Classifications

• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
  • Y02T10/00—Road transport of goods or passengers
  • Y02T10/80—Technologies aiming to reduce greenhouse gasses emissions common to all road transportation technologies
  • Y02T10/86—Optimisation of rolling resistance, e.g. weight reduction 

Definitions

• rubber compositions used in tire treads are required to have low fuel consumption performance.
• rubber compositions containing solid rubber, a specific modified liquid diene rubber, and a filler have been studied as rubber compositions suitable for use in tire treads for the purpose of improving such low fuel consumption performance (see Patent Documents 1 and 2).
• automobiles including passenger cars are being considered to be moving away from automobiles that are powered only by internal combustion engines and toward automobiles that use electric motors as at least a part of the power source (electric vehicles). In these electric vehicles, the state of transmission of driving force from the power source to the tires is different.
• the present invention has been made in consideration of the above-mentioned circumstances, and provides a rubber composition for tire treads, which can achieve both improved fuel economy and improved abrasion resistance without impairing wet grip performance, and a tire tread using the same at least in part.
• a tire tread using at least a portion of a rubber composition containing a specific solid rubber, a specific modified liquid diene rubber, and a filler can achieve both improved fuel economy and improved abrasion resistance without compromising wet grip performance, and thus completed the present invention.
• a rubber composition for a tire tread comprising 100 parts by mass of a solid rubber (A) including a natural rubber (A1), a butadiene rubber (A2), and a styrene-butadiene rubber (A3), 0.1 to 50 parts by mass of a modified liquid diene-based rubber (B) having a functional group derived from a silane compound represented by the following formula (1), and 20 to 200 parts by mass of a filler (C):
• the modified liquid diene rubber (B) has the following properties: (i) a weight average molecular weight (Mw) of 3,000 or more and 120,000 or less; (ii) a vinyl content of 70 mol% or less; (iii) the average number of functional groups derived from the silane compound per molecule of the modified liquid diene rubber (B) is 1 to 20;
• a rubber composition for tire treads comprising 100 parts by mass of a solid rubber (A) including a natural rubber (A1), a butadiene rubber (
• R1 is a divalent alkylene group having 1 to 6 carbon atoms
• R2 , R3 , and R4 each independently represent a methoxy group, an ethoxy group, a phenoxy group, a methyl group, an ethyl group, or a phenyl group, provided that at least one of R2 , R3 , and R4 is a methoxy group, an ethoxy group, or a phenoxy group.
• the present invention provides a rubber composition for tire treads that can simultaneously improve fuel economy and wear resistance without impairing wet grip performance, and a tire tread that uses this rubber composition at least in part.
• Solid rubber (A) used in the rubber composition for tire tread of the present invention means a rubber that can be handled in a solid form at 20° C.
• the Mooney viscosity ML 1+4 of the solid rubber (A) at 100° C. is usually in the range of 20 to 200.
• the solid rubber (A) contained in the rubber composition for tire tread of the present invention includes natural rubber (A1), butadiene rubber (A2) and styrene-butadiene rubber (A3).
• Natural rubber (A1) examples include unmodified natural rubbers such as TSR (Technically Specified Rubber) (SMR, TSR produced in Malaysia), SIR (TSR produced in Indonesia), STR (TSR produced in Thailand), and other natural rubbers commonly used in the tire industry, such as RSS (Ribbed Smoked Sheet), and high-purity natural rubber; and modified natural rubbers such as epoxidized natural rubber, hydroxylated natural rubber, hydrogenated natural rubber, and grafted natural rubber.
• unmodified natural rubber is preferred from the viewpoint of processability, and SMR20, STR20, and RSS#3 are more preferred from the viewpoints of less variation in quality and ease of availability.
• the glass transition temperature of the natural rubber (A1) varies depending on the amount of modification in modified natural rubber such as epoxidized natural rubber, but is preferably ⁇ 40° C. or lower, more preferably ⁇ 50° C. or lower. These natural rubbers (A1) may be used alone or in combination of two or more.
• butadiene rubber (A2) examples include Ziegler catalysts such as titanium tetrahalide-trialkylaluminum, diethylaluminum chloride-cobalt, trialkylaluminum-boron trifluoride-nickel, and diethylaluminum chloride-nickel; lanthanoid rare earth metal catalysts such as triethylaluminum-organic acid neodymium-Lewis acid; and commercially available butadiene rubbers polymerized using organic alkali metal compounds (e.g., n-butyllithium, sec-butyllithium, etc.) in the same manner as the solution-polymerized styrene-butadiene rubber described below.
• Ziegler catalysts such as titanium tetrahalide-trialkylaluminum, diethylaluminum chloride-cobalt, trialkylaluminum-boron trifluoride-nickel, and diethylaluminum chloride-
• butadiene rubbers polymerized using Ziegler catalysts are preferred because they have a high cis content.
• butadiene rubbers with an ultra-high cis content e.g., cis content of 95% or more
• a lanthanoid rare earth metal catalyst may be used as the butadiene rubber (A2).
• the vinyl content of the 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%, the rolling resistance performance (fuel economy performance) tends to deteriorate. There is no particular lower limit for the vinyl content.
• the glass transition temperature of the butadiene rubber (A2) varies depending on the vinyl content, but is preferably -40°C or less, and more preferably -50°C or less.
• the vinyl content refers to the proportion (mol%) of the total of 1,2-bond structural units (structural units other than 1,4-bonds) out of a total of 100 mol% of butadiene-derived structural units contained in the butadiene rubber.
• 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.
• Mw is within the above range, the processability of the rubber composition for tire treads is improved, and the wear resistance of tire treads using at least a part of the rubber composition for tire treads is also improved.
• the butadiene rubber (A2) may have a branched structure or a polar functional group formed by using a polyfunctional modifier, such as tin tetrachloride, silicon tetrachloride, an alkoxysilane having an epoxy group in the molecule, or an amino group-containing alkoxysilane, as long as the effect of the present invention is not impaired. From the viewpoint of processability, it is preferable that the butadiene rubber (A2) does not have a polar functional group. These butadiene rubbers (A2) may be used alone or in combination of two or more.
• the styrene butadiene rubber (A3) (hereinafter, “styrene butadiene rubber” is also referred to as "SBR") may be any rubber commonly used in tires. Specifically, the SBR (A3) preferably has a styrene content of 0.1 to 70 mass%, more preferably 5 to 60 mass%, and even more preferably 5 to 50 mass%. The SBR (A3) preferably has a vinyl content of 0.1 to 80 mol%, and more preferably 5 to 70 mol%.
• the vinyl content of SBR refers to the percentage (mol %) of the total of 1,2-bonded structural units (structural units other than 1,4-bonds) out of a total of 100 mol % of all structural units derived from butadiene contained in SBR.
• the weight average molecular weight (Mw) of the 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.
• Mw weight average molecular weight
• the processability of the rubber composition for tire treads is improved, and the wet grip performance of a tire having a tire tread obtained from the rubber composition for tire treads is improved, and furthermore, the mechanical strength, abrasion resistance, and steering stability are also improved.
• the weight average molecular weight in this specification is the weight average molecular weight calculated in terms of polystyrene obtained by measurement using gel permeation chromatography (GPC).
• 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, even more 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 above range, the viscosity of the rubber composition for tire treads can be prevented from increasing, making it easier to handle and also improving wet grip performance.
• the SBR (A3) that can be used in the present invention is obtained by copolymerizing styrene and butadiene.
• the method for producing SBR (A3) there are no particular limitations on the method for producing SBR (A3), and any of the emulsion polymerization method, solution polymerization method, gas phase polymerization method, and bulk polymerization method can be used, but among these production methods, the emulsion polymerization method and solution polymerization method are preferred.
• Emulsion-polymerized styrene butadiene rubber (hereinafter also referred to as E-SBR) can be produced by a known or similar normal emulsion polymerization method. For example, it can be obtained by emulsifying and dispersing a given amount of styrene and butadiene monomers in the presence of an emulsifier, and then emulsion-polymerizing them with a radical polymerization initiator.
• a salt of a long-chain fatty acid having 10 or more carbon atoms or a rosin acid salt is used.
• Specific examples include potassium salts or sodium salts of fatty acids such as capric acid, lauric acid, myristic acid, palmitic acid, oleic acid, and stearic acid.
• water is usually used, and it may contain a water-soluble organic solvent such as methanol or ethanol within a range that does not impair the stability during polymerization.
• a water-soluble organic solvent such as methanol or ethanol
• the radical polymerization initiator include persulfates such as ammonium persulfate and potassium persulfate, organic peroxides, and hydrogen peroxide.
• a chain transfer agent can also be used to adjust the molecular weight of the resulting E-SBR.
• chain transfer agents include mercaptans such as t-dodecyl mercaptan and n-dodecyl mercaptan; carbon tetrachloride, thioglycolic acid, diterpenes, terpinolene, ⁇ -terpinene, ⁇ -methylstyrene dimer, etc.
• the temperature of the emulsion polymerization can be appropriately selected depending on the type of radical polymerization initiator used, but is usually preferably 0 to 100°C, more preferably 0 to 60°C.
• the polymerization method may be either continuous polymerization or batch polymerization.
• the polymerization reaction can be stopped by adding a polymerization terminator.
• polymerization terminators examples include amine compounds such as isopropylhydroxylamine, diethylhydroxylamine, and hydroxylamine; quinone compounds such as hydroquinone and benzoquinone; and sodium nitrite.
• the polymerization reaction After the polymerization reaction is stopped, an antioxidant may be added as necessary. After the polymerization reaction is stopped, unreacted monomers are removed from the obtained latex as necessary. Next, the polymer is coagulated using a salt such as sodium chloride, calcium chloride, or potassium chloride as a coagulant, and an acid such as nitric acid or sulfuric acid is added as necessary to adjust the pH of the coagulation system to a predetermined value, and then the dispersion medium is separated to recover the polymer as crumbs. The crumbs are washed with water, dehydrated, and dried with a band dryer or the like to obtain E-SBR.
• a salt such as sodium chloride, calcium chloride, or potassium chloride
• an acid such as nitric acid or sulfuric acid
• the latex and extender oil that has been previously made into an emulsified dispersion may be mixed as necessary, and the product may be recovered as oil-extended rubber.
• extender oil is not included in solid rubber (A).
• E-SBR products include oil-extended styrene-butadiene rubber "ESBR1723" manufactured by ENEOS Materials Corporation.
• Solution-polymerized styrene butadiene rubber (hereinafter also referred to as S-SBR) can be produced by a conventional solution polymerization method.
• S-SBR Solution-polymerized styrene butadiene rubber
• styrene and butadiene are polymerized using an active metal capable of anionically polymerizing in a solvent, optionally in the presence of a polar compound.
• Solvents include, for example, 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 usually preferably used in a range in which the monomer concentration is 1 to 50% by mass.
• active metals capable of anion polymerization include alkali metals such as lithium, sodium, and potassium; alkaline earth metals such as beryllium, magnesium, calcium, strontium, and barium; and lanthanoid rare earth metals such as lanthanum and neodymium.
• alkali metals and alkaline earth metals are preferred, and alkali metals are more preferred.
• organic alkali metal compounds are more preferably used.
• the organic alkali metal compounds include, for example, organic monolithium compounds such as n-butyllithium, sec-butyllithium, t-butyllithium, hexyllithium, phenyllithium, and stilbenelithium; polyfunctional organic lithium compounds such as dilithiomethane, 1,4-dilithiobutane, 1,4-dilithio-2-ethylcyclohexane, and 1,3,5-trilithiobenzene; sodium naphthalene, potassium naphthalene, and the like.
• organic lithium compounds are preferred, and organic monolithium compounds are more preferred.
• the amount of the organic alkali metal compound used is determined appropriately according to the molecular weight of the required S-SBR.
• the organic alkali metal compounds can also be used as organic alkali metal amides by reacting them with secondary amines such as dibutylamine, dihexylamine, and dibenzylamine.
• the polar compound there are no particular limitations on the polar compound, so long as it is one that is normally used in anionic polymerization to adjust the microstructure of butadiene units and the distribution in the styrene copolymer chain without inactivating the reaction.
• 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.
• the temperature of the polymerization reaction is usually in the range of -80 to 150°C, preferably 0 to 100°C, and more preferably 30 to 90°C.
• the polymerization method may be either batchwise or continuous. In order to improve the random copolymerization of styrene and butadiene, it is preferable to continuously or intermittently supply styrene and butadiene to the reaction liquid so that the composition ratio of styrene and butadiene in the polymerization system is within a specific range.
• the polymerization reaction can be stopped by adding an alcohol such as methanol or isopropanol as a polymerization terminator. After the polymerization reaction has been stopped, the solvent can be separated from the polymerization solution by direct drying or steam stripping, and the desired S-SBR can be recovered. Note that before removing the solvent, the polymerization solution can be mixed with an extender oil and recovered as oil-extended rubber.
• an alcohol such as methanol or isopropanol
• the solvent can be separated from the polymerization solution by direct drying or steam stripping, and the desired S-SBR can be recovered. Note that before removing the solvent, the polymerization solution can be mixed with an extender oil and recovered as oil-extended rubber.
• modified SBR in which functional groups have been introduced may be used as long as the effects of the present invention are not impaired.
• functional groups include amino groups, alkoxysilyl groups, hydroxyl groups, epoxy groups, and carboxyl groups.
• a method for producing modified SBR includes, for example, a method of adding a coupling agent such as tin tetrachloride, tetrachlorosilane, dimethyldichlorosilane, dimethyldiethoxysilane, tetramethoxysilane, tetraethoxysilane, 3-aminopropyltriethoxysilane, tetraglycidyl-1,3-bisaminomethylcyclohexane, or 2,4-tolylenediisocyanate that can react with the polymerization active terminals, or a polymerization terminal modifier such as 4,4'-bis(diethylamino)benzophenone or N-vinylpyrrolidone, or other modifiers described in JP 2011-132298 A, before adding a polymerization terminator.
• the position of the polymer where the functional group is introduced may be the polymerization terminal or a side chain of the polymer chain.
• the content of natural rubber (A1) in 100% by mass of the solid rubber (A) is preferably 40 to 80% by mass, more preferably 45 to 75% by mass, and even more preferably 50 to 70% by mass.
• the content of natural rubber (A1) in the solid rubber (A) is within the above range, abrasion resistance is improved.
• 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.
• the content of butadiene rubber (A2) in the solid rubber (A) is within the above range, abrasion resistance is improved.
• the content of styrene-butadiene rubber (A3) in 100% by mass of the solid rubber (A) is preferably 5 to 50% by mass, more preferably 10 to 45% by mass, and even more preferably 10 to 40% by mass.
• the content of styrene-butadiene rubber (A3) in the solid rubber (A) is within the above range, fuel efficiency performance is improved.
• the mass ratio (A2)/(A3) of the butadiene rubber (A2) to the styrene butadiene rubber (A3) is preferably 0.12 to 3, more preferably 0.13 to 2.5, more preferably 0.14 to 2.0, even more preferably 0.14 to 1.8, and even more preferably 0.2 to 1.2.
• the mass ratio (A2)/(A3) in the solid rubber (A) is within the above range, the balance between wet grip performance, fuel efficiency, and abrasion resistance is improved.
• the total content of the natural rubber (A1), butadiene rubber (A2) and styrene butadiene rubber (A3) in 100% by mass of the solid rubber (A) is preferably 80% by mass or more, and more preferably 90% by mass or more. From the same viewpoint, it is preferable that the total content of the natural rubber (A1), butadiene rubber (A2) and styrene butadiene rubber (A3) in 100% by mass of the solid rubber (A) is 100% by mass, i.e., the solid rubber (A) consists only of the natural rubber (A1), butadiene rubber (A2) and styrene butadiene rubber (A3).
• the solid rubber (A) may contain solid rubbers other than the natural rubber (A1), butadiene rubber (A2) and styrene butadiene rubber (A3) within the scope of not impairing the effects of the present invention.
• solid rubbers other than the 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.
• the content of the solid rubbers other than the natural rubber (A1), the butadiene rubber (A2), and the styrene-butadiene rubber (A3) in 100 mass% of the solid rubber (A) is preferably 20 mass% or less, and more preferably 10 mass% or less.
• the modified liquid diene rubber (B) used in the rubber composition for tire treads of the present invention is a liquid polymer having a functional group derived from a silane compound represented by formula (1) described later (hereinafter also referred to as silane compound (1)), a weight average molecular weight (Mw) of 3,000 to 120,000 (requirement (i)), a vinyl content of 70 mol% or less (requirement (ii)), and an average number of functional groups derived from the silane compound (1) per molecule of the modified liquid diene rubber (B) being 1 to 20 (requirement (iii)).
• silane compound (1) a weight average molecular weight (Mw) of 3,000 to 120,000
• an average number of functional groups derived from the silane compound (1) per molecule of the modified liquid diene rubber (B) being 1 to 20 (requirement (iii)).
• the inclusion of the modified liquid diene rubber (B) improves the dispersibility of the filler (C) in the rubber composition and the interaction between the filler (C) and the solid rubber (A), and a tire tread using at least a part of the rubber composition can achieve both improved fuel economy and improved wear resistance.
• the unmodified liquid diene rubber (B') used as the raw material for the modified liquid diene rubber (B) contains conjugated diene units as monomer units constituting the polymer.
• conjugated dienes include 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-octatriene, myrcene, farnesene ( ⁇ -farnesene, ⁇ -farnesene), and chloroprene, and other conjugated dienes (b1) other than butadiene and isoprene.
• the conjugated diene units contained in the unmodified liquid diene rubber (B') preferably contain at least one selected from the group consisting of butadiene units, isoprene units, and ⁇ -farnesene units, more preferably contain at least one selected from the group consisting of butadiene units and isoprene units, even more preferably contain only at least one selected from the group consisting of butadiene units and isoprene units, and even more preferably contain only butadiene units.
• the unmodified liquid diene rubber (B') used as the raw material for the modified liquid diene rubber (B) preferably has a conjugated diene unit content of 50% by mass or more, more preferably 60 to 100% by mass, and even more preferably 70 to 100% by mass, of the total monomer units constituting the polymer (100% by mass).
• the monomer units of the unmodified liquid diene rubber (B') contain only conjugated diene units (100% by mass of the total monomer units is conjugated diene units).
• the unmodified liquid diene rubber (B') used as the raw material for the modified liquid diene rubber (B) preferably contains at least 50 mass% of monomer units of at least one conjugated diene (b1) selected from the group consisting of butadiene and isoprene out of 100 mass% of all monomer units constituting the polymer.
• the content of monomer units of at least one conjugated diene (b1) selected from the group consisting of butadiene and isoprene is preferably 60 to 100 mass%, more preferably 70 to 100 mass%, of the total monomer units of the unmodified liquid diene rubber (B').
• Examples of monomer units other than the conjugated diene units that may be contained in the unmodified liquid diene rubber (B') include aromatic vinyl compound (b2) units.
• aromatic vinyl compounds (b2) include styrene, ⁇ -methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 4-propylstyrene, 4-t-butylstyrene, 4-cyclohexylstyrene, 4-dodecylstyrene, 2,4-dimethylstyrene, 2,4-diisopropylstyrene, 2,4,6-trimethylstyrene, 2-ethyl-4-benzylstyrene, 4-(phenylbutyl)styrene, 1-vinylnaphthalene, 2-vinylnaphthalene, vinylanthracene, N,N-diethyl-4-aminoethylstyrene, vinylpyridine, 4-methoxystyrene, monochlorostyrene, dichlorostyrene, and divinylbenzene
• the content of monomer units other than conjugated dienes, such as aromatic vinyl compound (b2), in the unmodified liquid diene rubber (B') 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.
• aromatic vinyl compound (b2) units are within the above range or less, the processability of the rubber composition tends to improve.
• the bonding mode may be a random copolymer or a block copolymer.
• the block copolymer preferably contains a polymer block consisting of only butadiene units and a polymer block consisting of only isoprene units.
• 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.
• the unmodified liquid diene rubber (B') is preferably a polymer obtained by polymerizing a conjugated diene and, if necessary, other monomers other than the conjugated diene, for example, by emulsion polymerization or solution polymerization.
• a monomer containing a predetermined amount of conjugated diene is emulsified and dispersed in the presence of an emulsifier, and emulsion polymerized using a radical polymerization initiator.
• Emulsifiers include, for example, salts of long-chain fatty acids having 10 or more carbon atoms and rosin acid salts.
• Examples of salts of long-chain fatty acids include potassium salts or sodium salts of fatty acids such as capric acid, lauric acid, myristic acid, palmitic acid, oleic acid, and stearic acid.
• water is usually used, and it may contain a water-soluble organic solvent such as methanol or ethanol within a range that does not impair the stability during polymerization.
• a water-soluble organic solvent such as methanol or ethanol
• the radical polymerization initiator include persulfates such as ammonium persulfate and potassium persulfate, organic peroxides, and hydrogen peroxide.
• a chain transfer agent may be used to adjust the molecular weight of the resulting unmodified liquid diene rubber (B').
• chain transfer agents include mercaptans such as t-dodecyl mercaptan and n-dodecyl mercaptan; carbon tetrachloride, thioglycolic acid, diterpenes, terpinolene, ⁇ -terpinene, and ⁇ -methylstyrene dimer.
• the temperature of the emulsion polymerization can be set appropriately depending on the type of radical polymerization initiator used, but is usually in the range of 0 to 100°C, preferably 0 to 60°C.
• the polymerization method may be either continuous polymerization or batch polymerization.
• the polymerization reaction can be stopped by adding a polymerization terminator.
• polymerization terminators include amine compounds such as isopropylhydroxylamine, diethylhydroxylamine, and hydroxylamine, quinone compounds such as hydroquinone and benzoquinone, and sodium nitrite.
• an anti-aging agent may be added as necessary.
• unreacted monomers are removed from the obtained latex as necessary, and then the unmodified liquid diene rubber (B') is coagulated using a salt such as sodium chloride, calcium chloride, or potassium chloride as a coagulant, and an acid such as nitric acid or sulfuric acid is added as necessary to adjust the pH of the coagulation system to a predetermined value, and the dispersion medium is separated to recover the polymer.
• the unmodified liquid diene rubber (B') is then obtained by washing with water, dehydrating, and drying. Note that, during coagulation, the latex and an extender oil that has been previously made into an emulsified dispersion may be mixed as necessary, and the oil-extended unmodified liquid diene rubber (B') may be recovered.
• a monomer containing a conjugated diene is polymerized in a solvent using a Ziegler catalyst, a metallocene catalyst, or an anionically polymerizable active metal or active metal compound, if necessary in the presence of a polar compound.
• Solvents include, for example, 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.
• aliphatic hydrocarbons such as n-butane, n-pentane, isopentane, n-hexane, n-heptane, and isooctane
• alicyclic hydrocarbons such as cyclopentane, cyclohexane, and methylcyclopentane
• aromatic hydrocarbons such as benzene, toluene, and xylene.
• active metals capable of anion polymerization include alkali metals such as lithium, sodium, and potassium; alkaline earth metals such as beryllium, magnesium, calcium, strontium, and barium; and lanthanoid rare earth metals such as lanthanum and neodymium.
• alkali metals and alkaline earth metals are preferred, and alkali metals are more preferred.
• an organic alkali metal compound is preferred.
• the organic alkali metal compound include organic monolithium compounds such as methyllithium, ethyllithium, n-butyllithium, sec-butyllithium, t-butyllithium, hexyllithium, phenyllithium, and stilbenelithium; polyfunctional organic lithium compounds such as dilithiomethane, dilithionaphthalene, 1,4-dilithiobutane, 1,4-dilithio-2-ethylcyclohexane, and 1,3,5-trilithiobenzene; sodium naphthalene, potassium naphthalene, and the like.
• organic lithium compounds are preferred, and organic monolithium compounds are more preferred.
• the amount of organic alkali metal compound used can be appropriately set depending on 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 per 100 parts by mass of all monomers including conjugated dienes.
• organic alkali metal compounds can also be reacted with secondary amines such as dibutylamine, dihexylamine, and dibenzylamine to be used as organic alkali metal amides.
• secondary amines such as dibutylamine, dihexylamine, and dibenzylamine
• polar compounds are usually used to adjust the microstructure of the conjugated diene units (e.g., vinyl content) without deactivating the reaction.
• polar compounds include ether compounds such as dibutyl ether, tetrahydrofuran, and ethylene glycol diethyl ether; tertiary amines such as N,N,N',N'-tetramethylethylenediamine and trimethylamine; alkali metal alkoxides, and phosphine compounds.
• Polar compounds are usually used in an amount of 0.01 to 1,000 moles per mole of the organic alkali metal compound.
• the temperature for solution polymerization is usually in the range of -80 to 150°C, preferably in the range of 0 to 100°C, and more preferably in the range of 10 to 90°C.
• the polymerization method may be either continuous polymerization or batch polymerization.
• the polymerization reaction can be terminated by adding a polymerization terminator.
• the polymerization terminator include alcohols such as methanol and isopropanol.
• the obtained polymerization reaction liquid is poured into a poor solvent such as methanol to precipitate the unmodified liquid diene rubber (B'), or the polymerization reaction liquid is washed with water, separated, and then dried to isolate the unmodified liquid diene rubber (B').
• the solution polymerization method is preferred.
• the unmodified liquid diene rubber (B') is not modified with a functional group (e.g., a hydroxyl group) other than the functional group derived from the silane compound represented by formula (1) described later. Since the unmodified liquid diene rubber (B') is not modified with other functional groups, the stability of the resulting modified liquid diene rubber (B) tends to be superior.
• a functional group e.g., a hydroxyl group
• the interaction e.g., reactivity
• the functional group derived from the silane compound represented by formula (1) of the resulting modified liquid diene rubber (B) with the filler (C) e.g., silica
• the filler (C) e.g., silica
• the unmodified liquid diene rubber (B') is modified with a functional group derived from a silane compound (hereinafter also referred to as silane compound (1)) represented by the following formula (1) and used as modified liquid diene rubber (B).
• silane compound (1) a silane compound represented by the following formula (1)
• the modified liquid diene rubber (B) has a functional group derived from a silane compound (silane compound (1)) represented by the following formula (1).
• R 1 is a divalent alkylene group having 1 to 6 carbon atoms.
• the divalent alkylene group having 1 to 6 carbon atoms include a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, and a hexylene group.
• R 2 , R 3 , and R 4 each independently represent a methoxy group, an ethoxy group, a phenoxy group, a methyl group, an ethyl group, or a phenyl group. However, at least one of R 2 , R 3 , and R 4 is a methoxy group, an ethoxy group, or a phenoxy group.
• silane compound (1) examples include 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 may be used alone or in combination of two or more.
• 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, a partial structure represented by the following formula (2) as a functional group.
• R 1 , R 2 , R 3 and R 4 in the above formula (2) are the same as the definitions and specific examples of R 1 , R 2 , R 3 and R 4 in the formula (1).
• the average number of functional groups per molecule of the modified liquid diene rubber (B) having functional groups derived from the silane compound (1) is 1 to 20 (requirement (iii)). If the average number of functional groups is less than 1, the affinity with the filler (C) is low, the filler dispersion in the rubber composition cannot be improved, and it is difficult to manufacture a tire tread that is both improved in fuel economy performance. On the other hand, if the average number of functional groups exceeds 20, it is difficult to obtain an improved wear resistance effect in the tire tread obtained from that rubber composition.
• the average number of functional groups per molecule of the modified liquid diene rubber (B) having functional groups derived from the silane compound (1) is preferably 1 to 15, more preferably 1 to 12, even more preferably 1 to 9, even more preferably 1 to 5, particularly preferably 1 to 4, and more particularly preferably 2 to 4.
• the average number of functional groups per molecule of the modified liquid diene rubber (B) can be calculated by the following formula using the equivalent weight (g/eq) of the functional groups of the modified liquid diene rubber (B) and the number average molecular weight Mn in terms of styrene.
• 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 contained as necessary)]/(functional group equivalent)
• the equivalent of the functional group of the modified liquid diene rubber (B) means the mass of butadiene bonded to one functional group and other monomers other than butadiene contained as necessary.
• the equivalent of the functional group can be calculated from the area ratio of the peak derived from the functional group of the modified liquid diene rubber (B) to the peak derived from the main chain of the modified liquid diene rubber (B) using 1 H-NMR or 13 C-NMR.
• the peak derived from the functional group refers to the peak derived from the alkoxy group contained in the group derived from the silane compound (1) contained in the modified liquid diene rubber (B).
• the amount of silane compound (1) added in modified liquid diene rubber (B) is preferably 1 to 60 parts by mass, more preferably 1 to 50 parts by mass, and even more preferably 1 to 40 parts by mass, per 100 parts by mass of unmodified liquid diene rubber (B'). If the amount added is more than 60 parts by mass, the dispersion effect of filler (C) is poor, and the abrasion resistance of the resulting tire tread also tends to decrease. If it is less than 1 part by mass, the dispersion effect of filler (C) is poor, and the improvement in fuel efficiency and abrasion resistance of the resulting tire tread tends to be insufficient.
• the amount of silane compound (1) added in modified liquid diene rubber (B) can be determined, for example, using various analytical instruments such as NMR.
• the method of adding the silane compound (1) to the unmodified liquid diene rubber (B') is not particularly limited.
• a method can be adopted in which the silane compound (1) and, if necessary, a radical generator are added to the unmodified liquid diene rubber (B') and heated in the presence or absence of an organic solvent.
• the radical generator used, and commercially available organic peroxides, azo compounds, hydrogen peroxide, etc. can be used. It is not desirable to carry out the reaction of adding the silane compound (1) to the unmodified liquid diene rubber (B') only by heating without using a radical generator.
• the addition reaction does not occur sufficiently, and the average number of functional groups per molecule may not be in the desired range.
• the heating temperature is increased, the addition reaction may proceed, but the generation of radicals on the polymer main chain may also cause the polymer polymerization reaction to proceed at the same time, so if the Mw of the modified liquid diene rubber is not in the desired range, the viscosity of the modified liquid diene rubber may not be in the desired range. In these cases where the temperature during the addition reaction is high, the handling of the modified liquid diene rubber may deteriorate, and the physical properties of the resulting rubber composition for tires may be adversely affected.
• the addition reaction is carried out by adding a radical generator and heating, the addition reaction proceeds sufficiently even at a relatively low temperature while sufficiently suppressing side reactions such as polymerization reactions.
• the total area of the GPC chromatogram obtained by GPC measurement of the modified liquid diene rubber (B) derived from the modified liquid diene rubber (B) is taken as 100%, and it is preferable that the proportion of polymers in the region having a molecular weight of Mt x 1.45 or more is 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 more particularly preferably in the range of 0 to 8%.
• organic peroxides include, for example, methyl ethyl ketone peroxide, cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide, methylcyclohexanone peroxide, acetylacetone peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)-cyclohexane, 1,1-bis(t-hexylperoxy)cyclohexane, 2,2-bis(t-butylperoxy)butane, t-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, paramenthane hydroperoxide, 2,5-dimethylhexane 2,5-dihydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, di-t-butyl peroxide, t-buty
• the above azo compounds include, for example, 2,2'-azobisisobutyronitrile, 1,1'-azobis(cyclohexane-1-carbonitrile), 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethyl-4-methoxyvaleronitrile), 2,2'-azobis(2-(2-imidazolin-2-yl)propane), 2,2' -Azobis(2,4,4-trimethylpentane), 2,2'-azobis(2-methylpropane), 2,2'-azobis(2-hydroxymethylpropiononitrile), 4,4'-azobis(4-cyanovaleric acid), dimethyl 2,2'-azobis(2-methylpropionate), 2-cyano-2-propylazoformamide, 2-phenylazo-4-methoxy-2,4-dimethylvaleronitrile, etc.
• the organic solvents used in the above method generally include hydrocarbon solvents and halogenated hydrocarbon solvents.
• hydrocarbon solvents such as n-butane, n-hexane, n-heptane, cyclohexane, benzene, toluene, and xylene are preferred.
• an antioxidant may be added from the viewpoint of suppressing side reactions.
• the antioxidants include 2,6-di-t-butyl-4-methylphenol (BHT), 2,2'-methylenebis(4-methyl-6-t-butylphenol), 4,4'-thiobis(3-methyl-6-t-butylphenol), 4,4'-butylidenebis(3-methyl-6-t-butylphenol) (AO-40), 3,9-bis[1,1-dimethyl-2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyl]propionyl], and the like.
• the amount of the antioxidant added is preferably 0 to 10 parts by mass, more preferably 0 to 5 parts by mass, based on 100 parts by mass of the unmodified liquid diene rubber (B').
• the position of the functional group introduced may be the polymerization terminal or the side chain of the polymer chain. From the viewpoint of easily introducing a plurality of functional groups, the side chain of the polymer chain is preferable.
• the functional group may be contained alone or may be contained in two or more kinds. Therefore, the modified liquid diene rubber (B) may be modified with one kind of silane compound (1), or may be modified with two or more kinds of compounds.
• the mixing ratio of the unmodified liquid diene rubber (B') and the silane compound (1) may be appropriately set so that the average number of functional groups per molecule of the modified liquid diene rubber (B) is a desired value, for example, and the unmodified liquid diene rubber (B') and the silane compound (1) may be mixed so that the mass ratio (B')/(1) is 0.3 to 300.
• the temperature in the reaction for adding the silane compound (1) to the unmodified liquid diene rubber (B') is preferably 10 to 200°C, more preferably 50°C to 180°C, and even more preferably 50°C to 140°C.
• 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.
• the weight average molecular weight (Mw) of the modified liquid diene rubber (B) is 3,000 or more and 120,000 or less (requirement (i)).
• the Mw of the modified liquid diene rubber (B) is the weight average molecular weight calculated in terms of polystyrene obtained by measurement using gel permeation chromatography (GPC).
• GPC gel permeation chromatography
• 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, even more 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 more particularly preferably 5,500 or more and 9,000 or less.
• the Mw of the modified liquid diene rubber (B) is determined in terms of standard polystyrene molecular weight by GPC (gel permeation chromatography). Specifically, it can be determined by the method described in the examples.
• 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 above range, the viscosity of the resulting modified liquid diene rubber (B) will vary less, which is more preferable.
• the molecular weight distribution (Mw/Mn) refers to the ratio of the weight average molecular weight (Mw)/number average molecular weight (Mn) in terms of standard polystyrene, determined by GPC measurement.
• the vinyl content of the modified liquid diene rubber (B) is 70 mol % or less (requirement (ii)). If the vinyl content exceeds 70 mol %, fuel economy performance tends to deteriorate. From the viewpoint of fuel economy, the vinyl content of the modified liquid diene rubber (B) is preferably 65 mol% or less, more preferably 60 mol% or less, even more preferably 50 mol% or less, even more preferably 45 mol% or less, particularly preferably 40 mol% or less, and more particularly 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, even more preferably 7 mol% or more, and even more preferably 10 mol% or more.
• the preferred numerical range of the vinyl content of the modified liquid diene rubber (B) can be set by appropriately combining the above upper and lower limits.
• the "vinyl content” means the total mol% of conjugated diene units bonded via 1,2-bonds, 3,4-bonds (in the case of other than farnesene), and 3,13-bonds (in the case of farnesene) (conjugated diene units bonded via other than 1,4-bonds (in the case of other than farnesene) and 1,13-bonds (in the case of farnesene)) relative to the total 100 mol% of conjugated diene units contained in the modified liquid diene rubber (B).
• the vinyl content is calculated by analyzing the modified liquid diene rubber (B) using 1H -NMR and from the area ratio of the peaks derived from the conjugated diene units bonded via 1,2-bonds, 3,4-bonds (in the case of other than farnesene), and 3,13-bonds (in the case of farnesene) to the peaks derived from the conjugated diene units bonded via 1,4-bonds (in the case of other than farnesene) and 1,13-bonds (in the case of farnesene).
• the vinyl content of the modified liquid diene rubber (B) can be adjusted to a desired value by controlling, for example, the type of solvent used in producing the unmodified liquid diene rubber (B'), the polar compound used as necessary, the polymerization temperature, etc.
• 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.
• the melt viscosity of the modified liquid diene rubber (B) is within the above range, the flexibility of the resulting rubber composition is improved, and therefore the processability is improved.
• the melt viscosity of the liquid diene rubber (B) is a value measured at 38°C using a Brookfield viscometer.
• the glass transition temperature (Tg) of the modified liquid diene rubber (B) can vary depending on the vinyl content of the conjugated diene units, the type of conjugated diene, the content of units derived from monomers other than conjugated dienes, etc., but is preferably -150 to 50°C, more preferably -120 to 30°C, even more preferably -100 to 10°C, and even more preferably -100 to 0°C.
• Tg is in the above range, for example, the fuel economy and abrasion resistance of a tire tread obtained from the rubber composition are likely to be improved.
• the viscosity of the modified liquid diene rubber (B) can be prevented from increasing, making it easier to handle.
• the modified liquid diene rubber (B) may be used alone or in combination of two or more kinds.
• the modified liquid diene rubber (B) preferably has a catalyst residue amount derived from the polymerization catalyst used in its production in the range of 0 to 200 ppm in terms of metal.
• a catalyst residue amount derived from the polymerization catalyst used in its production in the range of 0 to 200 ppm in terms of metal.
• the metal that is the standard for the catalyst residue amount is an alkali metal such as lithium.
• the catalyst residue amount derived from the polymerization catalyst used in the production of the modified liquid diene rubber (B) is more preferably 0 to 150 ppm, and even more preferably 0 to 100 ppm in terms of metal.
• the catalyst residue amount can be measured, for example, by using a polarized Zeeman atomic absorption spectrophotometer.
• the method of making the amount of catalyst residue in the liquid diene rubber such a specific amount includes purifying the modified liquid diene rubber (B) or the raw material unmodified liquid diene rubber (B') and thoroughly removing the catalyst residue.
• a purification method washing with water or hot water, or an organic solvent such as methanol or acetone, or supercritical fluid carbon dioxide is preferable.
• the number of washings is preferably 1 to 20 times, more preferably 1 to 10 times.
• the washing temperature is preferably 20 to 100°C, more preferably 40 to 90°C.
• the amount of catalyst residue required can be reduced by removing impurities that inhibit polymerization before the polymerization reaction by distillation or using an adsorbent and increasing the purity of the monomer and solvent before polymerization.
• the amount of catalyst residue in the rubber composition for tire treads containing the solid rubber (A), modified liquid diene rubber (B) and filler (C) of the present invention is preferably 0 to 200 ppm, more preferably 0 to 150 ppm, and even more preferably 0 to 100 ppm, calculated as metal.
• the amount of catalyst residue may be the amount of catalyst residue derived from the polymerization catalyst used in the production of any one or more of the solid rubber (A), modified liquid diene rubber (B) and other optional components contained in the rubber composition for tire treads of the present invention.
• the content of the modified liquid diene rubber (B) relative to 100 parts by mass of the solid rubber (A) is 0.1 to 50 parts by mass, preferably 1 to 45 parts by mass, more preferably 1 to 40 parts by mass, even more preferably 2 to 40 parts by mass, even more preferably 5 to 40 parts by mass, particularly preferably 5 to 35 parts by mass, more particularly preferably 5 to 30 parts by mass, more particularly preferably 5 to 25 parts by mass, and more particularly preferably 10 to 25 parts by mass.
• the content of the modified liquid diene rubber (B) is within the above range, the dispersibility of the filler (C) in the rubber composition is improved, and the fuel economy and wear resistance of the resulting tire tread are improved.
• the filler (C) used in the rubber composition for tire treads of the present invention can be any filler generally used in rubber compositions for tire treads without any particular limitations. From the viewpoint of improving the fuel efficiency performance of the tire tread, however, it is preferable that the filler (C) contains silica (C1).
• silica (C1) examples include wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, etc.
• wet silica is preferred from the viewpoint of further improving processability, mechanical strength and abrasion resistance of the resulting tire tread, and further improving fuel efficiency performance.
• These silicas (C1) may be used alone or in combination of two or more types.
• the average particle size of the silica (C1) is preferably 0.5 nm or more, more preferably 2 nm or more, even more preferably 5 nm or more, even more preferably 8 nm or more, and particularly preferably 10 nm or more, from the viewpoints of processability of the rubber composition for tire treads, improvement of fuel efficiency performance of tire treads at least partially using the rubber composition for tire treads, and improvement of abrasion resistance.
• the average particle size is preferably 200 nm or less, more preferably 150 nm or less, even more 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.
• the average particle size of the silica can be determined by measuring the diameter of each particle in a field of view observed with a transmission electron microscope and calculating the average value.
• Examples of the carbon black (C2) include furnace black, channel black, thermal black, acetylene black, and ketjen black.
• furnace black is preferred from the viewpoints of improving the crosslinking rate, improving the mechanical strength of the resulting tire tread, improving abrasion resistance, and improving fuel efficiency.
• These carbon blacks may be used alone or in combination of two or more types.
• the average particle size of the carbon black (C2) is preferably 5 nm or more, more preferably 10 nm or more, and even more preferably 15 nm or more, from the viewpoint of improving the mechanical strength, abrasion resistance, and fuel efficiency of a tire tread at least partly using the rubber composition for tire treads.
• the 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.
• the average particle size of carbon black can be determined by measuring the diameter of each particle in a field of view observed with a transmission electron microscope and calculating the average value.
• the carbon black (C2) may be subjected to an acid treatment with nitric acid, sulfuric acid, hydrochloric acid or a mixture of these acids, or a surface oxidation treatment by heat treatment in the presence of air.
• the carbon black (C2) may be subjected to a heat treatment at 2,000 to 3,000° C. in the presence of a graphitization catalyst.
• the carbon black (C2) can also be used after adjusting the particle size by grinding or the like.
• High-speed rotary grinders hammer mills, pin mills, cage mills), various ball mills (rolling mills, vibrating mills, planetary mills), stirring mills (bead mills, attritors, flow-tube mills, annular mills), etc. can be used to grind carbon black.
• the rubber composition for tire treads of the present invention may contain fillers other than silica (C1) and carbon black (C2) for the purpose of improving the properties of the resulting tire tread, such as increasing its mechanical strength, and improving production costs by incorporating a filler as an extender.
• the amount of silica (C1) per 100 parts by mass of the solid rubber (A) is preferably 20 parts by mass or more, more preferably 30 parts by mass or more, even more 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, from the viewpoint of improving the wet grip performance, fuel efficiency, and abrasion resistance of a tire tread at least partly using the rubber composition for tire treads.
• 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.
• the amount of carbon black (C2) per 100 parts by mass of the 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, from the viewpoint of improving the abrasion resistance and fuel efficiency of a tire tread at least partly using the rubber composition for tire treads.
• 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.
• thiocarbamoyl tetrasulfide 3-triethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 2-trimethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropyl benzothiazole tetrasulfide, 3-triethoxysilylpropyl benzothiazole tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, and 3-octanoylthio-1-propyltriethoxysilane.
• Examples of the vinyl-based compound include vinyltriethoxysilane and vinyltrimethoxysilane.
• Examples of the amino compound include 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-(2-aminoethyl)aminopropyltriethoxysilane, and 3-(2-aminoethyl)aminopropyltrimethoxysilane.
• glycidoxy compounds include gamma-glycidoxypropyltriethoxysilane, gamma-glycidoxypropyltrimethoxysilane, gamma-glycidoxypropylmethyldiethoxysilane, and gamma-glycidoxypropylmethyldimethoxysilane.
• Examples of the nitro-based compound include 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane.
• Examples of the chloro-based compounds include 3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysilane, 2-chloroethyltrimethoxysilane, and 2-chloroethyltriethoxysilane.
• Other compounds include, for example, octyltriethoxysilane, methyltriethoxysilane, methyltrimethoxysilane, and hexadecyltrimethoxysilane.
• silane coupling agents may be used alone or in combination of two or more.
• silane coupling agents containing sulfur such as sulfide-based compounds and mercapto-based compounds
• sulfur such as sulfide-based compounds and mercapto-based compounds
• bis(3-triethoxysilylpropyl) disulfide, bis(3-triethoxysilylpropyl) tetrasulfide, and 3-mercaptopropyltriethoxysilane being more preferred.
• the silane coupling agent is preferably contained in an amount of 0.1 to 30 parts by mass, more preferably 0.5 to 20 parts by mass, and even more preferably 1 to 15 parts by mass, per 100 parts by mass of silica (C1).
• content of the silane coupling agent is within the above range, dispersibility, coupling effect, reinforcement, and abrasion resistance are improved.
• the rubber composition for tire treads of the present invention may further contain a vulcanizing agent (D) to crosslink the rubber.
• a vulcanizing agent (D) include sulfur and sulfur compounds.
• the sulfur compounds include morpholine disulfide and alkylphenol disulfide.
• These vulcanizing agents (D) may be used alone or in combination of two or more.
• the vulcanizing agent (D) is usually contained in an amount of 0.1 to 10 parts by mass, preferably 0.5 to 10 parts by mass, and more preferably 0.8 to 5 parts by mass, per 100 parts by mass of the solid rubber (A).
• the rubber composition for tire treads of the present invention may further contain a vulcanization accelerator (E) when it contains a vulcanizing agent (D) for crosslinking (vulcanizing) rubber.
• a vulcanization accelerator (E) examples include guanidine compounds, sulfenamide compounds, thiazole compounds, thiuram compounds, thiourea compounds, dithiocarbamic acid compounds, aldehyde-amine compounds, aldehyde-ammonia compounds, imidazoline compounds, and xanthate compounds.
• These vulcanization accelerators (E) may be used alone or in combination of two or more.
• the vulcanization accelerator (E) is usually contained in an amount of 0.1 to 15 parts by mass, preferably 0.1 to 10 parts by mass, per 100 parts by mass of the solid rubber (A).
• the rubber composition for tire treads of the present invention may further contain a vulcanization aid (F) when, for example, sulfur or a sulfur compound is contained as a vulcanizing agent (D) for crosslinking (vulcanizing) rubber.
• a vulcanization aid (F) include fatty acids such as stearic acid, metal oxides such as zinc oxide, and fatty acid metal salts such as zinc stearate. These vulcanization aids (F) may be used alone or in combination of two or more.
• the vulcanization aid (F) is usually contained in an amount of 0.1 to 15 parts by mass, preferably 1 to 10 parts by mass, per 100 parts by mass of the solid rubber (A).
• the rubber composition for tire treads may contain a crosslinking agent in addition to the vulcanizing agent (D).
• crosslinking agents include oxygen, organic peroxides, phenolic resins, amino resins, quinone and quinone dioxime derivatives, halogen compounds, aldehyde compounds, alcohol compounds, epoxy compounds, metal halides, organometallic halides, and silane compounds. These may be used alone or in combination of two or more.
• the amount of crosslinking agent is preferably 0.1 to 10 parts by mass per 100 parts by mass of the solid rubber (A).
• the rubber composition for tire treads of the present invention may contain, as necessary, softening agents such as silicone oil, aromatic oil, process oils such as TDAE (Treated Distilled Aromatic Extracts), MES (Mild Extracted Solvates), RAE (Residual Aromatic Extracts), paraffin oil, naphthenic oil, etc., resin components such as aliphatic hydrocarbon resins, alicyclic hydrocarbon resins, C9 resins, rosin resins, coumarone-indene resins, phenolic resins, and liquid polymers such as low molecular weight polybutadiene, low molecular weight polyisoprene, low molecular weight styrene-butadiene copolymers, and low molecular weight styrene-isoprene copolymers, for the purpose of improving processability, fluidity, etc., within the scope that does not impair the effects of the present invention.
• softening agents such as silicone oil, aromatic oil, process oils
• the rubber composition for tire treads of the present invention contains the above-mentioned process oil, resin, or liquid polymer as a softener, the content thereof is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 15 parts by mass or less, per 100 parts by mass of the solid rubber (A), from the viewpoint of bleeding resistance.
• the rubber composition for tire treads of the present invention may contain additives such as anti-aging agents, antioxidants, waxes, lubricants, light stabilizers, scorch inhibitors, processing aids, colorants such as pigments and dyes, flame retardants, antistatic agents, matting agents, antiblocking agents, UV absorbers, release agents, foaming agents, antibacterial agents, antifungal agents, fragrances, etc., as necessary, for the purpose of improving weather resistance, heat resistance, oxidation resistance, etc., within a range that does not impair the effects of the present invention.
• additives such as anti-aging agents, antioxidants, waxes, lubricants, light stabilizers, scorch inhibitors, processing aids, colorants such as pigments and dyes, flame retardants, antistatic agents, matting agents, antiblocking agents, UV absorbers, release agents, foaming agents, antibacterial agents, antifungal agents, fragrances, etc., as necessary, for the purpose of improving weather resistance, heat resistance, oxidation resistance, etc., within a
• antioxidant examples include hindered phenol compounds, phosphorus compounds, lactone compounds, and hydroxyl compounds.
• antiaging agent examples include amine-ketone compounds, imidazole compounds, amine compounds, phenol compounds, sulfur compounds, phosphorus compounds, etc. These additives may be used alone or in combination of two or more kinds.
• the method for producing the rubber composition for tire treads of the present invention is not particularly limited as long as it can uniformly mix the above-mentioned components.
• Examples of the apparatus used for producing the rubber composition for tire treads include tangential or intermeshing internal mixers such as kneader-ruders, Brabenders, Banbury mixers, and internal mixers, single-screw extruders, twin-screw extruders, mixing rolls, and rollers.
• the rubber composition can usually be produced at a temperature range of 70 to 270°C.
• the rubber composition for tire treads of the present invention is preferably used as a cross-linked product (vulcanized rubber) by cross-linking.
• vulcanized rubber vulcanized rubber
• the extraction rate of the modified liquid diene rubber (B) from the crosslinked product is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less.
• the extraction rate can be calculated from the amount of modified liquid diene rubber (B) extracted into toluene after immersing 2 g of the crosslinked product in 400 mL of toluene at 23° C. for 48 hours.
• the tire tread of the present invention is at least partially made of the rubber composition for tire treads, and can achieve both improved fuel economy and improved wear resistance without impairing wet grip performance.
• the tire tread is suitable for use in tires of electric vehicles, which are relatively heavy and characterized by electric motor drive characteristics (e.g., large initial torque).
• an electric vehicle is a vehicle (e.g., electric vehicle, hybrid vehicle, fuel cell vehicle) that uses an electric motor as at least a part of the power source.
• the tire tread of the present invention can be obtained by molding tire tread rubber having a predetermined cross-sectional shape from the rubber composition for tire tread obtained as described above using an extruder or the like, and using this tire tread rubber to produce tires for various applications such as passenger car tires (e.g., pneumatic tires, solid tires, airless tires) using a conventional method (generally including a crosslinking step), as a tire including the tire tread of the present invention (e.g., a pneumatic tire for an electric vehicle).
• passenger car tires e.g., pneumatic tires, solid tires, airless tires
• a conventional method generally including a crosslinking step
• a tire including the tire tread of the present invention e.g., a pneumatic tire for an electric vehicle.
• Production Example 1 Production of modified liquid diene rubber (B-1) A thoroughly dried 5L autoclave was substituted with nitrogen, 1150g of hexane and 154g of n-butyllithium (17% by mass hexane solution) were charged, and the temperature was raised to 50°C. Under stirring conditions, 10g of N,N,N',N'-tetramethylethylenediamine was added, and then 1250g of butadiene was added successively while controlling the polymerization temperature to 50°C, and polymerization was carried out for 1 hour. Methanol was then added to terminate the polymerization reaction, and a polymer solution was obtained. Water was added to the obtained polymer solution and stirred, and the polymer solution was washed with water.
• Production Example 2 Production of modified liquid diene rubber (B-2) A thoroughly dried 5L autoclave was substituted with nitrogen, and 1100g of hexane and 204g of n-butyllithium (17% by mass hexane solution) were charged. The temperature was raised to 50°C, and then 1300g of butadiene was added successively under stirring conditions while controlling the polymerization temperature to 50°C, and polymerization was carried out for 1 hour. Methanol was then added to terminate the polymerization reaction, and a polymer solution was obtained. Water was added to the obtained polymer solution and stirred, and the polymer solution was washed with water. After the stirring was terminated and it was confirmed that the polymer solution phase and the water phase were separated, the water was separated.
• B-2 modified liquid diene rubber
• Production Example 3 Production of modified liquid diene rubber (B-3) A thoroughly dried 5L autoclave was substituted with nitrogen, and 1280g of cyclohexane and 66g of sec-butyllithium (10.5% by mass cyclohexane solution) were charged, and the temperature was raised to 50°C. After that, under stirring conditions, 1350g of butadiene was successively added while controlling the polymerization temperature to 50°C, and polymerization was carried out for 1 hour. Methanol was then added to terminate the polymerization reaction, and a polymer solution was obtained. Water was added to the obtained polymer solution and stirred, and the polymer solution was washed with water.
• the Mw of the modified liquid diene rubber (B) was determined in terms of standard polystyrene equivalent molecular weight by GPC (gel permeation chromatography) using the following measuring device and conditions.
• GPC gel permeation chromatography
• Eluent Tetrahydrofuran Eluent flow rate: 1.0 mL/min Sample concentration: 5 mg/10 mL Column temperature: 40°C
• the vinyl content was calculated from the area ratio of the peak derived from the conjugated diene unit bonded through 1,2-bond and 3,4-bond to the peak derived from the conjugated diene unit bonded through 1,4-bond in the obtained spectrum.
• Glass Transition Temperature 10 mg of the modified liquid diene rubber (B) was placed in an aluminum pan, and a thermogram was measured by differential scanning calorimetry (DSC) at a heating rate of 10°C/min. The peak top value of DDSC (first derivative curve of DSC curve) was taken as the glass transition temperature (Tg).
• melt viscosity at 38°C The melt viscosity of the modified liquid diene rubber (B) at 38° C. was measured by a Brookfield viscometer (manufactured by BROOKFIELD ENGINEERING LABS. INC.).
• the average number of functional groups per molecule of the modified liquid diene rubber (B) was determined from the equivalent weight (g/eq) of the functional groups of the modified liquid diene rubber (B) and the number average molecular weight Mn in terms of styrene.
• (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 contained as necessary)]/(functional group equivalent)
• the equivalent of the functional group of the modified liquid diene rubber (B) means the mass of butadiene bonded to one functional group and other monomers other than butadiene contained as necessary.
• the equivalent of the functional group was calculated from the area ratio of the peak derived from the functional group and the peak derived from the polymer main chain obtained by using 1H -NMR or 13C -NMR of the modified liquid diene rubber (B).
• the peak derived from the functional group refers to the peak derived from the alkoxy group.
• Examples 1 to 10 and Comparative Examples 1 to 6 According to the compounding ratio (parts by mass) shown in Tables 2 and 3, the components other than the vulcanizing agent (sulfur) and the vulcanization accelerator were each put into an internal Banbury mixer, and the starting temperature was controlled to be 60°C and the resin temperature was controlled to be 155-160°C, and the mixture was kneaded for 4 minutes, then removed from the mixer and cooled to room temperature. Next, this mixture was put into the Banbury mixer again, and the starting temperature was controlled to be 60°C and the resin temperature was controlled to be 155-160°C, and the mixture was kneaded for 3 minutes, then removed from the mixer and cooled to room temperature.
• this mixture was put into the Banbury mixer again, and the vulcanizing agent (sulfur) and the vulcanization accelerator were added, and the mixture was kneaded for 75 seconds at a starting temperature of 50°C and a final temperature of 100°C to obtain a rubber composition.
• the obtained rubber composition was press molded (160°C, 20 to 30 minutes) to prepare a vulcanized rubber sheet (thickness 2 mm), and the fuel economy performance, abrasion resistance, and wet grip performance were evaluated according to the following methods. The results are shown in Tables 2 and 3. The measurement methods for each evaluation are as follows.
• Test pieces measuring 40 mm in length and 5 mm in width were cut out from the sheets of the rubber compositions prepared in the Examples and Comparative Examples, and tan ⁇ was measured using a dynamic viscoelasticity measuring device manufactured by GABO under conditions of a measurement temperature of 60° C., a frequency of 10 Hz, a static strain of 10%, and a dynamic strain of 2%, and was used as an index of fuel economy performance.
• the numerical values of each Example and Comparative Example in Table 2 are relative values when the value of Comparative Example 1 is taken as 100.
• ⁇ Measurement temperature 20°C Road surface: Noritake Coated Abrasives Co., Ltd., METABRIT, grain size 120, abrasive grain A ⁇ Road surface water supply amount: 1.0L/min ⁇ Road surface supply water temperature: 20°C ⁇ Speed: 30km/hrs Load: 50N ⁇ Slip ratio: 0-40%
• tire treads obtained from the rubber composition for tire treads of the present invention have improved fuel economy performance while maintaining the same or improved wet grip performance. Also, they have improved abrasion resistance while maintaining the same or improved wet grip performance. Therefore, they have achieved a good balance between the three performances of fuel economy performance, abrasion resistance, and wet grip performance, which was previously difficult to achieve. Therefore, they are useful as tire treads, and are particularly useful as tire treads for automobiles that are heavier than before, such as electric automobiles (electric automobiles, hybrid automobiles, fuel cell automobiles).

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• 2024
  • 2024-07-08 WO PCT/JP2024/024600 patent/WO2025018211A1/ja active Pending
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