JP7067526B2 - Rubber composition for tires and pneumatic tires using them - Google Patents

Description

The present invention relates to a rubber composition for a tire and a pneumatic tire using the same. Specifically, the present invention is a rubber composition for a tire that improves the dispersibility of silica with respect to rubber and has excellent low heat generation and breaking strength. It relates to objects and pneumatic tires using them.

In recent years, from the viewpoint of protecting the global environment, consideration for the environment has been required for pneumatic tires, and specifically, the performance of improving fuel efficiency while maintaining high strength is desired. For this purpose, a technique for blending silica into a rubber composition for tire tread is known. However, silica has a problem that it has a low affinity for diene-based rubber, its dispersibility deteriorates, desired physical properties cannot be obtained, and its elongation at break decreases. Therefore, in order to improve the dispersibility of silica, for example, a method such as increasing the amount of a silane coupling agent; using a modified rubber as a diene rubber; increasing the crosslink density of the rubber; etc. has been adopted. Then, all of them worsen the breaking elongation.

The following Patent Document 1 discloses a tetrazine compound used in the present invention, and it is said that the tetrazine compound improves the dispersibility of silica and brings about a low heat generation. However, in this industry, further reduction in heat generation is required. Further, there is a strong demand for the development of a rubber composition for a tire having low heat generation and high breaking strength, which are in a trade-off relationship as described above.

Japanese Patent No. 6148799

Therefore, it is an object of the present invention to improve the dispersibility of silica with respect to rubber, and to provide a rubber composition for a tire having excellent low heat generation and breaking strength, and a pneumatic tire using the same.

As a result of diligent research, the present inventors have solved the above-mentioned problems by blending silica, a specific tetrazine compound, zinc or a zinc compound with diene rubber, and specifying the amount ratio of the tetrazine compound to zinc. We found that it could be solved, and we were able to complete the present invention.
That is, the present invention is as follows.

1. 1. For 100 parts by mass of diene rubber
30 parts by mass or more of silica,
The tetrazine compound represented by the following formula (1) is blended in an amount of 0.7 to 5 parts by mass, and zinc or a zinc compound is blended so that the mass ratio of zinc / the tetrazine compound is 1.5 or more.
A rubber composition for tires, characterized in that.

[In the formula, X ¹ and X ² represent a hydrogen atom, an alkyl group, an alkylthio group, an arylthio group, a heterocyclic group, or an amino group, which are the same or different. Each of these groups may have one or more substituents. ]
2. 2. The rubber composition for a tire according to 1 above, wherein the zinc compound is zinc oxide and / or a zinc salt of a fatty acid.
3. 3. The rubber composition for a tire according to 1 or 2, wherein the silica has a CTAB specific surface area of 140 to 300 m ² / g.
4. The rubber composition for a tire according to any one of 1 to 3 above, wherein the silane coupling agent is further blended in a proportion of 1 to 20% by mass with respect to the silica.
5. A pneumatic tire using the tire rubber composition according to any one of 1 to 4 above for a cap tread.

The rubber composition for a tire of the present invention contains 30 parts by mass or more of silica, 0.7 to 5 parts by mass of a tetrazine compound represented by the above formula (1), and zinc or zinc with respect to 100 parts by mass of diene rubber. Since the compound is blended so that the mass ratio of zinc / the tetrazine compound is 1.5 or more, the dispersibility of silica with respect to diene rubber is improved, and the heat generation property and breaking strength are superior to those of the prior art. It is possible to provide a rubber composition for a tire and a pneumatic tire using the same.

Hereinafter, the present invention will be described in more detail.

(Diene rubber)
As the diene rubber used in the present invention, any diene rubber that can be blended in a normal rubber composition can be used, and for example, natural rubber (NR), isoprene rubber (IR), and butadiene rubber ( BR), styrene-butadiene copolymer rubber (SBR), acrylonitrile-butadiene copolymer rubber (NBR) and the like can be mentioned. These may be used alone or in combination of two or more. The molecular weight and microstructure thereof are not particularly limited, and may be terminal-modified with an amine, amide, silyl, alkoxysilyl, carboxyl, hydroxyl group or the like, or may be epoxidized.
Among these diene-based rubbers, it is preferable to use SBR and BR from the viewpoint of the effect of the present invention.

(silica)
As the silica used in the present invention, any silica conventionally known to be used in rubber compositions such as dry silica, wet silica, colloidal silica and precipitated silica is used alone or in combination of two or more. can.
Further, the silica used in the present invention preferably has a CTAB specific surface area of 140 to 300 m ² / g, more preferably 180 to 260 m ² / g.
When the CTAB specific surface area is 140 m ² / g or more, the effect of high reinforcing property is obtained. Further, since it is 300 m ² / g or less, the workability is not impaired.
In the present specification, the CTAB specific surface area is a value obtained by measuring the amount of CTAB adsorbed on the silica surface according to JIS K6217-3: 2001 "Part 3: How to obtain the specific surface area-CTAB adsorption method".

The blending amount of the silica is 30 parts by mass or more, preferably 50 to 200 parts by mass, and more preferably 70 to 150 parts by mass with respect to 100 parts by mass of the diene rubber. If the blending amount of silica is less than 30 parts by mass, low heat generation cannot be imparted.

(Tetrazine compound)
The tetrazine compound used in the present invention is represented by the following formula (1), and is disclosed and known in Patent Document 1.

[In the formula, X ¹ and X ² represent a hydrogen atom, an alkyl group, an alkylthio group, an arylthio group, a heterocyclic group, or an amino group, which are the same or different. Each of these groups may have one or more substituents. ]

In the present specification, the "alkyl group" is not particularly limited, and examples thereof include linear, branched or cyclic alkyl groups, and specific examples thereof include methyl, ethyl, n-propyl and isopropyl. , N-butyl, isobutyl, s-butyl, t-butyl, 1-ethylpropyl, n-pentyl, neopentyl, n-hexyl, isohexyl, 3-methylpentyl group, etc. with 1 to 6 carbon atoms (particularly 1 to 6 carbon atoms). 4) Linear or branched alkyl groups; cyclic alkyl groups having 3 to 8 carbon atoms (particularly 3 to 6 carbon atoms) such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl and the like can be mentioned. Preferred alkyl groups are linear or branched alkyl groups having 1 to 6 carbon atoms, more preferably methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, or n-pentyl groups. Particularly preferably, it is methyl or an ethyl group.

In the present specification, the "alkylthio group" is not particularly limited, and examples thereof include linear, branched or cyclic alkylthio groups, and specific examples thereof include methylthio, ethylthio, n-propylthio and isopropyl. 1 carbon number of thio, n-butylthio, isobutylthio, s-butylthio, t-butylthio, 1-ethylpropylthio, n-pentylthio, neopentylthio, n-hexylthio, isohexylthio, 3-methylpentylthio group, etc. Linear or branched alkylthio groups of up to 6 (particularly 1 to 4 carbon atoms); 3 to 8 carbon atoms of cyclopropylthio, cyclobutylthio, cyclopentylthio, cyclohexylthio, cycloheptylthio, cyclooctylthio groups, etc. Examples thereof include a cyclic alkylthio group having 3 to 6 carbon atoms. The preferred alkylthio group is a methylthio, ethylthio, isopropylthio or isobutylthio group, more preferably a methylthio group or an ethylthio group.

In the present specification, the "aralkyl group" is not particularly limited, and examples thereof include benzyl, phenethyl, trityl, 1-naphthylmethyl, 2- (1-naphthyl) ethyl, 2- (2-naphthyl) ethyl group and the like. Can be mentioned. The more preferable aralkyl group is a benzyl group or a phenethyl group, and more preferably a benzyl group.

In the present specification, the "aryl group" is not particularly limited, and examples thereof include phenyl, biphenyl, naphthyl, dihydroindenyl, and 9H-fluorenyl group. The more preferable aryl group is a phenyl group or a naphthyl group, and more preferably a phenyl group.

In the present specification, the "arylthio group" is not particularly limited, and examples thereof include phenylthio, biphenylthio, and naphthylthio groups.

In the present specification, the "heterocyclic group" is not particularly limited, and is, for example, 2-pyridyl, 3-pyridyl, 4-pyridyl, 2-pyrazinyl, 2-pyrimidyl, 4-pyrimidyl, 5-pyrimidyl, 3-. Pyridadil, 4-pyridadyl, 4- (1,2,3-triazil), 5- (1,2,3-triazil), 2- (1,3,5-triazil), 3- (1,2,4) -Triazil), 5- (1,2,4-Triazil), 6- (1,2,4-Triazil), 2-quinoline, 3-quinoline, 4-quinoline, 5-quinoline, 6-quinolyl, 7- Quinoline, 8-quinoline, 1-isoquinolyl, 3-isoquinolyl, 4-isoquinolyl, 5-isoquinolyl, 6-isoquinolyl, 7-isoquinolyl, 8-isoquinolyl, 2-quinoxalyl, 3-quinoxalyl, 5-quinoxalyl, 6-quinoxalyl, 7-quinolinexyl, 8-quinoxalyl, 3-cinnoline, 4-cinnolyl, 5-cinnolyl, 6-cinnoline, 7-cinnolyl, 8-cinnoline, 2-quinazolyl, 4-quinazolyl, 5-quinazolyl, 6-quinazolyl, 7- Thiadiazole, 8-quinazolyl, 1-phthalazyl, 4-phthalazyl, 5-phthalazyl, 6-phthalazyl, 7-phthalazyl, 8-phthalazyl, 1-tetrahydroquinoline, 2-tetrahydroquinoline, 3-tetrahydroquinolyl, 4- Tetrahydroquinoline, 5-tetrahydroquinoline, 6-tetrahydroquinoline, 7-tetrahydroquinoline, 8-tetrahydroquinoline, 1-pyrrolill, 2-pyrrolill, 3-pyrrolill, 2-furyl, 3-furyl, 2- Thienyl, 3-thienyl, 1-imidazolyl, 2-imidazolyl, 4-imidazolyl, 5-imidazolyl, 1-pyrazolyl, 3-pyrazolyl, 4-pyrazolyl, 5-pyrazolyl, 2-oxazolyl, 4-oxazolyl, 5-oxazolyl, 2-thiazolyl, 4-thiazolyl, 5-thiazolyl, 3-isoxazolyl, 4-isoxazolyl, 5-isoxazolyl, 3-isothiazolyl, 4-isothiazolyl, 5-isothiazolyl, 4- (1,2,3-thiadiazolezolyl), 5- (1,2,3-thiadiazole), 3- (1,2,5-thiadiazole), 2- (1,3,4-thiadiazole), 4- (1,2,3-oxadiazolyl), 5- (1) , 2,3-oxadiazolyl), 3- (1,2,4-oxadiazolyl), 5- (1,2,4-oxadiazolyl), 3- (1,2,5-oxal) Diazolyl), 2- (1,3,4-oxadiazolyl), 1- (1,2,3-triazolyl), 4- (1,2,3-triazolyl), 5- (1,2,3-triazolyl) , 1- (1,2,4-triazolyl), 3- (1,2,4-triazolyl), 5- (1,2,4-triazolyl), 1-tetrazolyl, 5-tetrazolyl, 1-indrill, 2 -Indrill, 3-Indrill, 4-Indrill, 5-Indrill, 6-Indrill, 7-Indrill, 1-isoindrill, 2-isoindrill, 3-isoindrill, 4-isoindrill, 5-isoindrill, 6-isoindrill, 7-isoindrill , 1-benzoimidazolyl, 2-benzoimidazolyl, 4-benzoimidazolyl, 5-benzoimidazolyl, 6-benzoimidazolyl, 7-benzoimidazolyl, 2-benzofuranyl, 3-benzofuranyl, 4-benzofuranyl, 5-benzofuranyl, 6-benzofuranyl, 7-benzofuranyl, 1 -Isobenzofuranyl, 3-isobenzofuranyl, 4-isobenzofuranyl, 5-isobenzofuranyl, 6-isobenzofuranyl, 7-isobenzofunyl, 2-benzothienyl, 3-benzothienyl, 4- Benzothienyl, 5-benzothienyl, 6-benzothienyl, 7-benzothienyl, 2-benzoxazolyl, 4-benzoxazolyl, 5-benzoxazolyl, 6-benzoxazolyl, 7-benzoxalyl Zoryl, 2-benzothiazolyl, 4-benzothiazolyl, 5-benzothiazolyl, 6-benzothiazolyl, 7-benzothiazolyl, 1-indazolyl, 3-indazolyl, 4-indazolyl, 5-indazolyl, 6-indazolyl, 7-indazolyl, 2-morpholyl , 3-Morphoryl, 4-Morphoryl, 1-Piperazil, 2-Piperazil, 1-Piperidyl, 2-Piperidyl, 3-Piperidyl, 4-Piperidyl, 2-Tetrahydropyranyl, 3-Tetrahydropyranyl, 4-Tetrahydropyranyl , 2-Tetrahydropyranyl, 3-Tetrahydropyranyl, 4-Tetrahydropyranyl, 1-Pyrrolidyl, 2-Pyrrolidyl, 3-Pyrrolidyl, 2-Tetrahydropyran, 3-Tetrahydropyranyl, 2-Tetrahydropyranyl, 3 -Tetrahydropyran and the like can be mentioned. Among them, the preferred heterocyclic group is pyridyl, furanyl, thienyl, pyrimidyl or pyrazil, and more preferably pyridyl.

In the present specification, the "amino group" includes not only the amino group represented by -NH ₂ , but also, for example, methylamino, ethylamino, n-propylamino, isopropylamino, n-butylamino, isobutylamino, s. -Butylamino, t-butylamino, 1-ethylpropylamino, n-pentylamino, neopentylamino, n-hexylamino, isohexylamino, 3-methylpentylamino group, etc. have 1 to 6 carbon atoms (particularly the number of carbon atoms). 1 to 4) linear or branched monoalkylamino group; linear or branched alkyl having 1 to 6 carbon atoms (particularly 1 to 4 carbon atoms) such as dimethylamino, ethylmethylamino, diethylamino group, etc. Substituted amino groups such as dialkylamino groups having two groups are also included.

Each of these alkyl group, alkylthio group, aralkyl group, aryl group, arylthio group, heterocyclic group and amino group may have one or more substituents. The "substituent" is not particularly limited, and is, for example, a halogen atom, an amino group, an aminoalkyl group, an alkoxycarbonyl group, an acyl group, an acyloxy group, an amide group, a carboxyl group, a carboxyalkyl group, a formyl group, and a nitrile group. , Nitro group, alkyl group, hydroxyalkyl group, hydroxyl group, alkoxy group, aryl group, aryloxy group, heterocyclic group, thiol group, alkylthio group, arylthio group and the like. The substituent may preferably have 1 to 5, more preferably 1 to 3.

In the present specification, examples of the "halogen atom" include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom, preferably a chlorine atom, a bromine atom, and an iodine atom.

In the present specification, the "aminoalkyl group" is not particularly limited, and examples thereof include aminoalkyl groups such as aminomethyl, 2-aminoethyl, and 3-aminopropyl group.

In the present specification, the "alkoxycarbonyl group" is not particularly limited, and examples thereof include methoxycarbonyl and ethoxycarbonyl groups.

In the present specification, the "acyl group" is not particularly limited, and examples thereof include linear or branched alkylcarbonyl groups having 1 to 4 carbon atoms such as acetyl, propionyl, and pivaloyl groups.

In the present specification, the "acyloxy group" is not particularly limited, and examples thereof include acetyloxy, propionyloxy, and n-butyryloxy group.

In the present specification, the "amide group" is not particularly limited, and for example, a carboxylic acid amide group such as acetamide or benzamide group; a thioamide group such as thioacetamide or thiobenzamide group; N-methylacetamide or N-benzylacetamide. N-substituted amide groups such as groups; and the like.

In the present specification, the "carboxyalkyl group" is not particularly limited, and is, for example, carboxymethyl, carboxyethyl, carboxy-n-propyl, carboxy-n-butyl, carboxy-n-butyl, carboxy-n-hexyl group. And the like (preferably an alkyl group having a carboxy group and having 1 to 6 carbon atoms).

In the present specification, the "hydroxyalkyl group" is not particularly limited, and for example, a hydroxy-alkyl group (preferably a hydroxy group) such as hydroxymethyl, hydroxyethyl, hydroxy-n-propyl, and hydroxy-n-butyl group is used. Alkyl groups having 1 to 6 carbon atoms) can be mentioned.

In the present specification, the "alkoxy group" is not particularly limited, and examples thereof include linear, branched or cyclic alkoxy groups, and specific examples thereof include methoxy, ethoxy, n-propoxy and iso. Propoxy, n-butoxy, t-butoxy, n-pentyloxy, neopentyloxy, n-hexyloxy groups with 1 to 6 carbon atoms (particularly 1 to 4 carbon atoms) linear or branched alkoxy groups; cyclo Examples thereof include cyclic alkoxy groups having 3 to 8 carbon atoms (particularly 3 to 6 carbon atoms) such as propyloxy, cyclobutyloxy, cyclopentyloxy, cyclohexyloxy, cycloheptyloxy, and cyclooctyloxy groups.

In the present specification, the "aryloxy group" is not particularly limited, and examples thereof include phenoxy, biphenyloxy, and naphthoxy groups.

The "salt" of the tetrazine compound represented by the formula (1) is not particularly limited and includes all kinds of salts. Examples of such salts include inorganic acid salts such as hydrochlorides, sulfates and nitrates; organic acid salts such as acetates and methanesulfonates; alkali metal salts such as sodium salts and potassium salts; magnesium salts and calcium. Alkaline earth metal salts such as salts; quaternary ammonium salts such as dimethylammonium and triethylammonium can be mentioned.

Among these tetrazine compounds (1), preferable compounds are an alkyl group in which X ¹ and X ² are the same or different and may have a substituent, an aralkyl group which may have a substituent, and a substitution. A compound which is an aryl group which may have a group or a heterocyclic group which may have a substituent.

In the more preferable tetrazine compound (1), X ¹ and X ² have an aralkyl group which may have a substituent, an aryl group which may have a substituent, or a substituent, which may be the same or different. It is a compound which is a heterocyclic group which may be used.

In a more preferable tetradine compound (1), X ¹ and X ² have the same or different benzyl group which may have a substituent, a phenyl group which may have a substituent, and a substituent. 2-pyridyl group which may have a substituent, 3-pyridyl group which may have a substituent, 4-pyridyl group which may have a substituent, and 2-franyl group which may have a substituent. , Thienyl group which may have a substituent, 1-pyrazolyl group which may have a substituent, 2-pyrimidyl group which may have a substituent, or may have a substituent. It is a compound which is a good 2-pyrazyl group, and among these, it has a 2-pyridyl group which may have a substituent, a 3-pyridyl group which may have a substituent, or a substituent. A compound which may be a 2-furanyl group may be particularly preferable.

Specifically, as the tetrazine compound (1), for example,
1,2,4,5-Tetrazine,
3,6-bis (2-pyridyl) -1,2,4,5-tetrazine,
3,6-bis (3-pyridyl) -1,2,4,5-tetrazine,
3,6-bis (4-pyridyl) -1,2,4,5-tetrazine,
3,6-Diphenyl-1,2,4,5-Tetrazine,
3,6-Dibenzyl-1,2,4,5-Tetrazine,
3,6-Bis (2-Franyl) -1,2,4,5-Tetrazine,
3-Methyl-6- (3-pyridyl) -1,2,4,5-tetrazine,
3,6-bis (3,5-dimethyl-1-pyrazolyl) -1,2,4,5-tetrazine,
3,6-bis (2-thienyl) -1,2,4,5-tetrazine,
3-Methyl-6- (2-pyridyl) -1,2,4,5-tetrazine,
3,6-bis (4-hydroxyphenyl) -1,2,4,5-tetrazine,
3,6-bis (3-hydroxyphenyl) -1,2,4,5-tetrazine,
3,6-bis (2-pyrimidinyl) -1,2,4,5-tetrazine,
Examples thereof include 3,6-bis (2-pyrazyl) -1,2,4,5-tetrazine.

Among them, the preferred tetrazine compound (1) is 3,6-bis (2-pyridyl) -1,2,4,5-tetrazine and 3,6-bis (3-pyridyl) -1,2,4,5-. Tetrazine, 3,6-bis (2-furanyl) -1,2,4,5-tetrazine, 3-methyl-6- (3-pyridyl) -1,2,4,5-tetrazine, and 3-methyl- 6- (2-Pyridyl) -1,2,4,5-tetrazine, and a more preferable tetrazine compound (1) is 3,6-bis (2-pyridyl) -1,2,4,5-tetrazine, And 3,6-bis (3-pyridyl) -1,2,4,5-tetrazine.

In the present invention, the blending amount of the tetrazine compound is 0.7 to 5 parts by mass, preferably 1.0 to 3.0 parts by mass with respect to 100 parts by mass of the diene rubber.
If the compounding amount of the tetrazine compound is less than 0.7 parts by mass, the compounding amount is too small to achieve the effect of the present invention. On the contrary, if it exceeds 5 parts by mass, the elongation at break deteriorates.

(Silane coupling agent)
In the present invention, a silane coupling agent can be added to further enhance the dispersibility of silica. The silane coupling agent used is not particularly limited, but a sulfur-containing silane coupling agent is preferable, for example, bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide, 3-. Examples thereof include trimethoxysilylpropylbenzothiazoletetrasulfide, γ-mercaptopropyltriethoxysilane, 3-octanoylthiopropyltriethoxysilane, and the like.
The blending amount of the silane coupling agent is preferably 1 to 20% by mass with respect to the mass of silica. If the blending amount of the silane coupling agent is less than 1% by mass with respect to the mass of silica, the blending amount is too small to improve the dispersibility of silica. On the contrary, if it exceeds 20% by mass, the workability and the elongation at break may deteriorate.
The blending amount of the silane coupling agent is preferably 5 to 15% by mass with respect to the mass of silica.

(Zinc and / or zinc compounds)
The rubber composition in the present invention contains zinc and / or a zinc compound.
As the zinc compound, zinc oxide and a fatty acid zinc salt are preferable.
Examples of the zinc fatty acid salt include zinc salts of saturated or unsaturated fatty acids having 8 to 24 carbon atoms, preferably 12 to 22 carbon atoms. Preferred fatty acids include, for example, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid and the like.

The rubber composition of the present invention needs to have a zinc and / or zinc compound compounding amount of 1.5 or more as a mass ratio of zinc / the tetrazine compound. When the mass ratio is less than 1.5, the effect of improving the dispersibility, heat generation and breaking strength of silica is poor.
The mass ratio is preferably 1.5 to 6.0, more preferably 1.5 to 3.0.
Further, for example, when zinc oxide and a fatty acid zinc salt are used in combination as the zinc compound, the blending amount thereof may be appropriately determined in consideration of the mass ratio of the zinc / the tetrazine compound, but the blending amount of zinc oxide is 1 mass. In the case of parts, the blending amount of the zinc fatty acid salt is preferably 0.5 to 30 parts by mass, more preferably 1.0 to 25.0 parts by mass.

(Other ingredients)
In addition to the above-mentioned components, the rubber composition in the present invention includes a vulcanization or cross-linking agent; a vulcanization or cross-linking accelerator; various fillers such as carbon black, clay, talc, and calcium carbonate; an antiaging agent; plastic. Various additives generally blended in rubber compositions such as agents can be blended, and such additives are kneaded by a general method to form a composition, which is used for vulcanization or cross-linking. Can be done. The blending amount of these additives can also be a conventional general blending amount as long as it does not contradict the object of the present invention.

Further, the rubber composition of the present invention is suitable for manufacturing a pneumatic tire according to a conventional method for manufacturing a pneumatic tire, and is preferably applied to a tread, particularly a cap tread.

Hereinafter, the present invention will be further described with reference to Examples and Comparative Examples, but the present invention is not limited to the following examples.

Examples 1 to 4 and Comparative Examples 1 to 5
Preparation of sample In the formulation (part by mass) shown in Table 1, the vulcanization accelerator and the sulfur-excluding component were kneaded with a 1.7 liter closed rubbery mixer for 5 minutes, and then the vulcanization accelerator and sulfur were added. It was kneaded to obtain a rubber composition. Next, the obtained unvulcanized rubber composition was press-vulcanized in a predetermined mold at 160 ° C. for 20 minutes to obtain a vulcanized rubber test piece, and the unvulcanized rubber composition was obtained by the test method shown below. Alternatively, the physical properties of the vulcanized rubber test piece were measured.

Elongation at break: Tested at room temperature according to JIS K 6251. The results are shown exponentially with the value of Comparative Example 1 as 100. The larger the index, the better the elongation at break.
Pain effect: G'(0.56% strain) was measured on RPA2000 according to ASTM P6204 using an unvulcanized rubber composition. The results are shown exponentially with the value of Comparative Example 1 as 100. The smaller the index, the higher the dispersibility of silica.
Heat generation: According to JIS K6394: 2007, using a viscoelastic spectrometer (manufactured by Toyo Seiki Seisakusho), tan δ (60 ° C) is applied under the conditions of a stretch deformation strain rate of 10 ± 2%, a frequency of 20 Hz, and a temperature of 60 ° C. It was measured. The results are shown exponentially with the value of Comparative Example 1 as 100. The smaller the index, the lower the heat generation and the better the fuel efficiency.
The results are shown in Table 1.

* 1: SBR (E581 manufactured by Asahi Kasei Corporation, oil spread S-SBR, oil spread amount = 37.5 parts by mass with respect to 100 parts by mass of SBR (the actual blending amount is shown in Table 1).
* 2: BR (Nipol BR1220 manufactured by Nippon Zeon Corporation)
* 3: Silica (Zeosil 9100GR manufactured by Solvay, CTAB specific surface area = 200 m ² / g)
* 4: Carbon black (Cabot Japan Co., Ltd. Show Black N234)
* 5: Stearic acid (YR stearic acid manufactured by NOF CORPORATION)
* 6: Anti-aging agent (Santoflex 6PPD manufactured by Solutia Europe)
* 7: Tetrazine compound (3,6-bis (2-pyridyl) -1,2,4,5-tetrazine manufactured by Otsuka Chemical Co., Ltd.)
* 8: Silane coupling agent (Si69 manufactured by Evonik Degussa, bis (3-triethoxysilylpropyl) tetrasulfide)
* 9: Process oil (Extract No. 4S manufactured by Showa Shell Sekiyu Co., Ltd.)
* 10: Sulfur (oil-treated sulfur from Karuizawa Smelter)
* 11: Vulcanization accelerator CZ (Noxeller CZ-G manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.)
* 12: Vulcanization accelerator DPG (Perkacit DPG manufactured by Flexsys)
* 13: Zinc oxide (3 types of zinc oxide manufactured by Shodo Chemical Industry Co., Ltd.)
* 14: Zinc stearate (Exton L-2-G manufactured by Kawaguchi Chemical Industry Co., Ltd., Table 1 shows the amount of zinc stearate)

From the results in Table 1, since the rubber composition of each example contains silica, a specific tetrazine compound, zinc or a zinc compound in a diene rubber, and the amount ratio of the tetrazine compound to zinc is in a specific range. As compared with Comparative Example 1, the elongation at break, the dispersibility of silica, and the exothermic property all showed excellent values.
On the other hand, Comparative Example 2 was an example in which the amount of zinc was smaller than that of Comparative Example 1, and the exothermic property was deteriorated.
In Comparative Examples 3 to 5, since the mass ratio of the zinc / tetrazine compound was less than the lower limit specified by the present invention, the dispersibility of silica was deteriorated and the exothermic property was also deteriorated.

Claims (4)

For 100 parts by mass of diene rubber
30 parts by mass or more of silica,
0.7 to 5 parts by mass of the tetrazine compound represented by the following formula (1) ,
The zinc compound is blended so that the mass ratio of zinc / the tetrazine compound is 1.5 or more .
The zinc compound is zinc oxide and a fatty acid zinc salt.
A rubber composition for tires, characterized in that.

[In the formula, X ¹ and X ² represent a hydrogen atom, an alkyl group, an alkylthio group, an arylthio group, a heterocyclic group, or an amino group, which are the same or different. Each of these groups may have one or more substituents. ] The rubber composition for a tire according to claim 1 , wherein the silica has a CTAB specific surface area of 140 to 300 m ² / g. The rubber composition for a tire according to claim 1 or 2 , wherein a silane coupling agent is further blended in a proportion of 1 to 20% by mass with respect to the silica. A pneumatic tire using the tire rubber composition according to any one of claims 1 to 3 for a cap tread.