JP2023105088A - Copolymer, production method of acryl rubber and acryl rubber - Google Patents

Abstract

To provide an acryl rubber excellent in the mechanical physical properties, the compressive permanent set and the flexural fatigue resistance.SOLUTION: A production method of acryl rubber is provided, the method includes a copolymer that contains at least one kind of a (meth)acrylic acid ester monomer unit (however, excluding (meth)acrylic acid tert-butyl monomer unit), at least one kind of a (meth)acrylic acid tert-butyl monomer unit and 2-ethyl acrylic acid tert-butyl monomer unit as a pyrolytic monomer unit, and a cross-linkable monomer unit having a crosslinkable functional group, the pyrolytic monomer unit of 0.1 to 10 pts.mass relative to 100 pts.mass of the (meth)acrylic acid ester monomer unit (however, excluding (meth)acrylic acid tert-butyl monomer unit), the crosslinkable monomer unit of 5 pts.mass or lower, and the step of heat treating the copolymer at 70 to 250°C.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a copolymer, a method for producing an acrylic rubber, an acrylic rubber, an acrylic rubber composition, a vulcanized product of the acrylic rubber composition, and uses of the vulcanized product.

Acrylic rubber and its vulcanizate have excellent physical properties such as heat aging resistance, oil resistance, mechanical properties, and compression set properties. It is widely used as a material such as

However, in recent years, with the increasing performance of automobiles, the properties required for acrylic rubber parts have become more and more stringent, and there is a strong need to improve the physical properties of acrylic rubber, such as bending fatigue resistance for hose applications and compression set for seal applications. It has been demanded.

Acrylic rubber is usually used by imparting rubber elasticity by cross-linking, and for this purpose, a cross-linkable monomer having a cross-linkable functional group is copolymerized. As the crosslinkable functional group, an epoxy group, a carboxyl group, an active chlorine group, etc. are mainly used, and they are used properly according to the characteristics.

(Meth)acrylic acid monomers, which are cross-linking monomers with good copolymerizability with (meth)acrylic acid ester monomers, which are the main component of acrylic rubber, are highly water-soluble and are used in the production of acrylic rubber. Sufficient reaction is difficult in the commonly used semi-batch emulsion polymerization.

The non-uniform distribution of the crosslinkable functional groups is a cause of deterioration in mechanical properties, compression set, bending fatigue resistance, etc., and thus improvement is desired.

For example, in Patent Document 1 and Non-Patent Document 1, a pressure-sensitive adhesive whose adhesiveness is changed by copolymerizing a tert-butyl acrylate monomer and then performing a modification reaction by heat to generate a carboxy group is disclosed. disclosed. The tert-butyl acrylate monomer has good copolymerizability with the (meth)acrylic acid ester monomer, and it is believed that the use of this monomer can achieve uniform distribution of crosslinkable functional groups.

Japanese Patent Publication No. 2006-511640

Shoichi Matsumoto, "Research on synthesis of degradable polymers by radical polymerization and design of degradable adhesive materials", Journal of Adhesion Society of Japan, Adhesion Society of Japan, 2014, Vol.50, No.3, p. 72-81

A main object of the present invention is to provide an acrylic rubber excellent in mechanical properties, compression set and bending fatigue resistance.

As a result of intensive research to achieve the above objects, the present inventors have found that the above objects can be achieved by using a specific copolymer containing a thermally decomposable monomer unit in a method for producing acrylic rubber. This led to the completion of the present invention.

That is, the present invention provides a (meth)acrylic acid ester monomer unit (excluding a tert-butyl (meth)acrylate monomer unit) and a tert (meth)acrylate monomer unit as a thermally decomposable monomer unit. -Butyl monomer unit and at least one of tert-butyl 2-ethylacrylate monomer unit and a crosslinkable monomer unit having a crosslinkable functional group, and the (meth)acrylic acid The thermally decomposable monomer unit is 0.1 to 10 parts by mass with respect to 100 parts by mass of the ester monomer unit (excluding the tert-butyl (meth)acrylate monomer unit), and the cross-linking Provided is a copolymer having a site monomer unit of 5 parts by mass or less.
The copolymer may contain ethylene monomer units, and in the copolymer, the ethylene monomer units are 100 parts by mass of the (meth)acrylic acid ester monomer units (however, (meth) 0.1 to 10 parts by mass relative to tert-butyl acrylate monomer units).
The crosslinkable monomer unit may have at least one selected from a carboxyl group, an epoxy group and a halogen group as the crosslinkable functional group.
The present invention provides a method for producing acrylic rubber, which comprises the step of heat-treating the copolymer at 70-250°C.
In the production method, heat treatment may be performed in the presence of an acid catalyst having an acid dissociation constant (pKa) of 5 to -10 in water at 25°C.
The acid catalyst may be p-toluenesulfonic acid.
The present invention provides an acrylic rubber produced by the above production method.
The present invention provides an acrylic rubber composition containing 100 parts by mass of the acrylic rubber and 30 to 80 parts by mass of carbon black.
The present invention provides a vulcanizate obtained by vulcanizing the above acrylic rubber composition and having a compression set of 27% or less and a bending fatigue resistance of 1,300,000 times or more.
The present invention provides a rubber hose using the vulcanizate.
The present invention provides a sealing part using the vulcanizate.

INDUSTRIAL APPLICABILITY According to the present invention, an acrylic rubber having excellent mechanical properties, compression set and bending fatigue resistance can be obtained.

Although the present invention will be described in detail below, the present invention is not limited to each embodiment shown below.

The method for producing an acrylic rubber according to the present embodiment comprises a (meth)acrylic acid ester monomer unit (excluding a tert-butyl (meth)acrylate monomer unit) and a thermally decomposable monomer unit as A copolymer containing at least one of tert-butyl (meth)acrylate monomer units and tert-butyl 2-ethylacrylate monomer units is heat-treated at 70 to 250 ° C., An acrylic rubber is produced by thermally decomposing a decomposable monomer unit to generate a cross-linking site unit having a carboxy group. The copolymer may further contain a crosslinkable monomer unit having a crosslinkable functional group.

<Copolymer>
The (meth)acrylic acid ester monomer forms the skeleton of the acrylic rubber, and is not particularly limited. is mentioned.

The (meth)acrylic acid alkyl ester monomer is not particularly limited, but examples thereof include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-(meth)acrylate, Butyl, isobutyl (meth)acrylate, n-pentyl (meth)acrylate, isoamyl (meth)acrylate, n-hexyl (meth)acrylate, 2-methylpentyl (meth)acrylate, n-(meth)acrylate -octyl, 2-ethylhexyl (meth)acrylate and cyclohexyl (meth)acrylate. Among these (meth)acrylic acid alkyl ester monomers, preferred are (meth)acrylic acid alkyl ester monomers having a linear alkyl group having 1 to 8 carbon atoms, such as methyl (meth)acrylate, (meth) Ethyl acrylate and n-butyl (meth)acrylate are more preferred, and ethyl acrylate and n-butyl acrylate are particularly preferred. These may be used singly or in combination of two or more.

The (meth)acrylic acid alkoxyalkyl ester monomer is not particularly limited, but examples thereof include methoxymethyl (meth)acrylate, ethoxymethyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, (meth)acrylate, 2-ethoxyethyl acrylate, 2-propoxyethyl (meth)acrylate, 2-butoxyethyl (meth)acrylate, 3-methoxypropyl (meth)acrylate, 4-methoxybutyl (meth)acrylate, (meth)acrylate 2-(2-ethoxyethoxy)ethyl acrylate and the like. Among these (meth)acrylic acid alkoxyalkyl ester monomers, a (meth)acrylic acid alkoxyalkyl ester monomer having a linear alkoxyalkyl group having 2 to 8 carbon atoms is preferable, and (meth)acrylic acid 2- Methoxyethyl, 2-ethoxyethyl (meth)acrylate and 2-(2-ethoxyethoxy)ethyl (meth)acrylate are more preferred, and 2-methoxyethyl acrylate and 2-(2-ethoxyethoxy)ethyl acrylate are preferred. Especially preferred. These may be used singly or in combination of two or more.

The content of the (meth) acrylic acid ester monomer unit is preferably 50 to 99.9% by mass, more preferably 60 to 99.5% by mass, particularly preferably 70% by mass, based on 100% by mass of the copolymer. ~99% by mass. By setting the content of the (meth)acrylic acid ester monomer unit within the above range, the heat resistance and oil resistance of the obtained vulcanized acrylic rubber can be made more excellent.

The thermally decomposable monomer units include at least one of tert-butyl (meth)acrylate monomer units and tert-butyl 2-ethylacrylate monomer units. The thermally decomposable monomer unit is heat-treated at 70 to 250° C. to form a carboxyl group, which is a cross-linkable functional group that enables intermolecular cross-linking of acrylic rubber. This intermolecular cross-linking makes it possible to adjust the hardness and elongation properties of the acrylic rubber vulcanizate to be obtained. In addition, this thermally decomposable monomer has excellent copolymerizability with a (meth)acrylic acid ester monomer, and the acrylic polymer obtained by uniformly arranging the crosslinkable functional groups in the acrylic rubber molecule The rubber vulcanizate can have excellent mechanical properties, compression set and bending fatigue resistance. These may be used singly or in combination of two or more.

The total content of thermally decomposable monomer units in the copolymer is based on 100 parts by mass of (meth)acrylic acid ester monomer units (excluding tert-butyl (meth)acrylate monomer units) and 0.1 to 10 parts by mass. The upper limit of the total content of thermally decomposable monomer units is preferably 5 parts by mass or less, more preferably 4 parts by mass or less, still more preferably 3 parts by mass or less, and particularly preferably 2 parts by mass. It is below. The lower limit of the total content of thermally decomposable monomer units is preferably 0.2 parts by mass or more, more preferably 0.3 parts by mass or more, and still more preferably 0.4 parts by mass or more, Particularly preferably, it is 0.5 parts by mass or more. By setting the total content of the thermally decomposable monomer units within the above range, it is possible to suppress scorching during processing in a state in which a vulcanizing agent or the like is added, and improve the mechanical properties of the obtained vulcanizate of acrylic rubber. can be made excellent.

The copolymer preferably further contains a crosslinkable monomer unit having a crosslinkable functional group. The crosslinkable monomer enables intermolecular crosslinkage of the obtained acrylic rubber by having a crosslinkable functional group.

Examples of crosslinkable functional groups include, but are not limited to, epoxy groups, carboxyl groups, halogen groups, amino groups, hydroxyl groups, phenol groups, hydrazide groups and unsaturated carbon bond groups. Among these crosslinkable functional groups, an epoxy group, a carboxyl group and a halogen group are preferable, and a carboxyl group is more preferable. These crosslinking site monomers having a crosslinkable functional group may be used singly or in combination of two or more.

A cross-linkable monomer having a carboxy group is a monomer copolymerizable with a (meth)acrylic acid ester monomer. For example, carboxylic acid monomers such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid; carboxylic acid ester monomers such as n-butyl, monomethyl fumarate, monoethyl fumarate, mono-n-butyl fumarate; and carboxylic acid anhydride monomers having a carboxylic acid anhydride group, such as maleic anhydride; . Among these carboxy group-containing crosslinking site monomers, carboxylic acid ester monomers are preferred, and butenedionate monoester monomers such as fumaric acid monoester and maleic acid monoester are more preferred, and maleic acid monoalkyl esters are preferred. Monomers are more preferred, and monobutyl maleate is particularly preferred.

A crosslinking site monomer having a halogen group is a monomer copolymerizable with a (meth)acrylic acid ester monomer. For example, unsaturated alcohol esters of halogen group-containing saturated carboxylic acids such as vinyl chloroacetate, allyl chloroacetate, vinyl fluoroacetate and allyl fluoroacetate; halogens such as chloromethyl vinyl ether, 2-chloroethyl vinyl ether and 2-fluoroethyl vinyl ether Group-containing unsaturated ethers; halogen group-containing aromatic vinyls such as p-chlorostyrene, p-fluorostyrene, vinylbenzyl chloride; trifluoromethyl (meth)acrylate, 2,2,2-(meth)acrylic acid halogen group-containing (meth)acrylic acid esters such as trifluoroethyl; and the like.

The crosslinking site monomer having an epoxy group is a monomer copolymerizable with the (meth)acrylic acid ester monomer. Examples thereof include unsaturated glycidyl esters such as glycidyl (meth)acrylate; unsaturated glycidyl ethers such as vinyl glycidyl ether and allyl glycidyl ether; and the like. Among these epoxy group-containing crosslinking monomers, unsaturated glycidyl esters are preferred, and glycidyl methacrylate is more preferred.

The total content of the crosslinking site monomer units in the copolymer is based on 100 parts by mass of (meth)acrylic acid ester monomer units (excluding tert-butyl (meth)acrylate monomer units) , 0 mass % or more and 5 mass parts or less. The upper limit of the total content of crosslinking site monomer units is preferably 4.7 parts by mass or less, more preferably 4.5 parts by mass or less, still more preferably 4 parts by mass or less, and particularly preferably It is 3 parts by mass or less. The lower limit of the total content of crosslinking site monomer units is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, still more preferably 0.3 parts by mass or more, and particularly Preferably, it is 0.5 parts by mass or more. By setting the cross-linkable monomer unit within the above range, scorching during processing in a state where a vulcanizing agent or the like is added can be suppressed, and the obtained acrylic rubber vulcanizate has excellent mechanical properties. be able to.

In order to improve the mechanical properties of the acrylic rubber vulcanizate to be obtained, the above copolymer preferably contains ethylene monomer units. The content of ethylene monomer units in the copolymer is preferably per 100 parts by mass of (meth)acrylic acid ester monomer units (excluding tert-butyl (meth)acrylate monomer units). is 10 parts by mass or less. The upper limit of the ethylene monomer content is more preferably 5 parts by mass or less, still more preferably 4 parts by mass or less, and particularly preferably 3 parts by mass or less. The lower limit of the ethylene monomer content is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and still more preferably 1 part by mass or more. By setting the content of the ethylene monomer unit in the copolymer within this numerical range, an acrylic rubber composition with improved vulcanizate elongation and cold resistance can be obtained.

The above copolymer may contain other monomers copolymerizable with the (meth)acrylic acid ester monomer and the crosslinking site monomer within a range that does not impair the object of the present invention. Examples of other copolymerizable monomers include, but are not limited to, alkyl vinyl ketones such as vinyl acetate and methyl vinyl ketone; vinyl and allyl ethers such as vinyl ethyl ether and allyl methyl ether; styrene, α-methyl Vinyl aromatic compounds such as styrene, vinyl toluene and vinyl naphthalene; vinyl nitriles such as acrylonitrile and methacrylonitrile, acrylamide, propylene, butadiene, isoprene, pentadiene, vinyl propionate, maleic acid diesters such as dimethyl maleate, dimethyl fumarate Dialkyl fumarate such as dialkyl itaconate such as dimethyl itaconate Dialkyl citraconic acid such as dimethyl citraconate Dialkyl mesaconate such as dimethyl mesaconate 2-pentenedioic acid such as dimethyl 2-pentenedioate Ethylenically unsaturated compounds such as dialkyl esters and acetylenedicarboxylic acid dialkyl esters such as dimethyl acetylenedicarboxylate; These may be used singly or in combination of two or more. In the above copolymer, the content of other monomer units copolymerizable with the (meth)acrylic acid ester monomer and the crosslinking site monomer is the (meth)acrylic acid ester monomer unit (however, It is preferably 40 parts by mass or less, more preferably 20 parts by mass or less, still more preferably 10 parts by mass or less per 100 parts by mass (excluding tert-butyl (meth)acrylate monomer units).

The above copolymer comprises a (meth)acrylic acid ester monomer, a thermally decomposable monomer, and a crosslinking site monomer having a crosslinkable functional group used as necessary, and optionally used It is obtained by copolymerizing other monomers copolymerizable with these. As for the form of the polymerization reaction, any of emulsion polymerization, suspension polymerization, bulk polymerization, and solution polymerization can be used. From the point of view of ease of control of the polymerization reaction, polymerization by emulsion polymerization, which is generally used as a conventionally known method for producing acrylic rubber, is preferable.

In the case of polymerization by emulsion polymerization, a conventional method may be used. As the polymerization initiator, the polymerization terminator, the emulsifier, and the like, conventionally known ones generally used can be used.

Examples of polymerization initiators include azo compounds such as azobisisobutyronitrile; organic peroxides such as diisopropylbenzene hydroperoxide, cumene hydroperoxide and benzoyl peroxide; inorganic peroxides such as sodium persulfate and ammonium persulfate. ; and the like. These polymerization initiators can be used singly or in combination of two or more. The amount of polymerization initiator to be used is preferably 0.01 to 1.0 parts by mass with respect to 100 parts by mass of all monomers used for polymerization.

Moreover, a peroxide initiator can be used as a redox polymerization initiator in combination with a reducing agent. Examples of the reducing agent include, but are not limited to, compounds containing metal ions in a reduced state such as ferrous sulfate and cuprous naphthenate; sulfonic acid compounds such as sodium methanesulfonate; amine compounds such as dimethylaniline. ; and the like. These reducing agents can be used singly or in combination of two or more. The amount of the reducing agent used is preferably 0.03 to 10 parts by mass with respect to 1 part by mass of the peroxide initiator.

Examples of the polymerization terminator include hydroxylamine, hydroxylamine sulfate, diethylhydroxyamine, hydroxylaminesulfonic acid and alkali metal salts thereof; sodium dimethyldithiocarbamate; and the like. The amount of the polymerization terminator used is not particularly limited, but is preferably 0.1 to 2 parts by mass with respect to 100 parts by mass of all the monomers used for polymerization.

Examples of emulsifiers include nonionic emulsifiers such as fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenol ethers, polyoxyethylene alkyl esters, polyoxyethylene sorbitan alkyl esters; myristic acid; Salts of fatty acids such as palmitic acid, oleic acid and linolenic acid; Alkylbenzenesulfonates such as sodium dodecylbenzenesulfonate; Anionic emulsifiers such as higher alcohol sulfates and alkylsulfosuccinates; Alkyltrimethylammonium chloride and dialkylammonium chloride , cationic emulsifiers such as benzylammonium chloride; α,β-unsaturated carboxylic acid sulfoesters, α,β-unsaturated carboxylic acid sulfate esters, sulfoalkylaryl ethers and other copolymerizable emulsifiers; can. Among these, partially saponified polyvinyl alcohol is preferred. These emulsifiers can be used singly or in combination of two or more. The amount of the emulsifier to be used is preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of all monomers used for polymerization.

The amount of water used is preferably 80 to 500 parts by mass, more preferably 100 to 300 parts by mass, per 100 parts by mass of all monomers 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.

Examples of molecular weight modifiers include mercaptans such as n-butyl mercaptan and t-dodecyl mercaptan; sulfides such as tetraethylthiuram sulfide and dipentamethylenethiuram hexasulfide; α-methylstyrene dimer; carbon tetrachloride; is mentioned.

Emulsion polymerization may be of a batch system, a semi-batch system, or a continuous system. The polymerization is preferably carried out in a temperature range of 0-80°C, more preferably 20-70°C.

<Method for producing acrylic rubber>
A method for producing an acrylic rubber according to the present embodiment includes a step of heat-treating the copolymer. By carrying out the heat treatment step, the thermally decomposable monomer unit is thermally decomposed to form a cross-linking site unit having a carboxyl group.

The copolymer to be heat-treated may be in the form of rubber emulsion, rubber solution, or rubbery. The heat treatment temperature is 70 to 250°C, preferably 70 to 230°C, more preferably 75 to 200°C. The heat treatment time is preferably 5 minutes or more, more preferably 5 minutes to 4 hours, and even more preferably 10 minutes to 2 hours. By performing the heat treatment step, the obtained vulcanized acrylic rubber can have excellent mechanical properties.

Moreover, in the heat treatment step, the heat treatment time can be shortened by using an acid catalyst. The acid catalyst preferably has an acid dissociation constant (pKa) in water at 25°C of 5 to -10, more preferably a pKa of 0 to -9, and still more preferably a pKa of - 1 to -5 acid catalyst. Here, pKa is a value defined by the formula: pKa=-log10Ka (Ka is an acid dissociation constant). For an acid compound containing an acid catalyst, the pKa can be calculated from its molecular structure.

The acid catalyst having a pKa within the range of 5 to −10 is not particularly limited, but examples thereof include carboxylic acids such as acetic acid, benzoic acid and trifluoroacetic acid; trifluoromethanesulfonic acid, sulfuric acid, monoalkylbenzenesulfonic acid, dialkylbenzene sulfonic acids such as sulfonic acid, trialkylbenzenesulfonic acid and alkylnaphthalenesulfonic acid; inorganic acids such as phosphoric acid, hydrochloric acid, aluminum silicate and zeolite; phenol; These acid catalysts may be used singly or in combination of two or more. Among these, sulfonic acids and carboxylic acids are preferred, monoalkylbenzenesulfonic acid is more preferred, and p-toluenesulfonic acid is particularly preferred. By using these acid catalysts, the decomposition reaction of the thermally decomposable monomer units in the heat treatment step can be efficiently advanced, and the heat treatment time can be shortened.

The upper limit of the amount of the acid catalyst having a pKa of 5 to −10 is preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 5 parts by mass or less, relative to 100 parts by mass of the copolymer. is. The lower limit of the amount of the acid catalyst to be added is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, and still more preferably 0.5 parts by mass with respect to 100 parts by mass of the copolymer. That's it. By setting the addition amount of the acid catalyst within this range, the heat treatment time can be effectively shortened.

<Acrylic rubber>
The acrylic rubber of this embodiment is produced by the production method described above. That is, the acrylic rubber of the present embodiment is obtained by heat-treating the above copolymer at 70 to 250°C. The acrylic rubber contains a cross-linked site unit having a carboxy group, which is generated by thermally decomposing the thermally decomposable monomer unit.

The upper limit of the carboxy group content in the acrylic rubber is preferably 10% by mass or less, more preferably 5% by mass or less, relative to 100% by mass of the acrylic rubber. The lower limit of the carboxy group content is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, relative to 100% by mass of the acrylic rubber.

<Acrylic rubber composition>
The acrylic rubber composition of the present embodiment contains the above acrylic rubber and carbon black. By using the above acrylic rubber, it is possible to improve the mechanical properties and heat resistance of the obtained acrylic rubber vulcanizate. Examples of carbon black include, but are not limited to, acetylene black, ketjen black, thermal black, channel black, furnace black, lamp black and graphitized carbon black. Among these carbon blacks, furnace black and acetylene black are preferred, and furnace black is more preferred, in order to further improve mechanical properties and heat resistance.

The content of the carbon black in the acrylic rubber composition is preferably 30 to 80 parts by mass, more preferably 40 to 75 parts by mass, and still more preferably 45 to 70 parts by mass with respect to 100 parts by mass of the acrylic rubber. . By setting the content of carbon black within the above range, it is possible to obtain an acrylic rubber composition having a good balance between tensile strength and elongation at break and excellent mechanical properties.

The acrylic rubber composition may further contain vulcanizing agents and vulcanization accelerators.

The vulcanizing agent may be appropriately selected according to the type of cross-linking monomer contained in the acrylic rubber and the molding application of the acrylic rubber composition, and is particularly limited as long as it can cross-link the acrylic rubber described above. not. Examples of such vulcanizing agents include polyvalent amine compounds such as diamine compounds and carbonates thereof, sulfur, sulfur donors, triazinethiol compounds, polyepoxy compounds, organic carboxylate ammonium salts, dithiocarbamate metal salts, Conventionally known vulcanizing agents such as polycarboxylic acids, quaternary onium salts, imidazole compounds, isocyanuric acid compounds and organic peroxides can be used. These vulcanizing agents may be used alone or in combination of two or more.

The acrylic rubber, which is the raw material of the acrylic rubber composition according to the present embodiment, contains carboxy groups generated by heat-treating the above-mentioned thermally decomposable monomer units. For this reason, polyvalent amine compounds and their carbonates are preferred as the vulcanizing agent.

Examples of the polyamine compound and the carbonate of the polyamine compound include, but are not particularly limited to, an aliphatic polyamine compound and its carbonate, and an aromatic polyamine compound. Among these, aliphatic polyvalent amine compounds and their carbonates are particularly preferred.

Examples of the aliphatic polyvalent amine compound and its carbonate include, but are not limited to, hexamethylenediamine, hexamethylenediamine carbamate, and N,N'-dicinnamylidene-1,6-hexanediamine. Among these, hexamethylenediamine carbamate is preferred.

Examples of aromatic polyvalent amine compounds include, but are not limited to, 4,4'-methylenedianiline, p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, and 3,4'-diaminodiphenyl ether. , 4,4′-(m-phenylenediisopropylidene)dianiline, 4,4′-(p-phenylenediisopropylidene)dianiline, 2,2′-bis[4-(4-aminophenoxy)phenyl]propane, 4,4'-diaminobenzanilide, 4,4'-bis(4-aminophenoxy)biphenyl, m-xylylenediamine, p-xylylenediamine, and 1,3,5-benzenetriamine. Among these, 2,2'-bis[4-(4-aminophenoxy)phenyl]propane is preferred.

Further, when the acrylic rubber contains an epoxy group, the vulcanizing agent may be hexamethylenediamine, aliphatic polyvalent amine compounds such as hexamethylenediamine carbamate and their carbonates; Aromatic polyvalent amine compounds such as aniline; carboxylic acid ammonium salts such as ammonium benzoate and ammonium adipate; dithiocarbamate metal salts such as zinc dimethyldithiocarbamate; polyvalent carboxylic acids such as tetradecanedioic acid; quaternary onium salts of; imidazole compounds such as 2-methylimidazole; isocyanuric acid compounds such as ammonium isocyanurate; Among these, carboxylate ammonium salts and dithiocarbamate metal salts are preferred, and ammonium benzoate is more preferred.

When the acrylic rubber contains a halogen group, the vulcanizing agent is preferably sulfur, a sulfur donor, or a triazinethiol compound.

Specific examples of sulfur donors include dipentamethylenethiuram hexasulfide and triethylthiuram disulfide.

Specific examples of triazinethiol compounds include 1,3,5-triazine-2,4,6-trithiol, 6-anilino-1,3,5-triazine-2,4-dithiol, 6-dibutylamino-1, 3,5-triazine-2,4-dithiol, 6-diallylamino-1,3,5-triazine-2,4-dithiol and 6-octylamino-1,3,5-triazine-2,4-dithiol, etc. is mentioned. Among these, 1,3,5-triazine-2,4,6-trithiol is preferred.

The content of the vulcanizing agent is not particularly limited, but is preferably 0.1 to 10 parts by mass, more preferably 0.3 to 5 parts by mass, based on 100 parts by mass of the acrylic rubber. A necessary and sufficient vulcanization treatment can be performed by setting the content within this range.

When the acrylic rubber composition of the present embodiment contains a vulcanizing agent, the acrylic rubber composition preferably further contains a vulcanization accelerator. A vulcanization accelerator is added to adjust the vulcanization rate. Examples of vulcanization accelerators include, but are not limited to, aliphatic monovalent secondary amine compounds, aliphatic monovalent tertiary amine compounds, guanidine compounds, imidazole compounds, quaternary onium salts, tertiary Examples include phosphine compounds, alkali metal salts of weak acids, and diazabicycloalkene compounds. Among these, diazabicycloalkene compounds are preferred.

The amount of the vulcanization accelerator to be added may be within a range that does not impair the properties of the vulcanizate obtained from the acrylic rubber composition of the present embodiment.

The aliphatic monovalent secondary amine compound is a compound in which two hydrogen atoms of ammonia are substituted with an aliphatic hydrocarbon group. Although there are no particular restrictions on the aliphatic hydrocarbon group that replaces the hydrogen atom, it preferably has 1 to 30 carbon atoms, more preferably 8 to 20 carbon atoms. Specific examples of aliphatic monovalent secondary amine compounds include dimethylamine, diethylamine, di-n-propylamine, diallylamine, diisopropylamine, di-n-butylamine, di-t-butylamine, di-sec-butylamine, and dipentyl. Amine, dihexylamine, diheptylamine, dioctylamine, dinonylamine, didecylamine, diundecylamine, didodecylamine, ditridecylamine, ditetradecylamine, dipentadecylamine, dicetylamine, di-2-ethylhexylamine, dioctadecylamine , di-cis-9-octadecenylamine, and dinonadecylamine.

The aliphatic monovalent tertiary amine compound is a compound obtained by substituting all three hydrogen atoms of ammonia with an aliphatic hydrocarbon group. Although there are no particular restrictions on the aliphatic hydrocarbon group that replaces the hydrogen atom, it preferably has 1 to 30 carbon atoms, more preferably 1 to 22 carbon atoms. Specific examples of aliphatic monovalent tertiary amine compounds include trimethylamine, triethylamine, tri-n-propylamine, triallylamine, triisopropylamine, tri-n-butylamine, tri-t-butylamine, tri-sec-butylamine, tripentylamine, trihexylamine, triheptylamine, trioctylamine, trinonylamine, tridecylamine, triundecylamine, tridodecylamine, tridecylamine, tritetradecylamine, tripentadecylamine, tricetylamine , tri-2-ethylhexylamine, trioctadecylamine, tri-cis-9-octadecenylamine, trinonadecylamine, N,N-dimethyldecylamine, N,N-dimethyldodecylamine, N,N-dimethyltetra Decylamine, N,N-dimethylcetylamine, N,N-dimethyloctadecylamine, N,N-dimethylbehenylamine, N-methyldidecylamine, N-methyldidodecylamine, N-methylditetradecylamine, N -methyldicetylamine, N-methyldioctadecylamine, N-methyldibehenylamine, and dimethylcyclohexylamine.

Specific examples of guanidine compounds include 1,3-di-o-tolylguanidine and 1,3-diphenylguanidine.

Specific examples of imidazole compounds include 2-methylimidazole and 2-phenylimidazole.

Specific examples of quaternary onium salts include tetra-n-butylammonium bromide and octadecyltri-n-butylammonium bromide.

Specific examples of tertiary phosphine compounds include triphenylphosphine and tri-p-tolylphosphine.

Specific examples of alkali metal salts of weak acids include weak inorganic acid salts such as sodium or potassium phosphate or carbonate; organic weak acid salts such as sodium or potassium stearate or laurate;

Specific examples of diazabicycloalkene compounds include 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5-diazabicyclo[4.3.0]no-5-ene ( DBN) and the like.

When sulfur is used as the vulcanizing agent, it is preferable to use an alkali metal carboxylate or a thiazole compound as the vulcanization accelerator. Examples of carboxylic acid alkali metal salts include sodium stearate, potassium stearate, sodium laurate, and potassium laurate. Thiazole compounds include, for example, mercaptobenzothiazole and dibenzothiazyl disulfide.

When a triazinethiol compound is used as a vulcanizing agent, it is preferable to use a thiuram-based accelerator or a dithiocarbamate-based accelerator as a vulcanization accelerator. Thiuram accelerators include, for example, tetraethylthiuram disulfide and tetrabutylthiuram disulfide. The dithiocarbamate-based accelerator is preferably at least one selected from zinc salts, copper salts, iron salts and tellurium salts of dithiocarbamates, more preferably zinc salts, and further zinc diethyldithiocarbamate and zinc dibutyldithiocarbamate. preferable.

The acrylic rubber composition of the present embodiment may contain fillers, reinforcing agents, plasticizers, lubricants, anti-aging agents, stabilizers, silane coupling agents and the like depending on the purpose of practical use.

Fillers and reinforcing agents other than carbon black may be used as long as they are commonly used in rubber applications, such as silica, talc, calcium carbonate, and the like. The total content of the filler and reinforcing agent is preferably in the range of 20 to 100 parts by mass with respect to 100 parts by mass of the acrylic rubber composition.

The plasticizer may be one that is commonly used for rubber applications, and includes, for example, ester plasticizers, polyoxyethylene ether plasticizers and trimellitate plasticizers. The content of the plasticizer is preferably 50 parts by mass or less with respect to 100 parts by mass of the acrylic rubber composition.

The anti-aging agent may be one commonly used for rubber applications, such as 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, N,N'-di-2-naphthyl-p -amine antioxidants such as phenylenediamine, N-phenyl-N'-isopropyl-p-phenylenediamine; 2,5-di-tert-butylhydroquinone, pentaerythritol tetrakis[3-(3,5-di-tert -butyl-4-hydroxyphenyl)propionate]; sulfur-based antioxidants such as 2-mercaptobenzimidazole; phosphorus-based antioxidants such as tris(nonylphenyl)phosphite; The content of the antioxidant is preferably 0.1 to 5 parts by mass with respect to 100 parts by mass of the acrylic rubber composition.

The acrylic rubber composition of the present embodiment may further contain a polymer other than the acrylic rubber described above as long as the effects of the present invention are not impaired. Polymers other than the above acrylic rubbers include acrylic rubbers other than the above acrylic rubbers, natural rubbers, polybutadiene rubbers, polyisoprene rubbers, styrene-butadiene rubbers, acrylonitrile-butadiene rubbers, silicone rubbers, rubbers such as fluororubbers; Resins such as resins, polystyrene-based resins, polyphenylene ether-based resins, polyester-based resins, polycarbonate-based resins, polyamide resins, vinyl chloride resins, and fluorine resins; The amount of the polymer other than the acrylic rubber is preferably 50 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 1 part by mass or less per 100 parts by mass of the acrylic rubber.

The method for producing the acrylic rubber composition of the present embodiment is not particularly limited. For example, the above acrylic rubber and each component excluding vulcanizing agents and heat-unstable vulcanizing auxiliaries are mixed at a temperature of preferably 10 to 200°C, more preferably 20 to 170°C, in a Banbury mixer. After kneading with a mixer such as a lavender mixer, an intermixer, or a kneader, transfer to a roll or the like, add a vulcanizing agent or a heat-unstable vulcanizing aid, and preferably at a temperature of 10 to 80 ° C. It can be produced by subsequent kneading.

<Vulcanized product of acrylic rubber composition>
A vulcanizate of the acrylic rubber composition according to the present embodiment is obtained by vulcanizing the acrylic rubber composition described above.

The vulcanizate of the acrylic rubber composition according to the present embodiment is formed by using the acrylic rubber composition described above, for example, using a molding machine corresponding to a desired shape, such as an extruder, an injection molding machine, a compressor, a roll, etc. and heating to cause a vulcanization reaction (primary vulcanization) to fix the shape as a vulcanizate. In this case, vulcanization may be performed after pre-molding, or vulcanization may be performed simultaneously with molding. The molding temperature is preferably 10-200°C, more preferably 25-120°C. The vulcanization temperature is preferably 100-200°C, more preferably 130-190°C. The vulcanization time is preferably 1 minute to 24 hours, more preferably 2 minutes to 12 hours, particularly preferably 3 minutes to 6 hours.

Further, depending on the shape, size, etc. of the vulcanizate, even if the surface is vulcanized, the interior may not be sufficiently vulcanized, so secondary vulcanization may be performed by further heating.

As the vulcanization method, general methods used for vulcanization of rubber such as steam vulcanization, press vulcanization, and oven vulcanization can be appropriately selected.

The vulcanizate of the acrylic rubber composition according to this embodiment preferably has a compression set of 27% or less when heated at 150° C. for 22 hours according to JISK6262:2013. A vulcanizate of such an acrylic rubber composition is suitable for sealing parts.

The vulcanizate of the acrylic rubber composition according to the present embodiment preferably has a bending fatigue count of 1,300,000 or more until cracking occurs, as measured in accordance with JISK6260:2010. A vulcanizate of such an acrylic rubber composition is suitable for rubber hoses and sealing parts.

The vulcanizate of the acrylic rubber composition according to the present embodiment is suitably used as sealing parts such as rubber hoses and gaskets and packings. The rubber hose and sealing parts may consist of only the vulcanized acrylic rubber composition, or may be combined with other parts.

Examples of rubber hoses include transmission oil cooler hoses for automobiles, construction machinery and hydraulic equipment, engine oil cooler hoses, air duct hoses, turbo intercooler hoses, hot air hoses, radiator hoses, power steering hoses, fuel system hoses and drain systems. There are hoses for

As for the structure of the rubber hose, as is generally done, a reinforcing thread or wire is provided in the middle of the hose or in the outermost layer of the rubber hose, or it has a laminated structure with rubber such as fluororubber and silicone rubber. Anything is fine.

Seal parts include, for example, engine head cover gaskets, oil pan gaskets, oil seals, lip seal packings, O-rings, transmission seal gaskets, crankshafts, camshaft seal gaskets, valve stems, power steering seal belt cover seals, constant velocity There are boot materials for joints and rack and pinion boot materials.

EXAMPLES The present invention will be described in more detail with examples below, but the present invention is not limited to these examples.

A rubber-like copolymer was produced under the following conditions.
<Copolymer A>
17 kg of an aqueous solution of 4% by mass of partially saponified polyvinyl alcohol, 22 g of sodium acetate, 56 g of ascorbic acid, 1.12 g of ethylenediaminetetraacetic acid, and 0.56 g of iron (II) sulfate heptahydrate were charged into a pressure-resistant reaction vessel having an inner volume of 40 liters. After replacing the air in the upper part of the tank with nitrogen while mixing well with a stirrer, 0.95 kg of ethylene was injected into the upper part of the tank to adjust the pressure to 3.5 MPa. After continuing stirring and maintaining the inside of the tank at 55° C., a monomer mixture of 7.84 kg of ethyl acrylate, 3.36 kg of n-butyl acrylate, 168 g of tert-butyl acrylate, and 2.7 g of tert-dodecylmercaptan was added. It was pressed in for 6 hours. At the same time, an aqueous t-butyl hydroperoxide solution (0.25% by mass, 2 liters) was injected from a separate injection port over 6 hours to carry out polymerization until the final polymerization rate was 95%. An aqueous sodium borate solution (3.5% by mass, 7 liters) was added as a coagulant to the resulting polymerization solution to solidify the polymer, which was then dehydrated and dried to obtain a copolymer A.

<Copolymer B>
A copolymer B was obtained in the same manner as for the copolymer A, but without ethylene injection.

<Copolymer C>
Copolymer C was obtained in the same manner as for Copolymer A, except that tert-butyl acrylate was changed to 784 g.

<Copolymer D>
A copolymer D was obtained in the same manner as for copolymer A, except that 112 g of tert-butyl acrylate was used and 180 g of monobutyl maleate was added.

<Copolymer E>
Copolymer E was obtained in the same manner as for Copolymer A except that 112 g of tert-butyl acrylate was used and 112 g of glycidyl methacrylate was added.

<Copolymer F>
Copolymer F was obtained in the same manner as for Copolymer A, except that 205 g of tert-butyl 2-ethylacrylate was used instead of tert-butyl acrylate.

<Copolymer G>
Copolymer G was obtained in the same manner as for copolymer A, except that 112 g of tert-butyl acrylate was used and 95 g of tert-butyl 2-ethylacrylate was added.

<Copolymer H>
Copolymer H was obtained in the same manner as for Copolymer A except that the amount of ethyl acrylate was changed to 10.4 kg and the amount of n-butyl acrylate to 0.8 kg.

<Copolymer I>
Copolymer I was obtained in the same manner as for Copolymer A except that the amount of ethyl acrylate was changed to 2.4 kg and the amount of n-butyl acrylate to 8.9 kg.

<Copolymer J>
Copolymer J was obtained in the same manner as for Copolymer A, except that tert-butyl acrylate was replaced with 275 g of monobutyl maleate.

<Copolymer K>
Copolymer K was obtained in the same manner as for Copolymer A except that 224 g of glycidyl methacrylate was used instead of tert-butyl acrylate.

<Copolymer L>
Copolymer L was obtained in the same manner as for Copolymer A, except that tert-butyl acrylate was changed to 1.5 kg.

<Copolymer M>
Copolymer M was obtained in the same manner as for Copolymer A except that 112 g of tert-butyl acrylate was used and 1070 g of monobutyl maleate was added.

<Acrylic rubber N>
Copolymer N was obtained in the same manner as for Copolymer A except that 112 g of tert-butyl acrylate was used and 870 g of glycidyl methacrylate was added.

<Identification of copolymer composition>
The composition of the resulting copolymer was identified using 13C NMR. The compositions of the identified copolymers are shown in Tables 2-4 below.

<Production of acrylic rubber>
The copolymer obtained by the above method was heat-treated using a gear oven (TG-100 manufactured by Suga Test Instruments Co., Ltd.) at the temperatures and times shown in Tables 2 to 4 below to produce acrylic rubbers. After that, the obtained acrylic rubber was allowed to cool in the atmosphere at 23° C. for 5 hours. When adding the acid catalysts listed in Tables 2 to 4 below in the heat treatment step, 3% by mass of the acid catalyst is added to the copolymer emulsion before the copolymer emulsion obtained by the above method solidifies. After addition, solidification, dehydration and drying were carried out to obtain a copolymer. The copolymer was then heat treated as described above.

Regarding the acid catalysts listed in Tables 2 to 4 below, "PTSA" is p-toluenesulfonic acid monohydrate manufactured by Wako Pure Chemical Industries, Ltd., and "TfOH" is trifluoromethanesulfonic acid manufactured by Wako Pure Chemical Industries, Ltd. .

<Measurement of carboxy group content>
The copolymer before the heat treatment and the acrylic rubber after the heat treatment were each dissolved in toluene, and the neutralization titration amount of carboxyl groups was measured using potassium hydroxide. Further, the reaction rate of the heat treatment was calculated by dividing the difference in the amount of carboxyl groups before and after the heat treatment by the amount of tert-butyl (meth)acrylate monomer units and tert-butyl 2-ethylacrylate monomer units. .

<Production of acrylic rubber composition>
The acrylic rubber obtained by the above method was kneaded with a 0.5 L pressure kneader for 15 minutes and then kneaded with a 6-inch open roll for 20 minutes to produce an acrylic rubber composition having the composition shown in Table 1 below. In addition, the unit of the numerical value described in Table 1 is a "mass part."

The reagents used for preparing the acrylic rubber composition are as follows.
・FEF carbon black: SEAST SO manufactured by Tokai Carbon Co., Ltd.
・Stearic acid: Lunax S-90 manufactured by Kao Corporation
· 4,4'-bis (α, α-dimethylbenzyl) diphenylamine: Naugard 445 manufactured by Addivant (antiaging agent)
・ Liquid paraffin: Hicol K-230 manufactured by Kaneda Corporation
・Stearylamine: Firmin 80 manufactured by Kao Corporation
· 6-Aminohexylcarbamic acid: Diak # 1 manufactured by DuPont (vulcanizing agent)
- 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU): XLA-60 manufactured by Lanxess (vulcanization accelerator)
・Trimethylthiourea (TMU): Noxceler TMU manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.
· 1-benzyl-2-methylimidazole: SB-25 manufactured by Shikoku Chemical Industry Co., Ltd.
・ Stearyltrimethylammonium bromide (STB): Catinal STB-100 manufactured by Toho Chemical Industry Co., Ltd.

<Production of Vulcanized Product of Acrylic Rubber Composition>
The obtained acrylic rubber composition was divided into sheets of 2.4 mm thickness, and after primary vulcanization in a press vulcanizer at 170°C for 40 minutes, secondary vulcanization in a gear oven at 170°C for 4 hours. Vulcanized to produce a vulcanizate.

<Physical property test>
The scorch time of the obtained acrylic rubber composition, and the tensile strength, elongation at break, hardness, compression set and bending fatigue resistance of the vulcanizate were evaluated under the following conditions, and the measurement results are shown in Tables 2 to 4 below. It was shown to.
(1) Scorch time Measured at 125°C in accordance with JISK6300:2013.
(2) Tensile strength and elongation at break Measured according to JISK6251:2010.
(3) Hardness Measured using a type A durometer in accordance with JISK6253:2012.
(4) Compression set Measured according to JISK6262:2013. It was determined that if the compression set was within 27% when heated at 150° C. for 22 hours, it would be suitable for sealing parts.
(5) Flex fatigue resistance (flex crack initiation test)
Measured according to JISK6260:2010. It was judged that the greater the number of times of bending fatigue until cracking occurred, the more excellent the resistance to bending fatigue was, and the more than 1,300,000 times was judged to be suitable for use in rubber hoses and sealing parts.

As shown in Tables 2 to 4, the vulcanizate of the acrylic rubber composition according to the present invention has excellent mechanical properties with a good balance between tensile strength and elongation at break. It was confirmed that the It was also suggested that vulcanized products of acrylic rubber compositions are suitable for use in rubber hoses and seals.

Comparative Examples 1 and 2, in which the heat treatment temperature was 280° C., decomposed the copolymer. Comparative Examples 3 and 4, in which the heat treatment temperature was 50° C., were not vulcanized. Comparative Example 5, which was not heat treated, was not vulcanized. Therefore, in Comparative Examples 1 to 5, desired acrylic rubber compositions and vulcanizates thereof could not be obtained. These results confirmed that the step of heat-treating the copolymer at 70 to 250° C. is essential.

Comparative Examples 6 and 7 using copolymers containing no thermally decomposable monomer units were inferior in compression set and bending fatigue resistance of the vulcanizates. These results confirmed that the thermally decomposable monomer unit is essential.

A copolymer containing more than 10 parts by mass of thermally decomposable monomer units per 100 parts by mass of (meth)acrylic acid ester monomer units (excluding tert-butyl (meth)acrylate monomer units) was inferior in elongation at break, compression set and bending fatigue resistance of the vulcanizate. From this result, the content of the thermally decomposable monomer unit in the copolymer is 100 mass of the (meth)acrylic acid ester monomer unit (excluding the tert-butyl (meth)acrylate monomer unit). It was suggested that 10 parts by mass or less is preferable with respect to parts.

A copolymer containing more than 5 parts by mass of crosslinking site monomer units per 100 parts by mass of (meth)acrylic acid ester monomer units (excluding tert-butyl (meth)acrylate monomer units) Comparative Examples 9 and 10 used were inferior in elongation at break, compression set and bending fatigue resistance of the vulcanizates. From these results, the content of the crosslinking site monomer unit in the copolymer is 100 mass of the (meth)acrylic acid ester monomer unit (excluding the tert-butyl (meth)acrylate monomer unit). It was suggested that 5 parts by mass or less is preferable with respect to parts.

Claims (11)

(meth)acrylic acid ester monomer units (excluding tert-butyl (meth)acrylate monomer units) and tert-butyl (meth)acrylate monomer units as thermally decomposable monomer units and at least one of tert-butyl 2-ethylacrylate monomer units, and a crosslinking site monomer unit having a crosslinkable functional group,
The thermally decomposable monomer unit is 0.1 to 10 mass parts per 100 parts by mass of the (meth)acrylic acid ester monomer unit (excluding the tert-butyl (meth)acrylate monomer unit). and the crosslinkable monomer unit is 5 parts by mass or less. The copolymer contains ethylene monomer units,
In the copolymer, the content of the ethylene monomer unit is 0.00 per 100 parts by mass of the (meth)acrylic acid ester monomer unit (excluding the tert-butyl (meth)acrylate monomer unit). The copolymer according to claim 1, which is 1 to 10 parts by mass. 3. The copolymer according to claim 1 or 2, wherein the crosslinkable monomer unit has at least one selected from a carboxyl group, an epoxy group and a halogen group as the crosslinkable functional group. A method for producing acrylic rubber, comprising a step of heat-treating the copolymer according to any one of claims 1 to 3 at 70 to 250°C. 5. The method for producing acrylic rubber according to claim 4, wherein the heat treatment is performed in the presence of an acid catalyst having an acid dissociation constant (pKa) of 5 to -10 in water at 25°C. 6. The method for producing acrylic rubber according to claim 5, wherein the acid catalyst is p-toluenesulfonic acid. An acrylic rubber produced by the production method according to any one of claims 4 to 6. An acrylic rubber composition containing 100 parts by mass of the acrylic rubber according to claim 7 and 30 to 80 parts by mass of carbon black. A vulcanizate obtained by vulcanizing the acrylic rubber composition according to claim 8 and having a compression set of 27% or less and a bending fatigue resistance of 1,300,000 times or more. A rubber hose using the vulcanizate according to claim 9. A sealing part using the vulcanizate according to claim 9.