Heavy-duty tires

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 4 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 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 1

Description

[Technical Field]

[0001] This invention relates to a heavy-duty tire that offers a balanced improvement in fuel efficiency, wet grip performance, wear resistance, chipping resistance, and tear resistance. [Background technology]

[0002] A known technique for improving the wear resistance of truck and bus tires involves micronizing or highly structuring carbon black (for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 6-279624 [Overview of the project] [Problems that the invention aims to solve]

[0004] The methods described above for micronizing or increasing the structure of carbon black are not sufficient to improve the fuel efficiency of tires. Furthermore, the deterioration of processability due to micronization can worsen the dispersibility of carbon black, which can conversely worsen the wear resistance of tires. Therefore, there were limitations to conventional methods of improving performance through the modification of carbon black.

[0005] Furthermore, due to the impact of recent environmental regulations, there is a growing demand for truck and bus tires to achieve a high level of balance not only in wear resistance, but also in fuel efficiency, wet grip performance, and chipping resistance.

[0006] The present invention aims to provide a heavy-duty tire that offers a balanced improvement in fuel efficiency, wet grip performance, wear resistance, chipping resistance, and tear resistance. [Means for solving the problem]

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

[0008] In other words, the present invention is [1] A heavy-duty tire having a carcass extending from the tread portion through the sidewall portion to the bead core of the bead portion, and a belt layer disposed on the radially outer side of the carcass and on the inner side of the tread portion, wherein the belt layer is formed by belt plies including a first belt layer, a second belt layer, and a third belt layer, which are laminated in order from the radially inner side of the tire, and the tread Department However, it has multiple main grooves that extend continuously in the circumferential direction of the tire, and the tread Department However, the cap rubber layer and the cap rubber layer that constitute the tread surface tire The cap rubber layer and the base rubber layer are made of a rubber composition containing rubber components, the rubber components constituting the cap rubber layer include isoprene rubber and butadiene rubber, and the rubber composition constituting the cap rubber layer has a nitrogen adsorption specific surface area (N2SA) of 180 m² per 100 parts by mass of rubber components. 2 A heavy-duty tire containing 30 parts by mass or more of silica at a concentration of / g or more, wherein the tanδ of the rubber composition constituting the base rubber layer at 70°C is 0.04 to 0.07. [2] In the tire meridian cross section including the tire rotation axis, the third belt layer Te is the thickness of the cap rubber layer along the normal line drawn from the end of the tire's rotation axis down to the tread surface, Tt2 is the distance from the third belt layer to the tread surface along the normal line, Tt1 is the distance from the second belt layer to the tread surface along the normal line, and Tt1 is the distance from the tire's equator down to the third belt layerWhen the thickness of the cap rubber layer at a position half the distance from the end of the tire's rotation axis is Tm, and the thickness of the cap rubber layer at the tire's equatorial plane is Tc, the following heavy load described in [1] above satisfies formulas (1) to (4). Use No, 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] A heavy-duty tire according to [1] or [2] above, wherein the rubber composition constituting the cap rubber layer contains 8 to 18 parts by mass of a sulfide-based silane coupling agent per 100 parts by mass of the silica contained in the rubber composition, [4] The rubber component constituting the cap rubber layer contains 65% by mass or more of isoprene-based rubber, as described in any of [1] to [3] above. Heavy load tire, [5] The modulus of the rubber composition constituting the base rubber layer at 23°C when stretched to 200% is 5.0 to 14.0 MPa The heavy-duty tires described in any of the above [1] to [4], [6] The rubber composition constituting the base rubber layer has an elongation at break of 380% or more, as described in any of [1] to [5] above. Heavy load tire, [7] The above [ 2 Heavy-duty tires as described in any of the following: [8] A heavy-duty tire according to any one of [1] to [7] above, wherein the ratio (Ec' / Eb') of the storage modulus Ec' of the rubber composition constituting the cap rubber layer to the storage modulus Eb' of the rubber composition constituting the base rubber layer at 70°C is 1.1 to 1.7. [9] A heavy-duty tire according to any of [1] to [8] above, wherein the ratio (Hm / Tt3) of the groove depth Hm of the main groove closest to the tire equator to the distance Tt3 from the tread surface to the outermost belt layer in the tire radial direction is 0.50 to 0.90. 〔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 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 (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 at least one selected from the group consisting of a phenol resin, a cresol resin, and a resorcin 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] It is a cross-sectional view showing a part of a heavy-duty tire according to an embodiment of the present disclosure. [Figure 2] It is an enlarged cross-sectional view showing a part of the heavy-duty tire of FIG. 1.

Mode for Carrying Out the Invention

[0011] A heavy-duty tire which is an 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 in the tire radial direction and inside the tread portion of the carcass, wherein 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, and the tread DepartmentHowever, it has multiple main grooves that extend continuously in the circumferential direction of the tire, and the tread Department However, the cap rubber layer and the cap rubber layer that constitute the tread surface tire The cap rubber layer and the base rubber layer are made of a rubber composition containing rubber components, the rubber components constituting the cap rubber layer include isoprene rubber and butadiene rubber, and the rubber composition constituting the cap rubber layer has a nitrogen adsorption specific surface area (N2SA) of 180 m² per 100 parts by mass of rubber components. 2 This is a heavy-duty tire containing 30 parts by mass or more of silica at a concentration of 1 / g or more, and the tanδ of the rubber composition constituting the base rubber layer at 70°C is 0.04 to 0.07.

[0012] While not intended to be theoretically bound, the following mechanisms are considered in this disclosure to be able to improve the fuel efficiency, wet grip performance, wear resistance, chipping resistance, and tear resistance of heavy-duty tires in a balanced manner: By setting a predetermined combination of rubber components, silica content, and nitrogen adsorption specific surface area (N2SA) to be compounded in the cap rubber layer, silica can be highly finely dispersed, forming a strong silica network and enabling a high degree of balance between the strength and elongation of the rubber composition during stretching. Furthermore, by compounding silica in the cap rubber layer, the hydrophilicity of the rubber composition is increased, improving its ability to follow wet road surfaces. In addition, by setting the tanδ of the rubber composition constituting the base rubber layer at 70°C within a predetermined range, the temperature rise at the belt end can be suppressed, preventing fracture originating from the steel filament end, and also suppressing a decrease in the fracture strength of the base rubber layer itself. Thus, it is believed that the aforementioned physical properties of the rubber composition constituting each layer of the tread, in cooperation with the tire structure, can improve fuel efficiency, wet grip performance, wear resistance, chipping resistance, and tear resistance in a balanced manner.

[0013] The heavy-duty tire of this disclosure has a third belt in the tire meridian cross section including the tire rotation axis. layerTe is the thickness of the cap rubber layer along the normal line drawn from the end of the tire's rotation axis down to the tread surface, Tt2 is the distance from the third belt layer to the tread surface along the normal line, Tt1 is the distance from the second belt layer to the tread surface along the normal line, and Tt1 is the distance from the tire's equator down to the third belt layer When the thickness of the cap rubber layer at a position half the distance from the end of the tire's rotation axis is Tm, and the thickness of the cap rubber layer at the tire's equatorial plane is Tc, it is preferable that the following equations (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 per 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 isoprene-based rubber.

[0016] The modulus of the rubber composition constituting the base rubber layer at 23°C when stretched to 200% 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 modulus Ec' of the rubber composition constituting the cap rubber layer to the storage modulus Eb' of the rubber composition constituting the base rubber layer at 70°C 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's equatorial plane to the distance Tt3 from the tread surface at the tire's equatorial plane to the outermost belt layer in the tire's radial direction is preferably 0.50 to 0.90.

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

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

[0023] Preferably, the rubber composition constituting the cap rubber layer contains one or more selected from the group consisting of phenolic resin, cresol resin, and resorcinol resin.

[0024] A heavy-duty tire, which is one embodiment of this disclosure, will be described in detail below. However, the following description is illustrative for the purpose of explaining this disclosure and is not intended to limit the technical scope of the present invention to this scope only. In this specification, when a numerical range is indicated using "~", it includes the numerical values ​​at both ends of the range.

[0025] Figure 1 is a cross-sectional view showing a part of a heavy-duty tire according to one embodiment of the present disclosure. In Figure 1, the vertical direction is the radial direction of the heavy-duty tire 2, the left-right direction is the tire axis direction of the heavy-duty tire 2, and the direction perpendicular to the plane of the paper is the circumferential direction of the heavy-duty tire 2. In Figure 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 comprises 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. The tread surface 22 has a plurality of main grooves 24 that extend continuously in the circumferential direction of the tire.

[0027] The outer end of the tread 4 in the axial direction of the tire rotation and its vicinity are referred to as the shoulder portion of the heavy-duty tire 2. In this disclosure, for clarity, the portion of the tire rotation axial direction that is outward from the main groove 24s closest to the tread end will be referred to as the shoulder portion.

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

[0029] The carcass 12 consists of carcass plies 36. The carcass plies 36 are stretched between the beads 10 on both sides and run along the tread 4 and sidewall 6. The carcass plies 36 are folded around the bead core 32 from the inside to the outside in the tire rotation axis direction. The carcass plies 36 consist 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 direction of the tire rotation axis. The belt layer 18 is located on the inside of the tread 4 in the tire radial direction. The belt layer 18 is located on the radially outside of the carcass 12 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 stacked in order from the inside in the radial direction of the tire. Figure 1 shows a case where a fourth belt layer 18d is placed on the radially outer side of the third belt layer 18c. The first belt layer 18a is stacked on the carcass 12. In Figure 1, the second belt layer 18b has the largest width among the four layers in the tire rotation axis direction, and the fourth belt layer 18d has the smallest width among the four layers, but the configuration is not limited to this.

[0032] Figure 2 is an enlarged cross-sectional view showing the vicinity of the shoulder portion of the heavy-duty tire 2 shown in Figure 1. As shown, 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 the ends of the second belt layer 18b and the third belt layer 18c.

[0033] The tread 4 comprises a base rubber layer 28 and a cap rubber layer 30, with the outer surface of the cap rubber layer 30 forming the tread surface 22, and the base rubber layer 28 adjacent to the inner side of the cap rubber layer 30 in the tire radial direction. In addition, there may be one or more further rubber layers between the base rubber layer 28 and the belt layer 18, as long as the effects of this disclosure are achieved.

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

[0035] In the heavy-duty tire of this disclosure, in a tire meridian cross-section including the tire rotation axis, the thickness of the cap rubber layer 30 on the normal N drawn from the tire rotation axis 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 N is Tt2, the distance from the second belt layer to the tread surface 22 on the normal N is Tt1, and the distance from the tire equatorial plane EQ to the third belt layer When Tm is the thickness of the cap rubber layer 30 at a position half the distance from the tire rotation axis end, and Tc is the thickness of the cap rubber layer 30 at the tire equatorial plane EQ, it is preferable that the following equations (1) to (4) are satisfied. Note that the normal N is a line that passes through the tire rotation axis end of the tire radial outer surface of the third belt layer and is perpendicular to the tangent at that tire rotation axis 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 becomes difficult to secure 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 stages of tire wear. Furthermore, the base rubber layer 28 is more likely to be exposed on the tire surface in the final stages of tire wear, leading to a decrease in tire life and a tendency for uneven wear. On the other hand, when Te / Tt2 is greater than 0.75, the volume of the base rubber layer 28 in the shoulder area is insufficient, causing the temperature to rise more easily during driving from the tire rotation axis end of the second belt layer to the vicinity of the tire rotation axis end of the third belt layer. This reduces the effect of suppressing adhesive failure between the steel filaments and rubber at the tire rotation axis end of the third belt layer. This adhesive failure at the tire rotation axis end of the third belt layer can result in a fracture inside the rubber between the second and third belt layers, propagating toward the tire equator and potentially causing damage to the entire tire. For similar reasons, it is preferable that Te and Tt1 satisfy formula (2) above.

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

[0038] If (Te / Tt2)-(Te / Tt1) is less than 0.20, it becomes more difficult to mitigate the shear between the axial end of the second belt layer and the axial end of the third belt layer due to changes in the shape of the tread during driving, and the aforementioned fracture tends to become more difficult to suppress. Also, if (Te / Tt2)-(Te / Tt1) is greater than 0.70, the distance between the axial end of the second belt layer and the axial end of the third belt layer becomes too large, and it tends to become more difficult to maintain an appropriate tread shape.

[0039] From the viewpoint of balancing tire performance after the later stages 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 of the groove depth Hm of the main groove 24m closest to the tire's equatorial plane (Hm / Tt3) to the distance Tt3 from the tread surface at the tire's equatorial plane to the outermost belt layer in the tire's radial direction (the fourth belt layer 18d in Figure 1) is preferably 0.50 or more, more preferably 0.55 or more, and even more preferably 0.60 or more. Furthermore, 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, chipping resistance can be further improved.

[0041] The ratio of Te to groove depth Hs of the main groove 24s closest to the tread edge (Te / Hs) is preferably 0.50 or higher, more preferably 0.55 or higher, and even more preferably 0.60 or higher. Furthermore, Te / Hs is preferably 0.90 or lower, more preferably 0.85 or lower, and even more preferably 0.80 or lower. Moreover, Te is preferably smaller than Tm and Tc. By placing a low-heat-generating base rubber layer 28 in the shoulder portion 26, which is a part that experiences large strain and generates large amounts of heat, the heat generation of the entire tread 4 can be reduced. As a result, the amount of base rubber layer 28 near the tire equator can be reduced, which in turn suppresses the situation where the base rubber layer 28 comes into contact with the road surface in the final stages of wear, thereby maintaining chipping resistance.

[0042] The distance Wa in the axial direction of the tire rotation from the tire equatorial plane to the edge of the outermost belt layer in the radial direction of the tire (fourth belt layer 18d in Figure 1) is relative to the distance Wb in the axial direction of the tire rotation from the tire equatorial plane to the groove edge of the main groove closest to the tire equatorial plane. ratio The (Wb / Wa) ratio is preferably 0.50 or higher, more preferably 0.55 or higher, and even more preferably 0.60 or higher. Furthermore, the Wb / Wa ratio is preferably 0.90 or lower, more preferably 0.85 or lower, and even more preferably 0.80 or lower. By setting the Wb / Wa ratio within the above range, chipping resistance can be further improved.

[0043] In this 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 10Hz. The ratio (Ec' / Eb') of the storage modulus Ec' of the rubber composition constituting the cap rubber layer 30 to the storage modulus Eb' of the rubber composition constituting the base rubber layer 28 at 70°C 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. Furthermore, 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. Note that the 70°C E' of each rubber layer can be appropriately adjusted depending on the type and amount of the rubber components, fillers, silane coupling agents, softeners, etc.

[0044] In this disclosure, "70°C tanδ" 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 10Hz. The 70°C tanδ of the rubber composition constituting the base rubber layer 28 is 0.04 or higher, preferably 0.05 or higher. If the 70°C tanδ of the rubber composition constituting the base rubber layer 28 is less than 0.04, the fracture strength of the base rubber compound itself decreases significantly, raising concerns about tearing due to the fracture 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 lower, preferably 0.06 or lower, from the viewpoint of suppressing temperature rise at the belt end and suppressing fracture originating from the steel filament end. Furthermore, from the viewpoint of exhibiting a better effect in improving fuel efficiency, it is preferable that the value of the 70°C tanδ of the rubber composition constituting the cap rubber layer 30 is greater than the value of the 70°C tanδ of the rubber composition constituting the base rubber layer 28. The 70°C tanδ of each rubber layer can be appropriately adjusted depending on the type and amount of rubber components, fillers, silane coupling agents, softeners, etc.

[0045] In this disclosure, the modulus at 200% stretch refers to the tensile stress at 100% elongation in the grain direction, measured in accordance with JIS K 6251:2017 under conditions of a 23°C atmosphere and a tensile speed of 3.3 mm / sec. From the viewpoint of ensuring the rigidity of the tread portion and suppressing uneven wear, the modulus of the base rubber layer 28 at 200% stretch is preferably 5.0 MPa or higher, more preferably 5.5 MPa or higher, even more preferably 6.0 MPa or higher, and particularly preferably 6.5 MPa or higher. On the other hand, the modulus of the base rubber layer 28 at 200% stretch is preferably 14.0 MPa or lower, and preferably 13.5 MPa. below More preferably, 13.0 MPa or less is even more preferred, and 12.5 MPa or less is particularly preferred. If the modulus of the base rubber layer 28 when stretched to 200% exceeds 14.0 MPa, external forces are difficult to dissipate, and the input concentrates at the interface between the cap rubber layer 30 and the base rubber layer 28, raising concerns about crack propagation at the interface. Furthermore, it is preferable that the modulus of the cap rubber layer 30 when stretched to 200% is greater than the modulus of the base rubber layer 28 when stretched to 200%. In this specification, "processing direction" means the rolling direction when forming a rubber sheet by extrusion or shearing.

[0046] In this disclosure, elongation at break (EB) refers to the elongation at break (elongation at snapping) measured in accordance with JIS K 6251:2017, under conditions of a tensile speed of 3.3 mm / second in a 23°C atmosphere. The EB of the cap rubber layer 30 is preferably 400% or more, and more preferably 420% or more, from the viewpoint of maintaining surface smoothness. The EB of the base rubber layer 28 is preferably 380% or more, and more preferably 400% or more, from the viewpoint of suppressing internal breakage of the rubber between the second belt layer 18b and the third belt layer 18c. There is no particular upper limit on the EB of the rubber compositions constituting the cap rubber layer 30 and the base rubber layer 28.

[0047] Furthermore, the modulus and EB of each rubber layer at 200% stretch can be appropriately adjusted depending on the type and amount of rubber components, fillers, silane coupling agents, softeners, etc.

[0048] [Rubber composition] The heavy-duty tire of this disclosure can improve fuel efficiency, wet grip performance, wear resistance, chipping resistance, and tear resistance in a balanced manner through the cooperation of the aforementioned tire structure and the aforementioned physical properties of the rubber composition constituting each layer of the tread.

[0049] <Rubber components> The rubber composition (tread rubber composition) constituting each rubber layer of the tread according to this 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 and BR, or it may consist only of isoprene rubber and BR. The rubber component constituting the base rubber layer 28 preferably includes isoprene rubber, or it may consist only of isoprene rubber.

[0050] (Isoprene rubber) As isoprene-based rubbers, for example, isoprene rubber (IR) and natural rubber, which are common in the tire industry, can be used. Natural rubber includes not only unmodified natural rubber (NR), but also 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-based rubbers may be used individually or in combination of two or more types.

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

[0052] In the rubber composition constituting the cap rubber layer 30, the content of 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 affinity with isoprene-based rubber, increasing the content of isoprene-based rubber in the rubber component and dispersing silica in the isoprene-based rubber phase which forms the sea phase tends to improve the overall strength of the matrix, and further improve the abrasion resistance and fracture characteristics. On the other hand, from the viewpoint of wet grip performance, 95% by mass or less is preferred, 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% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. The rubber component may consist solely of isoprene-based rubber.

[0054] (BR) BR is not particularly limited, and 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 butadiene rubber synthesized using a rare-earth element catalyst (rare-earth 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 may be used individually or in combination of two or more types.

[0055] High-cis BR can be commercially available from companies such as Nippon Zeon Co., Ltd., Ube Industries, Ltd., and JSR Corporation. Including high-cis BR can improve wear resistance. The cis content is preferably 95% by mass or more, more preferably 96% by mass or more, even 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.

[0056] Rare earth-based BR is synthesized using a rare earth element catalyst, and has a vinyl content of preferably 1.8 mol% or less, more preferably 1.0 mol% or less, and even more preferably 0.8 mol or less, and a cis content of preferably 95% by mass or more, more preferably 96% by mass or more, even more preferably 97% by mass or more, and particularly preferably 98% by mass or more. As rare earth-based BR, commercially available products from companies such as Lanxess can be used.

[0057] SPB-containing BR refers to a type in which 1,2-syndiotactic polybutadiene crystals are not simply dispersed in BR, but are chemically bonded to and dispersed in BR. Such SPB-containing BR can be commercially available from companies such as Ube Industries, Ltd.

[0058] Modified BRs include those obtained by polymerizing 1,3-butadiene with a lithium initiator and then adding a tin compound, with the ends of the modified BR molecule being linked by a tin-carbon bond (tin-modified BR), and butadiene rubber having a condensed alkoxysilane compound at the active end of the butadiene rubber (modified BR for silica). Examples of such modified BRs include BR1250H (tin-modified) and S-modified polymer (modified for silica) manufactured by ZS Elastomer Co., Ltd.

[0059] The weight-average molecular weight (Mw) of BR is preferably 300,000 or more, more preferably 350,000 or more, and even more preferably 400,000 or more, from the viewpoint of abrasion resistance and grip performance. Furthermore, from the viewpoint of crosslinking uniformity, it is preferably 2,000,000 or less, and more preferably 1,000,000 or less. Mw can be determined by converting the measured value by gel permeation chromatography (GPC) (for example, the GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMALTIPORE HZ-M manufactured by Tosoh Corporation) to standard polystyrene equivalent.

[0060] From the viewpoint of wear resistance, the content of BR in the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and particularly preferably 20% by mass or more. Furthermore, from the viewpoint of wet grip performance, it is preferably 40% by mass or less, more preferably 35% by mass or less, even more preferably 30% by mass or less, and particularly preferably 25% by mass or less.

[0061] (SBR) There are no particular limitations on SBR, and examples 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 in which the terminals and / or main chain are modified, and modified SBRs coupled with tin, silicon compounds, etc. (such as condensates and those with branched structures). Among these, E-SBR is preferred because it can significantly improve fuel efficiency and wear resistance. These SBRs may be used individually or in combination of two or more types.

[0062] (Other rubber components) The rubber components relating to this disclosure may include rubber components other than the isoprene-based rubber, SBR, and BR mentioned above. Other rubber components that can be crosslinked are commonly used in the tire industry, and examples include 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, polyethylene chloride rubber, fluororubber (FKM), acrylic rubber (ACM), hydrin rubber, and the like. These other rubber components may be used individually or in combination of two or more.

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

[0064] (Silica) By blending silica into the rubber composition for a tread according to the present disclosure, the low fuel consumption performance, wet grip performance, abrasion 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 preferable because it has many silanol groups. These silicas may be used alone or in combination of two or more.

[0065] 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. Further, 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. The N2SA of silica in this specification 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 rubber component, from the viewpoint of balancing fuel efficiency and wet grip performance. In the rubber composition constituting the cap rubber layer 30, the silica content per 100 parts by mass of 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. Furthermore, from the viewpoint of suppressing a decrease in fuel efficiency and wear resistance due to deterioration of silica dispersibility in 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.

[0067] In the rubber composition constituting the base rubber layer 28, the silica content per 100 parts by mass of 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. Furthermore, from the viewpoint of low fuel consumption performance and wear 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.

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

[0069] The nitrogen adsorption specific surface area (N2SA) of carbon black is 50m², considering its weather resistance and reinforcing properties. 2 Preferably 80m / g or more. 2 More preferably 100m / g or more, 2 A value of 250m or more is even more preferable. Furthermore, from the viewpoint of dispersibility, low fuel consumption, fracture characteristics, and durability, 250m is preferable. 2 Preferably less than / g, 220m 2 A value of less than / g is more preferable. In this specification, the N2SA of carbon black is the value measured in accordance with 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".

[0070] In the rubber composition constituting the cap rubber layer 30, the content of carbon black per 100 parts by mass of 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 reinforcing properties. Furthermore, 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.

[0071] In the rubber composition constituting the base rubber layer 28, the content of carbon black per 100 parts by mass of 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 properties. Furthermore, 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.

[0072] Other fillers commonly used in the tire industry, such as aluminum hydroxide, calcium carbonate, alumina, clay, and talc, can be used in addition to silica and carbon black.

[0073] In the rubber composition constituting the cap rubber layer 30, the silica content in 100% by mass of the total of silica and carbon black 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. Furthermore, the silica content 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 100% by mass of silica and carbon black is preferably 5% by mass or more, and more preferably 10% by mass or more. Furthermore, the silica content is preferably 30% by mass or less, and more preferably 25% by 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 wear resistance performance. Furthermore, from the viewpoint of suppressing a decrease in fuel efficiency and wear 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. Furthermore, 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 conventionally been used in combination with silica in the tire industry can be used, for example: mercapto-type silane coupling agents such as 3-mercaptopropyltrimethoxysilane, Momentive's NXT-Z100, NXT-Z45, and NXT; sulfide-type silane coupling agents such as bis(3-triethoxysilylpropyl) disulfide and bis(3-triethoxysilylpropyl) tetrasulfide; and thioester-type silane coupling agents such as 3-octanoylthio-1-propyltriethoxysilane, 3-hexanoylthio-1-propyltriethoxysilane, and 3-octanoylthio-1-propyltrimethoxysilane. Examples of coupling agents include: 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; and chloro-based silane coupling agents such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. 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 individually 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 part 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. Furthermore, from the viewpoint of preventing a decrease in wear resistance, it 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] From the viewpoint of improving silica dispersibility, the content of silane coupling agent (preferably sulfide-based silane coupling agent) per 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. 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 components mentioned above, the rubber composition relating to this 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 softening agents include resin components, oils, and liquid rubber.

[0082] The resin components are not particularly limited, but examples 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 individually or in combination of two or more.

[0083] Phenolic resins are not particularly limited, but examples include phenol-formaldehyde resin, alkylphenol-formaldehyde resin, alkylphenol-acetylene resin, and oil-modified phenol-formaldehyde resin.

[0084] When a resin component is included, the content of the resin component 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. Furthermore, from the viewpoint of suppressing heat generation, 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.

[0085] Examples of oils include process oils, vegetable oils, and animal oils. Examples of process oils include paraffinic process oils, naphthenic process oils, and aromatic process oils. Furthermore, for environmental reasons, process oils with a low content of polycyclic aromatic compounds (PCA) can be used. Examples of low-PCA process oils include light extraction solvates (MES), processed distillate aromatic extracts (TDAEs), and heavy naphthenic oils.

[0086] When oil is included, the oil content per 100 parts by mass of 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. Furthermore, from the viewpoint of wear resistance, it is preferably 120 parts by mass or less, more preferably 100 parts by mass or less, and even more preferably 90 parts by mass or less. In this specification, the oil content also includes the amount of oil contained in the oil-spread rubber.

[0087] Liquid rubber is not particularly limited as long as it is a polymer that is in a liquid state at room temperature (25°C), but examples 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 individually or in combination of two or more.

[0088] When liquid rubber is included, its content per 100 parts by mass of 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. Furthermore, the liquid rubber content is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 20 parts by mass or less.

[0089] When wax is included, the amount of wax per 100 parts by mass of 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. Furthermore, from the viewpoint of preventing whitening of the tire due to bloom, it is preferably 10 parts by mass or less, and more preferably 5 parts by mass or less.

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

[0091] When processing aids are included, the content per 100 parts by mass of rubber component is preferably 0.5 parts by mass or more, and more preferably 1 part by mass or more, from the viewpoint of exhibiting an effect of improving processability. Furthermore, from the viewpoint of abrasion resistance and fracture strength, it is preferably 10 parts by mass or less, and more preferably 8 parts by mass or less.

[0092] While not particularly limited, examples of anti-aging agents include amine-based, quinoline-based, quinone-based, phenol-based, and imidazole-based compounds, as well as metal carbamate salts. 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, and N-cyclohexyl-N'-phenyl-p-phenylenediamine are preferred, as are quinoline-based anti-aging agents such as 2,2,4-trimethyl-1,2-dihydroquinoline polymer and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline. These anti-aging agents may be used individually or in combination of two or more.

[0093] When an anti-aging agent is included, the content per 100 parts by mass of rubber component is preferably 0.5 parts by mass or more, and more preferably 1 part by mass or more, from the viewpoint of the rubber's resistance to ozone cracking. Furthermore, from the viewpoint of wear resistance and wet grip performance, it is preferably 10 parts by mass or less, and more preferably 5 parts by mass or less.

[0094] When stearic acid is included, its content 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 processability. Furthermore, from the viewpoint of vulcanization rate, it is preferably 10 parts by mass or less, and more preferably 5 parts by mass or less.

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

[0096] Sulfur is preferably used as a vulcanizing agent. Suitable sulfur varieties include powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur.

[0097] When sulfur is included as a vulcanizing agent, the amount of sulfur per 100 parts by mass of 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 a sufficient vulcanization reaction. Furthermore, from the viewpoint of preventing deterioration, it 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. When oil-containing sulfur is used as the vulcanizing agent, the amount of vulcanizing agent is the total amount of pure sulfur contained in the oil-containing sulfur.

[0098] Examples of vulcanizing agents other than sulfur include alkylphenol-sulfur chloride condensates, 1,6-hexamethylene-dithiosulfate sodium dihydrate, and 1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane). These non-sulfur vulcanizing agents can be purchased commercially from companies such as Taoka Chemical Industries, Ltd., Lanxess Corporation, and Flexis.

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

[0100] Examples of sulfenamide-based vulcanization accelerators include N-tert-butyl-2-benzothiazolyl sulfenamide (TBBS), N-cyclohexyl-2-benzothiazolyl sulfenamide (CBS), and N,N-dicyclohexyl-2-benzothiazolyl sulfenamide (DCBS). Among these, N-tert-butyl-2-benzothiazolyl sulfenamide (TBBS) is preferred.

[0101] Examples of guanidine-based vulcanization accelerators include 1,3-diphenylguanidine (DPG), 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, di-o-tolylguanidine salts of dicatecholborate, 1,3-di-o-cumenylguanidine, 1,3-di-o-biphenylguanidine, and 1,3-di-o-cumenyl-2-propionylguanidine. Among these, 1,3-diphenylguanidine (DPG) is preferred.

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

[0103] When a vulcanization accelerator is included, its content per 100 parts by mass of the rubber component is preferably 1 part by mass or more, and more preferably 2 parts by mass or more. Furthermore, 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 keeping the content of the vulcanization accelerator within the above range, it tends to be possible to ensure fracture strength and elongation.

[0104] The rubber composition relating to this disclosure can be manufactured by known methods. For example, it can be manufactured by kneading each of the above components using a rubber kneading device such as an open roll or a closed kneader (Banbury mixer, kneader, etc.).

[0105] The mixing process includes, for example, a base mixing process in which compounding agents and additives other than the vulcanizing agent and vulcanization accelerator are mixed, and a final mixing (F mixing) process in which the vulcanizing agent and vulcanization accelerator are added to the mixture obtained in the base mixing process and mixed. Furthermore, the base mixing process can be divided into multiple processes as desired.

[0106] There are no particular limitations on the mixing conditions, but for example, in the base mixing process, mixing is performed at a discharge temperature of 150-170°C for 3-10 minutes, and in the final mixing process, mixing is performed at 70-110°C for 1-5 minutes. There are no particular limitations on the vulcanization conditions, but for example, vulcanization is performed at 150-200°C for 10-30 minutes.

[0107] [tire] A heavy-duty tire having a tread including a cap rubber layer 30 and a base rubber layer 28 can be manufactured by conventional methods using the rubber composition described above. Specifically, an unvulcanized rubber composition, in which the above components are blended with the rubber component as needed, is extruded in an extruder equipped with a die of a predetermined shape to match the shape of the cap rubber layer 30 and the base rubber layer 28, bonded together with other tire components on a tire molding machine, and molded in conventional methods to form an unvulcanized tire. A heavy-duty tire can then be manufactured by heating and pressurizing this unvulcanized tire in a vulcanizing machine.

[0108] The heavy-duty tires described herein have excellent wear resistance and chipping resistance, making them suitable for driving on rough road surfaces (unpaved, uneven roads). [Examples]

[0109] The present disclosure will be described below 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 summarized below. NR:TSR20 BR: UBEPOL BR(registered trademark) 150B manufactured by Ube Industries, Ltd. (cis content: 97% by mass, Mw: 440,000) Carbon Black 1: Mitsubishi Chemical Corporation's Dia Black N220 (N2SA: 115m 2 / g) Carbon Black 2: Mitsubishi Chemical Corporation's Dia Black N134 (N2SA: 148ml) 2 / g) Silica 1: Evonik Degussa's UltraSil VN3 (N2SA: 175m 2 / g, average primary particle diameter: 18nm) Silica 2: Evonik Degussa's UltraSil 9100GR (N2SA: 230m 2 / g, average primary particle diameter: 15nm) Silane coupling agent: Si266 (bis(3-triethoxysilylpropyl) disulfide) manufactured by Evonik Degussa. Anti-aging agent: Nocrack 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Stearic acid: Beads of stearic acid 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: Noxellar CZ (N-cyclohexyl-2-benzothiazolyl sulfenamide (CBS)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator 2: Noxellar D (1,3-diphenylguanidine (DPG)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0111] (Examples and Comparative Examples) According to the formulations shown in Tables 1 and 2, chemicals other than sulfur and vulcanization accelerator were mixed in a 1.7 L sealed Banbury mixer for 1 to 10 minutes until the discharge temperature reached 150 to 160°C to obtain a mixture. Next, sulfur and vulcanization accelerator were added to the mixture using a twin-screw open roll mixer and mixed for 4 minutes until the temperature reached 105°C to obtain an unvulcanized rubber composition. Using the obtained unvulcanized rubber composition, the cap rubber layer and base rubber layer were extruded into shape using an extruder equipped with a die of a predetermined shape, and bonded together with other tire components to produce an unvulcanized tire in which the tread portion consisted of the two rubber layers described above. The test tires (12R22.5, truck / bus tires) described in Tables 3 and 4 were manufactured by press vulcanization at 170°C for 12 minutes.

[0112] The following evaluations were performed on the obtained test tires. 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, cut into pieces 4 mm wide, 40 mm long, and 2 mm thick, and measured using a viscoelastic spectrometer manufactured by Iwamoto Seisakusho Co., Ltd. under the conditions of a temperature of 70°C, initial strain of 10%, dynamic strain of ±2%, and frequency of 10 Hz, with storage modulus E' (MPa) and loss tangent (tanδ) being measured.

[0114] <Tensile Test> A 1 mm thick, dumbbell-shaped No. 7 test specimen was prepared by cutting from the base rubber layer of each test tire so that the tire circumference was the tensile direction. Tensile tests were conducted in accordance with JIS K 6251:2017 at a 23°C atmosphere and a tensile speed of 3.3 mm / second, and the modulus (MPa) at 200% stretch and elongation EB (%) at break were measured. The thickness direction of the sample was the tire radius direction.

[0115] <Fuel efficiency> Using a rolling resistance tester, the rolling resistance of the test tire was measured when it was driven at a rim size of 15×6JJ, an internal pressure of 230kPa, a load of 3.43kN, and a speed of 80km / h. The reciprocal of this value was expressed as an index, with Comparative Example 2 set to 100. A higher value indicates lower rolling resistance and superior fuel efficiency.

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

[0117] <Abrasion resistance> Each test tire was mounted on all wheels of a truck (2-D vehicle) with a maximum load capacity of 10 tons. The groove depth of the tire tread was measured after 8,000 km of driving, and the distance traveled when the tire groove depth decreased by 1 mm was determined. The results are shown as an index calculated using the following formula, with the distance traveled when the tire groove depth decreased by 1 mm in Comparative Example 1 set to 100. A higher index indicates better wear resistance. (Wear resistance index) = (Distance traveled when the tread of each test tire decreases by 1 mm) / (Distance traveled when the tread of the tire in Comparative Example 2 decreases 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 condition of the tread blocks after 8,000 km of driving was visually observed and scored. The results are shown as an index calculated using the following formula, with the score for Comparative Example 1 set at 100. A higher index indicates less tread block chipping and higher chipping resistance. (Chipping resistance index) = (Score of each test tire) / (Score of the tire in Comparative Example 2) × 100

[0119] <Tear resistance> After conducting the above wear resistance test, the presence or absence of tearing was visually checked for each test tire. Tires with tearing were marked with a "+", and those without tearing were marked with a "-".

[0120] [Table 1]

[0121] [Table 2]

[0122] [Table 3]

[0123] [Table 4]

[0124] The results in Tables 1 to 4 show that the heavy-duty tire of this disclosure, which has 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, shows a well-balanced improvement in fuel efficiency, 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 (Outer surface of the base rubber layer in the radial direction of the tire) EQ tire equatorial plane

Claims

1. A heavy-duty tire having a carcass extending from the tread portion through the sidewall portion to the bead core of the bead portion, and a belt layer positioned radially outward of the carcass and on the inside 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, which are stacked in order from the inside in the radial direction of the tire. The tread portion has a plurality of main grooves that extend continuously in the circumferential direction of the tire, The tread portion comprises a cap rubber layer that constitutes the tread surface and a base rubber layer adjacent to the inner side of the cap rubber layer in the tire radial direction. The cap rubber layer and the base rubber layer are composed of a rubber composition containing rubber components. The rubber components constituting the cap rubber layer include isoprene-based rubber and butadiene rubber. The rubber composition constituting the cap rubber layer has a nitrogen adsorption specific surface area (N) measured by the BET method in accordance with ASTM D3037-93, with respect to 100 parts by mass of the rubber component. 2 SA) is 180m 2 It contains 30 parts by mass or more and 110 parts by mass or less of silica at a concentration of / g or more. The loss tangent tanδ of the rubber composition constituting the base rubber layer is 0.04 to 0.07 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. A heavy-duty tire in which the rubber composition constituting the base rubber layer has a modulus of 5.0 to 14.0 MPa at 23°C when stretched to 200%.

2. A heavy-duty tire having a carcass extending from the tread portion through the sidewall portion to the bead core of the bead portion, and a belt layer positioned radially outward of the carcass and on the inside 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, which are stacked in order from the inside in the radial direction of the tire. The tread portion has a plurality of main grooves that extend continuously in the circumferential direction of the tire, The tread portion comprises a cap rubber layer that constitutes the tread surface and a base rubber layer adjacent to the inner side of the cap rubber layer in the tire radial direction. The cap rubber layer and the base rubber layer are composed of a rubber composition containing rubber components. The rubber components constituting the cap rubber layer include isoprene-based rubber and butadiene rubber. The rubber composition constituting the cap rubber layer has a nitrogen adsorption specific surface area (N) measured by the BET method in accordance with ASTM D3037-93, with respect to 100 parts by mass of the rubber component. 2 SA) is 180m 2 It contains 30 parts by mass or more of silica at a concentration of / g or more, In the rubber composition constituting the cap rubber layer, the silica content is 40% by mass or more out of a total of 100% by mass of silica and carbon black. The loss tangent tanδ of the rubber composition constituting the base rubber layer is 0.04 to 0.07 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. A heavy-duty tire in which the rubber composition constituting the base rubber layer has a modulus of 5.0 to 14.0 MPa at 23°C when stretched to 200%.

3. A heavy-duty tire according to claim 1 or 2, wherein, in a tire meridian cross-section including the tire rotation axis, the thickness of the cap rubber layer on the normal line drawn from the tire rotation axis 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 the distance from the tire equator to the tire rotation axis end of the third belt layer is Tm, and the thickness of the cap rubber layer at the tire equator is Tc, 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 of Te to groove depth Hs of the main groove closest to the tread edge (Te / Hs) is 0.50 to 0.

90.

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

7. The heavy-duty tire according to any one of claims 1 to 6, wherein the rubber component constituting the cap rubber layer contains 65% by mass or more of isoprene-based rubber.

8. A heavy-duty tire according to any one of claims 1 to 7, wherein the rubber composition constituting the base rubber layer has an elongation at break of 380% or more.

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

7.

10. A heavy-duty tire according to any one of claims 1 to 9, wherein the ratio of the groove depth Hm of the main groove closest to the tire equator (Hm / Tt3) to the distance Tt3 from the tread surface to the outermost belt layer in the tire radial direction at the tire equator is 0.50 to 0.

90.

11. A heavy-duty tire according to any one of claims 1 to 10, wherein the ratio (Wb / Wa) of the distance Wb from the tire equatorial plane to the groove edge of the main groove closest to the tire equatorial plane to the tire rotation axial distance Wa from the tire equatorial plane to the outermost edge of the belt layer in the radial direction of the tire 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 includes one or more selected from the group consisting of phenolic resin, cresol resin, and resorcinol resin.

13. The heavy-duty tire according to any one of claims 1 to 12, wherein the rubber composition constituting the cap rubber layer contains 1 to 25 parts by mass of carbon black per 100 parts by mass of rubber component.

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