JP7639277B2 - 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 on wet road surfaces at high temperatures.

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 steering stability on wet road surfaces at high temperatures.

The present invention relates to a rubber composition for tires, which has a crosslink density (νM) of a monosulfide bond and a total crosslink density (νT) determined by a swelling compression method that satisfy the following formula (1), and which contains 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) νM/νT≧0.20

It is preferable that the following formula is satisfied.
νM/νT≧0.25

It is preferable that the following formula is satisfied.
νM/νT≧0.30

It is preferable that the following formula is satisfied.
νM≧1.0×10 ⁻⁵ mol/cm ³

It is preferable that the content of the filler is 5 to 200 parts by mass per 100 parts by mass of the rubber component, and the content of the organosilicon compound is 0.1 to 20 parts by mass per 100 parts by mass of silica.

It is preferable that the silica content in 100% by mass of the filler is 30% by mass or more.

It is preferable that the styrene butadiene rubber content in 100% by mass of the rubber component is 30% by mass or more.

It is preferable that the styrene butadiene rubber content is 50 to 90 mass% and the butadiene rubber content is 10 to 40 mass% in 100 mass% of the rubber component.

The content of the dialkyldithiophosphate compound per 100 parts by mass of the rubber component is preferably 0.1 to 10 parts by mass.

It is preferable that the sulfur content per 100 parts by mass of the rubber component is 5.0 parts by mass or less.

It is preferable that the sulfur content per 100 parts by mass of the rubber component is 1.0 part by mass or less.

The plasticizer content is preferably 5 to 30 parts by mass per 100 parts by mass of the rubber component.

It is preferable that the contents of silica and plasticizer per 100 parts by mass of the rubber component satisfy the following formula.
2.4≦Silica content/Plasticizer content≦4.0

It is preferable that the contents of silica and resin per 100 parts by mass of the rubber component satisfy the following formula.
10≦Silica content/resin content≦20

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

According to the present invention, the rubber composition for tires has a monosulfide bond crosslink density (νM) and total crosslink density (νT) determined by the swelling compression method that satisfy the formula (1), and contains a filler containing silica and a silane coupling agent, and the silane coupling agent contains 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, thereby improving steering stability on wet road surfaces at high temperatures.

The present invention is a rubber composition for tires, the crosslink density (νM) and total crosslink density (νT) of monosulfide bonds determined by a swelling compression method satisfy the above formula (1), the rubber composition includes a filler containing silica, and a silane coupling agent, the silane coupling agent includes 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 rubber composition has excellent steering stability on wet road surfaces at high temperatures. That is, when the tire (tread, etc.) becomes hot, the effect of obtaining good steering stability on wet road surfaces is achieved. For example, the effect can be obtained in any case where the tire (tread, etc.) becomes hot, such as when the tire becomes hot directly due to high air temperature, when the road surface becomes hot due to high air temperature and the tire becomes hot as a result, or when the tire becomes hot due to high-speed driving regardless of the air temperature.

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, so that the distance between the polymers in the rubber phase becomes uniform. Furthermore, by increasing the "crosslink density (νM)/total crosslink density (νT)≧0.20 of the monosulfide bond", that is, the relatively short mono-crosslink ratio, the silica interface becomes flexible, and it is possible to obtain a followability in a small deformation and a sufficient heat generation property. In addition, since the mono-crosslink is strong against heat, even if heat is generated by continuous driving, there is little change, and it is possible to prevent the stress of the entire rubber from decreasing. Therefore, it is presumed that the steering stability on wet road surfaces at high temperatures is significantly improved.

The rubber composition (rubber composition after vulcanization) has a monosulfide bond crosslink density (νM (mol/cm ³ )) and a total crosslink density (νT (mol/cm ³ )) determined by a swelling compression method that satisfy the following formula (1).
(1) νM/νT≧0.20
From the viewpoint of steering stability on wet road surfaces at high temperatures, νM/νT is preferably 0.25 or more, more preferably 0.30 or more, and even more preferably 0.33 or more. The upper limit is not particularly limited, but is preferably 0.50 or less, more preferably 0.45 or less, even more preferably 0.43 or less, and particularly preferably 0.41 or less.

From the viewpoint of steering stability on wet road surfaces at high temperatures, the rubber composition (rubber composition after vulcanization) preferably has a crosslink density (νM (mol/cm ³ )) of monosulfide bonds determined by a swelling and compression method that satisfies the following formula:
νM≧1.0×10 ⁻⁵ mol/cm ³
νM is preferably 1.2×10 ⁻⁵ mol/cm ³ or more, more preferably 1.3×10 ⁻⁵ mol/cm ³ or more, even more preferably 1.4×10 ⁻⁵ mol/cm ³ or more, and particularly preferably 1.5×10 ⁻⁵ mol/cm ³ or more. The upper limit is preferably 3.5×10 ⁻⁵ mol/cm ³ or less, more preferably 3.0×10 ⁻⁵ mol/cm ³ or less, and even more preferably 2.8×10 ⁻⁵ mol/cm ³ or less.

From the viewpoint of steering stability on wet road surfaces at high temperatures, the rubber composition (rubber composition after vulcanization) preferably has a total crosslink density (νT (mol/cm ³ )) determined by a swelling compression method that satisfies the following formula:
νT≧4.0×10 ⁻⁵ mol/cm ³
νT is preferably 4.4×10 ⁻⁵ mol/cm ³ or more, more preferably 4.7×10 ⁻⁵ mol/cm ³ or more, even more preferably 4.9×10 ⁻⁵ mol/cm ³ or more, and particularly preferably 5.0×10 ⁻⁵ mol/cm ³ or more. The upper limit is preferably 8.0×10 ⁻⁵ mol/cm ³ or less, more preferably 7.0×10 ⁻⁵ mol/cm ³ or less, and particularly preferably 6.5×10 ⁻⁵ mol/cm ³ or less.

In the rubber composition (rubber composition after vulcanization), the crosslink density of the monosulfide bond and the total crosslink density can be determined by the swelling and compression method described in Hideo Nakauchi and 4 others, "Japan Rubber Association Journal", 1987, Vol. 60, No. 5, pp. 267-272, that is, by selectively cutting the crosslinks with a reagent such as LiAlH ₄ or propane 2-thiol, and calculating the crosslink density of the monosulfide bond (R-S ₁ -R) and the total crosslink density from the swelling degree before and after the selective cutting using the Flory-Rehner formula. Specifically, they can be measured by the method described in the examples below.

The νM and νT of a rubber composition (rubber composition after vulcanization) can be adjusted by adjusting the amount of sulfur, adjusting the amount of vulcanization accelerator, blending a dialkyldithiophosphate compound, blending the organosilicon compound, etc. Specifically, the νM value tends to increase by blending a dialkyldithiophosphate compound, blending the organosilicon compound, increasing the ratio of accelerator to sulfur, etc. The νT value tends to increase by increasing the amount of sulfur or vulcanization accelerator, etc.

(Rubber component)
As the rubber component usable in the rubber composition, for example, diene rubber can be used. Examples of diene rubber include 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. In addition, butyl rubber, fluororubber, etc. can also be mentioned. These may be used alone or in combination of two or more. Among them, from the viewpoint of steering stability on wet road surfaces at high temperatures, SBR, BR, and isoprene rubber are preferred, and SBR and BR are more preferred.

The diene rubber may be an unmodified diene rubber or a modified diene rubber.
The modified diene rubber may be any diene rubber having a functional group that interacts with a filler such as silica. Examples of the modified diene rubber include terminal-modified diene rubber (terminal-modified diene rubber having the functional group at the terminal) in which at least one terminal of the diene rubber has been modified with a compound (modifier) having the functional group, main-chain modified diene rubber having the functional group in the main chain, main-chain terminal-modified diene rubber having the functional group in the main chain and at least one terminal (for example, main-chain terminal-modified diene rubber having the functional group in the main chain and at least one terminal modified with the modifier), and terminal-modified diene rubber 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.

The above-mentioned 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), and alkoxysilyl groups (preferably alkoxysilyl groups having 1 to 6 carbon atoms) are preferred.

The SBR is not particularly limited, and for example, emulsion-polymerized styrene-butadiene rubber (E-SBR), solution-polymerized styrene-butadiene rubber (S-SBR), etc. can be used. These may be used alone or in combination of two or more types.

The styrene content of SBR is preferably 5.0% by mass or more, more preferably 8.0% by mass or more, and even more preferably 10.0% by mass or more. The styrene content is preferably 50.0% by mass or less, more preferably 35.0% by mass or less, even more preferably 30.0% by mass or less, particularly preferably 28.0% by mass or less, and most preferably 27.0% by mass or less. By keeping it within the above range, the steering stability on wet road surfaces at high temperatures tends to be improved.
In this specification, the styrene content can be measured by ¹ H-NMR measurement.

The vinyl bond content of SBR is preferably 15% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, particularly preferably 45% by mass or more, and most preferably 50% by mass or more. The vinyl bond content is preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 65% by mass or less. By keeping it within the above range, the steering stability on wet road surfaces at high temperatures tends to be improved.
In this specification, the vinyl bond amount (1,2-bonded butadiene unit amount) can be measured by infrared absorption spectroscopy.

The SBR may be unmodified or modified. Examples of modified SBR include modified SBR into which functional groups similar to those of modified diene rubber have been introduced. Hydrogenated styrene-butadiene copolymers (hydrogenated SBR) can also be used as SBR.

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 50% by mass or more, even more preferably 60% by mass or more, and particularly preferably 70% 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 it within the above range, the steering stability on wet road surfaces at high temperatures tends to be improved.

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 diene rubber have been introduced. BR may also be 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 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more. The upper limit is preferably 60% by mass or less, more preferably 40% by mass or less, even more preferably 35% by mass or less, and particularly preferably 30% by mass or less. By keeping it within the above range, the steering stability on wet road surfaces at high temperatures tends to be improved.

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.

When the rubber composition contains isoprene-based rubber, the content of isoprene-based rubber 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 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. By keeping it within the above range, the steering stability on wet road surfaces at high temperatures tends to be improved.

(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, and even more preferably ^150m2 /g or more. The upper limit of the _N2SA of silica is not particularly limited, but is preferably ^250m2 /g or less, more preferably ^220m2 /g or less, and even more preferably ^200m2 /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 60 parts by mass or more, and particularly preferably 70 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, steering stability on wet road surfaces at high temperatures tends to be improved.

（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 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 blending amount of the compound of the average composition formula (I-1), anhydrous sodium sulfide, and sulfur as necessary, so as to obtain the desired compound of the average composition formula (I). For example, if you want to make the compound of the average composition formula (I) have x 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, that is, a long-chain silane coupling agent, is used as a 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 that the dispersibility of the silica is significantly improved. In addition, the uniform dispersion of silica due to the long chain structure makes it possible to make the distance between polymers in the rubber phase uniform. Furthermore, as mentioned above, the relatively short mono-crosslinking ratio is high, so that it is possible to obtain tracking ability with small deformation and sufficient heat generation, and even if heat is generated by continuous driving, there is little change, and the stress of the entire rubber can be prevented from decreasing. Therefore, by using such a long-chain silane coupling agent, the steering stability on wet roads at high temperatures 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, there is a tendency for the steering stability on wet road surfaces at high temperatures to be improved. 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, the steering stability on wet road surfaces at high temperatures tends to be improved.

(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 55 parts by mass or more, even more preferably 65 parts by mass or more, and particularly preferably 75 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 it within the above range, the steering stability on wet road surfaces at high temperatures tends to be improved.

In the rubber composition, the silica content in 100% by mass of the filler is preferably 30% by mass or more, more preferably 50% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more, from the viewpoint of handling stability on wet road surfaces at high temperatures. 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 it within the above range, the steering stability on wet road surfaces at high temperatures tends to be improved.
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 content within the above range, the steering stability on wet road surfaces at high temperatures tends to be improved.

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, the steering stability on wet road surfaces at high temperatures tends to be improved.

(Plasticizer)
The rubber composition may contain a plasticizer. A plasticizer is a material that imparts plasticity to a rubber component, and examples of the plasticizer include liquid plasticizers (plasticizers that are in a liquid state at room temperature (25° C.)) and resins (resins that are in a solid state at room temperature (25° C.)). Among these, resins are preferred from the viewpoint of steering stability on wet road surfaces at high temperatures.

In the rubber composition, the plasticizer content (the total amount of liquid plasticizer (plasticizer in a liquid state at room temperature (25°C)) and resin (resin in a solid state at room temperature (25°C))) is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 15 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 40 parts by mass or less, and particularly preferably 30 parts by mass or less. By keeping it within the above range, there is a tendency for steering stability on wet road surfaces at high temperatures to be improved.

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

In the rubber composition, the content of the liquid plasticizer is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 15 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 40 parts by mass or less, and particularly preferably 30 parts by mass or less. By keeping the content within the above range, the steering stability on wet road surfaces at high temperatures tends to be improved.

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.

Liquid resins include terpene resins (including terpene phenol resins and aromatic modified terpene resins) that are liquid at 25°C, 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, acrylic resins, etc.

Liquid diene polymers include liquid styrene butadiene copolymers (liquid SBR), liquid butadiene polymers (liquid BR), liquid isoprene polymers (liquid IR), liquid styrene isoprene copolymers (liquid SIR), liquid styrene butadiene styrene block copolymers (liquid SBS block polymers), liquid styrene isoprene styrene block copolymers (liquid SIS block polymers), liquid farnesene polymers, liquid farnesene butadiene copolymers, etc. that are liquid at 25°C. The ends or main chains of these may be modified with polar groups.

The above resins (resins in a solid state at room temperature (25°C)) that can be used in the rubber composition include, for example, aromatic vinyl polymers in a solid state at room temperature (25°C), coumarone-indene resins, coumarone resins, indene resins, phenolic resins, rosin resins, petroleum resins, terpene resins, acrylic resins, and the like. The resins may also be hydrogenated. These may be used alone or in combination of two or more. Among these, aromatic vinyl polymers, coumarone-indene resins, phenolic resins, and petroleum resins are preferred from the viewpoint of steering stability on wet road surfaces at high temperatures.

In the rubber composition, the content of the above resin 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, even more preferably 20 parts by mass or less, and particularly preferably 10 parts by mass or less. By keeping the content within the above range, the steering stability on wet road surfaces at high temperatures tends to be improved. The same range is also suitable for the content of the aromatic vinyl polymer.

The softening point of the 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, the steering stability on wet road surfaces at high temperatures tends to be improved.
The softening point of the resin 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 that contains coumarone and indene as the main monomer components that make up the resin skeleton (main chain). Other monomer components contained in the skeleton besides coumarone and indene include styrene, α-methylstyrene, methylindene, vinyltoluene, etc.

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 above-mentioned rosin resins include rosin-based resins such as natural rosin, polymerized rosin, modified rosin, ester compounds thereof, and hydrogenated products thereof.

The petroleum resins include C5 resins, C9 resins, C5/C9 resins, dicyclopentadiene (DCPD) resins, etc. Among these, DCPD resins are preferred.

The terpene resin is a polymer that contains 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, pp. 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 plasticizer 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., and Taoka Chemical Co., Ltd.

From the viewpoint of steering stability on wet road surfaces at high temperatures, it is preferable that the rubber composition has a silica content (parts by mass) per 100 parts by mass of the rubber component and a plasticizer content (parts by mass) per 100 parts by mass of the rubber component that satisfy the following formula:
2.0≦Silica content/Plasticizer content≦4.5
The silica content/plasticizer content is preferably 2.4 or more, more preferably 2.6 or more, even more preferably 2.8 or more, and particularly preferably 3.0 or more. The lower limit is preferably 4.0 or less, more preferably 3.8 or less, even more preferably 3.6 or less, and particularly preferably 3.4 or less. By keeping it within the above range, the steering stability on wet road surfaces at high temperatures tends to improve.

From the viewpoint of steering stability on wet road surfaces at high temperatures, it is preferable that the rubber composition has a silica content (parts by mass) per 100 parts by mass of the rubber component and a resin content (parts by mass) per 100 parts by mass of the rubber component (a resin in a solid state at room temperature (25° C.)) that satisfies the following formula:
5≦Silica content/resin content≦25
The silica content/plasticizer content is preferably 10 or more, more preferably 12 or more, even more preferably 14 or more, and particularly preferably 15 or more. The lower limit is preferably 20 or less, more preferably 19 or less, even more preferably 18 or less, and particularly preferably 17 or less. By keeping it within the above range, the steering stability on wet road surfaces at high temperatures tends to be improved.

The rubber composition preferably contains a dialkyldithiophosphate compound from the viewpoint of handling stability on wet road surfaces at high temperatures.

The reason why such an effect is obtained is not entirely clear, but it is presumed that the effect is due to the following mechanism.
By introducing a compound such as zinc dithiophosphate, the alkyl group is compatible with the rubber, while zinc is accompanied by vulcanizing agents such as sulfur and accelerators, and relatively short mono-crosslinks are easily generated in the system. By increasing the relatively short mono-crosslink ratio, the silica interface becomes flexible, and it is possible to obtain sufficient heat generation while providing followability in small deformations. In addition, since the mono-crosslink is strong against heat, even if heat is generated by continuous running, there is little change, and it is possible to prevent the stress of the entire rubber from decreasing. Therefore, it is presumed that the use of a dialkyl dithiophosphate compound together with the organosilicon compound (long-chain silane coupling agent) significantly improves the steering stability on wet roads at high temperatures.

（式中、Ｒ^１～Ｒ^４はそれぞれ独立に炭素数１～１８の直鎖若しくは分岐鎖アルキル基、又は炭素数５～１２のシクロアルキル基を表す。） As the dialkyldithiophosphate compound, for example, a salt of a dialkyldithiophosphate with a metal such as zinc or molybdenum can be used. As a commercially available product, a product from Rhein Chemie can be used. These may be used alone or in combination of two or more. Among them, the compound represented by the following formula (zinc dialkyldithiophosphate) is preferred.

(In the formula, R ¹ to R ⁴ each independently represent a linear or branched alkyl group having 1 to 18 carbon atoms, or a cycloalkyl group having 5 to 12 carbon atoms.)

In the above formula, examples of the linear or branched alkyl group represented by R ¹ to R ⁴ include a methyl group, an ethyl group, an n-propyl group, an iso-propyl group, an n-butyl group, a 4-methylpentyl group, a 2-ethylhexyl group, an octyl group, an octadecyl group, etc., while examples of the cycloalkyl group include a cyclopentyl group, a cyclohexyl group, a cyclooctyl group, etc. Among these, from the viewpoints of easy dispersion in the rubber composition and easy production, R ¹ to R ⁴ are preferably linear or branched alkyl groups having 2 to 8 carbon atoms, more preferably an n-butyl group, an n-propyl group, an iso-propyl group, or an n-octyl group, and even more preferably an n-butyl group.

The content of the dialkyldithiophosphate compound 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, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, even more preferably 3 parts by mass or less, and particularly preferably 2 parts by mass or less. Within the above range, the effect tends to be better obtained. The content of the zinc dialkyldithiophosphate is also preferably in the same range.

(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 may be 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; N-isopropyl-N'-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, N,N'-di-2-naphthyl-p-phenylenediamine, Examples of such antioxidants include p-phenylenediamine antioxidants such as amines; quinoline antioxidants such as polymerized 2,2,4-trimethyl-1,2-dihydroquinoline; monophenol antioxidants such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol; and bis-, tris-, and polyphenol-based antioxidants such as tetrakis-[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane. Among these, p-phenylenediamine antioxidants and quinoline antioxidants are preferred, and N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine and polymerized 2,2,4-trimethyl-1,2-dihydroquinoline are more preferred. Commercially available products include those from Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinko Chemical Co., Ltd., and Flexis.

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, any known zinc oxide can be used, for example, 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., Seiko Chemical Co., Ltd., etc.

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 5.0 parts by mass or less, more preferably 2.5 parts by mass or less, even more preferably 1.5 parts by mass or less, and particularly preferably 1.0 part 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-benzothiazole 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 mixture.

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, tread, etc. 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. Among them, pneumatic tires are preferred. The tires can be used for passenger car tires, large passenger car and large SUV tires, heavy load tires such as trucks and buses, light truck tires, two-wheeled vehicle tires, racing tires (high performance tires), etc. Among them, the tires can be preferably used for passenger car tires, large passenger car tires, and large SUV 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.
SBR: HPR850 (styrene content 27.5% by mass, vinyl bond content 59.0% by mass) manufactured by JSR Corporation
BR: Ubepol BR150B (cis content 98% by mass) manufactured by Ube Industries, Ltd.
Carbon black: ^Diablack N220 ( _N2SA115m2 /g) manufactured by Mitsubishi Chemical Corporation
Silica: Ultrasil VN3 ( _N2SA ^175m2 /g) manufactured by Evonik Degussa
Organosilicon compound 1: A silane coupling agent synthesized in Production Example 1 below. Organosilicon compound 2: Si266 (bis(3-triethoxysilylpropyl)disulfide) manufactured by Evonik Degussa.
Oil: Diana Process NH-70S (aromatic process oil) manufactured by Idemitsu Kosan Co., Ltd.
Resin: Sylvares 4401 (copolymer of α-methylstyrene and styrene, softening point 85° C., Tg 43° C.) manufactured by Arizona Chemical Company
Wax: Ozoace wax manufactured by Nippon Seiro Co., Ltd. Anti-aging agent 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: NOF Corporation's "Tsubaki" stearic acid
Zinc oxide: Zinc oxide No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: Powdered sulfur manufactured by Tsurumi Chemical Co., Ltd.
Dialkyldithiophosphate compound: TP-50 manufactured by Rhein Chemie (mixture of zinc dithiophosphate and polymer, R ¹ to R ⁴ are n-butyl groups, active ingredient 50% by mass)
Vulcanization accelerator: Noccela NS (N-tert-butyl-) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
2-Benzothiazylsulfenamide (TBBS)

(Production Example 1: 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 recipes shown in each table, 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 physical property measurements and evaluations were carried out on the obtained test tires. The evaluation results are shown in the tables. Note that in Tables 1 and 2, Comparative Examples 1-1 and 2-1 were used as the reference comparative examples, respectively.

[Swelling compression method]
A test specimen (2 cm x 2 cm, thickness 1 mm (rubber composition after vulcanization)) taken from the tread of a test tire was immersed in a solution of tetrahydrofuran and toluene mixed in a 1:1 ratio for one day to cause swelling. The swelling compression of this swollen sample was measured using a thermomechanical analyzer (manufactured by Shimadzu Corporation, product name "TMA-50"). Then, the total network density (total crosslink density (νT)) (mol/cm ³ ) was calculated from the swelling compression of the swollen sample using the Flory-Rehner equation.
In addition, the sample was immersed for one day in a solution saturated with LiAlH ₄ and mixed in a 1:1 ratio of tetrahydrofuran and toluene to cause swelling. Similarly, the swelling compression degree of the swollen sample was measured, and the network density was calculated using the Flory-Rehner equation to be the network density of monosulfide (crosslink density of monosulfide bonds (νM)) (mol/cm ³ ).

<Handling stability on wet roads at high temperatures (actual vehicle)>
After mounting the test tires and driving around a test course with a wet road surface under conditions where the tires would be at high temperatures (at an air temperature of 20°C and an average speed of 120 km/h), the responsiveness during cornering was evaluated on a 10-point scale from 1 to 10 based on the driver's feeling. The same test was carried out by a total of 10 drivers, and the total score was calculated for each test tire, and indexed so that the total score of the reference comparative example (Comparative Example 1-1 in Table 1, Comparative Example 2-1 in Table 2) was 100. The higher the index, the better the handling stability on wet road surfaces at high temperatures.

From each table, the examples that satisfy the formula (1) "M300/M100 ≧ 4.0" and the formula (1) "νM/νT ≧ 0.20", and contain a filler containing silica and a silane coupling agent containing an organosilicon compound containing an alkoxysilyl group and a sulfur atom and having 6 or more carbon atoms connecting the alkoxysilyl group and the sulfur atom, had excellent steering stability on wet road surfaces at high temperatures.

Claims (15)

The crosslink density (νM) of the monosulfide bond and the total crosslink density (νT) determined by a swelling compression method satisfy the following formula (1),
The composition includes a styrene-butadiene rubber, a resin, a filler including silica, and a silane coupling agent,
The styrene butadiene rubber has a styrene content of 5.0 to 30.0 mass%;
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 rubber composition for tires, wherein the organosilicon compound is an organosilicon compound represented by the following average composition formula (I):
(1) νM/νT≧0.20

(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:
νM/νT≧0.25 The rubber composition for tires according to claim 1, which satisfies the following formula:
νM/νT≧0.30 The rubber composition for tires according to any one of claims 1 to 3, which satisfies the following formula:
νM≧1.0×10 ⁻⁵ mol/cm ³ The rubber composition for tires according to any one of claims 1 to 4, wherein the content of the filler per 100 parts by mass of the rubber component is 5 to 200 parts by mass, and the content of the organosilicon compound per 100 parts by mass of silica is 0.1 to 20 parts by mass. The rubber composition for tires according to any one of claims 1 to 5, wherein the silica content in 100% by mass of the filler is 30% by mass or more. The rubber composition for tires according to any one of claims 1 to 6, wherein the content of styrene butadiene rubber in 100% by mass of the rubber component is 30% by mass or more. The rubber composition for tires according to any one of claims 1 to 7, wherein the content of styrene butadiene rubber is 50 to 90 mass% and the content of butadiene rubber is 10 to 40 mass% in 100 mass% of the rubber component. The rubber composition for tires according to any one of claims 1 to 8, wherein the content of the dialkyldithiophosphate compound per 100 parts by mass of the rubber component is 0.1 to 10 parts by mass. The rubber composition for tires according to any one of claims 1 to 9, wherein the sulfur content per 100 parts by mass of the rubber component is 5.0 parts by mass or less. The rubber composition for tires according to any one of claims 1 to 9, wherein the sulfur content per 100 parts by mass of the rubber component is 1.0 part by mass or less. The rubber composition for tires according to any one of claims 1 to 11, wherein the content of the plasticizer per 100 parts by mass of the rubber component is 5 to 30 parts by mass. The rubber composition for tires according to any one of claims 1 to 12, wherein the contents of silica and plasticizer per 100 parts by mass of the rubber component satisfy the following formula:
2.4≦Silica content/Plasticizer content≦4.0 The rubber composition for tires according to any one of claims 1 to 13, wherein the contents of silica and resin per 100 parts by mass of the rubber component satisfy the following formula:
10≦Silica content/resin content≦20 A tire having a tread made of the rubber composition according to any one of claims 1 to 14.