tire

Abstract

To provide a tire improved in wear resistance performance.SOLUTION: The tire comprises a tread part and a belt layer. The tread part has a first layer constituting a tread surface and a second layer formed closer to inside in a tire radial direction than the first layer. The tread part has two or more circumferential grooves continuously extending in a circumferential direction. When a thickness of the first layer is set as t1 (mm), a thickness of the second layer is set as t2 (mm), a groove depth of a deepest part of the circumferential groove is set as H (mm) and a complex elastic modulus at 100°C of a rubber composition constituting the first layer is set as 100°CE*(MPa), t1 / H is less than 1.0 and 100°CE* / t2 is equal to 1.5 or less.SELECTED DRAWING: None

Description

[Technical field]

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

[0002] In recent years, due to growing interest in environmental issues, there has been an increased demand for tires with low fuel consumption, and various studies have been conducted to address this demand.

[0003] For example, Patent Document 1 describes that a rubber composition containing a specific compound in a specified ratio has excellent low heat generation properties and can be suitably used as a material for heavy-duty tires. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2021-185212 A Summary of the Invention [Problem to be solved by the invention]

[0005] On the other hand, as concern about environmental impact grows, there is a demand for improvements in tire life performance in addition to fuel efficiency, and in particular, there is a demand for further improvements in tire wear resistance.

[0006] An object of the present invention is to provide a tire having improved wear resistance. [Means for solving the problem]

[0007] The present invention relates to A tire having a tread portion and a belt layer, The tread portion has a first layer constituting a tread surface and a second layer located radially inward of the first layer, The tread portion has two or more circumferential grooves extending continuously in the circumferential direction, When the thickness of the first layer is t1 (mm), the thickness of the second layer is t2 (mm), the groove depth of the deepest portion of the circumferential groove is H (mm), and the complex modulus of elasticity at 100°C of the rubber composition constituting the first layer is 100°C E* (MPa), The present invention relates to a tire having a t1 / H of less than 1.0 and a 100°C E* / t2 of 1.5 or less. Effect of the Invention

[0008] According to the present invention, the wear resistance of a tire can be improved.

[0009] The reason why the wear resistance is improved in the tire of the present embodiment is thought to be as follows, without intending to be bound by theory.

[0010] When a vehicle is traveling, friction occurs between the road surface and the tire tread surface, causing the tread to deform. Therefore, (1) by making t1 / H less than 1.0, the interface between the first layer of the tread and layers other than the first layer is located radially outward of the deepest part of the circumferential groove. By having the interface located radially outward of the deepest part of the circumferential groove, the energy generated by the deformation of the tread during traveling can be absorbed. Therefore, the deformation energy applied to the first layer can be reduced.

[0011] In addition, the deformation of the tread portion during driving is likely to be a bulging deformation (rounding) due to the air pressure inside the tire and the centrifugal force acting on the tire. Rounding is particularly likely to occur when the thickness of the second layer t2 is small. When the tread portion is rounded, the tire's contact area becomes smaller and the deformation energy acting on the first layer becomes larger. Therefore, by (2) setting 100°CE* / t2 to 1.5 or less and reducing 100°CE* as t2 becomes smaller, the first layer constituting the tread surface also becomes more likely to deform even when the tread portion is rounded. This makes it easier for the tread surface to contact the road surface, and the deformation energy acting on the first layer can be reduced. It is believed that the cooperation of (1) and (2) provides a remarkable effect of improving the wear resistance of the tire. [Brief description of the drawings]

[0012] [Figure 1] 1 is a cross-sectional view showing a portion of a tire according to one embodiment of the present invention. [Diagram 2] 1 is a cross-sectional view of a tire tread portion taken along a tire rotation axis; [Diagram 3] FIG. 4 is a cross-sectional view showing a portion of a circumferential groove according to the embodiment. [Figure 4] 8 is a cross-sectional view showing a portion of another circumferential groove according to the embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] A tire according to one embodiment of the present invention is a tire having a tread portion and a belt layer, the tread portion having a first layer constituting a tread surface, and a second layer located radially inward of the first layer, the tread portion having two or more circumferential grooves extending continuously in the circumferential direction, and wherein, when the thickness of the first layer is t1 (mm), the thickness of the second layer is t2 (mm), the groove depth at the deepest part of the circumferential groove is H (mm), and the complex modulus at 100°C of the rubber composition constituting the first layer is 100°CE* (MPa), t1 / H is less than 1.0 and 100°CE* / t2 is 1.5 or less.

[0014] It is preferable that at least one of the circumferential grooves is a wide circumferential groove having a groove width wider than the groove width on the tread surface at any position on the radially inner side of the groove, and that the groove width at a 90% position of the deepest part of the wide circumferential groove is 1.0 mm or more and 4.0 mm or less.

[0015] It is believed that the wide circumferential grooves increase the voids inside the tread, making it easier for the tread to follow the road surface when in contact with the ground, improving ground contact. This reduces the deformation energy applied to the first layer, making it easier to improve wear resistance.

[0016] It is preferable that at least one of the circumferential grooves is a wide circumferential groove having a groove width wider than the groove width on the tread surface at any position on the radially inner side of the groove, and that the wide circumferential groove has a change point where the groove width widens from the tread surface toward the radially inner side of the tire.

[0017] It is believed that the changes can minimize the size of the voids and suppress excessive deformation of the tread portion, thereby making it easier to further improve the wear resistance.

[0018] The rubber composition constituting the second layer preferably contains recycled carbon black (rCB). It is believed that recycled carbon black is less likely to restrict the surrounding rubber molecular chains than conventional carbon black, making it flexible against deformation and capable of adequately reinforcing the rubber molecules.

[0019] The rubber composition constituting the second layer preferably contains vegetable oil, which has oxygen-containing functional groups on its molecule and is believed to suppress the movement of polymers in the rubber composition and reduce heat generation in the rubber composition.

[0020] The total styrene content in the polymer component of the rubber composition constituting the first layer is preferably 1.0% by mass or more and 20.0% by mass or less.

[0021] It is believed that by setting the total styrene amount in the first layer within the above range, the action of the styrene groups appropriately relieves the stress applied to the rubber composition, inhibits the development of cracks, and improves abrasion resistance.

[0022] When the complex modulus of elasticity at 70° C. of the rubber composition constituting the first layer is defined as 70° C.E*, it is preferable that 100° C.E* / 70° C.E* is less than 0.85.

[0023] By having the 100℃E* / 70℃E* ratio be less than 0.85, the surface, which becomes hotter during driving, can conform to the road surface while the inner part maintains its rigidity, which is thought to prevent excessive deformation and make it easier to improve wear resistance.

[0024] The belt layer preferably has two or more layers including steel cords inclined with respect to the tire circumferential direction, and one or more reinforcing layers including steel cords oriented in the tire circumferential direction. It is believed that the reinforcing layers suppress the change in the outer diameter of the tire caused by the centrifugal force during rolling, improve the ground contact of the tread portion, and facilitate the improvement of the wear resistance.

[0025] The elastic modulus of the steel cord of the reinforcing layer at 0.5% to 1.0% elongation is preferably 80 GPa or more and 250 GPa or less. By setting the elastic modulus of the steel cord of the reinforcing layer at 0.5% to 1.0% elongation in the above range, it is considered that the tread portion can be sufficiently restrained and stable ground contact during running can be obtained.

[0026] When the tan δ at 70°C of the rubber composition constituting the first layer is 70°C tan δ, 70°C tan δ × H is preferably 3.0 or less. It is believed that when 70°C tan δ × H is 2.5 or less, the greater the groove depth, the greater the deformation of the tread portion, and by sufficiently reducing heat buildup relative to the groove depth, it is believed that excessive heat buildup in the tread portion and a decrease in wear resistance can be suppressed.

[0027] The modulus of the rubber composition constituting the second layer at 200% elongation is preferably 9.0 MPa or less. It is believed that the low modulus of the second layer allows the surface of the first layer to easily conform to the road surface, making it easier to improve abrasion resistance.

[0028] <Definition> The "tread portion" is the portion that forms the tread surface (the tire's contact surface), and in the case where the tire has components that form the tire skeleton made of steel or textile materials, such as a belt layer, a belt reinforcing layer, and a carcass layer, in the radial cross section of the tire, the component is the component that is radially outward of these components.

[0029] The "belt layer" is a layer located radially outboard of the carcass layer, and includes multiple working layers in which the internal reinforcing material is inclined at an angle of about 10 to 60° relative to the tire circumferential direction and overlaps in the opposite direction, and a circumferential belt layer in which the internal reinforcing material is oriented at an angle of ±5° relative to the tire circumferential direction.

[0030] A "genuine rim" is a rim that is determined for each tire by the standard system that includes the standards on which the tire is based. In the case of JATMA, this is the standard rim described in the "JATMA YEAR BOOK." In the case of ETRTO (The European Tyre and Rim Technical Organisation), this is the "Measuring Rim" described in the "STANDARDS MANUAL." In the case of TRA (The Tire and Rim Association, Inc.), this is the "Design Rim" described in the "YEAR BOOK." JATMA, ETRTO, and TRA should be referred to in that order, and if there is an applicable size at the time of reference, that standard should be followed.

[0031] "Normal inner pressure" is the air pressure set for each tire by each standard in the standard system including the standard on which the tire is based. For JATMA, it is "maximum air pressure", for ETRTO, it is "INFLATION PRESSURE", and for TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES". As with normal rims, refer to JATMA, ETRTO, TRA in that order, and follow the standard if there is an applicable size at the time of reference.

[0032] "Normal condition" refers to a condition in which a tire is mounted on a normal rim, inflated to normal internal pressure, and no load is applied. In this specification, unless otherwise specified, the dimensions of each part of the tire are measured in the normal condition.

[0033] "Normal load" refers to the load that is determined for each tire by the standard system that includes the standard on which the tire is based. For example, for JATMA, it is "Maximum Load Capacity", for ETRTO, it is "LOAD CAPACITY", and for TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES". As with the case of normal rims and normal internal pressures, JATMA, ETRTO, and TRA should be referenced in that order, and if there is an applicable size at the time of reference, that standard should be followed. For tires not specified in the above standards, the normal load W is calculated as follows: L V is the virtual volume of the tire (mm 3 ), Dt is the outer diameter of the tire (mm), Ht is the section height of the tire (mm), and Wt is the section width of the tire (mm). In this specification, the term "maximum load capacity" is synonymous with the normal load. TIFF2025062518000001.tif1484

[0034] The "thickness of each rubber layer constituting the tread portion" refers to the thickness of each rubber layer on the tire equatorial plane in a cross section cut along a plane including the tire rotation axis, and is the average value of the tread thicknesses obtained at five positions by rotating the tire circumferentially at 72° intervals. For example, the thickness t1 of the first layer refers to the linear distance in the tire radial direction from the outermost surface of the tread to the tire radially inner interface of the first layer on the tire equatorial plane. In addition, when the tire has a circumferential groove on the tire equatorial plane, the thickness of each rubber layer constituting the tread portion is the thickness of each rubber layer at the tire width direction center of the land portion closest to the tire equatorial plane. The "land portion closest to the tire equatorial plane" refers to the land portion of the circumferential groove present on the tire equatorial plane that has the groove edge closest to the tire equatorial plane, and when such land portions exist on both sides in the tire width direction, the thickness of each rubber layer constituting the tread portion is the average value of the thicknesses of each rubber layer at the tire width direction center of the two land portions. In addition, when a conductive member or the like is present on the land portion on the tire equatorial plane and the interface is unclear, the interface obstructed by the conductive member or the like is virtually connected and measured.

[0035] A "groove", including circumferential grooves and wide circumferential grooves, refers to a recess with a depth of at least 3.0 mm. In particular, a groove with an opening width of less than 1.5 mm on the tire surface is called a "sipe".

[0036] The "groove depth H of the deepest part of the circumferential groove" is determined by the distance in the radial direction of the tire 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 circumferential groove that has the deepest groove depth among the circumferential grooves adjacent to the land portion.

[0037] "Total styrene content (S) in the polymer component" refers to the total content (mass%) of styrene moieties contained in 100% by mass of the polymer component, and is calculated by Σ(styrene content (mass%) of each styrene-containing rubber × content (mass%) of each styrene-containing rubber in the polymer component / 100). For example, when the polymer component is composed of 30% by mass of the first SBR (styrene content 25% by mass), 60% by mass of the second SBR (styrene content 27.5% by mass), and 10% by mass of NR, the total styrene content (S) in 100% by mass of the polymer component is 24.0% by mass (=25×30 / 100+27.5×60 / 100).

[0038] "Recycled carbon black" refers to carbon black obtained by crushing products such as used tires that contain carbon black and then calcining the crushed material, and refers to carbon black in which the mass ratio of ash (ash content), which is a component that does not burn, is 13% by mass or more when it is subjected to oxidative combustion by heating in air in a thermogravimetric measurement method conforming to JIS K 6226-2:2003. In other words, the mass (carbon content) of the part lost due to the oxidative combustion is less than 87% by mass. Recycled carbon black is also called recovered carbon black, and is sometimes expressed as rCB.

[0039] <Measurement method> "The thickness of each rubber layer constituting the tread portion" is measured in a state in which the tire is cut along a plane including the tire rotation axis and the width of the bead portion is adjusted to the width of a regular rim.

[0040] "100°CE*" is the complex modulus measured under the conditions of a temperature of 100°C, a frequency of 10Hz, an initial strain of 10%, and a dynamic strain of ±2.5%. The measurement sample is a vulcanized rubber composition with a length of 20mm, a width of 4mm, and a thickness of 1mm. When cutting out from a tire, the sample is cut out from the tread portion of the tire so that the long side is in the tire circumferential direction and the thickness direction is in the tire radial direction.

[0041] "70℃ tan δ" is the loss tangent measured under the conditions of temperature 70℃, frequency 10Hz, initial strain 10%, dynamic strain ±1%, and elongation mode. The sample for measuring 70℃ tan δ is prepared in the same manner as for 100℃E*.

[0042] The "elastic modulus of steel cord at 0.5% to 1.0% elongation" is calculated by carrying out a tensile test in accordance with JIS G 3510 "Test method for steel tire cord" at a tensile speed of 5 mm / min, measuring the tension (N) at 1.0% elongation and 0.5% elongation, and calculating it from the following formula. (Elastic modulus at 0.5% to 1.0% elongation) = 0.2 x (Tension at 1.0% elongation (N) - Tension at 0.5% elongation (N)) / Cross-sectional area of ​​steel cord (mm 2 )

[0043] "Modulus at 200% stretch" is the tensile stress (MPa) at 200% stretch in the grain direction (rolling direction when forming a rubber sheet by extrusion or shearing) measured in accordance with JIS K 6251:2017 using a No. 7 dumbbell sample at a tensile speed of 3.3 mm / sec in an atmosphere of 23°C. When preparing a measurement sample from a test tire, the sample is cut from the tread portion of the tire so that the long side is in the tire circumferential direction and the thickness direction is in the tire radial direction.

[0044] The "plasticizer content" includes the amount of plasticizer contained in the extended rubber component that has been extended in advance with a plasticizer such as oil, a resin component, a liquid rubber component, etc. The same applies to the oil content, the resin component content, and the liquid rubber content. For example, if the extended component is oil, the extended oil is included in the oil content.

[0045] "Styrene content" is 1It is a value calculated by H-NMR measurement, and is applied to, for example, polymer components having repeating units derived from styrene, such as SBR. "Vinyl content (amount of 1,2-bonded butadiene units)" is a value calculated by infrared absorption spectroscopy in accordance with JIS K 6239-2:2017, and is applied to, for example, polymer components having repeating units derived from butadiene, such as SBR, BR, and thermoplastic elastomers. "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 is applied to, for example, polymer components having repeating units derived from butadiene, such as BR.

[0046] The "weight average molecular weight (Mw)" can be determined by converting the measured value obtained by gel permeation chromatography (GPC) (for example, GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMALTIPORE HZ-M manufactured by Tosoh Corporation) into standard polystyrene equivalent. For example, this applies to SBR, BR, etc.

[0047] "Nitrogen adsorption specific surface area (N2SA) of carbon black" is measured in accordance with JIS K 6217-2:2017.

[0048] "Ash content (mass %)" refers to the ratio of the total mass of non-combustible components (ash) in a rubber composition to the total mass of the rubber composition, and is determined by the following method. A vulcanized rubber test piece cut from the tread of each test tire is placed in an alumina crucible and heated in an electric furnace at 550°C for 4 hours, and the mass of the vulcanized rubber test piece after heating is measured. The "ash content (mass %)" in the rubber composition can be determined from the mass of the vulcanized rubber test piece after heating, when the mass of the vulcanized rubber test piece before heating is taken as 100% by mass.

[0049] The "cross-sectional area of ​​the steel cord" is the cross-sectional area of ​​the steel cord when cut in a plane perpendicular to the longitudinal direction of the steel cord.

[0050] A procedure for producing a tire according to an embodiment of the present invention will be described in detail below. However, the following description is merely an example for explaining the present invention, and is not intended to limit the technical scope of the present invention to the described range.

[0051] <Tires> Fig. 1 illustrates an example of a tire according to an embodiment of the present invention. Fig. 1 shows a part of a cross section of the tire taken along a plane including the tire rotation axis. In Fig. 1, the up-down direction is the tire's radial direction, the left-right direction is the tire's axial direction, and the direction perpendicular to the paper surface is the tire's circumferential direction. In Fig. 1, a dashed dotted line CL represents the tire equator.

[0052] The tire in FIG. 1 has a tread portion 1, a pair of sidewall portions 2 extending radially outward, and a pair of bead portions 3. As shown in FIG. 1, a belt layer 5 is provided on the radially inner side of the tread portion 1. A carcass 4 and an inner liner 7 are laminated under the belt layer 5. A band layer may be provided between the tread portion 1 and the belt layer 5 (not shown). The bead portion 3 has a bead core 14 and a bead apex 13 extending radially outward from the core. The bead apex 13 tapers radially outward. In the bead portion 3, a clinch portion 10 that comes into contact with the rim when the rim is attached is provided on the outer side of the carcass 4.

[0053] In Fig. 1, the belt layer 5 is made up of multiple layers (5a, 5b, 5c, 5d). Each belt layer 5 includes multiple steel cords that are inclined with respect to the tire circumferential direction. Between each belt layer 5, there may be one or more reinforcing layers (not shown) including steel cords oriented in the tire circumferential direction.

[0054] In this embodiment, the belt layer 5 preferably has two or more layers including steel cords inclined with respect to the tire circumferential direction, and one or more reinforcing layers including steel cords oriented in the tire circumferential direction.

[0055] The tread portion 1 is made of a rubber composition. The tread portion 1 has a first layer 11 that constitutes the tread surface, and a second layer 12 that is located radially inward of the first layer 11. One or more intermediate rubber layers may be further present between the first layer 11 and the second layer 12.

[0056] Fig. 2 is a cross section of the tread portion of a tire taken along a line passing through the tire axis. In Fig. 2, the vertical direction is the tire radial direction, the horizontal direction is the tire width direction, and the direction perpendicular to the paper surface is the tire circumferential direction.

[0057] The tread portion 1 of the tire according to this embodiment has two or more circumferential grooves 20 that extend continuously in the circumferential direction. The circumferential grooves 20 may extend linearly along the circumferential direction, or may extend in a zigzag pattern along the circumferential direction.

[0058] The groove depth H of the deepest part of the circumferential groove 20 is obtained by the distance between an extension line 22 connecting two land portions 21 adjacent to the circumferential groove 20 and an extension line 23 of the deepest part of the groove bottom of the circumferential groove 20. Note that, for example, when there are multiple circumferential grooves 20, the groove depth H can be the groove depth of the deepest part of the circumferential groove having the deepest groove depth.

[0059] In this embodiment, the groove depth H of the deepest portion of the circumferential groove 20 is preferably 10.0 mm or more, more preferably 12.0 mm or more, and even more preferably 13.0 mm or more from the viewpoint of drainage. Also, the groove depth H of the deepest portion of the circumferential groove 20 is preferably 21.0 mm or less, more preferably 19.0 mm or less, and even more preferably 18.0 mm or less from the viewpoint of suppressing excessive deformation of the tread portion and facilitating improvement of wear resistance.

[0060] As shown in the figure, the tread portion 1 of the tire according to this embodiment includes a first layer 11 and a second layer 12, the outer surface of the first layer 11 constitutes the tread surface 30, and the second layer 12 is present radially inward of the first layer 11. The first layer 11 typically corresponds to a cap tread. The second layer 12 may be a cap tread or a base tread since a typical shape is not determined, but is preferably a base tread. In addition, one or more rubber layers may be further provided between the second layer 12 and the belt layer 5. When the tread portion 1 has three or more layers, the cap tread or the inner layer (base tread) may be composed of two or more layers.

[0061] In the tire according to the present embodiment, the total thickness of the tread, which is the sum (t1+t2) of the thickness t1 of the first layer 11 and the thickness t2 of the second layer 12 in Fig. 2, is preferably 15.0 mm or more, more preferably 16.0 mm or more, even more preferably 18.0 mm or more, and particularly preferably 19.0 mm or more, from the viewpoint of wear resistance. Also, from the viewpoint of the effect of the present invention, the total thickness of the tread is preferably 30.0 mm or less, more preferably 25.0 mm or less, and even more preferably 22.0 mm or less.

[0062] In this embodiment, the thickness t1 of the first layer 11 is preferably 10.0 mm or more, more preferably 11.0 mm or more, and even more preferably 12.0 mm or more, from the viewpoint of facilitating deformation so as to follow the road surface. Moreover, the thickness t1 of the first layer 11 is preferably 20.0 mm or less, more preferably 18.0 mm or less, even more preferably 15.0 mm or less, and particularly preferably 13.0 mm or less.

[0063] The thickness t2 of the second layer 12 is preferably 3.0 mm or more, more preferably 5.0 mm or more, and even more preferably 6.0 mm or more, from the viewpoint of absorbing deformation energy at the interface with the first layer when the tread portion deforms during running. The thickness t2 of the second layer 12 is preferably 11.0 mm or less, more preferably 10.0 mm or less, even more preferably 9.0 mm or less, and particularly preferably 8.0 mm or less.

[0064] The ratio of t1 to the sum of the thickness t1 of the first layer 11 and the thickness t2 of the second layer 12 (t1 / (t1+t2)) is preferably 0.90 or less, more preferably 0.80 or less, and even more preferably 0.74 or less, from the viewpoint of keeping the thickness ratio of the first layer at a constant level or less and facilitating the absorption of deformation energy at the interface with the first layer when the tread portion deforms during running. Moreover, t1 / (t1+t2) is preferably 0.50 or more, more preferably 0.55 or more, and even more preferably 0.60 or more, from the viewpoint of allowing the first layer to deform appropriately.

[0065] In this embodiment, the ratio of t1 to H (t1 / H) is less than 1.0, preferably less than 0.98, more preferably less than 0.97, even more preferably less than 0.96, and particularly preferably less than 0.94.

[0066] The complex elastic modulus (100°C E*) of the first layer 11 at 100°C is preferably 6.0 MPa or more, more preferably 7.0 MPa or more, even more preferably 8.0 MPa or more, even more preferably 8.5 MPa or more, and particularly preferably 8.8 MPa or more, from the viewpoint of suppressing excessive deformation of the first layer during driving. Also, from the viewpoint of making it easier for the surface of the first layer to follow the road surface during driving, the 100°C E* is preferably 12.0 MPa or less, more preferably 10.0 MPa or less, and even more preferably 9.0 MPa or less. The 100°C E* is measured by the above-mentioned method. The complex elastic modulus of the second layer 12 at 100°C is not particularly limited.

[0067] In this embodiment, the ratio of the complex elastic modulus at 100°C of the first layer 11 to the thickness t2 of the second layer 12 (100°CE* / t2) is 1.50 or less, preferably 1.45 or less, more preferably 1.40 or less, even more preferably 1.35 or less, and particularly preferably 1.30 or less. The lower limit of 100°CE* / t2 is not particularly limited, but may be, for example, 1.00 or more, 1.10 or more.

[0068] The complex modulus of elasticity at 70°C (70°C E*) of the first layer 11 is preferably 8.0 MPa or more, more preferably 9.0 MPa or more, even more preferably 9.5 MPa or more, even more preferably 10.0 MPa or more, and particularly preferably 11.0 MPa or more, from the viewpoint of ensuring rigidity inside the first layer. Also, from the viewpoint of allowing the first layer to deform moderately, 70°C E* is preferably 18.0 MPa or less, more preferably 15.0 MPa or less, and even more preferably 13.0 MPa or less. Note that 70°C E* is measured by the above-mentioned method. The complex modulus of elasticity at 70°C of the second layer 12 is not particularly limited.

[0069] The 100° C.E* / 70° C.E* ratio is preferably less than 0.90, more preferably less than 0.85, and even more preferably less than 0.76. The lower limit of the 100° C.E* / 70° C.E* ratio is not particularly limited, but may be, for example, 0.60 or more, 0.70 or more.

[0070] The tan δ at 70°C (70°C tan δ) of the first layer 11 is preferably 0.05 or more, more preferably 0.07 or more, even more preferably 0.09 or more, and particularly preferably 0.10 or more, from the viewpoint of facilitating internal absorption of deformation energy during rolling. Moreover, the tan δ at 70°C is preferably 0.18 or less, more preferably 0.16 or less, and even more preferably 0.15 or less, from the viewpoint of suppressing heat generation. The tan δ at 70°C of the second layer 12 is not particularly limited.

[0071] Since it is believed that the deeper the groove depth, the greater the deformation of the tread portion, the ratio of tan δ at 70°C of the first layer 11 to H (70°C tan δ×H) is preferably 3.0 or less, more preferably 2.5 or less, and even more preferably 2.2 or less, from the viewpoint of sufficiently reducing heat buildup relative to the groove depth and suppressing excessive heat buildup in the tread portion and a decrease in abrasion resistance. The lower limit of 70°C tan δ×H is not particularly limited, but can be, for example, 0.7 or more, 0.9 or more, or 1.0 or more.

[0072] The modulus (M200) of the second layer 12 at 200% stretching is preferably 2.0 MPa or more, more preferably 3.0 MPa or more, and even more preferably 4.0 MPa or more, from the viewpoint of suppressing excessive deformation of the first layer. The modulus of the second layer 12 at 200% stretching is preferably 10.0 MPa or less, more preferably 9.0 MPa or less, and even more preferably 8.0 MPa or less, from the viewpoint of facilitating the absorption of deformation energy at the interface with the first layer. The modulus at 200% stretching is measured by the above-mentioned method. The modulus of the first layer 11 is not particularly limited. The modulus at 200% stretching of each rubber layer can be appropriately adjusted by the type and amount of the polymer component, filler, plasticizer, etc. described below.

[0073] The 100°C E*, 70°C E*, and 70°C tan δ can be appropriately adjusted depending on the type and amount of the polymer component, filler, plasticizer, vulcanizing agent, vulcanization accelerator, etc. For example, the value of 70°C tan δ tends to increase by increasing the total amount of styrene in the polymer component, increasing the amount of filler, reducing the amount of vulcanizing agent and vulcanization accelerator, using a resin with a high glass transition temperature as a plasticizer, etc. In addition, the value of 70°C E* tends to increase by increasing the total amount of styrene in the polymer component, increasing the amount of filler, increasing the amount of vulcanizing agent and vulcanization accelerator, using a resin component with a high glass transition temperature as a plasticizer, etc., and reducing the amount of plasticizer. In addition, when the amount of recycled carbon black is reduced, the values ​​of 70°C tan δ and 70°C E* tend to decrease.

[0074] Fig. 3 is a cross-sectional view showing a part of a circumferential groove according to this embodiment. In Fig. 3, the up-down direction is the radial direction of the tire, the left-right direction is the axial direction of the tire, and the direction perpendicular to the paper surface is the circumferential direction of the tire.

[0075] In this embodiment, at least one of the circumferential grooves 20 is preferably a wide circumferential groove 25 having a groove width wider than the groove width W1 on the tread surface at any position on the inner side in the tire radial direction of the groove.

[0076] In Fig. 3, the wide circumferential groove 25 has a recess 27 recessed outward in the groove width direction from a groove edge 26 appearing on the tread surface 30. By providing a recess on the groove wall of the circumferential groove, a gap is formed inside the tread, and it is considered that the gap can absorb shock and suppress propagation. In Fig. 3, the wide circumferential groove 25 has a groove width that gradually increases from the end of the tread surface 30 toward the inside in the tire radial direction, but is not limited to such an embodiment.

[0077] The groove width W2 at the 90% position h of the deepest part of the wide circumferential groove is preferably 0.5 mm or more, more preferably 1.0 mm or more, even more preferably 1.5 mm or more, and particularly preferably 2.0 mm or more, from the viewpoint of suppressing deterioration of the wear appearance in the later stage of wear. Also, the groove width W2 at the 90% position h of the deepest part of the wide circumferential groove is preferably 4.0 mm or less, more preferably 3.5 mm or less, even more preferably 3.0 mm or less, and particularly preferably 2.5 mm or less, from the viewpoint of improving the ground contact of the tread surface.

[0078] Fig. 4 is a cross-sectional view showing a part of another wide circumferential groove 25 according to this embodiment. In Fig. 4, the wide circumferential groove 25 has a constant groove width within a distance L from the tread surface 30, and the groove width gradually increases from a change point P toward the tire radially inward direction to form a recess 27.

[0079] In this embodiment, at least one of the circumferential grooves 20 is a wide circumferential groove 25 having a groove width wider than the groove width W1 on the tread surface at any position on the radially inner side of the groove, and it is preferable that the wide circumferential groove 25 has a change point P that widens from the tread surface toward the radially inner side of the tire.

[0080] In a circumferential groove having a recess in the groove wall that is recessed outward in the groove width direction from the groove edge 26 appearing on the tread surface, the distance L from the tire radially outer end of the recess to the tread surface is preferably greater than t1. It is considered that the presence of the recess on the tire radially inner side of the first layer results in the generation of the void in the second layer and subsequent layers, which makes it easier to absorb shock and deformation 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, the upper limit of L / t1 is not particularly limited, but is preferably less than 4.0, more preferably less than 3.0, and even more preferably less than 2.0.

[0081] The distance L from the radially outer end of the recess of the wide circumferential groove 25 to the tread surface is preferably more than 6 mm, more preferably more than 8 mm, and even more preferably more than 9 mm. On the other hand, L is preferably less than 18 mm, more preferably less than 16 mm, and even more preferably less than 15 mm.

[0082] The total recession amount (c1+c2 in Figs. 3 and 4) of the wide circumferential grooves 25 is preferably 0.10 to 5.00 times, more preferably 0.20 to 3.00 times, and even more preferably 0.30 to 1.00 times the groove width W1 of the wide circumferential groove 25. When there are multiple wide circumferential grooves, it is sufficient that the total recession amount of any one of the wide circumferential grooves satisfies the above relationship, and all of the wide circumferential grooves may satisfy the above relationship.

[0083] [Rubber composition] The rubber composition constituting the tread portion of the present embodiment will be described below. Unless otherwise specified, the following description of the rubber composition is common to both the rubber composition constituting the first layer and the rubber composition constituting the second layer.

[0084] <Polymer component> The rubber composition according to the present embodiment includes a polymer component. In this specification, the polymer component includes the following rubber component and thermoplastic elastomer, and is a component that mainly forms the matrix of the composition, and is detected as a polymer component in a composition analysis using a thermogravimetric analyzer (TGA) or the like.

[0085] As the rubber component, a diene rubber is preferably used. Examples of the diene rubber include isoprene rubber, butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene rubber (SIR), styrene isoprene butadiene rubber (SIBR), chloroprene rubber (CR), and acrylonitrile butadiene rubber (NBR). These diene rubbers may be modified rubbers treated with a modifying group capable of interacting with fillers such as carbon black and silica, or may be hydrogenated rubbers in which a part of the unsaturated bonds is hydrogenated. The diene rubbers may be used alone or in combination of two or more. In addition, extended rubbers that have been previously extended using a plasticizer as described below may be used. In this specification, the term "rubber component" refers to a component that forms a chemical network with a vulcanizing agent such as sulfur and exhibits rubber elasticity.

[0086] The content of the diene rubber in the polymer 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. The polymer component may be composed of only the diene rubber.

[0087] As the diene rubber component, at least one selected from the group consisting of isoprene rubber, styrene butadiene rubber (SBR) and butadiene rubber (BR) is preferably used. The rubber components constituting the first layer and the second layer preferably contain at least one selected from the group consisting of isoprene rubber, styrene butadiene rubber (SBR) and butadiene rubber (BR). The rubber component constituting the first layer preferably contains isoprene rubber, more preferably contains isoprene rubber and SBR, and more preferably contains isoprene rubber, SBR and BR. The rubber component constituting the second layer preferably contains isoprene rubber.

[0088] (Isoprene rubber) As the isoprene-based rubber, for example, isoprene rubber (IR) and natural rubber, which are common in the tire industry, can be used. In addition to unmodified natural rubber (NR), natural rubber also includes modified natural rubber such as epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), deproteinized natural rubber (DPNR), high-purity natural rubber, and grafted natural rubber. These isoprene-based rubbers may be used alone or in combination of two or more.

[0089] The NR is not particularly limited, and any NR commonly used in the tire industry can be used, such as SIR20, RSS#3, and TSR20.

[0090] From the viewpoint of the effects of the present invention, the content of the isoprene-based rubber in the polymer component constituting the first layer is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 45% by mass or more, and particularly preferably 50% by mass or more. 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 even more preferably 90% by mass or less.

[0091] From the viewpoint of the effects of the present invention, the content of the isoprene-based rubber in the polymer component constituting the second layer is preferably 60% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, and may be 100% by mass.

[0092] (BR) The BR is not particularly limited, and can be one that is commonly used in the tire industry, such as BR with a cis content of less than 50 mol% (low cis BR), BR with a cis content of 90 mol% or more (high cis BR), rare earth butadiene rubber (rare earth BR) synthesized using a rare earth catalyst, BR containing syndiotactic polybutadiene crystals (SPB-containing BR), modified BR (high cis modified BR, low cis modified BR), etc. These BRs can be used alone or in combination of two or more.

[0093] As the high-cis BR, for example, those commercially available from Zeon Corporation, UBE Corporation, JSR Corporation, etc. can be used. By containing high-cis BR, the abrasion resistance performance can be improved. The cis content of the high-cis BR is preferably 95 mol % or more, more preferably 96 mol % or more, and further preferably 97 mol % or more. The cis content of BR is measured by the above-mentioned measuring method.

[0094] As the modified BR, a modified butadiene rubber (modified BR) in which the terminals and / or the main chain are modified with a functional group containing at least one element selected from the group consisting of silicon, nitrogen and oxygen is preferably used.

[0095] Other modified BRs include those obtained by polymerizing 1,3-butadiene with a lithium initiator and then adding a tin compound, and further having the terminals of the modified BR molecule bonded with tin-carbon bonds (tin-modified BR), etc. The modified BR may be either non-hydrogenated or hydrogenated.

[0096] From the viewpoint of abrasion resistance, the weight average molecular weight (Mw) of BR is preferably 300,000 or more, more preferably 350,000 or more, and even more preferably 400,000 or more. From the viewpoint of crosslinking uniformity, etc., it is preferably 2,000,000 or less, and more preferably 1,000,000 or less. The Mw of BR is measured by the above-mentioned measurement method.

[0097] The content of BR in the polymer component constituting the first layer is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less. The lower limit of the content is not particularly limited, but is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more. The content of BR in the polymer component constituting the second layer is not particularly limited.

[0098] (SBR) There is no particular limitation on the SBR, and examples thereof include unmodified solution-polymerized SBR (S-SBR) and emulsion-polymerized SBR (E-SBR), as well as modified SBRs (modified S-SBR, modified E-SBR). Modified SBRs include SBRs whose ends and / or main chains are modified, and modified SBRs (condensates, those having a branched structure, etc.) coupled with tin or silicon compounds. Of these, S-SBR and modified SBR are preferred. Furthermore, hydrogenated products of these SBRs (hydrogenated SBR) and the like can also be used. These SBRs may be used alone or in combination of two or more.

[0099] The SBR according to the present embodiment may be an extended SBR or a non-extended SBR. When an extended SBR is used, the amount of extension of the SBR, i.e., the content of the extended plasticizer contained in the SBR, is preferably 10 to 50 parts by mass per 100 parts by mass of the rubber solid content of the SBR.

[0100] The SBRs listed above may be used alone or in combination of two or more. As the SBRs listed above, for example, those commercially available from Sumitomo Chemical Co., Ltd., JSR Corporation, Asahi Kasei Corporation, Zeon Corporation, ZS Elastomers Co., Ltd., etc. may be used.

[0101] 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. The styrene content of SBR is preferably 5% by mass or more, more preferably 7% by mass or more, and even more preferably 10% by mass or more. The styrene content of SBR is measured by the above-mentioned measurement method.

[0102] 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. 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 above-mentioned measurement method.

[0103] The content of SBR in the polymer component constituting the first layer is preferably 70% by mass or less, more preferably 60% by mass or less, even more preferably 50% by mass or less, and particularly preferably 40% by mass or less. The lower limit of the content is not particularly limited, but is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, even more preferably 25% by mass or more, and particularly preferably 30% by mass or more. The content of SBR in the polymer component constituting the second layer is not particularly limited.

[0104] The total amount of styrene in the polymer component constituting the first layer is preferably less than 20% by mass, more preferably less than 15% by mass, and even more preferably less than 12% by mass. The lower limit of the total amount of styrene in the polymer component constituting the first layer is not particularly limited, but is preferably more than 1.0% by mass, more preferably more than 2.0% by mass, and even more preferably more than 3.0% by mass. The total amount of styrene in the polymer component constituting the second layer is not particularly limited.

[0105] (Other rubber components) The rubber component may contain other rubber components other than the diene rubber, as long as the effect of the present invention is not affected. As the rubber components other than the diene rubber, crosslinkable rubber components generally used in the tire industry can be used, and examples thereof include non-diene rubbers such as butyl rubber (IIR), halogenated butyl rubber, ethylene propylene rubber, polynorbornene rubber, silicone rubber, chlorinated polyethylene rubber, fluororubber (FKM), acrylic rubber (ACM), and hydrin rubber. These other rubber components may be used alone or in combination of two or more.

[0106] <Other polymer components> The rubber composition according to the present embodiment may or may not contain a thermoplastic elastomer as a polymer component in addition to the above-mentioned rubber component. The term "thermoplastic elastomer" refers to a thermoplastic resin material having elasticity. In this specification, the term "thermoplastic elastomer" does not include the above-mentioned rubber component.

[0107] The thermoplastic elastomer is not particularly limited, but examples thereof include styrene-based thermoplastic elastomers, polybutadiene-based thermoplastic elastomers, urethane-based thermoplastic elastomers, olefin-based thermoplastic elastomers, polyester-based thermoplastic elastomers, polyamide-based thermoplastic elastomers, etc., and among these, it is preferable to include at least one selected from the group consisting of styrene-based thermoplastic elastomers and polybutadiene-based thermoplastic elastomers, and it is more preferable to include polybutadiene-based thermoplastic elastomers. These thermoplastic elastomers may be used alone or in combination of two or more.

[0108] The vinyl content of the thermoplastic elastomer is preferably 50 mol % or more, more preferably 60 mol % or more, further preferably 80 mol % or more, and particularly preferably 85 mol % or more.

[0109] The thermoplastic elastomer may be a commercially available product or a synthetic product, such as those manufactured and sold by JSR Corporation, Asahi Kasei Corporation, Kuraray Co., Ltd., and Nippon Miractoran Co., Ltd.

[0110] The content of the thermoplastic elastomer in the polymer component constituting the first layer is preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 6% by mass or less. In addition, when the polymer component constituting the first layer contains a thermoplastic elastomer, the content is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more.

[0111] Monomers that are structural units of polymers such as SBR and BR may be derived from petroleum or may be recycled from rubber products such as tires or non-rubber products such as polystyrene. Monomers obtained by recycling (recycled monomers) are not particularly limited, and examples thereof include recycled butadiene and recycled aromatic vinyl. Examples of the butadiene include 1,2-butadiene and 1,3-butadiene. Examples of the aromatic vinyl include, but are not particularly limited, styrene. Among them, it is preferable to use recycled butadiene (recycled butadiene) and / or recycled styrene (recycled styrene) as raw materials.

[0112] The method for producing the recycled monomer is not particularly limited, and examples thereof include synthesis from recycle-derived naphtha obtained by decomposing rubber products such as tires. The method for producing the recycled naphtha is also not particularly limited, and examples thereof include decomposing rubber products such as tires under high temperature and pressure, decomposing with microwaves, or mechanically crushing and then extracting.

[0113] Furthermore, monomers that are structural units of polymers such as SBR and BR may be derived from biomass. Examples of monomers derived from biomass (biomass monomers) include, but are not limited to, butadiene derived from biomass and aromatic vinyl derived from biomass. Examples of butadiene include 1,2-butadiene and 1,3-butadiene. Examples of aromatic vinyl include, but are not limited to, styrene. In addition, the method for producing biomass monomers is not particularly limited, and examples include biological and / or chemical and / or physical conversion of animals and plants. Representative biological conversion is fermentation by microorganisms, and examples of chemical and / or physical conversion include those using catalysts, those using high heat, those using high pressure, those using electromagnetic waves, those using critical liquids, and combinations thereof. Examples of biomass sources for these monomers include sugar, wood, plant residues after useful components are obtained, plant-derived ethanol, biomass naphtha, etc.

[0114] The polymer (biomass polymer) synthesized from a biomass monomer component is not particularly limited, and examples thereof include polybutadiene rubber synthesized from butadiene derived from biomass, aromatic vinyl / butadiene copolymer synthesized from butadiene derived from biomass and / or aromatic vinyl derived from biomass, etc. Examples of the aromatic vinyl / butadiene copolymer include styrene butadiene rubber synthesized from butadiene derived from biomass and / or styrene derived from biomass.

[0115] Whether the raw material of a polymer is derived from biomass can be determined by the percent modern carbon (pMC) measured in accordance with ASTM D6866-10. pMC is the modern standard reference. 14 C concentration vs. sample 14 This is the ratio of the carbon concentration to the biomass concentration of the compound (rubber), and this value is used as an index of the biomass ratio of the compound (rubber). The significance of this value is described below.

[0116] 1 mole of carbon atoms (6.02 × 10 23 ) contains approximately 6.02 × 10 atoms, which is about one trillionth of the size of a normal carbon atom. 11 pcs 14 C exists. 14 The half-life of C is 5730 years, 14 C is decreasing regularly. Therefore, in fossil fuels such as coal, oil, and natural gas, which are thought to have been absorbed and fixed by plants and other organisms more than 226,000 years ago, C was also included in these fuels when they were first fixed. 14 All C elements have decayed. Therefore, in the 21st century, fossil fuels such as coal, oil, and natural gas are 14 There is no C element at all. Therefore, chemical substances produced using these fossil fuels as raw materials also 14 It does not contain any C elements.

[0117] on the other hand, 14 C is constantly produced by cosmic rays undergoing nuclear reactions in the atmosphere. Therefore, 14 C is balanced between its loss by radioactive decay and its generation by nuclear reactions, and in the Earth's atmospheric environment, 14 The amount of C is constant. Therefore, the amount of biomass-derived materials circulating in the current environment is 14 As mentioned above, the C concentration is about 1×10 -12 The value is about mole percent. Therefore, by utilizing the difference between these values, it is possible to calculate the ratio (biomass ratio) of compounds derived from natural resources (compounds derived from biomass resources) in a certain compound (rubber).

[0118] this 14 C is typically measured as follows: using accelerator mass spectrometry based on a tandem accelerator, 13 C concentration ( 13 C / 12 C). 14 C concentration ( 14 C / 12 C) is measured. 14The modern standard reference for the C concentration is the carbon circulating in nature in 1950. 14 The specific standard substance used is the oxalic acid standard provided by NIST (National Institute of Standards and Technology). The specific radioactivity of carbon in this oxalic acid (per gram of carbon) is 14 C) for each carbon isotope, 13 The standard value is the value corrected for decay from 1950 to the measurement date, with C corrected to a constant value. 14 This is used as the C concentration value (100%). The ratio of this value to the value actually measured for the sample is the pMC value.

[0119] Therefore, if rubber is made from 100% biomass (natural) derived materials, it will show a value of approximately 110 pMC, although there may be regional differences (currently, under normal conditions, it is often not 100). On the other hand, for chemical substances derived from petroleum and other fossil fuels, 14 When the C concentration is measured, it will show approximately 0 pMC (for example, 0.3 pMC). This value corresponds to the biomass ratio of 0% mentioned above.

[0120] For these reasons, it is preferable in terms of environmental protection to use a material such as rubber having a high pMC value, that is, a material such as rubber having a high biomass ratio, in a rubber composition.

[0121] <Filler> The rubber composition according to the present embodiment preferably contains a filler, and carbon black is preferably used as the filler.

[0122] (Carbon Black) Carbon black is not particularly limited, and examples thereof include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762. The raw material of carbon black may be a biomass material such as lignin or vegetable oil, or may be pyrolysis oil obtained by pyrolyzing waste tires. The carbon black may be produced by combustion such as a furnace method, hydrothermal carbonization (HTC), or pyrolysis of methane such as a thermal black method. Commercially available products include products from Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Corporation, Lion Corporation, Nippon Steel Carbon Co., Ltd., Columbia Carbon Co., Ltd., and the like. These may be used alone or in combination of two or more.

[0123] The nitrogen adsorption specific surface area (N2SA) of the carbon black contained in the rubber composition constituting the first layer and the second layer is set to 70 m from the viewpoint of reinforcement. 2 / g or more is preferable, and 90m 2 / g or more is more preferable, and 110m 2 / g or more is more preferable, and 130m 2 From the viewpoints of fuel economy and processability, it is particularly preferable that the tensile strength is 200 m 2 / g or less is preferable, and 180m 2 / g or less is more preferable, and 160m 2 / g or less is more preferable. The nitrogen adsorption specific surface area (N2SA) of the carbon black contained in the rubber composition constituting the third layer is not particularly limited. The N2SA of the carbon black is measured by the above-mentioned measuring method.

[0124] The content of carbon black per 100 parts by mass of the polymer component (total content when two or more types are contained) is preferably 20 parts by mass or more, more preferably 25 parts by mass or more, even more preferably 30 parts by mass or more, and particularly preferably 35 parts by mass or more, from the viewpoint of reinforcing properties, and is preferably 90 parts by mass or less, more preferably 85 parts by mass or less, even more preferably 80 parts by mass or less, and particularly preferably 75 parts by mass or less, from the viewpoints of fuel efficiency and processability.

[0125] (Recycled Carbon Black) Recycled carbon black can be obtained by crushing used pneumatic tires (scrap tires) or used tire tubes (scrap tire tubes) and calcining the crushed material. These scrap tires and scrap tire tubes preferably contain diene rubber. For example, European Patent Application Publication No. 3427975, referring to "Rubber Chemistry and Technology", Vol. 85, No. 3, pp. 408-449 (2012), especially pp. 438, 440, and 442, describes that carbon black can be obtained by pyrolysis of organic materials at 550-800°C with the exclusion of oxygen, or by vacuum pyrolysis at relatively low temperatures (

[0027] ). Carbon black obtained from such pyrolysis processes is usually devoid of functional groups on its surface, as mentioned in

[0004] of Japanese Patent No. 6856781 (Comparison of Surface Morphology and Chemistry of Pyrolytic Carbon Black and Commercial Carbon Black, Powder Technology 160 (2005) 190-193).

[0126] In this specification, the ash content of the recycled carbon black is 13% by mass or more. The recycled carbon black has a feature that it is difficult to absorb oil because of its high ash content. The ash content is preferably 14% by mass or more, more preferably 15% by mass or more, even more preferably 16% by mass or more, and particularly preferably 17% by mass or more. The ash content is measured by the above-mentioned method.

[0127] When the rubber composition constituting the first layer contains recycled carbon black, the content per 100 parts by mass of the polymer component is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, even more preferably 15 parts by mass or more, and particularly preferably 20 parts by mass or more from the viewpoint of reinforcement, and is preferably 90 parts by mass or less, more preferably 85 parts by mass or less, even more preferably 80 parts by mass or less, and particularly preferably 75 parts by mass or less from the viewpoint of fuel efficiency and processability.

[0128] When the rubber composition constituting the second layer contains recycled carbon black, the content per 100 parts by mass of the polymer component is preferably 20 parts by mass or more, more preferably 25 parts by mass or more, even more preferably 30 parts by mass or more, and particularly preferably 35 parts by mass or more, from the viewpoint of reinforcement, and is preferably 90 parts by mass or less, more preferably 85 parts by mass or less, even more preferably 80 parts by mass or less, and particularly preferably 75 parts by mass or less, from the viewpoints of fuel efficiency and processability.

[0129] (Other fillers) The filler other than carbon black is not particularly limited, and may be, for example, one that has been generally used in the tire industry, such as silica, aluminum hydroxide, alumina (aluminum oxide), calcium carbonate, magnesium sulfate, talc, clay, biochar, etc. These other fillers may be used alone or in combination of two or more.

[0130] (silica) The silica is not particularly limited, and can be, for example, silica prepared by a dry method (anhydrous silica), silica prepared by a wet method, or the like, which is generally used in the tire industry. The raw material of silica is not particularly limited, and can be, for example, a mineral-derived raw material such as quartz, a biological raw material such as rice husk (for example, silica made from a biomass material such as rice husk), or silica recycled from a product containing silica. Among them, hydrated silica prepared by a wet method is preferred because it has a large number of silanol groups. These silicas can be used alone or in combination of two or more types.

[0131] Silica made from biomass materials can be obtained, for example, by extracting silicate from rice husk ash obtained by burning rice husks using a sodium hydroxide solution, and then reacting the silicate with sulfuric acid in the same manner as conventional wet-process silica to produce a silicon dioxide precipitate, which is then filtered, washed with water, dried, and pulverized.

[0132] When silica crystallizes, it does not dissolve in water, and its component silicic acid cannot be used. By controlling the combustion temperature and combustion time, it is possible to suppress the crystallization of silica in rice husk ash (see JP 2009-2594 A, Akita Prefectural University Web Journal B / 2019, vol. 6, p. 216-222, etc.). Amorphous silica extracted from rice husks can be commercially available from Wilmar Co., Ltd., etc.

[0133] The silica recycled from a product containing silica can be, for example, silica recovered from a product containing silica, such as electronic parts such as semiconductors, tires, desiccants, and filtering materials such as diatomaceous earth. The recovery method is not particularly limited, and examples include pyrolysis and decomposition by electromagnetic waves. Among them, silica recovered from electronic parts such as semiconductors or tires is preferred.

[0134] When silica is contained, the content per 100 parts by mass of the polymer component is preferably 50 parts by mass or more, more preferably 55 parts by mass or more, and even more preferably 60 parts by mass or more, from the viewpoints of fuel economy performance, wet grip performance, and abrasion resistance performance. Also, from the viewpoint of suppressing the deterioration of fuel economy performance and abrasion resistance performance due to the deterioration of dispersibility of silica in rubber, the content is preferably 150 parts by mass or less, more preferably 120 parts by mass or less, and even more preferably 100 parts by mass or less.

[0135] <Other compounding agents> In addition to the above-mentioned components, the rubber composition according to the present embodiment may appropriately contain compounding agents generally used in the conventional tire industry, such as a plasticizer, vulcanized rubber particles, wax, stearic acid, zinc oxide, an antioxidant, a vulcanizing agent, and a vulcanization accelerator.

[0136] Examples of the plasticizer include oil, a resin component, liquid rubber, etc. The rubber composition constituting the first layer or the rubber composition constituting the second layer preferably contains vegetable oil, and it is more preferable that the rubber composition constituting the second layer contains vegetable oil.

[0137] Examples of the oil include process oil, vegetable oil, and animal oil. Examples of the process oil include paraffin-based process oil (mineral oil), naphthenic process oil, and aromatic process oil. Specific examples of the process oil include MES (Mild Extract Solvated), DAE (Distillate Aromatic Extract), TDAE (Treated Distillate Aromatic Extract), TRAE (Treated Residual Aromatic Extract), and RAE (Residual Aromatic Extract). In addition, as an environmental measure, a process oil with a low content of polycyclic aromatic compound (PCA) compounds can be used. Examples of the low PCA content process oil include MES, TDAE, and heavy naphthenic oil.

[0138] When the rubber composition constituting the first layer contains oil, the content (total content when two or more kinds are contained) per 100 parts by mass of the polymer component is preferably more than 0.1 parts by mass, more preferably more than 0.3 parts by mass, from the viewpoint of processability. The content of the oil 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.

[0139] When the rubber composition constituting the second layer contains oil, the content (total content when two or more types are contained) per 100 parts by mass of the polymer component is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and particularly preferably 3 parts by mass or more, from the viewpoint of processability. The content of the oil 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.

[0140] (vegetable oil) In this specification, examples of vegetable oils include linseed oil, rapeseed oil, safflower oil, soybean oil, corn oil, cottonseed oil, rice oil, tall oil, sesame oil, perilla oil, castor oil, paulownia oil, pine oil, pine tar oil, sunflower oil, coconut oil, palm oil, palm kernel oil, olive oil, camellia oil, jojoba oil, macadamia nut oil, peanut oil, grapeseed oil, and wood wax. In addition, examples of vegetable oils include refined oils (such as salad oils) obtained by refining the above oils, transesterified oils obtained by transesterifying the above oils, hardened oils obtained by hydrogenating the above oils, thermally polymerized oils obtained by thermally polymerizing the above oils, oxidatively polymerized oils obtained by oxidizing the above oils, and waste edible oils obtained by recovering oils that have been used as edible oils or the like. The vegetable oils may be liquid or solid at room temperature (25° C.). These may be used alone or in combination of two or more.

[0141] The vegetable oil according to the present embodiment preferably contains acylglycerol, and more preferably contains triacylglycerol. In this specification, acylglycerol refers to a compound in which a hydroxyl group of glycerin and a fatty acid are ester-bonded. The acylglycerol is not particularly limited, and may be 1-monoacylglycerol, 2-monoacylglycerol, 1,2-diacylglycerol, 1,3-diacylglycerol, or triacylglycerol. Furthermore, the acylglycerol may be a monomer, a dimer, or a polymer of trimer or more. Incidentally, dimer or more acylglycerols can be obtained by thermal polymerization, oxidative polymerization, or the like. Furthermore, the acylglycerol may be liquid or solid at room temperature (25°C).

[0142] The method for confirming whether the rubber composition contains the acylglycerol is not particularly limited, but may be any of the following methods: 1 For example, a rubber composition containing triacylglycerol is immersed in deuterated chloroform at room temperature (25°C) for 24 hours, and after removing the rubber composition, 1 When H-NMR was measured, signals were observed at around 5.26 ppm, around 4.28 ppm, and around 4.15 ppm when the signal of tetramethylsilane (TMS) was set at 0.00 ppm, and the signals were presumed to be signals derived from hydrogen atoms bonded to carbon atoms adjacent to oxygen atoms of ester groups. Note that "around" in this paragraph refers to a range of ±0.10 ppm.

[0143] The fatty acid is not particularly limited, and may be an unsaturated fatty acid or a saturated fatty acid. Examples of the unsaturated fatty acid include monounsaturated fatty acids such as oleic acid, and polyunsaturated fatty acids such as linoleic acid and linolenic acid.

[0144] As the vegetable oil, for example, commercially available oils from Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., ENEOS Corporation, Orisoi Co., Ltd., H&R Corporation, Toyokuni Oil Mills Co., Ltd., Fuji Kosan Co., Ltd., Nisshin Oillio Group Co., Ltd., etc. can be used.

[0145] When the rubber composition constituting the first layer contains vegetable oil, the content thereof per 100 parts by mass of the polymer component is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and particularly preferably 3 parts by mass or more. The content of the vegetable oil 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.

[0146] When the rubber composition constituting the second layer contains vegetable oil, the content thereof per 100 parts by mass of the polymer component is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and particularly preferably 3 parts by mass or more. The content of the vegetable oil 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] (Resin component) Examples of the resin component include petroleum resins, terpene resins, rosin resins, phenol resins, etc. These resin components may be used alone or in combination of two or more.

[0148] Examples of the terpene resin include polyterpene resins consisting of at least one selected from terpene compounds such as α-pinene, β-pinene, limonene, and dipentene; aromatic modified terpene resins made from the terpene compounds and aromatic compounds; terpene phenolic resins made from terpene compounds and phenolic compounds; and terpene resins obtained by subjecting these terpene resins to hydrogenation treatment (hydrogenated terpene resins). Examples of aromatic compounds that are raw materials for aromatic modified terpene resins include styrene, α-methylstyrene, vinyltoluene, and divinyltoluene. Examples of phenolic compounds that are raw materials for terpene phenolic resins include phenol, bisphenol A, cresol, and xylenol.

[0149] Examples of the petroleum resin include C5 petroleum resin, aromatic petroleum resin, and C5C9 petroleum resin.

[0150] In this specification, the term "C5 petroleum resin" refers to a resin obtained by polymerizing a C5 fraction, and may be a hydrogenated or modified resin. Examples of C5 fractions include petroleum fractions having 4 to 5 carbon atoms, such as cyclopentadiene, pentene, pentadiene, and isoprene. As the C5 petroleum resin, dicyclopentadiene resin (DCPD resin) is preferably used.

[0151] In this specification, the term "aromatic petroleum resin" refers to a resin obtained by polymerizing a C9 fraction, and may be a hydrogenated or modified resin. Examples of the C9 fraction include petroleum fractions having 8 to 10 carbon atoms, such as vinyltoluene, alkylstyrene, indene, and methylindene. Specific examples of aromatic petroleum resins that can be suitably used include coumarone-indene resins, coumarone resins, indene resins, and aromatic vinyl resins. As aromatic vinyl resins, homopolymers of α-methylstyrene or styrene or copolymers of α-methylstyrene and styrene are preferred, and copolymers of α-methylstyrene and styrene are more preferred, because they are economical, easy to process, and have excellent heat generation properties. As aromatic vinyl resins, for example, those commercially available from Kraton, Eastman Chemical, etc. can be used.

[0152] In this specification, the term "C5C9 petroleum resin" refers to a resin obtained by copolymerizing the C5 fraction and the C9 fraction, and may be a hydrogenated or modified resin. Examples of the C5 fraction and the C9 fraction include the petroleum fractions described above. As the C5C9 petroleum resin, for example, those commercially available from Tosoh Corporation, LUHUA, etc. can be used.

[0153] The rosin-based resin is not particularly limited, but examples thereof include natural rosin resin and rosin-modified resins obtained by modifying rosin by hydrogenation, disproportionation, dimerization, esterification, or the like.

[0154] The phenol-based resin is not particularly limited, but examples thereof include phenol formaldehyde resin, alkylphenol formaldehyde resin, alkylphenol acetylene resin, and oil-modified phenol formaldehyde resin.

[0155] When a resin component is contained, the content relative to 100 parts by mass of the polymer component is preferably more than 1.0 part by mass, more preferably more than 1.5 parts by mass, and even more preferably more than 2.0 parts by mass, and from the viewpoint of suppressing heat buildup, is preferably less than 40 parts by mass, more preferably less than 30 parts by mass, and even more preferably less than 20 parts by mass.

[0156] The liquid rubber is not particularly limited as long as it is a rubber that is in a liquid state at room temperature (25°C), but examples thereof include liquid butadiene rubber (liquid BR), liquid isoprene rubber (liquid IR), liquid styrene butadiene rubber (liquid SBR), liquid styrene isoprene rubber (liquid SIR), liquid rubber containing myrcene or farnesene, etc. These liquid rubbers may be used alone or in combination of two or more.

[0157] When the liquid rubber is contained, the content thereof 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, based on 100 parts by mass of the polymer component. The content of the liquid rubber 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.

[0158] The content of the plasticizer relative to 100 parts by mass of the polymer component (the total amount when multiple plasticizers 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. The content is also 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.

[0159] The vulcanized rubber particles are particles made of vulcanized rubber, and specifically, rubber powder or the like specified in JIS K 6316:2017 can be used. From the viewpoint of environmental consideration and cost, recycled rubber powder produced from crushed waste tires or the like is preferable. These may be used alone or in combination of two or more types.

[0160] The vulcanized rubber particles are not particularly limited, and may be unmodified or modified. Commercially available vulcanized rubber products include those from Lehigh, Muraoka Rubber Industries, and the like.

[0161] The wax is not particularly limited, and any wax commonly used in the tire industry can be suitably used, for example, petroleum wax, mineral wax, synthetic wax, etc., with petroleum wax being preferred. Petroleum waxes include, for example, paraffin wax, microcrystalline wax, and selected special waxes thereof, with paraffin wax being preferred. The wax according to this embodiment does not contain stearic acid. The wax may be, for example, a wax commercially available from Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., Paramelt Co., Ltd., etc. These waxes may be used alone or in combination of two or more.

[0162] When the wax is contained, the content thereof per 100 parts by mass of the polymer component is preferably more than 0.5 parts by mass, more preferably more than 0.8 parts by mass, from the viewpoint of weather resistance of the rubber, and is preferably less than 10 parts by mass, more preferably less than 5.0 parts by mass, from the viewpoint of preventing whitening of the tire due to bloom.

[0163] The antioxidant is not particularly limited, and examples thereof include naphthylamine-based antioxidants such as phenyl-α-naphthylamine; diphenylamine-based antioxidants such as octylated diphenylamine and 4,4'-bis(α,α'-dimethylbenzyl)diphenylamine; N-isopropyl-N'-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine (77PD), N,N'-diphenyl-p-phenylenediamine (DPPD), N,N'-ditolyl-p-phenylenediamine, and the like. p-phenylenediamine-based antioxidants such as N-isopropyl-N'-phenyl-p-phenylenediamine (DTPD), N-isopropyl-N'-phenyl-p-phenylenediamine (IPPD), and N,N'-di-2-naphthyl-p-phenylenediamine (DNPD); quinoline-based antioxidants such as 2,2,4-trimethyl-1,2-dihydroquinoline polymers; monophenol-based antioxidants such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol; and bis-, tris-, and polyphenol-based antioxidants such as tetrakis-[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane. Among them, p-phenylenediamine-based antioxidants and quinoline-based antioxidants are preferred, and N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine and 2,2,4-trimethyl-1,2-dihydroquinoline polymers are more preferred. Commercially available products include those from Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinko Chemical Co., Ltd., Flexis, and the like.

[0164] When an antioxidant is contained, the content relative to 100 parts by mass of the polymer component is preferably more than 0.5 parts by mass, more preferably more than 0.8 parts by mass, and even more preferably more than 1.0 part by mass from the viewpoint of ozone crack resistance of the rubber, and is preferably less than 10 parts by mass, more preferably less than 5.0 parts by mass from the viewpoint of abrasion resistance.

[0165] When stearic acid is contained, the content relative to 100 parts by mass of the polymer component is preferably more than 0.5 parts by mass, more preferably more than 1.0 parts by mass, and even more preferably more than 1.5 parts by mass from the viewpoint of processability, and is preferably less than 10 parts by mass, more preferably less than 5.0 parts by mass from the viewpoint of vulcanization speed.

[0166] When zinc oxide is contained, the content relative to 100 parts by mass of the polymer component is preferably more than 1.0 part by mass, more preferably more than 1.5 parts by mass, and even more preferably more than 2.0 parts by mass from the viewpoint of processability, and is preferably less than 10 parts by mass, more preferably less than 5.0 parts by mass from the viewpoint of abrasion resistance.

[0167] As the vulcanizing agent, sulfur is preferably used, and examples of the sulfur that can be used include powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur.

[0168] When sulfur is contained as a vulcanizing agent, the content relative to 100 parts by mass of the polymer 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 parts by mass, from the viewpoint of ensuring sufficient vulcanization reaction. Also, 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. Note that, when oil-containing sulfur is used as a vulcanizing agent, the content of the vulcanizing agent is the total content of the pure sulfur contained in the oil-containing sulfur.

[0169] Examples of vulcanizing agents other than sulfur include alkylphenol-sulfur chloride condensates, sodium 1,6-hexamethylene-dithiosulfate dihydrate, 1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane, etc. As these vulcanizing agents other than sulfur, commercially available products from Taoka Chemical Co., Ltd., Lanxess Co., Ltd., Flexis, etc. can be used.

[0170] Examples of the vulcanization accelerator include sulfenamide vulcanization accelerators, thiazole vulcanization accelerators, thiuram vulcanization accelerators, guanidine vulcanization accelerators, dithiocarbamate vulcanization accelerators, and caprolactam disulfide. These vulcanization accelerators may be used alone or in combination of two or more. Among them, from the viewpoint of more suitably obtaining the desired effect, one or more vulcanization accelerators selected from the group consisting of sulfenamide vulcanization accelerators, thiazole vulcanization accelerators, thiuram vulcanization accelerators, and guanidine vulcanization accelerators are preferred, and sulfenamide vulcanization accelerators are more preferred.

[0171] Examples of sulfenamide vulcanization accelerators include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N,N-dicyclohexyl-2-benzothiazolylsulfenamide (DCBS), etc. Among these, TBBS and CBS are preferred.

[0172] When a vulcanization accelerator is contained, the content relative to 100 parts by mass of the polymer component is preferably more than 0.5 parts by mass, more preferably more than 0.8 parts by mass, and even more preferably more than 1.0 parts by mass. The content of the vulcanization accelerator relative to 100 parts by mass of the polymer 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 setting the content of the vulcanization accelerator within the above range, breaking strength and elongation tend to be secured.

[0173] [Belt layer] The tire according to the present embodiment has a belt layer. The belt layer preferably has a steel cord, and the steel cord may be covered with a topping rubber. The belt layer preferably has two or more layers including steel cords inclined with respect to the tire circumferential direction, and one or more reinforcing layers including steel cords oriented in the tire circumferential direction.

[0174] (Steel cord) The steel cord according to the present embodiment has one or more steel wires, also called filaments. When one steel cord has multiple filaments, the twisted structure of the steel cord is not particularly limited, but may have an N×M structure in which N (N=3-5) strands, each of which is made up of M wires (M=5-10), are twisted together, or a 1×N structure, which is a single-twist steel cord.

[0175] When the belt layer includes the reinforcing layer, the elastic modulus of the steel cord of the reinforcing layer at 0.5 to 1.0% elongation is preferably 80 GPa or more, more preferably 90 GPa or more, and even more preferably 100 GPa or more, from the viewpoint of suppressing deformation of the tread portion during rolling. Also, from the viewpoint of absorbing and mitigating impact from the road surface, the elastic modulus is preferably 250 GPa or less, more preferably 220 GPa or less, and even more preferably 200 GPa or less. The elastic modulus of the steel cord at 0.5 to 1.0% elongation is measured by the above method with the steel cord taken out of the tire.

[0176] In this specification, the state in which the steel cord has been removed from the tire refers to a state in which the steel cord has been removed from the tire and the topping rubber covering the steel cord has been removed.

[0177] The cross-sectional area of ​​the steel cord is 0.05 mm 2 More than 0.07mm is preferable. 2 More preferably, 0.09 mm or more 2 More preferably, 0.11 mm or more 2 More preferably, the cross-sectional area S of the steel cord is 0.80 mm 2 Less than 0.60mm is preferable 2 Less than 0.40mm is more preferable. 2 Less than 0.30 mm is more preferable. 2 The following are particularly preferred:

[0178] Regarding the physical properties of the steel cords, it is sufficient that any one of the steel cords satisfies the above-mentioned range, and all of the steel cords may satisfy the above-mentioned range.

[0179] [Production of rubber composition] The rubber composition according to the present embodiment can be produced by a known method, for example, by kneading the above-mentioned components using a rubber kneading device such as an open roll or an internal kneader (such as a Banbury mixer or a kneader).

[0180] The kneading step includes, for example, a base kneading step in which compounding ingredients and additives other than the vulcanizing agent and the vulcanization accelerator are kneaded, and a final kneading (F kneading) step in which the vulcanizing agent and the vulcanization accelerator are added to the kneaded product obtained in the base kneading step and kneaded. Furthermore, the base kneading step can be divided into a plurality of steps as desired.

[0181] The kneading conditions are not particularly limited, but examples thereof include a method in which in the base kneading step, kneading is performed for 3 to 10 minutes at a discharge temperature of 150 to 170° C., and in the final kneading step, kneading is performed for 1 to 5 minutes at 70 to 110° C. The vulcanization conditions are not particularly limited, but examples thereof include a method in which vulcanization is performed for 10 to 30 minutes at 150 to 200° C.

[0182] [Tire manufacturing] Each rubber composition obtained above is extruded in the unvulcanized stage according to the shape of the desired tire component, or when used as a topping rubber, it is extruded once in a sheet shape or the like, and then used as a topping rubber to cover a steel cord to produce a desired tire component, and each tire component thus obtained is molded together with other tire components in a tire building machine by a normal method to produce an unvulcanized tire. The tire of this embodiment can be obtained by heating and pressurizing this unvulcanized tire in a vulcanizer (vulcanization). The vulcanization conditions are not particularly limited, and examples include a method of vulcanization at 150 to 200 ° C for 5 to 30 minutes.

[0183] [Tire Uses] The tire according to the present embodiment can be suitably used as a heavy-duty tire. Note that a heavy-duty tire is a tire that is intended to be mounted on a vehicle that runs on four wheels, 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

[0184] The following are examples (working examples) that are considered to be preferable for carrying out the present invention, but the scope of the present invention is not limited to these working examples. Using the various chemicals shown below, a tire having a first layer of a tread portion obtained according to the composition in Table 1 and a second layer obtained according to the composition in Table 2 was examined, and the results calculated based on the following evaluation method are shown in Tables 3 and 4.

[0185] Various chemicals used in the examples and comparative examples are listed below. NR:TSR20 SBR: SBR1502 manufactured by JSR Corporation (unmodified E-SBR, styrene content: 23.5% by mass, Tg: -56°C, Mw: 440,000, not oil-extended) BR1: UBEPOL BR (registered trademark) 150B manufactured by UBE Corporation (unmodified BR, cis content: 97 mol%, Mw: 440,000) BR2: VCR-617 manufactured by UBE Corporation (SPB-containing BR, cis content: 98 mol%, Mw: 480,000) Thermoplastic elastomer: RB810 (polybutadiene-based thermoplastic elastomer, vinyl content: 90 mol%) manufactured by JSR Corporation Carbon black 1: Show Black N220 (N2SA: 111m) manufactured by Cabot Japan Co., Ltd. 2 / g) Carbon black 2: Cabot Japan Co., Ltd. Show Black N330 (N2SA: 75m 2 / g) rCB: Carbon black obtained from the pyrolysis process of tires (ash content: 17% by mass) Oil 1: Diana Process Oil PW-380 (paraffin-based process oil) manufactured by Idemitsu Kosan Co., Ltd. Oil 2: Sunflower oil manufactured by Nisshin Oillio Group Co., Ltd. (Oleic acid content in constituent fatty acids: 55% by mass, total polyunsaturated fatty acid content in constituent fatty acids: 8% by mass) Wax: Ozoace 0355 (paraffin wax) by Nippon Seiro Co., Ltd. Anti-aging agent: Nocrac 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Stearic acid: Beads of stearic acid camellia manufactured by NOF Corporation Zinc oxide: Two types of zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: HK-200-5 (powdered sulfur containing 5% oil) manufactured by Hosoi Chemical Industry Co., Ltd. Vulcanization accelerator: Noccela NS (N-tert-butyl-2-benzothiazolyl sulfenamide (TBBS)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0186] Examples and Comparative Examples According to the compounding recipes shown in Tables 1 and 2, chemicals other than sulfur and vulcanization accelerator are kneaded for 1 to 10 minutes using a 1.7 L closed type Banbury mixer until the discharge temperature reaches 150 to 160°C, to obtain a kneaded product. Next, sulfur and vulcanization accelerator are added to the kneaded product using a two-axis open roll, and kneaded for 4 minutes until the temperature reaches 105°C, to obtain an unvulcanized rubber composition. The unvulcanized rubber composition is molded according to the shape of the first layer and the second layer of the tread, respectively, and laminated together with the belt layer and other tire components to prepare an unvulcanized tire, which is then vulcanized at 150°C to obtain each test tire shown in Tables 3 and 4.

[0187] <Measurement of 100°C E* of the rubber composition constituting the first layer> Each vulcanized rubber test piece is cut out from the first layer of the tread portion of each test tire to a length of 20 mm, width of 4 mm, and thickness of 1 mm, with the long side in the tire circumferential direction and the thickness direction in the tire radial direction, and the complex modulus E* of each test piece is measured using a dynamic viscoelasticity measuring device (Iplexer series manufactured by GABO) under the conditions of a temperature of 100°C, a frequency of 10 Hz, an initial strain of 10%, a dynamic strain of ±2.5%, and an elongation mode.

[0188] <Measurement of 70°C tan δ and 70°C E* of the rubber composition constituting the first layer> Each vulcanized rubber test piece is cut out from the first layer of the tread of each test tire to a length of 20 mm, width of 4 mm, and thickness of 1 mm, with the long side in the tire circumferential direction and the thickness direction in the tire radial direction, and is measured for tan δ and complex modulus E* using a dynamic viscoelasticity measuring device (Iplexer series manufactured by GABO) under conditions of a temperature of 70°C, a frequency of 10 Hz, a dynamic strain amplitude of ±1%, and an extension mode.

[0189] <Measurement of modulus at 100% elongation of rubber composition constituting second layer> A 1 mm thick No. 7 dumbbell shaped test piece was prepared from the second layer of the tread of each test tire so that the thickness direction was the radial direction of the tire. A tensile test was carried out in accordance with JIS K 6251 "Vulcanized rubber and thermoplastic rubber - Determination of tensile test characteristics" at an atmosphere of 23°C and a tensile speed of 3.3 mm / sec, and the stress at 200% elongation (MPa) was measured.

[0190] <Steel cord elastic modulus at 0.5% to 1.0% elongation> A 250 mm long steel cord is cut out from the reinforcing layer of the belt layer of each test tire, and a tensile test is carried out at a tensile speed of 5 mm / min in accordance with JIS G 3510 "Steel Tire Cord Test Method", and the elastic modulus at 0.5% to 1.0% elongation is calculated using the following formula. (Elastic modulus at 0.5% to 1.0% elongation) = 0.2 x (Tension at 1.0% elongation (N) - Tension at 0.5% elongation (N)) / Cross-sectional area of ​​steel cord (mm 2 )

[0191] <Wear resistance> Each test tire is fitted to all wheels of a vehicle (a 10-ton 2-D truck), which is driven on an asphalt road surface for 30,000 km, and the groove depth H of the deepest part of the circumferential groove of the tire tread after the drive is measured, and the driving distance until H decreases by 1.0 mm is calculated. The driving distance of the control tire (Comparative Example 8) is converted to 100, and the reciprocal of the driving distance of each test tire is expressed as an index according to the following formula. The higher the index, the more improved the wear resistance performance. (Wet grip performance index after wear) = (braking distance of control tire after wear) / (braking distance of each test tire after wear)

[0192] [Table 1]

[0193] [Table 2]

[0194] [Table 3]

[0195] [Table 4]

[0196] <Embodiment> Examples of embodiments of the present invention are given below. [1] A tire having a tread portion and a belt layer, The tread portion has a first layer constituting a tread surface and a second layer located radially inward of the first layer, The tread portion has two or more circumferential grooves extending continuously in the circumferential direction, When the thickness of the first layer is t1 (mm), the thickness of the second layer is t2 (mm), the groove depth of the deepest portion of the circumferential groove is H (mm), and the complex modulus of elasticity at 100°C of the rubber composition constituting the first layer is 100°C E* (MPa), A tire having a t1 / H of less than 1.0 and a 100°C E* / t2 of 1.5 or less. [2] The tire according to [1] above, wherein at least one of the circumferential grooves is a wide circumferential groove having a groove width wider than the groove width on the tread surface at any position on the radially inner side of the groove, and the groove width at the 90% position of the deepest part of the wide circumferential groove is 1.0 mm or more and 4.0 mm or less. [3] The tire described in [1] or [2] above, wherein at least one of the circumferential grooves is a wide circumferential groove having a groove width wider than the groove width on the tread surface at any position on the radially inner side of the groove, and the wide circumferential groove has a change point where the groove width widens from the tread surface toward the radially inner side of the tire. [4] The tire according to any one of the above [1] to [3], wherein the rubber composition constituting the second layer contains recycled carbon black. [5] The tire according to any one of the above [1] to [3], wherein the rubber composition constituting the second layer contains vegetable oil. [6] The tire according to any one of the above [1] to [5], wherein the total styrene content in the polymer component of the rubber composition constituting the first layer is 1.0% by mass or more and 20.0% by mass or less. [7] The tire according to any one of the above [1] to [6], wherein, when the complex modulus at 70°C of the rubber composition constituting the first layer is 70°CE*, 100°CE* / 70°CE* is less than 0.85. [8] The tire according to any one of the above [1] to [7], wherein the belt layer has two or more layers including steel cords inclined with respect to the tire circumferential direction, and one or more reinforcing layers including steel cords oriented in the tire circumferential direction. [9] The tire according to any one of the above [1] to [8], wherein the elastic modulus of the steel cord of the reinforcing layer at 0.5% to 1.0% elongation is 80 GPa or more and 250 GPa or less.

[10] The tire according to any one of the above [1] to [9], wherein, when tan δ at 70° C. of the rubber composition constituting the first layer is 70° C. tan δ, 70° C. tan δ×H is 3.0 or less.

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

[10] , wherein the rubber composition constituting the second layer has a modulus of 9.0 MPa or less when stretched 200%.

[12] The tire according to any one of the above [1] to

[11] , which is for heavy loads. [Explanation of symbols]

[0197] 1 Tread section 2 Sidewall 3 Bead section 4. Carcass 5 Belt Layer 7 Inner Liner 10 Clinch Section 11 First layer 12 Second layer 13 Bead Apex 14 Bead core 20 Circumferential groove 21 Land Department 22 Extension line connecting the two land areas 23 Extension of the deepest part of the bottom of the circumferential groove 25 Wide circumferential groove 26 Groove Edge 27 Recess 30 Tread surface CL Tire Equator H: Depth of the deepest part of the circumferential groove h 90% of the deepest part of the circumferential groove t1 Thickness of the first layer t2 Second layer thickness W1 Groove width on tread surface W2: Groove width at 90% of the deepest part of the circumferential groove P Changes L Distance from tread surface to change point

Claims

1. A tire having a tread portion and a belt layer, The tread portion has a first layer constituting a tread surface and a second layer located radially inward of the first layer, The tread portion has two or more circumferential grooves extending continuously in a circumferential direction, When the thickness of the first layer is t1 (mm), the thickness of the second layer is t2 (mm), the groove depth of the deepest portion of the circumferential groove is H (mm), and the complex modulus of elasticity at 100° C. of the rubber composition constituting the first layer is 100° C. E* (MPa), A tire having t1 / H of less than 1.0 and 100°C E* / t2 of 1.5 or less.

2. 2. The tire according to claim 1, wherein at least one of the circumferential grooves is a wide circumferential groove having a groove width wider than the groove width on the tread surface at any position on the radially inner side of the groove, and the groove width at a 90% position of the deepest part of the wide circumferential groove is 1.0 mm or more and 4.0 mm or less.

3. 3. The tire according to claim 1, wherein at least one of the circumferential grooves is a wide circumferential groove having a groove width wider than a groove width on the tread surface at any position on the radially inner side of the groove, and the wide circumferential groove has a change point where the groove width widens from the tread surface toward the radially inner side of the tire.

4. The tire according to claim 1 or 2, wherein the rubber composition constituting the second layer contains recycled carbon black.

5. The tire according to claim 1 or 2, wherein the rubber composition constituting the second layer contains vegetable oil.

6. 3. The tire according to claim 1, wherein a total styrene content in a polymer component of a rubber composition constituting the first layer is 1.0% by mass or more and 20.0% by mass or less.

7. 3. The tire according to claim 1, wherein, when the complex modulus at 70°C of the rubber composition constituting the first layer is defined as 70°C E*, 100°C E* / 70°C E* is less than 0.

85.

8. The tire according to claim 1 or 2, wherein the belt layer has two or more layers including steel cords inclined with respect to the tire circumferential direction, and one or more reinforcing layers including steel cords oriented in the tire circumferential direction.

9. 9. The tire according to claim 8, wherein the steel cord of the reinforcing layer has an elastic modulus of 80 GPa or more and 250 GPa or less at 0.5% to 1.0% elongation.

10. The tire according to claim 1 or 2, wherein, when tan δ at 70° C. of the rubber composition constituting the first layer is taken as 70° C. tan δ, 70° C. tan δ×H is 3.0 or less.

11. The tire according to claim 1 or 2, wherein the rubber composition constituting the second layer has a modulus of 9.0 MPa or less when stretched 200%.

12. 3. A tire according to claim 1 or 2, for heavy loads.

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