Heavy load reuse tire

Abstract

To provide a heavy load tire improved in low fuel consumption performance, wet grip performance, abrasion resistance, chipping resistance, and tear resistance.SOLUTION: A heavy load tire 2 is configured such that a tread has a plurality of main grooves 24 continuously extending in a tire circumferential direction; the tread has a cap rubber layer 30 constituting a tread surface, and a base rubber layer 28 adjacent to the cap rubber layer inward in a radial direction; the cap rubber layer and the base rubber layer are constituted by a rubber composition including a rubber constituent; the rubber constituent constituting the cap rubber layer includes isoprene rubber, styrene-butadiene rubber, and butadiene rubber; the rubber composition constituting the cap rubber layer includes, based on the rubber constituent 100 pts.mass, 30 mass% or more silica having a nitrogen adsorption specific surface (N2SA) of 180 m2 / g or more; and the rubber composition constituting the base rubber layer has tanδ of 0.04-0.07 at 70°C.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a heavy-duty tire in which low fuel consumption performance, wet grip performance, wear resistance, chipping resistance, and tear resistance are improved in a well-balanced manner.

Background Art

[0002] As a method for improving the wear resistance of truck and bus tires, a technique of making carbon black fine or highly structured is known (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above method of making carbon black fine or highly structured, the improvement of the low fuel consumption performance of the tire is not sufficient. In addition, due to the deterioration of processability accompanying the fineness, the dispersibility of carbon black also deteriorates, and conversely, the wear resistance of the tire may deteriorate. Therefore, there has been a limit to the conventional method of improving performance by improving carbon black.

[0005] In addition, due to the influence of recent environmental regulations, in truck and bus tires, not only wear resistance but also requirements for highly compatible low fuel consumption performance, wet grip performance, chipping resistance, etc. are increasing.

[0006] An object of the present invention is to provide a heavy-duty tire in which low fuel consumption performance, wet grip performance, wear resistance, chipping resistance, and tear resistance are improved in a well-balanced manner.

Means for Solving the Problems

[0007] As a result of intensive studies, the inventor of the present invention has found that in a tire having a predetermined configuration, by blending a predetermined rubber component and silica in a cap rubber layer constituting a tread and setting the loss tangent tan δ of a base rubber layer within a predetermined range, the above problems can be solved, and thus the present invention has been completed.

[0008] That is, the present invention provides: 〔1〕A heavy-duty tire having a carcass extending from a tread portion to a bead core of a bead portion via a sidewall portion, and a belt layer disposed on the outer side in the tire radial direction and inside the tread portion of the carcass, wherein the belt layer is formed of a belt ply including a first belt layer, a second belt layer, and a third belt layer laminated in order from the inner side in the tire radial direction, and the tread Part has a plurality of main grooves continuously extending in the tire circumferential direction, and the tread Part has a cap rubber layer constituting a tread surface and a base rubber layer adjacent to the inner side in the radial direction of the cap rubber layer, the cap rubber layer and the base rubber layer are formed of a rubber composition containing a rubber component, the rubber component constituting the cap rubber layer includes an isoprene-based rubber, a styrene-butadiene rubber, and a butadiene rubber, and the rubber composition constituting the cap rubber layer contains 30 parts by mass or more of silica having a nitrogen adsorption specific surface area (N2SA) of 180 m Tire / g or more per 100 parts by mass of the rubber component, and the tan δ of the rubber composition constituting the base rubber layer at 70 °C is 0.04 to 0.07. 2 A heavy-duty tire. 〔2〕In a tire meridian cross-section including a tire rotation axis, the thickness of the cap rubber layer on a normal line dropped from the end in the tire rotation axis direction of the third belt to the tread surface is Te, the distance from the third belt layer to the tread surface on the normal line is Tt2, the distance from the second belt layer to the tread surface on the normal line is Tt1, and from the tire equatorial plane to the third belt Layer layer... LayerWhen the thickness of the cap rubber layer at a position half the distance to the axial end of the tire rotation axis is Tm and the thickness of the cap rubber layer at the tire equatorial plane is Tc, the heavy load according to the above [1] satisfies the following formulas (1) to (4). For use in ear, 0.65 ≦ Te / Tt2 ≦ 0.75 ···(1) 0.60 ≦ Te / Tt1 ≦ 0.70 ···(2) 0.85 ≦ Tc / Tm ≦ 1.15 ···(3) 0.85 ≦ Tm / Te ≦ 1.15 ···(4) 〔3〕The tire for heavy loads according to the above [1] or [2], wherein 8 to 18 parts by mass of a sulfide-based silane coupling agent is contained with respect to 100 parts by mass of the silica contained in the rubber composition constituting the cap rubber layer. 〔4〕The tire according to any one of the above [1] to [3], wherein the rubber component constituting the cap rubber layer contains 65% by mass or more of an isoprene-based rubber, and the content of styrene-butadiene rubber in the total amount of 100% by mass of styrene-butadiene rubber and butadiene rubber is 50% by mass or more. For heavy load tire, 〔5〕The tire for heavy loads according to any one of the above [1] to [4], wherein the modulus at 200% elongation at 23°C of the rubber composition constituting the base rubber layer is 5.0 to 14.0 MPa is. 〔6〕The tire according to any one of the above [1] to [5], wherein the elongation at break of the rubber composition constituting the base rubber layer is 380% or more. For heavy load tire, 〔7〕The tire for heavy loads according to any one of the above 2 〕 to [6], wherein Te is smaller than Tm and Tc. 〔8〕The tire for heavy loads according to any one of the above [1] to [7], wherein the ratio (Ec’ / Eb’) of the storage elastic modulus Ec’ at 70°C of the rubber composition constituting the cap rubber layer to the storage elastic modulus Eb’ at 70°C of the rubber composition constituting the base rubber layer is 1.1 to 1.7. 〔9〕The ratio (Hm / Tt3) of the groove depth Hm of the main groove closest to the tire equatorial plane to the distance Tt3 from the tread surface in the tire equatorial plane to the outermost belt layer in the tire radial direction is 0.50 to 0.90, the heavy-duty tire according to any one of the above 〔1〕 to 〔8〕, 〔10〕The ratio (Te / Hs) of the Te to the groove depth Hs of the main groove closest to the tread end is 0.50 to 0.90, the heavy-duty tire according to any one of the above 〔 2 〕 to 〔9〕, 〔11〕The tire rotational axis direction distance Wb from the tire equatorial plane to the groove edge of the main groove closest to the tire equatorial plane with respect to the tire rotational axis direction distance Wa from the tire equatorial plane to the layer end of the outermost belt layer in the tire radial direction Ratio of (Wb / Wa) is 0.50 to 0.90, the heavy-duty tire according to any one of the above 〔1〕 to 〔10〕, 〔12〕The rubber composition constituting the cap rubber layer contains one or more selected from the group consisting of a phenol resin, a cresol resin, and a resorcinol resin, the heavy-duty tire according to any one of the above 〔1〕 to 〔11〕.

Advantages of the Invention

[0009] According to the present invention, a heavy-duty tire with well-balanced improvements in low fuel consumption performance, wet grip performance, wear resistance performance, chipping resistance performance, and tear resistance performance is provided.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0011] A heavy-duty tire according to one embodiment of the present disclosure is a heavy-duty tire having a carcass extending from a tread portion through a sidewall portion to a bead core of a bead portion, and a belt layer disposed on the outer side of the carcass in the tire radial direction and on the inner side of the tread portion, the belt layer being formed of a belt ply including a first belt layer, a second belt layer, and a third belt layer laminated in this order from the inner side in the tire radial direction, Part has a plurality of main grooves extending continuously in a tire circumferential direction, and the tread Part However, the cap rubber layer constituting the tread surface and the cap rubber layer Tire The rubber composition for the cap rubber layer has a nitrogen adsorption specific surface area (N2SA) of 180 m per 100 parts by mass of the rubber component, and the cap rubber layer and the base rubber layer are made of a rubber composition containing a rubber component, and the rubber component for the cap rubber layer contains an isoprene-based rubber, a styrene-butadiene rubber, and a butadiene rubber, and the rubber composition for the cap rubber layer has a nitrogen adsorption specific surface area (N2SA) of 180 m per 100 parts by mass of the rubber component. 2 The heavy-duty tire contains 30 parts by mass or more of silica having a silica content of 30 parts by mass or more and a silica content of 30 parts by mass or more and a tan δ at 70° C. of the rubber composition constituting the base rubber layer is 0.04 to 0.07.

[0012] Although not intended to be bound by theory, in the present disclosure, as a mechanism capable of improving the low fuel consumption performance, wet grip performance, wear resistance performance, chipping resistance performance, and tear resistance performance of a heavy load tire in a well-balanced manner, the following are considered. By setting the rubber component blended in the cap rubber layer, and the content of silica and the nitrogen adsorption specific surface area (N2SA) to a predetermined combination, silica can be highly finely dispersed, a strong silica network is formed, and it becomes possible to highly balance both the strength and elongation of the rubber composition during elongation. Further, by blending silica in the cap rubber layer, the hydrophilicity of the rubber composition is increased, and the followability to a wet road surface is improved. Furthermore, by setting the tanδ at 70° C. of the rubber composition constituting the base rubber layer to a predetermined range, the temperature rise at the belt end can be suppressed, the breakage starting from the steel filament end can be suppressed, and the decrease in the breaking strength of the base rubber layer itself can be suppressed. Thus, it is considered that the above-described physical properties of the rubber compositions constituting each layer of the tread and the structure of the tire cooperate to improve the low fuel consumption performance, wet grip performance, wear resistance performance, chipping resistance performance, and tear resistance performance in a well-balanced manner.

[0013] In the heavy load tire of the present disclosure, in the tire meridian cross section including the tire rotation axis, the third belt Layer When the thickness of the cap rubber layer on the normal line lowered from the tire rotation axis direction end to the tread surface is Te, the distance from the third belt layer to the tread surface on the normal line is Tt2, the distance from the second belt layer to the tread surface on the normal line is Tt1, and the thickness of the cap rubber layer at a position half of the distance from the tire equatorial plane to the tire rotation axis direction end of the third belt Layer is Tm, and the thickness of the cap rubber layer at the tire equatorial plane is Tc, it is preferable to satisfy the following formulas (1) to (4). 0.65 ≦ Te / Tt2 ≦ 0.75 ···(1) 0.60 ≦ Te / Tt1 ≦ 0.70 ···(2) 0.85 ≦ Tc / Tm ≦ 1.15 ···(3) 0.85 ≦ Tm / Te ≦ 1.15 ···(4)

[0014] It is preferable that the cap rubber layer contains 8 to 18 parts by mass of a sulfide - type silane coupling agent with respect to 100 parts by mass of the silica contained in the rubber composition constituting the cap rubber layer.

[0015] The rubber component constituting the cap rubber layer preferably contains 65% by mass or more of an isoprene - based rubber, and the content of styrene - butadiene rubber in the total amount of 100% by mass of styrene - butadiene rubber and butadiene rubber is 50% by mass or more.

[0016] The modulus at 200% elongation at 23°C of the rubber composition constituting the base rubber layer is preferably 5.0 to 14.0.

[0017] The elongation at break of the rubber composition constituting the base rubber layer is preferably 380% or more.

[0018] It is preferable that Te is smaller than Tm and Tc.

[0019] The ratio (Ec' / Eb') of the storage elastic modulus Ec' at 70°C of the rubber composition constituting the cap rubber layer to the storage elastic modulus Eb' at 70°C of the rubber composition constituting the base rubber layer is preferably 1.1 to 1.7.

[0020] The ratio (Hm / Tt3) of the groove depth Hm of the main groove closest to the tire equatorial plane to the distance Tt3 from the tread surface at the tire equatorial plane to the outermost belt layer in the tire radial direction is preferably 0.50 to 0.90.

[0021] The ratio (Te / Hs) of Te to the groove depth Hs of the main groove closest to the tread edge is preferably 0.50 to 0.90.

[0022] The distance Wb in the tire rotation axis direction from the tire equatorial plane to the groove edge of the main groove closest to the tire equatorial plane with respect to the distance Wa in the tire rotation axis direction from the tire equatorial plane to the layer end of the outermost belt layer in the tire radial direction Ratio of (Wb / Wa) is preferably 0.50 to 0.90.

[0023] The rubber composition constituting the cap rubber layer preferably contains one or more selected from the group consisting of a phenol resin, a cresol resin, and a resorcin resin.

[0024] The heavy-duty tire which is an embodiment of the present disclosure will be described in detail below. However, the following description is an exemplification for explaining the present disclosure, and is not intended to limit the technical scope of the present invention only to this description scope. In this specification, when a numerical range is indicated using "~", both end values thereof are included.

[0025] FIG. 1 is a cross-sectional view showing a part of a heavy-duty tire according to an embodiment of the present disclosure. In FIG. 1, the vertical direction is the radial direction of the heavy-duty tire 2, the horizontal direction is the tire axis direction of the heavy-duty tire 2, and the direction perpendicular to the paper surface is the circumferential direction of the heavy-duty tire 2. In FIG. 1, the center line CL of the heavy-duty tire 2 also represents the equatorial plane EQ of the heavy-duty tire 2. The shape of this heavy-duty tire 2 is symmetric with respect to the equatorial plane EQ except for the tread pattern.

[0026] This heavy-duty tire 2 includes a tread 4, a sidewall 6, a bead 10, a carcass 12, an inner liner 14, and a belt layer 18. The inner liner 14 is located inside the carcass 12. The tread 4 forms a tread surface 22 that contacts the road surface. A plurality of main grooves 24 extending continuously in the tire circumferential direction are formed in the tread surface 22.

[0027] The outer end in the tire rotation axis direction of the tread 4 and the vicinity thereof are referred to as the shoulder portion of the heavy-duty tire 2. In the present disclosure, hereinafter, for the sake of clarity, the portion outside the main groove 24s closest to the tread end in the tire rotation axis direction is referred to as the shoulder portion.

[0028] The bead 10 includes a bead core 32 and an apex 34 extending radially outward from the bead core 32. The bead core 32 is ring-shaped and includes a wound non-elastic wire. The apex 34 tapers outward in the tire radial direction.

[0029] The carcass 12 is composed of a carcass ply 36. The carcass ply 36 is spanned between the beads 10 on both sides and is along the tread 4 and the sidewall 6. The carcass ply 36 is folded around the bead core 32 from the inner side to the outer side in the tire rotation axis direction. The carcass ply 36 is composed of a number of parallel cords and topping rubber. The carcass 12 may be formed from two or more carcass plies 36.

[0030] The belt layer 18 extends in the tire rotation axis direction. The belt layer 18 is located inside the tread 4 in the tire radial direction. The belt layer 18 is located outside the carcass 12 in the tire radial direction and reinforces the carcass 12.

[0031] The belt layer 18 is formed of at least three belt plies including a first belt layer 18a, a second belt layer 18b, and a third belt layer 18c laminated in order from the inner side in the tire radial direction. In FIG. 1, a case where a fourth belt layer 18d is disposed outside the third belt layer 18c in the tire radial direction is shown. The first belt layer 18a is laminated on the carcass 12. In FIG. 1, in the tire rotation axis direction, the second belt layer 18b has the largest width among the four layers, and the fourth belt layer 18d has the smallest width among the four layers, but it is not limited to such a mode.

[0032] FIG. 2 is an enlarged cross-sectional view showing the vicinity of the shoulder portion of the heavy-duty tire 2 in FIG. 1. As shown in the figure, the cap rubber layer 30 extends to both outer ends of the tread 4 in the tire rotation axis direction. The covering rubber 20 covers each end of the second belt layer 18b and the third belt layer 18c.

[0033] The tread 4 includes a base rubber layer 28 and a cap rubber layer 30. The outer surface of the cap rubber layer 30 constitutes the tread surface 22, and the base rubber layer 28 is adjacent to the inner side in the tire radial direction of the cap rubber layer 30. Further, as long as the effects of the present disclosure are achieved, one or more additional rubber layers may be provided between the base rubber layer 28 and the belt layer 18.

[0034] In the present disclosure, unless otherwise specified, the dimensions and angles of each member of the tire are measured in a state where the tire is mounted on a standard rim and filled with air to a standard internal pressure. During the measurement, no load is applied to the tire. Here, the "standard rim" in this specification is the rim defined for each tire in the standard system including the standard on which the tire is based. For example, it is the standard rim in JATMA, "Design Rim" in TRA, and "Measuring Rim" in ETRTO. The "standard internal pressure" in this specification is the air pressure defined for each tire by the above standard. It is the maximum air pressure in JATMA, the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in TRA, and "INFLATION PRESSURE" in ETRTO.

[0035] In the heavy-duty tire of the present disclosure, in the tire meridian cross-section including the tire rotation axis, the thickness of the cap rubber layer 30 on the normal line N dropped from the tire rotation axis direction end of the third belt layer to the tread surface 22 is Te, the distance from the third belt layer to the tread surface 22 on the normal line N is Tt2, the distance from the second belt layer to the tread surface 22 on the normal line N is Tt1, and the thickness of the cap rubber layer 30 at a position half of the distance from the tire equatorial plane EQ to the tire rotation axis direction end of the third belt Layer is Tm, and the thickness of the cap rubber layer 30 at the tire equatorial plane EQ is Tc. It is preferable to satisfy the following formulas (1) to (4). The normal line N is a line passing through the tire rotation axis direction end of the outer surface in the tire radial direction of the third belt layer and perpendicular to the tangent line at that tire rotation axis direction end. 0.65 ≤ Te / Tt2 ≤ 0.75 ···(1) 0.60 ≤ Te / Tt1 ≤ 0.70 ···(2) 0.85 ≤ Tc / Tm ≤ 1.15 ···(3) 0.85 ≤ Tm / Te ≤ 1.15 ···(4)

[0036] When Te / Tt2 is less than 0.65, it is difficult to secure a sufficient volume of the cap rubber layer 30 to exhibit the wear resistance and chipping resistance performance of the cap rubber layer 30 in the latter stage of tire wear. Further, in the final stage of tire wear, the base rubber layer 28 is likely to be exposed on the tire surface, and there is a tendency for a decrease in tire life and uneven wear to occur. On the other hand, when Te / Tt2 exceeds 0.75, due to the insufficient volume of the base rubber layer 28 in the shoulder portion, the temperature during running in the vicinity of the tire rotation axis direction end of the third belt layer from the tire rotation axis direction end of the second belt layer tends to rise, and the effect of suppressing the adhesive failure between the steel filament and the rubber at the tire rotation axis direction end of the third belt layer is reduced. The adhesive failure at the tire rotation axis direction end of the third belt layer may be a breakage inside the rubber between the second belt layer and the third belt layer and progress toward the tire equator plane, resulting in damage to the entire tire. Also, for the same reason, Te and Tt1 preferably satisfy the above formula (2).

[0037] Also, Te, Tt1, and Tt2 preferably satisfy the following formula (5). 0.20 ≤ (Te / Tt2) - (Te / Tt1) ≤ 0.70 ···(5)

[0038] When (Te / Tt2) - (Te / Tt1) is less than 0.20, it becomes difficult to relieve the shear between the tire rotation axis direction end of the second belt layer and the tire rotation axis direction end of the third belt layer accompanying the shape change of the tread portion during running, and there is a tendency for it to be difficult to suppress the above-mentioned breakage. Also, when (Te / Tt2) - (Te / Tt1) exceeds 0.70, the distance between the tire rotation axis direction end of the second belt layer and the tire rotation axis direction end of the third belt layer becomes too large, and there is a tendency for it to be difficult to maintain an appropriate tread shape.

[0039] From the perspective of the tire performance balance after the late wear stage, it is preferable that the thickness distribution of the cap rubber layer 30 satisfies the above formulas (3) and (4).

[0040] The ratio (Hm / Tt3) of the groove depth Hm of the main groove 24m closest to the tire equatorial plane to the distance Tt3 from the tread surface at the tire equatorial plane to the outermost belt layer in the tire radial direction (the fourth belt layer 18d in FIG. 1) is preferably 0.50 or more, more preferably 0.55 or more, and even more preferably 0.60 or more. Also, Hm / Tt3 is preferably 0.90 or less, more preferably 0.85 or less, and even more preferably 0.80 or less. By setting Hm / Tt3 within the above range, the chipping resistance performance can be further improved.

[0041] The ratio (Te / Hs) of the above Te to the groove depth Hs of the main groove 24s closest to the tread edge is preferably 0.50 or more, more preferably 0.55 or more, and even more preferably 0.60 or more. Also, Te / Hs is preferably 0.90 or less, more preferably 0.85 or less, and even more preferably 0.80 or less. Further, it is preferable that Te is smaller than Tm and Tc. By disposing the low heat - generating base rubber layer 28 in the shoulder portion 26, which is a portion with large strain and large heat generation, the overall heat generation of the tread 4 can be reduced. Therefore, the amount of the base rubber layer 28 near the tire equatorial plane can be decreased, and accordingly, the situation where the base rubber layer 28 contacts the road surface at the end of wear can be suppressed, and the chipping resistance performance can be maintained.

[0042] The distance Wb in the tire rotational axis direction from the tire equatorial plane to the groove edge of the main groove closest to the tire equatorial plane with respect to the distance Wa in the tire rotational axis direction from the tire equatorial plane to the layer end of the outermost belt layer in the tire radial direction (the fourth belt layer 18d in FIG. 1) Ratio of (Wb / Wa) is preferably 0.50 or more, more preferably 0.55 or more, and even more preferably 0.60 or more. Also, Wb / Wa is preferably 0.90 or less, more preferably 0.85 or less, and even more preferably 0.80 or less. By setting Wb / Wa within the above range, the chipping resistance performance can be further improved.

[0043] "70°C E'" in the present disclosure refers to the storage modulus (MPa) δ 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. From the perspective of chipping resistance performance, the ratio (Ec' / Eb') of the storage modulus Ec' at 70°C of the rubber composition constituting the cap rubber layer 30 to the storage modulus Eb' at 70°C of the rubber composition constituting the base rubber layer 28 is preferably 1.1 to 1.7, more preferably 1.1 to 1.6, still more preferably 1.2 to 1.5, and particularly preferably 1.2 to 1.4. The 70°C E' of the rubber composition constituting the cap rubber layer 30 is preferably 4.4 to 11.0 MPa, more preferably 5.4 to 10.0 MPa, and still more preferably 6.0 to 9.5 MPa. Further, the 70°C E' of the rubber composition constituting the base rubber layer 28 is preferably 4.0 to 6.5 MPa, more preferably 4.5 to 6.3 MPa, and still more preferably 5.0 to 6.1 MPa. Note that the 70°C E' of each rubber layer can be appropriately adjusted by the types and blending amounts of the rubber component, filler, silane coupling agent, softening agent, etc.

[0044] "70°C tanδ" in the present disclosure refers to the loss tangent tanδ 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. The 70°C tanδ of the rubber composition constituting the base rubber layer 28 is 0.04 or more, preferably 0.05 or more. When the 70°C tanδ of the rubber composition constituting the base rubber layer 28 is less than 0.04, the breaking strength of the base rubber blend itself is significantly reduced, and there is a concern about tear generation due to the breakage of the base rubber itself. On the other hand, the 70°C tanδ of the rubber composition constituting the base rubber layer 28 is 0.07 or less, preferably 0.06 or less, from the perspective of suppressing the temperature rise at the belt end and suppressing the breakage starting from the steel filament end. Further, from the perspective of better exerting the effect of improving fuel efficiency, the value of the 70°C tanδ of the rubber composition constituting the cap rubber layer 30 is preferably greater than the value of the 70°C tanδ of the rubber composition constituting the base rubber layer 28. Note that the 70°C tanδ of each rubber layer can be appropriately adjusted by the types and blending amounts of the rubber component, filler, silane coupling agent, softening agent, etc.

[0045] The modulus at 200% elongation in the present disclosure refers to the tensile stress at 100% elongation in the machine direction, measured at a tensile speed of 3.3 mm / sec under a 23°C atmosphere in accordance with JIS K 6251:2017. From the viewpoint of ensuring the rigidity of the tread portion and suppressing uneven wear, the modulus at 200% elongation of the base rubber layer 28 is preferably 5.0 MPa or more, more preferably 5.5 MPa or more, still more preferably 6.0 MPa or more, and particularly preferably 6.5 MPa or more. On the other hand, the modulus at 200% elongation of the base rubber layer 28 is preferably 14.0 MPa or less, more preferably Below 13.5 MPa or more, still more preferably 13.0 MPa or less, and particularly preferably 12.5 MPa or less. When the modulus at 200% elongation of the base rubber layer 28 exceeds 14.0 MPa, it is difficult for external forces to escape, and there is a concern that crack propagation may occur at the interface due to the concentration of input at the interface between the cap rubber layer 30 and the base rubber layer 28. Further, the modulus at 200% elongation of the cap rubber layer 30 is preferably greater than the modulus at 200% elongation of the base rubber layer 28. In the present specification, the "machine direction" means the rolling direction when forming a rubber sheet by extrusion or shearing treatment.

[0046] The elongation at break (EB) in the present disclosure refers to the elongation at break (elongation at cut) measured at a tensile speed of 3.3 mm / sec under a 23°C atmosphere in accordance with JIS K 6251:2017. From the viewpoint of maintaining the smoothness of the surface, the EB of the cap rubber layer 30 is preferably 400% or more, more preferably 420% or more. Further, from the viewpoint of suppressing breakage inside the rubber between the second belt layer 18b and the third belt layer 18c, the EB of the base rubber layer 28 is preferably 380% or more, more preferably 400% or more. Note that the upper limit value of the EB of the rubber composition constituting the cap rubber layer 30 and the base rubber layer 28 is not particularly limited.

[0047] Note that the modulus and EB at 200% elongation of each rubber layer can be appropriately adjusted by the types and blending amounts of the above-mentioned rubber components, fillers, silane coupling agents, softening agents, etc.

[0048] [Rubber composition] The heavy-duty tire of the present disclosure can improve the low fuel consumption performance, wet grip performance, abrasion resistance performance, chipping resistance performance, and tear resistance performance in a well-balanced manner by the cooperation of the above-described tire structure and the above-described physical properties of the rubber composition constituting each layer of the tread.

[0049] [Rubber component] The rubber composition (tread rubber composition) constituting each rubber layer of the tread according to the present disclosure preferably contains at least one selected from the group consisting of isoprene rubber, styrene-butadiene rubber (SBR), and butadiene rubber (BR) as a rubber component. The rubber component constituting the cap rubber layer 30 may include isoprene rubber, SBR, and BR, and may be a rubber component consisting only of isoprene rubber, SBR, and BR. The rubber component constituting the base rubber layer 28 preferably includes isoprene rubber, and may be a rubber component consisting only of isoprene rubber.

[0050] [Isoprene rubber] As the isoprene rubber, for example, those generally used in the tire industry such as isoprene rubber (IR) and natural rubber can be used. Natural rubber includes, in addition to unmodified natural rubber (NR), modified natural rubbers such as epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), deproteinized natural rubber (DPNR), high-purity natural rubber (UPNR), and grafted natural rubber. These isoprene rubbers may be used alone or in combination of two or more.

[0051] NR is not particularly limited, and those generally used in the tire industry can be used, and examples thereof include SIR20, RSS#3, and TSR20.

[0052] In the rubber composition constituting the cap rubber layer 30, the content in the rubber component of the isoprene rubber is preferably 50% by mass or more, more preferably 55% by mass or more, still more preferably 60% by mass or more, and particularly preferably 65% by mass or more. Since silica has good compatibility with the isoprene rubber, by increasing the content in the rubber component of the isoprene rubber and dispersing silica in the isoprene rubber phase that becomes the sea phase, the strength of the entire matrix is improved, and the abrasion resistance performance and fracture characteristics tend to be further improved. On the other hand, from the viewpoint of wet grip performance, 95% by mass or less is preferable, 90% by mass or less is more preferable, 85% by mass or less is still more preferable, and 80% by mass or less is particularly preferable.

[0053] In the rubber composition constituting the base rubber layer 28, the content in the rubber component of the isoprene rubber is preferably 85% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, and it may also be a rubber component consisting only of isoprene rubber.

[0054] (SBR) The rubber composition constituting the cap rubber layer 30 contains SBR as a rubber component. By blending SBR, the wet grip performance and chipping resistance are significantly improved. The reasons for this are considered to be that SBR has excellent viscoelastic properties in a region highly correlated with wet grip performance, and the modulus (stress) at large deformation is higher than that of BR etc. Also, since SBR has excellent compatibility and reactivity with silica, it is considered to be effective in silica dispersion and the immobilization of silica to the polymer.

[0055] There are no particular limitations on the SBR, and examples thereof include solution-polymerized SBR (S-SBR), emulsion-polymerized SBR (E-SBR), and modified SBRs thereof (modified S-SBR, modified E-SBR). Examples of the modified SBR include SBRs with modified terminals and / or main chains, and modified SBRs coupled with tin, silicon compounds, etc. (condensates, those having a branched structure, etc.). Among these, E-SBR is preferred from the viewpoint of being able to well improve low fuel consumption performance and wear resistance performance. These SBRs may be used alone or in combination of two or more.

[0056] From the viewpoints of wet grip performance and wear resistance performance, the styrene content of the SBR is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more. Also, from the viewpoints of the temperature dependence of grip performance and wear resistance performance, it is preferably 25% by mass or less, and more preferably 24% by mass or less. In this specification, the styrene content of the SBR is 1 calculated by 1H-NMR measurement.

[0057] From the viewpoints of ensuring reactivity with silica, rubber strength, and wear resistance performance, the vinyl content of the SBR is preferably 10 mol% or more, more preferably 13 mol% or more, and even more preferably 16 mol% or more. Also, from the viewpoints of preventing an increase in temperature dependence, wet grip performance, elongation at break, and wear resistance performance, the vinyl content of the SBR is preferably 45 mol% or less, more preferably 40 mol% or less, and even more preferably 35 mol% or less. In this specification, the vinyl content (amount of 1,2-bonded butadiene units) of the SBR is measured by infrared absorption spectroscopy analysis.

[0058] From the viewpoint of wet grip performance, the glass transition point (Tg) of the SBR is preferably -80°C or higher, and more preferably -70°C or higher. Also, from the viewpoint of low fuel consumption performance, the Tg of the SBR is preferably -40°C or lower, and more preferably -45°C or lower. In this specification, the Tg of the SBR complies with JIS K 6229. After removing the extender oil using acetone, the pure SBR content is determined by differential scanning calorimetry (DSC) in accordance with JIS K 7121.

[0059] From the perspective of abrasion resistance performance, the weight average molecular weight (Mw) of SBR is preferably 200,000 or more, more preferably 300,000 or more, and even more preferably 500,000 or more. Also, from the perspective of crosslinking uniformity and the like, Mw is preferably 2.5 million or less, and more preferably 2 million or less. Note that Mw can be determined by standard polystyrene conversion based on the measured value by gel permeation chromatography (GPC) (for example, GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMALTIPORE HZ-M manufactured by Tosoh Corporation).

[0060] From the perspective of chipping resistance performance and wet grip performance, the content in the rubber component when containing SBR is preferably 10% by mass or more, more preferably 12% by mass or more, even more preferably 15% by mass or more, and particularly preferably 18% by mass or more. Also, from the perspective of abrasion resistance performance, it is preferably 30% by mass or less, more preferably 27% by mass or less, and even more preferably 25% by mass or less.

[0061] (BR) The rubber composition constituting the cap rubber layer 30 contains BR as a rubber component. Since isoprene rubber and SBR are incompatible, further blending of BR can make SBR and BR compatible, and by lowering the glass transition point (Tg) of the rubber composition, it is considered that the fracture characteristics and abrasion resistance performance can be further improved.

[0062] BR is not particularly limited. For example, BR with a cis content of less than 50% by mass (low cis BR), BR with a cis content of 90% by mass or more (high cis BR), rare earth-based butadiene rubber synthesized using a rare earth element-based catalyst (rare earth-based BR), BR containing syndiotactic polybutadiene crystals (SPB-containing BR), modified BR (high cis modified BR, low cis modified BR), etc., which are common in the tire industry, can be used. These BRs can be used alone or in combination of two or more.

[0063] As the high-cis BR, for example, those commercially available from Nippon Zeon Co., Ltd., Ube Industries, Ltd., JSR Corporation, etc. can be used. By containing high-cis BR, the wear resistance performance can be improved. The cis content is preferably 95% by mass or more, more preferably 96% by mass or more, still more preferably 97% by mass or more, and particularly preferably 98% by mass or more. In this specification, the cis content (amount of cis-1,4-bonded butadiene units) is a value calculated by infrared absorption spectroscopy.

[0064] As the rare earth-based BR, it is synthesized using a rare earth element-based catalyst, the vinyl content is preferably 1.8 mol% or less, more preferably 1.0 mol% or less, still more preferably 0.8 mol% or less, and the cis content is preferably 95% by mass or more, more preferably 96% by mass or more, still more preferably 97% by mass or more, and particularly preferably 98% by mass or more. As the rare earth-based BR, for example, those commercially available from Lanxess Co., Ltd., etc. can be used.

[0065] The SPB-containing BR is not simply one in which 1,2-syndiotactic polybutadiene crystals are dispersed in BR, but one in which they are dispersed after chemically bonding to BR. As such SPB-containing BR, those commercially available from Ube Industries, Ltd., etc. can be used.

[0066] As the modified BR, it can be obtained by polymerizing 1,3-butadiene with a lithium initiator and then adding a tin compound, and further those in which the ends of the modified BR molecules are bonded by tin-carbon bonds (tin-modified BR), butadiene rubbers having a condensed alkoxysilane compound at the active ends of the butadiene rubber (modified BR for silica), etc. can be mentioned. As such modified BR, for example, BR1250H (tin-modified) manufactured by ZS Elastomer Co., Ltd., S-modified polymer (modified for silica), etc. can be mentioned.

[0067] The weight average molecular weight (Mw) of BR is preferably 300,000 or more, more preferably 350,000 or more, and even more preferably 400,000 or more from the viewpoints of abrasion resistance and grip performance. Further, from the viewpoint of crosslinking uniformity, etc., it is preferably 2,000,000 or less, and more preferably 1,000,000 or less. Note that Mw can be determined by standard polystyrene conversion based on the measured value by gel permeation chromatography (GPC) (for example, GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMALTIPORE HZ-M manufactured by Tosoh Corporation).

[0068] The content in the rubber component of BR is preferably 5% by mass or more, more preferably 8% by mass or more, even more preferably 10% by mass or more, and particularly preferably 12% by mass or more from the viewpoint of abrasion resistance performance. Further, from the viewpoint of wet grip performance, it is preferably 25% by mass or less, more preferably 22% by mass or less, even more preferably 20% by mass or less, and particularly preferably 17% by mass or less.

[0069] The content of SBR in 100% by mass of the total amount of SBR and BR is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, and particularly preferably 55% by mass or more from the viewpoint of wet grip performance. Further, from the viewpoint of the compatibility of the rubber component, it is preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 85% by mass or less, and particularly preferably 80% by mass or less.

[0070] (Other rubber components) As the rubber component according to the present disclosure, a rubber component other than the above-mentioned isoprene rubber, SBR, and BR may be contained. As other rubber components, crosslinkable rubber components generally used in the tire industry can be used. For example, styrene-isoprene-butadiene copolymer rubber (SIBR), styrene-isobutylene-styrene block copolymer (SIBS), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), hydrogenated nitrile rubber (HNBR), butyl rubber (IIR), ethylene propylene rubber, polynorbornene rubber, silicone rubber, chlorinated polyethylene rubber, fluororubber (FKM), acrylic rubber (ACM), hydrin rubber, etc. can be mentioned. These other rubber components may be used alone or in combination of two or more.

[0071] <Filler> The tread rubber composition according to the present disclosure preferably contains a filler containing carbon black and / or silica. Further, the filler may be a filler consisting only of carbon black and silica. The rubber composition constituting the cap rubber layer 30 preferably contains silica as a filler, more preferably contains carbon black and silica, and may be a filler consisting only of carbon black and silica. The rubber composition constituting the base rubber layer 28 preferably contains carbon black as a filler, more preferably contains carbon black and silica, and may be a filler consisting only of carbon black and silica.

[0072] (Silica) By blending silica into the tread rubber composition according to the present disclosure, low fuel consumption performance, wet grip performance, wear resistance performance, and chipping resistance performance can be improved. The silica is not particularly limited, and for example, silica prepared by a dry method (anhydrous silica), silica prepared by a wet method (hydrous silica), etc., which are common in the tire industry, can be used. Among them, hydrous silica prepared by a wet method is preferred because it has many silanol groups. These silicas may be used alone or in combination of two or more.

[0073] The nitrogen adsorption specific surface area (N2SA) of silica is 180 m 2 / g or more from the viewpoints of abrasion resistance performance and fracture characteristics, preferably 185 m 2 / g or more, more preferably 190 m 2 / g or more, and even more preferably 200 m 2 / g or more. Also, from the viewpoints of low fuel consumption performance and processability, it is preferably 350 m 2 / g or less, more preferably 300 m 2 / g or less, and even more preferably 250 m 2 / g or less. Note that the N2SA of silica in this specification is a value measured by the BET method in accordance with ASTM D3037-93.

[0074] The rubber composition constituting the cap rubber layer 30 contains 30 parts by mass or more of silica with respect to 100 parts by mass of the rubber component from the viewpoint of the balance between low fuel consumption performance and wet grip performance. In the rubber composition constituting the cap rubber layer 30, the content of silica with respect to 100 parts by mass of the rubber component is preferably 35 parts by mass or more, more preferably 40 parts by mass or more, and even more preferably 45 parts by mass or more. Also, from the viewpoint of suppressing the deterioration of low fuel consumption performance and abrasion resistance performance due to the deterioration of the dispersibility of silica in the rubber, it is preferably 150 parts by mass or less, more preferably 130 parts by mass or less, and even more preferably 110 parts by mass or less.

[0075] In the rubber composition constituting the base rubber layer 28, the content of silica with respect to 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more. Also, from the viewpoints of low fuel consumption performance and abrasion resistance performance, it 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.

[0076] (Carbon black) The carbon black is not particularly limited, and for example, those common in the tire industry such as GPF, FEF, HAF, ISAF, SAF, etc. can be used. These carbon blacks may be used alone or in combination of two or more.

[0077] From the viewpoints of weather resistance and reinforcing property, the nitrogen adsorption specific surface area (N2SA) of the carbon black is preferably 50 m 2 / g or more, more preferably 80 m 2 / g or more, and even more preferably 100 m 2 / g or more. Also, from the viewpoints of dispersibility, low fuel consumption performance, fracture characteristics and durability, it is preferably 250 m 2 / g or less, and more preferably 220 m 2 / g or less. The N2SA of the carbon black in this specification is a value measured according to Method A of JIS K 6217-2 "Basic properties of carbon black for rubber - Part 2: Method for determining specific surface area - Nitrogen adsorption method - Single point method".

[0078] In the rubber composition constituting the cap rubber layer 30, the content of the carbon black relative to 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more from the viewpoints of weather resistance and reinforcing property. Also, from the viewpoint of low fuel consumption performance, it 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.

[0079] In the rubber composition constituting the base rubber layer 28, the content of the carbon black relative to 100 parts by mass of the rubber component is preferably 5 parts by mass or more, more preferably 15 parts by mass or more, and even more preferably 25 parts by mass or more from the viewpoint of reinforcing property. Also, from the viewpoint of low fuel consumption performance, it is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, and even more preferably 40 parts by mass or less.

[0080] As fillers other than silica and carbon black, for example, those common in the tire industry such as aluminum hydroxide, calcium carbonate, alumina, clay, talc, etc. can be used.

[0081] In the rubber composition constituting the cap rubber layer 30, the content of silica in a total of 100% by mass of silica and carbon black is preferably 40% by mass or more, more preferably 50% by mass or more, still more preferably 55% by mass or more, and particularly preferably 60% by mass or more. Further, the content of the silica is preferably 99% by mass or less, more preferably 97% by mass or less, and still more preferably 95% by mass or less.

[0082] In the rubber composition constituting the base rubber layer 28, the content of silica in a total of 100% by mass of silica and carbon black is preferably 5% by mass or more, and more preferably 10% by mass or more. Further, the content of the silica is preferably 30% by mass or less, and more preferably 25% by mass or less.

[0083] In the rubber composition constituting the cap rubber layer 30, the total content of silica and carbon black with respect to 100 parts by mass of the rubber component is preferably 40 parts by mass or more, more preferably 50 parts by mass or more, and still more preferably 55 parts by mass or more from the viewpoint of wear resistance performance. Further, from the viewpoint of suppressing the deterioration of low fuel consumption performance and wear resistance performance, it is preferably 180 parts by mass or less, more preferably 160 parts by mass or less, and still more preferably 140 parts by mass or less.

[0084] In the rubber composition constituting the base rubber layer 28, the total content of silica and carbon black with respect to 100 parts by mass of the rubber component is preferably 20 parts by mass or more, more preferably 30 parts by mass or more, and still more preferably 40 parts by mass or more. Further, the content is preferably 70 parts by mass or less, more preferably 60 parts by mass or less, and still more preferably 50 parts by mass or less.

[0085] (Silane coupling agent) Silica is preferably used in combination with a silane coupling agent. The silane coupling agent is not particularly limited, and in the tire industry, any silane coupling agent that has been conventionally used in combination with silica can be used. For example, mercapto-based silane coupling agents such as 3-mercaptopropyltrimethoxysilane, NXT-Z100, NXT-Z45, and NXT manufactured by Momentive; sulfide-based silane coupling agents such as bis(3-triethoxysilylpropyl)disulfide and bis(3-triethoxysilylpropyl)tetrasulfide; thioester-based silane coupling agents such as 3-octanoylthio-1-propyltriethoxysilane, 3-hexanoylthio-1-propyltriethoxysilane, and 3-octanoylthio-1-propyltrimethoxysilane; 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; chloro-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 sulfide-based silane coupling agents are more preferred. These silane coupling agents may be used alone or in combination of two or more.

[0086] From the viewpoint of enhancing the dispersibility of silica, the content of the silane coupling agent (preferably a sulfide-based silane coupling agent) relative to 100 parts by mass of the rubber component is preferably 0.5 part by mass or more, more preferably 1.0 part by mass or more, still more preferably 2.0 parts by mass or more, and particularly preferably 4.0 parts by mass or more. Also, from the viewpoint of preventing a decrease in wear resistance performance, it is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and still more preferably 10 parts by mass or less.

[0087] From the viewpoint of enhancing the dispersibility of silica, the content of the silane coupling agent (preferably a sulfide-based silane coupling agent) relative to 100 parts by mass of silica is preferably 1 part by mass or more, more preferably 3 parts by mass or more, still more preferably 5 parts by mass or more, and particularly preferably 8 parts by mass or more. Further, from the viewpoints of cost and processability, it is preferably 20 parts by mass or less, more preferably 18 parts by mass or less, and still more preferably 16 parts by mass or less.

[0088] <Other compounding agents> In addition to the above components, the rubber composition according to the present disclosure may appropriately contain compounding agents generally used in the conventional tire industry, such as softeners, waxes, processing aids, stearic acid, zinc oxide, anti-aging agents, vulcanizing agents, vulcanization accelerators, and the like.

[0089] Examples of the softener include resin components, oils, liquid rubbers, and the like.

[0090] The resin component is not particularly limited, and examples thereof include petroleum resins, terpene resins, rosin resins, phenolic resins, cresol resins, resorcinol resins, etc. commonly used in the tire industry. Among them, one or more selected from the group consisting of phenolic resins, cresol resins, and resorcinol resins are preferred. These resin components may be used alone or in combination of two or more.

[0091] The phenolic resin is not particularly limited, and examples thereof include phenol formaldehyde resins, alkylphenol formaldehyde resins, alkylphenol acetylene resins, oil-modified phenol formaldehyde resins, etc.

[0092] When contained, the content relative to 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and still more preferably 5 parts by mass or more from the viewpoint of wet grip performance. From the viewpoint of suppressing heat generation, it is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, still more preferably 40 parts by mass or less, and particularly preferably 30 parts by mass or less.

[0093] Examples of the oil include process oil, vegetable oil and animal oil. Examples of the process oil include paraffinic process oil, naphthenic process oil, aromatic process oil and the like. Further, a process oil having a low content of polycyclic aromatic compound (PCA) can also be used for environmental measures. Examples of the low-PCA content process oil include mildly extracted solvent solvate (MES), treated distillate aromatic extract (TDAE), heavy naphthenic oil and the like.

[0094] When contained, the content relative to 100 parts by mass of the rubber component is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and still more preferably 15 parts by mass or more from the viewpoint of processability. From the viewpoint of wear resistance performance, it is preferably 120 parts by mass or less, more preferably 100 parts by mass or less, still more preferably 90 parts by mass or less. In the present specification, the oil content also includes the amount of oil contained in the oil-extended rubber.

[0095] The liquid rubber is not particularly limited as long as it is a polymer in a liquid state at normal temperature (25°C). Examples thereof include liquid butadiene rubber (liquid BR), liquid styrene-butadiene rubber (liquid SBR), liquid isoprene rubber (liquid IR), liquid styrene-isoprene rubber (liquid SIR), liquid farnesene rubber and the like. These liquid rubbers may be used alone or in combination of two or more.

[0096] When containing liquid rubber, the content relative to 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 2 parts by mass or more, still more preferably 3 parts by mass or more, and particularly preferably 5 parts by mass or more. Also, the content of the liquid rubber is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and still more preferably 20 parts by mass or less.

[0097] When containing wax, the content relative to 100 parts by mass of the rubber component is preferably 0.5 part by mass or more, more preferably 1 part by mass or more, from the viewpoint of the weather resistance of the rubber. Also, from the viewpoint of preventing whitening of the tire due to blooming, it is preferably 10 parts by mass or less, more preferably 5 parts by mass or less.

[0098] Examples of the processing aid include fatty acid metal salts, fatty acid amides, amide esters, silica surfactants, fatty acid esters, mixtures of fatty acid metal salts and amide esters, mixtures of fatty acid metal salts and fatty acid amides, and the like. These processing aids may be used alone or in combination of two or more. As the processing aid, for example, those commercially available from Schill + Seilacher, Performance Additives, etc. can be used.

[0099] When containing a processing aid, the content relative to 100 parts by mass of the rubber component is preferably 0.5 part by mass or more, more preferably 1 part by mass or more, from the viewpoint of exerting the effect of improving processability. Also, from the viewpoints of abrasion resistance and breaking strength, it is preferably 10 parts by mass or less, more preferably 8 parts by mass or less.

[0100] The anti-aging agent is not particularly limited. For example, there are anti-aging agents such as amine-based, quinoline-based, quinone-based, phenol-based, imidazole-based compounds, and metal carbamates. Preferred are phenylenediamine-based anti-aging agents such as N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, N,N'-diphenyl-p-phenylenediamine, N,N'-di-2-naphthyl-p-phenylenediamine, N-cyclohexyl-N'-phenyl-p-phenylenediamine, and quinoline-based anti-aging agents such as 2,2,4-trimethyl-1,2-dihydroquinoline polymer, 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline. These anti-aging agents may be used alone or in combination of two or more.

[0101] When containing an anti-aging agent, the content based on 100 parts by mass of the rubber component is preferably 0.5 part by mass or more, more preferably 1 part by mass or more, from the viewpoint of ozone crack resistance of the rubber. Also, from the viewpoints of abrasion resistance performance and wet grip performance, it is preferably 10 parts by mass or less, more preferably 5 parts by mass or less.

[0102] When containing stearic acid, the content based on 100 parts by mass of the rubber component is preferably 0.5 part by mass or more, more preferably 1 part by mass or more, from the viewpoint of processability. Also, from the viewpoint of vulcanization rate, it is preferably 10 parts by mass or less, more preferably 5 parts by mass or less.

[0103] When containing zinc oxide, the content based on 100 parts by mass of the rubber component is preferably 0.5 part by mass or more, more preferably 1 part by mass or more, from the viewpoint of processability. Also, from the viewpoint of abrasion resistance performance, it is preferably 10 parts by mass or less, more preferably 5 parts by mass or less.

[0104] Sulfur is preferably used as the vulcanizing agent. As sulfur, powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersed sulfur, etc. can be used.

[0105] When sulfur is contained as a vulcanizing agent, the content thereof relative to 100 parts by mass of the rubber component is preferably 0.1 part by mass or more, more preferably 0.3 part by mass or more, and still more preferably 0.5 part by mass or more from the viewpoint of ensuring a sufficient vulcanization reaction. Further, from the viewpoint of deterioration prevention, it is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and still more preferably 3.0 parts by mass or less. In addition, when oil-containing sulfur is used as the vulcanizing agent, the content of the vulcanizing agent is the total content of the pure sulfur component contained in the oil-containing sulfur.

[0106] Examples of vulcanizing agents other than sulfur include alkylphenol sulfur chloride condensates, sodium 1,6-hexamethylene-dithiolsulfate dihydrate, 1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane, and the like. As these vulcanizing agents other than sulfur, those commercially available from Taoka Chemical Industry Co., Ltd., Rancess Co., Ltd., Flexsys Co., Ltd., etc. can be used.

[0107] Examples of vulcanization accelerators include sulfenamide-based, thiazole-based, thiuram-based, thiourea-based, guanidine-based, dithiocarbamic acid-based, aldehyde-amine-based or aldehyde-ammonia-based, imidazoline-based, or xanthate-based vulcanization accelerators. These vulcanization accelerators may be used alone or in combination of two or more. Among them, one or more vulcanization accelerators selected from the group consisting of sulfenamide-based, guanidine-based, and thiazole-based vulcanization accelerators are preferred.

[0108] Examples of sulfenamide-based vulcanization accelerators include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N,N-dicyclohexyl-2-benzothiazolylsulfenamide (DCBS), and the like. Among them, N-tert-butyl-2-benzothiazolylsulfenamide (TBBS) is preferred.

[0109] Examples of guanidine vulcanization accelerators include 1,3-diphenylguanidine (DPG), 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, the di-o-tolylguanidine salt of dicatecholborate, 1,3-di-o-cumenylguanidine, 1,3-di-o-biphenylguanidine, 1,3-di-o-cumenyl-2-propionylguanidine, and the like. Among them, 1,3-diphenylguanidine (DPG) is preferred.

[0110] Examples of thiazole vulcanization accelerators include 2-mercaptobenzothiazole, the cyclohexylamine salt of 2-mercaptobenzothiazole, di-2-benzothiazolyldisulfide, and the like. Among them, 2-mercaptobenzothiazole is preferred.

[0111] When the vulcanization accelerator is contained, the content thereof per 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 2 parts by mass or more. Also, the content of the vulcanization accelerator per 100 parts by mass of the rubber component is preferably 8 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 6 parts by mass or less. By setting the content of the vulcanization accelerator within the above range, the breaking strength and elongation tend to be ensured.

[0112] The rubber composition according to the present disclosure can be produced by a known method. For example, it can be produced by kneading the above-mentioned respective components using a rubber kneading device such as an open roll or a closed kneader (Banbury mixer, kneader, etc.).

[0113] The kneading process includes, for example, a base kneading process of kneading compounding agents and additives other than the vulcanizing agent and the vulcanization accelerator, and a final kneading (F kneading) process of adding the vulcanizing agent and the vulcanization accelerator to the kneaded product obtained in the base kneading process and kneading them. Further, the base kneading process can be divided into a plurality of processes if desired.

[0114] Although the kneading conditions are not particularly limited, for example, in the base kneading step, kneading is performed at a discharge temperature of 150 to 170°C for 3 to 10 minutes, and in the final kneading step, kneading is performed at 70 to 110°C for 1 to 5 minutes. The vulcanization conditions are not particularly limited, and for example, a method of vulcanizing at 150 to 200°C for 10 to 30 minutes can be mentioned.

[0115] [Tire] A heavy-duty tire provided with a tread including a cap rubber layer 30 and a base rubber layer 28 can be manufactured by a normal method using the above rubber composition. That is, an unvulcanized rubber composition in which each of the above components is blended with respect to the rubber component as necessary is extruded into the shapes of the cap rubber layer 30 and the base rubber layer 28 using an extruder equipped with a die of a predetermined shape, and is bonded together with other tire members on a tire molding machine and molded by a normal method to form an unvulcanized tire. By heating and pressurizing this unvulcanized tire in a vulcanizer, a heavy-duty tire can be manufactured.

[0116] The heavy-duty tire according to the present disclosure is excellent in wear resistance and chipping resistance, and is suitable for traveling on rough road surfaces (unpaved and rough road surfaces).

Example

[0117] Hereinafter, the present disclosure will be described based on examples, but the present disclosure is not limited only to these examples.

[0118] Hereinafter, various chemicals used in the examples and comparative examples are collectively shown. NR: TSR20 SBR: SBR1502 (E-SBR, styrene content: 23.5% by mass, vinyl content: 18 mol%, Mw: 420,000) manufactured by JSR Corporation BR: UBEPOL BR (registered trademark) 150B (cis content: 97% by mass, Mw: 440,000) manufactured by Ube Industries, Ltd. Carbon black 1: Diamond Black N220 (N2SA: 115 m 2 / g) manufactured by Mitsubishi Chemical Corporation Carbon black 2: Diablack N134 manufactured by Mitsubishi Chemical Corporation (N2SA: 148 m 2 / g) Silica 1: Ultrasil VN3 manufactured by Evonik Degussa (N2SA: 175 m 2 / g, average primary particle size: 18 nm) Silica 2: Ultrasil 9100GR manufactured by Evonik Degussa (N2SA: 230 m 2 / g, average primary particle size: 15 nm) Silane coupling agent: Si266 (bis(3-triethoxysilylpropyl)disulfide) manufactured by Evonik Degussa Antioxidant: Nocrack 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Stearic acid: Bead stearic acid Tsubaki manufactured by NOF Corporation Zinc oxide: Zinc white No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: Powder sulfur manufactured by Karuizawa Sulfur Co., Ltd. Vulcanization accelerator 1: Nocceler CZ (N-cyclohexyl-2-benzothiazolylsulfenamide (CBS)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator 2: Nocceler D (1,3-diphenylguanidine (DPG)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0119] (Examples and Comparative Examples) According to the compounding formulations shown in Table 1 and Table 2, using a 1.7 L sealed Banbury mixer, chemicals other than sulfur and vulcanization accelerators were kneaded for 1 - 10 minutes until the discharge temperature reached 150 - 160 °C to obtain a kneaded product. Next, using a twin - screw open roll, sulfur and vulcanization accelerators were added to the obtained kneaded product and kneaded for 4 minutes until the temperature reached 105 °C to obtain an unvulcanized rubber composition. Using the obtained unvulcanized rubber composition, it was extruded into the shapes of the cap rubber layer and the base rubber layer using an extruder equipped with a die of a predetermined shape, and bonded together with other tire members to produce an unvulcanized tire whose tread portion consisted of the above - mentioned two rubber layers. By press - vulcanizing at 170 °C for 12 minutes, each test tire (12R22.5, truck - bus tire) described in Table 3 and Table 4 was manufactured.

[0120] The following evaluations were carried out on the obtained test tires. The evaluation results are shown in Table 3 and Table 4.

[0121] <Viscoelasticity test> Vulcanized rubber was sampled from the cap rubber layer and the base rubber layer of each test tire, cut into pieces with a width of 4 mm, a length of 40 mm, and a thickness of 2 mm, and using a viscoelastic spectrometer manufactured by Iwamoto Seisakusho Co., Ltd., the storage elastic modulus E’ (MPa) and the loss tangent (tanδ) were measured 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.

[0122] <Tensile test> From the base rubber layer of each test tire, a dumbbell - shaped No. 7 test piece with a thickness of 1 mm was cut out so that the tire circumferential direction was the tensile direction, and in accordance with JIS K 6251:2017, a tensile test was carried out under the conditions of a 23 °C atmosphere and a tensile speed of 3.3 mm / second, and the modulus (MPa) at 200% elongation and the elongation at break EB (%) were measured. The thickness direction of the sample was the tire radial direction.

[0123] <Low fuel - consumption performance> Using a rolling resistance tester, the rolling resistance of the test tire was measured when the test tire was run at a speed of 80 km / h with a rim of 15×6JJ, an internal pressure of 230 kPa, and a load of 3.43 kN. The reciprocal was expressed exponentially with Comparative Example 2 as 100. The larger the numerical value, the smaller the rolling resistance, indicating excellent low fuel consumption performance.

[0124] <Wet Grip Performance Test> Each test tire was mounted on all wheels of a truck (2-D vehicle) with a maximum load capacity of 10 tons, and the braking distance from an initial speed of 100 km / h was measured on a wet road surface. It was expressed exponentially with Comparative Example 1 as 100 according to the following formula. The larger the index, the better the wet grip performance. Note that 100 or more is the minimum target value, and 105 or more is preferable. (Wet Grip Performance Index)= (Braking distance of the tire in Comparative Example 2) / (Braking distance of each test tire)×100

[0125] <Wear Resistance> Each test tire was mounted on all wheels of a truck (2-D vehicle) with a maximum load capacity of 10 tons, and the groove depth of the tire tread part after a driving distance of 8000 km was measured. The driving distance when the tire groove depth decreased by 1 mm was obtained. The results are shown as an index according to the following calculation formula with the driving distance when the tire groove of Comparative Example 1 decreased by 1 mm as 100. The larger the index, the better the wear resistance. (Wear Resistance Index)=(Driving distance when the tire groove of each test tire decreased by 1 mm) / (Driving distance when the tire groove of the tire in Comparative Example 2 decreased by 1 mm)×100

[0126] <Chipping Resistance> Each test tire was mounted on all wheels of a truck (2-D vehicle) with a maximum load capacity of 10 tons, and the block chipping state after a driving distance of 8000 km was visually observed and scored. The results are shown as an index according to the following calculation formula with the score of Comparative Example 1 as 100. The larger the index, the less block chipping has occurred, indicating high chipping resistance. (Chipping Resistance Index)= (Score of each test tire) / (Score of the tire in Comparative Example 2)×100

[0127] <Abrasion resistance performance> After conducting the above abrasion resistance performance test, the presence or absence of tears in each test tire was visually confirmed. Those with tears were marked as "+", and those without tears were marked as "-".

[0128]

Table 1

[0129]

Table 2

[0130]

Table 3

[0131]

Table 4

[0132] From the results of Tables 1 to 4, it can be seen that the heavy-duty tire of the present disclosure having a tread in which the cap rubber layer contains a predetermined rubber component and silica and the loss tangent tanδ of the base rubber layer is within a predetermined range has well-balanced improvements in low fuel consumption performance, wet grip performance, abrasion resistance performance, chipping resistance performance, and tear resistance performance.

Explanation of reference numerals

[0133] 2 Heavy-duty tire 4 Tread 6 Sidewall 10 Bead 12 Carcass 14 Inner liner 18 Belt layer 20 Capping rubber 22 Tread surface 24 Main groove 28 Base rubber layer 30 Cap rubber layer 32 Bead core 34 Apex 36 Carcass ply 38 Tire radial outer surface (of the base rubber layer) EQ Tire equatorial plane

Claims

1. A heavy-duty tire having a carcass extending from a tread portion through a sidewall portion to a bead core of a bead portion, and a belt layer disposed outside the tire in the radial direction and inside the tread portion, wherein the belt layer is formed of a belt ply including a first belt layer, a second belt layer, and a third belt layer laminated in order from the inner side in the tire radial direction, wherein the tread portion has a plurality of main grooves extending continuously in the tire circumferential direction, wherein the tread portion has a cap rubber layer constituting a tread surface and a base rubber layer adjacent to the inner side of the cap rubber layer in the tire radial direction, wherein the cap rubber layer and the base rubber layer are composed of a rubber composition containing a rubber component, wherein the rubber component constituting the cap rubber layer includes an isoprene-based rubber, a styrene-butadiene rubber, and a butadiene rubber, The rubber composition constituting the cap rubber layer contains 30 parts by mass or more and 110 parts by mass or less of silica having a nitrogen adsorption specific surface area (N 2 SA) of 180 m 2 / g or more per 100 parts by mass of the rubber component, wherein the storage elastic modulus Ec' of the rubber composition constituting the cap rubber layer at 70°C is 7.1 to 11.0 MPa, A heavy-duty tire wherein the tanδ of the rubber composition constituting the base rubber layer at 70°C is 0.04 to 0.

07.

2. A heavy-duty tire having a carcass extending from a tread portion through a sidewall portion to a bead core of a bead portion, and a belt layer disposed outside the tire in the radial direction and inside the tread portion, wherein the belt layer is formed of a belt ply including a first belt layer, a second belt layer, and a third belt layer laminated in order from the inner side in the tire radial direction, wherein the tread portion has a plurality of main grooves extending continuously in the tire circumferential direction, wherein the tread portion has a cap rubber layer constituting a tread surface and a base rubber layer adjacent to the inner side of the cap rubber layer in the tire radial direction, wherein the cap rubber layer and the base rubber layer are composed of a rubber composition containing a rubber component, wherein the rubber component constituting the cap rubber layer includes an isoprene-based rubber, a styrene-butadiene rubber, and a butadiene rubber, wherein the content of styrene-butadiene rubber in the rubber component constituting the cap rubber layer is 12% by mass or more, The rubber composition constituting the cap rubber layer contains 30 parts by mass or more of silica having a nitrogen adsorption specific surface area (N 2 SA) of 180 m 2 / g or more, based on 100 parts by mass of the rubber component. wherein the storage elastic modulus Ec' of the rubber composition constituting the cap rubber layer at 70°C is 7.1 to 11.0 MPa, A heavy-duty tire wherein the tanδ of the rubber composition constituting the base rubber layer at 70°C is 0.04 to 0.

07.

3. In a tire meridian cross-section including a tire rotation axis, when the thickness of the cap rubber layer on the normal line lowered from the tire rotation axis direction end of the third belt layer to the tread surface is Te, the distance from the third belt layer to the tread surface on the normal line is Tt2, the distance from the second belt layer to the tread surface on the normal line is Tt1, the thickness of the cap rubber layer at a position half of the distance from the tire equatorial plane to the tire rotation axis direction end of the third belt layer is Tm, and the thickness of the cap rubber layer at the tire equatorial plane is Tc, the heavy-duty tire according to claim 1 or 2, which satisfies the following formulas (1) to (4). 0.65 ≤ Te / Tt2 ≤ 0.75... (1) 0.60 ≤ Te / Tt1 ≤ 0.70... (2) 0.85 ≤ Tc / Tm ≤ 1.15... (3) 0.85 ≤ Tm / Te ≤ 1.15... (4)

4. The heavy-duty tire according to claim 3, wherein Te is smaller than Tm and Tc.

5. The heavy-duty tire according to claim 3 or 4, wherein the ratio (Te / Hs) of Te to the groove depth Hs of the main groove closest to the tread end is 0.50 to 0.

90.

6. The heavy-duty tire according to any one of claims 1 to 5, wherein 8 to 18 parts by mass of a sulfide-based silane coupling agent is contained with respect to 100 parts by mass of the silica contained in the rubber composition constituting the cap rubber layer.

7. The heavy-duty tire according to any one of claims 1 to 6, wherein the content of the isoprene-based rubber in the rubber component constituting the cap rubber layer is 65% by mass or more, and the content of the styrene-butadiene rubber in the total amount of 100% by mass of the styrene-butadiene rubber and the butadiene rubber is 50% by mass or more.

8. The heavy-duty tire according to any one of claims 1 to 7, wherein the modulus at 200% elongation at 23°C of the rubber composition constituting the base rubber layer is 5.0 to 14.0 MPa.

9. The heavy-duty tire according to any one of claims 1 to 8, wherein the elongation at break of the rubber composition constituting the base rubber layer is 380% or more.

10. The heavy-duty tire according to any one of claims 1 to 9, wherein the ratio (Ec' / Eb') of the storage elastic modulus Ec' at 70°C of the rubber composition constituting the cap rubber layer to the storage elastic modulus Eb' at 70°C of the rubber composition constituting the base rubber layer is 1.1 to 1.

7.

11. The ratio (Hm / Tt3) of the groove depth Hm of the main groove closest to the tire equatorial plane to the distance Tt3 from the tread surface in the tire equatorial plane to the outermost belt layer in the tire radial direction is 0.50 to 0.

90. The heavy-duty tire according to any one of claims 1 to 10.

12. The ratio (Wb / Wa) of the tire rotational axis direction distance Wb from the tire equatorial plane to the groove edge of the main groove closest to the tire equatorial plane to the tire rotational axis direction distance Wa from the tire equatorial plane to the layer end of the outermost belt layer in the tire radial direction is 0.50 to 0.

90. The heavy-duty tire according to any one of claims 1 to 11.

13. The rubber composition constituting the cap rubber layer contains one or more selected from the group consisting of a phenol resin, a cresol resin, and a resorcinol resin. The heavy-duty tire according to any one of claims 1 to 12.

14. The content of butadiene rubber in the rubber component constituting the cap rubber layer is 5 to 25% by mass. The heavy-duty tire according to any one of claims 1 to 13.

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