Rubber composition and crosslinked material

Abstract

Even relying on a rubber composition comprising, as a solid rubber, a highly modified solution-polymerized styrene-butadiene copolymer having a prescribed content of Si originating with an Si-containing functional group, and further comprising a fine filler (for example, fine silica) as a filler, provided are: a tire that is produced such that at least a portion thereof is formed from this rubber composition or a crosslinked material from this rubber composition, having the excellent elastic modulus intrinsically possessed by this rubber composition or crosslinked material from this rubber composition, with the rubber composition exhibiting an improved processability, and with the tire being expected to exhibit an improved fuel efficiency performance; a tire tread that uses this rubber composition in at least a portion thereof; and a pneumatic tire that uses this rubber composition in at least a portion thereof.　The rubber composition comprises the following per 100 parts by mass of a solid rubber (A) that contains at least 60 mass% of a modified solution-polymerized styrene-butadiene copolymer (A1) having an Si-containing functional group: 60 to 150 parts by mass of a silica (B1) as a filler (B), and 5 to 30 parts by mass of a liquid conjugated diene polymer (C) having a weight-average molecular weight in the range from 3,000 to 200,000. The content of Si originating with the Si-containing functional group contained in the modified solution-polymerized styrene-butadiene copolymer (A1) is 220 to 800 ppm, and the specific surface area (CTAB) of the silica (B1) is 180 to 500 m2 / g.

Description

Rubber composition and crosslinked product

[0001] The present invention relates to a rubber composition and a crosslinked product obtained by crosslinking the rubber composition.

[0002] Conventionally, rubber compositions in which mechanical strength is improved by compounding a filler such as silica or carbon black with a solid rubber component such as natural rubber or styrene-butadiene rubber have been widely used in tire applications requiring abrasion resistance and mechanical strength. For example, with the aim of improving the dispersibility of these fillers, rubber compositions containing a modified solution-polymerized styrene-butadiene copolymer having a functional group containing Si as a solid rubber component have been studied (see, for example, Patent Document 1). The rubber composition containing the solid rubber component of Patent Document 1 is said to have excellent interaction with carbon black and silica, good filler dispersibility, and be capable of producing tires with excellent low heat buildup, fracture properties, and abrasion resistance.

[0003] In recent years, rubber compositions used in tires have been required to further improve fuel economy, such as by reducing tire-derived energy loss and thinning tires, from the perspective of reducing carbon dioxide emissions. Furthermore, to achieve a reduction in carbon dioxide emissions from a different perspective, automobiles (e.g., electric automobiles, hybrid automobiles, hydrogen fuel cell automobiles, etc.) that replace part or all of their carbon dioxide-emitting internal combustion engines with electric motor drive have been considered. In order to achieve electric motor drive, these automobiles all require the installation of an additional storage battery. The increase in vehicle weight that accompanies the addition of such batteries is problematic, and tires are being required to address this issue.

[0004] International Publication No. 2009 / 133888 Pamphlet

[0005] Among the problems mentioned above, a possible solution to reduce energy loss from tires is to further improve the dispersibility of silica. To achieve this, one possible solution is to increase the concentration of Si-containing functional groups in the modified solution-polymerized styrene-butadiene copolymer having Si-containing functional groups used as the solid rubber component of the rubber composition (use of a highly modified solution-polymerized styrene-butadiene copolymer). Furthermore, increasing the elasticity of tire materials is considered effective in addressing thinner tires and increased vehicle weight. One possible solution for increasing the elasticity of tire materials is to use a fine filler with a small particle size (e.g., fine silica) as a filler in the rubber composition that will become the tire material. Given these factors, one possible solution for reducing carbon dioxide emissions from automobiles is to consider a rubber composition for use as tire material that includes a highly modified solution-polymerized styrene-butadiene copolymer with a high concentration of Si-containing functional groups as the solid rubber component, and further includes a fine filler (e.g., fine silica) as a filler.

[0006] However, according to the studies of the present inventors, it has been found that kneading the components to prepare a rubber composition containing the above-mentioned highly modified solution-polymerized styrene-butadiene copolymer and a fine filler (e.g., fine silica) can be difficult. For example, even when components other than the crosslinking component are kneaded using a Banbury mixer or the like, the Mooney viscosity increases significantly during kneading, making it difficult to sufficiently increase the rotation speed. Furthermore, it can be difficult to ensure sufficient kneading time to achieve good dispersion of the components. Furthermore, after kneading using the Banbury mixer, a sheet is formed using a roll to cool the rubber composition, but this sheet is prone to tearing, which can lead to reduced productivity. Furthermore, when components such as the crosslinking component are kneaded using roll kneading, the sheet formed by the roll is prone to tearing, making it difficult to sufficiently knead the components using roll kneading.

[0007] The present invention has been made in view of the above circumstances, and provides a rubber composition which is expected to have improved fuel economy performance and contains, as a solid rubber, a highly modified solution-polymerized styrene-butadiene copolymer in which the content of Si derived from a functional group containing Si is a specific amount, and which further contains a fine filler (for example, fine silica) as a filler, and which has improved processability and which has a good elastic modulus inherent to the rubber composition or a cross-linked product of the rubber composition, or which is made so that the cross-linked product of the rubber composition constitutes at least a part of the tire; a tire tread which uses the rubber composition at least in part; and a pneumatic tire which uses the rubber composition at least in part.

[0008] As a result of intensive investigations, the present inventors have found that the above-mentioned problems can be solved by adding a specific liquid conjugated diene polymer to a rubber composition containing, as a solid rubber, a modified solution-polymerized styrene-butadiene copolymer having a functional group containing Si at a certain content ratio or more, and further containing, as a filler, silica having a specific specific surface area. This has led to the completion of the present invention. That is, the present invention relates to the following [1] to

[11] .

[0009] [1] A rubber composition comprising 60 to 150 parts by mass of silica (B1) as a filler (B) and 5 to 30 parts by mass of a liquid conjugated diene-based polymer (C) having a weight-average molecular weight in the range of 3,000 to 200,000, per 100 parts by mass of solid rubber (A) containing 60% by mass or more of a modified solution-polymerized styrene-butadiene copolymer (A1) having a functional group containing Si, wherein the content of Si derived from the functional group containing Si contained in the modified solution-polymerized styrene-butadiene copolymer (A1) is 220 to 800 ppm, and the specific surface area (CTAB) of the silica (B1) is 180 to 500 m. 2 / g of the rubber composition.

[0010] [2] The average content of Si derived from functional groups containing Si in the solid rubber (A) is X ppm, and the amount of Si in 1 cm of the rubber composition is 3 The total specific surface area of ​​silica (B1) per unit area is Ym 2 / cm 3[1] The rubber composition according to [1], wherein the value of X×Y satisfies 9,000 or more when the liquid conjugated diene polymer (C) is expressed as follows: [3] The rubber composition according to [1] or [2], wherein the liquid conjugated diene polymer (C) has a melt viscosity at 38°C of 0.1 to 2,000 Pa s. [4] The rubber composition according to any one of [1] to [3], wherein the silica (B1) has an average particle size of 0.5 to 200 nm. [5] The rubber composition according to any one of [1] to [4], wherein the conjugated diene that is a unit derived from a conjugated diene contained in the liquid conjugated diene polymer (C) includes at least one selected from the group consisting of isoprene, butadiene, and farnesene. [6] The rubber composition according to any one of [1] to [5], wherein the liquid conjugated diene polymer (C) is at least one selected from the group consisting of liquid polyisoprene and liquid butadiene-farnesene copolymer. [7] The rubber composition according to any one of [1] to [6], wherein the liquid conjugated diene polymer (C) is liquid polyisoprene. [8] The rubber composition according to any one of [1] to [7], further comprising carbon black (B2) as the filler (B).

[0011] [9] A crosslinked product obtained by crosslinking the rubber composition according to any one of [1] to [8].

[10] A tire tread at least partially using the rubber composition according to any one of [1] to [8].

[11] A pneumatic tire at least partially using the rubber composition according to any one of [1] to [8].

[0012] According to the present invention, a rubber composition having improved processability can be obtained, even if the rubber composition contains a highly modified solution-polymerized styrene-butadiene copolymer as a solid rubber having a specific amount of Si derived from Si-containing functional groups, which is expected to have improved fuel economy performance, and further contains a fine filler as a filler. Furthermore, the rubber composition or a cross-linked product of the rubber composition has a good inherent elastic modulus. Furthermore, a tire (e.g., a pneumatic tire) manufactured so that the rubber composition or the cross-linked product of the rubber composition constitutes at least a part of the tire exhibits excellent low heat buildup.

[0013] [Solid Rubber (A)] The solid rubber (A) used in the rubber composition of the present invention refers to a rubber that can be handled in a solid state at 20°C. The Mooney viscosity ML of the solid rubber (A) at 100°C 1+4 is usually in the range of 20-200.

[0014] The solid rubber (A) contains 60% by mass or more of a modified solution-polymerized styrene-butadiene copolymer (A1) having a functional group containing Si, and the content of Si derived from the functional group containing Si contained in the modified solution-polymerized styrene-butadiene copolymer (A1) is 220 to 800 ppm (hereinafter, the styrene-butadiene copolymer will also be referred to as "SBR," and the solution-polymerized styrene-butadiene copolymer will also be referred to as "S-SBR"). As the modified S-SBR (A1), for example, a modified S-SBR used for tires can be used. By including a modified S-SBR satisfying the above requirements as the solid rubber (A), the dispersibility of the filler (B) containing silica (B1), described below, in the rubber composition tends to be superior compared to when the modified SBR is not included. If the silica (B1) can be sufficiently mixed into the rubber composition, a tire manufactured using at least a portion of the rubber composition or a cross-linked product of the rubber composition is expected to have excellent low heat buildup.

[0015] The modified S-SBR (A1) used in the present invention can be produced, for example, by producing unmodified S-SBR by a solution polymerization method and then introducing a functional group containing Si into this unmodified S-SBR. The position at which the functional group containing Si of this modified SBR is introduced may be the terminal of the polymer chain or a side chain of the polymer chain. When produced by the method described below, the functional group is usually introduced at the terminal of the polymer chain. Unmodified S-SBR can be produced by a conventional solution polymerization method. For example, there is a method in which styrene and butadiene are polymerized as monomers using an active metal capable of anion polymerization in a solvent, optionally in the presence of a polar compound.

[0016] Examples of anionically polymerizable active metals include alkali metals such as lithium, sodium, and potassium; alkaline earth metals such as beryllium, magnesium, calcium, strontium, and barium; and lanthanoid rare earth metals such as lanthanum and neodymium. Among these, alkali metals and alkaline earth metals are preferred, and alkali metals are more preferred. As anionically polymerizable active metal compounds, organic alkali metal compounds are preferred.

[0017] Examples of the solvent include aliphatic hydrocarbons such as n-butane, n-pentane, isopentane, n-hexane, n-heptane, and isooctane; alicyclic hydrocarbons such as cyclopentane, cyclohexane, and methylcyclopentane; and aromatic hydrocarbons such as benzene and toluene. These solvents are preferably used in such a manner that the monomer concentration in the solvent is in the range of 1 to 50% by mass.

[0018] Examples of organic alkali metal compounds include organic monolithium compounds such as n-butyllithium, sec-butyllithium, t-butyllithium, hexyllithium, phenyllithium, and stilbenelithium; polyfunctional organic lithium compounds such as dilithiomethane, 1,4-dilithiobutane, 1,4-dilithio-2-ethylcyclohexane, and 1,3,5-trilithiobenzene; sodium naphthalene, and potassium naphthalene. Among these, organic lithium compounds are preferred, and organic monolithium compounds are more preferred. The amount of the organic alkali metal compound used is determined appropriately depending on the molecular weight of the S-SBR to be produced.

[0019] The organic alkali metal compounds can also be reacted with secondary amines such as dibutylamine, dihexylamine, dibenzylamine, etc. to form organic alkali metal amides.

[0020] The polar compound is not particularly limited as long as it is one that is commonly used in anionic polymerization to adjust the microstructure of butadiene units and the distribution of styrene in the polymer chain without deactivating the reaction. Examples of the polar compound include ether compounds such as dibutyl ether, tetrahydrofuran, and ethylene glycol diethyl ether; tertiary amines such as N,N,N',N'-tetramethylethylenediamine and trimethylamine; alkali metal alkoxides; and phosphine compounds.

[0021] The temperature of the polymerization reaction is usually in the range of −80 to 150° C., preferably 0 to 100° C., and more preferably 30 to 90° C. The polymerization method may be either batch polymerization or continuous polymerization. In order to improve the random copolymerization of styrene and butadiene, it is preferable to continuously or intermittently supply styrene and butadiene to the reaction liquid so that the composition ratio of styrene and butadiene in the polymerization system falls within a specific range.

[0022] The modified S-SBR (A1) can be produced by introducing a Si-containing functional group into the unmodified S-SBR obtained in this manner. For example, the modified S-SBR (A1) can be produced by chemically bonding a modifying compound having a Si-containing functional group to the unmodified S-SBR via a carbon-Si bond. Generally, when silica is simply mixed with solid rubber, it has low affinity with the solid rubber, making it difficult to fully achieve the performance improvement (e.g., improved reinforcing performance) expected from the properties of silica. The modified S-SBR (A1) contains a Si-containing functional group, which can increase the affinity between the silica and the solid rubber component, making it easier to achieve the performance improvement expected from the properties of silica. The Si-containing functional group contained in the modified S-SBR (A1) is preferably a Si-containing functional group having an alkoxyl group, and more preferably an alkoxysilyl group. The modified S-SBR (A1) can be produced, for example, by completing the polymerization reaction of the above-mentioned S-SBR and then adding a modifying compound having a Si-containing functional group capable of reacting with the polymerization active terminal of the S-SBR.

[0023] An example of a modified compound having a functional group containing Si is a compound represented by the following formula (a1): Si(R 1 ) a (X 1 ) b (a1) In the above formula (a1), R 1 are each independently an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, or an aralkyl group having 7 to 20 carbon atoms; X 1 are each independently chlorine or bromine, a is an integer of 0 to 3, b is an integer of 1 to 4, and a+b=4. 1 The alkyl group represented by R is preferably a methyl group, an ethyl group, an n-butyl group, an n-octyl group, or a 2-ethylhexyl group. 1 The cycloalkyl group represented by R is preferably a cyclohexyl group. 1 The aryl group is preferably a phenyl group, and the aralkyl group is preferably a neophyl group.

[0024] The modifying compound having a functional group containing Si is preferably at least one selected from the group consisting of compounds represented by the following formula (a2) and compounds represented by the following formula (a3), in order to further enhance the affinity between the modified S-SBR (A1) and the silica (B1). Si(R 2 ) c (OR 3 ) d (a2) In the above formula (a2), R 2 and R 3 are each independently a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, c is an integer of 0 to 2, d is an integer of 2 to 4, and c+d=4. 3 If multiple are included, multiple OR 3 may be the same or different, and the compound does not contain an active proton.

[0025] Specific examples of the compound represented by the above formula (a2) include tetramethoxysilane, tetraethoxysilane, tetra-n-propoxysilane, tetraisopropoxysilane, tetra-n-butoxysilane, tetraisobutoxysilane, tetra-sec-butoxysilane, tetra-tert-butoxysilane, methyltrimethoxysilane, methyltriethoxysilane, methyltrippropoxysilane, methyltriisopropoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, ethyltripoxysilane, ethyltriisopropoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, ethyltriisoprop ... Examples of the silane include propyltriisopropoxysilane, ethyltriisopropoxysilane, propyltrimethoxysilane, propyltriethoxysilane, propyltripropoxysilane, propyltriisopropoxysilane, butyltrimethoxysilane, butyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, dimethoxydimethylsilane, methylphenyldimethoxysilane, dimethyldiethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, divinyldiethoxysilane, etc. Among these compounds, at least one selected from the group consisting of tetraethoxysilane, methyltriethoxysilane, and dimethyldiethoxysilane is preferred.

[0026]

[0027] In the above formula (a3), A 1 is a monovalent group having at least one functional group selected from the group consisting of an epoxy group, a glycidyloxy group, an isocyanate group, an imino group, a carboxylic acid ester group, a carboxylic acid anhydride group, a cyclic tertiary amino group, a non-cyclic tertiary amino group, a pyridine group, a silazane group, and a disulfide group, and R 4 is a single bond or a divalent hydrocarbon group, and R 5 and R 6 are each independently a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, e is an integer of 0 to 2, and OR 6 If there are multiple, multiple OR 6 may be the same or different, and the compound does not contain an active proton.

[0028] Specific examples of the compound represented by formula (a3) ​​include epoxy group-containing alkoxysilane compounds such as 2-glycidyloxyethyltrimethoxysilane, 2-glycidyloxyethyltriethoxysilane, (2-glycidyloxyethyl)methyldimethoxysilane, 3-glycidyloxypropyltrimethoxysilane, 3-glycidyloxypropyltriethoxysilane, (3-glycidyloxypropyl)methyldimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyl(methyl)dimethoxysilane. Among these compounds, the compound represented by formula (a3) ​​is preferably at least one selected from the group consisting of 3-glycidyloxypropyltrimethoxysilane and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

[0029] Furthermore, as the modifying compound having a functional group containing Si, a hydrocarbyloxysilane compound is one preferred embodiment because it has a high affinity for silica.

[0030] The hydrocarbyloxysilane compound used to produce the modified S-SBR (A1) includes, for example, the hydrocarbyloxysilane compound represented by the following formula (a4):

[0031]

[0032] In the formula (a4), f1, f3, and f4 each independently represent an integer of 0 to 3, f2 represents an integer of 1 to 4, and f1 to f4 satisfy the relationship f1+f2+f3+f4=4; 1is at least one functional group selected from the group consisting of a saturated cyclic tertiary amine compound residue, an unsaturated cyclic tertiary amine compound residue, a ketimine residue, a nitrile group, an isocyanate group, a thioisocyanate group, an epoxy group, a thioepoxy group, an isocyanuric acid trihydrocarbyl ester group, a carbonate dihydrocarbyl ester group, a nitrile group, a pyridine group, a ketone group, a thioketone group, an aldehyde group, a thioaldehyde group, an amide group, a carboxylic acid ester group, a thiocarboxylic acid ester group, a metal base of a carboxylic acid ester, a metal base of a thiocarboxylic acid ester, a carboxylic acid anhydride residue, a carboxylic acid halide compound residue, a primary amino group having a hydrolyzable group, a secondary amino group having a hydrolyzable group, and a mercapto compound residue having a hydrolyzable group; when f4 is 2 or more, B 1 may be the same or different, and two R a4 -B 1 may be taken together to form a divalent group having a cyclic structure bonded to Si, a1 is a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms, a monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms, or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, and when f1 is 2 or more, R a1 may be the same or different, R a2 represents a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms, a monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms, a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, or any of these groups which further contain a nitrogen atom and / or a silicon atom; when f2 is 2 or more, R a2 may be the same or different, and two R a2 O may be taken together to form a divalent organic group having a cyclic structure bonded to Si, R a3 represents a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms, a monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms, a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, or a halogen atom (fluorine, chlorine, bromine, or iodine), and when f3 is 2 or more, R a3 may be the same or different, R a4represents a divalent aliphatic hydrocarbon group having 1 to 20 carbon atoms, a divalent alicyclic hydrocarbon group having 3 to 20 carbon atoms, or a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms, and when f4 is 2 or more, they may be the same or different. 1 The hydrolyzable group contained in the primary amino group having a hydrolyzable group, the secondary amino group having a hydrolyzable group, and the mercapto compound residue having a hydrolyzable group, which can be any of the above, is preferably at least one selected from the group consisting of a trimethylsilyl group and a tert-butyldimethylsilyl group, and more preferably a trimethylsilyl group.

[0033] A preferred embodiment of the hydrocarbyloxysilane compound represented by the above formula (a4) is a hydrocarbyloxysilane compound represented by the following formula (a5):

[0034]

[0035] In the formula (a5), g1 and g3 each independently represent an integer of 0 to 1, g2 represents an integer of 1 to 2, and g1 to g3 satisfy the relationship g1+g2+g3=2; B 2 is NR aa (R aa is a monovalent hydrocarbon group, a monovalent hydrolyzable group, or a monovalent nitrogen-containing organic group, and the hydrolyzable group is preferably a trimethylsilyl group or a tert-butyldimethylsilyl group, more preferably a trimethylsilyl group; or a sulfur atom; R a5 is a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms, a monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms, or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms; R a7 is a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms, a monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms, a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, or a halogen atom (fluorine, chlorine, bromine, or iodine), and R a6 represents a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms, a monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms, a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, or any of these groups and further containing a nitrogen atom and / or a silicon atom; when g2 is 2, they may be the same or different from each other; and when two Ra6 O may be taken together to form a divalent group having a cyclic structure bonded to Si, R a8 is a divalent aliphatic hydrocarbon group having 1 to 20 carbon atoms, a divalent alicyclic hydrocarbon group having 3 to 20 carbon atoms, or a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms.

[0036] As the hydrocarbyloxysilane compound represented by the above formula (a4), a hydrocarbyloxysilane compound represented by the following formula (a6) or (a7) is a preferred embodiment.

[0037]

[0038] In the above formula (a6), h1 is an integer of 0 to 2, h2 is an integer of 1 to 3, and h1 and h2 satisfy h1+h2=3; R b1 is a divalent aliphatic hydrocarbon group having 1 to 20 carbon atoms, a divalent alicyclic hydrocarbon group having 3 to 20 carbon atoms, or a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms, b2 and R b3 are each independently a hydrolyzable group, a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms, a monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms, or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms; R b4 is a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms, a monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms, or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, and when h1 is 2, R b4 may be the same or different, R b5 is a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms, a monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms, or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, and when h2 is 2 or more, R b5 may be the same or different.

[0039]

[0040] In the above formula (a7), i1 is an integer of 1 to 3, i2 is an integer of 0 to 2, and i1 and i2 satisfy i1+i2=3; R b6 is a divalent aliphatic hydrocarbon group having 1 to 20 carbon atoms, a divalent alicyclic hydrocarbon group having 3 to 20 carbon atoms, or a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms,b7 is a dimethylaminomethyl group, a dimethylaminoethyl group, a diethylaminomethyl group, a diethylaminoethyl group, a methylsilyl(methyl)aminomethyl group, a methylsilyl(methyl)aminoethyl group, a methylsilyl(ethyl)aminomethyl group, a methylsilyl(ethyl)aminoethyl group, a dimethylsilylaminomethyl group, a dimethylsilylaminoethyl group, a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms, a monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms, or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms; when i1 is 2 or more, R b7 may be the same or different, R b8 is a hydrocarbyloxy group having 1 to 20 carbon atoms, a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms, a monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms, or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, and when i2 is 2, R b8 may be the same or different.

[0041] A preferred embodiment of the hydrocarbyloxysilane compound represented by the formula (a4) above is a hydrocarbyloxysilane compound having two or more nitrogen atoms represented by the following formula (a8) or (a9):

[0042]

[0043] In the above formula (a8), R c0 is a trimethylsilyl group (Si(CH3)3), a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms, a monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms, or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms; R c1 is a hydrocarbyloxy group having 1 to 20 carbon atoms, a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms, a monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms, or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms; R c2 is a divalent aliphatic hydrocarbon group having 1 to 20 carbon atoms, a divalent alicyclic hydrocarbon group having 3 to 20 carbon atoms, or a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms.

[0044]

[0045] In the above formula (a9), R c3 and R c4are each independently a divalent aliphatic hydrocarbon group having 1 to 20 carbon atoms, a divalent alicyclic hydrocarbon group having 3 to 20 carbon atoms, or a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms; R c5 is a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms, a monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms, or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, and a plurality of R c5 may be the same or different.

[0046] Another preferred embodiment of the hydrocarbyloxysilane compound represented by the formula (a4) is a hydrocarbyloxysilane compound represented by the following formula (a10):

[0047]

[0048] In the above formula (a10), j1 is an integer of 0 to 2, j2 is an integer of 1 to 3, and j1 and j2 satisfy j1+j2=3; R c6 is a divalent aliphatic hydrocarbon group having 1 to 20 carbon atoms, a divalent alicyclic hydrocarbon group having 3 to 20 carbon atoms, or a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms, c7 and R c8 are each independently a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms, a monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms, or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms; when j1 is 2, R c7 may be the same or different, and when j2 is an integer of 2 or more, R c8 may be the same or different.

[0049] Another preferred embodiment of the hydrocarbyloxysilane compound represented by the formula (a4) is a hydrocarbyloxysilane compound represented by the following formula (a11):

[0050]

[0051] In the above formula (a11), X2 is a halogen atom, and R d1 is a divalent aliphatic hydrocarbon group having 1 to 20 carbon atoms, a divalent alicyclic hydrocarbon group having 3 to 20 carbon atoms, or a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms, d2 and Rd3 are each independently a hydrolyzable group, a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms, a monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms, or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, or R d2 and R d3 may be a divalent organic group having a cyclic structure bonded to Si together, R d4 and R d5 are each independently a halogen atom, a hydrocarbyloxy group, a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms, a monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms, or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms. d2 and R d3 is preferably a hydrolyzable group, and among such hydrolyzable groups, a trimethylsilyl group or a tert-butyldimethylsilyl group is preferred, with a trimethylsilyl group being particularly preferred.

[0052] The hydrocarbyloxysilane compounds represented by the above formulae (a4) to (a11) are preferably used as modifying compounds to modify the active terminals of S-SBR produced by anionic polymerization during the production of modified S-SBR (A1). Furthermore, the hydrocarbyloxysilane compounds represented by formulae (a4) to (a11) are preferably alkoxysilane compounds. Among these hydrocarbyloxysilane compounds, 3,4-bis(trimethylsilyloxy)-1-vinylbenzene, 3,4-bis(trimethylsilyloxy)benzaldehyde, and 3,4-bis(tert-butyldimethylsilyloxy)benzaldehyde are preferred.

[0053] In addition, when producing the modified S-SBR (A1), it is also a preferred embodiment to use a lithium amide compound as an initiator for SBR, in which the initiator terminal is a functional group containing Si. Examples of such lithium amide compounds include lithium hexamethyleneimide, lithium pyrrolidide, lithium piperidide, lithium heptamethyleneimide, lithium dodecamethyleneimide, lithium dimethylamide, lithium diethylamide, lithium dibutylamide, lithium dipropylamide, lithium diheptylamide, lithium dihexylamide, lithium dioctylamide, lithium di-2-ethylhexylamide, lithium didecylamide, lithium-N-methylpiberazide, lithium ethylpropylamide, lithium ethylbutylamide, lithium ethylbenzylamide, and lithium methylphenethylamide. When such a lithium amide compound is used as an initiator, polymerization can be carried out under the same polymerization conditions as those for unmodified S-SBR, for example, as described above.

[0054] After the above-described modifying compound is added, a polymerization terminator (e.g., an alcohol such as methanol or isopropanol) is usually added to terminate the polymerization reaction. The modified S-SBR (A1) obtained in this manner can be recovered by, for example, directly drying or steam stripping the polymerization solution after the reaction has been terminated to separate the solvent. Before removing the solvent, the polymerization solution may be mixed with an extender oil and recovered as an oil-extended rubber.

[0055] The content of Si derived from the Si-containing functional group contained in the modified S-SBR (A1) is 220 to 800 ppm. By including such a modified S-SBR (A1) in the solid rubber (A), it is possible to improve the dispersibility of the filler (B) containing silica (B1) described below in the rubber composition. When a rubber composition in which the filler (B) containing silica (B1) is sufficiently mixed can be produced, the tire (typically a pneumatic tire) produced using the rubber composition or a cross-linked product of the rubber composition as at least a part thereof will have excellent low heat buildup properties. From the viewpoint of improving the dispersibility of the filler (B) containing silica (B1) in the rubber composition and the low heat buildup properties of a tire produced using the rubber composition or a cross-linked product of the rubber composition as at least a part thereof, the content of Si derived from the Si-containing functional group contained in the modified S-SBR (A1) is preferably 240 to 700 ppm, more preferably 250 to 600 ppm, and even more preferably 260 ppm to 500 ppm. The content of Si derived from the Si-containing functional groups contained in the modified S-SBR (A1) can be adjusted to a desired value by appropriately adjusting the amount of the modifying compound having the Si-containing functional group used to introduce the Si-containing functional group into the unmodified S-SBR relative to the unmodified S-SBR, the reaction conditions when introducing the modifying compound, and the like. The content of Si derived from the Si-containing functional groups in the modified S-SBR (A1) can be determined by ICP optical emission spectrometry. In the present invention, the content of Si derived from the Si-containing functional groups contained in the modified S-SBR (A1) means the content of the Si-containing functional groups contained in the modified S-SBR (A1) in terms of Si atoms.

[0056] The styrene content (styrene unit content, i.e., the content of units derived from styrene) of the modified S-SBR (A1) is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and still more preferably 20% by mass or more, from the viewpoints of improving the low heat buildup performance and grip performance (wet grip, dry grip) of a tire produced at least in part using the rubber composition or a cross-linked product of the rubber composition. From the above viewpoints, the styrene content of the modified S-SBR (A1) is preferably 70% by mass or less, more preferably 50% by mass or less, even more preferably 45% by mass or less, and still more preferably 40% by mass or less.

[0057] The content of the modified S-SBR (A1) in the solid rubber (A) is 60% by mass or more, preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, still more preferably 95% by mass or more, and may even be 100% by mass, from the viewpoint of improving the low heat buildup performance and grip performance (wet grip, dry grip) of a tire produced at least in part using the rubber composition or a cross-linked product of the rubber composition. The content of the modified S-SBR (A1) in the solid rubber (A) is preferably 100% by mass or less, more preferably 95% by mass or less, even more preferably 90% by mass or less, and still more preferably 85% by mass or less.

[0058] The weight average molecular weight (Mw) of the modified S-SBR (A1) is preferably 100,000 to 2,500,000, more preferably 150,000 to 2,000,000, and even more preferably 200,000 to 1,800,000. When the Mw of the modified S-SBR (A1) is within this range, the processability of the resulting rubber composition is ensured, and the modulus of elasticity of the cross-linked product of the rubber composition is sufficiently high. When the rubber composition or at least a part of the cross-linked product of the rubber composition is used in a tire, the low heat buildup performance and grip performance (wet grip and dry grip) are improved. Note that, in this specification, Mw refers to the weight average molecular weight in terms of polystyrene obtained by gel permeation chromatography (GPC).

[0059] The glass transition temperature (Tg) of the modified S-SBR (A1) determined by differential thermal analysis is preferably −95 to 0° C., more preferably −80 to −5° C., even more preferably −70 to −10° C., still more preferably −60 to −15° C., particularly preferably −50 to −20° C., and most preferably −40 to −20° C. When the glass transition temperature is within the above range, an increase in the viscosity of the rubber composition can be suppressed, making it easier to handle.

[0060] The vinyl content of the modified S-SBR (A1) is preferably 0.1 to 80 mol%, more preferably 10 to 80 mol%, still more preferably 20 to 80 mol%, and even more preferably 40 to 70 mol%.

[0061] In this specification, the vinyl content of the modified S-SBR (A1) means the total mol % of units derived from butadiene bonded via 1,2-bonds (units derived from butadiene bonded via bonds other than 1,4-bonds) out of a total of 100 mol % of units derived from butadiene contained in the modified S-SBR (A1). 1 It can be calculated using H-NMR in the same manner as in the case of the liquid conjugated diene polymer (C) described below.

[0062] [Rubber Other Than Modified S-SBR (A1)] The solid rubber (A) may contain a rubber other than the modified S-SBR (A1). Examples of the rubber other than the modified S-SBR (A1) include synthetic rubber other than the modified S-SBR (A1) and natural rubber. Preferred rubbers other than the modified S-SBR (A1) that can be used in the solid rubber (A) are styrene-butadiene copolymers other than the modified S-SBR (A1), isoprene rubber, butadiene rubber, butyl rubber, halogenated butyl rubber, ethylene propylene diene rubber, butadiene acrylonitrile polymer rubber, chloroprene rubber, and natural rubber. Of these, styrene-butadiene copolymers other than the modified S-SBR (A1), isoprene rubber, butadiene rubber, and natural rubber are more preferred. These may be used alone or in combination of two or more.

[0063] Examples of SBR other than the modified S-SBR (A1) include unmodified S-SBR, unmodified emulsion-polymerized styrene-butadiene copolymer (hereinafter, the emulsion-polymerized styrene-butadiene copolymer may be referred to as "E-SBR"), and modified SBR other than the modified S-SBR (A1).

[0064] (Unmodified S-SBR) A suitable example of unmodified S-SBR is unmodified S-SBR, which is a raw material for modified S-SBR. Preferred aspects of the unmodified S-SBR, such as the styrene content, Mw, Tg, and vinyl content, are the same as those of modified S-SBR (A1). Unmodified S-SBR can be produced, for example, by carrying out the polymerization reaction of unmodified S-SBR using the method described in the section on the production of modified S-SBR, and then adding a polymerization terminator (for example, an alcohol such as methanol or isopropanol) to terminate the polymerization reaction. The produced unmodified S-SBR can be recovered using the same method as for modified S-SBR (A1).

[0065] (Emulsion-Polymerized Styrene-Butadiene Rubber (E-SBR)) E-SBR can be produced by a conventional emulsion polymerization method, for example, by emulsifying and dispersing predetermined amounts of styrene and butadiene monomers in a dispersion medium in the presence of an emulsifier, and then emulsion-polymerizing the resulting mixture with a radical polymerization initiator.

[0066] As the emulsifier, for example, a salt of a long-chain fatty acid having 10 or more carbon atoms or a rosinate may be used. Specific examples include potassium salts or sodium salts of fatty acids such as capric acid, lauric acid, myristic acid, palmitic acid, oleic acid, and stearic acid.

[0067] Water is usually used as the dispersion medium. A water-soluble organic solvent such as methanol or ethanol may be contained within a range that does not impair stability during polymerization. Examples of the radical polymerization initiator include persulfates such as ammonium persulfate and potassium persulfate, organic peroxides, and hydrogen peroxide.

[0068] A chain transfer agent can also be used to adjust the molecular weight of the resulting E-SBR. Examples of the chain transfer agent include mercaptans such as t-dodecyl mercaptan and n-dodecyl mercaptan; carbon tetrachloride, thioglycolic acid, diterpenes, terpinolene, γ-terpinene, and α-methylstyrene dimer.

[0069] The temperature of the emulsion polymerization can be appropriately selected depending on the type of radical polymerization initiator used, but is usually 0 to 100°C, preferably 0 to 60°C. The polymerization may be carried out in either continuous or batch mode. The polymerization reaction can be terminated by adding a polymerization terminator.

[0070] Examples of the polymerization terminator include amine compounds such as isopropylhydroxylamine, diethylhydroxylamine, and hydroxylamine; quinone compounds such as hydroquinone and benzoquinone; and sodium nitrite.

[0071] After the polymerization reaction is terminated, an antioxidant may be added as needed. After the polymerization reaction is terminated, unreacted monomers are removed from the obtained latex as needed. Next, the polymer is coagulated using a salt such as sodium chloride, calcium chloride, or potassium chloride as a coagulant, and an acid such as nitric acid or sulfuric acid is added as needed to adjust the pH of the coagulation system to a predetermined value. The dispersion medium is then separated, and the polymer can be recovered as crumbs. The crumbs are washed with water, dehydrated, and dried with a band dryer or the like to obtain E-SBR. During coagulation, if necessary, the latex and an extender oil previously emulsified and dispersed may be mixed, and the resultant may be recovered as an oil-extended rubber. In the composition of the rubber composition herein, the extender oil is not included in the solid rubber (A).

[0072] The styrene content of the E-SBR (the content of styrene units, i.e., the content of units derived from styrene) is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and still more preferably 20% by mass or more, from the viewpoint of improving the low heat buildup performance and grip performance (wet grip, dry grip) of a tire produced at least in part using the rubber composition or a cross-linked product of the rubber composition. From the above viewpoints, the styrene content of the E-SBR is preferably 70% by mass or less, more preferably 50% by mass or less, even more preferably 45% by mass or less, and still more preferably 40% by mass or less.

[0073] The weight average molecular weight (Mw) of the E-SBR is preferably 100,000 to 2,500,000, more preferably 150,000 to 2,000,000, and even more preferably 150,000 to 1,800,000. When the Mw of the E-SBR is within the above range, the processability of the resulting rubber composition is ensured, and the modulus of elasticity of the cross-linked product of the rubber composition becomes sufficiently high, and when at least a part of the rubber composition or the cross-linked product of the rubber composition is used in a tire, the low heat buildup performance and grip performance (wet grip and dry grip) are improved.

[0074] The glass transition temperature (Tg) of the E-SBR determined by differential thermal analysis is preferably −70 to 0° C. The vinyl content of the E-SBR is preferably 5 to 40 mol %.

[0075] Commercially available E-SBR products include oil-extended styrene-butadiene rubber "ESBR1723" manufactured by ENEOS Materials Corporation.

[0076] (Modified SBR (excluding modified S-SBR (A1))) Modified SBRs other than modified S-SBR (A1) include modified SBRs into which a functional group other than a functional group containing Si has been introduced. Examples of the functional group other than a functional group containing Si include an amino group, a hydroxy group, an epoxy group, and a carboxyl group.

[0077] Examples of methods for producing modified SBR include a method in which, before adding a polymerization terminator, a coupling agent capable of reacting with an active polymerization terminal, such as tin tetrachloride, tetraglycidyl-1,3-bisaminomethylcyclohexane, or 2,4-tolylene diisocyanate, or a polymerization terminal modifier, such as 4,4′-bis(diethylamino)benzophenone or N-vinylpyrrolidone, is added.

[0078] In modified SBRs other than the modified S-SBR (A1), the position of the polymer into which the functional group is introduced may be the polymerization terminal or a side chain of the polymer chain. Preferred aspects of the styrene content, Mw, Tg, vinyl content, etc. of the modified SBR (excluding the modified S-SBR (A1)) are the same as those of the modified S-SBR (A1).

[0079] (Isoprene Rubber) Examples of isoprene rubber that can be used include commercially available isoprene rubber polymerized using Ziegler catalysts such as titanium tetrahalide-trialkylaluminum, diethylaluminum chloride-cobalt, trialkylaluminum-boron trifluoride-nickel, and diethylaluminum chloride-nickel; lanthanoid rare earth metal catalysts such as triethylaluminum-organic acid neodymium-Lewis acid; or organic alkali metal compounds, similar to S-SBR. Isoprene rubber polymerized using a Ziegler catalyst has a high cis-isomer content and is preferred. Isoprene rubber with an ultra-high cis-isomer content obtained using a lanthanoid rare earth metal catalyst may also be used.

[0080] The vinyl content of the isoprene rubber is preferably 50 mol% or less, more preferably 40 mol% or less, and even more preferably 30 mol% or less. If the vinyl content exceeds 50 mol%, rolling resistance performance (fuel economy performance) tends to deteriorate. There is no particular limitation on the lower limit of the vinyl content. In this specification, the vinyl content of the isoprene rubber means the total mol% of units derived from isoprene bonded via 1,2-bonds or 3,4-bonds (units derived from isoprene bonded via bonds other than 1,4-bonds) out of a total of 100 mol% of units derived from isoprene contained in the isoprene rubber. The vinyl content is 1The glass transition temperature can be calculated using H-NMR in the same manner as for the liquid conjugated diene polymer (C) described later. The glass transition temperature varies depending on the vinyl content, but is preferably −20° C. or lower, and more preferably −30° C. or lower.

[0081] The weight average molecular weight (Mw) of the isoprene rubber is preferably 90,000 to 2,000,000, and more preferably 150,000 to 1,500,000. When the weight average molecular weight of the isoprene rubber is within the above range, the processability and mechanical strength of the rubber composition are improved.

[0082] The isoprene rubber may have a branched structure or a polar functional group formed by using a polyfunctional modifier, such as tin tetrachloride, silicon tetrachloride, an alkoxysilane having an epoxy group in the molecule, or an amino group-containing alkoxysilane.

[0083] (Butadiene Rubber) Examples of butadiene rubber that can be used include commercially available butadiene rubbers polymerized using Ziegler catalysts such as titanium tetrahalide-trialkylaluminum, diethylaluminum chloride-cobalt, trialkylaluminum-boron trifluoride-nickel, and diethylaluminum chloride-nickel; lanthanoid rare earth metal catalysts such as triethylaluminum-organic acid neodymium-Lewis acid; or organic alkali metal compounds, similar to S-SBR. Butadiene rubbers polymerized using Ziegler catalysts have a high cis content and are preferred. Alternatively, butadiene rubbers with an ultra-high cis content (e.g., a cis content of 95% or more) obtained using a lanthanoid rare earth metal catalyst may be used.

[0084] The vinyl content of the butadiene rubber is preferably 50 mol% or less, more preferably 40 mol% or less, and even more preferably 30 mol% or less. If the vinyl content exceeds 50 mol%, rolling resistance performance (fuel economy performance) tends to deteriorate. The lower limit of the vinyl content is not particularly limited. The vinyl content of the butadiene rubber can be calculated using the same method as for the vinyl content of the modified S-SBR (A1) described above. The glass transition temperature of the butadiene rubber varies depending on the vinyl content, but is preferably -40°C or less, and more preferably -50°C or less.

[0085] The weight average molecular weight (Mw) of the butadiene rubber is preferably 90,000 to 2,000,000, and more preferably 150,000 to 1,500,000. When the weight average molecular weight (Mw) of the butadiene rubber is within this range, the processability of the resulting rubber composition is improved, and when at least a part of the rubber composition or a cross-linked product of the rubber composition is used as a tire, the wear performance of the tire is also improved.

[0086] The butadiene rubber may have a branched structure or a polar functional group formed by using a polyfunctional modifier, such as tin tetrachloride, silicon tetrachloride, an alkoxysilane having an epoxy group in the molecule, or an amino group-containing alkoxysilane.

[0087] In addition to SBR, one or more of butyl rubber, halogenated butyl rubber, ethylene propylene diene rubber, butadiene acrylonitrile polymer rubber, chloroprene rubber, etc. may be used. The method for producing these rubbers is not particularly limited, and commercially available rubbers may be used.

[0088] (Natural Rubber) Examples of natural rubber include TSR (Technically Specified Rubber) such as SMR (Malaysian TSR), SIR (Indonesian TSR), and STR (Thai TSR), and natural rubber commonly used in tire applications such as RSS (Ribbed Smoked Sheet), as well as modified natural rubber such as high-purity natural rubber, epoxidized natural rubber, hydroxylated natural rubber, hydrogenated natural rubber, and grafted natural rubber. Of these, SMR20, STR20, and RSS#3 are preferred as natural rubbers in terms of their low quality variation and ease of availability. These may be used alone or in combination of two or more.

[0089] In the present invention, the content of the solid rubber (A) in the rubber composition is preferably 25% by mass or more, more preferably 30% by mass or more, even more preferably 35% by mass or more, and even more preferably 40% by mass or more. The content of the solid rubber (A) in the rubber composition is preferably 80% by mass or less, more preferably 75% by mass or less, even more preferably 70% by mass or less, still more preferably 65% ​​by mass or less, and particularly preferably 60% by mass or less. When the content of the solid rubber (A) in the rubber composition is within the above range, the wear resistance of a tire using at least a part of the rubber composition or a cross-linked product of the rubber composition is improved.

[0090] [Filler (B)] The filler (B) used in the rubber composition of the present invention contains silica (B1). The specific surface area (CTAB) of the silica (B1) is 180 to 500 m 2 / g. When the rubber composition contains silica (B1) having such a specific surface area, the elastic modulus of the cross-linked product obtained from the rubber composition can be increased. From the viewpoint of further increasing the elastic modulus of the cross-linked product obtained from the rubber composition, the specific surface area (CTAB) of silica (B1) is 180 to 450 m 2 / g, and 180 to 400m 2 / g, and more preferably 180 to 350m 2 / g, and more preferably 180 to 300m 2The specific surface area (CTAB) of the filler is determined in accordance with JIS K 6217-3:2001, and is the specific surface area (m) determined by adsorbing CTAB (Cetyl Tri-methyl Ammonium Bromide) to the filler. 2 / g).

[0091] In the present invention, the average content of Si derived from the functional group containing Si in the solid rubber (A) (typically derived from the functional group containing Si contained in the modified solution-polymerized styrene-butadiene copolymer (A1)) is defined as X ppm, and the average content of Si derived from the functional group containing Si in the solid rubber (A) (typically derived from the functional group containing Si contained in the modified solution-polymerized styrene-butadiene copolymer (A1)) is defined as X ppm per 1 cm of the rubber composition. 3 The total specific surface area of ​​silica (B1) per unit area is Ym 2 / cm 3 When the value of X×Y (i.e., the product of X and Y) is set to 9,000 or more, more preferably 12,000 or more, even more preferably 15,000 or more, even more preferably 17,000 or more, and even more preferably 19,000 or more. By using such a rubber composition, the cross-linked product of the rubber composition has a higher elastic modulus, and the fuel economy of a tire manufactured using the rubber composition or a cross-linked product of the rubber composition as at least a part thereof is improved. The value of X×Y is preferably 50,000 or less, more preferably 40,000 or less, even more preferably 24,000 or less, and preferably 20,000 or less.

[0092] In the present invention, the average content X of Si derived from Si-containing functional groups in the solid rubber (A) means the average content, in terms of Si atoms, of the Si-containing functional groups contained in the solid rubber (A). The content of Si derived from Si-containing functional groups in the solid rubber (A) can be obtained by analyzing the solid rubber (A) by ICP atomic emission spectroscopy. When the only solid rubber having Si-containing functional groups in the solid rubber (A) is the modified S-SBR (A1), the average content of Si derived from Si-containing functional groups in the solid rubber (A) is determined by determining the content of Si derived from Si-containing functional groups contained in the modified S-SBR (A1), and then calculating this content and the proportion of the modified S-SBR (A1) in the solid rubber (A) using the following formula (1): (Average content X (ppm) of Si derived from functional groups containing Si in solid rubber (A)) = (content (ppm) of Si derived from functional groups containing Si contained in modified S-SBR (A1)) × (ratio (mass%) of modified S-SBR (A1) in solid rubber (A)) (1) 1 cm of rubber composition 3 The total specific surface area of ​​silica (B1) per unit area is Ym 2 / cm 3 The value of is calculated from the following formula (2): In this formula, the volume of the rubber composition is expressed as H cm 3 , its volume H cm 3 The specific surface area (CTAB) of the silica contained in the rubber composition is Im 2 / g, and the weight of the silica is Jg. The volume of the rubber composition is calculated from the blending amount and specific gravity of each component contained in the rubber composition. The specific gravity of the liquid conjugated diene polymer (C) can be measured by the method described in JIS K 2249-2:2011. Y=(I×J) / H (2)

[0093] From the viewpoint of improving the rolling resistance, mechanical strength, and abrasion resistance of a cross-linked product and a tire produced from the rubber composition, the average particle size of the silica (B1) is preferably 0.5 to 200 nm, more preferably 1 to 100 nm, even more preferably 1 to 50 nm, and even more preferably 3 to 30 nm. The average particle size of the silica can be determined by measuring the particle diameters using a transmission electron microscope and calculating the average value. More specifically, the average particle size can be determined by measuring the diameters of the primary particles of each silica in a field of view observed using a transmission electron microscope and calculating the average value.

[0094] Examples of the silica (B1) include wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, and aluminum silicate. Among these silicas, wet silica is preferred from the viewpoint of further improving mechanical strength and abrasion resistance. The silica (B1) may be used alone or in combination of two or more.

[0095] In the rubber composition of the present invention, the content of silica (B1) per 100 parts by mass of the solid rubber (A) is 60 to 150 parts by mass, preferably 65 to 140 parts by mass, and more preferably 70 to 130 parts by mass. When the content of silica (B1) is within this range, processability, rolling resistance, mechanical strength, and abrasion resistance are improved.

[0096] In one preferred embodiment, the filler (B) used in the rubber composition of the present invention further contains carbon black (B2).

[0097] The average particle size of the carbon black (B2) is preferably 5 to 100 nm, more preferably 5 to 80 nm, and even more preferably 5 to 70 nm, from the viewpoint of improving dispersibility, mechanical strength, hardness, etc. The average particle size of the carbon black can be determined by measuring the particle diameters using a transmission electron microscope and calculating the average value.

[0098] Examples of the carbon black (B2) include furnace black, channel black, thermal black, acetylene black, and ketjen black. Among these carbon blacks, furnace black is preferred from the viewpoint of improving the crosslinking rate and mechanical strength.

[0099] Commercially available furnace black products include, for example, "Diablack" manufactured by Mitsubishi Chemical Corporation and "Seast" manufactured by Tokai Carbon Co., Ltd. Commercially available acetylene black products include, for example, "Denka Black" manufactured by Denki Kagaku Kogyo Co., Ltd. Commercially available ketjen black products include, for example, "ECP600JD" manufactured by Lion Corporation.

[0100] To improve wettability and dispersibility in the solid rubber (A), the carbon black (B2) may be subjected to an acid treatment using nitric acid, sulfuric acid, hydrochloric acid, or a mixture thereof, or a surface oxidation treatment using heat treatment in the presence of air. Furthermore, to improve the mechanical strength of the rubber composition of the present invention or a cross-linked product obtained from this rubber composition, the carbon black (B2) may be subjected to a heat treatment at 2,000 to 3,000°C in the presence of a graphitization catalyst. Suitable graphitization catalysts include boron, boron oxides (e.g., BO, BO, BO, etc.), boron oxoacids (e.g., orthoboric acid, metaboric acid, tetraboric acid, etc.) and their salts, boron carbides (e.g., BC, BC), boron nitride (BN), and other boron compounds.

[0101] The carbon black (B2) can also be used after adjusting its particle size by pulverization, etc. For pulverization of carbon black, a high-speed rotary pulverizer (hammer mill, pin mill, cage mill), various ball mills (tumbling mill, vibration mill, planetary mill), stirring mill (bead mill, attritor, flow-tube mill, annular mill), etc. can be used.

[0102] The carbon black (B2) may be used alone or in combination of two or more kinds.

[0103] In the rubber composition of the present invention, the content of carbon black (B2) per 100 parts by mass of solid rubber (A) is preferably 0.5 to 100 parts by mass, more preferably 1 to 60 parts by mass, and even more preferably 3 to 30 parts by mass. When the content of carbon black (B2) is within the above range, the processability, weather resistance, etc. of the resulting rubber composition are improved.

[0104] The rubber composition of the present invention may contain a filler (B) other than silica (B1) and carbon black (B2). Examples of fillers other than silica (B1) and carbon black (B2) include inorganic fillers such as clay, mica, calcium carbonate, magnesium hydroxide, aluminum hydroxide, barium sulfate, titanium oxide, glass fiber, fibrous filler, and glass balloons; and organic fillers such as resin particles, wood flour, and cork powder. The inclusion of such fillers in the rubber composition can improve physical properties such as mechanical strength, heat resistance, and weather resistance, adjust hardness, and increase the amount of rubber.

[0105] When a filler other than silica (B1) and carbon black (B2) is used as the filler (B), the content thereof is usually 120 parts by mass or less, preferably 0.5 to 100 parts by mass, more preferably 1 to 50 parts by mass, and even more preferably 1 to 20 parts by mass, per 100 parts by mass of the solid rubber (A). The fillers other than silica (B1) and carbon black (B2) may be used singly or in combination of two or more types.

[0106] [Liquid Conjugated Diene Polymer (C)] The liquid conjugated diene polymer (C) used in the rubber composition of the present invention is a relatively low molecular weight polymer containing monomer units derived from conjugated dienes (hereinafter also referred to as "conjugated diene units"), and has a weight average molecular weight (Mw) in the range of 3,000 to 200,000. By using such a liquid conjugated diene polymer (C) together with the solid rubber (A) and the filler (B), the resulting rubber composition or a cross-linked product of the rubber composition has the inherently good elastic modulus, and a tire produced in which the rubber composition or the cross-linked product of the rubber composition constitutes at least a part thereof has excellent low heat buildup. Furthermore, the rubber composition has excellent processability.

[0107] The liquid conjugated diene polymer (C) contains a unit derived from a conjugated diene (conjugated diene unit) as a monomer unit constituting the polymer. Examples of conjugated dienes include butadiene, isoprene, and conjugated dienes (c1) other than butadiene and isoprene, such as 2,3-dimethylbutadiene, 2-phenylbutadiene, 1,3-pentadiene, 2-methyl-1,3-pentadiene, 1,3-hexadiene, 1,3-octadiene, 1,3-cyclohexadiene, 2-methyl-1,3-octadiene, 1,3,7-octatriene, myrcene, farnesene, and chloroprene. The conjugated diene that forms the conjugated diene unit contained in the liquid conjugated diene polymer (C) is preferably at least one selected from the group consisting of butadiene, isoprene, and farnesene, and more preferably isoprene.

[0108] In one preferred embodiment, the liquid conjugated diene polymer (C) contains 50% by mass or more of conjugated diene units relative to units derived from all monomers constituting the polymer (C) (hereinafter also referred to as "total monomer units"), i.e., relative to 100% by mass of the liquid conjugated diene polymer (C). The content of conjugated diene units in the liquid conjugated diene polymer (C) is preferably 60 to 100% by mass, and more preferably 70 to 100% by mass, relative to all monomer units. In another preferred embodiment, the liquid conjugated diene polymer (C) contains 100% by mass of conjugated diene units (i.e., the liquid conjugated diene polymer (C) is composed solely of conjugated diene units).

[0109] Examples of monomer units other than the conjugated diene units that can be contained in the liquid conjugated diene polymer (C) include aromatic vinyl compound (c2) units (units derived from aromatic vinyl compound (c2)).

[0110] Examples of the aromatic vinyl compound (c2) include styrene, α-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 4-propylstyrene, 4-t-butylstyrene, 4-cyclohexylstyrene, 4-dodecylstyrene, 2,4-dimethylstyrene, 2,4-diisopropylstyrene, 2,4,6-trimethylstyrene, 2-ethyl-4-benzylstyrene, 4-(phenylbutyl)styrene, 1-vinylnaphthalene, 2-vinylnaphthalene, vinylanthracene, N,N-diethyl-4-aminoethylstyrene, vinylpyridine, 4-methoxystyrene, monochlorostyrene, dichlorostyrene, and divinylbenzene. Among these aromatic vinyl compounds, styrene, α-methylstyrene, and 4-methylstyrene are preferred.

[0111] The content of other monomer units than the conjugated diene units in the liquid conjugated diene polymer (C) is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, based on 100% by mass (total monomer units) of the liquid conjugated diene polymer (C). For example, when the aromatic vinyl compound (c2) units are in the above range or less, the processability of the rubber composition tends to be improved.

[0112] When the liquid conjugated diene polymer (C) contains two or more types of conjugated diene units, the bonding mode of these conjugated diene units is not particularly limited, and the liquid conjugated diene polymer (C) may be a random copolymer or a block copolymer.

[0113] Among the liquid conjugated diene polymers (C), from the viewpoint of the processability of the rubber composition, at least one selected from the group consisting of liquid polybutadiene (liquid butadiene homopolymer), liquid polyisoprene (liquid isoprene homopolymer), liquid polyfarnesene (liquid farnesene homopolymer), and liquid butadiene-farnesene copolymer is preferred, at least one selected from the group consisting of liquid polyisoprene (liquid isoprene homopolymer), liquid polyfarnesene (liquid farnesene homopolymer), and liquid butadiene-farnesene copolymer is more preferred, at least one selected from the group consisting of liquid polyisoprene and liquid butadiene-farnesene copolymer is even more preferred, and liquid polyisoprene is even more preferred. In addition, in one preferred embodiment, the liquid conjugated diene polymer (C) is at least one selected from the group consisting of liquid polybutadiene (liquid butadiene homopolymer), liquid polyisoprene (liquid isoprene homopolymer), and liquid polyfarnesene (liquid farnesene homopolymer).

[0114] The liquid conjugated diene polymer (C) is preferably a polymer obtained by polymerizing a conjugated diene and, if necessary, other monomers other than the conjugated diene, for example, by emulsion polymerization or solution polymerization.

[0115] As the emulsion polymerization method, known methods or methods equivalent to known methods can be applied. For example, a predetermined amount of a monomer containing a conjugated diene is emulsified and dispersed in the presence of an emulsifier, and emulsion polymerized using a radical polymerization initiator.

[0116] Examples of emulsifiers include salts of long-chain fatty acids having 10 or more carbon atoms, rosinate salts, etc. Examples of long-chain fatty acid salts include potassium salts or sodium salts of fatty acids such as capric acid, lauric acid, myristic acid, palmitic acid, oleic acid, and stearic acid.

[0117] As the dispersion medium, water is usually used, and a water-soluble organic solvent such as methanol or ethanol may be contained within a range that does not impair stability during polymerization. Examples of the radical polymerization initiator include persulfates such as ammonium persulfate and potassium persulfate, organic peroxides, and hydrogen peroxide.

[0118] A chain transfer agent may be used to adjust the molecular weight of the resulting liquid conjugated diene polymer (C). Examples of the chain transfer agent include mercaptans such as t-dodecyl mercaptan and n-dodecyl mercaptan; carbon tetrachloride, thioglycolic acid, diterpenes, terpinolene, γ-terpinene, and α-methylstyrene dimer.

[0119] The temperature of the emulsion polymerization can be appropriately set depending on the type of radical polymerization initiator used, etc. Specifically, it is usually in the range of 0 to 100° C., preferably in the range of 0 to 60° C. The polymerization mode may be either continuous polymerization or batch polymerization.

[0120] The polymerization reaction can be terminated by adding a polymerization terminator, such as an amine compound such as isopropylhydroxylamine, diethylhydroxylamine, or hydroxylamine, a quinone compound such as hydroquinone or benzoquinone, or sodium nitrite.

[0121] After the polymerization reaction is terminated, an antioxidant may be added as needed. After the polymerization reaction is terminated, unreacted monomers are removed from the obtained latex as needed. Next, the liquid conjugated diene polymer (C) is coagulated using a salt such as sodium chloride, calcium chloride, or potassium chloride as a coagulant, and an acid such as nitric acid or sulfuric acid is added as needed to adjust the pH of the coagulation system to a predetermined value. The dispersion medium is then separated to recover the polymer. The polymer is then washed with water, dehydrated, and dried to obtain the liquid conjugated diene polymer (C). During the coagulation, the latex and an extender oil previously prepared as an emulsified dispersion may be mixed as needed, and the oil-extended liquid conjugated diene polymer (C) may be recovered.

[0122] As the solution polymerization method, a known method or a method equivalent to a known method can be applied. For example, a monomer containing a conjugated diene is polymerized in a solvent using a Ziegler catalyst, a metallocene catalyst, or an anionically polymerizable active metal or active metal compound, optionally in the presence of a polar compound.

[0123] Examples of the solvent include aliphatic hydrocarbons such as n-butane, n-pentane, isopentane, n-hexane, n-heptane, and isooctane; alicyclic hydrocarbons such as cyclopentane, cyclohexane, and methylcyclopentane; and aromatic hydrocarbons such as benzene, toluene, and xylene.

[0124] Examples of the anionically polymerizable active metal include alkali metals such as lithium, sodium, and potassium; alkaline earth metals such as beryllium, magnesium, calcium, strontium, and barium; and lanthanoid rare earth metals such as lanthanum and neodymium. Among the anionically polymerizable active metals, alkali metals and alkaline earth metals are preferred, and alkali metals are more preferred.

[0125] The anionically polymerizable active metal compound is preferably an organic alkali metal compound. Examples of the organic alkali metal compound include organic monolithium compounds such as methyllithium, ethyllithium, n-butyllithium, sec-butyllithium, t-butyllithium, hexyllithium, phenyllithium, and stilbenelithium; polyfunctional organic lithium compounds such as dilithiomethane, dilithionaphthalene, 1,4-dilithiobutane, 1,4-dilithio-2-ethylcyclohexane, and 1,3,5-trilithiobenzene; sodium naphthalene, potassium naphthalene, and the like. Among these organic alkali metal compounds, organic lithium compounds are preferred, and organic monolithium compounds are more preferred.

[0126] The amount of the organic alkali metal compound used can be appropriately set depending on the melt viscosity, molecular weight, etc. of the liquid conjugated diene polymer (C), but it is usually used in an amount of 0.01 to 3 parts by mass per 100 parts by mass of all monomers including conjugated dienes used to produce the liquid conjugated diene polymer (C).

[0127] The above organic alkali metal compounds can also be reacted with a secondary amine such as dibutylamine, dihexylamine, or dibenzylamine to form organic alkali metal amides.

[0128] In anionic polymerization, polar compounds are usually used to adjust the microstructure of the conjugated diene units (e.g., vinyl content) without deactivating the reaction. Examples of polar compounds include ether compounds such as dibutyl ether, tetrahydrofuran, and ethylene glycol diethyl ether; tertiary amines such as N,N,N',N'-tetramethylethylenediamine and trimethylamine; alkali metal alkoxides; and phosphine compounds. The polar compound is usually used in an amount of 0.01 to 1,000 moles per mole of the organic alkali metal compound.

[0129] The temperature for solution polymerization is usually in the range of −80 to 150° C., preferably in the range of 0 to 100° C., and more preferably in the range of 10 to 90° C. The polymerization may be carried out in either a batch or continuous manner.

[0130] The polymerization reaction can be terminated by adding a polymerization terminator. Examples of the polymerization terminator include alcohols such as methanol and isopropanol. The liquid conjugated diene polymer (C) can be isolated by pouring the resulting polymerization reaction solution into a poor solvent such as methanol to precipitate the liquid conjugated diene polymer (C), or by washing the polymerization reaction solution with water, separating it, and then drying it. Of the above methods, the solution polymerization method is preferred as a method for producing the unmodified liquid conjugated diene polymer (C).

[0131] The liquid conjugated diene polymer (C) thus obtained may be modified with a modifying compound after polymerization, or may be hydrogenated to hydrogenate at least a portion of its conjugated diene units. In consideration of improving the processability of the rubber composition, a preferred embodiment of the liquid conjugated diene polymer (C) is an unmodified liquid conjugated diene polymer that has not been modified after polymerization. In consideration of the processability of the rubber composition and the handleability of the liquid conjugated diene polymer (C), a preferred embodiment of the liquid conjugated diene polymer (C) is an unhydrogenated liquid conjugated diene polymer that has not been hydrogenated.

[0132] The weight average molecular weight (Mw) of the liquid conjugated diene polymer (C) is in the range of 3,000 to 200,000, preferably in the range of 7,000 to 160,000, more preferably in the range of 20,000 to 100,000, and even more preferably in the range of 30,000 to 60,000. Alternatively, the weight average molecular weight (Mw) of the liquid conjugated diene polymer (C) is preferably in the range of 10,000 to 140,000, more preferably in the range of 20,000 to 120,000, even more preferably in the range of 30,000 to 120,000, even more preferably in the range of 40,000 to 120,000, particularly preferably in the range of 40,000 to 100,000, and more particularly preferably in the range of 40,000 to 60,000. In the present invention, the Mw of the liquid conjugated diene polymer (C) is the weight average molecular weight in terms of polystyrene determined by gel permeation chromatography (GPC). When the Mw of the liquid conjugated diene polymer (C) is within the above range, the processability of the rubber composition can be improved, the rubber composition or a cross-linked product of the rubber composition has the good elastic modulus that it inherently has, and a tire produced using the rubber composition or a cross-linked product of the rubber composition as at least a part thereof has excellent low heat buildup. In the present invention, two or more liquid conjugated diene polymers (C) having different Mw may be used in combination.

[0133] The molecular weight distribution (Mw / Mn) of the liquid conjugated diene polymer (C) is preferably 1.0 to 20.0, more preferably 1.0 to 10.0, even more preferably 1.0 to 5.0, even more preferably 1.0 to 2.0, and particularly preferably 1.0 to 1.5. When Mw / Mn is within the above range, the viscosity of the resulting liquid conjugated diene polymer (C) varies less, which is more preferable. The molecular weight distribution (Mw / Mn) means the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) in terms of standard polystyrene, determined by GPC measurement.

[0134] The melt viscosity of the liquid conjugated diene polymer (C) measured at 38°C is preferably 0.1 to 2,000 Pa·s, more preferably 1 to 1,500 Pa·s, even more preferably 5 to 1,000 Pa·s, even more preferably 10 to 700 Pa·s, particularly preferably 50 to 700 Pa·s, more particularly preferably 150 to 700 Pa·s, and even more particularly preferably 300 to 700 Pa·s. When the melt viscosity of the liquid conjugated diene polymer (C) is within the above range, the flexibility of the resulting rubber composition is improved, thereby improving processability. In the present invention, the melt viscosity of the liquid conjugated diene polymer (C) is a value measured at 38°C using a Brookfield viscometer.

[0135] The vinyl content of the liquid conjugated diene polymer (C) is preferably 1 to 70 mol%, more preferably 1 to 50 mol%, even more preferably 1 to 30 mol%, and even more preferably 1 to 20 mol%. In the present invention, the "vinyl content" refers to the total mol% of conjugated diene units bonded via 1,2-bonds or 3,4-bonds (in the case of other than farnesene) and 3,13-bonds (in the case of farnesene) (conjugated diene units bonded via bonds other than 1,4-bonds (in the case of other than farnesene) and 1,13-bonds (in the case of farnesene)) out of a total of 100 mol% of conjugated diene (c1) units contained in the liquid conjugated diene polymer (C). The vinyl content is 1 Using H-NMR, the vinyl content can be calculated from the area ratio of the peaks derived from conjugated diene units bonded via 1,2-bonds or 3,4-bonds (in the case of rubbers other than farnesene) and 3,13-bonds (in the case of farnesene) to the peaks derived from conjugated diene units bonded via 1,4-bonds (in the case of rubbers other than farnesene) and 1,13-bonds (in the case of farnesene). Having the vinyl content within the above range improves, for example, the rolling resistance of tires manufactured so that the rubber composition or a crosslinked product of the rubber composition forms at least a part of the tire, and also improves the processability of the rubber composition. The vinyl content of the liquid conjugated diene polymer (C) can be adjusted to a desired value by controlling, for example, the type of solvent used in producing the liquid conjugated diene polymer (C), the polar compound used as needed, the polymerization temperature, etc.

[0136] The glass transition temperature (Tg) of the liquid conjugated diene polymer (C) may vary depending on the vinyl content of the conjugated diene units, the type of conjugated diene units, the content of units derived from monomers other than conjugated dienes, etc., but is preferably −150 to 50° C., more preferably −120 to 0° C., even more preferably −100 to −20° C., even more preferably −90 to −40° C., and even more preferably −80 to −40° C. When the Tg is within the above range, for example, the rolling resistance performance of a tire produced so that the rubber composition or a crosslinked product of the rubber composition constitutes at least a part of the tire is improved. In addition, an increase in viscosity can be suppressed, making the tire easier to handle.

[0137] The liquid conjugated diene polymer (C) may be used alone or in combination of two or more thereof.

[0138] The liquid conjugated diene polymer (C) preferably has a catalyst residue amount derived from the polymerization catalyst used in its production in the range of 0 to 200 ppm, calculated as metal. For example, when an organic alkali metal such as an organolithium compound is used as the polymerization catalyst for producing the liquid conjugated diene polymer (C), the metal used as the reference for the catalyst residue amount is an alkali metal such as lithium. Having the catalyst residue amount within the above range prevents a decrease in tackiness during processing, and improves the heat resistance and tire properties of the crosslinked product obtained from the rubber composition of the present invention. The catalyst residue amount derived from the polymerization catalyst used in the production of the liquid conjugated diene polymer (C), calculated as metal, is more preferably 0 to 150 ppm, even more preferably 0 to 100 ppm, even more preferably 0 to 50 ppm, and particularly preferably 0 to 20 ppm. The catalyst residue amount can be measured, for example, using a polarized Zeeman atomic absorption spectrophotometer.

[0139] Examples of methods for adjusting the catalyst residue content of the liquid conjugated diene polymer (C) to such a specific amount include purifying the liquid conjugated diene polymer (C) and thoroughly removing the catalyst residue. As a purification method, washing with water or hot water, or an organic solvent such as methanol or acetone, or supercritical fluid carbon dioxide is preferred. From an economical viewpoint, the number of washes is preferably 1 to 20 times, more preferably 1 to 10 times. Furthermore, the washing temperature is preferably 20 to 100°C, more preferably 40 to 90°C. Furthermore, by removing impurities that inhibit polymerization prior to the polymerization reaction using distillation or an adsorbent, and then increasing the purity of the monomer, the amount of polymerization catalyst required can be reduced, thereby reducing the amount of catalyst residue. From the same viewpoint as above, the amount of catalyst residue in the rubber composition of the present invention is preferably 0 to 200 ppm, more preferably 0 to 150 ppm, and even more preferably 0 to 100 ppm, in terms of metal. In this case, the amount of catalyst residue may be the amount of catalyst residue derived from a polymerization catalyst used to produce a component (such as solid rubber (A)) other than the liquid conjugated diene polymer (C) in the rubber composition.

[0140] In the rubber composition of the present invention, the content of the liquid conjugated diene polymer (C) per 100 parts by mass of the solid rubber (A) is 5 to 30 parts by mass, preferably 5 to 25 parts by mass, more preferably 5 to 20 parts by mass, and even more preferably 5 to 15 parts by mass. When the content of the liquid conjugated diene polymer (C) in the rubber composition is within the above range, the processability of the rubber composition can be improved, the good elastic modulus of the rubber composition or a cross-linked product of the rubber composition is not impaired, and the low heat buildup properties of a tire produced so that the rubber composition or a cross-linked product of the rubber composition constitutes at least a part of the tire are not impaired.

[0141] [Other Components] The rubber composition of the present invention may further contain a crosslinking agent (D) to crosslink the rubber. Examples of the crosslinking agent (D) include sulfur, sulfur compounds, oxygen, organic peroxides, phenolic resins, amino resins, quinones and quinone dioxime derivatives, halogen compounds, aldehyde compounds, alcohol compounds, epoxy compounds, metal halides and organometallic halides, and silane compounds. Examples of sulfur compounds include morpholine disulfide and alkylphenol disulfides. Examples of organic peroxides include cyclohexanone peroxide, methyl acetoacetate peroxide, t-butyl peroxyisobutyrate, t-butyl peroxybenzoate, benzoyl peroxide, lauroyl peroxide, dicumyl peroxide, di-t-butyl peroxide, and 1,3-bis(t-butylperoxyisopropyl)benzene. These crosslinking agents (D) may be used alone or in combination of two or more. From the viewpoint of the mechanical properties of the crosslinked product, the crosslinking agent (D) is contained in an amount of usually 0.1 to 10 parts by mass, preferably 0.5 to 10 parts by mass, and more preferably 0.8 to 5 parts by mass per 100 parts by mass of the solid rubber (A).

[0142] The rubber composition of the present invention may further contain a vulcanization accelerator (E) when, for example, sulfur or a sulfur compound is contained as the crosslinking agent (D) for crosslinking (vulcanizing) the rubber. Examples of the vulcanization accelerator (E) include guanidine compounds, sulfenamide compounds, thiazole compounds, thiuram compounds, thiourea compounds, dithiocarbamic acid compounds, aldehyde-amine compounds, aldehyde-ammonia compounds, imidazoline compounds, and xanthate compounds. These vulcanization accelerators (E) may be used alone or in combination of two or more. The vulcanization accelerator (E) is typically contained in an amount of 0.1 to 15 parts by mass, preferably 0.1 to 10 parts by mass, per 100 parts by mass of the solid rubber (A).

[0143] The rubber composition of the present invention may further contain a vulcanization aid (F) when, for example, sulfur or a sulfur compound is contained as the crosslinking agent (D) for crosslinking (vulcanizing) the rubber. Examples of the vulcanization aid (F) include fatty acids such as stearic acid, metal oxides such as zinc oxide, and fatty acid metal salts such as zinc stearate. These vulcanization aids (F) may be used alone or in combination of two or more. The vulcanization aid (F) is typically contained in an amount of 0.1 to 15 parts by mass, preferably 1 to 10 parts by mass, per 100 parts by mass of the solid rubber (A).

[0144] In one embodiment, the rubber composition of the present invention preferably contains a silane coupling agent, such as a sulfide compound, a mercapto compound, a vinyl compound, an amino compound, a glycidoxy compound, a nitro compound, or a chloro compound.

[0145] Examples of sulfide compounds include bis(3-triethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, bis(3-triethoxysilylpropyl)trisulfide, bis(3-trimethoxysilylpropyl)trisulfide, bis(3-triethoxysilylpropyl)disulfide, bis(3-trimethoxysilylpropyl)disulfide, and 3-trimethoxysilylpropyl-N,N-dimethylsilyl. thiocarbamoyl tetrasulfide, 3-triethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 2-trimethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropyl benzothiazole tetrasulfide, 3-triethoxysilylpropyl benzothiazole tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, 3-octanoylthio-1-propyltriethoxysilane, and the like.

[0146] Examples of mercapto compounds include 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, and 2-mercaptoethyltriethoxysilane.

[0147] Examples of vinyl compounds include vinyltriethoxysilane and vinyltrimethoxysilane, etc. Examples of amino compounds include 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-(2-aminoethyl)aminopropyltriethoxysilane, and 3-(2-aminoethyl)aminopropyltrimethoxysilane, etc.

[0148] Examples of glycidoxy compounds include γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, and γ-glycidoxypropylmethyldimethoxysilane.

[0149] Examples of nitro-based compounds include 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane. Examples of chloro-based compounds include 3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysilane, 2-chloroethyltrimethoxysilane, and 2-chloroethyltriethoxysilane. Other compounds include octyltriethoxysilane, methyltriethoxysilane, methyltrimethoxysilane, and hexadecyltrimethoxysilane.

[0150] These silane coupling agents may be used alone or in combination of two or more. Among these silane coupling agents, bis(3-triethoxysilylpropyl) disulfide, bis(3-triethoxysilylpropyl) tetrasulfide, and 3-mercaptopropyltriethoxysilane are preferred from the viewpoints of the large effect of addition and cost.

[0151] The silane coupling agent is preferably contained in an amount of 0.1 to 30 parts by mass, more preferably 0.5 to 20 parts by mass, and even more preferably 1 to 15 parts by mass, per 100 parts by mass of silica. When the content of the silane coupling agent is within the above range, dispersibility, coupling effect, reinforcement, and abrasion resistance are improved.

[0152] The rubber composition of the present invention may contain, as needed, softeners such as silicone oil, aromatic oil, TDAE (Treated Distilled Aromatic Extracts), MES (Mild Extracted Solvates), RAE (Residual Aromatic Extracts), process oils such as paraffin oil and naphthenic oil, and resin components such as aliphatic hydrocarbon resins, alicyclic hydrocarbon resins, C9 resins, rosin resins, coumarone-indene resins, and phenolic resins, for the purpose of improving processability, fluidity, etc., within a range that does not impair the effects of the present invention. When the rubber composition of the present invention contains the process oil as a softener, the content thereof is preferably less than 50 parts by mass per 100 parts by mass of the solid rubber (A).

[0153] The rubber composition of the present invention may contain additives such as antioxidants, waxes, antioxidants, lubricants, light stabilizers, scorch inhibitors, processing aids, colorants such as pigments and dyes, flame retardants, antistatic agents, matting agents, antiblocking agents, UV absorbers, mold release agents, foaming agents, antibacterial agents, antifungal agents, and fragrances, as needed, to improve weather resistance, heat resistance, and oxidation resistance, as long as the effects of the present invention are not impaired. Examples of antioxidants include hindered phenol compounds, phosphorus compounds, lactone compounds, and hydroxyl compounds. Examples of antioxidants include amine-ketone compounds, imidazole compounds, amine compounds, phenol compounds, sulfur compounds, and phosphorus compounds. These additives may be used alone or in combination of two or more.

[0154] [Method for Producing Rubber Composition] The method for producing the rubber composition of the present invention is not particularly limited as long as it can uniformly mix the above-mentioned components. Examples of equipment used for producing the rubber composition include tangential or intermeshing internal mixers such as kneader-ruders, Brabenders, Banbury mixers, and internal mixers, single-screw extruders, twin-screw extruders, mixing rolls, and rollers. The rubber composition can usually be produced at a temperature ranging from 70 to 270°C.

[0155] [Crosslinked Product] A crosslinked product can be obtained by crosslinking the rubber composition of the present invention. The crosslinking conditions for the rubber composition can be appropriately set depending on the application, etc. For example, when sulfur or a sulfur compound is used as a crosslinking agent and the rubber composition is crosslinked (vulcanized) in a mold, the crosslinking temperature is usually 120 to 200°C and the pressure condition is usually 0.5 to 2.0 MPa, and the crosslinking (vulcanization) can be performed.

[0156] The extraction rate of the liquid conjugated diene polymer (C) from the crosslinked product is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. The extraction rate can be calculated by immersing 2 g of the crosslinked product in 400 mL of toluene at 23° C. for 48 hours and then calculating the amount of the liquid conjugated diene polymer (C) extracted into the toluene.

[0157] [Tire Tread and Pneumatic Tire] A tire tread is a part of a tire, and is the part where the tire, which has a groove pattern usually called a pattern, comes into contact with the road surface. The tire tread of the present invention uses the rubber composition (or a cross-linked product of the rubber composition) in at least a part thereof, and exhibits a high elastic modulus and excellent low heat buildup. The structure of the tire tread of the present invention is not particularly limited, and may be a single-layer structure or a multi-layer structure. In the case of a multi-layer structure, it is preferable to use the rubber composition (or a cross-linked product of the rubber composition) in the layer that comes into contact with the road surface.

[0158] A pneumatic tire is a tire in which air is filled between a tire body, which is composed of the tire parts described below, and a wheel rim, and is the most common tire used for bicycles and automobiles. The pneumatic tire of the present invention uses the rubber composition or a cross-linked product of the rubber composition as at least a part of the tire, and a pneumatic tire using the tire tread as described above is particularly preferred. Because the pneumatic tire of the present invention uses the rubber composition or a cross-linked product of the rubber composition as at least a part of the pneumatic tire, the part composed of the rubber composition has a high elastic modulus, and the pneumatic tire exhibits excellent low heat buildup.

[0159] Furthermore, examples of tire parts in which the rubber composition (or a cross-linked product of the rubber composition) can be used include treads (cap treads and under treads), sidewalls, rubber reinforcing layers for run-flat tires (liners and the like), rim cushions, bead fillers, bead insulation, bead apexes, clinch apexes, belts, belt cushions, breakers, breaker cushions, chafers, chafer pads, and strip apexes.

[0160] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The components used in these examples and comparative examples are as follows.

[0161] <Solid rubber (A)> Modified solution-polymerized styrene-butadiene copolymer (A1-1) having a functional group containing Si: HPR850 (Si content derived from functional groups containing Si: 290 ppm, styrene content: 28% by mass, vinyl content: 59% by mass, specific gravity: 0.94; manufactured by ENEOS Material Corporation) Modified solution-polymerized styrene-butadiene copolymer (A1'-1) having functional groups containing Si: HPR355 (Si content derived from functional groups containing Si: 210 ppm, styrene content: 27% by mass, vinyl content: 58% by mass, specific gravity: 0.93; manufactured by ENEOS Material Corporation) Butadiene rubber BR01 (Mw: 550,000, cis content 95% by mass, specific gravity: 0.90; manufactured by ENEOS Material Corporation)

[0162] <Filler (B)> Silica (B1-1) Zeosil Premium 200MP (wet silica (precipitated silica) specific surface area (CTAB): 200 m 2 / g, average particle size: 10 nm, specific gravity: 2.0; manufactured by Solvay) Silica (B1'-1) Ultrasil 7000GR (wet silica (precipitated silica) specific surface area (CTAB): 160 m 2 / g, average particle size: 14 nm, specific gravity: 2.0; manufactured by Evonik) Carbon black (B2-1) SEAT 3 (furnace black HAF, nitrogen adsorption specific surface area 79 m 2 / g, specific gravity: 1.8; manufactured by Tokai Carbon Co., Ltd.) The specific surface area (CTAB) of silica was measured in accordance with JIS K 6217-3:2001. Specifically, CTAB was adsorbed onto the silica surface in a CTAB solution, and the amount of CTAB that was not adsorbed and remained in the solution was titrated and quantified with a di-2-ethylhexyl sodium sulfosuccinate solution to calculate the amount of CTAB adsorbed onto the silica, which was taken as the specific surface area (CTAB).

[0163] <Liquid Conjugated Diene Polymer (C)> Liquid conjugated diene polymers (C-1), (C-2), and (C-3) obtained in Production Examples 1, 2, and 3 described below

[0164] [Other Components] <Crosslinking Agent (D)> Sulfur: Myucron OT-20 (insoluble sulfur, specific gravity: 1.6; manufactured by Shikoku Chemical Industry Co., Ltd.) <Vulcanization Accelerator (E)> Vulcanization Accelerator (1): Noccelaer D (specific gravity: 1.2; manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) Vulcanization Accelerator (2): Noccelaer CZ-G (specific gravity: 1.3; manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) Vulcanization Accelerator (3): Noccelaer TBT-N (specific gravity: 1.1; manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) <Vulcanization Aid (F)> Zinc Oxide: Zinc Oxide (specific gravity: 5.6; manufactured by Sakai Chemical Industry Co., Ltd.) Stearic Acid: Lunac S-20 (specific gravity: 0.84; manufactured by Kao Corporation) <Additives> Silane Coupling Agent: Si-69 (specific gravity: 1.1; manufactured by Evonik) TDAE: VivaTec 500 (specific gravity: 0.96; manufactured by H&R) Anti-aging agent: Nocrac 6C (specific gravity: 1.1; manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) Wax: Suntite S (specific gravity: 0.93; manufactured by Seiko Chemical Co., Ltd.)

[0165] Production Example 1: Production of Liquid Conjugated Diene Polymer (C-1) A thoroughly dried pressure vessel was purged with nitrogen, and 600 g of hexane and 44.9 g of n-butyllithium (17% by mass hexane solution) were charged into the pressure vessel. The vessel was heated to 70°C, and then 2050 g of isoprene was added and polymerized for 1 hour while stirring and controlling the polymerization temperature to 70°C. Methanol was then added to terminate the polymerization reaction, yielding a polymerized solution (2695 g). Water was added to the resulting polymerized solution, and the mixture was stirred. The polymerized solution was washed with water. After stirring was terminated, it was confirmed that the polymerized solution phase and the aqueous phase had separated, and the water was then separated. The polymerized solution after washing was vacuum dried at 70°C for 24 hours to yield a liquid conjugated diene polymer (C-1), which was a liquid polyisoprene (liquid isoprene homopolymer).

[0166] Production Example 2: Production of Liquid Conjugated Diene Polymer (C-2) A thoroughly dried pressure vessel was purged with nitrogen, and 600 g of hexane and 13.9 g of n-butyllithium (17% by mass hexane solution) were charged into the pressure vessel. The vessel was heated to 70°C, and then 1,370 g of isoprene was added and polymerized for 1 hour under stirring conditions while controlling the polymerization temperature to 70°C. Methanol was then added to terminate the polymerization reaction, yielding a polymerized solution (1,980 g). Water was added to the resulting polymerized solution, and the mixture was stirred. The polymerized solution was washed with water. After stirring was terminated, it was confirmed that the polymerized solution phase and the aqueous phase had separated, and then the water was separated. The polymerized solution after washing was vacuum dried at 70°C for 24 hours to yield a liquid conjugated diene polymer (C-2), which was a liquid polyisoprene (liquid isoprene homopolymer).

[0167] Production Example 3: Production of Liquid Conjugated Diene Polymer (C-3) A thoroughly dried pressure vessel was purged with nitrogen, and 1200 g of hexane and 11 g of sec-butyllithium (10.5 mass % cyclohexane solution) were charged into the pressure vessel. The temperature was raised to 70°C, and then 1200 g of a previously prepared mixture of butadiene (a) and β-farnesene (b) (480 g of butadiene (a) and 720 g of β-farnesene (b) were mixed in a bomb) was added and polymerization was carried out for 1 hour. Thereafter, methanol was added to terminate the polymerization reaction, and a polymerized solution (2400 g) was obtained. Water was added to the obtained polymerized solution and the mixture was stirred, and the polymerized solution was washed with water. After stirring was stopped and it was confirmed that the polymerized solution phase and the aqueous phase had separated, the water was separated. After washing, the polymer solution was vacuum dried at 70° C. for 24 hours to obtain a liquid conjugated diene polymer (C-3), which was a liquid butadiene-farnesene copolymer (liquid butadiene-farnesene random copolymer).

[0168] The methods for measuring and calculating the various physical properties of the liquid conjugated diene polymers obtained in these production examples are as follows.

[0169] (Method for measuring weight average molecular weight (Mw)) The Mw of the liquid conjugated diene polymer (C) and the like was determined by GPC (gel permeation chromatography) in terms of standard polystyrene equivalent molecular weight. The measurement device and conditions are as follows: Device: GPC device "HLC-8320GPC" manufactured by Tosoh Corporation Separation column: "TSKgel Super HZ4000 x 2" manufactured by Tosoh Corporation Eluent: tetrahydrofuran Eluent flow rate: 0.35 mL / min Sample concentration: 5 mg / 10 mL Column temperature: 40°C

[0170] (Vinyl Content) The vinyl content of the liquid conjugated diene polymer (C) and the like was determined by the method of 1 Measurements were performed using H-NMR (500 MHz) at a sample / d-chloroform concentration of 50 mg / 1 mL, with an accumulation count of 32. The vinyl content was calculated from the area ratio of the peaks derived from conjugated diene units bonded via 1,2-bonds, 3,4-bonds (other than farnesene), and 3,13-bonds (in the case of farnesene) to the peaks derived from conjugated diene units bonded via 1,4-bonds (other than farnesene) and 1,13-bonds (in the case of farnesene).

[0171] (Glass transition temperature (Tg)) 10 mg of a sample such as the liquid conjugated diene polymer (C) was placed in an aluminum pan and measured by differential scanning calorimetry (DSC) at a heating rate of 10°C / min to obtain a thermogram. The value at the peak top of the DDSC in this thermogram was taken as the glass transition temperature (Tg) of the sample such as the liquid conjugated diene polymer (C).

[0172] (Melt Viscosity at 38° C.) The melt viscosity at 38° C. of the liquid conjugated diene polymer (C) and the like was measured using a Brookfield viscometer (manufactured by BROOKFIELD ENGINEERING LABS. INC.).

[0173] (Specific Gravity) The specific gravity of the liquid conjugated diene polymer (C) was measured by the method described in JIS K 2249-2:2011.

[0174] (Si Content Derived from Si-Containing Functional Groups in Modified Solution-Polymerized Styrene-Butadiene Copolymer (A1) Having Si-Containing Functional Groups) The Si content derived from Si-containing functional groups in the modified solution-polymerized styrene-butadiene copolymers having Si-containing functional groups used in the Examples and Comparative Examples was measured by ICP atomic emission spectroscopy. The apparatus and evaluation method were as follows. Apparatus: "iCAP6500Duo" manufactured by Thermo Fisher Scientific. Sample preparation method: Nitric acid and sulfuric acid were added to 2 g of the sample, and the mixture was heated to incinerate. Sodium carbonate was then added and the mixture was melted, and then ultrapure water was added to dissolve the sample. The solution was filtered, and the diluted solution was analyzed using an ICP atomic emission spectrometer to obtain the Si content derived from Si-containing functional groups. The average Si content X in the solid rubber (A) was calculated using this obtained content and the proportion of the modified solution-polymerized styrene-butadiene copolymer having Si-containing functional groups contained in the solid rubber (A). The results are shown in Table 2.

[0175] (1 cm of rubber composition 3 The total specific surface area Y of silica (B1) per 1 cm of the rubber compositions of the Examples and Comparative Examples 3 The total specific surface area Y of the silica (B1) per unit volume of the rubber composition calculated from the blending amount and specific gravity of each component contained in the rubber composition is expressed as H cm 3 , its volume H cm 3 The specific surface area (CTAB) of the silica contained in the rubber composition is Im 2 The silica content was calculated using the following formula (2) where Y is the total mass of silica and the weight of silica is Jg. The results are shown in Table 2. Y = (I × J) / H (2)

[0176] (Value of X×Y) The value of X×Y was calculated by multiplying X and Y obtained by the above-mentioned method. The results are shown in Table 2.

[0177] The physical properties of the liquid conjugated diene polymers (C-1), (C-2) and (C-3) obtained in Production Examples 1 to 3 are summarized in Table 1 below.

[0178]

[0179] Examples 1 to 3 and Comparative Examples 1 to 4 As described in detail below, rubber compositions were prepared by kneading each component according to the compounding ratios (parts by mass) listed in Table 2. First, two steps (NP1 and NP2) were performed to mix components other than the crosslinking agent (vulcanizing agent) and vulcanization accelerator to obtain an unvulcanized rubber mixture (unvulcanized rubber mixture (2)). Then, a step (FM) was performed to further knead the crosslinking agent and vulcanization accelerator into this unvulcanized rubber mixture (2), thereby preparing a rubber composition. Note that by performing the step of mixing components other than the crosslinking agent (vulcanizing agent) and vulcanization accelerator twice, the dispersibility of the filler (B) (particularly silica (B1)) was improved. [Kneading step (NP1)] According to the compounding ratios (parts by mass) listed in Table 2, solid rubber (A), filler (B), liquid conjugated diene polymer (C), TDAE, silane coupling agent, zinc oxide, stearic acid, wax, and antioxidant were each charged into an internal Banbury mixer, and the mixture was kneaded for 4 minutes at a starting temperature of 60 ° C. and a resin temperature of 155 to 160 ° C. After that, the mixture was removed from the mixer and cooled to room temperature to obtain an unvulcanized rubber mixture (1). [Kneading step (NP2)] The unvulcanized rubber mixture (1) obtained in the kneading step (NP1) was again charged into an internal Banbury mixer, and the mixture was kneaded for 3 minutes at a starting temperature of 60 ° C. and a resin temperature of 155 to 160 ° C. After that, the mixture was removed from the mixer and cooled to room temperature to obtain an unvulcanized rubber mixture (2). [Mixing step (FM)] The unvulcanized rubber mixture (2) obtained in the mixing step (NP2) was placed back into the Banbury mixer, and a crosslinking agent (vulcanizing agent) and a vulcanization accelerator were added. The mixture was mixed for 75 seconds to obtain a rubber composition, with the starting temperature being 50°C and the final temperature being 100°C. In each example and comparative example, the physical properties were evaluated as follows. The evaluation results of the physical properties are shown in Table 2.

[0180] (Mooney Viscosity) The Mooney viscosity (ML) of the rubber composition before vulcanization obtained through the kneading steps (NP1), (NP2) and (FM) was measured in accordance with JIS K 6300-1:2013. 1+4 ) was measured at 130°C. The values ​​for each Example and Comparative Example in Table 2 are relative values ​​when the value for Comparative Example 1 is set to 100. The smaller the value, the better the processability of the rubber composition.

[0181] (Elongation at break of unvulcanized rubber mixture (1)) A sample was prepared from the unvulcanized rubber mixture (1) obtained through the kneading process (NP1), and the elongation at break of this sample was evaluated. The sample was prepared by press-molding (100 ° C, 10 minutes) the unvulcanized rubber mixture (1) obtained through the kneading process (NP1) into an unvulcanized rubber sheet (thickness 2 mm). A JIS dumbbell-shaped No. 3 test piece was punched out from the prepared unvulcanized rubber sheet, and the tensile elongation at break was measured at a pulling rate of 50 cm / min using an Instron tensile tester. The values ​​in each example and comparative example are relative values ​​when the value of comparative example 1 is set to 100. The larger the value, the more difficult it is to break the sheet in the unvulcanized state, and the more likely it is to prevent a decrease in productivity.

[0182] (Fuel efficiency (60°C tan δ), 25°C modulus, 60°C modulus) The rubber compositions obtained through the kneading steps (NP1), (NP2) and (FM) prepared in the Examples and Comparative Examples were press-molded (160°C, 10-30 minutes) to prepare vulcanized rubber sheets (2 mm thick). Test pieces measuring 40 mm long x 5 mm wide were cut out from the resulting vulcanized rubber sheets, and using a dynamic viscoelasticity measuring device manufactured by GABO, under the conditions of a frequency of 10 Hz, a static strain of 10%, and a dynamic strain of 2%, tan δ was measured at a measurement temperature of 60°C, and E' (elastic modulus) was measured at measurement temperatures of 25°C and 60°C. The values ​​for each Example and Comparative Example are relative values ​​when the value for Comparative Example 1 in Table 2 is taken as 100. The smaller the value of tan δ, the better the fuel efficiency of the rubber composition (vulcanized rubber sheet), and the larger the value of E', the higher the elasticity of the resulting vulcanized rubber sheet.

[0183]

[0184] Compared to Comparative Example 1, Examples 1 to 3 incorporate a liquid conjugated diene polymer, which improves processability and productivity while providing high elasticity and tends to provide equivalent or superior fuel economy. Furthermore, compared to Comparative Examples 2 to 4, Examples 1 to 3 incorporate a modified solution-polymerized styrene-butadiene copolymer with an appropriate content of Si derived from Si-containing functional groups or silica with an appropriate specific surface area, which improves productivity while not reducing the elastic modulus and provides excellent fuel economy.

[0185] The rubber composition of the present invention contains a highly modified solution-polymerized styrene-butadiene copolymer having a high concentration of Si-containing functional groups as a solid rubber component, and even when the rubber composition further contains a fine filler as a filler, the rubber composition has excellent processability. Furthermore, the rubber composition or a cross-linked product of the rubber composition has the inherently good elastic modulus. Therefore, it can be suitably used for industrial component applications such as tires, industrial belts, and industrial rubber hoses, making it useful. Furthermore, when the rubber composition or a cross-linked product of the rubber composition is used for tires, it also has excellent fuel economy, making it useful.

Claims

1. The rubber composition comprises 60 to 150 parts by mass of silica (B1) as a filler (B) and 5 to 30 parts by mass of a liquid conjugated diene-based polymer (C) having a weight average molecular weight in the range of 3,000 to 200,000, relative to 100 parts by mass of a solid rubber (A) containing 60% by mass or more of a modified solution-polymerized styrene-butadiene copolymer (A1) having a functional group containing Si, the content of Si derived from the Si-containing functional group contained in the modified solution-polymerized styrene-butadiene copolymer (A1) is 220 to 800 ppm; The specific surface area (CTAB) of the silica (B1) is 180 to 500 m 2 / g of the rubber composition.

2. The average content of Si derived from the functional group containing Si in the solid rubber (A) is X ppm, and the average content of Si derived from the functional group containing Si in 1 cm of the rubber composition is 3 The total specific surface area of ​​silica (B1) per unit area is Ym 2 / cm 3 The rubber composition according to claim 1, wherein the value of X×Y satisfies 9,000 or more.

3. 2. The rubber composition according to claim 1, wherein the liquid conjugated diene polymer (C) has a melt viscosity at 38° C. of 0.1 to 2,000 Pa·s.

4. The rubber composition according to claim 1, wherein the silica (B1) has an average particle size of 0.5 to 200 nm.

5. 2. The rubber composition according to claim 1, wherein the conjugated diene unit derived from the conjugated diene contained in the liquid conjugated diene-based polymer (C) comprises at least one selected from the group consisting of isoprene, butadiene, and farnesene.

6. 2. The rubber composition according to claim 1, wherein the liquid conjugated diene polymer (C) is at least one selected from the group consisting of liquid polyisoprene and liquid butadiene-farnesene copolymer.

7. The rubber composition according to claim 1, wherein the liquid conjugated diene polymer (C) is liquid polyisoprene.

8. The rubber composition according to claim 1, further comprising carbon black (B2) as the filler (B).

9. A crosslinked product obtained by crosslinking the rubber composition according to any one of claims 1 to 8.

10. A tire tread at least partly comprising the rubber composition according to any one of claims 1 to 8.

11. A pneumatic tire at least partly using the rubber composition according to any one of claims 1 to 8.