Tire

Abstract

A tire includes a tread portion having a plurality of circumferential grooves, the tread portion including at least a first layer constituting a tread and a second layer adjacent to a radial inner side of the first layer, the first layer and the second layer each being configured from a rubber composition containing a rubber component and silica, the thickness of the first layer is t1 (mm), the depth of the deepest portion of the circumferential groove is H (mm), the content of silica in the rubber compositions constituting the first layer and the second layer is S1 (parts by mass) and S2 (parts by mass), respectively, the acetone extraction amounts of the rubber compositions constituting the first layer and the second layer are AE1 (% by mass) and AE2 (% by mass), respectively, and the complex elastic modulus at 30 DEG C of the second layer is 30 DEG C E * 2 (MPa). When the land ratio of the ground contact surface of the tread portion is R, t1 / H is 0.90 or less, the product of R and 30 DEG C E * 2 is 12.0 or less, and AE2 / S2 is greater than AE1 / S1.

Description

Technical Field

[0001] The present invention relates to a tire. Background Art

[0002] In the past, there have been various studies on methods for improving the traction performance of tires. For example, Patent Document 1 records that the comprehensive performance of wear resistance and traction performance at high temperatures can be improved by using a rubber composition containing specific styrene butadiene rubber, vulcanized rubber particles and carbon black in the tread. [Prior art literature] [Patent Literature]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2022-32428 Summary of the invention [Problems to be solved by the invention]

[0004] However, in recent years, there has been a demand for further improvement in the comprehensive performance of wet grip performance and traction performance of tires.

[0005] An object of the present invention is to provide a tire having improved comprehensive performance of wet grip performance and traction performance.

Methods to solve the problem

[0006] The present invention relates to a tire, which is a tire having a tread portion, wherein the tread portion has a plurality of circumferential grooves extending continuously in the circumferential direction of the tire, wherein the tread portion has at least a first layer constituting the tread, and a second layer adjacent to the radially inner side of the first layer, wherein the first layer and the second layer are respectively composed of a rubber composition containing a rubber component and silica, and when the thickness of the first layer is t1 (mm), the groove depth of the deepest part of the circumferential groove is H (mm), the content of silica relative to 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 relative to 100 parts by mass of the rubber component in the rubber composition constituting the first layer is S2 (parts by mass), and the content of silica relative to 100 parts by mass of the rubber component in the rubber composition constituting the first layer is S3 (parts by mass). 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 acetone extractable amount of the rubber composition constituting the first layer is AE1 (% by mass), the acetone extractable amount of the rubber composition constituting the second layer is AE2 (% by mass), the complex elastic modulus of the second layer at 30°C is 30°CE*2 (MPa), and when the land ratio of the contact surface of the tread portion is R, t1 / H is less than 0.90, the product of R and 30°CE*2 (R×30°CE*2) is less than 12.0, and AE2 / S2 is greater than AE1 / S1. [Effects of the invention]

[0007] According to the present invention, the comprehensive performance of the wet grip performance and traction performance of the tire can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0008]

Figure 1

[0009] A tire according to one embodiment of the present invention is a tire having a tread portion, wherein the tread portion has a plurality of circumferential grooves extending continuously in the circumferential direction of the tire, wherein the tread portion has at least a first layer constituting the tread, and a second layer adjacent to the radially inner side of the first layer, wherein the first layer and the second layer are respectively composed of a rubber composition containing a rubber component and silica, and when the thickness of the first layer is t1 (mm), the groove depth of the deepest part of the circumferential groove is H (mm), the content of silica relative to 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 relative to 100 parts by mass of the rubber component in the rubber composition constituting the first layer is S2 (parts by mass), and the content of silica relative to 100 parts by mass of the rubber component in the rubber composition constituting the second layer is S3 (parts by mass). The content of silica per 100 parts by mass of the rubber component in the rubber composition of the second layer is S2 (parts by mass), the acetone extract amount of the rubber composition constituting the first layer is AE1 (% by mass), the acetone extract amount of the rubber composition constituting the second layer is AE2 (% by mass), the complex elastic modulus of the second layer at 30°C is 30°CE*2 (MPa), when the land ratio of the contact surface of the tread portion is R, t1 / H is less than 0.90, the product of R and 30°CE*2 (R×30°CE*2) is less than 12.0 (preferably less than 8.0), and AE2 / S2 is greater than AE1 / S1.

[0010] Although not wishing to be bound by theory, the reason why the comprehensive performance of wet grip performance and traction performance is improved in the tire of the present invention is considered to be as follows.

[0011] It is believed that by making AE2 / S2 larger than AE1 / S1, the first layer becomes a highly rigid rubber due to silica, and the second layer becomes a soft rubber due to low molecular weight components, and the second layer becomes softer than the first layer. Therefore, when strain is applied to the tread portion during cornering, the soft and highly mobile second layer becomes easy to heat up. Moreover, it is believed that the wet grip performance is improved by the heat being conducted to the first layer and the road followability being instantly improved. In addition, it is believed that when the temperature of the tread portion drops after cornering, the first layer close to the road surface is air-cooled first, so the rigidity of the first layer becomes higher, and it becomes easy to generate gripping force, so that the traction performance can be efficiently exerted.

[0012] Furthermore, by setting t1 / H to be less than 0.90, the outer surface of the second layer is located further outward in the tire radial direction than the deepest part of the groove bottom of the circumferential groove, and the land portion and the inside of the pattern block are formed by two or more rubber layers. It is believed that the strain of the tread portion is easily transferred to the second layer with high heat generation, and the heat of the second layer is easily transferred to the first layer, so that the wet grip performance is more efficiently improved.

[0013] It is believed that as the land ratio further increases, by reducing the 30°C complex elastic modulus (30°C E*2) of the second layer, the mobility and heat generation of the second layer during cornering are high, and the first layer can obtain good rigidity during cornering and straight driving, thereby achieving the commendable effect of synergistic improvement of wet grip performance and traction performance.

[0014] 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 preferably both -10°C or lower, and more preferably both -20°C or lower.

[0015] It is considered that by setting Tg1 and Tg2 within the above range, the deformation speed of the tread rubber becomes faster, and the tread rubber can sufficiently follow the road surface even during high-speed running with high-frequency deformation.

[0016] The tan δ of the first layer at 30°C (tan δ1 at 30°C) and the tan δ of the second layer at 30°C (tan δ2 at 30°C) are preferably both 0.50 or less, and more preferably both 0.30 or less.

[0017] It is considered that by reducing tan δ in a temperature range close to the actual temperature during running, the phase difference between input and response can be reduced, and the force generated in the tread portion can be easily transmitted to the road surface instantaneously, thereby improving the turning performance.

[0018] The total amount of styrene Sty1 in the rubber component constituting the first layer and the total amount of styrene Sty2 in the rubber component constituting the second layer are preferably both 45% by mass or less, and more preferably both 35% by mass or less.

[0019] It is considered that by reducing the total amount of styrene in the rubber component, the risk of impairing the road surface followability due to the influence of the hard region caused by the excess styrene portion is reduced.

[0020] The average primary particle size of the silica is preferably 23 nm or less, more preferably 18 nm or less.

[0021] It is considered that by setting the average primary particle size of silica in the above range, a fine silica network is formed, and the force from the road surface can be easily transmitted through the network.

[0022] From the viewpoint of grip performance, it is preferred 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.

[0023] The product of R and Sty1 (R×Sty1) is preferably 20 or less.

[0024] It is believed that as the land ratio R increases, the contact area with the road surface can be increased by reducing Sty1, making it easier to obtain followability on the tread surface. On the other hand, it is believed that by increasing Sty1 when R is small, energy loss occurs even on the tread surface, making it easier to improve cornering performance.

[0025] The product of R and Sty2 (R×Sty2) is preferably 20 or less.

[0026] It is believed that as the land ratio R increases, by reducing Sty2, the second layer becomes easier to deform during cornering, and the first layer is softened by the heat, making it easier to follow the road surface. In addition, it is believed that by increasing Sty2 when R is small, the heat generation in the second layer can be increased, and the following performance of the entire tread portion can be improved.

[0027] It is preferable that the groove width of the circumferential groove gradually increases from the end portion on the tire surface side toward the inner side in the tire radial direction.

[0028] It is considered that by gradually increasing the groove width of the circumferential groove toward the inner side in the tire radial direction, the second layer becomes easier to deform, and heat can be easily generated in the second layer during cornering.

[0029] <Definition> The "tread portion" is the portion that forms the contact surface of the tire. In the radial cross-section of the tire, when there are components of the tire frame formed of steel or textile materials such as a belt layer or a belt reinforcement layer, a carcass layer, etc., it is the component that is radially outer than these components.

[0030] "Regular rim" refers to the rim specified for each tire in the specification system that includes the specifications on which the tire is based. If it is JATMA (Japan Automobile Tire Association), it refers to the "Standard Rim" recorded in the "JATMA Yearbook", if it is ETRTO (The European Tyre and Rim Technical Organisation), it refers to the "Measuring Rim" recorded in the "Standards Manual", and if it is TRA (The Tire and Rim Association, Inc.), it refers to the "Design Rim" recorded in the "Yearbook". Reference is made to JATMA, ETRTO, and TRA in this order, and when referring to them, if there is an applicable size, follow that specification. Furthermore, in the case of tires not specified in the aforementioned specifications, the rim refers to the rim with the narrowest rim width among the rims with the smallest diameter on which the tire can be assembled and on which the internal pressure can be maintained (i.e., no air leakage will occur between the rim and the tire).

[0031] The "regular internal pressure" is the air pressure specified for each tire in each specification system including the specifications on which the tire is based. In the case of JATMA, it refers to the "maximum air pressure", in the case of ETRTO, it refers to the "inflation pressure (INFLATION PRESSURE)", and in the case of TRA, it refers to the maximum value recorded in the table "Tire load limits at various cold inflation pressures (TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES)". As in the case of "regular rims", reference is made in the order of JATMA, ETRTO, and TRA. When referring, if there is an applicable size, the specification is followed. In addition, in the case of tires not specified in the above-mentioned specifications, it refers to the regular internal pressure (including 250 kPa or more) of other tire sizes (including tire sizes specified in the specifications) recorded as the above-mentioned regular rims as standard rims. In the case of multiple regular internal pressures of 250 kPa or more, it refers to the minimum value among them.

[0032] The "normal state" means that the tire is assembled on a normal rim and filled with a normal internal pressure and is in a state without load. In addition, in this specification, unless otherwise specified, the dimensions of each part of the tire are measured in the normal state.

[0033] "Groove" including circumferential groove and transverse groove refers to a concave groove with a width of at least 2.0 mm. On the other hand, "sipe" refers to a fine cut with a width of 2.0 mm or less, preferably 0.5 to 2.0 mm.

[0034] The "land ratio R" refers to the ratio of the total area of ​​the ground contact surface to the total surface area of ​​the tread (i.e., the area obtained by the outer contour in the ground contact shape of the tread portion) when the tire is in a normal state and a normal load is applied to the tire and the camber angle is 0 degrees. Here, all grooves refer to grooves that are not the above-mentioned circumferential grooves and lateral grooves.

[0035] The "total contact surface area" is calculated based on the contact shape of the tire. The contact shape is obtained by assembling it on a regular rim, applying regular internal pressure, leaving it at 25°C for 24 hours, applying ink to the tread surface, applying a load of the maximum load capacity and pressing it on thick paper (camber angle is 0°), and transferring it to the paper. Then, the tire is rotated 72° in the circumferential direction and transferred 5 times. That is, 5 contact shapes are obtained. The actual contact area is obtained by the average of the 5 areas of the ink part.

[0036] "The thickness of each rubber layer constituting the tread portion" is the thickness of each rubber layer on the equatorial plane of the tire in a cross section cut with a plane containing the rotation axis of the tire, and is the average value of the thickness of the tread obtained at 5 positions by rotating the tire 72° in sequence along the circumferential direction. For example, the thickness of the first layer refers to the straight-line distance in the tire radial direction from the outermost surface of the tread to the inner interface of the first layer in the tire radial direction on the equatorial plane of the tire. In addition, when there is a circumferential groove on the equatorial plane of the tire, the thickness of each rubber layer constituting the tread portion is set to the thickness of each rubber layer in the central part of the tire width direction of the land portion closest to the equatorial plane of the tire. "The land portion closest to the equatorial plane of the tire" is set to refer to: the land portion with the groove edge closest to the equatorial plane of the tire in the circumferential groove on the equatorial plane of the tire, and when such a land portion exists on both sides in the tire width direction, the thickness of each rubber layer constituting the tread portion is set to the average value of the thickness of each rubber layer in the central part of the tire width direction of the two land portions. In addition, when there is a conducting component or the like on the land portion on the equatorial plane of the tire and the interface is unclear, the interface blocked by the conducting component or the like is virtually connected and measured.

[0037] The "depth of the deepest part of the circumferential groove" is obtained by the distance in the tire radial direction between the tread and the deepest part of the groove bottom of the circumferential groove. In addition, the deepest part of the groove bottom of the circumferential groove refers to the deepest part of the groove bottom of the circumferential groove adjacent to the land portion or the pattern block portion and having the deepest groove depth.

[0038] "Softener" refers to a material that imparts plasticity to the rubber component and is a component extracted from the rubber composition using acetone. Softeners include softeners that are liquid at 25°C and softeners that are solid at 25°C. However, wax and stearic acid commonly used in the tire industry are not included.

[0039] The "softener content" also 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, liquid rubber component, etc. In addition, the same applies to the oil content, resin component content, and liquid rubber content. For example, when the extended component is oil, the extended oil is included in the oil content.

[0040] <Measurement method> The “thickness of each rubber layer constituting the tread portion” is measured after the tire is cut along a plane including the tire rotation axis and the width of the bead portion is made equal to the width of a regular rim.

[0041] The “acetone extractable amount” can be determined according to 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 component, measuring the mass of each test piece before and after the extraction, and using the following formula. (Acetone extraction amount (mass %)) = {(mass of the rubber test piece before extraction - mass of the rubber test piece after extraction) / (mass of the rubber test piece before extraction)} × 100

[0042] "30°C tanδ" is the loss tangent measured using a dynamic viscoelasticity measuring device (e.g., EPLEXOR series manufactured by GABO) at a temperature of 30°C, a frequency of 10 Hz, an initial strain of 5%, a dynamic strain of ±1%, and a tensile mode. The sample for the loss tangent measurement is a vulcanized rubber composition of 20 mm in length, 4 mm in width, and 1 mm in thickness. When cutting from a tire, the tire is cut from the tread portion with the tire circumferential direction being the long side and the tire radial direction being the thickness direction.

[0043] "30°C E*" is the complex elastic modulus measured using a dynamic viscoelasticity measuring device (e.g., EPLEXOR series manufactured by GABO Corporation) under the conditions of temperature 30°C, frequency 10 Hz, initial strain 5%, dynamic strain ±1%, and tensile mode. The sample for this measurement is prepared in the same manner as in the case of 30°C tanδ.

[0044] "The glass transition temperature (Tg) of the rubber composition" is obtained by measuring the temperature distribution curve of tanδ under the 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 using a dynamic viscoelasticity measuring device (e.g., EPLEXOR series manufactured by GABO Corporation), and taking the temperature corresponding to the maximum value in the range of -60°C to 40°C of the obtained temperature distribution curve (tanδ peak temperature) as the glass transition temperature. In addition, in the range of -60°C to 40°C, when tanδ continues to increase or decrease as the temperature rises, the glass transition temperature is set to 40°C or -60°C, respectively. In addition, when there are two points showing maximum values ​​in the range of -60°C to 40°C, the point with the lowest temperature among them is set as the glass transition temperature. The sample for this measurement is the same as that of 30°C tanδ.

[0045] The “styrene content” is a value calculated from 1H-NMR measurement, and is applied to a rubber component having a repeating unit derived from styrene, such as SBR.

[0046] The “vinyl bond content (1,2-bonded butadiene unit content)” is a value calculated from infrared absorption spectrum analysis in accordance with JIS K 6239-2:2017, and is applicable to rubber components having repeating units derived from butadiene, such as SBR and BR.

[0047] The “cis content (cis-1,4-bonded butadiene unit amount)” is a value calculated from infrared absorption spectrum analysis in accordance with JIS K 6239-2:2017, and is applied to rubber components having repeating units derived from butadiene, such as BR.

[0048] The "total amount of styrene in the rubber component" is the total content (mass %) of styrene units contained in 100 mass % of the rubber component, and is the sum of the values ​​obtained by multiplying the styrene content (mass %) by the mass fraction in the rubber component for each rubber component. Specifically, it is calculated according to Σ(styrene content (mass %) of each rubber containing styrene unit × content (mass %) of each rubber containing styrene unit in the rubber component / 100).

[0049] The “glass transition temperature (Tg) of the rubber component” was measured in accordance with JIS K 7121 using a differential scanning calorimeter (Q200) manufactured by TA Instruments Japan Co., Ltd. while increasing the temperature at a heating rate of 10° C. / min.

[0050] The "weight average molecular weight (Mw)" can be calculated based on the value measured by gel permeation chromatography (GPC) (e.g., GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMULTIPORE HZ-M manufactured by Tosoh Corporation) and converted to standard styrene. For example, it is applicable to SBR, BR, etc.

[0051] The “nitrogen adsorption specific surface area (N2SA) of carbon black” is measured in accordance with JIS K 6217-2: 2017. The “nitrogen adsorption specific surface area (N2SA) of silica” is measured by the BET method in accordance with ASTM D3037-93.

[0052] The "average primary particle size" is obtained by taking a picture of the particles with a transmission or scanning electron microscope and taking the arithmetic average of 400 particle sizes. For the particle size, when the shape of the particle is roughly circular, the diameter of the circle is used as the particle size. When it is needle-shaped or rod-shaped, the short diameter is used as the particle size. In other cases, the equivalent circle diameter is calculated from the electron microscope image as the particle size. The equivalent circle diameter is obtained by (4×(area of ​​the particle) / π)^0.5. The average primary particle size is applicable to silica, carbon black, etc.

[0053] The “softening point of the resin component” is a temperature at which a ball falls when the softening point specified in JIS K 6220-1:2015 7.7 is measured using a ring and ball softening point measuring apparatus.

[0054] The tire according to one embodiment of the present invention will be described using drawings as appropriate. The following description is an example for describing the present invention, and the technical scope of the present invention is not limited to the description.

[0055] <Tires> Figure 1 An example of a cross-sectional view showing a part of the tread portion of the tire according to the present embodiment is shown in FIG. Figure 1 In the figure, the up and down direction is the radial direction of the tire, the left and right direction is the axial direction of the tire, and the direction perpendicular to the paper surface is the circumferential direction of the tire.

[0056] As shown in the figure, the tread portion of the tire involved in this embodiment includes a first layer 11 and a second layer 12, the outer surface of the first layer 11 constitutes the tread, and the second layer 12 is adjacent to the inner side of the first layer 11 in the tire radial direction. In addition, as long as the purpose of the present invention can be achieved, there may be one or more rubber layers ( Figure 1 The third layer 13).

[0057] From the viewpoint of the effect 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 further preferably 5 mm or more. On the other hand, t1 is preferably 14 mm or less, more preferably 12 mm or less, and further preferably 10 mm or less.

[0058] From the viewpoint of the effect of the present invention, the thickness t2 of the second layer 12 is preferably 0.5 mm or more, 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 further preferably 6 mm or less.

[0059] From the viewpoint of the effect 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 further preferably 7 mm or more. On the other hand, H is preferably 16 mm or less, more preferably 14 mm or less, and further preferably 12 mm or less.

[0060] The tire involved in this embodiment is formed so that the deepest part of the groove bottom of the circumferential groove is located further inward in the tire radial direction than the outer surface of the second layer 12, and the land portion is formed by two or more rubber layers. From the viewpoint of the effect 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 further preferably 0.50 or more.

[0061] The second layer 12 preferably has a recessed portion that is recessed inward in the tire radial direction relative to the outermost portion of the second layer, and a portion of the first layer 11 is formed in the recessed portion of the second layer 12, and more preferably the surface of the recessed portion is formed by the first layer 11. It is believed that by setting such a configuration, when the tread portion is worn and the second layer is exposed, the second layer is present in the central portion of the land portion and the first layer is present in the edge portion of the land portion, making it easier to exert the effect of the present invention.

[0062] Figure 1 In the embodiment, the circumferential groove 3 is formed such that the deepest part of the groove bottom of the circumferential groove 3 is located further inward in the tire radial direction than the outermost part of the second layer 12 in the land portion adjacent to the circumferential groove 3 in the tire radial direction. Specifically, on the inner side of the circumferential groove 3 in the tire radial direction, the second layer 12 has a recessed portion that is recessed inward in the tire radial direction relative to its outermost part, and a part of the first layer 11 is formed in the recessed portion of the second layer 12 with a predetermined thickness. The circumferential groove 3 is formed such that it passes over the outermost part of the second layer 12 in the tire radial direction and enters the inner side of the recessed portion of the second layer 12.

[0063] Preferably, at least one groove wall of the circumferential groove is provided with a recessed portion that is recessed further outward in the groove width direction than the groove edge 2 that appears on the tread surface of the tread portion. It is believed that by providing such a recessed portion on the groove wall of the circumferential groove, the second layer becomes easier to deform, and heat can be easily generated in the second layer during cornering.

[0064] Figure 1 In the embodiment, the groove wall 10 on both sides of the circumferential groove 3 is provided with a concave portion 9 with a constant amount of depression in the tire circumferential direction. In the circumferential groove 3, the groove width gradually increases from the end on the tire surface side to the inner side of the tire radial direction. The groove wall 5 of the circumferential groove 3 extends from the outer side to the inner side of the tire radial direction in a straight line, but is not limited to this form, and may extend in a curved or stepped shape, for example.

[0065] Total depression of circumferential groove 3 ( Figure 1 c1+c2) is preferably 0.10 to 2.00 times, more preferably 0.20 to 1.50 times, and further preferably 0.30 to 0.90 times the groove width W1 of the circumferential groove 3. In addition, when there are multiple circumferential grooves having the recessed portion, as long as the total recessed amount of any circumferential groove satisfies the above relationship, all grooves having the recessed portion may satisfy the above relationship.

[0066] The land ratio R in the contact surface of the tread portion is preferably 0.50 or more, more preferably 0.55 or more, further preferably 0.60 or more, and particularly preferably 0.65 or more. In addition, the land ratio R is preferably 0.90 or less, more preferably 0.88 or less, further preferably 0.85 or less, and particularly preferably 0.82 or less.

[0067] The acetone extract (AE1) of the rubber composition constituting the first layer is preferably 8% by mass or more, more preferably 10% by mass or more, further preferably 12% by mass or more, and particularly preferably 14% by mass or more. In addition, AE1 is preferably 30% by mass or less, more preferably 27% by mass or less, and further preferably 24% by mass or less.

[0068] The acetone extract (AE2) of the rubber composition constituting the second layer is preferably 8% by mass or more, more preferably 10% by mass or more, further preferably 12% by mass or more, further preferably 14% by mass or more, further preferably 16% by mass or more, and particularly preferably 18% by mass or more. In addition, AE2 is preferably 32% by mass or less, more preferably 30% by mass or less, further preferably 28% by mass or less, and particularly preferably 26% by mass or less.

[0069] 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, further preferably 7 MPa or more, and particularly preferably 8 MPa or more. On the other hand, 30°C E*1 is preferably 40 MPa or less, more preferably 35 MPa or less, and further preferably 30 MPa or less.

[0070] 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 further preferably 4 MPa or more. On the other hand, 30°C E*2 is preferably 18 MPa or less, more preferably 16 MPa or less, and further preferably 14 MPa or less.

[0071] 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, further 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, further preferably 16 MPa or less, and particularly preferably 14 MPa or less.

[0072] The 30° C. E* of the rubber composition can be appropriately adjusted according to the types or blending amounts of the rubber component, filler, and softener described below.

[0073] From the viewpoint of the effect of the present invention, the 30°C tanδ (30°C tanδ1) of the rubber composition constituting the first layer is preferably 0.55 or less, more preferably 0.50 or less, further preferably 0.45 or less, further preferably 0.40 or less, further preferably 0.35 or less, and particularly preferably 0.30 or less. In addition, the 30°C tanδ (30°C tanδ2) of the rubber composition constituting the second layer is preferably 0.55 or less, more preferably 0.50 or less, further preferably 0.45 or less, further preferably 0.40 or less, further preferably 0.35 or less, and particularly preferably 0.30 or less. On the other hand, from the viewpoint of the effect of the present invention, 30°C tanδ1 and 30°C tanδ2 are preferably 0.06 or more, more preferably 0.08 or more, further preferably 0.10 or more, and particularly preferably 0.12 or more. In addition, the 30°C tanδ of the rubber composition can be appropriately adjusted according to the type or mixing amount of the following rubber components, fillers, and softeners.

[0074] The Tg (Tg1) of the rubber composition constituting the first layer is preferably -5°C or less, more preferably -10°C or less, further preferably -15°C or less, further preferably -20°C or less, and particularly preferably -24°C or less. In addition, the Tg (Tg2) of the rubber composition constituting the second layer is preferably -5°C or less, more preferably -10°C or less, further preferably -15°C or less, further preferably -20°C or less, and particularly preferably -24°C or less. On the other hand, the lower limits of Tg1 and Tg2 are not particularly limited, but are preferably -65°C or more, more preferably -60°C or more, further preferably -55°C or more, and particularly preferably -50°C or more. In addition, the Tg of the rubber composition can be appropriately adjusted according to the type or mixing amount of the following rubber components, fillers, and softeners.

[0075] The tire involved in the present embodiment is characterized in that: when the content of silica in the rubber composition constituting the first layer relative to 100 parts by mass of the rubber component is S1 (parts by mass), and the content of silica in the rubber composition constituting the second layer relative to 100 parts by mass of the rubber component 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 greater than 0.01, more preferably greater than 0.02, further preferably greater than 0.03, and particularly preferably greater than 0.04. On the other hand, the upper limit value of the difference between AE2 / S2 and AE1 / S1 (AE2 / S2-AE1 / S1) is not particularly limited, but is preferably less than 0.30, more preferably less than 0.25, and further preferably less than 0.20.

[0076] AE1 / S1 is preferably 0.10 or more, more preferably 0.12 or more, further 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 further preferably 0.24 or less.

[0077] AE2 / S2 is preferably 0.17 or more, more preferably 0.19 or more, further preferably 0.21 or more, and particularly preferably 0.23 or more. In addition, AE2 / S2 is preferably 0.47 or less, more preferably 0.45 or less, and further preferably 0.43 or less.

[0078] From the viewpoint of the effect of the present invention, the product of R and 30°C E*2 (R×30°C E*2) is 12.0 or less, preferably 11.5 or less, more preferably 11.0 or less, further 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×30°C E*2 is preferably 2.0 or more, more preferably 2.5 or more, and further preferably 3.0 or more.

[0079] When the total amount of styrene in the rubber component constituting the first layer is Sty1 (mass %), the product of R and Sty1 (R×Sty1) is preferably 35 or less, more preferably 30 or less, further preferably 25 or less, further preferably 20 or less, and particularly preferably 18 or less. In addition, the lower limit of R×Sty1 is not particularly limited, but is preferably 2 or more, more preferably 4 or more, further preferably 6 or more, and particularly preferably 8 or more.

[0080] When the total amount of styrene in the rubber component constituting the second layer is Sty2 (mass %), the product of R and Sty2 (R×Sty2) is preferably 35 or less, more preferably 30 or less, further preferably 25 or less, further preferably 20 or less, and particularly preferably 18 or less. In addition, the lower limit of R×Sty2 is not particularly limited, but is preferably 2 or more, more preferably 4 or more, further preferably 6 or more, and particularly preferably 8 or more.

[0081] [Rubber composition] The rubber composition constituting the tread of the tire of the present invention (the rubber composition involved in the present embodiment) is described below, and unless otherwise specified, it can also be applied to any rubber layer of the tread. The rubber composition involved in the present embodiment contains a rubber component and silica, and can further contain other admixtures.

[0082] <Rubber ingredients> In the rubber composition involved in the present embodiment, diene rubber is preferably used as the rubber component. As diene rubber, for example, isoprene rubber, butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene rubber (SIR), styrene isoprene butadiene rubber (SIBR), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), etc. can be cited. These diene rubbers can be modified rubbers treated with a modifying group that can interact with fillers such as carbon black or silica, or can be hydrogenated rubbers in which a part of the unsaturated bonds is hydrogenated. One type of diene rubber can be used alone, or two or more types can be used in combination. In addition, a volume-enhanced rubber pre-increased with the following softener can also be used.

[0083] The content of the diene rubber in the rubber component is preferably 70% by mass or more, more preferably 80% by mass or more, further preferably 90% by mass or more, and particularly preferably 95% by mass or more. Alternatively, the rubber component may be composed only of diene rubber.

[0084] As the diene rubber component, at least one selected from the group consisting of isoprene rubber, butadiene rubber (SBR) and butadiene rubber (BR) is preferably used. The rubber component constituting the first layer preferably contains SBR, more preferably contains SBR and BR. The rubber component constituting the second layer preferably contains SBR, more preferably contains SBR and BR.

[0085] (SBR) As SBR, there is no particular limitation, and examples include unmodified solution polymerization SBR (S-SBR) or emulsion polymerization SBR (E-SBR), these modified SBR (modified S-SBR, modified E-SBR), etc. As modified SBR, SBR with modified terminal and / or main chain, modified SBR (condensate, branched structure, etc.) coupled by tin, silicon compound, etc., etc., etc. can be listed. Among them, S-SBR and modified SBR are preferred. In addition, hydrides (hydrogenated SBR) of these SBRs, etc. can also be used. These SBRs can be used alone or in combination of two or more.

[0086] As the SBR involved in this embodiment, a volume-expanded SBR or a non-volume-expanded SBR may be used. When a volume-expanded SBR is used, the volume-expanded amount of the SBR, i.e., the content of the volume-expanded softener contained in the SBR relative to 100 parts by mass of the rubber solid content of the SBR, is preferably 10 to 50 parts by mass.

[0087] The SBR listed above may be used alone or in combination of two or more. As the SBR listed above, for example, commercially available products from Sumitomo Chemical Co., Ltd., JSR Corporation, Asahi Kasei Corporation, Nippon Zeon Co., Ltd., ZSElastomers Co., Ltd., etc. can be used.

[0088] The styrene content of SBR is preferably 50% by mass or less, more preferably 45% by mass or less, further preferably 40% by mass or less, further preferably 35% by mass or less, and particularly preferably 28% by mass or less. In addition, the styrene content of SBR is preferably 5% by mass or more, more preferably 7% by mass or more, and further preferably 10% by mass or more. In addition, the styrene content of SBR is measured according to the above-mentioned determination method.

[0089] From the viewpoint of ensuring reactivity with silica, rubber strength, and wear resistance, the vinyl content of SBR is preferably more than 10 mol%, more preferably more than 15 mol%, and more preferably more than 20 mol%. In addition, from the viewpoint of preventing temperature dependence from increasing, elongation at break, and wear resistance, the vinyl content of SBR is preferably less than 70 mol%, more preferably less than 65 mol%, and more preferably less than 60 mol%. In addition, the vinyl content of SBR is measured according to the above-mentioned determination method.

[0090] From the viewpoint of the effect 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 further preferably 180,000 or more. In addition, 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 further preferably 1,500,000 or less. In addition, the Mw of SBR is measured according to the above-mentioned measurement method.

[0091] From the viewpoint of wear resistance, the glass transition temperature (Tg) of SBR is preferably -90°C or higher, more preferably -80°C or higher, and further preferably -70°C or higher. In addition, the Tg of SBR is preferably -10°C or lower, more preferably -15°C or lower, and further preferably -20°C or lower. In addition, the Tg of SBR is measured according to the above-mentioned measurement method.

[0092] 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, further preferably 50% by mass or more, and particularly preferably 60% by mass or more. In addition, the upper limit of the content is not particularly limited, but is preferably 99% by mass or less, more preferably 95% by mass or less, and further preferably 90% by mass or less.

[0093] The total amount of styrene Sty1 in the rubber component constituting the first layer is preferably 45% by mass or less, preferably 42% by mass or less, further preferably 37% by mass or less, and particularly preferably 33% by mass or less. In addition, Sty1 is preferably 3% by mass or more, more preferably 5% by mass or more, and further preferably 7% by mass or more.

[0094] 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, further preferably 50% by mass or more, and particularly preferably 60% by mass or more. In addition, the upper limit of the content is not particularly limited, but is preferably 99% by mass or less, more preferably 95% by mass or less, and further preferably 90% by mass or less.

[0095] The total amount of styrene Sty2 in the rubber component constituting the second layer is preferably 45% by mass or less, preferably 42% by mass or less, further preferably 37% by mass or less, and particularly preferably 33% by mass or less. In addition, Sty2 is preferably 3% by mass or more, more preferably 5% by mass or more, and further preferably 7% by mass or more.

[0096] (BR) The BR is not particularly limited, and 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-based butadiene rubber synthesized using a rare earth element-based catalyst (rare earth-based BR), BR containing syndiotactic polybutadiene crystals (SPB-containing BR), modified BR (high cis-modified BR, low cis-modified BR), and the like that are commonly used in the tire industry can be used. These BRs can be used alone or in combination of two or more.

[0097] As high cis BR, for example, commercially available materials such as those from Japan Zeon Co., Ltd., Ube Industries, Ltd., and JSR Corporation can be used. By containing high cis BR, wear resistance can be improved. The cis content of high cis BR is preferably 95% by mass or more, more preferably 96% by mass or more, and further preferably 97% by mass or more. In addition, the cis content of BR is measured according to the above-mentioned measurement method.

[0098] As the modified BR, it is preferable to use a modified butadiene rubber (modified BR) in which the terminal and / or the main chain is modified with a functional group containing at least one element selected from the group consisting of silicon, nitrogen and oxygen.

[0099] Other modified BRs include those obtained by polymerizing 1,3-butadiene with a lithium initiator and then adding a tin compound, wherein the ends of the modified BR molecules are bonded via tin-carbon bonds (tin-modified BR), etc. The modified BR may be either unhydrogenated or hydrogenated.

[0100] From the viewpoint of wear resistance, the weight average molecular weight (Mw) of BR is preferably 300,000 or more, more preferably 350,000 or more, and further preferably 400,000 or more. In addition, from the viewpoint of crosslinking uniformity, it is preferably 2 million or less, and more preferably 1 million or less. In addition, the Mw of BR is measured according to the above-mentioned measurement method.

[0101] 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, further preferably 30% by mass or less, and particularly preferably 25% by mass or less. In addition, the lower limit of the content is not particularly limited, but is preferably 1% by mass or more, more preferably 5% by mass or more, and further preferably 10% by mass or more.

[0102] 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, further preferably 30% by mass or less, and particularly preferably 25% by mass or less. In addition, the lower limit of the content is not particularly limited, but is preferably 1% by mass or more, more preferably 5% by mass or more, and further preferably 10% by mass or more.

[0103] (Isoprene rubber) As the isoprene rubber, for example, materials commonly used in the tire industry such as isoprene rubber (IR) and natural rubber can be used. In addition to non-modified natural rubber (NR), natural rubber also includes modified natural rubbers such as epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), deproteinized natural rubber (DPNR), high-purity natural rubber, and grafted natural rubber. These isoprene rubbers can be used alone or in combination of two or more.

[0104] The NR is not particularly limited, and those generally used in the tire industry can be used, and examples thereof include SIR20, RSS#3, and TSR20.

[0105] The content of the isoprene-based rubber is preferably 40% by mass or less, more preferably 30% by mass or less, further preferably 20% by mass or less, and particularly preferably 15% by mass or less. In addition, the lower limit of the content is not particularly limited, but is preferably 1% by mass or more, and can be 3% by mass or more, or 5% by mass or more.

[0106] (Other rubber components) In the range that does not affect the effect of the present invention, the rubber component may also contain other rubber components other than the diene rubber. As other rubber components other than the diene rubber, crosslinkable rubber components conventionally used in the tire industry can be used, and 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 epichlorohydrin rubber can be cited. These other rubber components can be used alone or in combination of two or more. In addition, in addition to the above-mentioned rubber components, known thermoplastic elastomers may be contained or not contained.

[0107] <Packing> The rubber composition according to the present embodiment contains silica as a filler, and preferably contains carbon black and silica.

[0108] (Carbon Black) The carbon black is not particularly limited, and for example, materials commonly used in the tire industry such as GPF, FEF, HAF, ISAF, and SAF can be used. In addition to the carbon black generated by burning ordinary mineral oil, carbon black using biomass materials such as lignin can also be used. In addition, recycled carbon black obtained by thermally decomposing products containing carbon black such as tires or plastic products can also be used. These carbon blacks can be used alone or in combination of two or more.

[0109] From the perspective of reinforcement, the nitrogen adsorption specific surface area (N2SA) of carbon black is preferably 30 m2 / g or more, more preferably 50m 2 / g or more, more preferably 70m 2 / g or more. In addition, from the viewpoint of low fuel consumption performance and processability, 200 m 2 / g or less, more preferably 180m 2 / g or less, more preferably 160m 2 / g or less. In addition, the N2SA of carbon black is measured according to the above-mentioned measurement method.

[0110] From the viewpoint of reinforcement, the content of carbon black in the rubber composition constituting the first layer is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, further preferably 15 parts by mass or more, and particularly preferably 20 parts by mass or more, relative to 100 parts by mass of the rubber component. In addition, the content is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, further preferably 40 parts by mass or less, and particularly preferably 35 parts by mass or less.

[0111] From the viewpoint of reinforcement, the content of carbon black in the rubber composition constituting the second layer is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, further preferably 15 parts by mass or more, and particularly preferably 20 parts by mass or more, relative to 100 parts by mass of the rubber component. In addition, the content is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, further preferably 40 parts by mass or less, and particularly preferably 35 parts by mass or less.

[0112] (Silicon Dioxide) As silicon dioxide, there is no particular limitation, and materials conventionally used in the tire industry such as silicon dioxide prepared by a dry method (anhydrous silicon dioxide) and silicon dioxide prepared by a wet method (hydrous silicon dioxide) can be used. Among them, from the reason that there are many silanol groups, it is preferred to use hydrous silicon dioxide prepared by a wet method. In addition, in addition to the above-mentioned silicon dioxide, silicon dioxide made from biomass materials such as rice husks as raw materials can also be appropriately used. These silicon dioxides can be used alone or in combination of two or more.

[0113] From the viewpoint of low fuel consumption and wear resistance, the nitrogen adsorption specific surface area (N2SA) of silica is preferably 120 m 2 / g or more, more preferably 150m 2 / g or more, more preferably 170m 2 / g or more. In addition, from the viewpoint of low fuel consumption performance and processability, 350 m 2 / g or less, more preferably 300m 2 / g or less, more preferably 250m 2 / g or less. In addition, the N2SA of silica is measured according to the above-mentioned measurement method.

[0114] From the viewpoint of the effect of the present invention, the average primary particle size of silicon dioxide is preferably less than 25nm, more preferably less than 23nm, further preferably less than 20nm, and particularly preferably less than 18nm. The lower limit of the average primary particle size is not particularly limited, but from the viewpoint of the dispersibility of silicon dioxide, it is preferably more than 1nm, more preferably more than 3nm, and more preferably more than 5nm. In addition, the average primary particle size of silicon dioxide is measured according to the above-mentioned measuring method.

[0115] From the viewpoint of the effects of the present invention, in the rubber composition constituting the first layer, the content S1 of silica relative to 100 parts by mass of the rubber component is preferably 40 parts by mass or more, more preferably 50 parts by mass or more, further 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, further preferably 130 parts by mass or less, and particularly preferably 120 parts by mass or less.

[0116] From the viewpoint of the effect of the present invention, in the rubber composition constituting the second layer, the content S2 of silica relative to 100 parts by mass of the rubber component is preferably 40 parts by mass or more, more preferably 50 parts by mass or more, further 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, further preferably 130 parts by mass or less, and particularly preferably 120 parts by mass or less.

[0117] (Other fillers) Fillers other than silica and carbon black are not particularly limited, and materials conventionally used in the tire industry such as aluminum hydroxide, alumina, calcium carbonate, magnesium sulfate, talc, clay, and biochar can be mixed. These other fillers can be used alone or in combination of two or more.

[0118] The total content of the filler is preferably 40 parts by mass or more, more preferably 50 parts by mass or more, further preferably 60 parts by mass or more, and particularly preferably 65 parts by mass or more, relative to 100 parts by mass of the rubber component. In addition, the content is preferably 160 parts by mass or less, more preferably 150 parts by mass or less, further preferably 140 parts by mass or less, and particularly preferably 130 parts by mass or less.

[0119] The content of silica 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. It is further preferably 70% by mass or more, and particularly preferably 75% by mass or more. In addition, the upper limit of the content is not particularly limited, but is preferably 95% by mass or less, and more preferably 90% by mass or less.

[0120] The content of silica 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, further preferably 70% by mass or more, and particularly preferably 75% by mass or more. The upper limit of the content is not particularly limited, but is preferably 98% by mass or less, more preferably 95% by mass or less, and further preferably 92% by mass or less.

[0121] (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 used in combination with silica in the tire industry can be used, for example, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane and other mercapto-based silane coupling agents; bis(3-triethoxysilylpropyl)disulfide, bis(3-triethoxysilylpropyl)tetrasulfide and other sulfide-based silane coupling agents; 3-octanoylthio-1-propyltriethoxysilane, 3-hexanoylthio-1-propyltriethoxysilane, 3-octanoylthio-1-propyltrimeth ...3-octanoylthio-1-propyltrimethoxysilane, 3-octanoylthio-1-propyltrimethoxysilane, 3-octanoylthio-1-propyltrimethoxysilane, 3-octanoylthio-1-propyltrimethoxysilane, 3-octanoylthio-1-propyltrimethoxysilane, 3-octanoylthio-1-propyltrimethoxysilane, 3-octanoylthio-1-propyltrimethoxysilane, 3-octanoylthio-1-propyltrimethoxysilane, Thioester silane coupling agents such as oxysilane; vinyl silane coupling agents such as vinyl triethoxysilane and vinyl trimethoxysilane; amino silane coupling agents such as 3-aminopropyl triethoxysilane, 3-aminopropyl trimethoxysilane, and 3-(2-aminoethyl)aminopropyl triethoxysilane; glycidoxy silane coupling agents such as γ-glycidoxypropyl triethoxysilane and γ-glycidoxypropyl trimethoxysilane; nitro silane coupling agents such as 3-nitropropyl trimethoxysilane and 3-nitropropyl triethoxysilane; chlorine silane coupling agents such as 3-chloropropyl trimethoxysilane and 3-chloropropyl triethoxysilane. Among them, sulfide silane coupling agents and / or mercapto silane coupling agents are preferably contained. As the silane coupling agent, for example, commercially available substances such as Evonik Degussa and Momentive can be used. These silane coupling agents may be used alone or in combination of two or more.

[0122] From the viewpoint of improving the dispersibility of silica, the content of the silane coupling agent relative to 100 parts by mass of silica is preferably 1.0 parts by mass or more, more preferably 3.0 parts by mass or more, and further preferably 5.0 parts by mass or more. In addition, 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 further preferably 12 parts by mass or less.

[0123] <Other Mixtures> The rubber composition of the present embodiment may appropriately contain, in addition to the above-mentioned components, compounding agents conventionally used in the tire industry, such as softeners, waxes, stearic acid, zinc oxide, antioxidants, vulcanizers, and vulcanization accelerators.

[0124] Examples of the softener include resin components, oils, and liquid polymers.

[0125] The resin component is not particularly limited, and examples thereof include hydrocarbon resins such as petroleum resins, terpene resins, rosin resins, and phenolic resins that are commonly used in the tire industry.

[0126] Examples of the petroleum resin include C5-based petroleum resins, aromatic-based petroleum resins, and C5C9-based petroleum resins.

[0127] In this specification, "C5 petroleum resin" refers to a resin obtained by polymerizing a C5 fraction, and may also be a hydrogenated product or a modified product of these resins. Examples of C5 fractions include petroleum fractions corresponding to 4 to 5 carbon atoms such as cyclopentadiene, pentene, pentadiene, and isoprene. As C5 petroleum resin, dicyclopentadiene resin (DCPD resin) is preferably used.

[0128] In this specification, "aromatic petroleum resin" refers to a resin obtained by polymerizing a C9 fraction, and may also be a hydrogenated product or a modified product of these resins. As the C9 fraction, for example, vinyl toluene, alkyl styrene, indene, methyl indene and other petroleum fractions corresponding to 8 to 10 carbon atoms can be cited. As specific examples of aromatic petroleum resins, for example, coumarone-indene resin, coumarone resin, indene resin and aromatic vinyl resins are preferably used. As aromatic vinyl resins, from the reasons of economy, easy processing and excellent heat generation, 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. As aromatic vinyl resins, for example, commercially available substances from Kraton Company, Eastman Chemical Company, etc. can be used.

[0129] In this specification, "C5C9-based petroleum resin" refers to a resin obtained by copolymerizing the above-mentioned C5 fraction and the above-mentioned C9 fraction, and may also be a hydrogenated product or a modified product of these resins. Examples of the C5 fraction and the C9 fraction include the above-mentioned petroleum fractions. As the C5C9-based petroleum resin, for example, commercially available materials such as those from Tosoh Corporation and LUHUA Corporation can be used.

[0130] Examples of terpene resins include polyterpene resins composed of at least one selected from terpene compounds such as α-pinene, β-pinene, limonene, and dipentene; aromatic modified terpene resins containing the above terpene compounds and aromatic compounds as monomer components; terpene phenol resins containing terpene compounds and phenolic compounds as monomer components; and hydrogenated terpene resins (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.

[0131] The rosin-based resin is not particularly limited, and examples thereof include natural resin rosin and rosin-modified resins obtained by modifying the rosin by hydrogenation, disproportionation, dimerization, esterification, or the like.

[0132] The phenolic resin is not particularly limited, and examples thereof include phenolic resins, alkylphenolic resins, alkylphenolacetylene resins, and oil-modified phenolic resins.

[0133] 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, it 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 according to the above-mentioned measurement method.

[0134] When the resin component is contained, the content is preferably 1 part by mass or more, more preferably 3 parts by mass or more, further preferably 5 parts by mass or more, and particularly preferably 7 parts by mass or more relative to 100 parts by mass of the rubber component. In addition, from the viewpoint of suppressing heat generation, it is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, further preferably 30 parts by mass or less, and particularly preferably 25 parts by mass or less.

[0135] As oil, for example, process oil, vegetable oil, etc. can be cited. As process oil, paraffin-based process oil (mineral oil), naphthenic process oil, aromatic process oil, etc. can be cited. As specific examples of process oil, for example, MES (Mild Extract Solvated), DAE (Distillate Aromatic Extract), TDAE (Treated Distillate Aromatic Extract), TRAE (Treated Residual Aromatic Extract), RAE (Residual Aromatic Extract), etc. can be cited. In addition, due to environmental measures, process oils with low content of polycyclic aromatic compounds (PCA) can also be used. As the above-mentioned process oils with low PCA content, MES, TDAE, heavy naphthenic oils, etc. can be cited. In addition, from the perspective of life cycle assessment, products refined from waste oil used in rubber mixers or engines, or waste cooking oil used in restaurants can also be used.

[0136] From the viewpoint of the effects of the present invention, in the rubber composition constituting the first layer, the content of oil relative to 100 parts by mass of the rubber component 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.

[0137] From the viewpoint of the effects of the present invention, the content of oil in the rubber composition constituting the second layer is preferably 25 parts by mass or more, more preferably 30 parts by mass or more, further preferably 35 parts by mass or more, and particularly preferably 40 parts by mass or more, relative to 100 parts by mass of the rubber component. In addition, the content is preferably 90 parts by mass or less, more preferably 85 parts by mass or less, further preferably 80 parts by mass or less, and particularly preferably 75 parts by mass or less.

[0138] The liquid polymer is not particularly limited as long as it is a polymer in a liquid state at room temperature (25° C.), and examples thereof 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), a polymer containing myrcene or farnesene, etc. These liquid polymers may be used alone or in combination of two or more.

[0139] When the liquid polymer is contained, the content is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and further preferably 5 parts by mass or more relative to 100 parts by mass of the rubber component. In addition, the content of the liquid polymer is preferably 40 parts by mass or less, more preferably 30 parts by mass or less, and further preferably 20 parts by mass or less.

[0140] From the viewpoint of the effects of the present invention, in the rubber composition constituting the first layer, the content of the softener relative to 100 parts by mass of the rubber component (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, further preferably 20 parts by mass or more, further preferably 25 parts by mass or more, further preferably 30 parts by mass or more, and particularly preferably 35 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, further preferably 80 parts by mass or less, further preferably 75 parts by mass or less, and particularly preferably 70 parts by mass or less.

[0141] From the viewpoint of the effects of the present invention, in the rubber composition constituting the second layer, the content of the softener relative to 100 parts by mass of the rubber component (the total amount of all softeners when multiple softeners are used in combination) is preferably 30 parts by mass or more, more preferably 35 parts by mass or more, further preferably 40 parts by mass or more, further 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, further preferably 90 parts by mass or less, and particularly preferably 85 parts by mass or less.

[0142] The wax is not particularly limited, and any substance conventionally used in the tire industry is preferably used, and examples thereof include petroleum wax, mineral wax, synthetic wax, etc., and petroleum wax is preferred. Examples of petroleum wax include paraffin wax, microcrystalline wax, and selected special waxes thereof, and paraffin wax is preferred. In addition, the wax involved in the present embodiment is a substance that does not contain stearic acid. For example, the wax can use commercially available substances such as those from Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seira Co., Ltd., and Paramelt. These waxes can be used alone or in combination of two or more.

[0143] From the viewpoint of weather resistance of rubber, when wax is contained, the content is preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, relative to 100 parts by mass of the rubber component. In addition, from the viewpoint of preventing tire whitening due to blooming, the content is preferably 10 parts by mass or less, more preferably 5.0 parts by mass or less.

[0144] The antioxidant is not particularly limited, but examples thereof include amine-based, quinoline-based, quinone-based, phenol-based, imidazole-based compounds or carboxylic acid metal salts, preferably 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 and other phenylenediamine-based antioxidants, and quinoline-based antioxidants such as 2,2,4-trimethyl-1,2-dihydroquinoline polymers and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline. These antioxidants may be used alone or in combination of two or more.

[0145] From the viewpoint of the ozone cracking resistance of the rubber, when the antioxidant is contained, the content relative to 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. In addition, from the viewpoint of wear resistance, it is preferably 10 parts by mass or less, more preferably 5.0 parts by mass or less.

[0146] From the viewpoint of processability, when stearic acid is contained, the content relative to 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 further preferably 1.5 parts by mass or more. In addition, from the viewpoint of vulcanization speed, it is preferably 10 parts by mass or less, and more preferably 5.0 parts by mass or less.

[0147] From the viewpoint of processability, when zinc oxide is contained, the content relative to 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 further preferably 1.5 parts by mass or more. In addition, from the viewpoint of wear resistance, it is preferably 10 parts by mass or less, and more preferably 5.0 parts by mass or less.

[0148] As the vulcanizing agent, sulfur is preferably used. As the sulfur, powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, etc. can be used.

[0149] From the viewpoint of ensuring sufficient vulcanization reaction, when sulfur is contained as a vulcanizing agent, the content relative to 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 further preferably 1.0 parts by mass or more. In addition, from the viewpoint of preventing deterioration, it is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and further preferably 3.5 parts by mass or less. In addition, when oil-containing sulfur is used as a vulcanizing agent, the content of the vulcanizing agent is set to the total content of pure sulfur contained in the oil-containing sulfur.

[0150] Examples of the vulcanizing agent other than sulfur include alkylphenol·sulfur chloride condensate, 1,6-hexamethylene-sodium dithiosulfate·dihydrate, 1,6-bis(N,N'-dibenzylthiocarbamoyldisulfide)hexane, etc. These vulcanizing agents other than sulfur can be commercially available from Taoka Chemical Industry Co., Ltd., Lanxess Co., Ltd., Flexis Co., Ltd., etc.

[0151] Examples of the vulcanization accelerator include sulfenamide vulcanization accelerators, thiazole vulcanization accelerators, guanidine vulcanization accelerators, thiuram vulcanization accelerators, dithiocarbamate vulcanization accelerators, caprolactam disulfide, etc. These vulcanization accelerators may be used alone or in combination of two or more. Among them, from the point of more appropriately obtaining the desired effect, it is preferred to use one or more vulcanization accelerators selected from the group consisting of sulfenamide vulcanization accelerators, thiazole vulcanization accelerators, and guanidine vulcanization accelerators, and it is more preferred to use a sulfenamide vulcanization accelerator and a guanidine vulcanization accelerator in combination.

[0152] Examples of the sulfenamide vulcanization accelerator include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), and N,N-dicyclohexyl-2-benzothiazolylsulfenamide (DCBS). Among them, TBBS and CBS are preferred.

[0153] Examples of the thiazole vulcanization accelerator include 2-mercaptobenzothiazole (MBT) or its salts, di-2-benzothiazolyl disulfide (MBTS), 2-(2,4-dinitrophenyl)mercaptobenzothiazole, and 2-(2,6-diethyl-4-morpholinylthio)benzothiazole. Among them, MBTS and MBT are preferred, and MBTS is more preferred.

[0154] Examples of the guanidine vulcanization accelerator include 1,3-diphenylguanidine (DPG), 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, di-o-tolylguanidine salt of di-orthocatechol borate, 1,3-di-o-isopropylphenylguanidine, 1,3-di-o-biphenylguanidine, and 1,3-di-o-isopropylphenyl-2-propionylguanidine. Among them, DPG is preferred.

[0155] When a vulcanization accelerator is contained, the content relative to 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 further preferably 1.5 parts by mass or more. In addition, the content of the vulcanization accelerator relative to 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 further preferably 4.0 parts by mass or less. By making the content of the vulcanization accelerator within the above range, it tends to be possible to ensure the breaking strength and elongation.

[0156] [Manufacture 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 components using a rubber kneading device such as an open roll mill or a closed mixer (Banbury mixer, kneader, etc.).

[0157] The kneading process includes, for example, a basic kneading process for kneading a compounding agent and an additive other than a vulcanizing agent and a vulcanization accelerator, and a final kneading (F kneading) process for adding a vulcanizing agent and a vulcanization accelerator to the kneaded material obtained in the basic kneading process and kneading. Furthermore, the basic kneading process can be divided into a plurality of processes as desired.

[0158] The kneading conditions are not particularly limited, but examples thereof include kneading at a discharge temperature of 150 to 170° C. for 3 to 10 minutes in the basic kneading step and kneading at 70 to 110° C. for 1 to 5 minutes in the final kneading step. The vulcanization conditions are not particularly limited, but examples thereof include vulcanization at 150 to 200° C. for 10 to 30 minutes.

[0159] The tire of the present disclosure having a tread composed of the above-mentioned rubber composition can be manufactured according to a conventional method. That is, the unvulcanized rubber composition mixed with the above-mentioned components as required is extruded according to the shape of the first layer and the second layer of the tread, and is bonded together with other tire components on a tire molding machine, and molded by a conventional method to form an unvulcanized tire, and the unvulcanized tire is heated and pressurized in a vulcanizer, thereby manufacturing a tire. As vulcanization conditions, Although not particularly limited, examples thereof include a method of vulcanizing at 150 to 200° C. for 10 to 30 minutes.

[0160] [Use of tires] The tires involved in this embodiment are preferably used for passenger car tires, truck and bus tires, two-wheeled vehicle tires, and racing tires, and are preferably used for passenger car tires. In addition, passenger car tires refer to tires that are loaded on four-wheeled vehicles and have a maximum load capacity of less than 1000 kg. [Example]

[0161] The following are examples (embodiments) that are considered to be preferred when implemented, but the scope of the present invention is not limited to the examples. Using the various chemicals shown below, tires having a first layer, a second layer, and a third layer of a tread portion obtained according to the formulation of Table 1 were studied, and the results were calculated based on the following evaluation method, and the calculated results are shown in Tables 2 and 3.

[0162] The following summarizes various chemicals used in Examples and Comparative Examples. NR:TSR20 SBR1: SBR prepared according to the following Preparation Example 1 (S-SBR, styrene content: 46% by mass, vinyl content: 40 mol%, non-extended product) SBR2: Nipol NS522 manufactured by ZS ELASTOMERS Co., Ltd. (S-SBR, styrene content: 39% by mass, vinyl content: 40% by mol, Tg: -25°C, Mw: 1.2 million, containing 37.5 parts by mass of an extender based on 100 parts by mass of the rubber solid content) SBR3: SBR prepared according to the following Preparation Example 2 (S-SBR, styrene content: 25% by mass, vinyl content: 25 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-expanded 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-expanded product) BR: UBEPOL BR (registered trademark) 150B manufactured by Ube Industries, Ltd. (unmodified BR, cis content: 97% by mass, Mw: 440,000) Carbon black: Showblack N330 (N2SA: 75m 2 / g) Silica 1: Zeosil 1115MP (N2SA: 115m 2 / g, average primary particle size: 24nm) Silica 2: ZEOSIL 115GR (N2SA: 115m 2 / g, average primary particle size: 20nm) Silicon dioxide 3: ULTRASIL (registered trademark) VN3 (N2SA: 175m 2 / g, average primary particle size: 17nm) Silane coupling agent: Si266 (bis(3-triethoxysilylpropyl) disulfide) manufactured by Evonik Degussa Oil: VivaTec500 (TDAE oil) manufactured by H&R Corporation Resin component: Sylvares SA85 manufactured by Kraton Corporation (copolymer of α-methylstyrene and styrene, softening point: 85°C) Antioxidant: ANTIGENE 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd. Wax: SUNNOC N (paraffin wax) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Stearic acid: NOF Corporation's stearic acid beads "TSUBAKI" Zinc oxide: 2 types of zinc oxide produced by Mitsui Mining and Smelting Co., Ltd. Sulfur: Powdered sulfur manufactured by Karuizawa Sulfur Co., Ltd. Vulcanization accelerator 1: NOCCELER CZ (N-cyclohexyl-2-benzothiazolylsulfenamide (CBS)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator 2: NOCCELER D (1,3-diphenylguanidine (DPG)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0163] (Manufacturing Example 1: Manufacture of SBR1) Hexane, 1,3-butadiene, styrene, and tetrahydrofuran were added to the nitrogen-substituted autoclave reactor and stirred at 40°C. The ratio of styrene to 1,3-butadiene was adjusted so that the styrene content was 46% by mass. After adding 0.1 mol / L of n-butyl lithium / hexane solution and scavenge treatment, 4 mL of 0.1 mol / L of n-butyl lithium / hexane solution was added, and the stirring speed was set to 130 rpm and the jacket temperature was set to 80°C for stirring. After confirming that a polymer with a Mw of 1 million has been generated by GPC, 4 L of ethanol was injected into the polymerization solution to recover the precipitate. After the obtained precipitate was dried by air supply, it was dried under reduced pressure at 80°C / 10Pa or less until the drying loss became 0.1%, and SBR1 was obtained.

[0164] (Manufacturing Example 2: Manufacture of SBR2) SBR2 was obtained in the same manner as in Production Example 1 except that the ratio of styrene to 1,3-butadiene was adjusted so that the styrene content was 25% by mass.

[0165] (Examples and Comparative Examples) According to the mixing formula shown in Table 1 and Table 2, a 1.7L sealed Banbury mixer was used to mix for 1 to 10 minutes until the discharge temperature of the chemicals other than sulfur and vulcanization accelerator reached 150 to 160°C to obtain a kneaded product. Next, sulfur and a vulcanization accelerator were added to the kneaded product using a biaxial open roll mill, and kneaded for 4 minutes until the temperature reached 105°C to obtain an unvulcanized rubber composition. The unvulcanized rubber composition was extruded and formed into the shape of the first layer (thickness: 8.5mm) and the second layer (thickness: 1.5mm) of the tread portion in an extruder equipped with a metal cap of a specified shape, and an unvulcanized tire was laminated together with other tire components. The test tires described in Table 3 and Table 4 (size: 205 / 55R16, rim: 16×6.5J, internal pressure: 250kPa) were obtained by press vulcanization at 170°C for 12 minutes. Furthermore, the groove depth H of the deepest portion of the circumferential groove was set to 9.5 mm, the groove width of the circumferential groove was set to 9.0 mm, and the total recessed amount of the circumferential groove was set to 5.4 mm.

[0166] <Determination of Acetone Extraction Amount (AE Amount)> The AE amount was measured for the vulcanized rubber test pieces cut from the inside of each rubber layer of the tread portion of each test tire. The AE amount was obtained by immersing each vulcanized rubber test piece in acetone at room temperature (about 25°C) for 72 hours, extracting the soluble components, and measuring the mass of each test piece before and after extraction according to JIS K 6229:2015. (Acetone extraction amount (mass %)) = {(mass of the rubber test piece before extraction - mass of the rubber test piece after extraction) / (mass of the rubber test piece before extraction)} × 100

[0167] <Measurement of tanδ at 30°C and E* at 30°C> From the inside of each rubber layer of the tread portion of each test tire, a vulcanized rubber test piece of 20 mm in length × 4 mm in width × 1 mm in thickness was cut out with the tire circumferential direction as the long side and the tire radial direction as the thickness direction. The loss tangent tanδ and the complex elastic modulus E* were measured using a dynamic viscoelasticity measuring apparatus (EPLEXOR series manufactured by GABO Corporation) under the conditions of a temperature of 30°C, a frequency of 10 Hz, an initial strain of 5%, a dynamic strain of ±1%, and a tensile mode.

[0168] <Measurement of glass transition temperature (Tg)> From the inside of each rubber layer of the tread portion of each test tire, a vulcanized rubber test piece of 20 mm in length × 4 mm in width × 1 mm in thickness was cut out with the tire circumferential direction being the long side and the tire radial direction being the thickness direction. A dynamic viscoelasticity measuring apparatus (EPLEXOR series manufactured by GABO Corporation) was used to measure the temperature distribution curve of tan δ under the 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 maximum value of the obtained temperature distribution curve in the range of -60°C to 40°C (tan δ peak temperature) was taken as the glass transition temperature.

[0169] <Wet Grip Performance> A Japanese FF vehicle (displacement 2000cc) equipped with the above-mentioned test tires on all wheels was braked while driving on a wet asphalt road at an initial speed of 100 km / 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 as 100. The larger the index, the better the wet grip performance.

[0170] <Traction performance> A Japanese FF vehicle (displacement 2000cc) equipped with the above-mentioned test tires on all wheels was driven at 80 km / h on a dry asphalt road surface, and the traction performance was sensory evaluated based on the feeling when the accelerator was pressed at the corner exit. The evaluation was performed with integer values ​​of 1 to 5 points, and the total score of 20 test drivers was calculated based on the evaluation criteria that the higher the score, the better the traction performance. Then, the total score of the control tire (Comparative Example 1) was converted to a reference value (100), and the evaluation results of each test tire were expressed by indexing in proportion to the total score.

[0171]

Table 1

[0172]

Table 2

[0173]

Table 3

[0174]

Table 4

[0175] <Implementation Method> Examples of embodiments of the present invention are shown below.

[0176] [1] A tire comprising a tread portion, the tread portion having a plurality of circumferential grooves extending continuously in the circumferential direction of the tire, the tread portion comprising at least a first layer constituting the tread, and a second layer adjacent to the radially inner side of the first layer, the first layer and the second layer being respectively composed of a rubber composition containing a rubber component and silica, and assuming that the thickness of the first layer is t1 (mm), the groove depth of the deepest part of the circumferential groove is H (mm), 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 first layer is S2 (parts by mass), and the content of silica per 100 parts by mass of the rubber component in the rubber composition constituting the first layer is S3 (parts by mass). 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 extract of the rubber composition constituting the first layer is AE1 (% by mass), the amount of acetone extract of the rubber composition constituting the second layer is AE2 (% by mass), the complex elastic modulus of the second layer at 30°C is 30°CE*2 (MPa), and when the land ratio of the contact surface of the tread portion is R, t1 / H is less than 0.90, the product of R and 30°CE*2 (R×30°CE*2) is less than 12.0, and AE2 / S2 is greater than AE1 / S1. [2] The tire according to [1] above, wherein R×30°C E*2 is 8.0 or less. [3] The tire according to [1] or [2] above, 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 [3] above, wherein both Tg1 and Tg2 are -20°C or lower. [5] The tire according to any one of [1] to [4] above, wherein tan δ of the first layer at 30°C (tan δ1 at 30°C) and tan δ of the second layer at 30°C (tan δ2 at 30°C) are both 0.50 or less. [6] The tire according to [5] above, wherein tan δ1 at 30°C and tan δ2 at 30°C are both 0.30 or less. [7] The tire according to any one of [1] to [6] above, wherein the total amount of styrene Sty1 in the rubber component constituting the first layer and the total amount of styrene Sty2 in the rubber component constituting the second layer are both 45% by mass or less. [8] The tire according to [7] above, wherein Sty1 and Sty2 are both 35% by mass or less. [9] The tire according to any one of [1] to [8] above, wherein the average primary particle size 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 size of the silica is 18 nm or less.

[11] The tire according to any one of [1] to

[10] above, wherein the rubber component constituting the first layer and the rubber component constituting the second layer both 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 [7] to

[12] above, 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 groove width of the circumferential groove gradually increases from the end portion on the tire surface side toward the inner side in the tire radial direction.

Claims

1. A tire having a tread portion, characterized in that: The tread portion has a plurality of circumferential grooves extending continuously in the tire circumferential direction. The tread portion includes at least a first layer constituting the tread and a second layer adjacent to the radially inner side of the first layer. The first layer and the second layer are respectively composed of a rubber composition containing a rubber component and silica, Assuming that the thickness of the first layer is t1, the unit of the thickness t1 is mm, the groove depth of the deepest part of the circumferential groove is H, the unit of the groove depth H is mm, the content of silica relative to 100 parts by mass of the rubber component in the rubber composition constituting the first layer is S1, the unit of the content S1 is parts by mass, the content of silica relative to 100 parts by mass of the rubber component in the rubber composition constituting the second layer is S2, the unit of the content S2 is parts by mass, the acetone extractable amount of the rubber composition constituting the first layer is AE1, the unit of the extractable amount AE1 is mass %, the acetone extractable amount of the rubber composition constituting the second layer is AE2, the unit of the extractable amount AE2 is mass %, the complex elastic modulus of the second layer at 30°C is 30°CE*2, the unit of the complex elastic modulus 30°CE*2 is MPa, and the land ratio of the contact surface of the tread portion is R, t1 / H is less than 0.90, the product of R and 30°C E*2 R×30°C E*2 is less than 12.0, and AE2 / S2 is greater than AE1 / S1.

2. The tire according to claim 1, wherein: R×30°C E*2 is 8.0 or less.

3. 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.

4. The tire according to claim 3, wherein: Both Tg1 and Tg2 are below -20°C.

5. The tire according to claim 1, wherein: The tan δ of the first layer at 30°C, ie, 30°C tan δ1, and the tan δ of the second layer at 30°C, ie, 30°C tan δ2, are both 0.50 or less.

6. The tire according to claim 5, wherein: Both tan δ1 at 30°C and tan δ2 at 30°C are less than 0.

30.

7. The tire according to claim 1, wherein: The total amount of styrene Sty1 in the rubber component constituting the first layer and the total amount of styrene Sty2 in the rubber component constituting the second layer are both 45% by mass or less.

8. The tire according to claim 7, wherein: Sty1 and Sty2 are both 35 mass % or less.

9. The tire according to any one of claims 1 to 8, wherein The average primary particle size of the silicon dioxide is 23 nm or less.

10. The tire according to any one of claims 1 to 8, wherein The average primary particle size of the silicon dioxide is 18 nm or less.

11. 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 both contain 60% by mass or more of styrene butadiene rubber.

12. The tire according to claim 7 or 8, wherein: The product of R and Sty1, R×Sty1, is 20 or less.

13. The tire according to claim 7 or 8, wherein: The product of R and Sty2, R×Sty2, is 20 or less.

14. The tire according to any one of claims 1 to 8, wherein The groove width of the circumferential groove gradually increases from the end portion on the tire surface side toward the inner side in the tire radial direction.

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