "Irganox 1035", manufactured by BASF), 1,2-bis[3-(4-hydroxy-3,5-di-tert-butylphenyl)propionyl]hydrazine (trade name "Irganox MD1024", manufactured by BASF), octyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (trade name "Irganox Examples include "1135" (manufactured by BASF), N,N'-hexamethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanamide] (trade name "Irganox 1098", manufactured by BASF), 1,6-hexanediolbis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (trade name "Irganox 259", manufactured by BASF), and stearyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (trade name "Irganox 1076", manufactured by BASF).

[0042] A semi-hindered phenolic antioxidant is a phenolic compound in which either the 2nd or 6th position of the OH group (phenolic hydroxyl group) constituting the phenol structure is a hindered group, and the other is an alkyl group having 3 or fewer carbon atoms, such as a methyl group (preferably a methyl group).

[0043] Specific examples of semi-hindered phenolic antioxidants include 4,6-bis(octylthiomethyl)-o-cresol (trade name "Irganox 1520L", manufactured by BASF), 1,3,5-tris[[4-(1,1-dimethylethyl)-3-hydroxy-2,6-dimethylphenyl]methyl]-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (trade name "Irganox 1790", manufactured by BASF), and 3,9-bis[2-{3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy}-1,1-dimethylethyl]-2,4,8,10-tetraoxaspiro[5,5 Examples include undecane (for example, trade name "ADEKA Stab AO-80", manufactured by ADEKA Corporation), ethylenebis(oxyethylene)bis[3-(5-tert-butyl-hydroxy-m-tolyl)propionate] (for example, trade name "Irganox 245", manufactured by BASF Corporation), and triethylene glycol bis[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate] (for example, trade name "ADEKA Stab AO-70", manufactured by ADEKA Corporation).

[0044] Furthermore, less hindered phenolic antioxidants are phenolic compounds in which either the 2nd or 6th position of the OH group (phenolic hydroxyl group) constituting the phenol structure is a hindered group, and the other is a hydrogen atom.

[0045] Specific examples of less-hindered phenol-based antioxidants include 1,1,3-tris-(2-methyl-4-hydroxy-5-tert-butylphenyl)butane (e.g., trade name "ADEKA Stab AO-30", manufactured by ADEKA Corporation), 4,4'-butylidenebis(6-t-butyl-3-methylphenol) (e.g., trade name "ADEKA Stab AO-40", manufactured by ADEKA Corporation), and 4,4'-thiobis(6-t-butyl-3-methylphenol) (e.g., trade name "SumiLizer WX-R", manufactured by Sumitomo Chemical Co., Ltd.).

[0046] Phenolic antioxidants can be used individually or in combination of two or more. Among phenolic antioxidants, double-hindered phenolic antioxidants and semi-hindered phenolic antioxidants are preferred, and double-hindered phenolic antioxidants are preferred from the viewpoint of appropriately suppressing the generation of discoloration and odor.

[0047] Furthermore, as a phenolic antioxidant, one with a molecular weight of 470 or less is preferred, one with a molecular weight of 100 to 450 is more preferred, and one with a molecular weight of 150 to 400 is even more preferred. By using a phenolic antioxidant with a molecular weight of 500 or less, the generation of discoloration and odor can be suppressed more effectively.

[0048] The content of the phenolic antioxidant is preferably 0.1 to 5 parts by weight, more preferably 0.2 to 3.0 parts by weight, and even more preferably 0.3 to 2.0 parts by weight, per 100 parts by weight of the acrylic rubber component. By setting the content of the phenolic antioxidant within the above range, discoloration and odor generation can be more effectively suppressed.

[0049] The Mooney viscosity (ML1+4, 100°C) of the acrylic rubber of the present invention is not particularly limited, but is preferably in the range of 10 to 150, more preferably in the range of 20 to 100, and particularly preferably in the range of 25 to 70. By setting the Mooney viscosity within the above range, a high degree of balance can be achieved between the processability and strength characteristics of the acrylic rubber.

[0050] Furthermore, the pH of the acrylic rubber of the present invention is not particularly limited, but is preferably 6 or less, more preferably 2 to 6, even more preferably 2.5 to 5.5, and most preferably 3 to 5. By setting the pH within the above range, the storage stability of the acrylic rubber can be further enhanced.

[0051] Furthermore, the weight-average molecular weight (Mw) of the acrylic rubber of the present invention is not particularly limited, but from the viewpoint of providing good mechanical strength and processability, it is preferably 800,000 or more, more preferably 800,000 to 2,600,000, even more preferably 900,000 to 2,300,000, and particularly preferably 1,000,000 to 2,000,000. Furthermore, the molecular weight distribution of the acrylic rubber is not particularly limited, but the Mw / Mn value is preferably 1.50 to 10.0, more preferably 1.70 to 8.00, even more preferably 2.00 to 6.00, and the Mz / Mw value is preferably 1.30 to 3.00, more preferably 1.45 to 2.70, and even more preferably 1.60 to 2.50. Furthermore, the weight-average molecular weight and molecular weight distribution of acrylic rubber can be determined as absolute molecular weight and absolute molecular weight distribution, for example, by the GPC-MALS method using a GPC (Gel Permeation Chromatography) instrument incorporating a multi-angle laser light scattering photometer (MALS).

[0052] The method for producing the acrylic rubber of the present invention is not particularly limited, and any method may be used, but for example, the following method is preferred. That is, the acrylic rubber can be produced by emulsion polymerization of monomer components containing a (meth)acrylic acid ester monomer, a crosslinkable group-containing monomer, and a (meth)acrylamide monomer in the presence of a polymerization catalyst.

[0053] The monomer components used in emulsion polymerization include the monomers listed above, and the preferred monomers are also as described above. Furthermore, the amount of each monomer used should be appropriately selected so as to fall within the composition range described above.

[0054] For emulsion polymerization, a conventional method can be used, and emulsifiers, polymerization initiators, polymerization inhibitors, etc., can be used according to standard procedures.

[0055] While there are no particular limitations on the emulsifier, phosphate ester salts can be suitably used. As the phosphate ester salt, compounds represented by the following general formula (1) are preferred. [ka] (In the above general formula (1), R 1 R represents a linear or branched alkyl group having 4 to 20 carbon atoms, an alkylphenyl group, or an unsaturated alkyl group having 4 to 20 carbon atoms. 2 represents a linear or branched alkylene group having 2 or 3 carbon atoms, M represents an alkali metal, m is an integer from 1 to 20, and if m is 2 or greater, R 2 It may have multiple different groups, where n is 1 or 2, p is 1 or 2, and n+p is 3.

[0056] In the above general formula (1), R 1 R represents a linear or branched alkyl group having 4 to 20 carbon atoms, an alkylphenyl group, or an unsaturated alkyl group having 4 to 20 carbon atoms. 1 Preferably, the carbon number is 4 or more and 18 or less, more preferably 5 or more and 16 or less, and even more preferably 6 or more and 14 or less. 1 Specific examples include n-octyl group, n-decyl group, n-dodecyl group, n-tridecyl group, n-tetradecyl group, isooctyl group, isotridecyl group, n-octadecyl group, nonylphenyl group, etc.

[0057] In the above general formula (1), R 2 R represents a linear or branched alkylene group having 2 or 3 carbon atoms. 2 Specific examples include ethylene groups and propylene groups, with ethylene groups being more preferred among them.

[0058] In the general formula (1) above, M represents an alkali metal, and specific examples of M include sodium, potassium, lithium, rubidium, and cesium. Among these, sodium and potassium are preferred as M.

[0059] In the above general formula (1), m is an integer of 1 to 20, preferably an integer of 2 or more and 15 or less, more preferably an integer of 2 or more and 13 or less, and even more preferably an integer of 2 or more and 11 or less. When m is 2 or more, R 2 may have a plurality of different groups. That is, for example, R 2 may have both an ethylene group and a propylene group.

[0060] In the above general formula (1), n is 1 or 2, preferably 1. Also, p is 1 or 2, preferably 2. Note that n + p is 3.

[0061] These phosphate esters can be used alone, or in combination of two or more different ones in terms of the number n, or in combination of two or more with different ester species. Among these combinations, a mixture of different phosphate esters in terms of the number n is preferred, and a mixture of different phosphate esters in terms of the number n with the same ester species is more preferred. Note that the mixing ratio in the mixture of different phosphate esters in terms of the number n is not particularly limited. The usage amount of the phosphate ester is preferably 0.01 to 10 parts by weight, more preferably 0.1 to 5 parts by weight, and even more preferably 1 to 3 parts by weight based on 100 parts by weight of the monomer component used in the polymerization.

[0062] Examples of phosphate ester salts represented by the above general formula (1) include octyloxydi(oxyethylene) phosphate, dodecyloxydi(oxyethylene) phosphate, tridecyloxytri(oxyethylene) phosphate, hexyloxytetra(oxyethylene) phosphate, heptylhexaoxytetra(oxyethylene) phosphate, octyloxytetra(oxyethylene) phosphate, nonyloxytetra(oxyethylene) phosphate, decyloxytetra(oxyethylene) phosphate, decyloxytetra(oxyethylene) phosphate, and octadecyl Examples include alkali metal salts (e.g., Na salts, K salts, etc.) of oxytetra(oxyethylene) phosphate, nonylphenyloxytetra(oxyethylene) phosphate, tridecyloxytetra(oxyethylene) phosphate, octyloxyhexa(oxyethylene) phosphate, decyloxyhexa(oxyethylene) phosphate, tridecyloxyhexa(oxyethylene) phosphate, nonylphenyloxyhexa(oxyethylene) phosphate, octadecyloxyhepta(oxyethylene) phosphate, and tridecyloxydeca(oxyethylene) phosphate. The structure of the hydrophobic group of these phosphate ester salts is not limited and may be linear or branched, and may include an unsaturated structure.

[0063] Furthermore, in the present invention, emulsifiers other than phosphate ester salts can be used together with or in place of phosphate ester salts. Examples of emulsifiers other than phosphate ester salts include anionic emulsifiers other than phosphate ester salts, cationic emulsifiers, and nonionic emulsifiers. Among these, anionic emulsifiers other than phosphate ester salts and nonionic emulsifiers are preferred, and it is preferable to use an anionic emulsifier other than phosphate ester salts and a nonionic emulsifier in combination.

[0064] Anionic emulsifiers other than phosphate ester salts are not particularly limited, but include, for example, salts of fatty acids such as myristic acid, palmitic acid, oleic acid, and linolenic acid; alkylbenzene sulfonates such as sodium dodecylbenzenesulfonate; sulfate esters such as sodium lauryl sulfate; and alkyl sulfosuccinates.

[0065] Cationic emulsifiers are not particularly limited, but examples include alkyltrimethylammonium chloride, dialkylammonium chloride, and benzylammonium chloride.

[0066] Nonionic emulsifiers are not particularly limited, but examples include polyoxyalkylene fatty acid esters such as polyoxyethylene stearate; polyoxyalkylene alkyl ethers such as polyoxyethylene dodecyl ether; polyoxyalkylene alkylphenol ethers such as polyoxyethylene nonylphenyl ether; and polyoxyethylene sorbitan alkyl esters. Among these, polyoxyalkylene alkyl ethers and polyoxyalkylene alkylphenol ethers are preferred, and polyoxyethylene alkyl ethers and polyoxyethylene alkylphenol ethers are more preferred.

[0067] Emulsifiers other than phosphate ester salts can be used individually or in combination of two or more.

[0068] The amount of emulsifier used is preferably 0.01 to 10 parts by weight, more preferably 0.1 to 5 parts by weight, and even more preferably 1 to 3 parts by weight, relative to 100 parts by weight of monomer components used for polymerization. Furthermore, when an anionic emulsifier other than a phosphate ester salt is used in combination with a nonionic emulsifier, the amount of nonionic emulsifier used is more than 0 parts by weight and 4 parts by weight or less, preferably 0.1 to 3 parts by weight, more preferably 0.5 to 2 parts by weight, and even more preferably 0.7 to 1.7 parts by weight, relative to 100 parts by weight of monomer components used for polymerization. The amount of anionic emulsifier other than a phosphate ester salt used is more than 0 parts by weight and 4 parts by weight or less, preferably 0.1 to 3 parts by weight, more preferably 0.5 to 2 parts by weight, and even more preferably 0.35 to 0.75 parts by weight, relative to 100 parts by weight of monomer components used for polymerization. Furthermore, when using an anionic emulsifier other than a phosphate ester salt in combination with a nonionic emulsifier, the preferred usage ratio is 1 / 99 to 99 / 1 by weight of the nonionic emulsifier / anionic emulsifier other than a phosphate ester salt, more preferably 10 / 90 to 80 / 20, even more preferably 25 / 75 to 75 / 25, even more preferably 50 / 50 to 75 / 25, and particularly preferably 65 / 35 to 75 / 25.

[0069] In emulsion polymerization, it is preferable to first emulsify the monomer component mainly composed of (meth)acrylic acid ester with water and an emulsifier to obtain an emulsion, and then emulsion polymerize the obtained emulsion in the presence of a polymerization catalyst. In this case, there are no particular limitations on the method of emulsifying the monomer component mainly composed of (meth)acrylic acid ester with water and an emulsifier, but a method of mixing the monomer component, water and emulsifier is preferred, and a method of stirring the monomer component, water and emulsifier using a stirrer such as a homogenizer or a disk turbine is more preferred.

[0070] The amount of water used when emulsifying the monomer components is preferably 5 to 500 parts by weight, more preferably 10 to 300 parts by weight, and even more preferably 20 to 200 parts by weight, per 100 parts by weight of the monomer components used for polymerization.

[0071] The polymerization catalyst is not particularly limited, and any catalyst commonly used in emulsion polymerization can be used without restriction. For example, a redox catalyst consisting of a radical generator and a reducing agent can be used as the polymerization catalyst.

[0072] Examples of radical generators include peroxides and azo compounds, with peroxides being preferred among these. Either inorganic or organic peroxides may be used.

[0073] Examples of inorganic peroxides include sodium persulfate, potassium persulfate, hydrogen peroxide, and ammonium persulfate. Among these, potassium persulfate, hydrogen peroxide, and ammonium persulfate are preferred, with potassium persulfate being particularly preferred.

[0074] Examples of organic peroxides include 2,2-di(4,4-di-(t-butylperoxy)cyclohexyl)propane, 1-di-(t-hexylperoxy)cyclohexane, 1,1-di-(t-butylperoxy)cyclohexane, 4,4-di-(t-butylperoxy)n-butyl valerate, 2,2-di-(t-butylperoxy)butane, t-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, paramentane hydroperoxide, benzoyl peroxide, and 1,1,3,3-butyl peroxide. Traethylbutyl hydroperoxide, t-butylcumyl peroxide, di-t-butyl peroxide, di-t-hexyl peroxide, di(2-t-butylperoxyisopropyl)benzene, dicumyl peroxide, diisobutyryl peroxide, di(3,5,5-trimethylhexanoyl) peroxide, dilauroyl peroxide, disuccinate peroxide, dibenzoyl peroxide, di(3-methylbenzoyl) peroxide, benzoyl(3-methylbenzoyl) peroxide, diisobutyryl peroxide Peroxide, di-n-propyl peroxydicarbonate, di(2-ethylhexyl)peroxydicarbonate, di-sec-butyl peroxydicarbonate, 1,1,3,3-tetramethylbutyl peroxyneodecanate, t-hexyl peroxypivalate, t-butyl peroxyneodecanate, t-hexyl peroxypivalate, t-butyl peroxypivalate, 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane, 1,1,3,3-tetramethylbutyl peroxy-2-ethylhexanate, t-hex Examples include peroxy-2-ethylhexanate, t-butyl peroxy-3,5,5-trimethylhexanate, t-hexyl peroxyisopropyl monocarbonate, t-butyl peroxyisopropyl monocarbonate, t-butyl peroxy-2-ethylhexyl monocarbonate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-butyl peroxyacetate, t-hexyl peroxybenzoate, t-butyl peroxybenzoate, and 2,5-dimethyl-2,5-di(t-butylperoxy)hexane.Among these, diisopropylbenzene hydroperoxide, cumene hydroperoxide, paramentane hydroperoxide, and benzoyl peroxide are preferred.

[0075] Examples of azo compounds include azobisisobutyronitrile, 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis[2-(2-imidazolin-2-yl)propane, 2,2'-azobis(propane-2-carbomidine), 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropanamide], 2,2'-azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane}, 2,2'-azobis(1-imino-1-pyrrolidino-2-methylpropane), and 2,2'-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propanamide}.

[0076] These radical generators can be used individually or in combination of two or more. The amount of radical generator used is preferably 0.0001 to 5 parts by weight, more preferably 0.0005 to 1 part by weight, and even more preferably 0.001 to 0.5 parts by weight, per 100 parts by weight of monomer components used for polymerization.

[0077] The reducing agent used in combination with the radical generator can be any reducing agent that is used as a redox catalyst in emulsion polymerization. It is preferable to use at least two reducing agents, and among these, a combination of a metal ion compound in a reduced state and another reducing agent is preferred.

[0078] The metal ion compound in the reduced state is not particularly limited, but examples include ferrous sulfate, sodium ferric hexamethylenediaminetetraacetate, and cuprous naphthenate. Among these, ferrous sulfate is preferred.

[0079] The metal ion compounds in the reduced state can be used individually or in combination of two or more. The amount of metal ion compounds in the reduced state used is preferably in the range of 0.000001 to 0.01 parts by weight, more preferably 0.00001 to 0.001 parts by weight, and even more preferably 0.00005 to 0.0005 parts by weight, per 100 parts by weight of monomer components used for polymerization.

[0080] Reducing agents other than metal ion compounds in a reduced state are not particularly limited, but include, for example, ascorbic acid or its salts, such as ascorbic acid, sodium ascorbate, potassium ascorbate; erythorbic acid or its salts, such as erythorbic acid, sodium erythorbate, potassium erythorbate; sulfinates such as sodium hydroxymethanesulfinate (sodium formaldehyde sulfoxylate); sulfites of sodium sulfite, potassium sulfite, sodium bisulfite, aldehyde sodium bisulfite, potassium bisulfite; pyrosulfites such as sodium pyrosulfite, potassium pyrosulfite, sodium pyrosulfite, potassium pyrosulfite; thiosulfates such as sodium thiosulfate, potassium thiosulfate; phosphorous acid or its salts, such as phosphorous acid, sodium phosphite, potassium phosphite, sodium bisulfite, potassium bisulfite; pyrosulfites or its salts, such as pyrosulfite, sodium pyrosulfite, potassium pyrosulfite, sodium pyrosulfite, potassium pyrosulfite; and others. Among these, ascorbic acid or its salts, and sodium hydroxymethanesulfinate (sodium formaldehyde sulfoxylate) are preferred, with ascorbic acid or its salts being particularly preferred.

[0081] Reducing agents other than metal ion compounds in a reduced state can be used individually or in combination of two or more. The amount of reducing agent other than metal ion compounds in a reduced state used is preferably 0.001 to 1 part by weight, more preferably 0.005 to 0.5 parts by weight, and even more preferably 0.01 to 0.3 parts by weight, per 100 parts by weight of monomer components used for polymerization.

[0082] Preferred combinations of a metal ion compound in a reduced state and a reducing agent other than a metal ion compound in a reduced state include ferrous sulfate and ascorbic acid or its salt and / or sodium hydroxymethanesulfinate (sodium formaldehyde sulfoxylate), more preferably ferrous sulfate and ascorbate and / or sodium hydroxymethanesulfinate (sodium formaldehyde sulfoxylate), and particularly preferably ferrous sulfate and ascorbate. In this case, the amount of ferrous sulfate used is preferably 0.000001 to 0.01 parts by weight, more preferably 0.00001 to 0.001 parts by weight, and even more preferably 0.00005 to 0.0005 parts by weight, per 100 parts by weight of monomer components used for polymerization, and the amount of ascorbic acid or its salt and / or sodium hydroxymethanesulfinate (sodium formaldehyde sulfoxylate) used is preferably 0.001 to 1 part by weight, more preferably 0.005 to 0.5 parts by weight, and even more preferably 0.01 to 0.3 parts by weight, per 100 parts by weight of monomer components used for polymerization.

[0083] The amount of water used in emulsion polymerization is preferably 10 to 1000 parts by weight, more preferably 50 to 800 parts by weight, even more preferably 80 to 600 parts by weight, and particularly preferably 100 to 400 parts by weight, per 100 parts by weight of monomer components used for polymerization. The amount of water used in emulsion polymerization should be adjusted so that the amount taken into account the amount of water used to emulsify the monomer components falls within the above range. Emulsion polymerization may be carried out using only the water used to emulsify the monomer components, or further water may be added before emulsion polymerization.

[0084] Furthermore, during emulsion polymerization, polymerization auxiliary materials such as molecular weight modifiers, particle size modifiers, chelating agents, and oxygen scavengers can be used as needed.

[0085] Emulsion polymerization may be carried out by batch, semi-batch, or continuous methods, but the semi-batch method is preferred.

[0086] The polymerization temperature and polymerization time are not particularly limited and can be appropriately selected depending on the type of polymerization catalyst used, but the polymerization temperature is preferably 0 to 100°C, more preferably 5 to 80°C, and even more preferably 10 to 50°C. The polymerization time is preferably 0.5 to 100 hours, and more preferably 1 to 10 hours. The polymerization conversion rate is not particularly limited, but is preferably 80% by weight or more, more preferably 90% by weight or more, and even more preferably 95% by weight or more.

[0087] Furthermore, polymerization inhibitors can be used to stop the polymerization reaction. Examples of polymerization inhibitors include hydroxylamine, hydroxyamine sulfate, diethylhydroxyamine, hydroxyamine sulfonic acid and its alkali metal salts, sodium dimethyldithiocarbamate, and hydroquinone. The amount of polymerization inhibitor used is not particularly limited, but is preferably 0.1 to 2 parts by weight per 100 parts by weight of monomer components used for polymerization.

[0088] Furthermore, in the present invention, it is preferable to add a phenolic antioxidant to the emulsion polymerization solution of acrylic rubber obtained by emulsion polymerization. When adding the phenolic antioxidant to the emulsion polymerization solution of acrylic rubber, it is preferable to use either the following addition method (1) or addition method (2). Method of addition (1): A method of adding a phenolic antioxidant to an emulsion polymerization solution of acrylic rubber under conditions of a temperature above the melting point of the phenolic antioxidant. Method of addition (2): A dispersion is obtained by contacting a phenolic antioxidant with an aqueous solution of an emulsifier under conditions of a temperature above the melting point of the phenolic antioxidant, and the phenolic antioxidant is added to the emulsion polymerization solution of acrylic rubber in the form of the dispersion.

[0089] When adding a phenolic antioxidant to the emulsion polymerization solution of acrylic rubber, by employing either method (1) or method (2), the phenolic antioxidant can be uniformly dispersed in the emulsion polymerization solution. As a result, the dispersion of the phenolic antioxidant in the acrylic rubber after solidification can be made uniform, thereby ensuring that its additive effect is sufficient.

[0090] In addition method (1), there are no particular limitations on the specific method of adding the phenolic antioxidant to the emulsion polymerization solution of acrylic rubber under conditions of a temperature above the melting point of the phenolic antioxidant. However, it is preferable to heat the emulsion polymerization solution to a temperature above the melting point of the phenolic antioxidant and then add the phenolic antioxidant to the emulsion polymerization solution. In particular, since the amount of phenolic antioxidant added to the emulsion polymerization solution is usually very small compared to the amount of emulsion polymerization solution, it is convenient and preferable to heat the emulsion polymerization solution to a temperature above the melting point of the phenolic antioxidant used.

[0091] In addition method (1), when adding the phenolic antioxidant to the emulsion polymerization solution, it is sufficient to do so under temperature conditions above the melting point of the phenolic antioxidant used. However, it is more preferable to add the phenolic antioxidant under temperature conditions of the melting point + 10°C or higher, and even more preferable to add it under temperature conditions of the melting point + 15°C or higher.

[0092] Furthermore, in addition method (2), a dispersion of the phenolic antioxidant is first obtained by contacting the phenolic antioxidant with an aqueous solution of the emulsifier under conditions of a temperature above the melting point of the phenolic antioxidant.

[0093] While there are no particular limitations on the emulsifier, it is preferable to use the same emulsifier as used in the emulsion polymerization described above, from the viewpoint of dispersibility when a dispersion of phenolic antioxidants is added to the emulsion polymerization solution. Furthermore, if two or more emulsifiers are used in the emulsion polymerization described above, it is preferable to use at least one of the two or more emulsifiers.

[0094] The amount of emulsifier used is preferably such that the concentration of the emulsifier in the dispersion of the phenolic antioxidant is 0.5 to 20% by weight, more preferably 1.0 to 15% by weight, and even more preferably 2.0 to 10% by weight. By using an amount of emulsifier within the above range, the dispersion of the phenolic antioxidant in the dispersion can be sufficiently dispersed, thereby allowing the phenolic antioxidant to be dispersed more uniformly when the dispersion is added to the emulsion polymerization solution.

[0095] There are no particular limitations on the method for contacting a phenolic antioxidant with an aqueous solution of an emulsifier under conditions where the temperature is above the melting point of the phenolic antioxidant. However, a preferred method is to bring both the aqueous solution of the phenolic antioxidant and the aqueous solution of the emulsifier to a temperature above the melting point of the phenolic antioxidant, and then add the phenolic antioxidant to the aqueous solution of the emulsifier while stirring.

[0096] Furthermore, in addition method (2), when the phenolic antioxidant is brought into contact with the aqueous solution of the emulsifier, it is sufficient to do so under temperature conditions above the melting point of the phenolic antioxidant used. However, it is more preferable to add the phenolic antioxidant under temperature conditions of the melting point of the phenolic antioxidant + 10°C or higher, and even more preferable to add it under temperature conditions of the melting point of the phenolic antioxidant + 15°C or higher.

[0097] The content of the phenolic antioxidant in the dispersion of the phenolic antioxidant is not particularly limited, but it is preferable that the concentration of the phenolic antioxidant be 10 to 80% by weight, more preferably 25 to 75% by weight, and even more preferably 30 to 70% by weight. By setting the content of the phenolic antioxidant within the above range, the phenolic antioxidant can be dispersed more uniformly when the dispersion of the phenolic antioxidant is added to the emulsion polymerization solution.

[0098] Then, in addition method (2), the dispersion of the phenolic antioxidant prepared in this manner is added to the emulsion polymerization solution of acrylic rubber.

[0099] When adding an anti-aging agent, the amount of phenolic anti-aging agent added to the emulsion polymerization solution should be such that the content in the acrylic rubber falls within the range described above. Specifically, the amount added is preferably 0.1 to 5 parts by weight, more preferably 0.2 to 3 parts by weight, and even more preferably 0.3 to 2 parts by weight, per 100 parts by weight of the acrylic rubber component contained in the emulsion polymerization solution. Since the phenolic anti-aging agent usually remains in the acrylic rubber after solidification, even after the solidification operation described later, the amount of phenolic anti-aging agent to be added should be determined taking this into consideration.

[0100] Next, a coagulant is brought into contact with the emulsion polymerization solution to which a phenolic antioxidant has been added, thereby causing coagulation and generating a hydrated crumb.

[0101] The coagulant is not particularly limited, but examples include 1- to 3-valent metal salts. A 1- to 3-valent metal salt is a salt containing a metal that becomes a 1- to 3-valent metal ion when dissolved in water, and is not particularly limited, but examples include salts of inorganic acids selected from hydrochloric acid, nitric acid, sulfuric acid, etc., or organic acids such as acetic acid, and metals selected from sodium, potassium, lithium, magnesium, calcium, zinc, titanium, manganese, iron, cobalt, nickel, aluminum, tin, etc. Hydroxides of these metals can also be used.

[0102] Specific examples of 1-3 valent metal salts include metal chlorides such as sodium chloride, potassium chloride, lithium chloride, magnesium chloride, calcium chloride, zinc chloride, titanium chloride, manganese chloride, iron chloride, cobalt chloride, nickel chloride, aluminum chloride, and tin chloride; nitrates such as sodium nitrate, potassium nitrate, lithium nitrate, magnesium nitrate, calcium nitrate, zinc nitrate, titanium nitrate, manganese nitrate, iron nitrate, cobalt nitrate, nickel nitrate, aluminum nitrate, and tin nitrate; and sulfates such as sodium sulfate, potassium sulfate, lithium sulfate, magnesium sulfate, calcium sulfate, zinc sulfate, titanium sulfate, manganese sulfate, iron sulfate, cobalt sulfate, nickel sulfate, aluminum sulfate, and tin sulfate. Among these, calcium chloride, sodium chloride, aluminum sulfate, magnesium chloride, magnesium sulfate, zinc chloride, zinc sulfate, and sodium sulfate are preferred. Among these, 1- or 2-valent metal salts are preferred, 2-valent metal salts are more preferred, magnesium salts are more preferred, inorganic magnesium salts are even more preferred, and magnesium sulfate is particularly preferred. These can be used individually or in combination.

[0103] The amount of coagulant used is preferably 0.01 to 100 parts by weight, more preferably 0.1 to 50 parts by weight, and even more preferably 1 to 30 parts by weight, per 100 parts by weight of monomer components used in polymerization. By using the above range for the amount of coagulant, the acrylic rubber can be sufficiently solidified while the resulting acrylic rubber has excellent water resistance.

[0104] The method of bringing the emulsion polymerization solution into contact with the coagulant is not particularly limited, but examples include adding the emulsion polymerization solution to an aqueous solution containing a coagulant while stirring the aqueous solution containing the coagulant, or adding the aqueous solution containing the coagulant to an aqueous solution containing a coagulant while stirring the emulsion polymerization solution. Alternatively, a method of simply adding the emulsion polymerization solution to an aqueous solution containing a coagulant without stirring, or adding the aqueous solution containing a coagulant to an emulsion polymerization solution, may be employed. Among these, the method of adding the emulsion polymerization solution to an aqueous solution containing a coagulant while stirring the aqueous solution containing the coagulant is preferred, as employing such a method to perform the coagulation operation makes it possible to control the particle size of the water-containing crumb produced by coagulation to a relatively uniform range, thereby improving the washing efficiency of the produced water-containing crumb.

[0105] The concentration of magnesium salt in the aqueous solution containing the coagulant is not particularly limited, but from the viewpoint of more effectively controlling the particle size of the hydrated crumb produced by coagulation, it is preferably 0.1 to 20% by weight, more preferably 0.5 to 10% by weight, and even more preferably 1 to 5% by weight.

[0106] The temperature of the aqueous solution containing the coagulant (i.e., the coagulation temperature) is not particularly limited, but from the viewpoint of more effectively controlling the particle size of the water-containing crumb produced by coagulation, it is preferably 40°C or higher, and more preferably 50 to 90°C.

[0107] The stirring method for stirring an aqueous solution containing a coagulant is not particularly limited, but one method is to use a stirring device that uses a stirring blade. In this case, it is preferable to include the aqueous solution containing the coagulant in a stirring tank and add the emulsion polymerization solution while stirring the aqueous solution containing the coagulant with a stirring blade in the stirring tank.

[0108] Furthermore, the solid content concentration of the emulsion polymerization solution used for coagulation is not particularly limited, and it may be used as is after emulsion polymerization and the addition of an anti-aging agent. However, from the viewpoint of more favorably controlling the particle size of the water-containing crumb produced by coagulation, it is preferable to adjust the solid content concentration to a range of 5 to 50% by weight, more preferably to a range of 10 to 45% by weight, and particularly preferably to a range of 20 to 40% by weight.

[0109] Next, it is preferable to wash the hydrated crumb obtained by the coagulation operation. The washing method is not particularly limited, but for example, it is preferable to wash the hydrated crumb obtained by the coagulation operation with water, and preferably, it is preferable to mix the hydrated crumb obtained by the coagulation operation with water. The temperature during washing is not particularly limited, but 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.

[0110] Furthermore, while there are no particular limitations on the amount of water to be mixed with the hydrated crumb during washing, from the viewpoint of further improving washing efficiency, it is preferable to use an amount of 50 parts by weight or more per 100 parts by weight of monomer components used in polymerization, more preferably 50 to 15,000 parts by weight, even more preferably 100 to 10,000 parts by weight, and particularly preferably 500 to 5,000 parts by weight.

[0111] The rinsing time is not particularly limited, but is preferably 1 to 120 minutes, more preferably 2 to 60 minutes, and even more preferably 3 to 30 minutes.

[0112] Furthermore, the number of rinses is not particularly limited, but is preferably 1 to 10 times, more preferably 1 to 5 times, and even more preferably 1 to 3 times. In this invention, the number of rinses refers to the number of times in which the operation of adding water to the water-containing crumb, mixing for a predetermined time, and then separating the water-containing crumb from the water used for rinsing is considered as one rinse. That is, for example, two rinses means adding water to the water-containing crumb, mixing for a predetermined time, then separating the water-containing crumb from the water used for rinsing, and then, subsequently, adding water to the water-containing crumb again, mixing for a predetermined time, and then separating the water-containing crumb from the water used for rinsing. When the number of rinses is two or more, the temperature of the water used for rinsing, the amount of water, and the rinsing time may be the same or different.

[0113] Furthermore, in this invention, after rinsing with water, acid cleaning may be performed using an acid as the cleaning solution. After acid cleaning, it is preferable to rinse with water again, and the conditions for rinsing with water may be the same as those described above.

[0114] Furthermore, the washed, water-containing crumb may be dried. The drying method for the water-containing crumb is not particularly limited and can be any standard method, but examples include drying using a hot air dryer, vacuum dryer, expander dryer, kneader dryer, screw extruder, etc.

[0115] Furthermore, the drying temperature of the hydrated crumb is not particularly limited, but is preferably 80 to 250°C, and more preferably 100 to 200°C.

[0116] There are no particular limitations on the method for dewatering water-containing crumb, but examples include using a dewatering machine such as a centrifuge, squeezer, or screw extruder to remove moisture from the water-containing crumb. From the viewpoint of further reducing the moisture content of the water-containing crumb, methods using a squeezer and screw extruder are preferred, and methods using a screw extruder are particularly preferred. By using a screw extruder, the dewatering and drying of the water-containing crumb can be carried out in a continuous process, thereby increasing productivity.

[0117] As a screw-type extruder, a twin-screw extruder equipped with a barrel unit consisting of multiple barrel blocks and a pair of screws rotatably arranged inside the barrel unit can be suitably used.

[0118] The barrel unit may comprise, in order from the water-containing crumb supply side, a supply barrel section consisting of one or more supply barrel blocks, a dewatering barrel section consisting of one or more dewatering barrel blocks, and a drying barrel section consisting of one or more drying barrel blocks. A die for extruding the dewatered and dried acrylic rubber into a sheet is connected to the downstream side of the drying barrel section.

[0119] The supply barrel section is the area that supplies the water-containing crumb into the barrel unit. The dewatering barrel section is the area that separates and discharges the liquid (ceram water) containing the coagulant from the water-containing crumb. At least a portion of the dewatering barrel block that makes up the dewatering barrel section is equipped with slits for discharging the water generated by dewatering. The drying barrel section is the area that dries the crumb after it has been dewatered by the dewatering barrel section.

[0120] The set temperature in the dewatering barrel is preferably 60 to 150°C, more preferably 70 to 140°C, and even more preferably 80 to 130°C. The set temperature in the drying barrel is preferably 100 to 250°C, more preferably 110 to 200°C, and even more preferably 120 to 180°C.

[0121] The screw length (L) of the pair of screws arranged inside the barrel unit constituting the screw-type extruder is not particularly limited, but is preferably 3,000 to 15,000 mm, more preferably 4,000 to 10,000 mm, and even more preferably 4,500 to 8,000 mm. The screw diameter (D) of the screws is not particularly limited, but is preferably in the range of 50 to 250 mm, more preferably 100 to 200 mm, and even more preferably 120 to 160 mm. Furthermore, the ratio (L / D) of the screw length (L) to the screw diameter (D) is not particularly limited, but is preferably 10 to 100, more preferably 20 to 80, and even more preferably 30 to 60. By setting the screw length (L) and screw diameter (D) within the above ranges, dewatering and drying can be efficiently performed while effectively suppressing the decrease in molecular weight and the occurrence of burning of the acrylic rubber.

[0122] Furthermore, the operating conditions of a screw extruder when dewatering and drying water-containing crumb using a screw extruder are not particularly limited, but examples include the following conditions. In other words, the rotational speed N [rpm] of the pair of screws arranged inside the barrel unit is preferably 10 to 1000 rpm, more preferably 50 to 750 rpm, even more preferably 100 to 500 rpm, and particularly preferably 120 to 300 rpm, from the viewpoint of efficiently reducing the water content and gel amount of the acrylic rubber. The processing rate Q [kg / hr] of acrylic rubber dried per unit time in a screw-type extruder is preferably 100 to 1500 kg / hr, more preferably 300 to 1200 kg / hr, even more preferably 400 to 1000 kg / hr, and particularly preferably 500 to 800 kg / hr.

[0123] Furthermore, the ratio (Q / N) of the amount of acrylic rubber dried per unit time Q to the number of screw rotations N is not particularly limited, but is preferably 1 to 20, more preferably 2 to 10, even more preferably 3 to 8, and most preferably 4 to 6. By setting "Q / N" within the above range, acrylic rubber with appropriately reduced moisture content can be produced with high productivity. Furthermore, the rubber pressure (resin pressure or discharge pressure) in the die connected downstream of the drying barrel is not particularly limited, but from the viewpoint of effectively suppressing air entrapment while achieving high productivity, it is preferably 0.1 to 10 MPa, more preferably 0.5 to 5 MPa, and even more preferably 1 to 3 MPa.

[0124] The temperature of the water-containing crumb supplied to the screw-type extruder is not particularly limited, but it is preferable to set it to 60°C or higher, as this can improve dewatering and drying efficiency and thereby enhance the water resistance of the resulting acrylic rubber.

[0125] According to the present invention, acrylic rubber can be manufactured as described above. In this invention, the acrylic rubber may be obtained in granular form, or as baled rubber, i.e., as an acrylic rubber bale (acrylic rubber in the form of a predetermined shape).

[0126] <Rubber composition> The rubber composition of the present invention comprises a rubber component containing the acrylic rubber of the present invention described above, and a crosslinking agent. The proportion of the acrylic rubber component of the present invention in the rubber component can be appropriately selected depending on the intended use, but is preferably 30% by weight or more, more preferably 50% by weight or more, even more preferably 70% by weight or more, and particularly preferably 100% by weight (i.e., an embodiment in which the rubber component consists substantially only of the acrylic rubber component).

[0127] The rubber components of the present invention other than the acrylic rubber are not particularly limited, but include acrylic rubber other than the acrylic rubber of the present invention, natural rubber, polybutadiene rubber, polyisoprene rubber, styrene-butadiene rubber, acrylonitrile-butadiene rubber, silicone rubber, fluororubber, olefin-based elastomer, styrene-based elastomer, vinyl chloride-based elastomer, polyester-based elastomer, polyamide-based elastomer, polyurethane-based elastomer, and polysiloxane-based elastomer.

[0128] The rubbers other than acrylic rubber of the present invention can be used individually or in combination of two or more types. The shape of the acrylic rubber and the rubbers other than acrylic rubber of the present invention are not particularly limited, but may be in any form such as bale, sheet, or powder.

[0129] The crosslinking agent is not particularly limited, but conventionally known crosslinking agents such as polyhydric amine compounds such as diamine compounds and their carbonates; sulfur; sulfur donors; triazinethiol compounds; polyhydric epoxy compounds; ammonium salts of organic carboxylates; organic peroxides; metal salts of dithiocarbamate; polyhydric carboxylic acids; quaternary onium salts; imidazole compounds; isocyanuric acid compounds; etc. can be used. These crosslinking agents can be used individually or in combination of two or more. It is preferable to appropriately select the crosslinking agent according to the type of monomer unit containing the crosslinkable group.

[0130] Among these, if the acrylic rubber of the present invention has a carboxyl group-containing monomer unit as a crosslinkable group-containing monomer unit, it is preferable to use a polyhydric amine compound and its carbonate as the crosslinking agent.

[0131] The polyhydric amine compound and its carbonate are not particularly limited, but polyhydric amine compounds having 4 to 30 carbon atoms and their carbonates are preferred. Examples of such polyhydric amine compounds and their carbonates include aliphatic polyhydric amine compounds and their carbonates, as well as aromatic polyhydric amine compounds.

[0132] The aliphatic polyvalent amine compound and its carbonate are not particularly limited, but examples include hexamethylenediamine, hexamethylenediamine carbamate, and N,N'-disinnamyridene-1,6-hexanediamine. Among these, hexamethylenediamine carbamate is preferred.

[0133] The aromatic polyvalent amine compounds are not particularly limited, but examples include 4,4'-methylenedianiline, p-phenylenediamine, 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, and 1,3,5-benzenetriamine. Among these, 2,2'-bis[4-(4-aminophenoxy)phenyl]propane is preferred.

[0134] Furthermore, if the acrylic rubber of the present invention has halogen atom-containing monomer units as crosslinkable group-containing monomer units, it is preferable to use sulfur, sulfur donors, triazinethiol compounds, polyhydric amine compounds, or carbonates of polyhydric amine compounds as crosslinking agents. Examples of sulfur donors include dipentamethylenethuram hexasulfide and triethylthuram disulfide. Examples of triazine compounds include 2,4,6-trimercapto-s-triazine, 2-anilino-4,6-dithiol-s-triazine, 2-dibutylamino-4,6-dithiol-s-triazine, and 1-hexylamino-3,5-dimercaptotriazine. Among these, 2,4,6-trimercapto-s-triazine is preferred. As examples of polyvalent amine compounds and carbonates of polyvalent amine compounds, those mentioned above can be used.

[0135] The crosslinking agent content in the rubber composition of the present invention is preferably 0.001 to 20 parts by weight, more preferably 0.1 to 10 parts by weight, even more preferably 0.1 to 5 parts by weight, and particularly preferably 0.2 to 4 parts by weight, per 100 parts by weight of the rubber component containing the acrylic rubber of the present invention. By setting the crosslinking agent content within the above range, it is possible to achieve sufficient rubber elasticity while also providing excellent mechanical strength as a crosslinked rubber product.

[0136] Furthermore, if the acrylic rubber of the present invention has an epoxy group-containing monomer unit as a crosslinkable group-containing monomer unit, it is preferable to use polyhydric amine compounds, polyhydric amine compounds, carbonates of polyhydric amine compounds; ammonium carboxylate salts such as ammonium benzoate and ammonium adipate; metal dithiocarbamate salts such as zinc dimethyldithiocarbamate; polyhydric carboxylic acids such as tetradecanedioic acid; quaternary onium salts such as cetyltrimethylammonium bromide; imidazole compounds such as 2-methylimidazole; isocyanuric acid compounds such as ammonium isocyanurate; etc. as crosslinking agents. For example, the above-mentioned products can be used as polyhydric amine compounds and carbonates of polyhydric amine compounds. Among these, ammonium carboxylate salts and metal dithiocarbamate salts are preferred, and ammonium benzoate is more preferred.

[0137] Furthermore, it is preferable that the rubber composition of the present invention further contains a crosslinking accelerator. The crosslinking accelerator is not particularly limited, but if the acrylic rubber of the present invention has a carboxyl group as a crosslinkable group and the crosslinking agent is a polyvalent amine compound or its carbonate, then guanidine compounds, diazabicycloalkene compounds, imidazole compounds, quaternary onium salts, tertiary phosphine compounds, aliphatic monovalent secondary amine compounds, and aliphatic monovalent tertiary amine compounds can be used. Among these, guanidine compounds, diazabicycloalkene compounds, and aliphatic monovalent secondary amine compounds are preferred, and guanidine compounds and diazabicycloalkene compounds are particularly preferred. These basic crosslinking accelerators can be used individually or in combination of two or more.

[0138] Specific examples of guanidine compounds include 1,3-di-o-tolylguanidine and 1,3-diphenylguanidine. Specific examples of diazabicycloalkene compounds include 1,8-diazabicyclo[5.4.0]unde-7-cene and 1,5-diazabicyclo[4.3.0]no-5-nene. Specific examples of imidazole compounds include 2-methylimidazole and 2-phenylimidazole. Specific examples of quaternary onium salts include tetra-n-butylammonium bromide and octadecyltri-n-butylammonium bromide. Specific examples of tertiary phosphine compounds include triphenylphosphine and tri-p-tolylphosphine.

[0139] Aliphatic monovalent secondary amine compounds are compounds in which two hydrogen atoms of ammonia are replaced with aliphatic hydrocarbon groups. The aliphatic hydrocarbon groups that replace the hydrogen atoms are preferably those having 1 to 30 carbon atoms. Specific examples of aliphatic monovalent secondary amine compounds include dimethylamine, diethylamine, dipropylamine, diallylamine, diisopropylamine, di-n-butylamine, di-t-butylamine, di-sec-butylamine, dihexylamine, diheptylamine, dioctylamine, dinonylamine, didecylamine, diundecylamine, didodecylamine, ditridecylamine, ditetradecylamine, dipentadecylamine, dicetylamine, di-2-ethylhexylamine, and dioctadecylamine.

[0140] Aliphatic monovalent tertiary amine compounds are compounds in which all three hydrogen atoms of ammonia are replaced with aliphatic hydrocarbon groups. The aliphatic hydrocarbon groups that replace the hydrogen atoms are preferably those having 1 to 30 carbon atoms. Specific examples of aliphatic monovalent tertiary amine compounds include trimethylamine, triethylamine, tripropylamine, triallylamine, triisopropylamine, tri-n-butylamine, tri-t-butylamine, tri-sec-butylamine, trihexylamine, triheptylamine, trioctylamine, trinonylamine, tridecylamine, triundecylamine, and tridodecylamine.

[0141] The amount of the crosslinking accelerator in the rubber composition of the present invention is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 7.5 parts by weight, and particularly preferably 1 to 5 parts by weight, per 100 parts by weight of the rubber component containing the acrylic rubber of the present invention. By setting the amount of the crosslinking accelerator within the above range, the tensile strength and compression set resistance of the resulting crosslinked rubber can be further improved.

[0142] Furthermore, the rubber composition of the present invention may further contain a filler. The filler is not particularly limited, but examples include reinforcing fillers and non-reinforcing fillers, and among these, reinforcing fillers are preferred.

[0143] Examples of reinforcing fillers include carbon black such as furnace black, acetylene black, thermal black, channel black, and graphite; and silica such as wet silica, dry silica, and colloidal silica. Examples of non-reinforcing fillers include clay such as quartz powder and diatomaceous earth; zinc oxide; basic magnesium carbonate; activated calcium carbonate; magnesium silicate; aluminum silicate; titanium dioxide; talc; aluminum sulfate; calcium sulfate; and barium sulfate.

[0144] These fillers can be used individually or in combination of two or more. The amount of filler in the rubber composition of the present invention is not particularly limited, but is preferably 1 to 200 parts by weight, more preferably 10 to 150 parts by weight, and even more preferably 20 to 100 parts by weight, per 100 parts by weight of the rubber component containing the acrylic rubber of the present invention.

[0145] Furthermore, the rubber composition of the present invention may optionally contain an antioxidant. That is, in addition to the phenolic antioxidant optionally contained in the acrylic rubber, an additional antioxidant may be added. The antioxidant is not particularly limited, but may include the phenolic antioxidants mentioned above; phosphite ester antioxidants such as tris(nonylphenyl) phosphite, diphenylisodecyl phosphite, and tetraphenyldipropylene glycol diphosphite; sulfur ester antioxidants such as dilauryl thiodipropionate; phenyl-α-naphthylamine, phenyl-β-naphthylamine, p-(p-toluenesulfonylamide)-diphenylamine, and 4,4'-bis(α,α-dimethicone). Examples include amine-based anti-aging agents such as rubenzyl)diphenylamine, N,N-diphenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, and butyraldehyde-aniline condensate; imidazole-based anti-aging agents such as 2-mercaptobenzimidazole; quinoline-based anti-aging agents such as 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline; and hydroquinone-based anti-aging agents such as 2,5-di-(t-amyl)hydroquinone.

[0146] Anti-aging agents can be used individually or in combination of two or more. The amount of anti-aging agent in the rubber composition of the present invention is not particularly limited, but is preferably 0.01 to 15 parts by weight, more preferably 0.05 to 10 parts by weight, and even more preferably 0.1 to 5 parts by weight, per 100 parts by weight of the rubber component containing the acrylic rubber of the present invention.

[0147] Furthermore, the rubber composition of the present invention may contain, in addition to the above-mentioned components, compounding agents commonly used in the field of rubber processing. Examples of such compounding agents include light stabilizers, scorch inhibitors, plasticizers, processing aids, adhesives, lubricants, flame retardants, fungicides, antistatic agents, colorants, and crosslinking retarders. The amount of these compounding agents added is not particularly limited as long as it does not hinder the purpose or effect of the present invention, and appropriate amounts can be added depending on the purpose of compounding.

[0148] The rubber composition of the present invention is prepared by mixing the rubber component containing the acrylic rubber of the present invention described above with a crosslinking agent and various other compounding agents as needed, mixing and kneading with an open roll, Banbury mixer, various kneaders, etc., and then further kneading with a kneading roll.

[0149] The order in which each component is added is not particularly limited, but it is preferable to thoroughly mix components that are not easily reacted or decomposed by heat, and then quickly mix components that are easily reacted or decomposed by heat, such as crosslinking agents, at a temperature at which no reaction or decomposition occurs.

[0150] <Rubber Crosslinked Products> The rubber crosslinked material of the present invention is obtained by crosslinking the rubber composition of the present invention described above. The crosslinked rubber product of the present invention can be manufactured by using the acrylic rubber composition of the present invention, molding it using a molding machine corresponding to the desired shape, such as an extruder, injection molding machine, compressor, and roll, and then heating it to perform a crosslinking reaction and fix the shape as a crosslinked rubber product. In this case, crosslinking may be performed either after molding or simultaneously with molding. The molding temperature is usually 10 to 200°C, preferably 25 to 120°C. The crosslinking temperature is usually 130 to 220°C, preferably 150 to 190°C, and the crosslinking time is usually 2 minutes to 10 hours, preferably 3 minutes to 5 hours. As for the heating method, any method used for crosslinking rubber, such as press heating, steam heating, oven heating, and hot air heating, may be appropriately selected.

[0151] Furthermore, depending on the shape and size of the crosslinked rubber material, the crosslinked rubber material of the present invention may be further heated to perform secondary crosslinking. The duration of secondary crosslinking varies depending on the heating method, crosslinking temperature, and shape, but is preferably 1 to 48 hours. The heating method and heating temperature can be selected as appropriate.

[0152] The rubber crosslinked material of the present invention obtained in this manner is suitably used as a sealing material such as O-rings, packings, diaphragms, oil seals, shaft seals, bearing sheaths, mechanical seals, wellhead seals, seals for electrical and electronic equipment, and seals for air compressor equipment; various gaskets such as cylinder head gaskets fitted to the connection between the cylinder block and the cylinder head, rocker cover gaskets fitted to the connection between the rocker cover and the cylinder head, oil pan gaskets fitted to the connection between the oil pan and the cylinder head or transmission case, fuel cell separator gaskets fitted between a pair of housings that sandwich a unit cell equipped with a positive electrode, electrolyte plate, and negative electrode, and gaskets for the top cover of a hard disk drive; cushioning material, vibration damping material; wire insulation material; industrial belts; tubes and hoses; sheets; and the like.

[0153] Furthermore, the rubber crosslinked material of the present invention is suitably used as an extruded molded product and crosslinked product for automotive applications, such as fuel oil system hoses such as fuel tanks, fuel hoses, filler neck hoses, vent hoses, vapor hoses, and oil hoses; air system hoses such as turbo air hoses and transmission control hoses; and various other hoses such as radiator hoses, heater hoses, brake hoses, and air conditioning hoses. [Examples]

[0154] The present invention will be described in more detail below with reference to examples and comparative examples. Unless otherwise specified, the unit of "part" in each example is based on weight. Various physical properties were evaluated according to the following method.

[0155] [Monomer composition of acrylic rubber] The monomer composition of the acrylic rubber was calculated from the amount of each monomer used in the polymerization reaction and the polymerization conversion rate. Specifically, in the emulsion polymerization reaction in each example and comparative example, no unreacted monomers were found, and the polymerization conversion rate was approximately 100%. Therefore, the amount of each monomer used in the polymerization reaction was assumed to be the same as the content ratio of each monomer unit constituting the acrylic rubber.

[0156] [Mooney viscosity (ML1+4, 100℃)] The Mooney viscosity (polymer Mooney) of acrylic rubber was measured according to JIS K6300:2013.

[0157] [Measurement of roll processability of acrylic rubber composition] The tackiness of the acrylic rubber composition prepared using a roll was evaluated according to the following criteria. A higher score indicates superior processability. ◎: There was no stickiness on the roll surface, resulting in good operability. ○: Although some adhesion occurred on the roll surface, it was possible to reverse the process and pass the material through thinly. △: Significant adhesion occurred on the roll surface, making it impossible to reverse direction or pass the material through. ×: Significant adhesion occurred to the roll surface, and rubber stuck to both the front and back sides of the roll, making mixing impossible. The reversal operation is a mixing operation in which a portion (about half) of the rubber composition that is stuck to the roll is peeled off the roll, the peeled piece of rubber composition is placed on top of the other piece of rubber composition that is stuck to the roll, and then the roll is passed through again while the two pieces are still stacked. Furthermore, the thinning operation is a mixing operation in which, after the reversing operation, the rubber composition is passed through the rolls again with the gap between the rolls minimized, so that the longer side of the rubber composition intersects perpendicular to the axial direction of the rolls in the thickness direction of the sheet-like rubber composition.

[0158] [Tensile strength and elongation at break] An acrylic rubber composition was placed in a mold measuring 15 cm in length, 15 cm in width, and 0.2 cm in depth, and primary crosslinking was performed by compressing it at 170°C for 20 minutes under a pressure of 10 MPa. Subsequently, the obtained primary crosslinked material was further heated in a gear oven at 170°C for 4 hours to perform secondary crosslinking, thereby obtaining a sheet-like crosslinked rubber material. Test specimens were prepared by punching out the obtained crosslinked rubber material with a No. 3 dumbbell. Next, the tensile strength and elongation at break were measured using these test specimens in accordance with JIS K6251:2017.

[0159] [Compression permanent set test] An acrylic rubber composition was molded and crosslinked by pressing at 170°C for 20 minutes to produce a cylindrical test specimen with a diameter of 29 mm and a thickness of 12.5 mm. This specimen was then further heated at 150°C for 4 hours to induce secondary crosslinking. In accordance with JIS K6262:2006, the test specimen obtained after secondary crosslinking was compressed by 25% and left at 150°C for 70 hours. After releasing the compression, the compression set (%) was measured. A smaller compression set (%) value indicates superior resistance to compression set.

[0160] [Example 1] (Manufacturing of acrylic rubber (A-1)) In a mixing vessel equipped with a homomixer, 46.294 parts of deionized water, 46.8 parts of ethyl acrylate, 46.8 parts of n-butyl acrylate, 5 parts of acrylamide, and 1.4 parts of mono-n-butyl fumarate as monomer components, and 1.8 parts of tridecyloxyhexa(oxyethylene) phosphate sodium salt (anionic emulsifier) ​​as an emulsifier were charged and stirred to obtain a monomer emulsion.

[0161] Next, 170.853 parts of pure water and 2.962 parts of the monomer emulsion obtained above were added to a polymerization reactor equipped with a thermometer and a stirring device, and cooled to 12°C under a nitrogen stream. Then, 145.132 parts of the monomer emulsion obtained above, 0.00033 parts of ferrous sulfate (reducing agent), 0.264 parts of sodium ascorbate (reducing agent), and 7.72 parts of a 2.85% by weight aqueous solution of potassium persulfate (polymerization initiator) (0.22 parts of potassium persulfate) were continuously added dropwise over 3 hours while maintaining the temperature at 12°C. After that, the reaction was continued for 1 hour while maintaining the temperature in the polymerization reactor at 23°C, and it was confirmed that the polymerization conversion rate had reached approximately 100%. Hydroquinone was then added as a polymerization stopper to stop the polymerization reaction and obtain an emulsion polymerization solution.

[0162] Next, separately from the above, 50 parts of an aqueous solution of 12% by weight of tridecyloxyhexa(oxyethylene) phosphate sodium salt (anionic emulsifier) ​​and 50 parts of octyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (trade name "Irganox 1135", manufactured by BASF, a double-hindered phenolic antioxidant, molecular weight: 390, melting point: 10℃) were mixed and stirred at a temperature of 25℃ to obtain an antioxidant dispersion (concentration of tridecyloxyhexa(oxyethylene) phosphate sodium salt as an emulsifier: 6% by weight, concentration of phenolic antioxidant: 50% by weight).

[0163] Next, 0.36 parts of the antioxidant dispersion prepared above (an amount such that the phenolic antioxidant is 0.5 parts per 100 parts of rubber component in the emulsion polymerization solution) were added to 100 parts of the emulsion polymerization solution obtained above (temperature: 25°C), and the mixture was stirred.

[0164] Next, 60 parts of a 30% by weight magnesium sulfate aqueous solution, adjusted to 85°C, were added to a solidification tank equipped with a thermometer and a stirring device, and stirred with a stirring blade while heated to 85°C. Then, under stirring, 100 parts of the emulsion polymerization solution to which the antioxidant dispersion prepared above had been added was continuously added to the magnesium sulfate aqueous solution, causing the polymer to solidify and then filtered off to obtain a hydrated crumb.

[0165] Next, 388 parts of industrial water were added to 100 parts of the solid content of the hydrated crumb obtained above, and the mixture was stirred in a solidification tank at room temperature for 5 minutes. After the water was drained from the solidification tank, the hydrated crumb was washed with water. The washed hydrated crumb was then dried in a hot air dryer at 110°C for 1 hour to obtain solid acrylic rubber (A-1) with a 100% recovery rate. The Mooney viscosity of the obtained acrylic rubber (A-1) was measured according to the method described above. The results are shown in Table 1.

[0166] (Preparation of acrylic rubber composition) Using a Banbury mixer, 100 parts of the acrylic rubber (A-1) obtained above were mixed with 60 parts of carbon black (product name "Seasto SO", manufactured by Tokai Carbon Co., Ltd.), 1 part of stearic acid, 1 part of ester wax (product name "Grec 8205", manufactured by DIC Corporation), and 2 parts of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine (product name "Nocrack CD", manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) and mixed at 50°C for 5 minutes. The resulting mixture was transferred to a roll at 50°C, and 100 parts of acrylic rubber (A-1) were mixed with 0.5 parts of hexamethylenediamine carbamate (product name "Diak #1", manufactured by DuPont Daue Elastomers, Ltd.) and 2 parts of 1,3-di-o-tolylguanidine (product name "Noxela DT", manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) and kneaded with a roll to obtain an acrylic rubber composition. Furthermore, during the mixing process using rolls, the roll adhesion was evaluated according to the criteria described above. Then, the tensile strength and elongation at break, as well as the compression set test, were performed on the obtained acrylic rubber composition. The results are shown in Table 1.

[0167] [Example 2] Acrylic rubber (A-2) was obtained in the same manner as in Example 1, except that the amounts of each monomer component were changed to 48.8 parts ethyl acrylate, 48.8 parts n-butyl acrylate, 1 part acrylamide, and 1.4 parts mono-n-butyl fumarate. Acrylic rubber compositions were prepared in the same manner as in Example 1, except that the obtained acrylic rubber (A-2) was used, and these were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0168] [Example 3] Acrylic rubber (A-3) was obtained in the same manner as in Example 1, except that the amounts of each monomer component were changed to 41.8 parts ethyl acrylate, 41.8 parts n-butyl acrylate, 15 parts acrylamide, and 1.4 parts mono-n-butyl fumarate. Acrylic rubber compositions were prepared in the same manner as in Example 1, except that the obtained acrylic rubber (A-3) was used, and these were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0169] [Example 4] Acrylic rubber (A-4) was obtained in the same manner as in Example 1, except that ethyl acrylate was not used as a monomer component, and the amounts of the other monomer components were changed to 93.6 parts n-butyl acrylate, 5 parts acrylamide, and 1.4 parts mono-n-butyl fumarate, respectively. Acrylic rubber compositions were prepared in the same manner as in Example 1, except that the obtained acrylic rubber (A-4) was used, and these were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0170] [Example 5] (Manufacturing of acrylic rubber (A-5)) Acrylic rubber (A-5) was obtained in the same manner as in Example 1, except that 1.4 parts of monocyclohexyl fumarate were used as the monomer component instead of 1.4 parts of mono-n-butyl fumarate. Acrylic rubber compositions were prepared in the same manner as in Example 1, except that the obtained acrylic rubber (A-5) was used, and these were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0171] [Example 6] (Manufacturing of acrylic rubber (A-6)) Acrylic rubber (A-6) was obtained in the same manner as in Example 1, except that 1.4 parts of glycidyl methacrylate were used instead of 1.4 parts of mono-n-butyl fumarate as the monomer component. The obtained acrylic rubber (A-6) was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0172] (Preparation of acrylic rubber composition) Furthermore, an acrylic rubber composition was prepared in the same manner as in Example 1, except that the acrylic rubber (A-6) obtained above was used, and 1.5 parts of ammonium benzoate (trade name "Balnok AB-S", manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) were used instead of hexamethylenediamine carbamate and 1,3-di-o-tolylguanidine, and evaluated in the same manner. The results are shown in Table 1.

[0173] [Example 7] (Manufacturing of acrylic rubber (A-7)) Acrylic rubber (A-7) was obtained in the same manner as in Example 1, except that vinyl monochloroacetate was used as the monomer component instead of mono-n-butyl fumarate, and the amounts of each monomer component were changed to 46.2 parts ethyl acrylate, 46.2 parts n-butyl acrylate, 5 parts acrylamide, and 2.6 parts vinyl monochloroacetate. The obtained acrylic rubber (A-7) was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0174] (Preparation of acrylic rubber composition) Furthermore, using the acrylic rubber (A-7) obtained above, an acrylic rubber composition was prepared in the same manner as in Example 1, except that 3.0 parts of semi-hardened beef tallow fatty acid sodium soap (product name "NS Soap", manufactured by Kao Corporation), 0.5 parts of stearic acid (product name "Nonsal SK-1", manufactured by NOF Corporation), and 0.3 parts of sulfur (product name "Sulfax PMC", manufactured by Tsurumi Chemical Industries, Ltd.) were used instead of hexamethylenediamine carbamate and 1,3-di-o-tolylguanidine, and the composition was evaluated in the same manner. The results are shown in Table 1.

[0175] [Comparative Example 1] Acrylic rubber (A-8) was obtained in the same manner as in Example 1, except that acrylamide was not used as the monomer component, and the amounts of other monomer components were changed to 49.8 parts ethyl acrylate, 49.8 parts n-butyl acrylate, and 1.4 parts mono-n-butyl fumarate. Acrylic rubber compositions were prepared in the same manner as in Example 1, except that the obtained acrylic rubber (A-8) was used, and these were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0176] [Comparative Example 2] Emulsion polymerization was carried out in the same manner as in Example 1, except that the amounts of each monomer component were changed to 38.8 parts ethyl acrylate, 38.8 parts n-butyl acrylate, 20 parts acrylamide, and 1.4 parts mono-n-butyl fumarate. The resulting polymer was soluble in water and therefore could not be recovered by coagulation.

[0177] [Comparative Example 3] Acrylic rubber (A-10) was obtained in the same manner as in Example 1, except that ethyl acrylate and acrylamide were not used as monomer components, and the amount of n-butyl acrylate used was changed to 98.6 parts. Furthermore, acrylic rubber compositions were prepared in the same manner as in Example 1, except that the obtained acrylic rubber (A-10) was used, and these were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0178] [Table 1]

[0179] As shown in Table 1, an acrylic rubber containing a crosslinkable group-containing monomer unit, which is at least one selected from the group consisting of carboxyl group-containing monomer units, halogen atom-containing monomer units, and epoxy group-containing monomer units, and a (meth)acrylamide monomer unit, wherein the content of (meth)acrylamide monomer units in the total monomer units is 0.2 to 17.5% by weight, exhibits suppressed adhesion to rolls, excellent processability, and furthermore, the resulting crosslinked rubber product has high elongation at break and tensile strength (Examples 1 to 8).

[0180] On the other hand, when the acrylic rubber did not contain the acrylamide monomer, adhesion to the roll occurred, resulting in poor processability, and the resulting crosslinked rubber product had low elongation at break and low tensile strength (Comparative Examples 1 and 3). Furthermore, when the acrylamide monomer content was set to 20% by weight, the resulting polymer was soluble in water and therefore could not be recovered by coagulation (Comparative Example 2).

Claims

1. A monomer unit containing at least one crosslinkable group selected from the group consisting of carboxyl group-containing monomer units, halogen atom-containing monomer units, and epoxy group-containing monomer units, (Meth)acrylamide monomer units, Acrylic rubber containing (meth)acrylic acid ester monomer units, The (meth)acrylic acid ester monomer units include ethyl acrylate units and n-butyl acrylate units. Acrylic rubber having a content of the (meth)acrylamide monomer unit in the total monomer units of 0.2 to 17.5% by weight.

2. The acrylic rubber according to claim 1, wherein the content of the (meth)acrylamide monomer unit in the total monomer unit is 1 to 15% by weight.

3. The acrylic rubber according to claim 1 or 2, wherein the crosslinkable group-containing monomer unit is the carboxyl group-containing monomer unit.

4. A rubber composition containing a rubber component comprising the acrylic rubber described in any one of claims 1 to 3, and a crosslinking agent.

5. A crosslinked rubber product obtained by crosslinking the rubber composition described in claim 4.

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