US20200131293A1 - Nitrile group-containing copolymer rubber - Google Patents

Nitrile group-containing copolymer rubber Download PDF

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US20200131293A1
US20200131293A1 US16/493,270 US201816493270A US2020131293A1 US 20200131293 A1 US20200131293 A1 US 20200131293A1 US 201816493270 A US201816493270 A US 201816493270A US 2020131293 A1 US2020131293 A1 US 2020131293A1
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containing copolymer
copolymer rubber
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Atsuhiro SHIONO
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Zeon Corp
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    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F236/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, at least one having two or more carbon-to-carbon double bonds
    • C08F236/02—Copolymers of compounds having one or more unsaturated aliphatic radicals, at least one having two or more carbon-to-carbon double bonds the radical having only two carbon-to-carbon double bonds
    • C08F236/04—Copolymers of compounds having one or more unsaturated aliphatic radicals, at least one having two or more carbon-to-carbon double bonds the radical having only two carbon-to-carbon double bonds conjugated
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08C—TREATMENT OR CHEMICAL MODIFICATION OF RUBBERS
    • C08C19/00—Chemical modification of rubber
    • C08C19/02—Hydrogenation
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    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F220/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride ester, amide, imide or nitrile thereof
    • C08F220/02—Monocarboxylic acids having less than ten carbon atoms; Derivatives thereof
    • C08F220/42—Nitriles
    • C08F220/44—Acrylonitrile
    • C08F220/46—Acrylonitrile with carboxylic acids, sulfonic acids or salts thereof
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    • C08F236/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, at least one having two or more carbon-to-carbon double bonds
    • C08F236/02—Copolymers of compounds having one or more unsaturated aliphatic radicals, at least one having two or more carbon-to-carbon double bonds the radical having only two carbon-to-carbon double bonds
    • C08F236/04—Copolymers of compounds having one or more unsaturated aliphatic radicals, at least one having two or more carbon-to-carbon double bonds the radical having only two carbon-to-carbon double bonds conjugated
    • C08F236/14—Copolymers of compounds having one or more unsaturated aliphatic radicals, at least one having two or more carbon-to-carbon double bonds the radical having only two carbon-to-carbon double bonds conjugated containing elements other than carbon and hydrogen
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08C—TREATMENT OR CHEMICAL MODIFICATION OF RUBBERS
    • C08C1/00—Treatment of rubber latex
    • C08C1/14—Coagulation
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08C—TREATMENT OR CHEMICAL MODIFICATION OF RUBBERS
    • C08C19/00—Chemical modification of rubber
    • C08C19/22—Incorporating nitrogen atoms into the molecule
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F2/00—Processes of polymerisation
    • C08F2/12—Polymerisation in non-solvents
    • C08F2/16—Aqueous medium
    • C08F2/22—Emulsion polymerisation
    • C08F2/24—Emulsion polymerisation with the aid of emulsifying agents
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    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F2/00—Processes of polymerisation
    • C08F2/38—Polymerisation using regulators, e.g. chain terminating agents, e.g. telomerisation
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F220/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride ester, amide, imide or nitrile thereof
    • C08F220/02—Monocarboxylic acids having less than ten carbon atoms; Derivatives thereof
    • C08F220/42—Nitriles
    • C08F220/44—Acrylonitrile
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F236/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, at least one having two or more carbon-to-carbon double bonds
    • C08F236/02—Copolymers of compounds having one or more unsaturated aliphatic radicals, at least one having two or more carbon-to-carbon double bonds the radical having only two carbon-to-carbon double bonds
    • C08F236/04—Copolymers of compounds having one or more unsaturated aliphatic radicals, at least one having two or more carbon-to-carbon double bonds the radical having only two carbon-to-carbon double bonds conjugated
    • C08F236/06—Butadiene
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J3/00—Processes of treating or compounding macromolecular substances
    • C08J3/24—Crosslinking, e.g. vulcanising, of macromolecules
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K5/00—Use of organic ingredients
    • C08K5/0008—Organic ingredients according to more than one of the "one dot" groups of C08K5/01 - C08K5/59
    • C08K5/0025—Crosslinking or vulcanising agents; including accelerators
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K5/00—Use of organic ingredients
    • C08K5/16—Nitrogen-containing compounds
    • C08K5/17—Amines; Quaternary ammonium compounds
    • C—CHEMISTRY; METALLURGY
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    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K5/00—Use of organic ingredients
    • C08K5/16—Nitrogen-containing compounds
    • C08K5/205—Compounds containing groups, e.g. carbamates
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K5/00—Use of organic ingredients
    • C08K5/16—Nitrogen-containing compounds
    • C08K5/34—Heterocyclic compounds having nitrogen in the ring
    • C08K5/3442—Heterocyclic compounds having nitrogen in the ring having two nitrogen atoms in the ring
    • C08K5/3462—Six-membered rings
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K5/00—Use of organic ingredients
    • C08K5/16—Nitrogen-containing compounds
    • C08K5/34—Heterocyclic compounds having nitrogen in the ring
    • C08K5/3442—Heterocyclic compounds having nitrogen in the ring having two nitrogen atoms in the ring
    • C08K5/3462—Six-membered rings
    • C08K5/3465—Six-membered rings condensed with carbocyclic rings
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L13/00—Compositions of rubbers containing carboxyl groups
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L9/00—Compositions of homopolymers or copolymers of conjugated diene hydrocarbons
    • C08L9/02—Copolymers with acrylonitrile

Definitions

  • the present invention relates to a nitrile group-containing copolymer rubber, and more specifically relates to a nitrile group-containing copolymer rubber which has high processability, and can give a cross-linked rubber having high compression set resistance when made into a cross-linked rubber.
  • Nitrile rubber (acrylonitrile-butadiene copolymer rubber), because of its useful oil resistance, mechanical properties, resistance against chemicals, is conventionally used as a material for rubber parts such as hoses and seals for automobiles.
  • hydrogenated nitrile rubber (hydrogenated acrylonitrile-butadiene copolymer rubber) obtained through hydrogenation of carbon-carbon double bonds in the polymer main chain of nitrile rubber has higher mechanical properties and heat resistance, and is used for rubber parts such as belts, hoses, seals, diaphragms, and the like.
  • Patent Document 1 proposes a nitrile rubber composition comprising a hydrogenated nitrile rubber including an ⁇ , ⁇ -ethylenically unsaturated dicarboxylic acid monoester monomer unit, a polyamine cross-linking agent, and a basic cross-linking accelerator.
  • a hydrogenated nitrile rubber including an ⁇ , ⁇ -ethylenically unsaturated dicarboxylic acid monoester monomer unit
  • a polyamine cross-linking agent a polyamine cross-linking agent
  • a basic cross-linking accelerator for example, Patent Document 1 proposes a nitrile rubber composition comprising a hydrogenated nitrile rubber including an ⁇ , ⁇ -ethylenically unsaturated dicarboxylic acid monoester monomer unit, a polyamine cross-linking agent, and a basic cross-linking accelerator.
  • Patent Document 1 JP-A 2001-55471
  • An object of the present invention is to provide a nitrile group-containing copolymer rubber which has high processability and can give a cross-linked rubber having high compression set resistance when made into a cross-linked rubber.
  • the present inventors who have conducted extensive research to achieve the object above, have found that the object can be achieved by a nitrile group-containing copolymer rubber comprising an ⁇ , ⁇ -ethylenically unsaturated nitrile monomer unit and an ⁇ , ⁇ -ethylenically unsaturated dicarboxylic acid monoester monomer unit in specific amounts and having an iodine value of 120 or less, in which a processability index, which is the product of the carboxyl group content and the Absorbance area of a carboxylic anhydride group determined by infrared spectroscopy, is controlled within a predetermined range, and have completed the present invention.
  • a processability index which is the product of the carboxyl group content and the Absorbance area of a carboxylic anhydride group determined by infrared spectroscopy
  • the nitrile group-containing copolymer rubber according to the present invention preferably contains a conjugated diene monomer unit in an amount of 20 to 89 wt %.
  • a content of the ⁇ , ⁇ -ethylenically unsaturated dicarboxylic acid monoester monomer unit is preferably 1 to 10 wt %.
  • the ⁇ , ⁇ -ethylenically unsaturated dicarboxylic acid monoester monomer unit is preferably at least one selected from the group consisting of a mono-n-butyl maleate unit, a mono-n-butyl fumarate unit, and a monocyclohexyl fumarate unit.
  • the present invention also provides a cross-linkable rubber composition comprising the nitrile group-containing copolymer rubber and a cross-linking agent.
  • the cross-linkable rubber composition according to the present invention preferably further comprises a basic cross-linking accelerator having a cyclic amidine structure.
  • the present invention provides a cross-linked rubber prepared through cross-linking of the cross-linkable rubber composition.
  • the present invention can provide a nitrile group-containing copolymer rubber which has high processability and can give a cross-linked rubber having high compression set resistance when made into a cross-linked rubber, and a cross-linked rubber which can be prepared using such a nitrile group-containing copolymer rubber and has high compression set resistance.
  • FIG. 1 is a diagram illustrating a spectrum obtained by infrared spectroscopy of the nitrile group-containing copolymer rubber according to Production Example 11.
  • Any ⁇ , ⁇ -ethylenically unsaturated compound having a nitrile group can be used as the ⁇ , ⁇ -ethylenically unsaturated nitrile monomer forming the ⁇ , ⁇ -ethylenically unsaturated nitrile monomer unit without limitation.
  • examples thereof include acrylonitrile; ⁇ -halogenoacrylonitriles such as ⁇ -chloroacrylonitrile and ⁇ -bromoacrylonitrile; ⁇ -alkylacrylonitriles such as methacrylonitrile and ethacrylonitrile; and the like.
  • preferred are acrylonitrile and methacrylonitrile, and particularly preferred is acrylonitrile.
  • These ⁇ , ⁇ -ethylenically unsaturated nitrile monomers may be used alone or in combination.
  • the proportion of the ⁇ , ⁇ -ethylenically unsaturated nitrile monomer unit contained in the nitrile group-containing copolymer rubber according to the present invention is 10 to 60 wt %, preferably 10 to 50 wt %, more preferably 15 to 45 wt % of the total monomer units.
  • An excessively low proportion of the ⁇ , ⁇ -ethylenically unsaturated nitrile monomer unit results in a cross-linked rubber having reduced oil resistance.
  • an excessively high proportion thereof results in a cross-linked rubber having reduced cold resistance.
  • Examples of ⁇ , ⁇ -ethylenically unsaturated dicarboxylic acid monoester monomers forming the ⁇ , ⁇ -ethylenically unsaturated dicarboxylic acid monoester monomer unit include maleic acid monoalkyl esters such as monomethyl maleate, monoethyl maleate, monopropyl maleate, and mono-n-butyl maleate; maleic acid monocycloalkyl esters such as monocyclopentyl maleate, monocyclohexyl maleate, and monocycloheptyl maleate; maleic acid monoalkylcycloalkyl esters such as monomethylcyclopentyl maleate and monoethylcyclohexyl maleate; fumaric acid monoalkyl esters such as monomethyl fumarate, monoethyl fumarate, monopropyl fumarate, and mono-n-butyl fumarate; fumaric acid monocycloalkyl esters such as monocyclopentyl fumarate, mono
  • ⁇ , ⁇ -ethylenically unsaturated dicarboxylic acid monoester monomers may be used alone or in combination.
  • ⁇ , ⁇ -ethylenically unsaturated dicarboxylic acid monoalkyl ester monomers and ⁇ , ⁇ -ethylenically unsaturated dicarboxylic acid monocycloalkyl ester monomers are particularly preferred.
  • Particularly preferred are mono-n-butyl maleate, mono-n-butyl fumarate, and monocyclohexyl fumarate.
  • These alkyl esters preferably have C 2 to C 8 alkyl groups.
  • the proportion of the ⁇ , ⁇ -ethylenically unsaturated dicarboxylic acid monoester monomer unit contained in the nitrile group-containing copolymer rubber according to the present invention is 1 to 60 wt %, preferably 1 to 20 wt %, more preferably 1 to 10 wt %, still more preferably 3 to 8 wt % of the total monomer units.
  • An excessively low proportion of the ⁇ , ⁇ -ethylenically unsaturated dicarboxylic acid monoester monomer unit results in a cross-linked rubber having reduced compression set resistance.
  • an excessively high proportion thereof results in a reduction in elongation of the resulting cross-linked rubber, the elongation being one of the mechanical properties.
  • the nitrile group-containing copolymer rubber according to the present invention also contains a conjugated diene monomer unit to provide a cross-linked product having rubber elasticity.
  • Preferred conjugated diene monomers forming the conjugated diene monomer unit are C 4 to C 6 conjugated diene monomers such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, and chloroprene. 1,3-Butadiene and isoprene are more preferred, and 1,3-butadiene is particularly preferred. These conjugated diene monomers may be used alone or in combination.
  • the content of the conjugated diene monomer unit is preferably 20 to 89 wt %, more preferably 30 to 80 wt %, still more preferably 40 to 65 wt % of the total monomer units.
  • a content of the conjugated diene monomer unit within this range results in a cross-linked rubber maintaining favorable heat resistance and chemical stability and having excellent rubber elasticity.
  • a content of the conjugated diene monomer unit controlled to the lower limit value or higher can improve the polymerization conversion ratio.
  • the nitrile group-containing copolymer rubber according to the present invention also contains an ⁇ , ⁇ -ethylenically unsaturated monocarboxylic acid ester monomer unit when 30 wt % or less of the ⁇ , ⁇ -ethylenically unsaturated nitrile monomer unit is contained.
  • Examples of ⁇ , ⁇ -ethylenically unsaturated monocarboxylic acid ester monomers forming the ⁇ , ⁇ -ethylenically unsaturated monocarboxylic acid ester monomer unit include (meth)acrylic acid esters (abbreviation for “methacrylic acid esters and acrylate esters” and the same applies hereinafter) having C 1 to C 18 alkyl groups, such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, n-dodecyl acrylate, methyl methacrylate, and ethyl methacrylate; (meth)acrylic acid esters having C 2 to C 18 alkoxyalkyl groups, such as methoxymethyl acrylate, methoxyethyl acrylate, ethoxypropyl acrylate, methoxybutyl acrylate, ethoxydodecyl acrylate, methoxye
  • (meth)acrylic acid esters having C 1 to C 18 alkyl groups and (meth)acrylic acid esters having C 2 to C 18 alkoxyalkyl groups are particularly preferred.
  • n-butyl acrylate and methoxyethyl acrylate are particularly preferred.
  • These ⁇ , ⁇ -ethylenically unsaturated monocarboxylic acid ester monomers may be used alone or in combination.
  • the proportion of the ⁇ , ⁇ -ethylenically unsaturated monocarboxylic acid ester monomer unit in the nitrile group-containing copolymer rubber according to the present invention is preferably 0 to 60 wt %, more preferably 0 to 50 wt %, still more preferably 0 to 40 wt % of the total monomer units.
  • the nitrile group-containing copolymer rubber according to the present invention may also contain a unit of an additional monomer copolymerizable with the monomers which form these monomer units.
  • Examples of such an additional monomer include ⁇ , ⁇ -ethylenically unsaturated monocarboxylic acid monomers, ⁇ , ⁇ -ethylenically unsaturated polyvalent carboxylic acid monomers (excluding those categorized under the ⁇ , ⁇ -ethylenically unsaturated dicarboxylic acid monoester monomer), ethylene, ⁇ -olefin monomers, aromatic vinyl monomers, fluorine-containing vinyl monomers, copolymerizable antioxidants, and the like.
  • ⁇ , ⁇ -ethylenically unsaturated monocarboxylic acid monomers examples include acrylic acid, methacrylic acid, ethylacrylic acid, crotonic acid, cinnamic acid, and the like.
  • Examples of the ⁇ , ⁇ -ethylenically unsaturated polyvalent carboxylic acid monomers include butenedioic acids such as fumaric acid and maleic acid, itaconic acid, citraconic acid, mesaconic acid, glutaconic acid, allylmalonic acid, teraconic acid, and the like.
  • Examples of anhydrides of ⁇ , ⁇ -unsaturated polyvalent carboxylic acids include maleic anhydride, itaconic anhydride, citraconic anhydride, and the like.
  • Preferred ⁇ -olefin monomers are those having 3 to 12 carbon atoms. Examples thereof include propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, and the like.
  • aromatic vinyl monomers examples include styrene, ⁇ -methylstyrene, vinylpyridine, and the like.
  • fluorine-containing vinyl monomers examples include fluoroethyl vinyl ether, fluoropropyl vinyl ether, o-trifluoromethylstyrene, pentafluorovinyl benzoate, difluoroethylene, tetrafluoroethylene, and the like.
  • copolymerizable antioxidants examples include N-(4-anilinophenyl)acrylamide, N-(4-anilinophenyl)methacrylamide, N-(4-anilinophenyl)cinnamamide, N-(4-anilinophenyl)crotonamide, N-phenyl-4-(3-vinylbenzyloxy)aniline, N-phenyl-4-(4-vinylbenzyloxy)aniline, and the like.
  • the content of the unit of the additional monomer is preferably 50 wt % or less, more preferably 40 wt % or less, still more preferably 10 wt % or less of the total monomer units which form the nitrile group-containing copolymer rubber.
  • the nitrile group-containing copolymer rubber according to the present invention has an iodine value of 120 or less, preferably 60 or less, more preferably 50 or less, particularly preferably 30 or less.
  • An excessively high iodine value of the nitrile group-containing copolymer rubber may result in a cross-linked rubber having reduced heat resistance and reduced ozone resistance.
  • a processability of a nitrile group-containing copolymer rubber can be made excellent while making a compression set resistance of a cross-linked rubber excellent when made into a cross-linked rubber.
  • control of the processability index I pro to 0.0030 or less can reduce an increase in Mooney viscosity, which is caused when the cross-linking agent is compounded.
  • favorable forming properties can be provided when a variety of compounding agents including the cross-linking agent are compounded.
  • the present inventors have found that the processability is affected by the amount of free carboxyl groups contained in the nitrile group-containing copolymer rubber (the amount of free carboxyl groups which are not esterified and the like) and the amount of carboxylic anhydride groups (the amount of anhydrous carboxyl groups), and have completed the present invention.
  • the carboxyl group content C C is the number of moles of carboxyl groups per 100 g of nitrile group-containing copolymer rubber, and can be measured by the following method, for example.
  • a nitrile group-containing copolymer rubber is dissolved in a predetermined solvent to prepare a solution of the nitrile group-containing copolymer rubber.
  • the obtained solution is subjected to titration using an alkali, and the number of moles of carboxyl groups (the number of moles of free carboxyl groups which are not esterified and the like) per 100 g of rubber is calculated to determine the carboxyl group content C C .
  • the carboxyl group content C C is preferably 0.005 to 0.116 ephr, more preferably 0.005 to 0.058 ephr, particularly preferably 0.015 to 0.046 ephr. As the carboxyl group content C C increases, the processability index I pro also tends to increase. Opposed to this, the processability can be further enhanced by controlling the carboxyl group content C C to the upper limit value or lower. On the other hand, a cross-linked rubber having higher compression set resistance can be provided by controlling the carboxyl group content C C to the lower limit value or higher.
  • the absorbance area S A of a carboxylic anhydride group (anhydrous carboxyl group) determined by infrared spectroscopy is the area of the absorbance corresponding to the carboxylic anhydride group from infrared spectroscopy of the nitrile group-containing copolymer rubber. Although depending on the peak intensity, a peak corresponding to the carboxylic anhydride group usually appears in the range of 1765 to 1795 cm ⁇ 1 .
  • the spectrum obtained by infrared spectroscopy of the nitrile group-containing copolymer rubber according to Production Example 11 is shown in FIG. 1 .
  • infrared spectroscopy measurement can be performed on a solid nitrile group-containing copolymer rubber to measure absorbances at wavelengths by attenuted total reflection (ATR) method using a Fourier transform infrared spectrophotometer (FT-IR) as an infrared spectrophotometer according to “Analytical general rules for infrared spectroscopy” specified in JIS K 0117:2000.
  • ATR attenuted total reflection
  • FT-IR Fourier transform infrared spectrophotometer
  • the area of the peak corresponding to the carboxylic anhydride group (peak which appears in the range of 1770 to 1790 cm ⁇ 1 , and peak which appears in the range of 1765 to 1795 cm ⁇ 1 if the absorbance is relatively high) is determined, and can be defined as an absorbance area S A .
  • the absorbance area S A is the area of the absorbance in the peak range corresponding to the carboxylic anhydride group (the peak range of 1770 to 1790 cm ⁇ 1 , and the peak range of 1765 to 1795 cm ⁇ 1 if the absorbance is relatively high).
  • the absorbance area S A is an integrated value of the absorbance (e.g., absorbance in the ordinate in the spectrum shown in FIG. 1 ) with respect to the wave number (e.g., wave number in the abscissa in the spectrum shown in FIG. 1 ). Specifically, a bottom line connecting the rise points of the peak corresponding to the carboxylic anhydride group is drawn, and the Absorbance from the bottom line is integrated with respect to the wave number to determine the absorbance area S A .
  • the absorbance area S A can be determined using a standard measurement function included in a Fourier transform infrared spectrophotometer as the infrared spectrophotometer. If the absorbance area S A is measured using a diluted rubber sample (diluted with a highly transmissive material), the obtained absorbance value (measured value) is corrected according to the dilution proportion and the absorbance of the material used for dilution, and the absorbance area S A is calculated using the absorbance value after the correction.
  • the absorbance area S A is preferably 0.09 cm ⁇ 1 or less, more preferably 0.07 cm ⁇ 1 or less, still more preferably 0.06 cm ⁇ 1 or less.
  • An excessively large absorbance area S A tends to increase the processability index I pro .
  • the processability can be further enhanced through control thereof to the upper limit value specified above or lower.
  • the carboxyl group content C C , the Absorbance area S A of the carboxylic anhydride group determined by infrared spectroscopy, and the processability index I pro can be controlled within the ranges specified above by various methods.
  • examples thereof include a method of adjusting the content of the ethylenically unsaturated dicarboxylic acid monoester monomer unit in the nitrile group-containing copolymer rubber, a method of appropriately selecting the type of the ethylenically unsaturated dicarboxylic acid monoester monomer which forms the ethylenically unsaturated dicarboxylic acid monoester monomer unit, a method of controlling the thermal history of the nitrile group-containing copolymer rubber (such as a method of controlling the drying process, the drying temperature, and the drying time), a method using an appropriate combination thereof, and the like.
  • the method of adjusting the content of the ethylenically unsaturated dicarboxylic acid monoester monomer unit or the method of controlling the thermal history of the nitrile group-containing copolymer rubber can effectively prevent generation of acid anhydrides derived from the ethylenically unsaturated dicarboxylic acid monoester monomer unit, thereby enabling an appropriate reduction in processability index I pro .
  • the nitrile group-containing copolymer rubber according to the present invention has a polymer Mooney viscosity (ML1+4, 100° C.) of preferably 10 to 200, more preferably 15 to 100, still more preferably 20 to 80, particularly preferably 30 to 60.
  • a polymer Mooney viscosity within this range results in favorable processability, as well as a cross-linked rubber having appropriately enhanced mechanical properties.
  • the nitrile group-containing copolymer rubber according to the present invention can be produced by any method
  • the nitrile group-containing copolymer rubber can be produced by copolymerizing the monomers described above, and hydrogenating the carbon-carbon double bonds of the resulting copolymer.
  • Any polymerization method can be used without limitation, and a known emulsion polymerization or solution polymerization method may be used. Preferred is emulsion polymerization from the viewpoint of industrial productivity.
  • polymerization additives usully used can be used in addition to an emulsifier, a polymerization initiator, and a molecular weight adjuster.
  • emulsifier can be used without limitation.
  • examples thereof include nonionic emulsifiers such as polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenol ethers, polyoxyethylene alkyl esters, and polyoxyethylene sorbitan alkyl esters; anionic emulsifiers such as salts of fatty acids such as myristic acid, palmitic acid, oleic acid, and linolenic acid, salts of alkylbenzene sulfonates such as sodium dodecylbenzenesulfonate, polycondensates of naphthalene sulfonate salts with formalin, higher alcohol sulfuric acid ester salts, and alkyl sulfosuccinic acid salts; copolymerizable emulsifiers such as sulfo esters of ⁇ , ⁇ -unsaturated carboxylic acids, sulfate esters of ⁇ , ⁇ -unsaturated carboxylic
  • Any radical initiator can be used as the polymerization initiator without limitation.
  • examples thereof include inorganic peroxides such as potassium persulfate, sodium persulfate, ammonium persulfate, potassium perphosphate, and hydrogen peroxide; organic peroxides such as t-butyl peroxide, cumene hydroperoxide, p-menthane hydroperoxide, di-t-butyl peroxide, t-butylcumyl peroxide, acetyl peroxide, isobutyryl peroxide, octanoyl peroxide, dibenzoyl peroxide, 3,5,5-trimethylhexanoyl peroxide, and t-butylperoxy isobutyrate; azo compounds such as azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, azobiscyclohexanecarbonitrile, and methyl azobisisobutyrate; and the
  • polymerization initiators can be used alone or in combination.
  • Preferred polymerization initiators are inorganic or organic peroxides. If a peroxide is used as the polymerization initiator, a combination thereof with a reducing agent such as sodium bisulfite, ferrous sulfate, sodium formaldehyde sulfoxylate, or iron sodium ethylenediaminetetraacetate can be used as a redox polymerization initiator. Furthermore, a chelating agent such as ethylenediaminetetraacetic acid ferric sodium salt tetrahydrate, and a builder such as sodium carbonate or sodium sulfate can also be used.
  • the amount of the polymerization initiator to be added is preferably 0.01 to 2 parts by weight relative to 100 parts by weight of the monomers used in polymerization.
  • Any molecular weight adjuster can be used without limitation.
  • Examples thereof include mercaptans such as t-dodecyl mercaptan, n-dodecyl mercaptan, and octyl mercaptan; halogenated hydrocarbons such as carbon tetrachloride, methylene chloride, and methylene bromide; ⁇ -methylstyrene dimers; sulfur-containing compounds such as tetraethylthiuram disulfide, dipentamethylenethiuram disulfide, and diisopropyl xanthogen disulfide; and the like. These molecular weight adjusters can be used alone or in combination.
  • the amount of the molecular weight adjuster to be used is preferably 0.1 to 0.8 parts by weight relative to 100 parts by weight of the total monomers.
  • Water is usually used as the medium for emulsion polymerization.
  • the amount of water is preferably 80 to 500 parts by weight, more preferably 80 to 300 parts by weight relative to 100 parts by weight of the monomers used in polymerization.
  • polymerization additives such as a stabilizer, a dispersant, a pH adjuster, an oxygen absorbing agent, and a particle size adjuster can be used as needed.
  • the additives of any type can be used in any amount.
  • the resulting copolymer may be subjected to hydrogenation (hydrogenating reaction) as needed.
  • Hydrogenation may be performed by a known method. Examples thereof include an oil layer hydrogenation method of coagulating a latex of a copolymer prepared through emulsion polymerization, and hydrogenating the latex in an oil layer; an aqueous layer hydrogenation method of hydrogenating a latex of the resulting copolymer as it is; and the like.
  • the latex of the above copolymer prepared by emulsion polymerization is subjected to coagulation by salting-out or with an alcohol, filtration, and drying, and then is dissolved in an organic solvent.
  • a hydrogenating reaction oil layer hydrogenation
  • the resulting hydride is added into a large amount of water, and is subjected to coagulation, washing with water, filtration, and drying.
  • centrifugal dehydration may be performed.
  • the latex can be coagulated by salting-out using a known coagulant such as sodium chloride, calcium chloride, aluminum sulfate, magnesium sulfate, or the like.
  • the coagulation may be performed using an alcohol such as methanol or isopropyl alcohol, instead of coagulation by salting-out.
  • the solvent to be used in the oil layer hydrogenation method can be any liquid organic compound which dissolves a copolymer prepared through emulsion polymerization.
  • Benzene, chlorobenzene, toluene, xylene, hexane, cyclohexane, tetrahydrofuran, methyl ethyl ketone, ethyl acetate, cyclohexanone, acetone, and the like are preferably used.
  • the catalyst to be used in the oil layer hydrogenation method can be any known selective hydrogenation catalyst.
  • Preferred are palladium catalysts and rhodium catalysts, and more preferred are palladium catalysts (such as palladium acetate, palladium chloride, palladium hydroxide, and the like). These may be used in combination.
  • a palladium catalyst is preferably used as a main active component.
  • These catalysts are usually used as carried on carriers. Examples of the carriers include silica, silica-alumina, alumina, diatomite, activated carbon, and the like.
  • the amount of the catalyst to be used is preferably 10 to 20000 ppm by weight, more preferably 50 to 15000 ppm by weight relative to the copolymer.
  • a latex of the copolymer prepared through emulsion polymerization is diluted with water added, as needed, and is subjected to the hydrogenating reaction.
  • the aqueous layer hydrogenation method include an aqueous layer direct hydrogenation method of performing hydrogenation through feeding of hydrogen to a reaction system in the presence of a hydrogenation catalyst, and an aqueous layer indirect hydrogenation method of performing hydrogenation through reduction in the presence of an oxidizing agent, a reducing agent, and an activating agent.
  • an aqueous layer direct hydrogenation preferred is preferred.
  • the content of the copolymer in the aqueous layer is preferably 40 wt % or less to prevent aggregation.
  • the hydrogenation catalyst can be any compound which hardly decomposes in water.
  • palladium catalysts such as palladium salts of carboxylic acids such as formic acid, propionic acid, lauric acid, succinic acid, oleic acid, and phthalic acid; chlorinated palladium compounds such as palladium chloride, dichloro(cyclooctadiene)palladium, dichloro(norbonadiene)palladium, and ammonium hexachloropalladate(IV); iodides such as palladium iodide; palladium nitrate; palladium sulfate dihydrate; and the like.
  • palladium salts of carboxylic acids, palladium chloride, and palladium nitrate particularly preferred are palladium salts of carboxylic acids, palladium chloride, and palladium nitrate.
  • the amount of the hydrogenation catalyst to be used may be appropriately determined. The amount is preferably 5 to 20000 ppm by weight, more preferably 10 to 15000 ppm by weight relative to
  • the hydrogenation catalyst in the latex is removed after the hydrogenating reaction is completed.
  • This removal operation can be performed, for example, using a method comprising a step of adding an adsorbent such as an activated carbon or an ion exchange resin and adsorbing the hydrogenation catalyst under stirring or a step of forming a complex of the hydrogenation catalyst with a complexing agent in the presence of an oxidizing agent or a reducing agent, and then centrifuging and/or filtering the latex.
  • the hydrogenation catalyst can be left in the latex, rather than removed.
  • the nitrile group-containing copolymer rubber according to the present invention can be produced by performing coagulation with an alcohol such as methanol and isopropyl alcohol or by salting-out, washing with water, and filtration on the resulting latex after the hydrogenating reaction, and drying the resulting hydrous crumbs.
  • Coagulation by salting-out can be performed using a known coagulant such as sodium chloride, calcium chloride, aluminum sulfate, or magnesium sulfate. Centrifugal dehydration may be performed in some cases.
  • the oil layer hydrogenation method and the aqueous layer hydrogenation method both use hot air drying or kneading drying as the drying method.
  • a method of performing coagulation, washing with water, and drying in a single kneader can also be used.
  • the drying temperature for hot air drying is preferably 40 to 100° C., more preferably 60 to 90° C.
  • the drying time is preferably 0.5 to 12 hours, more preferably 1 to 6 hours.
  • the drying temperature for kneading drying is preferably 100 to 200° C., more preferably 120 to 170° C.
  • the drying time is preferably 1 to 20 minutes, more preferably 2 to 15 minutes.
  • a higher temperature or a longer drying time may increase the processability index I pro and reduce the processability.
  • a lower temperature or a shorter drying time is likely to cause undried and wet spots.
  • An antioxidant can also be added to the oil layer or the aqueous layer before coagulation. Any antioxidant can be used without limitation. Examples of usable antioxidants include 2,6-di-t-butyl-4-cresol (ANTAGE BHT, made by Kawaguchi Chemical Industry Co., LTD.), 2,2′-methylenebis(4-methyl-6-tert-butylphenol) (Sandant 2246, made by Sanshin Chemical Industry Co., Ltd.
  • the cross-linkable rubber composition according to the present invention comprises the nitrile group-containing copolymer rubber according to the present invention and a cross-linking agent.
  • cross-linking agent which can cross-linking the nitrile group-containing copolymer rubber according to the present invention can be used without limitation.
  • examples thereof include sulfur cross-linking agents, organic peroxide cross-linking agents, and polyamine cross-linking agents. Among these, preferred are polyamine cross-linking agents.
  • sulfur cross-linking agents examples include sulfur such as powdery sulfur, flowers of sulfur, precipitated sulfur, colloidal sulfur, surface-treated sulfur, and insoluble sulfur; sulfur-containing compounds such as sulfur chloride, sulfur dichloride, morpholine disulfide, alkylphenol disulfide, dibenzothiazyl disulfide, caprolactam disulfide (N,N′-dithio-bis(hexahydro-2H-azepin-2-one)), phosphorus-containing polysulfide, and polymeric polysulfide; sulfur-donating compounds such as tetramethylthiuram disulfide, selenium dimethyldithiocarbamate, and 2-(4′-morpholinodithio)benzothiazole; and the like. These can be used alone or in combination.
  • organic peroxide cross-linking agents examples include dicumyl peroxide, cumene hydroperoxide, t-butyl cumyl peroxide, paramenthane hydroperoxide, di-t-butyl peroxide, 1,3-bis(t-butylperoxyisopropyl)benzene, 1,4-bis(t-butylperoxyisopropyl)benzene, 1,1-di-t-butylperoxy-3,3-trimethylcyclohexane, 4,4-bis-(t-butyl-peroxy)-n-butyl valerate, 2,5-dimethyl-2,5-di-t-butylperoxyhexane, 2,5-dimethyl-2,5-di-t-butylperoxyhexyne-3,1,1-di-t-butylperoxy-3,5,5-trimethylcyclohexane, p-chlorobenzoyl peroxide, t-butyl
  • the polyamine cross-linking agents may be any compound having two or more amino groups or any compound which is converted into a form having two or more amino groups during cross-linking.
  • Preferred are compounds having an aliphatic hydrocarbon or aromatic hydrocarbon moiety with amino groups or hydrazide structures (the structures represented by —CONHNH 2 where CO represents a carbonyl group) replacing a plurality of hydrogen atoms and compounds which are converted into such a form during cross-linking.
  • polyamine cross-linking agents include aliphatic polyvalent amines such as hexamethylenediamine, hexamethylenediamine carbamate, N,N-dicinnamylidene-1,6-hexanediamine, tetramethylenepentamine, and hexamethylenediamine cinnamaldehyde adducts; aromatic polyvalent amines such as 4,4-methylenedianiline, m-phenylenediamine, 4,4-diaminodiphenyl ether, 3,4-diaminodiphenyl ether, 4,4-(m-phenylenediisopropylidene)dianiline, 4,4-(p-phenylenediisopropylidene)dianiline, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 4,4-diaminobenzanilide, 4,4-bis(4-aminophenoxy)bipheny
  • aliphatic polyvalent amines and aromatic polyvalent amines preferred are aliphatic polyvalent amines and aromatic polyvalent amines, more preferred are hexamethylenediamine carbamate and 2,2-bis[4-(4-aminophenoxy)phenyl]propane, and particularly preferred is hexamethylenediamine carbamate to more significantly enhance the effects of the present invention.
  • the cross-linkable rubber composition according to the present invention can contain the cross-linking agent in any amount, the content is preferably 0.1 to 20 parts by weight, more preferably 1 to 15 parts by weight relative to 100 parts by weight of the nitrile group-containing copolymer rubber.
  • a polyamine cross-linking agent is used as the cross-linking agent, it is preferred that a basic cross-linking accelerator be further contained.
  • basic cross-linking accelerator examples include compounds represented by General Formula (1), basic cross-linking accelerators having a cyclic amidine structure, basic guanidine cross-linking accelerators, basic aldehyde amine cross-linking accelerators, and the like.
  • R 1 and R 2 each independently represent a C 1 to C 12 alkyl group optionally having a substituent or a C 5 to C 12 cycloalkyl group optionally having a substituent).
  • R 1 and R 2 are a C 1 to C 12 alkyl group optionally having a substituent or a C 5 to C 12 cycloalkyl group optionally having a substituent.
  • Preferred is a C 5 to C 12 cycloalkyl group optionally having a substituent, and particularly preferred is a C 5 to C 8 cycloalkyl group optionally having a substituent.
  • R 1 and R 2 have no substituent.
  • R 1 and R 2 have a substituent
  • substituents include a hydroxyl group, an alkoxy group, an alkoxycarbonyl group, an amino group, halogen atoms, and the like.
  • R 3 and R 4 each independently represent a C 5 to C 8 cycloalkyl group optionally having a substituent.
  • R 3 and R 4 are a C 5 to C 8 cycloalkyl group optionally having a substituent, preferred are C 5 or C 6 cycloalkyl groups optionally having a substituent, and more preferred are C 6 cycloalkyl groups optionally having a substituent.
  • R 3 and R 4 have no substituent.
  • R 3 and R 4 have a substituent
  • substituents include a hydroxyl group, an alkoxy group, an alkoxycarbonyl group, an amino group, halogen atoms, and the like.
  • Specific examples of the compounds represented by General Formula (1) include dicycloalkylamines such as dicyclopentylamine, dicyclohexylamine, and dicycloheptylamine; secondary amines whose nitrogen atom is bonded to an alkyl group and a cycloalkyl group, such as N-methylcyclopentylamine, N-butylcyclopentylamine, N-heptylcyclopentylamine, N-octylcyclopentylamine, N-ethylcyclohexylamine, N-butylcyclohexylamine, N-heptylcyclohexylamine, and N-octylcyclooctylamine; secondary amines whose nitrogen atom is bonded to an alkyl group having a hydroxy group and a cycloalkyl group, such as N-hydroxymethylcyclopentylamine and N-hydroxybutylcyclohexylamine; secondary amines whose
  • Examples of the basic cross-linking accelerators having a cyclic amidine structure include 1,8-diazabicyclo[5,4,0]undecene-7 (hereinafter, abbreviated to “DBU” in some cases), 1,5-diazabicyclo[4,3,0]nonene-5 (hereinafter, abbreviated to “DBN” in some cases), 1-methylimidzole, 1-ethylimidzole, 1-phenylimidazole, 1-benzylimidzole, 1,2-dimethylimidzole, 1-ethyl-2-methylimidzole, 1-methoxyethylimidzole, 1-phenyl-2-methylimidzole, 1-benzyl-2-methylimidazole, 1-methyl-2-phenylimidzole, 1-methyl-2-benzylimidzole, 1,4-dimethylimidzole, 1,5-dimethylimidazole, 1,2,4-trimethylimidzole, 1,4-dimethyl-2-e
  • 1,8-diazabicyclo[5,4,0]undecene-7 and 1,5-diazabicyclo[4,3,0]nonene-5 preferred are 1,8-diazabicyclo[5,4,0]undecene-7.
  • guanidine basic cross-linking accelerators examples include tetramethylguanidine, tetraethyguanidine, diphenylguanidine, 1,3-di-ortho-tolylguanidine, orthotolylbiguanide, and the like.
  • aldehyde amine basic cross-linking accelerators examples include n-butylaldehyde aniline, acetaldehyde ammonia, and the like.
  • these basic cross-linking accelerators preferred are the compounds represented by General Formula (1), the basic guanidine cross-linking accelerators, and the basic cross-linking accelerators having a cyclic amidine structure, and more preferred are the compounds represented by General Formula (1) and the basic cross-linking accelerators having a cyclic amidine structure.
  • the compounds represented by General Formula (1) may be mixed with alcohols such as an alkylene glycol and a C 5 to C 20 alkyl alcohol, and such mixtures may further contain an inorganic acid and/or an organic acid.
  • the compounds represented by General Formula (1) may form (a) salt(s) with the inorganic acid and/or the organic acid, and may further form a composite with the alkylene glycol.
  • the basic cross-linking accelerator having a cyclic amidine structure may form a salt with an organic carboxylic acid, an alkyl phosphoric acid, or the like.
  • the compounding amount of the basic cross-linking accelerator in the cross-linkable rubber composition according to the present invention is preferably 0.1 to 20 parts by weight, more preferably 0.2 to 15 parts by weight, still more preferably 0.5 to 10 parts by weight relative to 100 parts by weight of the nitrile group-containing copolymer rubber.
  • the following compounding agents usually used in the rubber field can also be compounded with the cross-linkable rubber composition according to the present invention: for example, reinforcing agents such as carbon black and silica, fillers such as calcium carbonate, talc, and clay, metal oxides such as zinc oxide and magnesium oxide, ⁇ , ⁇ -ethylenically unsaturated carboxylic acid metal salts such as zinc methacrylate and zinc acrylate, co-cross-linking agents, cross-linking aids, cross-linking retarders, antiaging agents, antioxidants, light stabilizers, scorching preventing agents such as primary amines, activating agents such as diethylene glycol, coupling agents, plasticizers, processing aids, greases, adhesives, lubricants, flame retardants, antifungal agents, acid acceptors, antistatic agents, piyments, foaming agents, and the like.
  • reinforcing agents such as carbon black and silica
  • fillers such as calcium carbonate, talc, and clay
  • metal oxides such
  • the coupling agents include silane coupling agents, aluminum coupling agents, titanate coupling agents, and the like. Any silane coupling agent can be used without limitation. Specific examples thereof include sulfur-containing silane coupling agents such as ⁇ -mercaptopropyltrimethoxysilane, ⁇ -mercaptomethyltrimethoxysilane, ⁇ -mercaptomethyltriethoxysilane, ⁇ -mercaptohexamethyldisilazane, bis(3-triethoxysilylpropyl)tetrasulfane, and bis(3-triethoxysilylpropyl)dusulfane; epoxy group-containing silane coupling agents such as ⁇ -glycidoxypropyltrimethoxysilane, ⁇ -glycidoxypropylmethyldimethoxysilane, ⁇ -(3,4-epoxycyclohexyl)ethyltrimethoxysilane, ⁇ -mercaptopropyltrimethoxysilane,
  • Any aluminum coupling agent can be used without limitation. Specific examples thereof include acetoalkoxyaluminum diisopropylate, and the like.
  • titanate coupling agent can be used without limitation.
  • Specific examples thereof include isopropyltriisostearoyl titanate, isopropyltris(dioctylpyrophosphate) titanate, isopropyltri(N-aminoethyl-aminoethyl) titanate, tetraoctylbis(ditridecylphosphite) titanate, tetra(2,2-diallyloxymethyl-1-butyl)bis(ditridecyl)phosphite titanate, bis(dioctylpyrophosphate)oxyacetate titanate, bis(dioctylpyrophosphate)ethylene titanate, tetraisopropylbis(dioctylphosphite) titanate, isopropyltriisostearoyl titanate, and the like.
  • silane coupling agents, aluminum coupling agents, titanate coupling agents, and the like can be
  • carbon black examples include furnace black, acetylene black, thermal black, channel black, austin black, graphite, and the like. These can be used alone or in combination.
  • silica examples include natural silicas such as quartz powder and silica stone powder; synthetic silicas such as silicic anhydride (such as silica gel and aerosil) and hydrous silicic acid; and the like. Among these, preferred are synthetic silicas. These silicas may be surface-treated with a coupling agent or the like. Examples of coupling agents usable in the surface treatment include those listed above.
  • any co-cross-linking agent can be used without limitation.
  • examples thereof include polyfunctional vinyl compounds such as divinylbenzene and divinylnaphthalene; isocyanurates such as triallyl isocyanurate and trimethallyl isocyanurate; cyanurates such as triallyl cyanurate; maleimides such as N,N′-m-phenylenedimaleimide; allyl esters of polyvalent acids such as diallyl phthalate, diallyl isophthalate, diallyl maleate, diallyl fumarate, diallyl sebacate, and triallyl phosphate; diethylene glycol bisallyl carbonate; allyl ethers such as ethylene glycol diallyl ether, triallyl ether of trimethylolpropane, and partial allyl ether of pentaerythrite; allyl-modified resins
  • plasticizer can be used without limitation, for example, trimellitic acid plasticizers, pyromellitic acid plasticizers, ether ester plasticizers, polyester plasticizers, phthalic acid plasticizers, adipic acid ester plasticizers, phosphoric acid ester plasticizers, sebacic acid ester plasticizers, alkylsulfonic acid ester compound plasticizers, epoxidated vegetable oil plasticizers, and the like can be used.
  • trimellitic acid isononyl ester trimellitic acid mixed linear alkyl esters, dipentaerythritol esters, pyromellitic acid 2-ethylhexyl ester, polyether esters (molecular weight: about 300 to 5000), bis[2-(2-butoxyethoxy)ethyl] adipate, dioctyl adipate, adipic acid polyester (molecular weight: about 300 to 5000), dioctyl phthalate, diisononyl phthalate, dibutyl phthalate, tricresyl phosphate, dibutyl sebacate, alkylsulfonic acid phenyl ester, epoxidized soybean oil, diheptanoate, di-2-ethylhexanoate, didecanoate, and the like. These can be used alone or in combination.
  • a rubber other than the nitrile group-containing copolymer rubber according to the present invention described above may be compounded in the range not impairing the effects of the present invention.
  • Examples of such a rubber include acrylic rubber, ethylene-acrylic acid copolymer rubber, styrene-butadiene copolymer rubber, polybutadiene rubber, ethylene-propylene copolymer rubber, ethylene-propylene-diene ternary copolymer rubber, epichlorohydrin rubber, fluorocarbon rubber, urethane rubber, chloroprene rubber, silicone rubber, natural rubber, polyisoprene rubber, and the like.
  • the compounding amount in the cross-linkable rubber composition is preferably 30 parts by weight or less, more preferably 20 parts by weight or less, still more preferably 10 parts by weight or less relative to 100 parts by weight of the nitrile group-containing copolymer rubber according to the present invention.
  • the cross-linkable rubber composition according to the present invention is prepared by mixing the components above preferably in a nonaqueous system.
  • the cross-linkable rubber composition according to the present invention can be prepared by any method without limitation.
  • the cross-linkable rubber composition can be usually prepared as follows: The components other than the cross-linking agent and thermally unstable components are primarily kneaded with a mixer such as a Banbury mixer, an internal mixer, a kneader, or the like. The kneaded mixture is transferred into an open roll mill or the like. The cross-linking agent and the thermally unstable components are added thereto, and the mixture are secondarily kneaded.
  • the primary kneading is performed usually at a temperature of 10 to 200° C., preferably 30 to 180° C. for 1 minute to 1 hour, preferably 1 minute to 30 minutes.
  • the secondary kneading is performed at a temperature of usually 10 to 90° C., preferably 20 to 60° C. for 1 minute to 1 hour, preferably 1 minute to 30 minutes.
  • the cross-linked rubber according to the present invention is prepared through cross-linking of the cross-linkable rubber composition according to the present invention described above.
  • the cross-linked rubber according to the present invention can be prepared as follows:
  • the cross-linkable rubber composition according to the present invention is formed using a forming machine having a desired shape, such as an extruder, an injection molding machine, a compressor, or a roll, is subjected to a cross-linking reaction by heating, and is solidified into a cross-linked product.
  • the composition may be cross-linked after forming, or may be formed and cross-linked at the same time.
  • the forming temperature is usually 10 to 200° C., preferably 25 to 120° C.
  • the cross-linking temperature is usually 100 to 200° C., preferably 130 to 190° C.
  • the cross-linking time is usually 1 minute to 24 hours, preferably 2 minutes to 1 hour.
  • the cross-linked product although cross-linked on its surface, may be insufficiently cross-linked in its inside depending on the shape, the size, and the like.
  • the cross-linked rubber may be secondarily cross-linked by further heating.
  • the heating method may be appropriately selected from methods used to cross-link rubber, such as press heating, steam heating, oven heating, and hot air heating.
  • the cross-linked rubber according to the present invention thus obtained is prepared using the nitrile group-containing copolymer rubber according to the present invention described above, and has high compression set resistance.
  • the cross-linked rubber according to the present invention can be used in broad applications: for example, a variety of sealing materials such as O-rings, packings, diaphrayms, oil seals, shaft seals, bearing seals, wellhead seals, shock absorber seals, coolant seals as seals for sealing cooling solutions such as long life coolants (LLC), oil coolant seals, seals for pneumatic apparatuses and devices, seals for sealing Freon, fluorohydrocarbons, or carbon dioxide used in cooling apparatuses for air conditioners and compressors for refrigerators of air-conditioning systems, seals for sealing supercritical carbon dioxide or subcritical carbon dioxide used as washing media for precision cleaning, seals for roller devices (such as roller bearings, automotive hub units, automotive water pumps, linear guide devices, and ball screws), valves and valve sheets, blow out preventers (BOPs), and bladders; a variety of gaskets such as an intake manifold gasket attached to a connection between an intake manifold and a cylinder head
  • LLC long life coolants
  • infrared spectroscopy was performed on a solid nitrile group-containing copolymer rubber by attenuated total reflection (ATR) method using a Fourier transform infrared spectrophotometer (FT-IR) as an infrared spectrophotometer according to “Analytical general rules for infrared spectroscopy” specified in JIS K 0117:2000. From the results obtained by infrared spectroscopy, the area of the peak of the absorbance which appeared in the range of 1770 to 1790 cm ⁇ 1 was calculated, and was defined as the absorbance area S A (unit: cm ⁇ 1 ).
  • ATR attenuated total reflection
  • the absorbance area S A was calculated and was defined as the absorbance area S A .
  • the Fourier transform infrared spectrophotometer used in the measurement was “FTS7000” made by Agilent Technologies, Inc. using a diamond having an angle of incidence of 45° (Golden Gate 10542 made by Systems Engineering Inc.) as a prism. To minimize the errors of measurement of the absorbance area, the measurement was performed at room temperature while the rubber was pressed against the entire surface of the prism so as to cover the entire surface thereof without any gap. In the measurement, the sample for measurement was a nitrile group-containing copolymer rubber not diluted with any other material (namely, the state where the concentration was 100 wt %).
  • the absorbance area S A was determined using a standard measurement function included in the Fourier transform infrared spectrophotometer “FTS7000” to measure the Absorbance area.
  • the iodine value of the nitrile group-containing copolymer rubber was measured in accordance with JIS K 6235.
  • the proportions of the monomer units forming the nitrile group-containing copolymer rubber were determined according to the following method.
  • the proportions of the mono-n-butyl maleate unit, the mono-n-butyl fumarate unit, the monocyclohexyl fumarate unit, and the mono-n-butyl itaconate unit were calculated as follows: The number of moles of carboxyl groups relative to 100 g of nitrile group-containing copolymer rubber after hydrogenation was determined by the method of measuring the “carboxyl group content” described above, and the determined number of moles thereof was converted into the contents of the mono-n-butyl maleate unit, the mono-n-butyl fumarate unit, the monocyclohexyl fumarate unit, or the mono-n-butyl itaconate unit.
  • the proportion of the 1,3-butadiene unit was calculated from the iodine value of the nitrile group-containing copolymer rubber before hydrogenation, which was measured (in accordance with JIS K 6235).
  • the proportion of the acrylonitrile unit was calculated from the nitrogen content in the nitrile group-containing copolymer rubber after hydrogenation, which was measured in accordance with JIS K 6384 by a semi-micro Kjeldahl method or a modified Dumas method.
  • the proportions of the n-butyl acrylate unit and the acrylic acid methoxyethyl acrylate unit were calculated as the balance of the monomer units above.
  • the Mooney viscosity (polymer Mooney viscosity) (ML1+4, 100° C.) of the nitrile group-containing copolymer rubber was measured in accordance with JIS K 6300.
  • the cross-linkable rubber composition was visually observed, and was evaluted for the state of a sheet-shaped compound dough and the crack or fusion failure during preparation of the sample for a compression set test, which will be described later, according to the following criteria:
  • A The compound dough is smooth and well wound around a roll.
  • B Bagging occurs (float or drip from a roll).
  • the cross-linkable rubber composition was primarily cross-linked by pressing at a temperature of 170° C. for 25 minutes using a metal mold, yielding a cylindrical cross-linked rubber having a diameter of 29 mm and a height of 12.5 mm.
  • the resulting cross-linked rubber was placed into a gear oven, and was secondarily cross-linked at 170° C. for 4 hours, preparing a cylindrical cross-linked rubber.
  • JIS K 6262 the resulting cross-linked rubber was then left to stand under a 150° C. environment for 168 hours in the state where the cross-linked rubber was 25% compressed, and then the compression set was measured. A lower value indicates higher compression set resistance.
  • the reactor was kept at 10° C., and 0.1 parts of cumene hydroperoxide (polymerization initiator) and a reducing agent, a chelating agent, and a builder in appropriate amounts were placed thereinto.
  • the polymerization reaction was continued under stirring.
  • 4 parts of a 2.5 wt % aqueous solution of 2,2,6,6-tetramethylpiperidine-1-oxyl (polymerization terminator) was added to terminate the polymerization reaction.
  • residual monomers were removed at a water temperature of 60° C. to yield a latex of Nitrile group-containing copolymer rubber (X1) (solids content: 25 wt %).
  • the obtained latex of Nitrile group-containing copolymer rubber (X1) and the catalyst aqueous solution were added in an autoclave such that the palladium content relative to the dry weight of the rubber contained in the latex of Nitrile group-containing copolymer rubber (X1) was 2,500 ppm by weight.
  • a hydrogenating reaction was performed for 6 hours under the following conditions to prepare a latex of Nitrile group-containing copolymer rubber (n1) hydrogenated: hydrogen pressure 3 MPa, temperature 50° C., and solids content 20 wt %.
  • the pH of the resulting latex was adjusted to 7.0.
  • a mixed aqueous solution of dimethylglyoxime in a 5-fold molar amount of that of the Pd metal contained in palladium chloride used in the hydrogenating reaction and potassium hydroxide in a 2-fold molar amount of that of dimethylglyoxime was added, and a hydrogen peroxide solution in a 30-fold molar amount of that of the Pd metal was further added.
  • the mixed solution was heated to 80° C. and was stirred for 5 hours, an insoluble complex was precipitated in the latex. The insoluble complex was removed through filtration.
  • the resulting latex of Nitrile group-containing copolymer rubber (n1) was adjusted with 1 wt % sulfuric acid to have a pH of 4. Under stirring, the latex was coagulated by adding the latex to 3-fold volume of deionized water where 100 parts of dietary salt is added relative to 100 parts of the copolymer and the pH is adjusted to 3 with sulfuric acid.
  • the resulting hydrous crumbs of Nitrile group-containing copolymer rubber (n1) were washed with water two times with 1 L deionized water, and were subjected to centrifugal dehydration and then hot air drying at 80° C. for 4 hours to yield Nitrile group-containing copolymer rubber (n1).
  • the obtained Nitrile group-containing copolymer rubber (n1) had an iodine value of 11 and a polymer Mooney viscosity (ML1+4, 100° C.) of 45.
  • Solid Nitrile group-containing copolymer rubbers (n2), (n4), (n5), (n6), (n9), and (n13) were prepared in the same manner as in Production Example 1 except that the types and compounding amounts of the monomers used in polymerization were varied as shown in Table 1 and the polymerization conversion ratio of the polymerization reaction and the amount of the palladium catalyst used in the hydrogenating reaction were varied as shown in Table 1.
  • Solid Nitrile group-containing copolymer rubbers (n3), (n7), and (n8) were prepared in the same manner as in Production Example 1 except that the types and compounding amounts of the monomers used in polymerization were varied as shown in Table 1, the polymerization conversion ratio of the polymerization reaction and the amount of the palladium catalyst used in the hydrogenating reaction were varied as shown in Table 1, and the resulting hydrous crumbs were dried by kneading the hydrous crumbs with a Brabender at 150° C. for 5 minutes.
  • Nitrile group-containing copolymer rubber (n10) was prepared in the same manner as in Production Example 8 except that the drying condition for kneading using a Brabender was changed to 150° C. for 10 minutes.
  • Nitrile group-containing copolymer rubber (n11) was prepared in the same manner as in Production Example 8 except that the drying condition for kneading using a Brabender was changed to 150° C. for 20 minutes.
  • Nitrile group-containing copolymer rubber (n12) was prepared in the same manner as in Production Example 8 except that the drying condition for kneading using a Brabender was changed to 180° C. for 5 minutes.
  • DBU 1,8-diazabicyclo[5,4,0]undecene-7
  • RIENOGRAN XLA-60 GE2014
  • 2 parts of hexamethylenediamine carbamate (trade name “Diak#1”, made by E. I. du Pont de Nemours and Company, polyamine cross-linking agent belonging to aliphatic polyvalent amines) were added to and kneaded with the mixture to prepare a sheet-shaped cross-linkable rubber composition.
  • Cross-linkable rubber compositions were prepared in the same manner as in Example 1 except that Nitrile group-containing copolymer rubbers (n2) to (n10) prepared in Production Examples 2 to 10 were used instead of Nitrile group-containing copolymer rubber (n2) prepared in Production Example 1 and the compounding amount of hexamethylenediamine carbamate as the cross-linking agent was varied as shown in Table 2, and were evaluted in the same manner as in Example 1. The results are shown in Table 2.
  • Cross-linkable rubber compositions were prepared in the same manner as in Example 1 except that Nitrile group-containing copolymer rubbers (n11), (n12), and (n13) prepared in Production Examples 11, 12, and 13 were used instead of Nitrile group-containing copolymer rubber (n2) prepared in Production Example 1 and the compounding amount of hexamethylenediamine carbamate as the cross-linking agent was varied as shown in Table 2, and were evaluated in the same manner as in Example 1. The results are shown in Table 2.
  • Example 1 2 3 4 5 6 7 Type of nitrile group-containing copolymer rubber (n1) (n2) (n3) (n4) (n5) (n6) (n7) Monomer composition of nitrile group-containing copolymer rubber Acrylonitrile unit (wt %) 15 16 21 21 21 44 24 1,3-Butadiene unit (including saturated moiety) (wt %) 46 45 43 42.5 42 51 45 Methoxyethyl acrylate unit (wt %) 26 n-Butyl acrylate unit (wt %) 34 34 31 30 31 Mono-n-butyl maleate unit (wt %) 5 5 5 5 5 5 Mono-n-butyl fumarate unit (wt %) 6.5 Monocyclohexyl fumarate unit (wt %) 6 Mono-n-butyl itaconate unit (wt %) Iodine value of nitrile group-containing copolymer rubber 11 60 11 50 20 10 8 Carboxyl group content C c (ephr)
  • the compounding amount of hexamethylenediamine carbamate is expressed as the content relative to 100 parts of the nitrile group-containing copolymer rubber.
  • their cross-linkable rubber compositions compounded with the cross-linking agent had a small change amount ⁇ ML of the Mooney viscosity, had a favorable state of the compound dough, allowed appropriate prevention of crack or fusion failure in their compounds, and had high forming properties.
  • the cross-linked rubbers prepared using such nitrile group-containing copolymer rubbers had a reduced compression set and high compression set resistance (Examples 1 to 10).

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