pneumatic tires

Abstract

To provide a pneumatic tire excellent in wet turning performance at high speed.SOLUTION: A tire satisfies specific requirements regarding a tire cross-sectional width Wt and a belt layer width B. Mixture of rubber composition constituting a tread surface rubber layer 4 is a specific condition, and total styrene amount of the rubber composition constituting the tread surface rubber layer 4 is larger than total styrene amount of the rubber composition constituting a tread inner side rubber layer 5.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a pneumatic tire with improved wet grip performance during high-speed cornering. [Background technology]

[0002] It is desirable for passenger car tires to achieve high levels of performance, including reduced rolling resistance and wet grip performance.

[0003] Therefore, various pneumatic tires for passenger vehicles have been proposed, each having a tread rubber including a tread surface rubber layer located on the outermost surface of the tread and an inner tread rubber layer located radially inward of the tread surface rubber layer (for example, Patent Document 1). In such tires, the tread surface rubber layer is made of a rubber layer with relatively high rigidity, and the inner tread rubber layer is made of a rubber layer with relatively low rigidity. As a result, when the vehicle is traveling straight, the inner rubber layer with relatively low rigidity suppresses, for example, hysteresis loss, thereby reducing the rolling resistance of the tire. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-162242 Summary of the Invention [Problem to be solved by the invention]

[0005] However, with the recent development of expressways and improvements in vehicle performance, it is not uncommon to travel long distances at high speeds. In this environment, the high rigidity of the tread surface rubber layer of pneumatic tires described above means that they do not maintain sufficient contact with the road surface during cornering, and there is room for improvement in wet grip performance during high-speed cornering.

[0006] An object of the present disclosure is to provide a pneumatic tire with improved wet grip performance during high-speed cornering. [Means for solving the problem]

[0007] As a result of extensive investigation, it was found that the above-mentioned problems can be solved in a tire in which the tire cross-sectional width and the tire belt layer width satisfy predetermined requirements, by setting the compounding conditions of the rubber composition constituting the tread surface rubber layer to specific conditions and by making the total styrene amount of the rubber composition constituting the tread surface rubber layer greater than the total styrene amount of the rubber composition constituting the tread inner rubber layer.

[0008] That is, the present disclosure relates to a tire having a tread portion and a belt layer, wherein the tread portion comprises at least a first layer constituting a tread surface and a second layer adjacent to and radially inward of the first layer, wherein the rubber component constituting the first and second layers contains styrene-butadiene rubber, the content of butadiene rubber in the rubber component constituting the first layer is 25% by mass or less, the glass transition temperature Tg1 (°C) of the rubber composition constituting the first layer is −18°C or higher, the total styrene amount S1 (mass%) in the rubber component constituting the first layer is 1 to 35% by mass, and the total styrene amount S2 (mass%) in the rubber component constituting the second layer is smaller than S1, and the cross-sectional width Wt (mm) of the tire and the belt layer width B (mm) of the tire when the tread is pressed against a flat surface under a normal load in a normal state satisfy (B-16) / Wt≦0.75. [Effects of the Invention]

[0009] According to the present disclosure, a pneumatic tire is provided that has improved wet grip performance during high-speed cornering. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic partial cross-sectional view of a tire according to one embodiment of the present disclosure. [Figure 2] 1 is a schematic diagram of a tire when the tread is pressed against a flat surface. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present disclosure relates to a tire having a tread portion and a belt layer, wherein the tread portion comprises at least a first layer constituting a tread surface and a second layer adjacent to and radially inward of the first layer, wherein the rubber components constituting the first and second layers contain styrene-butadiene rubber, the butadiene rubber content in the rubber component constituting the first layer is 25% by mass or less, the glass transition temperature Tg1 (°C) of the rubber composition constituting the first layer is -18°C or higher, the total styrene content S1 (mass%) in the rubber component constituting the first layer is 1 to 35% by mass, and the total styrene content S2 (mass%) in the rubber component constituting the second layer is smaller than S1, and the tire cross-sectional width Wt (mm) and the tire belt layer width B (mm) satisfy (B-16) / Wt≦0.75 when the tread is pressed against a flat surface under a normal load under normal conditions.

[0012] Although not intending to be bound by theory, the mechanism by which the effects of the present disclosure are exhibited is thought to be, for example, as follows.

[0013] The tire disclosed herein has the following advantages: (1) the total styrene content S1 of the first layer constituting the tread surface is 1 to 35% by mass, which is believed to suppress cohesion of the styrene portion of the rubber component at the tread surface, thereby improving road-following performance even during high-speed driving; (2) the butadiene rubber content of the first layer constituting the tread surface is 25% by mass or less, and the glass transition temperature Tg1 (°C) is -18°C or higher, which is believed to increase the loss tangent tanδ at temperatures higher than Tg, thereby improving heat buildup during high-speed cornering; (3) the total styrene content S2 of the second layer adjacent to the first layer radially inward of the tire is smaller than S1, which further suppresses cohesion of the styrene in the styrene-butadiene rubber in the second layer, thereby improving road contact with the tread surface; and (4) the presence of styrene in both the first and second layers of the rubber component is believed to facilitate force transmission and generate reaction force during cornering. (4) The tire's cross-sectional width Wt (mm) and belt layer width B (mm) satisfy (B-16) / Wt≦0.75, which is believed to suppress an increase in contact pressure in the tread shoulder area, uniformize the contact pressure on the tread surface during high-speed cornering, and increase the force generated across the entire contact surface. Furthermore, the cooperation of the above (1) to (4) is believed to achieve the remarkable effect of uniforming the contact pressure across the tread surface even during high-speed driving, and improving wet grip performance during high-speed cornering because the tread surface rubber layer has high compliance and heat generation, making it easy to transmit the force generated on the tread surface into the tire.

[0014] It is preferable that Wt, B, and S1 satisfy the following formula (2). (S1×B-480) / Wt≦21 (2)

[0015] The product of the styrene content and belt layer width relative to the tire cross-sectional width is reduced so that Wt, B, and S1 satisfy the above formula (2). This makes it possible to prevent aggregation of the styrene portion in the surface rubber layer while improving the contact with the ground at the tread surface, which is thought to facilitate improved wet grip performance during high-speed cornering.

[0016] The rubber composition constituting the first layer and / or the second layer preferably contains silica having an average primary particle size of 20 nm or less.

[0017] When the average primary particle size of the silica is within the above range, interaction between the silica and the rubber component is more likely to occur, increasing heat buildup and further improving wet grip performance during high-speed driving.

[0018] The rubber composition constituting the first layer and / or the second layer preferably contains 40 to 120 parts by mass of silica per 100 parts by mass of the rubber component.

[0019] By setting the silica content in the rubber composition constituting the tread within the above range, it is believed that it is possible to achieve both good dispersibility and heat buildup of the silica, and further improve wet grip performance during high-speed driving.

[0020] The glass transition temperature Tg2 (°C) of the rubber composition constituting the second layer is preferably -30°C or higher.

[0021] By setting Tg2 (°C) to -30°C or higher, the loss tangent tanδ of the second layer does not become too low, and the second layer can obtain a certain level of heat buildup even during high-speed cornering, thereby achieving a high level of wet grip performance during high-speed cornering and reduced rolling resistance.

[0022] It is preferable that Tg1-Tg2 is 2°C or higher.

[0023] By setting the glass transition temperature Tg2 (°C) of the second layer lower than the glass transition temperature Tg1 (°C) of the first layer, the loss tangent tanδ of the second layer becomes relatively lower than the loss tangent tanδ of the first layer, which is thought to reduce the rolling resistance of the entire tread. By setting the difference between Tg1 and Tg2 within the above range, the loss tangent tanδ of the second layer becomes relatively lower than the loss tangent tanδ of the first layer, which is thought to reduce the deformation of the entire tread during braking, increase the contact area of ​​the tread surface with the road surface, and improve wet grip performance.

[0024] The content of butadiene rubber in the rubber component constituting the second layer is preferably 35% by mass or less.

[0025] By setting the content of butadiene rubber in the rubber component constituting the second layer within the above range, the Tg of the second layer does not become too low, and the second layer can achieve a certain level of heat buildup even during high-speed cornering, thereby achieving a high level of wet grip performance during high-speed cornering and reduced rolling resistance.

[0026] The total styrene content S2 in the rubber component constituting the second layer is preferably 15 to 35% by mass.

[0027] By setting S2 within the above range, aggregation of styrene in the styrene-butadiene rubber in the second layer is further suppressed, making it easier for the tread surface to contact the road surface and improving wet grip performance.

[0028] It is preferable that the tread includes a base rubber layer adjacent to the belt layer on the radially outer side of the tire, and that the base rubber layer is made of a rubber composition containing a rubber component including at least one of an isoprene-based rubber and a butadiene rubber.

[0029] The tread has a base rubber layer adjacent to the outer side of the belt layer in the tire radial direction, and the base rubber layer is made of a rubber composition containing a rubber component including at least one of an isoprene-based rubber and a butadiene rubber, so that the second layer and the base rubber layer reduce heat buildup throughout the tread and reduce rolling resistance. In addition, the second layer and the base rubber layer further suppress deformation of the entire tread during braking, thereby increasing the contact area of ​​the tread surface with the road surface and further improving wet grip performance.

[0030] When the outer diameter of the tire is Dt (mm), it is preferable that Wt and Dt satisfy the following formula (3). (π / 4)×(Dt 2 / Wt)≧1500 (3)

[0031] By setting the value of formula (3) in the above range and reducing the width of the tread relative to the lateral area of ​​the tire, it is possible to reduce heat generation originating from the tread, which contributes most to heat generation in the tire, thereby suppressing the temperature rise due to heat generation in the tread, preventing the temperature of the tire and the sidewalls from becoming too high, and reducing rolling resistance.

[0032] The tread has land portions partitioned by one or more circumferential grooves extending continuously in the tire circumferential direction, and at least one of the land portions has an opening area to the tread surface of 0.1 to 15 mm 2 It is preferable that the porous body has one or more small holes.

[0033] When the tread has one or more small holes, water can be removed from between the tread surface and the road surface when the tire comes into contact with a wet road surface, making it easier to obtain road surface conformability and improving wet grip performance, particularly when traveling at high speeds.

[0034] <Definition> The "total styrene content in the rubber component" refers to the total content (mass%) of styrene moieties contained in 100% by mass of the rubber component, and is calculated by Σ(styrene content (mass%) of each styrene-containing rubber × content (mass%) of each styrene-containing rubber in the rubber component / 100). For example, if the rubber component consists of 30% by mass of a first SBR (styrene content 25% by mass), 60% by mass of a second SBR (styrene content 27.5% by mass), and 10% by mass of NR, the total styrene content in 100% by mass of the rubber component is 24.0% by mass (= 25 × 30 / 100 + 27.5 × 60 / 100).

[0035] "Genuine rim" refers to the rim specified for each tire by the standard system that includes the standard on which the tire is based, for example, standard rim for JATMA, "Design Rim" for TRA, and "Measuring Rim" for ETRTO. In the case of a tire size that is not specified in the above standard system, it refers to the narrowest rim among the smallest diameter rims that can be mounted on the tire and do not cause air leakage between the rim and tire.

[0036] "Normal internal pressure" is the air pressure specified for each tire by each standard in the standard system, including the standard on which the tire is based. For JATMA, it is the "maximum air pressure," for TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES," and for ETRTO, it is the "INFLATION PRESSURE." For tires not specified in a standard, the normal internal pressure is 250 kPa.

[0037] "Normal condition" refers to a state in which a tire is mounted on a normal rim, inflated to the normal internal pressure, and no load is applied. For tires of sizes not specified in the above-mentioned standard system, this refers to a state in which the tire is mounted on the smallest rim, inflated to 250 kPa, and no load is applied. Unless otherwise specified, the dimensions of each part of the tire (such as the tire section width Wt) are measured in the normal condition.

[0038] "Normal load" means the load specified in the standard system, including the standard on which the tire is based. The normal load is the "maximum load capacity" in the JATMA standard, the "maximum value" listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard.

[0039] "Tire section width Wt" refers to the maximum width of the tire section in its normal state. However, if there are patterns or letters on the side of the tire, this is the maximum width between the outer surfaces of the sidewalls, excluding these. It can also be measured simply by taking a cross section cut out of the tire in the radial direction and determining the maximum linear distance in the width direction, excluding any letters on the sidewalls, with the distance between the beads aligned to the normal rim width.

[0040] "Tire belt layer width B" is the maximum length in the width direction of the tire belt layer in its normal state. Simply put, like the above-mentioned cross-sectional width, it can be measured by determining the linear distance in the width direction between the end points of the belt layer in a cross section cut out in the radial direction of the tire, with the distance between the bead portions aligned with the normal rim width. If the belt layer is made up of multiple belt layers, the longest of these will be taken as the "tire belt total width B."

[0041] "Outer diameter Dt of tire" is the diameter of the tire in a normal state.

[0042] The "aspect ratio (%) of a tire" is calculated by (Ht / Wt) x 100, where Ht (mm) is the tire section height and Wt (mm) in a normal state.

[0043] A "small hole" refers to a hole that extends from within the tread and opens onto the tread surface. It is not connected in the circumferential or widthwise directions of the tire, and is distinct from circumferential grooves, lateral grooves, decorative grooves, etc.

[0044] "Oil content" includes the amount of oil contained in oil-extended rubber.

[0045] <Measurement method> The "glass transition temperature (Tg) of a rubber composition" is determined by measuring a temperature distribution curve of tan δ for a test piece sample (e.g., 20 mm long x 4 mm wide x 1 mm thick) of the rubber composition using a dynamic viscoelasticity evaluation device (e.g., an Iplexer series manufactured by GABO) under conditions of a frequency of 10 Hz, an initial strain of 10%, an amplitude of ±0.5%, and a heating rate of 2°C / min, and the "glass transition temperature (Tg) of a rubber composition" is the temperature corresponding to the largest tan δ value in the temperature distribution curve obtained (tan δ peak temperature). For rubber compositions for tires, a test piece sample of the rubber composition is taken from a tire, and the longitudinal direction of the test piece sample is aligned with the circumferential direction of the tire.

[0046] "Tg" is a value determined by differential scanning calorimetry (DSC) in accordance with JIS K 7121, and is applied to, for example, SBR and resin components.

[0047] "Styrene content" is 1 This is a value calculated by H-NMR measurement, and is applied to rubber components having repeating units derived from styrene, such as SBR.

[0048] The "vinyl content (amount of 1,2-bonded butadiene units)" is a value calculated by infrared absorption spectroscopy in accordance with JIS K 6239-2:2017, and applies to rubber components having repeating units derived from butadiene, such as SBR and BR.

[0049] The "cis content (amount of cis-1,4-bonded butadiene units)" is a value calculated by infrared absorption spectroscopy in accordance with JIS K 6239-2:2017, and applies to rubber components having repeating units derived from butadiene, such as BR.

[0050] The "weight average molecular weight (Mw)" can be determined by converting the measured value into a standard polystyrene equivalent value based on the value measured by gel permeation chromatography (GPC) (for example, a GPC-8000 series manufactured by Tosoh Corporation, a differential refractometer as the detector, and a TSKGEL SUPERMALTIPORE HZ-M column manufactured by Tosoh Corporation). This applies to, for example, SBR, BR, resin components, liquid polymers, etc.

[0051] The "average primary particle size of silica" can be determined by observing with a transmission or scanning electron microscope, measuring 400 or more primary particles of silica observed within the field of view, and averaging the measurements.

[0052] "N2SA of silica" is measured by the BET method in accordance with ASTM D3037-93.

[0053] "N2SA of carbon black" is measured in accordance with JIS K 6217-2 "Basic properties of carbon black for rubber - Part 2: Determination of specific surface area - Nitrogen adsorption method - Single point method."

[0054] The "softening point of the resin component" is the temperature at which the ball drops when the softening point specified in JIS K 6220-1:2001 is measured using a ring and ball softening point tester.

[0055] <Tires> A tire according to one embodiment of the present disclosure is a tire having a tread portion and a belt layer, wherein the tread portion comprises at least a first layer constituting a tread surface and a second layer adjacent to the first layer on the radially inner side of the tire, wherein the rubber components constituting the first and second layers contain styrene-butadiene rubber, the total styrene content S1 (mass%) of the rubber component constituting the first layer is 1 to 35 mass%, the total styrene content S2 (mass%) of the rubber component constituting the second layer is smaller than S1, and when the tread is pressed against a flat surface under a normal load under normal conditions, the cross-sectional width Wt (mm) of the tire and the belt layer width B (mm) of the tire satisfy (B-16) / Wt≦0.75.

[0056] The tire of the present disclosure can improve wet grip performance by disposing a first layer that forms the tread surface and a second layer that is adjacent to and radially inward of the first layer.

[0057] A procedure for manufacturing a tire according to one embodiment of the present disclosure will be described in detail below. However, the following description is an example for explaining the present disclosure and is not intended to limit the technical scope of the present disclosure to the described range. In this specification, when a numerical range is indicated using "to," the range includes both ends of the numerical range.

[0058] <Tire dimensions> 1 is an enlarged cross-sectional view showing a portion of a tire according to the present disclosure, in which the vertical direction is the radial direction of the tire, the left-right direction is the tire width direction, and the direction perpendicular to the paper surface is the tire circumferential direction.

[0059] The tire of the present disclosure preferably has an aspect ratio of 45% or more, more preferably 50% or more, even more preferably 52% or more, and even more preferably 55% or more. On the other hand, the upper limit is preferably 80% or less, more preferably 75% or less, and even more preferably 70% or less. With the aspect ratio in this range, the side portions tend to flex appropriately during cornering, making it easier for the outermost tread surface to contact the ground, further improving wet grip performance during high-speed cornering.

[0060] The tire outer diameter Dt is preferably 585 mm or more, more preferably 600 mm or more, and even more preferably 625 mm or more. The tire outer diameter Dt is preferably less than 843 mm, more preferably less than 725 mm, and even more preferably less than 685 mm.

[0061] The tire section width Wt is preferably 125 mm or more, more preferably 150 mm or more, and even more preferably 175 mm or more, and is preferably less than 305 mm, more preferably less than 245 mm, and even more preferably less than 210 mm.

[0062] The tire of the present disclosure is characterized in that the tire cross-sectional width Wt (mm) and the tire belt layer width B (mm) satisfy the following formula (1) when a normal load is applied and the tread is pressed against a flat surface. (B-16) / Wt≦0.75 (1)

[0063] From the viewpoint of the effects of the present disclosure, the value of formula (1) is preferably 0.74 or less, more preferably 0.73 or less, and even more preferably 0.72 or less. The lower limit of formula (1) is not particularly limited, but is preferably 0.50 or more, more preferably 0.60 or more, and even more preferably 0.65 or more.

[0064] In the tire of the present disclosure, it is preferable that Wt, B, and S1 satisfy the following formula (2). (S1×B-480) / Wt≦21 (2)

[0065] The value of formula (2) is preferably 18 or less, more preferably 15 or less, and even more preferably 10 or less. The lower limit of formula (2) is not particularly limited, but is preferably 1 or more, and more preferably 2 or more.

[0066] In the tire of the present disclosure, when the tire section width is Wt (mm) and the tire outer diameter is Dt (mm), it is preferable that Wt and Dt satisfy the following formula (3). (π / 4)×(Dt 2 / Wt)≧1500 (3)

[0067] Here, as Dt increases, the value of equation (3) increases, and conversely, as Dt decreases, the value decreases. On the other hand, as Wt increases, the value of equation (3) decreases, and conversely, as Wt decreases, the value increases. Therefore, by focusing on this point and adjusting Dt and Wt, it is possible to adjust Dt and Wt so that they satisfy equation (3).

[0068] The value of formula (3) is preferably 1500 or more, more preferably 1520 or more, and even more preferably 1525 or more. There is no particular upper limit to the value of formula (3), but it is preferably 2800 or less, more preferably 2700 or less, and even more preferably 2600 or less.

[0069] Specific examples of tire sizes that satisfy formula (3) include 125 / 65R19, 145 / 60R18, 145 / 60R19, 155 / 55R18, 155 / 55R19, 155 / 70R17, 155 / 70R19, 165 / 55R20, 165 / 55R21, 165 / 60R19, 165 / 65R19, 165 / 70R18, 175 / 55R19, 175 / 55R20, 175 / 55R22, 175 / 60R18, 185 / 55R19, 185 / 60R20, 195 / 50R20, 195 / 55R20, 205 / 55R16, 195 / 65R15, and 205 / 55R16.

[0070] <Tread structure> As shown in Fig. 1, the tread portion of the tire of the present disclosure comprises a first layer 4 and a second layer 5, with the outer surface of the first layer 4 constituting the tread surface and the second layer 5 adjacent to the radially inner side of the first layer. It is also preferable to comprise a base rubber layer 6 adjacent to the radially outer side of the belt layer 3. As long as the object of the present disclosure is achieved, one or more rubber layers may be further present between the second layer 5 and the base rubber layer 6.

[0071] <Tread pattern> Fig. 2 is a schematic diagram of the contact patch when the tread is pressed against a flat surface. As shown in Fig. 2, the tread 10 constituting the tire according to the present disclosure has circumferential grooves 1 extending continuously in the tire circumferential direction C (extending linearly along the tire circumferential direction in the example of Fig. 2), lateral grooves 21 extending in the width direction, and sipes 22, 23.

[0072] The tread 10 has a plurality of circumferential grooves 1 extending continuously in the circumferential direction C. In Fig. 2, three circumferential grooves 1 are provided, but the number of circumferential grooves is not particularly limited and may be, for example, two to five. Furthermore, in the present disclosure, the circumferential grooves 1 extend linearly along the circumferential direction, but are not limited to this form and may extend, for example, in a wave-like, sinusoidal, or zigzag shape along the circumferential direction.

[0073] The tread 10 has land portions 2 separated by a plurality of circumferential grooves 1 in the tire width direction W. The shoulder land portions 11 are a pair of land portions formed between the circumferential groove 1 and the tread edge Te. The center land portion 12 is a land portion formed between the pair of shoulder land portions 11. In FIG. 3, two center land portions 12 are provided, but the number of center land portions is not particularly limited and may be, for example, one to five.

[0074] It is preferable that lateral grooves (widthwise grooves) and / or sipes are provided in the land portion 2. In Fig. 2, the shoulder land portion 11 is provided with a plurality of shoulder lateral grooves 21 whose ends open into the circumferential groove 1 and a plurality of shoulder sipes 22 whose one end opens into the circumferential groove 1, and the center land portion 12 is provided with a plurality of center sipes 23 whose one end opens into the circumferential groove 1. In the present disclosure, it is preferable that the center land portion 12 does not have lateral grooves (widthwise grooves) and sipes whose both ends open into the circumferential groove.

[0075] The land portion 2 preferably has one or more small holes. In FIG. 2, in the center land portion 12, two small holes 24 are arranged in the land portion surrounded by the tire width direction portion and tire circumferential direction portion of the center sipe 23 and the center sipe 23 adjacent to the center sipe 23 in the tire circumferential direction. The opening area of ​​the small holes on the tread surface is 0.1 to 15 mm 2 is preferable, and 0.5 to 10 mm 2 is more preferable, and 1.0 to 7.0 mm 2 is more preferable, and 1.5 to 5.0 mm 2is particularly preferred. By providing small holes with the above opening area, water can be removed from between the tread surface and the road surface when the tire comes into contact with a wet road, making it easier to obtain road conformity and improving wet grip performance, especially when traveling at high speeds. In addition, it is possible to increase the surface area of ​​the tread without adversely affecting other performance characteristics, which is thought to improve heat dissipation in the tread and make it possible to suppress temperature increases in the tire and sidewalls.

[0076] In this specification, the term "groove," including circumferential grooves and widthwise grooves, refers to a recess having a width of at least 2.0 mm, while the term "sipe" refers to a thin cut having a width of 2.0 mm or less, preferably 0.5 to 1.5 mm.

[0077] [Properties of rubber composition] In the present disclosure, the glass transition temperature Tg1 of the rubber composition constituting the first layer is −18° C. or higher. By setting the glass transition temperature Tg1 (° C.) to −18° C. or higher, the loss tangent tanδ in a temperature range higher than Tg becomes high, good heat buildup can be achieved during high-speed cornering, and wet grip performance during high-speed cornering is improved.

[0078] <tg1> Tg1 (°C) is preferably −17.5°C or lower, more preferably −17°C or higher, and even more preferably −16°C or higher. There is no particular upper limit to Tg1 (°C), but it is preferably −7°C or lower, more preferably −9°C or lower, and even more preferably −10°C or lower.

[0079] <tg2> In the present disclosure, the glass transition temperature Tg2 of the rubber composition constituting the second layer is preferably −30° C. or higher. By setting the glass transition temperature Tg2 (° C.) to −30° C. or higher, the loss tangent tanδ of the second layer does not become too low, allowing the second layer to achieve a certain level of heat buildup even during high-speed cornering, thereby achieving both excellent wet grip performance and reduced rolling resistance during high-speed cornering.

[0080] Tg2 (°C) is preferably −30°C or higher, more preferably −25°C or higher, particularly preferably −20°C or higher, and most preferably −19°C or higher. There is no particular upper limit for Tg2 (°C), but from the viewpoint of reducing rolling resistance, it is preferably −5°C or lower, more preferably −8°C or lower.

[0081] The Tg1 (°C) and Tg2 (°C) can be adjusted as appropriate by adjusting the ratio of the rubber components in the rubber composition forming each rubber layer, the amount of styrene in the rubber components, the Tg of each rubber component, and the type and amount of plasticizer. For example, Tg1 (°C) and Tg2 (°C) can be lowered by reducing the amount of styrene in the rubber components, using a styrene-butadiene rubber with a low Tg, or using an ester-based plasticizer with a low Tg as a plasticizer. On the other hand, Tg1 (°C) and Tg2 (°C) can be raised by increasing the amount of styrene in the rubber components, using a styrene-butadiene rubber with a high Tg, or using a resin component with a high Tg as a plasticizer.

[0082] In the present disclosure, Tg1-Tg2 is preferably equal to or greater than 2° C. When Tg1-Tg2 is equal to or greater than 2° C., the loss tangent tanδ of the second layer is relatively low compared to the loss tangent tanδ of the first layer, and therefore the second layer suppresses deformation of the entire tread during braking, increasing the contact area of ​​the tread surface with the road surface and improving wet grip performance.

[0083] Tg1-Tg2 is more preferably 3° C. or higher, even more preferably 5° C. or higher, and even more preferably 8° C. or higher. From the viewpoint of making it easier to generate heat in the entire second layer, the upper limit of Tg1-Tg2 is preferably 30° C. or lower, more preferably 28° C. or lower, even more preferably 24° C. or lower, and even more preferably 20° C. or lower.

[0084] [Rubber composition compounding] The rubber compositions constituting the first layer, the second layer, and the base rubber layer of the present disclosure are characterized in that the total styrene content of the rubber composition constituting the second layer is smaller than the total styrene content of the rubber composition constituting the first layer. The rubber compositions constituting each layer (hereinafter referred to as rubber compositions according to the present disclosure) can be produced using the raw materials described below. These will be described in detail below.

[0085] <Rubber component> Styrene-butadiene rubber (SBR), butadiene rubber (BR), and isoprene-based rubber are preferably used as rubber components for producing the rubber composition according to the present disclosure. Furthermore, in the present disclosure, the rubber compositions constituting the first and second layers contain SBR as an essential rubber component. Furthermore, in the present disclosure, the rubber composition constituting the base rubber layer does not necessarily contain SBR. These rubber components may be used alone, or two or more different rubber components may be used in combination.

[0086] In the present disclosure, the rubber compositions constituting the first and second layers preferably contain BR. Also, in the present disclosure, the rubber composition constituting the base rubber layer preferably contains an isoprene-based rubber, and more preferably contains an isoprene-based rubber and BR.

[0087] (SBR) The SBR is not particularly limited, and examples thereof include solution-polymerized SBR (S-SBR), emulsion-polymerized SBR (E-SBR), and modified SBRs thereof (modified S-SBR, modified E-SBR). Modified SBRs include SBRs whose ends and / or main chains are modified, and modified SBRs (condensates, those having a branched structure, etc.) coupled with tin, silicon compounds, etc. Among these, S-SBR and modified SBR are preferred, and modified S-SBR is more preferred. Furthermore, hydrogenated products of these SBRs (hydrogenated SBR) can also be used. These SBRs may be used alone or in combination of two or more.

[0088] Examples of S-SBR that can be used in the present disclosure include S-SBR manufactured and sold by JSR Corporation, Sumitomo Chemical Co., Ltd., Ube Industries, Ltd., Asahi Kasei Corporation, ZS Elastomers Co., Ltd., and the like.

[0089] From the viewpoint of grip performance, the styrene content of SBR is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 8% by mass or more. On the other hand, the styrene content of SBR is preferably 40% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less. If the styrene content of SBR exceeds 40% by mass, there is a concern that styrene groups will be adjacent to each other, causing the domains of the styrene groups to become too large, making it difficult to obtain good ground contact. In this specification, the styrene content of SBR is measured by the above-mentioned measurement method.

[0090] The vinyl content of SBR is preferably 10 mol% or more, more preferably 15 mol% or more, and even more preferably 20 mol% or more, from the viewpoints of ensuring reactivity with silica and improving rubber strength and abrasion resistance. Furthermore, the vinyl content of SBR is preferably 70 mol% or less, more preferably 65 mol% or less, and even more preferably 60 mol% or less, from the viewpoints of preventing an increase in temperature dependency and improving wet grip performance, elongation at break, and abrasion resistance. In this specification, the vinyl content (amount of 1,2-bonded butadiene units) of SBR is measured by the above-mentioned measurement method.

[0091] The weight average molecular weight (Mw) of SBR is preferably 200,000 or more from the viewpoint of wet grip performance and abrasion resistance, more preferably 300,000 or more, even more preferably 400,000 or more, and particularly preferably 500,000 or more. Furthermore, from the viewpoint of crosslinking uniformity, etc., Mw is preferably 2,000,000 or less, more preferably 1,500,000 or less, and even more preferably 1,000,000 or less. Mw is measured by the above-mentioned measurement method.

[0092] In the rubber composition constituting the first and second layers, the content of SBR in the rubber component is preferably 30% 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, from the viewpoint of wet grip performance. Furthermore, in the rubber composition constituting the first and second layers, the upper limit of the content of SBR in the rubber component is not particularly limited and can be 100% by mass, but from the viewpoint of abrasion resistance, it is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less.

[0093] (BR) The BR is not particularly limited, and examples thereof include BR having a cis-1,4 bond content of less than 50% (low-cis BR), BR having a cis-1,4 bond content of 90% or more (high-cis BR), rare earth butadiene rubber synthesized using a rare earth catalyst (rare earth BR), BR containing syndiotactic polybutadiene crystals (SPB-containing BR), and modified BR (high-cis modified BR, low-cis modified BR), which are commonly used in the tire industry.

[0094] Examples of high-cis BR include those manufactured and sold by JSR Corporation, Zeon Corporation, Ube Industries, Ltd., etc. The inclusion of high-cis BR can improve low-temperature properties and wear resistance. Examples of rare earth-based BR include those sold by Lanxess K.K.

[0095] An example of an SPB-containing BR is one in which 1,2-syndiotactic polybutadiene crystals are dispersed in BR after being chemically bonded to the BR, rather than simply being dispersed in the BR. Examples of such SPB-containing BR include the SPB-containing BR sold by Ube Industries, Ltd.

[0096] Modified BR includes those obtained by polymerizing 1,3-butadiene with a lithium initiator and then adding a tin compound, in which the terminals of the modified BR molecule are further bonded with a tin-carbon bond (tin-modified BR), and butadiene rubber having a condensed alkoxysilane compound at the active terminal of the butadiene rubber (silica-modified BR). Examples of such modified BR include tin-modified BR and S-modified polymer (silica-modified) manufactured by ZS Elastomer Co., Ltd.

[0097] The weight-average molecular weight (Mw) of BR is preferably 300,000 or more, more preferably 350,000 or more, and even more preferably 400,000 or more, from the viewpoint of abrasion resistance and grip performance. Furthermore, from the viewpoint of crosslink uniformity, it is preferably 2,000,000 or less, and more preferably 1,000,000 or less. Mw can be determined by the above-mentioned measurement method.

[0098] In the present disclosure, when the rubber composition constituting the first layer contains BR, the content of BR in the rubber component is 25% by mass or less. The content of BR in the rubber component of the rubber composition constituting the first layer is preferably 23% by mass or less, more preferably 22% by mass or less, and most preferably 21% by mass or less. Furthermore, from the viewpoint of wet grip performance, the content of BR in the rubber component of the rubber composition constituting the first layer is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and most preferably 18% by mass or more.

[0099] When the rubber composition constituting the second layer contains BR, the content of BR in the rubber component is preferably 45% by mass or less, more preferably 40% by mass or less, even more preferably 38% by mass or less, and particularly preferably 35% by mass or less, from the viewpoint of the effects of the present disclosure. Also, the content of BR in the rubber component of the rubber composition constituting the second layer is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and most preferably 20% by mass or more, from the viewpoint of wet grip performance.

[0100] When the rubber composition constituting the base rubber layer contains BR, the content of BR in the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, from the viewpoint of the effects of the present disclosure. Also, when the rubber composition constituting the base rubber layer contains BR, the content of BR in the rubber component is preferably 70% by mass or less, more preferably 60% by mass or less, from the viewpoint of the effects of the present disclosure.

[0101] (Isoprene rubber) Examples of isoprene-based rubbers that can be used include isoprene rubber (IR) and natural rubber, which are commonly used in the tire industry. Natural rubber includes unmodified natural rubber (NR), as well as modified natural rubbers such as epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), deproteinized natural rubber (DPNR), highly purified natural rubber (UPNR), and grafted natural rubber. These rubbers may be used alone or in combination of two or more.

[0102] The NR is not particularly limited, and those commonly used in the tire industry can be used, such as SIR20, RSS#3, and TSR20.

[0103] When the rubber composition constituting the first layer and the second layer contains an isoprene-based rubber, the amount of the isoprene-based rubber contained in the rubber component is not particularly limited.

[0104] When the rubber composition constituting the base rubber layer contains an isoprene-based rubber, the content of the isoprene-based rubber in the rubber component is, from the viewpoint of the effects of the present disclosure, preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, particularly preferably 60% by mass or more, and most preferably 50% by mass or more. In addition, in the rubber composition constituting the base rubber layer, the upper limit of the content of the isoprene-based rubber in the rubber component is not particularly limited, and can be 100% by mass.

[0105] (Other rubber components) The rubber component in the rubber composition according to the present disclosure may contain rubber components other than the SBR, BR, and isoprene-based rubber. Examples of other rubber components include crosslinkable rubber components commonly used in the tire industry, such as styrene-isoprene-butadiene copolymer rubber (SIBR), styrene-isobutylene-styrene block copolymer (SIBS), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), hydrogenated nitrile rubber (HNBR), butyl rubber (IIR), ethylene propylene rubber, polynorbornene rubber, silicone rubber, chlorinated polyethylene rubber, fluororubber (FKM), acrylic rubber (ACM), and hydrin rubber. These other rubber components may be used alone or in combination of two or more.

[0106] <s1> In the rubber composition according to the present disclosure, by setting the total styrene content (S1) in the first layer to 35% by mass or less, aggregation of the styrene portion in the rubber component at the tread surface is suppressed, and road conformability is easily obtained. It is preferably 25% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less.

[0107] In the rubber composition according to the present disclosure, wet grip performance can be improved by making the total styrene content (S1) in the first layer 1% by mass or more, preferably 2% by mass or more, and more preferably 5% by mass or more.

[0108] <s2> In the rubber composition according to the present disclosure, the total styrene amount (S2) of the second layer is smaller than the total styrene amount (S1) of the first layer. By making the total styrene amount (S2) of the second layer smaller than the total styrene amount (S1) of the first layer, aggregation of styrene in the styrene-butadiene rubber in the second layer is further suppressed, thereby making it easier for the tread surface to contact the road surface.

[0109] In the rubber composition according to the present disclosure, the total styrene content (S2) of the second layer is preferably 35% by mass or less, more preferably 25% by mass or less, even more preferably 20% by mass or less, and most preferably 10% by mass or less, from the viewpoint of the effects of the present disclosure. Also, the total styrene content (S2) of the second layer is preferably 1% by mass or more, more preferably 1.5% by mass or more, and even more preferably 2% by mass or more, from the viewpoint of the effects of the present disclosure.

[0110] In the rubber composition according to the present disclosure, the total styrene amount of the rubber composition constituting the base rubber layer is not particularly limited.

[0111] <Filler> The rubber compositions constituting the first and second layers preferably contain silica as a filler, more preferably carbon black and silica, and the rubber composition constituting the base rubber layer preferably contains carbon black as a filler.

[0112] (silica) By compounding silica into the rubber composition according to the present disclosure, it is possible to reduce rolling resistance and improve wet grip performance. The silica is not particularly limited, and for example, silica commonly used in the tire industry, such as silica prepared by a dry method (anhydrous silica) or silica prepared by a wet method (hydrated silica), can be used. Among these, hydrated silica prepared by a wet method is preferred because it contains a large number of silanol groups. Silica may be used alone or in combination of two or more types. In addition to silica made from hydrated silica or the like, silica made from biomass materials such as rice husks may also be used.

[0113] The nitrogen adsorption specific surface area (N2SA) of silica is 150m from the viewpoint of breaking elongation. 2 / g or more is preferable, and 180m 2 / g or more is more preferable, and 200m 2 / g or more is more preferable. From the viewpoint of reducing rolling resistance and processability, 2 / g or less is preferable, and 250m 2 / g or less is more preferable. The BET specific surface area of ​​silica in this specification can be measured by the above-mentioned measurement method.

[0114] The average primary particle size of silica is preferably 20 nm or less, more preferably 18 nm or less, and even more preferably 17 nm or less. The lower limit of the average primary particle size is not particularly limited, but from the viewpoint of silica dispersibility, it is preferably 1 nm or more, more preferably 3 nm or more, and even more preferably 5 nm or more. By having the average primary particle size of silica within the above range, the dispersibility of silica can be further improved, and the reinforcing properties, fracture properties, and abrasion resistance can be further improved. The average primary particle size of silica can be determined by the above-mentioned measurement method.

[0115] When the rubber composition constituting the first layer and the second layer contains silica, the content thereof per 100 parts by mass of the rubber component is preferably 40 parts by mass or more, preferably 50 parts by mass or more, and more preferably 60 parts by mass or more, from the viewpoint of reducing rolling resistance and improving wet grip performance. Furthermore, from the viewpoint of suppressing an increase in rolling resistance due to a deterioration in dispersibility of silica in the rubber, the content thereof is preferably 150 parts by mass or less, preferably 140 parts by mass or less, and more preferably 130 parts by mass or less. When the base rubber layer contains silica, the content thereof per 100 parts by mass of the rubber component is not particularly limited.

[0116] (carbon black) The carbon black is not particularly limited, and those commonly used in the tire industry, such as GPF, FEF, HAF, ISAF, and SAF, can be used. Specifically, N110, N115, N120, N125, N134, N135, N219, N220, N231, N234, N293, N299, N326, N330, N339, N343, N347, N351, N356, N358, N375, N539, N550, N582, N630, N642, N650, N660, N683, N754, N762, N765, N772, N774, N787, N907, N908, N990, and N991 can be preferably used. In addition to these, in-house synthesized products can also be preferably used. These may be used alone or in combination of two or more.

[0117] The nitrogen adsorption specific surface area (N2SA) of carbon black is 50m from the viewpoint of weather resistance and reinforcement. 2 / g or more is preferable, and 80m 2 / g or more is more preferable, and 100m 2 From the viewpoints of dispersibility, reduction of rolling resistance, fracture characteristics and durability, it is more preferable that the pore size is 250m / g or more. 2 / g or less is preferable, and 220m 2 / g or less is more preferable. The N2SA of carbon black in this specification can be measured by the above-mentioned measurement method.

[0118] When the rubber composition constituting the first layer contains carbon black, the content of carbon black per 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more from the viewpoints of weather resistance and reinforcement, and is preferably 40 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less from the viewpoint of reducing rolling resistance.

[0119] When the rubber composition constituting the second layer contains carbon black, the content of carbon black per 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more from the viewpoints of weather resistance and reinforcement, and is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, and even more preferably 40 parts by mass or less from the viewpoint of reducing rolling resistance.

[0120] When the base rubber layer contains carbon black, the content thereof per 100 parts by mass of the rubber component is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, from the viewpoint of reinforcement, and is preferably 100 parts by mass or less, more preferably 90 parts by mass or less, from the viewpoint of the effects of the present disclosure.

[0121] (Other fillers) Fillers other than carbon black and silica that have been conventionally used in the tire industry, such as aluminum hydroxide, calcium carbonate, alumina, clay, and talc, can be blended.

[0122] (Silane coupling agent) Silica is preferably used in combination with a silane coupling agent.The silane coupling agent is not particularly limited, and any silane coupling agent that is conventionally used in combination with silica in the tire industry can be used, for example, mercapto-based silane coupling agents such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane; sulfide-based silane coupling agents such as bis(3-triethoxysilylpropyl)disulfide, bis(3-triethoxysilylpropyl)tetrasulfide; 3-octanoylthio-1-propyltriethoxysilane, 3-hexanoylthio-1-propyltriethoxysilane, 3-octanoylthio-1-propyltrimethoxysilane Examples of suitable silane coupling agents include thioester-based silane coupling agents such as silane, vinyltriethoxysilane, vinyltrimethoxysilane, and the like; amino-based silane coupling agents such as 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, and 3-(2-aminoethyl)aminopropyltriethoxysilane; glycidoxy-based silane coupling agents such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro-based silane coupling agents such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; and chloro-based silane coupling agents such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. Among these, sulfide-based silane coupling agents and / or mercapto-based silane coupling agents are preferred. Examples of suitable silane coupling agents include those commercially available from Momentive, Inc. These silane coupling agents may be used alone or in combination.

[0123] The silane coupling agent having a mercapto group is preferably a compound represented by the following formula (4) and / or a compound containing a bonding unit A represented by the following formula (5) and a bonding unit B represented by the following formula (6). [ka] (In the formula, R 101 , R 102 , and R 103 are each independently an alkyl having 1 to 12 carbon atoms, an alkoxy having 1 to 12 carbon atoms, or -O-(R 111 -O) z -R 112 (z R 111 each independently represents a divalent hydrocarbon group having 1 to 30 carbon atoms; R 112 represents an alkyl having 1 to 30 carbon atoms, an alkenyl having 2 to 30 carbon atoms, an aryl having 6 to 30 carbon atoms, or an aralkyl having 7 to 30 carbon atoms; z represents an integer of 1 to 30; R 104 represents an alkylene having 1 to 6 carbon atoms) [ka] [ka] (wherein x represents an integer of 0 or more; y represents an integer of 1 or more; R 201 represents a hydrogen atom, a halogen atom, an alkyl having 1 to 30 carbon atoms, an alkenyl having 2 to 30 carbon atoms, or an alkynyl having 2 to 30 carbon atoms, which may be substituted with a hydroxyl or carboxyl; R 202 represents an alkylene having 1 to 30 carbon atoms, an alkenylene having 2 to 30 carbon atoms, or an alkynylene having 2 to 30 carbon atoms; 201 and R 202 may form a ring structure with

[0124] Examples of compounds represented by formula (4) include 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, and a compound represented by the following formula (7) (Si363 manufactured by Evonik Degussa GmbH), and the compound represented by the following formula can be preferably used. These compounds can be used alone or in combination of two or more. [ka]

[0125] Compounds containing the linking unit A represented by formula (5) and the linking unit B represented by formula (6) exhibit less viscosity increase during processing than sulfide-based silane coupling agents such as bis-(3-triethoxysilylpropyl)tetrasulfide. This results in better silica dispersibility, reduced rolling resistance, and improved wet grip performance and elongation at break. This is thought to be because the sulfide portion of linking unit A is a CSC bond, which is more thermally stable than tetrasulfides and disulfides, resulting in less increase in Mooney viscosity.

[0126] The content of the bonding unit A is preferably 30 to 99 mol%, more preferably 50 to 90 mol%, from the viewpoint of suppressing an increase in viscosity during processing. The content of the bonding unit B is preferably 1 to 70 mol%, more preferably 5 to 65 mol%, and even more preferably 10 to 55 mol%. The total content of the bonding 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 bonding units A and B includes cases where the bonding units A and B are located at the terminals of the silane coupling agent. When the bonding units A and B are located at the terminals of the silane coupling agent, the form of the bonding units A and B is not particularly limited, as long as they form units corresponding to the formulas (5) and (6) representing the bonding units A and B.

[0127] In a compound containing a bonding unit A represented by formula (5) and a bonding unit B represented by formula (6), the total number of repetitions (x+y) of the bonding unit A (x) and the bonding unit B (y) is preferably in the range of 3 to 300. Within this range, the mercaptosilane of the bonding unit B can be bonded to the -CH of the bonding unit A. 15 Since the surface is covered with the silica, the scorch time can be prevented from being shortened and good reactivity with the silica and rubber components can be ensured.

[0128] Examples of compounds containing a linking unit A represented by formula (5) and a linking unit B represented by formula (6) include NXT-Z30, NXT-Z45, NXT-Z60, and NXT-Z100 manufactured by Momentive Corp. These may be used alone or in combination of two or more.

[0129] The content of the mercapto group-containing silane coupling agent is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, even more preferably 2 parts by mass or more, and particularly preferably 4 parts by mass or more, per 100 parts by mass of silica, from the viewpoint of reducing rolling resistance. Also, from the viewpoint of rubber strength and abrasion resistance, the content is preferably 20 parts by mass or less, more preferably 12 parts by mass or less, even more preferably 10 parts by mass or less, and particularly preferably 9 parts by mass or less.

[0130] (Other compounding agents) In addition to the above components, the rubber composition according to the present disclosure may appropriately contain compounding agents conventionally commonly used in the tire industry, such as oil, ester-based plasticizer, resin component, liquid polymer, antioxidant, wax, zinc oxide, stearic acid, crosslinking agent such as sulfur, vulcanization accelerator, etc. The rubber compositions constituting the first and second layers preferably contain oil as a compounding agent, and more preferably contain oil and a resin component.

[0131] (oil) Examples of oils include process oils, vegetable oils, and mixtures thereof. Examples of process oils that can be used include paraffin-based process oils, aromatic process oils, and naphthenic process oils. Examples of vegetable oils include castor oil, cottonseed oil, linseed oil, rapeseed oil, soybean oil, palm oil, coconut oil, peanut oil, rosin, pine oil, pine tar, tall oil, corn oil, rice bran oil, safflower oil, sesame oil, olive oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, and tung oil. These oils may be used alone or in combination. From the perspective of life cycle assessment, lubricating oils used in rubber mixers or engines, or waste cooking oils used in restaurants, may also be used as appropriate. As the oil, for example, products from Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., Japan Energy Co., Ltd., Orisoi Co., Ltd., H&R Co., Ltd., Toyokuni Oil Mills Co., Ltd., Showa Shell Sekiyu KK, Fuji Kosan Co., Ltd., etc. can be used.

[0132] When the rubber compositions constituting the first layer, the second layer, and the base rubber layer contain oil, the content per 100 parts by mass of the rubber component is preferably 8 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 20 parts by mass or more, from the viewpoint of processability. Furthermore, from the viewpoint of abrasion resistance, the content is preferably 80 parts by mass or less, more preferably 75 parts by mass or less, and even more preferably 70 parts by mass or less. In this specification, the oil content includes the amount of oil contained in the oil-extended rubber.

[0133] (ester plasticizer) Examples of ester-based plasticizers include dibutyl adipate (DBA), diisobutyl adipate (DIBA), dioctyl adipate (DOA), di-2-ethylhexyl azelate (DOZ), dibutyl sebacate (DBS), diisononyl adipate (DINA), diethyl phthalate (DEP), dioctyl phthalate (DOP), diundecyl phthalate (DUP), dibutyl phthalate (DBP), dioctyl sebacate (DOS), tributyl phosphate (TBP), trioctyl phosphate (TOP), triethyl phosphate (TEP), trimethyl phosphate (TMP), thymidine triphosphate (TTP), tricresyl phosphate (TCP), and trixylenyl phosphate (TXP). These ester-based plasticizers may be used alone or in combination of two or more.

[0134] When the rubber compositions constituting the first layer, the second layer, and the base rubber layer contain an ester-based plasticizer, the content thereof (the total amount when multiple ester-based plasticizers are used) per 100 parts by mass of the rubber component is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 15 parts by mass or more from the viewpoint of wet grip performance. Also, from the viewpoint of processability, the content is preferably 120 parts by mass or less, more preferably 100 parts by mass or less, even more preferably 90 parts by mass or less, and particularly preferably 80 parts by mass or less.

[0135] (resin component) The resin component is not particularly limited, but examples thereof include petroleum resins, terpene resins, rosin resins, phenolic resins, etc. These resin components may be used alone or in combination of two or more.

[0136] As used herein, "C5 petroleum resin" refers to a resin obtained by polymerizing a C5 fraction. Examples of C5 fractions include petroleum fractions having 4 to 5 carbon atoms, such as cyclopentadiene, pentene, pentadiene, and isoprene. Dicyclopentadiene resin (DCPD resin) is preferably used as the C5 petroleum resin. The DCPD resin may be a resin that has been subjected to a hydrogenation treatment (hydrogenated DCPD resin). The hydrogenation treatment of the DCPD resin can be carried out by a known method, and commercially available hydrogenated resins can also be used.

[0137] As used herein, "aromatic petroleum resin" refers to a resin obtained by polymerizing a C9 fraction, and may be a hydrogenated or modified version of the resin. Examples of C9 fractions include petroleum fractions having 8 to 10 carbon atoms, such as vinyltoluene, alkylstyrene, indene, and methylindene. Specific examples of aromatic petroleum resins that are suitable for use include coumarone-indene resins, coumarone resins, indene resins, and aromatic vinyl resins. Preferred aromatic vinyl resins are homopolymers of α-methylstyrene or styrene, or copolymers of α-methylstyrene and styrene, with copolymers of α-methylstyrene and styrene being more preferred, due to their economical efficiency, ease of processing, and excellent heat generation properties. Examples of aromatic vinyl resins that can be used include commercially available products from Kraton, Eastman Chemical Company, and the like.

[0138] As used herein, the term "C5C9 petroleum resin" refers to a resin obtained by copolymerizing the C5 fraction and the C9 fraction, and may be a hydrogenated or modified resin. Examples of the C5 fraction and the C9 fraction include the petroleum fractions described above. As the C5C9 petroleum resin, for example, commercially available products from Tosoh Corporation, LUHUA, etc. can be used.

[0139] Examples of terpene resins include polyterpene resins made of at least one terpene compound selected from α-pinene, β-pinene, limonene, dipentene, and the like; aromatic modified terpene resins made from the terpene compound and an aromatic compound; terpene phenolic resins made from a terpene compound and a phenolic compound; and those obtained by subjecting these terpene resins to hydrogenation treatment (hydrogenated terpene resins). Examples of aromatic compounds used as raw materials for aromatic modified terpene resins include styrene, α-methylstyrene, vinyltoluene, and divinyltoluene. Examples of phenolic compounds used as raw materials for terpene phenolic resins include phenol, bisphenol A, cresol, and xylenol.

[0140] The rosin-based resin is not particularly limited, but examples thereof include natural resin rosin and rosin-modified resins obtained by modifying rosin by hydrogenation, disproportionation, dimerization, esterification, etc.

[0141] The phenolic resin is not particularly limited, but examples thereof include phenol formaldehyde resin, alkylphenol formaldehyde resin, alkylphenol acetylene resin, and oil-modified phenol formaldehyde resin.

[0142] From the viewpoint of grip performance, the softening point of the resin component is preferably 40° C. or higher, more preferably 60° C. or higher, and even more preferably 70° C. or higher. From the viewpoint of processability and improving the dispersibility of the rubber component and the filler, the softening point is preferably 150° C. or lower, more preferably 140° C. or lower, and even more preferably 130° C. or lower. The softening point of the resin component is measured by the above-mentioned measurement method.

[0143] When the rubber composition constituting the first and second layers contains a resin component, the content thereof per 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 2 parts by mass or more, even more preferably 3 parts by mass or more, and particularly preferably 4 parts by mass or more, from the viewpoint of wet grip performance. Furthermore, from the viewpoint of reduced rolling resistance and abrasion resistance, the content thereof is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, even more preferably 35 parts by mass or less, and particularly preferably 10 parts by mass or less. When the base rubber layer contains a resin component, the content thereof per 100 parts by mass of the rubber component is not particularly limited.

[0144] (liquid polymer) The liquid polymer is not particularly limited as long as it is a polymer that is in a liquid state at room temperature (25°C), and examples thereof include liquid diene polymers such as liquid styrene butadiene copolymer (liquid SBR), liquid butadiene polymer (liquid BR), liquid isoprene polymer (liquid IR), and liquid styrene isoprene copolymer (liquid SIR). A single liquid polymer may be used, or two or more liquid polymers may be used in combination. Among these, liquid BR is preferred from the viewpoint of grip performance. The weight-average molecular weight (Mw) of the liquid polymer can be determined by the above-mentioned method.

[0145] When the rubber compositions constituting the first layer, the second layer, and the base rubber layer contain a liquid polymer, the content (total amount when multiple liquid polymers are used) per 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more from the viewpoint of grip performance, and is preferably 40 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 25 parts by mass or less from the viewpoint of wear resistance.

[0146] (anti-aging agent) The antioxidant is not particularly limited, but examples thereof include amine-based, quinoline-based, quinone-based, phenol-based, and imidazole-based compounds, and carbamic acid metal salts, and examples thereof include N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, N,N'-diphenyl-p-phenylenediamine, N,N'-di-2-naphthyl-p-phenylenediamine, N-cyclohexyl-N'-phenyl-p-phenylenediamine, N,N'-bis(1-methylheptyl)-p-phenylenediamine, N,N'-bis(1,4-di Phenylenediamine-based antioxidants such as N,N'-bis(1-ethyl-3-methylpentyl)-p-phenylenediamine, N-4-methyl-2-pentyl-N'-phenyl-p-phenylenediamine, N,N'-diaryl-p-phenylenediamine, hindered diaryl-p-phenylenediamine, phenylhexyl-p-phenylenediamine, and phenyloctyl-p-phenylenediamine, as well as quinoline-based antioxidants such as 2,2,4-trimethyl-1,2-dihydroquinoline polymer and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline, are preferred. These antioxidants may be used alone or in combination of two or more.

[0147] When the rubber compositions constituting the first layer, the second layer, and the base rubber layer contain an antioxidant, the content thereof per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, from the viewpoint of ozone crack resistance of the rubber, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, from the viewpoint of abrasion resistance and wet grip performance.

[0148] When the rubber compositions constituting the first layer, the second layer, and the base rubber layer contain wax, the content of wax per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, from the viewpoint of weather resistance of the rubber, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, from the viewpoint of whitening of the tire due to bloom.

[0149] When the rubber compositions constituting the first layer, the second layer, and the base rubber layer contain stearic acid, the content thereof per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, from the viewpoint of processability, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, from the viewpoint of vulcanization rate.

[0150] When the rubber compositions constituting the first layer, the second layer, and the base rubber layer contain zinc oxide, the content thereof per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, from the viewpoint of processability, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, from the viewpoint of abrasion resistance.

[0151] (Crosslinking agent) As the crosslinking agent, sulfur is preferably used, and examples of sulfur that can be used include powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur.

[0152] When sulfur is contained, the content per 100 parts by mass of the rubber component is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.5 parts by mass or more, from the viewpoint of ensuring a sufficient vulcanization reaction. Furthermore, from the viewpoint of preventing deterioration, the content is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, even more preferably 3.0 parts by mass or less, and particularly preferably 2.5 parts by mass or less. When oil-containing sulfur is used as the crosslinking agent, the content of the vulcanizing agent is the total content of pure sulfur contained in the oil-containing sulfur.

[0153] Known organic crosslinking agents other than sulfur can also be used. The organic crosslinking agent is not particularly limited as long as it can form crosslinked chains other than polysulfide bonds. Examples of the organic crosslinking agent include alkylphenol-sulfur chloride condensate, sodium 1,6-hexamethylene-dithiosulfate dihydrate, 1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane, and dicumyl peroxide. 1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane is preferred. These organic crosslinking agents can be commercially available from Taoka Chemical Co., Ltd., Lanxess KK, Flexis, and other companies.

[0154] The vulcanization accelerator is not particularly limited, but examples thereof include sulfenamide-based, thiazole-based, thiuram-based, thiourea-based, guanidine-based, dithiocarbamic acid-based, aldehyde-amine-based or aldehyde-ammonia-based, imidazoline-based, and xanthate-based vulcanization accelerators. Among these, sulfenamide-based and thiuram-based vulcanization accelerators are preferred because they more suitably achieve the desired effects, and it is more preferred to use these two types in combination.

[0155] Examples of sulfenamide vulcanization accelerators include CBS (N-cyclohexyl-2-benzothiazolylsulfenamide), TBBS (Nt-butyl-2-benzothiazolylsulfenamide), N-oxyethylene-2-benzothiazolylsulfenamide, N,N'-diisopropyl-2-benzothiazolylsulfenamide, and N,N-dicyclohexyl-2-benzothiazolylsulfenamide. Examples of thiazole vulcanization accelerators include 2-mercaptobenzothiazole and dibenzothiazolyl disulfide. Examples of thiuram vulcanization accelerators include tetramethylthiuram monosulfide, tetramethylthiuram disulfide, and tetrabenzylthiuram disulfide (TBzTD). Examples of guanidine vulcanization accelerators include diphenylguanidine (DPG), di-orthotolylguanidine, and orthotolylbiguanidine. These may be used alone or in combination. Of these, the combination of CBS and TBzTD is particularly preferred because the desired effect can be more suitably obtained.

[0156] When a vulcanization accelerator is contained, the content thereof per 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 2 parts by mass or more. The content thereof per 100 parts by mass of the rubber component is preferably 8 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 6 parts by mass or less. By setting the content of the vulcanization accelerator within the above range, breaking strength and elongation tend to be ensured.

[0157] The rubber composition according to the present disclosure can be produced by a known method. For example, it can be produced by a method in which, among the above-mentioned components, components other than the vulcanizing agent (crosslinking agent) and vulcanization accelerator are kneaded in a known kneading machine generally used in the tire industry, such as a Banbury mixer, a kneader, or an open roll, and then the vulcanizing agent and vulcanization accelerator are added thereto and further kneaded, followed by vulcanization.

[0158] <Tires> The pneumatic tire according to the present disclosure has a tread constituted by the above-described rubber composition for a tread, and is suitably used as a passenger car tire, a high-performance passenger car tire, etc. It is particularly preferably used as a passenger car tire.

[0159] A tire having a tread made of the rubber composition for a tread can be manufactured by a conventional method using the rubber composition for a tread. That is, an unvulcanized rubber composition obtained by blending the above components with a rubber component as needed is extruded to match the shape of the tread, laminated together with other tire components in a tire building machine, and molded by a conventional method to form an unvulcanized tire, and the unvulcanized tire is heated and pressurized in a vulcanizer to manufacture the tire. [Example]

[0160] Hereinafter, the present disclosure will be described based on examples, but the present disclosure is not limited to these examples.

[0161] The various chemicals used in the examples and comparative examples are listed below. SBR1: HPR830E manufactured by JSR Corporation (styrene content: 39.5% by mass, vinyl content: 38.5% by mole, Tg: -23°C, oil extension amount: 10 parts by mass per 100 parts by mass of rubber component) SBR2: Modified solution-polymerized SBR produced in Production Example 2 described below (styrene content: 35% by mass, vinyl content: 50% by mole, Tg: −24° C., non-oil-extended product) SBR3: HPR850 manufactured by JSR Corporation (styrene content: 27.5% by mass, vinyl content: 59.0% by mole, Tg: -24°C, non-oil-extended) SBR4: HPR840 manufactured by JSR Corporation (styrene content: 10.0% by mass, vinyl content: 42.0% by mole, Tg: -60°C, non-oil-extended) NR:TSR20 BR: UBEPOL BR (registered trademark) 150B manufactured by Ube Industries, Ltd. (vinyl bond content: 1.5 mol%, cis-1,4-content: 97%, Mw: 440,000) Carbon black: Diablack N220 (N2SA: 115m) manufactured by Mitsubishi Chemical Corporation 2 / g) Silica 1: Evonik Degussa 9100GR (N2SA: 235 ml 2 / g, average primary particle diameter: 15.6nm) Silica 2: ZEOSIL 1115MP (N2SA:115m) manufactured by Solvay Japan Co., Ltd. 2 / g, average primary particle diameter: 23.8nm) Silane coupling agent: NXT-Z manufactured by Momentive Oil: H&R VivaTec 400 (TDAE oil) Ester-based plasticizer: TOP manufactured by Daihachi Chemical Industry Co., Ltd. Resin component 1: Sylvatraxx (registered trademark) 4401 manufactured by Arizona Chemical Company (a copolymer of α-methylstyrene and styrene, softening point: 85°C, Tg: 43°C) Resin component 2: P125 (hydrogenated polyterpene resin, softening point: 125°C, Tg: 67°C) manufactured by Yasuhara Chemical Co., Ltd. Resin component 3: ExxonMobil Oppa PR-120 (hydrogenated dicyclopentadiene resin, softening point: 120°C, Tg: 62°C) Resin component 4: Petrotack 100V (C5 / C9 mixed resin, softening point: 95°C, Tg: 62°C) manufactured by Tosoh Corporation Liquid polymer: RICON 134 (liquid BR, Mw: 8000, vinyl content: 28 mol%) manufactured by Cray Valley Antioxidant: Nocrac 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Antioxidant: Nocrac RD (poly(2,2,4-trimethyl-1,2-dihydroquinoline)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Wax: Ozoace 0355 manufactured by Nippon Seiro Co., Ltd. Stearic acid: Camellia stearic acid beads manufactured by NOF Corporation Zinc oxide: Zinc oxide No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: HK-200-5 (powdered sulfur containing 5% oil) manufactured by Hosoi Chemical Industry Co., Ltd. Vulcanization accelerator 1: Noccela CZ (N-cyclohexyl-2-benzothiazolyl sulfenamide (CBS)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator 2: Sancerer TBZTD (tetrabenzyl thiuram disulfide (TBzTD)) manufactured by Sanshin Chemical Industry Co., Ltd.

[0162] Production Example 2: Synthesis of SBR2 Cyclohexane, tetrahydrofuran, styrene, and ethylene glycol diethyl ether were charged into a nitrogen-purged autoclave reactor. After adjusting the temperature of the reactor contents to 20°C, bis(diethylamino)methylvinylsilane and n-butyllithium were charged as cyclohexane and n-hexane solutions, respectively, to initiate polymerization. The stirring speed was 130 rpm, the reactor temperature was 65°C, and copolymerization of 1,3-butadiene and styrene was carried out for 3 hours while continuously feeding the monomers into the reactor. Next, the resulting polymer solution was stirred at 130 rpm, N-(3-dimethylaminopropyl)acrylamide was added, and the reaction was carried out for 15 minutes. After the polymerization reaction was completed, 2,6-di-tert-butyl-p-cresol was added. The solvent was then removed by steam stripping and the mixture was dried on a heated roll heated to 110°C to obtain SBR2.

[0163] Examples and Comparative Examples According to the formulations shown in Tables 1 and 2, the chemicals other than sulfur and the vulcanization accelerator were mixed in a 1.7 L closed-type Banbury mixer for 1 to 10 minutes until the discharge temperature reached 150 to 160°C, yielding a kneaded mixture. Next, sulfur and the vulcanization accelerator were added to the resulting mixture using a two-screw open roll mill, and the mixture was mixed for 4 minutes until the temperature reached 105°C, yielding an unvulcanized rubber composition. The resulting unvulcanized rubber composition was molded to fit the shapes of the first layer (thickness: 3.5 mm), second layer (thickness: 3.5 mm), and base rubber layer (thickness: 1.0 mm) of the tread, and these were then bonded together with other tire components to produce unvulcanized tires. These were then vulcanized at 170°C to obtain the test tires (sizes: 205 / 65R16 or 195 / 65R15) listed in Tables 3 to 5. The circumferential groove depth (at its deepest point) was 6.5 mm.

[0164] <Measurement of glass transition temperature (Tg)> Each rubber test specimen was cut from the rubber layer of the tread portion of each test tire, measuring 20 mm in length, 4 mm in width, and 1 mm in thickness, with the long side aligned in the tire circumferential direction. A temperature distribution curve of the loss tangent (tanδ) was measured using a GABO Iplexer series under conditions of a frequency of 10 Hz, an initial strain of 10%, an amplitude of ±0.5%, and a heating rate of 2°C / min. The temperature corresponding to the largest tanδ value in the obtained temperature distribution curve (tanδ peak temperature) was taken as the glass transition temperature (Tg). The thickness direction of the sample was the radial direction of the tire.

[0165] <High-speed wet cornering> The obtained test tire was mounted on a regular rim, inflated with 250 kPa of air, and then attached to all wheels of a domestically produced FF vehicle (2000 cc). With the test tire mounted, the vehicle was driven on a wet road surface at a speed of 100 km / h, and the cornering performance was evaluated sensorily on a 5-point scale. The same evaluation was carried out by 20 drivers, and the total score of the evaluation results was calculated. The obtained results were indexed, with the result of Comparative Example 5 being set at 100, and the evaluation results for each tire were obtained. (High-speed wet cornering performance index) = (total score of each evaluated tire) / (total score of Comparative Example 5) × 100

[0166] [Table 1]

[0167] [Table 2]

[0168] [Table 3]

[0169] [Table 4]

[0170] [Table 5]

[0171] The results in Tables 3 and 4 show that tires in which the total tire width and tire breaker width meet specified requirements, the rubber composition constituting the tread surface rubber layer is compounded under specific conditions, and the total styrene content of the rubber composition constituting the tread surface rubber layer is greater than the total styrene content of the rubber composition constituting the tread inner rubber layer have excellent high-speed wet cornering performance.

[0172] <Embodiment> Examples of embodiments of the present disclosure are provided below.

[0173] [1] A tire having a tread portion and a belt layer, The tread portion includes at least a first layer constituting a tread surface and a second layer adjacent to the first layer on the inner side in the tire radial direction, the rubber component constituting the first layer and the second layer contains styrene-butadiene rubber, The content of butadiene rubber in the rubber component constituting the first layer is 25% by mass or less, The glass transition temperature Tg1 (°C) of the rubber composition constituting the first layer is -18°C or higher, a total styrene content S1 (mass%) in the rubber component constituting the first layer is 1 to 35 mass%, the total styrene content S2 (mass%) in the rubber component constituting the second layer is smaller than S1, A tire whose cross-sectional width Wt (mm) and belt layer width B (mm) satisfy the following formula (1) when the tread is pressed against a flat surface under normal load. (B-16) / Wt≦0.75 (1) [2] The tire according to the above [1], wherein Wt, B, and S1 satisfy the following formula (2): (S1×B-480) / Wt≦21 (2) [3] The tire according to [1] or [2] above, wherein the rubber composition constituting the first layer and / or the second layer contains silica having an average primary particle diameter of 20 nm or less. [4] The tire according to any one of the above [1] to [3], wherein the rubber composition constituting the first layer and / or the second layer contains 40 to 120 parts by mass of silica per 100 parts by mass of the rubber component. [5] The tire according to any one of the above [1] to [4], wherein the glass transition temperature Tg2 (°C) of the rubber composition constituting the second layer is -30°C or higher. [6] The tire according to any one of the above [1] to [5], wherein Tg1-Tg2 is 2°C or higher. [7] The tire according to any one of the above [1] to [6], wherein the content of butadiene rubber in the rubber component constituting the second layer is 30% by mass or less. [8] The tire according to any one of the above [1] to [7], wherein S2 is 15 to 35 mass %. [9] A tire according to any one of the above [1] to [8], wherein the tread portion comprises a base rubber layer adjacent to the outer side of the belt layer in the tire radial direction, and the base rubber layer is composed of a rubber composition containing a rubber component including at least one of an isoprene-based rubber and a butadiene rubber.

[10] The tire according to any one of the above [1] to [9], wherein Wt and Dt satisfy the following formula (3), where Dt (mm) is the outer diameter of the tire. (π / 4)×(Dt 2 / Wt)≧1500 (3)

[11] The tread portion has land portions partitioned by one or more circumferential grooves extending continuously in the tire circumferential direction, and at least one of the land portions has an opening area to the tread surface of 0.1 to 15 mm 2 The tire according to any one of the above [1] to

[10] , having one or more small holes. [Explanation of symbols]

[0174] Wt Section width B Belt layer width Ht Section height Dt Tire outer diameter 1 Circumferential groove 2 Land 3 Belt Layer 4 First layer 5 Second layer 6 Base rubber layer 7 Sidewall 8 Inner liner 9 Clinch 10 Tread C Circumferential direction of tire W Tire width direction Te tread edge 21 Yokomizo 22 sipes 23 Center sipe 24 Small hole 30 beads 31 Bead core 32 rims

Claims

1. A tire having a tread portion and a belt layer, the tread portion includes a first layer constituting a tread surface, a second layer adjacent to the first layer on the inner side in the tire radial direction, and a base rubber layer adjacent to the belt layer on the outer side in the tire radial direction, the rubber component constituting the first layer and the second layer contains styrene-butadiene rubber, the content of butadiene rubber in the rubber component constituting the first layer is 25% by mass or less, The glass transition temperature Tg of the rubber composition constituting the first layer 1 (°C) is -18°C or higher, a total styrene amount S1 (mass%) in the rubber component constituting the first layer is 1 to 35 mass%, the total styrene content S2 (mass%) in the rubber component constituting the second layer is smaller than S1, the rubber composition constituting the base rubber layer contains a resin component, A tire in which the cross-sectional width Wt (mm) and the belt layer width B (mm) of the tire satisfy the following formula (1) when the tread is pressed against a flat surface under a normal load in a normal state. (B-16) / Wt≦0.75...(1)

2. The tire according to claim 1, wherein Wt, B, and S1 satisfy the following formula (2): (S1 × B-480) / Wt≦21 (2)

3. The tire according to claim 1 or 2, wherein the rubber composition constituting the first layer and / or the second layer contains silica having an average primary particle diameter of 20 nm or less.

4. The tire according to any one of claims 1 to 3, wherein the rubber composition constituting the first layer and / or the second layer contains 40 to 120 parts by mass of silica per 100 parts by mass of the rubber component.

5. The glass transition temperature Tg of the rubber composition constituting the second layer 2 The tire according to any one of claims 1 to 4, wherein (°C) is -30°C or higher.

6. When the glass transition temperature of the rubber composition constituting the second layer is Tg 2 (°C), Tg 1 -Tg 2 The tire according to any one of claims 1 to 5, wherein the temperature is 2°C or higher.

7. The tire according to claim 6, wherein Tg 1 -Tg 2 is 12°C or higher.

8. The tire according to any one of claims 1 to 7, wherein the content of butadiene rubber in the rubber component constituting the second layer is 30% by mass or less.

9. The tire according to any one of claims 1 to 8, wherein S2 is 26.25 mass% or less.

10. A tire described in any one of claims 1 to 9, wherein the base rubber layer is composed of a rubber composition containing a rubber component including at least one of isoprene-based rubber and butadiene rubber.

11. The tire according to any one of claims 1 to 10, wherein Wt and Dt satisfy the following formula (3), where Dt (mm) is the tire outer diameter: (π / 4)×(Dt 2 / Wt)≧1500・・・(3)

12. The tread portion has land portions partitioned by one or more circumferential grooves extending continuously in the tire circumferential direction, and at least one of the land portions has an opening area to the tread surface of 0.1 to 15 mm 2 12. The tire according to claim 1, having one or more small holes.

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