JP7155594B2 - Method for manufacturing acrylic rubber - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing an acrylic rubber, and more particularly, a method for producing an acrylic rubber that can achieve excellent storage stability while maintaining good physical properties in a normal state, and that is excellent in resistance to compression set when crosslinked. Regarding.

Acrylic rubber is a polymer containing acrylic acid ester as a main component, and is generally known as a rubber having excellent heat resistance, oil resistance, and ozone resistance, and is widely used in automobile-related fields and the like.

Such acrylic rubber is usually prepared by emulsion polymerization of a monomer mixture that constitutes the acrylic rubber, adding a coagulant to the obtained emulsion polymerization solution to coagulate, and drying the water-containing crumbs obtained by coagulation. (see, for example, Patent Document 1). A hot air dryer is usually used for drying the wet crumbs, but from the viewpoint of productivity, a drying apparatus such as a belt conveyor type band dryer capable of drying in a continuous process is used. On the other hand, the acrylic rubber produced in this way has problems of poor storage stability such as Mooney scorch and scorching, and particularly poor compression set when crosslinked.

JP-A-7-145291

The object of the present invention has been made in view of such circumstances, and an acrylic resin that can achieve excellent storage stability while maintaining good physical properties in a normal state and has excellent compression set resistance when crosslinked An object of the present invention is to provide a method for producing rubber.

The present inventors emulsify-polymerize a monomer containing (meth)acrylic acid ester as a main component to obtain an emulsion-polymerized liquid, coagulate the obtained emulsion-polymerized liquid to form crumbs, and then The present inventors have found that acid washing significantly improves the storage stability of the produced acrylic rubber and the resistance to compression set when crosslinked.

The present inventors also found that when a crosslinkable acrylic rubber, particularly a carboxyl group-containing acrylic rubber, was produced by emulsion polymerization of a monomer used for polymerization including a crosslinkable monomer, the polymerization When emulsion polymerization is carried out using redox catalysts as initiators, especially with peroxides and ferrous sulfate, and also with other reducing agents, certain coagulants, especially sulfate compounds, are also used. When water-containing crumbs are obtained by coagulating using the above-mentioned method, the obtained crumbs are further subjected to acid washing with a specific acid concentration, and water washing is incorporated before and after that. It has been found that the improvement effect of the present invention is significantly improved.
The present inventors have completed the work based on these findings.

Thus, according to the present invention, an emulsion polymerization step of obtaining an emulsion polymerization liquid by emulsion polymerization of a monomer containing (meth)acrylic acid ester as a main component using a polymerization initiator, and a water-containing crumb by coagulating the emulsion polymerization liquid , a washing step of acid-washing the water-containing crumbs, and a drying step of drying the acid-washed water-containing crumbs.
According to the present invention, there is also provided the method for producing the above acrylic rubber, wherein the monomer contains a crosslinkable monomer.
According to the present invention, the crosslinkable monomer is at least one monomer selected from the group consisting of carboxyl group-containing monomers, epoxy group-containing monomers and halogen group-containing monomers. A method for manufacturing the acrylic rubber is provided.
According to the present invention, there is also provided the method for producing the above acrylic rubber, wherein the crosslinkable monomer is a carboxyl group-containing monomer.

According to the present invention, there is also provided the method for producing the above acrylic rubber, wherein the polymerization initiator is a redox catalyst.
According to the present invention, there is also provided the method for producing the above acrylic rubber, wherein the redox catalyst comprises a peroxide and a reducing agent.
According to the present invention, there is also provided the above-described method for producing an acrylic rubber using, as the reducing agent, a combination of a metal ion-containing compound in a reduced state and a reducing agent other than the metal ion-containing compound in a reduced state. be.
According to the present invention, there is also provided the method for producing the above acrylic rubber, wherein the metal ion-containing compound in the reduced state is ferrous sulfate.
According to the present invention, there is also provided the method for producing the acrylic rubber described above, wherein the reducing agent other than the metal ion-containing compound in the reduced state is ascorbic acid or an ascorbate.

According to the present invention, there is also provided the method for producing acrylic rubber described above, wherein the coagulation of the emulsion polymerization liquid in the coagulation step is performed using a monovalent to trivalent metal compound as a coagulant.
According to the present invention, there is also provided the method for producing acrylic rubber described above, wherein the coagulation of the emulsion polymerization liquid in the coagulation step is performed using a sulfate as a coagulant.
According to the present invention, there is also provided the method for producing the acrylic rubber described above, wherein the acid washing has a pH of 6 or less.
According to the present invention, there is also provided the method for producing acrylic rubber, wherein the washing step further includes washing with water.
According to the present invention, there is also provided a method for producing the above acrylic rubber, wherein the water washing is performed multiple times.
According to the present invention, there is also provided the method for producing the acrylic rubber described above, wherein the water washing is performed before and after the acid washing.

INDUSTRIAL APPLICABILITY According to the present invention, there is provided a method for producing an acrylic rubber that can achieve excellent storage stability while maintaining good physical properties in a normal state, and that has excellent resistance to compression set when crosslinked.

The method for producing an acrylic rubber of the present invention comprises an emulsion polymerization step of obtaining an emulsion polymerization liquid by emulsion polymerization of a monomer containing (meth)acrylic acid ester as a main component using a polymerization initiator, and coagulating the emulsion polymerization liquid. and a coagulating step of obtaining wet crumbs, a washing step of acid-cleaning the wet crumbs, and a drying step of drying the acid-washed wet crumbs.

<monomer>
The monomer used in the emulsion polymerization step of the present invention is characterized by containing (meth)acrylic acid ester as a main component. The (meth)acrylic acid ester, which is the main component, is not particularly limited, but examples thereof include (meth)acrylic acid alkyl esters and (meth)acrylic acid alkoxyalkyl esters.

As the (meth)acrylic acid alkyl ester, for example, an ester of an alkanol having 1 to 12 carbon atoms and (meth)acrylic acid is used, and an ester of an alkanol having 1 to 8 carbon atoms and (meth)acrylic acid is preferable. , an ester of an alkanol having 2 to 6 carbon atoms and (meth)acrylic acid is more preferable. Specifically, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, and isobutyl (meth)acrylate. , n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate and the like, among these, ethyl (meth)acrylate and n-butyl (meth)acrylate Ethyl acrylate and n-butyl acrylate are particularly preferred.

As the (meth)acrylic acid alkoxyalkyl ester, for example, an ester of an alkoxyalkyl alcohol having 2 to 12 carbon atoms and (meth)acrylic acid is preferable, and specifically, methoxymethyl (meth)acrylate, (meth) Ethoxymethyl acrylate, 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-propoxyethyl (meth)acrylate, 2-butoxyethyl (meth)acrylate, (meth)acrylic acid 3-methoxypropyl, 4-methoxybutyl (meth)acrylate and the like. Among these, 2-ethoxyethyl (meth)acrylate, 2-methoxyethyl (meth)acrylate and the like are preferable, 2-ethoxyethyl acrylate and 2-methoxyethyl acrylate are more preferable, and 2-methoxyethyl acrylate is preferable. is more preferred.

These (meth)acrylic acid esters may be used alone or in combination of two or more. The content of (meth)acrylic acid ester in the monomer used for polymerization is usually 50 to 99.9% by weight, preferably 60 to 99.7% by weight, more preferably 70 to 99.5% by weight. . If the content of the (meth)acrylic acid ester monomer is too low, the obtained rubber crosslinked product may deteriorate in weather resistance, heat resistance, and oil resistance. There is a possibility that the heat resistance of the crosslinked product may be lowered. In addition, as the (meth)acrylic acid ester, one containing 30 to 100% by weight of (meth)acrylic acid alkyl ester monomer and 70 to 0% by weight of (meth)acrylic acid alkoxyalkyl ester monomer should be used. is preferred.

As the monomers used for polymerization in the emulsion polymerization step of the present invention, it is preferable to contain a crosslinkable monomer together with the above (meth)acrylic acid ester. be.

The crosslinkable monomer is not particularly limited and includes, for example, a carboxyl group-containing monomer, an epoxy group-containing monomer, a halogen atom-containing monomer, a diene monomer, etc., preferably a carboxyl group. monomers, epoxy group-containing monomers and halogen atom-containing monomers, most preferably carboxyl group-containing monomers.

Although the carboxyl group-containing monomer is not particularly limited, for example, α,β-ethylenically unsaturated carboxylic acid can be preferably used. Examples of α,β-ethylenically unsaturated carboxylic acids include α,β-ethylenically unsaturated monocarboxylic acids with 3 to 12 carbon atoms, α,β-ethylenically unsaturated dicarboxylic acids with 4 to 12 carbon atoms, Examples include monoesters of α,β-ethylenically unsaturated dicarboxylic acids having 4 to 12 carbon atoms and alkanols having 1 to 8 carbon atoms. Use of an α,β-ethylenically unsaturated carboxylic acid is preferable because the compression set resistance of the resulting acrylic rubber in the form of a crosslinked rubber can be further enhanced.

Examples of α,β-ethylenically unsaturated monocarboxylic acids having 3 to 12 carbon atoms include acrylic acid, methacrylic acid, α-ethylacrylic acid, crotonic acid and cinnamic acid. Examples of α,β-ethylenically unsaturated dicarboxylic acids having 4 to 12 carbon atoms include butenedioic acids such as fumaric acid and maleic acid, itaconic acid, citraconic acid and chloromaleic acid. Examples of monoesters of α,β-ethylenically unsaturated dicarboxylic acids having 4 to 12 carbon atoms and alkanols having 1 to 8 carbon atoms include monomethyl fumarate, monoethyl fumarate, mono-n-butyl fumarate, and maleic acid. Butenedioic acid mono-chain alkyl esters such as monomethyl, monoethyl maleate, mono-n-butyl maleate; monocyclopentyl fumarate, monocyclohexyl fumarate, monocyclohexenyl fumarate, monocyclopentyl maleate, monocyclohexyl maleate, maleic acid butenedioic acid monoesters having an alicyclic structure such as monocyclohexenyl; itaconic acid monoesters such as monomethyl itaconate, monoethyl itaconate, mono-n-butyl itaconate and monocyclohexyl itaconate; and the like.

The carboxyl group-containing monomer is preferably an α,β-ethylenically unsaturated carboxylic acid, and a monoester of an α,β-ethylenically unsaturated dicarboxylic acid having 4 to 12 carbon atoms and an alkanol having 1 to 8 carbon atoms. is more preferable, and a butenedioic acid mono-chain alkyl ester and a butenedioic acid monoester having an alicyclic structure are particularly preferable. Preferred specific examples include mono-n-butyl fumarate, mono-n-butyl maleate, mono-cyclohexyl fumarate, and mono-cyclohexyl maleate, with mono-n-butyl fumarate being particularly preferred. Among the above monomers, the dicarboxylic acid includes those present as an anhydride.

The epoxy group-containing monomer is not particularly limited, but examples include epoxy group-containing (meth)acrylic acid esters such as glycidyl (meth)acrylate; epoxy group-containing styrenes such as p-vinylbenzyl glycidyl ether; glycidyl and vinyl glycidyl ethers, 3,4-epoxy-1-pentene, 3,4-epoxy-1-butene, 4,5-epoxy-2-pentene, 4-vinylcyclohexyl glycidyl ether, cyclohexenylmethyl glycidyl ether, epoxy group-containing ethers such as 3,4-epoxy-1-vinylcyclohexene and allylphenylglycidyl ether;

The halogen-containing monomer is not particularly limited, but examples include unsaturated alcohol esters of halogen-containing saturated carboxylic acids, haloalkyl (meth)acrylates, haloacyloxyalkyl (meth)acrylates, (meth) acrylic acid (haloacetylcarbamoyloxy) alkyl esters, halogen-containing unsaturated ethers, halogen-containing unsaturated ketones, halomethyl group-containing aromatic vinyl compounds, halogen-containing unsaturated amides, haloacetyl group-containing unsaturated monomers, and the like.

Examples of unsaturated alcohol esters of halogen-containing saturated carboxylic acids include vinyl chloroacetate, vinyl 2-chloropropionate, and allyl chloroacetate. (Meth)acrylate haloalkyl esters include, for example, chloromethyl (meth)acrylate, 1-chloroethyl (meth)acrylate, 2-chloroethyl (meth)acrylate, 1,2-dichloroethyl (meth)acrylate, Examples include 2-chloropropyl (meth)acrylate, 3-chloropropyl (meth)acrylate, and 2,3-dichloropropyl (meth)acrylate. (Meth)acrylic acid haloacyloxyalkyl esters include, for example, 2-(chloroacetoxy)ethyl (meth)acrylate, 2-(chloroacetoxy)propyl (meth)acrylate, 3-(chloroacetoxy)acrylate (meth)acrylate ) propyl, 3-(hydroxychloroacetoxy)propyl (meth)acrylate, and the like. Examples of (haloacetylcarbamoyloxy)alkyl esters of (meth)acrylic acid include 2-(chloroacetylcarbamoyloxy)ethyl (meth)acrylate and 3-(chloroacetylcarbamoyloxy)propyl (meth)acrylate. be done. Halogen-containing unsaturated ethers include, for example, chloromethyl vinyl ether, 2-chloroethyl vinyl ether, 3-chloropropyl vinyl ether, 2-chloroethyl allyl ether, 3-chloropropyl allyl ether and the like. Halogen-containing unsaturated ketones include, for example, 2-chloroethyl vinyl ketone, 3-chloropropyl vinyl ketone, 2-chloroethyl allyl ketone, and the like. Examples of halomethyl group-containing aromatic vinyl compounds include p-chloromethylstyrene, m-chloromethylstyrene, o-chloromethylstyrene, p-chloromethyl-α-methylstyrene and the like. Halogen-containing unsaturated amides include, for example, N-chloromethyl(meth)acrylamide. Haloacetyl group-containing unsaturated monomers include, for example, 3-(hydroxychloroacetoxy)propyl allyl ether, p-vinylbenzyl chloroacetate and the like.

Examples of diene monomers include conjugated dienes and non-conjugated dienes. Examples of conjugated dienes include 1,3-butadiene, isoprene, and piperylene. Examples of non-conjugated dienes include ethylidene norbornene, dicyclopentadiene, dicyclopentadienyl (meth)acrylate, and 2-dicyclopentadienylethyl (meth)acrylate.

These crosslinkable monomers may be used alone or in combination of two or more. The content of the crosslinkable monomer in the monomer is usually in the range of 0.01-20% by weight, preferably 0.1-10% by weight, more preferably 0.5-5% by weight. By setting the content of the crosslinkable monomer within this range, it is possible to achieve a high balance between the storage stability of the obtained acrylic rubber and the compression set resistance of the crosslinked product.

The monomers used for polymerization in the emulsion polymerization step of the present invention may optionally contain other copolymerizable monomers in addition to the (meth)acrylic acid ester and the crosslinkable monomer. Other copolymerizable monomers are not particularly limited as long as they are copolymerizable. Examples include aromatic vinyl monomers, α,β-ethylenically unsaturated nitrile monomers, acrylamide monomers, monomers, other olefinic monomers, and the like. Examples of aromatic vinyl monomers include styrene, α-methylstyrene, divinylbenzene and the like. Examples of α,β-ethylenically unsaturated nitrile monomers include acrylonitrile and methacrylonitrile. Examples of acrylamide-based monomers include acrylamide and methacrylamide. Other olefinic monomers include, for example, ethylene, propylene, vinyl chloride, vinylidene chloride, vinyl acetate, ethyl vinyl ether, butyl vinyl ether and the like. Among these other copolymerizable monomers, styrene, acrylonitrile, methacrylonitrile, ethylene and vinyl acetate are preferred, and acrylonitrile, methacrylonitrile and ethylene are more preferred.

These other copolymerizable monomers may be used alone or in combination of two or more. The content of these other copolymerizable monomers in the monomer is usually 49.99% by weight or less, preferably 39.9% by weight or less, more preferably 29.5% by weight or less.

<Emulsion polymerization step>
In the emulsion polymerization step of the present invention, a monomer containing the (meth)acrylic acid ester as a main component is emulsion-polymerized using a polymerization initiator to obtain an emulsion-polymerized liquid.

Emulsion polymerization may be carried out according to a conventional method. For example, a monomer containing (meth)acrylic acid ester as a main component is previously mixed with an emulsifier and water, and a polymerization initiator is added to carry out emulsion polymerization. methods and the like.

The emulsifier is not particularly limited, and examples thereof include nonionic emulsifiers, anionic emulsifiers and cationic emulsifiers.
Nonionic emulsifiers are not particularly limited, and examples include polyoxyalkylene alkyl ethers such as polyoxyethylene dodecyl ether; polyoxyalkylene alkylphenyl ethers such as polyoxyethylene nonylphenyl ether; oxyalkylene fatty acid esters; polyoxyethylene sorbitan alkyl esters; copolymers of two or more oxyalkylenes such as polyoxyethylene/polyoxypropylene copolymers; Among these, polyoxyalkylene alkyl ethers and polyoxyalkylene alkylphenyl ethers are preferred, and polyoxyethylene alkyl ethers and polyoxyethylene alkylphenyl ethers are particularly preferred. The weight average molecular weight of the nonionic emulsifier is not particularly limited, but is usually in the range of 300-50,000, preferably 500-30,000, more preferably 1,000-15,000. These nonionic emulsifiers may be used alone or in combination of two or more.

Examples of anionic emulsifiers include, but are not limited to, salts of fatty acids such as myristic acid, palmitic acid, oleic acid and linolenic acid; alkylbenzene sulfonates such as sodium dodecylbenzenesulfonate; higher alcohols such as sodium lauryl sulfate. Sulfuric acid ester salts, higher phosphate salts such as sodium alkyl phosphate; alkyl sulfosuccinates, and the like. Among these anionic emulsifiers, higher phosphate ester salts and higher alcohol sulfate ester salts are preferred.

Examples of cationic emulsifiers include alkyltrimethylammonium chloride, dialkylammonium chloride, and benzylammonium chloride.

These emulsifiers may be used alone or in combination of two or more. Among these emulsifiers, nonionic emulsifiers and anionic emulsifiers are preferable, and it is more preferable to use a combination of nonionic emulsifiers and anionic emulsifiers. By using a combination of a nonionic emulsifier and an anionic emulsifier, it is possible to effectively suppress the occurrence of contamination due to the adhesion of polymers and the like to a polymerization apparatus (for example, a polymerization tank) during emulsion polymerization, and use it in the coagulation step described later. It is possible to reduce the amount of coagulant used, and as a result, it is possible to reduce the amount of coagulant in the finally obtained acrylic rubber, thereby improving the storage stability of the resulting acrylic rubber composition. And, the water resistance as a rubber cross-linked product can be improved. In addition, by using a nonionic emulsifier and an anionic emulsifier in combination, the emulsifying action can be enhanced, so the amount of the emulsifier itself used can be reduced. It is possible to reduce the residual amount of the emulsifier contained in , thereby further enhancing the storage stability and water resistance of the obtained acrylic rubber.

The amount of the emulsifier used is usually 0.01 to 10 parts by weight, preferably 0.1 to 5 parts by weight, more preferably 1 to 3 parts by weight, based on 100 parts by weight of the monomers used for polymerization. is in the range of When a nonionic emulsifier and an anionic emulsifier are used in combination, the ratio by weight of the nonionic emulsifier/anionic emulsifier is usually 1/99 to 99/1, preferably 10/90 to 80/20. , more preferably 25/75 to 75/25, still more preferably 50/50 to 75/25, and most preferably 65/35 to 75/25, the object of the present application can be highly enhanced. .

Examples of polymerization initiators include azo compounds such as azobisisobutyronitrile; organic peroxides such as diisopropylbenzene hydroperoxide, cumene hydroperoxide, paramenthane hydroperoxide, and benzoyl peroxide; sodium persulfate, Inorganic peroxides such as potassium persulfate, hydrogen peroxide, and ammonium persulfate; and the like can be used. These polymerization initiators may be used alone or in combination of two or more. The amount of the polymerization initiator used is usually 0.001 to 5 parts by weight, preferably 0.01 to 1 part by weight, more preferably 0.05 to 0.5 parts by weight, per 100 parts by weight of the monomer used for polymerization. It is in the range of parts by weight.

When using an organic peroxide and/or an inorganic peroxide as a polymerization initiator, it is preferable to use it as a redox polymerization initiator in combination with a reducing agent. The reducing agent to be combined is not particularly limited, but for example, metal ion-containing compounds in a reduced state such as ferrous sulfate, sodium hexamethylenediaminetetraacetate, and cuprous naphthenate; ascorbic acid, sodium ascorbate, ascorbic ascorbic acid (salts) such as potassium sulfite; erythorbic acid (salts) such as erythorbic acid, sodium erythorbate, potassium erythorbate; sugars; sulfinates such as sodium hydroxymethanesulfinate; sodium sulfite, potassium sulfite, sodium bisulfite , Aldehyde Sodium bisulfite, Potassium bisulfite sulfites; Pyrosulfites such as sodium pyrosulfite, potassium pyrosulfite, sodium pyrosulfite, potassium pyrosulfite; Phosphorous acid (salt) of phosphoric acid, sodium phosphite, potassium phosphite, sodium hydrogen phosphite, potassium hydrogen phosphite; Pyrophosphorous acid (salt) such as potassium; sodium formaldehyde sulfoxylate;

These reducing agents can be used either alone or in combination of two or more. It is preferable to combine with a reducing agent other than the compound, particularly by combining ferrous sulfate and ascorbic acid (salt), because the object of the present application can be achieved to a higher degree. The amount of the reducing agent used is preferably 0.00001 to 1 part by weight, more preferably 0.0001 to 0.5 part by weight, per 100 parts by weight of the monomers used for polymerization.

When ferrous sulfate is used in combination with ascorbic acid and/or ascorbate, the amount of ferrous sulfate used is usually 0.00001-0. 01 parts by weight, preferably in the range of 0.0001 to 0.001 parts by weight, and the amount of ascorbic acid and/or ascorbate used is usually 0.001 to 5 parts by weight, preferably 0.01 to 1 part by weight. is in the range of

The amount of water used is preferably 80 to 500 parts by weight, more preferably 100 to 300 parts by weight, per 100 parts by weight of the monomer used for polymerization.

In the emulsion polymerization, auxiliary materials for polymerization such as molecular weight modifiers, particle size modifiers, chelating agents, and oxygen scavengers can be used as necessary.

Emulsion polymerization may be carried out by any of a batch system, a semi-batch system and a continuous system, but the semi-batch system is preferred. Specifically, in a reaction system containing a polymerization initiator and a reducing agent, a monomer used for polymerization is continuously added dropwise to the polymerization reaction system from the start of the polymerization reaction until an arbitrary time, and the polymerization reaction is performed. , For at least one of the monomers, the polymerization initiator, and the reducing agent used in the polymerization, it is preferable to carry out the polymerization reaction while continuously dropping it into the polymerization reaction system from the start of the polymerization reaction until an arbitrary time, It is more preferable to carry out the polymerization reaction while continuously dropping all of the monomers, the polymerization initiator, and the reducing agent used for the polymerization into the polymerization reaction system from the start of the polymerization reaction until an arbitrary time. By carrying out the polymerization reaction while dropping these continuously, the emulsion polymerization can be stably carried out, whereby the polymerization reaction rate can be improved. The polymerization is usually carried out in the temperature range of 0-70°C, preferably 5-50°C.

Further, when the polymerization reaction is performed while continuously dropping the monomer used for polymerization, the monomer used for polymerization is mixed with an emulsifier and water to obtain a monomer emulsion (emulsion preparation step), it is preferable to drop continuously in the state of the monomer emulsion. The method for preparing the monomer emulsion is not particularly limited, and a method of stirring the total amount of the monomers used in the polymerization, the total amount of the emulsifier, and water using a stirrer such as a homomixer or a disc turbine. mentioned. The amount of water used in the monomer emulsion is preferably 10 to 70 parts by weight, more preferably 20 to 50 parts by weight, per 100 parts by weight of the monomer used for polymerization.

Further, when the polymerization reaction is carried out while continuously dripping all of the monomers, polymerization initiator, and reducing agent used for the polymerization into the polymerization reaction system from the start of the polymerization reaction until an arbitrary time, these are separated. Alternatively, at least the polymerization initiator and the reducing agent are mixed in advance and, if necessary, are added dropwise to the polymerization system in the form of an aqueous solution from the same dropping device. may After completion of the dropwise addition, the reaction may be continued for an arbitrary period of time in order to further improve the polymerization reaction rate.

Emulsion polymerization can be terminated by adding a polymerization terminator, if necessary. Examples of the polymerization terminator include hydroxylamine, hydroxylamine sulfate, diethylhydroxyamine, hydroxylaminesulfonic acid and alkali metal salts thereof, sodium dimethyldithiocarbamate, and hydroquinone. The amount of the polymerization terminator used is not particularly limited, but is preferably 0.1 to 2 parts by weight with respect to 100 parts by weight of the monomer used for polymerization.

<Addition of compounding agent to emulsion polymerization solution>
In the emulsion polymerization step of the present invention, various compounding agents can be added as necessary to the emulsion polymerization solution before coagulation obtained by the emulsion polymerization, and uniformly dispersed in the resulting acrylic rubber. The compounding agent to be added is not particularly limited as long as it is a compounding agent for rubber, but for example, anti-aging agents, lubricants, alkylene oxide-based polymers, etc. are preferable, and anti-aging agents and alkylene oxide-based polymers are more preferable. .

For example, by preliminarily containing an anti-aging agent in the emulsion polymerization liquid before coagulation, it is possible to effectively suppress deterioration of the acrylic rubber due to heat during drying in the drying step described later. Specifically, it is possible to effectively suppress the decrease in Mooney viscosity caused by deterioration due to heating during drying. can be increased to In addition, by blending the anti-aging agent in the state of the emulsion polymerization liquid before coagulation, the anti-aging agent can be appropriately dispersed. It is possible to fully exhibit the effect of the addition. Specifically, the blending amount of the antioxidant is preferably 0.1 to 2 parts by weight, more preferably 0.2 to 1.2 parts by weight, with respect to 100 parts by weight of the acrylic rubber component in the emulsion polymerization liquid. Even with a relatively small blending amount, the effect of addition can be fully exhibited. Even if the anti-aging agent is contained in the emulsion polymerization liquid before coagulation, the added anti-aging agent is not substantially removed during subsequent coagulation, washing, drying, etc. , the addition effect can be fully exhibited. In addition, as a method for incorporating the anti-aging agent into the emulsion polymerization liquid, a method of adding it to the emulsion polymerization liquid after emulsion polymerization and before coagulation, or a method of adding it to the solution before emulsion polymerization is performed. However, if it is added to the solution before emulsion polymerization, aggregates are generated during emulsion polymerization, which may cause staining of the polymerization apparatus. Moreover, the method of adding to the emulsion polymerization liquid before coagulation is preferable.

The anti-aging agent is not particularly limited, but examples include 2,6-di-t-butyl-4-methylphenol, 2,6-di-t-butylphenol, butylhydroxyanisole, 2,6-di-t- butyl-α-dimethylamino-p-cresol, octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, mono (or di, or tri) (α-methylbenzyl)phenol, etc. styrenated phenol, 2,2'-methylene-bis(6-α-methylbenzyl-p-cresol), 4,4'-methylenebis(2,6-di-t-butylphenol), 2,2'-methylene- Bis(4-methyl-6-t-butylphenol), stearyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, alkylated bisphenol, butylation reaction of p-cresol and dicyclopentadiene Phenolic antioxidants containing no sulfur atoms such as products; 2,4-bis[(octylthio)methyl]-6-methylphenol, 2,2'-thiobis-(4-methyl-6-t-butylphenol) , 4,4′-thiobis-(6-t-butyl-o-cresol), 2,6-di-t-butyl-4-(4,6-bis(octylthio)-1,3,5-triazine- 2-ylamino)phenol and other thiophenol-based antioxidants; tris(nonylphenyl)phosphite, diphenylisodecylphosphite, tetraphenyldipropylene glycol diphosphite and other phosphite-based antioxidants; dilauryl thiodipropionate sulfur ester anti-aging agents such as; Amine antioxidants such as N-diphenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, butyraldehyde-aniline condensates; imidazole antioxidants such as 2-mercaptobenzimidazole; quinoline antioxidants such as 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline; hydroquinone antioxidants such as 2,5-di-(t-amyl)hydroquinone; . These antioxidants may be used alone or in combination of two or more.

The lubricant is not particularly limited, and examples thereof include hydrocarbon lubricants such as liquid paraffin, paraffin wax and synthetic polyethylene wax; fatty acid ester lubricants such as stearic acid alkyl ester; Fatty acid amide-based lubricants such as; calcium stearate, magnesium stearate, zinc stearate and other metal soap-based lubricants; phosphate ester lubricants such as polyoxyethylene higher alcohol phosphates such as ethylene tridecyl ether phosphate; higher fatty acid lubricants such as fatty acids having 10 to 30 carbon atoms, preferably 12 to 20 carbon atoms;

Among these lubricants, fatty acid ester lubricants, fatty acid amide lubricants, phosphate ester lubricants, and higher fatty acid lubricants, preferably phosphate ester lubricants and higher fatty acid lubricants, and more preferably polyoxyethylene stearyl ether phosphoric acid are used. When the acrylic rubber is dried, the handleability and roll workability of the produced acrylic rubber are highly improved, which is preferable.

These lubricants can be used alone or in combination of two or more. The amount added is appropriately selected according to the purpose of use. On the other hand, it is usually in the range of 0.0001 to 10 parts by weight, preferably 0.001 to 5 parts by weight, more preferably 0.01 to 1 part by weight.

By preliminarily containing the lubricant in the emulsion polymerization liquid before coagulation, the lubricant can be dispersed satisfactorily in the emulsion polymerization liquid before coagulation. A lubricant can be contained therein in a well-dispersed state. As a result, the lubricant can be appropriately contained in the obtained acrylic rubber (preferably, it can be contained in a uniformly dispersed state), thereby making the acrylic rubber obtained It can be excellent in handleability during drying and roll processability. Even when the lubricant is contained in the emulsion polymerization liquid before coagulation, the added lubricant is not substantially removed in the subsequent coagulation, washing, drying, etc., so the effect of the addition is limited. It can be fully demonstrated. On the other hand, when a lubricant is added after coagulation, it becomes difficult to disperse the lubricant in the acrylic rubber. It cannot be included in the state), and it becomes difficult to obtain the effect of suppressing adhesion, etc. during drying during the production of acrylic rubber.

The alkylene oxide polymer is not particularly limited as long as it is an alkylene oxide polymer, but a lower alkylene oxide polymer is usually used. Specific examples include polyethylene oxide, polypropylene oxide, ethylene oxide/propylene oxide copolymers, etc. Among these, polyethylene oxide is preferred. The weight average molecular weight of the alkylene oxide polymer is selected depending on the purpose of use, but is usually 10,000 to 6,000,000, preferably 30,000 to 1,000,000, more preferably 50,000. to 500,000, particularly preferably 50,000 to 300,000, most preferably 80,000 to 200,000. When the weight-average molecular weight of the alkylene oxide polymer is within this range, the object of the present invention can be achieved to a high degree, which is preferable.

These alkylene oxide polymers may be used alone or in combination of two or more. The amount to be blended is preferably 0.01 per 100 parts by weight of the acrylic rubber component in the emulsion polymerization liquid. ~1 part by weight, more preferably 0.01 to 0.6 part by weight, and still more preferably 0.02 to 0.5 part by weight. By preliminarily containing the alkylene oxide polymer in the emulsion polymerization liquid before coagulation, the coagulability of the emulsion polymerization liquid can be improved, thereby reducing the amount of coagulant in the coagulation step. Therefore, the residual amount in the finally obtained acrylic rubber can be reduced, and the compression set resistance and water resistance of the rubber crosslinked product can be improved.

<Coagulation process>
In the coagulation step of the present invention, water-containing crumbs are obtained by coagulating the above-mentioned emulsion polymerization solution to which an anti-aging agent, a lubricant and/or an alkylene oxide polymer are added as necessary.

The coagulation of the emulsion polymerization solution can be carried out according to a conventional method, for example, by contacting the emulsion polymerization solution with a coagulant.

The coagulant is not particularly limited, but includes, for example, monovalent to trivalent metal salts. The monovalent to trivalent metal salt is a salt containing a metal that becomes a monovalent to trivalent metal ion when dissolved in water, and is not particularly limited, but is, for example, an inorganic acid selected from hydrochloric acid, nitric acid, sulfuric acid, and the like. or acetic acid with a metal selected from sodium, potassium, lithium, magnesium, calcium, zinc, titanium, manganese, iron, cobalt, nickel, aluminum and tin. Hydroxides of these metals can also be used.

Specific examples of monovalent to trivalent metal salts include sodium chloride, potassium chloride, lithium chloride, magnesium chloride, calcium chloride, zinc chloride, titanium chloride, manganese chloride, iron chloride, cobalt chloride, nickel chloride, aluminum chloride, chloride Metal chlorides such as tin; metal nitrates such as sodium nitrate, potassium nitrate, lithium nitrate, magnesium nitrate, calcium nitrate, zinc nitrate, titanium nitrate, manganese nitrate, iron nitrate, cobalt nitrate, nickel nitrate, aluminum nitrate, tin nitrate; sulfuric acid metal sulfates such as sodium, potassium sulfate, lithium sulfate, magnesium sulfate, calcium sulfate, zinc sulfate, titanium sulfate, manganese sulfate, iron sulfate, cobalt sulfate, nickel sulfate, aluminum sulfate, tin sulfate; Among these, metal chlorides and metal sulfates are preferred, monovalent or divalent metal chlorides and monovalent or divalent metal sulfates are more preferred, and monovalent or divalent metal sulfates are particularly preferred. As the monovalent or divalent metal salt, calcium chloride, sodium chloride, magnesium sulfate and sodium sulfate are preferable, and magnesium sulfate and sodium sulfate are more preferable.

These coagulants may be used alone or in combination of two or more. The amount of the coagulant used is usually 0.01 to 100 parts by weight, preferably 0.1 to 50 parts by weight, more preferably 1 to 30 parts by weight, per 100 parts by weight of the acrylic rubber component in the emulsion polymerization liquid. Range. When the coagulant is in this range, it is possible to sufficiently coagulate the acrylic rubber and highly improve the compression set resistance and water resistance when the acrylic rubber is crosslinked, which is preferable.

The method of contacting the emulsion polymerization liquid and the coagulant may be carried out according to a conventional method, such as adding the coagulant to the emulsion polymerization liquid or adding the emulsion polymerization liquid to the solution or dispersion liquid of the coagulant. can be done. As the solution or dispersion of the coagulant when the emulsion polymerization solution is added, an aqueous solution is usually used, and the concentration of the coagulant in the aqueous solution is appropriately selected, usually 1 to 30% by weight, preferably 5 to 25% by weight. , more preferably in the range of 10 to 20% by weight. When a coagulant is added to the emulsion polymerization liquid, the coagulant may be added in the form of a solid powder, or may be dissolved in the form of an aqueous solution. When the coagulant is added as an aqueous solution, the concentration is appropriately selected depending on the purpose of use, and is usually in the range of 1 to 50% by weight, preferably 5 to 40% by weight, more preferably 10 to 30% by weight.

The contact (coagulation) temperature between the emulsion polymerization solution and the coagulant is not particularly limited, but is usually 60°C or higher, preferably 70 to 100°C, more preferably 75 to 90°C.

<Washing process>
In the washing step of the present invention, the wet crumbs obtained in the above coagulation step are washed with an acid.

According to the production method of the present invention, by carrying out acid washing, it is possible to further improve the compression set resistance in the case of making a rubber crosslinked product, and the carboxyl group-containing acrylic rubber in which the acrylic rubber has a carboxyl group. , the effect of improving the compression set resistance by this acid washing is particularly large. The acid used for acid washing is not particularly limited, and sulfuric acid, hydrochloric acid, phosphoric acid and the like can be used without limitation. In addition, when acid is added to the water-containing crumbs in acid washing, it is preferable to add the acid in the form of an aqueous solution. Preferably it is 3 or less. Although the lower limit of pH is not particularly limited, it is usually 1 or higher. The pH of the washing water used for acid washing can be determined, for example, by measuring the pH of the water contained in the water-containing crumb after acid washing.

The method of acid washing is not particularly limited, but for example, a method of mixing the water-containing crumbs with an aqueous solution of an added acid can be mentioned. The temperature during acid washing is not particularly limited, but is preferably 5 to 60° C., more preferably 10 to 50° C., and the mixing time is 1 to 60 minutes, more preferably 2 to 30 minutes.

In the production method of the present invention, the wet crumbs obtained in the coagulation step may be washed with an acid instead of washing with water. Since the water resistance can be further enhanced by this, it is preferable that the water-containing crumbs obtained in the coagulation step are washed with water and then washed with an acid. The method of washing with water is not particularly limited, but a method of washing with water by using water as a washing liquid and mixing the added water with the water-containing crumbs can be mentioned. The temperature for washing with water is not particularly limited, but is preferably 5 to 60° C., more preferably 10 to 50° C., and the mixing time is 1 to 60 minutes, more preferably 2 to 30 minutes.

In addition, the amount of water added to the water-containing crumbs during washing is not particularly limited. The amount of water per washing is preferably 50 to 9,800 parts by weight, more preferably 300 to 1,800 parts by weight, based on 100 parts by weight of the solid content (mainly the acrylic rubber component) contained in the water-containing crumbs. weight part.

The number of times of water washing is not particularly limited, and may be once, but from the viewpoint of reducing the residual amount of the coagulant in the finally obtained acrylic rubber, it is preferable to wash several times, preferably 2 to 10 times. , more preferably 3 to 8 times. From the viewpoint of reducing the residual amount of the coagulant in the finally obtained acrylic rubber, it is desirable to wash with water more often, but even if the number of washings exceeds the above range, the effect of removing the coagulant will not be obtained. Although the number of steps is small, the number of steps increases, and the effect of lowering productivity becomes greater.

Further, in the present invention, it is preferable to further wash with water after the above-described acid washing, and the conditions for water washing may be the same as those described above.

<Drying process>
In the drying step of the present invention, the wet crumbs washed in the washing step are dried.

The drying method in the drying step is not particularly limited. For example, drying can be performed using a dryer such as a screw extruder, a kneader dryer, an expander dryer, a hot air dryer, or a reduced pressure dryer. . Moreover, you may use the drying method which combined these. Furthermore, before drying in the drying step, the wet crumb may be filtered using a sieve such as a rotary screen or vibrating screen; a centrifugal dehydrator; or the like, if necessary.

For example, the drying temperature in the drying step is not particularly limited and varies depending on the dryer used for drying. For example, when using a hot air dryer, the drying temperature is preferably 80 to 200 ° C. It is more preferable to set the temperature to 170°C.

<Acrylic rubber>
According to the present invention, an acrylic rubber can be obtained by the production method described above. The acrylic rubber of the present invention thus produced has excellent storage stability while maintaining good physical properties under normal conditions.

The monomer composition in the acrylic rubber thus produced is appropriately selected according to the purpose of use. 99.7% by weight, more preferably 70 to 99.5% by weight. In addition, the (meth)acrylic acid ester monomer unit includes from 30 to 100% by weight of (meth)acrylic acid alkyl ester monomeric unit and from 70 to 0% by weight of (meth)acrylic acid alkoxyalkyl ester monomeric unit. preferably configured. The content of the crosslinkable monomer unit in the acrylic rubber is generally 0.01-20% by weight, preferably 0.1-10% by weight, more preferably 0.5-5% by weight. The content of other copolymerizable monomer units in the acrylic rubber is usually 0 to 49.99% by weight, preferably 0 to 39.9% by weight, more preferably 0 to 29.5% by weight. be.

The Mooney viscosity (ML1+4, 100°C) of the acrylic rubber produced in this manner is selected according to the purpose of use, but is usually in the range of 10 to 120, preferably 20 to 80, more preferably 25 to 60. .

The glass transition temperature (Tg) of the acrylic rubber thus produced is selected according to the purpose of use, and is usually 15°C or lower, preferably 0°C or lower.

<Rubber composition>
According to the present invention, by blending a rubber component containing acrylic rubber obtained by the above production method with a cross-linking agent, a rubber composition containing a rubber component containing acrylic rubber obtained by the above production method and a cross-linking agent can be obtained. can be obtained.

Examples of cross-linking agents include, but are not limited to, diamine compounds, polyvalent amine compounds such as dithiocarbamic acid, and carbonates thereof; sulfur compounds; sulfur donors; polyepoxy compounds; organic carboxylic acid ammonium salts; Conventionally known cross-linking agents such as oxides; polycarboxylic acids; isocyanuric acid compounds; organic peroxides; triazine compounds; Among these, polyvalent amine compounds and triazine compounds are preferred, and triazine compounds are particularly preferred.

In addition to the cross-linking agent, the rubber composition may contain at least one selected from a cross-linking accelerator, an anti-scorch agent, a filler and a silane coupling agent. In addition to at least one of these, dispersing agents such as higher fatty acids and metal amine salts thereof, plasticizers such as phthalic acid derivatives, adipic acid derivatives, sebacic acid derivatives, lubricating oils, process oils, coal tar, castor oil, stear Softeners such as calcium phosphate, antioxidants, light stabilizers, processing aids, adhesives, lubricants, flame retardants, anti-mold agents, antistatic agents, colorants, cross-linking retarders, polyolefin resins, polystyrene resins, poly Resins such as acrylic resins, polyphenylene ether-based resins, polyester-based resins, polycarbonate-based resins, polyamide resins, vinyl chloride resins, and fluorine resins may be blended.

<Rubber cross-linked product>
According to the present invention, a rubber cross-linked product can be obtained by cross-linking the rubber composition described above.

The rubber cross-linked product is obtained by molding the above-described rubber composition into a desired shape using a molding machine such as an extruder, an injection molding machine, a compressor, or a roll, and then heating to carry out a cross-linking reaction. , can be produced by fixing the shape as a rubber crosslinked product. In this case, the cross-linking may be performed after pre-molding, or the cross-linking may be performed at the same time as the molding. The molding temperature is usually 10-200°C, preferably 25-150°C. The crosslinking temperature is usually 100 to 250°C, preferably 130 to 220°C, more preferably 150 to 200°C, and the crosslinking time is usually 0.1 minute to 10 hours, preferably 1 minute to 5 hours. As the heating method, a method used for cross-linking rubber, such as press heating, steam heating, oven heating, and hot air heating, may be appropriately selected.

Further, the cross-linked rubber may be further heated for secondary cross-linking depending on the shape and size of the cross-linked rubber. The secondary cross-linking is preferably carried out for 1 to 48 hours, although it varies depending on the heating method, cross-linking temperature, shape and the like. A heating method and a heating temperature may be appropriately selected.

EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples. "Parts" in each example are by weight unless otherwise specified.
Various physical properties were evaluated according to the following methods.

[Mooney viscosity (ML1+4, 100°C)]
Mooney viscosity (Polymer Mooney) of acrylic rubber was measured according to JIS K6300.

[Glass-transition temperature]
The glass transition temperature (Tg) of acrylic rubber was measured according to JIS K6240.

[Normal physical properties (tensile strength, elongation)]
The acrylic rubber composition is placed in a mold of 15 cm long, 15 cm wide and 0.2 cm deep, and pressed at 180° C. for 10 minutes under a pressure of 10 MPa for cross-linking to obtain a cross-linked rubber sheet. rice field. The resulting crosslinked rubber product was punched out with a No. 3 dumbbell to prepare a test piece. The tensile strength and elongation of this test piece were measured according to JIS K6251.

[Mooney scorch test (ML125°C)]
The Mooney scorch time (t5 and t35) and Vmin of the acrylic rubber composition were measured at 145°C according to JIS K6300. In this measurement, the time when the Mooney viscosity increased by 5M from Vmin was defined as t5, and the time when the Mooney viscosity increased by 35M from Vmin was defined as t35. Moreover, the acrylic rubber composition used for the measurement was produced according to JIS K6299. The larger the values of t5 and t35, the longer it takes to vulcanize, and it can be judged that the rubber composition has excellent storage stability and the vulcanization acceleration effect is suppressed (well controlled). . A lower value of Vmin means less initial vulcanization of the rubber composition, and it can be judged that the storage stability is excellent.

[Compression set test]
The acrylic rubber composition was molded and crosslinked by pressing at 180°C for 10 minutes to prepare a cylindrical test piece with a diameter of 29 mm and a thickness of 12.5 mm, which was then heated at 180°C for 4 hours for secondary crosslinking. let me According to JIS K6262, the test piece after the secondary cross-linking obtained above was compressed by 25%, left for 72 hours in an environment of 150 ° C. and 175 ° C., and then released to be permanently compressed. A strain rate (%) was measured. The smaller the compression set rate (%), the better the compression set resistance.

[Example 1]
46.294 parts of pure water, 34.6 parts of ethyl acrylate, 49 parts of n-butyl acrylate, 15 parts of 2-methoxyethyl acrylate, and 1.4 parts of mono-n-butyl fumarate were placed in a mixing vessel equipped with a homomixer. part, 0.567 parts of sodium lauryl sulfate as an anionic emulsifier (trade name "Emal 2FG", manufactured by Kao Corporation), and polyoxyethylene dodecyl ether as a nonionic emulsifier (trade name "Emulgen 105", weight average molecular weight: Approximately 1500, manufactured by Kao Corporation) (1.4 parts) was charged and stirred to obtain a monomer emulsion.

Then, 170.853 parts of pure water and 2.98 parts of the monomer emulsion obtained above were added to a polymerization reactor equipped with a thermometer and a stirring device, and the temperature was 12° C. under a nitrogen stream. cooled to Next, in the polymerization reactor, 145.85 parts of the monomer emulsion obtained above, 0.00033 parts of ferrous sulfate as a reducing agent, 0.264 parts of sodium ascorbate as a reducing agent, and , 7.72 parts of a 2.85% by weight potassium persulfate aqueous solution (0.22 parts as the amount of potassium persulfate) as a polymerization initiator was continuously added dropwise over 3 hours. After that, the reaction was continued for 1 hour while maintaining the temperature in the polymerization reactor at 23° C. After confirming that the polymerization conversion rate reached 95%, hydroquinone was added as a polymerization terminator to polymerize. The reaction was stopped to obtain an emulsion polymerization liquid.

Then, 3-(3,5-di-tert-butyl-4-hydroxyphenyl) stearyl propionate as an antioxidant (trade name “Irganox 1076”, BASF Co., Ltd.) 0.3 parts (the total amount of monomers charged when producing the emulsion polymerization liquid (that is, ethyl acrylate, n-butyl acrylate, 2-methoxyethyl acrylate, mono-n-fumarate) 1 part per 100 parts of total butyl), 0.011 part of polyethylene oxide polymer (weight average molecular weight (Mw) = 100,000) (total of monomers charged when producing the emulsion polymerization liquid 0.039 parts per 100 parts) to obtain a mixed liquid. Then, the obtained mixed solution is transferred to a coagulation tank, 47.8 parts of industrial water is added to 100 parts of this mixed solution, the temperature is raised to 85 ° C., and the mixed solution is heated to 85 ° C. A sodium sulfate aqueous solution (20% by weight aqueous solution) obtained by mixing 13.2 parts of industrial water and 3.3 parts of sodium sulfate as a coagulant (11 parts per 100 parts of the polymer contained in the mixed solution) while stirring. ) was continuously added to coagulate the polymer, thereby obtaining hydrous crumbs of acrylic rubber.

Next, 388 parts of industrial water is added to 100 parts of the solid content of the water-containing crumb obtained above, and after stirring for 5 minutes at 15 ° C. in the coagulation tank, water is discharged from the coagulation tank, The wet crumbs were washed with water. In addition, in this production example, such washing with water was repeated four times.

Next, a sulfuric acid aqueous solution (pH = 2.6) obtained by mixing 388 parts of industrial water and 0.13 parts of concentrated sulfuric acid is added to 100 parts of the solid content of the water-containing crumbs washed with water as described above, and a coagulation tank is added. After stirring for 5 minutes at 15° C. inside, the water-containing crumb was pickled by draining water from the coagulation tank. Next, 388 parts of pure water is added to 100 parts of the solid content of the water-containing crumbs that have been pickled, and after stirring at 15 ° C. for 5 minutes in the coagulation tank, the water is discharged from the coagulation tank to remove the water. The crumbs were washed with pure water, and the water-containing crumbs washed with pure water were dried at 110° C. for 1 hour in a hot air dryer to obtain a solid acrylic rubber (A1).

The resulting acrylic rubber (A1) had a Mooney viscosity (ML1+4, 100°C) of 39 and a Tg of -35°C. The composition of the acrylic rubber is 34.6% by weight of ethyl acrylate units, 49% by weight of n-butyl acrylate units, 15% by weight of 2-methoxyethyl acrylate units, and 1.4% by weight of mono-n-butyl fumarate units. %Met.

Using a Banbury mixer, 100 parts of acrylic rubber (A1), 50 parts of carbon black (trade name “SEAST SO”, manufactured by Tokai Carbon), 1 part of stearic acid, polyoxyethylene stearyl ether phosphate (trade name “Phospha 2 parts of 4,4′-bis(α,α-dimethylbenzyl)diphenylamine (trade name “Nocrac CD”, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) were added. , 50° C. for 5 minutes. The resulting mixture was then transferred to a roll at 50° C., and 0.7 parts of 4,4′-diaminodiphenylmethane and 1,3-di-o-tolylguanidine (trade name “Noccellar DT”, Ouchi Shinko Kagaku) 2 parts of a cross-linking accelerator manufactured by Kogyosha Co., Ltd. were blended and kneaded to obtain an acrylic rubber composition. Using the obtained acrylic rubber composition, normal physical properties, Mooney scorch and compression set were measured according to the above methods, and the results are shown in Table 1.

[Example 2]
A sodium sulfate aqueous solution (5% by weight aqueous solution) obtained by mixing 60 parts of industrial water and 3.3 parts of sodium sulfate as a coagulant with 100 parts of the mixed solution prepared in the same manner as in Example 1 was added to the coagulation tank. After charging and heating to 85 ° C., solid acrylic rubber was obtained by performing the same operation as in Example 1 except that the polymer was solidified by continuously adding the mixed solution at 85 ° C. (A2) was obtained.

The resulting acrylic rubber (A2) had a Mooney viscosity (ML1+4, 100°C) of 39 and a Tg of -35°C. The composition of the acrylic rubber is 34.6% by weight of ethyl acrylate units, 49% by weight of n-butyl acrylate units, 15% by weight of 2-methoxyethyl acrylate units, and 1.4% by weight of mono-n-butyl fumarate units. %Met.
Then, an acrylic rubber composition was obtained in the same manner as in Example 1, except that the acrylic rubber (A2) obtained above was used. Using the obtained acrylic rubber composition, normal physical properties, Mooney scorch and compression set were measured, and the results are shown in Table 1.

[Example 3]
100 parts of the solid content of the water-containing crumbs washed with water in the same manner as in Example 1 was acid-washed with an aqueous sulfuric acid solution (pH = 2.8) obtained by mixing 388 parts of industrial water and 0.08 parts of concentrated sulfuric acid. A solid acrylic rubber (A3) was obtained by performing the same operation as in Example 1, except that the

The resulting acrylic rubber (A3) had a Mooney viscosity (ML1+4, 100°C) of 38 and a Tg of -35°C. The composition of the acrylic rubber is 34.6% by weight of ethyl acrylate units, 49% by weight of n-butyl acrylate units, 15% by weight of 2-methoxyethyl acrylate units, and 1.4% by weight of mono-n-butyl fumarate units. %Met.
Then, an acrylic rubber composition was obtained in the same manner as in Example 1, except that the acrylic rubber (A3) obtained above was used. Using the obtained acrylic rubber composition, normal physical properties, Mooney scorch and compression set were measured, and the results are shown in Table 1.

[Example 4]
100 parts of the solid content of the water-containing crumbs washed with water in the same manner as in Example 1 was acid-washed with an aqueous sulfuric acid solution (pH = 3.3) obtained by mixing 388 parts of industrial water and 0.04 parts of concentrated sulfuric acid. A solid acrylic rubber (A4) was obtained by performing the same operation as in Production Example 1 except that

The resulting acrylic rubber (A4) had a Mooney viscosity (ML1+4, 100°C) of 38 and a Tg of -35°C. The acrylic rubber composition is composed of 34.6% by weight of ethyl acrylate units, 49% by weight of n-butyl acrylate units, 15% by weight of 2-methoxyethyl acrylate units, and 1.4% by weight of mono-n-butyl fumarate units. Met.
Then, an acrylic rubber composition was obtained in the same manner as in Example 1, except that the acrylic rubber (A4) obtained above was used. Using the obtained acrylic rubber composition, normal physical properties, Mooney scorch and compression set were measured, and the results are shown in Table 1.

[Example 5]
100 parts of the solid content of the water-containing crumbs washed with water in the same manner as in Example 1 was acid-washed with an aqueous sulfuric acid solution (pH = 3.7) obtained by mixing 388 parts of industrial water and 0.02 parts of concentrated sulfuric acid. A solid acrylic rubber (A5) was obtained by performing the same operation as in Example 1, except that the

The resulting acrylic rubber (A5) had a Mooney viscosity (ML1+4, 100°C) of 38 and a Tg of -35°C. The composition of the acrylic rubber is 34.6% by weight of ethyl acrylate units, 49% by weight of n-butyl acrylate units, 15% by weight of 2-methoxyethyl acrylate units, and 1.4% by weight of mono-n-butyl fumarate units. %Met.
Then, an acrylic rubber composition was obtained in the same manner as in Example 1, except that the acrylic rubber (A5) obtained above was used. Using the obtained acrylic rubber composition, normal physical properties, Mooney scorch and compression set were measured, and the results are shown in Table 1.

[Comparative Example 1]
100 parts of the solid content of the wet crumb washed with water in the same manner as in Example 1 was washed with 388 parts of industrial water without adding concentrated sulfuric acid (that is, water washing was performed instead of acid washing). obtained a solid acrylic rubber (C1) by performing the same operation as in Production Example 1.

The resulting acrylic rubber (C1) had a Mooney viscosity (ML1+4, 100°C) of 39 and a Tg of -35°C. The composition of the acrylic rubber is 34.6% by weight of ethyl acrylate units, 49% by weight of n-butyl acrylate units, 15% by weight of 2-methoxyethyl acrylate units, and 1.4% by weight of mono-n-butyl fumarate units. %Met.
Then, an acrylic rubber composition was obtained in the same manner as in Example 1, except that the acrylic rubber (A5) obtained above was used. Using the obtained acrylic rubber composition, normal physical properties, Mooney scorch and compression set were measured, and the results are shown in Table 1.

From Table 1, the acid-washed acrylic rubbers (Examples 1 to 5) obtained by the production method of the present invention have almost the normal properties compared to the acrylic rubber (Comparative Example 1) that is washed only with water and not washed with an acid. Although there is no change, it can be seen that the initial characteristics (Vmin: the smaller the better) and the long-term characteristics (t5 and t35: the larger the better), which are indicators of the storage stability, are greatly improved. In particular, in the compression set test, the sulfuric acid aqueous solution with a pH of 3.7, which is relatively high in each of Examples 1 to 5, compared to the sample not washed with acid (Comparative Example 1). A significant improvement was observed in the 150°C test by acid washing alone (Example 5), and a further remarkable improvement effect was observed in the more severe 175°C test. 0.5 or less, it becomes even larger (Examples 1 to 4).

Claims (11)

A method for producing an acrylic rubber containing (meth)acrylic acid ester monomer units in a proportion of 70 to 99.9% by weight and carboxyl group-containing monomer units in a proportion of 0.1 to 20% by weight. hand,
an emulsion polymerization step of obtaining an emulsion polymerization liquid by emulsion polymerization of a monomer containing a (meth)acrylic acid ester monomer and a carboxyl group-containing monomer using a polymerization initiator;
a coagulation step of coagulating the emulsion polymerization liquid to obtain water-containing crumbs;
a washing step of acid washing the water-containing crumbs;
A drying step of drying the water-containing crumbs that have been washed with the acid;
with
A method for producing an acrylic rubber, wherein the acid washing has a pH of 4 or less. 2. The method for producing acrylic rubber according to claim 1 , wherein the polymerization initiator is a redox catalyst. 3. The method for producing acrylic rubber according to claim 2 , wherein said redox catalyst comprises a peroxide and a reducing agent. 4. The method for producing acrylic rubber according to claim 3 , wherein a metal ion-containing compound in a reduced state and a reducing agent other than the metal ion-containing compound in a reduced state are used in combination as the reducing agent. 5. The method for producing acrylic rubber according to claim 4 , wherein the metal ion-containing compound in a reduced state is ferrous sulfate. 6. The method for producing acrylic rubber according to claim 4 , wherein the reducing agent other than the metal ion-containing compound in the reduced state is ascorbic acid or ascorbate. 7. The method for producing acrylic rubber according to any one of claims 1 to 6 , wherein the coagulation of the emulsion polymerization liquid in the coagulation step is performed using a monovalent to trivalent metal compound as a coagulant. 8. The method for producing acrylic rubber according to any one of claims 1 to 7 , wherein the coagulation of the emulsion polymerization liquid in the coagulation step is performed using a sulfate as a coagulant. The method for producing acrylic rubber according to any one of claims 1 to 8 , wherein the washing step further includes washing with water. 10. The method for producing acrylic rubber according to claim 9 , wherein the washing with water is performed multiple times. 11. The method for producing acrylic rubber according to claim 9 , wherein the water washing is performed before and after the acid washing.