JP5503303B2 - 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.

In recent years, there has been an increasing demand for lower fuel consumption of vehicles, and reduction of rolling resistance (improvement of rolling resistance characteristics) is required not only in the tread but also in the sidewall.

As a method for improving rolling resistance characteristics, it is known to replace carbon black as a filler with silica. In this case, however, mechanical strength (breaking strength) is reduced, and cut resistance and separation resistance are reduced. Tended to get worse. Further, as a method for increasing the mechanical strength, a method for reducing the amount of oil is known, but in this case, the workability tends to deteriorate. Therefore, a method for improving rolling resistance characteristics, mechanical strength and workability in a well-balanced manner has been desired.

Patent Documents 1 to 3 propose to reduce rolling resistance using modified diene rubbers such as modified butadiene rubber and modified styrene butadiene rubber. However, there is still room for improvement in terms of improving the rolling resistance characteristics, mechanical strength, and workability in a well-balanced manner.

JP 2001-114939 A JP 2005-126604 A JP 2005-325206 A

The present invention solves the above-mentioned problems, and provides a rubber composition for a sidewall that can improve rolling resistance characteristics, mechanical strength and processability in a well-balanced manner, and a pneumatic tire having a sidewall produced using the rubber composition. With the goal.

（式中、Ｒ^１、Ｒ^２及びＲ^３は、同一若しくは異なって、アルキル基、アルコキシ基、シリルオキシ基、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、アルキル基又は環状エーテル基を表す。ｎは整数を表す。）

（式中、ｘ、ｙはそれぞれ１以上の整数である。Ｒ^６は水素、ハロゲン、分岐若しくは非分岐の炭素数１〜３０のアルキル基若しくはアルキレン基、分岐若しくは非分岐の炭素数２〜３０のアルケニル基若しくはアルケニレン基、分岐若しくは非分岐の炭素数２〜３０のアルキニル基若しくはアルキニレン基、又は該アルキル基若しくは該アルケニル基の末端の水素が水酸基若しくはカルボキシル基で置換されたものを示す。Ｒ^７は水素、分岐若しくは非分岐の炭素数１〜３０のアルキレン基若しくはアルキル基、分岐若しくは非分岐の炭素数２〜３０のアルケニレン基若しくはアルケニル基、又は分岐若しくは非分岐の炭素数２〜３０のアルキニレン基若しくはアルキニル基を示す。Ｒ^６とＲ^７とで環構造を形成してもよい。） The present invention includes a butadiene rubber containing a rubber component, a silane coupling agent and silica, wherein the rubber component is modified with a compound represented by the following formula (1), and the silane coupling agent is represented by the following formula (2): ) And the unit B is copolymerized at a ratio of 1 to 70 mol% with respect to the total amount of the bond unit B represented by the following formula (3). It is related with the rubber composition for side walls whose content of the said silica with respect to a mass part is 15-150 mass parts.

(Wherein R ¹ , R ² and R ³ are the same or different and each represents an alkyl group, an alkoxy group, a silyloxy group, an acetal group, a carboxyl group, a mercapto group or a derivative thereof. R ⁴ and R ⁵ are (The same or different and represents a hydrogen atom, an alkyl group or a cyclic ether group. N represents an integer.)

(Wherein, x and y are each an integer of 1 or more. R ⁶ is hydrogen, halogen, branched or unbranched C 1-30 alkyl group or alkylene group, branched or unbranched C 2-30 Or an alkenyl group or alkenylene group, a branched or unbranched alkynyl group or alkynylene group having 2 to 30 carbon atoms, or a hydrogen atom substituted at the terminal of the alkyl group or the alkenyl group with a hydroxyl group or a carboxyl group. ⁷ represents hydrogen, a branched or unbranched alkylene group or alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenylene group or alkenyl group having 2 to 30 carbon atoms, or a branched or unbranched carbon group having 2 to 30 carbon atoms. R represents an alkynylene group or an alkynyl group, and R ⁶ and R ⁷ may form a ring structure.)

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

According to the present invention, since it is a rubber composition containing a butadiene rubber modified with a specific compound, a specific silane coupling agent, and a predetermined amount of silica, it has rolling resistance characteristics, mechanical strength, and processability. Can be obtained in a balanced manner. Therefore, by using the rubber composition as a sidewall, it is possible to provide a pneumatic tire that is improved in rolling resistance characteristics and mechanical strength in a well-balanced manner and is easy to manufacture.

The rubber composition of the present invention comprises a butadiene rubber modified with a compound represented by the above formula (1) (hereinafter also referred to as “modified BR”), and a silane cup represented by the above formulas (2) and (3). Contains a ring agent and a predetermined amount of silica. Thereby, rolling resistance characteristics, mechanical strength, and workability can be obtained with a good balance.

In the compound represented by the above formula (1), R ¹ , R ² and R ³ are the same or different and are an alkyl group, an alkoxy group, a silyloxy group, an acetal group, a carboxyl group (—COOH), a mercapto group (— SH) or derivatives thereof.

As said alkyl group, C1-C4 alkyl groups, such as a methyl group, an ethyl group, n-propyl group, isopropyl group, n-butyl group, t-butyl group, etc. are mentioned, for example.

Examples of the alkoxy group include an alkoxy group having 1 to 8 carbon atoms (preferably 1 to 6 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. More preferably, C1-C4) etc. are mentioned. Examples of the alkoxy group include a cycloalkoxy group (such as a cycloalkoxy group having 5 to 8 carbon atoms such as a cyclohexyloxy group) and an aryloxy group (an aryloxy group having 6 to 8 carbon atoms such as a phenoxy group and a benzyloxy group). ) Is also included.

Examples of the 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, diethylisopropylsilyloxy group, t- Butyldimethylsilyloxy group, t-butyldiphenylsilyloxy group, tribenzylsilyloxy group, triphenylsilyloxy group, tri-p-xylylsilyloxy group, etc.).

Examples of the 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, mechanical strength and rolling resistance characteristics can be suitably achieved.

In the compound represented by the above formula (1), R ⁴ and R ⁵ are the same or different and each represents a hydrogen atom, an alkyl group or a cyclic ether group.

Examples of the alkyl group for R ⁴ and R ⁵ include the same groups as the above alkyl group.

Examples of the cyclic ether group of R ⁴ and R ⁵ include one ether bond such as an oxirane group, an oxetane group, an oxolane group, an oxane group, an oxepane group, an oxocan group, an oxonan group, an oxecan group, an oxet group, and an oxole group. A cyclic ether group having two ether bonds such as a cyclic ether group, a dioxolane group, a dioxane group, a dioxepane group and a dioxecan group, and a cyclic ether group having three ether bonds such as a trioxane group. Among these, a C2-C7 cyclic ether group having one ether bond is preferable, and a C3-C5 cyclic ether group having one ether bond is more preferable. The cyclic ether group preferably has no unsaturated bond in the ring skeleton.

As R ⁴ and R ⁵ , an alkyl group (preferably having 1 to 3 carbon atoms, more preferably 1 to 2 carbon atoms) is preferable, and an ethyl group is more preferable. Thereby, mechanical strength and rolling resistance characteristics can be suitably achieved.

As n (integer), 2-5 are preferable. Thereby, mechanical strength and rolling resistance characteristics can be suitably achieved. Furthermore, n is more preferably 2 to 4, and most preferably 3. If n is 1 or less, 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, the following formulas (4) to ( 11) and the like. These may be used alone or in combination of two or more. Of these, 3-diethylaminopropyltrimethoxysilane and a compound represented by the following formula (4) are preferred from the viewpoint that the effect of improving mechanical strength and rolling resistance characteristics is high.

Methods for modifying butadiene rubber with the compound represented by the above formula (1) (modifier) are described in JP-B-6-53768, JP-B-6-57767, JP-T2003-514078, and the like. Conventionally known methods such as the above method 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. The method etc. are mentioned.

The butadiene rubber (BR) to be modified is not particularly limited, and BR having a high cis content, BR containing a syndiotactic polybutadiene crystal, or the like can be used. In addition, BR obtained by polymerization using a catalyst containing a lanthanum series rare earth-containing compound described in JP-T-2003-514078 can also be used.

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, rolling resistance characteristics tend to deteriorate. The lower limit of the vinyl content is not particularly limited.
In the present invention, the vinyl content (1,2-bond butadiene unit amount) can be measured by infrared absorption spectrum analysis.

The content of the modified BR in 100% by mass of the rubber component is preferably 10% by mass or more, more preferably 30% by mass or more, and further preferably 50% by mass or more. If it is less than 10% by mass, the rolling resistance characteristics tend not to be sufficiently improved. The upper limit of the content of the modified BR is not particularly limited, but is preferably 90% by mass or less, more preferably 80% by mass or less, and still more preferably 70% by mass or less. If it exceeds 90 mass%, the mechanical strength tends to be insufficient.

Examples of rubber components other than the modified BR used in the rubber composition include natural rubber (NR), epoxidized natural rubber (ENR), non-modified BR, styrene butadiene rubber (SBR), isoprene rubber (IR), and ethylene. -Propylene-diene rubber (EPDM), butyl rubber (IIR), halogenated butyl rubber (X-IIR), chloroprene rubber (CR), acrylonitrile (NBR), halides of copolymers of isomonoolefin and paraalkylstyrene, etc. Diene rubber can be used. Especially, it is preferable to use NR with modified BR from the point that mechanical strength can be improved more.

The NR is not particularly limited, and for example, those commonly used in the tire industry such as SIR20, RSS # 3, TSR20, and the like can be used.

The content of NR in 100% by mass of the rubber component is preferably 10% by mass or more, more preferably 20% by mass or more, and further preferably 30% by mass or more. If it is less than 10% by mass, the mechanical strength tends not to be sufficiently improved. The NR content is preferably 90% by mass or less, more preferably 80% by mass or less. If it exceeds 90% by mass, the cut resistance tends to deteriorate.

The rubber composition of the present invention contains silica. By including silica together with the modified BR, good rolling resistance characteristics and mechanical strength can be obtained. Examples of silica include dry process silica (anhydrous silica), wet process silica (hydrous silica), and wet process silica is preferred because it has many silanol groups.

The average primary particle diameter of silica is preferably 10 nm or more, more preferably 15 nm or more. When the thickness is less than 10 nm, rolling resistance characteristics and workability tend to deteriorate. The average primary particle diameter of silica is preferably 40 nm or less, more preferably 30 nm or less. If it exceeds 40 nm, the mechanical strength tends to decrease.
In addition, the average primary particle diameter of silica can be calculated | required from the average value which observes a silica with an electron microscope, measures a particle diameter about 50 arbitrary particles, for example.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 120 m ² / g or more, more preferably 140 m ² / g or more, and further preferably 150 m ² / g or more. There exists a tendency for sufficient reinforcement property not to be acquired as it is less than 120 m < ² > / g. Further, N ₂ SA of silica is preferably 250 m ² / g or less, more preferably 200 m ² / g or less. When it exceeds 250 m < ² > / g, the viscosity of an unvulcanized rubber composition will become high and there exists a tendency for workability to deteriorate.
The _N 2 SA of silica is a value measured by the BET method in accordance with ASTM D3037-81.

The content of silica is 15 parts by mass or more, preferably 20 parts by mass or more, more preferably 30 parts by mass or more with respect to 100 parts by mass of the rubber component. If the amount is less than 15 parts by mass, the effect of incorporating silica tends to be insufficient. The content of the silica is 150 parts by mass or less, preferably 120 parts by mass or less, more preferably 80 parts by mass or less. When it exceeds 150 parts by mass, the viscosity of the unvulcanized rubber composition increases, and the processability tends to deteriorate.

The rubber composition, as a silane coupling agent, contains 1 to 70 bond units B with respect to the total amount of bond units A represented by the above formula (2) and bond units B represented by the above formula (3). It contains what is copolymerized at a mole percentage. By containing the silane coupling agent having the above structure, it is possible to improve rolling resistance characteristics without deteriorating workability.

The silane coupling agent having the above structure has an increased viscosity during processing as compared with polysulfide silanes such as bis- (3-triethoxysilylpropyl) tetrasulfide because the molar ratio of the bond unit A to the bond unit B satisfies the above conditions. Is suppressed. This is presumably because the increase in Mooney viscosity is small because the sulfide portion of the bond unit A is a C—S—C bond and is thermally stable compared to tetrasulfide and disulfide.

Moreover, when the molar ratio of the bond unit A and the bond unit B satisfies the above condition, the shortening of the scorch time is suppressed as compared with mercaptosilane such as 3-mercaptopropyltrimethoxysilane. This is because the bonding unit B has a structure of mercaptosilane, but the —C ₇ H ₁₅ portion of the bonding unit A covers the —SH group of the bonding unit B, so that it is difficult to react with the polymer. As a result, the scorch time is unlikely to be shortened and the viscosity is unlikely to increase.

Examples of the halogen for R ⁶ include chlorine, bromine, and fluorine.

Examples of the branched or unbranched alkyl group having 1 to 30 carbon atoms of R ⁶ and R ⁷ include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an iso-butyl group, and a sec-butyl group. Tert-butyl group, pentyl group, hexyl group, heptyl group, 2-ethylhexyl group, octyl group, nonyl group, decyl group and the like. The number of carbon atoms of the alkyl group is preferably 1-12.

Examples of the branched or unbranched alkylene group having 1 to 30 carbon atoms of R ⁶ and R ⁷ include ethylene group, propylene group, butylene group, pentylene group, hexylene group, heptylene group, octylene group, nonylene group, decylene group, Examples include undecylene group, dodecylene group, tridecylene group, tetradecylene group, pentadecylene group, hexadecylene group, heptadecylene group, octadecylene group and the like. The alkylene group preferably has 1 to 12 carbon atoms.

Examples of the branched or unbranched alkenyl group having 2 to 30 carbon atoms represented by R ⁶ and R ⁷ include a vinyl group, 1-propenyl group, 2-propenyl group, 1-butenyl group, 2-butenyl group, 1-pentenyl group, 2-pentenyl group, 1-hexenyl group, 2-hexenyl group, 1-octenyl group and the like can be mentioned. The alkenyl group preferably has 2 to 12 carbon atoms.

Examples of the branched or unbranched C 2-30 alkenylene group of R ⁶ and R ⁷ include vinylene group, 1-propenylene group, 2-propenylene group, 1-butenylene group, 2-butenylene group, 1-pentenylene group, 2-pentenylene group, 1-hexenylene group, 2-hexenylene group, 1-octenylene group and the like can be mentioned. The alkenylene group preferably has 2 to 12 carbon atoms.

Examples of the branched or unbranched alkynyl group having 2 to 30 carbon atoms represented by R ⁶ and R ⁷ include ethynyl group, propynyl group, butynyl group, pentynyl group, hexynyl group, heptynyl group, octynyl group, noninyl group, decynyl group, An undecynyl group, a dodecynyl group, etc. are mentioned. The alkynyl group preferably has 2 to 12 carbon atoms.

Examples of the branched or unbranched C2-C30 alkynylene group of R ⁶ and R ⁷ include an ethynylene group, a propynylene group, a butynylene group, a pentynylene group, a hexynylene group, a heptynylene group, an octynylene group, a noninylene group, a decynylene group, An undecynylene group, a dodecynylene group, etc. are mentioned. The alkynylene group preferably has 2 to 12 carbon atoms.

In the silane coupling agent having the above structure, the total repeating number (x + y) of the repeating number (x) of the bonding unit A and the repeating number (y) of the bonding unit B is preferably in the range of 3 to 300. Within this range, since the mercaptosilane of the bond unit B is covered by —C ₇ H ₁₅ of the bond unit A, it is possible to suppress the scorch time from being shortened and to have good reactivity with silica and rubber components. Can be secured.

As the silane coupling agent having the above structure, for example, NXT-Z30, NXT-Z45, NXT-Z60 and the like manufactured by Momentive can be used. These 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 4 parts by mass or more, and still more preferably 6 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 characteristics tend to deteriorate. Further, the content of the silane coupling agent is preferably 20 parts by mass or less, more preferably 16 parts by mass or less, and still more preferably 10 parts by mass or less. When it exceeds 20 parts by mass, there is a tendency that an effect commensurate with the increase in cost cannot be obtained.

In addition to the above components, the rubber composition of the present invention contains a compounding agent generally used in the production of a rubber composition, for example, a filler such as clay, an anti-aging agent, oil, sulfur, a vulcanization accelerator, and the like. It can mix | blend suitably.

As a method for producing the rubber composition of the present invention, a known method can be employed. For example, the above components are kneaded using a rubber kneading apparatus such as a Banbury mixer or an open roll.

A pneumatic tire can be manufactured by a normal method using the rubber composition of the present invention. That is, it can be produced by preparing a sidewall using the rubber composition, pasting it together with other members, and applying heat and pressure on a tire molding machine.

The pneumatic tire of the present invention can be used for passenger cars, trucks, buses, light trucks, and the like, and in particular, can be suitably used for passenger cars.

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
Non-modified BR: Nipol BR1220 (vinyl content: 1% by mass) manufactured by Nippon Zeon Co., Ltd.
Modified BR: Modified butadiene rubber manufactured by Sumitomo Chemical Co., Ltd. (vinyl content: 15% by mass, R ¹ , R ² and R ³ = —OCH ₃ , R ⁴ and R ⁵ = —CH ₂ CH ₃ , n = 3)
Silica: Ultrasil VN3 manufactured by Degussa (average primary particle size: 15 nm, N ₂ SA: 175 m ² / g)
Tetrasulfide silane: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by Degussa
Mercaptosilane: A1891 (3-mercaptopropyltriethoxysilane) manufactured by Momentive
Silane coupling agent A: NXT-Z15 manufactured by Momentive (copolymer of bond unit A and bond unit B (bond unit A: 85 mol%, bond unit B: 15 mol%))
Silane coupling agent B: NXT-Z45 manufactured by Momentive (copolymer of bond unit A and bond unit B (bond unit A: 55 mol%, bond unit B: 45 mol%))
Silane coupling agent C: NXT-Z80 manufactured by Momentive (copolymer of bonding unit A and bonding unit B (bonding unit A: 20 mol%, bonding unit B: 80 mol%))
Oil: Diana Process AH-24 manufactured by Idemitsu Kosan Co., Ltd.
Zinc oxide: Zinc oxide stearic acid manufactured by Mitsui Mining & Smelting Co., Ltd .: Stearic acid “Kashiwa” manufactured by NOF Corporation
Anti-aging agent: Antigen 6C manufactured by Sumitomo Chemical Co., Ltd.
Wax: Sunnock N manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Sulfur: Powder sulfur vulcanization accelerator manufactured by Karuizawa Sulfur Co., Ltd. (1): Noxeller CZ manufactured by Ouchi Shinsei Chemical Co., Ltd.
Vulcanization accelerator (2): Noxeller D manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

Examples 1-4 and Comparative Examples 1-6
According to the formulation shown in Table 1, chemicals other than sulfur and vulcanization accelerator were kneaded at about 150 ° C. for 3 minutes using a Banbury mixer to obtain a kneaded product. Next, sulfur and a vulcanization accelerator were added to the obtained kneaded product, and kneaded at about 80 ° C. for 5 minutes using a biaxial open roll to obtain an unvulcanized rubber composition.
The obtained unvulcanized rubber composition was press vulcanized at 150 ° C. for 35 minutes to obtain a vulcanized rubber sheet.

The following evaluation was performed using the obtained unvulcanized rubber composition and vulcanized rubber sheet. The results are shown in Table 1.

(Mooney viscosity index)
Based on JIS K6300, the Mooney viscosity of the unvulcanized rubber composition was measured at 130 ° C. And the Mooney viscosity of the comparative example 1 was set to 100, and the Mooney viscosity of each formulation was indicated by an index by the following calculation formula. It shows that it is excellent in workability, so that a value is small.
(Mooney viscosity index) = (Mooney viscosity of each formulation) / (Mooney viscosity of Comparative Example 1) × 100

(Scorch time index)
Based on JIS K6300, the scorch time of the unvulcanized rubber composition was measured at 130 ° C. And the scorch time of the comparative example 1 was set to 100, and the scorch time of each combination was displayed as an index according to the following formula. It shows that it is excellent in workability, so that a value is large.
(Scorch time index) = (Scorch time of each formulation) / (Scorch time of Comparative Example 1) × 100

(Strength index)
In accordance with JIS K6251 “Vulcanized rubber and thermoplastic rubber-Determination of tensile properties”, tensile tests were conducted using No. 3 dumbbell-shaped test pieces made of each vulcanized rubber sheet, breaking strength (TB) and breaking The time elongation (EB) was measured and the fracture energy (TB × EB / 2) was calculated. And the breaking energy of the comparative example 1 was set to 100, and the breaking energy of each combination was indicated by an index by the following calculation formula. The larger the value, the higher the mechanical strength and the better the cut resistance and separation resistance.
(Strength index) = (Fracture energy of each formulation) / (Fracture energy of Comparative Example 1) × 100

(Low fuel consumption index)
With respect to the vulcanized rubber sheet, tan δ of each formulation was measured under the conditions of a temperature of 70 ° C., an initial strain of 10%, and a dynamic strain of 2% using a viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.). Then, with tan δ of Comparative Example 1 as 100, tan δ of each formulation was displayed as an index according to the following calculation formula. It shows that it is excellent in low-fuel-consumption property (rolling resistance characteristic), so that a value is large.
(Low fuel consumption index) = (tan δ of Comparative Example 1) / (tan δ of each formulation) × 100

From Table 1, in Examples containing modified BR, a specific silane coupling agent, and a predetermined amount of silica, rolling resistance characteristics, mechanical strength and workability were improved in a well-balanced manner. On the other hand, the comparative examples not containing at least one of the modified BR and the specific silane coupling agent have a small effect of improving each performance, and some of the performances are greatly deteriorated.

Claims (2)

Containing a rubber component, a silane coupling agent , and silica having a nitrogen adsorption specific surface area of 120 to ²⁰⁰ m ² / g ,
The rubber component includes butadiene rubber modified with natural rubber and a compound represented by the following formula (1):
The silane coupling agent is combined at a ratio of 1 to 70 mol% with respect to the total amount of the bond unit A represented by the following formula (2) and the bond unit B represented by the following formula (3). Polymerized,
The content of the natural rubber in 100% by mass of the rubber component is 10 to 90% by mass, and the content of the modified butadiene rubber is 10 to 90% by mass.
A rubber composition for a sidewall, wherein the silica content is 15 to 150 parts by mass with respect to 100 parts by mass of the rubber component.

(Wherein R ¹ , R ² and R ³ are the same or different and each represents an alkyl group, an alkoxy group, a silyloxy group, an acetal group, a carboxyl group, a mercapto group or a derivative thereof. R ⁴ and R ⁵ are (The same or different and represents a hydrogen atom, an alkyl group or a cyclic ether group. N represents an integer.)

(Wherein, x and y are each an integer of 1 or more. R ⁶ is hydrogen, halogen, branched or unbranched C 1-30 alkyl group or alkylene group, branched or unbranched C 2-30 Or an alkenyl group or alkenylene group, a branched or unbranched alkynyl group or alkynylene group having 2 to 30 carbon atoms, or a hydrogen atom substituted at the terminal of the alkyl group or the alkenyl group with a hydroxyl group or a carboxyl group. ⁷ represents hydrogen, a branched or unbranched alkylene group or alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenylene group or alkenyl group having 2 to 30 carbon atoms, or a branched or unbranched carbon group having 2 to 30 carbon atoms. R represents an alkynylene group or an alkynyl group, and R ⁶ and R ⁷ may form a ring structure.) A pneumatic tire having a sidewall produced using the rubber composition according to claim 1.