JP5808305B2 - Rubber composition and pneumatic tire - Google Patents

Description

The present invention relates to a rubber composition and a pneumatic tire produced using the rubber composition.

In recent years, there is an increasing demand for tires to improve fuel economy, steering stability such as braking performance during high-speed driving, and riding comfort performance. As a method for improving steering stability, a method is known in which a phenol resin is blended with a fiber cord coating rubber composition to improve the complex elastic modulus (E ^* ) and increase the rigidity. However, this method has room for improvement in that tan δ increases and fuel efficiency deteriorates.

As a technique for improving E ^* and reducing tan δ, a cross-linked resin such as a resorcin condensate or a modified resorcin condensate is used as a partial condensate of hexamethylol melamine pentamethyl ether (HMMPME) or hexamethoxymethylol melamine (HMMM). A method of crosslinking with a methylene donor such as a partial condensate is known. Patent Document 1 discloses a rubber composition that has improved adhesion to a carcass cord and further suppresses crack growth, heat generation, and deterioration of rubber properties. However, in recent years, further improvement in fuel efficiency has been demanded.

JP 2006-328194 A

The present invention solves the above-described problems, and provides a rubber composition that can improve fuel efficiency while maintaining processability, rubber strength, resistance to flex crack growth, and cord adhesion, and a pneumatic tire produced using the rubber composition. The purpose is to provide.

（式中、Ｒ^１、Ｒ^２は、同一又は異なって、水素原子、炭素数１〜２０のアルキル基、炭素数１〜２０のアルケニル基又は炭素数１〜２０のアルキニル基である。Ｍ^ｒ＋は金属イオンを示し、ｒはその価数を表す。） The present invention includes a rubber component containing at least one diene rubber selected from the group consisting of isoprene rubber, butadiene rubber and styrene butadiene rubber, carbon black having a nitrogen adsorption specific surface area of 20 to 130 m ² / g, Compound represented by the following formula (I), sulfur, at least one cross-linked resin selected from the group consisting of cresol resin, resorcin resin and modified resorcin resin, partial condensate of hexamethoxymethylol melamine and hexamethylol Containing at least one methylene donor selected from the group consisting of partial condensates of melamine pentamethyl ether, and the content of the carbon black is 10 to 60 parts by mass with respect to 100 parts by mass of the rubber component. The sulfur content is 2 to 3.5 parts by mass, and the content of the crosslinked resin is 0.5 to 10 parts. The rubber whose content of said methylene donor is 0.1-3 mass parts, and whose content of following formula (I) is 0.5-20 mass parts with respect to 100 mass parts of said carbon black. Relates to the composition.

^(Wherein, R 1, ^{R 2} are the same or different, a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an alkenyl group or an alkynyl group having 1 to 20 carbon atoms having 1 to 20 carbon atoms ^{.M r +} Represents a metal ion, and r represents its valence.)

In 100% by mass of the rubber component, the content of isoprene-based rubber is preferably 50 to 100% by mass, the content of styrene butadiene rubber is 0 to 40% by mass, and the content of butadiene rubber is preferably 0 to 30% by mass. .

The compound represented by the formula (I) is preferably a compound represented by the following formula (I-1), (I-2) or (I-3).

The metal ion is preferably sodium ion, potassium ion or lithium ion.

The rubber composition is preferably used as a rubber composition for covering a fiber cord.

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

According to the invention, a rubber containing a predetermined amount of a specific rubber component, a specific carbon black, a compound represented by the formula (I), sulfur, a specific cross-linked resin, and a specific methylene donor. Since it is a composition, it is possible to provide a pneumatic tire in which processability, rubber strength, resistance to flex crack growth, cord adhesion, and fuel efficiency are improved in a well-balanced manner.

The rubber composition of the present invention contains a specific rubber component, a specific carbon black, a compound represented by the formula (I), sulfur, a specific cross-linked resin, and a specific methylene donor. The compound represented by the formula (I) can be bonded to carbon black by the reaction of the terminal nitrogen functional group with a functional group such as a carboxyl group present on the surface of the carbon black, and the carbon-carbon double The bonding portion can be bonded to the polymer by a reaction with a polymer radical or a reaction involving sulfur crosslinking. Therefore, the dispersibility of carbon black can be improved and the good dispersion state can be maintained even during use. Further, since the polymer restrains the carbon black through the compound represented by the formula (I), the exothermic property can be suppressed. The compound represented by the formula (I) having these functions is blended with a specific carbon black, sulfur, a specific cross-linked resin, and a specific methylene donor into a rubber composition containing a specific rubber component. As a result, the fuel efficiency can be greatly improved while maintaining the processability, rubber strength, flex crack growth resistance and cord adhesion of the rubber composition at a problem-free level.

The rubber composition of the present invention contains at least one selected from the group consisting of isoprene rubber, butadiene rubber (BR) and styrene butadiene rubber (SBR) as a rubber component.

Examples of the isoprene-based rubber include natural rubber (NR), isoprene rubber (IR), epoxidized natural rubber (ENR), and high-purity natural rubber (HPNR), and NR can be preferably used. In the isoprene-based rubber, a polymer chain is cut during kneading to generate radicals. The generated radical is captured by the compound represented by the formula (I), whereby the polymer chain and the compound represented by the formula (I) can be bonded. 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 SBR is not particularly limited, and emulsion polymerization SBR (E-SBR) and solution polymerization SBR (S-SBR) can be preferably used.

The BR is not particularly limited, and those commonly used in the tire industry can be used, and high-cis BR (high cis BR) or modified BR such as BR130B and BR150B manufactured by Ube Industries, Ltd. are preferably used. Can do. As the modified BR, tin-modified BR and modified BR modified with a compound containing a glycidylamino group in the molecule are preferable.

The content of the isoprene-based rubber in 100% by mass of the rubber component is preferably 50% by mass or more, more preferably 60% by mass or more, and further preferably 70% by mass or more. If it is less than 50% by mass, the fuel economy may not be sufficiently improved. In addition, sufficient rubber strength cannot be ensured, and the rubber composition may be broken by contact with road surface irregularities or foreign objects during tire travel. The content may be 100% by mass, preferably 90% by mass or less, more preferably 80% by mass or less.

The content of SBR in 100% by mass of the rubber component may be 0% by mass, but is preferably 10% by mass or more, more preferably 15% by mass or more. If it is less than 10% by mass, there is a possibility that the cord adhesiveness, rubber strength and bending crack growth resistance cannot be sufficiently secured. The content is preferably 40% by mass or less, more preferably 35% by mass or less. If it exceeds 40% by mass, fuel economy, cord adhesion, rubber strength, and flex crack growth resistance may be reduced.

The content of BR in 100% by mass of the rubber component may be 0% by mass, but is preferably 10% by mass or more, more preferably 12% by mass or more. If it is less than 10% by mass, the resistance to flex crack growth may be lowered. The content is preferably 30% by mass or less, more preferably 25% by mass or less. When it exceeds 30 mass%, in a kneading | mixing process, the winding to a roll worsens and there exists a possibility that workability may fall.

The rubber composition of the present invention contains carbon black having a specific nitrogen adsorption specific surface area. The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is 20 m ² / g or more, preferably 25 m ² / g or more, more preferably 30 m ² / g or more. If it is less than 20 m ² / g, sufficient rubber strength may not be ensured. The N ₂ SA is 130 m ² / g or less, preferably 120 m ² / g or less, more preferably 100 m ² / g or less. When it exceeds 130 m ² / g, the heat generation derived from carbon black is increased, and the reaction with the compound represented by the formula (I) is difficult to proceed, so that the fuel economy may not be sufficiently improved. is there.

Carbon black dibutyl phthalate (DBP) oil absorption is preferably 40 cm ^3/100 g or more, more preferably 70cm ^3/100 g or more. Is less than 40 cm ^3/100 g, it may not be possible to secure a sufficient rubber strength. Intake oil amount is preferably 180cm ^3/100 g or less, and more preferably not more than 160cm ³ / 100g. Exceeds 180cm ³ / 100g, it may be impossible to ensure a minimum breaking elongation.

The pH of carbon black is preferably 7.9 or less, more preferably 7.8 or less, still more preferably 7.7 or less, and particularly preferably 7.6 or less. If it exceeds 7.9, the amount of acidic functional groups of carbon black is small, so the reactivity (interaction) with the compound represented by formula (I) is small, and there is a possibility that fuel economy and the like cannot be improved sufficiently. is there. Although the minimum of this pH is not specifically limited, Preferably it is 3.0 or more, More preferably, it is 3.5 or more. If it is less than 3.0, the pH of the rubber composition is lowered, whereby the activity of the vulcanizing agent is lowered and the crosslinking efficiency tends to be lowered.

The volatile content of carbon black is preferably 0.8% by mass or more, more preferably 0.9% by mass or more, and further preferably 1.0% by mass or more. If it is less than 0.8% by mass, the reactivity (interaction) with the compound represented by the formula (I) becomes small, and there is a possibility that the fuel efficiency cannot be sufficiently improved. Although the upper limit of this volatile matter is not specifically limited, Preferably it is 3.5 mass% or less, More preferably, it is 3.0 mass% or less. If it exceeds 3.5 mass%, it is necessary to volatilize most of the volatile components in the vulcanization process and continue vulcanization until porosity does not occur. There is a tendency to get worse.

In this specification, the DBP oil absorption, pH, and volatile content of carbon black are values measured by JIS K6221 (1982), and N ₂ SA of carbon black is a value measured by the method described by JIS K6217 (2001).

The content of carbon black is 10 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 it is less than 10 parts by mass, there is a possibility that sufficient bending crack growth resistance cannot be ensured. The content is 60 parts by mass or less, preferably 55 parts by mass or less. When the amount exceeds 60 parts by mass, the rubber becomes too hard, and the flex crack growth resistance may be deteriorated. Moreover, there is a possibility that the fuel efficiency is deteriorated.

（式中、Ｒ^１、Ｒ^２は、同一又は異なって、水素原子、炭素数１〜２０のアルキル基、炭素数１〜２０のアルケニル基又は炭素数１〜２０のアルキニル基である。Ｍ^ｒ＋は金属イオンを示し、ｒはその価数を表す。） The rubber composition of the present invention contains a compound represented by the following formula (I).

^(Wherein, R 1, ^{R 2} are the same or different, a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an alkenyl group or an alkynyl group having 1 to 20 carbon atoms having 1 to 20 carbon atoms ^{.M r +} Represents a metal ion, and r represents its valence.)

Examples of the alkyl group for R ¹ and R ² include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, and a tert-butyl group.
Examples of the alkenyl group for R ¹ and R ² include a vinyl group, an allyl group, a 1-propenyl group, and a 1-methylethenyl group.
Examples of the alkynyl group for R ¹ and R ² include an ethynyl group and a propargyl group.

R ¹ and R ² are preferably a hydrogen atom or an alkyl group, more preferably a hydrogen atom or a methyl group, and still more preferably a hydrogen atom. That is, the compound represented by the above formula (I) is preferably a compound represented by the following formula (I-1), (I-2) or (I-3). It is more preferable that it is a compound represented by.

In the above formulas (I), (I-1), (I-2), and (I-3), examples of metal ions include sodium ions, potassium ions, and lithium ions, and sodium ions are preferable.

Content of the compound represented by Formula (I) is 0.5 mass part or more with respect to 100 mass parts of carbon black, Preferably it is 1 mass part or more, More preferably, it is 2 mass parts or more. If it is less than 0.5 parts by mass, the fuel economy may not be sufficiently improved. Content of the compound represented by Formula (I) is 20 mass parts or less, Preferably it is 15 mass parts or less, More preferably, it is 10 mass parts or less. If it exceeds 20 parts by mass, there is a possibility that sufficient bending crack growth resistance cannot be ensured.

The rubber composition of the present invention contains sulfur. The sulfur is not particularly limited, and those commonly used in the tire industry can be used, but insoluble sulfur is particularly preferable. The insoluble sulfur, heating the natural sulfur _{S 8, quenched,} refers to a sulfur which is a high molecular weight such that S x (x = 100,000~300,000). By using insoluble sulfur, blooming that normally occurs when sulfur is used as a rubber vulcanizing agent can be prevented.

The sulfur content is 2 parts by mass or more, preferably 2.2 parts by mass or more, and more preferably 2.4 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 2 parts by mass, sufficient sulfur is not supplied to the adhesive layer with the cord, and the cord adhesion may be lowered. The content is 3.5 parts by mass or less, preferably 3.0 parts by mass or less, more preferably 2.8 parts by mass or less. If it exceeds 3.5 parts by mass, the density of sulfur crosslinks increases, and the resistance to flex crack growth, particularly the resistance to flex crack growth after thermal oxidation degradation, may be reduced.

The rubber composition of the present invention contains at least one cross-linked resin selected from the group consisting of a cresol resin, a resorcin resin (condensate) and a modified resorcin resin (condensate). Thereby, code adhesiveness can be improved.

（式中、ｎは１以上の整数である。） Cresol resin is a compound represented by the following formula.

(In the formula, n is an integer of 1 or more.)

（式中、ｎは１以上の整数である。） Resorcin resin (condensate) is a compound represented by the following formula.

(In the formula, n is an integer of 1 or more.)

（式中、ｎは１以上の整数であり、Ｒはアルキル基である。） The modified resorcin resin (condensate) is a compound represented by the following formula. R in the formula is an alkyl group. Examples of the modified resorcin resin (condensate) include resorcin / alkylphenol / formalin copolymer (such as Sumikanol 620 manufactured by Taoka Chemical Co., Ltd.), resorcin / formalin reactant penacolite resin (such as 1319S manufactured by India Spec). Etc.

(In the formula, n is an integer of 1 or more, and R is an alkyl group.)

The content of the cross-linked resin is 0.5 parts by mass or more, preferably 1 part by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 0.5 part by mass, the crosslinking density is small, and there is a possibility that sufficient rubber strength cannot be secured. The content is 10 parts by mass or less, preferably 5 parts by mass or less, more preferably 2 parts by mass or less. When the amount exceeds 10 parts by mass, heat generation increases and the fuel efficiency tends to decrease.

The rubber composition of the present invention contains at least one methylene donor selected from the group consisting of a partial condensate of hexamethoxymethylol melamine and a partial condensate of hexamethylol melamine pentamethyl ether together with the cross-linked resin.

（式中、ｎは１以上の整数である。） A partial condensate of hexamethoxymethylolmelamine (HMMM) is a compound represented by the following formula. N in a formula is an integer greater than or equal to 1, and is usually 1-3.

(In the formula, n is an integer of 1 or more.)

（式中、ｎは１以上の整数である。） Moreover, the partial condensate of hexamethylol melamine pentamethyl ether (HMMPME) is a compound represented by the following formula. N in a formula is an integer greater than or equal to 1, and is usually 1-3.

(In the formula, n is an integer of 1 or more.)

The content of the methylene donor is 0.1 parts by mass or more, preferably 0.5 parts by mass or more, more preferably 0.6 parts by mass or more, and further preferably 1 part by mass with respect to 100 parts by mass of the rubber component. That's it. If the amount is less than 0.1 parts by mass, sufficient rubber strength may not be ensured. The content is 3 parts by mass or less, preferably 2.5 parts by mass or less. When it exceeds 3 parts by mass, heat generation tends to increase and fuel efficiency tends to decrease.

The rubber composition of the present invention may contain other reinforcing filler in addition to the carbon black. Examples of other reinforcing fillers include silica, calcium carbonate, aluminum hydroxide, clay, talc, and alumina. Of these, silica is preferable.

When the rubber composition of the present invention contains silica, the content of silica is preferably 1 part by mass or more, more preferably 5 parts by mass from the viewpoint that good cord adhesion and bending crack growth resistance can be obtained. It is above, Preferably it is 20 mass parts or less, More preferably, it is 15 mass parts or less.

The total content of the reinforcing filler is preferably 10 parts by mass or more, more preferably 40 parts by mass or more with respect to 100 parts by mass of the rubber component. If the amount is less than 10 parts by mass, sufficient reinforcement may not be obtained. The total content is preferably 70 parts by mass or less, more preferably 65 parts by mass or less. When it exceeds 70 parts by mass, the hardness becomes too high and the flex crack growth resistance tends to decrease.

In addition to the above-mentioned components, the rubber composition of the present invention contains compounding agents generally used in the production of rubber compositions such as silane coupling agents, zinc oxide, anti-aging agents, oils, waxes, stearic acid, additives. A sulfur accelerator or the like can be appropriately blended.

Examples of the anti-aging agent include amine-ketone type, bisphenol type, polyphenol type, aromatic secondary amine type, thiourea type anti-aging agent and the like. Among these, it is preferable to use an amine-ketone type anti-aging agent from the viewpoint that good cord adhesion can be obtained. As the amine-ketone antioxidant, 2,2,4-trimethyl-1,2-dihydroquinoline polymer can be used preferably.

As a method for producing the rubber composition of the present invention, a known method, for example, a method of kneading each component with a known mixer such as a roll or Banbury can be used.

The rubber composition of the present invention can be suitably used as a fiber cord coating rubber composition (topping rubber composition), and is particularly suitable for a carcass or belt having a fiber cord.

The fiber cord is obtained from raw materials such as polyester, nylon, rayon and polyethylene terephthalate. Among these, it is preferable to use polyester because it is excellent in thermal stability and inexpensive.

The pneumatic tire of the present invention is formed by coating a fiber cord with the rubber composition of the present invention to form a carcass, a belt, or the like, and then bonding to another tire member to form an unvulcanized tire and vulcanize it. Can be produced. By using the rubber composition of the present invention as a rubber composition for covering a fiber cord, there is an advantage that fuel efficiency can be improved while maintaining processability, rubber strength, resistance to flex crack growth, and cord adhesion.

The pneumatic tire of the present invention is well suited not only for passenger car tires but also for light truck tires because processability, rubber strength, resistance to flex crack growth, cord adhesion and fuel economy are improved in a well-balanced manner. It is.

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

架橋樹脂：田岡化学工業（株）製のスミカノール６２０（変性レゾルシン樹脂）
メチレン供与体：田岡化学工業（株）製のスミカノール５０７Ａ（ＨＭＭＰＭＥの部分縮合物を６５質量％、シリカ及びオイルを３５質量％含有、化学式ｎ＝１〜３、下記表１、２においては樹脂分の量を記載）
不溶性硫黄：日本乾溜工業（株）製のセイミサルファー（オイル分１０％含有、二硫化炭素による不溶物６０％以上のもの、下記表１、２においてはオイル分及び硫黄分の合計量を記載）
酸化亜鉛：東邦亜鉛（株）製の銀嶺Ｒ
老化防止剤：大内新興化学工業（株）製のノクラック２２４（２，２，４−トリメチル−１，２−ジヒドロキノリン重合体）
オイル：（株）ジャパンエナジー製のプロセスＰＸ−１４０
ステアリン酸：日油（株）製のステアリン酸「椿」
加硫促進剤：大内新興化学工業（株）製のノクセラーＮＳ（Ｎ−ｔｅｒｔ−ブチル−２−ベンゾチアゾリルスルファンアミド） Below, various chemical | medical agents used by the Example and the comparative example are demonstrated.
NR: RSS # 3
SBR: Nipol 1502 manufactured by ZEON CORPORATION
BR: BR150B manufactured by Ube Industries, Ltd.
Modified BR (1): Nipol BR1250H manufactured by Nippon Zeon Co., Ltd. (lithium initiator: lithium, tin atom content: 250 ppm, Mw / Mn: 1.5, vinyl bond content: 10-13 mass%)
Modified BR (2): terminal-modified BR polymerized using a lithium initiator and modified with tetraglycidyl-1,3-bisaminomethylcyclohexane at the polymerization terminal of BR (vinyl content: 12% by mass, cis content: 38 (Mass%, trans content: 50 mass%, Mw / Mn: 1.19, Mw: 550,000)
Carbon black: Cabot Japan Ltd. of SHOWBLACK ^{_{N330 (N 2 SA: 75m 2}} / g, DBP oil ^absorption: 102cm 3 ^{/100g,pH:7.5,} volatile matter: 1.0 wt%)
Silica: VN3 manufactured by EVONIK DEGUSSA
Compound (I): (2Z) -4-[(4-aminophenyl) amino] -4-oxo-2-butenoic acid sodium (compound represented by the following formula) manufactured by Sumitomo Chemical Co., Ltd.

Cross-linked resin: Sumikanol 620 (modified resorcin resin) manufactured by Taoka Chemical Co., Ltd.
Methylene donor: Sumikanol 507A manufactured by Taoka Chemical Co., Ltd. (65% by mass of HMMPME partial condensate, 35% by mass of silica and oil, chemical formula n = 1 to 3, in Tables 1 and 2 below, resin content The amount of
Insoluble sulfur: Seimisulfur manufactured by Nippon Kiboshi Kogyo Co., Ltd. (containing 10% oil, 60% or more insoluble matter due to carbon disulfide, Tables 1 and 2 below indicate the total amount of oil and sulfur)
Zinc oxide: Silver candy R made by Toho Zinc Co., Ltd.
Anti-aging agent: NOCRACK 224 (2,2,4-trimethyl-1,2-dihydroquinoline polymer) manufactured by Ouchi Shinsei Chemical Co., Ltd.
Oil: Process PX-140 manufactured by Japan Energy Co., Ltd.
Stearic acid: Stearic acid “椿” manufactured by NOF Corporation
Vulcanization accelerator: Noxeller NS (N-tert-butyl-2-benzothiazolylsulfanamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

<Examples and Comparative Examples>
(Production of rubber sheet for test)
In accordance with the formulations shown in Tables 1 and 2, various chemicals excluding sulfur and a vulcanization accelerator were kneaded with a Banbury mixer. Sulfur and a vulcanization accelerator were added to the obtained kneaded product and kneaded with an open roll to obtain an unvulcanized rubber composition. And the rubber sheet for a test was produced by vulcanizing the unvulcanized rubber composition at 170 ° C. for 12 minutes.
(Production of carcass coated with fiber cord)
A fiber cord (polyester manufactured by Teijin Ltd. (raw materials: terephthalic acid and ethylene glycol)) is immersed in a mixed solution of resorcinol and formaldehyde to form a resorcin resin film (dip treatment). The unvulcanized carcass was formed by coating with a vulcanized rubber composition. Then, vulcanized carcass was obtained by vulcanization at 180 ° C. for 40 minutes.

The following evaluation was performed about the obtained unvulcanized rubber composition, the test rubber sheet, and the vulcanized carcass. The results are shown in Tables 1 and 2. In the following evaluation, the reference comparative example in Table 1 was set as Comparative Example 1, and the reference comparative example in Table 2 was set as Comparative Example 7.

(Roll processability index)
In the kneading step in the open roll, the wrapping of the unvulcanized rubber composition around the roll was visually evaluated, and the value of the reference comparative example was set as 100 (roll workability index). A larger index indicates that kneading in the open roll advances to lubrication and is excellent in workability.

(Low fuel consumption index)
Using a viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.), the loss tangent (tan δ) of each test rubber sheet was measured under conditions of a temperature of 70 ° C., an initial strain of 10%, a dynamic strain of 2%, and a frequency of 10 Hz. Then, assuming that the loss tangent tan δ of the reference comparative example is 100, the tan δ of each formulation is displayed as an index (low fuel consumption index) by the following formula. A larger index indicates lower rolling resistance and better fuel efficiency.
(Low fuel efficiency index) = (tan δ of reference comparative example) / (tan δ of each formulation) × 100

(Destruction energy index)
The tensile strength and elongation at break of each test rubber sheet were measured according to JIS K6251 "Vulcanized rubber and thermoplastic rubber-Determination of tensile properties". Then, the breaking energy was calculated by tensile strength × breaking elongation / 2, and the breaking energy index of the reference comparative example was set to 100, and the breaking energy of each formulation was displayed as an index by the following formula. The larger the index, the better the rubber strength.
(Fracture energy index) = (Fracture energy of each formulation) / (Fracture energy of reference comparative example) × 100

(Bending crack growth resistance index)
A flex crack growth test was conducted in accordance with JIS K6301 using a test rubber sheet that had been thermally oxidized and deteriorated for 12 minutes at a temperature of 170 ° C. In the test, 70% elongation was repeated 300,000 times to bend the test rubber sheet, and then the length of the cracks generated was measured. Then, the reciprocal of the measured value was taken, and the reciprocal of the reference comparative example was taken as 100, and the reciprocal of each formulation was displayed as an index (flexible crack growth resistance index). The larger the index, the more the crack growth is suppressed and the better the resistance to flex crack growth.

(Adhesion index)
Using a vulcanized carcass, the tensile resistance between rubber and fiber cord was measured with a tensile tester (Instron), and the tensile resistance of each compound was indexed with the tensile resistance of the reference comparative example being 100 (adhesion) Sex index). The larger the index, the better the cord adhesion.

From the results in Table 1,
In Comparative Example 2 in which the amount of sulfur was reduced compared to Comparative Example 1 in which the compound represented by the formula (I) was not blended, the fuel economy and flex crack growth resistance were reduced. Further, the cord adhesiveness was greatly reduced.
In Comparative Example 3 in which the amount of sulfur was increased, although the fuel efficiency was improved, the rubber strength was greatly reduced.
In Comparative Example 4, the compound represented by the formula (I) was blended, but since the amount thereof was small, the effect of improving the fuel efficiency was low as compared with the Examples.
In Comparative Example 5, the compound represented by the formula (I) was blended, but since the amount thereof was large, the fuel efficiency was good, but other performances were lowered.
In Comparative Example 6, the compound represented by the formula (I) was blended, but since the fuel content was improved because the sulfur content was small, the cord adhesion was greatly reduced.
On the other hand, in the examples in which a predetermined amount of sulfur and the compound represented by the formula (I) were blended, the workability, rubber strength, flex crack growth resistance, and cord adhesion were maintained at a problem-free level while being low. Fuel efficiency has been greatly improved.

From the results in Table 2, the same tendency as in Table 1 was obtained when NR, SBR and BR were blended as rubber components. In particular,
In Examples 5 to 10 in which the compound represented by the formula (I) was blended, the processability, rubber strength, bending crack growth resistance and cord adhesiveness were maintained at a problem-free level as compared with Comparative Example 7. However, fuel efficiency has been greatly improved.
In Examples 6, 8, and 10 in which part of the carbon black was substituted with silica, both rubber strength and fuel efficiency were greatly improved, although the processability was slightly reduced.

Claims (6)

Rubber components including isoprene-based rubber and butadiene rubber and / or styrene butadiene rubber;
Carbon black having a nitrogen adsorption specific surface area of 20 to 130 m ² / g;
A compound represented by the following formula (I):
Sulfur and
At least one cross-linked resin selected from the group consisting of a cresol resin, a resorcin resin and a modified resorcin resin;
Containing at least one methylene donor selected from the group consisting of a partial condensate of hexamethoxymethylol melamine and a partial condensate of hexamethylol melamine pentamethyl ether;
With respect to 100 parts by mass of the rubber component, the content of the carbon black is 10 to 60 parts by mass, the content of the sulfur is 2.4 to 3.5 parts by mass, and the content of the crosslinked resin is 0.5 to 10 parts by mass, the methylene donor content is 0.1-3 parts by mass,
The rubber composition whose content of following formula (I) is 0.5-20 mass parts to 100 mass parts of carbon black.

^(Wherein, R 1, ^{R 2,} identical or different, a hydrogen atom, an alkyl group having 1-20 carbon atoms or an alkynyl group having alkenyl or C2-20 C2-20 ^{.M r +} Represents a metal ion, and r represents its valence.) The content of isoprene-based rubber is 50 to 100% by mass, the content of styrene-butadiene rubber is 0 to 40% by mass, and the content of butadiene rubber is 0 to 30% by mass in 100% by mass of the rubber component. The rubber composition as described. The rubber composition according to claim 1 or 2, wherein the compound represented by the formula (I) is a compound represented by the following formula (I-1), (I-2) or (I-3).

The rubber composition according to claim 1 or 2 , wherein the metal ion is sodium ion, potassium ion or lithium ion. The rubber composition according to any one of claims 1 to 4, which is used as a rubber composition for covering a fiber cord. A pneumatic tire produced using the rubber composition according to claim 1.