Tire

Abstract

The present application provides a tire with improved overall performance in terms of low fuel consumption, wet grip performance in new condition, and wet grip performance after wear. A tire has a tread that includes at least a first layer constituting a tread surface and a second layer adjacent to a radially inner side of the first layer, wherein the tread has land portions separated by a plurality of circumferential grooves extending continuously in a tire circumferential direction, the first layer and the second layer are composed of a rubber composition containing a rubber component and a plasticizer, a ratio of a complex elastic modulus of the first layer at 30°C to a complex elastic modulus of the second layer at 30°C is 0.85 or greater, and a ratio of tan δ of the first layer at 30°C to tan δ of the second layer at 30°C is 1.0 or greater.

Description

Technical Field

[0001] This invention relates to tires. Background Technology

[0002] Patent Document 1 describes a tire with improved handling stability and low fuel consumption by setting the tread portion as a two-layer structure (so-called tread / base structure) consisting of a base rubber located radially inside the tire and a tread rubber located radially outside the tire, and applying a rubber composition with a small loss tangent (tanδ) to the base rubber.

[0003] [Existing technical documents]

[0004] [Patent Literature]

[0005] [Patent Document 1] Japanese Patent No. 3213127 Summary of the Invention

[0006] [The problem the invention aims to solve]

[0007] In the case of the tires described above, the high wear tangent (tanδ) of the tread rubber layer results in high wet grip performance when new. However, there are concerns that with continuous driving, the tread rubber layer will undergo thermal degradation and hardening due to its own heat generation. At the same time, the groove volume decreases, the rigidity of the tread contact surface increases, resulting in a loss of road surface responsiveness and a decline in wet grip performance.

[0008] The purpose of this invention is to provide a tire with improved overall performance in terms of low fuel consumption, wet grip when new, and wet grip after wear.

[0009] [Methods used to solve problems]

[0010] After conducting in-depth research, the inventors discovered that by setting two or more rubber layers in the tread area and ensuring that the complex elastic modulus E* and the loss tangent tanδ of the rubber layers satisfy a specified relationship, the above-mentioned problems can be solved, thus completing the present invention.

[0011] That is, the present invention relates to:

[0012] [1] A tire having a tread, the tread having at least a first layer constituting a tread surface and a second layer adjacent to the radially inner side of the first layer, wherein the tread has land portions separated by a plurality of circumferential grooves extending continuously in the tire circumferential direction, the first layer and the second layer being composed of a rubber composition containing a rubber component and a plasticizer, the ratio of the complex elastic modulus of the first layer at 30°C to the complex elastic modulus of the second layer at 30°C being 0.85 or more, and the ratio of the tanδ of the first layer at 30°C to the tanδ of the second layer at 30°C being 1.0 or more;

[0013] [2] According to the tire described in [1] above, the ratio of the tanδ of the first layer at 30°C to the tanδ of the second layer at 30°C is 1.2 or more;

[0014] [3] According to the tire described in [1] or [2] above, wherein the ratio of the tanδ of the first layer at 30°C to the tanδ of the second layer at 30°C is 1.4 to 2.0;

[0015] [4] The tire according to any one of [1] to [3] above, wherein the content of butadiene rubber in the rubber component constituting the first layer is 35% by mass or less;

[0016] [5] The tire according to any one of [1] to [4] above, wherein the difference |AE1-AE2| between the acetone extraction amount AE1 of the rubber composition constituting the first layer and the acetone extraction amount AE2 of the rubber composition constituting the second layer is 10% by mass or less;

[0017] [6] The tire according to any one of [1] to [5] above, wherein the rubber composition constituting the first layer and the rubber composition constituting the second layer each contain a resin component;

[0018] [7] The tire according to any one of [1] to [6] above, wherein at least one of the rubber composition constituting the first layer and the rubber composition constituting the second layer contains an aromatic petroleum resin;

[0019] [8] The tire according to any one of [1] to [7] above, wherein the ratio of the content of resin component in the rubber composition constituting the second layer to the content of resin component in the rubber composition constituting the first layer to 100 parts by mass of rubber component is 2.4 or less;

[0020] [9] The tire according to any one of [1] to [8] above, wherein the tire has a third layer that is radially inner adjacent to the second layer;

[0021]

[10] The tire according to any one of [1] to [9] above, wherein the ratio of the thickness of the first layer to the total thickness of the first layer and the second layer is 0.40 or more;

[0022]

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

[10] above, wherein the second layer has a complex elastic modulus of 5 MPa or more at 30°C;

[0023]

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

[11] above, wherein the second layer has a tanδ of 0.30 or less at 30°C;

[0024]

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

[12] above, wherein the glass transition temperature of the first layer is -15°C or higher;

[0025]

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

[13] above, wherein the Shore hardness (Hs) of the second layer is 50 to 80 as measured by a type A hardness tester at a temperature of 23°C in accordance with JIS K6253-3:2012;

[0026]

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

[14] above, wherein the modulus of the first layer at 100% elongation is greater than the modulus of the second layer at 100% elongation;

[0027]

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

[15] above, wherein the deepest part of the bottom of any one of the circumferential grooves is located closer to the radial inner side of the tire than the outermost part of the second layer in the land adjacent to the circumferential groove;

[0028]

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

[16] above, wherein the land portion has sipes at both ends that are not open to the circumferential groove;

[0029]

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

[17] above, wherein the tire has: a portion in the width direction of the land portion closest to the tire equatorial plane that increases as it moves from the radially outer side of the tire toward the inner side.

[0030] [The effects of the invention]

[0031] This invention provides a tire with improved overall performance in terms of low fuel consumption, wet grip when new, and wet grip after wear. Attached Figure Description

[0032] [ Figure 1 This image shows an enlarged cross-sectional view of a portion of the tread of a tire according to an embodiment of the present invention.

[0033] [ Figure 2 This image shows an enlarged cross-sectional view of a portion of the tread of a tire according to an embodiment of the present invention.

[0034] [ Figure 3 This image shows an enlarged cross-sectional view of a portion of the tread of a tire according to an embodiment of the present invention.

[0035] [ Figure 4This image shows an enlarged cross-sectional view of a portion of the tread of a tire according to an embodiment of the present invention.

[0036] [ Figure 5 This image shows an enlarged cross-sectional view of a portion of the tread of a tire according to an embodiment of the present invention.

[0037] [ Figure 6 This image shows an enlarged cross-sectional view of a portion of the tread of a tire according to an embodiment of the present invention.

[0038] [ Figure 7 A diagram showing the tire's contact patch with the ground when the tread is pressed onto a flat surface.

[0039] [ Figure 8 A diagram showing the tire's contact patch with the ground when the tread is pressed onto a flat surface.

[0040] [Figure Labels]

[0041] 1…Zhouxianggou

[0042] 2… Land Department

[0043] 3…tread surface

[0044] 4…Extension of the land section

[0045] 5…The extension line of the deepest part of the bottom of Zhouxiang Ditch

[0046] 6…First floor

[0047] 7…Second layer

[0048] 8…Third floor

[0049] 9…Extension of the outermost line of the second layer

[0050] 10… The outermost extension line of the third layer

[0051] 11…Fetal shoulder land

[0052] 12…Central Army Department

[0053] 21… Tire shoulder transverse groove

[0054] 22… Tire shoulder groove

[0055] 23…Central Tool Groove Detailed Implementation

[0056] A tire according to one embodiment of the present invention has a tread comprising at least a first layer constituting the tread surface and a second layer adjacent to the radially inner side of the first layer, wherein the tread has land portions separated by a plurality of circumferential grooves extending continuously in the tire circumferential direction, the first layer and the second layer being composed of a rubber composition containing a rubber component and a plasticizer, wherein the ratio of the complex elastic modulus of the first layer at 30°C to the complex elastic modulus of the second layer at 30°C is 0.85 or more, and the ratio of the tanδ of the first layer at 30°C to the tanδ of the second layer at 30°C is 1.0 or more (preferably 1.2 or more, more preferably 1.4 to 2.0).

[0057] While not intending to be bound by theory, the following mechanism can be considered as a way to suppress the decline in wet grip performance after tire wear in this invention.

[0058] In the tread of this invention, when the ratio of the complex elastic modulus of the first layer at 30°C to that of the second layer at 30°C is 0.85 or more but less than 1.00, the first layer exhibits softness when new. At this time, because the first layer easily deforms significantly following the road surface during braking, and the tanδ of the first layer at 30°C is also larger than that of the second layer, good wet grip performance can be obtained when new. Simultaneously, the internal mobility of the first layer increases, making it easier for plasticizers to migrate from the first layer to the second layer. It is believed that, therefore, when the second layer is exposed, since the second layer is also in a soft state, good traction can be obtained even with a reduced tread volume, and good wet grip performance can be obtained even with wear.

[0059] It is believed that when the ratio of the complex elastic modulus of the first layer at 30°C to that of the second layer at 30°C is 1.00 or higher, during braking, the entire land area moves and flexes around the second layer, while the first layer generates heat between itself and the road surface, thus achieving wet grip performance. Furthermore, when the second layer is exposed, it is in a soft state, therefore good traction can be achieved even with reduced tread volume, and good wet grip performance can be maintained even during wear.

[0060] On the other hand, it is believed that when the ratio of the complex elastic modulus of the first layer at 30°C to that of the second layer at 30°C is less than 0.85, the first layer is too soft relative to the second layer. Therefore, the deformation of the first layer in the land area becomes excessive, causing chunking to occur from the parts that cannot withstand the deformation. This results in a premature reduction of the contact area when the product is new, failing to achieve good wet grip performance. Furthermore, it is believed that insufficient transfer of plasticizer to the second layer also leads to inadequate wet grip performance during wear.

[0061] In the tire of the present invention, preferably, the deepest part of the bottom of any one of the circumferential grooves is located closer to the radial inner side of the tire than the outermost part of the second layer in the land portion adjacent to the circumferential groove.

[0062] The land portion preferably has cutter grooves at both ends that do not open into the circumferential groove.

[0063] The tire of the present invention preferably has a portion in which the width-direction length of the land portion closest to the tire equatorial plane increases as it moves from the radially outer side of the tire toward the inner side.

[0064] The following describes a tire according to an embodiment of the present invention in detail. The description below is merely illustrative and the scope of the invention is not limited to this description. Furthermore, in this specification, when "~" is used to indicate a numerical range, it includes the values ​​at both ends.

[0065] Figures 1-6 It is an enlarged cross-sectional view showing a portion of the tire tread. Figures 1-6 In the diagram, the vertical direction is the tire's radial direction, the horizontal direction is the tire's width direction, and the direction perpendicular to the paper is the tire's circumferential direction.

[0066] As shown in the figure, the tire tread of the present invention includes a first rubber layer 6 and a second rubber layer 7, and may have a third rubber layer 8 (hereinafter sometimes simply referred to as "first layer 6", "second layer 7", or "third layer 8"). The outer surface of the first layer 6 forms the tread surface 3. The second layer 7 is adjacent to the radially inner side of the first layer 6, and the third layer 8 is adjacent to the radially inner side of the second layer 7. The first layer 6 typically corresponds to the cap tread. The third layer 8 typically corresponds to the base tread or the under tread. The typical shape of the second layer 7 is not fixed, and therefore it may be the base tread or the under tread. Furthermore, as long as the purpose of the present invention can be achieved, one or more rubber layers may be further provided between the third layer 8 and the belt layer. Figure 1 , Figure 2 , Figure 3 and Figure 6 In the middle, the tread consists of a first layer 6, a second layer 7, and a third layer 8. Figure 4 and Figure 5 In the middle, the tread is composed of the first layer 6 and the second layer 7.

[0067] exist Figures 1-6 In the diagram, double arrow t1 represents the maximum thickness of the first layer 6, double arrow t2 represents the maximum thickness of the second layer 7, and double arrow t3 represents the maximum thickness of the third layer 8. Figures 1-6In this specification, any point on the ungrouted tread surface is denoted by the symbol P. The symbol N represents a straight line (normal) that passes through point P and is perpendicular to the tangent plane at point P. Figures 1-6 In the cross section, starting from point P on the tread surface at the grooveless position, draw a normal line N, and measure the thicknesses t1, t2 and t3 along this normal line N.

[0068] In this invention, the maximum thickness t1 of the first layer 6 is not particularly limited, but from the viewpoint of wet grip performance, it is preferably 1.0 mm or more, more preferably 1.5 mm or more, and even more preferably 2.0 mm or more. On the other hand, from the viewpoint of heat generation, the maximum thickness t1 of the first layer 6 is preferably 7.0 mm or less, more preferably 6.5 mm or less, and even more preferably 6.0 mm or less.

[0069] In this invention, the maximum thickness t2 of the second layer 7 is not particularly limited, but is preferably 1.0 mm or more, more preferably 1.5 mm or more. Furthermore, the maximum thickness t2 of the second layer 7 is preferably 10.0 mm or less, more preferably 9.0 mm or less, and even more preferably 8.0 mm or less.

[0070] In this invention, the maximum thickness t3 of the third layer 8 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. Furthermore, the maximum thickness t3 of the third layer 8 is preferably 10.0 mm or less, more preferably 9.0 mm or less, and even more preferably 8.0 mm or less.

[0071] From the viewpoint of the effects of the present invention, the ratio of the thickness of the second layer 7 to the total thickness of the first layer 6 and the second layer 7 (t2 / (t1+t2)) is preferably 0.30 or more, more preferably 0.40 or more, and even more preferably 0.45 or more.

[0072] The tread of the present invention has a land portion 2 divided by a circumferential groove 1 in the tire width direction.

[0073] The depth H1 of the circumferential trench 1 is obtained by the distance between the extension line 4 of the land portion 2 and the extension line 5 of the deepest part of the bottom of the circumferential trench 1. Alternatively, when there are multiple circumferential trenches 1, the depth H1 can be, for example, the distance between the extension line 4 of the land portion 2 and the extension line 5 of the deepest part of the bottom of the circumferential trench 1 with the deepest trench depth.

[0074] exist Figure 1 and Figure 2In the plurality of circumferential grooves 1, the deepest part of the bottom of the circumferential groove 1 with the deepest groove depth is located closer to the radial inner side of the tire than the outermost part of the third layer 8 in the land portion 2 adjacent to the circumferential groove. That is, the extension line 5 of the deepest part of the bottom of the circumferential groove 1 with the deepest groove depth is located closer to the radial inner side of the tire than the extension line 10 of the outermost part of the third layer 8 in the land portion 2 adjacent to the circumferential groove. Directly below the circumferential groove 1 with the deepest groove depth (radially inner side of the tire), there is a recess that is recessed radially inner side of the tire relative to the outermost part of the third layer 8 in the land portion 2 adjacent to the circumferential groove, and a portion of the first layer 6 and the second layer 7 are formed in the recess of the third layer 8 with a predetermined thickness.

[0075] exist Figures 3-6 In the plurality of circumferential grooves 1, the deepest part of the bottom of the circumferential groove 1 with the deepest groove depth is located closer to the radial inner side of the tire than the outermost part of the second layer 7 in the land portion 2 adjacent to the circumferential groove. That is, the extension line 5 of the deepest part of the bottom of the circumferential groove 1 with the deepest groove depth is located closer to the radial inner side of the tire than the extension line 9 of the outermost part of the second layer 7 in the land portion 2 adjacent to the circumferential groove. Directly below the circumferential groove 1 with the deepest groove depth (radially inner side of the tire), there is a recess that is recessed radially inner side of the tire relative to the outermost part of the second layer 7 in the land portion 2 adjacent to the circumferential groove, and a portion of the first layer 6 is formed in the recess of the second layer 7 with a predetermined thickness.

[0076] It is believed that, as described above, by forming the first layer 6, the second layer 7, and the third layer 8, the complex elastic modulus of the first layer 6 remaining around the circumferential groove 1 after tire wear is higher than that of the second layer 7. Therefore, it is easier to play an edge role during turning, and the snow traction is improved.

[0077] The tire of the present invention, such as Figures 1-4 As shown, preferably, the width-direction length of at least one land portion 2 increases as it moves from the radial outer side of the tire towards the inner side; more preferably, the width-direction length of the land portion 2 gradually increases as it moves from the radial outer side of the tire towards the inner side. By employing this method, the wear-prone area along with the contact patch during driving can be increased, thus maintaining wet grip performance until the end of driving. Furthermore, the groove wall of the circumferential groove 1 of the present invention extends in a straight line from the radial outer side of the tire towards the inner side, but is not limited to this form; for example, it may extend in a curved or stepped shape.

[0078] The tire of the present invention, such as Figure 1As shown, in the radial section of the tire including the tire's axis of rotation, at least one of the land portions 2 may have a third layer 8 formed asymmetrically with respect to the normal N passing through the center of the tire's width direction. By forming the third layer 8 asymmetrically, the hardness distribution of the land portion becomes uneven, affecting the ground contact pressure. In the portion with high ground contact pressure, a portion appears where the water film does not shrink upwards and touches the ground, improving wet grip performance, thus reducing the difference in wet grip performance between new and worn parts. This land portion 2 with the asymmetrical third layer 8 may be a land portion 2 located on the outer side of the vehicle relative to the tire equator, or it may be a land portion 2 located on the inner side of the vehicle relative to the tire equator. In addition, the land portion 2 with the asymmetrical third layer 8 may be a land portion held by multiple circumferential grooves 1, or it may be a tire shoulder land portion held by the circumferential grooves 1 and the tread contact end, preferably a land portion held by multiple circumferential grooves 1.

[0079] Figure 7 and Figure 8 This diagram shows the contact patch when the tire tread is pressed onto a flat surface. (Example) Figure 7 and Figure 8 As shown, the tread 10 constituting the tire of the present invention has: a circumferential groove 1 extending continuously in the tire circumferential direction C, a transverse groove 21 extending in the width direction, and sipes 22 and 23.

[0080] The tread has multiple circumferential grooves 1 that extend continuously in the circumferential direction C. Figure 7 and Figure 8 The invention includes three circumferential grooves 1, but the number of circumferential grooves is not particularly limited, for example, it can be 2 to 5. In addition, in this invention, the circumferential grooves 1 extend in a straight line along the circumferential direction C, but are not limited to this manner. For example, they can extend in a wavy, sinusoidal, or sawtooth shape along the circumferential direction C.

[0081] The tread has land portions 2 separated by multiple circumferential grooves 1 in the tire width direction W. Shoulder land portions 11 are a pair of land portions formed between the circumferential grooves 1 and the tread end Te. A central land portion 12 is a land portion formed between the pair of shoulder land portions 11. Figure 7 and Figure 8 There are two central land divisions 12, but the number of central land divisions is not particularly limited, for example, it can be 1 to 5.

[0082] Preferably, the land portion 2 is provided with a transverse groove and / or a cutting groove that runs through the land portion 2. Furthermore, more preferably, the land portion 2 has a cutting groove whose two ends do not open into the circumferential groove 1. Figure 7 In the tire shoulder land portion 11, there are multiple shoulder transverse grooves 21 with one end opening towards the circumferential groove 1, and multiple shoulder slits 22 with one end opening towards the circumferential groove 1. In the central land portion 12, there are multiple central slits 23 with one end opening towards the circumferential groove 1. Figure 8In the tire shoulder land portion 11, there are multiple shoulder transverse grooves 21 with their ends opening toward the circumferential groove 1, and multiple shoulder slits 22 with their ends not opening toward the circumferential groove 1. In the central land portion 12, there are multiple central slits 23 with one end opening toward the circumferential groove 1.

[0083] Furthermore, in this specification, the term "groove," including circumferential grooves and transverse grooves, refers to a recess with a width of at least 2.0 mm. On the other hand, the term "groove" in this specification refers to a fine groove with a width of 2.0 mm or less, preferably 0.5 to 2.0 mm.

[0084] In this invention, unless otherwise specified, the dimensions of the tire components are measured with the tire mounted on a standard rim and inflated with air to achieve the standard internal pressure. During measurement, the tire is not under load.

[0085] "Standard rim" refers to the rim specified for each tire within the specification system that the tire is based on. In JATMA, it refers to "standard rim," in TRA it refers to "design rim," and in ETRTO it refers to "measuring rim." Additionally, in the case of tires whose dimensions are not specified in the aforementioned specification system, it refers to the narrowest of the smallest diameter rims that can be assembled with the tire without causing air leakage between the rim and the tire.

[0086] "Standard tire pressure" refers to the air pressure specified for each tire within the tire specification system, including the tire's base specification. In JATMA, it refers to the "maximum pressure"; in TRA, it refers to the maximum value recorded in "TIRE LOAD LIMITS AT VARIOUS COLDINFLATION PRESSURES"; and in ETRTO, it refers to "INFLATION PRESSURE". Additionally, for tires of sizes not specified in the aforementioned specification system, the standard tire pressure is set to 250 kPa.

[0087] In this invention, "30℃E*" refers to the complex elastic modulus E* under the conditions of a temperature of 30℃, an initial strain of 10%, a dynamic strain of 1%, and a frequency of 10Hz. From the viewpoint of handling stability performance, the 30℃E* of the first layer 6 is preferably 7 MPa or more, more preferably 8 MPa or more, even more preferably 9 MPa or more, and particularly preferably 10 MPa or more. From the viewpoint of handling stability performance, the 30℃E* of the second layer 7 is preferably 4 MPa or more, more preferably 5 MPa or more, and even more preferably 6 MPa or more. The 30℃E* of the third layer 8 is preferably 4 MPa or more, more preferably 5 MPa or more, and even more preferably 6 MPa or more. On the other hand, from the viewpoint of wet grip performance, the 30℃E* of the first layer 6, the second layer 7, and the third layer 8 is preferably 25 MPa or less, more preferably 20 MPa or less, and even more preferably 18 MPa or less. In this invention, the ratio of 30°C E* of the first layer 6 to 30°C E* of the second layer 7 is 0.85 or more, preferably 1.0 or more, more preferably 1.1 or more, even more preferably 1.2 or more, even more preferably 1.3 or more, and particularly preferably 1.4 or more. When the ratio of 30°C E* of the first layer 6 to 30°C E* of the second layer 7 is 0.85 or more but less than 1.00, good wet grip performance can be obtained when the product is new. At the same time, the mobility inside the first layer 6 increases, and the plasticizer can easily move from the first layer 6 to the second layer 7. It is believed that, therefore, when the second layer 7 is exposed, the second layer 7 is also in a soft state, so even if the tread volume is reduced, good traction can be obtained, and good wet grip performance can be obtained even when worn. It is believed that when the ratio of the complex elastic modulus of the first layer 6 at 30°C to that of the second layer 7 at 30°C is 1.00 or higher, during braking, the entire land area moves and flexes around the second layer 7, while the first layer 6 generates heat between itself and the road surface, thereby achieving wet grip performance. Furthermore, it is believed that when the second layer 7 is exposed, since it is in a soft state, good traction can be achieved even with a reduction in tread volume, and good wet grip performance can be maintained during wear. Additionally, there is no particular upper limit to the ratio of the 30°C E* of the first layer 6 to that of the second layer 7, but it is preferably 3.0 or less, more preferably 2.5 or less, even more preferably 2.2 or less, and particularly preferably 2.0 or less. Furthermore, the 30°C E* of each rubber layer can be appropriately adjusted according to the type or mixing amount of the rubber composition, fillers, plasticizers, etc. (especially plasticizers).

[0088] In this invention, "30℃tanδ" refers to the loss tangent tanδ under the conditions of 30℃ temperature, 10% initial strain, 1% dynamic strain, and 10Hz frequency. From the viewpoint of wet grip performance, the 30℃tanδ of the first layer 6 is preferably 0.18 or more, more preferably 0.20 or more, even more preferably 0.22 or more, and particularly preferably 0.24 or more. The 30℃tanδ of the second layer 7 is preferably 0.10 or more, more preferably 0.12 or more, and even more preferably 0.14 or more. The 30℃tanδ of the third layer 8 is preferably 0.10 or more, more preferably 0.12 or more, and even more preferably 0.14 or more. On the other hand, from the viewpoint of low fuel consumption performance, the 30℃tanδ of the rubber composition constituting the first layer 6, the second layer 7, and the third layer 8 is preferably 0.40 or less, more preferably 0.35 or less, and even more preferably 0.30 or less. It is believed that, in this invention, the ratio of the 30°C tanδ of the first layer 6 to the 30°C tanδ of the second layer 7 is 1.0 or more, preferably 1.1 or more, more preferably 1.2 or more, even more preferably 1.3 or more, and particularly preferably 1.4 or more. By having the ratio of the 30°C tanδ of the first layer 6 to the 30°C tanδ of the second layer 7 be 1.0 or more, the heat generated in the first layer during driving increases, resulting in good wet grip performance. Simultaneously, when the complex elastic modulus E* of the first layer is less than that of the second layer, the internal mobility of the first layer can be improved, achieving the effect of transferring plasticizer to the second layer. Furthermore, there is no particular upper limit to the ratio of the 30°C tanδ of the first layer 6 to the 30°C tanδ of the second layer 7, but it is preferably 2.5 or less, more preferably 2.2 or less, even more preferably 2.0 or less, and particularly preferably 1.8 or less. Additionally, the 30°C tanδ of each rubber layer can be appropriately adjusted according to the type or mixing amount of the rubber composition, fillers, plasticizers, etc. (especially plasticizers), as described later.

[0089] The acetone extraction yield of this invention is an indicator of the concentration of low-molecular-weight organic compounds in the plasticizer contained in the vulcanized rubber composition. The acetone extraction yield can be determined according to JIS K 6229-3:2015, by immersing each vulcanized rubber test piece in acetone for 24 hours, extracting the soluble components, measuring the mass of each test piece before and after extraction, and then calculating it using the following formula.

[0090] Acetone extraction yield (%) = {(mass of rubber test pieces before extraction - mass of rubber test pieces after extraction) / (mass of rubber test pieces before extraction)} × 100

[0091] The difference between the acetone extraction amount AE1 of the rubber composition constituting the first layer 6 and the acetone extraction amount AE2 of the rubber composition constituting the second layer 7, |AE1-AE2|, is preferably 10% by mass or less, more preferably 8% by mass or less, even more preferably 6% by mass or less, and particularly preferably 4% by mass or less. It is believed that by setting the difference in acetone extraction amounts to the aforementioned range, the transfer of acetone-extracted components from the second layer 7 to the first layer 6 during driving can be suppressed, thus maintaining the hardness of the tread rubber even after wear, and preserving wet grip performance for a long time. Furthermore, as long as the difference between AE1 and AE2 is within the aforementioned range, the larger value of either one is acceptable. The values ​​of AE1 and AE2 are not particularly limited, but are preferably 1 to 40% by mass, more preferably 5 to 30% by mass, respectively.

[0092] In this invention, the glass transition temperature (Tg) refers to the tanδ peak temperature determined by the following method: For a rubber test piece (e.g., 20 mm long × 4 mm wide × 1 mm thick) cut from the interior of the rubber layer of each test tire tread with the tire circumference as the long side, a dynamic viscoelasticity evaluation device (e.g., the Eplexor series manufactured by GABO) is used to measure the temperature distribution curve of tanδ under conditions of 10% initial strain, 1% dynamic strain, and 10 Hz frequency. The temperature corresponding to the largest tanδ value in the obtained temperature distribution curve (tanδ peak temperature) is taken as the glass transition temperature (Tg) in this invention. From the viewpoint of wet grip performance, the Tg of the first layer 6 is preferably -15°C or higher, more preferably -13°C or higher, and even more preferably -11°C or higher. Furthermore, from the viewpoint of wet grip performance, the Tg of the second layer 7 is preferably -20°C or higher, more preferably -15°C or higher, and even more preferably -12°C or higher. Furthermore, there is no particular limitation on the upper limit of the Tg of the first layer 6 and the second layer 7, but it is preferably below 20°C, more preferably below 15°C, and even more preferably below 10°C. In addition, the Tg of each rubber layer can be appropriately adjusted according to the type or mixing amount of the rubber components, etc.

[0093] The rubber hardness of the present invention refers to the Shore hardness (Hs) measured using a type A durometer at a temperature of 23°C, in accordance with JIS K 6253-3:2012. The Shore hardness (Hs) of the first layer 6 is preferably 80 or less, more preferably 75 or less, and even more preferably 70 or less. Furthermore, the Shore hardness (Hs) of the second layer 7 is preferably 80 or less, more preferably 75 or less, and even more preferably 70 or less. By setting the Shore hardness (Hs) of the first layer 6 and the second layer 7 to the aforementioned range, the wet grip performance is improved when the tire is new because it does not impair road surface traction and easily generates reaction force. Moreover, since sufficient traction is easily obtained even after wear, the decline in wet grip performance after tire wear can be suppressed. On the other hand, based on the viewpoint of maintaining the rigidity of the tire tread blocks, the Shore hardness (Hs) of the first layer 6 and the second layer 7 is preferably 50 or more, more preferably 55 or more. Furthermore, the rubber hardness of each rubber layer can be appropriately adjusted according to the type or mixing amount of the rubber composition, fillers, plasticizers, etc., as described below.

[0094] In this invention, the modulus at 100% elongation refers to the tensile stress at 100% elongation in the grain direction (the calendering direction when forming a rubber sheet through extrusion or shearing), measured according to JIS K 6251 at 23°C and a stretching speed of 3.3 mm / s. The modulus of the first layer 6 at 100% elongation is preferably 1.0 MPa or more, more preferably 1.2 MPa or more, further preferably 1.4 MPa or more, and particularly preferably 1.6 MPa or more. Furthermore, the modulus of the second layer 7 at 100% elongation is preferably 1.0 MPa or more, more preferably 1.2 MPa or more, further preferably 1.4 MPa or more, and particularly preferably 1.6 MPa or more. Additionally, there is no particular upper limit to the modulus of the first layer 6 and the second layer 7 at 100% elongation; it is typically 4.0 MPa or less, and preferably 3.5 MPa or less. In this invention, it is preferable that the modulus of the first layer 6 at 100% elongation is greater than that of the second layer 7 at 100% elongation. The difference between the modulus of the second layer 7 at 100% elongation and the modulus of the first layer 6 at 100% elongation is preferably 0.1 MPa or more, more preferably 0.2 MPa or more, and even more preferably 0.3 MPa or more. Furthermore, the modulus of each rubber layer at 100% elongation can be appropriately adjusted according to the type or mixing amount of the rubber composition, filler, plasticizer, etc., as described below.

[0095] [Rubber Composition]

[0096] The tire of the present invention, through the cooperation of the above-described tire structure (especially the shape of the tread) and the physical properties of the rubber composition constituting each layer of the tread, can more effectively suppress the decline in wet grip performance after tire wear.

[0097] <Rubber Composition>

[0098] In the rubber composition of the present invention, the rubber component preferably contains at least one selected from isoprene rubber, styrene-butadiene rubber (SBR), and butadiene rubber (BR). The rubber components constituting the first layer 6 and the second layer 7 preferably contain SBR, more preferably contain both SBR and BR, and can be configured as a rubber component consisting only of SBR and BR. The rubber component constituting the third layer 8 preferably contains isoprene rubber, more preferably contains both isoprene rubber and BR, and can be configured as a rubber component consisting only of isoprene rubber and BR.

[0099] (Isoprene-based rubber)

[0100] As isoprene-based rubbers, those commonly used in the tire industry include, for example, isoprene rubber (IR) and natural rubber. Natural rubber, in addition to unmodified natural rubber (NR), includes epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), deproteinized natural rubber (DPNR), high-purity natural rubber, grafted natural rubber, and other modified natural rubbers. These isoprene-based rubbers can be used alone or in combination of two or more.

[0101] As for NR, there are no special restrictions, and commonly used ones in the tire industry can be used, such as SIR20, RSS#3, TSR20, etc.

[0102] When the rubber components constituting the first layer 6 and the second layer 7 contain isoprene-based rubber (preferably natural rubber, more preferably unmodified natural rubber (NR)), from the viewpoint of wet grip performance, its content in the rubber components is preferably 50% by mass or less, more preferably 40% by mass or less, further preferably 30% by mass or less, and particularly preferably 20% by mass or less. On the other hand, there is no particular limitation on the lower limit value of the isoprene-based rubber content in the rubber components, for example, it can be set to 1% by mass or more, 3% by mass or more, 5% by mass or more, 10% by mass or more, or 15% by mass or more.

[0103] When the rubber component constituting the third layer 8 contains isoprene-based rubber (preferably natural rubber, more preferably unmodified natural rubber (NR)), its content in the rubber component is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more. Furthermore, there is no particular limit to the upper limit of the isoprene-based rubber content in the rubber component, and it can be 100% by mass.

[0104] (SBR)

[0105] There are no particular limitations on the type of SBR used, and examples include solution-polymerized SBR (S-SBR), emulsion-polymerized SBR (E-SBR), and their modified SBRs (modified S-SBR, modified E-SBR). Examples of modified SBRs include SBRs with modified ends and / or main chains, and modified SBRs coupled to tin, silicon compounds, etc. (condensates, those with branched structures, etc.). Among these, S-SBR and modified SBRs are preferred. Additionally, hydrides of these SBRs (hydrogenated SBRs) can also be used. These SBRs can be used individually or in combination of two or more.

[0106] Examples of S-SBRs that can be used in this invention include those manufactured and sold by JSR Corporation, Sumitomo Chemical Co., Ltd., Ube Industries, Ltd., Asahi Kasei Corporation, and ZS Elastomers Co., Ltd.

[0107] Based on 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. Furthermore, based on the viewpoints of temperature dependence of grip performance and burst resistance, this content is preferably 60% by mass or less, more preferably 55% by mass or less, and even more preferably 50% by mass or less. Additionally, in this specification, the styrene content of SBR can be determined by… 1 Calculated by H-NMR measurements.

[0108] Based on considerations of reactivity with silica, wet grip, rubber strength, and abrasion resistance, 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. Furthermore, based on considerations of preventing increased temperature dependence, elongation at break, and abrasion resistance, the vinyl content of SBR is preferably 70 mol% or less, more preferably 65 mol% or less, and even more preferably 60 mol% or less. Additionally, in this specification, the vinyl content (1,2-binding butadiene unit weight) of SBR can be determined by infrared absorption spectroscopy.

[0109] From the perspective 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. Furthermore, from the perspective of crosslinking uniformity, the weight-average molecular weight is preferably 2,000,000 or less, more preferably 1,800,000 or less, and even more preferably 1,500,000 or less. Additionally, in this specification, the weight-average molecular weight of SBR can be calculated from standard polystyrene based on the measured value obtained by gel permeation chromatography (GPC) (e.g., GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, chromatographic column: TSKGEL SUPERMALTIPORE HZ-M manufactured by Tosoh Corporation).

[0110] When the rubber components constituting the first layer 6 and the second layer 7 contain SBR, from the viewpoint of wet grip performance, its content in the rubber components is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 65% ​​by mass or more, and particularly preferably 70% by mass or more. On the other hand, there is no particular limit to the upper limit of the SBR content in the rubber components, and it can be 100% by mass. In addition, when the rubber components constituting the third layer 8 contain SBR, its content in the rubber components is not particularly limited.

[0111] (BR)

[0112] As for BR, there are no particular limitations, and BRs commonly used in the tire industry can be used, such as BRs with a cis content of less than 50% by mass (low cis BR), BRs with a cis content of more than 90% by mass (high cis BR), rare earth-based butadiene rubber synthesized using rare earth element-based catalysts (rare earth-based BR), BRs containing syndiotactic polybutadiene crystals (BRs containing SPB), and modified BRs (high cis modified BRs, low cis modified BRs), etc. As for modified BRs, examples include BRs modified with the same functional groups described in the above-mentioned SBRs. These BRs can be used alone or in combination of two or more.

[0113] As a high-cis BR, commercially available products from companies such as Zeon Corporation, Ube Industries, and JSR Corporation can be used. By containing a high-cis BR, low-temperature properties and wear resistance can be improved. The cis content is preferably 95% by mass or more, more preferably 96% by mass or more, even more preferably 97% by mass or more, and particularly preferably 98% by mass or more. Furthermore, in this specification, the cis content (cis-1,4-bound butadiene unit content) is a value calculated by infrared absorption spectroscopy analysis.

[0114] As a rare earth-based BR, it is synthesized using a rare earth element-based catalyst. The vinyl content is preferably 1.8 mol% or less, more preferably 1.0 mol% or less, and even more preferably 0.8 mol% or less. The cis content is preferably 95% by mass or more, more preferably 96% by mass or more, even more preferably 97% by mass or more, and particularly preferably 98% by mass or more. Commercially available products such as those from Lanxess Corporation can be used as the rare earth-based BR.

[0115] Examples of SPB-containing BRs include those in which 1,2-syndiotactic polybutadiene crystals are dispersed after chemical bonding with the BR, rather than those in which 1,2-syndiotactic polybutadiene crystals are simply dispersed in the BR. Commercially available products from companies such as Ube Industries, Ltd. can be used as such SPB-containing BRs.

[0116] As a modified BR, it is suitable to use modified butadiene rubber (modified BR) obtained by modifying the ends and / or main chain with functional groups containing at least one element selected from silicon, nitrogen and oxygen.

[0117] Other examples of modified BR include those obtained by polymerizing 1,3-butadiene with a lithium initiator and adding a tin compound, and those further modified by bonding the ends of the BR molecules through tin-carbon bonds (tin-modified BR). Furthermore, the modified BR can be either unhydrogenated or hydrogenated.

[0118] The BRs listed above can be used alone or in combination of two or more.

[0119] 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. Furthermore, from the viewpoint of crosslinking uniformity, this weight-average molecular weight is preferably 2 million or less, more preferably 1 million or less. Additionally, Mw can be calculated from standard polystyrene based on the measured value obtained by gel permeation chromatography (GPC) (e.g., GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, chromatographic column: TSKGEL SUPERMALTIPORE HZ-M manufactured by Tosoh Corporation).

[0120] When the rubber components constituting the first layer 6 and the second layer 7 contain BR, from the viewpoint of wet grip performance, its content in the rubber components is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, and particularly preferably 20% by mass or less. On the other hand, there is no particular limitation on the lower limit value of the BR content in the rubber components, for example, it can be 1% by mass or more, 3% by mass or more, 5% by mass or more, 10% by mass or more, or 15% by mass or more.

[0121] When the rubber component constituting the third layer 8 contains BR, its content in the rubber component is preferably 80% by mass or less, more preferably 70% by mass or less, even more preferably 65% ​​by mass or less, and particularly preferably 60% by mass or less. On the other hand, there is no particular limitation on the lower limit value of the BR content in the rubber component, for example, it can be 1% by mass or more, 3% by mass or more, 5% by mass or more, 10% by mass or more, or 15% by mass or more.

[0122] (Other rubber components)

[0123] The rubber components of this invention may contain other rubber components besides the isoprene-based rubbers, SBR, and BR mentioned above. Other rubber components may be crosslinkable rubber components commonly used in the tire industry, such as styrene-isoprene-butadiene copolymer rubber (SIBR), styrene-isobutylene-styrene block copolymer (SIBS), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), hydrogenated nitrile butadiene rubber (HNBR), butyl rubber (IIR), ethylene propylene rubber, polynorbornene rubber, silicone rubber, chlorinated polyethylene rubber, fluororubber (FKM), acrylate rubber (ACM), epichlorohydrin rubber, etc. These other rubber components may be used alone or in combination of two or more.

[0124] <packing>

[0125] In the rubber composition of the present invention, fillers containing carbon black and / or silica are suitable for use. In the rubber composition constituting the first layer 6 and the second layer 7, silica is preferably contained as a filler, more preferably containing both carbon black and silica, and a filler consisting only of carbon black and silica may be used. In the rubber composition constituting the third layer 8, carbon black is preferably contained as a filler, and a filler consisting only of carbon black may be used.

[0126] (Carbon black)

[0127] As carbon black, those commonly used in the tire industry can be appropriately used, such as GPF, FEF, HAF, ISAF, and SAF. These carbon blacks can be used alone or in combination of two or more.

[0128] From a reinforcing perspective, the nitrogen adsorption specific surface area (N2SA) of carbon black is preferably 10 m² / s. 2 / g or more, preferably 30m 2 / g or higher, further optimized for 50m 2 / g or more. Furthermore, based on the viewpoints of low fuel consumption and processability, the nitrogen adsorption specific surface area is preferably 200 m². 2 / g or less, preferably 150m 2 Below / g, 125m is further preferred. 2 / g or less. In addition, the N2SA of carbon black is the value determined in accordance with JIS K 6217-2:2017 "Basic properties of carbon black for rubber - Part 2: Calculation of specific surface area - Nitrogen adsorption method - Single point method".

[0129] When the rubber composition constituting the first layer 6 and the second layer 7 contains carbon black, from the viewpoint of abrasion resistance and wet grip performance, its content 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, relative to 100 parts by mass of rubber component. Furthermore, from the viewpoint of low fuel consumption performance, this content 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.

[0130] When the rubber composition constituting the third layer 8 contains carbon black, from the viewpoint of reinforcement, its content is preferably 30 parts by mass or more, more preferably 40 parts by mass or more, and even more preferably 50 parts by mass or more, relative to 100 parts by mass of rubber component. Furthermore, from the viewpoint of low fuel consumption performance, this content is preferably 100 parts by mass or less, more preferably 90 parts by mass or less, and even more preferably 80 parts by mass or less.

[0131] (Silicon dioxide)

[0132] There are no particular limitations on the silica used; for example, silica prepared by a dry process (anhydrous silica) and silica prepared by a wet process (hydrated silica), commonly used in the tire industry, can be used. Among these, hydrated silica prepared by a wet process is preferred due to the high number of silanol groups. One type of silica can be used alone, or two or more types can be used in combination.

[0133] Based on the considerations of low fuel consumption and wear resistance, the nitrogen adsorption specific surface area (N2SA) of silica is preferably 140 m². 2 / g or more, preferably 170m 2 / g or more, further optimized for 200m 2 / g or more. Furthermore, based on the viewpoints of low fuel consumption and processability, the nitrogen adsorption specific surface area is preferably 350 m². 2 / g or less, preferably 300m 2 Below / g, 250m is further preferred. 2 / g or less. Additionally, the N2SA of silica in this specification is the value determined by the BET method according to ASTM D 3037-93.

[0134] When the rubber composition constituting the first layer 6 and the second layer 7 contains silica, from the viewpoint of wet grip performance, its content is preferably 20 parts by mass or more, more preferably 40 parts by mass or more, further preferably 50 parts by mass or more, and particularly preferably 60 parts by mass or more, relative to 100 parts by mass of rubber component. Furthermore, from the viewpoint of abrasion resistance performance, this content is preferably 130 parts by mass or less, more preferably 120 parts by mass or less, and further preferably 110 parts by mass or less. Additionally, when the rubber composition constituting the third layer 8 contains silica, its content relative to 100 parts by mass of rubber component is not particularly limited.

[0135] In the rubber composition constituting the first layer 6 and the second layer 7, from the viewpoint of abrasion resistance, the total content of silica and carbon black relative to 100 parts by weight of rubber component is preferably 40 parts by weight or more, more preferably 50 parts by weight or more, and even more preferably 60 parts by weight or more. Furthermore, from the viewpoint of low fuel consumption and elongation at break, this content is preferably 160 parts by weight or less, more preferably 140 parts by weight or less, and even more preferably 120 parts by weight or less.

[0136] Based on the viewpoint of balancing low fuel consumption, wet grip, and abrasion resistance, the rubber composition constituting the first layer 6 and the second layer 7 preferably has a higher content of silica than carbon black relative to 100 parts by mass of the rubber component. In the first layer 6 and the second layer 7, the ratio of silica to the total content of silica and carbon black is preferably 60% by mass or more, more preferably 70% by mass or more, further preferably 80% by mass or more, and particularly preferably 85% by mass or more. Furthermore, there are no particular limitations on the content ratio of silica and carbon black in the rubber composition constituting the third layer 8.

[0137] (Other fillers)

[0138] As a filler other than silica and carbon black, it can be mixed with aluminum hydroxide, calcium carbonate, alumina, clay, talc and other commonly used in the tire industry.

[0139] (Silane coupling agent)

[0140] Silica is preferably used in combination with a silane coupling agent. There are no particular limitations on the silane coupling agent; any silane coupling agent that has been conventionally used with silica in the rubber industry can be used. Examples include, for instance, the following mercapto-based silane coupling agents; sulfide-based silane coupling agents such as bis(3-triethoxysilylpropyl) disulfide and bis(3-triethoxysilylpropyl) tetrasulfide; vinyl-based silane coupling agents such as vinyltriethoxysilane and vinyltrimethoxysilane; 3-aminopropyltriethoxysilane, Amino-based silane coupling agents such as 3-aminopropyltrimethoxysilane and 3-(2-aminoethyl)aminopropyltriethoxysilane; epoxy-based silane coupling agents such as γ-epoxypropoxypropyltriethoxysilane and γ-epoxypropoxypropyltrimethoxysilane; nitro-based silane coupling agents such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; and chlorinated 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, with mercapto-based silane coupling agents being more preferred. These silane coupling agents can be used alone or in combination of two or more.

[0141] The mercaptosilane coupling agent is preferably a compound represented by formula (1) and / or a compound containing binding unit A represented by formula (2) and binding unit B represented by formula (3).

[0142]

[0143] (where R is in the formula) 101 R 102 and R 103 Each of the following can be independently represented as an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, or -O-(R 111 -O) z -R 112 (z R) 111 Each of the following groups independently represents a divalent hydrocarbon group with 1 to 30 carbon atoms; R 112 The radical (z) represents an alkyl group with 1 to 30 carbon atoms, an alkenyl group with 2 to 30 carbon atoms, an aryl group with 6 to 30 carbon atoms, or an aralkyl group with 7 to 30 carbon atoms; z represents an integer from 1 to 30; R 104 This refers to alkylene groups having 1 to 6 carbon atoms.

[0144]

[0145]

[0146] (In the formula, x represents an integer greater than or equal to 0; y represents an integer greater than or equal to 1; R) 201Represents an alkyl group with 1 to 30 carbon atoms, an alkenyl group with 2 to 30 carbon atoms, or an alkynyl group with 2 to 30 carbon atoms, which can be substituted by hydrogen atoms, halogen atoms, hydroxyl groups, or carboxyl groups; R 202 This indicates an alkylene group having 1 to 30 carbon atoms, an alkenyl group having 2 to 30 carbon atoms, or an ynylene group having 2 to 30 carbon atoms; here, R 201 With R 202 It can form a ring structure.

[0147] Examples of compounds represented by formula (1) include, for example, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, or compounds represented by formula (4) below (Si363 manufactured by Evonik Degussa), etc., and compounds represented by formula (4) below may be used appropriately. These may be used alone or in combination of two or more.

[0148]

[0149] Compounds comprising binding unit A as shown in formula (2) and binding unit B as shown in formula (3) can be exemplified by manufacturers and sellers such as Momentive. These can be used alone or in combination of two or more.

[0150] When a silane coupling agent is included, from the viewpoint of improving the dispersibility of silica, the total content of the silane coupling agent relative to 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, even more preferably 2.0 parts by mass or more, and particularly preferably 4.0 parts by mass or more. Furthermore, from the viewpoint of preventing a decrease in abrasion resistance, this total content is preferably 20 parts by mass or less, more preferably 12 parts by mass or less, even more preferably 10 parts by mass or less, and particularly preferably 9.0 parts by mass or less.

[0151] From the viewpoint of improving the dispersibility of silica, the content of silane coupling agent (total amount when multiple silane coupling agents are used) relative to 100 parts by mass of silica is preferably 1.0 parts by mass or more, more preferably 3.0 parts by mass or more, and even more preferably 5.0 parts by mass or more. Furthermore, from the viewpoint of cost and processability, this 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.

[0152] Besides carbon black and silica, other fillers can also be used as fillers. There are no particular limitations on the type of filler used; for example, commonly used fillers in this field such as aluminum hydroxide, bauxite (alumina), calcium carbonate, magnesium sulfate, talc, and clay can all be used. These fillers can be used individually or in combination.

[0153] <Plasticizer>

[0154] The rubber composition of the present invention preferably contains a plasticizer. Examples of plasticizers include resin components, oils, liquid rubbers, ester-based plasticizers, etc.

[0155] The rubber composition constituting the first layer 6 and the second layer 7 preferably contains a resin component. There are no particular limitations on the resin component; examples include petroleum resins, terpene resins, rosin resins, and phenolic resins commonly used in the tire industry. One of these resin components may be used alone, or two or more may be used in combination. Furthermore, preferably, at least one of the rubber composition constituting the first layer 6 and the rubber composition constituting the second layer 7 contains an aromatic petroleum resin.

[0156] In this specification, "C5 series petroleum resin" refers to resin obtained by polymerizing C5 fractions. Examples of C5 fractions include petroleum fractions with 4 to 5 carbon atoms, such as cyclopentadiene, pentene, pentadiene, and isoprene. Dicyclopentadiene resin (DCPD resin) is a suitable C5 series petroleum resin.

[0157] In this specification, "aromatic petroleum resin" refers to resins obtained by polymerizing C9 fractions, or their hydrides or modifications. Examples of C9 fractions include, for example, vinyltoluene, alkylstyrene, indene, methylindene, and other petroleum fractions with 8 to 10 carbon atoms. Specific examples of aromatic petroleum resins include, for example, benzofuran-indene resins, benzofuran resins, indene resins, and aromatic vinyl resins. As aromatic vinyl resins, homopolymers of α-methylstyrene or styrene, or copolymers of α-methylstyrene and styrene, are preferred for their economic efficiency, ease of processing, and excellent exothermic properties; copolymers of α-methylstyrene and styrene are more preferred. Commercially available products from companies such as CLAYTON and Eastman Chemical can be used as aromatic vinyl resins.

[0158] In this specification, "C5C9 series petroleum resin" refers to a resin obtained by copolymerizing the C5 fraction with the C9 fraction, or it may be a hydride or modified form of the same. Examples of C5 and C9 fractions include the aforementioned petroleum fractions. Commercially available products from companies such as Tosoh Corporation and Luhua Corporation can be used as C5C9 series petroleum resins.

[0159] Examples of terpene resins include polyterpene resins formed from at least one terpene compound selected from α-pinene, β-pinene, limonene, and dipentene; aromatic modified terpene resins made from said terpene compounds and aromatic compounds; terpene phenolic resins made from terpene compounds and phenolic compounds; and those obtained by hydrogenating these terpene resins (hydrogenated terpene resins). Examples of aromatic compounds used as raw materials for aromatic modified terpene resins include, for example, styrene, α-methylstyrene, vinyltoluene, and divinyltoluene. Examples of phenolic compounds used as raw materials for terpene phenolic resins include, for example, phenol, bisphenol A, cresol, and xylenol.

[0160] As a rosin-based resin, there are no particular limitations; examples include natural rosin resin and rosin-modified resins that have been modified through hydrogenation, disproportionation, dimerization, esterification, etc.

[0161] As a phenolic resin, there are no particular limitations; examples include phenolic resin, alkylphenolic resin, alkylphenol acetylene resin, and oil-modified phenolic resin.

[0162] From the viewpoint of wet grip performance, the softening point of the resin component is preferably 60°C or higher, more preferably 65°C or higher. Furthermore, from the viewpoint of processability and improving the dispersibility of the rubber component and filler, this softening point is preferably 150°C or lower, more preferably 140°C or lower, and even more preferably 130°C or lower. Additionally, the softening point in this specification can be defined as the temperature at which the ball falls, as specified in JIS K 6220-1:2001, measured using a ring-and-ball softening point measuring device.

[0163] When the resin component is present, from the viewpoint of wet grip performance, its content relative to 100 parts by weight of rubber component is preferably 1 part by weight or more, more preferably 3 parts by weight or more, and even more preferably 5 parts by weight or more. Furthermore, from the viewpoint of suppressing heat generation, this content is preferably 60 parts by weight or less, more preferably 50 parts by weight or less, even more preferably 40 parts by weight or less, and particularly preferably 30 parts by weight or less.

[0164] The ratio of the resin content in the rubber composition constituting the second layer 7 to the resin content in the rubber composition constituting the first layer 6 relative to 100 parts by mass of the rubber component is preferably 3.0 or less, more preferably 2.4 or less, even more preferably 1.9 or less, and particularly preferably 1.4 or less. When this ratio exceeds 3.0, localized rigidity differences are easily generated at the interface between the first layer 6 and the second layer 7, and the first layer 6 is more prone to large deformation, thus raising concerns about partial peeling of the first layer 6 and decreased wet grip performance. Furthermore, this ratio is preferably 0.3 or more, more preferably 0.5 or more, even more preferably 0.7 or more, and particularly preferably 1.0 or more. When this ratio is less than 0.3, the liquid component, which is the plasticizer in the second layer, increases, raising concerns about plasticizer migrating from the second layer 7 to the first layer 6 during driving.

[0165] Examples of oils include processing oils, vegetable oils, and animal fats. Examples of processing oils include paraffin-based processing oils, naphthenic processing oils, and aromatic processing oils. Furthermore, for environmental reasons, processing oils with low polycyclic aromatic compounds (PCA) content can also be used. Examples of processing oils with low PCA content include moderately solvent-extracted oils (MES), treated distillate aromatic oils (TDAE), and heavy naphthenic oils.

[0166] When oil is present, from a processability perspective, the oil content is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 15 parts by mass or more, relative to 100 parts by mass of the rubber component. Furthermore, from a wear resistance perspective, this content is preferably 120 parts by mass or less, more preferably 100 parts by mass or less, and even more preferably 90 parts by mass or less. Additionally, in this specification, the oil content also includes the amount of oil contained in the oil-extended rubber.

[0167] Liquid rubber is any polymer that is liquid at room temperature (25°C) without any particular limitations. Examples include liquid butadiene rubber (liquid BR), liquid styrene-butadiene rubber (liquid SBR), liquid isoprene rubber (liquid IR), liquid styrene-isoprene rubber (liquid SIR), and liquid farnesene rubber. These liquid rubbers can be used alone or in combination of two or more.

[0168] When liquid rubber is present, its content relative to 100 parts by mass of rubber component is preferably 1 part by mass or more, more preferably 2 parts by mass or more, even more preferably 3 parts by mass or more, and particularly preferably 5 parts by mass or more. Furthermore, the content of 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.

[0169] Examples of ester-based plasticizers include dibutyl adipate (DBA), diisobutyl adipate (DIBA), dioctyl adipate (DOA), di(2-ethylhexyl) azelaate (DOZ), dibutyl sebacate (DBS), diisononyl adipate (DINA), diethyl phthalate (DEP), dioctyl phthalate (DOP), diundecyl phthalate (DUP), dibutyl phthalate (DBP), dioctyl sebacate (DOS), tributyl phosphate (TBP), trioctyl phosphate (TOP), triethyl phosphate (TEP), trimethyl phosphate (TMP), thymidine triphosphate (TTP), tricresyl phosphate (TCP), and tri(xyl) phosphate (TXP). These ester-based plasticizers can be used alone or in combination of two or more.

[0170] From the viewpoint of wet grip performance, the content of plasticizer (total amount when multiple plasticizers are used) is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 15 parts by mass or more, relative to 100 parts by mass of rubber component. Furthermore, from the viewpoint of processability, this content is preferably 120 parts by mass or less, more preferably 100 parts by mass or less, even more preferably 90 parts by mass or less, and particularly preferably 80 parts by mass or less.

[0171] <Other compounding agents>

[0172] In addition to the above-mentioned components, the rubber composition of the present invention may also contain appropriate compounding agents commonly used in the tire industry, such as waxes, processing aids, stearic acid, zinc oxide, antioxidants, vulcanizing agents, vulcanization accelerators, etc.

[0173] When wax is present, from the viewpoint of improving the weather resistance of rubber, the wax content is preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, and even more preferably 1.5 parts by mass or more, relative to 100 parts by mass of rubber component. Furthermore, from the viewpoint of preventing tire whitening due to blooming, this content is preferably 10 parts by mass or less, more preferably 5.0 parts by mass or less.

[0174] Examples of processing aids include, for example, 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 can be used alone or in combination of two or more. Commercially available products from companies such as Schill+Seilacher and Performance Additives can be used as processing aids.

[0175] When processing aids are included, from the viewpoint of improving processability, the content of processing aids is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 1.5 parts by mass or more, relative to 100 parts by mass of rubber component. Furthermore, from the viewpoint of abrasion resistance and tensile strength, this content is preferably 10 parts by mass or less, more preferably 8.0 parts by mass or less.

[0176] There are no particular limitations on the antioxidants used, and examples include various compounds of the amine, quinoline, quinone, phenol, and imidazole series, or metal carbamate salts. Preferred antioxidants include 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, as well as quinoline-based antioxidants such as 2,2,4-trimethyl-1,2-dihydroquinoline polymers and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline. These antioxidants can be used alone or in combination of two or more.

[0177] When an antioxidant is included, based on the viewpoint of the rubber's resistance to ozone cracking, the antioxidant content is preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, and even more preferably 1.5 parts by mass or more, relative to 100 parts by mass of the rubber component. Furthermore, based on the viewpoint of abrasion resistance and wet grip performance, this content is preferably 10 parts by mass or less, more preferably 5 parts by mass or less.

[0178] When stearic acid is present, from a processability perspective, the stearic acid content is preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, and even more preferably 1.5 parts by mass or more, relative to 100 parts by mass of the rubber component. Furthermore, from a vulcanization rate perspective, this content is preferably 10 parts by mass or less, more preferably 5.0 parts by mass or less.

[0179] When zinc oxide is present, from a processability perspective, the zinc oxide content is preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, and even more preferably 1.5 parts by mass or more, relative to 100 parts by mass of the rubber component. Furthermore, from a wear resistance perspective, this content is preferably 10 parts by mass or less, more preferably 5.0 parts by mass or less.

[0180] Sulfur can be used as a vulcanizing agent. Powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersed sulfur can be used.

[0181] When sulfur is included as a vulcanizing agent, from the viewpoint of ensuring a sufficient vulcanization reaction, its content relative to 100 parts by weight of rubber component is preferably 0.1 parts by weight or more, more preferably 0.3 parts by weight or more, and even more preferably 0.5 parts by weight or more. Furthermore, from the viewpoint of preventing deterioration, this content is preferably 5.0 parts by weight or less, more preferably 4.0 parts by weight or less, and even more preferably 3.0 parts by weight or less. Moreover, when oil-containing sulfur is used as a vulcanizing agent, the content of the vulcanizing agent is the total content of pure sulfur components contained in the oil-containing sulfur.

[0182] Examples of vulcanizing agents other than desulfurization include alkylphenol-sulfur chloride condensate, sodium 1,6-hexamethylene dithiosulfate dihydrate, and 1,6-bis(N,N'-dibenzylthiocarbamoyl dithio)hexane. These vulcanizing agents, other than desulfurization agents, can be commercially available from companies such as Taoka Chemical Industry Co., Ltd., Lanxess Co., Ltd., and Flexis Co., Ltd.

[0183] Examples of vulcanization accelerators include, for example, sulfenamide-based, thiazole-based, thiuram-based, thiourea-based, guanidine-based, dithiocarbamate-based, aldehyde-amine-based or aldehyde-amine-based, imidazoline-based, or xanthate-based vulcanization accelerators. These vulcanization accelerators can be used alone or in combination of two or more. Preferably, one or more vulcanization accelerators selected from sulfenamide-based, guanidine-based, and thiazole-based vulcanization accelerators are used, and sulfenamide-based vulcanization accelerators are more preferred.

[0184] Examples of sulfenamide-based vulcanization accelerators include, for example, N-tert-butyl-2-benzothiazolyl sulfenamide (TBBS), N-cyclohexyl-2-benzothiazolyl sulfenamide (CBS), and N,N-dicyclohexyl-2-benzothiazolyl sulfenamide (DCBS). Among these, N-cyclohexyl-2-benzothiazolyl sulfenamide (CBS) is preferred.

[0185] Examples of guanidine-based vulcanization accelerators include, for example, 1,3-diphenylguanidine (DPG), 1,3-di-o-tolylguanidine, 1-o-tolylbiguanidine, di-o-tolylguanidine salts of biscatechol borate, 1,3-di-o-isopropylphenylguanidine, 1,3-di-o-biphenylguanidine, and 1,3-di-o-isopropylphenyl-2-propionylguanidine. Among these, 1,3-diphenylguanidine (DPG) is preferred.

[0186] Examples of thiazole-based sulfidation accelerators include 2-mercaptobenzothiazole, cyclohexylamine salts of 2-mercaptobenzothiazole, and di-2-benzothiazole disulfides. Among these, 2-mercaptobenzothiazole is preferred.

[0187] When a vulcanization accelerator is included, the content of the vulcanization accelerator relative to 100 parts by weight of the rubber component is preferably 1 part by weight or more, more preferably 2 parts by weight or more. Furthermore, the content of the vulcanization accelerator relative to 100 parts by weight of the rubber component is preferably 8 parts by weight or less, more preferably 7 parts by weight or less, and even more preferably 6 parts by weight or less. By setting the content of the vulcanization accelerator within the above range, there is a tendency to ensure both breaking strength and elongation.

[0188] The rubber composition of the present invention can be manufactured by known methods. For example, it can be manufactured by mixing the above-mentioned components using a rubber mixing apparatus such as an open roller mill or a closed mixing mill (Banbury mill, kneader, etc.).

[0189] The kneading process includes, for example, a basic kneading process that mixes compounding agents and additives other than vulcanizing agents and vulcanization accelerators, and a final kneading process (F-kneading) that adds vulcanizing agents and vulcanization accelerators to the mixture obtained in the basic kneading process. Furthermore, the basic kneading process may be divided into multiple steps as needed.

[0190] There are no particular limitations on the mixing conditions. For example, in the basic kneading process, mixing can be carried out at a discharge temperature of 150–170°C for 3–10 minutes, and in the final kneading process, mixing can be carried out at 70–110°C for 1–5 minutes. There are no particular limitations on the vulcanization conditions. For example, vulcanizing can be carried out at 150–200°C for 10–30 minutes.

[0191] [tire]

[0192] The tire of the present invention has a tread comprising a first layer 6, a second layer 7, and a third layer 8, and can be a pneumatic tire or a non-pneumatic tire. Furthermore, it is suitable for use in racing tires, passenger car tires, large passenger car tires, large SUV tires, and motorcycle tires, and can be used as their respective summer tires, winter tires, and studless tires.

[0193] Tires having a tread comprising a first layer 6, a second layer 7, and a third layer 8 can be manufactured using the aforementioned rubber composition by conventional methods. Specifically, an uncured rubber composition, in which the aforementioned components are mixed as needed relative to the rubber components, is extruded into the shapes of the first layer 6, the second layer 7, and the third layer 8 using an extruder with a die of a predetermined shape. This composition is then bonded to other tire components on a tire forming machine and molded using conventional methods to form an uncured tire. The uncured tire can then be manufactured by heating and pressurizing it in a vulcanizing machine.

[0194] [Example]

[0195] The present invention is illustrated based on the embodiments, but the present invention is not limited to the embodiments.

[0196] The following summarizes the various chemicals used in the examples and comparative examples.

[0197] NR: TSR20

[0198] SBR1: Tufdene 4850 manufactured by Asahi Kasei Corporation (unmodified S-SBR, styrene content: 40% by mass, vinyl content: 46% by mole, Mw: 350,000, contains 50 parts by mass of oil relative to 100 parts by mass of rubber solids).

[0199] SBR2: Modified S-SBR manufactured in Manufacturing Example 1 described later (styrene content: 40% by mass, vinyl content: 25% by mol%, Mw: 1 million, non-oil-extended).

[0200] SBR3: Modified S-SBR manufactured in Manufacturing Example 2 described later (styrene content: 25% by mass, vinyl content: 25% by mol%, Mw: 1 million, non-oil-extended).

[0201] BR: Ube Industries, Inc. UBEPOL BR (registered trademark) 150B (vinyl content: 1.5 mol%, cis content: 97% by mass, Mw: 440,000)

[0202] Carbon Black 1: SHOWBLACK N330 (N2SA: 75m) manufactured by Cabot Japan Co., Ltd. 2 / g)

[0203] Carbon Black 2: SHOWBLACK N220 (N2SA: 110m) manufactured by Cabot Japan Co., Ltd. 2 / g)

[0204] Silica: Ultrasil VN3 (N2SA: 175m) manufactured by Evonik Degussa 2 / g)

[0205] Silane coupling agent 1: NXT-Z45 (thiol-based silane coupling agent) manufactured by Momentive.

[0206] Silane coupling agent 2: Si266 (bis(3-triethoxysilylpropyl) disulfide) manufactured by Evonik Degussa.

[0207] Oil: VivaTec 500 (TDAE oil) manufactured by H&R.

[0208] Resin composition: Sylvares SA85 (a copolymer of α-methylstyrene and styrene, softening point: 85℃) manufactured by CLAYTON.

[0209] Antioxidant: ANTIGENE 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd.

[0210] Wax: SUNNOC N manufactured by Ouchi Shinshin Chemical Industry Co., Ltd.

[0211] Stearic acid: Stearic acid beads "Tsubaki" manufactured by Nippon Oil Co., Ltd.

[0212] Zinc oxide: Zinc oxide No. 2 manufactured by Mitsui Metals & Minerals Co., Ltd.

[0213] Sulfur: Powdered sulfur manufactured by Karuizawa Sulfur Co., Ltd.

[0214] Vulcanization accelerator 1: NOCCELER CZ (N-cyclohexyl-2-benzothiazolyl sulfenamide) manufactured by Ouchi Shinsei Chemical Co., Ltd.

[0215] Vulcanization accelerator 2: NOCCELER D (1,3-diphenylguanidine (DPG)) manufactured by Ouchi Shinsei Chemical Co., Ltd.

[0216] Manufacturing Example 1: Synthesis of SBR2

[0217] Cyclohexane, tetrahydrofuran, styrene, and 1,3-butadiene were added to a nitrogen-purged autoclave reactor. The ratio of styrene to 1,3-butadiene was adjusted to achieve a styrene content of 40% by mass. After adjusting the reactor contents temperature to 20°C, n-butyllithium was added to initiate polymerization. Polymerization was carried out under adiabatic conditions, reaching a maximum temperature of 80°C. When the polymerization conversion reached 99%, 1,3-butadiene was added, and after another 5 minutes of polymerization, N,N-bis(trimethylsilyl)-3-aminopropyltrimethoxysilane was added as a modifier. After the polymerization reaction was completed, 2,6-di-tert-butyl-p-cresol was added. Then, the solvent was removed by stripping, and the product was dried by hot roller drying at 110°C to obtain SBR2.

[0218] Manufacturing Example 2: Synthesis of SBR3

[0219] Except for adjusting the ratio of styrene and 1,3-butadiene to make the styrene content 25% by mass, the rest was obtained by the same method as in manufacturing example 1 to obtain SBR3.

[0220] (Examples and Comparative Examples)

[0221] Following the formulations shown in Tables 1, 2, and 4, a 1.7L closed-type Banbury mixer was used to mix the chemicals, excluding sulfur and vulcanization accelerators, for 1–10 minutes until the discharge temperature reached 150–160°C, yielding a compound. Then, using a 2-axis open roll mill, sulfur and vulcanization accelerators were added to the resulting compound, and kneading was continued for 4 minutes until reaching 105°C, yielding an unvulcanized rubber composition. Using the obtained unvulcanized rubber composition, the first, second, and third layers of the tread were shaped and bonded to other tire components to produce unvulcanized tires. These tires were then vulcanized at 170°C to obtain the test tires shown in Tables 3 and 5 (size: 195 / 65R15, rim: 15×6.0J, internal pressure: 230kPa).

[0222] <Determination of loss tangent tanδ, complex elastic modulus E*, and glass transition temperature (Tg)>

[0223] Rubber test pieces, 20 mm long × 4 mm wide × 1 mm thick, were cut from the inner rubber layer of the tread of each test tire, with the tire circumference as the long side. For these rubber test pieces, the loss tangent (tanδ) and complex elastic modulus (E*) were measured using an Eplexor series instrument manufactured by GABO at 30°C, 10% initial strain, 1% dynamic strain, and 10 Hz. Additionally, the temperature distribution curve of the loss tangent (tanδ) was measured under the conditions of 10% initial strain, 1% dynamic strain, and 10 Hz. The temperature corresponding to the maximum tanδ value in the obtained temperature distribution curve (tanδ peak temperature) was taken as the glass transition temperature (Tg). Furthermore, the thickness direction of the sample was radial to the tire.

[0224] <Determination of Acetone Extraction Volume (AE Volume)>

[0225] Each vulcanized rubber test piece was immersed in acetone for 24 hours to extract the soluble components. The mass of each test piece before and after extraction was measured, and the amount of acetone extracted was calculated using the following formula.

[0226] Acetone extraction yield (%) = {(mass of rubber test pieces before extraction - mass of rubber test pieces after extraction) / (mass of rubber test pieces before extraction)} × 100

[0227] In addition, each rubber test piece was cut from the inside of the rubber layer of the tread of each test tire.

[0228] <Determination of Rubber Hardness (Hs)>

[0229] In accordance with JIS K 6253-3:2012, the Shore hardness (Hs) of each rubber test piece at 23°C was determined using a type A durometer. Furthermore, each rubber test piece was cut from the inside of the rubber layer of the tread of each test tire.

[0230] Tensile Test

[0231] Dumbbell-shaped test pieces (size 7) with a thickness of 1 mm were prepared by cutting from the inside of the rubber layer of the tread of each test tire, with the tire circumferential direction as the tensile direction. Tensile tests were conducted according to JIS K 6251:2017 "Vulcanized rubber and thermoplastic rubber - Determination of tensile test properties" at 23°C and a tensile speed of 3.3 mm / s, and the modulus (MPa) at 100% elongation was measured. The thickness direction of the sample was radial to the tire.

[0232] Low fuel consumption performance

[0233] Using a rolling resistance tester, the rolling resistance of each test tire when new was measured under the conditions of a rim of 15×6.0J, internal pressure of 230kPa, load of 4.24kN, and speed of 80km / h. The reciprocal of the rolling resistance was expressed as an exponent, with the benchmark comparison examples (Comparative Example 1 in Table 3 and Comparative Example 3 in Table 5, the same below) set to 100. A higher value indicates lower rolling resistance and better fuel economy.

[0234] <Wet grip performance of tires when new and after wear>

[0235] Each test tire (size: 195 / 65R15, rim: 15×6.0J, internal pressure: 230kPa) was installed on all wheels of a vehicle (domestic FF2000cc). Braking distances from the braking point at 100km / h were measured on a wet asphalt surface. Alternatively, after subjecting the tires to 7 days of thermal degradation at 80°C, the tread was worn along the tread radius until the tread thickness was 50% of its new thickness. The worn test tires were then installed on all wheels of the same vehicle, and braking distances from the braking point at 100km / h were measured on a wet asphalt surface. The braking distances of the test tires in Comparative Example 1, both when new and after wear, were 100km / h. The wet grip performance of each tire, both when new and after wear, was expressed as an index using the following formula. A higher index indicates better wet grip performance.

[0236] (Wet grip performance index when new) = (Braking distance of the benchmark tire when new) / (Braking distance of each test tire when new) × 100

[0237] (Wear-worn wet grip performance index) = (Braking distance of the benchmark tire after wear) / (Braking distance of each test tire after wear) × 100

[0238] The performance target value for the comprehensive performance of low fuel consumption performance, wet grip performance when new, and wet grip performance after wear (the sum of the low fuel consumption performance index, the wet grip performance index when new, and the wet grip performance index after wear) is set to be over 300.

[0239] [Table 1]

[0240]

[0241] [Table 2]

[0242] Table 2

[0243]

[0244] [Table 3]

[0245]

[0246] [Table 4]

[0247]

[0248] [Table 5]

[0249]

[0250] As can be seen from the results in Tables 1 to 5, the tire of the present invention, which has two or more rubber layers in the tread and whose complex elastic modulus E* and loss tangent tanδ of the rubber layer satisfy the specified relationship, has improved overall performance in terms of low fuel consumption, wet grip performance when new, and wet grip performance after wear.

Claims

1. A tire having a tread, said tread comprising at least a first layer constituting a tread surface and a second layer radially inwardly adjacent to the first layer, characterized in that, The tread has a land portion separated by a plurality of circumferential grooves extending continuously in the tire circumferential direction. The first and second layers are composed of a rubber composition containing rubber components and plasticizers. The ratio of the complex elastic modulus of the first layer at 30°C to that of the second layer at 30°C is 1.5 to 3.

0. The ratio of the tanδ of the first layer at 30°C to the tanδ of the second layer at 30°C is 1.0~2.

2. The rubber composition constituting the first layer and the rubber composition constituting the second layer also each contain a resin component. The ratio of the resin component content in the rubber composition constituting the second layer to the resin component content in the rubber composition constituting the first layer relative to 100 parts by mass of the rubber component is 2.4 or less.

2. The tire according to claim 1, wherein, The ratio of the tanδ of the first layer at 30°C to the tanδ of the second layer at 30°C is greater than 1.

2.

3. The tire according to claim 1 or 2, wherein, The ratio of the tanδ of the first layer at 30°C to the tanδ of the second layer at 30°C is 1.4 to 2.

0.

4. The tire according to claim 1 or 2, wherein, The butadiene rubber content in the rubber component constituting the first layer is less than 35% by mass.

5. The tire according to claim 1 or 2, wherein, The difference between the acetone extraction amount AE1 of the rubber composition constituting the first layer and the acetone extraction amount AE2 of the rubber composition constituting the second layer, |AE1-AE2|, is less than 10% by mass.

6. The tire according to claim 1 or 2, wherein, At least one of the rubber compositions constituting the first layer and the rubber compositions constituting the second layer contains an aromatic petroleum resin.

7. The tire according to claim 1 or 2, wherein, The tire has a third layer that is radially inner to the second layer.

8. The tire according to claim 1 or 2, wherein, The ratio of the thickness of the first layer to the total thickness of the first and second layers is 0.40 or more.

9. The tire according to claim 1 or 2, wherein, The second layer has a complex elastic modulus of more than 5 MPa at 30°C.

10. The tire according to claim 1 or 2, wherein, The second layer has a tanδ of less than 0.30 at 30°C.

11. The tire according to claim 1 or 2, wherein, The glass transition temperature of the first layer is above -15°C.

12. The tire according to claim 1 or 2, wherein, The second layer, measured according to JIS K 6253-3:2012 using a type A hardness tester at 23°C, has a Shore hardness Hs of 50~80.

13. The tire according to claim 1 or 2, wherein, The modulus of the first layer at 100% elongation is greater than that of the second layer at 100% elongation.

14. The tire according to claim 1 or 2, wherein, The deepest part of the bottom of any of the circumferential grooves is located closer to the radial inner side of the tire than the outermost part of the second layer in the land adjacent to the circumferential groove.

15. The tire according to claim 1 or 2, wherein, The land portion has cutter grooves at both ends that do not open into the circumferential groove.

16. The tire according to claim 1 or 2, wherein, The tire has a portion in which the width of the land portion closest to the tire's equatorial plane increases as it moves from the radially outer side of the tire toward the inner side.

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