tire

Abstract

To provide a tire capable of maintaining wet grip performance even after the tire has worn out.SOLUTION: A tire has a tread including at least a first layer forming a tread surface and a second layer adjacent to the radial direction inner side of the first layer. The first layer and the second layer are each formed of a rubber composition containing a rubber component and plasticizers. A rubber composition composing the rubber composition forming the first layer contains 3.0 pts.mass or more of a plasticizer A, 1.0 pts.mass or more of a plasticizer B, and 1.0 pts.mass or more of a plasticizer C, based on 100 pts.mass of the rubber component. The plasticizer A has a glass transition point of - 40°C or lower and a weight-average molecular weight of less than 1000. The plasticizer B has a glass transition point of 30°C or higher. The plasticizer C has a glass transition point of higher than - 70°C and lower than 30°C, and a weight-average molecular weight of 1000 or more. The content of the plasticizer A based on 100 pts.mass of the rubber component in the rubber composition forming the second layer is more than the content of the plasticizer A based on 100 pts.mass of the rubber component in the rubber composition forming the first layer. A difference (AE2-AE1) between an amount AE2 of acetone extract from the rubber composition forming the second layer and an amount AE1 of acetone extract from the rubber composition forming the first layer is 3.0 mass% or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to tires. [Background technology]

[0002] Patent Document 1 discloses a tire having a tread portion including a cap rubber layer that comes into contact with the road surface and a base rubber layer that is arranged radially inward of the cap rubber. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-162242 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the case of a tire with a tread having multiple rubber layers as described above, the cap rubber layer that comes into contact with the road surface hardens over time as the tire is driven, and this hardening causes a problem of reduced wet grip performance. Here, since the hardness of the rubber varies greatly depending on the thickness of the rubber and the roughness of the surface, it is desirable to develop a method for predicting and controlling the change in hardness of the cap rubber layer over time.

[0005] An object of the present disclosure is to provide a tire that can maintain wet grip performance even after wear. [Means for solving the problem]

[0006] As a result of extensive research, it was discovered that in a tire having a tread including at least a first layer constituting the tread surface and a second layer adjacent to the first layer radially inward, changes in rubber hardness over time are caused by diffusion of a plasticizer into the adjacent rubber layer, and that the degree of plasticizer diffusion can be determined by changes in the amount of acetone extractables over time. Further extensive research led to the discovery that the above-mentioned problem can be solved by blending plasticizers with different diffusion rates into the rubber compositions constituting the first and second layers, respectively, and by setting the difference between the amount of acetone extractables of the rubber composition constituting the second layer and the rubber composition constituting the first layer within a predetermined range.

[0007] That is, the present disclosure relates to a tire having a tread including at least a first layer constituting a tread surface and a second layer adjacent to the first layer on the radially inner side, wherein the first layer and the second layer are constituted by a rubber composition containing a rubber component and a plasticizer, and the rubber composition constituting the first layer contains 3.0 parts by mass or more of plasticizer A, 1.0 part by mass or more of plasticizer B, and 1.0 part by mass or more of plasticizer C per 100 parts by mass of the rubber component, and the plasticizer A has a glass transition point of -40°C or less and a weight average molecular weight of less than 1000, and the plasticizer B has a glass transition point of 30°C or higher, the plasticizer C has a glass transition point of more than -70°C and less than 30°C and a weight average molecular weight of 1,000 or higher, the content of the plasticizer A per 100 parts by mass of the rubber component of the rubber composition constituting the second layer is greater than the content of the plasticizer A per 100 parts by mass of the rubber component of the rubber composition constituting the first layer, and the difference (AE2-AE1) between the acetone extractable amount AE2 of the rubber composition constituting the second layer and the acetone extractable amount AE1 of the rubber composition constituting the first layer is 3.0% by mass or higher. [Effects of the Invention]

[0008] According to the present disclosure, a tire is provided that can maintain wet grip performance even after wear. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view of a portion of a tread of a tire according to one embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0010] A tire according to one embodiment of the present disclosure has a tread including at least a first layer constituting a tread surface and a second layer adjacent to the first layer on the radially inner side thereof, wherein the first layer and the second layer are constituted by a rubber composition containing a rubber component and a plasticizer, and the rubber composition constituting the first layer contains 3.0 parts by mass or more of plasticizer A, 1.0 part by mass or more of plasticizer B, and 1.0 part by mass or more of plasticizer C per 100 parts by mass of the rubber component, and the plasticizer A has a glass transition point of -40°C or less and a weight average molecular weight of less than 1,000. the plasticizer B has a glass transition point of 30°C or higher, and the plasticizer C has a glass transition point of more than -70°C and less than 30°C and a weight average molecular weight of 1,000 or higher, the content of the plasticizer A per 100 parts by mass of the rubber component of the rubber composition constituting the second layer is greater than the content of the plasticizer A per 100 parts by mass of the rubber component of the rubber composition constituting the first layer, and the difference (AE2 - AE1) between the acetone extractable amount AE2 of the rubber composition constituting the second layer and the acetone extractable amount AE1 of the rubber composition constituting the first layer is 3.0% by mass or higher.

[0011] While not intending to be bound by theory, the mechanism by which the tire of the present disclosure suppresses changes in tread hardness over time is thought to be as follows: Specifically, by blending plasticizers with different diffusion rates into the rubber compositions constituting the first and second layers, and by setting the difference between the acetone extractable amount of the rubber composition constituting the second layer and the acetone extractable amount of the rubber composition constituting the first layer within a predetermined range, it is possible to appropriately control the diffusion of the plasticizer into the adjacent rubber layer. This is thought to achieve the remarkable effect of appropriately controlling changes in hardness of the tread surface rubber layer due to tire use and maintaining wet grip performance for a long period of time, even after the second layer is exposed.

[0012] In the tire of the present disclosure, the rubber composition constituting the first layer preferably has a tan δ at 30° C. of less than 0.20, and more preferably less than 0.15.

[0013] When the tan δ of the rubber composition constituting the first layer is less than the above value, heat generation during running is reduced, and it is believed that hardening of the first layer over time is suppressed.

[0014] The difference (AE2-AE1) between the acetone extractable amount AE2 of the rubber composition constituting the second layer and the acetone extractable amount AE1 of the rubber composition constituting the first layer is preferably 20% by mass or less.

[0015] It is believed that by setting AE2-AE1 within the above range, it is possible to prevent the plasticizer from diffusing too quickly from the second layer to the first layer.

[0016] The plasticizer A is preferably at least one of an oil and an ester-based plasticizer, the plasticizer B is preferably a resin component, and the plasticizer C is preferably a liquid polymer.

[0017] When the first and second layers are bonded together and subjected to dynamic stimulation for 120 hours under conditions of a dynamic stress of 0.45 MPa, a frequency of 50 Hz, and a temperature of 80°C, the rate of change in the complex modulus at 0°C (0°C E*) of the rubber composition constituting the first layer before and after the dynamic stimulation is preferably more than -20% and less than 20%, and the rate of change in tan δ at 0°C (0°C tan δ) is preferably more than -20% and less than 20%. By controlling the rate of change in 0°C E* and 0°C tan δ of the rubber composition constituting the first layer before and after the dynamic stimulation to more than -20% and less than 20%, it is believed that hardening of the first layer over time with use can be further suppressed, and wet grip performance can be maintained until the end of the wear stage.

[0018] In view of the effects of the present disclosure, the 0°C E* of the rubber composition constituting the first layer is preferably 4.0 MPa or more.

[0019] In view of the effects of the present disclosure, the 0° C. tan δ of the rubber composition constituting the first layer is preferably 0.10 or more.

[0020] The glass transition temperature of the rubber composition constituting the first layer is preferably −40° C. or higher.

[0021] When the glass transition temperature of the rubber composition constituting the first layer is -40°C or higher, the loss tangent tanδ tends to be higher in the temperature range higher than Tg compared to when the glass transition temperature is lower than -40°C, and it is believed that the effects of the present disclosure are more easily exhibited.

[0022] The rubber composition constituting the first layer preferably has an elongation at break measured in accordance with JIS K 6251:2017 of 200% or more.

[0023] By making the elongation at break of the rubber composition constituting the first layer 200% or more, it is believed that the surface condition is more likely to be maintained smoother when the tire wears, reducing the reduction in the actual contact area and, as a result, reducing the deterioration of wet grip performance after tire wear.

[0024] <Definition> A "genuine rim" is a rim that is determined for each tire by the standard system that includes the standard on which the tire is based. For JATMA, it is a "standard rim," for TRA, it is a "design rim," and for ETRTO, it is a "measuring rim."

[0025] "Normal internal pressure" is the air pressure specified for each tire by each standard in the standard system, including the standard on which the tire is based. For JATMA, it is the "maximum air pressure," for TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES," and for ETRTO, it is the "INFLATION PRESSURE."

[0026] "Normal condition" refers to a condition in which a tire is mounted on a normal rim, inflated to a normal internal pressure, and no load is applied. In this specification, unless otherwise specified, the dimensions of each part of the tire (t1, t2, etc.) are measured in the normal condition.

[0027] A "plasticizer" is a material that imparts plasticity to a rubber component and is extracted from the rubber composition using acetone. Plasticizers include liquid plasticizers (plasticizers that are liquid at 25°C) and solid plasticizers (plasticizers that are solid at 25°C).

[0028] "Plasticizer diffusion rate" refers to the rate at which a plasticizer diffuses from one rubber layer to the adjacent rubber layer. The diffusion rate of different plasticizers can be evaluated using the following method. Specifically, a vulcanized rubber sheet containing a certain plasticizer as a first layer is laminated with a vulcanized rubber sheet containing no plasticizer but with the same formulation and manufacturing method as a second layer, but without the plasticizer. The vulcanized rubber sheet is left standing at 80°C for 480 hours while a 500g load is applied from the first layer to the second layer in the thickness direction. After that, the vulcanized rubber sheet is separated into the first and second layers, and the weight of the second layer is measured. This procedure is repeated for several different plasticizers, and the initial weight of the second layer before the load is applied is indexed, with 100 representing the index. A higher index indicates a greater amount of plasticizer from the first layer diffuses into the second layer, indicating a faster diffusion rate of the plasticizer.

[0029] "Dynamic stimulation" refers to repeatedly applying dynamic stress in a direction perpendicular to the bonded surface of the first and second layers. Applying such dynamic stimulation to the bonded rubber layers promotes the diffusion of plasticizer from the first layer to the second layer. The magnitude of the dynamic stress is set as described below so that the rubber composition constituting the first and second layers is not destroyed, i.e., so that the dynamic stress can be repeatedly applied. In this disclosure, various physical properties (acetone extractables, loss tangent tanδ, complex modulus E*, etc.) of the rubber composition constituting the first layer are measured before and after the dynamic stimulation.

[0030] "Oil content" includes the amount of oil contained in oil-extended rubber.

[0031] <Measurement method> The "acetone extractable amount" can be calculated according to JIS K 6229:2015 by immersing each vulcanized rubber test piece in acetone for 72 hours to extract the soluble components, measuring the mass of each test piece before and after extraction, and then using the following formula. The sample for measuring the acetone extractable amount is a vulcanized rubber composition having a length of 1 mm, a width of 1 mm, and a thickness of 1 mm. When preparing the sample by cutting it out from a tire, the sample is cut out from the tread portion of the tire so that the long side is in the tire circumferential direction and the thickness direction is in the tire radial direction. (Amount of acetone extracted (mass%)) = {(mass of rubber test piece before extraction - mass of rubber test piece after extraction) / (mass of rubber test piece before extraction)} × 100

[0032] The "difference in acetone extractable amount" can be determined from the difference in acetone extractable amount between the rubber compositions constituting adjacent rubber layers. For example, when the acetone extractable amount of the rubber composition constituting the first layer is AE1 (mass%) and the acetone extractable amount of the rubber composition constituting the second layer is AE2 (mass%), the difference can be determined by AE2 - AE1.

[0033] The "dynamic test" is performed by applying dynamic stress to the bonded first and second layers in a direction perpendicular to the bonded surfaces for 120 hours using a dynamic viscoelasticity measuring device (e.g., an Iplexer series manufactured by GABO) under conditions of a dynamic stress of 0.45 MPa, a frequency of 50 Hz, and a temperature of 80°C. When preparing the sample by cutting it out from the tire, a sample is cut out from the tread portion of the tire, measuring 30 mm in length, 30 mm in width, and 10 mm in thickness, including the interface between the first and second layers, so that the thickness of the first and second layers is the same. The long side of the sample is in the tire circumferential direction, and the thickness direction of the sample is in the tire radial direction.

[0034] The "change rate (%) in the amount of acetone extractables before and after applying dynamic stimulation" can be calculated by measuring the amount of acetone extractables before and after applying dynamic stimulation to each vulcanized rubber test piece and using the following formula. (Change in acetone extractables before and after dynamic stimulation (%)) = {(acetone extractable amount after dynamic stimulation) / (acetone extractable amount before dynamic stimulation) × 100}-100

[0035] "Tan δ at 30°C (30°C tan δ)" is the loss tangent measured using a dynamic viscoelasticity measuring device (for example, the Iplexer series manufactured by GABO) under conditions of a temperature of 30°C, an initial strain of 5%, a dynamic strain of 1%, and a frequency of 10 Hz. The sample for measuring the loss tangent is a vulcanized rubber composition having a length of 20 mm, a width of 4 mm, and a thickness of 1 mm. When cutting out a sample from a tire, the sample is cut out from the tread portion of the tire so that the long side is in the tire circumferential direction and the thickness direction is in the tire radial direction.

[0036] "Tan δ at 0°C (0°C tan δ)" is the loss tangent measured using a dynamic viscoelasticity measuring device (for example, the Iplexer series manufactured by GABO) under the conditions of a temperature of 0°C, an initial strain of 10%, a dynamic strain of 2.5%, and a frequency of 10 Hz. The sample for this measurement is prepared in the same manner as for 30°C tan δ.

[0037] The "change rate (%) of 0°C tan δ before and after applying dynamic stimulation" can be calculated by measuring 0°C tan δ before and after applying dynamic stimulation to each vulcanized rubber test piece and using the following formula. (Change in 0℃ tanδ before and after dynamic stimulation (%)) = {(0℃ tanδ after dynamic stimulation) / (0℃ tanδ before dynamic stimulation) × 100}-100

[0038] The "complex modulus E* at 0°C (0°C E*)" is the complex modulus measured using a dynamic viscoelasticity measuring device (e.g., the Iplexer series manufactured by GABO) under the conditions of a temperature of 0°C, an initial strain of 10%, a dynamic strain of 2.5%, and a frequency of 10 Hz. The sample for this measurement is prepared in the same manner as for the 30°C tan δ.

[0039] The "rate of change in 0°C E* before and after applying dynamic stimulation" can be calculated by measuring the 0°C E* before and after applying dynamic stimulation to each vulcanized rubber test piece and using the following formula. (Percentage change in 0℃E* before and after dynamic stimulation (%)) = {(0℃E* after dynamic stimulation) / (0℃E* before dynamic stimulation) × 100}-100

[0040] The "Tg of the rubber composition" is determined by measuring the temperature distribution curve of tan δ using a dynamic viscoelasticity measuring device (e.g., an Iplexer series manufactured by GABO) under conditions of a frequency of 10 Hz, an initial strain of 10%, an amplitude of ±0.5%, and a heating rate of 2°C / min, and is determined as the temperature corresponding to the largest tan δ value in the obtained temperature distribution curve (tan δ peak temperature). The measurement sample is prepared in the same manner as for 30°C tan δ.

[0041] "Elongation at break (EB)" was measured by cutting a 1 mm thick No. 7 dumbbell-shaped test piece from inside the rubber layer of the tread portion of each test tire so that the tensile direction was the tire circumferential direction, and conducting a tensile test in accordance with JIS K 6251:2017 at a temperature of 23°C and a tensile speed of 3.3 mm / sec. The thickness direction of the sample was the tire radial direction.

[0042] "Styrene content" is 1 It is a value calculated by H-NMR measurement, and is applied to, for example, rubber components having repeating units derived from styrene, such as SBR. "Vinyl content (amount of 1,2-bonded butadiene units)" is a value calculated by infrared absorption spectroscopy in accordance with JIS K 6239-2:2017, and is applied to, for example, rubber components having repeating units derived from butadiene, such as SBR and BR. "Cis content (amount of cis-1,4-bonded butadiene units)" is a value calculated by infrared absorption spectroscopy in accordance with JIS K 6239-2:2017, and is applied to, for example, rubber components having repeating units derived from butadiene, such as BR.

[0043] The "softening point of the resin component" can be defined as the temperature at which the ball drops when the softening point specified in JIS K 6220-1:2001 is measured using a ring and ball softening point tester.

[0044] The "weight average molecular weight (Mw)" can be determined by converting the measured value into standard polystyrene equivalents using gel permeation chromatography (GPC) (for example, a GPC-8000 series manufactured by Tosoh Corporation, a differential refractometer as the detector, and a TSKGEL SUPERMALTIPORE HZ-M column manufactured by Tosoh Corporation). This applies to, for example, SBR, BR, plasticizers, etc.

[0045] "N2SA of carbon black" is measured in accordance with JIS K 6217-2:2017. "N2SA of silica" is measured by the BET method in accordance with ASTM D3037-93.

[0046] The "Tg of the plasticizer" is a value measured by differential scanning calorimetry (DSC) at a temperature rise rate of 10°C / min in accordance with JIS K 7121:2012.

[0047] A procedure for manufacturing a tire according to an embodiment of the present disclosure will be described in detail below. However, the following description is merely an example for explaining the present disclosure, and is not intended to limit the technical scope of the present disclosure to the scope of the description.

[0048] [tire] Fig. 1 is a cross-sectional view showing a portion of the tread of a tire according to the present disclosure, in which an enlarged portion of the tread surface where no grooves are formed is shown.

[0049] As shown in the figure, the tread portion of the tire of the present disclosure includes a first layer 2 and a second layer 3, with the outer surface of the first layer 2 forming a tread surface 1 and the second layer 3 adjacent to the radially inner side of the first layer 2. The first layer 2 typically corresponds to a cap tread. The second layer 3 typically corresponds to a base tread or undertread. Furthermore, as long as the objectives of the present disclosure are achieved, one or more rubber layers (third layer 4 in FIG. 1 ) may be further included between the second layer 3 and the belt layer.

[0050] In Figure 1, the double arrow t1 indicates the thickness of the first layer 2, and the double arrow t2 indicates the thickness of the second layer 3. In Figure 1, an arbitrary point on the tread surface where no grooves are formed is indicated by the symbol P. The line indicated by the symbol N is a line (normal) that passes through point P and is perpendicular to the tangent plane at point P. In this specification, the thicknesses t1 and t2 are measured along the normal N drawn from point P on the tread surface at a position where no grooves exist in the cross section of Figure 1.

[0051] In the present disclosure, the thickness t1 of the first layer 2 is not particularly limited, but from the viewpoint of wet grip performance, it is preferably 1.5 mm or more, more preferably 2.0 mm or more, and even more preferably 2.5 mm or more. On the other hand, from the viewpoint of heat buildup, the thickness t1 of the first layer 2 is preferably 10.0 mm or less, more preferably 9.0 mm or less, and even more preferably 8.0 mm or less.

[0052] In the present disclosure, the thickness t2 of the second layer 3 is not particularly limited, but is preferably 1.0 mm or more, more preferably 1.5 mm or more, and even more preferably 2.0 mm or more. The thickness t2 of the second layer 3 is preferably 10.0 mm or less, more preferably 9.0 mm or less, and even more preferably 8.0 mm or less.

[0053] The ratio (t2 / t1) of the thickness t2 of the second layer 3 to the thickness t1 of the first layer 2 is preferably 0.1 or more, more preferably 0.2 or more, from the viewpoint of fuel economy, while it is preferably 1.1 or less, more preferably 0.9 or less, even more preferably 0.7 or less, and particularly preferably 0.5 or less, from the viewpoint of wet grip performance.

[0054] <Acetone extraction amount> In the present disclosure, the diffusion of plasticizer from the second layer to the first layer can be measured by the acetone extractables. The acetone extractables are measured by the above-described measurement method. The acetone extractables AE2 of the second layer 3 before application of the dynamic stimulus are preferably 8.0% by mass or more, more preferably 11.0% by mass or more, even more preferably 14.0% by mass or more, and particularly preferably 17.0% by mass or more. The acetone extractables AE2 of the second layer 3 before application of the dynamic stimulus are preferably 45.0% by mass or less, more preferably 40.0% by mass or less, even more preferably 35.0% by mass or less, and particularly preferably 30.0% by mass or less. The acetone extractables AE1 of the first layer 2 before application of the dynamic stimulus are preferably 5.0% by mass or more, more preferably 8.0% by mass or more, even more preferably 11.0% by mass or more, and particularly preferably 14.0% by mass or more. The acetone extractable amount AE1 of the first layer 2 before the dynamic stimulus is applied is preferably 42.0 mass % or less, more preferably 37.0 mass % or less, even more preferably 32.0 mass % or less, and particularly preferably 27.0 mass % or less.

[0055] <Difference in acetone extraction amount> In the present disclosure, the difference (AE2-AE1) between the acetone extractable amount AE2 of the rubber composition constituting the second layer and the acetone extractable amount AE1 of the rubber composition constituting the first layer is 3.0% by mass or more, preferably 3.3% by mass or more, more preferably 3.6% by mass or more, and even more preferably 3.9% by mass or more. Furthermore, AE2-AE1 is preferably 20% by mass or less, more preferably 17% by mass or less, even more preferably 14% by mass or less, and particularly preferably 11% by mass or less. By setting AE2-AE1 within the above range, it is believed that diffusion of plasticizer into adjacent rubber layers can be appropriately controlled, and that changes in hardness of the tread surface rubber layer due to tire use can be appropriately controlled.

[0056] <<Change in acetone extractable amount>> When the dynamic stimulus is applied to the first layer and the second layer in a bonded state, the rate of change in the amount of acetone extractable from the rubber composition constituting the first layer before and after the dynamic stimulus is preferably more than -30% and less than 30%, more preferably more than -20% and less than 20%, even more preferably more than -10% and less than 18%, and particularly preferably more than -5% and less than 16%, from the viewpoint of maintaining wet grip performance until the end of wear.

[0057] <30℃ tanδ> The 30°C tan δ of the rubber composition constituting the first layer 2 is preferably less than 0.20, more preferably less than 0.18, even more preferably less than 0.16, even more preferably less than 0.15, and particularly preferably less than 0.14, from the viewpoints of reducing heat generation during running and preventing hardening of the first layer over time. The 30°C tan δ of the rubber composition constituting the second layer 3 is preferably less than 0.40, more preferably less than 0.30, and even more preferably less than 0.20. The 30°C tan δ of the rubber compositions constituting the first layer 2 and the second layer 3 is preferably 0.05 or greater, more preferably 0.06 or greater, even more preferably 0.08 or greater, and particularly preferably 0.09 or greater. The 30°C tan δ of the rubber composition constituting the first layer 2 is preferably greater than the 30°C tan δ of the rubber composition constituting the second layer 3. The difference between the 30°C tan δ of the rubber composition constituting the first layer 2 and the 30°C tan δ of the rubber composition constituting the second layer 3 is preferably 0.01 or more, more preferably 0.02 or more, even more preferably 0.03 or more, and particularly preferably 0.04 or more. The 30°C tan δ of the rubber composition can be appropriately adjusted by the types and amounts of rubber components, plasticizers, etc.

[0058] <0℃ tan δ change rate (%)> When the dynamic stimulus is applied to the first and second layers in a bonded state, the rate of change in 0°C tan δ of the rubber composition constituting the first layer before and after the dynamic stimulus is preferably more than -20% and less than 20%, more preferably more than -15% and less than 15%, even more preferably more than -10% and less than 10%, even more preferably more than -8% and less than 8%, and particularly preferably more than -6% and less than 6%, from the viewpoint of maintaining wet grip performance until the end of wear.

[0059] <0℃E* change rate> When the dynamic stimulus is applied to the first and second layers in a bonded state, the rate of change in 0°C E* of the rubber composition constituting the first layer before and after the dynamic stimulus is preferably more than -25% and less than 25%, more preferably more than -20% and less than 20%, and even more preferably more than -18% and less than 10%, from the viewpoint of maintaining wet grip performance until the end of wear.

[0060] <0℃ tanδ> From the viewpoint of wet grip performance, the 0°C tan δ of the rubber composition constituting the first layer 2 is preferably 0.10 or greater, more preferably 0.12 or greater, even more preferably 0.14 or greater, and particularly preferably 0.16 or greater. The 0°C tan δ of the rubber composition constituting the second layer 3 is preferably 0.07 or greater, more preferably 0.09 or greater, even more preferably 0.11 or greater, and particularly preferably 0.13 or greater. From the viewpoint of fuel economy, the 0°C tan δ of the rubber compositions constituting the first layer 2 and the second layer 3 is preferably 0.80 or less, more preferably 0.60 or less, even more preferably 0.50 or less, and particularly preferably 0.40 or less. The 0°C tan δ of the rubber composition constituting the first layer 2 is preferably greater than the 0°C tan δ of the rubber composition constituting the second layer 3. The difference between the 0°C tan δ of the rubber composition constituting the first layer 2 and the 0°C tan δ of the rubber composition constituting the second layer 3 is preferably 0.01 or more, more preferably 0.02 or more, even more preferably 0.03 or more, and particularly preferably 0.04 or more. The 0°C tan δ of the rubber composition can be appropriately adjusted by the types and amounts of rubber components, plasticizers, etc.

[0061] <0℃E*> From the viewpoint of wet grip performance, the 0°C E* of the rubber composition constituting the first layer 2 is preferably 5.0 MPa or more, more preferably 6.0 MPa or more, even more preferably 7.0 MPa or more, and particularly preferably 8.0 MPa or more. The 0°C E* of the rubber composition constituting the second layer 3 is preferably 4.0 MPa or more, more preferably 5.0 MPa or more, even more preferably 6.0 MPa or more, and particularly preferably 7.0 MPa or more. On the other hand, from the viewpoint of road conformity, the 0°C E* of the rubber compositions constituting the first layer 2 and the second layer 3 is preferably 100 MPa or less, more preferably 70 MPa or less, even more preferably 40 MPa or less, and particularly preferably 30 MPa or less. The 0°C E* value of the rubber composition constituting the first layer 2 is preferably greater than the 0°C E* value of the rubber composition constituting the second layer 3. The difference between the 0°C E* of the rubber composition constituting the first layer 2 and the 0°C E* of the rubber composition constituting the second layer 3 is preferably 0.5 MPa or more, more preferably 1.0 MPa or more, and even more preferably 1.5 MPa or more. By setting the 0°C E* in the above range, it is thought that the balance between road surface following ability and anchor friction can be improved and the deterioration of wet grip performance after tire wear can be suppressed. The 0°C E* of the rubber composition can be appropriately adjusted by the types and amounts of rubber components, plasticizers, etc.

[0062] <Glass transition temperature (Tg)> From the viewpoint of wet grip performance, the Tg of the rubber composition constituting the first layer 2 is preferably -40°C or higher, more preferably -37°C or higher, even more preferably -34°C or higher, and particularly preferably -31°C or higher. When the Tg is higher than -40°C, the loss tangent (tanδ) tends to be higher in the temperature range above Tg compared to when the Tg is lower than -40°C. The Tg of the rubber composition constituting the second layer 3 is preferably -60°C or higher, more preferably -55°C or higher, even more preferably -50°C or higher, and particularly preferably -45°C or higher. The upper limit of the Tg of the rubber compositions constituting the first layer 2 and the second layer 3 is not particularly limited, but is preferably 20°C or lower, more preferably 10°C or lower, and even more preferably 0°C or lower. The Tg of the rubber composition can be adjusted appropriately by changing the type and amount of rubber components, plasticizers, etc.

[0063] <Elongation at break (EB)> From the viewpoint of abrasion resistance, the EB of the rubber composition constituting the first layer 2 is preferably 200% or more, more preferably 300% or more, even more preferably 400% or more, and particularly preferably 500% or more. The EB of the rubber composition constituting the second layer 3 is preferably 200% or more, more preferably 300% or more, even more preferably 400% or more, and particularly preferably 450% or more. By setting the EB within the above range, it is believed that the surface condition during tire wear is more easily maintained smooth, reducing the reduction in the actual contact area, and as a result, reducing the deterioration of wet grip performance after tire wear. There is no particular upper limit for the EB of the rubber compositions constituting the first layer 2 and the second layer 3. The EB of the rubber composition can be adjusted appropriately by changing the type and amount of rubber components, plasticizers, etc.

[0064] [Rubber composition for tread] The tread portion of the present disclosure comprises at least a first layer 2 constituting the tread surface and a second layer 3 adjacent to the first layer 2 on the radially inward side, and is characterized in that the difference between the acetone extractable amount of the rubber composition constituting the second layer 3 and the acetone extractable amount of the rubber composition constituting the first layer 2 is within a predetermined range. The rubber compositions constituting each layer of the tread portion can be manufactured using the raw materials described below according to the required acetone extractable amount, etc., as described in detail below.

[0065] <Rubber component> The rubber composition according to the present disclosure preferably uses a diene rubber as the rubber component. Examples of diene rubber include isoprene rubber, butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene rubber (SIR), styrene isoprene butadiene rubber (SIBR), chloroprene rubber (CR), and acrylonitrile butadiene rubber (NBR). These rubber components may be used alone or in combination of two or more.

[0066] The content of the diene rubber in 100% by mass of the rubber component is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. The rubber component may also consist solely of the diene rubber.

[0067] The rubber composition according to the present disclosure preferably contains at least one rubber component selected from the group consisting of isoprene-based rubber, styrene-butadiene rubber (SBR), and butadiene rubber (BR). The rubber components constituting the first layer 2 and the second layer 3 preferably contain isoprene-based rubber, more preferably contain isoprene-based rubber and BR, and even more preferably contain isoprene-based rubber, BR, and SBR. The rubber components may consist solely of isoprene-based rubber, BR, and SBR.

[0068] (Isoprene rubber) Examples of isoprene-based rubbers that can be used include those commonly used in the tire industry, such as isoprene rubber (IR) and natural rubber. Natural rubber includes unmodified natural rubber (NR) as well as modified natural rubbers such as epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), deproteinized natural rubber (DPNR), highly purified natural rubber, and grafted natural rubber. These isoprene-based rubbers may be used alone or in combination of two or more.

[0069] The NR is not particularly limited, and those commonly used in the tire industry can be used, such as SIR20, RSS#3, and TSR20.

[0070] When an isoprene-based rubber is contained, the content thereof in 100% by mass of the rubber component 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, from the viewpoint of wet grip performance. When an isoprene-based rubber is contained, the content thereof is not particularly limited to a lower limit, but is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, and particularly preferably 40% by mass or more.

[0071] (SBR) The SBR is not particularly limited, and examples thereof include unmodified solution-polymerized SBR (S-SBR) and emulsion-polymerized SBR (E-SBR), as well as modified SBRs (modified S-SBR, modified E-SBR). Modified SBRs include SBRs whose ends and / or main chains are modified, and modified SBRs (condensates, those having a branched structure, etc.) coupled with tin or silicon compounds. Of these, S-SBR and modified SBR are preferred. Furthermore, hydrogenated products of these SBRs (hydrogenated SBR) can also be used. These SBRs may be used alone or in combination of two or more.

[0072] The SBR may be either oil-extended or non-oil-extended. When oil-extended SBR is used, the amount of oil extension of the SBR, i.e., the content of the oil-extending oil contained in the SBR, is preferably 10 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the rubber solids content of the SBR.

[0073] As the S-SBR that can be used in the present disclosure, commercially available products from JSR Corporation, Sumitomo Chemical Co., Ltd., Ube Industries, Ltd., Asahi Kasei Corporation, ZS Elastomers Co., Ltd., and the like can be used.

[0074] From the viewpoints of wet grip performance and abrasion resistance, the styrene content of SBR is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more. From the viewpoints of temperature dependency of grip performance and blow resistance, the styrene content is preferably 60% by mass or less, more preferably 55% by mass or less, and even more preferably 50% by mass or less. The styrene content of SBR is measured by the above-mentioned measurement method.

[0075] The vinyl content of SBR is preferably 10 mol% or more, more preferably 15 mol% or more, and even more preferably 20 mol% or more, from the viewpoints of ensuring reactivity with silica, wet grip performance, rubber strength, and abrasion resistance. Furthermore, the vinyl content of SBR is preferably 80 mol% or less, more preferably 70 mol% or less, and even more preferably 65 mol% or less, from the viewpoints of preventing an increase in temperature dependency, elongation at break, and abrasion resistance. The vinyl content of SBR is measured by the above-mentioned measurement method.

[0076] From the viewpoint of wet grip performance, the weight average molecular weight (Mw) of SBR is preferably 200,000 or more, more preferably 250,000 or more, and even more preferably 300,000 or more. From the viewpoint of crosslink uniformity, the Mw of SBR is preferably 2,000,000 or less, more preferably 1,800,000 or less, and even more preferably 1,500,000 or less. The Mw of SBR is measured by the above-mentioned measurement method.

[0077] When SBR is contained, the content in 100% by mass of the rubber component is preferably 1% by mass or more, more preferably 5% by mass or more, even more preferably 8% by mass or more, and particularly preferably 9% by mass or more, from the viewpoint of wet grip performance. The content of SBR in the rubber component is preferably 60% by mass or less, more preferably 50% by mass or less, even more preferably 40% by mass or less, and particularly preferably 30% by mass or less.

[0078] (BR) The BR is not particularly limited, and examples include BR with a cis content of less than 50 mol% (low-cis BR), BR with a cis content of 90 mol% or more (high-cis BR), rare earth butadiene rubber (rare earth BR) synthesized using a rare earth catalyst, BR containing syndiotactic polybutadiene crystals (SPB-containing BR), and modified BR (high-cis modified BR, low-cis modified BR), which are commonly used in the tire industry. Modified BRs include BRs modified with functional groups similar to those described above for SBR. These BRs may be used alone or in combination of two or more.

[0079] As the high-cis BR, for example, commercially available products from Zeon Corporation, Ube Industries, Ltd., JSR Corporation, etc. can be used. The inclusion of high-cis BR can improve low-temperature properties and wear resistance. The cis content is preferably 95 mol% or more, more preferably 96 mol% or more, even more preferably 97 mol% or more, and particularly preferably 98 mol% or more.

[0080] The rare earth BR is synthesized using a rare earth catalyst and has a vinyl content of preferably 1.8 mol% or less, more preferably 1.0 mol% or less, and even more preferably 0.8 mol% or less, and a cis content of preferably 95 mol% or more, more preferably 96 mol% or more, even more preferably 97 mol% or more, and particularly preferably 98 mol% or more. Commercially available rare earth BRs, such as those sold by Lanxess K.K., can be used. The vinyl content and cis content of the BR are measured by the above-mentioned methods.

[0081] The SPB-containing BR is not one in which 1,2-syndiotactic polybutadiene crystals are simply dispersed in the BR, but one in which the 1,2-syndiotactic polybutadiene crystals are dispersed after being chemically bonded to the BR. As such SPB-containing BR, commercially available products from Ube Industries, Ltd. and the like can be used.

[0082] As the modified BR, a modified butadiene rubber (modified BR) whose terminals and / or main chain are modified with a functional group containing at least one element selected from the group consisting of silicon, nitrogen, and oxygen is preferably used.

[0083] Other examples of modified BR include tin-modified BR, which is obtained by polymerizing 1,3-butadiene with a lithium initiator and then adding a tin compound, and in which the terminals of the modified BR molecule are further bonded with a tin-carbon bond (tin-modified BR).Modified BR may be either non-hydrogenated or hydrogenated.

[0084] The BRs listed above may be used alone or in combination of two or more.

[0085] From the viewpoint of abrasion resistance, the weight-average molecular weight (Mw) of BR is preferably 300,000 or more, more preferably 350,000 or more, and even more preferably 400,000 or more. From the viewpoint of crosslinking uniformity, it is preferably 2,000,000 or less, more preferably 1,000,000 or less. The Mw of BR is measured by the above-mentioned measurement method.

[0086] When BR is contained, the content thereof in 100% by mass of the rubber component is preferably 60% by mass or less, more preferably 50% by mass or less, even more preferably 40% by mass or less, and particularly preferably 35% by mass or less, from the viewpoint of wet grip performance. When BR is contained, the content thereof 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 more.

[0087] (Other rubber components) The rubber component may contain other rubber components besides the diene rubber, as long as the effects of the present disclosure are not affected. Examples of other rubber components besides the diene rubber include crosslinkable rubber components commonly used in the tire industry, such as butyl rubber (IIR), halogenated butyl rubber, ethylene propylene rubber, polynorbornene rubber, silicone rubber, chlorinated polyethylene rubber, fluororubber (FKM), acrylic rubber (ACM), and hydrin rubber. These other rubber components may be used alone or in combination of two or more. In addition to the above rubber components, a known thermoplastic elastomer may or may not be contained.

[0088] <Plasticizer> The rubber composition according to the present disclosure contains a plasticizer. A plasticizer is a material that imparts plasticity to a rubber component, and is a concept that includes liquid plasticizers (plasticizers that are liquid (liquid) at room temperature (25°C)) and solid plasticizers (plasticizers that are solid at room temperature (25°C)). Specifically, it is a component that can be extracted from a rubber composition using acetone. One type of plasticizer may be used alone, or two or more types may be used in combination.

[0089] The plasticizers of the present disclosure are classified into Plasticizer A, Plasticizer B, Plasticizer C, and other plasticizers according to the rate at which the plasticizer diffuses from the first layer to the second layer, using the method for evaluating the diffusion rate of plasticizers described above and in the Reference Examples below. Plasticizer A, which has a fast diffusion rate, has a glass transition point of -40°C or lower and a weight average molecular weight of less than 1,000. Plasticizer B, which has a medium diffusion rate, has a glass transition point of 30°C or higher. Plasticizer C, which has a slow diffusion rate, has a glass transition point of more than -70°C and less than 30°C and a weight average molecular weight of 1,000 or higher.

[0090] Plasticizer A is preferably at least one of an oil and an ester-based plasticizer, Plasticizer B is preferably a resin component, and Plasticizer C is preferably a liquid polymer.

[0091] The resin component is not particularly limited, but examples thereof include petroleum resins, terpene resins, rosin resins, phenolic resins, etc. These resin components may be used alone or in combination of two or more.

[0092] As used herein, "C5 petroleum resin" refers to a resin obtained by polymerizing a C5 fraction. Examples of C5 fractions include petroleum fractions having 4 to 5 carbon atoms, such as cyclopentadiene, pentene, pentadiene, and isoprene. Dicyclopentadiene resin (DCPD resin) is preferably used as the C5 petroleum resin.

[0093] In this specification, "aromatic petroleum resin" refers to a resin obtained by polymerizing a C9 fraction, and may be a hydrogenated or modified version of the C9 fraction. Examples of C9 fractions include petroleum fractions having 8 to 10 carbon atoms, such as vinyltoluene, alkylstyrene, indene, and methylindene. Specific examples of aromatic petroleum resins include: Coumarone-indene resin, coumarone resin, indene resin, and aromatic vinyl resin are preferably used. As the aromatic vinyl resin, a homopolymer of α-methylstyrene or styrene or a copolymer of α-methylstyrene and styrene is preferred, and a copolymer of α-methylstyrene and styrene is more preferred, because they are economical, easy to process, and have excellent heat generation properties. As the aromatic vinyl resin, for example, commercially available products from Arizona Chemical Company, Eastman Chemical Company, etc. can be used.

[0094] As used herein, the term "C5C9 petroleum resin" refers to a resin obtained by copolymerizing the C5 fraction and the C9 fraction, and may be a hydrogenated or modified resin. Examples of the C5 fraction and the C9 fraction include the petroleum fractions described above. As the C5C9 petroleum resin, for example, commercially available products from Tosoh Corporation, LUHUA, etc. can be used.

[0095] Examples of terpene resins include polyterpene resins made of at least one terpene compound selected from α-pinene, β-pinene, limonene, dipentene, and the like; aromatic modified terpene resins made from the terpene compound and an aromatic compound; terpene phenolic resins made from a terpene compound and a phenolic compound; and those obtained by subjecting these terpene resins to hydrogenation treatment (hydrogenated terpene resins). Examples of aromatic compounds used as raw materials for aromatic modified terpene resins include styrene, α-methylstyrene, vinyltoluene, and divinyltoluene. Examples of phenolic compounds used as raw materials for terpene phenolic resins include phenol, bisphenol A, cresol, and xylenol.

[0096] The rosin-based resin is not particularly limited, but examples thereof include natural resin rosin and rosin-modified resins obtained by modifying rosin by hydrogenation, disproportionation, dimerization, esterification, etc.

[0097] The phenolic resin is not particularly limited, but examples thereof include phenol formaldehyde resin, alkylphenol formaldehyde resin, alkylphenol acetylene resin, and oil-modified phenol formaldehyde resin.

[0098] When a resin component is contained, the content per 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 3 parts by mass or more, even more preferably 5 parts by mass or more, and particularly preferably 7 parts by mass or more from the viewpoint of wet grip performance, and 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 from the viewpoint of suppressing heat buildup.

[0099] Examples of oils include process oil, vegetable oils, and animal fats. Examples of the process oil include paraffinic process oil, naphthenic process oil, and aromatic process oil. Furthermore, as an environmental measure, process oil with a low content of polycyclic aromatic compounds (PCA) can also be used. Examples of the low-PCA process oil include mild extract solvates (MES), treated distillate aromatic extract (TDAE), and heavy naphthenic oil. Furthermore, from the perspective of life cycle assessment, refined waste oil from rubber mixers and engines, or waste cooking oil from restaurants, can also be used.

[0100] When oil is contained, the content per 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 3 parts by mass or more, even more preferably 5 parts by mass or more, and particularly preferably 7 parts by mass or more from the viewpoint of processability, and is preferably 120 parts by mass or less, more preferably 100 parts by mass or less, even more preferably 80 parts by mass or less, and particularly preferably 60 parts by mass or less from the viewpoint of abrasion resistance.

[0101] The liquid polymer is not particularly limited as long as it is a polymer that is in a liquid state at room temperature (25°C), and examples thereof 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 alone or in combination of two or more.

[0102] When a liquid polymer is contained, the content thereof per 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 3 parts by mass or more, even more preferably 5 parts by mass or more, and particularly preferably 7 parts by mass or more. The content of the liquid rubber 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.

[0103] Examples of ester-based plasticizers include dibutyl adipate (DBA), diisobutyl adipate (DIBA), dioctyl adipate (DOA), di-2-ethylhexyl azelate (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 alone or in combination of two or more.

[0104] The content of plasticizer A (total amount of all plasticizers A when multiple plasticizers A are used) per 100 parts by mass of the rubber component of the rubber composition constituting the first layer 2 is 3.0 parts by mass or more, preferably 5.0 parts by mass or more, more preferably 8.0 parts by mass or more, even more preferably 10 parts by mass or more, and particularly preferably 12 parts by mass or more. The content of plasticizer A (total amount of all plasticizers A when multiple plasticizers A are used) per 100 parts by mass of the rubber component of the rubber composition constituting the second layer 3 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. On the other hand, the content of plasticizer A per 100 parts by mass of the rubber component of the rubber compositions constituting the first layer 2 and the second layer 3 is preferably 100 parts by mass or less, more preferably 90 parts by mass or less, even more preferably 80 parts by mass or less, and particularly preferably 70 parts by mass or less. The content of plasticizer A per 100 parts by mass of the rubber component of the rubber composition constituting the second layer 3 is greater than the content of plasticizer A per 100 parts by mass of the rubber component of the rubber composition constituting the first layer 2. The difference between the content of plasticizer A per 100 parts by mass of the rubber component of the rubber composition constituting the second layer 3 and the content of plasticizer A per 100 parts by mass of the rubber component of the rubber composition constituting the first layer 2 is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, even more preferably 15 parts by mass or more, and particularly preferably 20 parts by mass or more.

[0105] The content of plasticizer B (the total amount when multiple plasticizers B are used) per 100 parts by mass of the rubber component of the rubber composition constituting the first layer 2 is 1.0 part by mass or more, preferably 3.0 parts by mass or more, more preferably 5.0 parts by mass or more, even more preferably 8.0 parts by mass or more, even more preferably 10 parts by mass or more, and particularly preferably 12 parts by mass or more. The content of plasticizer B per 100 parts by mass of the rubber component of the rubber composition constituting the first layer 2 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. The content of plasticizer B per 100 parts by mass of the rubber component of the rubber composition constituting the second layer 3 is not particularly limited, but is preferably less than 20 parts by mass, more preferably less than 10 parts by mass, even more preferably less than 5 parts by mass, and particularly preferably less than 1 part by mass. Plasticizer B may not be present.

[0106] The content of plasticizer C per 100 parts by mass of the rubber component of the rubber composition constituting the first layer 2 (the total amount when multiple plasticizers C are used) is 1.0 part by mass or more, preferably 3.0 parts by mass or more, and more preferably 5.0 parts by mass or more. The content of plasticizer C per 100 parts by mass of the rubber component of the rubber composition constituting the first layer 2 is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, even more preferably 30 parts by mass or less, and particularly preferably 20 parts by mass or less. The content of plasticizer C per 100 parts by mass of the rubber component of the rubber composition constituting the second layer 3 is not particularly limited, but is preferably less than 20 parts by mass, more preferably less than 10 parts by mass, even more preferably less than 5 parts by mass, and particularly preferably less than 1 part by mass, and the rubber composition may not contain plasticizer C.

[0107] The content of other plasticizers per 100 parts by mass of the rubber component of the rubber composition constituting the first layer 2 and the second layer 3 (the total amount when multiple other plasticizers are used in combination) is preferably less than 20 parts by mass, more preferably less than 10 parts by mass, even more preferably less than 5 parts by mass, and particularly preferably less than 1 part by mass, and other plasticizers may not be contained.

[0108] <Filler> The rubber composition according to the present disclosure preferably uses a filler containing carbon black and / or silica. The rubber compositions constituting the first layer 2 and the second layer 3 more preferably contain silica as a filler, and even more preferably contain carbon black and silica.

[0109] (carbon black) As the carbon black, any carbon black commonly used in the tire industry can be used as appropriate, such as GPF, FEF, HAF, ISAF, SAF, etc. These carbon blacks may be used alone or in combination of two or more.

[0110] The nitrogen adsorption specific surface area (N2SA) of carbon black is 10m from the viewpoint of reinforcement. 2 / g or more is preferable, and 20m 2 / g or more is more preferable, and 35m 2 / g or more is more preferable, and 50m 2 / g or more is particularly preferable. From the viewpoint of fuel economy and processability, 200m 2 / g or less is preferable, and 160m 2 / g or less is more preferable, and 140m 2 / g or less is more preferable. The N2SA of carbon black is measured by the above-mentioned measurement method.

[0111] From the viewpoint of reinforcing properties, the oil absorption (DBP oil absorption (OAN)) of carbon black is preferably 80 mL / 100 g or more, more preferably 90 mL / 100 g or more, and even more preferably 100 mL / 100 g or more. From the viewpoint of processability, the OAN is preferably 250 mL / 100 g or less, more preferably 200 mL / 100 g or less, and even more preferably 160 mL / 100 g or less. The OAN of carbon black is measured by the above-mentioned measurement method.

[0112] When carbon black is contained, the content per 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more from the viewpoints of abrasion resistance and wet grip performance, and is preferably 50 parts by mass or less, more preferably 35 parts by mass or less, even more preferably 20 parts by mass or less, and particularly preferably 10 parts by mass or less from the viewpoint of fuel economy.

[0113] (silica) The silica is not particularly limited, and can be, for example, silica prepared by a dry method (anhydrous silica) or silica prepared by a wet method (hydrated silica), which are commonly used in the tire industry. Among them, hydrated silica prepared by a wet method is preferred because it contains a large number of silanol groups. These silicas can be used alone or in combination of two or more.

[0114] The nitrogen adsorption specific surface area (N2SA) of silica is 100m from the viewpoint of fuel efficiency and wear resistance. 2 / g or more is preferable, and 120m 2 / g or more is more preferable, and 140m 2 / g or more is more preferable, and 160m 2 / g or more is particularly preferable. From the viewpoint of fuel efficiency and processability, 2 / g or less is preferable, and 300m 2 / g or less is more preferable, and 250m 2 / g or less is more preferable. The N2SA of silica is measured by the above-mentioned measuring method.

[0115] When silica is contained, the content per 100 parts by mass of the 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 wet grip performance, and is preferably 110 parts by mass or less, more preferably 90 parts by mass or less, even more preferably 70 parts by mass or less, and particularly preferably 50 parts by mass or less, from the viewpoint of abrasion resistance.

[0116] The total content of silica and carbon black per 100 parts by mass of the rubber component is preferably 20 parts by mass or more, more preferably 25 parts by mass or more, and even more preferably 30 parts by mass or more from the viewpoint of abrasion resistance, and is preferably 140 parts by mass or less, more preferably 120 parts by mass or less, even more preferably 100 parts by mass or less, and particularly preferably 80 parts by mass or less from the viewpoint of fuel economy and elongation at break.

[0117] From the viewpoint of a balance between fuel economy, wet grip performance, and abrasion resistance, the rubber composition constituting the first layer 2 and the second layer 3 preferably contains more silica than carbon black per 100 parts by mass of the rubber component. The proportion of silica to the total content of silica and carbon black in the first layer 2 and the second layer 3 is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more.

[0118] (Silane coupling agent) Silica is preferably used in combination with a silane coupling agent.The silane coupling agent is not particularly limited, and any silane coupling agent that has been conventionally used in combination with silica in the tire industry can be used, for example, mercapto-based silane coupling agents such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane; sulfide-based silane coupling agents such as bis(3-triethoxysilylpropyl)disulfide, bis(3-triethoxysilylpropyl)tetrasulfide; 3-octanoylthio-1-propyltriethoxysilane, 3-hexanoylthio-1-propyltriethoxysilane, 3-octanoylthio-1-propyltrimethoxysilane; Examples of suitable silane coupling agents include thioester-based silane coupling agents such as silane; vinyl-based silane coupling agents such as vinyltriethoxysilane and vinyltrimethoxysilane; amino-based silane coupling agents such as 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, and 3-(2-aminoethyl)aminopropyltriethoxysilane; glycidoxy-based silane coupling agents such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro-based silane coupling agents such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; and chloro-based silane coupling agents such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. Among these, sulfide-based silane coupling agents and / or mercapto-based silane coupling agents are preferred. Examples of suitable silane coupling agents include those commercially available from Momentive, Inc. These silane coupling agents may be used alone or in combination.

[0119] When a silane coupling agent is contained, the content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, even more preferably 2.0 parts by mass or more, and particularly preferably 3.0 parts by mass or more, from the viewpoint of improving the dispersibility of silica, and is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, even more preferably 12 parts by mass or less, and particularly preferably 9.0 parts by mass or less, from the viewpoint of preventing a decrease in abrasion resistance.

[0120] The content of the silane coupling agent relative to 100 parts by mass of silica is preferably 1.0 part by mass or more, more preferably 3.0 parts by mass or more, and even more preferably 5.0 parts by mass or more, from the viewpoint of improving the dispersibility of silica. From the viewpoint of cost and processability, the content 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] As the filler, in addition to carbon black and silica, other fillers may also be used. Such fillers are not particularly limited, and any fillers commonly used in this field, such as aluminum hydroxide, alumina (aluminum oxide), calcium carbonate, magnesium sulfate, talc, clay, etc., may be used. These other fillers may be used alone or in combination of two or more.

[0122] <Other compounding agents> In addition to the above components, the rubber composition according to the present disclosure may appropriately contain compounding agents that are conventionally commonly used in the tire industry, such as wax, processing aids, stearic acid, zinc oxide, antioxidants, vulcanizing agents, and vulcanization accelerators.

[0123] When wax is contained, the content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, and more preferably 1 part by mass or more, from the viewpoint of weather resistance of the rubber, and is preferably 10 parts by mass or less, and more preferably 5 parts by mass or less, from the viewpoint of preventing whitening of the tire due to bloom.

[0124] 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 alone or in combination of two or more. Examples of processing aids that can be used include those commercially available from Schill + Seilacher, Performance Additives, etc.

[0125] When a processing aid is contained, the content thereof per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, from the viewpoint of improving processability, and is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, from the viewpoint of abrasion resistance and breaking strength.

[0126] The antioxidant is not particularly limited, but examples thereof include amine-based, quinoline-based, quinone-based, phenol-based, and imidazole-based compounds, as well as metal carbamates. Preferred are phenylenediamine-based antioxidants such as N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, N,N'-diphenyl-p-phenylenediamine, N,N'-di-2-naphthyl-p-phenylenediamine, and N-cyclohexyl-N'-phenyl-p-phenylenediamine, and quinoline-based antioxidants such as 2,2,4-trimethyl-1,2-dihydroquinoline polymer and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline. These antioxidants may be used alone or in combination of two or more.

[0127] When an antioxidant is contained, the content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, from the viewpoint of ozone crack resistance of the rubber, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, from the viewpoint of abrasion resistance and wet grip performance.

[0128] When stearic acid is contained, the content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, from the viewpoint of processability, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, from the viewpoint of vulcanization rate.

[0129] When zinc oxide is contained, the content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, from the viewpoint of processability, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, from the viewpoint of abrasion resistance.

[0130] As the vulcanizing agent, sulfur is preferably used, and examples of sulfur that can be used include powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur.

[0131] When sulfur is contained as a vulcanizing agent, the content per 100 parts by mass of the rubber component is preferably 0.1 parts by mass or more, more preferably 0.3 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, the content is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.0 parts by mass or less. When oil-containing sulfur is used as the vulcanizing agent, the content of the vulcanizing agent is the total content of pure sulfur contained in the oil-containing sulfur.

[0132] Examples of vulcanizing agents other than sulfur include alkylphenol-sulfur chloride condensate, sodium 1,6-hexamethylene-dithiosulfate dihydrate, 1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane, etc. These vulcanizing agents other than sulfur can be commercially available from Taoka Chemical Co., Ltd., Lanxess K.K., Flexis, etc.

[0133] Examples of vulcanization accelerators include sulfenamide-based, thiazole-based, thiuram-based, thiourea-based, guanidine-based, dithiocarbamic acid-based, aldehyde-amine-based or aldehyde-ammonia-based, imidazoline-based, and xanthate-based vulcanization accelerators. These vulcanization accelerators may be used alone or in combination of two or more. Among them, one or more vulcanization accelerators selected from the group consisting of sulfenamide-based, guanidine-based, and thiazole-based vulcanization accelerators are preferred, and sulfenamide-based vulcanization accelerators are more preferred.

[0134] Examples of sulfenamide vulcanization accelerators include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N,N-dicyclohexyl-2-benzothiazolylsulfenamide (DCBS), etc. Among these, N-cyclohexyl-2-benzothiazolylsulfenamide (CBS) is preferred.

[0135] Examples of guanidine vulcanization accelerators include 1,3-diphenylguanidine (DPG), 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, di-o-tolylguanidine salt of dicatechol borate, 1,3-di-o-cumenylguanidine, 1,3-di-o-biphenylguanidine, 1,3-di-o-cumenyl-2-propionylguanidine, etc. Among these, 1,3-diphenylguanidine (DPG) is preferred.

[0136] Examples of the thiazole vulcanization accelerator include 2-mercaptobenzothiazole, cyclohexylamine salt of 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, etc. Among these, 2-mercaptobenzothiazole is preferred.

[0137] When a vulcanization accelerator is contained, the content (total amount when multiple vulcanization accelerators are used) 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, and even more preferably 3 parts by mass or more. The content of the vulcanization accelerator per 100 parts by mass of the rubber component is preferably 8 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 6 parts by mass or less. By keeping the content of the vulcanization accelerator within the above range, breaking strength and elongation tend to be ensured.

[0138] The rubber composition according to the present disclosure can be produced by a known method, for example, by kneading the above-described components using a rubber kneading device such as an open roll or an internal kneader (such as a Banbury mixer or kneader).

[0139] The kneading step includes, for example, a base kneading step in which compounding ingredients and additives other than the vulcanizing agent and vulcanization accelerator are kneaded, and a final kneading (F kneading) step in which the vulcanizing agent and vulcanization accelerator are added to the kneaded product obtained in the base kneading step and kneaded. Furthermore, the base kneading step can be divided into multiple steps as desired.

[0140] The kneading conditions are not particularly limited, but examples include a method in which the base kneading step involves kneading for 3 to 10 minutes at a discharge temperature of 150 to 170°C, and a method in which the final kneading step involves kneading for 1 to 5 minutes at 70 to 110°C. The vulcanization conditions are not particularly limited, but examples include a method in which vulcanization is carried out for 10 to 30 minutes at 150 to 200°C.

[0141] The tire according to the present disclosure has a tread including a first layer 2 and a second layer 3, and may be a pneumatic tire or a non-pneumatic tire. Examples of pneumatic tires include passenger car tires, truck and bus tires, motorcycle tires, and high-performance tires, and the tire is particularly suitable for use as a passenger car tire. In this specification, a high-performance tire is a tire with particularly excellent grip performance, and is a concept that also includes racing tires used on racing vehicles.

[0142] A tire having a tread including the first layer 2 and the second layer 3 can be manufactured by a conventional method using the rubber composition. That is, an unvulcanized rubber composition obtained by blending the above-mentioned components with a rubber component as needed is extruded to match the shapes of the first layer 2 and the second layer 3 using an extruder equipped with a die of a predetermined shape, and the extruded composition is then laminated together with other tire components on a tire building machine and molded by a conventional method to form an unvulcanized tire. A tire can be manufactured by heating and pressurizing this unvulcanized tire in a vulcanizer. [Example]

[0143] The present disclosure will be described based on examples, but the present disclosure is not limited to only the examples.

[0144] The various chemicals used in the examples and comparative examples are listed below. SBR: SBR produced according to Production Example 1 below (unmodified S-SBR, styrene content: 25% by mass, vinyl content: 59% by mole, Mw: 250,000, non-oil extended) BR: UBEPOL BR (registered trademark) 150B (unmodified BR, vinyl content: 1.5 mol%, cis content: 97 mol%, Mw: 440,000) manufactured by Ube Industries, Ltd. NR:TSR20 Carbon black: SEAT 6 manufactured by Tokai Carbon Co., Ltd. (DBP oil absorption: 114 mL / 100 g, N2SA: 119 m 2 / g) Silica: Zeosil 1115MP (N2SA: 160m) manufactured by Solvay 2 / g) Silane coupling agent: Si75 (bis(3-triethoxysilylpropyl) disulfide) manufactured by Evonik Degussa Plasticizer 1: PS-32 (paraffinic process oil, Tg: -86°C, Mw: 300) manufactured by Idemitsu Kosan Co., Ltd. Plasticizer 2: Process X-140 (aromatic process oil, Tg: -41°C, Mw: 600) manufactured by ENEOS Corporation Plasticizer 3: YS Polystar T80 (terpene phenol resin, Tg: 62°C, Mw: 1000) manufactured by Yasuhara Chemical Co., Ltd. Plasticizer 4: PX1150N (non-hydrogenated polyterpene resin, Tg: 62°C, Mw: 3000) manufactured by Yasuhara Chemical Co., Ltd. Plasticizer 5: Liquid SBR (Tg: -25°C, Mw: 5000) produced according to Production Example 2 below Plasticizer 6: Liquid SBR (Tg: -5°C, Mw: 5000) produced according to Production Example 3 below Plasticizer 7: TOP (tris(2-ethylhexyl)phosphate, Tg: -74°C, Mw: 435) manufactured by Daihachi Chemical Industry Co., Ltd. Stearic acid: Camellia stearic acid beads manufactured by NOF Corporation Zinc oxide: Zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. Vulcanization accelerator 1: Noccela CZ (N-cyclohexyl-2-benzothiazole sulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator 2: Noccela D (DPG, 1,3-diphenylguanidine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Sulfur: Powdered sulfur manufactured by Karuizawa Sulfur Co., Ltd.

[0145] (Production Example 1: Production of SBR) A nitrogen-purged autoclave reactor was charged with 600 mL of hexane, 75 g of 1,3-butadiene, 25 g of styrene, and 60 mL of tetrahydrofuran and stirred at 40°C. After scavenging by adding 0.5 mL of a 0.1 mol / L n-butyllithium / hexane solution in 0.5 mL increments, 4 mL of a 0.1 mol / L n-butyllithium / hexane solution was added, and the stirring speed was increased to 130 rpm and the jacket temperature to 80°C. After confirming the formation of a polymer with a Mw of 250,000 by GPC, the polymerization solution was poured into 4 L of ethanol and the precipitate was collected. The resulting precipitate was blown dry and then vacuum dried at 80°C / 10 Pa or less until the loss on drying reached 0.1%, yielding SBR.

[0146] (Production Example 2: Production of Plasticizer 5) A nitrogen-purged autoclave reactor was charged with 20 mL of a 1.0 mol / L n-butyllithium / hexane solution, 200 mL of hexane, and 60 mL of tetrahydrofuran. A monomer solution (75 g of 1,3-butadiene and 25 g of styrene dissolved in 400 mL of hexane) was then added, with stirring at 80 rpm and a jacket temperature of 80°C, while the reaction temperature did not exceed 90°C. After confirming the formation of a polymer with a Mw of 5000 by GPC, the polymerization solution was poured into 4 L of ethanol, and the precipitate was recovered. The resulting precipitate was blown dry and then vacuum dried at 80°C / 10 Pa or less until the loss on drying reached 0.1%. DSC analysis of the resulting liquid indicated a Tg of -25°C.

[0147] (Production Example 3: Production of Plasticizer 6) A nitrogen-purged autoclave reactor was charged with 20 mL of a 1.0 mol / L n-butyllithium / hexane solution, 200 mL of hexane, and 60 mL of tetrahydrofuran. A monomer solution (60 g of 1,3-butadiene and 40 g of styrene dissolved in 400 mL of hexane) was then added, with stirring at 80 rpm and a jacket temperature of 80°C, while the reaction temperature did not exceed 90°C. After confirming the formation of a polymer with a Mw of 5000 by GPC, the polymerization solution was poured into 4 L of ethanol, and the precipitate was recovered. The resulting precipitate was blown dry and then vacuum dried at 80°C / 10 Pa or less until the loss on drying reached 0.1%. DSC analysis of the resulting liquid revealed a Tg of -5°C.

[0148] [Reference example] (Creating vulcanized rubber sheets) According to the formulations shown in Tables 1 and 2, the chemicals other than sulfur and the vulcanization accelerator were kneaded in a 1.7 L closed-type Banbury mixer for 1 to 10 minutes until the discharge temperature reached 150 to 160°C, yielding a kneaded mixture. Next, sulfur and the vulcanization accelerator were added to the resulting kneaded mixture using a two-screw open roll mill, and the mixture was kneaded for 4 minutes until the temperature reached 105°C, yielding an unvulcanized rubber composition. The resulting unvulcanized rubber composition was vulcanized at 160°C for 8 minutes, and then cut into a 40 mm long x 40 mm wide x 2 mm thick piece to produce a vulcanized rubber sheet.

[0149] (Measurement of the diffusion rate of plasticizer) First and second vulcanized rubber sheets were laminated together according to the combinations shown in Table 3, and then left to stand at 80°C for 480 hours while a 500g load was applied from the first layer to the second layer. The vulcanized rubber sheets were then separated into the first and second layers, and the weight of the second layer was measured. The initial weight of the second layer before the load was applied was indexed, with 100 representing the weight. A higher index indicates a greater amount of plasticizer blended into the first layer that diffused into the second layer, indicating a faster diffusion rate of the plasticizer. The results in Table 3 show that the diffusion rate of the plasticizers was fastest in the following order: Plasticizer 1, Plasticizer 2, Plasticizer 3, Plasticizer 4, Plasticizer 5, and Plasticizer 6.

[0150] [Table 1]

[0151] [Table 2]

[0152] [Table 3]

[0153] Examples and Comparative Examples According to the formulation shown in Table 4, chemicals other than sulfur and vulcanization accelerator were mixed in a 1.7 L closed-type Banbury mixer for 1 to 10 minutes until the discharge temperature reached 150 to 160°C, yielding a kneaded mixture. Next, sulfur and vulcanization accelerator were added to the resulting mixture using a two-screw open roll mill, and the mixture was mixed for 4 minutes until the temperature reached 105°C, yielding an unvulcanized rubber composition. The resulting unvulcanized rubber composition was molded to fit the shapes of the first and second layers of the tread, and then bonded together with other tire components to produce unvulcanized tires. These were then vulcanized at 170°C to obtain the test tires (size: 205 / 65R15, rim: 15x6JJ, internal pressure: 230 kPa) shown in Table 2.

[0154] <Dynamic Test> Vulcanized rubber test pieces measuring 30 mm in length, 30 mm in width, and 10 mm in thickness were cut from the tire tread, including the interface between the first and second layers, so that the thickness of the first and second layers was the same. The long side of the sample was circumferentially aligned with the tire, and the thickness direction of the sample was radially aligned with the tire. Each vulcanized rubber test piece was subjected to dynamic stress of 0.45 MPa, a frequency of 50 Hz, and a temperature of 80°C for 120 hours in a direction perpendicular to the bonded surfaces using a dynamic viscoelasticity measuring device (GABO's Iplexer series).

[0155] <Measurement of acetone extractables (AE amount)> The AE amount was measured for each vulcanized rubber test piece before and after application of the dynamic stimulus. The AE amount was calculated by immersing each vulcanized rubber test piece (length 1 mm x width 1 mm x thickness 1 mm) in acetone for 24 hours to extract the soluble components, measuring the mass of each test piece before and after extraction, and calculating it using the following formula. The change (%) in the acetone extractable amount of the rubber composition constituting the first layer before and after application of the dynamic stimulus was also calculated using the following formula. Acetone extractable amount (mass%) = {(mass of vulcanized rubber test piece before extraction - mass of vulcanized rubber test piece after extraction) / (mass of rubber test piece before extraction)} × 100 (Change in acetone extractables before and after dynamic stimulation (%)) = {(acetone extractable amount after dynamic stimulation) / (acetone extractable amount before dynamic stimulation) × 100}-100

[0156] <Measurement of 0℃ tanδ and 0℃ E*> The 0°C tan δ and 0°C E* of the vulcanized rubber test pieces were measured before and after the dynamic stimulation. The 0°C tan δ and 0°C E* of each vulcanized rubber test piece (20 mm long x 4 mm wide x 1 mm thick) were measured using a dynamic viscoelasticity measuring device (GABO's Iplexar series) under the following conditions: temperature of 0°C, initial strain of 10%, dynamic strain of 2.5%, and frequency of 10 Hz. The percentage change in 0°C tan δ and percentage change in 0°C E* of the rubber composition constituting the first layer before and after the dynamic stimulation were calculated using the following formulas. (Change in 0℃ tanδ before and after dynamic stimulation (%)) = {(0℃ tanδ after dynamic stimulation) / (0℃ tanδ before dynamic stimulation) × 100}-100 (Percentage change in 0℃E* before and after dynamic stimulation (%)) = {(0℃E* after dynamic stimulation) / (0℃E* before dynamic stimulation) × 100}-100

[0157] <Measurement of tan δ at 30°C> Each vulcanized rubber specimen was cut from the inside of the rubber layer in the tread portion of each test tire, measuring 20 mm in length, 4 mm in width, and 1 mm in thickness, with the long side aligned in the tire circumferential direction. The loss tangent (tanδ) of each specimen was measured using a dynamic viscoelasticity measuring device (GABO's Iplexer series) under conditions of a temperature of 30°C, an initial strain of 5%, a dynamic strain of 1%, and a frequency of 10 Hz. The thickness direction of the sample was the radial direction of the tire.

[0158] <Measurement of glass transition temperature (Tg)> Each vulcanized rubber specimen was cut from the rubber layer of the tread of each test tire, measuring 20 mm in length, 4 mm in width, and 1 mm in thickness, with the long side aligned in the tire circumferential direction. A dynamic viscoelasticity measuring device (GABO's Iplexer series) was used to measure the temperature distribution curve of the loss tangent (tanδ) under conditions of a frequency of 10 Hz, an initial strain of 10%, an amplitude of ±0.5%, and a heating rate of 2°C / min. The temperature corresponding to the largest tanδ value in the obtained temperature distribution curve (tanδ peak temperature) was taken as the glass transition temperature (Tg). The thickness direction of the sample was the radial direction of the tire.

[0159] <Tensile test> A 1mm thick dumbbell-shaped No. 7 test piece was cut from inside the rubber layer of the tread portion of each test tire so that the tensile direction was the tire circumferential direction, and a tensile test was carried out in accordance with JIS K 6251:2017 "Vulcanized rubber and thermoplastic rubber - Determination of tensile test properties" at 23°C in an atmosphere and at a tensile speed of 3.3mm / sec to measure the elongation at break EB (%). The thickness direction of the sample was the tire radial direction.

[0160] <Wet grip performance after wear> The tread portion of each test tire was worn along the tread radius so that the thickness of the first layer was 50% of that of a new tire, and these tires were mounted on all wheels of a vehicle (a domestic FF 2000cc) and the braking distance from the point where the brakes were applied at a speed of 100 km / h on a wet asphalt road surface was measured. The braking distance of the control tire (Comparative Example 3) was set at 100, and the reciprocal of the braking distance of each test tire was expressed as an index using the following formula. A higher index indicates that the wet grip performance is maintained after wear. (Wet grip performance index after wear) = (braking distance after wear of control tire) / (braking distance after wear of each test tire)

[0161] [Table 4]

[0162] [Table 5]

[0163] The results in Tables 4 and 5 show that the tires of the present disclosure suppress changes in tread hardness over time and maintain high wet grip performance even after wear.

[0164] <Embodiment> Examples of embodiments of the present disclosure are provided below.

[0165] [1] A tire having a tread including at least a first layer constituting a tread surface and a second layer adjacent to the first layer on the radially inner side, wherein the first layer and the second layer are constituted by a rubber composition containing a rubber component and a plasticizer, and the rubber composition constituting the first layer contains 3.0 parts by mass or more of plasticizer A, 1.0 part by mass or more of plasticizer B, and 1.0 part by mass or more of plasticizer C per 100 parts by mass of the rubber component, and the plasticizer A has a glass transition point of -40°C or less and a weight average molecular weight of less than 1000, a tire in which plasticizer B has a glass transition point of 30°C or higher, plasticizer C has a glass transition point of more than -70°C and less than 30°C and a weight average molecular weight of 1,000 or higher, the content of plasticizer A per 100 parts by mass of the rubber component of the rubber composition constituting the second layer is greater than the content of plasticizer A per 100 parts by mass of the rubber component of the rubber composition constituting the first layer, and the difference (AE2-AE1) between the acetone extractable amount AE2 of the rubber composition constituting the second layer and the acetone extractable amount AE1 of the rubber composition constituting the first layer is 3.0% by mass or higher. [2] The tire according to the above [1], wherein the rubber composition constituting the first layer has a tan δ at 30°C of less than 0.20. [3] The tire according to [1] above, wherein the rubber composition constituting the first layer has a tan δ at 30°C of less than 0.15. [4] The tire according to any one of the above [1] to [3], wherein the difference (AE2-AE1) between the acetone extractable amount AE2 of the rubber composition constituting the second layer and the acetone extractable amount AE1 of the rubber composition constituting the first layer is 20 mass% or less. [5] The tire according to any one of the above [1] to [4], wherein the plasticizer A is at least one of oil and ester-based plasticizers. [6] The tire according to any one of the above [1] to [5], wherein the plasticizer B is a resin component. [7] The tire according to any one of the above [1] to [6], wherein the plasticizer C is a liquid polymer. [8] The tire according to any one of the above [1] to [7], wherein when a dynamic stimulus is applied for 120 hours under conditions of a dynamic stress of 0.45 MPa, a frequency of 50 Hz, and a temperature of 80°C with the first and second layers bonded together, the rate of change in the complex modulus at 0°C (0°C E*) of the rubber composition constituting the first layer before and after the dynamic stimulus is more than -20% and less than 20%. [9] The tire according to [8] above, wherein the rate of change in tan δ (0°C tan δ) at 0°C of the rubber composition constituting the first layer before and after application of the dynamic stimulus is more than -20% and less than 20%.

[10] The tire according to any one of the above [1] to [9], wherein the rubber composition constituting the first layer has an E* at 0°C of 4.0 MPa or more.

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

[10] , wherein the rubber composition constituting the first layer has a 0°C tan δ of 0.10 or more.

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

[11] , wherein the glass transition temperature of the rubber composition constituting the first layer is −40° C. or higher.

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

[12] above, wherein the rubber composition constituting the first layer has an elongation at break of 200% or more as measured in accordance with JIS K 6251:2017. [Explanation of symbols]

[0166] 1. Tread surface 2...first layer 3...Second layer 4...Third layer

Claims

1. A tire having a tread including at least a first layer constituting a tread surface and a second layer adjacent to the radially inner side of the first layer, the first layer and the second layer are made of a rubber composition containing a rubber component and a plasticizer, the rubber composition constituting the first layer contains, per 100 parts by mass of the rubber component, 3.0 parts by mass or more of a plasticizer A, 1.0 part by mass or more of a plasticizer B, and 1.0 part by mass or more of a plasticizer C; The plasticizer A has a glass transition point of −40° C. or lower and a weight average molecular weight of less than 1,000, The plasticizer B has a glass transition point of 30°C or higher, the plasticizer C has a glass transition point of more than −70° C. and less than 30° C. and a weight average molecular weight of 1,000 or more; a content of the plasticizer A per 100 parts by mass of the rubber component of the rubber composition constituting the second layer is greater than a content of the plasticizer A per 100 parts by mass of the rubber component of the rubber composition constituting the first layer, Acetone extractable amount AE of the rubber composition constituting the second layer 2 and the acetone extractable amount AE of the rubber composition constituting the first layer. 1 Difference with (AE 2 -AE 1 ) is 3.0% by mass or more, When a dynamic stimulus is applied for 120 hours under conditions of a dynamic stress of 0.45 MPa, a frequency of 50 Hz, and a temperature of 80°C with the first and second layers bonded together, the rate of change in the complex modulus at 0°C (0°C E*) of the rubber composition constituting the first layer before and after the dynamic stimulus is more than -20% and less than 20%.

2. A tire having a tread comprising at least a first layer constituting a tread surface and a second layer adjacent to the radially inner side of the first layer, the first layer and the second layer are made of a rubber composition containing a rubber component and a plasticizer, the rubber composition constituting the first layer contains, per 100 parts by mass of the rubber component, 3.0 parts by mass or more of a plasticizer A, 1.0 part by mass or more of a plasticizer B, and 1.0 part by mass or more of a plasticizer C; The plasticizer A has a glass transition point of −40° C. or lower and a weight average molecular weight of less than 1,000, The plasticizer B has a glass transition point of 30°C or higher, the plasticizer C has a glass transition point of more than −70° C. and less than 30° C. and a weight average molecular weight of 1,000 or more; a content of the plasticizer A per 100 parts by mass of the rubber component of the rubber composition constituting the second layer is greater than a content of the plasticizer A per 100 parts by mass of the rubber component of the rubber composition constituting the first layer, the difference (AE 2 −AE 1 ) between the acetone extractable amount AE 2 of the rubber composition constituting the second layer and the acetone extractable amount AE 1 of the rubber composition constituting the first layer is 3.0% by mass or more; When a dynamic stimulus is applied for 120 hours under conditions of a dynamic stress of 0.45 MPa, a frequency of 50 Hz, and a temperature of 80°C with the first and second layers bonded together, the rate of change in the complex modulus at 0°C (0°C E*) of the rubber composition constituting the first layer before and after the dynamic stimulus is more than -20% and less than 20%, and the rate of change in tan δ at 0°C (0°C tan δ) of the rubber composition constituting the first layer before and after the dynamic stimulus is more than -20% and less than 20%.

3. A tire having a tread comprising at least a first layer constituting a tread surface and a second layer adjacent to the radially inner side of the first layer, the first layer and the second layer are made of a rubber composition containing a rubber component and a plasticizer, the rubber composition constituting the first layer contains, per 100 parts by mass of the rubber component, 3.0 parts by mass or more of a plasticizer A, 1.0 part by mass or more of a plasticizer B, and 1.0 part by mass or more of a plasticizer C; The plasticizer A has a glass transition point of −40° C. or lower and a weight average molecular weight of less than 1,000, The plasticizer B has a glass transition point of 30°C or higher, the plasticizer C has a glass transition point of more than −70° C. and less than 30° C. and a weight average molecular weight of 1,000 or more; a content of the plasticizer A per 100 parts by mass of the rubber component of the rubber composition constituting the second layer is greater than a content of the plasticizer A per 100 parts by mass of the rubber component of the rubber composition constituting the first layer, the difference (AE 2 −AE 1 ) between the acetone extractable amount AE 2 of the rubber composition constituting the second layer and the acetone extractable amount AE 1 of the rubber composition constituting the first layer is 3.0% by mass or more; The tire wherein the rubber composition constituting the first layer has a 0°C tan δ of 0.10 or more and 0.40 or less.

4. The tire according to any one of claims 1 to 3, wherein the rubber composition constituting the first layer has a tan δ at 30°C of less than 0.

20.

5. The tire according to any one of claims 1 to 3, wherein the rubber composition constituting the first layer has a tan δ at 30°C of less than 0.

15.

6. Acetone extractable amount AE of the rubber composition constituting the second layer 2 and the acetone extractable amount AE of the rubber composition constituting the first layer. 1 Difference with (AE 2 -AE 1 6. The tire according to claim 1, wherein the amount of hydroxyapatite is 20% by mass or less.

7. The tire according to any one of claims 1 to 6, wherein the plasticizer A is at least one of an oil and an ester-based plasticizer.

8. The tire according to any one of claims 1 to 7, wherein the plasticizer B is a resin component.

9. The tire according to any one of claims 1 to 8, wherein the plasticizer C is a liquid polymer.

10. The tire according to any one of claims 1 to 9, wherein the rubber composition constituting the first layer has an E* at 0°C of 4.0 MPa or more.

11. The tire according to any one of claims 1 to 10, wherein the rubber composition constituting the first layer has a glass transition temperature of -40°C or higher.

12. The tire according to any one of claims 1 to 11, wherein the rubber composition constituting the first layer has an elongation at break measured in accordance with JIS K 6251:2017 of 200% or more.

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