Heavy-duty tires

Abstract

To provide a heavy-duty tire improved in chipping resistance performance on a rough road surface.SOLUTION: A heavy-duty tire comprises a tread part which comprises a first layer constituting a tread surface and a second layer located inside the first layer. The tread surface comprises: a plurality of main grooves extending continuously in a tire circumferential direction; lateral grooves extending from the main grooves in a tire axial direction; and blocks demarcated by the main grooves and the lateral grooves. Each of the blocks comprises a sipe. When a depth (mm) of the sipe is D, and when a thickness (mm) of the first layer is H, D and H satisfy the following relational expression: D / H≤0.95 (1). In the heavy-duty tire, a rubber composition constituting the first layer comprises: a rubber component comprising isoprene-based rubber; and a filler comprising carbon black and silica.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] Chipping refers to a phenomenon in which a part of the rubber forming the surface layer of the tread peels off in scales. During driving, when the surface of the tread contacts the road surface, a part of the rubber on the tread surface is damaged (initial crack), and the shear stress generated during turning or sudden braking concentrates on this damage, causing the crack to progress and chipping to occur. Patent Document 1 describes a tread rubber composition having a predetermined formulation with chipping resistance performance.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to improve the chipping resistance performance of a heavy-duty tire on a rough road surface.

Means for Solving the Problems

[0005] The present invention relates to a heavy-duty tire as follows. A heavy-duty tire having a tread portion including a first layer constituting a tread surface and a second layer located inside the first layer, where the tread surface has a plurality of main grooves extending continuously in the tire circumferential direction, lateral grooves extending from the main grooves in the tire axial direction, and blocks defined by the main grooves and the lateral grooves, the blocks have sipes, when the depth (mm) of the sipes is D and the thickness (mm) of the first layer is H, D and H satisfy the following relational expression, The heavy-duty tire in which the rubber composition constituting the first layer contains a rubber component including an isoprene-based rubber and a filler including carbon black and silica. D / H ≦ 0.95 (1)

Advantages of the Invention

[0006] According to the present invention, it is possible to improve the chipping resistance performance of a heavy-duty tire on a rough road surface.

Brief Description of the Drawings

[0007] [Figure 1] It is a cross-sectional view in a plane including the tire rotation axis of the tire according to an embodiment of the present invention. [Figure 2] It is a plan view showing the tread surface and the tread contact surface of the tire according to an embodiment of the present invention. The enclosed area in the figure is the tread contact surface. [Figure 3] In the tire according to an embodiment of the present invention, it is a plan view showing the tread contact surface. The enclosed area in the figure is the tread contact surface.

Mode for Carrying Out the Invention

[0008] Hereinafter, the present invention will be described. However, the following description is an exemplification for explaining the present invention, and is not intended to limit the technical scope of the present invention only to this description range.

[0009] The heavy-duty tire of the present invention is a heavy-duty tire having a tread portion comprising a first layer constituting the tread surface and a second layer located inside the first layer, wherein the tread surface has a plurality of main grooves extending continuously in the circumferential direction of the tire, transverse grooves extending from the main grooves in the axial direction of the tire, and blocks partitioned by the main grooves and the transverse grooves, the blocks having sipes, and when the depth of the sipes (mm) is D and the thickness of the first layer (mm) is H, D and H satisfy the following relationship, and the rubber composition constituting the first layer comprises a rubber component containing isoprene-based rubber and a filler containing carbon black and silica. D / H ≤ 0.95 (1)

[0010] While not intended to be constrained by theory, the following mechanisms are considered to be how the heavy-duty tire of the present invention can improve chipping resistance on rough road surfaces: (1) By incorporating isoprene-based rubber (IR-based rubber) into the rubber composition constituting the tread surface, the tire becomes more resistant to deformation and chipping on the tread surface and deformation of the entire pattern block; (2) By forming sipes with a depth of less than a predetermined value relative to the thickness of the first tread layer, and keeping the depth of the sipes within the first layer, the rubber can deform flexibly within the pattern block, and the sipes do not pass through the interface of the rubber layer, making them less likely to break off; (3) By using carbon black and silica in combination, carbon black can reduce the amount of rubber deformation, and silica can improve the elongation at break of the rubber, thus contributing to improved chipping resistance. It is thought that these (1) to (3) work together to improve the fracture characteristics of the first layer rubber composition while allowing it to deform flexibly, making fracture less likely and thus improving chipping resistance.

[0011] The right-hand side of equation (1) is preferably 0.80.

[0012] This is because it is believed that chipping resistance can be further improved by moving the deformation initiation point of the sipe away from the interface of the first layer.

[0013] The carbon black preferably contains carbon black with an average primary particle size of 19 nm or less.

[0014] This is because carbon black is expected to improve the reinforcing properties of the rubber composition, thereby further enhancing its chipping resistance.

[0015] Preferably, the content of carbon black with an average primary particle diameter of 19 nm or less in the total carbon black is 100% by mass.

[0016] This is because carbon black is expected to improve the reinforcing properties of the rubber composition, thereby further enhancing its chipping resistance.

[0017] When the content of carbon black (parts by mass) per 100 parts by mass of rubber component in the rubber composition constituting the above layer is A1 and the content of silica (parts by mass) is B1, it is preferable that A1 and B1 satisfy the following relationship. B1 / (A1+B1)<0.50 (2)

[0018] When the above formula (2) is satisfied, the ratio of silica to the total amount of carbon black and silica used as fillers becomes less than half, which suppresses poor dispersion of silica and makes it easier to exhibit the combined effect of carbon black and silica on chipping resistance.

[0019] The right-hand side of equation (2) is preferably 0.20.

[0020] It is believed that the combined effect of carbon black and silica on chipping resistance is easily achieved.

[0021] Preferably, the rubber composition constituting the above layer further contains a resin component.

[0022] By further incorporating resin components, it is believed that the chipping resistance will be improved because impacts and other stresses will be more easily converted into heat.

[0023] The rubber composition comprising the above layer further contains sulfur, preferably with a sulfur content of 2.00 parts by mass or less per 100 parts by mass of the rubber component. Here, "sulfur content" is the amount defined below.

[0024] By reducing the sulfur content, it is possible to maintain the rubber's degradation margin even in the final stages of wear, which is thought to contribute to chipping resistance.

[0025] When A1 is the amount of carbon black (parts by mass) per 100 parts by mass of rubber component in the rubber composition constituting the above layer, and C is the land ratio (%) of the tread surface of the tread portion, it is preferable that A1 and C satisfy the following relationship. A1 × C / 1000 > 3.00 (3)

[0026] Both the land ratio and the carbon black content are thought to increase tread rigidity and suppress deformation. Therefore, by ensuring that the product of these two factors is above a certain value, deformation on the tread surface is suppressed, and good chipping resistance is achieved.

[0027] When A1 is the amount of carbon black (parts by mass) per 100 parts by mass of rubber component in the rubber composition constituting the above layer, it is preferable that A1 and D / H satisfy the following relationship. A1 / (D / H)>250 (4)

[0028] The higher the carbon black content A1 in the aforementioned first layer, the greater the rigidity. On the other hand, the smaller the D / H ratio, the further the deformation initiation point is from the interface of the first layer when the sipe portion deforms, thus contributing to improved chipping resistance. Therefore, The quotient obtained by dividing the former by the latter. It is believed that when these factors are harmonized above a certain value, it contributes to improved chipping resistance.

[0029] The number of main grooves is three or more, and of these main grooves, the pair of main grooves on the outermost side in the tire width direction are designated as shoulder main grooves, and the other main grooves are designated as center main grooves. The groove width (mm) of the shoulder main groove with the smallest groove width is GW. SH And, the groove width (mm) of the largest of the aforementioned center main grooves is GW. CE When the following relationship is satisfied, and the land area on the outer side in the tire width direction, demarcated by the pair of shoulder main grooves, is defined as a pair of shoulder land areas, the sum of the maximum contact widths (mm) of each shoulder land area is W. SH Preferably, the tread contact width (mm), TW, satisfies the following relationship. Golden Week CE / GW SH <1.00 (5) W SH / TW<0.50 (6)

[0030] By setting the groove width of the center main groove to be narrower than the groove width of the shoulder main groove, it is thought that the shoulder portion can make contact with the ground more easily, thereby reducing the force received per unit area of ​​the contact surface. Furthermore, by positioning the shoulder main groove on the outer side in the tire width direction so that the contact width of the shoulder portion is less than half of the tread contact width, it is thought that the tread portion can deform radially more easily near the shoulder portion, which is difficult to make contact with the ground, thereby improving contact performance. As a result, improved contact performance reduces the force that the tread surface receives from the road surface, which is thought to contribute to improved chipping resistance.

[0031] The rubber composition constituting the above layer preferably has a rubber hardness of 62 to 72 at 23°C.

[0032] It is believed that appropriate chipping resistance can be ensured by controlling the hardness range.

[0033] Preferably, the block has a shallow groove with a groove depth shallower than the groove depth of the main groove, and the shallow groove opens into at least one of the main groove and the lateral groove adjacent to the block.

[0034] By providing shallow grooves as described above, it is believed that preventing mud from accumulating will contribute to improving chipping resistance.

[0035] When A1 is the amount of carbon black per 100 parts by mass of rubber component in the rubber composition constituting the first layer, and the rubber composition constituting the second layer contains a rubber component including isoprene rubber and a filler including carbon black, and A2 is the amount of carbon black per 100 parts by mass of rubber component in the rubber composition constituting the second layer, it is preferable that A1 and A2 satisfy the following relationship. A2 / A1<1.00 (7) (However, A2 is 20 or higher.)

[0036] By creating a concentration gradient in the carbon black content, the tread layer, which consists of at least two layers, is expected to absorb impact more easily, contributing to improved chipping resistance.

[0037] When B1 is the silica content (parts by mass) per 100 parts by mass of rubber component in the rubber composition constituting the first layer, and the rubber composition constituting the second layer contains a rubber component including isoprene rubber and a filler containing silica, and B2 is the silica content (parts by mass) per 100 parts by mass of rubber component in the rubber composition constituting the second layer, it is preferable that B1 and B2 satisfy the following relationship. B2 / B1<1.00 (8) (However, B2 must be 3 or higher.)

[0038] By creating a concentration gradient in the silica content, the tread layer, consisting of at least two layers, is expected to absorb impact more easily, contributing to improved chipping resistance.

[0039] [Definition] "Normal condition" refers to the state of a tire that is mounted on a normal rim, filled to the normal internal pressure, and unloaded.

[0040] A "standard rim" refers to the rim specified for each tire within the standards system that the tire is based on. For example, for JATMA (Japan Automobile Tire Manufacturers Association), it refers to the standard rim for the applicable size listed in the "JATMA YEAR BOOK," for ETRTO (The European Tyre and Rim Technical Organisation), it refers to the "Measuring Rim" listed in the "STANDARDS MANUAL," and for TRA (The Tire and Rim Association, Inc.), it refers to the "Design Rim" listed in the "YEAR BOOK." Refer to JATMA, ETRTO, and TRA in that order, and if an applicable size is available at the time of reference, follow that standard. In the case of tires not specified in the standards, it refers to the rim with the smallest diameter and the narrowest rim width among rims that can be mounted on and can maintain internal pressure, i.e., rims that do not cause air leakage from between the rim and tire.

[0041] "Regular internal pressure" refers to the air pressure specified for each tire in the tire standard system, including the standard on which the tire is based. For JATMA, it is the "maximum air pressure," for TRA, it is the "maximum value" listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES," and for ETRTO, it is the "INFLATION PRESSURE." Similar to regular rims, refer to JATMA, ETRTO, and TRA in that order, and if an applicable size is found during the reference, follow that standard.

[0042] "Regular load" refers to the load specified in the standards system, including the standard on which the tire is based. The "maximum load capacity" in the JATMA standard, the "maximum value" listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are all regular loads. Similar to regular rims and regular in-tire pressure, refer to JATMA, ETRTO, and TRA in that order, and if applicable to the size at the time of reference, follow that standard.

[0043] "Sulfur content" refers to the amount of sulfur element per 100 parts by mass of rubber component in the rubber composition. This amount of sulfur element includes the amount of sulfur element contained in the vulcanizing agent, as well as the amount of sulfur element contained in the vulcanization accelerator and coupling agent, etc. The "amount of sulfur element per 100 parts by mass of rubber component" is calculated as a mass % by dividing the "amount of rubber component (PC amount (mass %))" and the "amount of total sulfur (TS amount (mass %))" contained in the rubber composition, which are measured by a predetermined method, by the formula TS amount ÷ PC amount × 100.

[0044] "Main grooves" refer to grooves that extend continuously in the circumferential direction on the tread surface of the tire, with a groove width exceeding 2.0 mm. There are shoulder main grooves and center main grooves. "Shoulder main grooves" are a pair of main grooves located on the outermost side in the tire width direction. "Center main grooves" are main grooves other than the shoulder main grooves.

[0045] "Main groove width" refers to the width (mm) of the main groove in the tire rotation axis direction on the tread surface, and is measured under normal conditions. If the main groove width changes along the tire circumference, it can be calculated by dividing the sum of the groove areas of the main grooves by the tire circumference. When calculating the sum of the groove areas of the main grooves, the ends of adjacent blocks in the circumferential direction should be connected by straight lines to recognize the groove area of ​​the main groove. SH " is the groove width of the shoulder main groove with the smallest groove width. CE " is the groove width of the center main groove, which has the widest groove width.

[0046] A "lateral groove" is a groove that extends from the main groove in the direction of the tire's axis. Lateral grooves connect adjacent main grooves to form blocks.

[0047] A "block" is an area on the tread demarcated by main grooves and lateral grooves. Blocks can be formed, for example, (1) by two adjacent main grooves and two adjacent lateral grooves connecting those two main grooves, or (2) by one shoulder main groove and two adjacent lateral grooves extending outward from that shoulder main groove in the tire width direction. The block in case (1) is called a "center block," and the block in case (2) is called a "shoulder block." In a shoulder block, the ends of two adjacent lateral grooves on the tread contact end side may or may not reach the tread contact end. Furthermore, if the ends of two adjacent lateral grooves on the tread contact end side do not reach the tread contact end, those ends may or may not be in communication with each other.

[0048] A "sipe" refers to a narrow cut with a width of 2.0 mm or less, preferably 0.5 to 2.0 mm. Sipes are formed on a block.

[0049] "Thickness of the first layer constituting the tread surface (H)" refers to the thickness (mm) of the first layer constituting the tread surface at the midpoint of the sipe, and is measured when the tire is cut in a plane containing the tire's axis of rotation and held at the normal rim width. This thickness of the first layer is recognized as the thickness that fills the sipe. The midpoint of the sipe is the point on the tread surface that is equal in distance from both ends of the sipe.

[0050] "Sipe depth (D)" refers to the depth (mm) of the sipe from the tread surface at the midpoint of the sipe, and is measured when the tire is cut in a plane containing the tire's axis of rotation and held at the standard rim width.

[0051] The "land ratio" refers to the ratio (%) of the area of the tread contact surface excluding the areas of the grooves and sipes present on the contact surface to the total area of the contact surface when all the grooves and sipes present on the contact surface of a tire in its normal state are filled, under a normal load. For example, in Fig. 2, the framed part represents the tread contact surface of a tire in its normal state under a normal load. Therefore, the ratio (%) of the area of the contact surface excluding the areas of the grooves and sipes present on the contact surface to the total area of the contact surface when all the grooves and sipes present on the contact surface are filled is the land ratio.

[0052] The "tread contact width (TW)" is the maximum distance in the width direction of the tread contact surface.

[0053] The "total ground contact width of each shoulder land (W SH )" is the sum (mm) of the maximum values of the ground contact widths in the tire axial direction of each of the pair of shoulder lands in the region within the tread contact width (TW) (Fig. 2).

[0054] A "shallow groove" is a groove formed in a block and having a groove depth shallower than that of the main groove. The shallow groove opens into at least one of the main grooves or transverse grooves partitioning the block.

[0055] [Measurement method] The "styrene content" is 1 calculated by H-NMR measurement.

[0056] The "vinyl content (amount of 1,2-bonded butadiene units)" is measured in accordance with JIS K 6239-2:2017.

[0057] The "weight-average molecular weight (Mw)" can be determined by standard polystyrene conversion based on the measured values obtained by gel permeation chromatography (GPC) (GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMALTIPORE HZ-M manufactured by Tosoh Corporation).

[0058] The "cis content (amount of cis-1,4-bonded butadiene units)" is measured according to JIS K 6239-2:2017.

[0059] The "average primary particle size of carbon black" can be determined by measuring more than 400 primary particles observed within the field of view using a transmission electron microscope and averaging those measurements.

[0060] The "N2SA of carbon black" is a value determined according to JIS K 6217-2:2017.

[0061] "N2SA of silica" is a value measured by the BET method in accordance with ASTM D3037-93.

[0062] "Rubber hardness" is a value measured by cutting out a tread portion from the tread area that forms the contact surface of the tire so that the tire radius direction is the thickness direction, creating a sample for hardness measurement, and then pressing a Type A durometer against the sample from the contact surface side at 23°C in accordance with JIS K 6253.

[0063] Unless otherwise specified, the "softening point" is the temperature at which the sphere descends when the softening point specified in JIS K 6220-1:2015 is measured using a ring-type softening point measuring device. If the softening point is measured by another method, this will be noted.

[0064] The "total sulfur content" is the amount of sulfur element (TS amount (mass%)) used to calculate the sulfur content, and is measured as mass% using the oxygen combustion flask method in accordance with JIS K 6233 for test pieces cut from the tread of a test tire.

[0065] The "amount of rubber component" refers to the amount of rubber component (PC amount (mass%)) used in calculating the sulfur content. A test piece cut from the tread of a test tire is placed in a Soxhlet extractor, and acetone extraction is performed under the following conditions: test piece: 10g or less, acetone: 150ml, constant temperature bath temperature: 95~100℃, extraction time: 72 hours. After acetone extraction, the amount of organic matter in the test piece is measured as the loss (mass (%)) when the organic matter is thermally decomposed and vaporized by heating in nitrogen (raising the temperature from room temperature to 750℃), in accordance with JIS K 6226-1:2003.

[0066] [tire] The heavy-duty tire of the present invention will be described below with reference to the drawings as appropriate. However, the drawings are for illustrative purposes only.

[0067] The heavy-duty tire of the present invention is a heavy-duty tire having a tread portion comprising a first layer constituting the tread surface and a second layer located inside the first layer, wherein the tread surface has a plurality of main grooves extending continuously in the circumferential direction of the tire, transverse grooves extending from the main grooves in the axial direction of the tire, and blocks partitioned by the main grooves and the transverse grooves, the blocks having sipes, and when the depth of the sipes (mm) is D and the thickness of the first layer (mm) is H, D and H satisfy the following relationship. D / H ≤ 0.95 (1)

[0068] Figure 1 is a cross-sectional view in plan including the tire rotation axis of a heavy-duty tire according to one embodiment of the present invention. The tire 1 in Figure 1 has a tread 3 including a first layer 4 that constitutes the tread surface 2 and a second layer 5 located inside the first layer, and the tread surface 2 has four main grooves that extend continuously in the circumferential direction of the tire. Of these main grooves, the pair of main grooves on the outermost side in the tire width direction are represented as shoulder main grooves 8, and the two main grooves other than the shoulder main grooves are represented as center main grooves 7.

[0069] Figure 2 is a plan view showing the tread surface and tread contact surface of a heavy-duty tire according to one embodiment of the present invention. The enclosed area in Figure 2 is the tread contact surface. TW indicates the tread contact width. The tread surface in Figure 2 has two center main grooves 7, two shoulder main grooves 8, and lateral grooves 9 communicating with the main grooves. The block 10 consists of a center block partitioned by two adjacent main grooves from the center main groove 7 and shoulder main grooves 8 and two circumferentially adjacent lateral grooves 9, and a shoulder block partitioned by one shoulder main groove 8 and two circumferentially adjacent lateral grooves 9. The center block and the shoulder block each have two sipes 11. GW SH The width of the groove with the smallest width among the shoulder main grooves is GW CE The numbers indicate the groove width of the widest of the center main grooves. In Figure 2, GW CE It's Golden Week SH It is narrower than that. Also, in Figure 2, W SH This is the sum (mm) of the maximum contact widths in the tire axial direction of each of the pair of shoulder land areas within the tread contact width (TW) region.

[0070] Figure 3 is a plan view showing the tread surface and tread contact surface of a heavy-duty tire according to one embodiment of the present invention. The enclosed area in the figure is the tread contact surface. Figure 3 differs from Figure 2 in the number of sipes and groove pattern of each center block (block 10). 3 The center block has one sipe 11 and a shallow groove 12. The shallow groove 12 consists of a groove depth shallower than the groove depth of the adjacent center main groove 7 and opening into the adjacent center main groove 7, and a groove depth shallower than the groove depth of the adjacent shoulder main groove 8 and opening into the adjacent shoulder main groove 8.

[0071] <Main groove> The main grooves may be zigzag or straight. For example, in Figure 2 or Figure 3, the main grooves that extend continuously in the circumferential direction of the tire both extend in a zigzag pattern while oscillating in the tire width direction. Here, "zigzag" means that the center of the main groove in the width direction oscillates in the tire width direction while extending in the tire circumferential direction. Therefore, the zigzag pattern includes not only a form in which straight grooves repeatedly bend, but also a form in which curved grooves repeatedly curve in a wave-like pattern.

[0072] The number of main grooves is two or more. When there are two main grooves, these two main grooves form a pair of shoulder main grooves. When there are three or more main grooves, the number of center main grooves increases in proportion to the number of main grooves. Figures 1 to 3 all show examples with four main grooves. The number of main grooves may be five, six or more.

[0073] <Yokomizo> The lateral grooves extend from the main grooves in the direction of the tire axis and, together with the main grooves, demarcate the blocks. The angle of the lateral grooves with respect to the tire axis is not particularly limited, but is preferably, for example, 3° to 7°.

[0074] <Block, sipe> The main grooves and lateral grooves demarcate the blocks, and each demarcated block has sipes. The depth D (mm) of the sipes is less than or equal to a predetermined value relative to the thickness H (mm) of the first layer, as described above. The number of sipes on each block is not particularly limited; the optimal number of sipes can be determined according to the shape of the block, the area of ​​the block, the length of the sipes, etc. In Figure 2, each block has two sipes, and in Figure 3, the shoulder block has two sipes and the center block has one sipe.

[0075] <Tread section> The tread portion includes a first layer constituting the tread surface and a second layer located inside the first layer. The thickness of the first layer is preferably more than 12 mm, more preferably more than 14 mm, and even more preferably more than 16 mm. On the other hand, the thickness of the first layer is preferably less than 24 mm, more preferably less than 22 mm, and even more preferably less than 20 mm. The thickness of the second layer is preferably more than 2.0 mm, more preferably more than 3.0 mm, and even more preferably more than 4.0 mm. On the other hand, the thickness of the second layer is preferably less than 8.0 mm, more preferably less than 7.0 mm, and even more preferably less than 6.0 mm.

[0076] The heavy-duty tire of the present invention may further include an intermediate layer in addition to the first and second layers. Such an intermediate layer may be a layer similar in composition to the first layer and placed inside it, or a layer similar in composition to the second layer and placed outside it, or a layer with a different composition from the first and second layers and placed in between them. Furthermore, the intermediate layer may consist of one layer or two or more layers.

[0077] <Rubber hardness> The rubber hardness of the rubber composition constituting the above layer is preferably 62 or more and 72 or less at 23°C. Preferably, the rubber hardness is greater than 62, more preferably greater than 64, and even more preferably greater than 65. On the other hand, preferably the rubber hardness is less than 72, more preferably less than 69, even more preferably 68 or less, even more preferably 67 or less, and even more preferably less than 67.

[0078] The rubber hardness of a rubber composition can be adjusted by conventional methods in the tire industry. Specifically, it can be adjusted by changing the type and amount of chemicals (e.g., rubber components, fillers, softeners, sulfur, vulcanization accelerators, silane coupling agents, etc.) blended into the rubber composition. For example, increasing the oil content can lower the rubber hardness, while decreasing it can increase it. Therefore, those skilled in the art can adjust the rubber hardness as appropriate.

[0079] <Formula (1)> When the depth of the sipe (mm) is D and the thickness of the first layer (mm) is H, the relationship between D and H satisfies the following equation. D / H ≤ 0.95 (1)

[0080] The right-hand side of equation (1) is preferably 0.90, more preferably 0.87, even more preferably 0.80, even more preferably 0.70, even more preferably 0.60, even more preferably 0.50, even more preferably 0.40, even more preferably 0.30, even more preferably 0.20, and even more preferably 0.12. On the other hand, there are no particular limitations on the lower limit of D / H, but it is usually preferably greater than 0.05, more preferably greater than 0.07, and even more preferably greater than 0.10.

[0081] <Formula (2)> When the content of carbon black (parts by mass) per 100 parts by mass of rubber component in the rubber composition constituting the above layer is A1 and the content of silica (parts by mass) is B1, it is preferable that A1 and B1 satisfy the following relationship. B1 / (A1+B1)<0.50 (2)

[0082] The right-hand side of equation (2) is preferably 0.45, more preferably 0.40, even more preferably 0.35, even more preferably 0.20, and even more preferably 0.18. On the other hand, there are no particular limitations on the lower limit of B1 / (A1+B1), but it is usually preferably greater than 0.05, more preferably greater than 0.07, and even more preferably greater than 0.10.

[0083] <Formula (3)> When A1 is the amount of carbon black (parts by mass) per 100 parts by mass of rubber component in the rubber composition constituting the above layer, and C is the land ratio (%) of the tread surface of the tread portion, it is preferable that A1 and C satisfy the following relationship. A1 × C / 1000 > 3.00 (3)

[0084] The right-hand side of equation (3) is preferably 3.20, more preferably 3.30, and even more preferably 3.40. On the other hand, there is no particular upper limit to A1 × C / 1000, but it is usually preferably less than 9.00, more preferably less than 7.00, and even more preferably less than 5.00.

[0085] Furthermore, the land ratio (%) C is preferably greater than 60%, more preferably greater than 65%, even more preferably greater than 70%, and even more preferably greater than 75%. In addition, C is preferably less than 90%, and preferably less than 85%.

[0086] <Formula (4)> When A1 is the amount of carbon black (parts by mass) per 100 parts by mass of rubber component in the rubber composition constituting the above layer, it is preferable that A1 and D / H satisfy the following relationship. A1 / (D / H)>250 (4)

[0087] The right-hand side of equation (4) is preferably 275, more preferably 300, and even more preferably 350. On the other hand, there is no particular upper limit to A1 / (D / H), but it is usually preferably less than 1000, more preferably less than 700, and even more preferably less than 500.

[0088] <Formula (5)> The groove width (mm) of the smallest groove among the shoulder main grooves is GW. SH And, the groove width (mm) of the largest of the aforementioned center main grooves is GW. CE Preferably, the following relationship is satisfied. Golden Week CE / GW SH <1.00 (5)

[0089] The right-hand side of equation (5) is preferably 0.95, more preferably 0.90, even more preferably 0.85, even more preferably 0.80, even more preferably 0.76, even more preferably 0.70, even more preferably 0.65, and even more preferably 0.61. On the other hand, GW CE / GW SH There are no particular limitations on the lower limit, but it is usually preferable to be greater than 0.20, more preferably greater than 0.40, and even more preferably greater than 0.50.

[0090] <Formula (6)> When the outer part of the tire in the width direction, demarcated by the pair of shoulder main grooves, is considered a pair of shoulder land sections, the sum of the maximum contact widths (mm) of each shoulder land section is W. SH Preferably, the following relationship is satisfied between the tread contact width (mm), TW, and the tread contact width. W SH / TW<0.50 (6)

[0091] The right-hand side of equation (6) is preferably 0.49, more preferably 0.48, even more preferably 0.47, even more preferably 0.46, even more preferably 0.45, even more preferably 0.44, even more preferably 0.43, even more preferably 0.42, and even more preferably 0.41. On the other hand, W SH There are no particular limitations on the lower limit of / TW, but it is generally preferable to be greater than 0.35, more preferably greater than 0.37, and even more preferably greater than 0.39.

[0092] <Formula (7)> When A1 is the amount of carbon black per 100 parts by mass of rubber component in the rubber composition constituting the first layer, and A2 is the amount of carbon black per 100 parts by mass of rubber component in the rubber composition constituting the second layer, it is preferable that A1 and A2 satisfy the following relationship. A2 / A1<1.00 (7) (However, A2 is 20 or higher.)

[0093] The right-hand side of equation (7) is preferably 0.95, more preferably 0.90, and even more preferably 0.86. On the other hand, there are no particular limitations on the lower limit of A2 / A1, but it is usually preferably greater than 0.50, more preferably greater than 0.60, and even more preferably greater than 0.70.

[0094] <Formula (8)> When B1 is the silica content (parts by mass) per 100 parts by mass of rubber component in the rubber composition constituting the first layer, and B2 is the silica content (parts by mass) per 100 parts by mass of rubber component in the rubber composition constituting the second layer, it is preferable that B1 and B2 satisfy the following relationship. B2 / B1<1.00 (8) (However, B2 must be 3 or higher.)

[0095] The right-hand side of equation (8) is preferably 0.90, more preferably 0.80, even more preferably 0.70, even more preferably 0.60, even more preferably 0.50, even more preferably 0.40, even more preferably 0.30, and even more preferably 0.21. On the other hand, there are no particular limitations on the lower limit of B2 / B1, but it is usually preferably greater than 0.10, more preferably greater than 0.15, and even more preferably greater than 0.18.

[0096] [Rubber composition] The following describes the rubber composition (the rubber composition of the present invention) that constitutes the first layer of the tread portion of the heavy-duty tire of the present invention. The rubber composition of the present invention comprises a rubber component containing isoprene-based rubber and a filler containing carbon black and silica.

[0097] <Rubber components> The rubber component includes isoprene-based rubber.

[0098] (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, and grafted natural rubber. Of these, natural rubber is preferred, and unmodified natural rubber (NR) is more preferred. These isoprene-based rubbers may be used individually or in combination of two or more types.

[0099] NR is not particularly limited and can be any tire that is common in the tire industry, such as SIR20, RSS#3, and TSR20.

[0100] (Other rubber components) The rubber component may contain rubber components other than the isoprene-based rubber mentioned above. Other rubber components that can be crosslinked are commonly used in the tire industry. Examples include diene-based rubbers such as styrene-butadiene rubber (SBR), butadiene rubber (BR), styrene-isoprene-butadiene copolymer rubber (SIBR), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), and polynorbornene rubber, as well as non-diene rubbers such as butyl rubber (IIR), hydrogenated nitrile rubber (HNBR), ethylene propylene rubber, silicone rubber, polyethylene chloride rubber, fluororubber (FKM), acrylic rubber (ACM), and hydrin rubber. Of these, diene-based rubber is preferred. These other rubber components may be used individually or in combination of two or more.

[0101] Among other rubber components, SBR and BR are preferred. Therefore, preferred forms of the rubber component include, for example, a mixture containing isoprene rubber and SBR, a mixture consisting only of isoprene rubber and SBR, a mixture containing isoprene rubber and BR, a mixture consisting only of isoprene rubber and BR, a mixture containing isoprene rubber, SBR and BR, and a mixture consisting only of isoprene rubber, SBR and BR.

[0102] ≪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. (condensates, those with branched structures, etc.). Among these, S-SBR and modified SBR are preferred. Furthermore, hydrogenated products of these SBRs (hydrogenated SBRs) can also be used. These SBRs may be used individually or in combination of two or more types.

[0103] For SBR, either oil-expanded SBR or non-oil-expanded SBR can be used. When using oil-expanded SBR, the amount of oil expanded in the SBR, that is, the amount of oil-expanding oil contained in the SBR, is preferably 10 to 50 parts by mass per 100 parts by mass of rubber solids in the SBR.

[0104] S-SBRs that can be used in this invention are commercially available from companies such as JSR Corporation, Sumitomo Chemical Co., Ltd., Ube Industries, Ltd., Asahi Kasei Corporation, ZS Elastomers Co., Ltd., and ARLANXEO.

[0105] Modified SBR may be one in which the main chain and / or terminals are modified with a modifying agent, or it may be modified with a polyfunctional modifying agent such as tin tetrachloride or silicon tetrachloride and have a partially branched structure, but SBR modified with a modifying agent having functional groups that interact with silica in the main chain and / or terminals (silica-modified SBR) is preferred. It is particularly preferable to contain modified SBR in the first layer and / or second layer.

[0106] Examples of functional groups that interact with silica include amino groups, amide groups, alkoxysilyl groups, isocyanate groups, imino groups, imidazole groups, urea groups, ether groups, carbonyl groups, oxycarbonyl groups, sulfide groups, disulfide groups, sulfonyl groups, sulfinyl groups, thiocarbonyl groups, ammonium groups, imide groups, hydrazo groups, azo groups, diazo groups, carboxyl groups, nitrile groups, pyridyl groups, alkoxy groups, hydrocarbon groups, hydroxyl groups, oxy groups, and epoxy groups. These functional groups may have substituents. Among these, amino groups, epoxy groups, hydroxyl groups, alkoxy groups, and alkoxysilyl groups are preferred from the viewpoint of improving the dispersibility of silica, and amino groups and alkoxysilyl groups are more preferred.

[0107] From the viewpoint of chipping resistance and abrasion resistance, the styrene content of SBR is preferably more than 5% by mass, more preferably more than 8% by mass, and even more preferably more than 10% by mass. Furthermore, from the viewpoint of temperature dependence, it is preferably less than 50% by mass, more preferably less than 30% by mass, and even more preferably less than 25% by mass. In this specification, the styrene content of SBR is calculated by the method described above.

[0108] The vinyl content of SBR is preferably more than 10 mol%, more preferably more than 13 mol%, and even more preferably more than 15 mol%, from the viewpoint of ensuring reactivity with silica, chipping resistance, and abrasion resistance. Furthermore, the vinyl content of SBR is preferably less than 70 mol%, more preferably less than 60 mol%, and even more preferably less than 40 mol%, from the viewpoint of preventing increased temperature dependence, elongation at break, and abrasion resistance. In this specification, the vinyl content of SBR (amount of 1,2-bonded butadiene units) is measured by the method described above.

[0109] From the viewpoint of chipping resistance, the weight-average molecular weight (Mw) of SBR is preferably greater than 200,000, more preferably greater than 250,000, and even more preferably greater than 300,000. Furthermore, from the viewpoint of crosslinking uniformity, the weight-average molecular weight is preferably less than 2 million, more preferably less than 1.5 million, and even more preferably less than 1 million. In this specification, the weight-average molecular weight of SBR can be determined by the method described above.

[0110] ≪BR≫ BR is not particularly limited, and for example, BR with a cis content of less than 50 mol% (low-cis BR), BR with a cis content of 90 mol% 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.

[0111] For example, commercially available high-cis butadiene (H-BR) from companies such as Nippon Zeon Co., Ltd., Ube Industries, Ltd., and JSR Corporation can be used. The cis content is preferably more than 94 mol%, more preferably more than 95 mol%, even more preferably 96 mol% 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 the value calculated by the method described above.

[0112] Rare-earth BRs are synthesized using rare-earth element catalysts, and have a vinyl content of preferably less than 1.8 mol%, more preferably less than 1.0 mol%, and even more preferably less than 0.8 mol%, and a cis content of preferably more than 94 mol%, more preferably more than 95 mol%, and even more preferably 96 mol% or more. As rare-earth BRs, commercially available products from companies such as Lanxess K.K. and ARLANXEO can be used.

[0113] 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.

[0114] 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 tin-carbon bonds (tin-modified BR), and butadiene rubber modified with a modifying agent having functional groups that interact with silica on the main chain and / or ends of the butadiene rubber (silica-modified BR). Furthermore, the modified BR may be either unhydrogenated or hydrogenated.

[0115] From the viewpoint of wear resistance, the weight-average molecular weight (Mw) of BR is preferably greater than 300,000, more preferably greater than 350,000, and even more preferably greater than 400,000. From the viewpoint of crosslinking uniformity, it is preferably less than 2,000,000, more preferably less than 1,500,000, and even more preferably less than 1,000,000. The weight-average molecular weight of BR can be determined by the method described above.

[0116] The isoprene-based rubber and other rubber components described above may be modified to interact with the filler, or they may remain unmodified. Furthermore, these isoprene-based rubber and other rubber components may have their double bond content reduced by hydrogenation, or stretched rubber with the plasticizer component described later may be used.

[0117] (Content) The content of isoprene-based rubber in the rubber component is preferably more than 50% by mass, more preferably more than 55% by mass, even more preferably 60% by mass or more, even more preferably more than 70% by mass, even more preferably 80% by mass or more, and even more preferably more than 90% by mass. The content may also be 100% by mass.

[0118] When SBR is included, its content in the rubber component is preferably less than 20% by mass, more preferably less than 15% by mass, and even more preferably 10% by mass or less. On the other hand, its content is preferably more than 5% by mass, more preferably more than 7% by mass, and even more preferably 10% by mass or more. The SBR content may be 0% by mass.

[0119] When BR is included, its content in the rubber component is preferably less than 50% by mass, more preferably less than 40% by mass, even more preferably less than 35% by mass, even more preferably 30% by mass or less, and even more preferably 20% by mass or less. On the other hand, the BR content is preferably more than 5 parts by mass, more preferably more than 10 parts by mass, even more preferably more than 15 parts by mass, and even more preferably 20 parts by mass or more. The BR content may be 0% by mass.

[0120] Preferred embodiments of the rubber component include, for example, a rubber component having an isoprene-based rubber content of 60% to 100% by mass, an SBR content of 0% to 10% by mass, and a BR content of 0% to 30% by mass.

[0121] <Filler> The rubber composition of the present invention comprises carbon black and silica.

[0122] (Carbon Black) The carbon black used is not particularly limited and includes N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, N600, N660, N762, etc. Commercially available products from Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Corporation, Lion Corporation, Shin-Nippon Chemical Carbon Co., Ltd., Columbia Carbon, etc. can be used. These carbon blacks may be used individually or in combination of two or more types.

[0123] In addition to the above, from a life cycle assessment perspective, carbon black may also be made from biomass materials such as lignin, or from recycled carbon refined by thermal decomposition of products containing carbon black, such as tires.

[0124] In particular, fine-particle carbon black with an average primary particle diameter of 19 nm or less is preferred as the carbon black. As the fine-particle carbon black, those commonly used in the tire industry can be used as appropriate, for example, those manufactured and sold by Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Corporation, Lion Corporation, Nippon Steel Carbon Co., Ltd., Columbia Carbon Corporation, etc. The fine-particle carbon black may be used alone or in combination of two or more types.

[0125] The average primary particle diameter of the fine-particle carbon black is preferably less than 19 nm, and more preferably 18 nm or less. The lower limit of the average primary particle diameter is not particularly limited, but may be greater than 1 nm, greater than 3 nm, or greater than 5 nm. The average primary particle diameter of the fine-particle carbon black can be measured by the method described above.

[0126] The nitrogen adsorption specific surface area (N2SA) of fine-particle carbon black is 130 m² from the perspective of reinforcing properties. 2 Preferably more than / g, 135m 2 More preferably than / g, 140m 2 A value exceeding / g is even more preferable. Furthermore, from the viewpoint of low fuel consumption and processability, 300m 2 Less than / g is preferable, 200m 2 Less than / g is more preferable, 180m 2 A value of less than / g is even more preferable. The N2SA of fine-particle carbon black can be measured by the method described above.

[0127] The carbon black content per 100 parts by mass of rubber component is preferably more than 20 parts by mass, more preferably more than 30 parts by mass, and even more preferably more than 40 parts by mass. On the other hand, the carbon black content is preferably less than 150 parts by mass, more preferably less than 100 parts by mass, even more preferably less than 80 parts by mass, and even more preferably less than 60 parts by mass.

[0128] The content of fine particle carbon black relative to the total amount of carbon black is not particularly limited and may be 0% by mass or 100% by mass, but from the viewpoint of the effects of the present invention, it is preferable to be 100% by mass. The content is preferably more than 40% by mass, more preferably 50% by mass or more, even more preferably more than 75% by mass, and even more preferably more than 90% by mass.

[0129] (silica) The silica used is not particularly limited, and common silica used in the tire industry can be used, such as silica prepared by the dry method (anhydrous silica) or silica prepared by the wet method (hydrated silica). Among these, hydrated silica prepared by the wet method is preferred because it contains a large number of silanol groups. These silicas may be used individually or in combination of two or more types.

[0130] In addition to the above, silica derived from biomass materials such as rice husks may also be used, from the perspective of life cycle assessment.

[0131] The nitrogen adsorption specific surface area (N2SA) of silica is 120 m² from the perspective of chipping resistance. 2 Preferably 140m / g or more. 2 More preferably 160m / g or more, 2 A value of 350m or more is even more preferable. Furthermore, from the viewpoint of low fuel consumption and processability, 350m 2 Preferably less than / g, 300m 2 More preferably less than / g, 250m 2 A value of less than or equal to / g is even more preferable. The N2SA of silica as used herein is the value measured by the BET method in accordance with ASTM D3037-93.

[0132] The silica content per 100 parts by mass of rubber component is preferably more than 1 part by mass, more preferably more than 3 parts by mass, even more preferably more than 5 parts by mass, and still more preferably 8.5 parts by mass or more. On the other hand, the silica content is preferably less than 75 parts by mass, more preferably less than 50 parts by mass, even more preferably 25 parts by mass or less, even more preferably less than 10 parts by mass, and still more preferably 8.5 parts by mass or less.

[0133] Regarding the silica content and carbon black content, it is preferable that the silica content is less than the carbon black content. That is, when the carbon black content (parts by mass) is A1 and the silica content (parts by mass) is B1 per 100 parts by mass of the rubber component, it is preferable that A1 and B1 satisfy the following formula (2). B1 / (A1+B1)<0.50 (2)

[0134] The right-hand side of equation (2) above is preferably 0.40, more preferably 0.30, even more preferably 0.25, even more preferably 0.20, even more preferably 0.15, and even more preferably 0.13.

[0135] The total content of silica and fine-particle carbon black per 100 parts by mass of rubber component is preferably more than 25 parts by mass, more preferably more than 35 parts by mass, and still more preferably more than 45 parts by mass. Furthermore, the total content is preferably less than 200 parts by mass, more preferably less than 160 parts by mass, still more preferably less than 120 parts by mass, still more preferably less than 80 parts by mass, and still more preferably less than 60 parts by mass.

[0136] (Other fillers) In addition to the fine-particle carbon black and silica mentioned above, other fillers may be used as fillers. Such fillers are not particularly limited, and any filler commonly used in this field can be used, for example, carbon black other than the fine-particle carbon black, aluminum hydroxide, alumina (aluminum oxide), calcium carbonate, magnesium sulfate, talc, clay, biochar (BIO CHAR), etc. These fillers may be used individually or in combination of two or more. Preferably, the filler consists only of fine-particle carbon black and silica, without any other fillers.

[0137] (Silane coupling agent) A silane coupling agent can be used in the rubber composition of the present invention. The silane coupling agent is not particularly limited, and any silane coupling agent conventionally used in combination with silica in the tire industry can be used. Examples include sulfide-based silane coupling agents such as bis(3-triethoxysilylpropyl) disulfide and bis(3-triethoxysilylpropyl) tetrasulfide; vinyl-based silane coupling agents such as vinyltriethoxysilane and vinyltrimethoxysilane; amino-based silane coupling agents such as 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, and 3-(2-aminoethyl)aminopropyltriethoxysilane; glycidoxy-based silane coupling agents such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro-based silane coupling agents such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; chloro-based silane coupling agents such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane; and mercapto-based silane coupling agents. Among these, sulfide-based silane coupling agents and / or mercapto-based silane coupling agents are preferred. These silane coupling agents may be used individually or in combination of two or more.

[0138] The mercapto-silane coupling agent is preferably a compound represented by the following chemical formula (1), and / or a compound containing a bonding unit A represented by the following chemical formula (2) and a bonding unit B represented by the following chemical formula (3). [ka] (In the formula, R 101 , R 102 , and R 103 Each of these is independently an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, or -O-(R 111 -O) z -R 112 (z R 111 Each of these independently represents a divalent hydrocarbon group having 1 to 30 carbon atoms; R 112 R represents an alkyl group with 1 to 30 carbon atoms, an alkenyl group with 2 to 30 carbon atoms, an aryl group with 6 to 30 carbon atoms, or an aralkyl group with 7 to 30 carbon atoms; z represents an integer from 1 to 30. 104 (This represents alkylenes with 1 to 6 carbon atoms.) [ka] [ka] (In the formula, x represents an integer greater than or equal to 0; y represents an integer greater than or equal to 1; R 201 R represents a hydrogen atom, or an alkyl group having 1 to 30 carbon atoms, an alkenyl group having 2 to 30 carbon atoms, or an alkynyl group having 2 to 30 carbon atoms, which may be substituted with a halogen atom, hydroxyl, or carboxyl; 202 R represents alkylene with 1 to 30 carbon atoms, alkenylene with 2 to 30 carbon atoms, or alkynylene with 2 to 30 carbon atoms; where R 201 and R 202 (They may form a ring structure.)

[0139] Examples of compounds represented by chemical formula (1) include 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, and the compound represented by the following chemical formula (4) (Si363 manufactured by Evonik Degussa). The compound represented by the following chemical formula (4) can be preferably used. These may be used individually or in combination of two or more. [ka]

[0140] Examples of compounds containing the bonding unit A shown in chemical formula (2) and the bonding unit B shown in chemical formula (3) include those manufactured and sold by Momentive, Inc., among others. These may be used individually or in combination of two or more types.

[0141] The silane coupling agent content is preferably more than 1.0 part by mass, more preferably more than 3.0 parts by mass, and even more preferably more than 5.0 parts by mass, per 100 parts by mass of silica, from the viewpoint of improving silica dispersibility. Furthermore, from the viewpoint of cost and processability, it is preferably less than 20 parts by mass, more preferably less than 15 parts by mass, and even more preferably less than 12 parts by mass.

[0142] <Resin components> The resin component is not particularly limited, but examples include petroleum resins, terpene resins, rosin resins, and phenolic resins commonly used in the tire industry. The resin component is preferably a thermoplastic resin. These resin components may be used individually or in combination of two or more.

[0143] Examples of petroleum resins include C5-based petroleum resins, aromatic petroleum resins, and C5C9-based petroleum resins. Of these, C5-based petroleum resins refer to resins obtained by polymerizing a C5 fraction. Examples of C5 fractions include petroleum fractions with 4 to 5 carbon atoms, such as cyclopentadiene, pentene, pentadiene, and isoprene. Dicyclopentadiene resin (DCPD resin) is preferably used as a C5-based petroleum resin.

[0144] Aromatic petroleum resins refer to resins obtained by polymerizing C9 fractions, and may be hydrogenated or modified. Examples of C9 fractions include petroleum fractions with 8 to 10 carbon atoms, such as vinyltoluene, alkylstyrene, indene, and methylindene. Specific examples of aromatic petroleum resins that are suitably used include coumarone indene resin, coumarone resin, indene resin, and aromatic vinyl resins. For aromatic vinyl resins, homopolymers of α-methylstyrene or styrene, or copolymers of α-methylstyrene and styrene are preferred, and copolymers of α-methylstyrene and styrene are more preferred, due to their economical nature, ease of processing, and excellent heat generation properties. Aromatic vinyl resins that are commercially available from companies such as Braskem, Kraton, and Eastman Chemical can be used.

[0145] C5C9 petroleum resin refers to a resin obtained by copolymerizing the C5 fraction and the C9 fraction, and may be hydrogenated or modified. Examples of the C5 and C9 fractions include the petroleum fractions mentioned above. As C5C9 petroleum resin, commercially available products from companies such as Tosoh Corporation and LUHUA can be used.

[0146] Examples of terpene resins include polyterpene resins consisting of at least one terpene compound selected from α-pinene, β-pinene, limonene, dipentene, etc.; aromatically modified terpene resins made from the terpene compound and an aromatic compound; terpene-phenol resins made from the terpene compound and a phenolic compound; and these terpene resins that have been hydrogenated (hydrogenated terpene resins). Examples of aromatic compounds used as raw materials for aromatically modified terpene resins include styrene, α-methylstyrene, vinyltoluene, and divinyltoluene. Examples of phenolic compounds used as raw materials for terpene-phenol resins include phenol, bisphenol A, cresol, and xylenol.

[0147] Rosin-based resins are not particularly limited, but examples include natural resin rosins such as tall rosin, gum rosin, and wood rosin, as well as rosin-modified resins obtained by hydrogenation, disproportionation, dimerization, esterification, etc.

[0148] Phenolic resins are not particularly limited, but examples include phenol-formaldehyde resin, alkylphenol-formaldehyde resin, alkylphenol-acetylene resin, and oil-modified phenol-formaldehyde resin.

[0149] From the viewpoint of wet grip performance, the softening point of the resin component is preferably 60°C or higher, more preferably 65°C or higher, and even more preferably 70°C or higher. Furthermore, from the viewpoint of processability and improved dispersibility between the rubber component and the filler, it is preferably 150°C or lower, more preferably 140°C or lower, and even more preferably 130°C or lower. The softening point can be defined as the temperature at which the sphere descends when the softening point specified in JIS K 6220-1:2001 is measured using a ring-type softening point measuring device.

[0150] When a resin component is included, the content per 100 parts by mass of the rubber component is preferably more than 0.1 parts by mass, more preferably more than 0.2 parts by mass, and even more preferably more than 0.3 parts by mass, from the viewpoint of chipping resistance. On the other hand, from the viewpoint of suppressing heat generation, the content is preferably less than 20 parts by mass, more preferably less than 10 parts by mass, even more preferably less than 5 parts by mass, even more preferably less than 3 parts by mass, and even more preferably less than 1 part by mass.

[0151] <Other compounding agents> In addition to the components mentioned above, the rubber composition constituting each layer of the tread according to the present invention may appropriately contain compounding agents commonly used in the tire industry, such as plasticizers other than resin components, waxes, processing aids, stearic acid, zinc oxide, antioxidants, vulcanizing agents, vulcanization accelerators, and the like.

[0152] (Plasticizers other than resin components) The rubber composition constituting each layer of the tread according to the present invention preferably contains a plasticizer other than the resin component. Examples of plasticizers include oil, liquid rubber, and ester-based plasticizers.

[0153] 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.

[0154] Furthermore, from a life cycle assessment perspective, lubricating oil used in rubber mixers and engines, or waste cooking oil used in restaurants, etc., may be appropriately refined and used in equal amounts as replacement for these oils.

[0155] When oil is included, the oil content per 100 parts by mass of rubber component is preferably more than 1 part by mass, more preferably more than 3 parts by mass, even more preferably more than 5 parts by mass, and particularly preferably more than 7 parts by mass, from the viewpoint of processability. Furthermore, from the viewpoint of wear resistance, it is preferably less than 50 parts by mass, more preferably less than 25 parts by mass, and even more preferably less than 10 parts by mass. In this specification, the oil content also includes the amount of oil contained in the oil-spread rubber.

[0156] 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.

[0157] When liquid rubber is included, its content per 100 parts by mass of rubber component is preferably more than 1 part by mass, more preferably more than 3 parts by mass, even more preferably more than 5 parts by mass, and particularly preferably more than 7 parts by mass. Furthermore, the liquid rubber content is preferably less than 50 parts by mass, more preferably less than 25 parts by mass, and even more preferably less than 10 parts by mass.

[0158] Examples of ester-based plasticizers include dibutyl adipate (DBA), diisobutyl adipate (DIBA), dioctyl adipate (DOA), di-2-ethylhexyl azelaate (DOZ), dibutyl sebacate (DBS), diisononyl adipate (DINA), diethyl phthalate (DEP), dioctyl phthalate (DOP), diundecyl phthalate (DUP), dibutyl phthalate (DBP), dioctyl sebacate (DOS), tributyl phosphate (TBP), trioctyl phosphate (TOP), triethyl phosphate (TEP), trimethyl phosphate (TMP), thymidine triphosphate (TTP), tricresyl phosphate (TCP), and trixylenyl phosphate (TXP). These ester-based plasticizers may be used individually or in combination of two or more.

[0159] (wax) When wax is included, the amount of wax per 100 parts by mass of rubber component is preferably more than 0.5 parts by mass, and more preferably more than 1 part by mass, 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 less than 10 parts by mass, and more preferably less than 5 parts by mass.

[0160] (Processing aid) 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.

[0161] When processing aids are included, the content per 100 parts by mass of rubber component is preferably more than 0.5 parts by mass, and more preferably more than 1 part by mass, from the viewpoint of exhibiting an effect of improving processability. Furthermore, from the viewpoint of wear resistance and fracture strength, it is preferably less than 10 parts by mass, and more preferably less than 8 parts by mass.

[0162] (Anti-aging agent) 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, and 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 are preferred. These anti-aging agents may be used individually or in combination of two or more.

[0163] When an anti-aging agent is included, the content per 100 parts by mass of rubber component is preferably more than 0.5 parts by mass, more preferably more than 1.0 part by mass, and even more preferably more than 1.5 parts by mass, 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 less than 10.0 parts by mass, and more preferably less than 5.0 parts by mass.

[0164] (Stearic acid) When stearic acid is included, its content per 100 parts by mass of rubber component is preferably more than 0.5 parts by mass, more preferably 1.0 part by mass or more, and even more preferably more than 1.5 parts by mass, from the viewpoint of processability. Furthermore, from the viewpoint of vulcanization rate, it is preferably less than 10.0 parts by mass, and more preferably less than 5.0 parts by mass.

[0165] (Zinc oxide) When zinc oxide is included, its content per 100 parts by mass of rubber component is preferably more than 0.5 parts by mass, more preferably more than 1.0 part by mass, and even more preferably more than 1.5 parts by mass, from the viewpoint of processability. Furthermore, from the viewpoint of wear resistance, it is preferably less than 10.0 parts by mass, and more preferably less than 5.0 parts by mass.

[0166] (Vulcanizing agent) 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.

[0167] When sulfur is used as a vulcanizing agent, the content per 100 parts by mass of rubber component is preferably more than 0.1 parts by mass, more preferably more than 0.3 parts by mass, and even more preferably more than 0.5 parts by mass, from the viewpoint of ensuring a sufficient vulcanization reaction. Furthermore, from the viewpoint of preventing deterioration, it is preferably less than 3.0 parts by mass, more preferably less than 1.5 parts by mass, even more preferably less than 1.25 parts by mass, and even more preferably 1.15 parts by mass or less. When oil-containing sulfur is used as a vulcanizing agent, the content of the vulcanizing agent shall be the total content of pure sulfur contained in the oil-containing sulfur.

[0168] 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.

[0169] (Vulcanization accelerator) 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, with sulfenamide vulcanization accelerators being more preferred.

[0170] 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.

[0171] 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.

[0172] 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.

[0173] When a vulcanization accelerator is included, its content per 100 parts by mass of rubber component is preferably more than 1.0 part by mass, more preferably more than 1.25 parts by mass, and even more preferably 1.5 parts by mass or more. Furthermore, the content of the vulcanization accelerator per 100 parts by mass of rubber component is preferably less than 8.0 parts by mass, more preferably less than 6.0 parts by mass, and even more preferably less than 3.0 parts by mass. By keeping the content of the vulcanization accelerator within the above range, it tends to be possible to ensure fracture strength and elongation.

[0174] (Sulfur content) The sulfur content (amount of sulfur element per 100 parts by mass of rubber component in the rubber composition) is preferably less than 2.00% by mass, more preferably 1.98% by mass or less, even more preferably less than 1.85% by mass, and even more preferably 1.82% by mass or less, from the viewpoint of chipping resistance. On the other hand, there is no particular limit on the lower limit of the sulfur content, but it is usually around 1.50%.

[0175] [Rubber composition constituting the second layer of the tread] The second layer of the tread portion of the heavy-duty tire of the present invention is a component known as the base tread. As the rubber composition constituting this second layer, a base tread rubber composition commonly used in this field can be used. Specific examples of such base tread rubber compositions include those described in the Examples section.

[0176] [Rubber composition that makes up the other layers of the tread] The tread portion of the heavy-duty tire of the present invention may further have one or more intermediate layers between the first layer and the second layer. As the rubber composition constituting such intermediate layers, a rubber composition for intermediate layers commonly used in this art can be used. Specific examples of such intermediate layer rubber compositions include, for example, those described in the Examples section.

[0177] [Application] The heavy-duty tires of the present invention are a concept that includes not only large trucks and buses, but also small trucks, buses, and vans, and are tires with a normal load capacity exceeding 1000 kg. Furthermore, when applying the heavy-duty tires of the present invention to small vehicles, it is preferable that the belt reinforcement layer and / or carcass cords be textile cords. The heavy-duty tires of the present invention are preferably tires mounted on large vehicles such as trucks, buses, and construction vehicles, and are tires with a normal load capacity of 1400 kg or more.

[0178] [Manufacturing method] <Manufacturing of rubber compositions> The rubber composition of the present invention 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.). The kneading process includes, for example, a base kneading step in which compounding agents and additives other than the vulcanizing agent and vulcanization accelerator are kneaded, and a final kneading (F kneading) step in which the vulcanizing agent and 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 multiple steps if desired. The kneading conditions are not particularly limited, but for example, in the base kneading step, kneading is performed at a discharge temperature of 150 to 170°C for 3 to 10 minutes, and in the final kneading step, kneading is performed at 50 to 110°C for 1 to 5 minutes.

[0179] <Tire Manufacturing> A rubber composition containing the above components can be extruded to the desired shape of each layer of a tread at the pre-vulcanization stage, and then molded together with other tire components in a conventional manner on a tire molding machine to produce an unvulcanized tire. By heating and pressurizing (vulcanizing) this unvulcanized tire in a vulcanizing machine, the tire of the present invention can be obtained. The vulcanization conditions are not particularly limited, but for example, a method of vulcanization at 150 to 200°C for 5 to 30 minutes can be used. [Examples]

[0180] The following examples (case studies) are considered preferable for implementation, but the scope of the present invention is limited. This is not limited to the examples provided.

[0181] The tires obtained using the various chemicals listed below, according to each table, were examined, and the results calculated based on the evaluation method described below are shown at the bottom of each table as the chipping resistance index.

[0182] [Examples and Comparative Examples] <Various chemicals> The various chemicals used in the examples and comparative examples are summarized below. NR:TSR20 BR: BUNA CB24 manufactured by ARLANXEO (BR synthesized using an Nd-based catalyst, cis content: 96 mol%, vinyl content: 0.7 mol%, Mw: 500,000) SBR: SBR1502 manufactured by ARLANXEO (Styrene content: 23.5% by mass, Vinyl content: 18 mol%, Mw: 500,000) Carbon Black 1: N134 (N2SA: 148m 2 / g, average primary particle diameter: 18nm) Carbon Black 2: N220 (N2SA: 115m) made by Birla Carbon Brasil Ltda 2 / g, average primary particle diameter: 22nm) Silica: OSC Siam Silica's TOKUSIL USG-A (N2SA: 175m 2 / g) Silane coupling agent: Si266 (bis(3-triethoxysilylpropyl) disulfide) manufactured by Evonik Degussa. Resin component: UNILEN A-100 manufactured by Braskem (aromatic petroleum resin, softening point 96-105°C (the softening point was measured according to ASTM D6943)). Oil: Diana Process Oil PA32 manufactured by Idemitsu Kosan Co., Ltd. Zinc oxide: Two types of zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. 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 Wax: Sunnock N manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Sulfur: Powdered sulfur manufactured by Karuizawa Sulfur Co., Ltd. Vulcanization accelerator: Noxellar NS-P (N-tert-butyl-2-benzothiazolyl sulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0183] <Unvulcanized rubber composition> According to the formulation shown in Table 1, the chemicals other than sulfur and vulcanization accelerator are mixed in a 1.7 L sealed Banbury mixer for 1 to 10 minutes until the discharge temperature reaches 150 to 160°C to obtain a mixture. Next, using a twin-screw open roll mixer, sulfur and vulcanization accelerator are added to the mixture and mixed for 4 minutes until the temperature reaches 105°C to obtain an unvulcanized rubber composition.

[0184] <Two-layer tread tire> Using the obtained unvulcanized rubber composition, the first layer (thickness: 17.2 mm) and second layer (thickness: 5.0 mm) of the tread were molded according to the shapes shown in Table 2, and then bonded together with other tire components to produce an unvulcanized tire. The tire was then vulcanized at 170°C to obtain each test tire (size: 12R22.5, for trucks and buses). Each block on the tread surface of the first layer has two sipes.

[0185] <Triple-layer tread tire> Using an unvulcanized rubber composition, the first layer (thickness: 17.2 mm), intermediate layer (thickness: 3.0 mm), and second layer (thickness: 2.0 mm) of the tread were molded according to the shapes in Table 3, and then bonded together with other tire components to produce an unvulcanized tire. The tire was then vulcanized at 170°C to obtain each test tire (size: 12R22.5, for trucks and buses).

[0186] (Sulfur content) Sulfur content refers to the amount of sulfur element per 100 parts by mass of rubber component (mass %), and is measured for rubber composition samples cut from each test tire. The "amount of sulfur element per 100 parts by mass of rubber component" is calculated by dividing the amount of sulfur element contained in the vulcanizing agent, as well as the amount of sulfur element contained in the vulcanization accelerator and coupling agent, etc., by the total sulfur amount (TS amount) and the amount of rubber component (PC amount), and then multiplying by PC amount. Here, the "TS amount" is measured as mass % for test pieces cut from the tread of the test tire using the oxygen combustion flask method in accordance with JIS K 6233. On the other hand, the "polymer content" is measured by setting a test piece cut from the tread of a test tire into a Soxhlet extractor, and performing acetone extraction under the following conditions: test piece: 10g or less, acetone: 150ml, constant temperature bath temperature: 95~100°C, extraction time: 72 hours. After acetone extraction, the test piece is measured as the loss in mass (%) when organic matter is thermally decomposed and vaporized by heating in nitrogen (raising the temperature from room temperature to 750°C), in accordance with JIS K 6226-1:2003.

[0187] (Chipping resistance) Each test tire is mounted on a rim (7.50 x 22.5) and the internal pressure is adjusted to 750 kPa. This tire is then mounted on the drive wheel of a test vehicle (2-D truck). After 8000 km of driving on this test vehicle (load capacity: 8 tons), the condition of the tread blocks is visually observed and scored. The results are expressed as an index, with the score of the standard example set at 100. A higher index indicates less tread block chipping and higher chipping resistance.

[0188] [Table 1]

[0189] [Table 2]

[0190] [Table 3]

[0191] <Embodiment> The following describes preferred embodiments.

[0192] [1] A heavy-duty tire having a tread portion including a first layer that constitutes the tread surface and a second layer located inside the first layer, The tread surface has a plurality of main grooves that extend continuously in the circumferential direction of the tire, transverse grooves that extend from the main grooves in the axial direction of the tire, and blocks that are partitioned by the main grooves and the transverse grooves. The aforementioned block has sipes, When the depth of the sipe (mm) is D and the thickness of the first layer (mm) is H, D and H satisfy the following relationship, preferably the right-hand side of equation (1) is 0.90, and more preferably 0.87. A heavy-duty tire comprising a rubber composition in the aforementioned layer, comprising a rubber component containing isoprene rubber and a filler containing carbon black and silica. D / H ≤ 0.95 (1) [2] The heavy-duty tire according to [1] above, wherein the right-hand side of formula (1) is 0.80, preferably 0.70, more preferably 0.60, even more preferably 0.50, even more preferably 0.40, even more preferably 0.30, even more preferably 0.20, and even more preferably 0.12. [3] The heavy-duty tire according to [1] or [2] above, wherein the carbon black comprises carbon black with an average primary particle size of 19 nm or less, preferably 18 nm or less. [4] The heavy-duty tire according to [3] above, wherein the carbon black with an average primary particle diameter of 19 nm or less, preferably 18 nm or less, is included in 100% by mass of the total carbon black. [5] A heavy-duty tire according to any one of the above [1] to [4], wherein A1 is the content of carbon black (parts by mass) and B1 is the content of silica (parts by mass) in the rubber composition constituting the first layer, and A1 and B1 satisfy the following relationship, preferably the right-hand side of equation (2) is 0.45, more preferably 0.40, and even more preferably 0.35. B1 / (A1+B1)<0.50 (2) [6] The heavy-duty tire according to [5] above, wherein the right-hand side of formula (2) is 0.20, preferably 0.18. [7] The heavy-duty tire according to any one of the above [1] to [6], wherein the rubber composition constituting the layer further contains a resin component. [8] The heavy-duty tire according to any one of the above [1] to [7], wherein the rubber composition constituting the first layer further contains sulfur, and the sulfur content per 100 parts by mass of the rubber component is 2.00% by mass or less, preferably 1.98% by mass or less, more preferably less than 1.85% by mass, and even more preferably 1.82% by mass or less. [9] A heavy-duty tire according to any one of the above [1] to [8], wherein A1 is the content (parts by mass) of carbon black relative to 100 parts by mass of rubber component in the rubber composition constituting the first layer, and C is the land ratio (%) of the tread surface of the tread portion, and A1 and C satisfy the following relationship, preferably the right-hand side of equation (3) is 3.20, more preferably 3.30, and even more preferably 3.40. A1 × C / 1000 > 3.00 (3)

[10] The heavy-duty tire according to any one of the above [1] to [9], wherein A1 is the amount of carbon black in the rubber composition constituting the first layer with respect to 100 parts by mass of rubber components, and A1 and D / H satisfy the following relationship, preferably the right-hand side of equation (4) is 275, more preferably 300, and even more preferably 350. A1 / (D / H)>250 (4)

[11] The number of main grooves is 3 or more, When the pair of main grooves on the outermost side in the tire width direction are designated as shoulder main grooves and the other main grooves as center main grooves, the groove width (mm) of the shoulder main groove with the smallest groove width is GW. SH And, the groove width (mm) of the largest of the aforementioned center main grooves is GW. CE The following relationship is satisfied, preferably the right-hand side of equation (5) is 0.95, more preferably 0.90, even more preferably 0.85, even more preferably 0.80, even more preferably 0.76, even more preferably 0.70, even more preferably 0.65, and even more preferably 0.61. When the outer part of the tire in the width direction, demarcated by the pair of shoulder main grooves, is considered a pair of shoulder land sections, the sum of the maximum contact widths (mm) of each shoulder land section is W. SH A heavy-duty tire according to any one of the above [1] to

[10] , wherein the tread contact width (mm) TW satisfies the following relationship, preferably the right-hand side of equation (6) is 0.49, more preferably 0.48, even more preferably 0.47, even more preferably 0.46, even more preferably 0.45, even more preferably 0.44, even more preferably 0.43, even more preferably 0.42, and even more preferably 0.41. Golden Week CE / GW SH <1.00 (5) W SH / TW<0.50 (6)

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

[11] , wherein the rubber composition constituting the layer has a rubber hardness of 62 to 72 at 23°C.

[13] The block has shallow grooves with a groove depth shallower than the groove depth of the main groove, A heavy-duty tire according to any one of the above [1] to

[12] , wherein the shallow groove opens into at least one of the main groove and the lateral groove adjacent to the block.

[14] A heavy-duty tire according to any one of the above [1] to

[13] , wherein A1 is the amount of carbon black per 100 parts by mass of rubber component in the rubber composition constituting the first layer, and the rubber composition constituting the second layer contains a rubber component including isoprene rubber and a filler including carbon black, and A2 is the amount of carbon black per 100 parts by mass of rubber component in the rubber composition constituting the second layer, such that A1 and A2 satisfy the following relationship, preferably the right-hand side of equation (7) is 0.95, more preferably 0.90, and even more preferably 0.86. A2 / A1<1.00 (7) (However, A2 is 20 or higher.)

[15] A heavy-duty tire according to any one of the above [1] to

[14] , wherein B1 is the silica content (parts by mass) per 100 parts by mass of rubber component in the rubber composition constituting the first layer, and the rubber composition constituting the second layer contains a rubber component including isoprene rubber and a filler containing silica, and B2 is the silica content (parts by mass) per 100 parts by mass of rubber component in the rubber composition constituting the second layer, such that B1 and B2 satisfy the following relationship, preferably the right-hand side of equation (8) is 0.90, more preferably 0.80, even more preferably 0.70, even more preferably 0.60, even more preferably 0.50, even more preferably 0.40, even more preferably 0.30, and even more preferably 0.21. B2 / B1<1.00 (8) (However, B2 must be 3 or higher.) [Explanation of Symbols]

[0193] 1. Tire 2. Tread surface 3. Tread 4...First layer 5...Second layer 6...Main groove 7. Center main groove 8. Shoulder main groove 9.. Yokomizo 10 blocks 11. Sipes 12. Shallow groove H...Tread's first layer thickness C...Tire centerline TW...Tread contact width Golden Week SH • Groove width of the shoulder main groove with the smallest groove width Golden Week CE • Groove width is the width of the main center groove. W SH • The sum of the maximum contact widths of each shoulder's land portion.

Claims

1. A heavy-duty tire having a tread portion including a first layer that constitutes the tread surface and a second layer located inside the first layer, The tread surface has a plurality of main grooves that extend continuously in the circumferential direction of the tire, transverse grooves that extend from the main grooves in the axial direction of the tire, and blocks that are partitioned by the main grooves and the transverse grooves. The block has sipes, When the depth of the sipe (mm) is D and the thickness of the first layer (mm) is H, D and H satisfy the following relationship (1): The rubber composition comprising the above layer comprises a rubber component containing isoprene rubber and a filler containing carbon black and silica. When A1 is the amount of carbon black (parts by mass) per 100 parts by mass of rubber component in the rubber composition constituting the above layer, A1 and D / H satisfy the following relation (4): The rubber composition constituting the second layer comprises a rubber component containing isoprene rubber and a filler containing silica. When B1 is the silica content (parts by mass) per 100 parts by mass of rubber component in the rubber composition constituting the first layer, and B2 is the silica content (parts by mass) per 100 parts by mass of rubber component in the rubber composition constituting the second layer, B1 and B2 satisfy the following relation (8): Heavy-duty tires. D / H≦0.95 (1) A 1 / (D / H)>250 (4) B 2 / B 1 <1.00 (8) (However, B2 must be 3 or higher.)

2. The heavy-duty tire according to claim 1, wherein the right-hand side of formula (1) is 0.

80.

3. The heavy-duty tire according to claim 1, wherein the carbon black includes carbon black with an average primary particle size of 19 nm or less.

4. The heavy-duty tire according to claim 3, wherein the carbon black with an average primary particle diameter of 19 nm or less accounts for 100% by mass of the total carbon black.

5. The amount of carbon black (parts by mass) in the rubber composition constituting the above layer, relative to 100 parts by mass of rubber component, is A. 1 The silica content (parts by mass) is set to B 1 In that case, A 1 and B 1 A heavy-duty tire according to any one of claims 1 to 4, wherein the following relation satisfies the relationship between and the tire. B 1 / (A 1 +B 1 )<0.50 (2)

6. The heavy-duty tire according to claim 5, wherein the right-hand side of formula (2) is 0.

20.

7. The heavy-duty tire according to any one of claims 1 to 4, wherein the rubber composition constituting the above layer further contains a resin component.

8. The heavy-duty tire according to any one of claims 1 to 4, wherein the rubber composition constituting the first layer further contains sulfur, and the sulfur content relative to 100 parts by mass of the rubber component is 2.00% by mass or less.

9. Let the content (parts by mass) of carbon black with respect to 100 parts by mass of the rubber component in the rubber composition constituting the first layer be A 1 When the land ratio (%) of the tread surface of the tread portion is C, the heavy load tire according to any one of claims 1 to 4, wherein A 1 and C satisfy the following relational expression A 1 ×C / 1000>3.00 (3)

10. The heavy-duty tire according to any one of claims 1 to 4, wherein the right-hand side of formula (4) is 275.

11. The number of main grooves is three or more, When the pair of main grooves on the outermost side in the tire width direction are designated as shoulder main grooves and the other main grooves as center main grooves, the groove width (mm) of the shoulder main groove with the smallest groove width is GW. SH And, the groove width (mm) of the largest groove among the aforementioned center main grooves is GW. CE And satisfy the following relationship, When the outer part of the tire in the width direction, demarcated by the pair of shoulder main grooves, is considered a pair of shoulder land sections, the sum of the maximum contact widths (mm) of each shoulder land section is W. SH A heavy-duty tire according to any one of claims 1 to 4, wherein the tread contact width (mm), TW, satisfies the following relationship. GW CE / GW SH <1.00 (5) W SH / TW<0.50 (6)

12. A heavy-duty tire according to any one of claims 1 to 4, wherein the rubber composition constituting the above layer has a rubber hardness of 62 to 72 at 23°C.

13. The block has shallow grooves with a groove depth shallower than the groove depth of the main groove, The heavy-duty tire according to any one of claims 1 to 4, wherein the shallow groove opens into at least one of the main groove and the lateral groove adjacent to the block.

14. The amount of carbon black (parts by mass) in the rubber composition constituting the above layer, relative to 100 parts by mass of rubber component, is A. 1 The rubber composition constituting the second layer comprises a rubber component containing isoprene rubber and a filler containing carbon black, and the carbon black content (parts by mass) in the rubber composition constituting the second layer relative to 100 parts by mass of the rubber component is A 2 In that case, A 1 and A 2 A heavy-duty tire according to any one of claims 1 to 4, wherein the following relation satisfies the relationship between and the tire. A 2 / A 1 <1.00 (7) (However, A 2 (It is 20 or more.)

15. The heavy-duty tire according to any one of claims 1 to 4, wherein the right-hand side of formula (8) is 0.90.

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