Rubber composition, crosslinkable rubber composition, and rubber crosslinked article

Abstract

Provided is a rubber composition comprising: a nitrile copolymer rubber (A) containing an α,β-ethylenically unsaturated nitrile monomer unit; and a vinyl chloride resin (B), wherein a fitting error value RMSE is 0.1 or less when a value of a loss tangent (tanδ) measured by dynamic viscoelasticity measurements in a temperature range of 50-220°C is fitted to a Doniach-Sunjic function.

Description

Rubber composition, crosslinkable rubber composition, and crosslinked rubber

[0001] The present invention relates to a rubber composition capable of giving a cross-linked rubber product having excellent ozone resistance, and to a cross-linkable rubber composition and cross-linked rubber product obtained using the rubber composition.

[0002] Conventionally, rubber containing α,β-ethylenically unsaturated nitrile monomer units and conjugated diene monomer units (nitrile copolymer rubber) has been known as a rubber having excellent oil resistance, and has been used mainly as a material for rubber products used in automobiles around various oils, such as fuel hoses, gaskets, packings, and oil seals.

[0003] Such rubber products are constantly required to have further improved overall performance such as ozone resistance, cold resistance, and compression set resistance, and therefore, improvements in these properties are also required in rubber compositions containing nitrile copolymer rubber.

[0004] For example, Patent Document 1 discloses a rubber composition containing an unsaturated nitrile-conjugated diene polymer containing a specific amount of specific alkylthio groups and having a Mooney viscosity within a specific range, and a vinyl chloride resin. However, the rubber composition obtained by the technique of Patent Document 1 does not necessarily have sufficient ozone resistance when made into a cross-linked rubber, and therefore further improvement has been desired.

[0005] Japanese Patent Application Publication No. 8-73661

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a rubber composition that can give a cross-linked rubber product having excellent ozone resistance, as well as a cross-linkable rubber composition and a cross-linked rubber product obtained using the rubber composition.

[0007] As a result of intensive research into achieving the above object, the present inventors have found that the above object can be achieved by controlling the fitting error value RMSE within a predetermined range when a loss tangent (tan δ) value measured by dynamic viscoelasticity measurement in a temperature range of 50 to 220°C is fitted to a Doniak-Schonitch function in a rubber composition containing a nitrile copolymer rubber (A) containing an α,β-ethylenically unsaturated nitrile monomer unit and a vinyl chloride resin (B) in a predetermined ratio, and have thus completed the present invention.

[0008] That is, according to the present invention, the following rubber composition, cross-linkable rubber composition, and cross-linked rubber product are provided. [1] A rubber composition containing a nitrile copolymer rubber (A) containing α,β-ethylenically unsaturated nitrile monomer units and a vinyl chloride resin (B), wherein the fitting error value RMSE when the loss tangent (tan δ) value measured by dynamic viscoelasticity measurement in the temperature range of 50 to 220°C is fitted to a Doniak-Schunich function is 0.1 or less. [2] The rubber composition according to [1], wherein the weight ratio (A / B) of the nitrile copolymer rubber (A) to the vinyl chloride resin (B) is 90 / 10 to 30 / 70. [3] The rubber composition according to [1] or [2], wherein the content of the α,β-ethylenically unsaturated nitrile monomer units in the nitrile copolymer rubber (A) is 15 to 55% by weight. [4] The rubber composition according to any one of [1] to [3], wherein the vinyl chloride resin (B) has an average degree of polymerization of 500 to 2800. [5] The rubber composition according to any one of [1] to [4], further containing a plasticizer. [6] The rubber composition according to any one of [1] to [5], further containing a stabilizer. [7] A cross-linkable rubber composition obtained by blending a cross-linking agent with the rubber composition according to any one of [1] to [6]. [8] A cross-linked rubber obtained by cross-linking the cross-linkable rubber composition according to [7].

[0009] According to the present invention, it is possible to provide a rubber composition that can give a cross-linked rubber product having excellent ozone resistance, and a cross-linked rubber product having excellent ozone resistance that is obtained using such a rubber composition.

[0010] FIG. 1(A) is a graph showing the relationship between the tan δ value of dynamic viscoelasticity measurement in the temperature range of 50 to 220°C, measured for the rubber composition of Example 3, and the Doniak-Schunich function obtained by fitting. FIG. 1(B) is a graph showing the relationship between the tan δ value of dynamic viscoelasticity measurement in the temperature range of 50 to 220°C, measured for the rubber composition of Comparative Example 1, and the Doniak-Schunich function obtained by fitting.

[0011] Rubber Composition The rubber composition of the present invention is a rubber composition containing a nitrile copolymer rubber (A) containing α,β-ethylenically unsaturated nitrile monomer units and a vinyl chloride resin (B), and the rubber composition has a fitting error value RMSE of 0.1 or less when the loss tangent (tan δ) value measured by dynamic viscoelasticity measurement in the temperature range of 50 to 220°C is fitted to a Doniak-Schunich function.

[0012] The nitrile copolymer rubber (A) used in the present invention is a rubber containing at least α,β-ethylenically unsaturated nitrile monomer units.

[0013] The α,β-ethylenically unsaturated nitrile monomer that forms the α,β-ethylenically unsaturated nitrile monomer unit 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. These can be used alone or in combination.

[0014] The nitrile copolymer rubber (A) used in the present invention preferably also contains diene monomer units or α-olefin monomer units so that the resulting cross-linked rubber has rubber elasticity.

[0015] Examples of the diene monomer that forms the diene monomer unit include conjugated dienes preferably having 4 or more carbon atoms, such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, and 1,3-pentadiene; and non-conjugated dienes preferably having 5 to 12 carbon atoms, such as 1,4-pentadiene, 1,4-hexadiene, vinylnorbornene, and dicyclopentadiene. Of these, conjugated dienes are preferred, and 1,3-butadiene is more preferred.

[0016] The α-olefin monomer forming the α-olefin monomer unit preferably has 2 to 12 carbon atoms, and examples thereof include ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene.

[0017] The content of the α,β-ethylenically unsaturated nitrile monomer units is not particularly limited, but is preferably 15 to 55% by weight, more preferably 20 to 54% by weight, even more preferably 25 to 52% by weight, still more preferably 28 to 50% by weight, and particularly preferably 30 to 48% by weight, based on the total monomer units. By setting the content of the α,β-ethylenically unsaturated nitrile monomer units within the above range, the obtained cross-linked rubber product can be made to have excellent ozone resistance and cold resistance.

[0018] In the present invention, when rubbers having different monomer compositions are combined to be used as the nitrile copolymer rubber (A), it is preferable that the content of the α,β-ethylenically unsaturated nitrile monomer unit in the entire mixture of rubbers having different monomer compositions (i.e., the entire mixture of nitrile copolymer rubbers (A) having different monomer compositions) be within the above-mentioned range. For example, when a 50:50 (weight ratio) mixture of rubber (α) having an α,β-ethylenically unsaturated nitrile monomer unit content of 25% by weight and rubber (β) having an α,β-ethylenically unsaturated nitrile monomer unit content of 35% by weight is used as the nitrile copolymer rubber (A), the content of the α,β-ethylenically unsaturated nitrile monomer unit in the entire nitrile copolymer rubber (A) will be 30% by weight. The same applies hereinafter to diene monomer units or α-olefin monomer units, etc.

[0019] The content of diene monomer units or α-olefin monomer units in the nitrile copolymer rubber (A) used in the present invention is preferably 45 to 85% by weight, more preferably 46 to 80% by weight, even more preferably 48 to 75% by weight, even more preferably 50 to 72% by weight, and particularly preferably 52 to 70% by weight, based on the total monomer units. By setting the content of diene monomer units or α-olefin monomer units within the above range, the obtained cross-linked rubber product can be made to have excellent ozone resistance, cold resistance, and compression set resistance. In addition, rubber elasticity can be appropriately improved.

[0020] The nitrile copolymer rubber (A) used in the present invention may contain, in addition to the above-mentioned α,β-ethylenically unsaturated nitrile monomer units and diene monomer units or α-olefin monomer units, units of other monomers copolymerizable with the monomers forming these monomer units. The content of such other monomer units is preferably 30% by weight or less, more preferably 20% by weight or less, and even more preferably 10% by weight or less, based on the total monomer units.

[0021] Examples of such copolymerizable other monomers include aromatic vinyl compounds such as styrene, α-methylstyrene, and vinyltoluene; fluorine-containing vinyl compounds such as fluoroethyl vinyl ether, fluoropropyl vinyl ether, o-trifluoromethylstyrene, vinyl pentafluorobenzoate, difluoroethylene, and tetrafluoroethylene; α-olefin compounds such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene; acrylic acid, methacrylic acid, maleic acid, and anhydride. α,β-ethylenically unsaturated carboxylic acids and anhydrides thereof, such as maleic acid, itaconic acid, itaconic anhydride, fumaric acid, and fumaric anhydride; α,β-ethylenically unsaturated monocarboxylic acid alkyl esters, such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; monoethyl maleate, diethyl maleate, monobutyl maleate, dibutyl maleate, monoethyl fumarate, diethyl fumarate, monobutyl fumarate, dibutyl fumarate, and monocyclohexyl fumarate. monoesters and diesters of α,β-ethylenically unsaturated polycarboxylic acids such as methyl acrylate, dicyclohexyl fumarate, monoethyl itaconate, diethyl itaconate, monobutyl itaconate, and dibutyl itaconate; alkoxyalkyl esters of α,β-ethylenically unsaturated carboxylic acids such as methoxyethyl (meth)acrylate, methoxypropyl (meth)acrylate, and butoxyethyl (meth)acrylate; α,β-ethylenically unsaturated carboxylic acids such as 2-hydroxyethyl (meth)acrylate and 3-hydroxypropyl (meth)acrylate; Examples of suitable ethylenically unsaturated monomers include polyfunctional ethylenically unsaturated monomers such as hydroxyalkyl esters of carboxylic acid; divinyl compounds such as divinylbenzene; di(meth)acrylic acid esters such as ethylene di(meth)acrylate, diethylene glycol di(meth)acrylate, and ethylene glycol di(meth)acrylate; and trimethacrylic acid esters such as trimethylolpropane tri(meth)acrylate, as well as self-crosslinking compounds such as N-methylol(meth)acrylamide and N,N'-dimethylol(meth)acrylamide.

[0022] The nitrile copolymer rubber (A) may be a nitrile copolymer rubber that is in a solid state at 25°C (has no fluidity at 25°C), or may be a liquid nitrile rubber. The liquid nitrile rubber used in the present invention is a nitrile copolymer rubber that is in a liquid state at 25°C (has fluidity at 25°C). The liquid nitrile rubber used in the present invention usually has a Mooney viscosity of 1 or less, measured in accordance with JIS K6300, or a viscosity that is so low that the Mooney viscosity cannot be measured. When a liquid nitrile rubber is used in the present invention, it is preferable to use a combination of a nitrile copolymer rubber that is in a solid state at 25°C and a liquid nitrile rubber. In this case, from the viewpoint of strength, it is preferable that the weight ratio of the nitrile copolymer rubber that is in a solid state at 25°C is higher than the weight ratio of the liquid nitrile rubber, and it is more preferable that the weight ratio of the nitrile copolymer rubber that is in a solid state at 25°C: the liquid nitrile rubber is 70:30 to 90:10.

[0023] The Mooney viscosity (ML1+4, 100°C) of the nitrile copolymer rubber (A) is usually 3 to 250, preferably 15 to 180, and more preferably 20 to 160. If the polymer Mooney viscosity of the nitrile copolymer rubber (A) is too low, the strength properties of the resulting cross-linked rubber may be reduced. On the other hand, if the polymer Mooney viscosity is too high, processability may be impaired. The Mooney viscosity of the nitrile copolymer rubber (A) can be measured, for example, in accordance with JIS K6300. When two or more types of rubber are used in combination as the nitrile copolymer rubber (A), the Mooney viscosity of the two or more types of nitrile copolymer rubbers when mixed may be set within the above range.

[0024] The method for producing the nitrile copolymer rubber (A) used in the present invention is not particularly limited, but it can be produced by copolymerizing the above-mentioned monomers and, if necessary, hydrogenating the carbon-carbon double bonds in the resulting copolymer. The polymerization method is not particularly limited, and known emulsion polymerization methods or solution polymerization methods may be used, but emulsion polymerization methods are preferred from the viewpoint of industrial productivity. During emulsion polymerization, commonly used polymerization secondary materials can be used in addition to emulsifiers, polymerization initiators, and molecular weight modifiers.

[0025] The emulsifier is not particularly limited, but examples thereof include nonionic emulsifiers such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenol 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, alkylbenzenesulfonates such as sodium dodecylbenzenesulfonate, higher alcohol sulfates, and alkyl sulfosuccinates; and copolymerizable emulsifiers such as sulfoesters of α,β-unsaturated carboxylic acids, sulfate esters of α,β-unsaturated carboxylic acids, and sulfoalkylaryl ethers. The amount of emulsifier added is preferably 0.1 to 10 parts by weight, and more preferably 0.5 to 5 parts by weight, per 100 parts by weight of the monomers used in the polymerization.

[0026] The polymerization initiator is not particularly limited as long as it is a radical initiator, and 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-butylperoxyisobutyrate; and azo compounds such as azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, azobiscyclohexanecarbonitrile, and methyl azobisisobutyrate. These polymerization initiators can be used alone or in combination of two or more. Inorganic or organic peroxides are preferred as the polymerization initiator. When a peroxide is used as a polymerization initiator, it can be used as a redox polymerization initiator in combination with a reducing agent such as sodium bisulfite, ferrous sulfate, etc. The amount of the polymerization initiator added is preferably 0.01 to 2 parts by weight based on 100 parts by weight of the monomers used in the polymerization.

[0027] The molecular weight modifier is not particularly limited, but 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; 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. Among these, mercaptans are preferred, and t-dodecyl mercaptan is more preferred. The amount of molecular weight modifier used is preferably 0.1 to 1.5 parts by weight per 100 parts by weight of the monomers used in the polymerization when producing a nitrile copolymer rubber that is in a solid state at 25°C, and preferably 5 to 15 parts by weight per 100 parts by weight of the monomers used in the polymerization when producing a liquid nitrile rubber.

[0028] Water is usually used as the medium for emulsion polymerization, and the amount of water is preferably 80 to 500 parts by weight, more preferably 80 to 300 parts by weight, per 100 parts by weight of the monomers used in the polymerization.

[0029] In emulsion polymerization, if necessary, polymerization auxiliary materials such as stabilizers, dispersants, pH adjusters, oxygen scavengers, particle size adjusters, etc. When these are used, the types and amounts used are not particularly limited.

[0030] The nitrile copolymer rubber (A) used in the present invention may be a hydrogenated nitrile copolymer rubber obtained by hydrogenating (by hydrogenation reaction) at least a portion of the unsaturated bond moieties in the diene monomer units of the copolymer obtained by copolymerization as described above. The hydrogenation method is not particularly limited, and any known method may be used. When the nitrile copolymer rubber (A) is made into a hydrogenated nitrile copolymer rubber, its iodine value is preferably in the range of 0 to 70, more preferably in the range of 4 to 60.

[0031] The polymerization reaction solution thus obtained is coagulated with an alcohol such as methanol or isopropyl alcohol or by salting out, washed with water, and filtered, and the resulting hydrous crumbs are dried to obtain the nitrile copolymer rubber (A). For coagulation by salting out, known coagulants such as sodium chloride, calcium chloride, aluminum sulfate, and magnesium sulfate can be used. Centrifugal dehydration may also be performed, if necessary.

[0032] Alternatively, an antioxidant may be added to the polymerization reaction solution before coagulation, and the coagulation may be carried out in a state containing the antioxidant. The antioxidant is not particularly limited, but examples thereof include 2,6-di-t-butyl-4-cresol (ANTAGE BHT, manufactured by Kawaguchi Chemical Industry Co., Ltd.), 2,2'-methylenebis(4-methyl-6-tert-butylphenol) (Sandant 2246, manufactured by Sanshin Chemical Industry Co., Ltd.), bis(3,5-di-tert-butyl-4-hydroxybenzyl)sulfide (Sandant 103, manufactured by Sanshin Chemical Industry Co., Ltd.), pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (Irganox 1010, manufactured by BASF Japan), octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (Irganox 1076, manufactured by BASF Japan), isooctyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (Irganox 1135, manufactured by BASF Japan), hexamethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (Irganox 259, manufactured by BASF Japan), 4,6-bis(octylthiomethyl)-o-cresol (Irganox 1520L, manufactured by BASF Japan), and the like can be used.

[0033] When a crosslinkable rubber composition described later is obtained using the rubber composition of the present invention, in addition to the nitrile copolymer rubber (A) contained in the rubber composition of the present invention, depending on the compounding agents used in obtaining the crosslinkable rubber composition, the nitrile copolymer rubber (A) may be additionally added together with a crosslinking agent when obtaining the crosslinkable rubber composition described later.

[0034] The rubber composition of the present invention contains a vinyl chloride resin (B) in addition to the above-mentioned nitrile copolymer rubber (A).

[0035] The vinyl chloride resin (B) is not particularly limited as long as it is a resin whose main constituent monomer is vinyl chloride, but the content of vinyl chloride units as the main constituent monomer is preferably 50 to 100% by weight, more preferably 60 to 100% by weight, and even more preferably 70 to 100% by weight.

[0036] The average degree of polymerization of the vinyl chloride resin (B) is not particularly limited, but its lower limit is preferably 500 or more, more preferably 700 or more, even more preferably 850 or more, even more preferably 900 or more, particularly preferably 950 or more, and particularly preferably 1000 or more, and its upper limit is preferably 2800 or less, more preferably 2750 or less, even more preferably 2700 or less, even more preferably 2600 or less, particularly preferably 2500 or less, and particularly preferably 2400 or less. By setting the average degree of polymerization of the vinyl chloride resin (B) within the above range, the obtained cross-linked rubber product can be made to have excellent ozone resistance while being appropriately mixed with the nitrile copolymer rubber (A). Specifically, by setting the average degree of polymerization of the vinyl chloride resin (B) within the above range, the Mooney viscosity of the rubber composition can be controlled within an appropriate range, thereby improving the processability when obtaining the rubber composition. The average degree of polymerization of the vinyl chloride resin (B) can be measured, for example, by the solution viscosity method specified in JIS K6721. The glass transition temperature (Tg) of the vinyl chloride resin (B) is preferably 50 to 180°C.

[0037] The vinyl chloride resin (B) used in the present invention may be a copolymer of vinyl chloride, which is the main constituent monomer, with other monomers copolymerizable with vinyl chloride. Examples of such other monomers include (meth)acrylic acid alkyl esters having an alkyl group of 1 to 20 carbon atoms; aromatic vinyl compounds such as styrene, vinyltoluene, and α-methylstyrene; vinyl cyanide compounds such as acrylonitrile, methacrylonitrile, and vinylidene cyanide; vinyl ester compounds such as vinyl acetate and vinyl propionate; vinyl ether compounds such as ethyl vinyl ether, cetyl vinyl ether, and hydroxybutyl vinyl ether; and hydroxyl group- or alkoxy group-containing unsaturated carboxylic acid ester compounds such as α-hydroxyethyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and butoxyethyl (meth)acrylate.

[0038] The polymerization method for producing the vinyl chloride resin (B) used in the present invention is not particularly limited, and examples thereof include emulsion polymerization, seed emulsion polymerization, fine suspension polymerization, and suspension polymerization.

[0039] As the vinyl chloride resin (B), a suspension vinyl chloride resin, a paste vinyl chloride resin, or the like is preferably used.

[0040] The vinyl chloride resin suspension is preferably a particle having a porous structure, more specifically, an irregular particle having many voids inside. The vinyl chloride resin suspension can be obtained, for example, by suspension polymerization. The average particle diameter of the vinyl chloride resin suspension is usually 50 to 200 μm. In particular, from the viewpoint of further improving the dispersion state of the nitrile copolymer rubber (A) and the vinyl chloride resin (B), the average particle diameter of the vinyl chloride resin suspension is preferably 50 to 150 μm. The average particle diameter can be measured, for example, as the 50% cumulative diameter (D50 diameter) on a volume basis using a laser diffraction scattering measurement device.

[0041] The paste vinyl chloride resin is preferably spherical particles, more specifically, preferably true spheres with few internal and surface voids. Paste vinyl chloride resins can be obtained, for example, by emulsion polymerization or microsuspension polymerization. Paste vinyl chloride resins include pulverized and granular grades. Since fine-grained paste vinyl chloride resins (pulverized) have small particle diameters and excellent dispersibility, the use of fine-grained paste vinyl chloride resins can further improve the dispersion state of the nitrile copolymer rubber (A) and the vinyl chloride resin (B). On the other hand, granular paste vinyl chloride resins have excellent handleability, so the use of granular paste vinyl chloride resins can improve the workability of obtaining a rubber composition. Therefore, taking these properties into consideration, fine-grained paste vinyl chloride resins or granular paste vinyl chloride resins can be appropriately selected and used, and both can be used suitably. The average particle size of the paste vinyl chloride resin is broad, usually less than 100 μm, preferably 0.02 to 50 μm, more preferably 0.02 to 10 μm, and even more preferably 0.02 to 1 μm.

[0042] In the rubber composition of the present invention, the weight ratio (A / B) of the nitrile copolymer rubber (A) to the vinyl chloride resin (B) is not particularly limited, but is preferably 90 / 10 to 30 / 70, more preferably 85 / 15 to 35 / 65, even more preferably 80 / 20 to 40 / 60, still more preferably 75 / 25 to 45 / 55, and particularly preferably 70 / 30 to 50 / 50. By setting the weight ratio (A / B) of the nitrile copolymer rubber (A) to the vinyl chloride resin (B) within the above range, the obtained cross-linked rubber product can be made more excellent in ozone resistance, and the polymer Mooney viscosity of the mixture of the nitrile copolymer rubber (A) and the vinyl chloride resin (B) can be controlled within an appropriate range, thereby improving the processability when obtaining the rubber composition.

[0043]

[0033] The rubber composition of the present invention may contain other compounding agents in addition to the nitrile copolymer rubber (A) and the vinyl chloride resin (B). Examples of such other compounding agents include a plasticizer, a stabilizer, and an antioxidant.

[0044] Specific examples of the plasticizer include ester compounds of adipic acid and an ether bond-containing alcohol, such as dibutoxyethyl adipate and di(butoxyethoxyethyl) adipate; ester compounds of azelaic acid and an ether bond-containing alcohol, such as dibutoxyethyl azelaate and di(butoxyethoxyethyl) azelaate; ester compounds of sebacic acid and an ether bond-containing alcohol, such as dibutoxyethyl sebacate and di(butoxyethoxyethyl) sebacate; dibutoxyethyl phthalate and di(butoxyethoxyethyl) phthalate; ester compounds of isophthalic acid and ether bond-containing alcohols such as dibutoxyethyl isophthalate and di(butoxyethoxyethyl) isophthalate; dialkyl adipic acid esters such as di-(2-ethylhexyl) adipate, diisodecyl adipate, diisononyl adipate, and dibutyl adipate; dialkyl azelaic acid esters such as di-(2-ethylhexyl) azelaate, diisooctyl azelaate, and di-n-hexyl azelaate; di-sebacic acid di- Sebacic acid dialkyl esters such as n-butyl and di-(2-ethylhexyl) sebacate; phthalic acid dialkyl esters such as dibutyl phthalate, di-(2-ethylhexyl) phthalate, di-n-octyl phthalate, diisobutyl phthalate, diheptyl phthalate, diisodecyl phthalate, diundecyl phthalate, and diisononyl phthalate; phthalic acid dicycloalkyl esters such as dicyclohexyl phthalate; phthalic acid aryl esters such as diphenyl phthalate and butyl benzyl phthalate; di-(2-ethylhexyl) isophthalate, isophthalic acid dialkyl esters such as diisooctyl isophthalate; tetrahydrophthalic acid dialkyl esters such as di-(2-ethylhexyl) tetrahydrophthalate, di-n-octyl tetrahydrophthalate, and diisodecyl tetrahydrophthalate; trimellitic acid derivatives such as tri-(2-ethylhexyl) trimellitate, tri-n-octyl trimellitate, triisodecyl trimellitate, triisooctyl trimellitate, tri-n-hexyl trimellitate, triisononyl trimellitate, and triisodecyl trimellitate;Examples of suitable plasticizers include epoxy-based plasticizers such as epoxidized soybean oil and epoxidized linseed oil; and phosphate ester-based plasticizers such as tricresyl phosphate. These may be used alone or in combination.

[0045] Among these, from the viewpoint of being able to improve the cold resistance and oil resistance of the obtained cross-linked rubber product, preferred are ester compounds of dibasic acids such as adipic acid, azelaic acid, sebacic acid and phthalic acid with ether bond-containing alcohols, more preferred are ester compounds of adipic acid with ether bond-containing alcohols, and di(butoxyethoxyethyl) adipate is particularly preferred.

[0046] The content of the plasticizer in the rubber composition of the present invention is preferably 40 parts by weight or less, more preferably 0.1 to 40 parts by weight, even more preferably 0.5 to 30 parts by weight, and particularly preferably 1 to 25 parts by weight, per 100 parts by weight of the total of the nitrile copolymer rubber (A) and the vinyl chloride resin (B). By setting the content of the plasticizer within the above range, the effect of adding the plasticizer can be further enhanced.

[0047] Examples of stabilizers include lead-based stabilizers such as tribasic lead sulfate, dibasic lead phosphite, basic lead sulfite, and lead silicate; stabilizers containing metals such as potassium, magnesium, barium, zinc, cadmium, and lead, and 2-ethylhexanoic acid, lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, hydroxystearic acid, oleic acid, ricinoleic acid, linoleic acid, behenic acid, isodecanoic acid, triethanolamine, and the like; metal soap stabilizers derived from one or more fatty acids such as alkylacetic acid, naphthenic acid, benzoic acid, salicylic acid, etc.; complex metal soap stabilizers derived from two or more metals such as Ca-Zn, Ba-Zn, Mg-Zn, Na-Zn, Pb-Sn, Ca-Mg-Zn, Ba-Ca-Sn, Ca-Mg-Sn, Ca-Zn-Sn, Pb-Ba-Ca, etc., and the above fatty acids; Mg ４．５ Al ２ (OH) １３ CO ３ ・3.5H ２ O, Mg ４．５ Al ２(OH) １３ CO ３ , Mg ４ Al ２ (OH) １２ CO ３ ・3.5H ２ O, Mg ６ Al ２ (OH) １６ CO ３ ・4H ２ O, Mg ５ Al ２ (OH) １４ CO ３ ・4H ２ O, Mg ３ Al ２ (OH) １０ CO ３ ・1.7H ２ General formula Mg ｘ Al ｙ (OH) ２ｘ＋３ｙ－２ CO ３ ・wH ２ 0 (where x is a number from 1 to 10, y is a number from 1 to 5, and w is a real number); and organotin stabilizers derived from alkyl groups, ester groups, etc., and fatty acid salts, maleates, sulfides, etc. Among these, Ca-Mg-Zn, Ba-Zn, and Ca-Zn composite metal soap stabilizers and hydrotalcite stabilizers are preferred, Ca-Mg-Zn composite metal soap stabilizers and hydrotalcite stabilizers are more preferred, and Ca-Mg-Zn composite metal soap stabilizers are even more preferred. These may be used alone or in combination. The content of the stabilizer in the rubber composition of the present invention is preferably 0.01 to 10 parts by weight, more preferably 0.1 to 5 parts by weight, and even more preferably 0.2 to 3 parts by weight, per 100 parts by weight of the total of the nitrile copolymer rubber (A) and the vinyl chloride resin (B). By setting the content of the stabilizer within the above range, it is possible to realize excellent ozone resistance while maintaining a good hue, and to broaden the range of applications, thereby further increasing the value of the product.

[0048] The antioxidant is not particularly limited, but may be a phenol-based, amine-based, benzimidazole-based, phosphoric acid-based, etc. The content of the antioxidant in the rubber composition of the present invention is preferably 0.5 to 20 parts by weight, more preferably 1 to 15 parts by weight, and even more preferably 1.5 to 10 parts by weight, per 100 parts by weight of the total of the nitrile copolymer rubber (A) and the vinyl chloride resin (B).

[0049] The rubber composition of the present invention has a fitting error value RMSE of 0.1 or less when the loss tangent (tan δ) value measured by dynamic viscoelasticity measurement in the temperature range of 50 to 220°C is fitted to a Doniak-Schunich function. According to the present invention, by making the fitting error value RMSE 0.1 or less, the rubber composition can be made to give a cross-linked rubber product with excellent ozone resistance. The value of the fitting error value RMSE is preferably 0.099 or less, more preferably 0.095 or less. The lower limit of the fitting error value RMSE of the rubber composition of the present invention is not particularly limited, but is usually 0.001 or more, preferably 0.005 or more, and more preferably 0.01. If the fitting error value RMSE is too large, the resulting cross-linked rubber product will have poor ozone resistance.

[0050] According to the findings of the present inventors, in a rubber composition containing a nitrile copolymer rubber (A) and a vinyl chloride resin (B), when the value of the loss tangent (tan δ) measured by dynamic viscoelasticity measurement in the temperature range of 50 to 220°C, particularly the relationship between the measurement temperature and the loss tangent (tan δ), is approximated by a Doniak-Schunich function, the closer the value is to the ideal Doniak-Schunich function, the more excellent the ozone resistance of a cross-linked rubber product obtained using the rubber composition, which led to the completion of the present invention. Specifically, the inventors have discovered that the smaller the fitting error value RMSE, which represents the deviation from the ideal Doniak-Schunich function when fitting to the Doniak-Schunich function, i.e., the closer the value is to the ideal Doniak-Schunich function, the more excellent the ozone resistance of a cross-linked rubber product obtained using the rubber composition.

[0051] Here, Figure 1(A) is a graph showing the relationship between the tan δ value of dynamic viscoelasticity measurement in the temperature range of 50 to 220°C, measured for the rubber composition of Example 3, and the Doniak-Schunich function obtained by fitting. As can be seen from Figure 1(A), the rubber composition of the present invention has a loss tangent (tan δ) value with respect to measurement temperature that approximates the Doniak-Schunich function, and has a small fitting error value RMSE. In contrast, Figure 1(B) is a graph showing the relationship between the tan δ value of dynamic viscoelasticity measurement in the temperature range of 50 to 220°C, measured for the rubber composition of Comparative Example 1, and the Doniak-Schunich function obtained by fitting. As is clear from Figure 1(B), the rubber composition of Comparative Example 1 has a large fitting error value RMSE, and the resulting cross-linked rubber product has poor ozone resistance.

[0052] The fitting error value RSME of a rubber composition can be determined as follows: First, dynamic viscoelasticity measurement is performed on the rubber composition to measure tan δ in a temperature range of 50 to 220° C. Next, the measured tan δ is used to fit a Doniak-Schunich function represented by the following formula (1) by the least squares method, and the Doniak-Schunich function fitted to the measured tan δ (with the smallest error) is determined. In this case, A (amplitude), which is one of the parameters determining the Doniak-Schunich function expressed by the above formula (1), is initially set to 1 and its value is changed within a range from a minimum value of 1 to a maximum value of ∞. Similarly, μ (center), which is another parameter determining the Doniak-Schunich function expressed by the above formula (1), is initially set to 150 and its value is changed within a range from a minimum value of 0 to a maximum value of 250, σ (sigma) is initially set to 20 and its value is changed within a range from a minimum value of 10 to a maximum value of 60, and γ (gamma) is initially set to 0.15 and its value is changed within a range from a minimum value of 0 to a maximum value of 1, thereby obtaining a Doniak-Schunich function (with the smallest error) fitted to the measurement results from among the Doniak-Schunich functions expressed by the above formula (1). By calculating the error value between the measurement results and the Doniak-Schunich function with the smallest error obtained in this way, a fitting error value RMSE can be calculated. The fitting can be performed, for example, by using the limfit module of Python and using the Doniach Model as the above formula (1). Furthermore, the least squares method can be, for example, the Levenberg-Marquardt method.

[0053] Dynamic viscoelasticity measurement can be performed, for example, using a dynamic viscoelasticity measuring device under conditions of a dynamic strain of ±0.5% and 5 Hz. Measurement of the tan δ value by dynamic viscoelasticity measurement may be performed in a temperature range of 50 to 220° C., but it is preferable to measure the tan δ value in increments of 1 to 15° C. in the temperature range of 50 to 220° C. and use the results; for example, measurement of the tan δ value in increments of 10° C. in the temperature range of 50 to 220° C. and use the results.

[0054] The rubber composition of the present invention is prepared by mixing the components including the nitrile copolymer rubber (A) and the vinyl chloride resin (B), preferably in a non-aqueous system, using, for example, an open mixer such as a roll, an internal mixer such as a Banbury mixer, an internal mixer such as a kneader or a Brabender, or a continuous mixer such as a single-screw extruder or a twin-screw extruder.

[0055] The mixing start temperature (the set temperature of the kneader) when mixing the components including the nitrile copolymer rubber (A) and the vinyl chloride resin (B) is not particularly limited, but can be appropriately set between 20 and 200°C, and preferably between 20 and 100°C.

[0056] When mixing the components including the nitrile copolymer rubber (A) and the vinyl chloride resin (B), the temperature of the mixture often rises due to frictional forces generated by kneading as the mixing proceeds. In the present invention, it is preferable to control the maximum temperature reached by the temperature rise of the mixture (referred to as the maximum ultimate mixing temperature in the present invention) within a predetermined range. Specifically, it is preferable to set the maximum ultimate mixing temperature when mixing the components including the nitrile copolymer rubber (A) and the vinyl chloride resin (B) to a temperature equal to or higher than the gelation temperature of the vinyl chloride resin (B). More specifically, the maximum ultimate mixing temperature is preferably 140°C or higher, more preferably 160°C or higher, even more preferably 170°C or higher, and particularly preferably 180°C or higher, with the upper limit being preferably 210°C or lower, more preferably 200°C or lower. By setting the maximum ultimate mixing temperature within the above range, the dispersion state of the nitrile copolymer rubber (A) and the vinyl chloride resin (B) can be improved, and the fitting error value RMSE can be suitably controlled within the above range. The maximum mixing temperature may be determined by taking the temperature of the mixture when it is discharged from the kneader (discharge temperature) as the maximum mixing temperature.

[0057] When mixing the components including the nitrile copolymer rubber (A) and the vinyl chloride resin (B), the total mixing time from the start of mixing to the discharge of the mixture can be appropriately set depending on the kneading conditions, but is usually 2 to 20 minutes, and preferably 2 to 10 minutes.

[0058] In the present invention, the nitrile copolymer rubber (A) and the vinyl chloride resin (B) are preferably mixed under conditions in which a shear force is applied, and a method using a kneading device capable of applying a shear force, such as an internal kneader such as a Banbury mixer, an intermix, a kneader, or a Brabender, or a continuous kneader such as a single-screw extruder or a twin-screw extruder, is preferred. By mixing under such conditions, the dispersion state of the nitrile copolymer rubber (A) and the vinyl chloride resin (B) can be improved, and the fitting error value RMSE can be suitably controlled within the above range.

[0059] When the nitrile copolymer rubber (A) and the vinyl chloride resin (B) are mixed under the above conditions, the nitrile copolymer rubber (A) and the vinyl chloride resin (B) may be mixed alone, but from the viewpoint of improving the color, it is preferable to mix them in the presence of a stabilizer, and it is more preferable to mix them in the presence of a plasticizer in addition to the stabilizer. In this case, the amounts of the stabilizer and the plasticizer used may be within the above-mentioned ranges.

[0060] Crosslinkable Rubber Composition The crosslinkable rubber composition of the present invention is obtained by compounding the above-mentioned rubber composition of the present invention with a crosslinking agent. Examples of the crosslinking agent include sulfur-based crosslinking agents and organic peroxide crosslinking agents. These may be used alone or in combination of two or more types, but it is preferable to use a sulfur-based crosslinking agent.

[0061] Examples of sulfur-based crosslinking agents include sulfur such as powdered sulfur, sulfur flowers, 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, phosphorus-containing polysulfide, and polymeric polysulfides; and sulfur-donating compounds such as tetramethylthiuram disulfide, dimethyldithiocarbamate selenium, and 2-(4'-morpholinodithio)benzothiazole. These may be used alone or in combination of two or more.

[0062] Examples of organic peroxide crosslinking agents include dicumyl peroxide, cumene hydroperoxide, t-butylcumyl 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-butylperoxy)-n-butylvalerate, 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-butylperoxyisopropyl carbonate, and t-butylperoxybenzoate. These may be used alone or in combination.

[0063] From the viewpoint of obtaining a good cross-linked rubber product, the content of the cross-linking agent in the cross-linkable rubber composition of the present invention is preferably 0.1 to 10 parts by weight, more preferably 0.3 to 8 parts by weight, and even more preferably 0.5 to 6 parts by weight, per 100 parts by weight of the total of the nitrile copolymer rubber (A) and the vinyl chloride resin (B).

[0064] When a sulfur-based crosslinking agent is used, it can be used in combination with a crosslinking aid such as active zinc oxide, zinc oxide, stearic acid, etc.; or a crosslinking accelerator such as a guanidine-based, aldehyde-amine-based, aldehyde-ammonia-based, thiazole-based, sulfenamide-based, or thiourea-based. The amount of these crosslinking aids and crosslinking accelerators used is preferably in the range of 0.1 to 20 parts by weight per 100 parts by weight of the total of the nitrile copolymer rubber (A) and the vinyl chloride resin (B).

[0065] When an organic peroxide crosslinking agent is used, a polyfunctional monomer such as trimethylolpropane trimethacrylate, divinylbenzene, ethylene dimethacrylate, triallyl isocyanurate, etc. may be used in combination as a crosslinking aid. The amount of these crosslinking aids used is preferably in the range of 0.5 to 20 parts by weight per 100 parts by weight of the total of the nitrile copolymer rubber (A) and the vinyl chloride resin (B).

[0066] The cross-linkable rubber composition of the present invention preferably further contains an aromatic amine-based antioxidant and / or a quinoline-based antioxidant, more preferably contains at least an aromatic amine-based antioxidant, and particularly preferably contains both an aromatic amine-based antioxidant and a quinoline-based antioxidant. By further containing an aromatic amine-based antioxidant and / or a quinoline-based antioxidant, the obtained cross-linked rubber product can be made more excellent in ozone resistance.

[0067] Specific examples of aromatic amine antioxidants include 4,4'-bis(α,α'-dimethylbenzyl)diphenylamine (also called "p.p'-dicumyldiphenylamine"), p. Examples include diaryl secondary monoamine antioxidants such as octylated diphenylamines such as p'-dioctyldiphenylamine, styrenated diphenylamine, and phenyl-α-naphthylamine; diaryl-p-phenylenediamine antioxidants such as diphenyl-p-phenylenediamine, mixed diaryl-p-phenylenediamine, and dinaphthyl-p-phenylenediamine; and alkylaryl-p-phenylenediamine antioxidants such as N-isopropyl-N'-phenyl-p-phenylenediamine, N-1,3-dimethylbutyl-N'-phenyl-p-phenylenediamine, N-(3-methacryloyloxy-2-hydroxypropyl)-N'-phenyl-p-phenylenediamine, and N-(methacryloyl)-N'-phenyl-p-phenylenediamine. These can be used alone or in combination of two or more. Among these, alkylaryl-p-phenylenediamine antioxidants are preferred, and N-isopropyl-N'-phenyl-p-phenylenediamine is more preferred.

[0068] Examples of quinoline antioxidants include 2,2,4-trimethyl-1,2-dihydroquinoline polymers and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline polymers. These can be used alone or in combination. Of these, 2,2,4-trimethyl-1,2-dihydroquinoline polymers are preferred.

[0069] The content of the aromatic amine-based antioxidant and / or quinoline-based antioxidant in the crosslinkable rubber composition of the present invention is preferably 0.3 to 15 parts by weight, more preferably 0.5 to 12 parts by weight, and even more preferably 0.8 to 10 parts by weight, per 100 parts by weight of the total of the nitrile copolymer rubber (A) and the vinyl chloride resin (B). By setting the content of the aromatic amine-based antioxidant and / or quinoline-based antioxidant within the above range, the ozone resistance of the obtained crosslinked rubber can be more appropriately improved.

[0070] The cross-linkable rubber composition of the present invention preferably further contains a hydrocarbon wax. By further containing a hydrocarbon wax, the obtained cross-linked rubber product can be made to have better ozone resistance.

[0071] Examples of hydrocarbon waxes include polyolefin waxes such as polyethylene wax and polypropylene wax; Fischer-Tropsch wax; and petroleum-based waxes such as paraffin wax and microcrystalline wax. Of these, Fischer-Tropsch wax and petroleum-based wax are preferred, with petroleum-based waxes being more preferred.

[0072] The content of the hydrocarbon wax in the cross-linkable rubber composition of the present invention is preferably 0.1 to 5 parts by weight, more preferably 0.3 to 4 parts by weight, and even more preferably 0.5 to 3 parts by weight, per 100 parts by weight of the total of the nitrile copolymer rubber (A) and the vinyl chloride resin (B). By setting the content of the aromatic hydrocarbon wax within the above range, the ozone resistance of the obtained cross-linked rubber can be more appropriately improved.

[0073] Furthermore, the cross-linkable rubber composition of the present invention preferably contains a plasticizer, and the same plasticizer as in the rubber composition described above can be used. The content of the plasticizer in the cross-linkable rubber composition of the present invention is preferably 3 to 300 parts by weight, more preferably 5 to 200 parts by weight, and even more preferably 10 to 150 parts by weight, per 100 parts by weight of the total of the nitrile copolymer rubber (A) and the vinyl chloride resin (B). By setting the content of the plasticizer within the above range, the effect of adding the plasticizer can be further enhanced. The content of the plasticizer in the cross-linkable rubber composition of the present invention may be adjusted so that the total content, including the plasticizer contained in the rubber composition of the present invention described above, falls within the above range.

[0074] Furthermore, the crosslinkable rubber composition of the present invention may contain other compounding agents used in general rubbers, such as crosslinking retarders, reinforcing agents, fillers, slip agents, adhesives, lubricants, processing aids, flame retardants, antifungal agents, antistatic agents, colorants, and coupling agents, as needed.

[0075] Furthermore, the crosslinkable rubber composition of the present invention may contain rubbers other than the nitrile copolymer rubber (A) as long as the effects of the present invention are not impaired. Examples of rubbers other than the nitrile copolymer rubber (A) include acrylic rubber, ethylene-acrylic acid copolymer rubber, fluororubber, styrene-butadiene copolymer rubber, polybutadiene rubber, ethylene-propylene copolymer rubber, ethylene-propylene-diene terpolymer rubber, epichlorohydrin rubber, urethane rubber, chloroprene rubber, silicone rubber, fluorosilicone rubber, chlorosulfonated polyethylene rubber, natural rubber, and polyisoprene rubber. When a rubber other than the nitrile copolymer rubber (A) is contained, the amount of the rubber contained therein is preferably 30 parts by weight or less, more preferably 20 parts by weight or less, and particularly preferably 10 parts by weight or less, per 100 parts by weight of the total nitrile copolymer rubber (A).

[0076] The method for preparing the crosslinkable rubber composition of the present invention is not particularly limited, but may be such that the crosslinking agent and other compounding ingredients are added to the rubber composition obtained by the above-mentioned method and kneaded with a kneading machine such as a roll, a Banbury mixer, a kneader, etc. In this case, the order of compounding is not particularly limited, but may be such that the components that are resistant to reaction or decomposition by heat are thoroughly mixed, and then the components that are liable to be decomposed by heat (crosslinking agent, crosslinking accelerator, etc.) are mixed for a short time at a temperature below which decomposition does not occur.

[0077] Cross-linked Rubber Product The cross-linked rubber product of the present invention is obtained by cross-linking the cross-linkable rubber composition of the present invention described above. When cross-linking the cross-linkable rubber composition, molding is carried out using a molding machine, such as an extruder, injection molding machine, compressor, or roll, that corresponds to the shape of the molded product (cross-linked rubber product) to be produced, and then a cross-linking reaction is carried out to fix the shape of the cross-linked product. When cross-linking is carried out, cross-linking may be carried out after molding in advance, or may be carried out simultaneously with molding. The molding 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, and the cross-linking time is usually 1 minute to 24 hours, preferably 2 minutes to 1 hour.

[0078] Depending on the shape, size, etc., the cross-linked rubber product may not be sufficiently cross-linked to the inside even if the surface is cross-linked, so it may be further heated to cause secondary cross-linking.

[0079] The cross-linked rubber product of the present invention thus obtained is excellent in ozone resistance because it is obtained using the above-mentioned nitrile rubber composition and cross-linkable rubber composition of the present invention. Specifically, the cross-linked rubber product of the present invention has excellent ozone resistance, such that when a static ozone degradation test is conducted in accordance with JIS K6259 in which the cross-linked rubber product is exposed to an atmosphere at 40°C and an ozone concentration of 50 pphm for 72 hours, the tensile strain until cracks occur in the cross-linked rubber product is preferably 20% or more.

[0080] Therefore, the cross-linked rubber product of the present invention is suitable for sealing members such as packings, gaskets, O-rings and oil seals; hoses such as oil hoses, fuel hoses, inlet hoses, gas hoses, brake hoses and refrigerant hoses; diaphragms; accumulator bladder; boots; and is more preferably used as a hose, particularly preferably used as a gas hose for transporting air, nitrogen, oxygen, hydrogen, carbon dioxide, carbon monoxide, methane, ethane, propane, dimethyl ether, water vapor and the like, and is particularly preferably used as a hose or tube.

[0081] 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.

[0082] RMSE For the rubber composition, tan δ was measured in the temperature range of 50 to 220 ° C. using a dynamic viscoelasticity measuring device (product name "PREMIER RPA", manufactured by ALPHA TECHNOLOGIES) under conditions of dynamic strain ±0.5% and 5 Hz. Next, using the measured tan δ, fitting was performed to the Doniach-Schunich function represented by the following formula (1) by the least squares method, and the Doniach-Schunich function with the smallest error for the measured tan δ was obtained. The fitting was performed using Python's limfit module and the Doniach Model as the above formula (1). The least squares method was also performed using the Levenberg-Marquardt method. In this case, the initial values ​​and selection ranges of the parameters (A, μ, σ, γ) that determine the Doniak-Schunich function expressed by the above formula (1) were set as follows, and the Doniak-Schunich function with the smallest error for the measurement results was obtained from among the Doniak-Schunich functions expressed by the above formula (1). The fitting error value RMSE was calculated by calculating the error value between the Doniak-Schunich function with the smallest error for the measurement results obtained in this way and the measurement results. A (amplitude): initial value 1, minimum value 1, maximum value ∞ μ (center): initial value 150, minimum value 0, maximum value 250 σ (sigma): initial value 20, minimum value 10, maximum value 60 γ (gamma): initial value 0.15, minimum value 0, maximum value 1

[0083] Here, Fig. 1(A) shows the relationship between the tan δ value measured by the above method and the Doniak-Schunich function obtained by fitting by the above method for the rubber composition of Example 3. Fig. 1(B) shows the relationship between the tan δ value measured by the above method and the Doniak-Schunich function obtained by fitting by the above method for the rubber composition of Comparative Example 1.

[0084] Mooney Viscosity The Mooney viscosity of the nitrile copolymer rubber and the rubber composition was measured in accordance with JIS K6300 (unit: [ML1+4, 100°C]).

[0085] Hue The hue of the rubber composition was visually observed and evaluated according to the following criteria. Note that, in the following, colors lighter than yellow include light yellow, light pink, milky white, and white. A: Yellow or colors lighter than yellow B: Orange C: Vermilion D: Brown

[0086] Static Ozone Degradation Test (Ozone Resistance) The crosslinkable rubber composition was placed in a mold measuring 15 cm in length, 15 cm in width, and 0.2 cm in depth, and press-molded at 160°C for 20 minutes while applying pressure to obtain a sheet-shaped crosslinked rubber product. The resulting sheet-shaped crosslinked rubber product was punched into a No. 1 dumbbell shape to obtain a dumbbell-shaped test piece. The resulting dumbbell-shaped test piece was subjected to a static ozone degradation test using an ozone weather meter (product name "OMS-HN", manufactured by Suga Test Instruments Co., Ltd.) in accordance with JIS K6259 at a test temperature of 40°C, an ozone concentration of 50 pphm, tensile strains of 20%, 30%, 40%, and 50%, and a test time of 72 hours. After the ozone degradation test, the test piece was inspected for cracking, and the ozone resistance was evaluated according to the following criteria: NC: No cracking was observed; A1-5, B1-5, C1-5: Cracks were observed. Cut: The cracks grew large enough to break the test piece. Furthermore, when cracks were found in the test piece after the ozone degradation test (A1 to 5, B1 to 5, C1 to 5 above), the number and size of the cracks in the test piece were observed using the crack state observation method in accordance with JIS K6259, and the ozone resistance was evaluated in detail. Specifically, the number and size of the cracks in the test piece were evaluated according to the following criteria: A: Few cracks. B: Many cracks. C: Countless cracks. 1: No cracks visible to the naked eye, but cracks visible with a 10x magnifying glass. 2: Cracks visible to the naked eye. 3: Deep and relatively large cracks (less than 1 mm). 4: Deep and large cracks (1 mm or more, less than 3 mm). 5: Cracks of 3 mm or more or likely to break.

[0087] Hardness The hardness of the sheet-like cross-linked rubber product used in the static ozone degradation test was measured using a durometer hardness tester (type A) in accordance with JIS K6253-3.

[0088] Compression Set The crosslinkable rubber composition was crosslinked by pressing it using a mold at a temperature of 160°C for 20 minutes, to obtain a cylindrical crosslinked rubber product having a diameter of 29 mm and a height of 12.5 mm. Then, using the obtained cylindrical crosslinked rubber product, the crosslinked rubber product was placed in a 100°C environment for 70 hours in a state compressed by 25%, and the compression set was measured according to JIS K6262. The smaller this value, the better the compression set resistance can be judged to be. If the compression set is 55% or less, it can be judged that the product has sufficient compression set resistance for practical use.

[0089] Gehman torsion test (cold resistance) The sheet-like cross-linked rubber product used in the static ozone degradation test was subjected to a Gehman torsion test in accordance with JIS K6261-3: 2017, and the temperature T5 at which the specific modulus becomes 5 times the modulus at room temperature (23°C) was measured. The lower the T5 value, the more excellent the cold resistance can be judged to be.

[0090] Production Example 1 (Production of Nitrile Copolymer Rubber (A-1)) A reaction vessel was charged with 240 parts of water, 48 parts of acrylonitrile, and 2.5 parts of sodium dodecylbenzenesulfonate (emulsifier), and the temperature was adjusted to 5°C. Next, the gas phase was reduced in pressure and thoroughly degassed, and then 52 parts of 1,3-butadiene, 0.04 parts of p-menthane hydroperoxide as a polymerization initiator, 0.02 parts of sodium ethylenediaminetetraacetate, 0.006 parts of ferrous sulfate (heptahydrate), and 0.06 parts of sodium formaldehyde sulfoxylate, and 1 part of t-dodecyl mercaptan as a chain transfer agent were added to initiate the first-stage reaction of emulsion polymerization. Thereafter, when the polymerization conversion rate based on the total monomers charged reached 90% by weight, 0.3 parts of hydroxylamine sulfate and 0.2 parts of potassium hydroxide were added to terminate the polymerization reaction. After the reaction was stopped, the content of the reaction vessel was heated to 70°C, and the unreacted monomer was recovered by steam distillation under reduced pressure to obtain a latex of nitrile copolymer rubber (A-1) (solid content concentration 27% by weight).

[0091] Next, a double volume of methanol was added to the obtained latex to coagulate it, and then the coagulated latex was dried in a vacuum at 60° C. for 12 hours to obtain a nitrile copolymer rubber (A-1). １The composition of each monomer unit of the obtained nitrile copolymer rubber (A-1) was measured by H-NMR and found to be 50% by weight of acrylonitrile units and 50% by weight of 1,3-butadiene units, and the polymer Mooney viscosity [ML1+4, 100°C] was 78.

[0092] Production Example 2 (Production of Nitrile Copolymer Rubber (A-2)) A latex of nitrile copolymer rubber (A-2) (solid content concentration 27% by weight) was obtained in the same manner as in Production Example 1, except that the charged monomers in the first stage reaction of emulsion polymerization in Production Example 1 were changed to 37 parts of acrylonitrile and 63 parts of 1,3-butadiene.

[0093] Next, the obtained latex was coagulated by adding twice the volume of methanol, and then vacuum dried at 60° C. for 12 hours to obtain a nitrile copolymer rubber (A-2). １ The composition of each monomer unit of the obtained nitrile copolymer rubber (A-2) was measured by H-NMR, and as a result, it was found that the acrylonitrile unit was 40.5% by weight and the 1,3-butadiene unit was 59.5% by weight, and the polymer Mooney viscosity [ML1+4, 100°C] was 80.

[0094] Production Example 3 (Production of Nitrile Copolymer Rubber (A-3)) A latex of nitrile copolymer rubber (A-3) (solid content concentration 27% by weight) was obtained in the same manner as in Production Example 1, except that the charged monomers in the first stage reaction of emulsion polymerization in Production Example 1 were changed to 32 parts of acrylonitrile and 68 parts of 1,3-butadiene.

[0095] Next, the obtained latex was coagulated by adding twice the volume of methanol, and then vacuum dried at 60° C. for 12 hours to obtain a nitrile copolymer rubber (A-3). １ The composition of each monomer unit of the obtained nitrile copolymer rubber (A-3) was measured by H-NMR, and as a result, it was found that the acrylonitrile unit was 31% by weight, the 1,3-butadiene unit was 69% by weight, and the polymer Mooney viscosity [ML1+4, 100°C] was 65.

[0096] Production Example 4 (Production of Nitrile Copolymer Rubber (A-4)) A latex of nitrile copolymer rubber (A-4) (solid content concentration 26% by weight) was obtained in the same manner as in Production Example 1, except that the monomers charged in the first stage reaction of emulsion polymerization in Production Example 1 were changed to 26 parts of acrylonitrile and 74 parts of 1,3-butadiene.

[0097] Next, the obtained latex was coagulated by adding twice the volume of methanol, and then vacuum dried at 60° C. for 12 hours to obtain a nitrile copolymer rubber (A-4). １ The composition of each monomer unit of the obtained nitrile copolymer rubber (A-4) was measured by H-NMR, and as a result, it was found that the acrylonitrile unit was 27.5% by weight and the 1,3-butadiene unit was 72.5% by weight, and the polymer Mooney viscosity [ML1+4, 100°C] was 63.

[0098] Production Example 5 (Production of Nitrile Copolymer Rubber (A-5)) In Production Example 1, the charged monomers for the first stage reaction of emulsion polymerization were changed to 10 parts of acrylonitrile and 90 parts of 1,3-butadiene, and when the polymerization conversion rate reached 30% by weight and 50% by weight, 5 parts and 5 parts of acrylonitrile were additionally added to the reaction vessel to carry out second and third stage polymerization reactions, and the polymerization reactions were stopped when the polymerization conversion rate reached 80% by weight, and a latex of nitrile copolymer rubber (A-5) (solid concentration 26% by weight) was obtained in the same manner as in Production Example 1, except that

[0099] Next, the obtained latex was coagulated by adding twice the volume of methanol, and then vacuum dried at 60° C. for 12 hours to obtain a nitrile copolymer rubber (A-5). １ The composition of each monomer unit of the obtained nitrile copolymer rubber (A-5) was measured by H-NMR, and as a result, it was found that the acrylonitrile unit was 18% by weight, the 1,3-butadiene unit was 82% by weight, and the polymer Mooney viscosity [ML1+4, 100°C] was 78.

[0100] Production Example 6 (Production of Liquid Nitrile Rubber (A-6)) A reaction vessel was charged with 240 parts of water, 33 parts of acrylonitrile, 67 parts of 1,3-butadiene, 3 parts of sodium dodecyl sulfate, and 0.5 parts of potassium persulfate, and 8 parts of t-dodecyl mercaptan as a molecular weight modifier was further added. The mixture was maintained at 30°C while stirring thoroughly to achieve uniformity, and when the polymerization conversion rate based on the total charged monomers reached 90% by weight, 0.1 part of hydroxylamine sulfate and 0.1 part of sodium hydroxide were added to terminate the polymerization reaction, and the residual monomers were removed by heating. The resulting polymer (liquid nitrile rubber (A-6)) had a number average molecular weight of 5,000, 29% by weight of acrylonitrile units, and 71% by weight of 1,3-butadiene units.

[0101] Example 1 (Preparation of Rubber Composition) To 70 parts of the nitrile copolymer rubber (A-1) obtained in Production Example 1, 30 parts of a suspension vinyl chloride resin (B-3) (product name "TH-1300", manufactured by Taiyo Vinyl Corporation, average degree of polymerization 1300), 5 parts of di(butoxyethoxyethyl) adipate (plasticizer), and 0.5 parts of a Ca-Mg-Zn complex metal soap stabilizer were added, and kneading was started in a Brabender set at 50°C. After kneading for 4 minutes from the start of kneading so that the maximum mixing temperature reached 192°C, the kneaded product was discharged to obtain a rubber composition. The temperature of the kneaded product when discharged from the Brabender (discharge temperature) was 192°C. Using the obtained rubber composition, the fitting error value RMSE and Mooney viscosity were measured, and the hue was evaluated.

[0102] (Preparation of Cross-Linkable Rubber Composition) Next, 60 parts of SRF carbon, 5 parts of zinc oxide (activated zinc oxide), 1 part of stearic acid, and 15 parts of di(butoxyethoxyethyl) adipate (plasticizer) were added to the rubber composition obtained above, and the mixture was kneaded in a kneader at 140°C. This was wound around an 8-inch roll heated to 50°C, and 0.5 parts of 325 mesh sulfur, 1.5 parts of di-2-benzothiazolyl disulfide (cross-linking accelerator), and 1.5 parts of tetramethylthiuram disulfide (cross-linking accelerator) were added, and the mixture was kneaded with the roll to obtain a cross-linkable rubber composition. The amount of di(butoxyethoxyethyl) adipate added when obtaining the cross-linkable rubber composition was set so that the total amount added during preparation of the rubber composition and during preparation of the cross-linkable rubber composition was 20 parts. In addition, the amount of Ca-Mg-Zn composite metal soap stabilizer added when obtaining the cross-linkable rubber composition was set so that the total amount added when preparing the rubber composition and when preparing the cross-linkable rubber composition was 0.5 parts.

[0103] The crosslinkable rubber composition thus obtained was subjected to measurements and tests for static ozone degradation (ozone resistance), hardness, compression set, and Gehman torsion test (cold resistance). The results are shown in Table 1.

[0104] Examples 2 to 11 Rubber compositions and cross-linkable rubber compositions were obtained in the same manner as in Example 1, and evaluated in the same manner, except that the nitrile copolymer rubber and vinyl chloride resin shown in Table 1 were used in the amounts shown in Table 1, and the materials were kneaded so that the discharge temperature when obtaining the rubber compositions was the temperature shown in Table 1. Examples 5 to 8 also differed from Example 1 in that no stabilizer was used when obtaining the rubber compositions. Furthermore, in Examples 5 to 8, 0.5 parts of a Ca-Mg-Zn complex metal soap stabilizer was added when obtaining the cross-linkable rubber composition, so that the total amount of the Ca-Mg-Zn complex metal soap stabilizer added when preparing the rubber composition and the cross-linkable rubber composition was 0.5 parts. The results are shown in Table 1.

[0105] Examples 12 to 22 Rubber compositions and cross-linkable rubber compositions were obtained in the same manner as in Example 1, and evaluated in the same manner, except that the nitrile copolymer rubber and vinyl chloride resin shown in Table 2 were used in the amounts shown in Table 2, and the materials were kneaded so that the discharge temperature when obtaining the rubber compositions was the temperature shown in Table 2. Example 19 differed from Example 1 in that di(butoxyethoxyethyl) adipate was not used when obtaining the rubber composition. Furthermore, in Example 19, the amount of di(butoxyethoxyethyl) adipate used when obtaining the cross-linkable rubber composition was changed to 20 parts, so that the total amount of di(butoxyethoxyethyl) adipate added when preparing the rubber composition and when preparing the cross-linkable rubber composition was 20 parts. The results are shown in Table 2.

[0106] Examples 23 to 33 Rubber compositions and crosslinkable rubber compositions were obtained and evaluated in the same manner as in Example 1, except that the nitrile copolymer rubber and vinyl chloride resin shown in Table 3 were used in the amounts shown in Table 3 and the materials were kneaded so that the discharge temperature when obtaining the rubber compositions was the temperature shown in Table 3. Example 25 differed from Example 1 in that no di(butoxyethoxyethyl) adipate was used when obtaining the rubber composition, and Example 26 differed from Example 1 in that 20 parts of di(butoxyethoxyethyl) adipate was used when obtaining the rubber composition. In addition, in Example 25, the amount of di(butoxyethoxyethyl) adipate used when obtaining the cross-linkable rubber composition was changed to 20 parts so that the total amount of di(butoxyethoxyethyl) adipate added when preparing the rubber composition and when preparing the cross-linkable rubber composition was 20 parts, and in Example 26, no di(butoxyethoxyethyl) adipate was added when obtaining the cross-linkable rubber composition. The results are shown in Table 3.

[0107] Examples 34 to 44 Rubber compositions and cross-linkable rubber compositions were obtained in the same manner as in Example 1, and evaluated in the same manner, except that the nitrile copolymer rubber and vinyl chloride resin shown in Table 4 were used in the amounts shown in Table 4, and the materials were kneaded so that the discharge temperature when obtaining the rubber compositions was the temperature shown in Table 4. Examples 34 to 41 also differed from Example 1 in that di(butoxyethoxyethyl) adipate was not used when obtaining the rubber compositions. Furthermore, in Examples 34 to 41, the amount of di(butoxyethoxyethyl) adipate used when obtaining the cross-linkable rubber compositions was changed to 20 parts so that the total amount of di(butoxyethoxyethyl) adipate added when preparing the rubber compositions and when preparing the cross-linkable rubber compositions was 20 parts. The results are shown in Table 4.

[0108] Comparative Examples 1 to 9 Rubber compositions and cross-linkable rubber compositions were obtained in the same manner as in Example 1, and evaluated in the same manner, except that the nitrile copolymer rubber and vinyl chloride resin shown in Table 5 were used in the amounts shown in Table 5, and the materials were kneaded so that the discharge temperature when obtaining the rubber compositions was the temperature shown in Table 5. Comparative Example 3 differed from Example 1 in that di(butoxyethoxyethyl) adipate was not used. Furthermore, in Comparative Example 3, the amount of di(butoxyethoxyethyl) adipate used when obtaining the cross-linkable rubber composition was changed to 20 parts, so that the total amount of di(butoxyethoxyethyl) adipate added when preparing the rubber composition and when preparing the cross-linkable rubber composition was 20 parts. The results are shown in Table 5.

[0109]

[0110]

[0111]

[0112]

[0113] The vinyl chloride resin suspensions (B-1) to (B-6) and vinyl chloride resin pastes (B-7) to (B-9) used were as follows: Suspension vinyl chloride resin (B-1): Trade name "Kanevinyl S1008", manufactured by Kaneka Corporation, average degree of polymerization 800. Suspension vinyl chloride resin (B-2): Trade name "TK-1000", manufactured by Shin-Etsu Chemical Co., Ltd., average degree of polymerization 1000. Suspension vinyl chloride resin (B-3): Trade name "TH-1300", manufactured by Taiyo Vinyl Corporation, average degree of polymerization 1300. Suspension vinyl chloride resin (B-4): Trade name "TK-1700E", manufactured by Shin-Etsu Chemical Co., Ltd., average degree of polymerization 1700. Suspension vinyl chloride resin (B-5): Trade name "ZEST 2000Z", manufactured by Shin-Dai Vinyl Corporation, average degree of polymerization 2000. Suspension vinyl chloride resin (B-6): Trade name "Kanevinyl KS-2500", manufactured by Kaneka Corporation, average degree of polymerization 2500. Paste vinyl chloride resin (B-7): Trade name "ZEST PQ92" manufactured by Shin-Daiichi Vinyl Corporation, average degree of polymerization 900 (fine powder) Paste vinyl chloride resin (B-8): trade name "Kane Vinyl Paste PSH-180" manufactured by Kaneka Corporation, average degree of polymerization 1700 (granules) Paste vinyl chloride resin (B-9): trade name "Ryuron Paste 761" manufactured by Tosoh Corporation, average degree of polymerization 2100 (fine powder)

[0114] As shown in Tables 1 to 4, the rubber compositions contained a nitrile copolymer rubber (A) containing an α,β-ethylenically unsaturated nitrile monomer unit and a vinyl chloride resin (B) in a predetermined ratio, and the rubber compositions had a fitting error value RMSE of 0.1 or less when the loss tangent (tan δ) value measured by dynamic viscoelasticity measurement in the temperature range of 50 to 220°C was fitted to a Doniak-Schunich function, and the cross-linked rubber products obtained using these rubber compositions had excellent ozone resistance (Examples 1 to 44).

[0115] On the other hand, as shown in Table 5, when a rubber composition having a fitting error value RMSE of more than 0.1 was used, the obtained cross-linked rubber product had poor ozone resistance (Comparative Examples 1 to 9).

Claims

1. A rubber composition containing a nitrile copolymer rubber (A) containing α,β-ethylenically unsaturated nitrile monomer units and a vinyl chloride resin (B), wherein the fitting error value RMSE when the loss tangent (tanδ) value measured by dynamic viscoelasticity measurement in the temperature range of 50 to 220°C is fitted to a Doniak-Schunich function is 0.1 or less.

2. The rubber composition according to claim 1, wherein the weight ratio (A / B) of the nitrile copolymer rubber (A) to the vinyl chloride resin (B) is 90 / 10 to 30 / 70.

3. The rubber composition according to claim 1 or 2, wherein the content of the α,β-ethylenically unsaturated nitrile monomer units in the nitrile copolymer rubber (A) is 15 to 55% by weight.

4. A rubber composition according to any one of claims 1 to 3, wherein the vinyl chloride resin (B) has an average degree of polymerization of 500 to 2,800.

5. The rubber composition according to any one of claims 1 to 4, further comprising a plasticizer.

6. The rubber composition according to any one of claims 1 to 5, further comprising a stabilizer.

7. A crosslinkable rubber composition obtained by compounding a crosslinking agent with the rubber composition according to any one of claims 1 to 6.

8. A cross-linked rubber product obtained by cross-linking the cross-linkable rubber composition according to claim 7.

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