JP2019167469A - Rubber composition for base tread - Google Patents

Abstract

To provide a rubber composition for a base tread with improved fracture characteristics while maintaining and improving low heat generation properties, and thereby to provide a tire with improved fuel consumption performance and durability performance.SOLUTION: A rubber composition for a base tread includes 30-50 pts.mass carbon black in which 24M4DBP oil absorption is 90 ml/100 g or less and CTAB absorption specific surface area is 50 m/g or less, as a reinforcement filler, based on 100 pts.mass diene rubber component containing 15-30 mass% polybutadiene rubber containing 2.5-20 mass% 1,2-syndiotactic poly butadiene crystal, and 70-85 mass% isoprene rubber. A tire includes a base tread composed thereof.SELECTED DRAWING: None

Description

  The present invention relates to a rubber composition for a base tread and a tire provided with a base tread composed of the rubber composition for a base tread.

  2. Description of the Related Art Conventionally, for the purpose of energy saving, with increasing demand for low fuel consumption performance of tires, not only tread rubber but also internal components constituting the skeleton of the tire itself have been required to reduce heat generation at a high level. Among them, efforts have also been made to reduce heat generation, such as a technique for lowering the carbon filling amount for the base tread, a technique for using silica as a reinforcing filler, and a technique for increasing the blending amount of the vulcanizing agent.

  Furthermore, in Patent Document 1, as a rubber for a base tread, a polybutadiene rubber containing 2.5 to 20% by mass of 1,2-syndiotactic polybutadiene crystals, a butadiene rubber synthesized using a rare earth catalyst, a lithium initiator A predetermined amount of a reinforcing filler containing sulfur and silica is added to 100 parts by mass of a predetermined tin-modified polybutadiene rubber polymerized by the above, a rubber component containing a predetermined amount of a predetermined modified butadiene rubber for silica and natural rubber, and the like. Thus, it is described that steering stability, rolling resistance characteristics and durability are improved without deteriorating extrusion processability.

JP 2014-189774 A

  However, the heat generation and fracture characteristics of rubber generally tend to contradict each other, and tires that require high-speed turning performance cannot be used for low-heat generation base tread rubber in terms of ensuring durability. There is a tendency.

  In addition, when the above method is used to reduce the fuel consumption of the base tread, in any case, the destruction characteristics of the rubber are deteriorated. For example, in sports tires that require high-speed turning performance, There is a problem that it cannot withstand the input from the surface and peels in the vicinity of the interface with the adjacent compound (cap tread).

  Furthermore, in Patent Document 1, although it is said that steering stability, rolling resistance characteristics and durability can be improved without deteriorating extrudability, maintenance and improvement of low exothermic property and fracture characteristics of the resulting tire can be improved. There is still room for improvement.

  Accordingly, to provide a rubber composition for base treads having improved fracture characteristics while maintaining and improving low heat build-up, and to provide tires with improved ride comfort, fuel efficiency and durability. Objective.

  In view of the above problems, the present inventor uses a butadiene rubber containing a 1,2-syndiotactic polybutadiene crystal having strength in a polymer itself, and blends a predetermined amount of flexible grade carbon, thereby reducing low heat build-up. The present inventors have found that the fracture characteristics can be improved while maintaining and improving the present invention.

That is, this disclosure
[1] 2.5 to 20% by mass of 1,2-syndiotactic polybutadiene crystals, preferably 5 to 19% by mass, more preferably 7 to 18% by mass, still more preferably 10 to 18% by mass, particularly preferably. 100 parts by mass of a diene rubber component containing 15 to 30% by mass of polybutadiene rubber containing 12 to 16% by mass, and 70 to 85% by mass, preferably 70 to 80% by mass, more preferably 75 to 80% by mass of isoprene-based rubber. On the other hand, the 24M4DBP oil absorption as a reinforcing filler is 90 ml / 100 g or less, preferably 60 to 87 ml / 100 g, more preferably 65 to 85 ml / 100 g, still more preferably 70 to 84 ml / 100 g, and the CTAB adsorption specific surface area. 50 m ² / g or less, preferably 25~45m ² / g, more preferably 30~43m ² / g, Et preferably a 30~42m ² / g, particularly preferably 30 to 40 m ² / g, even more preferably 30 to 50 parts by weight of carbon black as a 30~37m ² / g, preferably 33 to 48 parts by weight, More preferably, rubber composition for base tread containing 35 to 45 parts by mass,
[2] The rubber composition for a base tread according to the above [1], wherein the content of the polybutadiene rubber in the diene rubber component is 20 to 30% by mass, preferably 25 to 30% by mass,
[3] 2-10 parts by mass, preferably 3-8 parts by mass, more preferably 3-6 parts by mass, of a copolymerized hydrocarbon resin obtained by copolymerizing an aromatic component and / or a naphthene component and an aliphatic component, More preferably, the rubber composition for base treads according to [1] or [2] above containing 4 to 5 parts by mass, and [4] the rubber composition for base treads according to any of [1] to [3] above. The present invention relates to a tire provided with a base tread.

With respect to 100 parts by mass of the diene rubber component containing 15 to 30% by mass of polybutadiene rubber containing 2.5 to 20% by mass of 1,2-syndiotactic polybutadiene crystal and 70 to 85% by mass of isoprene rubber according to the present invention. The base tread rubber composition containing 30-50 parts by mass of carbon black having a 24M4DBP oil absorption of 90 ml / 100 g or less and a CTAB adsorption specific surface area of 50 m ² / g or less as a reinforcing filler has been improved. A tire including a base tread having low heat build-up and improved fracture characteristics and composed of the base tread rubber composition can improve riding comfort, durability, and fuel efficiency.

The rubber composition for a base tread of the present invention is a diene system containing 15 to 30% by mass of polybutadiene rubber containing 2.5 to 20% by mass of 1,2-syndiotactic polybutadiene crystals and 70 to 85% by mass of isoprene-based rubber. The rubber component contains 30 to 50 parts by mass of carbon black having a 24M4DBP oil absorption of 90 ml / 100 g or less and a CTAB adsorption specific surface area of 50 m ² / g or less as a reinforcing filler.

  The reason why such a low exothermic maintenance and improvement effect and an improvement effect on fracture characteristics are not clear, but a polybutadiene rubber containing 2.5 to 20% by mass of 1,2-syndiotactic polybutadiene crystals is a polymer itself. In combination with a flexible grade of carbon black that is strong, has a relatively large particle size, and does not adversely affect exothermic properties, it can obtain sufficient fracture characteristics while preventing exothermic deterioration. it is conceivable that.

  Further, if the content in the rubber component of the polybutadiene rubber containing 2.5 to 20% by mass of 1,2-syndiotactic polybutadiene crystal is further limited to 20 to 30% by mass, sufficient fracture characteristics are obtained depending on its strength. Can be obtained.

  As one embodiment of the present invention, it is preferable to blend a predetermined amount of a copolymer hydrocarbon resin obtained by copolymerizing an aromatic component and / or a naphthene component and an aliphatic component. In the copolymerized hydrocarbon resin in which the aromatic component and / or naphthene component and the aliphatic component are copolymerized, the aliphatic component is compatible with the rubber component, and the aromatic component and / or naphthene component is compatible with carbon black. In order to dissolve, the dispersibility of the carbon black in the rubber component is improved, and in addition to the combination of the polybutadiene rubber containing 2.5 to 20% by mass of the above 1,2-syndiotactic polybutadiene crystal and the predetermined carbon black Further, it is considered that low heat buildup and fracture resistance can be improved.

(Rubber component)
The diene rubber component contains 15 to 30% by mass of polybutadiene rubber (SPB-containing BR) containing 2.5 to 20% by mass of 1,2-syndiotactic polybutadiene crystals and 70 to 85% by mass of isoprene rubber.

  The SPB-containing BR is preferably a non-orientated dispersion in which 1,2-syndiotactic polybutadiene crystals (SPB) are not simply dispersed in BR but chemically bonded to BR. When the crystal is chemically bonded to BR and then dispersed, crack generation and propagation tend to be suppressed. Examples of such SPB-containing BR include VCR-303, VCR-412 and VCR-617 manufactured by Ube Industries.

  The melting point of SPB is preferably 180 ° C. or higher, more preferably 190 ° C. or higher, and further preferably 200 ° C. or higher. When the melting point of SPB is less than 180 ° C., crystals melt during vulcanization of the tire by pressing, and the hardness tends to decrease. The melting point of SPB is preferably 220 ° C. or lower, more preferably 210 ° C. or lower, and further preferably 200 ° C. or lower. When the melting point of SPB exceeds 220 ° C., the molecular weight of the rubber component increases, so that dispersibility tends to deteriorate in the rubber composition.

  The content of the boiling n-hexane insoluble matter in the SPB-containing BR is preferably 2.5% by mass or more, more preferably 8% by mass or more, further preferably 10% by mass or more, and particularly preferably 15% by mass or more. When the content of boiling n-hexane insoluble matter is less than 2.5% by mass, the hardness of the rubber composition tends to be insufficient. Further, the content of the boiling n-hexane insoluble matter is preferably 22% by mass or less, more preferably 20% by mass or less, and further preferably 18% by mass or less. When the content of the boiling n-hexane insoluble matter exceeds 22% by mass, the viscosity of the SPB-containing BR itself is high, and the dispersibility of the SPB-containing BR and the reinforcing filler in the rubber composition tends to deteriorate. Here, the boiling n-hexane insoluble means 1,2-syndiotactic polybutadiene (SPB) in the SPB-containing BR.

  The SPB content in the SPB-containing BR is 2.5 mass% or more, preferably 5 mass% or more, more preferably 7 mass% or more, further preferably 10 mass% or more, and particularly preferably 12 mass% or more. When the SPB content is less than 2.5% by mass, sufficient hardness tends not to be obtained. Further, the SPB content in the SPB-containing BR is 20% by mass or less, preferably 19% by mass or less, more preferably 18% by mass or less, and further preferably 16% by mass or less. When the SPB content exceeds 20% by mass, the SPB-containing BR cannot be sufficiently dispersed in the rubber composition, and good extrudability tends to be not obtained.

  The content of SPB-containing BR in the rubber component is 15% by mass or more, preferably 20% by mass or more, and more preferably 25% by mass or more. When the content of SPB-containing BR is less than 15% by mass, sufficient fracture characteristics tend not to be obtained. Moreover, content of SPB containing BR in a rubber component is 30 mass% or less. When the content of the SPB-containing BR exceeds 30% by mass, the exothermic property and elongation at break tend to deteriorate.

  Examples of the isoprene-based rubber include natural rubber (NR) and polyisoprene rubber (IR).

  The NR is not particularly limited, and those commonly used in the tire industry can be used, and examples thereof include SIR20, RSS # 3, and TSR20. Further, as the IR, those generally used in the tire industry can be used.

  The content of the isoprene-based rubber in the rubber component is 70% by mass or more. When the content of the isoprene-based rubber is less than 70% by mass, the heat generation tends to deteriorate. Further, the content of the isoprene-based rubber in the rubber component is 85% by mass or less, preferably 80% by mass or less, and more preferably 75% by mass or less. When the content of the isoprene-based rubber exceeds 85% by mass, sufficient fracture characteristics tend not to be obtained.

  The diene rubber component may contain a diene rubber in addition to the SPB-containing BR and the isoprene rubber. Such a diene rubber is not particularly limited. For example, butadiene rubber (BR), deproteinized natural rubber (DPNR), high-purity natural rubber (HPNR), epoxidized natural rubber (ENR), Examples include solution polymerized styrene butadiene rubber (S-SBR), emulsion polymerized styrene butadiene rubber (E-SBR), and modified styrene butadiene rubber (modified S-SBR, modified E-SBR). Among these, BR is preferable from the viewpoints of excellent handling stability, elongation at break and rolling resistance. In addition, these rubber components may be used independently and may use 2 or more types together.

  As the BR, a low-cis 1,4-polybutadiene rubber (low-cis BR), a high-cis 1,4-polybutadiene rubber (high-cis BR), 1,3-butadiene is polymerized with a lithium initiator, and then a tin compound is added. Further, modified BR molecules whose ends are bonded with tin-carbon bonds (tin-modified BR), butadiene rubber synthesized using a rare earth catalyst (rare earth BR), butadiene rubber Examples include butadiene rubber (modified BR for silica) having a condensed alkoxysilane compound at the active end. Examples of such modified BR include BR1250H (tin modified) manufactured by Nippon Zeon Co., Ltd., S modified polymer (modified for silica) manufactured by Sumitomo Chemical Co., Ltd., and the like.

  The high cis BR is a butadiene rubber having a cis 1,4 bond content of 90% by weight or more. Examples of such high-sis BR include BR1220 manufactured by Nippon Zeon Co., Ltd., BR130B and BR150B manufactured by Ube Industries, Ltd. By containing the high cis BR, low temperature characteristics and wear resistance can be improved.

  Butadiene rubber (rare earth BR) synthesized using a rare earth catalyst has a high cis content and a low vinyl content. As the rare earth BR, a general-purpose product in tire manufacture can be used.

  Tin-modified BR is polymerized by a lithium initiator, tin-modified polybutadiene rubber having a tin atom content of 50 to 3000 ppm, a vinyl bond content of 5 to 50% by mass, and a molecular weight distribution (Mw / Mn) of 2 or less. Tin-modified BR). This tin-modified BR is obtained by polymerizing 1,3-butadiene with a lithium initiator and then adding a tin compound. Further, the tin-modified BR is bonded with a tin-carbon bond at the end of the modified BR molecule. Polybutadiene rubber is preferred.

(Carbon black)
The carbon black is not particularly limited as long as it has a 24M4DBP oil absorption of 90 ml / 100 g or less and a CTAB adsorption specific surface area of 50 m ² / g or less. GPF, FEF, HAF, ISAF, SAF, etc., alone or 2 A combination of more than one species can be used.

  Carbon black has a 24M4DBP oil absorption (compressed dibutyl phthalate oil absorption) of 90 ml / 100 g or less, preferably 87 ml / 100 g or less, more preferably 85 ml / 100 g or less, and even more preferably 84 ml / 100 g or less. If the 24M4DBP oil absorption of carbon black exceeds 90 ml / 100 g, sufficient fracture characteristics tend to be obtained, but it is difficult to maintain and improve heat generation and riding comfort in a well-balanced manner. There is no particular lower limit to the 24M4DBP oil absorption amount of carbon black, but the 24M4DBP oil absorption amount of carbon black is preferably 60 ml / 100 g or more and 63 ml / 100 g or more in consideration of use in a rubber composition for a base tread. More preferred is 70 ml / 100 g or more. Carbon black can use 1 type (s) or 2 or more types. Here, the 24M4DBP oil absorption is a value measured based on ASTM D3493-91 (Standard Test Method for Carbon Black-n-Division 1 Phthalate Number of Compressed Sample).

Cetyltrimethylammonium bromide (CTAB) adsorption specific surface area of carbon black is not more than 50 m ² / g, preferably 45 m ² / g or less, more preferably ^{43m 2 / g, 42m 2 /} g and more preferably less, 40 m ² / g or less is particularly preferable, and 37 m ² / g or less is even more preferable. There is no particular lower limit to the CTAB adsorption specific surface area of carbon black, but the CTAB adsorption specific surface area of carbon black is preferably 25 m ² / g or more in consideration of use in a rubber composition for base tread, and 30 m ² / G or more is more preferable. Such carbon black can be used singly or in combination of two or more. When the CTAB adsorption specific surface area of the carbon black exceeds 50 m ² / g, the heat generation tends to deteriorate. Here, the CTAB adsorption specific surface area is a value that correlates with the particle size of carbon black, and the larger the CTAB adsorption specific surface area, the smaller the particle size of carbon black. The CTAB adsorption specific surface area can be measured according to JIS K 6217-3: 2001.

  The content of carbon black with respect to 100 parts by mass of the rubber component is 30 parts by mass or more, more preferably 33 parts by mass or more, and further preferably 35 parts by mass or more. When the content of carbon black is less than 30 parts by mass, the effects of the invention tend to be hardly exhibited. The content of carbon black with respect to 100 parts by mass of the rubber component is 50 parts by mass or less, more preferably 48 parts by mass or less, and further preferably 45 parts by mass or less. If the carbon black content exceeds 50 parts by mass, the exothermicity may deteriorate.

(Compatibilized resin)
The rubber composition of this embodiment suitably contains a compatibilizing resin. In the present embodiment, the compatibilizing resin has good affinity for both rubber and filler and contributes to improvement of durability by reducing the voids around the filler, and is an aromatic component and / or naphthene component. And a copolymerized hydrocarbon resin in which an aliphatic component is copolymerized. As an example, the compatibilizing resin is an ethylene propylene styrene copolymer resin or the like. A compatibilizing resin may be used in combination. The rubber composition of the present embodiment more preferably contains an ethylene propylene styrene copolymer resin from the viewpoint of improving the durability of the resulting rubber composition and being inexpensive.

  The ethylene-propylene-styrene copolymer resin is a copolymer resin obtained by polymerizing a styrene monomer, an ethylene monomer, and a propylene monomer, and the following general formula (wherein, m, n, and o are all integers of 1 or more). ) Is included. The rubber composition contains the ethylene propylene styrene copolymer resin, so that the durability is maintained at the same level as compared with the case where the terpene resin is contained.

  The total amount of the structural unit derived from ethylene and the structural unit derived from propylene in the ethylene-propylene-styrene copolymer resin (EP content, sum of m and n in the above formula with respect to the number of all the structural units) is not particularly limited.

  In the present embodiment, a commercially available product may be used as the ethylene propylene styrene copolymer resin. Examples of such commercially available products include those manufactured and sold by Straktor, Flow Polymers Inc., performance additive, LANXESS, and the like.

  The content of the compatibilizing resin with respect to 100 parts by mass of the rubber component is preferably 2 parts by mass or more, more preferably 3 parts by mass or more, and still more preferably 4 parts by mass or more. By setting the content of the compatibilizing resin to 2 parts by mass or more, sufficient fracture characteristics tend to be obtained. Moreover, 10 mass parts or less are preferable with respect to 100 mass parts of rubber components, 8 mass parts or less are more preferable, 6 mass parts or less are more preferable, and 5 mass parts or less are especially preferable. By setting the content of the compatibilizing resin to 10 parts by mass or less, the exothermic deterioration can be suppressed.

(Other ingredients)
In addition to the above components, the rubber composition for base tread includes, as necessary, compounding agents generally used in the conventional rubber industry, for example, reinforcing fillers such as silica other than carbon black, various softeners, oils , Liquid diene polymers, various anti-aging agents, waxes, zinc oxide, stearic acid, vulcanizing agents, vulcanization accelerators and the like can be appropriately contained.

(silica)
The silica is not particularly limited, and examples thereof include dry process silica (anhydrous silicic acid), wet process silica (hydrous silicic acid), etc., but there are many silanol groups and there are many reactive points with the silane coupling agent. Therefore, wet method silica is preferable.

(Silane coupling agent)
When silica is contained, it is preferable to use a silane coupling agent. Examples of the silane coupling agent include sulfide systems such as bis (3-triethoxysilylpropyl) disulfide and bis (3-triethoxysilylpropyl) tetrasulfide, 3-mercaptopropyltrimethoxysilane, and 3-mercaptopropyltriethoxy. Mercapto series such as silane, 3-octanoylthio-1-propyltriethoxysilane, 3-hexanoylthio-1-propyltriethoxysilane, thioether series such as 3-octanoylthio-1-propyltrimethoxysilane, vinyltriethoxysilane, etc. Vinyl type, amino type such as 3-aminopropyltriethoxysilane, glycidoxy type such as γ-glycidoxypropyltriethoxysilane, nitro type such as 3-nitropropyltrimethoxysilane, 3-chloropropyltrimethyl Chloro-based such as Kishishiran like. These may be used alone or in combination of two or more. Of these, sulfide coupling agents, particularly bis (3-triethoxysilylpropyl) tetrasulfide and 3 are particularly preferred from the viewpoints of easy control of the temperature of the reaction with silica and the effect of improving the reinforcing property of the rubber composition. -Trimethoxysilylpropylbenzothiazolyl tetrasulfide is preferred.

(Softener)
Softeners include petroleum-based softeners such as process oil, lubricating oil, paraffin, liquid paraffin, petroleum asphalt and petroleum jelly, and fatty oil-based softeners such as soybean oil, palm oil, castor oil, linseed oil, rapeseed oil and coconut oil. Agents, waxes such as tall oil, sub, beeswax, carnauba wax and lanolin, and fatty acids such as linoleic acid, palmitic acid, stearic acid and lauric acid.

(oil)
Examples of the oil include process oils such as paraffinic, aroma-based, and naphthenic process oils.

(Anti-aging agent)
The antiaging agent is not particularly limited, but examples thereof include naphthylamines such as phenyl-α-naphthylamine, phenyl-β-naphthylamine, aldol-α-trimethyl1,2-naphthylamine; 2,2,4- Quinoline such as trimethyl-1,2-dihydroquinoline polymer, 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline; p-isopropoxydiphenylamine, p- (p-toluenesulfonylamide)- Diphenylamines such as diphenylamine, N, N-diphenylethylenediamine, octylated diphenylamine; N-phenyl-N ′-(1,3-dimethylbutyl) -p-phenylenediamine, N-isopropyl-N′-phenyl-p-phenylene Diamine, N, N'-diphenyl-p-phenylenediam N, N′-di-2-naphthyl-p-phenylenediamine, N-cyclohexyl-N′-phenyl-p-phenylenediamine, N, N′-bis (1-methylheptyl) -p-phenylenediamine, N , N′-bis (1,4-dimethylpentyl) -p-phenylenediamine, N, N′-bis (1-ethyl-3-methylpentyl) -p-phenylenediamine, N-4-methyl-2-pentyl -N'-phenyl-p-phenylenediamine, N, N'-diaryl-p-phenylenediamine, hindered diaryl-p-phenylenediamine, phenylhexyl-p-phenylenediamine, phenyloctyl-p-phenylenediamine, etc. -Phenylenediamine series; 2,5-di- (tert-amyl) hydroquinone, 2,5-di-tert-butylhydroxy Hydroquinone derivatives such as phenol; phenolic (2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-ethylphenol, 2,6-di-tert-butylphenol, 1 -Oxy-3-methyl-4-isopropylbenzene, butylhydroxyanisole, 2,4-dimethyl-6-tert-butylphenol, n-octadecyl-3- (4'-hydroxy-3 ', 5'-di-tert- Monophenols such as butylphenyl) propionate and styrenated phenol; 2,2′-methylene-bis- (4-methyl-6-tert-butylphenol), 2,2′-methylene-bis- (4-ethyl-6) -Tert-butylphenol), 4,4'-butylidene-bis- (3-methyl-6-tert-butylphenol) ), 1,1′-bis- (4-hydroxyphenyl) -cyclohexane and the like; trisphenol type; tetrakis- [methylene-3- (3 ′, 5′-di-tert-butyl-4′-hydroxy] Phenyl) propionate] polyphenols such as methane); 4,4′-thiobis- (6-tert-butyl-3-methylphenol), 2,2′-thiobis- (6-tert-butyl-4-methylphenol) Thiobisphenol such as 2-mercaptomethylbenzimidazole; thiourea such as tributylthiourea; phosphorous acid such as tris (nonylphenyl) phosphite; organic thioacid such as dilauryl thiodipropionate Antiaging agent etc. are mentioned. These anti-aging agents may be used alone or in combination of two or more. Among them, N-phenyl-N ′-(1,3-dimethylbutyl) -p-phenylenediamine and 2,2,4-trimethyl-1,2-dihydroquinoline heavy are preferable in terms of both heat resistance and fatigue resistance. It is preferable to use a combination.

  In addition, as stearic acid, zinc oxide, wax, etc., those conventionally used in the rubber industry can be used.

(Vulcanizing agent)
The vulcanizing agent is not particularly limited, and those commonly used in the tire industry can be used. Among them, sulfur is preferable, and insoluble sulfur is more preferable.

(Vulcanization accelerator)
The vulcanization accelerator is not particularly limited. For example, sulfenamide, thiazole, thiuram, thiourea, guanidine, dithiocarbamic acid, aldehyde-amine or aldehyde-ammonia, imidazoline. And xanthate vulcanization accelerators. Among them, sulfenamide vulcanization accelerators are preferable from the viewpoint that the effects of the present invention can be obtained more suitably.

  Examples of the sulfenamide vulcanization accelerator include CBS (N-cyclohexyl-2-benzothiazylsulfenamide), TBBS (Nt-butyl-2-benzothiazylsulfenamide), N-oxyethylene- Examples include 2-benzothiazylsulfenamide, N, N′-diisopropyl-2-benzothiazylsulfenamide, N, N-dicyclohexyl-2-benzothiazylsulfenamide, and the like. Examples of thiazole vulcanization accelerators include 2-mercaptobenzothiazole, dibenzothiazolyl disulfide and the like. Examples of the thiuram vulcanization accelerator include tetramethylthiuram monosulfide, tetramethylthiuram disulfide, and tetrabenzylthiuram disulfide (TBzTD). Examples of the guanidine vulcanization accelerator include diphenyl guanidine (DPG), diortolyl guanidine, orthotolyl biguanidine and the like. These may be used alone or in combination of two or more. Especially, it is preferable to use TBBS from the point from which the effect of this invention is acquired more suitably.

(Method for producing rubber composition for base tread)
It does not specifically limit as a manufacturing method of the rubber composition for base treads, A well-known method can be used. For example, each of the above components can be produced by a method of kneading using a rubber kneading apparatus such as an open roll, a Banbury mixer, a closed kneader, and then vulcanizing.

(Tire manufacturing method)
A tire including a base tread composed of the base tread rubber composition can be produced by a normal method using the base tread rubber composition. That is, the rubber composition in which the compounding agent is blended as necessary with respect to the diene rubber component is extruded according to the shape of the base tread, and bonded together with other tire members on a tire molding machine, An unvulcanized tire is formed by molding by a normal method, and the tire can be manufactured by heating and pressurizing the unvulcanized tire in a vulcanizer.

  The tire can be used for tires such as tires for passenger cars, high performance tires for passenger cars, heavy duty tires such as trucks and buses, and tires for competition.

  EXAMPLES Hereinafter, although this invention is demonstrated based on an Example, this invention is not limited only to these Examples.

Hereinafter, various chemicals used in Examples and Comparative Examples are shown together.
・ NR: TSR20 (natural rubber)
SPB-containing BR: VCR617 manufactured by Ube Industries, Ltd. (polybutadiene rubber containing 1,2-syndiotactic polybutadiene crystal, 1,2-syndiotactic polybutadiene crystal (SPB) content: 12% by mass, SPB Melting point: 200 ° C., content of boiling n-hexane insoluble matter: 15 to 18% by mass)
-Tin-modified BR: BR1250 manufactured by Nippon Zeon Co., Ltd. (tin-modified polybutadiene rubber (tin-modified BR), polymerization using lithium as an initiator, vinyl bond amount: 10 to 13% by mass, Mw / Mn: 1.5 , Tin atom content: 250 ppm)
Carbon black 1: Seast 3 (HAF) manufactured by Tokai Carbon Co., Ltd. (24M4DBP oil absorption: 98 ml / 100 g, CTAB adsorption specific surface area: 89 m ² / g, N ₂ SA: 79 m ² / g)
Carbon black 2: Seast SO (FEF) manufactured by Tokai Carbon Co., Ltd. (24M4DBP oil absorption: 85 ml / 100 g, CTAB adsorption specific surface area: 42 m ² / g, N ₂ SA: 40 m ² / g)
Carbon black 3: Seast V (GPF) manufactured by Tokai Carbon Co., Ltd. (24M4DBP oil absorption: 84 ml / 100 g, CTAB adsorption specific surface area: 37 m ² / g, N ₂ SA: 36 m ² / g)
・ Zinc flower: Zinc flower No. 1 made by Mitsui Mining & Smelting Co., Ltd. ・ Stearic acid: Bead stearic acid Tsubaki made by NOF Corporation ・ Wax: Ozoace 355 made by Nippon Seiwa Co., Ltd.
Anti-aging agent 1: Antigen 6C (N-phenyl-N ′-(1,3-dimethylbutyl) -p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd.
Anti-aging agent 2: ANTAGE RD (2,2,4-trimethyl-1,2-dihydroquinoline polymer) manufactured by Kawaguchi Chemical Industry Co., Ltd.
・ Oil: Diana Process AH-24 (Aroma Oil) manufactured by Idemitsu Kosan Co., Ltd.
-Compatibilized resin 1: Stractol 40MS manufactured by Straktor (mixture of aromatic hydrocarbon resin and aliphatic hydrocarbon resin (ethylene propylene styrene copolymer), softening point: 98-106 ° C)
Compatibilizing resin 2: Promix (registered trademark) 400 manufactured by Flow Polymer Co., Ltd. (copolymerized hydrocarbon resin (ethylene propylene styrene copolymer) in which an aromatic component and / or a naphthene component and an aliphatic component are copolymerized), (Softening point: 98-106 ° C)
・ Insoluble sulfur: Seimi sulfur manufactured by Nihon Kiboshi Kogyo Co., Ltd. (containing 10% oil, insoluble matter due to carbon disulfide: 60% or more)
-Vulcanization accelerator 1: Noxeller NS-P (N-tert-butyl-2-benzothiazolylsulfenamide (TBBS)) manufactured by Ouchi Shinsei Chemical Co., Ltd.

Examples and Comparative Examples In accordance with the formulation shown in Tables 1 and 2, using a 1.7 L Banbury mixer manufactured by Kobe Steel Co., Ltd., chemicals other than insoluble sulfur and a vulcanization accelerator were added, and the discharge temperature was 155. It knead | mixed for 5 minutes so that it might become ° C. Next, insoluble sulfur and a vulcanization accelerator were added to the obtained kneaded material in the amounts shown in Table 1, and then kneaded for 3 minutes using an open roll at a discharge temperature of 80 ° C. A rubber composition was obtained. The obtained unvulcanized rubber composition was molded into a tread shape, bonded to another member, and vulcanized at 170 ° C. for 15 minutes to obtain a pneumatic tire (size 195 / 65R15). Moreover, the unvulcanized rubber composition was used as a test piece, and vulcanized at 170 ° C. for 15 minutes to obtain a vulcanized rubber test piece. In Tables 1 and 2, the oil content includes the amount of oil contained in the oil-extended rubber and the amount of oil contained in insoluble sulfur.

  The pneumatic tires or vulcanized rubber test pieces obtained in the examples and comparative examples were evaluated for fuel efficiency, riding comfort, and durability by the following tests. The results are shown in Tables 1 and 2.

<Fuel efficiency test>
Using a rolling resistance tester, the rolling resistance when each test tire was run at a rim (15 × 6JJ), internal pressure (230 kPa), load (3.43 kN), speed (80 km / h) was measured, Comparative example 1 was taken as 100 and displayed as an index. The larger the fuel efficiency index is, the better the fuel efficiency is, and 110 or more is set as the target value.

<Ride comfort test>
Each test tire was mounted on all wheels of domestic FF2000cc and the vehicle was actually driven on the test course. The ride comfort after the start of the meandering and 30 minutes after the start was evaluated by sensory evaluation of the driver. Overall, the above evaluations were made relative evaluations with the riding comfort of Comparative Example 1 as 100 points. The higher the score, the better the ride comfort, and the target value is 110 or more.

<Durability>
Each test tire was mounted on a passenger car with a displacement of 2000 cc, and the damage form after 35 round laps on the asphalt road surface was evaluated. When no peeling occurred, 100 was assumed, and when peeling occurred, the number of laps / 35 laps was indexed.

Claims (4)

For reinforcement with respect to 100 parts by mass of a diene rubber component containing 15 to 30% by mass of polybutadiene rubber containing 2.5 to 20% by mass of 1,2-syndiotactic polybutadiene crystals and 70 to 85% by mass of isoprene-based rubber A rubber composition for a base tread comprising 30 to 50 parts by mass of carbon black having a 24M4DBP oil absorption of 90 ml / 100 g or less and a CTAB adsorption specific surface area of 50 m ² / g or less as a filler. The rubber composition for a base tread according to claim 1, wherein the content of the polybutadiene rubber in the diene rubber component is 20 to 30% by mass. The rubber composition for base treads according to claim 1 or 2, comprising 2 to 10 parts by mass of a copolymerized hydrocarbon resin obtained by copolymerizing an aromatic component and / or a naphthene component and an aliphatic component. A tire provided with the base tread comprised with the rubber composition for base treads of Claims 1-3.