Crosslinkable acrylic rubber composition

Abstract

This crosslinkable acrylic rubber composition is obtained by containing: (A) an acrylic elastomer copolymer constituted from a copolymerizable anti-aging agent represented by general formula [I] (R1 is a monovalent aliphatic hydrocarbon group having 1-20 carbon atoms, R2 is a hydrogen atom or a methyl group, and A is a direct bond, an oxygen atom or a sulfur atom), an alkyl (meth)acrylate monomer and / or an alkoxyalkyl (meth)acrylate monomer, and an α,β-unsaturated carboxylic acid monomer; (B) a phenothiazine-based anti-aging agent; (C) a polyvalent amine crosslinking agent; and (D) a crosslinking accelerator.

Description

Crosslinkable acrylic rubber composition

[0001] The present invention relates to a crosslinkable acrylic rubber composition, and more particularly to a crosslinkable acrylic rubber composition that can minimize deterioration in mechanical properties of a crosslinked product due to thermal oxidative degradation.

[0002] From the perspective of global climate change countermeasures and efficient energy use, regulations on emissions of carbon dioxide, NOx gases, and other gases emitted by internal combustion engines, such as automobile engines, are becoming increasingly strict. As a response, automobile engines are required to have higher output, higher thermal efficiency, and reduced and harmless exhaust gases, which has resulted in a tendency for temperatures inside the engine compartment to rise. Accordingly, polymeric materials used in the vicinity, such as rubber and plastics, are required to have even greater heat resistance.

[0003] As a specific example, vehicles equipped with turbocharger systems to improve engine fuel efficiency are becoming more common. The air that is guided from the turbocharger to the intercooler and engine is at high temperature and pressure, so the rubber hose material that transports this air must have high heat resistance.

[0004] As a result of the demand for higher temperatures and longer life for the polymeric materials used in automobile engines, measures have been taken to address these demands, such as improving the heat resistance of the raw rubber material itself used in rubber product components, and adding appropriate antioxidants to rubber product components.

[0005] Typical antioxidants used for rubber members include phenol-based antioxidants and amine-based antioxidants, and amine-based antioxidants are used particularly for rubber members used in higher temperature environments.

[0006] For example, in the case of acrylic rubber, an amine-based antioxidant, typified by 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, is used as the antioxidant (Patent Documents 1 to 4).

[0007] In addition, in an effort to improve the heat resistance of acrylic rubber itself, the crosslinking site monomer has been changed from an active chlorine-containing unsaturated monomer to an α,β-unsaturated carboxylic acid monomer, thereby forming a strong crosslinked structure that can withstand use in high-temperature environments.

[0008] However, even with the improvement of the heat resistance of the raw rubber itself and the addition of amine-based antioxidants, it is not possible to fully satisfy the current demand for heat resistance.

[0009] Patent Document 5 describes that a phenothiazine-based antioxidant is effective as an antioxidant for rubber materials.

[0010] This document discloses a rubber material that is excellent in vulcanization properties, mechanical properties, and heat aging properties and is particularly suitable for use as a vibration-proof rubber, and that contains (A) a diene rubber, (B) a bismaleimide compound, and (C) the following phenothiazine compound: R 1 , R 2 R: Hydrogen atom, C1-C8 alkyl group which may be substituted with an aromatic ring, alkoxy group, halogen atom, cyano group 3 m, n: 0 to 2; phenothiazine compounds in which the sulfur atom at the 5th position is -SO2- are also known, and are described in, for example, Patent Document 6.

[0011] Patent Document 6 describes a fused heterocyclic compound represented by the following general formula and an organic material composition containing the same, and states that the compound can impart high processing stability, heat resistance, and long life to organic materials such as polymers that are susceptible to oxidative, thermal, or light-induced degradation. Y: Chemical single bond, -S(=O)-, -SO2- R a , R b : C1-C optionally having a substituent 30 organic group Z a , Zb : Chemical single bond, -SO2- X 1 , X 2 : Hydrogen atom, halogen atom, alkyl group, cyano group, nitro group, -OR 1 , -O-CO-R 1 , -CO-OR 1 , -O-CO-OR 1 , -NR 2 R 3 , -NR 2 -CO-R 1 , -CO-NR 2 R 3 , -O-CO-NR 2 R 3 n, m: 0 to 2, but either one is not 0

[0012] Furthermore, in order to prevent the volatilization of amine-based antioxidants from rubber components, studies have been conducted to increase the molecular weight and melting point of the amine-based antioxidants. However, as the molecular weight and melting point of the antioxidant increase, problems arise, such as a decrease in dispersibility in rubber and migration within the rubber.

[0013] In order to prevent the volatilization of antioxidants and extend the life of rubber parts in high-temperature environments, a method of copolymerizing antioxidants having polymerizable unsaturated groups with raw rubber has also been investigated (Patent Document 7).

[0014] For example, Non-Patent Documents 1 and 2 list anti-aging agents having a polymerizable unsaturated group, such as Nocrac G-1 (Ouchi Shinko Chemical Industry Co., Ltd.) and APMA (Seiko Chemical Industry Co., Ltd.).

[0015] However, the radical copolymerization of the above antioxidants with polymerizable unsaturated monomers is practically difficult due to the radical polymerization inhibiting effect of the diphenylamino group.

[0016] In addition, several methods have been disclosed for introducing a diphenylamino structure into an elastomeric polymer by a modification reaction. For example, a method in which the side chain of an elastomer having an olefinically unsaturated group is hydroformylated and then a diphenylamino group is introduced (Patent Document 8), and a method in which maleic anhydride is added to a diene copolymer in the presence of a free radical generator and then a diphenylamino group is introduced (Patent Document 9) are known. However, these methods require an additional modification step of introducing a diphenylamino group after producing the base copolymer, making them impractical in terms of production cost.

[0017] Furthermore, a method of crosslinking acrylic rubber in the presence of 4-aminodiphenylamine is known (Patent Documents 10 and 11), but in this method, there is a concern that 4-aminodiphenylamine may deteriorate compression set resistance.

[0018] As described above, the conventional techniques cannot fully satisfy the current demand for heat resistance, regardless of whether they are achieved by improving the heat resistance of the raw rubber itself, by improving the performance of various antioxidants, or by chemically bonding a heat aging prevention component to the raw rubber.

[0019] JP 11-21411 A WO 2011 / 58918 A1 JP 2010-254579 A WO 2006 / 001299 A1 JP 2015-227402 A WO 2011 / 093443 A1 JP 2009-209268 A JP 4-264106 A JP 5-230132 A WO 2020 / 158132 A1 JP 2009-84514 A JP 2020-111552 A

[0020] Rubber Chem. Technol., Vol. 46, p. 106 (1973) Rubber Chem. Technol., Vol. 52, p. 883 (1979)

[0021] In response to the above-mentioned problems, the present inventors have investigated whether it is possible to improve the heat resistance of acrylic rubber by using a crosslinkable acrylic rubber composition comprising an antiaging component, a carboxyl group-containing acrylic rubber, a phenothiazine-based antiaging agent, a crosslinking agent, and a crosslinking accelerator. In particular, the inventors have investigated to suppress the significant softening degradation observed in the early stages of thermooxidative degradation of acrylic rubber made primarily from ethyl acrylate, as well as the significant hardening degradation observed in the later stages.

[0022] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a cross-linkable acrylic rubber composition that suppresses the significant softening deterioration observed in the early stage of thermo-oxidative deterioration of a cross-linked acrylic rubber product and the significant hardening deterioration observed in the later stage, thereby minimizing the decrease in mechanical strength.

[0023] The object of the present invention is to provide a compound comprising: (A) a compound of general formula [I] (where R 1 is a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms, and R 2 (B) a copolymerizable antioxidant represented by the general formula [II]: (A) is a hydrogen atom or a methyl group, and (B) is a direct bond, an oxygen atom, or a sulfur atom; an acrylic elastomer copolymer composed of an alkyl (meth)acrylate monomer and / or an alkoxyalkyl (meth)acrylate monomer and an α,β-unsaturated carboxylic acid monomer; and (C) a phenothiazine-based antioxidant represented by the general formula [II]: [where R 3 represents a hydrogen atom, a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms, an aralkyl group having 7 to 20 carbon atoms, or a group represented by the following general formula [III]: (where R 5 is a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms), and R 4 is an aralkyl group having 7 to 20 carbon atoms], (C) a polyamine crosslinking agent, and (D) a crosslinking accelerator.

[0024] The acrylic elastomer copolymer used in the crosslinkable acrylic rubber composition of the present invention contains an antiaging component in its polymer side chain, stabilizing the copolymer itself against thermal oxidative degradation. Furthermore, in molded parts obtained by crosslinking it, the antiaging component is prevented from volatilizing into the air or being extracted by liquid media such as oils and fats or organic solvents, thereby enabling the acrylic elastomer molded parts to have a long life even under various deteriorating environments.

[0025] Furthermore, the crosslinking action of the anti-aging component chemically bonded to the polymer side chains can suppress the softening and deterioration observed in the early stages of thermal oxidative deterioration, thereby preventing a decrease in mechanical strength.

[0026] Furthermore, the phenothiazine-based antioxidant constituting the composition of the present invention exhibits the effect of significantly suppressing hardening degradation in the later stage of thermo-oxidative degradation of the cross-linked acrylic rubber copolymerized with the copolymerizable antioxidant. As a result, the molded part obtained by cross-linking the cross-linkable acrylic rubber composition of the present invention exhibits the excellent effect of minimizing the deterioration of its mechanical properties throughout the entire thermo-oxidative degradation process.

[0027] Figure 1 shows a diagram of the change over time in the 100% modulus of a cross-linked acrylic rubber product at 190°C (Example 1: -●-, Comparative Example 1: - - ● - -, Comparative Example 2: - -▲- -, Comparative Example 3: - - ◆ - -; common to Figures 1 to 3). Figure 2 shows a diagram of the change over time in the strength at break of a cross-linked acrylic rubber product at 190°C. Figure 3 shows a diagram of the change over time in the elongation at break of a cross-linked acrylic rubber product at 190°C. Figure 4 shows the percentage change in strength at break (black bars) after a combined test consisting of air heating (175°C, 150 hours), IRM903 oil immersion (150°C, 168 hours), and air heating (190°C, 300 hours), compared with the percentage change in strength at break (white bars) after an air heating aging test (190°C, 300 hours). 8 shows a comparison of the change in elongation at break (black bars) after a combined test consisting of air heating (175°C, 150 hours), IRM903 oil immersion (150°C, 168 hours), and air heating (190°C, 300 hours), with the change in elongation at break (white bars) after an air heating aging test (190°C, 300 hours). The change over time in the 100% modulus of a cross-linked acrylic rubber product at 190°C is diagrammed (Example 2: -●-, Comparative Example 4: - - ● - -, Comparative Example 5: - -▲- -, Comparative Example 6: - - ◆ - -; common to Figures 6 to 8). The change over time in the strength at break of a cross-linked acrylic rubber product at 190°C is diagrammed. The change over time in the elongation at break of a cross-linked acrylic rubber product at 190°C is diagrammed. 1 is a diagram showing the change over time in the 100% modulus of a cross-linked acrylic rubber product at 190°C (Example 3: -●-, Comparative Example 7: - - ● - -, Comparative Example 8: - -▲- -, Comparative Example 9: - - ◆ - -; common to Figures 9 to 11). This is a diagram showing the change over time in the strength at break of a cross-linked acrylic rubber product at 190°C. This is a diagram showing the change over time in the elongation at break of a cross-linked acrylic rubber product at 190°C. This is a diagram showing the change over time in the 100% modulus of a cross-linked acrylic rubber product at 190°C (Example 4: -●-, Comparative Example 10: - - ● - -, Comparative Example 11: - -▲- -, Comparative Example 12: - - ◆ - -; common to Figures 12 to 14). This is a diagram showing the change over time in the strength at break of a cross-linked acrylic rubber product at 190°C.This is a diagram showing the change over time in the elongation at break of a cross-linked acrylic rubber at 190°C. The percentage change in elongation at break (black bars) after a combined test consisting of toluene immersion (room temperature, 168 hours) and air heating (190°C, 300 hours) is compared with the percentage change in elongation at break (white bars) after an air heating aging test (190°C, 300 hours).

[0028] The crosslinkable acrylic rubber composition of the present invention comprises: (A) a compound represented by the general formula [I] (where R 1 is a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms, and R 2 (B) a copolymerizable antioxidant represented by the general formula [II]: (A) is a hydrogen atom or a methyl group, and (B) is a direct bond, an oxygen atom, or a sulfur atom; an acrylic elastomer copolymer composed of an alkyl (meth)acrylate monomer and / or an alkoxyalkyl (meth)acrylate monomer and an α,β-unsaturated carboxylic acid monomer; and (C) a phenothiazine-based antioxidant represented by the general formula [II]: [where R 3 represents a hydrogen atom, a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms, an aralkyl group having 7 to 20 carbon atoms, or a group represented by the following general formula [III]: (where R 5 is a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms), and R 4 is an aralkyl group having 7 to 20 carbon atoms), (C) a polyamine crosslinking agent, and (D) a crosslinking accelerator. Here, (meth)acrylate refers to acrylate or methacrylate.

[0029] The copolymerizable antioxidant represented by general formula [I] used in the acrylic elastomer copolymer (A) can be easily produced from phenothiazine, phenoxazine, carbazole, etc. An example of the production method is shown below. After N-alkylation in the first step, the aromatic ring is formylated or acetylated, and then the carbonyl group is converted to an olefin, thereby producing the desired copolymerizable antioxidant.

[0030] Specific examples of copolymerizable antioxidants include: etc.

[0031] In copolymerizing the copolymerizable antioxidant with the polymerizable unsaturated monomer, the copolymerizable antioxidant [I] is used in a ratio of about 0.05 to 5 parts by weight, preferably about 0.1 to 3 parts by weight, per 100 parts by weight of the alkyl (meth)acrylate and / or alkoxyalkyl (meth)acrylate monomer. If it is used in a ratio less than this, a sufficient antiaging effect cannot be expected, while if it is used in a ratio greater than this, no improvement in the antiaging effect can be expected, and it is uneconomical.

[0032] As the alkyl(meth)acrylate monomer and / or alkoxyalkyl(meth)acrylate monomer constituting the acrylic elastomer copolymer of the present invention, at least one (meth)acrylate selected from alkyl(meth)acrylates having an alkyl group with 1 to 8 carbon atoms, aralkyl(meth)acrylates having an aralkyl group with 7 to 20 carbon atoms, and alkoxyalkyl(meth)acrylates having an alkoxyalkyl group with 2 to 8 carbon atoms is used.

[0033] Examples of alkyl (meth)acrylates that can be used include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, and cyclohexyl (meth)acrylate. Two or more of these can be used in combination, and preferably, two types of alkyl acrylates, ethyl acrylate and butyl acrylate, are used.

[0034] As the aralkyl(meth)acrylate, for example, benzyl(meth)acrylate is used.

[0035] Examples of alkoxyalkyl (meth)acrylates that can be used include methoxymethyl (meth)acrylate, methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, n-butoxyethyl (meth)acrylate, ethoxypropyl (meth)acrylate, methoxyethoxyethyl (meth)acrylate, and ethoxyethoxyethyl (meth)acrylate.

[0036] The α,β-unsaturated carboxylic acid monomer constituting the component (A) acrylic elastomer copolymer may be a monobasic α,β-unsaturated carboxylic acid, a dibasic α,β-unsaturated carboxylic acid, or a dibasic α,β-unsaturated carboxylic acid monoalkyl ester.

[0037] Examples of the monobasic α,β-unsaturated carboxylic acid include acrylic acid and methacrylic acid.

[0038] Examples of the dibasic α,β-unsaturated carboxylic acid include maleic acid, fumaric acid, itaconic acid, and citraconic acid.

[0039] Examples of dibasic α,β-unsaturated carboxylic acid monoalkyl esters include monoalkyl esters of maleic acid, fumaric acid, itaconic acid, and citraconic acid. Specific examples include monomethyl maleate, monoethyl maleate, mono-n-propyl maleate, monoisopropyl maleate, mono-n-butyl maleate, monoisobutyl maleate, mono-n-hexyl maleate, monocyclohexyl maleate, monomethyl fumarate, monoethyl fumarate, mono-n-propyl fumarate, monoisopropyl fumarate, mono-n-butyl fumarate, monoisobutyl fumarate, mono-n-hexyl fumarate, and monocyclohexyl fumarate.

[0040] The crosslinking site monomer in the acrylic elastomer copolymer (A) is copolymerized in a proportion of 0.1 to 5% by weight, preferably 0.5 to 3% by weight.

[0041] In addition to the main component of the acrylic elastomer copolymer (A), other polymerizable unsaturated monomers may be used as needed.

[0042] Examples of the polymerizable unsaturated monomer include styrene, α-methylstyrene, 3-methylstyrene, 4-methylstyrene, 1-vinylnaphthalene, 2-vinylnaphthalene, acrylonitrile, methacrylonitrile, acrylic acid amide, vinyl acetate, methyl vinyl ether, ethyl vinyl ether, ethylene, propylene, piperylene, butadiene, isoprene, chloroprene, cyclopentadiene, vinyl chloride, and vinylidene chloride.

[0043] The acrylic elastomer copolymer (A) is produced by a common copolymerization method for acrylic rubber. The copolymerization reaction can be carried out by any method, such as emulsion polymerization, suspension polymerization, solution polymerization, or bulk polymerization, but emulsion polymerization or suspension polymerization is preferred, and the reaction is carried out at a temperature of about -10 to 100°C, preferably about 5 to 80°C.

[0044] As the polymerization initiator for the reaction, organic peroxides or hydroperoxides such as benzoyl peroxide, dicumyl peroxide, tert-butyl hydroperoxide, cumyl hydroperoxide, and p-methylene hydroperoxide, diazo compounds such as azobisisobutyronitrile and azobisisobutylamidine, and peroxide salts such as ammonium salts typified by ammonium persulfate, sodium salts, and potassium salts may be used alone or as redox initiators.

[0045] A particularly preferred emulsifier for use in emulsion polymerization is an aqueous solution of an anionic or nonionic surfactant, the pH of which is adjusted with an acid or base as necessary, and which is buffered with an inorganic salt.

[0046] The polymerization reaction is continued until the conversion rate of the monomer mixture reaches 90% or more. The resulting aqueous latex is coagulated by a salt-acid coagulation method, a method using salts such as calcium chloride, magnesium sulfate, sodium sulfate, or ammonium sulfate, a method using boron compounds such as boric acid or borax, a thermal coagulation method, or a freeze coagulation method, and the resulting copolymer is thoroughly washed with water and dried. This acrylic rubber has a Mooney viscosity (PML) of about 5 to 100, preferably about 20 to 80. 1+4 (100°C).

[0047] The acrylic elastomer copolymer (A) is a copolymer of 0.1 to 5% by weight of a copolymerizable antioxidant represented by general formula [I], 90 to 99.8% by weight of an alkyl (meth)acrylate and / or alkoxyalkyl (meth)acrylate monomer, and 0.1 to 5% by weight of an α,β-unsaturated carboxylic acid monomer, preferably 0.3 to 3% by weight of a copolymerizable antioxidant represented by general formula [I], 94 to 99.2% by weight of an alkyl (meth)acrylate and / or alkoxyalkyl (meth)acrylate monomer, and 0.5 to 3% by weight of a crosslinking site monomer, and preferably an acrylic elastomer copolymer composed of a copolymerizable antioxidant represented by general formula [I], an alkyl acrylate monomer, and an α,β-unsaturated carboxylic acid monomer is used.

[0048] As component (B), which is a constituent of the composition of the present invention, a phenothiazine-based antioxidant represented by general formula [II] is used. [where R 3 represents a hydrogen atom, a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms, an aralkyl group having 7 to 20 carbon atoms, or a group represented by the following general formula [III]: (where R 5 is a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms), and R 4 is an aralkyl group having 7 to 20 carbon atoms.

[0049] R 3Specific examples of when is an aliphatic hydrocarbon group having 1 to 20 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, an n-undecyl group, an n-pentadecyl group, an n-heptadecyl group, an isopropyl group, a 2-butyl group, a 2-pentyl group, a 3-pentyl group, a 2-hexyl group, a 3-hexyl group, a 2-heptyl group, a 3-heptyl group, a 4-heptyl group, a 2-octyl group, a 3-octyl group, a 4 ... Examples thereof include a butyl group, a 1,1-dimethyl-1-propyl group, a 1,1-dimethyl-1-butyl group, a 1,1-dimethyl-1-pentyl group, a 1,1-dimethyl-1-hexyl group, a 3-methyl-3-pentyl group, a 3-ethyl-3-pentyl group, a 3-methyl-3-hexyl group, a 2-ethylhexyl group, a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a 1-methyl-1-cyclopentyl group, a 1-methyl-1-cyclohexyl group, and a 1-adamantyl group.

[0050] R 3 Specific examples of when is an aralkyl group having 7 to 20 carbon atoms include a benzyl group, an α-methylbenzyl group, and a 9-fluorenylmethyl group.

[0051] R 5is a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms. Examples of the aliphatic hydrocarbon group having 1 to 20 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, an n-undecyl group, an n-pentadecyl group, an n-heptadecyl group, an isopropyl group, a 2-butyl group, a 2-pentyl group, a 3-pentyl group, a 2-hexyl group, a 3-hexyl group, a 2-heptyl group, a 3-heptyl group, a 4-heptyl group, a 2-octyl group, a 3-octyl group, a 4-octyl group, and a tert-butyl group. , 1,1-dimethyl-1-propyl group, 1,1-dimethyl-1-butyl group, 1,1-dimethyl-1-pentyl group, 1,1-dimethyl-1-hexyl group, 3-methyl-3-pentyl group, 3-ethyl-3-pentyl group, 3-methyl-3-hexyl group, 2-ethylhexyl group, cyclopropyl group, cyclobutyl group, cyclopentyl group, cyclohexyl group, cycloheptyl group, 1-methyl-1-cyclopentyl group, 1-methyl-1-cyclohexyl group, and 1-adamantyl group.

[0052] Particularly preferred are monovalent aliphatic hydrocarbon groups having 4 to 20 carbon atoms in which the carbon at the α-position relative to the carbonyl group is a tertiary carbon, and preferred examples thereof include tert-butyl, 1,1-dimethylpropyl, 1,1-dimethyl-1-butyl, 1,1-dimethyl-1-pentyl, 1,1-dimethyl-1-hexyl, 3-methyl-3-pentyl, 3-ethyl-3-pentyl, 3-methyl-3-hexyl, 2-ethylhexyl, 1-methyl-1-cyclopentyl, 1-methyl-1-cyclohexyl, and 1-adamantyl.

[0053] R 4 Examples of the aralkyl group represented by the formula (I) include a benzyl group, an α-methylbenzyl group, and an α,α-dimethylbenzyl group, with an α,α-dimethylbenzyl group being particularly preferred.

[0054] R 3A phenothiazine-based antioxidant in which is a hydrogen atom can be produced by the method described in Patent Document 6. For example, phenothiazine is reacted with α-methylstyrene in the presence of an acidic catalyst to form 3,7-bis(α,α-dimethylbenzyl)-10H-phenothiazine (hereinafter abbreviated as CD-S), and then the sulfur atom is oxidized with an oxidizing agent to produce 3,7-bis(α,α-dimethylbenzyl)-10H-phenothiazine-5,5-dioxide (hereinafter abbreviated as CD-SO2).

[0055] R 3 In the case of a phenothiazine antioxidant in which is an aliphatic hydrocarbon group having 1 to 20 carbon atoms, the desired phenothiazine antioxidant can be produced by treating CD-S with a base, followed by N-alkylation with a halide of an aliphatic hydrocarbon having 1 to 20 carbon atoms, and then oxidizing the sulfur atom. Alternatively, CD-SO2 obtained in Patent Document 6 may be treated with a base, followed by reaction with a halide of an aliphatic hydrocarbon having 1 to 20 carbon atoms.

[0056] R 3 When is an acyl group represented by general formula [III], it can be produced by the method described in Patent Document 12. Specifically, the desired phenothiazine antioxidant can be produced by N-acylating CD-S with an acyl halide in the presence of a basic organic compound or a basic inorganic compound, and then oxidizing the sulfur atom.

[0057] It can also be produced by N-acylation from CD-SO2 using a similar method.

[0058] Specific examples of the phenothiazine antioxidant represented by the general formula [III] include 3,7-bis(α,α-dimethylbenzyl)-10H-phenothiazine-5,5-dioxide, 10-methyl-3,7-bis(α,α-dimethylbenzyl)-10H-phenothiazine-5,5-dioxide, 10-n-propyl-3,7-bis(α,α-dimethylbenzyl)-10H-phenothiazine-5,5-dioxide, 10-isopropyl-3,7-bis(α,α-dimethylbenzyl)-10H-phenothiazine-5,5-dioxide, 10-benzyl-3,7-bis(α,α-dimethylbenzyl)-10H-phenothiazine-5,5-dioxide, Examples thereof include 10-pivaloyl-3,7-bis(α,α-dimethylbenzyl)-10H-phenothiazine-5,5-dioxide, 10-(2,2-dimethylbutanoyl)-3,7-bis(α,α-dimethylbenzyl)-10H-phenothiazine-5,5-dioxide, and 10-(1-adamantanecarbonyl)-3,7-bis(α,α-dimethylbenzyl)-10H-phenothiazine-5,5-dioxide.

[0059] The phenothiazine antioxidant (B) is used in an amount of about 0.01 to 5 parts by weight, preferably about 0.1 to 5 parts by weight, per 100 parts by weight of the acrylic elastomer copolymer (A). If the amount of antioxidant is less than this amount, the crosslinked acrylic rubber will suffer a significant decrease in mechanical properties due to thermo-oxidative degradation. In particular, it will be difficult to suppress significant hardening degradation in the later stages of thermo-oxidative degradation. On the other hand, if the amount is greater than this amount, not only will it promote softening degradation in the early stages of thermo-oxidative degradation, but it will not be expected to have any further effect in suppressing hardening degradation in the later stages of thermo-oxidative degradation, making it uneconomical.

[0060] As the polyamine crosslinking agent (C), an aliphatic polyamine compound, a carbonate of an aliphatic polyamine compound, an aliphatic polyamine compound in which the amino group is protected with an organic group, an aromatic polyamine compound, etc. can be used.

[0061] Examples of aliphatic polyamine compounds include hexamethylenediamine. Examples of carbonates of aliphatic polyamine compounds include hexamethylenediamine carbamate. Examples of aliphatic polyamines in which amino groups are protected with organic groups include N,N'-dicinnamylidene-1,6-hexanediamine and the compounds disclosed in Patent Document 11.

[0062] Examples of aromatic polyvalent amine compounds include 4,4'-methylenedianiline, m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenyl ether, 4,4'-bis(4-aminophenoxy)biphenyl, m-xylylenediamine, p-xylylenediamine, 1,3,5-benzenetriamine, 4,4'-(m-phenylenediisopropylidene)dianiline, 4,4'-(p-phenylenediisopropylidene)dianiline, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, and 4,4'-diaminobenzanilide.

[0063] The polyamine compounds listed above can be used alone or in combination of two or more, and hexamethylenediamine carbamate, 4,4'-diaminodiphenyl ether, and 2,2-bis[4-(4-aminophenoxy)phenyl]propane are preferred.

[0064] The amount of the crosslinking agent added is adjusted appropriately depending on the desired crosslinking rate, mechanical strength of the crosslinked product, resistance to compression set and resistance to thermal oxidative degradation.

[0065] The polyamine crosslinking agent (C) is used in an amount of about 0.01 to 5 parts by weight, preferably about 0.05 to 3 parts by weight, per 100 parts by weight of the acrylic elastomer copolymer (A). If the amount of polyamine crosslinking agent is less than this amount, no improvement in compression set resistance can be expected. On the other hand, if more than this amount is used, the thermal oxidation degradation resistance of the acrylic rubber may be deteriorated.

[0066] Examples of the crosslinking accelerator (D) include crosslinking accelerators such as guanidine compounds, diazabicycloalkene compounds or organic acid salts thereof.

[0067] Examples of the guanidine compound include tetramethylguanidine, tetraethylguanidine, 1,3-diphenylguanidine, 1,3-di-o-tolylguanidine, etc. Preferred are 1,3-diphenylguanidine, 1,3-di-o-tolylguanidine, or a combination thereof.

[0068] The diazabicycloalkene compound is preferably 1,8-diazabicyclo[5.4.0]-7-undecene.

[0069] The organic acid salt of the diazabicycloalkene compound is preferably an organic acid salt of 1,8-diazabicyclo[5.4.0]-7-undecene.

[0070] The organic acid used for the organic acid salt of 1,8-diazabicyclo[5.4.0]-7-undecene includes an organic monobasic acid or an organic dibasic acid.

[0071] Examples of organic monobasic acids include n-hexanoic acid, n-heptanoic acid, n-octanoic acid, 2-ethylhexanoic acid, n-capric acid, n-lauric acid, p-toluenesulfonic acid, phenol, etc. Examples of organic dibasic acids include adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, terephthalic acid, orthophthalic acid, phthalic acid, etc., and monocarboxylic or dicarboxylic acids having 6 to 18 carbon atoms are preferred.

[0072] The crosslinking accelerator (D) is used in an amount of about 0.1 to 5 parts by weight, preferably about 0.3 to 3 parts by weight, per 100 parts by weight of the acrylic elastomer copolymer (A). Less than this amount of crosslinking accelerator can significantly reduce the crosslinking rate, and can also reduce the mechanical properties of the acrylic rubber after crosslinking and after heat aging. On the other hand, more than this amount can worsen the acrylic rubber's resistance to thermal oxidation degradation or compression set resistance.

[0073] The crosslinkable acrylic rubber composition of the present invention may be blended with various additives, as needed, such as fillers, processing aids, plasticizers, softeners, colorants, stabilizers, adhesion aids, release agents, electrical conductivity imparting agents, thermal conductivity imparting agents, surface non-stick agents, tackifiers, flexibility imparting agents, heat resistance improvers, flame retardants, ultraviolet absorbers, oil resistance improvers, scorch inhibitors, and lubricants.

[0074] Examples of fillers include silica such as basic silica and acidic silica; metal oxides such as zinc oxide, calcium oxide, titanium oxide and aluminum oxide; metal hydroxides such as magnesium hydroxide, aluminum hydroxide and calcium hydroxide; carbonates such as magnesium carbonate, aluminum carbonate, calcium carbonate and barium carbonate; silicates such as magnesium silicate, calcium silicate, sodium silicate and aluminum silicate; sulfates such as aluminum sulfate, calcium sulfate and barium sulfate; metal sulfides such as molybdenum disulfide, iron sulfide and copper sulfide; synthetic hydrotalcite, diatomaceous earth, asbestos, lithopone (zinc sulfide / barium sulfide), graphite, carbon black (MT carbon black, SRF carbon black, FEF carbon black, etc.), carbon fluoride, calcium fluoride, coke, quartz fine powder, zinc oxide, talc, mica powder, wollastonite, carbon fiber, aramid fiber, various whiskers, glass fiber, organic reinforcing agents, and organic fillers.

[0075] Examples of processing aids include higher fatty acids such as stearic acid, oleic acid, palmitic acid, and lauric acid; higher fatty acid salts such as sodium stearate and zinc stearate; higher fatty acid amides such as stearamide and oleamide; higher fatty acid esters such as ethyl oleate, higher aliphatic amines such as stearylamine and oleylamine; petroleum waxes such as carnauba wax and ceresin wax; polyglycols such as ethylene glycol, glycerin, and diethylene glycol; aliphatic hydrocarbons such as petrolatum and paraffin; silicone oils, silicone polymers, low-molecular-weight polyethylene, phthalate esters, phosphate esters, rosin, (halogenated) dialkylamines, (halogenated) dialkylsulfones, and surfactants.

[0076] Examples of plasticizers include epoxy resins, phthalic acid derivatives, and sebacic acid derivatives; examples of softeners include lubricating oils, process oils, coal tar, castor oil, and calcium stearate; and examples of antioxidants include phenylenediamines, phosphates, quinolines, cresols, phenols, and dithiocarbamate metal salts.

[0077] The above compounding ingredients, which are used as needed, are blended into the crosslinkable acrylic rubber composition of the present invention, which comprises acrylic rubber, a phenothiazine-based antioxidant, a crosslinking agent, and a crosslinking accelerator, and mixed using a Banbury mixer, a pressure kneader, an open roll, etc. The crosslinking of the resulting crosslinkable mixture is carried out by primary crosslinking at about 120 to 250°C for about 1 to 60 minutes, and, as needed, oven crosslinking (secondary crosslinking) at about 120 to 200°C for about 1 to 20 hours.

[0078] The present invention will now be described in detail with reference to examples, although the present invention, including its effects, is not limited to these examples.

[0079] Reference Example 1: Preparation of Compound (a) Compound (a) was produced by the following method.

[0080] [Step 1] [PTZ] → (a-1): 60.0 g (301 mmol) of phenothiazine [PTZ] and 300 ml of N,N-dimethylformamide were placed in a 1000 ml four-neck flask equipped with a magnetic stirrer, a thermometer, a dropping funnel, a nitrogen gas inlet tube, and an outlet tube. The system was cooled to below 5°C under a nitrogen atmosphere. While maintaining the system temperature below 10°C, 10.9 g (452 ​​mmol) of sodium hydride was added and the reaction was carried out for 1 hour. While maintaining the system temperature below 20°C, 51.3 g (361 mmol) of iodomethane was added dropwise, and the reaction was carried out for another 1 hour. After the reaction was completed, the reaction mixture was added to a saturated aqueous solution of sodium chloride. The precipitated colorless solid was filtered and dissolved in ethyl acetate. After washing with a saturated aqueous solution of sodium chloride, the organic layer was dried over anhydrous magnesium sulfate, and the insoluble matter was filtered off. Volatile components were distilled off from the filtrate under reduced pressure to obtain 67.8 g of a crude product (crude yield 106%). Recrystallization from ethanol gave 59.9 g of 10-methyl-10H-phenothiazine (a-1) as colorless needle crystals (yield 93%). 1 H NMR (400MHz, Acetone-d6, δ ppm): 3.39 (s, 3H, N-CH3) 6.91-6.98 (m, 4H, Ar) 7.14 (dd, J=7.6Hz, J=1.6Hz, 2H, Ar) 7.21 (td, J=7.6Hz, J=1.6Hz, 2H, Ar)

[0081] ​[Step 2] (a-1) → (a-2): 210 ml of N,N-dimethylformamide was placed in a 500 ml four-neck flask equipped with a magnetic stirrer, a dropping funnel, a thermometer, a gas inlet / outlet, and a reflux condenser. Under a nitrogen atmosphere, 129.2 g (843 mmol) of phosphoryl chloride was added dropwise while maintaining the internal temperature of the system below 10°C, and the reaction was continued for an additional 30 minutes. Next, 30 g (141 mmol) of N-methyl-10H-phenothiazine (a-1) obtained in Step 1 above was added, and the reaction was continued at 60°C for 24 hours. After the reaction was completed, the contents were poured into an aqueous sodium acetate solution and neutralized with sodium bicarbonate. The product was extracted from the resulting aqueous solution using ethyl acetate, and the organic layer was washed once with saturated aqueous sodium chloride. The organic layer was dried over anhydrous magnesium sulfate, and the insoluble matter was filtered off. The volatile components were then distilled off under reduced pressure to obtain 33.8 g (99% crude yield) of crude product as a red oil. Low-Rf components were removed from the crude product by column chromatography (Wakogel C300) using ethyl acetate as the eluent, yielding 33.6 g (98% yield) of the desired low-Rf-removed crude product as a yellow solid. Further recrystallization using 70 ml of ethyl acetate yielded 30.1 g (88% yield) of 10-methyl-10H-phenothiazine-3-carbaldehyde (a-2) as yellow crystals. 1 H NMR (400MHz, Acetone d6, δ ppm): 3.49 (s, 3H, N-CH3) 7.00-7.06 (m, 2H, Ar) 7.10 (d, J=8.4Hz, 1H, Ar) 7.15-7.19 (m, 1H, Ar) 7.22-7.28 (m, 1H, Ar) 7.61(d, J=1.6Hz, 1H, Ar) 7.75(dd, J=8.4Hz, J=1.6Hz, 1H, Ar) 9.85(s, 1H, -CHO)

[0082] ​[Step 3] (a-2) → (a): 220 ml of tetrahydrofuran was placed in a 500 ml four-neck flask equipped with a magnetic stirrer, thermometer, gas inlet tube, and gas outlet tube. The reaction vessel was cooled to below 10°C while purging with nitrogen. 8.4 g (74.9 mmol) of potassium tert-butoxide was added, followed by 26.9 g (75.3 mmol) of methyltriphenylphosphonium bromide, and the reaction was carried out for 30 minutes. 15.0 g (62.2 mmol) of compound (a-2) was added to the reaction mixture and the reaction was carried out for 2 hours at 10-30°C. The resulting reaction mixture was added to a saturated aqueous sodium chloride solution, and the product was extracted with dichloromethane. After drying over anhydrous magnesium sulfate, insoluble matter was filtered off, and the volatile components were removed from the filtrate by distillation under reduced pressure, yielding 35.1 g of residue. The residue was subjected to column chromatography (carrier: Wakogel C300) using dichloromethane as an eluent to remove triphenylphosphine oxide, and then recrystallized from ethanol to obtain 8.7 g (yield 58%) of compound (a) as a pale yellow solid. 1 H NMR (400 MHz, CDCl3, δ ppm): 3.37 (s, 3H, N-CH3), 5.14 (d, J = 10.8 Hz, 1H, CH2 = CH-Ph (trans to the phenyl group)), 5.61 (d, J = 17.6 Hz, 1H, CH2 = CH-Ph (cis to the phenyl group)), 6.59 (dd, J = 10.8 Hz, 17.6 Hz, 1H, CH2 = CH-Ph), 6.75 (d, J = 8.4 Hz, 1H, Ar), 6.81 (d, J = 9.2 Hz, 1H, Ar), 6.92 (td, J = 7.6 Hz, 1.2 Hz, 1H, Ar), 7.11-7.23 (m, 4H, Ar).

[0083] Reference Example 2 Preparation of 10-pivaloyl-3,7-bis(α,α-dimethylbenzyl)-10H-phenothiazine-5,5-dioxide [CD-SO2-PIV] Into a 1000 ml four-neck flask equipped with a magnetic stirrer, a thermometer, a nitrogen gas inlet and outlet, and a reflux condenser, 119.6 g (0.6 mol) of phenothiazine, 2.88 g of p-toluenesulfonic acid, and 480 ml of toluene were placed, and the mixture was heated to 80°C. After that, 141.9 g (1.2 mol) of α-methylstyrene was added, and the mixture was allowed to react for 1 hour under a nitrogen gas atmosphere.

[0084] After cooling the reaction mixture to room temperature, the toluene was distilled off under reduced pressure to obtain 265.5 g of a purple solid reaction product. This was recrystallized from 1500 ml of ethanol to obtain 179 g (68% yield) of crude 3,7-bis(α,α-dimethylbenzyl)-10H-phenothiazine [CD-S] as light reddish-purple crystals. This crude CD-S was further recrystallized from ethanol to obtain 161 g of purified CD-S as colorless flake crystals.

[0085] A 500 mL three-neck flask equipped with a magnetic stirrer, thermometer, and reflux condenser was charged with 68.7 g (158 mmol) of crude CD-S, 24.8 g (206 mmol) of pivaloyl chloride, and 60 g of pyridine, in that order, and the mixture was reacted at 120°C for 1.5 hours. The pyridine was removed from the resulting reaction mixture by distillation under reduced pressure, and the residue was then dissolved in 300 mL of dichloromethane. The organic layer was washed three times with 300 mL of saturated aqueous sodium chloride solution and dried over anhydrous magnesium sulfate. After filtering the magnesium sulfate, the volatile components were removed from the filtrate by distillation under reduced pressure, yielding 81.7 g of a highly viscous red liquid.

[0086] This highly viscous liquid was dissolved in 250 ml of toluene and placed in a 1000 ml three-necked flask equipped with a magnetic stirrer, a thermometer, and a reflux condenser. 80 g of acetic acid and 107 g of 30% hydrogen peroxide were then added, and the mixture was allowed to react at 100°C for 2 hours.

[0087] After cooling to room temperature, the upper toluene layer was removed and the volatiles were distilled off under reduced pressure. The resulting pale red solid (89 g) was recrystallized from a mixed solvent of ethanol and toluene (volume ratio 9:1) to obtain 70.3 g of CD-SO2-PIV as colorless needles (81% yield based on CD-S).1 H NMR (300MHz, CDCl3, δ ppm): 1.22 (s, 9H, -C(CH3)3) 1.71 (s, 12H, -C(CH3)2-) 7.19~7.30 (m, 12H) 7.42 (d, J=9.0Hz, 2H) 8.03 (d, J=1.8Hz, 2H)

[0088] Reference Example 3 Preparation of 3,7-bis(α,α-dimethylbenzyl)-10H-phenothiazine-5,5-dioxide [CD-SO2] 24.9 g (0.125 mol) of phenothiazine, 0.6 g of p-toluenesulfonic acid, and 115 ml of toluene were placed in a 500 ml four-neck flask equipped with a magnetic stirrer, a thermometer, a nitrogen gas inlet and outlet, and a reflux condenser. The mixture was heated to 80°C, and then 29.5 g (0.25 mol) of α-methylstyrene was added and reacted for 1 hour under a nitrogen gas atmosphere.

[0089] Next, 30 g of acetic acid was added to the reaction mixture, followed by the addition of 42.5 g of 30% aqueous hydrogen peroxide in five portions, and the reaction was continued at 80°C for another 2 hours. The contents were cooled to room temperature and allowed to stand, after which the upper toluene layer was poured into 500 ml of methanol. After standing overnight at room temperature, 42.5 g (72% yield) of crude CD-SO2 was obtained as pale yellow crystals. This was recrystallized from ethanol to obtain 38 g (65% yield) of CD-SO2 as pale yellow needle-like crystals.

[0090] Reference Example 4 [Production of Acrylic Elastomer Copolymer A] A separable flask equipped with a thermometer, a stirrer, a nitrogen gas inlet tube, and a Dimroth condenser was charged with the following monomer mixture: water 187 parts by weight, sodium lauryl sulfate 2 parts by weight, polyoxyethylene lauryl ether 2 parts by weight, ethyl acrylate [EA] 97.4 parts by weight, mono-n-butyl fumarate [MBF] 1.6 parts by weight, and compound (a) from Reference Example 1 1.0 parts by weight. The system was then purged with nitrogen gas to thoroughly remove oxygen from the system, and then 0.008 parts by weight of sodium formaldehyde sulfoxylate (Rongalite, a product of Fujifilm Wako Pure Chemical Industries, Ltd.) and 0.0047 parts by weight of tert-butyl hydroperoxide (Perbutyl H69, a product of NOF Corp.) were added to initiate the polymerization reaction at room temperature and continued until the polymerization conversion rate reached 90% or more. The obtained aqueous latex was coagulated with a 10% by weight aqueous solution of sodium sulfate, then washed with water and dried to obtain acrylic rubber A. The Mooney viscosity PML of the obtained acrylic rubber elastomer copolymer A was 1+4 (100℃) was 31.

[0091] Its mole fraction composition is: lThe composition was determined from H-NMR (400 MHz, Acetone d6, δ ppm) using the following equation: Compound (a): 0.41 mol %, EA + MBF: 99.59 mol %. α: Integrated value of signals from 6.5 to 7.5 ppm β: Integrated value of signals from 3.2 to 5.0 ppm Compound (a) (mol %) = 200 × α / (2α + 7β) EA + MBF (mol %) = 100 - Compound (a) The approximate weight fraction composition was determined from the following equation: Compound (a): 1.0 wt %, EA + MBF: 99.0 wt %. Compound (a) (wt%) = (Compound (a) (mol%) × 239.34 × 100) / [Compound (a) (mol%) × 239.34 + (EA + MBF (mol%)) × 100.8)] EA + MBF (wt%) = 100 - Compound (a) (wt%)

[0092] Comparative Example 1: A copolymerization reaction was carried out in the same manner as in Reference Example 4, except that the following monomer mixture was used, to obtain an acrylic rubber B. The Mooney viscosity PML of the obtained acrylic elastomer copolymer B was l+4 (100°C) was 32. Charged monomer mixture: Ethyl acrylate (EA) 98.4 parts by weight Mono-n-butyl fumarate (MBF) 1.6 parts by weight

[0093] Reference Example 5 [Production of Acrylic Elastomer Copolymer C] A copolymerization reaction was carried out in the same manner as in Reference Example 4, except that the following charged monomer mixture was used, to obtain an acrylic rubber C. Mooney viscosity PML of the obtained acrylic elastomer copolymer C l+4 (100°C) was 30. Ethyl acrylate [EA] 97.9 parts by weight Mono-n-butyl fumarate [MBF] 1.6 parts by weight Compound (a) of Reference Example 1 0.5 parts by weight

[0094] The molar fraction composition was calculated from the formula in Reference Example 4 as follows: Compound (a): 0.20 mol %, EA + MBF: 99.80 mol %. The approximate weight fraction composition was calculated from the formula in Reference Example 4 as follows: Compound (a): 0.5 wt %, EA + MBF: 99.5 wt %.

[0095] Reference Example 6 [Production of Acrylic Elastomer Copolymer D] A copolymerization reaction was carried out in the same manner as in Reference Example 4, except that the following charged monomer mixture was used, to obtain an acrylic rubber D. The Mooney viscosity PML of the obtained acrylic elastomer copolymer D was l+4 (100°C) was 26. Ethyl acrylate [EA] 57.7 parts by weight n-Butyl acrylate [BA] 40.0 parts by weight Mono-n-butyl fumarate [MBF] 1.6 parts by weight Compound (a) of Reference Example 1 0.7 parts by weight

[0096] The molar fraction composition was calculated using the formula in Reference Example 4, and was found to be: Compound (a): 0.31 mol %, EA + BA + MBF: 99.69 mol %. The approximate weight fraction composition was calculated using the following formula: Compound (a): 0.7 wt %, EA + BA + MBF: 99.3 wt %. Compound (a) (wt %) = (Compound (a) (mol %) × 239.34 × 100) / [Compound (a) (mol %) × 239.34 + (EA + BA + MBF (mol %)) × 110.6)] EA + BA + MBF (wt %) = 100 - Compound (a) (wt %)

[0097] Comparative Example 2: A copolymerization reaction was carried out in the same manner as in Reference Example 4, except that the following monomer mixture was used, to obtain an acrylic rubber E. The Mooney viscosity PML of the obtained acrylic elastomer copolymer E was l+4The temperature (100°C) was 26. Charged monomer mixture Ethyl acrylate [EA] 58.4 parts by weight n-butyl acrylate [BA] 40.0 parts by weight Mono-n-butyl fumarate [MBF] 1.6 parts by weight

[0098] Reference Example 7 [Production of Acrylic Elastomer Copolymer F] A copolymerization reaction was carried out in the same manner as in Reference Example 4, except that the following charged monomer mixture was used, to obtain an acrylic rubber F. Mooney viscosity PML of the obtained acrylic elastomer copolymer F l+4 The viscosity (100°C) was 24. Ethyl acrylate [EA] 57.9 parts by weight n-butyl acrylate [BA] 40.0 parts by weight Mono-n-butyl fumarate [MBF] 1.6 parts by weight Compound (a) of Reference Example 1 0.5 parts by weight The molar fraction composition, calculated from the formula in Reference Example 4, was Compound (a): 0.24 mol%, EA + BA + MBF: 99.76 mol%. The approximate weight fraction composition, calculated from the formula in Reference Example 6, was Compound (a): 0.5 wt%, EA + BA + MBF: 99.5 wt%.

[0099] Example 1 Acrylic elastomer copolymer A 100 parts by weight SRF carbon black (Tokai Carbon's Seast GS) 60 parts by weight Stearic acid (Miyoshi Oil & Fats' TST) 1 part by weight Polyoxyethylene stearyl ether phosphate 0.5 parts by weight (Toho Chemical Industry's Phosphanol RL-210) Crosslinking accelerator (Safic-Alcan's Vulcofac ACT55) 1 part by weight Hexamethylenediamine carbamate (Unimatec's Cheminox AC6F) 0.6 parts by weight CD-SO2-PIV 1 part by weight Of the above components, acrylic elastomer copolymer A, SRF carbon black, stearic acid, and polyoxyethylene stearyl ether phosphate were mixed in a Banbury mixer. The resulting mixture and the remaining components were mixed using an open roll mill to obtain a crosslinkable acrylic rubber composition.

[0100] This was subjected to primary crosslinking at 180°C for 8 minutes using a 100-ton press molding machine, and then further oven crosslinking at 175°C for 4 hours, yielding a sheet-like crosslinked product with a thickness of approximately 2 mm and a cylindrical crosslinked product with a diameter of approximately 29 mm and a height of approximately 12.5 mm.

[0101] The crosslinking characteristics of the acrylic rubber composition and the physical properties of the crosslinked product were measured as follows: Mooney scorch test: Conforms to JIS K6300-1 (125°C), which corresponds to ISO 289-1. A Toyo Seiki Seisakusho Mooney Viscometer AM-3 was used to measure the minimum Mooney viscosity (ML min) and scorch time (t5). Crosslinking test: Conforms to JIS K6300-2 (180°C, 12 minutes), which corresponds to ISO 6502. A Toyo Seiki Seisakusho Rotorless Rheometer RLR-3 was used to measure the ML, MH, tc(10), and tc(90). ML: Minimum torque MH: Maximum torque tc(10): Time required for the crosslinking torque to reach ML + (MH - ML) x 0.1 tc(90): Time required for the crosslinking torque to reach ML + (MH - ML) x 0.9. Normal physical properties: Post-cured sheets were measured in accordance with JIS K6251, which corresponds to ISO 37, and JIS K6253, which corresponds to ISO 37. Air heating aging test: Post-cured sheets were measured in accordance with JIS K6257, which corresponds to ISO 188 (190°C: 100 hours, 200 hours, 300 hours, 400 hours, 500 hours, 600 hours). Oil immersion test: After immersion in oil (IRM903 oil) at 150°C for 168 hours in accordance with JIS K6258, which corresponds to ISO 1817, the rate of change from normal physical properties before oil immersion and the volume swelling ratio were determined. Air heating aging test - oil immersion - air heating aging combined test: An air heating aging test was conducted at 175°C for 150 hours in accordance with JIS K6257, which corresponds to ISO 188, and the rate of change from normal physical properties before oil immersion and the volume swelling ratio were determined. In accordance with JIS K6258, an oil (IRM903 oil) immersion test was conducted at 150°C for 168 hours, followed by an air heating aging test at 190°C for 300 hours in accordance with JIS K6257, which corresponds to ISO 188. After this, the percentage change in each physical property from the normal state was determined. Compression set test: In accordance with JIS K6262, which corresponds to ISO 815-1 (175°C: 70 hours, 500 hours).

[0102] Comparative Example 1 In Example 1, CD-SO2-PIV was not used.

[0103] Comparative Example 2 In Example 1, acrylic elastomer copolymer B was used in place of acrylic elastomer copolymer A.

[0104] Comparative Example 3 In Comparative Example 2, 1 part by weight of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine (Nocrac CD, a product of Ouchi Shinko Chemical Industry Co., Ltd.) was used in place of CD-SO2-PIV.

[0105] Example 2 In Example 1, the following components were used for the crosslinkable acrylic rubber composition. Acrylic elastomer copolymer C 100 parts by weight SRF carbon black (Seast GS) 70 parts by weight Stearic acid (TST) 1 part by weight Polyoxyethylene stearyl ether phosphate 0.5 parts by weight (Phosphanol RL-210) Crosslinking accelerator (Vulcofac ACT55) 1 part by weight 2,2-bis[4-(4-aminophenoxy)phenyl]propane 1.2 parts by weight (Tokyo Chemical Industry Co., Ltd. CD-SO2 1 part by weight)

[0106] Comparative Example 4 In Example 2, CD-SO2 was not used.

[0107] Comparative Example 5 In Example 2, the acrylic elastomer copolymer B was used in place of the acrylic elastomer copolymer C.

[0108] Comparative Example 6 In Comparative Example 5, 1 part by weight of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine (Nocrac CD) was used in place of CD-SO2.

[0109] Example 3 In Example 1, the following components were used for the crosslinkable acrylic rubber composition: Acrylic elastomer copolymer D 100 parts by weight SRF carbon black (Seast GS) 70 parts by weight Stearic acid (TST) 1 part by weight Polyoxyethylene stearyl ether phosphate 0.5 parts by weight (Phosphanol RL-210) Stearylamine (Farmin 80S) 1 part by weight Crosslinking accelerator (Vulcofac ACT55) 1 part by weight Hexamethylenediamine carbamate (ChemiNox AC6F) 0.6 parts by weight CD-SO2 1 part by weight

[0110] Comparative Example 7 In Example 3, CD-SO2 was not used.

[0111] Comparative Example 8 In Example 3, acrylic elastomer copolymer E was used in place of acrylic elastomer copolymer D.

[0112] Comparative Example 9 In Comparative Example 8, 1 part by weight of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine (Nocrac CD) was used in place of CD-SO2.

[0113] Example 4 In Example 1, the following components were used as the crosslinkable acrylic rubber composition, and the crosslinked acrylic rubber composition was subjected to a combined toluene immersion / air heating aging test. Acrylic elastomer copolymer F 100 parts by weight SRF carbon black (Seast GS) 70 parts by weight Stearic acid (TST) 1 part by weight Polyoxyethylene stearyl ether phosphate 0.5 parts by weight (Phosphanol RL-210) Crosslinking accelerator (Vulcofac ACT55) 1 part by weight 2,2-bis[4-(4-aminophenoxy)phenyl]propane 1.2 parts by weight (Tokyo Chemical Industry Co., Ltd.) CD-SO2 1 part by weight Toluene immersion - air heating aging combined test: In accordance with JIS K6258, which corresponds to ISO 1817, a toluene immersion test was carried out at room temperature for 168 hours, after which the toluene was removed from the test piece by air drying, and a further air heating aging test was carried out at 190°C for 300 hours in accordance with JIS K6257, which corresponds to ISO 188.

[0114] Comparative Example 10 In Example 4, CD-SO2 was not used.

[0115] Comparative Example 11 In Example 4, acrylic elastomer copolymer E was used in place of acrylic elastomer copolymer F.

[0116] Comparative Example 12 In Comparative Example 11, 1 part by weight of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine (Nocrac CD) was used in place of CD-SO2.

[0117] The results obtained in Examples 1 to 4 and Comparative Examples 1 to 12 are shown in the following Tables 1 to 4 and Figures 1 to 15. Table 1 Example Comparative Example Measurement results 1 1 2 3 Mooney scorch test (125°C) ML min (pts) 65 65 61 64 t5 (min) 1.6 1.5 2.8 2.4 Crosslinking test (180°C) tc(10) (min) 0.53 0.52 0.50 0.50 tc(90) (min) 5.34 5.43 4.76 4.87 ML (N・m) 0.23 0.24 0.21 0.23 MH (N・m) 0.94 0.96 0.94 0.97 Physical properties at room temperature (post cure) Hardness (Duro A) 65 65 62 63 100% modulus (MPa) 4.9 5.2 4.3 4.4 Strength at break (MPa) 17.0 17.1 16.1 15.8 Elongation at break (%) 260 260 240 260 Heat aging test (190°C, 100 hours) Change in hardness (Duro A) +12 +9 +4 +0 100% change in modulus (%) +65 +62 -19 -36 Change in strength at break (%) -12 -8 -27 -35 Change in elongation at break (%) -33 -30 +25 +28 Heat aging test (190°C, 200 hours) Change in hardness (Duro A) +11 +10 +5 +0 100% change in modulus (%) +51+37 -37 -52 Change in strength at break (%) -21 -23 -43 -60 Change in elongation at break (%) -28 -29 +46 +31 Heat aging test (190℃, 300 hours) Change in hardness (Duro A) +13 +13 +6 +3 Change in 100% modulus (%) +29 +17 -51 -48 Change in strength at break (%) -34 -41 -60 -70 Change in elongation at break (%) -25 -29 +52 +33 Heat aging test (190℃, 400 hours) Change in hardness (Duro A) +15 +16 +9 +15 Change in 100% modulus (%) +16 +8 -51 -25 Change in strength at break (%) -45 -59 -70 -69 Change in elongation at break +31 -56 +14 Change in strength at break (%) -53 -58 -76 -65 Change in elongation at break (%) -29 -61 +64 -51 Heat aging test (190°C, 600 hours) Change in hardness (Duro A) +19 +23 +17 +22 Change in 100% modulus (%) +4 -47 Change in strength at break (%) -60 -54 -80 -61 Change in elongation at break (%) -34 -72 +35 -77 Oil immersion test (150°C, 168 hours)Change in hardness (Duro A) -6 -6 -6 -7 Change in 100% modulus (%) -2 -6 -5 +5 Change in strength at break (%) -9 -10 -11 -6 Change in elongation at break (%) -3 -4 +1 -6 Volume swelling (%) +11 +11 +11 +10 Combined air aging-oil immersion-air aging test Change in hardness (Duro A) +17 +17 +12 +19 Change in 100% modulus (%) +24 +15 -40 +9 Change in strength at break (%) -51 -51 -65 -68 Change in elongation at break (%) -37 -39 +27 -60 Compression set test 175°C, 70 hours (%) 17 16 14 15 175°C, 500 hours (%) 34 34 27 27 Table 2 Example Comparative Example Measurement results 2 4 5 6 Mooney scorch test (125°C) ML min (pts) 62 62 63 63 t5 (min) 6.4 5.7 6.3 5.0 Crosslinking test (180°C) tc(10) (min) 1.08 1.03 1.25 1.16 tc(90) (min) 8.21 8.11 8.26 8.13 ML (N・m) 0.27 0.28 0.26 0.27 MH (N・m) 0.820.90 0.88 0.93 Physical properties at normal temperature (post cure) Hardness (Duro A) 69 70 66 66 100% modulus (MPa) 6.0 6.3 6.7 5.2 Strength at break (MPa) 16.8 17.4 16.8 16.2 Elongation at break (%) 220 230 220 230 Heat aging test (190°C, 100 hours) Change in hardness (Duro A) +12 +11 +10 +5 Change in 100% modulus (%) +15 +22 -33 -25 Change in strength at break (%) -16 -11 -29 -28 Change in elongation at break (%) -10 -14 +27 +20 Heat aging test (190°C, 200 hours) Change in hardness (Duro A) +12 +13 +9 +9 Change in 100% modulus (%) +10 +0 -42 -42 Change in strength at break (%) -26 -29 -40 -56 Change in elongation at break (%) -13 -12 +27 +28 Heat aging test (190°C, 300 hours) Change in hardness (Duro A) +12 +14 +10 +13 Change in 100% modulus (%) -10 -25 -55 -40 Change in strength at break (%) -43 -59 -58 -69 Change in elongation at break (%) -8 -10 +40 +11 Heat aging test (190°C, 400 hours) Change in hardness (Duro A) +13 +17 +13 +20 Change in 100% modulus (%) -25 -14 -58 -12Change in strength at break (%) -56 -63 -69 -67 Change in elongation at break (%) +2 -35 +50 -32 Heat aging test (190℃, 500 hours) Change in hardness (Duro A) +16 +20 +13 +24 Change in 100% modulus (%) -23 -57 Change in strength at break (%) -63 -60 -75 -60 Change in elongation at break (%) -9 -69 +32 -69 Heat aging test (190℃, 600 hours) Change in hardness (Duro A) +17 +22 +17 +27 Change in 100% modulus (%) -25 -52 Change in strength at break (%) -69 -47 -77 -43 Change in elongation at break (%) -16 -81 +14 -85 Oil immersion test (150°C, 168 hours) Change in hardness (Duro A) -3 -5 -3 -4 Change in 100% modulus (%) -5 -8 -15 +12 Change in strength at break (%) -7 -5 -7 -1 Change in elongation at break (%) +4 +7 +7 -3 Volume swelling (%) +11 +12 +11 +11 Compression set test 175°C, 70 hours (%) 24 24 22 22 175°C, 500 hours (%) 39 38 34 33 Table 3 Example Comparative Example Measurement results 3 7 89 Mooney scorch test (125°C) ML min (pts) 46 48 47 47 t5 (min) 4.9 4.0 4.2 3.6 Crosslinking test (180°C) tc(10) (min) 0.55 0.51 0.55 0.52 tc(90) (min) 6.54 6.27 6.53 6.35 ML (N・m) 0.231 0.22 0.21 0.21 MH (N・m) 0.80 0.84 0.83 0.84 Physical properties at normal condition (post cure) Hardness (Duro A) 66 65 63 62 100% modulus (MPa) 4.9 5.1 4.9 4.9 Strength at break (MPa) 13.4 14.5 12.3 12.7 Elongation at break (%) 230 240 200 220 Heat aging test (190℃, 100h) Change in hardness (Duro A) +8 +12 +7 +6 Change in 100% modulus (%) +38 +29 -20 -24 Change in strength at break (%) -13 -13 -16 -17 Change in elongation at break (%) -29 -28 +16 +14 Heat aging test (190℃, 200h) Change in hardness (Duro A) +9 +12 +5 +5 Change in 100% modulus (%) +56 +57 -27 -29 Change in strength at break (%) -10 -14 -24 -28 Change in elongation at break (%) -29 -35 +9 +6 Heat aging test (190℃, 300 hours)Change in hardness (Duro A) +10 +14 +7 +9 Change in 100% modulus (%) +33 +39 -37 -22 Change in strength at break (%) -23 -30 -37 -40 Change in elongation at break (%) -28 -37 +11 -14 Heat aging test (190°C, 400 hours) Change in hardness (Duro A) +12 +16 +10 +16 Change in 100% modulus (%) +19 +35 -39 +18 Change in strength at break (%) -34 -39 -46 -39 Change in elongation at break (%) -27 -42 +25 -36 Heat aging test (190°C, 500 hours) Change in hardness (Duro A) +11 +17 +9 +18 Change in 100% modulus (%) +17 +53 -35 +67 Change in strength at break (%) -40 -43 -51 -35 Change in elongation at break (%) -31 -54 +3 -54 Heat aging test (190℃, 600 hours) Change in hardness (Duro A) +13 +19 +12 +23 Change in 100% modulus (%) +6 -33 Change in strength at break (%) -50 -46 -55 -43 Change in elongation at break (%) -36 -67 -5 -73 Oil immersion test (150℃, 168 hours) Change in hardness (Duro A) -18 -16 -15 -15 Change in 100% modulus (%) -20 -21 -18 -14 Change in strength at break (%) -22 -22 -19 -17Change in elongation at break (%) -14 -13 -5 -14 Volume swelling (%) +28 +28 +28 +27 Compression set test 175°C, 70 hours (%) 23 22 21 21 175°C, 500 hours (%) 40 40 37 34 Table 4 Examples Comparative Examples Measurement results 4 10 11 12 Mooney scorch test (125°C) ML min (pts) 47 48 50 50 t5 (min) 7.1 7.2 7.7 8.0 Crosslinking test (180°C) tc(10) (min) 0.94 0.84 1.15 1.16 tc(90) (min) 8.13 8.04 8.34 8.25 ML (N・m) 0.21 0.21 0.20 0.19 MH (N・m) 0.70 0.74 0.69 0.68 Physical properties at normal condition (post cure) Hardness (Duro A) 66 65 66 65 100% modulus (MPa) 5.0 5.7 5.8 5.4 Strength at break (MPa) 13.7 14.6 13.0 13.4 Elongation at break (%) 200 220 190 210 Heat aging test (190℃, 100 hours) Change in hardness (Duro A) +7 +11 +4 +6 Change in 100% modulus (%) +26 +18 -31 -33 Change in strength at breakChange in hardness (Duro A) +8 +12 -2 +8 Change in 100% modulus (%) +16 +12 -38 -26 Change in strength at break (%) -25 -25 -32 -42 Change in elongation at break (%) -11 -25 +18 -1 Heat aging test (190°C, 300 hours) Change in hardness (Duro A) +10 +16 +10 +17 Change in 100% modulus (%) -4 +23 -41 +28 Change in strength at break (%) -39 -42 -45 -40 Change in elongation at break (%) -9 -40 +15 -41 Heat aging test (190℃, 400 hours) Change in hardness (Duro A) +15 +19 +13 +22 Change in 100% modulus (%) -8 -36 Change in strength at break (%) -47 -44 -53 -35 Change in elongation at break (%) -15 -60 +2 -68 Heat aging test (190℃, 500 hours) Change in hardness (Duro A) +18 +23 +16 +27 Change in 100% modulus (%) +2 -24 Change in strength at break (%) -50 -35 -56 -26 Change in elongation at break (%) -24 -74 -19 -80Heat aging test (190°C, 600 hours) Change in hardness (Duro A) +19 +26 +17 +29 Change in 100% modulus (%) +4 -14 Change in strength at break (%) -55 -30 -57 -8 Change in elongation at break (%) -33 -80 -34 -86 Toluene immersion (room temperature, 168 hours) - Air heat aging (190°C, 300 hours) Combined test Change in hardness (Duro A) +12 +14 +12 +24 Change in 100% modulus (%) +18 +32 -2 Change in strength at break (%) -35 -40 -33 -37 Change in elongation at break (%) -16 -47 -13 -29 Compression set test 175°C, 70 hours (%) 26 25 25 26 175℃, 500 hours (%) 41 41 40 39

[0118] For Example 1 and Comparative Examples 1 to 3, ΔΔEb, which indicates the degree of extraction of the antioxidant from the crosslinked product in the oil immersion test, was calculated using the following formula, and was found to be -12 for Example 1, -10 for Comparative Example 1, -25 for Comparative Example 2, and -95 for Comparative Example 3. ΔΔEb = ΔEb (change in elongation at break in combined test of air heating aging test-oil immersion test-air heating aging) - ΔEb (change in elongation at break in air heating aging test at 190°C for 300 hours)

[0119] For Example 4 and Comparative Examples 10 to 12, ΔΔEb, which indicates the degree of extraction of the antioxidant from the crosslinked product in the toluene immersion test, was calculated using the following formula, and was found to be -7 for Example 4, -7 for Comparative Example 10, -28 for Comparative Example 11, and -38 for Comparative Example 12. ΔΔEb = ΔEb (change in elongation at break in combined toluene immersion test and air heating aging test) - ΔEb (change in elongation at break in 190°C, 300-hour air heating aging test).

[0120] The above results reveal the following: (1) In the air heating aging test, it was found that the decrease in strength at break in Example 1 was suppressed compared to Comparative Examples 2 and 3. This is thought to be mainly due to the crosslinking action of the antiaging component chemically bonded to the acrylic elastomer. Similar trends are also seen in Comparative Examples 5 and 6 and Example 2, Comparative Examples 8 and 9 and Example 3, and Comparative Examples 11 and 12 and Example 4. (2) In Examples 1 to 3 (after a slight decrease in elongation at break at the beginning of the test), the elongation at break remained at a nearly constant value, and rubber elasticity was maintained for a long period of time, whereas in Comparative Examples 1, 4, and 7, the elongation at break decreased from the middle of the test, and rubber elasticity was lost. On the other hand, in Comparative Examples 2, 3, 5, 6, 8, 9, 11, and 12, a significant increase in elongation at break and a significant decrease in strength at break due to softening and degradation were observed from the beginning of the test, suggesting a decrease in the mechanical strength of the crosslinked product. (3) In the combined oil immersion test and air heating aging test, the elongation at break of Comparative Example 3 was significantly lower than that of Example 1 and Comparative Example 1. This is presumably due to the extraction of the antioxidant from the crosslinked product during the oil immersion test. Conversely, an increase in elongation at break was observed in Comparative Example 2. This is presumably due to the phenothiazine-based antioxidant being difficult to extract with oil and remaining in the rubber. This is also indicated by the small absolute values ​​of the ΔΔEb values, which indicate the degree of extraction of the antioxidant from the crosslinked product in the oil immersion test. On the other hand, in Example 1 and Comparative Example 1, the antioxidant component is chemically bonded to the acrylic elastomer copolymer, preventing extraction with oil. As a result, the decrease in elongation at break is presumably suppressed. (4) The larger the absolute value of ΔΔEb, which indicates the degree of extraction of the antioxidant from the crosslinked product in the toluene immersion test, the more antioxidant is extracted, and the lower the residual rate in the crosslinked product. Therefore, these results suggest that the antioxidant component originating from the copolymerizable aging agent (a) is not easily extracted with toluene, and most of it remains in the crosslinked product (Example 4, Comparative Example 10). Furthermore, when Example 4 is compared with Comparative Example 12, the decrease in elongation at break in Example 4 is clearly small, which can be said to be due to the effect of using the copolymerizable aging agent (a) in combination with the phenothiazine-based antioxidant CD-SO2.(5) The decrease in strength at break in Example 1 and Comparative Example 1 is smaller than that in Comparative Examples 2 and 3, which is thought to be mainly due to the crosslinking action of the antioxidant component chemically bonded to the acrylic elastomer copolymer. In Comparative Example 2, the decrease in strength at break due to softening and deterioration is significant. This is a phenomenon specific to rubber compounded with a phenothiazine-based antioxidant. (6) Rubber parts obtained by crosslinking the composition of the present invention can maintain their mechanical strength and rubber elasticity for long periods of time under severe thermal oxidative deterioration conditions or severe extraction / chemical deterioration conditions using liquid media such as oil.

Claims

1. (A) General formula [I] (where R 1 is a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms, and R 2 (B) a copolymerizable antioxidant represented by the general formula [II]: (A) is a hydrogen atom or a methyl group, and (B) is a direct bond, an oxygen atom, or a sulfur atom; an acrylic elastomer copolymer composed of an alkyl (meth)acrylate monomer and / or an alkoxyalkyl (meth)acrylate monomer and an α,β-unsaturated carboxylic acid monomer; and (C) a phenothiazine-based antioxidant represented by the general formula [II]: [where R 3 represents a hydrogen atom, a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms, an aralkyl group having 7 to 20 carbon atoms, or a group represented by the following general formula [III]: (where R 5 is a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms), and R 4 is an aralkyl group having 7 to 20 carbon atoms), (C) a polyamine crosslinking agent, and (D) a crosslinking accelerator.

2. The crosslinkable acrylic rubber composition according to claim 1, wherein A in the copolymerizable antioxidant represented by general formula [I] is a sulfur atom.

3. A crosslinkable acrylic rubber composition according to claim 1, wherein component (A) is an acrylic elastomer copolymer composed of a copolymerizable antioxidant represented by general formula [I], an alkyl acrylate monomer, and an α,β-unsaturated carboxylic acid monomer.

4. The crosslinkable acrylic rubber composition according to claim 3, wherein the alkyl acrylate monomer is ethyl acrylate and / or n-butyl acrylate.

5. A crosslinkable acrylic rubber composition according to claim 1, wherein the polyamine crosslinking agent (C) is hexamethylenediamine carbamate, 4,4'-diaminodiphenyl ether or 2,2-bis[4-(4-aminophenoxy)phenyl]propane.

6. A crosslinkable acrylic rubber composition according to claim 1, wherein the crosslinking accelerator (D) is 1,8-diazabicyclo[5.4.0]-7-undecene or an organic acid salt thereof.