JP2024176462A - tire - Google Patents

Abstract

The present invention provides a tire that can improve the overall performance of wet grip performance and traction performance.
[Solution] A tire with a tread portion, the tread portion having a plurality of circumferential grooves extending continuously in the tire circumferential direction, the tread portion having at least a first layer constituting a tread surface and a second layer adjacent to the radially inward side of the first layer, the first layer and the second layer each being composed of a rubber composition containing a rubber component and silica, the thickness of the first layer being t1 (mm), the groove depth at the deepest part of the circumferential groove being H (mm), the content of silica per 100 parts by mass of the rubber component in the rubber composition constituting the first layer being S1 (parts by mass), a tire in which, when a silica content per 100 parts by mass of the rubber component in the rubber composition constituting the second layer is S2 (parts by mass), an acetone extractable amount of the rubber composition constituting the first layer is AE1 (% by mass), an acetone extractable amount of the rubber composition constituting the second layer is AE2 (% by mass), a complex modulus of elasticity at 30°C of the second layer is 30°CE*2 (MPa), and a land ratio at the contact surface of the tread portion is R, t1/H is 0.90 or less, the product of R and 30°CE*2 (R×30°CE*2) is 12.0 or less, and AE2/S2 is greater than AE1/S1.
[Selection diagram] None

Description

The present invention relates to a tire.

Various methods for improving the traction performance of tires have been studied for some time. For example, Patent Document 1 describes that the overall performance of wear resistance and traction performance at high temperatures can be improved by using a rubber composition containing a specific styrene-butadiene rubber, vulcanized rubber particles, and carbon black in the tread.

JP 2022-32428 A

However, in recent years, there has been a demand for further improvement in the overall wet grip and traction performance of tires.

The present invention aims to provide a tire that can improve the overall performance of wet grip performance and traction performance.

The present invention relates to a tire having a tread portion, the tread portion having a plurality of circumferential grooves extending continuously in the tire circumferential direction, the tread portion having at least a first layer constituting a tread surface and a second layer adjacent to the radially inner side of the first layer, the first layer and the second layer each being composed of a rubber composition containing a rubber component and silica, the thickness of the first layer being t1 (mm), the groove depth of the deepest part of the circumferential groove being H (mm), the content of silica per 100 parts by mass of the rubber component in the rubber composition constituting the first layer being S1 (parts by mass), and the The tire relates to a tire in which, when the content of silica per 100 parts by mass of the rubber component in the rubber composition constituting the two layers is S2 (parts by mass), the amount of acetone extractable from the rubber composition constituting the first layer is AE1 (% by mass), the amount of acetone extractable from the rubber composition constituting the second layer is AE2 (% by mass), the complex modulus of elasticity at 30°C of the second layer is 30°CE*2 (MPa), and the land ratio at the contact surface of the tread portion is R, t1/H is 0.90 or less, the product of R and 30°CE*2 (R x 30°CE*2) is 12.0 or less, and AE2/S2 is greater than AE1/S1.

The present invention can improve the overall wet grip and traction performance of a tire.

1 is a cross-sectional view showing a portion of a tread portion of a tire according to an embodiment of the present invention.

A tire according to one embodiment of the present invention is a tire having a tread portion, the tread portion having a plurality of circumferential grooves extending continuously in the tire circumferential direction, the tread portion having at least a first layer constituting a tread surface and a second layer adjacent to the radially inner side of the first layer, the first layer and the second layer each being composed of a rubber composition containing a rubber component and silica, the thickness of the first layer being t1 (mm), the groove depth of the deepest part of the circumferential groove being H (mm), the content of silica per 100 parts by mass of the rubber component in the rubber composition constituting the first layer being S1 (parts by mass), and the The tire has a silica content of S2 (parts by mass) per 100 parts by mass of the rubber component in the rubber composition constituting the two layers, an acetone extractable amount of the rubber composition constituting the first layer is AE1 (% by mass), an acetone extractable amount of the rubber composition constituting the second layer is AE2 (% by mass), a complex elastic modulus of the second layer at 30°C is 30°CE*2 (MPa), and a land ratio of the contact surface of the tread portion is R. t1/H is 0.90 or less, the product of R and 30°CE*2 (R x 30°CE*2) is 12.0 or less (preferably 8.0 or less), and AE2/S2 is greater than AE1/S1.

Without intending to be bound by theory, the reason why the overall wet grip performance and traction performance of the tire of the present invention is improved is thought to be as follows.

By making AE2/S2 larger than AE1/S1, the first layer is a rubber with high rigidity due to silica, and the second layer is a soft rubber due to low molecular weight components, and it is believed that the second layer is relatively softer than the first layer. For this reason, when the tread is distorted during turning, the soft, highly maneuverable second layer is more likely to generate heat. This heat is then transferred to the first layer, instantly improving the ability to follow the road surface, which is believed to improve wet grip performance. In addition, when the temperature of the tread drops after turning, the first layer, which is closer to the road surface, is air-cooled first, so the rigidity of the first layer increases, making it easier to generate force to scratch the road surface, which is believed to enable efficient traction performance.

In addition, by setting t1/H to 0.90 or less, the outer surface of the second layer is positioned radially outward of the deepest part of the bottom of the circumferential groove, and the land portion and the inside of the block are formed of two or more rubber layers. This makes it easier for distortion in the tread portion to be transmitted to the second layer, which has a high heat generation rate, and easier for heat from the second layer to be transmitted to the first layer, which is thought to improve wet grip performance more efficiently.

Furthermore, by decreasing the complex modulus of elasticity at 30°C (30°C E*2) of the second layer as the land ratio increases, the high maneuverability and heat generation of the second layer during cornering allows the first layer to obtain good rigidity during cornering and straight driving, which is believed to have the remarkable effect of synergistically improving wet grip performance and traction performance.

The glass transition temperature Tg1 of the rubber composition constituting the first layer and the glass transition temperature Tg2 of the rubber composition constituting the second layer are both preferably -10°C or lower, and more preferably -20°C or lower.

By setting Tg1 and Tg2 within the above ranges, it is believed that the deformation speed of the tread rubber increases, allowing it to adequately follow the road surface even during high-speed driving, when deformation occurs at high frequency.

The tan δ of the first layer at 30°C (30°C tan δ1) and the tan δ of the second layer at 30°C (30°C tan δ2) are preferably both 0.50 or less, and more preferably both 0.30 or less.

By reducing tan δ in a temperature range close to the actual temperature during driving, it is possible to reduce the phase difference between input and response, making it easier to instantly transmit the force generated in the tread to the road surface, which is thought to improve cornering performance.

The total styrene amount Sty1 in the rubber component constituting the first layer and the total styrene amount Sty2 in the rubber component constituting the second layer are each preferably 45% by mass or less, and more preferably 35% by mass or less.

It is believed that by reducing the total amount of styrene in the rubber component, the risk of impaired road conformity due to the effect of hard domains caused by excess styrene is reduced.

The average primary particle size of the silica is preferably 23 nm or less, and more preferably 18 nm or less.

By setting the average primary particle size of silica within the above range, it is believed that a fine silica network can be formed, and force from the road surface can be easily transmitted through this network.

From the viewpoint of grip performance, it is preferable that the rubber component constituting the first layer and the rubber component constituting the second layer each contain 60% by mass or more of styrene-butadiene rubber.

The product of R and Sty1 (R x Sty1) is preferably 20 or less.

By decreasing Sty1 as the land ratio R increases, it is believed that it is possible to increase the contact area with the road surface while making it easier to obtain tracking performance on the tread surface. On the other hand, by increasing Sty1 when R is small, it is believed that it is possible to generate energy loss on the tread surface as well, making it easier to improve cornering performance.

The product of R and Sty2 (R x Sty2) is preferably 20 or less.

By decreasing Sty2 as the land ratio R increases, the second layer becomes more likely to deform during cornering, and the heat also softens the first layer, making it easier to obtain conformability to the road surface. In addition, by increasing Sty2 when R is small, it becomes possible to increase heat generation within the second layer, which is thought to improve conformability of the entire tread portion.

It is preferable that the width of the circumferential grooves gradually increases from the end on the tire surface side toward the inside in the tire radial direction.

It is believed that by gradually increasing the groove width of the circumferential grooves toward the inside of the tire in the radial direction, the second layer becomes more easily deformed, making it easier for heat to be generated in the second layer during cornering.

<Definition>
The "tread portion" refers to the portion that forms the contact surface of the tire, and in the case where the tire includes components that form the tire skeleton made of steel or textile materials, such as a belt layer, a belt reinforcing layer, and a carcass layer, in the radial cross section of the tire, the component that is radially outward of these components.

"Genuine rim" refers to the rim that is specified for each tire by the standard system that includes the standard on which the tire is based. For JATMA, this refers to the "standard rim" described in the "JATMA YEAR BOOK." For ETRTO (The European Tire and Rim Technical Organisation), this refers to the "Measuring Rim" described in the "STANDARDS MANUAL." For TRA (The Tire and Rim Association, Inc.), this refers to the "Design Rim" described in the "YEAR BOOK." JATMA, ETRTO, and TRA are referred to in that order, and if there is an applicable size at the time of reference, that standard is followed. For tires not specified in the above standards, this refers to the narrowest rim among the smallest diameter rims that can be assembled with the tire and can hold internal pressure (i.e., no air leaks from between the rim and tire).

"Regular internal pressure" refers to the air pressure set for each tire by each standard in the standard system, including the standard on which the tire is based. For JATMA, it refers to the "Maximum Air Pressure", for ETRTO, it refers to the "INFLATION PRESSURE", and for TRA, it refers to the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES". As with regular rims, refer to JATMA, ETRTO, and TRA in that order, and follow the standard if there is an applicable size at the time of reference. Note that in the case of tires not specified in the above standards, the regular internal pressure refers to the regular internal pressure (250 kPa or more) of another tire size (defined in the standard) for which the regular rim is listed as the standard rim, and if multiple regular internal pressures of 250 kPa or more are listed, it refers to the smallest value among them.

"Normal condition" refers to a state in which the tire is mounted on a normal rim, inflated to normal internal pressure, and unloaded. In this specification, unless otherwise specified, the dimensions of each part of the tire are measured in the normal condition.

A "groove," including circumferential and lateral grooves, is a recess with a width of at least 2.0 mm. On the other hand, a "sipe" is a thin cut with a width of 2.0 mm or less, preferably 0.5 to 2.0 mm.

"Land ratio R" is the ratio of the total area of the contact surface to the total surface area of the tread surface (i.e., the area obtained by the outer contour of the contact shape of the tread portion) when a tire in a normal state is loaded with a normal load and in contact with a flat surface with a camber angle of 0 degrees, assuming that all grooves are filled. Here, "all grooves" includes grooves that do not fall under the above-mentioned circumferential grooves and lateral grooves.

The "total area of the contact patch" is calculated from the tire's contact shape. The contact shape is obtained by mounting the tire on a standard rim, applying standard internal pressure, and leaving it at 25°C for 24 hours, then applying ink to the tread surface, and pressing it against cardboard under a load of maximum load capacity (camber angle is 0°) to transfer the shape to the paper. The tire is then rotated 72° in circumferential directions, and the shape is transferred at five locations. In other words, five contact shapes are obtained. The actual contact area is calculated as the average area of the ink parts at five locations.

"The thickness of each rubber layer constituting the tread" refers to the thickness of each rubber layer on the tire equatorial plane in a cross section of the tire cut along a plane including the tire rotation axis, and is the average value of the tread thicknesses obtained at five positions by rotating the tire circumferentially at 72° intervals. For example, the thickness of the first layer refers to the linear distance in the tire radial direction from the outermost tread surface to the tire radially inner interface of the first layer on the tire equatorial plane. In addition, when the tire has a circumferential groove on the tire equatorial plane, the thickness of each rubber layer constituting the tread is the thickness of each rubber layer at the tire widthwise center of the land portion closest to the tire equatorial plane. "The land portion closest to the tire equatorial plane" refers to the land portion of the circumferential groove present on the tire equatorial plane that has the groove edge closest to the tire equatorial plane, and when such land portions exist on both sides in the tire width direction, the thickness of each rubber layer constituting the tread is the average value of the thicknesses of each rubber layer at the tire widthwise center of the two land portions. In addition, if there is a conductive member or the like on the land portion of the tire's equatorial plane and the interface is unclear, the interface that is blocked by the conductive member or the like is virtually connected and measured.

The "groove depth at the deepest part of the circumferential groove" is determined by the distance in the tire radial direction between the tread surface and the deepest part of the groove bottom of the circumferential groove. The deepest part of the groove bottom of the circumferential groove is the deepest part of the groove bottom of the circumferential groove that has the deepest groove depth among the circumferential grooves adjacent to the land portion or block portion.

A "softener" is a material that imparts plasticity to a rubber component, and is a component that is extracted from a rubber composition using acetone. Softeners include softeners that are liquid (liquid-like) at 25°C and softeners that are solid at 25°C. However, this does not include wax and stearic acid that are commonly used in the tire industry.

"Softener content" includes the amount of softener contained in the extended rubber component that has been extended in advance with a softener such as oil, resin component, or liquid rubber component. The same applies to the oil content, resin component content, and liquid rubber content. For example, if the extended component is oil, the extended oil is included in the oil content.

<Measurement method>
"The thickness of each rubber layer constituting the tread portion" is measured in a state in which the tire is cut along a plane including the tire rotation axis and the width of the bead portion is adjusted to the width of a regular rim.

The "acetone extractable amount" can be calculated in accordance with JIS K 6229:2015 by immersing each vulcanized rubber test piece in acetone at room temperature (about 25°C) for 72 hours to extract the soluble components, measuring the mass of each test piece before and after extraction, and then calculating the amount of acetone extractable from the following formula.
(Amount of acetone extracted (mass %))={(mass of rubber test piece before extraction−mass of rubber test piece after extraction)/(mass of rubber test piece before extraction)}×100

"30°C tan δ" is the loss tangent measured using a dynamic viscoelasticity measuring device (e.g., the Iplexer series manufactured by GABO) under the following conditions: temperature 30°C, frequency 10 Hz, initial strain 5%, dynamic strain ±1%, and extension mode. The sample for measuring the loss tangent is a vulcanized rubber composition having a length of 20 mm, width 4 mm, and thickness of 1 mm. When cutting out from a tire, the sample is cut out from the tread portion of the tire so that the long side is in the tire circumferential direction and the thickness direction is in the tire radial direction.

"30℃E*" is the complex modulus measured using a dynamic viscoelasticity measuring device (e.g., the Iplexer series manufactured by GABO) under the following conditions: temperature 30℃, frequency 10Hz, initial strain 5%, dynamic strain ±1%, and extension mode. The sample for this measurement is prepared in the same manner as for 30℃tan δ.

The "glass transition temperature (Tg) of the rubber composition" is determined by measuring the temperature distribution curve of tan δ using a dynamic viscoelasticity measuring device (e.g., the 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. The glass transition temperature is the temperature (tan δ peak temperature) corresponding to the maximum value in the range of -60°C to 40°C on the obtained temperature distribution curve. Note that in the range of -60°C to 40°C, if tan δ continues to gradually increase or decrease with increasing temperature, the glass transition temperature is 40°C or -60°C, respectively. In addition, if there are two points showing maximum values in the range of -60°C to 40°C, the lowest temperature point is taken as the glass transition temperature. The measurement sample is prepared in the same manner as for 30°C tan δ.

The "styrene content" is a value calculated by ¹ H-NMR measurement, and is applied to a rubber component having repeating units derived from styrene, such as SBR.

"Vinyl content (amount of 1,2-bonded butadiene units)" is a value calculated by infrared absorption spectrum analysis in accordance with JIS K 6239-2:2017, and applies to rubber components that have repeating units derived from butadiene, such as SBR and BR.

"Cis content (amount of cis-1,4-bonded butadiene units)" is a value calculated by infrared absorption spectrum analysis in accordance with JIS K 6239-2:2017, and applies to rubber components that have repeating units derived from butadiene, such as BR.

"Total styrene content in rubber component" refers to the total content (mass%) of styrene units contained in 100% by mass of rubber component, calculated by multiplying the styrene content (mass%) of each rubber component by the mass fraction in the rubber component, and adding up the values obtained. Specifically, it is calculated by Σ(styrene content (mass%) of each styrene unit-containing rubber × content (mass%) of each styrene unit-containing rubber in the rubber component/100).

The "glass transition temperature (Tg) of the rubber component" is measured in accordance with JIS K 7121 using a differential scanning calorimeter (Q200) manufactured by TA Instruments Japan Ltd., while increasing the temperature at a rate of 10°C/min.

The "weight average molecular weight (Mw)" can be calculated based on the measured value by gel permeation chromatography (GPC) (e.g., GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMALTIPORE HZ-M manufactured by Tosoh Corporation) and converted into standard polystyrene. For example, it is applicable to SBR, BR, etc.

"Nitrogen adsorption specific surface area (N ₂ SA) of carbon black" is measured in accordance with JIS K 6217-2: 2017. "Nitrogen adsorption specific surface area (N ₂ SA) of silica" is measured by the BET method in accordance with ASTM D3037-93.

The "average primary particle size" is calculated by photographing particles with a transmission or scanning electron microscope and taking the arithmetic average of 400 particle sizes. If the particle shape is nearly circular, the diameter of the circle is used as the particle size. If the particle shape is needle-like or rod-like, the minor axis is used as the particle size. In other cases, the equivalent circle diameter is calculated from the electron microscope image. The equivalent circle diameter is calculated as (4 x (particle area)/π)^0.5. The average primary particle size applies to silica, carbon black, etc.

The "softening point of the resin component" is the temperature at which the ball drops when the softening point as specified in JIS K 6220-1:2015 7.7 is measured using a ring and ball softening point tester.

A tire, which is one embodiment of the present invention, will be described with reference to the appropriate drawings. However, the following description is merely an example for explaining the present invention, and is not intended to limit the technical scope of the present invention to the scope of this description.

<Tires>
An example of a cross-sectional view showing a part of a tread portion of a tire according to the present embodiment is shown in Fig. 1. In Fig. 1, the up-down direction is the radial direction of the tire, the left-right direction is the axial direction of the tire, and the direction perpendicular to the paper surface is the circumferential direction of the tire.

As shown in the figure, the tread portion of the tire according to this embodiment comprises a first layer 11 and a second layer 12, with the outer surface of the first layer 11 forming the tread surface, and the second layer 12 adjacent to the first layer 11 on the radially inner side of the tire. In addition, as long as the object of the present invention is achieved, one or more rubber layers (third layer 13 in FIG. 1) may be further provided between the second layer 13 and the belt layer (not shown).

From the viewpoint of the effects of the present invention, the thickness t1 of the first layer 11 is preferably 3 mm or more, more preferably 4 mm or more, and even more preferably 5 mm or more. On the other hand, t1 is preferably 14 mm or less, more preferably 12 mm or less, and even more preferably 10 mm or less.

From the viewpoint of the effects of the present invention, the thickness t2 of the second layer 12 is preferably 0.5 mm or more, and more preferably 1.0 mm or more. On the other hand, t2 is preferably 10 mm or less, more preferably 8 mm or less, and even more preferably 6 mm or less.

From the viewpoint of the effects of the present invention, the groove depth H of the circumferential groove is preferably 5 mm or more, more preferably 6 mm or more, and even more preferably 7 mm or more. On the other hand, H is preferably 16 mm or less, more preferably 14 mm or less, and even more preferably 12 mm or less.

The tire according to this embodiment is formed so that the deepest part of the bottom of the circumferential groove is located radially inward of the outer surface of the second layer 12, and the land portion is formed of two or more rubber layers. From the viewpoint of the effects of the present invention, t1/H is 0.90 or less, preferably 0.88 or less, and more preferably 0.85 or less. On the other hand, the lower limit of t1/H is not particularly limited, but is preferably 0.30 or more, more preferably 0.40 or more, and even more preferably 0.50 or more.

It is preferable that the second layer 12 has a recess that is recessed radially inward from the outermost portion of the second layer, and that a part of the first layer 11 is formed within the recess of the second layer 12, and it is more preferable that the surface of the recess is formed by the first layer 11. With this configuration, when the tread portion wears and the second layer is exposed, the second layer is present in the center of the land portion and the first layer is present in the edge portion of the land portion, and it is believed that the effect of the present invention is easily achieved.

In FIG. 1, the circumferential groove 3 is formed so that the deepest part of the groove bottom of the circumferential groove 3 is located radially inward of the outermost part of the second layer 12 in the tire radial direction in the land portion adjacent to the circumferential groove 3. Specifically, on the radially inner side of the circumferential groove 3, the second layer 12 has a recess that is recessed radially inward from its outermost part, and a part of the first layer 11 is formed with a predetermined thickness within the recess of the second layer 12. The circumferential groove 3 is formed so as to extend beyond the outermost part of the second layer 12 in the tire radial direction and enter inside the recess of the second layer 12.

It is preferable that at least one groove wall of the circumferential groove has a recess that is recessed outward in the groove width direction from the groove edge 2 that appears on the tread surface of the tread portion. It is believed that providing a recess on the groove wall of the circumferential groove makes it easier for the second layer to deform, making it easier to generate heat in the second layer during cornering.

In FIG. 1, the circumferential groove 3 has recesses 9 on both sides of the groove wall 10, the recesses being constant in the circumferential direction of the tire. The groove width of the circumferential groove 3 gradually increases from the end on the tire surface side toward the inside in the tire radial direction. The groove wall 5 of the circumferential groove 3 extends linearly from the outside toward the inside in the tire radial direction, but is not limited to this form and may extend, for example, in a curved or stepped manner.

The total recess amount of the circumferential groove 3 (c1+c2 in FIG. 1) is preferably 0.10 to 2.00 times the groove width W1 of the circumferential groove 3, more preferably 0.20 to 1.50 times, and even more preferably 0.30 to 0.90 times. If there are multiple circumferential grooves having the recess, it is sufficient that the total recess amount of any one of the circumferential grooves satisfies the above relationship, and all grooves having recesses may satisfy the above relationship.

The land ratio R at the contact surface of the tread portion is preferably 0.50 or more, more preferably 0.55 or more, even more preferably 0.60 or more, and particularly preferably 0.65 or more. The land ratio R is preferably 0.90 or less, more preferably 0.88 or less, even more preferably 0.85 or less, and particularly preferably 0.82 or less.

The acetone extractable amount ( _AE1 ) of the rubber composition constituting the first layer is preferably 8 mass% or more, more preferably 10 mass% or more, even more preferably 12 mass% or more, and particularly preferably 14 mass% or more. Also, _AE1 is preferably 30 mass% or less, more preferably 27 mass% or less, and even more preferably 24 mass% or less.

The acetone extractable amount ( _AE2 ) of the rubber composition constituting the second layer is preferably 8 mass% or more, more preferably 10 mass% or more, even more preferably 12 mass% or more, still more preferably 14 mass% or more, even more preferably 16 mass% or more, and particularly preferably 18 mass% or more. Also, _AE2 is preferably 32 mass% or less, more preferably 30 mass% or less, even more preferably 28 mass% or less, and particularly preferably 26 mass% or less.

The 30°C E* (30°C E*1) of the rubber composition constituting the first layer is preferably 5 MPa or more, more preferably 6 MPa or more, even more preferably 7 MPa or more, and particularly preferably 8 MPa or more. On the other hand, the 30°C E*1 is preferably 40 MPa or less, more preferably 35 MPa or less, and even more preferably 30 MPa or less.

The 30°C E* (30°C E*2) of the rubber composition constituting the second layer is preferably 2 MPa or more, more preferably 3 MPa or more, and even more preferably 4 MPa or more. On the other hand, the 30°C E*2 is preferably 18 MPa or less, more preferably 16 MPa or less, and even more preferably 14 MPa or less.

The difference between 30°C E*1 and 30°C E*2 (30°C E*1-30°C E*2) is preferably 1 MPa or more, more preferably 2 MPa or more, even more preferably 3 MPa or more, and particularly preferably 4 MPa or more. On the other hand, the upper limit of 30°C E*1-30°C E*2 is not particularly limited, but is preferably 20 MPa or less, more preferably 18 MPa or less, even more preferably 16 MPa or less, and particularly preferably 14 MPa or less.

The 30°C E* of the rubber composition can be adjusted as appropriate by adjusting the types and amounts of the rubber components, fillers, and softeners described below.

From the viewpoint of the effects of the present invention, the 30°C tan δ (30°C tan δ1) of the rubber composition constituting the first layer is preferably 0.55 or less, more preferably 0.50 or less, even more preferably 0.45 or less, even more preferably 0.40 or less, even more preferably 0.35 or less, and particularly preferably 0.30 or less. Also, the 30°C tan δ (30°C tan δ2) of the rubber composition constituting the second layer is preferably 0.55 or less, more preferably 0.50 or less, even more preferably 0.45 or less, even more preferably 0.40 or less, even more preferably 0.35 or less, and particularly preferably 0.30 or less. On the other hand, from the viewpoint of the effects of the present invention, the 30°C tan δ1 and 30°C tan δ2 are preferably 0.06 or more, more preferably 0.08 or more, even more preferably 0.10 or more, and particularly preferably 0.12 or more. The 30°C tan δ of the rubber composition can be adjusted as appropriate by adjusting the types and amounts of the rubber components, fillers, and softeners described below.

The Tg (Tg1) of the rubber composition constituting the first layer is preferably -5°C or lower, more preferably -10°C or lower, even more preferably -15°C or lower, even more preferably -20°C or lower, and particularly preferably -24°C or lower. The Tg (Tg2) of the rubber composition constituting the second layer is preferably -5°C or lower, more preferably -10°C or lower, even more preferably -15°C or lower, even more preferably -20°C or lower, and particularly preferably -24°C or lower. On the other hand, the lower limit values of Tg1 and Tg2 are not particularly limited, but are preferably -65°C or higher, more preferably -60°C or higher, even more preferably -55°C or higher, and particularly preferably -50°C or higher. The Tg of the rubber composition can be appropriately adjusted by the type and amount of the rubber component, filler, and softener described below.

The tire according to the present embodiment is characterized in that, when the content of silica per 100 parts by mass of the rubber component in the rubber composition constituting the first layer is S1 (parts by mass), and the content of silica per 100 parts by mass of the rubber component in the rubber composition constituting the second layer is S2 (parts by mass), AE2/S2 is greater than AE1/S1. The difference between AE2/S2 and AE1/S1 (AE2/S2-AE1/S1) is preferably 0.01 or more, more preferably 0.02 or more, even more preferably 0.03 or more, and particularly preferably 0.04 or more. On the other hand, the upper limit of the difference between AE2/S2 and AE1/S1 (AE2/S2-AE1/S1) is not particularly limited, but is preferably 0.30 or less, more preferably 0.25 or less, and even more preferably 0.20 or less.

AE1/S1 is preferably 0.10 or more, more preferably 0.12 or more, even more preferably 0.14 or more, and particularly preferably 0.16 or more. AE1/S1 is preferably 0.30 or less, more preferably 0.27 or less, and even more preferably 0.24 or less.

AE2/S2 is preferably 0.17 or more, more preferably 0.19 or more, even more preferably 0.21 or more, and particularly preferably 0.23 or more. AE2/S2 is preferably 0.47 or less, more preferably 0.45 or less, and even more preferably 0.43 or less.

From the viewpoint of the effect of the present invention, the product of R and 30°C E*2 (R x 30°C E*2) is 12.0 or less, preferably 11.5 or less, more preferably 11.0 or less, even more preferably 10.5 or less, and particularly preferably 10.0 or less. On the other hand, from the viewpoint of the mobility and heat generation of the rubber composition constituting the second layer, R x 30°C E*2 is preferably 2.0 or more, more preferably 2.5 or more, and even more preferably 3.0 or more.

When the total styrene content Sty1 (mass%) in the rubber component constituting the first layer is taken as the product of R and Sty1 (R x Sty1) is preferably 35 or less, more preferably 30 or less, even more preferably 25 or less, even more preferably 20 or less, and particularly preferably 18 or less. There is no particular lower limit for R x Sty1, but it is preferably 2 or more, more preferably 4 or more, even more preferably 6 or more, and particularly preferably 8 or more.

When the total styrene content Sty2 (mass%) in the rubber component constituting the second layer is taken as the total styrene content Sty2, the product of R and Sty2 (R x Sty2) is preferably 35 or less, more preferably 30 or less, even more preferably 25 or less, even more preferably 20 or less, and particularly preferably 18 or less. There is no particular lower limit for R x Sty2, but it is preferably 2 or more, more preferably 4 or more, even more preferably 6 or more, and particularly preferably 8 or more.

[Rubber composition]
The rubber composition constituting the tread portion of the tire of the present invention (rubber composition according to the present embodiment) will be described below, but unless otherwise specified, it can be applied to any rubber layer of the tread portion. The rubber composition according to the present embodiment contains a rubber component and silica, and may further contain other compounding ingredients.

<Rubber component>
In the rubber composition according to the present embodiment, a diene rubber is preferably used as the rubber component. Examples of diene rubber include isoprene rubber, butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene rubber (SIR), styrene isoprene butadiene rubber (SIBR), chloroprene rubber (CR), and acrylonitrile butadiene rubber (NBR). These diene rubbers may be modified rubbers treated with a modifying group capable of interacting with fillers such as carbon black and silica, or may be hydrogenated rubbers in which a portion of the unsaturated bonds has been hydrogenated. The diene rubber may be used alone or in combination of two or more types. In addition, an extended rubber that has been previously extended using a softener described later may be used.

The content of diene rubber in the rubber component is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. The rubber component may also consist of only diene rubber.

As the diene rubber component, at least one selected from the group consisting of isoprene rubber, styrene butadiene rubber (SBR), and butadiene rubber (BR) is preferably used. The rubber component constituting the first layer preferably contains SBR, and more preferably contains SBR and BR. The rubber component constituting the second layer preferably contains SBR, and more preferably contains SBR and BR.

(SBR)
The SBR is not particularly limited, and examples thereof include unmodified solution-polymerized SBR (S-SBR) and emulsion-polymerized SBR (E-SBR), as well as modified SBRs thereof (modified S-SBR, modified E-SBR). Examples of modified SBR include SBR 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. Furthermore, hydrogenated products of these SBRs (hydrogenated SBR), etc. can also be used. These SBRs may be used alone or in combination of two or more.

As the SBR according to this embodiment, either extended SBR or non-extended SBR can be used. When extended SBR is used, the amount of extension of the SBR, i.e., the content of the extension softener contained in the SBR, is preferably 10 to 50 parts by mass per 100 parts by mass of the rubber solid content of the SBR.

The SBRs listed above may be used alone or in combination of two or more. As the SBRs listed above, for example, commercially available products from Sumitomo Chemical Co., Ltd., JSR Corporation, Asahi Kasei Corporation, Nippon Zeon Co., Ltd., ZS Elastomers Co., Ltd., etc. can be used.

The styrene content of SBR is preferably 50% by mass or less, more preferably 45% by mass or less, even more preferably 40% by mass or less, even more preferably 35% by mass or less, and particularly preferably 28% by mass or less. The styrene content of SBR is preferably 5% by mass or more, more preferably 7% by mass or more, and even more preferably 10% by mass or more. The styrene content of SBR is measured by the above-mentioned measurement method.

From the viewpoints of ensuring reactivity with silica, rubber strength, and abrasion resistance, 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 preventing an increase in temperature dependency, breaking elongation, and abrasion resistance, 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. The vinyl content of SBR is measured by the above-mentioned measurement method.

From the viewpoint of the effects of the present invention, the weight average molecular weight (Mw) of SBR is preferably 100,000 or more, more preferably 140,000 or more, and even more preferably 180,000 or more. From the viewpoint of crosslinking uniformity, the weight average molecular weight is preferably 2,000,000 or less, more preferably 1,800,000 or less, and even more preferably 1,500,000 or less. The Mw of SBR is measured by the above-mentioned measurement method.

From the viewpoint of abrasion resistance, the glass transition temperature (Tg) of SBR is preferably -90°C or higher, more preferably -80°C or higher, and even more preferably -70°C or higher. The Tg of SBR is preferably -10°C or lower, more preferably -15°C or lower, and even more preferably -20°C or lower. The Tg of SBR is measured by the above-mentioned measurement method.

The content of SBR in the rubber component constituting the first layer 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. There is no upper limit to the content, but it is preferably 99% by mass or less, more preferably 95% by mass or less, and even more preferably 90% by mass or less.

The total styrene content Sty1 in the rubber component constituting the first layer is preferably 45% by mass or less, more preferably 42% by mass or less, more preferably 37% by mass or less, and particularly preferably 33% by mass or less. Sty1 is preferably 3% by mass or more, more preferably 5% by mass or more, and even more preferably 7% by mass or more.

The content of SBR in the rubber component constituting the second layer 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. There is no upper limit to the content, but it is preferably 99% by mass or less, more preferably 95% by mass or less, and even more preferably 90% by mass or less.

The total styrene content Sty2 in the rubber component constituting the second layer is preferably 45% by mass or less, more preferably 42% by mass or less, more preferably 37% by mass or less, and particularly preferably 33% by mass or less. Sty2 is preferably 3% by mass or more, more preferably 5% by mass or more, and even more preferably 7% by mass or more.

(BR)
The BR is not particularly limited, and can be, for example, BR having a cis content of less than 50% by mass (low cis BR), BR having a cis content of 90% by mass or more (high cis BR), rare earth butadiene rubber (rare earth BR) synthesized using a rare earth catalyst, BR containing syndiotactic polybutadiene crystals (SPB-containing BR), modified BR (high cis modified BR, low cis modified BR), etc. These BRs can be used alone or in combination of two or more.

As the high cis BR, for example, commercially available products from Zeon Corporation, Ube Industries, Ltd., JSR Corporation, etc. can be used. The inclusion of high cis BR can improve abrasion resistance. The cis content of high cis BR is preferably 95% by mass or more, more preferably 96% by mass or more, and even more preferably 97% by mass or more. The cis content of BR is measured by the above-mentioned measurement method.

As the modified BR, a modified butadiene rubber (modified BR) in which the terminals and/or the main chain are modified with a functional group containing at least one element selected from the group consisting of silicon, nitrogen, and oxygen is preferably used.

Other modified BRs include those obtained by polymerizing 1,3-butadiene with a lithium initiator and then adding a tin compound, in which the ends of the modified BR molecules are further bonded with tin-carbon bonds (tin-modified BR). In addition, the modified BR may be either non-hydrogenated or hydrogenated.

From the viewpoint of abrasion resistance, 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 crosslinking uniformity, etc., it is preferably 2,000,000 or less, and more preferably 1,000,000 or less. The Mw of BR is measured by the above-mentioned measurement method.

The content of BR in the rubber component constituting the first layer is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, and particularly preferably 25% by mass or less. There is no particular lower limit for the content, but it is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more.

The content of BR in the rubber component constituting the second layer is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, and particularly preferably 25% by mass or less. There is no particular lower limit for the content, but it is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more.

(Isoprene rubber)
As the isoprene-based rubber, for example, isoprene rubber (IR) and natural rubber, which are common in the tire industry, can be used. In addition to unmodified natural rubber (NR), natural rubber also includes modified natural rubber such as epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), deproteinized natural rubber (DPNR), high-purity natural rubber, and grafted natural rubber. These isoprene-based rubbers may be used alone or in combination of two or more.

There are no particular limitations on NR, and any commonly used NR in the tire industry can be used, such as SIR20, RSS#3, TSR20, etc.

The content of isoprene-based rubber is preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 20% by mass or less, and particularly preferably 15% by mass or less. There is no particular lower limit to the content, but it is preferably 1% by mass or more, and can be, for example, 3% by mass or more, or 5% by mass or more.

(Other rubber components)
The rubber component may contain other rubber components other than the diene rubber, as long as the effect of the present invention is not affected. As the rubber component other than the diene rubber, a crosslinkable rubber component generally used in the tire industry can be used, and examples thereof include non-diene rubbers such as butyl rubber (IIR), halogenated butyl rubber, 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. In addition to the above rubber components, a known thermoplastic elastomer may or may not be contained.

<Filler>
The rubber composition according to the present embodiment contains silica as a filler, and preferably contains carbon black and silica.

(Carbon Black)
The carbon black is not particularly limited, and for example, GPF, FEF, HAF, ISAF, SAF, and other carbon blacks commonly used in the tire industry can be used. In addition to carbon blacks produced by burning common mineral oils, carbon blacks using biomass materials such as lignin can also be used. In addition, recycled carbon blacks obtained by pyrolyzing products containing carbon black, such as tires and plastic products, can also be used. These carbon blacks can be used alone or in combination of two or more.

From the viewpoint of reinforcing properties, the nitrogen adsorption specific surface area ( _N2SA ) of carbon black is preferably 30 ^m2 /g or more, more preferably 50 ^m2 /g or more, and even more preferably 70 ^m2 /g or more. From the viewpoints of fuel efficiency and processability, it is preferably 200 ^m2 /g or less, more preferably 180 ^m2 /g or less, and even more preferably 160 ^m2 /g or less. The _N2SA of carbon black is measured by the above-mentioned measurement method.

From the viewpoint of reinforcement, the carbon black content per 100 parts by mass of the rubber component in the rubber composition constituting the first layer is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, even more preferably 15 parts by mass or more, and particularly preferably 20 parts by mass or more. The content is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, even more preferably 40 parts by mass or less, and particularly preferably 35 parts by mass or less.

From the viewpoint of reinforcement, the carbon black content per 100 parts by mass of the rubber component in the rubber composition constituting the second layer is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, even more preferably 15 parts by mass or more, and particularly preferably 20 parts by mass or more. The content is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, even more preferably 40 parts by mass or less, and particularly preferably 35 parts by mass or less.

(silica)
The silica is not particularly limited, and can be, for example, silica prepared by a dry method (anhydrous silica), silica prepared by a wet method (hydrated silica), or other silica commonly used in the tire industry. Among them, hydrated silica prepared by a wet method is preferred because it has a large number of silanol groups. In addition to the above silica, silica made from biomass materials such as rice husks can be used as appropriate. These silicas can be used alone or in combination of two or more types.

From the viewpoints of fuel economy and wear resistance, the nitrogen adsorption specific surface area ( _N2SA ) of silica is preferably 120 ^m2 /g or more, more preferably 150 ^m2 /g or more, and even more preferably 170 ^m2 /g or more. From the viewpoints of fuel economy and processability, it is preferably 350 ^m2 /g or less, more preferably 300 ^m2 /g or less, and even more preferably 250 ^m2 /g or less. The _N2SA of silica is measured by the above-mentioned measurement method.

From the viewpoint of the effects of the present invention, the average primary particle diameter of silica is preferably 25 nm or less, more preferably 23 nm or less, even more preferably 20 nm or less, and particularly preferably 18 nm or less. The lower limit of the average primary particle diameter is not particularly limited, but from the viewpoint of the dispersibility of silica, it is preferably 1 nm or more, more preferably 3 nm or more, and even more preferably 5 nm or more. The average primary particle diameter of silica is measured by the above-mentioned measurement method.

From the viewpoint of the effects of the present invention, the silica content S1 per 100 parts by mass of the rubber component in the rubber composition constituting the first layer is preferably 40 parts by mass or more, more preferably 50 parts by mass or more, even more preferably 60 parts by mass or more, and particularly preferably 65 parts by mass or more. In addition, the content is preferably 150 parts by mass or less, more preferably 140 parts by mass or less, even more preferably 130 parts by mass or less, and particularly preferably 120 parts by mass or less.

From the viewpoint of the effects of the present invention, the silica content S2 per 100 parts by mass of the rubber component in the rubber composition constituting the second layer is preferably 40 parts by mass or more, more preferably 50 parts by mass or more, even more preferably 60 parts by mass or more, and particularly preferably 65 parts by mass or more. In addition, the content is preferably 150 parts by mass or less, more preferably 140 parts by mass or less, even more preferably 130 parts by mass or less, and particularly preferably 120 parts by mass or less.

(Other fillers)
The filler other than silica and carbon black is not particularly limited, and may be, for example, one that has been generally used in the tire industry, such as aluminum hydroxide, alumina (aluminum oxide), calcium carbonate, magnesium sulfate, talc, clay, biochar, etc. These other fillers may be used alone or in combination of two or more.

The total filler content per 100 parts by mass of the rubber component is preferably 40 parts by mass or more, more preferably 50 parts by mass or more, even more preferably 60 parts by mass or more, and particularly preferably 65 parts by mass or more. The content is preferably 160 parts by mass or less, more preferably 150 parts by mass or less, even more preferably 140 parts by mass or less, and particularly preferably 130 parts by mass or less.

The silica content in the filler contained in the rubber composition constituting the first layer is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and particularly preferably 75% by mass or more. There is no particular upper limit to the content, but it is preferably 95% by mass or less, and more preferably 90% by mass or less.

The silica content in the filler contained in the rubber composition constituting the second layer is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and particularly preferably 75% by mass or more. The upper limit of the silica content is not particularly limited, but is preferably 98% by mass or less, more preferably 95% by mass or less, and even more preferably 92% by mass or less.

(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 has been 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, and 2-mercaptoethyltriethoxysilane; sulfide-based silane coupling agents such as bis(3-triethoxysilylpropyl)disulfide and bis(3-triethoxysilylpropyl)tetrasulfide; 3-octanoylthio-1-propyltriethoxysilane, 3-hexanoylthio-1-propyltriethoxysilane, and 3-octanoylthio-1-propyltrimethoxysilane. Examples of the silane coupling agent include thioester-based silane coupling agents such as silane; vinyl-based silane coupling agents such as vinyltriethoxysilane and vinyltrimethoxysilane; 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, it is preferable to contain a sulfide-based silane coupling agent and/or a mercapto-based silane coupling agent. As the silane coupling agent, for example, those commercially available from Evonik Degussa, Momentive, etc. can be used. These silane coupling agents may be used alone or in combination of two or more.

The content of the silane coupling agent relative to 100 parts by mass of silica 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, from the viewpoint of increasing the dispersibility of the silica. Also, from the viewpoint of cost and processability, it is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 12 parts by mass or less.

<Other compounding agents>
In addition to the above-mentioned components, the rubber composition according to the present embodiment may appropriately contain compounding agents that are generally used in the tire industry, such as a softener, wax, stearic acid, zinc oxide, an antioxidant, a vulcanizing agent, and a vulcanization accelerator.

Examples of softeners include resin components, oils, liquid polymers, etc.

The resin component is not particularly limited, but examples include hydrocarbon resins commonly used in the tire industry, such as petroleum resins, terpene resins, rosin resins, and phenolic resins.

Examples of petroleum resins include C5 petroleum resins, aromatic petroleum resins, C5C9 petroleum resins, etc.

In this specification, "C5 petroleum resin" refers to a resin obtained by polymerizing a C5 fraction, and may be a hydrogenated or modified resin. Examples of C5 fractions include petroleum fractions with 4 to 5 carbon atoms, such as cyclopentadiene, pentene, pentadiene, and isoprene. Dicyclopentadiene resin (DCPD resin) is preferably used as a C5 petroleum resin.

In this specification, "aromatic petroleum resin" refers to a resin obtained by polymerizing a C9 fraction, and may be a hydrogenated or modified 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 preferably used include coumarone-indene resins, coumarone resins, indene resins, and aromatic vinyl resins. As aromatic vinyl resins, homopolymers of α-methylstyrene or styrene or copolymers of α-methylstyrene and styrene are preferred, and copolymers of α-methylstyrene and styrene are more preferred, because they are economical, easy to process, and have excellent heat generation properties. As aromatic vinyl resins, for example, those commercially available from Kraton, Eastman Chemical, etc. can be used.

In this specification, "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, those commercially available from Tosoh Corporation, LUHUA Corporation, etc. can be used.

Examples of terpene resins include polyterpene resins made of at least one terpene compound selected from α-pinene, β-pinene, limonene, dipentene, and other terpene compounds; aromatic modified terpene resins containing the terpene compound and an aromatic compound as monomer components; terpene phenol resins containing a terpene compound and a phenol compound as monomer components; and terpene resins that have been subjected to a hydrogenation treatment (hydrogenated terpene resins). Examples of aromatic compounds that are monomer components of aromatic modified terpene resins include styrene, α-methylstyrene, vinyltoluene, and divinyltoluene. Examples of phenolic compounds that are monomer components of terpene phenol resins include phenol, bisphenol A, cresol, and xylenol.

Rosin-based resins are not particularly limited, but examples include natural resin rosin and rosin-modified resins obtained by modifying rosin through hydrogenation, disproportionation, dimerization, esterification, etc.

Examples of phenol-based resins include, but are not limited to, phenol formaldehyde resin, alkylphenol formaldehyde resin, alkylphenol acetylene resin, oil-modified phenol formaldehyde resin, etc.

From the viewpoint of grip performance, the softening point of the resin component is preferably 60°C or higher, more preferably 70°C or higher, and even more preferably 80°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.

When a resin component is contained, the content 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, even more preferably 5 parts by mass or more, and particularly preferably 7 parts by mass or more. From the viewpoint of suppressing heat generation, the content is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, even more preferably 30 parts by mass or less, and particularly preferably 25 parts by mass or less.

Examples of the oil include process oil and vegetable oil. Examples of the process oil include paraffin-based process oil (mineral oil), naphthenic process oil, and aromatic process oil. Specific examples of the process oil include MES (Mild Extract Solvated), DAE (Distillate Aromatic Extract), TDAE (Treated Distillate Aromatic Extract), TRAE (Treated Residual Aromatic Extract), and RAE (Residual Aromatic Extract). In addition, as an environmental measure, process oil with a low content of polycyclic aromatic compounds (PCA) compounds can be used. Examples of the low PCA content process oil include MES, TDAE, and heavy naphthenic oil. In addition, from the viewpoint of life cycle assessment, waste oil after use in rubber mixers and engines, and refined waste edible oil used in cooking restaurants may be used.

From the viewpoint of the effects of the present invention, the oil content per 100 parts by mass of the rubber component in the rubber composition constituting the first layer is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, and even more preferably 20 parts by mass or more. In addition, 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.

From the viewpoint of the effects of the present invention, the oil content per 100 parts by mass of the rubber component in the rubber composition constituting the second layer is preferably 25 parts by mass or more, more preferably 30 parts by mass or more, even more preferably 35 parts by mass or more, and particularly preferably 40 parts by mass or more. In addition, the content is preferably 90 parts by mass or less, more preferably 85 parts by mass or less, even more preferably 80 parts by mass or less, and particularly preferably 75 parts by mass or less.

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), but examples include liquid butadiene polymer (liquid BR), liquid isoprene rubber polymer (liquid IR), liquid styrene butadiene copolymer (liquid SBR), liquid styrene isoprene rubber copolymer (liquid SIR), polymers containing myrcene or farnesene, etc. These liquid polymers may be used alone or in combination of two or more types.

When a liquid polymer is contained, the content 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. The content of the liquid polymer 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.

The content of the softener per 100 parts by mass of the rubber component in the rubber composition constituting the first layer (the total amount when multiple softeners are used in combination) is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, even more preferably 20 parts by mass or more, even more preferably 25 parts by mass or more, even more preferably 30 parts by mass or more, and particularly preferably 35 parts by mass or more, from the viewpoint of the effects of the present invention. The content is preferably 90 parts by mass or less, more preferably 85 parts by mass or less, even more preferably 80 parts by mass or less, even more preferably 75 parts by mass or less, and particularly preferably 70 parts by mass or less.

From the viewpoint of the effects of the present invention, the content of the softener per 100 parts by mass of the rubber component in the rubber composition constituting the second layer (the total amount of all softeners when multiple softeners are used) is preferably 30 parts by mass or more, more preferably 35 parts by mass or more, even more preferably 40 parts by mass or more, even more preferably 45 parts by mass or more, and particularly preferably 50 parts by mass or more. In addition, the content is preferably 100 parts by mass or less, more preferably 95 parts by mass or less, even more preferably 90 parts by mass or less, and particularly preferably 85 parts by mass or less.

The wax is not particularly limited, and any wax commonly used in the tire industry can be suitably used. Examples of the wax include petroleum wax, mineral wax, and synthetic wax, with petroleum wax being preferred. Examples of the petroleum wax include paraffin wax, microcrystalline wax, and selected special waxes thereof, with paraffin wax being preferred. The wax according to this embodiment does not contain stearic acid. The wax may be commercially available from, for example, Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., Paramelt Co., Ltd., etc. These waxes may be used alone or in combination of two or more types.

When wax is contained, the content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, and more preferably 1.0 parts by mass or more, from the viewpoint of weather resistance of the rubber. Also, from the viewpoint of preventing whitening of the tire due to bloom, the content is preferably 10 parts by mass or less, and more preferably 5.0 parts by mass or less.

The anti-aging agent 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. Phenylenediamine-based anti-aging agents such as 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, and N-cyclohexyl-N'-phenyl-p-phenylenediamine, and quinoline-based anti-aging agents such as 2,2,4-trimethyl-1,2-dihydroquinoline polymer and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline are preferred. These anti-aging agents may be used alone or in combination of two or more.

When an antioxidant is contained, the content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, and more preferably 1.0 parts by mass or more, from the viewpoint of the ozone crack resistance of the rubber. Also, from the viewpoint of abrasion resistance, the content is preferably 10 parts by mass or less, and more preferably 5.0 parts by mass or less.

When stearic acid is contained, the content per 100 parts by mass of the rubber component 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, from the viewpoint of processability. Also, from the viewpoint of vulcanization speed, the content is preferably 10 parts by mass or less, and more preferably 5.0 parts by mass or less.

When zinc oxide is contained, the content per 100 parts by mass of the rubber component 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, from the viewpoint of processability. Also, from the viewpoint of abrasion resistance, the content is preferably 10 parts by mass or less, and more preferably 5.0 parts by mass or less.

Sulfur is preferably used as a vulcanizing agent. Examples of sulfur that can be used include powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur.

When sulfur is used as a vulcanizing agent, the content per 100 parts by mass of the rubber component is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 1.0 parts by mass or more, from the viewpoint of ensuring a sufficient vulcanization reaction. Also, 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, and even more preferably 3.5 parts by mass or less. Note that when oil-containing sulfur is used as the vulcanizing agent, the content of the vulcanizing agent is the total content of the pure sulfur contained in the oil-containing sulfur.

Examples of vulcanizing agents other than sulfur include alkylphenol-sulfur chloride condensates, sodium 1,6-hexamethylene-dithiosulfate dihydrate, 1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane, etc. These vulcanizing agents other than sulfur can be commercially available from Taoka Chemical Co., Ltd., LANXESS Co., Ltd., Flexis, etc.

Examples of vulcanization accelerators include sulfenamide-based vulcanization accelerators, thiazole-based vulcanization accelerators, guanidine-based vulcanization accelerators, thiuram-based vulcanization accelerators, dithiocarbamate-based vulcanization accelerators, and caprolactam disulfide. These vulcanization accelerators may be used alone or in combination of two or more. Among them, from the viewpoint of more suitably obtaining the desired effect, one or more vulcanization accelerators selected from the group consisting of sulfenamide-based vulcanization accelerators, thiazole-based vulcanization accelerators, and guanidine-based vulcanization accelerators are preferred, and it is more preferred to use a sulfenamide-based vulcanization accelerator and a guanidine-based vulcanization accelerator in combination.

Examples of sulfenamide vulcanization accelerators include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), and N,N-dicyclohexyl-2-benzothiazolylsulfenamide (DCBS). Of these, TBBS and CBS are preferred.

Examples of thiazole-based vulcanization accelerators include 2-mercaptobenzothiazole (MBT) or its salts, di-2-benzothiazolyl disulfide (MBTS), 2-(2,4-dinitrophenyl)mercaptobenzothiazole, 2-(2,6-diethyl-4-morpholinothio)benzothiazole, etc. Among these, MBTS and MBT are preferred, and MBTS is more preferred.

Examples of guanidine vulcanization accelerators include 1,3-diphenylguanidine (DPG), 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, di-o-tolylguanidine salt of dicatechol borate, 1,3-di-o-cumenylguanidine, 1,3-di-o-biphenylguanidine, 1,3-di-o-cumenyl-2-propionylguanidine, etc. Among these, DPG is preferred.

When a vulcanization accelerator is contained, the content per 100 parts by mass of the rubber component 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. The content per 100 parts by mass of the rubber component is preferably 8.0 parts by mass or less, more preferably 6.0 parts by mass or less, and even more preferably 4.0 parts by mass or less. By keeping the content of the vulcanization accelerator within the above range, breaking strength and elongation tend to be ensured.

[Production of rubber composition and tire]
The rubber composition according to the present embodiment can be produced by a known method, for example, by kneading the above-mentioned components using a rubber kneading device such as an open roll or an internal kneader (such as a Banbury mixer or a kneader).

The kneading process includes, for example, a base kneading process in which compounding ingredients and additives other than the vulcanizing agent and vulcanization accelerator are kneaded, and a final kneading (F kneading) process in which the vulcanizing agent and vulcanization accelerator are added to the kneaded product obtained in the base kneading process and kneaded. Furthermore, the base kneading process can be divided into multiple processes as desired.

The kneading conditions are not particularly limited, but examples include a method in which the base kneading process involves kneading for 3 to 10 minutes at a discharge temperature of 150 to 170°C, and in the final kneading process, kneading for 1 to 5 minutes at 70 to 110°C. The vulcanization conditions are not particularly limited, but examples include a method in which vulcanization is performed for 10 to 30 minutes at 150 to 200°C.

The tire of the present disclosure, which has a tread composed of the rubber composition, can be manufactured by a conventional method. That is, an unvulcanized rubber composition in which the above-mentioned components are blended with the rubber component as necessary is extruded to match the shape of the first and second layers of the tread, laminated together with other tire components on a tire building machine, and molded by a conventional method to form an unvulcanized tire, which can then be heated and pressurized in a vulcanizer to manufacture the tire. The vulcanization conditions are not particularly limited, and examples include a method of vulcanizing at 150 to 200°C for 10 to 30 minutes.

[Tire applications]
The tire according to the present embodiment can be suitably used as a passenger car tire, a truck/bus tire, a motorcycle tire, or a racing tire, and is preferably used as a passenger car tire. Note that a passenger car tire is a tire that is intended to be mounted on a four-wheeled vehicle and has a maximum load capacity of 1000 kg or less.

The following are examples (working examples) that are considered to be preferable for carrying out the present invention, but the scope of the present invention is not limited to these working examples. Using the various chemicals shown below, tires having first, second, and third layers in the tread portion obtained according to the formulations in Table 1 were examined, and the results calculated based on the evaluation method described below are shown in Tables 2 and 3.

Various chemicals used in the examples and comparative examples are listed below.
NR: TSR20
SBR1: SBR produced by Production Example 1 below (S-SBR, styrene content: 46% by mass, vinyl content: 40% by mole, non-extended product)
SBR2: Nipol NS522 manufactured by ZS Elastomers Co., Ltd. (S-SBR, styrene content: 39 mass%, vinyl content: 40 mol%, Tg: -25°C, Mw: 1.2 million, contains 37.5 mass parts of oil extension oil per 100 mass parts of rubber solids)
SBR3: SBR produced according to Production Example 2 below (S-SBR, styrene content: 25% by mass, vinyl content: 25% by mol, non-extended product)
SBR4: HPR850 manufactured by JSR Corporation (S-SBR, styrene content: 27.5% by mass, vinyl content: 59 mol%, Tg: -24°C, Mw: 200,000, non-extended product)
SBR5: HPR840 manufactured by JSR Corporation (S-SBR, styrene content: 10% by mass, vinyl content: 42 mol%, Tg: -60°C, Mw: 190,000, non-extended product)
BR: UBEPOL BR (registered trademark) 150B manufactured by Ube Industries, Ltd. (unmodified BR, cis content: 97% by mass, Mw: 440,000)
Carbon black: Show Black N330 ( _N2SA : ^75m2 /g) manufactured by Cabot Japan Co., Ltd.
Silica 1: Zeosil 1115MP manufactured by Solvay ( _N2SA : 115 ^m2 /g, average primary particle size: 24 nm)
Silica 2: ZEOSIL 115GR manufactured by Solvay ( _N2SA : 115 ^m2 /g, average primary particle size: 20 nm)
Silica 3: ULTRASIL (registered trademark) VN3 manufactured by Evonik Degussa (N ₂ SA: 175 m ² /g, average primary particle size: 17 nm)
Silane coupling agent: Si266 (bis(3-triethoxysilylpropyl)disulfide) manufactured by Evonik Degussa
Oil: VivaTec 500 (TDAE oil) manufactured by H&R Corporation
Resin component: Sylvares SA85 manufactured by Kraton (a copolymer of α-methylstyrene and styrene, softening point: 85° C.)
Anti-aging agent: Antigen 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd.
Wax: Sunnock N (paraffin wax) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Stearic acid: Beads of stearic acid camellia manufactured by NOF Corp. Zinc oxide: Zinc oxide type 2 manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: Powder manufactured by Karuizawa Sulfur Co., Ltd. Sulfur vulcanization accelerator 1: Noccela CZ (N-cyclohexyl-2-benzothiazolyl sulfenamide (CBS)) 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.

(Production Example 1: Production of SBR1)
Hexane, 1,3-butadiene, styrene, and tetrahydrofuran are charged into a nitrogen-substituted autoclave reactor and stirred at 40°C. The ratio of styrene and 1,3-butadiene is adjusted so that the styrene content is 46% by mass. After adding a 0.1 mol/L n-butyllithium/hexane solution and performing a scavenging treatment, 4 mL of a 0.1 mol/L n-butyllithium/hexane solution is added and stirred at a stirring speed of 130 rpm and a jacket temperature of 80°C. After confirming the production of a polymer with Mw of 1 million by GPC, the polymerization solution is poured into 4 L of ethanol and the precipitate is collected. The obtained precipitate is dried by blowing air, and then dried under reduced pressure at 80°C/10 Pa or less until the loss on drying is 0.1%, to obtain SBR1.

(Production Example 2: Production of SBR2)
SBR2 is obtained in the same manner as in Production Example 1, except that the ratios of styrene and 1,3-butadiene are adjusted so that the styrene content is 25 mass %.

Examples and Comparative Examples
According to the compounding recipes shown in Tables 1 and 2, chemicals other than sulfur and vulcanization accelerator are kneaded for 1 to 10 minutes using a 1.7 L closed type Banbury mixer until the discharge temperature reaches 150 to 160°C, to obtain a kneaded product. Next, sulfur and vulcanization accelerator are added to the kneaded product using a two-screw open roll, and the mixture is kneaded for 4 minutes until the temperature reaches 105°C, to obtain an unvulcanized rubber composition. The unvulcanized rubber composition is extruded into the shapes of the first layer (thickness: 8.5 mm) and the second layer (thickness: 1.5 mm) of the tread part using an extruder equipped with a die of a predetermined shape, and laminated together with other tire components to prepare an unvulcanized tire, which is press-vulcanized for 12 minutes under the condition of 170°C, to obtain each test tire (size: 205/55R16, rim: 16×6.5J, internal pressure: 250 kPa) shown in Tables 3 and 4. The groove depth H of the deepest portion of the circumferential groove is 9.5 mm, the groove width of the circumferential groove is 9.0 mm, and the total recess amount of the circumferential groove is 5.4 mm.

<Measurement of acetone extractable amount (AE amount)>
The AE amount is measured for each vulcanized rubber test piece cut out from the inside of each rubber layer of the tread portion of each test tire. The AE amount is calculated according to the following formula by immersing each vulcanized rubber test piece in acetone at room temperature (about 25°C) for 72 hours in accordance with JIS K 6229:2015 to extract soluble components, measuring the mass of each test piece before and after extraction.
(Amount of acetone extracted (mass %))={(mass of rubber test piece before extraction−mass of rubber test piece after extraction)/(mass of rubber test piece before extraction)}×100

<Measurement of 30° C. tan δ and 30° C. E*>
Each vulcanized rubber test piece was cut out from inside each rubber layer of the tread portion of each test tire to a length of 20 mm, a width of 4 mm, and a thickness of 1 mm, with the long side in the tire circumferential direction and the thickness direction in the tire radial direction. The loss tangent tan δ and complex modulus of elasticity E* of each test piece were measured using a dynamic viscoelasticity measuring device (Iplexer series manufactured by GABO Corporation) under conditions of a temperature of 30°C, a frequency of 10 Hz, an initial strain of 5%, a dynamic strain of ±1%, and an elongation mode.

<Measurement of Glass Transition Temperature (Tg)>
For each vulcanized rubber test piece prepared by cutting out a length of 20 mm x width of 4 mm x thickness of 1 mm from inside each rubber layer of the tread portion of each test tire, with the long side in the tire circumferential direction and the thickness direction in the tire radial direction, a temperature distribution curve of tan δ was measured using a dynamic viscoelasticity measuring device (Iplexer series manufactured by GABO Corporation) 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 temperature (tan δ peak temperature) corresponding to the maximum value of the obtained temperature distribution curve in the range of -60°C to 40°C was determined as the glass transition temperature.

<Wet grip performance>
The above test tires were fitted to all wheels of a domestically produced FF vehicle (engine displacement 2000cc), and the vehicle was driven on a wet asphalt road surface at an initial speed of 100km/h, and the braking distance was measured. The reciprocal value of the braking distance was expressed as an index, with the braking distance of Comparative Example 1 set at 100. The larger the index, the better the wet grip performance.

<Traction performance>
The above test tires were fitted to all wheels of a domestically produced FF vehicle (engine displacement 2000cc), which was driven at 80km/h on a dry asphalt road surface, and the traction performance was evaluated based on the feeling when stepping on the accelerator at the corner exit. The evaluation was performed using integer values from 1 point to 5 points, and the total score of the 20 test drivers was calculated based on the evaluation criteria that the higher the score, the better the traction performance. The total score of the control tire (Comparative Example 1) was then converted to a standard value (100), and the evaluation results of each test tire were displayed as an index proportional to the total score.

<Embodiment>
Examples of embodiments of the present invention are given below.

[1] A tire having a tread portion, the tread portion having a plurality of circumferential grooves extending continuously in a tire circumferential direction, the tread portion having at least a first layer constituting a tread surface and a second layer adjacent to the radially inner side of the first layer, the first layer and the second layer each being composed of a rubber composition containing a rubber component and silica, the first layer having a thickness t1 (mm), the groove depth of the deepest part of the circumferential groove being H (mm), the content of silica relative to 100 parts by mass of the rubber component in the rubber composition constituting the first layer being S1 (parts by mass), and the a tire in which, when the content of silica per 100 parts by mass of the rubber component in the rubber composition constituting the second layer is S2 (parts by mass), the amount of acetone extractable from the rubber composition constituting the first layer is AE1 (% by mass), the amount of acetone extractable from the rubber composition constituting the second layer is AE2 (% by mass), the complex modulus of elasticity at 30°C of the second layer is 30°CE*2 (MPa), and R is a land ratio at the contact surface of the tread portion, t1/H is 0.90 or less, the product of R and 30°CE*2 (R×30°CE*2) is 12.0 or less, and AE2/S2 is greater than AE1/S1.
[2] The tire according to the above [1], wherein R×30° C. E*2 is 8.0 or less.
[3] The tire according to the above [1] or [2], wherein the glass transition temperature Tg1 of the rubber composition constituting the first layer and the glass transition temperature Tg2 of the rubber composition constituting the second layer are both −10° C. or lower.
[4] The tire according to the above [3], wherein both Tg1 and Tg2 are −20° C. or lower.
[5] The tire according to any one of the above [1] to [4], wherein the tan δ at 30° C. (30° C. tan δ1) of the first layer and the tan δ at 30° C. (30° C. tan δ2) of the second layer are both 0.50 or less.
[6] The tire according to the above [5], wherein both of 30° C. tan δ1 and 30° C. tan δ2 are 0.30 or less.
[7] The tire according to any one of the above [1] to [6], wherein a total styrene amount Sty1 in the rubber component constituting the first layer and a total styrene amount Sty2 in the rubber component constituting the second layer are both 45 mass% or less.
[8] The tire according to the above [7], wherein both Sty1 and Sty2 are 35 mass% or less.
[9] The tire according to any one of the above [1] to [8], wherein the average primary particle diameter of the silica is 23 nm or less.
[10] The tire according to any one of [1] to [8] above, wherein the average primary particle diameter of the silica is 18 nm or less.
[11] The tire according to any one of the above [1] to [10], wherein the rubber component constituting the first layer and the rubber component constituting the second layer each contain 60% by mass or more of styrene-butadiene rubber.
[12] The tire according to any one of [7] to [11] above, wherein the product of R and Sty1 (R × Sty1) is 20 or less.
[13] The tire according to any one of the above [7] to [12], wherein the product of R and Sty2 (R × Sty2) is 20 or less.
[14] The tire according to any one of [1] to [13] above, wherein the circumferential groove has a groove width that gradually increases from the end portion on the tire surface side toward the inside in the tire radial direction.

REFERENCE SIGNS LIST 1 tread portion 2 groove edge 3 circumferential groove 9 recess 10 groove wall 11 first layer 12 second layer 13 third layer 14 tread surface

Claims (14)

A tire having a tread portion,
The tread portion has a plurality of circumferential grooves extending continuously in a circumferential direction of the tire,
The tread portion includes at least a first layer constituting a tread surface and a second layer adjacent to the radially inner side of the first layer,
the first layer and the second layer are each made of a rubber composition containing a rubber component and silica,
when a thickness of the first layer is t1 (mm), a groove depth of the deepest portion of the circumferential groove is H (mm), a silica content per 100 parts by mass of the rubber component in the rubber composition constituting the first layer is S1 (parts by mass), a silica content per 100 parts by mass of the rubber component in the rubber composition constituting the second layer is S2 (parts by mass), an acetone extractable amount of the rubber composition constituting the first layer is AE1 (mass%), an acetone extractable amount of the rubber composition constituting the second layer is AE2 (mass%), a complex modulus of elasticity at 30°C of the second layer is 30°CE*2 (MPa), and a land ratio at the contact surface of the tread portion is R,
A tire in which t1/H is 0.90 or less, the product of R and 30° C.E*2 (R×30° C.E*2) is 12.0 or less, and AE2/S2 is greater than AE1/S1. The tire according to claim 1, in which R x 30°C E*2 is 8.0 or less. The tire according to claim 1, wherein the glass transition temperature Tg1 of the rubber composition constituting the first layer and the glass transition temperature Tg2 of the rubber composition constituting the second layer are both -10°C or lower. The tire according to claim 3, in which Tg1 and Tg2 are both -20°C or lower. The tire of claim 1, wherein the tan δ (30°C tan δ1) of the first layer at 30°C and the tan δ (30°C tan δ2) of the second layer at 30°C are both 0.50 or less. The tire according to claim 5, in which 30°C tan δ1 and 30°C tan δ2 are both 0.30 or less. The tire according to claim 1, wherein the total styrene content Sty1 in the rubber component constituting the first layer and the total styrene content Sty2 in the rubber component constituting the second layer are both 45 mass% or less. The tire according to claim 7, in which Sty1 and Sty2 are both 35 mass% or less. A tire according to any one of claims 1 to 8, wherein the average primary particle size of the silica is 23 nm or less. A tire according to any one of claims 1 to 8, wherein the average primary particle size of the silica is 18 nm or less. The tire according to any one of claims 1 to 8, wherein the rubber component constituting the first layer and the rubber component constituting the second layer each contain 60% by mass or more of styrene-butadiene rubber. The tire according to claim 7 or 8, in which the product of R and Sty1 (R x Sty1) is 20 or less. The tire according to claim 7 or 8, in which the product of R and Sty2 (R x Sty2) is 20 or less. The tire according to any one of claims 1 to 8, wherein the circumferential grooves have a groove width that gradually increases from the end on the tire surface side toward the tire radially inward.

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