Acrylic rubber composition, crosslinked rubber object, hose material, sealing material, tube material, belt material, and boot material

Abstract

Provided is an acrylic rubber composition comprising an acrylic rubber and an aromatic-polyvalent-amine crosslinking agent, wherein the acrylic rubber comprises units of an alkyl (meth)acrylate monomer and / or an alkoxyalkyl (meth)acrylate monomer, and units of a carboxylated monomer. The acrylic rubber has a crosslinking-point equivalent of 10-25 mephr. When a section of an uncrosslinked solid rubber formed from the acrylic rubber composition is subjected to examination with an optical microscope to examine five areas in a 30 mm × 2 mm field of view, then secondary particles of the aromatic-polyvalent-amine crosslinking agent observed in the section have a maximum diameter of 200 μm or smaller.

Description

Acrylic rubber composition, rubber crosslinked product, hose material, sealing material, tube material, belt material, and boot material

[0001] The present invention relates to an acrylic rubber composition, a rubber crosslinked product, a hose material, a sealing material, a tube material, a belt material, and a boot material.

[0002] As a method for crosslinking an acrylic rubber composition, usually, as a primary crosslinking, after heating at about 150°C to 190°C for several minutes to several tens of minutes, as a secondary crosslinking, heating is performed for several hours in a heated air environment of 140°C to 200°C (for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2003-201380

[0004] From the viewpoints of productivity, energy saving, and carbon neutrality of the rubber crosslinked product, there is a demand for an acrylic rubber composition capable of producing a rubber crosslinked product having good crosslinked physical properties without requiring secondary crosslinking.

[0005] The present invention has been made in view of such circumstances, and an object thereof is to provide an acrylic rubber composition that has good scorch stability, has sufficient mechanical properties without performing secondary crosslinking, and can provide a rubber crosslinked product excellent in tensile strength after heat aging.

[0006] As a result of intensive studies by the present inventors, it has been found that in an acrylic rubber composition containing a predetermined acrylic rubber and an aromatic polyvalent amine crosslinking agent, the above object can be achieved by controlling the state of existence of the aromatic polyvalent amine crosslinking agent in the acrylic rubber composition, and the present invention has been completed.

[0007] In other words, the present invention provides the following acrylic rubber compositions, rubber crosslinked products, hose materials, sealing materials, tube materials, belt materials and boot materials. [1] An acrylic rubber composition comprising acrylic rubber and an aromatic polyhydric amine crosslinking agent, wherein the acrylic rubber comprises (meth)acrylate alkyl ester monomer units and / or (meth)acrylate alkoxyalkyl ester monomer units and carboxyl group-containing monomer units, the crosslinking point equivalent of the acrylic rubber is 10 to 25 mephr, and when the cross-section of an uncrosslinked rubber solid made of the acrylic rubber composition is observed with an optical microscope at five locations within a field of view of 30 mm × 2 mm, the maximum secondary particle diameter of the aromatic polyhydric amine crosslinking agent observed in the cross-section is 200 μm or less. [2] The acrylic rubber composition according to [1], wherein when the cross-section of an uncrosslinked rubber solid made of the acrylic rubber composition is observed with an optical microscope at five locations within a field of view of 30 mm × 2 mm, the number of aromatic polyhydric amine crosslinkers present in the cross-section, each having a secondary particle diameter of 100 μm or more, is 3 or less. [3] An acrylic rubber crosslinked product obtained by crosslinking the acrylic rubber composition according to [1] or [2]. [4] A hose material, seal material, tube material, belt material, or boot material made of the acrylic rubber crosslinked product according to [3]. [5] A hose material or seal material made of the acrylic rubber crosslinked product according to [3]. [6] A method for producing the acrylic rubber composition according to [1] or [2], comprising the step of mixing the acrylic rubber and the aromatic polyhydric amine crosslinker at a temperature equal to or greater than the melting temperature of the aromatic polyhydric amine crosslinker. [7] A method for producing the acrylic rubber composition described in [1] or [2], comprising the steps of: grinding an aromatic polyhydric amine crosslinking agent so that the average secondary particle diameter is 30 μm or less; and mixing the acrylic rubber with the ground aromatic polyamine crosslinking agent.

[0008] According to the present invention, it is possible to provide an acrylic rubber composition that has good scorch stability, sufficient mechanical properties without secondary crosslinking, and excellent tensile strength after thermal aging, thereby providing a crosslinked rubber product.

[0009] Figure 1 is a cross-sectional photograph of the acrylic rubber composition (uncrosslinked rubber sheet) of Example 4. Figure 2 is a cross-sectional photograph of the acrylic rubber composition (uncrosslinked rubber sheet) of Comparative Example 3. Figure 3 is a cross-sectional photograph of the same acrylic rubber composition (uncrosslinked rubber sheet) of Comparative Example 3 as in Figure 2, with the measurement area of ​​the maximum diameter of the aggregate (i.e., secondary particle diameter) indicated by the white line.

[0010] The acrylic rubber composition of the present invention is an acrylic rubber composition containing acrylic rubber and an aromatic polyhydric amine crosslinking agent, wherein the acrylic rubber comprises (meth)acrylate alkyl ester monomer units and / or (meth)acrylate alkoxyalkyl ester monomer units and carboxyl group-containing monomer units, the crosslinking point equivalent of the acrylic rubber is 10 to 25 mephr, and when the cross-section of an uncrosslinked rubber solid made of the acrylic rubber composition is observed with an optical microscope at five locations within a field of view of 30 mm × 2 mm, the maximum secondary particle diameter of the aromatic polyhydric amine crosslinking agent observed in the cross-section is 200 μm or less.

[0011] The acrylic rubber composition of the present invention not only contains the above-mentioned specific acrylic rubber and a polyhydric amine crosslinking agent in combination, but is also adjusted so that when the cross-section of an uncrosslinked rubber solid made of the acrylic rubber composition is observed with an optical microscope at five locations within a 30 mm × 2 mm field of view, the maximum secondary particle size of the aromatic polyhydric amine crosslinking agent observed in the cross-section is 200 μm or less. With this configuration, the acrylic rubber composition of the present invention can provide a rubber crosslinked product that has good scorch stability, sufficient mechanical properties (specifically, tensile properties and resistance to compression set) without secondary crosslinking, and excellent tensile strength after thermal aging.

[0012] <Acrylic Rubber> The acrylic rubber used in the present invention includes (meth)acrylate alkyl ester monomer units and / or (meth)acrylate alkoxyalkyl ester monomer units, as well as carboxyl group-containing monomer units.

[0013] The acrylic rubber used in the present invention comprises at least one (meth)acrylic acid monomer unit selected from alkyl (meth)acrylate monomer units and alkoxyalkyl (meth)acrylate monomer units.

[0014] Furthermore, (meth)acrylate alkyl ester means alkyl acrylate and / or alkyl methacrylate, and (meth)acrylate alkoxyalkyl ester means alkoxyalkyl acrylate and / or alkoxyalkyl methacrylate. Hereafter, the term "(meth)acrylic" will be understood similarly.

[0015] The alkyl (meth)acrylate monomer that forms the alkyl (meth)acrylate monomer unit is not particularly limited, but an ester of an alkanol having 1 to 12 carbon atoms and (meth)acrylic acid (a (meth)acrylic acid ester having an alkyl group having 1 to 12 carbon atoms) is preferred, an ester of an alkanol having 1 to 8 carbon atoms and (meth)acrylic acid (a (meth)acrylic acid ester having an alkyl group having 1 to 8 carbon atoms) is more preferred, and an ester of an alkanol having 2 to 6 carbon atoms and (meth)acrylic acid (a (meth)acrylic acid ester having an alkyl group having 2 to 6 carbon atoms) is even more preferred.

[0016] Specific examples of alkyl (meth)acrylate monomers include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and cyclohexyl (meth)acrylate. Among these, ethyl (meth)acrylate and n-butyl (meth)acrylate are preferred, and ethyl acrylate and n-butyl acrylate are more preferred. These can be used individually or in combination of two or more.

[0017] For example, the acrylic rubber used in the present invention may contain both ethyl acrylate units and n-butyl acrylate units as (meth)acrylate alkyl ester monomer units. In this case, the weight ratio of the content of the two monomer units [content of ethyl acrylate units: content of n-butyl acrylate units] is preferably 1:99 to 99:1, more preferably 10:90 to 90:10, even more preferably 20:30 to 85:15, and particularly preferably 30:70 to 80:20.

[0018] The (meth)acrylate alkoxyalkyl ester monomer that forms the (meth)acrylate alkoxyalkyl ester monomer unit is not particularly limited, but an ester of an alkoxyalkyl alcohol having 2 to 12 carbon atoms and (meth)acrylic acid (a (meth)acrylate ester having an alkoxyalkyl group having 2 to 12 carbon atoms) is preferred, an ester of an alkoxyalkyl alcohol having 2 to 8 carbon atoms and (meth)acrylic acid (a (meth)acrylate ester having an alkoxyalkyl group having 2 to 8 carbon atoms) is more preferred, and an ester of an alkoxyalkyl alcohol having 2 to 6 carbon atoms and (meth)acrylic acid (a (meth)acrylate ester having an alkoxyalkyl group having 2 to 6 carbon atoms) is even more preferred.

[0019] Specific examples of (meth)acrylate alkoxyalkyl ester monomers include methoxymethyl (meth)acrylate, ethoxymethyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-propoxyethyl (meth)acrylate, 2-butoxyethyl (meth)acrylate, 3-methoxypropyl (meth)acrylate, and 4-methoxybutyl (meth)acrylate. Among these, 2-ethoxyethyl (meth)acrylate and 2-methoxyethyl (meth)acrylate are preferred, and 2-ethoxyethyl acrylate and 2-methoxyethyl acrylate are particularly preferred. These can be used individually or in combination of two or more.

[0020] The total content of alkyl (meth)acrylate monomer units and alkoxyalkyl (meth)acrylate monomer units in the total monomer units constituting the acrylic rubber used in the present invention is preferably 50 to 98.7% by weight, more preferably 70 to 98.7% by weight, even more preferably 80 to 98.6% by weight, particularly preferably 85 to 98.5% by weight, and most preferably 90 to 98% by weight. By having a (meth)acrylate monomer unit content within the above range, the resulting rubber crosslinked product will have even better mechanical properties.

[0021] The acrylic rubber used in the present invention may contain only one of either (meth)acrylate alkyl ester monomer units or (meth)acrylate alkoxyalkyl ester monomer units, or both. Preferably, the acrylic rubber used in the present invention contains at least (meth)acrylate alkyl ester monomer units.

[0022] When the acrylic rubber used in the present invention contains alkyl (meth)acrylate monomer units, the content thereof is preferably 1 to 98.7% by weight, more preferably 1 to 98.6% by weight, even more preferably 5 to 98.5% by weight, and particularly preferably 5 to 98% by weight, of the total monomer units constituting the acrylic rubber.

[0023] When the acrylic rubber used in the present invention contains (meth)acrylate alkoxyalkyl ester monomer units, the content thereof is preferably 1 to 70% by weight, more preferably 1 to 60% by weight, even more preferably 2 to 60% by weight, and particularly preferably 3 to 50% by weight, of the total monomer units constituting the acrylic rubber.

[0024] When the acrylic rubber used in the present invention contains alkyl (meth)acrylate monomer units and alkoxyalkyl (meth)acrylate monomer units, the weight ratio of the content of both monomer units [content of alkyl (meth)acrylate monomer units: content of alkoxyalkyl (meth)acrylate monomer units] is preferably 1:99 to 99:1, more preferably 50:50 to 98:2, and even more preferably 80:20 to 95:5.

[0025] The acrylic rubber used in the present invention includes carboxyl group-containing monomer units in addition to alkyl (meth)acrylate monomer units and / or alkoxyalkyl (meth)acrylate monomer units.

[0026] The carboxyl group-containing monomers that form carboxyl group-containing monomer units are not particularly limited, but examples include α,β-ethylenically unsaturated dicarboxylic acid monoester monomers, α,β-ethylenically unsaturated monocarboxylic acids, and α,β-ethylenically unsaturated dicarboxylic acids.

[0027] As α,β-ethylenically unsaturated dicarboxylic acid monoester monomers, monoesters of an α,β-ethylenically unsaturated dicarboxylic acid having 4 to 12 carbon atoms and an alkanol having 1 to 12 carbon atoms are preferred, monoesters of an α,β-ethylenically unsaturated dicarboxylic acid having 4 to 6 carbon atoms and an alkanol having 2 to 8 carbon atoms are more preferred, and monoesters of an α,β-ethylenically unsaturated dicarboxylic acid having 4 carbon atoms and an alkanol having 2 to 6 carbon atoms are even more preferred.

[0028] Specific examples of α,β-ethylenically unsaturated dicarboxylic acid monoester monomers include monochain alkyl esters of butendionate such as monomethyl fumarate, monoethyl fumarate, mono-n-butyl fumarate, monomethyl maleate, monoethyl maleate, and mono-n-butyl maleate; monocyclic butendionate monoesters of butendionate having an alicyclic structure such as monocyclopentyl fumarate, monocyclohexyl fumarate, monocyclohexenyl fumarate, monocyclopentyl maleate, monocyclohexyl maleate, and monocyclohexenyl maleate; and monoesters of itaconic acid such as monomethyl itaconate, monoethyl itaconate, mono-n-butyl itaconate, and monocyclohexyl itaconate. These can be used individually or in combination of two or more. Note that among the above monomers, dicarboxylic acids also exist as anhydrides.

[0029] Specific examples of α,β-ethylenically unsaturated monocarboxylic acids include acrylic acid, methacrylic acid, α-ethylacrylic acid, crotonic acid, and cinnamic acid.

[0030] Specific examples of α,β-ethylenically unsaturated dicarboxylic acids include butendionic acids such as fumaric acid and maleic acid; itaconic acid; citraconic acid; and chloromaleic acid. Note that some of the above monomers also exist as anhydrides.

[0031] Among these, α,β-ethylenically unsaturated dicarboxylic acid monoester monomers are preferred, monochain alkyl butendionates and butendionates having an alicyclic structure are more preferred, mono-n-butyl fumarate, mono-n-butyl maleate, monocyclohexyl fumarate, and monocyclohexyl maleate are even more preferred, and mono-n-butyl fumarate is particularly preferred.

[0032] The acrylic rubber used in this invention is a crosslinkable acrylic rubber because it contains carboxyl group-containing monomer units and therefore has carboxyl groups as crosslinking sites. The acrylic rubber used in this invention has a crosslinking point equivalent in the range of 10 to 25 mephr.

[0033] In the present invention, the crosslinking point equivalent (mephr) is expressed as 1000 times the equivalent (ephr) of the crosslinking point in 100 parts by weight of acrylic rubber, and its unit is mephr (millieequivalent per hundred red rubber). For example, if the monomer units having crosslinking points in acrylic rubber consist only of monomer units having one carboxyl group, such as α,β-ethylenically unsaturated dicarboxylic acid monoester monomer units and / or monocarboxylic acid monomer units, the crosslinking point equivalent is equal to 1000 times the equivalent (ephr) of the monomer units having one carboxyl group in 100 parts by weight of acrylic rubber.

[0034] If the crosslinking point equivalent is too low, it becomes difficult to produce a primary crosslinked material with sufficient mechanical properties. On the other hand, it is not easy to manufacture acrylic rubber with too high a crosslinking point equivalent, and it also becomes difficult to achieve both scorch stability and the mechanical properties of the primary crosslinked material.

[0035] The crosslinking point equivalent is not particularly limited as long as it is between 10 mephr and 25 mephr, but is preferably 11 to 22 mephr, more preferably 12 to 20 mephr, even more preferably 12.5 to 18 mephr, and particularly preferably 12.5 to 16 mephr. By having the crosslinking point equivalent within the above preferred range, it is possible to achieve an even higher level of balance between scorch stability and the mechanical properties of the primary crosslinked material.

[0036] The content of carboxyl group-containing monomer units in the total monomer units constituting the acrylic rubber used in this invention is not particularly limited as long as the amount is such that the crosslinking point equivalent falls within the above range, but is preferably 1.3 to 7.5% by weight, more preferably 1.5 to 5.0% by weight, even more preferably 1.7 to 4.0% by weight, particularly preferably 1.9 to 3.5% by weight, and most preferably 2.0 to 3.0% by weight. By having a carboxyl group-containing monomer unit content within the above range, it is possible to achieve a higher level of balance between scorch stability and the mechanical properties of the primary crosslinked material.

[0037] The acrylic rubber used in the present invention preferably contains α,β-ethylenically unsaturated dicarboxylic acid monoester monomer units as carboxyl group-containing monomer units. In this case, the weight ratio of the content of α,β-ethylenically unsaturated dicarboxylic acid monoester monomer units to the content of carboxyl group-containing monomer units in the acrylic rubber used in the present invention [(content of α,β-ethylenically unsaturated dicarboxylic acid monoester monomer units / content of carboxyl group-containing monomer units) × 100] is preferably 50 to 100% by weight, more preferably 70 to 100% by weight, and even more preferably 90 to 100% by weight. In one embodiment of the present invention, the acrylic rubber may contain only α,β-ethylenically unsaturated dicarboxylic acid monoester monomer units as carboxyl group-containing monomer units. That is, the above weight ratio may be substantially 100% by weight.

[0038] The acrylic rubber used in the present invention may have other monomer units copolymerizable with the monomer units described above. Examples of such copolymerizable monomers are not particularly limited, but include conjugated diene monomers, unconjugated diene monomers, aromatic vinyl monomers, α,β-ethylenically unsaturated nitrile monomers, acrylamide monomers, α,β-ethylenically unsaturated dicarboxylic acid diester monomers, and other olefin monomers.

[0039] Examples of conjugated diene monomers include 1,3-butadiene, isoprene, and piperine.

[0040] Examples of non-conjugated diene monomers include ethylidene norbornene, dicyclopentadiene, dicyclopentadienyl (meth)acrylate, and 2-dicyclopentadienylethyl (meth)acrylate.

[0041] Examples of aromatic vinyl monomers include styrene, α-methylstyrene, and divinylbenzene.

[0042] Examples of the α,β-ethylenically unsaturated nitrile monomer include acrylonitrile and methacrylonitrile. Examples of the acrylamide monomer include acrylamide and methacrylamide.

[0043] Examples of the α,β-ethylenically unsaturated dicarboxylic acid diester monomer include dialkyl maleates such as dimethyl maleate and di-n-butyl maleate, where the alkyl group has 1 to 18 carbon atoms; dialkyl fumarates such as dimethyl fumarate and di-n-butyl fumarate, where the alkyl group has 1 to 18 carbon atoms; dicycloalkyl maleates such as dicyclopentyl maleate and dicyclohexyl maleate, where the cycloalkyl group has 4 to 16 carbon atoms; dicycloalkyl fumarates such as dicyclopentyl fumarate and dicyclohexyl fumarate, where the cycloalkyl group has 4 to 16 carbon atoms; dialkyl itaconates such as dimethyl itaconate and di-n-butyl itaconate, where the alkyl group has 1 to 18 carbon atoms; dicycloalkyl itaconates such as dicyclohexyl itaconate, where the cycloalkyl group has 4 to 16 carbon atoms; and the like.

[0044] Examples of the other olefin monomers include ethylene, propylene, vinyl chloride, vinylidene chloride, vinyl acetate, ethyl vinyl ether, butyl vinyl ether, and the like.

[0045] The other copolymerizable monomers can be used alone or in combination of two or more. The content of the units of the other copolymerizable monomers in the monomer units constituting the acrylic rubber used in the present invention is preferably 48.7% by weight or less, more preferably 28.5% by weight or less, still more preferably 18.5% by weight or less, particularly preferably 13.5% by weight or less, and most preferably 8.0% by weight or less.

[0046] The acrylic rubber used in the present invention can be obtained by polymerizing the above monomers. As the form of the polymerization reaction, any of emulsion polymerization method, suspension polymerization method, bulk polymerization method, and solution polymerization method can be used. However, from the viewpoint of ease of controlling the polymerization reaction, etc., it is preferable to use the emulsion polymerization method under normal pressure.

[0047] Emulsion polymerization may be carried out in any of batchwise, semi-batchwise, and continuous modes. The polymerization is usually carried out in a temperature range of 0 to 70°C, preferably 5 to 50°C. The above monomers do not necessarily have to be supplied to the reaction site in all species and in all amounts from the beginning of the reaction. Considering the copolymerization reactivity ratio, reaction conversion rate, etc., they may be continuously or intermittently added over the entire reaction time, or may be introduced in one batch or dividedly in the middle or in the latter half. Also, the charging ratio of each monomer in the polymerization reaction may be adjusted according to the reactivity of each monomer. However, since the polymerization reaction often proceeds almost quantitatively, considering such circumstances, etc., the charging ratio may be determined according to the monomer unit composition of the acrylic rubber to be produced. After polymerization, through coagulation and drying, a solid acrylic rubber can be obtained. <着

[0048] The shape of the acrylic rubber used in the present invention is not particularly limited, and it may be in any shape such as veil shape, sheet shape, powder shape, etc.

[0049] <Aromatic polyvalent amine crosslinking agent> The acrylic rubber composition of the present invention contains an aromatic polyvalent amine crosslinking agent in addition to the above-mentioned acrylic rubber. Since the acrylic rubber composition of the present invention contains an acrylic rubber having a crosslinking point equivalent within the above range and an aromatic polyvalent amine crosslinking agent as a crosslinking agent, it exhibits crosslinkability (is crosslinkable). That is, it can be said that the acrylic rubber composition of the present invention is a crosslinkable acrylic rubber composition.

[0050] The aromatic polyvalent amine crosslinking agent is not particularly limited as long as it is an aromatic compound having two or more amino groups or a compound that forms an aromatic compound having two or more amino groups during crosslinking.

[0051] Aromatic polyvalent amine crosslinking agents are not particularly limited, but examples include 4,4'-methylenedianiline, p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-(m-phenylenediisopropylidene)dianiline, 4,4'-(p-phenylenediisopropylidene)dianiline, 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), 4,4'-diaminobenzanilide, 4,4'-bis(4-aminophenoxy)biphenyl, m-xylylenediamine, p-xylylenediamine, and 1,3,5-benzenetriamine. Among these, 2,2'-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) is preferred.

[0052] Among the above, as aromatic polyhydric amine crosslinking agents, diamine compounds, that is, compounds having two amino groups, or compounds that become compounds having two amino groups when crosslinked, are preferred. Using diamine compounds is preferable because it results in a more uniform crosslinking structure, thereby achieving excellent mechanical properties.

[0053] In the acrylic rubber composition of the present invention, the content of the aromatic polyhydric amine crosslinking agent is preferably 0.4 to 1.6 parts by weight, more preferably 0.6 to 1.2 parts by weight, and even more preferably 0.75 to 1.1 parts by weight, per 100 parts by weight of acrylic rubber. By setting the content of the aromatic polyhydric amine crosslinking agent within the above range, it is possible to achieve an even higher level of balance between scorch stability and the mechanical properties of the primary crosslinked product.

[0054] The acrylic rubber composition of the present invention may contain crosslinking agents other than aromatic polyhydric amine crosslinking agents, but the content is preferably 0.5 parts by weight or less, more preferably 0.1 parts by weight or less, per 100 parts by weight of acrylic rubber, and even more preferably does not contain any crosslinking agents other than aromatic polyhydric amine crosslinking agents.

[0055] Furthermore, the acrylic rubber composition of the present invention controls the state of the aromatic polyhydric amine crosslinking agent within the acrylic rubber composition to a specific state. Specifically, when observing five locations within a 30 mm × 2 mm field of view of an uncrosslinked rubber solid (an acrylic rubber composition that has not been crosslinked (before being subjected to a crosslinking reaction) and has a predetermined shape) made of the acrylic rubber composition using an optical microscope, the maximum secondary particle size of the aromatic polyhydric amine crosslinking agent observed in the cross-section is controlled to be 200 μm or less. In other words, the present invention controls the acrylic rubber composition so that there are no aggregates of aromatic polyhydric amine crosslinking agent with a secondary particle size exceeding 200 μm. As a result, according to the present invention, it is possible to provide a rubber crosslinked material that has good scorch stability, sufficient mechanical properties (specifically, tensile properties and resistance to compression set), and excellent tensile strength after thermal aging, without performing secondary crosslinking.

[0056] Here, the maximum secondary particle diameter of the aromatic polyhydric amine crosslinking agent is the secondary particle diameter of the aggregate with the largest secondary particle diameter among the aggregates of aromatic polyhydric amine crosslinking agent observed when observing five locations within a 30 mm × 2 mm field of view of the cross-section of the uncrosslinked rubber solid made of acrylic rubber composition using an optical microscope.

[0057] In this invention, when observing the cross-section of an acrylic rubber composition, the uncrosslinked rubber solid made of the acrylic rubber composition is cut crosswise using a sharp blade such as a knife, and the cut cross-section is observed using an optical microscope. Furthermore, the cross-sectional observation range is sufficient to be 30 mm × 2 mm in five locations. According to the inventors' findings, by setting the cross-sectional observation range to such a range (30 mm × 2 mm in a field of view, five locations), the state of presence of aromatic polyhydric amine crosslinking agents in the acrylic rubber composition can be sufficiently determined. In other words, according to the inventors' findings, by setting the cross-sectional observation range to such a range, the number of aggregates of aromatic polyhydric amine crosslinking agents per unit area in the acrylic rubber composition and the maximum secondary particle size of the aggregates of aromatic polyhydric amine crosslinking agents contained in the acrylic rubber composition can be appropriately measured (i.e., it is a sufficient measurement range for measuring these).

[0058] Cross-sectional observation can be performed at any five locations within a 30 mm x 2 mm area on any cross-section of the uncrosslinked rubber solid made of acrylic rubber composition. The uncrosslinked rubber solid made of acrylic rubber composition only needs to be uncrosslinked and in a solid state; its shape is not particularly limited and can be any shape, whether molded or unmolded, and can be various shapes such as sheets or blocks. From the viewpoint of providing a suitable 30 mm x 2 mm cross-section, a sheet shape with a width of 30 mm and a thickness of 2 mm is also preferable. However, depending on the shape and size of the uncrosslinked rubber solid, it may not be possible to obtain a 30 mm x 2 mm cross-section. In such cases, it is not necessarily required to measure at five locations within a 30 mm x 2 mm area; the total area range should be 300 mm. ２ The above measurement should be performed on a cross-sectional area that is (30 mm x 2 mm x 5 locations). In other words, in the present invention, the cross-section of the uncrosslinked rubber solid made of acrylic rubber composition is 300 mm ２Regarding the field of view, when observed with an optical microscope, the maximum secondary particle size of the aromatic polyvalent amine crosslinking agent observed in the cross-section may be controlled to 200 μm or less.

[0059] The acrylic rubber composition of the present invention is acceptable as long as the maximum secondary particle diameter of the aromatic polyhydric amine crosslinking agent observed in the above cross-section is controlled to be 200 μm or less. However, from the viewpoint of making the effects of the present invention even more remarkable, the maximum secondary particle diameter is preferably 150 μm or less, more preferably 100 μm or less, and even more preferably 50 μm or less. Furthermore, in the present invention, it is also a preferred embodiment that no aggregates of the aromatic polyhydric amine crosslinking agent are observed in the cross-sectional observation. In this case, since no aggregates are observed and the maximum secondary particle diameter of the aromatic polyhydric amine crosslinking agent cannot be measured, the maximum secondary particle diameter of the aromatic polyhydric amine crosslinking agent is 0 μm or undetectable.

[0060] Furthermore, the acrylic rubber composition of the present invention is measured in five locations (or 300 mm) within a field of view of 30 mm x 2 mm on the cross-section of an uncrosslinked rubber solid made of the acrylic rubber composition. ２ When observing the field of view (of the field of view) with an optical microscope, it is preferable that the number of aromatic polyhydric amine crosslinking agents with a secondary particle diameter of 100 μm or more observed in the cross-section be 3 or less, more preferably less than 3, even more preferably 2 or less, even more preferably 1 or less, and particularly preferably 0. By setting the number of aromatic polyhydric amine crosslinking agents with a secondary particle diameter of 100 μm or more within the above range, the effects of the present invention can be made even more remarkable.

[0061] In this invention, the secondary particle diameter observed in the cross-section may be the maximum diameter of the observed aromatic polyhydric amine crosslinking agent aggregates. For example, if the aromatic polyhydric amine crosslinking agent aggregates are observed to be elliptical in shape, the major axis may be used as the secondary particle diameter. Figure 2 is a cross-sectional photograph of the acrylic rubber composition (uncrosslinked rubber sheet) of Comparative Example 3. While the aggregates of the aromatic polyhydric amine crosslinking agent can be observed in a state where their shape can be sufficiently identified through cross-sectional observation, they are often not observed to be perfectly spherical. Therefore, in this invention, the secondary particle diameter observed in the cross-section is set to be the maximum diameter of the observed aromatic polyhydric amine crosslinking agent aggregates.

[0062] <Crosslinking retarder> The acrylic rubber composition of the present invention may further contain a crosslinking retarder.

[0063] The crosslinking retarder is preferably a monoamine-based crosslinking retarder, and more preferably a monomajor amine compound. Monomajor amine compounds are compounds in which one hydrogen atom of ammonia is replaced with a hydrocarbon group, and include aliphatic monomajor amines, alicyclic monomajor amines, aromatic monomajor amines, amino alcohols, and aminooxo compounds. Among these, aliphatic monomajor amines are preferred, and aliphatic monomajor amines having 8 to 20 carbon atoms are particularly preferred. When an aromatic polyhydric amine crosslinking agent is used in combination with an aliphatic monomajor amine as a crosslinking retarder, scorch stability is extremely good.

[0064] Examples of aliphatic monoprimary amines include methylamine, ethylamine, propylamine, allylamine, isopropylamine, n-butylamine, t-butylamine, sec-butylamine, hexylamine, heptylamine, octylamine, nonylamine, decylamine, undecylamine, dodecylamine, tridecylamine, tetradecylamine, pentadecylamine, cetylamine, 2-ethylhexylamine, octadecylamine, cis-9-octadecenylamine, and nonadecylamine. Among these, aliphatic monoprimary amines having 8 to 20 carbon atoms, such as octylamine, decylamine, dodecylamine, tetradecylamine, cetylamine, octadecylamine, cis-9-octadecenylamine, and nonadecylamine, are preferred.

[0065] Examples of alicyclic monoprimary amines include cyclopropylamine, cyclobutylamine, cyclopentylamine, and cyclohexylamine.

[0066] Examples of aromatic monoprimary amines include aniline, o-toluidine, m-toluidine, benzylamine, α-naphthylamine, and β-naphthylamine.

[0067] Examples of amino alcohols include aminoethanol, aminopropanol, D,L-alaninol, 2-minobutyl alcohol, 2-amino-2-methylpropanol, 2-amino-2-hydroxymethyl-1,3-propanediol, 2-amino-2-methylpropane-1,3-diol, 2-amino-2-ethyl-1,3-propanediol, 1-chloro-3-aminopropan-2-ol, 3-amino-1,2-propanediol, and 2-amine-1,3-propanediol.

[0068] Examples of aminooxo compounds include 3-methoxypropylamine and 3-ethoxypropylamine.

[0069] The crosslinking retarder content in the acrylic rubber composition of the present invention is preferably 0.4 to 1.5 parts by weight, more preferably 0.6 to 1.25 parts by weight, and even more preferably 0.7 to 1.1 parts by weight, per 100 parts by weight of acrylic rubber. By setting the crosslinking retarder content within the above range, it is possible to achieve an even higher level of balance between scorch stability and the mechanical properties of the primary crosslinked material.

[0070] <Other components> Furthermore, it is preferable that the acrylic rubber composition of the present invention contains a crosslinking accelerator.

[0071] Examples of crosslinking accelerators include guanidine compounds, diazabicycloalkene compounds, imidazole compounds, quaternary onium salts, tertiary phosphine compounds, aliphatic monovalent secondary amine compounds, and aliphatic monovalent tertiary amine compounds. These basic crosslinking accelerators can be used individually or in combination of two or more.

[0072] Specific examples of guanidine compounds include 1,3-di-o-tolylguanidine and 1,3-diphenylguanidine. Specific examples of diazabicycloalkene compounds include 1,8-diazabicyclo[5.4.0]unde-7-cene (DBU) and 1,5-diazabicyclo[4.3.0]no-5-nene. Specific examples of imidazole compounds include 2-methylimidazole and 2-phenylimidazole. Specific examples of quaternary onium salts include tetra-n-butylammonium bromide and octadecyltri-n-butylammonium bromide. Specific examples of tertiary phosphine compounds include triphenylphosphine and tri-p-tolylphosphine.

[0073] Aliphatic monovalent secondary amine compounds are compounds in which two hydrogen atoms of ammonia are replaced with aliphatic hydrocarbon groups. The aliphatic hydrocarbon groups that replace the hydrogen atoms preferably have 1 to 30 carbon atoms. Specific examples of aliphatic monovalent secondary amine compounds include dialkylmonoamine compounds such as dimethylamine, diethylamine, dipropylamine, 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, and dioctadecylamine.

[0074] Aliphatic monovalent tertiary amine compounds are compounds in which all three hydrogen atoms of ammonia are replaced with aliphatic hydrocarbon groups. The aliphatic hydrocarbon groups that replace the hydrogen atoms are preferably those having 1 to 30 carbon atoms. Specific examples of aliphatic monovalent tertiary amine compounds include trimethylamine, triethylamine, tripropylamine, triallylamine, triisopropylamine, tri-n-butylamine, tri-t-butylamine, tri-sec-butylamine, trihexylamine, triheptylamine, trioctylamine, trinonylamine, tridecylamine, triundecylamine, and tridodecylamine, which are all trialkylmonoamines.

[0075] Among these, guanidine compounds, diazabicycloalkene compounds, and aliphatic monovalent secondary amine compounds are preferred, guanidine compounds and diazabicycloalkene compounds are more preferred, and 1,3-di-o-tolylguanidine and 1,8-diazabicyclo[5.4.0]unde-7-cene (DBU) are even more preferred.

[0076] The crosslinking accelerator content in the acrylic rubber composition of the present invention is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 6 parts by weight, and even more preferably 1 to 4 parts by weight, per 100 parts by weight of acrylic rubber. By setting the crosslinking accelerator content within the above range, it is possible to achieve a higher level of balance between scorch stability and the mechanical properties of the primary crosslinked product.

[0077] The acrylic rubber composition of the present invention may contain rubber other than acrylic rubber.

[0078] The rubbers other than acrylic rubber that can be used in the present invention are not particularly limited, but include acrylic rubbers other than those used in the present invention, natural rubber, polybutadiene rubber, polyisoprene rubber, styrene-butadiene rubber, acrylonitrile-butadiene rubber, silicone rubber, fluororubber, olefin-based elastomers, styrene-based elastomers, vinyl chloride-based elastomers, polyester-based elastomers, polyamide-based elastomers, polyurethane-based elastomers, and polysiloxane-based elastomers. These can be used individually or in combination of two or more.

[0079] The proportion of acrylic rubber component in the rubber component of the acrylic rubber composition can be appropriately selected depending on the intended use, but is preferably 70% by weight or more, more preferably 90% by weight or more, even more preferably 95% by weight or more, and particularly preferably 100% by weight (i.e., the rubber component of the acrylic rubber composition consists substantially only of acrylic rubber component).

[0080] The acrylic rubber composition of the present invention preferably contains fillers such as reinforcing fillers and non-reinforcing fillers.

[0081] Examples of reinforcing fillers include carbon black such as furnace black, acetylene black, thermal black, channel black, and graphite; and silica such as wet silica, dry silica, and colloidal silica. Examples of non-reinforcing fillers include clay such as quartz powder and diatomaceous earth; zinc oxide; basic magnesium carbonate; activated calcium carbonate; magnesium silicate; aluminum silicate; titanium dioxide; talc; aluminum sulfate; calcium sulfate; and barium sulfate. Fillers can be used individually or in combination of two or more types.

[0082] The amount of filler in the acrylic rubber composition of the present invention is not particularly limited, but is preferably 1 to 200 parts by weight, more preferably 10 to 150 parts by weight, and even more preferably 20 to 100 parts by weight, per 100 parts by weight of the rubber component containing acrylic rubber in the acrylic rubber composition.

[0083] The acrylic rubber composition of the present invention may optionally contain an antioxidant. The antioxidant is not particularly limited, but examples include phenolic antioxidants such as double-hindered phenolic antioxidants, semi-hindered phenolic antioxidants, less-hindered phenolic antioxidants, and phenolic antioxidants without a hindered group; phosphite ester antioxidants; sulfur ester antioxidants; secondary amine antioxidants such as phenyl-α-naphthylamine, phenyl-β-naphthylamine, p-(p-toluenesulfonylamide)-diphenylamine, 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, N,N-diphenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, and butyraldehyde-aniline condensates; imidazole antioxidants; quinoline antioxidants; hydroquinone antioxidants; and the like.

[0084] Anti-aging agents can be used individually or in combination of two or more. The amount of anti-aging agent in the rubber composition of the present invention is not particularly limited, but is preferably 0.01 to 15 parts by weight, more preferably 0.05 to 10 parts by weight, and even more preferably 0.1 to 5 parts by weight, per 100 parts by weight of the rubber component containing the copolymer rubber of the present invention.

[0085] Furthermore, the acrylic rubber composition of the present invention may contain, in addition to the above-mentioned components, compounding agents commonly used in the rubber processing field. Examples of such compounding agents include light stabilizers, plasticizers, softeners, processing aids, adhesives, lubricants, flame retardants, fungicides, antistatic agents, and colorants. The amount of these compounding agents added is not particularly limited as long as it does not hinder the purpose or effects of the present invention, and appropriate amounts can be added depending on the purpose of compounding.

[0086] <Method for producing the acrylic rubber composition> The acrylic rubber composition of the present invention can be prepared by mixing an aromatic polyhydric amine crosslinking agent, a crosslinking retarder, and various other compounding agents as needed with a rubber component containing acrylic rubber, mixing and kneading with an open roll, Banbury mixer, various kneaders, etc., and then kneading further with a kneading roll.

[0087] In the present invention, from the viewpoint of being able to suitably control the state of presence of the aromatic polyhydric amine crosslinking agent in the acrylic rubber composition to the specific state described above, it is preferable to use a method of mixing the acrylic rubber and the aromatic polyhydric amine crosslinking agent at a temperature above the melting temperature of the aromatic polyhydric amine crosslinking agent when compounding the acrylic rubber with the aromatic polyhydric amine crosslinking agent. In this case, it is sufficient to mix at a temperature above the melting temperature of the aromatic polyhydric amine crosslinking agent, but it is preferable to mix at a temperature of 5°C or higher above the melting temperature, and more preferably at a temperature of 10°C or higher above the melting temperature, and the upper limit is preferably below the temperature at which the aromatic polyhydric amine crosslinking agent acts as a crosslinking agent.

[0088] Alternatively, the state of the aromatic polyamine crosslinking agent in the acrylic rubber composition can be suitably controlled to the specific state described above by grinding the aromatic polyamine crosslinking agent so that its average secondary particle diameter is 30 μm or less, and then mixing the pulverized aromatic polyamine crosslinking agent with acrylic rubber. Aromatic polyamine crosslinking agents often exhibit agglomeration, usually in a state where their average secondary particle diameter is 200 μm or more, and they often agglomerate even when mixed with acrylic rubber. In contrast, by grinding the aromatic polyamine crosslinking agent beforehand so that its average secondary particle diameter is 30 μm or less, and then mixing the pulverized aromatic polyamine crosslinking agent with acrylic rubber, the state of the aromatic polyamine crosslinking agent in the acrylic rubber composition can be suitably controlled to the specific state described above. When grinding the aromatic polyamine crosslinking agent beforehand, the average secondary particle diameter after grinding is preferably 20 μm or less, more preferably 15 μm or less, and although there is no particular lower limit, it is preferably 2 μm or more from the viewpoint of handling. The average secondary particle diameter after grinding should be defined as the particle diameter (D50) at which the cumulative volume calculated from the smallest diameter side in the particle diameter distribution (volume-based) measured using a laser diffraction particle size distribution analyzer becomes 50%.

[0089] The Mooney viscosity (ML1+4, 100°C) of the acrylic rubber composition of the present invention is preferably 10 to 80, more preferably 20 to 70, and even more preferably 30 to 60.

[0090] <Crosslinked Rubber Product> The crosslinked rubber product of the present invention is obtained by crosslinking the acrylic rubber composition of the present invention described above.

[0091] The crosslinked rubber product of the present invention can be manufactured by using the acrylic rubber composition of the present invention, molding it using a molding machine corresponding to the desired shape, such as an extruder, injection molding machine, compressor, and roll, and then heating it to carry out a crosslinking reaction and fix the shape as a crosslinked rubber product. In this case, crosslinking may be performed either after molding or simultaneously with molding. The molding temperature is usually 10 to 140°C, preferably 25 to 120°C.

[0092] The crosslinking temperature is typically 150 to 190°C, preferably 160 to 180°C, and the crosslinking time is typically 2 to 60 minutes, preferably 3 to 40 minutes. As for the heating method, any method used for crosslinking rubber, such as press heating, steam heating, oven heating, and hot air heating, can be appropriately selected.

[0093] In the method for manufacturing a crosslinked rubber product of the present invention, secondary crosslinking is not necessarily required, but it may be performed. Secondary crosslinking is usually carried out in a heated air environment at 130 to 220°C for 1 to 48 hours.

[0094] From the viewpoint of productivity, energy saving, and carbon neutrality, the rubber crosslinked product of the present invention is preferably a primary crosslinked product of the acrylic rubber composition of the present invention. For example, the rubber crosslinked product of the present invention is preferably a primary crosslinked product obtained by heating and crosslinking the acrylic rubber composition of the present invention at a temperature of 150°C to 190°C for 2 to 60 minutes.

[0095] The crosslinked rubber material of the present invention is suitably used as a sealing material such as O-rings, packings, diaphragms, oil seals, shaft seals, bearing sheaths, mechanical seals, wellhead seals, seals for electrical and electronic equipment, and seals for air compressor equipment; various gaskets such as cylinder head gaskets fitted to the connection between the cylinder block and the cylinder head, rocker cover gaskets fitted to the connection between the rocker cover and the cylinder head, oil pan gaskets fitted to the connection between the oil pan and the cylinder head or transmission case, fuel cell separator gaskets fitted between a pair of housings that sandwich a unit cell equipped with a positive electrode, electrolyte plate, and negative electrode, and gaskets for the top cover of a hard disk drive; cushioning material, vibration damping material; wire insulation material; industrial belts; tube material and hose material; belt material; boot material; sheets; and the like.

[0096] Furthermore, the rubber crosslinked material of the present invention is suitably used as an extruded molded product and crosslinked product for automotive applications, such as fuel oil system hoses such as fuel tanks, fuel hoses, filler neck hoses, vent hoses, vapor hoses, and oil hoses; air system hoses such as turbo air hoses and transmission control hoses; and various hose materials such as radiator hoses, heater hoses, brake hoses, and air conditioning hoses.

[0097] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, the "parts" below refer to weight. Various physical properties were measured as follows.

[0098] <Crosslinking point equivalent> The crosslinking point equivalent in acrylic rubber was calculated by dissolving the rubber sample in acetone and performing potentiometric titration with potassium hydroxide solution.

[0099] <Cross-sectional observation of acrylic rubber composition> To observe the secondary particles of aromatic polyhydric amine crosslinking agents contained in the acrylic rubber composition, cross-sectional observation of an uncrosslinked acrylic rubber sheet was performed. Specifically, the cross-section of the uncrosslinked acrylic rubber sheet was exposed by cutting it with a sharp blade, and the exposed cross-section was observed using an optical microscope. The observation cross-section was 30 mm x 2 mm in size, and five observation points were set. The measurement magnification was selected in the range of 50 to 500 times, depending on the size of the secondary particles of aromatic polyhydric amine crosslinking agents that appeared in the cross-section. The tilt angle during measurement was set to 0°. In the cross-sectional observation, the secondary particle diameter (maximum secondary particle diameter) of the aromatic polyhydric amine crosslinking agent aggregate with the largest secondary particle diameter contained in the five cross-sections was measured, and the number of aromatic polyhydric amine crosslinking agent aggregates with a secondary particle diameter of 100 μm or more contained in the five cross-sections was counted. In cross-sectional observation, the largest diameter of the observed aggregate of aromatic polyvalent amine crosslinking agent was defined as its secondary particle diameter.

[0100] <Mooney scorch time [t5]> The Mooney scorch time [t5] of the acrylic rubber composition was measured at a temperature of 125°C in accordance with JIS K6300. A Mooney scorch time [t5] of 15 minutes or more indicates good scorch stability.

[0101] <Maximum Torque [MH]> The crosslinking properties of the acrylic rubber composition were tested using a rubber vulcanization tester (moving dileometer MDR, manufactured by Alpha Technologies) at 170°C for 20 minutes. The maximum torque [MH] was then measured from the results of the crosslinking properties test.

[0102] <Normal Physical Properties of Acrylic Rubber Crosslinked Material (Primary Crosslinked Material)> In accordance with JIS K6251, test specimens were cut from sheet-like acrylic rubber crosslinked material (primary crosslinked material), and the tensile strength, elongation, and 100% elongation stress of the obtained test specimens were measured. If the 100% elongation stress is 3 MPa or higher, it can be determined that the acrylic rubber crosslinked material has sufficient mechanical properties.

[0103] <Physical Properties of Acrylic Rubber Crosslinked Material (Primary Crosslinked Material) After Heating> Sheet-shaped acrylic rubber crosslinked material (primary crosslinked material) was subjected to an air heating aging test at 175°C for 72 hours in accordance with JIS K6257. Then, in accordance with JIS K6251, test specimens were cut from the acrylic rubber crosslinked material after the air heating aging test, and the tensile strength and elongation of the obtained test specimens were measured.

[0104] <Compression set [Cs] of acrylic rubber crosslinked material (primary crosslinked material)> Using a cylindrical acrylic rubber crosslinked material (primary crosslinked material), the compression set [Cs] was determined in accordance with JIS K6262 under compression conditions of 25% compressibility, 175°C, and 72 hours.

[0105] <Increase in 100% tensile stress due to secondary crosslinking> A secondary crosslinked material was obtained by heating a sheet-like acrylic rubber crosslinked material (primary crosslinked material) in an oven at 170°C for 4 hours. In accordance with JIS K6251, test pieces were cut from the secondary crosslinked material, and the 100% tensile stress of the obtained test pieces was measured. Then, the increase in 100% tensile stress due to secondary crosslinking was calculated according to the following formula: Increase in 100% tensile stress due to secondary crosslinking (%) = {(100% tensile stress of secondary crosslinked material - 100% tensile stress of primary crosslinked material) / 100% tensile stress of primary crosslinked material} × 100 The smaller the increase in 100% tensile stress due to secondary crosslinking, the better it can be judged that the crosslinking reaction is proceeding by primary crosslinking alone.

[0106] <Example 1> (Production of acrylic rubber) In a polymerization reactor equipped with a thermometer, a stirrer, a nitrogen inlet pipe, and a vacuum device, 200 parts of water, 3 parts of sodium lauryl sulfate, 60.00 parts of ethyl acrylate, 37.00 parts of n-butyl acrylate, and 3.00 parts of mono-n-butyl fumarate were charged. After that, oxygen was thoroughly removed by repeatedly degassing under reduced pressure and purging with nitrogen, and then 0.002 parts of sodium formaldehyde sulfoxylate and 0.005 parts of cumene hydroperoxide were added to start the emulsion polymerization reaction at atmospheric pressure and room temperature, and the reaction was continued until the polymerization conversion rate reached 95%. The obtained emulsion polymerization solution was solidified with an aqueous magnesium sulfate solution, washed with water, and dried to obtain acrylic rubber (ACM-1). The content of mono-n-butyl fumarate units in the obtained acrylic rubber (ACM-1) was 2.42% by weight, and the content of ethyl acrylate units and n-butyl acrylate units, other than mono-n-butyl fumarate units, corresponded to the proportions used in the initial charge. Furthermore, the crosslinking point equivalent of the acrylic rubber (ACM-1) was measured according to the method described above and was found to be 14.07 mephr.

[0107] (Production of Acrylic Rubber Composition) A mixture was obtained by kneading 100 parts of acrylic rubber (ACM-1), 60 parts of carbon black (product name "Seist SO", manufactured by Tokai Carbon Co., Ltd.), 2 parts of stearic acid (dispersant and softener for carbon black), 1 part of ester wax (product name "Greg G-8205", manufactured by DIC Corporation), 0.70 parts of octadecylamine (Lipomin 18D, manufactured by Lion Specialty Chemicals, monoamine crosslinking retarder), 2 parts of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine (anti-aging agent), and 1.00 part of 2,2'-bis[4-(4-aminophenoxy)phenyl]propane (product name "BAPP", manufactured by Seika Co., Ltd., polyvalent amine crosslinking agent (divalent), average secondary particle size (D50): 212 μm) in a Banbury. During kneading in Banbury, the discharge temperature was set to 130°C or higher to ensure that 2,2'-bis[4-(4-aminophenoxy)phenyl]propane melted and dispersed. Next, 2.00 parts of crosslinking accelerator 1 (trade name "Noxellar DT", manufactured by Ouchi Shinko Chemical Industry Co., Ltd., 1,3-di-o-tolylguanidine) were added to the resulting mixture and kneaded at 50°C in an open roll to obtain a sheet-like acrylic rubber composition (uncrosslinked rubber sheet) with a width of 30 mm and a thickness of 2 mm. Using the obtained acrylic rubber composition (uncrosslinked rubber sheet), cross-sectional observation (observation of secondary particles of aromatic polyvalent amine crosslinking agent contained in the acrylic rubber composition), as well as measurement of Mooney scorch time [t5] and maximum torque [MH] were performed according to the above method. The results are shown in Table 1.

[0108] (Manufacturing of Acrylic Rubber Crosslinked Material) An acrylic rubber composition was molded and crosslinked by pressing at 10 MPa at 170°C for 20 minutes to obtain a sheet-like acrylic rubber crosslinked material (primary crosslinked material) measuring 15 cm × 15 cm × 2 mm. Using the obtained sheet-like acrylic rubber crosslinked material (primary crosslinked material), the normal physical properties, physical properties after heating, and the percentage increase in 100% elongation stress due to secondary crosslinking were measured. The results are shown in Table 1. In addition, an acrylic rubber composition was molded and crosslinked by pressing at 10 MPa at 170°C for 20 minutes to produce a cylindrical acrylic rubber crosslinked material (primary crosslinked material) with a diameter of 29 mm and a thickness of 12.5 mm, and the compression set [Cs] was measured. The results are shown in Table 1.

[0109] <Examples 2, 3, 7-9> (Production of acrylic rubber) Acrylic rubber (ACM-2, ACM-3, ACM-4, ACM-5) was obtained in the same manner as in Example 1, except that the monomers listed in Table 1 were used in the amounts listed in Table 1 instead of 60.00 parts ethyl acrylate, 37.00 parts n-butyl acrylate, and 3.00 parts mono-n-butyl fumarate. The content ratio of mono-n-butyl fumarate units in the obtained acrylic rubber (ACM-2, ACM-3, ACM-4, ACM-5) was as shown in Table 1, and the content ratios of ethyl acrylate units, n-butyl acrylate units, and 2-methoxyethyl acrylate units, other than mono-n-butyl fumarate units, corresponded to the charge ratios. Furthermore, the crosslinking point equivalents of the acrylic rubber (ACM-2, ACM-3, ACM-4, ACM-5) were measured according to the above method, and the results are as shown in Table 1.

[0110] (Production of Acrylic Rubber Composition) Except that the acrylic rubbers (ACM-2, ACM-3, ACM-4, ACM-5) obtained above were used instead of acrylic rubber (ACM-1), and the amount of octadecylamine (crosslinking retarder) and / or 2,2'-bis[4-(4-aminophenoxy)phenyl]propane (aromatic polyhydric amine crosslinking agent) and the type and amount of the crosslinking accelerator were changed as shown in Table 1, a sheet-like acrylic rubber composition (uncrosslinked rubber sheet) was obtained in the same manner as in Example 1. That is, in Examples 2, 3, 7 to 9, the timing of blending 2,2'-bis[4-(4-aminophenoxy)phenyl]propane was set to the time of kneading in Banbury, and the discharge temperature was set to 130°C or higher so that 2,2'-bis[4-(4-aminophenoxy)phenyl]propane would melt and disperse during kneading in Banbury. In Example 9, crosslinking accelerator 2 (product name "Rhenogran XLA-60", manufactured by Rhein Chemie, 60% 1,8-diazabicyclo[5.4.0]undeca-7-ene (DBU) (including the portion of DBU that is a zinc dialkyl diphosphonate salt), acrylic acid polymer and 40% dispersant) was used as the crosslinking accelerator. The obtained acrylic rubber composition (uncrosslinked rubber sheet) was measured in the same manner as in Example 1. The results are shown in Table 1.

[0111] <Example 4> (Grinding of polyvalent amine crosslinking agent) Powder of 2,2'-bis[4-(4-aminophenoxy)phenyl]propane (trade name "BAPP", manufactured by Seika Co., Ltd., polyvalent amine crosslinking agent (divalent), average secondary particle size (D50): 212 μm) was added to a porcelain mortar and pestle, and the mortar was used to grind the powder for more than 10 minutes. A pulverized product of 2,2'-bis[4-(4-aminophenoxy)phenyl]propane was obtained, in which the average secondary particle size (D50) of the particle size distribution (volume basis) measured using a laser diffraction particle size distribution analyzer was 7 μm.

[0112] (Production of Acrylic Rubber Composition) A mixture was obtained by kneading 100 parts of acrylic rubber (ACM-1) obtained in the same manner as in Example 1, 60 parts of carbon black (product name "Seast SO", manufactured by Tokai Carbon Co., Ltd.), 2 parts of stearic acid (dispersant and softener for carbon black), 1 part of ester wax (product name "Greg G-8205", manufactured by DIC Corporation), 0.80 parts of octadecylamine (Lipomin 18D, manufactured by Lion Specialty Chemicals, a monoamine crosslinking retarder), and 2 parts of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine (anti-aging agent) in a Banbury. Next, 1.00 part of the pulverized 2,2'-bis[4-(4-aminophenoxy)phenyl]propane obtained above, and 2.00 parts of crosslinking accelerator 1 (product name "Noxellar DT", manufactured by Ouchi Shinko Chemical Industry Co., Ltd., 1,3-di-o-tolylguanidine) were added to the obtained kneaded mixture and kneaded in an open roll at 50°C to obtain a sheet-like acrylic rubber composition (uncrosslinked rubber sheet) with a width of 30 mm and a thickness of 2 mm. Measurements were performed using the obtained acrylic rubber composition (uncrosslinked rubber sheet) in the same manner as in Example 1. The results are shown in Table 1.

[0113] <Examples 5 and 6> (Production of acrylic rubber composition) Using the acrylic rubber (ACM-1) obtained in the same manner as in Example 1, a sheet-like acrylic rubber composition (uncrosslinked rubber sheet) was obtained in the same manner as in Example 1, except that the amount of octadecylamine (crosslinking retarder) and / or 2,2'-bis[4-(4-aminophenoxy)phenyl]propane (aromatic polyhydric amine crosslinking agent) was changed as shown in Table 1. In other words, in Example 5 and 6, the timing of blending 2,2'-bis[4-(4-aminophenoxy)phenyl]propane was set to the time of kneading in Banbury, and the discharge temperature was set to 130°C or higher so that 2,2'-bis[4-(4-aminophenoxy)phenyl]propane would melt and disperse during kneading in Banbury. Measurements were performed using the obtained acrylic rubber composition (uncrosslinked rubber sheet) in the same manner as in Example 1. The results are shown in Table 1.

[0114] <Comparative Example 1> (Production of Acrylic Rubber) Acrylic rubber (ACM-6) was obtained in the same manner as in Example 1, except that the monomers listed in Table 2 were used in the amounts listed in Table 2 instead of 60.00 parts ethyl acrylate, 37.00 parts n-butyl acrylate, and 3 parts mono-n-butyl fumarate. The content ratio of mono-n-butyl fumarate units in the obtained acrylic rubber (ACM-6) was as shown in Table 2, and the content ratios of ethyl acrylate units, n-butyl acrylate units, and 2-methoxyethyl acrylate units, other than mono-n-butyl fumarate units, corresponded to the charge ratios. Furthermore, the crosslinking point equivalent of the acrylic rubber (ACM-6) was measured according to the above method, and the results are as shown in Table 2.

[0115] (Production of acrylic rubber composition) A mixture was obtained by kneading 100 parts of acrylic rubber (ACM-6), 60 parts of carbon black (product name "Seasto SO", manufactured by Tokai Carbon Co., Ltd.), 2 parts of stearic acid (dispersant and softener for carbon black), 1 part of ester wax (product name "Greg G-8205", manufactured by DIC Corporation), 0.50 parts of octadecylamine (Lipomin 18D, manufactured by Lion Specialty Chemicals, a monoamine crosslinking retarder), and 2 parts of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine (anti-aging agent) in a Banbury. Next, 0.80 parts of 2,2'-bis[4-(4-aminophenoxy)phenyl]propane (trade name "BAPP", manufactured by Seika Co., Ltd., polyvalent amine crosslinking agent (divalent), average secondary particle size (D50): 212 μm) and 2.00 parts of crosslinking accelerator 1 (trade name "Noxellar DT", manufactured by Ouchi Shinko Chemical Industry Co., Ltd., 1,3-di-o-tolylguanidine) were added to the obtained kneaded mixture and kneaded in an open roll at 50°C to obtain a sheet-like acrylic rubber composition (uncrosslinked rubber sheet) with a width of 30 mm and a thickness of 2 mm. Measurements were performed using the obtained acrylic rubber composition (uncrosslinked rubber sheet) in the same manner as in Example 1. The results are shown in Table 2.

[0116] <Comparative Examples 2 and 5> (Production of Acrylic Rubber) Acrylic rubber (ACM-7, ACM-8) was obtained in the same manner as in Example 1, except that the monomers listed in Table 2 were used in the amounts listed in Table 2 instead of 60.00 parts ethyl acrylate, 37.00 parts n-butyl acrylate, and 3 parts mono-n-butyl fumarate. The content ratio of mono-n-butyl fumarate units in the obtained acrylic rubber (ACM-7, ACM-8) was as shown in Table 2, and the content ratios of ethyl acrylate units and n-butyl acrylate units other than mono-n-butyl fumarate units corresponded to the charge ratios. Furthermore, the crosslinking point equivalent of the acrylic rubber (ACM-7, ACM-8) was measured according to the above method, and the results are as shown in Table 2.

[0117] (Preparation of Acrylic Rubber Composition) A sheet-like acrylic rubber composition (uncrosslinked rubber sheet) was obtained in the same manner as in Comparative Example 1, except that the acrylic rubbers (ACM-7, ACM-8) obtained above were used instead of acrylic rubber (ACM-6), and the amounts of octadecylamine (crosslinking retarder) and 2,2'-bis[4-(4-aminophenoxy)phenyl]propane (aromatic polyhydric amine crosslinking agent) and the type and amount of the crosslinking accelerator were changed as shown in Table 2. In Comparative Example 2, crosslinking accelerator 2 (trade name "Rhenogran XLA-60", manufactured by Rhein Chemie, 1,8-diazabicyclo[5.4.0]undeca-7-ene (DBU) 60% (including the portion of DBU that is a zinc dialkyl diphosphonate salt), acrylic acid polymer and dispersant 40%) were used. The obtained acrylic rubber composition (uncrosslinked rubber sheet) was measured in the same manner as in Example 1. The results are shown in Table 2.

[0118] <Comparative Examples 3 and 4> (Production of Acrylic Rubber Composition) Except that acrylic rubber (ACM-1) obtained in the same manner as in Example 1 was used instead of acrylic rubber (ACM-6), and the amounts of octadecylamine (crosslinking retarder) and 2,2'-bis[4-(4-aminophenoxy)phenyl]propane (aromatic polyhydric amine crosslinking agent) were changed as shown in Table 2, a sheet-like acrylic rubber composition (uncrosslinked rubber sheet) was obtained in the same manner as in Comparative Example 1. Measurements were performed using the obtained acrylic rubber composition (uncrosslinked rubber sheet) in the same manner as in Example 1. The results are shown in Table 2.

[0119] In Table 1, a value of "-" for the maximum secondary particle size of the aromatic polyhydric amine crosslinking agent in the acrylic rubber composition means that no aggregates of the aromatic polyhydric amine crosslinking agent were observed within the measurement field of view.

[0120]

[0121] As shown in Table 1, in acrylic rubber compositions containing acrylic rubber with a predetermined crosslinking point equivalent and an aromatic polyhydric amine crosslinking agent, by controlling the maximum secondary particle size of the aromatic polyhydric amine crosslinking agent in the acrylic rubber composition to 200 μm or less, it was possible to obtain a crosslinked rubber product with good scorch stability (processing stability), sufficient mechanical properties, and excellent tensile strength after thermal aging without performing secondary crosslinking (Examples 1 to 9).

[0122] On the other hand, when the maximum secondary particle size of the aromatic polyvalent amine crosslinking agent in the acrylic rubber composition exceeded 200 μm, the compression set resistance was insufficient, and the increase in 100% elongation stress due to secondary crosslinking was large, resulting in insufficient properties being obtained with primary crosslinking alone (Comparative Examples 1-5). Furthermore, Comparative Examples 3-5 also showed lower tensile strength after heating.

[0123] Figure 1 shows a cross-sectional photograph of the acrylic rubber composition (uncrosslinked rubber sheet) of Example 4, and Figure 2 shows a cross-sectional photograph of the acrylic rubber composition (uncrosslinked rubber sheet) of Comparative Example 3. In Figure 1, minute aggregates of aromatic polyhydric amine crosslinking agent can be seen in the center of the photograph in the vertical direction and on the right side of the rubber cross-section. In Figure 2, coarse aggregates of aromatic polyhydric amine crosslinking agent can be seen in the center of the photograph in the vertical direction and on the left side of the rubber cross-section. The aggregates of aromatic polyhydric amine crosslinking agent observed in Figure 2 are roughly rectangular in shape with rounded corners, and their longest diameter has an inclination of about 20 to 30° with respect to the vertical direction of the photograph and lies on a straight line passing through the approximate center (on a straight line connecting opposite rounded corners). Therefore, the particle length on this straight line was defined as the secondary particle diameter. Figure 3 is a cross-sectional photograph of the same acrylic rubber composition (uncrosslinked rubber sheet) as Comparative Example 3 in Figure 2. In Figure 3, the measurement points for the maximum diameter of the aggregates (i.e., the secondary particle diameter in Figure 2) are indicated by white lines on the aggregates. In Figures 1, 2, and 3, a 100 μm scale bar is also shown in the lower right portion of the photographs.

Claims

1. An acrylic rubber composition comprising acrylic rubber and an aromatic polyhydric amine crosslinking agent, wherein the acrylic rubber comprises (meth)acrylate alkyl ester monomer units and / or (meth)acrylate alkoxyalkyl ester monomer units and carboxyl group-containing monomer units, the crosslinking point equivalent of the acrylic rubber is 10 to 25 mephr, and when the cross-section of an uncrosslinked rubber solid made of the acrylic rubber composition is observed with an optical microscope at five locations within a 30 mm × 2 mm field of view, the maximum secondary particle diameter of the aromatic polyhydric amine crosslinking agent observed in the cross-section is 200 μm or less.

2. The acrylic rubber composition according to claim 1, wherein when the cross-section of an uncrosslinked rubber solid made of the acrylic rubber composition is observed with an optical microscope at five locations within a field of view of 30 mm × 2 mm, the number of aromatic polyvalent amine crosslinking agents present in the cross-section, each having a secondary particle diameter of 100 μm or more, is 3 or less.

3. An acrylic rubber crosslinked product obtained by crosslinking the acrylic rubber composition according to claim 1 or 2.

4. A hose material, sealing material, tube material, belt material, or boot material made of the acrylic rubber crosslinked material described in claim 3.

5. A hose material or sealing material made of the acrylic rubber crosslinked material described in claim 3.

6. A method for producing the acrylic rubber composition according to claim 1 or 2, comprising the step of mixing the acrylic rubber and the aromatic polyhydric amine crosslinking agent at a temperature equal to or greater than the melting temperature of the aromatic polyhydric amine crosslinking agent.

7. A method for producing the acrylic rubber composition according to claim 1 or 2, comprising the steps of: grinding an aromatic polyhydric amine crosslinking agent so that its average secondary particle diameter is 30 μm or less; and mixing the acrylic rubber with the ground aromatic polyhydric amine crosslinking agent.

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