JP2010285512A - Rubber composition for sidewall and tire for truck and bus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for a sidewall which can be suitably used for restraining the deterioration by hardening of rubber, which results in the long life of the resultant tire. <P>SOLUTION: The rubber composition includes a rubber component including by 30 mass% or more of an isoprene rubber, silica and a compound represented by formula (I) and/or formula (II), (wherein R<SP>1</SP>and R<SP>2</SP>may be the same or different, and are each hydrogen, alkyl, aryl or aralkyl). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a rubber composition for a sidewall and a truck / bus tire using the rubber composition.

Conventionally, anti-aging agents have been used in rubber compositions used for sidewalls of tires for trucks and buses in order to increase the heat resistance of the rubber compositions. Anti-aging agents include amines such as N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine (6PPD) and N-phenyl-N′-isopropyl-p-phenylenediamine (IPPD). Anti-aging agents are widely used.

However, in recent years, the demand for improved heat resistance has further increased, and further life extension has been demanded. Although a long life can be achieved by increasing the amount of the anti-aging agent, there is a problem that the surface is browned by the precipitation of 6PPD or IPPD on the tire surface, resulting in poor appearance of the tire. Therefore, it is desired to provide a rubber composition that can improve heat resistance and extend the life without increasing the amount of anti-aging agent.

Patent Document 1 discloses a rubber composition in which N- (1-methylheptyl) -N′-phenyl-p-phenylenediamine as an antiaging agent and a wax are blended with a diene rubber. However, there is still room for improvement in terms of improving heat resistance.

Japanese Patent Laid-Open No. 10-324779

The present invention solves the above-mentioned problems, improves the heat resistance without increasing the amount of anti-aging agent, particularly suppresses the deterioration of rubber curing, and can extend the life of the sidewall rubber composition, and the tire The object is to provide tires for trucks and buses used for sidewalls.

The present invention relates to a rubber composition for a sidewall containing a rubber component containing 30% by mass or more of isoprene-based rubber, silica, and a compound represented by the following formula (I) and / or (II).

（式（Ｉ）、（ＩＩ）において、Ｒ^１及びＲ^２は、同一若しくは異なって、水素原子、アルキル基、アリール基又はアラルキル基を表す。但し、Ｒ^１及びＲ^２が同時に水素原子である場合を除く。）

(In the formula (I), (II), ^{R 1} and ^{R 2} are the same or different and each represents a hydrogen atom, an alkyl group, an aryl group or an aralkyl group. However, ^{R 1} and ^{R 2} is simultaneously hydrogen atom Except in cases.)

The isoprene-based rubber is preferably at least one selected from the group consisting of isoprene rubber, natural rubber and modified natural rubber.

The compound is preferably a compound represented by the following formula (III).

The rubber composition preferably contains 1 to 6 parts by mass of sulfur with respect to 100 parts by mass of the rubber component. Moreover, it is preferable that the said rubber composition contains 1-6 mass parts of zinc oxide with respect to 100 mass parts of said rubber components.

The present invention also relates to a truck / bus tire having a sidewall manufactured using the rubber composition.

According to the present invention, since the rubber component containing a specific amount of isoprene-based rubber contains silica and the compound represented by the above formula (I) and / or (II), the heat resistance can be improved. It is possible to suppress the curing deterioration of rubber. Therefore, the life of the rubber composition can be extended without increasing the amount of the anti-aging agent such as 6PPD, and the rubber composition can be suitably applied to the tire sidewall.

The rubber composition of the present invention contains a rubber component containing isoprene-based rubber, silica, and a compound represented by the above formula (I) and / or (II). By using isoprene-based rubber as a rubber component and further compounding silica and the compounds represented by the above formulas (I) and (II), heat resistance can be improved, and in particular, suppression of deterioration of rubber can be suppressed. Become.

Here, the curing deterioration of rubber is a deterioration phenomenon in which the rubber becomes harder than the initial state when heat is applied under the condition where oxygen is present as a deterioration factor. Can be effectively suppressed. Such curing deterioration suppressing effect is a so-called heat fatigue resistance (preventing blow and chunk generation) and heat sag resistance, and is an effect different from that of isoprene-based rubber, silica, and formulas (I) and (II). It is specifically produced when three components with a compound are used.

Further, when these three components are used, the effect of improving heat resistance (particularly, the effect of suppressing curing deterioration) is generated synergistically. For example, silica and compounds of formulas (I) and (II) are added to styrene butadiene rubber. Compared with the case where is blended, a very large curing deterioration suppressing effect is produced.
Therefore, in the present invention, since the heat resistance (particularly, the effect of suppressing curing deterioration) can be improved without increasing the amount of the anti-aging agent, it can be suitably used for a tire sidewall and the life of the tire can be extended.

In the present invention, isoprene-based rubber is used as the rubber component. In the present invention, the heat resistance (particularly, the effect of suppressing the curing deterioration) can be improved despite using a rubber having an isoprene skeleton. Examples of the isoprene-based rubber include isoprene rubber (IR), natural rubber (NR), and modified natural rubber. NR includes deproteinized natural rubber (DPNR) and high-purity natural rubber (HPNR). Modified natural rubber includes epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), and grafted natural rubber. Etc. Moreover, as NR, what is common in tire industry, such as SIR20, RSS # 3, TSR20, can be used, for example. Moreover, it does not specifically limit as IR, A thing common in the rubber industry can be used.

In the present invention, 100% by mass of the rubber component contains 30% by mass or more of isoprene-based rubber, preferably 35% by mass or more, more preferably 40% by mass or more, and further preferably 45% by mass or more. If it is less than 30% by mass, the effect of suppressing the curing deterioration may not be sufficiently obtained. Further, the content of the isoprene-based rubber is preferably 80% by mass or less, more preferably 70% by mass or less. If it exceeds 80% by mass, the crack resistance tends to be inferior.

In addition to isoprene-based rubber, butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), ethylene propylene diene rubber (EPDM), chloroprene rubber (CR) can be used as rubber components. And acrylonitrile butadiene rubber (NBR). A rubber component may be used independently and may use 2 or more types together. Among these, BR is preferable for the reason of improving crack resistance.

The BR is not particularly limited. For example, BR1220 manufactured by Nippon Zeon Co., Ltd., BR130B manufactured by Ube Industries, Ltd., BR150B having a high cis content such as BR150B, VCR412 manufactured by Ube Industries, Ltd. BR containing syndiotactic polybutadiene crystals can be used.

The content of BR in 100% by mass of the rubber component is preferably 20% by mass or more, more preferably 30% by mass or more, and further preferably 40% by mass or more. There exists a tendency for it to be inferior to crack-proof performance as it is less than 20 mass%. The content of BR in 100% by mass of the rubber component is preferably 70% by mass or less, more preferably 60% by mass or less. When it exceeds 70 mass%, there exists a possibility that the curing deterioration inhibitory effect may not fully be acquired.

In the present invention, silica is used. Thereby, heat resistance (especially hardening deterioration inhibitory effect) can be improved. Examples of the silica include, but are not limited to, dry method silica (anhydrous silicic acid), wet method silica (anhydrous silicic acid), and the like, and wet method silica is preferable because it has many silanol groups. Silica may be used alone or in combination of two or more.

The nitrogen adsorption specific surface area (N ₂ SA) of the silica is preferably 50 m ² / g or more, more preferably 80 m ² / g or more, and still more preferably 100 m ² / g or more. If it is less than 50 m ² / g, the reinforcing property tends to be inferior. Further, N ₂ SA of silica is preferably 200 m ² / g or less, more preferably 150 m ² / g or less, and further preferably 130 m ² / g or less. If it exceeds 200 m ² / g, it may be difficult to ensure dispersibility.
The nitrogen adsorption specific surface area of silica is a value measured by the BET method according to ASTM D3037-81.

The content of silica is preferably 20 parts by mass or more, more preferably 25 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 20 parts by mass, there is a possibility that the curing deterioration suppressing effect cannot be sufficiently obtained. Content of this silica becomes like this. Preferably it is 100 mass parts or less, More preferably, it is 80 mass parts or less, More preferably, it is 60 mass parts or less. If it exceeds 100 parts by mass, it may be difficult to ensure dispersibility.

The rubber composition of the present invention preferably contains a silane coupling agent together with silica.
As the silane coupling agent, any silane coupling agent conventionally used in combination with silica can be used in the rubber industry. For example, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-tri Ethoxysilylethyl) tetrasulfide, bis (4-triethoxysilylbutyl) tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilylethyl) tetrasulfide, bis (4-trimethoxysilyl) Butyl) tetrasulfide, bis (3-triethoxysilylpropyl) trisulfide, bis (2-triethoxysilylethyl) trisulfide, bis (4-triethoxysilylbutyl) trisulfide, bis (3-trimethoxysilylpropyl) Trisulfi Bis (2-trimethoxysilylethyl) trisulfide, bis (4-trimethoxysilylbutyl) trisulfide, bis (3-triethoxysilylpropyl) disulfide, bis (2-triethoxysilylethyl) disulfide, bis (4 -Triethoxysilylbutyl) disulfide, bis (3-trimethoxysilylpropyl) disulfide, bis (2-trimethoxysilylethyl) disulfide, bis (4-trimethoxysilylbutyl) disulfide, 3-trimethoxysilylpropylbenzothiazoli And sulfide systems such as tetratetrasulfide and 3-triethoxysilylpropylbenzothiazole tetrasulfide. Moreover, mercapto type, vinyl type, glycidoxy type, nitro type, chloro type and the like can also be mentioned. Of these, bis (3-triethoxysilylpropyl) tetrasulfide and bis (3-triethoxysilylpropyl) disulfide are preferably used from the viewpoint of the reinforcing effect and processability of the silane coupling agent. These silane coupling agents may be used alone or in combination of two or more.

6 mass parts or more are preferable with respect to 100 mass parts of silica content, as for content of a silane coupling agent, 8 mass parts or more are more preferable, and 12 mass parts or more are still more preferable. If it is less than 6 mass parts, there exists a tendency for a fracture strength to fall large. Further, the content of the silane coupling agent is preferably 25 parts by mass or less, and more preferably 20 parts by mass or less. When the amount exceeds 25 parts by mass, effects such as an increase in fracture strength and a reduction in rolling resistance due to the addition of the silane coupling agent tend not to be obtained.

In the present invention, a compound represented by the following formula (I) and / or (II) is used. The compound is a vulcanization accelerator, but can improve the heat resistance (suppression of curing deterioration) of the vulcanized rubber.

（式（Ｉ）、（ＩＩ）において、Ｒ^１及びＲ^２は、同一若しくは異なって、水素原子、アルキル基、アリール基又はアラルキル基を表す。但し、Ｒ^１及びＲ^２が同時に水素原子である場合を除く（即ち、同一の環に結合しているＲ^１及びＲ^２がともに水素原子である化合物を除く）。）

(In the formulas (I) and (II), R ¹ and R ² are the same or different and each represents a hydrogen atom, an alkyl group, an aryl group, or an aralkyl group, provided that R ¹ and R ² are hydrogen atoms at the same time. Except for the case (that is, excluding compounds in which R ¹ and R ² bonded to the same ring are both hydrogen atoms).

As R ¹ and R ² , the alkyl group preferably has 1 to 10 carbon atoms, the aryl group has 6 to 10 carbon atoms, and the aralkyl group has 7 to 10 carbon atoms. Examples of the alkyl group include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, iso-butyl group, sec-butyl group, tert-butyl group, pentyl group, hexyl group, heptyl group, Examples include 2-ethylhexyl group, octyl group, nonyl group, decyl group and the like. Examples of the aryl group include a phenyl group, a tolyl group, a xylyl group, a biphenyl group, a naphthyl group, an anthryl group, and a phenanthryl group. Examples of the aralkyl group include a benzyl group and a phenethyl group. The hydrocarbon group of R ^{1 to} R ² may be linear, branched or cyclic. Of the alkyl group, aryl group, and aralkyl group, an alkyl group is preferable, and the alkyl group preferably has 1 to 4 carbon atoms, more preferably 1 to 2 carbon atoms. Further, ^{R 1} is an alkyl group, ^{R 2} is preferably a hydrogen atom. In this case, the effect of suppressing curing deterioration can be obtained satisfactorily.

Specific examples of the compound represented by the formula (I) include bis (4-methylbenzothiazolyl-2) -disulfide, bis (4-ethylbenzothiazolyl-2) -disulfide, bis (5- Methylbenzothiazolyl-2) -disulfide, bis (5-ethylbenzothiazolyl-2) -disulfide, bis (6-methylbenzothiazolyl-2) -disulfide, bis (6-ethylbenzothiazolyl) -2) -disulfide, bis (4,5-dimethylbenzothiazolyl-2) -disulfide, bis (4,5-diethylbenzothiazolyl-2) -disulfide, bis (4-phenylbenzothiazolyl-) 2) -disulfide, bis (5-phenylbenzothiazolyl-2) -disulfide, bis (6-phenylbenzothiazolyl-2) -disulfide, etc. That. Specific examples of the compound represented by the above formula (II) include 2-mercapto-4-methylbenzothiazole, 2-mercapto-4-ethylbenzothiazole, 2-mercapto-5-methylbenzothiazole, 2-mercapto- 5-ethylbenzothiazole, 2-mercapto-6-methylbenzothiazole, 2-mercapto-6-ethylbenzothiazole, 2-mercapto-4,5-dimethylbenzothiazole, 2-mercapto-4,5-diethylbenzothiazole, Examples include 2-mercapto-4-phenylbenzothiazole, 2-mercapto-5-phenylbenzothiazole, 2-mercapto-6-phenylbenzothiazole and the like. Of these, bis (4-methylbenzothiazolyl-2) -disulfide, bis (5-methylbenzothiazolyl-2) -disulfide, mercapto-4-methylbenzothiazole, and mercapto-5-methylbenzothiazole are preferable. . In the formulas (I) and (II), the compound represented by the formula (I) is preferably used. Furthermore, among the compounds described above, the compound (4m-MBTS) represented by the formula (III) is particularly preferably used. When using the above compounds, the effect of suppressing curing deterioration can be obtained satisfactorily.

式（Ｉ）、（ＩＩ）で表される化合物は、単独で用いてもよく、２種以上を併用してもよい。該化合物の市販品として、例えば、ＮＯＣＩＬ社の製品を使用することができる。

The compounds represented by the formulas (I) and (II) may be used alone or in combination of two or more. As a commercial product of the compound, for example, a product of NOCIL can be used.

The total content of the compounds represented by the above formulas (I) and (II) is preferably 1.0 part by mass or more, more preferably 1.3 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 1.0 mass part, there exists a possibility that the hardening deterioration inhibitory effect may not fully be acquired. The total content is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less. If it exceeds 5.0 parts by mass, it may be difficult to maintain an appropriate crosslinking density and crosslinking form.

The rubber composition of the present invention preferably contains zinc oxide. When blending zinc oxide, the content of zinc oxide is preferably 1 part by mass or more, more preferably 2 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 1 part by mass, the reinforcing property tends to be inferior. Further, the content of zinc oxide is preferably 6 parts by mass or less, more preferably 5 parts by mass or less. If it exceeds 6 parts by mass, the cost tends to increase.

In addition to the components described above, the rubber composition of the present invention includes compounding agents conventionally used in the rubber industry, for example, inorganic and organic fillers such as carbon black, softeners such as oil, and vulcanization acceleration of stearic acid and the like. Auxiliaries, various anti-aging agents, ozone degradation inhibitors, vulcanizing agents such as wax, sulfur or sulfur compounds, vulcanization accelerators, and the like can be appropriately blended as necessary.

Examples of carbon black that can be used include GPF, FEF, HAF, ISAF, and SAF, but are not particularly limited. By blending carbon black, it is possible to enhance the reinforcement.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 20 m ² / g or more, more preferably 40 m ² / g or more. If it is less than 20 m ² / g, the reinforcing property tends to be inferior. Further, the N ₂ SA of the carbon black is preferably 200 m ² / g or less, more preferably 100 m ² / g or less. When it exceeds 200 m ² / g, crack resistance tends to be inferior.
In addition, the nitrogen adsorption specific surface area of carbon black is calculated | required by A method of JISK6217.

When carbon black is blended, the carbon black content is preferably 10 parts by mass or more, and more preferably 15 parts by mass or more with respect to 100 parts by mass of the rubber component.
If it is less than 10 parts by mass, the reinforcing property tends to be inferior. Further, the carbon black content is preferably 100 parts by mass or less, more preferably 50 parts by mass or less. If it exceeds 100 parts by mass, the dispersibility of the filler may be deteriorated.

In the present invention, an amine-based anti-aging agent is preferably used as an anti-aging agent because of its excellent destructive properties, and heat resistance (especially an effect of inhibiting curing deterioration) can be improved without increasing the amount used. is there. Examples of amine-based antioxidants include diphenylamine-based and p-phenylenediamine-based amine derivatives. Examples of the diphenylamine derivative include p- (p-toluenesulfonylamide) -diphenylamine, octylated diphenylamine, and the like. Examples of p-phenylenediamine derivatives include N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine (6PPD), N-phenyl-N′-isopropyl-p-phenylenediamine (IPPD). ), N, N′-di-2-naphthyl-p-phenylenediamine, and the like.

The content of the amine anti-aging agent is preferably 1 part by mass or more, more preferably 1.5 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 1 part by mass, the fracture characteristics may not be improved. Moreover, this content becomes like this. Preferably it is 6 mass parts or less, More preferably, it is 4 mass parts or less. If it exceeds 6 parts by mass, bloom may be generated on the surface.

In the present invention, sulfur can be suitably used as a vulcanizing agent. Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur.
The sulfur content is preferably 1 part by mass or more and more preferably 1.5 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 1 part by mass, the effect may be small. Moreover, this content becomes like this. Preferably it is 6 mass parts or less, More preferably, it is 5 mass parts or less. If it exceeds 6 parts by mass, the effect of suppressing the curing deterioration may not be sufficiently obtained.

In the present invention, other vulcanization accelerators may be blended together with the compounds represented by the above formulas (I) and (II), and even in this case, the effect of suppressing the curing deterioration can be suitably obtained.
Other vulcanization accelerators include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N, N′-dicyclohexyl- Examples include 2-benzothiazolylsulfenamide (DZ), mercaptobenzothiazole (MBT), dibenzothiazolyl disulfide (MBTS), and diphenylguanidine (DPG). 0.1 to 2.0 parts by mass may be blended.

The rubber composition of the present invention is produced by a general method. That is, it can be produced by a method of kneading the above components with a Banbury mixer, a kneader, an open roll or the like and then vulcanizing.

The rubber composition of the present invention can be suitably used for sidewalls of tires (particularly, truck / bus tires).

The truck / bus tire of the present invention can be produced by a conventional method using the rubber composition. That is, the rubber composition is extruded in accordance with the shape of the sidewall at an unvulcanized stage, molded by a normal method on a tire molding machine, and bonded together with other tire members to form an unvulcanized tire. Form. This unvulcanized tire can be heated and pressurized in a vulcanizer to produce a tire.

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

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
IR: Nippon IR2200 made by Nippon Zeon Co., Ltd.
BR: BR150B manufactured by Ube Industries, Ltd.
Silica: Silica 115Gr (N ₂ SA: 110 m ² / g) manufactured by Rhodia Japan Co., Ltd.
Silane coupling agent: Si266 (bis (3-triethoxysilylpropyl) disulfide) manufactured by Degussa
Carbon black: Dia Black (N ₂ SA: 50 m ² / g) manufactured by Mitsubishi Chemical Corporation
Zinc oxide: 2 types of zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: “Kashiwa” manufactured by NOF Corporation
Anti-aging agent: Anti-aging agent 6C (SANTOFLEX, 6PPD) manufactured by FLEXSYS Corporation
Sulfur: Powder sulfur vulcanization accelerator manufactured by Tsurumi Chemical Co., Ltd. 1: Noxeller NS (N-tert-butyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Vulcanization accelerator 2: Noxeller DM (dibenzothiazolyl disulfide) manufactured by Ouchi Shinsei Chemical Co., Ltd.
Vulcanization accelerator 3: bis (4-methylbenzothiazolyl-2) -disulfide (formula (III)) manufactured by NOCIL
Vulcanization accelerator 4: Soxinol D (diphenylguanidine) manufactured by Sumitomo Chemical Co., Ltd.

Examples 1-3 and Comparative Examples 1-4
According to the contents shown in Table 1, materials other than sulfur and a vulcanization accelerator were kneaded for 5 minutes under a condition of 130 ° C. using a 1.7 L Banbury mixer to obtain a kneaded product. Next, sulfur and a vulcanization accelerator were added to the obtained kneaded product, and kneaded for 3 minutes at 60 ° C. using an open roll to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was press vulcanized with a 0.5 mm thick mold at 170 ° C. for 10 to 20 minutes to obtain a vulcanized rubber composition. The obtained vulcanized rubber composition was used as a new sample.

(Deterioration conditions)
The new sample prepared above was thermally deteriorated in an oven at 100 ° C. for 7 days. The obtained sample was used as a deteriorated sample.

The following evaluation was performed using the obtained new samples and deteriorated samples. Each test result is shown in Table 1. In the table, the value of the deteriorated sample is shown as an index when the new sample is set to 100, and the closer to 100, the less the hardening deterioration is in hardness, swelling, and M100 as compared with the new sample.

<Hardness>
Using the prepared sample, the hardness of the rubber was measured using a hardness meter at a temperature of 25 ° C. in accordance with JIS K6253 (Shore-A measurement). It shows that it is so hard that a numerical value is large.

<Swelling rate>
The immersion test of the prepared sample was performed according to JIS K6258, and the volume of the sample after being immersed in toluene at 40 ° C. for 24 hours and swollen was measured and calculated from the volume change. The smaller the value, the higher the crosslink density.

<Stress at 100% elongation (M100)>
Using a No. 3 dumbbell-shaped test piece made of the prepared sample, a tensile test was performed at a pulling speed of 500 mm / min in accordance with JIS K6251 “vulcanized rubber and thermoplastic rubber—determining tensile properties”. The stress at 100% elongation at 23 ° C. (M100 (MPa)) was measured. Larger numbers indicate higher modulus and hardness. M100 is also an index of crosslink density.

According to Table 1, Examples 1 to 3 in which 4m-MBTS is blended with silica and IR improve the effect of suppressing curing deterioration as compared with Comparative Examples 1 to 3 in which conventional accelerators such as TBBS and MBTS are blended. I was able to. Moreover, in the comparative example 4 which mix | blended 4m-MBTS, without mix | blending IR, the inhibitory effect of hardening deterioration was not fully acquired.

Claims (6)

A rubber composition for a sidewall, comprising a rubber component containing 30% by mass or more of isoprene-based rubber, silica, and a compound represented by the following formula (I) and / or (II).

(In the formula (I), (II), ^{R 1} and ^{R 2} are the same or different and each represents a hydrogen atom, an alkyl group, an aryl group or an aralkyl group. However, ^{R 1} and ^{R 2} is simultaneously hydrogen atom Except in cases.) The rubber composition for a sidewall according to claim 1, wherein the isoprene-based rubber is at least one selected from the group consisting of isoprene rubber, natural rubber and modified natural rubber. The rubber composition for a sidewall according to claim 1 or 2, wherein the compound is a compound represented by the following formula (III).

The rubber composition for a sidewall according to any one of claims 1 to 3, comprising 1 to 6 parts by mass of sulfur with respect to 100 parts by mass of the rubber component. The rubber composition for a sidewall according to any one of claims 1 to 4, comprising 1 to 6 parts by mass of zinc oxide with respect to 100 parts by mass of the rubber component. A truck / bus tire having a sidewall produced using the rubber composition according to claim 1.