Heavy-duty tires

Abstract

To provide a tire for heavy loads that can be improved in uneven wear resistance performance.SOLUTION: A tire for heavy loads comprises a tread part. The tread part has a plurality of circumferential grooves extending continuously in a tire circumferential direction. The tread part comprises at least a first layer constituting a tread surface, a second layer formed adjacently to inside in a tire radial direction of the first layer and a third layer existing inside in the tire radial direction of the second layer. The first layer, the second layer and the third layer respectively are constituted of rubber compositions containing rubber components. A ratio (70°Ctanδ1 / 70°Ctanδ2) of tanδ(70°Ctanδ1) at 70°C of the rubber compositions constituting the first layer to tanδ(70°Ctanδ2) at 70°C of the rubber compositions constituting the second layer is less than 1.0, where when an outer diameter of the tire is defined as Dt(m), a thickness of the first layer is defined as t1(mm) and groove depths of deepest parts of the circumferential grooves are defined as H(mm), 70°Ctanδ2 / Dt is over 0.09 and t1 / H is equal to 0.90 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a heavy-duty tire. [Background technology]

[0002] Patent Document 1 describes a pneumatic tire that has a tread section consisting of a cap rubber layer and a base rubber layer, achieving low fuel consumption without worsening wear resistance. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2007-126523 [Overview of the project] [Problems that the invention aims to solve]

[0004] In Patent Document 1, the tread's land portion (block) is composed of a single layer of rubber. Therefore, when applied to tires that carry heavy loads, such as heavy-duty tires, there is a concern that uneven wear may occur when a large load is applied locally to the tread rubber.

[0005] The present invention aims to improve resistance to uneven wear. [Means for solving the problem]

[0006] The present invention relates to a heavy-duty tire having a tread portion, wherein the tread portion has a plurality of circumferential grooves extending continuously in the circumferential direction of the tire, and the tread portion comprises at least a first layer constituting the tread surface, a second layer adjacent to the inner side of the first layer in the tire radial direction, and a third layer located on the inner side of the second layer in the tire radial direction, wherein the first layer, the second layer, and the third layer are each composed of a rubber composition containing a rubber component, and the ratio of the tanδ(70°C tanδ1) of the rubber composition constituting the first layer at 70°C to the tanδ(70°C tanδ2) of the rubber composition constituting the second layer at 70°C (70°C tanδ1 / 70°C tanδ2) is less than 1.0, and when the outer diameter of the tire is Dt (m), the thickness of the first layer is t1 (mm), and the groove depth of the deepest part of the circumferential groove is H (mm), the 70°C tanδ2 / Dt is greater than 0.09 and t1 / H is 0.90 or less. [Effects of the Invention]

[0007] According to the present invention, a heavy-duty tire is provided that can improve resistance to uneven wear. [Brief explanation of the drawing]

[0008] [Figure 1] This is a flat-layout diagram of the tread pattern of a tire according to one embodiment of the present invention. [Figure 2] This is a cross-sectional view showing a portion of the circumferential groove according to this embodiment. [Figure 3] This is a cross-sectional view showing a portion of another circumferential groove according to this embodiment. [Modes for carrying out the invention]

[0009] A tire according to one embodiment of the present invention is a heavy-duty tire having a tread portion, wherein the tread portion has a plurality of circumferential grooves extending continuously in the circumferential direction of the tire, and the tread portion comprises at least a first layer constituting the tread surface, a second layer adjacent to the radially inward side of the first layer, and a third layer located radially inward of the second layer, wherein the first layer, the second layer, and the third layer are each composed of a rubber composition containing a rubber component, and the ratio of the tanδ(70°C tanδ1) of the rubber composition constituting the first layer at 70°C to the tanδ(70°C tanδ2) of the rubber composition constituting the second layer at 70°C (70°C tanδ1 / 70°C tanδ2) is less than 1.0, and when the outer diameter of the tire is Dt (m), the thickness of the first layer is t1 (mm), and the groove depth of the deepest part of the circumferential groove is H (mm), the heavy-duty tire has 70°C tanδ2 / Dt greater than 0.09 and t1 / H 0.90 or less.

[0010] While we do not intend to be bound by theory, the reason why the uneven wear resistance of the tire of this invention is improved can be considered as follows.

[0011] By setting the ratio of the thickness of the first layer to the groove depth at the deepest part of the circumferential groove (t1 / H) to 0.90 or less, the deepest part of the groove bottom of the circumferential groove is formed to be located radially inward of the outer surface of the second layer, so that the inside of the block is formed of two or more rubber layers. Furthermore, by making the 70°C tanδ of the second layer greater than that of the first layer, deformation energy during driving can be dissipated as heat inside the block, which is thought to improve wear resistance on land. Also, by making the value of 70°C tanδ of the first layer smaller, heat generation outside the block is suppressed, and it is thought that the deterioration of wear resistance due to the block surface becoming hot and soft can be prevented. In addition, by making the tread part of three or more layers, when deformation and impact are transmitted from the first layer to the inside of the tread, there is an additional interface on the radially inward side of the second layer, which is thought to make it easier to absorb at this interface.

[0012] On the one hand, as the outer diameter of the tire increases, the energy due to the inertia of the tire increases, and the time during which any point on the tread touches the road surface becomes longer. Therefore, as the outer diameter of the tire increases, the energy transmitted to the tread also increases, and the time of contact with the road surface when traveling a unit distance also becomes longer. From this, it is considered that by making the ratio of the 70°C tanδ of the second layer to the outer diameter of the tire larger than a predetermined value, the effect of absorbing deformation inside the tread can be enhanced.

[0013] And because these cooperate, it is possible to absorb local deformation from the road surface at the second layer and the interface in each land portion, and to suppress the softening of the rubber due to the heat generation of the first layer. Therefore, it is considered that the abrasion resistance performance in the land portion where the deformation becomes large during grounding is improved and the wear becomes uniform, so that the uneven wear resistance performance can be improved.

[0014] From the viewpoint of allowing the second layer to release energy by generating heat when a load is applied to the tire, it is preferable that 70°C tanδ2 exceeds 0.11.

[0015] From the viewpoint of suppressing the softening of the rubber due to the temperature rise of the first layer, it is preferable that 70°C tanδ1 is less than 0.10.

[0016] The ratio of 70°C tanδ1 to the land ratio R at the grounding surface of the tread portion (70°C tanδ1 / R) is preferably less than 0.120.

[0017] By setting 70°C tanδ1 / R within the above range and increasing the land ratio R as the 70°C tanδ of the first layer increases, it is considered that the deformation of the first layer decreases and heat generation is suppressed. As a result, it is considered that the softening of the first layer is reduced and the uneven wear resistance performance is improved.

[0018] The Shore hardness (Hs) of the first layer is preferably 65 or more.

[0019] It is believed that by setting the Shore hardness (Hs) of the first layer within the aforementioned range and suppressing the deformation of the first layer, the resistance to uneven wear can be improved.

[0020] The tanδ² / R at 70℃ is preferably 0.165 or higher.

[0021] By setting 70°C tanδ² / R within the aforementioned range and increasing the 70°C tanδ of the second layer relative to the land ratio R, it is believed that the energy absorption efficiency in the second layer will be increased, improving resistance to uneven wear.

[0022] The modulus M2 of the rubber composition constituting the second layer when stretched to 200% is preferably 9.0 MPa or less.

[0023] By setting the modulus of the rubber composition constituting the second layer at 200% stretch within the aforementioned range, it is believed that when deformation from the road surface occurs that could not be fully absorbed by the first layer, the second layer can deform flexibly, making it easier to absorb the deformation.

[0024] The mass content ratio of silica to carbon black in the rubber composition constituting the second layer is preferably 0.50 or higher.

[0025] By incorporating silica into the second layer, which is the intermediate rubber layer, to improve elongation, it is possible to mitigate the impact received by the block, and thus improve resistance to uneven wear.

[0026] The elongation EB2 at break of the rubber composition constituting the second layer is preferably 500% or more.

[0027] By setting the elongation at break of the rubber composition constituting the second layer within the aforementioned range, it is thought that the second layer can be made more easily deformable.

[0028] From the viewpoint of the effects of the present invention, the rubber component constituting the first layer preferably contains isoprene-based rubber.

[0029] The total amount of styrene in the rubber component constituting the second layer is preferably less than 20% by mass.

[0030] By setting the total amount of styrene in the rubber component constituting the second layer within the aforementioned range, it is thought that fine styrene domains can be formed within the second layer, making it easier to absorb external deformation at the interface between the styrene domains and the surrounding rubber molecular chains.

[0031] The ratio of 70°C tanδ2 to 70°C tanδ3 (70°C tanδ2 / 70°C tanδ3) of the rubber composition constituting the third layer is preferably greater than 1.0.

[0032] By increasing the heat generation properties of the second layer relative to the heat generation properties of the rubber composition constituting the third layer, it is thought that even if deformation occurs that cannot be fully absorbed by the first layer, the deformation can be more easily absorbed by the second layer.

[0033] From the viewpoint of the effects of the present invention, H is preferably greater than 10 mm and less than 20 mm.

[0034] It is preferable that at least one groove wall of the circumferential groove has a recess that is recessed outward in the groove width direction from the groove edge that appears on the tread surface of the tread portion.

[0035] By providing recesses in the groove walls of the circumferential grooves, it is possible to create voids within the tread, allowing for the absorption and suppression of impact transmission within these voids.

[0036] In a circumferential groove, where a recess is provided in the groove wall that is recessed outward in the groove width direction from the groove edge that appears on the tread surface of the tread portion, when L is the distance from the radially outer end of the recess to the tread surface, it is preferable that L / t1 is greater than 1.0.

[0037] The presence of a recess on the radially inward side of the tire compared to the first layer creates the aforementioned void in the second layer and beyond, which is thought to make it easier to absorb shocks and deformations inside the tire.

[0038] Preferably, the tread portion has a plurality of lateral grooves extending in the tire width direction.

[0039] The presence of lateral grooves in the tread section is thought to make the block section more susceptible to deformation in the circumferential direction of the tire.

[0040] <Definition> The "tread portion" is the part that forms the contact surface of the tire, and in the radial cross-section of the tire, if the tire has components that form the tire skeleton using steel or textile materials such as belt layers, belt reinforcement layers, and carcass layers, the tread portion is the component that is radially outward from these components.

[0041] A "standard rim" is the rim specified for each tire in the standards system that the tire is based on. For example, it is called a "standard rim" for JATMA, a "design rim" for TRA, and a "measuring rim" for ETRTO. Refer to JATMA, ETRTO, and TRA in that order, and if there is an applicable size at the time of reference, follow that standard.

[0042] "Regular internal pressure" refers to the air pressure specified for each tire in the tire standard system, including the standard on which the tire is based. For JATMA, it is the "maximum air pressure," for TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES," and for ETRTO, it is the "INFLATION PRESSURE." Similar to the regular rim, refer to JATMA, ETRTO, and TRA in that order, and if an applicable size is available at the time of reference, follow that standard.

[0043] "Normal condition" refers to a state in which the tire is mounted on a normal rim, filled to the normal internal pressure, and under no load. In this specification, unless otherwise specified, the dimensions of each part of the tire are measured under the aforementioned normal condition.

[0044] "Regular load" refers to the load specified for each tire in the standards system, including the standard on which the tire is based. For JATMA, it is the "maximum load capacity," for TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES," and for ETRTO, it is the "LOAD CAPACITY." Similar to the regular rim and regular internal pressure mentioned above, refer to JATMA, ETRTO, and TRA in that order, and if there is an applicable size at the time of reference, follow that standard.

[0045] The "contact point" is the outermost contact point in the tire's width direction when a tire in a normal state is subjected to a normal load, has a camber angle of 0 degrees, and is in contact with a flat surface.

[0046] "The thickness of each rubber layer constituting the tread" refers to the thickness of each rubber layer on the tire's equatorial plane in a cross-section obtained by cutting the tire with respect to the plane containing the tire's axis of rotation. For example, the thickness of the first layer refers to the straight-line distance in the tire's radial direction from the outermost surface of the tread to the inner radial interface of the first layer on the tire's equatorial plane. If the tire has circumferential grooves on its equatorial plane, the thickness of each rubber layer constituting the tread shall be the thickness of each rubber layer at the center of the tire's width direction of the land area closest to the tire's equatorial plane. "The land area closest to the tire's equatorial plane" refers to the land area of ​​a circumferential groove on the tire's equatorial plane that has the groove edge closest to the tire's equatorial plane. If such land areas exist on both sides in the tire's width direction, the thickness of each rubber layer constituting the tread shall be the average value of the thicknesses of each rubber layer at the center of the tire's width direction of the two land areas. Furthermore, if there are conductive members or the like on the land area of ​​the tire's equatorial plane and the interface is unclear, the interface obstructed by the conductive members or the like shall be virtually connected and measured.

[0047] A "groove," including circumferential and lateral grooves, refers to a recess with a depth of at least 3 mm. In particular, those with an opening width of 2 mm or less on the tire surface are called "sipes."

[0048] "Block" refers to the area on the tread surface formed in the tread portion that is demarcated by circumferential grooves, transverse grooves, and contact edges with an opening width greater than 2.0 mm. If there are no widthwise grooves, it refers to the land portion demarcated by the circumferential grooves and contact edges.

[0049] "Land ratio R" is the ratio of the total surface area of ​​the contact surface to the total surface area of ​​the tread surface when a tire in a normal state is subjected to a normal load, with a camber angle of 0 degrees, and making contact with a flat surface, assuming that all grooves are filled. Here, "all grooves" includes grooves that do not fall under the circumferential grooves and lateral grooves mentioned above.

[0050] The "deepest groove depth of the circumferential groove" is determined by the distance between the tread surface and the deepest part of the groove bottom of the circumferential groove. The deepest part of the groove bottom of the circumferential groove is the deepest part of the groove bottom of the circumferential groove with the deepest groove depth among the circumferential grooves adjacent to the block.

[0051] In a circumferential groove, where a recess is provided in the groove wall that is recessed outward in the groove width direction from the groove edge that appears on the tread surface of the tread portion, the distance L from the outer end of the recess in the tire radial direction to the tread surface refers to the straight-line distance from the inflection point where the groove width widens from the tire surface side toward the tire side to the straight line connecting the ends of the circumferential groove on the tire's outermost surface side in the tire radial cross-section (Figure 3). If the groove width of the circumferential groove continues to gradually increase from the end on the tire surface side toward the tire side, then L is 0.

[0052] A "softener" is a material that imparts plasticity to rubber components and is extracted from rubber compositions using acetone. Softeners include those that are liquid at 25°C and those that are solid at 25°C. However, waxes and stearic acid commonly used in the tire industry are excluded.

[0053] "Softener content" includes the amount of softener contained in the stretchable rubber component that has been pre-stretched with softeners such as oil, resin components, and liquid rubber components. The same applies to the oil content, resin component content, and liquid rubber content; for example, if the stretchable component is oil, the stretchable oil is included in the oil content.

[0054] <Measurement method> The thickness of each rubber layer that makes up the tread is measured by cutting the tire along the plane containing the tire's rotation axis, with the width of the bead area matched to the width of the standard rim.

[0055] "70℃tanδ" is the loss loss tangent measured under the conditions of a temperature of 70℃, a frequency of 10Hz, an initial strain of 10%, a dynamic strain of 1%, and the extension mode. The sample for measuring 70℃tanδ is a vulcanized rubber composition measuring 20mm in length, 4mm in width, and 1mm in thickness. When preparing the sample by cutting it from a tire, it should be cut from the tire tread so that the tire circumference is the longer side and the tire radius is the thickness direction.

[0056] Shore hardness is measured in accordance with JIS K 6253-3:2012, using a durometer type A at a temperature of 23°C (Hs). The Shore hardness measurement sample is prepared by cutting a piece from the tread so that the tire radius is oriented in the thickness direction. The measurement is performed by pressing the measuring instrument against the sample from the contact surface side.

[0057] "Elongation at Break (EB)" is the elongation at break (elongation at rupture) (%) measured in accordance with JIS K 6251:2017, under conditions of 23°C atmosphere and a tensile speed of 3.3 mm / second. The sample for EB measurement is a 1 mm thick, dumbbell-shaped vulcanized rubber test piece of type 7. When preparing it by cutting from a tire, it should be cut from the tire tread so that the tire circumference is the tensile direction and the tire radius is the thickness direction.

[0058] The "modulus at 200% elongation" is the tensile stress (MPa) at 200% elongation in the shear direction (the rolling direction when forming a rubber sheet by extrusion or shearing), measured under conditions of 3.3 mm / second at a tensile speed in a 23°C atmosphere, in accordance with JIS K 6251:2017. The sample for this measurement is prepared in the same manner as in the case of EB.

[0059] The "total contact area" is calculated from the tire's contact shape. The contact shape is obtained by mounting the tire to a standard rim, applying standard internal pressure, letting it stand at 25°C for 24 hours, then applying ink to the tread surface, applying a load of the maximum load capacity, pressing it onto cardboard (camber angle 0 degrees), and transferring the shape to the paper. The tire is then rotated 72 degrees in the circumferential direction, and the shape is transferred at five different points. In other words, the contact shape is obtained five times. The actual contact area is determined by the average of the areas of the ink-covered parts at these five points.

[0060] "Styrene content" is, 1 This value is calculated by 1H-NMR measurement and applies, for example, to rubber components having repeating units derived from styrene, such as SBR. "Cis content (amount of cis-1,4-bonded butadiene units)" is a value calculated by infrared absorption spectroscopy in accordance with JIS K 6239-2:2017 and applies, for example, to rubber components having repeating units derived from butadiene, such as BR.

[0061] "Total styrene content in rubber components" refers to the total amount of styrene units contained in 100% by mass of the rubber components (by mass%). For each rubber component, the value obtained by multiplying the styrene content (by mass%) by the mass fraction in the rubber components is calculated, and these values ​​are then summed up. Specifically, it is calculated as Σ(styrene content (by mass%) of each styrene-containing rubber × styrene content (by mass%) in the rubber components of each styrene-containing rubber / 100).

[0062] The "weight-average molecular weight (Mw)" can be determined by converting the measured value using gel permeation chromatography (GPC) (for example, the GPC-8000 series from Tosoh Corporation, with a differential refractometer as the detector and TSKGEL SUPERMALTIPORE HZ-M column from Tosoh Corporation) to a standard polystyrene equivalent. This method is applicable, for example, to SBR, BR, etc.

[0063] 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.

[0064] The "softening point of the resin component" is the temperature at which the sphere descends when the softening point specified in JIS K 6220-1:2015 7.7 is measured using a ring-type softening point measuring device.

[0065] The procedure for manufacturing a tire, which is one embodiment of the present invention, will be described in detail below. However, the following description is illustrative for explaining the present invention and is not intended to limit the technical scope of the present invention to this scope only.

[0066] [tire] Figure 1 shows an example of a flattened unfolded view of the tread pattern of a tire according to one embodiment of the present invention, but the present invention is not limited thereto. As shown in Figure 1, the tread portion 1 is provided with a pair of center land portions 6, 6, middle land portions 7, 7, and shoulder land portions 8, 8 by circumferential grooves 3, 4, 5 that extend continuously in the circumferential direction of the tire. The center land portion 6 is formed between the center circumferential groove 3 and the middle circumferential groove 4. The middle land portion 7 is formed between the middle circumferential groove 4 and the shoulder circumferential groove 5. The shoulder land portion 8 is formed between the shoulder circumferential groove 5 and the contact end Te.

[0067] The center land section 6 is provided with multiple center lateral grooves 19 that traverse the center land section 6 and communicate with the center circumferential groove 3 and the middle circumferential groove 4, forming an independent block. The middle land section 7 is provided with multiple middle lateral grooves 20 that traverse the middle land section 7 and communicate with the middle circumferential groove 4 and the shoulder circumferential groove 5, forming an independent block. The shoulder land section 8 is provided with multiple shoulder lateral grooves 21 that communicate with the shoulder circumferential groove 5.

[0068] In Figure 1, the center circumferential groove 3 extends in a zigzag pattern. The center circumferential groove 3 also alternately includes a center long side portion 3A and a center short side portion 3B. The center long side portion 3A is inclined to one side with respect to the tire circumferential direction. The center short side portion 3B is inclined in the opposite direction to the center long side portion 3A.

[0069] In Figure 1, the center lateral groove 19 and the middle lateral groove 20 extend in a straight line, but the design is not limited to this configuration. For example, they may extend in a wavy, sinusoidal, or zigzag pattern.

[0070] The center land portion 6 is provided with a center sipe 22 that communicates with the center circumferential groove 3 and the middle circumferential groove 4. When the block edge in the circumferential direction of the tire makes contact with the ground, the sipe deforms in a direction that closes its width, so that the walls of adjacent sipes come into close contact and support each other, thereby suppressing a decrease in the rigidity of the land portion. The center sipe 22 extends in a zigzag shape, but is not limited to this configuration, and may extend in a wave-like, sinusoidal, or linear shape, for example.

[0071] The land ratio R at the contact surface of the tread is preferably 0.65 or higher, more preferably 0.70 or higher, and even more preferably 0.75 or higher. Furthermore, the land ratio R is preferably 0.95 or lower, more preferably 0.90 or lower, and even more preferably 0.85 or lower.

[0072] Figure 2 is a cross-sectional view showing a portion of the circumferential groove according to this embodiment. In Figure 2, the vertical direction is the radial direction of the tire, the left-right direction is the axial direction of the tire, and the direction perpendicular to the plane of the paper is the circumferential direction of the tire.

[0073] As shown in the figures, the tread portion of the tire according to this embodiment comprises a first layer 11, a second layer 12, and a third layer 13, with the outer surface of the first layer 11 forming the tread surface, the second layer 12 adjacent to the radially inward side of the first layer 11, and the third layer 13 located radially inward of the second layer 12. Furthermore, to the extent that the objective of the present invention is achieved, there may be one or more additional rubber layers between the second layer 12 and the third layer 13, and / or between the third layer 13 and a belt layer (not shown).

[0074] From the viewpoint of the effects of the present invention, the thickness t1 of the first layer 11 is preferably 5 mm or more, more preferably 8 mm or more, and even more preferably 10 mm or more. On the other hand, t1 is preferably 20 mm or less, more preferably 18 mm or less, and even more preferably 15 mm or less.

[0075] From the viewpoint of the effects of the present invention, the thickness t2 of the second layer 12 is preferably 1 mm or more, more preferably 3 mm or more, and even more preferably 5 mm or more. On the other hand, t2 is preferably 15 mm or less, more preferably 12 mm or less, and even more preferably 10 mm or less.

[0076] From the viewpoint of the effects of the present invention, the groove depth H of the circumferential groove is preferably greater than 4 mm, more preferably greater than 7 mm, even more preferably greater than 10 mm, and particularly preferably greater than 12 mm. On the other hand, H is preferably less than 26 mm, more preferably less than 24 mm, even more preferably less than 22 mm, and particularly preferably less than 20 mm.

[0077] In this embodiment, the tire is formed such that the deepest part of the groove bottom of the circumferential groove is located radially inward from the outer surface of the second layer 12, and the inside of the block is formed of two or more rubber layers. From the viewpoint of the effects of the present invention, t1 / H is 0.90 or less, preferably 0.85 or less, and more preferably 0.80 or less. On the other hand, the lower limit of t1 / H is not particularly limited, but is preferably 0.20 or more, more preferably 0.30 or more, and even more preferably 0.40 or more.

[0078] It is preferable that at least one groove wall of the circumferential groove has a recess that is recessed outward in the groove width direction from the groove edge 2 that appears on the tread surface of the tread portion. By providing a recess in the groove wall of the circumferential groove, it is thought that a void can be formed inside the tread, and that impact can be absorbed and its propagation suppressed in this void. In Figure 2, the circumferential groove 3 has recesses 9 on both groove walls 10. In Figure 2, the groove width of the circumferential groove 3 gradually increases from the end on the tire surface side toward the inside in the tire radial direction, but the configuration is not limited to this.

[0079] Figure 3 is a cross-sectional view showing a portion of another circumferential groove according to this embodiment. In Figure 3, the circumferential groove 3 has a constant groove width in a range of distance L from the tread surface 14, and from there the groove width gradually increases toward the radially inward direction of the tire, forming a recess 9.

[0080] In a circumferential groove, where a recess is provided in the groove wall that is recessed outward in the groove width direction from the groove edge that appears on the tread surface of the tread portion, the distance L from the outer end of the recess in the tire radial direction to the tread surface is preferably greater than t1. It is believed that the presence of a recess radially inward from the first layer creates the aforementioned void in the second layer and beyond, making it easier to absorb shocks and deformations inside the tire. L / t1 is preferably greater than 1.0, more preferably greater than 1.1, and even more preferably greater than 1.2. On the other hand, there is no particular upper limit to L / t1, but it is preferably less than 4.0, more preferably less than 3.0, and even more preferably less than 2.0.

[0081] L is preferably greater than 0 mm, more preferably greater than 5 mm, and even more preferably greater than 8 mm. On the other hand, L is preferably less than 25 mm, more preferably less than 21 mm, and even more preferably less than 16 mm.

[0082] The total recess amount of the circumferential groove 3 (c1 + c2 in Figures 2 and 3) is preferably 0.10 to 5.00 times the groove width W1 of the circumferential groove 3, more preferably 0.20 to 3.00 times, and even more preferably 0.30 to 1.00 times. If there are multiple circumferential grooves having such recesses, it is sufficient if the total recess amount of any one of the circumferential grooves satisfies the above relationship, and it is also acceptable if all grooves having recesses satisfy the above relationship.

[0083] The tanδ (70°C tanδ1) of the rubber composition constituting the first layer at 70°C is preferably less than 0.20, more preferably less than 0.16, even more preferably less than 0.12, and particularly preferably less than 0.10, from the viewpoint of suppressing the softening of the rubber due to the temperature rise of the first layer. On the other hand, from the viewpoint of absorbing deformation from the road surface, it is preferably 0.03 or higher, more preferably 0.04 or higher, and even more preferably 0.05 or higher.

[0084] The tanδ (70°C tanδ²) of the rubber composition constituting the second layer at 70°C is preferably greater than 0.07, more preferably greater than 0.09, even more preferably greater than 0.10, and particularly preferably greater than 0.11, from the viewpoint of allowing energy to be dissipated by the second layer generating heat when a load is applied to the tire. On the other hand, from the viewpoint of suppressing excessive heat generation inside the block, it is preferably 0.30 or less, more preferably 0.25 or less, even more preferably 0.20 or less, and particularly preferably 0.18 or less.

[0085] The tanδ (70°C tanδ3) of the rubber composition constituting the third layer at 70°C is preferably 0.24 or less, more preferably 0.19 or less, even more preferably 0.14 or less, and particularly preferably 0.09 or less, from the viewpoint of suppressing excessive heat generation inside the block. Furthermore, the 70°C tanδ3 is preferably 0.03 or more, more preferably 0.04 or more, and even more preferably 0.05 or more.

[0086] In this embodiment, 70°C tanδ1 / 70°C tanδ2 is less than 1.0, and 0.95 A value less than 0.90 is preferred, less than 0.85 is even more preferred, and less than 0.80 is particularly preferred. By setting 70℃tanδ1 / 70℃tanδ2 within the above range, it is thought that energy can be dissipated as heat within the block, thereby improving resistance to uneven wear. Furthermore, it is thought that heat generation outside the block is suppressed, and the surface of the block becomes hot and soft, thereby suppressing the worsening of uneven wear. On the other hand, there is no particular limit to the lower limit of 70℃tanδ1 / 70℃tanδ2, but a value greater than 0.40 is preferred, more than 0.50 is preferred, and more than 0.60 is even more preferred.

[0087] The 70°C tanδ² / 70°C tanδ³ ratio is preferably greater than 1.0, more preferably greater than 1.2, and even more preferably greater than 1.4. By increasing the heat generation of the second layer relative to the heat generation of the rubber composition constituting the third layer, it is thought that even if deformation occurs that cannot be fully absorbed by the first layer, the deformation can be more easily absorbed by the second layer. On the other hand, there is no particular upper limit to the 70°C tanδ² / 70°C tanδ³ ratio, but it is preferably less than 4.0, and more preferably less than 3.0.

[0088] Furthermore, the 70°C tanδ of each rubber layer can be appropriately adjusted depending on the type and amount of rubber components, fillers, and softeners described below.

[0089] The modulus (M1) of the rubber composition constituting the first layer at 200% stretch is preferably 15.0 MPa or less, more preferably 14.0 MPa or less, even more preferably 13.0 MPa or less, and particularly preferably 12.0 MPa or less. The modulus (M2) of the rubber composition constituting the second layer at 200% stretch is preferably 13.0 MPa or less, more preferably 11.0 MPa or less, even more preferably 10.0 MPa or less, and particularly preferably 9.0 MPa or less. On the other hand, the lower limits of M1 and M2 are not particularly limited, but are preferably 2.0 MPa or more, more preferably 3.0 MPa or more, and even more preferably 4.0 MPa or more. The modulus of the rubber composition constituting the third layer at 200% stretch is not particularly limited.

[0090] The elongation at break (EB1) of the rubber composition constituting the first layer is preferably 420% or more, more preferably 440% or more, and even more preferably 460% or more. Similarly, the elongation at break (EB2) of the rubber composition constituting the second layer is preferably 440% or more, more preferably 470% or more, and even more preferably 500% or more. There are no particular upper limits on EB1 and EB2.

[0091] Furthermore, the EB and modulus at 200% stretch of each rubber layer can be appropriately adjusted by the type and amount of rubber components, fillers, softeners, etc., as described below.

[0092] The Shore hardness (Hs) of the first layer is preferably 55 or higher, more preferably 60 or higher, and even more preferably 65 or higher. It is believed that by setting the Shore hardness (Hs) of the first layer within the above range and suppressing deformation of the first layer, the resistance to uneven wear can be improved. Furthermore, the Shore hardness (Hs) of the first layer is preferably 80 or lower, more preferably 75 or lower, and even more preferably 70 or lower. The Shore hardness can be appropriately adjusted depending on the type and amount of rubber components, fillers, plasticizers, etc.

[0093] The tire outer diameter Dt is preferably 0.70m or more, more preferably 0.80m or more, and even more preferably 0.90m or more. Furthermore, Dt is preferably 1.20m or less, and more preferably 1.10m or less.

[0094] In this embodiment, 70°C tanδ² / Dt is greater than 0.09, preferably greater than 0.10, more preferably greater than 0.12, and even more preferably greater than 0.14. It is believed that setting 70°C tanδ² / Dt within the above range can greatly enhance the effect of absorbing deformation inside the tread. On the other hand, there is no particular upper limit to 70°C tanδ² / Dt, but it is preferably less than 0.24, and more preferably less than 0.22.

[0095] The 70°C tanδ1 / R is preferably less than 0.150, more preferably less than 0.140, even more preferably less than 0.130, even more preferably less than 0.120, and particularly preferably less than 0.115. By setting the 70°C tanδ1 / R within the above range and increasing the land ratio R as the 70°C tanδ of the first layer increases, it is thought that the deformation of the first layer decreases and heat generation is suppressed. On the other hand, there is no particular limit to the lower limit of the 70°C tanδ1 / R, but it is preferably 0.030 or higher, more preferably 0.040 or higher, even more preferably 0.050 or higher, and particularly preferably 0.060 or higher.

[0096] The 70°C tanδ² / R is preferably 0.100 or higher, more preferably 0.130 or higher, even more preferably 0.160 or higher, and particularly preferably 0.165 or higher. By setting the 70°C tanδ² / R within the above range and reducing the land ratio R relative to the 70°C tanδ of the second layer, it is thought that the second layer deforms and generates heat, making it easier to dissipate energy. On the other hand, there is no particular upper limit to the 70°C tanδ² / R, but it is preferably 0.270 or lower, more preferably 0.230 or lower, and even more preferably 0.200 or lower.

[0097] [Rubber composition] The tire according to this embodiment can improve resistance to uneven wear through the cooperation of the aforementioned tire and tread configuration and the aforementioned physical properties of the rubber composition constituting each layer of the tread. The rubber composition according to this embodiment will be described below, and unless otherwise specified, it will be applicable to any rubber layer of the tread.

[0098] <Rubber components> The rubber composition according to this embodiment preferably contains at least one rubber component selected from the group consisting of isoprene rubber, styrene-butadiene rubber (SBR), and butadiene rubber (BR), and more preferably contains isoprene rubber. These rubber components may be used individually or in combination of two or more. Furthermore, these rubber components may be modified rubbers treated with modifying groups that can interact with fillers such as carbon black or silica, or hydrogenated rubbers in which some of the unsaturated bonds have been hydrogenated. The rubber components constituting the first and second layers preferably contain isoprene rubber, and more preferably contain isoprene rubber and BR.

[0099] (Isoprene rubber) As isoprene-based rubbers, for example, isoprene rubber (IR) and natural rubber, which are common in the tire industry, can be used. Natural rubber includes not only unmodified natural rubber (NR), but also 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-based rubbers may be used individually or in combination of two or more types.

[0100] NR is not particularly limited and can be any tire that is common in the tire industry, such as SIR20, RSS#3, and TSR20.

[0101] From the viewpoint of the effects of the present invention, the content of isoprene-based rubber in the rubber component is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, and particularly preferably 50% by mass or more. Furthermore, there is no particular upper limit to the content, but for example, it can be 100% by mass, 99% by mass or less, 95% by mass or less, 90% by mass or less, or 85% by mass or less.

[0102] (BR) BR is not particularly limited, and for example, BR with a cis content of less than 50% by mass (low-cis BR), BR with a cis content of 90% by mass or more (high-cis BR), rare-earth butadiene rubber synthesized using a rare-earth element catalyst (rare-earth BR), BR containing syndiotactic polybutadiene crystals (SPB-containing BR), modified BR (high-cis modified BR, low-cis modified BR), etc., which are common in the tire industry, can be used. These BRs may be used individually or in combination of two or more types.

[0103] High-sis BR can be commercially available from companies such as Nippon Zeon Co., Ltd., Ube Industries, Ltd., and JSR Corporation. The inclusion of high-sis BR improves wear resistance. The cis content of high-sis BR is preferably 95% by mass or more, more preferably 96% by mass or more, and even more preferably 97% by mass or more. The cis content of BR is measured by the measurement method described above.

[0104] As the modified BR, a modified butadiene rubber (modified BR) is preferably used in which the terminal and / or main chain is modified with a functional group containing at least one element selected from the group consisting of silicon, nitrogen, and oxygen.

[0105] Other modified BRs include those obtained by polymerizing 1,3-butadiene with a lithium initiator and then adding a tin compound, and in which the ends of the modified BR molecule are linked by a tin-carbon bond (tin-modified BR). Furthermore, the modified BR may be either unhydrogenated or hydrogenated.

[0106] 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 even more preferably 400,000 or more. From the viewpoint of crosslinking uniformity, it is preferably 2,000,000 or less, and more preferably 1,000,000 or less. The Mw of BR is measured by the measurement method described above.

[0107] From the viewpoint of the effects of the present invention, the BR content in the rubber component is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, and particularly preferably 25% by mass or less. Furthermore, there is no particular lower limit to the content, but for example, it can be 1% by mass or more, 3% by mass or more, 5% by mass or more, or 7% by mass or more.

[0108] (SBR) There are no particular limitations on SBR, and examples include unmodified solution-polymerized SBR (S-SBR), emulsion-polymerized SBR (E-SBR), and modified SBRs thereof (modified S-SBR, modified E-SBR). Modified SBRs include SBRs with modified terminals and / or main chains, and modified SBRs coupled with tin, silicon compounds, etc. (condensates, those with branched structures, etc.). Among these, S-SBR and modified SBRs are preferred. Furthermore, hydrogenated versions of these SBRs (hydrogenated SBRs) can also be used. These SBRs may be used individually or in combination of two or more types.

[0109] In this embodiment, stretchable SBR can be used, or non-stretchable SBR can be used. When stretchable SBR is used, the amount of stretch of the SBR, that is, the amount of stretchable softener contained in the SBR, is preferably 10 to 50 parts by mass per 100 parts by mass of rubber solids in the SBR.

[0110] The SBRs listed above may be used individually or in combination of two or more. Examples of the SBRs listed above include those commercially available from companies such as Sumitomo Chemical Co., Ltd., JSR Corporation, Asahi Kasei Corporation, Nippon Zeon Corporation, and ZS Elastomer Co., Ltd.

[0111] The styrene content of SBR is preferably 40% by mass or less, more preferably 36% by mass or less, even more preferably 32% by mass or less, and particularly preferably 28% by mass or less. Furthermore, the styrene content of SBR is preferably 5% by mass or more, more preferably 7% by mass or more, and even more preferably 10% by mass or more. The styrene content of SBR is measured by the measurement method described above.

[0112] From the viewpoint of the effects of the present invention, the weight-average molecular weight (Mw) of SBR is preferably 100,000 or more, more preferably 200,000 or more, and even more preferably 300,000 or more. Furthermore, from the viewpoint of crosslinking uniformity, the weight-average molecular weight is preferably 2,000,000 or less, more preferably 1,800,000 or less, and even more preferably 1,500,000 or less. The weight-average molecular weight of SBR is measured by the measurement method described above.

[0113] The SBR content in the rubber component constituting the second layer can be appropriately selected, for example, so that the total styrene content in the rubber component satisfies the range described below, but is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, and particularly preferably 20% by mass or less. Furthermore, there is no particular lower limit to the content, but it can be, for example, 1% by mass or more, 3% by mass or more, 5% by mass or more, or 7% by mass or more. The SBR content in the rubber components constituting the first and third layers is not particularly limited.

[0114] From the viewpoint of the effects of the present invention, the total amount of styrene in the rubber component constituting the second layer is preferably less than 20% by mass, more preferably less than 16% by mass, even more preferably less than 12% by mass, and particularly preferably less than 8.0% by mass. Furthermore, there is no particular lower limit to the total amount of styrene in the rubber component constituting the second layer, but it can be, for example, greater than 1.0% by mass, greater than 2.0% by mass, or greater than 3.0% by mass. The total amount of styrene in the rubber components constituting the first and third layers is not particularly limited.

[0115] (Other rubber components) The rubber component according to this embodiment may include rubber components other than the isoprene-based rubber, SBR, and BR mentioned above. Other rubber components that can be crosslinked are commonly used in the tire industry and include isoprene-based rubbers such as styrene-isoprene rubber (SIR), styrene-isoprene butadiene rubber (SIBR), chloroprene rubber (CR), and acrylonitrile butadiene rubber (NBR), diene-based rubbers other than SBR and BR; and non-diene-based rubbers such as butyl rubber (IIR), halogenated butyl rubber, ethylene propylene rubber, polynorbornene rubber, silicone rubber, polyethylene chloride rubber, fluororubber (FKM), acrylic rubber (ACM), and hydrin rubber. These other rubber components may be used individually or in combination of two or more.

[0116] The rubber component according to this embodiment preferably contains 80% by mass or more of diene rubber, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 98% by mass or more. It may also be a rubber component consisting solely of diene rubber. In addition to the above rubber component, it may or may not contain a known thermoplastic elastomer.

[0117] <Filler> The rubber composition according to this embodiment preferably uses a filler containing carbon black and / or silica. The rubber composition constituting the first and second layers preferably contains carbon black as a filler, and more preferably contains carbon black and silica. The rubber composition constituting the third layer preferably contains carbon black as a filler.

[0118] (Carbon Black) The carbon black used is not particularly limited; for example, common types used in the tire industry such as GPF, FEF, HAF, ISAF, and SAF can be used. In addition to carbon black produced by burning common mineral oil, carbon black made from biomass materials such as lignin may also be used. These carbon blacks may be used individually or in combination of two or more types.

[0119] The nitrogen adsorption specific surface area (N2SA) of the carbon black contained in the rubber composition constituting the first layer is preferably 70 m 2 / g or more, more preferably 90 m 2 / g or more, even more preferably 110 m 2 / g or more, particularly preferably 130 m 2 / g or more. Further, from the viewpoints of low fuel consumption performance and processability, it is preferably 200 m 2 / g or less, more preferably 180 m 2 / g or less, even more preferably 160 m 2 / g or less. The N2SA of the carbon black is measured by the above measurement method.

[0120] The nitrogen adsorption specific surface area (N2SA) of the carbon black contained in the rubber compositions constituting the second and third layers is preferably 10 m 2 / g or more, more preferably 30 m 2 / g or more, even more preferably 50 m 2 / g or more. Further, from the viewpoints of low fuel consumption performance and processability, it is preferably 200 m 2 / g or less, more preferably 160 m 2 [[ID=三十一]] / g or less, even more preferably 120 m 2 / g or less.

[0121] From the viewpoint of reinforcement, the content of carbon black with respect to 100 parts by mass of the rubber component is preferably 5 parts by mass or more, more preferably 8 parts by mass or more, even more preferably 15 parts by mass or more, and particularly preferably 25 parts by mass or more. Further, the content is preferably 90 parts by mass or less, more preferably 80 parts by mass or less, even more preferably 70 parts by mass or less, and particularly preferably 60 parts by mass or less.

[0122] (Silica) The silica used is not particularly limited, and common silica used in the tire industry can be used, such as silica prepared by the dry method (anhydrous silica) or silica prepared by the wet method (hydrated silica). Among these, hydrated silica prepared by the wet method is preferred because it contains a large number of silanol groups. In addition to the silica mentioned above, silica made from biomass materials such as rice husks may also be used as appropriate. These silicas may be used individually or in combination of two or more types.

[0123] The nitrogen adsorption specific surface area (N2SA) of silica is 120 m², from the perspective of low fuel consumption and wear resistance. 2 Preferably 150m / g or more 2 More preferably 170m / g or more. 2 A value of 350m or more is even more preferable. Furthermore, from the viewpoint of low fuel consumption and processability, 350m 2 Preferably less than / g, 300m 2 More preferably less than / g, 250m 2 A value of less than / g is even more preferable. The N2SA of silica is measured by the measurement method described above.

[0124] From the viewpoint of the effects of the present invention, the silica content of the rubber composition constituting the first and second layers, per 100 parts by mass of rubber components, is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, even more preferably 10 parts by mass or more, and particularly preferably 15 parts by mass or more. Furthermore, the silica content is preferably 90 parts by mass or less, more preferably 80 parts by mass or less, even more preferably 70 parts by mass or less, and particularly preferably 60 parts by mass or less. The silica content of the rubber composition constituting the third layer, per 100 parts by mass of rubber components, is not particularly limited.

[0125] (Other fillers) Other fillers besides silica and carbon black are not particularly limited and can include, for example, aluminum hydroxide, alumina (aluminum oxide), calcium carbonate, magnesium sulfate, talc, clay, biochar, and other materials commonly used in the tire industry. These other fillers may be used individually or in combination of two or more.

[0126] The total filler content per 100 parts by mass of rubber component is preferably 25 parts by mass or more, more preferably 30 parts by mass or more, even more preferably 35 parts by mass or more, and particularly preferably 40 parts by mass or more. Furthermore, the content is preferably 150 parts by mass or less, more preferably 130 parts by mass or less, even more preferably 110 parts by mass or less, and particularly preferably 90 parts by mass or less.

[0127] The mass content ratio of silica to carbon black in the rubber composition constituting the second layer is preferably 0.30 or higher, more preferably 0.40 or higher, even more preferably 0.50 or higher, particularly preferably 0.75 or higher, and particularly preferably greater than 1.0. By incorporating silica into the second layer, which is an intermediate rubber layer, and improving elongation, it is possible to mitigate the impact received by the block and improve the resistance to uneven wear. Furthermore, from the viewpoint of the effects of the present invention, the content ratio is preferably 20 or less, more preferably 15 or less, even more preferably 10 or less, and particularly preferably 5.0 or less. The mass content ratio of silica to carbon black in the rubber compositions constituting the first and third layers is not particularly limited.

[0128] (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 conventionally been used in combination with silica in the tire industry can be used, for example: mercapto-based silane coupling agents such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, and 2-mercaptoethyltriethoxysilane; sulfide-based silane coupling agents such as bis(3-triethoxysilylpropyl) disulfide and bis(3-triethoxysilylpropyl) tetrasulfide; 3-octanoylthio-1-propyltriethoxysilane, 3-hexanoylthio-1-propyltriethoxysilane, and 3-octanoylthio-1-propyltrimethoxysilane. Examples include thioester silane coupling agents such as lan; vinyl silane coupling agents such as vinyltriethoxysilane and vinyltrimethoxysilane; amino silane coupling agents such as 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, and 3-(2-aminoethyl)aminopropyltriethoxysilane; glycidoxy silane coupling agents such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro silane coupling agents such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; and chloro silane coupling agents such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. Among these, it is preferable to contain a sulfide silane coupling agent and / or a mercapto silane coupling agent. As silane coupling agents, for example, those commercially available from Momentive, etc., can be used. These silane coupling agents may be used individually or in combination of two or more.

[0129] From the viewpoint of improving silica dispersibility, the content of the silane coupling agent per 100 parts by mass of silica is preferably 1.0 part by mass or more, more preferably 3.0 parts by mass or more, and even more preferably 5.0 parts by mass or more. Furthermore, from the viewpoint of cost and processability, it is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 12 parts by mass or less.

[0130] <Other compounding agents> In addition to the components mentioned above, the rubber composition according to this embodiment may also appropriately contain compounding agents commonly used in the tire industry, such as softeners, waxes, stearic acid, zinc oxide, antioxidants, vulcanizing agents, and vulcanization accelerators.

[0131] Examples of softening agents include resin components, oils, and liquid polymers.

[0132] The resin components are not particularly limited, but examples include hydrocarbon resins commonly used in the tire industry, such as petroleum resins, terpene resins, rosin resins, and phenolic resins.

[0133] Examples of petroleum resins include C5-based petroleum resins, aromatic petroleum resins, and C5C9-based petroleum resins.

[0134] In this specification, "C5-based petroleum resin" refers to a resin obtained by polymerizing a C5 fraction, and may be hydrogenated or modified. Examples of C5 fractions include petroleum fractions with 4 to 5 carbon atoms, such as cyclopentadiene, pentene, pentadiene, and isoprene. Dicyclopentadiene resin (DCPD resin) is preferably used as the C5-based petroleum resin.

[0135] In this specification, "aromatic petroleum resin" refers to a resin obtained by polymerizing a C9 fraction, and may be hydrogenated or modified. Examples of C9 fractions include petroleum fractions with 8 to 10 carbon atoms, such as vinyltoluene, alkylstyrene, indene, and methylindene. Specific examples of aromatic petroleum resins that are preferably used include coumarone indene resin, coumarone resin, indene resin, and aromatic vinyl resins. As aromatic vinyl resins, homopolymers of α-methylstyrene or styrene, or copolymers of α-methylstyrene and styrene are preferred, and copolymers of α-methylstyrene and styrene are more preferred, for reasons of being economical, easy to process, and having excellent heat generation properties. As aromatic vinyl resins, commercially available products from companies such as Kraton, Eastman Chemical, etc., can be used.

[0136] In this specification, "C5C9 petroleum resin" refers to a resin obtained by copolymerizing the C5 fraction and the C9 fraction, and may be hydrogenated or modified. Examples of the C5 fraction and C9 fraction include the petroleum fractions mentioned above. As C5C9 petroleum resin, commercially available products from companies such as Tosoh Corporation and LUHUA can be used.

[0137] Examples of terpene resins include polyterpene resins consisting of at least one terpene compound selected from α-pinene, β-pinene, limonene, dipentene, etc.; aromatically modified terpene resins made from the terpene compound and an aromatic compound; terpene-phenol resins made from the terpene compound and a phenolic compound; and these terpene resins that have been hydrogenated (hydrogenated terpene resins). Examples of aromatic compounds used as raw materials for aromatically modified terpene resins include styrene, α-methylstyrene, vinyltoluene, and divinyltoluene. Examples of phenolic compounds used as raw materials for terpene-phenol resins include phenol, bisphenol A, cresol, and xylenol.

[0138] Rosin-based resins are not particularly limited, but examples include natural resin rosin and rosin-modified resins obtained by hydrogenation, disproportionation, dimerization, esterification, etc.

[0139] Phenolic resins are not particularly limited, but examples include phenol-formaldehyde resin, alkylphenol-formaldehyde resin, alkylphenol-acetylene resin, and oil-modified phenol-formaldehyde resin.

[0140] 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. Furthermore, from the viewpoint of processability and improved dispersibility between the rubber component and 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 by the measurement method described above.

[0141] When a resin component is included, the content per 100 parts by mass of the rubber component is preferably more than 1 part by mass, more preferably more than 3 parts by mass, and even more preferably more than 5 parts by mass. Furthermore, from the viewpoint of suppressing heat generation, it is preferably less than 50 parts by mass, more preferably less than 40 parts by mass, and even more preferably less than 30 parts by mass.

[0142] Examples of oils include process oils, vegetable oils, and animal fats. Examples of process oils include paraffinic process oils (mineral oil), naphthenic process oils, and aromatic process oils. Specific examples of process oils include MES (Mild Extract Solvated), DAE (Distillate Aromatic Extract), TDAE (Treated Distillate Aromatic Extract), TRAE (Treated Residual Aromatic Extract), and RAE (Residual Aromatic Extract). Furthermore, for environmental reasons, process oils with a low content of polycyclic aromatic compounds (PCA) can be used. Examples of low-PCA process oils include MES, TDAE, and heavy naphthenic oils. Additionally, from a life cycle assessment perspective, refined waste oil from rubber mixers and engines, or waste cooking oil used in restaurants, may be used.

[0143] When oil is included, the content of oil per 100 parts by mass of rubber component is preferably more than 1 part by mass, more preferably more than 3 parts by mass, and even more preferably more than 5 parts by mass, from the viewpoint of processability. Furthermore, from the viewpoint of wear resistance, it is preferably less than 90 parts by mass, more preferably less than 70 parts by mass, even more preferably less than 50 parts by mass, and particularly preferably less than 30 parts by mass.

[0144] The liquid polymer is not particularly limited as long as it is a polymer that is in a liquid state at room temperature (25°C), but examples include liquid butadiene polymer (liquid BR), liquid isoprene rubber polymer (liquid IR), liquid styrene-butadiene copolymer (liquid SBR), liquid styrene-isoprene rubber copolymer (liquid SIR), and polymers containing myrcene or farnesene. These liquid polymers may be used individually or in combination of two or more.

[0145] When a liquid polymer is included, its content per 100 parts by mass of the rubber component is preferably more than 1 part by mass, more preferably more than 3 parts by mass, and even more preferably more than 5 parts by mass. Furthermore, the liquid polymer content is preferably less than 50 parts by mass, more preferably less than 40 parts by mass, and even more preferably less than 30 parts by mass.

[0146] The amount of softener per 100 parts by mass of rubber component (total amount if multiple softeners are used in combination) is not particularly limited, but is preferably more than 1 part by mass, more preferably more than 3 parts by mass, and even more preferably more than 5 parts by mass. Furthermore, the amount is preferably less than 90 parts by mass, more preferably less than 70 parts by mass, even more preferably less than 50 parts by mass, and particularly preferably less than 30 parts by mass.

[0147] The wax is not particularly limited, and any wax commonly used in the tire industry can be suitably used. Examples include petroleum-based waxes, mineral-based waxes, and synthetic waxes, with petroleum-based waxes being preferred. Examples of petroleum-based waxes include paraffin wax, microcrystalline wax, and selected special waxes thereof, with paraffin wax being preferred. The wax according to this embodiment does not contain stearic acid. The wax can be commercially available from companies such as Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., and Paramelt Co., Ltd. These waxes may be used individually or in combination of two or more types.

[0148] When wax is included, the amount of wax per 100 parts by mass of rubber component is preferably more than 0.5 parts by mass, and more preferably more than 0.8 parts by mass, from the viewpoint of weather resistance of the rubber. Furthermore, from the viewpoint of preventing whitening of the tire due to bloom, it is preferably less than 10 parts by mass, and more preferably less than 5.0 parts by mass.

[0149] While not particularly limited, examples of anti-aging agents include amine-based, quinoline-based, quinone-based, phenol-based, and imidazole-based compounds, as well as metal carbamate salts. Phenylenediamine-based anti-aging agents such as N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, N,N'-diphenyl-p-phenylenediamine, N,N'-di-2-naphthyl-p-phenylenediamine, and N-cyclohexyl-N'-phenyl-p-phenylenediamine are preferred, as are quinoline-based anti-aging agents such as 2,2,4-trimethyl-1,2-dihydroquinoline polymer and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline. These anti-aging agents may be used individually or in combination of two or more.

[0150] When an anti-aging agent is included, the content per 100 parts by mass of rubber component is preferably more than 0.5 parts by mass, and more preferably more than 0.8 parts by mass, from the viewpoint of the rubber's resistance to ozone cracking. Furthermore, from the viewpoint of wear resistance, it is preferably less than 10 parts by mass, and more preferably less than 5.0 parts by mass.

[0151] When stearic acid is included, its content per 100 parts by mass of rubber component is preferably more than 0.5 parts by mass, more preferably more than 1.0 part by mass, and even more preferably more than 1.5 parts by mass, from the viewpoint of processability. Furthermore, from the viewpoint of vulcanization rate, it is preferably less than 10 parts by mass, and more preferably less than 5.0 parts by mass.

[0152] When zinc oxide is included, its content per 100 parts by mass of rubber component is preferably more than 0.5 parts by mass, more preferably more than 1.0 part by mass, and even more preferably more than 1.5 parts by mass, from the viewpoint of processability. Furthermore, from the viewpoint of wear resistance, it is preferably less than 10 parts by mass, and more preferably less than 5.0 parts by mass.

[0153] Sulfur is preferably used as a vulcanizing agent. Suitable sulfur varieties include powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur.

[0154] When sulfur is included as a vulcanizing agent, the amount of sulfur per 100 parts by mass of rubber component is preferably more than 0.1 parts by mass, more preferably more than 0.5 parts by mass, and even more preferably more than 1.0 part by mass, from the viewpoint of ensuring a sufficient vulcanization reaction. Furthermore, from the viewpoint of preventing deterioration, it is preferably less than 5.0 parts by mass, more preferably less than 4.0 parts by mass, and even more preferably less than 3.5 parts by mass. When oil-containing sulfur is used as the vulcanizing agent, the amount of vulcanizing agent is the total amount of pure sulfur contained in the oil-containing sulfur.

[0155] Examples of vulcanizing agents other than sulfur include alkylphenol-sulfur chloride condensates, 1,6-hexamethylene-dithiosulfate sodium dihydrate, and 1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane. These non-sulfur vulcanizing agents can be purchased commercially from companies such as Taoka Chemical Industries, Ltd., Lanxess Corporation, and Flexis.

[0156] Examples of vulcanization accelerators include sulfenamide-based vulcanization accelerators, thiazole-based vulcanization accelerators, thiram-based vulcanization accelerators, guanidine-based vulcanization accelerators, dithiocarbamate-based vulcanization accelerators, and caprolactam disulfide. These vulcanization accelerators may be used individually or in combination of two or more. In particular, from the viewpoint of obtaining the desired effect more favorably, one or more vulcanization accelerators selected from the group consisting of sulfenamide-based vulcanization accelerators, thiazole-based vulcanization accelerators, and guanidine-based vulcanization accelerators are preferred, and the combination of sulfenamide-based vulcanization accelerators and guanidine-based vulcanization accelerators is even more preferred.

[0157] Examples of sulfenamide-based vulcanization accelerators include N-tert-butyl-2-benzothiazolyl sulfenamide (TBBS), N-cyclohexyl-2-benzothiazolyl sulfenamide (CBS), and N,N-dicyclohexyl-2-benzothiazolyl sulfenamide (DCBS). Among these, TBBS and CBS are preferred.

[0158] Examples of thiazole-based vulcanization accelerators include 2-mercaptobenzothiazole (MBT) or its salts, di-2-benzothiazolyl disulfide (MBTS), 2-(2,4-dinitrophenyl)mercaptobenzothiazole, and 2-(2,6-diethyl-4-morpholinothio)benzothiazole. Of these, MBTS and MBT are preferred, with MBTS being more preferred.

[0159] Examples of guanidine-based vulcanization accelerators include 1,3-diphenylguanidine (DPG), 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, di-o-tolylguanidine salts of dicatecholborate, 1,3-di-o-cumenylguanidine, 1,3-di-o-biphenylguanidine, and 1,3-di-o-cumenyl-2-propionylguanidine. Among these, DPG is preferred.

[0160] When a vulcanization accelerator is included, its content per 100 parts by mass of rubber component is preferably more than 0.5 parts by mass, more preferably more than 1.0 part by mass, and even more preferably more than 1.5 parts by mass. Furthermore, the content of the vulcanization accelerator per 100 parts by mass of rubber component is preferably less than 8.0 parts by mass, more preferably less than 6.0 parts by mass, and even more preferably less than 4.0 parts by mass. By keeping the content of the vulcanization accelerator within the above range, it tends to be possible to ensure fracture strength and elongation.

[0161] [Manufacturing of rubber compositions and tires] The rubber composition according to this embodiment can be manufactured by known methods. For example, it can be manufactured by kneading each of the above components using a rubber kneading device such as an open roll or a closed kneader (Banbury mixer, kneader, etc.).

[0162] The mixing process includes, for example, a base mixing process in which compounding agents and additives other than the vulcanizing agent and vulcanization accelerator are mixed, and a final mixing (F mixing) process in which the vulcanizing agent and vulcanization accelerator are added to the mixture obtained in the base mixing process and mixed. Furthermore, the base mixing process can be divided into multiple processes as desired.

[0163] There are no particular limitations on the mixing conditions, but for example, in the base mixing process, mixing is performed at a discharge temperature of 150-170°C for 3-10 minutes, and in the final mixing process, mixing is performed at 70-110°C for 1-5 minutes. There are no particular limitations on the vulcanization conditions, but for example, vulcanization is performed at 150-200°C for 10-30 minutes.

[0164] A tire having a tread including a first layer 11, a second layer 12, and a third layer 13 can be manufactured by conventional methods using the rubber composition described above. Specifically, an unvulcanized rubber composition, in which the above components are blended with the rubber component as needed, is extruded in an extruder equipped with a die of a predetermined shape to match the shapes of the first layer 11, the second layer 12, and the third layer 13, and then bonded together with other tire components on a tire molding machine and molded in conventional methods to form an unvulcanized tire. This unvulcanized tire is then heated and pressurized in a vulcanizing machine to manufacture the tire. The vulcanization conditions are not particularly limited, and for example, a method of vulcanization at 150 to 200°C for 10 to 30 minutes can be used.

[0165] [Tire Uses] The tire according to this embodiment can be suitably used as a heavy-duty tire. A heavy-duty tire is a tire intended to be mounted on a four-wheeled vehicle and has a maximum load capacity of 1000 kg or more. The maximum load capacity of a heavy-duty tire is preferably 1200 kg or more, and more preferably 1400 kg or more. [Examples]

[0166] The following examples (case studies) are shown as preferred for implementation, but the scope of the present invention is not limited to these examples. Using the various chemicals shown below, a heavy-duty tire having a first, second, and third tread layer obtained according to the formulations in Table 1 was examined, and the results calculated based on the evaluation method below are shown in Tables 2 and 3.

[0167] The various chemicals used in the examples and comparative examples are summarized below. NR:TSR20 SBR: SBR1502 manufactured by JSR Corporation (unmodified E-SBR, styrene content: 23.5% by mass, Mw: 440,000, non-oil-based) BR: UBEPOL BR(registered trademark) 150B manufactured by Ube Industries, Ltd. (unmodified BR, cis content: 97% by mass, Mw: 440,000) Carbon Black 1: VULCAN10H (N134, N2SA: 144m) manufactured by Cabot Japan Co., Ltd. 2 / g) Carbon Black 2: Show Black N220 (N2SA: 111m) manufactured by Cabot Japan Co., Ltd. 2 / g) Carbon Black 3: Show Black N330 (N2SA: 75m) manufactured by Cabot Japan Co., Ltd. 2 / g) Silica: ULTRASIL(registered trademark) VN3 (N2SA: 175m) manufactured by Evonik Degussa. 2 / g) Silane coupling agent: Si266 (bis(3-triethoxysilylpropyl) disulfide) manufactured by Evonik Degussa. Oil: Diana Process NH-70S (aromatic process oil) manufactured by Idemitsu Kosan Co., Ltd. Resin component: Sylvatraxx® 4401 (a copolymer of α-methylstyrene and styrene, manufactured by Kraton Corporation; softening point: 85°C) Wax: Ozoace 0355 (paraffin wax) from Nippon Seiro Co., Ltd. Anti-aging agent: Nocrack 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Stearic acid: Beads of stearic acid manufactured by NOF Corporation Zinc oxide: Two types of zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: HK-200-5 (5% oil-containing powdered sulfur) manufactured by Hosoi Chemical Industry Co., Ltd. Vulcanization accelerator 1: Noxellar NS (N-tert-butyl-2-benzothiazolyl sulfenamide (TBBS)) 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. Vulcanization accelerator 1: Nocceler CZ (N-cyclohexyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0168] (Examples and Comparative Examples) According to the formulation shown in Table 1, using a 1.7 L closed Banbury mixer, chemicals other than sulfur and vulcanization accelerators are kneaded for 1 to 10 minutes until the discharge temperature reaches 150 to 160 °C to obtain a kneaded product. Next, using a two-roll open mill, sulfur and vulcanization accelerators are added to the kneaded product and kneaded for 4 minutes until it reaches 105 °C to obtain an unvulcanized rubber composition. Using the unvulcanized rubber composition, it is molded according to the shapes of the first layer, second layer (thickness: 10 mm), and third layer (thickness: 3 mm) of the tread, and laminated together with other tire members to produce an unvulcanized tire, which is vulcanized at 150 °C to obtain each test tire described in Tables 2 and 3. Note that the groove width W1 of the circumferential groove is 5 mm, and the total recess amount of the circumferential groove is 2 mm.

[0169] <Measurement of tanδ> For each vulcanized rubber test piece prepared by cutting out from each rubber layer inside the tread part of each test tire, with the tire circumferential direction as the long side and the tire radial direction as the thickness direction, having a length of 20 mm × width of 4 mm × thickness of 1 mm, using a dynamic viscoelasticity measuring device (Epsilon series manufactured by GABO), measure tanδ under the conditions of a temperature of 70 °C, a frequency of 10 Hz, an initial strain of 10%, a dynamic strain of 1%, and an elongation mode.

[0170] <Tensile test> For each dumbbell-shaped No. 7 test piece cut out with a thickness of 1 mm from each rubber layer inside the tread part of each test tire, with the tire circumferential direction as the tensile direction and the tire radial direction as the thickness direction, according to JIS K 6251:2017, conduct a tensile test under the conditions of a temperature of 23 °C and a tensile speed of 3.3 mm / second, and measure the elongation at break EB (%) and the modulus (MPa) at a 200% elongation respectively.

[0171] <Measurement of rubber hardness (Hs)> For each vulcanized rubber test specimen, which is prepared by cutting out a piece from the first layer of the tread of each test tire so that the tire radius direction is the thickness direction, the Shore hardness (Hs) of each rubber test specimen is measured at a temperature of 23°C using a durometer type A in accordance with JIS K6253-3:2012.

[0172] <Abrasion resistance> Each test tire is mounted on all wheels of a truck (2-D vehicle) with a maximum load capacity of 10 tons. After driving 10,000 km on a dry asphalt test course at an average speed of 80 km / h, the difference in wear on both sides of the tire's circumferential direction for the center block, middle block, and shoulder block of the rear wheel is measured. For each block, eight blocks with approximately equal pitch in the circumferential direction of the tire are used for measurement, and the average value of all measurements is calculated. The measurement results are then expressed as an index using the following formula. A higher index indicates better resistance to uneven wear. The control tires are Comparative Example 3 in Table 2 and Comparative Example 10 in Table 3. (Abrasion resistance index) = (Difference in wear of the control tire) / (Difference in wear of each test tire) × 100

[0173] [Table 1]

[0174] [Table 2]

[0175] [Table 3]

[0176] <Embodiment> Examples of embodiments of the present invention are shown below.

[0177] [1] A heavy-duty tire having a tread portion, wherein the tread portion has a plurality of circumferential grooves extending continuously in the circumferential direction of the tire, and the tread portion comprises at least a first layer constituting the tread surface, a second layer adjacent to the inner side of the first layer in the radial direction of the tire, and a third layer located on the inner side of the second layer in the radial direction of the tire, wherein the first layer, the second layer, and the third layer are each composed of a rubber composition containing a rubber component, and the ratio of the tanδ(70°C tanδ1) of the rubber composition constituting the first layer at 70°C to the tanδ(70°C tanδ2) of the rubber composition constituting the second layer at 70°C (70°C tanδ1 / 70°C tanδ2) is less than 1.0, and when the outer diameter of the tire is Dt (m), the thickness of the first layer is t1 (mm), and the groove depth of the deepest part of the circumferential groove is H (mm), 70°C tanδ2 / Dt is greater than 0.09 and t1 / H is 0.90 or less. [2] The heavy-duty tire described in [1] above, wherein the tanδ² at 70℃ is greater than 0.11. [3] A heavy-duty tire as described in [1] or [2] above, wherein the 70°C tanδ1 is less than 0.10. [4] A heavy-duty tire according to any of [1] to [3] above, wherein the ratio of 70°C tanδ1 to the land ratio R at the contact surface of the tread portion (70°C tanδ1 / R) is less than 0.120. [5] A heavy-duty tire according to any of [1] to [4] above, wherein the Shore hardness (Hs) of the first layer is 65 or higher. [6] A heavy-duty tire according to any of [1] to [5] above, wherein the ratio of 70°C tanδ2 to the land ratio R at the contact surface of the tread portion (70°C tanδ2 / R) is 0.165 or more. [7] A heavy-duty tire according to any one of [1] to [6] above, wherein the modulus M2 of the rubber composition constituting the second layer when stretched to 200% is 9.0 MPa or less. [8] A heavy-duty tire according to any one of [1] to [7] above, wherein the mass content ratio of silica to carbon black in the rubber composition constituting the second layer is 0.50 or more. [9] A heavy-duty tire according to any one of [1] to [8] above, wherein the elongation EB2 at break of the rubber composition constituting the second layer is 500% or more.

[10] A heavy-duty tire according to any one of [1] to [9] above, wherein the rubber component constituting the above layer includes isoprene rubber.

[11] A heavy-duty tire according to any one of [1] to

[10] above, wherein the total amount of styrene in the rubber component constituting the second layer is less than 20% by mass.

[12] A heavy-duty tire according to any one of [1] to

[11] above, wherein the ratio of 70°C tanδ2 to 70°C tanδ3 (70°C tanδ2 / 70°C tanδ3) of the rubber composition constituting the third layer is greater than 1.0.

[13] A heavy-duty tire as described in any of [1] to

[12] above, wherein H is greater than 10 mm but less than 20 mm.

[14] A heavy-duty tire according to any one of [1] to

[13] above, wherein at least one groove wall of the circumferential groove is provided with a recess that is recessed outward in the groove width direction from the groove edge that appears on the tread surface of the tread portion.

[15] A heavy-duty tire according to

[14] above, wherein a circumferential groove is provided in the groove wall, the recess being recessed outward in the groove width direction from the groove edge that appears on the tread surface of the tread portion, and when the distance from the radially outer end of the recess to the tread surface is L, L / t1 is greater than 1.0. [Explanation of Symbols]

[0178] 1. Tread section 2 groove edge 3. Center circumferential groove 4. Middle circumferential grooves 5. Shoulder circumferential grooves 6 Center Track and Field Club 7 Middle Track and Field Club 8 Shoulder Track and Field Club 9 recesses 10 trench wall 11 First layer 12 Second layer 13 Third layer 14 Tread surface 19 Center horizontal groove 20 Middle Horizontal Groove 21 Shoulder lateral groove 22 Center Sipes Te grounding end

Claims

1. A heavy-duty tire having a tread section, The tread portion has a plurality of circumferential grooves that extend continuously in the circumferential direction of the tire, The tread portion comprises at least a first layer constituting the tread surface, a second layer adjacent to the first layer on the radially inward side of the tire, and a third layer located on the radially inward side of the second layer. The first layer, the second layer, and the third layer are each composed of a rubber composition containing a rubber component. The ratio of the tanδ at 70°C of the rubber composition constituting the first layer (70°C tanδ1 / 70°C tanδ2) to the tanδ at 70°C of the rubber composition constituting the second layer (70°C tanδ2) is less than 1.

0. When the outer diameter of the tire is Dt (m), the thickness of the first layer is t1 (mm), and the groove depth of the deepest part of the circumferential groove is H (mm), A heavy-duty tire with a 70°C tanδ² / Dt greater than 0.09 and a t1 / H of 0.90 or less.

2. A heavy-duty tire according to claim 1, wherein the 70°C tanδ² is greater than 0.

11.

3. A heavy-duty tire according to claim 1 or 2, wherein the 70°C tanδ1 is less than 0.

10.

4. The heavy-duty tire according to claim 1 or 2, wherein the ratio of 70°C tanδ1 to the land ratio R at the contact surface of the tread portion (70°C tanδ1 / R) is less than 0.

120.

5. The heavy-duty tire according to claim 1 or 2, wherein the Shore hardness (Hs) of the first layer is 65 or higher.

6. The heavy-duty tire according to claim 1 or 2, wherein the ratio of 70°C tanδ² to the land ratio R at the contact surface of the tread portion (70°C tanδ² / R) is 0.165 or more.

7. The heavy-duty tire according to claim 1 or 2, wherein the modulus M2 of the rubber composition constituting the second layer when stretched to 200% is 9.0 or less and MPa or less.

8. The heavy-duty tire according to claim 1 or 2, wherein the mass content ratio of silica to carbon black in the rubber composition constituting the second layer is 0.50 or more.

9. The heavy-duty tire according to claim 1 or 2, wherein the elongation EB2 at break of the rubber composition constituting the second layer is 500% or more.

10. The heavy-duty tire according to claim 1 or 2, wherein the rubber component constituting the above layer includes isoprene-based rubber.

11. The heavy-duty tire according to claim 1 or 2, wherein the total amount of styrene in the rubber component constituting the second layer is less than 20% by mass.

12. The heavy-duty tire according to claim 1 or 2, wherein the ratio of tanδ2 at 70°C to tanδ3 at 70°C (tanδ2 / tanδ3) of the rubber composition constituting the third layer is greater than 1.

0.

13. A heavy-duty tire according to claim 1 or 2, wherein H is greater than 10 mm and less than 20 mm.

14. The heavy-duty tire according to claim 1 or 2, wherein at least one groove wall of the circumferential groove is provided with a recess that is recessed outward in the groove width direction from the groove edge that appears on the tread surface of the tread portion.

15. A heavy-duty tire according to claim 14, wherein a circumferential groove is provided in the groove wall, the recess being recessed outward in the groove width direction from the groove edge that appears on the tread surface of the tread portion, and when the distance from the radially outer end of the recess to the tread surface is L, L / t1 is greater than 1.0.

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