Rubber composition, crosslinked product thereof, and method for producing acrylic rubber

Abstract

To achieve both water resistance and breaking tensile strength in a crosslinked product of acrylic rubber.SOLUTION: A rubber composition contains an acrylic rubber and a nonionic emulsifier, wherein more than 0 mass% and 80 mass% or less of the total mass of the nonionic emulsifier is fixed to the acrylic rubber.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a rubber composition, a crosslinked product thereof, and a method for producing an acrylic rubber.

Background Art

[0002] Acrylic rubber and its crosslinked product are excellent in physical properties such as heat resistance, oil resistance, and mechanical properties, and are therefore used as materials for, for example, hoses and seal parts in the engine room of automobiles. For example, Patent Document 1 discloses an acrylic rubber containing an alkyl acrylate and a crosslinking site monomer as monomer units, wherein the content of the nonionic emulsifier in the acrylic rubber is 0.5 to 2% by mass.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As disclosed in Patent Document 1, studies have been conducted focusing on the content of the nonionic emulsifier coexisting with the acrylic rubber. However, according to the studies of the present inventors, even when the content of the nonionic emulsifier coexisting with the acrylic rubber is the same, the water resistance and tensile strength at the time of cutting of the crosslinked product of the acrylic rubber can vary, and in some cases, the water resistance or tensile strength at the time of cutting may deteriorate.

[0005] Therefore, one aspect of the present invention aims to achieve both water resistance and tensile strength at the time of cutting of the crosslinked product of acrylic rubber.

Means for Solving the Problems

[0006] Even when simply referred to as a nonionic emulsifier coexisting with an acrylic rubber, the inventors have found that there can be a nonionic emulsifier that is fixed to the acrylic rubber and is relatively difficult to desorb, and a nonionic emulsifier that is not fixed to the acrylic rubber and is relatively easy to desorb.

[0007] And even when the same total amount of nonionic emulsifier is made to coexist with acrylic rubbers having the same monomer composition, if there is no nonionic emulsifier fixed to the acrylic rubber (only nonionic emulsifiers not fixed to the acrylic rubber are present), the tensile strength at break of the crosslinked product of the acrylic rubber decreases, while if there is more than the required amount of nonionic emulsifier fixed to the acrylic rubber, the water resistance of the crosslinked product of the acrylic rubber deteriorates. Therefore, when the same total amount of nonionic emulsifier is made to coexist with acrylic rubbers having the same monomer composition, in order to balance the water resistance and the tensile strength at break of the crosslinked product of the acrylic rubber (without reducing or deteriorating either one), it is important to keep the proportion of the nonionic emulsifier fixed to the acrylic rubber within a specific range.

[0008] The present invention includes the following aspects. [1] A rubber composition containing an acrylic rubber and a nonionic emulsifier, wherein more than 0% by mass and 80% by mass or less of the total mass of the nonionic emulsifier is fixed to the acrylic rubber. [2] The rubber composition according to [1], wherein the total mass of the nonionic emulsifier is 5 parts by mass or less with respect to 100 parts by mass of the total mass of the acrylic rubber. [3] The rubber composition according to [1] or [2], wherein the acrylic rubber contains at least one monomer unit selected from the group consisting of an alkyl acrylate, an alkyl methacrylate, and an alkoxyalkyl acrylate. [4] The rubber composition according to any one of [1] to [3], further containing a crosslinking agent. [5] A crosslinked product of the rubber composition according to any one of [1] to [4]. [6] A step of polymerizing an acrylic monomer in the presence of a nonionic emulsifier to obtain a latex of an acrylic polymer, and a step of coagulating and washing the acrylic polymer to obtain an acrylic rubber, wherein more than 0% by mass and 70% by mass or less of the total mass of the nonionic emulsifier in the latex is fixed to the acrylic polymer. A method for producing an acrylic rubber. [7] The method for producing an acrylic rubber according to [6], wherein the total mass of the nonionic emulsifier in the latex is 6 parts by mass or less with respect to 100 parts by mass of the total mass of the acrylic polymer. [8] The method for producing an acrylic rubber according to [6] or [7], wherein the acrylic rubber contains at least one monomer unit selected from the group consisting of an alkyl acrylate, an alkyl methacrylate, and an alkoxyalkyl acrylate. [Advantages of the Invention]

[0009] According to one aspect of the present invention, it is possible to achieve both water resistance and tensile strength at the time of cutting of a crosslinked product of an acrylic rubber.

[0010] According to another aspect of the present invention, the toluene-insoluble content of the acrylic rubber can be lowered. According to another aspect of the present invention, the flex fatigue resistance of a crosslinked product of an acrylic rubber can be improved. According to another aspect of the present invention, the copper corrosion resistance of a crosslinked product of an acrylic rubber can be improved. [Embodiments for Carrying Out the Invention]

[0011] One embodiment of the present invention includes a step of polymerizing an acrylic monomer in the presence of a nonionic emulsifier to obtain a latex of an acrylic polymer (hereinafter also referred to as "step S1"), and a step of coagulating and washing the acrylic polymer to obtain an acrylic rubber (hereinafter also referred to as "step S2"). A method for producing an acrylic rubber.

[0012] In step S1, for example, a polymerization initiator and a monomer mixture containing an acrylic monomer are added to a suspension of a nonionic emulsifier to polymerize the acrylic monomer. As a result, a latex in which the acrylic polymer is dispersed in water is obtained.

[0013] The acrylic monomer may contain at least one monomer selected from the group consisting of an alkyl acrylate, an alkyl methacrylate, and an alkoxyalkyl acrylate.

[0014] The alkyl acrylate is represented by the following formula (1).

Chemical formula

[0015] The alkyl group (R 1 ) in the alkyl acrylate may be linear or branched. The number of carbon atoms in the alkyl group (R 1 ) in the alkyl acrylate may be 1 or more and may be 16 or less. Specific examples of the alkyl acrylate include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-pentyl acrylate, isoamyl acrylate, n-hexyl acrylate, 2-methylpentyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, hexadecyl acrylate, 1-adamantyl acrylate, cyclohexyl acrylate, and the like. These alkyl acrylates may be used alone or in combination of two or more.

[0016] The content of the alkyl acrylate may be 40% by mass or more, 50% by mass or more, or 60% by mass or more, and may be 99% by mass or less, 95% by mass or less, or 90% by mass or less based on the total mass of the acrylic monomer.

[0017] The alkyl acrylate may include an alkyl acrylate (first alkyl acrylate) having an alkyl group with 3 or fewer carbon atoms (where R 1 is an alkyl group with 3 or fewer carbon atoms) and an alkyl acrylate (second alkyl acrylate) having an alkyl group with 4 or more carbon atoms (where R 1 is an alkyl group with 4 or more carbon atoms).

[0018] The number of carbon atoms of the alkyl group in the first alkyl acrylate may be 1 or more, 2 or less, or may be 2. The first alkyl acrylate is preferably ethyl acrylate. The number of carbon atoms of the alkyl group in the second alkyl acrylate may be 8 or less, 6 or less, or 5 or less, or may be 4. The second alkyl acrylate is preferably n-butyl acrylate.

[0019] The content of the first alkyl acrylate may be 10% by mass or more, 20% by mass or more, or 30% by mass or more, and may be 70% by mass or less, 60% by mass or less, or 50% by mass or less based on the total mass of the acrylic monomers.

[0020] The content of the second alkyl acrylate may be 20% by mass or more, 30% by mass or more, or 40% by mass or more, and may be 70% by mass or less, 60% by mass or less, or 50% by mass or less based on the total mass of the acrylic monomers.

[0021] The alkyl methacrylate is represented by the following formula (2). [Chemical formula] In the formula, R 2 represents an alkyl group.

[0022] The alkyl group (R 2) may be linear or branched. The alkyl group (R 2 ) in the alkyl methacrylate may have 1 or more carbon atoms, may have 4 or fewer carbon atoms, preferably has 2 or more or 3 or more carbon atoms, and may have 3 carbon atoms. Specific examples of the alkyl methacrylate include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, and the like. These alkyl methacrylates may be used alone or in combination of two or more. The alkyl methacrylate is preferably n-butyl methacrylate.

[0023] The content of the alkyl methacrylate (preferably an alkyl methacrylate having an alkyl group with 3 or more carbon atoms) may be 3% by mass or more, 5% by mass or more, or 7% by mass or more, and may be 40% by mass or less, 35% by mass or less, 30% by mass or less, 25% by mass or less, 20% by mass or less, 15% by mass or less, or 13% by mass or less based on the total mass of the acrylic monomer.

[0024] The alkoxyalkyl acrylate is represented by the following formula (3).

Chemical formula

[0025] The alkylene group (R 3 ) and the alkyl group (R 4 ) in the alkoxyalkyl acrylate may each be linear or branched. The alkylene group (R 3 ) in the alkoxyalkyl acrylate may have 1 or more or 2 or more carbon atoms, and may have 4 or fewer or 3 or fewer carbon atoms. The alkyl group (R 4 ) in the alkoxyalkyl acrylate may have 1 or more carbon atoms, and may have 4 or fewer, 3 or fewer, or 2 or fewer carbon atoms.

[0026] Specific examples of the alkoxyalkyl acrylate include 2-methoxyethyl acrylate, 2-ethoxyethyl acrylate, 2-(n-propoxy)ethyl acrylate, 2-(n-butoxy)ethyl acrylate, 3-methoxypropyl acrylate, 3-ethoxypropyl acrylate, 2-(n-propoxy)propyl acrylate, and 2-(n-butoxy)propyl acrylate. These alkoxyalkyl acrylates may be used alone or in combination of two or more.

[0027] The content of the alkoxyalkyl acrylate may be 5% by mass or more, 10% by mass or more, or 12% by mass or more, and may be 30% by mass or less, 25% by mass or less, or 20% by mass or less based on the total mass of the acrylic monomer.

[0028] The acrylic monomer may further contain a crosslinking site monomer. The crosslinking site monomer is a monomer that is copolymerizable with an alkyl acrylate (more preferably an alkyl methacrylate and an alkoxyalkyl acrylate) and has a crosslinkable group that forms a crosslinking site (also referred to as a crosslinking point). The crosslinking site monomer has a polymerizable carbon-carbon double bond, and for example, has an acryloyl group, a methacryloyl group, an allyl group, a methallyl group, a vinyl group, or an alkenylene group. Examples of the crosslinkable group include a carboxyl group, an epoxy group, and an active chlorine group. The crosslinking site monomer may have one or more of these functional groups.

[0029] Examples of the crosslinking site monomer having a carboxyl group as the crosslinkable group include acrylic acid, methacrylic acid, crotonic acid, 2-pentenoic acid, maleic acid, fumaric acid, itaconic acid, and maleic acid monoalkyl ester.

[0030] Examples of the crosslinking-site monomer having an epoxy group as the crosslinkable group include glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, and methallyl glycidyl ether.

[0031] Examples of the crosslinking-site monomer having an active chlorine group as the crosslinkable group include 2-chloroethyl vinyl ether, 2-chloroethyl acrylate, vinyl benzyl chloride, vinyl chloroacetate, and allyl chloroacetate.

[0032] The content of the crosslinking-site monomer may be 0.5% by mass or more, 1% by mass or more, or 1.2% by mass or more, and may be 8% by mass or less, 5% by mass or less, or 3% by mass or less, based on the total mass of the acrylic monomer.

[0033] The acrylic monomer may further contain other monomers copolymerizable with the above-described monomers. Examples of the other monomers include ethylene, alkoxy esters of methacrylic acid, alkyl vinyl ketones, vinyl ethers, allyl ethers, vinyl aromatic compounds, vinyl nitriles, dialkyl esters of maleic acid, dialkyl esters of fumaric acid, dialkyl esters of itaconic acid, dialkyl esters of citraconic acid, dialkyl esters of mesaconic acid, dialkyl esters of 2-pentenedioic acid, dialkyl esters of acetylenedicarboxylic acid, and the like.

[0034] The nonionic emulsifier may contain at least one selected from the group consisting of ether-type nonionic emulsifiers, ester-type nonionic emulsifiers, ether-ester-type nonionic emulsifiers, nitrogen-containing nonionic emulsifiers, and polyvinyl alcohol-based emulsifiers.

[0035] Examples of ether-type nonionic emulsifiers include polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, polyoxyalkylene alkyl ethers, polyoxyethylene alkenyl ethers, polyoxyethylene alkyl phenol ethers, polyoxyethylene polyoxypropylene copolymers, polyoxyethylene lauryl glycols, and polyoxypropylene glycols.

[0036] Examples of ester-type nonionic emulsifiers include sorbitan fatty acid esters and glycerin fatty acid esters. The sorbitan fatty acid ester may be, for example, a monoester. The glycerin fatty acid ester may be, for example, a monoester or a diester.

[0037] Examples of ether-ester type nonionic emulsifiers include polyoxyethylene fatty acid esters and polyoxyethylene sorbitan fatty acid esters. The polyoxyethylene fatty acid ester may be, for example, a monoester or a diester. The polyoxyethylene sorbitan fatty acid ester may be, for example, a monoester.

[0038] Examples of nitrogen-containing type nonionic emulsifiers include polyoxyethylene alkyl amines, polyoxyethylene fatty acid monoethanolamides, and fatty acid diethanolamides.

[0039] The polyvinyl alcohol-based emulsifier may be fully saponified polyvinyl alcohol or partially saponified polyvinyl alcohol, preferably partially saponified polyvinyl alcohol. The degree of saponification in polyvinyl alcohol may be 60 mol% or more, 70 mol% or more, or 80 mol% or more, and may be 100 mol% or less, 99 mol% or less, or 90 mol% or less. The degree of saponification of polyvinyl alcohol means the value measured according to JIS K6726 "3.5 Degree of Saponification".

[0040] The addition amount of the nonionic emulsifier may be 1 part by mass or more, 1.5 parts by mass or more, 2 parts by mass or more, 2.5 parts by mass or more, 3 parts by mass or more, 3.5 parts by mass or more, 4 parts by mass or more, or 4.5 parts by mass or more with respect to 100 parts by mass of the total mass of the acrylic monomer. From the viewpoint of further improving the water resistance of the crosslinked product, lowering the toluene-insoluble content of the acrylic rubber, and improving the flexural fatigue resistance of the crosslinked product, the addition amount of the nonionic emulsifier is preferably 10 parts by mass or less, 9 parts by mass or less, 8 parts by mass or less, 7 parts by mass or less, 6 parts by mass or less, or 5 parts by mass or less with respect to 100 parts by mass of the total mass of the acrylic monomer.

[0041] The polymerization initiator may be, for example, an azo compound such as azobisisobutyronitrile, an organic peroxide such as tert-butyl hydroperoxide, cumene hydroperoxide, benzoyl peroxide, or an inorganic peroxide such as sodium persulfate or ammonium persulfate, and is preferably tert-butyl hydroperoxide.

[0042] When polymerizing the acrylic monomer, a pH adjuster may be further used. The pH adjuster may be, for example, an alkali metal salt such as sodium acetate, sodium hydroxide, potassium hydroxide, sodium phosphate, or sodium citrate, and is preferably sodium acetate. The addition amount of the pH adjuster may be, for example, 0.1 part by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the total amount of the monomers.

[0043] The acrylic polymer in the latex obtained by step S1 may contain the above-described acrylic monomer as a monomer unit. That is, the acrylic polymer may contain at least one monomer unit selected from the group consisting of an alkyl acrylate, an alkyl methacrylate, and an alkoxyalkyl acrylate.

[0044] In this latex, more than 0% by mass and at most 70% by mass of the total mass of the nonionic emulsifier is fixed to the acrylic polymer. In this specification, the amount of the nonionic emulsifier fixed to the acrylic polymer is determined by subtracting the amount of the nonionic emulsifier not fixed to the acrylic polymer from the total amount (charged amount) of the nonionic emulsifier in the latex. The amount of the nonionic emulsifier not fixed to the acrylic polymer is defined as the amount of the nonionic emulsifier contained in the supernatant after separating the precipitated solid content by centrifuging the latex at 10,000 rpm for 30 minutes using a centrifuge. Note that the amount of the nonionic emulsifier contained in the supernatant is measured by a method appropriately selected according to the type of the nonionic emulsifier. For example, when the nonionic emulsifier is polyvinyl alcohol, the amount of polyvinyl alcohol contained in the supernatant is measured by the method described in the examples.

[0045] That is, in this specification, the nonionic emulsifier fixed to the acrylic polymer is defined as the nonionic emulsifier (the nonionic emulsifier that does not desorb from the acrylic polymer) contained in the precipitated solid content when the latex is centrifuged at 10,000 rpm for 30 minutes. Also, in this specification, the nonionic emulsifier not fixed to the acrylic polymer is defined as the nonionic emulsifier (the nonionic emulsifier that has desorbed from the acrylic polymer) contained in the supernatant when the latex is centrifuged at 10,000 rpm for 30 minutes.

[0046] The lower limit of the amount of the nonionic emulsifier fixed to the acrylic polymer is preferably 0.1% by mass or more, 0.5% by mass or more, 1% by mass or more, 1.5% by mass or more, 2% by mass or more, 3% by mass or more, 4% by mass or more, 5% by mass or more, 6% by mass or more, 7% by mass or more, 8% by mass or more, 9% by mass or more, 10% by mass or more, 12% by mass or more, 14% by mass or more, 16% by mass or more, 18% by mass or more, 20% by mass or more, 25% by mass or more, 30% by mass or more, 40% by mass or more, or 45% by mass or more from the viewpoint of further improving the tensile strength at break of the crosslinked product and improving the copper corrosion resistance of the crosslinked product, based on the total mass of the nonionic emulsifier. The upper limit of the amount of the nonionic emulsifier fixed to the acrylic polymer is preferably 68% by mass or less, 65% by mass or less, 60% by mass or less, 55% by mass or less, 50% by mass or less, 40% by mass or less, 30% by mass or less, 25% by mass or less, 20% by mass or less, 15% by mass or less, or 10% by mass or less from the viewpoint of further improving the water resistance of the crosslinked product, lowering the toluene-insoluble content of the acrylic rubber, and improving the flex fatigue resistance of the crosslinked product.

[0047] The amount of the nonionic emulsifier not fixed to the acrylic polymer, based on the total mass of the nonionic emulsifier, is preferably 30% by mass or more, 32% by mass or more, 35% by mass or more, 40% by mass or more, 45% by mass or more, 50% by mass or more, 60% by mass or more, 70% by mass or more, 75% by mass or more, 80% by mass or more, 85% by mass or more, or 90% by mass or more from the viewpoint of further improving the water resistance of the crosslinked product, lowering the toluene-insoluble content of the acrylic rubber, and improving the flex fatigue resistance of the crosslinked product. The amount of the nonionic emulsifier not fixed to the acrylic polymer, based on the total mass of the nonionic emulsifier, is preferably less than 100% by mass, 99.9% by mass or less, 99.5% by mass or less, 99% by mass or less, 98.5% by mass or less, 98% by mass or less, 97% by mass or less, 96% by mass or less, 95% by mass or less, 94% by mass or less, 93% by mass or less, 92% by mass or less, 91% by mass or less, 90% by mass or less, 88% by mass or less, 86% by mass or less, 84% by mass or less, 82% by mass or less, 80% by mass or less, 75% by mass or less, 70% by mass or less, 60% by mass or less, or 55% by mass or less from the viewpoint of further improving the tensile strength at break of the crosslinked product and improving the copper corrosion resistance of the crosslinked product.

[0048] The total mass of the nonionic emulsifier in the latex may be 1 part by mass or more, 1.5 parts by mass or more, 2 parts by mass or more, 2.5 parts by mass or more, 3 parts by mass or more, 3.5 parts by mass or more, 4 parts by mass or more, or 4.5 parts by mass or more with respect to 100 parts by mass of the total mass of the acrylic polymer. The total mass of the nonionic emulsifier in the latex is preferably 10 parts by mass or less, 9 parts by mass or less, 8 parts by mass or less, 7 parts by mass or less, 6 parts by mass or less, or 5 parts by mass or less with respect to 100 parts by mass of the total mass of the acrylic polymer from the viewpoint of further improving the water resistance of the crosslinked product, lowering the toluene-insoluble content of the acrylic rubber, and improving the flex fatigue resistance of the crosslinked product.

[0049] In order for a specific amount of the nonionic emulsifier in the latex to be fixed to the acrylic polymer, in step S1, it is important to separately add a monomer mixture containing an acrylic monomer and a polymerization initiator to the suspension of the nonionic emulsifier, and to adjust the addition amount of the polymerization initiator within a specific range. Also, in step S1, the amount of the nonionic emulsifier fixed to the acrylic polymer can be adjusted by increasing or decreasing the addition amount of the acrylic monomer at the initial stage of the polymerization of the acrylic monomer, or by adjusting the polymerization temperature and the polymerization time.

[0050] Subsequently, in step S2, a coagulant is added to the latex obtained in step S1 to coagulate the acrylic polymer. Examples of the coagulant include ammonium salts, monovalent to trivalent metal salts, inorganic acids, and organic acids. Examples of the ammonium salts include ammonium borate, ammonium sulfate, and ammonium chloride. Examples of the monovalent to trivalent metal salts include sodium salts, magnesium salts, calcium salts, aluminum salts, and zinc salts. Examples of the sodium salts include sodium borate, sodium sulfate, and sodium chloride. Examples of the magnesium salts include magnesium sulfate, magnesium chloride, and magnesium nitrate. Examples of the calcium salts include calcium sulfate, calcium chloride, and calcium nitrate. Examples of the aluminum salts include aluminum sulfate and aluminum chloride. Examples of the zinc salts include zinc chloride and zinc acetate. Examples of the inorganic acids include hydrochloric acid, sulfuric acid, and nitric acid. Examples of the organic acids include formic acid and acetic acid.

[0051] The addition amount of the coagulant may be 0.5 part by mass or more, 1 part by mass or more, or 2 part by mass or more, and may be 150 parts by mass or less, 50 parts by mass or less, or 20 parts by mass or less with respect to 100 parts by mass of the total mass of the acrylic polymer.

[0052] In step S2, next, the solidified acrylic polymer is washed with water and dried. When washing with water, a part of the nonionic emulsifier not fixed to the acrylic polymer in the latex (the nonionic emulsifier that can be removed by washing with water even without performing the centrifugation described above) is removed. Therefore, by passing through step S2, in the resulting acrylic rubber (rubber composition), the amount of the nonionic emulsifier not fixed to the acrylic rubber can be less than that of the nonionic emulsifier not fixed to the acrylic polymer in the latex.

[0053] By the above production method, an acrylic rubber (rubber composition containing an acrylic rubber and a nonionic emulsifier) coexisting with a nonionic emulsifier is obtained. That is, another embodiment of the present invention is a rubber composition containing an acrylic rubber and a nonionic emulsifier.

[0054] The acrylic rubber contains the above-described acrylic monomer as a monomer unit. That is, the acrylic polymer may contain at least one monomer unit selected from the group consisting of an alkyl acrylate, an alkyl methacrylate, and an alkoxyalkyl acrylate. The acrylic rubber may further contain a crosslinking site monomer as a monomer unit, and may further contain other monomers.

[0055] The nonionic emulsifier contained in the rubber composition may be derived from the nonionic emulsifier used in step S1 described above. The details of the nonionic emulsifier are as described above. In the rubber composition, more than 0% by mass and 80% by mass or less of the total mass of the nonionic emulsifier is fixed to the acrylic rubber.

[0056] In this specification, the amount of the nonionic emulsifier fixed to the acrylic rubber is obtained by subtracting the amount of the nonionic emulsifier not fixed to the acrylic rubber (moreover, when the acrylic rubber is washed, the amount of the nonionic emulsifier removed by washing) from the total amount (charged amount) of the nonionic emulsifier. The amount of the nonionic emulsifier not fixed to the acrylic rubber is defined as the amount of the nonionic emulsifier contained in the supernatant after centrifuging the solution in which the acrylic rubber is dissolved (see Examples for details) at 10,000 rpm for 30 minutes using a centrifuge. Note that the amount of the nonionic emulsifier contained in the supernatant is measured by a method appropriately selected according to the type of the nonionic emulsifier. For example, when the nonionic emulsifier is polyvinyl alcohol, the amount of polyvinyl alcohol contained in the supernatant is measured by the method described in the Examples.

[0057] That is, in this specification, the nonionic emulsifier fixed to the acrylic rubber is defined as the nonionic emulsifier (the nonionic emulsifier that does not desorb from the acrylic rubber) contained in the precipitated solid matter when the solution of the acrylic rubber is centrifuged at 10,000 rpm for 30 minutes. Further, in this specification, the nonionic emulsifier not fixed to the acrylic rubber is defined as the nonionic emulsifier (the nonionic emulsifier that has desorbed from the acrylic rubber) contained in the supernatant when the solution of the acrylic rubber is centrifuged at 10,000 rpm for 30 minutes.

[0058] The lower limit of the amount of the nonionic emulsifier fixed to the acrylic rubber, based on the total mass of the nonionic emulsifier, is preferably 0.1% by mass or more, 0.5% by mass or more, 1% by mass or more, 1.5% by mass or more, 2% by mass or more, 3% by mass or more, 4% by mass or more, 5% by mass or more, 6% by mass or more, 7% by mass or more, 8% by mass or more, 9% by mass or more, 10% by mass or more, 12% by mass or more, 14% by mass or more, 16% by mass or more, 18% by mass or more, 20% by mass or more, 25% by mass or more, 30% by mass or more, 40% by mass or more, 45% by mass or more, or 50% by mass or more from the viewpoint of further improving the tensile strength at break of the crosslinked product and improving the copper resistance of the crosslinked product. The upper limit of the amount of the nonionic emulsifier fixed to the acrylic rubber, based on the total mass of the nonionic emulsifier, is preferably 75% by mass or less, 70% by mass or less, 68% by mass or less, 65% by mass or less, 60% by mass or less, 55% by mass or less, 50% by mass or less, 40% by mass or less, 30% by mass or less, 25% by mass or less, 20% by mass or less, or 15% by mass or less from the viewpoint of further improving the water resistance of the crosslinked product, lowering the toluene-insoluble content of the acrylic rubber, and improving the flex fatigue resistance of the crosslinked product.

[0059] The amount of the nonionic emulsifier not fixed to the acrylic rubber, based on the total mass of the nonionic emulsifier, is preferably 20% by mass or more, 25% by mass or more, 30% by mass or more, 32% by mass or more, 35% by mass or more, 40% by mass or more, 45% by mass or more, 50% by mass or more, 60% by mass or more, 70% by mass or more, 75% by mass or more, 80% by mass or more, or 85% by mass or more from the viewpoint of further improving the water resistance of the crosslinked product, reducing the toluene-insoluble content of the acrylic rubber, and improving the flexural fatigue resistance of the crosslinked product. The amount of the nonionic emulsifier not fixed to the acrylic rubber, based on the total mass of the nonionic emulsifier, is preferably less than 100% by mass, 99.9% by mass or less, 99.5% by mass or less, 99% by mass or less, 98.5% by mass or less, 98% by mass or less, 97% by mass or less, 96% by mass or less, 95% by mass or less, 94% by mass or less, 93% by mass or less, 92% by mass or less, 91% by mass or less, 90% by mass or less, 88% by mass or less, 86% by mass or less, 84% by mass or less, 82% by mass or less, 80% by mass or less, 75% by mass or less, 70% by mass or less, 60% by mass or less, 55% by mass or less, or 50% by mass or less from the viewpoint of further improving the tensile strength at break of the crosslinked product and improving the copper corrosion resistance of the crosslinked product.

[0060] The total mass of the nonionic emulsifier in the rubber composition may be 0.5 part by mass or more, 1 part by mass or more, 1.5 parts by mass or more, 2 parts by mass or more, 2.5 parts by mass or more, 3 parts by mass or more, 3.5 parts by mass or more, or 4 parts by mass or more with respect to 100 parts by mass of the total mass of the acrylic rubber. The total mass of the nonionic emulsifier in the rubber composition is preferably 10 parts by mass or less, 9 parts by mass or less, 8 parts by mass or less, 7 parts by mass or less, 6 parts by mass or less, 5 parts by mass or less, 4.5 parts by mass or less, or 4 parts by mass or less with respect to 100 parts by mass of the total mass of the acrylic rubber from the viewpoint of further improving the water resistance of the crosslinked product, reducing the toluene-insoluble content of the acrylic rubber, and improving the flexural fatigue resistance of the crosslinked product.

[0061] The rubber composition may further contain a crosslinking agent. The rubber composition may further contain a crosslinking accelerator. In this case, after kneading the rubber composition at a temperature below the crosslinking temperature, a crosslinked product can be obtained by heating at a predetermined crosslinking temperature. Another embodiment of the present invention is a crosslinked product of the above rubber composition.

[0062] The heating conditions during crosslinking can be appropriately set according to the formulation of the rubber composition and the type of crosslinking agent. The heating temperature may be 100°C or higher and may be 200°C or lower. The heating time may be 1 hour or longer and may be 10 hours or shorter. As the heating method, methods used for crosslinking rubber such as hot press heating, steam heating, and oven heating can be used.

[0063] For the apparatus for kneading, molding, and crosslinking the rubber composition, and the apparatus for kneading and molding the crosslinked product of the rubber composition, apparatuses usually used for rubber compositions can be used. As the kneading apparatus, rolls, kneaders, Banbury mixers, internal mixers, twin-screw extruders, etc. can be used.

[0064] The crosslinking agent may be any one usually used for crosslinking acrylic rubber and is not particularly limited. For example, when the acrylic rubber contains a crosslinking monomer having a carboxyl group as a monomer unit, the crosslinking agent is preferably a polyvalent amine compound and a carbonate of the polyvalent amine compound, more preferably a polyvalent amine compound having 4 to 30 carbon atoms and its carbonate.

[0065] Specific examples of the polyvalent amine compound include aromatic polyamine compounds such as 4,4'-bis(4-aminophenoxy)biphenyl, 4,4'-diaminodiphenyl sulfide, 1,3-bis(4-aminophenoxy)-2,2-dimethylpropane, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)pentane, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]sulfone, 4,4'-diaminodiphenyl sulfone, bis(4-3-aminophenoxy)phenyl sulfone, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 4,4'-diaminobenzanilide, bis[4-(4-aminophenoxy)phenyl]sulfone; aliphatic polyamine compounds such as hexamethylenediamine, hexamethylenediamine carbamate, N,N'-dicyclohexylidene-1,6-hexanediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, etc.

[0066] The content of the crosslinking agent in the rubber composition may be 0.1 part by mass or more, 0.2 part by mass or more, or 0.3 part by mass or more, and may be 5 parts by mass or less, 4 parts by mass or less, or 3 parts by mass or less, based on 100 parts by mass of the acrylic rubber.

[0067] The crosslinking accelerator is not particularly limited. However, when the crosslinking agent is a polyvalent amine compound or its carbonate, examples include aliphatic monovalent secondary amine compounds, aliphatic monovalent tertiary amine compounds, guanidine compounds, imidazole compounds, quaternary onium salts, tertiary phosphine compounds, alkali metal salts of weak acids, and diazabicycloalkene compounds. The crosslinking accelerator can be used alone or in combination of two or more.

[0068] Examples of aliphatic monovalent secondary amine compounds include dimethylamine, diethylamine, di-n-propylamine, diallylamine, diisopropylamine, di-n-butylamine, di-t-butylamine, di-sec-butylamine, dihexylamine, diheptylamine, dioctylamine, dinonylamine, didecylamine, diundecylamine, didodecylamine, ditridecylamine, ditetradecylamine, dipentadecylamine, dicetylamine, di-2-ethylhexylamine, dioctadecylamine, di-cis-9-octadecenylamine, and dinonadecylamine, etc.

[0069] Examples of aliphatic monovalent tertiary amine compounds include trimethylamine, triethylamine, tri-n-propylamine, triallylamine, triisopropylamine, tri-n-butylamine, tri-t-butylamine, tri-sec-butylamine, tripentylamine, trihexylamine, triheptylamine, trioctylamine, trinonylamine, tridecylamine, triundecylamine, tridodecylamine, tridecylamine, tritetradecylamine, tripentadecylamine, tricetylamine, tri-2-ethylhexylamine, trioctadecylamine, tri-cis-9-octadecenylamine, trinonadecylamine, N,N-dimethyldecylamine, N,N-dimethyldodecylamine, N,N-dimethyltetradecylamine, N,N-dimethylcetylamine, N,N-dimethyloctadecylamine, N,N-dimethylbehenylamine, N-methyldidecylamine, N-methyldidodecylamine, N-methylditetradecylamine, N-methyldicetylamine, N-methyldioctadecylamine, N-methyldibehenylamine, and dimethylcyclohexylamine, etc.

[0070] Examples of guanidine compounds include 1,3-di-o-tolylguanidine, 1,3-diphenylguanidine, etc.

[0071] Examples of imidazole compounds include 2-methylimidazole, 2-phenylimidazole, etc.

[0072] Although there are no particular restrictions on the quaternary onium salt, examples thereof include ammonium salts such as tetra-n-butylammonium chloride, trimethylphenylammonium chloride, trimethylstearylammonium chloride, trimethyldodecylammonium chloride, trimethylcetylammonium chloride, dimethyldistearylammonium chloride, tributylbenzylammonium chloride, tetra-n-butylammonium bromide, methyltriphenylammonium bromide, ethyltriphenylammonium bromide, trimethylphenylammonium bromide, trimethylbenzylammonium bromide, trimethylstearylammonium bromide, tetrabutylammonium thiocyanate, and phosphonium salts such as tetra-n-butylphosphonium chloride, tetra-n-butylphosphonium bromide, methyltriphenylphosphonium bromide, ethyltriphenylphosphonium bromide, butyltriphenylphosphonium bromide, hexyltriphenylphosphonium bromide, benzyltriphenylphosphonium bromide, tetraphenylphosphonium chloride, tetraphenylphosphonium bromide, 4-butoxybenzyltriphenylphosphonium bromide, allyltributylphosphonium chloride, 2-propynyltriphenylphosphonium bromide, and methoxypropyltributylphosphonium chloride.

[0073] Examples of the tertiary phosphine compound include triphenylphosphine and tri-p-tolylphosphine.

[0074] Examples of the alkali metal salts of weak acids include inorganic weak acid salts such as phosphates and carbonates of sodium and potassium, and organic weak acid salts such as stearates and laurates of sodium and potassium.

[0075] Examples of the diazabicycloalkene compound include 1,8-diazabicyclo[5.4.0]undecene-7 (DBU), 1,5-diazabicyclo[4.3.0]nonene-5 (DBN), 1,4-diazabicyclo[2.2.2]octane (DABCO), etc. These diazabicycloalkene compounds may form salts with, for example, hydrochloric acid, sulfuric acid, carboxylic acid, sulfonic acid, phenol, etc. Examples of the carboxylic acid include octylic acid, oleic acid, formic acid, phthalic acid, adipic acid, etc. Examples of the sulfonic acid include benzenesulfonic acid, toluenesulfonic acid, dodecylbenzenesulfonic acid, naphthalenesulfonic acid, etc.

[0076] The content of the crosslinking accelerator may be 0.1 part by mass or more, 0.2 part by mass or more, or 0.3 part by mass or more, and 5 parts by mass or less, 4 parts by mass or less, or 3 parts by mass or less with respect to 100 parts by mass of the acrylic rubber.

[0077] The rubber composition may further contain other additives. Examples of the other additives include fillers (reinforcing agents), plasticizers, lubricants, anti-aging agents, stabilizers, silane coupling agents, etc.

[0078] The total content of the other additives in the rubber composition may be 0.1 part by mass or more or 0.2 part by mass or more, and 90 parts by mass or less or 80 parts by mass or less with respect to 100 parts by mass of the acrylic rubber.

[0079] The above-described rubber composition is suitably used as a rubber composition for a seal (also referred to as a seal member) or a hose (also referred to as a hose member). Further, the rubber composition can also be used as a rubber composition for a vibration isolator rubber (also referred to as a vibration isolator rubber member). The crosslinked product of the above-described rubber composition is suitably used as a seal or a hose. That is, another embodiment of the present invention is a seal or a hose including the above crosslinked product. Further, the crosslinked product can also be used as a vibration isolator rubber. That is, another embodiment of the present invention is a vibration isolator rubber including the above crosslinked product. Examples of the hose (hose member) include a rubber hose. Examples of the seal (seal member) include a gasket, packing, and the like. These members may consist only of the crosslinked product of the rubber composition, or may include the crosslinked product and other components.

[0080] Specific examples of the hose (hose member) include, for example, a transmission oil cooler hose, an engine oil cooler hose, an air duct hose, a turbo intercooler hose, a hot air hose, a radiator hose, a power steering hose, a fuel system hose, a drain system hose, etc. for automobiles, construction machines, hydraulic equipment, etc. The hose member may have a reinforcing thread or wire in the intermediate layer or the outermost layer of the hose.

[0081] Specific examples of the seal (seal member) include, for example, an engine head cover gasket, an oil pan gasket, an oil seal, a lip seal packing, an O-ring, a transmission seal gasket, a crankshaft, a camshaft seal gasket, a valve stem, a power steering seal, a belt cover seal, a boot material for a constant velocity joint, a boot material for a rack and pinion, etc.

[0082] Specific examples of the vibration isolator rubber (vibration isolator rubber member) include, for example, a damper pulley, a center support cushion, a suspension bush, etc.

Examples

[0083] Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

[0084] (Example 1) 16.8 kg of an aqueous solution of 4% by mass of a nonionic emulsifier (polyvinyl alcohol) and 22 g of sodium acetate were charged into a pressure-resistant reaction vessel with an internal volume of 40 liters, and they were thoroughly mixed in advance with a stirrer to prepare a uniform suspension. After replacing the air in the upper part of the container with nitrogen, stirring was continued, and after maintaining the inside of the container at 45°C, 11.2 kg of a monomer mixture consisting of a (meth)acrylic monomer containing ethyl acrylate and n-butyl acrylate and monobutyl maleate and 2 liters of an aqueous solution of t-butyl hydroperoxide (0.25% by mass) were separately press-fitted and added to initiate polymerization. The temperature inside the container was maintained at 45°C, and the reaction was terminated after 6.5 hours. As a result, a latex containing an acrylic polymer dispersed in water and a nonionic emulsifier was obtained. To the obtained latex, 20 liters of an aqueous solution of sodium borate (3.5% by mass) as a coagulant was added to coagulate the acrylic polymer. Next, the coagulated acrylic polymer was washed with water and then dehydrated and dried to obtain an acrylic rubber (a rubber composition containing an acrylic rubber and a nonionic emulsifier).

[0085] The above acrylic polymer and acrylic rubber had a monomer composition of 50.0% by mass of ethyl acrylate, 48.5% by mass of n-butyl acrylate, and 1.5% by mass of monobutyl maleate (hereinafter referred to as "monomer composition A"). Tables 1 and 2 show the total mass (parts by mass) of the nonionic emulsifier in the latex with respect to 100 parts by mass of the total mass of the acrylic polymer in the latex, the ratio of the nonionic emulsifier fixed to the acrylic polymer in the latex (mass% based on the total mass of the nonionic emulsifier in the latex), the total mass (parts by mass) of the nonionic emulsifier in the rubber composition with respect to 100 parts by mass of the total mass of the acrylic rubber in the rubber composition, and the ratio of the nonionic emulsifier fixed to the acrylic rubber in the rubber composition (mass% based on the total mass of the nonionic emulsifier in the rubber composition).

[0086] The proportion of the nonionic emulsifier fixed to the acrylic polymer in the latex was measured by the following procedure. First, 50 g of a sample obtained by diluting M E (g) of latex M containing a nonionic emulsifier 20-fold with pure water was placed in a centrifuge tube, and centrifuged at 10,000 rpm for 30 minutes using a centrifuge (Hitachi "CT15D"). The supernatant after centrifugation was taken into a 100 mL plastic bottle, and the mass M L (g) of the supernatant was weighed. 1 mL of this supernatant, 15 mL of a 4 mass% boric acid aqueous solution, and 3 mL of a 0.05 mol iodine solution were put in, and pure water was added to make up to 50 mL to obtain a measurement sample (a sample obtained by diluting the latex 1000-fold). The absorbance Abs at a wavelength of 650 nm of this measurement sample was measured with a spectrophotometer. S (g) was measured. 1 mL of this supernatant, 15 mL of a 4 mass% boric acid aqueous solution, and 3 mL of a 0.05 mol iodine solution were put in, and pure water was added to make up to 50 mL to obtain a measurement sample (a sample obtained by diluting the latex 1000-fold). The absorbance Abs at a wavelength of 650 nm of this measurement sample was measured with a spectrophotometer. Subsequently, the concentration C free (g / kg) of the nonionic emulsifier not fixed to the acrylic polymer in the latex was calculated by the following formula: C free (g / kg)=α (mg / L)×Abs×M S (g) / 50 (g) was determined.

[0087] In the above formula, the density of the supernatant was converted to 1 g / mL, and since the measurement sample was obtained by diluting the latex 1000-fold, the unit of C free is g / kg. Also, the concentration coefficient α (mg / L) was determined by preparing measurement samples and measuring the absorbance at a wavelength of 650 nm in the same manner as the above supernatant for each aqueous solution of nonionic emulsifier (the same polyvinyl alcohol as above) with concentrations of 2, 10, 20, 30, and 40 mg / L, and approximating α assuming that the concentration of each aqueous solution = α × absorbance.

[0088] Then, using the above C free (g / kg), the mass M free (g) of the nonionic emulsifier not fixed to the acrylic polymer in the latex was calculated as follows: M free (g)=C L(kg) was determined. Finally, the ratio (mass %) of the nonionic emulsifier fixed to the acrylic polymer in the latex = [M E (g) - M free (g)] / M E (g) × 100 was determined.

[0089] Also, the ratio of the nonionic emulsifier fixed to the acrylic rubber in the rubber composition was measured by the following procedure. First, 0.3 g of the rubber composition was prepared and precisely weighed into a 100 mL Erlenmeyer flask. Approximately 20 mL of chloroform (CHCl3) was added to this rubber composition and shaken to dissolve the rubber composition. Then, 10 mL of dimethyl sulfoxide (DMSO) was added, and it was heated in a water bath at 90 °C or higher for 1 hour. Next, 20 mL of hot water at 80 °C or higher was added little by little, and it was heated in a water bath for about 30 minutes to remove chloroform, and then allowed to cool. The sample after cooling was centrifuged in a centrifuge (Hitachi's "CT15D") under the conditions of 10000 rpm × 30 minutes. The supernatant after centrifugation was made up to 100 mL and then filtered through a 200-mesh wire mesh to obtain a sample containing the nonionic emulsifier not fixed to the acrylic rubber. For this sample, the concentration C free (g / kg) of the nonionic emulsifier not fixed to the acrylic polymer in the above latex was determined in the same manner, and the ratio of the nonionic emulsifier not fixed to the acrylic rubber in the rubber composition was determined. By subtracting the amount of the nonionic emulsifier not fixed to the acrylic rubber thus obtained and the amount of the nonionic emulsifier removed by washing with water from the charged amount of the nonionic emulsifier, the amount of the nonionic emulsifier fixed to the acrylic rubber was determined.

[0090] (Example 2) An acrylic rubber (rubber composition) was obtained in the same manner as in Example 1 except that the addition amount of the aqueous solution of t-butyl hydroperoxide (0.25 mass %) was changed to 0.75 times.

[0091] (Example 3) The amount of the aqueous solution of t-butyl hydroperoxide (0.25% by mass) was changed to 0.75 times, and an acrylic rubber (rubber composition) was obtained in the same manner as in Example 1 except that the amount of the monomer mixture at the initial stage of polymerization was reduced by about 20%.

[0092] (Example 4) An acrylic rubber (rubber composition) was obtained in the same manner as in Example 1 except that the amount of the aqueous solution of t-butyl hydroperoxide (0.25% by mass) was changed to 0.75 times, the amount of the monomer mixture at the initial stage of polymerization was reduced by about 40%, and the polymerization temperature was changed to 35°C.

[0093] (Example 5) An acrylic rubber (rubber composition) was obtained in the same manner as in Example 1 except that the amount of the aqueous solution of t-butyl hydroperoxide (0.25% by mass) was changed to 0.5 times, the amount of the monomer mixture at the initial stage of polymerization was reduced by about 75%, the polymerization temperature was changed to 35°C, and the reaction time was changed to 12 hours.

[0094] (Comparative Example 1) An acrylic rubber (rubber composition) was obtained in the same manner as in Example 1 except that the amount of the aqueous solution of t-butyl hydroperoxide (0.25% by mass) was changed to 2 times and the polymerization temperature was changed to 55°C.

[0095] (Comparative Example 2) An acrylic rubber (rubber composition) was obtained in the same manner as in Example 1 except that the nonionic emulsifier was changed to an anionic emulsifier.

[0096] (Example 6) An acrylic rubber (rubber composition) was obtained in the same manner as in Example 2 except that the concentration of the aqueous solution of the nonionic emulsifier was changed from 4% by mass to 8% by mass.

[0097] (Example 7) By adjusting the blending ratios of ethyl acrylate, n-butyl acrylate, and monobutyl maleate in the monomer mixture, the monomer composition A of the acrylic polymer and acrylic rubber was changed to monomer composition B (68.5% by mass of ethyl acrylate, 30.0% by mass of n-butyl acrylate, and 1.5% by mass of monobutyl maleate). Also, an acrylic rubber (rubber composition) was obtained in the same manner as in Example 1, except that the addition amount of the aqueous solution of t-butyl hydroperoxide (0.15% by mass) was changed to 1.8 L.

[0098] (Example 8) By changing the monomer mixture to a monomer mixture consisting of ethyl acrylate, n-butyl acrylate, n-butyl methacrylate, 2-methoxyethyl acrylate, and monobutyl maleate, the monomer composition A of the acrylic polymer and acrylic rubber was changed to monomer composition C (35.0% by mass of ethyl acrylate, 39.5% by mass of n-butyl acrylate, 9.5% by mass of n-butyl methacrylate, 14.5% by mass of 2-methoxyethyl acrylate, and 1.5% by mass of monobutyl maleate). Also, an acrylic rubber (rubber composition) was obtained in the same manner as in Example 1, except that the addition amount of the aqueous solution of t-butyl hydroperoxide (0.25% by mass) was changed to 1.5 L and the polymerization temperature was changed to 45°C.

[0099] (Example 9) An acrylic rubber (rubber composition) was obtained in the same manner as in Example 8, except that the addition amount of the aqueous solution of t-butyl hydroperoxide (0.25% by mass) was changed to 0.7 times.

[0100] (Example 10) By changing the monomer mixture to a monomer mixture consisting of ethyl acrylate, n-butyl acrylate, n-butyl methacrylate, and monobutyl maleate, the monomer composition A of the acrylic polymer and acrylic rubber was changed to monomer composition D (25.0% by mass of ethyl acrylate, 43.5% by mass of n-butyl acrylate, 30.0% by mass of n-butyl methacrylate, and 1.5% by mass of monobutyl maleate). Also, an acrylic rubber (rubber composition) was obtained in the same manner as in Example 1.

[0101] (Example 11) By changing the monomer mixture to a monomer mixture consisting of ethyl acrylate, n-butyl acrylate, n-butyl methacrylate, and monobutyl maleate, the monomer composition A of the acrylic polymer and the acrylic rubber was changed to monomer composition E (35.0% by mass of ethyl acrylate, 48.5% by mass of n-butyl acrylate, 15.0% by mass of n-butyl methacrylate, and 1.5% by mass of monobutyl maleate). An acrylic rubber (rubber composition) was obtained in the same manner as in Example 1, except for the change.

[0102] (Example 12) By changing the monomer mixture to a monomer mixture consisting of ethyl acrylate, n-butyl acrylate, 2-methoxyethyl acrylate, and monobutyl maleate, the monomer composition A of the acrylic polymer and the acrylic rubber was changed to monomer composition F (70.0% by mass of ethyl acrylate, 13.5% by mass of n-butyl acrylate, 15.0% by mass of 2-methoxyethyl acrylate, and 1.5% by mass of monobutyl maleate). An acrylic rubber (rubber composition) was obtained in the same manner as in Example 1, except for the change.

[0103] (Example 13) By changing the monomer mixture to a monomer mixture consisting of ethyl acrylate, n-butyl acrylate, 2-methoxyethyl acrylate, and monobutyl maleate, the monomer composition A of the acrylic polymer and the acrylic rubber was changed to monomer composition G (5.0% by mass of ethyl acrylate, 68.5% by mass of n-butyl acrylate, 25.0% by mass of 2-methoxyethyl acrylate, and 1.5% by mass of monobutyl maleate). An acrylic rubber (rubber composition) was obtained in the same manner as in Example 1, except for the change.

[0104] The Mooney viscosity ML(1+4) at 100 °C of the acrylic rubber (rubber composition) obtained in each example and comparative example was measured according to the method specified in JIS K6300. The results are shown in Tables 1 and 2.

[0105] Also, to 100 parts by mass of the acrylic rubber (rubber composition) obtained in each of the examples and comparative examples, the following components were blended and kneaded using an 8-inch open roll. Filler: 55 parts by mass of carbon black (Seast SO manufactured by Tokai Carbon Co., Ltd.) Lubricant a: 1 part by mass of stearic acid (Beads Stearic Acid Camellia manufactured by NOF Corporation) Lubricant b: 0.3 part by mass of stearylamide (Amide AP-1 manufactured by Mitsubishi Chemical Corporation) Lubricant c: 1 part by mass of liquid paraffin (High Cold K-230 manufactured by Kaneda Co., Ltd.) Release agent: 0.5 part by mass of a fatty acid·fatty acid ester·amine·wetting agent mixture (MoldWiz INT-21G manufactured by Kao Corporation) Antioxidant: 0.5 part by mass of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine (Naugard#445 manufactured by AdvanTech) Crosslinking agent: 0.5 part by mass of hexamethylenediamine carbamate (Diak#1 manufactured by DuPont) Crosslinking accelerator: 1.0 part by mass of a synthetic mixture of an active amine and a retarder (XLA-60 manufactured by Rancess)

[0106] After the kneaded rubber composition was separated into a sheet with a thickness of 2.4 mm, heating and pressurization were performed at 170 °C and a pressure of 10 MPa for 20 minutes using a press vulcanizer. Subsequently, heating was performed in a gear oven at 170 °C for 4 hours to obtain a crosslinked product of the rubber composition.

[0107] (Evaluation of water resistance) According to the "immersion test" of JIS K6258:2016, the crosslinked product was subjected to an immersion test (80 °C, 72 hours) with distilled water, and the volume change rate of the crosslinked product before and after the test was calculated based on the following formula. Volume change rate (%) = (Volume after test - Volume before test) / Volume before test × 100 The results are shown in Tables 1 and 2. The smaller the volume change rate, the better the water resistance.

[0108] (Measurement of tensile strength at break) In accordance with JIS K6251:2017, the tensile strength at break Tb of the crosslinked product was measured. The results are shown in Tables 1 and 2.

[0109] [Table 1]

[0110] [Table 2]

[0111] For Examples 1 to 13, the following evaluations of toluene insoluble content, flex fatigue resistance, and copper corrosion resistance were also carried out. The results are shown in Tables 3 and 4.

[0112] (Measurement of toluene insoluble content) 1 g of acrylic rubber was precisely weighed and dissolved in 100 mL of toluene at 25°C over 48 hours. Then, the solution was transferred to a centrifuge tube with a volume of 250 mL whose mass had been previously measured (designated as X (g)). Subsequently, using an angle rotor with a maximum centrifugal radius of 13.8 cm, the solution was centrifuged at 10°C, 8500 rpm for 60 minutes, and then the non-precipitate was removed by decantation. The precipitate in the centrifuge tube was dried in a vacuum dryer at 70°C for 24 hours, and the mass of the centrifuge tube after drying (designated as Y (g)) was measured. From the measured X and Y, the toluene insoluble content was calculated by the following formula. Toluene insoluble content (mass %) = (Y - X) × 100 The lower the toluene insoluble content, the more preferable.

[0113] (Evaluation of flex fatigue resistance) In accordance with JIS K6260:2010, in an environment of 100°C, the number of flexing cycles until a crack of 0.5 mm occurred in the crosslinked product was measured. The number of flexing cycles was the average value of the results of similar measurements for five samples. The more the number of flexing cycles, the better the flex fatigue resistance.

[0114] (Evaluation of copper corrosion resistance) The crosslinked product formed in the shape of a No. 3 dumbbell was used as a test piece. 5 g of a slurry obtained by mixing engine oil (Mobil 15W-30 manufactured by EMG Lubricants Co., Ltd.) and copper powder (CE-1110 manufactured by Fukuda Metal Foil & Powder Co., Ltd.) at a ratio of engine oil / copper powder = 3 / 1 (mass ratio) was applied using a brush so as to completely cover the area between the gauge lines of the test piece, and dried at room temperature for 12 hours. Subsequently, a copper corrosion resistance test was conducted by heating the test piece in a gear oven at 150°C for 500 hours. Thereafter, the copper paste was peeled off from the test piece using a spatula, and the elongation of the test piece was measured in accordance with JIS K6251:2010. The change rate of elongation (%) before and after the test was calculated based on the following formula. Change rate of elongation (%) = (Elongation after test - Elongation before test) / Elongation before test × 100 The smaller the absolute value of the change rate of elongation, the better the copper corrosion resistance.

[0115]

Table 3

[0116]

Table 4

Claims

1. Contains acrylic rubber and a nonionic emulsifier, A rubber composition, in which more than 0 mass % and 80 mass % or less of the total mass of the nonionic emulsifier is fixed to the acrylic rubber.

2. The rubber composition according to claim 1, wherein a total mass of the nonionic emulsifier is 5 parts by mass or less per 100 parts by mass of a total mass of the acrylic rubber.

3. 2. The rubber composition according to claim 1, wherein the acrylic rubber contains at least one monomer unit selected from the group consisting of an alkyl acrylate, an alkyl methacrylate, and an alkoxyalkyl acrylate.

4. The rubber composition according to any one of claims 1 to 3, further comprising a crosslinking agent.

5. A crosslinked product of the rubber composition according to claim 4.

6. A step of polymerizing an acrylic monomer in the presence of a nonionic emulsifier to obtain a latex of an acrylic polymer; and coagulating and washing the acrylic polymer to obtain an acrylic rubber. The method for producing an acrylic rubber, wherein more than 0 mass % and 70 mass % or less of the total mass of the nonionic emulsifier in the latex is fixed to the acrylic polymer.

7. The method for producing an acrylic rubber according to claim 6, wherein a total mass of the nonionic emulsifier in the latex is 6 parts by mass or less per 100 parts by mass of a total mass of the acrylic polymer.

8. The method for producing an acrylic rubber according to claim 6 or 7, wherein the acrylic polymer contains at least one monomer unit selected from the group consisting of an alkyl acrylate, an alkyl methacrylate, and an alkoxyalkyl acrylate.

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