JP6248621B2 - Rubber composition and pneumatic tire using the same - Google Patents

Description

  The present invention relates to a rubber composition for a cap tread of a heavy duty vehicle tire and a pneumatic tire using the same.

Generally, a compound for a cap of a heavy-duty vehicle tire (heavy-duty tire) such as a truck or a bus is worn or unevenly worn (uneven wear means that the tire road surface portion does not wear evenly and wears. It is necessary to achieve both suppression of low temperature and heat generation. As a general method for increasing the hardness of a vulcanized rubber, for example, a method of increasing the amount of carbon black, a method of increasing the crosslinking density, and the like are known.
On the other hand, the crosslinking of the diene rubber is generally formed by a sulfide bond or peroxide crosslinking derived from sulfur or the like. In addition, in the case of peroxide crosslinking that can be applied to saturated rubber in addition to diene rubber, a crosslinking aid such as triallyl isocyanurate is used (for example, Patent Document 1).

JP 2012-197421 A

However, the inventor of the present application has clarified that the low exothermic property deteriorates when carbon black is simply increased in order to increase the hardness of the vulcanized rubber, and the heat aging resistance deteriorates when sulfur is increased. Further, it has been clarified that when an isocyanurate compound having an allyl group such as triallyl isocyanurate is used as a crosslinking agent, the hardness, wear resistance and uneven wear resistance are deteriorated.
Therefore, the present invention is a rubber for a cap tread of a heavy-duty vehicle, which can achieve both excellent wear resistance and uneven wear resistance and excellent low heat build-up, and is excellent in heat aging resistance while maintaining high hardness. An object is to provide a composition and a pneumatic tire using the composition.

As a result of earnestly examining the above problems, the present inventor has 0.1 to 10 parts by mass of an isocyanuric acid derivative and / or a carboxylic acid derivative having a specific structure with respect to 100 parts by mass of a diene rubber containing natural rubber. And 40 to 60 parts by mass of carbon black having a nitrogen adsorption specific surface area of 90 to 150 m ³ / g, and the amount of the natural rubber is 40 to 100 parts by mass in 100 parts by mass of the diene rubber Rubber for cap treads of tires for heavy-duty vehicles, which can achieve both excellent wear resistance and uneven wear resistance and excellent low heat build-up, and excellent heat aging resistance while maintaining high hardness The present invention has been completed by finding that it can be a composition.

That is, the present inventors have found that the above problem can be solved by the following configuration.
1. For 100 parts by mass of diene rubber containing natural rubber,
0.1 to 10 parts by mass of an isocyanuric acid derivative represented by the following formula (1) and / or a carboxylic acid derivative represented by the following formula (2);
Including 40 to 60 parts by mass of carbon black having a nitrogen adsorption specific surface area of 90 to 150 m ³ / g,
A rubber composition for a cap tread of a heavy-duty vehicle tire, wherein the amount of the natural rubber is 40 to 100 parts by mass in 100 parts by mass of the diene rubber.

[In the formula (1), R ¹ , R ² and R ³ are each independently —C _a H _2a OC (═O) C _b H _2b SH, and a and b are each independently an integer of 1 or more. , R ¹ , R ² and R ³ may be the same or different. ]

[In the formula (2), R ⁴ , R ⁵ and R ⁶ are each independently —OC (═O) C _n H _2n SH, R ⁷ is —OC (═O) C _n H _2n SH, an alkyl group or hydrogen atom, n is independently an integer of 2 or _{more, -OC (= O) C n} H 2n SH may be the same or different. ]
2. 2. The rubber composition according to 1 above, wherein the molecular weight of the isocyanuric acid derivative or the carboxylic acid derivative is 1,000 or less.
3. 3. The rubber composition according to 1 or 2 above, wherein n is 2 in the formula (2).
4). 4. The rubber composition according to any one of 1 to 3, wherein the diene rubber further contains a butadiene rubber.
5). Furthermore, the rubber composition in any one of said 1-4 containing a filler (except the said carbon black).
6). A pneumatic tire for heavy-duty vehicles, comprising a cap tread formed using the rubber composition according to any one of 1 to 5 above.

  According to the present invention, a tire cap tread for a heavy-duty vehicle that can achieve both excellent wear resistance and uneven wear resistance and excellent low heat build-up, and is excellent in heat aging resistance while maintaining high hardness. The rubber composition for this and a pneumatic tire using the same can be provided.

FIG. 1 is a partial cross-sectional schematic view of a tire representing an example of an embodiment of the pneumatic tire of the present invention.

  Below, the rubber composition of this invention and the pneumatic tire of this invention are demonstrated.

[Rubber composition]
The rubber composition of the present invention is based on 100 parts by mass of a diene rubber containing natural rubber.
0.1 to 10 parts by mass of an isocyanuric acid derivative represented by the above formula (1) and / or a carboxylic acid derivative represented by the above formula (2);
Including 40 to 60 parts by mass of carbon black having a nitrogen adsorption specific surface area of 90 to 150 m ³ / g,
The amount of the natural rubber is 40 to 100 parts by mass in 100 parts by mass of the diene rubber.
A rubber composition for a cap tread of a heavy-duty vehicle tire.

Since the rubber composition of the present invention has such a configuration, it can achieve both excellent wear resistance and uneven wear resistance and excellent low heat build-up, and is excellent in heat aging resistance while maintaining high hardness. .
The reason why these properties are excellent is not clear, but is estimated as follows.
That is, the isocyanuric acid derivative and / or carboxylic acid derivative having a specific structure is an unsaturated bond (for example, vinylene group, vinyl group, etc. derived from a conjugated diene monomer) possessed by a diene rubber at the time of vulcanization, for example. It is thought that the cross-linking point of the network chain is formed by a monosulfide bond by interacting with or reacting with.
In addition, crosslinking with an isocyanuric acid derivative and / or carboxylic acid derivative is a three-dimensional network structure unlike a crosslinking point (sulfide bond) by sulfur vulcanization, so that the crosslinking density of rubber can be increased. It is thought that flexibility can be imparted because the distance between the points is long.
Such a structure is considered to contribute to the above characteristics.

  The diene rubber will be described below. The diene rubber contained in the rubber composition of the present invention contains natural rubber and is not particularly limited except that the amount of natural rubber is 40 to 100 parts by mass in 100 parts by mass of the diene rubber. All of the diene rubber can be natural rubber.

Natural rubber is not particularly limited. For example, a conventionally well-known thing is mentioned. Natural rubbers can be used alone or in combination of two or more.
When the diene rubber further contains a diene rubber other than natural rubber (for example, butadiene rubber described later), the amount of the natural rubber can be 40 parts by mass or more in 100 parts by mass of the diene rubber.
The amount of the natural rubber is preferably 60 to 100 parts by mass and more preferably 62 to 100 parts by mass in 100 parts by mass of the diene rubber.

The diene rubber preferably contains a butadiene rubber from the viewpoint of excellent wear resistance and uneven wear resistance and excellent heat aging resistance while maintaining high hardness.
The butadiene rubber that the diene rubber can contain is not particularly limited. For example, a conventionally well-known thing is mentioned.

The weight average molecular weight of the butadiene rubber is preferably 200,000 to 700,000, more preferably 300,000 to 600,000, from the viewpoint of excellent processability. The weight average molecular weight (Mw) of butadiene is determined in terms of standard polystyrene by gel permeation chromatography (GPC) using tetrahydrofuran as a solvent (the same applies hereinafter).
Butadiene rubbers can be used alone or in combination of two or more.

  The amount of butadiene rubber is a diene rubber 100 from the viewpoint that it is possible to achieve both excellent wear resistance and uneven wear resistance and excellent low heat build-up, and is excellent in heat aging resistance while maintaining high hardness. It can be 0-60 mass parts in a mass part, 0-40 mass parts is preferable and it is more preferable that it is 38 mass parts or less.

The isocyanuric acid derivative represented by the formula (1) and the carboxylic acid derivative represented by the formula (2) will be described below.
In the present invention, an isocyanuric acid derivative represented by the formula (1) (sometimes referred to simply as an isocyanuric acid derivative) and a carboxylic acid derivative represented by the formula (2) (sometimes referred to simply as a carboxylic acid derivative). ) Can function as a diene rubber crosslinking agent and / or chain transfer agent and plasticizer.

The isocyanuric acid derivative that can be used in the present invention is an isocyanuric acid derivative represented by the following formula (1).

[In the formula (1), R ¹ , R ² and R ³ are each independently —C _a H _2a OC (═O) C _b H _2b SH, and a and b are each independently an integer of 1 or more. , R ¹ , R ² and R ³ may be the same or different. ]
“OC (═O)” in —C _a H _2a OC (═O) C _b H _2b SH means an ester bond.
a can achieve both excellent wear resistance and uneven wear resistance and excellent low heat build-up, and is excellent in heat aging resistance while maintaining high hardness, elastic modulus, fracture property (for example, elongation at break) In the following, the integer is preferably an integer of 1 or more, more preferably an integer of 1 to 18, and still more preferably 2.
From the viewpoint of being able to achieve both excellent wear resistance and uneven wear resistance and more excellent low heat build-up, b is excellent in heat aging resistance while maintaining high hardness, and is excellent in elastic modulus and fracture properties. It is preferably an integer of 1 or more, more preferably an integer of 1 to 12, and still more preferably 2.
-C _a H _2a OC (═O) C _b H _2b SH can achieve both higher wear resistance and uneven wear resistance and better low heat build-up, while maintaining high hardness and heat aging From the viewpoint of superiority in properties and excellent elasticity and fracture properties, —C ₂ H ₄ OC (═O) C ₂ H ₄ SH (a = b = 2) is preferred.

The carboxylic acid derivative used in the rubber composition of the present invention is a carboxylic acid derivative represented by the following formula (2).

[In the formula (2), R ⁴ , R ⁵ and R ⁶ are each independently —OC (═O) C _n H _2n SH, n is each independently an integer of 2 or more, and R ⁷ is —OC (═O) C _n H _2n SH, an alkyl group or a hydrogen atom, and —OC (═O) C _n H _2n SH may be the same or different. ]
“OC (═O)” in —OC (═O) C _n H _2n SH means an ester bond.
From the viewpoint that n can achieve both excellent wear resistance and uneven wear resistance and more excellent low heat build-up, excellent heat aging resistance while maintaining high hardness, and excellent elasticity and fracture properties. It is preferably an integer of 2 or more, more preferably an integer of 2 to 18, and even more preferably 2.
The alkyl group is not particularly limited. Examples thereof include a methyl group, an ethyl group, a propyl group, a butyl group, and an octyl group.
—OC (═O) C _n H _2n SH can achieve both excellent wear resistance and uneven wear resistance and excellent low heat build-up, and is excellent in heat aging resistance while maintaining high hardness. From the viewpoint of excellent elasticity and fracture properties, —OC (═O) C ₂ H ₄ SH (n = 2) is preferred.
R ⁷ is a viewpoint that it is possible to achieve both higher wear resistance and uneven wear resistance and better low heat build-up, excellent heat aging resistance while maintaining high hardness, and excellent elasticity and fracture properties. Accordingly, —OC (═O) C ₂ H ₄ SH (n = 2) and a methyl group are preferable.

  The molecular weight of the isocyanuric acid derivative or carboxylic acid derivative is able to achieve both excellent wear resistance and uneven wear resistance and excellent low heat build-up, and is excellent in heat aging resistance while maintaining high hardness. From the viewpoint of excellent fracture physical properties, it is preferably 1,000 or less, more preferably 150 to 1,000.

  In the present invention, the amount of the isocyanuric acid derivative and / or the carboxylic acid derivative (the total amount when both are used together) is 0.1 to 10 parts by mass with respect to 100 parts by mass of the diene rubber. From the viewpoint of being able to achieve both excellent wear resistance and uneven wear resistance and more excellent low heat build-up, excellent heat aging resistance while maintaining high hardness, and excellent elasticity and fracture properties. The amount is preferably 1 to 8 parts by mass, and more preferably 1 to 6 parts by mass. The amount of the above isocyanuric acid derivative and / or carboxylic acid derivative may be the amount of the isocyanuric acid derivative and / or carboxylic acid derivative when sulfur is not contained or further sulfur is contained in the present invention.

  In the present invention, at least a part of sulfur generally used in a diene rubber can be replaced with an isocyanuric acid derivative and / or a carboxylic acid derivative. In this case, the rigidity is excellent.

  In the present invention, when the rubber composition further contains sulfur, sulfur is not particularly limited. For example, a conventionally well-known thing is mentioned. The amount of sulfur is able to achieve both better wear resistance and uneven wear resistance and better low heat build-up, and is excellent in heat aging resistance while maintaining high hardness, and excellent in elastic modulus and fracture properties. From a viewpoint, it is preferable that it is 0.1-5 mass parts with respect to 100 mass parts of diene rubbers, 0.1 mass part or more and less than 3.5 mass parts are more preferable, 0.1-3 mass parts is preferable. More preferably.

  In the present invention, when sulfur and an isocyanuric acid derivative and / or carboxylic acid derivative are used in combination, the mass ratio [sulfur / (isocyanuric acid derivative and / or carboxylic acid derivative)] is more excellent in wear resistance and uneven resistance. From the viewpoint of being able to achieve both wear and better low heat build-up, excellent heat aging resistance while maintaining high hardness, and excellent elasticity and fracture properties, it is preferably 0.1 to 100, More preferably, it is 0.1-40, and it is still more preferable that it is 0.1-20.

The carbon black will be described below. The carbon black contained in the rubber composition of the present invention is a carbon black having a nitrogen adsorption specific surface area (N ₂ SA) of 90 to 150 m ³ / g.
The nitrogen adsorption specific surface area of carbon black in the present invention is a value determined by the A method of JIS K6217.

Examples of carbon black include SAF and ISAF, which are generally used in the tire industry.
Carbon blacks can be used alone or in combination of two or more.

  In the present invention, the amount of carbon black is 40 to 60 parts by mass with respect to 100 parts by mass of the diene rubber. The amount of carbon black is preferably 45 to 60 parts by mass with respect to 100 parts by mass of the diene rubber from the viewpoint of being excellent in low exothermic property and heat aging resistance.

  The rubber composition of the present invention can further contain a filler (excluding the carbon black). Examples of the filler include white fillers such as silica, talc, clay, calcium carbonate, mica, and aluminum hydroxide; and carbon blacks other than the above. The fillers can be used alone or in combination of two or more. Of these, silica is preferable.

Silica will be described below. The silica that can be further contained in the rubber composition of the present invention is not particularly limited. Examples thereof include wet method silica, dry method silica, and surface-treated silica.
The amount of silica is preferably 5 to 95 parts by mass, more preferably 10 to 95 parts by mass with respect to 100 parts by mass of the diene rubber, from the viewpoint of excellent heat aging resistance and excellent elasticity and fracture properties. Is more preferable.

  When the rubber composition of the present invention further contains silica, the rubber composition further contains a silane coupling agent from the viewpoint that the dispersibility of the silica can be improved and the reinforcement to the diene rubber can be enhanced. Is mentioned as one of the preferred embodiments.

  The silane coupling agent is not particularly limited. For example, sulfur-containing silane coupling agents are preferred, such as bis- (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide, 3-trimethoxysilylpropylbenzothiazole tetrasulfide. A sulfide-based silane coupling agent; a mercapto-based silane coupling agent such as γ-mercaptopropyltriethoxysilane; a thioester-based silane coupling agent such as 3-octanoylthiopropyltriethoxysilane; a polysiloxane skeleton and a mercapto group. The silane coupling agent which has is mentioned. Of these, a sulfide-based silane coupling agent is preferable from the viewpoint of excellent fracture property. The silane coupling agents can be used alone or in combination of two or more.

  The amount of the silane coupling agent is preferably 3 to 20% by mass of the amount of silica, from the viewpoint of improving the dispersibility of the silica and increasing the reinforcement to the diene rubber. More preferably, it is 15 mass%.

[Optional ingredients]
The rubber composition of the present invention may further contain an additive as required, as long as the effect and purpose are not impaired. Examples of additives include zinc oxide (zinc white), stearic acid, anti-aging agent, processing aid, oil (eg, aroma oil, process oil), terpene resin, thermosetting resin, vulcanization accelerator, formula Various additives generally used for rubber compositions, such as crosslinking agents (for example, peroxide) other than the isocyanuric acid derivative represented by (1) or the carboxylic acid derivative represented by formula (2), can be mentioned. The amount of the additive can be set to, for example, the same amount as conventionally known, within a range that does not impair the effect and purpose, depending on the use of the rubber composition.

[Method for producing rubber composition]
The method for producing the rubber composition of the present invention is not particularly limited, and examples thereof include a method of kneading the above-described components using a known method and apparatus (for example, a Banbury mixer, a kneader, a roll, etc.). . Specifically, for example, first, a masterbatch is prepared by mixing components excluding sulfur, a vulcanization accelerator, an isocyanuric acid derivative and / or a carboxylic acid derivative, and sulfur and a vulcanization accelerator are added to the obtained masterbatch. And a method of producing a rubber composition by mixing an isocyanuric acid derivative and / or a carboxylic acid derivative.
The rubber composition of the present invention can be vulcanized or crosslinked under conventionally known vulcanization or crosslinking conditions.
In the present invention, a network chain crosslink is formed by the interaction and / or reaction between the unsaturated bond of the diene rubber and three or more mercapto groups of the isocyanuric acid derivative and / or carboxylic acid derivative. Such a crosslinked structure is considered to have an advantageous effect on the aging resistance. The cross-linking of the network structure can be formed in rubber simultaneously with sulfur vulcanization.

  The use of the rubber composition of the present invention is a rubber composition for cap treads of tires (for example, pneumatic tires) for heavy duty vehicles. Other examples include rubber compositions for anti-vibration rubber and seismic isolation rubber; rubber compositions for automotive parts such as packing.

[Pneumatic tire]
The pneumatic tire of the present invention is a pneumatic tire for heavy-duty vehicles having a cap tread formed using the rubber composition of the present invention.
The rubber composition used for the cap tread of the pneumatic tire of the present invention is not particularly limited as long as it is the rubber composition of the present invention.
FIG. 1 shows a schematic partial sectional view of a tire representing an example of an embodiment of the pneumatic tire of the present invention, but the pneumatic tire of the present invention is not limited to the attached drawings.

In FIG. 1, the pneumatic tire includes a pair of left and right bead portions 1 and side treads (sidewall portions) 2 and a cap tread 3 connected to both side treads 2. Steel cords are embedded between the bead portions 1 and 1. The carcass layer 4 is mounted, and the ends of the carcass layer 4 are folded back around the bead core 5 and the bead filler 6 from the inside to the outside of the tire. In the tread portion 3, a belt layer 7 is disposed on the outer side of the carcass layer 4 over the circumference of the tire. Belt cushions 8 are disposed at both ends of the belt layer 7. An inner liner 9 is provided on the inner surface of the pneumatic tire to prevent the air filled inside the tire from leaking to the outside of the tire, and a tie rubber 10 for bonding the inner liner 9 is attached to the carcass layer 4. It is laminated between the inner liner 9. The pneumatic tire shown in FIG. 1 is a heavy-duty vehicle tire.
In the present invention, a cap tread is formed using the rubber composition of the present invention.

  The pneumatic tire of the present invention can be manufactured, for example, according to a conventionally known method. Moreover, as gas with which a tire is filled, inert gas, such as nitrogen, argon, helium other than the air which adjusted normal or oxygen partial pressure, can be used.

  The pneumatic tire of the present invention can be used as a tire (heavy load tire) of a heavy load vehicle. Examples of heavy-duty vehicles include trucks, buses, and tractors.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these.

<Manufacture of rubber composition>
The components shown in the following table were blended in the proportions (unit: parts by mass) shown in the table.
Specifically, first, among the components shown in the following table, components other than sulfur, a vulcanization accelerator, an isocyanuric acid derivative and / or a carboxylic acid derivative are mixed for 5 minutes using a 1.7 liter closed Banbury mixer. When the temperature reached 150 ± 5 ° C., it was released and cooled to room temperature to obtain a master batch. Furthermore, using the Banbury mixer, sulfur, a vulcanization accelerator, an isocyanuric acid derivative and / or a carboxylic acid derivative were mixed with the obtained master batch to produce a rubber composition.

<Manufacture of vulcanized rubber sheet>
The rubber composition produced as described above was press-vulcanized at 148 ° C. for 30 minutes in a 15 cm long × 15 cm wide × 0.2 cm thick mold to produce a vulcanized rubber sheet.

<Manufacture of pneumatic tires for heavy-duty vehicles>
The rubber composition produced as described above was used for a cap tread, and a known tire and other conditions were adopted for other tire parts to produce a heavy duty vehicle pneumatic tire (295 / 80R22.5).

<Evaluation>
The following evaluation was performed using the vulcanized rubber sheet or rubber composition produced as described above. The results are shown in the table below. In the same table, the evaluation results other than the hardness are displayed as an index with the result of Standard Example 1 being 100.
Hardness: Measured under the condition of 20 ° C. according to JIS K 6253.
・ Abrasion resistance: Pneumatic tires for heavy-duty vehicles manufactured as described above are assembled to a rim of size 22.5 × 8.25, mounted on the front shaft of the tractor head, and per tire under conditions of air pressure 900 kPa The vehicle was allowed to travel 50,000 km under a load of 3650 kg. The remaining groove at that time was measured, and a value of “groove depth at new article−remaining groove after running” was obtained. It means that it is excellent in abrasion resistance, so that an index | exponent is large.
Uneven wear resistance: Pneumatic tires for heavy-duty vehicles manufactured as described above are assembled on a rim of size 22.5 x 8.25, mounted on the front shaft of the tractor head, and one tire under conditions of air pressure 900 kPa The vehicle was run for 50,000 km under a load of 3650 kg per hit. The inflated profile after running is compared with the new inflated profile, and the amount of uneven wear is determined from the value of “amount of wear at the end of the shoulder in the tire width direction−the amount of wear at the shoulder adjacent to the main groove”. The amount of shoulder wear at the shoulder was measured. It means that it is excellent in uneven wear resistance, so that an index | exponent is large.
Exothermicity: 11R22.5 size tires using each rubber composition as a cap tread were prepared. Using a drum tester with a drum diameter of 1707mm, mounted on a 22.5X7.5 rim, measured the resistance force of this pneumatic tire under the conditions of air pressure 900kPa, load 33.8kN, speed 80km / h, and rolled this It was resistance. A smaller index indicates lower rolling resistance (lower heat generation).
Heat aging resistance (index of decrease in elongation at break after heat aging): A rubber composition produced as described above was pressure vulcanized at 160 ° C. for 60 minutes, and a 2 mm thick sheet in accordance with JIS K6251. A dumbbell-shaped No. 3 test piece is punched from the sheet, further subjected to air heat aging treatment under conditions of 80 ° C. and 168 hours, and measured elongation at break before and after the treatment. The amount of decrease in elongation at break later was determined.
Reduction in elongation at break after heat aging (%) = [(break elongation before treatment−break elongation after treatment) / (break elongation before treatment)] × 100
It shows with the index | exponent which made the standard example 1 the reference | standard (100), and shows that it is excellent in heat aging resistance (maintenance of the elongation at break after heat aging), so that this index | exponent is small.

The detail of each component shown by the said table | surface is as follows.
NR: natural rubber, RSS # 1
BR: Nippon Synthetic Rubber Co., Ltd., BR01, cis 1,4 structure 97%, weight average molecular weight 500,000
CB (ISAF): carbon black, grade ISAF, Shiyo Black N234 manufactured by Cabot Japan, nitrogen adsorption specific surface area 123 m ² / g
CB (FEF): carbon black, grade FEF, manufactured by Nippon Kayaku Co., Ltd., trade name N550, nitrogen adsorption specific surface area 38 m ² / g
・ Stearic acid: NOF Corporation, “Stearic acid YR”
・ Sulfur: Made by Karuizawa Refinery, “Oil treatment sulfur”
・ Vulcanization accelerator: “Noxeller NS” manufactured by Ouchi Shinsei Chemical Industry

Isocyanur compound 1 (allyl group): triallyl isocyanurate represented by the following formula, TAIC (allyl group) manufactured by Nippon Kasei Co., Ltd.

Isocyanur compound 2: Tris-[(3-mercaptopropionyloxy) -ethyl] -isocyanurate represented by the following formula, SC Organic Chemicals Corporation TEMPIC (SH = 3), MW 525.62

Propionate 1: Trimethylolpropane tris (3-mercaptopropionate) represented by the following formula, TMMP (SH = 3) manufactured by SC Organic Chemical Co., MW 398.50

In the above table, since Standard Example 1 contains sulfur, the rubber cross-linking is due to sulfide bonds including polysulfide bonds.
As is clear from the results shown in the table, Comparative Example 1 in which the amount of carbon black exceeds 60 parts by mass with respect to 100 parts by mass of the diene rubber was lower in heat generation and heat aging resistance than in Standard Example 1. In Comparative Example 2 in which the nitrogen adsorption specific surface area of carbon black was less than 90 m ³ / g, the wear resistance, uneven wear resistance, and heat aging resistance were lower than in Standard Example 1. Comparative Example 3 which did not use a specific isocyanuric acid derivative or carboxylic acid derivative and simply increased the amount of sulfur was inferior in heat aging resistance to that of Standard Example 1. Comparative Example 4 using the isocyanuric compound 1 having an allyl group instead of using a specific isocyanuric acid derivative or carboxylic acid derivative was inferior in hardness, wear resistance, and uneven wear resistance to the standard example 1.
On the other hand, Examples 1 to 3 can achieve both excellent wear resistance and uneven wear resistance and excellent low heat build-up compared to Standard Example 1, and heat aging while maintaining high hardness. Excellent in properties.

1 Bead part 2 Side tread (side wall part)
3 Cap tread 4 Carcass layer 5 Bead core 6 Bead filler 7 Belt layer 8 Belt cushion 9 Inner liner 10 Thai rubber

Claims (6)

For 100 parts by mass of diene rubber containing natural rubber,
0.1 to 10 parts by mass of an isocyanuric acid derivative represented by the following formula (1) and / or a carboxylic acid derivative represented by the following formula (2);
Including 40 to 60 parts by mass of carbon black having a nitrogen adsorption specific surface area of 90 to 150 m ² / g,
A rubber composition for a cap tread of a heavy-duty vehicle tire, wherein the amount of the natural rubber is 40 to 100 parts by mass in 100 parts by mass of the diene rubber.
[In the formula (1), R ¹ , R ² and R ³ are each independently —C _a H _2a OC (═O) C _b H _2b SH, and a and b are each independently an integer of 1 or more. , R ¹ , R ² and R ³ may be the same or different. ]

Wherein ^{(2), R 4, R} 5, R 6 are each independently _{-OC (= O) C n H} 2n SH, R 7 is an A alkyl group or a hydrogen atom, n represents each independently It is an integer of 2 or more, and —OC (═O) C _n H _2n SH may be the same or different. ]   The rubber composition according to claim 1, wherein the isocyanuric acid derivative or the carboxylic acid derivative has a molecular weight of 1,000 or less.   The rubber composition according to claim 1 or 2, wherein n is 2 in the formula (2).   The rubber composition according to any one of claims 1 to 3, wherein the diene rubber further contains a butadiene rubber.   The rubber composition according to any one of claims 1 to 4, further comprising a filler (excluding the carbon black).   A pneumatic tire for a heavy-duty vehicle, comprising a cap tread formed using the rubber composition according to claim 1.