Heavy-duty retread tire

Abstract

To provide a heavy-duty tire excellent in chipping resistance performance on high speed traveling.SOLUTION: A heavy-duty tire includes a tread part which has a shoulder part in a tire axial direction outer side compared with a vertical main groove in a tire circumferential direction arranged at a tire axial direction outermost side. A tread rubber arranged in the tread part is made of multi-layered structure consisting of a cap rubber layer of a tread external surface and a base rubber layer arranged in a tire radial direction innermost side. The cap rubber layer in the shoulder part includes a rubber constituent containing butadiene rubber and carbon black. The heavy-duty tire satisfies the following expressions (1)-(3) when thickness Tc and complex modulus of elasticity Ec' of the cap rubber layer in the shoulder part, thickness Tb and complex modulus of elasticity Eb' of the base rubber layer in the shoulder part, and content Bca of the butadiene rubber in the rubber constituent 100 mass% contained in the cap rubber layer are given: (1)Tb / Tc≤0.50; (2)Eb' / Ec'≤0.60; (3)Bca / (Tb / Tc)≥40.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a heavy-duty tire.

Background Art

[0002] Conventionally, various methods for improving the chipping resistance performance of tires have been studied in heavy-duty vehicles such as trucks and buses. In recent years, it has been desired to improve the chipping resistance performance during high-speed driving.

Summary of the Invention

Problems to be Solved by the Invention

[0003] An object of the present disclosure is to solve the above problems and provide a heavy-duty tire having excellent chipping resistance performance during high-speed driving.

Means for Solving the Problems

[0004] The present disclosure is a heavy-duty tire having a tread portion, the tread portion includes a shoulder portion outside the tire axial direction of a circumferential longitudinal main groove arranged at the outermost side in the tire axial direction, the tread rubber arranged in the tread portion is composed of a multilayer structure including a cap rubber layer forming the tread outer surface and a base rubber layer arranged at the innermost side in the tire radial direction, the cap rubber layer in the shoulder portion includes a rubber component containing butadiene rubber and carbon black, the present disclosure relates to a heavy-duty tire in which the thickness Tc and complex elastic modulus Ec' of the cap rubber layer in the shoulder portion, the thickness Tb and complex elastic modulus Eb' of the base rubber layer in the shoulder portion, and the content Bca of the butadiene rubber in 100% by mass of the rubber component contained in the cap rubber layer satisfy the following formulas (1) to (3). (1) Tb / Tc ≦ 0.50 (2) Eb' / Ec' ≦ 0.60 (3) Bca / (Tb / Tc) ≧ 40

Effects of the Invention

[0005] The present disclosure relates to a heavy-duty tire having a tread portion, wherein the tread portion includes a shoulder portion axially outside the tire in the axial direction of the tire relative to a circumferential main groove in the circumferential direction of the tire disposed at the outermost side in the axial direction of the tire, and the tread rubber disposed in the tread portion is composed of a multilayer structure including a cap rubber layer forming the tread outer surface and a base rubber layer disposed at the innermost side in the radial direction of the tire. The cap rubber layer in the shoulder portion includes a rubber component containing butadiene rubber and carbon black, and since it is a heavy-duty tire satisfying the formulas (1) to (3), it has excellent chipping resistance performance during high-speed running.

Brief Description of the Drawings

[0006]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0007] The present disclosure relates to a heavy-duty tire having a tread portion, wherein the tread portion includes a shoulder portion axially outside the tire in the axial direction of the tire relative to a circumferential main groove in the circumferential direction of the tire disposed at the outermost side in the axial direction of the tire, and the tread rubber disposed in the tread portion is composed of a multilayer structure including a cap rubber layer forming the tread outer surface and a base rubber layer disposed at the innermost side in the radial direction of the tire. The cap rubber layer in the shoulder portion includes a rubber component containing butadiene rubber and carbon black, and it is a heavy-duty tire satisfying the formulas (1) to (3).

[0008] The reason why the above-described effects are obtained with the heavy-duty tire is presumed as follows. By adopting a cap rubber layer / base rubber layer structure incorporating a base rubber layer with excellent low heat generation properties in the tread portion, it is known that heat generation in the shoulder portion of the tread portion is suppressed and low fuel consumption performance is improved. However, when an input is applied from the road surface aggregate, since an interface exists in the tread portion, there is a concern that chipping may occur in which the tread portion chips off. In particular, when driving at high speed, since the input transmitted to the tread portion also increases, there is a concern that this tendency becomes more prominent. On the other hand, in the present disclosure, by setting the ratio of the thickness Tb of the base rubber layer to the thickness Tc of the cap rubber layer in the shoulder portion to be half or less, that is, the formula (1) "Tb / Tc ≤ 0.50", the thickness of the cap rubber layer in the shoulder portion is sufficiently ensured, and it is considered that when hitting the aggregate, the cap rubber layer deforms and it becomes easy to escape the input from the road surface. In addition, since the interface of the rubber layer can be moved away from the road surface, it is considered that the load applied to the interface can be reduced. Furthermore, by setting the ratio of the complex elastic modulus Eb' of the base rubber layer to the complex elastic modulus Ec' of the cap rubber layer in the shoulder portion to be in a state where the base rubber layer side is small, that is, the formula (2) "Eb' / Ec' ≤ 0.60", the base rubber layer also becomes easier to deform, and it is considered that it becomes possible to suppress stress concentration at the interface. In addition, since the cap rubber layer can also be deformed from the inner side in the tire radial direction, it is considered that stress concentration on the tread surface can be prevented. At the same time, by increasing the amount Bca of butadiene rubber in the cap rubber layer with respect to the ratio (Tb / Tc) of the thickness Tb of the base rubber layer to the thickness Tc of the cap rubber layer in the shoulder portion, that is, by satisfying the relational expression of the formula (3) "Bca / (Tb / Tc) ≥ 40", even when the cap rubber layer is relatively thin within the range of Tb / Tc ≤ 0.50, by increasing the amount of butadiene rubber that can move flexibly, it is considered that the chipping resistance performance is improved. From the above, it is inferred that it has become possible to improve the chipping resistance performance in the shoulder portion during high-speed driving in a heavy load tire.

[0009] Hereinafter, an embodiment of the heavy-duty tire of the present disclosure will be described together with the illustrated examples, but the present disclosure is not limited to such an embodiment. In this specification, the heavy-duty tire refers to one with a maximum load capacity of 1400 kg or more. Here, the maximum load capacity is the maximum load capacity determined for each tire in the standard system including the standard on which the tire is based. For example, in the case of the JATMA standard (Japan Automobile Tire Manufacturers Association standard), it is the maximum load capacity based on the load index (LI); in the case of TRA, it is the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES"; in the case of ETRTO, it is "LOAD CAPACITY".

[0010] Also, in this specification, unless otherwise specified, the dimensions of each part of the tire and the like are taken as the values specified in the reference state where the tire is mounted on the regular rim and filled with the regular internal pressure. Note that the "regular rim" is the rim determined for each tire in the standard system including the standard on which the tire is based. For example, in the case of JATMA, it means the standard rim; in the case of TRA, it means "Design Rim"; in the case of ETRTO, it means "Measuring Rim".

[0011] FIG. 1 is a cross-sectional view showing the reference state in which the heavy-duty tire of the present disclosure is filled with an internal pressure of 50 kPa, and FIG. 2 is an enlarged cross-sectional view showing the tread portion thereof. As an example, the heavy-duty tire 1 in FIG. 1 is shown in a form including at least a carcass 6 extending from a tread portion 2 through a sidewall portion 3 to a bead core 5 of a bead portion 4, and a belt layer 7 disposed radially outside the carcass 6 and inside the tread portion 2.

[0012] The carcass 6 is shown in a form formed from at least one, in this example one, carcass ply 6A in which carcass cords are arranged at an angle of, for example, 80 to 90° with respect to the tire equator. As the carcass cords, steel cords are preferably used, but organic fiber cords such as nylon, rayon, polyester, and aromatic polyamide can also be used as required. The carcass ply 6A is shown in a form having ply turned-up portions 6b that are folded back and locked from the inner side to the outer side in the tire axial direction around the bead cores 5 on both sides of a toroidal ply main body portion 6a that straddles between the bead cores 5, 5. In this form, a bead apex rubber 8 that tapers and extends radially outward from the bead core 5 is disposed between the ply main body portion 6a and the ply turned-up portion 6b, reinforcing from the bead portion 4 to the sidewall portion 3. Note that a wind bead structure in which the ply turned-up portion 6b is wound around the bead core 5 and its tip portion is clamped between the bead core 5 and the bead apex rubber 8, or the bead apex may be divided into two or more layers, etc. may be employed.

[0013] The belt layer 7 is shown in a form formed from a plurality of, usually 3 to 4, belt plies using steel cords as belt cords. In this form, the case of a four-ply structure of the belt layer 7 including a first belt ply 7A that is the innermost in the radial direction in which belt cords are arranged at an angle of, for example, 60 ± 15° with respect to the tire circumferential direction, and second to fourth belt plies 7B to 7D that are arranged at a small angle of, for example, 10 to 35° with respect to the tire circumferential direction is illustrated.

[0014] Among these belt plies 7A to 7D, the second belt ply 7B has the maximum width, and its width is, for example, 0.80 to 0.95 times the tread width TW. At the same time, the widths of the first and third belt plies 7A and 7C are, for example, 85 to 95% of the width of the second belt ply 7B. In this way, substantially the entire width of the tread portion 2 is reinforced with the tag effect, and the concentration of stress generated at the outer ends in the tire axial direction of each belt ply is alleviated. Note that at least the outer end in the tire axial direction of the second belt ply 7A, and in this embodiment, the outer ends in the tire axial direction of the first to third belt plies 7A to 7C are covered and protected in a U shape by the thin covering rubber 13, showing a form that prevents damage from the belt cord ends. The rubber hardness of this covering rubber 13 is preferably in the range of 60 to 70°, and its thickness is preferably in the range of 0.1 to 1.5 mm, more preferably 0.3 to 0.6 mm. Note that the hardness is the Shore A hardness, measured under the conditions of conforming to JIS K 6253, type A durometer (Shore A), and temperature 23°C.

[0015] Both ends of the belt layer 7 are gradually separated from the carcass 6, and a belt cushion rubber 10 having a triangular cross-section is arranged in this separated portion. This belt cushion rubber 10 has the maximum thickness at the position of the outer end 7Be of the second belt ply 7B, and extends along the outer surface of the carcass 6 while gradually decreasing in thickness from the position of the outer end 7Be. This belt cushion rubber 10 is preferably of the same rubber hardness of 60 to 70° as the covering rubber 13. In this way, it is possible to alleviate the shearing force between the belt cord and the carcass cord, maintain the tag effect of the belt layer 7, and maintain the tread shape. Also, by extending from the outer end 7Be of the second belt ply 7B with the maximum width, it is possible to protect the outer end of the inner belt ply 7A, which is likely to be the starting point of structural damage.

[0016] On the outer side in the tire radial direction of the belt layer 7, a form in which the tread rubber 2G is disposed is shown. The tread rubber is composed of a multilayer structure including a cap rubber layer forming a tread outer surface in contact with the road surface and a base rubber layer disposed on the innermost side in the tire radial direction. In FIGS. 1 and 2, as an example thereof, a form of the tread rubber 2G having a two-layer structure composed of a cap rubber layer 2Gc forming a tread outer surface 2S in contact with the road surface and a base rubber layer 2Gb disposed on the inner side in the tire radial direction thereof is shown. However, a form including one or more rubber layers may be provided between the cap rubber layer 2Gc and the base rubber layer 2Gb.

[0017] The outer end portion 2Ge in the tire axial direction of the tread rubber 2G extends radially inward beyond a horizontal reference line X extending in the tire axial direction from the outer end 7Be in the tire axial direction of the belt ply 7B having the maximum width and terminates in contact with the belt cushion rubber 10. Also, the sidewall rubber 3G disposed on the outer side of the carcass 6 and in the sidewall portion 3 has a form in which its outer end portion 3Ge in the radial direction covers the outer end portion 2Ge in the tire axial direction of the tread rubber 2G and terminates beyond the horizontal reference line X in the radial direction outward.

[0018] In the tread portion 2, tread grooves g are formed in various patterns in order to secure wet grip performance and the like. And, as shown in FIG. 2, the tread rubber 2G has a shoulder portion Ye. Here, the shoulder portion Ye means a land portion (shoulder land portion) on the outer side in the tire axial direction than the longitudinal main groove ge in the tire circumferential direction disposed on the outermost side in the tire axial direction.

[0019] For the heavy load tire 1, the thickness Tc (mm) of the cap rubber layer 2Gc in the shoulder portion Ye and the thickness Tb (mm) of the base rubber layer 2Gb in the shoulder portion Ye satisfy the following formula (1). (1) Tb / Tc ≦ 0.50 The upper limit of Tb / Tc is preferably 0.45 or less, more preferably 0.40 or less, still more preferably 0.35 or less, and particularly preferably 0.30 or less. The lower limit of Tb / Tc is preferably 0.10 or more, more preferably 0.15 or more, and still more preferably 0.20 or more. When within the above range, the effect tends to be better obtained.

[0020] The lower limit of the above Tc is preferably 10 mm or more, more preferably 13 mm or more, and still more preferably 15 mm or more. On the other hand, the upper limit of the above Tc is not particularly limited, but preferably 25 mm or less, more preferably 20 mm or less, and still more preferably 18 mm or less. When within the above range, the effect tends to be better obtained.

[0021] The lower limit of the above Tb is preferably 1.5 mm or more, more preferably 2.0 mm or more, and still more preferably 2.5 mm or more. On the other hand, the upper limit of the above Tb is preferably 8.0 mm or less, more preferably 6.0 mm or less, still more preferably 5.0 mm or less, and particularly preferably 4.5 mm or less. When within the above range, the effect tends to be better obtained.

[0022] The reason for obtaining such an effect is presumed as follows. By adjusting the thickness Tc of the cap rubber layer and the thickness Tb of the base rubber layer within the above range, in the shoulder portion Ye of the multilayer structure, the thickness of the cap rubber layer is sufficiently ensured and it becomes a state where it is easy to escape the input from the road surface, and the interface of the rubber layer is farther from the road surface and the load applied to the interface becomes smaller, which is more effectively realized. Therefore, it is presumed that the chipping resistance performance in the shoulder portion during high-speed driving is further improved.

[0023] In the present disclosure, the thickness Tc of the cap rubber layer 2Gc in the shoulder portion Ye and the thickness Tb of the base rubber layer 2Gb in the shoulder portion Ye are measured by the following method. In FIG. 2, reference symbol P represents a point on the outer tread surface 2S. The double-headed arrow Tc represents the thickness of the cap rubber layer 2Gc in the shoulder portion Ye at point P, and the double-headed arrow Tb represents the thickness of the base rubber layer 2Gb in the shoulder portion Ye at point P. Tc and Tb are measured along the normal line of the outer tread surface 2S at point P. The thickness Tc of the cap rubber layer 2Gc in the shoulder portion Ye and the thickness Tb of the base rubber layer 2Gb in the shoulder portion Ye respectively represent the average value of the thickness of the cap rubber layer 2Gc at each point on the outer tread surface 2S of the portion of the shoulder that contacts the road surface, and the average value of the thickness of the base rubber layer 2Gb. Here, when a belt layer or a belt reinforcing layer is provided, the outermost location in the width direction of their width direction ends is defined as the grounding end portion.

[0024] For the heavy-duty tire 1, the complex elastic modulus Ec’ (MPa) of the cap rubber layer 2Gc in the shoulder portion Ye and the complex elastic modulus Eb’ (MPa) of the base rubber layer 2Gb in the shoulder portion Ye satisfy the following formula (2). (2) Eb’ / Ec’ ≦ 0.60 The upper limit of Eb’ / Ec’ is preferably 0.55 or less, more preferably 0.50 or less, still more preferably 0.49 or less, and particularly preferably 0.47 or less. The lower limit of Eb’ / Ec’ is preferably 0.20 or more, more preferably 0.30 or more, and still more preferably 0.35 or more. When within the above range, the effect tends to be obtained more favorably.

[0025] The lower limit of the Ec’ is preferably 7.0 MPa or more, more preferably 8.0 MPa or more, still more preferably 9.0 MPa or more, and particularly preferably 10.0 MPa or more. The upper limit of the Ec’ is preferably 20.0 MPa or less, more preferably 17.0 MPa or less, and still more preferably 15.0 MPa or less. When within the above range, the effect tends to be obtained more favorably.

[0026] The lower limit of the said Eb’ is preferably 2.0 MPa or more, more preferably 2.5 MPa or more, still more preferably 3.0 MPa or more. The upper limit of the said Eb’ is preferably 8.0 MPa or less, more preferably 6.0 MPa or less, still more preferably 5.0 MPa or less, and particularly preferably 4.7 MPa or less. When it is within the above range, the effect tends to be obtained more favorably.

[0027] The reason for obtaining such an effect is presumed as follows. By adjusting the complex elastic modulus Ec’ of the cap rubber layer 2Gc and the complex elastic modulus Eb of the base rubber layer 2Gb within the above range, in the shoulder part of the multilayer structure, the base rubber layer is more likely to deform and stress concentration at the interface is suppressed, and it becomes possible to deform from the inner side in the tire radial direction with the cap rubber layer, preventing stress concentration on the tread surface, which is more effectively realized. Therefore, it is presumed that the chipping resistance performance in the shoulder part during high-speed driving is further improved.

[0028] The complex elastic modulus E’ can be adjusted by the type and amount of chemicals (particularly, rubber components, fillers, plasticizers, sulfur, vulcanization accelerators) compounded in the rubber composition (cap rubber layer 2Gc, base rubber layer 2Gb). For example, increasing the amount of filler or increasing the amount of sulfur or vulcanization accelerator tends to increase E’.

[0029] In this specification, Ec’ and Eb’ are the complex elastic moduli measured under the conditions of a temperature of 70 °C, an initial strain of 10%, a dynamic strain of ±2%, a frequency of 10 Hz, and an elongation mode. Specifically, Ec’ and Eb’ are the complex elastic moduli measured at a temperature of 70 °C, an initial strain of 10%, a dynamic strain of ±2%, and a frequency of 10 Hz using a viscoelasticity tester such as the Iplexer series of GABO Co., Ltd. for a test piece sample cut out from the cap rubber layer and the base rubber layer of the tire with a size of 4 mm in width, 40 mm in length, and 2 mm in thickness. When measuring, the longitudinal direction of the sample is made to coincide with the circumferential direction of the tire, and the dynamic strain is applied in the longitudinal direction of the sample.

[0030] From the viewpoint of obtaining better effects, it is desirable that the loss tangent tanδc of the cap rubber layer 2Gc in the shoulder portion Ye and the loss tangent tanδb of the base rubber layer 2Gb in the shoulder portion Ye satisfy the following formula. tanδb / tanδc≧0.40 The lower limit of tanδb / tanδc is preferably 0.45 or more, more preferably 0.47 or more, still more preferably 0.50 or more, and particularly preferably 0.54 or more. The upper limit of tanδb / tanδc is preferably 1.50 or less, more preferably 1.20 or less, and still more preferably 1.00 or less. When within the above range, there is a tendency to obtain better effects.

[0031] The reason for obtaining such an effect is presumably as follows. In the shoulder portion, by making the ratio of the loss tangent tanδb of the base rubber layer 2Gb to the loss tangent tanδc of the cap rubber layer 2Gc relatively large, that is, by setting "tanδb / tanδc≧0.50", it becomes easier for the base rubber layer to absorb the impact due to deformation, so it is considered possible to suppress the concentration of stress at the interface. Also, in the cap rubber layer, since it is possible to deform from the inner side in the tire radial direction, it is considered possible to prevent stress concentration on the tread surface. From the above, it is presumed that in the heavy load tire, it has become possible to improve the chipping resistance performance in the shoulder portion during high-speed running.

[0032] The lower limit of the tanδc is preferably 0.11 or more, more preferably 0.12 or more, and still more preferably 0.13 or more. The upper limit of the tanδc is preferably 0.20 or less, more preferably 0.18 or less, and still more preferably 0.17 or less. When within the above range, there is a tendency to obtain better effects.

[0033] The lower limit of the above-mentioned tanδb is preferably 0.01 or more, more preferably 0.02 or more, and still more preferably 0.04 or more. The upper limit of the above-mentioned tanδb is preferably 0.09 or less, more preferably 0.08 or less, and still more preferably 0.07 or less. When within the above range, the effect tends to be obtained more favorably.

[0034] The reason for obtaining such an effect is presumed as follows. By adjusting the loss tangent tanδc of the cap rubber layer 2Gc and the loss tangent tanδb of the base rubber layer 2Gb within the above range, in the shoulder portion of the multilayer structure, it becomes easier to absorb impact in the base rubber layer, so that it becomes possible to deform from the inner side in the tire radial direction in the cap rubber layer, and it is more effectively realized to prevent stress concentration on the tread surface. Therefore, it is presumed that the chipping resistance performance in the shoulder portion during high-speed driving is further improved.

[0035] The loss tangent tanδ can be adjusted by the types and amounts of chemicals (particularly, rubber components, fillers, plasticizers, sulfur, vulcanization accelerators, silane coupling agents) compounded in the rubber composition. For example, increasing the content of isoprene-based rubber, reducing the amount of filler, or reducing the amount of liquid plasticizer tends to reduce tanδ.

[0036] In this specification, tanδc and tanδb are loss tangents measured under the conditions of a temperature of 70°C, an initial strain of 10%, a dynamic strain of ±2%, a frequency of 10 Hz, and an elongation mode. Specifically, tanδc and tanδb mean the loss tangents measured at a temperature of 70°C, an initial strain of 10%, a dynamic strain of ±2%, and a frequency of 10 Hz using a viscoelasticity tester such as the Iplexer series of GABO for a test piece sample cut out from the cap rubber layer and the base rubber layer of the tire with a size of 4 mm in width, 40 mm in length, and 2 mm in thickness. When measuring, the longitudinal direction of the sample is made to coincide with the circumferential direction of the tire, and the dynamic strain is applied in the longitudinal direction of the sample.

[0037] The cap rubber layer 2Gc in the shoulder part Ye is composed of a rubber composition for the cap rubber layer, and the base rubber layer 2Gb in the shoulder part Ye is composed of a rubber composition for the base rubber layer.

[0038] The rubber compositions for the cap rubber layer and the base rubber layer contain a rubber component. In the rubber compositions for the cap rubber layer and the base rubber layer, the rubber component is a component that contributes to crosslinking. Generally, it is a polymer with a weight average molecular weight (Mw) of 10,000 or more, and the polymer component that is not extracted by acetone corresponds to the rubber component.

[0039] The weight average molecular weight of the rubber component is preferably 50,000 or more, more preferably 150,000 or more, still more preferably 200,000 or more, and preferably 2,000,000 or less, more preferably 1,500,000 or less, still more preferably 1,000,000 or less. When within the above range, the effect tends to be obtained more favorably.

[0040] In this specification, the weight average molecular weight (Mw) can be determined by standard polystyrene conversion based on the measured value by gel permeation chromatography (GPC) (GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMULTIPORE HZ-M manufactured by Tosoh Corporation).

[0041] The rubber component is not particularly limited, and those known in the tire field can be used. For example, diene rubbers such as isoprene rubber, butadiene rubber (BR), styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), butyl rubber (IIR), and styrene-isoprene-butadiene copolymer rubber (SIBR) can be mentioned. These may be used alone or in combination of two or more. Among them, isoprene rubber, BR, and SBR are preferred.

[0042] Examples of isoprene rubbers include natural rubber (NR), isoprene rubber (IR), modified NR, denatured NR, denatured IR, etc. As NR, for example, those commonly used in the tire industry such as SIR20, RSS#3, TSR20, etc. can be used. IR is not particularly limited, and for example, those commonly used in the tire industry such as IR2200, etc. can be used. Examples of modified NR include deproteinized natural rubber (DPNR), high-purity natural rubber (UPNR), etc., examples of denatured NR include epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), grafted natural rubber, etc., and examples of denatured IR include epoxidized isoprene rubber, hydrogenated isoprene rubber, grafted isoprene rubber, etc. These can be used alone or in combination of two or more. Among them, NR is preferred.

[0043] SBR is not particularly limited, and for example, emulsion polymerization styrene-butadiene rubber (E-SBR), solution polymerization styrene-butadiene rubber (S-SBR), etc. can be used. Examples of commercially available products include products of Sumitomo Chemical Co., Ltd., JSR Corporation, Asahi Kasei Corporation, Zeon Corporation, etc.

[0044] The styrene content of SBR is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 15% by mass or more, particularly preferably 20% by mass or more, and most preferably 25% by mass or more. Also, the styrene content is preferably 60% by mass or less, more preferably 50% by mass or less, still more preferably 40% by mass or less, particularly preferably 35% by mass or less. When within the above range, the effect tends to be obtained more favorably. In addition, in this specification, the styrene content of SBR 1 is calculated by H-NMR measurement.

[0045] BR is not particularly limited. For example, BRs with a high cis content such as BR1220 manufactured by Nippon Zeon Co., Ltd., BR150B manufactured by Ube Industries, Ltd., BR1280 manufactured by LG Chem, etc., BRs containing 1,2-syndiotactic polybutadiene crystals (SPB) such as VCR412 and VCR617 manufactured by Ube Industries, Ltd., butadiene rubbers synthesized using rare earth element-based catalysts (rare earth-based BR), etc., which are common in the tire industry, can be used. These may be used alone or in combination of two or more.

[0046] The cis amount (cis content) of BR is preferably 80% by mass or more, more preferably 85% by mass or more, still more preferably 90% by mass or more, and preferably 99% by mass or less, more preferably 98% by mass or less, still more preferably 97% by mass or less. When within the above range, the effect tends to be obtained more favorably. Incidentally, the cis amount of BR can be measured by infrared absorption spectrum analysis.

[0047] The rubber component may be an oil-extended rubber extended with oil or a resin-extended rubber extended with resin. These may be used alone or in combination of two or more. Among them, oil-extended rubber is preferred. Incidentally, the oil used for the oil-extended rubber and the resin used for the resin-extended rubber are the same as those described for the plasticizer below. Also, the oil content in the oil-extended rubber and the resin content in the resin-extended rubber are not particularly limited, but are usually about 10 to 50 parts by mass with respect to 100 parts by mass of the rubber solid content.

[0048] The rubber component may have a functional group introduced by modification that interacts with a filler such as silica. Examples of the functional group include, for example, a silicon-containing group (-SiR3, where R is the same or different and is hydrogen, a hydroxyl group, a hydrocarbon group, an alkoxy group, etc.), an amino group, an amide group, an isocyanate group, an imino group, an imidazole group, a urea group, an ether group, a carbonyl group, an oxycarbonyl group, a mercapto group, a sulfide group, a disulfide group, a sulfonyl group, a sulfinyl group, a thiocarbonyl group, an ammonium group, an imide group, a hydrazo group, an azo group, a diazo group, a carboxyl group, a nitrile group, a pyridyl group, an alkoxy group, a hydroxyl group, an oxy group, an epoxy group, etc. These functional groups may have substituents. Among them, a silicon-containing group is preferable, and -SiR3 (R is the same or different and is hydrogen, a hydroxyl group, a hydrocarbon group (preferably a hydrocarbon group having 1 to 6 carbon atoms (more preferably an alkyl group having 1 to 6 carbon atoms)) or an alkoxy group (preferably an alkoxy group having 1 to 6 carbon atoms)), and at least one of R is a hydroxyl group) is more preferable.

[0049] Specific examples of the compound (modifying agent) for introducing the functional group include 2-dimethylaminoethyltrimethoxysilane, 3-dimethylaminopropyltrimethoxysilane, 2-dimethylaminoethyltriethoxysilane, 3-dimethylaminopropyltriethoxysilane, 2-diethylaminoethyltrimethoxysilane, 3-diethylaminopropyltrimethoxysilane, 2-diethylaminoethyltriethoxysilane, 3-diethylaminopropyltriethoxysilane, etc.

[0050] Regarding the aforementioned rubber component, the rubber composition for the cap rubber layer contains at least BR, but from the viewpoint of obtaining better effects, it is desirable to further contain an isoprene-based rubber. Also, from the viewpoint of obtaining better effects, the rubber composition for the base rubber layer desirably contains an isoprene-based rubber.

[0051] In the rubber composition for the cap rubber layer, the content of isoprene rubber in 100% by mass of the rubber component is preferably 20% by mass or more, more preferably 40% by mass or more, still more preferably 50% by mass or more, and particularly preferably 60% by mass or more. The upper limit is preferably 90% by mass or less, more preferably 80% by mass or less, still more preferably 70% by mass or less. When it is within the above range, the effect tends to be obtained more favorably.

[0052] In the rubber composition for the cap rubber layer, the content of BR in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 20% by mass or more, still more preferably 30% by mass or more, and particularly preferably 40% by mass or more, and is preferably 70% by mass or less, more preferably 60% by mass or less, still more preferably 50% by mass or less. When it is within the above range, the effect tends to be obtained more favorably. The reason for obtaining such an effect is presumed as follows. In the rubber composition for the cap rubber layer, by setting the content of BR within the above range, particularly 20% by mass or more, that is, increasing the amount of butadiene rubber that can move flexibly, it is considered that the cap rubber layer becomes more movable. Therefore, it is presumed that the chipping resistance performance in the shoulder portion during high-speed driving is further improved.

[0053] In the rubber composition for the cap rubber layer, the total content of isoprene rubber and BR in 100% by mass of the rubber component is preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and may be 100% by mass. When it is within the above range, the effect tends to be obtained more favorably.

[0054] In the rubber composition for the base rubber layer, the content of isoprene rubber in 100% by mass of the rubber component is preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and may be 100% by mass. When it is within the above range, the effect tends to be obtained more favorably.

[0055] The rubber compositions for the cap rubber layer and the base rubber layer preferably contain a filler. From the viewpoint of obtaining better effects, carbon black is preferable as the filler, and the rubber composition for the cap rubber layer contains at least carbon black.

[0056] The carbon black is not particularly limited, and examples include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, N762, etc. The raw material of the carbon black may be a biomass material such as lignin or vegetable oil. Also, the production method of the carbon black may be by combustion such as the furnace method, or may be by hydrothermal carbonization (HTC). As commercially available products, products of Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Corporation, Lion Corporation, Shin Nippon Carbon Co., Ltd., Columbia Carbon Company, etc. can be used. These may be used alone or in combination of two or more.

[0057] The nitrogen adsorption specific surface area (N2SA) of the carbon black is preferably 50 m 2 / g or more, more preferably 70 m 2 / g or more, and still more preferably 75 m 2 / g or more. Also, the above N2SA is preferably 200 m 2 / g or less, more preferably 170 m 2 / g or less, and still more preferably 150 m 2 / g or less. When within the above range, the effects tend to be obtained better. Note that the nitrogen adsorption specific surface area of the carbon black is determined according to JIS K6217-2:2001.

[0058] Examples of the filler that can be used in addition to carbon black include inorganic fillers. Examples of the inorganic filler include silica, clay, alumina, talc, calcium carbonate, magnesium carbonate, aluminum hydroxide, magnesium hydroxide, magnesium oxide, titanium oxide, etc. These may be used alone or in combination of two or more. Among them, silica is preferred.

[0059] Examples of silica include dry-process silica (anhydrous silicic acid), wet-process silica (hydrous silicic acid), etc. Wet-process silica is preferred because of its large number of silanol groups. The raw material of silica may be water glass (sodium silicate) or biomass materials such as rice husks. As commercially available products, products of Evonik, Tosoh Silica Corporation, Solvay Japan Co., Ltd., Tokuyama Corporation, etc. can be used. These may be used alone or in combination of two or more.

[0060] The nitrogen adsorption specific surface area (N2SA) of silica is preferably 50 m 2 / g or more, more preferably 100 m 2 / g or more, still more preferably 150 m 2 / g or more. Also, the upper limit of N2SA of silica is not particularly limited, but is preferably 350 m 2 / g or less, more preferably 250 m 2 / g or less, still more preferably 200 m 2 / g or less. When within the above range, the effect tends to be obtained better. Note that the N2SA of silica is a value measured by the BET method in accordance with ASTM D3037-93.

[0061] Regarding the above-mentioned filler, from the viewpoint of obtaining better effects, the rubber composition for the cap rubber layer preferably contains carbon black with N2SA of 80 to 150 m 2 / g, more preferably N2SA of 110 to 150 m 2 / g, still more preferably N2SA of 130 to 150 m 2 / g. The rubber composition for the base rubber layer has N2SA of 60 to 120 m 2 / g, more preferably N2SA of 70 to 100 m 2 / g, more preferably N2SA 75 to 85 m 2 It is preferable to contain carbon black of / g.

[0062] In the rubber composition for the cap rubber layer, the content of carbon black is preferably 30 parts by mass or more, more preferably 40 parts by mass or more, still more preferably 50 parts by mass or more, particularly preferably 55 parts by mass or more, based on 100 parts by mass of the rubber component. Also, it is preferably 150 parts by mass or less, more preferably 100 parts by mass or less, still more preferably 80 parts by mass or less, particularly preferably 75 parts by mass or less. When it is within the above range, the effect tends to be obtained more favorably.

[0063] In the rubber composition for the cap rubber layer, the content (total amount) of the filler is preferably 30 parts by mass or more, more preferably 40 parts by mass or more, still more preferably 50 parts by mass or more, particularly preferably 55 parts by mass or more, based on 100 parts by mass of the rubber component. Also, it is preferably 150 parts by mass or less, more preferably 100 parts by mass or less, still more preferably 80 parts by mass or less, particularly preferably 75 parts by mass or less. When it is within the above range, the effect tends to be obtained more favorably.

[0064] From the viewpoint of obtaining a better effect, in the rubber composition for the cap rubber layer, the carbon black content rate in 100% by mass of the filler is preferably 50% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and may be 100% by mass. When it is within the above range, the effect tends to be obtained more favorably.

[0065] In the rubber composition for the base rubber layer, the content of carbon black is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, still more preferably 30 parts by mass or more, particularly preferably 40 parts by mass or more, based on 100 parts by mass of the rubber component. Also, it is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, still more preferably 70 parts by mass or less, particularly preferably 60 parts by mass or less. When it is within the above range, the effect tends to be obtained more favorably.

[0066] In the rubber composition for the base rubber layer, the content (total amount) of the filler is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, still more preferably 30 parts by mass or more, particularly preferably 40 parts by mass or more, and preferably 100 parts by mass or less, more preferably 80 parts by mass or less, still more preferably 70 parts by mass or less, particularly preferably 60 parts by mass or less, based on 100 parts by mass of the rubber component. When within the above range, the effect tends to be obtained more favorably.

[0067] From the viewpoint of obtaining a better effect, in the rubber composition for the base rubber layer, the carbon black content in 100% by mass of the filler is preferably 50% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and may be 100% by mass. When within the above range, the effect tends to be obtained more favorably.

[0068] The rubber composition for the cap rubber layer and the base rubber layer may contain a plasticizer. Here, the plasticizer is a material that imparts plasticity to the polymer component, and examples include liquid plasticizers (plasticizers in a liquid state at room temperature (25°C)), resins (resins in a solid state at room temperature (25°C)), and the like.

[0069] The liquid plasticizer (plasticizer in a liquid state at room temperature (25°C)) that can be used in the rubber composition for the cap rubber layer and the base rubber layer is not particularly limited, and examples include oils, liquid polymers (liquid resins, liquid diene-based polymers, liquid farnesene-based polymers, etc.). These may be used alone or in combination of two or more.

[0070] Examples of the oil include process oil, vegetable oil, or a mixture thereof. As the process oil, for example, paraffinic process oil, aromatic process oil, naphthenic process oil, etc. can be used. Examples of the vegetable oil include castor oil, cottonseed oil, linseed oil, rapeseed oil, soybean oil, palm oil, coconut oil, peanut oil, rosin, pine oil, pine tar, tall oil, corn oil, rice bran oil, safflower oil, sesame oil, olive oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, tung oil, etc. Among them, process oil (such as paraffinic process oil, aromatic process oil, naphthenic process oil, etc.) and vegetable oil are preferred. In addition, from the perspective of life cycle assessment, these process oils and vegetable oils may be appropriately used with oils after being used as lubricating oils for rubber mixers, engines, etc., and waste cooking oils.

[0071] Examples of the liquid resin include terpene resins (including terpene phenol resins and aromatic modified terpene resins), rosin resins, styrene resins, C5 resins, C9 resins, C5 / C9 resins, dicyclopentadiene (DCPD) resins, coumarone indene resins (including coumarone and indene monomer resins), phenol resins, olefin resins, polyurethane resins, acrylic resins, etc. In addition, hydrogenated products thereof can also be used.

[0072] Examples of the liquid diene polymer include liquid styrene-butadiene copolymer (liquid SBR) in a liquid state at 25°C, liquid butadiene polymer (liquid BR), liquid isoprene polymer (liquid IR), liquid styrene-isoprene copolymer (liquid SIR), liquid styrene-butadiene-styrene block copolymer (liquid SBS block polymer), liquid styrene-isoprene-styrene block copolymer (liquid SIS block polymer), liquid farnesene polymer, liquid farnesene-butadiene copolymer, etc. These may have their terminals or main chains modified with polar groups. In addition, hydrogenated products thereof can also be used.

[0073] Examples of the resin (resin in a solid state at normal temperature (25°C)) that can be used in the rubber composition for the cap rubber layer and the base rubber layer include, for example, an aromatic vinyl polymer, a coumarone-indene resin, a coumarone resin, an indene resin, a phenol resin, a rosin resin, a petroleum resin, a terpene resin, an acrylic resin, etc. in a solid state at normal temperature (25°C). The resin may be hydrogenated. These may be used alone or in combination of two or more. Among them, an aromatic vinyl polymer, a petroleum resin, and a terpene resin are preferable.

[0074] The softening point of the above resin is preferably 50°C or higher, more preferably 55°C or higher, and still more preferably 60°C or higher. The upper limit is preferably 160°C or lower, more preferably 150°C or lower, and still more preferably 145°C or lower. When within the above range, the effect tends to be obtained more favorably. The softening point of the above resin is the temperature at which the ball drops when measured with a ring and ball softening point measuring device according to the softening point defined in JIS K6220-1:2001.

[0075] In the rubber composition for the cap rubber layer, the content of the plasticizer (total amount of the plasticizer) is preferably 5 parts by mass or less, more preferably 1 part by mass or less, still more preferably 0.1 part by mass or less, particularly preferably 0.01 part by mass or less, and may be 0 part by mass, based on 100 parts by mass of the rubber component. When within the above range, the effect tends to be obtained more favorably.

[0076] In the rubber composition for the base rubber layer, the content of the plasticizer (total amount of the plasticizer) is preferably 5 parts by mass or less, more preferably 1 part by mass or less, still more preferably 0.1 part by mass or less, particularly preferably 0.01 part by mass or less, and may be 0 part by mass, based on 100 parts by mass of the rubber component. When within the above range, the effect tends to be obtained more favorably.

[0077] As the plasticizer, for example, products of Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., Nippon Energy Corporation, Orisoy Co., H&R Co., Toyokuni Oil Co., Ltd., Showa Shell Sekiyu K.K., Fuji Kogyo Co., Ltd., Nisshin Oillio Group, Ltd., Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Yasuhara Chemical Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF SE, Arizona Chemical Company, Nippon Paint Chemical Co., Ltd., Nippon Shokubai Co., Ltd., ENEOS Corporation, Arakawa Chemical Industries, Ltd., Takeoka Chemical Industry Co., Ltd., etc. can be used.

[0078] The rubber compositions for the cap rubber layer and the base rubber layer may contain a silane coupling agent. The silane coupling agent is not particularly limited. For example, bis(3-triethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, bis(2-triethoxysilylethyl)trisulfide, bis(4-trimethoxysilylbutyl)trisulfide, bis(3-triethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)disulfide, bis(4-triethoxysilylbutyl)disulfide, bis(3-trimethoxysilylpropyl)disulfide, bis(2-trimethoxysilylethyl)disulfide, bis(4-trimethoxysilylbutyl)disulfide, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide and other sulfide-based ones, 3-mercaptopropyltrimethoxysilane, 2-mercaptoethyltriethoxysilane and other mercapto-based ones, vinyltriethoxysilane, vinyltrimethoxysilane and other vinyl-based ones, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane and other amino-based ones, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane and other glycidoxy-based ones, 3-nitropropyltrimethoxysilane, 3-nitropropyltriethoxysilane and other nitro-based ones, 3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysilane and other chloro-based ones can be mentioned. As commercially available products, for example, products of Evonik Degussa, Momentive, Shin-Etsu Silicone Co., Ltd., Tokyo Chemical Industry Co., Ltd., Azmax Co., Ltd., Toray Dow Corning Co., Ltd. etc. can be used. These may be used alone or in combination of two or more kinds.

[0079] In the rubber composition for the cap rubber layer and the base rubber layer, the content of the silane coupling agent is preferably 3 parts by mass or more, more preferably 6 parts by mass or more, still more preferably 8 parts by mass or more, and preferably 16 parts by mass or less, more preferably 14 parts by mass or less, still more preferably 12 parts by mass or less, based on 100 parts by mass of silica. When it is within the above range, the effect tends to be obtained more favorably.

[0080] The rubber composition for the cap rubber layer and the base rubber layer may contain an anti-aging agent. Examples of the anti-aging agent include naphthylamine-based anti-aging agents such as phenyl-α-naphthylamine; diphenylamine-based anti-aging agents such as octylated diphenylamine and 4,4′-bis(α,α′-dimethylbenzyl)diphenylamine; p-phenylenediamine-based anti-aging agents such as N-isopropyl-N′-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine, and N,N′-di-2-naphthyl-p-phenylenediamine; quinoline-based anti-aging agents such as polymers of 2,2,4-trimethyl-1,2-dihydroquinoline; monophenol-based anti-aging agents such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol; bis, tris, polyphenol-based anti-aging agents such as tetrakis-[methylene-3-(3′,5′-di-t-butyl-4′-hydroxyphenyl)propionate]methane, etc. As commercially available products, products of Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinsei Chemical Industry Co., Ltd., Flexsys Co., etc. can be used. These may be used alone or in combination of two or more.

[0081] In the rubber composition for the cap rubber layer and the base rubber layer, the content of the anti-aging agent is preferably 0.5 parts by mass or more, more preferably 0.8 parts by mass or more, still more preferably 1.0 parts by mass or more, and preferably 10.0 parts by mass or less, more preferably 6.0 parts by mass or less, still more preferably 4.0 parts by mass or less, based on 100 parts by mass of the rubber component. When it is within the above range, the effect tends to be obtained more favorably.

[0082] The rubber compositions for the cap rubber layer and the base rubber layer may contain wax. The wax is not particularly limited, and examples thereof include petroleum waxes such as paraffin wax and microcrystalline wax; natural waxes such as plant waxes and animal waxes; and synthetic waxes such as polymers of ethylene, propylene, etc. As commercially available products, products of Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., Seiko Chemical Co., Ltd., etc. can be used. These may be used alone or in combination of two or more.

[0083] In the rubber compositions for the cap rubber layer and the base rubber layer, the content of the wax is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and preferably 10 parts by mass or less, more preferably 6 parts by mass or less, based on 100 parts by mass of the rubber component. When within the above range, the effect tends to be obtained more favorably.

[0084] The rubber compositions for the cap rubber layer and the base rubber layer may contain stearic acid. As the stearic acid, conventionally known ones can be used. As commercially available products, products of NOF Corporation, Kao Corporation, Fuji Film Wako Pure Chemical Corporation, Chiba Fatty Acids Co., Ltd., etc. can be used. These may be used alone or in combination of two or more.

[0085] In the rubber compositions for the cap rubber layer and the base rubber layer, the content of the stearic acid is preferably 1.0 part by mass or more, more preferably 2.0 parts by mass or more, still more preferably 3.0 parts by mass or more, and preferably 10.0 parts by mass or less, more preferably 6.0 parts by mass or less, based on 100 parts by mass of the rubber component. When within the above range, the effect tends to be obtained more favorably.

[0086] The rubber compositions for the cap rubber layer and the base rubber layer may contain zinc oxide. As the zinc oxide, those conventionally known can be used, and as commercially available products, products of Mitsui Mining & Smelting Co., Ltd., Toho Zinc Co., Ltd., Hakusui Tech Co., Ltd., Shoindo Chemical Industry Co., Ltd., Sakai Chemical Industry Co., Ltd., etc. can be used. These may be used alone or in combination of two or more.

[0087] In the rubber composition for the cap rubber layer and the base rubber layer, the content of zinc oxide is preferably 1.0 part by mass or more, more preferably 2.5 parts by mass or more, still more preferably 3.0 parts by mass or more, and preferably 10.0 parts by mass or less, more preferably 6.0 parts by mass or less, based on 100 parts by mass of the rubber component. When it is within the above range, the effect tends to be obtained more favorably.

[0088] The rubber composition for the cap rubber layer and the base rubber layer may contain sulfur. Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersed sulfur, soluble sulfur, etc., which are generally used as crosslinking agents in the rubber industry. As commercially available products, products of Tsurumi Chemical Industry Co., Ltd., Karuizawa Sulfur Co., Ltd., Shikoku Kasei Kogyo Co., Ltd., Flexsys, Nippon Kankyo Kogyo Co., Ltd., Hosoi Chemical Industry Co., Ltd., etc. can be used. These may be used alone or in combination of two or more.

[0089] In the rubber composition for the cap rubber layer and the base rubber layer, the content of sulfur is preferably 0.5 part by mass or more, more preferably 0.8 part by mass or more, still more preferably 1.0 part by mass or more, and preferably 3.5 parts by mass or less, more preferably 2.8 parts by mass or less, still more preferably 2.5 parts by mass or less, based on 100 parts by mass of the rubber component. When it is within the above range, the effect tends to be obtained more favorably.

[0090] The rubber composition for the cap rubber layer and the base rubber layer may contain a vulcanization accelerator. Examples of vulcanization accelerators include thiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole and di-2-benzothiazolyldisulfide; thiuram-based vulcanization accelerators such as tetramethylthiuram disulfide (TMTD) and tetrakis(2-ethylhexyl)thiuram disulfide (TOT-N); sulfenamide-based vulcanization accelerators such as N-cyclohexyl-2-benzothiazylsulfenamide (CBS), N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-oxyethylene-2-benzothiazolesulfenamide, and N,N′-diisopropyl-2-benzothiazolesulfenamide; and guanidine-based vulcanization accelerators such as diphenylguanidine, diorthotolylguanidine, and orthotolylbiguanidine. As commercially available products, products of Sumitomo Chemical Co., Ltd., Ouchi Shinsei Chemical Industry Co., Ltd., etc. can be used. These may be used alone or in combination of two or more.

[0091] In the rubber compositions for the cap rubber layer and the base rubber layer, the content of the vulcanization accelerator is preferably 0.5 part by mass or more, more preferably 0.8 part by mass or more, still more preferably 1.0 part by mass or more, and preferably 10.0 parts by mass or less, more preferably 8.0 parts by mass or less, still more preferably 7.0 parts by mass or less, based on 100 parts by mass of the rubber component. When within the above range, the effect tends to be obtained more favorably.

[0092] In addition to the above components, the rubber compositions for the cap rubber layer and the base rubber layer may further be blended with additives generally used in the tire industry, such as organic peroxides. The content of these additives is preferably 0.1 to 200 parts by mass based on 100 parts by mass of the rubber component.

[0093] The rubber compositions for the cap rubber layer and the base rubber layer can be produced, for example, by kneading the above-mentioned respective components using a rubber kneading device such as an open roll or a Banbury mixer, and then vulcanizing.

[0094] As for the kneading conditions, in the base kneading step of kneading additives other than the vulcanizing agent and the vulcanization accelerator, the kneading temperature is usually 100 to 180 °C, preferably 120 to 170 °C. In the finishing kneading step of kneading the vulcanizing agent and the vulcanization accelerator, the kneading temperature is usually 120 °C or lower, preferably 85 to 110 °C. Further, the composition kneaded with the vulcanizing agent and the vulcanization accelerator is usually subjected to a vulcanization treatment such as press vulcanization. As the vulcanization temperature, it is usually 140 to 190 °C, preferably 150 to 185 °C. The vulcanization time is usually 5 to 15 minutes.

[0095] In the heavy load tire 1 shown in FIGS. 1 and 2, the thickness Tc (mm) of the cap rubber layer 2Gc in the shoulder portion Ye, the thickness Tb (mm) of the base rubber layer 2Gb in the shoulder portion Ye, and the content Bca (%) of butadiene rubber in 100% by mass of the rubber component contained in the cap rubber layer 2Gc in the shoulder portion Ye satisfy the following formula (3). (3) Bca / (Tb / Tc) ≥ 40 The lower limit of Bca / (Tb / Tc) [mass%] is preferably 60 or more, more preferably 100 or more, still more preferably 120 or more, and particularly preferably 130 or more. The upper limit of Bca / (Tb / Tc) [mass%] is preferably 200 or less, more preferably 170 or less, still more preferably 160 or less, and particularly preferably 150 or less. When within the above range, the effect tends to be obtained more favorably.

[0096] As described above, the particularly preferred embodiments of the present disclosure have been described in detail. However, the present disclosure is not limited to the illustrated embodiments and can be implemented in various forms.

Examples

[0097] The present disclosure will be specifically described based on the examples, but the present disclosure is not limited to these only.

[0098] Hereinafter, various chemicals used in the examples and comparative examples will be described. NR: TSR20 BR: BR150B manufactured by Ube Industries, Ltd. (vinyl content 1% by mass, cis content 97% by mass) Carbon black N220: Shaw black N220 (N2SA114m 2 / g) manufactured by Cabot Japan Co., Ltd. Carbon black N134: Shaw black N134 (N2SA148m 2 / g) manufactured by Cabot Japan Co., Ltd. Carbon black N330: Shaw black N330 (N2SA78m 2 / g) manufactured by Cabot Japan Co., Ltd. Wax: Oz Ace 0355 manufactured by Nippon Seiro Co., Ltd. Antioxidant: Nocrack 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Stearic acid: Stearic acid "Tsubaki" manufactured by NOF Corporation Zinc oxide: Zinc white No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: HK-200-5 (powder sulfur containing 5% by mass of oil) manufactured by Hosoi Chemical Industry Co., Ltd. Vulcanization accelerator: Nocceler NS (N-tert-butyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0099] (Examples and Comparative Examples) According to the formulation contents shown in the rubber compositions for the cap rubber layer in Tables 1 and 2 and the rubber compositions for the base rubber layer in Table 3, using a 1.7 L Banbury mixer manufactured by Kobe Steel, Ltd., materials other than sulfur and the vulcanization accelerator were kneaded at 150 °C for 5 minutes to obtain a kneaded product. Next, sulfur and the vulcanization accelerator were added to the obtained kneaded product, and it was kneaded at 80 °C for 5 minutes using an open roll to obtain an unvulcanized rubber composition for the cap rubber layer and an unvulcanized rubber composition for the base rubber layer. According to the specifications in Tables 1 and 2, the unvulcanized rubber composition for the cap rubber layer was formed into the shape of the cap rubber layer, and the unvulcanized rubber composition for the base rubber layer was formed into the shape of the base rubber layer. They were bonded together with other tire members to form an unvulcanized tire, which was press-vulcanized at 150 °C for 30 minutes to obtain a test tire (heavy-duty tire, size: 11R22.5).

[0100] The following evaluations were performed using the obtained test tires, and the results are shown in Tables 1 and 2. In the following evaluations, the evaluation criteria for calculating the indices are as follows. Tables 1 and 2: Comparative Example 8

[0101] <Viscoelasticity test> Regarding Ec’ and Eb’, tanδc and tanδb, test piece samples with a width of 4 mm, a length of 40 mm, and a thickness of 2 mm were cut out from the cap rubber layer and the base rubber layer of the test tire, and the complex elastic modulus and loss tangent were measured using a viscoelasticity tester of the Iplexer series manufactured by GABO under the conditions of a temperature of 70 °C, an initial strain of 10%, a dynamic strain of ±2%, and a frequency of 10 Hz.

[0102] <Chipping resistance during high-speed driving> Regarding the test tire, a drum-type driving tester was used, and metal slats (protrusions) were attached to two locations in the circumferential direction on the drum, and it was run for 30 minutes at 80 km / h and a load of 26.72 kN. Then, regarding the chips generated on the tire surface, the number of chips × the depth of the damage was measured and indexed. A larger numerical value indicates better chip resistance performance.

[0103]

Table 1

[0104]

Table 2

[0105]

Table 3

[0106] From Tables 1 and 2, the examples had excellent chipping resistance performance during high-speed driving.

[0107] The present disclosure (1) is a heavy-duty tire having a tread portion, The tread portion includes a shoulder portion that is axially outside of the longitudinal main groove in the tire circumferential direction disposed at the outermost side in the tire axial direction. The tread rubber disposed in the tread portion is formed of a multilayer structure including a cap rubber layer forming the tread outer surface and a base rubber layer disposed at the innermost side in the tire radial direction. The cap rubber layer in the shoulder portion includes a rubber component containing butadiene rubber and carbon black. The tire for heavy loads satisfies the following formulas (1) to (3) with respect to the thickness Tc and complex elastic modulus Ec' of the cap rubber layer in the shoulder portion, the thickness Tb and complex elastic modulus Eb' of the base rubber layer in the shoulder portion, and the content Bca of the butadiene rubber in 100% by mass of the rubber component contained in the cap rubber layer. (1) Tb / Tc ≤ 0.50 (2) Eb' / Ec' ≤ 0.60 (3) Bca / (Tb / Tc) ≥ 40

[0108] The tire for heavy loads according to the present disclosure (2) satisfies the following formula with respect to the tire for heavy loads according to the present disclosure (1). Tb / Tc ≤ 0.30

[0109] The tire for heavy loads according to the present disclosure (3) satisfies the following formula with respect to the tire for heavy loads according to the present disclosure (1) or (2). Eb' / Ec' ≤ 0.50

[0110] The tire for heavy loads according to the present disclosure (4) satisfies the following formula with respect to any one of the tires for heavy loads according to the present disclosures (1) to (3). Bca / (Tb / Tc) ≥ 60

[0111] The tire for heavy loads according to the present disclosure (5) satisfies the following formula with respect to any one of the tires for heavy loads according to the present disclosures (1) to (3). Bca / (Tb / Tc) ≥ 120

[0112] The present disclosure (6) is a heavy-duty tire according to any one of the present disclosures (1) to (5), in which the loss tangent tanδc of the cap rubber layer in the shoulder portion and the loss tangent tanδb of the base rubber layer in the shoulder portion satisfy the following formula. tanδb / tanδc≧0.50

[0113] The present disclosure (7) is a heavy-duty tire according to any one of the present disclosures (1) to (6), which satisfies the following formula. Tc≧13mm

[0114] The present disclosure (8) is a heavy-duty tire according to any one of the present disclosures (1) to (7), which satisfies the following formula. Eb’≦5.0MPa

[0115] The present disclosure (9) is a heavy-duty tire according to any one of the present disclosures (6) to (8), which satisfies the following formula. tanδb≧0.04

[0116] The present disclosure (10) is a heavy-duty tire according to any one of the present disclosures (1) to (9), in which the cap rubber layer in the shoulder portion has a butadiene rubber content of 20% by mass or more in 100% by mass of the rubber component.

Explanation of Signs

[0117] 1 Heavy-duty tire 2 Tread portion 2S Tread outer surface 2G Tread rubber 2Gb Base rubber layer 2Gc Cap rubber layer 3 Sidewall portion 3G Sidewall rubber 4 Bead portion 5 Bead core 6 Carcass 7 Belt layer Ye Shoulder portion Tc Thickness of the cap rubber layer 2Gc in the shoulder portion Ye Thickness of the base rubber layer 2Gb in the shoulder portion Ye of the Tb ge longitudinal main groove Point on the outer surface 2S of the P tread C tire equator

Claims

1. A heavy-duty tire having a tread portion, wherein the tread portion includes a shoulder portion axially outside the tire in the tire axial direction than a circumferential longitudinal main groove disposed at the outermost side in the tire axial direction, the tread rubber disposed in the tread portion is composed of a multilayer structure including a cap rubber layer forming the tread outer surface and a base rubber layer disposed at the innermost side in the tire radial direction, the cap rubber layer in the shoulder portion includes a rubber component containing butadiene rubber and carbon black, a heavy-duty tire in which the thickness Tc of the cap rubber layer in the shoulder portion, the temperature of the cap rubber layer at 70 ° C, an initial strain of 10%, a dynamic strain of ± 2%, a frequency of 10 Hz, the complex elastic modulus Ec' measured under the conditions of the elongation mode, the thickness Tb of the base rubber layer in the shoulder portion, the temperature of the base rubber layer at 70 ° C, an initial strain of 10%, a dynamic strain of ± 2%, a frequency of 10 Hz, the complex elastic modulus Eb' measured under the conditions of the elongation mode, and the content Bca of the butadiene rubber in 100% by mass of the rubber component contained in the cap rubber layer satisfy the following formulas (1) to (3). (1) Tb / Tc ≤ 0.50 (2) Eb' / Ec' ≤ 0.60 (3) Bca / (Tb / Tc) ≥ 40

2. The heavy-duty tire according to Claim 1, which satisfies the following formula. Tb / Tc ≤ 0.30

3. The heavy-duty tire according to Claim 1 or 2, which satisfies the following formula. Eb' / Ec' ≤ 0.50

4. The heavy-duty tire according to any one of Claims 1 to 3, which satisfies the following formula. Bca / (Tb / Tc) ≥ 60

5. The heavy-duty tire according to any one of Claims 1 to 3, which satisfies the following formula. Bca / (Tb / Tc) ≥ 120

6. The loss tangent tanδc measured under the conditions of the temperature of the cap rubber layer in the shoulder portion at 70 ° C, an initial strain of 10%, a dynamic strain of ± 2%, a frequency of 10 Hz, and the elongation mode, and the loss tangent tanδb measured under the conditions of the temperature of the base rubber layer in the shoulder portion at 70 ° C, an initial strain of 10%, a dynamic strain of ± 2%, a frequency of 10 Hz, and the elongation mode, the heavy-duty tire according to any one of Claims 1 to 5, which satisfies the following formula. tanδb / tanδc ≥ 0.50

7. The heavy-duty tire according to any one of Claims 1 to 6, which satisfies the following formula. Tc ≥ 13 mm

8. The heavy-duty tire according to any one of Claims 1 to 7, which satisfies the following formula. Eb' ≤ 5.0 MPa

9. The heavy load tire according to any one of claims 6 to 8, which satisfies the following formula. tan δb ≥ 0.04

10. The heavy load tire according to any one of claims 1 to 9, wherein the cap rubber layer in the shoulder portion has a butadiene rubber content of 20% by mass or more in 100% by mass of the rubber component.

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