Rubber composition, rubber product, and pneumatic tire

Abstract

To provide a rubber composition capable of yielding a rubber product having low rolling resistance, a rubber product obtained from the rubber composition, and a pneumatic tire as the rubber product.SOLUTION: A rubber composition comprises a diene-based rubber (A), silica (B), carbon black (C), a silane coupling agent (D), and a (meth)acrylic acid ester-based polymer (E), where one terminal of the (meth)acrylic acid ester-based polymer (E) has a group represented by the general formula (1).SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] Conventionally, in the automotive industry, there has been a demand for reducing the fuel consumption of automobiles, and a tread rubber composition capable of providing a tire with low rolling resistance has been required.

[0003] As a rubber composition for reducing the rolling resistance of a tire, for example, in a rubber composition containing a diene rubber, a rubber composition in which a (meth)acrylic polymer having an acryloyl group capable of reacting during vulcanization of the diene rubber at the ends of molecular fragments is blended is known (see Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When the present inventors studied, when the rubber composition disclosed in Patent Document 1 was used, although the rolling resistance of the tire was reduced, further improvement was required.

[0006] The present invention has been made in view of the above problems, and an object thereof is to provide a rubber-like composition capable of obtaining a rubber product having low rolling resistance, a rubber product obtained from the rubber composition, and a pneumatic tire as the rubber product.

Means for Solving the Problems

[0007] The inventor has found that by blending a (meth)acrylic polymer having a specific substituent at one end instead of the (meth)acrylic polymer having an acryloyl group at the molecular fragment end disclosed in Patent Document 1, the above problems can be solved, and the present invention has been completed.

[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)acrylate polymer (E), The rubber composition, wherein one end of the (meth)acrylate polymer (E) has a group represented by the following general formula (1).

Chemical formula

[0010] According to the present invention, it is possible to provide a rubber-like composition capable of obtaining a rubber product with low rolling resistance, a rubber product obtained from the rubber composition, and a pneumatic tire as the rubber product. [Embodiments for Carrying out the Invention]

[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)acrylate polymer (E) described later.

[0012] According to the rubber composition of the present embodiment, by containing the (meth)acrylate polymer (E) described later, a rubber product with low rolling resistance can be obtained. Hereinafter, essential or optional components that the rubber composition may contain will be described.

[0013] <Diene Rubber (A)> The diene rubber (A) is not particularly limited as long as it is a rubber obtained from monomers 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, chloroprene rubber, and the like. The styrene-butadiene copolymer rubber (SBR) may be either emulsion polymerization SBR or solution polymerization SBR. Further, the diene rubber (A) may be a rubber into which a functional group is 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 of these.

[0014] In addition, an olefin polymer rubber may be used in combination with these diene rubbers (A). Examples of the olefin polymer rubber include butyl rubber, chlorinated butyl rubber, brominated butyl rubber, ethylene-propylene-diene rubber, and the like.

[0015] <Silica (B)> The silica (B) is not particularly limited, and examples thereof include wet silica, dry silica, ground silica, and the like. Among these, wet silica is preferable in terms of excellent abrasion resistance, mechanical properties, and economy.

[0016] The content of the 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 with respect to 100 parts by weight of the diene rubber (A).

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

[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 with respect to 100 parts by weight of the 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-mercaptoethyltrimethoxysilane, 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-(triethoxysilyl)-1-propanamine, vinyltrimethoxysilane, vinyltriethoxysilane, γ-acryloxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-acryloxypropyltriethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, β-(3,Examples include (4-epoxycyclohexyl)ethyltriethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, γ-mercaptopropylmethyldimethoxysilane, styryltrimethoxysilane, styryltriethoxysilane, γ-mercaptopropylmethyldiethoxysilane, etc.

[0020] Among these, bis(3-triethoxysilylpropyl)tetrasulfide, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, γ-acryloxypropyltriethoxysilane, γ-methacryloxypropyltriethoxysilane, vinyltriethoxysilane, and styryltriethoxysilane are preferred in terms of excellent abrasion resistance and improving reinforcement.

[0021] The silane coupling agent (D) can be used 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 with respect to 100 parts by weight of the diene rubber (A).

[0023] <(meth)acrylate polymer (E)> (The (meth)acrylate polymer (E) has a group represented by the following general formula (1) at one end of the main chain of the (meth)acrylate polymer. [Chemical formula] (In formula (1), R 1 and R 2 represent the same or different hydrogen atoms, alkyl groups having 1 to 20 carbon atoms, or aryl groups having 6 to 20 carbon atoms. However, R 1 and R 2 are not simultaneously hydrogen atoms. R 3represents a hydrogen atom or a methyl group. However, the alkyl group or aryl group may be partially substituted with one or more selected from the group consisting of an oxygen atom, a halogen atom, NHR 4 , and NR 4 R 5 . Here, R 4 and R 5 are the same or different and each represents a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, or an aryl group having 6 to 11 carbon atoms. Y represents an alkylene group having 1 to 18 carbon atoms or a single bond.)

[0024] ((Meth)acrylate polymer) In the (meth)acrylate polymer, the structural unit derived from the (meth)acrylate monomer is contained in an amount of 50 mol% or more and less than 50 mol% of the structural units derived from monomers other than the (meth)acrylate monomer, based on 100 mol% of all the constituent units contained in the polymer.

[0025] Examples of the (meth)acrylic acid ester monomer include 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, cyclohexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, phenyl (meth)acrylate, toluyl (meth)acrylate, benzyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, stearyl (meth)acrylate, glycidyl (meth)acrylate, (3-trimethoxysilyl)propyl (meth)acrylate, (3-dimethoxymethylsilyl)propyl (meth)acrylate, (2-trimethoxysilyl)ethyl (meth)acrylate, (2-dimethoxymethylsilyl)ethyl (meth)acrylate, trimethoxysilylmethyl (meth)acrylate, (dimethoxymethylsilyl)methyl (meth)acrylate, an ethylene oxide adduct of (meth)acrylic acid, trifluoromethylmethyl (meth)acrylate, 2-trifluoromethylethyl (meth)acrylate, 2-perfluoroethylethyl (meth)acrylate, 2-perfluoroethyl-2-perfluorobutylethyl (meth)acrylate, perfluoroethyl (meth)acrylate, trifluoromethyl (meth)acrylate, bis(trifluoromethyl)methyl (meth)acrylate, 2-trifluoromethyl-2-perfluoroethylethyl (meth)acrylate, 2-perfluorohexylethyl (meth)acrylate, 2-perfluorodecylethyl (meth)acrylate, 2-perfluorohexadecylethyl (meth)acrylate, etc. These monomers may be used alone or in combination of two or more. Here, “(meth)acrylic” represents acrylic and / or methacrylic.

[0026] Monomers other than (meth)acrylate monomers (hereinafter sometimes referred to as "other monomers") are not particularly limited as long as they are vinyl monomers copolymerizable with (meth)acrylate monomers. Examples of other monomers 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, vinyltriethoxysilane; maleic anhydride, maleic acid, monoalkyl esters and dialkyl esters of maleic acid; fumaric acid, monoalkyl esters and dialkyl esters of fumaric acid; maleimide monomers such as maleimide, methylmaleimide, ethylmaleimide, propylmaleimide, butylmaleimide, hexylmaleimide, octylmaleimide, dodecylmaleimide, stearylmaleimide, phenylmaleimide, cyclohexylmaleimide; nitrile group-containing vinyl monomers such as acrylonitrile, methacrylonitrile; amide group-containing vinyl monomers such as acrylamide, methacrylamide; vinyl ester monomers such as vinyl acetate, vinyl propionate, vinyl pivalate, vinyl benzoate, vinyl cinnamate; alkenyl monomers such as ethylene, propylene; conjugated diene monomers such as butadiene, isoprene; vinyl chloride, vinylidene chloride, allyl chloride, allyl alcohol and the like. These other monomers may be used alone or in combination of two or more.

[0027] (The group represented by formula (1)) R 1 and R 2Examples of the alkyl group having 1 to 20 carbon atoms represented by 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 preferable.

[0028] R 1 and R 2 Examples of the aryl group having 6 to 20 carbon atoms represented by include a phenyl group, a 1-naphthyl group, a 2-naphthyl group, a 3-phenanthryl group, a 2-anthryl group, etc. Among these, from the viewpoint of obtaining a rubber product with low rolling resistance, a phenyl group and a 1-naphthyl group are preferable.

[0029] R 4 and R 5 Examples of the alkyl group having 1 to 8 carbon atoms represented by 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, etc.

[0030] R 4 and R 5 Examples of the aryl group having 6 to 11 carbon atoms represented by include a phenyl group, a 1-naphthyl group, a 2-naphthyl group, etc.

[0031] 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, a decane-1,10-diyl group, etc.

[0032] Among the alkylene group having 1 to 18 carbon atoms represented by Y and single bonds, a single bond is preferred from the viewpoint of obtaining a rubber product with low rolling resistance.

[0033] The number average molecular weight of the (meth)acrylate polymer (E) is not particularly limited, and in terms of the polystyrene-equivalent molecular weight using size exclusion chromatography (SEC), 1,000 to 50,000 is preferred, 1,000 to 20,000 is more preferred, and 1,000 to 15,000 is even more preferred.

[0034] The molecular weight distribution (Mw / Mn) of the (meth)acrylate polymer (E) is not particularly limited. For example, 3.0 or less is preferred, 2.0 or less is more preferred, 1.8 or less is even more preferred, 1.6 or less is still more preferred, and 1.4 or less is particularly preferred. The lower limit is not particularly limited, but it may be 1 or more.

[0035] The content of the (meth)acrylate 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 with respect to 100 parts by weight of the diene rubber (A).

[0036] (Method for producing the (meth)acrylate polymer (E)) The (meth)acrylate polymer (E) can be obtained by a conventionally known polymerization method. Among them, 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, a radical polymerization method or anionic polymerization method is preferred. The radical polymerization method can be classified into a "chain transfer agent method" and a "living radical polymerization method". As the chain transfer agent method, as described in JP-A-9-104718, in the presence of a chain transfer agent having a carboxyl group, the above-mentioned (meth)acrylate monomer and, if necessary, the above-mentioned other monomers are polymerized, and then an unsaturated carboxylic acid described later is reacted to introduce a group represented by the formula (1) to one end of the (meth)acrylate polymer. This method is common. As the living radical polymerization method, for example, as described in JP-A-2005-232419 and JP-A-2006-291073, an organic halide is used as an initiator, and a transition metal complex is used as a polymerization catalyst to polymerize the aforementioned (meth)acrylate monomer and, if necessary, the aforementioned other monomers, and the terminal halogen functional group can be converted into a group represented by the formula (1).

[0037] Atom transfer radical polymerization will be briefly described below.

[0038] 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 or the like as an initiator.

[0039] There are no particular restrictions on the (meth)acrylate monomer used in atom transfer radical polymerization and, if necessary, other monomers, and all of the exemplified (meth)acrylate monomers and, if necessary, other monomers can be suitably used.

[0040] The transition metal complex used as the overlapping catalyst is not particularly limited, but is preferably a metal complex having a Group 7, 8, 9, 10, or 11 element 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 the monovalent copper compound used to form the copper complex include cuprous chloride, cuprous bromide, cuprous iodide, cuprous cyanide, cuprous oxide, cuprous perchlorate, and the like. When a copper compound is used, 2,2'-bipyridyl or its derivative, 1,10-phenanthroline or its derivative, tetramethylethylenediamine, pentamethyldiethylenetriamine, hexamethyltriethylenetetramine, or a polyamine such as hexamethyltris(2-aminoethyl)amine is added as a ligand to enhance the catalytic activity.

[0041] 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. Polymerization can also be carried out in an emulsion system or a system using supercritical fluid CO2 as a medium.

[0042] The polymerization temperature is not limited, but can be carried out in the range of 0 to 200 °C, preferably in the range of room temperature to 150 °C.

[0043] Examples of the method for introducing the group represented by the above formula (1) include the methods described in paragraphs

[0080] to

[0091] of JP-A-2004-203932. Among these methods, from the viewpoint of easier control, it is preferably produced by substituting the terminal halogen group of the (meth)acrylate polymer with an unsaturated carboxylic acid that gives the group represented by the above formula (1).

[0044] (Meth)acrylate polymers having a terminal halogen group are produced by a method of polymerizing the above-described organic halides or sulfonyl halide compounds using an initiator and a transition metal complex as a catalyst, or a method of polymerizing using a halogen compound as a chain transfer agent, but the former is preferred.

[0045] As the above unsaturated carboxylic acid, a compound represented by the following general formula (2) is preferred.

Chemical formula

[0046] In formula (2), the alkyl group having 1 to 20 carbon atoms represented by R 1 and R 2 , the aryl group having 6 to 20 carbon atoms represented by R 1 and R 2 , the alkyl group having 1 to 8 carbon atoms represented by R 4 and R 5 , the aryl group having 6 to 11 carbon atoms represented by R 4 and R 5 , and the alkylene group having 1 to 18 carbon atoms represented by Y are the same as R 1 and R 2 in the above formula (1).An alkyl group having 1 to 20 carbon atoms represented by R 1 and R 2 An aryl group having 6 to 20 carbon atoms represented by R 4 and R 5 An alkyl group having 1 to 8 carbon atoms represented by R 4 and R 5 Examples of the group similar to the alkylene group having 1 to 18 carbon atoms represented by Y include an aryl group having 6 to 11 carbon atoms.

[0047] Among the compounds represented by the formula (2), 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 preferable.

[0048] The solvent used in this reaction is not particularly limited, and usually, tetrahydrofuran, dioxane, diethyl ether, acetone, ethyl acetate, butyl acetate, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, hexamethylphosphoric triamide, acetonitrile and the like are used.

[0049] The reaction temperature is not particularly limited, and generally it is 0 to 150°C, and preferably room temperature to 120°C.

[0050] (Other components) The rubber composition may contain components other than the above-mentioned diene rubber (A), silica (B), carbon black (C), silane coupling agent (D), and (meth)acrylate 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 such as fillers, plasticizers, vulcanizing agents, vulcanization accelerators, vulcanization accelerator aids, anti-aging agents, etc., which are usually used in the rubber industry, can be appropriately compounded according to their purposes and uses.

[0051] 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, flake graphite and the like.

[0052] Examples of the plasticizer include petroleum 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 because of their compatibility with the rubber component.

[0053] Examples of the vulcanizing agent include sulfur, phenol resin, metal oxide, peroxide, and the like.

[0054] Examples of the vulcanization accelerator include thiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole (M), 2,2-dithiobisbenzothiazole (DM), zinc salt of mercaptobenzothiazole (MZ), cyclohexylamine salt of mercaptobenzothiazole (M60), 2,4-dinitrophenylthiobenzothiazole (DBM), and N,N-diethylthiocarbamoylthiobenzothiazole (64); sulfenamide-based vulcanization accelerators such as N-cyclohexyl-2-benzothiazoyl sulfenamide (CZ), N-tert-butyl-2-benzothiazole sulfenamide (NS), N-oxydiethylene-2-benzothiazoyl sulfenamide (NOBS), N,N-dicyclohexyl-2-benzothiazoyl sulfenamide (DZ), and morpholinodithiobenzothiazole (MDB); amine-based vulcanization accelerators such as hexamethylenetetramine (H); aldehyde ammonia-based vulcanization accelerators such as butyraldehyde aniline (B) and butyraldehyde monobutylamine (833); guanidine-based ones such as diphenylguanidine (D), di-o-tolylguanidine (DT), o-tolylguanidine (BG), and di-o-tolylguanidine salt of dicatecholboric acid (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.

[0055] These other components are usually used in an amount of 0.2 to 40 parts by weight based on 100 parts by weight of the diene rubber (A). The vulcanization accelerator may be used alone or in combination of two or more.

[0056] <Method for producing rubber composition> The method for producing the rubber composition is not particularly limited as long as it employs a method conventionally used in the rubber industry. Examples thereof include a method of kneading the above-described respective components using a known method and apparatus (e.g., Banbury mixer, kneader, roll, etc.).

[0057] As for the kneading conditions, when additives other than vulcanizing agents and vulcanization accelerators are compounded, 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.

[0058] When vulcanizing agents and vulcanization accelerators are compounded, the kneading temperature is usually 100 °C or lower, preferably room temperature to 80 °C. Further, the composition containing vulcanizing agents and vulcanization accelerators is usually used after being vulcanized by press vulcanization or the like. The vulcanization temperature is usually 120 to 200 °C, preferably 140 to 180 °C.

[0059] <Rubber product> The rubber product is obtained from the aforementioned rubber composition. That is, a rubber composition blended with various additives as necessary is formed into a molded article at the unvulcanized stage. The rubber product can be manufactured by heating and pressurizing this unvulcanized molded article in a vulcanizer.

[0060] Examples of rubber products include pneumatic tires, cable coatings, hoses, transmission belts, conveyor belts, roll covers, shoe bodies or soles, sealing rings, vibration-proof rubbers, and the like.

[0061] <Pneumatic tire> The pneumatic tire is manufactured by a conventional method using the aforementioned rubber composition. That is, a rubber composition blended with various additives as necessary is extruded at the unvulcanized stage according to the shape of the tire tread, molded by a conventional method on a tire molding machine, bonded together with other tire members to form an unvulcanized tire. The pneumatic tire of the present invention can be manufactured by heating and pressurizing this unvulcanized tire in a vulcanizer.

[0062] The pneumatic tire can be suitably used as a passenger car tire or a truck / bus tire (heavy-duty tire).

[0063] When the rubber composition is used for a pneumatic tire, the performance of the tire is estimated by the following indexes.

[0064] The rolling resistance is the vibration around 10 - 100 Hz near 60°C, and is represented by tanδ at 40°C - 70°C at 10 Hz.

[0065] The wet grip property is considered to depend on the deformation near the surface of the tire. This deformation near the surface is known to be vibration at a very high frequency. Using temperature-frequency conversion, the wet grip property is represented by tanδ at -20°C - 0°C at 10 Hz.

Example

[0066] Hereinafter, the present invention will be described more specifically based on examples and comparative examples, but the present invention is not limited to the following examples.

[0067] [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)acrylate polymer were measured by the standard polystyrene conversion method using size exclusion chromatography (SEC). The specifications of the SEC are as follows. · SEC system: HLC-8320 (Tosoh Corporation) · Stationary phase: TSKgel SuperHM-N (Tosoh Corporation) · Mobile phase: chloroform (2) Rolling resistance A test piece with a length of 40 mm, a width of 5 mm, and a thickness of 2 mm was cut out from the vulcanized rubber cured product, and tanδ at 60°C was measured using a dynamic viscoelasticity measuring device DVA-200 (IT Measurement and Control Co., Ltd.). This property was indicated by an index with a reference sample (Comparative Example 1 described later) set to 100. The smaller this index, the better the rolling resistance. The measurement conditions were as follows. · Measurement temperature: -20°C - 80°C · Heating rate: 2°C / min · Initial strain: 10% · Amplitude: ±1% · Frequency: 10 Hz (3) Wet grip property In the same manner as the rolling resistance, tanδ at 0°C was measured. This property was indicated by an index with a reference sample (Comparative Example 1 described later) being 100. The larger this index, the better the wet grip property.

[0068] [Materials] The materials used in the examples and comparative examples are as follows. Diene rubber (A): Toughden 2000R (Asahi Kasei Corporation) Silica (B): Nipsil AQ (Tokyo Sojitz Silica Corporation) Carbon black (C): Diablack N339 (Mitsubishi Chemical Corporation) Silane coupling agent (D): Si69 (Evonik) (Meth)acrylate polymer (E): The following Polymers 1 to 6 · Polymer 1: The one obtained in Production Example 1 · Polymer 2: The one obtained in Production Example 2 · Polymer 3: The one obtained in Production Example 3 · Polymer 4: The one obtained in Production Example 4 · Polymer 5: The one obtained in Production Example 5 · Polymer 6: The one obtained in Production Example 6

[0069] [Other components] · Antioxidant: Nocrack 6C (Ouchi Shinko Chemical Industry Co., Ltd.) · Plasticizer: Aromax 3 (ENEOS Corporation) · Vulcanizing agent: Sulfur (Fuji Film Wako Pure Chemical Corporation) · Vulcanization accelerator: 1,3-Diphenylguanidine (Tokyo Chemical Industry Co., Ltd.), N-tert-butyl-2-benzothiazolesulfenamide (Fuji Film Wako Pure Chemical Corporation) · Vulcanization accelerator coagent: Stearic acid (Fuji Film Wako Pure Chemical Corporation), Zinc oxide (Fuji Film Wako Pure Chemical Corporation)

[0070] [Production Example 1: Production of Polymer 1] 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 0.2247 g (0.9753 mmol) of tris[2-(dimethylamino)ethyl]amine with a purity of 96%) was mixed therewith. After nitrogen bubbling was carried out for 30 minutes, 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 nitrogen-bubbled in advance for 30 minutes, and this ascorbic acid solution was added dropwise to initiate polymerization. The dropping rate of the ascorbic acid solution was set such that 0.0281 g (0.1597 mmol) of ascorbic acid was introduced into the polymerization system per hour. During the polymerization, the polymerization solution was withdrawn as needed, and the consumption rate of butyl acrylate was measured by gas chromatography. It was confirmed that 52.1% of butyl acrylate had been consumed 120 minutes after the start of dropping the ascorbic acid solution. Then, 660 g (5.15 mol) of butyl acrylate that had been nitrogen-bubbled in advance for 30 minutes was added dropwise over 120 minutes. It was confirmed that 95.2% of butyl acrylate had been consumed 340 minutes after the start of dropping the ascorbic acid solution, and the dropping of the ascorbic acid solution was stopped. The number average molecular weight of the polymer of butyl acrylate at this point was 3,080, and the molecular weight distribution was 1.09. Next, the reaction solution was concentrated under reduced pressure at 80°C for 1 hour. 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 to the concentrated reaction solution, and the mixture was stirred at 100°C for 1 hour. Next, the obtained reaction solution was filtered to obtain filtrate A. To 220 g of filtrate A, 6.519 g (0.04400 mol) of cinnamic acid, 3.547 g (0.02567 mol) of potassium carbonate, 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 charged, and the mixture was stirred at 120 °C for 5 hours. The resulting reaction solution was filtered, and the obtained filtrate was concentrated under reduced pressure at 120 °C for 3 hours to obtain Polymer 1. By 1H NMR measurement of the obtained Polymer 1, it was confirmed that 0.97 groups derived from cinnamic acid were introduced per Polymer 1 molecule at the molecular terminals. The number average molecular weight of the obtained Polymer 1 was 3,180, and the molecular weight distribution was 1.10.

[0071] [Production Example 2: Production of Polymer 2] Polymer 2 was obtained in the same manner as in Production Example 1, except that 3.788 g (0.04400 mol) of crotonic acid was used instead of cinnamic acid. By 1H NMR measurement of the obtained Polymer 2, it was confirmed that 0.92 groups derived from crotonic acid were introduced per Polymer 1 molecule at the molecular terminals. The number average molecular weight of the obtained Polymer 2 was 2,970, and the molecular weight distribution was 1.13.

[0072] [Production Example 3: Production of Polymer 3] Polymer 3 was obtained by concentrating the above filtrate A under reduced pressure at 120 °C for 3 hours. The number average molecular weight of the obtained Polymer 3 was 3,110, and the molecular weight distribution was 1.10.

[0073] [Production Example 4: Production of Polymer 4] Polymer 4 was obtained in the same manner as in Production Example 1, except that potassium acrylate 4.847 g (0.04400 mol) was used instead of cinnamic acid and potassium carbonate, and the mixture was heated and stirred for 4 hours. By 1H NMR measurement of the obtained Polymer 4, it was confirmed that 0.92 acryloyl groups were introduced per Polymer 1 molecule at the molecular terminals. The number average molecular weight of the obtained Polymer 4 was 3,150, and the molecular weight distribution was 1.11.

[0074] [Production Example 5: Production of Polymer 5] Instead of cinnamic acid, 6.608 g (0.06600 mol) of 4-pentenoic acid was used, the amount of potassium carbonate used was 5.068 g (0.03667 mol), the amount of tetra-n-butylammonium bromide used was 0.132 g, and the mixture was heated and stirred for 3 hours. Polymer 5 was obtained in the same manner as in Production Example 1. By 1H NMR measurement of the obtained Polymer 5, it was confirmed that 0.96 groups derived from 4-pentenoic acid were introduced per polymer molecule at the molecular terminals. The number average molecular weight of the obtained Polymer 5 was 3,250, and the molecular weight distribution was 1.10.

[0075] [Production Example 6: Production of Polymer 6] 20.00 g (0.1560 mol) of butyl acrylate, 12 g of toluene, and 1.6231 g (4.6963 mmol) of 2-cyano-2-propyl dodecyl trithiocarbonate (CPDT) as a RAFT agent were charged. To this, 0.9604 g of a separately prepared V-59 solution (a solution prepared by dissolving 0.1000 g (0.5201 mmol) of V-59 in 9.9000 g of toluene) was added. After nitrogen bubbling was performed for 30 minutes, polymerization was started by stirring at 70°C. During the polymerization, the polymerization solution was withdrawn as needed, and the consumption rate of butyl acrylate was measured by gas chromatography. After 8 hours from the start of polymerization, it was confirmed that 77.1% of butyl acrylate had been consumed, and the heating was stopped. Next, the reaction solution was concentrated under reduced pressure at 105°C for 1 hour to obtain Polymer 6. By absorbance measurement of the obtained Polymer 6, it was confirmed that 0.95 groups derived from CPDT were introduced per polymer molecule at the molecular terminals. The number average molecular weight of the obtained Polymer 6 was 3,950, and the molecular weight distribution was 1.06.

[0076] [Examples 1 to 2, Comparative Examples 1 to 5] The components shown in Table 1 were prepared (unit: parts by weight). Components other than the vulcanizing agent and the vulcanization accelerator were kneaded for 15 minutes using a Laboplastomill (manufactured by Toyo Seiki Seisakusho Co., Ltd., model number "4C150") set at 100°C. Then, the mixture was taken out once and cooled. The mixture was put into the Laboplastomill again, and the vulcanizing agent and the vulcanization accelerator were added while ensuring that the resin temperature did not exceed 90°C, followed by kneading for 5 minutes to obtain a rubber composition. The rubber composition was press-molded at 170°C for 30 minutes using a press machine (manufactured by Shindo Metal Industry Co., Ltd., model number "NSF-50") to produce a sheet with a thickness of 2 mm. Test pieces were cut out from the sheet, and the dynamic viscoelasticity was measured to evaluate the rolling resistance and the wet grip property. The results are shown in Table 1.

[0077] As can be seen from Table 1, the sheet obtained from the rubber composition according to the example has almost the same wet grip property as the sheet obtained from the rubber composition according to the comparative example, and the rolling resistance is improved.

[0078]

Table 1

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), wherein the (meth)acrylate polymer (E) has a group represented by the following general formula (1) at one end thereof. 【Chemical Formula 1】 (In formula (1), R １ and R ２ are the same or different and each represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or an aryl group having 6 to 20 carbon atoms, provided that R １ and R ２ are not simultaneously hydrogen atoms. R ３ represents a hydrogen atom or a methyl group. The alkyl group or aryl group may be partially substituted with one or more selected from the group consisting of an oxygen atom, a halogen atom, NHR ４ , and NR ４ R ５ . Here, R ４ and R ５ are the same or different and each represents a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, or an aryl group having 6 to 11 carbon atoms. Y represents an alkylene group having 1 to 18 carbon atoms or a single bond.)

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

3. 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.

4. A rubber product obtained from the rubber composition according to Claim 1 or 2.

5. A pneumatic tire which is the rubber product according to Claim 4.

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