JP2012025802A - Rubber composition for tire, method for producing the same, and pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for a tire that can improve low fuel consumption, rubber strength, abrasion resistance, and processability in a balanced manner, a method for producing the same, and a pneumatic tire produced by using the rubber composition.SOLUTION: The rubber composition for a tire contains a rubber component, silica, and at least two silane coupling agents including a tetrasulfide-based coupling agent, wherein the rubber composition for a tire is obtained by kneading the tetrasulfide-based coupling agent under the conditions that the highest achieving temperature is 95-135°C.

Description

The present invention relates to a tire rubber composition, a method for producing the same, and a pneumatic tire manufactured using the tire rubber composition.

Conventionally, in order to improve the fuel efficiency of a tire, a method of reducing the amount of a reinforcing agent in a rubber composition, a method of blending silica and a silane coupling agent, and a method of increasing the amount of a crosslinking agent such as sulfur are used. I came. However, in the method of reducing the amount of the reinforcing agent in the rubber composition, sufficient reinforcing properties cannot be obtained, and the rubber strength and wear resistance tend to be reduced. Also, the method of blending silica and a silane coupling agent and the method of increasing the amount of a crosslinking agent such as sulfur tend to decrease the rubber strength and wear resistance due to the excessive crosslinking density between polymers.

In addition, fuel efficiency can be improved by increasing the blending ratio of natural rubber, but reversion is likely to occur, and as a result, rubber strength may decrease. Thus, it is difficult to achieve both low fuel consumption and tire durability, and a method for improving both performances in a well-balanced manner is desired.

Patent Document 1 proposes a method in which silica is dispersed well using two or more silane coupling agents to improve fuel efficiency, rubber strength, etc., but the improvement effect is not sufficient. . Further, Patent Document 2 proposes a method for improving fuel efficiency by using a silane coupling agent having a mercapto group highly reactive with silica. However, when this method is used, there is room for improvement in that the scorch time is significantly shortened and the workability may be deteriorated.

Japanese Patent Laid-Open No. 11-181160 JP 2009-126907 A

The present invention solves the above-mentioned problems and provides a tire rubber composition capable of improving fuel economy, rubber strength, wear resistance and processability in a well-balanced manner, a method for producing the same, and a pneumatic produced using the rubber composition. The object is to provide a tire.

The present invention is a tire rubber composition containing a rubber component, silica, and two or more silane coupling agents including a tetrasulfide coupling agent. The present invention relates to a tire rubber composition obtained by kneading at a temperature of 95 to 135 ° C.

In the rubber composition, the content of the silica is preferably 10 to 150 parts by mass and the content of the tetrasulfide coupling agent is 1 to 12 parts by mass with respect to 100 parts by mass of the rubber component.

（式中、Ｒ^１、Ｒ^２及びＲ^３は、同一若しくは異なって、炭素数５〜１２のアルキル基を示す。ｘ及びｙは、同一若しくは異なって、２〜４の整数を示す。ｎは０〜１０の整数を示す。）
ＭＯ_３Ｓ−Ｓ−（ＣＨ_２）_ｐ−Ｓ−ＳＯ_３Ｍ （２）
（式中、ｐは３〜１０の整数を表す。Ｍは、同一若しくは異なって、リチウム、カリウム、ナトリウム、マグネシウム、カルシウム、バリウム、亜鉛、ニッケル又はコバルトを表す。）
Ｒ^４−Ｓ−Ｓ−（ＣＨ_２）_ｑ−Ｓ−Ｓ−Ｒ^５ （３）
（式中、ｑは２〜１０の整数を表す。Ｒ^４及びＲ^５は、同一若しくは異なって、チッ素原子を含む１価の有機基を表す。） The rubber component is selected from the group consisting of a compound represented by any one of the following formulas (1) to (3) and a hydrate of a compound represented by the following formula (2) with respect to 100 parts by mass of the rubber component. It is preferable to contain 0.3 to 6 parts by mass of at least one kind.

^(Wherein, R 1, ^{R 2} and ^{R 3} are the same or different, .x and y represents an alkyl group having 5 to 12 carbon atoms are the same or different, .n indicating the integer of 2 to 4 is Represents an integer of 0 to 10.)
_{MO 3 S-S- (CH 2} ) p -S-SO 3 M (2)
(In the formula, p represents an integer of 3 to 10. M is the same or different and represents lithium, potassium, sodium, magnesium, calcium, barium, zinc, nickel, or cobalt.)
R ⁴ —S—S— (CH ₂ ) _q —S—S—R ⁵ (3)
(In the formula, q represents an integer of 2 to 10. R ⁴ and R ⁵ are the same or different and each represents a monovalent organic group containing a nitrogen atom.)

The hydrate of the compound represented by the formula (2) is 1,6-hexamethylene-sodium dithiosulfate dihydrate, and the compound represented by the formula (3) is 1,6-bis (N, N′-dibenzylthiocarbamoyldithio) hexane is preferred.

（式中、Ｒ^６、Ｒ^７及びＲ^８は、同一若しくは異なって、アルキル基、アルコキシ基、シリルオキシ基、アセタール基、カルボキシル基、メルカプト基又はこれらの誘導体を表す。Ｒ^９及びＲ^１０は、同一若しくは異なって、水素原子又はアルキル基を表す。ｍは整数を表す。） In 100% by mass of the rubber component, the total content of styrene butadiene rubber and butadiene rubber modified with a compound represented by the following formula (4) is preferably 10% by mass or more.

(Wherein R ⁶ , R ⁷ and R ⁸ are the same or different and each represents an alkyl group, an alkoxy group, a silyloxy group, an acetal group, a carboxyl group, a mercapto group, or a derivative thereof. R ⁹ and R ¹⁰ are (The same or different and represents a hydrogen atom or an alkyl group. M represents an integer.)

The present invention also includes a step (I) of kneading the rubber component, the silica, and a silane coupling agent other than the tetrasulfide coupling agent, a kneaded product obtained in the step (I), and the And a step (II) of kneading a tetrasulfide coupling agent under the condition that the maximum temperature reached 95 to 135 ° C.
The present invention also relates to a pneumatic tire produced using the rubber composition.

According to the present invention, the rubber component, silica, and two or more silane coupling agents including a tetrasulfide coupling agent are contained, and the tetrasulfide coupling agent is added at the highest temperature within a specific range. Since the rubber composition is obtained by kneading, by using the rubber composition for a tire, it is possible to provide a pneumatic tire excellent in balance between low fuel consumption, rubber strength, and wear resistance. Further, the unvulcanized rubber composition is excellent in processability.

The tire rubber composition of the present invention contains a rubber component, silica, and two or more silane coupling agents including a tetrasulfide coupling agent, and the tetrasulfide coupling agent is the highest. It is obtained by kneading under the condition that the ultimate temperature (temperature at which kneading is finished) is 95 to 135 ° C. By kneading the tetrasulfide coupling agent with other components at a low temperature as described above, an unreacted tetrasulfide coupling agent can be present around the silica, and in the vicinity of the silica during vulcanization. Sulfur can be supplied efficiently. As a result, the crosslink density in the vicinity of the silica can be selectively improved without greatly changing the crosslink density of the entire polymer, and the fuel efficiency, rubber strength, and wear resistance can be improved. Moreover, the effect which suppresses shortening of a scorch time can be anticipated by making an unreacted tetrasulfide coupling agent exist in an unvulcanized rubber composition. These effects can improve fuel economy, rubber strength, wear resistance, and processability in a well-balanced manner.

The rubber composition of the present invention includes, for example, a rubber component, silica, and a silane coupling agent other than the tetrasulfide coupling agent (of the two or more silane coupling agents, other than the tetrasulfide coupling agent). And kneading the kneaded product obtained in the step (I) and the tetrasulfide coupling agent under the condition that the maximum reached temperature is 95 to 135 ° C. It is suitably obtained by the manufacturing method including.

(Process (I))
In the step (I), a silane coupling agent other than the tetrasulfide coupling agent among the two or more silane coupling agents is kneaded together with the rubber component and silica. The kneading method is not particularly limited, and a known method such as a Banbury mixer can be used. Moreover, it does not specifically limit as kneading | mixing temperature and kneading | mixing time of process (I), For example, it kneads about 2 to 10 minutes (preferably 2 to 6 minutes at 150-170 degreeC) in the range of 140-180 degreeC. do it.

（式中、Ｒ^６、Ｒ^７及びＲ^８は、同一若しくは異なって、アルキル基、アルコキシ基、シリルオキシ基、アセタール基、カルボキシル基、メルカプト基又はこれらの誘導体を表す。Ｒ^９及びＲ^１０は、同一若しくは異なって、水素原子又はアルキル基を表す。ｍは整数を表す。） The rubber component used in step (I) preferably includes styrene butadiene rubber (modified SBR) and / or butadiene rubber (modified BR) modified with a compound represented by the following formula (4). Thereby, silica can be dispersed well and fuel economy, rubber strength, wear resistance and processability can be improved in a well-balanced manner. Among these, modified SBR is preferable because it is advantageous for low fuel consumption.

(Wherein R ⁶ , R ⁷ and R ⁸ are the same or different and each represents an alkyl group, an alkoxy group, a silyloxy group, an acetal group, a carboxyl group, a mercapto group, or a derivative thereof. R ⁹ and R ¹⁰ are (The same or different and represents a hydrogen atom or an alkyl group. M represents an integer.)

In the compound represented by the above formula (4), R ⁶ , R ⁷ and R ⁸ are the same or different and are alkyl group, alkoxy group, silyloxy group, acetal group, carboxyl group (—COOH), mercapto group (— SH) or derivatives thereof.

As said alkyl group, C1-C4 alkyl groups, such as a methyl group, an ethyl group, n-propyl group, isopropyl group, n-butyl group, t-butyl group, etc. are mentioned, for example.

Examples of the alkoxy group include an alkoxy group having 1 to 8 carbon atoms (preferably 1 to 6 carbon atoms) such as a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, an n-butoxy group, and a t-butoxy group. More preferably, C1-C4) etc. are mentioned. Examples of the alkoxy group include a cycloalkoxy group (such as a cycloalkoxy group having 5 to 8 carbon atoms such as a cyclohexyloxy group) and an aryloxy group (an aryloxy group having 6 to 8 carbon atoms such as a phenoxy group and a benzyloxy group). ) Is also included.

Examples of the silyloxy group include a silyloxy group substituted with an aliphatic group having 1 to 20 carbon atoms and an aromatic group (trimethylsilyloxy group, triethylsilyloxy group, triisopropylsilyloxy group, diethylisopropylsilyloxy group, t- Butyldimethylsilyloxy group, t-butyldiphenylsilyloxy group, tribenzylsilyloxy group, triphenylsilyloxy group, tri-p-xylylsilyloxy group, etc.).

Examples of the acetal group include groups represented by -C (RR ')-OR "and -OC (RR')-OR". Examples of the former include a methoxymethyl group, an ethoxymethyl group, a propoxymethyl group, a butoxymethyl group, an isopropoxymethyl group, a t-butoxymethyl group, and a neopentyloxymethyl group. The latter includes a methoxymethoxy group, an ethoxy group, and the like. Methoxy group, propoxymethoxy group, i-propoxymethoxy group, n-butoxymethoxy group, t-butoxymethoxy group, n-pentyloxymethoxy group, n-hexyloxymethoxy group, cyclopentyloxymethoxy group, cyclohexyloxymethoxy group, etc. Can be mentioned.

As R < ⁶ >, R < ⁷ > and R < ⁸ >, an alkoxy group is preferable and an ethoxy group is more preferable. Thereby, low fuel consumption, rubber strength, wear resistance, and workability can be improved in a high level and in a well-balanced manner.

In the compound represented by the above formula (4), R ⁹ and R ¹⁰ are the same or different and each represents a hydrogen atom or an alkyl group.

Examples of the alkyl group for R ⁹ and R ¹⁰ include the same groups as the above alkyl groups.

R ⁹ and R ¹⁰ are preferably an alkyl group (preferably having 1 to 3 carbon atoms, more preferably 1 to 2 carbon atoms), and more preferably an ethyl group. Thereby, low fuel consumption, rubber strength, wear resistance, and workability can be improved in a high level and in a well-balanced manner.

As m (integer), 2-5 are preferable. Thereby, low fuel consumption, rubber strength, wear resistance, and workability can be improved in a high level and in a well-balanced manner. Furthermore, m is more preferably 2 to 4, and most preferably 3. If m is 1 or less, the denaturation reaction may be inhibited, and if m is 6 or more, the effect as a denaturing agent is reduced.

Specific examples of the compound represented by the above formula (4) include 3-aminopropyldimethylmethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylethyldimethoxysilane, 3-aminopropyltrimethoxysilane, 3- Aminopropyldimethylethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyldimethylbutoxysilane, 3-aminopropylmethyldibutoxysilane, dimethylaminomethyltrimethoxysilane, 2-dimethyl Aminoethyltrimethoxysilane, 3-dimethylaminopropyltrimethoxysilane, 4-dimethylaminobutyltrimethoxysilane, dimethylaminomethyldimethoxymethylsilane, 2-dimethylaminoethyldimethoxy Methylsilane, 3-dimethylaminopropyldimethoxymethylsilane, 4-dimethylaminobutyldimethoxymethylsilane, dimethylaminomethyltriethoxysilane, 2-dimethylaminoethyltriethoxysilane, 3-dimethylaminopropyltriethoxysilane, 4-dimethylaminobutyl Triethoxysilane, dimethylaminomethyldiethoxymethylsilane, 2-dimethylaminoethyldiethoxymethylsilane, 3-dimethylaminopropyldiethoxymethylsilane, 4-dimethylaminobutyldiethoxymethylsilane, diethylaminomethyltrimethoxysilane, 2- Diethylaminoethyltrimethoxysilane, 3-diethylaminopropyltrimethoxysilane, 4-diethylaminobutyltrimethoxysilane, diethylamino Tildimethoxymethylsilane, 2-diethylaminoethyldimethoxymethylsilane, 3-diethylaminopropyldimethoxymethylsilane, 4-diethylaminobutyldimethoxymethylsilane, diethylaminomethyltriethoxysilane, 2-diethylaminoethyltriethoxysilane, 3-diethylaminopropyltriethoxysilane 4-diethylaminobutyltriethoxysilane, diethylaminomethyldiethoxymethylsilane, 2-diethylaminoethyldiethoxymethylsilane, 3-diethylaminopropyldiethoxymethylsilane, 4-diethylaminobutyldiethoxymethylsilane, and the like. These may be used alone or in combination of two or more. Of these, 3-diethylaminopropyltriethoxysilane is preferred from the viewpoint that the effect of improving fuel economy is high.

Examples of the method for modifying styrene butadiene rubber (SBR) and butadiene rubber (BR) with the compound represented by the above formula (4) (modifier) include JP-B-6-53768, JP-B-6-57767, A conventionally known method such as the method described in Table 2003-514078 can be used. For example, SBR or BR may be brought into contact with a modifying agent, SBR or BR is polymerized, and a predetermined amount of the modifying agent is added to the polymer rubber solution, or the modifying agent is added to the SBR or BR solution. The method of making it react is mentioned.

SBR and BR to be modified are not particularly limited, and those commonly used in the tire industry can be used. For example, SBR includes solution polymerization SBR, emulsion polymerization SBR, and the like, and BR includes high cis content BR, BR containing syndiotactic polybutadiene crystals, and the like.

In the rubber composition of the present invention obtained by the above production method, the content of the modified SBR in 100% by mass of the rubber component is preferably 10% by mass or more, more preferably 30% by mass or more. If it is less than 10% by mass, sufficient silica dispersion cannot be ensured, and the fuel efficiency may deteriorate. The content of the modified SBR is preferably 90% by mass or less, more preferably 70% by mass or less. When it exceeds 90 mass%, workability may be significantly deteriorated.

In the rubber composition of the present invention obtained by the above production method, the content of the modified BR in 100% by mass of the rubber component is preferably 10% by mass or more, more preferably 30% by mass or more. If it is less than 10% by mass, sufficient silica dispersion cannot be ensured, and the fuel efficiency may deteriorate. The content of the modified BR is preferably 90% by mass or less, more preferably 70% by mass or less. When it exceeds 90 mass%, workability may be significantly deteriorated.

In the rubber composition of the present invention obtained by the above production method, the total content of the modified SBR and the modified BR in 100% by mass of the rubber component is preferably 10% by mass or more, more preferably 20% by mass or more, and still more preferably. Is 30% by mass or more. If it is less than 10% by mass, sufficient silica dispersion cannot be obtained, and the effect of improving fuel economy tends to be low. Although the upper limit of this total content is not specifically limited, Preferably it is 90 mass% or less, More preferably, it is 80 mass% or less. When it exceeds 90% by mass, the Mooney viscosity increases rapidly during kneading, and the kneading processability tends to deteriorate.

In the step (I), it is preferable to mix other rubber components together with the modified SBR and / or the modified BR. Thereby, workability, wear resistance, etc. can be improved. As other rubber components, for example, natural rubber (NR), modified natural rubber, non-modified SBR, non-modified BR and the like can be used. These may be used alone or in combination of two or more. Of these, NR and modified natural rubber are preferable, and NR is more preferable in that good rubber strength and wear resistance can be obtained. As NR, deproteinized natural rubber, high-purity natural rubber (HPNR) and the like can be suitably used. As the modified natural rubber, epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), grafted natural rubber, and the like can be suitably used.

In the rubber composition of the present invention obtained by the above production method or the like, the content of NR in 100% by mass of the rubber component is preferably 10% by mass or more, more preferably 20% by mass or more. If it is less than 10% by mass, the effect of improving the rubber strength and wear resistance by NR may not be sufficiently obtained. The NR content is preferably 60% by mass or less, more preferably 40% by mass or less. If it exceeds 60% by mass, the ratio of other rubber components decreases, and there is a possibility that low fuel consumption, wear resistance and wet grip performance cannot be obtained in a well-balanced manner.

The silica used in the step (I) is not particularly limited, and for example, those commonly used in the tire industry such as dry method silica (anhydrous silica) and wet method silica (hydrous silica) can be used. These may be used alone or in combination of two or more.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 50 m ² / g or more, more preferably 80 m ² / g or more. If it is less than 50 m ² / g, the reinforcing effect is small, and the wear resistance tends to decrease. Further, N ₂ SA of silica is preferably 300 m ² / g or less, more preferably 250 m ² / g or less. When it exceeds 300 m ² / g, silica is difficult to disperse, hysteresis loss increases, and fuel economy tends to deteriorate.
The _N 2 SA of silica is measured by BET method in accordance with ASTM D3037-81.

In the rubber composition of the present invention obtained by the above production method or the like, the content of silica is preferably 10 parts by mass or more, more preferably 60 parts by mass or more with respect to 100 parts by mass of the rubber component. If the amount is less than 10 parts by mass, sufficient wear resistance may not be obtained. The silica content is preferably 150 parts by mass or less, more preferably 100 parts by mass or less. If it exceeds 150 parts by mass, the workability tends to deteriorate.

In step (I), of the two or more silane coupling agents used, those other than the tetrasulfide coupling agent are kneaded. Examples of such silane coupling agents include bis (3-triethoxysilylpropyl) disulfide, bis (2-triethoxysilylethyl) disulfide, bis (4-triethoxysilylbutyl) disulfide, and bis (3-triethoxy). Disulfide systems such as methoxysilylpropyl) disulfide, bis (2-trimethoxysilylethyl) disulfide, bis (4-trimethoxysilylbutyl) disulfide; 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2- Mercapto compounds such as mercaptoethyltrimethoxysilane and 2-mercaptoethyltriethoxysilane are preferred. Among these, a mercapto silane coupling agent is preferable from the viewpoint that good fuel economy can be obtained.

（式中、ｚ、ｗはそれぞれ１以上の整数である。Ｒ^１１は水素、ハロゲン、分岐若しくは非分岐の炭素数１〜３０のアルキル基若しくはアルキレン基、分岐若しくは非分岐の炭素数２〜３０のアルケニル基若しくはアルケニレン基、分岐若しくは非分岐の炭素数２〜３０のアルキニル基若しくはアルキニレン基、又は該アルキル基若しくは該アルケニル基の末端の水素が水酸基若しくはカルボキシル基で置換されたものを示す。Ｒ^１２は水素、分岐若しくは非分岐の炭素数１〜３０のアルキレン基若しくはアルキル基、分岐若しくは非分岐の炭素数２〜３０のアルケニレン基若しくはアルケニル基、又は分岐若しくは非分岐の炭素数２〜３０のアルキニレン基若しくはアルキニル基を示す。Ｒ^１１とＲ^１２とで環構造を形成してもよい。） Moreover, as a mercapto type | system | group silane coupling agent, 1-70 mol of bond units b are with respect to the total amount of the bond unit a shown by following formula (5), and the bond unit b shown by following formula (6). What was copolymerized in the ratio of% can be used conveniently.

(In the formula, each of z and w is an integer of 1 or more. R ¹¹ is hydrogen, halogen, branched or unbranched C1-C30 alkyl group or alkylene group, branched or unbranched C2-C30. Or an alkenyl group or alkenylene group, a branched or unbranched alkynyl group or alkynylene group having 2 to 30 carbon atoms, or a hydrogen atom substituted at the terminal of the alkyl group or the alkenyl group with a hydroxyl group or a carboxyl group. ¹² is hydrogen, a branched or unbranched alkylene group or alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenylene group or alkenyl group having 2 to 30 carbon atoms, or a branched or unbranched carbon group having 2 to 30 carbon atoms. R represents an alkynylene group or an alkynyl group, and R ¹¹ and R ¹² may form a ring structure.)

In the silane coupling agent having the above structure, since the molar ratio of the bond unit a and the bond unit b satisfies the above condition, an increase in viscosity during processing is suppressed. This is presumably because the increase in Mooney viscosity is small because the sulfide portion of the bond unit a is thermally stable with a C—S—C bond.

Moreover, when the molar ratio of the bond unit a and the bond unit b satisfies the above conditions, the shortening of the scorch time is suppressed as compared with mercaptosilane such as 3-mercaptopropyltrimethoxysilane. This is because the bonding unit b has a mercaptosilane structure, but the —C ₇ H ₁₅ portion of the bonding unit a covers the —SH group of the bonding unit b, and thus it is difficult to react with the polymer. As a result, the scorch time is unlikely to be shortened and the viscosity is unlikely to increase.

Examples of the halogen for R ¹¹ include chlorine, bromine, and fluorine.

Examples of the branched or unbranched alkyl group having 1 to 30 carbon atoms of R ¹¹ and R ¹² include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an iso-butyl group, and a sec-butyl group. Tert-butyl group, pentyl group, hexyl group, heptyl group, 2-ethylhexyl group, octyl group, nonyl group, decyl group and the like. The number of carbon atoms of the alkyl group is preferably 1-12.

Examples of the branched or unbranched alkylene group having 1 to 30 carbon atoms of R ¹¹ and R ¹² include ethylene group, propylene group, butylene group, pentylene group, hexylene group, heptylene group, octylene group, nonylene group, decylene group, Examples include an undecylene group, a dodecylene group, a tridecylene group, a tetradecylene group, a pentadecylene group, a hexadecylene group, a heptadecylene group, and an octadecylene group. The alkylene group preferably has 1 to 12 carbon atoms.

Examples of the branched or unbranched alkenyl group having 2 to 30 carbon atoms represented by R ¹¹ and R ¹² include a vinyl group, 1-propenyl group, 2-propenyl group, 1-butenyl group, 2-butenyl group, 1-pentenyl group, 2-pentenyl group, 1-hexenyl group, 2-hexenyl group, 1-octenyl group and the like can be mentioned. The alkenyl group preferably has 2 to 12 carbon atoms.

Examples of the branched or unbranched C2-C30 alkenylene group represented by R ¹¹ and R ¹² include a vinylene group, a 1-propenylene group, a 2-propenylene group, a 1-butenylene group, a 2-butenylene group, a 1-pentenylene group, 2-pentenylene group, 1-hexenylene group, 2-hexenylene group, 1-octenylene group and the like can be mentioned. The alkenylene group preferably has 2 to 12 carbon atoms.

Examples of the branched or unbranched alkynyl group having 2 to 30 carbon atoms represented by R ¹¹ and R ¹² include ethynyl group, propynyl group, butynyl group, pentynyl group, hexynyl group, heptynyl group, octynyl group, noninyl group, decynyl group, An undecynyl group, a dodecynyl group, etc. are mentioned. The alkynyl group preferably has 2 to 12 carbon atoms.

Examples of the branched or unbranched alkynylene group having 2 to 30 carbon atoms of R ¹¹ and R ¹² include ethynylene group, propynylene group, butynylene group, pentynylene group, hexynylene group, heptynylene group, octynylene group, noninylene group, decynylene group, An undecynylene group, a dodecynylene group, etc. are mentioned. The alkynylene group preferably has 2 to 12 carbon atoms.

In the silane coupling agent having the above structure, the total repeating number (z + w) of the repeating number (z) of the bonding unit a and the repeating number (w) of the bonding unit b is preferably in the range of 3 to 300. Within this range, since the mercaptosilane of the bond unit b is covered with —C ₇ H ₁₅ of the bond unit a, it is possible to suppress the scorch time from being shortened and to have good reactivity with silica and rubber components. Can be secured.

As a commercial item of the silane coupling agent having the above structure, for example, NXT-Z30, NXT-Z45, NXT-Z60 manufactured by Momentive Performance Materials, Inc. can be used.

In the rubber composition of the present invention obtained by the above production method, the content of the silane coupling agent used in the step (I) is preferably 4 parts by mass or more, more preferably 100 parts by mass of silica. It is 6 parts by mass or more. If the amount is less than 4 parts by mass, the reaction between silica and the silane coupling agent becomes insufficient, and the fuel economy, rubber strength, and wear resistance may not be sufficiently improved. The content of the silane coupling agent is preferably 12 parts by mass or less, more preferably 10 parts by mass or less. If it exceeds 12 parts by mass, there is a possibility that an effect commensurate with the increase in cost cannot be obtained.

In step (I), carbon black is preferably blended as a reinforcing agent. Thereby, good rubber strength and wear resistance can be obtained. Carbon black that can be used is not particularly limited, and those generally used in the tire industry such as GPF, FEF, HAF, ISAF, and SAF can be used. These may be used alone or in combination of two or more.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 80 m ² / g or more, more preferably 100 m ² / g or more. If it is less than 80 m ² / g, sufficient wet grip performance cannot be obtained, and rubber strength and wear resistance tend to be reduced. The N ₂ SA of the carbon black is preferably 280 m ² / g or less, more preferably 250 m ² / g or less. If it exceeds 280 m ² / g, the workability tends to deteriorate.
In addition, the nitrogen adsorption specific surface area of carbon black is measured by the A method of JIS K6217.

In the rubber composition of the present invention obtained by the above production method or the like, the content of carbon black is preferably 2 parts by mass or more, more preferably 5 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 2 parts by mass, the rubber strength and wear resistance tend to decrease. The carbon black content is preferably 50 parts by mass or less, more preferably 20 parts by mass or less. If it exceeds 50 parts by mass, the workability tends to deteriorate. In addition, hysteresis loss increases and fuel efficiency tends to deteriorate.

(Process (II))
In step (II), for example, a tetrasulfide coupling agent is added to the kneaded product obtained in step (I) and kneaded under the condition that the maximum temperature reached 95 to 135 ° C.

The tetrasulfide coupling agent is not particularly limited as long as it is a coupling agent having a tetrasulfide bond, and general ones can be used. Of these, bis (3-triethoxysilyl) tetrasulfide can be preferably used from the viewpoint that the effects of the present invention can be obtained satisfactorily.

The maximum temperature reached in step (II) is 95 ° C or higher, preferably 100 ° C or higher. If it is lower than 95 ° C., the tetrasulfide coupling agent cannot be sufficiently dispersed, and the effect of improving rubber strength and wear resistance may be reduced. The maximum temperature reached is 135 ° C. or lower, preferably 130 ° C. or lower, more preferably 120 ° C. or lower. When it exceeds 135 ° C., a part of the tetrasulfide coupling agent is decomposed and there is a possibility that sulfur cannot be supplied during vulcanization.

It does not specifically limit as a kneading | mixing method of process (II), The method similar to process (I) can be used. Moreover, what is necessary is just to adjust the kneading | mixing time of process (II) suitably in the range which does not exceed the said highest ultimate temperature, for example, should just be about 1 to 8 minutes (preferably 2 to 5 minutes).

In the rubber composition of the present invention obtained by the above production method or the like, the content of the tetrasulfide coupling agent used in the step (II) is preferably 1 part by mass or more with respect to 100 parts by mass of the rubber component. More preferably, it is 3 mass parts or more, More preferably, it is 4 mass parts or more. If it is less than 1 part by mass, sulfur cannot be sufficiently supplied, and the effect of improving rubber strength and wear resistance may be reduced. The content is preferably 12 parts by mass or less, more preferably 10 parts by mass or less. If it exceeds 12 parts by mass, there is a possibility that an effect commensurate with the increase in cost cannot be obtained.

After performing the step (II), the kneaded product, the crosslinking agent, the vulcanization accelerator and the like obtained in the step (II) are kneaded by a known method, and then vulcanized to obtain the rubber of the present invention. A composition can be obtained.

（式中、Ｒ^１、Ｒ^２及びＲ^３は、同一若しくは異なって、炭素数５〜１２のアルキル基を示す。ｘ及びｙは、同一若しくは異なって、２〜４の整数を示す。ｎは０〜１０の整数を示す。）
ＭＯ_３Ｓ−Ｓ−（ＣＨ_２）_ｐ−Ｓ−ＳＯ_３Ｍ （２）
（式中、ｐは３〜１０の整数を表す。Ｍは、同一若しくは異なって、リチウム、カリウム、ナトリウム、マグネシウム、カルシウム、バリウム、亜鉛、ニッケル又はコバルトを表す。）
Ｒ^４−Ｓ−Ｓ−（ＣＨ_２）_ｑ−Ｓ−Ｓ−Ｒ^５ （３）
（式中、ｑは２〜１０の整数を表す。Ｒ^４及びＲ^５は、同一若しくは異なって、チッ素原子を含む１価の有機基を表す。） The rubber composition of the present invention is selected from the group consisting of a compound represented by any one of the following formulas (1) to (3) and a hydrate of a compound represented by the following formula (2) as a crosslinking agent. It is preferable to use at least one kind. As a result, a good cross-linked structure can be formed, and the fuel economy, rubber strength, wear resistance and processability can be improved in a well-balanced manner. Further, the compound represented by the following formula (2) and the hydrate thereof can have a highly heat-stable —S— (CH ₂ ) _p —S— bond in the rubber composition, Abrasion resistance can be further improved. Similarly, the compound represented by the following formula (3) can also have a highly heat-stable -C-C- bond in the rubber composition, and the -C-C- bond is -S- Since the flexibility is lower than that of the S-bond, the elastic modulus can be increased to improve the rubber strength and the wear resistance.

^(Wherein, R 1, ^{R 2} and ^{R 3} are the same or different, .x and y represents an alkyl group having 5 to 12 carbon atoms are the same or different, .n indicating the integer of 2 to 4 is Represents an integer of 0 to 10.)
_{MO 3 S-S- (CH 2} ) p -S-SO 3 M (2)
(In the formula, p represents an integer of 3 to 10. M is the same or different and represents lithium, potassium, sodium, magnesium, calcium, barium, zinc, nickel, or cobalt.)
R ⁴ —S—S— (CH ₂ ) _q —S—S—R ⁵ (3)
(In the formula, q represents an integer of 2 to 10. R ⁴ and R ⁵ are the same or different and each represents a monovalent organic group containing a nitrogen atom.)

In the formula (1), n is an integer of 0 to 10 from the viewpoint of good dispersibility of the compound represented by the formula (1) (alkylphenol / sulfur chloride condensate) in the rubber component. An integer of is preferred. x and y are integers of 2 to 4 from the viewpoint that high hardness can be efficiently expressed (reversion suppression), and both are preferably 2. R ^{1 to} R ³ are alkyl groups having 5 to 12 carbon atoms, preferably alkyl groups having 6 to 9 carbon atoms, from the viewpoint of good dispersibility of the alkylphenol / sulfur chloride condensate in the rubber component.

The alkylphenol / sulfur chloride condensate can be prepared by a known method and is not particularly limited. For example, a method of reacting alkylphenol and sulfur chloride at a molar ratio of 1: 0.9 to 1.25, etc. Is mentioned.

Specific examples of the alkylphenol / sulfur chloride condensate include Takkol V200 (following formula (7)) manufactured by Taoka Chemical Industry Co., Ltd.

（式中、ｎは０〜１０の整数を表す。）

(In the formula, n represents an integer of 0 to 10.)

The sulfur content of the alkylphenol / sulfur chloride condensate is a ratio obtained by heating to 800 to 1000 ° C. in a combustion furnace and converting it into SO ₂ gas or SO ₃ gas, optically quantifying it from the amount of gas generated. Say.

In formula (2), p is an integer of 3 to 10, preferably 3 to 6. If it is less than 3, the rubber strength and wear resistance may not be sufficiently improved, and if it exceeds 10, the effect of improving the rubber strength and wear resistance tends to be small although the molecular weight increases.

In formula (2), M is preferably lithium, potassium, sodium, magnesium, calcium, barium, zinc, nickel or cobalt, more preferably potassium or sodium. Examples of the hydrate of the compound represented by the formula (2) include sodium salt monohydrate and sodium salt dihydrate.

As a compound represented by the formula (2) and a hydrate thereof, a derivative derived from sodium thiosulfate, for example, 1,6-hexamethylene-sodium dithiosulfate dihydrate is preferable for economic reasons.

In formula (3), q is an integer of 2 to 10, preferably 4 to 8. When q is 1, thermal stability is poor and the effect of having an alkylene group tends not to be obtained, and when 11 or more, it is represented by —SS— (CH ₂ ) _q —S—S—. It tends to be difficult to form a crosslinked chain.

Examples of the alkylene group satisfying the above conditions include ethylene group, trimethylene group, tetramethylene group, pentamethylene group, hexamethylene group, heptamethylene group, octamethylene group, decamethylene group and the like. Among these, a hexamethylene group is preferable because a bridge represented by —SS— (CH ₂ ) _q —S—S— is smoothly formed between the polymers and is thermally stable.

In formula (3), R ⁴ and R ⁵ are not particularly limited as long as they are monovalent organic groups containing nitrogen atoms, but those containing at least one aromatic ring are preferred, and carbon atoms are bonded to dithio groups. And those containing a linking group represented by N—C (═S) —. R ⁴ and R ⁵ may be the same or different, but are preferably the same for reasons such as ease of production.

Examples of the compound represented by the above formula (3) include 1,2-bis (N, N′-dibenzylthiocarbamoyldithio) ethane, 1,3-bis (N, N′-dibenzylthiocarbamoyldithio). ) Propane, 1,4-bis (N, N′-dibenzylthiocarbamoyldithio) butane, 1,5-bis (N, N′-dibenzylthiocarbamoyldithio) pentane, 1,6-bis (N, N '-Dibenzylthiocarbamoyldithio) hexane, 1,7-bis (N, N'-dibenzylthiocarbamoyldithio) heptane, 1,8-bis (N, N'-dibenzylthiocarbamoyldithio) octane, 1, Examples include 9-bis (N, N′-dibenzylthiocarbamoyldithio) nonane and 1,10-bis (N, N′-dibenzylthiocarbamoyldithio) decane.Among these, 1,6-bis (N, N′-dibenzylthiocarbamoyldithio) hexane is preferable because it is thermally stable and has excellent polarizability.

In the rubber composition of the present invention obtained by the above production method, the content of the compound represented by the formula (1) is preferably 0.3 parts by mass or more, more preferably 100 parts by mass with respect to the rubber component. Is 0.5 parts by mass or more. The content is preferably 6 parts by mass or less, more preferably 3 parts by mass or less, and still more preferably 2 parts by mass or less.

In the rubber composition of the present invention obtained by the above production method or the like, the total content of the compound represented by the above formula (2) and its hydrate is preferably 0.3 with respect to 100 parts by mass of the rubber component. It is at least 0.5 parts by mass, more preferably at least 0.5 parts by mass. The total content is preferably 6 parts by mass or less, more preferably 3 parts by mass or less, and still more preferably 2 parts by mass or less.

In the rubber composition of the present invention obtained by the above production method, the content of the compound represented by the above formula (3) is preferably 0.3 parts by mass or more, more preferably 100 parts by mass of the rubber component. Is 0.5 parts by mass or more. The content is preferably 6 parts by mass or less, more preferably 3 parts by mass or less, and still more preferably 2 parts by mass or less.
In addition, about content of Formula (1), (2), its hydrate, and (3), there exists a possibility that sufficient improvement effect may not be acquired as it is less than a minimum, and when it exceeds an upper limit, low-fuel-consumption property There is a possibility that the balance of rubber strength, wear resistance and workability is deteriorated.

The rubber composition of the present invention preferably uses sulfur as a crosslinking agent. By using the hydrate of the above formulas (1) to (3) or formula (2) and sulfur together, different cross-linked forms can be retained in the rubber composition, compared with the case where each is used alone. Thus, the performance improvement effect can be synergistically enhanced.

In the rubber composition of the present invention obtained by the above production method, the sulfur content is preferably 0.5 parts by mass or more, more preferably 1.5 parts by mass or more, with respect to 100 parts by mass of the rubber component. . If the amount is less than 0.5 parts by mass, a sufficient improvement effect may not be obtained. Moreover, this content becomes like this. Preferably it is 3.5 mass parts or less, More preferably, it is 2.5 mass parts or less. If it exceeds 3.5 parts by mass, the crosslink density becomes too high, and the rubber strength and wear resistance tend to deteriorate.

In the rubber composition of the present invention obtained by the above production method and the like, a compound represented by any one of the above formulas (1) to (3), a hydrate of the compound represented by the above formula (2), The total content with sulfur is preferably 0.8 parts by mass or more, more preferably 2 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 0.8 part by mass, a sufficient improvement effect may not be obtained. Moreover, this total content becomes like this. Preferably it is 9.5 mass parts or less, More preferably, it is 4.5 mass parts or less. If it exceeds 9.5 parts by mass, the crosslinking density becomes too high, and the rubber strength and wear resistance tend to deteriorate.

In the rubber composition of the present invention, various materials generally used in the tire industry such as zinc oxide, stearic acid and anti-aging agent may be appropriately blended in addition to the above materials.

The rubber composition of the present invention can be used for each member of a tire, and in particular, can be suitably used for a tread, a sidewall, a clinch apex and the like.

The pneumatic tire of the present invention is produced by a usual method using the rubber composition. That is, a rubber composition containing various additives as necessary is extruded in accordance with the shape of each member of the tire at an unvulcanized stage and molded by a normal method on a tire molding machine. After forming an unvulcanized tire by heating, it can be manufactured by heating and pressing in a vulcanizer.

The present invention will be specifically described based on examples, but the present invention is not limited to these examples.

Hereinafter, various chemicals used in the production examples will be described together. In addition, the chemical | medical agent refine | purified according to the usual method as needed.
n-hexane: Kanto Chemical Co., Ltd. Styrene: Kanto Chemical Co., Ltd. 1,3-Butadiene: Takachiho Chemical Co., Ltd. Tetrahydrofuran: Kanto Chemical Co., Ltd. 1.6M n-butyllithium hexane solution: Kanto Chemical 3-diethylaminopropyltriethoxysilane manufactured by: Amax Co., Ltd. Methanol: manufactured by Kanto Chemical Co., Ltd. Oil: Process X-140 manufactured by Japan Energy Co., Ltd.
2,6-tert-butyl-p-cresol: manufactured by Kanto Chemical Co., Inc.

The analysis of the polymer obtained by the following manufacture example was performed with the following method.

(Measurement of weight average molecular weight)
The weight average molecular weight (Mw) was calibrated with standard polystyrene using a differential refractometer as a detector using a GPC-8000 series apparatus manufactured by Tosoh Corporation.

(Polymer structure identification)
The structural identification of the polymer was measured using a JNM-ECA series device manufactured by JEOL Ltd. From the measurement results, the styrene content and vinyl content of the polymer were determined.

Production Example 1 (Synthesis of Polymer 1)
Add 1500 ml of n-hexane, 42 g of styrene, 92 g of 1,3-butadiene, and 3 g of tetrahydrofuran to a heat-resistant container sufficiently substituted with nitrogen, and then add 0.7 ml of 1.6 M n-butyllithium hexane solution, and at 50 ° C. for 4 hours. Stir. Thereafter, 0.3 g of 3-diethylaminopropyltriethoxysilane was added and stirred for 30 minutes. 1 g of methanol was added to the polymer solution to stop the reaction, and 27 g of oil and 1 g of 2,6-tert-butyl-p-cresol were added to the reaction solution, followed by drying under reduced pressure at 50 ° C. for 24 hours to obtain polymer 1. . The obtained polymer 1 had a weight average molecular weight Mw of 230000, a styrene content of 32% by mass, and a vinyl content of 42% by mass.

Production Example 2 (Synthesis of Polymer 2)
To a heat-resistant container sufficiently purged with nitrogen, 1500 ml of n-hexane, 134 g of 1,3-butadiene and 3 g of tetrahydrofuran were added, and further 0.7 ml of 1.6M n-butyllithium hexane solution was added, followed by stirring at 50 ° C. for 4 hours. Thereafter, 0.3 g of 3-diethylaminopropyltriethoxysilane was added and stirred for 30 minutes. 1 g of methanol was added to the polymer solution to stop the reaction, and 27 g of oil and 1 g of 2,6-tert-butyl-p-cresol were added to the reaction solution, followed by drying under reduced pressure at 50 ° C. for 24 hours to obtain a polymer 2. .

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
NR: TSR20
SBR1: Asaprene E15 manufactured by Asahi Kasei Co., Ltd. (S-SBR modified (coupled) with a polyfunctional compound having two or more epoxy groups in the molecule, styrene content: 23 mass%, vinyl content: 63 mass%)
SBR2: Polymer 1 synthesized in Production Example 1 (S-SBR modified with the compound represented by the above formula (4), styrene content: 32% by mass, vinyl content: 42% by mass)
BR: Polymer 2 synthesized in Production Example 2 (BR modified with the compound represented by Formula (4) above)
Carbon Black: Show Black N220 (N ₂ SA: 111 m ² / g) manufactured by Cabot Japan
Silica: ULTRASIL VN3 manufactured by Degussa (N ₂ SA: 175 m ² / g)
Silane coupling agent 1: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by Degussa
Silane coupling agent 2: Si75 (bis (3-triethoxysilylpropyl) disulfide) manufactured by Degussa
Silane coupling agent 3: NXT-Z45 manufactured by Momentive Performance Materials (copolymer of bond unit a and bond unit b (bond unit a: 55 mol%, bond unit b: 45 mol%))
Zinc oxide: Zinc Hana No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: Stearic acid “Kashiwa” manufactured by NOF Corporation
Aroma oil: Process X-140 manufactured by Japan Energy Co., Ltd.
Anti-aging agent: Antigen 6C (N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd.
Wax: Sunnock N manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
V200: Tachiroll V200 manufactured by Taoka Chemical Industry Co., Ltd.
HTS: DURALINK HTS (sodium 1,6-hexamethylene-dithiosulfate dihydrate) manufactured by Flexis
KA9188: 1,6-bis (N, N′-dibenzylthiocarbamoyldithio) hexane sulfur manufactured by LANXESS, Inc .: powder sulfur vulcanization accelerator manufactured by Karuizawa Sulfur Co., Ltd .: manufactured by Ouchi Shinsei Chemical Industry Co., Ltd. Noxeller CZ (N-cyclohexyl-2-benzothiazolylsulfenamide)

Examples 1-30 and Comparative Examples 1-18
According to the formulation shown in Tables 1-6, the chemical shown in step (I) was kneaded at 150 ° C. for 4 minutes using a Banbury mixer to obtain a kneaded product. Next, using a Banbury mixer, the chemicals shown in step (II) were added and kneaded until a predetermined maximum temperature was reached. Furthermore, the chemical | medical agent shown to process (III) was added to the obtained kneaded material using an open roll, and it knead | mixed for 4 minutes at 95 degreeC, and obtained the unvulcanized rubber composition.
The obtained unvulcanized rubber composition was press vulcanized for 12 minutes at 170 ° C. to obtain a vulcanized rubber sheet.
In Comparative Examples 1, 6, 7, 12, 13, and 18, step (II) was not performed.

The following evaluation was performed using the unvulcanized rubber composition and the vulcanized rubber sheet. The results are shown in Tables 1-6. In addition, the reference comparative example in Tables 1 and 2 was set as Comparative Example 1, the reference comparative example in Tables 3 and 4 was set as Comparative Example 7, and the reference comparative example in Tables 5 and 6 was set as Comparative Example 13.

(Low exothermic index)
Using a viscoelastic spectrometer manufactured by Iwamoto Seisakusho, loss tangent tan δ of the vulcanized rubber sheet at 70 ° C. was measured under conditions of a frequency of 10 Hz, an initial strain of 10% and a dynamic strain of 2%. Then, the low exothermic index of the reference comparative example was set to 100, and tan δ of each formulation was displayed as an index by the following calculation formula. A larger index indicates less heat generation and better fuel economy.
(Low exothermic index) = (tan δ of reference comparative example) / (tan δ of each formulation) × 100

(Rubber strength index)
The vulcanized rubber sheet was subjected to a tensile test according to JIS K6251 and the elongation at break was measured. The measurement results were displayed as an index according to a lower calculation formula with the reference comparative example being 100. The larger the index, the higher the rubber strength and the better the durability.
(Rubber strength index) = (breaking elongation of each compound) / (breaking elongation of reference comparative example) × 100

(Abrasion resistance index)
A wear test of the vulcanized rubber sheet was performed using a Lambone-type wear tester at room temperature and a slip rate of 20%. The measurement results were displayed as an index according to the following calculation formula with the reference comparative example being 100. It shows that it is excellent in abrasion resistance, so that an index | exponent is large.
(Abrasion resistance index) = (Abrasion amount of reference comparative example) / (Abrasion amount of each formulation) × 100

(Kneading workability index)
The Mooney viscosity of the unvulcanized composition was measured at 130 ° C. according to JIS K6300. The measurement results were displayed as an index according to the following calculation formula with the reference comparative example being 100. The larger the index, the lower the Mooney viscosity and the easier the processing (excellent processability).
(Kneading workability index) = (Mooney viscosity of reference comparative example) / (Mooney viscosity of each formulation) × 100

(Extrudability index)
The scorch time of the unvulcanized composition was measured at 130 ° C. according to JIS K6300. The measurement results were displayed as an index according to the following calculation formula with the reference comparative example being 100. The larger the index, the longer the scorch time and the easier the processing (excellent processability).
(Extrudability index) = (Scorch time of each formulation) / (Scorch time of reference comparative example) × 100

From Tables 1 to 6, examples containing silica and two or more silane coupling agents, and obtained by kneading Si69 (tetrasulfide coupling agent) at low temperatures are fuel efficiency, rubber strength, Wear resistance and workability were improved in a well-balanced manner.

Claims (7)

A rubber composition for a tire containing a rubber component, silica, and two or more silane coupling agents including a tetrasulfide coupling agent,
A rubber composition for tires obtained by kneading the tetrasulfide coupling agent under conditions where the maximum temperature reached is 95 to 135 ° C. The rubber composition for a tire according to claim 1, wherein the content of the silica is 10 to 150 parts by mass and the content of the tetrasulfide coupling agent is 1 to 12 parts by mass with respect to 100 parts by mass of the rubber component. . At least selected from the group consisting of a compound represented by any of the following formulas (1) to (3) and a hydrate of a compound represented by the following formula (2) with respect to 100 parts by mass of the rubber component. The rubber composition for tires according to claim 1 or 2 which contains 0.3-6 mass parts of 1 sort.

^(Wherein, R 1, ^{R 2} and ^{R 3} are the same or different, .x and y represents an alkyl group having 5 to 12 carbon atoms are the same or different, .n indicating the integer of 2 to 4 is Represents an integer of 0 to 10.)
_{MO 3 S-S- (CH 2} ) p -S-SO 3 M (2)
(In the formula, p represents an integer of 3 to 10. M is the same or different and represents lithium, potassium, sodium, magnesium, calcium, barium, zinc, nickel, or cobalt.)
R ⁴ —S—S— (CH ₂ ) _q —S—S—R ⁵ (3)
(In the formula, q represents an integer of 2 to 10. R ⁴ and R ⁵ are the same or different and each represents a monovalent organic group containing a nitrogen atom.) The hydrate of the compound represented by the formula (2) is 1,6-hexamethylene-sodium dithiosulfate dihydrate, and the compound represented by the formula (3) is 1,6-bis (N, The tire rubber composition according to claim 1, which is N′-dibenzylthiocarbamoyldithio) hexane. The total content of styrene butadiene rubber and butadiene rubber modified with a compound represented by the following formula (4) in 100% by mass of the rubber component is 10% by mass or more. Rubber composition for tires.

(Wherein R ⁶ , R ⁷ and R ⁸ are the same or different and each represents an alkyl group, an alkoxy group, a silyloxy group, an acetal group, a carboxyl group, a mercapto group, or a derivative thereof. R ⁹ and R ¹⁰ are (The same or different and represents a hydrogen atom or an alkyl group. M represents an integer.) Step (I) of kneading the rubber component, the silica, and a silane coupling agent other than the tetrasulfide coupling agent, the kneaded product obtained in the step (I), and the tetrasulfide coupling The method for producing a rubber composition for a tire according to any one of claims 1 to 5, further comprising a step (II) of kneading the agent under a condition that the maximum reached temperature is 95 to 135 ° C. The pneumatic tire produced using the rubber composition in any one of Claims 1-5.