JP2013224393A - Rubber composition for sidewall, and pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for a sidewall, which is well balancedly improved in processability, low fuel consumption, breaking strength and flexing crack-growth resistance, and a pneumatic tire using the same.SOLUTION: A rubber composition for a sidewall contains a butadiene rubber modified with a sulfur compound and having a cis content of ≥70 mass% and Mooney viscosity (ML, 100°C) of 30 to 120, silica, and a silane coupling agent having a mercapto group.

Description

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

Conventionally, reduction in tire rolling resistance (improvement in rolling resistance performance) has led to lower fuel consumption of vehicles. Since the rolling resistance of a tire greatly depends on the low heat build-up property of rubber used for the tire, development for realizing the low heat build-up property (low fuel consumption) of the tire rubber is actively performed. Furthermore, in recent years, the demand for lower fuel consumption of cars has become stronger, and not only rubber that produces cap treads with a high occupation ratio among tire members but also rubber that produces sidewalls. Excellent fuel economy is required.

On the other hand, as a reinforcing filler, a rubber component blended with natural rubber, which exhibits excellent tensile strength and tear strength, and butadiene rubber, which exhibits excellent resistance to flex crack growth, has been used for tire sidewalls. Although rubber compositions containing carbon black have been used, there has been a problem of poor fuel economy.

Therefore, in order to improve fuel efficiency, it has been studied to replace a part of carbon black, or in some cases, all with silica. However, since silica has hydrophilic silanol groups on its surface, it has lower affinity with rubber (especially natural rubber, butadiene rubber, styrene butadiene rubber, etc. often used for tire applications) compared to carbon black, There has been a problem that it is often inferior in terms of bending crack growth resistance and breaking strength (breaking strength and elongation at break).

In general, methods for increasing the cis content of the butadiene rubber to be blended and increasing the molecular weight are known for improving the balance between breaking strength and fuel efficiency. However, although a certain effect can be obtained with the carbon black compounding system, the silica compounding system causes poor dispersion of silica, and tends to deteriorate the fuel economy, fracture strength, and flex crack growth resistance.

Further, in Patent Documents 1 to 3, for the purpose of improving fuel economy, in a compound containing silica, by adding a specific polar group to rubber, it has an affinity for silica, thereby improving the dispersibility of silica. Although a method for obtaining a rubber composition excellent in fuel efficiency is described, provision of other methods is also demanded.

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

The present invention solves the above problems and provides a rubber composition for sidewalls that can improve the workability, fuel efficiency, fracture strength, and flex crack growth resistance in a well-balanced manner, and a pneumatic tire using the rubber composition. The purpose is to do.

The present invention includes a butadiene rubber modified with a sulfur compound, having a cis content of 70% by mass or more and a Mooney viscosity (ML _{1 + 4} , 100 ° C.) of 30 to 120, silica, and a silane coupling agent having a mercapto group. It is related with the rubber composition for side walls containing.

The rubber composition preferably has a silica content of 50% by mass or more in 100% by mass of the reinforcing filler.

The rubber composition preferably contains a modified natural rubber having a phosphorus content of 200 ppm or less.

The nitrogen content of the modified natural rubber is preferably 0.3% by mass or less.

The butadiene rubber preferably has a ratio of z + 1 average molecular weight to number average molecular weight in terms of polystyrene by gel permeation chromatography of 3.5 or more.

The butadiene rubber preferably has a ratio of 5% toluene solution viscosity (Tcp) to Mooney viscosity (ML _{1 + 4} , 100 ° C.) of 1.8 to 6.0.

（式（１）中、Ｒ^１０１〜Ｒ^１０３は、分岐若しくは非分岐の炭素数１〜１２のアルキル基、分岐若しくは非分岐の炭素数１〜１２のアルコキシ基、又は−Ｏ−（Ｒ^１１１−Ｏ）_ｚ−Ｒ^１１２（ｚ個のＲ^１１１は、分岐若しくは非分岐の炭素数１〜３０の２価の炭化水素基を表す。ｚ個のＲ^１１１はそれぞれ同一でも異なっていてもよい。Ｒ^１１２は、分岐若しくは非分岐の炭素数１〜３０のアルキル基、分岐若しくは非分岐の炭素数２〜３０のアルケニル基、炭素数６〜３０のアリール基、又は炭素数７〜３０のアラルキル基を表す。ｚは１〜３０の整数を表す。）で表される基を表す。Ｒ^１０１〜Ｒ^１０３はそれぞれ同一でも異なっていてもよい。Ｒ^１０４は、分岐若しくは非分岐の炭素数１〜６のアルキレン基を表す。）

（式（２）及び（３）中、Ｒ^２０１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、分岐若しくは非分岐の炭素数２〜３０のアルケニル基、分岐若しくは非分岐の炭素数２〜３０のアルキニル基、又は該アルキ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表す。Ｒ^２０２は分岐若しくは非分岐の炭素数１〜３０のアルキレン基、分岐若しくは非分岐の炭素数２〜３０のアルケニレン基、又は分岐若しくは非分岐の炭素数２〜３０のアルキニレン基を表す。Ｒ^２０１とＲ^２０２とで環構造を形成してもよい。） The silane coupling agent includes a compound represented by the following formula (1) and / or a binding unit A represented by the following formula (2) and a binding unit B represented by the following formula (3). It is preferable.

(In the formula (1), R ^{101 to} R ¹⁰³ are each a branched or unbranched C 1-12 alkyl group, a branched or unbranched C 1-12 alkoxy group, or —O— (R ¹¹¹ — O) _z- R ¹¹² (z R ¹¹¹ represents a branched or unbranched divalent hydrocarbon group having 1 to 30 carbon atoms. The z R ^{111 s} may be the same as or different from each other. ¹¹² represents a branched or unbranched alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenyl group having 2 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms, or an aralkyl group having 7 to 30 carbon atoms. Z represents an integer of 1 to 30.) R ^{101 to} R ¹⁰³ may be the same as or different from each other, and R ¹⁰⁴ has 1 to 6 carbon atoms which are branched or unbranched. Represents an alkylene group of

(In the formulas (2) and (3), R ²⁰¹ is hydrogen, halogen, branched or unbranched alkyl group having 1 to 30 carbon atoms, branched or unbranched alkenyl group having 2 to 30 carbon atoms, branched or unbranched. Or an alkyl group substituted with a hydroxyl group or a carboxyl group, and R ²⁰² represents a branched or unbranched C 1-30 alkylene group, branched or It represents an unbranched C2-C30 alkenylene group or a branched or unbranched C2-C30 alkynylene group, and R ²⁰¹ and R ²⁰² may form a ring structure.)

The rubber composition contains 5 to 100 parts by mass of the silica and 0 to 60 parts by mass of carbon black with respect to 100 parts by mass of the rubber component containing 5 to 60% by mass of the butadiene rubber in 100% by mass of the rubber component. It is preferable that 0.1-15 mass parts of said silane coupling agents are included with respect to 100 mass parts of silica.

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

According to the present invention, a butadiene coupling agent modified with a sulfur compound, having a cis content of 70% by mass or more and a Mooney viscosity (ML _{1 + 4} , 100 ° C.) of 30 to 120, silica, and a mercapto group. Therefore, processability, fuel efficiency, fracture strength, and flex crack growth resistance can be improved in a well-balanced manner.

The rubber composition for a side wall of the present invention is modified with a sulfur compound, has a cis content of 70% by mass or more, a Mooney viscosity (ML _{1 + 4} , 100 ° C.) of 30 to 120, silica, and a mercapto group. And having a silane coupling agent.

Butadiene rubber modified with a sulfur compound and having a specific molecular structure (cis content of 70% by mass or more, Mooney viscosity (ML _{1 + 4} , 100 ° C.) of 30 to 120), silica, and a specific functional group (mercapto group) By using in combination with a silane coupling agent having the above, processability and fuel efficiency can be synergistically improved, and processability, fuel efficiency, fracture strength, and flex crack growth resistance can be improved in a balanced manner.

In the present invention, a butadiene rubber (sulfur-modified butadiene rubber) modified with a sulfur compound, having a cis content of 70% by mass or more and a Mooney viscosity (ML _{1 + 4} , 100 ° C.) of 30 to 120 is used as the rubber component.

In general, a butadiene rubber having a high cis content (for example, having a cis content of 70% by mass or more) is difficult to be modified, and only a low modification rate can be achieved even after modification, resulting in sufficient modification. In many cases, the effect (modification effect) cannot be obtained. On the other hand, modification with a sulfur compound can achieve a high modification rate even in a butadiene rubber having a high cis content, and an excellent modification effect can be obtained. By blending sulfur-modified butadiene rubber, processability, fuel efficiency, breaking strength, and flex crack growth resistance can be improved in a well-balanced manner.

The cis content of the sulfur-modified butadiene rubber is 70% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, and particularly preferably 95% by mass or more. If it is less than 70% by mass, sufficient fuel economy, wear resistance, fracture strength and flex crack growth resistance cannot be obtained. The cis content can be measured by, for example, a calculation method by NMR peak comparison, a calculation method by an absorption area of an infrared absorption spectrum, or the like, and specifically, a value obtained by a measurement method described in Examples described later. .

The Mooney viscosity (ML _{1 + 4} , 100 ° C.) of the sulfur-modified butadiene rubber is 30 to 120. The lower limit is preferably 40 and more preferably 60. When the Mooney viscosity is less than 30, sufficient fracture strength cannot be obtained, and when it exceeds 120, workability is deteriorated.

The sulfur-modified butadiene rubber preferably has a ratio (Tcp / ML _{1 + 4} , 100 ° C.) of 5% toluene solution viscosity (Tcp) to Mooney viscosity (ML _{1 + 4} , 100 ° C.) of 1.8 to 6.0. More preferably, it is 0.0-5.0, and it is still more preferable that it is 2.0-3.5. The ratio is an index of the degree of branching of butadiene rubber and is known to those skilled in the art. The larger the ratio, the smaller the degree of branching of the butadiene rubber, that is, the higher the linearity. When the ratio is less than 1.8, the tan δ of the vulcanized rubber increases, and sufficient fuel efficiency tends not to be obtained. Moreover, when this ratio is larger than 6.0, workability tends to deteriorate. In addition, 5% toluene solution viscosity (Tcp) and Mooney viscosity (ML _{1 + 4} , 100 ° C.) are values obtained by the measurement methods described in Examples described later.

The sulfur-modified butadiene rubber has a ratio (M _{z + 1} / M _n ) of z + 1 average molecular weight (M _{z + 1} ) and number average molecular weight (M _n ) in terms of polystyrene by gel permeation chromatography (GPC) of 3.5 or more. Is preferably 4 or more, more preferably 5 or more, particularly preferably 10 or more, and most preferably 15 or more. If the ratio is less than 3.5, processability, fuel economy, fracture strength, and flex crack growth resistance (particularly processability) may not be sufficiently obtained. The upper limit of the ratio is not particularly limited, but is preferably 35 or less, more preferably 25 or less. When it exceeds 35, rubber | gum will gelatinize and there exists a tendency for workability to deteriorate.
The z + 1 average molecular weight (M _{z + 1} ) is an amount represented by the following formula, assuming that n _i (mol) of molecules having a molecular weight Mi exist.
M _{z + 1} = ΣM _i ⁴ × n _i / (ΣM _i ³ × n _i )
M z _{+ 1} becomes an index of the content of the high molecular weight component, indicating that a large amount of high molecular weight component as M z _{+ 1} is large. M _{z + 1} and M _n are values converted from standard polystyrene using GPC, and specifically, values obtained by the measurement methods described in Examples described later.

The storage elastic modulus when the loss elastic modulus in the viscoelasticity of a solution obtained by diluting sulfur-modified butadiene rubber to 30% by mass with liquid paraffin is 100 Pa is preferably 20 Pa or more, more preferably 25 Pa or more, and further preferably 30 Pa or more. . If it is less than 20 Pa, the content of the high molecular weight component is small, and there is a possibility that processability, fuel efficiency, fracture strength, and flex crack growth resistance (particularly processability) may not be sufficiently obtained. The storage elastic modulus is preferably 60 Pa or less, more preferably 45 Pa or less.
When it exceeds 60 Pa, workability may be deteriorated. In addition, this storage elastic modulus is a value obtained by the measuring method described in the examples described later.

The sulfur-modified butadiene rubber is obtained by modifying butadiene rubber with a sulfur compound. Specifically, the sulfur-modified butadiene rubber can be produced by a known method, for example, by the method described in JP 2012-17416 A or JP 8-208751 A. A person skilled in the art can modify the butadiene rubber with a sulfur compound based on the contents described in the present specification and the above publication and the common general technical knowledge at the time of filing, and then obtain a desired molecular structure (cis content is 70% by mass). As described above, selection of a butadiene rubber to be modified (determination of a desirable molecular structure as a modified butadiene rubber) so as to obtain a sulfur-modified butadiene rubber having a Mooney viscosity (ML _{1 + 4} , 100 ° C.) of 30 to 120, etc. It is possible to appropriately set the addition amount of the sulfur compound, the conditions for the modification reaction, and the like.

The butadiene rubber modified with the sulfur compound may be actually polymerized or a commercially available product may be used.

Commercially available products include BR1220 manufactured by Nippon Zeon Co., Ltd., BR130B manufactured by Ube Industries, Ltd., BR150B, BR150L, BRANACB21 manufactured by LANXESS Co., Ltd., BunaCB22, etc., and Ube Industries, Ltd. BR containing a syndiotactic polybutadiene crystal such as VCR412 and VCR617 manufactured by the same company can be used.

The catalyst for polymerizing the butadiene rubber is not particularly limited, but is a cobalt-based catalyst or a rare earth element-based catalyst (for example, a neodymium-based catalyst (neodymium (Nd) -containing compound, organoaluminum compound, aluminoxane, halogen-containing compound, necessary Accordingly, a catalyst containing a Lewis base)) and the like can be mentioned. In particular, by modifying a butadiene rubber polymerized using a cobalt-based catalyst with a sulfur compound, a sulfur-modified butadiene rubber having a high molecular weight component content while having a molecular structure with a low degree of branching is obtained. A cobalt-based catalyst is preferred because the effects of the invention can be obtained more suitably.

As the cobalt-based catalyst, a catalyst system composed of a cobalt compound, a halogen-containing aluminum compound, and water, and a catalyst system composed of a cobalt compound, a halogen-containing aluminum compound, water, and an organoaluminum compound are preferable.

The polymerization temperature is preferably -30 to 100 ° C. The polymerization time is preferably 10 minutes to 12 hours. Further, the polymerization pressure may be arbitrarily selected depending on other conditions.

The modification reaction of the sulfur compound and butadiene rubber may be carried out subsequently after the polymerization reaction, or after the polymerization reaction is stopped after the polymerization, or after the polymerization reaction is stopped after the polymerization, the reaction product It may be carried out after resolving a dried product of butadiene rubber obtained by removing the solvent and unreacted monomers remaining therein by a steam stripping method or a vacuum drying method with a solvent such as cyclohexane.

That is, modification with a sulfur compound is performed by adding a sulfur compound to a reaction solution after polymerizing butadiene rubber or a solution obtained by dissolving a commercially available butadiene rubber or polymerized butadiene rubber in a solvent such as cyclohexane. Just do.

Sulfur compounds include disulfur dichloride, disulfur dibromide, disulfur difluoride, disulfur diiodide, etc., disulfur dihalides, sulfur dichloride, sulfur dibromide, sulfur difluoride, disulfide Examples thereof include sulfur dihalides such as sulfur iodide, thionyl chloride such as thionyl chloride, thionyl bromide, thionyl fluoride, thionyl iodide, and the like. Of these, disulfur dihalide is preferable, and disulfur dichloride is more preferable.

The addition amount of the sulfur compound is preferably 0.05 to 0.5 parts by mass, more preferably 0.1 to 0.4 parts by mass with respect to 100 parts by mass of the butadiene rubber. Moreover, it is preferable to stir and mix the modification reaction for 10 to 150 minutes. Moreover, about the reaction temperature of modification | denaturation reaction, Preferably it is 20-100 degreeC, More preferably, it is 30-80 degreeC. After the denaturation reaction, the inside of the reaction vessel may be released as necessary, and washed, dried, or the like.

The content of the sulfur-modified butadiene rubber in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, and further preferably 20% by mass or more. If it is less than 5% by mass, sufficient processability, fuel efficiency, fracture strength, and bending crack growth resistance may not be obtained. The content of the sulfur-modified butadiene rubber is preferably 60% by mass or less, more preferably 50% by mass or less. If it exceeds 60% by mass, the mechanical strength (breaking strength) of the rubber is insufficient, and damage such as chipping may occur.

Examples of rubber components other than the sulfur-modified butadiene rubber used in the rubber composition include natural rubber (NR), butadiene rubber (BR) other than sulfur-modified butadiene rubber, styrene butadiene rubber (SBR), isoprene rubber (IR), Diene rubbers such as butyl rubber (IIR), halogenated butyl rubber (X-IIR), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), styrene-isoprene-butadiene copolymer rubber (SIBR) can be used. These rubber components may be used alone or in combination of two or more. Further, the main chain and / or terminal thereof may be modified, or may be modified with a polyfunctional compound such as tin tetrachloride or silicon tetrachloride to have a branched structure.

As a rubber component other than the sulfur-modified butadiene rubber, NR is preferable because processability, fuel efficiency, fracture strength, and flex crack growth resistance can be obtained in a more balanced manner.

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 5% by mass or more, more preferably 20% by mass or more, and further preferably 40% by mass or more. If it is less than 5% by mass, the workability, fuel efficiency, fracture strength, and flex crack growth resistance may not be improved in a well-balanced manner. The NR content is preferably 95% by mass or less, more preferably 90% by mass or less, and still more preferably 80% by mass or less. If it exceeds 95% by mass, the content of the sulfur-modified butadiene rubber decreases, and there is a possibility that sufficient processability, low fuel consumption, fracture strength, and flex crack growth resistance cannot be obtained.

Further, as the rubber component other than the sulfur-modified butadiene rubber, a modified natural rubber having a phosphorus content of 200 ppm or less is preferable because the fuel efficiency, fracture strength, and flex crack growth resistance can be further improved.

Natural rubber (modified natural rubber) from which phospholipids contained in natural rubber (NR) have been reduced and removed (modified natural rubber, preferably from which protein and gel content have also been removed) has the property of not generating heat. Compared with the use of, further reduction in fuel consumption can be achieved. In addition, the unvulcanized rubber composition containing the modified natural rubber is excellent in processability and can be sufficiently kneaded without performing a special mastication step. A decrease in bending crack growth resistance and the like can be suppressed, and low fuel consumption, fracture strength, bending crack growth resistance, and the like can be effectively enhanced.

The modified natural rubber (HPNR) has a phosphorus content of 200 ppm or less. If it exceeds 200 ppm, the gel amount will increase during storage, and the tan δ of the vulcanized rubber will increase and the fuel efficiency will deteriorate, or the Mooney viscosity of the unvulcanized rubber will increase and the processability will tend to deteriorate. In addition, there is a possibility that low fuel consumption, breaking strength, and resistance to flex crack growth cannot be improved in a well-balanced manner. The phosphorus content is preferably 150 ppm or less, and more preferably 100 ppm or less. Here, the phosphorus content can be measured by a conventional method such as ICP emission analysis. Phosphorus is derived from phospholipids (phosphorus compounds).

In the modified natural rubber, the nitrogen content is preferably 0.3% by mass or less, and more preferably 0.15% by mass or less. If the nitrogen content exceeds 0.3% by mass, the Mooney viscosity will increase during storage and the processability tends to deteriorate, and the fuel economy, fracture strength, and flex crack growth resistance cannot be improved in a well-balanced manner. There is also a fear. The nitrogen content can be measured by a conventional method such as Kjeldahl method. Nitrogen is derived from protein.

The gel content in the modified natural rubber is preferably 20% by mass or less, more preferably 10% by mass or less, and still more preferably 7% by mass or less. If it exceeds 20% by mass, the Mooney viscosity tends to increase and the workability tends to deteriorate, and there is a possibility that the fuel economy, fracture strength, and flex crack growth resistance cannot be improved in a well-balanced manner. The gel content means a value measured as an insoluble content with respect to toluene which is a nonpolar solvent, and may be simply referred to as “gel content” or “gel content” below. The measuring method of the content rate of a gel part is as follows. First, a natural rubber sample is soaked in dehydrated toluene, light-shielded in the dark and left for 1 week, and then the toluene solution is centrifuged at 1.3 × 10 ⁵ rpm for 30 minutes to obtain an insoluble gel content and a toluene soluble content. Isolate. Methanol is added to the insoluble gel and solidified, and then dried, and the gel content is determined from the ratio between the mass of the gel and the original mass of the sample.

The modified natural rubber is preferably substantially free of phospholipids. “Substantially no phospholipid is present” represents a state in which a natural rubber sample is extracted with chloroform and a peak due to phospholipid does not exist at −3 ppm to 1 ppm in ³¹ P NMR measurement of the extract. The peak of phosphorus present at -3 ppm to 1 ppm is a peak derived from the phosphate structure of phosphorus in the phospholipid.

As a method for producing the modified natural rubber, for example, the production method described in JP 2010-138359 A, that is, the step (A) of obtaining a saponified natural rubber latex by saponifying the natural rubber latex, and the obtained Examples of the method include a step (B) of washing the saponified natural rubber latex until the phosphorus content in the rubber is 200 ppm or less. Specifically, first, a natural rubber latex is saponified with an alkali to prepare a saponified natural rubber latex, and then the agglomerated rubber obtained by agglomerating the saponified natural rubber latex contains phosphorus to the rubber content. A modified natural rubber (saponified natural rubber) can be produced by a method of repeatedly washing with water until the rate becomes 200 ppm or less and drying.

According to the above production method, the phosphorus compound separated by saponification is washed away, so that the phosphorus content of the natural rubber can be suppressed. Moreover, since the protein in natural rubber is decomposed by the saponification treatment, the nitrogen content of the natural rubber can be suppressed.

The content of the modified natural rubber in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 20% by mass or more, and further preferably 40% by mass or more. If it is less than 5% by mass, the workability, fuel efficiency, fracture strength, and flex crack growth resistance may not be improved in a well-balanced manner. The content of the modified natural rubber is preferably 95% by mass or less, more preferably 90% by mass or less, and still more preferably 80% by mass or less. If it exceeds 95% by mass, the content of the sulfur-modified butadiene rubber decreases, and there is a possibility that sufficient processability, low fuel consumption, fracture strength, and flex crack growth resistance cannot be obtained.

The rubber composition of the present invention contains silica. Thereby, workability, fuel efficiency, fracture strength, and flex crack growth resistance can be improved in a well-balanced manner. Examples of the silica include dry process silica (anhydrous silicic acid), wet process silica (hydrous silicic acid), and the like, but wet process silica is preferred because it has many silanol groups.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 40 m ² / g or more, more preferably 100 m ² / g or more, and further preferably 150 m ² / g or more. If it is less than 40 m ² / g, the fracture strength tends to deteriorate. The N ₂ SA is preferably 500 m ² / g or less, more preferably 300 m ² / g or less, still more preferably 250 m ² / g or less, and particularly preferably 200 m ² / g or less. If it exceeds 500 m ² / g, the workability, fuel efficiency, fracture strength, and flex crack growth resistance tend 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 preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and still more preferably 20 parts by mass or more with respect to 100 parts by mass of the rubber component. If the amount is less than 5 parts by mass, sufficient fuel economy may not be obtained. The content is preferably 100 parts by mass or less, more preferably 70 parts by mass or less. When the amount exceeds 100 parts by mass, the dispersibility of silica tends to decrease, and the workability, fuel efficiency, fracture strength, and flex crack growth resistance tend to deteriorate.

The rubber composition of the present invention contains a silane coupling agent having a mercapto group. As a result, silica is well dispersed and processability, fuel efficiency, fracture strength, and flex crack growth resistance can be improved in a well-balanced manner.

（式（１）中、Ｒ^１０１〜Ｒ^１０３は、分岐若しくは非分岐の炭素数１〜１２のアルキル基、分岐若しくは非分岐の炭素数１〜１２のアルコキシ基、又は−Ｏ−（Ｒ^１１１−Ｏ）_ｚ−Ｒ^１１２（ｚ個のＲ^１１１は、分岐若しくは非分岐の炭素数１〜３０の２価の炭化水素基を表す。ｚ個のＲ^１１１はそれぞれ同一でも異なっていてもよい。Ｒ^１１２は、分岐若しくは非分岐の炭素数１〜３０のアルキル基、分岐若しくは非分岐の炭素数２〜３０のアルケニル基、炭素数６〜３０のアリール基、又は炭素数７〜３０のアラルキル基を表す。ｚは１〜３０の整数を表す。）で表される基を表す。Ｒ^１０１〜Ｒ^１０３はそれぞれ同一でも異なっていてもよい。Ｒ^１０４は、分岐若しくは非分岐の炭素数１〜６のアルキレン基を表す。）

（式（２）及び（３）中、Ｒ^２０１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、分岐若しくは非分岐の炭素数２〜３０のアルケニル基、分岐若しくは非分岐の炭素数２〜３０のアルキニル基、又は該アルキ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表す。Ｒ^２０２は分岐若しくは非分岐の炭素数１〜３０のアルキレン基、分岐若しくは非分岐の炭素数２〜３０のアルケニレン基、又は分岐若しくは非分岐の炭素数２〜３０のアルキニレン基を表す。Ｒ^２０１とＲ^２０２とで環構造を形成してもよい。） Examples of the silane coupling agent having a mercapto group include a compound represented by the following formula (1) and / or a binding unit A represented by the following formula (2) and a binding unit B represented by the following formula (3). The compound containing can be used conveniently. Especially, the compound containing the bond unit A shown by following formula (2) and the bond unit B shown by following formula (3) is more preferable.

(In the formula (1), R ^{101 to} R ¹⁰³ are each a branched or unbranched C 1-12 alkyl group, a branched or unbranched C 1-12 alkoxy group, or —O— (R ¹¹¹ — O) _z- R ¹¹² (z R ¹¹¹ represents a branched or unbranched divalent hydrocarbon group having 1 to 30 carbon atoms. The z R ^{111 s} may be the same as or different from each other. ¹¹² represents a branched or unbranched alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenyl group having 2 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms, or an aralkyl group having 7 to 30 carbon atoms. Z represents an integer of 1 to 30.) R ^{101 to} R ¹⁰³ may be the same as or different from each other, and R ¹⁰⁴ has 1 to 6 carbon atoms which are branched or unbranched. Represents an alkylene group of

(In the formulas (2) and (3), R ²⁰¹ is hydrogen, halogen, branched or unbranched alkyl group having 1 to 30 carbon atoms, branched or unbranched alkenyl group having 2 to 30 carbon atoms, branched or unbranched. Or an alkyl group substituted with a hydroxyl group or a carboxyl group, and R ²⁰² represents a branched or unbranched C 1-30 alkylene group, branched or It represents an unbranched C2-C30 alkenylene group or a branched or unbranched C2-C30 alkynylene group, and R ²⁰¹ and R ²⁰² may form a ring structure.)

Hereinafter, the compound represented by Formula (1) is demonstrated.

By using the compound represented by the formula (1), silica is well dispersed, and the workability, fuel efficiency, fracture strength, and flex crack growth resistance can be improved in a balanced manner.

R ^{101 to} R ¹⁰³ are each a branched or unbranched alkyl group having 1 to 12 carbon atoms, a branched or unbranched alkoxy group having 1 to 12 carbon atoms, or —O— (R ¹¹¹ —O) _z —R ¹¹² . Represents the group represented. From the viewpoint that the effect of the present invention can be obtained satisfactorily, at least one of R ^{101 to} R ¹⁰³ is preferably a group represented by —O— (R ¹¹¹ —O) _z —R ¹¹² , and two of them are — More preferably, it is a group represented by O— (R ¹¹¹ —O) _z —R ¹¹² , and one is a branched or unbranched C 1-12 alkoxy group.

Examples of the branched or unbranched alkyl group having 1 to 12 carbon atoms (preferably 1 to 5 carbon atoms) represented by R ^{101 to} R ¹⁰³ include, for example, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, and n-butyl. Group, iso-butyl group, sec-butyl group, tert-butyl group, pentyl group, hexyl group, heptyl group, 2-ethylhexyl group, octyl group, nonyl group and the like.

Examples of the branched or unbranched alkoxy group having 1 to 12 carbon atoms (preferably 1 to 5 carbon atoms) of R ^{101 to} R ¹⁰³ include, for example, methoxy group, ethoxy group, n-propoxy group, isopropoxy group, n- Examples include butoxy, iso-butoxy, sec-butoxy, tert-butoxy, pentyloxy, hexyloxy, heptyloxy, 2-ethylhexyloxy, octyloxy, nonyloxy and the like.

In —O— (R ¹¹¹ —O) _z —R ¹¹² of R ^{101 to} R ¹⁰³ , R ¹¹¹ represents a branched or unbranched carbon number of 1 to 30 (preferably having 1 to 15 carbon atoms, more preferably 1 carbon number). To 3) a divalent hydrocarbon group.
Examples of the hydrocarbon group include a branched or unbranched alkylene group having 1 to 30 carbon atoms, a branched or unbranched alkenylene group having 2 to 30 carbon atoms, and a branched or unbranched alkynylene group having 2 to 30 carbon atoms. And an arylene group having 6 to 30 carbon atoms. Of these, a branched or unbranched alkylene group having 1 to 30 carbon atoms is preferable.

Examples of the branched or unbranched alkylene group having 1 to 30 carbon atoms (preferably 1 to 15 carbon atoms, more preferably 1 to 3 carbon atoms) of R ¹¹¹ include, for example, a methylene group, an ethylene group, a propylene group, and a butylene group. Pentylene group, hexylene group, heptylene group, octylene group, nonylene group, decylene group, undecylene group, dodecylene group, tridecylene group, tetradecylene group, pentadecylene group, hexadecylene group, heptadecylene group, octadecylene group and the like.

Examples of the branched or unbranched carbon atoms 2-30 alkenylene group (preferably 2 to 15 carbon atoms, more preferably 2 to 3 carbon atoms) of R ^111, for example, vinylene group, 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.

Examples of the branched or unbranched carbon atoms 2-30 alkynylene group (preferably 2 to 15 carbon atoms, more preferably 2 to 3 carbon atoms) of R ^111, for example, ethynylene group, propynylene group, butynylene group, pentynylene group Hexynylene group, heptynylene group, octynylene group, noninylene group, decynylene group, undecynylene group, dodecynylene group and the like.

Examples of the arylene group having 6 to 30 carbon atoms (preferably 6 to 15 carbon atoms) of R ¹¹¹ include a phenylene group, a tolylene group, a xylylene group, and a naphthylene group.

z represents an integer of 1 to 30 (preferably 2 to 20, more preferably 3 to 7, further preferably 5 to 6).

R ¹¹² represents a branched or unbranched alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenyl group having 2 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms, or an aralkyl group having 7 to 30 carbon atoms. Represent. Of these, a branched or unbranched alkyl group having 1 to 30 carbon atoms is preferable.

Examples of the branched or unbranched alkyl group having 1 to 30 carbon atoms (preferably 3 to 25 carbon atoms, more preferably 10 to 15 carbon atoms) of R ¹¹² include, for example, a methyl group, an ethyl group, an n-propyl group, Isopropyl, n-butyl, iso-butyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, 2-ethylhexyl, octyl, nonyl, decyl, undecyl , Dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, octadecyl group and the like.

Examples of the branched or unbranched alkenyl group having 2 to 30 carbon atoms (preferably 3 to 25 carbon atoms, more preferably 10 to 15 carbon atoms) for R ¹¹² include, for example, a vinyl group, a 1-propenyl group, and 2-propenyl. Group, 1-butenyl group, 2-butenyl group, 1-pentenyl group, 2-pentenyl group, 1-hexenyl group, 2-hexenyl group, 1-octenyl group, decenyl group, undecenyl group, dodecenyl group, tridecenyl group, tetradecenyl group Group, pentadecenyl group, octadecenyl group and the like.

Examples of the aryl group having 6 to 30 carbon atoms (preferably 10 to 20 carbon atoms) of R ¹¹² include a phenyl group, a tolyl group, a xylyl group, a naphthyl group, and a biphenyl group.

Examples of the aralkyl group having 7 to 30 carbon atoms (preferably 10 to 20 carbon atoms) of R ¹¹² include a benzyl group and a phenethyl group.

Specific examples of the group represented by —O— (R ¹¹¹ —O) _z —R ¹¹² include, for example, —O— (C ₂ H ₄ —O) ₅ —C ₁₁ H ₂₃ , —O— (C _{2 H 4 -O) 5 -C 12 H} 25, -O- (C 2 H 4 -O) 5 -C 13 H 27, -O- (C 2 H 4 -O) 5 -C 14 H 29, -O _{- (C 2 H 4 -O)} 5 -C 15 H 31, -O- (C 2 H 4 -O) 3 -C 13 H 27, -O- (C 2 H 4 -O) 4 -C 13 H _{27, -O- (C 2 H 4} -O) 6 -C 13 H 27, such as _{-O- (C 2 H 4 -O)} 7 -C 13 H 27 and the like. Among _{these, -O- (C 2 H 4 -O} ) 5 -C 11 H 23, -O- (C 2 H 4 -O) 5 -C 13 H 27, -O- (C 2 H 4 -O) 5 _{-C 15 H 31, -O- (C} 2 H 4 -O) 6 -C 13 H 27 are preferable.

Examples of the branched or unbranched alkylene group having 1 to 6 carbon atoms (preferably 1 to 5 carbon atoms) of R ¹⁰⁴ include the same groups as the branched or unbranched alkylene group having 1 to 30 carbon atoms of R ^111. Can give.

Examples of the compound represented by the formula (1) include 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, and the following formula: The compound represented by the following formula (Si363 manufactured by EVONIK-DEGUSSA) and the like can be used, and a compound represented by the following formula can be preferably used. These may be used alone or in combination of two or more.

Next, the compound containing the bond unit A represented by the formula (2) and the bond unit B represented by the formula (3) will be described.

By using the compound containing the bond unit A represented by the formula (2) and the bond unit B represented by the formula (3), the silica is well dispersed, processability, fuel efficiency, breaking strength, and bending resistance. Crack growth can be improved in a more balanced manner.

The compound containing the bond unit A represented by the formula (2) and the bond unit B represented by the formula (3) is more viscous during processing than a polysulfide silane such as bis- (3-triethoxysilylpropyl) tetrasulfide. The rise 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, 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 part of the bonding unit A covers the —SH group of the bonding unit B, so that it does not easily react with the polymer and scorch is less likely to occur. This is probably because of this.

In the silane coupling agent having the above structure, the content of the bond unit A is preferably 30 from the viewpoint that the effect of suppressing the increase in viscosity during processing and the effect of suppressing the shortening of the scorch time can be enhanced. It is at least mol%, more preferably at least 50 mol%, preferably at most 99 mol%, more preferably at most 90 mol%. Further, the content of the bond unit B is preferably 1 mol% or more, more preferably 5 mol% or more, further preferably 10 mol% or more, preferably 70 mol% or less, more preferably 65 mol% or less, More preferably, it is 55 mol% or less. Further, the total content of the binding units A and B is preferably 95 mol% or more, more preferably 98 mol% or more, and particularly preferably 100 mol%.
The content of the bond units A and B is an amount including the case where the bond units A and B are located at the terminal of the silane coupling agent. The form in which the bonding units A and B are located at the end of the silane coupling agent is not particularly limited, as long as the units corresponding to the formulas (2) and (3) indicating the bonding units A and B are formed. .

Examples of the halogen for R ²⁰¹ include chlorine, bromine, and fluorine.

^Examples of the branched or unbranched alkyl group having 1 to 30 carbon atoms of R ²⁰¹ include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, iso-butyl group, sec-butyl group, tert- Examples thereof include a butyl group, a pentyl group, a hexyl group, a heptyl group, a 2-ethylhexyl group, an octyl group, a nonyl group, and a decyl group. The number of carbon atoms of the alkyl group is preferably 1-12.

^Examples of the branched or unbranched C 2-30 alkenyl group of R ²⁰¹ include a vinyl group, 1-propenyl group, 2-propenyl group, 1-butenyl group, 2-butenyl group, 1-pentenyl group, and 2-pentenyl. Group, 1-hexenyl group, 2-hexenyl group, 1-octenyl group and the like. The alkenyl group preferably has 2 to 12 carbon atoms.

^Examples of the branched or unbranched alkynyl group having 2 to 30 carbon atoms of R ²⁰¹ include ethynyl group, propynyl group, butynyl group, pentynyl group, hexynyl group, heptynyl group, octynyl group, nonynyl group, decynyl group, undecynyl group, And dodecynyl group. The alkynyl group preferably has 2 to 12 carbon atoms.

Examples of the branched or unbranched alkylene group having 1 to 30 carbon atoms of R ²⁰² include an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, a heptylene group, an octylene group, a nonylene group, a decylene group, an undecylene group, Examples include 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 C2-C30 alkenylene group of R202 include vinylene group, 1-propenylene group, 2-propenylene group, 1-butenylene group, 2-butenylene group, 1-pentenylene group and 2-pentenylene. Group, 1-hexenylene group, 2-hexenylene group, 1-octenylene group and the like. The alkenylene group preferably has 2 to 12 carbon atoms.

Examples of the branched or unbranched alkynylene group having 2 to 30 carbon atoms of R ²⁰² include ethynylene group, propynylene group, butynylene group, pentynylene group, hexynylene group, heptynylene group, octynylene group, noninylene group, decynylene group, undecynylene group, And dodecynylene group. The alkynylene group preferably has 2 to 12 carbon atoms.

In the compound containing the bond unit A represented by the formula (2) and the bond unit B represented by the formula (3), the repetition of the total of the repeating number (x) of the bonding unit A and the repeating number (y) of the bonding unit B The number (x + y) 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.

For example, NXT-Z30, NXT-Z45, NXT-Z60, etc. manufactured by Momentive are used as the compound containing the binding unit A represented by the formula (2) and the coupling unit B represented by the formula (3). Can do. These may be used alone or in combination of two or more.

The content of the silane coupling agent having a mercapto group is preferably 0.1 parts by mass or more, more preferably 3 parts by mass or more, and further preferably 6 parts by mass or more with respect to 100 parts by mass of silica. If it is less than 0.1 part by mass, the viscosity of the unvulcanized rubber composition is high, and there is a possibility that good processability and low fuel consumption cannot be ensured. Moreover, content of the silane coupling agent which has a mercapto group becomes like this. Preferably it is 15 mass parts or less, More preferably, it is 12 mass parts or less. If it exceeds 15 parts by mass, the workability tends to decrease.

In the rubber composition of the present invention, other silane coupling agents may be used in combination with the silane coupling agent having a mercapto group. Examples of other silane coupling agents include bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) trisulfide, bis (3-triethoxysilylpropyl) disulfide, and bis (2- Triethoxysilylethyl) tetrasulfide, 3-trimethoxysilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilylethyl) tetrasulfide, 3 -Triethoxysilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N, N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropylbenzothiazolyl tetras Fido, 3-triethoxysilylpropylbenzothiazolyl tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, bis (3-diethoxymethylsilylpropyl) tetrasulfide, 3- Examples include mercaptopropyldimethoxymethylsilane, dimethoxymethylsilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide, dimethoxymethylsilylpropylbenzothiazolyl tetrasulfide and the like.

The rubber composition of the present invention may contain a reinforcing filler other than silica. Examples of the reinforcing filler include carbon black, clay, calcium carbonate, aluminum hydroxide, alumina, talc, glass balloon, cellulose, and montmorillonite. Especially, it is preferable to mix | blend carbon black. Thereby, workability, fuel efficiency, fracture strength, and flex crack growth resistance can be improved in a balanced manner. Carbon blacks that can be used include furnace black (furnace carbon black) such as SAF, ISAF, HAF, MAF, FEF, SRF, GPF, APF, FF, CF, SCF and ECF; acetylene black (acetylene carbon black); FT And thermal black (thermal carbon black) such as MT; channel black (channel carbon black) such as EPC, MPC and CC; graphite and the like. Carbon black may be used independently and may use 2 or more types together.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 5 m ² / g or more, and more preferably 15 m ² / g or more. If it is less than 5 m ² / g, sufficient reinforcing properties cannot be obtained, and sufficient fracture strength and resistance to flex crack growth may not be obtained. The N ₂ SA is preferably 100 m ² / g or less, more preferably 60 m ² / g or less, and still more preferably 40 m ² / g or less. When it exceeds 100 m ² / g, the dispersibility is poor, and the workability and fuel efficiency tend to deteriorate.
Incidentally, _N 2 SA of carbon black, JIS K 6217-2: determined by 2001.

When the rubber composition of the present invention contains carbon black, the content of carbon black is preferably 5 parts by mass or more, more preferably 15 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 5 parts by mass, sufficient reinforcing properties cannot be obtained, and sufficient fracture strength and resistance to flex crack growth may not be obtained. The content is preferably 60 parts by mass or less, more preferably 40 parts by mass or less. If it exceeds 60 parts by mass, heat generation will increase and processability and fuel efficiency will tend to deteriorate.

The content of silica in 100% by mass of the reinforcing filler (preferably the total of silica and carbon black) is preferably 50% by mass or more, more preferably 60% by mass or more, and still more preferably 80% by mass or more. It may be 100% by mass. When the content is within the above range, the effects of the present invention are more suitably obtained.

In addition to the above components, the rubber composition of the present invention includes compounding agents generally used in the production of rubber compositions, such as zinc oxide, stearic acid, processing aids, various anti-aging agents, and oil softeners. Vulcanizing agents such as aromatic petroleum resins, waxes, sulfur, vulcanization accelerators, and the like can be appropriately blended.

Although it does not specifically limit as a softener which can be used by this invention, For example, mineral oils, such as aromatic oil, a process oil, paraffin oil, will be mentioned if it is oil. These softeners may be used alone or in combination of two or more.

In the present invention, the amount of oil is preferably 1 to 20 parts by mass, more preferably 5 to 15 parts by mass with respect to 100 parts by mass of the rubber component, because the effects of the present invention can be suitably obtained. . Here, the amount of oil contained in the oil-extended rubber is also included in the amount of oil blended.

Examples of the vulcanization accelerator include sulfenamide, thiazole, thiuram, thiourea, guanidine, dithiocarbamic acid, aldehyde-amine or aldehyde-ammonia, imidazoline, or xanthate vulcanization accelerators. Etc. These vulcanization accelerators may be used alone or in combination of two or more. Of these, sulfenamide vulcanization accelerators are preferred.

Examples of the sulfenamide vulcanization accelerator include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N, N -Dicyclohexyl-2-benzothiazolylsulfenamide (DCBS) and the like. Of these, TBBS is preferable.

The content of the vulcanization accelerator is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and preferably 5 parts by mass or less, more preferably 100 parts by mass of the rubber component. Is 3 parts by mass or less. By adjusting within the above range, the effect of the present invention can be obtained more suitably.

As a method for producing the rubber composition of the present invention, known methods can be used. For example, the above components are kneaded using a rubber kneader such as an open roll, a Banbury mixer, a closed kneader, and then added. It can be manufactured by a method of sulfurating.

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 necessary is extruded in accordance with the shape of the sidewall, etc. in an unvulcanized stage, molded by a normal method on a tire molding machine, etc. After being bonded together with the tire member to form an unvulcanized tire, the tire can be manufactured by heating and pressing in a vulcanizer.

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

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

(Production Example 1)
UBEPOL BR150L 100 g made by Ube Industries, Ltd. obtained by cobalt-based catalytic polymerization was dissolved in 1000 ml of dehydrated cyclohexane, charged into a 1.5 liter stainless steel autoclave, and the inside was sufficiently purged with nitrogen. 0.18 parts by mass of sulfur was added and a denaturation reaction was performed at 40 ° C. for 40 minutes at normal pressure. After completion of the modification reaction, the inside of the autoclave was opened, ethanol was added to the polymerization solution to recover the polybutadiene rubber, and an anti-aging agent was added thereto, followed by vacuum drying at 40 ° C. for 3 hours. BR1 (sulfur modified butadiene) Rubber).

(Production Example 2)
100 g of polybutadiene with Mooney viscosity 67, 5% toluene solution viscosity 190 obtained by cobalt-based catalytic polymerization was dissolved in 1000 ml of dehydrated cyclohexane, charged into a 1.5 liter stainless steel autoclave, and the inside was sufficiently purged with nitrogen. Thereafter, 0.18 parts by mass of disulfur dichloride was added, and a denaturing reaction was carried out at normal pressure and 40 ° C. for 40 minutes. After completion of the modification reaction, the inside of the autoclave was opened, ethanol was added to the polymerization solution to recover the polybutadiene rubber, and an anti-aging agent was added thereto, followed by vacuum drying at 40 ° C. for 3 hours. BR2 (sulfur modified butadiene) Rubber).

(Production Example 3)
BR3 (sulfur modified butadiene rubber) was obtained in the same manner as in Production Example 1 except that BunaCB22 manufactured by LANXESS obtained by neodymium-based catalytic polymerization was used as polybutadiene.

(Production Example 4)
In a glass bottle with a rubber brace volume of 100 ml, dried and nitrogen-substituted, in the following order, 7.11 g of cyclohexane solution of butadiene (15.2% by mass), cyclohexane solution of neodymium neodecanoate (0.56) Mol / liter) 0.59 ml, toluene solution of methylaluminoxane MAO (PMAO manufactured by Toso-Akzo Co.) (aluminum concentration: 3.23 mol / liter) 10.32 ml, diisobutylaluminum hydride (manufactured by Kanto Chemical Co., Inc.) 1.77 ml of a hexane solution (0.90 mol / liter) was added and aged at room temperature for 2 minutes, and then a hexane solution (0.95 mol / liter) of chlorinated diethylaluminum (manufactured by Kanto Chemical). 45 ml was added and aged at room temperature for 15 minutes with occasional stirring. The reaction solution thus obtained was used as a polymerization catalyst solution for the next reaction.
A 1-liter glass bottle with a rubber stopper was dried and purged with nitrogen, and a dry-purified butadiene cyclohexane solution and a dry cyclohexane solution were respectively added thereto, and 400 g of a 12.5 mass% cyclohexane solution of butadiene was charged. Next, 2.28 ml of the catalyst solution prepared above (0.025 mmol in terms of neodymium) was added, and polymerization was performed in a 50 ° C. hot water bath for 1.0 hour. The polymerization was stopped by adding 2 ml of a 5% solution of isopropanol 2,2′-methylene-bis (4-ethyl-6-tert-butylphenol) (NS-5) in isopropanol to the polymerization system. Reprecipitation was performed in isopropanol containing -5, and drum-dried to obtain an unmodified polybutadiene rubber. This was subjected to sulfur modification in the same manner as in Production Example 1 to obtain BR4 (sulfur modified butadiene rubber).

The following evaluation was performed on the sulfur-modified butadiene rubber (BR1-4) obtained in Production Examples 1 to 4 and UBEPOL BR150L manufactured by Ube Industries, Ltd. The results are shown in Table 1.

(Cis content)
The cis content was measured using an AV400 NMR apparatus manufactured by BRUKER and data analysis software TOP SPIN2.1.

(Glass transition temperature (Tg))
According to JIS-K7121, the glass transition temperature (Tg) was measured on the conditions of the temperature increase rate of 10 degree-C / min using the automatic differential scanning calorimeter (DSC-60A) by Shimadzu Corporation.

(Mooney viscosity (ML _{1 + 4} , 100 ° C.) In Table 1, abbreviated as ML)
In accordance with JIS-K6300, using a Mooney viscometer (SMV-200) manufactured by Shimadzu Corporation, preheated at 100 ° C for 1 minute, then measured for 4 minutes, and Mooney viscosity of rubber (ML _{1 + 4} , 100 ° C) Was measured.

(5% toluene solution viscosity (Tcp))
After dissolving 2.28 g of the polymer in 50 ml of toluene, the standard solution for calibration of the viscometer (JIS Z8809) was used as the standard solution. 400 was used to measure the 5% toluene solution viscosity (Tcp) at 25 ° C.

(Z + 1 average molecular weight (M _{z + 1} ), number average molecular weight (M _n ))
Performing gel permeation (permeation) chromatography (GPC, manufactured by Tosoh Corporation) at a temperature of 40 ° C. using tetrahydrofuran as a solvent with polystyrene as a standard substance, and using a calibration curve obtained from the obtained molecular weight distribution curve, The z + 1 average molecular weight and the number average molecular weight were determined.

(Storage elastic modulus when the loss elastic modulus in the viscoelasticity of the solution diluted to 30% by mass with liquid paraffin is 100 Pa)
The polymer was dissolved in liquid paraffin to 30% by mass, and the resulting solution was measured for storage elastic modulus and loss elastic modulus at a dynamic strain of 1% using DSR500 manufactured by Rheometric Co., and when the loss elastic modulus was 100 Pa. The storage modulus was determined.

Hereinafter, various chemicals used in Production Examples 5 and 6 will be described together.
Natural rubber latex: Field latex surfactant obtained from Muhibah Lateks, Inc .: Emal-E27C (polyoxyethylene lauryl ether sodium sulfate) manufactured by Kao Corporation
NaOH: NaOH manufactured by Wako Pure Chemical Industries, Ltd.

(Production of saponified natural rubber)
(Production Example 5)
After adjusting solid content concentration (DRC) of natural rubber latex to 30% (w / v), 25 g of 10% Emal-E27C aqueous solution and 50 g of 40% NaOH aqueous solution are added to 1000 g of natural rubber latex (wet state), A saponification reaction was carried out at room temperature for 48 hours to obtain a saponified natural rubber latex. Water was added to the latex to dilute to DRC 15% (w / v), and then formic acid was added with slow stirring to adjust the pH to 4.0 for aggregation.
The agglomerated rubber was pulverized, washed repeatedly with 1000 ml of water, and then dried at 90 ° C. for 4 hours to obtain a solid rubber (saponified natural rubber A).

(Production Example 6)
A solid rubber (saponified natural rubber B) was obtained in the same manner as in Production Example 1 except that the amount of the 40% NaOH aqueous solution was changed to 25 g.

The solid content (saponified natural rubber A, B) and TSR obtained in Production Examples 5 and 6 were measured for nitrogen content, phosphorus content, and gel content by the methods described below. The results are shown in Table 2.

(Measurement of nitrogen content)
The nitrogen content was measured using CHN CORDER MT-5 (manufactured by Yanaco Analytical Industries). For the measurement, first, a calibration curve for determining the nitrogen content was prepared using antipyrine as a standard substance. Next, about 10 mg of the sample was weighed, and an average value was obtained from the measurement results of three times to obtain the nitrogen content of the sample.

(Measurement of phosphorus content)
The phosphorus content of the sample was determined using an ICP emission spectrometer (ICPS-8100, manufactured by Shimadzu Corporation).
In addition, ³¹ P-NMR measurement of phosphorus uses an NMR analyzer (400 MHz, AV400M, manufactured by Nippon Bruker Co., Ltd.), and uses a measurement peak of P atom in an 80% aqueous phosphoric acid solution as a reference point (0 ppm), and raw rubber with chloroform. More extracted components were purified, dissolved in CDCl ₃ and measured.

(Measurement of gel content)
A raw rubber sample 70.00 mg cut to 1 mm × 1 mm was weighed, 35 mL of toluene was added thereto, and the mixture was allowed to stand in a cool dark place for 1 week. Subsequently, centrifugation was performed to precipitate a gel component insoluble in toluene, the soluble component of the supernatant was removed, and only the gel component was solidified with methanol, and then dried and the mass was measured. The gel content (%) was determined by the following formula.
Gel content (mass%) = [mass mg after drying / mg of initial sample] × 100

As shown in Table 2, the saponified natural rubbers A and B had a reduced nitrogen content, phosphorus content, and gel content as compared with TSR.
In ³¹ P-NMR measurement, the saponified natural rubbers A and B did not have a peak due to phospholipid at -3 ppm to 1 ppm.

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
NR: TSR
Saponified natural rubber A: Modified natural rubber obtained by Production Example 5 Saponified natural rubber B: Modified natural rubber obtained by Production Example 6 BR1: BR1 (sulfur modified butadiene rubber) prepared by Production Example 1 (Tg) : -108 ° C)
BR2: BR2 (sulfur-modified butadiene rubber) prepared according to Production Example 2 (Tg: −108 ° C.)
BR3: BR3 (sulfur-modified butadiene rubber) prepared according to Production Example 3 (Tg: −109 ° C.)
BR4: BR4 (sulfur-modified butadiene rubber) prepared according to Production Example 4 (Tg: -110 ° C)
BR5: Polybutadiene rubber (sulfur non-modified butadiene rubber) UBEPOL BR150L (Tg: −108 ° C.) manufactured by Ube Industries, Ltd.
Silica: Ultrasil VN3 (N ₂ SA: 175 m ² / g) manufactured by EVONIK-DEGUSSA
Carbon black: Niteron # 55S (N ₂ SA: 28 m ² / g) manufactured by Shin-Nikka Carbon Co., Ltd.
Silane coupling agent 1: NXT-Z45 manufactured by Momentive (compound containing bonding unit A and bonding unit B (bonding unit A: 55 mol%, bonding unit B: 45 mol%))
Silane coupling agent 2: Si363 manufactured by EVONIK-DEGUSSA
Silane coupling agent 3: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by EVONIK-DEGUSSA
Process oil: Process X-140 (aromatic process oil) manufactured by Japan Energy
Wax: Sunnock N manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Stearic acid: Stearic acid “paulownia” manufactured by NOF Corporation
Zinc oxide: 2 types of anti-aging of zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd .: NOCRACK 6C (N- (1,3-dimethylbutyl) -N-phenyl-p-phenylene manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.) Diamine)
Sulfur: Powdered sulfur vulcanization accelerator manufactured by Tsurumi Chemical Industry Co., Ltd .: Noxeller NS (N-tert-butyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

(Examples and Comparative Examples)
According to the formulation shown in Table 3, materials other than sulfur and a vulcanization accelerator were kneaded for 3 minutes at 150 ° 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 5 minutes at 50 ° 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 12 minutes to obtain a vulcanized rubber composition.

The following evaluation was performed about the obtained unvulcanized rubber composition and vulcanized rubber composition. The results are shown in Table 3.

(Processability)
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

(Low fuel consumption)
Using a viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.), tan δ of each vulcanized rubber composition was measured and compared at a temperature of 70 ° C., an initial strain of 10%, and a dynamic strain of 2%. The tan δ in Example 1 was set to 100, and the index was displayed by 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

(destruction strength)
The obtained vulcanized rubber composition was subjected to a tensile test using a No. 3 dumbbell according to JIS K6251 and measured for breaking strength (TB) and elongation at break (EB) (%). The numerical value of TB × EB / 2 was used as the breaking strength, and the breaking strength of each formulation was displayed as an index with the breaking strength of Comparative Example 1 as 100. The larger the index, the better the breaking strength.

(Flexible crack growth resistance)
Using the obtained vulcanized rubber composition, a sample was prepared based on JIS K6260 “vulcanized rubber and thermoplastic rubber-dematcher bending crack test method”, a bending crack growth test was performed, 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 is, the more the crack growth is suppressed and the resistance to flex crack growth is excellent.
(Bending crack growth resistance index) = (Measured value of Comparative Example 1) / (Measured value of each formulation) × 100

From the results of Table 3, butadiene rubber (BR1-4) modified with a sulfur compound, having a cis content of 70% by mass or more and a Mooney viscosity (ML _{1 + 4} , 100 ° C.) of 30 to 120, silica, and a mercapto group Examples including the silane coupling agent (silane coupling agents 1 and 2) had improved workability, fuel efficiency, fracture strength, and flex crack growth resistance in a well-balanced manner.

By comparison of Comparative Examples 1, 2, 3, and Example 1, a butadiene rubber modified with a sulfur compound, having a cis content of 70% by mass or more and a Mooney viscosity (ML _{1 + 4} , 100 ° C.) of 30 to 120, and a mercapto group It was found that processability and low fuel consumption can be improved synergistically by using a silane coupling agent having the above.

Claims (9)

For a sidewall containing a butadiene rubber modified with a sulfur compound and having a cis content of 70% by mass or more and a Mooney viscosity (ML _{1 + 4} , 100 ° C.) of 30 to 120, silica, and a silane coupling agent having a mercapto group Rubber composition. The rubber composition for a sidewall according to claim 1, wherein the content of silica in 100% by mass of the reinforcing filler is 50% by mass or more. The rubber composition for a sidewall according to claim 1 or 2, comprising a modified natural rubber having a phosphorus content of 200 ppm or less. The rubber composition for a sidewall according to claim 3, wherein the nitrogen content of the modified natural rubber is 0.3% by mass or less. The rubber composition for a sidewall according to any one of claims 1 to 4, wherein the butadiene rubber has a ratio of z + 1 average molecular weight and number average molecular weight in terms of polystyrene by gel permeation chromatography of 3.5 or more. The rubber for a sidewall according to any one of claims 1 to 5, wherein the butadiene rubber has a ratio of 5% toluene solution viscosity (Tcp) to Mooney viscosity (ML _{1 + 4} , 100 ° C) of 1.8 to 6.0. Composition. The silane coupling agent is a compound containing a compound represented by the following formula (1) and / or a binding unit A represented by the following formula (2) and a binding unit B represented by the following formula (3). The rubber composition for side walls in any one of Claims 1-6.

(In the formula (1), R ^{101 to} R ¹⁰³ are each a branched or unbranched C 1-12 alkyl group, a branched or unbranched C 1-12 alkoxy group, or —O— (R ¹¹¹ — O) _z- R ¹¹² (z R ¹¹¹ represents a branched or unbranched divalent hydrocarbon group having 1 to 30 carbon atoms. The z R ^{111 s} may be the same as or different from each other. ¹¹² represents a branched or unbranched alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenyl group having 2 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms, or an aralkyl group having 7 to 30 carbon atoms. Z represents an integer of 1 to 30.) R ^{101 to} R ¹⁰³ may be the same as or different from each other, and R ¹⁰⁴ has 1 to 6 carbon atoms which are branched or unbranched. Represents an alkylene group of

(In the formulas (2) and (3), R ²⁰¹ is hydrogen, halogen, branched or unbranched alkyl group having 1 to 30 carbon atoms, branched or unbranched alkenyl group having 2 to 30 carbon atoms, branched or unbranched. Or an alkyl group substituted with a hydroxyl group or a carboxyl group, and R ²⁰² represents a branched or unbranched C 1-30 alkylene group, branched or It represents an unbranched C2-C30 alkenylene group or a branched or unbranched C2-C30 alkynylene group, and R ²⁰¹ and R ²⁰² may form a ring structure.) 100 parts by mass of rubber component containing 5-60% by mass of the butadiene rubber in 100% by mass of rubber component, 5-100 parts by mass of silica, 0-60 parts by mass of carbon black, and 100 parts by mass of silica The rubber composition for a sidewall according to any one of claims 1 to 7, comprising 0.1 to 15 parts by mass of the silane coupling agent. A pneumatic tire having a sidewall produced using the rubber composition according to claim 1.