Rubber composition, rubber product, and pneumatic tire

Abstract

The present invention provides: a rubber composition from which it is possible to obtain a rubber product that has low rolling resistance; a rubber product which is obtained from this rubber composition; and a pneumatic tire which is the rubber product.　The present invention uses a rubber composition which contains a diene rubber (A), silica (B), carbon black (C), a silane coupling agent (D), and a (meth)acrylate ester polymer (E) that satisfies the following condition (a) and the like. (a) The polymer has a first end and a second end as both ends of the polymer, and has a group represented by general formula (1) at the first end. (In formula (1), R1 and R2 are the same or different and each represent a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or an aryl group having 6 to 20 carbon atoms. R3 represents a hydrogen atom or a methyl group. Y represents an alkylene group having 1 to 18 carbon atoms or a single bond.)

Description

Rubber composition, rubber product, and pneumatic tire

[0001] The present invention relates to a rubber composition, a rubber product, and a pneumatic tire.

[0002] BACKGROUND ART In the automobile industry, there has been a demand for improved fuel efficiency of automobiles, and there has been a demand for rubber compositions for treads that can provide tires with low rolling resistance.

[0003] As a rubber composition that reduces the rolling resistance of a tire, for example, a rubber composition containing a diene rubber, which is compounded with a (meth)acrylic polymer having an acryloyl group at one molecular end that can react during vulcanization of the diene rubber, is known (see Patent Document 1).

[0004] JP 2014-084363 A

[0005] According to the inventors' investigations, although the use of the rubber composition disclosed in Patent Document 1 reduces the rolling resistance of tires, further improvement is required.

[0006] The present invention has been made in view of the above-mentioned problems, and aims to provide a rubber composition from which a rubber product having low rolling resistance can be obtained, a rubber product obtained from the rubber composition, and a pneumatic tire as the rubber product.

[0007] The present inventors have found that the above problems can be solved by blending a specific copolymer as a (meth)acrylic acid ester polymer having an acryloyl group at one end, and have completed the present invention.

[0008] Aspects of the present disclosure relate to the following rubber compositions, rubber products, and pneumatic tires.

[0009] [1] A rubber composition containing a diene rubber (A), silica (B), carbon black (C), a silane coupling agent (D), and a (meth)acrylic acid ester polymer (E) that satisfies the following conditions (a) to (d): (a) the polymer has a first end and a second end as both ends thereof, and the first end has a group represented by the following general formula (1): (In formula (1), R １ and R２ are the same or different and represent a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or an aryl group having 6 to 20 carbon atoms. ３ represents a hydrogen atom or a methyl group. Y represents an alkylene group having 1 to 18 carbon atoms or a single bond. (b) Contains a structural unit (2) derived from a monomer represented by the following general formula (2) and a structural unit (3) derived from a monomer represented by the following general formula (3): (In formula (2), R ４ are the same or different and represent a hydrogen atom or a methyl group. ５ represents an alkyl group having 1 to 20 carbon atoms, provided that the alkyl group is partially substituted with one or more atoms selected from the group consisting of oxygen atoms, nitrogen atoms, and halogen atoms. ６ are the same or different and represent a hydrogen atom or a methyl group. ７represents an alkyl group having 1 to 20 carbon atoms. However, the alkyl group consists only of carbon atoms and hydrogen atoms.) (c) In a first region consisting of 30 mol % of all structural units from the first terminal, the structural unit (2) is contained in an amount of 50 mol % or more of all structural units in the first region. (d) In a second region consisting of 30 mol % of all structural units from the second terminal, the structural unit (3) is contained in an amount of 50 mol % or more of all structural units in the second region. [2] The rubber composition according to [1], wherein, in the (meth)acrylic acid ester polymer (E), under condition (c), the content of the structural unit (2) is 65 mol % or more, and under condition (d), the content of the structural unit (3) is 95 mol % or more. [3] The rubber composition according to [1], wherein the (meth)acrylic acid ester polymer (E) has a content of the structural unit (2) of 80 mol% or more under the condition (c) and a content of the structural unit (3) of 95 mol% or more under the condition (d). [4] The rubber composition according to any one of [1] to [3], wherein the diene rubber (A) is at least one selected from the group consisting of natural rubber, isoprene rubber, styrene-butadiene copolymer rubber, and butadiene rubber. [5] The rubber composition according to any one of [1] to [4], wherein the silica (B), 0.5 to 50 parts by weight of the carbon black (C), 0.5 to 20 parts by weight of the silane coupling agent (D), and 1 to 20 parts by weight of the (meth)acrylic acid ester polymer (E) are contained relative to 100 parts by weight of the diene rubber (A). [6] A rubber product obtained from the rubber composition according to any one of [1] to [5]. [7] A pneumatic tire that is the rubber product according to [6].

[0010] According to the present invention, it is possible to provide a rubber composition from which a rubber product having low rolling resistance can be obtained, a rubber product obtained from the rubber composition, and a pneumatic tire as the rubber product.

[0011] <Rubber Composition> The rubber composition of the present embodiment contains a diene rubber (A), silica (B), carbon black (C), a silane coupling agent (D), and a (meth)acrylic acid ester polymer (E) described later.

[0012] According to the rubber composition of the present embodiment, a rubber product having low rolling resistance can be obtained by containing the (meth)acrylic acid ester polymer (E) described later. Essential and optional components that the rubber composition may contain will be described below.

[0013] <Diene Rubber (A)> The diene rubber (A) is not particularly limited as long as it is a rubber obtained from a monomer containing a diene compound. Examples of the diene rubber (A) include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), acrylonitrile butadiene rubber, ethylene-propylene-diene copolymer rubber, styrene-isoprene copolymer rubber, isoprene-butadiene copolymer rubber, styrene-isoprene-butadiene copolymer rubber, and chloroprene rubber. The styrene-butadiene copolymer rubber (SBR) may be either an emulsion polymerization SBR or a solution polymerization SBR. The diene rubber (A) may also be a rubber into which a functional group has been introduced, such as a modified butadiene rubber. More preferably, the diene rubber (A) is natural rubber, isoprene rubber, styrene-butadiene copolymer rubber, butadiene rubber, or a blend of two or more thereof.

[0014] These diene rubbers (A) may be used in combination with olefin polymer rubbers, such as butyl rubber, chlorinated butyl rubber, brominated butyl rubber, and ethylene-propylene-diene rubber.

[0015] <Silica (B)> Silica (B) is not particularly limited, and examples thereof include wet silica, dry silica, pulverized silica, etc. Among these, wet silica is preferred because it has excellent abrasion resistance, mechanical properties, and is also economical.

[0016] The content of silica (B) is preferably 5 to 200 parts by weight, more preferably 10 to 150 parts by weight, and even more preferably 20 to 100 parts by weight, per 100 parts by weight of diene rubber (A).

[0017] <Carbon Black (C)> The carbon black (C) is not particularly limited as long as it can be generally compounded as a filler in a rubber composition. Examples of the carbon black (C) include FEF, SRF, HAF, ISAF, and SAF grades. In terms of further improving mechanical properties and abrasion resistance, HAF, ISAF, and SAF grades are preferred for the carbon black (C). The carbon black (C) may be used alone or in combination of two or more types.

[0018] The content of carbon black (C) is preferably 0.5 to 50 parts by weight, more preferably 0.5 to 40 parts by weight, and even more preferably 1.0 to 20 parts by weight, based on 100 parts by weight of diene rubber (A).

[0019] <Silane Coupling Agent (D)> Examples of the silane coupling agent (D) include bis(3-triethoxysilylpropyl)tetrasulfide, bis(3-triethoxysilylpropyl)trisulfide, bis(3-triethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, 3-mercaptopropyltriethoxysilane, 2-mercaptoethylsilane, 2 ... methyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-triethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropyl benzothiazole tetrasulfide, 3-triethoxysilylpropyl benzothiazole tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, bis(3-diethoxymethylsilylpropyl)tetrasulfide, 3-mercaptopropyldimethoxymethylsilane, dimethoxymethylsilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, dimethoxymethylsilylpropyl benzothiazole tetrasulfide, N-(1,3-dimethylbutylidene)-3-(triethoxysilylpropyl)benzothiazole tetrasulfide (3,4-epoxycyclohexyl)ethyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltriethoxy ...4-epoxycyclohexyl)ethyltriethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, γ-mercaptopropylmethyldimethoxysilane, styryltrimethoxysilane, styryltriethoxysilane, γ-mercaptopropylmethyldiethoxysilane, etc.

[0020] Among these, from the viewpoint of superior abrasion resistance and improved reinforcement, bis(3-triethoxysilylpropyl)tetrasulfide, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, γ-acryloxypropyltriethoxysilane, γ-methacryloxypropyltriethoxysilane, vinyltriethoxysilane, and styryltriethoxysilane are preferred.

[0021] The silane coupling agents (D) can be used either alone or in combination of two or more.

[0022] The content of the silane coupling agent (D) is preferably 0.5 to 20 parts by weight, more preferably 0.5 to 15 parts by weight, and even more preferably 1.0 to 10 parts by weight, per 100 parts by weight of the diene rubber (A).

[0023] <(Meth)acrylic acid ester polymer (E)> The (meth)acrylic acid ester polymer (E) is a copolymer satisfying the following conditions (a) to (d): (a) The polymer has a first end and a second end as both ends thereof, and the first end has a group represented by the following general formula (1): (In formula (1), R １ and R ２ are the same or different and represent a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or an aryl group having 6 to 20 carbon atoms. ３ represents a hydrogen atom or a methyl group. Y represents an alkylene group having 1 to 18 carbon atoms or a single bond. (b) Contains a structural unit (2) derived from a monomer represented by the following general formula (2) and a structural unit (3) derived from a monomer represented by the following general formula (3): (In formula (2), R ４are the same or different and represent a hydrogen atom or a methyl group. ５ represents an alkyl group having 1 to 20 carbon atoms, provided that the alkyl group is partially substituted with one or more atoms selected from the group consisting of oxygen atoms, nitrogen atoms, and halogen atoms. ６ are the same or different and represent a hydrogen atom or a methyl group. ７ represents an alkyl group having 1 to 20 carbon atoms. However, the alkyl group consists only of carbon atoms and hydrogen atoms. (c) In a first region consisting of 30 mol % of all structural units from the first terminal, the structural unit (2) is contained in an amount of 50 mol % or more of all structural units in the first region. (d) In a second region consisting of 30 mol % of all structural units from the second terminal, the structural unit (3) is contained in an amount of 50 mol % or more of all structural units in the second region. In this specification, "(meth)acrylic" represents acrylic and / or methacrylic.

[0024] When the rubber composition of the present embodiment contains the (meth)acrylic acid ester polymer (E), a rubber product having low rolling resistance and excellent tensile stress can be obtained.

[0025] Under condition (b), the structural unit (2) derived from the monomer represented by general formula (2) is a structural unit with a higher polarity than the structural unit (3) derived from the monomer represented by general formula (3). Under conditions (c) and (d), the first region consisting of 30 mol% of all structural units from the first end, and the second region consisting of 30 mol% of all structural units from the second end, are each an invariant region in the main chain of the (meth)acrylic acid ester polymer (E). That is, the (meth)acrylic acid ester polymer (E) has a group represented by general formula (1) at the first end, and contains, in order from the first end to the other end, the second end, a first region and a second region, with the first region containing a large amount of the highly polar structural unit (2) and the second region containing a large amount of the less polar structural unit (3). In this way, by blending a (meth)acrylic acid ester-based polymer (E) that includes, from the first end to the second end, a group represented by general formula (1), a first region containing a large number of high-polarity structural units, and a second region containing a large number of low-polarity structural units, into a rubber composition, a rubber product with low rolling resistance and excellent tensile stress can be obtained.

[0026] (Group represented by formula (1) in condition (a)) In formula (1), R １ and R ２ Examples of the alkyl group having 1 to 20 carbon atoms represented by the formula (I) include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, a 2,2-dimethylpropyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, an n-decyl group, an n-undecyl group, an n-dodecyl group, an n-tridecyl group, an n-tetradecyl group, an n-pentadecyl group, etc. Among these, from the viewpoint of obtaining a rubber product with low rolling resistance, a methyl group, an ethyl group, and a propyl group are preferred.

[0027] In formula (1), R １ and R ２Examples of the aryl group having 6 to 20 carbon atoms represented by the formula (1) include a phenyl group, a 1-naphthyl group, a 2-naphthyl group, a 3-phenanthryl group, and a 2-anthryl group. Among these, a phenyl group and a 1-naphthyl group are preferred from the viewpoint of obtaining a rubber product with low rolling resistance. １ and R ２ The group represented by the formula (I) is preferably a hydrogen atom, from the viewpoint of obtaining a rubber product with low rolling resistance.

[0028] In formula (1), examples of the alkylene group having 1 to 18 carbon atoms represented by Y include a methylene group, an ethane-1,2-diyl group, a propane-1,3-diyl group, a butane-1,4-diyl group, a pentane-1,5-diyl group, a hexane-1,6-diyl group, a heptane-1,7-diyl group, an octane-1,8-diyl group, a nonane-1,9-diyl group, and a decane-1,10-diyl group.

[0029] Of the alkylene group having 1 to 18 carbon atoms represented by Y and the single bond, the single bond is preferred from the viewpoint of obtaining a rubber product with low rolling resistance.

[0030] (Constituent unit (2) derived from a monomer represented by formula (2) under condition (b)) In formula (2), R ５ The alkyl group represented by the formula (I) is an alkyl group having 1 to 20 carbon atoms, and the alkyl group is partially substituted with one or more atoms selected from the group consisting of oxygen atoms, nitrogen atoms, and halogen atoms. Examples of the alkyl group having 1 to 20 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, 2,2-dimethylpropyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, and n-pentadecyl groups. Among these, methyl, ethyl, propyl, and butyl groups are preferred from the viewpoint of obtaining rubber products with low rolling resistance. Examples of halogen atoms include fluorine, chlorine, bromine, and iodine.

[0031] Examples of the monomer represented by formula (2) include 2-methoxyethyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, glycidyl (meth)acrylate, 2-aminoethyl (meth)acrylate, γ-(methacryloyloxypropyl)trimethoxysilane, ethylene oxide adducts of (meth)acrylic acid, trifluoromethylmethyl (meth)acrylate, 2-trifluoromethylethyl (meth)acrylate, 2-perfluoroethylethyl (meth)acrylate, 2-perfluoroethyl-2-perfluorobutylethyl (meth)acrylate, 2-perfluoroethyl (meth)acrylate, perfluoromethyl (meth)acrylate, diperfluoromethylmethyl (meth)acrylate, 2-perfluoromethyl-2-perfluoroethylmethyl (meth)acrylate, 2-perfluorohexylethyl (meth)acrylate, 2-perfluorodecylethyl (meth)acrylate, and 2-perfluorohexadecylethyl (meth)acrylate.

[0032] (Constituent unit (3) derived from a monomer represented by formula (3) under condition (b)) In formula (3), R ７ is an alkyl group having 1 to 20 carbon atoms, and the alkyl group consists solely of carbon atoms and hydrogen atoms. Examples of the alkyl group having 1 to 20 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, 2,2-dimethylpropyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, and benzyl. Of these, from the viewpoint of obtaining a rubber product with low rolling resistance, methyl, ethyl, propyl, butyl, 2-ethylhexyl, and benzyl are preferred.

[0033] Examples of the monomer represented by formula (3) include (meth)acrylic acid, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, phenyl (meth)acrylate, toluyl (meth)acrylate, and benzyl (meth)acrylate.

[0034] (Conditions (c) and (d)) Under condition (c), the content of the structural unit (2) is 50 mol% or more, preferably 65 mol% or more, and more preferably 80 mol% or more, relative to all structural units in the first region. Under condition (d), the content of the structural unit (3) is 50 mol% or more, preferably 95 mol% or more, and more preferably 98 mol% or more, relative to all structural units in the second region. Regarding the contents of the structural units (2) and (3), under condition (c), the content of the structural unit (2) is preferably 65 mol% or more, and under condition (d), the content of the structural unit (3) is preferably 95 mol% or more. Under condition (c), the content of the structural unit (2) is preferably 80 mol% or more, and under condition (d), the content of the structural unit (3) is preferably 95 mol% or more. More preferably, under condition (c), the content of the structural unit (2) is 80 mol% or more, and under condition (d), the content of the structural unit (3) is 95 mol% or more.

[0035] (First Region) The first region contains the structural unit (2) as an essential structural unit, but may also contain a structural unit other than the structural unit (2) (hereinafter also referred to as "other structural unit (A)"). The other structural unit (A) may be, for example, the structural unit (3) described above, or a structural unit other than the structural unit (2) and the structural unit (3) described above (hereinafter also referred to as "other structural unit (a)"). When the first region contains the structural unit (2) and the other structural unit (A), the first region may be a random copolymer or a block copolymer.

[0036] (Second Region) The second region contains the structural unit (3) as an essential structural unit, but may also contain a structural unit other than the structural unit (3) (hereinafter also referred to as "other structural unit (B)"). The other structural unit (B) may be, for example, the structural unit (2) described above, or a structural unit other than the structural unit (2) and the structural unit (3) (the aforementioned "other structural unit (a)"). When the second region contains the structural unit (3) and the other structural unit (B), the second region may be a random copolymer or a block copolymer.

[0037] (Intermediate Region) The (meth)acrylic acid ester polymer (E) has an intermediate region between the first region and the second region, which corresponds to 40 mol % of all structural units in the polymer main chain. The structural unit contained in the intermediate region is not particularly limited, and may be any of the structural unit (2), the structural unit (3), and the other structural unit (a). When the intermediate region contains two or more structural units selected from the group consisting of the structural unit (2), the structural unit (3), and the other structural unit (a), the intermediate region may be a random copolymer or a block copolymer.

[0038] The monomer that provides the other structural unit (a) is not particularly limited as long as it is a vinyl monomer copolymerizable with the monomer represented by the above formula (2) or the monomer represented by the above formula (3). Examples of the vinyl monomer include styrene monomers such as styrene, vinyltoluene, α-methylstyrene, chlorostyrene, styrenesulfonic acid and its salts; fluorine-containing vinyl monomers such as perfluoroethylene, perfluoropropylene, vinylidene fluoride; silicon-containing vinyl monomers such as vinyltrimethoxysilane and vinyltriethoxysilane; maleic anhydride, maleic acid, monoalkyl esters and dialkyl esters of maleic acid; fumaric acid, monoalkyl esters and dialkyl esters of fumaric acid; maleimide, methylmaleimide, ethylmaleimide, propylmaleimide, butylmaleimide, Examples of suitable vinyl monomers include maleimide monomers such as hexylmaleimide, octylmaleimide, dodecylmaleimide, stearylmaleimide, phenylmaleimide, and cyclohexylmaleimide; nitrile group-containing vinyl monomers such as acrylonitrile and methacrylonitrile; amide group-containing vinyl monomers such as acrylamide and methacrylamide; vinyl ester monomers such as vinyl acetate, vinyl propionate, vinyl pivalate, vinyl benzoate, and vinyl cinnamate; alkenyl monomers such as ethylene and propylene; conjugated diene monomers such as butadiene and isoprene; vinyl chloride, vinylidene chloride, allyl chloride, and allyl alcohol. These vinyl monomers may be used alone or in combination of two or more.

[0039] The number average molecular weight of the (meth)acrylic acid ester polymer (E) is not particularly limited, and is preferably 1,000 to 50,000, more preferably 1,000 to 20,000, and even more preferably 1,000 to 15,000, in terms of polystyrene equivalent molecular weight measured by size exclusion chromatography (SEC).

[0040] The molecular weight distribution (Mw / Mn) of the (meth)acrylic acid ester polymer (E) is not particularly limited, and is, for example, preferably 3.0 or less, more preferably 2.0 or less, even more preferably 1.8 or less, even more preferably 1.6 or less, and particularly preferably 1.4 or less. The lower limit is not particularly limited, but it is sufficient as long as it is 1 or more.

[0041] The content of the (meth)acrylic acid ester polymer (E) is preferably 1 to 20 parts by weight, more preferably 1 to 15 parts by weight, and even more preferably 1 to 10 parts by weight, based on 100 parts by weight of the diene rubber (A).

[0042] (Method for Producing (Meth)acrylic Acid Ester Polymer (E)) The (meth)acrylic acid ester polymer (E) can be obtained by a conventionally known polymerization method. Among these, radical polymerization methods and anionic polymerization methods are preferred from the viewpoints of the versatility of the monomer and the ease of introducing the group represented by the above formula (1) to the terminal. Radical polymerization methods can be classified into "chain transfer agent methods" and "living radical polymerization methods." As for the chain transfer agent method, as described in JP-A-9-104718, a common method involves polymerizing the above-mentioned (meth)acrylic acid ester monomer, and, if necessary, the above-mentioned other monomers, in the presence of a chain transfer agent having a carboxyl group, and then reacting the polymer with an unsaturated carboxylic acid described below, thereby introducing the group represented by formula (1) to one terminal of the (meth)acrylic acid ester polymer. As described in, for example, JP-A Nos. 2005-232419 and 2006-291073, the living radical polymerization method can be carried out by polymerizing the above-mentioned (meth)acrylic acid ester monomer and, if necessary, the above-mentioned other monomers using an organic halide as an initiator and a transition metal complex as a polymerization catalyst, and converting the terminal halogen functional group into a group represented by formula (1).

[0043] Atom transfer radical polymerization will be briefly described below.

[0044] In atom transfer radical polymerization, it is preferable to use an organic halide, particularly an organic halide having a highly reactive carbon-halogen bond (for example, a carbonyl compound having a halogen at the α-position or a compound having a halogen at the benzyl position), or a sulfonyl halide compound as an initiator.

[0045] The (meth)acrylic acid ester-based monomer used in atom transfer radical polymerization and other monomers used as needed are not particularly limited, and all of the exemplified (meth)acrylic acid ester-based monomers and other monomers used as needed can be suitably used.

[0046] The transition metal complex used as the polymerization catalyst is not particularly limited, but is preferably a metal complex having an element of Group 7, 8, 9, 10, or 11 of the periodic table as the central metal, more preferably a transition metal complex having zero-valent copper, monovalent copper, divalent ruthenium, divalent iron, or divalent nickel as the central metal, and particularly preferably a copper complex. Specific examples of monovalent copper compounds used to form copper complexes include cuprous chloride, cuprous bromide, cuprous iodide, cuprous cyanide, cuprous oxide, and cuprous perchlorate. When a copper compound is used, 2,2'-bipyridyl or a derivative thereof, 1,10-phenanthroline or a derivative thereof, or a polyamine such as tetramethylethylenediamine, pentamethyldiethylenetriamine, hexamethyltriethylenetetraamine, or hexamethyltris(2-aminoethyl)amine may be added as a ligand to enhance catalytic activity.

[0047] The polymerization reaction can be carried out without a solvent, but can also be carried out in various solvents. The type of solvent is not particularly limited, and examples include the solvents described in paragraph

[0067] of JP-A 2005-232419. These may be used alone or in combination of two or more. In addition, emulsion systems or supercritical fluid CO ２ Polymerization can also be carried out in a system using the medium.

[0048] The polymerization temperature is not limited, but can be in the range of 0 to 200°C, preferably in the range of room temperature to 150°C.

[0049] Examples of methods for introducing the group represented by formula (1) include the methods described in paragraphs

[0080] to

[0091] of JP-A 2004-203932. Among these methods, those produced by substituting the terminal halogen groups of a (meth)acrylic acid ester polymer with an unsaturated carboxylic acid or a compound having an acryloyl group are preferred because they are easier to control.

[0050] The (meth)acrylic acid ester polymer having a terminal halogen group is produced by a polymerization method using the above-mentioned organic halide or halogenated sulfonyl compound as an initiator and a transition metal complex as a catalyst, or by a polymerization method using a halogen compound as a chain transfer agent, but the former is preferred.

[0051] The unsaturated carboxylic acid is preferably a compound represented by the following general formula (4). (In formula (4), R １ and R ２ are the same or different and represent a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or an aryl group having 6 to 20 carbon atoms. ３ represents a hydrogen atom or a methyl group. Y represents an alkylene group having 1 to 18 carbon atoms or a single bond.

[0052] In formula (4), R １ and R ２ an alkyl group having 1 to 20 carbon atoms represented by the formula: １ and R ２ The aryl group having 6 to 20 carbon atoms represented by the formula (1) and the alkylene group having 1 to 18 carbon atoms represented by the formula (1) are R １ and R ２ an alkyl group having 1 to 20 carbon atoms represented by the formula: １ and R ２ and the same groups as the alkylene group represented by Y having 1 to 18 carbon atoms.

[0053] Among the compounds represented by formula (4), cinnamic acid, p-coumaric acid, caffeic acid, ferulic acid, crotonic acid, oleic acid, trans-2-pentenoic acid, trans-2-hexenoic acid, and the like are preferred.

[0054] The solvent used in this reaction is not particularly limited, and typically, tetrahydrofuran, dioxane, diethyl ether, acetone, ethyl acetate, butyl acetate, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, hexamethylphosphoric triamide, acetonitrile, etc. are used.

[0055] As the compound having an acryloyl group, a compound represented by the following general formula (5) can be used: M ＋－ OC(O)C(R)=CH2 (5) Specific examples of R in formula (5) include, for example, -H, -CH ３ , -CH ２ CH ３ , -(CH ２ ) ｎ CH ３ (n represents an integer of 2 to 19), -C ６ H ５ , -CH ２ -OH, -CN, etc., and preferably -H, -CH ３ is.

[0056] M in the above formula (5) ＋ is the counter cation of the oxyanion, and M ＋ Examples of the ion include alkali metal ions, specifically lithium ions, sodium ions, potassium ions, and quaternary ammonium ions. Examples of the quaternary ammonium ions include tetramethylammonium ions, tetraethylammonium ions, tetrabenzylammonium ions, trimethyldodecylammonium ions, tetrabutylammonium ions, and dimethylpiperidinium ions. In view of reactivity and availability, sodium ions and potassium ions are preferred.

[0057] The reaction temperature is not particularly limited, but is generally 0 to 150°C, preferably room temperature to 120°C.

[0058] (Other Components) The rubber composition may contain components other than the diene rubber (A), silica (B), carbon black (C), silane coupling agent (D), and (meth)acrylic acid ester polymer (E) (hereinafter also referred to as "other components") as long as the effects of the present invention are not impaired. As other components, compounding agents typically used in the rubber industry, such as fillers, plasticizers, vulcanizing agents, vulcanization accelerators, vulcanization accelerator assistants, and antioxidants, can be appropriately blended depending on the purpose and application.

[0059] Examples of the filler include, in addition to the above-mentioned silica (B) and carbon black (C), aluminum oxide, organic short fibers, (meth)acrylic resin fine particles, epoxy resin fine particles, glass fine particles, glass fibers, and flake graphite.

[0060] Examples of plasticizers include petroleum-based process oils such as paraffinic process oil, naphthenic process oil, and aromatic process oil, dialkyl dibasic acids such as diethyl phthalate, dioctyl phthalate, and dibutyl adipate, low-molecular-weight liquid polymers such as liquid polybutene and liquid polyisoprene, and natural oils such as orange oil. Among these, liquid polybutene, liquid polyisoprene, and aromatic process oil are preferred in terms of compatibility with the rubber component.

[0061] Examples of the vulcanizing agent include sulfur, phenolic resin, metal oxide, and peroxide.

[0062] Examples of the vulcanization accelerator include thiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole (M), 2,2-dithiobisbenzothiazole (DM), mercaptobenzothiazole zinc salt (MZ), mercaptobenzothiazole cyclohexylamine salt (M60), 2,4-dinitrophenylthiobenzothiazole (DBM), and N,N-diethylthiocarbamoylthiobenzothiazole (64); N-cyclohexyl-2-benzothiazoylsulfenamide (CZ), N-tert-butyl-2-benzothiazolesulfenamide (NS), N-oxydiethylene-2-benzothiazoylsulfenamide (NOBS), N,N-dicyclohexyl-2-benzothiazoylsulfenamide (DZ), and morpholinodithiobenzothiazole ( Examples of suitable vulcanization accelerators include sulfenamide-based vulcanization accelerators such as butyraldehyde aniline (B) and butyraldehyde monobutylamine (833), aldehyde ammonia-based vulcanization accelerators such as butyraldehyde aniline (B) and butyraldehyde monobutylamine (833), guanidine-based vulcanization accelerators such as diphenyl guanidine (D), di-o-tolyl guanidine (DT), o-tolyl guanidine (BG), and dicatechol borate-di-o-tolyl guanidine salt (PR), and thiuram-based vulcanization accelerators such as tetramethylthiuram monosulfide (TS), tetramethylthiuram disulfide (TT), tetraethylthiuram disulfide (TET), tetrabutylthiuram disulfide (TBT), dipentamethylenethiuram hexasulfide (TRA), and tetrabenzylthiuram disulfide.

[0063] These other components are usually used in an amount of 0.2 to 40 parts by weight per 100 parts by weight of the diene rubber (A). The vulcanization accelerators may be used alone or in combination of two or more.

[0064] <Method for Producing Rubber Composition> The method for producing the rubber composition is not particularly limited as long as it is a method conventionally used in the rubber industry, and examples thereof include a method in which the above-mentioned components are kneaded using a known method or apparatus (e.g., a Banbury mixer, a kneader, a roll, etc.).

[0065] As for the kneading conditions, when additives other than the vulcanizing agent and the vulcanization accelerator are blended, the kneading temperature is usually 50 to 200°C, preferably 80 to 190°C, and the kneading time is usually 30 seconds to 30 minutes, preferably 1 minute to 30 minutes.

[0066] When a vulcanizing agent and a vulcanization accelerator are blended, the kneading temperature is usually 100°C or lower, preferably room temperature to 80°C. Furthermore, a composition blended with a vulcanizing agent and a vulcanization accelerator is usually used by subjecting it to a vulcanization treatment such as press vulcanization. The vulcanization temperature is usually 120 to 200°C, preferably 140 to 180°C. The (meth)acrylic acid ester polymer (E) may be blended in the vulcanization step, or may be blended in advance with the diene rubber (A), or may be reacted with the diene rubber (A) in advance. Blending in the vulcanization step is preferred because of the ease of operation.

[0067] <Rubber Products> Rubber products can be obtained from the rubber composition described above. That is, the rubber composition, to which various additives are optionally added, is molded into a molded product before vulcanization. This unvulcanized molded product can be heated and pressurized in a vulcanizer to produce a rubber product.

[0068] Examples of rubber products include pneumatic tires, cable coverings, hoses, transmission belts, conveyor belts, roll covers, shoe bodies or shoe soles, sealing rings, and vibration-isolating rubber.

[0069] <Pneumatic Tire> A pneumatic tire is manufactured by a conventional method using the above-described rubber composition. That is, the rubber composition, to which various additives are optionally added, is extruded to match the shape of the tire tread while still unvulcanized, molded by a conventional method on a tire building machine, and then bonded together with other tire components to form an unvulcanized tire. This unvulcanized tire can be heated and pressurized in a vulcanizer to manufacture the pneumatic tire of the present invention.

[0070] The pneumatic tire can be suitably used as a tire for a passenger car, or a tire for a truck or bus (heavy duty tire).

[0071] <Tire Performance> When the rubber composition is used in a pneumatic tire, the performance of the tire is estimated by the following indexes.

[0072] (Rolling Resistance) Rolling resistance is a vibration of about 10 to 100 Hz at around 60° C., and is therefore expressed as tan δ from 40° C. to 70° C. at 10 Hz.

[0073] (Wet Grip Performance) Wet grip performance is believed to depend on deformation near the tire surface. This deformation near the surface is known to be a very high frequency vibration, and when temperature frequency conversion is used, wet grip performance is expressed as tan δ from -20°C to 0°C at 10 Hz.

[0074] (Tensile Stress) Tensile stress is considered to be related to the rigidity, strength, and durability of a tire. The tensile stress can be determined using the stress at 300% elongation (M300) as an index.

[0075] (Hardness) Hardness is considered to be related to handling stability.

[0076] The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0077] [Measurement Method] (1) Molecular Weight The number average molecular weight (Mn), weight average molecular weight (Mw), and molecular weight distribution (Mw / Mn) of the (meth)acrylic acid ester polymer were measured by standard polystyrene conversion using size exclusion chromatography (SEC). The SEC specifications are as follows: SEC system: HLC-8320 (Tosoh Corporation) Stationary phase: TSKgel Super HM-N (Tosoh Corporation) Mobile phase: Chloroform (2) Rolling Resistance Test specimens measuring 40 mm in length, 5 mm in width, and 2 mm in thickness were cut from the vulcanized cured rubber, and tan δ at 60°C was measured using a dynamic viscoelasticity measuring device DVA-200 (IT Measurement Control Co., Ltd.). This characteristic is expressed as an index, with the reference sample (Comparative Example 2 described below) set to 100. The smaller the index, the better the rolling resistance. The measurement conditions were as follows. Measurement temperature: -20°C to 80°C Heating rate: 2°C / min Initial strain: 10% Amplitude: ±1% Frequency: 10 Hz (3) Wet grip performance Tan δ at 0°C was measured in the same manner as for rolling resistance. This characteristic was expressed as an index, with the reference sample (Comparative Example 2 described below) being 100. The higher this index, the better the wet grip performance. (4) Stress at 300% elongation (M300) A dumbbell size 7 was punched out of the vulcanized cured rubber, and a tensile test was performed to measure the stress at 300% elongation. An AGS-J (Shimadzu Corporation) was used for the measurement. The tensile speed during the measurement was 500 mm / min. This characteristic was expressed as an index, with the reference sample (Comparative Example 2 described below) being 100. The higher this index, the better the rigidity, strength, and durability are expected to be. (5) Hardness: The vulcanized cured rubber was stacked to a thickness of 6 mm and measured using a Type A durometer. This property was expressed as an index, with the reference sample (Comparative Example 2 described below) being set at 100. A higher index is expected to provide better handling stability.

[0078] [Materials] The materials used in the examples and comparative examples are as follows. Diene rubber (A): Tufden 2000R (Asahi Kasei Corporation) Silica (B): Nipsil AQ (Tosoh Silica Corporation) Carbon black (C): Diablack N339 (Mitsubishi Chemical Corporation) Silane coupling agent (D): Si69 (Evonik) (Meth)acrylic acid ester polymer (E): Polymers 1 to 6 shown below: Polymer 1: obtained in Production Example 1 Polymer 2: obtained in Production Example 2 Polymer 3: obtained in Production Example 3 Polymer 4: obtained in Production Example 4

[0079] (Other ingredients) Antioxidant: Nocrac 6C (Ouchi Shinko Chemical Industry Co., Ltd.) Plasticizer: Aromax 3 (ENEOS Corporation) Vulcanizing agent: sulfur (Fujifilm Wako Pure Chemical Industries Co., Ltd.) Vulcanization accelerator: 1,3-diphenylguanidine (Tokyo Chemical Industry Co., Ltd.), N-tert-butyl-2-benzothiazole sulfenamide (Fujifilm Wako Pure Chemical Industries Co., Ltd.) Vulcanization accelerator aid: stearic acid (Fujifilm Wako Pure Chemical Industries Co., Ltd.), zinc oxide (Fujifilm Wako Pure Chemical Industries Co., Ltd.), 1,3-diphenylguanidine (Tokyo Chemical Industry Co., Ltd.), N-tert-butyl-2-benzothiazole sulfenamide (Fujifilm Wako Pure Chemical Industries Co., Ltd.)

[0080] [Production Example 1: Production of Polymer 1] 198.5 g (1.549 mol) of butyl acrylate, 80 g of methanol, 0.70 g (6.9 mmol) of triethylamine, and 13.42 g (0.06882 mol) of ethyl 2-bromobutyrate were charged, and a separately prepared copper complex solution (a solution prepared by dissolving 0.0769 g (0.344 mmol) of copper(II) bromide in 8 g of methanol and mixing with 0.0793 g (0.344 mmol) of 96%-purity tris[2-(dimethylamino)ethyl]amine) was mixed therein. Nitrogen bubbling was performed for 30 minutes, and then the mixture was stirred at 40°C. 0.0606 g (0.344 mmol) of ascorbic acid and 0.0696 g (0.688 mmol) of triethylamine were dissolved in 12.00 g of methanol that had been previously bubbled with nitrogen for 30 minutes, and the ascorbic acid solution was added dropwise to initiate polymerization. The polymerization solution was sampled at regular intervals during the polymerization, and the consumption rate of butyl acrylate was measured by gas chromatography. 2.5 hours after the start of dropwise addition of the ascorbic acid solution, it was confirmed that 84.9% of the butyl acrylate had been consumed. 201.5 g (1.549 mol) of 2-methoxyethyl acrylate, which had been previously bubbled with nitrogen for 30 minutes, was then added dropwise over 1 hour. Five hours after the start of dropwise addition of the ascorbic acid solution, it was confirmed that 98.4% of the butyl acrylate and 96.4% of the 2-methoxyethyl acrylate had been consumed, and the dropwise addition of the ascorbic acid solution was stopped. The rate of addition of the ascorbic acid solution was 0.0048 g (0.028 mmol) per hour from the start of addition until 2.5 hours, 0.0036 g (0.020 mmol) per hour from 2.5 to 3.5 hours, and 0.0024 g (0.014 mmol) per hour from 3.5 to 5 hours. The reaction solution was then concentrated under reduced pressure at 80°C for 1 hour. To the concentrated reaction solution, 400 g of butyl acetate, 4 g of Kyoward 500SH (Kyowa Chemical Industry Co., Ltd.), and 4 g of Kyoward 700SEN-S (Kyowa Chemical Industry Co., Ltd.) were added and stirred at 100°C for 1 hour. The resulting reaction solution was then filtered to obtain a filtrate.To the obtained filtrate, 15.51 g (0.1408 mol) of potassium acrylate, 1.6 g of Kyoward 700SEN-S (Kyowa Chemical Industry Co., Ltd.), 0.040 g of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl, and 0.440 g of tetra-n-butylammonium bromide were added and stirred at 120°C for 3 hours. The resulting reaction solution was filtered, and the resulting filtrate was concentrated under reduced pressure at 120°C for 3 hours to obtain Polymer 1. 1H NMR measurement of the obtained Polymer 1 confirmed that 0.95 acryloyl groups per polymer molecule had been introduced at the molecular terminals. The number average molecular weight of the obtained Polymer 1 was 5,840, and the molecular weight distribution was 1.09. Polymer 1 is a copolymer having a block primarily composed of units derived from butyl acrylate and a block primarily composed of units derived from 2-methoxyethyl acrylate. The acryloyl group was introduced at the end of a block primarily composed of units derived from 2-methoxyethyl acrylate (first end). The polymerization solution was sampled at regular intervals during the polymerization, and the consumption rates of butyl acrylate and 2-methoxyethyl acrylate were measured by gas chromatography. It was confirmed that 93.8% of the butyl acrylate and 43.0% of the 2-methoxyethyl acrylate had been consumed three hours after the start of the dropwise addition of the ascorbic acid solution. The proportion of the units contained from that point to the first end to all units constituting Polymer 1 is 30 mol % (100 - (("amount of butyl acrylate charged" (mol) x "consumption rate of butyl acrylate at that point" (%) + "amount of 2-methoxyethyl acrylate charged" (mol) x "consumption rate of 2-methoxyethyl acrylate at that point" (%)) / ("amount of butyl acrylate charged" (mol) x "consumption rate of butyl acrylate at the time of termination of polymerization" (%) + "amount of 2-methoxyethyl acrylate charged" (mol) x "consumption rate of 2-methoxyethyl acrylate at the time of completion of polymerization" (%))) x 100).Furthermore, the proportion of units derived from 2-methoxyethyl acrylate in the units contained from that point to the first terminal is 92 mol% (("amount of 2-methoxyethyl acrylate charged" (mol) × "consumption rate of 2-methoxyethyl acrylate at the end of polymerization" (%) - "amount of 2-methoxyethyl acrylate charged" (mol) × "consumption rate of 2-methoxyethyl acrylate at the end of polymerization" (%)) / (("amount of butyl acrylate charged" (mol) × "consumption rate of butyl acrylate at the end of polymerization" (%) + "amount of 2-methoxyethyl acrylate charged" (mol) × "consumption rate of 2-methoxyethyl acrylate at the end of polymerization" (%)) - ("amount of butyl acrylate charged" (mol) × "consumption rate of butyl acrylate at the end of polymerization" (%) + "amount of 2-methoxyethyl acrylate charged" (mol) × "consumption rate of 2-methoxyethyl acrylate at the end of polymerization" (%))) × 100). The units constituting the portion comprising 30 mol % of all units from the second terminal consist solely of units derived from butyl acrylate. Polymer 1 contains 92 mol % of units derived from 2-methoxyethyl acrylate in the first region relative to all units in the first region, and 100 mol % of units derived from butyl acrylate in the second region relative to all units in the second region.

[0081] [Production Example 2: Production of Polymer 2] Polymerization was initiated in the same manner as in Production Example 1, except that 201.5 g (1.549 mol) of 2-methoxyethyl acrylate was used instead of 198.5 g of butyl acrylate as the initially charged monomer. The polymerization solution was sampled at regular intervals during the polymerization, and the consumption rate of 2-methoxyethyl acrylate was measured by gas chromatography. It was confirmed that 93.3% of the 2-methoxyethyl acrylate had been consumed 140 minutes after the start of the dropwise addition of the ascorbic acid solution. To this solution, 198.5 g (1.549 mol) of butyl acrylate, which had been previously bubbled with nitrogen for 30 minutes, was added dropwise over 1 hour. 310 minutes after the start of the dropwise addition of the ascorbic acid solution, it was confirmed that 99.8% of the 2-methoxyethyl acrylate and 96.3% of the butyl acrylate had been consumed, and the dropwise addition of the ascorbic acid solution was stopped. The rate of addition of the ascorbic acid solution was 0.0024 g (0.014 mmol) per hour from the start of addition until 140 minutes, and 0.0048 g (0.028 mmol) of ascorbic acid per hour from 140 minutes to 310 minutes. Polymer 2 was obtained by the same procedure as in Production Example 1. H NMR analysis of the resulting polymer 2 confirmed that 0.91 acryloyl groups were introduced at the molecular terminals per polymer molecule. The number-average molecular weight of the resulting polymer 2 was 5,890, and the molecular weight distribution was 1.10. Polymer 2 was a copolymer having a block primarily composed of units derived from 2-methoxyethyl acrylate and a block primarily composed of units derived from butyl acrylate. The acryloyl group was introduced at the terminal of the block primarily composed of units derived from butyl acrylate (first terminal). The polymerization solution was sampled from time to time during the polymerization, and the consumption rates of 2-methoxyethyl acrylate and butyl acrylate were measured by gas chromatography. It was confirmed that 98.0% of 2-methoxyethyl acrylate and 38.0% of butyl acrylate had been consumed 200 minutes after the start of dropwise addition of the ascorbic acid solution. Calculations made in the same manner as in Production Example 1 revealed that the proportion of units contained from that point through the first terminal to all units constituting Polymer 2 was 30 mol %.Furthermore, the proportion of units derived from 2-methoxyethyl acrylate in the units contained from that point to the first terminal is 3 mol %. The units constituting the portion containing 30 mol % of all units from the second terminal consist only of units derived from 2-methoxyethyl acrylate. Polymer 2 contains 3 mol % of units derived from 2-methoxyethyl acrylate in the first region relative to all units in the first region, and 0 mol % of units derived from butyl acrylate in the second region relative to all units in the second region.

[0082] [Production Example 3: Production of Polymer 3] 440 g (3.43 mol) of butyl acrylate, 220 g of methanol, 5.92 g (58.5 mmol) of triethylamine, and 76 g (0.39 mol) of ethyl 2-bromoisobutyrate were charged, and a separately prepared copper complex solution (a solution prepared by dissolving 0.2178 g (0.9753 mmol) of copper(II) bromide in 22 g of methanol and mixing with 0.2247 g (0.9753 mmol) of 96%-purity tris[2-(dimethylamino)ethyl]amine) was mixed therewith. Nitrogen bubbling was performed for 30 minutes, and then the mixture was stirred at 40° C. 0.3435 g (1.951 mmol) of ascorbic acid and 0.3947 g (3.901 mmol) of triethylamine were dissolved in 68.00 g of methanol that had been previously bubbled with nitrogen for 30 minutes, and the ascorbic acid solution was added dropwise to initiate polymerization. The ascorbic acid solution was added dropwise at a rate of 0.0281 g (0.1597 mmol) of ascorbic acid per hour to the polymerization system. The polymerization solution was sampled at regular intervals during the polymerization, and the butyl acrylate consumption rate was measured by gas chromatography. 120 minutes after the start of the ascorbic acid solution addition, it was confirmed that 52.1% of the butyl acrylate had been consumed. To this solution, 660 g (5.15 mol) of butyl acrylate, which had been previously bubbled with nitrogen for 30 minutes, was added dropwise over 120 minutes. 340 minutes after the start of the ascorbic acid solution addition, it was confirmed that 95.2% of the butyl acrylate had been consumed, and the addition of the ascorbic acid solution was stopped. The reaction solution was then concentrated under reduced pressure at 80°C for 1 hour. To the concentrated reaction solution, 1100 g of butyl acetate, 11 g of Kyoward 500SH (Kyowa Chemical Industry Co., Ltd.), and 11 g of Kyoward 700SEN-S (Kyowa Chemical Industry Co., Ltd.) were added and stirred at 100°C for 1 hour. The resulting reaction solution was then filtered to obtain a filtrate. To 220 g of the resulting filtrate, 4.847 g (0.04400 mol) of potassium acrylate, 0.44 g of Kyoward 700SEN-S (Kyowa Chemical Industry Co., Ltd.), 0.011 g of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl, and 0.264 g of tetra-n-butylammonium bromide were added and stirred at 120°C for 4 hours.The resulting reaction solution was filtered, and the resulting filtrate was concentrated under reduced pressure at 120°C for 3 hours to obtain polymer 3. 1H NMR measurement of the resulting polymer 3 confirmed that 0.92 acryloyl groups were introduced per polymer molecule at the molecular terminals. The resulting polymer 3 had a number average molecular weight of 3,150 and a molecular weight distribution of 1.11. In polymer 3, the first region contained 0 mol% of units derived from 2-methoxyethyl acrylate relative to all units in the first region, and the second region contained 100 mol% of units derived from butyl acrylate relative to all units in the second region.

[0083] [Production Example 4: Production of Polymer 4] 440 g (3.38 mol) of 2-methoxyethyl acrylate, 220 g of methanol, 5.83 g (57.6 mmol) of triethylamine, and 75 g (0.38 mol) of ethyl 2-bromoisobutyrate were charged, and a separately prepared copper complex solution (a solution prepared by dissolving 0.2145 g (0.9605 mmol) of copper(II) bromide in 22 g of methanol and mixing with 0.2213 g (0.9605 mmol) of 96% pure tris[2-(dimethylamino)ethyl]amine) was mixed therewith. Nitrogen bubbling was performed for 30 minutes, and then the mixture was stirred at 40°C. 0.3383 g (1.921 mmol) of ascorbic acid and 0.3888 g (3.842 mmol) of triethylamine were dissolved in 66.94 g of methanol that had been previously bubbled with nitrogen for 30 minutes, and the ascorbic acid solution was added dropwise to initiate polymerization. The ascorbic acid solution was added dropwise at a rate of 0.0278 g (0.1579 mmol) of ascorbic acid per hour to the polymerization system. The polymerization solution was sampled at regular intervals during the polymerization, and the consumption rate of 2-methoxyethyl acrylate was measured by gas chromatography. 1.5 hours after the start of the ascorbic acid solution addition, it was confirmed that 67.3% of the 2-methoxyethyl acrylate had been consumed. To this solution, 660 g (5.07 mol) of 2-methoxyethyl acrylate, which had been previously bubbled with nitrogen for 30 minutes, was added dropwise over 120 minutes. 4 hours after the start of the ascorbic acid solution addition, it was confirmed that 95.8% of the 2-methoxyethyl acrylate had been consumed, and the addition of the ascorbic acid solution was stopped. The reaction solution was then concentrated under reduced pressure at 80°C for 1 hour. To the concentrated reaction solution, 1100 g of butyl acetate, 11 g of Kyoward 500SH (Kyowa Chemical Industry Co., Ltd.), and 11 g of Kyoward 700SEN-S (Kyowa Chemical Industry Co., Ltd.) were added and stirred at 100°C for 1 hour. The resulting reaction solution was then filtered to obtain a filtrate. To the resulting filtrate, 48.47 g (0.4400 mol) of potassium acrylate, 4.4 g of Kyoward 700SEN-S (Kyowa Chemical Industry Co., Ltd.), 0.11 g of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl, and 2.64 g of tetra-n-butylammonium bromide were added and stirred at 120°C for 4 hours.The resulting reaction solution was filtered, and the resulting filtrate was concentrated under reduced pressure at 120°C for 3 hours to obtain polymer 4. 1H NMR measurement of the resulting polymer 4 confirmed that 0.91 acryloyl groups were introduced per polymer molecule at the molecular terminals. The resulting polymer 4 had a number average molecular weight of 2,820 and a molecular weight distribution of 1.13. Polymer 4 contained 100 mol% of units derived from 2-methoxyethyl acrylate in the first region relative to all units in the first region, and 0 mol% of units derived from butyl acrylate in the second region relative to all units in the second region.

[0084] [Example 1, Comparative Examples 1-4] The components listed in Table 1 were prepared (unit: parts by weight). All components except the vulcanizing agent and vulcanization accelerator were kneaded for 15 minutes using a Labo Plastomill (Toyo Seiki Seisakusho, Ltd., model number "4C150") set at 100°C, and the mixture was then removed and cooled. The mixture was then recharged into the Labo Plastomill, and the vulcanizing agent and vulcanization accelerator were added, ensuring that the resin temperature did not exceed 90°C. The mixture was then kneaded for 5 minutes to obtain a rubber composition. The rubber composition was press-molded at 170°C for 30 minutes using a press (Kamito Metal Industries, Ltd., model number "NSF-50") to produce a 2 mm thick sheet. Test specimens were cut from the sheet, and rolling resistance, wet grip performance, stress at 300% elongation (M300), and hardness were measured. The results are shown in Table 1.

[0085] As can be seen from Table 1, the sheets obtained from the rubber compositions according to the Examples have almost the same wet grip performance and hardness as the sheets obtained from the rubber compositions according to the Comparative Examples, but have improved rolling resistance and M300.

[0086]

Claims

1. A rubber composition containing a diene rubber (A), silica (B), carbon black (C), a silane coupling agent (D), and a (meth)acrylate polymer (E) that satisfies the following conditions (a) to (d). (a) It has a first end and a second end as both ends of the polymer, and the first end has a group represented by the following general formula (1). (In formula (1), R １ and R ２ are the same or different and represent a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or an aryl group having 6 to 20 carbon atoms. R ３ represents a hydrogen atom or a methyl group. Y represents an alkylene group having 1 to 18 carbon atoms or a single bond.) (b) It has a structural unit (2) derived from a monomer represented by the following general formula (2) and a structural unit (3) derived from a monomer represented by the following general formula (3). (In formula (2), R ４ are the same or different and represent a hydrogen atom or a methyl group. R ５ represents an alkyl group having 1 to 20 carbon atoms. However, the alkyl group is partially substituted with one or more selected from the group consisting of an oxygen atom, a nitrogen atom, and a halogen atom. In formula (3), R ６ are the same or different and represent a hydrogen atom or a methyl group. R ７ represents an alkyl group having 1 to 20 carbon atoms. However, the alkyl group consists of only carbon atoms and hydrogen atoms.) (c) In a first region consisting of 30 mol% of the total structural units from the first end, the structural unit (2) is contained in an amount of 50 mol% or more based on the total structural units of the first region. (d) In a second region consisting of 30 mol% of the total structural units from the second end, the structural unit (3) is contained in an amount of 50 mol% or more based on the total structural units of the second region.

2. The rubber composition according to claim 1, wherein in the condition (c), the content of the constitutional unit (2) in the (meth)acrylate polymer (E) is 65 mol% or more, and in the condition (d), the content of the constitutional unit (3) is 95 mol% or more.

3. The rubber composition according to claim 1, wherein in the condition (c), the content of the constitutional unit (2) in the (meth)acrylate polymer (E) is 80 mol% or more, and in the condition (d), the content of the constitutional unit (3) is 95 mol% or more.

4. The rubber composition according to claim 1 or 2, wherein the diene rubber (A) is at least one selected from the group consisting of natural rubber, isoprene rubber, styrene-butadiene copolymer rubber, and butadiene rubber.

5. The rubber composition according to claim 1 or 2, containing 5 to 200 parts by weight of the silica (B), 0.5 to 50 parts by weight of the carbon black (C), 0.5 to 20 parts by weight of the silane coupling agent (D), and 1 to 20 parts by weight of the (meth)acrylate polymer (E) with respect to 100 parts by weight of the diene rubber (A).

6. A rubber product obtained from the rubber composition according to claim 1 or 2.

7. A pneumatic tire which is the rubber product according to claim 6.

Images