WO2024225185A1 - Acrylic rubber, acrylic rubber composition for crosslinking, and crosslinked object obtained therefrom - Google Patents

Abstract

The purpose of the present invention is to provide: an acrylic rubber which comes to have sufficient mechanical properties through primary crosslinking only without necessitating secondary crosslinking, from the standpoints of energy saving and production efficiency; an acrylic rubber composition for crosslinking; and a crosslinked object obtained therefrom.　These inventors have found that a crosslinked acrylic rubber obtained using an acrylic rubber at least including a constituent unit derived from an organic iodine compound having two or more iodine atoms in the molecule and a constituent unit derived from an alkyl ester of acrylic acid, even when being a product of primary crosslinking, has mechanical strength comparable to that of the product of secondary crosslinking.

Description

Acrylic rubber, composition for crosslinking acrylic rubber and crosslinked product thereof

　This article relates to acrylic rubber and rubber materials made from it, and more specifically to acrylic rubber, a composition for cross-linking acrylic rubber, and cross-linked acrylic rubber, which have small differences in physical properties between the primary cross-linked product and the secondary cross-linked product and have a fast cross-linking rate.

Acrylic rubber exhibits its properties as a rubber material by copolymerizing reactive groups such as halogen groups, epoxy groups, and carboxyl groups on the side chains as crosslinking points and reacting them with various crosslinking agents. However, in order to obtain sufficient rubber properties, the crosslinking process requires not only primary crosslinking but also secondary crosslinking at high temperatures for a long period of time, and from the standpoint of energy consumption and productivity, a milder and simpler method is required.

In light of this situation, Patent Document 1 discloses that an acrylic rubber compound containing a halogen group and a carboxyl group, trithiocyanuric acid, a metal dithiocarbamate, and/or thiuram sulfide provides good rubber properties even without secondary crosslinking.

Patent Document 2 also discloses that by crosslinking reactive halogen-containing acrylic rubber with an alkali metal or alkaline earth metal iodide or bromide, it is possible to omit the secondary crosslinking and shorten the primary crosslinking while still obtaining good rubber properties.

However, even in References 1 and 2, there is a large difference in the physical properties between the primary crosslinked product and the secondary crosslinked product, and from the perspective of the quality of the final product, it is desirable for these differences in physical properties to be small.

Patent No. 2622739 Japanese Patent Application Publication No. 8-311289

In view of the above problems, the present invention aims to provide an acrylic rubber cross-linked product in which the difference in physical properties between the primary cross-linked product and the secondary cross-linked product is small.

As a result of various investigations conducted by the inventors to achieve the above object, it was discovered that an acrylic rubber cross-linked product using an acrylic rubber containing at least a structural unit (A) derived from an organic iodine compound containing two or more iodine atoms in one molecule and a structural unit (B) derived from an alkyl acrylate ester has mechanical strength equivalent to that of a secondary cross-linked product, even though it is a primary cross-linked product, and thus the present invention was completed.

（Ｒ１は炭素数２～４の炭化水素基である。Ｒ２、Ｒ３は水素原子、炭素数１～４のアルキル基、または置換基を有していてもよい芳香族炭化水素基である。Ｒ２およびＲ３は同一であってもよいし、異なっていてもよい。ｎは２～４の整数である）

（Ｒ４は炭素数２～４の炭化水素基、または置換基を有していてもよい芳香族炭化水素基である。Ｒ５、Ｒ６は水素原子、炭素数１～４のアルキル基、置換基を有していてもよい芳香族炭化水素基、または－ＣＯＯＲ７であり、ここでＲ７は炭素数１～３のアルキル基である。Ｒ５およびＲ６は同一であってもよいし、異なっていてもよい。Ｒ７は同一であってもよいし、異なっていてもよい。ｎは２～４の整数である）
項２
　さらにアクリル酸アルコキシアルキルエステルに由来する構成単位（Ｃ）を含む項１に記載のアクリルゴム。
項３
　さらにメタクリル酸アルキルエステルに由来する構成単位（Ｄ）を含む項１又は２に記載のアクリルゴム。
項４
　前記アクリルゴムの重量平均分子量が５０万～２３０万である項１～３のいずれか１項に記載のアクリルゴム。
項５
　項１～４のいずれか１項に記載のアクリルゴムと、架橋剤を少なくとも含むアクリルゴム架橋用組成物。
項６
　項５に記載のアクリルゴム架橋用組成物を架橋してなるアクリルゴム架橋物。 That is, the present invention provides an invention having the following configuration.
Item 1
The acrylic rubber includes at least a structural unit (A) derived from an organic iodine compound containing two or more iodine atoms in one molecule and represented by the following general formula (1) or the following general formula (2), and a structural unit (B) derived from an alkyl acrylate,
The acrylic rubber has a content of the structural unit (A) of 0.015 to 0.099 mass% based on 100 mass% of the acrylic rubber.

(R1 is a hydrocarbon group having 2 to 4 carbon atoms. R2 and R3 are a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or an aromatic hydrocarbon group which may have a substituent. R2 and R3 may be the same or different. n is an integer of 2 to 4.)

(R4 is a hydrocarbon group having 2 to 4 carbon atoms, or an aromatic hydrocarbon group which may have a substituent. R5 and R6 are a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an aromatic hydrocarbon group which may have a substituent, or -COOR7, where R7 is an alkyl group having 1 to 3 carbon atoms. R5 and R6 may be the same or different. R7 may be the same or different. n is an integer of 2 to 4.)
Item 2
Item 2. The acrylic rubber according to item 1, further comprising a structural unit (C) derived from an alkoxyalkyl acrylate.
Item 3
Item 3. The acrylic rubber according to item 1 or 2, further comprising a structural unit (D) derived from an alkyl methacrylate ester.
Item 4
Item 4. The acrylic rubber according to any one of Items 1 to 3, wherein the weight average molecular weight of the acrylic rubber is 500,000 to 2,300,000.
Item 5
Item 5. A composition for crosslinking acrylic rubber comprising at least the acrylic rubber according to any one of items 1 to 4 and a crosslinking agent.
Item 6
Item 6. A cross-linked acrylic rubber product obtained by cross-linking the composition for cross-linking acrylic rubber according to item 5.

The acrylic rubber cross-linked product of the present invention, which is produced by cross-linking the acrylic rubber, has a small difference in mechanical strength between the primary cross-linked product and the secondary cross-linked product, so the secondary cross-linking process can be omitted. This allows for a shorter manufacturing process and industrial production with less energy.

<Acrylic rubber>
The acrylic rubber of the present invention contains at least a structural unit (A) derived from an organic iodine compound containing two or more iodine atoms in one molecule, and a structural unit (B) derived from an alkyl acrylate.

Structural unit (A) derived from an organic iodine compound containing two or more iodine atoms in one molecule
Examples of the structural unit derived from an organic iodine compound containing two or more iodine atoms in one molecule include structural units derived from an organic iodine compound represented by the following general formula (1) or the following general formula (2). The structural unit (A) may be used alone or in combination of two or more. Among them, the structural unit derived from an organic iodine compound represented by the following general formula (1) is preferred.

（Ｒ１は炭素数２～４の炭化水素基である。Ｒ２、Ｒ３は水素原子、炭素数１～４のアルキル基、または置換基を有していてもよい芳香族炭化水素基である。Ｒ２およびＲ３は同一であってもよいし、異なっていてもよい。ｎは２～４の整数である） In the following general formula (1), R1 is preferably a hydrocarbon group having 2 to 4 carbon atoms, more preferably a saturated hydrocarbon group having 2 to 4 carbon atoms, and even more preferably a saturated hydrocarbon group having 2 to 3 carbon atoms. R2 and R3 are preferably a hydrogen atom, a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, or a phenyl group, more preferably a hydrogen atom, a methyl group, an ethyl group, or a phenyl group, even more preferably a hydrogen atom, a methyl group, or a phenyl group, and particularly preferably a hydrogen atom or a methyl group. R2 and R3 are also preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. R2 and R3 may be the same or different. n is preferably an integer of 2 to 3.

(R1 is a hydrocarbon group having 2 to 4 carbon atoms. R2 and R3 are a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or an aromatic hydrocarbon group which may have a substituent. R2 and R3 may be the same or different. n is an integer of 2 to 4.)

The organic iodine compounds represented by the general formula (1) include, for example, ethylene glycol bisiodoacetic acid, ethylene glycol bis(2-iodopropionic acid), ethylene glycol bis(2-iodoisobutyric acid), ethylene glycol bis(2-iodo-2-phenylacetic acid), ethylene glycol bis(2-iodo-2-phenylpropionic acid), ethylene glycol bis(2-iodo-2-phenylisobutyric acid), glycerol 1,2-bisiodoacetic acid, glycerol 1,3-bisiodoacetic acid, glycerol 1,2-bis(2-iodopropionic acid), glycerol 1,3-bis(2-iodopropionic acid), glycerol 1,2-bis(2-iodoisobutyric acid), glycerol 1,3-bis(2-iodoisobutyric acid), glycerol 1,2 -bis(2-iodo-2-phenylacetic acid), glycerol 1,3-bis(2-iodo-2-phenylacetic acid), glycerol 1,2-bis(2-iodo-2-phenylpropionic acid), glycerol 1,3-bis(2-iodo-2-phenylpropionic acid), glycerol 1,2-bis(2-iodo-2-phenylisobutyric acid), glycerol 1,3-bis(2-iodo-2-phenylisobutyric acid), glycerol tris-iodoacetate, glycerol tris(2-iodopropionic acid), glycerol tris(2-iodoisobutyric acid) TBTP, glycerol tris(2-iodo-2-phenylacetic acid), glycerol tris(2-iodo-2-phenylpropionic acid), glycerol tris(2-iodo-2-phenylisobutyric acid). Among these, ethylene glycol bis(2-iodoisobutyric acid), ethylene glycol bis(2-iodo-2-phenylacetic acid), glycerol tris(2-iodoisobutyric acid), and glycerol tris(2-iodo-2-phenylacetic acid) are preferred, and ethylene glycol bis(2-iodoisobutyric acid), ethylene glycol bis(2-iodo-2-phenylacetic acid), and glycerol tris(2-iodoisobutyric acid) are more preferred.

（Ｒ４は炭素数２～４の炭化水素基、または置換基を有していてもよい芳香族炭化水素基である。Ｒ５、Ｒ６は水素原子、炭素数１～４のアルキル基、置換基を有していてもよい芳香族炭化水素基、または－ＣＯＯＲ７であり、ここでＲ７は炭素数１～３のアルキル基である。Ｒ５およびＲ６は同一であってもよいし、異なっていてもよい。Ｒ７は同一であってもよいし、異なっていてもよい。ｎは２～４の整数である） In the following general formula (2), R4 is preferably a hydrocarbon group or an aromatic hydrocarbon group having 2 to 4 carbon atoms, more preferably a saturated hydrocarbon group or an aromatic hydrocarbon group having 2 to 4 carbon atoms, and even more preferably a saturated hydrocarbon group or an aromatic hydrocarbon group having 2 to 3 carbon atoms. R5 and R6 are preferably a hydrogen atom, a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, or a phenyl group, and R7 is preferably a methyl group (-COOCH3), an ethyl group (-COOCH2CH3), or a propyl group (-COOCH2CH2CH3), more preferably a hydrogen atom, a methyl group, an ethyl group, a phenyl group, and R7 is preferably an ethyl group (-COOCH2CH3), and even more preferably a hydrogen atom, a methyl group, a phenyl group, and R7 is preferably an ethyl group (-COOCH2CH3). R5 and R6 may be the same or different. n is preferably an integer of 2 to 3.

(R4 is a hydrocarbon group having 2 to 4 carbon atoms, or an aromatic hydrocarbon group which may have a substituent. R5 and R6 are a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an aromatic hydrocarbon group which may have a substituent, or -COOR7, where R7 is an alkyl group having 1 to 3 carbon atoms. R5 and R6 may be the same or different. R7 may be the same or different. n is an integer of 2 to 4.)

Examples of organic iodine compounds represented by general formula (2) include 1,4-diiodobutane, 1,1-diiodoisobutane, 1,4-diphenyl-1,4-diiodobutane, 2,5-diiododidiethyl acid, p-xylylene diiodide, o-xylylene diiodide, m-xylylene diiodide, 1,4-bis(1'-iodoethyl)benzene, 2,2,4-triiodobutane, and 1,3,5-tris(1'-iodoethyl)benzene. Among these, 2,5-diiododidiethyl acid, p-xylylene diiodide, 1,4-bis(1'-iodoethyl)benzene, and 1,3,5-tris(1'-iodoethyl)benzene are preferred.

The content of structural unit (A) in 100% by mass of the acrylic rubber of the present invention is preferably 0.015 to 0.099% by mass. More specifically, the lower limit is preferably 0.015% by mass or more, more preferably 0.025% by mass or more, and even more preferably 0.035% by mass or more. The upper limit is preferably 0.099% by mass or less, more preferably 0.09% by mass or less, and even more preferably 0.085% by mass or less. By being in this range, an acrylic rubber having a good balance between crosslinking speed and mechanical strength can be obtained.

Structural unit (B) derived from alkyl acrylate
The acrylic rubber of the present invention preferably contains a structural unit derived from an alkyl acrylate, more preferably a structural unit derived from an alkyl acrylate having an alkyl group having 1 to 8 carbon atoms, even more preferably a structural unit derived from an alkyl acrylate having an alkyl group having 2 to 8 carbon atoms, and particularly preferably a structural unit derived from an alkyl acrylate having an alkyl group having 2 to 6 carbon atoms. The structural unit (B) may be used alone or in combination of two or more kinds.

Examples of structural units derived from alkyl acrylate esters having an alkyl group with 1 to 8 carbon atoms include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-pentyl acrylate, n-hexyl acrylate, n-heptyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, and cyclohexyl acrylate, with structural units derived from ethyl acrylate and n-butyl acrylate being preferred. These may be used alone or in combination of two or more.

In 100% by mass of the acrylic rubber of the present invention, the content of the structural unit (B) is preferably 50% by mass to 99.985% by mass. More specifically, the lower limit is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, particularly preferably 80% by mass or more, most preferably 89% by mass or more, and even more preferably 90% by mass or more. The upper limit is preferably 99.985% by mass or less, more preferably 99.975% by mass or less, and even more preferably 99.965% by mass or less. Being in the above range tends to result in good physical properties in terms of the cold resistance and oil resistance of the acrylic rubber.

Structural unit (C) derived from alkoxyalkyl acrylate
The acrylic rubber of the present invention may contain a structural unit derived from an alkoxyalkyl acrylate, and in that case, it is preferable that the structural unit is derived from an alkoxyalkyl acrylate having an alkoxyalkyl group having 2 to 6 carbon atoms, more preferably that the structural unit is derived from an alkoxyalkyl acrylate having an alkoxyalkyl group having 2 to 5 carbon atoms, and even more preferably that the structural unit is derived from an alkoxyalkyl acrylate having an alkoxyalkyl group having 2 to 4 carbon atoms. The structural unit (C) may be used alone or in combination of two or more kinds.

Examples of structural units derived from alkoxyalkyl acrylate esters having an alkoxyalkyl group with 2 to 8 carbon atoms include structural units derived from acrylic esters such as methoxymethyl acrylate, ethoxymethyl acrylate, 2-methoxyethyl acrylate, 2-ethoxyethyl acrylate, 2-propoxyethyl acrylate, 2-butoxyethyl acrylate, 2-methoxypropyl acrylate, 2-ethoxypropyl acrylate, 3-methoxypropyl acrylate, 3-ethoxypropyl acrylate, 4-methoxybutyl acrylate, and 4-ethoxybutyl acrylate, with 2-methoxyethyl acrylate being preferred.

In 100% by mass of the acrylic rubber of the present invention, the content of the structural unit (C) is preferably 0% by mass to 30% by mass. More specifically, the lower limit is preferably 0% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, and particularly preferably 4% by mass or more. The upper limit is preferably 30% by mass or less, more preferably 25% by mass or less, even more preferably 20% by mass or less, particularly preferably 15% by mass or less, and most preferably 10% by mass or less. Being in the above range provides good physical properties in terms of the mechanical strength of the acrylic rubber, and also tends to be favorable in terms of cold resistance and oil resistance.

Structural unit (D) derived from alkyl methacrylate ester
The acrylic rubber of the present invention may contain a structural unit derived from an alkyl methacrylate ester, in which case it is preferably a structural unit derived from an alkyl methacrylate ester having an alkyl group having 1 to 8 carbon atoms, more preferably a structural unit derived from an alkyl methacrylate ester having an alkyl group having 1 to 7 carbon atoms, even more preferably a structural unit derived from an alkyl methacrylate ester having an alkyl group having 1 to 6 carbon atoms, and particularly preferably a structural unit derived from an alkyl methacrylate ester having an alkyl group having 1 to 4 carbon atoms. The structural unit (D) may be used alone or in combination of two or more kinds.

Examples of structural units derived from alkyl methacrylate esters having an alkyl group with 1 to 8 carbon atoms include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-pentyl methacrylate, n-hexyl methacrylate, n-heptyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, and cyclohexyl methacrylate, with structural units derived from methyl methacrylate, ethyl methacrylate, and n-butyl methacrylate being preferred. These may be used alone or in combination of two or more.

In 100% by mass of the acrylic rubber of the present invention, the content of the structural unit (D) is preferably 0% by mass to 30% by mass. More specifically, the lower limit is preferably 0% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more. The upper limit is preferably 30% by mass or less, more preferably 25% by mass or less, even more preferably 20% by mass or less, and particularly preferably 15% by mass or less. Being in the above range tends to result in good physical properties in terms of the mechanical strength of the acrylic rubber.

Furthermore, in addition to the above-mentioned structural units, the acrylic rubber of the present invention may contain structural units derived from other monomers copolymerizable therewith. Examples of other structural units include structural units derived from ethylenically unsaturated nitriles, structural units derived from acrylamide monomers, structural units derived from aromatic vinyl monomers, structural units derived from conjugated diene monomers, structural units derived from non-conjugated dienes, structural units derived from other olefins, and the like. These may be used alone or in combination of two or more.

Examples of structural units derived from ethylenically unsaturated nitriles include structural units derived from compounds such as acrylonitrile, methacrylonitrile, α-methoxyacrylonitrile, and vinylidene cyanide.

　Examples of structural units derived from acrylamide monomers include structural units derived from compounds such as acrylamide, methacrylamide, diacetone acrylamide, diacetone methacrylamide, N-butoxymethyl acrylamide, N-butoxymethyl methacrylamide, N-butoxyethyl acrylamide, N-butoxyethyl methacrylamide, N-methoxymethyl acrylamide, N-methoxymethyl methacrylamide, N-propoxymethyl acrylamide, N-propoxymethyl methacrylamide, N-methyl acrylamide, N-methyl methacrylamide, N,N-dimethyl acrylamide, N,N-dimethyl methacrylamide, N,N-diethyl acrylamide, N,N-diethyl methacrylamide, N-methylolacrylamide, N-methylolacrylamide, ethacrylamide, crotonamide, cinnamic acid amide, maleindiamide, itacondiamide, methylmaleamide, methyl itaconamide, maleimide, and itaconimide.

　Examples of structural units derived from aromatic vinyl monomers include structural units derived from compounds such as styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, o-ethylstyrene, p-ethylstyrene, α-fluorostyrene, p-trifluoromethylstyrene, p-methoxystyrene, p-aminostyrene, p-dimethylaminostyrene, p-acetoxystyrene, styrenesulfonic acid or its salts, α-vinylnaphthalene, 1-vinylnaphthalene-4-sulfonic acid or its salts, 2-vinylfluorene, 2-vinylpyridine, 4-vinylpyridine, divinylbenzene, diisopropenylbenzene, and vinylbenzyl chloride.

　Examples of structural units derived from conjugated diene monomers include structural units derived from compounds such as 1,3-butadiene, 2-methyl-1,3-butadiene, 2-chloro-1,3-butadiene, 1,2-dichloro-1,3-butadiene, 2,3-dichloro-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-neopentyl-1,3-butadiene, 2-bromo-1,3-butadiene, 2-cyano-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, chloroprene, and piperylene.

Furthermore, examples of structural units derived from non-conjugated dienes include structural units derived from non-conjugated diene compounds such as 1,4-pentadiene, 1,4-hexadiene, ethylidenenorbornene, norbornadiene, and dicyclopentadiene.

Other structural units derived from olefin monomers include esters such as dicyclopentadienyl acrylate, dicyclopentadienyl methacrylate, dicyclopentadienyl ethyl acrylate, and dicyclopentadienyl ethyl methacrylate, as well as structural units derived from compounds such as ethylene, propylene, vinyl chloride, vinylidene chloride, 1,2-dichloroethylene, vinyl acetate, vinyl fluoride, vinylidene fluoride, 1,2-difluoroethylene, vinyl bromide, vinylidene bromide, 1,2-dibromoethylene, ethyl vinyl ether, and butyl vinyl ether.

When the acrylic rubber of the present invention contains structural units derived from these other copolymerizable monomers, the content of the total structural units may be 0 to 15% by mass, 0 to 10% by mass, or 0 to 5% by mass.

In 100% by mass of the acrylic rubber of the present invention, the total content of the structural unit (A) and the structural unit (B) is preferably 85% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, particularly preferably 98% by mass or more, and may be 100% by mass.

In 100% by mass of the acrylic rubber of the present invention, the total content of the structural units (A), (B), and (C) is preferably 85% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, particularly preferably 98% by mass or more, and may be 100% by mass.

In 100% by mass of the acrylic rubber of the present invention, the total content of the structural units (A), (B), and (D) is preferably 85% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, particularly preferably 98% by mass or more, and may be 100% by mass.

In 100% by mass of the acrylic rubber of the present invention, the total content of the structural units (A), (B), (C) and (D) is preferably 85% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, particularly preferably 98% by mass or more, and may be 100% by mass.

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

The weight average molecular weight (Mw) of the acrylic rubber of the present invention obtained as described above is preferably 500,000 to 2,300,000 from the viewpoint of roll kneading and moldability. More specifically, the lower limit is preferably 500,000 or more, more preferably 750,000 or more, and even more preferably 1,000,000 or more. The upper limit is preferably 2,300,000 or less, more preferably 2,000,000 or less, and even more preferably 1,900,000 or less.

The molecular weight distribution (weight average molecular weight/number average molecular weight (Mn)) is preferably 2.0 to 4.5. More specifically, the lower limit is preferably 2.0 or more, more preferably 2.1 or more, and even more preferably 2.2 or more. The upper limit is preferably 4.5 or less, more preferably 4.2 or less, and even more preferably 4.0 or less. Having the molecular weight distribution in the above range makes it possible to achieve a balance between processability and rubber physical properties.
In this specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) of the acrylic rubber are measured by the method described in the examples.

<Method of manufacturing acrylic rubber>
The acrylic rubber used in the present invention can be obtained by polymerizing various monomers. The monomers used may be commercially available products and are not particularly limited.

As the form of the polymerization reaction, any of the emulsion polymerization method, suspension polymerization method, bulk polymerization method, and solution polymerization method can be used, but from the viewpoint of ease of control of the polymerization reaction, it is preferable to use the suspension polymerization method or emulsion polymerization method, which are commonly used as the conventional method for manufacturing acrylic rubber.

The polymerization initiator, chain transfer agent, polymerization terminator, etc. commonly used in the suspension polymerization method and emulsion polymerization method can be any commonly used conventionally known agent.

The polymerization initiator is not particularly limited, and polymerization initiators generally used in suspension polymerization and emulsion polymerization can be used. Specific examples include inorganic polymerization initiators such as persulfates, such as potassium persulfate, sodium persulfate, and ammonium persulfate, 2,2-di(4,4-di(t-butylperoxy)cyclohexyl)propane, 1-di(t-hexylperoxy)cyclohexane, 1,1-di(t-butylperoxy)cyclohexane, 4,4-di(t-butylperoxy)n-butyl valerate, 2,2-di(t-butylperoxy)butane, t-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, p-menthane hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, t-butylcumyl peroxide, di-t-butyl peroxide, di-t-hexyl peroxide, di(2-t-butyl di(3,5,5-trimethylhexanoyl) peroxide, dilauroyl peroxide, disuccinic acid peroxide, benzoyl peroxide, di(3-methylbenzoyl) peroxide, benzoyl(3-methylbenzoyl) peroxide, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di(4-t-butylcyclohexyl) peroxydicarbonate, di(2-ethylhexyl) peroxydicarbonate, di-sec-butyl peroxydicarbonate, cumyl peroxyneodecanate, 1,1,3,3-tetramethylbutyl peroxyneodecanate, t-hexyl peroxyneodecanate, t-butyl peroxyneodecanate decanate, t-hexylperoxypivalate, t-butylperoxypivalate, 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanate, t-hexylperoxy-2-ethylhexanate, t-butylperoxy-2-ethylhexanate, t-butylperoxylaurate, t-butylperoxy-3,5,5-trimethylhexanate, t-hexylperoxyisopropylmonocarbonate, t-butylperoxyisopropylmonocarbonate, t-butylperoxy2-ethylhexylmonocarbonate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-butylperoxyacetate, t-hexylperoxybenzoate, t-butylperoxy Oxybenzoate, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane and other organic peroxide-based polymerization initiators, hydroperoxides, azobisisobutyronitrile, 4-4'-azobis(4-cyanovaleric acid), 2-2'-azobis[2-(2-imidazolin-2-yl)propane, 2-2'-azobis(propane-2-carboxamidine), 2-2'-azobis[N-(2-carboxamidine), Examples of the polymerization initiators include azo-based initiators such as 2-2'-azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane}, 2-2'-azobis(1-imino-1-pyrrolidino-2-methylpropane) and 2-2'-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propanamide}. These polymerization initiators may be used alone or in combination of two or more.

The amount of polymerization initiator used is preferably in the range of 0.0001 to 0.1 parts by mass per 100 parts by mass of charged monomer. More specifically, the lower limit is preferably 0.0001 parts by mass or more, more preferably 0.0005 parts by mass or more, and even more preferably 0.001 parts by mass or more. The upper limit is preferably 0.1 parts by mass or less, more preferably 0.05 parts by mass or less, and even more preferably 0.01 parts by mass or less. If the amount is less than this range, the polymerization reaction may not start, or the polymerization rate may be significantly slowed. On the other hand, if the amount is too high, the polymerization rate may become too fast, or functional groups derived from the polymerization initiator may be introduced at the ends of the acrylic rubber, making it impossible to obtain the desired acrylic rubber.

Alternatively, it is preferably 0.01 to 200 mol per 1 mol of the organic iodine compound represented by general formula (1) or general formula (2). More specifically, the lower limit is preferably 0.01 mol or more, more preferably 0.02 mol or more, and even more preferably 0.03 mol or more. The upper limit is preferably 40 mol or less, more preferably 20 mol or less, and even more preferably 4 mol or less.

As the chain transfer agent, chain transfer agents generally used in suspension polymerization and emulsion polymerization can be used. For example, alkyl mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, and n-stearyl mercaptan; xanthogen compounds such as 2,4-diphenyl-4-methyl-1-pentene, 2,4-diphenyl-4-methyl-2-pentene, dimethyl xanthogen disulfide, and diisopropyl xanthogen disulfide; thiuram compounds such as terpinolene, tetramethylthiuram disulfide, tetraethylthiuram disulfide, and tetramethylthiuram monosulfide. Examples of suitable chain transfer agents include phenolic compounds such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol, allyl compounds such as allyl alcohol, halogenated hydrocarbon compounds such as dichloromethane, dibromomethane and carbon tetrabromide, vinyl ethers such as α-benzyloxystyrene, α-benzyloxyacrylonitrile and α-benzyloxyacrylamide, triphenylethane, pentaphenylethane, acrolein, methacrolein, thioglycolic acid, thiomalic acid, and 2-ethylhexyl thioglycolate, and these may be used alone or in combination. The amount of these chain transfer agents is not particularly limited, but is usually 0 to 0.1 parts by mass relative to 100 parts by mass of the charged monomer, and may be 0.01 to 0.05 parts by mass.

As the polymerization terminator, any polymerization terminator commonly used in suspension polymerization or emulsion polymerization can be used. Examples include hydroxylamine, hydroxylamine sulfate, diethylhydroxyamine, hydroxylamine sulfonic acid and its alkali metal salts, sodium dimethyldithiocarbamate, and quinone compounds such as hydroquinone. There are no particular limitations on the amount of polymerization terminator used, but it is usually 0 to 2 parts by mass per 100 parts by mass of charged monomer.

The emulsifier used in the emulsion polymerization method is not particularly limited, and commonly used nonionic emulsifiers and anionic emulsifiers can be used. Examples of nonionic emulsifiers include polyoxyethylene alkyl ethers, polyoxyethylene alcohol ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene polycyclic phenyl ethers, polyoxyalkylene alkyl ethers, sorbitan fatty acid esters, polyoxyethylene fatty acid esters, and polyoxyethylene sorbitan fatty acid esters. Examples of anionic emulsifiers include alkylbenzene sulfonates, alkyl sulfate salts, polyoxyethylene alkyl ether sulfate salts, polyoxyalkylene alkyl ether phosphate esters or salts thereof, and fatty acid salts. One or more of these may be used. Representative examples of anionic emulsifiers include sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and triethanolamine dodecyl sulfate.

The amount of emulsifier used in the present invention may be any amount generally used in emulsion polymerization methods. Specifically, it is preferably 0.01 to 10% by mass based on the amount of charged monomer. More specifically, the lower limit is preferably 0.01% by mass or more, more preferably 0.03% by mass or more, and even more preferably 0.05% by mass or more. The upper limit is preferably 10% by mass or less, more preferably 7% by mass or less, and even more preferably 5% by mass or less. When a reactive surfactant is used as the monomer component, the addition of an emulsifier is not necessarily required.

The dispersant used in the suspension polymerization method is not particularly limited, and any commonly used dispersant can be used. For example, the above-mentioned emulsifiers used in emulsion polymerization can also be used as dispersants, and examples of the dispersant include nonionic polymer compounds such as polyvinyl alcohol, polyvinylpyrrolidone, polyethylene oxide, and cellulose derivatives, anionic polymer compounds such as polyacrylic acid and its salts, polymethacrylic acid and its salts, and rubbers of methacrylic acid esters and methacrylic acid and/or its salts, and poorly water-soluble inorganic compounds such as calcium phosphate, calcium carbonate, and aluminum hydroxide.

These dispersants can be used alone or in combination of two or more. The amount of dispersant used in the present invention may be any amount generally used in suspension polymerization methods. Specifically, the amount is preferably in the range of 0.01 to 10% by mass relative to the amount of charged monomer. More specifically, it is preferably 0.01% by mass or more, more preferably 0.03% by mass or more, and even more preferably 0.05% by mass or more. The upper limit is preferably 10% by mass or less, more preferably 7% by mass or less, and even more preferably 5% by mass or less.

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

　In addition to the above, particle size regulators, chelating agents, oxygen scavengers and other polymerization secondary materials can be used as needed.

Suspension polymerization and emulsion polymerization may be batch, semi-batch, or continuous. There are no particular limitations on the polymerization time and temperature. They can be selected appropriately based on the type of polymerization initiator used, but generally, the polymerization temperature is 10 to 100°C, and the polymerization time is 0.5 to 100 hours.

There is no particular restriction on the method for recovering the polymer obtained by the above method, and any commonly used method can be used. One example of such a method is to continuously or batchwise supply the polymerization liquid to an aqueous solution containing a coagulant, and this operation produces a coagulated slurry. The temperature of the aqueous solution containing the coagulant is affected by the coagulation conditions, such as the type and amount of monomer used, and the shear force caused by stirring, and cannot be uniformly determined, but is generally 50°C or higher, preferably in the range of 60°C to 100°C.

The coagulated slurry obtained by the above method is preferably washed with water to remove the coagulant. If washing with water is not performed at all or washing is insufficient, there is a risk that ionic residues derived from the coagulant will be precipitated during the molding process.

Acrylic rubber can be obtained by removing water from the solidified slurry after washing and drying. There are no particular limitations on the drying method, but it is generally dried using a flash dryer or fluidized bed dryer. In addition, a dehydration process using a centrifuge or similar machine may be used prior to the drying process.

<Acrylic rubber crosslinking composition>
The composition for crosslinking acrylic rubber of the present invention can be obtained by containing at least the above-mentioned acrylic rubber and a crosslinking agent.

In the acrylic rubber cross-linking composition of the present invention, the content of the acrylic rubber of the present invention in 100% by mass of acrylic rubber is preferably 85% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, particularly preferably 98% by mass or more, and may be 100% by mass.

As the crosslinking agent, conventionally known crosslinking agents that are commonly used for crosslinking rubber, such as organic peroxides, polyamine compounds, polyepoxy compounds, polyisocyanate compounds, aziridine compounds, sulfur compounds, basic metal oxides, and organometallic halides, can be used. Of these, organic peroxides are preferably used because the acrylic rubber of the present invention contains iodine.

The organic peroxide may be any organic peroxide that can easily generate peroxy radicals in the presence of heat or an oxidation-reduction system, such as 1,1-bis(t-butylperoxy)-3,5,5-trimethylcyclohexane, 2,5-dimethylhexane-2,5-dihydroperoxide, di-t-butyl peroxide, t-butylcumyl peroxide, dicumyl peroxide, α,α-bis(t-butylperoxy)-p-diisopropylbenzene, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di(t-butylperoxy)-hexyne-3, benzoyl peroxide, t-butylperoxybenzene, t-butylperoxymaleic acid, t-butylperoxyisopropylcarbonate, and t-butylperoxybenzoate. Among these, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane and 2,5-dimethyl-2,5-di(t-butylperoxy)-hexyne-3 are preferred.

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

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

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

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

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

Examples of basic metal oxides include zinc oxide, lead oxide, calcium oxide, magnesium oxide, etc.

Examples of organometallic halides include dicyclopentadienyl metal dihalides, and examples of metals include titanium and zirconium.

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

When the crosslinking agent is an organic peroxide, it is preferable that the acrylic rubber crosslinking composition further contains a crosslinking aid. Examples of crosslinking aids include triallyl cyanurate, triallyl isocyanurate (TAIC), triacrylformal, triallyl trimellitate, N,N'-m-phenylene bismaleimide, dipropargyl terephthalate, diallyl phthalate, tetraallyl terephthalate amide, triallyl phosphate, bismaleimide, fluorinated triallyl isocyanurate (1,3,5-tris(2,3,3-trifluoro-2-propenyl)-1,3,5-triazine, etc. -2,4,6-trione), tris(diallylamine)-S-triazine, N,N-diallylacrylamide, 1,6-divinyldodecafluorohexane, hexaallyl phosphoramide, N,N,N',N'-tetraallylphthalamide, N,N,N',N'-tetraallylmalonamide, trivinyl isocyanurate, 2,4,6-trivinylmethyltrisiloxane, tri(5-norbornene-2-methylene) cyanurate, triallyl phosphite, etc. Among these, triallyl isocyanurate (TAIC) is preferred because of its excellent crosslinkability, mechanical properties, and flexibility.

The amount of cross-linking aid is preferably 0.01 to 10 parts by mass, more preferably 0.01 to 7.0 parts by mass, and even more preferably 0.1 to 5.0 parts by mass, per 100 parts by mass of acrylic rubber. If the amount of cross-linking aid is less than 0.01 parts by mass, the mechanical properties and flexibility will decrease. If the amount exceeds 10 parts by mass, the heat resistance will be poor and the durability of the molded product will also tend to decrease. The cross-linking aids can be used alone or in combination of two or more types.

The acrylic rubber crosslinking composition of the present invention can also contain any of the other additives commonly used in the art, such as lubricants, antioxidants, light stabilizers, fillers, reinforcing agents, plasticizers, processing aids, pigments, colorants, crosslinking accelerators, crosslinking retarders, antistatic agents, foaming agents, etc. These can be used alone or in combination of two or more.

An example of a reinforcing agent is carbon black, and the content thereof is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 30 parts by mass or more, and is preferably 120 parts by mass or less, and more preferably 100 parts by mass or less, relative to 100 parts by mass of acrylic rubber.

Lubricants include, for example, metal soaps such as zinc stearate, calcium stearate, and magnesium stearate; higher fatty acids such as lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, and oleic acid; higher fatty acid esters such as methyl esters, isopropyl esters, butyl esters, and octyl esters of higher fatty acids; higher alcohols such as myristyl alcohol, cetyl alcohol, and stearyl alcohol; and hydrocarbon lubricants such as liquid paraffin, paraffin wax, and synthetic polyethylene wax. Among these, higher fatty acids are preferred in the present invention, and stearic acid is more preferred.

The amount of lubricant blended is preferably 0.1 to 10 parts by mass per 100 parts by mass of acrylic rubber. More specifically, the lower limit is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 1 part by mass or more. The upper limit is preferably 10 parts by mass or less, more preferably 7 parts by mass or less, even more preferably 5 parts by mass or less, and especially preferably 3 parts by mass or less.

Examples of anti-aging agents include amine-based, phosphate-based, quinoline-based, cresol-based, phenol-based, and dithiocarbamate metal salts. In the present invention, it is preferable to use amine-based and phenol-based anti-aging agents. These may be used alone or in combination of two or more types.

Examples of amine-based anti-aging agents include phenyl-α-naphthylamine, phenyl-β-naphthylamine, p-(p-toluenesulfonylamido)-diphenylamine, 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, N,N-diphenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, and butyraldehyde-aniline condensate.

Phenol-based antioxidants include, for example, 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, styrenated phenol, 2,2'-methylene-bis(6-α-methyl-benzyl-p-cresol), 4,4'-methylenebis( 2,6-di-t-butylphenol), 2,2'-methylene-bis(4-methyl-6-t-butylphenol), 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-triazin-2-ylamino)phenol, etc.

The content of the anti-aging agent is preferably 0.01 to 10 parts by mass, more preferably 0.01 to 5 parts by mass, and particularly preferably 0.03 to 3 parts by mass, per 100 parts by mass of acrylic rubber.

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

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

The acrylic rubber crosslinking composition of the present invention can be compounded using any method conventionally used in the field of polymer processing, such as an open roll, a Banbury mixer, or various kneaders.

The compounding procedure can be the usual procedure used in the field of polymer processing. For example, the polymer alone is first mixed, then compounding ingredients other than the crosslinking agent and crosslinking aid are added to prepare compound A, and then compound B is mixed with the crosslinking agent and crosslinking aid.

A rubber material can be made from the composition of the present invention (specifically, it is usually crosslinked by heating to 100-250°C). The crosslinking time varies depending on the temperature, but is usually between 0.5 and 300 minutes. Crosslinking molding can be performed in any of the following ways: crosslinking and molding can be performed together, a previously molded acrylic rubber crosslinking composition can be heated again to form a crosslinked product, or the crosslinked product can be heated first and then processed for molding. Specific methods for crosslinking molding include compression molding using a mold, injection molding, heating using a steam can, air bath, infrared rays, or microwaves, among others.

The acrylic rubber of the present invention and the composition for crosslinking acrylic rubber of the present invention containing the acrylic rubber of the present invention can provide an acrylic rubber crosslinked product having a small difference in physical properties between the primary crosslinked product and the secondary crosslinked product. Therefore, since the acrylic rubber of the present invention and the composition for crosslinking acrylic rubber of the present invention can produce an acrylic rubber crosslinked product having sufficient physical properties by the primary crosslinking step, it is preferable not to carry out the secondary crosslinking step. In other words, it is preferable that the crosslinked acrylic rubber of the present invention is produced by carrying out only the primary crosslinking step as a crosslinking step, without carrying out the secondary crosslinking step, on the acrylic rubber of the present invention and the composition for crosslinking acrylic rubber of the present invention.
In this specification, the primary crosslinking step means a step in which the acrylic rubber of the present invention or the composition for crosslinking the acrylic rubber of the present invention is allowed to exist under conditions of preferably 140 to 200°C, more preferably 150 to 180°C, for preferably 5 to 50 minutes, more preferably 10 to 40 minutes, and the secondary crosslinking step means a step in which, after carrying out the primary crosslinking step, the acrylic rubber of the present invention or the composition for crosslinking the acrylic rubber of the present invention is allowed to exist under conditions of preferably 140 to 200°C, more preferably 150 to 180°C, for preferably 1 to 5 hours, more preferably 1 to 3 hours.

The crosslinked product produced from the composition containing the acrylic rubber of the present invention thus obtained has excellent resistance to scorching at high temperatures and a fast crosslinking rate.

As a result, the rubber material of the present invention can obtain hardness and rubber properties equivalent to those of secondary crosslinking with only primary crosslinking, and therefore can be used to produce various gaskets such as O-rings, packings, diaphragms, oil seals, shaft seals, bearing seals, mechanical seals, wellhead seals, seals for electrical and electronic equipment, seals for pneumatic equipment, cylinder head gaskets attached to the joint between the cylinder block and cylinder head, rocker cover gaskets attached to the joint between the rocker cover and cylinder head, oil pan gaskets attached to the joint between the oil pan and the cylinder block or transmission case, gaskets for fuel cell separators attached between a pair of housings that sandwich a unit cell having a positive electrode, electrolyte plate and negative electrode, and gaskets for the top cover of hard disk drives, as well as extrusion molded products and mold crosslinked products used in automotive applications such as fuel oil hoses around fuel tanks such as fuel hoses, filler neck hoses, vent hoses, vapor hoses and oil hoses, air hoses such as turbo air hoses and emission control hoses, and various hoses such as radiator hoses, heater hoses, brake hoses and air conditioner hoses, with less energy consumption than before. In addition, the crosslinking speed is fast, and hardness and rubber properties equivalent to secondary crosslinking can be obtained with only primary crosslinking, so there is little lot-to-lot variation in the properties of the crosslinked product, and there is little variation in the quality of the final product.

The present invention will be specifically explained using examples and comparative examples. However, the present invention is not limited to these. In the event of any discrepancy between the descriptions in the text and the descriptions in the tables, the descriptions in the tables take precedence.

[Production Example 1] (Production of Acrylic Rubber A)
In a polymerization reactor equipped with a thermometer, a stirrer, a nitrogen inlet tube and a pressure reducing device, 200 parts by mass of water, 1.9 parts by mass of polyoxyalkylene alkyl ether phosphate ester, 50 parts by mass of ethyl acrylate as a monomer, 50 parts by mass of n-butyl acrylate, and 0.05 parts by mass of ethylene glycol bis(2-iodoisobutyric acid) (manufactured by Godo Shigen Co., Ltd., hereinafter abbreviated as BBDG) as an organic iodine compound were charged, and oxygen was sufficiently removed by repeatedly degassing under reduced pressure and replacing with nitrogen, and then 0.004 parts by mass of benzoyl peroxide was added, and the polymerization reaction was carried out by heating the inside of the polymerization reactor to 65°C until the polymerization conversion rate reached 80%. The obtained polymerization liquid was coagulated with an aqueous sodium sulfate solution, washed with water and dried to obtain acrylic rubber A. The following tests were carried out using the obtained acrylic rubber, and the results are shown in Table 1.

<Molecular Weight Measurement>
The weight average molecular weight (Mw) and number average molecular weight (Mn) of the acrylic rubber were measured by gel permeation chromatography (GPC), and the molecular weight distribution was calculated from Mw and Mn. Specifically, the measurement was performed using a column in which two TSKgel Super HM-H (manufactured by Tosoh Corporation, column size 6.0 mm x 15 cm) were connected in series to a liquid chromatograph (manufactured by Waters Corporation). Tetrahydrofuran was used as the eluent, and the column temperature was set to 50°C. The weight average molecular weight (Mw) and number average molecular weight (Mn) were measured as polystyrene equivalent values.

<Polymer Mooney Viscosity (ML ₁₊₄ , 100° C.)>
For the acrylic rubber, the Mooney viscosity (ML ₁₊₄ ) was measured at a measurement temperature of 100° C. using a Mooney Viscometer AM-3 manufactured by Toyo Seiki Seisakusho Co., Ltd. in accordance with the Mooney viscosity test of the uncrosslinked rubber physical testing method of JIS K6300.

<Mooney scorch time t5 (scorch stability)>
The acrylic rubber composition was kneaded with a kneader and an open roll to prepare an uncrosslinked sheet having a thickness of 2 to 2.5 mm. The Mooney scorch test specified in JIS K 6300 was carried out at 145°C using a Mooney Viscometer AM-3 manufactured by Toyo Seiki Seisakusho, and the time required for the Mooney viscosity to increase by 5 points from the minimum Mooney viscosity was measured to evaluate the scorch stability.

[Production Example 2] (Production of Acrylic Rubber B)
The same procedure as in Production Example 1 was carried out, except that the iodine compound charged was changed to 0.08 parts by mass of glycerol tris(2-iodoisobutyric acid) (manufactured by Godo Shigen Co., Ltd., hereinafter abbreviated as TBTP), to obtain acrylic rubber B. The above tests were carried out using the obtained acrylic rubber, and the results are shown in Table 1.

[Production Example 3] (Production of Acrylic Rubber C)
The same procedure as in Production Example 1 was carried out except that the iodine compound charged was changed to 0.05 parts by mass of TBTP, to obtain acrylic rubber C. The above tests were carried out using the obtained acrylic rubber, and the results are shown in Table 1.

[Production Example 4] (Production of Acrylic Rubber D)
The same procedure as in Production Example 1 was carried out except that the monomers and their amounts charged were changed to 40 parts by mass of ethyl acrylate and 60 parts by mass of n-butyl acrylate, to obtain acrylic rubber D. The obtained acrylic rubber was subjected to the above tests, and the results are shown in Table 1.

[Production Example 5] (Production of Acrylic Rubber E)
The same procedure as in Production Example 1 was carried out except that the monomers and their amounts charged were changed to 70 parts by mass of ethyl acrylate, 25 parts by mass of n-butyl acrylate, and 5 parts by mass of 2-methoxyethyl acrylate, to obtain acrylic rubber E. The above tests were carried out using the obtained acrylic rubber, and the results are shown in Table 1.

[Production Example 6] (Production of Acrylic Rubber F)
The same procedure as in Production Example 1 was carried out except that the monomers and their amounts charged were changed to 50 parts by mass of ethyl acrylate, 40 parts by mass of n-butyl acrylate, and 10 parts by mass of n-butyl methacrylate, to obtain acrylic rubber F. The above tests were carried out using the obtained acrylic rubber, and the results are shown in Table 1.

[Production Example 7] (Production of Acrylic Rubber G)
Acrylic rubber G was obtained in the same manner as in Production Example 1, except that the amount of BBDG, an iodine compound, was changed to 0.01 parts by mass from Production Example 1. The above tests were performed using the obtained acrylic rubber, and the results are shown in Table 1.

[Production Example 8] (Production of Acrylic Rubber H)
The same procedure as in Production Example 1 was carried out except that the amount of BBDG, an iodine compound, was changed to 0.1 parts by mass, to obtain acrylic rubber H. The above tests were carried out using the obtained acrylic rubber, and the results are shown in Table 1.

[Example 1]
To 100 parts by mass of the acrylic rubber obtained in Production Example 1, 60 parts by mass of carbon black N550, 2 parts by mass of stearic acid, and 4 parts by mass of triallyl isocyanurate were added and kneaded to obtain kneaded compound A. 1.5 parts by mass of Perhexa 25B (manufactured by NOF Corporation, chemical name 2,5-dimethyl-2,5-di(t-butylperoxy)hexane) was added to this kneaded compound A and kneaded with an open roll to obtain kneaded compound B, and an uncrosslinked sheet having a thickness of 2 to 2.5 mm was prepared. The obtained uncrosslinked sheet was evaluated as follows, and the results are shown in Table 2.

<Normal physical property test>
The uncrosslinked sheet obtained above was pressed at 180°C for 15 minutes to obtain a primary crosslinked sheet. This was further heated in an air oven at 180°C for 3 hours to obtain a secondary crosslinked sheet. Using the crosslinked sheets of the primary crosslinked product and the secondary crosslinked product, tensile tests (strength TB, elongation EB) were performed in accordance with the method described in JIS K 6251 using an AGS-5KNY manufactured by Shimadzu Corporation. In addition, type A durometer hardness HS (JIS A) was performed in accordance with the method described in JIS K6253. Comparative evaluation of the primary crosslinked product and the secondary crosslinked product was performed as follows. The smaller the rate of change and amount of change in physical properties between the primary crosslinked product and the secondary crosslinked product, the more sufficient normal physical properties were obtained with the primary crosslinked product.
ΔTB=(strength of primary crosslinked product−strength of secondary crosslinked product)/strength of secondary crosslinked product×100
ΔEB = (elongation of primary crosslinked product - elongation of secondary crosslinked product) / elongation of secondary crosslinked product x 100
ΔHS = (hardness of primary crosslinked product - hardness of secondary crosslinked product)

[Examples 2 to 6, Comparative Examples 1 to 2]
For Examples 2 to 6 and Comparative Examples 1 and 2, the procedures shown in Table 2 were carried out to obtain compositions for crosslinking acrylic rubber, and the evaluations were carried out as described above. The results are shown in Table 2.

As shown in Examples 1 to 6, the acrylic rubbers A to F of the present invention obtained in Production Examples 1 to 6 showed small changes in physical properties between the primary crosslinked product and the secondary crosslinked product of ±10% compared to Comparative Examples 1 and 2, suggesting that sufficient crosslinking had progressed with only the primary crosslinking. Therefore, it was found that the acrylic rubber crosslinked product obtained by crosslinking the acrylic rubber of the present invention has small differences in physical properties between the primary crosslinked product and the secondary crosslinked product, making it possible to omit the secondary crosslinking process, shortening the manufacturing process and enabling industrial production with less energy.

The acrylic rubber, composition for cross-linking acrylic rubber, and cross-linked product thereof of the present invention show only small changes in physical properties between the primary cross-linked product and the secondary cross-linked product, and therefore can be used to produce materials for various rubber products and resin products by primary cross-linking alone, making them extremely useful from the standpoint of low energy and labor saving.

Claims (6)

The acrylic rubber includes at least a structural unit (A) derived from an organic iodine compound containing two or more iodine atoms in one molecule and represented by the following general formula (1) or the following general formula (2), and a structural unit (B) derived from an alkyl acrylate,
The acrylic rubber has a content of the structural unit (A) of 0.015 to 0.099 mass% based on 100 mass% of the acrylic rubber.

(R1 is a hydrocarbon group having 2 to 4 carbon atoms. R2 and R3 are a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or an aromatic hydrocarbon group which may have a substituent. R2 and R3 may be the same or different. n is an integer of 2 to 4.)

(R4 is a hydrocarbon group having 2 to 4 carbon atoms, or an aromatic hydrocarbon group which may have a substituent. R5 and R6 are a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an aromatic hydrocarbon group which may have a substituent, or -COOR7, where R7 is an alkyl group having 1 to 3 carbon atoms. R5 and R6 may be the same or different. R7 may be the same or different. n is an integer of 2 to 4.) The acrylic rubber according to claim 1 further contains a structural unit (C) derived from an alkoxyalkyl acrylate. The acrylic rubber according to claim 1 further contains a structural unit (D) derived from an alkyl methacrylate ester. The acrylic rubber according to claim 1, wherein the weight average molecular weight of the acrylic rubber is 500,000 to 2,300,000. A composition for cross-linking acrylic rubber comprising at least the acrylic rubber according to any one of claims 1 to 4 and a cross-linking agent. A cross-linked acrylic rubber product obtained by cross-linking the composition for cross-linking acrylic rubber according to claim 5.