JP7501193B2 - Rubber composition for tires and tires - Google Patents

Description

The present invention relates to a rubber composition for tires and a tire.

Automobile tires are required to have various performance characteristics such as wet grip performance. For example, Patent Document 1 proposes a technology to improve wet steering stability by blending silica, a silane coupling agent, a liquid resin, etc. However, in recent years, from the viewpoint of safety, etc., there is a demand for improving steering stability, particularly when turning while braking on wet road surfaces.

JP 2007-186567 A

The present invention aims to solve the above problems and provide a rubber composition for tires and a tire that improves cornering performance while braking on wet road surfaces.

The present invention relates to a rubber composition for tires, which has a 300% modulus (M300) and a 100% modulus (M100) that satisfy the following formula (1), and which comprises a filler containing silica, and a silane coupling agent, wherein the silane coupling agent contains an alkoxysilyl group and a sulfur atom, and the number of carbon atoms connecting the alkoxysilyl group and the sulfur atom is 6 or more.
(1) M300/M100≧4.0

It is preferable that the following formula is satisfied.
M300/M100≧4.2

It is preferable that the following formula is satisfied.
M100≦5.0MPa

It is preferable that the following formula is satisfied.
M300≧8.0MPa

Preferably contains isoprene-based rubber, styrene butadiene rubber and butadiene rubber.

It is preferable that the rubber composition further contains a resin component, and the contents of silica and the resin component per 100 parts by mass of the rubber component satisfy the following formula:
1.5≦Silica content/Resin component content≦5.0

It is preferable that the resin component content is 20 parts by mass or more per 100 parts by mass of the rubber component.

Further comprising a resin component and a liquid polymer,
It is preferable that the content of silica, the content of the resin component and the total content of the liquid polymer per 100 parts by mass of the rubber component satisfy the following formula.
1.0≦Silica content/total content of resin component and liquid polymer≦4.5

The total content of the resin component and liquid polymer per 100 parts by mass of the rubber component is preferably 30 parts by mass or more.

The present invention also relates to a tire using the above rubber composition in the tread.

According to the present invention, the 300% modulus (M300) and 100% modulus (M100) satisfy the formula (1), and the tire rubber composition contains a filler containing silica and a silane coupling agent, and the silane coupling agent contains an organosilicon compound containing an alkoxysilyl group and a sulfur atom, and the number of carbon atoms connecting the alkoxysilyl group and the sulfur atom is 6 or more, so that the tire rubber composition can improve cornering performance while braking on wet road surfaces.

The present invention is a rubber composition for tires, which has a 300% modulus (M300) and a 100% modulus (M100) that satisfy the above formula (1), and contains a filler containing silica, and a silane coupling agent containing an organosilicon compound that contains an alkoxysilyl group and a sulfur atom and has 6 or more carbon atoms connecting the alkoxysilyl group and the sulfur atom. The rubber composition can improve cornering performance while braking on wet road surfaces.

The reason why the above-mentioned effects are obtained is not entirely clear, but it is presumed that they are due to the following mechanism.
By using an organic silicon compound containing an alkoxysilyl group and a sulfur atom as a silane coupling agent, and the number of carbon atoms connecting the alkoxysilyl group and the sulfur atom is 6 or more, that is, a long-chain silane coupling agent, the dispersion of silica is promoted, and the distance between the polymer/polymer becomes uniform, so that stress is easily generated in the polymer phase and tracking ability is generated in the micro region. In addition, since it is bonded to silica by a long chain, the distance between the polymer/polymer is easily kept long. Furthermore, by satisfying M300/M100≧4.0, it is possible to increase the stress at the time of large deformation compared to the time of small deformation, so that the stress on the rubber surface where the deformation amount is relatively large while generating stress in the entire tread part can be made high. As a result, it is possible to exert micro tracking ability and stress, so that braking performance and response performance are simultaneously exerted, and the steering stability when turning while applying the brakes can be improved. Therefore, it is presumed that the rubber composition significantly improves the turning performance while applying the brakes on a wet road surface.

The rubber composition (rubber composition after vulcanization) has a 300% modulus (M300 (MPa)) and a 100% modulus (M100 (MPa)) that satisfy the following formula (1).
(1) M300/M100≧4.0
From the viewpoint of cornering performance while braking on a wet road surface, M300/M100 is preferably 4.2 or more, more preferably 4.4 or more, and even more preferably 4.5 or more. There is no particular upper limit, but it is preferably 10.0 or less, more preferably 6.0 or less, and even more preferably 5.5 or less.

From the viewpoint of cornering performance while braking on a wet road surface, it is preferable that the 300% modulus (M300 (MPa)) of the rubber composition (rubber composition after vulcanization) satisfies the following formula:
M300≧8.0MPa
M300 is preferably 8.2 MPa or more, more preferably 8.4 MPa or more, and even more preferably 8.6 MPa or more. There is no particular upper limit, but it is preferably 15.0 MPa or less, more preferably 14.5 MPa or less, even more preferably 14.0 MPa or less, and particularly preferably 13.5 MPa or less.

From the viewpoint of cornering performance while braking on a wet road surface, it is preferable that the rubber composition (rubber composition after vulcanization) has a 100% modulus (M100 (MPa)) satisfying the following formula:
M100≦5.0MPa
M100 is preferably 4.8 MPa or less, more preferably 4.7 MPa or less, and even more preferably 4.6 MPa or less. There is no particular lower limit, but it is preferably 1.5 MPa or more, more preferably 1.7 MPa or more, even more preferably 1.9 MPa or more, and particularly preferably 2.0 MPa or more.

The M300 and M100 of a rubber composition (rubber composition after vulcanization) can be adjusted by increasing or decreasing the amount of filler, plasticizer, styrene butadiene rubber, resin component, and vulcanizing agent. Specifically, the values of M300 and M100 tend to be higher by increasing the amount of filler, decreasing the amount of plasticizer, increasing the amount of styrene butadiene rubber, decreasing the amount of resin component, and increasing the amount of vulcanizing agent.

The rubber composition (rubber composition after vulcanization) can achieve "M300/M100 ≧ 4.0" by using techniques such as the above-mentioned method of adjusting M300 and M100, using the above-mentioned organosilicon compound, using high molecular weight styrene-butadiene rubber, and improving the dispersion of fillers.

Note that M300 (300% modulus) and M100 (100% modulus) are values measured using a method based on JIS K6251:2010, as described in the examples.

(Rubber component)
As the rubber component usable in the rubber composition, for example, diene rubber can be used. As the diene rubber, isoprene rubber, butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), etc. can be mentioned. In addition, butyl rubber, fluororubber, etc. can be mentioned. These may be used alone or in combination of two or more. Among them, isoprene rubber, SBR, and BR are preferable from the viewpoint of cornering performance while stepping on the brake on a wet road surface.

Isoprene-based rubbers include natural rubber (NR), isoprene rubber (IR), modified NR, modified NR, modified IR, etc. NR can be, for example, SIR20, RSS#3, TSR20, etc., which are common in the rubber industry. IR is not particularly limited, and can be, for example, IR2200, etc., which are common in the rubber industry. Modified NR can be, for example, deproteinized natural rubber (DPNR), high-purity natural rubber (UPNR), etc. Modified NR can be, for example, epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), grafted natural rubber, etc. Modified IR can be, for example, epoxidized isoprene rubber, hydrogenated isoprene rubber, grafted isoprene rubber, etc. These can be used alone or in combination of two or more.

The content of isoprene-based rubber in 100% by mass of the rubber component is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more. The upper limit is preferably 50% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less. By keeping it within the above range, cornering performance while braking on wet roads tends to improve.

The SBR is not particularly limited, and can be any SBR commonly used in the tire industry, such as emulsion-polymerized SBR (E-SBR) or solution-polymerized SBR (S-SBR). Of these, S-SBR is preferred from the viewpoint of cornering performance while braking on wet roads. These can be used alone or in combination of two or more types.

From the viewpoint of cornering performance while braking on wet roads, the weight average molecular weight (Mw) of the SBR is preferably 200,000 or more, more preferably 600,000 or more, even more preferably 800,000 or more, and particularly preferably 820,000 or more. In particular, when a long-chain silane coupling agent is combined with a high molecular weight SBR, it is presumed that the M300/M100 ratio becomes large and the cornering performance is significantly improved. There is no particular upper limit, but it is preferably 1.5 million or less, more preferably 1.3 million or less, even more preferably 1.1 million or less, and particularly preferably 1 million or less.

The styrene content of the SBR is preferably 25% by mass or more, more preferably 28% by mass or more, even more preferably 31% by mass or more, and particularly preferably 33% by mass or more. The styrene content is preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less. By keeping it within the above range, cornering performance while braking on wet roads tends to improve.

The vinyl bond amount of SBR is preferably 20 mol% or more, more preferably 25 mol% or more, even more preferably 30 mol% or more, and particularly preferably 32 mol% or more. The vinyl bond amount is preferably 60 mol% or less, more preferably 50 mol% or less, even more preferably 45 mol% or less, and particularly preferably 42 mol% or less. By keeping it within the above range, cornering performance while braking on wet road surfaces tends to improve.

In this specification, the weight average molecular weight (Mw) can be determined in terms of standard polystyrene based on a measurement value obtained by gel permeation chromatography (GPC) (GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMULTIPORE HZ-M manufactured by Tosoh Corporation). The styrene content can be measured by ¹ H-NMR measurement. The vinyl bond amount (amount of 1,2-bonded butadiene units) can be measured by infrared absorption spectroscopy.

As SBR, either oil-extended styrene-butadiene copolymer or non-oil-extended styrene-butadiene copolymer can be used, but from the viewpoint of cornering performance while braking on wet roads, oil-extended styrene-butadiene copolymer is particularly suitable.

Oil-extended styrene-butadiene copolymer is a styrene-butadiene copolymer that has been oil-extended using an extender oil. By containing an oil-extended styrene-butadiene copolymer that has already been oil-extended with an extender oil in this way, the dispersibility of the extender oil and filler in the rubber component can be improved compared to compounded rubber in which oil is kneaded during compounding of the rubber composition.

The oil-extended styrene-butadiene copolymer is preferably one in which a branched structure has been introduced. Examples of styrene-butadiene copolymers in which a branched structure has been introduced include those in which the polymer ends have been modified with at least one polyfunctional coupling agent selected from the group consisting of epoxy compounds, halogen-containing silicon compounds, and alkoxysilane compounds, and those polymerized in the presence of a small amount of a branching agent. Among these, those in which the polymer ends have been modified with a polyfunctional coupling agent are preferred.

The styrene-butadiene copolymer can be prepared, for example, by copolymerizing styrene and butadiene using a polymerization initiator. As the polymerization initiator, a lithium-based initiator is preferable. As the lithium-based initiator, an organic lithium compound is preferable. Examples of the organic lithium compound include alkyl lithium such as n-butyl lithium, sec-butyl lithium, and t-butyl lithium; alkylene dilithium such as 1,4-dilithium butane; aromatic hydrocarbon lithium such as reaction products of alkyl lithium such as phenyl lithium, stilbene lithium, diisopropenylbenzene lithium, and butyl lithium with divinylbenzene; polynuclear hydrocarbon lithium such as lithium naphthalene; amino lithium, tributyltin lithium, and the like.

During polymerization, if necessary, an ether compound or an amine can be used as a styrene randomizer during copolymerization or as an adjuster for the amount of vinyl bonds. Examples of ether compounds or amines include dimethoxybenzene, tetrahydrofuran, dimethoxyethane, diethylene glycol dibutyl ether, diethylene glycol dimethyl ether, triethylamine, pyridine, N-methylmorpholine, N,N,N',N'-tetramethylethylenediamine, and dipiperidinoethane. Activators such as potassium dodecylbenzenesulfonate, potassium linoleate, potassium benzoate, potassium phthalate, and potassium tetradecylbenzenesulfonate can also be used for the same purpose.

As the polymerization solvent, n-hexane, cyclohexane, heptane, benzene, etc. can be used. The polymerization method may be either batch polymerization method or continuous polymerization method, but it is preferable to use the continuous polymerization method from the viewpoint of suitably obtaining a styrene-butadiene copolymer having the various properties described above. As polymerization conditions, the polymerization temperature is usually 0 to 130°C, preferably 10 to 100°C. The polymerization time is usually 5 minutes to 24 hours, preferably 10 minutes to 10 hours. The monomer concentration in the polymerization solvent (total of monomers/(total of monomers+polymerization solvent)) is usually 5 to 50 mass%, preferably 10 to 35 mass%.

In general, when a lithium initiator is used, the polymerization reaction rate of styrene and the polymerization reaction rate of butadiene are different. In addition, each polymerization reaction rate is affected by the polymerization temperature and the monomer concentration. Therefore, when a simple reaction is performed, in the latter half of the reaction when the polymerization temperature increases, due to the influence of the polymerization temperature and the high concentration of styrene monomer, a lot of styrene reacts, and many long styrene chains are generated, and the content of long styrene chains may increase. Therefore, as a method for adjusting the content of single styrene chains and long styrene chains to an appropriate value, there is a method of controlling the polymerization temperature to a point where the reaction rates of styrene and butadiene are the same, or a method of increasing the amount of styrene taken up in the early stages of polymerization by starting the reaction with a reduced amount of butadiene charged before the reaction, and then continuously introducing the reduced amount of butadiene.

Specific methods for introducing a branched structure into a styrene-butadiene copolymer include, in the case of modification with a polyfunctional coupling agent, reacting an active polymer having a lithium active end obtained by a batch polymerization method or a continuous polymerization method with at least one polyfunctional coupling agent selected from the group consisting of halogen-containing silicon compounds such as silicon tetrachloride, alkoxysilane compounds, alkoxysilane sulfide compounds, (poly)epoxy compounds, urea compounds, amide compounds, imide compounds, thiocarbonyl compounds, lactam compounds, ester compounds, and ketone compounds. Among these, halogen-containing silicon compounds such as silicon tetrachloride, alkoxysilane compounds, alkoxysilane sulfide compounds, and (poly)epoxy compounds are preferred, and halogen-containing silicon compounds, alkoxysilane compounds, and (poly)epoxy compounds are more preferred. In addition, when polymerization is performed in the presence of a small amount of a branching agent, a specific example of the branching agent is divinylbenzene. The amount of introduction is preferably 10% by mass or less relative to 100% by mass of the styrene-butadiene copolymer.

Examples of the extender oil used for oil extension of styrene-butadiene copolymer include naphthenic, paraffinic, and aromatic oil extenders. Examples of the oil extension method include adding an extender oil after polymerization is complete, and removing the solvent and drying using a conventional method.

The amount of extender oil used is preferably 5 to 50 parts by mass, and more preferably 10 to 40 parts by mass, per 100 parts by mass of styrene-butadiene copolymer.

The SBR may be unmodified or modified. In addition, hydrogenated styrene butadiene copolymer (hydrogenated SBR) may also be used.

The modified SBR may be any SBR having a functional group that interacts with a filler such as silica. Examples of the modified SBR include terminally modified SBR (terminally modified SBR having the above-mentioned functional group at the terminal) in which at least one terminal of the SBR has been modified with a compound (modifier) having the above-mentioned functional group, main-chain modified SBR having the above-mentioned functional group in the main chain, main-chain terminal-modified SBR having the above-mentioned functional group in the main chain and at least one terminal (for example, main-chain terminal-modified SBR having the above-mentioned functional group in the main chain and at least one terminal modified with the above-mentioned modifier), and terminal-modified SBR modified (coupled) with a polyfunctional compound having two or more epoxy groups in the molecule and having a hydroxyl group or epoxy group introduced therein. These may be used alone or in combination of two or more types.

The functional groups include, for example, amino groups, amide groups, silyl groups, alkoxysilyl groups, isocyanate groups, imino groups, imidazole groups, urea groups, ether groups, carbonyl groups, oxycarbonyl groups, mercapto groups, sulfide groups, disulfide groups, sulfonyl groups, sulfinyl groups, thiocarbonyl groups, ammonium groups, imide groups, hydrazo groups, azo groups, diazo groups, carboxyl groups, nitrile groups, pyridyl groups, alkoxy groups, hydroxyl groups, oxy groups, and epoxy groups. These functional groups may have a substituent. Among them, amino groups (preferably amino groups in which the hydrogen atoms of the amino groups are substituted with alkyl groups having 1 to 6 carbon atoms), alkoxy groups (preferably alkoxy groups having 1 to 6 carbon atoms), alkoxysilyl groups (preferably alkoxysilyl groups having 1 to 6 carbon atoms), and amide groups are preferred.

As SBR, for example, SBR manufactured and sold by Sumitomo Chemical Co., Ltd., JSR Corporation, Asahi Kasei Corporation, Nippon Zeon Co., Ltd., etc. can be used.

The content of SBR in 100% by mass of the rubber component is preferably 30% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and particularly preferably 80% by mass or more. The upper limit is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less. By keeping the content within the above range, cornering performance while braking on wet roads tends to improve.

The BR is not particularly limited, and examples of the BR that can be used include high cis BR with a high cis content, BR containing syndiotactic polybutadiene crystals, and BR synthesized using a rare earth catalyst (rare earth BR). These may be used alone or in combination of two or more. In particular, the BR preferably contains high cis BR with a cis content of 90% by mass or more. The cis content is more preferably 95% by mass or more. The cis content can be measured by infrared absorption spectroscopy.

The BR may be unmodified or modified. Examples of modified BR include modified BR into which functional groups similar to those of modified SBR have been introduced. The BR may also be a hydrogenated butadiene polymer (hydrogenated BR).

For example, products from Ube Industries, Ltd., JSR Corporation, Asahi Kasei Corporation, Zeon Corporation, etc. can be used as BR.

The BR content in 100% by mass of the rubber component is preferably 3% by mass or more, more preferably 5% by mass or more, and even more preferably 7% by mass or more. The upper limit is preferably 50% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less. By keeping it within the above range, cornering performance while braking on wet roads tends to improve.

(silica)
Silica is compounded as a filler in the rubber composition. Examples of silica that can be used include dry process silica (anhydrous silica) and wet process silica (hydrated silica). Among them, wet process silica is preferred because it has a large number of silanol groups. Commercially available products include those from Degussa, Rhodia, Tosoh Silica, Solvay Japan, and Tokuyama. These may be used alone or in combination of two or more.

The nitrogen adsorption specific surface area ( _N2SA ) of silica is preferably ^50m2 /g or more, more preferably ^100m2 /g or more, even more preferably ^150m2 /g or more, and particularly preferably ^200m2 /g or more. The upper limit of the _N2SA of silica is not particularly limited, but is preferably ^300m2 /g or less, more preferably ^250m2 /g or less. By keeping it within the above range, high-speed cornering performance on wet road surfaces tends to improve.
The N ₂ SA of silica is a value measured by the BET method in accordance with ASTM D3037-93.

In the rubber composition, the content of silica is preferably 5 parts by mass or more, more preferably 50 parts by mass or more, even more preferably 75 parts by mass or more, and particularly preferably 95 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit of the content is preferably 250 parts by mass or less, more preferably 200 parts by mass or less, even more preferably 150 parts by mass or less, and particularly preferably 120 parts by mass or less. By keeping the content within the above range, cornering performance while braking on wet road surfaces tends to improve.

（式中、ｘは、硫黄原子の平均個数を表し、３．５以上である。ｍは、６以上の整数を表す。Ｒ^１～Ｒ^６は、同一若しくは異なって炭素数１～６のアルキル基又はアルコキシ基を表し、Ｒ^１～Ｒ^３の少なくとも１つ及びＲ^４～Ｒ^６の少なくとも１つが前記アルコキシ基である。なお、Ｒ^１～Ｒ^６は、前記アルキル基又は前記アルコキシ基が結合した環構造を形成したものでもよい。） (Silane coupling agent)
The silane coupling agent used in the rubber composition is an organosilicon compound that contains an alkoxysilyl group and a sulfur atom, and the number of carbon atoms connecting the alkoxysilyl group and the sulfur atom is 6 or more. Such organosilicon compounds may be used alone or in combination of two or more. Among the organosilicon compounds, the organosilicon compound represented by the following average composition formula (I) is preferred.

(In the formula, x represents the average number of sulfur atoms and is 3.5 or more; m represents an integer of 6 or more; R ¹ to R ⁶ are the same or different and represent an alkyl group or an alkoxy group having 1 to 6 carbon atoms, and at least one of R ¹ to R ³ and at least one of R ⁴ to R ⁶ is the alkoxy group. Note that R ¹ to R ⁶ may form a ring structure by bonding the alkyl groups or the alkoxy groups.)

x represents the average number of sulfur atoms in the organosilicon compound. x is preferably 3.5 or more and 12 or less. Here, the average number of sulfur atoms and the number of silicon atoms are values calculated from the molecular weights of the sulfur and silicon amounts in the composition measured by fluorescent X-rays.

m represents an integer of 6 or more, preferably 6 or more and 14 or less.

The number of carbon atoms in the alkyl group (R ¹ to R ⁶ ) is preferably 1 to 5. The alkyl group may be linear, branched, or cyclic. Specific examples include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, and a tert-butyl group.

The alkoxy group (R ¹ to R ⁶ ) preferably has 1 to 5 carbon atoms. The hydrocarbon group in the alkoxy group may be linear, branched, or cyclic. Specific examples include a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, and an n-butoxy group.

At least one of R ¹ to R ³ and at least one of R ⁴ to R ⁶ is an alkoxy group having 1 to 6 carbon atoms, and preferably at least two of R ¹ to R ³ and R ⁴ to R ⁶ are alkoxy groups having 1 to 6 carbon atoms.

R ¹ to R ⁶ may each be a ring structure formed by bonding an alkyl group or alkoxy group having 1 to 6 carbon atoms. For example, when (i) R ¹ is an ethoxy group and R ² is a ring structure formed by bonding a methyl group, or (ii) R ¹ is an ethyl group and R ² is a ring structure formed by bonding a methyl group, R ¹ and R ² form divalent groups such as "-O-C ₂ H ₄ -CH ₂ -" and "-C ₂ H ₄ -CH ₂ -", respectively, and these groups are bonded to Si.

The organosilicon compound can be prepared, for example, by the manufacturing method described in JP 2018-65954 A. Specifically, the organosilicon compound can be produced by reacting the halogen-containing organosilicon compound of formula (I-1) described in JP 2018-65954 A, anhydrous sodium sulfide represented by Na ₂ S, and sulfur as necessary. When carrying out the above reaction, the addition of sulfur is optional for adjusting the sulfide chain, and may be determined from the compound of the average composition formula (I-1), anhydrous sodium sulfide, and, if necessary, sulfur, so as to obtain the desired compound of the average composition formula (I). For example, if you want to make the x of the compound of the average composition formula (I) 3.5, you can react 1.0 mol of anhydrous sodium sulfide, 2.5 mol of sulfur, and 2.0 mol of the compound of formula (I-1).

And, when an organic silicon compound containing an alkoxysilyl group and a sulfur atom and having 6 or more carbon atoms connecting the alkoxysilyl group and the sulfur atom is used as a silane coupling agent, that is, a long-chain silane coupling agent, the alkoxy group in the compound reacts with the hydroxyl group on the silica surface to hydrophobize the silica surface, and the effect of hydrophobization is greater than that of conventional silane coupling agents due to the long carbon chain of the compound, so the dispersibility of the silica is significantly improved. Therefore, the distance between the polymers becomes uniform, making it easier to generate stress in the polymer phase and allowing tracking in the microscopic region to be generated. In addition, since it is bonded to silica by a long chain, it is easier to maintain the distance between the polymers. Therefore, by using such a long-chain silane coupling agent, the cornering performance while braking on a wet road surface can be significantly improved.

In the rubber composition, the content of the organosilicon compound is preferably 0.1 parts by mass or more, more preferably 3 parts by mass or more, even more preferably 5 parts by mass or more, and particularly preferably 7 parts by mass or more, per 100 parts by mass of silica. The upper limit of the content is preferably 50 parts by mass, more preferably 20 parts by mass or less, even more preferably 15 parts by mass or less, and particularly preferably 10 parts by mass or less. By keeping it within the above range, cornering performance while braking on wet road surfaces tends to improve. The content of the organosilicon compound represented by the average composition formula (I) is also preferably in the same range.

The rubber composition may contain a silane coupling agent other than the organosilicon compound that contains an alkoxysilyl group and a sulfur atom and has 6 or more carbon atoms connecting the alkoxysilyl group and the sulfur atom.
The other silane coupling agent is not particularly limited, and examples thereof include bis(3-triethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, bis(2-triethoxysilylethyl)trisulfide, bis(4-trimethoxysilylbutyl)trisulfide, bis(3-triethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)disulfide, bis(4-triethoxysilylbutyl)disulfide, bis(3-trimethoxysilylpropyl)disulfide, bis(2-trimethoxysilylethyl)disulfide, bis(4-trimethoxysilylbutyl)disulfide, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl silane, and the like. Examples of such silanes include sulfide-based silanes such as rubamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, and 3-triethoxysilylpropyl methacrylate monosulfide; mercapto-based silanes such as 3-mercaptopropyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, and Momentive's NXT and NXT-Z; vinyl-based silanes such as vinyltriethoxysilane and vinyltrimethoxysilane; amino-based silanes such as 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane; glycidoxy-based silanes such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro-based silanes such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; and chloro-based silanes such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. As commercially available products, products of Degussa, Momentive, Shin-Etsu Silicone Co., Ltd., Tokyo Chemical Industry Co., Ltd., Azumax Co., Ltd., Dow Corning Toray Co., Ltd., etc. can be used. These may be used alone or in combination of two or more kinds.

In the rubber composition, the content of the silane coupling agent (total amount of the organosilicon compound and other silane coupling agents) is preferably 0.1 parts by mass or more, more preferably 3 parts by mass or more, even more preferably 5 parts by mass or more, and particularly preferably 7 parts by mass or more, per 100 parts by mass of silica. The upper limit of the content is preferably 50 parts by mass, more preferably 20 parts by mass or less, even more preferably 15 parts by mass or less, and particularly preferably 10 parts by mass or less. By keeping it within the above range, cornering performance while braking on wet roads tends to improve.

(Other fillers)
The filler other than silica is not particularly limited, and materials known in the rubber field can be used, such as inorganic fillers such as carbon black, calcium carbonate, talc, alumina, clay, aluminum hydroxide, aluminum oxide, and mica. Of these, carbon black and aluminum hydroxide are preferred.

In the rubber composition, the content of the filler (total content of the fillers) is preferably 5 parts by mass or more, more preferably 50 parts by mass or more, even more preferably 80 parts by mass or more, and particularly preferably 100 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit of the content is preferably 250 parts by mass or less, more preferably 200 parts by mass or less, even more preferably 160 parts by mass or less, and particularly preferably 130 parts by mass or less. By keeping the content within the above range, cornering performance while braking on wet roads tends to improve.

In the rubber composition, the silica content in 100% by mass of the filler is preferably 50% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more, from the viewpoint of cornering performance while braking on a wet road surface. There is no particular upper limit, but it is preferably 98% by mass or less, and more preferably 97% by mass or less.

The carbon black that can be used in the rubber composition is not particularly limited, but examples include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762. Commercially available products include those from Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Corporation, Lion Corporation, Shin-Nichika Carbon Co., Ltd., Columbia Carbon Co., Ltd., and the like. These may be used alone or in combination of two or more types.

The nitrogen adsorption specific surface area ( _N2SA ) of the carbon black is preferably ⁵⁰ m2/g or more, more preferably ⁷⁰ m2/g or more, and even more preferably ⁹⁰ m2/g or more. The _N2SA is preferably ²⁰⁰ m2/g or less, more preferably ¹⁵⁰ m2/g or less, and even more preferably 130 ^m2 /g or less. By keeping the N2SA within the above range, cornering performance while braking on wet road surfaces tends to improve.
The nitrogen adsorption specific surface area of carbon black is determined in accordance with JIS K6217-2:2001.

In the rubber composition, the carbon black content is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit of the content is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 10 parts by mass or less. By keeping the carbon black content within the above range, cornering performance while braking on wet road surfaces tends to improve.

The aluminum hydroxide is not particularly limited, and any aluminum hydroxide commonly used in the tire industry can be used. These may be used alone or in combination of two or more types.

The average primary particle size of aluminum hydroxide is preferably 0.6 μm or more, more preferably 0.7 μm or more. The average primary particle size of aluminum hydroxide is preferably 10 μm or less, more preferably 5 μm or less, even more preferably 1.3 μm or less, and particularly preferably 1.2 μm or less. Within the above range, the effect tends to be better obtained.
In this specification, the average primary particle size of aluminum hydroxide is a number average particle size, which is measured by a transmission electron microscope.

In the rubber composition, the content of aluminum hydroxide is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit of the content is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, and even more preferably 40 parts by mass or less. By keeping the content within the above range, cornering performance while braking on wet road surfaces tends to improve.

(Plasticizer)
It is preferable to compound a plasticizer in the rubber composition. The plasticizer is a material that imparts plasticity to the rubber component, and examples of the plasticizer include liquid plasticizers (plasticizers that are in a liquid state at room temperature (25° C.)), resin components (resins that are in a liquid state at room temperature (25° C.) and resins that are in a solid state at room temperature (25° C.)). In particular, when a resin component is compounded, cornering performance while braking on wet road surfaces can be significantly improved.

In the rubber composition, the content of the plasticizer (total amount of plasticizer) is preferably 20 parts by mass or more, more preferably 30 parts by mass or more, even more preferably 50 parts by mass or more, and particularly preferably 60 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit of the content is preferably 200 parts by mass or less, more preferably 150 parts by mass or less, even more preferably 120 parts by mass or less, and particularly preferably 100 parts by mass or less. By keeping the content within the above range, cornering performance while braking on wet roads tends to improve.

Liquid plasticizers (plasticizers that are liquid at room temperature (25°C)) that can be used in the rubber composition are not particularly limited, and examples include oils and liquid polymers. Examples of liquid polymers include liquid rubber and liquid farnesene-based polymers. These may be used alone or in combination of two or more.

In the rubber composition, the content of the liquid plasticizer (total amount of oil, liquid rubber, and liquid farnesene-based polymer) is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, and even more preferably 17 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit of the content is preferably 100 parts by mass or less, more preferably 60 parts by mass or less, even more preferably 50 parts by mass or less, and particularly preferably 45 parts by mass or less. By keeping it within the above range, cornering performance while braking on wet roads tends to improve.

Examples of the oil include process oil, vegetable oil, or a mixture thereof. Examples of the process oil include paraffin-based process oil, aromatic process oil, and naphthenic process oil. Examples of the vegetable oil include castor oil, cottonseed oil, linseed oil, rapeseed oil, soybean oil, palm oil, coconut oil, peanut oil, rosin, pine oil, pine tar, tall oil, corn oil, rice oil, safflower oil, sesame oil, olive oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, and tung oil. Examples of commercially available products include those from Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., Japan Energy Co., Ltd., Orisoi Co., Ltd., H&R Co., Ltd., Toyokuni Seiyu Co., Ltd., Showa Shell Sekiyu K.K., Fuji Kosan Co., Ltd., and Nisshin Oillio Group Co., Ltd. Among these, process oils (paraffin-based process oils, aromatic process oils, naphthenic process oils, etc.) and vegetable oils are preferred.

In the rubber composition, the oil content is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 13 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit of the content is preferably 70 parts by mass or less, more preferably 50 parts by mass or less, and even more preferably 35 parts by mass or less. By keeping the content within the above range, cornering performance while braking on wet road surfaces tends to improve. The oil content also includes the oil contained in the extended oil.

Examples of liquid rubber include liquid diene rubbers that can be extracted with acetone. Specific examples include liquid diene rubbers that are liquid at 25°C, such as liquid styrene butadiene copolymer (liquid SBR), liquid butadiene polymer (liquid BR), liquid isoprene polymer (liquid IR), liquid styrene isoprene copolymer (liquid SIR), liquid styrene butadiene styrene block copolymer (liquid SBS block polymer), and liquid styrene isoprene styrene block copolymer (liquid SIS block polymer). The ends or main chains of these may be modified with polar groups. Hydrogenated versions of these rubbers can also be used.

In the rubber composition, the content of the liquid rubber is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit of the content is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less. By keeping the content within the above range, cornering performance while braking on wet road surfaces tends to improve. The content of the liquid diene rubber is also preferably in a similar range.

Liquid farnesene polymers are polymers obtained by polymerizing farnesene and have structural units based on farnesene. Farnesene includes isomers such as α-farnesene ((3E,7E)-3,7,11-trimethyl-1,3,6,10-dodecatetraene) and β-farnesene (7,11-dimethyl-3-methylene-1,6,10-dodecatriene), but (E)-β-farnesene having the following structure is preferred.

The liquid farnesene-based polymer may be a homopolymer of farnesene (farnesene homopolymer) or a copolymer of farnesene and a vinyl monomer (farnesene-vinyl monomer copolymer).

Vinyl monomers include aromatic vinyl compounds such as styrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, α-methylstyrene, 2,4-dimethylstyrene, 2,4-diisopropylstyrene, 4-tert-butylstyrene, 5-t-butyl-2-methylstyrene, vinylethylbenzene, divinylbenzene, trivinylbenzene, divinylnaphthalene, tert-butoxystyrene, vinylbenzyldimethylamine, (4-vinylbenzyl)dimethylaminoethylether, N,N-dimethylaminoethylstyrene, N,N-dimethylaminomethylstyrene, 2-ethylstyrene, 3-ethylstyrene, 4-ethylstyrene, 2-t-butylstyrene, 3-t-butylstyrene, 4-t-butylstyrene, vinylxylene, vinylnaphthalene, vinyltoluene, vinylpyridine, diphenylethylene, and tertiary amino group-containing diphenylethylene, as well as conjugated diene compounds such as butadiene and isoprene. These may be used alone or in combination of two or more. Among these, butadiene is preferred. That is, as the farnesene-vinyl monomer copolymer, a copolymer of farnesene and butadiene (farnesene-butadiene copolymer) is preferred.

In the farnesene-vinyl monomer copolymer, the copolymerization ratio by mass of farnesene and vinyl monomer (farnesene/vinyl monomer) is preferably 40/60 to 90/10.

The liquid farnesene polymer that can be used preferably has a weight average molecular weight (Mw) of 3,000 to 300,000. The Mw of the liquid farnesene polymer is preferably 8,000 or more, more preferably 10,000 or more, and is preferably 100,000 or less, more preferably 60,000 or less, and even more preferably 50,000 or less.

In the rubber composition, the content of the liquid farnesene polymer is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, and even more preferably 7 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit of the content is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less. By keeping the content within the above range, cornering performance while braking on wet road surfaces tends to be improved.

In addition, in the rubber composition, the content of the resin components (the total amount of resins in a liquid state at room temperature (25°C) and resins in a solid state at room temperature (25°C)) is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, even more preferably 30 parts by mass or more, and particularly preferably 35 parts by mass or more. The upper limit of the content is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, even more preferably 60 parts by mass or less, and particularly preferably 50 parts by mass or less. By keeping it within the above range, cornering performance while braking on wet roads tends to improve.

The resin component that is in a liquid state at room temperature (25°C) can be a liquid resin. The liquid resin may be one that has a softening point below room temperature and is in a liquid state at room temperature. Examples of liquid resins include terpene resins (including terpene phenol resins and aromatic modified terpene resins), rosin resins, styrene resins, C5 resins, C9 resins, C5/C9 resins, dicyclopentadiene (DCPD) resins, coumarone-indene resins (including coumarone and indene simple resins), phenol resins, olefin resins, polyurethane resins, and acrylic resins. Hydrogenated versions of these resins can also be used.

In the rubber composition, the content of the liquid resin is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, and even more preferably 7 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit of the content is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less. By keeping the content within the above range, cornering performance while braking on wet road surfaces tends to improve.

Examples of the resin component that is in a solid state at room temperature (25°C) (hereinafter also referred to as "solid resin") include aromatic vinyl polymers, coumarone-indene resins, coumarone resins, indene resins, phenolic resins, rosin resins, petroleum resins, terpene resins, acrylic resins, and alicyclic hydrocarbon resins that are in a solid state at room temperature (25°C). The resins may also be hydrogenated. These may be used alone or in combination of two or more. Among these, from the viewpoint of cornering performance while braking on wet road surfaces, aromatic vinyl polymers, terpene resins, petroleum resins, and alicyclic hydrocarbon resins are preferred, and petroleum resins are more preferred.

In the rubber composition, the content of the solid resin is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, even more preferably 30 parts by mass or more, and particularly preferably 35 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit of the content is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, even more preferably 60 parts by mass or less, and particularly preferably 50 parts by mass or less. By keeping the content within the above range, cornering performance while braking on wet road surfaces tends to improve. The contents of aromatic vinyl polymer, terpene resin, and petroleum resin are also preferably in the same range.

The softening point of the solid resin is preferably 60° C. or higher, more preferably 70° C. or higher, and even more preferably 80° C. or higher. The upper limit is preferably 160° C. or lower, more preferably 130° C. or lower, and even more preferably 115° C. or lower. By keeping the softening point within the above range, cornering performance while braking on wet road surfaces tends to improve.
The softening point of the resin component is the temperature at which the ball drops when the softening point specified in JIS K6220-1:2001 is measured using a ring and ball softening point tester.

The aromatic vinyl polymer is a polymer containing an aromatic vinyl monomer as a constituent unit. For example, it can be a resin obtained by polymerizing α-methylstyrene and/or styrene, and specifically, it can be a homopolymer of styrene (styrene resin), a homopolymer of α-methylstyrene (α-methylstyrene resin), a copolymer of α-methylstyrene and styrene, a copolymer of styrene and another monomer, etc.

The coumarone-indene resin is a resin containing coumarone and indene as the main monomer components constituting the resin skeleton (main chain). Other monomer components contained in the skeleton besides coumarone and indene include styrene, α-methylstyrene, methylindene, vinyltoluene, etc. The content of the coumarone-indene resin is preferably 1 to 200 parts by mass per 100 parts by mass of the rubber component.

The above coumarone resin is a resin that contains coumarone as the main monomer component that constitutes the resin skeleton (main chain).

The above-mentioned indene resin is a resin that contains indene as the main monomer component that constitutes the resin skeleton (main chain).

The phenolic resin may be, for example, a known polymer obtained by reacting phenol with an aldehyde such as formaldehyde, acetaldehyde, or furfural using an acid or alkali catalyst. Among these, those obtained by reacting with an acid catalyst (such as novolac-type phenolic resin) are preferred.

The rosin resin may be a rosin-based resin such as natural rosin, polymerized rosin, modified rosin, ester compounds thereof, or hydrogenated products thereof. The content of the rosin resin is preferably 1 to 200 parts by mass per 100 parts by mass of the rubber component.

The petroleum resins include C5 resins, C9 resins, C5/C9 resins, dicyclopentadiene (DCPD) resins, and hydrogenated versions of these resins. Of these, DCPD resins, hydrogenated DCPD resins, and C9 resins are preferred, with hydrogenated DCPD resins being more preferred.

The terpene resin is a polymer containing terpene as a structural unit. Examples include polyterpene resins obtained by polymerizing terpene compounds, and aromatic modified terpene resins obtained by polymerizing terpene compounds and aromatic compounds. Hydrogenated products of these resins can also be used.

The polyterpene resin is a resin obtained by polymerizing a terpene compound. The terpene compound is a hydrocarbon represented by the composition (C ₅ H ₈ ) _n and its oxygen-containing derivatives, and is a compound having a basic skeleton of a terpene classified into monoterpene (C ₁₀ H ₁₆ ), sesquiterpene (C ₁₅ H ₂₄ ), diterpene (C ₂₀ H ₃₂ ), etc., and examples thereof include α-pinene, β-pinene, dipentene, limonene, myrcene, alloocimene, ocimene, α-phellandrene, α-terpinene, γ-terpinene, terpinolene, 1,8-cineole, 1,4-cineole, α-terpineol, β-terpineol, and γ-terpineol.

The polyterpene resins mentioned above include pinene resin, limonene resin, dipentene resin, pinene/limonene resin, etc., which are made from the above-mentioned terpene compounds. Of these, pinene resin is preferred. Pinene resins usually contain both α-pinene and β-pinene, which are isomers, but depending on the components they contain, they are classified into β-pinene resins, which are mainly made of β-pinene, and α-pinene resins, which are mainly made of α-pinene.

The aromatic modified terpene resin may be a terpene phenol resin made from the above terpene compound and a phenolic compound, or a terpene styrene resin made from the above terpene compound and a styrene compound. Terpene phenol styrene resin made from the above terpene compound, a phenolic compound, and a styrene compound may also be used. Examples of phenolic compounds include phenol, bisphenol A, cresol, and xylenol. Examples of styrene compounds include styrene and α-methylstyrene.

The acrylic resin is a polymer containing an acrylic monomer as a constituent unit. For example, there is a styrene-acrylic resin such as a styrene-acrylic resin that has a carboxyl group and is obtained by copolymerizing an aromatic vinyl monomer component and an acrylic monomer component. Among them, a solvent-free carboxyl group-containing styrene-acrylic resin can be preferably used.

The above-mentioned solvent-free carboxyl group-containing styrene acrylic resin is a (meth)acrylic resin (polymer) synthesized by a high-temperature continuous polymerization method (high-temperature continuous bulk polymerization method) (methods described in U.S. Pat. No. 4,414,370, JP-A-59-6207, JP-B-5-58005, JP-A-1-313522, U.S. Pat. No. 5,010,166, Toa Gosei Kenkyuu Nenpo TREND 2000 Vol. 3, p. 42-45, etc.) with minimal use of auxiliary raw materials such as polymerization initiators, chain transfer agents, and organic solvents. In this specification, (meth)acrylic means methacryl and acrylic.

Examples of the acrylic monomer components constituting the acrylic resin include (meth)acrylic acid, (meth)acrylic acid esters (alkyl esters such as 2-ethylhexyl acrylate, aryl esters, aralkyl esters, etc.), (meth)acrylamide, and (meth)acrylic acid derivatives such as (meth)acrylamide derivatives. Note that (meth)acrylic acid is a general term for acrylic acid and methacrylic acid.

Examples of the aromatic vinyl monomer components constituting the acrylic resin include aromatic vinyls such as styrene, α-methylstyrene, vinyltoluene, vinylnaphthalene, divinylbenzene, trivinylbenzene, and divinylnaphthalene.

In addition, other monomer components may be used in addition to (meth)acrylic acid, (meth)acrylic acid derivatives, and aromatic vinyl as monomer components constituting the acrylic resin.

Examples of the plasticizers that can be used include products from Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Yasuhara Chemical Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF, Arizona Chemical Company, Nitto Chemical Co., Ltd., Nippon Shokubai Co., Ltd., JXTG Nippon Oil & Energy Corporation, Arakawa Chemical Industries Co., Ltd., Taoka Chemical Co., Ltd., Novares Rutgers, etc.

From the viewpoint of cornering performance while braking on a wet road surface, it is preferable that the content (parts by mass) of the silica per 100 parts by mass of the rubber component and the content (parts by mass) of the resin component per 100 parts by mass of the rubber component satisfy the following formula:
1.5≦Silica content/Resin component content≦5.0
The silica content/resin content is preferably 1.8 or more, more preferably 2.0 or more, even more preferably 2.2 or more, and particularly preferably 2.3 or more. The lower limit is preferably 4.0 or less, more preferably 3.5 or less, even more preferably 3.0 or less, and particularly preferably 2.7 or less. By keeping it within the above range, cornering performance while braking on wet road surfaces tends to improve.

In the rubber composition, the total content (parts by mass) of the resin component and the liquid polymer per 100 parts by mass of the rubber component is preferably 15 parts by mass or more, more preferably 30 parts by mass or more, even more preferably 40 parts by mass or more, and particularly preferably 45 parts by mass or more per 100 parts by mass of the rubber component. The upper limit of the content is preferably 110 parts by mass or less, more preferably 90 parts by mass or less, even more preferably 70 parts by mass or less, and particularly preferably 60 parts by mass or less. By keeping the content within the above range, cornering performance while braking on wet road surfaces tends to be improved.

From the viewpoint of cornering performance while braking on a wet road surface, it is preferable that the content (parts by mass) of the silica per 100 parts by mass of the rubber component and the total content (parts by mass) of the resin component and the liquid polymer per 100 parts by mass of the rubber component satisfy the following formula:
1.0≦Silica content/total content of resin component and liquid polymer≦4.5
Silica content / total content of liquid polymer and resin components is
It is preferably 1.4 or more, more preferably 1.6 or more, even more preferably 1.8 or more, and particularly preferably 1.9 or more. The lower limit is preferably 3.6 or less, more preferably 3.1 or less, even more preferably 2.6 or less, and particularly preferably 2.3 or less. By keeping it within the above range, cornering performance while braking on a wet road surface tends to improve.

(Other materials)
From the viewpoints of crack resistance, ozone resistance, and the like, the rubber composition preferably contains an antioxidant.

The anti-aging agent is not particularly limited, but examples thereof include naphthylamine-based anti-aging agents such as phenyl-α-naphthylamine; diphenylamine-based anti-aging agents such as octylated diphenylamine and 4,4'-bis(α,α'-dimethylbenzyl)diphenylamine; p-phenylenediamine-based anti-aging agents such as N-isopropyl-N'-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine and N,N'-di-2-naphthyl-p-phenylenediamine; quinoline-based anti-aging agents such as polymers of 2,2,4-trimethyl-1,2-dihydroquinoline; monophenol-based anti-aging agents such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol; and bis-, tris- and polyphenol-based anti-aging agents such as tetrakis-[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane. Among these, p-phenylenediamine-based antiaging agents and quinoline-based antiaging agents are preferred, and N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine and 2,2,4-trimethyl-1,2-dihydroquinoline polymers are more preferred. Commercially available products include those from Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinko Chemical Co., Ltd., Flexis, and others.

In the rubber composition, the content of the antioxidant is preferably 0.2 parts by mass or more, and more preferably 0.5 parts by mass or more, per 100 parts by mass of the rubber component. The content is preferably 7.0 parts by mass or less, and more preferably 4.0 parts by mass or less.

The rubber composition preferably contains stearic acid. The content of stearic acid in the rubber composition is preferably 0.5 to 10 parts by mass, more preferably 0.5 to 5 parts by mass, per 100 parts by mass of the rubber component.

The stearic acid used can be any known product, such as products from NOF Corp., NOF Corporation, Kao Corp., Fujifilm Wako Pure Chemical Industries, Ltd., Chiba Fatty Acid Co., Ltd., etc.

The rubber composition preferably contains zinc oxide. In the rubber composition, the content of zinc oxide is preferably 0.5 to 10 parts by mass, more preferably 1 to 5 parts by mass, per 100 parts by mass of the rubber component.

As zinc oxide, conventionally known products can be used, such as products from Mitsui Mining & Smelting Co., Ltd., Toho Zinc Co., Ltd., Hakusui Tech Co., Ltd., Seido Chemical Industry Co., Ltd., Sakai Chemical Industry Co., Ltd., etc.

The rubber composition may contain wax. The amount of wax in the rubber composition is preferably 0.5 to 10 parts by mass, and more preferably 1 to 5 parts by mass, per 100 parts by mass of the rubber component.

The wax is not particularly limited, and examples include petroleum-based waxes and natural waxes. Synthetic waxes obtained by refining or chemically processing multiple waxes can also be used. These waxes may be used alone or in combination of two or more types.

Petroleum-based waxes include paraffin wax, microcrystalline wax, etc. Natural waxes are not particularly limited as long as they are derived from resources other than petroleum, and examples include vegetable waxes such as candelilla wax, carnauba wax, Japan wax, rice wax, and jojoba wax; animal waxes such as beeswax, lanolin, and spermaceti; mineral waxes such as ozokerite, ceresin, and petrolactam; and refined products thereof. Commercially available products include those from Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., and Seiko Chemical Co., Ltd.

It is preferable to add sulfur to the rubber composition, as this forms appropriate cross-linked chains in the polymer chains and provides good performance.

In the rubber composition, the sulfur content is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.5 parts by mass or more, per 100 parts by mass of the rubber component. The content is preferably 4.0 parts by mass or less, more preferably 3.0 parts by mass or less, and even more preferably 2.0 parts by mass or less.

Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, and soluble sulfur, which are commonly used in the rubber industry. Commercially available products include those from Tsurumi Chemical Industry Co., Ltd., Karuizawa Sulfur Co., Ltd., Shikoku Chemical Industry Co., Ltd., Flexis Corporation, Nippon Kanzuri Kogyo Co., Ltd., and Hosoi Chemical Industry Co., Ltd. These may be used alone or in combination of two or more types.

The rubber composition preferably contains a vulcanization accelerator.
In the rubber composition, the content of the vulcanization accelerator is not particularly limited and may be freely determined according to the desired vulcanization speed and crosslink density, but is preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, and even more preferably 1.5 parts by mass or more, relative to 100 parts by mass of the rubber component. The upper limit is preferably 8.0 parts by mass or less, more preferably 6.0 parts by mass or less, and even more preferably 5.0 parts by mass or less.

There are no particular restrictions on the type of vulcanization accelerator, and any commonly used accelerator can be used. Examples of the vulcanization accelerator include thiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, and N-cyclohexyl-2-benzothiazyl sulfenamide; thiuram-based vulcanization accelerators such as tetramethylthiuram disulfide (TMTD), tetrabenzylthiuram disulfide (TBzTD), and tetrakis(2-ethylhexyl)thiuram disulfide (TOT-N); sulfenamide-based vulcanization accelerators such as N-cyclohexyl-2-benzothiazole sulfenamide, N-t-butyl-2-benzothiazolyl sulfenamide, N-oxyethylene-2-benzothiazole sulfenamide, N-oxyethylene-2-benzothiazole sulfenamide, and N,N'-diisopropyl-2-benzothiazole sulfenamide; and guanidine-based vulcanization accelerators such as diphenyl guanidine, di-orthotolyl guanidine, and orthotolyl biguanidine. These may be used alone or in combination of two or more. Among them, sulfenamide-based, guanidine-based, and benzothiazole-based vulcanization accelerators are preferred.

In addition to the above components, the rubber composition may contain compounding agents that are commonly used in the tire industry, such as release agents, as appropriate.

The rubber composition can be produced by a known method, for example, by kneading the components using a rubber kneading device such as an open roll or a Banbury mixer, and then vulcanizing the components.

As for the kneading conditions, in the base kneading process where additives other than the vulcanizing agent and vulcanization accelerator are kneaded, the kneading temperature is usually 50 to 200°C, preferably 80 to 190°C, and the kneading time is usually 30 seconds to 30 minutes, preferably 1 minute to 30 minutes. In the finish kneading process where the vulcanizing agent and vulcanization accelerator are kneaded, the kneading temperature is usually 100°C or less, preferably room temperature to 80°C. Furthermore, the composition kneaded with the vulcanizing agent and vulcanization accelerator is usually subjected to a vulcanization treatment such as press vulcanization. The vulcanization temperature is usually 120 to 200°C, preferably 140 to 180°C.

The rubber composition can be used in various pneumatic tire components such as tread (cap tread), sidewall, base tread, bead apex, clinch apex, inner liner, under tread, breaker topping, brim topping, and tread. In particular, it can be used in tread (cap tread).

Tires are manufactured by the usual method using a rubber composition. That is, the rubber composition containing the above components is extruded in the unvulcanized stage to match the shape of the tread, etc., and molded together with other tire components in a tire building machine by the usual method to form an unvulcanized tire. The unvulcanized tire is then heated and pressurized in the vulcanizer to obtain a tire.

The tires include pneumatic tires and non-pneumatic tires. Of these, pneumatic tires are preferred. The tires can be used as passenger car tires, tires for large passenger cars and large SUVs, heavy-duty tires such as trucks and buses, light truck tires, motorcycle tires, and racing tires (high-performance tires). Of these, the tires are particularly suitable for use as passenger car tires.

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

Various chemicals used in the examples and comparative examples will be collectively described below.
SBR1: Modified solution-polymerized SBR synthesized in Production Example 1-1 below (styrene content 35% by mass, vinyl bond content 34 mol%, Mw 850,000, Tg -30°C, oil-extended product containing 25 parts by mass of oil per 100 parts by mass of rubber component)
SBR2: Modified solution-polymerized SBR synthesized in Production Example 1-2 below (styrene content 30% by mass, vinyl bond amount 52 mol%, Mw 250,000, Tg -23°C, non-oil extended product)
SBR3: SLR6430 manufactured by Styron (styrene content 40% by mass, vinyl bond content 24 mol%, Mw 1,070,000, Tg -31°C, oil-extended and non-oil-extended product containing 37.5 parts by mass of oil per 100 parts by mass of rubber component)
BR: Ubepol BR150B (cis content 98% by mass) manufactured by Ube Industries, Ltd.
NR: TSR20
Silica 1: Ultrasil VN3 (N ₂ SA 175 m ² /g) manufactured by Evonik Degussa
Silica 2: Ultrasil 9100Gr ( _N2SA235m2 /g) manufactured by Evonik ^Degussa
Carbon black: ^Diablack N220 ( _N2SA115m2 /g) manufactured by Mitsubishi Chemical Corporation
Organosilicon compound 1: A silane coupling agent synthesized in Production Example 2 below. Organosilicon compound 2: Si266 (bis(3-triethoxysilylpropyl)disulfide) manufactured by Evonik Degussa.
Solid resin 1: T-REZ PR801 (hydrogenated DCPD/C9, softening point 87-93°C) manufactured by JXTG Nippon Oil & Energy Corporation
Solid resin 2: Sylvares 4401 (copolymer of α-methylstyrene and styrene, softening point 85° C., Tg 43° C.) manufactured by Arizona Chemical Co.
Solid resin 3: YS Resin PX1150 (polyterpene (β-pinene resin), softening point 115°C) manufactured by Yasuhara Chemical Co., Ltd.
Liquid polymer: CRAY VALLEY's RICON 130 (polybutadiene, Mn 2500)
Zinc oxide: Zinc oxide type 2 manufactured by Mitsui Metals Co., Ltd. Wax: Ozoace wax manufactured by Nippon Seiro Co., Ltd.
Antioxidant 1: Nocrac 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Antioxidant 2: Nocrac RD (poly(2,2,4-trimethyl-1,2-dihydroquinoline)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Stearic acid: "Tsubaki" manufactured by NOF Corporation
Vulcanization accelerator CZ: Noccela CZ (N-cyclohexyl-2-benzothiazolyl sulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Vulcanization accelerator DPG: Noccela D manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Sulfur: Powdered sulfur manufactured by Karuizawa Sulfur Co., Ltd.

(Production Example 1-1: Synthesis of SBR1)
An autoclave reactor (capacity 20 L) equipped with a stirrer and a jacket was purged with nitrogen, and the temperature was controlled at 70° C. while continuously charging styrene at a rate of 10.5 g/min, 1,3-butadiene containing 100 ppm of 1,2-butadiene at a rate of 19.5 g/min, cyclohexane at a rate of 150 g/min, tetrahydrofuran at a rate of 1.5 g/min, and n-butyllithium at a rate of 0.117 mmol/min. At the top outlet of the first reaction vessel, silicon tetrachloride was continuously added at a rate of 0.04 mmol/min, and this was introduced into the second reaction vessel connected to the first reaction vessel to carry out a modification reaction. 2,6-di-tert-butyl-p-cresol was added to the polymer solution after the modification reaction was completed. Next, 25 parts by mass of extender oil (VivaTec 400 manufactured by H&R) was added per 100 parts by mass of the polymer, and the solvent was removed by steam stripping, followed by drying with a heated roll adjusted to 110° C. to obtain SBR1.

(Production Example 1-2: Synthesis of SBR2)
Cyclohexane, tetrahydrofuran, styrene, and 1,3-butadiene were charged into a nitrogen-substituted autoclave reactor. After adjusting the temperature of the reactor contents to 20°C, n-butyllithium was added to initiate polymerization. Polymerization was performed under adiabatic conditions, with the maximum temperature reaching 85°C. When the polymerization conversion reached 99%, 1,3-butadiene was added, and polymerization was continued for another 5 minutes, after which N,N-bis(trimethylsilyl)-3-aminopropyltrimethoxysilane was added as a modifier to carry out the reaction. After completion of the polymerization reaction, 2,6-di-tert-butyl-p-cresol was added. Next, the solvent was removed by steam stripping, and the mixture was dried with a heated roll adjusted to 110°C to obtain SBR2.

(Production Example 2: Synthesis of Organosilicon Compound 1)
In a 2L separable flask equipped with a stirrer, a reflux condenser, a dropping funnel and a thermometer, 78.0g (1.0 mol) of anhydrous sodium sulfide, 80.3g (2.5 mol) of sulfur and 480g of ethanol were charged and heated to 80°C. 566g (2.0 mol) of 6-chlorohexyltriethoxysilane was added dropwise therein and heated and stirred at 80°C for 10 hours. The reaction liquid was filtered under pressure using a filter plate to obtain a filtrate from which the salt generated as the reaction proceeded was removed. The obtained filtrate was heated to 100°C, and ethanol was distilled off under a reduced pressure of 10mmHg or less to obtain an organosilicon compound 1 (silane coupling agent) as a reaction product. The obtained organosilicon compound 1 had a sulfur content of 18.5% by mass, the average number of sulfur atoms x contained in one molecule of the organosilicon compound was 3.5, and the value of m was 6.

<Examples and Comparative Examples>
According to the compounding recipe shown in Table 1, polymers and compounding chemicals were added using a 1.7 L Banbury mixer, and the mixture was kneaded for 3 minutes at 150°C to obtain a kneaded product. Sulfur and a vulcanization accelerator were added, and the mixture was kneaded for 2 minutes at 100°C using an open roll to obtain an unvulcanized rubber composition. Each of the obtained unvulcanized rubber compositions was molded into a cap tread shape, laminated together with other tire components, and vulcanized at 170°C for 15 minutes to produce a test tire (tire size: 195/65R15).

The following evaluations were performed on the obtained test tires. The evaluation results are shown in Table 1. Comparative Example 1 was used as the reference comparative example.

<Turning performance while braking on wet roads (actual vehicle)>
The test was carried out by actual vehicle evaluation on a test course, and the cornering performance while braking on a wet road surface was evaluated on a scale of 1 to 10 for each test vehicle equipped with each test tire on all wheels, based on the feeling of 10 drivers. The total score was calculated as a score, and the standard comparative example was set to 100, and this was expressed as an index. The higher the index, the better the cornering performance while braking on a wet road surface.

From Table 1, it can be seen that the examples that satisfied the formula (1) "M300/M100≧4.0" and contained a filler containing silica and a silane coupling agent that contained an alkoxysilyl group and a sulfur atom and had 6 or more carbon atoms connecting the alkoxysilyl group and the sulfur atom, had excellent cornering performance while braking on wet road surfaces.

Claims (10)

The 300% modulus (M300) and the 100% modulus (M100) satisfy the following formula (1),
The rubber composition includes a rubber component, a filler containing silica, a silane coupling agent , and a solid resin ,
The silane coupling agent includes an organosilicon compound that contains an alkoxysilyl group and a sulfur atom, and the number of carbon atoms connecting the alkoxysilyl group and the sulfur atom is 6 or more,
The organosilicon compound is an organosilicon compound represented by the following average composition formula (I):
The content of the solid resin in the rubber composition for tires is 35 to 100 parts by mass per 100 parts by mass of the rubber component .
(1) M300/M100≧4.0

(In the formula, x represents the average number of sulfur atoms and is 3.5 or more; m represents an integer of 6 or more; R ¹ to R ⁶ are the same or different and represent an alkyl group or an alkoxy group having 1 to 6 carbon atoms, and at least one of R ¹ to R ³ and at least one of R ⁴ to R ⁶ is the alkoxy group. Note that R ¹ to R ⁶ may form a ring structure by bonding the alkyl groups or alkoxy groups.) The rubber composition for tires according to claim 1, which satisfies the following formula:
M300/M100≧4.2 3. The rubber composition for tires according to claim 1 or 2, which satisfies the following formula:
M100≦5.0MPa The rubber composition for tires according to any one of claims 1 to 3, which satisfies the following formula:
M300≧8.0MPa The rubber composition for tires according to any one of claims 1 to 4, which contains isoprene-based rubber, styrene-butadiene rubber, and butadiene rubber. The 300% modulus (M300) and the 100% modulus (M100) satisfy the following formula (1),
The rubber composition includes a rubber component, a filler containing silica, and a silane coupling agent,
The silane coupling agent includes an organosilicon compound that contains an alkoxysilyl group and a sulfur atom, and the number of carbon atoms connecting the alkoxysilyl group and the sulfur atom is 6 or more,
Further contains a resin component,
The contents of silica and resin components per 100 parts by mass of the rubber component satisfy the following formula,
The content of the silica is 5 to 250 parts by mass based on 100 parts by mass of the rubber component,
The content of the resin component in the rubber composition for tires is 10 to 100 parts by mass per 100 parts by mass of the rubber component .
1.5≦Silica content/resin component content≦ 4.0
(1) M300/M100≧4.0 The rubber composition for tires according to any one of claims 1 to 6, wherein the content of the resin component per 100 parts by mass of the rubber component is 20 parts by mass or more. Further comprising a resin component and a liquid polymer (excluding the resin component) ,
8. The rubber composition for tires according to claim 1, wherein the content of silica, the content of the resin component and the total content of the liquid polymer per 100 parts by mass of the rubber component satisfy the following formula:
1.0≦Silica content/total content of resin component and liquid polymer≦4.5 9. The rubber composition for tires according to claim 1, wherein the total content of the resin component and the liquid polymer (excluding the resin component) is 30 parts by mass or more per 100 parts by mass of the rubber component. A tire having a tread made of the rubber composition according to any one of claims 1 to 9.