JP2024078409A - tire - Google Patents

Abstract

[Problem] To provide a tire that is excellent in overall performance in terms of abrasion resistance, wet grip performance, and bleed resistance. [Solution] A tire has a tread made of a rubber composition containing a rubber component and a branched conjugated diene polymer, the branched conjugated diene polymer being a copolymer having at least branched conjugated diene, butadiene, and styrene as structural units, and A defined as A=42.9/√α+0.14 (wherein α represents the weight average molecular weight of the branched conjugated diene polymer) and a groove area ratio S [%] in the contact surface of the tread satisfy the following formulas (1) and (2): Formula (1) 0.25<A≦1.50 Formula (2) A×S≦27.0 [Selected Figure] None

Description

The present invention relates to a tire.

Various performance characteristics are required of tires, but in recent years, there has been a particular demand for balanced improvements in wear resistance, wet grip performance, and bleed resistance.

The present invention aims to solve the above problems and provide a tire that has excellent overall performance in terms of wear resistance, wet grip performance, and bleed resistance.

The present invention provides a tire having a tread made of a rubber composition containing a rubber component and a branched conjugated diene-based polymer,
The branched conjugated diene polymer is a copolymer having at least a branched conjugated diene, a butadiene, and a styrene as structural units,
The tire has A defined as A=42.9/√α+0.14 (wherein α represents the weight-average molecular weight of the branched conjugated diene polymer), and a groove area ratio S [%] in the contact surface of the tread, which satisfy the following formulas (1) and (2):
Formula (1)
0.25<A≦1.50
Equation (2)
A×S≦27.0

According to the present invention, a tire is provided that has a tread made of a rubber composition containing a rubber component and a branched conjugated diene polymer, the branched conjugated diene polymer being a copolymer having at least branched conjugated diene, butadiene and styrene as structural units, and that satisfies the above formulas (1) and (2). As a result, a tire that has excellent overall performance in terms of abrasion resistance, wet grip performance and bleed resistance can be provided.

1 is a cross-sectional view taken along a meridian direction of a tire 1 according to an embodiment of the present invention. 1 is a cross-sectional view of a tread 2 of a tire 1 taken along a plane including the tire axis.

〔tire〕
The present invention provides a tire having a tread made of a rubber composition containing a rubber component and a branched conjugated diene-based polymer, wherein the branched conjugated diene-based polymer is a copolymer having at least branched conjugated diene, butadiene and styrene as constituent units, and satisfies formula (1) "0.25<A≦1.50" and formula (2) "A×S≦27.0".

The mechanism by which the above-mentioned effects are obtained is not clear, but is presumed to be as follows.
The branched conjugated diene polymer having at least branched conjugated diene, butadiene and styrene as structural units improves compatibility with rubber components such as butadiene rubber and styrene-butadiene rubber, and in particular, by adjusting the weight average molecular weight of the branched conjugated diene polymer to fall within a predetermined range by adjusting the weight average molecular weight to fall within the predetermined range, the number of single domain phases is reduced, and compatibility is further improved. The reduction in the number of single domain phases suppresses bleeding of the branched conjugated diene polymer, and improves bleeding resistance and wear resistance.
The branched conjugated diene polymer having styrene as a structural unit provides a high Tg and improves wet grip performance.
By adjusting A and the groove area ratio S [%] to satisfy the formula (2) "A × S ≦ 27.0" and decreasing the weight average molecular weight of the branched conjugated diene polymer while increasing the contact area of the tread (reducing the groove area ratio), grip performance is ensured, wear is suppressed, and wet grip performance and wear resistance are improved.
It is presumed that the above results in improved overall performance in terms of abrasion resistance, wet grip performance and bleed resistance.

In this way, the tire is configured to satisfy formula (1) "0.25<A≦1.50" and formula (2) "A×S≦27.0", thereby solving the problem (objective) of improving the overall performance of wear resistance, wet grip performance, and bleed resistance. In other words, these formulas do not define the problem (objective), and the object of the present application is to improve the overall performance of wear resistance, wet grip performance, and bleed resistance, and the tire is configured to satisfy these parameters as a means to achieve this.

The formulas (1) and (2) can be adjusted to be satisfied by appropriately selecting the weight average molecular weight of the branched conjugated diene polymer used and the groove area ratio on the contact surface of the tread.

In the tire, the tread is made of a rubber composition containing a rubber component and a branched conjugated diene polymer.

(Rubber component)
The rubber composition includes a rubber component.
The weight average molecular weight of the rubber component is preferably 50,000 or more, more preferably 150,000 or more, and even more preferably 200,000 or more, and is preferably 2,000,000 or less, more preferably 1,500,000 or less, and even more preferably 1,000,000 or less. Within the above ranges, the effect tends to be better obtained.

In this specification, the weight average molecular weight (Mw) of the rubber component can be determined by converting it into standard polystyrene 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).

The rubber component is not particularly limited, and any rubber known in the field of tires can be used. Examples of the rubber include diene rubbers such as isoprene rubber, butadiene rubber (BR), styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), chloroprene rubber (CR), butyl rubber (IIR), and styrene-isoprene-butadiene copolymer rubber (SIBR). These may be used alone or in combination of two or more. Among them, from the viewpoint of obtaining a better effect, it is preferable to use any one of BR, SBR, and isoprene rubber, it is more preferable to use any one of BR and SBR, and it is even more preferable to use both BR and SBR.
The mechanism by which such an effect is obtained by using at least one of isoprene-based rubber, butadiene rubber, and styrene-butadiene rubber is not clear, but it is presumed that the good abrasion resistance and wet grip performance inherent to these rubbers are exhibited, and that the use of these rubbers in combination with a branched conjugated diene-based polymer further exhibits the effect of preventing bleeding, thereby improving the overall performance of the abrasion resistance, wet grip performance, and bleeding resistance.

The BR is not particularly limited, and may be any of those commonly used in the tire industry, such as BR with a high cis content, such as BR1220 manufactured by Zeon Co., Ltd., BR150B manufactured by Ube Industries, Ltd., and BR1280 manufactured by LG Chem, BR containing 1,2-syndiotactic polybutadiene crystals (SPB), such as VCR412 and VCR617 manufactured by Ube Industries, and butadiene rubber synthesized using a rare earth element catalyst (rare earth BR). These may be used alone or in combination of two or more types. In addition, hydrogenated butadiene polymer (hydrogenated BR) may also be used as the BR.

The cis amount (cis content) of BR is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, still more preferably 95% by mass or more, and is preferably 99% by mass or less, more preferably 98% by mass or less, and even more preferably 97% by mass or less. When it is within the above range, the effect tends to be more favorably obtained.
The cis amount of BR can be measured by infrared absorption spectroscopy.
The cis content of BR means the cis content of the BR when there is one type of BR, and means the average cis content when there are multiple types of BR.
The average cis content of BR can be calculated by {Σ(content of each BR × cis content of each BR)}/total content of all BRs. For example, when 100% by mass of the rubber component contains 20% by mass of BR with a cis content of 90% by mass and 10% by mass of BR with a cis content of 40% by mass, the average cis content of BR is 73.3% by mass (=(20×90+10×40)/(20+10)).

When the rubber composition contains BR, the content of BR in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, and is preferably 60% by mass or less, more preferably 50% by mass or less, even more preferably 40% by mass or less. Within the above range, the effect tends to be better obtained.

The SBR is not particularly limited, and examples of the SBR that can be used include emulsion-polymerized styrene-butadiene rubber (E-SBR) and solution-polymerized styrene-butadiene rubber (S-SBR). Commercially available products include those from Sumitomo Chemical Co., Ltd., JSR Corporation, Asahi Kasei Corporation, and Nippon Zeon Co., Ltd. In addition, hydrogenated styrene-butadiene copolymers (hydrogenated SBR) can also be used as SBR.

The styrene content of the SBR is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and even more preferably 19.4% by mass or more, and is preferably 60% by mass or less, more preferably 55% by mass or less, and even more preferably 50% by mass or less. Within the above ranges, the effect tends to be better obtained.
In this specification, the styrene content of SBR is calculated by ¹ H-NMR measurement.

In particular, for summer tires, the styrene content of the SBR is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 25% by mass or more, and is preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less. If it is within the above range, the effect tends to be better.

In particular, for winter tires, 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, and is preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less. Within the above ranges, the effect tends to be better.

The vinyl content of the SBR is preferably 15% by mass or more, more preferably 20% by mass or more, and even more preferably 24% by mass or more, and is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 35% by mass or less. Within the above ranges, the effect tends to be better obtained.
In this specification, the vinyl content (amount of 1,2-bonded butadiene units) of SBR can be measured by infrared absorption spectroscopy.

Here, the styrene content of the SBR mentioned above means the styrene content of the SBR when there is one type of SBR, and means the average styrene content when there are multiple types of SBR.
The average styrene amount of SBR can be calculated by {Σ(content of each SBR × styrene amount of each SBR)}/total content of all SBRs. For example, when 100% by mass of the rubber component contains 85% by mass of SBR with a styrene amount of 40% by mass and 5% by mass of SBR with a styrene amount of 25% by mass, the average styrene amount of the SBR is 39.2% by mass (=(85×40+5×25)/(85+5)).

Also, for example, if the rubber component consists of 70 mass% SBR (A) (styrene amount 35 mass%, Mw 650,000), 10 mass% SBR (B) (styrene amount 40 mass%, Mw 950,000), 10 mass% NR, and 10 mass% BR, the content ratios of SBR (A) and (B) are 0.875 (= 70/(70 + 10)) and 0.125 (= 10/(70 + 10)), respectively, and the average molecular weight of SBR is 687,500 (= 0.875 x 650,000 + 0.125 x 950,000).
The styrene content of SBR is 35.86 mass% (= {70/(70+10)×350×650,000+10/(70+10)×400×950,000}/687,500).

The vinyl content of SBR is the proportion of vinyl bonds when the total mass of the butadiene parts in SBR is taken as 100 (unit: mass %), and is expressed as vinyl content [mass %] + cis content [mass %] + trans content [mass %] = 100 [mass %]. When there is one type of SBR, it means the vinyl content of that SBR, and when there are multiple types of SBR, it means the average vinyl content.
The average vinyl content of the SBR can be calculated by Σ{content of each SBR×(100[mass%]−styrene content of each SBR[mass%])×vinyl content of each SBR[mass%]}/Σ{content of each SBR×(100[mass%]−styrene content of each SBR[mass%])}. For example, in 100 parts by mass of the rubber component, 75 parts by mass of SBR having a styrene content of 40% by mass and a vinyl content of 30% by mass and a styrene content of 25% by mass are used. , vinyl amount: When 15 parts by mass of 20% by mass SBR is used and the remaining 10 parts by mass is a part other than SBR, the average vinyl amount of the SBR is 28% by mass (={75 x (100[% by mass] - 40[% by mass]) x 30[% by mass] + 15 x (100[% by mass] - 25[% by mass]) x 20[% by mass]} / {75 x (100[% by mass] - 40[% by mass]) + 15 x (100[% by mass] - 25[% by mass])}.

When the rubber composition contains SBR, the content of SBR in 100% by mass of the rubber component is preferably 10% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, and particularly preferably 60% by mass or more, and is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less. Within the above range, the effect tends to be better obtained.

The rubber composition has a total content of BR and SBR of preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more, or may be 100% by mass, based on 100% by mass of the rubber component. When the total content is within the above range, the effect tends to be better.

In particular, in the case of summer tires, the total content of BR and SBR in the rubber composition is preferably 40% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, and may be 100% by mass, based on 100% by mass of the rubber component. When it is within the above range, the effect tends to be better.

In particular, in the case of winter tires, the total content of BR and SBR in the rubber composition is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, and may be 100% by mass, based on 100% by mass of the rubber component. When it is within the above range, the effect tends to be better.

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 tire industry. IR is not particularly limited, and can be, for example, IR2200, etc., which are common in the tire 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. Of these, NR is preferred.

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 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and is preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 25% by mass or less. Within the above range, the effect tends to be better obtained.

The rubber component may be an extended rubber extended with a plasticizer component such as oil, resin, or liquid polymer. These may be used alone or in combination of two or more. Examples of plasticizers used in extended rubber include those described below. The amount of plasticizer in the extended rubber is not particularly limited, but is usually about 10 to 50 parts by mass per 100 parts by mass of rubber solids.

The rubber component may be modified to introduce a functional group that interacts with a filler such as silica.
Examples of the functional group include silicon-containing groups (-SiR ₃ (R are the same or different and are hydrogen, a hydroxyl group, a hydrocarbon group, an alkoxy group, etc.), amino groups, amide 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. Of these, silicon-containing groups are preferred, and -SiR ₃ (R are the same or different and are hydrogen, a hydroxyl group, a hydrocarbon group (preferably a hydrocarbon group having 1 to 6 carbon atoms (more preferably an alkyl group having 1 to 6 carbon atoms)) or an alkoxy group (preferably an alkoxy group having 1 to 6 carbon atoms)), and at least one of R is a hydroxyl group) is more preferred.

Specific examples of compounds (modifiers) that introduce the above functional groups include 2-dimethylaminoethyltrimethoxysilane, 3-dimethylaminopropyltrimethoxysilane, 2-dimethylaminoethyltriethoxysilane, 3-dimethylaminopropyltriethoxysilane, 2-diethylaminoethyltrimethoxysilane, 3-diethylaminopropyltrimethoxysilane, 2-diethylaminoethyltriethoxysilane, 3-diethylaminopropyltriethoxysilane, etc.

(Branched conjugated diene polymer)
The rubber composition contains a branched conjugated diene polymer having at least a branched conjugated diene, butadiene and styrene as structural units. The branched conjugated diene polymer may be used alone or in combination of two or more.

In the present invention, a branched conjugated diene refers to a compound having a branched structure with a conjugated diene structure in which a double bond is separated by one single bond, and may be a compound that further has or does not have another double bond.

Examples of branched conjugated dienes constituting the branched conjugated diene polymer include 2,3-dimethyl-1,3-butadiene, 2,4-dimethyl-1,3-pentadiene, 3-methyl-1,3-pentadiene, farnesene, and myrcene. Among these, farnesene and myrcene are preferred, and farnesene is more preferred, from the viewpoint of obtaining better effects. One or more branched conjugated dienes can be used.
The mechanism by which the use of farnesene provides such an effect is not clear, but it is presumed that the improved compatibility with rubber improves abrasion resistance and wet grip performance while also suppressing bleeding, thereby improving the overall performance of abrasion resistance, wet grip performance, and bleed resistance.

Farnesene includes isomers such as α-farnesene ((3E,7E)-3,7,11-trimethyl-1,3,6,10-dodecatetraene) and β-farnesene (7,11-dimethyl-3-methylene-1,6,10-dodecatriene). Among them, (E)-β-farnesene (7,11-dimethyl-3-methylene-1,6,10-dodecatriene) having the following structure is preferred.

Myrcene includes both α-myrcene (2-methyl-6-methyleneocta-1,7-diene) and β-myrcene, with β-myrcene (7-methyl-3-methyleneocta-1,6-diene) having the following structure being particularly preferred.

As the butadiene that constitutes the branched conjugated diene polymer, 1,3-butadiene is preferable.

In addition, branched conjugated diene polymers can be used to replace plasticizers such as oils that are conventionally used.

The branched conjugated diene polymer is not particularly limited as long as it is a copolymer having at least branched conjugated diene, butadiene, and styrene as constituent units. Among them, from the viewpoint of obtaining a better effect, a copolymer having at least farnesene, butadiene, and styrene as constituent units, or a copolymer having at least myrcene, butadiene, and styrene as constituent units is preferable, and a copolymer of farnesene, butadiene, and styrene, or a copolymer of myrcene, butadiene, and styrene is more preferable.

The weight average molecular weight (Mw) of the branched conjugated diene polymer is preferably 1000 or more, more preferably 4000 or more, even more preferably 5000 or more, still more preferably 9000 or more, particularly preferably 10000 or more, and is preferably 100000 or less, more preferably 30000 or less, even more preferably 25000 or less, still more preferably 20000 or less, still more preferably 15000 or less, and still more preferably 12000 or less. Within the above ranges, the effect tends to be better obtained.
The mechanism by which such an effect is obtained by adjusting the Mw within a specified range is not clear, but it is presumed that compatibility with the rubber is ensured to ensure good abrasion resistance and wet grip performance, and that a Mw within the specified range sufficiently suppresses bleeding, thereby improving the overall performance of abrasion resistance, wet grip performance, and bleed resistance.
In this specification, the weight average molecular weight (Mw) of the branched conjugated diene polymer can be determined in terms of standard polystyrene based on a measurement value obtained by gel permeation chromatography (GPC) (GPC apparatus "HLC-8320" manufactured by Tosoh Corporation, detector: differential refractometer, column: column "TSKgelSuperHZM-M" manufactured by Tosoh Corporation).

In the branched conjugated diene polymer, the content of the branched conjugated diene in 100% by mass of the monomer component (amount of branched conjugated diene units in 100% by mass of the branched conjugated diene polymer) is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, and is preferably 80% by mass or less, more preferably 70% by mass or less, even more preferably 60% by mass or less. Within the above range, the effect tends to be better obtained.

In the branched conjugated diene polymer, the butadiene content in 100% by mass of the monomer component (butadiene unit amount in 100% by mass of the branched conjugated diene polymer) is preferably 5% by mass or more, more preferably 18% by mass or more, even more preferably 20% by mass or more, even more preferably 25% by mass or more, even more preferably 30% by mass or more, and is preferably 70% by mass or less, more preferably 50% by mass or less, even more preferably 40% by mass or less, even more preferably 35% by mass or less. Within the above range, the effect tends to be better obtained.

In the branched conjugated diene polymer, the styrene content in 100% by mass of the monomer component (amount of styrene units in 100% by mass of the branched conjugated diene polymer) is preferably 2% by mass or more, more preferably 5% by mass or more, even more preferably 8% by mass or more, even more preferably 10% by mass or more, and is preferably 40% by mass or less, more preferably 35% by mass or less, even more preferably 30% by mass or less, even more preferably 25% by mass or less, and even more preferably 20% by mass or less. Within the above range, the effect tends to be better obtained.

In the branched conjugated diene polymer, it is desirable that the butadiene content (the amount of butadiene units (mass %) in 100 mass % of the branched conjugated diene polymer) and the styrene content (the amount of styrene units (mass %) in 100 mass % of the branched conjugated diene polymer) satisfy the following formula:
0.40≦0.013×butadiene unit amount+0.071×styrene unit amount≦2.70
The lower limit is preferably 0.70 or more, more preferably 0.80 or more, even more preferably 0.90 or more, and particularly preferably 0.97 or more, and the upper limit is preferably 2.50 or less, more preferably 2.30 or less, even more preferably 2.23 or less, still more preferably 2.20 or less, and still more preferably 1.68 or less. Within the above ranges, the effect tends to be better obtained.
The mechanism by which such an effect is obtained by setting 0.013 x the amount of butadiene units + 0.071 x the amount of styrene units in a predetermined range is not clear, but it is presumed that the compatibility with the rubber component is improved, the abrasion resistance is improved, and the bleed resistance is improved by reducing the number of single domain phases. Furthermore, the styrene achieves a high Tg, improving wet grip performance, and thereby improving the overall abrasion resistance, wet grip performance, and bleed resistance.

The synthesis of branched conjugated diene polymers can be carried out by known methods. For example, in the case of synthesis by anionic polymerization, hexane, branched conjugated diene, butadiene, styrene, sec-butyllithium, and other vinyl monomers as necessary are charged into a pressure-resistant vessel that has been fully substituted with nitrogen, and then the mixture is heated and stirred for several hours. The resulting polymerization solution is quenched and then vacuum dried to obtain a branched conjugated diene polymer.

In the polymerization for preparing the branched conjugated diene polymer, the polymerization procedure is not particularly limited. For example, all monomers may be randomly copolymerized at once, or specific monomers (e.g., only branched conjugated diene monomers, only butadiene monomers, only styrene monomers, etc.) may be polymerized in advance and the remaining monomers may be added and copolymerized, or specific monomers may be polymerized in advance and block copolymerized.

In the rubber composition, the content of the branched conjugated diene polymer is preferably 3 parts by mass or more, more preferably 6 parts by mass or more, and even more preferably 8 parts by mass or more, per 100 parts by mass of the rubber component, and is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less. Within the above range, the effect tends to be better obtained.

(Filling material)
In order to obtain a better effect, it is preferable that the rubber composition contains a filler.
In the rubber composition, the content of the filler is preferably 30 parts by mass or more, more preferably 70 parts by mass or more, even more preferably 100 parts by mass or more, particularly preferably 120 parts by mass or more, and is preferably 250 parts by mass or less, more preferably 200 parts by mass or less, even more preferably 170 parts by mass or less, particularly preferably 150 parts by mass or less, based on 100 parts by mass of the rubber component. Within the above ranges, the effect tends to be better obtained.
The mechanism by which such an effect is obtained by setting the amount of filler within a predetermined range is not clear, but it is presumed that the sufficient reinforcing properties of the rubber are exerted, thereby improving abrasion resistance and wet grip performance, thereby improving the overall performance of abrasion resistance, wet grip performance and bleed resistance.

As the filler, materials known in the rubber field can be used, and examples thereof include inorganic fillers such as silica, carbon black, calcium carbonate, talc, alumina, clay, aluminum hydroxide, aluminum oxide, mica, biochar, regenerated carbon black, etc. Among these, carbon black and silica are preferred from the viewpoint of obtaining better effects.
The mechanism by which such effects are obtained by using silica and carbon black is not clear, but it is presumed that by using them in combination to fully exert their reinforcing properties on the rubber, abrasion resistance and wet grip performance are exerted, thereby improving the overall performance of abrasion resistance, wet grip performance and bleed resistance.

The carbon black is not particularly limited, but examples thereof 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 others. In addition to the carbon black made from mineral oils and the like, carbon black made from biomass materials such as lignin may also be used. These may be used alone or in combination of two or more types.

The nitrogen adsorption specific surface area ( _N2SA ) of carbon black is preferably ³⁰ m2/g or more, more preferably ³⁵ m2/g or more, and even more preferably ⁴⁰ m2/g or more, and is preferably ²⁰⁰ m2/g or less, more preferably ¹⁷⁰ m2/g or less, even more preferably ¹⁵⁰ m2/g or less, and even more preferably 148 ^m2 /g or less. If it is within the above range, the effect tends to be better.
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 5 parts by mass or more, more preferably 8 parts by mass or more, and even more preferably 10 parts by mass or more, per 100 parts by mass of the rubber component, and is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 30 parts by mass or less. Within the above range, the effect tends to be better obtained.

Examples of silica include dry process silica (anhydrous silica) and wet process silica (hydrated silica). Of these, 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. Silica made from biomass materials such as rice husks can also be used. These may be used alone or in combination of two or more.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 50 m ² /g or more, more preferably 100 m ² /g or more, even more preferably 150 m ² /g or more, and particularly preferably 170 m ² /g or more. The upper limit of the N ₂ SA of silica is not particularly limited, but is preferably 350 m ² /g or less, more preferably 300 m ² /g or less, and even more preferably 250 m ² /g or less. Within the above range, the effect tends to be better obtained. In addition, when multiple types of silica are used, it is desirable that the total N ₂ SA of the silica used is within the above range. It is also desirable that the N ₂ SA of each silica of the multiple types of silica blended is within the above range.
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 20 parts by mass or more, more preferably 60 parts by mass or more, even more preferably 90 parts by mass or more, and particularly preferably 110 parts by mass or more, per 100 parts by mass of the rubber component, and is preferably 250 parts by mass or less, more preferably 200 parts by mass or less, even more preferably 160 parts by mass or less, and particularly preferably 140 parts by mass or less. Within the above range, the effect tends to be better obtained.

(Silane coupling agent)
When the rubber composition contains silica, it is preferable that the rubber composition further contains a silane coupling agent.
The silane coupling agent is not particularly limited, and those known in the rubber field can be used. For example, 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, bis(3-trimethoxysilylpropyl)disulfide, bis(2-trimethoxysilylethyl)disulfide, bis(4-trimethoxysilylbutyl)disulfide, 3-trimethoxysilylpropyl-N, Examples of such silylsilanes include sulfide-based silylsilanes such as N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, and 3-triethoxysilylpropyl methacrylate monosulfide; mercapto-based silylsilanes such as 3-mercaptopropyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, and Momentive's NXT and NXT-Z; vinyl-based silylsilanes such as vinyltriethoxysilane and vinyltrimethoxysilane; amino-based silylsilanes such as 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane; glycidoxy-based silylsilanes such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro-based silylsilanes such as 3-nitropropyltriethoxysilane and 3-nitropropyltriethoxysilane; and chloro-based silylsilanes such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. Among them, sulfide-based and mercapto-based are preferred, and mercapto-based are more preferred. Commercially available products include those from Degussa, Momentive, Shin-Etsu Silicone Co., Ltd., Tokyo Chemical Industry Co., Ltd., Azumax Co., Ltd., and Dow Corning Toray Co., Ltd. These may be used alone or in combination of two or more.
The mechanism by which such an effect is obtained by using a mercapto-based silane coupling agent is not clear, but it is presumed that the reinforcing effect of the rubber composition containing silica is fully exerted, thereby improving abrasion resistance and wet grip performance, thereby improving the overall performance of abrasion resistance, wet grip performance and bleed resistance.

As the mercapto-based silane coupling agent, in addition to compounds having a mercapto group, compounds having a structure in which the mercapto group is protected by a protecting group (for example, a compound represented by the following formula (S1)) can also be used.

（式中、Ｒ^１００１は－Ｃｌ、－Ｂｒ、－ＯＲ^１００６、－Ｏ（Ｏ＝）ＣＲ^１００６、－ＯＮ＝ＣＲ^１００６Ｒ^１００７、－ＮＲ^１００６Ｒ^１００７及び－（ＯＳｉＲ^１００６Ｒ^１００７）_ｈ（ＯＳｉＲ^１００６Ｒ^１００７Ｒ^１００８）から選択される一価の基（Ｒ^１００６、Ｒ^１００７及びＲ^１００８は同一でも異なっていても良く、各々水素原子又は炭素数１～１８の一価の炭化水素基であり、ｈは平均値が１～４である。）であり、Ｒ^１００２はＲ^１００１、水素原子又は炭素数１～１８の一価の炭化水素基、Ｒ^１００３は－［Ｏ（Ｒ^１００９Ｏ）_ｊ］－基（Ｒ^１００９は炭素数１～１８のアルキレン基、ｊは１～４の整数である。）、Ｒ^１００４は炭素数１～１８の二価の炭化水素基、Ｒ^１００５は炭素数１～１８の一価の炭化水素基を示し、ｘ、ｙ及びｚは、ｘ＋ｙ＋２ｚ＝３、０≦ｘ≦３、０≦ｙ≦２、０≦ｚ≦１の関係を満たす数である。）

（式中、ｖは０以上の整数、ｗは１以上の整数である。Ｒ^１１は水素、ハロゲン、分岐若しくは非分岐の炭素数１～３０のアルキル基、分岐若しくは非分岐の炭素数２～３０のアルケニル基、分岐若しくは非分岐の炭素数２～３０のアルキニル基、又は該アルキル基の末端の水素が水酸基若しくはカルボキシル基で置換されたものを示す。Ｒ^１２は分岐若しくは非分岐の炭素数１～３０のアルキレン基、分岐若しくは非分岐の炭素数２～３０のアルケニレン基、又は分岐若しくは非分岐の炭素数２～３０のアルキニレン基を示す。Ｒ^１１とＲ^１２とで環構造を形成してもよい。） Particularly suitable mercapto-based silane coupling agents include silane coupling agents represented by the following formula (S1) and silane coupling agents containing a bond unit A represented by the following formula (I) and a bond unit B represented by the following formula (II).

(In the formula, R ¹⁰⁰¹ is a monovalent group selected from -Cl, -Br, -OR ¹⁰⁰⁶ , -O(O═)CR ¹⁰⁰⁶ , -ON═CR ¹⁰⁰⁶ R ¹⁰⁰⁷ , -NR ¹⁰⁰⁶ R ¹⁰⁰⁷ and -(OSiR ¹⁰⁰⁶ R ¹⁰⁰⁷ ) _h (OSiR ¹⁰⁰⁶ R ¹⁰⁰⁷ R ¹⁰⁰⁸ ) (R ¹⁰⁰⁶ , R ¹⁰⁰⁷ and R ¹⁰⁰⁸ may be the same or different and each is a hydrogen atom or a monovalent hydrocarbon group having 1 to 18 carbon atoms, and h has an average value of 1 to 4), R ¹⁰⁰² is R ¹⁰⁰¹ , a hydrogen atom or a monovalent hydrocarbon group having 1 to 18 carbon atoms, R ¹⁰⁰³ is a -[O(R ¹⁰⁰⁹ O) _j ]- group (R R ¹⁰⁰⁹ is an alkylene group having 1 to 18 carbon atoms, j is an integer from 1 to 4. R ¹⁰⁰⁴ is a divalent hydrocarbon group having 1 to 18 carbon atoms, R ¹⁰⁰⁵ is a monovalent hydrocarbon group having 1 to 18 carbon atoms, and x, y, and z are numbers that satisfy the relationship of x+y+2z=3, 0≦x≦3, 0≦y≦2, and 0≦z≦1.

(In the formula, v is an integer of 0 or more, and w is an integer of 1 or more. R ¹¹ represents hydrogen, halogen, a branched or unbranched alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenyl group having 2 to 30 carbon atoms, a branched or unbranched alkynyl group having 2 to 30 carbon atoms, or an alkyl group in which the terminal hydrogen atom is substituted with a hydroxyl group or a carboxyl group. R ¹² represents a branched or unbranched alkylene group having 1 to 30 carbon atoms, a branched or unbranched alkenylene group having 2 to 30 carbon atoms, or a branched or unbranched alkynylene group having 2 to 30 carbon atoms. R ¹¹ and R ¹² may form a ring structure.)

In formula (S1), R ¹⁰⁰⁵ , R ¹⁰⁰⁶ , R ¹⁰⁰⁷ and R ¹⁰⁰⁸ are each preferably independently a group selected from the group consisting of a linear, cyclic or branched alkyl group, alkenyl group, aryl group and aralkyl group having 1 to 18 carbon atoms. When R ¹⁰⁰² is a monovalent hydrocarbon group having 1 to 18 carbon atoms, it is preferably a group selected from the group consisting of a linear, cyclic or branched alkyl group, alkenyl group, aryl group and aralkyl group. R ¹⁰⁰⁹ is preferably a linear, cyclic or branched alkylene group, particularly preferably a linear one. Examples of R ¹⁰⁰⁴ include an alkylene group having 1 to 18 carbon atoms, an alkenylene group having 2 to 18 carbon atoms, a cycloalkylene group having 5 to 18 carbon atoms, a cycloalkylalkylene group having 6 to 18 carbon atoms, an arylene group having 6 to 18 carbon atoms, and an aralkylene group having 7 to 18 carbon atoms. The alkylene group and the alkenylene group may be either linear or branched, and the cycloalkylene group, the cycloalkylalkylene group, the arylene group, and the aralkylene group may have a functional group such as a lower alkyl group on the ring. As this R ¹⁰⁰⁴ , an alkylene group having 1 to 6 carbon atoms is preferable, and a linear alkylene group, such as a methylene group, an ethylene group, a trimethylene group, a tetramethylene group, a pentamethylene group, or a hexamethylene group, is particularly preferable.

Specific examples of R ¹⁰⁰² , R ¹⁰⁰⁵ , R ¹⁰⁰⁶ , R ¹⁰⁰⁷ and R ¹⁰⁰⁸ in formula (S1) 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, a tert-butyl group, a pentyl group, a hexyl group, an octyl group, a decyl group, a dodecyl group, a cyclopentyl group, a cyclohexyl group, a vinyl group, a propenyl group, an allyl group, a hexenyl group, an octenyl group, a cyclopentenyl group, a cyclohexenyl group, a phenyl group, a tolyl group, a xylyl group, a naphthyl group, a benzyl group, a phenethyl group and a naphthylmethyl group.
Examples of R ¹⁰⁰⁹ in formula (S1) include linear alkylene groups such as methylene, ethylene, n-propylene, n-butylene, and hexylene groups, and branched alkylene groups such as isopropylene, isobutylene, and 2-methylpropylene groups.

Specific examples of silane coupling agents represented by formula (S1) include 3-hexanoylthiopropyltriethoxysilane, 3-octanoylthiopropyltriethoxysilane, 3-decanoylthiopropyltriethoxysilane, 3-lauroylthiopropyltriethoxysilane, 2-hexanoylthioethyltriethoxysilane, 2-octanoylthioethyltriethoxysilane, 2-decanoylthioethyltriethoxysilane, 2-lauroylthioethyltriethoxysilane, 3-hexanoylthiopropyltrimethoxysilane, 3-octanoylthiopropyltrimethoxysilane, 3-decanoylthiopropyltrimethoxysilane, 3-lauroylthiopropyltrimethoxysilane, 2-hexanoylthioethyltrimethoxysilane, 2-octanoylthioethyltrimethoxysilane, 2-decanoylthioethyltrimethoxysilane, 2-lauroylthioethyltrimethoxysilane, and the like. These may be used alone or in combination of two or more. Of these, 3-octanoylthiopropyltriethoxysilane is particularly preferred.

In the silane coupling agent comprising the bond unit A represented by formula (I) and the bond unit B represented by formula (II), the content of the bond unit A is preferably 30 mol% or more, more preferably 50 mol% or more, and preferably 99 mol% or less, more preferably 90 mol% or less.The content of the bond unit B is preferably 1 mol% or more, more preferably 5 mol% or more, even more preferably 10 mol% or more, and preferably 70 mol% or less, more preferably 65 mol% or less, even more preferably 55 mol% or less.The total content of the bond units A and B is preferably 95 mol% or more, more preferably 98 mol% or more, and particularly preferably 100 mol%.
The content of the bond units A and B includes the case where the bond units A and B are located at the terminals of the silane coupling agent. When the bond units A and B are located at the terminals of the silane coupling agent, the form of the bond units A and B is not particularly limited, and it is sufficient that the bond units A and B form units corresponding to the formulas (I) and (II) shown in the formulas.

With respect to R ¹¹ in formulae (I) and (II), examples of the halogen include chlorine, bromine, and fluorine. Examples of the branched or unbranched alkyl group having 1 to 30 carbon atoms include a methyl group, an ethyl group, and the like. Examples of the branched or unbranched alkenyl group having 2 to 30 carbon atoms include a vinyl group, a 1-propenyl group, and the like. Examples of the branched or unbranched alkynyl group having 2 to 30 carbon atoms include an ethynyl group, a propynyl group, and the like.

With respect to R ¹² in formulas (I) and (II), examples of the branched or unbranched alkylene group having 1 to 30 carbon atoms include an ethylene group, a propylene group, etc. Examples of the branched or unbranched alkenylene group having 2 to 30 carbon atoms include a vinylene group, a 1-propenylene group, etc. Examples of the branched or unbranched alkynylene group having 2 to 30 carbon atoms include an ethynylene group, a propynylene group, etc.

In a silane coupling agent containing a bonding unit A represented by formula (I) and a bonding unit B represented by formula (II), the total number of repetitions (v+w) of the number of repetitions of bonding unit A (v) and the number of repetitions of bonding unit B (w) is preferably in the range of 3 to 300.

In the rubber composition, the content of the silane coupling agent is preferably 3 parts by mass or more, and more preferably 6 parts by mass or more, per 100 parts by mass of silica. The content is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 10 parts by mass or less. The content of the mercapto-based silane coupling agent is also preferably in the same range.

(Plasticizer)
The rubber composition may contain a plasticizer.
Here, the plasticizer is a material that imparts plasticity to the rubber component, and examples thereof include liquid plasticizers (plasticizers that are in a liquid state at room temperature (25°C)), resins (resins that are in a solid state at room temperature (25°C)), and ester-based plasticizers.

In the present invention, the aforementioned "branched conjugated diene polymer" is included in the "plasticizer" if it is a material that imparts plasticity to the rubber component. In this case, the content of the plasticizer (total amount of plasticizer) is the total content of the branched conjugated diene polymer (with plasticity) and other plasticizers.

In the rubber composition, the content of the plasticizer (total amount of the plasticizer) is preferably 10 parts by mass or more, more preferably 30 parts by mass or more, even more preferably 40 parts by mass or more, particularly preferably 47 parts by mass or more, and is preferably 100 parts by mass or less, more preferably 70 parts by mass or less, and even more preferably 60 parts by mass or less, based on 100 parts by mass of the rubber component. When the content is within the above range, the effect tends to be better obtained.
The amount of the plasticizer used in the extended rubber is also included in the amount of the plasticizer.

The liquid plasticizer (a plasticizer in a liquid state at room temperature (25° C.)) is not particularly limited, and examples thereof include oil and liquid polymer (liquid resin, liquid diene-based polymer, etc.). Among these, from the viewpoint of obtaining a greater effect, oil, liquid resin, and liquid diene-based polymer are preferable. These may be used alone or in combination of two or more kinds.
The mechanism by which the use of oil, liquid resin, and liquid diene polymer provides such an effect is not clear, but it is presumed that these plasticizers provide good grip performance, thereby improving the overall performance of the tire, including abrasion resistance, wet grip performance, and bleed resistance.

In the rubber composition, the content of the liquid plasticizer is preferably 5 parts by mass or more, more preferably 8 parts by mass or more, and even more preferably 10 parts by mass or more, and is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less, based on 100 parts by mass of the rubber component. When the content is within the above range, the effect tends to be better obtained.
The amount of liquid plasticizer included in the oil-extended rubber is also included in the amount of oil.
When the branched conjugated diene polymer corresponds to a plasticizer that is in a liquid state at room temperature (25° C.), the content of the liquid plasticizer is the total content of the branched conjugated diene polymer and other liquid plasticizers.

The oil may be, for example, a process oil, a vegetable oil, or a mixture thereof. The process oil may be, for example, a paraffin-based process oil, an aromatic process oil, or a naphthenic process oil. The vegetable oil may be, for example, 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, or tung oil. Among these, process oils (paraffin-based process oil, aromatic process oil, naphthenic process oil, etc.) and vegetable oils are preferred. From the viewpoint of life cycle assessment, these process oils and vegetable oils may be appropriately used as oils after being used as lubricants for rubber mixing mixers and engines, or waste edible 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.

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), and liquid styrene isoprene styrene block copolymers (liquid SIS block polymers), which 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.

Examples of the resin (resin in a solid state at room temperature (25°C)) include 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, p-t-butylphenol acetylene resins, acrylic resins, and the like. The resins may also be hydrogenated. These may be used alone or in combination of two or more.

In the rubber composition, the content of the resin is preferably 5 parts by mass or more, more preferably 7 parts by mass or more, and even more preferably 9 parts by mass or more, and is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less, based on 100 parts by mass of the rubber component. When the content is within the above range, the effect tends to be better obtained.
The mechanism by which such an effect is obtained by setting the resin amount within a specified range is not clear, but it is presumed that the improved compatibility with the rubber results in improved abrasion resistance and wet grip performance as well as suppressed bleeding, thereby improving the overall performance of abrasion resistance, wet grip performance and bleed resistance.

The softening point of the resin is preferably 50° C. or higher, more preferably 55° C. or higher, even more preferably 60° C. or higher, and even more preferably 85° C. or higher. The upper limit is preferably 160° C. or lower, more preferably 150° C. or lower, and even more preferably 145° C. or lower. Within the above range, the effect tends to be better obtained.
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 softening point of the resin is usually about 50° C.±5° C., which is the glass transition temperature of the resin component.

The aromatic vinyl polymer is a polymer containing an aromatic vinyl monomer as a constituent unit, and examples thereof include styrene-based resins. Examples of styrene-based resins include resins obtained by polymerizing α-methylstyrene and/or styrene, and specific examples thereof include homopolymers of styrene (styrene resins), homopolymers of α-methylstyrene (α-methylstyrene resins), copolymers of α-methylstyrene and styrene, and copolymers of styrene and other monomers.

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

The 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 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.

Examples of the rosin resin 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 constituent unit, and examples thereof include polyterpene resins obtained by polymerizing terpene compounds, and aromatic modified terpene resins obtained by polymerizing terpene compounds and aromatic compounds. Examples of aromatic modified terpene resins include terpene phenol resins made from terpene compounds and phenolic compounds, terpene styrene resins made from terpene compounds and styrene compounds, and terpene phenol styrene resins made from terpene compounds, phenolic compounds, and styrene compounds. Examples of terpene compounds include α-pinene, β-pinene, etc., examples of phenolic compounds include phenol, bisphenol A, etc., and examples of aromatic compounds include styrene compounds (styrene, α-methylstyrene, etc.).

The p-t-butylphenol acetylene resin is a solid resin obtained by a condensation reaction between p-t-butylphenol and acetylene.

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

Among the above-mentioned resins, from the viewpoint of obtaining a greater effect, it is desirable to include at least one resin selected from the group consisting of styrene-based resins, coumarone-indene resins, terpene-based resins, p-t-butylphenol acetylene resins, acrylic-based resins, dicyclopentadiene-based resins, C5-based resins, C9-based resins, and C5C9-based resins.
Although the mechanism by which the use of these resins provides such an effect is not clear, it is presumed that these resins provide good grip performance, thereby improving the overall performance of abrasion resistance, wet grip performance, and bleed resistance.

The ester plasticizer is not particularly limited as long as it is a compound having an ester group that is in a liquid state at room temperature (25°C), but examples include phthalic acid derivatives, long-chain fatty acid derivatives, phosphoric acid derivatives, sebacic acid derivatives, adipic acid derivatives, etc. These may be used alone or in combination of two or more. Among them, phosphoric acid derivatives, sebacic acid derivatives, and adipic acid derivatives are preferred, and sebacic acid derivatives are more preferred.

The phthalic acid derivatives include, but are not limited to, phthalic acid esters such as di-2-ethylhexyl phthalate (DOP) and diisodecyl phthalate (DIDP). The long-chain fatty acid derivatives include, but are not limited to, long-chain fatty acid glycerin esters. The phosphoric acid derivatives include, but are not limited to, phosphoric acid esters such as tris(2-ethylhexyl)phosphate (TOP) and tributyl phosphate (TBP). The sebacic acid derivatives include, but are not limited to, sebacic acid esters such as di(2-ethylhexyl)sebacate (DOS) and diisooctylsebacate (DIOS). The adipic acid derivatives include, but are not limited to, adipic acid esters such as di(2-ethylhexyl)adipate (DOA) and diisooctyladipate (DIOA).
Among these, phosphate ester, sebacic acid ester, and adipic acid ester are preferred, and sebacic acid ester is more preferred. Specific examples of the compound include TOP, DOS, and DOA, and DOS is more preferred.

The glass transition temperature (Tg) of the ester plasticizer is preferably −110° C. or higher, more preferably −100° C. or higher, even more preferably −80° C. or higher, and is preferably −20° C. or lower, more preferably −40° C. or lower, even more preferably −55° C. or lower. By keeping it within the above range, the above-mentioned effects tend to be more suitably obtained.
In this specification, the glass transition temperature is a value measured in accordance with JIS-K7121 using a differential scanning calorimeter (Q200) manufactured by TA Instruments Japan Ltd. at a temperature rise rate of 10° C./min.

The content of the ester plasticizer is preferably 1 to 20 parts by mass per 100 parts by mass of the rubber component.

As plasticizers, for example, products from Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., ENEOS Corporation, Orisoi Corporation, H&R Corporation, Toyokuni Oil Mills Co., Ltd., Showa Shell Sekiyu K.K., Fuji Kosan Co., Ltd., Nisshin Oillio Group Ltd., 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., Arakawa Chemical Industries Co., Ltd., Taoka Chemical Co., Ltd., Daihachi Chemical Industry Co., Ltd., etc. can be used.

The rubber composition may contain a processing aid.
Examples of processing aids include metal salts (compounds in which the hydrogen atoms of an acid are replaced with metal ions), fatty acid amides, amide esters, fatty acid esters, etc. These may be used alone or in combination of two or more. Among these, metal salts and fatty acid amides are preferred, and metal salts are more preferred.

Metals used in metal salts include, for example, alkali metals such as potassium and sodium, and alkaline earth metals such as calcium and barium. Magnesium, zinc, nickel, molybdenum, etc. can also be used. Of these, alkali metals are preferred.

Examples of acids used in metal salts include fatty acids such as lauric acid, myristic acid, and palmitic acid. In addition, boric acid, carbonic acid, hydrochloric acid, nitric acid, and sulfuric acid can also be used.

Commercially available processing aids include products from Kishida Chemical Co., Ltd., Kenei Pharmaceutical Co., Ltd., Struktol Co., Ltd., Performance Additives Co., Ltd., etc.

In the rubber composition, the content of the processing aid is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and even more preferably 3 parts by mass or more, per 100 parts by mass of the rubber component, and is preferably 12 parts by mass or less, more preferably 9 parts by mass or less, and even more preferably 6 parts by mass or less. Within the above range, the effect tends to be better obtained.

(Other ingredients)
The rubber composition may contain an antioxidant.
Examples of the antiaging agent include naphthylamine-based antiaging agents such as phenyl-α-naphthylamine; diphenylamine-based antiaging agents such as octylated diphenylamine and 4,4'-bis(α,α'-dimethylbenzyl)diphenylamine; p-phenylenediamine-based antiaging agents such as N-isopropyl-N'-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine and N,N'-di-2-naphthyl-p-phenylenediamine; quinoline-based antiaging agents such as polymers of 2,2,4-trimethyl-1,2-dihydroquinoline; monophenol-based antiaging agents such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol; and bis-, tris-, and polyphenol-based antiaging agents such as tetrakis-[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane. As commercially available products, products available from Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinko Chemical Co., Ltd., Flexis Co., Ltd., etc. may be used alone or in combination of two or more kinds.

In the rubber composition, the content of the antioxidant is preferably 1.0 part by mass or more, more preferably 3.0 parts by mass or more, and even more preferably 4.5 parts by mass or more, per 100 parts by mass of the rubber component, and is preferably 10.0 parts by mass or less, more preferably 8.0 parts by mass or less, and even more preferably 6.0 parts by mass or less. Within the above range, the effect tends to be better.

The rubber composition may contain a wax.
The wax is not particularly limited, and examples thereof include petroleum waxes such as paraffin wax and microcrystalline wax; natural waxes such as vegetable wax and animal wax; and synthetic waxes such as polymers of ethylene, propylene, etc. Commercially available products include those from Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., Seiko Chemical Co., Ltd., etc. These may be used alone or in combination of two or more kinds.

In the rubber composition, the wax content is preferably 1.0 part by mass or more, more preferably 2.0 parts by mass or more, and even more preferably 2.5 parts by mass or more, per 100 parts by mass of the rubber component, and is preferably 10.0 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. Within the above ranges, the effect tends to be better.

The rubber composition may contain stearic acid.
As the stearic acid, a conventionally known one can be used, and as a commercially available product, a product from NOF Corp., Kao Corp., Fujifilm Wako Pure Chemical Industries, Ltd., Chiba Fatty Acid 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 stearic acid is preferably 1.0 part by mass or more, more preferably 3.0 parts by mass or more, and even more preferably 4.0 parts by mass or more, per 100 parts by mass of the rubber component, and is preferably 10.0 parts by mass or less, and more preferably 6.0 parts by mass or less. Within the above range, the effect tends to be better obtained.

The rubber composition may contain sulfur.
Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, soluble sulfur, etc., which are generally used as crosslinking agents 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., Hosoi Chemical Industry Co., Ltd., etc. These may be used alone or in combination of two or more kinds.

In the rubber composition, the sulfur content 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, per 100 parts by mass of the rubber component, and is preferably 3.5 parts by mass or less, more preferably 2.8 parts by mass or less, and even more preferably 2.5 parts by mass or less. Within the above range, the effect tends to be better obtained.

The rubber composition may contain a vulcanization accelerator.
Examples of the vulcanization accelerator include thiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole and di-2-benzothiazolyl disulfide; thiuram-based vulcanization accelerators such as tetramethylthiuram disulfide (TMTD) and tetrakis(2-ethylhexyl)thiuram disulfide (TOT-N); sulfenamide-based vulcanization accelerators such as N-cyclohexyl-2-benzothiazylsulfenamide (CBS), N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-oxyethylene-2-benzothiazolesulfenamide, and N,N'-diisopropyl-2-benzothiazolesulfenamide; and guanidine-based vulcanization accelerators such as diphenylguanidine, di-orthotolylguanidine, and orthotolylbiguanidine. Commercially available products include products from Sumitomo Chemical Co., Ltd. and Ouchi Shinko Chemical Co., Ltd. These may be used alone or in combination of two or more.

In the rubber composition, the content of the vulcanization accelerator is preferably 1.0 part by mass or more, more preferably 3.0 parts by mass or more, and even more preferably 5.0 parts by mass or more, per 100 parts by mass of the rubber component, and is preferably 10.0 parts by mass or less, more preferably 8.0 parts by mass or less, and even more preferably 7.0 parts by mass or less. Within the above range, the effect tends to be better obtained.

In addition to the above components, the rubber composition may further contain additives commonly used in the tire industry, such as organic peroxides. The content of these additives is preferably 0.1 to 200 parts by mass per 100 parts by mass of the rubber component.

The rubber composition can be produced using known methods, for example, by kneading the above-mentioned 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 is used as a tread for a tire.
Examples of tires that can be applied to the present invention include pneumatic tires and non-pneumatic tires, and among these, pneumatic tires are preferred. In particular, they can be used preferably as summer tires (summer tires), winter tires (studless tires, tires for low-temperature road surfaces, snow tires, stud tires, etc.), and all-season tires. Among these, they can be used preferably as summer tires and winter tires. In addition, the tires can be used as passenger car tires, large passenger car tires, large SUV tires, heavy load tires such as trucks and buses, light truck tires, two-wheeled automobile tires, and racing tires (high performance tires). Among these, it is preferable to use them as passenger car tires.

Tires are manufactured by the usual method using the rubber composition. For example, a rubber composition containing various materials is extruded to match the shape of the tread while still unvulcanized, and molded together with other tire components in a tire building machine by the usual method to form an unvulcanized tire, which is then heated and pressurized in the vulcanizer to manufacture the tire.

The tire of the present invention has a tread constituted by the rubber composition containing a rubber component and a branched conjugated diene-based polymer, and A defined as A = 42.9/√α + 0.14 (wherein α represents the weight average molecular weight of the branched conjugated diene-based polymer) satisfies formula (1).
Formula (1)
0.25<A≦1.50
The lower limit of A is preferably 0.28 or more, more preferably 0.30 or more, even more preferably 0.39 or more, even more preferably 0.40 or more, even more preferably 0.44 or more, even more preferably 0.50 or more, even more preferably 0.53 or more, even more preferably 0.57 or more, even more preferably 0.59 or more, and the upper limit is preferably 1.20 or less, more preferably 0.82 or less, even more preferably 0.80 or less, even more preferably 0.75 or less, even more preferably 0.70 or less. Within the above range, the effect tends to be better obtained.
The mechanism by which such an effect is obtained by setting A within a predetermined range, particularly 0.30≦A≦0.80, is not clear, but it is presumed that the improved compatibility with rubber reduces the number of single domain phases and improves abrasion resistance, and that the reduced number of single domain phases suppresses bleeding of the branched conjugated diene polymer and improves bleed resistance, thereby improving the overall abrasion resistance, wet grip performance, and bleed resistance.

The tire has a tread made of the rubber composition, and A defined as A=42.9/√α+0.14 (wherein α represents the weight average molecular weight of the branched conjugated diene polymer) and a groove area ratio S [%] in the contact surface of the tread satisfy the following formula (2):
Equation (2)
A×S≦27.0
The upper limit of A×S is preferably 26.6 or less, more preferably 26.1 or less, even more preferably 25.5 or less, even more preferably 25.0 or less, even more preferably 23.1 or less, even more preferably 23.0 or less, even more preferably 22.2 or less, particularly preferably 22.0 or less. The lower limit is not particularly limited, but is preferably 10.0 or more, more preferably 10.8 or more, even more preferably 15.0 or more, even more preferably 15.1 or more, even more preferably 17.3 or more, even more preferably 17.8 or more, even more preferably 18.0 or more. Within the above range, the effect tends to be better obtained.
The mechanism by which such an effect is obtained by setting A×S to a predetermined value or less, in particular A×S≦22.0, is not clear, but it is presumed that sufficient grip performance is ensured, wear is suppressed, and wet grip performance and wear resistance are improved, thereby improving the overall performance of wear resistance, wet grip performance, and bleed resistance.

It is preferable that the tire has a groove area ratio S [%] of 50% or less in the contact surface of the tread.
S is preferably 45% or less, more preferably 44% or less, even more preferably 43% or less, even more preferably 41% or less, even more preferably 39% or less. The lower limit of the groove area ratio is preferably 10% or more, more preferably 15% or more, even more preferably 20% or more, even more preferably 30% or more, even more preferably 33% or more, even more preferably 35% or more. Within the above range, the effect tends to be better obtained.
The mechanism by which such an effect is obtained by setting S within a predetermined range, particularly 15%≦S≦45%, is not clear, but it is presumed that sufficient grip performance is ensured, wear is suppressed, and wet grip performance and wear resistance are improved, thereby improving the overall performance of wear resistance, wet grip performance and bleed resistance.

The mechanism by which the above-mentioned effects are obtained is not clear, but is presumed to be as follows.
The branched conjugated diene polymer having at least branched conjugated diene, butadiene and styrene as structural units improves compatibility with rubber components such as butadiene rubber and styrene-butadiene rubber, and in particular, by adjusting the weight average molecular weight of the branched conjugated diene polymer to satisfy the formula (1) "0.25<A≦1.50" and adjusting the weight average molecular weight of the branched conjugated diene polymer to fall within a predetermined range, the number of single domain phases is reduced, and the wear resistance is improved. Furthermore, the reduction in the number of single domain phases suppresses bleeding of the branched conjugated diene polymer, and the bleeding resistance is improved.
The branched conjugated diene polymer having styrene as a structural unit provides a high Tg and improves wet grip performance.
By adjusting A and the groove area ratio S [%] to satisfy the formula (2) "A × S ≦ 27.0" and decreasing the weight average molecular weight of the branched conjugated diene polymer while increasing the contact area of the tread (reducing the groove area ratio), grip performance is ensured, wear is suppressed, and wet grip performance and wear resistance are improved.
It is presumed that the above results in improved overall performance in terms of abrasion resistance, wet grip performance and bleed resistance.

The groove area ratio S (negative ratio) in the ground contact surface of the tread is the ratio of the total groove area in the ground contact surface to the total area of the ground contact surface, and is measured by the following method.
In this specification, when the tire is a pneumatic tire, the groove area ratio S is calculated from the ground contact shape under normal rim, normal internal pressure, and normal load conditions. In the case of a non-pneumatic tire, it can be measured in the same manner without requiring normal internal pressure.
"Genuine rim" refers to a rim that is determined for each tire by the standard system that includes the standard on which the tire is based. For example, this refers to the standard rim in the case of JATMA, the "Design Rim" in the case of TRA, or the "Measuring Rim" in the case of ETRTO.
"Normal internal pressure" refers to the air pressure set by the standard for each tire, and in the case of JATMA, it refers to the maximum air pressure, in the case of TRA, it refers to the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES", and in the case of ETRTO, it refers to "INFLATION PRESSURE".
"Normal load" refers to the load determined for each tire by the above-mentioned standard, and means the maximum load capacity in the case of JATMA, the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the case of TRA, and "LOAD CAPACITY" in the case of ETRTO.
The contact shape is obtained by assembling the tire on a standard rim, applying standard internal pressure, and leaving it at 25°C for 24 hours. Then, ink is applied to the surface of the tire tread, and the tire is pressed against cardboard under a standard load (camber angle is 0°) to transfer the shape to the paper.
The tire is rotated 72° in the circumferential direction and the transfer is performed at five locations. In other words, the contact shape is obtained five times.
The area of the figure obtained by smoothly connecting the contours of the five contact shapes is the total area, and the total area transferred is the contact area. The average value of the results for these five locations is calculated, and the groove area ratio S (%) is calculated as [1 - {average area of the five contact shapes (black parts) transferred to the cardboard / average area of the total area of the five transferred areas (figures obtained by the contours)}] x 100 (%).
Here, the average value of the length or area is the simple average of the five values.

The tire has a tread thickness G (mm) of preferably 3.0 mm or more, more preferably 3.5 mm or more, even more preferably 4.0 mm or more, and even more preferably 6.0 mm or more. There is no particular upper limit, but it is preferably 15.0 mm or less, more preferably 10.0 mm or less, even more preferably 9.0 mm or less, and particularly preferably 8.0 mm or less. Within the above range, the effect tends to be better obtained.
The mechanism by which such an effect is obtained is not clear, but it is presumed that by setting the tread thickness within a specified range, the rigidity is improved, thereby improving abrasion resistance and wet grip performance, and the thickness also improves bleed resistance, thereby improving the overall performance of abrasion resistance, wet grip performance, and bleed resistance.

In the present invention, the thickness G of the tread is the thickness on the equatorial plane of the radial cross section of the tread, specifically, the distance from the tread surface on the equatorial plane to the interface of the reinforcing layer containing other fiber materials such as the belt reinforcing layer, belt layer, and carcass layer on the tire's outermost surface side in the cross section cut along a plane including the tire's rotation axis. In addition, when the tire has grooves on the equatorial plane of the tire, the thickness G is the straight line distance from the intersection of the straight line connecting the ends of the grooves on the outermost surface side in the radial direction of the tire with the equatorial plane.

Figure 1 is a cross-sectional view taken along the meridian line, showing a portion of a tire 1 according to one embodiment of the present invention. Note that the tire of the present invention is not limited to the following form.

In FIG. 1, the up-down direction is the tire radial direction (hereinafter also simply referred to as the radial direction), the left-right direction is the tire axial direction (hereinafter also simply referred to as the axial direction), and the direction perpendicular to the paper surface is the tire circumferential direction (hereinafter also simply referred to as the circumferential direction). This tire 1 has a shape that is approximately symmetrical with respect to a center line CL in FIG. 1. This center line CL is also called the tread center line, and represents the equatorial plane EQ of the tire 1.

The tire 1 has a tread 2, a sidewall 3, a bead 4, a carcass 5, and a belt 6. The tire 1 is of a tubeless type.

The tread portion 2 has a tread surface 7. In a cross section taken along the meridian of the tire 1, the tread surface 7 has a shape that is convex radially outward. This tread surface 7 comes into contact with the road surface. The tread surface 7 has a plurality of grooves 8 that extend circumferentially. These grooves 8 form a tread pattern. The outer portion of the tread 2 in the axial direction (tire width direction) is called a shoulder portion 15. The sidewall 3 extends radially inward from the end of the tread 2. This sidewall 3 is made of cross-linked rubber or the like.

As shown in FIG. 1, the bead 4 is located approximately radially inward from the sidewall 3. The bead 4 includes a core 10 and an apex 11 extending radially outward from the core 10. The core 10 has a ring shape along the circumferential direction of the tire. The core 10 is formed by winding a non-elastic wire. Typically, a steel wire is used for the core 10. The apex 11 tapers radially outward. The apex 11 is made of a high-hardness crosslinked rubber or the like.

In this embodiment, the carcass 5 is made of a carcass ply 12. The carcass ply 12 is laid between the beads 4 on both sides and runs along the inside of the tread 2 and sidewall 3. The carcass ply 12 is folded around the core 10 from the inside to the outside in the axial direction of the tire. Although not shown, the carcass ply 12 is made of a large number of cords arranged in parallel and a topping rubber. The absolute value of the angle that each cord makes with respect to the equatorial plane EQ (CL) is usually 70° to 90°. In other words, the carcass 5 has a radial structure.

In this embodiment, the belt 6 is located radially outside the carcass 5. The belt 6 is laminated on the carcass 5. The belt 6 reinforces the carcass 5. The belt 6 may be composed of an inner layer belt 13 and an outer layer belt 14. In this embodiment, the widths of the two belts 13 and 14 are different.

Although not shown, each of the inner layer belt 13 and the outer layer belt 14 typically consists of a large number of parallel cords and a topping rubber. It is preferable that each cord is inclined with respect to the equatorial plane EQ. It is preferable that the inclination direction of the cords of the inner layer belt 13 is opposite to the inclination direction of the cords of the outer layer belt 14.

Although not shown, a band may be laminated on the radially outer side of the belt 6. The width of this band is greater than the width of the belt 6. The band may be made of a cord and a topping rubber. The cord is wound in a spiral shape. The belt is restrained by the cord, so lifting of the belt 6 is suppressed. The cord is desirably made of organic fibers. Examples of preferred organic fibers include nylon fibers, polyester fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

Although not shown, an edge band may be disposed radially outward of the belt 6 and near the widthwise end (edge portion) of the belt 6. This edge band may be made of cords and topping rubber, similar to the above-mentioned band. One example of the above-mentioned edge band is one that is layered on the upper surface of the step 20 portion of the wide inner layer belt 13. The cords of this edge band may be inclined in the same direction as the direction of the cords of the narrow outer layer belt 14, and may be biased against the cords of the wide inner layer belt 13.

Although not shown, a cushion rubber layer may be laminated with the carcass 5 near the widthwise end of the belt 6. The cushion layer may be made of soft crosslinked rubber. The cushion layer absorbs stress at the end of the belt.

Figure 2 shows a cross section of the tread 2 of this tire 1 cut on a plane including the tire axis. In Figures 1 and 2, the crown center 17, which is the position of the equator EQ, corresponds to the "equatorial plane of the tire radial cross section of the tread 2."

In tire 1, the thickness G of tread 2 (thickness G of tread 2 on the equatorial plane of the tire radial cross section) is the distance from tread surface 7 on the equatorial plane (a straight line connecting the ends of grooves 8 on the tire radial outermost surface side, since tire 1 has grooves on the tire equatorial plane) to the interface of outer layer belt 14 on the tire outermost surface side in the cross section cut on a plane including the tire axis.

In the tire 1, the tread rubber composition constituting the tread 2 contains a rubber component and a branched conjugated diene polymer, and the branched conjugated diene polymer is a copolymer having at least branched conjugated diene, butadiene and styrene as structural units, and A defined as A = 42.9/√α + 0.14 (wherein α represents the weight average molecular weight of the branched conjugated diene polymer) satisfies the formula (1) "0.25 < A ≦ 1.50". In addition, A and the groove area ratio S [%] on the contact surface of the tread 2 satisfy the formula (2) "A × S ≦ 27.0".

Below are examples (embodiments) that are considered to be preferable for implementation, but the scope of the present invention is not limited to these examples.

The results of examining tires obtained by varying the formulation according to Table 1 using the various chemicals shown below and calculating them based on the evaluation method below are shown in Table 1.

(Rubber component)
SBR1: Tufuden 3830 manufactured by Asahi Kasei Corporation (styrene content: 36% by mass, butadiene content: 64% by mass, Mw: 420,000, contains 37.5 parts by mass of oil per 100 parts by mass of rubber solids)
SBR2: JSR1723 manufactured by JSR Corporation (styrene content: 24% by mass, butadiene content: 76% by mass, containing 37.5 parts by mass of oil per 100 parts by mass of rubber solids)
SBR3: JSR1502 manufactured by JSR Corporation (styrene content: 25% by mass, butadiene content: 75% by mass)
BR: BR150B (cis content 95% by mass or more) manufactured by Ube Industries, Ltd.

(Chemicals other than rubber components)
Oil: Diana Process PA32 (mineral oil) manufactured by Idemitsu Kosan Co., Ltd.
Carbon black: N134 ( _N2SA : ^148m2 /g) manufactured by Cabot Japan Co., Ltd.
Silica 1: Ultrasil VN3 (N ₂ SA: 175 m ² /g) manufactured by Degussa
Silica 2: ZEOSIL 1115MP (N ₂ SA: 115 m ² /g) manufactured by Solvay
Silica 3: 9100Gr ( _N2SA : ^235m2 /g) manufactured by Degussa
Silane coupling agent: NXT (3-octanoylthiopropyltriethoxysilane) manufactured by Momentive
Resin: Sylvatraxx 4401 (copolymer of α-methylstyrene and styrene, softening point: 85° C.) manufactured by Arizona Chemical Co.
Polyisoprene: LIR50 (Mw: 54,000) manufactured by Kuraray Co., Ltd.
Styrene-butadiene copolymer: RICON 100 manufactured by Clay Valley (styrene content 23% by mass, butadiene content 77% by mass, Mw: 4500)
Styrene-farnesene copolymer: Septon 1020 manufactured by Kuraray Co., Ltd. (styrene content 36% by mass, farnesene content 64% by mass, Mw: 1000)
Copolymer 1: butadiene/farnesene copolymer of Production Example 1 belowCopolymer 2: styrene/butadiene/farnesene copolymer of Production Example 2 belowCopolymer 3: styrene/butadiene/farnesene copolymer of Production Example 3 belowCopolymer 4: styrene/butadiene/farnesene copolymer of Production Example 4 belowCopolymer 5: styrene/butadiene/farnesene copolymer of Production Example 5 belowCopolymer 6: styrene/butadiene/farnesene copolymer of Production Example 6 belowCopolymer 7: styrene/butadiene/farnesene copolymer of Production Example 7 below Polymer 8: Styrene/butadiene/farnesene copolymer of Production Example 8 below Copolymer 9: Styrene/butadiene/farnesene copolymer of Production Example 9 below Copolymer 10: Styrene/butadiene/farnesene copolymer of Production Example 10 below Copolymer 11: Styrene/butadiene/farnesene copolymer of Production Example 11 below Copolymer 12: Styrene/butadiene/farnesene copolymer of Production Example 12 below Copolymer 13: Styrene/butadiene/farnesene copolymer of Production Example 13 below Wax: OZOACE 0355 manufactured by Nippon Seiro Co., Ltd.
Antioxidant 1: Nocrac 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Antioxidant 2: Nocrac 224 (2,2,4-trimethyl-1,2-dihydroquinoline polymer) 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: HK-200-5 (powdered sulfur containing 5% by mass of oil) manufactured by Hosoi Chemical Industry Co., Ltd.
Vulcanization accelerator 1: Noccela CZ (N-cyclohexyl-2-benzothiazolyl sulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Vulcanization accelerator 2: Noccelaer D (1,3-diphenylguanidine (DPG)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

The materials used in the following manufacturing examples are as follows.
Butadiene: 1,3-butadiene manufactured by Tokyo Chemical Industry Co., Ltd. Styrene: styrene manufactured by Tokyo Chemical Industry Co., Ltd. Cyclohexane: cyclohexane manufactured by Tokyo Chemical Industry Co., Ltd. Tetrahydrofuran: tetrahydrofuran manufactured by Tokyo Chemical Industry Co., Ltd. β-farnesene: trans-β-farnesene manufactured by Tokyo Chemical Industry Co., Ltd. Methanol: methanol manufactured by Tokyo Chemical Industry Co., Ltd. sec-butyllithium: butyllithium manufactured by Tokyo Chemical Industry Co., Ltd. (10.5% by mass solution in cyclohexane, approximately 2.3 mol/L)

<Method for measuring weight average molecular weight>
The weight average molecular weight of the polymer is determined in terms of standard polystyrene by gel permeation chromatography (GPC) using the following measuring device and conditions:
・Apparatus: Tosoh Corporation GPC device "HLC-8320"
Separation column: Tosoh Corporation column "TSKgel Super HZM-M"
Eluent: Tetrahydrofuran Eluent flow rate: 0.7 ml/min Sample concentration: 5 mg/10 ml
Column temperature: 40°C

<Production of Copolymer>
(Production Example 1: Production of butadiene/farnesene copolymer)
A dried and nitrogen-purged pressure vessel was charged with 1,140 g of cyclohexane as a solvent and 156 g of sec-butyllithium (10.5 mass % cyclohexane solution) as an initiator, and the temperature was raised to 50° C., after which 3.5 g of tetrahydrofuran was added, and 1,800 g of a previously prepared mixture of butadiene and β-farnesene (720 g of butadiene and 1,080 g of β-farnesene were mixed in a bomb) was added at a rate of 10 ml/min and polymerization was carried out for 1 hour.
The polymerization reaction liquid thus prepared is treated with methanol, and then washed with water.
After washing, the polymerization reaction liquid is separated from water and dried at 70° C. for 12 hours to obtain Copolymer 1 having the physical properties shown in Table 1.

(Production Example 2: Production of styrene/butadiene/farnesene copolymer)
A dried and nitrogen-purged pressure vessel was charged with 1,140 g of cyclohexane as a solvent and 12 g of sec-butyllithium (10.5 mass % cyclohexane solution) as an initiator, and the temperature was raised to 50° C., after which 3.5 g of tetrahydrofuran was added, and 1,800 g of a previously prepared mixture of styrene, butadiene, and β-farnesene (180 g of styrene, 360 g of butadiene, and 1,260 g of β-farnesene were mixed in a bomb) was added at a rate of 10 ml/min, and polymerization was carried out for 2 hours.
The polymerization reaction liquid thus prepared is treated with methanol, and then washed with water.
The washed polymerization reaction solution is separated from water and dried at 70° C. for 12 hours to obtain Copolymer 2 having the physical properties shown in Table 1.

(Production Example 3: Production of styrene/butadiene/farnesene copolymer)
A dried and nitrogen-purged pressure vessel was charged with 1,140 g of cyclohexane as a solvent and 156 g of sec-butyllithium (10.5 mass % cyclohexane solution) as an initiator, and the temperature was raised to 50° C., after which 3.5 g of tetrahydrofuran was added, and 1,800 g of a previously prepared mixture of styrene, butadiene, and β-farnesene (180 g of styrene, 360 g of butadiene, and 1,260 g of β-farnesene mixed in a bomb) was added at 10 ml/min and polymerization was carried out for 1 hour.
The polymerization reaction liquid thus prepared is treated with methanol, and then washed with water.
The washed polymerization reaction solution is separated from water and dried at 70° C. for 12 hours to obtain Copolymer 3 having the physical properties shown in Table 1.

(Production Example 4: Production of styrene/butadiene/farnesene copolymer)
Copolymer 4 having the physical properties shown in Table 1 is obtained under the same production conditions as in Production Example 3, except that the amount of sec-butyllithium (10.5% by mass in cyclohexane solution) is changed to 74 g.

(Production Example 5: Production of styrene/butadiene/farnesene copolymer)
Copolymer 5 having the physical properties shown in Table 1 is obtained under the same production conditions as in Production Example 3, except that the amount of sec-butyllithium (10.5% by mass solution in cyclohexane) is changed to 52 g.

(Production Example 6: Production of styrene/butadiene/farnesene copolymer)
Copolymer 6 having the physical properties shown in Table 1 is obtained under the same production conditions as in Production Example 3, except that the amount of sec-butyllithium (10.5% by mass solution in cyclohexane) is changed to 346 g.

(Production Example 7: Production of styrene/butadiene/farnesene copolymer)
Copolymer 7 having the physical properties shown in Table 1 was obtained under the same production conditions as in Production Example 3, except that the amounts of the previously prepared mixture of styrene, butadiene and β-farnesene were changed to 36 g of styrene, 324 g of butadiene and 1,440 g of β-farnesene.

(Production Example 8: Production of styrene/butadiene/farnesene copolymer)
Copolymer 8 having the physical properties shown in Table 1 was obtained under the same production conditions as in Production Example 3, except that the amounts of the previously prepared mixture of styrene, butadiene and β-farnesene were changed to 360 g of styrene, 360 g of butadiene and 1,080 g of β-farnesene.

(Production Example 9: Production of styrene/butadiene/farnesene copolymer)
Copolymer 9 having the physical properties shown in Table 1 was obtained under the same production conditions as in Production Example 3, except that the amounts of the previously prepared mixture of styrene, butadiene and β-farnesene were changed to 450 g of styrene, 630 g of butadiene and 720 g of β-farnesene.

(Production Example 10: Production of styrene/butadiene/farnesene copolymer)
Copolymer 10 having the physical properties shown in Table 1 was obtained under the same production conditions as in Production Example 3, except that the amounts of the previously prepared mixture of styrene, butadiene and β-farnesene were changed to 630 g of styrene, 450 g of butadiene and 720 g of β-farnesene.

(Production Example 11: Production of styrene/butadiene/farnesene copolymer)
Copolymer 11 having the physical properties shown in Table 1 is obtained under the same production conditions as in Production Example 2, except that the amount of sec-butyllithium (10.5% by mass solution in cyclohexane) is changed to 15 g.

(Production Example 12: Production of styrene/butadiene/farnesene copolymer)
Copolymer 12 having the physical properties shown in Table 1 is obtained under the same production conditions as in Production Example 3, except that the amount of sec-butyllithium (10.5% by mass solution in cyclohexane) is changed to 434 g.

(Production Example 13: Production of styrene/butadiene/farnesene copolymer)
Copolymer 13 having the physical properties shown in Table 1 is obtained under the same production conditions as in Production Example 3, except that the amount of sec-butyllithium (10.5% by mass solution in cyclohexane) is changed to 124 g.

<Production of test tires>
According to the compounding recipes shown in Tables 2 and 3, chemicals other than sulfur and vulcanization accelerators are kneaded at 160° C. for 4 minutes using a 16L Banbury mixer manufactured by Kobe Steel, Ltd. to obtain a kneaded mixture.
Next, sulfur and a vulcanization accelerator are added to the kneaded mixture, and the mixture is kneaded for 4 minutes at 80° C. using an open roll to obtain an unvulcanized polymer composition.
The unvulcanized polymer composition is molded into a tread shape, and laminated together with other tire components on a tire building machine to form an unvulcanized tire. The unvulcanized tire is then vulcanized at 170° C. for 12 minutes to produce a test tire (size: 195/65R15, specifications: Tables 2 and 3).

<Wear resistance>
The above test tire is mounted on a vehicle, and the groove depth of the tread portion is measured after driving 10,000 km. The amount of wear of the tread portion is calculated from the measured value, and expressed as an index with Comparative Example 1 being set at 100. The larger the index, the smaller the amount of wear and the better the wear resistance performance.

<Wet grip performance>
Each test tire was mounted on a vehicle, and the braking distance from an initial speed of 100 km/h on a wet asphalt road surface was determined, and expressed as an index with Comparative Example 1 taken as 100. A higher index indicates a shorter braking distance and better wet grip performance.

<Acetone Extraction Amount (AE Amount)>
For rubber test pieces cut from the tread of the test tire, the amount of material extracted by acetone contained in the test piece is measured according to the method for measuring acetone extractables in accordance with JIS K 6229. The amount of acetone extractables of each rubber test piece is expressed as an index based on Comparative Example 1. The larger the index, the smaller the amount of acetone extractables and the better the bleed resistance performance.
Acetone extractable amount (mass %)=(mass of sample before extraction−mass of sample after extraction)/mass of sample before extraction×100

<Overall performance>
The overall performance of abrasion resistance, wet grip performance and bleed resistance is evaluated as the average of abrasion resistance (index), wet grip performance (index) and acetone extractables (index). The higher the index, the better the overall performance.

The present invention (1) provides a tire having a tread made of a rubber composition containing a rubber component and a branched conjugated diene-based polymer,
The branched conjugated diene polymer is a copolymer having at least a branched conjugated diene, a butadiene, and a styrene as structural units,
The tire has A defined as A=42.9/√α+0.14 (wherein α represents the weight average molecular weight of the branched conjugated diene polymer), and a groove area ratio S [%] in the contact surface of the tread, which satisfy the following formulas (1) and (2):
Formula (1)
0.25<A≦1.50
Equation (2)
A×S≦27.0

The present invention (2) is a tire according to the present invention (1), in which the thickness of the tread is 3.0 mm or more.

The present invention (3) is a tire according to the present invention (1) or (2), in which the rubber component contains at least one selected from the group consisting of isoprene-based rubber, butadiene rubber, and styrene-butadiene rubber.

The present invention (4) is a tire that is any combination of the present inventions (1) to (3) in which the branched conjugated diene is farnesene.

The present invention (5) is a tire in any combination with any of the present inventions (1) to (4) in which the branched conjugated diene polymer has a weight average molecular weight of 1,000 to 20,000.

The present invention (6) is a tire in any combination with any of the present inventions (1) to (5) that satisfies the following formula:
0.30≦A≦0.80

The present invention (7) is a tire in any combination with any of the present inventions (1) to (6) that satisfies the following formula:
15%≦S≦45%

The present invention (8) is a tire in any combination with any of the present inventions (1) to (7) that satisfy the following formula:
A×S≦22.0

The present invention (9) is a tire in any combination with any of the present inventions (1) to (8), in which the butadiene unit amount (mass%) and the styrene unit amount (mass%) in 100 mass% of the branched conjugated diene polymer satisfy the following formula:
0.40≦0.013×butadiene unit amount+0.071×styrene unit amount≦2.70

The present invention (10) is a tire in any combination with any of the present inventions (1) to (9), in which the rubber composition contains at least one liquid plasticizer selected from the group consisting of oil, liquid resin, and liquid diene-based polymer.

The present invention (11) is a tire in any combination with any of the present inventions (1) to (10), in which the rubber composition contains at least one resin selected from the group consisting of styrene-based resins, coumarone-indene resins, terpene-based resins, p-t-butylphenol acetylene resins, acrylic resins, dicyclopentadiene-based resins, C5-based resins, C9-based resins, and C5C9-based resins.

The present invention (12) is a tire that is any combination of the present inventions (1) to (11) in which the rubber composition contains silica and carbon black.

The present invention (13) is a tire that is any combination of the present inventions (1) to (12) in which the rubber composition contains a mercapto-based silane coupling agent.

The present invention (14) is a tire in any combination with any of the present inventions (1) to (13) in which the rubber component contains butadiene rubber and styrene-butadiene rubber.

The present invention (15) is a tire that is any combination of the present inventions (1) to (14) in which the rubber composition contains oil.

The present invention (16) is a tire in any combination with any of the present inventions (1) to (15) in which the rubber composition contains a styrene-based resin.

Reference Signs List 1 Tire 2 Tread 3 Sidewall 4 Bead 5 Carcass 6 Belt 7 Tread surface 8 Groove 10 Core 11 Apex 12 Carcass ply 13 Inner layer belt 14 Outer layer belt 15 Shoulder portion 17 Crown center (tread center line CL, equatorial plane EQ of tire 1)
20 Step G Thickness of the tread portion on the equatorial plane of the tire radial cross section

Claims (13)

A tire having a tread made of a rubber composition containing a rubber component and a branched conjugated diene-based polymer,
The branched conjugated diene polymer is a copolymer having at least a branched conjugated diene, a butadiene, and a styrene as structural units,
A tire in which A defined as A=42.9/√α+0.14 (wherein α represents the weight average molecular weight of the branched conjugated diene polymer) and a groove area ratio S [%] in the contact surface of the tread satisfy the following formulas (1) and (2):
Formula (1)
0.25<A≦1.50
Equation (2)
A×S≦27.0 The tire according to claim 1, wherein the thickness of the tread is 3.0 mm or more. The tire according to claim 1, wherein the rubber component includes at least one selected from the group consisting of isoprene-based rubber, butadiene rubber, and styrene-butadiene rubber. The tire of claim 1, wherein the branched conjugated diene is farnesene. The tire according to claim 1, wherein the branched conjugated diene polymer has a weight average molecular weight of 1,000 to 20,000. 2. The tire according to claim 1, which satisfies the following formula:
0.30≦A≦0.80 2. The tire according to claim 1, which satisfies the following formula:
15%≦S≦45% 2. The tire according to claim 1, which satisfies the following formula:
A×S≦22.0 The tire according to claim 1 , wherein the butadiene unit amount (mass %) and the styrene unit amount (mass %) in 100 mass % of the branched conjugated diene polymer satisfy the following formula:
0.40≦0.013×butadiene unit amount+0.071×styrene unit amount≦2.70 The tire according to claim 1, wherein the rubber composition contains at least one liquid plasticizer selected from the group consisting of oil, liquid resin, and liquid diene-based polymer. The tire according to claim 1, wherein the rubber composition contains at least one resin selected from the group consisting of styrene-based resin, coumarone-indene resin, terpene-based resin, p-t-butylphenol acetylene resin, acrylic resin, dicyclopentadiene-based resin, C5-based resin, C9-based resin, and C5C9-based resin. The tire according to claim 1, wherein the rubber composition contains silica and carbon black. The tire according to claim 1, wherein the rubber composition contains a mercapto-based silane coupling agent.

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