JP7543748B2 - 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 performance by blending silica, a silane coupling agent, a liquid resin, etc. However, in recent years, there has been a demand for suppressing the deterioration of wet grip performance, especially after aging.

JP 2007-186567 A

The present invention aims to provide a rubber composition for tires and a tire that can solve the above problems and suppress the deterioration of wet grip performance after aging.

The present invention relates to a rubber composition for tires, which has a ratio (Hsa/Hso x 100) of room temperature hardness (Hso) measured within 180 days after vulcanization to room temperature hardness (Hsa) after heat treatment for 168 hours in an 80°C atmosphere after the room temperature hardness measurement of 107 or less, and which contains a filler containing silica and a silane coupling agent, and the silane coupling agent contains an alkoxysilyl group and a sulfur atom, and contains an organosilicon compound having 6 or more carbon atoms connecting the alkoxysilyl group and the sulfur atom.

The rubber composition for tires preferably has Hsa/Hso×100 of 105 or less.

The rubber composition for tires preferably has an Hso of 55 to 70 and an Hsa of 57 to 72.

It is preferable that the content of the silica is 5 to 150 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 the silica.

It is preferable that the silica content in 100% by mass of the filler is 50% by mass or more.

The carbon black content per 100 parts by mass of the rubber component is preferably 1 to 10 parts by mass.

It is preferable that the content of styrene butadiene rubber in 100% by mass of the rubber component is 50% by mass or more.

The rubber composition for tires preferably has a ratio (AS/TS x 100) of the amount of sulfur after acetone extraction (AS) to the amount of sulfur before acetone extraction (TS) measured within 180 days after vulcanization of 75 or less, and a toluene swelling index (Swell) measured within 180 days after vulcanization of 330 or less.

The rubber composition for tires preferably has an AS/TS×100 of 70 or less.

The rubber composition for tires preferably has a TS of 1.00 to 1.60 mass % and an AS of 0.60 to 1.30 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.

The present invention also relates to a tire having a tread made of the rubber composition.

According to the present invention, the ratio (Hsa/Hso x 100) of the room temperature hardness (Hso) measured within 180 days after vulcanization to the room temperature hardness (Hsa) measured after heat treatment for 168 hours in an atmosphere at 80°C after the room temperature hardness measurement is 107 or less, and the tire rubber composition 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, so that the deterioration of wet grip performance after aging can be suppressed.

The present invention is a rubber composition for tires (rubber composition after vulcanization) having Hsa/Hso x 100 of 107 or less, and containing 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. The rubber composition can suppress the deterioration of wet grip performance after aging.

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.
Hsa/Hso×100≦107, that is, by adjusting the hardness change before and after heat treatment to be small, it is possible to suppress the deterioration of wet grip performance due to the aging of the tire. Furthermore, by using an organosilicon compound containing an alkoxysilyl group and a sulfur atom as a silane coupling agent, and having 6 or more carbon atoms connecting the alkoxysilyl group and the sulfur atom, it is possible to prevent silica from re-aggregating in the rubber component because the steric hindrance increases due to the influence of the long chain of the compound. Therefore, these functions not only suppress the macroscopic hardness change, but also make it possible to suppress the hardness change in the system in the microscopic dimension, so that it is possible to improve the maintenance of wet grip performance. Therefore, the rubber composition (rubber composition after vulcanization) can suppress the deterioration of wet grip performance after aging.

In this way, the rubber composition satisfies "Hsa/Hso x 100 ≦ 107" and contains a filler containing silica and a silane coupling agent containing 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, thereby solving the problem (objective) of being able to suppress the deterioration of wet grip performance after aging. In other words, the configuration of "Hsa/Hso x 100 ≦ 107" does not define the problem (objective), and the object of the present application is to suppress the deterioration of wet grip performance after aging, and the composition that satisfies the parameters is used as a means to solve this problem.

The rubber composition (rubber composition after vulcanization) has a room temperature hardness (Hso: hardness at 25 ° C.) measured within 180 days after vulcanization and a room temperature hardness (Hsa: hardness at 25 ° C. after heat treatment) measured for 168 hours in an atmosphere of 80 ° C. after the measurement of the room temperature hardness (Hsa / Hso × 100) of 107 or less. It is preferably 105 or less, more preferably 104 or less, particularly preferably 103 or less, and most preferably 102 or less. The lower limit is not particularly limited, but is preferably 50 or more, more preferably 70 or more, and even more preferably 90 or more. By setting it within the above range, there is a tendency that the deterioration of wet grip performance after aging can be suppressed.
Hso and Hsa can be measured by the method described in the Examples below.

Hso may be adjusted as appropriate within the range that satisfies "Hsa/Hso x 100 is 107 or less", but is preferably 75 or less, more preferably 70 or less, even more preferably 67 or less, and is preferably 50 or more, more preferably 55 or more, and even more preferably 60 or more. Similarly, Hsa is preferably 77 or less, more preferably 72 or less, and even more preferably 69 or less, and is preferably 52 or more, more preferably 57 or more, and even more preferably 62 or more. By keeping it within the above range, it tends to be possible to suppress the deterioration of wet grip performance after aging.

The method of adjusting Hso and Hsa is not particularly limited, but Hso can be increased by, for example, increasing the amount of reinforcing agent, decreasing the amount of softener, increasing the amount of sulfur, or increasing the amount of vulcanization accelerator, and can be decreased by, for example, decreasing the amount of reinforcing agent, increasing the amount of softener, decreasing the amount of sulfur, or decreasing the amount of vulcanization accelerator. On the other hand, Hsa can be increased by, for example, increasing Hso, increasing the amount of sulfur and decreasing the amount of vulcanization accelerator, decreasing the amount of zinc oxide and stearic acid, or decreasing the amount of heat applied during vulcanization, and can be decreased by, for example, using a (co)polymer with fewer conjugated diene units as the rubber component, decreasing Hso, decreasing the amount of sulfur and increasing the amount of vulcanization accelerator, increasing the amount of zinc oxide and stearic acid, blending a plasticizer with an iodine value of 100 to 150 g/100 g, or increasing the amount of heat applied during vulcanization (increasing the time/increasing the temperature).

Hsa/Hso x 100 ≦ 107, i.e., the method of adjusting to reduce the change in hardness before and after heat treatment, can be achieved, for example, by using 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, or by reducing the amount of sulfur.

From the viewpoint of suppressing the deterioration of wet grip performance after aging, the rubber composition (rubber composition after vulcanization) preferably has a ratio (AS/TS×100) of the amount of sulfur after acetone extraction (AS) measured within 180 days after vulcanization to the amount of sulfur before acetone extraction (TS) measured within 180 days after vulcanization of 80 or less. AS/TS×100 is more preferably 75 or less, even more preferably 70 or less, and particularly preferably 65 or less. The lower limit is not particularly limited, but is preferably 30 or more, more preferably 40 or more, and even more preferably 50 or more.
Incidentally, TS and AS can be measured by the method described in the Examples below.

TS is preferably 1.80 mass% or less, more preferably 1.70 mass% or less, even more preferably 1.60 mass% or less, and also preferably 1.00 mass% or more, more preferably 1.20 mass% or more, and even more preferably 1.30 mass% or more. Similarly, AS is preferably 1.40 mass% or less, more preferably 1.30 mass% or less, and even more preferably 1.20 mass% or less, and also preferably 0.60 mass% or more, more preferably 0.80 mass% or more, and even more preferably 0.85 mass% or more. By keeping it within the above range, it tends to be possible to suppress the deterioration of wet grip performance after aging.

The method of adjusting TS and AS is not particularly limited, but TS can be increased by, for example, increasing the compounding ratio of chemicals containing sulfur atoms, such as sulfur, vulcanization accelerators, and silane coupling agents, and can be decreased by, for example, decreasing the compounding ratio of chemicals containing sulfur atoms. AS can be increased by, for example, increasing the compounding ratio of chemicals containing sulfur atoms, such as sulfur, vulcanization accelerators, and silane coupling agents, in the same way as TS, and increasing the amount of sulfur atoms bonded to the rubber component.

AS/TS x 100 ≦ 80, i.e., the AS/TS value can be adjusted to a smaller value by, for example, adding a plasticizer with an iodine value of 100 to 150 g/100 g, adding a smaller amount of vulcanization accelerator relative to sulfur, or reducing the amount of unsaturated bonds in the rubber component.

From the viewpoint of suppressing deterioration of wet grip performance after aging, the rubber composition (rubber composition after vulcanization) preferably has a Swell (%) of 330 or less, more preferably 320 or less, even more preferably 315 or less, particularly preferably 310 or less, and also preferably 200 or more, more preferably 230 or more, even more preferably 240 or more, particularly preferably 245 or more.
Swell can be measured by the method described in the Examples below.

The method for adjusting Swell is not particularly limited, but for example, it can be increased by reducing the amount of sulfur or vulcanization accelerator, increasing the amount of softener, reducing the amount of reinforcing agent, increasing the amount of plasticizer, or increasing the iodine value of the plasticizer, and it can be decreased by increasing the amount of sulfur or vulcanization accelerator, decreasing the amount of softener, increasing the amount of reinforcing agent, decreasing the amount of plasticizer, or decreasing the iodine value of the plasticizer.

(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), and acrylonitrile butadiene rubber (NBR). In addition, butyl rubber and fluororubber can be mentioned. These may be used alone or in combination of two or more. Among them, from the viewpoint of suppressing the deterioration of wet grip performance after aging, SBR, BR, and isoprene rubber are preferable, and SBR and BR are more preferable.

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 the SBR is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more. The styrene content is preferably 45% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less. By keeping the styrene content within the above range, it is possible to suppress the deterioration of wet grip performance after aging.
In this specification, the styrene content can be measured by ¹ H-NMR measurement.

The vinyl bond content of the SBR is preferably 3% by mass or more, more preferably 5% by mass or more, and even more preferably 7% by mass or more. The vinyl bond content is preferably 60% by mass or less, more preferably 45% by mass or less, even more preferably 25% by mass or less, particularly preferably 15% by mass or less, and most preferably 13% by mass or less. By keeping it within the above range, it tends to be possible to suppress the deterioration of wet grip performance after aging.
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 copolymer (hydrogenated SBR) can also be used as SBR.

The weight average molecular weight (Mw) of the hydrogenated SBR is preferably 100,000 or more, more preferably 120,000 or more, even more preferably 200,000 or more, particularly preferably 300,000 or more, and is preferably 1,000,000 or less, more preferably 600,000 or less, and even more preferably 400,000 or less. By keeping it within the above range, there is a tendency that deterioration of wet grip performance after aging can be suppressed.
The weight average molecular weight (Mw) can be determined by standard polystyrene conversion based on the measured 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). In the case of a polymer having a modifying group, the modifying group interacts with the silica gel of the column, making it impossible to obtain an accurate Mw, so that the Mw is measured before carrying out the modification treatment.

The hydrogenation rate of the hydrogenated SBR is preferably 75 mol% or more, more preferably 80 mol% or more, and even more preferably 90 mol% or more, and is preferably 98 mol% or less, more preferably 95 mol% or less, based on the total butadiene units before hydrogenation being 100 mol%. By keeping the hydrogenation rate within the above range, deterioration of wet grip performance after aging tends to be suppressed.
The hydrogenation rate can be calculated from the rate of decrease in the spectrum of unsaturated bonds obtained by measuring ¹ H-NMR.

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 70% by mass or more, and particularly preferably 80% by mass or more. There is no particular upper limit, and it may be 100% by mass. By keeping it within the above range, it tends to be possible to suppress the deterioration of wet grip performance after aging.

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 rubbers have been introduced. Hydrogenated butadiene polymer (hydrogenated BR) may also be used as the BR. The Mw and hydrogenation rate of the hydrogenated BR are preferably in the same range as those of the hydrogenated SBR.

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 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. There is no particular lower limit, and it may be 0% by mass. By keeping it within the above range, it tends to be possible to suppress the deterioration of wet grip performance after aging.

In the rubber composition, the total content of SBR and BR in 100% by mass of the rubber component is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more. There is no particular upper limit, and it may be 100% by mass. By keeping it within the above range, it tends to be possible to suppress the deterioration of wet grip performance after aging.

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 an isoprene-based rubber, the content of the 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 30% by mass or less, and even more preferably 20% by mass or less. By keeping the content within the above range, it tends to be possible to suppress the deterioration of wet grip performance after aging.

(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 ^350m2 /g or less, more preferably ^250m2 /g or less, and even more preferably ^200m2 /g or less. By keeping it within the above range, there is a tendency that the deterioration of wet grip performance after aging can be suppressed.
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 15 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, it tends to be possible to suppress the deterioration of wet grip performance after aging.

（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 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 that the dispersibility of silica is significantly improved. In addition, the steric hindrance caused by the long chain of the compound is large, so that re-aggregation of silica in the rubber component can be prevented. Furthermore, by adjusting the rubber composition so that Hsa/Hso×100≦107, that is, the hardness change before and after heat treatment is small, the deterioration of wet grip performance due to changes over time can be suppressed. Therefore, by using such a long-chain silane coupling agent, the deterioration of wet grip performance after aging can be suppressed.

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 that the deterioration of wet grip performance after aging can be suppressed. 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, there is a tendency that the deterioration of wet grip performance after aging can be suppressed.

(Other fillers)
The filler other than silica is not particularly limited, and materials known in the rubber field can be used, for example, inorganic fillers such as carbon black, calcium carbonate, talc, alumina, clay, aluminum hydroxide, aluminum oxide, mica, etc. Among them, carbon black is preferable.

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 60 parts by mass or more, and particularly preferably 65 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 130 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, there is a tendency that the deterioration of wet grip performance after aging can be suppressed.

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, and even more preferably 90% by mass or more, from the viewpoint of suppressing deterioration of wet grip performance after aging. There is no particular upper limit, but it is preferably 98% by mass or less, and more preferably 96% 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 Co., Ltd., Lion Co., Ltd., 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, there is a tendency that the deterioration of wet grip performance after aging can be suppressed.
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 200 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 carbon black content within the above range, there is a tendency that the deterioration of wet grip performance after aging can be suppressed.

(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.)).

In the rubber composition, the content of the plasticizer (total amount of 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 70 parts by mass or less, even more preferably 50 parts by mass or less, and particularly preferably 30 parts by mass or less. By keeping the content within the above range, it tends to be possible to suppress the deterioration of wet grip performance after aging.

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 and liquid polymers (liquid resins, liquid diene-based polymers, etc.). 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 70 parts by mass or less, even more preferably 50 parts by mass or less, and particularly preferably 30 parts by mass or less. By keeping the content within the above range, there is a tendency that the deterioration of wet grip performance after aging can be suppressed.

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 7 parts by mass or more, and even more preferably 10 parts by mass or more. The upper limit of the content is preferably 100 parts by mass or less, more preferably 70 parts by mass or less, even more preferably 50 parts by mass or less, and particularly preferably 30 parts by mass or less. By keeping the content within the above range, there is a tendency that the deterioration of wet grip performance after aging can be suppressed. The oil content also includes the oil contained in the oil extension oil.

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, acrylic resins, etc. Hydrogenated versions of these resins can also be used.

In the rubber composition, the content of the liquid resin is preferably 5 parts by mass or more, more preferably 7 parts by mass or more, and even more preferably 10 parts by mass or more. The upper limit of the content is preferably 100 parts by mass or less, more preferably 70 parts by mass or less, even more preferably 50 parts by mass or less, and particularly preferably 30 parts by mass or less. By keeping the content within the above range, there is a tendency that the deterioration of wet grip performance after aging can be suppressed.

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, and liquid farnesene butadiene copolymers that are liquid at 25°C. The ends or main chains of these may be modified with polar groups. Hydrogenated versions of these polymers may also be used.

In the rubber composition, the content of the liquid diene polymer is preferably 5 parts by mass or more, more preferably 7 parts by mass or more, and even more preferably 10 parts by mass or more. The upper limit of the content is preferably 100 parts by mass or less, more preferably 70 parts by mass or less, even more preferably 50 parts by mass or less, and particularly preferably 30 parts by mass or less. By keeping the content within the above range, there is a tendency that the deterioration of wet grip performance after aging can be suppressed.

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, and acrylic resins. The resins may also be hydrogenated. These may be used alone or in combination of two or more. Among these, aromatic vinyl polymers, petroleum resins, and terpene resins are preferred.

When the rubber composition contains the above resin, 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 200 parts by mass or less, more preferably 100 parts by mass or less, even more preferably 50 parts by mass or less, and particularly preferably 20 parts by mass or less. By keeping the content within the above range, there is a tendency that the deterioration of wet grip performance after aging can be suppressed.

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, there is a tendency that deterioration of wet grip performance after aging can be suppressed.
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, and hydrogenated versions of these resins. Of these, DCPD resins and hydrogenated DCPD resins are 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, 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.

(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-phenylene Examples of such antioxidants include p-phenylenediamine antioxidants such as diamines; 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 manufactured by Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinko Chemical Co., Ltd., and Flexis Co., Ltd.

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. The content of zinc oxide in the rubber composition 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.

Wax may be compounded in the rubber composition. The wax content in the rubber composition 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.

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 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-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. 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.
SBR: SBR1502 (non-oil extended, styrene content 25% by mass) manufactured by Zeon Corporation
Hydrogenated SBR 1: Production Example 1-1 below (hydrogenation rate 95 mol%, aromatic vinyl (styrene) unit 33 mass%, Mw 300,000)
Hydrogenated SBR2: Production Example 1-2 below (hydrogenation rate 80 mol%, aromatic vinyl (styrene) unit 33 mass%, Mw 300,000)
BR: Ubepol BR150B (cis content 97% by mass) manufactured by Ube Industries, Ltd.
NR: TSR20
Carbon black: Seast N220 (N ₂ SA 114 m ² /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 2 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.
Liquid resin: Ricon 340 manufactured by Cray Valley (C9 fraction/C5 fraction copolymer resin, glass transition temperature -35°C, Mw 1200, iodine value 113g/100g)
Wax: Ozoace wax manufactured by Nippon Seiro Co., Ltd. Antioxidant 6C: Nocrac 6C (N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine) (6PPD) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Antioxidant RD: Nocrac RD (poly(2,2,4-trimethyl-1,2-dihydroquinoline)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Stearic acid: Paulownia produced by NOF Corp. Zinc oxide: Zinc oxide type 2 produced by Mitsui Mining & Smelting Co., Ltd. Sulfur: Powdered sulfur produced by Tsurumi Chemical Industry Co., Ltd. Vulcanization accelerator: Noccela NS (N-tert-butyl-2-benzothiazylsulfenamide (TBBS)) produced by Ouchi Shinko Chemical Industry Co., Ltd.

(Production Example 1-1: Production of hydrogenated SBR1)
n-Hexane, styrene, 1,3-butadiene, TMEDA (N,N,N',N'-tetramethylethylenediamine), and n-butyllithium were added to a heat-resistant reaction vessel that had been thoroughly substituted with nitrogen, and the mixture was stirred at 50°C for 5 hours to carry out a polymerization reaction. Thereafter, the mixture was stirred for 20 minutes while hydrogen gas was supplied at a pressure of 0.4 MPa-Gauge, and reacted with the unreacted lithium at the polymer end to produce lithium hydride. The hydrogen gas supply pressure was set to 0.7 MPa-Gauge, the reaction temperature was set to 90°C, and hydrogenation was carried out using a catalyst mainly composed of titanocene dichloride. When the absorption of hydrogen reached an integrated amount that would result in the desired hydrogenation rate, the reaction temperature was set to room temperature, the hydrogen pressure was returned to normal pressure, and the mixture was removed from the reaction vessel, the reaction solution was stirred and poured into water, and the solvent was removed by steam stripping, to obtain hydrogenated SBR1. The polymerization conversion rate was nearly 100%.

(Production Example 1-2: Production of hydrogenated SBR2)
Hydrogenated SBR 2 was obtained in the same manner as in Production Example 1-1, except that the amounts of each chemical used and the cumulative amount of hydrogen absorption were changed. The polymerization conversion rate was nearly 100%.

(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 formulations shown in each table, materials other than sulfur and vulcanization accelerator were kneaded for 5 minutes using a 1.7 L Banbury mixer manufactured by Kobe Steel, Ltd., and discharged at 150° C. to obtain a kneaded product. Next, sulfur and vulcanization accelerator were added to the obtained kneaded product, and the mixture was kneaded for 5 minutes under the condition of 80° C. using an open roll to obtain an unvulcanized rubber composition.
The unvulcanized rubber composition was molded into a tread shape, and was laminated together with other tire components on a tire building machine to form an unvulcanized tire, which was then vulcanized at 170° C. for 10 minutes to obtain a test tire.

The following evaluations were performed using the above test tires. The results are shown in the tables. The reference comparative examples in Tables 1 and 2 are Comparative Examples 1-4 and 2-1, respectively. All measurements were performed within 180 days after the manufacture (vulcanization) of the above test tires.

(hardness)
For the test specimens cut out from the tread of the test tire, the hardness (JIS-A hardness) at room temperature (25°C) was measured (Hso) using a type A durometer in accordance with JIS K6253-3 (2012) "Vulcanized rubber and thermoplastic rubber - Determination of hardness - Part 3: Durometer hardness".
In addition, the test pieces after the measurement were heat-treated at 80° C. for 168 hours under conditions of an oxygen concentration of 20%, and then their hardness (Hsa) at room temperature was measured in the same manner.

(Sulfur content)
For a test specimen cut out from the tread of the test tire, the amount of sulfur (mass%) in the test specimen was calculated by the oxygen combustion flask method in accordance with JIS-K6233:2016 (TS).
In addition, a test piece cut from the tread of the test tire was set in a Soxhlet extractor, and acetone extraction was performed under the following conditions: test piece: 10 g or less, acetone: 150 ml, thermostatic bath temperature: 95 to 100° C., extraction time: 24 to 72 hours. The test piece after acetone extraction was placed in an oven and heated at 100° C. for 30 minutes to remove the solvent in the test piece, and then the amount of sulfur (mass%) in the test piece was calculated by the oxygen combustion flask method in accordance with JIS-K6233:2016 (AS).
In the measurements of TS and AS, test pieces of the same size were used.

(Volume change before and after immersion)
A test piece cut out from the tread of the test tire was immersed in toluene at 25° C. for 24 hours, and the change in volume (Swell (%)) before and after the immersion was measured.

<Wet grip performance (actual vehicle)>
Test tires (new) were fitted to all wheels of a domestically manufactured 2000cc automobile, and the braking distance on a wet road surface when the tires were new was measured. The test tires were also heat-treated in an oven at 80°C for two weeks, and the braking distance on a wet road surface after aging was measured.
A wet grip performance degradation suppression index was calculated from the braking distance of each test by the following calculation method, with the reference comparative example being set at 100. A larger index indicates that the degradation of wet grip performance after aging can be suppressed more effectively.
Wet grip performance maintenance rate = Braking distance of test tire (new) / Braking distance of test tire (aged) Wet grip performance degradation suppression index = Wet grip performance maintenance rate of each test tire / Wet grip performance maintenance rate of test tire of standard comparative example × 100

From each table, it can be seen that the examples containing a filler containing silica and a silane coupling agent containing an organosilicon compound containing an alkoxysilyl group and a sulfur atom, and in which the number of carbon atoms connecting the alkoxysilyl group and the sulfur atom is 6 or more, and in which Hsa/Hso x 100) is 107 or less, suppressed the deterioration of wet grip performance after aging.

Claims (13)

The ratio (Hsa/Hso×100) of the room temperature hardness (Hso) measured within 180 days after vulcanization to the room temperature hardness (Hsa) after heat treatment for 168 hours in an atmosphere at 80° C. after the room temperature hardness measurement is 107 or less,
The rubber component includes a styrene-butadiene rubber, a filler includes silica, and a silane coupling agent,
The silane coupling agent is a rubber composition for tires, which contains an organosilicon compound that contains an alkoxysilyl group and a sulfur atom, and in which the number of carbon atoms connecting the alkoxysilyl group and the sulfur atom is 6 or more,
the ratio (AS/TS×100) of the amount of sulfur after acetone extraction (AS) to the amount of sulfur before acetone extraction (TS) measured within 180 days after vulcanization is 75 or less;
A rubber composition for tires having a toluene swelling index (Swell) of 330 or less measured within 180 days after vulcanization . The ratio (Hsa/Hso×100) of the room temperature hardness (Hso) measured within 180 days after vulcanization to the room temperature hardness (Hsa) after heat treatment for 168 hours in an atmosphere at 80° C. after the room temperature hardness measurement is 107 or less,
The rubber component includes a styrene-butadiene rubber, a filler includes silica, and a silane coupling agent,
The silane coupling agent is a rubber composition for tires, which contains an organosilicon compound that contains an alkoxysilyl group and a sulfur atom, and in which the number of carbon atoms connecting the alkoxysilyl group and the sulfur atom is 6 or more,
A rubber composition for tires having a sulfur content (TS) before acetone extraction of 1.00 to 1.60 mass %, and a sulfur content (AS) after acetone extraction measured within 180 days after vulcanization of 0.60 to 1.30 mass %. 3. The rubber composition for tires according to claim 1, wherein Hsa/Hso×100 is 105 or less. 4. The rubber composition for tires according to claim 1, wherein Hso is 55-70 and Hsa is 57-72. The rubber composition for tires according to any one of claims 1 to 4 , wherein the content of the silica is 5 to 150 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 the silica. 6. The rubber composition for tires according to claim 1 , wherein the silica content in 100% by mass of the filler is 50% by mass or more. 7. The rubber composition for tires according to claim 1 , wherein the content of the carbon black is 1 to 10 parts by mass based on 100 parts by mass of the rubber component. The rubber composition for tires according to any one of claims 1 to 7 , wherein the content of the styrene-butadiene rubber in 100% by mass of the rubber component is 50% by mass or more. the ratio (AS/TS×100) of the amount of sulfur after acetone extraction (AS) to the amount of sulfur before acetone extraction (TS) measured within 180 days after vulcanization is 75 or less;
3. The rubber composition for tires according to claim 2 , which has a toluene swelling index (Swell) of 330 or less measured within 180 days after vulcanization. 10. The rubber composition for tires according to claim 1 , wherein AS/TS×100 is 70 or less. 2. The rubber composition for tires according to claim 1 , wherein TS is from 1.00 to 1.60 mass % and AS is from 0.60 to 1.30 mass %. The rubber composition for tires according to any one of claims 1 to 11 , wherein the content of sulfur per 100 parts by mass of the rubber component is 5.0 parts by mass or less. A tire having a tread made of the rubber composition according to any one of claims 1 to 12 .