Rubber composition for tire tread and tire tread

Abstract

Provided are: a rubber composition for tire treads, which does not impair wet grip performance and can achieve both an improvement in low fuel consumption performance and an improvement in wear resistance; and a tire tread which is obtained by using the rubber composition for at least a part of the tire tread. This rubber composition for tire treads contains 0.1-50 parts by mass of a modified liquid diene rubber (B) having a functional group derived from a specific silane compound and 20-200 parts by mass of a filler (C) per 100 parts by mass of a specific solid rubber (A).

Description

Technical Field

[0001] The present invention relates to a rubber composition for tire tread and to the use of the same composition in at least a portion of a tire tread. Background Technology

[0002] Research has been conducted on rubber compositions obtained by blending diene rubbers and other rubber components with fillers such as carbon black and silica for use in tire components, such as tire treads. In order to improve vehicle safety, excellent braking performance (wet grip) on wet roads is required in such tire treads.

[0003] Furthermore, in recent years, from the perspective of reducing environmental burden, low fuel consumption performance has been required for rubber compositions used in tire treads. For example, as a rubber composition applicable to tire treads with the aim of improving such low fuel consumption performance, rubber compositions comprising solid rubber, specific modified liquid diene rubber, and fillers have been studied (see Patent Documents 1 and 2).

[0004] From the same perspective of reducing environmental burden, research is underway in the automotive industry, particularly in passenger cars, on a shift from vehicles powered solely by internal combustion engines to those using electric motors as at least a part of their power source (electric vehicles). In these electric vehicles, the transmission of driving force from the power source to the tires differs. Furthermore, to ensure stable operation of the electric motor over extended periods, batteries are typically mounted on the vehicle. Therefore, compared to conventional vehicles powered solely by internal combustion engines, electric vehicles tend to experience greater initial forces on the tires and an increase in vehicle weight; consequently, the rubber composition used in the tire treads of electric vehicles requires high abrasion resistance.

[0005] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2013-249359 Patent Document 2: International Publication No. 2019 / 044892. Summary of the Invention

[0006] The problem that the invention aims to solve In electric vehicles, the transmission of driving force from the power source to the tires differs from that of conventional vehicles, as mentioned above. In particular, the initial force applied to the tires is relatively large. In addition, electric vehicles are heavier than conventional vehicles. Therefore, the tire tread used in electric vehicles requires not only good wet grip performance but also improved fuel efficiency and, more importantly, wear resistance.

[0007] However, achieving a balance between improved wear resistance and good wet grip is challenging. Furthermore, achieving a balance between improved fuel efficiency and good wet grip is also difficult. Therefore, a tire tread that achieves a good balance of these three properties is desirable.

[0008] The present invention is made in view of the above-mentioned actual situation, and provides a tire tread rubber composition that does not compromise wet grip performance and can simultaneously improve low fuel consumption performance and wear resistance, and a tire tread obtained by using the composition in at least a portion thereof.

[0009] means for solving problems The inventors conducted in-depth research and found that using a rubber composition comprising a specific solid rubber, a specific modified liquid diene rubber, and fillers in at least a portion of the tire tread results in tires with undamaged wet grip performance, while simultaneously improving low fuel consumption and wear resistance. This led to the completion of the present invention.

[0010] That is, the present invention relates to the following [1] to [9].

[0011] [1] A rubber composition for tire tread, wherein, relative to 100 parts by weight of a solid rubber (A) comprising natural rubber (A1), butadiene rubber (A2), and styrene-butadiene rubber (A3), it contains 0.1 to 50 parts by weight of a modified liquid diene rubber (B) having functional groups derived from silane compounds represented by the following formula (1), and 20 to 200 parts by weight of filler (C), The modified liquid diene rubber (B) has the following characteristics (i) to (iii): (i) Weight-average molecular weight (Mw) is above 3,000 and below 120,000; (ii) The vinyl content is less than 70 mol%; (iii) The average number of functional groups derived from the silane compound in each molecule of modified liquid diene rubber (B) is 1 to 20.

[0012] [Chemistry 1] (In equation (1), R) 1 R is a divalent alkylene group having 1 to 6 carbon atoms. 2 R 3 and R 4 Each can independently represent methoxy, ethoxy, phenoxy, methyl, ethyl, or phenyl. Among them, R... 2 R 3 and R 4 At least one of them is methoxy, ethoxy, or phenoxy. [2] The tire tread rubber composition according to [1], wherein the aforementioned modified liquid diene rubber (B) has a melt viscosity of 0.1 to 4,000 Pa·s at 38°C.

[0013] [3] The tire tread rubber composition according to [1] or [2], wherein the content of natural rubber (A1) in the aforementioned solid rubber (A) 100% by mass is 40 to 80% by mass.

[0014] [4] The tire tread rubber composition according to any one of [1] to [3], wherein the mass ratio of butadiene rubber (A2) to styrene-butadiene rubber (A3) contained in the aforementioned solid rubber (A) is 0.12 or more and 3 or less.

[0015] [5] A rubber composition for tire tread according to any one of [1] to [4], wherein silica is contained as the aforementioned filler (C).

[0016] [6] The tire tread rubber composition according to [5] further comprises carbon black as the aforementioned filler (C).

[0017] [7] A crosslinked compound obtained by crosslinking the rubber composition for tire tread described in any one of [1] to [6].

[0018] [8] A tire tread, at least a portion thereof using any one of [1] to [7] a tire tread rubber composition.

[0019] [9] An inflatable tire for an electric vehicle, comprising the tire tread described in [8].

[0020] Invention Effects According to the present invention, a tire tread rubber composition that provides wet grip performance without damage and improves both low fuel consumption and wear resistance can be used in at least a portion of the tire tread. Detailed Implementation

[0021] [Solid Rubber (A)] The solid rubber (A) used in the tire tread rubber composition of the present invention refers to a rubber that can be processed in a solid state at 20°C. The Mooney viscosity (ML) of solid rubber (A) at 100°C is... 1＋4 It is usually in the range of 20 to 200.

[0022] The solid rubber (A) included in the tire tread rubber composition of the present invention includes natural rubber (A1), butadiene rubber (A2) and styrene-butadiene rubber (A3).

[0023] [Natural Rubber (A1)] As for natural rubber (A1), examples include unmodified natural rubbers commonly used in the tire industry, such as SMR (Malaysian TSR), SIR (Indonesian TSR), STR (Thailand TSR), etc., TSR (Technically Specified Rubber) and / or RSS (Ribbed Smoked Sheet), high-purity natural rubber, etc.; and modified natural rubbers such as epoxidized natural rubber, hydroxylated natural rubber, hydrogenated natural rubber, grafted natural rubber, etc. Among these, from the viewpoint of processability, unmodified natural rubber is preferred, and from the viewpoints of minimal quality deviation and ease of acquisition, SMR20, STR20, and / or RSS#3 are more preferred.

[0024] In addition, the glass transition temperature of natural rubber (A1) varies depending on the quality of modification when natural rubber is modified, such as by epoxidizing natural rubber, and is preferably below -40°C, more preferably below -50°C.

[0025] These natural rubbers can be used alone or in combination of two or more types.

[0026] [Butadiene rubber (A2)] Examples of butadiene rubber (A2) include Ziegler-based catalysts such as titanium tetrahalide-trialkylaluminum, diethylaluminum chloride-cobalt, trialkylaluminum-boron trifluoride-nickel, and diethylaluminum chloride-nickel; lanthanide-based rare earth metal catalysts such as triethylaluminum-neodymium organic acid-Lewis acid; and commercially available butadiene rubbers obtained by polymerization using organoalkali metal compounds (e.g., n-butyllithium, sec-butyllithium, etc.) similar to those used in the solution polymerization of styrene-butadiene rubber described later. Among these, butadiene rubber obtained by polymerization using Ziegler-based catalysts is preferred due to its high cis content. Furthermore, butadiene rubber (A2) with an ultra-high cis content (e.g., cis content of 95% or more) obtained using lanthanide-based rare earth metal catalysts can be used.

[0027] The vinyl content of butadiene rubber (A2) 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%, there is a tendency for the rotational resistance performance (low fuel consumption performance) to deteriorate. There is no particular limitation on the lower limit of the vinyl content. Furthermore, the glass transition temperature of butadiene rubber (A2) varies depending on the vinyl content, and is preferably -40°C or less, more preferably -50°C or less. Vinyl content refers to the total proportion (mol%) of 1,2-bonded structural units (excluding 1,4-bonded structural units) out of a total of 100 mol% of butadiene-derived structural units contained in the butadiene rubber.

[0028] The weight-average molecular weight (Mw) of the butadiene rubber (A2) is preferably 90,000 to 2,000,000, more preferably 150,000 to 1,500,000. When Mw is within the above range, the processability of the tire tread rubber composition is improved, and the wear resistance of the tire tread obtained by using the tire tread rubber composition in at least a portion is also improved.

[0029] In the aforementioned butadiene rubber (A2), a portion may have a branched structure or polar functional groups formed by using a multifunctional modifier, such as tin tetrachloride, silicon tetrachloride, alkoxysilanes with intramolecular epoxy groups, or alkoxysilanes containing amino groups. From a processability point of view, the aforementioned butadiene rubber (A2) preferably does not have polar functional groups.

[0030] These butadiene rubbers (A2) can be used alone or in combination of two or more types.

[0031] [Styrene-butadiene rubber (A3)] As the aforementioned styrene-butadiene rubber (A3) (hereinafter also referred to as "SBR"), conventional materials used in tire applications can be used. Specifically, as SBR (A3), the styrene content is preferably 0.1 to 70% by mass, more preferably 5 to 60% by mass, and even more preferably 5 to 50% by mass. Furthermore, as SBR (A3), the vinyl content is preferably 0.1 to 80 mol%, more preferably 5 to 70 mol%.

[0032] It should be noted that the vinyl content of SBR in this specification refers to the total proportion (mol%) of 1,2-bonded structural units (excluding 1,4-bonded structural units) out of a total of 100 mol% of structural units derived from all butadiene in the SBR.

[0033] The weight-average molecular weight (Mw) of SBR (A3) is preferably 100,000 to 2,500,000, more preferably 150,000 to 2,000,000, and even more preferably 150,000 to 1,500,000. When the weight-average molecular weight (Mw) of SBR is within the above range, the processability of the tire tread rubber composition is improved, and the wet grip performance of the tire with tire tread obtained from the tire tread rubber composition is improved, further improving mechanical strength, wear resistance, and handling stability. It should be noted that the weight-average molecular weight in this specification refers to the weight-average molecular weight of polystyrene determined by gel permeation chromatography (GPC).

[0034] The glass transition temperature (Tg) of SBR (A3), determined by differential thermal analysis, is preferably -95 to 0°C, more preferably -90 to -5°C, further preferably -85 to -10°C, even more preferably -80 to -15°C, and particularly preferably -70 to -20°C. If the glass transition temperature is within the aforementioned range, the viscosity of the rubber composition for tire tread can be suppressed, processing becomes easier, and wet grip performance is improved.

[0035] The SBR (A3) that can be used in this invention is obtained by copolymerizing styrene and butadiene. There are no particular limitations on the manufacturing method of SBR (A3), and emulsion polymerization, solution polymerization, gas-phase polymerization, and bulk polymerization can all be used. Among these manufacturing methods, emulsion polymerization and solution polymerization are preferred.

[0036] Emulsion-polymerized styrene-butadiene rubber (hereinafter also referred to as E-SBR) can be manufactured by conventional emulsion polymerization methods known or based on known standards. For example, a specified amount of styrene and butadiene monomers are emulsified and dispersed in the presence of an emulsifier, and then obtained by emulsion polymerization using a free radical polymerization initiator.

[0037] As emulsifiers, long-chain fatty acid salts with 10 or more carbon atoms and rosin salts can be used. Specific examples include potassium or sodium salts of fatty acids such as decanoic acid, lauric acid, myristic acid, palmitic acid, oleic acid, and stearic acid.

[0038] Water is typically used as the dispersion medium, and water-soluble organic solvents such as methanol and ethanol may be included, provided that they do not impede the stability of the polymerization process.

[0039] Examples of free radical polymerization initiators include ammonium persulfate, potassium persulfate and other persulfates, organic peroxides, and hydrogen peroxide.

[0040] To adjust the molecular weight of the obtained E-SBR, chain transfer agents can be used. Examples of chain transfer agents include thiols such as tert-dodecyl mercaptan and n-dodecyl mercaptan; carbon tetrachloride; thioglycolic acid; diterpenes; terpinene; γ-terpinene; and α-methylstyrene dimer.

[0041] The temperature for emulsion polymerization can be appropriately set depending on the type of free radical polymerization initiator used, and is generally preferred to be 0~100℃, more preferably 0~60℃. The polymerization method can be either continuous polymerization or batch polymerization. The polymerization reaction can be terminated by adding a polymerization inhibitor.

[0042] Examples of polymerization inhibitors include amine compounds such as isopropyl hydroxylamine, diethyl hydroxylamine, and hydroxylamine; quinone compounds such as hydroquinone and benzoquinone; and sodium nitrite.

[0043] After the polymerization reaction is terminated, antioxidants may be added as needed. After the polymerization reaction is terminated, unreacted monomers are removed from the resulting latex as needed. Next, salts such as sodium chloride, calcium chloride, and potassium chloride are used as coagulants, and acids such as nitric acid and sulfuric acid are added as needed to adjust the pH of the coagulation system to a specified value. Simultaneously, after the polymer coagulates, it can be recovered in the form of debris by separating the dispersion medium. The debris is washed with water, then dehydrated, and dried using a belt dryer or similar method to obtain E-SBR. It should be noted that during coagulation, the latex and the stretching oil used to prepare the emulsion dispersion can be mixed beforehand as needed, and it can be recovered as oil-extended rubber. It should be noted that in the composition of the tire tread rubber composition in this specification, the stretching oil is not included in the solid rubber (A).

[0044] Commercially available E-SBR products include oil-extended styrene-butadiene rubber "ESBR1723" manufactured by ENEOS Materials Co., Ltd.

[0045] Solution-polymerized styrene-butadiene rubber (hereinafter also referred to as S-SBR) can be manufactured by conventional solution polymerization. For example, an active metal capable of anionic polymerization is used in the solvent, and styrene and butadiene are polymerized in the presence of a polar compound as desired.

[0046] Examples of solvents 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 generally preferred to be used in the range of 1 to 50% by mass to achieve a monomer concentration.

[0047] Examples of active metals capable of anionic polymerization include alkali metals such as lithium, sodium, and potassium; alkaline earth metals such as beryllium, magnesium, calcium, strontium, and barium; and lanthanide rare earth metals such as lanthanum and niobium. Among these active metals, alkali metals and alkaline earth metals are preferred, and alkali metals are more preferred. Furthermore, among alkali metals, organoalkali metal compounds are more preferred.

[0048] Examples of organoalkali metal compounds include, for instance, monolithium organometallic compounds such as n-butyllithium, sec-butyllithium, tert-butyllithium, hexyllithium, phenyllithium, and stilbene; multifunctional organolithium compounds such as dilithium methane, 1,4-dilithium butane, 1,4-dilithium-2-ethylcyclohexane, and 1,3,5-trilithium benzene; and sodium naphthalene and potassium naphthalene. Among these, organolithium compounds are preferred, and monolithium organometallic compounds are more preferred. The amount of organoalkali metal compound used is appropriately determined according to the required molecular weight of the S-SBR. Organoalkali metal compounds can also react with secondary amines such as dibutylamine, dihexylamine, and diphenylmethylamine to prepare organoalkali metal amines for use.

[0049] As polar compounds, there are no particular limitations as long as they do not deactivate the reaction in anionic polymerization, are commonly used to adjust the microstructure of butadiene units, or the distribution of styrene in the copolymer chain. Examples include ether compounds such as dibutyl ether, tetrahydrofuran, and ethylene glycol diethyl ether; tertiary amines such as tetramethylethylenediamine and trimethylamine; alkali metal alkoxides, and phosphine compounds.

[0050] The polymerization temperature is typically in the range of -80 to 150°C, preferably 0 to 100°C, and more preferably 30 to 90°C. The polymerization can be either batch or continuous. Furthermore, to improve the random copolymerization of styrene and butadiene, it is preferable to continuously or intermittently supply styrene and butadiene to the reaction solution in a manner that achieves a specific range in the styrene-to-butadiene ratio within the polymer system.

[0051] The polymerization reaction can be terminated by adding alcohols such as methanol or isopropanol as polymerization inhibitors. The polymerization solution after termination can be dried directly or stripped to separate the solvent, thereby recovering the target S-SBR. It should be noted that before solvent removal, the polymerization solution and stretching oil can be premixed to recover oil-extended rubber.

[0052] As for the aforementioned SBR (A3), any modified SBR in which functional groups have been introduced into the SBR can be used, as long as it does not impair the effects of the present invention. Examples of functional groups include amino, alkoxysilyl, hydroxyl, epoxy, and carboxyl groups.

[0053] Examples of methods for manufacturing modified SBR include adding coupling agents capable of reacting with polymer active ends, such as tin tetrachloride, tetrachlorosilane, dimethyldichlorosilane, dimethyldiethoxysilane, tetramethoxysilane, tetraethoxysilane, 3-aminopropyltriethoxysilane, tetraglycidyl-1,3-diaminomethylcyclohexane, and 2,4-toluene diisocyanate, before adding a polymerization inhibitor; polymerization end modifiers such as 4,4'-bis(diethylamino)benzophenone and N-vinylpyrrolidone; or other modifiers described in Japanese Patent Application Publication No. 2011-132298. In this modified SBR, the position of the introduced functional group in the polymer can be either the polymerization end or a side chain of the polymer chain.

[0054] In the aforementioned solid rubber (A) 100% by mass, the content of natural rubber (A1) is preferably 40-80% by mass, more preferably 45-75% by mass, and even more preferably 50-70% by mass. If the content of natural rubber (A1) in the solid rubber (A) is within the above range, the wear resistance is improved.

[0055] In the aforementioned solid rubber (A) at 100% by mass, the content of butadiene rubber (A2) is preferably 3 to 45% by mass, more preferably 3 to 40% by mass, and even more preferably 5 to 35% by mass. If the content of butadiene rubber (A2) in the solid rubber (A) is within the above range, the wear resistance is improved.

[0056] In the aforementioned solid rubber (A) at 100% by mass, the content of styrene-butadiene rubber (A3) is preferably 5-50% by mass, more preferably 10-45% by mass, and even more preferably 10-40% by mass. If the content of styrene-butadiene rubber (A3) in the solid rubber (A) is within the above range, the low fuel consumption performance is improved.

[0057] In the aforementioned solid rubber (A), the mass ratio (A2) / (A3) of butadiene rubber (A2) to styrene-butadiene rubber (A3) is preferably 0.12 or more and 3 or less, preferably 0.13 or more and 2.5 or less, more preferably 0.14 or more and 2.0 or less, even more preferably 0.14 or more and 1.8 or less, and even more preferably 0.2 or more and 1.2 or less. If the mass ratio (A2) / (A3) in the solid rubber (A) is within the above range, the balance between wet grip performance, low fuel consumption performance, and abrasion resistance is improved.

[0058] From the viewpoint of producing tire treads with further improved fuel efficiency and wear resistance, it is preferable that the total content of natural rubber (A1), butadiene rubber (A2), and styrene-butadiene rubber (A3) in 100% by mass of the aforementioned solid rubber (A) is 80% by mass or more, more preferably 90% by mass or more. Furthermore, from the same viewpoint, it is preferable that the total content of natural rubber (A1), butadiene rubber (A2), and styrene-butadiene rubber (A3) in 100% by mass of the aforementioned solid rubber (A) is 100% by mass, meaning that the solid rubber (A) consists only of natural rubber (A1), butadiene rubber (A2), and styrene-butadiene rubber (A3).

[0059] The aforementioned solid rubber (A) may include solid rubbers other than natural rubber (A1), butadiene rubber (A2), and styrene-butadiene rubber (A3) without impairing the effects of the present invention. Examples of solid rubbers other than natural rubber (A1), butadiene rubber (A2), and styrene-butadiene rubber (A3) include isoprene rubber, butyl rubber, halogenated butyl rubber, ethylene propylene diene rubber, butadiene acrylonitrile copolymer rubber, chloroprene rubber, acrylic rubber, fluororubber, and urethane rubber.

[0060] When the solid rubber (A) contains solid rubber other than natural rubber (A1), butadiene rubber (A2) and styrene-butadiene rubber (A3), the content of solid rubber other than natural rubber (A1), butadiene rubber (A2) and styrene-butadiene rubber (A3) in 100% by mass of the solid rubber (A) is preferably 20% by mass or less, more preferably 10% by mass or less.

[0061] [Modified Liquid Diene Rubber (B)] The modified liquid diene rubber (B) used in the tire tread rubber composition of the present invention refers to a liquid polymer having functional groups derived from a silane compound (hereinafter also referred to as silane compound (1)) shown in formula (1) below, having a weight-average molecular weight (Mw) of 3,000 or more and 120,000 or less (necessary condition (i)), a vinyl content of 70 mol% or less (necessary condition (ii)), and an average number of functional groups derived from silane compound (1) in each molecule of modified liquid diene rubber (B) of 1 to 20 (necessary condition (iii)). In the tire tread rubber composition of the present invention, by including the modified liquid diene rubber (B), the dispersibility of the filler (C) in the rubber composition and the interaction between the filler (C) and the solid rubber (A) become good, and the tire tread obtained by using this rubber composition in at least a portion can achieve both improved low fuel consumption performance and improved wear resistance.

[0062] Regarding the unmodified liquid diene rubber (B') that serves as the raw material for the modified liquid diene rubber (B), the monomer units constituting the polymer include conjugated diene units. Examples of conjugated dienes include, for instance, butadiene, isoprene; 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-octtriene, geraniol, farnesene (α-farnesene, β-farnesene), and chloroprene, etc., other than butadiene and isoprene (b1). The conjugated diene units contained in the unmodified liquid diene rubber (B') preferably include at least one selected from butadiene units, isoprene units and β-farnesene units, more preferably include at least one selected from butadiene units and isoprene units, further preferably include only at least one selected from butadiene units and isoprene units, and even more preferably include only butadiene units.

[0063] Regarding the unmodified liquid diene rubber (B') used as a raw material for the modified liquid diene rubber (B), the content of conjugated diene units is preferably 50% by mass or more, more preferably 60 to 100% by mass, and even more preferably 70 to 100% by mass, out of 100% by mass of all monomer units constituting the polymer. Furthermore, it is also a preferred embodiment for the unmodified liquid diene rubber (B') to contain only conjugated diene units (100% by mass of conjugated diene units out of 100% by mass of all monomer units).

[0064] Regarding the unmodified liquid diene rubber (B') used as a raw material for the modified liquid diene rubber (B), preferably 50% or more of the monomer units constituting the polymer, out of 100% by mass, are monomer units selected from at least one conjugated diene (b1) chosen from butadiene and isoprene. The content of monomer units selected from at least one conjugated diene (b1) chosen from butadiene and isoprene is preferably 60 to 100% by mass, more preferably 70 to 100% by mass, relative to the total monomer units of the unmodified liquid diene rubber (B').

[0065] Other monomer units that may be included in the unmodified liquid diene rubber (B') besides the conjugated diene unit include aromatic vinyl compound (b2) units, etc.

[0066] Examples of aromatic vinyl compounds (b2) include styrene, α-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 4-propylstyrene, 4-tert-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, at least one selected from styrene, α-methylstyrene, and 4-methylstyrene is preferred.

[0067] In the unmodified liquid diene rubber (B') described above, the content of monomer units other than conjugated dienes, such as aromatic vinyl compounds (b2), is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, relative to 100% by mass of all monomer units. For example, if the content of aromatic vinyl compound (b2) units is below the above range, there is a tendency for the processability of the rubber composition to be improved.

[0068] When the unmodified liquid diene rubber (B') contains two or more monomer units, its bonding mode can be either a random copolymer or a block copolymer. When the unmodified liquid diene rubber (B') is a block copolymer, the block copolymer preferably contains polymer blocks composed only of butadiene units and polymer blocks composed only of isoprene units. In the case of this block copolymer, the content of butadiene units in 100% by mass of all monomer units contained in the unmodified liquid diene rubber (B') is preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less.

[0069] The unmodified liquid diene rubber (B') is preferably a polymer obtained by polymerizing a conjugated diene and other monomers other than the conjugated diene as needed, such as by emulsion polymerization or solution polymerization.

[0070] As the emulsion polymerization method described above, known methods or methods based on known methods can be applied. For example, a monomer containing a specified amount of conjugated diene is emulsified and dispersed in the presence of an emulsifier, and emulsion polymerization is carried out using a free radical polymerization initiator.

[0071] Examples of emulsifiers include long-chain fatty acid salts with 10 or more carbon atoms and rosin salts. Examples of long-chain fatty acid salts include potassium or sodium salts of fatty acids such as decanoic acid, lauric acid, myristic acid, palmitic acid, oleic acid, and stearic acid.

[0072] Water is typically used as a dispersion medium, and water-soluble organic solvents such as methanol and ethanol can be included within a range that does not impair the stability during polymerization.

[0073] Examples of free radical polymerization initiators include persulfates such as ammonium persulfate and / or potassium persulfate, organic peroxides, and hydrogen peroxide.

[0074] To adjust the molecular weight of the resulting unmodified liquid diene rubber (B'), chain transfer agents can be used. Examples of chain transfer agents include thiols such as tert-dodecyl mercaptan and n-dodecyl mercaptan; carbon tetrachloride; mercaptoacetic acid; diterpenes; terpinene; γ-terpinene; and α-methylstyrene dimers.

[0075] The temperature of emulsion polymerization can be appropriately set according to the type of free radical polymerization initiator used, typically in the range of 0~100℃, preferably in the range of 0~60℃. The polymerization method can be either continuous polymerization or batch polymerization.

[0076] Polymerization reactions can be stopped by adding polymerization stoppers. Examples of polymerization stoppers include amine compounds such as isopropyl hydroxylamine, diethyl hydroxylamine, and hydroxylamine; quinone compounds such as hydroquinone and / or benzoquinone; and sodium nitrite.

[0077] After the polymerization reaction stops, an antioxidant may be added as needed. After the polymerization reaction stops, unreacted monomers are removed from the resulting latex as needed. Then, using salts such as sodium chloride, calcium chloride, and potassium chloride as coagulants, the pH of the coagulation system is adjusted to a specified value by adding acids such as nitric acid and sulfuric acid as needed. The unmodified liquid diene rubber (B') is then coagulated, and the dispersion medium is separated, thereby recovering the polymer. Next, after washing and dehydration, it is dried to obtain the unmodified liquid diene rubber (B'). It should be noted that during coagulation, the latex may be pre-mixed with an emulsifying oil to form an unmodified liquid diene rubber (B') for recovery.

[0078] As for the solution polymerization method described above, known methods or methods based on known methods can be applied. For example, a Ziegler catalyst, a metallocene catalyst, an active metal or active metal compound capable of anionic polymerization can be used in a solvent to polymerize a monomer containing a conjugated diene in the presence of a polar compound, as needed.

[0079] Examples of solvents 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.

[0080] Examples of active metals capable of anionic polymerization include alkali metals such as lithium, sodium, and potassium; alkaline earth metals such as beryllium, magnesium, calcium, strontium, and barium; and lanthanide rare earth metals such as lanthanum and neodymium. Among active metals capable of anionic polymerization, alkali metals and alkaline earth metals are preferred, and alkali metals are more preferred.

[0081] As the active metal compound capable of anionic polymerization, an organoalkali metal compound is preferred. Examples of organoalkali metal compounds include, for instance, monolithium organic compounds such as methyllithium, ethyllithium, n-butyllithium, sec-butyllithium, tert-butyllithium, hexyllithium, phenyllithium, and lithium mesimilar; multifunctional organolithium compounds such as dilithium methane, dilithium naphthalene, 1,4-dilithium butane, 1,4-dilithium-2-ethylcyclohexane, and 1,3,5-trilithiumbenzene; and sodium naphthalene and potassium naphthalene. Among these organoalkali metal compounds, organolithium compounds are preferred, and monolithium organic compounds are more preferred.

[0082] The amount of organoalkali metal compound used can be appropriately set according to the melt viscosity, molecular weight, etc. of the unmodified liquid diene rubber (B') and the modified liquid diene rubber (B). For example, it is usually used in an amount of 0.01 to 3 parts by mass relative to 100 parts by mass of all monomers containing the conjugated diene.

[0083] The aforementioned organoalkali metal compounds can also react with secondary amines such as dibutylamine, dihexylamine, and dibenzylamine to be used in the form of organoalkali metal amides.

[0084] Polar compounds typically do not deactivate the reaction in anionic polymerization; they are used to adjust the microstructure of the conjugated diene units (e.g., vinyl content). Examples of polar compounds include ethers 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. Polar compounds are typically used in amounts ranging from 0.01 to 1000 moles relative to 1 mole of the organoalkali metal compound.

[0085] The solution polymerization temperature is typically in the range of 80–150°C, preferably in the range of 0–100°C, and more preferably in the range of 10–90°C. The polymerization method can be either continuous polymerization or batch polymerization.

[0086] The polymerization reaction can be stopped by adding a polymerization stopper. Examples of polymerization stoppers include alcohols such as methanol and isopropanol. The unmodified liquid diene rubber (B') can be separated by injecting the resulting polymerization reaction solution into a poor solvent such as methanol, or by washing and separating the polymerization reaction solution with water and then drying it.

[0087] Of the methods for manufacturing the aforementioned unmodified liquid diene rubber (B'), solution polymerization is preferred.

[0088] Regarding the unmodified liquid diene rubber (B') obtained by such operation, in order to more easily manufacture tire treads that do not suffer from wet grip performance and also improve low fuel consumption performance and wear resistance, it is desirable to directly (in the unhydrogenated state) modify it using functional groups derived from the silane compound shown in formula (1) below.

[0089] Furthermore, regarding the aforementioned unmodified liquid diene rubber (B'), from the viewpoint of exhibiting the properties of the functional groups derived from the silane compound shown in formula (1) in a more preferred state, it is preferable not to modify it using functional groups other than those derived from the silane compound shown in formula (1) (e.g., hydroxyl groups). Since the unmodified liquid diene rubber (B') is not modified using other functional groups, there is a tendency for the resulting modified liquid diene rubber (B) to have better stability. In addition, there is a tendency for the functional groups derived from the silane compound shown in formula (1) of the resulting modified liquid diene rubber (B) to have better interaction (e.g., reactivity) with the filler (C) (e.g., silica).

[0090] The unmodified liquid diene rubber (B') is modified using functional groups derived from the silane compound (hereinafter also referred to as silane compound (1)) shown in formula (1) below, and is used in the form of modified liquid diene rubber (B). In other words, the modified liquid diene rubber (B) has functional groups derived from the silane compound (silane compound (1)) shown in formula (1) below.

[0091] [Chemistry 2] In the above formula (1), R 1 It is a divalent alkylene group having 1 to 6 carbon atoms. Examples of divalent alkylene groups having 1 to 6 carbon atoms include methylene, ethylene, propylene, butylene, pentylene, and hexylene. 2 R 3 and R 4 Each can independently represent methoxy, ethoxy, phenoxy, methyl, ethyl, or phenyl. Among them, R... 2 R 3 and R 4 At least one of them is methoxy, ethoxy, or phenoxy.

[0092] Examples of the aforementioned silane compounds (1) include, for instance, mercaptomethylenemethyldiethoxysilane, mercaptomethylenetriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, 2-mercaptoethylmethoxydimethylsilane, 2-mercaptoethylethoxydimethylsilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropyldimethoxymethylsilane, 3-mercaptopropyldiethoxymethylsilane, 3-mercaptopropyldimethoxyethylsilane, 3-mercaptopropyldiethoxyethylsilane, 3-mercaptopropylmethoxydimethylsilane, and 3-mercaptopropylethoxydimethylsilane. These silane compounds can be used alone or in combination of two or more.

[0093] The mercapto group (-SH) of the silane compound (1) undergoes a radical addition reaction with the carbon-carbon unsaturated bond contained in the unmodified liquid diene rubber (B'), thereby obtaining a modified liquid diene rubber (B) having a functional group derived from the silane compound (1), specifically having a partial structure as shown in the following formula (2) as a functional group.

[0094] [Chemistry 3] R in equation (2) above 1 R 2 R 3 and R 4 The definition and specific examples are equivalent to R in equation (1). 1 R 2 R 3 and R 4 The definition and specific examples are the same.

[0095] The average number of functional groups in the modified liquid diene rubber (B) having a functional group derived from silane compound (1) per molecule is 1 to 20 (necessary condition (iii)). When the aforementioned average number of functional groups is less than 1, the affinity with filler (C) is low, the filler dispersion in the rubber composition cannot be improved, and it is difficult to manufacture a tire tread that also improves low fuel consumption performance. On the other hand, when the aforementioned average number of functional groups exceeds 20, it is difficult to obtain the effect of improved wear resistance for the tire tread obtained from the rubber composition. From the perspective of the tendency to further improve the low fuel consumption performance and the tendency to further improve the wear resistance of the obtained tire tread, the average number of functional groups in the modified liquid diene rubber (B) having a functional group derived from silane compound (1) per molecule is preferably 1 to 15, more preferably 1 to 12, further preferably 1 to 9, even more preferably 1 to 5, particularly preferably 1 to 4, and even more particularly preferably 2 to 4.

[0096] The average number of functional groups in each molecule of modified liquid diene rubber (B) can be calculated using the equivalent (g / eq) of the functional groups of modified liquid diene rubber (B) and the number-average molecular weight Mn converted from styrene, and by the following formula.

[0097] (Average number of functional groups per molecule) = [(Number average molecular weight Mn) ÷ (Molecular weight of styrene unit) × (Average molecular weight of conjugated diene and other monomer units other than conjugated diene included as needed)] / (Equivalent number of functional groups) It should be noted that the functional group equivalent of the modified liquid diene rubber (B) refers to the mass of butadiene bonded to one functional group and, as needed, other monomers besides butadiene. The functional group equivalent can be expressed using... 1H-NMR or 13 C-NMR is calculated based on the area ratio of peaks originating from functional groups of the modified liquid diene rubber (B) to peaks originating from the main chain of the modified liquid diene rubber (B). It should be noted that peaks originating from functional groups refer to alkoxy groups contained in the silane compound (1) contained in the modified liquid diene rubber (B).

[0098] The amount of silane compound (1) added to the modified liquid diene rubber (B) is preferably 1 to 60 parts by mass relative to 100 parts by mass of the unmodified liquid diene rubber (B'), more preferably 1 to 50 parts by mass, and even more preferably 1 to 40 parts by mass. When the amount added is greater than 60 parts by mass, there is a tendency for a lack of dispersion effect of filler (C) and a decrease in the wear resistance of the resulting tire tread. When the amount added is less than 1 part by mass, there is a tendency for a lack of dispersion effect of filler (C), insufficient improvement in the low fuel consumption performance of the resulting tire tread, and insufficient improvement in wear resistance. It should be noted that the amount of silane compound (1) added to the modified liquid diene rubber (B) can be determined using various analytical instruments such as NMR.

[0099] There are no particular limitations on the method for adding silane compound (1) to unmodified liquid diene rubber (B'). For example, a method can be used that involves adding silane compound (1) to unmodified liquid diene rubber (B'), then adding a free radical generator as needed, and heating the mixture with or without an organic solvent. There are no particular limitations on the free radical generator used; commercially available organic peroxides, azo compounds, hydrogen peroxide, etc., can be used. It is not desirable for the reaction of adding silane compound (1) to unmodified liquid diene rubber (B') to proceed solely by heating without the use of a free radical generator. For example, if the heating temperature is too low, the addition reaction may not occur sufficiently, and the average number of functional groups per molecule may not be within the desired range. Furthermore, if the heating temperature is increased, the addition reaction may occur, but since free radicals are generated on the polymer backbone, polymerization may also occur simultaneously. Therefore, there may be cases where the Mw of the modified liquid diene rubber is not within the desired range, and the viscosity of the modified liquid diene rubber is not within the desired range. At high temperatures during addition reactions, the processability of modified liquid diene rubber deteriorates, negatively impacting the physical properties of the resulting tire rubber composition. On the other hand, if the addition reaction is carried out by adding a free radical generator and heating, side reactions such as polymerization are sufficiently suppressed at lower temperatures, and the addition reaction proceeds fully.

[0100] When the maximum peak molecular weight of the modified liquid diene rubber (B) obtained by GPC determination is set as Mt, the total area of ​​the modified liquid diene rubber (B) in the GPC chromatogram obtained by GPC determination is set as 100%. The proportion of polymers in the region with a molecular weight of Mt×1.45 or higher is preferably in the range of 0 to 30%, more preferably in the range of 0 to 20%, even more preferably in the range of 0 to 18%, even more preferably in the range of 0 to 15%, particularly preferably in the range of 0 to 10%, and even more particularly preferably in the range of 0 to 8%. It can be inferred that by incorporating this modified liquid diene rubber (B) into the rubber composition, the processability of the rubber composition is improved, and the interaction with the filler (C) described later in the resulting rubber composition is enhanced. Therefore, it is easy to have the filler (C) present in the vicinity when making the rubber composition. As a result, the dispersion state of the filler (C) and the like in the rubber composition is excellent, which is ideal for improving the physical properties of the resulting tire tread (e.g., improving low fuel consumption performance and improving wear resistance).

[0101] Examples of the aforementioned organic peroxides include, for instance, methyl ethyl ketone peroxide, cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide, methylcyclohexanone peroxide, acetylacetone peroxide, 1,1-bis(tert-butylperoxide)-3,3,5-trimethylcyclohexane, 1,1-bis(tert-butylperoxide)cyclohexane, 1,1-bis(tert-hexylperoxide)cyclohexane, 2,2-bis(tert-butylperoxide)butane, tert-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, p-menthol hydroperoxide, 2,5-dimethylhexane 2,5-disperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, di-tert-butyl peroxide, tert-butylcumyl peroxide, dicumyl peroxide, bis(tert-butylperoxide isopropyl)benzene, 2 5-Dimethyl-2,5-di(tert-butylperoxide)hexane, 2,5-hexanoylperoxide, lauroylperoxide, succinic acid peroxide, benzoyl peroxide and its substituted derivatives, 2,4-dichlorobenzoylperoxide, m-toluylperoxide, diisopropyl peroxide dicarbonate, tert-butyl 2-ethylhexanoate, di(2-ethylhexyl) peroxide dicarbonate, dimethoxyisopropyl peroxide dicarbonate, di(3-methyl-3-methoxybutyl) peroxide dicarbonate, tert-butyl peracetic acid, tert-butyl perpentanoate, tert-butyl perdecanoate, tert-butyl peroctanoate, tert-butyl peroxyoctanoate, tert-butyl peroxy3,3,5-trimethylhexanoate, tert-butyl perlaurate, tert-butyl percarbonate, tert-butyl perbenzoate, tert-butyl perisobutyrate, etc.

[0102] Examples of the aforementioned azo compounds include 2,2'-azobisisobutyronitrile, 1,1'-azobis(cyclohexane-1-carboxylonitrile), 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2,4-dimethylpentanitrile), 2,2'-azobis(2,4-dimethyl-4-methoxypentanitrile), 2,2'-azobis(2-(2-imidazoline-2-yl)propane), 2,2'-azobis(2,4,4-trimethylpentane), 2,2'-azobis(2-methylpropane), 2,2'-azobis(2-hydroxymethylpropionitrile), 4,4'-azobis(4-cyanopentanoic acid), dimethyl 2,2'-azobis(2-methylpropionate), 2-cyano-2-propylazocarboxamide, and 2-phenylazo-4-methoxy-2,4-dimethylpentanitrile.

[0103] Organic solvents used in the above methods typically include hydrocarbon solvents and halogenated hydrocarbon solvents. Among these organic solvents, hydrocarbon solvents such as n-butane, n-hexane, n-heptane, cyclohexane, benzene, toluene, and xylene are preferred.

[0104] Furthermore, when carrying out the reaction of adding silane compound (1) by the above method, from the viewpoint of suppressing side reactions, an antioxidant may be added.

[0105] Preferred antioxidants for use at this time include, for example, 2,6-di-tert-butyl-4-methylphenol (BHT), 2,2'-methylenebis(4-methyl-6-tert-butylphenol), 4,4'-thiobis(3-methyl-6-tert-butylphenol), 4,4'-butidenebis(3-methyl-6-tert-butylphenol) (AO-40), 3,9-bis[1,1-dimethyl-2-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]ethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane (AO-80), 2,4-bis[(octylthio)methyl]-6-methylphenol (Irganox 1520L), 2,4-bis[(dodecylthio)methyl]-6-methylphenol (Irganox 1726), 2-[ 1-(2-hydroxy-3,5-di-tert-pentylphenyl)ethyl]-4,6-di-tert-pentylphenyl acrylate (SumilizerGS), 2-tert-butyl-6-(3-tert-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate (SumilizerGM), 6-tert-butyl-4-[3-(2,4,8,10-tetra-tert-butyldibenzo[d,f][1,3,2]dioxaphosphatane-6-yloxy)propyl]-2-methylphenol (SumilizerGP), tris(2,4-di-tert-butylphenyl) phosphite (Irgafos168), dioctadecyl 3,3'-dithiodipropionate, hydroquinone, p-methoxyphenol, N-phenyl-N'-(1,3-dimethylbutyl)p-phenylenediamine (NOCRAC) Examples of antioxidants include 6C, bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate (LA-77Y), N,N-bis(octadecylhydroxylamine) (IrgastabFS042), and bis(4-tert-octylphenyl)amine (Irganox5057). These antioxidants can be used alone or in combination of two or more.

[0106] The amount of antioxidant added is preferably 0 to 10 parts by weight relative to 100 parts by weight of unmodified liquid diene rubber (B'), more preferably 0 to 5 parts by weight.

[0107] In this modified liquid diene rubber (B), the introduced functional group can be located at the polymerization end or as a side chain of the polymer chain. From the viewpoint that multiple functional groups can be easily introduced, a side chain of the polymer chain is preferred. In addition, the aforementioned functional group can be a single type or two or more types. Therefore, the modified liquid diene rubber (B) can be modified using one silane compound (1), or it can be modified using two or more compounds.

[0108] The mixing ratio of unmodified liquid diene rubber (B') to silane compound (1) can be appropriately set, for example, in such a way that the average number of functional groups in each molecule of modified liquid diene rubber (B) is a desired value. For example, it can be mixed in such a way that the mass ratio (B') / (1) of unmodified liquid diene rubber (B') to silane compound (1) is 0.3 to 300.

[0109] As a method for manufacturing modified liquid diene rubber (B) with specific properties, it is effective to allow the reaction of the silane compound (1) to undergo free radical addition at an appropriate reaction temperature and for a sufficient reaction time. For example, the temperature for the reaction in which the silane compound (1) is added to the unmodified liquid diene rubber (B') is preferably 10°C to 200°C, more preferably 50°C to 180°C, and even more preferably 50°C to 140°C. In addition, the reaction time is preferably 1 to 200 hours, more preferably 1 to 100 hours, even more preferably 1 to 50 hours, and even more preferably 1 to 25 hours.

[0110] The modified liquid diene rubber (B) has a weight-average molecular weight (Mw) of 3,000 or more and 120,000 or less (necessary condition (i)). In this invention, the Mw of the modified liquid diene rubber (B) is the weight-average molecular weight of polystyrene determined by gel permeation chromatography (GPC). If the Mw of the modified liquid diene rubber (B) is within the aforementioned range, the process compliance during manufacturing is excellent, and the economy becomes good. In addition, the processability of the rubber composition of this invention is improved, the dispersibility of the filler (C) is excellent, and the physical properties of the resulting tire tread can be improved (improved fuel efficiency and improved wear resistance).

[0111] From the viewpoint of improving the low fuel consumption performance and wear resistance of the obtained tire tread, the Mw of the modified liquid diene rubber (B) is preferably 4,000 or more and 80,000 or less, more preferably 4,500 or more and 60,000 or less, further preferably 5,000 or more and 40,000 or less, even more preferably 5,500 or more and 35,000 or less, particularly preferably 5,500 or more and 12,000 or less, and even more particularly preferably 5,500 or more and 9,000 or less. The Mw of the modified liquid diene rubber (B) is determined using GPC (gel permeation chromatography) and converted to molecular weight according to standard polystyrene. Specifically, it can be determined using the method described in the examples.

[0112] The molecular weight distribution (Mw / Mn) of the modified liquid diene rubber (B) is preferably 1.0 to 20.0, more preferably 1.0 to 15.0, even more preferably 1.0 to 10.0, even more preferably 1.0 to 5.0, and even more preferably 1.0 to 2.0. If Mw / Mn is within the aforementioned range, the resulting modified liquid diene rubber (B) has a smaller viscosity deviation, which is more preferred. It should be noted that the molecular weight distribution (Mw / Mn) refers to the ratio of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) of standard polystyrene, determined by GPC measurement.

[0113] The vinyl content of the modified liquid diene rubber (B) is less than 70 mol% (necessary condition (ii)). If the vinyl content exceeds 70 mol%, there is a tendency for the low fuel consumption performance to deteriorate.

[0114] From the viewpoint of low fuel consumption performance, the vinyl content of the modified liquid diene rubber (B) is preferably 65 mol% or less, more preferably 60 mol% or less, further preferably 50 mol% or less, even more preferably 45 mol% or less, particularly preferably 40 mol% or less, and even more preferably 30 mol% or less. The vinyl content of the modified liquid diene rubber (B) is preferably 3 mol% or more, more preferably 5 mol% or more, further preferably 7 mol% or more, and even more preferably 10 mol% or more. The preferred range of vinyl content for the modified liquid diene rubber (B) can be set by appropriately combining the above-mentioned upper and lower limits.

[0115] In this invention, "vinyl content" refers to: the total mole percentage of conjugated diene units contained in the modified liquid diene rubber (B) that are bonded by means of 1,2-bonding, 3,4-bonding (except for farnesene), and 3,13-bonding (in the case of farnesene). The vinyl content is calculated as follows: using... 1 H-NMR analysis of modified liquid diene rubber (B) was performed based on the area ratio of peaks originating from conjugated diene units bonded by 1,2-bonding, 3,4-bonding (except for farnesene) and 3,13-bonding (in the case of farnesene) to peaks originating from conjugated diene units bonded by 1,4-bonding (except for farnesene) and 1,13-bonding (in the case of farnesene).

[0116] It should be noted that the vinyl content of the modified liquid diene rubber (B) can be set to a desired value by, for example, controlling the type of solvent used in the manufacture of the unmodified liquid diene rubber (B'), the polar compound used as needed, the polymerization temperature, etc.

[0117] The melt viscosity of the modified liquid diene rubber (B) measured at 38°C is preferably 0.1 to 4,000 Pa·s, more preferably 0.1 to 2,000 Pa·s, even more preferably 0.1 to 1,000 Pa·s, particularly preferably 0.1 to 500 Pa·s, and even more preferably 0.1 to 200 Pa·s. If the melt viscosity of the modified liquid diene rubber (B) is within the aforementioned range, the resulting rubber composition exhibits improved softness, and therefore, improved processability. It should be noted that in this invention, the melt viscosity of the liquid diene rubber (B) is a value measured at 38°C using a Brookfield viscometer.

[0118] The glass transition temperature (Tg) of the modified liquid diene rubber (B) may vary depending on the vinyl content of the conjugated diene units, the type of conjugated diene, and the content of units derived from monomers other than the conjugated diene. It is preferably -150 to 50°C, more preferably -120 to 30°C, further preferably -100 to 10°C, and even more preferably -100 to 0°C. If Tg is within the above range, for example, the low fuel consumption performance and fuel consumption resistance of tire treads obtained from the rubber composition can be easily improved. Furthermore, the viscosity of the modified liquid diene rubber (B) can be suppressed from increasing, making it easier to handle.

[0119] The modified liquid diene rubber (B) described above can be used alone or in combination with two or more types.

[0120] In the modified liquid diene rubber (B) described above, the amount of catalyst residue derived from the polymerization catalyst used in its manufacture is preferably in the range of 0 to 200 ppm in metal conversion. For example, when using an organic alkali metal such as an organolithium compound as the polymerization catalyst for manufacturing the unmodified liquid diene rubber (B'), which is a raw material for the modified liquid diene rubber (B), the metal used as the benchmark for the amount of catalyst residue becomes an alkali metal such as lithium. By keeping the amount of catalyst residue within the above range, the viscosity does not decrease during processing, and the performance of the tire tread obtained from the rubber composition of the present invention is improved. As for the amount of catalyst residue derived from the polymerization catalyst used in the manufacture of the modified liquid diene rubber (B), it is more preferably 0 to 150 ppm, and even more preferably 0 to 100 ppm in metal conversion. It should be noted that the amount of catalyst residue can be determined, for example, using a polarized Zeeman atomic absorption spectrophotometer.

[0121] Methods for setting the catalyst residue amount of liquid diene rubber to this specific amount include: purifying the modified liquid diene rubber (B) or the unmodified liquid diene rubber (B') used as raw material to thoroughly remove catalyst residue. As a purification method, washing with water or warm water, or organic solvents such as methanol or acetone, or supercritical fluid carbon dioxide is preferred. From an economic point of view, the number of washing cycles 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. In addition, by removing impurities that hinder polymerization using distillation and / or adsorbents before the polymerization reaction, and improving the purity of the monomer and / or solvent before polymerization, a smaller amount of polymerization catalyst is required, thus reducing the amount of catalyst residue. Furthermore, from the same perspective as above, the amount of catalyst residue in the tire tread rubber composition of the present invention, containing solid rubber (A), modified liquid diene rubber (B), and filler (C), is preferably 0 to 200 ppm, more preferably 0 to 150 ppm, and even more preferably 0 to 100 ppm in metal conversion. This amount of catalyst residue is simply the amount of catalyst residue derived from any one or more of the polymerization catalyst used in the manufacture of the solid rubber (A), the modified liquid diene rubber (B), and other optional components included in the tire tread rubber composition of the present invention.

[0122] In the rubber composition of the present invention, the content of modified liquid diene rubber (B) relative to 100 parts by weight of solid rubber (A) is 0.1 to 50 parts by weight, preferably 1 to 45 parts by weight, more preferably 1 to 40 parts by weight, further preferably 2 to 40 parts by weight, even more preferably 5 to 40 parts by weight, particularly preferably 5 to 35 parts by weight, even more preferably 5 to 30 parts by weight, even more preferably 5 to 25 parts by weight, and even more preferably 10 to 25 parts by weight. If the content of modified liquid diene rubber (B) is within the above range, the dispersibility of filler (C) in the rubber composition is improved, and the low fuel consumption performance and wear resistance of the resulting tire tread are improved.

[0123] [Packaging (C)] As for the filler (C) used in the tire tread rubber composition of the present invention, any substance commonly used in tire tread rubber compositions may be used without particular limitation. From the viewpoint of improving the low fuel consumption performance of tire tread, the filler (C) preferably contains silica (C1).

[0124] Examples of silica (C1) include wet silica (hydrated silica), dry silica (anhydrous silica), calcium silicate, and aluminum silicate. Among these silicas, wet silica is preferred from the viewpoint of further improving processability, the mechanical strength and wear resistance of the resulting tire tread, and further improving fuel efficiency.

[0125] From the viewpoint of improving the processability of the rubber composition for tire tread, and enhancing the low fuel consumption performance and wear resistance of the tire tread obtained by using the rubber composition for tire tread in at least a portion, the average particle size of silica (Cl) is preferably 0.5 nm or more, more preferably 2 nm or more, further preferably 5 nm or more, even more preferably 8 nm or more, and particularly preferably 10 nm or more. Furthermore, the aforementioned average particle size is preferably 200 nm or less, more preferably 150 nm or less, further preferably 100 nm or less, even more preferably 50 nm or less, particularly preferably 30 nm or less, and most preferably 20 nm or less. It should be noted that the average particle size of silica can be determined by measuring the diameter of each particle in the field of view observed using a transmission electron microscope and calculating its average value.

[0126] From the viewpoint of improving the mechanical strength and wear resistance of the tire tread rubber composition of the present invention, the filler (C) used in the tire tread rubber composition of the present invention preferably includes carbon black (C2). In other words, the filler (C) used in the tire tread rubber composition of the present invention preferably includes silica (C1) and carbon black (C2).

[0127] Examples of carbon black (C2) include furnace black, channel black, thermal black, acetylene black, and Ketjen black. From the perspectives of increased crosslinking speed, improved mechanical strength of the resulting tire tread, improved wear resistance, and improved low fuel consumption performance, furnace black is preferred among these carbon blacks. One type of carbon black may be used alone, or two or more may be used in combination.

[0128] From the viewpoint of improving the mechanical strength, wear resistance, and low fuel consumption performance of tire treads obtained by using a tire tread rubber composition in at least a portion, the average particle size of carbon black (C2) is preferably 5 nm or more, more preferably 10 nm or more, and even more preferably 15 nm or more. Furthermore, the aforementioned average particle size is preferably 100 nm or less, more preferably 80 nm or less, even more preferably 60 nm or less, and even more preferably 40 nm or less. It should be noted that the average particle size of carbon black can be determined by measuring the diameter of each particle within the field of view observed using a transmission electron microscope and calculating its average value.

[0129] Commercially available products of the aforementioned furnace blacks include, for example, "DIABLACK" manufactured by Mitsubishi Chemical Corporation and "SEAST" manufactured by Tokai Rubber & Plastics Corporation. Commercially available products of acetylene blacks include, for example, "DENKABLACK" manufactured by Electrochemical Industries Co., Ltd. Commercially available products of Ketjen blacks include, for example, "ECP600JD" manufactured by Lion Corporation.

[0130] From the viewpoint of improving the wettability and dispersibility of solid rubber (A), the aforementioned carbon black (C2) can be acid-treated with nitric acid, sulfuric acid, hydrochloric acid, or mixtures thereof, and / or surface-oxidized by heat treatment in the presence of air. Furthermore, from the viewpoint of improving the mechanical strength of the tire tread rubber composition of the present invention and the tire tread obtained from the composition, heat treatment can be performed at 2,000 to 3,000 °C in the presence of a graphitization catalyst. It should be noted that suitable graphitization catalysts include boron, boron oxides (e.g., B2O2, B2O3, B4O3, B4O5, etc.), oxyacids of boron (e.g., orthoboric acid, metaboric acid, tetraboric acid, etc.) and their salts, boron carbides (e.g., B4C, B6C, etc.), boron nitride (BN), and other boron compounds.

[0131] The carbon black (C2) mentioned above can also be used after its particle size has been adjusted by crushing or other methods. Carbon black can be crushed using high-speed rotary mills (hammer mills, pin mills, cage mills) and / or various ball mills (rotary mills, vibratory mills, planetary mills), stirred mills (bead mills, grinding mills, flow-through mills, ring mills), etc.

[0132] Regarding the rubber composition for tire tread of the present invention, for the purposes of improving the mechanical strength and other properties of the resulting tire tread, and improving manufacturing costs by using compounded fillers as extenders, it may contain fillers other than silica (C1) and carbon black (C2).

[0133] As fillers other than silica (C1) and carbon black (C2), organic fillers and / or inorganic fillers such as clay, talc, mica, calcium carbonate, magnesium hydroxide, aluminum hydroxide, barium sulfate, titanium dioxide, glass fiber, fibrous fillers, and hollow glass spheres can be used. These fillers can be used alone or in combination of two or more.

[0134] The filler (C) is present in an amount of 20 to 200 parts by weight relative to 100 parts by weight of solid rubber (A), preferably 20 to 150 parts by weight. If the amount of filler (C) is within the aforementioned range, both improved fuel efficiency and improved wear resistance can be achieved when the tire tread rubber composition is used in at least a portion of the tire tread. From the aforementioned viewpoint, the amount of filler (C) relative to 100 parts by weight of solid rubber (A) is more preferably 30 parts by weight or more, further preferably 50 parts by weight or more, even more preferably 70 parts by weight or more, and preferably 140 parts by weight or less, more preferably 130 parts by weight or less, even more preferably 120 parts by weight or less, and even more preferably 110 parts by weight or less.

[0135] Furthermore, when silica (C1) is included as filler (C), from the viewpoint of improving the wet grip performance, low fuel consumption performance, and wear resistance of the tire tread obtained by using the tire tread rubber composition in at least a portion, the amount of silica (C1) relative to 100 parts by mass of solid rubber (A) is preferably 20 parts by mass or more, more preferably 30 parts by mass or more, further preferably 40 parts by mass or more, even more preferably 50 parts by mass or more, and particularly preferably 60 parts by mass or more. Moreover, the amount of silica (C1) is preferably 145 parts by mass or less, more preferably 135 parts by mass or less, and even more preferably 105 parts by mass or less.

[0136] When carbon black (C2) is further included as filler (C), from the viewpoint of improving the wear resistance and low fuel consumption performance of the tire tread obtained by using the tire tread rubber composition in at least a portion, the amount of carbon black (C2) relative to 100 parts by mass of solid rubber (A) is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, even more preferably 20 parts by mass or more, and particularly preferably 30 parts by mass or more. Furthermore, the amount of carbon black (C2) is preferably 80 parts by mass or less, more preferably 60 parts by mass or less, and even more preferably 40 parts by mass or less.

[0137] When silica (C1) and carbon black (C2) are included as filler (C), from the viewpoint that the low fuel consumption performance and wear resistance of the tire tread obtained from the rubber composition for tire tread of the present invention can be further improved, the ratio of silica (C1) to carbon black (C2) (mass ratio = (C1) / (C2)) is preferably 1 / 99 to 99 / 1, more preferably 10 / 90 to 95 / 5, and even more preferably 30 / 70 to 90 / 10. Furthermore, from the same viewpoint, 1 / 99 to 99 / 1 is preferred, more preferably 10 / 90 to 95 / 5, even more preferably 50 / 50 to 95 / 5, and even more preferably 70 / 30 to 95 / 5.

[0138] [Other ingredients] In the tire tread rubber composition of the present invention, when silica (Cl) or the like is used as filler (C), a preferred embodiment is a silane coupling agent. Examples of silane coupling agents include, for instance, sulfide compounds, mercapto compounds, vinyl compounds, amino compounds, epoxypropoxy compounds, nitro compounds, and chlorine compounds.

[0139] 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-dimethylthiocarbamoyl tetrasulfide, 3-triethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 2-trimethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropylbenzothiazole tetrasulfide, 3-triethoxysilylpropylbenzothiazole tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, 3-octanoylthio-1-propyltriethoxysilane, etc.

[0140] Examples of thiol compounds include 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, and 2-mercaptoethyltriethoxysilane.

[0141] Examples of vinyl compounds include vinyltriethoxysilane and vinyltrimethoxysilane.

[0142] Examples of amino compounds include 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-(2-aminoethyl)aminopropyltriethoxysilane, and 3-(2-aminoethyl)aminopropyltrimethoxysilane.

[0143] Examples of epoxypropoxy compounds include γ-epoxypropoxypropyltriethoxysilane, γ-epoxypropoxypropyltrimethoxysilane, γ-epoxypropoxypropylmethyldiethoxysilane, and γ-epoxypropoxypropylmethyldimethoxysilane.

[0144] Examples of nitro compounds include 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane.

[0145] Examples of chlorine compounds include 3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysilane, 2-chloroethyltrimethoxysilane, and 2-chloroethyltriethoxysilane.

[0146] Other examples of such compounds include octyltriethoxysilane, methyltriethoxysilane, methyltrimethoxysilane, and hexadecyltrimethoxysilane.

[0147] These silane coupling agents can be used alone or in combination of two or more. Among these silane coupling agents, from the viewpoint of maximizing the reinforcing effect, sulfur-containing silane coupling agents such as sulfide compounds and mercapto compounds are preferred, and bis(3-triethoxysilylpropyl) disulfide, bis(3-triethoxysilylpropyl) tetrasulfide, and 3-mercaptopropyltriethoxysilane are more preferred.

[0148] For example, the silane coupling agent described above preferably contains 0.1 to 30 parts by mass relative to 100 parts by mass of silicon dioxide (Cl), more preferably 0.5 to 20 parts by mass, and even more preferably 1 to 15 parts by mass. If the content of the silane coupling agent is within the aforementioned range, the dispersibility, coupling effect, reinforcement, and wear resistance are improved.

[0149] In the tire tread rubber composition of the present invention, a vulcanizing agent (D) may be further contained for crosslinking the rubber. Examples of vulcanizing agents (D) include sulfur and sulfur compounds. Examples of sulfur compounds include morpholine disulfide and alkylphenol disulfide. One of these vulcanizing 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 vulcanizing agent (D) is typically contained in 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 solid rubber (A).

[0150] When the tire tread rubber composition of the present invention contains, for example, a vulcanizing agent (D) for crosslinking (vulcanizing) rubber, it may also contain a vulcanization accelerator (E). Examples of vulcanization accelerators (E) include, for example, guanidine compounds, sulfinamide compounds, thiazole compounds, thiuram compounds, thiourea compounds, dithiocarbamate compounds, aldehyde-amine compounds, aldehyde-amine 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 present in 0.1 to 15 parts by weight, preferably 0.1 to 10 parts by weight, relative to 100 parts by weight of solid rubber (A).

[0151] In the tire tread rubber composition of the present invention, when sulfur, sulfur compounds, etc., are included as a vulcanizing agent (D) for crosslinking (vulcanizing) the rubber, a vulcanizing aid (F) may also be included. Examples of vulcanizing aids (F) include fatty acids such as stearic acid, metal oxides such as zinc oxide, and fatty acid metal salts such as zinc stearate. One of these vulcanizing aids (F) may be used alone, or two or more may be used in combination. The vulcanizing aid (F) typically contains 0.1 to 15 parts by weight, and preferably 1 to 10 parts by weight, relative to 100 parts by weight of solid rubber (A).

[0152] In addition to a vulcanizing agent (D), the rubber composition for tire tread may also contain a crosslinking agent. Examples of such crosslinking agents include oxygen, organic peroxides, phenolic resins, amino resins, quinones and quinone dioxime derivatives, halogen compounds, aldehyde compounds, alcohol compounds, epoxy compounds, metal halides, organometallic halides, and silane compounds. One type may be used alone, or two or more may be used in combination. The amount of crosslinking agent is preferably 0.1 to 10 parts by weight relative to 100 parts by weight of solid rubber (A).

[0153] In the tire tread rubber composition of the present invention, without hindering the effect of the present invention, for the purpose of improving processability, flowability, etc., it may contain, as needed, silicone oil, aromatic oil, TDAE (Treated Distilled Aromatic Extracts), MES (Mild Extracted Solvates), RAE (Residual Aromatic Extracts), alkane oil, cycloalkane oil and other process oils, aliphatic hydrocarbon resins, alicyclic hydrocarbon resins, C9 series resins, rosin resins, coumarone-indene resins, phenolic resins and other resin components, as well as liquid polymers such as low molecular weight polybutadiene, low molecular weight polyisoprene, low molecular weight styrene-butadiene copolymer and low molecular weight styrene-isoprene copolymer as softeners. When the tire tread rubber composition of the present invention contains the above-mentioned process oil, resin, and liquid polymer as a softener, from the viewpoint of bleed resistance, its content relative to 100 parts by weight of solid rubber (A) is preferably 50 parts by weight or less, more preferably 30 parts by weight or less, and even more preferably 15 parts by weight or less.

[0154] In the tire tread rubber composition of the present invention, without hindering the effect of the present invention, additives such as antioxidants, waxes, lubricants, light stabilizers, anti-scorching agents, processing aids, colorants such as pigments and / or dyes, flame retardants, antistatic agents, matting agents, anti-blocking agents, ultraviolet absorbers, release agents, foaming agents, antibacterial agents, mildew inhibitors, and fragrances may be included as needed to improve weather resistance, heat resistance, oxidation resistance, etc.

[0155] Examples of antioxidants include hindered phenolic compounds, phosphorus compounds, lactone compounds, and hydroxyl compounds.

[0156] Examples of antioxidants include amine-ketone compounds, imidazole compounds, amine compounds, phenolic compounds, sulfur compounds, and phosphorus compounds. These additives can be used individually or in combination of two or more.

[0157] [Method for manufacturing rubber composition for tire tread] The method for manufacturing the tire tread rubber composition of the present invention is not particularly limited as long as the above-mentioned components can be uniformly mixed. Examples of apparatus for manufacturing the tire tread rubber composition include, for example, tangential or interlocking closed mixing mills such as KNEADER-RUDER, Brabender, and Banbury internal mixers with internal agitators, single-screw extruders, twin-screw extruders, open mill rolls, and rollers. The manufacturing of the above-mentioned rubber composition can generally be carried out in a temperature range of 70 to 270°C.

[0158] The tire tread rubber composition of the present invention is preferably used in the form of a crosslinked product (vulcanized rubber) through crosslinking. The vulcanization conditions and methods are not particularly limited, but it is preferred to use a vulcanization mold at a vulcanization temperature of 120-200°C and a vulcanization pressure of 0.5-20 MPa.

[0159] The extraction rate of modified liquid diene rubber (B) from the crosslinked material is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less.

[0160] It should be noted that the above extraction rate can be calculated as follows: after immersing 2g of crosslinked material in 400mL of toluene at 23°C for 48 hours, the amount of modified liquid diene rubber (B) extracted into the toluene is used for calculation.

[0161] [Tire tread] The tire tread of the present invention is obtained by using the aforementioned tire tread rubber composition in at least a portion, without compromising wet grip performance, and simultaneously improving fuel efficiency and wear resistance. It is particularly suitable for tire treads used in electric vehicles, which are characterized by relatively heavy vehicle weight and electric motor drive characteristics (e.g., high initial torque). An electric vehicle is a vehicle (e.g., electric car, hybrid vehicle, fuel cell vehicle) that uses an electric motor as at least a part of its power source.

[0162] Regarding the tire tread of the present invention, a tire tread rubber with a specified cross-sectional shape is formed by using a tire tread rubber composition obtained by the above operation through an extruder or the like, and the tire tread rubber is used to manufacture tires for various purposes such as passenger car tires (e.g., pneumatic tires, solid tires, and airless tires) using conventional methods (generally including a crosslinking process), thereby enabling the tire to be obtained in the form of a tire containing the tire tread of the present invention (e.g., a pneumatic tire for an electric vehicle). Example

[0163] The present invention will be described in more detail below through embodiments, but the present invention is not limited to these embodiments.

[0164] The components used in this embodiment and comparative example are shown below.

[0165] <Solid Rubber (A)> Natural rubber (A1): STR20 (natural rubber from Thailand) Butadiene rubber (A2): BR01 (manufactured by ENEOS Materials, Mw: 550,000, cis content: 95% by mass) Styrene-butadiene rubber (A3): Solution polymerized styrene-butadiene copolymer HPR850 (manufactured by ENEOS Materials Co., Ltd., styrene content 27.5% by mass, vinyl content 59% by mass). <Modified Liquid Diene Rubber (B)> The modified liquid diene rubbers obtained in Examples 1-3 described later <Packaging (C)> Silica: ULTRASIL9100GR (Evonik Degussa, Japan, wet silica) Carbon black: DIABLACK I (manufactured by Mitsubishi Chemical Corporation, average particle size 23nm) <Vulcanizing Agent (D)> Sulfur: MUCRON OT-20 (manufactured by Shikoku Chemical Industry Co., Ltd., insoluble sulfur, oil content: 18~22%) <Vulcanization Accelerator (E)> Vulcanization accelerator (1): Nocceler CZ-G (manufactured by Ouchi Shinshin Chemical Industry Co., Ltd.) Vulcanization accelerator (2): Nocceler D (manufactured by Ouchi Shinshin Chemical Industry Co., Ltd.) <Vulcanizing aid (F)> Stearic acid: Lunac S-20 (manufactured by Kao Corporation) Zinc white: Zinc oxide (manufactured by Sakai Chemical Industry Co., Ltd.) <Optional Ingredients> TDAE: VivaTec500 (made by H&R) Silane coupling agent: Si-75 (manufactured by Evonik Degussa Japan Co., Ltd.) Antioxidant: Nocrac 6C (manufactured by Ouchi Shinshin Chemical Industry Co., Ltd.) Wax: SUNTIGHT S (manufactured by Seiko Chemical Co., Ltd.)

[0166] Manufacturing Example 1: Manufacturing of Modified Liquid Diene Rubber (B-1) A thoroughly dried 5L autoclave was purged with nitrogen. 1150g of hexane and 154g of n-butyllithium (17% by mass hexane solution) were added. The mixture was heated to 50°C, and under stirring, 10g of N,N,N',N'-tetramethylethylenediamine was added. While maintaining the polymerization temperature at 50°C, 1250g of butadiene was added sequentially, and polymerization was carried out for 1 hour. Subsequently, methanol was added to stop the polymerization reaction, yielding a polymer solution. Water was added to the resulting polymer solution and stirred to wash the polymer solution. After stirring was stopped, and the polymer solution phase was confirmed to have separated from the aqueous phase, the water was separated. The washed polymer solution was then vacuum-dried at 70°C for 24 hours to obtain unmodified liquid diene rubber (B'1).

[0167] Next, 700g of the unmodified liquid diene rubber (B'1) was added to a 1L high-pressure reactor, and nitrogen degassing was carried out while stirring at 60°C for 3 hours. 0.1g of 1,1-bis(tert-butylperoxy)cyclohexane and 119g of (3-mercaptopropyl)triethoxysilane were added, and the mixture was reacted at 120°C for 3 hours to obtain the modified liquid diene rubber (B-1).

[0168] Manufacturing Example 2: Manufacturing of Modified Liquid Diene Rubber (B-2) A thoroughly dried 5L autoclave was purged with nitrogen. 1100g of hexane and 204g of n-butyllithium (17% by mass hexane solution) were added. After heating to 50°C, butadiene was added sequentially while stirring to maintain a polymerization temperature of 50°C. Polymerization was carried out for 1 hour. Subsequently, methanol was added to stop the polymerization reaction, yielding a polymer solution. Water was added to the resulting polymer solution and stirred to wash the polymer solution. After stirring was stopped, and the polymer solution phase was confirmed to have separated from the aqueous phase, the water was separated. The washed polymer solution was then vacuum-dried at 70°C for 24 hours to obtain unmodified liquid diene rubber (B'2).

[0169] Next, 700g of the obtained unmodified liquid diene rubber (B'2) was added to a 1L high-pressure reactor, and nitrogen degassing was carried out while stirring at 60°C for 3 hours. 2.0g of 1,1-bis(tert-butylperoxy)cyclohexane and 119g of (3-mercaptopropyl)triethoxysilane were added, and the mixture was reacted at 120°C for 3 hours to obtain the modified liquid diene rubber (B-2).

[0170] Manufacturing Example 3: Manufacturing of Modified Liquid Diene Rubber (B-3) A thoroughly dried 5L autoclave was purged with nitrogen. 1280g of cyclohexane and 66g of sec-butyllithium (10.5% by mass cyclohexane solution) were added. After heating to 50°C, butadiene 1350g was added sequentially while stirring to maintain a polymerization temperature of 50°C. Polymerization was carried out for 1 hour. Subsequently, methanol was added to stop the polymerization reaction, yielding a polymer solution. Water was added to the resulting polymer solution and stirred to wash the polymer solution. After stirring was stopped, and the polymer solution phase was confirmed to have separated from the aqueous phase, the water was separated. The washed polymer solution was then vacuum-dried at 70°C for 24 hours to obtain unmodified liquid diene rubber (B'3).

[0171] Next, 700g of the obtained unmodified liquid diene rubber (B'3) was added to a 1L high-pressure reactor, and nitrogen degassing was carried out while stirring at 60°C for 3 hours. 1.0g of 1,1-bis(tert-butylperoxy)cyclohexane and 50g of (3-mercaptopropyl)triethoxysilane were added, and the mixture was reacted at 105°C for 8 hours to obtain the modified liquid diene rubber (B-3).

[0172] It should be noted that the methods for determining and calculating the various physical properties of the modified liquid diene rubbers, etc., obtained in the manufacturing examples are as follows.

[0173] (Method for determining weight-average molecular weight) The molecular weight (Mw) of the modified liquid diene rubber (B) was determined using GPC (gel permeation chromatography) and converted to the molecular weight of standard polystyrene. The apparatus and conditions for determination are shown below.

[0174] • Device: GPC device "GPC8020" manufactured by Tosoh Corporation • Separation column: Tosoh Corporation's "TSKgel G4000HXL" • Detector: Tosoh Corporation's "RI-8020" • Eluent: Tetrahydrofuran • Elution flow rate: 1.0 mL / min • Sample concentration: 5 mg / 10 mL • Column temperature: 40℃.

[0175] (Vinyl content) The vinyl content of the modified liquid diene rubber (B) was determined using an AVANCEIII 400 NanoBay NMR spectrometer manufactured by BRUKER JAPAN, at a concentration of 50 mg / 1 mL of modified liquid diene rubber (B) and 1024 NMR measurements. The vinyl content was calculated based on the area ratio of peaks originating from conjugated diene units bonded via 1,2- and 3,4-bonds to peaks originating from conjugated diene units bonded via 1,4-bonds.

[0176] (Glass transition temperature) 10 mg of modified liquid diene rubber (B) was placed in an aluminum pan and the temperature spectrum was measured by differential scanning calorimetry (DSC) at a heating rate of 10 °C / min. The peak value of the DDSC (the first derivative curve of the DSC curve) was set as the glass transition temperature (Tg).

[0177] (Method for determining melt viscosity at 38℃) The melt viscosity of the modified liquid diene rubber (B) at 38°C was measured using a Brookfield viscometer (manufactured by Brookfield Engineering Labs, Inc.).

[0178] (Average number of functional groups in each molecule of modified liquid diene rubber (B)) The number average molecular weight Mn of the modified liquid diene rubber (B) was determined by using the average number of functional groups in each molecule of the modified liquid diene rubber (B), the equivalent amount of functional groups (g / eq) of the modified liquid diene rubber (B), and the number average molecular weight Mn converted from styrene.

[0179] (Average number of functional groups per molecule) = [(Number average molecular weight Mn) ÷ (Molecular weight of styrene unit) × (Average molecular weight of conjugated diene and other monomer units other than conjugated diene included as needed)] / (Equivalent number of functional groups) It should be noted that the functional group equivalent of the modified liquid diene rubber (B) refers to the mass of butadiene bonded to one functional group and, as needed, other monomers besides butadiene. The functional group equivalent is determined by the use of the modified liquid diene rubber (B). 1 H-NMR or 13 The calculation is based on the area ratio of peaks originating from functional groups to peaks originating from the polymer backbone obtained by C-NMR. It should be noted that peaks originating from functional groups refer to peaks originating from alkoxy groups.

[0180] The physical properties of the modified liquid diene rubbers (B-1) to (B-3) obtained in Examples 1 to 3 are summarized in Table 1.

[0181] [Table 1] .

[0182] Examples 1-10 and Comparative Examples 1-6 According to the mixing ratios (parts by mass) recorded in Tables 2 and 3, all components except the vulcanizing agent (sulfur) and vulcanization accelerator were added separately to a closed Banbury mixer. The mixing was controlled with an initial temperature of 60°C and a resin temperature of 155-160°C. After mixing for 4 minutes, the mixture was removed from the mixer and cooled to room temperature. Next, the mixture was added back to the Banbury mixer, and the mixing was controlled with an initial temperature of 60°C and a resin temperature of 155-160°C. After mixing for 3 minutes, the mixture was removed from the mixer and cooled to room temperature. Then, the mixture was added back to the Banbury mixer, and the vulcanizing agent (sulfur) and vulcanization accelerator were added. The mixture was then mixed at an initial temperature of 50°C and a final temperature of 100°C for 75 seconds to obtain the rubber composition.

[0183] The obtained rubber composition was press-molded (160°C, 20-30 minutes) to produce vulcanized rubber sheets (2 mm thick). The low fuel consumption performance, abrasion resistance, and wet grip performance were evaluated according to the following method. The results are shown in Tables 2 and 3.

[0184] It should be noted that the measurement methods for each evaluation are as follows.

[0185] (Low fuel consumption performance) Test pieces measuring 40 mm in length and 5 mm in width were cut from the rubber compositions prepared in the examples and comparative examples. The tanδ was measured using a dynamic viscoelasticity measuring device manufactured by GABO at a measurement temperature of 60°C, a frequency of 10 Hz, a static deformation of 10%, and a dynamic deformation of 2%, and was set as an indicator of low fuel consumption performance.

[0186] The values ​​for each embodiment and comparative example in Table 2 are relative values ​​when the value of Comparative Example 1 is set to 100. It should be noted that when the relative value relative to Comparative Example 1 is 100±5 (95~105), it is equivalent to Comparative Example 1. When the relative value is less than 95, the low fuel consumption performance of the rubber composition is good compared to Comparative Example 1. When the relative value is greater than 105, the low fuel consumption performance of the rubber composition is poor compared to Comparative Example 1.

[0187] Furthermore, Table 3 examines rubber compositions containing resin. The values ​​for each example and comparative example in Table 3 are relative values ​​with Comparative Example 2 set to 100. Performance was evaluated based on Comparative Example 2, using the same judgment criteria as in Table 2.

[0188] (Abrasion resistance, FPS abrasion tester) Test pieces with holes the size of a dedicated metal core, 50 mm in diameter and 10 mm thick, were made from the rubber compositions prepared in the examples and comparative examples. The abrasion amount was measured using an FPS abrasion tester manufactured by Ueshima Corporation, with the abrasion road surface being METABRIT (particle size 240, abrasive A) manufactured by Noritake Coated Abrasive Co., Ltd., the test piece speed being 80 m / min, the load being 40 N, the talc feeder being 0.4 rpm, the set temperature being 35 °C, and the slip ratio being 15%.

[0189] The values ​​for each embodiment and comparative example in Table 2 are relative values ​​when the value of Comparative Example 1 is set to 100. When the relative value relative to Comparative Example 1 is 100±5 (95~105), it is equivalent to Comparative Example 1. When the relative value is less than 95, it indicates that the wear amount is small and the wear resistance is good compared with Comparative Example 1. When the relative value is greater than 105, the wear amount is large and the wear resistance is poor compared with Comparative Example 1.

[0190] Furthermore, Table 3 examines rubber compositions containing resin. The values ​​for each example and comparative example in Table 3 are relative values ​​with Comparative Example 2 set to 100. Performance was evaluated based on Comparative Example 2, using the same judgment criteria as in Table 2.

[0191] (Wet grip performance) The coefficient of friction (μ) on wet pavement is used as an indicator of the wet grip performance of the rubber composition.

[0192] The coefficient of friction of wet road surfaces was determined using cylindrical friction coefficient measuring test pieces prepared in the examples and comparative examples. The measuring apparatus and conditions are as follows.

[0193] The coefficient of friction was measured within a range of 0 to 40% of the tire-road slip ratio, and the maximum value of the obtained coefficient of friction was taken as the coefficient of friction (μ) of the wet road surface.

[0194] The values ​​for each embodiment and comparative example in Table 2 are relative values ​​when the value of Comparative Example 1 is set to 100. When the relative value relative to Comparative Example 1 is 100±5 (95~105), it is equivalent to Comparative Example 1. When the relative value is greater than 105, it indicates that the wet grip performance is good compared to Comparative Example 1. When the relative value is less than 95, the wet grip performance is poor compared to Comparative Example 1.

[0195] Furthermore, Table 3 examines rubber compositions containing resin. The values ​​for each example and comparative example in Table 3 are relative values ​​with the value of Comparative Example 2 set to 100. Performance was evaluated based on Comparative Example 2, using the same judgment criteria as in Table 2.

[0196] [Measuring Apparatus and Measuring Conditions] • Apparatus: RTM friction testing machine manufactured by Uejima Manufacturing Co., Ltd. • Measurement temperature: 20℃ • Road surface: Noritake Coated Abrasive Co., Ltd., METABRIT, grit size 120, abrasive A • Road surface water supply rate: 1.0L / min • Road surface water supply temperature: 20℃ • Speed: 30km / hrs • Load: 50N • Slip ratio: 0~40%.

[0197] [Table 2] .

[0198] [Table 3] .

[0199] Industrial utilization The tire tread obtained from the rubber composition of the present invention, compared with the tire tread obtained from conventional rubber compositions, achieves improved fuel efficiency while maintaining or improving wet grip performance. Furthermore, it also improves abrasion resistance while maintaining or improving wet grip performance. Therefore, it is possible to achieve a balanced and effective improvement in the three previously difficult-to-achieve properties: fuel efficiency, abrasion resistance, and wet grip performance. Thus, it is useful as a tire tread, particularly for vehicles with increased weight, such as electric vehicles (electric cars, hybrid vehicles, fuel cell vehicles), etc.

Claims

1. A rubber composition for tire tread, wherein, Relative to 100 parts by weight of solid rubber (A) comprising natural rubber (A1), butadiene rubber (A2), and styrene-butadiene rubber (A3), 0.1 to 50 parts by weight of modified liquid diene rubber (B) having functional groups derived from silane compounds represented by formula (1) below, and 20 to 200 parts by weight of filler (C), The modified liquid diene rubber (B) has the following characteristics (i) to (iii): (i) Weight-average molecular weight (Mw) is above 3,000 and below 120,000; (ii) The vinyl content is less than 70 mol%; (iii) The average number of functional groups derived from the silane compound in each molecule of modified liquid diene rubber (B) is 1 to 20. [Chemistry 1] In equation (1), R 1 R is a divalent alkylene group having 1 to 6 carbon atoms. 2 R 3 and R 4 Each can independently represent methoxy, ethoxy, phenoxy, methyl, ethyl, or phenyl, where R 2 R 3 and R 4 At least one of them is methoxy, ethoxy, or phenoxy.

2. The rubber composition for tire tread according to claim 1, wherein, The aforementioned modified liquid diene rubber (B) has a melt viscosity of 0.1~4,000 Pa·s at 38°C.

3. The rubber composition for tire tread according to claim 1 or 2, wherein, The content of natural rubber (A1) in the aforementioned solid rubber (A) 100% by mass is 40-80% by mass.

4. The rubber composition for tire tread according to any one of claims 1 to 3, wherein, The mass ratio of butadiene rubber (A2) to styrene-butadiene rubber (A3) contained in the aforementioned solid rubber (A) is 0.12 or more and 3 or less.

5. The rubber composition for tire tread according to any one of claims 1 to 4, wherein, It contains silica as the aforementioned filler (C).

6. The rubber composition for tire tread according to claim 5, wherein, It also contains carbon black as the aforementioned filler (C).

7. A crosslinked compound obtained by crosslinking the rubber composition for tire tread according to any one of claims 1 to 6.

8. A tire tread, at least a portion thereof using the rubber composition for tire tread as described in any one of claims 1 to 7.

9. A pneumatic tire for an electric vehicle, comprising the tire tread as described in claim 8.

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