Acrylic rubber, composition containing acrylic rubber and rubber cross-linked product

Abstract

The present invention newly explains the problem that when acrylic rubber is cross-linked, the cross-linking shrinkage increases, and finds that maintaining good normal physical properties and reducing cross-linking shrinkage are new issues. The present invention finds that the above-mentioned issue can be solved by making the high molecular weight part and the low molecular weight part of the molecular weight distribution in the acrylic rubber have a specific distribution. Specifically, it is found that the above-mentioned issue can be solved by the following acrylic rubber: the ratio of molecular weights below 500,000 is 32 to 65%, and the ratio of molecular weights above 2,000,000 is 3 to 20%.

Description

Technical Field

[0001] The present invention relates to an acrylate rubber, a composition containing the acrylate rubber and a rubber crosslinked product. Background Art

[0002] It is known that acrylic rubber is obtained by copolymerizing (meth)acrylic acid ester by emulsion polymerization or the like, adding the copolymer to an aqueous coagulant solution to obtain a water-containing crumb, and drying the obtained water-containing crumb.

[0003] Acrylic rubber is generally known as a rubber having excellent heat resistance, oil resistance and ozone resistance, and its cross-linked products are widely used in automotive components such as sealing materials, pipe materials, vibration-proof materials, duct materials, belt materials or boot materials.

[0004] When acrylic rubber is used for these automobile parts, it is necessary to process it. Patent Document 1 describes that the processability can be improved without reducing the heat resistance of acrylic rubber.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2009-40922 Summary of the invention

[0008] Problem that the invention aims to solve

[0009] However, the results of the studies conducted by the present inventors have revealed that there is a problem in that crosslinking shrinkage increases when acrylic rubber is crosslinked, and thus it has been newly revealed that it is a problem to reduce crosslinking shrinkage while maintaining good normal physical properties.

[0010] Solutions for solving problems

[0011] The inventors of the present invention have conducted various studies to solve the new problems found by the inventors of the present invention. As a result, they have found that the above problems can be solved by making the high molecular weight part and the low molecular weight part of the molecular weight distribution of the acrylic rubber into a specific distribution. Specifically, the inventors of the present invention have found that the acrylic rubber having a molecular weight of 500,000 or less at a ratio of 32 to 65% and a molecular weight of 2,000,000 or less at a ratio of 3 to 20% can maintain good normal physical properties and reduce crosslinking shrinkage.

[0012] The scheme of the present invention is as follows.

[0013] Item 1. An acrylic rubber, wherein the ratio of the acrylic rubber having a molecular weight of 500,000 or less is 32 to 65%, and the ratio of the acrylic rubber having a molecular weight of 2,000,000 or more is 3 to 20%.

[0014] Item 2. The acrylic rubber according to Item 1, wherein the proportion of the acrylic rubber having a molecular weight of 500,000 or less is 35 to 55%, and the proportion of the acrylic rubber having a molecular weight of 2,000,000 or more is 4 to 18%.

[0015] Item 3. The acrylic rubber according to Item 1 or 2, wherein the proportion of the acrylic rubber having a molecular weight of 500,000 or less is 38 to 51%, and the proportion of the acrylic rubber having a molecular weight of 2,000,000 or more is 5 to 15%.

[0016] Item 4. The acrylic rubber according to any one of Items 1 to 3, which has a structural unit selected from a structural unit derived from an unsaturated monomer having a halogen group, a structural unit derived from an unsaturated monomer having a carboxyl group, and a structural unit derived from an unsaturated monomer having an epoxy group.

[0017] Item 5. An acrylic rubber-containing composition comprising: the acrylic rubber according to any one of Items 1 to 4 and a cross-linking agent.

[0018] Item 6. A cross-linked rubber product produced using the acrylic rubber-containing composition according to Item 5.

[0019] Effects of the Invention

[0020] The acrylic rubber of the present invention can maintain good normal physical properties and reduce cross-linking shrinkage, and therefore can be suitably used in products produced using the acrylic rubber. DETAILED DESCRIPTION

[0021] The acrylic rubber of the present invention has a molecular weight of 500,000 or less in a ratio of 32 to 65%, and a molecular weight of 2,000,000 or more in a ratio of 3 to 20%. This can maintain good normal physical properties and reduce crosslinking shrinkage.

[0022] The reason why the above-mentioned effects are obtained by the above-mentioned acrylic rubber is presumed as follows.

[0023] Acrylic rubbers with a molecular weight of more than 2,000,000 have good rubber properties, such as normal physical properties, but poor processability and a tendency to further increase cross-linking shrinkage. On the other hand, acrylic rubbers with a molecular weight of less than 500,000 have a low cross-linking shrinkage, but poor rubber properties. Acrylic rubbers containing a certain amount of each component can achieve both suppression of cross-linking shrinkage and good rubber properties.

[0024] The acrylic rubber of the present invention is preferably a polymer having a structural unit derived from (meth)acrylate as a main component, and the main component means: containing 50% by mass or more of a structural unit derived from (meth)acrylate. It should be noted that "(meth)acrylate" means "acrylate or methacrylate", and the same applies to similar expressions in this application.

[0025] As the structural unit derived from the (meth)acrylate, there can be exemplified a structural unit derived from an alkyl (meth)acrylate and a structural unit derived from an alkoxyalkyl (meth)acrylate. Among them, a structural unit derived from an alkyl acrylate having an alkyl group with 1 to 8 carbon atoms and a structural unit derived from an alkoxyalkyl acrylate having an alkoxyalkyl group with 2 to 8 carbon atoms are preferred, a structural unit derived from an alkyl acrylate having an alkyl group with 2 to 6 carbon atoms and / or a structural unit derived from an alkoxyalkyl acrylate having an alkoxyalkyl group with 2 to 6 carbon atoms are more preferred, and a structural unit derived from an alkyl acrylate having an alkyl group with 2 to 4 carbon atoms and / or a structural unit derived from an alkoxyalkyl acrylate having an alkoxyalkyl group with 2 to 4 carbon atoms are particularly preferred. The structural unit derived from the (meth)acrylate may be a structural unit derived from one or more types of (meth)acrylate.

[0026] Specific examples of (meth)acrylic acid alkyl esters include (meth)acrylic acid methyl (meth)acrylate, (meth)acrylic acid ethyl ester, (meth)acrylic acid n-propyl ester, (meth)acrylic acid isopropyl ester, (meth)acrylic acid n-butyl ester, (meth)acrylic acid isobutyl ester, (meth)acrylic acid n-pentyl ester, (meth)acrylic acid n-hexyl ester, (meth)acrylic acid n-heptyl ester, (meth)acrylic acid n-octyl ester, (meth)acrylic acid 2-ethylhexyl ester, (meth)acrylic acid cyclohexyl ester and the like. These may be used alone or in combination of two or more. Among them, (meth)acrylic acid ethyl ester and (meth)acrylic acid n-butyl ester are preferred.

[0027] Specific examples of alkoxyalkyl (meth)acrylates include methoxymethyl (meth)acrylate, methoxyethyl (meth)acrylate, ethoxymethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-propoxyethyl (meth)acrylate, 2-butoxyethyl (meth)acrylate, 2-methoxypropyl (meth)acrylate, 2-ethoxypropyl (meth)acrylate, 3-methoxypropyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate, 4-methoxybutyl (meth)acrylate, 4-ethoxybutyl (meth)acrylate, and the like. These may be used alone or in combination of two or more. Among them, 2-methoxyethyl (meth)acrylate is preferred.

[0028] The content of the structural unit derived from (meth)acrylate in the acrylic rubber of the present invention is preferably 50% by mass or more, particularly preferably 60% by mass or more, and may be 70% by mass or more, and may be 80% by mass or more, in all the structural units of the acrylic rubber, and the upper limit is preferably 99.5% by mass or less, and more preferably 99% by mass or less.

[0029] The acrylic rubber of the present invention preferably contains a structural unit derived from an unsaturated monomer having a crosslinking group. As the structural unit derived from the unsaturated monomer having a crosslinking group, there can be exemplified a structural unit derived from an unsaturated monomer having a halogen group (e.g., a chloro group, etc.), a structural unit derived from an unsaturated monomer having a carboxyl group, and a structural unit derived from an unsaturated monomer having an epoxy group. They can be used alone or in combination of two or more. Among them, structural units derived from unsaturated monomers having a halogen group (especially a chloro group) and a carboxyl group are particularly preferred, and structural units derived from unsaturated monomers having a carboxyl group are most preferred.

[0030] As unsaturated monomers having a halogen group, for example, monochloroacetic acid vinyl ester, allyl chloroacetate, etc. can be mentioned. These can be used alone or in combination of two or more. Among them, monochloroacetic acid vinyl ester is preferred.

[0031] As unsaturated monomers having a carboxyl group, for example, unsaturated monocarboxylic acids such as (meth) acrylic acid, crotonic acid, 2-pentenoic acid, and cinnamic acid, unsaturated dicarboxylic acids such as fumaric acid, maleic acid, and itaconic acid, carboxylic anhydrides such as maleic anhydride and citraconic anhydride, monomethyl fumarate, monoethyl fumarate, mono-n-butyl fumarate, monomethyl maleate, monoethyl maleate, mono-2-ethylhexyl maleate, and mono-n-butyl maleate, monocyclic alkyl maleates such as monocyclopentyl fumarate, monocyclohexyl fumarate, monocyclopentyl maleate, and monocyclohexyl maleate, monomethyl itaconate, monoethyl itaconate, mono-n-butyl itaconate, etc. can be cited. These can be used alone or in combination of two or more. Among them, unsaturated dicarboxylic acid monoesters such as monoethyl fumarate, monopropyl fumarate, monobutyl fumarate, monoethyl itaconate, monopropyl itaconate, and monobutyl itaconate are preferred.

[0032] Examples of the unsaturated monomer having an epoxy group include glycidyl (meth)acrylate and (meth)allyl glycidyl ether, etc. These may be used alone or in combination of two or more.

[0033] The content ratio of the structural unit derived from the unsaturated monomer having a crosslinking group in the acrylic rubber is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, particularly preferably 0.5% by mass or more, and preferably 10% by mass or less, more preferably 5% by mass or less, particularly preferably 2.5% by mass or less, in all the structural units of the acrylic rubber. The structural unit derived from the unsaturated monomer having a crosslinking group is preferably within the above range in terms of physical properties such as strength and compression set and processability.

[0034] The total content of the structural units derived from the (meth)acrylate and the structural units derived from the unsaturated monomer having a crosslinking group in the acrylic rubber of the present invention is preferably 55% by mass or more, more preferably 65% ​​by mass or more, further preferably 75% by mass or more, particularly preferably 85% by mass or more, in all the structural units of the acrylic rubber, and may be 100% by mass.

[0035] Furthermore, the acrylic rubber of the present invention may contain copolymerizable monomers other than the above-mentioned monomers as structural units of the acrylic rubber as long as it does not deviate from the gist of the present invention, and examples of other monomers include ethylenically unsaturated nitrile monomers, (meth)acrylamide monomers, aromatic vinyl monomers, conjugated diene monomers, non-conjugated diene monomers, other olefin monomers, etc. These monomers may be used alone or in combination of two or more.

[0036] Examples of the ethylenically unsaturated nitrile monomer include acrylonitrile, methacrylonitrile, α-methoxyacrylonitrile, vinylidene cyanide, etc. These may be used alone or in combination of two or more.

[0037] Examples of the (meth)acrylamide monomer include acrylamide, methacrylamide, diacetone acrylamide, diacetone methacrylamide, N-butoxymethyl acrylamide, N-butoxymethyl methacrylamide, N-butoxyethyl acrylamide, N-butoxyethyl methacrylamide, N-methoxymethyl acrylamide, N-methoxymethyl methacrylamide, N-propoxymethyl acrylamide, N-propoxymethyl methacrylamide, N-methyl acrylamide, N-methyl methacrylamide, N,N-dimethyl acrylamide, N,N-dimethyl methacrylamide, N,N-diethyl acrylamide, N,N-diethyl methacrylamide, N-hydroxymethyl acrylamide, N-hydroxymethyl methacrylamide, ethyl acrylamide, crotonamide, cinnamamide, maleic acid diamide, itaconamide, methyl maleic acid diamide, methyl itaconamide, maleimide, itaconimide, etc. These monomers may be used alone or in combination of two or more.

[0038] Examples of the aromatic vinyl monomer include styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, o-ethylstyrene, p-ethylstyrene, α-fluorostyrene, p-trifluoromethylstyrene, p-methoxystyrene, p-aminostyrene, p-dimethylaminostyrene, p-acetoxystyrene, styrenesulfonic acid or its salts, α-vinylnaphthalene, 1-vinylnaphthalene-4-sulfonic acid or its salts, 2-vinylfluorene, 2-vinylpyridine, 4-vinylpyridine, divinylbenzene, diisopropenylbenzene, vinylbenzyl chloride, etc. These monomers may be used alone or in combination of two or more thereof.

[0039] Examples of the conjugated diene monomer include 1,3-butadiene, 2-methyl-1,3-butadiene, 2-chloro-1,3-butadiene, 1,2-dichloro-1,3-butadiene, 2,3-dichloro-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-neopentyl-1,3-butadiene, 2-bromo-1,3-butadiene, 2-cyano-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, chloroprene, piperylene, etc. These monomers may be used alone or in combination of two or more.

[0040] Examples of the non-conjugated diene monomer include 1,4-pentadiene, 1,4-hexadiene, ethylidene norbornene, norbornadiene, dicyclopentadiene, etc. These may be used alone or in combination of two or more.

[0041] As other olefin monomers, for example, esters such as dicyclopentadienyl acrylate, dicyclopentadienyl methacrylate, dicyclopentadienyl ethyl acrylate, and dicyclopentadienyl ethyl methacrylate, ethylene, propylene, vinyl chloride, vinylidene chloride, 1,2-dichloroethylene, vinyl acetate, vinyl fluoride, vinylidene fluoride, 1,2-dichloroethylene, vinyl bromide, vinylidene bromide, 1,2-dibromoethylene, ethyl vinyl ether, and butyl vinyl ether can be mentioned. These monomers can be used alone or in combination of two or more.

[0042] The content of the structural unit in the acrylic rubber of the present invention can be determined based on the nuclear magnetic resonance spectrum of the obtained polymer.

[0043] The acrylic rubber of the present invention has a molecular weight of 500,000 or less in a ratio of 32 to 65%, preferably 35 to 55%, more preferably 38 to 51%, further preferably 44 to 51%, particularly preferably 48 to 51%.

[0044] The acrylic rubber of the present invention has a molecular weight of 2,000,000 or more in a ratio of 3 to 20%, preferably 4 to 18%, particularly preferably 6 to 18%, most preferably 8 to 18%, and most preferably 10 to 18%.

[0045] The ratio of the molecular weight of 500,000 or less and the ratio of the molecular weight of 2,000,000 or more in the acrylic rubber of the present invention can be determined in terms of polystyrene by gel permeation chromatography (GPC) using tetrahydrofuran (THF) as a solvent.

[0046] The ratio of molecular weights below 500,000 and the ratio of molecular weights above 2,000,000 are calculated as follows: a molecular weight distribution curve formed by the slice molecular weight and the slice area is plotted as an integral value curve of the slice area, and the integral value (%) when the slice molecular weight is below 500,000 and the integral value (%) when it is above 2,000,000 is calculated.

[0047] The acrylic rubber of the present invention has a molecular weight distribution (Mw (weight average molecular weight) / Mn (number average molecular weight)) of preferably 4.0 or more, more preferably 5.0 or more, further preferably 6.0 or more, and particularly preferably 6.3 or more, and the upper limit is not particularly limited.

[0048] The molecular weight distribution (Mw / Mn) of the acrylic rubber can be determined in terms of polystyrene by gel permeation chromatography (GPC) using tetrahydrofuran (THF) as a solvent.

[0049] <Acrylic rubber>

[0050] The acrylic rubber used in the present invention can be obtained by polymerizing various monomers. The monomers used may be commercially available products without any particular limitation.

[0051] It should be noted that the acrylic rubber of the present invention is characterized in that the high molecular weight part and the low molecular weight part of the molecular weight distribution are specific distributions. The molecular weight distribution of the acrylic rubber only needs to specify the target molecular weight distribution, and it is possible for those skilled in the art to manufacture acrylic rubbers with desired molecular weight distributions without excessive burden. For example, by changing the type and amount of the polymerization initiator and chain transfer agent used in the polymerization of the acrylic rubber, the molecular weight distribution can be adjusted. In addition, in order to make the high molecular weight part and the low molecular weight part of the molecular weight distribution in the acrylic rubber specific distributions, two or more acrylic rubbers (e.g., low molecular weight acrylic rubber and high molecular weight acrylic rubber prepared separately) can be mixed.

[0052] As the form of the polymerization reaction, emulsion polymerization, suspension polymerization, bulk polymerization, and solution polymerization can be used. However, from the perspective of ease of controlling the polymerization reaction, emulsion polymerization under normal pressure, which is conventionally known as a method for producing acrylic rubber, is preferred.

[0053] In the case of polymerization by emulsion polymerization, a common method may be used, and conventionally known substances commonly used such as a polymerization initiator, an emulsifier, a chain transfer agent, and a polymerization inhibitor may be used.

[0054] The emulsifier used in the present invention is not particularly limited, and nonionic emulsifiers and anionic emulsifiers commonly used in emulsion polymerization can be used. As nonionic emulsifiers, for example, polyoxyethylene alkyl ethers, polyoxyethylene alcohol ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene polycyclic phenyl ethers, polyoxyalkylene alkyl ethers, sorbitan fatty acid esters, polyoxyethylene fatty acid esters, and polyoxyethylene sorbitan fatty acid esters can be cited. As anionic emulsifiers, alkylbenzene sulfonates, alkyl sulfate ester salts, polyoxyethylene alkyl ether sulfate ester salts, polyoxyalkylene alkyl ether phosphates or their salts, fatty acid salts, etc. can be cited, and they can be used alone or in combination. As representative examples of anionic emulsifiers, sodium lauryl sulfate, sodium dodecylbenzene sulfonate, and triethanolamine lauryl sulfate can be cited.

[0055] The amount of the emulsifier used in the present invention can be any amount commonly used in the emulsion polymerization method. Specifically, it is in the range of 0.01 to 10 parts by mass, preferably 0.03 to 7 parts by mass, and more preferably 0.05 to 5 parts by mass, relative to 100 parts by mass of the monomer constituting the acrylic rubber. When a reactive surfactant is used as a monomer component, an emulsifier may not necessarily be added.

[0056] The polymerization initiator used in the present invention is not particularly limited, and a polymerization initiator commonly used in the emulsion polymerization method can be used. Specific examples thereof include inorganic polymerization initiators represented by persulfates such as potassium persulfate, sodium persulfate, and ammonium persulfate, 2,2-bis(4,4-bis(tert-butylperoxide)cyclohexyl)propane, 1-bis(tert-hexylperoxide)cyclohexane, 1,1-bis(tert-butylperoxide)cyclohexane, 4,4-bis(tert-butylperoxide)n-butyl valerate, 2,2-bis(tert-butylperoxide)butane, tert-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, p-menthane hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, tert-butyl isopropyl peroxide, di-tert-butyl peroxide, di-tert-hexyl peroxide, di(2-tert-butyl isopropyl peroxide)benzene, and the like. , diisopropyl peroxide, diisobutyryl peroxide, di(3,5,5-trimethylhexanoyl) peroxide, dilauroyl peroxide, disuccinic acid peroxide, dibenzoyl peroxide, di(3-methylbenzoyl) peroxide, benzoyl(3-methylbenzoyl) peroxide, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di(4-tert-butylcyclohexyl) peroxydicarbonate, di(2-ethylhexyl) peroxydicarbonate, di-sec-butyl peroxydicarbonate, isopropyl peroxyneodecanoate, 1,1,3,3-tetramethylbutyl peroxyneodecanoate, tert-hexyl peroxyneodecanoate, tert-butyl peroxyneodecanoate, tert-hexyl peroxypivalate, tert-tert-heptyl peroxypivalate tert-Butyl peroxylaurate, ... ) hexane and other organic peroxide-based polymerization initiators, hydrogen peroxide, azobisisobutyronitrile, 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis[2-(2-imidazolin-2-yl)propane, 2,2'-azobis(propane-2-carboxamidine), 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamide, 2,2'-azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane}, 2,2'-azobis(1-imino-1-pyrrolidine-2-methylpropane) and azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propionamide} and the like. These polymerization initiators may be used alone or in combination of two or more.

[0057] The amount of the polymerization initiator used in the present invention may be an amount generally used in the emulsion polymerization method, and specifically, it is in the range of 0.01 to 5 parts by mass based on 100 parts by mass of the monomer constituting the acrylic rubber.

[0058] In addition, organic peroxides and inorganic peroxides as polymerization initiators can be used as redox polymerization initiators by combining with reducing agents. The reducing agents used in combination are not particularly limited, and examples thereof include compounds containing metal ions in a reduced state such as ferrous sulfate and cuprous naphthenate, methane compounds such as sodium formaldehyde sulfoxylate and sodium methanesulfonate, amine compounds such as dimethylaniline, ascorbic acid and its salts, alkali metal salts of sulfurous acid and thiosulfuric acid, and other reducing inorganic salts. These reducing agents can be used alone or in combination of two or more. The amount of the reducing agent used is preferably 0.0003 to 10.0 parts by mass relative to 100 parts by mass of the monomer constituting the acrylic rubber.

[0059] A chain transfer agent may be used as needed. Specific examples of the chain transfer agent include alkyl mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, tert-octyl mercaptan, n-dodecyl mercaptan, tert-dodecyl mercaptan, and n-stearyl mercaptan, xanthate compounds such as 2,4-diphenyl-4-methyl-1-pentene, 2,4-diphenyl-4-methyl-2-pentene, dimethyl xanthate disulfide, and diisopropyl xanthate disulfide, terpinolene, tetramethylthiuram disulfide, tetraethylthiuram disulfide, and tetramethylthiuram monosulfide, etc. Thiuram compounds, phenolic compounds such as 2,6-di-tert-butyl-4-methylphenol and styrenated phenol, allyl compounds such as allyl alcohol, halogenated hydrocarbon compounds such as dichloromethane, dibromomethane and carbon tetrabromide, vinyl ethers such as α-benzyloxystyrene, α-benzyloxyacrylonitrile and α-benzyloxyacrylamide, triphenylethane, pentaphenylethane, acrolein, methacrolein, thioglycolic acid, thiomalic acid, 2-ethylhexyl thioglycolate, etc., these can be used alone or in combination. The amount of these chain transfer agents is not particularly limited, and is usually used in an amount of 0 to 5 parts by mass, or 0.01 to 3 parts by mass, relative to 100 parts by mass of the monomers constituting the acrylic rubber.

[0060] Examples of the polymerization inhibitor include hydroxylamine, hydroxylamine sulfate, diethylhydroxylamine, hydroxylamine sulfonic acid and alkali metal salts thereof, sodium dimethyldithiocarbamate, and quinone compounds such as hydroquinone. These can be used alone or in combination of two or more. The amount of the polymerization inhibitor used is not particularly limited, but is usually 0 to 2 parts by mass relative to 100 parts by mass of the monomers constituting the acrylic rubber.

[0061] Furthermore, the polymer obtained by the above method can be adjusted in pH by using a base as a pH adjuster as needed. Specific examples of the base include sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium bicarbonate, ammonia, inorganic ammonium compounds, organic amine compounds, etc. The pH range is pH 1 to 11, preferably pH 1.5 to 10.5, and more preferably pH 2 to 10.

[0062] In addition, polymerization auxiliary materials such as a particle size regulator, a chelating agent, and an oxygen scavenger may be used as necessary.

[0063] The emulsion polymerization can be carried out in batch, semi-batch or continuous mode. The polymerization time and polymerization temperature are not particularly limited. They can be appropriately selected from the type of polymerization initiator used, but the polymerization temperature is usually 10°C to 100°C and the polymerization time is 0.5 hour to 100 hours.

[0064] There is no particular limitation on the method for recovering the polymer obtained by the above method, and a commonly used method can be used. As an example of the method, the following method can be cited: a polymer solution obtained by emulsion polymerization or the like is continuously or intermittently supplied to an aqueous solution containing a coagulant, and water-containing crumbs are obtained by this operation. At this time, the temperature of the aqueous solution containing the coagulant is affected by coagulation conditions such as the type and amount of the monomer, the shear force generated by stirring, etc., and therefore cannot be generally limited, but is usually in the range of 50°C to 100°C, preferably 60°C to 100°C.

[0065] Furthermore, an antioxidant may be added during the solidification process. Specific examples of the antioxidant include phenolic antioxidants, amine antioxidants, phosphanol antioxidants, hindered amine antioxidants, etc. These may be used alone or in combination of two or more.

[0066] Furthermore, the water-containing crumbs obtained by the above method can be adjusted in pH by using an alkali as a pH adjuster as needed. Specific examples of the alkali include sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium bicarbonate, ammonia, inorganic ammonium compounds, organic amine compounds, etc. The pH range is pH 1 to 11, preferably pH 2 to 10, and more preferably pH 4 to 8.

[0067] The water-containing scraps obtained by the above method are preferably washed with water to remove the coagulant. If no water washing is performed or the washing is insufficient, there is a concern that ion residues derived from the coagulant may precipitate during the molding process.

[0068] The acrylic rubber can be obtained by removing water from the water-containing scraps after washing and drying. The drying method is not particularly limited, and is usually dried using a flash dryer, a fluidized dryer, etc. In addition, a dehydration step using a centrifuge, etc. may also be performed before the drying step.

[0069] The molecular weight range of the acrylic copolymer of the present invention produced in this way is preferably 10 to 100, more preferably 15 to 90, and even more preferably 20 to 80, as represented by the Mooney viscosity (ML1+4) at 100° C. in the Mooney scorch test specified in JIS K 6300, from the viewpoint of processability.

[0070] <Composition containing acrylic rubber>

[0071] The acrylic rubber-containing composition of the present invention can be obtained by containing the above-mentioned acrylic rubber and at least a crosslinking agent.

[0072] As the crosslinking agent, conventionally known crosslinking agents commonly used for crosslinking of rubbers such as polyamine compounds, polyepoxy compounds, polyisocyanate compounds, aziridine compounds, sulfides, basic metal oxides and organometallic halides can be used. Among them, polyamine compounds can be preferably used.

[0073] Examples of the polyamine compound include aliphatic polyamine compounds such as hexamethylenediamine, hexamethylenediamine carbamate, and N,N'-biscinnamaldehyde-1,6-hexanediamine, and aromatic polyamine compounds such as 4,4'-methylenedianiline, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-(m-phenylenediisopropylidene)diphenylamine, 4,4'-(p-phenylenediisopropylidene)diphenylamine, 2,2'-bis[4-(4-aminophenoxy)phenyl]propane, 4,4'-diaminobenzanilide, 4,4'-bis(4-aminophenoxy)biphenyl, m-phenylenediamine, p-phenylenediamine, 1,3,5-phenyltriamine, 1,3,5-phenyltriaminomethyl, and isophthalic acid dihydrazide. Among these, aliphatic polyamine compounds are preferred.

[0074] Examples of the polyvalent epoxy compound include phenol novolac epoxy compounds, cresol novolac epoxy compounds, cresol epoxy compounds, bisphenol A epoxy compounds, bisphenol F epoxy compounds, brominated bisphenol A epoxy compounds, brominated bisphenol F epoxy compounds, hydrogenated bisphenol A epoxy compounds, and other glycidyl ether epoxy compounds, alicyclic epoxy compounds, glycidyl ester epoxy compounds, glycidyl amine epoxy compounds, isocyanurate epoxy compounds, and other polyvalent epoxy compounds.

[0075] Examples of the polyisocyanate compound include 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4′-diphenylmethane diisocyanate, hexamethylene diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, 1,5-naphthalene diisocyanate, 1,3,6-hexamethylene triisocyanate, 1,6,11-undecyl triisocyanate, and bicycloheptane triisocyanate.

[0076] Examples of the aziridine compound include 2,4,6-tris(1-aziridinyl)-1,3,5-triazine, tris[1-(2-methyl)aziridinyl]phosphine oxide, and hexa[1-(2-methyl)aziridinyl]triphosphorus triazine.

[0077] Examples of the sulfide include sulfur, 4,4′-dithiomorpholine, tetramethylthiuram disulfide, and tetraethylthiuram disulfide.

[0078] Examples of the basic metal oxide include zinc oxide, lead oxide, calcium oxide, and magnesium oxide.

[0079] As the organometallic halide, for example, a dicyclopentadienyl metal dihalide is exemplified, and as the metal, titanium, zirconium, and the like can be cited.

[0080] These crosslinking agents may be used alone or in combination of two or more. The amount of the crosslinking agent is 0.05 to 20 parts by mass, preferably 0.1 to 10 parts by mass, based on 100 parts by mass of the acrylic rubber of the present invention.

[0081] In addition, the acrylic rubber-containing composition of the present invention can be arbitrarily compounded with other additives commonly used in the technical field, such as lubricants, antioxidants, light stabilizers, fillers, reinforcing agents, plasticizers, processing aids, pigments, colorants, crosslinking accelerators, crosslinking aids, crosslinking retarders, antistatic agents, foaming agents, etc.

[0082] As the filler, known fillers can be used, specifically, calcium carbonate, talc, silica, clay, carbon fiber, glass fiber, carbon black, titanium oxide, magnesium oxide, hydrotalcite, magnesium hydroxide, antimony oxide, zinc oxide, carbon black, etc. can be mentioned. They can be used alone or in combination of two or more. Among them, silica and carbon black are preferred.

[0083] The amount of the filler compounded may be 15 to 100 parts by mass, preferably 20 to 80 parts by mass, based on 100 parts by mass of the acrylic rubber of the present invention.

[0084] Examples of the softener include lubricating oil, process oil, coal tar, castor oil, stearic acid, calcium stearate, etc. These may be used alone or in combination of two or more.

[0085] The blending amount of the softener may be 0.3 to 10 parts by mass, preferably 0.5 to 5 parts by mass, based on 100 parts by mass of the acrylic rubber of the present invention.

[0086] As antioxidants, for example, amines, phosphates, quinolines, cresols, phenols, dithiocarbamate metal salts, etc. can be cited. They can be used alone or in combination of two or more. Among them, amines such as diphenylamine derivatives and phenylenediamine derivatives are preferred.

[0087] The amount of the antioxidant compounded may be 0.3 to 10 parts by mass, preferably 0.5 to 5 parts by mass, based on 100 parts by mass of the acrylic rubber of the present invention.

[0088] Further, without departing from the scope of the gist of the present invention, it is also possible to carry out blending with commonly used rubber, resin, etc. in the technical field. As commonly used rubber that can be used in the present invention, for example, butadiene rubber, styrene-butadiene rubber, isoprene rubber, natural rubber, nitrile rubber, acrylonitrile-butadiene-isoprene rubber, EPDM rubber, epichlorohydrin rubber, etc. can be enumerated, and as resin, for example, PMMA (polymethyl methacrylate) resin, PS (polystyrene) resin, PUR (polyurethane) resin, PVC (polyvinyl chloride) resin, EVA (ethylene / vinyl acetate) resin, AS (styrene / acrylonitrile) resin, PE (polyethylene) resin, etc. can be enumerated. They can be used alone, and two or more kinds can also be used in combination.

[0089] The total amount of the rubber and the resin blended is 50 parts by mass or less, preferably 10 parts by mass or less, and more preferably 1 part by mass or less, based on 100 parts by mass of the acrylic rubber of the present invention.

[0090] As a compounding method for the composition containing acrylic rubber for obtaining the rubber cross-linked product of the present invention, any device used in the field of rubber processing in the past, such as an open roll mill, a Banbury mixer, various kneading machines, etc. can be used. As its compounding steps, it can be carried out in the usual steps carried out in the field of rubber processing. For example, it can be carried out in the following steps: firstly, only the rubber is kneaded, and then compounding agents other than the crosslinking agent and the crosslinking accelerator are added to prepare the A kneading compound, and then the crosslinking agent and the crosslinking accelerator are added to carry out B kneading.

[0091] <Rubber cross-linked products>

[0092] The cross-linked rubber of the present invention can be obtained by cross-linking the above-mentioned acrylic rubber-containing composition.

[0093] The cross-linked rubber of the present invention can be formed by heating the above-mentioned acrylic rubber-containing composition to 100°C to 250°C. The cross-linking time varies depending on the temperature and is generally between 0.5 minutes and 300 minutes. In addition to the case where cross-linking and molding are performed integrally, and the case where the previously molded acrylic rubber-containing composition is reheated to form a cross-linked rubber, the cross-linked rubber can also be molded and processed by heating first. As a specific method for cross-linking molding, any method such as compression molding based on a mold, injection molding, and heat based on a steam tank, an air bath, infrared rays, or microwaves can be used.

[0094] The acrylic rubber-containing composition of the present invention obtained in this way is excellent in roll processability during processing, and the rubber cross-linked product of the present invention is excellent in normal physical properties and heat resistance at high temperatures for a long period of time.

[0095] Therefore, the rubber cross-linked product of the present invention is suitable for use as various gaskets such as O-rings, seals, separators, oil seals, shaft seals, bearing seals, mechanical seals, wellhead seals, seals for electrical / electronic equipment, seals for pneumatic equipment, cylinder head gaskets mounted at the connection between a cylinder block and a cylinder head, rocker cover gaskets mounted at the connection between a rocker cover and a cylinder head, oil pan gaskets mounted at the connection between an oil pan and a cylinder block or a transmission, gaskets for fuel cell separators mounted between a pair of housings that sandwich a unit element having a positive electrode, an electrolyte plate, and a negative electrode, and gaskets for upper covers of hard disk drives, by utilizing the above-mentioned properties.

[0096] The cross-linked rubber product of the present invention can be suitably used as extrusion molded products and cross-linked products used in automobile applications, for example, various hoses such as fuel hoses, filler neck hoses, breather hoses, steam hoses, and oil hoses for fuel tanks, air hoses such as turbo air hoses and emission control hoses, radiator hoses, heater hoses, brake hoses, and air conditioning hoses.

[0097] Example

[0098] The present invention will be specifically described based on Examples and Comparative Examples, but the present invention is not limited to these.

[0099] (Determination of Molecular Weight)

[0100] As a method for measuring the molecular weight, an acrylic rubber is dissolved in tetrahydrofuran (THF) as a solvent, and the molecular weight is measured in terms of polystyrene by gel permeation chromatography (GPC).

[0101] The measurement was performed using a GPC device Alliance HPLC system manufactured by Waters Corp. connected to two TSK gel HM-2 columns manufactured by Tosoh Corporation, with a flow rate of 0.6 mL / min, a concentration of polymer (acrylic rubber) of 10 mg / THF8 mL, an injection volume of 40 μL, and a column temperature of 50°C.

[0102] The ratio of the molecular weight of acrylic rubber (polymer) below 500,000 and above 2,000,000 is calculated as follows: Based on the molecular weight distribution curve formed by the slice molecular weight and the slice area, an integral value curve of the slice area is drawn, and the integral value (%) when the slice molecular weight is below 500,000 and the integral value (%) when it is above 2,000,000 is calculated.

[0103] Furthermore, the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the acrylic rubber (polymer) were calculated, and based on the calculated results, the molecular weight distribution (Mw / Mn) of the acrylic rubber (polymer) was calculated.

[0104] <Mooney viscosity (ML1+4, 100℃)>

[0105] The acrylic copolymer was measured for Mooney viscosity (ML1+4) at a measurement temperature of 100° C. using Mooney Viscometer AM-3 manufactured by Toyo Seiki Co., Ltd. in accordance with the Mooney viscosity test of uncrosslinked rubber physical testing methods of JIS K6300.

[0106] (Manufacture of Acrylic Rubber A)

[0107] In a polymerization reactor equipped with a thermometer, a stirring device, a nitrogen inlet pipe and a decompression device, 150 parts by mass of water, 1.2 parts by mass of sodium salt of polyoxyalkylene alkyl ether phosphate, 68.5 parts by mass of ethyl acrylate as monomers, 20 parts by mass of butyl acrylate, 10 parts by mass of 2-methoxyethyl acrylate and 1.5 parts by mass of monobutyl fumarate, and 0.055 parts by mass of n-dodecyl mercaptan as a chain transfer agent were added, and degassing and nitrogen replacement based on reduced pressure were repeated to fully remove oxygen, and then 0.072 parts by mass of sodium formaldehyde sulfoxylate and 0.06 parts by mass of potassium persulfate were added to initiate emulsion polymerization at normal pressure and room temperature, and the reaction was continued until the polymerization conversion rate reached 95% to obtain a polymerization liquid. The obtained polymerization liquid was coagulated in sodium sulfate, washed with water and dried to obtain acrylic rubber A. The Mooney viscosity ML (1+4) at 100°C was 29. The ratio of molecular weights of 500,000 or less and 2,000,000 or more is shown in Table 1.

[0108] (Manufacture of Acrylate Rubber B)

[0109] Acrylate rubber B was obtained in the same manner as in the production of acrylate rubber A except that n-dodecyl mercaptan was not used. Mooney viscosity ML (1+4) at 100° C. was 49. Table 1 shows the ratio of molecular weights of 500,000 or less and 2,000,000 or more.

[0110] (Manufacture of Acrylic Rubber C)

[0111] Acrylic rubber C was obtained in the same manner as in the production of acrylic rubber A except that 0.025 parts by mass of n-dodecyl mercaptan, 0.12 parts by mass of sodium formaldehyde sulfoxylate and 0.01 parts by mass of potassium persulfate were used. The Mooney viscosity ML (1+4) at 100° C. was 36. The ratio of molecular weights of 500,000 or less and 2,000,000 or more are shown in Table 1.

[0112] (Manufacture of Acrylic Rubber D)

[0113] Acrylic rubber D was obtained in the same manner as in the production of acrylic rubber A except that n-dodecyl mercaptan was changed to 0.07 parts by mass, and Mooney viscosity ML (1+4) at 100° C. was 24. Table 1 shows the ratio of molecular weights of 500,000 or less and 2,000,000 or more.

[0114] (Manufacture of Acrylic Rubber E)

[0115] 67 parts by mass of acrylic rubber A and 33 parts by mass of acrylic rubber B were mixed to obtain acrylic rubber E. Table 1 shows the ratio of the molecular weight of 500,000 or less and the ratio of the molecular weight of 2,000,000 or more.

[0116] (Manufacture of Acrylic Rubber F)

[0117] 50 parts by mass of acrylic rubber A and 50 parts by mass of acrylic rubber B were mixed to obtain acrylic rubber F. Table 1 shows the ratio of the molecular weight of 500,000 or less and the ratio of the molecular weight of 2,000,000 or more.

[0118] (Manufacture of Acrylic Rubber G)

[0119] 33 parts by mass of acrylic rubber A and 67 parts by mass of acrylic rubber B were mixed to obtain acrylic rubber E. Table 1 shows the ratio of the molecular weight of 500,000 or less and the ratio of the molecular weight of 2,000,000 or more.

[0120] (Manufacture of Acrylic Rubber H)

[0121] Acrylic rubber H was obtained in the same manner as in the production of acrylic rubber C except that 0.015 parts by weight of n-dodecyl mercaptan was used and 0.03 parts by weight of 1-thioglycerol was added when the polymerization addition rate reached 60%. The Mooney viscosity ML (1+4) at 100°C was 37. The ratio of molecular weights of 500,000 or less and 2,000,000 or more are shown in Table 1.

[0122] [Table 1]

[0123] Ratio of less than 500,000 (%) Ratio of 2 million or more (%) Mw / Mn Acrylic rubber A 47 8 3.2 Acrylic rubber E (A:B=67:33) 42 12 3.7 Acrylic rubber F (A:B=50:50) 40 14 4.1 Acrylic rubber G (A:B=33:67) 37 17 3.7 Acrylic rubber B 31 21 3.7 Acrylic rubber C 53 7 4.3 Acrylic rubber D 51 13 5.0 Acrylic rubber H 51 11 6.6

[0124] (Manufacture of acrylic rubber composition)

[0125] First, the acrylic rubber, carbon black (Seast SO (Tokai Carbon Co., Ltd.)), stearic acid (STEARIC ACID CHERRY (NOF Corporation)), and antioxidant (Noklak CD (Ouchi Shinko Chemical Industry Co., Ltd.)) shown in Table 2 were kneaded in a kneader at 100°C to prepare a kneaded compound A. The kneaded compound A was kneaded in an open roll at room temperature, and hexamethylenediamine urethane and an accelerator (Rhenogran XLA60 (LANXESS)) were kneaded to prepare a kneaded compound B, and an uncrosslinked sheet with a thickness of 2 to 2.5 mm was prepared. The unit of the compounding agent in Table 2 is set to mass parts.

[0126] [Table 2]

[0127]

[0128] (Evaluation of extrudability)

[0129] According to the Gerber die extrusion test of ASTM-D-2230, the uncrosslinked sheet was extruded at L / D=10, rotation speed: 60 rpm, temperature: barrel 60°C, die 80°C. The length of the extruded product was evaluated in three stages: ◎: 80 cm / min or more, ○: 80 to 60 cm / min, and ×: 60 cm / min or less. The results are shown in Table 3.

[0130] (Evaluation of cross-linking shrinkage)

[0131] The length of the extrusion molded product obtained above was measured before and after heating at 180° C. for 3 hours in an air oven, and the crosslinking shrinkage was calculated using the following formula. The results are shown in Table 3. The smaller the crosslinking shrinkage, the more the crosslinking shrinkage can be reduced.

[0132]

[0133] (Preparation of Secondary Cross-linked Product)

[0134] The uncrosslinked rubber sheet was subjected to a press treatment at 180° C. for 10 minutes to obtain a primary crosslinked product having a thickness of 2 mm, and then heated in an air oven at 180° C. for 3 hours to obtain a secondary crosslinked product.

[0135] (Test of normal physical properties)

[0136] The obtained secondary crosslinked product was subjected to evaluation by a tensile test and a hardness test. The tensile test was conducted in accordance with JIS K6251, and the hardness test was conducted in accordance with the method described in JIS K6253.

[0137] Table 3 shows the test results of Examples and Comparative Examples obtained by each test method.

[0138] In each table, tensile strength and elongation refer to the tensile strength and elongation specified in the tensile test of JIS K6251, respectively, and hardness refers to the hardness specified in the hardness test of JIS K6253. The results are shown in Table 3. When the tensile strength is 8 MPa or more, the elongation is 200% or more, and the hardness is 60 or more, it is judged that the normal physical properties expected as acrylic rubber are maintained.

[0139] [Table 3]

[0140]

[0141] Table 3 shows that the acrylic rubber-containing compositions using acrylic rubbers having a molecular weight ratio of 500,000 or less to 2,000,000 or more as defined in the present invention in Examples 1 to 7 have good extrudability and reduced crosslinking shrinkage, and their crosslinked products can maintain the normal physical properties expected of acrylic rubbers.

[0142] On the other hand, it was found that Comparative Example 1 was inferior to Examples 1 to 7 in cross-linking shrinkage.

[0143] Industrial Applicability

[0144] The present invention can provide an acrylic rubber having a small cross-linking shrinkage. A rubber cross-linked product prepared using a composition containing the acrylic rubber is suitable for use as automotive components such as seals, pipes, vibration-proof materials, ducts, belts, or boots.

Claims

1. An acrylic rubber, wherein the proportion of the molecular weight of the acrylic rubber is 500,000 or less is 32 to 65%, and the proportion of the molecular weight of the acrylic rubber is 2,000,000 or more is 3 to 20%, The acrylic rubber contains a structural unit derived from (meth)acrylate and a structural unit derived from an unsaturated monomer having a crosslinking group. The structural unit derived from the unsaturated monomer having a crosslinking group is one or more selected from the group consisting of a structural unit derived from an unsaturated monomer having a halogen group, a structural unit derived from an unsaturated monomer having a carboxyl group, and a structural unit derived from an unsaturated monomer having an epoxy group. Among all structural units of the acrylic rubber, the content of the structural unit derived from (meth)acrylate is 50 mass % to 99 mass %, and the content of the structural unit derived from the unsaturated monomer having a crosslinking group is 0.1 mass % to 10 mass %.

2. The acrylic rubber according to claim 1, wherein the proportion of the acrylic rubber having a molecular weight of 500,000 or less is 35 to 55%, and the proportion of the acrylic rubber having a molecular weight of 2,000,000 or more is 4 to 18%.

3. The acrylic rubber according to claim 1 or 2, wherein the proportion of the acrylic rubber having a molecular weight of 500,000 or less is 38 to 51%, and the proportion of the acrylic rubber having a molecular weight of 2,000,000 or more is 5 to 15%. 4 . An acrylic rubber-containing composition comprising: the acrylic rubber according to claim 1 and a crosslinking agent.

5. A rubber cross-linked product produced by using the acrylic rubber-containing composition according to claim 4.

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