JP7009869B2 - Rubber composition for heavy-duty tires and its manufacturing method - Google Patents

Description

The present invention relates to a rubber composition for heavy-duty tires having excellent wear resistance and low rolling resistance, and a method for producing the same.

It is important that heavy-duty tires used as tires for trucks and buses have excellent wear resistance and a long tire life. On the other hand, in recent years, regulations on rolling resistance have become stricter, and there is an increasing demand for improvement in low rolling resistance. In order to impart low rolling resistance, it is considered to add silica to the rubber composition for heavy-duty tires, but there is a problem that the wear resistance is lowered.

Therefore, Patent Document 1 describes a rubber composition obtained by blending carbon black, silica, and a sulfur-containing silane compound having a specific structure with a rubber component made of natural rubber, styrene-butadiene copolymer rubber, and / or polybutadiene rubber. We propose to improve wear resistance and low rolling resistance by using pneumatic tires for heavy loads used for the cap rubber. However, the level of wear resistance required for heavy-duty pneumatic tires has been higher, and further improvements have been required.

Japanese Unexamined Patent Publication No. 2008-38119

An object of the present invention is to provide a heavy-duty tire rubber composition having improved wear resistance and low rolling resistance beyond the conventional level, and a method for producing the same.

The heavy-duty tire of the present invention that achieves the above object has a CTAB adsorption specific surface area of 180 to 300 m ² / g in 100 parts by mass of a rubber component composed of 55 to 70% by mass of natural rubber and 30 to 45% by mass of butadiene rubber. 40 to 60 parts by mass of silica and 3 to 10 parts by mass of carbon black having a nitrogen adsorption specific surface area of 110 to 150 m ² / g, and a silane coupling agent having a sulfide bond is added in an amount of 6 to 15 of the silica. The silane coupling agent containing mass% and having the sulfide bond is bis- (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide, 3-trimethoxysilylpropylbenzothiazole tetrasulfide. It is characterized by being one of .

Further, the method for producing a heavy-duty tire of the present invention is a method for producing the rubber composition for a heavy-duty tire of the present invention by a kneading step, a roll step, and a final step, in which the kneading step is a sulfide-based compounding agent. This is a step of kneading the raw materials other than the above with a Banbury mixer, in which the roll step applies the mixture obtained in the kneading step to a roll and mixes the mixture at a roll gap of 0.5 to 5 mm and a temperature of the mixture of 40 to 100 ° C. It is a step, and the final step is a step of adding a sulfide-based compounding agent to the mixture obtained in the roll step and mixing the mixture.

The rubber composition for heavy-duty tires of the present invention is prepared by blending a predetermined amount of natural rubber and butadiene rubber with silica having a fine particle size and a small amount of carbon black, and blending a silane coupling agent having a sulfide bond. Therefore, the wear resistance and the low rolling resistance can be improved more than the conventional level.

The content ratio of the cis 1,4 bond of the butadiene rubber is preferably 90% or more. Further, the butadiene rubber may contain a modified butadiene rubber.

The method for producing a rubber composition for a heavy-duty tire of the present invention is produced by a kneading step, a roll step, and a final step, and the mixture obtained in the kneading step is applied to a roll, and the roll gap is 0.5 to 5 mm. By carrying out the rolling step of mixing at a temperature of 40 to 100 ° C., the balance between wear resistance and low rolling resistance can be improved, and in particular, wear resistance can be further improved.

The temperature of the mixture in the kneading step is 135 to 155 ° C., and the temperature Ti of the mixture at that time is measured at every measurement interval Δt (seconds) and converted to 150 ° C. obtained by the following formula (1). The history amount HHS is preferably 50 to 250 seconds.
HHS = Σ [Δt × exp (Ea / R × (1 / To-1 / Ti))] ・ ・ ・ (1)
(In the formula, HHS is the amount of heat history converted to 150 ° C., Δt is the measurement interval (seconds), Ea is the activation energy, Ea = 22000cal / mol, and R is the gas constant, R = 1.987cal / (mol. K), To is the reference temperature, To = 150 + 273K, and Ti is the i-th kneading temperature (K) measured every Δt.)

A heavy-duty tire having a tread portion composed of a rubber composition for a heavy-duty tire and having an outer diameter of 700 to 1400 mm has excellent wear resistance, rolling resistance can be reduced to a level higher than the conventional level, and a truck and a tire can be used. Suitable as a bus tire.

In the present specification, the heavy-duty tire refers to a large pneumatic tire mounted on a truck, a bus, or a construction vehicle, and the rubber composition for the heavy-duty tire is a component of the heavy-duty tire, preferably a tread rubber or a side rubber. Refers to a rubber composition that forms a tire.

In the rubber composition for heavy-duty tires, the rubber component is composed of 55 to 70% by mass of natural rubber and 30 to 45% by mass of butadiene rubber. As the natural rubber, those usually used for a rubber composition for a tire can be used, and modified natural rubber may be used. The content of the natural rubber is preferably 55 to 70% by mass, preferably 60 to 70% by mass in 100% by mass of the rubber component. If the content of the natural rubber is less than 55% by mass, the chipping resistance deteriorates. Further, when the content of natural rubber exceeds 70% by mass, the wear resistance is lowered.

On the other hand, the content of the butadiene rubber is preferably 30 to 45% by mass, preferably 30 to 40% by mass in 100% by mass of the rubber component. By containing butadiene rubber, wear resistance can be improved. When the content of the butadiene rubber is less than 30% by mass, the wear resistance is lowered and the rolling resistance is increased. Further, when the content of the butadiene rubber exceeds 45% by mass, the tensile breaking strength of the rubber composition is lowered and the chipping resistance is deteriorated when the tire is used for heavy load.

In the present invention, the butadiene rubber preferably has a cis 1,4 bond content of 90% or more, more preferably 93 to 98%. Abrasion resistance is improved by setting the content ratio of the cis 1 and 4 bonds to 90% or more. The butadiene rubber having a cis 1,4 bond content of 90% or more may be produced by a usual method, or may be appropriately selected from commercially available products and used.

Further, the butadiene rubber can contain a modified butadiene rubber and is suitable for reducing the rolling resistance. The modified butadiene rubber is a butadiene rubber having a functional group reactive with silica. Examples of such a functional group include a hydroxy group, a hydroxysilyl group, an alcohol group, a carboxy group, an amino group and the like. The modified butadiene rubber may be produced by a usual method, or may be appropriately selected from commercially available products and used.

In the rubber composition for heavy-duty tires, 40 to 60 parts by mass, preferably 45 to 55 parts by mass of silica is blended with 100 parts by mass of the above-mentioned rubber component. By blending 40 parts by mass or more of silica, rolling resistance can be reduced and wear resistance can be improved. Rolling resistance can be reduced by blending 60 parts by mass or less of silica.

The CTAB adsorption specific surface area of silica is 180 to 300 m ² / g, preferably 180 to 250 m ² / g. If the N ₂ SA of silica is less than 180 m ² / g, the effect of improving wear resistance and low rolling resistance may not be sufficiently obtained. Further, if the N ₂ SA of silica exceeds 300 m ² / g, the workability may be deteriorated. In the present specification, N ₂ SA of silica shall be measured in accordance with JIS K6430.

In the present invention, a silane coupling agent having a sulfide bond is blended with silica. By blending a silane coupling agent having a sulfide bond, the dispersibility of silica with respect to the rubber component can be improved, and the action of improving wear resistance and low rolling resistance can be enhanced.

Examples of the type of silane coupling agent having a sulfide bond include bis- (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide, 3-trimethoxysilylpropylbenzothiazole tetrasulfide, and the like. It can be exemplified.

The blending amount of the silane coupling agent is 6 to 15% by mass, preferably 7 to 13% by mass with respect to the mass of silica. If the blending amount of the silane coupling agent is less than 6% by mass of the silica blending amount, the silica dispersion may not be sufficiently improved. If the blending amount of the silane coupling agent exceeds 15% by mass of the silica blending amount, the silane coupling agents are condensed with each other, and the desired hardness and strength in the rubber composition cannot be obtained.

In the rubber composition for heavy-duty tires, carbon black is blended in an amount of 3 to 10 parts by mass, preferably 5 to 10 parts by mass, in 100 parts by mass of the above-mentioned rubber component. By blending 3 parts by mass or more of carbon black, the rubber can be blackened. By blending 10 parts by mass or less of carbon black, it is possible to blacken the rubber without reinforcing it.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is 110 to 150 m ² / g, preferably 110 to 140 m ² / g. If the N ₂ SA of carbon black is less than 110 m ² / g, the wear resistance may decrease. Further, if the N ₂ SA of carbon black exceeds 150 m ² / g, carbon black may become expensive. In the present specification, N ₂ SA of carbon black shall be measured in accordance with JIS K6217-2.

In the present invention, other inorganic fillers other than silica and carbon black can be blended. Examples of other inorganic fillers include clay, talc, mica, calcium carbonate and the like. By blending other inorganic fillers, the rubber composition becomes cheaper.

Rubber compositions for heavy-duty tires are generally used for tire rubber compositions such as vulcanizing agents / cross-linking agents, vulcanization accelerating aids, anti-aging agents, scouring accelerators, various oils, and plasticizing agents. Various additives can be blended within a range that does not interfere with the composition of the present invention, and such additives are kneaded by a general method to obtain a rubber composition for heavy-duty tires, which is used for vulcanization or crosslinking. can do.

The method for producing a rubber composition for a heavy-duty tire of the present invention comprises a kneading step, a roll step, and a final step. In the kneading step, raw materials other than the vulcanizing compounding agent are kneaded with a Banbury mixer, and in the roll step, kneading is performed. The mixture obtained in the step is subjected to a roll and mixed at a roll gap of 0.5 to 5 mm and a temperature of the mixture of 40 to 100 ° C. In the final step, a vulcanization-based compounding agent is added to the mixture obtained in the roll step. And mixed to obtain a rubber composition for heavy-duty tires.

The kneading step is a step of kneading the raw materials other than the vulcanization-based compounding agent among the raw materials used for the rubber composition for heavy-duty tires with a Banbury mixer. Here, as the vulcanization-based compounding agent, a vulcanization agent / cross-linking agent, a vulcanization accelerating aid, and the like can be exemplified. It also refers to raw materials such as hollow fine particles and heat-expandable microcapsules that are destroyed or lose their function due to the addition of high shearing force.

In this kneading step, the strength of the shearing force, the kneading temperature and the time can be appropriately adjusted in the same manner as in the usual method for producing a rubber composition. The kneading temperature in the kneading step is preferably 135 to 155 ° C, more preferably 140 to 150 ° C. By setting the kneading temperature in the kneading step to 135 ° C. or higher, the viscosity is lowered and the workability is improved. Further, by setting the kneading temperature in the kneading step to 155 ° C. or lower, the wear resistance is improved. Here, the kneading temperature in the kneading step shall be the temperature of the mixture in the kneading step.

In the kneading step, the kneading time is not particularly limited, but is preferably 200 to 500 seconds, more preferably 200 to 300 seconds. When the kneading time is 200 seconds or more, the dispersibility of silica is improved. Further, when the kneading time is 500 seconds or less, the rubber hardness can be secured.

By specifying the amount of heat history in the kneading step, the wear resistance and low rolling resistance of the obtained rubber composition for heavy-duty tires can be further improved. That is, the temperature of the mixture in the kneading step was 135 to 155 ° C., and the temperature Ti of the mixture at that time was measured at every measurement interval Δt (seconds) and converted to 150 ° C. obtained by the following formula (1). The heat history amount HHS is preferably 50 to 250 seconds, more preferably 100 to 150 seconds.
HHS = Σ [Δt × exp (Ea / R × (1 / To-1 / Ti))] ・ ・ ・ (1)
(In the formula, HHS is the amount of heat history converted to 150 ° C., Δt is the measurement interval (seconds), Ea is the activation energy, Ea = 22000cal / mol, and R is the gas constant, R = 1.987cal / (mol. K), To is the reference temperature, To = 150 + 273K, and Ti is the i-th kneading temperature (K) measured every Δt.)

In the present invention, the heat history amount HHS converted to 150 ° C. measures the kneading temperature Ti (K) of the mixture every measurement interval Δt seconds, and as in the above formula (1), the reference temperature To and the kneading temperature Ti (K). It is obtained by multiplying the exponential value calculated from the difference between the reciprocals of each by the measurement interval Δt and adding them together. The measurement interval time Δt (seconds) can be arbitrarily set, but is preferably 0.2 to 2.0 seconds, more preferably 0.5 to 1.0 seconds. Here, Σ (Δt) seconds is the total kneading time of kneading. The subscript i in the formula (1) is a natural number indicating the order from 1 to the end of measurement. For example, when Σ (Δt) = 180 seconds and Δt = 0.5 seconds, i is a natural number from 1 to 360. When the heat history amount HHS is 50 seconds or more, the dispersibility of silica can be improved. Further, when the heat history amount HHS is 250 seconds or less, the rubber hardness can be secured. The heat history amount HHS can be adjusted by increasing or decreasing the kneading temperature (Ti) and the total kneading time (ΣΔt).

The mixture obtained in the kneading step is taken out from the kneader and subjected to the rolling step. At this time, the mixture taken out from the kneader may be subjected to the roll as it is, or may be appropriately cooled to lower the temperature of the mixture and then subjected to the roll.

In the roll step, the mixture obtained in the kneading step is repeatedly mixed at a roll gap of 0.5 to 5 mm and a temperature of 40 to 100 ° C. By further mixing the mixture kneaded with the Banbury mixer in the roll step, the dispersibility of silica in natural rubber and butadiene rubber is improved, so that the wear resistance of the rubber composition can be further improved. can. The temperature of the mixture in the rolling step is 40 to 100 ° C, preferably 60 to 80 ° C. By setting the temperature of the mixture to 40 ° C. or higher, it is possible to prevent an excessive load from being applied to the roll. Further, by setting the temperature of the mixture to 100 ° C. or lower, high shear can be given to the rubber and the dispersibility of silica can be enhanced.

The size (roll diameter) of the mixing roll machine used in the roll process is not particularly limited and can be appropriately selected based on the amount of the mixture to be processed. Here, the roll gap between adjacent rolls is preferably 0.5 to 5 mm, preferably 1.0 to 2.0 mm, regardless of the size of the rolls. By setting the roll gap to 0.5 mm or more, the risk of the rolls coming into contact with each other can be reduced. Further, by setting the roll gap to 5 mm or less, high shear can be given to the rubber and the dispersibility of silica can be improved. Here, the roll gap refers to the minimum distance between the outer surfaces of adjacent rolls.

The mixing time in the roll step is not particularly limited, but is preferably 100 to 600 seconds, more preferably 300 to 500 seconds. By setting the mixing time in such a range, the dispersibility of silica is improved, so that the wear resistance of the rubber composition can be further improved. The roll step may be performed once or a plurality of times. Here, one roll step means mixing at a predetermined roll gap, temperature and mixing time, and performing the roll step multiple times means that the mixture after the first roll step is mixed from the mixing roll. Taking out, subjecting to another mixing roll or the same mixing roll without adjusting or adjusting the temperature, and mixing under different roll mixing conditions or the same roll mixing conditions means repeating this any number of times.

In the production method of the present invention, after the roll step, the temperature of the mixture is cooled if necessary, and then the mixture is subjected to the final step, and the vulcanization-based compounding agent is added to and mixed with the mixture obtained in the roll step. A normal rubber kneading machine, for example, a Banbury mixer, a roll, a kneader, or the like can be used for the final step, and the final step can be performed in the same manner as the final step in the usual method for producing a rubber composition.

The rubber composition for heavy-duty tires of the present invention is prepared by blending a predetermined amount of natural rubber and butadiene rubber with silica having a fine particle size and a small amount of carbon black, and blending a silane coupling agent having a sulfide bond. Therefore, the wear resistance and the low rolling resistance can be improved more than the conventional level. Further, the method for producing a rubber composition for a heavy-duty tire of the present invention can efficiently produce a rubber composition for a heavy-duty tire having an improved balance between wear resistance and low rolling resistance, and is particularly wear-resistant. Can be made even better. A heavy-duty tire having a tread portion composed of a rubber composition for a heavy-duty tire and having an outer diameter of 700 to 1400 mm has excellent wear resistance, rolling resistance can be reduced to a level higher than the conventional level, and a truck and a tire can be used. Suitable as a bus tire. The heavy-duty tire targeted by the present invention preferably has a tire outer diameter of 900 to 1200 mm. The weight of the heavy-duty tire is not particularly limited, but is preferably 20 to 70 kg, more preferably 30 to 60 kg.

Hereinafter, the present invention will be further described with reference to Examples, but the scope of the present invention is not limited to these Examples.

Thirteen types of rubber compositions for heavy-duty tires (Examples 1 to 10 and Comparative Examples 1 to 3) having the common formulations shown in Table 2 and having the formulations shown in Table 1 are prepared. Weigh the components excluding the vulcanization-based compounding agent, which consists of sulfur and vulcanization accelerator, and knead with a 270L sealed Banbury mixer for about 4 to 8 minutes. After performing the kneading step, the obtained mixture is released and at room temperature. Cooled. At this time, from the time when the kneading temperature reaches 120 ° C. or higher to the end of the kneading process (until the mixture is discharged from the 1.7 L closed Banbury mixer), the kneading temperature Ti is measured every measurement interval Δt = 1 second. , The heat history amount HHS converted to 150 ° C. was calculated based on the above-mentioned equation (1). The obtained heat history amount HHS is shown in Tables 1 and 2.

The mixture discharged from the 270 L closed Banbury mixer and cooled to room temperature was again subjected to a 270 L closed Banbury mixer or a mixing roll (diameter 660 mm). When it was used in a 270L sealed Banbury mixer, it was described as "mixer" in the "remil form" column in Table 1, and when it was used in a mixing roll, it was described as "roll" in the "remil form" column. .. The remill using the 270 L sealed Banbury mixer was carried out at a kneading temperature of 130 to 140 ° C. for about 2 to 3 minutes. For the remill using the mixing roll, the roll step was carried out at the roll gap and the kneading temperature of the mixture shown in Table 1, and this roll step was repeated twice.

After cooling the mixture obtained by remiling at room temperature, it is subjected to a roll, a vulcanization-based compounding agent consisting of sulfur and a vulcanization accelerator is added and mixed, and a final step is performed to prepare a rubber composition for heavy-duty tires. did.

Using the obtained rubber composition, vulcanize and mold at 160 ° C. for 30 minutes using a mold having a predetermined shape to prepare a test sample, and use the method shown below to prepare a dynamic viscoelastic tan δ (60 ° C.). Abrasion resistance and tensile elongation at break were evaluated.

Dynamic viscoelastic tan δ (60 ° C)
The dynamic viscoelasticity of the obtained test sample was measured at an initial strain of 10%, an amplitude of ± 2%, and a frequency of 20 Hz using a viscoelasticity spectrometer manufactured by Toyo Seiki Seisakusho Co., Ltd., and tan δ was determined at a temperature of 60 ° C. .. The obtained results are shown in Table 1 as an index with the value of Comparative Example 1 as 100. The smaller the index of tan δ (60 ° C.) at a temperature of 60 ° C., the smaller the heat generation, which means that the rolling resistance is small and excellent when a heavy-duty tire is used.

Abrasion resistance The runbone wear of the obtained test sample was carried out using a Ramborn wear tester manufactured by Iwamoto Seisakusho Co., Ltd. in accordance with JIS K6264-2, under conditions of load 49N, slip ratio 25%, time 4 minutes, and room temperature. Measured at. The obtained results are shown in Table 1 as an index with Comparative Example 1 as 100. The larger the index of Rambone wear, the better the wear resistance.

Tension fracture elongation A JIS No. 3 dumbbell type test piece was cut out from the obtained test sample in accordance with JIS K6251. A tensile test was conducted under the conditions of a temperature of 20 ° C. and a tensile speed of 500 mm / min according to JIS K6251, and the tensile elongation at break was measured. The obtained results are shown in Table 1 as an index with the value of Comparative Example 1 as 100. The larger the index of tensile elongation at break, the better the chipping resistance when a heavy-duty tire is used.

The types of raw materials used in Tables 1 and 2 are shown below.
・ NR: Natural rubber, TSR20
-BR: NIPOL BR1220 (unmodified BR, manufactured by Zeon Corporation), content ratio of cis 1,4 bond is 96%
-Modified BR: Modified polybutadiene (CB24 manufactured by LANXESS), content ratio of cis 1,4 bond is 96%
-Silica 1: ZEOSIL Premium 200MP manufactured by Rhodia, CTAB adsorption specific surface area: 200m ² / g
-Silica 2: ZEOSIL 1165MP manufactured by Rhodia, CTAB adsorption specific surface area: 160 m ² / g
・ CB1: Carbon black, Tokai Carbon Co., Ltd. Seast 6, Nitrogen adsorption specific surface area: 119m ² / g
・ CB2: Carbon black, Tokai Carbon Co., Ltd. Seast 9H, Nitrogen adsorption specific surface area: 142 m ² / g
-Silane coupling agent: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide, manufactured by Evonik Degussa)

The types of raw materials used in Table 2 are shown below.
・ Zinc oxide: Zinc oxide 3 types, manufactured by Shodo Chemical Industry Co., Ltd. ・ Anti-aging agent 1: Nocrack 6C manufactured by Ouchi Shinko Chemical Co., Ltd.
・ Anti-aging agent 2: Non-flex RD manufactured by Seiko Kagaku Co., Ltd.
・ Wax: Sanknock, manufactured by Ouchi Shinko Kagaku Co., Ltd. ・ Stearic acid: beaded stearic acid, manufactured by NOF Corporation ・ Sulfur: Muclon OT-20 (sulfur content is 80% by mass), manufactured by Shikoku Chemicals Corporation ・ Vulcanization accelerator : Noxeller CZ manufactured by Ouchi Shinko Kagaku Co., Ltd.

As is clear from Table 1, the rubber compositions for heavy-duty tires of Examples 1 to 10 are excellent in low rolling resistance, wear resistance, and chipping resistance.

Since the rubber composition for heavy-duty tires of Comparative Example 1 has a CTAB adsorption specific surface area of silica of less than 180 m ² / g, its low rolling resistance and wear resistance are inferior to those of the rubber composition of Examples.
In the rubber composition for a heavy-duty tire of Comparative Example 2, since natural rubber exceeds 70% by mass and butadiene rubber is less than 30% by mass, low rolling resistance and wear resistance deteriorate.
In the rubber composition for a heavy-duty tire of Comparative Example 3, the natural rubber is less than 55% by mass and the butadiene rubber is more than 45% by mass, so that the chipping resistance is deteriorated.

Claims (6)

40 to 60 parts by mass of silica having a CTAB adsorption specific surface area of 180 to 300 m ² / g and nitrogen adsorption specific surface area in 100 parts by mass of a rubber component composed of 55 to 70% by mass of natural rubber and 30 to 45% by mass of butadiene rubber. Contains 3 to 10 parts by mass of carbon black having a specific surface area of 110 to 150 m ² / g and a silane coupling agent having a sulfide bond in an amount of 6 to 15% by mass based on the amount of the silica.
The silane coupling agent having a sulfide bond is
A rubber composition for heavy-duty tires, which is one of bis- (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide, and 3-trimethoxysilylpropylbenzothiazole tetrasulfide. thing. The rubber composition for a heavy-duty tire according to claim 1, wherein the content ratio of the cis 1,4 bond of the butadiene rubber is 90% or more. The rubber composition for a heavy-duty tire according to claim 1 or 2, wherein the butadiene rubber contains a modified butadiene rubber. A method for producing the rubber composition for a heavy-duty tire according to any one of claims 1 to 3 by a kneading step, a rolling step, and a final step.
The kneading step is a step of kneading raw materials other than the vulcanization-based compounding agent with a Banbury mixer, and the roll step applies the mixture obtained in the kneading step to a roll, a roll gap of 0.5 to 5 mm, and the mixture. The heavy-duty tire is a step of mixing at a temperature of 40 to 100 ° C., wherein the final step is a step of adding a vulcanization-based compounding agent to the mixture obtained in the roll step and mixing the mixture. A method for producing a rubber composition for use. The temperature of the mixture in the kneading step is 135 to 155 ° C., and the temperature Ti of the mixture at that time is measured at every measurement interval Δt (seconds) and converted to 150 ° C. obtained by the following formula (1). The method for producing a rubber composition for a heavy-duty tire according to claim 4, wherein the history amount HHS is set to 50 to 250 seconds.
HHS = Σ [Δt × exp (Ea / R × (1 / To-1 / Ti))] ・ ・ ・ (1)
(In the formula, HHS is the amount of heat history converted to 150 ° C., Δt is the measurement interval (seconds), Ea is the activation energy, Ea = 22000cal / mol, and R is the gas constant, R = 1.987cal / (.
mol · K), To is the reference temperature, To = 150 + 273K, and Ti is the i-th kneading temperature (K) measured every Δt. ) A heavy-duty tire having a tread portion formed of the rubber composition for a heavy-duty tire according to any one of claims 1 to 3 and having an outer diameter of 700 to 1400 mm.