tire

Abstract

A tire having a tread provided with at least a first layer constituting a tread surface, a second layer adjacent to the first layer on the radially inward side thereof, and a third layer adjacent to the second layer on the radially inward side thereof, wherein the first layer, the second layer, and the third layer are formed from a rubber composition containing a rubber component and a plasticizer, 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 technology]

[0002] Patent Document 1 discloses a pneumatic tire having a tread rubber including a tread surface rubber layer located on the outermost surface of the tread and a tread inner rubber layer located radially inward of the tread surface rubber layer. In such a tire, the tread surface rubber layer is a rubber layer having a relatively high rigidity, and the tread inner rubber layer is a rubber layer having a relatively low rigidity. As a result, the tread surface rubber layer improves the rigidity of the land portion in the tire circumferential direction of the tire surface, for example, to improve the wear resistance, and the tread inner rubber layer improves the fuel efficiency of the tire, for example, by suppressing hysteresis loss. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2014-162242 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the case of such a tire, when the tread surface rubber layer wears away and the low heat generating inner tread rubber layer is exposed, there is a risk that the wet grip performance will rapidly deteriorate.

[0005] An object of the present invention is to provide a tire that can improve fuel economy while maintaining wet grip performance even after wear. [Means for solving the problem]

[0006] As a result of extensive research, the inventors have found that the above-mentioned problems can be solved by providing three or more rubber layers in the tread portion and providing a plasticizer concentration gradient of a certain level or more from the rubber layer on the outer side in the tire's radial direction to the rubber layer on the inner side in the tire's radial direction, and have thus completed the present invention.

[0007] That is, the present invention provides [1] A tire having a tread including at least a first layer constituting a tread surface, a second layer adjacent to the radially inner side of the first layer, and a third layer adjacent to the radially inner side of the second layer, wherein the first layer, the second layer, and the third layer are made of a rubber composition containing a rubber component and a plasticizer, and the acetone extractable amount AE of the rubber composition constituting the first layer is 1 and the acetone extractable amount AE of the rubber composition constituting the second layer. 2 Difference from (AE 1 -AE 2 ) is 1.0 mass % or more, and the acetone extractable amount AE of the rubber composition constituting the second layer is 1.0 mass % or more. 2 and the acetone extractable amount AE of the rubber composition constituting the third layer. 3 Difference from (AE 2 -AE 3 ) is 1.0 mass % or more, [2] The above-mentioned AE 1 -AE 2 The tire according to the above [1], [3] The above-mentioned AE 2 -AE 3 The tire according to the above [1] or [2], wherein the amount of the carbide is 2.0 mass% or more. [4] The tire according to any one of the above [1] to [3], wherein the tan δ at 0 ° C. of the rubber composition constituting the first layer is 1.00 or more. [5] The tire according to any one of the above [1] to [4], wherein the rubber composition constituting the first layer has a breaking elongation of 610% or more as measured in accordance with JIS K 6251. [6] The tire according to any one of the above [1] to [5], wherein the complex modulus at 0 ° C. (0 ° C. E*) of the rubber composition constituting the first layer is 50 MPa or more. [7] The tire according to any one of the above [1] to [6], wherein the glass transition temperature of the rubber composition constituting the first layer is −10° C. or higher. [8] The tire according to any one of the above [1] to [7], wherein the glass transition temperature of the rubber composition constituting the first layer is −7° C. or higher. [9] The tire according to any one of the above [1] to [8], wherein the rubber composition constituting the first layer has a tan δ at 30°C of 0.25 or more.

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

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

[10] , wherein the tan δ at 0 ° C. of the rubber composition constituting the second layer is 0.60 or more.

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

[11] , wherein the rubber composition constituting the second layer has a breaking elongation of 500% or more as measured in accordance with JIS K 6251.

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

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

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

[13] , wherein the rubber composition constituting the first layer and the second layer contains 40 to 160 parts by mass of silica and carbon black in total per 100 parts by mass of the rubber component, and the ratio of the content of silica to the total content of silica and carbon black is 60% by mass or more.

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

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

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

[15] , wherein the rubber composition constituting the first layer and the second layer contains 10 parts by mass or more of a plasticizer per 100 parts by mass of the rubber component.

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

[16] , wherein the rubber components constituting the first layer and the second layer contain 50% by mass or more of styrene-butadiene rubber.

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

[17] , further comprising at least one selected from the group consisting of a sealant, a noise damper, and an electronic component for tire monitoring in the tire cavity. Effect of the Invention

[0008] According to the present invention, there is provided a tire that can improve fuel economy while maintaining wet grip performance even after wear. [Brief description of the drawings]

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

[0010] A tire according to one embodiment of the present disclosure is a tire having a tread including at least a first layer constituting a tread surface, a second layer adjacent to the radially inner side of the first layer, and a third layer adjacent to the radially inner side of the second layer, wherein the first layer, the second layer, and the third layer are made of a rubber composition containing a rubber component and a plasticizer, and the acetone extractable amount AE of the rubber composition constituting the first layer is 100% or more. 1 and the acetone extractable amount AE of the rubber composition constituting the second layer. 2 Difference from (AE 1 -AE 2 ) is 1.0 mass % or more (preferably 2.0 mass % or more), and the acetone extractable amount AE of the rubber composition constituting the second layer is 1.0 mass % or more (preferably 2.0 mass % or more). 2 and the acetone extractable amount AE of the rubber composition constituting the third layer. 3 Difference from (AE 2 -AE 3 ) is 1.0 mass % or more (preferably 2.0 mass % or more).

[0011] The tire of the present disclosure has a second layer adjacent to the radially inner side of a first layer that constitutes the tread surface and that generates less heat than the first layer, thereby enabling improvement in fuel efficiency while maintaining wet grip performance.

[0012] In the tire of the present disclosure, by providing a plasticizer concentration gradient of a certain level or more from the rubber layer on the radially outer side of the tire to the rubber layer on the radially inner side of the tire, stimulation during driving promotes the migration of the plasticizer from the rubber layer on the radially outer side of the tire to the rubber layer on the radially inner side of the tire, and wet grip performance can be ensured even when the second layer is exposed due to wear, so it is believed that wet grip performance can be maintained for a long period of time.

[0013] A procedure for producing a tire according to an embodiment of the present disclosure will be described in detail below. However, the following description is merely an example for explaining the present invention, and is not intended to limit the technical scope of the present invention to the described range. In this specification, when a numerical range is indicated using "to" it is intended to include both ends of the numerical range.

[0014] Fig. 1 is an enlarged cross-sectional view showing a part of the tread of a tire according to the present disclosure. Fig. 1 shows an enlarged view of a part of the tread of the present disclosure in which no grooves are formed on the tread surface. In Fig. 2, the up-down direction is the radial direction of the tire, the left-right direction is the axial direction of the tire, and the direction perpendicular to the paper surface is the circumferential direction of the tire.

[0015] 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, with the outer surface of the first layer 2 constituting a tread surface 1, the second layer 3 adjacent to the radially inner side of the first layer 2, and the third layer 4 adjacent to the radially inner side of the second layer 3. The first layer 2 typically corresponds to a cap tread. The second layer 3 and the third layer 4 typically correspond to a base tread or an undertread. In addition, one or more rubber layers may be further provided between the third layer 4 and the belt layer, as long as the object of the present invention is achieved.

[0016] In Fig. 1, double arrow t1 indicates the thickness of the first layer 2, double arrow t2 indicates the thickness of the second layer 3, and double arrow t3 indicates the thickness of the third layer 4. In Fig. 1, an arbitrary point on the tread surface where no grooves are formed is indicated by the symbol P. The straight line indicated by the symbol N is a straight line (normal line) that passes through point P and is perpendicular to the tangent plane at point P. In this specification, thicknesses t1, t2, and t3 are measured along the normal line N drawn from point P on the tread surface at a position where no grooves exist in the cross section of Fig. 1.

[0017] In the present disclosure, the thickness t1 of the first layer 2 is not particularly limited, but from the viewpoint of wet grip performance, it is preferably 1.0 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 thickness t1 of the first layer 2 is preferably 10.0 mm or less, more preferably 9.0 mm or less, and even more preferably 8.0 mm or less.

[0018] In the present disclosure, the thickness t2 of the second layer 3 is not particularly limited, but is preferably 1.5 mm or more, more preferably 2.0 mm or more, and even more preferably 2.5 mm or more. The thickness t2 of the second layer 3 is preferably 10.0 mm or less, more preferably 9.0 mm or less, and even more preferably 8.0 mm or less.

[0019] In the present disclosure, the thickness t3 of the third layer 4 is not particularly limited, but is preferably 1.0 mm or more, more preferably 1.5 mm or more. Also, the thickness t3 of the third layer 4 is preferably 10.0 mm or less, more preferably 9.0 mm or less, and even more preferably 8.0 mm or less.

[0020] 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, even more preferably 0.7 or more, and particularly preferably 0.9 or more, from the viewpoint of fuel economy performance, while it is preferably 5.0 or less, more preferably 4.5 or less, even more preferably 4.0 or less, and particularly preferably 3.5 or less, from the viewpoint of wet grip performance.

[0021] From the viewpoint of better exerting 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 viewpoint of better exerting 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.

[0022] The tire of the present disclosure may be provided with a sealant, a sound damper, electronic components for tire monitoring, and the like in the tire cavity.

[0023] As the sealant, a sealant generally used on the inner peripheral surface of the tire tread portion for puncture prevention can be suitably used. Specific examples of such a sealant layer include those described in JP 2020-23152 A. The thickness of the sealant is usually preferably 1 to 10 mm. The width of the sealant is usually preferably 85 to 115% of the maximum width of the belt layer, and preferably 95 to 105%.

[0024] Any sound-damping body can be suitably used as long as it can exert a sound-damping effect in the tire cavity. Specific examples of such sound-damping bodies include those described in JP 2019-142503 A. The sound-damping body is, for example, made of a porous sponge material. The sponge material is a spongy porous structure, and includes, for example, a so-called sponge having continuous bubbles formed by foaming rubber or synthetic resin, as well as a web-like structure in which animal fibers, plant fibers, synthetic fibers, etc. are intertwined and connected together. In addition, the "porous structure" includes those having not only continuous bubbles but also closed bubbles. An example of the sound-damping body is a sponge material having continuous bubbles made of polyurethane. Suitable sponge materials include synthetic resin sponges such as ether-based polyurethane sponge, ester-based polyurethane sponge and polyethylene sponge, and rubber sponges such as chloroprene rubber sponge (CR sponge), ethylene propylene rubber sponge (EDPM sponge) and nitrile rubber sponge (NBR sponge). In particular, polyurethane-based or polyethylene-based sponges including ether-based polyurethane sponge are preferred from the standpoints of sound-damping properties, light weight, foaming adjustability, durability, and the like.

[0025] The sound-damping body is in the form of a long strip having a bottom surface fixed to the inner surface of the tread portion and extends in the circumferential direction of the tire. In this case, the outer ends in the circumferential direction may be butted against each other to form a substantially annular shape, or the outer ends may be spaced apart from each other in the circumferential direction.

[0026] In the present disclosure, "0°C tan δ" refers to the loss tangent tan δ under the conditions of a temperature of 0°C, a frequency of 10Hz, and an elongation strain of 2.5%. From the viewpoint of wet grip performance, the 0°C tan δ of the rubber composition constituting the first layer 2 is preferably 1.00 or more, more preferably 1.05 or more, even more preferably 1.10 or more, and particularly preferably 1.15 or more. The 0°C tan δ of the rubber composition constituting the second layer 3 is preferably 0.60 or more, more preferably 0.64 or more, and even more preferably 0.68 or more. On the other hand, the 0°C tan δ 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 even more preferably 1.50 or less, from the viewpoint of fuel efficiency performance. The 0°C tan δ value of the rubber composition constituting the first layer 2 is preferably larger than the 0°C tan δ value of the rubber composition constituting the second layer 3. The difference between the 0°C tan δ of the rubber composition constituting the first layer 2 and the 0°C tan δ of the rubber composition constituting the second layer 3 is preferably 0.10 or more, more preferably 0.20 or more, even more preferably 0.30 or more, and particularly preferably 0.40 or more.

[0027] In the present disclosure, "30°C tan δ" refers to the loss tangent tan δ under the conditions of a temperature of 30°C, a frequency of 10Hz, and an elongation strain of 2.5%. From the viewpoint of wet grip performance, the 30°C tan δ of the rubber composition constituting the first layer 2 is preferably 0.25 or more, more preferably 0.28 or more, even more preferably 0.29 or more, even more preferably 0.30 or more, even more preferably 0.31 or more, even more preferably 0.32 or more, and particularly preferably 0.33 or more. The 30°C tan δ of the rubber composition constituting the second layer 3 is preferably 0.15 or more, more preferably 0.17 or more, even more preferably 0.19 or more, and particularly preferably 0.21 or more. On the other hand, the 30°C tan δ of the rubber composition 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, even more preferably 0.55 or less, even more preferably 0.50 or less, and particularly preferably 0.45 or less, from the viewpoint of fuel efficiency. The 30°C tan δ value of the rubber composition constituting the first layer 2 is preferably greater than the 30°C tan δ value of the rubber composition constituting the second layer 3. The difference between the 30°C tan δ of the rubber composition constituting the first layer 2 and the 30°C tan δ of the rubber composition constituting the second layer 3 is preferably 0.02 or greater, more preferably 0.04 or greater, even more preferably 0.06 or greater, and particularly preferably 0.08 or greater.

[0028] In the present disclosure, EB refers to the elongation at break (elongation at break) measured in accordance with JIS K 6251 at a tensile speed of 3.3 mm / sec in an atmosphere of 23°C. From the viewpoint 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, even more preferably 630% or more, and particularly preferably 640% or more. The EB of the rubber composition constituting the second layer 3 is preferably 500% or more, more preferably 510% or more, even more preferably 520% ​​or more, and particularly preferably 530% or more. By setting the EB within the above range, it is believed that the surface state during tire wear is more easily maintained smooth, the reduction in the actual contact area is suppressed, and as a result, the deterioration of wet grip performance after tire wear can be suppressed. The upper limit value of the EB of the rubber composition constituting the first layer 2, the second layer 3, and the third layer 4 is not particularly limited.

[0029] In the present disclosure, "0°C E*" refers to the complex modulus E* under the conditions of a temperature of 0°C, a frequency of 10Hz, and an elongation strain of 2.5%. The 0°C E* of the rubber composition constituting the first layer 2 is preferably 50MPa or more, more preferably 55MPa or more, and even more preferably 60MPa or more, from the viewpoint of anchor friction. The 0°C E* of the rubber composition constituting the second layer 3 is preferably 25MPa or more, more preferably 30MPa or more, and even more preferably 35MPa or more, from the viewpoint of anchor friction. On the other hand, the 0°C E* of the rubber composition constituting the first layer 2, the second layer 3, and the third layer 4 is preferably 85MPa or less, more preferably 80MPa or less, and even more preferably 75MPa or less, from the viewpoint of road surface following ability. The 0°C E* value of the rubber composition constituting the first layer 2 is preferably larger than the 0°C E* value of the rubber composition constituting the second layer 3. The difference between the 0°C E* of the rubber composition constituting the first layer 2 and the 0°C E* of the rubber composition constituting the second layer 3 is preferably 5 MPa or more, more preferably 8 MPa or more, and even more preferably 12 MPa or more. By setting the 0°C E* in the above range, it is believed that the balance between road surface following performance and anchor friction can be improved, and the deterioration of wet grip performance after tire wear can be suppressed.

[0030] The glass transition temperature (Tg) in the present disclosure refers to the tan δ peak temperature measured by the following method. That is, for a rubber test piece (for example, 20 mm long x 4 mm wide x 1 mm thick) cut out from the inside of the rubber layer of the tread portion of each test tire so that the long side is in the tire circumferential direction, a temperature distribution curve of tan δ is measured under conditions of a frequency of 10 Hz and an elongation strain of 2.5% using a dynamic viscoelasticity evaluation device (Iplexer series manufactured by GABO Corporation), and the temperature corresponding to the largest tan δ value in the obtained temperature distribution curve (tan δ peak temperature) is defined as the glass transition temperature (Tg) in the present disclosure. From the viewpoint 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, even more preferably -7°C or higher, even more preferably -6°C or higher, even more preferably -5°C or higher, and particularly preferably -4°C or higher. When the Tg is -10°C or higher, the loss tangent tan δ in the temperature range higher than Tg tends to be higher than when it is lower than -10°C. The Tg of the rubber composition constituting the second layer 3 is preferably -25°C or higher, more preferably -22°C or higher, and even more preferably -19°C or higher. The upper limit of the Tg of the rubber compositions constituting the first layer 2, the second layer 3, and the third layer 4 is not particularly limited, but is preferably 20°C or lower, more preferably 15°C or lower, even more preferably 10°C or lower, even more preferably 5°C or lower, and particularly preferably 0°C or lower. The Tg of each rubber layer can be appropriately adjusted by the type and amount of the rubber component, etc.

[0031] The rubber composition constituting the first layer 2 preferably has a 30°C tan δ of 0.25 to 0.65 and a Tg of -10°C to 20°C; more preferably has a 30°C tan δ of 0.28 to 0.60 and a Tg of -8°C to 15°C; even more preferably has a 30°C tan δ of 0.30 to 0.55 and a Tg of -7°C to 10°C; and particularly preferably has a 30°C tan δ of 0.32 to 0.50 and a Tg of -6°C to 5°C.

[0032] In this disclosure, unless otherwise specified, the dimensions and angles of each component of the tire are measured when the tire is mounted on a standard rim and inflated to a standard internal pressure. No load is applied to the tire during measurement. In this specification, the term "standard rim" refers to a rim that is determined for each tire by a standard system that includes the standard on which the tire is based, such as a standard rim for JATMA, a "Design Rim" for TRA, and a "Measuring Rim" for ETRTO. In this specification, the term "standard internal pressure" refers to the air pressure determined for each tire by the standard, such as the maximum air pressure for JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA, and "INFLATION PRESSURE" for ETRTO.

[0033] [Rubber composition for tread] As described above, the rubber composition constituting each rubber layer of the tread (rubber composition for tread) contains a rubber component and a plasticizer.

[0034] <Rubber component> The rubber composition for treads according to the present disclosure preferably contains at least one rubber component selected from the group consisting of isoprene-based rubber, styrene butadiene rubber (SBR) and butadiene rubber (BR). The rubber components constituting the first layer 2 and the second layer 3 preferably contain SBR, more preferably contain SBR and BR, and may be rubber components consisting of only SBR and BR. The rubber component constituting the third layer 4 preferably contains isoprene-based rubber, more preferably contains isoprene-based rubber and BR, and may be rubber components consisting of only isoprene-based rubber and BR.

[0035] (Isoprene rubber) As the isoprene-based rubber, for example, isoprene rubber (IR) and natural rubber, which are common in the tire industry, can be used. In addition to unmodified natural rubber (NR), natural rubber also includes modified natural rubber such as epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), deproteinized natural rubber (DPNR), high-purity natural rubber, and grafted natural rubber. These isoprene-based rubbers may be used alone or in combination of two or more.

[0036] The NR is not particularly limited, and any NR commonly used in the tire industry can be used, such as SIR20, RSS#3, and TSR20.

[0037] When the rubber composition constituting the first layer 2 and the second layer 3 contains an isoprene-based rubber (preferably natural rubber, more preferably unmodified natural rubber (NR)), the content in 100% by mass of the rubber component 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, from the viewpoint of wet grip performance. In addition, the lower limit of the content when the isoprene-based rubber is contained is not particularly limited, but 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. When the rubber composition constituting the third layer 4 contains an isoprene-based rubber, the content in 100% by mass of the rubber component is not particularly limited, but can be, for example, 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.

[0038] (SBR) There are no particular limitations on the 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). Modified SBRs include SBRs whose ends and / or main chains are modified, and modified SBRs (condensates, those having a branched structure, etc.) coupled with tin or silicon compounds. Of these, S-SBR and modified SBR are preferred. Furthermore, hydrogenated products of these SBRs (hydrogenated SBR), etc. can also be used. These SBRs may be used alone or in combination of two or more.

[0039] As the SBR, oil-extended SBR or non-oil-extended SBR can be used. When oil-extended SBR is used, the amount of oil extension of SBR, i.e., the content of oil extension oil contained in SBR, is preferably 10 to 50 parts by mass per 100 parts by mass of rubber solid content of SBR.

[0040] As the S-SBR that can be used in the present disclosure, commercially available products from JSR Corporation, Sumitomo Chemical Co., Ltd., Ube Industries, Ltd., Asahi Kasei Corporation, ZS Elastomers Co., Ltd., and the like can be used.

[0041] From the viewpoints of wet grip performance and abrasion resistance, the styrene content of SBR is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more. From the viewpoints of temperature dependency of grip performance and blow resistance, the styrene content is preferably 60% by mass or less, more preferably 55% by mass or less, and even more preferably 50% by mass or less. In this specification, the styrene content of SBR is 1 It is calculated by H-NMR measurement.

[0042] The vinyl content of SBR is preferably 10 mol% or more, more preferably 15 mol% or more, and even more preferably 20 mol% or more, from the viewpoints of ensuring reactivity with silica, wet grip performance, rubber strength, and abrasion resistance. Also, the vinyl content of SBR is preferably 70 mol% or less, more preferably 65 mol% or less, and even more preferably 60 mol% or less, from the viewpoints of preventing an increase in temperature dependency, breaking elongation, and abrasion resistance. In this specification, the vinyl content of SBR (amount of 1,2-bonded butadiene units) is measured by infrared absorption spectroscopy.

[0043] From the viewpoint of wet grip performance, the weight average molecular weight (Mw) of SBR is preferably 200,000 or more, more preferably 250,000 or more, and even more preferably 300,000 or more. From the viewpoint of crosslinking uniformity, the weight average molecular weight is preferably 2,000,000 or less, more preferably 1,800,000 or less, and even more preferably 1,500,000 or less. In this specification, the weight average molecular weight of SBR can be calculated in terms of standard polystyrene based on the measured value by gel permeation chromatography (GPC) (for example, GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMALTIPORE HZ-M manufactured by Tosoh Corporation).

[0044] When the rubber composition constituting the first layer 2 and the second layer 3 contains SBR, the content of SBR in 100% by mass of the rubber component 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, from the viewpoint of wet grip performance. The upper limit of the content of SBR in the rubber component is not particularly limited, and may be 100% by mass. 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.

[0045] (BR) The BR is not particularly limited, and can be one that is commonly used in the tire industry, such as BR with a cis content of less than 50% (low cis BR), BR with a cis content of 90% or more (high cis BR), rare earth butadiene rubber (rare earth BR) synthesized using a rare earth catalyst, BR containing syndiotactic polybutadiene crystals (SPB-containing BR), and modified BR (high cis modified BR, low cis modified BR). Modified BR can be BR modified with the same functional groups as those described above for SBR. These BRs can be used alone or in combination of two or more.

[0046] As the high cis BR, for example, those commercially available from Zeon Corporation, Ube Industries, Ltd., JSR Corporation, etc. can be used. By containing high cis BR, low temperature properties and wear resistance can be improved. The cis content is preferably 95% or more, more preferably 96% or more, further preferably 97% or more, and particularly preferably 98% or more. In this specification, the cis content (amount of cis-1,4-bonded butadiene units) is a value calculated by infrared absorption spectrum analysis.

[0047] The rare earth BR is synthesized using a rare earth catalyst, and has a vinyl content of preferably 1.8 mol% or less, more preferably 1.0 mol% or less, and even more preferably 0.8 mol% or less, and a cis content of preferably 95% or more, more preferably 96% or more, even more preferably 97% or more, and particularly preferably 98% or more. As the rare earth BR, for example, commercially available products from LANXESS Co., Ltd. can be used.

[0048] The SPB-containing BR is not one in which 1,2-syndiotactic polybutadiene crystals are simply dispersed in the BR, but one in which the 1,2-syndiotactic polybutadiene crystals are dispersed after being chemically bonded to the BR. As such an SPB-containing BR, commercially available products from Ube Industries, Ltd. can be used.

[0049] As the modified BR, a modified butadiene rubber (modified BR) in which the terminals and / or the main chain are modified with a functional group containing at least one element selected from the group consisting of silicon, nitrogen and oxygen is preferably used.

[0050] Other modified BRs include those obtained by polymerizing 1,3-butadiene with a lithium initiator and then adding a tin compound, and further having the terminals of the modified BR molecule bonded with tin-carbon bonds (tin-modified BR), etc. The modified BR may be either non-hydrogenated or hydrogenated.

[0051] The BRs listed above may be used alone or in combination of two or more.

[0052] From the viewpoint of wear resistance, the weight average molecular weight (Mw) of BR is preferably 300,000 or more, more preferably 350,000 or more, and even more preferably 400,000 or more. From the viewpoint of crosslinking uniformity, it is preferably 2,000,000 or less, and more preferably 1,000,000 or less. The weight average molecular weight of BR can be determined by standard polystyrene conversion based on the measured value obtained by gel permeation chromatography (GPC) (for example, GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMALTIPORE HZ-M manufactured by Tosoh Corporation).

[0053] When the rubber compositions constituting the first layer 2, the second layer 3 and the third layer 4 contain BR, the content thereof in 100% by mass of the rubber component 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, from the viewpoint of wet grip performance. Furthermore, when BR is contained, the lower limit of the content is not particularly limited, and 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.

[0054] (Other rubber components) The rubber component according to the present disclosure may contain rubber components other than the isoprene-based rubber, SBR, and BR. As the other rubber components, crosslinkable rubber components generally 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, chlorinated polyethylene rubber, fluororubber (FKM), acrylic rubber (ACM), hydrin rubber, etc. These other rubber components may be used alone or in combination of two or more.

[0055] <Filler> The rubber composition for treads according to the present disclosure preferably uses a filler containing carbon black and / or silica. The rubber compositions constituting the first layer 2 and the second layer 3 preferably contain silica as a filler, more preferably carbon black and silica. The rubber composition constituting the third layer 4 preferably contains carbon black as a filler.

[0056] (Carbon Black) As the carbon black, any carbon black commonly used in the tire industry can be appropriately used, such as GPF, FEF, HAF, ISAF, SAF, etc. These carbon blacks may be used alone or in combination of two or more kinds.

[0057] The nitrogen adsorption specific surface area of ​​carbon black (N 2 SA) is 10m from the viewpoint of reinforcement. 2 / g or more is preferable, and 20m 2 / g or more is more preferable, and 35m 2 / g or more is more preferable, and 50m 2 From the viewpoints of fuel economy and processability, it is particularly preferable that the tensile strength is 200 m 2 / g or less is preferable, and 150m 2 / g or less is more preferable, and 100m 2 / g or less is more preferable, and 80m 2 / g or less is more preferable. 2 SA is a value measured in accordance with JIS K 6217-2 "Basic properties of carbon black for rubber - Part 2: Determination of specific surface area - Nitrogen adsorption method - Single point method".

[0058] When carbon black is contained, the content per 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more from the viewpoint of abrasion resistance and wet grip performance, and is preferably 50 parts by mass or less, more preferably 35 parts by mass or less, even more preferably 20 parts by mass or less, and particularly preferably 10 parts by mass or less from the viewpoint of fuel economy.

[0059] (silica) The silica is not particularly limited, and can be, for example, silica prepared by a dry method (anhydrous silica), silica prepared by a wet method (hydrated silica), or other silica commonly used in the tire industry. Among them, hydrated silica prepared by a wet method is preferred because it contains a large number of silanol groups. These silicas can be used alone or in combination of two or more.

[0060] The nitrogen adsorption specific surface area of ​​silica (N 2 SA) is a 140m 2 / g or more is preferable, and 150m 2 / g or more is more preferable, and 170m 2 / g or more is more preferable, and 200m 2 From the viewpoints of fuel economy and processability, it is particularly preferable that the tensile strength is 350 m 2 / g or less is preferable, and 300m 2 / g or less is more preferable, and 250m 2 / g or less is more preferable. 2 SA is a value measured by the BET method in accordance with ASTM D3037-93.

[0061] When silica is contained, the content per 100 parts by mass of the rubber component is preferably 20 parts by mass or more, more preferably 40 parts by mass or more, even more preferably 50 parts by mass or more, and particularly preferably 60 parts by mass or more. When silica is contained, the content per 100 parts by mass of the rubber component is preferably 160 parts by mass or less, more preferably 130 parts by mass or less, even more preferably 120 parts by mass or less, and particularly preferably 110 parts by mass or less.

[0062] When the rubber composition constituting the first layer contains silica, the content per 100 parts by mass of the rubber component is preferably 50 parts by mass or more, more preferably 70 parts by mass or more, even more preferably 90 parts by mass or more, and particularly preferably 100 parts by mass or more from the viewpoint of wet grip performance, and is preferably 160 parts by mass or less, more preferably 130 parts by mass or less, even more preferably 120 parts by mass or less, and particularly preferably 110 parts by mass or less from the viewpoint of abrasion resistance.

[0063] When the rubber composition constituting the second layer contains silica, the content thereof per 100 parts by mass of the rubber component is preferably 40 parts by mass or more, more preferably 50 parts by mass or more, even more preferably 60 parts by mass or more, and particularly preferably 70 parts by mass or more. From the viewpoint of abrasion resistance, the content is preferably 130 parts by mass or less, more preferably 120 parts by mass or less, even more preferably 110 parts by mass or less, and particularly preferably 100 parts by mass or less.

[0064] The total content of silica and carbon black per 100 parts by mass of the rubber component is preferably 40 parts by mass or more, more preferably 50 parts by mass or more, and even more preferably 60 parts by mass or more from the viewpoint of abrasion resistance, and is preferably 160 parts by mass or less, more preferably 140 parts by mass or less, and even more preferably 120 parts by mass or less from the viewpoint of fuel economy and elongation at break.

[0065] From the viewpoint of a balance between fuel economy performance, wet grip performance, and abrasion resistance, the rubber composition constituting the first layer 2 and the second layer 3 preferably has a silica content greater than the carbon black content per 100 parts by mass of the rubber component. The ratio of silica to the total content of silica and carbon black in the first layer 2 and the second layer 3 is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 85% by mass or more, and particularly preferably 90% by mass or more. The ratio of silica and carbon black to the total content of silica and carbon black in the third layer 4 is not particularly limited, but the ratio of carbon black to the total content of silica and 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.

[0066] (Silane coupling agent) Silica is preferably used in combination with a silane coupling agent. The silane coupling agent is not particularly limited, and any silane coupling agent conventionally used in combination with silica in the tire industry can be used. Examples of the silane coupling agent include 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 vinyl triethoxysilane and vinyl trimethoxysilane; amino-based silane coupling agents such as 3-aminopropyl triethoxysilane, 3-aminopropyl trimethoxysilane and 3-(2-aminoethyl) aminopropyl triethoxysilane; glycidoxy-based silane coupling agents such as γ-glycidoxypropyl triethoxysilane and γ-glycidoxypropyl trimethoxysilane; nitro-based silane coupling agents such as 3-nitropropyl trimethoxysilane and 3-nitropropyl triethoxysilane; and chloro-based silane coupling agents such as 3-chloropropyl trimethoxysilane and 3-chloropropyl triethoxysilane. 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 may be used alone or in combination of two or more.

[0067] The mercapto-based silane coupling agent is preferably a compound represented by the following formula (1) and / or a compound containing a bonding unit A represented by the following formula (2) and a bonding unit B represented by the following formula (3). [ka] (In the formula, R 101 , R 102 , and R 103 are each independently 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 independently represents a divalent hydrocarbon group having 1 to 30 carbon atoms; R112 represents an alkyl group having 1 to 30 carbon atoms, an alkenyl group having 2 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms, or an aralkyl group having 7 to 30 carbon atoms; z represents an integer of 1 to 30; 104 represents an alkylene having 1 to 6 carbon atoms. [ka] [ka] (wherein x represents an integer of 0 or more; y represents an integer of 1 or more; R 201 represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 30 carbon atoms, an alkenyl group having 2 to 30 carbon atoms, or an alkynyl group having 2 to 30 carbon atoms, which may be substituted by a hydroxyl or carboxyl group; R 202 represents an alkylene having 1 to 30 carbon atoms, an alkenylene having 2 to 30 carbon atoms, or an alkynylene having 2 to 30 carbon atoms; 201 and R 202 may form a ring structure.)

[0068] Examples of the compound represented by formula (1) include 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 following formula (4) can be preferably used. These may be used alone or in combination of two or more. [ka]

[0069] Examples of compounds containing a bond unit A represented by formula (2) and a bond unit B represented by formula (3) include those manufactured and sold by Momentive, Inc. These may be used alone or in combination of two or more.

[0070] When a silane coupling agent is contained, the total content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, even more preferably 2.0 parts by mass or more, and particularly preferably 4.0 parts by mass or more, from the viewpoint of improving the dispersibility of silica, and is preferably 20 parts by mass or less, more preferably 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, from the viewpoint of preventing a decrease in abrasion resistance.

[0071] The content of silane coupling agent with respect to 100 parts by mass of silica (when multiple silane coupling agents are used, the total amount of all of them) 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, from the viewpoint of increasing the dispersibility of silica.Furthermore, from the viewpoint of cost and processability, it is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 12 parts by mass or less.

[0072] As the filler, in addition to carbon black and silica, other fillers may be used. Such fillers are not particularly limited, and any fillers generally used in this field, such as aluminum hydroxide, alumina (aluminum oxide), calcium carbonate, magnesium sulfate, talc, clay, etc., may be used. These fillers may be used alone or in combination of two or more.

[0073] <Plasticizer> The rubber composition for a tread according to the present disclosure contains a plasticizer, such as a resin component, oil, liquid rubber, or an ester-based plasticizer.

[0074] The resin component is not particularly limited, but examples thereof include petroleum resins, terpene resins, rosin resins, phenol resins, etc. These resin components may be used alone or in combination of two or more.

[0075] In this specification, the term "C5 petroleum resin" refers to a resin obtained by polymerizing a C5 fraction. Examples of C5 fractions include petroleum fractions having 4 to 5 carbon atoms, such as cyclopentadiene, pentene, pentadiene, and isoprene. As the C5 petroleum resin, dicyclopentadiene resin (DCPD resin) is preferably used.

[0076] In this specification, the term "aromatic petroleum resin" refers to a resin obtained by polymerizing a C9 fraction, and may be a hydrogenated or modified resin. Examples of C9 fractions include petroleum fractions having 8 to 10 carbon atoms, such as vinyl toluene, alkyl styrene, indene, and methyl indene. Specific examples of aromatic petroleum resins include, for example, Coumarone-indene resin, coumaron resin, indene resin, and aromatic vinyl resin are preferably used. As the aromatic vinyl resin, a homopolymer of α-methylstyrene or styrene, or a copolymer of α-methylstyrene and styrene is preferred, and a copolymer of α-methylstyrene and styrene is more preferred, because they are economical, easy to process, and have excellent heat generation properties. As the aromatic vinyl resin, for example, commercially available products from Kraton, Eastman Chemical, etc. can be used.

[0077] In this specification, the term "C5C9 petroleum resin" refers to a resin obtained by copolymerizing the C5 fraction and the C9 fraction, and may be a hydrogenated or modified resin. Examples of the C5 fraction and the C9 fraction include the petroleum fractions described above. As the C5C9 petroleum resin, for example, those commercially available from Tosoh Corporation, LUHUA, etc. can be used.

[0078] Examples of the terpene resin include polyterpene resins consisting of at least one selected from terpene compounds such as α-pinene, β-pinene, limonene, and dipentene; aromatic modified terpene resins made from the terpene compounds and aromatic compounds; terpene phenolic resins made from terpene compounds and phenolic compounds; and terpene resins obtained by subjecting these terpene resins to hydrogenation treatment (hydrogenated terpene resins). Examples of aromatic compounds that are raw materials for aromatic modified terpene resins include styrene, α-methylstyrene, vinyltoluene, and divinyltoluene. Examples of phenolic compounds that are raw materials for terpene phenolic resins include phenol, bisphenol A, cresol, and xylenol.

[0079] The rosin-based resin is not particularly limited, but examples thereof include natural rosin resin and rosin-modified resins obtained by modifying rosin by hydrogenation, disproportionation, dimerization, esterification, or the like.

[0080] The phenol-based resin is not particularly limited, but examples thereof include phenol formaldehyde resin, alkylphenol formaldehyde resin, alkylphenol acetylene resin, and oil-modified phenol formaldehyde resin.

[0081] From the viewpoint of wet grip performance, the softening point of the resin component is preferably 60° C. or higher, and more preferably 65° C. or higher. From the viewpoint of processability and improving the dispersibility of the rubber component and the filler, the softening point is preferably 150° C. or lower, more preferably 140° C. or lower, and even more preferably 130° C. or lower. In this specification, the softening point may be defined as the temperature at which the ball drops when the softening point specified in JIS K 6220-1:2001 is measured using a ring and ball softening point tester.

[0082] When a resin component is contained, the content per 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 3 parts by mass or more, even more preferably 5 parts by mass or more, and particularly preferably 7 parts by mass or more from the viewpoint of wet grip performance, and is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, even more preferably 40 parts by mass or less, and particularly preferably 30 parts by mass or less from the viewpoint of suppressing heat buildup.

[0083] Examples of the oil include process oil, vegetable oil, and animal oil. Examples of the process oil include paraffin-based process oil, naphthenic process oil, and aromatic process oil. In addition, as an environmental measure, process oil with a low content of polycyclic aromatic compound (PCA) compounds can be used. Examples of the low PCA content process oil include light extract solvate (MES), treated distillate aromatic extract (TDAE), and heavy naphthenic oil.

[0084] When oil is contained, the content per 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 3 parts by mass or more, even more preferably 5 parts by mass or more, and particularly preferably 7 parts by mass or more, from the viewpoint of processability. Also, from the viewpoint of abrasion resistance, the content is preferably 120 parts by mass or less, more preferably 100 parts by mass or less, even more preferably 80 parts by mass or less, and particularly preferably 60 parts by mass or less. In this specification, the content of oil includes the amount of oil contained in the oil-extended rubber.

[0085] 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 thereof include liquid butadiene rubber (liquid BR), liquid styrene butadiene rubber (liquid SBR), liquid isoprene rubber (liquid IR), liquid styrene isoprene rubber (liquid SIR), liquid farnesene rubber, etc. These liquid rubbers may be used alone or in combination of two or more kinds.

[0086] When the liquid rubber is contained, the content per 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 3 parts by mass or more, even more preferably 5 parts by mass or more, and particularly preferably 7 parts by mass or more. The content of the liquid rubber is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 20 parts by mass or less.

[0087] Examples of ester-based plasticizers include dibutyl adipate (DBA), diisobutyl adipate (DIBA), dioctyl adipate (DOA), di-2-ethylhexyl azelate (DOZ), dibutyl sebacate (DBS), diisononyl adipate (DINA), diethyl phthalate (DEP), dioctyl phthalate (DOP), diundecyl phthalate (DUP), dibutyl phthalate (DBP), dioctyl sebacate (DOS), tributyl phosphate (TBP), trioctyl phosphate (TOP), triethyl phosphate (TEP), trimethyl phosphate (TMP), thymidine triphosphate (TTP), tricresyl phosphate (TCP), trixylenyl phosphate (TXP), etc. These ester-based plasticizers may be used alone or in combination of two or more.

[0088] In the rubber composition constituting the first layer 2, the content of the plasticizer per 100 parts by mass of the rubber component (when multiple plasticizers are used in combination, the total amount of all of them) is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, even more preferably 30 parts by mass or more, and particularly preferably 40 parts by mass or more, from the viewpoint of wet grip performance. In the rubber composition constituting the second layer 3, the content of the plasticizer per 100 parts by mass of the rubber component 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. In addition, in the rubber compositions constituting the first layer 2, the second layer 3, and the third layer 4, the content of the plasticizer per 100 parts by mass of the rubber component 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, from the viewpoint of processability.

[0089] <Other compounding agents> In addition to the above-mentioned components, the rubber composition according to the present disclosure may appropriately contain compounding agents commonly used in the tire industry, such as wax, processing aids, stearic acid, zinc oxide, antioxidants, vulcanizing agents, and vulcanization accelerators.

[0090] When the wax is contained, the content thereof per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, and more preferably 1 part by mass or more, from the viewpoint of weather resistance of the rubber, and is preferably 10 parts by mass or less, and more preferably 5 parts by mass or less, from the viewpoint of preventing whitening of the tire due to bloom.

[0091] Examples of the processing aid include 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 may be used alone or in combination of two or more. Examples of the processing aids that can be used include those commercially available from Schill+Seilacher, Performance Additives, etc.

[0092] When a processing aid is contained, the content thereof per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, from the viewpoint of improving processability, and is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, from the viewpoints of abrasion resistance and breaking strength.

[0093] The antiaging agent is not particularly limited, but examples thereof include amine-based, quinoline-based, quinone-based, phenol-based, and imidazole-based compounds, and carbamic acid metal salts, and the like. Phenylenediamine-based antiaging agents such as N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, N,N'-diphenyl-p-phenylenediamine, N,N'-di-2-naphthyl-p-phenylenediamine, and N-cyclohexyl-N'-phenyl-p-phenylenediamine, and quinoline-based antiaging agents such as 2,2,4-trimethyl-1,2-dihydroquinoline polymer and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline are preferred. These antiaging agents may be used alone or in combination of two or more.

[0094] When an antioxidant is contained, the content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, from the viewpoint of ozone crack resistance of the rubber, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, from the viewpoint of abrasion resistance and wet grip performance.

[0095] When stearic acid is contained, the content thereof per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, from the viewpoint of processability, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, from the viewpoint of vulcanization speed.

[0096] When zinc oxide is contained, the content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, from the viewpoint of processability, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, from the viewpoint of abrasion resistance.

[0097] As the vulcanizing agent, sulfur is preferably used, and examples of the sulfur that can be used include powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur.

[0098] When sulfur is contained as a vulcanizing agent, the content per 100 parts by mass of the rubber component is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.5 parts by mass or more, from the viewpoint of ensuring sufficient vulcanization reaction. Also, from the viewpoint of preventing deterioration, the content is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.0 parts by mass or less. Note that, when oil-containing sulfur is used as a vulcanizing agent, the content of the vulcanizing agent is the total content of the pure sulfur contained in the oil-containing sulfur.

[0099] Examples of vulcanizing agents other than sulfur include alkylphenol-sulfur chloride condensates, sodium 1,6-hexamethylene-dithiosulfate dihydrate, 1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane, etc. As these vulcanizing agents other than sulfur, commercially available products from Taoka Chemical Co., Ltd., Lanxess Co., Ltd., Flexis, etc. can be used.

[0100] Examples of the vulcanization accelerator include sulfenamide-based, thiazole-based, thiuram-based, thiourea-based, guanidine-based, dithiocarbamic acid-based, aldehyde-amine-based or aldehyde-ammonia-based, imidazoline-based, and xanthate-based vulcanization accelerators. These vulcanization accelerators may be used alone or in combination of two or more. Among them, one or more vulcanization accelerators selected from the group consisting of sulfenamide-based, guanidine-based, and thiazole-based vulcanization accelerators are preferred, and sulfenamide-based vulcanization accelerators are more preferred.

[0101] Examples of sulfenamide vulcanization accelerators include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N,N-dicyclohexyl-2-benzothiazolylsulfenamide (DCBS), etc. Among them, N-cyclohexyl-2-benzothiazolylsulfenamide (CBS) is preferred.

[0102] Examples of the guanidine vulcanization accelerator include 1,3-diphenylguanidine (DPG), 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, di-o-tolylguanidine salt of dicatechol borate, 1,3-di-o-cumenylguanidine, 1,3-di-o-biphenylguanidine, 1,3-di-o-cumenyl-2-propionylguanidine, etc. Among them, 1,3-diphenylguanidine (DPG) is preferable.

[0103] Examples of the thiazole-based vulcanization accelerator include 2-mercaptobenzothiazole, cyclohexylamine salt of 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, etc. Among these, 2-mercaptobenzothiazole is preferred.

[0104] When a vulcanization accelerator is contained, the content per 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 2 parts by mass or more. The content per 100 parts by mass of the rubber component is preferably 8 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 6 parts by mass or less. By setting the content of the vulcanization accelerator within the above range, breaking strength and elongation tend to be secured.

[0105] The rubber composition according to the present disclosure can be produced by a known method, for example, by kneading the above-mentioned components using a rubber kneading device such as an open roll or an internal kneader (such as a Banbury mixer or kneader).

[0106] The kneading step includes, for example, a base kneading step in which compounding ingredients and additives other than the vulcanizing agent and the vulcanization accelerator are kneaded, and a final kneading (F kneading) step in which the vulcanizing agent and the vulcanization accelerator are added to the kneaded product obtained in the base kneading step and kneaded. Furthermore, the base kneading step can be divided into a plurality of steps as desired.

[0107] The kneading conditions are not particularly limited, but examples thereof include a method in which in the base kneading step, kneading is performed for 3 to 10 minutes at a discharge temperature of 150 to 170° C., and in the final kneading step, kneading is performed for 1 to 5 minutes at 70 to 110° C. The vulcanization conditions are not particularly limited, but examples thereof include a method in which vulcanization is performed for 10 to 30 minutes at 150 to 200° C.

[0108] Acetone extractable amount AE of the rubber composition constituting the first layer 2 1 and the acetone extractable amount AE of the rubber composition constituting the second layer 3. 2 Difference from (AE 1 -AE 2 ) is 1.0% by mass or more, preferably 1.5% by mass or more, more preferably 2.0% by mass or more, even more preferably 2.5% by mass or more, and particularly preferably 3.0% by mass or more. By setting the difference in acetone extractables within the above range, the concentration gradient makes it easier for acetone extractable components such as oil to migrate from the first layer 2 to the second layer 3 during driving, and by the time the second layer 3 is exposed due to wear of the tread portion, the second layer 3 contains a sufficient amount of plasticizer, making it possible to maintain wet grip performance for a long period of time. In addition, 1 -AE 2 The upper limit is not particularly limited, but is generally 30% by mass or less, preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less.

[0109] Acetone extractable amount AE of the rubber composition constituting the second layer 3 2 and the acetone extractable amount AE of the rubber composition constituting the third layer 4. 3 Difference from (AE 2 -AE 3 ) is 1.0 mass% or more, preferably 1.5 mass% or more, more preferably 2.0 mass% or more, even more preferably 2.5 mass% or more, and particularly preferably 3.0 mass% or more. 2 -AE 3 The upper limit is not particularly limited, but is generally 30% by mass or less, preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less.

[0110] The acetone extractable amount is an index of the concentration of organic low molecular weight compounds in the plasticizer contained in the vulcanized rubber composition. The acetone extractable amount can be calculated by immersing each vulcanized rubber test piece in acetone for 24 hours in accordance with JIS K 6229-3:2015 to extract soluble components, measuring the mass of each test piece before and after extraction, and using the following formula: Acetone extractable amount (mass%)={(mass of rubber test piece before extraction-mass of rubber test piece after extraction) / (mass of rubber test piece before extraction)}×100

[0111] [tire] The tire according to the present disclosure has a tread including a first layer 2, a second layer 3, and a third layer 4, and may be a pneumatic tire or a non-pneumatic tire. Examples of pneumatic tires include passenger car tires, truck and bus tires, motorcycle tires, and high performance tires, and are particularly suitable for use as passenger car tires. In this specification, the high performance tire is a tire that is particularly excellent in grip performance, and is a concept that also includes racing tires used on racing vehicles.

[0112] A tire having a tread including the first layer 2, the second layer 3, and the third layer 4 can be manufactured by a normal method using the above rubber composition. That is, an unvulcanized rubber composition in which the above components are blended with the rubber component as necessary is extruded into the shapes of the first layer 2, the second layer 3, and the third layer 4 using an extruder equipped with a die of a predetermined shape, and then laminated together with other tire components on a tire building machine and molded by a normal method to form an unvulcanized tire, and the unvulcanized tire is heated and pressurized in a vulcanizer to manufacture a tire. EXAMPLES

[0113] The present disclosure will be described based on examples, but the present disclosure is not limited to only the examples.

[0114] The various chemicals used in the examples and comparative examples are listed below. NR:TSR20 SBR: Tufuden 4850 manufactured by Asahi Kasei Corporation (unmodified S-SBR, styrene content: 40% by mass, vinyl content: 46 mol%, Mw: 350,000, contains 50 parts by mass of oil per 100 parts by mass of rubber solids) BR: UBEPOL BR (registered trademark) 150B manufactured by Ube Industries, Ltd. (vinyl content: 1.5 mol%, cis content: 97%, Mw: 440,000) Carbon black: Show Black N330 (N) manufactured by Cabot Japan Co., Ltd. 2 SA:75m 2 / g) Silica: Ultrasil VN3 (N) manufactured by Evonik Degussa 2 SA: 175m 2 / g, average primary particle diameter: 15nm) Silane coupling agent: Momentive's NXT-Z45 (mercapto-based silane coupling agent) Resin component: Petrotac 100V manufactured by Tosoh Corporation (C5C9 petroleum resin, softening point: 96°C, Mw: 3800, SP value: 8.3) Liquid rubber: Cray Valley Ricon 100 (liquid SBR) Oil: VivaTec500 (TDAE oil) manufactured by H&R Corporation Anti-aging agent: Antigen 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd. Wax: Sannock N manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Stearic acid: Beads of stearic acid camellia manufactured by NOF Corporation Zinc oxide: Two types of zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: Powdered sulfur manufactured by Karuizawa Sulfur Co., Ltd. Vulcanization accelerator: Noccela CZ (N-cyclohexyl-2-benzothiazolyl sulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0115] Examples and Comparative Examples According to the compounding recipe shown in Table 1, chemicals other than sulfur and vulcanization accelerator were kneaded for 1 to 10 minutes using a 1.7 L closed type Banbury mixer until the discharge temperature reached 150 to 160 ° C., and a kneaded product was obtained. Next, sulfur and vulcanization accelerator were added to the kneaded product obtained using a two-axis open roll, and the mixture was kneaded for 4 minutes until the temperature reached 105 ° C., and an unvulcanized rubber composition was obtained. The unvulcanized rubber composition obtained was molded according to the shape of the first layer, second layer, and third layer of the tread, and laminated together with other tire components to prepare an unvulcanized tire, which was vulcanized at 170 ° C. to obtain each test tire (size: 205 / 65R15, rim: 15 × 6JJ, internal pressure: 230 kPa) shown in Table 2.

[0116] <Measurement of acetone extractables (AE amount) from the first, second and third layers> After vulcanization, each rubber test piece was immersed in acetone for 24 hours to extract the soluble components. The mass of each test piece was measured before and after extraction, and the amount of acetone extracted was calculated using the following formula. Acetone extractable amount (mass%)={(mass of rubber test piece before extraction-mass of rubber test piece after extraction) / (mass of rubber test piece before extraction)}×100

[0117] The rubber test pieces for the first, second and third layers were cut out from the inside of the rubber layer in the tread portion of each test tire. 1 and the acetone extractable amount AE of the rubber composition constituting the second layer. 2 Difference from (AE 1 -AE 2 ) and the acetone extractable amount AE of the rubber composition constituting the second layer 2 and the acetone extractable amount AE of the rubber composition constituting the second layer. 3 Difference from (AE 2 -AE 3 ) values ​​are shown in Table 2.

[0118] <Loss tangent tanδ and complex elastic modulus E* measurement> For each rubber test piece cut from the inside of the rubber layer of the tread portion of each test tire with a length of 20 mm, width of 4 mm, and thickness of 1 mm, with the tire circumferential direction as the long side, a dynamic viscoelasticity measuring device Iplexer (registered trademark) series manufactured by GABO was used to measure the loss tangent tanδ at temperatures of 0°C and 30°C, a frequency of 10 Hz, and an elongation strain of 2.5%. In addition, the complex modulus E* of each rubber test piece was measured at temperatures of 0°C, a frequency of 10 Hz, and an elongation strain of 2.5%. The thickness direction of the sample was the tire radial direction.

[0119] <Measurement of glass transition temperature (Tg)> For each rubber test piece cut from the inside of the rubber layer of the tread of each test tire with a length of 20 mm, width of 4 mm, and thickness of 1 mm, with the long side in the tire circumferential direction, a temperature distribution curve of loss tangent tanδ was measured using an Iplexer series manufactured by GABO under the conditions of a frequency of 10 Hz and an elongation strain of 2.5%, and the temperature corresponding to the largest tanδ value in the obtained temperature distribution curve (tanδ peak temperature) was taken as the glass transition temperature (Tg). The thickness direction of the sample was the tire radial direction.

[0120] <Tensile test> A 1mm-thick dumbbell-shaped No. 7 test piece was cut from inside the rubber layer of the tread of each test tire so that the tensile direction was the tire circumferential direction, and a tensile test was carried out in accordance with JIS K 6251:2017 "Vulcanized rubber and thermoplastic rubber - Determination of tensile test properties" at a 23°C atmosphere and a tensile speed of 3.3 mm / sec to measure the elongation at break EB (%). The thickness direction of the sample was the tire radial direction.

[0121] <Wet grip maintenance performance> Each test tire was attached to all wheels of a vehicle (domestic FF2000cc) and the braking distance from the point where the brakes were applied at a speed of 100km / h on a wet asphalt road surface was measured. Furthermore, after the above tires were thermally deteriorated at 80°C for 7 days, each test tire was worn along the tread radius so that the thickness of the tread portion was 50% of that of a new tire, and then the braking distance from the point where the brakes were applied at a speed of 100km / h on a wet asphalt road surface was measured. Then, for each test tire, the wet grip performance maintenance index before and after wear was calculated using the following formula, and the maintenance index of the control tire (Comparative Example 6) was converted to 100 to determine the wet grip maintenance performance of each test tire. The higher the value, the smaller the change in wet grip performance before and after wear, and the wet grip performance of the new tire is maintained. (Wet grip performance maintenance index of control tire) = (braking distance of control tire when new) / (braking distance of control tire after worn) (Wet grip performance maintenance index of each test tire) = (braking distance of each test tire when it is new) / (braking distance of each test tire after it has been worn) (Wet grip maintenance performance of each test tire) = (Wet grip performance maintenance index of each test tire) / (Wet grip performance maintenance index of control tire) × 100

[0122] <Low fuel consumption performance> Using a rolling resistance tester, the rolling resistance of each test tire was measured when it was run on a rim of 15×6JJ, with an internal pressure of 230 kPa, a load of 3.43 kN, and at a speed of 80 km / h. The rolling resistance of the control tire (Comparative Example 6) was set at 100, and the results were expressed as an index using the following calculation formula. The larger the value, the better the fuel efficiency performance. (Fuel economy performance index) = (Rolling resistance of control tire when new) / (Rolling resistance of each test tire when new) x 100

[0123] The target performance value for the overall wet grip maintenance performance and fuel efficiency performance (the sum of the wet grip maintenance performance index and the fuel efficiency performance index) is over 200.

[0124] [Table 1]

[0125] [Table 2]

[0126] The results in Tables 1 and 2 show that tires of the present disclosure, which have three or more rubber layers in the tread portion and in which the amount of plasticizer is gradient at least to a certain level from the rubber layer on the radially outer side of the tire to the rubber layer on the radially outer side of the tire, have improved overall wet grip maintenance performance and fuel efficiency performance. [Explanation of symbols]

[0127] 1. Tread surface 2...first layer 3...Second layer 4...Third layer

Claims

1. A tire having a tread including at least a first layer constituting a tread surface, a second layer adjacent to the radially inner side of the first layer, and a third layer adjacent to the radially inner side of the second layer, the first layer, the second layer and the third layer are made of a rubber composition containing a rubber component and a plasticizer, The acetone extractable amount AE of the rubber composition constituting the first layer 1 and the acetone extractable amount AE of the rubber composition constituting the second layer 2 Difference with (AE 1 -A.E. 2 ) is 1.0 mass% or more, The acetone extractable amount AE of the rubber composition constituting the second layer 2 and the acetone extractable amount AE of the rubber composition constituting the third layer 3 Difference with (AE 2 -A.E. 3 ) is 1.0 mass% or more, The tire in which the rubber composition constituting the first layer has a tan δ at 0° C. of 1.00 or more.

2. A tire having a tread including at least a first layer constituting a tread surface, a second layer adjacent to the radially inward side of the first layer, and a third layer adjacent to the radially inward side of the second layer, the first layer, the second layer and the third layer are made of a rubber composition containing a rubber component and a plasticizer, a difference (AE1-AE2) between an acetone extractable amount AE1 of a rubber composition constituting the first layer and an acetone extractable amount AE2 of a rubber composition constituting the second layer is 1.0 mass% or more; the difference (AE 2 - AE 3 ) between the acetone extractable amount AE 2 of the rubber composition constituting the second layer and the acetone extractable amount AE 3 of the rubber composition constituting the third layer is 1.0 mass % or more, The tire wherein the complex modulus of elasticity at 0° C. (0° C. E*) of the rubber composition constituting the first layer is 50 MPa or more.

3. A tire having a tread including at least a first layer constituting a tread surface, a second layer adjacent to the radially inward side of the first layer, and a third layer adjacent to the radially inward side of the second layer, the first layer, the second layer and the third layer are made of a rubber composition containing a rubber component and a plasticizer, a difference (AE1-AE2) between an acetone extractable amount AE1 of a rubber composition constituting the first layer and an acetone extractable amount AE2 of a rubber composition constituting the second layer is 1.0 mass% or more; the difference (AE 2 - AE 3 ) between the acetone extractable amount AE 2 of the rubber composition constituting the second layer and the acetone extractable amount AE 3 of the rubber composition constituting the third layer is 1.0 mass % or more, The tire wherein the rubber composition constituting the first layer has a glass transition temperature of -10°C or higher.

4. A tire having a tread including at least a first layer constituting a tread surface, a second layer adjacent to the radially inward side of the first layer, and a third layer adjacent to the radially inward side of the second layer, the first layer, the second layer and the third layer are made of a rubber composition containing a rubber component and a plasticizer, a difference (AE1-AE2) between an acetone extractable amount AE1 of a rubber composition constituting the first layer and an acetone extractable amount AE2 of a rubber composition constituting the second layer is 1.0 mass% or more; the difference (AE 2 - AE 3 ) between the acetone extractable amount AE 2 of the rubber composition constituting the second layer and the acetone extractable amount AE 3 of the rubber composition constituting the third layer is 1.0 mass % or more, The tire wherein the rubber composition constituting the first layer has a glass transition temperature of -7°C or higher.

5. A tire having a tread including at least a first layer constituting a tread surface, a second layer adjacent to the radially inward side of the first layer, and a third layer adjacent to the radially inward side of the second layer, the first layer, the second layer and the third layer are made of a rubber composition containing a rubber component and a plasticizer, a difference (AE1-AE2) between an acetone extractable amount AE1 of a rubber composition constituting the first layer and an acetone extractable amount AE2 of a rubber composition constituting the second layer is 1.0 mass% or more; the difference (AE 2 - AE 3 ) between the acetone extractable amount AE 2 of the rubber composition constituting the second layer and the acetone extractable amount AE 3 of the rubber composition constituting the third layer is 1.0 mass % or more, The tire wherein the rubber composition constituting the first layer has a tan δ at 30° C. of 0.25 or more.

6. A tire having a tread including at least a first layer constituting a tread surface, a second layer adjacent to the radially inward side of the first layer, and a third layer adjacent to the radially inward side of the second layer, the first layer, the second layer and the third layer are made of a rubber composition containing a rubber component and a plasticizer, a difference (AE1-AE2) between an acetone extractable amount AE1 of a rubber composition constituting the first layer and an acetone extractable amount AE2 of a rubber composition constituting the second layer is 1.0 mass% or more; the difference (AE 2 - AE 3 ) between the acetone extractable amount AE 2 of the rubber composition constituting the second layer and the acetone extractable amount AE 3 of the rubber composition constituting the third layer is 1.0 mass % or more, The tire wherein the rubber composition constituting the first layer has a tan δ at 30° C. of 0.30 or more.

7. A tire having a tread including at least a first layer constituting a tread surface, a second layer adjacent to the radially inward side of the first layer, and a third layer adjacent to the radially inward side of the second layer, the first layer, the second layer and the third layer are made of a rubber composition containing a rubber component and a plasticizer, a difference (AE1-AE2) between an acetone extractable amount AE1 of a rubber composition constituting the first layer and an acetone extractable amount AE2 of a rubber composition constituting the second layer is 1.0 mass% or more; the difference (AE 2 - AE 3 ) between the acetone extractable amount AE 2 of the rubber composition constituting the second layer and the acetone extractable amount AE 3 of the rubber composition constituting the third layer is 1.0 mass % or more, The tire wherein the rubber composition constituting the second layer has a tan δ at 0° C. of 0.60 or more.

8. A tire having a tread including at least a first layer constituting a tread surface, a second layer adjacent to the radially inward side of the first layer, and a third layer adjacent to the radially inward side of the second layer, the first layer, the second layer and the third layer are made of a rubber composition containing a rubber component and a plasticizer, a difference (AE1-AE2) between an acetone extractable amount AE1 of a rubber composition constituting the first layer and an acetone extractable amount AE2 of a rubber composition constituting the second layer is 1.0 mass% or more; the difference (AE 2 - AE 3 ) between the acetone extractable amount AE 2 of the rubber composition constituting the second layer and the acetone extractable amount AE 3 of the rubber composition constituting the third layer is 1.0 mass % or more, The tire wherein the rubber composition constituting the second layer has a complex modulus at 0°C (0°C E*) of 25 MPa or more.

9. The AE 1 -A.E. 2 The tire according to any one of claims 1 to 8, wherein the amount of the sintered body is 2.0 mass% or more.

10. The AE 2 -A.E. 3 The tire according to any one of claims 1 to 9, wherein the amount of the sintered body is 2.0 mass% or more.

11. The tire according to any one of claims 1 to 10, wherein the rubber composition constituting the first layer has an elongation at break measured in accordance with JIS K 6251 of 610% or more.

12. The tire according to any one of claims 1 to 11, wherein the rubber composition constituting the second layer has an elongation at break measured in accordance with JIS K 6251 of 500% or more.

13. The tire according to any one of claims 1 to 12, wherein the rubber compositions constituting the first layer and the second layer contain 40 to 160 parts by mass of silica and carbon black in total per 100 parts by mass of the rubber component, and a ratio of the content of silica to the total content of silica and carbon black is 60% by mass or more.

14. The tire according to any one of claims 1 to 13, wherein the rubber composition constituting the first layer contains 100 parts by mass or more of silica per 100 parts by mass of the rubber component.

15. The tire according to any one of claims 1 to 14, wherein the rubber compositions constituting the first layer and the second layer contain 10 parts by mass or more of a plasticizer per 100 parts by mass of a rubber component.

16. The tire according to any one of claims 1 to 15, wherein the rubber components constituting the first layer and the second layer contain 50 mass % or more of styrene-butadiene rubber.

17. The tire according to any one of claims 1 to 16, further comprising at least one selected from the group consisting of a sealant, a sound-damping material, and an electronic component for tire monitoring, in a tire cavity.

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