tire

Abstract

To provide a tire that can improve steering stability performance.SOLUTION: A tire has a tread part. The tread part has a first layer constituting a tread surface and a second layer arranged adjacently to inside in a tire radial direction of the first layer. The first layer and the second layer are constituted of rubber compositions containing rubber components and vulcanized rubber particles respectively. A ratio R1 of areas of a domain derived from the vulcanized rubber particles to areas of a whole of a cut surface is over 0.05 and 0.50 or less, on the cut surface parallel to the tread surface of the first layer, and a ratio R2 of areas of a domain derived from the vulcanized rubber particles to areas of the whole of a cut surface is over 0.05 or more and less than 0.50, on the cut surface parallel to the tread surface of the second layer, where R1 is larger than R2.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to tires. [Background technology]

[0002] In recent years, there has been a strong demand in the tire market for improved handling stability, particularly at high speeds. Patent Document 1 discloses that by incorporating a predetermined chitin fiber and / or chitosan fiber into the base rubber that constitutes the tread, heat generation can be reduced, the rigidity of the rubber can be increased, and handling stability can be improved. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2009-1672 [Overview of the project] [Problems that the invention aims to solve]

[0004] The present invention aims to provide a tire that can improve handling stability. [Means for solving the problem]

[0005] The present invention relates to a tire having a tread portion, wherein the tread portion comprises a first layer constituting a tread surface and a second layer adjacent to the radially inward side of the first layer, and the first layer and the second layer are each composed of a rubber composition containing a rubber component and vulcanized rubber particles, wherein, in a cross-section parallel to the tread surface of the first layer, the ratio R1 of the area of ​​domains derived from vulcanized rubber particles to the total area of ​​the cross-section is greater than 0.05 and less than or equal to 0.50, and in a cross-section parallel to the tread surface of the second layer, the ratio R2 of the area of ​​domains derived from vulcanized rubber particles to the total area of ​​the cross-section is 0.05 or more and less than 0.50, and R1 is greater than R2. [Effects of the Invention]

[0006] According to the present invention, it is possible to improve the handling stability performance of the tires. [Brief explanation of the drawing]

[0007] [Figure 1] This is an enlarged cross-sectional view showing a portion of the tread of a tire according to one embodiment of the present invention. [Modes for carrying out the invention]

[0008] One embodiment of the present invention is a tire having a tread portion, wherein the tread portion comprises a first layer constituting the tread surface and a second layer adjacent to the radially inward side of the first layer, and the first layer and the second layer are each composed of a rubber composition containing a rubber component and vulcanized rubber particles, wherein in a cross-section parallel to the tread surface of the first layer, the ratio R1 of the area of ​​domains derived from vulcanized rubber particles to the total area of ​​the cross-section is greater than 0.05 and less than or equal to 0.50, and in a cross-section parallel to the tread surface of the second layer, the ratio R2 of the area of ​​domains derived from vulcanized rubber particles to the total area of ​​the cross-section is 0.05 or more and less than 0.50, and R1 is greater than R2.

[0009] A tire obtained by laminating two or more rubber layers in the tread area, and by making the area of ​​domains derived from vulcanized rubber particles smaller than the area ratio of domains derived from vulcanized rubber particles in the outermost layer (first layer) of the tread cross-section of the second layer from the tread surface, exhibits significantly improved handling stability. While we do not intend to be bound by theory, the reason for this can be considered as follows.

[0010] By incorporating vulcanized rubber particles into the first layer of the tread, domains of vulcanized rubber particles are formed. Heat is generated due to friction at the interface between the vulcanized rubber particles and the rubber matrix, and the gripping effect of the vulcanized rubber particles is obtained, thereby improving the frictional performance of the tread surface against the road surface. Furthermore, by incorporating vulcanized rubber particles into the second layer, heat can be generated through friction at the interface between the vulcanized rubber particles and the rubber matrix, similar to the first layer. In this way, it is believed that the grip performance can be improved by obtaining heat generation throughout the tread and adding the gripping effect on the tread surface.

[0011] Here, the second layer needs to play a role in transmitting the force (grip force) generated by friction on the tread surface to the inside of the tire. However, if the amount of vulcanized rubber particles in the second layer is large, the heat generation (phase difference) will increase, making it difficult to transmit the grip force to the inside of the tire. Therefore, by making the area ratio of domains derived from vulcanized rubber particles to the total area of ​​the tread cross-section of the second layer smaller than the area ratio of domains derived from vulcanized rubber particles to the total area of ​​the tread cross-section of the first layer, it is thought that the grip force can be more easily transmitted to the inside of the tire, and the force that changes the direction of the vehicle can be more easily generated. And it is thought that the remarkable effect of improving ice grip performance is achieved through the cooperation of these factors.

[0012] The ratio (t1 / t2) of the thickness of the first layer to the thickness of the second layer (t2 / mm) is preferably greater than 0.15.

[0013] By setting t1 / t2 within the aforementioned range, it is thought that friction can be more easily generated on the tread surface, making it easier to generate a large force.

[0014] The tanδ (70°C tanδ) of the second layer at 70°C is preferably between 0.02 and 0.25.

[0015] By setting the tanδ of the second layer within the above range, the phase difference during force transmission can be reduced, and it is considered that the force generated by friction on the tread surface can be more easily transmitted to the inside of the tire.

[0016] The product (R1×(t1 / t2)) of the ratio (t1 / t2) of the thickness t1 (mm) of the first layer to the thickness t2 (mm) of the second layer and R1 is preferably more than 0.015.

[0017] As described above, it is considered that the vulcanized rubber particles in the first layer can easily generate friction by the first layer. On the other hand, when the ratio of the thickness of the first layer is small, it is considered that the force generated in the first layer becomes small. From this, by setting the product (R1×(t1 / t2)) of the area ratio R1 occupied by the vulcanized rubber particles in the first layer and the ratio (t1 / t2) of the thickness of the first layer to the thickness of the second layer within the above range, it is considered that the frictional force on the tread surface can be ensured and the force can be easily transmitted to the inside of the tire.

[0018] The rubber component constituting the first layer preferably contains styrene-butadiene rubber. Further, the total styrene amount in the rubber component constituting the first layer is preferably 10% by mass or more and 20% by mass or less.

[0019] By containing styrene-butadiene rubber as the rubber component constituting the first layer, minute domains derived from the styrene portion are formed in the rubber layer, and it is considered that frictional heat generated by friction between these and other molecular chains and the engagement of the domains derived from the styrene portion with the road surface can easily obtain frictional force. Also, by setting the total styrene amount in the rubber component constituting the first layer within the above range, it is considered that domains derived from the styrene portion can be easily formed in the system.

[0020] The total content of butadiene rubber and styrene-butadiene rubber in the rubber component constituting the first layer is preferably 75% by mass or more.

[0021] By setting the total content of butadiene rubber and styrene-butadiene rubber in the rubber component constituting the first layer within the aforementioned range, it is thought that it is possible to facilitate the formation of domains derived from the styrene portion within the system.

[0022] Preferably, the total content of silica and carbon black in the rubber composition constituting the first layer is 60 parts by mass or less per 100 parts by mass of rubber component.

[0023] By setting the total content of silica and carbon black in the rubber composition constituting the first layer within the aforementioned range, it is possible to suppress the hardening of the entire rubber layer by silica and carbon black, thereby creating a hardness distribution in the microscopic region, and making it easier for the domains formed within the rubber layer to grip the road surface.

[0024] The glass transition temperature of the aforementioned first layer is preferably -25°C or higher.

[0025] By setting the glass transition temperature of the first layer within the aforementioned range, it is possible to increase the energy loss corresponding to the frequency of vibrations generated during rolling in normal driving, thereby making it easier to absorb vibrations.

[0026] The Shore hardness (Hs) of the second layer is preferably between 50 and 80.

[0027] By setting the Shore hardness (Hs) of the second layer within the aforementioned range, it is believed that good macroscopic followability can be easily obtained.

[0028] The modulus of the second layer at 100% stretch is preferably greater than the modulus of the first layer at 100% stretch.

[0029] By making the modulus of the second layer at 100% stretch greater than that of the first layer at 100% stretch, it becomes easier to generate a large force in the second layer, which is expected to improve steering stability during high-speed driving. Furthermore, from the viewpoint of the effects of the present invention, the modulus of the second layer at 100% stretch is preferably 2.2 MPa or higher.

[0030] The tread portion has circumferential grooves that extend continuously in the circumferential direction of the tire, and it is preferable that the ratio of t1 to the groove depth H at the deepest part of the circumferential groove (t1 / H) is 0.40 to 0.90.

[0031] By setting t1 / H within the aforementioned range, it is thought that it becomes easier to generate force in the first layer, thereby improving handling stability.

[0032] <Definition> The "tread portion" is the part that forms the contact surface of the tire, and in the radial cross-section of the tire, if the tire has components that form the tire skeleton using steel or textile materials such as belt layers, belt reinforcement layers, and carcass layers, the tread portion is the component that is radially outward from these components.

[0033] A "standard rim" is the rim specified for each tire in the standards system that the tire is based on. For example, it is called a "standard rim" for JATMA, a "measuring rim" for ETRTO, or a "design rim" for TRA. Refer to JATMA, ETRTO, and TRA in that order, and if there is an applicable size at the time of reference, follow that standard.

[0034] "A cross-section parallel to the tread surface" refers to a cross-section parallel to the surface in contact with the tread surface on the tire's centerline.

[0035] A "circumferential groove" refers to a groove that extends continuously in the circumferential direction of the tire, and is defined as a recess with an opening width of at least 2.0 mm or more on the tread surface.

[0036] "Circumferential groove depth H" refers to the distance between the tread surface and the deepest part of the groove bottom of the circumferential groove. If there are multiple circumferential grooves, the groove depth H of the circumferential groove with the deepest groove depth will be used as the "circumferential groove depth H".

[0037] "The thickness of each rubber layer constituting the tread" refers to the thickness of each rubber layer on the tire's equatorial plane in a cross-section obtained by cutting the tire with respect to the plane containing the tire's axis of rotation. For example, the thickness of the first layer refers to the straight-line distance in the tire's radial direction from the outermost surface of the tread to the inner radial interface of the first layer on the tire's equatorial plane. If the tire has circumferential grooves on its equatorial plane, the thickness of each rubber layer constituting the tread shall be the thickness of each rubber layer at the center of the tire's width direction of the land area closest to the tire's equatorial plane. "The land area closest to the tire's equatorial plane" refers to the land area of ​​a circumferential groove on the tire's equatorial plane that has the groove edge closest to the tire's equatorial plane. If such land areas exist on both sides in the tire's width direction, the thickness of each rubber layer constituting the tread shall be the average value of the thicknesses of each rubber layer at the center of the tire's width direction of the two land areas. Furthermore, if there are conductive members or the like on the land area of ​​the tire's equatorial plane and the interface is unclear, the interface obstructed by the conductive members or the like shall be virtually connected and measured.

[0038] A "softener" is a material that imparts plasticity to rubber components and is extracted from rubber compositions using acetone. Softeners include those that are liquid at 25°C and those that are solid at 25°C. However, waxes and stearic acid commonly used in the tire industry are excluded.

[0039] "Softener content" includes the amount of softener contained in the stretchable rubber component that has been pre-stretched with softeners such as oil, resin components, and liquid rubber components. The same applies to the oil content, resin component content, and liquid rubber content; for example, if the stretchable component is oil, the stretchable oil is included in the oil content.

[0040] <Measurement method> The area of ​​domains derived from vulcanized rubber particles in a cross-section parallel to the tread surface of each rubber layer constituting the tread can be determined, for example, by observing a vulcanized rubber test piece cut from the tread using a scanning electron microscope (SEM). Specifically, for example, each vulcanized rubber test piece is prepared by cutting it from the tire tread so that the longer side is in the circumferential direction of the tire, with dimensions of 20 mm in length, 30 mm in width, and 2 mm in thickness. The obtained rubber test piece is placed in a scanning electron microscope (ThermoFishershasei Teneo) so that the surface parallel to the tread surface becomes the observation cross-section, and imaging is performed with an acceleration voltage of 15 kV to obtain an electron microscope image at a magnification of 50x. Then, the area of ​​domains derived from vulcanized rubber particles is calculated in a 2.54 mm x 1.69 mm area of ​​the obtained image, and the ratio of this area to the total area of ​​the cross-section is calculated. This is done for three fields of view per sample, and the average value is taken as the area ratio of the rubber powder.

[0041] The thickness of each rubber layer that makes up the tread is measured by cutting the tire along the plane containing the tire's rotation axis, with the width of the bead area matched to the width of the standard rim.

[0042] "70℃tanδ" is the loss tangent measured under the conditions of a temperature of 70℃, a frequency of 10Hz, an initial strain of 10%, a dynamic strain of ±1%, and the extension mode. The sample for measuring 70℃tanδ is a vulcanized rubber composition measuring 20mm in length, 4mm in width, and 1mm in thickness. When preparing the sample by cutting it from a tire, it should be cut from the tire tread so that the tire circumference is the longer side and the tire radius is the thickness direction.

[0043] The glass transition temperature (Tg) of the rubber layer is determined by measuring the temperature distribution curve of tanδ in the range of -60°C to 40°C using a dynamic viscoelasticity measuring device (e.g., the Iplexer series from GABO) under conditions of frequency 10 Hz, initial strain 1%, amplitude ±0.1%, and heating rate 3°C / min. The temperature corresponding to the largest tanδ value in the obtained temperature distribution curve (tanδ peak temperature) is determined as Tg. If there are two points with maximum values ​​of tanδ in the range of -60°C to 40°C, the one with the lower temperature is taken as Tg. Furthermore, if a temperature distribution curve is obtained in the range of -60°C to 40°C where tanδ gradually decreases with increasing temperature, Tg is set to -60°C according to the above definition. The sample for this measurement is prepared in the same manner as for 70°C tanδ.

[0044] Shore hardness is measured in Hs using a durometer type A under conditions of 23°C, in accordance with JIS K 6253-3:2012. A sample for Shore hardness measurement is prepared by cutting a piece from the tread so that the tire radius is oriented in the thickness direction. The measurement is performed by pressing the measuring instrument against the sample from the contact surface side.

[0045] The "modulus at 100% elongation (M100)" is the tensile stress (MPa) at 100% elongation in the grain direction (the rolling direction when forming a rubber sheet by extrusion or shearing), measured under conditions of 3.3 mm / second at a tensile speed in a 23°C atmosphere, in accordance with JIS K 6251:2017. The sample for M100 measurement is a 1 mm thick, dumbbell-shaped No. 7 vulcanized rubber test piece. When preparing it by cutting from a tire, it should be cut from the tire tread so that the tire circumference is the tensile direction and the tire radius is the thickness direction.

[0046] "Styrene content" is, 1 This value is calculated by 1H-NMR measurement and is applied, for example, to rubber components having repeating units derived from styrene, such as SBR.

[0047] "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 rubber components having repeating units derived from butadiene, such as SBR and BR.

[0048] "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, for example, to rubber components having repeating units derived from butadiene, such as BR.

[0049] "Total styrene content in rubber components" refers to the total amount of styrene units contained in 100% by mass of the rubber components (by mass%). For each rubber component, the value obtained by multiplying the styrene content (by mass%) by the mass fraction in the rubber components is calculated, and these values ​​are then summed up. Specifically, it is calculated as Σ(styrene content (by mass%) of each styrene-containing rubber × styrene content (by mass%) in the rubber components of each styrene-containing rubber / 100).

[0050] The "weight-average molecular weight (Mw)" can be determined by converting the measured value using gel permeation chromatography (GPC) (for example, the GPC-8000 series from Tosoh Corporation, with a differential refractometer as the detector and TSKGEL SUPERMALTIPORE HZ-M column from Tosoh Corporation) to a standard polystyrene equivalent. This method is applicable, for example, to SBR, BR, etc.

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

[0052] The procedure for manufacturing a tire, which is one embodiment of the present invention, will be described in detail below. However, the following description is illustrative for explaining the present invention and is not intended to limit the technical scope of the present invention to this scope only.

[0053] [tire] A tire according to one embodiment of the present invention will be described below with reference to the drawings. Note that the embodiments shown below are merely examples, and the tire of the present invention is not limited to the embodiments described below.

[0054] Figure 1 is an enlarged cross-sectional view showing a portion of the tire tread. In Figure 1, the vertical direction is the tire radius direction, the horizontal direction is the tire width direction, and the direction perpendicular to the plane of the paper is the tire circumferential direction.

[0055] As shown in the figure, the tread portion 8 of the tire according to this embodiment comprises a first layer 6 and a second layer 7, the outer surface of the first layer 6 constitutes the tread surface 3, and the second layer 7 is adjacent to the radially inward side of the first layer 6. The first layer 6 typically corresponds to a cap tread. The second layer 7 does not have a typical shape and may be a base tread or an under tread. Furthermore, as long as the objective of the present invention is achieved, there may be one or more additional rubber layers between the second layer 7 and the belt layer. If the tread portion 8 has three or more layers, the cap tread or inner layer (base tread) may be composed of two or more layers. For example, if there are two cap tread layers, the rubber layer located radially inward of the cap tread corresponds to the second layer of the present invention, and if there are two base tread layers, the rubber layer located radially outward of the base tread corresponds to the second layer of the present invention.

[0056] In Figure 1, the deepest part of the groove bottom of the circumferential groove 1 having the deepest groove depth among the multiple circumferential grooves 1 is formed to be located radially inward of the tire beyond the outermost edge of the second layer 7 in the land area 2 adjacent to that circumferential groove. That is, the deepest part of the groove bottom of the circumferential groove 1 having the deepest groove depth among the multiple circumferential grooves 1 is located radially inward of the tire beyond the extension of the outermost edge of the second layer 7 in the land area 2 adjacent to that circumferential groove. Directly below the circumferential groove 1 having the deepest groove depth among the multiple circumferential grooves 1 (radially inward of the tire), there is a recess that is indented radially inward of the tire relative to the outermost edge of the second layer 7 in the land area 2 adjacent to that circumferential groove, and a part of the first layer 6 is formed with a predetermined thickness within the recess of the second layer 7.

[0057] In Figure 1, the groove width of the circumferential groove 1 is constant from the outside to the inside in the radial direction of the tire, but the design is not limited to this configuration and may vary from the outside to the inside in the radial direction of the tire. Also, the groove wall 5 of the circumferential groove extends linearly from the outside to the inside in the radial direction of the tire, but the design is not limited to this configuration and may extend in a curved or stepped shape, for example.

[0058] In this embodiment, the thickness t1 of the first layer 6 is not particularly limited, but from the viewpoint of steering stability performance, it is preferably 0.8 mm or more, more preferably 1.1 mm or more, and even more preferably 1.4 mm or more. On the other hand, from the viewpoint of heat generation, the thickness t1 of the first layer 6 is preferably 6.0 mm or less, more preferably 5.0 mm or less, even more preferably 4.0 mm or less, and particularly preferably 3.0 mm or less.

[0059] In this embodiment, the thickness t2 of the second layer 7 is not particularly limited, but is preferably 1.0 mm or more, more preferably 2.0 mm or more, even more preferably 3.0 mm or more, and particularly preferably 4.0 mm or more. Furthermore, the thickness t2 of the second layer 7 is preferably 10.0 mm or less, more preferably 9.0 mm or less, even more preferably 8.5 mm or less, and particularly preferably 8.0 mm or less.

[0060] The ratio of the thickness t1 of the first layer 6 to the thickness t2 of the second layer 7 (t1 / t2) is preferably greater than 0.10, more preferably greater than 0.12, even more preferably greater than 0.15, even more preferably greater than 0.17, and particularly preferably greater than 0.20. It is believed that setting t1 / t2 within the above range makes it easier to transmit the force generated by friction on the tread surface to the inside of the tire. Furthermore, t1 / t2 is preferably less than 8.0, more preferably less than 6.0, even more preferably less than 4.0, even more preferably less than 2.0, even more preferably less than 1.0, even more preferably less than 0.80, and particularly preferably less than 0.60.

[0061] The ratio of t1 to the groove depth H (mm) at the deepest part of the circumferential groove (t1 / H) is preferably 0.10 or more, more preferably 0.15 or more, even more preferably 0.20 or more, and particularly preferably 0.25 or more. On the other hand, t1 / H is preferably 0.90 or less, more preferably 0.75 or less, even more preferably 0.60 or less, and particularly preferably 0.45 or less. It is believed that setting t1 / H within the above range makes it easier to generate force in the first layer and improves steering stability.

[0062] The 70°C tanδ of the first layer 6 is preferably 0.25 or less, more preferably 0.22 or less, even more preferably 0.19 or less, and particularly preferably 0.16 or less. The 70°C tanδ of the second layer 7 is preferably 0.35 or less, more preferably 0.30 or less, even more preferably 0.28 or less, and particularly preferably 0.25 or less, from the viewpoint of facilitating force transmission into the tire interior. On the other hand, the 70°C tanδ of the first layer 6 and the second layer 7 is preferably 0.02 or more, more preferably 0.04 or more, even more preferably 0.06 or more, and particularly preferably 0.10 or more, from the viewpoint of steering stability performance.

[0063] The 70°C tanδ can be adjusted as appropriate depending on the type and amount of rubber components, fillers, softeners, vulcanizing agents, and vulcanization accelerators described below. For example, increasing the total amount of styrene in the rubber components tends to increase the 70°C tanδ value. Also, increasing the amount of fillers (especially carbon black) or softeners (especially oil) tends to increase the 70°C tanδ value.

[0064] The Tg of the first layer 6 is preferably -30°C or higher, more preferably -28°C or higher, and even more preferably -26°C or higher. By setting the glass transition temperature of the first layer 6 within the above range, it is possible to increase the energy loss corresponding to the frequency of vibrations generated during rolling in normal driving, and thus make it easier to absorb vibrations. The Tg of the second layer 7 is preferably -30°C or higher, more preferably -28°C or higher, and even more preferably -26°C or higher. There are no particular upper limits on the Tg of the first layer 6 and the second layer 7, but it is preferably 20°C or lower, more preferably 15°C or lower, even more preferably 10°C or lower, and particularly preferably 5°C or lower. The Tg of each rubber layer can be appropriately adjusted depending on the type and amount of rubber components described later.

[0065] The Shore hardness (Hs) of the first layer 6 is preferably 80 or less, more preferably 75 or less, and even more preferably 70 or less. Similarly, the Shore hardness (Hs) of the second layer 7 is preferably 80 or less, more preferably 75 or less, and even more preferably 70 or less. By setting the Shore hardness (Hs) of the first layer 6 and the second layer 7 within the above ranges, it is believed that the ability to follow the road surface is not impaired, and reaction force is easily obtained. On the other hand, the Shore hardness (Hs) of the first layer 6 and the second layer 7 is preferably 50 or more, and more preferably 55 or more, from the viewpoint of maintaining the block rigidity of the tire. The rubber hardness of each rubber layer can be appropriately adjusted by the type and amount of rubber components, fillers, softeners, etc., as described later.

[0066] The modulus (M100) of the first layer 6 at 100% stretch is preferably 1.0 MPa or higher, more preferably 1.2 MPa or higher, even more preferably 1.4 MPa or higher, and particularly preferably 1.6 MPa or higher. The modulus of the second layer 7 at 100% stretch is preferably 1.3 MPa or higher, more preferably 1.6 MPa or higher, even more preferably 1.9 MPa or higher, and particularly preferably 2.2 MPa or higher. There is no particular upper limit to the modulus of the first layer 6 and second layer 7 at 100% stretch, but it is usually 4.0 MPa or lower, and preferably 3.5 MPa or lower. In this embodiment, it is preferable that the modulus of the second layer 7 at 100% stretch is greater than that of the first layer 6 at 100% stretch. By making the modulus of the second layer 7 at 100% stretch greater than that of the first layer 6 at 100% stretch, it is possible to generate a larger force in the second layer 7, which is thought to improve steering stability during high-speed driving. The difference between the modulus of the second layer 7 at 100% stretch and the modulus of the first layer 6 at 100% stretch is preferably 0.1 MPa or more, more preferably 0.2 MPa or more, and even more preferably 0.3 MPa or more. The modulus of each rubber layer at 100% stretch can be appropriately adjusted by the type and amount of rubber components, fillers, softeners, etc., as described below.

[0067] The product of the ratio (t1 / t2) of the thickness of the first layer 6 to the thickness t2 (mm) of the second layer 7 and R1 (R1 × (t1 / t2)) is preferably greater than 0.007, more preferably greater than 0.010, even more preferably greater than 0.012, even more preferably greater than 0.014, even more preferably greater than 0.016, and particularly preferably greater than 0.017. By setting R1 × (t1 / t2) within the above range, it is considered possible to ensure frictional force on the tread surface while making it easier to transmit that force to the inside of the tire. Furthermore, R1 × (t1 / t2) is preferably less than 0.045, more preferably less than 0.040, even more preferably less than 0.035, and particularly preferably less than 0.030.

[0068] [Rubber composition] The tread portion according to this embodiment consists of two or more rubber layers, characterized in that the rubber compositions constituting the first and second layers each contain vulcanized rubber particles. Each rubber composition constituting the tread portion can be manufactured using the raw materials described below, according to the ratio of the area of ​​domains derived from vulcanized rubber particles to the total area of ​​the tread cross-section, etc. The rubber compositions according to this embodiment will be described below, and unless otherwise specified, they are applicable to any rubber layer of the tread portion according to this embodiment.

[0069] <Rubber components> The rubber composition according to this embodiment preferably uses diene rubber as the rubber component, and preferably contains at least one selected from the group consisting of isoprene rubber, styrene-butadiene rubber (SBR), and butadiene rubber (BR). These rubber components may be used individually or in combination of two or more. Furthermore, these rubber components may be modified rubbers treated with modifying groups that can interact with fillers such as carbon black or silica, or hydrogenated rubbers in which some of the unsaturated bonds have been hydrogenated. Note that the rubber components according to this embodiment do not contain vulcanized rubber particles, which will be described later.

[0070] The rubber component constituting the first layer preferably contains BR, and more preferably contains BR and isoprene rubber and / or BR. On the other hand, the rubber component constituting the second layer is not particularly limited, but can be, for example, a rubber component containing SBR, a rubber component containing isoprene rubber and BR, or a rubber component containing isoprene rubber and SBR.

[0071] (Isoprene rubber) As isoprene-based rubbers, for example, isoprene rubber (IR) and natural rubber, which are common in the tire industry, can be used. Natural rubber includes not only unmodified natural rubber (NR), but also modified natural rubbers such as epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), deproteinized natural rubber (DPNR), high-purity natural rubber, and grafted natural rubber. These isoprene-based rubbers may be used individually or in combination of two or more types.

[0072] NR is not particularly limited and can be any tire that is common in the tire industry, such as SIR20, RSS#3, and TSR20.

[0073] From the viewpoint of the effects of the present invention, the content of isoprene-based rubber in the rubber component constituting the first layer is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, and particularly preferably 20% by mass or less. Furthermore, there is no particular lower limit to the content, but for example, it can be 1% by mass or more, 3% by mass or more, 5% by mass or more, or 10% by mass or more.

[0074] From the viewpoint of the effects of the present invention, the content of isoprene-based rubber in the rubber component constituting the second layer is preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 70% by mass or less, and particularly preferably 60% by mass or less. Furthermore, there is no particular lower limit to the content, but for example, it can be 1% by mass or more, 3% by mass or more, 5% by mass or more, or 10% by mass or more.

[0075] (SBR) There are no particular limitations on SBR, and examples include unmodified solution-polymerized SBR (S-SBR), emulsion-polymerized SBR (E-SBR), and modified SBRs thereof (modified S-SBR, modified E-SBR). Modified SBRs include SBRs with modified terminals and / or main chains, and modified SBRs coupled with tin, silicon compounds, etc. (condensates, those with branched structures, etc.). Among these, S-SBR and modified SBRs are preferred. Furthermore, hydrogenated versions of these SBRs (hydrogenated SBRs) can also be used. These SBRs may be used individually or in combination of two or more types.

[0076] As for SBR, either stretchable SBR or non-stretchable SBR can be used. When stretchable SBR is used, the amount of stretchable SBR, that is, the amount of stretchable softener contained in the SBR, is preferably 10 to 50 parts by mass per 100 parts by mass of rubber solids in the SBR.

[0077] The SBRs listed above may be used individually or in combination of two or more. Examples of the SBRs listed above include those commercially available from companies such as Sumitomo Chemical Co., Ltd., JSR Corporation, Asahi Kasei Corporation, Nippon Zeon Corporation, and ZS Elastomer Co., Ltd.

[0078] The styrene content of SBR can be appropriately selected so that the total amount of styrene in the rubber component satisfies the range described below, but is preferably 40% by mass or less, more preferably 36% by mass or less, even more preferably 32% by mass or less, and particularly preferably 28% by mass or less. Furthermore, the styrene content of SBR is preferably 5% by mass or more, more preferably 7% by mass or more, even more preferably 10% by mass or more, even more preferably 13% by mass or more, and particularly preferably 16% by mass or more. The styrene content of SBR is measured by the measurement method described above.

[0079] The vinyl content of SBR is preferably 10 mol% or more, more preferably 15 mol% or more, and even more preferably 20 mol% or more, from the viewpoint of ensuring reactivity with silica and abrasion resistance. Furthermore, the vinyl content of SBR is preferably 70 mol% or less, more preferably 65 mol% or less, and even more preferably 60 mol% or less, from the viewpoint of elongation at break and abrasion resistance. In this specification, the vinyl content of SBR is measured by the measurement method described above.

[0080] From the viewpoint of handling stability performance, the weight-average molecular weight (Mw) of SBR is preferably 200,000 or more, and more preferably 250,000 or more. Furthermore, from the viewpoint of crosslinking uniformity, the weight-average molecular weight is preferably 2,000,000 or less, more preferably 1,800,000 or less, and even more preferably 1,500,000 or less. In this specification, the weight-average molecular weight of SBR is measured by the measurement method described above.

[0081] The SBR content in the rubber component constituting the first layer can be appropriately selected so that the total amount of styrene in the rubber component satisfies the range described below, but is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, and particularly preferably 30% by mass or more. On the other hand, the content is preferably 80% by mass or less, more preferably 75% by mass or less, even more preferably 70% by mass or less, and particularly preferably 65% ​​by mass or less.

[0082] From the viewpoint of the effects of the present invention, the SBR content in the rubber component constituting the second layer is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and particularly preferably 20% by mass or less. On the other hand, there is no particular upper limit to the content.

[0083] (BR) BR is not particularly limited, and for example, BR with a cis content of less than 50% by mass (low-cis BR), BR with a cis content of 90% by mass or more (high-cis BR), rare-earth butadiene rubber synthesized using a rare-earth element catalyst (rare-earth BR), BR containing syndiotactic polybutadiene crystals (SPB-containing BR), modified BR (high-cis modified BR, low-cis modified BR), etc., which are common in the tire industry, can be used. These BRs may be used individually or in combination of two or more types.

[0084] High-sis BR can be commercially available from companies such as Nippon Zeon Co., Ltd., Ube Industries, Ltd., and JSR Corporation. Including high-sis BR can improve low-temperature properties and wear resistance. The cis content of high-sis BR is preferably 95% by mass or more, more preferably 96% by mass or more, and even more preferably 97% by mass or more. In this specification, the cis content is measured by the measurement method described above.

[0085] As the modified BR, a modified butadiene rubber (modified BR) is preferably used in which the terminal and / or main chain is modified with a functional group containing at least one element selected from the group consisting of silicon, nitrogen, and oxygen.

[0086] Other modified BRs include those obtained by polymerizing 1,3-butadiene with a lithium initiator and then adding a tin compound, and in which the ends of the modified BR molecule are linked by a tin-carbon bond (tin-modified BR). Furthermore, the modified BR may be either unhydrogenated or hydrogenated.

[0087] From the viewpoint of wear resistance, the weight-average molecular weight (Mw) of BR is preferably 300,000 or more, more preferably 350,000 or more, and even more preferably 400,000 or more. From the viewpoint of crosslinking uniformity, it is preferably 2,000,000 or less, and more preferably 1,000,000 or less. The weight-average molecular weight of BR is measured by the measurement method described above.

[0088] From the viewpoint of the effects of the present invention, the BR content in the rubber component constituting the first layer is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, and particularly preferably 30% by mass or more. On the other hand, the content is preferably 80% by mass or less, more preferably 75% by mass or less, even more preferably 70% by mass or less, and particularly preferably 65% ​​by mass or less.

[0089] From the viewpoint of the effects of the present invention, the BR content in the rubber component constituting the second layer is preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 70% by mass or less, and particularly preferably 60% by mass or less. Furthermore, there is no particular lower limit to the content, but for example, it can be 1% by mass or more, 3% by mass or more, 5% by mass or more, or 10% by mass or more.

[0090] The total content of BR and SBR in the rubber component constituting the first layer is preferably 60% by mass or more, more preferably 65% ​​by mass or more, even more preferably 70% by mass or more, even more preferably 75% by mass or more, and particularly preferably 80% by mass or more. On the other hand, there is no particular upper limit on the total content of BR and SBR in the rubber component constituting the first layer.

[0091] (Other rubber components) The rubber component according to this embodiment may contain rubber components other than the isoprene-based rubber, SBR, and BR mentioned above. Other rubber components that can be crosslinked are commonly used in the tire industry and include isoprene-based rubbers such as styrene-isoprene rubber (SIR), styrene-isoprene butadiene rubber (SIBR), chloroprene rubber (CR), and acrylonitrile butadiene rubber (NBR), diene-based rubbers other than SBR and BR; and rubber components other than diene-based rubbers such as butyl rubber (IIR), halogenated butyl rubber, ethylene propylene rubber, polynorbornene rubber, silicone rubber, polyethylene chloride rubber, fluororubber (FKM), acrylic rubber (ACM), and hydrin rubber. These other rubber components may be used individually or in combination of two or more. The rubber component according to this embodiment preferably contains 80% by mass or more of diene-based rubber, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 98% by mass or more, and may consist only of diene-based rubber. In addition to the rubber components mentioned above, the product may or may not contain known thermoplastic elastomers.

[0092] From the viewpoint of the effects of the present invention, the total amount of styrene in the rubber component constituting the first layer is preferably 4% by mass or more, more preferably 7% by mass or more, and even more preferably 10% by mass or more. Furthermore, from the viewpoint of the effects of the present invention, the total amount of styrene in the rubber component constituting the first layer is preferably 25% by mass or less, more preferably 20% by mass or less, even more preferably 18% by mass or less, and particularly preferably 16% by mass or less.

[0093] From the viewpoint of the effects of the present invention, the total amount of styrene in the rubber component constituting the second layer is preferably 35% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less. On the other hand, there is no particular lower limit to the total amount of styrene in the rubber component constituting the second layer, but it can be, for example, 1% by mass or more, 2% by mass or more, 3% by mass or more, or 4% by mass or more.

[0094] <Vulcanized rubber particles> "Vulcanized rubber particles" refer to a rubber composition obtained by a process separate from the rubber matrix constituting the rubber composition according to this embodiment, and which forms domains that can be distinguished from the rubber matrix constituting the rubber composition according to this embodiment by image analysis such as SEM. Generally, these are recycled rubber and powdered rubber as described later, but are not limited to these, and depending on the application, a rubber composition different from the rubber composition according to this embodiment may be prepared and crushed to obtain them. Vulcanized rubber particles may be used alone, or two or more may be used in combination.

[0095] "Recycled rubber" refers to recycled rubber from used automobile tires, tubes, and other rubber products as defined in JIS K 6313:2012, as well as rubber having equivalent properties. Powdered rubber is excluded. Furthermore, recycled rubber undergoes desulfurization treatment.

[0096] The recycled rubber can be any type of recycled rubber, such as recycled tube rubber, recycled tire rubber, or other types, and multiple types can be combined. Among these, recycled tire rubber is preferred.

[0097] Recycled rubber can be obtained by known manufacturing methods, including the most common pan process (oil process), as well as methods using a Banbury mixer and twin-screw reaction extruder, microwave methods, ultrasonic methods, and electron beam irradiation methods, but any method of production is acceptable. Commercially available recycled rubber may also be used. One specific example of manufacturing recycled rubber is to put vulcanized rubber powder into a closed mixer or extruder, heat it to 100-250°C, and treat it for 5-50 minutes while applying mechanical shear force to desulfurize it. Commercially available recycled rubber can be used, for example, those manufactured and sold by companies such as Muraoka Rubber Industries Co., Ltd. and Asahi Recycled Rubber Co., Ltd.

[0098] Recycled rubber may be used alone or in combination of two or more types.

[0099] "Powdered rubber" refers to vulcanized powdered rubber recycled from waste rubber products. From the perspective of environmental considerations and cost, it is preferable to use crushed tread rubber from used tires, spew burrs from harvesting, etc. (crushed waste tire material) as the raw material for powdered rubber. Furthermore, there are no particular limitations on the type of waste rubber, but examples include diene-based rubbers such as NR, SBR, BR, and IR. In addition, powdered rubber can be made from 30-mesh or 40-mesh passed Tyler Mesh products. Powdered rubber may be used alone or in combination of two or more types.

[0100] The average particle size of the rubber powder is preferably 70 μm or more, and more preferably 100 μm or more. The average particle size is preferably 1 mm or less, and more preferably 750 μm or less. In this specification, the average particle size of the rubber powder is the mass-based average particle size calculated from the particle size distribution measured in accordance with JIS Z 8815:1994.

[0101] Powdered rubber can be used, for example, those manufactured and sold by companies such as Muraoka Rubber Industries Co., Ltd., Asahi Recycled Rubber Co., Ltd., and Lehigh Technologies.

[0102] The rubber component in the vulcanized rubber particles preferably has a natural rubber content of 40% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more. When the natural rubber content is within the above range, excellent elongation at break tends to be obtained. The natural rubber content is determined by measurement using pyrolysis gas chromatography (PyGC).

[0103] In a cross-section parallel to the tread surface of the first layer, the ratio R1 of the area of ​​domains derived from vulcanized rubber particles to the total area of ​​the cross-section is, from the viewpoint of the effects of the present invention, greater than 0.05, preferably greater than 0.06, more preferably 0.07 or higher, even more preferably 0.08 or higher, and particularly preferably 0.09 or higher. Furthermore, from the viewpoint of the effects of the present invention, R1 is 0.50 or less, preferably 0.40 or less, more preferably 0.35 or less, even more preferably 0.30 or less, even more preferably 0.25 or less, even more preferably 0.20 or less, and particularly preferably 0.15 or less.

[0104] In a cross-section parallel to the tread surface of the second layer, the ratio R2 of the area of ​​domains derived from vulcanized rubber particles to the total area of ​​the cross-section is, from the viewpoint of the effects of the present invention, 0.05 or more, preferably 0.06 or more, and more preferably 0.07 or more. Furthermore, from the viewpoint of the effects of the present invention, R2 is less than 0.50, preferably less than 0.40, more preferably less than 0.35, even more preferably less than 0.30, even more preferably less than 0.25, even more preferably less than 0.20, and particularly preferably less than 0.15.

[0105] R1 and R2 can be adjusted as appropriate by the amount of vulcanized rubber particles blended and the average particle size. For example, increasing the amount of vulcanized rubber particles blended with the rubber component tends to increase the values ​​of R1 and R2.

[0106] The content of vulcanized rubber particles relative to 100 parts by mass of rubber component in the rubber composition constituting the first layer can be appropriately selected so that R1 satisfies the above range, but is preferably 5 parts by mass or more, more preferably 6 parts by mass or more, even more preferably 7 parts by mass or more, and particularly preferably 8 parts by mass or more. On the other hand, the content is preferably 70 parts by mass or less, more preferably 60 parts by mass or less, even more preferably 50 parts by mass or less, even more preferably 40 parts by mass or less, and particularly preferably 30 parts by mass or less.

[0107] The content of vulcanized rubber particles relative to 100 parts by mass of rubber component in the rubber composition constituting the second layer can be appropriately selected so that R2 satisfies the above range, but is preferably 5 parts by mass or more, more preferably 6 parts by mass or more, and still preferably 7 parts by mass or more. On the other hand, the content is preferably 70 parts by mass or less, more preferably 60 parts by mass or less, still preferably 50 parts by mass or less, still preferably 40 parts by mass or less, still still preferably 30 parts by mass or less, and particularly preferably 20 parts by mass or less.

[0108] <Filler> The rubber composition according to this embodiment preferably uses a filler containing carbon black and / or silica. The rubber composition constituting the first layer preferably contains silica as a filler, and more preferably contains carbon black and silica. The rubber composition constituting the second layer preferably contains carbon black as a filler.

[0109] (Carbon Black) The carbon black used is not particularly limited; for example, common types used in the tire industry such as GPF, FEF, HAF, ISAF, and SAF can be used. In addition to carbon black produced by burning common mineral oil, carbon black made from biomass materials such as lignin may also be used. These carbon blacks may be used individually or in combination of two or more types.

[0110] The nitrogen adsorption specific surface area (N2SA) of carbon black is 10 m² from the perspective of reinforcing properties. 2 Preferably 30m / g or more. 2 More preferably 50m 2 A value of 200m or more is even more preferable. Furthermore, from the viewpoint of low fuel consumption and processability, 200m 2 Preferably less than / g, 150m 2 / g or less is more preferable, 120m 2 A value of less than / g is even more preferable. The N2SA of carbon black is measured by the measurement method described above.

[0111] From the perspective of wear resistance performance and wet grip performance, the content of carbon black with respect to 100 parts by mass of the rubber component of the rubber composition constituting the first layer is preferably 1 part by mass or more, more preferably 5 parts by mass or more, still more preferably 10 parts by mass or more, and particularly preferably 15 parts by mass or more. Also, from the perspective of low fuel consumption performance, it is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, still more preferably 40 parts by mass or less, and particularly preferably 30 parts by mass or less.

[0112] From the perspective of wear resistance performance, the content of carbon black with respect to 100 parts by mass of the rubber component of the rubber composition constituting the second layer is preferably 20 parts by mass or more, more preferably 25 parts by mass or more, and still more preferably 30 parts by mass or more. Also, the content is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, and still more preferably 60 parts by mass or less.

[0113] (Silica) The silica is not particularly limited, and for example, silica prepared by a dry method (anhydrous silica), silica prepared by a wet method (hydrous silica), etc., which are common in the tire industry, can be used. Among them, hydrous silica prepared by a wet method is preferred because of its large number of silanol groups. In addition to the above silica, silica made from biomass materials such as rice husks may be appropriately used as raw materials. These silicas may be used alone or in combination of two or more.

[0114] From the perspective of low fuel consumption performance and wear resistance performance, the nitrogen adsorption specific surface area (N2SA) of silica is preferably 120 m 2 / g or more, more preferably 150 m 2 / g or more, and still more preferably 170 m 2 / g or more. Also, from the perspective of low fuel consumption performance and processability, it is preferably 350 m 2 / g or less, more preferably 300 m 2 / g or less, and still more preferably 250 m 2 / g or less. Note that the N2SA of silica is measured by the above measurement method.

[0115] From the viewpoint of wet grip performance, the silica content of the first layer rubber composition per 100 parts by mass of rubber component is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, even more preferably 20 parts by mass or more, and particularly preferably 25 parts by mass or more. From the viewpoint of abrasion resistance performance, it is preferably 70 parts by mass or less, more preferably 60 parts by mass or less, even more preferably 50 parts by mass or less, and particularly preferably 45 parts by mass or less. The silica content of the second layer rubber composition per 100 parts by mass of rubber component is not particularly limited.

[0116] From the viewpoint of wear resistance, the total content of silica and carbon black per 100 parts by mass of rubber component in the rubber composition constituting the first layer is preferably 20 parts by mass or more, more preferably 30 parts by mass or more, even more preferably 35 parts by mass or more, and particularly preferably 40 parts by mass or more. Furthermore, the content is preferably 80 parts by mass or less, more preferably 70 parts by mass or less, even more preferably 65 parts by mass or less, even more preferably 60 parts by mass or less, and particularly preferably 55 parts by mass or less. By setting the total content of silica and carbon black in the rubber composition constituting the first layer within the above range, it is thought that the hardening of the entire rubber layer by silica and carbon black is suppressed, a distribution of hardness in the microscopic region can be created, and domains formed within the rubber layer can be made to grip the road surface more easily.

[0117] The rubber composition constituting the first layer preferably contains more silica per 100 parts by mass of rubber components than carbon black, from the viewpoint of balancing fuel efficiency, wet grip performance, and wear resistance. The ratio of silica to the total content of silica and carbon black in the rubber composition constituting the first layer is preferably 55% by mass or more, and more preferably 60% by mass or more. The ratio of silica to carbon black in the rubber composition constituting the second layer is not particularly limited.

[0118] (Other fillers) In addition to carbon black and silica, other fillers may be used. Such fillers are not particularly limited and may include, for example, aluminum hydroxide, alumina (aluminum oxide), calcium carbonate, magnesium sulfate, talc, clay, biochar, and other materials commonly used in the tire industry. These other fillers may be used individually or in combination of two or more.

[0119] (Silane coupling agent) Silica is preferably used in combination with a silane coupling agent. The silane coupling agent is not particularly limited, and any silane coupling agent that has conventionally been used in combination with silica in the tire industry can be used, for example: mercapto-based silane coupling agents such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, and 2-mercaptoethyltriethoxysilane; sulfide-based silane coupling agents such as bis(3-triethoxysilylpropyl) disulfide and bis(3-triethoxysilylpropyl) tetrasulfide; 3-octanoylthio-1-propyltriethoxysilane, 3-hexanoylthio-1-propyltriethoxysilane, and 3-octanoylthio-1-propyltrimethoxysilane. Examples include thioester silane coupling agents such as lan; vinyl silane coupling agents such as vinyltriethoxysilane and vinyltrimethoxysilane; amino silane coupling agents such as 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, and 3-(2-aminoethyl)aminopropyltriethoxysilane; glycidoxy silane coupling agents such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro silane coupling agents such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; and chloro silane coupling agents such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. In particular, it is preferable to contain a sulfide silane coupling agent and / or a mercapto silane coupling agent. As silane coupling agents, for example, those commercially available from Evonik Degussa, Momentive, etc., can be used. These silane coupling agents may be used individually or in combination of two or more.

[0120] From the viewpoint of improving silica dispersibility, the content of the silane coupling agent per 100 parts by mass of silica is preferably 1.0 part by mass or more, more preferably 3.0 parts by mass or more, and even more preferably 5.0 parts by mass or more. Furthermore, from the viewpoint of cost and processability, it is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 12 parts by mass or less.

[0121] <Other compounding agents> In addition to the components mentioned above, the rubber composition according to this embodiment may appropriately contain compounding agents commonly used in the tire industry, such as softeners, waxes, processing aids, stearic acid, zinc oxide, antioxidants, vulcanizing agents, and vulcanization accelerators.

[0122] (Softener) The rubber composition according to this embodiment preferably contains a softening agent. Examples of softening agents include resin components, oils, liquid rubber, ester-based plasticizers, and the like.

[0123] The resin components are not particularly limited, but examples include hydrocarbon resins commonly used in the tire industry, such as petroleum resins, terpene resins, rosin resins, and phenolic resins.

[0124] Examples of petroleum resins include C5-based petroleum resins, aromatic petroleum resins, and C5C9-based petroleum resins.

[0125] In this specification, "C5-based petroleum resin" refers to a resin obtained by polymerizing a C5 fraction, and may be hydrogenated or modified. Examples of C5 fractions include petroleum fractions with 4 to 5 carbon atoms, such as cyclopentadiene, pentene, pentadiene, and isoprene. Dicyclopentadiene resin (DCPD resin) is preferably used as the C5-based petroleum resin.

[0126] In this specification, "aromatic petroleum resin" refers to a resin obtained by polymerizing a C9 fraction, and may be hydrogenated or modified. Examples of C9 fractions include petroleum fractions with 8 to 10 carbon atoms, such as vinyltoluene, alkylstyrene, indene, and methylindene. Specific examples of aromatic petroleum resins that are preferably used include coumarone indene resin, coumarone resin, indene resin, and aromatic vinyl resins. As aromatic vinyl resins, homopolymers of α-methylstyrene or styrene, or copolymers of α-methylstyrene and styrene are preferred, and copolymers of α-methylstyrene and styrene are more preferred, for reasons of being economical, easy to process, and having excellent heat generation properties. As aromatic vinyl resins, commercially available products from companies such as Kraton, Eastman Chemical, etc., can be used.

[0127] In this specification, "C5C9 petroleum resin" refers to a resin obtained by copolymerizing the C5 fraction and the C9 fraction, and may be hydrogenated or modified. Examples of the C5 fraction and C9 fraction include the petroleum fractions mentioned above. As C5C9 petroleum resin, commercially available products from companies such as Tosoh Corporation and LUHUA can be used.

[0128] Examples of terpene resins include polyterpene resins consisting of at least one terpene compound selected from α-pinene, β-pinene, limonene, dipentene, etc.; aromatically modified terpene resins made from the terpene compound and an aromatic compound; terpene-phenol resins made from the terpene compound and a phenolic compound; and these terpene resins that have been hydrogenated (hydrogenated terpene resins). Examples of aromatic compounds used as raw materials for aromatically modified terpene resins include styrene, α-methylstyrene, vinyltoluene, and divinyltoluene. Examples of phenolic compounds used as raw materials for terpene-phenol resins include phenol, bisphenol A, cresol, and xylenol.

[0129] Among terpene resins, hydrogenated terpene resins are preferred, and hydrogenated polyterpene resins are even more preferred because they allow for near 100% hydrogenation and also offer superior durability. Hydrogenation of terpene resins can be carried out by known methods, and in this embodiment, commercially available hydrogenated terpene resins can also be used.

[0130] Rosin-based resins are not particularly limited, but examples include natural resin rosin and rosin-modified resins obtained by hydrogenation, disproportionation, dimerization, esterification, etc.

[0131] Phenolic resins are not particularly limited, but examples include phenol-formaldehyde resin, alkylphenol-formaldehyde resin, alkylphenol-acetylene resin, and oil-modified phenol-formaldehyde resin.

[0132] The softening point of the resin component (preferably a terpene-based resin) is preferably 60°C or higher, and more preferably 65°C or higher, from the viewpoint of wet grip performance. Furthermore, from the viewpoint of processability and improved dispersibility between the rubber component and filler, it is preferably 150°C or lower, more preferably 140°C or lower, and even more preferably 130°C or lower. The softening point of the resin component is measured by the measurement method described above. In addition, the glass transition temperature of the resin component usable in this embodiment is approximately 40 to 50°C lower than the softening point.

[0133] When a resin component (preferably a terpene resin) is included, its content per 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more. Furthermore, the content of the resin component is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, even more preferably 40 parts by mass or less, and particularly preferably 30 parts by mass or less.

[0134] Examples of oils include process oils, vegetable oils, and animal fats. Examples of process oils include paraffinic process oils (mineral oil), naphthenic process oils, and aromatic process oils. Specific examples of process oils include MES (Mild Extract Solvated), DAE (Distillate Aromatic Extract), TDAE (Treated Distillate Aromatic Extract), TRAE (Treated Residual Aromatic Extract), and RAE (Residual Aromatic Extract). Furthermore, for environmental reasons, process oils with a low content of polycyclic aromatic compounds (PCA) can be used. Examples of low-PCA process oils include MES, TDAE, and heavy naphthenic oils. Additionally, from a life cycle assessment perspective, refined waste oil from rubber mixers and engines, or waste cooking oil used in restaurants, may be used.

[0135] When oil is included, the content of oil per 100 parts by mass of rubber component is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, from the viewpoint of processability. Furthermore, from the viewpoint of wear resistance, it is preferably 80 parts by mass or less, more preferably 60 parts by mass or less, and even more preferably 40 parts by mass or less.

[0136] Liquid rubber is not particularly limited as long as it is a polymer that is in a liquid state at room temperature (25°C), but examples include liquid butadiene rubber (liquid BR), liquid styrene butadiene rubber (liquid SBR), liquid isoprene rubber (liquid IR), liquid styrene isoprene rubber (liquid SIR), liquid farnesene rubber, etc. These liquid rubbers may be used individually or in combination of two or more.

[0137] When liquid rubber is included, its content per 100 parts by mass of rubber component is preferably 1 part by mass or more, more preferably 2 parts by mass or more, even more preferably 3 parts by mass or more, and particularly preferably 5 parts by mass or more. Furthermore, the liquid rubber content is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 20 parts by mass or less.

[0138] Examples of ester-based plasticizers include dibutyl adipate (DBA), diisobutyl adipate (DIBA), dioctyl adipate (DOA), di-2-ethylhexyl azelaate (DOZ), dibutyl sebacate (DBS), diisononyl adipate (DINA), diethyl phthalate (DEP), dioctyl phthalate (DOP), diundecyl phthalate (DUP), dibutyl phthalate (DBP), dioctyl sebacate (DOS), tributyl phosphate (TBP), trioctyl phosphate (TOP), triethyl phosphate (TEP), trimethyl phosphate (TMP), thymidine triphosphate (TTP), tricresyl phosphate (TCP), and trixylenyl phosphate (TXP). These ester-based plasticizers may be used individually or in combination of two or more.

[0139] When an ester-based plasticizer is included, its content per 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 2 parts by mass or more, even more preferably 3 parts by mass or more, and particularly preferably 5 parts by mass or more. Furthermore, the content of the ester-based plasticizer is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 15 parts by mass or less.

[0140] When a softening agent is included, the content per 100 parts by mass of the rubber component (total amount if multiple softening agents are used in combination) is preferably 1 part by mass or more, more preferably 3 parts by mass or more, even more preferably 5 parts by mass or more, and particularly preferably 7 parts by mass or more. Furthermore, the content of the softening agent is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, even more preferably 60 parts by mass or less, and particularly preferably 40 parts by mass or less.

[0141] The wax is not particularly limited, and any wax commonly used in the tire industry can be suitably used. Examples include petroleum-based waxes, mineral-based waxes, and synthetic waxes, with petroleum-based waxes being preferred. Examples of petroleum-based waxes include paraffin wax, microcrystalline wax, and selected special waxes thereof, with paraffin wax being preferred. The wax according to this embodiment does not contain stearic acid. The wax can be commercially available from companies such as Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., and Paramelt Co., Ltd. These waxes may be used individually or in combination of two or more types.

[0142] When wax is included, the amount of wax per 100 parts by mass of rubber component is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, and even more preferably 1.5 parts by mass or more, from the viewpoint of weather resistance of the rubber. Furthermore, from the viewpoint of preventing whitening of the tire due to bloom, it is preferably 10 parts by mass or less, and more preferably 5.0 parts by mass or less.

[0143] Examples of processing aids include fatty acid metal salts, fatty acid amides, amide esters, silica surfactants, fatty acid esters, mixtures of fatty acid metal salts and amide esters, and mixtures of fatty acid metal salts and fatty acid amides. These processing aids may be used individually or in combination of two or more. Examples of processing aids that can be used are those commercially available from companies such as Schill+Seilacher and Performance Additives.

[0144] When processing aids are included, the content per 100 parts by mass of rubber components is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, and even more preferably 1.5 parts by mass or more, from the viewpoint of exhibiting an effect of improving processability. Furthermore, from the viewpoint of abrasion resistance and fracture strength, it is preferably 10 parts by mass or less, and more preferably 8.0 parts by mass or less.

[0145] While not particularly limited, examples of anti-aging agents include amine-based, quinoline-based, quinone-based, phenol-based, and imidazole-based compounds, as well as metal carbamate salts. Phenylenediamine-based anti-aging agents such as N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, N,N'-diphenyl-p-phenylenediamine, N,N'-di-2-naphthyl-p-phenylenediamine, and N-cyclohexyl-N'-phenyl-p-phenylenediamine are preferred, as are quinoline-based anti-aging agents such as 2,2,4-trimethyl-1,2-dihydroquinoline polymer and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline. These anti-aging agents may be used individually or in combination of two or more.

[0146] When an anti-aging agent is included, the content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, and even more preferably 1.5 parts by mass or more, from the viewpoint of the rubber's resistance to ozone cracking. Furthermore, from the viewpoint of wear resistance and wet grip performance, it is preferably 10 parts by mass or less, and more preferably 5.0 parts by mass or less.

[0147] When stearic acid is included, its content per 100 parts by mass of rubber component is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, and even more preferably 1.5 parts by mass or more, from the viewpoint of processability. Furthermore, from the viewpoint of vulcanization rate, it is preferably 10 parts by mass or less, and more preferably 5.0 parts by mass or less.

[0148] When zinc oxide is included, its content per 100 parts by mass of rubber component is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, and even more preferably 1.5 parts by mass or more, from the viewpoint of processability. Furthermore, from the viewpoint of wear resistance, it is preferably 10 parts by mass or less, and more preferably 5.0 parts by mass or less.

[0149] Sulfur is preferably used as a vulcanizing agent. Suitable sulfur varieties include powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur.

[0150] When sulfur is included as a vulcanizing agent, the amount of sulfur per 100 parts by mass of rubber component is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.5 parts by mass or more, from the viewpoint of ensuring a sufficient vulcanization reaction. Furthermore, from the viewpoint of preventing deterioration, it is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, even more preferably 3.0 parts by mass or less, and particularly preferably 2.5 parts by mass or less. When oil-containing sulfur is used as the vulcanizing agent, the amount of vulcanizing agent is the total amount of pure sulfur contained in the oil-containing sulfur.

[0151] Examples of vulcanizing agents other than sulfur include alkylphenol-sulfur chloride condensates, 1,6-hexamethylene-dithiosulfate sodium dihydrate, and 1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane. These non-sulfur vulcanizing agents can be purchased commercially from companies such as Taoka Chemical Industries, Ltd., Lanxess Corporation, and Flexis.

[0152] Examples of vulcanization accelerators include sulfenamide-based vulcanization accelerators, thiazole-based vulcanization accelerators, thiram-based vulcanization accelerators, guanidine-based vulcanization accelerators, dithiocarbamate-based vulcanization accelerators, and caprolactam disulfide. These vulcanization accelerators may be used individually or in combination of two or more. Among these, one or more vulcanization accelerators selected from the group consisting of sulfenamide-based vulcanization accelerators, thiazole-based vulcanization accelerators, and guanidine-based vulcanization accelerators are preferred because they more favorably produce the desired effect.

[0153] Examples of sulfenamide-based vulcanization accelerators include N-tert-butyl-2-benzothiazolyl sulfenamide (TBBS), N-cyclohexyl-2-benzothiazolyl sulfenamide (CBS), and N,N-dicyclohexyl-2-benzothiazolyl sulfenamide (DCBS). Among these, TBBS and CBS are preferred.

[0154] Examples of thiazole-based vulcanization accelerators include 2-mercaptobenzothiazole (MBT) or its salts, di-2-benzothiazolyl disulfide (MBTS), 2-(2,4-dinitrophenyl)mercaptobenzothiazole, and 2-(2,6-diethyl-4-morpholinothio)benzothiazole. Among these, MBTS and MBT are preferred.

[0155] Examples of guanidine-based vulcanization accelerators include 1,3-diphenylguanidine (DPG), 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, di-o-tolylguanidine salts of dicatecholborate, 1,3-di-o-cumenylguanidine, 1,3-di-o-biphenylguanidine, and 1,3-di-o-cumenyl-2-propionylguanidine. Among these, DPG is preferred.

[0156] When a vulcanization accelerator is included, the content per 100 parts by mass of the rubber component (total amount if multiple vulcanization accelerators are used in combination) is preferably 1.0 part by mass or more, more preferably 2.0 parts by mass or more, and even more preferably 2.5 parts by mass or more. Furthermore, the content is preferably 8.0 parts by mass or less, more preferably 7.0 parts by mass or less, and even more preferably 6.0 parts by mass or less. By keeping the content of the vulcanization accelerator within the above range, it tends to be possible to ensure fracture strength and elongation.

[0157] [Manufacturing of rubber compositions and tires] The rubber composition according to this embodiment can be manufactured by known methods. For example, it can be manufactured by kneading each of the above components using a rubber kneading device such as an open roll or a closed kneader (Banbury mixer, kneader, etc.).

[0158] The mixing process includes, for example, a base mixing process in which compounding agents and additives other than the vulcanizing agent and vulcanization accelerator are mixed, and a final mixing (F mixing) process in which the vulcanizing agent and vulcanization accelerator are added to the mixture obtained in the base mixing process and mixed. Furthermore, the base mixing process can be divided into multiple processes as desired.

[0159] There are no particular limitations on the mixing conditions, but for example, in the base mixing process, mixing is performed at a discharge temperature of 150-170°C for 3-10 minutes, and in the final mixing process, mixing is performed at 70-110°C for 1-5 minutes. There are no particular limitations on the vulcanization conditions, but for example, vulcanization is performed at 150-200°C for 10-30 minutes.

[0160] A tire having a tread including a first layer 6 and a second layer 7 can be manufactured by conventional methods using the corresponding rubber compositions. Specifically, the unvulcanized rubber compositions corresponding to each rubber layer obtained by the above method are extruded in an extruder equipped with a die of a predetermined shape to match the shape of each rubber layer, bonded together with other tire components on a tire molding machine, and molded in conventional methods to form an unvulcanized tire. This unvulcanized tire is then heated and pressurized in a vulcanizer to manufacture the tire. The vulcanization conditions are not particularly limited, and for example, a method of vulcanization at 150 to 200°C for 10 to 30 minutes can be used.

[0161] [Tire Uses] The tire according to this embodiment can be suitably used for passenger car tires, truck and bus tires, motorcycle tires, and racing tires, and is particularly preferred for passenger car tires. A passenger car tire is a tire intended to be mounted on a four-wheeled vehicle and has a maximum load capacity of 1000 kg or less. Here, maximum load capacity refers to the maximum load capacity specified for each tire in the standards system, including the standard on which the tire is based. For example, in the case of JATMA, it refers to the "maximum load capacity" based on the load index (LI), in the case of ETRTO it refers to "LOAD CAPACITY", and in the case of TRA it refers to the "maximum value" listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES". Refer to JATMA, ETRTO, and TRA in that order, and if there is an applicable size at the time of reference, follow that standard. In addition, the tire according to this embodiment can be used for all-season tires, summer tires, and winter tires such as studless tires. [Examples]

[0162] The following examples (case studies) are shown as preferred for implementation, but the scope of the present invention is not limited to these examples. Using the various chemicals shown below, we examined tires having the first and second layers of the tread obtained according to the formulations in Tables 1 and 2, and the results calculated based on the evaluation method below are shown in Tables 3, 4, and 5.

[0163] <Manufacturing of rubber compositions and tires> The various chemicals used in the examples and comparative examples are summarized below. NR:TSR20 BR: UBEPOL BR(registered trademark) 150B manufactured by Ube Industries, Ltd. (cis content: 97 mol%, Mw: 440,000) SBR: SBR1502 manufactured by JSR Corporation (unmodified E-SBR, styrene content: 23.5% by mass, vinyl content: 16 mol%, Mw: 500,000, non-oil-based) Carbon Black: Cabot Japan Co., Ltd. Show Black N220 (N2SA: 111m 2 / g) Silica: Evonik Degussa's UltraSil VN3 (N2SA: 175m 2 / g) Silane coupling agent: Si266 (bis(3-triethoxysilylpropyl) disulfide) manufactured by Evonik Degussa. Vulcanized rubber particles: Powdered rubber W2-A (30 mesh vulcanized rubber powder) manufactured by Asahi Recycled Rubber Co., Ltd. Oil: Diana Process NH-705 manufactured by Idemitsu Kosan Co., Ltd. Zinc oxide: Zinc oxide No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Anti-aging agent 1: Nocrack 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Anti-aging agent 2: Nocrack FR (2,2,4-trimethyl-1,2-dihydroquinoline polymer) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Stearic acid: Beads of stearic acid manufactured by NOF Corporation Wax: Ozoace 0355 from Nippon Seiro Co., Ltd. Sulfur: Powdered sulfur manufactured by Tsurumi Chemical Industries Co., Ltd. (5% oil-containing powdered sulfur) Vulcanization accelerator 1: Noxellar D (1,3-diphenylguanidine (DPG)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator 2: Noxellar CZ (N-cyclohexyl-2-benzothiazolyl sulfenamide (CBS)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0164] (Examples and Comparative Examples) According to the formulations shown in Tables 1 and 2, the chemicals other than sulfur and vulcanization accelerator were mixed in a 1.7 L sealed Banbury mixer for 1 to 10 minutes until the discharge temperature reached 150 to 160°C to obtain a mixture. Next, sulfur and vulcanization accelerator were added to the mixture using a twin-screw open roll mixer and mixed for 4 minutes until the temperature reached 105°C to obtain an unvulcanized rubber composition. Using this unvulcanized rubber composition, it was molded to match the shape of the first and second layers of the tread, and bonded together with other tire components to produce an unvulcanized tire. The tire was then vulcanized at 170°C to obtain the test tires described in Tables 3, 4, and 5.

[0165] <Measurement of Domain Size and Elastic Modulus> Each vulcanized rubber test piece after vulcanization is cut out from the first and second layers of the tread part with a length of 20 mm × width of 30 mm × thickness of 2 mm so that the tire circumferential direction is the long side and the tire radial direction is the thickness direction. The rubber test piece is placed in a scanning electron microscope (ThermoFishershasei Teneo) so that the surface parallel to the tread surface becomes the observation cross-section, and imaged at an acceleration voltage of 15 kV to obtain an electron microscope image with a magnification of 50 times. Then, in the range of 2.54 mm × 1.69 mm of the obtained image, the area of the domain derived from the vulcanized rubber particles is calculated, and the ratio occupied with respect to the area of the entire cut surface is calculated. This is performed for 3 fields of view for each sample, and R1 and R2 are obtained from the average value.

[0166] <Measurement of tanδ and Glass Transition Temperature (Tg)> Regarding each vulcanized rubber test piece prepared by cutting out from the first and second layers inside the tread part of each test tire with a length of 20 mm × width of 4 mm × thickness of 1 mm so that the tire circumferential direction is the long side and the tire radial direction is the thickness direction, using a dynamic viscoelasticity measuring device (Implex series manufactured by GABO), measure 70°C tanδ under the conditions of a temperature of 70°C, a frequency of 10 Hz, an initial strain of 10%, a dynamic strain of ±1%, and an elongation mode. Further, measure the temperature distribution curve of tanδ from -60 to 40°C under the conditions of a frequency of 10 Hz, an initial strain of 1%, an amplitude of ±0.1%, and a heating rate of 3°C / min, and take the temperature (tanδ peak temperature) corresponding to the largest tanδ value in the obtained temperature distribution curve as the glass transition temperature (Tg).

[0167] <Measurement of Rubber Hardness (Hs)> Regarding each vulcanized rubber test piece prepared by cutting out from inside each rubber layer of the tread part of each test tire so that the tire radial direction is the thickness direction, in accordance with JIS K6253-3:2012, using a durometer type A, measure the shore hardness (Hs) of each rubber test piece at a temperature of 23°C.

[0168] <Tensile Test> For each test tire, a dumbbell-shaped No. 7 test specimen, 1 mm thick, is cut from the first and second layers of the tread, such that the tire circumferential direction is the tensile direction and the tire radial direction is the thickness direction. Tensile tests are performed in accordance with JIS K 6251:2017 at a 23°C atmosphere and a tensile speed of 3.3 mm / second, and the modulus (M100) (MPa) at 100% elongation is measured.

[0169] <Handling Stability Performance> Each test tire is mounted on the four wheels of a 2000cc front-wheel-drive passenger car, and the vehicle is driven on a dry asphalt test course. The handling characteristics are evaluated based on the feeling of straight driving, lane changes, and acceleration / deceleration while driving at 100 km / h by a test driver. The evaluation is given as an integer value from 1 to 5 points, with higher scores indicating better handling characteristics. The total scores of 20 test drivers are calculated. The total scores of the control tires (Comparative Example 1 in Table 3, Comparative Example 11 in Table 4, and Comparative Example 21 in Table 5) are converted to a baseline value (100), and the evaluation results of each test tire are indexed and displayed in proportion to the total score.

[0170] [Table 1]

[0171] [Table 2]

[0172] [Table 3]

[0173] [Table 4]

[0174] [Table 5]

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

[0176] [1] A tire having a tread portion, wherein the tread portion comprises a first layer constituting a tread surface and a second layer adjacent to the radially inward side of the first layer, and the first layer and the second layer are each composed of a rubber composition containing a rubber component and vulcanized rubber particles, wherein in a cross-section parallel to the tread surface of the first layer, the ratio R1 of the area of ​​domains derived from vulcanized rubber particles to the total area of ​​the cross-section is greater than 0.05 and less than or equal to 0.50, and in a cross-section parallel to the tread surface of the second layer, the ratio R2 of the area of ​​domains derived from vulcanized rubber particles to the total area of ​​the cross-section is 0.05 or more and less than 0.50, and R1 is greater than R2. [2] The tire according to [1] above, wherein the ratio (t1 / t2) of the thickness of the first layer to the thickness t2 (mm) of the second layer is greater than 0.15. [3] The tire according to [1] or [2] above, wherein the tanδ (70°C tanδ) of the second layer at 70°C is 0.02 or more and 0.25 or less. [4] A tire according to any of [1] to [3] above, wherein the product of the ratio (t1 / t2) of the thickness of the first layer to the thickness t2 (mm) of the second layer and R1 (R1 × (t1 / t2)) is greater than 0.015. [5] The tire according to any one of [1] to [4] above, wherein the rubber component constituting the above layer contains styrene-butadiene rubber. [6] The tire according to any one of [1] to [5] above, wherein the total amount of styrene in the rubber component constituting the first layer is 10% by mass or more and 20% by mass or less. [7] The tire according to any one of [1] to [6] above, wherein the total content of butadiene rubber and styrene-butadiene rubber in the rubber component constituting the above layer is 75% by mass or more. [8] The tire according to any one of [1] to [7] above, wherein the total content of silica and carbon black in the rubber composition constituting the first layer is 60 parts by mass or less per 100 parts by mass of rubber component. [9] The tire according to any of [1] to [8] above, wherein the glass transition temperature of the first layer is -30°C or higher.

[10] The tire according to any of [1] to [9] above, wherein the Shore hardness (Hs) of the second layer is 50 or more and 80 or less.

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

[10] above, wherein the modulus of the second layer when stretched to 100% is greater than the modulus of the first layer when stretched to 100%.

[12] The tire according to any of [1] to

[11] above, wherein the modulus of the second layer when stretched to 100% is 2.2 MPa or more.

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

[12] above, wherein the tread portion has circumferential grooves that extend continuously in the circumferential direction of the tire, and the ratio of t1 to the groove depth H of the deepest part of the circumferential groove (t1 / H) is 0.10 to 0.90. [Explanation of symbols]

[0177] 1 Circumferential groove 2 Land 3. Tread surface 5. Trench wall 6 First layer 7 Second layer 8 Tread section H Circumferential groove groove bottom depth CL Tire Equatorial Plane

Claims

1. A tire having a tread portion, The tread portion comprises a first layer that constitutes the tread surface and a second layer adjacent to the first layer on the radially inward side of the tire. The first layer and the second layer are each composed of a rubber composition containing a rubber component and vulcanized rubber particles, In the aforementioned cross-section parallel to the tread surface, the ratio R of the area of ​​domains derived from vulcanized rubber particles to the total area of ​​the cross-section. 1 The value is greater than 0.05 and less than or equal to 0.

50. In the cross-section parallel to the tread surface of the second layer, the ratio R of the area of ​​domains derived from vulcanized rubber particles to the total area of ​​the cross-section. 2 is 0.05 or more and less than 0.50, and R 1 R 2 Larger tires.

2. The tire according to claim 1, wherein the ratio (t1 / t2) of the thickness of the first layer to the thickness t2 (mm) of the second layer is greater than 0.

15.

3. The tire according to claim 1 or 2, wherein the tanδ (70°C tanδ) of the second layer at 70°C is 0.02 or more and 0.25 or less.

4. The ratio of the thickness of the first layer t1 (mm) to the thickness t2 (mm) of the second layer (t1 / t2) and R 1 The product of (R 1 The tire according to claim 1 or 2, wherein ×(t1 / t2)) is greater than 0.

015.

5. The tire according to claim 1 or 2, wherein the rubber component constituting the above layer contains styrene-butadiene rubber.

6. The tire according to claim 1 or 2, wherein the total amount of styrene in the rubber component constituting the above layer is 10% by mass or more and 20% by mass or less.

7. The tire according to claim 1 or 2, wherein the total content of butadiene rubber and styrene-butadiene rubber in the rubber component constituting the above layer is 75% by mass or more.

8. The tire according to claim 1 or 2, wherein the total content of silica and carbon black in the rubber composition constituting the first layer is 60 parts by mass or less per 100 parts by mass of rubber component.

9. The tire according to claim 1 or 2, wherein the glass transition temperature of the first layer is -30°C or higher.

10. The tire according to claim 1 or 2, wherein the Shore hardness (Hs) of the second layer is 50 or more and 80 or less.

11. The tire according to claim 1 or 2, wherein the modulus of the second layer when stretched to 100% is greater than the modulus of the first layer when stretched to 100%.

12. The tire according to claim 1 or 2, wherein the modulus of the second layer when fully stretched is 2.2 MPa or more.

13. The tread portion has circumferential grooves that extend continuously in the circumferential direction of the tire, The tire according to claim 1 or 2, wherein the ratio of t1 to the groove depth H at the deepest part of the circumferential groove (t1 / H) is 0.10 to 0.90.

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