Tire for heavy load

Abstract

To provide a tire for a heavy load improved in low fuel consumption performance, wet grip performance, abrasion resistance, chipping resistance and tear resistance.SOLUTION: A tread has a plurality of main grooves 24 extending continuously in a tire circumferential direction. The tread has a cap rubber layer 30 constituting a tread face 22 and a base rubber layer 28 formed adjacent to inside in a tire radial direction of the cap rubber layer. The cap rubber layer and the base rubber layer are composed of rubber compositions containing rubber constituents. The rubber constituents constituting the cap rubber layer include isoprene-system rubber and styrene-butadiene rubber. The rubber compositions constituting the cap rubber layer contain 30 pts.mass or more of silica whose nitrogen adsorption specific surface areas (N2SA) are 180 m2 / g or more, with respect to 100 pts.mass of rubber constituents, and tanδ at 70°C of the rubber compositions constituting the base rubber layer is 0.04-0.07.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a heavy-duty tire having improved fuel economy, wet grip performance, wear resistance, chipping resistance, and tear resistance in a well-balanced manner. [Background technology]

[0002] As a method for improving the wear resistance of truck and bus tires, a technique for finely dividing or highly structuring carbon black is known (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 6-279624 Summary of the Invention [Problem to be solved by the invention]

[0004] The above-mentioned methods of finely dividing or highly structuring carbon black are not sufficient to improve the fuel economy of tires. In addition, the deterioration of processability associated with finely dividing carbon black can also deteriorate the dispersibility of carbon black, which can in turn deteriorate the abrasion resistance of tires. For this reason, there are limitations to the performance improvement methods based on the conventional improvement of carbon black.

[0005] Furthermore, due to the influence of recent environmental regulations, there is an increasing demand for truck and bus tires to not only have high wear resistance, but also high levels of fuel efficiency, wet grip performance, chipping resistance, etc.

[0006] An object of the present invention is to provide a heavy-duty tire which has improved fuel economy, wet grip performance, wear resistance, chipping resistance and tear resistance in a well-balanced manner. [Means for solving the problem]

[0007] As a result of intensive research, the present inventors have found that the above-mentioned problems can be solved by compounding a predetermined rubber component and silica into a cap rubber layer constituting a tread, and by setting the loss tangent tanδ of a base rubber layer within a predetermined range in a tire having a predetermined configuration, and have completed the present invention.

[0008] That is, the present invention provides [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 on the radially outer side of the carcass 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 radially inner side of the tire, the tread portion having a plurality of main grooves extending continuously in the tire circumferential direction, the tread portion having a cap rubber layer forming a tread surface and a base rubber layer adjacent to the radially inner side of the cap rubber layer, the cap rubber layer and the base rubber layer being formed of a rubber composition containing a rubber component, the rubber component constituting the cap rubber layer containing an isoprene-based rubber and a styrene-butadiene rubber, and the rubber composition constituting 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 a heavy-duty tire containing 30 parts by mass or more of silica having a silica content of 30 parts by mass or more per 100 parts by mass of 1 / g or more, and a rubber composition constituting the base rubber layer having a tan δ at 70°C of 0.04 to 0.07; [2] A heavy-duty tire according to the above [1], which satisfies the following formulas (1) to (4) when, in a tire meridian cross section including the tire rotation axis, a thickness of the cap rubber layer on a normal line from an end of the third belt layer in the tire rotation axis direction down to the tread surface is Te, a distance from the third belt layer to the tread surface on the normal line is Tt2, a distance from the second belt layer to the tread surface on the normal line is Tt1, a thickness of the cap rubber layer at a position of 1 / 2 the distance from the tire equatorial plane to the end of the third belt layer in the tire rotation axis direction is Tm, and a thickness of the cap rubber layer at the tire equatorial plane is Tc: 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 heavy-duty tire according to the above [1] or [2], wherein the rubber composition constituting the cap rubber layer contains 8 to 18 parts by mass of a sulfide-based silane coupling agent relative to 100 parts by mass of the silica contained therein. [4] The heavy-duty 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. [5] The heavy-duty tire according to any one of the above [1] to [4], wherein the modulus of the rubber composition constituting the base rubber layer at 200% elongation at 23°C is 5.0 to 14.0 MPa. [6] The heavy-duty 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. [7] The heavy-duty tire according to any one of [2] to [6] above, wherein Te is smaller than Tm and Tc. [8] The heavy-duty tire according to any one of the above [1] to [7], wherein a ratio (Ec' / Eb') of a storage modulus Ec' at 70 ° C. of a rubber composition constituting the cap rubber layer to a storage modulus Eb' at 70 ° C. of a rubber composition constituting the base rubber layer is 1.1 to 1.7. [9] The heavy-duty tire according to any one of the above [1] to [8], wherein 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 0.50 to 0.90.

[10] A heavy-duty tire according to any one of the above [2] to [9], wherein a ratio (Te / Hs) of the Te to a groove depth Hs of the main groove closest to a tread end is 0.50 to 0.90.

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

[10] , wherein a ratio (Wb / Wa) of a distance Wb in the tire rotational axis direction from the tire equatorial plane to a groove edge of the main groove closest to the tire equatorial plane to a distance Wa in the tire rotational axis direction from the tire equatorial plane to a layer end of the belt layer outermost in the tire radial direction is 0.50 to 0.90.

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

[11] , wherein the rubber composition constituting the cap rubber layer contains at least one resin selected from the group consisting of a phenol resin, a cresol resin, and a resorcinol resin. Effect of the Invention

[0009] According to the present invention, there is provided a heavy-duty tire having improved fuel economy, wet grip performance, wear resistance, chipping resistance, and tear resistance in a well-balanced manner. [Brief description of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view showing a portion of a heavy duty tire according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is an enlarged cross-sectional view showing a part of the heavy duty tire of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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, the tread portion having a plurality of main grooves extending continuously in the tire circumferential direction, the tread portion having a cap rubber layer forming a tread surface and a base rubber layer adjacent to the inner side in the tire radial direction of the cap rubber layer, the cap rubber layer and the base rubber layer being formed of a rubber composition containing a rubber component, the rubber component constituting the cap rubber layer includes an isoprene-based rubber and a styrene-butadiene rubber, and the rubber composition constituting 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 intending to be bound by theory, the following mechanism is considered to improve the fuel economy, wet grip, wear resistance, chipping resistance, and tear resistance of heavy-duty tires in a well-balanced manner in the present disclosure. By using a predetermined combination of the rubber component to be compounded in the cap rubber layer, the silica content, and the nitrogen adsorption specific surface area (N2SA), the silica can be highly finely dispersed, a strong silica network is formed, and it becomes possible to achieve a high balance between the strength and elongation of the rubber composition when stretched. In addition, by compounding silica in the cap rubber layer, the hydrophilicity of the rubber composition is increased, and the ability to follow wet road surfaces is improved. Furthermore, by setting the tan δ at 70°C of the rubber composition constituting the base rubber layer within a predetermined range, the temperature rise at the belt end can be suppressed, the fracture originating from the steel filament end can be suppressed, and the fracture strength reduction of the base rubber layer itself can be suppressed. It is believed that the above-described physical properties of the rubber compositions constituting each layer of the tread cooperate with the tire structure to achieve a balanced improvement in fuel economy, wet grip performance, abrasion resistance, chipping resistance, and tear resistance.

[0013] In the heavy-duty tire of the present disclosure, in a tire meridian cross section including the tire rotation axis, when the thickness of the cap rubber layer on a normal line from the tire rotational 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 that is 1 / 2 the distance from the tire equatorial plane to the tire rotational 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 that the following formulas (1) to (4) are satisfied. 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] The cap rubber layer preferably contains 8 to 18 parts by mass of a sulfide-based 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.

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

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

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

[0019] The ratio (Ec' / Eb') of the storage modulus Ec' at 70°C of the rubber composition constituting the cap rubber layer to the storage 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 end is preferably 0.50 to 0.90.

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

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

[0024] A heavy-duty tire according to an embodiment of the present disclosure will be described in detail below. However, the following description is merely an example for explaining the present disclosure, and is not intended to limit the technical scope of the present invention to the described range. In this specification, when a numerical range is indicated using "to", the numerical range is intended to include both ends of the range.

[0025] Fig. 1 is a cross-sectional view showing a portion of a heavy duty tire according to an embodiment of the present disclosure. In Fig. 1, the up-down direction is the radial direction of the heavy duty tire 2, the left-right direction is the tire axial 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 symmetrical 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, beads 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 comes into contact with the road surface. A plurality of main grooves 24 are formed on the tread surface 22, which extend continuously in the circumferential direction of the tire.

[0027] The outer end of the tread 4 in the tire rotational axis direction and its vicinity are referred to as the shoulder portion of the heavy duty tire 2. In the following description of the present disclosure, for the sake of clarity, the portion that is outer in the tire rotational axis direction than the main groove 24s that is closest to the tread end 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-stretchable wire. The apex 34 tapers radially outward of the tire.

[0029] The carcass 12 is made of a carcass ply 36. The carcass ply 36 is laid between the beads 10 on both sides and extends along the tread 4 and the sidewall 6. The carcass ply 36 is folded around the bead core 32 from the inside to the outside in the tire rotational axis direction. The carcass ply 36 is made of a large number of cords and a topping rubber arranged in parallel. The carcass 12 may be formed of two or more carcass plies 36.

[0030] The belt layer 18 extends in the tire rotational 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, which are laminated in order from the inner side in the tire radial direction. FIG. 1 shows a case where a fourth belt layer 18d is arranged on the outer side in the tire radial direction of the third belt layer 18c. The first belt layer 18a is laminated on the carcass 12. In FIG. 1, the second belt layer 18b has the largest width of the above four layers in the tire rotation axis direction, and the fourth belt layer 18d has the smallest width of the above four layers, but is not limited to such an embodiment.

[0032] Fig. 2 is an enlarged cross-sectional view showing the vicinity of a 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 in the tire rotational axis direction of the tread 4. 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. In addition, one or more rubber layers may be further provided between the base rubber layer 28 and the belt layer 18, as long as the effects of the present disclosure are achieved.

[0034] In this disclosure, unless otherwise specified, the dimensions and angles of each component of the tire are measured when the tire is mounted on a standard rim and inflated to a standard internal pressure. No load is applied to the tire during measurement. In this specification, the term "standard rim" refers to a rim that is determined for each tire by a standard system that includes the standard on which the tire is based, such as a standard rim for JATMA, a "Design Rim" for TRA, and a "Measuring Rim" for ETRTO. In this specification, the term "standard internal pressure" refers to the air pressure determined for each tire by the standard, such as the maximum air pressure for JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA, and "INFLATION PRESSURE" for ETRTO.

[0035] In the heavy duty tire of the present disclosure, in a tire meridian cross section including the tire rotation axis, the thickness of the cap rubber layer 30 on a normal line N extending from the end of the third belt layer in the tire rotation axis direction 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, the thickness of the cap rubber layer 30 at a position of 1 / 2 the distance from the tire equatorial plane EQ to the end of the third belt layer in the tire rotation axis direction is Tm, and the thickness of the cap rubber layer 30 at the tire equatorial plane EQ is Tc, preferably satisfying the following formulas (1) to (4). The normal line N is a line passing through the end of the tire rotation axis direction of the third belt layer on the tire radial outer surface and perpendicular to the tangent at the end of the tire rotation axis direction. 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] If Te / Tt2 is less than 0.65, it is difficult to ensure a sufficient volume of the cap rubber layer 30 to exhibit the wear resistance and chipping resistance of the cap rubber layer 30 in the later stage of tire wear, and furthermore, the base rubber layer 28 is likely to be exposed to the tire surface in the final stage of tire wear, which tends to shorten the tire's lifespan and cause uneven wear. On the other hand, if Te / Tt2 is more than 0.75, the volume of the base rubber layer 28 in the shoulder portion is insufficient, which makes it easier for the temperature to rise during running from the end of the second belt layer in the tire rotational axis direction to the end of the third belt layer in the tire rotational axis direction, and the effect of suppressing adhesion failure between the steel filament and the rubber at the end of the third belt layer in the tire rotational axis direction is reduced. The adhesion failure at the end of the third belt layer in the tire rotational axis direction may progress toward the tire equatorial plane as a break inside the rubber between the second belt layer and the third belt layer, resulting in damage to the entire tire. For the same reason, it is preferable that Te and Tt1 satisfy the above formula (2).

[0037] Moreover, it is preferable that Te, Tt1, and Tt2 satisfy the following formula (5). 0.20≦(Te / Tt2)-(Te / Tt1)≦0.70 ···(5)

[0038] If (Te / Tt2)-(Te / Tt1) is less than 0.20, it becomes difficult to alleviate the shear between the end of the second belt layer in the tire rotational axis direction and the end of the third belt layer in the tire rotational axis direction due to the shape change of the tread portion during running, and it tends to be difficult to suppress the above-mentioned breakage. Also, if (Te / Tt2)-(Te / Tt1) is more than 0.70, the distance between the end of the second belt layer in the tire rotational axis direction and the end of the third belt layer in the tire rotational axis direction becomes too large, and it tends to be difficult to maintain an appropriate tread shape.

[0039] From the viewpoint of the balance of tire performance after the later stage of wear, 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. Moreover, 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 in the above range, chipping resistance can be further improved.

[0041] The ratio (Te / Hs) of Te to the groove depth Hs of the main groove 24s closest to the tread end is preferably 0.50 or more, more preferably 0.55 or more, and even more preferably 0.60 or more. Te / Hs is preferably 0.90 or less, more preferably 0.85 or less, and even more preferably 0.80 or less. Te is preferably smaller than Tm and Tc. By disposing the low heat generation base rubber layer 28 in the shoulder portion 26, which is a portion where distortion is large and heat generation is large, the heat generation of the entire tread 4 can be reduced, and the amount of the base rubber layer 28 near the tire equatorial plane can be reduced, and accordingly, the base rubber layer 28 can be prevented from contacting the road surface at the end of the wear stage, thereby maintaining chipping resistance.

[0042] 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 (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. Moreover, 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 in the above range, chipping resistance can be further improved.

[0043] In the present disclosure, "70°C E'" 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. 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, even more preferably 1.2 to 1.5, and particularly preferably 1.2 to 1.4, from the viewpoint of chipping resistance. 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 even more preferably 6.0 to 9.5 MPa. 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 even more preferably 5.0 to 6.1 MPa. The 70°C E' of each rubber layer can be appropriately adjusted depending on the types and amounts of the rubber components, filler, silane coupling agent, softener, etc.

[0044] In the present disclosure, "70°C tan δ" refers to the loss tangent tan 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. The 70°C tan δ of the rubber composition constituting the base rubber layer 28 is 0.04 or more, preferably 0.05 or more. If the 70°C tan δ of the rubber composition constituting the base rubber layer 28 is less than 0.04, the breaking strength of the base rubber compound itself is significantly reduced, and there is a concern that tears may occur due to the breakage of the base rubber itself. On the other hand, the 70°C tan δ of the rubber composition constituting the base rubber layer 28 is 0.07 or less, preferably 0.06 or less, from the viewpoint of suppressing the temperature rise at the belt end and suppressing the breakage starting from the steel filament end. In addition, from the viewpoint of better exerting the effect of improving fuel efficiency performance, the value of 70°C tan δ of the rubber composition constituting the cap rubber layer 30 is preferably larger than the value of 70°C tan δ of the rubber composition constituting the base rubber layer 28. The 70° C. tan δ of each rubber layer can be appropriately adjusted by the types and amounts of the rubber component, filler, silane coupling agent, softener, etc.

[0045] In the present disclosure, the modulus at 200% stretching refers to the tensile stress at 100% elongation in the grain direction measured in accordance with JIS K 6251:2017 at a 23°C atmosphere and a tensile speed of 3.3 mm / sec. The modulus of the base rubber layer 28 at 200% stretching is preferably 5.0 MPa or more, more preferably 5.5 MPa or more, even more preferably 6.0 MPa or more, and particularly preferably 6.5 MPa or more, from the viewpoint of ensuring the rigidity of the tread portion and suppressing uneven wear. On the other hand, the modulus of the base rubber layer 28 at 200% stretching is preferably 14.0 MPa or less, more preferably 13.5 MPa or less, even more preferably 13.0 MPa or less, and particularly preferably 12.5 MPa or less. If the modulus of the base rubber layer 28 at 200% stretch exceeds 14.0 MPa, external force is difficult to release, and input is concentrated at the interface between the cap rubber layer 30 and the base rubber layer 28, which may cause cracks to grow at the interface. In addition, the modulus of the cap rubber layer 30 at 200% stretch is preferably greater than the modulus of the base rubber layer 28 at 200% stretch. In this specification, the term "grain direction" refers to the rolling direction when a rubber sheet is formed by extrusion or shearing.

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

[0047] The modulus and EB at 200% stretching of each rubber layer can be appropriately adjusted by the types and amounts of the rubber component, filler, silane coupling agent, softener, etc., mentioned above.

[0048] [Rubber composition] The heavy-duty tire of the present disclosure can achieve a balanced improvement in fuel economy performance, wet grip performance, abrasion resistance, chipping resistance, and tear resistance by combining the above-described tire structure with the above-described physical properties of the rubber composition constituting each layer of the tread.

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

[0050] (Isoprene rubber) As the isoprene-based rubber, for example, isoprene rubber (IR) and natural rubber, which are common in the tire industry, can be used. In addition to unmodified natural rubber (NR), natural rubber also includes modified natural rubber such as epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), deproteinized natural rubber (DPNR), highly purified natural rubber (UPNR), and grafted natural rubber. These isoprene-based rubbers may be used alone or in combination of two or more.

[0051] The NR is not particularly limited, and any NR commonly used in the tire industry can be used, such as SIR20, RSS#3, and TSR20.

[0052] In the rubber composition constituting the cap rubber layer 30, the content of the isoprene-based rubber in the rubber component is preferably 50% by mass or more, more preferably 55% by mass or more, even more preferably 60% by mass or more, and particularly preferably 65% ​​by mass or more. Since silica has good compatibility with isoprene-based rubber, by increasing the content of the isoprene-based rubber in the rubber component and dispersing silica in the isoprene-based rubber phase that becomes the sea phase, the strength of the entire matrix tends to be improved, and the wear resistance and fracture properties tend to be further improved. On the other hand, from the viewpoint of wet grip performance, 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.

[0053] In the rubber composition constituting the base rubber layer 28, the content of isoprene-based rubber in the rubber component is preferably 85 mass% or more, more preferably 90 mass% or more, and even more preferably 95 mass% or more, and the rubber component may consist only of isoprene-based rubber.

[0054] (SBR) The rubber composition constituting the cap rubber layer 30 contains SBR as a rubber component. By blending SBR, wet grip performance and chipping resistance are significantly improved. The reason for this is thought to be that SBR has excellent viscoelastic properties in an area highly correlated with wet grip performance, and that its modulus (stress) at large deformation is higher than that of BR and the like. In addition, SBR has excellent compatibility and reactivity with silica, so it is thought to be effective in dispersing silica and fixing silica to polymers.

[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). Modified SBRs include SBRs whose ends and / or main chains are modified, and modified SBRs (condensates, those having a branched structure, etc.) coupled with tin, silicon compounds, etc. Among these, E-SBR is preferred from the viewpoint of being able to satisfactorily improve fuel economy and abrasion resistance. These SBRs may be used alone or in combination of two or more.

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

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

[0058] From the viewpoint of wet grip performance, the glass transition point (Tg) of SBR is preferably -80°C or higher, and more preferably -70°C or higher. From the viewpoint of fuel economy performance, the Tg of SBR is preferably -40°C or lower, and more preferably -45°C or lower. Note that the Tg of SBR in this specification is determined in accordance with JIS K 6229 by removing the extender oil with acetone and then subjecting the pure SBR content to differential scanning calorimetry (DSC) in accordance with JIS K 7121.

[0059] The weight average molecular weight (Mw) of SBR is preferably 200,000 or more from the viewpoint of abrasion resistance, more preferably 300,000 or more, and even more preferably 500,000 or more. From the viewpoint of crosslinking uniformity, Mw is preferably 2.5 million or less, more preferably 2 million or less. Mw can be calculated 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) in terms of standard polystyrene.

[0060] When SBR is contained, the content in the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, more preferably 15% by mass or more, and particularly preferably 20% by mass or more from the viewpoint of chipping resistance and wet grip performance, and is preferably 40% by mass or less, more preferably 35% by mass or less, further preferably 30% by mass or less, and particularly preferably 25% by mass or less from the viewpoint of abrasion resistance.

[0061] (BR) The BR is not particularly limited, and can be one that is commonly used in the tire industry, such as BR with a cis content of less than 50% by mass (low cis BR), BR with a cis content of 90% by mass or more (high cis BR), rare earth butadiene rubber (rare earth BR) synthesized using a rare earth catalyst, BR containing syndiotactic polybutadiene crystals (SPB-containing BR), modified BR (high cis modified BR, low cis modified BR), etc. These BRs can be used alone or in combination of two or more.

[0062] (Other rubber components) The rubber component according to the present disclosure may contain rubber components other than the isoprene-based rubber, SBR, and BR. As the other rubber components, crosslinkable rubber components generally used in the tire industry can be used, such as styrene-isoprene-butadiene copolymer rubber (SIBR), styrene-isobutylene-styrene block copolymer (SIBS), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), hydrogenated nitrile rubber (HNBR), butyl rubber (IIR), ethylene propylene rubber, polynorbornene rubber, silicone rubber, chlorinated polyethylene rubber, fluororubber (FKM), acrylic rubber (ACM), hydrin rubber, etc. These other rubber components may be used alone or in combination of two or more.

[0063] <Filler> The rubber composition for tread according to the present disclosure preferably contains a filler containing carbon black and / or silica. The filler may be a filler consisting of only 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, or may be a filler consisting of only 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, or may be a filler consisting of only carbon black and silica.

[0064] (silica) By blending silica in the rubber composition for tread according to the present disclosure, fuel economy 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 (hydrated silica), and other silicas commonly used in the tire industry can be used. Among them, hydrated silica prepared by a wet method is preferred because it contains a large number of silanol groups. These silicas may be used alone or in combination of two or more types.

[0065] The nitrogen adsorption specific surface area (N2SA) of silica is 180m from the viewpoint of wear resistance and fracture characteristics. 2 / g or more, 185m 2 / g or more is preferable, and 190m 2 / g or more is more preferable, and 200m 2 From the viewpoints of fuel efficiency and processability, it is more preferable that the tensile strength is 350 m 2 / g or less is preferable, and 300m 2 / g or less is more preferable, and 250m 2 / g or less is more preferable. In this specification, the N2SA of silica is a value measured by the BET method in accordance with ASTM D3037-93.

[0066] The rubber composition constituting the cap rubber layer 30 contains 30 parts by mass or more of silica per 100 parts by mass of the rubber component from the viewpoint of a balance between fuel economy performance and wet grip performance. In the rubber composition constituting the cap rubber layer 30, the content of silica per 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. In addition, from the viewpoint of suppressing a decrease in fuel economy performance and abrasion resistance performance due to deterioration of dispersibility of silica in rubber, the content 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.

[0067] In the rubber composition constituting the base rubber layer 28, the content of silica per 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more. From the viewpoints of fuel economy and abrasion resistance, the content is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, even more preferably 40 parts by mass or less, and particularly preferably 30 parts by mass or less.

[0068] (Carbon Black) The carbon black is not particularly limited, and may be, for example, one commonly used in the tire industry, such as GPF, FEF, HAF, ISAF, SAF, etc. These carbon blacks may be used alone or in combination of two or more.

[0069] From the viewpoint of weather resistance and reinforcement, the nitrogen adsorption specific surface area (N2SA) of carbon black is 50m 2 / g or more is preferable, and 80m 2 / g or more is more preferable, and 100m 2 From the viewpoints of dispersibility, fuel efficiency, breakage characteristics and durability, it is more preferable that the content is 250 m 2 / g or less is preferable, and 220m 2 In this specification, the N2SA of carbon black is a value measured in accordance with Method A of JIS K 6217-2 "Basic properties of carbon black for rubber use - Part 2: Determination of specific surface area - Nitrogen adsorption method - Single point method".

[0070] In the rubber composition constituting the cap rubber layer 30, the content of 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 viewpoint of weather resistance and reinforcement. Also, from the viewpoint of fuel efficiency performance, the content is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, even more preferably 40 parts by mass or less, and particularly preferably 30 parts by mass or less.

[0071] In the rubber composition constituting the base rubber layer 28, the content of carbon black per 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 reinforcement, and 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 from the viewpoint of fuel efficiency.

[0072] As fillers other than silica and carbon black, for example, aluminum hydroxide, calcium carbonate, alumina, clay, talc, and the like, which are commonly used in the tire industry, can be used.

[0073] In the rubber composition constituting the cap rubber layer 30, the content of silica in the total of silica and carbon black (100% by mass) is preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 55% by mass or more, and particularly preferably 60% by mass or more. The content of silica is preferably 99% by mass or less, more preferably 97% by mass or less, and even more preferably 95% by mass or less.

[0074] In the rubber composition constituting the base rubber layer 28, the silica content in the total of 100 mass% of silica and carbon black is preferably 5 mass% or more, and more preferably 10 mass% or more. The silica content is preferably 30 mass% or less, and more preferably 25 mass% or less.

[0075] In the rubber composition constituting the cap rubber layer 30, the total content of silica and carbon black per 100 parts by mass of the rubber component is preferably 40 parts by mass or more, more preferably 50 parts by mass or more, and even more preferably 55 parts by mass or more, from the viewpoint of abrasion resistance performance. Also, from the viewpoint of suppressing deterioration of fuel economy performance and abrasion resistance performance, it is preferably 180 parts by mass or less, more preferably 160 parts by mass or less, and even more preferably 140 parts by mass or less.

[0076] In the rubber composition constituting the base rubber layer 28, the total content of silica and carbon black per 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 even more preferably 40 parts by mass or more. Also, the content is preferably 70 parts by mass or less, more preferably 60 parts by mass or less, and even more preferably 50 parts by mass or less.

[0077] (Silane coupling agent) Silica is preferably used in combination with a silane coupling agent. The silane coupling agent is not particularly limited, and any silane coupling agent that has been used in combination with silica in the tire industry can be used, for example, mercapto-based silane coupling agents such as 3-mercaptopropyltrimethoxysilane, NXT-Z100, NXT-Z45, and NXT manufactured by Momentive Corporation; 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. Examples of the coupling agents include: vinyl triethoxysilane, vinyl trimethoxysilane, and other vinyl-based silane coupling agents; amino-based silane coupling agents such as 3-aminopropyl triethoxysilane, 3-aminopropyl trimethoxysilane, and 3-(2-aminoethyl) aminopropyl triethoxysilane; glycidoxy-based silane coupling agents such as γ-glycidoxypropyl triethoxysilane and γ-glycidoxypropyl trimethoxysilane; nitro-based silane coupling agents such as 3-nitropropyl trimethoxysilane and 3-nitropropyl triethoxysilane; chloro-based silane coupling agents such as 3-chloropropyl trimethoxysilane and 3-chloropropyl triethoxysilane; and the like. Among these, 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.

[0078] The content of the silane coupling agent (preferably a sulfide-based silane coupling agent) per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, even more preferably 2.0 parts by mass or more, and particularly preferably 4.0 parts by mass or more, from the viewpoint of improving the dispersibility of silica. Also, from the viewpoint of preventing a decrease in abrasion resistance, the content is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 10 parts by mass or less.

[0079] The content of the silane coupling agent (preferably sulfide-based silane coupling agent) with respect to 100 parts by mass of silica is preferably 1 part by mass or more, more preferably 3 parts by mass or more, even more preferably 5 parts by mass or more, and particularly preferably 8 parts by mass or more, from the viewpoint of increasing the dispersibility of silica.Furthermore, from the viewpoint of cost and processability, it is preferably 20 parts by mass or less, more preferably 18 parts by mass or less, and even more preferably 16 parts by mass or less.

[0080] <Other compounding agents> In addition to the above-mentioned components, the rubber composition according to the present disclosure may appropriately contain compounding agents commonly used in the tire industry, such as softeners, waxes, processing aids, stearic acid, zinc oxide, antioxidants, vulcanizing agents, and vulcanization accelerators.

[0081] Examples of the softener include a resin component, oil, and liquid rubber.

[0082] The resin component is not particularly limited, but examples thereof include petroleum resins, terpene resins, rosin resins, phenolic resins, cresol resins, and resorcinol resins commonly used in the tire industry. Among these, 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.

[0083] The phenol-based resin is not particularly limited, but examples thereof include phenol formaldehyde resin, alkylphenol formaldehyde resin, alkylphenol acetylene resin, and oil-modified phenol formaldehyde resin.

[0084] When a resin component is contained, the content per 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more from the viewpoint of wet grip performance, and is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, even more preferably 40 parts by mass or less, and particularly preferably 30 parts by mass or less from the viewpoint of suppressing heat buildup.

[0085] Examples of the oil include process oil, vegetable oil, and animal oil. Examples of the process oil include paraffin-based process oil, naphthenic process oil, and aromatic process oil. In addition, as an environmental measure, process oil with a low content of polycyclic aromatic compound (PCA) compounds can be used. Examples of the low PCA content process oil include light extract solvate (MES), treated distillate aromatic extract (TDAE), and heavy naphthenic oil.

[0086] When oil is contained, the content per 100 parts by mass of the rubber component is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 15 parts by mass or more from the viewpoint of processability. Also, from the viewpoint of abrasion resistance, the content is preferably 120 parts by mass or less, more preferably 100 parts by mass or less, and even more preferably 90 parts by mass or less. In this specification, the content of oil includes the amount of oil contained in the oil-extended rubber.

[0087] The liquid rubber is not particularly limited as long as it is a polymer that is in a liquid state at room temperature (25° C.), and examples thereof include liquid butadiene rubber (liquid BR), liquid styrene butadiene rubber (liquid SBR), liquid isoprene rubber (liquid IR), liquid styrene isoprene rubber (liquid SIR), liquid farnesene rubber, etc. These liquid rubbers may be used alone or in combination of two or more kinds.

[0088] When the liquid rubber is contained, the content per 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 2 parts by mass or more, even more preferably 3 parts by mass or more, and particularly preferably 5 parts by mass or more. The content of the liquid rubber is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 20 parts by mass or less.

[0089] When the wax is contained, the content thereof per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, and more preferably 1 part by mass or more, from the viewpoint of weather resistance of the rubber, and is preferably 10 parts by mass or less, and more preferably 5 parts by mass or less, from the viewpoint of preventing whitening of the tire due to bloom.

[0090] Examples of the processing aid include fatty acid metal salts, fatty acid amides, amide esters, silica surfactants, fatty acid esters, mixtures of fatty acid metal salts and amide esters, mixtures of fatty acid metal salts and fatty acid amides, etc. These processing aids may be used alone or in combination of two or more. Examples of the processing aids that can be used include those commercially available from Schill+Seilacher, Performance Additives, etc.

[0091] When a processing aid is contained, the content thereof per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, from the viewpoint of improving processability, and is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, from the viewpoints of abrasion resistance and breaking strength.

[0092] The antiaging agent is not particularly limited, but examples thereof include amine-based, quinoline-based, quinone-based, phenol-based, and imidazole-based compounds, and carbamic acid metal salts, and the like. Phenylenediamine-based antiaging agents such as N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, N,N'-diphenyl-p-phenylenediamine, N,N'-di-2-naphthyl-p-phenylenediamine, and N-cyclohexyl-N'-phenyl-p-phenylenediamine, and quinoline-based antiaging agents such as 2,2,4-trimethyl-1,2-dihydroquinoline polymer and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline are preferred. These antiaging agents may be used alone or in combination of two or more.

[0093] When an antioxidant is contained, the content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, from the viewpoint of ozone crack resistance of the rubber, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, from the viewpoint of abrasion resistance and wet grip performance.

[0094] When stearic acid is contained, the content thereof per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, from the viewpoint of processability, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, from the viewpoint of vulcanization speed.

[0095] When zinc oxide is contained, the content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, from the viewpoint of processability, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, from the viewpoint of abrasion resistance.

[0096] As the vulcanizing agent, sulfur is preferably used, and examples of the sulfur that can be used include powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur.

[0097] When sulfur is contained as a vulcanizing agent, the content per 100 parts by mass of the rubber component is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.5 parts by mass or more, from the viewpoint of ensuring sufficient vulcanization reaction. Also, from the viewpoint of preventing deterioration, the content is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.0 parts by mass or less. Note that, when oil-containing sulfur is used as a vulcanizing agent, the content of the vulcanizing agent is the total content of the pure sulfur contained in the oil-containing sulfur.

[0098] Examples of vulcanizing agents other than sulfur include alkylphenol-sulfur chloride condensates, sodium 1,6-hexamethylene-dithiosulfate dihydrate, 1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane, etc. As these vulcanizing agents other than sulfur, commercially available products from Taoka Chemical Co., Ltd., Lanxess Co., Ltd., Flexis, etc. can be used.

[0099] Examples of the vulcanization accelerator include sulfenamide-based, thiazole-based, thiuram-based, thiourea-based, guanidine-based, dithiocarbamic acid-based, aldehyde-amine-based or aldehyde-ammonia-based, imidazoline-based, and xanthate-based vulcanization accelerators. These vulcanization accelerators may be used alone or in combination of two or more. Among them, one or more vulcanization accelerators selected from the group consisting of sulfenamide-based, guanidine-based, and thiazole-based vulcanization accelerators are preferred.

[0100] Examples of sulfenamide vulcanization accelerators include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N,N-dicyclohexyl-2-benzothiazolylsulfenamide (DCBS), etc. Among them, N-tert-butyl-2-benzothiazolylsulfenamide (TBBS) is preferred.

[0101] Examples of the guanidine vulcanization accelerator include 1,3-diphenylguanidine (DPG), 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, di-o-tolylguanidine salt of dicatechol borate, 1,3-di-o-cumenylguanidine, 1,3-di-o-biphenylguanidine, 1,3-di-o-cumenyl-2-propionylguanidine, etc. Among them, 1,3-diphenylguanidine (DPG) is preferable.

[0102] Examples of the thiazole-based vulcanization accelerator include 2-mercaptobenzothiazole, cyclohexylamine salt of 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, etc. Among these, 2-mercaptobenzothiazole is preferred.

[0103] When a vulcanization accelerator is contained, the content per 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 2 parts by mass or more. The content per 100 parts by mass of the rubber component is preferably 8 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 6 parts by mass or less. By setting the content of the vulcanization accelerator within the above range, breaking strength and elongation tend to be secured.

[0104] The rubber composition according to the present disclosure can be produced by a known method, for example, by kneading the above-mentioned components using a rubber kneading device such as an open roll or an internal kneader (such as a Banbury mixer or kneader).

[0105] The kneading step includes, for example, a base kneading step in which compounding ingredients and additives other than the vulcanizing agent and the vulcanization accelerator are kneaded, and a final kneading (F kneading) step in which the vulcanizing agent and the vulcanization accelerator are added to the kneaded product obtained in the base kneading step and kneaded. Furthermore, the base kneading step can be divided into a plurality of steps as desired.

[0106] The kneading conditions are not particularly limited, but examples thereof include a method in which in the base kneading step, kneading is performed for 3 to 10 minutes at a discharge temperature of 150 to 170° C., and in the final kneading step, kneading is performed for 1 to 5 minutes at 70 to 110° C. The vulcanization conditions are not particularly limited, but examples thereof include a method in which vulcanization is performed for 10 to 30 minutes at 150 to 200° C.

[0107] [tire] A heavy-duty tire having a tread including the cap rubber layer 30 and the base rubber layer 28 can be manufactured by a normal method using the above-mentioned rubber composition. That is, an unvulcanized rubber composition obtained by blending the above-mentioned components with the rubber component as necessary is extruded in an extruder equipped with a die of a predetermined shape to match the shapes of the cap rubber layer 30 and the base rubber layer 28, laminated together with other tire components on a tire building machine, and molded by a normal method to form an unvulcanized tire, and the unvulcanized tire is heated and pressurized in a vulcanizer to manufacture a heavy-duty tire.

[0108] The heavy-duty tire according to the present disclosure has excellent wear resistance and chipping resistance, and is therefore suitable for running on rough road surfaces (rough unpaved road surfaces). EXAMPLES

[0109] Hereinafter, the present disclosure will be described based on examples, but the present disclosure is not limited to these examples.

[0110] The various chemicals used in the examples and comparative examples are listed below. NR:TSR20 SBR: SBR1502 manufactured by JSR Corporation (E-SBR, styrene content: 23.5% by mass, vinyl content: 18% by mole, Mw: 420,000) Carbon black 1: Diablack N220 (N2SA: 115m) manufactured by Mitsubishi Chemical Corporation 2 / g) Carbon black 2: Diablack N134 (N2SA:148m) manufactured by Mitsubishi Chemical Corporation 2 / g) Silica 1: Ultrasil VN3 (N2SA: 175 m) manufactured by Evonik Degussa 2 / g, average primary particle diameter: 18nm) Silica 2: Ultrasil 9100GR (N2SA: 230m) manufactured by Evonik Degussa 2 / g, average primary particle diameter: 15nm) Silane coupling agent: Si266 (bis(3-triethoxysilylpropyl) disulfide) manufactured by Evonik Degussa Anti-aging agent: Nocrac 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Stearic acid: Beads of stearic acid camellia manufactured by NOF Corporation Zinc oxide: Zinc oxide No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: Powdered sulfur manufactured by Karuizawa Sulfur Co., Ltd. Vulcanization accelerator 1: Noccela CZ (N-cyclohexyl-2-benzothiazolyl sulfenamide (CBS)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator 2: Noccelaer D (1,3-diphenylguanidine (DPG)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0111] Examples and Comparative Examples According to the compounding recipes shown in Tables 1 and 2, the chemicals other than sulfur and the vulcanization accelerator were kneaded for 1 to 10 minutes using a 1.7 L closed type Banbury mixer until the discharge temperature reached 150 to 160 ° C., to obtain a kneaded product. Next, using a two-axis open roll, sulfur and the vulcanization accelerator were added to the kneaded product obtained, and the mixture was 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 shape of the cap rubber layer and the base rubber layer using an extruder equipped with a predetermined shape of a die, and laminated together with other tire components to produce an unvulcanized tire whose tread portion is composed of the above two rubber layers, and press-vulcanized for 12 minutes under the condition of 170 ° C. to produce each test tire (12R22.5, truck and bus tires) shown in Tables 3 and 4.

[0112] The test tires thus obtained were subjected to the following evaluations. The evaluation results are shown in Tables 3 and 4.

[0113] <Viscoelasticity test> Vulcanized rubber was collected from the cap rubber layer and base rubber layer of each test tire and cut into pieces 4 mm wide, 40 mm long and 2 mm thick. The storage modulus E' (MPa) and loss tangent (tan δ) were measured using a viscoelasticity spectrometer manufactured by Iwamoto Seisakusho Co., Ltd. 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.

[0114] <Tensile test> A 1 mm thick dumbbell-shaped No. 7 test piece was cut from the base rubber layer of each test tire so that the tensile direction was the tire circumferential direction, and a tensile test was carried out in accordance with JIS K 6251:2017 at a 23°C atmosphere and a tensile speed of 3.3 mm / sec to measure the modulus (MPa) at 200% elongation and the elongation at break EB (%). The thickness direction of the sample was the tire radial direction.

[0115] <Low fuel consumption performance> Using a rolling resistance tester, the rolling resistance was measured when the test tire was run with a rim of 15×6JJ, an internal pressure of 230 kPa, a load of 3.43 kN, and a speed of 80 km / h, and the reciprocal was expressed as an index, with Comparative Example 2 being set at 100. The larger the value, the smaller the rolling resistance and the more excellent the fuel economy performance.

[0116] <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 was measured from an initial speed of 100 km / h on a wet road surface. The results were expressed as an index using the following formula, with Comparative Example 1 being set at 100. A higher index indicates better wet grip performance. The minimum target value is 100 or more, and 105 or more is preferable. (Wet grip performance index) = (Braking distance of the tire of Comparative Example 2) / (Braking distance of each test tire)×100

[0117] <Wear resistance> Each test tire was fitted to all wheels of a truck (2-D vehicle) with a maximum load capacity of 10 tons, and the tire tread groove depth after a driving distance of 8000 km was measured, and the driving distance when the tire groove depth was reduced by 1 mm was calculated. The results are expressed as an index according to the following calculation formula, with the driving distance when the tire groove depth of Comparative Example 1 was reduced by 1 mm being set at 100. The higher the index, the better the wear resistance. (Wear resistance index)=(Distance traveled when the tire tread of each test tire is reduced by 1 mm) / (Distance traveled when the tire tread of Comparative Example 2 is reduced by 1 mm)×100

[0118] <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 state of block chipping after a driving distance of 8000 km was visually observed and scored. The results are expressed as an index according to the following formula, with the score of Comparative Example 1 being set at 100. The higher the index, the less block chipping occurred and the higher the chipping resistance. (Chipping resistance performance index) = (Score of each test tire) / (Score of Comparative Example 2 tire)×100

[0119] <Tear resistance> After the above-mentioned wear resistance performance test was performed, each test tire was visually inspected for the presence or absence of taring. Tear was indicated as "+" when taring occurred, and "-" when no taring occurred.

[0120] [Table 1]

[0121] [Table 2]

[0122] [Table 3]

[0123] [Table 4]

[0124] The results in Tables 1 to 4 show that a heavy-duty tire of the present disclosure having a tread in which the cap rubber layer contains a specified rubber component and silica and the loss tangent tan δ of the base rubber layer is within a specified range exhibits well-balanced improvements in fuel economy, wet grip performance, wear resistance, chipping resistance, and tear resistance. [Explanation of symbols]

[0125] 2. Heavy duty tires 4 Tread 6 Sidewall 10 Beads 12. Carcass 14 Inner liner 18 Belt layer 20 Covering rubber 22 Tread surface 24 Main groove 28 Base rubber layer 30 Cap rubber layer 32 Bead core 34 Apex 36 Carcass ply 38 (Base rubber layer) tire radial outer surface 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 on the outer side of the carcass in the tire radial direction and on the inner side of the tread portion, The belt layer is formed by 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, The tread has a plurality of main grooves extending continuously in a tire circumferential direction, The tread has a cap rubber layer constituting a tread surface and a base rubber layer adjacent to the radially inner side of the cap rubber layer, the cap rubber layer and the base rubber layer are made of a rubber composition containing a rubber component, the rubber component constituting the cap rubber layer contains an isoprene-based rubber and a styrene-butadiene rubber, The rubber composition constituting the cap rubber layer has a nitrogen adsorption specific surface area (N 2 SA) is 180m 2 / g or more of silica, The heavy duty tire has a rubber composition constituting the base rubber layer, the rubber composition having a tan δ at 70° C. of 0.04 to 0.

07.

2. 2. The heavy-duty pneumatic tire according to claim 1, wherein in a tire meridian cross section including the tire rotation axis, the following formulas (1) to (4) are satisfied, where Te is a thickness of the cap rubber layer on a normal line from an end of the third belt in the tire rotation axis direction down to the tread surface, Tt2 is a distance from the third belt layer to the tread surface on the normal line, Tt1 is a distance from the second belt layer to the tread surface on the normal line, Tm is a thickness of the cap rubber layer at a position that is 1 / 2 the distance from the tire equatorial plane to the end of the third belt in the tire rotation axis direction, and Tc is a thickness of the cap rubber layer at the tire equatorial plane. 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. 3. The heavy duty tire according to claim 1, further comprising a sulfide-based silane coupling agent in an amount of 8 to 18 parts by mass per 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 claims 1 to 3, wherein a rubber component constituting the cap rubber layer contains 65 mass % or more of an isoprene-based rubber.

5. The heavy duty tire according to any one of claims 1 to 4, wherein the modulus of the rubber composition constituting the base rubber layer at 200% elongation at 23°C is 5.0 to 14.

0.

6. The tire according to any one of claims 1 to 5, wherein the rubber composition constituting the base rubber layer has an elongation at break of 380% or more.

7. The heavy duty tire according to any one of claims 1 to 6, wherein the Te is smaller than the Tm and the Tc.

8. The heavy load tire according to any one of claims 1 to 7, wherein a ratio (Ec' / Eb') of a storage modulus Ec' at 70°C of a rubber composition constituting the cap rubber layer to a storage modulus Eb' at 70°C of a rubber composition constituting the base rubber layer is 1.1 to 1.

7.

9. The tire for heavy loads according to any one of claims 1 to 8, wherein a ratio (Hm / Tt3) of a groove depth Hm of the main groove closest to the tire equatorial plane to a distance Tt3 from a tread surface at the tire equatorial plane to the outermost belt layer in the tire radial direction is 0.50 to 0.

90.

10. The heavy duty tire according to any one of claims 1 to 9, wherein a ratio (Te / Hs) of the Te to a groove depth Hs of the main groove closest to a tread end is 0.50 to 0.

90.

11. The heavy load tire according to any one of claims 1 to 10, wherein a distance Wb (Wb / Wa) in the tire rotational axis direction from the tire equatorial plane to a groove edge of the main groove closest to the tire equatorial plane relative to a distance Wa in the tire rotational axis direction from the tire equatorial plane to a layer end of the belt layer outermost in the tire radial direction is 0.50 to 0.

90.

12. The heavy duty tire according to any one of claims 1 to 11, wherein the rubber composition constituting the cap rubber layer contains at least one resin selected from the group consisting of a phenol resin, a cresol resin, and a resorcinol resin.

Images