Method for producing acrylic rubber

Abstract

The purpose of the present invention is to provide a method for producing an acrylic rubber having excellent storage stability.　This method for producing an acrylic rubber comprises: an emulsion polymerization step for obtaining an emulsion polymerization solution by subjecting monomers to an emulsion polymerization; a coagulation step for coagulating the emulsion polymerization solution with a coagulant to obtain a hydrous crumb; and a drying step for drying the hydrous crumb, the method being characterized in that when a base step for adding a base is included in steps after the emulsion polymerization step and an ester compound other than the monomer constituting the acrylic rubber is used up to the base step, the amount of the base used for the ester compound is adjusted.

Description

Technical Field

[0001] The present invention relates to a method for producing an acrylic rubber, and more particularly to a method for producing an acrylic rubber having excellent storage stability.

Background Art

[0002] Acrylic rubber is a polymer mainly composed of an acrylate ester, and is generally known as a rubber having excellent heat resistance, oil resistance and ozone resistance, and is widely used in the automotive industry.

[0003] Such an acrylic rubber is usually obtained by emulsion-polymerizing a monomer mixture constituting the acrylic rubber and drying a hydrous crumb obtained by adding a coagulant to the obtained emulsion polymerization liquid.

[0004] In the method for producing an acrylic rubber, the production conditions of each step have been studied, and Patent Document 1 discloses that by adjusting the residual calcium concentration and pH of the polymer, the cross-linked product of the obtained acrylic rubber has excellent physical properties.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, as a result of investigations by the present inventors, it was confirmed that in acrylic rubbers, the storage stability of the obtained acrylic rubber varies depending on the production method. The present invention has been made in view of such circumstances, and an object thereof is to provide a method for producing an acrylic rubber having excellent storage stability.

Means for Solving the Problems

[0007] As a result of intensive research to achieve the above object, the present inventors have found that in a method for producing an acrylic rubber including an emulsion polymerization step of obtaining an emulsion polymerization liquid by emulsion polymerizing a monomer, a coagulation step of coagulating the emulsion polymerization liquid with a coagulant to obtain a water-containing crumb, and a drying step of drying the water-containing crumb, in the steps after the emulsion polymerization step, a base addition step of adding a base is included, and when using an ester compound other than the monomer constituting the acrylic rubber up to the base addition step, by adjusting the amount of the base used, an acrylic rubber excellent in storage stability can be produced, and the present invention has been completed.

[0008] Aspects of the present invention are as follows. Item 1 An emulsion polymerization step of obtaining an emulsion polymerization liquid by emulsion polymerizing a monomer, A coagulation step of coagulating the emulsion polymerization liquid with a coagulant to obtain a water-containing crumb, and A drying step of drying the water-containing crumb including Furthermore, in the steps after the emulsion polymerization step, a base addition step of adding a base is included, An ester compound other than the monomer constituting the acrylic rubber is used up to the base addition step, When the amount of the base used in the base addition step is X parts by mass, the molecular weight of the base used is Y, and the valence (Z) of the base used with respect to 100 parts by mass of the ester compound 0.15 ≦ (X / Y) / Z ≦ 2.5 A method for producing an acrylic rubber that satisfies the above. Item 2 The method for producing an acrylic rubber according to Item 1, wherein the ester compound is a phosphoric acid ester compound and / or a sulfuric acid ester compound. Item 3 A method for producing an acrylic rubber-containing composition further including a step of blending a crosslinking agent with the acrylic rubber obtained by the method for producing an acrylic rubber according to Item 1 or 2. Item 4 A method for producing a crosslinked acrylic rubber further including a step of crosslinking the acrylic rubber composition obtained by the method for producing an acrylic rubber-containing composition according to Item 3.

Effects of the Invention

[0009] The present invention relates to a method for producing an acrylic rubber having excellent storage stability. Since the acrylic rubber obtained by the production method of the present invention has excellent storage stability, even when stored for a long period of time, the processability does not deteriorate extremely, and it is possible to prevent scorch (crosslinking before the crosslinking step).

Embodiments for Carrying Out the Invention

[0010] The acrylic rubber produced by the production method of the present invention is a polymer mainly composed of structural units derived from (meth)acrylic acid esters. Here, the main component means containing 50% by mass or more of structural units derived from (meth)acrylic acid esters. Note that “(meth)acrylic acid ester” means “acrylic acid ester or methacrylic acid ester”, and the same applies to similar expressions in this application.

[0011] Examples of the structural units derived from the (meth)acrylic acid ester include structural units derived from (meth)acrylic acid alkyl esters and structural units derived from (meth)acrylic acid alkoxyalkyl esters. The structural units derived from the (meth)acrylic acid ester are preferably structural units derived from (meth)acrylic acid alkyl esters having an alkyl group with 1 to 8 carbon atoms and structural units derived from (meth)acrylic acid alkoxyalkyl esters having an alkoxyalkyl group with 2 to 8 carbon atoms, more preferably having structural units derived from (meth)acrylic acid alkyl esters having an alkyl group with 2 to 6 carbon atoms and / or structural units derived from (meth)acrylic acid alkoxyalkyl esters having an alkoxyalkyl group with 2 to 6 carbon atoms, and particularly preferably having structural units derived from (meth)acrylic acid alkyl esters having an alkyl group with 2 to 4 carbon atoms and / or structural units derived from (meth)acrylic acid alkoxyalkyl esters having an alkoxyalkyl group with 2 to 4 carbon atoms. The structural units derived from the (meth)acrylic acid ester may be single or structural units derived from two or more (meth)acrylic acid esters.

[0012] Specific examples of the (meth)acrylic acid alkyl ester 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, cyclohexyl (meth)acrylate, etc., and ethyl (meth)acrylate and n-butyl (meth)acrylate are preferred. Specific examples of the (meth)acrylic acid alkoxyalkyl ester 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, 4-ethoxybutyl (meth)acrylate, etc., and methoxyethyl (meth)acrylate is preferred.

[0013] In the acrylic rubber of the present invention, the content of the structural unit derived from the (meth)acrylic acid ester is more preferably 50% by mass or more, particularly preferably 60% 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, more preferably 99% by mass or less, and particularly preferably 98.5% by mass or less.

[0014] In the acrylic rubber of the present invention, it contains a structural unit derived from an unsaturated monomer having a crosslinking group. Examples of the structural unit derived from an unsaturated monomer having a crosslinking group include a structural unit derived from an unsaturated monomer having a halogen group (for example, a chlorine group, etc.), 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. Among them, a structural unit derived from an unsaturated monomer having a halogen group (particularly a chlorine group) and a carboxyl group is particularly preferable.

[0015] Examples of the unsaturated monomer having a halogen group include vinyl monochloroacetate, allyl chloroacetate, etc., and vinyl monochloroacetate is preferable.

[0016] Examples of the unsaturated monomer having a carboxy group include unsaturated monocarboxylic acids such as (meth)acrylic acid, crotonic acid, 2-pentenoic acid, cinnamic acid, unsaturated dicarboxylic acids such as fumaric acid, maleic acid, itaconic acid, carboxylic anhydrides such as maleic anhydride, citraconic anhydride, monoesters of butenedioic acid such as monomethyl fumarate, monoethyl fumarate, mono-n-butyl fumarate, monomethyl maleate, monoethyl maleate, mono-2-ethylhexyl maleate, mono-n-butyl maleate; monocyclic alkyl esters of butenedioic acid such as monocyclopentyl fumarate, monocyclohexyl fumarate, monocyclopentyl maleate, monocyclohexyl maleate; monoesters of itaconic acid such as monomethyl itaconate, monoethyl itaconate, mono-n-butyl itaconate, monocyclohexyl itaconate; etc. Among these, monoesters of unsaturated dicarboxylic acids such as monoethyl fumarate, monopropyl fumarate, monobutyl fumarate, monoethyl itaconate, monopropyl itaconate, monobutyl itaconate, etc. can be mentioned.

[0017] Examples of the unsaturated monomer having an epoxy group include glycidyl (meth)acrylate, (meth)allyl glycidyl ether, etc.

[0018] 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, preferably 10% by mass or less, more preferably 5% by mass or less, and particularly preferably 2.5% by mass or less in all the structural units of the acrylic rubber. When the structural unit derived from the unsaturated monomer having a crosslinking group is within the above range, it is preferable in terms of physical properties such as strength and compression set, and processability.

[0019] Furthermore, the acrylic rubber of the present invention may contain, in addition to the above structural units, structural units derived from other monomers copolymerizable therewith. Examples of the other structural units include structural units derived from ethylenically unsaturated nitriles, structural units derived from (meth)acrylamide-based monomers, structural units derived from aromatic vinyl-based monomers, structural units derived from conjugated diene-based monomers, structural units derived from non-conjugated dienes, and structural units derived from other olefins.

[0020] Examples of the ethylenically unsaturated nitrile include compounds such as acrylonitrile, methacrylonitrile, α-methoxyacrylonitrile, and vinylidene cyanide.

[0021] Examples of (meth)acrylamide monomers include compounds such as 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-propioxymethyl acrylamide, N-propioxymethyl methacrylamide, N-methyl acrylamide, N-methyl methacrylamide, N,N-dimethyl acrylamide, N,N-dimethyl methacrylamide, N,N-diethyl acrylamide, N,N-diethyl methacrylamide, N-methylol acrylamide, N-methylol methacrylamide, ethacrylamide, crotonamide, cinnamic acid amide, maleic diamide, itaconic diamide, methyl maleic amide, methyl itaconic amide, maleimide, itaconimide, etc.

[0022] Examples of aromatic vinyl monomers include compounds such as styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, o-ethylstyrene, p-ethylstyrene, α-fluorostyrene, p-trifluoromethylstyrene, p-methoxystyrene, p-aminostyrene, p-dimethylaminostyrene, p-acetoxystyrene, styrene sulfonic acid or its salt, α-vinylnaphthalene, 1-vinylnaphthalene-4-sulfonic acid or its salt, 2-vinylfluorene, 2-vinylpyridine, 4-vinylpyridine, divinylbenzene, diisopropenylbenzene, vinylbenzyl chloride, etc.

[0023] Examples of conjugated diene monomers include compounds such as 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.

[0024] In addition, examples of the structural unit derived from non-conjugated dienes include structural units derived from compounds of non-conjugated dienes such as 1,4-pentadiene, 1,4-hexadiene, ethylidene norbornene, norbornadiene, and dicyclopentadiene.

[0025] Examples of other olefin monomers include esters such as dicyclopentadienyl acrylate, dicyclopentadienyl methacrylate, dicyclopentadienyl ethyl acrylate, and dicyclopentadienyl ethyl methacrylate, and compounds such as ethylene, propylene, vinyl chloride, vinylidene chloride, 1,2-dichloroethylene, vinyl acetate, vinyl fluoride, vinylidene fluoride, 1,2-difluoroethylene, vinyl bromide, vinylidene bromide, 1,2-dibromoethylene, ethyl vinyl ether, and butyl vinyl ether.

[0026] In the acrylic rubber of the present invention, when containing structural units derived from these copolymerizable other monomers, the content rate in all the structural units is preferably 0 to 45% by mass, more preferably 0 to 20% by mass.

[0027] The method for producing the acrylic rubber of the present invention includes an emulsion polymerization step of obtaining an emulsion polymerization liquid by emulsion polymerizing monomers, a coagulation step of coagulating the emulsion polymerization liquid with a coagulant to obtain a water-containing crumb, and a drying step of drying the water-containing crumb. Further, in the steps after the emulsion polymerization step, it includes a base addition step of adding a base, and an ester compound other than the monomers constituting the acrylic rubber is used (added) up to the base addition step.

[0028] The step of obtaining an emulsion polymerization liquid by emulsion polymerizing monomers will be described. Hereinafter, it may also be described as the emulsion polymerization step.

[0029] The emulsion polymerization step is a step of obtaining an emulsion polymerization liquid by emulsion polymerizing the monomers that will constitute the acrylic rubber.

[0030] In the emulsion polymerization process, ordinary methods can be used, and conventionally known substances such as emulsifiers, polymerization initiators, chain transfer agents, polymerization terminators, etc. can be used.

[0031] The emulsifier is not particularly limited, and nonionic emulsifiers and anionic emulsifiers generally used in the emulsion polymerization method can be used. Examples of nonionic emulsifiers include polyoxyethylene alkyl ethers, polyoxyethylene alcohol ethers, polyoxyethylene alkyl phenyl 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 sulfate esters, polyoxyethylene alkyl ether sulfate esters, polyoxyalkylene alkyl ether phosphate esters or their salts, polyoxyalkylene alkyl phenyl ether phosphate esters or their salts, and fatty acid salts such as sodium lauryl sulfate. These may be used alone or in combination of two or more. Examples of salts include alkali metals such as sodium and potassium, ammonia, and amines.

[0032] The amount of the emulsifier used may be an amount generally used in the emulsion polymerization method. Specifically, it is in the range of 0.01 to 10% by mass, preferably 0.03 to 7% by mass, and more preferably 0.05 to 5% by mass based on the monomer amount charged. When a reactive surfactant is used as the monomer component, the addition of an emulsifier is not necessarily required.

[0033] The polymerization initiator is not particularly limited, and polymerization initiators generally used in the emulsion polymerization method 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, n-butyl 4,4-di-(t-butylperoxy)valerate, 2,2-di(t-butylperoxy)butane, t-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, p-menthane hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, t-butyl cumyl 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 peroxide, 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 peroxyneodecanoate, 1,1,3,3-tetramethylbutyl peroxyneodecanoate, t-hexyl peroxyneodecanoate, t-butyl peroxyneodecanoate, t-hexyl peroxypivalate, t-butyl peroxypivalate, 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane, 1,1,3,3-tetramethylbutyl peroxy-2-ethylhexanoate, t-hexyl peroxy-2-ethylhexanoate, t-butyl peroxy-2-ethylhexanoate, t-butyl peroxylaurate, t-butyl peroxy-3,5,Organic peroxide-based polymerization initiators such as 5-trimethylhexanate, t-hexyl peroxyisopropyl monocarbonate, t-butyl peroxyisopropyl monocarbonate, t-butyl peroxy 2-ethylhexyl monocarbonate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-butyl peroxyacetate, t-hexyl peroxybenzoate, t-butyl peroxybenzoate, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, hydroperoxides, 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-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] and other azo initiators and the like can be mentioned. These polymerization initiators may be used alone or in combination of two or more kinds.,

[0034] The amount of the polymerization initiator used may be an amount generally used in the emulsion polymerization method. Specifically, it is in the range of 0.01 to 5% by mass, preferably 0.01 to 4% by mass, and more preferably 0.02 to 3% by mass with respect to the amount of the monomer charged.,

[0035] In addition, organic peroxides and inorganic peroxides as polymerization initiators can be used as redox polymerization initiators by combining them with a reducing agent. The reducing agent used in combination is not particularly limited, but examples 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, and inorganic salts having reducing properties such as alkali metal salts of sulfurous acid and thiosulfuric acid. 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 with respect to 100 parts by mass of the charged monomer.

[0036] 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, thiuram compounds such as terpinolene, tetramethylthiuram disulfide, tetraethylthiuram disulfide, and tetramethylthiuram monosulfide, 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. One or more of these can be used. The amount of these chain transfer agents is not particularly limited, but is usually used in an amount of 0 to 5 parts by mass with respect to 100 parts by mass of the charged monomer amount.

[0037] Examples of the polymerization terminator include hydroxylamine, hydroxylamine sulfate, diethylhydroxylamine, hydroxylamine sulfonic acid and its alkali metal salts, sodium dimethyldithiocarbamate, and quinone compounds such as hydroquinone. The amount of the polymerization terminator used is not particularly limited, but is usually 0 to 2 parts by mass with respect to 100 parts by mass of the total monomers.

[0038] In addition, polymerization auxiliary materials such as a particle size adjuster, a chelating agent, and an oxygen scavenger can be used as necessary.

[0039] The emulsion polymerization may be carried out in any of a batch system, a semi-batch system, and a continuous system. The polymerization time and the polymerization temperature are not particularly limited and can be appropriately selected from the type of the polymerization initiator used, etc. Generally, the polymerization temperature is 10 to 100 °C, and the polymerization time is 0.5 to 100 hours.

[0040] The step of coagulating the emulsion polymerization liquid with a coagulant to obtain a water-containing clam will be described. Hereinafter, it may also be described as a coagulation step.

[0041] The coagulant used in the coagulation step is not particularly limited and is preferably an inorganic metal salt. Specific examples thereof include sodium sulfate, magnesium sulfate, aluminum sulfate, sodium chloride, calcium chloride, and the like.

[0042] The method of coagulating with a coagulant is not particularly limited, and a generally used method can be adopted. As an example of the method, a method of continuously or batchwise supplying the emulsion polymerization liquid to an aqueous solution containing a coagulant can be mentioned, and a water-containing clam is obtained by this operation. At this time, the temperature of the aqueous solution containing the coagulant is affected by factors such as the type and amount of the monomer, and the shear force due to stirring, etc., and thus cannot be uniformly specified, but generally, it is 50 °C or higher, preferably in the range of 60 °C to 100 °C.

[0043] In the present invention, there may be a step of washing the obtained water-containing crumb with water. Hereinafter, it may also be described as a water-washing step. The purpose of the water-washing step is to remove the coagulant contained in the water-containing crumb.

[0044] In the present invention, there is a step of drying the water-containing crumb. Hereinafter, it may also be described as a drying step.

[0045] Acrylic rubber can be obtained by removing moisture from the water-containing crumb and drying it. The drying method is not particularly limited, but generally, it is dried using a flash dryer, a fluidized dryer, or the like.

[0046] The drying temperature is not particularly limited, but it is preferably 50°C to 250°C, and more preferably 80 to 200°C. The drying time varies depending on the drying temperature.

[0047] Before the drying step, a dehydration step using a centrifuge or the like may be performed.

[0048] In the production method of the present invention, in the steps after the emulsion polymerization step, it includes a base step of adding a base, and an ester compound other than the monomers constituting the acrylic rubber is used up to the base step.

[0049] Examples of the ester compound other than the monomers constituting the acrylic rubber include phosphate ester compounds and sulfate ester compounds. Since the ester compound other than the monomers constituting the acrylic rubber does not constitute the acrylic rubber, it does not have a (meth)acryloyl group.

[0050] Examples of the phosphate ester compound include alkyl ether phosphate esters, alkyl phosphate esters, and salts thereof.

[0051] Examples of the alkyl ether phosphate ester and its salts include polyoxyalkylene 2-ethylhexyl ether phosphate ester, polyoxyalkylene stearyl ether phosphate ester, polyoxyalkylene myristyl ether phosphate ester, polyoxyalkylene lauryl ether phosphate ester, polyoxyalkylene palmityl ether phosphate ester, polyoxyalkylene oleyl ether phosphate ester, polyoxyalkylene tridecyl ether phosphate ester, and other polyoxyalkylene alkyl ether phosphate esters. Examples of polyoxyalkylene include polyoxyethylene and polyoxypropylene. Examples of its salts include alkali metals such as sodium and potassium, ammonia, and amines.

[0052] Examples of the alkyl phosphate ester and its salts preferably include mono- or dialkyl phosphate esters having 12 to 24 carbon atoms and their salts, and mono- or dialkyl phosphate esters having 16 to 18 carbon atoms and their salts. Specific examples include stearyl phosphate ester, myristyl phosphate ester, lauryl phosphate ester, palmityl phosphate ester, etc. Examples of its salts include alkali metals such as sodium and potassium, ammonia, and amines.

[0053] Examples of the sulfate ester compound include alkyl ether sulfate ester, alkyl sulfate ester, and their salts.

[0054] Examples of the alkyl ether sulfate ester and its salts include polyoxyalkylene stearyl ether sulfate ester, polyoxyalkylene myristyl ether sulfate ester, polyoxyalkylene lauryl ether sulfate ester, polyoxyalkylene palmityl ether sulfate ester, etc. Examples of polyoxyalkylene include polyoxyethylene and polyoxypropylene. Examples of its salts include alkali metals such as sodium and potassium, ammonia, and amines.

[0055] As for the alkyl sulfate and its salts, mono- or dialkyl sulfates having 12 to 24 carbon atoms, their salts, mono- or dialkyl sulfates having 16 to 18 carbon atoms, and their salts are preferred. Specific examples include stearyl sulfate, myristyl sulfate, lauryl sulfate, palmityl sulfate, etc. Examples of the salts include alkali metals such as sodium and potassium, ammonia, amines, etc.

[0056] The ester compound other than the monomer constituting the acrylic rubber may be used up to the base step. Specifically, it may be used in the emulsion polymerization step, coagulation step, water washing step, or further between the steps of the emulsion polymerization step, coagulation step, and water washing step.

[0057] In the production method of the present invention, the ester compound may function as an emulsifier in the emulsion polymerization step, a lubricant for improving workability after drying, etc., and is not particularly limited by the purpose of use. The ester compound is particularly preferably used as an emulsifier in the emulsion polymerization step.

[0058] In the step after the emulsion polymerization step, as the base step of adding a base, when the amount of the base used in the base step is X parts by mass, the molecular weight of the base used is Y, and the valence (Z) of the base used with respect to 100 parts by mass of the ester compound other than the monomer constituting the acrylic rubber, 0.15 ≦ (X / Y) / Z ≦ 2.5 is satisfied.

[0059] Examples of the base used in the base step include hydroxide compounds such as sodium hydroxide, potassium hydroxide, calcium hydroxide, carbonate compounds such as sodium hydrogen carbonate, potassium carbonate, ammonia, inorganic ammonium compounds, organic amine compounds such as triethylamine, etc. Sodium hydrogen carbonate and sodium hydroxide are preferred. The base is mainly compounded for the purpose of neutralizing the ester in which hydrolysis proceeds in the production process of the acrylic rubber, rather than directly acting on the above ester compound.

[0060] In the present invention, when the amount of the base used in the base step is X parts by mass, the molecular weight of the base used is Y, and the valence (Z) of the base used, with respect to 100 parts by mass of the ester compound other than the monomers constituting the acrylic rubber, it is preferably satisfied that 0.15 ≦ (X / Y) / Z ≦ 2.5, more preferably satisfied that 0.18 ≦ (X / Y) / Z ≦ 2.3, and still more preferably satisfied that 0.18 ≦ (X / Y) / Z ≦ 1.5.

[0061] The base step is after the emulsion polymerization step, and is not particularly limited as long as it is after the ester compound is used, but it is preferably carried out before the drying step or the dehydration step carried out before the drying step, and may be after the coagulation step.

[0062] From the viewpoint of processability, the molecular weight range of the acrylic rubber used in the present invention produced in this way is the Mooney viscosity (ML 1+4 ) expressed at 100 °C in the Mooney scorch test defined in JIS K 6300, and is preferably 10 to 100, more preferably 15 to 90, and still more preferably 20 to 80.

[0063] <Acrylic rubber-containing composition> The acrylic rubber-containing composition of the present invention contains at least the above acrylic rubber and a crosslinking agent.

[0064] As the crosslinking agent, conventionally known crosslinking agents such as polyvalent amine compounds, polyvalent epoxy compounds, polyvalent isocyanate compounds, aziridine compounds, sulfur compounds, higher fatty acid metal salts (fatty acid metal soaps), and thiol compounds can be used.

[0065] Examples of the higher fatty acid metal salts include alkali metal salts or alkaline earth metal salts of fatty acids having 8 to 18 carbon atoms in the alkyl group or alkenyl group, such as sodium stearate, potassium stearate, potassium myristate, sodium palmitate, calcium stearate, magnesium stearate, sodium oleate, potassium oleate, barium oleate, etc., and one or more of these may be used.

[0066] Examples of the polyvalent amine compounds include aliphatic polyvalent amine compounds such as hexamethylenediamine, hexamethylenediamine carbamate, and N,N'-dicyclohexylidene-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.

[0067] Examples of the polyvalent epoxy compounds include glycidyl ether type epoxy compounds such as phenol novolak type epoxy compounds, cresol novolak 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; and other polyvalent epoxy compounds such as alicyclic epoxy compounds, glycidyl ester type epoxy compounds, glycidyl amine type epoxy compounds, and isocyanurate type epoxy compounds.

[0068] Examples of the polyvalent isocyanate 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.

[0069] Examples of the aziridine compound include tris-2,4,6-(1-aziridinyl)-1,3,5-triazine, tris[1-(2-methyl)aziridinyl]phosphine oxide, hexa[1-(2-methyl)aziridinyl]triphosphatotriazine, and the like.

[0070] Examples of the sulfur compound include sulfur, 4,4'-dithiomorpholine, tetramethylthiuram disulfide, tetraethylthiuram disulfide, and the like.

[0071] Examples of the thiol compound include 1,3,5-triazine dithiol or its derivatives, 1,3,5-triazine trithiol such as 1,3,5-triazine-2,4,6-trithiol, and the like.

[0072] 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, respectively, based on 100 parts by mass of the acrylic rubber of the present invention.

[0073] In addition, the acrylic rubber-containing composition of the present invention can be arbitrarily blended with other additives commonly used in the art, such as lubricants, anti-aging agents, light stabilizers, fillers, reinforcing agents, plasticizers, processing aids, pigments, colorants, crosslinking accelerators, crosslinking aids, crosslinking retarders, antistatic agents, foaming agents, and the like.

[0074] Examples of the anti-aging agent include amines, phosphates, quinolines, cresols, phenols, metal salts of dithiocarbamate, etc., and diphenylamine derivatives such as 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, and amines such as phenylenediamine derivatives are preferred.

[0075] Examples of the crosslinking accelerator include guanidine compounds, amine compounds, thiourea compounds, thiazole compounds, sulfenamide compounds, thiuram compounds, quaternary ammonium salts, etc., and guanidine compounds and amine compounds are preferred.

[0076] Furthermore, within the scope not departing from the gist of the present invention, it is also possible to perform blending with rubber, resin, etc., which are commonly carried out in the art. Examples of the rubber used in the present invention include butadiene rubber, styrene-butadiene rubber, isoprene rubber, natural rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene-isoprene rubber, ethylene-propylene-diene rubber, epichlorohydrin rubber, etc. Examples of the resin include PMMA (polymethyl methacrylate) resin, PS (polystyrene) resin, PUR (polyurethane) resin, PVC (polyvinyl chloride) resin, EVA (ethylene / vinyl acetate) resin, AS (styrene / acrylonitrile) resin, PE (polyethylene) resin, etc.

[0077] The total blending amount of the above rubber and resin is 50 parts by mass or less, preferably 10 parts by mass or less, more preferably 1 part by mass or less, based on 100 parts by mass of the acrylic rubber of the present invention.

[0078] The production method of the acrylic rubber-containing composition of the present invention includes a step of blending a crosslinking agent with the acrylic rubber obtained by the above production method of the acrylic rubber.

[0079] As the blending method of the acrylic rubber-containing composition of the present invention, any means conventionally used in the field of polymer processing, such as an open roll, a Banbury mixer, various kneaders, etc., can be used.

[0080] The blending procedure can be carried out according to the usual procedures carried out in the field of polymer processing. For example, it can be carried out in a procedure where first only the polymer is kneaded, then an A-kneaded compound is prepared by adding compounding agents other than the crosslinking agent and the crosslinking accelerator, and then B-kneading is carried out by adding the crosslinking agent and the crosslinking accelerator.

[0081] The acrylic rubber crosslinked product is obtained by crosslinking the acrylic rubber-containing composition. The production method of the acrylic rubber crosslinked product includes a step of crosslinking the acrylic rubber-containing composition obtained by the above production method of the acrylic rubber-containing composition.

[0082] As a step of crosslinking the acrylic rubber-containing composition, the acrylic rubber-containing composition can be made into a crosslinked product by heating it usually at 100 to 250°C. Although the crosslinking time varies depending on the temperature, it is usually carried out within 0.5 to 300 minutes. Crosslinking molding can be carried out in any of the following cases: when crosslinking and molding are carried out integrally, when the previously molded acrylic rubber-containing composition is heated again to obtain a crosslinked product, or when the previously heated crosslinked product is processed for molding. As a specific method of crosslinking molding, any method such as compression molding using a mold, injection molding, heating by a steam can, an air bath, infrared rays, or microwaves can be used.

[0083] Therefore, by taking advantage of the above characteristics, the crosslinked product of the present invention is 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 devices, seals for pneumatic devices, cylinder head gaskets mounted at the connecting portion between the cylinder block and the cylinder head, rocker cover gaskets mounted at the connecting portion between the rocker cover and the cylinder head, oil pan gaskets mounted at the connecting portion between the oil pan and the cylinder block or the transmission case, fuel cell separator gaskets mounted between a pair of housings sandwiching a unit cell including a positive electrode, an electrolyte plate, and a negative electrode, and gaskets for the top cover of a hard disk drive.

[0084] In addition, the crosslinked product in the present invention can be used as a rubber material, and as extrusion-molded products and mold-crosslinked products used in automotive applications, it is suitably used for various hoses such as fuel hoses around the fuel tank, such as fuel hoses, filler neck hoses, vent hoses, vapor hoses, oil hoses, air hoses such as turbo air hoses and emission control hoses, and various hoses such as radiator hoses, heater hoses, brake hoses, and air conditioner hoses.

Example

[0085] The present invention will be specifically described by way of examples and comparative examples. However, the present invention is not limited thereto. In the examples and comparative examples, the production of acrylic rubber, the acrylic rubber-containing composition containing the obtained acrylic rubber and a crosslinking agent, and the physical properties of the rubber material (specifically, a crosslinked product formed by crosslinking) produced using the acrylic rubber-containing composition were evaluated.

[0086] (Production of Emulsion Polymerization Liquid A) Into a polymerization reactor equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a decompression device, 150 parts by mass of water, 1.2 parts by mass of sodium salt of polyoxyethylene 2-ethylhexyl ether phosphate as an ester compound, 98.0 parts by mass of ethyl acrylate as a monomer, and 2.0 parts by mass of vinyl monochloroacetate were charged. After repeating degassing under reduced pressure and nitrogen substitution to sufficiently remove oxygen, 0.12 parts by mass of sodium formaldehyde sulfoxylate and 0.1 parts by mass of cumene hydroperoxide were added, and the emulsion polymerization reaction was started at normal pressure and room temperature. The reaction was continued until the polymerization conversion rate reached 95% to obtain emulsion polymerization liquid A.

[0087] (Production of Emulsion Polymerization Liquid B) The monomers to be charged and their amounts were changed to 48.0 parts by mass of ethyl acrylate, 25.0 parts by mass of n-butyl acrylate, 25.0 parts by mass of 2-methoxyethyl acrylate, and 2.0 parts by mass of vinyl monochloroacetate. Otherwise, the production was carried out in the same manner as for emulsion polymerization liquid A to obtain emulsion polymerization liquid B. The polymerization conversion rate at this time was 99%.

[0088] (Production of Emulsion Polymerization Liquid C) The emulsifier to be charged was changed to 0.42 parts by mass of sodium lauryl sulfate (i.e., sodium salt of lauryl sulfate) as an ester compound and 0.6 parts by mass of polyoxyethylene alkyl ether. Otherwise, the production was carried out in the same manner as for emulsion polymerization liquid B to obtain emulsion polymerization liquid C. The polymerization conversion rate at this time was 99%.

[0089] Next, using the above emulsion polymerization liquid, an acrylic rubber is produced through a coagulation process and a drying process. Here, when there is further a base process, for 100 parts by mass of an ester compound other than the monomers constituting the acrylic rubber, the amount of the base used in the base process is X parts by mass, the molecular weight of the base used is Y, and the valence (Z) of the base used, the value of (X / Y) / Z is also described.

[0090] [Example 1] (Production of Acrylic Rubber A) 100 parts by mass of water and 6 parts by mass of sodium sulfate were added to a beaker and heated to 90°C. Next, 100 parts by mass of emulsion polymerization liquid A was dropped to coagulate the polymer to obtain a water-containing crumb, and then 0.24 parts by mass of sodium hydrogen carbonate was added as a base. Thereafter, the polymer was washed twice with 250 parts by mass of water and dried at 85°C for 16 hours to obtain acrylic rubber A. Here, the value of (X / Y) / Z is 0.60.

[0091] [Example 2] (Production of Acrylic Rubber B) It was produced in the same manner as acrylic rubber A except that the base was changed to 0.36 parts by mass of a 10 wt% aqueous sodium hydroxide solution. Here, the value of (X / Y) / Z is 0.19.

[0092] [Example 3] (Production of Acrylic Rubber C) It was produced in the same manner as acrylic rubber A except that the base was changed to 0.36 parts by mass of sodium hydrogen carbonate. Here, the value of (X / Y) / Z is 0.89.

[0093] [Example 4] (Production of Acrylic Rubber D) It was produced in the same manner as acrylic rubber A except that the emulsion polymerization liquid was changed to emulsion polymerization liquid B. Here, the value of (X / Y) / Z is 0.60.

[0094] [Example 5] (Production of Acrylic Rubber E) It was produced in the same manner as acrylic rubber D, except that 3.6 parts by mass of 10% by weight sodium hydroxide was changed. Here, the value of (X / Y) / Z is 1.88.

[0095] [Example 6] (Production of acrylic rubber F) It was produced in the same manner as acrylic rubber A, except that the emulsion polymerization liquid was changed to emulsion polymerization liquid C and 0.24 part by mass of sodium hydrogen carbonate was changed. Here, the value of (X / Y) / Z is 2.27.

[0096] (Production of acrylic rubber G) [Comparative Example 1] It was produced in the same manner as acrylic rubber A, except that no base was added.

[0097] (Production of acrylic rubber H) [Comparative Example 2] It was produced in the same manner as acrylic rubber D, except that no base was added.

[0098] (Production of acrylic rubber I) [Comparative Example 3] It was produced in the same manner as acrylic rubber F, except that no base was added.

[0099] [Comparative Example 4] (Production of acrylic rubber J) It was produced in the same manner as acrylic rubber D, except that 0.04 part by mass of sodium hydrogen carbonate was changed. Here, the value of (X / Y) / Z is 0.10.

[0100] [Comparative Example 5] (Production of acrylic rubber K) It was produced in the same manner as acrylic rubber D, except that 1.21 parts by mass of sodium hydrogen carbonate was changed. Here, the value of (X / Y) / Z is 3.00.

[0101] (Method for promoting storage of acrylic rubber) Each of the manufactured acrylic rubbers was stored for 7 days in a thermo-hygrostat (ESPEC, PR-3K) adjusted to an atmosphere of 80 °C and 75% humidity. After that, each acrylic rubber was taken out and dried sufficiently.

[0102] (Evaluation method for storage stability) Using the formulations in the table, acrylic rubber compositions were produced by kneading the acrylic rubber without storage promotion and the acrylic rubber after storage promotion respectively, and the physical properties were compared depending on the presence or absence of promotion.

[0103] (Production of acrylic rubber composition) First, each compounding agent shown in Table 1 was kneaded in a kneader at 100 °C to prepare an A-kneaded compound. This A-kneaded compound was kneaded on an open roll at room temperature to prepare a B-kneaded compound. A in the table is the raw material of the A-kneaded compound, and B indicates the raw material to be compounded into the A-kneaded compound when preparing the B-kneaded compound. The unit for the compounding agents in Table 1 is parts by mass. As the antioxidant, 4,4'-bis(α,α-dimethylbenzyl) diphenylamine was used.

[0104] (Preparation of unvulcanized sheet) Each acrylic copolymer-containing composition obtained above was kneaded with a kneader and an open roll to prepare an unvulcanized sheet with a thickness of 2 - 2.5 mm.

[0105] (Mooney scorch test) Using the obtained unvulcanized sheet, the Mooney scorch test defined in JIS K 6300-1 was measured at 125 °C using a Mooney Viscometer AM-3 manufactured by Toyo Seiki Co., Ltd. The results are shown in Table 1.

[0106] (Preparation of secondary crosslinked product) The unvulcanized rubber sheet obtained above was press-treated at 180 °C for 10 minutes to obtain a primary crosslinked product with a thickness of 2 mm. Further, this was heated in an air oven at 180 °C for 3 hours to obtain a secondary crosslinked product.

[0107] (Test of physical properties under normal conditions) Using the obtained secondary crosslinked product, tensile tests and hardness tests were conducted. The tensile test was carried out according to the method described in JIS K 6251, and the hardness test was carried out according to the method described in JIS K6253.

[0108] Table 1 shows the test results of the examples and comparative examples obtained from each test method. In each table, the minimum Mooney value Vm and t5 represent the minimum Mooney viscosity and Mooney scorch time (scorch time (t5)) defined in the Mooney scorch test of JIS K6300-1. 100M, tensile strength, and elongation represent the tensile stress, tensile strength, and elongation at 100% elongation defined in the tensile test of JIS K6251, and hardness represents the hardness defined in the hardness test of JIS K6253. The results are shown in Table 1.

[0109]

Table 1

[0110] From Table 1, it is shown that the acrylic rubber of the examples obtained by the production method of the present invention maintains the scorch time (t5) (10 minutes or more) while having little change in the minimum Mooney value in both the acrylic rubber without storage promotion and the acrylic rubber after storage promotion, indicating excellent storage stability. On the other hand, the acrylic rubber of the comparative example shows that the scorch time (t5) becomes shorter (less than 10 minutes) or the minimum Mooney value changes greatly, indicating inferior storage stability compared to the acrylic rubber of the examples.

Industrial Applicability

[0111] The acrylic rubber obtained by the production method of the acrylic rubber of the present invention has excellent storage stability, and the rubber material (specifically, a crosslinked product formed by crosslinking) produced using the composition containing the obtained acrylic rubber is excellent in heat resistance and oil resistance, so it is suitable as a rubber material for various members for automobiles, such as sealing materials, hose materials, vibration-proof materials, tube materials, belt materials, or boot materials.

Claims

1. An emulsion polymerization step of obtaining an emulsion polymerization liquid by emulsion polymerizing monomers, A coagulation step of coagulating the emulsion polymerization liquid with a coagulant to obtain a water-containing crumb, and A drying step of drying the water-containing crumb comprising, furthermore, in the steps after the emulsion polymerization step, including a base addition step of adding a base before the drying step, not including a water washing step of washing the water-containing crumb until the base addition step, using an ester compound other than the monomers constituting the acrylic rubber until the base addition step, the ester compound being a phosphoric acid ester compound, the phosphoric acid ester compound being at least one selected from the group consisting of polyoxyalkylene 2-ethylhexyl ether phosphoric acid ester, polyoxyalkylene stearyl ether phosphoric acid ester, polyoxyalkylene myristyl ether phosphoric acid ester, polyoxyalkylene lauryl ether phosphoric acid ester, polyoxyalkylene palmityl ether phosphoric acid ester, polyoxyalkylene oleyl ether phosphoric acid ester, polyoxyalkylene tridecyl ether phosphoric acid ester, and alkali metal salts thereof, and these polyoxyalkylenes being polyoxyethylene or polyoxypropylene, When the amount of the base used in the base addition step is X parts by mass, the molecular weight of the base used is Y, and the valence (Z) of the base used in the base addition step with respect to 100 parts by mass of the ester compound other than the monomers constituting the acrylic rubber used until the base addition step in the base addition step 0.15 ≦ (X / Y) / Z ≦ 2.5 is satisfied, the valence (Z) of the base is 1, a method for producing an acrylic rubber.

2. A method for producing an acrylic rubber-containing composition, further comprising a step of blending a crosslinking agent with the acrylic rubber obtained by the method for producing an acrylic rubber according to Claim 1.

3. A method for producing a crosslinked acrylic rubber, further comprising a step of crosslinking the acrylic rubber composition obtained by the method for producing an acrylic rubber-containing composition according to Claim 2.

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