Tire

Abstract

Provided is a tire having a tread, the tread being provided with a first layer constituting the tread surface, a second layer adjacent to the first layer on its radially inner side, and a third layer adjacent to the second layer on its radially inner side, wherein the first layer, the second layer, and the third layer are formed of a rubber composition containing a rubber component and a plasticizer, and 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 1.0 mass% or more, and the difference (AE2 - AE3) between the acetone extraction amount AE2 of the rubber composition constituting the second layer and the acetone extraction amount AE3 of the rubber composition constituting the third layer is 1.0 mass% or more.

Description

Technical Field

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

[0002] Patent Document 1 discloses a pneumatic tire that includes tread rubber, which includes a tread surface rubber layer located on the uppermost surface of the tread and a tread inner rubber layer located on the inner side of the tread surface rubber layer in the tire radial direction. In such a tire, the tread surface rubber layer is made of a rubber layer having relatively high rigidity, while the tread inner rubber layer is made of a rubber layer having relatively low rigidity. In this way, the tread surface rubber layer improves the rigidity of the land portion on the tire surface in the tire circumferential direction (e.g., resulting in improved wear resistance), and the tread inner rubber layer suppresses hysteresis loss (e.g., causing improved fuel efficiency of the tire).

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: JP 2014-162242 A Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] However, with the tire as described above, when the tread surface rubber layer wears and the low heat-dissipating tread inner rubber layer is exposed, the wet grip performance drops sharply.

[0008] An object of the present invention is to provide a tire that enables improvement in fuel efficiency while maintaining wet grip performance even after wear.

[0009] Means for Solving the Problems

[0010] As a result of in-depth research, the inventors have found that the aforementioned problems can be solved by the following means: providing a tread portion having three or more rubber layers, and imparting at least a predetermined level of plasticizer concentration gradient from the rubber layer on the outer side in the tire radial direction toward the rubber layer on the inner side in the tire radial direction, and thus completing the present invention.

[0011] In other words, the present invention relates to:

[0012] [1]A tire having a tread, wherein the tread comprises at least a first layer constituting the tread surface, a second layer disposed adjacent to the inner side of the first layer in the radial direction, and a third layer disposed adjacent to the inner side of the second layer in the radial direction, wherein the first layer, the second layer, and the third layer are composed of a rubber composition containing a rubber component and a plasticizer, 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 1.0% by mass or more, and wherein the difference (AE2 - AE3) between the acetone extraction amount AE2 of the rubber composition constituting the second layer and the acetone extraction amount AE3 of the rubber composition constituting the third layer is 1.0% by mass or more.

[0013] [2]The tire according to [1] above, wherein AE1 - AE2 is 2.0% by mass or more.

[0014] [3]The tire according to [1] or [2] above, wherein AE2 - AE3 is 2.0% by mass or more.

[0015] [4]The tire according to any one of [1] to [3] above, wherein the tanδ of the rubber composition constituting the first layer at 0°C is 1.00 or more.

[0016] [5]The tire according to any one of [1] to [4] above, wherein the elongation at break of the rubber composition constituting the first layer measured according to JIS K 6251 is 610% or more.

[0017] [6]The tire according to any one of [1] to [5] above, wherein the complex modulus (E* at 0°C) of the rubber composition constituting the first layer is 50 MPa or more.

[0018] [7]The tire according to any one of [1] to [6] above, wherein the glass transition temperature of the rubber composition constituting the first layer is -10°C or more.

[0019] [8]The tire according to any one of [1] to [7] above, wherein the glass transition temperature of the rubber composition constituting the first layer is -7°C or more.

[0020] [9]The tire according to any one of [1] to [8] above, wherein the tanδ of the rubber composition constituting the first layer at 30°C is 0.25 or more.

[0021]

[10] The tire according to any one of [1] to [9] above, wherein the tanδ of the rubber composition constituting the first layer at 30°C is 0.30 or more.

[0022]

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

[10] above, wherein the rubber composition constituting the second layer has a tanδ of 0.60 or more at 0°C.

[0023]

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

[11] above, wherein the rubber composition constituting the second layer has an elongation at break measured according to JIS K 6251 of 500% or more.

[0024]

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

[12] above, wherein the rubber composition constituting the second layer has a complex modulus (E* at 0°C) of 25 MPa or more at 0°C.

[0025]

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

[13] above, wherein, based on 100 parts by mass of the rubber component, the rubber compositions constituting the first layer and the second layer each contain a total of 40 to 160 parts by mass of silica and carbon black, and the proportion of the silica content is 60% by mass or more relative to the total content of silica and carbon black.

[0026]

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

[14] above, wherein, based on 100 parts by mass of the rubber component, the rubber composition constituting the first layer contains 100 parts by mass or more of silica.

[0027]

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

[15] above, wherein, based on 100 parts by mass of the rubber component, the rubber compositions constituting the first layer and the second layer each contain 10 parts by mass or more of a plasticizer.

[0028]

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

[16] above, wherein the rubber components constituting the first layer and the second layer each include 50% by mass of styrene-butadiene rubber.

[0029]

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

[17] above, wherein at least one selected from the group consisting of a sealant, a noise damper, and an electronic component for tire monitoring is provided in the tire inner cavity.

[0030] Advantages of the Invention

[0031] According to the present invention, a tire is provided which enables improvement in fuel efficiency while maintaining wet grip performance even after wear. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is an enlarged cross-sectional view showing a part of the tread of a tire according to an embodiment of the present disclosure. Detailed Embodiment

[0033] A tire according to an embodiment of the present invention is a tire having a tread, the tread including at least a first layer constituting the tread surface, a second layer disposed adjacent to the inner side of the first layer in the radial direction, and a third layer disposed adjacent to the inner side of the second layer in the radial direction, wherein the first layer, the second layer, and the third layer are composed of a rubber composition containing a rubber component and a plasticizer, 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 1.0 mass% or more, and wherein the difference (AE2 - AE3) between the acetone extraction amount AE2 of the rubber composition constituting the second layer and the acetone extraction amount AE3 of the rubber composition constituting the third layer is 1.0 mass% or more (2.0 mass% or more).

[0034] In the tire of the present disclosure, the second layer is disposed adjacent to the inner side of the first layer in the radial direction, the first layer constituting the tread surface, and is lower than the first layer in terms of heat dissipation, so that an improvement in fuel efficiency can be achieved while maintaining wet grip performance.

[0035] It is considered that in the tire of the present disclosure, a plasticizer concentration gradient of at least a predetermined level is imparted from the rubber layer on the outer side in the tire radial direction to the rubber layer on the inner side in the tire radial direction, allowing the plasticizer to be promoted to transfer from the rubber layer on the outer side in the tire radial direction to the rubber layer on the inner side in the tire radial direction due to the stimulation during driving, and ensuring wet grip performance even when the second layer is exposed due to wear, so that the wet grip performance can be maintained for a long period of time.

[0036] The steps of manufacturing a tire according to an embodiment of the present disclosure will be described in detail below. Note that the following description is for illustrative purposes of the present invention and is not intended to limit the technical scope of the present invention only to the described scope. Further, in the specification, a numerical range shown using the expression "to" includes the numerical values at both ends thereof.

[0037] Figure 1 is an enlarged cross-sectional view showing a part of the tread of the tire according to the present disclosure. In Figure 1 is shown in an enlarged manner a part of the tread surface of the tread according to the present disclosure, in which no grooves are formed. In Figure 1 the up-down direction is the tire radial direction, the left-right direction is the tire axial direction, and the direction perpendicular to the paper surface is the tire circumferential direction.

[0038] As shown in the figure, the tread portion of the tire of the present disclosure includes a first layer 2, a second layer 3, and a third layer 4. The outer surface of the first layer 2 constitutes the tread surface 1. The second layer 3 is disposed adjacent to the inner side of the first layer 2 in the radial direction, and the third layer 4 is disposed adjacent to the inner side of the second layer 3 in the radial direction. The first layer 2 generally corresponds to the cap tread. The second layer 3 and the third layer 4 generally correspond to the base tread or the under tread. In addition, as long as the object of the present invention is achieved, one or more rubber layers may be provided between the third layer 4 and the belt layer.

[0039] In Figure 1 it, the double-headed arrow t1 is the thickness of the first layer 2, the double-headed arrow t2 is the thickness of the second layer 3, and the double-headed arrow t3 is the thickness of the third layer 4. In Figure 1 it, any point on the tread surface (where no groove is formed) is shown as the symbol P. The straight line shown by the symbol N is a straight line (normal line) passing through the point P and perpendicular to the contact plane of the point P. In this specification, in Figure 1 the cross-section of, the thicknesses t1, t2, and t3 are measured along the normal line N drawn from the point P on the tread surface, and there is no groove at the point P.

[0040] In the present disclosure, the thickness t1 of the first layer 2 is not particularly limited, but from the perspective of wet grip performance, it is preferably 1.0 mm or more, more preferably 1.5 mm or more, and still more preferably 2.0 mm or more. On the other hand, from the perspective of heat generation, the thickness t1 of the first layer 2 is preferably 10.0 mm or less, more preferably 9.0 mm or less, and still more preferably 8.0 mm or less.

[0041] In the present disclosure, the thickness t2 of the second layer 3 is not particularly limited, but it is preferably 1.5 mm or more, more preferably 2.0 mm or more, and still more preferably 2.5 mm or more. In addition, the thickness t2 of the second layer 3 is preferably 10.0 mm or less, more preferably 9.0 mm or less, and still more preferably 8.0 mm or less.

[0042] In the present disclosure, the thickness t3 of the third layer 4 is not particularly limited, but it is preferably 1.0 mm or more, more preferably 1.5 mm or more. In addition, the thickness t3 of the third layer 4 is preferably 10.0 mm or less, more preferably 9.0 mm or less, and still more preferably 8.0 mm or less.

[0043] From the perspective of fuel efficiency, the ratio (t2 / t1) of the thickness t2 of the second layer 3 to the thickness t1 of the first layer 2 is preferably 0.4 or more, more preferably 0.5 or more, further preferably 0.7 or more, and particularly preferably 0.9 or more. On the other hand, from the perspective of wet grip performance, it is preferably 5.0 or less, more preferably 4.5 or less, more preferably 4.0 or less, and particularly preferably 3.5 or less.

[0044] From the perspective of better demonstrating the effects of the present disclosure, the ratio (t3 / t2) of the thickness t3 of the third layer 4 to the thickness t2 of the second layer 3 is preferably 0.2 or more, more preferably 0.3 or more, and even more preferably 0.4 or more. On the other hand, from the perspective of better demonstrating the effects of the present disclosure, the ratio (t3 / t2) of the thickness t3 of the third layer 4 to the thickness t2 of the second layer 3 is preferably 3.0 or less, more preferably 2.0 or less, even more preferably 1.5 or less, and particularly preferably 0.9 or less.

[0045] For the tire of the present disclosure, a sealant, a noise damping body, an electronic component for tire monitoring, etc. may be provided in the tire cavity.

[0046] As the sealant, those sealants commonly used for the inner peripheral surface of the tread portion for puncture prevention can be appropriately used. Specific examples of such a sealant layer include, for example, the sealant layer disclosed in JP 2020-023152 A. Generally, the thickness of the sealant is preferably 1 mm to 10 mm. Generally, the width of the sealant is preferably 85% to 115% of the maximum width of the belt layer, and preferably 95% to 105%.

[0047] Any one of the noise damping bodies can be appropriately used as long as it can exhibit a noise damping effect in the tire cavity. For example, specific examples of the noise damping body include those disclosed in JP 2019-142503 A. For example, the noise damping body is composed of a porous sponge material. The sponge material is a multi-chambered porous structure, and in addition to the so-called sponge itself having interconnected small chambers in which, for example, rubber or synthetic resin is foamed, it also includes a reticulate body, which is an animal fiber, a plant fiber, or a synthetic fiber, etc. that are intertwined or integrally coupled with each other. In addition, the "porous structure" includes a body having not only interconnected small chambers but also closed small chambers. Examples of the noise damping body include a sponge material having interconnected small chambers made of polyurethane. As the sponge material, for example, synthetic resin sponges such as ether-based polyurethane sponges, ester-based polyurethane sponges, and polyethylene sponges; and rubber sponges such as chloroprene rubber sponges (CR sponges), ethylene-propylene rubber sponges (EDPM sponges), and nitrile rubber sponges (NBR sponges) can be appropriately used. In particular, from the perspectives of noise damping properties, light weight properties, controllability of foaming, durability, etc., polyurethane sponges including ether-based polyurethane sponges or polyethylene-based sponges are preferred.

[0048] The noise damping body has an elongated strip shape, which has a bottom surface fixed to the inner cavity surface of the tread portion and extending in the circumferential direction of the tire. At this time, the outer ends thereof in the circumferential direction can be made to contact each other to form a substantially annular shape, or the outer ends thereof can be spaced apart in the circumferential direction.

[0049] The "tanδ at 0°C" in the present disclosure refers to the tangent of the loss angle tanδ under the conditions of a temperature of 0°C, a frequency of 10 Hz, and an elongation strain of 2.5%. From the perspective of wet grip performance, the tanδ at 0°C of the rubber composition constituting the first layer 2 is preferably 1.00 or more, more preferably 1.05 or more, still more preferably 1.10 or more, and particularly preferably 1.15 or more. In addition, the tanδ at 0°C of the rubber composition constituting the second layer 3 is preferably 0.60 or more, more preferably 0.64 or more, and still more preferably 0.68 or more. On the other hand, from the perspective of fuel efficiency, the tanδ at 0°C of the rubber compositions constituting the first layer 2, the second layer 3, and the third layer 4 is preferably 1.60 or less, more preferably 1.55 or less, and still more preferably 1.50 or less. In addition, the value of the tanδ at 0°C of the rubber composition constituting the first layer 2 is preferably greater than the value of the tanδ at 0°C of the rubber composition constituting the second layer 3. The difference between the tanδ at 0°C of the rubber composition constituting the first layer 2 and the tanδ at 0°C of the rubber composition constituting the second layer 3 is preferably 0.10 or more, more preferably 0.20 or more, further preferably 0.30 or more, and particularly preferably 0.40 or more.

[0050] The "tanδ at 30°C" in the present disclosure refers to the tangent of the loss angle tanδ under the conditions of a temperature of 30°C, a frequency of 10 Hz, and an elongation strain of 2.5%. From the perspective of wet grip performance, the tanδ at 30°C of the rubber composition constituting the first layer 2 is preferably 0.25 or more, more preferably 0.28 or more, further preferably 0.29 or more, further preferably 0.30 or more, further preferably 0.31 or more, further preferably 0.32 or more, and particularly preferably 0.33 or more. In addition, the tanδ at 30°C of the rubber composition constituting the second layer 3 is preferably 0.15 or more, more preferably 0.17 or more, more preferably 0.19 or more, and particularly preferably 0.21 or more. On the other hand, from the perspective of fuel efficiency, the tanδ at 30°C of the rubber compositions constituting the first layer 2, the second layer 3, and the third layer 4 is preferably 0.65 or less, more preferably 0.60 or less, more preferably 0.55 or more, more preferably 0.50 or more, and particularly preferably 0.45 or more. In addition, the value of the tanδ at 30°C of the rubber composition constituting the first layer 2 is preferably greater than the value of the tanδ at 30°C of the rubber composition constituting the second layer 3. The difference between the tanδ at 30°C of the rubber composition constituting the first layer 2 and the tanδ at 30°C of the rubber composition constituting the second layer 3 is preferably 0.02 or more, more preferably 0.04 or more, further preferably 0.06 or more, and particularly preferably 0.08 or more.

[0051] In the present disclosure, EB refers to the elongation at break (elongation at the time of break) measured according to Japanese Industrial Standard JIS K 6251 under the conditions of an atmospheric temperature of 23°C and a tensile speed of 3.3 mm / second. From the perspective of maintaining the smoothness of the surface, the EB of the rubber composition constituting the first layer 2 is preferably 610% or more, more preferably 620% or more, still more preferably 630% or more, and particularly preferably 640% or more. In addition, the EB of the rubber composition constituting the second layer 3 is preferably 500% or more, more preferably 510% or more, still more preferably 520% or more, and particularly preferably 530% or more. It is considered that keeping EB within the previously described range allows the state of the surface during tire wear to be maintained in a smoother state, thereby suppressing the reduction in the actual ground contact area, and thus making it possible to suppress the deterioration of wet grip performance after the tire is worn. In addition, there is no particular limitation on the upper limit of EB of the rubber compositions constituting the first layer 2, the second layer 3, and the third layer 4.

[0052] "E* at 0°C" in the present disclosure refers to the complex modulus E under the conditions of a temperature of 0°C, a frequency of 10 Hz, and an elongation strain of 2.5%. * . From the perspective of anchoring friction, the E* at 0°C of the rubber composition constituting the first layer 2 is preferably 50 MPa or more, more preferably 55 MPa or more, still more preferably 60 MPa or more. In addition, from the perspective of anchoring friction, the E* at 0°C of the rubber composition constituting the second layer 3 is preferably 25 MPa or more, more preferably 30 MPa or more, still more preferably 35 MPa or more. On the other hand, from the perspective of road surface followability, the E* at 0°C of the rubber compositions constituting the first layer 2, the second layer 3, and the third layer 4 is preferably 85 MPa or less, more preferably 80 MPa or less, still more preferably 75 MPa or less. In addition, the value of E* at 0°C of the rubber composition constituting the first layer 2 is preferably greater than the value of E* at 0°C of the rubber composition constituting the second layer 3. The difference between the E* at 0°C of the rubber composition constituting the first layer 2 and the E* at 0°C of the rubber composition constituting the second layer 3 is preferably 5 MPa or more, more preferably 8 MPa or more, and still more preferably 12 MPa or more. It is considered that E* at 0°C within the aforementioned range * allows the balance between road surface followability and anchoring friction to be improved, making it possible to suppress the deterioration of wet grip performance after the tire is worn.

[0053] The glass transition temperature (Tg) in the present disclosure refers to the peak temperature of tanδ measured by the following method. In other words, for each of the rubber test pieces produced by cutting from the inside of the rubber layer in the tread portion of each test tire (for example, length 20 mm × width 4 mm × thickness 1 mm), with the tire circumferential direction being the long side, using a dynamic viscoelasticity evaluation device (EPLEXOR series manufactured by GABO Qualimeter Testanlagen GmbH), the temperature distribution curve of tanδ is measured under the conditions of a frequency of 10 Hz and an elongation strain of 2.5%, and the temperature (tanδ peak temperature) corresponding to the maximum tanδ value in the obtained temperature distribution curve is set as the glass transition temperature (Tg) in the present disclosure. From the perspective of wet grip performance, the Tg of the rubber composition constituting the first layer 2 is preferably -10°C or higher, more preferably -8°C or higher, further preferably -7°C or higher, further preferably -6°C or higher, more preferably -5°C or higher, and particularly preferably -4°C or higher. Compared with the case where Tg is set below -10°C, setting Tg to 10°C or higher results in a tendency for the loss tangent tanδ in the temperature region above Tg to be higher. In addition, the Tg of the rubber composition constituting the second layer 3 is preferably -25°C or higher, more preferably -22°C or higher, more preferably -19°C or higher. In addition, there is no particular limitation on the upper limit of the Tg of the rubber compositions constituting the first layer 2, the second layer 3, and the third layer 4, and the Tg is preferably 20°C or lower, more preferably 15°C or lower, further preferably 10°C or lower, further preferably 5°C or lower, and particularly preferably 0°C or lower. In addition, the Tg of each rubber layer can be appropriately adjusted according to the type and compounding amount of the aforementioned rubber components, etc.

[0054] For the rubber composition constituting the first layer 2, it is preferred that tanδ is 0.25 to 0.65 at 30°C and Tg is -10°C to 20°C; more preferably, tanδ is 0.28 to 0.60 at 30°C and Tg is -8°C to 15°C; further preferably, tanδ is 0.30 to 0.55 at 30°C and Tg is -7°C to 10°C; particularly preferably, tanδ is 0.32 to 0.50 at 30°C and Tg is -6°C to 5°C.

[0055] In the present disclosure, unless otherwise specified, the dimensions and angles of each component of the tire are measured when the tire is mounted on a normal rim and filled with air to achieve a normal internal pressure. When measuring, no load is applied to the tire. Further, in the specification, the "normal rim" is the rim defined by the standard for each tire in a standard system including the standard on which the tire is based, and is, for example, the standard rim of JATMA, the "design rim" of TRA, and the "measuring rim" of ETRTO. In the specification, the "normal internal pressure" is the air pressure defined by the standard for each tire, and is the maximum air pressure of JATMA, the maximum value described in the TRA table "Tire Load Limits at Various Cold Inflation Pressures", and the "inflation pressure" of ETRTO.

[0056] [Rubber composition for tread]

[0057] As described above, the rubber composition (rubber composition for tread) of each rubber layer constituting the tread includes a rubber component and a plasticizer.

[0058] [Rubber component]

[0059] The rubber composition for tread according to the present disclosure preferably includes at least one selected from the group consisting of isoprene rubber, styrene-butadiene rubber (SBR), and butadiene rubber (BR) as the rubber component. The rubber component constituting the first layer 2 and the second layer 3 preferably contains SBR, more preferably contains SBR and BR, or may be a rubber component consisting only of SBR and BR. The rubber component constituting the third layer 4 preferably includes isoprene rubber, more preferably includes isoprene rubber and BR, or may be a rubber component consisting only of isoprene rubber and BR.

[0060] [Isoprene rubber]

[0061] As the isoprene rubber, those commonly used in the tire industry can be used, such as isoprene rubber (IR), natural rubber, etc. In natural rubber, in addition to unmodified natural rubber (NR), it includes epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), deprotected natural rubber (DPNR), ultra-pure natural rubber, modified natural rubber including grafted natural rubber, etc. These isoprene rubbers can be used alone, or two or more of them can be used in combination.

[0062] There is no particular limitation on NR, and those commonly used in the tire industry can be used, such as SIR20, RSS#3, TSR20, etc.

[0063] From the perspective of wet grip performance, when the rubber compositions constituting the first layer 2 and the second layer 3 contain isoprene rubber, in 100% by mass of the rubber component, the content of isoprene rubber (preferably natural rubber, more preferably unmodified natural rubber (NR)) 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. In addition, although the lower limit of the content of isoprene rubber when the rubber composition contains isoprene rubber is not particularly limited, it may be, for example, 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. For example, when the rubber composition constituting the third layer 4 contains isoprene rubber, in 100% by mass of the rubber component, the content of isoprene rubber is not particularly limited, and it may be 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, 50% by mass or more, or 60% by mass or more.

[0064] (SBR)

[0065] There is no particular limitation on SBR, and examples thereof include solution-polymerized SBR (S-SBR), emulsion-polymerized SBR (E-SBR), and modified SBRs thereof (modified S-SBR, modified E-SBR), etc. Examples of modified SBR include SBR modified at its terminal and / or main chain, and modified SBR coupled with tin, silicon compounds, etc. (condensates or modified SBRs having a branched structure, etc.), and so on. Among them, S-SBR and modified SBR are preferred. In addition, hydrogenated additives (hydrogenated SBR) of these SBRs can also be used. These SBRs can be used alone, or two or more of them can be used in combination.

[0066] As SBR, oil-extended SBR can be used, or non-oil-extended SBR can be used. When using oil-extended SBR, based on 100 parts by mass of the rubber solid content of SBR, the oil extension amount of SBR (i.e., the content of oil-extended SBR contained in SBR) is preferably 10 to 50 parts by mass.

[0067] S-SBR that can be used in the present disclosure includes those that can be commercially obtained from JSR Corporation, Sumitomo Chemical Co., Ltd., Ube Industries, Ltd., Asahi Kasei Corporation, ZS Elastomer Corporation, etc.

[0068] From the perspectives 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 still more preferably 20% by mass or more. In addition, from the perspectives of grip performance and temperature dependence of scratch resistance, it is preferably 60% by mass or less, more preferably 55% by mass or less, and still more preferably 50% by mass or less. In addition, in this specification, the styrene content of SBR is determined by1 H-NMR measurement and calculation.

[0069] From the perspectives of ensuring reactivity with silica, wet grip performance, rubber strength, and abrasion resistance, the vinyl content of SBR is preferably 10 mol% or more, more preferably 15 mol% or more, and still more preferably 20 mol% or more. In addition, from the perspectives of preventing an increase in 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 still more preferably 60 mol% or less. In addition, in this specification, the vinyl content (amount of 1,2-bonded butadiene units) of SBR is measured by infrared absorption spectroscopy.

[0070] 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 still preferably 300,000 or more. In addition, 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 still more preferably 1,500,000 or less. In addition, in this specification, the weight-average molecular weight of SBR can be determined based on the measured values obtained by gel permeation chromatography (GPC) (for example, the GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMULTIPORE HZ-M, manufactured by Tosoh Corporation) according to standard polystyrene.

[0071] From the perspective of wet grip performance, when the rubber compositions constituting the first layer 2 and the second layer 3 contain SBR, in 100% by mass of the rubber component, the content of SBR is preferably 50% by mass or more, more preferably 60% by mass or more, further preferably 65% by mass or more, and particularly preferably 70% by mass or more. In addition, the upper limit of the content of SBR in the rubber component is not particularly limited and can be 100% by mass. In addition, when the rubber composition constituting the third layer 4 contains SBR, the content of SBR in 100% by mass of the rubber component is not particularly limited.

[0072] (BR)

[0073] There are no particular restrictions on BR, and those commonly used in the tire industry can be used. For example, BR with a cis content of less than 50% by mass (low-cis BR), BR with a cis content of more than 90% (high-cis BR), rare-earth butadiene rubber synthesized using rare-earth element catalysts (rare-earth BR), BR containing syndiotactic polybutadiene crystals (BR containing SPB), modified BR (high-cis modified BR, low-cis modified BR), etc. Examples of modified BR include BR modified with functional groups similar to those described for SBR above. These BRs can be used alone or two or more of them can be used in combination.

[0074] As high-cis BR, for example, those commercially available from Zeon Corporation, Ube Industries, Ltd., JSR Corporation, etc. can be used. When high-cis BR is included, the low-temperature properties and abrasion resistance can be improved. The cis content is preferably 95% by mass or more, more preferably 96% by mass or more, further preferably 97% by mass or more, and particularly preferably 98% by mass or more. In addition, in this specification, the cis content (cis-1,4-bonded butadiene unit amount) is a value calculated by infrared absorption spectroscopy.

[0075] As rare-earth BR, those synthesized using rare-earth element catalysts can be used, which have a vinyl content of preferably 1.8 mol% or less, more preferably 1.0 mol% or less, further preferably 0.8 mol% or less, and a cis content of preferably 95% by mass or more, more preferably 96% by mass or more, further preferably 97% by mass or more, and particularly preferably 98% by mass or more. As rare-earth BR, for example, those commercially available from LANXESS, etc. can be used.

[0076] Examples of BR containing SPS include those in which 1,2-syndiotactic polybutadiene crystals are chemically bonded and dispersed with BR, but not those in which the crystals are simply dispersed in BR. Thus, those commercially available from Ube Industries, Ltd. can be used.

[0077] As modified BR, modified butadiene rubber (modified BR) is suitably used, and the modified butadiene rubber (modified BR) is modified at its terminal and / or main chain with a functional group including at least one element selected from the group consisting of silicon, nitrogen, and oxygen.

[0078] Examples of other modified BRs include those obtained by polymerizing 1,3-butadiene with a lithium initiator and then adding a tin compound, and in which the modified BR molecules are bonded by a tin-carbon bond at their terminals (tin-modified BR). In addition, the modified BR can be hydrogenated or not hydrogenated.

[0079] The previously listed BRs can be used alone, or two or more of them can be used in combination.

[0080] From the perspective 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. In addition, from the perspective of crosslinking uniformity, it is preferably 2,000,000 or less, more preferably 1,000,000 or less. In addition, the weight-average molecular weight of BR can be determined based on the measured values obtained by gel permeation chromatography (GPC) (for example, the GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMTOREHZ-M, manufactured by Tosoh Corporation) according to standard polystyrene.

[0081] From the perspective of wet grip performance, when the rubber compositions constituting the first layer 2, the second layer 3, and the third layer 4 contain BR, in 100% by mass of the rubber component, the content of BR 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. In addition, although the lower limit of the content of BR when the rubber composition contains BR is not particularly limited, it can be, for example, 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.

[0082] (Other rubber components)

[0083] As the rubber component according to the present disclosure, rubber components other than the above-mentioned isoprene rubber, SBR, and BR can be included. As other rubber components, crosslinkable rubber components commonly used in the tire industry can be used, such as styrene-isoprene-butadiene copolymer rubber (SIBR), styrene-isobutylene-styrene block copolymer (SIBS), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), hydrogenated nitrile rubber (HNBR), butyl rubber (IIR), ethylene propylene rubber, polynorbornene rubber, silicone rubber, polyvinyl chloride rubber, fluororubber (FKM), acrylic rubber (ACM), chlorinated ether rubber, etc. These other rubber components can be used alone, or two or more of them can be used in combination.

[0084] <Filler>

[0085] In the tread rubber composition, according to the present disclosure, a filler containing carbon black and / or silica is appropriately used. The rubber compositions constituting the first layer 2 and the second layer 3 preferably include silica, and more preferably carbon black and silica as the filler. The rubber composition constituting the third layer 4 preferably contains carbon black as the filler.

[0086] (Carbon black)

[0087] As the carbon black, those commonly used in the tire industry can be appropriately used. For example, examples thereof include GPF, FEF, HAF, ISAF, SAF, etc. These carbon blacks can be used alone, or two or more of them can be used in combination.

[0088] From the perspective of reinforcement properties, the nitrogen adsorption specific surface area (N2SA) of the carbon black is preferably 10 m 2 / g or more, more preferably 20 m 2 / g or more, further preferably 35 m 2 / g or more, particularly preferably 50 m 2 / g or more. In addition, from the perspectives of fuel efficiency and processability, it is preferably 200 m 2 / g or less, more preferably 150 m 2 / g or less, further preferably 100 m 2 / g or less, further preferably 80 m 2 / g or less. In addition, the N2SA of the carbon black is a value measured according to Japanese Industrial Standard JIS K 6217-2 "Carbon black for rubber - Basic characteristics - Part 2: Determination of specific surface area - Nitrogen adsorption method - Single point method".

[0089] When the rubber composition contains carbon black, from the perspectives of abrasion resistance and wet grip performance, its content based on 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 further preferably 5 parts by mass or more. In addition, from the perspective of fuel efficiency, it is preferably 50 parts by mass or less, more preferably 35 parts by mass or less, further preferably 20 parts by mass or less, and particularly preferably 10 parts by mass or less.

[0090] (Silica)

[0091] The silica is not particularly limited, and those commonly used in the tire industry can be used, such as silica prepared by a dry process (anhydrous silica), silica prepared by a wet process (hydrous silica), etc. Among them, hydrous silica prepared by a wet process is preferred because it has many silanol groups. These silicas can be used alone, or two or more of them can be used in combination.

[0092] From the perspectives of fuel efficiency and abrasion resistance, the nitrogen adsorption specific surface area (N2SA) of the silica is preferably 140 m 2 / g or more, more preferably 150 m 2 / g or more, further preferably 170 m 2 / g or more, and particularly preferably 200 m 2 / g or more. In addition, from the perspectives of fuel efficiency and processability, it is preferably 350 m 2 / g or less, more preferably 300 m 2 / g or less, and even more preferably 250 m 2 / g or less. In addition, the N2SA of the silica in this specification is the value measured by the BET method according to ASTM D3037-93.

[0093] When the rubber composition contains silica, based on 100 parts by mass of the rubber component, the silica content in the rubber composition 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. In addition, when the rubber composition contains silica, based on 100 parts by mass of the rubber component, the silica content in the rubber composition is preferably 160 parts by mass or less, more preferably 130 parts by mass or less, further preferably 120 parts by mass or less, and particularly preferably 110 parts by mass or less.

[0094] When the rubber composition constituting the first layer contains silica, from the perspective of wet grip performance, based on 100 parts by mass of the rubber component, the silica content is preferably 50 parts by mass or more, more preferably 70 parts by mass or more, further preferably 90 parts by mass or more, and particularly preferably 100 parts by mass or more of silica. In addition, from the perspective of abrasion resistance, it is preferably 160 parts by mass or less, more preferably 130 parts by mass or less, further preferably 120 parts by mass or less, and particularly preferably 110 parts by mass or less.

[0095] When the rubber composition constituting the second layer contains silica, based on 100 parts by mass of the rubber component, the silica content is preferably 40 parts by mass or more, more preferably 50 parts by mass or more, further preferably 60 parts by mass or more, and particularly preferably 70 parts by mass or more of silica. In addition, from the perspective of abrasion resistance, it is preferably 130 parts by mass or less, more preferably 120 parts by mass or less, further preferably 110 parts by mass or less, and particularly preferably 100 parts by mass or less.

[0096] From the perspective of abrasion resistance, based on 100 parts by mass of the rubber component, the total content of silica and carbon black is preferably 40 parts by mass or more, more preferably 50 parts by mass or more, and further preferably 60 parts by mass or more. In addition, from the perspectives of fuel efficiency and elongation at break, it is preferably 160 parts by mass or less, more preferably 140 parts by mass or less, and further preferably 120 parts by mass or less.

[0097] From the perspective of the balance of fuel efficiency, wet grip performance, and abrasion resistance, in the rubber compositions constituting the first layer 2 and the second layer 3, based on 100 parts by mass of the rubber component, the silica content is greater than the carbon black content. In the first layer 2 and the second layer 3, the proportion of silica is preferably 60% by mass or more, more preferably 70% by mass or more, further preferably 80% by mass or more, still further preferably 85% by mass or more, and particularly preferably 90% by mass or more, relative to the total content of silica and carbon black. In addition, the percentage content of silica and carbon black in the third layer 4 is not particularly limited, but the proportion of carbon black can be, for example, 50% by mass or more, 70% by mass or more, 90% by mass or more, or 100% by mass or more, relative to the total content of silica and carbon black.

[0098] (Silane coupling agent)

[0099] Silica is preferably used in combination with a silane coupling agent. The silane coupling agent is not particularly limited, and any silane coupling agent conventionally used in combination with silica in the tire industry can be used, and examples thereof include, for example, the following mercapto-based silane coupling agents; sulfide-based silane coupling agents such as bis(3-triethoxysilylpropyl) disulfide, bis(3-triethoxysilylpropyl) tetrasulfide, etc.; vinyl-based silane coupling agents such as vinyltriethoxysilane, vinyltrimethoxysilane, etc.; amino-based silane coupling agents such as 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-(2-aminoethyl)aminopropyltriethoxysilane, etc.; glycidoxy-based silane coupling agents such as γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, etc.; nitro-based silane coupling agents such as 3-nitropropyltrimethoxysilane, 3-nitropropyltriethoxysilane, etc.; chloro-based silane coupling agents such as 3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysilane, etc.; and so on. Among them, sulfide-based silane coupling agents and / or mercapto-based silane coupling agents are preferred, and mercapto-based silane coupling agents are more preferred. These silane coupling agents can be used alone or two or more of them can be used in combination.

[0100] The mercapto-based silane coupling agent is preferably a compound represented by the following formula (1) and / or a compound containing a bond unit A represented by the following formula (2) and a bond unit B represented by the following formula (3):

[0101] [Chemical formula 1]

[0102]

[0103] (wherein, R 101 , R 102 and R 103 each independently represents an alkyl group of C 1-12 alkyl, C1-12 An alkoxy group or -O-(R 111 -O) z -R 112 group (wherein z R's 111 each independently represent a divalent hydrocarbon group having 1 to 30 carbon atoms; R 112 represents C 1-30 alkyl, C 2-30 alkenyl, C 6-30 aryl or C 7-30 aralkyl; z represents an integer from 1 to 30); and R 104 represents C 1-6 alkylene.)

[0104] [Chemical Formula 2]

[0105]

[0106] [Chemical Formula 3]

[0107]

[0108] (wherein x represents an integer of 0 or more; y represents an integer of 1 or more; R 201 represents a hydrogen atom or C 1-30 alkyl, C 2-30 alkenyl or C 2-30 alkynyl, which may be substituted by a halogen atom, a hydroxyl group or a carboxyl group; R 202 represents C 1-30 alkylene, C 2-30 alkenylene or C 2-30 alkynylene; wherein R 201 and R 202 may form a ring structure.)

[0109] Examples of the compound represented by the formula (1) include, for example, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, and the compound represented by the following formula (4) (Si363 manufactured by Evonik Degussa), and the compound represented by the formula (4) can be used appropriately. They may be used alone, or two or more of them may be used in combination.

[0110] [Chemical Formula 4]

[0111]

[0112] Examples of compounds including the key unit A represented by formula (2) and the key unit B represented by formula (3) include, for example, those manufactured by Momentive Performance Materials, and so on. They can be used alone, or two or more of them can be used in combination.

[0113] When the rubber composition contains a silane coupling agent, from the viewpoint of enhancing the dispersibility of silica, based on 100 parts by mass of the rubber component, the total content of the silane coupling agent is preferably 0.5 part by mass or more, more preferably 1.0 part by mass or more, further preferably 2.0 part by mass or more, and particularly preferably 4.0 part by mass or more. In addition, from the viewpoint of preventing a decrease in abrasion resistance, it is preferably 20 parts by mass or less, more preferably 12 parts by mass or less, further preferably 10 parts by mass or less, and particularly preferably 9.0 parts by mass or less.

[0114] From the viewpoint of improving the dispersibility of silica, based on 100 parts by mass of silica, the content of the silane coupling agent (when multiple silane coupling agents are used, the total content of all silane coupling agents) is preferably 1.0 part by mass or more, more preferably 3.0 part by mass or more, still more preferably 5.0 part by mass or more. In addition, from the viewpoints of cost and processability, it is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and also preferably 12 parts by mass or less.

[0115] As fillers, in addition to carbon black and silica, other fillers can also be used. Although such fillers are not particularly limited, any of the fillers commonly used in the art can be used, such as aluminum hydroxide, alumina (aluminum oxide), calcium carbonate, magnesium sulfate, talc, clay, and the like. These fillers can be used alone, or two or more of them can be used in combination.

[0116] <Plasticizer>

[0117] According to the present disclosure, the rubber composition for a tread preferably contains a plasticizer. For example, examples of the plasticizer include a resin component, oil, liquid rubber, an ester plasticizer, and the like.

[0118] The resin component is not particularly limited, and examples thereof include petroleum resins, terpene resins, rosin resins, phenolic resins, and the like that are commonly used in the tire industry. These resin components can be used alone, or two or more of them can be used in combination.

[0119] In the present specification, "C5 petroleum resin" refers to a resin obtained by polymerizing a C5 fraction. Examples of the C5 fraction include, for example, petroleum fractions corresponding to 4 to 5 carbon atoms, such as cyclopentadiene, pentene, pentadiene, isoprene, and the like. As the C5 petroleum resin, a dicyclopentadiene resin (DCPD resin) is suitably used.

[0120] In the present specification, "aromatic petroleum resin" refers to a resin obtained by polymerizing a C9 fraction and can be hydrogenated or modified. Examples of the C9 fraction include petroleum fractions corresponding to 8 to 10 carbon atoms, such as vinyltoluene, alkylstyrene, indene, and methylindene. As specific examples of the aromatic petroleum resin, for example, coumarone-indene resin, coumarone resin, indene resin, and aromatic vinyl resins are suitably 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 it is economical, easy to process, and good in terms of heat generation. As the aromatic vinyl resin-based, for example, those commercially available from Kraton Corporation, Eastman Chemical Company, etc. can be used.

[0121] In the present specification, "C5-C9 petroleum resin" refers to a resin obtained by copolymerizing a C5 fraction and a C9 fraction and can be hydrogenated or modified. Examples of the C5 fraction and the C9 fraction include the above-mentioned petroleum fractions. As the C5-C9 petroleum resin, for example, those commercially available from Tosoh Corporation, Zibo Luhua Hongjin New Materials Group Co., Ltd. (LUHUA) can be used.

[0122] Examples of terpene resins include: polyterpene resins composed of at least one selected from terpene compounds (such as α-pinene, β-pinene, limonene, dipentene, etc.); aromatic modified terpene resins made from terpene compounds and aromatic compounds; terpene phenol resins made from terpene compounds and phenol-based compounds; and those obtained by hydrogenating these terpene resins (hydrogenated terpene resins). Examples of the aromatic compounds used as raw materials for aromatic modified terpene resins include, for example, styrene, α-methylstyrene, vinyltoluene, divinyltoluene, etc. Examples of the phenol-based compounds used as raw materials for terpene phenol resins include, for example, phenol, bisphenol A, cresol, xylenol, etc.

[0123] The rosin resin is not particularly limited, and examples thereof include natural resin rosin and rosin modified resins, which are natural resin rosins modified by hydrogenation, disproportionation, dimerization, or esterification.

[0124] The phenol resin is not particularly limited, and examples thereof include phenolic resin, alkylphenol formaldehyde resin, alkylphenol acetylene resin, oil-modified phenolic resin, etc.

[0125] From the perspective of wet grip performance, the softening point of the resin component is preferably 60 °C or higher, more preferably 65 °C or higher. Further, from the perspectives of processability and improvement of the dispersibility of the rubber component and the filler, it is preferably 150 °C or lower, more preferably 140 °C or lower, and still more preferably 130 °C or lower. In addition, in the present specification, the softening point can be defined as the temperature at which the sphere descends when measuring the softening point specified in Japanese Industrial Standard JIS K 6220-1:2001 using a ring and ball softening point measuring device.

[0126] When the rubber composition contains a resin component, based on 100 parts by mass of the rubber component, its content is preferably 1 part by mass or more, more preferably 3 parts by mass or more, still more preferably 5 parts by mass or more, and particularly preferably 7 parts by mass or more. Further, from the perspective of suppressing heat generation, it is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, still more preferably 40 parts by mass or less, and particularly preferably 30 parts by mass or less.

[0127] Examples of the oil include, for example, processing oils, vegetable oils, animal oils, etc. Examples of the processing oil include paraffin-based processing oils, naphthenic-based processing oils, aromatic-based processing oils, etc. Further, as an environmental measure, a processing oil having a low content of polycyclic aromatic compounds (PCA) can also be used. Examples of the processing oil having a low PCA content include mild extraction solvent compounds (MES), treated distillate aromatic extracts (TDAE), heavy naphthenic oils, etc.

[0128] When the rubber composition contains the oil, from the perspective of processability, based on 100 parts by mass of the rubber component, its content is preferably 1 part by mass or more, more preferably 3 parts by mass or more, still more preferably 5 parts by mass or more, and particularly preferably 7 parts by mass or more. Further, from the perspective of abrasion resistance, it is preferably 120 parts by mass or less, more preferably 100 parts by mass or less, still more preferably 80 parts by mass or less, and particularly preferably 60 parts by mass or less. In addition, in the specification, the content of the oil also includes the amount of oil contained in the oil-extended rubber.

[0129] The liquid rubber is not particularly limited as long as it is a polymer that is in a liquid state at room temperature (25 °C), and examples of the liquid rubber include, for example, liquid butadiene rubber (liquid BR), liquid styrene-butadiene rubber (liquid SBR), liquid isoprene rubber (liquid IR), liquid styrene-isoprene polymer (liquid SIR), liquid farnesene rubber, etc. These can be used alone, or two or more of them can be used in combination.

[0130] When the rubber composition contains liquid rubber, based on 100 parts by mass of the rubber component, its content is preferably 1 part by mass or more, more preferably 3 parts by mass or more, still more preferably 5 parts by mass or more, and particularly preferably 7 parts by mass or more. In addition, the content of the liquid rubber is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, still more preferably 20 parts by mass or less.

[0131] Examples of the ester plasticizer include, for example, dibutyl adipate (DBA), diisobutyl adipate (DIBA), dioctyl adipate (DOA), bis(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), trixylenyl phosphate (TXP), etc. These ester plasticizers can be used alone or two or more of them can be used in combination.

[0132] From the perspective of wet grip performance, in the rubber composition constituting the first layer 2, based on 100 parts by mass of the rubber component, the content of the plasticizer (when multiple plasticizers are used, the total content of all plasticizers) is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, still more preferably 30 parts by mass or more, and particularly preferably 40 parts by mass or more. In the rubber composition constituting the second layer 3, based on 100 parts by mass of the rubber component, the plasticizer content is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, still more preferably 15 parts by mass or more. In addition, from the perspective of processability, in the rubber compositions constituting the first layer 2, the second layer 3, and the third layer 4, based on 100 parts by mass of the rubber component, the plasticizer content is preferably 120 parts by mass or less, more preferably 100 parts by mass or less, still more preferably 90 parts by mass or less, and particularly preferably 80 parts by mass or less.

[0133] <Other compounding reagents>

[0134] In addition to the foregoing components, the rubber composition according to the present disclosure may also appropriately contain compounding agents commonly used in the tire industry, such as wax, processing aids, stearic acid, zinc oxide, antioxidants, vulcanizing agents, vulcanization accelerators, etc.

[0135] When the rubber composition contains wax, from the perspective of the weather resistance of the rubber, based on 100 parts by mass of the rubber component, its content is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more. In addition, from the perspective of preventing tire whitening caused by blooming, it is preferably 10 parts by mass or less, more preferably 5 parts by mass or less.

[0136] 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, mixtures of fatty acid metal salts and fatty acid amides, etc. These processing aids can be used alone, or two or more of them can be used in combination. As processing aids, those commercially available from companies such as Schill&Seilacher and Performance Additives can be used, for example.

[0137] When the rubber composition contains a processing aid, from the perspective of exhibiting an improved effect of processability, based on 100 parts by mass of the rubber component, its content is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more. In addition, from the perspectives of abrasion resistance and breaking strength, it is preferably 10 parts by mass or less, more preferably 8 parts by mass or less.

[0138] The antioxidant is not particularly limited, and examples thereof include, for example, amine compounds, quinoline compounds, quinone compounds, phenolic compounds, and imidazole compounds, as well as antioxidants such as metal carbamate salts, preferably phenylenediamine 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, N-cyclohexyl-N'-phenyl-p-phenylenediamine, etc.; and quinoline antioxidants such as 2,2,4-trimethyl-1,2-dihydroquinoline polymer, 6-ethoxy-2,4-trimethyl-1,2-dihydroquinoline, etc. These antioxidants can be used alone, or two or more of them can be used in combination.

[0139] When the rubber composition contains an antioxidant, from the perspective of ozone cracking resistance, based on 100 parts by mass of the rubber component, its content is preferably 0.5 parts by mass, more preferably 1 part by mass or more. In addition, from the perspectives of abrasion resistance and wet grip performance, it is preferably 10 parts by mass or less, more preferably 5 parts by mass or less.

[0140] When the rubber composition contains stearic acid, from the perspective of processability, based on 100 parts by mass of the rubber component, its content is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more. In addition, from the perspective of vulcanization rate, it is preferably 10 parts by mass or less, more preferably 5 parts by mass or less.

[0141] When the rubber composition contains zinc oxide, from the perspective of processability, based on 100 parts by mass of the rubber component, its content is preferably 0.5 part by mass or more, more preferably 1 part by mass or more. In addition, from the perspective of abrasion resistance, it is preferably 10 parts by mass or less, more preferably 5 parts by mass or less.

[0142] Sulfur is suitable as a vulcanizing agent. As sulfur, powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersed sulfur, etc. can be used.

[0143] When the rubber composition contains sulfur as a vulcanizing agent, from the perspective of ensuring a sufficient vulcanization reaction, based on 100 parts by mass of the rubber component, the content of sulfur is preferably 0.1 part by mass or more, more preferably 0.3 part by mass or more, and still more preferably 0.5 part by mass or more. In addition, from the perspective of preventing deterioration, it is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and still more preferably 3.0 parts by mass or less. In addition, when using oil-containing sulfur as a vulcanizing agent, the content of the vulcanizing agent shall be the total content of the pure sulfur contained in the oil-containing sulfur.

[0144] Examples of vulcanizing agents other than sulfur include, for example, alkylphenol-sulfur chloride condensates, 1,6-hexamethylene-disodium dithiocarbamate dihydrate, 1,6-bis(N,N'-dibenzylthiocarbamoyl disulfide) hexane, etc. As these vulcanizing agents other than sulfur, those commercially available from Taoka Chemical Company, LANXESS, Flexsys, etc. can be used.

[0145] Examples of vulcanization accelerators include, for example, sulfenamides, thiazoles, thiurams, thioureas, guanidines, dithiocarbamates, aldehyde-amines or aldehyde-ammonias, imidazolines, and xanthate vulcanization accelerators. These vulcanization accelerators can be used alone or two or more of them can be used in combination. Among them, vulcanization accelerators selected from one or more of sulfenamides, guanidines, and thiazole vulcanization accelerators are preferred, and sulfenamide vulcanization accelerators are more preferred.

[0146] Examples of sulfenamide vulcanization accelerators include, for example, N-tert-butyl-2-benzothiazolesulfenamide (TBBS), N-cyclohexyl-2-benzothiazolesulfenamide (CBS), N,N-dicyclohexyl-2-benzothiazolesulfenamide (DCBS), etc. Among them, N-cyclohexyl-2-benzothiazolesulfenamide (CBS) is preferred.

[0147] Examples of guanidine vulcanization accelerators include, for example, 1,3-diphenylguanidine (DPG), 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, di-o-tolylguanidine salt of biscatecholborate, 1,3-di-o-cumylguanidine, 1,3-di-o-biphenylguanidine, 1,3-di-o-cumyl-2-propylguanidine, etc. Among them, 1,3-diphenylguanidine (DPG) is preferred.

[0148] Examples of thiazole vulcanization accelerators include, for example, 2-mercaptobenzothiazole, cyclohexylamine salt of 2-mercaptobenzothiazole, di-2-benzothiazole disulfide, etc. Among them, 2-mercaptobenzothiazole is preferred.

[0149] When the rubber composition contains a vulcanization accelerator, based on 100 parts by mass of the rubber component, its content is preferably 1 part by mass or more, more preferably 2 parts by mass or more. In addition, based on 100 parts by mass of the rubber component, the content of the vulcanization accelerator is preferably 8 parts by mass or less, more preferably 7 parts by mass or less, and further preferably 6 parts by mass or less. When the content of the vulcanization accelerator is within the above range, there is a tendency to ensure the breaking strength and elongation at break.

[0150] The rubber composition according to the present disclosure can be produced by known methods. It can be produced by kneading each of the aforementioned components using a rubber kneading device such as an open roll, a closed kneader (Banbury mixer, kneader, etc.).

[0151] The kneading step includes: for example, a basic kneading step of kneading compounding agents and additives other than the vulcanizing agent and the vulcanization accelerator, and a final kneading (F kneading) step of adding the vulcanizing agent and the vulcanization accelerator to the kneaded product obtained by the basic kneading step and kneading them. In addition, if necessary, the basic kneading step can be divided into multiple steps.

[0152] The kneading conditions are not particularly limited, and for example, a method of kneading at a discharge temperature of 150°C to 170°C for 3 to 10 minutes in the basic kneading step and kneading at 70°C to 110°C for 1 to 5 minutes in the final kneading step. The vulcanization conditions are not particularly limited, and for example, a method of vulcanizing at 150°C to 200°C for 10 to 30 minutes is exemplified.

[0153] The difference (AE1 - AE2) between the acetone extraction amount AE1 of the rubber composition constituting the first layer 2 and the acetone extraction amount AE2 of the rubber composition constituting the second layer 3 is 1.0% by mass or more, preferably 1.5% by mass or more, more preferably 2.0% by mass or more, further preferably 2.5% by mass or more, and particularly preferably 3.0% by mass or more. It is considered that setting the difference in acetone extraction amount within the aforementioned range makes it easier for acetone extraction components (such as oil, etc.) to transfer from the first layer 2 to the second layer 3 due to the concentration gradient during driving, and enables the wet grip performance to be maintained for a long time because when the second layer 3 is exposed due to wear of the tread portion, the second layer 3 contains a sufficient amount of plasticizer. In addition, although the upper limit of (AE1 - AE2) is not particularly limited, it is generally 30% by mass or less, preferably 20% by mass or less, more preferably 15% by mass or less, and still more preferably 10% by mass or less.

[0154] The difference (AE2 - AE3) between the acetone extraction amount AE2 of the rubber composition constituting the second layer 3 and the acetone extraction amount AE3 of the rubber composition constituting the third layer 4 is 1.0% by mass or more, preferably 1.5% by mass or more, more preferably 2.0% by mass or more, further preferably 2.5% by mass or more, and particularly preferably 3.0% by mass or more. In addition, although the upper limit of (AE2 - AE3) is not particularly limited, it is generally 30% by mass or less, preferably 20% by mass or less, more preferably 15% by mass or less, and still more preferably 10% by mass or less.

[0155] In addition, the acetone extraction amount is an index of the concentration of organic low-molecular compounds contained in the plasticizer in the vulcanized rubber composition. According to Japanese Industrial Standard JIS K 6229-3:2015, the acetone extraction amount can be determined by soaking each vulcanized rubber test piece in acetone for 24 hours to extract soluble components and measuring the mass of each test piece before and after extraction using the following equation:

[0156] Acetone extraction amount (mass%) = { (mass of rubber test piece before extraction - mass of rubber test piece after extraction) / (mass of rubber test piece before extraction)} × 100.

[0157] [Tire]

[0158] The tire according to the present disclosure includes a tread, which includes a first layer 2, a second layer 3, and a third layer 4, and can be a pneumatic tire or a non-pneumatic tire. In addition, examples of pneumatic tires include tires for passenger cars, tires for trucks / buses, tires for motorcycles, high-performance tires, etc., and pneumatic tires are suitably used as tires for passenger cars. In addition, the high-performance tires in the specification are tires having particularly good grip performance and are a concept including racing tires for racing cars.

[0159] A tire including a tread having a first layer 2, a second layer 3, and a third layer 4 can be manufactured by a conventional method using the aforementioned rubber composition. In other words, the tire can be manufactured by the following steps: extruding an unvulcanized rubber composition, which is compounded as needed with each of the above components based on the rubber component, into the shapes of the first layer 2, the second layer 3, and the third layer 4 using an extruder including a base having a predetermined shape, attaching them to other tire components on a tire molding machine, and molding them by a conventional method to form an unvulcanized tire, and then heating and pressurizing the unvulcanized tire in a vulcanizer.

[0160] Examples

[0161] Although the present disclosure will be described based on examples, the present disclosure is not limited to these examples.

[0162] The following shows various chemicals used in the examples and comparative examples:

[0163] NR: TSR20

[0164] SBR: Tufdene 4850 (unmodified S-SBR, styrene content: 40% by mass, vinyl content: 46 mol%, Mw: 350,000, oil content including 50 parts by mass based on 100 parts by mass of rubber solids), manufactured by Asahi Kasei Corporation.

[0165] BR: UBEPOL BR (registered trademark) 150B (vinyl content: 1.5 mol%, cis content: 97% by mass, Mw: 440,000), manufactured by Ube Industries, Ltd.

[0166] Carbon black: Show Black N330 (N2SA: 75 m 2 / g), manufactured by Cabot Japan K.K.

[0167] Silica: Ultrasil VN3 (N2SA: 175 m 2 / g, average primary particle size: 15 nm), manufactured by Evonik Degussa.

[0168] Silane coupling agent: NXT-Z45 (mercapto-based silane coupling agent), manufactured by Momentive Performance Materials.

[0169] Resin component: PetroTac 100V (C5-C9 petroleum resin, softening point: 96°C, Mw: 3800, SP value: 8.3), manufactured by Tosoh Corporation.

[0170] Liquid rubber: Ricon 100 (liquid SBR), manufactured by Clay Valley Company.

[0171] Oil: Vivatec 500 (TDAE oil), manufactured by H&R Group.

[0172] Antioxidant: Antigen 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine), manufactured by Sumitomo Chemical Co., Ltd.

[0173] Wax: Sunnock N, manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

[0174] Stearic acid: Pearl stearic acid "Tsubaki", manufactured by NOF Corporation.

[0175] Zinc oxide: Zinc oxide No. 2, manufactured by Mitsui Mining & Smelting Co., Ltd.

[0176] Sulfur: Powdered sulfur, manufactured by Tsurumi Chemical Industry Co., Ltd.

[0177] Vulcanization accelerator: Nocceler CZ (N-cyclohexyl-2-benzothiazolesulfonamide), manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

[0178] (Examples and Comparative Examples)

[0179] According to the compounding formula shown in Table 1, using a 1.7L enclosed Banbury mixer, all chemicals except sulfur and vulcanization accelerator were kneaded for 1 to 10 minutes until the discharge temperature reached 150°C to 160°C to obtain a kneaded product. Next, using a twin-screw open roll, sulfur and vulcanization accelerator were added to the obtained kneaded product, and the mixture was kneaded for 4 minutes until the temperature reached 105°C to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was extruded into the shapes of the first, second, and third layers of the tread, and connected to other tire components to produce an unvulcanized tire, which was then vulcanized at 170°C to obtain each test tire shown in Table 2 (size: 205 / 65R15, rim: 15x6JJ, internal pressure: 230 kPa).

[0180] <Measure the acetone extraction amount (AE amount) of the first, second, and third layers>

[0181] Each vulcanized rubber test piece was soaked in acetone for 24 hours to extract soluble components. The mass of each vulcanized rubber test piece before and after extraction was measured, and the acetone extraction amount was determined by the following calculation equation.

[0182] Acetone extraction amount (mass %) = { (mass of the rubber test piece before extraction - mass of the rubber test piece after extraction) / (mass of the rubber test piece before extraction)} × 100.

[0183] In addition, for each rubber test piece of the first layer, second layer, and third layer, the first layer, second layer, and third layer are used which are cut out from the inside of the rubber layer of the tread portion of each test tire. The differences (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, and (AE2 - AE3) between the acetone extraction amount AE2 of the rubber composition constituting the second layer and the acetone extraction amount AE3 of the rubber composition constituting the third layer are shown in Table 2.

[0184] <Measurement of loss tangent tanδ and complex modulus E*>

[0185] For each rubber test piece produced by cutting out a length of 20 mm x width 4 mm x thickness 1 mm from the inside of the rubber layer of the tread portion of each test tire, with the tire circumferential direction as the long side, using a dynamic viscoelasticity measuring device EPLEXOR (registered trademark) series, manufactured by GABO Qualimeter Testanlagen GmbH, the loss tangent tanδ is measured under the conditions of a temperature of 0°C and 30°C, a frequency of 10 Hz, and a strain of 2.5%. In addition, the complex modulus E is measured under the conditions of a temperature of 0°C, a frequency of 10 Hz, and a strain of 2.5%. * In addition, the thickness direction of the sample is set to the tire radial direction.

[0186] <Measurement of glass transition temperature (Tg)>

[0187] For each rubber test piece produced by cutting out a length of 20 mm x width 4 mm x thickness 1 mm from the inside of the rubber layer of the tread portion of each test tire, with the tire circumferential direction as the long side, using a dynamic viscoelasticity measuring device EPLEXOR (registered trademark) series, manufactured by GABO Qualimeter Testanlagen GmbH, the temperature distribution curve of the loss tangent tanδ is measured under the conditions of a frequency of 10 Hz and a strain of 2.5%, and the temperature (tanδ peak temperature) corresponding to the maximum tanδ value in the obtained temperature distribution curve is set as the glass transition temperature (Tg). In addition, the thickness direction of the sample is set to the tire radial direction.

[0188] <Tensile test>

[0189] Produce dumbbell-shaped test piece No. 7 with a thickness of 1 mm, which is cut out from the inside of the rubber layer of the tread part of each test tire, such that the tire circumferential direction is the stretching direction. Under the conditions of an atmospheric temperature of 23 °C and a stretching speed of 3.3 mm / second, a tensile test is carried out in accordance with Japanese Industrial Standard JIS K 6251:2017 "Vulcanized Rubber and Thermoplastic Rubber - Determination of Tensile Test Properties", and the elongation at break EB (%) is measured. In addition, the thickness direction of the sample is set to the tire radial direction.

[0190] <Wet Grip Maintenance Performance>

[0191] Each test tire is installed on all the wheels of a (2000 cc Japanese-made FF) vehicle, and the braking distance is measured starting from the time point when braking is applied while driving at a speed of 100 km / h on a wet asphalt road surface. In addition, the aforementioned tires are thermally deteriorated at 80 °C for 7 days, and then each test tire (which has a tread part worn along the tread radius such that the thickness of the tread part is 50% of the thickness of the newly used tire) is installed on all the wheels of the aforementioned vehicle, and the braking distance is measured starting from the time point when braking is applied while driving at a speed of 100 km / h on a wet asphalt road surface. Then, for each test tire, the wet grip performance maintenance index before and after wear is calculated by the following calculation equation, the wet grip performance maintenance index is converted with the maintenance index of a reference tire (Comparative Example 6) set to 100, and the wet grip maintenance performance of each test tire is obtained. It shows that the higher the value, the smaller the change in the wet grip performance before and after wear, thus maintaining the wet grip performance when the tire is newly used.

[0192] (Wet grip performance maintenance index of the reference tire) = (Braking distance of the reference tire when newly used) / (Braking distance of the reference tire after wear)

[0193] (Wet grip performance maintenance index of each test tire) = (Braking distance of each test tire when newly used) / (Braking distance of each test tire after wear)

[0194] (Wet grip maintenance performance of each test tire) = (Wet grip performance maintenance index of each test tire) / (Wet grip performance maintenance index of the reference tire) x 100

[0195] <Fuel Efficiency>

[0196] Using a rolling resistance test machine, the rolling resistance is measured, and each test tire operates under the conditions of a rim 15×6JJ, an internal pressure of 230 kPa, a load of 3.43 kN, and a speed of 80 km / h. With the rolling resistance of the reference tire (Comparative Example 6) set to 100, the rolling resistance is expressed as an index value using the following calculation equation. It shows that the larger the value, the better the fuel efficiency.

[0197] (Fuel efficiency index) = (Rolling resistance of the reference tire when newly used) / (Rolling resistance of each test tire when newly used) x 100

[0198] For the overall performance of wet grip retention performance and fuel efficiency (the sum of the wet grip retention performance index and the fuel efficiency index), exceeding 200 is set as the target performance value.

[0199]

[0200]

[0201] Based on the results of Tables 1 and 2, it is obvious that for the tires of the present disclosure, in which the tread portion is provided with more than three rubber layers and a plasticizer compounding gradient of at least a predetermined level is imparted from the rubber layer on the outer side in the tire radial direction to the rubber layer on the outer side in the tire radial direction, there is an improvement in the overall performance of wet grip retention performance and fuel efficiency.

[0202] Reference numeral

[0203] 1 Tread surface

[0204] 2 First layer

[0205] 3 Second layer

[0206] 4 Third layer

Claims

1. A tire having a tread, said tread comprising at least a first layer constituting the tread surface, a second layer disposed on the inner side adjacent to said first layer in the radial direction, and a third layer disposed on the inner side adjacent to said second layer in the radial direction. Wherein, The first layer, the second layer, and the third layer are composed of a rubber composition containing a rubber component and a plasticizer. Among them, 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 1.0% by mass or more, and Among them, the difference AE2 - AE3 between the acetone extraction amount AE2 of the rubber composition constituting the second layer and the acetone extraction amount AE3 of the rubber composition constituting the third layer is 1.0% by mass or more. Among them, the acetone extraction amount is determined by the following formula by soaking each vulcanized rubber test piece in acetone for 24 hours to extract soluble components and measuring the mass of each test piece before and after extraction according to Japanese Industrial Standard JIS K 6229 - 3:2015: Acetone extraction amount = {((mass of rubber test piece before extraction - mass of rubber test piece after extraction) / (mass of rubber test piece before extraction))}×100%.

2. The tire according to claim 1, wherein, AE1 - AE2 is 2.0% by mass or more.

3. The tire according to claim 1 or 2, wherein, AE2 - AE3 is 2.0% by mass or more.

4. The tire according to claim 1 or 2, wherein, The tanδ of the rubber composition constituting the first layer at 0°C is 1.00 or more.

5. The tire according to claim 1 or 2, wherein, The elongation at break of the rubber composition constituting the first layer measured according to JIS K6251 is 610% or more.

6. The tire according to claim 1 or 2, wherein, The complex modulus E* of the rubber composition constituting the first layer at 0°C is 50 MPa or more.

7. The tire according to claim 1 or 2, wherein, The glass transition temperature of the rubber composition constituting the first layer is -10°C or more.

8. The tire according to claim 1 or 2, wherein, The glass transition temperature of the rubber composition constituting the first layer is -7°C or more.

9. The tire according to claim 1 or 2, wherein, The tanδ of the rubber composition constituting the first layer at 30°C is 0.25 or more.

10. The tire according to claim 1 or 2, wherein, The tanδ of the rubber composition constituting the first layer at 30°C is 0.30 or more.

11. The tire according to claim 1 or 2, wherein, The tanδ of the rubber composition constituting the second layer at 0°C is 0.60 or more.

12. The tire according to claim 1 or 2, wherein, The elongation at break of the rubber composition constituting the second layer measured according to JIS K6251 is 500% or more.

13. The tire according to claim 1 or 2, wherein, The complex modulus E* of the rubber composition constituting the second layer at 0°C is 25 MPa or more.

14. The tire according to claim 1 or 2, wherein, Based on 100 parts by mass of the rubber component, each of the rubber compositions constituting the first layer and the second layer contains a total of 40 to 160 parts by mass of silica and carbon black, and the proportion of the silica content is 60% by mass or more relative to the total content of silica and carbon black.

15. The tire according to claim 1 or 2, wherein, Based on 100 parts by mass of the rubber component, the rubber composition constituting the first layer contains 100 parts by mass or more of silica.

16. The tire according to claim 1 or 2, wherein, Based on 100 parts by mass of the rubber component, each of the rubber compositions constituting the first layer and the second layer contains 10 parts by mass or more of a plasticizer.

17. The tire according to claim 1 or 2, wherein, Based on 100% by mass of the rubber component, each of the rubber components constituting the first layer and the second layer includes 50% by mass of styrene - butadiene rubber.

18. The tire according to claim 1 or 2, wherein,At least one selected from the group consisting of a sealant, a noise damping body, and an electronic component for tire monitoring is provided in the tire inner cavity.

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