JP4286653B2 - Rubber composition and pneumatic tire using the same - Google Patents

Description

  The present invention relates to a rubber composition and a pneumatic tire using the rubber composition, and particularly improves heat fatigue resistance without reducing high operability (dry grip performance) on a dry road surface by using the tire in a tire tread. The present invention relates to a rubber composition that can be used.

  A tire tread is required to have high steering stability (dry grip performance) on a dry road surface. Conventionally, in order to improve dry grip properties, in a rubber composition for a tread, an amount of oil components such as a resin, an aromatic oil, and a liquid polymer in the rubber composition has been increased. However, when the amount of the oil component is increased, particularly dynamic heat fatigue resistance is lowered, and there is a problem that cracks are likely to occur due to heat generation and deformation inside the tire during running.

  In response to this problem, thiuram compounds, dithiocarbamic acid metal salts, and dithiophosphoric acid metal salts are applied as vulcanization accelerators capable of increasing monosulfide, mainly for the purpose of improving the thermal stability of crosslinking. Possible (see Patent Document 1). However, when the compounding amount of these compounds is excessively increased, the static heat resistance is improved, but the fatigue resistance is lowered. As a result, there is a problem that the heat fatigue resistance is not improved.

  In addition, the use of a heat-resistant cross-linking agent such as phenylene bismaleimide, PK900, 1,6-hexamethylenedithiosulfate sodium dihydrate, etc. is also considered (see Patent Document 2). These compounds include natural rubber and isoprene rubber. However, it has low reactivity with polybutadiene rubber and styrene-butadiene copolymer rubber with high vinyl bond. There was a problem that fatigue did not improve.

  As described above, there has not yet been provided a technology that can greatly improve the thermal fatigue resistance of a tire while maintaining high dry grip performance.

JP-A-5-262916 JP 2000-301908 A

  Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art, and by using the tire tread, a rubber composition capable of improving the thermal fatigue resistance of the tire while maintaining high grip performance, and The object is to provide a high-performance tire using the rubber composition in a tread.

  As a result of intensive studies to achieve the above object, the present inventors have formulated a specific rubber component in combination with a specific vulcanization accelerator and a specific vulcanizing agent, thereby achieving high grip performance. It has been found that a rubber composition capable of improving the heat fatigue resistance of a tire can be obtained while maintaining the present invention, and the present invention has been completed.

（式中、Ｒ¹、Ｒ²、Ｒ³及びＲ⁴は、それぞれ独立に炭素数３〜１２の直鎖若しくは分岐鎖アルキル基又は炭素数７〜１２のアラルキル基を示す。）

（式中、Ｒ⁵及びＲ⁶は、それぞれ独立に炭素数７〜１２の直鎖若しくは分岐鎖アルキル基又は炭素数７〜１２のアラルキル基を示し、Ｍ¹は２価以上の金属であり、ｎはＭ¹の金属の原子価に等しい数である。）

（式中、Ｒ⁷、Ｒ⁸、Ｒ⁹及びＲ¹⁰は、それぞれ独立に炭素数３〜１２の直鎖若しくは分岐鎖アルキル基又は素数７〜１２のアラルキル基を示す。）
Ｍ²Ｏ₃Ｓ−Ｓ−(ＣＨ₂)_n−Ｓ−ＳＯ₃Ｍ² ・・・ (IV)
（式中、ｎは３〜１０を表し、Ｍ²はリチウム、カリウム、ナトリウム、マグネシウム、カルシウム、バリウム、亜鉛、ニッケル又はコバルトの１当量を表す。また、該化合物は、結晶水を含有していてもよい。） That is, the rubber composition of the present invention comprises (1) a rubber component containing at least one of a polybutadiene rubber and a styrene / butadiene copolymer rubber having a vinyl bond amount of 30% or more, and (2) the following formula (I): At least one compound selected from the group consisting of a compound represented by the following formula (II) and a compound represented by the following formula (III); and (3) represented by the following formula (IV): The total amount of the compound represented by the following formula (I), the compound represented by the following formula (II) and the compound represented by the following formula (III): The compounding amount of the compound represented by the following formula (IV) is 1 to 10 parts by mass with respect to 100 parts by mass of the rubber component. And Here, the vinyl bond amount is preferably 40% or more.

(In the formula, R ¹ , R ² , R ³ and R ⁴ each independently represents a linear or branched alkyl group having 3 to 12 carbon atoms or an aralkyl group having 7 to 12 carbon atoms.)

(In the formula, R ⁵ and R ⁶ each independently represent a linear or branched alkyl group having 7 to 12 carbon atoms or an aralkyl group having 7 to 12 carbon atoms, M ¹ is a divalent or higher metal, n is a number equal to the valence of the metal of M ^1. )

(In the formula, R ⁷ , R ⁸ , R ⁹ and R ¹⁰ each independently represents a linear or branched alkyl group having 3 to 12 carbon atoms or an aralkyl group having 7 to 12 carbon atoms.)
M ² O ₃ S—S— (CH ₂ ) _n —S—SO ₃ M ² (IV)
(In the formula, n represents 3 to 10, M ² represents one equivalent of lithium, potassium, sodium, magnesium, calcium, barium, zinc, nickel, or cobalt. Further, the compound contains crystal water. May be.)

In a preferred example of the rubber composition of the present invention, R ¹ , R ² , R ³ and R ^{4 of the} compound represented by the formula (I) are each independently a linear or branched chain having 8 to 12 carbon atoms. It is an alkyl group. Here, it is particularly preferred that R ¹ , R ² , R ³ and R ⁴ are 2-ethylhexyl groups.

  In another preferred embodiment of the rubber composition of the present invention, the styrene / butadiene copolymer rubber has a bound styrene content of 20 to 60% by mass. Here, the bound styrene content is more preferably 30 to 45% by mass.

  In another preferred embodiment of the rubber composition of the present invention, the content of the styrene / butadiene copolymer rubber (SBR) in the rubber component is 50 to 100% by mass. Here, the content of the SBR in the rubber component is more preferably 70 to 100% by mass.

  In another preferred embodiment of the rubber composition of the present invention, the organic thiosulfate compound represented by the formula (IV) is 1,6-hexamethylenedithiosulfate sodium dihydrate.

In the rubber composition of the present invention, the amount of the compound represented by the above formula (I), more preferably in the range of 0.5 to 10 parts by mass with respect to 100 parts by mass of the rubber component, 1 to 7 parts by weight It is particularly preferred.

In the rubber composition of the present invention, the amount of the compound represented by the above formula (IV), and even more preferably from 2 to 6 parts by weight.

  The pneumatic tire of the present invention is characterized by using the above rubber composition in a tread. Here, in the tire of the present invention, examples of the gas filled in the tire include normal or air with a changed oxygen partial pressure, or an inert gas such as nitrogen.

  ADVANTAGE OF THE INVENTION According to this invention, the rubber composition which can improve durability, such as heat fatigue resistance of a tire, can be provided, maintaining a high grip performance by using for the tread of a tire. Moreover, the high performance tire which used this rubber composition for the tread can be provided.

  The present invention is described in detail below. The rubber composition of the present invention includes (1) a rubber component containing at least one of a polybutadiene rubber and a styrene / butadiene copolymer rubber having a vinyl bond content of 30% or more, and (2) represented by the above formula (I). At least one compound selected from the group consisting of a compound represented by the above formula (II) and a compound represented by the above formula (III), and (3) an organic represented by the above formula (IV) It is blended with a thiosulfate compound.

  The organic thiosulfate compound represented by the formula (IV) is highly reactive with natural rubber and cis-1,4-polybutadiene rubber, but has high vinyl bond polybutadiene rubber and styrene / butadiene copolymer rubber. Because of low reactivity, these rubber components having a high vinyl bond amount did not function sufficiently as a vulcanizing agent, and the heat fatigue resistance of the rubber composition could not be improved. However, the rubber composition of the present invention contains a compound represented by any one of the above formula (I), formula (II) and formula (III) as a vulcanization accelerator, and the compound is the vinyl compound. In order to promote the reaction between the rubber component having a high binding amount and the organic thiosulfate compound, the heat fatigue resistance is remarkably improved.

From the viewpoint of improving heat resistance, the rubber component used in the rubber composition of the present invention has a polybutadiene rubber (BR) and a styrene / butadiene copolymer rubber (SBR) having a vinyl bond content of 30% or more, preferably 40% or more. ). Here, the styrene / butadiene copolymer rubber preferably has a bonded styrene unit content, that is, a bonded styrene content of 20 to 60% by mass. If the styrene-butadiene copolymer rubber has a bound styrene content of less than 20% by mass, the desired grip strength in the low and high temperature ranges cannot be obtained, and if it exceeds 60% by mass, the block rigidity is unnecessarily high. Thus, the amount of tread rubber biting into the road surface is reduced, and a desired grip force cannot be obtained. Moreover, since these effects become remarkable, it is more preferable that the styrene / butadiene copolymer rubber has a bound styrene content of 30 to 45% by mass. The vinyl bond amount can be determined by analyzing the microstructure by the infrared method (Morero method), and the bound styrene content can be determined by calculating the integral ratio of the spectrum by ¹ H-NMR. it can. The styrene / butadiene copolymer rubber may be synthesized by any polymerization method such as emulsion polymerization or solution polymerization. Further, as BR and SBR having a high vinyl bond amount, oil-extended ones can be preferably used. When BR and SBR having a high vinyl bond amount are oil-extended, slipping does not occur when kneading using a Banbury mixer or the like, and the kneading can be performed easily and reliably.

  The rubber component includes BR and SBR having a high vinyl bond content, natural rubber (NR), isoprene rubber (IR), acrylonitrile butadiene rubber (NBR), chloroprene rubber, ethylene / propylene rubber (EPM), Ethylene / propylene terpolymer, butyl rubber, acrylic rubber, etc. may be blended.

The compound of formula (I) (thiuram compound), the compound of formula (II) (dithiocarbamate compound) and the compound of formula (III) used in the rubber composition of the present invention function as a vulcanization accelerator. In the formula (I), R ¹ , R ² , R ³ and R ⁴ each independently represent a linear or branched alkyl group having 3 to 12 carbon atoms or an aralkyl group having 7 to 12 carbon atoms, Examples of the -12 linear or branched alkyl group include a 2-ethylhexyl group, an isopropyl group, an isobutyl group, and a dodecyl group, and examples of the aralkyl group having 7 to 12 carbon atoms include a benzyl group. . When the carbon number of R ^{1 to} R ⁴ is 2 or less, the dispersion into the rubber component is deteriorated and the heat resistance is deteriorated, and when the carbon number is 13 or more, the vulcanization rate is extremely delayed. Specific examples of the compound of formula (I) include tetrakis-2-ethylhexyl thiuram disulfide, tetrakis-isopropyl thiuram disulfide, tetrakis-isobutyl thiuram disulfide, tetrakis-dodecyl thiuram disulfide, tetrakis-benzyl thiuram disulfide and the like.

In the formula (II), R ⁵ and R ⁶ each independently represent a linear or branched alkyl group having 7 to 12 carbon atoms or an aralkyl group having 7 to 12 carbon atoms, Examples of the branched alkyl group include a 2-ethylhexyl group and a dodecyl group, and examples of the aralkyl group having 7 to 12 carbon atoms include a benzyl group. When the carbon number of R ^{5 to} R ⁶ is 6 or less, the dispersion into the rubber component is deteriorated and the heat resistance is deteriorated, and when the carbon number is 13 or more, the vulcanization rate is extremely delayed. M ¹ is a metal having a valence of 2 or more, and n is a number equal to the valence of the metal of M ^1. Examples of the metal include zinc, antimony, iron, copper, nickel, lead, tellurium, and the like. Among these, zinc is preferable. Specifically, examples of the compound of the formula (II) include 2-ethylhexyl dithiocarbamate zinc, dodecyl dithiocarbamate zinc, and benzyldithiocarbamate zinc.

In the formula (III), R ⁷ , R ⁸ , R ⁹ and R ¹⁰ each independently represent a linear or branched alkyl group having 3 to 12 carbon atoms or an aralkyl group having 7 to 12 carbon atoms, Examples of the -12 linear or branched alkyl group include a 2-ethylhexyl group, an isopropyl group, an isobutyl group, and a dodecyl group, and examples of the aralkyl group having 7 to 12 carbon atoms include a benzyl group. . When the carbon number of R ^{7 to} R ¹⁰ is 2 or less, the dispersion into the rubber component is deteriorated and the heat resistance is deteriorated, and when the carbon number is 13 or more, the vulcanization rate is extremely delayed. Specifically, the compound of the formula (III) includes 1,6-bis (N, N′-dibenzylthiocarbamoyldithio) -hexane, 1,6-bis (N, N′-di (2-ethylhexyl) And thiocarbamoyldithio) -hexane.

  Since the compound of the formula (III) includes a part of the structure of the formula (I) and a part of the structure of the formula (IV), it functions as a vulcanization accelerator and also as a vulcanizing agent. Therefore, when the rubber composition contains BR and / or SBR having a high vinyl bond amount and the compound of formula (III), the rubber composition does not need to be further blended with the compound of formula (IV). High dry grip and high heat fatigue resistance.

  Among the compounds of the above formula (I), the compound of formula (II) and the compound of formula (III), a thiuram compound containing an alkyl group is preferable from the viewpoint of heat resistance, fracture resistance and cost, and tetrakis-2-ethylhexyl thiuram disulfide. Is most preferred.

  The total amount of the compound of formula (I), the compound of formula (II) and the compound of formula (III) is 0.5 to 10 parts by mass with respect to 100 parts by mass of the rubber component. When the total amount of these compounds is less than 0.5 parts by mass, the effect of sufficiently activating the organic thiosulfate compound described later cannot be obtained, and when it exceeds 10 parts by mass, the fracture characteristics of the rubber composition are deteriorated. Here, the compounding amount of the compound of formula (I) is more preferably 0.5 to 10 parts by mass, and particularly preferably 1 to 7 parts by mass with respect to 100 parts by mass of the rubber component.

  The rubber composition of the present invention contains an organic thiosulfate compound represented by the above formula (IV) together with sulfur as a vulcanizing agent. The total amount of the vulcanizing agent comprising this mixture is in the range of 1.0 to 10.0 parts by mass, preferably in the range of 2.0 to 6.0 parts by mass, with respect to 100 parts by mass of the rubber component. When the total amount of the vulcanizing agent is less than 1.0 part by mass, a sufficient elastic modulus cannot be secured, and when it exceeds 10.0 parts by mass, the elongation at break is lowered and the rib chipping resistance is significantly lowered. Here, the compounding amount of the compound of formula (IV) is more preferably 1.0 to 10.0 parts by mass, and further preferably 2.0 to 6.0 parts by mass with respect to 100 parts by mass of the rubber component. When the compounding amount of the compound of formula (IV) is less than 1.0 part by mass, the heat fatigue resistance cannot be sufficiently improved, and when it exceeds 10.0 parts by mass, the elongation at break is lowered and the rib chipping resistance is remarkably lowered. To do.

In the above formula (IV), the number of methylene chains represented by m needs to be 3 to 10. If the number is 2 or less, the effect of improving the heat fatigue resistance is not sufficiently obtained, and if it is 11 or more, the molecular weight is low. Although it increases, the effect of improving heat fatigue resistance is small. Furthermore, from the viewpoint of suppressing intramolecular cyclization reaction, the number of methylene chains is preferably 3-6. M ² represents one equivalent of lithium, potassium, sodium, magnesium, calcium, barium, zinc, nickel or cobalt, and potassium, sodium and the like are preferable in consideration of availability and effects. This compound may be a hydrate having crystal water in the molecule. Specific examples of the compound of formula (IV) include sodium salt monohydrate, sodium salt dihydrate and the like. For economic reasons, derivatives from sodium thiosulfate such as 1,6-hexamethylene Sodium dithiosulfate dihydrate is most preferred.

The rubber composition of the present invention preferably further contains carbon black having a nitrogen adsorption specific surface area (N ₂ SA) of 80 to 280 m ² / g as a filler. When the nitrogen adsorption specific surface area of carbon black is less than 80 m ² / g, sufficient elastic modulus cannot be obtained and the wear resistance deteriorates, and when it exceeds 280 m ² / g, the improvement in grip strength and wear resistance cannot be expected. In addition, the kneading workability is deteriorated. Examples of the carbon black include HAF, ISAF, and SAF, and commercially available products can be used. Among these, SAF is preferable from the viewpoint of coexistence of grip force on a wet road surface in a low temperature region and grip force on a wet road surface or a semi-wet road surface in a high temperature region. The said carbon black may be used individually by 1 type, and may use 2 or more types together.

  The compounding amount of the carbon black is preferably 70 to 200 parts by mass, more preferably 95 to 130 parts by mass with respect to 100 parts by mass of the rubber component. If the blending amount of the carbon black is less than 70 parts by mass, the dry grip property and elastic modulus (E ′) of the rubber composition are not sufficient, and general properties such as strength are not sufficient, and the ground contact property is deteriorated. The lap time gets worse. On the other hand, when the blending amount of the carbon black exceeds 200 parts by mass, the rubber composition becomes too hard, and on the contrary, the wear resistance is lowered, and the processability of the rubber composition is extremely deteriorated.

The rubber composition of the present invention further preferably blended the C ₉ aromatic petroleum resin and / or alkylphenol resin. Here, the C ₉ aromatic petroleum resin means a polymer of C ₉ aromatic monomer, as the C ₉ aromatic monomer, vinyl toluene, alpha-methyl styrene, coumarone, indene, and the like. The C ₉ aromatic monomer may be used alone or in combination of two or more. On the other hand, alkylphenol-based resins include alkylphenol-acetylene resins such as pt-butylphenol-acetylene, and alkylphenol-formaldehyde resins including cresols, xylenols, pt-butylphenol, and pt-octylphenols. Can be mentioned. These resins preferably have a softening point of 60 to 150 ° C. If the softening point of the resin is less than 60 ° C, sufficient grip on the wet and semi-wet road surfaces in the high temperature range cannot be obtained, and if it exceeds 150 ° C, the resin is not evenly dispersed during kneading and wear resistance The performance is significantly reduced. These C ₉ aromatic petroleum resins and alkylphenol resins may be used alone or in combination of two or more. The compounding quantity of these resin is 3-50 mass parts with respect to 100 mass parts of said rubber components, and it is preferable that it is 5-40 mass parts. When the blending amount of these resins is less than 3 parts by mass, the effect of addition in wet performance such as grip strength cannot be sufficiently obtained, and when it exceeds 50 parts by mass, the workability in kneading the rubber composition is significantly deteriorated.

  The rubber composition of the present invention requires that the acetone / chloroform extract after vulcanization is 30 to 270 parts by mass with respect to 100 parts by mass of the rubber component. If the extracted amount is less than 30 parts by mass or exceeds 270 parts by mass, the kneading workability deteriorates although the improvement in gripping force and wear resistance cannot be expected. The extracted amount is preferably 30 to 200 parts by mass from the viewpoints of both grip strength and wear resistance and kneading workability.

In the rubber composition of the present invention, the rubber component, vulcanization accelerator, vulcanizing agent, carbon black, C ₉ aromatic petroleum resin, other alkylphenol-based resins, various compounding agents in the rubber industry is normally used, For example, oil such as process oil, inorganic filler, softener, dibenzothiazyl disulfide, 4,4′-dimethyldibenzothiazyl disulfide, N-cyclohexyl-2-benzothiazyl-sulfenamide, Nt-butyl-2 -Both benzothiazyl-sulfenamide, Nt-butyl-2-benzothiazyl-sulfenimide, N-oxydiethylene-benzothiazyl-sulfenamide, N, N'-dicyclohexyl-2-benzothiazyl-sulfenamide, etc. Accelerators, vulcanization aids, anti-aging agents, zinc oxide, stearic acid, antiozonants, colorants, antistatic agents, lubricants, antioxidants, A pulling agent, a foaming agent, a foaming aid, and the like can be appropriately blended within a range that does not impair the object of the present invention. As these compounding agents, commercially available products can be suitably used.

  The oil content of the process oil and the like is not particularly limited and may be appropriately selected depending on the intended purpose. However, aromatic oil, naphthenic oil, paraffin oil, ester oil, solution conjugated diene rubber, solution hydrogen Addition conjugated diene rubber and the like are preferable. When the oil composition such as process oil is contained in the rubber composition, the fluidity of the rubber composition can be controlled, the viscosity of the rubber composition before vulcanization is lowered, and the fluidity is increased. Therefore, extrusion can be performed very well.

  When the polybutadiene rubber and / or styrene / butadiene copolymer rubber is oil-extended, the content of oil such as the process oil in the rubber composition includes the oil component and the rubber component. The amount is preferably 35 to 200 parts by mass, more preferably 40 to 150 parts by mass with respect to 100 parts by mass. When the content of oil such as process oil is less than 35 parts by mass, the Mooney viscosity of the unvulcanized rubber composition becomes extremely high, the workability deteriorates, the dry grip property deteriorates, and the content exceeds 200 parts by mass. Further, the Mooney viscosity of the unvulcanized rubber composition becomes extremely low and the processability deteriorates, or the rubber after vulcanization becomes too soft and the wear resistance deteriorates.

  The rubber composition of the present invention is produced by kneading, heating, extruding, vulcanizing, etc., the rubber component, vulcanization accelerator and vulcanizing agent, and various compounding agents appropriately selected as necessary. The

  The kneading conditions are not particularly limited, and various conditions such as the input volume to the kneading apparatus, the rotational speed of the rotor, the ram pressure, the kneading temperature, the kneading time, the type of the kneading apparatus, and the like depending on the purpose. Can be selected as appropriate. Examples of the kneading apparatus include a Banbury mixer, an intermix, and a kneader that are usually used for kneading a rubber composition.

  The heating conditions are not particularly limited, and various conditions such as the heating temperature, the heating time, and the heating apparatus can be appropriately selected according to the purpose. Examples of the heating device include a roll machine ordinarily used for heating a rubber composition.

  The conditions for the extrusion are not particularly limited, and various conditions such as an extrusion time, an extrusion speed, an extrusion apparatus, and an extrusion temperature can be appropriately selected according to the purpose. As said extrusion apparatus, the extruder etc. which are normally used for extrusion of the rubber composition for tires are mentioned, for example. The extrusion temperature can be appropriately determined.

  There is no restriction | limiting in particular about the apparatus, system, conditions, etc. which perform the said vulcanization | cure, According to the objective, it can select suitably. Examples of the vulcanizing apparatus include a molding vulcanizer using a mold usually used for vulcanizing a rubber composition for tires. As the vulcanization conditions, the temperature is usually about 100 to 190 ° C.

  As described above, the rubber composition of the present invention is suitable for a tread of a high-performance tire because heat resistance such as heat fatigue resistance is improved while maintaining high grip performance.

  The pneumatic tire of the present invention is characterized by using the rubber composition of the present invention as a tread. There is no restriction | limiting in particular except for using the said rubber composition for a tread, and the tire of this invention can employ | adopt the structure of a well-known tire as it is.

  As an example of the pneumatic tire of the present invention, a pair of bead portions, a pair of side portions, a tread portion, a carcass extending in a toroid shape between the bead portions, and a crown portion of the carcass are arranged. A tire provided with a belt is preferably exemplified. The tire may have a radial structure or a bias structure.

  The structure of the tread is not particularly limited, and may be a single layer structure or a multilayer structure. An upper cap portion that directly contacts the road surface and an inner side in the tire radial direction of the cap portion are adjacent to each other. You may have what is called a cap base structure comprised from the base part of the lower layer arrange | positioned. In the present invention, it is preferable that at least the cap portion is formed of the rubber composition of the present invention.

  The production method of the pneumatic tire of the present invention is not particularly limited. For example, the rubber composition of the present invention is prepared, and the rubber composition is not added to the crown portion of the raw tire case in advance. It can be manufactured by pasting on a sulfur base and vulcanization molding with a predetermined mold at a predetermined temperature and pressure.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

(1) Thermal fatigue time measurement (lab test)
Various rubber compositions were prepared using a Banbury mixer according to the formulation shown in Table 1. After the obtained rubber composition was vulcanized at 145 ° C. for 45 minutes, a constant stress measurement was performed with a flexometer described in JIS K6265, and the time until a crack occurred inside the sample was defined as a heat fatigue time. The index is shown with 1 being 100. The results are shown in Tables 1 and 2. In addition, it shows that heat resistance fatigue time is so long that an index value is large, and heat fatigue resistance is favorable.

(2) Thermal fatigue evaluation (actual vehicle test)
Trial tires for passenger cars of size 225 / 40R18 using the rubber compositions described above as treads, mounting each test tire on a test vehicle, running the same lap on the test course, and the inside and appearance of the tire after running Observations were made and evaluated according to the following criteria. In addition, about the comparative example 4 and Example 2, 4, 7, and 13, the actual vehicle test is not implemented. The results are shown in Tables 1 and 2.
0 ... No chunks are generated. -1 ... Internal crack is less than 0.5mm.-2 ... Internal crack is 0.5mm or more. A state

  Examples 1 to 14 in which SBR having a vinyl bond amount of 30% or more is used as a rubber component, and a vulcanization accelerator represented by any one of formulas (I) to (III) and an organic thiosulfate compound are blended. The rubber composition had a long heat fatigue time, and the tire using the rubber composition in the tread had a high heat fatigue resistance. On the other hand, the rubber compositions of Comparative Examples 2 to 6 that do not satisfy the conditions defined in claim 1 of the present application are insufficient in improving the heat fatigue time as compared with Comparative Example 1, and the rubber composition is used as a tread. The tire used had many cracks and insufficient heat fatigue resistance.

Claims (8)

(1) A rubber component containing at least one of a polybutadiene rubber and a styrene / butadiene copolymer rubber having a vinyl bond amount of 30% or more,
(2) at least one compound selected from the group consisting of a compound represented by the following formula (I), a compound represented by the following formula (II), and a compound represented by the following formula (III);
(3) comprising an organic thiosulfate compound represented by the following formula (IV) :
The total amount of the compound represented by the following formula (I), the compound represented by the following formula (II), and the compound represented by the following formula (III) is 0.5 to 10 mass with respect to 100 parts by mass of the rubber component. Department,
The compounding amount of the compound represented by the following formula (IV) is 1 to 10 parts by mass with respect to 100 parts by mass of the rubber component.
The rubber composition characterized by the above-mentioned .

(In the formula, R ¹ , R ² , R ³ and R ⁴ each independently represents a linear or branched alkyl group having 3 to 12 carbon atoms or an aralkyl group having 7 to 12 carbon atoms.)

(In the formula, R ⁵ and R ⁶ each independently represent a linear or branched alkyl group having 7 to 12 carbon atoms or an aralkyl group having 7 to 12 carbon atoms, M ¹ is a divalent or higher metal, n is a number equal to the valence of the metal of M ^1. )

^{(Wherein, R 7, R 8, R} 9 and R ^10, a linear or branched alkyl group or an aralkyl group having 7 to 12 carbon atoms of 3 to 12 carbon atoms independently.)
M ² O ₃ S—S— (CH ₂ ) _m —S—SO ₃ M ² (IV)
(In the formula, m represents 3 to 10, M ² represents 1 equivalent of lithium, potassium, sodium, magnesium, calcium, barium, zinc, nickel or cobalt. The compound contains crystal water. May be.) In the compound represented by the formula (I), R ¹ , R ² , R ³ and R ⁴ are each independently a linear or branched alkyl group having 8 to 12 carbon atoms. The rubber composition as described in 2. The rubber composition according to claim 2, wherein in the compound represented by the formula (I), R ¹ , R ² , R ³ and R ⁴ are 2-ethylhexyl groups.   The rubber composition according to claim 1, wherein the styrene-butadiene copolymer rubber has a bound styrene content of 20 to 60% by mass.   The rubber composition according to claim 1, wherein the content of the styrene-butadiene copolymer rubber in the rubber component is 50 to 100% by mass.   2. The rubber composition according to claim 1, wherein the organic thiosulfate compound represented by the formula (IV) is sodium 1,6-hexamethylenedithiosulfate dihydrate. 2. The rubber composition according to claim 1 , wherein the compounding amount of the compound represented by the formula (I) is 0.5 to 10 parts by mass with respect to 100 parts by mass of the rubber component. A pneumatic tire using the rubber composition according to claim 1 as a tread.