Heavy-duty tires

Abstract

To provide a heavy duty tire having excellent durability.SOLUTION: A heavy duty tire comprises a bead apex rubber having the inside and outside apex parts. At least one selected from the group consisting of the inside and outside apex parts includes isoprene rubber, carbon black and a modified rubber material functionalized by thiuram sulfide-based compound. The complex elastic modulus (Ei*) of the inside apex part and that modulus (Eo*) of the outside apex part satisfy the following expressions (1) and (2): (1) Ei*>Eo* and (2) Ei* / Eo*≤7.0 (here, Ei* and Eo* are complex elastic moduli measured under conditions of 70°C, initial strain of 5%, dynamic strain of 1%, frequency of 10 Hz and elongation mode).SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a heavy-duty tire. [Background technology]

[0002] Heavy-duty tires, like other tires, require various performance characteristics, but durability is a particularly important requirement. [Overview of the Initiative] [Problems that the invention aims to solve]

[0003] The present invention aims to solve the aforementioned problems and provide a heavy-duty tire with excellent durability. [Means for solving the problem]

[0004] The present invention relates to a heavy-duty tire equipped with a bead apex rubber having an inner apex portion and an outer apex portion, At least one selected from the group consisting of the inner apex portion and the outer apex portion comprises isoprene rubber, carbon black, and a modified rubber material functionalized with a thiram sulfide compound. The complex modulus of elasticity (E) of the inner apex portion i *) The complex modulus of elasticity (E) of the outer apex portion. o *) pertains to heavy-duty tires that satisfy the following equations (1) and (2). (1)E i *>E o * (2)E i * / E o *≦7.0 (Ei* and Eo* are the complex modulus of elasticity measured under the conditions of a temperature of 70°C, initial strain of 5%, dynamic strain of 1%, frequency of 10Hz, and extension mode.) [Brief explanation of the drawing]

[0005] [Figure 1] This is a cross-sectional view showing one embodiment of the heavy-duty tire of the present invention. [Figure 2] It is an enlarged cross-sectional view showing a bead portion. MODE FOR CARRYING OUT THE INVENTION

[0006] The present invention provides a heavy-load tire comprising a bead apex rubber having an inner apex portion and an outer apex portion, wherein at least one selected from the group consisting of the inner apex portion and the outer apex portion contains an isoprene-based rubber, carbon black, and a modified rubber material functionalized with a thiuram sulfide-based compound, and satisfies the above formulas (1) to (2). The heavy-load tire is excellent in durability.

[0007] Although the mechanism (reason) why such operational effects are obtained is not clear, it is presumed as follows. From the perspective of life cycle assessment (LCA), it is desirable to use recycled materials for large heavy-load tires used in trucks, buses and the like. Since heavy-load tires are subjected to higher loads than normal tires, a two-layer structure that softens the tip of the bead apex rubber has been studied. However, if rubber powder is used in either the inner part (lower part) or the outer part (upper part) of the bead apex rubber, there is a concern that adhesion at the interface will be insufficient, and damage will occur starting from the interface when traveling under a high load. Therefore, it is considered that by dispersing modified reclaimed rubber in the isoprene-based rubber, the parts functionalized by the thiuram sulfide-based compound bond to each other, and while suppressing a decrease in rubber strength, further reinforcement is provided by carbon black, making it possible to ensure adhesion at the interface of the bead apex rubber and suppress crack propagation from the interface. In addition, the complex modulus of elasticity (E i *, E o *) is adjusted to satisfy formulas (1) to (2), and by setting the difference in complex modulus of elasticity to a predetermined value or less, it is considered that strain generated at the interface between the inner part (lower part) and the outer part (upper part) can be suppressed, and damage originating from the interface can be suppressed. Therefore, it is presumed that excellent durability is imparted to the heavy-load tire.

[0008] Thus, in a bead apex rubber comprising an inner apex portion and an outer apex portion, wherein at least one of the inner apex portion and the outer apex portion contains a modified rubber material functionalized with an isoprene-based rubber, carbon black, and a thiuram sulfide-based compound, formula (1) "E i *>E o *", formula (2) "E i * / E o *≦7.0" by adopting a configuration that satisfies this, the problem (object) of imparting excellent durability is solved. That is, the parameters of formula (1) "E i *>E o *", formula (2) "E i * / E o *≦7.0" do not define the problem (object); the problem of the present application is to impart excellent durability, and the configuration is made so as to satisfy the above parameters as a means for solving the problem.

[0009] Hereinafter, one embodiment of the present invention will be described with reference to illustrated examples. Figure 1 is a cross-sectional view showing, as an example, a 5% normal internal pressure state when the heavy-duty tire of the present invention is a tubeless tire for trucks, buses, etc., and Figure 2 is an enlarged cross-sectional view showing the bead portion thereof.

[0010] In Figure 1, the heavy-duty tire 1 comprises a carcass 6 extending from a tread portion 2 through a sidewall portion 3 to a bead core 5 in a bead portion 4, and a belt layer 7 arranged radially outside the carcass 6 and inward of the tread portion 2.

[0011] In the example shown in Figure 1, the belt layer 7 is formed from three or more belt plies using belt cords. In this example, the belt layer 7 is shown as having a four-ply structure consisting of a first belt ply 7A, the innermost in the radial direction, in which steel cords are arranged at an angle of, for example, 60 ± 15° with respect to the tire circumferential direction, and second to fourth belt plies 7B to 7D, in which they are arranged at a small angle of, for example, 10 to 35° with respect to the tire circumferential direction. These belt plies 7A to 7D are stacked with the belt cords intersecting each other at one or more points between the plies, thereby increasing the belt rigidity and reinforcing the tread portion 2 with a hoop effect. In addition, a belt reinforcement layer may be provided on the radially outer side of the belt layer 7, in which cords are arranged at an angle of ±10° with respect to the tire circumferential direction.

[0012] In this example, the carcass 6 is formed from a single carcass ply 6A in which carcass cords are arranged at an angle of 70 to 90° with respect to the circumferential direction of the tire. Steel cords are preferred as the carcass cords, but organic fiber cords such as nylon, rayon, polyester, and aromatic polyamides may also be used as needed. The carcass ply 6A has a series of ply return portions 6b on both sides of the ply body portion 6a that spans between the bead cores 5, 5, which are folded back from the inside to the outside in the tire axial direction around the bead core 5.

[0013] The bead core 5 is a ring-shaped body formed by winding, for example, a steel bead wire in multiple stages and rows. In this example, a bead core with a horizontally elongated, flattened hexagonal cross-section is shown. The bead core 5 enhances the engagement force with the rim J over a wide range by having its radially lower surface substantially parallel to the rim seat J1 of the regular rim J. In this example, the regular rim J is shown as a 15° tapered rim for tubeless tires, and therefore, the radially lower surface of the bead core 5 is inclined at an angle of 15° with respect to the tire axial line. The cross-sectional shape of the bead core 5 can also be a regular hexagon, rectangle, or circle, as needed.

[0014] Next, as shown in Figure 2, the bead portion 4 is provided with a bead apex rubber 8 that extends tapered outward from the bead core 5 in the radial direction of the tire, passing between the ply body portion 6a and the ply folded portion 6b of the carcass 6, and a reinforcing cord layer 9 that surrounds the bead core 5 in a U-shape via the carcass 6.

[0015] The reinforcing cord layer 9 has a U-shaped cross-section, with an inner piece 9a extending along the inner surface of the ply body 6a and an outer piece 9b that passes radially inward through the bead core 5 and rises radially outward along the outer surface of the ply folded portion 6b. In this example, the reinforcing cord layer 9 is exemplified as being made of a single cord ply in which steel reinforcing cords are arranged at an angle of 10 to 60° with respect to the tire circumferential direction.

[0016] Next, the bead apex rubber 8 has an inner apex portion 8A and an outer apex portion 8B. In this example, the inner apex portion 8A is made of hard rubber having a small triangular cross-section with a slope that inclines from the outside to the inside in the tire axial direction toward the radially outward direction of the tire, and the outer apex portion 8B is made of soft rubber extending radially outward from the bottom surface in contact with the slope, so that the bead apex rubber 8 has a two-layer structure consisting of the inner apex portion 8A and the outer apex portion 8B.

[0017] The complex modulus of elasticity (E) of the inner apex portion 8A i *) The complex modulus of elasticity of the outer apex portion 8B (E o *) satisfies the following equations (1) and (2). (1)E i *>E o * (2)E i * / E o *≦7.0 (Ei* and Eo* are the complex modulus of elasticity measured under the conditions of a temperature of 70°C, initial strain of 5%, dynamic strain of 1%, frequency of 10Hz, and extension mode.)

[0018] E i * / E o* is preferably 6.0 or less, more preferably 5.0 or less, even more preferably 4.5 or less, and particularly preferably 4.0 or less. The lower limit is not particularly limited, but is preferably 2.0 or more, more preferably 3.0 or more, even more preferably 3.5 or more, and particularly preferably 3.8 or more. When it is within the above range, the effect tends to be better obtained.

[0019] E i * is preferably 13.0 MPa or higher, more preferably 15.0 MPa or higher, even more preferably 18.0 MPa or higher, and particularly preferably 20.0 MPa or higher. The upper limit is not particularly limited, but is preferably 30.0 MPa or lower, more preferably 26.0 MPa or lower, even more preferably 24.0 MPa or lower, and particularly preferably 22.0 MPa or lower. When the value is within the above range, the effect tends to be better obtained.

[0020] The mechanism (reason) by which these effects are obtained is not clear, but it can be inferred as follows. It is believed that by setting the complex modulus of elasticity of the inner apex to a predetermined level or higher, deformation of the bead apex can be suppressed. Therefore, it is presumed that the heavy-duty tire will be given excellent durability.

[0021] E o * is preferably 2.0 MPa or higher, more preferably 3.0 MPa or higher, even more preferably 3.5 MPa or higher, and particularly preferably 4.0 MPa or higher. The upper limit is not particularly limited, but is preferably 7.0 MPa or lower, more preferably 6.0 MPa or lower, even more preferably 5.5 MPa or lower, and particularly preferably 5.0 MPa or lower. When the value is within the above range, the effect tends to be better obtained.

[0022] The complex modulus (E*) can be adjusted, for example, by adjusting the compounding of modified rubber materials functionalized with isoprene-based rubber or thiram sulfide-based compounds, as well as the type and amount of carbon black, other fillers, vulcanizing agents, and vulcanization accelerators. Specifically, E* tends to increase when modified rubber materials functionalized with isoprene-based rubber or thiram sulfide-based compounds are incorporated, when the amount of fillers and carbon black is increased, or when the particle size of the carbon black is reduced.

[0023] Note that Ei* and Eo* are the complex modulus of elasticity measured under the conditions of a temperature of 70°C, initial strain of 5%, dynamic strain of 1%, frequency of 10Hz, and extension mode. Ei* and Eo* are values ​​for the rubber composition after vulcanization.

[0024] The inner apex portion 8A and the outer apex portion 8B are composed of a rubber composition for the inner apex portion and a rubber composition for the outer apex portion, respectively, and at least one of the inner apex portion rubber composition and the outer apex portion rubber composition contains isoprene-based rubber, carbon black, and a modified rubber material functionalized with a thiram sulfide-based compound. From the viewpoint of obtaining better effects, it is desirable that both the inner apex portion rubber composition and the outer apex portion rubber composition contain these components.

[0025] Examples of isoprene-based rubbers that can be used in the rubber compositions for the inner and outer apex sections include natural rubber (NR), isoprene rubber (IR), modified NR, modified NR, and modified IR. For NR, examples include SIR20, RSS#3, TSR20, etc., which are common in the rubber industry. For IR, there are no particular limitations, and examples include IR2200, etc., which are common in the rubber industry. Examples of modified NR include deproteinized natural rubber (DPNR) and high-purity natural rubber (UPNR). Examples of modified NR include epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), and grafted natural rubber. Examples of modified IR include epoxidized isoprene rubber, hydrogenated isoprene rubber, and grafted isoprene rubber. These may be used individually or in combination of two or more types.

[0026] When the rubber composition for the inner apex contains isoprene-based rubber, the isoprene-based rubber content in 100% by mass of the rubber component is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and particularly preferably 80% by mass or more. The upper limit is not particularly limited and may be 100% by mass, but is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less. When the content is within the above range, a better effect tends to be obtained.

[0027] When the rubber composition for the outer apex contains isoprene-based rubber, the isoprene-based rubber content in 100% by mass of the rubber component is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more, and may also be 100% by mass. Within the above range, a better effect tends to be obtained.

[0028] The rubber composition for the inner apex and the rubber composition for the outer apex may contain rubber components other than isoprene-based rubber. Other rubber components include, for example, other diene-based rubbers. Examples of other diene-based rubbers include butadiene rubber (BR), styrene-butadiene rubber (SBR), styrene-isoprene-butadiene rubber (SIBR), ethylene-propylene-diene rubber (EPDM), chloroprene rubber (CR), and acrylonitrile-butadiene rubber (NBR). Butyl-based rubber and fluororubber are also examples. These may be used individually or in combination of two or more. In particular, from the viewpoint of obtaining better effects, it is preferable that the rubber composition for the inner apex contains SBR and the rubber composition for the outer apex contains BR.

[0029] The SBR is not particularly limited; for example, emulsion-polymerized styrene-butadiene rubber (E-SBR), solution-polymerized styrene-butadiene rubber (S-SBR), etc., can be used. These may be used individually or in combination of two or more types.

[0030] The styrene content of SBR is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more. Furthermore, the styrene content is preferably 60% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less. When the content is within the above range, the effect tends to be better obtained. Furthermore, the styrene content of SBR is 1 It is calculated by 1H-NMR measurement.

[0031] The vinyl content in the butadiene portion of SBR is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more. The vinyl content is preferably 80% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less. When the content is within the above range, the effect tends to be better obtained. The vinyl content of SBR can be measured by infrared absorption spectroscopy.

[0032] For example, SBR manufactured and sold by companies such as Sumitomo Chemical Co., Ltd., JSR Corporation, Asahi Kasei Corporation, and Nippon Zeon Co., Ltd. can be used.

[0033] SBR can be either unmodified SBR or modified SBR. Modified SBRs can be any SBR having a functional group that interacts with a packing material such as silica. Examples include terminally modified SBRs (terminally modified SBRs having the functional group at the terminal) in which at least one end of the SBR is modified with a compound having the functional group (modifying agent), main-chain modified SBRs having the functional group in the main chain, main-chain terminally modified SBRs having the functional group in both the main chain and the terminal (for example, main-chain terminally modified SBRs having the functional group in the main chain and at least one end modified with the modifying agent), and terminally modified SBRs that are modified (coupled) with a polyfunctional compound having two or more epoxy groups in the molecule, and in which hydroxyl groups or epoxy groups are introduced.

[0034] Examples of the above functional groups include amino groups, amide groups, silyl groups, alkoxysilyl groups, isocyanate groups, imino groups, imidazole groups, urea groups, ether groups, carbonyl groups, oxycarbonyl groups, mercapto groups, sulfide groups, disulfide groups, sulfonyl groups, sulfinyl groups, thiocarbonyl groups, ammonium groups, imide groups, hydrazo groups, azo groups, diazo groups, carboxyl groups, nitrile groups, pyridyl groups, alkoxy groups, hydroxyl groups, oxy groups, epoxy groups, and the like. These functional groups may have substituents. Among these, amino groups (preferably amino groups in which the hydrogen atoms of the amino group are substituted with C1-C6 alkyl groups), alkoxy groups (preferably alkoxy groups having C1-C6), and alkoxysilyl groups (preferably alkoxysilyl groups having C1-C6) are preferred.

[0035] BR is not particularly limited, and for example, high-cis BR with a high cis content, BR containing syndiotactic polybutadiene crystals, and BR synthesized using a rare-earth catalyst (rare-earth BR) can be used. Among these, high-cis BR with a cis content of 90% by mass or more is preferred because it improves wear resistance. These may be used individually or in combination of two or more types.

[0036] Furthermore, BR may be undenatured or modified. Modified BR can be modified BR in which functional groups similar to those introduced in modified SBR have been introduced.

[0037] For example, products from companies such as Ube Industries, Ltd., JSR Corporation, Asahi Kasei Corporation, and Nippon Zeon Corporation can be used as BRs.

[0038] When the rubber composition for the inner apex contains SBR, the SBR content in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and particularly preferably 20% by mass or more. There is no particular upper limit, but it is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. When it is within the above range, a better effect tends to be obtained.

[0039] When the rubber composition for the outer apex contains BR, the BR content in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and particularly preferably 20% by mass or more. There is no particular upper limit, but it is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. When it is within the above range, a better effect tends to be obtained.

[0040] Suitable carbon blacks for use in the inner apex rubber composition and the outer apex rubber composition include, but are not limited to, GPF, FEF, HAF, ISAF, and SAF. Commercially available products from Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Corporation, Lion Corporation, Nippon Steel Carbon Co., Ltd., Columbia Carbon Corporation, etc. These may be used individually or in combination of two or more types.

[0041] In the rubber composition for the inner apex, the nitrogen adsorption specific surface area (N2SA) of carbon black is preferably 20 m². 2 / g or more, comfortably 50m 2 / g or more, more preferably 70m 2 The value is 150m or more. The upper limit of N2SA in carbon black is not particularly limited, but preferably 150m 2 Less than / g, more preferably 100m 2 / g or less, more preferably 90m 2 It is less than or equal to / g. Within the above range, there is a tendency for better results to be obtained.

[0042] In the rubber composition for the inner apex, the carbon black content is preferably 30 parts by mass or more, more preferably 50 parts by mass or more, even more preferably 65 parts by mass or more, and particularly preferably 70 parts by mass or more, per 100 parts by mass of the rubber component. Furthermore, the carbon black content is preferably 150 parts by mass or less, more preferably 120 parts by mass or less, even more preferably 100 parts by mass or less, and particularly preferably 90 parts by mass or less. When the content is within the above range, a better effect tends to be obtained.

[0043] In the rubber composition for the outer apex, the nitrogen adsorption specific surface area (N2SA) of carbon black is preferably 20 m². 2 / g or more, comfortably within 30m 2 / g or more, more preferably 40m 2 The value is 150m or more. The upper limit of N2SA in carbon black is not particularly limited, but preferably 150m 2Less than / g, more preferably 100m 2 / g or less, more preferably 80m 2 / g or less, particularly preferably 60m 2 It is less than or equal to / g. Within the above range, there is a tendency for better results to be obtained. The specific surface area for nitrogen adsorption of carbon black is determined by Method A of JIS K6217.

[0044] In the rubber composition for the outer apex, the carbon black content is preferably 20 parts by mass or more, more preferably 30 parts by mass or more, even more preferably 35 parts by mass or more, and particularly preferably 40 parts by mass or more, per 100 parts by mass of the rubber component. Furthermore, the carbon black content is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, even more preferably 70 parts by mass or less, and particularly preferably 60 parts by mass or less. When the content is within the above range, a better effect tends to be obtained.

[0045] Other fillers that can be used in the rubber compositions for the inner and outer apex sections include those known in the rubber field, such as silica, calcium carbonate, talc, alumina, clay, aluminum hydroxide, aluminum oxide, and mica. Among these, silica is preferred.

[0046] Examples of silica that can be used in the rubber composition for the inner apex and the rubber composition for the outer apex include dry silica (anhydrous silica) and wet silica (hydrated silica). Among these, wet silica is preferred because it has a high silanol group content.

[0047] When the rubber composition for the inner apex and the rubber composition for the outer apex contain silica, the silica content is preferably 50 parts by mass or less, more preferably 20 parts by mass or less, even more preferably 10 parts by mass or less, and particularly preferably 5 parts by mass or less, per 100 parts by mass of the rubber component. The lower limit is not particularly limited, but is preferably 3 parts by mass or more, and more preferably 5 parts by mass or more. When the content is within the above range, a better effect tends to be obtained.

[0048] The nitrogen adsorption specific surface area (N2SA) of silica is preferably 50 m². 2 / g or more, comfortably 100m 2 / g or more, more preferably 150m 2 It is 1 / g or more. Furthermore, the N2SA content of silica is preferably 250m 2 / g or less, more preferably 220m 2 / g or less, more preferably 200m 2 It is less than or equal to / g. Within the above range, there is a tendency for better results to be obtained. Note that the N2SA value of silica is measured by the BET method in accordance with ASTM D3037-93.

[0049] For example, silica products from companies such as Degussa, Rhodia, Tosoh Silica Co., Ltd., Solvay Japan Co., Ltd., and Tokuyama Corporation can be used.

[0050] The rubber composition for the inner apex and the rubber composition for the outer apex preferably contain a silane coupling agent together with silica. Silane coupling agents are not particularly limited and include, for example, sulfide-based agents such as bis(3-triethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)tetrasulfide, and bis(3-trimethoxysilylpropyl)tetrasulfide; mercapto-based agents such as 3-mercaptopropyltrimethoxysilane; vinyl-based agents such as vinyltriethoxysilane; amino-based agents such as 3-aminopropyltriethoxysilane; glycidoxy-based agents such as γ-glycidoxypropyltriethoxysilane; nitro-based agents such as 3-nitropropyltrimethoxysilane; and chloro-based agents such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. Among these, sulfide-based agents are preferred from the viewpoint of obtaining better effects.

[0051] Examples of silane coupling agents that can be used include products from companies such as Degussa, Momentive, Shin-Etsu Silicone Co., Ltd., Tokyo Chemical Industry Co., Ltd., Azumax Co., Ltd., and Toray Dow Corning Co., Ltd.

[0052] When the rubber composition for the inner apex and the rubber composition for the outer apex contain a silane coupling agent, the content of the silane coupling agent is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, even more preferably 8 parts by mass or more, and also preferably 25 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 15 parts by mass or less, per 100 parts by mass of silica. Within the above range, a better effect tends to be obtained.

[0053] The modified rubber material functionalized with a thiuram sulfide compound that can be used in the rubber composition for the inner apex and the rubber composition for the outer apex is not particularly limited, and any rubber material modified with a thiuram sulfide compound can be used. In this specification, modified rubber materials functionalized with thiuram sulfide compounds are not considered to be part of the aforementioned rubber components.

[0054] The thiuram sulfide compounds are not particularly limited, and examples include alkyl thiuram sulfides, aryl thiuram sulfides, heterocyclic thiuram sulfides, thiuram disulfides, thiuram polysulfides, tetrabenzyl thiuram disulfide, tetraalkyl thiuram disulfide, tetramethyl thiuram disulfide, tetraethyl thiuram disulfide, and dipentamethyl thiuram monosulfide. These may be used individually or in combination of two or more.

[0055] The rubber functionalized with thiuram sulfide compounds (the rubber that forms the skeleton) is not particularly limited, and examples include the rubber components mentioned above.

[0056] From the viewpoint of life cycle assessment (LCA), modified recycled rubber is suitably used as the modified rubber material functionalized with the aforementioned thiram sulfide compound. In this specification, "modified recycled rubber" refers to a rubber material obtained by crushing a portion of used rubber products (waste rubber products) such as tires, then desulfurizing them, and further functionalizing them with a thiram sulfide compound. Using modified recycled rubber functionalized with a thiram sulfide compound tends to yield better results.

[0057] Modified recycled rubber is advantageous in improving problems such as reduced reinforcing properties that are a concern when using recycled materials, because its reactivity is increased by breaking some of the crosslinked structures in the rubber through desulfurization and functionalization. For example, it is produced by functionalizing recycled rubber or vulcanized rubber powder (powdered rubber) that has functional groups that can act on unvulcanized diene-based rubber with a modifying compound (introducing a modifying compound). Here, recycled rubber is not particularly limited and includes crushed rubber that has been mechanically crushed at room temperature or frozen, desulfurized rubber that has been further desulfurized, recycled rubber from used automobile tires, tubes and other rubber products as specified in JIS K6313, and recycled rubber having equivalent properties.

[0058] Furthermore, modified recycled rubber products from companies such as Lehigh can be used.

[0059] In the rubber composition for the inner apex, the content of the modified rubber material functionalized with a thiuram sulfide compound is preferably 3 parts by mass or more, more preferably 6 parts by mass or more, even more preferably 8 parts by mass or more, and particularly preferably 10 parts by mass or more, per 100 parts by mass of the rubber component. Furthermore, the content is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, even more preferably 15 parts by mass or less, and particularly preferably 13 parts by mass or less. When the content is within the above range, a better effect tends to be obtained.

[0060] In the rubber composition for the outer apex, the content of the modified rubber material functionalized with a thiuram sulfide compound is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, even more preferably 15 parts by mass or more, and particularly preferably 20 parts by mass or more, per 100 parts by mass of the rubber component. Furthermore, the content is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, even more preferably 30 parts by mass or less, and particularly preferably 25 parts by mass or less. When the content is within the above range, a better effect tends to be obtained.

[0061] From the viewpoint of obtaining a better effect, at least one of the rubber composition for the inner apex and the rubber composition for the outer apex should preferably have a content ratio of modified rubber material functionalized with a thiram sulfide compound to isoprene rubber (content of the modified rubber material in the rubber composition (parts by mass) / content of isoprene rubber in the rubber composition (parts by mass)) of 0.33 or less, more preferably 0.25 or less, even more preferably 0.22 or less, and particularly preferably 0.20 or less. The lower limit of this content ratio is not particularly limited, but preferably 0.10 or more, more preferably 0.12 or more, even more preferably 0.14 or more, and particularly preferably 0.16 or more. When it is within the above range, a better effect tends to be obtained. It is desirable that both the rubber composition for the inner apex and the rubber composition for the outer apex satisfy the above relationship.

[0062] The mechanism (reason) by which these effects are obtained is not clear, but it can be inferred as follows. When the ratio of modified rubber material to isoprene-based rubber, particularly the ratio of modified recycled rubber to isoprene-based rubber, increases, the contribution of modified recycled rubber in the rubber becomes larger, leading to concerns about decreased interfacial adhesion and impaired durability. However, it is believed that such concerns are reduced when the ratio is kept below a certain level, especially below 0.25. Therefore, it is presumed that excellent durability is imparted to the heavy-duty tire.

[0063] From the viewpoint of obtaining a better effect, at least one of the rubber composition for the inner apex and the rubber composition for the outer apex should preferably have a content ratio of carbon black to a modified rubber material functionalized with a thiram sulfide compound (content of carbon black in the rubber composition (parts by mass) / content of the modified rubber material in the rubber composition (parts by mass)) of 1.5 or more, more preferably 2.0 or more, even more preferably 2.5 or more, and particularly preferably 3.0 or more. The upper limit of this content ratio is not particularly limited, but preferably 5.0 or less, more preferably 4.5 or less, even more preferably 4.0 or less, and particularly preferably 3.5 or less. When the ratio is within the above range, a better effect tends to be obtained. It is desirable that both the rubber composition for the inner apex and the rubber composition for the outer apex satisfy the above relationship.

[0064] The mechanism (reason) by which these effects are obtained is not clear, but it can be inferred as follows. It is believed that dispersing carbon black around modified rubber material, particularly modified recycled rubber, can reinforce the entire rubber and suppress crack growth from the interface. Therefore, it is presumed that this will impart excellent durability to the heavy-duty tire.

[0065] Powdered recycled rubber may be incorporated into the rubber composition for the inner apex and the rubber composition for the outer apex. "Powdered recycled rubber" refers to pulverized rubber that has been mechanically crushed at room temperature or frozen, desulfurized rubber that has been further desulfurized, recycled used rubber from automobile tires, tubes and other rubber products as specified in JIS K6313, and recycled rubber having equivalent properties, and is a material that has not undergone modification treatment such as desulfurization or functionalization. In this specification, recycled powdered rubber is not considered to be a rubber component.

[0066] When the rubber composition for the inner apex and the rubber composition for the outer apex contain recycled powder rubber, the content of the recycled powder rubber is preferably 3 parts by mass or more, more preferably 6 parts by mass or more, even more preferably 8 parts by mass or more, and particularly preferably 10 parts by mass or more, per 100 parts by mass of the rubber component. Alternatively, the content is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, even more preferably 15 parts by mass or less, and particularly preferably 13 parts by mass or less.

[0067] The rubber composition for the inner apex and the rubber composition for the outer apex may contain a plasticizer. In this specification, "plasticizer" refers to a material that imparts plasticity to rubber components, and is a concept that includes liquid plasticizers (plasticizers that are liquid at 25°C) and solid plasticizers (plasticizers that are solid at 25°C). Specifically, this includes components that can be extracted from rubber compositions using acetone. These may be used individually or in combination of two or more types.

[0068] In the rubber composition for the inner apex and the rubber composition for the outer apex, the total content of plasticizers (total content of liquid and solid plasticizers) is preferably 10.0 parts by mass or less, more preferably 5.0 parts by mass or less, even more preferably 3.0 parts by mass or less, and particularly preferably 2.0 parts by mass or less, per 100 parts by mass of rubber component. Within this range, a better effect tends to be obtained. Furthermore, the plasticizer content includes the amount of oil contained in rubber (oil-applied rubber) and sulfur (oil-containing sulfur).

[0069] Examples of liquid plasticizers include oils, liquid polymers (diene-based, olefin-based, ester-based, etc.), liquid resins, essential oils derived from natural products such as turpentine oil, and ester-based plasticizers. Examples of solid plasticizers include solid resins that are solid at 25°C and commonly used in the tire industry. These may be used individually or in combination of two or more. In particular, the liquid plasticizer is preferably at least one selected from the group consisting of oils, liquid polymers, and liquid resins, with oil being more preferred, and process oil being even more preferred.

[0070] The above oils are not particularly limited, and conventionally known oils can be used, such as process oils like paraffinic process oils, aromatic process oils, and naphthenic process oils, low PCA (polycyclic aromatic) process oils such as TDAE and MES, vegetable oils, and mixtures thereof. These may be used individually or in combination of two or more. Among these, paraffinic process oils are preferred.

[0071] As for the oil, products from companies such as Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., ENEOS Corporation, Orisoy Co., Ltd., H&R Co., Ltd., Toyokuni Oil Co., Ltd., Showa Shell Sekiyu K.K., and Fuji Kosan Co., Ltd. can be used.

[0072] Examples of liquid resins include terpene resins (including terpene phenol resins and aromatically modified terpene resins) that are liquid at 25°C, rosin resins, styrene resins, C5 resins, C5C9 resins, coumarone-indene resins (including coumarone and indene-only resins), olefin resins, polyurethane resins, and acrylic resins.

[0073] Examples of liquid resins that can be used include those from Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Yasuhara Chemical Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF, Arizona Chemical Company, Nippon Paint Chemical Co., Ltd., Nippon Shokubai Co., Ltd., ENEOS Corporation, Arakawa Chemical Industries, Ltd., Taoka Chemical Industries, Ltd., and others.

[0074] Examples of liquid diene polymers include liquid styrene-butadiene copolymers (liquid SBR), liquid butadiene polymers (liquid BR), liquid isoprene polymers (liquid IR), liquid styrene-isoprene copolymers (liquid SIR), liquid styrene-butadiene-styrene block copolymers (liquid SBS block polymers), and liquid styrene-isoprene-styrene block copolymers (liquid SIS block polymers), which are liquid at 25°C. These polymers may have polar groups attached to their ends or main chains.

[0075] Examples of liquid diene polymers that can be used include products from companies such as Sartomer and Kuraray Co., Ltd.

[0076] In the rubber composition for the inner apex and the rubber composition for the outer apex, the content of liquid plasticizer (preferably oil) is preferably 10.0 parts by mass or less, more preferably 5.0 parts by mass or less, even more preferably 3.0 parts by mass or less, and particularly preferably 2.0 parts by mass or less, per 100 parts by mass of rubber component. Within the above range, a better effect tends to be obtained. Furthermore, the liquid plasticizer content includes the amount of oil contained in rubber (oil-applied rubber) and sulfur (oil-containing sulfur).

[0077] As solid plasticizers, solid resins commonly used in tire compounding can be used. Specifically, examples include terpene resins, rosin resins, styrene resins, olefin resins, C5 resins, C9 resins, C5 / C9 resins, coumarone resins, indene resins, coumarone-indene resins, acrylic resins, and urethane resins. These may be used individually or as mixtures of two or more, and the resin itself may be a copolymer of monomer components of multiple origins.

[0078] Examples of solid plasticizers that can be used include products from Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Yasuhara Chemical Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF, Arizona Chemical Company, Nippon Paint Chemical Co., Ltd., Nippon Shokubai Co., Ltd., ENEOS Corporation, Arakawa Chemical Industries, Ltd., and Taoka Chemical Industries, Ltd.

[0079] The softening point of the solid plasticizer is preferably 30°C or higher, more preferably 50°C or higher, even more preferably 80°C or higher, preferably 200°C or lower, more preferably 160°C or lower, even more preferably 140°C or lower, and particularly preferably 120°C or lower. Within this range, the aforementioned effects tend to be more favorably obtained. In this specification, the softening point of a solid plasticizer is defined as the temperature at which the sphere descends when the softening point specified in JIS K 6220-1:2001 is measured using a ring-type softening point measuring device.

[0080] In the rubber composition for the inner apex and the rubber composition for the outer apex, the content of the solid plasticizer (preferably resin) is preferably 10.0 parts by mass or less, more preferably 5.0 parts by mass or less, even more preferably 3.0 parts by mass or less, and particularly preferably 2.0 parts by mass or less, per 100 parts by mass of the rubber component. Within this range, a better effect tends to be obtained.

[0081] The rubber composition for the inner apex and the rubber composition for the outer apex preferably contain sulfur. Examples of sulfur commonly used in the rubber industry include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, and soluble sulfur. These may be used individually or in combination of two or more types.

[0082] For sulfur, products from companies such as Tsurumi Chemical Industries, Ltd., Karuizawa Sulfur Co., Ltd., Shikoku Chemicals Co., Ltd., Flexis Co., Ltd., Nippon Dry Distillation Co., Ltd., and Hosoi Chemical Industries Co., Ltd. can be used.

[0083] In the rubber composition for the inner apex and the rubber composition for the outer apex, the sulfur content is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 0.8 parts by mass or more, per 100 parts by mass of the rubber component. Furthermore, the above content is preferably 10.0 parts by mass or less, more preferably 7.0 parts by mass or less, even more preferably 5.5 parts by mass or less, and particularly preferably 4.0 parts by mass or less. When the content is within the above range, a better effect tends to be obtained.

[0084] The rubber composition for the inner apex and the rubber composition for the outer apex preferably contain a vulcanization accelerator. Examples of vulcanization accelerators include thiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole and di-2-benzothiazolyl disulfide; thiuram-based vulcanization accelerators such as tetramethylthiuram disulfide (TMTD), tetrabenzylthiuram disulfide (TBzTD), and tetrakis(2-ethylhexyl)thiuram disulfide (TOT-N); sulfenamide-based vulcanization accelerators such as N-cyclohexyl-2-benzothiazolyl sulfenamide, Nt-butyl-2-benzothiazolyl sulfenamide, N-oxyethylene-2-benzothiazole sulfenamide, and N,N'-diisopropyl-2-benzothiazole sulfenamide; and guanidine-based vulcanization accelerators such as diphenylguanidine, diortototrilguanidine, and orthotrilbiguanidine. These may be used individually or in combination of two or more. Among these, sulfenamide-based vulcanization accelerators are preferred.

[0085] Products from companies such as Kawaguchi Chemical Co., Ltd., Ouchi Shinko Chemical Co., Ltd., and Rhein Chemie can be used as vulcanization accelerators.

[0086] In the rubber composition for the inner apex and the rubber composition for the outer apex, the content of the vulcanization accelerator is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, and preferably 10.0 parts by mass or less, and more preferably 5.0 parts by mass or less, per 100 parts by mass of the rubber component. When the content is within the above range, a better effect tends to be obtained.

[0087] The rubber composition for the inner apex and the rubber composition for the outer apex preferably contain stearic acid. Conventional known stearic acid can be used, for example, products from NOF Corporation, Kao Corporation, Fujifilm Wako Pure Chemical Corporation, Chiba Fatty Acid Co., Ltd., etc.

[0088] In the rubber composition for the inner apex and the rubber composition for the outer apex, the stearic acid content is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, per 100 parts by mass of the rubber component. Furthermore, the above content is preferably 5 parts by mass or less, more preferably 3 parts by mass or less. When the content is within the above range, a better effect tends to be obtained.

[0089] The rubber composition for the inner apex and the rubber composition for the outer apex may contain zinc oxide. Conventional zinc oxides can be used, such as products from Mitsui Mining & Smelting Co., Ltd., Toho Zinc Co., Ltd., Hakusui Tech Co., Ltd., Seido Chemical Industry Co., Ltd., and Sakai Chemical Industry Co., Ltd.

[0090] In the rubber composition for the inner apex and the rubber composition for the outer apex, the zinc oxide content is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and preferably 10 parts by mass or less, and more preferably 5 parts by mass or less, per 100 parts by mass of the rubber component. Within this range, a better effect tends to be obtained.

[0091] The rubber composition for the inner apex and the rubber composition for the outer apex may contain an anti-aging agent. Examples of anti-aging agents include naphthylamine-based anti-aging agents such as phenyl-α-naphthylamine; diphenylamine-based anti-aging agents 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, and N,N′-di-2-naphthyl-p-phenylenediamine. Examples include p-phenylenediamine-based antioxidants such as 2,2,4-trimethyl-1,2-dihydroquinoline polymers and other quinoline-based antioxidants; 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. These may be used individually or in combination of two or more types. Among these, p-phenylenediamine-based antioxidants and quinoline-based antioxidants are preferred, and p-phenylenediamine-based antioxidants are more preferred.

[0092] Products from companies such as Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinko Chemical Co., Ltd., and Flexis Co., Ltd. can be used as anti-aging agents.

[0093] In the rubber composition for the inner apex and the rubber composition for the outer apex, the content of the anti-aging agent is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and preferably 10 parts by mass or less, and more preferably 5 parts by mass or less, per 100 parts by mass of the rubber component. When the content is within the above range, a better effect tends to be obtained.

[0094] The rubber composition for the inner apex and the rubber composition for the outer apex may contain wax. The waxes are not particularly limited and include petroleum-based waxes such as paraffin wax and microcrystalline wax; natural waxes such as plant-based waxes and animal-based waxes; and synthetic waxes such as polymers of ethylene and propylene. These may be used individually or in combination of two or more types.

[0095] Examples of waxes that can be used include those from Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., and Seiko Chemical Co., Ltd.

[0096] In the rubber composition for the inner apex and the rubber composition for the outer apex, the wax content is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, per 100 parts by mass of the rubber component. Furthermore, the above content is preferably 10 parts by mass or less, more preferably 7 parts by mass or less. When the content is within the above range, a better effect tends to be obtained.

[0097] The rubber composition for the inner apex and the rubber composition for the outer apex may contain additives commonly used in the tire industry, in addition to the above-mentioned components, such as vulcanizing agents other than sulfur (e.g., organic crosslinking agents, organic peroxides). The content of each of these components is preferably 0.1 parts by mass or more, and preferably 200 parts by mass or less, per 100 parts by mass of the rubber component.

[0098] It is preferable that the carbon black content (Cao) (parts by mass) per 100 parts by mass of rubber component in the rubber composition for the outer apex part, and the Ei* / Eo* ratio satisfy the following formula. Cao / (Ei* / Eo*)≧4.0 Cao / (Ei* / Eo*) is more preferably 6.0 or higher, even more preferably 7.0 or higher, and particularly preferably 8.0 or higher. The upper limit is preferably 20.0 or lower, more preferably 17.0 or lower, even more preferably 15.0 or lower, and particularly preferably 12.0 or lower. Within the above range, a better effect tends to be obtained.

[0099] It is preferable that the carbon black content (Cai) (parts by mass) per 100 parts by mass of rubber component in the rubber composition for the inner apex part, and the Ei* / Eo* ratio satisfy the following formula. Cai / (Ei* / Eo*)≧9.0 Cai / (Ei* / Eo*) is more preferably 11.0 or higher, even more preferably 13.0 or higher, and particularly preferably 15.0 or higher. The upper limit is preferably 30.0 or lower, more preferably 25.0 or lower, even more preferably 20.0 or lower, and particularly preferably 18.0 or lower. Within the above range, a better effect tends to be obtained.

[0100] The above rubber composition can be manufactured, for example, by kneading each of the components using a rubber kneading device such as an open roll or Banbury mixer, and then vulcanizing them.

[0101] Regarding the mixing conditions, in the base mixing step where additives other than the crosslinking agent (vulcanizing agent) and vulcanization accelerator are mixed, the mixing temperature is usually 100 to 180°C, preferably 120 to 170°C. In the finish mixing step where the vulcanizing agent and vulcanization accelerator are mixed, the mixing temperature is usually 120°C or lower, preferably 80 to 110°C. Furthermore, the composition mixed with the vulcanizing agent and vulcanization accelerator is usually subjected to a vulcanization treatment such as press vulcanization. The vulcanization temperature is usually 140 to 190°C, preferably 150 to 185°C.

[0102] Heavy-duty tires are manufactured using the above-mentioned rubber composition by conventional methods. Specifically, a rubber composition, with various additives added as needed, is extruded to match the shapes of the inner and outer apex portions at the unvulcanized stage, molded in a conventional manner on a tire molding machine, bonded together with other tire components to form an unvulcanized tire, and then heated and pressurized in a vulcanizing machine to manufacture the tire.

[0103] Heavy-duty tires are not particularly limited and include, for example, pneumatic tires, solid tires, and airless tires. Among these, pneumatic tires are preferred.

[0104] The heavy-duty tire 1 shown in Figure 1 can be used for various types of tires, such as pneumatic tires for heavy loads and non-pneumatic tires that do not contain pressurized air. Examples of heavy-duty tires 1 include truck tires and bus tires.

[0105] Heavy-duty tires are defined as those with a maximum load capacity of 1400 kg or more. Here, maximum load capacity refers to the maximum load capacity specified for each tire in the standard system that the tire is based on. For example, in the case of JATMA standards (Japan Automobile Tire Manufacturers Association standards), it is the maximum load capacity based on the load index (LI); in the case of TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES"; and in the case of ETRTO, it is "LOAD CAPACITY".

[0106] Although particularly preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the illustrated embodiments and can be implemented in various modified forms. [Examples]

[0107] The present invention will be specifically described based on the examples provided, but the present invention is not limited to these examples.

[0108] The various chemicals used in the examples and comparative examples are described below. NR:TSR20 SBR: SBR1502 manufactured by Sumitomo Chemical Co., Ltd. (styrene content 23.5% by mass) BR: BR150B (98% cis content by mass) manufactured by Ube Industries, Ltd. Carbon Black 1: N550 (N2SA41m) manufactured by Cabot Japan Co., Ltd. 2 / g) Carbon Black 2: N330 (N2SA75m) manufactured by Cabot Japan Co., Ltd. 2 / g) Modified rubber material: EkoDyne (modified recycled rubber functionalized with thiuram sulfide compounds) manufactured by Lehigh. Recycled rubber (unmodified): GF-80 REPROCESSED GROUND RUBBER from Lehigh (powdered recycled rubber, particle size 80 mesh) Resin: PR12686 (cashew oil modified phenolic resin) manufactured by Sumitomo Bakelite Co., Ltd. Oil: Diana Process NH-70S (aroma-type process oil) manufactured by Idemitsu Kosan Co., Ltd. Anti-aging agent: Nocrack RD (poly(2,2,4-trimethyl-1,2-dihydroquinoline)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Stearic acid: Paulownia wood manufactured by NOF Corporation. Zinc oxide: Two types of zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur 1: Powdered sulfur manufactured by Tsurumi Chemical Industries, Ltd. Sulfur 2: Flexis's Cristex (contains oil-treated insoluble sulfur, 80% insoluble sulfur, and 20% oil; the table shows the total amount of oil-treated insoluble sulfur including oil). Vulcanization accelerator 1: Noxellar NS (N-tert-butyl-2-benzothiadylsulfenamide (TBBS)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator 2: Noxellar D (N,N'-diphenylguanidine (DPG)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator 3: Noxellar H (hexamethylenetetramine (HMT)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0109] (Examples and Comparative Examples) According to the formulations shown in Tables 1 and 2, chemicals other than sulfur and vulcanization accelerator were mixed for 5 minutes at 150°C using a 1.7L Banbury mixer manufactured by Kobe Steel, Ltd. to obtain a mixture. Next, sulfur and vulcanization accelerator were added to the obtained mixture and mixed for 5 minutes at 80°C using an open roll to obtain an unvulcanized rubber composition for the outer apex and an unvulcanized rubber composition for the inner apex. The obtained unvulcanized rubber compositions for the outer apex and inner apex were molded into a two-layer bead apex structure consisting of an outer apex and an inner apex, according to the specifications in Table 3. These were then bonded together with other tire components to produce an unvulcanized tire, which was then press-vulcanized at 150°C for 30 minutes to obtain a test tire (heavy-duty tire, size: 11R22.5).

[0110] The obtained test tires were evaluated as follows. The results are shown in Table 3.

[0111] <Viscoelasticity Test> Viscoelasticity measurement samples (vulcanized rubber) measuring 20 mm in length, 4 mm in width, and 1 mm in thickness were taken from the outer and inner apex portions of the bead apex of each test tire, with the tire circumference being the longer side. The complex modulus E of each sample was then measured. o *(Outer apex), E i *The inner apex portion was measured using a GABO iplexer series under the following conditions: temperature 70°C, initial strain 5%, dynamic strain 1%, frequency 10Hz, and extension mode. The thickness direction of the sample was considered to be the tire radius direction.

[0112] <Durability> Using a drum testing machine, test tires were driven at a speed of 20 km / h under the conditions of rim (8.25 × 22.5), internal pressure (700 kPa), and load (26.72 kN × 2.5). The driving time until damage occurred to the bead area was expressed as an index with Comparative Example 1 set to 100. A higher value indicates better durability.

[0113] [Table 1]

[0114] [Table 2]

[0115] [Table 3]

[0116] From the table, the heavy-duty tire of the embodiment that comprises bead apex rubber having an inner apex portion and an outer apex portion, wherein at least one selected from the group consisting of the inner apex portion and the outer apex portion comprises isoprene-based rubber, carbon black, and a modified rubber material functionalized with a thiuram sulfide-based compound, and satisfies formulas (1) to (2), exhibited excellent durability.

[0117] The present invention (1) is a heavy-duty tire equipped with a bead apex rubber having an inner apex portion and an outer apex portion, At least one selected from the group consisting of the inner apex portion and the outer apex portion comprises isoprene rubber, carbon black, and a modified rubber material functionalized with a thiram sulfide compound. The complex modulus of elasticity (E) of the inner apex portion i *) The complex modulus of elasticity (E) of the outer apex portion. o *) is a heavy-duty tire that satisfies the following equations (1) to (2). (1)E i *>E o * (2)E i * / E o *≦7.0 (Ei* and Eo* are the complex modulus of elasticity measured under the conditions of a temperature of 70°C, initial strain of 5%, dynamic strain of 1%, frequency of 10Hz, and extension mode.)

[0118] The present invention (2) is a heavy-duty tire according to the present invention (1), wherein at least one selected from the group consisting of the inner apex portion and the outer apex portion has a content ratio of the modified rubber material to the isoprene-based rubber (content of the modified rubber material / content of the isoprene-based rubber) of 0.25 or less.

[0119] The present invention (3) is a heavy-duty tire according to the present invention (1) or (2), wherein at least one selected from the group consisting of the inner apex portion and the outer apex portion has a content ratio of carbon black to the modified rubber material (content of carbon black / content of the modified rubber material) of 2.0 or more.

[0120] The present invention (4) is E i *This is a heavy-duty tire according to any of the present invention (1) to (3), wherein the pressure is 15.0 MPa or higher.

[0121] The present invention (5) is a heavy-duty tire according to any one of the present inventions (1) to (4) such that the carbon black content (Cao) in the outer apex portion relative to 100 parts by mass of rubber component and the Ei* / Eo* satisfy the following formula. Cao / (Ei* / Eo*)≧6.0

[0122] The present invention (6) is a heavy-duty tire according to any one of the present inventions (1) to (5) such that the carbon black content (Cai) in the inner apex portion relative to 100 parts by mass of rubber component and the Ei* / Eo* satisfy the following formula. Cai / (Ei* / Eo*)≧11.0 [Explanation of Symbols]

[0123] 2 Tread section 3. Sidewall section 4. Bead section 5 Bead core 6 Carcass 6A Carcass Ply 6a Main body 6b Ply folded section 8 Bead Apex Rubber 8A Inner apex section 8B Outer apex section 9. Reinforcement cord layer 9a inner piece 9b outer piece

Claims

1. A heavy-duty tire equipped with a bead apex rubber having an inner apex portion and an outer apex portion, At least one selected from the group consisting of the inner apex portion and the outer apex portion comprises isoprene rubber, carbon black, and a modified rubber material functionalized with a thiram sulfide compound. At least one selected from the group consisting of the inner apex portion and the outer apex portion has a content ratio of the modified rubber material to the isoprene-based rubber (content of the modified rubber material / content of the isoprene-based rubber) of 0.25 or less. The complex modulus of elasticity (E) of the inner apex portion ｉ *), the complex modulus of elasticity of the outer apex portion (E ｏ *) refers to a heavy-duty tire that satisfies the following equations (1) to (2). (1)E ｉ *>E ｏ * (2)E ｉ * / E ｏ *≦7.0 (Ei* and Eo* are the complex modulus of elasticity measured under the conditions of a temperature of 70°C, initial strain of 5%, dynamic strain of 1%, frequency of 10Hz, and extension mode.)

2. A heavy-duty tire equipped with a bead apex rubber having an inner apex portion and an outer apex portion, At least one selected from the group consisting of the inner apex portion and the outer apex portion comprises isoprene rubber, carbon black, and a modified rubber material functionalized with a thiram sulfide compound. At least one selected from the group consisting of the inner apex portion and the outer apex portion has a content ratio of carbon black to the modified rubber material (content of carbon black / content of the modified rubber material) of 2.0 or more. The complex modulus of elasticity (E) of the inner apex portion ｉ *), the complex modulus of elasticity of the outer apex portion (E ｏ *) refers to a heavy-duty tire that satisfies the following equations (1) to (2). (1)E ｉ *>E ｏ * (2)E ｉ * / E ｏ *≦7.0 (Ei* and Eo* are the complex modulus of elasticity measured under the conditions of a temperature of 70°C, initial strain of 5%, dynamic strain of 1%, frequency of 10Hz, and extension mode.)

3. A heavy-duty tire equipped with a bead apex rubber having an inner apex portion and an outer apex portion, At least one selected from the group consisting of the inner apex portion and the outer apex portion comprises isoprene rubber, carbon black, and a modified rubber material functionalized with a thiram sulfide compound. The complex modulus of elasticity (E) of the inner apex portion ｉ *), the complex modulus of elasticity of the outer apex portion (E ｏ *) satisfies the following equations (1) to (2), (1)E ｉ *>E ｏ * (2)E ｉ * / E ｏ *≦7.0 (Ei* and Eo* are the complex modulus of elasticity measured under the conditions of a temperature of 70°C, initial strain of 5%, dynamic strain of 1%, frequency of 10Hz, and extension mode.) A heavy-duty tire in which the carbon black content (Cao) per 100 parts by mass of rubber component in the outer apex portion and the E i * / E o * satisfy the following formula. Cao / (E i * / E o *)≧6.0

4. A heavy-duty tire equipped with a bead apex rubber having an inner apex portion and an outer apex portion, At least one selected from the group consisting of the inner apex portion and the outer apex portion comprises isoprene rubber, carbon black, and a modified rubber material functionalized with a thiram sulfide compound. The complex modulus of elasticity (E) of the inner apex portion ｉ *), the complex modulus of elasticity of the outer apex portion (E ｏ *) satisfies the following equations (1) to (2), (1)E ｉ *>E ｏ * (2)E ｉ * / E ｏ *≦7.0 (Ei* and Eo* are the complex modulus of elasticity measured under the conditions of a temperature of 70°C, initial strain of 5%, dynamic strain of 1%, frequency of 10Hz, and extension mode.) A heavy-duty tire in which the carbon black content (Cai) per 100 parts by mass of rubber component in the inner apex portion and the E i * / E o * satisfy the following formula. Cai / (E i * / E o *)≧11.0

5. A heavy-duty tire according to any one of claims 2 to 4, wherein at least one selected from the group consisting of the inner apex portion and the outer apex portion has a content ratio of the modified rubber material to the isoprene-based rubber (content of the modified rubber material / content of the isoprene-based rubber) of 0.25 or less.

6. The heavy-duty tire according to claim 1, 3, or 4, wherein at least one selected from the group consisting of the inner apex portion and the outer apex portion has a content ratio of carbon black to the modified rubber material (carbon black content / modified rubber material content) of 2.0 or more.

7. The heavy-duty tire according to claim 1, 2, or 4, wherein the carbon black content (Cao) in the outer apex portion relative to 100 parts by mass of rubber component and the Ei* / Eo* satisfy the following formula. Cao / (Ei* / Eo*)≧6.0

8. A heavy-duty tire according to any one of claims 1 to 3, wherein the carbon black content (Cai) in the inner apex portion relative to 100 parts by mass of rubber component and the Ei* / Eo* satisfy the following formula. Cai / (Ei* / Eo*)≧11.0

9. The aforementioned E ｉ A heavy-duty tire according to any one of claims 1 to 4, wherein * is 15.0 MPa or more.

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