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

Abstract

Upon discovering the issue that crosslinking shrinkage increases during crosslinking of acrylic rubber, the present invention was developed to address the problem of reducing the crosslinking shrinkage while maintaining good normal physical properties. In developing the present invention, it was discovered that the problem can be solved by causing a high molecular weight part and a low molecular weight part of the molecular weight distribution in acrylic rubber to have a specific distribution. Specifically, it was discovered that the problem can be solved by acrylic rubber 32-65% of which is accounted for by a part having a molecular weight of not more than 0.5 million and 3-20% of which is accounted for by a part having a molecular weight of not less than 2 million.

Description

[Technical Field]

[0001] The present invention relates to an acrylic rubber, an acrylic rubber-containing composition, and a cross-linked rubber product. [Background technology]

[0002] It is known that acrylic rubber can be obtained by copolymerizing (meth)acrylic acid esters by emulsion polymerization or the like, adding the copolymer to an aqueous coagulant solution, and then drying the resulting hydrous crumbs.

[0003] Acrylic rubber is generally known as a rubber having excellent heat resistance, oil resistance, and ozone resistance, and cross-linked products thereof are widely used in automotive components, such as seal materials, hose materials, vibration-proof materials, tube materials, belt materials, and boot materials.

[0004] Acrylic rubber requires processing when used in these automotive components. Patent Document 1 describes how the processability of acrylic rubber can be improved without reducing its heat resistance. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-40922 Summary of the Invention [Problem to be solved by the invention]

[0006] However, as a result of investigations by the present inventors, it became clear that there is a problem in that crosslinking shrinkage increases when acrylic rubber is crosslinked, and it became clear that a new challenge is to reduce crosslinking shrinkage while maintaining good normal physical properties. [Means for solving the problem]

[0007] As a result of various investigations to solve the new problems that the inventors have discovered, they have found that the above problems can be solved by adjusting the high-molecular-weight and low-molecular-weight portions of the molecular weight distribution of the acrylic rubber to a specific distribution. Specifically, the inventors have found that by using an acrylic rubber in which the proportion of molecular weights of 500,000 or less is 32 to 65% and the proportion of molecular weights of 2,000,000 or less is 3 to 20%, crosslinking shrinkage can be reduced while maintaining good normal physical properties.

[0008] The aspects of the present invention are as follows. Item 1: Acrylic rubber in which the proportion of those with a molecular weight of 500,000 or less is 32 to 65% and the proportion of those with a molecular weight of 2,000,000 or more is 3 to 20%. Item 2. The acrylic rubber according to Item 1, wherein the proportion of those having a molecular weight of 500,000 or less is 35 to 55%, and the proportion of those having a molecular weight of 2,000,000 or more is 4 to 18%. Item 3. The acrylic rubber according to Item 1 or 2, wherein the proportion of those having a molecular weight of 500,000 or less is 38 to 51%, and the proportion of those having a molecular weight of 2,000,000 or more is 5 to 15%. 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 carboxy group, and a structural unit derived from an unsaturated monomer having an epoxy group. Item 5. An acrylic rubber-containing composition comprising the acrylic rubber according to any one of items 1 to 4 and a crosslinking agent. Item 6. A cross-linked rubber product produced using the acrylic rubber composition according to item 5. [Effects of the Invention]

[0009] The acrylic rubber of the present invention can reduce crosslinking shrinkage while maintaining good normal physical properties, and therefore can be suitably used in products manufactured using acrylic rubber. DETAILED DESCRIPTION OF THE INVENTION

[0010] In the acrylic rubber of the present invention, the proportion of molecular weights of 500,000 or less is 32 to 65%, and the proportion of molecular weights of 2,000,000 or more is 3 to 20%, which makes it possible to reduce crosslinking shrinkage while maintaining good normal physical properties.

[0011] The reason why the above-mentioned effects can be obtained with the acrylic rubber is presumed to be as follows. Acrylic rubber containing a large amount of components with a molecular weight of 2 million or more has good rubber properties, including normal physical properties, but tends to be less processable and have a high crosslinking shrinkage rate. On the other hand, acrylic rubber containing a large amount of components with a molecular weight of 500,000 or less has a low crosslinking shrinkage rate, but poor rubber properties. Acrylic rubber with a composition containing a certain amount of each component can achieve both reduced crosslinking shrinkage and good rubber properties.

[0012] The acrylic rubber of the present invention is preferably a polymer mainly composed of structural units derived from (meth)acrylic acid esters, and the term "main component" refers to a polymer containing 50 mass % or more of structural units derived from (meth)acrylic acid esters. Note that "(meth)acrylic acid esters" means "acrylic acid esters or methacrylic acid esters," and the same applies to similar expressions in the present application.

[0013] Examples of the structural unit derived from a (meth)acrylic acid ester include a structural unit derived from an alkyl (meth)acrylate and a structural unit derived from an alkoxyalkyl (meth)acrylate. Among these, a structural unit derived from an alkyl acrylate having an alkyl group containing 1 to 8 carbon atoms and a structural unit derived from an alkoxyalkyl acrylate having an alkoxyalkyl group containing 2 to 8 carbon atoms are preferred, a structural unit derived from an alkyl acrylate having an alkyl group containing 2 to 6 carbon atoms and / or a structural unit derived from an alkoxyalkyl acrylate having an alkoxyalkyl group containing 2 to 6 carbon atoms are more preferred, and a structural unit derived from an alkyl acrylate having an alkyl group containing 2 to 4 carbon atoms and / or a structural unit derived from an alkoxyalkyl acrylate having an alkoxyalkyl group containing 2 to 4 carbon atoms is particularly preferred. The structural unit derived from a (meth)acrylic acid ester may be a structural unit derived from a single (meth)acrylic acid ester or two or more types of (meth)acrylic acid esters.

[0014] Specific examples of (meth)acrylic acid alkyl esters include (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and cyclohexyl (meth)acrylate. These may be used alone or in combination of two or more. Among these, ethyl (meth)acrylate and n-butyl (meth)acrylate are preferred. Specific examples of (meth)acrylic acid alkoxyalkyl esters include (meth)acrylic acid esters such as 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, and 4-ethoxybutyl (meth)acrylate. These may be used alone or in combination of two or more. Among these, 2-methoxyethyl (meth)acrylate is preferred.

[0015] The content of the structural units derived from (meth)acrylic acid ester in the acrylic rubber of the present invention is preferably 50% by mass or more, more preferably 60% by mass or more, and may be 70% by mass or more, or 80% by mass or more, based on all structural units of the acrylic rubber. The upper limit is preferably 99.5% by mass or less, and more preferably 99% by mass or less.

[0016] The acrylic rubber of the present invention preferably contains a structural unit derived from an unsaturated monomer having a crosslinking group. Examples of structural units derived from an unsaturated monomer having a crosslinking group include structural units derived from an unsaturated monomer having a halogen group (e.g., a chlorine group), structural units derived from an unsaturated monomer having a carboxy group, and structural units derived from an unsaturated monomer having an epoxy group. These may be used alone or in combination of two or more. Among these, structural units derived from unsaturated monomers having a halogen group (especially a chlorine group) or a carboxyl group are particularly preferred, and structural units derived from unsaturated monomers having a carboxyl group are most preferred.

[0017] Examples of unsaturated monomers having a halogen group include vinyl monochloroacetate and allyl chloroacetate. These may be used alone or in combination of two or more. Among these, vinyl monochloroacetate is preferred.

[0018] Examples of unsaturated monomers having a carboxyl group include 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; butenedioic acid mono-chain alkyl esters such as monomethyl fumarate, monoethyl fumarate, mono-n-butyl fumarate, monomethyl maleate, monoethyl maleate, mono-2-ethylhexyl maleate, and mono-n-butyl maleate; butenedioic acid mono-cyclic alkyl esters such as monocyclopentyl fumarate, monocyclohexyl fumarate, monocyclopentyl maleate, and monocyclohexyl maleate; and itaconic acid monoesters such as monomethyl itaconate, monoethyl itaconate, mono-n-butyl itaconate, and monocyclohexyl itaconate. These may be used alone or in combination of two or more. Among these, unsaturated dicarboxylic acid monoesters such as monoethyl fumarate, monopropyl fumarate, monobutyl fumarate, monoethyl itaconate, monopropyl itaconate, and monobutyl itaconate are preferred.

[0019] Examples of the unsaturated monomer having an epoxy group include glycidyl (meth)acrylate, (meth)allyl glycidyl ether, etc. These may be used alone or in combination of two or more.

[0020] The content of the structural units derived from unsaturated monomers having a crosslinking group in the acrylic rubber is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and particularly preferably 0.5% by mass or more, and is preferably 10% by mass or less, more preferably 5% by mass or less, and particularly preferably 2.5% by mass or less, of all the structural units of the acrylic rubber. Having the structural units derived from unsaturated monomers having a crosslinking group in the above range is preferable in terms of physical properties such as strength and compression set, and processability.

[0021] In the acrylic rubber of the present invention, the total content of structural units derived from (meth)acrylic acid esters and structural units derived from unsaturated monomers having a crosslinking group is preferably 55% by mass or more, more preferably 65% ​​by mass or more, even more preferably 75% by mass or more, particularly preferably 85% by mass or more, and may be 100% by mass, based on all structural units of the acrylic rubber.

[0022] 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, provided that the purpose of the present invention is not exceeded. 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 may be used alone or in combination of two or more.

[0023] Examples of ethylenically unsaturated nitrile monomers include acrylonitrile, methacrylonitrile, α-methoxyacrylonitrile, vinylidene cyanide, etc. These may be used alone or in combination of two or more.

[0024] Examples of (meth)acrylamide monomers include acrylamide, methacrylamide, diacetone acrylamide, diacetone methacrylamide, N-butoxymethyl acrylamide, N-butoxymethyl methacrylamide, N-butoxyethyl acrylamide, N-butoxyethyl methacrylamide, N-methoxymethyl acrylamide, N-methoxymethyl methacrylamide, N-propoxymethyl acrylamide, N-propoxymethyl methacrylamide, N-methyl acrylamide, N-methyl methacrylamide, N,N-dimethyl acrylamide, N,N-dimethyl methacrylamide, N,N-diethyl acrylamide, N,N-diethyl methacrylamide, N-methylolacrylamide, N-methylol methacrylamide, ethacrylamide, crotonamide, cinnamic acid amide, maleindiamide, itacondiamide, methylmaleamide, methylitaconamide, maleinimide, itaconimide, etc. These may be used alone or in combination of two or more.

[0025] Examples of aromatic vinyl monomers include styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, o-ethylstyrene, p-ethylstyrene, α-fluorostyrene, p-trifluoromethylstyrene, p-methoxystyrene, p-aminostyrene, p-dimethylaminostyrene, p-acetoxystyrene, styrenesulfonic acid or a salt thereof, α-vinylnaphthalene, 1-vinylnaphthalene-4-sulfonic acid or a salt thereof, 2-vinylfluorene, 2-vinylpyridine, 4-vinylpyridine, divinylbenzene, diisopropenylbenzene, vinylbenzyl chloride, etc. These may be used alone or in combination of two or more.

[0026] Examples of conjugated diene monomers include 1,3-butadiene, 2-methyl-1,3-butadiene, 2-chloro-1,3-butadiene, 1,2-dichloro-1,3-butadiene, 2,3-dichloro-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-neopentyl-1,3-butadiene, 2-bromo-1,3-butadiene, 2-cyano-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, chloroprene, piperylene, etc. These may be used alone or in combination of two or more.

[0027] Examples of non-conjugated diene monomers include 1,4-pentadiene, 1,4-hexadiene, ethylidene norbornene, norbornadiene, dicyclopentadiene, etc. These may be used alone or in combination of two or more.

[0028] Other olefin-based monomers include, for example, esters such as dicyclopentadienyl acrylate, dicyclopentadienyl methacrylate, dicyclopentadienyl ethyl acrylate, dicyclopentadienyl ethyl methacrylate, ethylene, propylene, vinyl chloride, vinylidene chloride, 1,2-dichloroethylene, vinyl acetate, vinyl fluoride, vinylidene fluoride, 1,2-difluoroethylene, vinyl bromide, vinylidene bromide, 1,2-dibromoethylene, ethyl vinyl ether, butyl vinyl ether, etc. These may be used alone or in combination of two or more.

[0029] In the acrylic rubber of the present invention, the content of the structural units can be determined by the nuclear magnetic resonance spectrum of the obtained polymer.

[0030] In the acrylic rubber of the present invention, the proportion of molecular weights of 500,000 or less is 32 to 65%, preferably 35 to 55%, more preferably 38 to 51%, even more preferably 44 to 51%, and particularly preferably 48 to 51%.

[0031] In the acrylic rubber of the present invention, the proportion of those having a molecular weight of 2 million or more is 3 to 20%, preferably 4 to 18%, particularly preferably 6 to 18%, most preferably 8 to 18%, and even most preferably 10 to 18%.

[0032] The proportion of molecular weights of 500,000 or less and the proportion of molecular weights of 2,000,000 or more in the acrylic rubber of the present invention can be determined in terms of polystyrene using gel permeation chromatography (GPC) with tetrahydrofuran (THF) as a solvent.

[0033] The proportion of molecular weights of 500,000 or less and the proportion of molecular weights of 2,000,000 or more are calculated by drawing an integral curve of the slice area from a molecular weight distribution curve consisting of the slice molecular weight and the slice area, and then calculating the integral (%) when the slice molecular weight is 500,000 or less and the integral (%) when the slice molecular weight is 2,000,000 or more.

[0034] 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, even more preferably 6.0 or more, and particularly preferably 6.3 or more, with no particular upper limit. The molecular weight distribution (Mw / Mn) of the acrylic rubber can be determined in terms of polystyrene using gel permeation chromatography (GPC) with tetrahydrofuran (THF) as a solvent.

[0035] <Acrylic rubber> The acrylic rubber used in the present invention can be obtained by polymerizing various monomers. The monomers used may be commercially available products and are not particularly limited.

[0036] The acrylic rubber of the present invention is characterized by a specific distribution of high and low molecular weight portions in the molecular weight distribution. As long as the target molecular weight distribution of the acrylic rubber is determined, a person skilled in the art can easily produce an acrylic rubber having the desired molecular weight distribution. For example, the molecular weight distribution can be adjusted by changing the type and amount of polymerization initiator and chain transfer agent used in the polymerization of the acrylic rubber. Furthermore, two or more types of acrylic rubber (e.g., separately prepared low-molecular weight acrylic rubber and high-molecular weight acrylic rubber) may be mixed to achieve a specific distribution of the high-molecular weight and low-molecular weight portions in the molecular weight distribution of the acrylic rubber.

[0037] The polymerization reaction may be carried out by any of emulsion polymerization, suspension polymerization, bulk polymerization, and solution polymerization. However, from the standpoint of ease of control of the polymerization reaction, it is preferable to carry out emulsion polymerization under normal pressure, which is a method generally used as a conventional method for producing acrylic rubber.

[0038] In the case of emulsion polymerization, a conventional method may be used, and conventionally known polymerization initiators, emulsifiers, chain transfer agents, polymerization terminators, etc. that are commonly used may be used.

[0039] The emulsifier used in the present invention is not particularly limited, and nonionic emulsifiers and anionic emulsifiers commonly used in emulsion polymerization methods can be used. Examples of nonionic emulsifiers include 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. Examples of anionic emulsifiers include alkylbenzene sulfonates, alkyl sulfates, polyoxyethylene alkyl ether sulfates, polyoxyalkylene alkyl ether phosphates or their salts, and fatty acid salts. These may be used alone or in combination. Representative examples of anionic emulsifiers include sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, and triethanolamine dodecyl sulfate.

[0040] The amount of emulsifier used in the present invention may be any amount generally used in emulsion polymerization. Specifically, it is in the range of 0.01 to 10 parts by mass, preferably 0.03 to 7 parts by mass, and more preferably 0.05 to 5 parts by mass, relative to 100 parts by mass of the monomers constituting the acrylic rubber. When a reactive surfactant is used as a monomer component, the addition of an emulsifier is not necessarily required.

[0041] The polymerization initiator used in the present invention is not particularly limited, and polymerization initiators generally used in emulsion polymerization methods can be used. Specific examples thereof include inorganic polymerization initiators typified by persulfates such as potassium persulfate, sodium persulfate, and ammonium persulfate, 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, and cumene hydroperoxide. Side, diisopropylbenzene hydroperoxide, p-menthane hydroperoxide, 1,1,3,3-tetramethylbutyl 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, disuccinic acid peroxide oxide, dibenzoyl peroxide, di(3-methylbenzoyl) peroxide, benzoyl(3-methylbenzoyl) peroxide, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di(4-t-butylcyclohexyl) peroxydicarbonate, di(2-ethylhexyl) peroxydicarbonate, di-sec-butyl peroxydicarbonate, cumyl peroxyneodecanate, 1,1,3,3-tetramethylbutylperoxyneodecanate Canate, t-hexylperoxyneodecanate, t-butylperoxyneodecanate, t-hexylperoxypivalate, t-butylperoxypivalate, 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanate, t-hexylperoxy-2-ethylhexanate, t-butylperoxy-2-ethylhexanate, t-butylperoxylaurate, t-butylperoxy-3,5,Organic peroxide polymerization initiators such as 5-trimethylhexanate, t-hexylperoxyisopropyl monocarbonate, t-butylperoxyisopropyl monocarbonate, t-butylperoxy2-ethylhexyl monocarbonate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-butylperoxyacetate, t-hexylperoxybenzoate, t-butylperoxybenzoate, and 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, hydroperoxides, azobisisobutyronitrile, 4-4'-azobis(4- Examples of suitable polymerization initiators include azo initiators such as 2-2'-azobis[2-(2-imidazolin-2-yl)propane, 2-2'-azobis(propane-2-carboxamidine), 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}. These polymerization initiators can be used alone or in combination of two or more.

[0042] The amount of the polymerization initiator used in the present invention may be any amount generally used in emulsion polymerization, specifically, in the range of 0.01 to 5 parts by mass per 100 parts by mass of the monomers constituting the acrylic rubber.

[0043] In addition, organic peroxides and inorganic peroxides used as polymerization initiators can be used as redox polymerization initiators by combining them with a reducing agent. Reducing agents that can be used in combination include, but are not limited to, compounds containing reduced metal ions such as ferrous sulfate and cuprous naphthenate, methane compounds such as sodium formaldehyde sulfoxylate and sodium methanesulfonate, amine compounds such as dimethylaniline, and inorganic salts with reducing properties such as ascorbic acid and its salts, and alkali metal salts of sulfite and thiosulfate. These reducing agents can be used alone or in combination of two or more. The amount of reducing agent used is preferably 0.0003 to 10.0 parts by mass per 100 parts by mass of the monomers that make up the acrylic rubber.

[0044] A chain transfer agent can be used as needed. Specific examples of the chain transfer agent include alkyl mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, and n-stearyl mercaptan, xanthogen compounds such as 2,4-diphenyl-4-methyl-1-pentene, 2,4-diphenyl-4-methyl-2-pentene, dimethyl xanthogen disulfide, and diisopropyl xanthogen disulfide, terpinolene, tetramethylthiuram disulfide, tetraethylthiuram disulfide, and tetramethylthiuram monosulfide. Examples of suitable chain transfer agents include thiuram compounds, phenolic compounds such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol, allyl compounds such as allyl alcohol, halogenated hydrocarbon compounds such as dichloromethane, dibromomethane and carbon tetrabromide, vinyl ethers such as α-benzyloxystyrene, α-benzyloxyacrylonitrile and α-benzyloxyacrylamide, triphenylethane, pentaphenylethane, acrolein, methacrolein, thioglycolic acid, thiomalic acid and 2-ethylhexyl thioglycolate, and the like. These may be used alone or in combination of two or more. The amount of these chain transfer agents is not particularly limited, but is usually 0 to 5 parts by mass, and may be 0.01 to 3 parts by mass, per 100 parts by mass of the monomers constituting the acrylic rubber.

[0045] Examples of polymerization terminators include hydroxylamine, hydroxylamine sulfate, diethylhydroxyamine, hydroxylamine sulfonic acid and its alkali metal salts, sodium dimethyldithiocarbamate, and quinone compounds such as hydroquinone. These may be used alone or in combination of two or more. The amount of polymerization terminator used is not particularly limited, but is usually 0 to 2 parts by mass per 100 parts by mass of the monomers that make up the acrylic rubber.

[0046] Furthermore, the pH of the polymer obtained by the above method can be adjusted, if necessary, by using a base as a pH adjuster. Specific examples of bases include sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium bicarbonate, ammonia, inorganic ammonium compounds, and organic amine compounds. The pH range is 1 to 11, preferably 1.5 to 10.5, and more preferably 2 to 10.

[0047] In addition, if necessary, polymerization secondary materials such as particle size adjusters, chelating agents, and oxygen scavengers can be used.

[0048] The emulsion polymerization may be carried out in a batch, semi-batch, or continuous manner. The polymerization time and temperature are not particularly limited. They can be appropriately selected depending on the type of polymerization initiator used, but generally, the polymerization temperature is 10°C to 100°C, and the polymerization time is 0.5 to 100 hours.

[0049] The method for recovering the polymer obtained by the above method is not particularly limited, and a commonly used method can be used. One example of such a method is to continuously or batchwise supply the polymerization solution obtained by emulsion polymerization or the like to an aqueous solution containing a coagulant, thereby obtaining hydrous crumbs. The temperature of the aqueous solution containing the coagulant is affected by coagulation conditions such as the type and amount of monomer used, and shear force due to stirring, so it cannot be uniformly determined, but is generally 50°C to 100°C, preferably 60°C to 100°C.

[0050] Furthermore, an antioxidant can be added during the coagulation process. Specific examples of the antioxidant include phenol-based antioxidants, amine-based antioxidants, phosphanol-based antioxidants, and hindered amine-based antioxidants. These antioxidants can be used alone or in combination of two or more.

[0051] Furthermore, the pH of the hydrous crumb obtained by the above method can be adjusted as needed by using a base as a pH adjuster. Specific examples of bases include sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium bicarbonate, ammonia, inorganic ammonium compounds, and organic amine compounds. The pH range is 1 to 11, preferably 2 to 10, and more preferably 4 to 8.

[0052] The hydrous crumb obtained by the above method is preferably washed with water to remove the coagulant. If washing with water is not performed at all or is performed insufficiently, ionic residues derived from the coagulant may precipitate during the molding process.

[0053] The acrylic rubber can be obtained by removing water from the water-containing crumbs after washing and drying them. The drying method is not particularly limited, but is generally performed using a flash dryer or fluidized bed dryer. Furthermore, a dehydration step using a centrifuge or the like may be performed before the drying step.

[0054] From the viewpoint of processability, the molecular weight range of the acrylic copolymer of the present invention thus produced is preferably 10 to 100, more preferably 15 to 90, and even more preferably 20 to 80, expressed as Mooney viscosity (ML1+4) at 100°C in the Mooney scorch test specified in JIS K 6300.

[0055] <Acrylic rubber-containing composition> 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.

[0056] As the crosslinking agent, a conventionally known crosslinking agent that is usually used for crosslinking rubber, such as a polyamine compound, a polyepoxy compound, a polyisocyanate compound, an aziridine compound, a sulfur compound, a basic metal oxide, and an organometallic halide, can be used. Among these, a polyamine compound can be preferably used.

[0057] Examples of polyvalent amine compounds include aliphatic polyvalent amine compounds such as hexamethylenediamine, hexamethylenediamine carbamate, and N,N'-dicinnamylidene-1,6-hexanediamine, and aromatic polyvalent amine compounds such as 4,4'-methylenedianiline, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-(m-phenylenediisopropylidene)dianiline, 4,4'-(p-phenylenediisopropylidene)dianiline, 2,2'-bis[4-(4-aminophenoxy)phenyl]propane, 4,4'-diaminobenzanilide, 4,4'-bis(4-aminophenoxy)biphenyl, m-xylylenediamine, p-xylylenediamine, 1,3,5-benzenetriamine, 1,3,5-benzenetriaminomethyl, and isophthalic acid dihydrazide. Among these, aliphatic polyamine compounds are preferred.

[0058] Examples of the polyfunctional epoxy compound include glycidyl ether type epoxy compounds such as phenol novolac type epoxy compounds, cresol novolac type epoxy compounds, cresol type epoxy compounds, bisphenol A type epoxy compounds, bisphenol F type epoxy compounds, brominated bisphenol A type epoxy compounds, brominated bisphenol F type epoxy compounds, and hydrogenated bisphenol A type epoxy compounds, as well as other polyfunctional epoxy compounds such as alicyclic epoxy compounds, glycidyl ester type epoxy compounds, glycidyl amine type epoxy compounds, and isocyanurate type epoxy compounds.

[0059] Examples of polyisocyanate compounds include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, 1,5-naphthylene diisocyanate, 1,3,6-hexamethylene triisocyanate, 1,6,11-undecane triisocyanate, and bicycloheptane triisocyanate.

[0060] Examples of the aziridine compound include tris-2,4,6-(1-aziridinyl)-1,3,5-triazine, tris[1-(2-methyl)aziridinyl]phosphinoxide, and hexa[1-(2-methyl)aziridinyl]triphosphatriazine.

[0061] Examples of sulfur compounds include sulfur, 4,4'-dithiomorpholine, tetramethylthiuram disulfide, and tetraethylthiuram disulfide.

[0062] Examples of basic metal oxides include zinc oxide, lead oxide, calcium oxide, and magnesium oxide.

[0063] The organic metal halide may be, for example, a dicyclopentadienyl metal dihalide, and the metal may be titanium, zirconium, or the like.

[0064] These crosslinking agents can be used alone or in combination of two or more. The amount of each crosslinking agent is 0.05 to 20 parts by mass, preferably 0.1 to 10 parts by mass, per 100 parts by mass of the acrylic rubber of the present invention.

[0065] The acrylic rubber-containing composition of the present invention may also contain any of other additives commonly used in the art, such as lubricants, antioxidants, light stabilizers, fillers, reinforcing agents, plasticizers, processing aids, pigments, colorants, crosslinking accelerators, crosslinking aids, crosslinking retarders, antistatic agents, and foaming agents.

[0066] As the filler, known fillers can be used, and specific examples include calcium carbonate, talc, silica, clay, carbon fiber, glass fiber, carbon black, titanium oxide, magnesium oxide, hydrotalcite, magnesium hydroxide, antimony oxide, zinc oxide, and carbon black. These may be used alone or in combination of two or more. Among these, silica and carbon black are preferred.

[0067] The amount of the filler to be blended may be 15 to 100 parts by mass, and preferably 20 to 80 parts by mass, based on 100 parts by mass of the acrylic rubber of the present invention.

[0068] Examples of softeners 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.

[0069] The blending amount of the softener may be 0.3 to 10 parts by mass, and preferably 0.5 to 5 parts by mass, based on 100 parts by mass of the acrylic rubber of the present invention.

[0070] Examples of antioxidants include amines, phosphates, quinolines, cresols, phenols, and dithiocarbamate metal salts. These may be used alone or in combination of two or more. Among these, amines such as diphenylamine derivatives and phenylenediamine derivatives are preferred.

[0071] The blending amount of the antioxidant may be 0.3 to 10 parts by mass, and preferably 0.5 to 5 parts by mass, based on 100 parts by mass of the acrylic rubber of the present invention.

[0072] Furthermore, it is also possible to blend with rubbers, resins, etc. that are commonly used in the relevant technical field without departing from the spirit of the present invention. Examples of commonly used rubbers that can be used in the present invention include butadiene rubber, styrene-butadiene rubber, isoprene rubber, natural rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene-isoprene rubber, ethylene-propylene-diene rubber, and epichlorohydrin rubber. Examples of resins that can be used in the present invention include PMMA (polymethyl methacrylate) resin, PS (polystyrene) resin, PUR (polyurethane) resin, PVC (polyvinyl chloride) resin, EVA (ethylene / vinyl acetate) resin, AS (styrene / acrylonitrile) resin, and PE (polyethylene) resin. These may be used alone or in combination of two or more.

[0073] The total amount of the rubber and resin is 50 parts by mass or less, preferably 10 parts by mass or less, and more preferably 1 part by mass or less, per 100 parts by mass of the acrylic rubber of the present invention.

[0074] The acrylic rubber-containing composition can be compounded to obtain the cross-linked rubber product of the present invention using any means conventionally used in the field of rubber processing, such as an open roll, a Banbury mixer, or various kneaders. The compounding procedure can be the usual procedure used in the field of rubber processing. For example, the compounding can be performed by first kneading only the rubber, then adding compounding ingredients other than the cross-linking agent and cross-linking accelerator to prepare kneaded compound A, and then adding the cross-linking agent and cross-linking accelerator to perform kneading compound B.

[0075] <Rubber cross-linked products> The cross-linked rubber of the present invention can be obtained by cross-linking the acrylic rubber-containing composition.

[0076] The cross-linked rubber of the present invention can be obtained by heating the acrylic rubber-containing composition to a temperature of usually 100°C to 250°C. The cross-linking time varies depending on the temperature, but is usually between 0.5 and 300 minutes. Cross-linking molding may involve integrally performing cross-linking and molding, or may involve heating a previously molded acrylic rubber-containing composition to form a cross-linked rubber, or may involve first heating the cross-linked rubber and then processing it for molding. Specific methods for cross-linking molding include compression molding using a mold, injection molding, heating using a steam can, an air bath, infrared radiation, or microwaves, among other methods.

[0077] The acrylic rubber-containing composition of the present invention thus obtained has excellent roll processability during processing, and the cross-linked rubber of the present invention has excellent normal physical properties and heat resistance under long-term high temperature conditions.

[0078] Therefore, taking advantage of the above-mentioned properties, the cross-linked rubber product of the present invention can be suitably used as various gaskets such as O-rings, packings, diaphragms, oil seals, shaft seals, bearing seals, mechanical seals, wellhead seals, seals for electric and electronic equipment, seals for pneumatic equipment, cylinder head gaskets attached to the joint between a cylinder block and a cylinder head, rocker cover gaskets attached to the joint between a rocker cover and a cylinder head, oil pan gaskets attached to the joint between an oil pan and a cylinder block or a transmission case, fuel cell separator gaskets attached between a pair of housings sandwiching a unit cell having a positive electrode, an electrolyte plate, and a negative electrode, and gaskets for the top covers of hard disk drives.

[0079] The cross-linked rubber product of the present invention is also suitable for use as an extrusion molded product or a mold cross-linked product for automobile applications, for example, various hoses such as fuel oil hoses around fuel tanks, such as fuel hoses, filler neck hoses, vent hoses, vapor hoses and oil hoses, air hoses such as turbo air hoses and emission control hoses, radiator hoses, heater hoses, brake hoses and air conditioner hoses. [Example]

[0080] The present invention will be specifically explained by way of examples and comparative examples, but the present invention is not limited to these.

[0081] (Measurement of molecular weight) The molecular weight was measured by dissolving the acrylic rubber in tetrahydrofuran (THF) as a solvent and measuring the molecular weight in terms of polystyrene using gel permeation chromatography (GPC). The measurements were performed using a Waters Corp. GPC Alliance HPLC system and two Tosoh Corp. TSK gel HM-2 columns connected together at a flow rate of 0.6 mL / min, a polymer (acrylic rubber) concentration of 10 mg / THF 8 mL, an injection volume of 40 μL, and a column temperature of 50°C.

[0082] The proportion of acrylic rubber (polymer) with a molecular weight of 500,000 or less and the proportion of 2,000,000 or more was determined by drawing an integral curve of the slice area from the molecular weight distribution curve consisting of the slice molecular weight and slice area, and then calculating the integral (%) when the slice molecular weight was 500,000 or less and the integral (%) when the slice molecular weight was 2,000,000 or more. The weight average molecular weight (Mw) and number average molecular weight (Mn) of the acrylic rubber (polymer) were also calculated, and the molecular weight distribution (Mw / Mn) of the acrylic rubber (polymer) was calculated based on the calculation results.

[0083] <Mooney viscosity (ML1+4, 100°C)> The Mooney viscosity (ML1+4) of the acrylic copolymer was measured at a measurement temperature of 100°C using a Mooney Viscometer AM-3 manufactured by Toyo Seiki Seisakusho, in accordance with the Mooney viscosity test of JIS K6300, a physical testing method for uncrosslinked rubber.

[0084] (Production of acrylic rubber A) A polymerization reactor equipped with a thermometer, stirrer, nitrogen inlet, and pressure reducer was charged with 150 parts by weight of water, 1.2 parts by weight of polyoxyalkylene alkyl ether phosphate ester sodium salt, 68.5 parts by weight of ethyl acrylate, 20 parts by weight of butyl acrylate, 10 parts by weight of 2-methoxyethyl acrylate, and 1.5 parts by weight of monobutyl fumarate as monomers, and 0.055 parts by weight of n-dodecyl mercaptan as a chain transfer agent. After repeated degassing and nitrogen substitution under reduced pressure to thoroughly remove oxygen, 0.072 parts by weight of sodium formaldehyde sulfoxylate and 0.06 parts by weight of potassium persulfate were added to initiate the emulsion polymerization reaction at ambient pressure and temperature. The reaction was continued until the polymerization conversion reached 95%, yielding a polymerization solution. The resulting polymerization solution was coagulated with sodium sulfate, washed with water, and dried to yield Acrylic Rubber A. The Mooney viscosity (ML(1+4)) at 100°C was 29. The proportions of molecular weights below 500,000 and above 2,000,000 are shown in Table 1.

[0085] (Manufacture of acrylic rubber B) Acrylic Rubber B was obtained in the same manner as in the production of Acrylic Rubber A, except that n-dodecyl mercaptan was not used. The Mooney viscosity ML(1+4) at 100°C was 49. The proportions of molecular weights of 500,000 or less and 2,000,000 or more are shown in Table 1.

[0086] (Manufacture of acrylic rubber C) Acrylic Rubber C was obtained in the same manner as in the production of Acrylic Rubber A, except that the ingredients were changed to 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. The Mooney viscosity ML(1+4) at 100°C was 36. The proportions of molecular weights of 500,000 or less and 2,000,000 or more are shown in Table 1.

[0087] (Manufacture of acrylic rubber D) 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. The Mooney viscosity ML(1+4) at 100°C was 24. The proportions of molecular weights of 500,000 or less and 2,000,000 or more are shown in Table 1.

[0088] (Manufacture of acrylic rubber E) 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 proportions of those with molecular weights of 500,000 or less and those with molecular weights of 2,000,000 or more.

[0089] (Manufacture of acrylic rubber F) 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 proportions of those with molecular weights of 500,000 or less and those with molecular weights of 2,000,000 or more.

[0090] (Manufacture of acrylic rubber G) 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 proportions of those with molecular weights of 500,000 or less and those with molecular weights of 2,000,000 or more.

[0091] (Manufacture of acrylic rubber H) Acrylic Rubber H was obtained in the same manner as in the production of Acrylic Rubber C, except that n-dodecyl mercaptan was changed to 0.015 parts by mass 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 proportions of molecular weights of 500,000 or less and 2,000,000 or more are shown in Table 1.

[0092] [Table 1]

[0093] (Production of acrylic rubber composition) First, the acrylic rubber, carbon black (Seast SO (Tokai Carbon Co., Ltd.)), stearic acid (Sakura Stearate (NOF Corporation)), and antioxidant (Nocrac CD (Ouchi Shinko Chemical Industry Co., Ltd.)) shown in Table 2 were kneaded in a kneader at 100°C to prepare Compound A. This Compound A was kneaded in an open roll at room temperature, and hexamethylenediamine carbamate and an accelerator (Rhenogran XLA60 (Lanxess)) were kneaded to prepare Compound B, from which an uncrosslinked sheet 2 to 2.5 mm thick was produced. The units for the compounding ingredients in Table 2 are parts by mass.

[0094] [Table 2]

[0095] (Evaluation of extrusion properties) The uncrosslinked sheet was extruded in accordance with the Garvey die extrusion test of ASTM-D-2230, with an L / D ratio of 10, a rotation speed of 60 rpm, and temperatures of 60°C for the cylinder and 80°C for the die. The length of the extruded product was evaluated on a three-point scale: ◎: 80 cm / min or more, ○: 80 to 60 cm / min, and ×: 60 cm / min or less. The results are shown in Table 3.

[0096] (Evaluation of crosslinking shrinkage) The length of the extrusion molded product obtained above was measured before and after heating in an air oven at 180°C for 3 hours, and the crosslinking shrinkage was calculated using the formula below. The results are shown in Table 3. The smaller the crosslinking shrinkage, the more successfully reduced the crosslinking shrinkage.

number

[0097] (Preparation of secondary cross-linked product) The uncrosslinked rubber sheet was pressed at 180°C for 10 minutes to obtain a 2mm thick primary crosslinked product, which was then heated in an air oven at 180°C for 3 hours to obtain a secondary crosslinked product.

[0098] (Normal physical property test) The resulting secondary cross-linked product was subjected to a tensile test and a hardness test, which were performed in accordance with the methods specified in JIS K6251 and JIS K6253, respectively.

[0099] Table 3 shows the test results of the Examples and Comparative Examples obtained by each test method. In each table, tensile strength and elongation refer to those specified in the tensile test of JIS K6251, and hardness refers to those specified in the hardness test of JIS K6253. The results are shown in Table 3. When the tensile strength was 8 MPa or more, the elongation was 200% or more, and the hardness was 60 or more, it was determined that the normal physical properties expected of acrylic rubber were maintained.

[0100] [Table 3]

[0101] Table 3 shows that the acrylic rubber-containing compositions of Examples 1 to 7, which are made using acrylic rubbers having a molecular weight of 500,000 or less and 2,000,000 or more as specified in the present invention, have good extrudability, have reduced crosslinking shrinkage, and maintain the normal physical properties expected of acrylic rubber. On the other hand, it was shown that Comparative Example 1 was inferior to Examples 1 to 7 in crosslinking shrinkage. [Industrial Applicability]

[0102] The present invention can provide an acrylic rubber with small crosslinking shrinkage. Crosslinked rubber products produced using compositions containing the acrylic rubber are suitable for use in automobile components, such as seals, hoses, vibration-proofing materials, tubes, belts, and boots.

Claims

1. An acrylic rubber in which, in a molecular weight distribution curve consisting of slice molecular weight and slice area, the proportion of slice molecular weights of 500,000 or less is 35 to 55%, and the proportion of slice molecular weights of 2,000,000 or more is 4 to 18%, and the Mooney viscosity (ML1+4) at 100°C in the Mooney scorch test specified in JIS K 6300 is 10 to 100.

2. An acrylic rubber as described in claim 1, wherein the proportion of slice molecular weights of 500,000 or less is 38 to 51%, and the proportion of slice molecular weights of 2,000,000 or more is 5 to 15%.

3. 3. The acrylic rubber according to claim 1 or 2, which comprises 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 carboxy group, and a structural unit derived from an unsaturated monomer having an epoxy group.

4. An acrylic rubber-containing composition comprising the acrylic rubber according to any one of claims 1 to 3 and a crosslinking agent.

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

Images