Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
  • B60C1/00—Tyres characterised by the chemical composition or the physical arrangement or mixture of the composition
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F8/00—Chemical modification by after-treatment
  • C08F8/34—Introducing sulfur atoms or sulfur-containing groups
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F8/00—Chemical modification by after-treatment
  • C08F8/42—Introducing metal atoms or metal-containing groups
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/02—Elements
  • C08K3/04—Carbon
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/34—Silicon-containing compounds
  • C08K3/36—Silica
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L15/00—Compositions of rubber derivatives
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L7/00—Compositions of natural rubber
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L9/00—Compositions of homopolymers or copolymers of conjugated diene hydrocarbons

Definitions

• the present invention relates to a rubber composition for sidewalls and a sidewall that uses the same at least in part.
• Rubber compositions containing solid rubber, liquid diene-based rubber, and fillers have been studied as materials for use in various tire components, including treads and sidewalls, because they can maintain or improve various properties while improving processability.
• rubber compositions containing solid rubber and silica have been considered as materials for tire treads.
• rubber compositions containing solid rubber, a specific modified liquid diene rubber, and a filler have been considered as rubber compositions suitable for use in the treads of heavy-duty tires that are subjected to high loads, such as buses and trucks (see Patent Document 1).
• a tire is composed of various components in addition to the tread described above, and each component is required to have its own characteristics.
• the sidewall which is one example of a tire component, is required to have improved characteristics different from those of the tread, such as weather resistance and flex fatigue resistance.
• a rubber composition containing a diene-based rubber component, a reinforcing filler, and a specific liquid diene-based rubber has been investigated (see Patent Document 2).
• rubber compositions that can improve the fuel economy of tires include rubber compositions containing solid rubber and filler (typically silica).
• filler particles typically silica
• a rubber composition containing a filler (typically silica) with a small surface area where friction occurs, that is, a large particle size, and solid rubber is considered to be useful.
• a filler typically silica
• simply adding a large particle size filler (typically silica) to solid rubber does not necessarily provide sufficient affinity between the solid rubber and the filler, and therefore the sidewall obtained using the rubber composition does not necessarily have sufficient flex fatigue resistance. Therefore, there has been a demand for a rubber composition that can improve fuel economy while maintaining the characteristics required for the sidewall.
• the present invention was made in consideration of the above-mentioned circumstances, and provides a rubber composition for sidewalls that can be used to manufacture sidewalls that have excellent flex fatigue resistance and can also improve fuel efficiency, and a sidewall that uses this rubber composition at least in part.
• the inventors discovered that by producing a sidewall using at least a part of a rubber composition containing a specific solid rubber, a specific modified liquid diene rubber, and a filler, the sidewall obtained from the rubber composition has excellent flex fatigue resistance and improved fuel economy performance, which led to the completion of the present invention.
• a rubber composition for a sidewall comprising 100 parts by mass of a solid rubber (A) containing a natural rubber and/or an isoprene rubber (A1) and a butadiene rubber (A2), 0.1 to 30 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 5 to 80 parts by mass of a filler (C): the filler (C) contains silica (C1), and the BET specific surface area of the silica (C1) is less than 170 (m 2 /g);
• the modified liquid diene rubber (B) comprises the following (i) to (iii): (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
• R 1 is a divalent alkylene group having 1 to 6 carbon atoms
• 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, provided that at least one of R 2 , R 3 and R 4 is a methoxy group, an ethoxy group or a phenoxy group.
• [5] A crosslinked product obtained by crosslinking the rubber composition for a sidewall according to any one of [1] to [4].
• [6] A sidewall, at least a part of which uses the rubber composition for a sidewall according to any one of [1] to [5].
• the present invention provides a rubber composition for sidewalls that has excellent flex fatigue resistance and can be used to manufacture sidewalls that can improve fuel economy, and a sidewall that uses this rubber composition at least in part.
• Solid rubber (A) used in the rubber composition for sidewalls of the present invention refers to a rubber that can be handled in a solid form at 20° C.
• the solid rubber (A) usually has a Mooney viscosity ML1 +4 at 100° C. in the range of 20 to 200, and is usually selected from at least one of synthetic rubber and natural rubber.
• the solid rubber (A) contained in the rubber composition for a sidewall of the present invention contains natural rubber and/or isoprene rubber (A1) and butadiene rubber (A2).
• Natural rubber and/or isoprene 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, grafted natural rubber, and other modified natural rubbers.
• 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.
• These natural rubbers may be used alone or in combination of two or more.
• isoprene rubber that can be component (A1) 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 isoprene rubber polymerized using an organic alkali metal compound in the same manner as S-SBR (solution-polymerized styrene butadiene rubber).
• 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 triethy
• isoprene rubber polymerized using a Ziegler catalyst is preferred because it has a high cis content.
• isoprene rubber with an ultra-high cis content obtained using a lanthanoid rare earth metal catalyst may be used as the isoprene rubber.
• the vinyl content of the isoprene rubber is preferably 50 mol% or less, more preferably 40 mol% or less, and even more preferably 30 mol% or less. If the vinyl content exceeds 50 mol%, the rolling resistance performance tends to deteriorate. There is no particular limit to the lower limit of the vinyl content.
• the glass transition temperature varies depending on the vinyl content, but is preferably -20°C or less, and more preferably -30°C or less.
• the vinyl content refers to the percentage (mol%) of the total of structural units derived from 1,2-bonds or 3,4-bonds (structural units other than 1,4-bonds) out of a total of 100 mol% of structural units derived from isoprene contained in the isoprene rubber.
• the weight average molecular weight (Mw) of the isoprene rubber is preferably 90,000 to 2,000,000, and more preferably 150,000 to 1,500,000. When Mw is within the above range, the processability and mechanical strength are good.
• the isoprene rubber may have a branched structure or a polar functional group 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, in part of the isoprene rubber, so long as the effect of the present invention is not impaired. From the viewpoint of processability, it is preferable that the isoprene rubber does not have a polar functional group. These isoprene rubbers may be used alone or in combination of two or more kinds.
• Component (A1) may be natural rubber alone or isoprene rubber alone, or may be used as a mixture of natural rubber and isoprene rubber. From the standpoint of mechanical strength, natural rubber is preferred as component (A1).
• 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 similar to S-SBR.
• lanthanoid rare earth metal catalysts such as triethylaluminum-organic acid neodymium-Lewis acid
• butadiene rubbers polymerized using Ziegler catalysts are preferred because of their high cis content.
• butadiene rubbers with an ultra-high cis content e.g., cis content of 95% or more
• lanthanoid rare earth metal catalysts may be used as
• 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 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, and more preferably 150,000 to 1,500,000.
• Mw is within the above range, the processability of the rubber composition for the sidewall is improved, and the flex fatigue resistance of the sidewall that uses the rubber composition for the sidewall in part 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 total content of component (A1) and butadiene rubber (A2) 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 component (A1) and butadiene rubber (A2) in 100% by mass of the solid rubber (A) is 100% by mass, i.e., the solid rubber (A) consists only of component (A1) and butadiene rubber (A2).
• the mass ratio (A1)/(A2) of the component (A1) to the butadiene rubber (A2) contained in the solid rubber (A) is preferably 20/80 or more and 60/40 or less, more preferably 25/75 or more and 55/45 or less, even more preferably 30/70 or more and 50/50 or less, and even more preferably 40/60 or more and 50/50 or less.
• the solid rubber (A) may contain solid rubber other than the component (A1) and the butadiene rubber (A2) within the scope of not impairing the effects of the present invention.
• solid rubber other than the component (A1) and the butadiene rubber (A2) include styrene butadiene rubber (hereinafter also referred to as "SBR"), butyl rubber, halogenated butyl rubber, ethylene propylene diene rubber, butadiene acrylonitrile copolymer rubber, chloroprene rubber, acrylic rubber, fluororubber, and urethane rubber.
• SBR styrene butadiene rubber
• the content of the solid rubbers other than the component (A1) and the butadiene rubber (A2) 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 sidewalls of the present invention is a liquid polymer and has a functional group derived from a silane compound represented by formula (1) (hereinafter also referred to as silane compound (1)) described later.
• silane compound (1) a silane compound represented by formula (1)
• the weight average molecular weight (Mw) is 3,000 to 120,000 (requirement (i))
• the vinyl content is 70 mol% or less
• the average number of functional groups derived from the silane compound (1) per molecule of the modified liquid diene rubber (B) is 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).
• a sidewall using at least a part of the rubber composition has good flex fatigue resistance and improves fuel economy.
• 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, 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 unmodified liquid diene rubber (B') contains only conjugated diene units as its monomer 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) has 50 mass% or more 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 the 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 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 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 contained in the unmodified liquid diene rubber (B').
• aromatic vinyl compound (b2) units are within the above range, the processability of the rubber composition tends to improve.
• 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 antioxidant 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 salts such as sodium chloride, calcium chloride, and potassium chloride as coagulants, 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') thus obtained has excellent flexural fatigue resistance and, in order to facilitate the production of sidewalls that can improve fuel economy, it is desirable to modify it as is (without hydrogenation) with a functional group derived from a silane compound represented by formula (1) described below.
• 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 sidewall that is excellent in flex fatigue resistance and can improve fuel economy. On the other hand, if the average number of functional groups exceeds 20, it is difficult to manufacture a sidewall that is excellent in flex fatigue resistance with the sidewall 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 the 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 the unmodified liquid diene rubber (B'). If the amount added is more than 60 parts by mass, the effect of improving the flexural fatigue resistance of the resulting sidewall tends to be impaired. If it is less than 1 part by mass, the dispersion effect of the filler (C) is poor, and the flexural fatigue resistance of the resulting sidewall tends not to be excellent.
• the amount of silane compound (1) added in the modified liquid diene rubber (B) can be determined 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 may 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 polymer polymerization reaction may also proceed at the same time due to the generation of radicals on the polymer main chain. Therefore, 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 sidewalls may be adversely affected.
• the addition reaction is carried out by adding a radical generator and heating, the addition reaction proceeds sufficiently while sufficiently suppressing side reactions such as polymerization reactions even at a relatively low heating temperature.
• the total area of the GPC chromatogram obtained by GPC measurement of the modified liquid diene-based rubber (B) derived from the modified liquid diene-based rubber (B) is taken as 100%, and it is preferable that the proportion of the modified liquid diene-based rubber (B) 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.
• 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°C 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 processability during production is excellent and the economic efficiency is good.
• the processability of the rubber composition of the present invention is good, the dispersibility of the filler (C) is excellent, and the physical properties of the obtained sidewall can be improved (for example, improved fuel efficiency and improved flex fatigue resistance).
• 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, even more preferably 5,500 or more and 12,000 or less, and 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 particularly 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) calculated using standard polystyrene standards, 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 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" of the modified liquid diene rubber (B) 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) (i.e., conjugated diene units bonded 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 1 H-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, even more preferably 0.1 to 500 Pa ⁇ s, and particularly 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 -130 to 50°C, even more preferably -130 to 30°C, and even more preferably -100 to 0°C.
• Tg is in the above range, for example, the flex fatigue resistance of the sidewall obtained from the rubber composition is good.
• the viscosity can be prevented from increasing, making handling easier.
• 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.
• an organic alkali metal such as an organolithium compound
• 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 for 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 sidewalls 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 catalyst residue in this case may be catalyst residue derived from a 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 sidewalls of the present invention.
• the content of the modified liquid diene rubber (B) per 100 parts by mass of the solid rubber (A) is 0.1 to 30 parts by mass, preferably 0.5 to 25 parts by mass, more preferably 1 to 25 parts by mass, even more preferably 2 to 25 parts by mass, even more preferably 5 to 20 parts by mass, and even more preferably 5 to 15 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 resulting sidewall has good flex fatigue resistance and improved fuel economy.
• the filler (C) used in the rubber composition for a sidewall of the present invention can be any filler that is generally used in rubber compositions for a sidewall without any particular limitation. From the viewpoint of improving the fuel economy performance of the sidewall, 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 and fuel efficiency of the resulting sidewall.
• the BET specific surface area of the silica (C1) is less than 170 (m 2 /g).
• the BET specific surface area of the silica (C1) is preferably less than 130 (m 2 /g), and more preferably less than 110 (m 2 /g).
• the BET specific surface area of the silica (C1) is preferably 50 (m 2 /g) or more, more preferably 80 (m 2 /g) or more, and even more preferably 90 (m 2 /g) or more.
• the BET specific surface area is a value obtained by the BET method in accordance with ASTM D3037-81.
• the average particle size of the silica (C1) is preferably 10 nm or more, more preferably 15 nm or more, even more preferably 20 nm or more, and even more preferably 25 nm or more. And, it 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 silica can be obtained by measuring the diameter of each particle in a visual field observed by a transmission electron microscope and calculating the average value.
• These silicas (C1) may be used alone or in combination of two or more kinds.
• the filler (C) used in the rubber composition for the sidewall of the present invention contains carbon black (C2).
• the filler (C) used in the rubber composition for the sidewall of the present invention contains silica (C1) and carbon black (C2).
• 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 and improving the mechanical strength of the resulting sidewall.
• 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 and fuel economy of a sidewall at least partially using the rubber composition for sidewalls.
• the average particle size is preferably 100 nm or less, more preferably 80 nm or less, even more preferably 70 nm or less, and even more preferably 60 nm or less.
• the average particle size of the 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.
• furnace black products include, for example, "Diablack” manufactured by Mitsubishi Chemical Corporation and “Seat” manufactured by Tokai Carbon Co., Ltd.
• acetylene black products include, for example, “Denka Black” manufactured by Denki Kagaku Kogyo Co., Ltd.
• ketjen black products include, for example, "ECP600JD” manufactured by Lion Corporation.
• 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, from the viewpoint of improving the wettability and dispersibility in the solid rubber (A). Also, from the viewpoint of improving the mechanical strength of the rubber composition for sidewalls of the present invention and the sidewalls obtained from this composition, the carbon black may be subjected to a heat treatment at 2,000 to 3,000° C. in the presence of a graphitization catalyst.
• boron As the graphitization catalyst, boron, boron oxides (e.g., B 2 O 2 , B 2 O 3 , B 4 O 3 , B 4 O 5 , etc.), boron oxoacids (e.g., orthoboric acid, metaboric acid, tetraboric acid, etc.) and salts thereof, boron carbides (e.g., B 4 C, B 6 C, etc.), boron nitride (BN), and other boron compounds are preferably used.
• boron carbides e.g., B 4 C, B 6 C, etc.
• BN boron nitride
• the carbon black (C2) can also be used after adjusting the particle size by pulverization, etc.
• a high-speed rotary pulverizer hammer mill, pin mill, cage mill
• various ball mills rolling mill, vibration mill, planetary mill
• stirring mill be used.
• These carbon blacks (C2) may be used alone or in combination of two or more kinds.
• the rubber composition for sidewalls may contain fillers other than silica (C1) and carbon black (C2) as filler (C) for the purpose of improving the properties of the resulting sidewall, such as improving the mechanical strength, and improving production costs by blending the filler as an extender.
• fillers other than silica (C1) and carbon black (C2) as filler (C) for the purpose of improving the properties of the resulting sidewall, such as improving the mechanical strength, and improving production costs by blending the filler as an extender.
• Fillers other than silica (C1) and carbon black (C2) that can be used include, for example, organic fillers and inorganic fillers such as clay, talc, mica, calcium carbonate, magnesium hydroxide, aluminum hydroxide, barium sulfate, titanium oxide, glass fiber, fibrous fillers, and glass balloons. These fillers may be used alone or in combination of two or more types.
• the amount of filler (C) per 100 parts by mass of solid rubber (A) is 5 to 80 parts by mass, and preferably 20 to 60 parts by mass.
• the amount of filler (C) is within the above range, the flex fatigue resistance and fuel economy of the sidewall obtained from the rubber composition for sidewalls of the present invention are improved.
• the amount of silica (C1) relative to 100 parts by mass of solid rubber (A) is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, even more preferably 20 parts by mass or more, even more preferably 25 parts by mass or more, and particularly preferably 30 parts by mass or more, from the viewpoint of improving the fuel efficiency performance of the sidewall obtained from the rubber composition for sidewalls. And it is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, and even more preferably 40 parts by mass or less.
• the amount of silica (C1) relative to 100 parts by mass of solid rubber (A) is preferably 10 parts by mass or more and 60 parts by mass or less, more preferably 15 parts by mass or more and 50 parts by mass or less, even more preferably 20 parts by mass or more and 40 parts by mass or less, and even more preferably 25 parts by mass or more and 40 parts by mass or less.
• the amount of carbon black (C2) per 100 parts by mass of solid rubber (A) is preferably 1 part by mass or more, more preferably 1.5 parts by mass or more, and even more preferably 2 parts by mass or more, from the viewpoint of improving the mechanical strength and weather resistance of the sidewall obtained from the rubber composition for sidewalls of the present invention. It is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 10 parts by mass or less.
• the ratio of silica (C1) to carbon black (C2) is preferably 1/99 to 99/1, more preferably 10/90 to 97/3, even more preferably 30/70 to 95/5, even more preferably 50/50 to 95/5, and particularly preferably 70/30 to 95/5, in order to improve the flex fatigue resistance of the sidewall obtained from the rubber composition for sidewalls of the present invention and to further improve fuel economy performance.
• the rubber composition for sidewalls of the present invention contains silica (C1) as the filler (C), it is preferable to contain a silane coupling agent.
• the silane coupling agent include sulfide compounds, mercapto compounds, vinyl compounds, amino compounds, glycidoxy compounds, nitro compounds, and chloro compounds.
• Sulfide compounds include, for example, bis(3-triethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, bis(3-triethoxysilylpropyl)trisulfide, bis(3-trimethoxysilylpropyl)trisulfide, bis(3-triethoxysilylpropyl)disulfide, bis(3-trimethoxysilylpropyl)disulfide, and 3-trimethoxysilylpropyl-N,N-dimethylsilyl.
• thiocarbamoyl tetrasulfide 3-triethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 2-trimethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropyl benzothiazole tetrasulfide, 3-triethoxysilylpropyl benzothiazole tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, and 3-octanoylthio-1-propyltriethoxysilane.
• Examples of mercapto compounds include 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, and 2-mercaptoethyltriethoxysilane.
• 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).
• silica C1
• the content of the silane coupling agent is within the above range, the dispersibility of the filler, the coupling effect, the reinforcement property, the resistance to bending fatigue, and other properties are improved.
• the rubber composition for sidewalls 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 solid rubber (A).
• the rubber composition for sidewalls 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 solid rubber (A).
• the rubber composition for sidewalls 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 sidewalls 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 solid rubber (A).
• the rubber composition for sidewalls 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, etc., 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
• 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 solid rubber (A), from the viewpoint of bleeding resistance.
• the rubber composition for sidewalls 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 sidewalls 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 sidewalls 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 sidewalls of the present invention is preferably used as a cross-linked product (vulcanized rubber) by cross-linking.
• vulcanized rubber a cross-linked product
• 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 sidewall of the present invention is at least partially made of the rubber composition for sidewall, and has excellent flexural fatigue resistance and improved fuel economy.
• the rubber composition for sidewall has excellent flexural fatigue resistance, the sidewall can be made thinner (lighter), and the weight of the tire can be reduced to obtain a tire with excellent fuel economy.
• the sidewall of the present invention can be obtained by molding a sidewall rubber having a predetermined cross-sectional shape from the rubber composition for a sidewall obtained as described above using an extruder or the like, and using this sidewall rubber to produce various tires (pneumatic tires) such as passenger car tires, large tires for trucks and buses, and motorcycle tires by a conventional method (generally including a crosslinking step), thereby resulting in a tire including the sidewall of the present invention.
• the structure of the sidewall of the present invention is not particularly limited and may be a single-layer structure or a multi-layer structure. In the case of a multi-layer structure, it is preferable to apply the above-mentioned rubber composition for sidewalls to the outermost layer.
• Carbon black Diablack H (manufactured by Mitsubishi Chemical Corporation, average particle size 31 nm, specific surface area 79 m 2 /g)
• the specific surface area of the carbon black is a value obtained in accordance with JIS K 6217-2:2001.
• Production Example 1-1 Production of Unmodified Liquid Diene Rubber (B'-1) 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. The temperature was raised to 50°C, and then 1350g 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, it was confirmed that the polymer solution phase and the water phase were separated, and then the water was separated. The polymer solution after washing was vacuum dried at 70°C for 24 hours to obtain an unmodified liquid diene rubber (B'-1).
• Production Example 1-2 Production of modified liquid diene rubber (B-1)
• B'-1 unmodified liquid diene rubber obtained in Production Example 1-1
• 1.0 g of 1,1-bis(t-hexylperoxy)cyclohexane and 50 g of (3-mercaptopropyl)triethoxysilane were added and reacted at 105° C. for 8 hours to obtain modified liquid diene rubber (B-1).
• Production Example 2-1 Production of Unmodified Liquid Diene Rubber (B'-2) A thoroughly dried 5L autoclave was replaced 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.
• B'-2 Unmodified Liquid Diene Rubber
• Production Example 2-2 Production of Modified Liquid Diene Rubber (B-2)
• B-2 Modified Liquid Diene Rubber
• 700 g of the unmodified liquid diene rubber (B'-2) obtained in Production Example 2-1 was charged and degassed with nitrogen while stirring for 3 hours at 60° C.
• 0.1 g of 1,1-bis(t-butylperoxy)cyclohexane and 119 g of (3-mercaptopropyl)triethoxysilane were added and reacted at 120° C. for 3 hours to obtain a modified liquid diene rubber (B-2).
• Production Example 3-1 Production of Unmodified Liquid Diene Rubber (B'-3) A thoroughly dried 5L autoclave was substituted with nitrogen, and 1580g of cyclohexane and 336g of s-butyllithium (0.99 mol/L, cyclohexane solution) were charged, and the temperature was raised to 50°C. After that, under stirring conditions, 23.4g of tetrahydrofuran was added, and then 218g of butadiene, 776g of isoprene, and 234g of butadiene were successively added to polymerize while controlling the polymerization temperature to 50°C. Methanol was then added to terminate the polymerization reaction, and a polymer solution was obtained.
• B'-3 is a triblock copolymer consisting of a linear butadiene homopolymer block-isoprene homopolymer block-butadiene homopolymer block.
• Production Example 3-2 Production of Modified Liquid Diene Rubber (B-3) Into a 1 L autoclave, 481 g of the unmodified liquid diene rubber (B'-3) obtained in Production Example 3-1 was charged, and the mixture was degassed with nitrogen while stirring for 3 hours at 60° C. 4.9 g of 1,1-bis(t-hexylperoxy)cyclohexane and 79 g of (3-mercaptopropyl)triethoxysilane were added, and the mixture was reacted for 8 hours at 105° C.
• modified liquid diene rubber (B-3) which is a triblock copolymer consisting of a linear butadiene homopolymer block-isoprene homopolymer block-butadiene homopolymer block modified with a functional group derived from the silane compound (1).
• Production Example 4-1 Production of Unmodified Liquid Diene Rubber (B'-4) A thoroughly dried 5L autoclave was replaced 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 successively added 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. The polymer solution after washing was vacuum dried at 70°C for 24 hours to obtain an unmodified liquid diene rubber (B'-4).
• Production Example 4-2 Production of modified liquid diene rubber (B-4) Into a 1 L autoclave, 700 g of the unmodified liquid diene rubber (B'-4) obtained was charged and degassed with nitrogen while stirring for 3 hours at 60° C. 2.0 g of 1,1-bis(t-butylperoxy)cyclohexane and 119 g of (3-mercaptopropyl)triethoxysilane were added and reacted at 120° C. for 3 hours to obtain modified liquid diene rubber (B-4).
• the methods for measuring and calculating the various physical properties of the modified liquid diene rubber obtained in the manufacturing examples are as follows.
• 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 peaks derived from the conjugated diene units bonded via 1,2-bonds and 3,4-bonds to the peaks derived from the conjugated diene units bonded via 1,4-bonds 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 calculated from 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 was calculated from the area ratio of the peak derived from the functional group 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 was the peak derived from the alkoxy group.
• Examples 1 to 11 and Comparative Examples 1 to 7 According to the compounding ratio (parts by mass) described in Table 2 (Examples) and Table 3 (Comparative Examples), the components other than the vulcanizing agent (sulfur) and the vulcanization accelerator (in the Examples, solid rubber (A), modified liquid diene rubber (B), filler (C), TDAE, silane coupling agent, zinc oxide, stearic acid, and antioxidant) were each charged into an internal Banbury mixer, and the mixture was kneaded for 4 minutes while controlling the starting temperature to 60°C and the resin temperature to 155 to 160°C, and then taken out of the mixer and cooled to room temperature.
• the components other than the vulcanizing agent (sulfur) and the vulcanization accelerator in the Examples, solid rubber (A), modified liquid diene rubber (B), filler (C), TDAE, silane coupling agent, zinc oxide, stearic acid, and antioxidant
• this mixture was again put into the Banbury mixer, 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 (150°C, 20 to 40 minutes) to prepare vulcanized rubber sheets (thickness 2 mm) and test pieces for flex crack growth tests, and the hardness, fuel economy performance, and flex fatigue resistance 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 long x 5 mm wide 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 the 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 used as an index of fuel economy performance.
• the values of each Example and Comparative Example are relative values when the value of Comparative Example 1 in Table 2 is taken as 100. The smaller the value, the better the fuel economy performance of the rubber composition.
• the rubber composition for sidewalls of the present invention contains a filler (silica) with a relatively large particle size, the rubber composition can be used to produce sidewalls that have excellent resistance to flex fatigue and improved fuel economy. Therefore, the rubber composition for sidewalls of the present invention is useful.

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