JP5657927B2 - Sidewall rubber composition and pneumatic tire - Google Patents

Description

The present invention relates to a rubber composition for a sidewall and a pneumatic tire using the same.

Conventionally, the fuel consumption of automobiles has been reduced by reducing the rolling resistance of tires (improving rolling resistance characteristics). For example, a tire tread has a two-layer structure (an inner surface layer (base tread) and a surface layer (cap tread)), and a rubber composition having excellent low heat generation is used for the base tread. However, in recent years, the demand for lower fuel consumption has become stronger, and not only treads with a high occupation ratio in tires but also more excellent low heat generation are required not only for treads (for example, sidewalls). Yes.

In the rubber composition for the sidewall, unlike the rubber composition for the cap tread, carbon black having a large particle diameter has been conventionally used. Even if the carbon black is changed to silica, the effect of improving the low heat generation is so large. Absent. In addition, when silica is blended, it also has the disadvantage that the flex crack resistance required for the sidewall is inferior. Therefore, there is a demand for a rubber composition that can achieve both low exothermic properties and bending crack resistance at a high level. Further, if the blending amount of the filler is reduced for improving the low heat buildup, the strength is lowered and the breaking strength is deteriorated.

Patent Document 1 discloses a tire rubber composition in which a reversion inhibitor is blended with isoprene-based rubber to reduce rolling resistance and improve wear resistance. However, there is room for improvement in improving the balance between rubber strength and rolling resistance.

JP 2006-45471 A

The present invention solves the above-mentioned problems, and can improve fuel economy and flex crack resistance in a high level in a well-balanced manner, and can secure a steering stability and breaking strength, and a rubber composition for the sidewall It is an object of the present invention to provide a pneumatic tire using an object as a tire sidewall.

（式（１）中、Ｒ^１、Ｒ^２及びＲ^３は、同一若しくは異なって、分岐若しくは非分岐のアルキル基、分岐若しくは非分岐のアルコキシ基、分岐若しくは非分岐のシリルオキシ基、分岐若しくは非分岐のアセタール基、カルボキシル基、メルカプト基又はこれらの誘導体を表す。Ｒ^４及びＲ^５は、同一若しくは異なって、水素原子又は分岐若しくは非分岐のアルキル基を表す。ｎは整数を表す。）
Ｒ^６−Ｓ−Ｓ−Ａ−Ｓ−Ｓ−Ｒ^７ （２）
（式（２）において、Ａは分岐若しくは非分岐の炭素数２〜１０のアルキレン基、Ｒ^６及びＲ^７は、同一若しくは異なって、チッ素原子を含む１価の有機基を表す。） The present invention relates to a rubber composition for a sidewall comprising a rubber component containing a butadiene rubber modified with a compound represented by the following formula (1), silica, sulfur, and a compound represented by the following formula (2). Related to things.

(In formula (1), R ¹ , R ² and R ³ are the same or different and are branched or unbranched alkyl groups, branched or unbranched alkoxy groups, branched or unbranched silyloxy groups, branched or unbranched. R ⁴ and R ⁵ are the same or different and each represents a hydrogen atom or a branched or unbranched alkyl group, and n represents an integer.
R ⁶ —S—S—A—S—S—R ⁷ (2)
(In Formula (2), A represents a branched or unbranched alkylene group having 2 to 10 carbon atoms, and R ⁶ and R ⁷ are the same or different and represent a monovalent organic group containing a nitrogen atom.)

The sidewall rubber composition preferably contains 0.2 to 20 parts by mass of the compound represented by the above formula (2) with respect to 100 parts by mass of the rubber component.

The rubber component preferably contains isoprene-based rubber.

The present invention also relates to a pneumatic tire having a sidewall produced using the rubber composition.

According to the present invention, for a sidewall comprising a rubber component containing a butadiene rubber modified with a compound represented by the above formula (1), silica, sulfur, and a compound represented by the above formula (2). Since it is a rubber composition, fuel economy and bending crack resistance can be improved in a well-balanced manner, and steering stability and breaking strength can be secured. Moreover, since the bending crack resistance after heat deterioration can also be improved, it is excellent also in durability. Therefore, by using the rubber composition for the tire sidewall, the pneumatic tire is excellent in balance between low fuel consumption and bending crack resistance, ensuring driving stability and breaking strength, and having excellent durability. Can be provided.

The rubber composition for a sidewall of the present invention includes a rubber component containing a butadiene rubber modified with a compound represented by the above formula (1), silica, sulfur, and a compound represented by the above formula (2). including.

When carbon black is replaced with silica, although low fuel consumption can be improved, resistance to flex crack growth, fracture strength, and steering stability are reduced. Further, by replacing carbon black with silica and blending butadiene rubber modified with the compound represented by the above formula (1), the fracture strength and steering stability resulting from the replacement of carbon black with silica are improved. Although the decrease can be suppressed, the bending crack growth resistance is decreased. Therefore, in the present invention, carbon black is substituted with silica, and sulfur and a compound represented by the above formula (2) are blended together with a butadiene rubber modified with the compound represented by the above formula (1). Thus, the reduction in fracture strength and steering stability resulting from the replacement of carbon black with silica is suppressed, and the improvement in fuel efficiency is achieved by butadiene rubber modified with silica and the compound represented by the above formula (1). The bending crack growth resistance can be improved while maintaining the effect. This is because, by cross-linking rubber molecules with the compound represented by the above formula (2), (a) the cross-linking strength is improved over the conventional cross-linking by sulfide bond (sulfur cross-linking), (b) cross-linking It is presumed that the flexibility of the rubber molecular chain was improved by the longer chain (high molecular weight). In addition, since the bonding strength of the cross-linking is improved compared to the conventional cross-linking by sulfide bond (sulfur cross-linking), it is difficult to break the bond due to heat, the resistance to bending cracking after heat deterioration can be improved, and it is presumed to be excellent in durability. .

In the present invention, the rubber component includes butadiene rubber (modified butadiene rubber (modified BR)) whose terminal is modified with a compound represented by the following formula (1). By including the modified BR, the movement of the polymer terminal in the rubber can be suppressed, and further, the dispersibility of the silica can be improved, so that both low fuel consumption and flex crack resistance can be achieved. Moreover, breaking strength and handling stability can be improved.

R ¹ , R ² and R ³ in the above formula (1) are the same or different and each represents a branched or unbranched alkyl group, a branched or unbranched alkoxy group, a branched or unbranched silyloxy group, a branched or unbranched group. An acetal group, a carboxyl group (—COOH), a mercapto group (—SH) or a derivative thereof is represented. Examples of the branched or unbranched alkyl group include alkyl groups having 1 to 4 carbon atoms such as methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, and t-butyl group. . Examples of the branched or unbranched alkoxy group include an alkoxy group having 1 to 8 carbon atoms such as a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, an n-butoxy group, and a t-butoxy group (preferably C1-C6, More preferably, C1-C4) etc. are mentioned. The alkoxy group includes a cycloalkoxy group (cycloalkoxy group having 5 to 8 carbon atoms such as cyclohexyloxy group) and an aryloxy group (aryloxy group having 6 to 8 carbon atoms such as phenoxy group and benzyloxy group). ) Is also included.

Examples of the branched or unbranched silyloxy group include a silyloxy group substituted with an aliphatic group having 1 to 20 carbon atoms and an aromatic group (trimethylsilyloxy group, triethylsilyloxy group, triisopropylsilyloxy group, diethylisopropylsilyl group). Oxy group, t-butyldimethylsilyloxy group, t-butyldiphenylsilyloxy group, tribenzylsilyloxy group, triphenylsilyloxy group, tri-p-xylylsilyloxy group, and the like.

Examples of the branched or unbranched acetal group include groups represented by -C (RR ')-OR "and -O-C (RR')-OR". Examples of the former include a methoxymethyl group, an ethoxymethyl group, a propoxymethyl group, a butoxymethyl group, an isopropoxymethyl group, a t-butoxymethyl group, and a neopentyloxymethyl group. The latter includes a methoxymethoxy group, an ethoxy group, and the like. Methoxy group, propoxymethoxy group, i-propoxymethoxy group, n-butoxymethoxy group, t-butoxymethoxy group, n-pentyloxymethoxy group, n-hexyloxymethoxy group, cyclopentyloxymethoxy group, cyclohexyloxymethoxy group, etc. Can be mentioned. R ¹ , R ² and R ³ are preferably alkoxy groups, and more preferably methoxy groups. Thereby, both low fuel consumption and bending crack resistance can be achieved.

Examples of the branched or unbranched alkyl group of R ⁴ and R ^{5 in} the formula (1) include the same groups as the branched or unbranched alkyl group. R ⁴ and R ⁵ are preferably branched or unbranched alkyl groups (preferably having 1 to 3 carbon atoms, more preferably 1 to 2 carbon atoms), and more preferably ethyl groups. Thereby, both low fuel consumption and bending crack resistance can be achieved.

As n (integer) of said Formula (1), 1-5 are preferable. Thereby, both low fuel consumption and bending crack resistance can be achieved. Furthermore, n is more preferably 2 to 4, and most preferably 3. If n is 0, the denaturation reaction may be inhibited, and if n is 6 or more, the effect as a denaturing agent is reduced.

Specific examples of the compound represented by the above formula (1) include 3-aminopropyldimethylmethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylethyldimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, Aminopropyldimethylethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyldimethylbutoxysilane, 3-aminopropylmethyldibutoxysilane, dimethylaminomethyltrimethoxysilane, 2-dimethyl Aminoethyltrimethoxysilane, 3-dimethylaminopropyltrimethoxysilane, 4-dimethylaminobutyltrimethoxysilane, dimethylaminomethyldimethoxymethylsilane, 2-dimethylaminoethyldimethoxy Methylsilane, 3-dimethylaminopropyldimethoxymethylsilane, 4-dimethylaminobutyldimethoxymethylsilane, dimethylaminomethyltriethoxysilane, 2-dimethylaminoethyltriethoxysilane, 3-dimethylaminopropyltriethoxysilane, 4-dimethylaminobutyl Triethoxysilane, dimethylaminomethyldiethoxymethylsilane, 2-dimethylaminoethyldiethoxymethylsilane, 3-dimethylaminopropyldiethoxymethylsilane, 4-dimethylaminobutyldiethoxymethylsilane, diethylaminomethyltrimethoxysilane, 2- Diethylaminoethyltrimethoxysilane, 3-diethylaminopropyltrimethoxysilane, 4-diethylaminobutyltrimethoxysilane, diethylamino Tildimethoxymethylsilane, 2-diethylaminoethyldimethoxymethylsilane, 3-diethylaminopropyldimethoxymethylsilane, 4-diethylaminobutyldimethoxymethylsilane, diethylaminomethyltriethoxysilane, 2-diethylaminoethyltriethoxysilane, 3-diethylaminopropyltriethoxysilane 4-diethylaminobutyltriethoxysilane, diethylaminomethyldiethoxymethylsilane, 2-diethylaminoethyldiethoxymethylsilane, 3-diethylaminopropyldiethoxymethylsilane, 4-diethylaminobutyldiethoxymethylsilane, and the like. These may be used alone or in combination of two or more.

The vinyl content of the modified BR is preferably 35% by mass or less, more preferably 25% by mass or less, and still more preferably 20% by mass or less. When the vinyl content exceeds 35% by mass, the low exothermic property tends to be impaired. The lower limit of the vinyl content is not particularly limited.
The vinyl content (1,2-bond butadiene unit amount) can be measured by infrared absorption spectrum analysis.

Examples of the modification method of butadiene rubber with the compound (modifier) represented by the above formula (1) include conventionally known methods such as methods described in JP-B-6-53768 and JP-B-6-57767. Techniques can be used. For example, the butadiene rubber may be brought into contact with the modifying agent, the butadiene rubber is polymerized, and a predetermined amount of the modifying agent is added to the polymer rubber solution, and the modifying agent is added to the butadiene rubber solution and reacted. Methods and the like.

The butadiene rubber (BR) to be modified is not particularly limited. For example, BR1220 manufactured by Nippon Zeon Co., Ltd., BR130B manufactured by Ube Industries, Ltd., BR150B and other high cis content BR, Ube Industries, Ltd. BR containing a syndiotactic polybutadiene crystal such as VCR412 and VCR617 manufactured by the same company can be used.

The content of the modified BR in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 30% by mass or more. If it is less than 5% by mass, the effect of improving fuel economy may not be obtained as expected. The content of the modified butadiene rubber is preferably 70% by mass or less, more preferably 60% by mass or less, and still more preferably 50% by mass or less. If it exceeds 70% by mass, sufficient fracture strength cannot be obtained, and processability tends to deteriorate.

The rubber component that can be used in the present invention other than the modified BR is not particularly limited, and isoprene-based rubber, butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), chloroprene rubber (CR), Examples thereof include diene rubbers such as acrylonitrile butadiene rubber (NBR) and butyl rubber (IIR). Diene rubbers may be used alone or in combination of two or more. Among these, it is preferable to use a combination of isoprene-based rubber, BR and modified BR, a combination of isoprene-based rubber and modified BR, because the fracture strength and bending crack resistance can be secured, and a combination of isoprene-based rubber and modified BR. Is more preferable.

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. Among isoprene-based rubbers, NR is preferable because the fracture strength and bending crack resistance can be secured in a well-balanced manner.

The content of isoprene-based rubber is preferably 20% by mass or more, more preferably 40% by mass or more, and still more preferably 50% by mass or more, in 100% by mass of the rubber component. If it is less than 20% by mass, sufficient fracture strength and low heat build-up may not be ensured. The content of isoprene-based rubber is preferably 80% by mass or less, and more preferably 70% by mass or less. If it exceeds 80% by mass, the ratio of other polymers (modified BR, BR, etc.) may decrease, and a sufficient low heat generation effect may not be obtained.

The total content of isoprene-based rubber and modified BR in 100% by mass of the rubber component is preferably 80% by mass or more, more preferably 90% by mass or more, and further preferably 100% by mass. If it is less than 80% by mass, the fuel economy and flex crack resistance may not be improved in a well-balanced manner, and steering stability and fracture strength may not be ensured.

As BR (non-modified), the same BR as the above-mentioned modified BR can be used.

The content of BR (non-modified) in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 15% by mass or more. If it is less than 5% by mass, sufficient low heat build-up may not be ensured. The BR (non-modified) content is preferably 80% by mass or less, more preferably 60% by mass or less. If it exceeds 80% by mass, the ratio of other polymers (modified BR, NR, etc.) decreases, and there is a possibility that sufficient fracture strength cannot be obtained.

In the present invention, silica is used. By blending silica with the modified BR, good low heat buildup and high rubber strength can be obtained, and both low fuel consumption and breaking strength can be achieved. The silica is not particularly limited, and examples thereof include dry process silica (anhydrous silicic acid), wet process silica (hydrous silicic acid), and the like, but wet process silica is preferable because of its large number of silanol groups.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 40 m ² / g or more, more preferably 75 m ² / g or more, and still more preferably 100 m ² / g or more. If it is less than 40 m < ² > / g, there exists a tendency for the fracture strength after vulcanization to fall. The _N 2 SA of the silica is preferably 220 m ² / g or less, more preferably ^{150m 2 / g, 125m 2 /} g or less is more preferable. If it exceeds 220 m ² / g, the low heat build-up and kneading workability tend to be reduced.
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 10 parts by mass or more, more preferably 20 parts by mass or more, and further preferably 30 parts by mass or more with respect to 100 parts by mass of the rubber component. When the amount is less than 10 parts by mass, there is a tendency that a sufficient effect due to silica blending cannot be obtained. The content of the silica is preferably 150 parts by mass or less, more preferably 100 parts by mass or less, and still more preferably 75 parts by mass or less. When the amount exceeds 150 parts by mass, it is difficult to disperse silica in rubber, and the processability of rubber tends to deteriorate.
In the present invention, it is not necessary to reduce the blending amount of the filler (silica) in order to improve fuel economy (because the silica content can be the above amount), the strength is reduced and the breaking strength is deteriorated. Can be prevented.

In the rubber composition of the present invention, it is preferable to further contain a silane coupling agent. By blending a silane coupling agent, reduction in rolling resistance (improvement in fuel efficiency) and improvement in workability can be achieved at the same time. As the silane coupling agent, a conventionally known silane coupling agent can be used. For example, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) tetrasulfide, 3-trimethoxy Sulfide systems such as silylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropylbenzothiazolyl tetrasulfide, 3-trimethoxysilylpropyl methacrylate monosulfide; 3-mercaptopropyltrimethoxysilane, 3- Mercapto type such as mercaptopropyltriethoxysilane; Vinyl type such as vinyltriethoxysilane and vinyltrimethoxysilane; 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, -Amino compounds such as (2-aminoethyl) aminopropyltriethoxysilane and 3- (2-aminoethyl) aminopropyltrimethoxysilane; γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane , Glycidoxy systems such as γ-glycidoxypropylmethyldiethoxysilane and γ-glycidoxypropylmethyldimethoxysilane; nitro systems such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; 3-chloropropyl And chloro-based compounds such as trimethoxysilane, 3-chloropropyltriethoxysilane, 2-chloroethyltrimethoxysilane, and 2-chloroethyltriethoxysilane. Of these, bis (3-triethoxysilylpropyl) tetrasulfide and bis (3-triethoxysilylpropyl) disulfide are preferred from the viewpoint of good processability. These silane coupling agents may be used alone or in combination of two or more.

The content of the silane coupling agent is preferably 2 parts by mass or more, more preferably 6 parts by mass or more, and still more preferably 8 parts by mass or more with respect to 100 parts by mass of silica. If it is less than 2 parts by mass, the rolling resistance reduction effect (improvement of fuel efficiency) may not be sufficiently obtained. The content is preferably 20 parts by mass or less, more preferably 15 parts by mass or less. When it exceeds 20 parts by mass, there is a possibility that the rolling resistance reduction effect (improvement of fuel efficiency) corresponding to the amount of the expensive silane coupling agent blended cannot be obtained.

In the present invention, sulfur is used. Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur. For example, oil-treated insoluble sulfur is preferably used.

The sulfur content is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and still more preferably 0.5 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 0.1 parts by mass, the rubber strength tends to deteriorate. The sulfur content is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, still more preferably 5.0 parts by mass or less, and particularly preferably 1.0 part by mass or less. When it exceeds 20 parts by mass, the elongation at break and the resistance to flex crack growth of rubber tend to deteriorate. When the sulfur content is 1.0 part by mass or less, the effect of improving the flex crack growth resistance by the compound represented by the following formula (2) is particularly high.

In the present invention, a compound (crosslinking agent) represented by the following formula (2) is used. By compounding the compound represented by the following formula (2), the rubber composition can have a CC bond having high binding energy and high thermal stability. Therefore, the reduction in fracture strength and steering stability due to the replacement of carbon black with silica is suppressed, and the improvement in fuel efficiency is achieved by butadiene rubber modified with silica and the compound represented by the above formula (1). The bending crack growth resistance can be improved while maintaining the effect.
R ⁶ —S—S—A—S—S—R ⁷ (2)
(In Formula (2), A represents a branched or unbranched alkylene group having 2 to 10 carbon atoms, and R ⁶ and R ⁷ are the same or different and represent a monovalent organic group containing a nitrogen atom.)
The alkylene group for A is preferably an unbranched alkylene group.

2-10 are preferable and, as for carbon number of an alkylene group, 4-8 are more preferable. When the carbon number of the alkylene group is 1, thermal stability is poor, and there is a tendency that the effect of having the alkylene group is not obtained. When the alkylene group has 11 or more carbon atoms, —S—S—A—S There is a tendency that formation of a crosslinked chain represented by -S- becomes difficult.

Examples of the alkylene group satisfying the above conditions include ethylene group, trimethylene group, tetramethylene group, pentamethylene group, hexamethylene group, heptamethylene group, octamethylene group, decamethylene group and the like. Among these, a hexamethylene group is preferred because a cross-link represented by -S-S-ASS- is formed smoothly between the polymers and is thermally stable.

R ⁶ and R ⁷ are not particularly limited as long as they are monovalent organic groups containing a nitrogen atom, and those containing at least one aromatic ring are preferred, and N—C (= Those containing a linking group represented by S)-are more preferred.

R ⁶ and R ⁷ may be the same or different from each other, but are preferably the same for reasons such as ease of production.

Examples of the compound satisfying the above conditions include 1,2-bis (N, N′-dibenzylthiocarbamoyldithio) ethane, 1,3-bis (N, N′-dibenzylthiocarbamoyldithio) propane, 1, 4-bis (N, N′-dibenzylthiocarbamoyldithio) butane, 1,5-bis (N, N′-dibenzylthiocarbamoyldithio) pentane, 1,6-bis (N, N′-dibenzylthio) Carbamoyldithio) hexane, 1,7-bis (N, N′-dibenzylthiocarbamoyldithio) heptane, 1,8-bis (N, N′-dibenzylthiocarbamoyldithio) octane, 1,9-bis (N , N′-dibenzylthiocarbamoyldithio) nonane, 1,10-bis (N, N′-dibenzylthiocarbamoyldithio) decane and the like. Among these, 1,6-bis (N, N′-dibenzylthiocarbamoyldithio) hexane is preferable because it is thermally stable and has excellent polarizability.

The content of the compound represented by the formula (2) is preferably 0.2 parts by mass or more, more preferably 0.3 parts by mass or more, further preferably 0.4 parts by mass with respect to 100 parts by mass of the rubber component. That's it. If the amount is less than 0.2 parts by mass, the effect of improving the bending crack resistance may not be observed. Content of the compound represented by Formula (2) becomes like this. Preferably it is 20 mass parts or less, More preferably, it is 15 mass parts or less, More preferably, it is 10 mass parts or less, Most preferably, it is 5 mass parts or less. If it exceeds 20 parts by mass, the rubber strength (breaking strength), steering stability, and bending crack resistance may be deteriorated.

In addition to the above components, the rubber composition of the present invention includes compounding agents generally used in the production of rubber compositions, for example, reinforcing fillers such as carbon black and clay, zinc oxide, stearic acid, various anti-aging agents. Agents, softeners such as oil, waxes, vulcanization accelerators and the like can be appropriately blended.

As the oil, for example, process oil, vegetable oil or fat, or a mixture thereof may be used. Examples of the process oil include paraffinic process oil, naphthenic process oil, and aromatic process oil (aromatic oil). Vegetable oils include castor oil, cottonseed oil, sesame oil, rapeseed oil, soybean oil, palm oil, palm oil, peanut oil, rosin, pine oil, pineapple, tall oil, corn oil, rice bran oil, beet flower oil, sesame oil, Examples include olive oil, sunflower oil, palm kernel oil, cocoon oil, jojoba oil, macadamia nut oil, safflower oil, and tung oil. Of these, aromatic process oils are preferred because of their good compatibility with the rubber component.

The oil content is preferably 2 parts by mass or more, more preferably 5 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 2 parts by mass, the workability may be deteriorated. The oil content is preferably 25 parts by mass or less, more preferably 20 parts by mass or less, and still more preferably 15 parts by mass or less. When the amount exceeds 25 parts by mass, the rubber becomes too soft, the filler dispersion is deteriorated, and there is a risk that the fuel efficiency, the flex crack resistance, the steering stability, and the breaking strength are lowered.

Examples of the vulcanization accelerator include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N, N′-dicyclohexyl-2- Examples include benzothiazolylsulfenamide (DZ), mercaptobenzothiazole (MBT), dibenzothiazolyl disulfide (MBTS), and diphenylguanidine (DPG). Among them, sulfenamide-based vulcanization accelerators such as TBBS, CBS, and DZ are excellent because of their excellent vulcanization characteristics, excellent physical properties of rubber after vulcanization, excellent low heat build-up, and great effect of improving fracture strength. Are preferred, and CBS is more preferred.

As a method for producing the rubber composition of the present invention, a known method can be used. For example, the above components are kneaded using a rubber kneader such as an open roll or a Banbury mixer, and then vulcanized. Can be manufactured.

The rubber composition of the present invention can be suitably used for tire sidewalls.

The pneumatic tire of the present invention is produced by a usual method using the rubber composition. That is, a rubber composition containing various additives as required is extruded according to the shape of the sidewall of the tire at an unvulcanized stage, and molded by a normal method on a tire molding machine, After bonding together with other tire members to form an unvulcanized tire, the tire can be manufactured by heating and pressing in a vulcanizer.

The tire of the present invention is suitably used as a passenger car tire, bus tire, truck tire, and the like.

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.
NR: RSS # 3
BR1: BR130B manufactured by Ube Industries, Ltd. (cis content: 96% by mass)
BR2: Modified butadiene rubber (modified BR) manufactured by Sumitomo Chemical Co., Ltd. (vinyl content: 15% by mass, R ¹ , R ² and R ^{3 of} the above formula (1) = — OCH ₃ , R ⁴ and R ⁵ = − CH ₂ CH ₃ , modified by n = 3 compound)
Carbon black: Diamond black N550 manufactured by Mitsubishi Chemical Corporation (N ₂ SA: 42 m ² / g)
Silica: Zeosil 1115MP manufactured by Rhodia (nitrogen adsorption specific surface area (N ₂ SA): 115 m ² / g)
Silane coupling agent: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by Degussa
Process oil: Process X-140 (aromatic process oil) manufactured by Japan Energy
Wax: Sanno Wax N manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Anti-aging agent: Antigen 6C (N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd.
Stearic acid: Zinc oxide manufactured by NOF Corporation: Zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: Powdered sulfur vulcanization accelerator manufactured by Karuizawa Sulfur Co., Ltd. CZ: Ouchi Shinsei Chemical Co., Ltd. Noxeller CZ (N-cyclohexyl-2-benzothiazolylsulfenamide)
KA9188: Vulcuren KA9188 (1,6-bis (N, N′-dibenzylthiocarbamoyldithio) hexane) manufactured by Bayer

Examples 1-4 and Comparative Examples 1-3
In accordance with the formulation shown in Table 1, materials other than sulfur, a vulcanization accelerator, and KA9188 were kneaded for 3 minutes at 150 ° C. using a 1.7 L Banbury mixer to obtain a kneaded product. Next, sulfur, a vulcanization accelerator, and KA9188 were added to the obtained kneaded material, and kneaded for 5 minutes under a condition of 50 ° C. using an open roll, to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was press vulcanized at 170 ° C. for 12 minutes to obtain a vulcanized rubber composition.
The obtained unvulcanized rubber composition was molded into a sidewall shape, bonded to another tire member, and vulcanized under conditions of 25 kgf for 12 minutes at 170 ° C., so that a test tire (tire size: 195 / 65R15).

The following evaluation was performed about the obtained unvulcanized rubber composition, the vulcanized rubber composition, and the test tire. The results are shown in Table 1.

(Thermal degradation conditions)
The obtained vulcanized rubber composition was thermally deteriorated (aged) for 168 hours in an oven at 80 ° C. The obtained sample was used as a thermally deteriorated sample (flexible crack resistance test sample after heat deterioration).

(1) Mooney viscosity The Mooney viscosity of a predetermined unvulcanized rubber composition was measured at 130 ° C. according to JIS K6300. The measurement results were indexed according to the following calculation formula, with Comparative Example 1 being 100. The larger the index, the lower the viscosity and the easier the processing.
(Mooney viscosity index) = (Mooney viscosity of Comparative Example 1) / (Mooney viscosity of each formulation) × 100

(2) Tan δ of each vulcanized rubber composition using a rolling resistance viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.) at a temperature of 70 ° C., an initial strain of 10%, and a dynamic strain of 2%. The tan δ of Comparative Example 1 was set to 100, and an index was displayed according to the following calculation formula. The larger the index, the better the rolling resistance characteristics (low fuel consumption).
(Rolling resistance index) = (tan δ of Comparative Example 1) / (tan δ of each formulation) × 100

(3) Breaking strength The vulcanized rubber composition was subjected to a tensile test using a No. 3 dumbbell according to JIS K6251, and the breaking strength (TB) was measured as the elongation at break (EB) (%). The numerical value of TB × EB / 2 was taken as the breaking strength. The fracture strength of Comparative Example 1 was taken as 100, and the index was expressed by the following calculation formula. The larger the index, the better the breaking strength.
(Destructive strength index) = (Destructive strength of each formulation) / (Destructive strength of Comparative Example 1) × 100

(4) Steering stability test tires were mounted on all the wheels of a vehicle (domestic FF2000cc), and the vehicle was run on the test course, and the steering stability was evaluated by sensory evaluation of the driver. At that time, relative evaluation was performed with 10 points being the perfect score and the steering stability of Comparative Example 1 being 6 points. The larger the value, the better the steering stability.

(5) (Bending crack resistance)
Using a vulcanized rubber composition, a sample was prepared based on JIS-K-6260 “Vulcanized Rubber and Thermoplastic Rubber—Dematcher Bending Crack Test Method”, a bending crack growth test was conducted, and 70% elongation was 1 million times. After repeatedly bending the sample, the length of the generated crack was measured.
And the measured value (length) of the comparative example 1 was set to 100, and it displayed by the index | exponent by the following formula. The larger the index, the more the crack growth is suppressed and the better the flex crack resistance.
(Bending crack resistance index) = (Measured value of Comparative Example 1) / (Measured value of each formulation) × 100
Moreover, the same test was done using the heat-degraded sample, and the index was expressed by the following formula.
The larger the index is, the more the crack growth is suppressed and the better the resistance to bending cracking (durability) after thermal degradation.
(Bending crack resistance index after thermal degradation) = (Measured value of Comparative Example 1) / (Measured value of each formulation) × 100

Examples including a rubber component containing a butadiene rubber modified with a compound represented by the above formula (1), silica, sulfur, and a compound represented by the above formula (2) have low fuel consumption, Bending crack resistance and resistance to bending cracking (durability) after heat deterioration can be improved in a well-balanced manner, and steering stability and fracture strength can be secured.

On the other hand, the comparative example 1 which mix | blended only carbon black was inferior in the fuel-efficient property, the bending crack resistance, and the bending crack resistance (durability) after heat deterioration compared with the Example. In Comparative Example 2 in which the compound represented by the above formula (1) and the compound represented by the above formula (2) are not blended, fuel efficiency, fracture strength, steering stability, and flex crack resistance compared to the Examples The growth property and resistance to flex cracking (durability) after heat deterioration were inferior. The comparative example 3 which does not mix | blend the compound represented by the said Formula (2) was inferior in the bending crack growth resistance and the bending crack resistance (durability) after heat deterioration compared with the Example.

Claims (4)

A rubber component containing a butadiene rubber modified with a compound represented by the following formula (1);
A silica with a nitrogen adsorption specific surface area of 40 to 125 m ² / g;
Sulfur and
A compound represented by the following formula (2):
The content of the butadiene rubber modified with the compound represented by the formula (1) in 100% by mass of the rubber component is 5% by mass or more,
The content of the silica is 30 to 150 parts by mass, the sulfur content is 0.1 to 20 parts by mass, and the content of the compound represented by the formula (2) is 100 parts by mass of the rubber component. A rubber composition for a sidewall, which is 0.2 to 20 parts by mass.

(In formula (1), R ¹ , R ² and R ³ are the same or different and are branched or unbranched alkyl groups, branched or unbranched alkoxy groups, branched or unbranched silyloxy groups, branched or unbranched. An acetal group, a carboxyl group, a mercapto group, or a derivative thereof, wherein R ⁴ and R ⁵ represent an ethyl group, and n represents an integer.)
R ⁶ —S—S—A—S—S—R ⁷ (2)
(In Formula (2), A represents a branched or unbranched alkylene group having 2 to 10 carbon atoms, and R ⁶ and R ⁷ are the same or different and represent a monovalent organic group containing a nitrogen atom.) The rubber composition for a sidewall according to claim 1, wherein the content of oil is 2 to 25 parts by mass with respect to 100 parts by mass of the rubber component. The rubber composition for a sidewall according to claim 1 or 2, wherein the rubber component contains an isoprene-based rubber. The pneumatic tire which has a side wall produced using the rubber composition in any one of Claims 1-3.