Rubber composition for tires

Abstract

Provide is a rubber composition for tires having a high level of tread durability when traveling on rough roads, heat generation resistance, and processability. The rubber composition is characterized by blending 0.1-3.0 mass parts of a compound represented by general formula (1), 0.5-6.0 mass parts of a processing aid containing a fatty acid ester, and 40-80 mass parts of carbon black per 100 mass parts of diene rubber containing 40 mass% or more isoprene rubber and by the nitrogen absorption specific surface area of the carbon black being 60-200 m2 / g. (In formula (1), R1, R2, R3, and R4 are the same or different and represent a hydrogen atom, an alkyl group, an aralkyl group, an aryl group, or a heterocyclic group. R3 and R4 together may form an alkylidene group, and any two of R2, R3, and R4 together may form an alkylene group. Each of these groups may optionally have one or more substituents.)

Description

Rubber composition for tires

[0001] The present invention relates to a rubber composition for tires that combines high levels of tread durability during running on rough roads, heat resistance, and processability.

[0002] For heavy-duty tires mounted on large vehicles such as dump trucks that travel off-road, primarily at construction and civil engineering sites, it is important that they have excellent tread durability and heat resistance when traveling on rough roads. To improve tread durability when traveling on rough roads, it is necessary to improve the tensile elongation at break and tear strength of the rubber composition that constitutes the tire. For example, methods for improving tensile elongation at break include reducing the vulcanization density or the amount of reinforcing filler. However, reducing the vulcanization density leads to poor heat resistance, and reducing the amount of reinforcing filler reduces rubber hardness, resulting in problems such as poor abrasion resistance.

[0003] Patent Document 1 describes that a rubber composition containing a rubber component, carbon black and / or inorganic filler, and a specific pyrazolone compound and its salt can exhibit low heat buildup. However, the invention described in Patent Document 1 has the problem of reduced processability, such as an increase in the viscosity of the rubber composition and a slower vulcanization rate. Furthermore, the reduced processability can also lead to a reduction in tread durability, such as chipping resistance, of the vulcanized rubber. Thus, it is difficult to achieve high levels of tread durability, heat buildup resistance, and processability when driving on rough roads, which are required for heavy-duty tires.

[0004] Japanese Patent Application Publication No. 2020-33453

[0005] An object of the present invention is to provide a rubber composition for tires which has high levels of tread durability when traveling on rough roads, heat resistance and processability.

[0006] The rubber composition for a tire of the present invention, which achieves the above object, comprises 100 parts by mass of a diene rubber containing 40% by mass or more of an isoprene rubber, 0.1 to 3.0 parts by mass of a compound represented by the following general formula (1), 0.5 to 6.0 parts by mass of a processing aid containing a fatty acid ester, and 40 to 80 parts by mass of a reinforcing filler containing carbon black, wherein the carbon black has a nitrogen adsorption specific surface area of ​​60 to 200 m:2 / g. (In formula (1), R 1 , R 2 , R 3 and R 4 are the same or different and represent a hydrogen atom, an alkyl group, an aralkyl group, an aryl group, or a heterocyclic group. 3 and R 4 may be taken together to form an alkylidene group, and R 2 , R 3 and R 4 Any two of these may be combined to form an alkylene group. Each of these groups may optionally have one or more substituents.

[0007] The rubber composition for tires of the present invention comprises 100 parts by mass of diene rubber containing 40% by mass or more of isoprene rubber, 0.1 to 3.0 parts by mass of a compound represented by general formula (1), 0.5 to 6.0 parts by mass of a processing aid containing a fatty acid ester, and a rubber having a nitrogen adsorption specific surface area of ​​60 to 200 m 2 The tire contains 40 to 80 parts by mass of a reinforcing filler containing carbon black having a carbon content of 1 / g, so that the tire can have higher levels of tread durability when traveling on rough roads, heat resistance, and processability than ever before.

[0008] The rubber composition for a tire of the present invention may further contain a fatty acid metal salt as the processing aid, and the amount of the fatty acid metal salt may be 0.5 to 5.5 parts by mass and 0.5 to 5.5 parts by mass of the processing aid containing the fatty acid ester may be 0.5 to 5.5 parts by mass per 100 parts by mass of the diene rubber. By blending both the fatty acid ester and the fatty acid metal salt as processing aids, the compound represented by general formula (1) may be retained within the rubber composition, thereby achieving higher levels of tread durability, heat resistance, and processability. The fatty acid ester may be a fatty acid glyceride. The fatty acid metal salt may be a zinc fatty acid. The total amount of the compound represented by general formula (1) and the processing aid may be 0.01 to 0.1 times by mass the amount of the carbon black. The amount of the fatty acid metal salt may be 0.3 to 3.0 times by mass the amount of the compound represented by general formula (1). The reinforcing filler may contain silica, and the amount of silica may be 5 parts by mass or more per 100 parts by mass of the diene rubber.

[0009] A tire having a tread made of the above-described rubber composition for a tire can achieve both tread durability and heat buildup resistance when traveling on rough roads at levels higher than ever before. In particular, in heavy-duty tires that are mainly mounted on large vehicles traveling off-road, if the tread is made of the above-described rubber composition for a tire, it can achieve both tread durability and heat buildup resistance at high levels even when traveling on rough roads.

[0010] The method for producing a rubber composition for tires of the present invention is characterized by comprising a step of mixing the diene rubber and the fatty acid metal salt, and then adding and mixing the compound represented by general formula (1) thereto, or a step of simultaneously mixing the compound represented by general formula (1) and the fatty acid metal salt with the diene rubber.

[0011] The rubber composition for tires of the present invention contains 40% by mass or more of isoprene-based rubber based on 100% by mass of diene-based rubber. By containing 40% by mass or more of isoprene-based rubber, excellent tread durability when driving on rough roads (hereinafter, "tread durability when driving on rough roads" may be simply referred to as "tread durability") and heat buildup resistance can be achieved. The isoprene-based rubber is at least one selected from natural rubber, epoxidized natural rubber, isoprene rubber, and modified isoprene rubber. These isoprene-based rubbers can be appropriately selected from those typically used in rubber compositions for tires. The isoprene-based rubber preferably accounts for 50% by mass or more, more preferably 60 to 100% by mass, even more preferably 70 to 100% by mass, and even more preferably 80 to 100% by mass, based on 100% by mass of diene-based rubber. Furthermore, all of the diene-based rubber may be isoprene-based rubber. One type of isoprene-based rubber may be used, or two or more types may be used in combination.

[0012] The rubber composition for tires may contain other diene rubbers besides isoprene rubber. Examples of other diene rubbers include butadiene rubber, styrene-butadiene rubber, butyl rubber, halogenated butyl rubber, acrylonitrile-butadiene rubber, and modified diene rubbers in which functional groups have been added to these diene rubbers. Compounding butadiene rubber is particularly effective, as it is advantageous for improving tread durability and abrasion resistance. These other diene rubbers may be used alone or in any blend. The content of the other diene rubber is preferably 60% by mass or less, preferably 50% by mass or less, more preferably 0 to 40% by mass, even more preferably 0 to 30% by mass, and even more preferably 0 to 20% by mass, based on 100% by mass of the diene rubber.

[0013] The rubber composition for tires contains a reinforcing filler containing carbon black. By compounding the reinforcing filler containing carbon black, it is possible to achieve excellent tread durability and wear resistance. The reinforcing filler is compounded in an amount of 40 to 80 parts by mass, preferably 42 to 75 parts by mass, and more preferably 45 to 70 parts by mass, per 100 parts by mass of diene rubber. If the amount of the reinforcing filler containing carbon black is less than 40 parts by mass, tread durability and wear resistance will decrease. Furthermore, if it exceeds 80 parts by mass, heat resistance will deteriorate.

[0014] The carbon black content of the reinforcing filler is preferably 60% by mass or more, more preferably 65% ​​by mass or more, even more preferably 70% by mass or more, and particularly preferably 75% by mass or more. A carbon black content of 60% by mass or more is preferable because it can provide excellent tread durability and abrasion resistance. The carbon black content of the reinforcing filler is preferably 100% by mass or less, more preferably 95% by mass or less, even more preferably 90% by mass or less, and even more preferably 85% by mass or less.

[0015] The rubber strength of a rubber composition for tires can be improved by blending carbon black. Examples of carbon black that may be blended include furnace black, acetylene black, thermal black, channel black, and graphite. Among these, furnace black is preferred, and specific examples thereof include SAF, ISAF, ISAF-HS, ISAF-LS, IISAF, IISAF-HS, HAF, HAF-HS, HAF-LS, and FEF. Of these, SAF, ISAF, IISAF, and HAF are more preferred, with ISAF, IISAF, and HAF being even more preferred. These carbon blacks can be used alone or in combination of two or more. Surface-treated carbon blacks, which are obtained by chemically modifying these carbon blacks with various acid compounds or the like, can also be used.

[0016] The nitrogen adsorption specific surface area (N2SA) of carbon black is 60 to 200 m 2 / g, preferably 65 to 180 m2 / g, more preferably 70 to 150 m 2 / g. By setting the N2SA of the carbon black within this range, tread durability and abrasion resistance can be further improved. In this specification, the N2SA of the carbon black conforms to JIS K6217-2.

[0017] The reinforcing filler may optionally contain silica, which can improve heat resistance and wet performance. The amount of silica is not particularly limited, as long as the total amount with carbon black is 40 to 80 parts by mass per 100 parts by mass of diene rubber. A total of 40 parts by mass or more of carbon black and silica is preferred because it increases tear strength and improves tread durability and abrasion resistance. A total of 80 parts by mass or less is preferred because it increases tensile elongation at break and improves tread durability and heat resistance. The total amount of carbon black and silica is more preferably 45 to 75 parts by mass, and even more preferably 50 to 70 parts by mass. The amount of silica is preferably 5 parts by mass or more, more preferably 5 to 35 parts by mass, and even more preferably 10 to 25 parts by mass per 100 parts by mass of diene rubber.

[0018] The silica preferably has a CTAB adsorption specific surface area of ​​140 m 2 / g or more. The CTAB adsorption specific surface area of ​​silica is 140 m 2 / g or more is advantageous for improving tread durability and abrasion resistance. The CTAB adsorption specific surface area is more preferably 140 to 280 m 2 / g, more preferably 140 to 240 m 2 In this specification, the CTAB adsorption specific surface area of ​​silica is in accordance with ISO 5794.

[0019] The silica may be one typically used in rubber compositions for tires. Examples of silica that can be used include wet-process silica, dry-process silica, carbon-silica (dual-phase filler) in which silica is supported on the surface of carbon black, and silica surface-treated with a compound reactive or compatible with both silica and rubber, such as a silane coupling agent or polysiloxane. Among these, wet-process silica primarily composed of hydrated silicic acid is preferred. Silica may be used alone or in combination of two or more types. Furthermore, silica derived from biomass materials such as rice husks may also be used.

[0020] It is also preferable to blend a silane coupling agent together with silica, as this improves the dispersibility of the silica and further improves wet performance. The type of silane coupling agent is not particularly limited, but sulfur-containing silane coupling agents are preferred, such as bis-(3-triethoxysilylpropyl)tetrasulfide, bis(3-triethoxysilylpropyl)trisulfide, bis(3-triethoxysilylpropyl)disulfide, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyldimethoxymethylsilane, 3-mercaptopropyldimethylmethoxysilane, and 3-mercaptopropyltriethoxysilane.

[0021] The silane coupling agent is preferably blended in an amount of 3 to 20% by mass, more preferably 5 to 15% by mass, based on the mass of silica. When the blending amount of the silane coupling agent is 3% by mass or more of the silica mass, the effect of improving the dispersibility of the silica is sufficiently obtained, which is preferable. Furthermore, when the blending amount of the silane coupling agent is 20% by mass or less, gelation of the diene rubber component is suppressed, and the desired effect is obtained, which is preferable.

[0022] The rubber composition for tires may also contain fillers other than carbon black and silica. This increases the strength of the rubber composition and ensures tire durability. Examples of other fillers include inorganic fillers such as talc, mica, aluminum oxide, titanium oxide, and barium sulfate, and organic fillers such as cellulose, lecithin, lignin, and dendrimers.

[0023] The rubber composition for tires contains 0.1 to 3.0 parts by mass of a compound represented by the following general formula (1) (hereinafter sometimes abbreviated as "pyrazolone derivative") per 100 parts by mass of diene rubber. (In formula (1), R 1 , R 2 , R 3 and R 4 are the same or different and represent a hydrogen atom, an alkyl group, an aralkyl group, an aryl group, or a heterocyclic group. 3 and R 4 may be taken together to form an alkylidene group, and R 2 , R 3 and R 4 Any two of these may be combined to form an alkylene group. Each of these groups may optionally have one or more substituents.

[0024] In general formula (1), R 1 , R 2 , R 3 and R 4 are the same or different and represent a hydrogen atom, an alkyl group, an aralkyl group, an aryl group, or a heterocyclic group. 1 , R 2 , R 3 and R 4 When is hydrogen, the compound of general formula (1) is 5-pyrazolone. Therefore, in this specification, the compound represented by general formula (1) may be referred to as a "pyrazolone derivative."

[0025] In the present specification, examples of the "alkyl group" include linear, branched, and cyclic alkyl groups. Specific examples include linear or branched alkyl groups having 1 to 4 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, s-butyl, t-butyl, and 1-ethylpropyl; linear or branched alkyl groups having 1 to 18 carbon atoms, such as n-pentyl, isopentyl, neopentyl, n-hexyl, isohexyl, 3-methylpentyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, 5-propylnonyl, n-tridecyl, n-tetradecyl, n-pentadecyl, hexadecyl, heptadecyl, and octadecyl; and cyclic alkyl groups having 3 to 8 carbon atoms, such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl.

[0026] Examples of the "aralkyl group" include benzyl, phenethyl, trityl, 1-naphthylmethyl, 2-(1-naphthyl)ethyl, and 2-(2-naphthyl)ethyl groups.

[0027] Examples of the "aryl group" include phenyl, biphenyl, naphthyl, dihydroindenyl, and 9H-fluorenyl groups.

[0028] Examples of the "heterocyclic group" include pyridyl, pyrimidyl, triazyl, quinolyl, isoquinolyl, quinoxalyl, cinnolyl, quinazolyl, phthalazyl, tetrahydroquinolyl, pyrrolyl, furyl, thienyl, imidazolyl, pyrazolyl, oxazolyl, thiazolyl, isoxazolyl, isothiazolyl, thiadiazolyl, oxadiazolyl, triazolyl, tetrazolyl, indolyl, isoindolyl, benzimidazolyl, benzofuranyl, isobenzofuranyl, benzothienyl, benzoxazolyl, benzothiazolyl, indazolyl, morpholyl, piperazyl, 2-piperazyl, piperidyl, tetrahydropyranyl, tetrahydrothiopyranyl, pyrrolidyl, furanyl, tetrahydrofuranyl, tetrahydrothienyl, 5-methyl-3-oxo-2,3-dihydro-1H-pyrazol-4-yl group, and the like.

[0029] Examples of the "alkylidene group" include methylidene, ethylidene, propylidene, isopropylidene, and butylidene groups.

[0030] Examples of the "alkylene group" include an ethylene group, a trimethylene group, a tetramethylene group, a pentamethylene group, a hexamethylene group, a heptamethylene group, etc. These alkylene groups may contain a nitrogen atom, an oxygen atom, or a sulfur atom, and may be connected via a phenylene group.

[0031] Each of these alkyl groups, aralkyl groups, aryl groups, heterocyclic groups, alkylidene groups, and alkylene groups may have one or more substituents at any substitutable position. Examples of "substituents" include halogen atoms, amino groups, aminoalkyl groups, alkoxycarbonyl groups, acyl groups, acyloxy groups, amide groups, carboxyl groups, carboxyalkyl groups, formyl groups, nitrile groups, nitro groups, alkyl groups, hydroxyalkyl groups, hydroxyl groups, alkoxy groups, aryl groups, aryloxy groups, heterocyclic groups, thiol groups, alkylthio groups, and arylthio groups. The number of substituents may be preferably 1 to 5, and more preferably 1 to 3.

[0032] In general formula (1), R 1 , R 3 and R 4 may be the same or different and may be a hydrogen atom, a linear or branched alkyl group having 1 to 4 carbon atoms, an aralkyl group, an aryl group, or a heterocyclic group.

[0033] In general formula (1), R 1 is preferably a hydrogen atom. 2 is preferably a hydrogen atom, a linear or branched alkyl group having 1 to 4 carbon atoms, an aralkyl group, an aryl group, or a heterocyclic group, more preferably a hydrogen atom, a linear or branched alkyl group having 1 to 4 carbon atoms, a benzyl group, a phenyl group, a naphthyl group, or a furyl group, and particularly preferably a hydrogen atom or a linear alkyl group having 1 to 4 carbon atoms.

[0034] In general formula (1), R 3 and R 4A compound in which at least one of R 3 and R 4 A compound in which both are hydrogen atoms is more preferred.

[0035] The compound represented by general formula (1) is R 1 is a hydrogen atom, R 2 is a hydrogen atom, a linear or branched alkyl group having 1 to 4 carbon atoms, an aralkyl group, an aryl group, or a heterocyclic group, and R 3 and R 4 and R 1 is a hydrogen atom, R 2 is a hydrogen atom, a linear or branched alkyl group having 1 to 4 carbon atoms, an aralkyl group, an aryl group, or a heterocyclic group, R 3 and R 4 More preferred are compounds in which R 1 is a hydrogen atom, and R 2 is a hydrogen atom or a linear alkyl group having 1 to 4 carbon atoms, and R 3 and R 4 Particularly preferred are compounds in which both are hydrogen atoms.

[0036] Examples of the pyrazolone derivative represented by general formula (1) include 5-pyrazolone, 3-methyl-5-pyrazolone, 3-(naphthalen-2-yl)-1H-pyrazol-5(4H)-one, 3-(furan-2-yl)-1H-pyrazol-5(4H)-one, 3-phenyl-1H-pyrazol-5(4H)-one, and 3-propyl-1H-pyrazol-5(4H)-one.

[0037] Some compounds represented by general formula (1) produce tautomers, and these tautomers are also included. When tautomerization is possible (e.g., in solution), chemical equilibrium between the tautomers can be reached. Furthermore, salts of the compounds represented by general formula (1) are also included. Examples of salts of the compounds represented by general formula (1) include inorganic acid salts such as hydrochloride, sulfate, and nitrate; organic acid salts such as acetate and methanesulfonate; alkali metal salts such as sodium salt and potassium salt; alkaline earth metal salts such as magnesium salt and calcium salt; and ammonium salts such as dimethylammonium and triethylammonium.

[0038] The rubber composition for tires contains 0.1 to 3.0 parts by mass of a compound represented by general formula (1) (pyrazolone derivative) blended with 100 parts by mass of diene rubber. By blending the pyrazolone derivative, tear strength and tensile elongation at break can be improved, resulting in excellent tread durability and wear resistance. The pyrazolone derivative is preferably blended in an amount of 0.1 to 2.8 parts by mass, more preferably 0.5 to 2.5 parts by mass, and even more preferably 0.8 to 2.0 parts by mass. If the pyrazolone derivative is less than 0.1 part by mass, tread durability and wear resistance cannot be improved beyond conventional levels. Furthermore, if the amount exceeds 3.0 parts by mass, tear strength decreases, tread durability cannot be improved, and wear resistance and heat resistance decrease. Furthermore, the raw material cost of the rubber composition for tires increases. The pyrazolone derivative may be blended alone or in combination of two or more types. When two or more pyrazolone derivatives are blended, the total amount should preferably be within the above-mentioned range.

[0039] A rubber composition for tires is formulated with 0.5 to 6.0 parts by mass of a processing aid containing a fatty acid ester per 100 parts by mass of diene rubber. By incorporating a processing aid containing a fatty acid ester, the viscosity of the rubber composition for tires can be lowered. When the above-mentioned pyrazolone derivative is incorporated into a diene rubber, the viscosity of the rubber composition increases. However, by incorporating a processing aid containing a fatty acid ester, the viscosity can be further reduced. Furthermore, incorporating a pyrazolone derivative into a diene rubber slows the vulcanization rate of the rubber composition, making it difficult to uniformly vulcanize the tire. Therefore, when a vulcanization accelerator is incorporated to increase the vulcanization rate, rubber compositions containing isoprene rubber are prone to reversion, which can lead to reduced chipping resistance. Typically, processing aids only lower the viscosity and do not affect the vulcanization rate of the rubber composition. However, unexpectedly, incorporating a processing aid containing a fatty acid ester into a rubber composition containing isoprene rubber and a pyrazolone derivative can increase the vulcanization rate. Furthermore, by using a processing aid containing a fatty acid ester in combination with a pyrazolone derivative, it is possible to suppress reversion of a rubber composition containing an isoprene-based rubber, and to improve mechanical properties such as tensile strength and tear strength, as well as tire durability and abrasion resistance.

[0040] The amount of the processing aid containing a fatty acid ester is preferably 0.7 to 5.0 parts by mass, more preferably 1.0 to 4.0 parts by mass, and even more preferably 1.5 to 3.0 parts by mass per 100 parts by mass of diene rubber. By incorporating the fatty acid ester within this range, excellent processability can be achieved, such as by lowering the viscosity and increasing the vulcanization rate, thereby improving tread durability and abrasion resistance. The processing aid may contain only one type of fatty acid ester or two or more types of fatty acid esters. Fatty acid glycerides are a suitable example of a fatty acid ester. The processing aid may contain fatty acid glycerides and / or fatty acid esters other than fatty acid glycerides, each of which may contain one or more types. Furthermore, the processing aid may contain fatty acids, fatty acid metal salts, fatty acid amides, etc. in addition to fatty acid glycerides and / or fatty acid esters other than fatty acid glycerides.

[0041] In the present invention, the desired effects can be achieved by blending a processing aid containing a fatty acid ester together with a pyrazolone derivative. The total blend amount of the processing aid containing a fatty acid ester and the pyrazolone derivative is preferably 0.01 to 0.1 times by mass, more preferably 0.02 to 0.08 times by mass, relative to the blend amount of carbon black. When the total blend amount of the processing aid containing a fatty acid ester and the pyrazolone derivative is 0.01 times by mass or more relative to the blend amount of carbon black, chipping resistance and heat resistance become good, which is preferable. Furthermore, when it is 0.1 times by mass or less, a good balance between processability and vulcanization speed is achieved, which is preferable.

[0042] Fatty acid esters are compounds in which a fatty acid and an alcohol are ester-bonded. In this specification, the fatty acid may be saturated or unsaturated and may have a linear, branched, or cyclic structure. The number of carbon atoms in the fatty acid is preferably 3 or more, more preferably 8 or more, and even more preferably 12 or more. The number of carbon atoms in the fatty acid is preferably 30 or less, more preferably 24 or less, and even more preferably 20 or less. Specific examples of these fatty acids include saturated fatty acids such as propionic acid, butanoic acid, butyric acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, dodecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, palmitoleic acid, heptadecanoic acid, octadecenoic acid, octadecadienoic acid, octadecatrienoic acid, nonadecanoic acid, icosanoic acid, docosanoic acid, hexadocosanoic acid, and octadocosanoic acid. Examples of unsaturated fatty acids include monounsaturated fatty acids such as crotonic acid, myristoleic acid, palmitoleic acid, oleic acid, elaidic acid, vaccenic acid, gadoleic acid, erucic acid, and nervonic acid; diunsaturated fatty acids such as linoleic acid; triunsaturated fatty acids such as α-linolenic acid and eleostearic acid; tetraunsaturated fatty acids such as stearidonic acid and arachidonic acid; pentaunsaturated fatty acids such as eicosapentaenoic acid and sardine acid; and hexaunsaturated fatty acids such as docosahexaenoic acid. The fatty acid moiety constituting the fatty acid ester may be not only one having one fatty acid residue, such as a stearic acid ester, but also one having two fatty acid residues, such as a diglyceride, or even one having three or more fatty acid residues, such as a triglyceride. When the fatty acid moiety constituting the fatty acid ester has multiple fatty acid residues, the number of carbon atoms in the aforementioned fatty acid corresponds to the number of carbon atoms per ester group.

[0043] Examples of the alcohol moiety constituting the fatty acid ester include aliphatic alcohols and phenols. The hydrocarbon moiety of the aliphatic alcohol may be saturated or unsaturated and may have a linear, branched, or cyclic structure. The aliphatic alcohol and phenol may be monohydric alcohols, monohydric phenols, dihydric or higher alcohols, or dihydric or higher phenols, with trihydric alcohols being preferred.

[0044] The number of carbon atoms in the aliphatic alcohol is, for example, preferably 3 or more, more preferably 8 or more, and even more preferably 12 or more. The number of carbon atoms in the aliphatic alcohol is preferably 30 or less, more preferably 24 or less, and even more preferably 20 or less. Specific examples include 1-octanol (C8), 1-decanol (C10), lauryl alcohol (C12), myristyl alcohol (C14), palmitoleic alcohol (C16), stearyl alcohol (C18), oleyl alcohol (C18), linolenyl alcohol (C18), behenyl alcohol (C22), and myricyl alcohol (C30). Examples of dihydric or higher aliphatic alcohols include glycol, glycerin, erythritol, and sorbitol.

[0045] The processing aid preferably contains a fatty acid glyceride. The fatty acid glyceride is a mono-, di-, or triglyceride in which a fatty acid is ester-bonded to glycerol (glycerin). The fatty acid glyceride may be one type or a combination of two or more types. The fatty acid may be, for example, one or more selected from the fatty acids described above. The saturated fatty acid glyceride may be any of saturated fatty acid monoglycerides, saturated fatty acid diglycerides, and saturated fatty acid triglycerides. Examples of saturated fatty acid monoglycerides include glycerol monostearate, glycerol monolaurate, glycerol monomyristate, glycerol monopalmitate, glycerol monoarachidylate, glycerol monobeherate, glycerol monocaprate, glycerol monomargarate, glycerol monolignocerate, and glycerol monocerotylate. Furthermore, examples of saturated fatty acid diglycerides include glycerol distearate, glycerol dilaurate, glycerol dimyristate, glycerol dipalmitate, glycerol diarachidylate, glycerol dibeherate, glycerol dicaprate, glycerol dimargarate, glycerol dilignocerate, glycerol dicerotylate, glycerol monostearate monolaurate, etc. Furthermore, examples of saturated fatty acid triglycerides include glycerol tristearate, glycerol trilaurate, glycerol trimyristate, glycerol tripalmitate, glycerol triarachidylate, glycerol tribeherate, glycerol tricaprate, glycerol trimargallate, glycerol trilignocerate, glycerol tricerotylate, glycerol distearate monolaurate, etc.

[0046] The unsaturated fatty acid glyceride may be any of unsaturated fatty acid monoglycerides, unsaturated fatty acid diglycerides, and unsaturated fatty acid triglycerides. Examples of unsaturated fatty acid monoglycerides include glycerol monooleate, glycerol monomyristoleate, glycerol monopalmitoleate, glycerol monogadoleate, glycerol monotonate, glycerol monolinoleate, and glycerol monolinolenate. Examples of unsaturated fatty acid diglycerides include glycerol dioleate, glycerol dimyristoleate, glycerol dipalmitoleate, glycerol digadoleate, glycerol dicrotonate, glycerol dilinoleate, glycerol dilinolenate, and glycerol monooleate monomyristoleate. Examples of unsaturated fatty acid triglycerides include glycerol trioleate, glycerol trimyristoleate, glycerol tripalmitoleate, glycerol trigladeate, glycerol tricrotonate, glycerol trilinoleate, glycerol trilinolenate, and glycerol dioleate monomyristoleate.

[0047] In the present invention, by blending a processing aid containing a fatty acid ester with a pyrazolone derivative, an excellent effect can be achieved, such as providing tread durability, heat resistance, and processability on rough roads at levels higher than ever before. To further enhance this effect, it is preferable to use a fatty acid ester and a fatty acid metal salt in combination as processing aids. That is, it is preferable to include 0.5 to 5.5 parts by mass of a fatty acid metal salt and 0.5 to 5.5 parts by mass of a processing aid containing a fatty acid ester other than a fatty acid metal salt per 100 parts by mass of diene rubber. The total amount of the fatty acid metal salt and the processing aid containing a fatty acid ester is preferably 1.0 to 6.0 parts by mass. By blending a processing aid containing a fatty acid metal salt and a fatty acid ester, the compound represented by general formula (1) (pyrazolone derivative) is retained within the rubber composition, thereby providing tread durability, heat resistance, and processability at higher levels. When the pyrazolone derivative comes into contact with the fatty acid metal salt, it forms a metal complex of the pyrazolone derivative, which can improve thermal properties. For example, when 3-methyl-5-pyrazolone comes into contact with a fatty acid zinc, a complex is formed in which four molecules of 3-methyl-5-pyrazolone are present for one molecule of zinc. When 3-methyl-5-pyrazolone is exposed to high temperatures of approximately 130°C or higher during kneading of the rubber composition, its content in the rubber composition may decrease due to sublimation or the like. In contrast, by forming a complex with a metal such as zinc in advance, the sublimation of 3-methyl-5-pyrazolone is suppressed, and 3-methyl-5-pyrazolone is retained inside the rubber composition, allowing the coexistence of the 3-methyl-5-pyrazolone with the fatty acid ester to achieve the desired effect.

[0048] The fatty acid metal salt is a metal salt of a fatty acid. The type of fatty acid is the same as the fatty acid described above. Preferred fatty acids constituting the fatty acid metal salt include stearic acid (octadecanoic acid), lauric acid, ricinoleic acid, octylic acid, caprylic acid, undecylenic acid, myristic acid, palmitic acid, margaric acid, araginic acid, lignoceric acid, cerotic acid, melissic acid, myristoleic acid, oleic acid, linoleic acid, linolenic acid, behenic acid, and capric acid. The metal may include, for example, zinc, barium, calcium, magnesium, potassium, sodium, lithium, copper, and nickel, with zinc, calcium, and magnesium being preferred. The fatty acid metal salt is preferably a zinc fatty acid.

[0049] The amount of fatty acid metal salt is preferably 0.3 to 3.0 times by mass the amount of the compound (pyrazolone derivative) represented by general formula (1). When the amount of fatty acid metal salt is within this range, it is easy to form a complex with the pyrazolone derivative, which is preferable because it can suppress sublimation of the pyrazolone derivative during production of the rubber composition. The amount of fatty acid metal salt is more preferably 0.4 to 2.0 times by mass, and even more preferably 0.5 to 1.5 times by mass the amount of the pyrazolone derivative.

[0050] The method for producing a rubber composition for tires is not particularly limited, and a typical method for producing a rubber composition for tires can be applied. When the rubber composition for tires contains a fatty acid metal salt, it is preferable to mix and knead the compound represented by general formula (1) (pyrazolone derivative) in the presence of the fatty acid metal salt. That is, it is preferable to heat the pyrazolone derivative in the presence of the fatty acid metal salt. For example, it is preferable to have a process of mixing a diene rubber and a fatty acid metal salt, and then adding and mixing the pyrazolone derivative thereto, or a process of simultaneously mixing the compound represented by general formula (1) (pyrazolone derivative) and the fatty acid metal salt with the diene rubber. By producing a rubber composition for tires by mixing the pyrazolone derivative in the presence of a fatty acid metal salt, the pyrazolone derivative and the metal of the fatty acid metal salt are more likely to form a complex, which is preferable because it can prevent the pyrazolone derivative from sublimating during the production of the rubber composition. In the above-mentioned method for producing a rubber composition for tires, the compounding ingredients excluding vulcanizing agents such as sulfur and vulcanization accelerators can be added to a mixer and mixed and kneaded at the same time as the diene rubber. That is, the processing aid containing the fatty acid ester, the reinforcing filler containing carbon black, and other compounding ingredients are preferably added to the mixer at the same time as the diene rubber, and mixed and kneaded, and the vulcanizing agent is preferably mixed in a subsequent step.

[0051] In addition to the above components, various compounding agents commonly used in rubber compositions for tires, such as vulcanizing or crosslinking agents, vulcanization accelerators, antioxidants, and thermosetting resins, can be compounded into the rubber composition for tires in a conventional manner. Such compounding agents can be kneaded in a conventional manner to form a rubber composition, which can then be used for vulcanization or crosslinking. The compounding amounts of these compounding agents can be conventional amounts as long as they do not deviate from the objectives of the present invention. The rubber composition for tires can be prepared by mixing the above components using a known rubber kneading machine, such as a Banbury mixer, kneader, or roll.

[0052] The rubber composition for tires is suitable for forming the tread and sidewalls of tires, and is particularly suitable for forming cap treads. The tires may be either passenger tires or heavy-duty tires, and are particularly suitable for use in heavy-duty tires designed for rough road driving. In particular, in heavy-duty tires designed for use on large vehicles primarily traveling off-road, if the cap tread is made of the above-described rubber composition for tires, high levels of tread durability and heat buildup resistance can be achieved even when traveling on rough roads. Examples of heavy-duty tires include tires having at least four belt layers on the radially inner side of the tread. The tires may be either pneumatic or non-pneumatic. The present invention will be further described below with reference to examples, but the scope of the present invention is not limited to these examples.

[0053] To prepare rubber compositions for tires (Examples 1-9, Reference Example 1, and Comparative Examples 1-6) having the common additive formulation shown in Table 3 and the formulations shown in Tables 1 and 2, the components except for sulfur and vulcanization accelerator were weighed and mixed in a 1.7-liter internal Banbury mixer for 5 minutes, and the resulting masterbatch was then discharged from the mixer and cooled to room temperature. This masterbatch was then fed to the Banbury mixer, and sulfur and vulcanization accelerator were added and mixed to obtain rubber compositions for tires. The amounts of the additives in the formulations in Table 3 are listed in parts by mass relative to 100 parts by mass of the diene rubber shown in Tables 1 and 2.

[0054] Each of the rubber compositions for tires obtained above was vulcanized in a mold of a predetermined shape at 160°C for 20 minutes to prepare an evaluation sample. The obtained evaluation sample was used to measure the tensile elongation at break, tear strength, and heat resistance by the following methods.

[0055] Tensile Breaking Elongation The evaluation samples obtained above, each 2 mm thick, were punched into a JIS No. 3 dumbbell shape, and a tensile test was carried out at a pulling rate of 500 mm / min at 23°C in accordance with the measurement method specified in JIS K6251 "Vulcanized rubber and thermoplastic rubber - Determination of tensile properties," to measure the tensile breaking elongation (%). The results obtained are shown in the "Tensile Breaking Elongation" column in Tables 1 and 2 as an index, with the value of Reference Example 1 being set to 100. A higher index means a higher tensile breaking elongation.

[0056] Tear Strength Trouser-shaped test pieces according to JIS K6252 were punched out from the evaluation samples obtained above with a thickness of 2 mm, and a tear test was carried out at a pulling rate of 100 mm / min at 23°C in accordance with the measurement method specified in JIS K6252 "Vulcanized rubber and thermoplastic rubber - Determination of tear strength" to measure the tear strength (kN / m). The results obtained are shown in the "Tear Strength" column in Tables 1 and 2 as an index, with the value of Reference Example 1 being 100. A higher index means a higher tear strength.

[0057] Chipping resistance (tread durability) The average values ​​of the tensile breaking elongation index and tear strength index obtained above were recorded as the tread durability index in the "chipping resistance" column of Tables 1 and 2. A higher index indicates better chipping resistance, and an index of 97 or higher is considered to be excellent for practical use.

[0058] Heat Resistance Using the obtained evaluation samples, tan δ at 60°C was measured using a viscoelasticity spectrometer (manufactured by Toyo Seiki Seisakusho, Ltd.) in accordance with JIS K6394:2007 under conditions of an elongation deformation strain rate of 10%±2%, a frequency of 20 Hz, and a temperature of 60°C. The reciprocals of the obtained results were calculated and shown in the "Heat Resistance" column of Tables 1 and 2 as indexes, with the value of Reference Example 1 being 100. The larger this index, the smaller the heat generation and the better the heat resistance. An index of 97 or more is considered to be excellent for practical use.

[0059] Processability The Mooney viscosity of the rubber composition for tires was measured in accordance with JIS K6300 using a Mooney viscometer with an L-type rotor (38.1 mm diameter, 5.5 mm thickness) under the conditions of a 1 minute preheat time, a 4 minute rotor rotation time, 100°C, and 2 rpm. The reciprocals of the obtained results were calculated and shown in the "Processability" column of Tables 1 and 2 as an index, with the value of Reference Example 1 being 100. The larger this index, the lower the viscosity and the better the molding processability. An index of 105 or higher is considered to be practical.

[0060] Vulcanization Speed ​​A vulcanization curve of the tire rubber composition was obtained in accordance with JIS K6300, showing the torque obtained at a temperature of 160°C versus the vulcanization time, and the vulcanization time (T30) required to reach 30% of the maximum torque was measured. The reciprocals of the obtained results were calculated and shown in the "vulcanization speed" column in Tables 1 and 2 as an index, with the value of Reference Example 1 being 100. The larger this value, the faster the vulcanization speed. An index of 105 or more and 135 or less was considered practical.

[0061]

[0062]

[0063] The types of raw materials used in Tables 1 and 2 are as follows: NR: Natural rubber, SIR Carbon black-1: SAF grade carbon black, Nitelon #430 manufactured by Nippon Steel Carbon Co., Ltd., N2SA is 125 m 2 / g Carbon black-2: ISAF grade carbon black, SEAST 7HM manufactured by Nippon Steel Carbon Co., Ltd., N2SA is 110m 2 / g Carbon black-3: HAF grade carbon black, Seast KH manufactured by Tokai Carbon Co., Ltd., N2SA is 93m 2 / g Carbon black-4: HAF grade carbon black, manufactured by Tokai Carbon Co., Ltd., SEAT NHT, N2SA 70m 2 / g Silica-1: ULTRASIL VN3GR manufactured by Evonik, CTAB adsorption specific surface area is 150 m 2 / g Silica-2: ULTRASIL 9100GR manufactured by Evonik, CTAB adsorption specific surface area is 200 m 2 / g Compound-1: 3-methyl-5-pyrazolone, a compound represented by general formula (1) (R 1 , R 3 and R 4 is a hydrogen atom, R 2 is a methyl group), EN-01 manufactured by Otsuka Chemical Co., Ltd. Compound-2: hydrazide compound, N'-(1,3-dimethylbutylidene)-3-hydroxy-2-naphthohydrazide, a compound not represented by general formula (1), DC-01 manufactured by Otsuka Chemical Co., Ltd. Processing aid-1: zinc stearate, A50P manufactured by SKRUKTOL Processing aid-2: processing aid containing fatty acid glyceride, HT207 manufactured by SKRUKTOL Vulcanization accelerator: Noccela CZ-G manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Sulfur: Myucron OT-20 manufactured by Shikoku Chemical Industry Co., Ltd.

[0064]

[0065] The types of raw materials used in Table 3 are as follows: Zinc oxide: Three types of zinc oxide manufactured by Seido Chemical Co., Ltd. Antioxidant: 6PPD manufactured by Eastman Co., Ltd. Wax: OZOACE-0355 manufactured by Nippon Seiro Co., Ltd.

[0066] As is clear from Table 2, it was confirmed that the rubber compositions for tires of Examples 1 to 9 had improved tensile elongation at break and tear strength, and also had higher levels of chipping resistance (tread durability), heat resistance, processability (Mooney viscosity), and vulcanization speed than conventional rubber compositions.

[0067] As is clear from Table 1, the rubber composition for a tire of Comparative Example 1 does not contain a pyrazolone derivative but a hydrazide compound, and the processing aid does not contain a fatty acid ester, so chipping resistance (tread durability) cannot be improved. The rubber composition for a tire of Comparative Example 2 contains more than 80 parts by mass of a reinforcing filler containing carbon black, so heat resistance and processability (Mooney viscosity) are deteriorated. The rubber composition for a tire of Comparative Example 3 contains less than 40 parts by mass of a reinforcing filler containing carbon black, so it has low tear strength and a poor vulcanization rate. The rubber composition for a tire of Comparative Example 4 contains more than 6.0 parts by mass of a processing aid containing a fatty acid ester, so it has a poor vulcanization rate. The rubber composition for a tire of Comparative Example 5 contains more than 3.0 parts by mass of a pyrazolone derivative, so it has poor processability (Mooney viscosity) and a poor vulcanization rate. In the rubber composition for tires of Comparative Example 6, the vulcanization rate was increased by increasing the amount of vulcanization accelerator instead of blending a processing aid containing a fatty acid ester, so the tensile elongation at break and tear strength were reduced and chipping resistance was poor.

[0068] Rubber compositions for tires (Examples 10-19, Reference Example 2, and Comparative Examples 7-9) were prepared using the common additive formulation shown in Table 6 and the formulations shown in Tables 4-5. In the manufacturing methods for Reference Example 2, Examples 10, 11, 14-19, and Comparative Examples 7-9, the components excluding sulfur and vulcanization accelerator were weighed and mixed in a 1.7-liter internal Banbury mixer for 5 minutes to form a masterbatch, which was then discharged and cooled to room temperature. This masterbatch was fed to the same Banbury mixer, and sulfur and vulcanization accelerator were added and mixed to obtain a rubber composition for tires. When a fatty acid metal salt was added in these manufacturing methods, it was added and mixed simultaneously with the compound represented by general formula (1) (pyrazolone derivative). The amounts of the additives in the formulations in Table 6 are listed in parts by mass relative to 100 parts by mass of the diene rubber listed in Tables 4-5.

[0069] In the manufacturing method of Example 12, all components except for sulfur, a vulcanization accelerator, and a general formula pyrazolone derivative were weighed and kneaded in a 1.7-liter internal Banbury mixer for 3 minutes, and the pyrazolone derivative was added and kneaded for another 2 minutes to form a masterbatch, which was then discharged from the mixer and cooled to room temperature. This masterbatch was fed to the same Banbury mixer, and sulfur and a vulcanization accelerator were added and mixed to obtain a rubber composition for tires. In this manufacturing method, the fatty acid metal salt was first added and mixed, and then the pyrazolone derivative was added and mixed.

[0070] In the manufacturing method of Example 13, all components except sulfur, vulcanization accelerator, and fatty acid metal salt were weighed and kneaded in a 1.7-liter internal Banbury mixer for 3 minutes, and the fatty acid metal salt was added and kneaded for another 2 minutes to form a masterbatch, which was then discharged from the mixer and cooled at room temperature. This masterbatch was then fed to the same Banbury mixer, and sulfur and vulcanization accelerator were added and mixed to obtain a rubber composition for tires. In this manufacturing method, the pyrazolone derivative was first added and mixed, and then the fatty acid metal salt was added and mixed.

[0071] Each of the rubber compositions for tires obtained above was vulcanized in a mold of a predetermined shape at 160°C for 20 minutes to prepare an evaluation sample. The obtained evaluation sample was used to measure the tensile elongation at break, tear strength, and heat resistance by the following methods.

[0072] Tensile Breaking Elongation The evaluation samples obtained above, each 2 mm thick, were punched into a JIS No. 3 dumbbell shape and subjected to a tensile test at a pulling rate of 500 mm / min at 23°C in accordance with the measurement method specified in JIS K6251 "Vulcanized rubber and thermoplastic rubber - Determination of tensile properties," to measure the tensile breaking elongation (%). The results obtained are shown in the "Tensile Breaking Elongation" column in Tables 4 and 5 as an index, with the value of Reference Example 2 set to 100. A higher index means a higher tensile breaking elongation.

[0073] Tear Strength Trouser-shaped test pieces according to JIS K6252 were punched out from the evaluation samples with a thickness of 2 mm obtained above, and a tear test was carried out at a tensile speed of 100 mm / min at 23°C in accordance with the measurement method prescribed in JIS K6252 "Vulcanized rubber and thermoplastic rubber - Determination of tear strength" to measure the tear strength (kN / m). The results obtained are shown in the "Tear Strength" column of Tables 4 and 5 as an index, with the value of Reference Example 2 being 100. A higher index means a higher tear strength.

[0074] Chipping resistance (tread durability) The average values ​​of the tensile breaking elongation index and tear strength index obtained above were recorded as the tread durability index in the "chipping resistance" column of Tables 4 and 5. The larger this index, the better the chipping resistance, and an index of 97 or more is judged to be excellent in practical use.

[0075] Heat resistance Using the obtained evaluation samples, tan δ at 60°C was measured using a viscoelasticity spectrometer (manufactured by Toyo Seiki Seisakusho, Ltd.) in accordance with JIS K6394:2007 under conditions of an elongation deformation strain rate of 10%±2%, a frequency of 20 Hz, and a temperature of 60°C. The reciprocals of the obtained results were calculated and shown in the "heat resistance" column of Tables 4 and 5 as indexes, with the value of Reference Example 2 being 100. The larger this index, the smaller the heat generation and the better the heat resistance. An index of 97 or more is considered to be excellent for practical use.

[0076] Processability The Mooney viscosity of the rubber composition for tires was measured in accordance with JIS K6300 using a Mooney viscometer with an L-type rotor (38.1 mm diameter, 5.5 mm thickness) under the conditions of a preheating time of 1 minute, a rotor rotation time of 4 minutes, 100°C, and 2 rpm. The reciprocals of the obtained results were calculated and shown in the "Processability" column of Tables 4 and 5 as indexes, with the value of Reference Example 2 being 100. The higher the index, the lower the viscosity and the better the molding processability. An index of 105 or higher is considered to be practical.

[0077] Vulcanization Speed ​​A vulcanization curve of the tire rubber composition was obtained in accordance with JIS K6300, showing the torque obtained at a temperature of 160°C versus the vulcanization time, and the vulcanization time (T30) required to reach 30% of the maximum torque was measured. The reciprocals of the obtained results were calculated and shown in the "vulcanization speed" column of Tables 4 and 5 as an index, with the value of Reference Example 2 being 100. The larger this value, the faster the vulcanization speed. An index of 105 or more and 135 or less was considered practical.

[0078] Sublimation of Compound-1 (Pyrazolone Derivative) During Processing In the above-described method for preparing a rubber composition for tires, when the masterbatch was removed from the mixer, the state of the masterbatch was visually observed, and the presence or absence of sublimation of Compound-1 (pyrazolone derivative) was evaluated according to the following criteria, and the results are shown in the column "Presence or absence of sublimation of Compound-1 during processing" in Tables 4 and 5. Present: Emission of clear white smoke from the masterbatch was visually observed. Slightly present: Emission of white smoke from the masterbatch was visually observed, although less than above. Minimal: Even less, slight white smoke from the masterbatch was visually observed. Absent: White smoke could not be visually confirmed from the masterbatch.

[0079]

[0080]

[0081] The types of raw materials used in Tables 4 and 5 are as follows: NR: Natural rubber, SIR BR: Butadiene rubber, NIPOL BR1220 manufactured by Nippon Zeon Co., Ltd. Carbon black-1: SAF grade carbon black, Nitelon #430 manufactured by Nippon Steel Carbon Co., Ltd., N2SA is 125m 2 / g Carbon black-2: ISAF grade carbon black, SEAST 7HM manufactured by Nippon Steel Carbon Co., Ltd., N2SA is 110m 2 / g Carbon black-3: HAF grade carbon black, Seast KH manufactured by Tokai Carbon Co., Ltd., N2SA is 93m 2 / g Silica-1: ULTRASIL VN3GR manufactured by Evonik, CTAB adsorption specific surface area is 150 m 2 / g Compound-1: 3-methyl-5-pyrazolone, a compound represented by general formula (1) (R1 , R 3 and R 4 is a hydrogen atom, R 2 is a methyl group), EN-01 manufactured by Otsuka Chemical Co., Ltd. Compound-2: hydrazide compound, N'-(1,3-dimethylbutylidene)-3-hydroxy-2-naphthohydrazide, compound not represented by general formula (1), DC-01 manufactured by Otsuka Chemical Co., Ltd. Processing aid-1: zinc stearate, A50P manufactured by SKRUKTOL Processing aid-2: processing aid containing fatty acid glyceride, HT207 manufactured by SKRUKTOL Processing aid-3: processing aid containing fatty acid glyceride, HT204 manufactured by SKRUKTOL Processing aid-4: magnesium stearate, magnesium stearate manufactured by Taihei Chemical Industry Co., Ltd.

[0082]

[0083] The types of raw materials used in Table 6 are as follows: Zinc oxide: Three types of zinc oxide manufactured by Seido Chemical Co., Ltd. Antioxidant: 6PPD manufactured by Eastman Co., Ltd. Wax: OZOACE-0355 manufactured by Nippon Seiro Co., Ltd. Vulcanization accelerator: Noccela CZ-G manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Sulfur: Myucron OT-20 manufactured by Shikoku Chemical Industry Co., Ltd.

[0084] As is clear from Tables 4 and 5, it was confirmed that the rubber compositions for tires of Examples 10 to 18 had improved tensile elongation at break and tear strength, and also had higher levels of chipping resistance (tread durability), heat resistance, processability (Mooney viscosity), and vulcanization speed than conventional rubber compositions.

[0085] As is clear from Table 4, the rubber composition for a tire of Comparative Example 7 contains a hydrazide compound without a pyrazolone derivative, and the processing aid does not contain a fatty acid ester, so chipping resistance (tread durability) cannot be improved. The rubber composition for a tire of Comparative Example 8 contains more than 3.0 parts by mass of the pyrazolone derivative, so its processability (Mooney viscosity) is poor. The rubber composition for a tire of Comparative Example 9 contains more than 6.0 parts by mass of the processing aid containing a fatty acid ester, so its vulcanization speed is poor.

[0086] The present disclosure includes the following inventions: Invention [1] A rubber composition comprising 100 parts by mass of a diene rubber containing 40% by mass or more of an isoprene rubber, 0.1 to 3.0 parts by mass of a compound represented by the following general formula (1), 0.5 to 6.0 parts by mass of a processing aid containing a fatty acid ester, and 40 to 80 parts by mass of a reinforcing filler containing carbon black, wherein the carbon black has a nitrogen adsorption specific surface area of ​​60 to 200 m 2 / g. (In formula (1), R 1 , R 2 , R 3 and R 4 are the same or different and represent a hydrogen atom, an alkyl group, an aralkyl group, an aryl group, or a heterocyclic group. 3 and R 4 may be taken together to form an alkylidene group, and R 2 , R 3 and R 4Any two of the above may combine to form an alkylene group. Each of these groups may optionally have one or more substituents.) Invention [2] The rubber composition for a tire according to Invention [1], further comprising a fatty acid metal salt as the processing aid, the composition comprising 0.5 to 5.5 parts by mass of the fatty acid metal salt and 0.5 to 5.5 parts by mass of the processing aid containing the fatty acid ester per 100 parts by mass of the diene rubber. Invention [3] The rubber composition for a tire according to Invention [1] or [2], characterized in that the fatty acid ester is a fatty acid glyceride. Invention [4] The rubber composition for a tire according to any of Inventions [1] to [3], characterized in that the fatty acid metal salt is a zinc fatty acid. Invention [5] The rubber composition for a tire according to any of Inventions [1] to [4], characterized in that the total amount of the compound represented by General Formula (1) and the processing aid is 0.01 to 0.1 times by mass the amount of the carbon black. Invention [6] The rubber composition for a tire according to any one of Inventions [1] to [5], wherein the blending amount of the fatty acid metal salt is 0.3 to 3.0 times by mass the blending amount of the compound represented by General Formula (1). Invention [7] The rubber composition for a tire according to any one of Inventions [1] to [6], wherein the reinforcing filler contains silica, and the amount of this silica is 5 parts by mass or more per 100 parts by mass of the diene rubber. Invention [8] A tire having a tread made from the rubber composition for a tire according to any one of Inventions [1] to [7]. Invention [9] A heavy-duty tire having a tread made from the rubber composition for a tire according to any one of Inventions [1] to [7], and having at least four belt layers on the radially inner side of the tread. Invention

[10] A method for producing a rubber composition for a tire according to any one of Inventions [2] to [7], comprising the steps of: mixing the diene rubber and the fatty acid metal salt; and then adding and mixing the compound represented by General Formula (1) thereto; or simultaneously mixing the compound represented by General Formula (1) and the fatty acid metal salt with the diene rubber.

Claims

1. A rubber composition comprising 100 parts by mass of a diene rubber containing 40% by mass or more of an isoprene rubber, 0.1 to 3.0 parts by mass of a compound represented by the following general formula (1), 0.5 to 6.0 parts by mass of a processing aid containing a fatty acid ester, and 40 to 80 parts by mass of a reinforcing filler containing carbon black, wherein the carbon black has a nitrogen adsorption specific surface area of ​​60 to 200 m 2 / g. (In formula (1), R 1 , R 2 , R 3 and R 4 are the same or different and represent a hydrogen atom, an alkyl group, an aralkyl group, an aryl group, or a heterocyclic group. 3 and R 4 may be taken together to form an alkylidene group, and R 2 , R 3 and R 4 Any two of these may be combined to form an alkylene group. Each of these groups may optionally have one or more substituents.

2. The rubber composition for tires according to claim 1, further comprising a fatty acid metal salt as the processing aid, wherein the composition contains 0.5 to 5.5 parts by mass of the fatty acid metal salt and 0.5 to 5.5 parts by mass of the processing aid containing the fatty acid ester per 100 parts by mass of the diene rubber.

3. The rubber composition for tires according to claim 1 or 2, wherein the fatty acid ester is a fatty acid glyceride.

4. The rubber composition for tires according to claim 1 or 2, wherein the fatty acid metal salt is a fatty acid zinc salt.

5. The rubber composition for tires according to claim 1 or 2, characterized in that the total amount of the compound represented by general formula (1) and the processing aid is 0.01 to 0.1 times by mass the amount of the carbon black.

6. The rubber composition for tires according to claim 1 or 2, characterized in that the amount of the fatty acid metal salt blended is 0.3 to 3.0 times by mass the amount of the compound represented by general formula (1).

7. A rubber composition for tires according to claim 1 or 2, characterized in that the reinforcing filler contains silica, and the amount of this silica is 5 parts by mass or more per 100 parts by mass of the diene rubber.

8. A tire having a tread made of the rubber composition for tires according to claim 1 or 2.

9. A heavy-duty tire having a tread made of the rubber composition for tires according to claim 1 or 2, and at least four belt layers on the radially inner side of the tread.

10. A method for producing a rubber composition for tires according to claim 2, comprising the steps of: mixing the diene rubber and the fatty acid metal salt; and then adding and mixing the compound represented by general formula (1); or simultaneously mixing the compound represented by general formula (1) and the fatty acid metal salt with the diene rubber.

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