Crosslinkable rubber and method for producing same, and rubber crosslinked product

Abstract

Provided is a crosslinkable rubber containing a rubber component having a carboxyl group as a crosslinkable group. When a pulse NMR measurement is performed on a rubber crosslinked product having undergone high temperature storage, obtained by crosslinking the crosslinkable rubber to obtain a rubber crosslinked product before undergoing high temperature storage and causing the rubber crosslinked product before undergoing high temperature storage to be stored at a high temperature of 150°C for 1008 hours, the sum of intensities within a relaxation time of 0-8 msec is 19.0 or less.

Description

Crosslinkable rubber, its manufacturing method, and crosslinked rubber

[0001] The present invention relates to a crosslinkable rubber, a method for producing the same, and a crosslinked rubber product.

[0002] Crosslinkable rubbers such as acrylic rubber and nitrile rubber are widely used in the automotive industry, taking advantage of their excellent heat resistance, oil resistance, and ozone resistance.

[0003] For example, Patent Document 1 proposes an acrylic rubber having a residual coagulant content of 10 ppm by weight or more and 10,000 ppm by weight or less. The technology of Patent Document 1 aims to provide an acrylic rubber with excellent resistance to compression set that can be suitably used for automotive components such as seal materials, hose materials, vibration-proof materials, tube materials, belt materials, and boot materials.

[0004] On the other hand, when crosslinkable rubbers such as acrylic rubber and nitrile rubber are used as sealing materials, particularly for gasket applications, they are required to have excellent cold resistance and excellent compressive stress relaxation properties (high residual stress after a predetermined time has elapsed when compressed at a predetermined compression rate under predetermined temperature conditions). However, conventional crosslinkable rubbers such as the acrylic rubber described in Patent Document 1 have excellent compression set resistance, but have had the problem that their compressive stress relaxation properties are not necessarily sufficient.

[0005] International Publication No. 2018 / 079783

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a cross-linkable rubber that can give a cross-linked rubber product that is excellent in cold resistance and compressive stress relaxation property.

[0007] As a result of intensive research into achieving the above-mentioned object, the present inventors have found that by focusing on the relaxation time determined by performing pulse NMR measurement on the cross-linked rubber after high-temperature storage, which is obtained by cross-linking a cross-linkable rubber to form a cross-linked rubber before high-temperature storage and then storing the cross-linked rubber before high-temperature storage at a high temperature of 150°C for 1008 hours, and by setting the sum of intensities for a relaxation time of 0 to 8 msec within a predetermined range, it is possible to obtain a cross-linked rubber which is excellent in cold resistance and also in compressive stress relaxation property (when compressed at a predetermined compression rate under predetermined temperature conditions, the residual stress after a predetermined time has elapsed is high), and have thereby completed the present invention.

[0008] That is, according to the present invention, there is provided a crosslinkable rubber containing a rubber component having a carboxyl group as a crosslinkable group, wherein the crosslinkable rubber is crosslinked to form a cross-linked rubber before high-temperature storage, and then the cross-linked rubber before high-temperature storage is stored at high temperature at 150°C for 1008 hours to obtain a cross-linked rubber after high-temperature storage, and the cross-linked rubber after high-temperature storage has a sum of intensities over a relaxation time of 0 to 8 msec of 19.0 or less as determined by pulse NMR measurement.

[0009] In the cross-linkable rubber of the present invention, the sum of intensities over a relaxation time of 0 to 8 msec, as determined by pulse NMR measurement of the cross-linked rubber product after high-temperature storage, is preferably 17.0 to 18.0. In the cross-linkable rubber of the present invention, the sum of intensities over a relaxation time of 0 to 8 msec, as determined by cross-linking the cross-linkable rubber to form a cross-linked rubber product before high-temperature storage and performing pulse NMR measurement of the cross-linked rubber product before high-temperature storage, is preferably 19.0 or less. In the cross-linkable rubber of the present invention, the sum of intensities over a relaxation time of 0 to 8 msec, as determined by pulse NMR measurement of the cross-linked rubber product before high-temperature storage, is preferably 15.0 to 17.0.

[0010] In the crosslinkable rubber of the present invention, the measurement conditions for pulse NMR measurement can be configured as follows: Measurement time: 0 to 8 msec Interval between 90-degree pulse and 180-degree pulse in the first measurement: 0.04 msec Interval between 90-degree pulse and 180-degree pulse in the last measurement: 4 msec Total number of measurements: 30 points Timing of n-th measurement: T ｎ : T ｎ－１ +0.08×(DF) ｎ－１ +C [msec] (T ｎ [msec] indicates the measurement timing in the nth measurement as the elapsed time from the start of the measurement, and T ０ = 0 [msec], DF is a coefficient for specifying the measurement timing calculated by the formula "DF = exp(1 / (total number of measurements - 1) * ln (interval between 90-degree pulse and 180-degree pulse in the last measurement / interval between 90-degree pulse and 180-degree pulse in the first measurement)"), and C is a correction constant [msec].

[0011] In the cross-linkable rubber of the present invention, the rubber component is preferably a carboxyl group-containing acrylic rubber. In the cross-linkable rubber of the present invention, the carboxyl group-containing acrylic rubber preferably contains 50 to 99.9% by weight of (meth)acrylic acid ester monomer units and 0.1 to 10% by weight of carboxyl group-containing monomer units. In the cross-linkable rubber of the present invention, the rubber component is preferably a carboxyl group-containing nitrile rubber. In the cross-linkable rubber of the present invention, the carboxyl group-containing nitrile rubber preferably contains 5 to 60% by weight of α,β-ethylenically unsaturated nitrile monomer units, 10 to 80% by weight of conjugated diene monomer units, 1 to 30% by weight of carboxyl group-containing monomer units, and 10 to 50% by weight of α,β-ethylenically unsaturated monocarboxylic acid ester monomer units. In the cross-linkable rubber of the present invention, the cross-linkable rubber preferably contains a bisphenol-based antioxidant and / or a benzimidazole-based antioxidant.

[0012] The present invention also provides a cross-linked rubber product obtained by cross-linking the above-mentioned cross-linkable rubber.Furthermore, the present invention provides a method for producing the above-mentioned cross-linkable rubber, comprising the step of kneading the rubber component and the bisphenol-based antioxidant and / or benzimidazole-based antioxidant in a kneader.Alternatively, the present invention provides a method for producing the above-mentioned cross-linkable rubber, comprising the step of adding the bisphenol-based antioxidant and / or benzimidazole-based antioxidant to a latex containing the rubber component, followed by coagulation.

[0013] According to the present invention, it is possible to provide a cross-linkable rubber that can give a cross-linked rubber product that is excellent in cold resistance and compressive stress relaxation property.

[0014] FIG. 1 is a graph showing the relationship between relaxation time and relaxation intensity obtained by pulse NMR measurement in Examples and Comparative Examples.

[0015] The cross-linkable rubber of the present invention contains a rubber component having a carboxyl group as a cross-linkable group, and the cross-linkable rubber is cross-linked to form a cross-linked rubber before high-temperature storage, and then the cross-linked rubber before high-temperature storage is stored at high temperature at 150°C for 1008 hours to obtain a cross-linked rubber after high-temperature storage, which cross-linked rubber has a sum of intensities over a relaxation time of 0 to 8 msec of 19.0 or less as determined by pulse NMR measurement.

[0016] The crosslinkable rubber of the present invention is not particularly limited as long as it contains a rubber component having a carboxyl group as a crosslinkable group.

[0017] The cross-linkable rubber of the present invention is one in which the sum of intensities over a relaxation time of 0 to 8 msec is 19.0 or less, as determined by pulse NMR measurement of the cross-linked rubber obtained by cross-linking the rubber to form a cross-linked rubber product and then storing the cross-linked rubber product at a high temperature of 150°C for 1008 hours.

[0018] Here, the pulse NMR measurement is carried out using a pulse NMR device, and a predetermined pulse is applied to the cross-linked rubber product after high-temperature storage as the measurement target, and a response signal to the pulse is detected, and the １ In pulsed NMR measurements, a free induction decay curve is obtained as a pulse response. In the present invention, when the sum of the intensities for relaxation times of 0 to 8 msec is calculated from the free induction decay curve thus obtained, the sum of the intensities for relaxation times of 0 to 8 msec is configured to be 19.0 or less.

[0019] Figure 1 shows a graph of the relationship between relaxation time and relaxation strength obtained by pulse NMR measurement in the examples and comparative examples. Note that Figure 1 shows the measurement data of Example 4 and Comparative Example 1, which will be described later, and shows a total of four pieces of data: the measurement data of the cross-linked rubber product before high-temperature storage under conditions of 150°C for 1008 hours, and the measurement data of the cross-linked rubber product after high-temperature storage under conditions of 150°C for 1008 hours. In Figure 1, these are shown as Example 4 (before high-temperature storage), Example 4 (after high-temperature storage), Comparative Example 1 (before high-temperature storage), and Comparative Example 1 (after high-temperature storage), respectively.

[0020] As shown in Fig. 1, in pulsed NMR measurement, after the start of measurement, the relaxation intensity corresponding to the response signal to the pulse decreases as the relaxation time elapses. In the present invention, the sum of the intensities for the relaxation times of 0 to 8 msec shown in Fig. 1 is calculated. In this case, the relaxation intensity immediately after the start of measurement is normalized to 1 as the relaxation intensity, and the sum of the intensities for the relaxation times of 0 to 8 msec is calculated using a normalized relaxation intensity. Specifically, the relaxation intensity for each relaxation time is normalized by dividing it by the relaxation intensity at a relaxation time of 0, and the normalized value is used.

[0021] According to the findings of the present inventors, when a cross-linkable rubber is made into a cross-linked rubber product and pulse NMR measurement is performed after high-temperature storage at 150°C for 1008 hours, the cold resistance and compressive stress relaxation property can be improved by controlling the sum of intensities for a relaxation time of 0 to 8 msec to be a predetermined value or less, thereby finding a cross-linked rubber product excellent in cold resistance and compressive stress relaxation property. Specifically, when a cross-linkable rubber is made into a cross-linked rubber product and pulse NMR measurement is performed after high-temperature storage at 150°C for 1008 hours, the sum of intensities for a relaxation time of 0 to 8 msec is set to a value in the range of 19.0 or less, preferably in the range of 17.0 to 19.0, and more preferably in the range of 17.0 to 18.0. If this value is too large, the compressive stress relaxation property will deteriorate. As is clear from the graph in FIG. 1 , the decrease in relaxation strength over the relaxation time in Comparative Example 1 (after high-temperature storage) is slower than that in Example 4 (after high-temperature storage), and therefore the sum of the strengths is also larger, actually exceeding 19.0, resulting in poor compressive stress relaxation properties.

[0022] In the present invention, the sum of intensities for a relaxation time of 0 to 8 msec after high-temperature storage at 150°C for 1008 hours in the form of a cross-linked rubber product is sufficient as long as it is within the above-mentioned range, but the sum of intensities for a relaxation time of 0 to 8 msec in the condition before high-temperature storage at 150°C for 1008 hours, that is, when pulse NMR measurement is carried out on the cross-linked rubber in the form of a cross-linked rubber product without high-temperature storage, is preferably 19.0 or less, more preferably 15.0 to 17.0. By setting the sum of intensities for a relaxation time of 0 to 8 msec within the above-mentioned range before high-temperature storage, it is possible to further improve the compressive stress relaxation property. In the present invention, the difference between the sum of intensities for a relaxation time of 0 to 8 msec after high-temperature storage and the sum of intensities for a relaxation time of 0 to 8 msec before high-temperature storage (sum of intensities after high-temperature storage - sum of intensities before high-temperature storage) is preferably 1.5 or less, more preferably 1 or less, and even more preferably 0.1 to 0.8.

[0023] In the present invention, the specific measurement method and conditions for pulse NMR measurement can be the same as those described in the Examples below. Furthermore, when pulse NMR measurement is performed in the present invention, the cross-linked rubber product to be measured may be measured in a state containing a filler such as carbon black, or may be measured in a state free of compounding ingredients. However, measurement in a state free of compounding ingredients makes pulse NMR measurement relatively simple. Meanwhile, according to the findings of the present inventors, pulse NMR measurement can obtain data attributable to the rubber component regardless of the presence or absence of compounding ingredients, and therefore, it is possible to obtain substantially the same measurement data regardless of the presence or absence of fillers such as carbon black.

[0024] In the present invention, when pulse NMR measurement is performed, the crosslinkable rubber is crosslinked to form a crosslinked rubber product. The conditions for forming the crosslinked rubber product are not particularly limited, but the rubber component contained in the crosslinkable rubber should be sufficiently crosslinked. For example, crosslinking can be performed by blending approximately 0.4 to 0.5 times the molar equivalent of the crosslinking agent relative to the carboxyl groups (crosslinkable groups) contained in the rubber component contained in the crosslinkable rubber, at a crosslinking temperature of typically 130 to 250°C, preferably 150 to 240°C, and for a crosslinking time of typically 1 minute to 10 hours, preferably 2 minutes to 5 hours. Secondary crosslinking may also be performed. Furthermore, the crosslinking agent used in this case is not particularly limited, but polyamine compounds and their carbonates can be suitably used. Specific examples of polyamine compounds and their carbonates will be described later.

[0025] Specific crosslinking conditions are not particularly limited, but for example, when hexamethylenediamine carbamate is used as the crosslinking agent, a typical method is to prepare a crosslinked rubber product by adjusting the amount of hexamethylenediamine carbamate to 0.46 molar equivalents relative to the amount of carboxyl groups contained in the rubber component, and applying pressure at a temperature of 230°C and a pressure of 10 MPa for 3 minutes.

[0026] In the present invention, the method for making the cross-linkable rubber into a cross-linked rubber and adjusting the sum of intensities at a relaxation time of 0 to 8 msec within the above range after high-temperature storage at 150°C for 1008 hours is not particularly limited, but examples thereof include the following: For example, when producing the rubber component, the amount of molecular weight modifier is kept low or no molecular weight modifier is used, thereby reducing the low molecular weight components contained in the rubber component; a method for adjusting the amount of carboxyl groups as cross-linkable groups (for example, a method for increasing the amount of carboxyl groups); a method for adjusting the amount of monomers with short side chains (for example, methyl acrylate or methyl methacrylate) used as monomers constituting the rubber component (for example, a method for reducing the amount of monomers with short side chains used); and a method for blending a specific antioxidant into the cross-linkable rubber, and it is desirable to combine these methods appropriately.

[0027] In the present invention, from the viewpoint of being able to suitably control the sum of intensities at a relaxation time of 0 to 8 msec after high-temperature storage at 150°C for 1008 hours, the crosslinkable rubber preferably contains a bisphenol-based antioxidant and / or a benzimidazole-based antioxidant in addition to the rubber component. In this case, the crosslinkable rubber can be said to be a rubber composition containing the rubber component and the bisphenol-based antioxidant and / or the benzimidazole-based antioxidant.

[0028] Examples of bisphenol-based antioxidants include bisphenol alkanes such as 2,2'-methylenebis(4-methyl-6-tert-butylphenol) and 4,4'-butylidenebis(3-methyl-6-tert-butylphenol); and bisphenol sulfides such as 4,4'-thiobis(3-methyl-6-t-butylphenol). Of these, bisphenol alkanes are preferred, and 2,2'-methylenebis(4-methyl-6-tert-butylphenol) is more preferred.

[0029] Examples of the benzimidazole-based antioxidant include 2-mercaptobenzimidazole, zinc salt of 2-mercaptobenzimidazole, 2-mercaptomethylbenzimidazole, etc. Among these, 2-mercaptobenzimidazole is preferred.

[0030] The crosslinkable rubber of the present invention preferably contains at least one of a bisphenol-based antioxidant and a benzimidazole-based antioxidant, but preferably contains both a bisphenol-based antioxidant and a benzimidazole-based antioxidant from the viewpoint of more suitably controlling the sum of intensities at a relaxation time of 0 to 8 msec after the crosslinkable rubber is made into a crosslinked rubber and stored at a high temperature of 150°C for 1008 hours. In this case, the ratio (weight ratio) of the bisphenol-based antioxidant to the benzimidazole-based antioxidant is preferably 0.3:0.7-0.7-0.3, more preferably 0.4:0.6-0.6-0.4.

[0031] The total content of the bisphenol-based antioxidant and the benzimidazole-based antioxidant in the crosslinkable rubber of the present invention is preferably 1 to 5 parts by weight, more preferably 2 to 5 parts by weight, and even more preferably 2 to 4 parts by weight, per 100 parts by weight of the rubber component contained in the crosslinkable rubber.

[0032] The method for incorporating the bisphenol-based antioxidant and / or benzimidazole-based antioxidant into the crosslinkable rubber of the present invention is not particularly limited, and examples thereof include a method of kneading a rubber component and the bisphenol-based antioxidant and / or benzimidazole-based antioxidant in a kneader, and a method of adding the bisphenol-based antioxidant and / or benzimidazole-based antioxidant to a latex containing a rubber component, followed by coagulation.

[0033] The crosslinkable rubber of the present invention is not particularly limited as long as it contains a rubber component having a carboxyl group as a crosslinkable group, and examples thereof include carboxyl group-containing acrylic rubber, carboxyl group-containing nitrile rubber, and carboxyl group-containing synthetic polyisoprene rubber. Of these, carboxyl group-containing acrylic rubber and carboxyl group-containing nitrile rubber are preferred.

[0034] <Carboxyl Group-Containing Acrylic Rubber> The carboxyl group-containing acrylic rubber used in the present invention has, in its molecule, as the main component (for example, 50% by weight or more of all monomer units in the acrylic rubber), (meth)acrylic acid ester monomer units (meaning acrylic acid ester monomers and / or methacrylic acid ester monomers; hereinafter, the same applies to methyl (meth)acrylate, etc.) and carboxyl group-containing monomer units.

[0035] The (meth)acrylic acid ester monomer forming the (meth)acrylic acid ester monomer unit as the main component of the carboxyl group-containing acrylic rubber used in the present invention is not particularly limited, but examples thereof include (meth)acrylic acid alkyl ester monomers and (meth)acrylic acid alkoxyalkyl ester monomers.

[0036] The (meth)acrylic acid alkyl ester monomer is not particularly limited, but is preferably an ester of an alkanol having 1 to 8 carbon atoms with (meth)acrylic acid, and specific examples thereof 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, with ethyl acrylate and n-butyl acrylate being particularly preferred. These may be used alone or in combination of two or more.

[0037] The (meth)acrylic acid alkoxyalkyl ester monomer is not particularly limited, but is more preferably an ester of an alkoxyalkyl alcohol having 2 to 12 carbon atoms with (meth)acrylic acid, and more preferably an ester of an alkoxyalkyl alcohol having 2 to 8 carbon atoms with (meth)acrylic acid. Specific examples 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. Of these, 2-ethoxyethyl (meth)acrylate and 2-methoxyethyl (meth)acrylate are preferred, and 2-ethoxyethyl acrylate and 2-methoxyethyl acrylate are particularly preferred. These may be used alone or in combination of two or more.

[0038] The content of (meth)acrylic acid ester monomer units in the carboxyl group-containing acrylic rubber used in the present invention is preferably 50 to 99.9% by weight, more preferably 70 to 99.5% by weight, even more preferably 90 to 99.5% by weight, and particularly preferably 95 to 99% by weight. By setting the content of (meth)acrylic acid ester monomer units within the above range, the weather resistance, heat resistance, and oil resistance of the obtained cross-linked rubber can be improved.

[0039] In the present invention, the (meth)acrylic acid ester monomer units preferably consist of 30 to 100% by weight of (meth)acrylic acid alkyl ester monomer units and 70 to 0% by weight of (meth)acrylic acid alkoxyalkyl ester monomer units.

[0040] The carboxyl group-containing monomer constituting the carboxyl group-containing monomer unit is not particularly limited, but examples thereof include α,β-ethylenically unsaturated monocarboxylic acids having 3 to 12 carbon atoms, α,β-ethylenically unsaturated dicarboxylic acids having 4 to 12 carbon atoms, and monoesters of α,β-ethylenically unsaturated dicarboxylic acids having 4 to 12 carbon atoms and alkanols having 1 to 8 carbon atoms.

[0041] Specific examples of the α,β-ethylenically unsaturated monocarboxylic acid having 3 to 12 carbon atoms include acrylic acid, methacrylic acid, α-ethylacrylic acid, crotonic acid, and cinnamic acid. Specific examples of the α,β-ethylenically unsaturated dicarboxylic acid having 4 to 12 carbon atoms include butenedioic acids such as fumaric acid and maleic acid, itaconic acid, citraconic acid, and chloromaleic acid. Specific examples of monoesters of α,β-ethylenically unsaturated dicarboxylic acids having 4 to 12 carbon atoms and alkanols having 1 to 8 carbon atoms include butenedioic acid mono-chain alkyl esters such as monomethyl fumarate, monoethyl fumarate, mono-n-butyl fumarate, monomethyl maleate, monoethyl maleate, and mono-n-butyl maleate; butenedioic acid monoesters having an alicyclic structure such as monocyclopentyl fumarate, monocyclohexyl fumarate, monocyclohexenyl fumarate, monocyclopentyl maleate, monocyclohexyl maleate, and monocyclohexenyl maleate; and itaconic acid monoesters such as monomethyl itaconate, monoethyl itaconate, mono-n-butyl itaconate, and monocyclohexyl itaconate. Among these, butenedioic acid mono-chain alkyl esters or butenedioic acid monoesters having an alicyclic structure are preferred, mono-n-butyl fumarate, mono-n-butyl maleate, monocyclohexyl fumarate, and monocyclohexyl maleate are more preferred, and mono-n-butyl fumarate and monocyclohexyl maleate are even more preferred. These carboxyl group-containing monomers can be used alone or in combination of two or more. Among the above-mentioned monomers, dicarboxylic acids also include those that exist as anhydrides.

[0042] The content of the carboxyl group-containing monomer unit is preferably 0.1 to 10% by weight, more preferably 0.5 to 7% by weight, and even more preferably 1 to 5% by weight. When the content of the carboxyl group-containing monomer unit is within the above range, the compressive stress relaxation property of the obtained cross-linked rubber product can be further improved.

[0043] The content of carboxyl groups, i.e., the number of moles (ephr) of carboxyl groups per 100 g of carboxyl group-containing acrylic rubber, is preferably 4×10 －４ ~4 x 10 －１ (ephr), more preferably 1 x 10 －３ ~2 x 10 －１ (ephr), more preferably 5 x 10 －３ ~1 x 10 －１ (ephr).

[0044] In addition, the carboxyl group-containing acrylic rubber used in the present invention may have other crosslinkable monomer units as required.The crosslinkable monomers that form other crosslinkable monomer units include epoxy group-containing monomers such as epoxy group-containing (meth)acrylic acid esters and epoxy group-containing ethers; monomers having halogen atoms such as unsaturated alcohol esters of halogen-containing saturated carboxylic acids, (meth)acrylic acid haloalkyl esters, (meth)acrylic acid haloacyloxyalkyl esters, (meth)acrylic acid (haloacetylcarbamoyloxy) alkyl esters, halogen-containing unsaturated ethers, halogen-containing unsaturated ketones, halomethyl group-containing aromatic vinyl compounds, halogen-containing unsaturated amides, and haloacetyl group-containing unsaturated monomers; diene monomers such as conjugated diene monomers and non-conjugated diene monomers.

[0045] Furthermore, the carboxyl group-containing acrylic rubber used in the present invention may, in addition to the (meth)acrylic acid ester monomer units and the carboxyl group-containing monomer units, optionally contain units of other monomers copolymerizable with the (meth)acrylic acid ester monomer or the carboxyl group-containing monomer.

[0046] The copolymerizable other monomer is not particularly limited, but examples thereof include aromatic vinyl monomers, α,β-ethylenically unsaturated nitrile monomers, monomers having two or more acryloyloxy groups (hereinafter sometimes referred to as "polyfunctional acrylic monomers"), olefin-based monomers, and vinyl ether compounds.

[0047] Specific examples of aromatic vinyl monomers include styrene, α-methylstyrene, and divinylbenzene. Specific examples of α,β-ethylenically unsaturated nitrile monomers include acrylonitrile and methacrylonitrile. Specific examples of polyfunctional acrylic monomers include ethylene glycol di(meth)acrylate and propylene glycol di(meth)acrylate. Specific examples of olefinic monomers include ethylene, propylene, 1-butene, and 1-octene. Specific examples of vinyl ether compounds include vinyl acetate, ethyl vinyl ether, and n-butyl vinyl ether.

[0048] Among these, styrene, acrylonitrile, methacrylonitrile, ethylene and vinyl acetate are preferred, and acrylonitrile, methacrylonitrile, ethylene and vinyl acetate are more preferred.

[0049] The copolymerizable other monomers may be used alone or in combination of two or more. The content of units of the other monomers in the carboxyl group-containing acrylic rubber is preferably 30% by weight or less, more preferably 10% by weight or less.

[0050] The weight average molecular weight (Mw) of the carboxyl group-containing acrylic rubber used in the present invention is not particularly limited, but is preferably 50,000 to 5,000,000, more preferably 100,000 to 4,000,000, and even more preferably 150,000 to 3,500,000. The weight average molecular weight of the carboxyl group-containing acrylic rubber can be measured, for example, by gel permeation chromatography as a polystyrene-equivalent value.

[0051] The Mooney viscosity (ML1+4, 100°C) (polymer Mooney) of the carboxyl group-containing acrylic rubber used in the present invention is preferably 10-150, more preferably 10-80, even more preferably 20-70, and particularly preferably 25-60.

[0052] The carboxyl group-containing acrylic rubber used in the present invention can be produced by polymerizing the above-mentioned monomers. The polymerization reaction can be carried out using any of emulsion polymerization, suspension polymerization, bulk polymerization, and solution polymerization methods, but emulsion polymerization is preferred from the standpoint of ease of control of the polymerization reaction. During emulsion polymerization, commonly used polymerization auxiliary materials can be used in addition to an emulsifier and a polymerization initiator. Emulsion polymerization can be carried out in any of batch, semi-batch, and continuous modes. Polymerization is usually carried out at a temperature ranging from 0 to 70°C, preferably from 5 to 50°C.

[0053] Furthermore, during emulsion polymerization, a molecular weight modifier may or may not be used, but as described above, from the viewpoint of reducing the low molecular weight components contained in the carboxyl group-containing acrylic rubber, thereby converting the crosslinkable rubber into a cross-linked rubber, and suitably controlling the sum of the intensities over a relaxation time of 0 to 8 msec after high-temperature storage at 150°C for 1008 hours within the above range, it is preferable to keep the amount of molecular weight modifier low or to adopt an embodiment in which no molecular weight modifier is used. The amount of molecular weight modifier used is preferably 0 to 0.2 parts by weight, more preferably 0 to 0.05 parts by weight, per 100 parts by weight of the monomers used in the polymerization. Examples of the molecular weight modifier include, but are not limited to, mercaptans such as t-dodecyl mercaptan, n-dodecyl mercaptan, and octyl mercaptan; halogenated hydrocarbons such as carbon tetrachloride, methylene chloride, and methylene bromide; α-methylstyrene dimer; and sulfur-containing compounds such as tetraethylthiuram disulfide, dipentamethylenethiuram disulfide, and diisopropylxanthogen disulfide. These may be used alone or in combination of two or more.

[0054] The latex of the carboxyl group-containing acrylic rubber obtained by emulsion polymerization is then coagulated, and if necessary, washed and dried to obtain a solid carboxyl group-containing acrylic rubber. In this case, a bisphenol-based antiaging agent and / or a benzimidazole-based antiaging agent may be added to the latex of the carboxyl group-containing acrylic rubber in advance, followed by coagulation, and if necessary, washing and drying to obtain a solid carboxyl group-containing acrylic rubber containing the bisphenol-based antiaging agent and / or the benzimidazole-based antiaging agent.

[0055] <Carboxyl Group-Containing Nitrile Rubber> The carboxyl group-containing nitrile rubber used in the present invention is not particularly limited, but examples thereof include those obtained by copolymerizing an α,β-ethylenically unsaturated nitrile monomer, a carboxyl group-containing monomer, and other copolymerizable monomers that are added as necessary.

[0056] The α,β-ethylenically unsaturated nitrile monomer is not particularly limited as long as it is an α,β-ethylenically unsaturated compound having a nitrile group, and examples thereof include acrylonitrile; α-halogenoacrylonitriles such as α-chloroacrylonitrile and α-bromoacrylonitrile; and α-alkylacrylonitriles such as methacrylonitrile. Of these, acrylonitrile and methacrylonitrile are preferred, and acrylonitrile is more preferred. The α,β-ethylenically unsaturated nitrile monomer may be used alone or in combination.

[0057] The content of the α,β-ethylenically unsaturated nitrile monomer unit in the carboxyl group-containing nitrile rubber used in the present invention is preferably 5 to 60% by weight, more preferably 10 to 50% by weight, and even more preferably 15 to 40% by weight. By setting the content of the α,β-ethylenically unsaturated nitrile monomer unit within the above range, it is possible to achieve a well-balanced and excellent oil resistance and cold resistance.

[0058] As the carboxyl group-containing monomer, for example, the same ones as those exemplified for the carboxyl group-containing acrylic rubber described above can be used, and the preferred ones are also the same.

[0059] The content of the carboxyl group-containing monomer unit in the carboxyl group-containing nitrile rubber used in the present invention is preferably 1 to 30% by weight, more preferably 2 to 25% by weight, and even more preferably 2 to 20% by weight. When the content of the carboxyl group-containing monomer unit is within the above range, the compressive stress relaxation property of the obtained cross-linked rubber can be further improved.

[0060] The carboxyl group-containing nitrile rubber used in the present invention preferably further contains conjugated diene monomer units so that the resulting cross-linked rubber has rubber elasticity.

[0061] As the conjugated diene monomer forming the conjugated diene monomer unit, conjugated diene monomers having 4 to 6 carbon atoms such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, and chloroprene are preferred, 1,3-butadiene and isoprene are more preferred, and 1,3-butadiene is particularly preferred. The conjugated diene monomers may be used alone or in combination.

[0062] The content of the conjugated diene monomer units (including hydrogenated portions) is preferably 10 to 80% by weight, more preferably 25 to 75% by weight, and even more preferably 45 to 65% by weight, based on the total monomer units. By setting the content of the conjugated diene monomer units within the above range, the obtained cross-linked rubber product can be made excellent in rubber elasticity while maintaining good heat resistance and chemical resistance stability.

[0063] Moreover, from the viewpoint of further enhancing the cold resistance of the resulting cross-linked rubber, the carboxyl group-containing nitrile rubber used in the present invention preferably further contains an α,β-ethylenically unsaturated monocarboxylic acid ester monomer unit.

[0064] The α,β-ethylenically unsaturated monocarboxylic acid ester monomer is not particularly limited, but examples thereof include (meth)acrylic acid ester monomers, and as the (meth)acrylic acid ester monomer, for example, the same ones as those exemplified in the above-mentioned carboxyl group-containing acrylic rubber can be used, and preferred ones are also the same.

[0065] The content of the α,β-ethylenically unsaturated monocarboxylic acid ester monomer unit in the carboxyl group-containing nitrile rubber used in the present invention is preferably 10 to 50% by weight, more preferably 20 to 45% by weight, and even more preferably 25 to 40% by weight. By setting the content of the α,β-ethylenically unsaturated monocarboxylic acid ester monomer unit within the above range, the cold resistance of the obtained cross-linked rubber can be further improved.

[0066] Furthermore, the carboxyl group-containing nitrile rubber used in the present invention may contain, in addition to the α,β-ethylenically unsaturated nitrile monomer units, the carboxyl group-containing monomer units, and the conjugated diene monomer units and the α,β-ethylenically unsaturated monocarboxylic acid ester monomer units copolymerized as necessary, units of other monomers copolymerizable with the monomers forming these units. Examples of such other monomers include ethylene, α-olefin monomers, aromatic vinyl monomers, fluorine-containing vinyl monomers, and copolymerizable antioxidants.

[0067] The α-olefin monomer preferably has 3 to 12 carbon atoms, and examples thereof include propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene.

[0068] Examples of the aromatic vinyl monomer include styrene, α-methylstyrene, and vinylpyridine.

[0069] Examples of the fluorine-containing vinyl monomer include fluoroethyl vinyl ether, fluoropropyl vinyl ether, o-trifluoromethylstyrene, vinyl pentafluorobenzoate, difluoroethylene, and tetrafluoroethylene.

[0070] Examples of the copolymerizable antioxidant include N-(4-anilinophenyl)acrylamide, N-(4-anilinophenyl)methacrylamide, N-(4-anilinophenyl)cinnamamide, N-(4-anilinophenyl)crotonamide, N-phenyl-4-(3-vinylbenzyloxy)aniline, and N-phenyl-4-(4-vinylbenzyloxy)aniline.

[0071] A plurality of types of these copolymerizable other monomers may be used in combination. The content of the units of the other monomers is preferably 30% by weight or less, more preferably 10% by weight or less, based on the total monomer units constituting the carboxyl group-containing nitrile rubber.

[0072] The carboxyl group-containing nitrile rubber used in the present invention may be hydrogenated. In this case, the iodine value of the carboxyl group-containing nitrile rubber is preferably 120 or less, more preferably 50 or less, and even more preferably 30 or less.

[0073] The content of carboxyl groups in the carboxyl group-containing nitrile rubber used in the present invention, i.e., the number of moles (ephr) of carboxyl groups per 100 g of the carboxyl group-containing nitrile rubber, is preferably 5×10 －４ ~5 x 10 －１ (ephr), more preferably 1 x 10 －３ ~1 x 10 －１ (ephr), more preferably 5 x 10 －３ ~6 x 10 －２ (ephr).

[0074] The carboxyl group-containing nitrile rubber used in the present invention preferably has a Mooney viscosity (ML1+4, 100°C) (polymer Mooney) of 15 to 200, more preferably 30 to 100, and even more preferably 45 to 90.

[0075] The method for producing the carboxyl group-containing nitrile rubber used in the present invention is not particularly limited, but it can be produced by copolymerizing the above-mentioned monomers by emulsion polymerization and, if necessary, hydrogenating the carbon-carbon double bonds in the resulting copolymer. During emulsion polymerization, in addition to an emulsifier and a polymerization initiator, commonly used polymerization auxiliary materials can be used. The emulsion polymerization may be any of a batch system, a semi-batch system, and a continuous system. The polymerization is usually carried out at a temperature range of 0 to 70°C, preferably 5 to 50°C.

[0076] Furthermore, during emulsion polymerization, a molecular weight modifier may or may not be used, but as described above, from the viewpoint of reducing the low molecular weight components contained in the carboxyl group-containing acrylic rubber, thereby converting the crosslinkable rubber into a cross-linked rubber, and suitably controlling the sum of the intensities over a relaxation time of 0 to 8 msec after high-temperature storage at 150°C for 1008 hours within the above range, it is preferable to keep the amount of molecular weight modifier low or to adopt an embodiment in which no molecular weight modifier is used. The amount of molecular weight modifier used is preferably 0 to 0.5 parts by weight, more preferably 0 to 0.2 parts by weight, per 100 parts by weight of the monomers used in polymerization. Examples of the molecular weight modifier include, but are not limited to, mercaptans such as t-dodecyl mercaptan, n-dodecyl mercaptan, and octyl mercaptan; halogenated hydrocarbons such as carbon tetrachloride, methylene chloride, and methylene bromide; α-methylstyrene dimer; and sulfur-containing compounds such as tetraethylthiuram disulfide, dipentamethylenethiuram disulfide, and diisopropylxanthogen disulfide. These may be used alone or in combination of two or more.

[0077] Furthermore, the obtained copolymer is subjected to hydrogenation (hydrogenation reaction) as necessary. Hydrogenation may be carried out by a known method, but aqueous phase hydrogenation is preferred. Examples of aqueous phase hydrogenation include direct aqueous phase hydrogenation, in which hydrogen is supplied to a reaction system in the presence of a hydrogenation catalyst to carry out hydrogenation, and indirect aqueous phase hydrogenation, in which hydrogenation is carried out by reduction in the presence of an oxidizing agent, a reducing agent, and an activating agent. Of these, direct aqueous phase hydrogenation is preferred.

[0078] In the aqueous phase direct hydrogenation method, the concentration of the copolymer in the aqueous phase (concentration in the latex state) is preferably 40% by weight or less to prevent aggregation. The hydrogenation catalyst is not particularly limited as long as it is a compound that is not easily decomposed by water. Specific examples of palladium catalysts include palladium metal; palladium oxide; palladium hydroxide; palladium salts of carboxylic acids such as formic acid, acetic acid, propionic acid, lauric acid, succinic acid, oleic acid, and phthalic acid; palladium chlorides such as palladium chloride, dichloro(cyclooctadiene)palladium, dichloro(norbornadiene)palladium, and ammonium hexachloropalladate(IV); iodides such as palladium iodide; and palladium sulfate dihydrate. Among these, palladium metal, palladium salts of carboxylic acids, palladium chloride, dichloro(norbornadiene)palladium, and ammonium hexachloropalladate(IV) are particularly preferred. The amount of the hydrogenation catalyst used may be determined as appropriate, but is preferably 5 to 6000 ppm by weight, more preferably 10 to 4000 ppm by weight, based on the copolymer obtained by polymerization.

[0079] Then, the latex of the carboxyl group-containing nitrile rubber obtained by emulsion polymerization and hydrogenated as needed is coagulated, and washed and dried as needed, to obtain a solid carboxyl group-containing nitrile rubber. In this case, a bisphenol-based antioxidant and / or a benzimidazole-based antioxidant may be added to the latex of the carboxyl group-containing nitrile rubber in advance, followed by coagulation, and washed and dried as needed, to obtain a solid carboxyl group-containing nitrile rubber containing the bisphenol-based antioxidant and / or the benzimidazole-based antioxidant.

[0080] <Compounding Agents, etc.> The crosslinkable rubber of the present invention may contain various compounding agents in addition to a rubber component such as the above-mentioned carboxyl group-containing acrylic rubber or carboxyl group-containing acrylic rubber, and a bisphenol-based antioxidant and / or a benzimidazole-based antioxidant added as needed. In this case, the crosslinkable rubber of the present invention can be said to be a rubber composition containing the rubber component, the bisphenol-based antioxidant and / or the benzimidazole-based antioxidant added as needed, and the compounding agents.

[0081] An example of such compounding agent is a crosslinking agent. Since the crosslinkable rubber of the present invention contains a rubber component having a carboxyl group as a crosslinkable group, the crosslinking agent is not particularly limited as long as it can crosslink the carboxyl group, but polyamine compounds and carbonates thereof are preferably used.

[0082] The polyamine compound and carbonate thereof are not particularly limited, but polyamine compounds having 4 to 30 carbon atoms and carbonates thereof are preferred. Examples of such polyamine compounds and carbonates thereof include aliphatic polyamine compounds and carbonates thereof, and aromatic polyamine compounds.

[0083] The aliphatic polyamine compounds and carbonates thereof are not particularly limited, but examples thereof include hexamethylenediamine, hexamethylenediamine carbamate, and N,N'-dicinnamylidene-1,6-hexanediamine, etc. Among these, hexamethylenediamine carbamate is preferred.

[0084] The aromatic polyvalent amine compound is not particularly limited, but examples thereof 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, 4,4'-diaminobenzanilide, 4,4'-bis(4-aminophenoxy)biphenyl, m-xylylenediamine, p-xylylenediamine, and 1,3,5-benzenetriamine. Of these, 2,2'-bis[4-(4-aminophenoxy)phenyl]propane is preferred.

[0085] The content of the crosslinking agent is preferably 0.1 to 10 parts by weight, more preferably 0.1 to 5 parts by weight, and even more preferably 0.2 to 4 parts by weight, based on 100 parts by weight of the rubber component.

[0086] The crosslinkable rubber of the present invention may further contain a crosslinking accelerator. The crosslinking accelerator is not particularly limited, but may include guanidine compounds, diazabicycloalkene compounds, imidazole compounds, quaternary onium salts, tertiary phosphine compounds, aliphatic monovalent secondary amine compounds, and aliphatic monovalent tertiary amine compounds. Among these, guanidine compounds, diazabicycloalkene compounds, and aliphatic monovalent secondary amine compounds are preferred, and guanidine compounds and diazabicycloalkene compounds are particularly preferred. These basic crosslinking accelerators may be used alone or in combination of two or more.

[0087] 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]undec-7-ene and 1,5-diazabicyclo[4.3.0]non-5-ene. 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.

[0088] The aliphatic monovalent secondary amine compound is a compound in which two hydrogen atoms of ammonia are substituted with an aliphatic hydrocarbon group. The aliphatic hydrocarbon group substituting the hydrogen atom preferably has 1 to 30 carbon atoms. Specific examples of the aliphatic monovalent secondary amine compound include 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.

[0089] The aliphatic monovalent tertiary amine compound is a compound in which all three hydrogen atoms of ammonia have been substituted with aliphatic hydrocarbon groups. The aliphatic hydrocarbon group substituting the hydrogen atoms preferably has 1 to 30 carbon atoms. Specific examples of the aliphatic monovalent tertiary amine compound include trimethylamine, triethylamine, tripropylamine, triallylamine, triisopropylamine, tri-n-butylamine, tri-t-butylamine, tri-sec-butylamine, trihexylamine, triheptylamine, trioctylamine, trinonylamine, tridecylamine, triundecylamine, and tridodecylamine.

[0090] The content of the crosslinking accelerator is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 7.5 parts by weight, and particularly preferably 1 to 5 parts by weight, based on 100 parts by weight of the rubber component.

[0091] The crosslinkable rubber of the present invention may further contain a filler. The filler is not particularly limited, but examples thereof include reinforcing fillers and non-reinforcing fillers, and among these, reinforcing fillers are preferred.

[0092] Examples of reinforcing fillers include carbon blacks such as furnace black, acetylene black, thermal black, channel black, and graphite; and silicas such as wet silica, dry silica, and colloidal silica. Non-reinforcing fillers include quartz powder, clays such as diatomaceous earth, zinc oxide, basic magnesium carbonate, activated calcium carbonate, magnesium silicate, aluminum silicate, titanium dioxide, talc, aluminum sulfate, calcium sulfate, and barium sulfate. Among these, carbon black is preferred because it can further improve the compressive stress relaxation property. It is preferable to use carbon black with a relatively small specific surface area because it can further improve the compressive stress relaxation property. The BET specific surface area of ​​the carbon black is preferably 50.0 m ２ / g or less.

[0093] These fillers can be used alone or in combination of two or more. The content of the filler is not particularly limited, but is preferably 10 to 200 parts by weight, more preferably 30 to 100 parts by weight, and even more preferably 40 to 80 parts by weight, per 100 parts by weight of the rubber component. By setting the filler content within the above range, the compressive stress relaxation property can be further improved. In particular, the lower the content of carbon black as a filler within the above range, the more excellent the compressive stress relaxation property can be.

[0094] In addition to the above-mentioned compounding agents, the crosslinkable rubber of the present invention can also be compounded with compounding agents commonly used in the field of rubber processing. Examples of such compounding agents include light stabilizers, scorch inhibitors, plasticizers, processing aids, adhesives, slip agents, lubricants, flame retardants, mildew inhibitors, antistatic agents, colorants, crosslinking retarders, etc. The amount of these compounding agents to be compounded is not particularly limited as long as it does not impair the purpose and effects of the present invention, and they can be compounded in amounts appropriate to the purpose of compounding.

[0095] The method for blending the various compounding agents into the crosslinkable rubber of the present invention is not particularly limited, but the rubber component is blended with the crosslinking agent and various other compounding agents used as needed, and the mixture is mixed and kneaded using an open roll, a Banbury mixer, various kneaders, or the like, and then further kneaded using a kneading roll to prepare the crosslinkable rubber.

[0096] The order of mixing the components is not particularly limited, but it is preferable to thoroughly mix the components that are resistant to reaction or decomposition by heat, and then mix the crosslinking agent and other components that are resistant to reaction or decomposition by heat for a short period of time at a temperature at which they will not react or decompose.

[0097] <Rubber Cross-Linked Product> The cross-linked rubber product of the present invention can be obtained by cross-linking the cross-linkable rubber of the present invention described above. The cross-linked rubber product of the present invention can be produced by using the cross-linkable rubber of the present invention to mold into the desired shape using a molding machine such as an extruder, injection molding machine, compressor, or roll, and then heating to cause a cross-linking reaction and fix the shape as a cross-linked rubber product. In this case, cross-linking may be carried out after molding in advance or simultaneously with molding. The molding temperature is usually 10 to 200°C, preferably 25 to 120°C. The cross-linking temperature is usually 130 to 250°C, preferably 150 to 240°C, and the cross-linking time is usually 1 minute to 10 hours, preferably 2 minutes to 5 hours. The heating method may be appropriately selected from methods used for cross-linking rubber, such as press heating, steam heating, oven heating, and hot air heating.

[0098] Depending on the shape, size, etc. of the cross-linked rubber product, the cross-linked rubber product of the present invention may be further heated to carry out secondary cross-linking. The secondary cross-linking time varies depending on the heating method, cross-linking temperature, shape, etc., but is preferably carried out for 1 to 48 hours. The heating method and heating temperature may be selected appropriately.

[0099] The cross-linked rubber product of the present invention thus obtained is obtained by cross-linking the above-mentioned cross-linkable rubber of the present invention, and therefore the sum of intensities at a relaxation time of 0 to 8 msec, as determined by pulse NMR measurement after high-temperature storage at 150°C for 1008 hours, is 19.0 or less, preferably in the range of 17.0 to 19.0, and more preferably in the range of 17.0 to 18.0. Furthermore, the cross-linked rubber product of the present invention, when pulse NMR measurement is performed under the conditions before high-temperature storage at 150°C for 1008 hours or without high-temperature storage, preferably has a sum of intensities at a relaxation time of 0 to 8 msec of 19.0 or less, more preferably 15.0 to 17.0.

[0100] The cross-linked rubber product of the present invention is suitably used as sealing materials such as O-rings, packings, diaphragms, oil seals, shaft seals, bearing sheaths, mechanical seals, wellhead seals, seals for electric and electronic devices, and seals for air compressors; various gaskets such as cylinder head gaskets attached to the joint between a cylinder block and a cylinder head, rocker cover gaskets attached to the joint between a rocker cover and a cylinder head, oil pan gaskets attached to the joint between an oil pan and a cylinder head or a transmission case, gaskets for fuel cell separators attached between a pair of housings sandwiching a unit cell comprising a positive electrode, an electrolyte plate, and a negative electrode, and gaskets for the top covers of hard disk drives; cushioning materials, vibration-isolating materials; wire coating materials; industrial belts; tubes and hoses; sheets; etc. In particular, the cross-linked rubber product of the present invention has excellent cold resistance and compressive stress relaxation property, and is therefore suitably used in applications requiring such properties, particularly gasket applications.

[0101] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. In the following, "parts" are by weight unless otherwise specified. The methods for testing or evaluating physical properties and characteristics are as follows.

[0102] [Monomer Composition of Carboxyl Group-Containing Acrylic Rubber] The monomer composition of the carboxyl group-containing acrylic rubber was calculated from the amount of each monomer used in the polymerization reaction and the polymerization conversion rate. Specifically, in the emulsion polymerization reaction in each example and comparative example, no unreacted monomer was found, and the polymerization conversion rate was approximately 100%, so the amount of each monomer used in the polymerization reaction was considered to be the same as the content ratio of each monomer unit constituting the carboxyl group-containing acrylic rubber.

[0103] [Pulse NMR Measurement] The crosslinkable rubber composition for pulse NMR measurement was crosslinked by applying pressure at a temperature of 230°C and a pressure of 10 MPa for 3 minutes using a press molding machine (product name "NF-50T", manufactured by Shinto Metal Industries Co., Ltd.) to produce a sheet with a thickness of 1.0 mm. The sheet was then cut into a length of 10 mm x width of 10 mm x thickness of 1.0 mm, thereby obtaining a crosslinked rubber product for pulse NMR measurement (measurement sample) before high-temperature storage.

[0104] Next, the cross-linked rubber for pulse NMR measurement (measurement sample) prepared above before high-temperature storage was placed in a TD-NMR sample tube (10 mmφ) and packed into the pulse NMR inner tube, and pulse NMR measurement was carried out. Pulse NMR is a method of detecting a response signal to a pulse and determining the １ This is a method for determining the H nuclear magnetic relaxation time, and in pulse NMR measurement, a free induction decay curve is obtained as a pulse response. The measurement equipment used was a pulse NMR device (trade name "minispec mq20", manufactured by Bruker), the measurement method was the spin echo method, and the measurement nuclear frequency was 19.95 MHz ( １ H nucleus).

[0105] The measurement conditions were as follows. That is, first, the measurement sample was held at 150°C for 15 minutes, and then the measurement was performed under the following conditions: Measurement time: 0 to 8 msec Interval between 90-degree pulse and 180-degree pulse in the first measurement: 0.04 msec Interval between 90-degree pulse and 180-degree pulse in the last measurement: 4 msec Total number of measurements: 30 times Number of integrations: 8 times Spin echo repetition time: 2 sec Measurement temperature: 150°C. In this measurement, the total number of measurements was 30, and the measurement timing for each measurement was as follows. Here, T ｎ [msec] indicates the measurement timing in the nth measurement as the elapsed time from the start of the measurement, and T ０ = 0 [msec], DF is a coefficient for defining the measurement timing calculated by the following formula, C is a correction constant [msec], which is a value caused by the measurement system, etc., and is usually the first measurement timing T １ DF is a value between 0 and 15% of the time corresponding to the measurement time. DF = exp(1 / (total number of measurements - 1) * ln (interval between 90 degree pulse and 180 degree pulse in the last measurement / interval between 90 degree pulse and 180 degree pulse in the first measurement)) In this measurement, DF is calculated as follows: DF = exp(1 / (30-1) * ln(4 / 0.04)). (Each measurement timing) First measurement timing T １ : 0.08 + C [msec] Second measurement timing T ２ : T １ +0.08×DF+C [msec] Third measurement timing T ３ : T ２ +0.08×(DF) ２ +C [msec] nth measurement timing T ｎ : T ｎ－１ +0.08×(DF) ｎ－１ +C [msec] The value of "0.08" at each of the above measurement timings is twice the 0.04 msec interval between the 90-degree pulse and the 180-degree pulse in the initial measurement (first measurement). In this example and the comparative example, the correction constant C was set to 0.00868 [msec].

[0106] Then, a free induction decay curve (relaxation strength y versus relaxation time x) in spin-spin relaxation of the measurement sample is created, and the relaxation strength y at each relaxation time of the obtained free induction decay curve is calculated. ｎ The intensity was normalized by dividing by the relaxation intensity at the relaxation time of 0. That is, the relaxation intensity at the relaxation time of 0 was normalized as 1. Next, the normalized relaxation intensity y ｎ By summing these values, the sum of the intensities of the cross-linked rubber for pulse NMR measurement at a relaxation time of 0 to 8 msec before high-temperature storage (sum of intensities before high-temperature storage) was determined.

[0107] Furthermore, in the same manner as above, a cross-linked rubber product for pulse NMR measurement before high-temperature storage was prepared, and this was stored at high temperature under conditions of 150°C for 1008 hours to obtain a cross-linked rubber product for pulse NMR measurement after high-temperature storage, and by carrying out NMR measurement on the cross-linked rubber product for pulse NMR measurement after high-temperature storage obtained in the same manner as above, the sum of intensities over a relaxation time of 0 to 8 msec of the cross-linked rubber product for pulse NMR measurement after high-temperature storage (sum of intensities after high-temperature storage) was determined.

[0108] Fig. 1 shows a graph of the free induction decay curves obtained by measuring Example 4 and Comparative Example 1. Fig. 1 also shows the measurement results for the cross-linked rubber for pulse NMR measurement before high-temperature storage and the measurement results for the cross-linked rubber for pulse NMR measurement before high-temperature storage.

[0109] <Normal State Physical Properties (Hardness)> The crosslinkable rubber composition for evaluating physical properties was placed in a mold having a length of 15 cm, a width of 15 cm, and a depth of 0.2 cm, and press-molded at 170°C for 20 minutes while applying a pressure of 10 MPa to obtain a sheet-like primary crosslinked product. The obtained primary crosslinked product was then transferred to a gear oven and subjected to secondary crosslinking at 170°C for 4 hours, and the obtained sheet-like crosslinked product was punched out with a No. 3 dumbbell to prepare a test specimen. Then, using this obtained test specimen, the hardness of the crosslinked rubber product was measured using a durometer hardness tester (Type A) in accordance with JIS K6253.

[0110] <Compression Stress Relaxation Test> A crosslinkable rubber composition for evaluating physical properties was molded and crosslinked by pressing at 170°C for 20 minutes to prepare a cylindrical cross-linked rubber product having a diameter of 13 mm and a thickness of 6.3 mm. The product was then heated at 170°C for 4 hours to cause secondary cross-linking. The obtained cylindrical cross-linked rubber product was then compressed by 25% in the thickness direction and held in an environment at 150°C to conduct a compression stress relaxation test. In the compression stress relaxation test, first, the compressive stress of the cylindrical cross-linked rubber product was measured 30 minutes after the start of the test, and this was used as the initial compressive stress. Next, the compressive stress of the cylindrical cross-linked rubber product was measured 1008 hours after the start of the test to determine how much the compressive stress had been maintained relative to the initial compressive stress 30 minutes after the start of the test. Specifically, in the compression stress relaxation test, a compression stress relaxation index was calculated as "compressive stress relaxation index = compressive stress after 1008 hours ÷ initial compressive stress." A larger compression stress relaxation index indicates better compressive stress relaxation.

[0111] <Low-Temperature Sealing Property> A sheet-like cross-linked rubber product was obtained in the same manner as in the evaluation of the normal physical properties described above, and the obtained sheet-like cross-linked rubber product was used to carry out a TR test (low-temperature elastic recovery test) in a state elongated by 50% in accordance with JIS K6261. Specifically, the cross-linked rubber product elongated by 50% was frozen at -70°C, and the temperature was continuously raised to measure the recoverability of the elongated test piece, and the temperature TR10 at which the length of the cross-linked product contracted (recovered) by 10% due to the temperature increase was measured. The lower the TR10, the better the sealability at low temperatures and the better the low-temperature properties can be judged to be.

[0112] Example 1 (Production of Carboxyl Group-Containing Acrylic Rubber (A-1)) A mixing vessel equipped with a homomixer was charged with 46.294 parts of ion-exchanged water, 48.1 parts of ethyl acrylate, 49.1 parts of n-butyl acrylate, and 2.8 parts of mono-n-butyl fumarate as monomer components, and 1.8 parts of tridecyloxyhexa(oxyethylene) phosphate sodium salt (anionic emulsifier), and the mixture was stirred to obtain a monomer emulsion. Note that in Example 1, no molecular weight modifier such as tert-dodecyl mercaptan was used.

[0113] Next, 170.853 parts of pure water and 2.962 parts of the monomer emulsion obtained above were added to a polymerization reactor equipped with a thermometer and a stirrer, and the mixture was cooled to 12 ° C. under a nitrogen stream. Next, 145.132 parts of the monomer emulsion obtained above, 0.00033 parts of ferrous sulfate (reducing agent), 0.264 parts of sodium ascorbate (reducing agent), and 7.72 parts of a 2.85 wt% aqueous potassium persulfate solution (polymerization initiator) (0.22 parts as the amount of potassium persulfate) were continuously added dropwise to the polymerization reactor over a period of 3 hours while maintaining the temperature at 12 ° C. Thereafter, the reaction was continued for 1 hour while maintaining the temperature in the polymerization reactor at 23 ° C., and it was confirmed that the polymerization conversion rate had reached approximately 100%, and hydroquinone was added as a polymerization terminator to terminate the polymerization reaction, thereby obtaining an emulsion polymerization liquid.

[0114] Next, 60 parts of a 30 wt % aqueous magnesium sulfate solution adjusted to 85° C. was added to a coagulation tank equipped with a thermometer and a stirrer, and stirred with a stirring blade while heated to 85° C. Then, 100 parts of the emulsion polymerization liquid was continuously added to the aqueous magnesium sulfate solution while stirring, whereby the polymer was coagulated and filtered off, yielding hydrous crumbs.

[0115] Next, 388 parts of industrial water was added to 100 parts of the solid content of the obtained hydrous crumbs, and the mixture was stirred at room temperature for 5 minutes in a coagulation tank, and then the water was discharged from the coagulation tank, thereby washing the hydrous crumbs with water. The washed hydrous crumbs were then dried in a hot air dryer at 110°C for 1 hour, thereby obtaining a solid carboxyl group-containing acrylic rubber (A-1).

[0116] (Preparation of Crosslinkable Rubber Composition for Pulse NMR Measurement) Then, to 100 parts of the carboxyl group-containing acrylic rubber (A-1) obtained above, 2 parts of 2,2'-methylenebis(4-methyl-6-tert-butylphenol) (trade name "Nocrac NS-6", manufactured by Ouchi Shinko Chemical Industry Co., Ltd., a bisphenol-based antioxidant) and 2 parts of 2-mercaptobenzimidazole (trade name "Nocrac MB", manufactured by Ouchi Shinko Chemical Industry Co., Ltd., a benzimidazole-based antioxidant) were added, and the mixture was kneaded with rolls at 50°C. The resulting mixture was then blended with 2 parts of 1,3-o-tolylguanidine (trade name "Noccela DT", manufactured by Ouchi Shinko Chemical Industry Co., Ltd., a crosslinking accelerator) and 1.2 parts of hexamethylenediamine carbamate (trade name "Diak#1", manufactured by DuPont Elastomers Co., Ltd., a crosslinking agent), and kneaded to obtain a crosslinkable rubber composition for pulse NMR measurement. Pulse NMR measurement was carried out according to the method described above. The results are shown in Table 1.

[0117] (Preparation of a crosslinkable rubber composition for evaluating physical properties) Using a Banbury mixer, 100 parts of the carboxyl group-containing acrylic rubber (A-1) obtained above was mixed with carbon black (product name "Seast SO", manufactured by Tokai Carbon Co., Ltd., BET specific surface area: 42 m ２ 50 parts of 2,2'-methylenebis(4-methyl-6-tert-butylphenol) (trade name "Nocrac NS-6", manufactured by Ouchi Shinko Chemical Industry Co., Ltd., a bisphenol-based antioxidant), 2 parts of 2-mercaptobenzimidazole (trade name "Nocrac MB", manufactured by Ouchi Shinko Chemical Industry Co., Ltd., a benzimidazole-based antioxidant), and the mixture were mixed at 50°C for 5 minutes. The resulting mixture was then transferred to a 50°C roll, and 2 parts of 1,3-o-tolylguanidine (trade name "Noccela DT", manufactured by Ouchi Shinko Chemical Industry Co., Ltd., crosslinking accelerator) and 1.2 parts of hexamethylenediamine carbamate (trade name "Diak#1", manufactured by DuPont Elastomers Co., Ltd., crosslinking agent) were blended and kneaded to obtain a crosslinkable rubber composition for physical property evaluation, and normal state physical properties (hardness), compression stress relaxation test, and low temperature sealability (TR10 at 50% elongation) were measured and evaluated according to the methods described above. The results are shown in Table 1.

[0118] Example 2 (Preparation of crosslinkable rubber composition for pulse NMR measurement, crosslinkable rubber composition for physical property evaluation) A crosslinkable rubber composition for pulse NMR measurement was obtained in the same manner as in Example 1, using the carboxyl group-containing acrylic rubber (A-1) obtained in the same manner as in Example 1. Furthermore, a crosslinkable rubber composition for physical property evaluation was obtained in the same manner as in Example 1, except that the amount of carbon black used was changed to 60 parts. Then, using each of the obtained compositions, evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0119] Example 3 (Production of Carboxyl Group-Containing Acrylic Rubber (A-2)) A solid carboxyl group-containing acrylic rubber (A-2) was obtained by carrying out polymerization, coagulation, water washing, and drying in the same manner as in Example 1, except that the amounts of ethyl acrylate, n-butyl acrylate, and mono-n-butyl fumarate used as monomers were changed to 48.8 parts, 49.8 parts, and 1.4 parts, respectively, in preparing the monomer emulsion.

[0120] (Preparation of crosslinkable rubber composition for pulse NMR measurement and crosslinkable rubber composition for physical property evaluation) A crosslinkable rubber composition for pulse NMR measurement and a crosslinkable rubber composition for physical property evaluation were prepared and evaluated in the same manner as in Example 2, except that 100 parts of the carboxyl group-containing acrylic rubber (A-2) obtained above was used instead of the carboxyl group-containing acrylic rubber (A-1) and the amount of hexamethylenediamine carbamate used was changed to 0.6 parts. The results are shown in Table 1.

[0121] Example 4 (Production of Carboxyl Group-Containing Acrylic Rubber (A-3)) A solid carboxyl group-containing acrylic rubber (A-3) was obtained by carrying out polymerization, coagulation, water washing, and drying in the same manner as in Example 3, except that 0.05 parts of tert-dodecyl mercaptan was further used as a molecular weight modifier when preparing the monomer emulsion.

[0122] (Preparation of crosslinkable rubber composition for pulse NMR measurement and crosslinkable rubber composition for physical property evaluation) A crosslinkable rubber composition for pulse NMR measurement and a crosslinkable rubber composition for physical property evaluation were prepared and evaluated in the same manner as in Example 3, except that 100 parts of the carboxyl group-containing acrylic rubber (A-3) obtained above was used instead of the carboxyl group-containing acrylic rubber (A-2). The results are shown in Table 1.

[0123] Example 5 (Preparation of crosslinkable rubber composition for pulse NMR measurement and crosslinkable rubber composition for physical property evaluation) Except for not blending 2-mercaptobenzimidazole, a crosslinkable rubber composition for pulse NMR measurement and a crosslinkable rubber composition for physical property evaluation were prepared and evaluated in the same manner as in Example 3. The results are shown in Table 1.

[0124] Example 6 (Preparation of crosslinkable rubber composition for pulse NMR measurement and crosslinkable rubber composition for physical property evaluation) Except for not compounding 2,2'-methylenebis(4-methyl-6-tert-butylphenol), a crosslinkable rubber composition for pulse NMR measurement and a crosslinkable rubber composition for physical property evaluation were prepared and evaluated in the same manner as in Example 3. The results are shown in Table 1.

[0125] Example 7 (Production of Carboxyl Group-Containing Acrylic Rubber (A-4)) A solid carboxyl group-containing acrylic rubber (A-4) was obtained by carrying out polymerization, coagulation, washing with water, and drying in the same manner as in Example 1, except that, when preparing the monomer emulsion, the amounts of ethyl acrylate used were 48.8 parts, n-butyl acrylate used 24.8 parts, and mono-n-butyl fumarate used 1.4 parts, and 25 parts of methyl acrylate were further used, and 0.05 parts of tert-dodecyl mercaptan was further used as a molecular weight modifier.

[0126] (Preparation of crosslinkable rubber composition for pulse NMR measurement and crosslinkable rubber composition for physical property evaluation) A crosslinkable rubber composition for pulse NMR measurement and a crosslinkable rubber composition for physical property evaluation were prepared and evaluated in the same manner as in Example 3, except that 100 parts of the carboxyl group-containing acrylic rubber (A-4) obtained above was used instead of the carboxyl group-containing acrylic rubber (A-2). The results are shown in Table 1.

[0127] Example 8 (Production of Carboxyl Group-Containing Acrylic Rubber (A-5)) A solid carboxyl group-containing acrylic rubber (A-5) was obtained by carrying out polymerization, coagulation, water washing, and drying in the same manner as in Example 1, except that, when preparing the monomer emulsion, the amounts of ethyl acrylate and n-butyl acrylate used as monomers were 48.1 parts and 49.1 parts, respectively, and 2.8 parts of monocyclohexyl fumarate was used instead of mono-n-butyl fumarate.

[0128] (Preparation of crosslinkable rubber composition for pulse NMR measurement and crosslinkable rubber composition for physical property evaluation) A crosslinkable rubber composition for pulse NMR measurement and a crosslinkable rubber composition for physical property evaluation were prepared and evaluated in the same manner as in Example 2, except that 100 parts of the carboxyl group-containing acrylic rubber (A-5) obtained above was used instead of the carboxyl group-containing acrylic rubber (A-1). The results are shown in Table 1.

[0129] Example 9 (Production of Carboxyl Group-Containing Nitrile Rubber (A-6)) A reactor was charged with 220 parts of ion-exchanged water, 5 parts of a 10% aqueous solution of sodium dodecylbenzenesulfonate, 21.8 parts of acrylonitrile, 3 parts of mono-n-butyl maleate, 30.0 parts of n-butyl acrylate, and 0.2 parts of t-dodecyl mercaptan, in this order. The gas inside was replaced with nitrogen three times, and then 45.2 parts of 1,3-butadiene was charged. The reactor was then maintained at 10°C, and 0.1 parts of cumene hydroperoxide (polymerization initiator), a reducing agent, and an appropriate amount of a chelating agent were charged. The polymerization reaction was continued with stirring, and when the polymerization conversion rate reached 90%, 0.1 parts of a 10 wt% aqueous solution of hydroquinone (polymerization terminator) was added to terminate the polymerization reaction. Next, residual monomer was removed at a water temperature of 60°C, and a copolymer latex (solids concentration 30 wt%) was obtained.

[0130] Then, the copolymer latex and a palladium catalyst (a solution obtained by mixing a 1 wt % palladium acetate acetone solution with an equal weight of ion-exchanged water) were added to an autoclave so that the palladium content relative to the dry weight of rubber contained in the copolymer latex obtained above would be 2,000 ppm by weight, and a hydrogenation reaction was carried out at a hydrogen pressure of 3 MPa and a temperature of 50°C for 6 hours, thereby obtaining a latex of a carboxyl group-containing nitrile rubber (A-6).

[0131] An aqueous solution of sodium chloride (coagulant concentration: 25% by weight) was prepared in a tank as a coagulation liquid, and the above latex was slowly poured into the tank, followed by vigorously mixing and coagulation, after which filtration was carried out to remove solid matter (crumbs), which were then vacuum dried at 60°C for 12 hours to obtain a solid carboxyl group-containing nitrile rubber (A-6). The monomer composition of the carboxyl group-containing nitrile rubber (A-6) was almost equal to the amount of the monomers used.

[0132] (Preparation of crosslinkable rubber composition for pulse NMR measurement and crosslinkable rubber composition for physical property evaluation) A crosslinkable rubber composition for pulse NMR measurement and a crosslinkable rubber composition for physical property evaluation were prepared and evaluated in the same manner as in Example 2, except that 100 parts of the carboxyl group-containing nitrile rubber (A-6) obtained above was used instead of the carboxyl group-containing acrylic rubber (A-1). The results are shown in Table 1.

[0133] Example 10 (Production of Carboxyl Group-Containing Acrylic Rubber (A-7)) A mixing vessel equipped with a homomixer was charged with 46.294 parts of ion-exchanged water, 47.4 parts of ethyl acrylate, 49.8 parts of n-butyl acrylate, and 2.8 parts of mono-n-butyl fumarate as monomer components, and 1.8 parts of tridecyloxyhexa(oxyethylene) phosphate ester sodium salt (anionic emulsifier), and the mixture was stirred to obtain a monomer emulsion. Note that in Example 10, no molecular weight modifier such as tert-dodecyl mercaptan was used.

[0134] Next, 170.853 parts of pure water and 2.962 parts of the monomer emulsion obtained above were added to a polymerization reactor equipped with a thermometer and a stirrer, and the mixture was cooled to 12 ° C. under a nitrogen stream. Next, 145.132 parts of the monomer emulsion obtained above, 0.00033 parts of ferrous sulfate (reducing agent), 0.264 parts of sodium ascorbate (reducing agent), and 7.72 parts of a 2.85 wt% aqueous potassium persulfate solution (polymerization initiator) (0.22 parts as the amount of potassium persulfate) were continuously added dropwise to the polymerization reactor over a period of 3 hours while maintaining the temperature at 12 ° C. Thereafter, the reaction was continued for 1 hour while maintaining the temperature in the polymerization reactor at 23 ° C., and it was confirmed that the polymerization conversion rate had reached approximately 100%, and hydroquinone was added as a polymerization terminator to terminate the polymerization reaction, thereby obtaining an emulsion polymerization liquid.

[0135] Next, separately from the above, 50 parts of a 12 wt % aqueous solution of tridecyloxyhexa(oxyethylene) phosphate sodium salt (anionic emulsifier), 25 parts of 2,2′-methylenebis(4-methyl-6-tert-butylphenol) (trade name "Nocrac NS-6", manufactured by Ouchi Shinko Chemical Industry Co., Ltd., a bisphenol-based antioxidant), and 25 parts of 2-mercaptobenzimidazole (trade name "Nocrac MB", manufactured by Ouchi Shinko Chemical Industry Co., Ltd., a benzimidazole-based antioxidant) were mixed and stirred at a temperature of 25° C. to obtain an antioxidant dispersion (concentration of tridecyloxyhexa(oxyethylene) phosphate sodium salt as an emulsifier: 6 wt %, concentration of each antioxidant: 50 wt %).

[0136] Next, 1.44 parts of the antioxidant dispersion liquid prepared above (an amount such that the amount of each antioxidant was 2.0 parts per 100 parts of the rubber component in the emulsion polymerization liquid) was added to 100 parts of the emulsion polymerization liquid obtained above (temperature: 25°C), and the mixture was stirred.

[0137] Next, 60 parts of a 30 wt % aqueous magnesium sulfate solution adjusted to 85° C. was added to a coagulation tank equipped with a thermometer and a stirrer, and stirred with a stirring blade while heated to 85° C. Then, 100 parts of the emulsion polymerization liquid was continuously added to the aqueous magnesium sulfate solution while stirring, whereby the polymer was coagulated and filtered off, yielding hydrous crumbs.

[0138] Next, 388 parts of industrial water was added to 100 parts of the solid content of the obtained hydrous crumbs, and the mixture was stirred at room temperature for 5 minutes in a coagulation tank. After that, the water was drained from the coagulation tank, thereby washing the hydrous crumbs with water. The washed hydrous crumbs were then dried in a hot air dryer at 110°C for 1 hour, yielding a solid carboxyl group-containing acrylic rubber (A-7) with a recovery rate of 100%. The carboxyl group-containing acrylic rubber (A-7) contained 2 parts of 2,2'-methylenebis(4-methyl-6-tert-butylphenol) and 2 parts of 2-mercaptobenzimidazole per 100 parts of the rubber component.

[0139] (Preparation of crosslinkable rubber composition for pulse NMR measurement and crosslinkable rubber composition for physical property evaluation) A crosslinkable rubber composition for pulse NMR measurement and a crosslinkable rubber composition for physical property evaluation were prepared and evaluated in the same manner as in Example 1, except that the carboxyl group-containing acrylic rubber (A-7) obtained above was used in an amount of 100 parts in terms of rubber component instead of the carboxyl group-containing acrylic rubber (A-1), and that 2,2'-methylenebis(4-methyl-6-tert-butylphenol) and 2-mercaptobenzimidazole were not blended. The results are shown in Table 1.

[0140] Comparative Example 1 (Preparation of crosslinkable rubber composition for pulse NMR measurement and crosslinkable rubber composition for physical property evaluation) A crosslinkable rubber composition for pulse NMR measurement and a crosslinkable rubber composition for physical property evaluation were prepared in the same manner as in Example 4, except that 2,2'-methylenebis(4-methyl-6-tert-butylphenol) and 2-mercaptobenzimidazole were not compounded and instead 2 parts of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine (trade name "Nocrac CD", manufactured by Ouchi Shinko Chemical Industry Co., Ltd., amine-based antioxidant) was used, and evaluations were carried out in the same manner. The results are shown in Table 1.

[0141] Comparative Example 2 (Production of Carboxyl Group-Containing Acrylic Rubber (A-8)) A solid carboxyl group-containing acrylic rubber (A-8) was obtained by carrying out polymerization, coagulation, washing with water, and drying in the same manner as in Example 1, except that, when preparing the monomer emulsion, the amounts of ethyl acrylate used as monomers were 48.8 parts, the amount of mono-n-butyl fumarate used was 1.4 parts, 49.8 parts of methyl acrylate was used instead of n-butyl acrylate, and 0.05 parts of tert-dodecyl mercaptan was further used as a molecular weight modifier.

[0142] (Preparation of crosslinkable rubber composition for pulse NMR measurement and crosslinkable rubber composition for physical property evaluation) A crosslinkable rubber composition for pulse NMR measurement and a crosslinkable rubber composition for physical property evaluation were prepared and evaluated in the same manner as in Comparative Example 1, except that 100 parts of the carboxyl group-containing acrylic rubber (A-8) obtained above was used instead of the carboxyl group-containing acrylic rubber (A-3). The results are shown in Table 1.

[0143] Comparative Example 3 (Production of Carboxyl Group-Containing Acrylic Rubber (A-9)) A solid carboxyl group-containing acrylic rubber (A-9) was obtained by carrying out polymerization, coagulation, washing with water, and drying in the same manner as in Example 1, except that, when preparing the monomer emulsion, the amounts of ethyl acrylate used were 47.4 parts, n-butyl acrylate used 49.8 parts, and mono-n-butyl fumarate used 2.8 parts as monomers, and 0.05 parts of tert-dodecyl mercaptan was further used as a molecular weight modifier.

[0144] (Preparation of crosslinkable rubber composition for pulse NMR measurement and crosslinkable rubber composition for physical property evaluation) A crosslinkable rubber composition for pulse NMR measurement and a crosslinkable rubber composition for physical property evaluation were prepared and evaluated in the same manner as in Comparative Example 1, except that 100 parts of the carboxyl group-containing acrylic rubber (A-9) obtained above was used instead of the carboxyl group-containing acrylic rubber (A-3) and the amount of hexamethylenediamine carbamate used was changed to 1.2 parts. The results are shown in Table 1.

[0145] In Example 10, 2,2'-methylenebis(4-methyl-6-tert-butylphenol) and 2-mercaptobenzimidazole were blended with the latex of the carboxyl group-containing acrylic rubber (A-7).

[0146] As shown in Table 1, when the sum of the intensities for a relaxation time of 0 to 8 msec, as determined by pulse NMR measurement on the cross-linked rubber product after high-temperature storage obtained by storing the cross-linked rubber product at a high temperature of 150°C for 1008 hours, is 19.0 or less, the cross-linked rubber product obtained has a low TR10 in the evaluation of low-temperature sealability and is excellent in low-temperature properties, and also has a high compressive stress relaxation index and is excellent in compressive stress relaxation property (Examples 1 to 10). On the other hand, when the sum of the intensities for a relaxation time of 0 to 8 msec, as determined by pulse NMR measurement on the cross-linked rubber product after high-temperature storage obtained by storing the cross-linked rubber product at a high temperature of 150°C for 1008 hours, exceeds 19.0, the cross-linked rubber product obtained has a low compressive stress relaxation index and is poor in compressive stress relaxation property (Comparative Examples 1 to 3).

Claims

1. A crosslinkable rubber containing a rubber component having a carboxyl group as a crosslinkable group, A cross-linkable rubber, wherein the sum of intensities over a relaxation time of 0 to 8 msec is 19.0 or less, as determined by pulse NMR measurement of the cross-linked rubber after high-temperature storage obtained by cross-linking the cross-linkable rubber to form a cross-linked rubber before high-temperature storage, and then storing the cross-linked rubber before high-temperature storage at a high temperature of 150°C for 1008 hours.

2. The cross-linkable rubber according to claim 1, wherein the sum of intensities over a relaxation time of 0 to 8 msec determined by pulse NMR measurement of the cross-linked rubber after high-temperature storage is 17.0 to 18.

0.

3. The cross-linkable rubber according to claim 1 or 2, wherein the cross-linkable rubber is cross-linked to obtain a cross-linked rubber before high-temperature storage, and the cross-linked rubber before high-temperature storage is subjected to pulse NMR measurement, and the sum of intensities over a relaxation time of 0 to 8 msec is determined to be 19.0 or less.

4. The cross-linkable rubber according to claim 3, wherein the sum of intensities over a relaxation time of 0 to 8 msec determined by pulse NMR measurement of the cross-linked rubber before high-temperature storage is 15.0 to 17.

0.

5. 3. The crosslinkable rubber according to claim 1, wherein the pulse NMR measurement is carried out under the following conditions: Measurement time: 0~8msec Interval between 90-degree pulse and 180-degree pulse in the first measurement: 0.04 msec Interval between 90-degree pulse and 180-degree pulse in the last measurement: 4 msec Total number of measurements: 30 points nth measurement timing T ｎ : T ｎ－１ +0.08×(DF) ｎ－１ + C [msec] (T ｎ [msec] indicates the measurement timing in the nth measurement as the elapsed time from the start of the measurement, and T ０ = 0 [msec], DF is a coefficient for specifying the measurement timing calculated by the formula "DF = exp(1 / (total number of measurements - 1) * ln (interval between 90-degree pulse and 180-degree pulse in the last measurement / interval between 90-degree pulse and 180-degree pulse in the first measurement)"), and C is a correction constant [msec].

6. 3. The crosslinkable rubber according to claim 1, wherein the rubber component is a carboxyl group-containing acrylic rubber.

7. The crosslinkable rubber according to claim 6, wherein the carboxyl group-containing acrylic rubber contains 50 to 99.9% by weight of (meth)acrylic acid ester monomer units and 0.1 to 10% by weight of carboxyl group-containing monomer units.

8. 3. The crosslinkable rubber according to claim 1, wherein the rubber component is a carboxyl group-containing nitrile rubber.

9. The crosslinkable rubber according to claim 8, wherein the carboxyl group-containing nitrile rubber contains 5 to 60% by weight of α,β-ethylenically unsaturated nitrile monomer units, 10 to 80% by weight of conjugated diene monomer units, 1 to 30% by weight of carboxyl group-containing monomer units, and 10 to 50% by weight of α,β-ethylenically unsaturated monocarboxylic acid ester monomer units.

10. 3. The crosslinkable rubber according to claim 1, wherein the crosslinkable rubber contains a bisphenol-based antioxidant and / or a benzimidazole-based antioxidant.

11. A cross-linked rubber product obtained by cross-linking the cross-linkable rubber according to claim 1 or 2.

12. 11. A method for producing the cross-linkable rubber according to claim 10, comprising a step of kneading the rubber component and the bisphenol-based antioxidant and / or the benzimidazole-based antioxidant in a kneader.

13. 11. A method for producing the crosslinkable rubber according to claim 10, comprising the steps of adding the bisphenol-based antioxidant and / or the benzimidazole-based antioxidant to a latex containing the rubber component, and then coagulating the latex.