Heavy duty tire

Abstract

To provide a tire for a heavy load for improving total performance of wet grip performance, low fuel consumption performance and rib tear resistance performance.SOLUTION: A heavy duty tire including a tread portion, the tread portion including at least a first layer forming a tread surface, a second layer adjacent to an inner side of the first layer in a tire radial direction, and a third layer adjacent to an inner side of the second layer in the tire radial direction, each of the first layer, the second layer, and the third layer being formed of a rubber composition containing a rubber component and a filler, when contents of silica with respect to 100 parts by mass of rubber components in the rubber compositions constituting the first layer, the second layer, and the third layer are defined as S1 (parts by mass), S2 (parts by mass), and S3 (parts by mass), respectively, a maximum value of S1, S2, and S3 is defined as Smax, and a tire outer diameter is defined as Dt (m), S1 ≥ 0, S2 ≥ 0, S3 ≥ 0, Smax> 30, Dt> 0.80, and Smax / Dt <100.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] The tread portion of a heavy-duty tire often has multiple circumferential grooves and multiple land portions. During running, strain tends to concentrate at the groove bottoms of the circumferential grooves located closer to the tread edge than at the groove bottoms of the circumferential grooves located closer to the tire equator. Therefore, if a crack occurs at the groove bottom of a circumferential groove located closer to the tread edge and the crack reaches the inside of the tread portion, the land portion located closer to the tread edge will partially tear, resulting in a so-called rib tear.

[0003] As a method for improving the breaking strength of heavy-duty tires, there is a technique for microparticulating or highly structuring carbon black, as disclosed in Patent Document 1, for example.

[0004] Heavy-duty tires also require wet grip performance and low fuel consumption. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 6-279624 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a heavy-duty tire that improves the overall performance of wet grip performance, fuel economy, and rib tear resistance. [Means for solving the problem]

[0007] The present invention provides A heavy-duty tire having a tread portion, the tread portion includes at least a first layer constituting a tread surface, a second layer adjacent to the first layer on the radially inner side of the tire, and a third layer adjacent to the second layer on the radially inner side of the tire, the first layer, the second layer, and the third layer are each made of a rubber composition containing a rubber component and a filler, The silica contents per 100 parts by mass of the rubber component in the rubber compositions constituting the first layer, the second layer, and the third layer are defined as S1 (parts by mass), S2 (parts by mass), and S3 (parts by mass), respectively, and the maximum value of S1, S2, and S3 is defined as S max and the tire outer diameter is Dt(m), S1 ≥ 0, S2 ≥ 0, S3 ≥ 0, S max >30, Dt>0.80, S max / Dt<100. [Effects of the Invention]

[0008] According to the present invention, a heavy-duty tire is provided which has improved wet grip performance, fuel economy, and rib tear resistance. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view in the tread width direction showing half of a tread portion of a heavy-duty pneumatic tire according to one embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing the tire section width Wt, tire section height Ht, and tire outer diameter Dt in a tire cross section. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, a tire according to one embodiment of the present invention will be described. The tire according to this embodiment is a heavy-duty tire having a tread portion, the tread portion comprising at least a first layer constituting a tread surface, a second layer adjacent to the first layer on the radially inner side of the tire, and a third layer adjacent to the second layer on the radially inner side of the tire, the first layer, the second layer, and the third layer being made of a rubber composition containing a rubber component and a filler, the contents of silica in the rubber compositions constituting the first layer, the second layer, and the third layer per 100 parts by mass of the rubber component are respectively defined as S1 (parts by mass), S2 (parts by mass), and S3 (parts by mass), and the maximum value of S1, S2, and S3 is defined as S max If the tire outer diameter is Dt (m), then S1 ≥ 0, S2 ≥ 0, S3 ≥ 0, S max >30, Dt>0.80, S max / Dt<100, it is a heavy-duty tire.

[0011] Although not intending to be bound by theory, the reason why the present invention improves the overall wet grip performance, fuel economy, and rib tear resistance of a heavy duty tire is thought to be as follows.

[0012] First, (1) the tread portion has at least a first layer constituting the tread surface, a second layer adjacent to the first layer on the radially inner side of the tire, and a third layer adjacent to the second layer on the radially inner side of the tire. Therefore, even if a crack occurs in the tire groove bottom, the crack is less likely to reach the inside of the tread portion, and the occurrence of rib tears can be suppressed. max By satisfying Dt > 30, it becomes easier to increase the heat build-up (tan δ) of the tread rubber around 0°C, improving wet grip performance. Furthermore, silica can contribute to fuel efficiency. (3) By satisfying Dt > 0.80, the tire outer diameter becomes larger to a certain extent, making it suitable for installation on industrial vehicles such as trucks and buses. And, (4) S max By setting / Dt<100, the maximum silica content relative to the tire outer diameter is kept below a certain level, improving fuel efficiency.

[0013] It is believed that the cooperation of the above (1) to (4) achieves the remarkable effect of providing a heavy-duty tire with improved wet grip performance, fuel economy, and rib tear resistance.

[0014] S max The rubber component constituting the layer corresponding to the above preferably contains more than 10% by mass, more preferably more than 30% by mass of styrene-butadiene rubber.

[0015] S max The rubber component constituting the layer corresponding to the above preferably contains more than 10% by mass, and more preferably more than 30% by mass, of isoprene-based rubber.

[0016] Silica is also thought to contribute to improving fuel economy, but it also chemically bonds with styrene-butadiene rubber or isoprene-based rubber via a silane coupling agent, reinforcing the rubber composition. Therefore, if the layer with the highest silica content contains a certain amount of styrene-butadiene rubber, the styrene groups can improve the dispersibility of the silica, improving the flexibility of the rubber composition and further improving wet grip performance.

[0017] Furthermore, when the layer with the highest silica content contains a certain amount of isoprene-based rubber, an isoprene-based rubber phase that has a relatively weak interaction with silica is formed in the rubber matrix, which is thought to improve the flexibility of the rubber composition and further improve wet grip performance.

[0018] The rubber component constituting the first layer preferably contains 1% by mass or more of styrene-butadiene rubber.

[0019] The heat generated by the styrene group can increase the 0°C tan δ of the first layer, which is thought to further contribute to improved wet grip performance.

[0020] S1 is preferably greater than 30.

[0021] When the first layer that makes up the tread surface contains more than 30 parts by mass of silica, heat generation at around 0°C on the tread surface is improved, which is thought to improve the tire's ability to follow the road surface and further improve wet grip performance.

[0022] It is preferable that S1 is greater than S2 and S3, and it is more preferable that S1>S2>S3.

[0023] By making S1 larger than S2 and S3, it is possible to increase the heat buildup near 0°C on the tread surface compared to the interior of the tread, which is thought to improve the tire's ability to follow the road surface and further improve wet grip performance. Furthermore, by making S1 > S2 > S3, it is thought that the above effects can be further improved.

[0024] Dt is preferably 1.00 m or more, since this makes it more suitable for installation on industrial vehicles.

[0025] From the viewpoint of further improving wet grip performance, the tan δ at 0° C. (0° C. tan δ1) of the rubber composition constituting the first layer is preferably 0.21 or more.

[0026] It is preferable that 0°C tan δ1 × Dt is 0.190 or more.

[0027] It is believed that the larger Dt is, the more likely it is that energy loss will occur due to deformation at the ends of the land and block portions. Therefore, by increasing the product of 0°C tan δ1 and Dt, energy loss will occur in the land and block portions, making it easier to improve wet grip performance after wear.

[0028] The complex modulus of elasticity at 0° C. (0° C. E*1) of the rubber composition constituting the first layer is preferably 15.0 MPa or more, from the viewpoint of further improving wet grip performance.

[0029] The elongation at break (EB1) of the rubber composition constituting the first layer is preferably 400% or more from the viewpoint of rib tear resistance.

[0030] By setting the breaking elongation of the rubber composition constituting the first layer within the above range, it is believed that the surface condition is more likely to be maintained smoother when the tire is worn, and the reduction in the actual contact area is suppressed, and as a result, the deterioration of wet grip performance after tire wear can be suppressed.

[0031] [Definition] The "tread portion" refers to a component that includes the portion that forms the tire's contact surface, and in the case where the tire includes components that form the tire skeleton from steel or textile materials, such as a belt layer, a belt reinforcing layer, and a carcass layer, the "tread portion" is a component that is located radially outward of these components in the tire radial cross section.

[0032] "Tire outer diameter Dt" refers to the outer diameter of a tire in a normal state. In this specification, unless otherwise specified, the unit of Dt is "m."

[0033] "Normal condition" means that the tire is mounted on a normal rim, inflated to the normal internal pressure, and unloaded. Unless otherwise specified, the tire must be in its normal condition.

[0034] "Genuine rim" refers to the rim specified for each tire in the standard system that includes the standard on which the tire is based. 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 Organization), 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." JATMA, ETRTO, and TRA are referenced in that order, and if an applicable size is available at the time of reference, that standard is followed. In the case of a tire not specified in the above standards, it refers to the narrowest rim among the smallest diameter rims that can be mounted on the tire and can maintain internal pressure (i.e., no air leaks from between the rim and tire).

[0035] "Normal internal pressure" refers to the air pressure specified for each tire in the standard system that includes the standard on which the tire is based. For example, for JATMA, it is "maximum air pressure," for ETRTO, it is "INFLATION PRESSURE," and for TRA, it refers to the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES." As with regular rims, refer to JATMA, ETRTO, and TRA in that order, and follow that standard if there is an applicable size at the time of reference. In the case of tires not specified in the above standards, it refers to the normal internal pressure (250kPa or more) of another tire size (defined in the standard) that is specified using the regular rim as the standard rim, and if there are multiple normal internal pressures of 250kPa or more listed, it refers to the smallest value among them.

[0036] "Normal load (kg)" is the load specified for each tire in the standard system including the standard on which the tire is based, for example, "Maximum Load Capacity" for JATMA, "Load Capacity" for ETRTO, and the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA. As with normal rims and normal internal pressures, JATMA, ETRTO, and TRA should be referenced in that order, and if there is an applicable size at the time of reference, that standard should be followed. For tires not specified in the above standards, the maximum load capacity W calculated separately should be used. L is the normal load.

[0037] "Maximum load capacity W L (kg)" is calculated using the following formula: "V" is the virtual volume of the tire (mm 3 ), "Ht" is the tire's cross-sectional height (mm) in the radial direction of the tire in a cross section of the tire taken along a plane including the tire's rotation axis, and "Wt" is the tire's cross-sectional width (mm) in the normal state. In the calculation formula below, Dt is in mm. If the tire rim diameter is R, Ht can be calculated by (Dt-R) / 2. If there are any patterns or letters on the tire sidewall, Wt is the value obtained by excluding these. Note that maximum load capacity is synonymous with the normal load mentioned above.

[0038]

number

[0039] The term "circumferential groove" refers to a groove that extends continuously in the circumferential direction of the tire. The circumferential groove may extend linearly along the circumferential direction, or may extend in a wavy, sinusoidal, or zigzag pattern along the circumferential direction.

[0040] "The thickness of each rubber layer constituting the tread" refers to the thickness of each rubber layer constituting the tread in the radial direction of the tire at the tire's equatorial plane. When the tread is formed from multiple rubber layers, the sum of their thicknesses is the "thickness of the tread." Also, when the tire has grooves on the equatorial plane, the thickness of the rubber layer at the center in the tire width direction of the land portion closest to the tire's equatorial plane is considered to be the thickness of each rubber layer constituting the tread, or the thickness of the tread.

[0041] The "loss tangent and complex modulus of a rubber composition" are the loss tangent (tanδ) and complex modulus E* (MPa) measured under various conditions in extension mode using a dynamic viscoelasticity measuring device (for example, the Iplexer series manufactured by GABO). The sample used for dynamic viscoelasticity measurement is a vulcanized rubber composition having a length of 20 mm, a width of 4 mm, and a thickness of 1 mm. When preparing a sample by cutting it out from a tire, if the component from which the sample is prepared is a tread portion, a belt reinforcing layer, a belt layer, or an inner liner, the length direction of the sample should be aligned with the circumferential direction of the tire, and the thickness direction of the sample should be aligned with the radial direction of the tire.

[0042] "0°C tanδ" and "0°C E*" are the loss tangent (tanδ) and the complex modulus E* (MPa), respectively, measured under the conditions of a temperature of 0°C, a frequency of 10 Hz, an initial strain of 10%, a dynamic strain of ±2.5%, and an extension mode.

[0043] The "breaking elongation EB of the rubber composition" is the breaking elongation (%) when a tensile test is carried out on a 1 mm thick No. 7 dumbbell-shaped test piece in accordance with JIS K 6251:2017 at a temperature of 23°C and a tensile speed of 3.3 mm / sec.

[0044] "Styrene content" is measured by pyrolysis gas chromatography and NMR measurement ( 1 H-NMR and 13The amount of components such as "styrene content" is calculated by C-NMR. Unlike physical property values ​​such as complex modulus (E*), the amount of components such as "styrene content" has a true value that is independent of the measurement method, so it is preferable to use a measurement method with as high accuracy as possible. In this specification, "pyrolysis gas chromatography" refers to a method in which a sample is heated in a pyrolysis device, the individual components contained in the gas phase components generated by this heating are separated using a separation column, and each isolated component is analyzed.

[0045] "Vinyl content (amount of 1,2-bonded butadiene units)" can be measured by pyrolysis gas chromatography or NMR measurement ( 1 H-NMR and 13 It is calculated using C-NMR. As with the "styrene content," there is a true value for the "vinyl content" that is independent of the measurement method, so it is preferable to use a measurement method with as high accuracy as possible.

[0046] "Cis content (cis-1,4-bonded butadiene unit amount)" is measured by infrared absorption spectroscopy or NMR measurement ( 1 H-NMR and 13 This is a value measured by C-NMR and is applied to rubber components that have repeating units derived from butadiene, such as BR. As with the "styrene content," the "cis content" also has a true value that is independent of the measurement method, so it is preferable to use a measurement method with as high accuracy as possible.

[0047] The "weight average molecular weight (Mw)" can be determined by converting the measured value into standard polystyrene equivalents using gel permeation chromatography (GPC) (for example, a GPC-8000 series manufactured by Tosoh Corporation, a differential refractometer as the detector, and a TSKgel SuperMultipore HZ-M column manufactured by Tosoh Corporation). This applies to, for example, SBR, BR, plasticizers, etc.

[0048] The "glass transition temperature of the rubber component" refers to the static glass transition temperature of each rubber component determined by a differential scanning calorimeter (for example, Q200 manufactured by TA Instruments Japan Co., Ltd.).

[0049] The "nitrogen adsorption specific surface area (N2SA) of carbon black" is measured in accordance with JIS K 6217-2:2017.

[0050] The "nitrogen adsorption specific surface area (N2SA) of silica" is measured by the BET method in accordance with ASTM D3037-93.

[0051] The "average primary particle size" is a value obtained by photographing particles with a transmission or scanning electron microscope and calculating the arithmetic mean of the particle sizes of 400 particles. If the particle shape is spherical, the particle size is the diameter of the sphere, and if the particle shape is non-spherical, the particle size is calculated from the microscope image as the circle-equivalent diameter (positive square root of {4 × (particle area) / π}).

[0052] "Plasticizer" is a material that imparts plasticity to rubber components and is a component that is extracted from rubber compositions using acetone. Plasticizers include those that are liquid (fluid) at 25°C and those that are solid at 25°C. However, this does not include waxes and stearic acid, which are commonly used in the tire industry.

[0053] The "plasticizer content" also includes the amount of plasticizer in the rubber component extended by the plasticizer.

[0054] [tire] A tire according to one embodiment of the present invention will be described below with reference to the drawings. Note that the embodiment described below is merely an example, and the tire of the present invention is not limited to the following embodiment.

[0055] Fig. 1 shows a cross-sectional view in the tread width direction of half of the tread portion of a heavy-duty pneumatic tire according to one embodiment of the present invention. In Fig. 1, the up-down direction is the tire radial direction, the left-right direction is the tire axial direction, and the direction perpendicular to the paper surface is the tire circumferential direction.

[0056] The tire of FIG. 1 includes a tread portion 1, a pair of sidewalls 9 arranged on both sides of the tread portion, at least one layer of carcass 2, and at least one layer of belt 3 arranged radially outward of the carcass 2.

[0057] The tread portion 1 includes a first layer 4 that forms a tread surface 7, a second layer 5 adjacent to the first layer 4 on the radially inner side of the tire, and a third layer 6 adjacent to the second layer 5 on the radially inner side of the tire. The tread portion 1 can also include a further rubber layer between the third layer 6 and the belt layer 3, making it possible to have four or more layers.

[0058] In Fig. 1, the carcass 2 is laminated in two layers, and the belt layer 3 is laminated in five layers, but this is not limited to this. In a heavy-duty tire of one embodiment according to the present invention, it is preferable that the carcass and belt layer have two or more layers. In Fig. 1, a reinforcing rubber layer 8 is present between the third layer 6 and the belt layer 3, but the heavy-duty tire of this embodiment may or may not have a reinforcing rubber layer.

[0059] The tan δ at 0°C (0°C tan δ1) of the rubber composition constituting the first layer is preferably 0.18 or more, more preferably 0.19 or more, even more preferably 0.20 or more, and particularly preferably 0.21 or more. From the viewpoint of fuel economy at low temperatures, the 0°C tan δ1 is preferably 0.45 or less, more preferably 0.40 or less, even more preferably 0.35 or less, and particularly preferably 0.30 or less. The tan δ at 0°C of the rubber compositions constituting the second and third layers is not particularly limited.

[0060] The 0°C tan δ of the rubber composition can be adjusted appropriately by changing the types and amounts of the rubber components, vulcanized rubber particles, plasticizers, etc. For example, by reducing the content of silica or plasticizer, the value of 0°C tan δ can be reduced, and conversely, by increasing the content of silica or plasticizer, the value of 0°C tan δ can be increased.

[0061] From the viewpoint of wet grip performance, the complex modulus at 0°C (0°C E*1) of the rubber composition constituting the first layer is preferably 15.0 MPa or more, more preferably 16.0 MPa or more, even more preferably 17.5 MPa or more, and particularly preferably 18.0 MPa or more. Furthermore, 0°C E*1 is preferably 50.0 MPa or less, more preferably 45.0 MPa or less, and even more preferably 40.0 MPa or less. The E* at 0°C of the rubber compositions constituting the second and third layers is not particularly limited. The 0°C E* of the rubber composition can be adjusted appropriately by adjusting the types and amounts of the rubber components, vulcanized rubber particles, resins, oils, etc., described below.

[0062] The elongation at break (EB1) of the rubber composition constituting the first layer is preferably 400% or more, more preferably 410% or more, and even more preferably 430% or more, from the viewpoint of rib tear resistance. On the other hand, the upper limit of EB1 is not particularly limited, but can be, for example, 600% or less, 500% or less, or 480% or less.

[0063] The elongation at break (EB2 and EB3) of the second layer and the rubber composition constituting the second layer is preferably 480% or more, more preferably 500% or more, and even more preferably 510% or more. There are no particular upper limits for EB2 and EB3.

[0064] The breaking elongation of the rubber composition can be adjusted by the amount of rubber component, the amount of plasticizer, the type of plasticizer, etc. For example, the breaking elongation can be increased by reducing the content of isoprene-based rubber.

[0065] FIG. 2 is a diagram showing the tire section width Wt, tire section height Ht, and tire outer diameter Dt in a tire cross section.

[0066] In the heavy-duty tire according to the present embodiment, the tire outer diameter Dt is greater than 0.80 m, preferably 0.85 m or greater, more preferably 0.88 m or greater, even more preferably 0.90 m or greater, still more preferably 0.92 m or greater, still more preferably 0.95 m or greater, particularly preferably 0.98 m or greater, and most preferably 1.00 m or greater. From the viewpoint of the effects of the present invention, the tire outer diameter Dt is preferably less than 3.00 m, more preferably less than 2.50 m, and even more preferably less than 2.00 m.

[0067] In the heavy duty tire according to this embodiment, S max In view of the effects of the present invention, / Dt is less than 100, preferably less than 90, more preferably less than 80, even more preferably less than 70, and particularly preferably less than 60.

[0068] From the viewpoint of wet grip performance after wear, 0°C tan δ1 × Dt is preferably 0.190 or more, more preferably 0.200 or more, more preferably 0.210 or more, even more preferably 0.214 or more, and particularly preferably 0.220 or more. Also, 0°C tan δ1 × Dt is preferably 0.500 or less, more preferably 0.450 or less, and even more preferably 0.400 or less.

[0069] [Rubber composition] The tread portion according to the present embodiment includes at least three layers: a first layer, a second layer adjacent to the first layer on the radially inner side thereof, and a third layer adjacent to the second layer in the radial direction thereof, the first layer, the second layer, and the third layer being each made of a rubber composition containing a rubber component and a filler, and the contents of silica per 100 parts by mass of the rubber component in the rubber compositions constituting the first layer, the second layer, and the third layer being defined as S1 (parts by mass), S2 (parts by mass), and S3 (parts by mass), respectively, and the maximum value of S1, S2, and S3 being defined as S max If S1 ≥ 0, S2 ≥ 0, S3 ≥ 0, S max >30. The rubber compositions constituting each layer of the tread portion can be produced using the raw materials described below in accordance with the required 0°C tan δ, 0°C E*, elongation at break, etc. The rubber composition according to this embodiment will be described below.

[0070] <Rubber component> The rubber composition according to the present embodiment preferably contains a diene rubber as a rubber component, and more preferably contains at least one selected from the group consisting of isoprene rubber, styrene butadiene rubber (SBR), and butadiene rubber (BR). The rubber composition constituting the first layer preferably contains an isoprene rubber as a rubber component, and more preferably contains an isoprene rubber and BR. The rubber composition constituting the second layer preferably contains an isoprene rubber as a rubber component, and more preferably contains an isoprene rubber and BR, and may be a rubber component consisting only of an isoprene rubber and BR. The rubber composition constituting the third layer preferably contains an isoprene rubber, and may be a rubber component consisting only of an isoprene rubber. These rubber components may be modified with a functional group capable of interacting with filler components such as silica or carbon black, and from the viewpoint of optimizing the crosslinking form and suppressing deterioration, some of the unsaturated bonds may be hydrogenated to form saturated bonds.

[0071] As the diene rubber, any of those commonly used in the tire industry can be suitably used. Specific examples include isoprene rubber, butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene rubber (SIR), styrene isoprene butadiene rubber (SIBR), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), etc. These diene rubbers may be used alone or in combination of two or more.

[0072] The content of the diene rubber in the rubber component is preferably more than 70% by mass, more preferably more than 80% by mass, even more preferably more than 90% by mass, and particularly preferably more than 95% by mass.

[0073] (Isoprene rubber) Examples of isoprene-based rubbers that can be used include those commonly used in the tire industry, such as isoprene rubber (IR) and natural rubber. Natural rubber includes unmodified natural rubber (NR) as well as modified natural rubbers such as epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), deproteinized natural rubber (DPNR), highly purified natural rubber, and grafted natural rubber. These isoprene-based rubbers may be used alone or in combination of two or more.

[0074] The NR is not particularly limited, and those commonly used in the tire industry can be used, such as SIR20, RSS#3, and TSR20.

[0075] The content of isoprene-based rubber in the rubber component constituting the first layer is preferably 50% by mass or more, more preferably 55% by mass or more, even more preferably 60% by mass or more, and particularly preferably 65% ​​by mass or more, from the viewpoint of wet grip performance. Also, from the viewpoint of containing SBR and obtaining silica dispersibility due to styrene groups, the content is preferably less than 100% by mass, more preferably 90% by mass or less, and even more preferably 80% by mass or less.

[0076] From the viewpoint of fuel economy, the content of the isoprene-based rubber in the rubber component constituting the second layer is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more. The content of the isoprene-based rubber in the rubber component constituting the third layer is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more.

[0077] S max From the viewpoint of wet grip performance, the content of isoprene-based rubber in the rubber component constituting the layer corresponding to is preferably more than 5 mass%, more preferably more than 10 mass%, even more preferably more than 20 mass%, and particularly preferably more than 30 mass%.

[0078] (BR) The BR is not particularly limited, and can be one commonly used in the tire industry, such as 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 (rare earth BR) synthesized using a rare earth catalyst, BR containing syndiotactic polybutadiene crystals (SPB-containing BR), modified BR (high-cis modified BR, low-cis modified BR), etc. These BRs may be used alone or in combination of two or more.

[0079] As the high-cis BR, for example, commercially available products from Zeon Corporation, UBE Corporation, JSR Corporation, etc. can be used. The inclusion of high-cis BR can improve low-temperature properties and wear resistance. The cis content of the high-cis BR is preferably more than 95 mol%, more preferably more than 96 mol%, and even more preferably more than 97 mol%. The cis content of BR is measured by the above-mentioned measurement method.

[0080] The rare earth BR is synthesized using a rare earth catalyst and has a vinyl content of preferably less than 1.8 mol%, more preferably less than 1.6 mol%, and even more preferably 1.5 mol% or less, and a cis content of preferably more than 95 mol%, more preferably more than 96 mol%, and even more preferably 97 mol% or more. As the rare earth BR, for example, commercially available products from LANXESS K.K. can be used.

[0081] The SPB-containing BR is not simply 1,2-syndiotactic polybutadiene crystals dispersed in the BR, but is dispersed after being chemically bonded to the BR. As such SPB-containing BR, commercially available products from UBE Corporation and the like can be used.

[0082] As the modified BR, for example, a modified butadiene rubber (modified BR) whose terminals and / or main chain are modified with a functional group containing at least one element selected from the group consisting of silicon, nitrogen, and oxygen can be suitably used.

[0083] Other examples of modified BR include tin-modified BR, which is obtained by polymerizing 1,3-butadiene with a lithium initiator and then adding a tin compound, and in which the terminals of the modified BR molecule are further bonded with a tin-carbon bond (tin-modified BR).Modified BR may be either non-hydrogenated or hydrogenated.

[0084] From the viewpoint of abrasion resistance, the weight-average molecular weight (Mw) of BR is preferably more than 300,000, more preferably more than 350,000, and even more preferably more than 400,000. From the viewpoint of crosslink uniformity, etc., it is preferably less than 2,000,000, more preferably less than 1,000,000, and even more preferably less than 500,000. Mw can be determined by the above-mentioned method.

[0085] The BR content in the rubber component constituting the first layer is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, and is preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less.

[0086] The BR content in the rubber component constituting the second layer is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more. The content is preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less. The BR content in the rubber component constituting the third layer is not particularly limited, and the third layer may not contain BR.

[0087] (SBR) The SBR is not particularly limited, and examples thereof include solution-polymerized SBR (S-SBR), emulsion-polymerized SBR (E-SBR), and modified SBRs thereof (modified S-SBR, modified E-SBR). Modified SBRs include SBRs whose ends and / or main chains are modified, and modified SBRs (condensates, those having a branched structure, etc.) coupled with tin, silicon compounds, etc. Furthermore, hydrogenated products of these SBRs (hydrogenated SBRs) can also be used. These SBRs may be used alone or in combination of two or more.

[0088] As the SBR, either oil-extended or non-oil-extended SBR can be used. In this specification, commercially available SBRs from JSR Corporation, Sumitomo Chemical Co., Ltd., UBE Corporation, Asahi Kasei Corporation, ZS Elastomers Co., Ltd., ARLANXEO, etc. can be used.

[0089] 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 9% by mass. On the other hand, the styrene content of SBR is preferably less than 30% by mass, more preferably less than 20% by mass, and even more preferably less than 15% by mass. In this specification, the styrene content of SBR is measured by the above-mentioned measurement method.

[0090] The vinyl content of SBR is preferably more than 20 mol%, more preferably more than 30 mol%, and even more preferably more than 40 mol%. The vinyl content of SBR is preferably less than 70 mol%, more preferably less than 65 mol%, and even more preferably less than 60 mol%. In this specification, the vinyl content of SBR is measured by the above-mentioned measurement method.

[0091] From the viewpoint of wet grip performance, the glass transition temperature (Tg) of the SBR is preferably −80° C. or higher, more preferably −70° C. or higher, and even more preferably −65° C. or higher. From the viewpoint of fuel economy, the Tg of the SBR is preferably −40° C. or lower, more preferably −45° C. or lower, even more preferably −50° C. or lower, and even more preferably −55° C. or lower.

[0092] From the viewpoint of improving the dispersibility of silica, the content of SBR in the rubber component constituting the first layer is preferably 1% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, and particularly preferably 20% by mass or more. The content of SBR in the rubber component is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. The content of SBR in the rubber components constituting the second layer and the third layer is not particularly limited, and they may not contain SBR.

[0093] S max From the viewpoint of improving the dispersibility of silica, the content of SBR in the rubber component constituting the layer corresponding to is preferably more than 1 mass%, more preferably more than 5 mass%, even more preferably more than 10 mass%, and particularly preferably more than 30 mass%.

[0094] (Other rubber components) The rubber component may contain a rubber component other than the diene rubber (non-diene rubber) to the extent that it does not affect the effects of the invention. Examples of non-diene rubbers include rubber components commonly used in the tire industry, such as butyl rubber, ethylene propylene rubber, polynorbornene rubber, silicone rubber, chlorinated polyethylene rubber, fluororubber (FKM), acrylic rubber (ACM), and hydrin rubber. These other rubber components may be used alone or in combination of two or more. In addition to the above rubber components, a known thermoplastic elastomer may or may not be contained.

[0095] (Rubber components synthesized from recycled and biomass-derived raw materials) Monomers, which are structural units of synthetic rubbers such as IR, SBR, and BR, may be derived from underground resources such as petroleum and natural gas, or may be recycled from rubber products such as tires or non-rubber products such as polystyrene. Monomers obtained by recycling (recycled monomers) are not particularly limited, and examples include recycled polyisoprene, recycled butadiene, and recycled aromatic vinyl compounds. Examples of butadienes include 1,2-butadiene and 1,3-butadiene. Examples of aromatic vinyl compounds include, but are not limited to, styrene. Among these, recycled polyisoprene (recycled isoprene), recycled butadiene (recycled butadiene), and / or recycled styrene (recycled styrene) are preferably used as raw materials.

[0096] The method for producing the recycled monomer is not particularly limited, and examples thereof include synthesis from recycled naphtha obtained by decomposing rubber products such as tires. The method for producing recycled naphtha is also not particularly limited, and examples thereof include decomposing rubber products such as tires under high temperature and pressure, decomposing with microwaves, or mechanically crushing and then extracting.

[0097] Furthermore, the monomers that are the structural units of polymers such as IR, SBR, and BR may be derived from biomass. In this specification, biomass refers to materials derived from natural resources such as plants. Examples of biomass include, but are not limited to, agricultural, forestry, and fishery products, sugar, wood chips, plant residues after useful components have been extracted, plant-derived ethanol, and biomass naphtha.

[0098] Monomers derived from biomass (biomass monomers) are not particularly limited, and examples thereof include biomass-derived butadiene and biomass-derived aromatic vinyl compounds. Examples of butadienes include 1,2-butadiene and 1,3-butadiene. Examples of aromatic vinyl compounds include, but are not limited to, styrene. The method for producing biomass monomers is not particularly limited, and examples include biological and / or chemical and / or physical conversion of animals and plants. A representative example of biological conversion is fermentation by microorganisms, and examples of chemical and / or physical conversion include catalytic conversion, high heat conversion, high pressure conversion, electromagnetic wave conversion, critical fluid conversion, and combinations thereof.

[0099] Polymers synthesized from biomass monomer components (biomass polymers) are not particularly limited and include polybutadiene rubber synthesized from biomass-derived butadiene, aromatic vinyl / butadiene copolymers synthesized from biomass-derived butadiene and / or biomass-derived aromatic vinyl compounds, etc. Examples of the aromatic vinyl / butadiene copolymers include styrene-butadiene rubber synthesized from biomass-derived butadiene and / or biomass-derived styrene.

[0100] Whether a polymer's raw material is biomass-derived can be determined by its pMC (percent modern carbon) measured in accordance with ASTM D6866-10. pMC is the modern standard reference carbon. 14 of sample against C concentration 14 This is the ratio of C concentrations and is a value used as an index of the biomass ratio of a compound. The significance of this value is explained below.

[0101] 1 mole of carbon atoms (6.02 × 10 23 ) contains approximately 6.02 × 10 atoms, which is about one trillionth of the number of ordinary carbon atoms. 11 pieces 14 C exists. 14The half-life of C is 5730 years, 14 Therefore, in the case of fossil fuels such as coal, oil, and natural gas, which are thought to have been absorbed and fixed by plants and other organisms more than 226,000 years ago, carbon dioxide was included in these when they were first fixed. 14 All C elements have decayed. Therefore, in the 21st century, fossil fuels such as coal, oil, and natural gas contain 14 Therefore, chemicals produced from these fossil fuels do not contain any C element. 14 It does not contain any C element.

[0102] on the other hand, 14 C is constantly produced by cosmic rays undergoing nuclear reactions in the atmosphere. 14 The amount of C is balanced between radioactive decay and nuclear reaction, and in the Earth's atmospheric environment, 14 Therefore, the amount of carbon derived from biomass resources currently circulating in the environment is constant. 14 As mentioned above, the C concentration is approximately 1 × 10 -12 The value is approximately mol %. Therefore, the biomass ratio in a compound can be calculated by using the difference between these values.

[0103] this 14 C is typically measured using accelerator mass spectrometry based on a tandem accelerator. 13 C concentration ( 13 C / 12 C). 14 C concentration ( 14 C / 12 C) is measured. 14 The modern standard reference for the C concentration is the carbon circulating in nature as of 1950. 14The specific standard substance used is the oxalic acid standard provided by NIST (National Institute of Standards and Technology). The specific activity of carbon in this oxalic acid (per gram of carbon) is 14 The radioactivity of C is separated into carbon isotopes, 13 The standard value is the value corrected for decay from 1950 to the measurement date. 14 This is used as the C concentration value (100%). The ratio of this value to the value of the actually measured sample is the pMC value.

[0104] Therefore, if rubber is made from 100% biomass-derived materials, although there are regional differences, it will usually not reach 100 under normal conditions, so it will show a value of approximately 110 pMC. On the other hand, for chemical substances derived from petroleum and other fossil fuels, 14 When the carbon concentration is measured, it will show a value of about 0 pMC (for example, 0.3 pMC), which corresponds to the above-mentioned biomass ratio of 0%.

[0105] From the above, it is preferable in terms of environmental protection to use a material such as rubber having a high pMC value, that is, a material such as rubber having a high biomass ratio, in a rubber composition.

[0106] [Filler] The rubber composition according to the present embodiment contains a filler. The filler preferably contains silica, and more preferably contains carbon black and silica. Alternatively, the filler may be composed only of carbon black and silica.

[0107] <Silica> The silica is not particularly limited, and can be, for example, silica prepared by a dry method (anhydrous silica), silica prepared by a wet method (hydrated silica), or other silica commonly used in the tire industry. The raw material for silica is also not particularly limited, and can be, for example, a mineral-derived raw material such as quartz, a biological raw material such as rice husk (for example, silica made from biomass materials such as rice husk), or silica recycled from silica-containing products. Among these, hydrated silica prepared by a wet method is preferred because it contains a large number of silanol groups. These silicas can be used alone or in combination of two or more types.

[0108] Silica made from biomass materials can be obtained, for example, by extracting silicate from rice husk ash obtained by burning rice husks using a sodium hydroxide solution, and then reacting the silicate with sulfuric acid in the same manner as conventional wet-process silica to produce a silicon dioxide precipitate, which is then filtered, washed with water, dried, and pulverized.

[0109] Silica recycled from silica-containing products can be, for example, silica recovered from products containing silica, such as electronic components such as semiconductors, tires, desiccants, and filtering materials such as diatomaceous earth. The recovery method is not particularly limited, and examples include thermal decomposition and decomposition by electromagnetic waves. Among these, silica recovered from electronic components such as semiconductors or tires is preferred.

[0110] When silica crystallizes, it becomes insoluble in water, and its component, silicic acid, cannot be utilized. By controlling the combustion temperature and duration, the crystallization of silica in rice husk ash can be suppressed (see, for example, JP 2009-2594 A, Akita Prefectural University Web Journal B / 2019, vol. 6, pp. 216-222). Amorphous silica extracted from rice husks can be commercially available from Wilmar, Inc.

[0111] From the viewpoint of reinforcement, the nitrogen adsorption specific surface area (N2SA) of silica is 100m 2 / g or more is preferable, and 120m 2 / g is more preferable, and 150m2 From the viewpoint of heat buildup and processability, it is more preferable that the tensile strength is more than 300 m / g. 2 / g is preferable, and 280m 2 / g is more preferable, and 250m 2 / g or less is more preferable. The N2SA of silica is measured by the above-mentioned measurement method.

[0112] The average primary particle size of the silica contained in the rubber composition constituting the first layer is preferably greater than 8 nm, more preferably greater than 10 nm, and even more preferably greater than 12 nm. The average primary particle size is preferably less than 25 nm, more preferably less than 22 nm, even more preferably less than 20 nm, even more preferably less than 18 nm, and particularly preferably less than 16 nm. The average primary particle size of silica is measured by the above-mentioned measurement method.

[0113] The average primary particle size of the silica contained in the rubber composition constituting the second layer and the third layer is preferably greater than 12 nm, more preferably greater than 14 nm, and even more preferably greater than 15 nm. The average primary particle size is preferably less than 25 nm, more preferably less than 22 nm, and even more preferably less than 20 nm. The average primary particle size of silica is measured by the above-mentioned measurement method.

[0114] The content S1 of silica per 100 parts by mass of the rubber component in the rubber composition constituting the first layer is 0 or more, and is preferably greater than 10, more preferably greater than 20, and even more preferably greater than 30. From the viewpoint of rib tear resistance, S1 is preferably less than 80, more preferably less than 70, even more preferably less than 60, and particularly preferably less than 50.

[0115] The content S2 of silica per 100 parts by mass of the rubber component in the rubber composition constituting the second layer is 0 or more, and is preferably greater than 3, more preferably greater than 5, and even more preferably greater than 8. From the viewpoint of rib tear resistance, S2 is preferably less than 60, more preferably less than 50, and even more preferably less than 40.

[0116] The content S3 of silica per 100 parts by mass of the rubber component in the rubber composition constituting the third layer is 0 or greater, and is preferably greater than 1, more preferably greater than 2, and even more preferably greater than 4. From the viewpoint of rib tear resistance, S3 is preferably less than 40, more preferably less than 20, and even more preferably less than 10.

[0117] In the heavy duty tire according to this embodiment, the maximum value S of S1, S2, and S3 max is more than 30, preferably 31 or more. max is preferably less than 120, more preferably less than 100, and even more preferably less than 80.

[0118] S1 is preferably greater than S2 and S3, S2 is preferably greater than S3, and more preferably S1>S2>S3.

[0119] <Silane coupling agent> Silica is preferably used in combination with a silane coupling agent.Silane coupling agent is not particularly limited, but for example, sulfide-based silane coupling agent such as bis(3-triethoxysilylpropyl) disulfide, bis(3-triethoxysilylpropyl) tetrasulfide; mercapto-based silane coupling agent such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane; vinyl-based silane coupling agent such as vinyltriethoxysilane, vinyltrimethoxysilane; 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane Examples of suitable silane coupling agents include amino-based silane coupling agents such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro-based silane coupling agents such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; and chloro-based silane coupling agents such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. Among these, sulfide-based silane coupling agents and / or mercapto-based silane coupling agents are preferred. Examples of suitable silane coupling agents include those commercially available from Evonik Industries, Momentive, and the like. These silane coupling agents may be used alone or in combination.

[0120] The content of the silane coupling agent is preferably more than 3 parts by mass, more preferably more than 6 parts by mass, and even more preferably more than 9 parts by mass relative to 100 parts by mass of silica from the viewpoint of improving the dispersibility of silica. Also, from the viewpoint of cost and processability, the content is preferably less than 30 parts by mass, more preferably less than 20 parts by mass, and even more preferably less than 15 parts by mass relative to 100 parts by mass of silica.

[0121] The content of the silane coupling agent per 100 parts by mass of the rubber component (the total amount when multiple silane coupling agents are used) is preferably more than 1 part by mass, more preferably more than 2 parts by mass, and even more preferably 3 parts by mass or more, from the viewpoint of improving the dispersibility of silica. Also, from the viewpoint of preventing a decrease in abrasion resistance, the content is preferably less than 15 parts by mass, more preferably less than 10 parts by mass, and particularly preferably less than 5 parts by mass.

[0122] <Carbon black> Carbon black is not particularly limited, and examples thereof include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762. The raw material for carbon black may be a biomass material such as lignin or vegetable oil, or pyrolysis oil obtained by pyrolysis of waste tires. Carbon black may be produced by combustion, such as in a furnace process, by hydrothermal carbonization (HTC), or by pyrolysis of methane, such as in a thermal black process. Commercially available carbon blacks include those from Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Corporation, Lion Corporation, Nippon Steel Carbon Co., Ltd., and Columbia Carbon Co., Ltd. These carbon blacks may be used alone or in combination.

[0123] In addition to the above, from the viewpoint of life cycle assessment, carbon black may be made from a biomass material such as lignin, or recycled carbon black obtained by pyrolysis and purification of a product containing carbon black, such as a tire.

[0124] As used herein, "recycled carbon black" refers to carbon black obtained by crushing used tires or other products containing carbon black and calcining the crushed material, and refers to carbon black in which, when subjected to oxidative combustion by heating in air as measured by thermogravimetry in accordance with JIS K 6226-2:2003, the proportion of the mass of ash (ash content), which is the non-combustible component, is 13% by mass or more. In other words, the proportion of the mass (carbon content) of the recycled carbon black lost due to oxidative combustion is 87% by mass or less. Recycled carbon black is sometimes expressed as rCB.

[0125] Recycled carbon black can be obtained from the pyrolysis process of used pneumatic tires. For example, European Patent Application Publication No. 3427975, citing "Rubber Chemistry and Technology," Vol. 85, No. 3, pp. 408-449 (2012), particularly pp. 438, 440, and 442, describes the carbon black as being obtained by pyrolysis of organic materials at 550-800°C in the absence of oxygen, or by vacuum pyrolysis at relatively low temperatures (

[0027] ). Carbon black obtained from such pyrolysis processes typically lacks functional groups on its surface, as mentioned in

[0004] of Japanese Patent Publication No. 6856781 (Comparison of the Surface Morphology and Chemistry of Pyrolytic Carbon Black with Commercial Carbon Black, Powder Technology 160 (2005) pp. 190-193).

[0126] Recycled carbon black may lack functional groups on its surface, or may be treated to include functional groups on its surface. Treatment to include functional groups on the surface of recycled carbon black can be carried out by conventional methods. For example, in European Patent Application Publication No. 3,173,251, carbon black obtained from a pyrolysis process is treated with potassium permanganate under acidic conditions to obtain carbon black containing hydroxyl and / or carboxyl groups on its surface. Furthermore, in Japanese Patent Publication No. 6,856,781, carbon black obtained from a pyrolysis process is treated with an amino acid compound containing at least one thiol or disulfide group to obtain surface-activated carbon black. The recycled carbon black of this embodiment also includes carbon blacks treated to include functional groups on their surfaces.

[0127] As the recycled carbon black, commercially available products from Strable Green Carbon, LD Carbon, etc. can be used.

[0128] The nitrogen adsorption specific surface area (N2SA) of carbon black is 50m from the viewpoint of reinforcement. 2 / g or more is preferable, and 70m 2 / g is more preferable, and 100m 2 / g or more is more preferable, and 120m 2 From the viewpoint of heat buildup and processability, it is particularly preferable that the tensile strength is more than 250 m / g. 2 / g is preferable, and 200m 2 / g is more preferable, and 180m 2 / g or less is more preferable. The N2SA of carbon black is measured by the above-mentioned measurement method.

[0129] The average primary particle diameter of the carbon black contained in the rubber composition constituting the first layer is preferably greater than 8 nm, more preferably greater than 10 nm, and even more preferably greater than 15 nm. The average primary particle diameter is preferably less than 25 nm, more preferably less than 22 nm, and even more preferably less than 20 nm. The average primary particle diameter of the carbon black is measured by the above-mentioned measurement method.

[0130] The average primary particle diameter of the carbon black contained in the rubber composition constituting the second layer and the third layer is preferably greater than 15 nm, more preferably greater than 18 nm, and even more preferably greater than 20 nm, and is preferably less than 40 nm, more preferably less than 35 nm, and even more preferably less than 31 nm.

[0131] The amount of carbon black per 100 parts by mass of the rubber component is preferably more than 8 parts by mass, more preferably more than 15 parts by mass, even more preferably more than 20 parts by mass, and particularly preferably more than 25 parts by mass. The amount of carbon black per 100 parts by mass of the rubber component is preferably less than 100 parts by mass, more preferably less than 80 parts by mass, and even more preferably less than 50 parts by mass.

[0132] <Other fillers> The filler may contain fillers other than silica and carbon black. The other fillers are not particularly limited, but may include, for example, fillers that have been commonly used in the tire industry, such as aluminum hydroxide, calcium carbonate, alumina, clay, and talc.

[0133] [Other compounding agents] In addition to the rubber component and filler, the rubber composition may contain, as appropriate, compounding agents that are generally used in the tire industry, such as plasticizers, processing aids, vulcanized rubber particles, wax, stearic acid, zinc oxide, antioxidants, vulcanizing agents, and vulcanization accelerators.

[0134] <Plasticizer> A plasticizer is a material that imparts plasticity to rubber components and encompasses both liquid and solid plasticizers at 25°C. Examples of plasticizers include resins, oils, liquid rubbers, and ester-based plasticizers. These plasticizers may be derived from mineral resources such as petroleum and natural gas, biomass-derived materials, or naphtha recycled from rubber and non-rubber products. Low-molecular-weight hydrocarbon components obtained by pyrolysis and extraction of used tires or products containing various components may also be used as plasticizers. Plasticizers may be used singly or in combination.

[0135] (resin) Of the other compounding ingredients, the rubber composition preferably contains a resin. The resin is not particularly limited, but resins commonly used in the tire industry can be used, such as aromatic vinyl resins, dicyclopentadiene resins, C9 resins, C5 resins, C5C9 resins, terpene resins, rosin resins, and phenolic resins. Of these, petroleum resins, aromatic vinyl resins, dicyclopentadiene resins, C9 resins, and terpene resins are preferred. One type of resin may be used alone, or two or more types may be used in combination.

[0136] <Aromatic vinyl resin> The term "aromatic vinyl resin" refers to a resin containing at least one aromatic vinyl compound selected from the group consisting of styrene, α-methylstyrene, vinyltoluene, p-chlorostyrene, etc., as the monomer component with the largest content, preferably at least 50 mol %, and may be hydrogenated or modified. As the aromatic vinyl resin, a homopolymer of α-methylstyrene or styrene or a copolymer of α-methylstyrene and styrene is preferred, and a copolymer of α-methylstyrene and styrene is more preferred, because they are economical, easy to process, and have excellent heat generation properties. As the aromatic vinyl resin, commercially available products available from, for example, Kraton, Eastman Chemical, Mitsui Chemicals, Inc., etc., can be used. One type of resin may be used alone, or two or more types may be used in combination.

[0137] <Dicyclopentadiene resin> The term "dicyclopentadiene-based resin" refers to a resin containing dicyclopentadiene (DCPD) as the monomer component with the highest content, and may be a hydrogenated or modified resin. Examples of dicyclopentadiene-based resins include DCPD / C9 resins obtained by copolymerizing dicyclopentadiene with the C9 fraction, with DCPD / C9 resins being preferred. Examples of DCPD resins that can be used include those commercially available from ExxonMobil Corporation, ENEOS Corporation, Nippon Zeon Co., Ltd., Maruzen Petrochemical Co., Ltd., and the like. These resins may be used singly or in combination of two or more.

[0138] <C9 resin> The term "C9 resin" refers to a resin obtained by polymerizing a C9 fraction. It may be a C9 fraction polymerized alone or a copolymer obtained by copolymerizing a C9 fraction with other components. For example, a resin obtained by copolymerizing dicyclopentadiene (DCPD) with a C9 fraction is called a DCPD / C9 resin. It may also be a hydrogenated or modified version of such a resin. Examples of C9 fractions include at least one petroleum fraction having 8 to 10 carbon atoms selected from the group consisting of vinyltoluene, alkylstyrene, coumarone, indene, methylindene, dicyclopentadiene, etc. Specific examples of C9 resins include coumarone-indene resin, coumarone resin, and indene resin. These resins may be used alone or in combination.

[0139] <C5 resin> "C5 resin" refers to a resin obtained by polymerizing a C5 fraction other than dicyclopentadiene, and may be a hydrogenated or modified version of such a resin. Examples of C5 fractions other than dicyclopentadiene include at least one petroleum fraction having 4 to 5 carbon atoms selected from the group consisting of cyclopentadiene, isoprene, pentane, isopentane, neopentane, pentene, pentadiene, etc. Such resins may be used alone or in combination of two or more.

[0140] <C5C9 resin> The term "C5C9 resin" refers to a resin obtained by copolymerizing the C5 fraction and the C9 fraction, and may be a hydrogenated or modified resin. As the C5C9 petroleum resin, for example, commercially available products from Tosoh Corporation, LUHUA, etc. can be used. The resin may be used alone or in combination of two or more.

[0141] <Terpene resin> Terpene resins refer to resins containing at least one terpene compound selected from the group consisting of α-pinene, β-pinene, limonene, dipentene, etc., as the most abundant monomer component, preferably at least 50 mol %, and may be hydrogenated or modified. Specific examples of terpene resins include polyterpene resins containing only one or more of the terpene compounds as monomer components; aromatic-modified terpene resins containing the terpene compound and an aromatic compound as monomer components; and terpene phenolic resins containing the terpene compound and a phenolic compound as monomer components. Examples of aromatic compounds that serve as monomer components for aromatic-modified terpene resins include at least one selected from the group consisting of styrene, α-methylstyrene, vinyltoluene, divinyltoluene, etc. Examples of phenolic compounds that serve as monomer components for terpene phenolic resins include at least one selected from the group consisting of phenol, bisphenol A, cresol, xylenol, etc. These resins may be used alone or in combination.

[0142] <Rosin-based resin> The rosin-based resin refers to a resin containing at least one rosin acid compound selected from the group consisting of abietic acid, neoabietic acid, palustric acid, isopimaric acid, etc., and may be a hydrogenated or modified version of such a rosin-based resin. Examples of the rosin-based resin include, but are not limited to, natural rosin and rosin-modified resins obtained by modifying rosin through hydrogenation, disproportionation, dimerization, esterification, etc. Such resins may be used singly or in combination of two or more.

[0143] <Phenol-based resin> The phenolic resin refers to a resin containing a phenolic compound such as phenol or cresol as the monomer component with the largest content, preferably 50 mol% or more. Examples of the phenolic resin include, but are not limited to, phenol-formaldehyde resin, alkylphenol-formaldehyde resin, alkylphenol-acetylene resin, and oil-modified phenol-formaldehyde resin. These resins may be used alone or in combination of two or more.

[0144] (Plasticizers other than resins) Plasticizers other than resins, such as oil, liquid rubber, and ester-based plasticizers, will now be explained.

[0145] (oil) Examples of oils include mineral oil, vegetable oil, and animal oil. From the viewpoint of life cycle assessment, waste oils used in rubber mixers and engines, and refined waste cooking oils used in restaurants may also be used. One type of oil may be used alone, or two or more types may be used in combination.

[0146] As used herein, mineral oil refers to oil derived from mineral resources such as petroleum and natural gas. Examples of mineral oil include paraffinic oil (mineral oil), naphthenic oil, and aromatic oil. Specific examples of mineral oil include mild extracted solvate (MES), distillate aromatic extract (DAE), treated distillate aromatic extract (TDAE), treated residual aromatic extract (TRAE), and residual aromatic extract (RAE). Furthermore, as an environmental measure, oils with a low content of polycyclic aromatic compounds (PCA) can also be used. Examples of low PCA oils include MES, TDAE, and heavy naphthenic oil.

[0147] In this specification, examples of vegetable oils include linseed oil, rapeseed oil, safflower oil, soybean oil, corn oil, cottonseed oil, rice oil, tall oil, sesame oil, perilla oil, castor oil, tung oil, pine oil, pine tar oil, sunflower oil, coconut oil, palm oil, palm kernel oil, olive oil, camellia oil, jojoba oil, macadamia nut oil, peanut oil, grapeseed oil, and Japan wax. Further examples of vegetable oils include refined oils (such as salad oil) obtained by refining the above oils, interesterified oils obtained by interesterifying the above oils, hardened oils obtained by hydrogenating the above oils, thermally polymerized oils obtained by thermally polymerizing the above oils, oxidatively polymerized oils obtained by oxidizing the above oils, and waste edible oils recovered from edible oils. Vegetable oils may be liquid or solid at 25°C.

[0148] (liquid rubber) The liquid rubber is not particularly limited as long as it is a polymer that is in a liquid state at 25° C., and examples thereof include liquid butadiene rubber (liquid BR), liquid styrene butadiene rubber (liquid SBR), liquid isoprene rubber (liquid IR), liquid styrene isoprene rubber (liquid SIR), liquid farnesene rubber, etc. One type of liquid rubber may be used alone, or two or more types may be used in combination.

[0149] (ester plasticizer) Examples of ester-based plasticizers include dibutyl adipate (DBA), diisobutyl adipate (DIBA), dioctyl adipate (DOA), di-2-ethylhexyl azelate (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). One type of ester-based plasticizer may be used alone, or two or more types may be used in combination.

[0150] The amount of plasticizer per 100 parts by mass of the rubber component (the total amount when multiple plasticizers are used) is preferably 0 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 3 parts by mass or more from the viewpoint of wet grip performance. Furthermore, from the viewpoint of processability, the amount is preferably less than 50 parts by mass, more preferably less than 40 parts by mass, and even more preferably less than 30 parts by mass. The rubber composition may not contain a plasticizer. The amount of plasticizer also includes the amount of extender plasticizers, such as extender oil, extender resin, extender liquid rubber component, and extender ester-based plasticizer, used to extend the rubber component.

[0151] (vulcanized rubber particles) The vulcanized rubber particles are particles made of vulcanized rubber, and specifically, rubber powder as specified in JIS K 6316:2017 can be used. From the standpoint of environmental considerations and cost, recycled rubber powder produced from crushed waste tires is preferred. One type of vulcanized rubber particle may be used alone, or two or more types may be used in combination.

[0152] The vulcanized rubber particles are not particularly limited, and may be unmodified vulcanized rubber particles or modified vulcanized rubber particles.

[0153] As commercially available vulcanized rubber, for example, products from Lehigh, Muraoka Rubber Industries, Ltd., etc. can be used.

[0154] (processing aids) Examples of processing aids include fatty acid metal salts, fatty acid amides, amide esters, silica surfactants, 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 alone or in combination of two or more. Examples of processing aids that can be used include those commercially available from Schill + Seilacher, Performance Additives, etc.

[0155] When a processing aid is contained, the content thereof per 100 parts by mass of the rubber component is preferably more than 0.5 parts by mass, more preferably more than 1 part by mass, and even more preferably more than 1.5 parts by mass from the viewpoint of improving processability, and is preferably less than 10 parts by mass, more preferably less than 8.0 parts by mass, and even more preferably less than 5.0 parts by mass from the viewpoint of abrasion resistance and breaking strength.

[0156] (wax) The wax is not particularly limited, and any wax commonly used in the tire industry can be suitably used, such as mineral waxes and plant-derived waxes. Mineral waxes refer to waxes derived from mineral resources such as oil and natural gas. Plant-derived waxes refer to waxes derived from natural resources such as plants. Among these, mineral waxes are preferred. Examples of plant-derived waxes include rice wax, carnauba wax, and candelilla wax. Examples of mineral waxes include paraffin wax, microcrystalline wax, and selected special waxes thereof, with paraffin wax being preferred. The wax according to this embodiment does not contain stearic acid. Waxes commercially available from, for example, Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., Paramelt Co., Ltd., etc. can be used. One type of wax may be used alone, or two or more types may be used in combination.

[0157] When wax is contained, the content per 100 parts by mass of the rubber component is preferably 0 part by mass or more, more preferably more than 0.5 part by mass, and even more preferably more than 1.0 part by mass from the viewpoint of weather resistance of the rubber, and is preferably less than 10 parts by mass, more preferably less than 7.0 parts by mass, and even more preferably less than 5.0 parts by mass from the viewpoint of preventing whitening of the tire due to bloom.

[0158] (anti-aging agent) The antioxidant is not particularly limited, but examples thereof include naphthylamine-based antioxidants such as phenyl-α-naphthylamine; diphenylamine-based antioxidants such as octylated diphenylamine and 4,4'-bis(α,α'-dimethylbenzyl)diphenylamine; N-isopropyl-N'-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine (77PD), N,N'-diphenyl-p-phenylenediamine (DPPD), N,N'-ditolyl ... p-phenylenediamine-based antioxidants such as diphenyldiamine (DTPD), N-isopropyl-N'-phenyl-p-phenylenediamine (IPPD), and N,N'-di-2-naphthyl-p-phenylenediamine (DNPD); quinoline-based antioxidants such as 2,2,4-trimethyl-1,2-dihydroquinoline polymers; monophenol-based antioxidants such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol; and bis-, tris-, and polyphenol-based antioxidants such as tetrakis-[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane. Among these, p-phenylenediamine-based antioxidants and quinoline-based antioxidants are preferred, and polymers of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine and 2,2,4-trimethyl-1,2-dihydroquinoline are more preferred. Commercially available products that can be used include those from Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinko Chemical Industry Co., Ltd., and Flexis Co., Ltd. One type of antioxidant may be used alone, or two or more types may be used in combination.

[0159] When an antioxidant is contained, the content per 100 parts by mass of the rubber component is preferably more than 0.5 parts by mass, more preferably more than 1.0 parts by mass, and even more preferably more than 1.4 parts by mass from the viewpoint of ozone crack resistance of the rubber, and is preferably less than 2.5 parts by mass, more preferably less than 2.0 parts by mass, and even more preferably less than 1.8 parts by mass from the viewpoint of abrasion resistance and wet grip performance.

[0160] (stearic acid) When stearic acid is contained, the content per 100 parts by mass of the 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, and is preferably less than 10 parts by mass, more preferably less than 8.0 parts by mass, and even more preferably less than 5.0 parts by mass from the viewpoint of vulcanization rate.

[0161] (zinc oxide) When zinc oxide is contained, the content per 100 parts by mass of the 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, and preferably less than 10 parts by mass, more preferably less than 8.0 parts by mass, and even more preferably less than 5.0 parts by mass from the viewpoint of abrasion resistance.

[0162] (vulcanizing agent) Sulfur is preferably used as the vulcanizing agent. Examples of sulfur that can be used include powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur. The vulcanizing agent may be used alone or in combination of two or more.

[0163] When sulfur is contained, the content per 100 parts by mass of the rubber component is preferably more than 0.5 parts by mass, more preferably more than 0.8 parts by mass, and even more preferably more than 1.2 parts by mass, from the viewpoint of ensuring a sufficient vulcanization reaction. Furthermore, from the viewpoint of preventing deterioration, the content is preferably less than 5.0 parts by mass, more preferably less than 4.0 parts by mass, and even more preferably less than 3.0 parts by mass. When oil-containing sulfur is used as the vulcanizing agent, the content of the vulcanizing agent is the total content of pure sulfur contained in the oil-containing sulfur.

[0164] Known organic crosslinking agents can also be used as vulcanizing agents other than sulfur. The organic crosslinking agent is not particularly limited as long as it can form crosslinked chains other than polysulfide bonds. Examples of the organic crosslinking agent include alkylphenol-sulfur chloride condensate, sodium 1,6-hexamethylene-dithiosulfate dihydrate, 1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane, and dicumyl peroxide. 1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane is preferred. These organic crosslinking agents can be commercially available from Taoka Chemical Co., Ltd., Lanxess K.K., Flexis, and other companies.

[0165] (Vulcanization accelerator) The vulcanization accelerator is not particularly limited, but examples thereof include sulfenamide vulcanization accelerators, thiazole vulcanization accelerators, guanidine vulcanization accelerators, thiuram vulcanization accelerators, thiourea vulcanization accelerators, dithiocarbamate vulcanization accelerators, aldehyde-amine vulcanization accelerators, aldehyde-ammonia vulcanization accelerators, imidazoline vulcanization accelerators, xanthate vulcanization accelerators, and caprolactam disulfide. These vulcanization accelerators may be used alone or in combination of two or more. Among them, one or more vulcanization accelerators selected from the group consisting of sulfenamide vulcanization accelerators, thiazole vulcanization accelerators, and guanidine vulcanization accelerators are preferred, as they more suitably achieve the desired effects. The vulcanization accelerators may be used alone or in combination of two or more.

[0166] Examples of sulfenamide vulcanization accelerators include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), and N,N-dicyclohexyl-2-benzothiazolylsulfenamide (DCBS).

[0167] Examples of thiazole vulcanization accelerators include 2-mercaptobenzothiazole (MBT) or a salt thereof, di-2-benzothiazolyl disulfide (MBTS), 2-(2,4-dinitrophenyl)mercaptobenzothiazole, and 2-(2,6-diethyl-4-morpholinothio)benzothiazole.

[0168] Examples of guanidine vulcanization accelerators include 1,3-diphenylguanidine (DPG), 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, di-o-tolylguanidine salt of dicatechol borate, 1,3-di-o-cumenylguanidine, 1,3-di-o-biphenylguanidine, and 1,3-di-o-cumenyl-2-propionylguanidine.

[0169] Examples of thiuram vulcanization accelerators include tetrakis(2-ethylhexyl)thiuram disulfide (TOT-N), tetramethylthiuram disulfide (TMTD), tetraethylthiuram disulfide, tetramethylthiuram monosulfide (TMTM), dipentamethylene thiuram disulfide, and dipentamethylene thiuram tetrasulfide.

[0170] Examples of the thiourea vulcanization accelerator include thiourea compounds such as thiacarbamide, diethylthiourea, dibutylthiourea, trimethylthiourea and diorthotolylthiourea, N,N'-diphenylthiourea, trimethylthiourea and N,N'-diethylthiourea.

[0171] Examples of dithiocarbamate vulcanization accelerators include piperidinium pentamethylenedithiocarbamate (PPDC), zinc dimethyldithiocarbamate (ZnMDC), zinc diethyldithiocarbamate (ZnEDC), zinc dibutyldithiocarbamate (ZnBDC), zinc dibenzyldithiocarbamate (ZDBzC), zinc N-ethyl-N-phenyldithiocarbamate (ZnEPDC), zinc N-pentamethylenedithiocarbamate (ZnPDC), sodium dibutyldithiocarbamate (NaBDC), copper dimethyldithiocarbamate (CuMDC), iron dimethyldithiocarbamate (FeMDC), and tellurium diethyldithiocarbamate (TeEDC).

[0172] When a vulcanization accelerator is contained, the content (total amount when multiple vulcanization accelerators are used) per 100 parts by mass of the rubber component is preferably more than 1.0 part by mass, more preferably more than 1.5 parts by mass, and even more preferably more than 2.0 parts by mass. The content of the vulcanization accelerator per 100 parts by mass of the rubber component is preferably less than 8.0 parts by mass, more preferably less than 5.0 parts by mass, and even more preferably less than 4.0 parts by mass.

[0173] In this specification, various materials containing carbon atoms (for example, rubber, oil, resin, vulcanization accelerator, antioxidant, surfactant, etc.) may be derived from atmospheric carbon dioxide. The various materials may be obtained from carbon dioxide by directly converting carbon dioxide or by converting methane obtained through a methanation process in which methane is synthesized from carbon dioxide.

[0174] [Manufacturing] The rubber composition can be produced by a known method, for example, by kneading the above-mentioned components using a rubber kneading device such as an open roll or an internal kneader (such as a Banbury mixer or kneader).

[0175] The kneading process may include, for example, a base kneading process in which compounding ingredients and additives other than the vulcanizing agent and vulcanization accelerator are kneaded, and a final kneading (F kneading) process in which the vulcanizing agent and vulcanization accelerator are added to the kneaded product obtained in the base kneading process and kneaded. Furthermore, the base kneading process may be divided into multiple processes as desired. When the base kneading process is divided, the method may be (1) a method in which some of the compounding ingredients and additives are pre-mixed to form a masterbatch, and then the remaining compounding ingredients and additives are added to the resulting masterbatch and kneaded, or (2) a method in which all of the compounding ingredients and additives to be kneaded in the base kneading process are kneaded at once, and then the kneaded product is remilled one or more times. In the above method (1), the number of masterbatches is not limited and may be two or more. Furthermore, when the number of masterbatches is two or more, all of the compounding ingredients and additives used in the base kneading process may be allocated to one of the masterbatches.

[0176] The kneading conditions are not particularly limited, but examples include a method in which the base kneading step involves kneading for 3 to 10 minutes at a discharge temperature of 150 to 170°C, and a method in which the final kneading step involves kneading for 1 to 5 minutes at 70 to 110°C. The vulcanization conditions are not particularly limited, but examples include a method in which vulcanization is carried out for 10 to 30 minutes at 150 to 200°C.

[0177] The tire according to the present embodiment can be manufactured by a conventional method using the rubber composition. That is, the unvulcanized rubber composition is extruded in an extruder equipped with a die of a predetermined shape to match the shape of the first, second, or third layer of the tread portion, and then bonded together with other tire components in a tire building machine while adjusting the structure to obtain a predetermined tire structure. The tire is then molded by a conventional method to form an unvulcanized tire, and the unvulcanized tire is then heated and pressurized in a vulcanizer to manufacture the tire. The vulcanization conditions are not particularly limited, and examples include a method of vulcanizing at 140 to 170°C for 10 to 40 minutes.

[0178] [Application] The heavy-duty tires according to this embodiment are tires with a standard load of more than 1000 kg, including tires for not only large trucks and buses but also small trucks, buses, vans, etc. The heavy-duty tires according to this embodiment are preferably tires mounted on large vehicles such as trucks, buses, and construction vehicles, and have a standard load of 1400 kg or more. [Example]

[0179] Examples (working examples) that are considered preferable for carrying out the present invention are shown below, but the scope of the present invention is not limited to these working examples. Using the various chemicals shown below, rubber compositions obtained according to Table 1 and tires obtained according to Tables 2 and 3 were examined, and the results calculated based on the following evaluation methods are shown in Tables 2 and 3.

[0180] <Various chemicals> The chemicals used in the examples and comparative examples are summarized below. NR:TSR20 SBR: HPR840 (S-SBR, styrene content: 10% by mass, vinyl content: 42% by mole, Tg: -60°C, non-oil-extended) manufactured by JSR Corporation BR: UBEPOL BR (registered trademark) 150B (unmodified BR, cis content: 97 mol%, Mw: 440,000) manufactured by UBE Corporation Carbon black 1: Show Black N134 (N2SA: 148m) manufactured by Cabot Japan Co., Ltd. 2 / g, average primary particle diameter: 18nm) Carbon black 2: Show Black N220 (N2SA: 115m) manufactured by Cabot Japan Co., Ltd. 2 / g, average primary particle diameter: 22nm) Carbon black 3: Show Black N330 (N2SA: 75 ml) manufactured by Cabot Japan Co., Ltd. 2 / g, average primary particle diameter: 30nm) Silica 1: Ultrasil 9100GR (N2SA: 230m) manufactured by Evonik Industries 2 / g, average primary particle diameter: 15nm) Silica 2: Ultrasil VN3 (N2SA: 175 ml) manufactured by Evonik Industries 2 / g, average primary particle diameter: 18nm) Silane coupling agent: Si266 (bis(3-triethoxysilylpropyl) disulfide) manufactured by Evonik Industries Antioxidant: Nocrac 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Stearic acid: Camellia stearic acid beads manufactured by NOF Corporation Zinc oxide: Zinc oxide No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: Powdered sulfur manufactured by Karuizawa Sulfur Co., Ltd. Vulcanization accelerator 1: Noccela NS (Nt-butyl-2-benzothiazole sulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator 2: Noccelaer D (1,3-diphenylguanidine (DPG)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0181] Examples and Comparative Examples According to the formulation shown in Table 1, chemicals other than sulfur and vulcanization accelerators were mixed in a 1.7 L closed-type Banbury mixer for 1 to 10 minutes until the discharge temperature reached 150 to 160°C, yielding a kneaded mixture. Next, sulfur and vulcanization accelerators were added to the resulting mixture using a two-screw open roll mill, and the mixture was mixed for 4 minutes until the temperature reached 105°C, yielding an unvulcanized rubber composition. The resulting unvulcanized rubber composition was molded to match the shapes of the first, second, and third layers of the tread, and then bonded together with other tire components to produce an unvulcanized tire. The tire was then press-vulcanized at 150°C for 35 minutes, yielding the test tires listed in Tables 2 and 3.

[0182] <Measurement of 0℃ tanδ and 0℃ E*> Each vulcanized rubber test piece is cut out from the first layer of the tread portion of each test tire to a length of 20 mm, width of 4 mm, and thickness of 1 mm, with the long side aligned in the tire circumferential direction and the thickness direction aligned in the tire radial direction. Using a dynamic viscoelasticity measuring device (Iplexer series manufactured by GABO), the loss tangent tanδ and complex modulus of elasticity E* are measured under the conditions of a temperature of 0°C, a frequency of 10 Hz, an initial strain of 10%, a dynamic strain of ±2.5%, and an extension mode.

[0183] <Measurement of breaking elongation EB> A No. 7 dumbbell-shaped test piece with a thickness of 1 mm is prepared from the first layer of the tread portion of each test tire, and a tensile test is carried out in accordance with JIS K 6251 "Vulcanized rubber and thermoplastic rubber - Determination of tensile test properties" at a temperature of 23°C and a pulling speed of 3.3 mm / sec, and the breaking elongation EB (%) is measured.

[0184] <Wet grip performance> Each test tire is mounted on a rim, which is then attached to the rear wheel of a bus, which is a test vehicle. The braking distance of this test vehicle is measured from an initial speed of 100 km / h on a wet asphalt road surface. The result of the reference comparative example (Comparative Example 1) is set to 100, and the results are expressed as an index. A higher index indicates better wet grip performance. (Wet grip performance index) = (Braking distance of the reference comparative example) / (Braking distance of each test tire) x 100

[0185] <Low fuel consumption performance> The rolling resistance coefficient (RRC) of each test tire was measured in accordance with JIS D 4234:2009 (ISO28580), and the reciprocal value of the rolling resistance coefficient was expressed as an index, with the result of the reference comparative example (Comparative Example 1) set at 100. The higher the index, the lower the rolling resistance and the better the fuel economy performance. (Fuel efficiency index) = (Rolling resistance coefficient of the reference comparative example) / (Rolling resistance coefficient of each test tire) × 100

[0186] <Rib tear resistance> Each test tire is mounted on a rim, and this is attached to the rear wheel of a bus, which is a test vehicle. This test vehicle is driven on an asphalt road surface. After traveling 10,000 km, the appearance of the tire is observed, and if cracks are found at the bottom of the circumferential grooves, the length and depth of the cracks are measured. The reciprocal of the product of the length and depth of the crack is calculated, and this is used as an index of rib tear resistance. The result of the reference comparative example (Comparative Example 2) is set to 100, and the index is expressed as an index. The larger the value, the less likely rib tear will occur and the better the rib tear resistance. (Rib tear resistance performance index) = (crack length of reference comparative example × crack depth of reference comparative example) / (crack length of each test tire × crack depth of each test tire) × 100

[0187] <Overall performance> The total value of the wet grip performance, fuel economy performance, and rib tear resistance performance is shown as an overall performance index.

[0188] [Table 1]

[0189] [Table 2]

[0190] [Table 3]

[0191] <Embodiment> Examples of embodiments of the present invention are given below. [1] A heavy-duty tire having a tread portion, the tread portion includes at least a first layer constituting a tread surface, a second layer adjacent to the first layer on the radially inner side of the tire, and a third layer adjacent to the second layer on the radially inner side of the tire, the first layer, the second layer, and the third layer are each made of a rubber composition containing a rubber component and a filler, The silica contents per 100 parts by mass of the rubber component in the rubber compositions constituting the first layer, the second layer, and the third layer are defined as S1 (parts by mass), S2 (parts by mass), and S3 (parts by mass), respectively, and the maximum value of S1, S2, and S3 is defined as S max and the tire outer diameter is Dt(m), S1 ≥ 0, S2 ≥ 0, S3 ≥ 0, S max >30, Dt>0.80, S max / Dt<100, heavy duty tires. [2] S max The heavy duty tire according to [1] above, wherein the rubber component constituting the layer corresponding to the above contains more than 10% by mass of styrene-butadiene rubber. [3] S max The heavy duty tire according to [1] above, wherein the rubber component constituting the layer corresponding to the above contains more than 30% by mass of styrene-butadiene rubber. [4] S max The heavy duty tire according to any one of the above [1] to [3], wherein the rubber component constituting the layer corresponding to the above contains more than 10% by mass of isoprene-based rubber. [5] S max The heavy duty tire according to any one of the above [1] to [3], wherein the rubber component constituting the layer corresponding to the above contains more than 30% by mass of isoprene-based rubber. [6] The heavy duty tire according to any one of the above [1] to [5], wherein the rubber component constituting the first layer contains 1% by mass or more of styrene-butadiene rubber. [7] The heavy-duty tire according to any one of the above [1] to [6], wherein S1 is greater than 30. [8] The heavy-duty tire according to any one of the above [1] to [7], wherein S1 is larger than S2 and S3. [9] The heavy-duty tire according to any one of the above [1] to [8], wherein S1>S2>S3.

[10] The heavy-duty tire according to any one of the above [1] to [9], wherein Dt is 1.00 m or more.

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

[10] , wherein the rubber composition constituting the first layer has a tan δ at 0° C. (0° C. tan δ1) of 0.21 or more.

[12] The heavy-duty tire according to the above

[11] , wherein the product of 0°C tan δ1 and Dt (0°C tan δ1 × Dt) is 0.190 or more.

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

[12] , wherein the complex modulus of elasticity at 0°C (0°C E*1) of the rubber composition constituting the first layer is 15.0 MPa or more.

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

[13] , wherein the rubber composition constituting the first layer has a breaking elongation (EB1) of 400% or more. [Explanation of symbols]

[0192] 1 Tread section 2. Carcass 3 Belt Layer 3a, 3b, 3c, 3d, 3e belt layer 4 First layer 5 Second layer 6 Third layer 7 Tread surface 8 Reinforced rubber layer 9 Sidewall E Tire equatorial plane Wt Tire section width

Claims

1. A heavy-duty tire having a tread portion, the tread portion includes at least a first layer constituting a tread surface, a second layer adjacent to the first layer on the radially inner side of the tire, and a third layer adjacent to the second layer on the radially inner side of the tire, the first layer, the second layer, and the third layer are each made of a rubber composition containing a rubber component and a filler, The silica contents per 100 parts by mass of the rubber component in the rubber compositions constituting the first layer, the second layer, and the third layer are defined as S1 (parts by mass), S2 (parts by mass), and S3 (parts by mass), respectively, and the maximum value of S1, S2, and S3 is defined as S max and the tire outer diameter is Dt (m), S1≧0, S2≧0, S3≧0, S max >30, Dt>0.80, S max / Dt<100.

2. S max 2. The heavy duty tire according to claim 1, wherein the rubber component constituting the layer corresponding to the first layer contains more than 10% by mass of styrene-butadiene rubber.

3. S max 2. The heavy duty tire according to claim 1, wherein the rubber component constituting the layer corresponding to the first layer contains more than 30% by mass of styrene-butadiene rubber.

4. S max 3. The heavy duty tire according to claim 1, wherein the rubber component constituting the layer corresponding to the first layer contains more than 10% by mass of an isoprene-based rubber.

5. S max 3. The heavy duty tire according to claim 1, wherein the rubber component constituting the layer corresponding to the first layer contains more than 30% by mass of isoprene-based rubber.

6. 3. The heavy duty tire according to claim 1, wherein the rubber component constituting the first layer contains 1% by mass or more of styrene-butadiene rubber.

7. The heavy duty tire according to claim 1 or 2, wherein S1 is greater than 30.

8. 3. The heavy duty tire according to claim 1, wherein S1 is greater than S2 and S3.

9. 3. The heavy duty tire according to claim 1, wherein S1 > S2 > S3.

10. The heavy duty tire according to claim 1 or 2, wherein Dt is 1.00 m or more.

11. 3. The heavy-duty tire according to claim 1, wherein the rubber composition constituting the first layer has a tan δ at 0° C. (0° C. tan δ1) of 0.21 or more.

12. The heavy duty tire according to claim 11, wherein the product of 0° C. tan δ1 and Dt (0° C. tan δ1 × Dt) is 0.190 or more.

13. The heavy-duty tire according to claim 1 or 2, wherein the rubber composition constituting the first layer has a complex modulus at 0°C (0°C E*1) of 15.0 MPa or more.

14. 3. The heavy duty tire according to claim 1, wherein the rubber composition constituting the first layer has an elongation at break (EB1) of 400% or more.

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