Heavy-duty pneumatic tires

Abstract

To provide a pneumatic tire for a heavy load improved in low fuel consumption performance and rib tear resistance performance.SOLUTION: A pneumatic tire for a heavy load comprises a tread 1. The tread has a cap rubber layer 5 constituting a tread face and a base rubber layer 4 arranged adjacent to inside in a tire radial direction of the cap rubber layer. The cap rubber layer and the base rubber layer are constituted of rubber compositions containing rubber constituents. Extraction amounts of acetone of the rubber compositions constituting the base rubber layer are less than 4.0 mass%. When modulus at the time when the rubber compositions constituting the base rubber layer is stretched by 200% at 23°C is defined as M200b (MPa) and modulus at the time when the rubber compositions constituting the cap rubber layer is stretched by 200% at 23°C is defined as M200c (MPa), M200b and M200c satisfy the following formula (1): 0≤M200c-M200b≤5 (1).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a pneumatic tire for heavy loads. [Background technology]

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

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

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

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

[0006] The present invention aims to provide a heavy-duty pneumatic tire with improved fuel efficiency and rib tear resistance. [Means for solving the problem]

[0007] The inventors of the present invention have found that the above problems can be solved by setting the difference in modulus between the base rubber layer and the cap rubber layer at 200% stretch within a predetermined range, and by setting the amount of acetone extracted from the base rubber layer within a predetermined range, and have completed the present invention.

[0008] In other words, the present invention is [1] A heavy-duty pneumatic tire having a tread, wherein the tread has a cap rubber layer constituting the tread surface and a base rubber layer adjacent to the inner side of the cap rubber layer in the tire radial direction, the cap rubber layer and the base rubber layer are composed of a rubber composition containing rubber components, the amount of acetone extracted from the rubber composition constituting the base rubber layer is less than 4.0% by mass, and when the modulus of the rubber composition constituting the base rubber layer at 23°C and 200% stretch is M200b (MPa), and the modulus of the rubber composition constituting the cap rubber layer at 23°C and 200% stretch is M200c (MPa), M200b and M200c satisfy the following formula (1), 0 ≤ M200c - M200b ≤ 5 ···(1) [2] The heavy-duty pneumatic tire described in [1] above, wherein the tanδ (70°C tanδ) of the rubber composition constituting the base rubber layer is less than 0.040. [3] When the breaking strength at 23°C of the rubber composition constituting the base rubber layer is TB (MPa) and the breaking elongation at 23°C is EB (%), the tanδ (70°C tanδ), TB, and EB of the rubber composition constituting the base rubber layer satisfy the following formula (2), the heavy-duty pneumatic tire described in [1] or [2] above, TB × EB / 70℃ tanδ ≥ 4.5 × 10 5 ...(2) [4] A heavy-duty pneumatic tire according to any one of [1] to [3] above, wherein the rubber component constituting the base rubber layer contains butadiene rubber. [5] A heavy-duty pneumatic tire according to any of [1] to [4] above, wherein the thickness of the base rubber layer is 1 to 70% of the total thickness of the tread. 〔6〕The pneumatic heavy-duty tire according to any one of the above [1] to [5], comprising four or more belt layers on the inner side in the tire radial direction of the base rubber layer, and covering at least one of the outer surface in the tire radial direction of the belt layer on the outermost side in the tire radial direction and the outer surface in the tire radial direction of the widest belt layer with a reinforcing rubber layer that ends without reaching the tire equatorial plane, and the value of tanδ(70°C tanδ) at 70°C of the rubber composition constituting the reinforcing rubber layer is larger than the value of tanδ(70°C tanδ) at 70°C of the rubber composition constituting the base rubber layer. 〔7〕The pneumatic heavy-duty tire according to any one of the above [1] to [6], wherein the width w of the reinforcing rubber layer is 10 to 40% of the tread contact width W of the tread. 〔8〕The pneumatic heavy-duty tire according to any one of the above [1] to [7], wherein the maximum thickness of the reinforcing rubber layer is 5 to 25% of the groove depth of the width direction groove existing at the position of 1 / 4 of the tread contact width from the tire equatorial line. 〔9〕Relates to the pneumatic heavy-duty tire according to any one of the above [1] to [8], wherein the rubber composition constituting the base rubber layer contains glycerin fatty acid ester.

Advantages of the Invention

[0009] According to the present invention, a pneumatic heavy-duty tire with improved low fuel consumption performance and rib tear resistance performance is provided.

Brief Description of the Drawings

[0010] [Figure 1] It is a cross-sectional view in the tread width direction showing a half part of the tread portion of the pneumatic heavy-duty tire of the present disclosure. [Figure 2] It is a front view schematically showing an example of a test device used for evaluating the rib tear resistance performance of the pneumatic heavy-duty tire in the present disclosure. ​​​​​​​​​

[0011] The heavy-duty pneumatic tire according to this disclosure is a heavy-duty pneumatic tire equipped with a tread, wherein the tread has a cap rubber layer constituting the tread surface and a base rubber layer adjacent to the inner side of the cap rubber layer in the tire radial direction, the cap rubber layer and the base rubber layer are composed of a rubber composition containing rubber components, the amount of acetone extracted from the rubber composition constituting the base rubber layer is less than 4.0% by mass, and when the modulus of the rubber composition constituting the base rubber layer at 23°C and 200% stretch is M200b (MPa), and the modulus of the rubber composition constituting the cap rubber layer at 23°C and 200% stretch is M200c (MPa), M200b and M200c satisfy the following formula (1). 0 ≤ M200c - M200b ≤ 5 ···(1)

[0012] While we do not intend to be bound by theory, the mechanisms by which the effects of this disclosure are realized can be thought of as follows, for example.

[0013] If the modulus balance between the base rubber layer and the cap rubber layer is poor, it may lead to tread damage such as delamination at the interface between the cap rubber layer and the base rubber layer, or cracks within the base tread rubber.

[0014] Therefore, by setting the difference in modulus between the base rubber layer and the cap rubber layer at 200% stretch within a predetermined range, and by setting the amount of acetone extracted from the base rubber layer within a predetermined range, it is believed that the modulus balance between the base rubber layer and the cap rubber layer was optimized, thereby suppressing heat generation in the tread rubber while improving rib tear resistance.

[0015] Furthermore, it is believed that the combination of the structure of the reinforcing rubber layer, described later, and the aforementioned physical properties of the rubber composition constituting each layer of the tread, resulted in improved fuel efficiency and rib tear resistance.

[0016] Preferably, the tanδ (70°C tanδ) of the rubber composition constituting the base rubber layer is less than 0.040.

[0017] When the breaking strength at 23°C of the rubber composition constituting the base rubber layer is TB (MPa) and the elongation at 23°C is EB (%), it is preferable that the tanδ (70°C tanδ), TB, and EB of the rubber composition constituting the base rubber layer at 70°C satisfy the following formula (2). TB × EB / 70℃ tanδ ≥ 4.5 × 10 5 ...(2)

[0018] The rubber component constituting the base rubber layer preferably includes butadiene rubber.

[0019] The thickness of the base rubber layer is preferably 1 to 70% of the total thickness of the tread.

[0020] The heavy-duty pneumatic tire according to this disclosure comprises four or more belt layers on the radially inward side of the base rubber layer, and preferably, at least one of the radially outer surface of the outermost belt layer and the radially outer surface of the widest belt layer is covered with a reinforcing rubber layer that ends without reaching the tire equator, and preferably the tanδ (70°C tanδ) value of the rubber composition constituting the reinforcing rubber layer at 70°C is greater than the tanδ (70°C tanδ) value of the rubber composition constituting the base rubber layer at 70°C.

[0021] The width w of the reinforcing rubber layer is preferably 10 to 40% of the tread width W of the tread.

[0022] The maximum thickness of the reinforcing rubber layer is preferably 5 to 25% of the groove depth of the widthwise groove located at a position 1 / 4 of the tread width from the tire equator.

[0023] The rubber composition constituting the base rubber layer preferably contains a glycerin fatty acid ester.

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

[0025] <Heavy-duty pneumatic tires> Figure 1 shows a cross-sectional view in the tread width direction of half of the tread portion of the heavy-duty pneumatic tire of the present disclosure, but the present disclosure is not limited thereto.

[0026] In Figure 1, 1 represents the tread portion, 2 represents a carcass consisting of one or more carcass plies that toroidally extend between one bead core and the other bead core, and 3 represents a belt consisting of five laminated belt layers 3a to 3e arranged on the radially outer side of the carcass 2. A base rubber layer 4 and a cap rubber layer 5 are laminated on the radially outer side of the belt 3.

[0027] Here, at least one of the radially outer surfaces of the outermost belt layer 3e and the widest belt layer 3c (in Figure 1, the radially outer surface of the outermost belt layer 3e) is covered with a reinforcing rubber layer 7 that ends on the radially inner side of the tread rubber 6 without reaching the tire equatorial plane E.

[0028] By making the tanδ (70°C tanδ) value of the rubber composition constituting the reinforcing rubber layer 7 greater than the tanδ (70°C tanδ) value of the rubber composition constituting the base rubber layer, it is possible to achieve a high level of both heat resistance of the tire and durability of the belt.

[0029] The width w of the reinforcing rubber layer 7 is preferably 10-40% of the tread width W, and more preferably 15-30%. The maximum thickness t of the reinforcing rubber layer 7 is preferably 5-25% of the groove depth of the widthwise groove located at a position 1 / 4 of the tread width from the tire equator, and more preferably 7-20%. According to these, it is possible to effectively prevent the progression of damage into the base rubber 4, allow the low-heat-generating base rubber layer 4 to fully perform its original function, and impart high durability to the tread rubber 6. In this disclosure, "tread width" refers to the tread contact width which is the straight-line distance parallel to the tire axis between the outermost contact points (contact edges) in the tire axial direction when the tire is mounted on an applicable rim, filled with the specified air pressure, placed perpendicular to a flat plate with a camber angle of zero degrees, and subjected to a load equivalent to the maximum load capacity.

[0030] In this disclosure, "70°C tanδ" refers to the loss tangent tanδ under the conditions of a temperature of 70°C, initial strain of 5%, dynamic strain of ±1%, and frequency of 10Hz, in accordance with JIS K 6394:2007.

[0031] From the viewpoint of low fuel consumption performance, the 70°C tanδ of the rubber composition constituting the base rubber layer 4 is preferably less than 0.040, more preferably less than 0.039, and even more preferably less than 0.037.

[0032] The 70°C tanδ of the base rubber layer 4 can be appropriately adjusted depending on the type and amount of rubber components, fillers, silane coupling agents, oils, glycerin fatty acid esters, etc., as described later.

[0033] In this disclosure, the strength at break (TB) (MPa) and elongation at break (EB) (%) refer to the strength at break and elongation at break (elongation at rupture) measured in accordance with JIS K 6251:2017, under conditions of a tensile speed of 3.3 mm / second in a 23°C atmosphere.

[0034] In this disclosure, the modulus at 200% elongation refers to the tensile stress at 200% elongation in the grain direction, measured in a 23°C atmosphere and at a tensile speed of 3.3 mm / sec, in accordance with JIS K 6251:2017.

[0035] The modulus M200b of the rubber composition constituting the base rubber layer 4 when stretched to 200% is preferably 4.0 MPa or higher, more preferably 4.5 MPa or higher, even more preferably 5.0 MPa or higher, and particularly preferably 5.5 MPa or higher, from the viewpoint of suppressing deterioration of fuel efficiency due to rubber distortion, suppressing a decrease in handling stability, and suppressing uneven wear. On the other hand, M200b is preferably 15.0 MPa or lower, more preferably 14.0 MPa or higher, even more preferably 13.0 MPa or lower, and particularly preferably 12.0 MPa or lower. If M200b exceeds 15.0 MPa, external forces are difficult to dissipate, and there is a concern that crack propagation may occur at the interface due to the concentration of input at the interface between the cap rubber layer 5 and the base rubber layer 4.

[0036] When the modulus of the rubber composition constituting the base rubber layer 4 of this disclosure is M200b (MPa) at 23°C and the modulus of the rubber composition constituting the cap rubber layer 5 is M200c (MPa) at 23°C and the modulus is M200c (MPa), M200b and M200c satisfy the following formula (1). 0 ≤ M200c - M200b ≤ 5 ···(1)

[0037] By setting the M200c-M200b pressure to 5 MPa or less and improving the modulus balance between the base rubber layer 4 and the cap rubber layer 5, it is believed that tread damage such as delamination at the interface between the base rubber layer 4 and the cap rubber layer 5, and cracks within the base rubber layer 4, can be suppressed.

[0038] For M200c-M200b, a pressure of 4 MPa or less is preferred, and 3 MPa or less is more preferred.

[0039] Furthermore, the modulus, TB, and EB of each rubber layer at 200% stretch can be appropriately adjusted by the type and amount of rubber components, fillers, silane coupling agents, softeners, etc., as described later.

[0040] The acetone extraction amount in this disclosure is an indicator of the concentration of organic low-molecular-weight compounds in the plasticizer contained in the vulcanized rubber composition. The acetone extraction amount can be determined by immersing each vulcanized rubber test piece in acetone for 24 hours in accordance with JIS K 6229-3:2015 to extract soluble components, measuring the mass of each test piece before and after extraction, and using the following formula. Acetone extraction amount (%) = {(Mass of rubber test piece before extraction - Mass of rubber test piece after extraction) / (Mass of rubber test piece before extraction)} × 100

[0041] The amount of acetone extracted from the rubber composition constituting the base rubber layer 4 is less than 4.0% by mass, preferably less than 3.9% by mass, more preferably less than 3.8% by mass, even more preferably less than 3.7% by mass, and particularly preferably less than 3.6% by mass. By keeping the difference in the amount of acetone extracted within the above range, a high level of balance between low fuel consumption performance and fracture resistance performance can be achieved.

[0042] From the viewpoint of balancing tire durability and fuel efficiency, it is preferable that the tanδ at 70°C, the breaking strength TB (MPa) at 23°C, and the elongation at 23°C EB (%) of the rubber composition constituting the base rubber layer 4 satisfy the following formula (2). TB × EB / 70℃ tanδ ≥ 4.5 × 10 5 ...(2)

[0043] TB × EB / 70℃ tanδ is 4.6 × 10 5 The above is preferable, 4.7 × 10 5 The above is more preferable, 4.8 × 10 5 The above is even more preferable, 4.9 × 10 5 The above are particularly preferable.

[0044] [Rubber composition] The heavy-duty pneumatic tire of this disclosure can improve fuel efficiency and rib tear resistance through the cooperation of the aforementioned reinforcing rubber layer structure and the aforementioned physical properties of the rubber composition constituting each layer of the tread.

[0045] <Rubber components> The rubber composition constituting each rubber layer of the tread according to this disclosure (tread rubber composition) preferably contains at least one selected from the group consisting of isoprene rubber, styrene-butadiene rubber (SBR), and butadiene rubber (BR) as a rubber component. Natural rubber is particularly preferably included to ensure durability and wear resistance. The rubber component constituting each rubber layer of the tread may consist only of isoprene rubber, or it may consist only of isoprene rubber and BR.

[0046] (Isoprene rubber) As isoprene-based rubbers, for example, isoprene rubber (IR) and natural rubber, which are common in the tire industry, can be used. Natural rubber includes not only unmodified natural rubber (NR), but also modified natural rubbers such as epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), deproteinized natural rubber (DPNR), high-purity natural rubber, and grafted natural rubber. These isoprene-based rubbers may be used individually or in combination of two or more types.

[0047] NR is not particularly limited and can be any tire that is common in the tire industry, such as SIR20, RSS#3, and TSR20.

[0048] The content of isoprene-based rubber in 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 rubber component may consist solely of isoprene-based rubber.

[0049] (BR) The type of BR is not particularly limited, and common types used in the tire industry can be used, such as BR with a cis content (cis-1,4 bond content) of 90% by mass or more (high-cis BR), rare-earth butadiene rubber synthesized using a rare-earth element catalyst (rare-earth BR), BR containing syndiotactic polybutadiene crystals (SPB-containing BR), and modified BR (high-cis modified BR, low-cis modified BR). Modified BR is preferred as the BR from the viewpoint of reinforcing properties with fillers. In addition, SPB-containing BR can be used to ensure strength when the amount of filler is reduced.

[0050] Examples of high-cis BR include those manufactured by Nippon Zeon Co., Ltd., Ube Industries, Ltd., and JSR Corporation. Including high-cis BR can improve low-temperature properties and wear resistance. The cis content of high-cis BR is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 96% by mass or more, and particularly preferably 97% by mass or more. In this specification, the cis content is a value calculated by infrared absorption spectroscopy.

[0051] Rare earth-based BR is synthesized using a rare earth element catalyst, and the vinyl bond content (amount of 1,2-bonded butadiene units) is preferably 1.8 mol% or less, more preferably 1.0 mol% or less, and even more preferably 0.8 mol% or less. The cis content (cis-1,4 bond content) is preferably 95% by mass or more, more preferably 96% by mass or more, and even more preferably 97% by mass or more. As rare earth-based BR, for example, those manufactured by Lanxess K.K. can be used.

[0052] SPB-containing BR refers to BR in which 1,2-syndiotactic polybutadiene crystals are not simply dispersed in BR, but are chemically bonded to and dispersed in BR. Examples of such SPB-containing BR include those manufactured by Ube Industries, Ltd.

[0053] Preferably, modified BRs include terminally modified BRs coupled with tin, and terminally modified BRs having alkoxysilyl groups and / or amino groups. Furthermore, the modified BRs may be either unhydrogenated or hydrogenated. Examples of such modified BRs include those manufactured by Nippon Zeon Co., Ltd. and Asahi Kasei Chemicals Corporation.

[0054] As a tin-coupled terminally modified BR, it is preferable to obtain one in which 1,3-butadiene is polymerized with a lithium initiator, followed by the addition of a tin compound, and the terminals of the modified BR molecule are further bonded by a tin-carbon bond. Examples of lithium initiators include lithium-based compounds such as alkyllithium, aryllithium, vinyllithium, organotinlithium, and organonitrogen lithium compounds, as well as lithium metal. By using the above lithium initiator as the initiator for modified BR, modified BR with high vinyl and low cis content can be produced. Examples of tin compounds include tin tetrachloride, butyltin trichloride, dibutyltin dichloride, dioctyltin dichloride, tributyltin chloride, triphenyltin chloride, diphenyldibutyltin, triphenyltin ethoxide, diphenyldimethyltin, ditolylstin chloride, diphenyltin dioctanoate, divinyldiethyltin, tetrabenzyltin, dibutyltin distearate, tetraalyltin, and p-tributyltin styrene. These tin compounds may be used individually or in combination of two or more.

[0055] The BRs listed above may be used individually or in combination of two or more.

[0056] The weight-average molecular weight (Mw) of BR is preferably 300,000 or more, more preferably 350,000 or more, and even more preferably 400,000 or more, from the viewpoint of abrasion resistance and grip performance. Furthermore, from the viewpoint of crosslinking uniformity, it is preferably 2,000,000 or less, and more preferably 1,000,000 or less. Mw can be determined by converting the measured value by gel permeation chromatography (GPC) (GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMALTPORE HZ-M manufactured by Tosoh Corporation) to standard polystyrene equivalent.

[0057] When BR is included, the content in the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 12% by mass or more, and particularly preferably 15% by mass or more, from the viewpoint of low fuel consumption performance. Furthermore, from the viewpoint of breaking strength, the content is preferably 28% by mass or less, more preferably 25% by mass or less, even more preferably 22% by mass or less, and particularly preferably 20% by mass or less.

[0058] (SBR) There are no particular limitations on SBR, and examples include solution-polymerized SBR (S-SBR), emulsion-polymerized SBR (E-SBR), and modified SBRs thereof (modified S-SBR, modified E-SBR). Modified SBRs include SBRs in which the terminals and / or main chain are modified, and modified SBRs coupled with tin, silicon compounds, etc. (such as condensates and those with branched structures). Among these, E-SBR is preferred because it can significantly improve fuel efficiency and wear resistance. These SBRs may be used individually or in combination of two or more types.

[0059] The amount of SBR in the rubber component when SBR is included is not particularly limited, and can be, for example, 1% by mass or more, 5% by mass or more, 10% by mass or more, 30% by mass or less, 25% by mass or less, or 20% by mass or less.

[0060] (Other rubber components) The rubber components relating to this disclosure may include rubber components other than the isoprene-based rubber, SBR, and BR mentioned above. Other rubber components that can be crosslinked are commonly used in the tire industry, and examples include styrene-isoprene-butadiene copolymer rubber (SIBR), styrene-isobutylene-styrene block copolymer (SIBS), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), hydrogenated nitrile rubber (HNBR), butyl rubber (IIR), ethylene propylene rubber, polynorbornene rubber, silicone rubber, polyethylene chloride rubber, fluororubber (FKM), acrylic rubber (ACM), hydrin rubber, and the like. These other rubber components may be used individually or in combination of two or more.

[0061] <Filler> The tread rubber composition according to this disclosure preferably contains a filler comprising carbon black and / or silica. The filler may consist solely of carbon black, or solely of carbon black and silica.

[0062] (silica) By incorporating silica into the tread rubber composition according to this disclosure, fuel efficiency, fracture resistance, and wear resistance can be improved. The silica is not particularly limited, and common types used in the tire industry can be used, such as silica prepared by a dry process (anhydrous silica) or silica prepared by a wet process (hydrated silica). Among these, hydrated silica prepared by a wet process is preferred because it contains a large number of silanol groups. These silicas may be used individually or in combination of two or more types.

[0063] The average particle size of the silica is preferably 50 nm or less, more preferably 40 nm or less, and even more preferably 30 nm or less. Also, the average particle size of the silica is preferably 13 nm or more, more preferably 15 nm or more, and even more preferably 17 nm or more. When the average particle size of the silica is within the above range, the effects of the present disclosure tend to be more favorably exhibited. The average particle size of the silica is the number average particle size and is measured as the average value for any 100 particles by a transmission electron microscope.

[0064] The cetyltrimethylammonium bromide (CTAB) specific surface area of the silica is preferably 80 m 2 / g or more, more preferably 90 m 2 / g or more, and even more preferably 100 m 2 / g or more. Also, the CTAB specific surface area of the silica is more preferably 300 m 2 / g or less, even more preferably 170 m 2 / g or less, and even more preferably 150 m 2 / g or less. When the CTAB specific surface area of the silica is within the above range, the effects of the present disclosure tend to be more favorably exhibited. The CTAB specific surface area of the silica in this specification is a value measured in accordance with ASTM D3765-92.

[0065] The nitrogen adsorption specific surface area (N2SA) of the silica is preferably 80 m 2 / g or more, more preferably 110 m 2 / g or more, even more preferably 140 m 2 / g or more, and particularly preferably 170 m 2 / g or more. Also, the N2SA of the silica is preferably 350 m 2 / g or less, more preferably 300 m 2 / g or less, and even more preferably 250 m 2 / g or less. When the N2SA of the silica is within the above range, the effects of the present disclosure tend to be more favorably exhibited. The N2SA of the silica in this specification is a value measured by the BET method in accordance with ASTM D3037-93.

[0066] From the viewpoint of low fuel consumption performance, the silica content per 100 parts by mass of rubber component is preferably 20 parts by mass or less, more preferably 18 parts by mass or less, even more preferably 15 parts by mass or less, and particularly preferably 10 parts by mass or less. On the other hand, from the viewpoint of elongation at break, the content is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more.

[0067] (Carbon Black) The carbon black used is not particularly limited; for example, common types used in the tire industry such as GPF, FEF, HAF, ISAF, and SAF can be used. These carbon blacks may be used individually or in combination of two or more types.

[0068] The average particle diameter of the carbon black is preferably 90 nm or less, more preferably 70 nm or less, and even more preferably 50 nm or less. Furthermore, the average particle diameter of the carbon black is preferably 13 nm or more, more preferably 15 nm or more, and even more preferably 17 nm or more. When the average particle diameter of the carbon black is within the above range, the effects of this disclosure tend to be better exhibited. Note that the average particle diameter of the carbon black is the number-average particle diameter and is measured as the average value of any 100 particles using a transmission electron microscope.

[0069] The specific surface area of ​​cetyltrimethylammonium bromide (CTAB) in carbon black is 80 m². 2 Preferably 1 / g or more, 90m 2 More preferably 100m / g or more, 2 A value of 1 / g or higher is even more preferable. Furthermore, the specific surface area of ​​carbon black (CTAB) is 170 m². 2 More preferably less than / g, 165m 2 More preferably less than / g, 160m 2 A value of less than or equal to / g is even more preferable. When the CTAB specific surface area of ​​carbon black is within the above range, the effects of this disclosure tend to be better realized. The CTAB specific surface area of ​​carbon black in this specification is a value measured in accordance with JIS K 6217-3:2001.

[0070] The nitrogen adsorption specific surface area (N2SA) of carbon black is 40 m², from the perspective of fracture strength. 2 Preferably 60m / g or more. 2 More preferably 80m 2 A value of 1 / g or more is even more preferable. Also, from the viewpoint of processability, 200m 2 Preferably less than / g, 150m 2 More preferably less than / g, 130m 2 A value of less than or equal to / g is even more preferable. Note that the N2SA of carbon black as used herein is the value measured according to Method A of JIS K 6217-2 "Basic properties of carbon black for rubber - Part 2: Method for determining specific surface area - Nitrogen adsorption method - Single point method".

[0071] From the viewpoint of low fuel consumption, the content of carbon black per 100 parts by mass of rubber component is preferably 20 parts by mass or more, more preferably 25 parts by mass or more, and even more preferably 30 parts by mass or more. Furthermore, from the viewpoint of low fuel consumption, the content is preferably 60 parts by mass or less, more preferably 55 parts by mass or less, even more preferably 50 parts by mass or less, and particularly preferably 45 parts by mass or less.

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

[0073] The silica content in 100% by mass of the total silica and carbon black is preferably 1% by mass or more, more preferably 3% by mass or more, even more preferably 5% by mass or more, and particularly preferably 7% by mass or more. Furthermore, the silica content is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less.

[0074] From the viewpoint of wear resistance, the total content of silica and carbon black per 100 parts by mass of rubber component is preferably 25 parts by mass or more, more preferably 30 parts by mass or more, and even more preferably 35 parts by mass or more. Furthermore, from the viewpoint of suppressing a decrease in fuel efficiency and wear resistance, it is preferably 80 parts by mass or less, more preferably 70 parts by mass or less, even more preferably 60 parts by mass or less, and particularly preferably 55 parts by mass or less.

[0075] (Silane coupling agent) Silica is preferably used in combination with a silane coupling agent. The silane coupling agent is not particularly limited, but examples include: silane coupling agents having a sulfide group such as bis(3-triethoxysilylpropyl) disulfide and bis(3-triethoxysilylpropyl) tetrasulfide; silane coupling agents having a mercapto group such as 3-mercaptopropyltrimethoxysilane, Momentive's NXT-Z100, NXT-Z45, and NXT; silane coupling agents having a vinyl group such as vinyltriethoxysilane and vinyltrimethoxysilane; and 3-aminopropyltriethoxysilane. Examples of silane coupling agents include those having an amino group, such as silane and 3-(2-aminoethyl)aminopropyltriethoxysilane; glycidoxy-based silane coupling agents, such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro-based silane coupling agents, such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; and chloro-based silane coupling agents, such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. Silane coupling agents having a sulfide group are preferred. These silane coupling agents may be used individually or in combination of two or more.

[0076] When a silane coupling agent is included, the content per 100 parts by mass of silica is preferably 8.0 parts by mass or more, more preferably 8.5 parts by mass or more, even more preferably 9.0 parts by mass or more, and particularly preferably 9.5 parts by mass or more, from the viewpoint of improving the dispersibility of silica. Furthermore, from the viewpoint of preventing a decrease in wear resistance, it is preferably 18 parts by mass or less, more preferably 16 parts by mass or less, even more preferably 14 parts by mass or less, and particularly preferably 12 parts by mass or less.

[0077] <Other compounding agents> In addition to the components mentioned above, the tread rubber composition according to this disclosure may appropriately contain compounding agents commonly used in the tire industry, such as oils, waxes, glycerin fatty acid esters, processing aids, antioxidants, vulcanizing agents such as stearic acid, zinc oxide, and sulfur, and vulcanization accelerators.

[0078] Examples of oils include process oils, vegetable oils, and animal oils. Examples of process oils include paraffinic process oils, naphthenic process oils, and aromatic process oils. Furthermore, for environmental reasons, process oils with a low content of polycyclic aromatic compounds (PCA) can be used. Examples of low-PCA process oils include light extraction solvates (MES), processed distillate aromatic extracts (TDAEs), and heavy naphthenic oils.

[0079] When oil is included, the amount of oil per 100 parts by mass of rubber component is preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 4 parts by mass or less, from the viewpoint of balancing fuel efficiency and fracture strength. In this specification, the oil content also includes the amount of oil contained in the oil-spread rubber.

[0080] When wax is included, the amount of wax per 100 parts by mass of rubber component is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, and even more preferably 1.5 parts by mass or more, from the viewpoint of weather resistance of the rubber. Furthermore, from the viewpoint of preventing whitening of the tire due to bloom, it is preferably 8.0 parts by mass or less, and more preferably 6.0 parts by mass or less.

[0081] Glycerin fatty acid esters are formed in which a fatty acid is esterified to at least one of the three OH groups of glycerin, and are classified into glycerin fatty acid monoesters, glycerin fatty acid diesters, and glycerin fatty acid triesters depending on the number of fatty acids. The fatty acids constituting glycerin fatty acid esters are preferably those having 8 to 28 carbon atoms, more preferably 8 to 22 carbon atoms, even more preferably 10 to 18 carbon atoms, and particularly preferably 12 to 18 carbon atoms. The fatty acids may be saturated or unsaturated, linear or branched, but linear saturated fatty acids are preferred. Specific examples of fatty acids include capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, oleic acid, and linoleic acid.

[0082] When glycerin fatty acid ester is included, its content per 100 parts by mass of the rubber component is not particularly limited, but is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 1.0 part by mass or more. Furthermore, the content is preferably 10.0 parts by mass or less, more preferably 8.0 parts by mass or less, and even more preferably 6.0 parts by mass or less. By setting the content of glycerin fatty acid ester within the above range, the dispersibility of the filler in the rubber composition is improved, and the fuel efficiency and wear resistance can be further improved.

[0083] Examples of processing aids include fatty acid metal salts, fatty acid amides, amide esters, silica surfactants, fatty acid esters, mixtures of fatty acid metal salts and amide esters, and mixtures of fatty acid metal salts and fatty acid amides. These processing aids may be used individually or in combination of two or more. Examples of processing aids that can be used are those commercially available from companies such as Schill+Seilacher and Performance Additives.

[0084] When processing aids are included, the content per 100 parts by mass of rubber component is preferably 0.5 parts by mass or more, and more preferably 1 part by mass or more, from the viewpoint of exhibiting an effect of improving processability. Furthermore, from the viewpoint of abrasion resistance and fracture strength, it is preferably 10 parts by mass or less, and more preferably 8 parts by mass or less.

[0085] While not particularly limited, examples of anti-aging agents include amine-based, quinoline-based, quinone-based, phenol-based, and imidazole-based compounds, as well as metal carbamate salts. Phenylenediamine-based anti-aging agents such as N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, N,N'-diphenyl-p-phenylenediamine, N,N'-di-2-naphthyl-p-phenylenediamine, and N-cyclohexyl-N'-phenyl-p-phenylenediamine are preferred, as are quinoline-based anti-aging agents such as 2,2,4-trimethyl-1,2-dihydroquinoline polymer and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline. These anti-aging agents may be used individually or in combination of two or more.

[0086] When an anti-aging agent is included, the content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, and even more preferably 1.5 parts by mass or more, from the viewpoint of the rubber's resistance to ozone cracking. Furthermore, from the viewpoint of wear resistance and wet grip performance, it is preferably 10.0 parts by mass or less, and more preferably 5.0 parts by mass or less.

[0087] When stearic acid is included, its content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, and more preferably 1 part by mass or more, from the viewpoint of processability. Furthermore, from the viewpoint of vulcanization rate, it is preferably 10 parts by mass or less, and more preferably 5 parts by mass or less.

[0088] When zinc oxide is included, its content per 100 parts by mass of rubber component is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, and even more preferably 1.5 parts by mass or more, from the viewpoint of processability. Furthermore, from the viewpoint of wear resistance, it is preferably 10.0 parts by mass or less, and more preferably 5.0 parts by mass or less.

[0089] Sulfur is preferably used as a vulcanizing agent. Suitable sulfur varieties include powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur.

[0090] When sulfur is included as a vulcanizing agent, the amount of sulfur per 100 parts by mass of rubber component is preferably 0.5 parts by mass or more, and more preferably 1.0 part by mass or more, from the viewpoint of ensuring a sufficient vulcanization reaction and obtaining good grip performance and abrasion resistance. Furthermore, from the viewpoint of degradation, it is preferably 3.0 parts by mass or less, more preferably 2.5 parts by mass or less, and even more preferably 2.0 parts by mass or less. When oil-containing sulfur is used as the vulcanizing agent, the amount of vulcanizing agent shall be the total amount of pure sulfur contained in the oil-containing sulfur.

[0091] Examples of vulcanizing agents other than sulfur include alkylphenol-sulfur chloride condensates, 1,6-hexamethylene-dithiosulfate sodium dihydrate, and 1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane. These non-sulfur vulcanizing agents can be purchased commercially from companies such as Taoka Chemical Industries, Ltd., Lanxess Corporation, and Flexis.

[0092] Examples of vulcanization accelerators include sulfenamide, thiazole, thiuram, thiourea, guanidine, dithiocarbamate, aldehyde-amine or aldehyde-ammonia, imidazoline, or xanthate vulcanization accelerators. These vulcanization accelerators may be used individually or in combination of two or more. Among these, one or more vulcanization accelerators selected from the group consisting of sulfenamide, guanidine, and thiazole vulcanization accelerators are preferred.

[0093] Examples of sulfenamide-based vulcanization accelerators include N-tert-butyl-2-benzothiazolyl sulfenamide (TBBS), N-cyclohexyl-2-benzothiazolyl sulfenamide (CBS), and N,N-dicyclohexyl-2-benzothiazolyl sulfenamide (DCBS). Among these, N-tert-butyl-2-benzothiazolyl sulfenamide (TBBS) is preferred.

[0094] Examples of guanidine-based vulcanization accelerators include 1,3-diphenylguanidine (DPG), 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, di-o-tolylguanidine salts of dicatecholborate, 1,3-di-o-cumenylguanidine, 1,3-di-o-biphenylguanidine, and 1,3-di-o-cumenyl-2-propionylguanidine. Among these, 1,3-diphenylguanidine (DPG) is preferred.

[0095] Examples of thiazole-based vulcanization accelerators include 2-mercaptobenzothiazole, cyclohexylamine salt of 2-mercaptobenzothiazole, and di-2-benzothiazolyl disulfide. Among these, 2-mercaptobenzothiazole is preferred.

[0096] When a vulcanization accelerator is included, its content per 100 parts by mass of the rubber component is preferably 1 part by mass or more, and more preferably 2 parts by mass or more. Furthermore, the content of the vulcanization accelerator per 100 parts by mass of the rubber component is preferably 8 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 6 parts by mass or less. By keeping the content of the vulcanization accelerator within the above range, it tends to be possible to ensure fracture strength and elongation.

[0097] The rubber composition relating to this disclosure can be manufactured by known methods. For example, it can be manufactured by kneading each of the above components using a rubber kneading device such as an open roll or closed kneader (Banbury mixer, kneader, etc.).

[0098] The mixing process includes, for example, a base mixing process in which compounding agents and additives other than the vulcanizing agent and vulcanization accelerator are mixed, and a final mixing (F mixing) process in which the vulcanizing agent and vulcanization accelerator are added to the mixture obtained in the base mixing process and mixed. Furthermore, the base mixing process can be divided into multiple processes as desired.

[0099] There are no particular limitations on the mixing conditions, but for example, in the base mixing process, mixing is performed at a discharge temperature of 150-170°C for 3-10 minutes, and in the final mixing process, mixing is performed at 70-110°C for 1-5 minutes. There are no particular limitations on the vulcanization conditions, but for example, vulcanization is performed at 150-200°C for 10-30 minutes.

[0100] A tire having a tread including a cap rubber layer and a base rubber layer can be manufactured by conventional methods using the rubber composition described above. Specifically, an unvulcanized rubber composition, in which the above components are blended with the rubber component as needed, is extruded in an extruder equipped with a die of a predetermined shape to match the shape of the cap rubber layer and the base rubber layer, bonded together with other tire components on a tire molding machine, and molded in conventional methods to form an unvulcanized tire. The tire of this disclosure can then be manufactured by heating and pressurizing this unvulcanized tire in a vulcanizing machine. [Examples]

[0101] The present disclosure will be described below based on examples, but the present disclosure is not limited to these examples.

[0102] The various chemicals used in the examples and comparative examples are summarized below. NR:TSR20 BR1: UBEPOL BR150B manufactured by Ube Industries, Ltd. (cis content: 97% by mass, Mw: 440,000) BR2: BR1250H manufactured by Nippon Zeon Co., Ltd. (Tin-modified BR, polymerized using lithium as an initiator, cis content: 42% by mass, Mw: 570,000) Carbon Black 1: Carbon black produced by the following manufacturing example 1 (average particle size: 19 nm, CTAB: 150 nm) 2 / g, N2SA: 155m 2 / g) Carbon Black 2: DiaBlack N330 manufactured by Mitsubishi Chemical Corporation (average particle size: 31nm, CTAB: 78nm) 2 / g, N2SA:79m 2 / g) Carbon Black 3: DiaBlack N220 manufactured by Mitsubishi Chemical Corporation (average particle size: 23nm, CTAB: 110m) 2 / g, N2SA:114m 2 / g) Silica: UltraSil VN3 manufactured by Evonik Degussa (average particle size: 18 nm, CTAB: 153 nm) 2 / g, N2SA: 175m 2 / g) Wax: Ozoace 0355 manufactured by Nippon Seiro Co., Ltd. Anti-aging agent 1: Nocrack 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Anti-aging agent 2: Nocrack RD (poly(2,2,4-trimethyl-1,2-dihydroquinoline)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Stearic acid: Beads of stearic acid manufactured by NOF Corporation Zinc oxide: Zinc oxide No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur 1: HK-200-5 (5% oil-containing powdered sulfur) manufactured by Hosoi Chemical Industry Co., Ltd. Sulfur 2: Seimi OT (10% oil-containing insoluble sulfur) manufactured by Nippon Dry Distillation Industry Co., Ltd. Vulcanization accelerator: Noxellar NS (N-tert-butyl-2-benzothiazolyl sulfenamide (TBBS)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0103] (Manufacturing Example 1) A carbon black reactor was used, consisting of a combustion zone with an inner diameter of 800 mm and a length of 1600 mm equipped with an air intake duct and a combustion burner, a raw material introduction zone with an inner diameter of 175 mm and a length of 1000 mm connected to the combustion zone and with raw material nozzles passing through from the periphery, and a rear reaction zone with an inner diameter of 400 mm and a length of 3000 mm equipped with a quenching device, all connected in sequence. Using heavy fuel oil C as the fuel and creosote oil as the raw material hydrocarbon, carbon black 1 was produced by setting various conditions.

[0104] (Examples and Comparative Examples) According to the formulations shown in Tables 1 and 2, chemicals other than sulfur and vulcanization accelerator were mixed in a 1.7 L sealed Banbury mixer for 5 minutes until the discharge temperature reached 170°C to obtain a mixture. Furthermore, the obtained mixture was mixed again in the Banbury mixer for 4 minutes at a discharge temperature of 150°C (remilling). Next, sulfur and vulcanization accelerator were added to the obtained mixture using a twin-screw open roll and mixed for 4 minutes until the temperature reached 105°C to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was press-vulcanized at 170°C for 12 minutes to prepare a test vulcanized rubber composition.

[0105] Furthermore, the unvulcanized rubber composition was extruded into the shape of a cap rubber layer and a base rubber layer using an extruder equipped with a die of a predetermined shape, bonded together with other tire components to form an unvulcanized tire, and then press-vulcanized to produce the test tire (12R22.5, for trucks and buses) described in Table 3.

[0106] The obtained test vulcanized rubber compositions and test tires were evaluated as follows. The evaluation results are shown in Tables 1 to 3.

[0107] <Measurement of acetone extraction amount (AE amount)> Each rubber test specimen, prepared from vulcanized rubber compositions B1 to B12 for the base rubber layer, was immersed in acetone for 24 hours to extract soluble components. The mass of each test specimen was measured before and after extraction, and the amount of acetone extracted was calculated using the following formula. Acetone extraction amount (%) = {(Mass of rubber test piece before extraction - Mass of rubber test piece after extraction) / (Mass of rubber test piece before extraction)} × 100

[0108] <Viscoelasticity Test> Vulcanized rubber compositions B1 to B12 for the base rubber layer were prepared as sheet-shaped vulcanized rubber test pieces. In accordance with JIS K 6394:2007, the loss tangent (tanδ) was measured using a viscoelastic spectrometer RSA-G2 manufactured by TA Instruments at a temperature of 70°C, initial strain of 5%, dynamic strain of ±1%, and frequency of 10Hz. Furthermore, the reciprocal value of the 70°C tanδ of the base rubber layer was expressed as an index, with Comparative Example 1 set to 100 (fuel efficiency performance index). A higher index indicates better fuel efficiency performance. (Fuel efficiency index) = (70°C tanδ of the base rubber layer of Comparative Example 1) / (70°C tanδ of the base rubber layer of each test tire) × 100

[0109] <Tensile Test> Dumbbell-shaped No. 7 test specimens were prepared from vulcanized rubber composition A1 for the cap rubber layer and vulcanized rubber compositions B1 to B12 for the base rubber layer. Tensile tests were conducted in accordance with JIS K 6251:2017 at a 23°C atmosphere and a tensile speed of 3.3 mm / sec, and the modulus (MPa), strength at break (TB) (MPa), and elongation at break (EB) (%) at 200% stretch were measured.

[0110] <Durability Test> The rib tear resistance of each test tire was evaluated using the test apparatus 52 shown in Figure 2, as described in Japanese Patent Publication No. 2020-26257. Figure 3 is a plan view of the projection jig and reference surface of the test apparatus 52. The projection jig 56 had the external shape shown in Figure 4, was made of steel, and had an upper surface 56a with a length L of 200 mm, a width W of 50 mm, a projection 72 height H of 150 mm, and an inclination angle θ of the upper surface 56a of 3°. This projection jig 56 was attached to the base member 58 of the test apparatus 52.

[0111] (1) Tire assembly Each test tire was mounted onto a standard rim to form a tire assembly 51.

[0112] (2) Pretreatment process The tire assembly 51 was placed in a dry heat oven at 90°C and heated for 10 days. After that, the tire assembly 51 was removed from the oven and allowed to return to room temperature.

[0113] (3) Main processing step The pre-treated tire assembly 51 was mounted on the test apparatus 52. At this time, the tire assembly 51 and the projection jig 56 were aligned so that only the shoulder rib (not shown) of the tread portion 1 (a rib formed between the outermost circumferential groove in the tire axial direction and the tread contact edge) made contact with the upper surface 56a of the projection jig 56. Then, the tire assembly 51 (axis 66) was lowered at a speed of 50.0 mm / min and the lowering was continued until each test tire slid off the projection jig 56.

[0114] (4) Evaluation process After completing this processing step, the tire assembly 51 was removed from the test apparatus 52, and the area of ​​the tire 2 pressed against the protruding jig 56 was visually inspected. Tires in which no rib tear was observed were marked with "+", and tires in which rib tear was observed were marked with "-".

[0115] [Table 1]

[0116] [Table 2]

[0117] [Table 3]

[0118] The results in Tables 1 to 3 show that the heavy-duty pneumatic insert of this disclosure, in which the difference in modulus between the base rubber layer and the cap rubber layer at 200% stretch is within a predetermined range, and the amount of acetone extracted from the base rubber layer is within a predetermined range, exhibits improved fuel efficiency and rib tear resistance. [Explanation of symbols]

[0119] 1. Tread section 2 carcasses 3 belts 3a, 3b, 3c, 3d, 3e belt layer 4. Base rubber layer 5. Cap rubber layer 6 Tread Rubber E Tire Equatorial Plane w Reinforcement rubber layer width W Tread width t Maximum thickness of the reinforcing rubber layer 51 Tire Assembly 52 Test equipment 56. Protruding jig 56a Top surface of the projection jig 58 Base member 58a Top surface (reference surface) of the base member 62 Slide Bar 64 Vertical movement section 66 axes 71 Pedestal 72 Protrusion 74 Inner edge of projection jig

Claims

1. A heavy-duty pneumatic tire with a tread, The tread comprises a cap rubber layer constituting the tread surface and a base rubber layer adjacent to the inner side of the cap rubber layer in the tire radial direction, and the cap rubber layer and the base rubber layer are composed of a rubber composition containing rubber components and sulfur. The amount of acetone extracted from the rubber composition constituting the base rubber layer is less than 4.0% by mass. When the modulus of the rubber composition constituting the base rubber layer at 23°C and 200% stretch is M200b (MPa), and the modulus of the rubber composition constituting the cap rubber layer at 23°C and 200% stretch is M200c (MPa), then M200b and M200c satisfy the following formula (1), 0 ≤ M200c - M200b ≤ 4 ... (1) A heavy-duty pneumatic tire wherein, when the breaking strength at 23°C of the rubber composition constituting the base rubber layer is TB (MPa) and the elongation at 23°C is EB (%), the tanδ (70°C tanδ), TB, and EB of the rubber composition constituting the base rubber layer satisfy the following formula (2). TB × EB / 70°C tanδ ≥ 4.5 × 10⁵ ... (2)

2. A heavy-duty pneumatic tire with a tread, The tread comprises a cap rubber layer constituting the tread surface and a base rubber layer adjacent to the inner side of the cap rubber layer in the tire radial direction, and the cap rubber layer and the base rubber layer are composed of a rubber composition containing rubber components and sulfur. The amount of acetone extracted from the rubber composition constituting the base rubber layer is less than 4.0% by mass. When the modulus of the rubber composition constituting the base rubber layer at 23°C and 200% stretch is M200b (MPa), and the modulus of the rubber composition constituting the cap rubber layer at 23°C and 200% stretch is M200c (MPa), then M200b and M200c satisfy the following formula (1), 0 ≤ M200c - M200b ≤ 4 ... (1) A heavy-duty pneumatic tire in which the modulus M200b of the rubber composition constituting the base rubber layer is 13.0 MPa or less when stretched to 200%.

3. A heavy-duty pneumatic tire with a tread, The tread comprises a cap rubber layer constituting the tread surface and a base rubber layer adjacent to the inner side of the cap rubber layer in the tire radial direction, and the cap rubber layer and the base rubber layer are composed of a rubber composition containing rubber components and sulfur. The amount of acetone extracted from the rubber composition constituting the base rubber layer is less than 4.0% by mass. When the modulus of the rubber composition constituting the base rubber layer at 23°C and 200% stretch is M200b (MPa), and the modulus of the rubber composition constituting the cap rubber layer at 23°C and 200% stretch is M200c (MPa), then M200b and M200c satisfy the following formula (1), 0 ≤ M200c - M200b ≤ 4 ... (1) A heavy-duty pneumatic tire in which the butadiene rubber content in the rubber component of the rubber composition constituting the base rubber layer is 28% by mass or less.

4. A heavy-duty pneumatic tire with a tread, The tread comprises a cap rubber layer constituting the tread surface and a base rubber layer adjacent to the inner side of the cap rubber layer in the tire radial direction, and the cap rubber layer and the base rubber layer are composed of a rubber composition containing rubber components and sulfur. The amount of acetone extracted from the rubber composition constituting the base rubber layer is less than 4.0% by mass. When the modulus of the rubber composition constituting the base rubber layer at 23°C and 200% stretch is M200b (MPa), and the modulus of the rubber composition constituting the cap rubber layer at 23°C and 200% stretch is M200c (MPa), then M200b and M200c satisfy the following formula (1), 0 ≤ M200c - M200b ≤ 4 ... (1) A heavy-duty pneumatic tire in which the oil content of the rubber composition constituting the base rubber layer is 4 parts by mass or less per 100 parts by mass of rubber component.

5. A heavy-duty pneumatic tire according to any one of claims 1 to 4, satisfying that the maximum value of M200c - M200b in formula (1) above is 3 or less.

6. A heavy-duty pneumatic tire with a tread, The tread comprises a cap rubber layer constituting the tread surface and a base rubber layer adjacent to the inner side of the cap rubber layer in the tire radial direction, and the cap rubber layer and the base rubber layer are composed of a rubber composition containing rubber components and sulfur. The amount of acetone extracted from the rubber composition constituting the base rubber layer is less than 3.9% by mass. When the modulus of the rubber composition constituting the base rubber layer at 23°C and 200% stretch is M200b (MPa), and the modulus of the rubber composition constituting the cap rubber layer at 23°C and 200% stretch is M200c (MPa), then M200b and M200c satisfy the following formula (1), 0 ≤ M200c - M200b ≤ 5 ... (1') A heavy-duty pneumatic tire wherein, when the breaking strength at 23°C of the rubber composition constituting the base rubber layer is TB (MPa) and the elongation at 23°C is EB (%), the tanδ (70°C tanδ), TB, and EB of the rubber composition constituting the base rubber layer satisfy the following formula (2). TB × EB / 70°C tanδ ≥ 4.5 × 10⁵ ... (2)

7. The heavy-duty pneumatic tire according to any one of claims 1 to 5, wherein the amount of acetone extracted from the rubber composition of the base rubber layer is less than 3.9% by mass.

8. The heavy-duty pneumatic tire according to claim 6 or 7, wherein the amount of acetone extracted from the rubber composition of the base rubber layer is less than 3.8% by mass.

9. The heavy-duty pneumatic tire according to claim 8, wherein the amount of acetone extracted from the rubber composition of the base rubber layer is less than 3.7% by mass.

10. The heavy-duty pneumatic tire according to claim 9, wherein the amount of acetone extracted from the rubber composition of the base rubber layer is less than 3.6% by mass.

11. A heavy-duty pneumatic tire according to any one of claims 1 to 10, wherein the tanδ (70°C tanδ) of the rubber composition constituting the base rubber layer is less than 0.

040.

12. The heavy-duty pneumatic tire according to claim 11, wherein the tanδ (70°C tanδ) of the rubber composition constituting the base rubber layer is less than 0.

039.

13. The heavy-duty pneumatic tire according to claim 12, wherein the tanδ (70°C tanδ) of the rubber composition constituting the base rubber layer is less than 0.

038.

14. The heavy-duty pneumatic tire according to claim 13, wherein the tanδ (70°C tanδ) of the rubber composition constituting the base rubber layer is less than 0.

037.

15. A heavy-duty pneumatic tire according to any one of claims 2 to 5, wherein when the breaking strength at 23°C of the rubber composition constituting the base rubber layer is TB (MPa) and the elongation at 23°C is EB (%), the tanδ (70°C tanδ), TB, and EB of the rubber composition constituting the base rubber layer satisfy the following formula (2). TB×EB / 70℃tanδ≧4.5×10 5 ・・・(2)

16. A heavy-duty pneumatic tire according to claim 6 or 15, satisfying that the minimum value of TB × EB / 70°C tanδ in formula (2) above is 4.6 × 10⁵ or greater.

17. A heavy-duty pneumatic tire according to claim 6 or 16, wherein the minimum value of TB × EB / 70°C tanδ in formula (2) above is 4.7 × 10⁵ or greater.

18. A heavy-duty pneumatic tire according to claim 6 or 17, wherein the minimum value of TB × EB / 70°C tanδ in formula (2) above is 4.8 × 10⁵ or greater.

19. A heavy-duty pneumatic tire according to claim 6 or 18, satisfying that the minimum value of TB × EB / 70°C tanδ in formula (2) above is 4.9 × 10⁵ or greater.

20. The heavy-duty pneumatic tire according to any one of claims 1 to 19, wherein the rubber composition constituting the base rubber layer contains 5 parts by mass or more of silica per 100 parts by mass of rubber components.

21. A heavy-duty pneumatic tire according to any one of claims 1 to 20, wherein the rubber component constituting the base rubber layer includes butadiene rubber.

22. A heavy-duty pneumatic tire according to any one of claims 1 to 21, wherein the thickness of the base rubber layer is 1 to 70% of the total thickness of the tread.

23. The base rubber layer is provided with four or more belt layers on the radially inward side of the tire. At least one of the outermost radial surface of the belt layer in the tire's radial direction and the widest radial surface of the belt layer is covered with a reinforcing rubber layer that ends without reaching the tire's equatorial plane. A heavy-duty pneumatic tire according to any one of claims 1 to 22, wherein the tanδ (70°C tanδ) value of the rubber composition constituting the reinforcing rubber layer is greater than the tanδ (70°C tanδ) value of the rubber composition constituting the base rubber layer.

24. The heavy-duty pneumatic tire according to claim 23, wherein the width w of the reinforcing rubber layer is 10 to 40% of the tread width W of the tread.

25. The base rubber layer is provided with four or more belt layers on the radially inward side of the tire. At least one of the outermost radial surface of the belt layer in the tire's radial direction and the widest radial surface of the belt layer is covered with a reinforcing rubber layer that ends without reaching the tire's equatorial plane. The pneumatic tire for heavy loads according to claim 24, wherein the width w of the reinforcing rubber layer is 15 to 30% of the tread width W of the tread.

26. The base rubber layer is provided with four or more belt layers on the radially inward side of the tire. At least one of the outermost radial surface of the belt layer in the tire's radial direction and the widest radial surface of the belt layer is covered with a reinforcing rubber layer that ends without reaching the tire's equatorial plane. The heavy-duty pneumatic tire according to any one of claims 1 to 25, wherein the maximum thickness of the reinforcing rubber layer is 5 to 25% of the groove depth of the widthwise groove located at a position 1 / 4 of the tread width from the tire equator.

27. The base rubber layer is provided with four or more belt layers on the radially inward side of the tire. At least one of the outermost radial surface of the belt layer in the tire's radial direction and the widest radial surface of the belt layer is covered with a reinforcing rubber layer that ends without reaching the tire's equatorial plane. The heavy-duty pneumatic tire according to any one of claims 1 to 26, wherein the maximum thickness of the reinforcing rubber layer is 7 to 20% of the groove depth of the widthwise groove located at a position 1 / 4 of the tread width from the tire equator.

28. A heavy-duty pneumatic tire according to any one of claims 1 to 27, wherein the rubber composition constituting the base rubber layer contains a glycerin fatty acid ester.

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