tire

Abstract

The present invention provides a tire having improved combined performance in fuel economy, new wet grip performance, and worn wet grip performance. A tire is provided, comprising at least a first rubber layer constituting a tread surface, a second rubber layer radially inwardly adjacent to the first rubber layer, and a third rubber layer radially inwardly adjacent to the second rubber layer. The third rubber layer has a lower complex elastic modulus at 30°C than the first and second rubber layers, and the first rubber layer has a higher tan delta at 30°C than the second and third rubber layers. The tread includes land portions separated by a plurality of circumferential grooves extending continuously in the tire circumferential direction. In a tire meridian cross-section containing the tire's rotational axis, at least one of the land portions includes the third rubber layer formed bilaterally asymmetrically with respect to a normal line passing through the tire's widthwise center.

Description

Technical Field

[0001] The present invention relates to tires. Background Art

[0002] Patent document 1 states that the tread portion is formed of a two-layer structure (the so-called cap / base structure) consisting of a base rubber located radially inside the tire and a cap rubber located radially outside the tire. By applying a rubber composition having a small loss tangent tanδ to the base rubber, the handling stability and fuel efficiency of the tire are improved.

[0003]

Prior art literature

[0004] [Patent Literature]

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

[0006] [Problems to be solved by the invention]

[0007] In tires like these, the cap rubber layer has a high loss tangent (tanδ), resulting in excellent wet grip performance when new. However, as the cap rubber layer wears, the circumferential groove volume decreases, making it more susceptible to slippage. This, combined with exposure of the low-heat-generating base rubber layer, can lead to a sharp decline in wet grip performance.

[0008] An object of the present invention is to provide a tire having improved comprehensive performance of fuel efficiency, new wet grip performance, and worn wet grip performance.

[0009]

Methods for solving the problem

[0010] As a result of intensive research, the inventors discovered that the aforementioned problems can be solved by providing three or more rubber layers in the tread portion, setting the complex elastic modulus E* and loss tangent tanδ of the rubber layers to a predetermined relationship, and forming the inner base rubber layer corresponding to the bottom of the land portion asymmetrically in the tire width direction, thereby completing the present invention.

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

[0012] [1] A tire having a tread comprising at least a first rubber layer constituting a tread surface, a second rubber layer adjacent to the radially inner side of the first rubber layer, and a third rubber layer adjacent to the radially inner side of the second rubber layer,

[0013] The third rubber layer has a lower complex elastic modulus at 30°C than the first rubber layer and the second rubber layer, and the first rubber layer has a higher tan δ at 30°C than the second rubber layer and the third rubber layer, the tread includes land portions separated by a plurality of circumferential grooves extending continuously in the tire circumferential direction, and in a tire meridian cross-section including the tire rotation axis, at least one of the land portions includes the third rubber layer formed bilaterally asymmetrically with respect to a normal line passing through the center of the tire in the width direction.

[0014] [2] The tire according to [1], wherein a thickness ratio of the third rubber layer to the total thickness of the first rubber layer, the second rubber layer, and the third rubber layer is 0.30 or greater,

[0015] [3] The tire according to [1] or [2], wherein the complex elastic modulus of the second rubber layer at 30°C is lower than the complex elastic modulus of the first rubber layer at 30°C.

[0016] [4] The tire according to any one of [1] to [3], wherein the second rubber layer has a complex elastic modulus at 30°C of 8 MPa or more,

[0017] [5] The tire according to any one of [1] to [4], wherein the second rubber layer has a tan δ at 30°C of 0.25 or more,

[0018] [6] The tire according to any one of [1] to [5], wherein the glass transition temperature of the first rubber layer is -15°C or higher.

[0019] [7] The tire according to any one of [1] to [6], wherein the glass transition temperature of the second rubber layer is -20°C or higher.

[0020] [8] The tire according to any one of [1] to [7], wherein the first rubber layer has an elongation at break of 500% or more as measured in accordance with JIS K6251.

[0021] [9] The tire according to any one of [1] to [8], wherein the second rubber layer has an elongation at break of 450% or more as measured in accordance with JIS K6251.

[0022]

[10] The tire according to any one of [1] to [9], wherein the modulus of the second rubber layer at 100% stretch is greater than the modulus of the first rubber layer at 100% stretch,

[0023]

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

[10] , wherein the deepest portion of the groove bottom of any one of the circumferential grooves is formed to be located closer to the tire radial direction than the outermost portion of the second rubber layer in the land portion adjacent to the circumferential groove,

[0024]

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

[11] , wherein the land portion has a sipe whose ends do not open to the circumferential groove.

[0025] Effects of the invention

[0026] The present invention can provide a tire with improved comprehensive performance of low fuel consumption, new wet grip performance, and worn wet grip performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027]

Figure 1

[0028]

Figure 2

[0029]

Explanation of symbols

[0030] 1…Circumferential groove

[0031] 2…Lubu

[0032] 3…Tread surface

[0033] 4…Extension of the land department

[0034] 5…Extension line of the deepest part of the groove bottom of the circumferential groove

[0035] 6…first floor

[0036] 7…Second floor

[0037] 8…Third floor

[0038] 9…Extension cable on the outermost side of the second layer

[0039] 10…The outermost extension line of the third layer DETAILED DESCRIPTION

[0040] A tire according to one embodiment of the present invention is a tire having a tread including at least a first rubber layer constituting a tread surface, a second rubber layer adjacent to the radially inner side of the first rubber layer, and a third rubber layer adjacent to the radially inner side of the second rubber layer, wherein the third rubber layer has a lower complex elastic modulus at 30°C than the complex elastic moduli at 30°C of the first rubber layer and the second rubber layer, and the tan δ of the first rubber layer at 30°C is higher than the tan δ of the second rubber layer and the third rubber layer at 30°C, the tread having land portions partitioned by a plurality of circumferential grooves extending continuously in the tire circumferential direction, and at least one of the land portions has the third rubber layer formed bilaterally asymmetrically with respect to a normal line passing through the center in the tire width direction, in a tire meridian cross section containing the tire rotation axis.

[0041] While not being bound by theory, the present invention considers the following mechanism as a mechanism for suppressing the deterioration of wet grip performance after tire wear. Specifically, by minimizing the complex elastic modulus E* of the third rubber layer and forming the third rubber layer asymmetrically in the land portion, a deviation in the hardness distribution of the land portion is created, affecting the ground contact pressure. This improves wet grip performance by creating areas of high ground contact pressure where no water film forms, thereby reducing the difference in wet grip performance between new and worn tires.

[0042] The thickness ratio of the third rubber layer to the total thickness of the first rubber layer, the second rubber layer, and the third rubber layer is preferably 0.30 or greater.

[0043] The complex elastic modulus of the second rubber layer at 30°C is preferably lower than the complex elastic modulus of the first rubber layer at 30°C.

[0044] The second rubber layer preferably has a complex elastic modulus at 30° C. of 8 MPa or more.

[0045] The second rubber layer preferably has a tan δ at 30° C. of 0.25 or more.

[0046] The glass transition temperature of the first rubber layer is preferably -15°C or higher.

[0047] The glass transition temperature of the second rubber layer is preferably -20°C or higher.

[0048] The first rubber layer preferably has an elongation at break measured in accordance with JIS K 6251 of 500% or more.

[0049] The second rubber layer preferably has an elongation at break measured in accordance with JIS K 6251 of 450% or more.

[0050] The modulus of the second rubber layer at 100% stretching is preferably greater than the modulus of the first rubber layer at 100% stretching.

[0051] The deepest portion of the groove bottom of any one of the circumferential grooves is preferably located further inward in the tire radial direction than the outermost portion of the second rubber layer in the land portion adjacent to the circumferential groove, and more preferably is located further inward in the tire radial direction than the outermost portions of the second rubber layer and the third rubber layer in the land portion adjacent to the circumferential groove.

[0052] Preferably, a recessed portion is provided immediately below any one of the circumferential grooves, recessed inward in the tire radial direction relative to the outermost portion of the second rubber layer within the land portion adjacent to the circumferential groove, with a portion of the first rubber layer being formed within the recessed portion of the second rubber layer to a predetermined thickness. Furthermore, more preferably, a recessed portion is provided immediately below any one of the circumferential grooves, recessed inward in the tire radial direction relative to the outermost portions of the second and third rubber layers within the land portion adjacent to the circumferential groove, with a portion of the first and second rubber layers being formed within the recessed portion of the third rubber layer to a predetermined thickness.

[0053] Preferably, the land portion has a sipe with both ends not opening into the circumferential groove.

[0054] A tire according to one embodiment of the present invention is described in detail below. However, the following description is provided for illustrative purposes only and is not intended to limit the technical scope of the present invention to the description. Furthermore, in this specification, when "to" is used to indicate a numerical range, both ends of the numerical range are inclusive.

[0055] Figure 1 An enlarged cross-sectional view showing a portion of a tire tread. Figure 2 In the figure, the up and down direction is the tire radial direction, the left and right direction is the tire width direction, and the direction perpendicular to the paper surface is the tire circumferential direction.

[0056] As shown in the figure, the tread portion of the tire of the present invention includes a first rubber layer 6, a second rubber layer 7, and a third rubber layer 8 (hereinafter simply labeled as "first layer 6," "second layer 7," and "third layer 8"). The outer surface of the first layer 6 constitutes the tread surface 3, the second layer 7 is adjacent to the radial inner side of the first layer 6, and the third layer 8 is adjacent to the radial inner side of the second layer 7. Typically, the first layer 6 corresponds to the crown tread. Typically, the second layer 7 and the third layer 8 correspond to the base tread or under tread. In addition, as long as the purpose of the present invention is achieved, there may be one or more rubber layers between the third layer 8 and the belt layer.

[0057] Figure 1In FIG. 6 , the double arrow t1 represents the thickness of the first layer 6 , the double arrow t2 represents the thickness of the second layer 7 , and the double arrow t3 represents the thickness of the third layer 8 . Figure 1 In the tire width direction, the midpoint of the land portion 2 is represented by the symbol P. The straight line represented by the symbol N is a straight line (normal line) passing through the point P and perpendicular to the tangent plane at the point P. In this specification, Figure 1 In the cross section, the thicknesses t1 , t2 , and t3 are measured along a normal line N drawn from a point P on the tread surface at a position where no groove exists.

[0058] In the present invention, the thickness t1 of the first layer 6 is not particularly limited. From the perspective of wet grip performance, it is preferably 1.0 mm or greater, more preferably 1.5 mm or greater, and even more preferably 2.0 mm or greater. On the other hand, from the perspective of heat generation, the thickness t1 of the first layer 6 is preferably 6.0 mm or less, more preferably 5.5 mm or less, and even more preferably 5.0 mm or less.

[0059] In the present invention, the thickness t2 of the second layer 7 is not particularly limited, but is preferably 1.0 mm or more, more preferably 2.0 mm or more, and further preferably 3.0 mm or more. Furthermore, the thickness t2 of the second layer 7 is preferably 10.0 mm or less, more preferably 9.0 mm or less, and further preferably 8.0 mm or less.

[0060] In the present invention, the thickness t3 of the third layer 8 is not particularly limited, but is preferably 1.0 mm or greater, more preferably 2.0 mm or greater, and further preferably 3.0 mm or greater. Furthermore, the thickness t3 of the third layer 8 is preferably 10.0 mm or less, more preferably 9.0 mm or less, and further preferably 8.0 mm or less.

[0061] From the perspective of the effect of the present invention, the thickness ratio of the third layer to the total thickness of the first layer 6, the second layer 7 and the third layer 8 (t3 / (t1+t2+t3)) is preferably greater than 0.25, more preferably greater than 0.28, further preferably greater than 0.30, further preferably greater than 0.32, and particularly preferably greater than 0.35.

[0062] The thickness of the first layer 6 is preferably thinner than the thickness of the second layer 7 .

[0063] The groove depth H1 of the circumferential groove 1 is calculated based on the distance between the extension line 4 of the land portion 2 and the extension line 5 of the deepest portion of the groove bottom of the circumferential groove 1. Alternatively, for example, when there are multiple circumferential grooves 1, the groove depth H1 may be the distance between the extension line 4 of the land portion 2 and the extension line 5 of the deepest portion of the groove bottom of the circumferential groove 1 having the deepest groove depth among the multiple circumferential grooves 1.

[0064] In the present invention, the circumferential groove 1 having the deepest groove depth among the plurality of circumferential grooves 1 ( Figure 1The deepest portion of the groove bottom of the circumferential groove 1 (left side in the middle) is formed to be located closer to the tire radial direction inner side than the outermost portion of the second layer 7 and the outermost portion of the third layer 8 in the land portion 2 adjacent to the circumferential groove. That is, the circumferential groove 1 ( Figure 1 The extension line 5 of the deepest part of the groove bottom of the circumferential groove 1 on the left side is located closer to the tire radial inside than the outermost extension line 9 of the second layer 7 and the outermost extension line 10 of the third layer 7 in the land portion 2 adjacent to the circumferential groove.

[0065] In the present invention, the circumferential groove 1 having the deepest groove depth among the plurality of circumferential grooves 1 ( Figure 1 Directly below the circumferential groove 1 on the left side (inside the tire radial direction), there is a recessed portion that is recessed toward the inside of the tire radial direction compared to the outermost portions of the second layer 7 and the third layer 8 in the land portion 2 adjacent to the circumferential groove, and a portion of the first layer 6 and the second layer 7 is formed in the above-mentioned recessed portion of the third layer 8 with a specified thickness.

[0066] The tire of the present invention has, in a tire meridian cross-section containing the tire's rotational axis, at least one land portion 2 having a third layer 8 formed bilaterally asymmetrically with respect to a normal line N passing through the tire's widthwise center. Thus, the land portion 2 having the bilaterally asymmetrical third layer 8 can be either located on the vehicle's outer side relative to the tire's equator when installed on the vehicle, or located on the vehicle's inner side relative to the tire's equator when installed on the vehicle. Furthermore, the land portion 2 having the bilaterally asymmetrical third layer 8 can be a land portion sandwiched between a plurality of circumferential grooves 1 or a shoulder land portion sandwiched between a circumferential groove 1 and a tread contact edge, preferably a land portion sandwiched between a plurality of circumferential grooves 1.

[0067] Unless otherwise specified, the dimensions and angles of various tire components are measured with the tire mounted on a conventional rim and filled with air to a conventional internal pressure. No load is applied to the tire during measurement. Furthermore, the term "conventional rim" as used herein refers to a standard system encompassing tires based on standards. These standards are defined for each tire, such as the standard rim for JATMA, the "Design Rim" for TRA, and the "Measuring Rim" for ETRTO. "Conventional internal pressure" as used herein refers to the air pressure defined for each tire, such as the maximum air pressure for JATMA, the maximum value listed in the "TIRE LOAD LIMITS AT VARIOUS COLDINFLATION PRESSURES" table for TRA, and the "INFLATION PRESSURE" table for ETRTO.

[0068] In the present invention, "30°C E*" refers to the complex elastic modulus E* under the conditions of a temperature of 30°C, an initial strain of 10%, a dynamic strain of 1%, and a frequency of 10 Hz. From the perspective of handling stability, the 30°C E* of the first layer 6 is preferably 9 MPa or higher, more preferably 10 MPa or higher, even more preferably 11 MPa or higher, and particularly preferably 12 MPa or higher. From the perspective of handling stability, the 30°C E* of the second layer 7 is preferably 7 MPa or higher, more preferably 8 MPa or higher, and even more preferably 9 MPa or higher. The 30°C E* of the third layer 8 is preferably 5 MPa or higher, more preferably 6 MPa or higher, and even more preferably 7 MPa or higher. On the other hand, from the perspective of wet grip performance, the 0°C E* of the first, second, and third layers 6, 7, and 8 is preferably 25 MPa or lower, more preferably 20 MPa or lower, and even more preferably 18 MPa or lower. In the present invention, the 30°C E* of the third layer 8 is also lower than the 30°C E* of the first and second layers 6, 7. Furthermore, the 30°E* of the second layer 7 is preferably lower than the 30°E* of the first layer 6. The 30°E* of each rubber layer can be appropriately adjusted according to the types and mixing amounts of the rubber components, fillers, softeners, etc.

[0069] In the present invention, "tan δ at 30°C" refers to the loss tangent tan δ under the conditions of a temperature of 30°C, an initial strain of 10%, a dynamic strain of 1%, and a frequency of 10 Hz. From the perspective of wet grip performance, the tan δ at 30°C of the first layer 6 is preferably 0.30 or greater, more preferably 0.35 or greater, and even more preferably 0.40 or greater. The tan δ at 30°C of the second layer 7 is preferably 0.20 or greater, more preferably 0.25 or greater, and even more preferably 0.30 or greater. The tan δ at 30°C of the third layer 8 is preferably 0.10 or greater, more preferably 0.15 or greater, and even more preferably 0.20 or greater. On the other hand, from the perspective of fuel efficiency, the tan δ at 30°C of the rubber composition constituting the first, second, and third layers 6, 7, and 8 is preferably 0.65 or less, more preferably 0.60 or less, and even more preferably 0.55 or less. In the present invention, the tan δ at 30°C of the first layer 6 is also higher than the tan δ at 30°C of the second and third layers 7 and 8. Furthermore, the tanδ at 30°C of the second layer 7 is preferably higher than that of the third layer 8. The tanδ at 30°C of each rubber layer can be appropriately adjusted according to the types and blending amounts of the rubber components, fillers, softeners, etc.

[0070] The elongation at break (EB) of the present invention refers to the elongation at break (elongation at break) measured in accordance with JIS K 6251 under the conditions of a 23°C atmosphere and a tensile speed of 3.3 mm / second. From the perspective of maintaining surface smoothness, the EB of the first layer 6 is preferably 500% or more, more preferably 510% or more, and even more preferably 520% ​​or more. Furthermore, the EB of the second layer 7 is preferably 450% or more, more preferably 460% or more, and even more preferably 470% or more. The upper limit of the EB of the rubber composition constituting the first layer 6, the second layer 7, and the third layer 8 is not particularly limited.

[0071] The modulus at 100% stretching in the present invention refers to the tensile stress when stretched 100% in the grain direction, measured in accordance with JIS K 6251 under the conditions of an atmosphere at 23°C and a stretching speed of 3.3 mm / sec. The modulus at 100% stretching of the first layer 6 is preferably 1.0 MPa or more, more preferably 1.1 MPa or more, further preferably 1.2 MPa or more, and particularly preferably 1.3 MPa or more. Furthermore, the modulus at 100% stretching of the second layer 7 is preferably 1.0 MPa or more, more preferably 1.1 MPa or more, further preferably 1.3 MPa or more, and particularly preferably 1.5 MPa or more. The upper limit of the modulus at 100% stretching of the first layer 6, the second layer 7, and the third layer 8 is not particularly limited. In the present invention, the modulus at 100% stretching of the second layer 7 is also preferably greater than the modulus at 100% stretching of the first layer 6. The difference between the modulus at 100% stretch of the second layer 7 and the modulus at 100% stretch of the first layer 6 is preferably 0.1 MPa or more, more preferably 0.2 MPa or more, and even more preferably 0.3 MPa or more. In this specification, "grain direction" refers to the rolling direction when forming a rubber sheet by extrusion or shearing.

[0072] The EB and 100% elongation modulus of each rubber layer can be appropriately adjusted according to the types and compounding amounts of the rubber component, filler, softener, etc.

[0073] The glass transition temperature (Tg) of the present invention refers to the tan δ peak temperature measured by the following method. Specifically, a rubber test piece (e.g., 20 mm in length, 4 mm in width, and 1 mm in thickness) is cut from the rubber layer of the tread portion of each test tire, with the longer side in the tire circumferential direction. Using a dynamic viscoelasticity evaluation device (e.g., the Eplexor series manufactured by GABO), a tan δ temperature profile is measured under the conditions of an initial strain of 10%, a dynamic strain of 1%, and a frequency of 10 Hz. The temperature corresponding to the maximum tan δ value in the obtained temperature profile (tan δ peak temperature) is defined as the glass transition temperature (Tg) of the present invention. From the perspective of wet grip performance, the Tg of the rubber composition constituting the first layer 6 is preferably -15°C or higher, more preferably -12°C or higher, and even more preferably -10°C or higher. Furthermore, from the perspective of wet grip performance, the Tg of the rubber composition constituting the second layer 7 is preferably -20°C or higher, more preferably -15°C or higher, and even more preferably -12°C or higher. The upper limit of the Tg of the rubber composition constituting the first layer 6, the second layer 7, and the third layer 8 is not particularly limited, but is preferably 20°C or lower, more preferably 15°C or lower, and even more preferably 10°C or lower. The Tg of each rubber layer can be appropriately adjusted depending on the type and compounding amount of the rubber component, etc.

[0074] [Rubber composition]

[0075] The tire of the present invention can more effectively suppress the reduction in wet grip performance after tire wear by combining the aforementioned tire structure, especially the shape of the tread, and the aforementioned physical properties of the rubber composition constituting each tread layer.

[0076] <Rubber Components>

[0077] The rubber composition of the present invention preferably contains, as a rubber component, at least one selected from the group consisting of isoprene-based rubber, styrene-butadiene rubber (SBR), and butadiene rubber (BR). The rubber component constituting the first layer 6 and the second layer 7 preferably contains SBR, more preferably contains SBR and BR, and may be a rubber component consisting solely of SBR and BR. The rubber component constituting the third layer 8 preferably contains isoprene-based rubber, more preferably contains isoprene-based rubber and BR, and may be a rubber component consisting solely of isoprene-based rubber and BR.

[0078] (Isoprene rubber)

[0079] Isoprene-based rubbers that can be used include rubbers commonly used in the tire industry, such as isoprene rubber (IR) and natural rubber. Natural rubbers include unmodified natural rubber (NR) and modified natural rubbers such as epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), deproteinized natural rubber (DPNR), high-purity natural rubber, and grafted natural rubber. These isoprene-based rubbers can be used alone or in combination of two or more.

[0080] The NR is not particularly limited, and NR commonly used in the tire industry can be used, and examples thereof include SIR20, RSS#3, and TSR20.

[0081] In the rubber component constituting the first layer 6 and the second layer 7, from the perspective of wet grip performance, the content of isoprene-based rubber (preferably natural rubber, more preferably unmodified natural rubber (NR)) 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, relative to 100% by mass of the rubber component when the isoprene-based rubber is included. Furthermore, when the isoprene-based rubber is included, the lower limit of the content is not particularly limited and 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.

[0082] In the rubber component constituting the third layer 8, when the isoprene-based rubber (preferably natural rubber, more preferably unmodified natural rubber (NR)) is included, the content of the isoprene-based rubber is preferably 20% by mass or greater, more preferably 30% by mass or greater, and even more preferably 40% by mass or greater, based on 100% by mass of the rubber component. The upper limit of the content of the isoprene-based rubber in the rubber component is not particularly limited and may be 100% by mass.

[0083] (SBR)

[0084] Examples of SBR include solution-polymerized SBR (S-SBR), emulsion-polymerized SBR (E-SBR), and modified SBRs thereof (modified S-SBR, modified E-SBR).

[0085] As modified SBR, SBR with modified ends and / or main chains, modified SBR coupled with tin, silicon compounds, etc. (condensates, SBR with branched structures, etc.) etc. can be listed. Among them, S-SBR and modified SBR are preferred. Furthermore, hydrides of these SBRs (hydrogenated SBR) etc. can also be used. These SBRs can be used alone or in combination of two or more.

[0086] Examples of the S-SBR used in the present invention include those manufactured and sold by JSR Corporation, Sumitomo Chemical Corporation, Ube Industries, Ltd., Asahi Kasei Corporation, and ZS Elastomers Corporation.

[0087] From the viewpoint of wet grip performance and wear resistance, the styrene content of SBR is preferably 10% by mass or more, more preferably 15% by mass or more, and further preferably 20% by mass or more. In addition, from the viewpoint of temperature dependence of grip performance and blow mold resistance, it is preferably 60% by mass or less, more preferably 55% by mass or less, and further preferably 50% by mass or less. 1 The styrene content of SBR was calculated by H-NMR measurement.

[0088] From the viewpoint of ensuring reactivity with silica, wet grip performance, rubber strength and wear resistance, the vinyl content of SBR is preferably more than 10 mol %, more preferably more than 15 mol %, further preferably more than 20 mol %. In addition, from the viewpoint of preventing the increase of temperature dependence, elongation at break and wear resistance, the vinyl content of SBR is preferably less than 70 mol %, more preferably less than 65 mol %, further preferably less than 60 mol %. In addition, in this specification, the vinyl content (1,2-bonded butadiene unit amount) of SBR is measured by infrared absorption spectroscopy.

[0089] 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 further preferably 300,000 or more. In addition, from the perspective of crosslinking uniformity, the weight average molecular weight is preferably 2 million or less, more preferably 1.8 million or less, and further preferably 1.5 million or less. In addition, in this specification, the weight average molecular weight of SBR can be obtained by converting to standard polystyrene based on the measured value using gel permeation chromatography (GPC) (e.g., GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, chromatographic column: TSK GEL SUPERMALTIPORE HZ-M manufactured by Tosoh Corporation).

[0090] In the rubber component constituting the first layer 6 and the second layer 7, from the viewpoint of wet grip performance, when SBR is contained, its content 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 the rubber component 100% by mass. 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, in the rubber component constituting the third layer 8, the content of SBR in the rubber component 100% by mass is not particularly limited.

[0091] (BR)

[0092] BR is not particularly limited, and examples thereof include BR with a cis content of less than 50% by mass (low-cis BR), BR with a cis content of 90% or more by mass (high-cis BR), rare earth butadiene rubber synthesized using a rare earth element catalyst (rare earth BR), BR containing syndiotactic polybutadiene crystals (SPB-containing BR), and modified BR (high-cis modified BR, low-cis modified BR), commonly used in the tire industry. Examples of modified BR include BR modified with the same functional groups as described above for SBR. These BRs may be used alone or in combination of two or more.

[0093] High-cis BR can be used, for example, from commercially available suppliers such as Japan Zeon Co., Ltd., Ube Industries, Ltd., and JSR Corporation. The inclusion of high-cis BR improves low-temperature properties and wear resistance. The cis content is preferably 95% by mass or greater, more preferably 96% by mass or greater, even more preferably 97% by mass or greater, and particularly preferably 98% by mass or greater. In this specification, the cis content (amount of cis-1,4-linked butadiene units) is a value calculated based on infrared absorption spectroscopy.

[0094] Rare earth BR is synthesized using a rare earth element 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. The cis content is preferably 95 mass% or more, more preferably 96 mass% or more, even more preferably 97 mass% or more, and particularly preferably 98 mass% or more. Rare earth BR commercially available, for example, from LANXESS Co., Ltd. can be used.

[0095] Examples of SPB-containing BR include BRs in which 1,2-syndiotactic polybutadiene crystals are dispersed not simply as crystals but chemically bonded to BR. Such SPB-containing BRs can be commercially available from Ube Industries, Ltd. or the like.

[0096] As the modified BR, a modified butadiene rubber (modified BR) in which the terminal and / or main chain is modified with a functional group containing at least one element selected from the group consisting of silicon, nitrogen, and oxygen can be suitably used.

[0097] Other modified BRs include those obtained by polymerizing 1,3-butadiene with a lithium initiator and then adding a tin compound, where the ends of the modified BR molecules are further bonded via tin-carbon bonds (tin-modified BR). Furthermore, the modified BR may be either unhydrogenated BR or hydrogenated BR.

[0098] The above-mentioned BRs may be used alone or in combination of two or more.

[0099] From the perspective of wear resistance, the weight-average molecular weight (Mw) of BR is preferably 300,000 or greater, more preferably 350,000 or greater, and even more preferably 400,000 or greater. Furthermore, from the perspective of crosslinking uniformity, it is preferably 2,000,000 or less, and more preferably 1,000,000 or less. The Mw can be determined by converting the measured value using gel permeation chromatography (GPC) (e.g., GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMALTIPORE HZ-M manufactured by Tosoh Corporation) to standard polystyrene.

[0100] In the rubber component constituting the first layer 6 and the second layer 7, from the perspective of wet grip performance, when BR is included, 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, out of 100% by mass of the rubber component. Furthermore, the lower limit of the BR content when included is not particularly limited and 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.

[0101] When BR is included in the rubber component constituting the third layer 8, its content is preferably 80% by mass or less, more preferably 70% by mass or less, further preferably 65% ​​by mass or less, and particularly preferably 60% by mass or less, based on 100% by mass of the rubber component. Furthermore, the lower limit of the BR content when included is not particularly limited and 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.

[0102] (Other rubber components)

[0103] As the rubber component of the present invention, the rubber component other than the above-mentioned isoprene-based rubber, SBR and BR can also be contained. As other rubber components, the rubber component that can be crosslinked 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, chlorinated polyethylene rubber, fluororubber (FKM), acrylate rubber (ACM), epichlorohydrin rubber etc. can be enumerated. These other rubber components can be used alone or in combination with two or more.

[0104] <Padding>

[0105] The rubber composition of the present invention can preferably contain fillers such as carbon black and / or silica. The rubber composition constituting the first layer 6 and the second layer 7 preferably contains silica as a filler, and more preferably contains carbon black and silica. The rubber composition constituting the third layer 8 preferably contains carbon black as a filler.

[0106] (Carbon Black)

[0107] The rubber composition of the present invention preferably contains carbon black. The inclusion of carbon black can improve weather resistance, antistatic properties, and rubber strength. Carbon black commonly used in the tire industry can be appropriately used, including, for example, GPF, FEF, HAF, ISAF, and SAF. These carbon blacks may be used alone or in combination of two or more.

[0108] From the perspective of reinforcement, the nitrogen adsorption specific surface area (N2SA) of carbon black is preferably 10 m 2 / g or more, more preferably 20m 2 / g or more. In addition, from the perspective of low fuel consumption performance and processability, 200m 2 / g or less, more preferably 150m 2 / g or less, more preferably 100m 2 / g or less, more preferably 80m 2 / g or less, particularly preferably 50m 2 The N2SA of carbon black is a value measured in accordance with JIS K 6217-2 "Basic properties of carbon black for rubber use - Part 2: Determination of specific surface area - Nitrogen adsorption method - Single-point method".

[0109] When carbon black is contained, from the viewpoints of wear resistance and wet grip performance, the content is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more per 100 parts by mass of the rubber component. Furthermore, from the viewpoint of fuel efficiency, the content is preferably 50 parts by mass or less, more preferably 35 parts by mass or less, even more preferably 20 parts by mass or less, and particularly preferably 10 parts by mass or less.

[0110] (Silicon dioxide)

[0111] Silica is not particularly limited, and silica commonly used in the tire industry, such as dry-processed silica (anhydrous silica) and wet-processed silica (hydrous silica), can be used. Hydrous silica produced by a wet process is preferred due to its high silanol group content. These silicas may be used alone or in combination of two or more.

[0112] From the perspective of low fuel consumption and wear resistance, the nitrogen adsorption specific surface area (N2SA) of silica is preferably 140 m2 / g or more, more preferably 170m 2 / g or more, more preferably 200m 2 / g or more. In addition, from the perspective of low fuel consumption performance and processability, 350 m 2 / g or less, more preferably 300m 2 / g or less, more preferably 250m 2 In addition, the N2SA of silica in this specification is a value measured according to the BET method based on ASTM D3037-93.

[0113] When silica is present, from the perspective of wet grip performance, its content is preferably 20 parts by mass or greater, more preferably 40 parts by mass or greater, even more preferably 50 parts by mass or greater, and particularly preferably 60 parts by mass or greater, relative to 100 parts by mass of the rubber component. Furthermore, from the perspective of wear resistance, its content is preferably 130 parts by mass or less, more preferably 120 parts by mass or less, and even more preferably 110 parts by mass or less.

[0114] From the perspective of wear resistance, the total content of silica and carbon black per 100 parts by mass of the rubber component is preferably 40 parts by mass or greater, more preferably 50 parts by mass or greater, and even more preferably 60 parts by mass or greater. Furthermore, from the perspective of fuel economy and elongation at break, the total content 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.

[0115] In the rubber composition constituting the first and second layers 6 and 7, the silica content is preferably greater than the carbon black content per 100 parts by mass of the rubber component, from the perspective of achieving a balance between fuel efficiency, wet grip performance, and wear resistance. The ratio of silica to the total content of silica and carbon black in the first and second layers 6 and 7 is preferably 60% by mass or greater, more preferably 70% by mass or greater, even more preferably 80% by mass or greater, and particularly preferably 85% by mass or greater. The ratio of silica to carbon black in the rubber composition constituting the third layer 8 is not particularly limited.

[0116] (Other fillers)

[0117] As fillers other than silica and carbon black, fillers commonly used in the tire industry, such as aluminum hydroxide, calcium carbonate, alumina, clay, and talc, may be mixed.

[0118] (Silane coupling agent)

[0119] Silica is preferably used in combination with a silane coupling agent. As the silane coupling agent, there is no particular limitation. In the tire industry, any silane coupling agent that has been used in combination with silica in the past can be used. Examples 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 vinyltriethoxysilane and vinyltrimethoxysilane; amino-based silane coupling agents such as 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, and 3-(2-aminoethyl)aminopropyltriethoxysilane; glycidoxy-based silane coupling agents such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro-based silane coupling agents such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; chlorine-based silane coupling agents such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane, etc. 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 in combination of two or more kinds.

[0120] The mercapto-based silane coupling agent preferably includes 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).

[0121]

Chemical Formula 1

[0122]

[0123] (In the formula, R 101 , R 102 and R 103 each independently represent an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, or a group represented by -O-(R 111 -O)z-R 112 (z R 111 each independently represent a divalent hydrocarbon group having 1 to 30 carbon atoms; R 112 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 from 1 to 30).); R 104 represents an alkylene group having 1 to 6 carbon atoms.)

[0124]

Chemical Formula 2

[0125]

[0126]

Chemical Formula 3

[0127]

[0128] (wherein, x represents an integer greater than 0; y represents an integer greater than 1; R 201 represents 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 with a hydrogen atom, a halogen atom, a hydroxyl group, or a carboxyl group; R 202 represents an alkylene group having 1 to 30 carbon atoms, an alkenylene group having 2 to 30 carbon atoms, or an alkynylene group having 2 to 30 carbon atoms; wherein R 201 and R 202 Can form a ring structure.)

[0129] Examples of the compound represented by formula (1) include 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, and compounds represented by formula (4) (Si363 manufactured by Evonik Degussa). Compounds represented by formula (4) may be suitably used. These compounds may be used alone or in combination of two or more.

[0130]

Chemistry 4

[0131]

[0132] Examples of the compound comprising the bonding unit A represented by formula (2) and the bonding unit B represented by formula (3) include compounds manufactured and sold by Momentive Corp. These may be used alone or in combination of two or more.

[0133] When a silane coupling agent is present, the total amount thereof is preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, further preferably 2.0 parts by mass or more, and particularly preferably 4.0 parts by mass or more, relative to 100 parts by mass of the rubber component, from the viewpoint of improving the dispersibility of silica. Furthermore, from the viewpoint of preventing a decrease in wear resistance, the total amount 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.

[0134] The content of the silane coupling agent relative to 100 parts by mass of silica (the total amount of all silane coupling agents when multiple silane coupling agents are used in combination) 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 improving 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.

[0135] As fillers, in addition to carbon black and silica, other fillers can be further used. Such fillers are not particularly limited, and any of the fillers commonly used in this field, such as aluminum hydroxide, aluminum oxide (aluminum trioxide), calcium carbonate, magnesium sulfate, talc, and clay, can be used. These fillers can be used alone or in combination of two or more.

[0136] <Plasticizer>

[0137] The rubber composition of the present invention preferably contains a plasticizer. Examples of the plasticizer include resin components, oils, liquid rubbers, and ester plasticizers.

[0138] The resin component is not particularly limited, and examples thereof include petroleum resins, terpene resins, rosin resins, phenolic resins, etc. commonly used in the tire industry. These resin components may be used alone or in combination of two or more.

[0139] As used herein, "C5 petroleum resin" refers to a resin obtained by polymerizing a C5 fraction. Examples of C5 fractions include petroleum fractions having 4 to 5 carbon atoms, such as cyclopentadiene, pentene, pentadiene, and isoprene. Dicyclopentadiene resin (DCPD resin) is a suitable C5 petroleum resin.

[0140] In this specification, "aromatic petroleum resin" refers to a resin obtained by polymerizing a C9 fraction, which may also be hydrogenated or modified. Examples of the C9 fraction include petroleum fractions having 8 to 10 carbon atoms, such as vinyltoluene, alkylstyrene, indene, and methylindene. Specific examples of aromatic petroleum resins include coumarone indene resin, coumarone resin, indene resin, and aromatic vinyl resins. As aromatic vinyl resins, α-methylstyrene or a homopolymer of styrene or a copolymer of α-methylstyrene and styrene is preferred for reasons of economy, ease of processing, and excellent heat generation, and a copolymer of α-methylstyrene and styrene is more preferred. As aromatic vinyl resins, commercially available products such as Kraton and Eastman Chemical can be used.

[0141] In this specification, "C5C9-based petroleum resin" refers to a resin obtained by copolymerizing the aforementioned C5 fraction and the aforementioned C9 fraction, which may be hydrogenated or modified. Examples of the C5 and C9 fractions include the aforementioned petroleum fractions. Commercially available C5C9-based petroleum resins, such as those from Tosoh Corporation and Luhua, can be used.

[0142] Examples of terpene resins include polyterpene resins formed from at least one terpene compound selected from α-pinene, β-pinene, limonene, and dipentene; aromatic modified terpene resins derived from these terpene compounds and aromatic compounds; terpene phenol resins derived from terpene compounds and phenolic compounds; and hydrogenated terpene resins (hydrogenated terpene resins). Examples of aromatic compounds used as raw materials for aromatic modified terpene resins include styrene, α-methylstyrene, vinyltoluene, and divinyltoluene. Examples of phenolic compounds used as raw materials for terpene phenolic resins include phenol, bisphenol A, cresol, and xylenol.

[0143] The rosin-based resin is not particularly limited, and examples thereof include natural resin rosin and rosin-modified resins obtained by modifying the natural resin rosin by hydrogenation, disproportionation, dimerization, esterification, or the like.

[0144] The phenolic resin is not particularly limited, and examples thereof include phenol formaldehyde resin, alkylphenol formaldehyde resin, alkylphenol acetylene resin, and oil-modified phenol formaldehyde resin.

[0145] 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. Furthermore, from the perspective of processability and improved dispersibility of the rubber component and filler, it is preferably 150°C or lower, more preferably 140°C or lower, and even more preferably 130°C or lower. In this specification, the softening point specified in JIS K 6220-1:2001 is measured using a ring and ball softening point measuring apparatus, and the softening point is defined as the temperature at which the ball descends.

[0146] When a resin component is included, from the perspective of wet grip performance, its content is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more per 100 parts by mass of the rubber component. Furthermore, from the perspective of suppressing heat buildup, its content 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.

[0147] Examples of oils include process oils, vegetable oils, and animal oils. Examples of these process oils include paraffinic process oils, naphthenic process oils, and aromatic process oils. Furthermore, for environmental reasons, process oils low in polycyclic aromatic compounds (PCA) can also be used. Examples of these low-PCA process oils include mild extraction solvates (MES), treated distillate aroma extracts (TDAE), and heavy naphthenic oils.

[0148] When oil is present, from the perspective of processability, the amount 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, per 100 parts by mass of the rubber component. Furthermore, from the perspective of wear resistance, the amount is preferably 120 parts by mass or less, more preferably 100 parts by mass or less, and even more preferably 90 parts by mass or less. In this specification, the oil content also includes the amount of oil contained in the oil-extended rubber.

[0149] The liquid rubber is not particularly limited as long as it is a polymer that is liquid 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), and liquid farnesene rubber. These liquid rubbers may be used alone or in combination of two or more.

[0150] When liquid rubber is included, its content is preferably 1 part by mass or more, more preferably 2 parts by mass or more, further preferably 3 parts by mass or more, and particularly preferably 5 parts by mass or more, relative to 100 parts by mass of the rubber component. Furthermore, the liquid rubber content is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 20 parts by mass or less.

[0151] Examples of the ester plasticizer include dibutyl adipate (DBA), diisobutyl adipate (DIBA), dioctyl adipate (DOA), di-2-ethylhexyl azelate (DOZ), dibutyl sebacate (DBS), diisononyl adipate (DINA), diethyl phthalate (DEP), dioctyl phthalate (DOP), diundecyl phthalate (DUP), dibutyl phthalate (DBP), dioctyl sebacate (DOS), tributyl phosphate (TBP), trioctyl phosphate (TOP), triethyl phosphate (TEP), trimethyl phosphate (TMP), thymidine triphosphate (TTP), tricresyl phosphate (TCP), and trixylyl phosphate (TXP). These ester plasticizers may be used alone or in combination of two or more.

[0152] From the perspective of wet grip performance, the plasticizer content (the total amount when multiple plasticizers are used) is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 15 parts by mass or more, relative to 100 parts by mass of the rubber component. Furthermore, from the perspective of processability, the plasticizer content is preferably 120 parts by mass or less, more preferably 100 parts by mass or less, even more preferably 90 parts by mass or less, and particularly preferably 80 parts by mass or less.

[0153] <Other mixtures>

[0154] The rubber composition of the present invention may appropriately contain, in addition to the above-mentioned components, compounding agents commonly used in the tire industry, such as wax, processing aids, stearic acid, zinc oxide, antioxidants, vulcanizing agents, and vulcanization accelerators.

[0155] When wax is present, from the perspective of weather resistance of the rubber, the content is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, per 100 parts by mass of the rubber component. Furthermore, from the perspective of preventing tire whitening due to blooming, the content is preferably 10 parts by mass or less, more preferably 5 parts by mass or less.

[0156] Examples of processing aids include fatty acid metal salts, fatty acid amides, amide esters, silica surfactants, fatty acid esters, mixtures of fatty acid metal salts and amide esters, and mixtures of fatty acid metal salts and fatty acid amides. These processing aids may be used alone or in combination of two or more. Commercially available products from, for example, Schill & Seilacher and Performance Additives may be used.

[0157] When a processing aid is present, its content is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, per 100 parts by mass of the rubber component, from the viewpoint of achieving an effect of improving processability. Furthermore, from the viewpoint of abrasion resistance and breaking strength, its content is preferably 10 parts by mass or less, more preferably 8 parts by mass or less.

[0158] As antioxidant, there is no particular limitation, and examples thereof include amine-based, quinoline-based, quinone-based, phenol-based, imidazole-based compounds, metal carbamate-based antioxidants, and preferably 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 and other phenylenediamine-based antioxidants, and quinoline-based antioxidants such as 2,2,4-trimethyl-1,2-dihydroquinoline polymers and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline. These antioxidants may be used alone or in combination of two or more.

[0159] When an antioxidant is included, from the perspective of ozone cracking resistance of the rubber, its content is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, relative to 100 parts by mass of the rubber component. Furthermore, from the perspective of wear resistance and wet grip performance, its content is preferably 10 parts by mass or less, more preferably 5 parts by mass or less.

[0160] When stearic acid is contained, from the viewpoint of processability, its content is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, relative to 100 parts by mass of the rubber component. In addition, from the viewpoint of vulcanization speed, it is preferably 10 parts by mass or less, more preferably 5 parts by mass or less.

[0161] When zinc oxide is contained, its content is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, per 100 parts by mass of the rubber component from the viewpoint of processability, and preferably 10 parts by mass or less, more preferably 5 parts by mass or less from the viewpoint of wear resistance.

[0162] Sulfur is preferably used as the vulcanizing agent, 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.

[0163] When sulfur is contained as a vulcanizing agent, from the perspective of ensuring a sufficient vulcanization reaction, the content 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 per 100 parts by mass of the rubber component. Furthermore, from the perspective of preventing degradation, 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. Furthermore, when oil-containing sulfur is used as the vulcanizing agent, the content of the vulcanizing agent is the total content of pure sulfur components contained in the oil-containing sulfur.

[0164] Examples of vulcanizing agents other than sulfur include alkylphenol / sulfur chloride condensates, sodium 1,6-hexamethylenedithiosulfate / dihydrate, and 1,6-bis(N,N'-dibenzylthiocarbamoyldisulfide)hexane. Commercially available products from companies such as Taoka Chemical Industry Co., Ltd., Lanxess Co., Ltd., and Flexsys Co., Ltd. can be used for these vulcanizing agents other than sulfur.

[0165] Examples of the vulcanization accelerator include sulfenamide-based, thiazole-based, thiuram-based, thiourea-based, guanidine-based, dithiocarbamic acid-based, aldehyde-amine-based or aldehyde-ammonium-based, imidazoline-based, and xanthate-based vulcanization accelerators. These vulcanization accelerators may be used alone or in combination of two or more. Preferably, one or more vulcanization accelerators are selected from the group consisting of sulfenamide-based, thiazole-based, and guanidine-based vulcanization accelerators, and more preferably, sulfenamide-based vulcanization accelerators.

[0166] Examples of sulfenamide-based vulcanization accelerators include N-tert-butyl-2-benzothiazolesulfenamide (TBBS), N-cyclohexyl-2-benzothiazolesulfenamide (CBS), and N,N-dicyclohexyl-2-benzothiazolesulfenamide (DCBS). Among them, N-tert-butyl-2-benzothiazolesulfenamide (TBBS) is preferred.

[0167] Examples of the guanidine-based vulcanization accelerator include 1,3-diphenylguanidine (DPG), 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, di-o-tolylguanidine salt of diphenol borate, 1,3-di-o-isopropylphenylguanidine, 1,3-di-o-biphenylguanidine, and 1,3-di-o-isopropylphenyl-2-propionylguanidine. Among them, 1,3-diphenylguanidine (DPG) is preferred.

[0168] Examples of the thiazole vulcanization accelerator include 2-mercaptobenzothiazole, cyclohexylamine salt of 2-mercaptobenzothiazole, and di-2-benzothiazole disulfide. Among them, 2-mercaptobenzothiazole is preferred.

[0169] When a vulcanization accelerator is present, its content is preferably 1 part by mass or more, more preferably 2 parts by mass or more, relative to 100 parts by mass of the rubber component. Furthermore, the content of the vulcanization accelerator 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, relative to 100 parts by mass of the rubber component. By adjusting the content of the vulcanization accelerator within the above range, it tends to be possible to ensure sufficient breaking strength and elongation.

[0170] The rubber composition of the present invention can be produced by a known method, for example, by kneading the above-mentioned components using a rubber kneading apparatus such as an open roll mill or a closed mixer (Banbury mixer, kneader, etc.).

[0171] The kneading process includes, for example, a basic kneading process for kneading the compounding agents and additives other than the vulcanizing agent and the vulcanization accelerator, and a final kneading (F kneading) process for adding the vulcanizing agent and the vulcanization accelerator to the kneaded product obtained in the basic kneading process and kneading. Furthermore, the basic kneading process can be divided into multiple processes as desired.

[0172] The kneading conditions are not particularly limited, and examples thereof include kneading at a discharge temperature of 150 to 170°C for 3 to 10 minutes in the basic kneading step and kneading at 70 to 110°C for 1 to 5 minutes in the final kneading step. The vulcanization conditions are not particularly limited, and examples thereof include vulcanization at 150 to 200°C for 10 to 30 minutes.

[0173] [tire]

[0174] The tire of the present invention comprises a tread comprising a first layer 6, a second layer 7, and a third layer 8, and can be used as either a pneumatic or non-pneumatic tire. Furthermore, the tire is suitable for use as a racing tire, a passenger car tire, a large passenger car tire, a large SUV tire, or a motorcycle tire, and can also be used as a summer tire, a winter tire, or a studless tire.

[0175] A tire having a tread including the first layer 6, the second layer 7, and the third layer 8 can be manufactured using the above-mentioned rubber composition by conventional methods. Specifically, an unvulcanized rubber composition, to which the above-mentioned components are mixed as needed for the rubber component, is extruded into the shapes of the first layer 6, the second layer 7, and the third layer 8 using an extruder equipped with a die of a predetermined shape. The composition is then laminated together with other tire components in a tire molding machine and molded using conventional methods to form an unvulcanized tire. The unvulcanized tire is then heated and pressurized in the vulcanizer to manufacture the tire.

[0176] [Example]

[0177] The present invention is described based on the examples, but the present invention is not limited to the examples.

[0178] Hereinafter, various chemical reagents used in Examples and Comparative Examples will be described.

[0179] NR:TSR20

[0180] SBR: Tufdene 4850 manufactured by Asahi Kasei Corporation (unmodified S-SBR, styrene content: 40% by mass, vinyl content: 46 mol%, Mw: 350,000, containing 50 parts by mass of oil per 100 parts by mass of rubber solids)

[0181] BR: UBEPOL BR (registered trademark) 150B manufactured by Ube Industries, Ltd. (vinyl content: 1.5 mol%, cis content: 97% by mass, Mw: 440,000)

[0182] Carbon black: SHOBLACK N330 (N2SA: 75m 2 / g)

[0183] Silicon dioxide: ULTRASIL VN3 (N2SA: 175m 2 / g)

[0184] Silane coupling agent: NXT-Z45 (mercapto-based silane coupling agent) manufactured by Momentive

[0185] Oil: VivaTec500 (TDAE oil) manufactured by H&R Co., Ltd.

[0186] Antioxidant: Sumitomo Chemical Co., Ltd.'s ANTIGENE 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine)

[0187] Wax: Sonnoc N manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0188] Stearic acid: NOF Corporation's beaded stearic acid "Tsubaki"

[0189] Zinc oxide: Zinc oxide No. 2 manufactured by Mitsui Mining & Smelting Co., Ltd.

[0190] Sulfur: Powdered sulfur manufactured by Karuizawa Sulfur Co., Ltd.

[0191] Vulcanization accelerator: NOCCELER CZ (N-cyclohexyl-2-benzothiazolesulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0192] (Examples and Comparative Examples)

[0193] According to the mixing formula shown in Table 1, the chemical reagents other than sulfur and the vulcanization accelerator were kneaded in a 1.7L sealed Banbury mixer for 1 to 10 minutes until the discharge temperature reached 150-160°C to obtain a kneaded product. Subsequently, sulfur and the vulcanization accelerator were added to the kneaded product using a biaxial open mill and kneaded for 4 minutes until the temperature reached 105°C to obtain an unvulcanized rubber composition. The resulting unvulcanized rubber composition was molded into the shapes of the first, second, and third layers of the tread and laminated together with other tire components to produce unvulcanized tires. These tires were vulcanized at 170°C to obtain the test tires listed in Table 3 (size: 195 / 65R15 91V, rim: 15×6.0J, internal pressure: 240 kPa).

[0194] In addition, as tires of Examples 1 to 9 and Comparative Examples 1 and 5, Figure 1 As shown, the tread comprises a first rubber layer constituting the tread surface, a second rubber layer adjacent to the radially inner side of the first rubber layer, and a third rubber layer adjacent to the radially inner side of the second rubber layer. In a tire meridian cross section containing the tire rotation axis, the third rubber layer is formed asymmetrically with respect to a normal line of the center in the tire width direction of the land portion sandwiched by the circumferential grooves. In addition, as tires of Comparative Examples 2 to 4, as shown Figure 2 As shown, the tread includes a first rubber layer constituting the tread surface, a second rubber layer adjacent to the radially inner side of the first rubber layer, and a third rubber layer adjacent to the radially inner side of the second rubber layer. In a tire meridian cross section including the tire rotation axis, the third rubber layer is formed to be bilaterally symmetrical with respect to a normal line of the center in the tire width direction of a land portion sandwiched by the circumferential grooves.

[0195] <Determination of Loss Tangent tanδ, Complex Elastic Modulus E*, and Glass Transition Temperature (Tg)>

[0196] From the rubber layer of each test tire's tread, a rubber test piece measuring 20 mm in length, 4 mm in width, and 1 mm in thickness was cut, with the tire's circumferential direction as the long side. Using a GABO EPLEXOR (registered trademark) series dynamic viscoelasticity measuring instrument, the loss tangent (tanδ) and complex elastic modulus (E*) were measured under the conditions of a temperature of 30°C, an initial strain of 10%, a dynamic strain of 1%, and a frequency of 10 Hz. Furthermore, a temperature profile of the loss tangent (tanδ) was measured under the conditions of an initial strain of 10%, a dynamic strain of 1%, and a frequency of 10 Hz. The temperature corresponding to the maximum tanδ value in the obtained temperature profile (tanδ peak temperature) was defined as the glass transition temperature (Tg). The thickness direction of the sample was the tire radial direction.

[0197] <Tensile test>

[0198] From the rubber layer of each test tire's tread, a dumbbell-shaped No. 7 test piece with a thickness of 1 mm was cut, with the tire's circumferential direction as the tensile direction. Tensile testing was conducted in accordance with JIS K 6251:2017, "Rubber, vulcanized and thermoplasticized—Determination of tensile properties," at a temperature of 23°C and a tensile speed of 3.3 mm / s. The elongation at break (EB) (%) and the modulus (MPa) at 100% tension were measured. The thickness direction of the sample was defined as the tire's radial direction.

[0199] <Low fuel consumption performance>

[0200] Using a rolling resistance tester, the rolling resistance of each new test tire was measured under the conditions of a 15×6.0J rim, an internal pressure of 230 kPa, a load of 4.24 kN, and a speed of 80 km / h. The reciprocal of the rolling resistance was expressed as an index, with Comparative Example 1 being 100. A larger value indicates lower rolling resistance and better fuel efficiency.

[0201] <Wet grip performance of new and worn tires>

[0202] Each test tire (size: 195 / 65R15, rim: 15×6.0J, internal pressure: 230kPa) was mounted on all wheels of a vehicle (Japanese-made FF2000cc). The braking distance from the point where braking was initiated at 100km / h was measured on a wet asphalt road surface. Furthermore, the tires were heat-degraded at 80°C for 7 days, with the tread thickness reduced to 50% of the new thickness. Each test tire, with the tread worn along the tread radius, was mounted on all wheels of the vehicle. The braking distance from the point where braking was initiated at 100km / h was measured on a wet asphalt road surface. The braking distances of the new and worn test tires of Comparative Example 1 were set as 100, respectively. The wet grip performance of each tire, both when new and after wear, was expressed as an index according to the following formula. A larger index indicates superior wet grip performance.

[0203] (Wet grip performance index when new) =

[0204] (Braking distance of the tire of Comparative Example 1 when it was new) / (Braking distance of each test tire when it was new)×100

[0205] (Wet grip performance index after wear) =

[0206] (Braking distance of the tire of Comparative Example 1 after wear) / (Braking distance of each test tire after wear)×100

[0207] The comprehensive performance of low fuel consumption performance, new wet grip performance and worn wet grip performance (the sum of low fuel consumption performance index, new wet grip performance index and worn wet grip performance index) is greater than 300 as the performance target value.

[0208]

[0209]

Table 2

[0210]

[0211]

[0212] The results in Tables 1 to 3 show that the tire of the present invention, in which three or more rubber layers are provided in the tread portion, the complex elastic modulus E* and the loss tangent tanδ of the rubber layers are in a prescribed relationship, and the third layer corresponding to the bottom of the land portion is formed asymmetrically in the width direction of the tire, has improved comprehensive performance in terms of low fuel consumption, new wet grip performance, and wet grip performance after wear.

Claims

1. A tire comprising a tread comprising at least a first rubber layer constituting a tread surface, a second rubber layer adjacent to a radially inner side of the first rubber layer, and a third rubber layer adjacent to a radially inner side of the second rubber layer, The complex elastic modulus of the third rubber layer at 30° C. is lower than the complex elastic moduli of the first rubber layer and the second rubber layer at 30° C. The tan δ of the first rubber layer at 30° C. is higher than the tan δ of the second rubber layer and the third rubber layer at 30° C. The tread has land portions separated by a plurality of circumferential grooves extending continuously in the tire circumferential direction, In a tire meridian cross section including the tire rotation axis, at least one of the land portions includes the third rubber layer formed bilaterally asymmetrically with respect to a normal line passing through the center in the tire width direction.

2. The tire according to claim 1, wherein A thickness ratio of the third rubber layer to the total thickness of the first rubber layer, the second rubber layer, and the third rubber layer is 0.30 or greater.

3. The tire according to claim 1 or 2, wherein: The complex elastic modulus of the second rubber layer at 30° C. is lower than the complex elastic modulus of the first rubber layer at 30° C.

4. The tire according to any one of claims 1 to 3, wherein The second rubber layer has a complex elastic modulus at 30° C. of 8 MPa or more.

5. The tire according to any one of claims 1 to 4, wherein The second rubber layer has a tan δ at 30° C. of 0.25 or more.

6. The tire according to any one of claims 1 to 5, wherein The glass transition temperature of the first rubber layer is -15°C or higher.

7. The tire according to any one of claims 1 to 6, wherein The glass transition temperature of the second rubber layer is -20°C or higher.

8. The tire according to any one of claims 1 to 7, wherein The first rubber layer has an elongation at break measured in accordance with JIS K6251 of 500% or more.

9. The tire according to any one of claims 1 to 8, wherein The second rubber layer has an elongation at break measured in accordance with JIS K6251 of 450% or more.

10. The tire according to any one of claims 1 to 9, wherein The modulus of the second rubber layer at 100% stretching is greater than the modulus of the first rubber layer at 100% stretching.

11. The tire according to any one of claims 1 to 10, wherein The deepest portion of the groove bottom of any one of the circumferential grooves is formed to be located further inward in the tire radial direction than the outermost portion of the second rubber layer in the land portion adjacent to the circumferential groove.

12. The tire according to any one of claims 1 to 11, wherein The land portion has a sipe with both ends not opening to the circumferential groove.

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