JP5457007B2 - Rubber composition for tire and pneumatic tire - Google Patents

Description

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

A rubber composition used for a tire breaker is required to improve the excellent rigidity, breaking strength, adhesion to a cord such as a steel cord and performance of low fuel consumption in a balanced manner. For example, since the rubber composition for breaker topping requires high breaking strength, natural rubber / isoprene rubber close to 100% is generally used, but it is not sufficient in terms of low fuel consumption.

On the other hand, modified butadiene and solution polymerization modified styrene butadiene rubber that can form a strong bond with carbon black or silica is effective in reducing the tan δ of the rubber and reducing fuel consumption. There is a problem that decreases. Further, as a method for improving fuel economy, a method of reducing the content of fillers such as carbon black and silica, and a method of replacing part or all of carbon black with silica are known. ^* ) Decreases, and there is a problem that rigidity decreases or steering stability decreases.

As described above, the reduction in fuel consumption of breaker topping rubber is accompanied by a decrease in durability and adhesiveness, and a rubber composition that simultaneously satisfies all the characteristics of low fuel consumption, rigidity, breaking strength, and adhesiveness with cords. The current situation is that it has not been obtained.

For example, in Patent Document 1, rigidity is obtained by using a butadiene rubber containing 1,2-syndiotactic polybutadiene crystals and a modified butadiene rubber and / or a modified styrene butadiene rubber as a rubber component of a rubber composition for a breaker topping. It has been proposed to improve fuel efficiency while maintaining elongation at break and peel strength. Patent Document 2 also includes a rubber composition for coating a steel cord in which hexamethylene bisthiosulfate disodium salt dihydrate is blended with a specific amount of sulfur to suppress a decrease in tensile properties and peeling from the steel cord. It is disclosed that it can be done.

Furthermore, by using cresol resin, hexamethylol melamine pentamethyl ether, organic acid cobalt, etc., it is disclosed that the deterioration due to aging of the breaking strength is suppressed and the adhesiveness with a metal material is improved (patent document). 3). However, even if these rubber compositions are used, the above-mentioned performance such as fuel efficiency cannot be obtained in a well-balanced manner, and there is still room for improvement.

JP 2007-277289 A JP 2006-124474 A JP 2005-272815 A

The present invention solves the above-mentioned problems, and a tire rubber composition capable of obtaining all the performances of low fuel consumption, rigidity, breaking strength, and adhesion to a cord in a well-balanced manner, and covering this with a breaker cord It aims at providing the pneumatic tire which has a breaker obtained.

The present invention provides a tin-modified polybutadiene rubber and / or the following formula (1);

（式中、Ｒ^１、Ｒ^２及びＲ^３は、同一若しくは異なって、アルキル基、アルコキシ基、シリルオキシ基、アセタール基、カルボキシル基、メルカプト基又はこれらの誘導体を表す。Ｒ^４及びＲ^５は、同一若しくは異なって、水素原子又はアルキル基を表す。ｎは整数を表す。）で表される化合物により変性されたポリブタジエンゴム５〜５０質量部と天然ゴム及び／又はイソプレンゴム５０〜９５質量部とを含むゴム成分１００質量部に対して、ヘキサメチレンビスチオサルフェート２ナトリウム塩２水和物を０．１〜３質量部、硫黄を２．５〜７質量部含有するタイヤ用ゴム組成物に関する。

(Wherein R ¹ , R ² and R ³ are the same or different and each represents an alkyl group, an alkoxy group, a silyloxy group, an acetal group, a carboxyl group, a mercapto group or a derivative thereof. R ⁴ and R ⁵ are The same or different and each represents a hydrogen atom or an alkyl group, n represents an integer.) 5 to 50 parts by mass of a polybutadiene rubber modified with a compound represented by the following formula, and 50 to 95 parts by mass of natural rubber and / or isoprene rubber: It is related with the rubber composition for tires which contains 0.1-3 mass parts of hexamethylenebisthiosulfate disodium salt dihydrate, and 2.5-7 mass parts of sulfur with respect to 100 mass parts of rubber components containing.

Furthermore, it contains silica and carbon black, the content of the silica is 5 to 60 parts by mass, and the total content of the silica and carbon black is 40 to 60 parts by mass with respect to 100 parts by mass of the rubber component. preferable.

The tin-modified polybutadiene rubber is polymerized with a lithium initiator, the tin atom content is 50 to 3000 ppm, the vinyl bond content is 5 to 50% by mass, and the molecular weight distribution (Mw / Mn) is 2 or less. It is preferable that the vinyl bond content of the resulting polybutadiene rubber is 35% by mass or less.

The rubber composition is preferably used for a breaker topping, a breaker edge strip, or a breaker lower rubber between a breaker and a ply.

The present invention also relates to a pneumatic tire having a breaker obtained by coating a breaker cord with the rubber composition.

According to the present invention, by blending a predetermined amount of hexamethylene bisthiosulfate disodium salt dihydrate and sulfur into a specific rubber component, a balance between low fuel consumption, rigidity, breaking strength, and adhesion to cords is achieved. It is possible to provide a tire rubber composition that can be obtained well and a pneumatic tire having a breaker obtained by coating the rubber composition on a breaker cord.

The rubber composition for tires of the present invention includes a tin-modified polybutadiene rubber (tin-modified BR) and / or a polybutadiene rubber (S-modified BR) modified with a compound represented by the above formula (1) and a natural rubber (NR). Further, a predetermined amount of hexamethylene bisthiosulfate disodium salt dihydrate (HTS) and sulfur are further blended with a rubber component containing isoprene rubber (IR) in a predetermined blend. By using such a mixture of tin-modified BR or S-modified BR and NR or IR, fuel consumption can be reduced, and further by blending HTS, the cord adhesion and the breaking strength can be reduced by synthetic rubber. Can be suppressed. Accordingly, it is possible to obtain all the performances of low fuel consumption, rigidity, breaking strength, and adhesiveness with the cord in a well-balanced manner.

By using tin-modified BR, a low exothermic effect can be obtained and fuel consumption can be reduced.
The tin-modified BR is obtained by polymerizing 1,3-butadiene with a lithium initiator and then adding a tin compound, and the end of the tin-modified BR molecule is further bonded with a tin-carbon bond. Those are preferred.

Examples of the lithium initiator include lithium compounds such as alkyl lithium, aryl lithium, vinyl lithium, organic tin lithium, and organic nitrogen lithium compounds, and lithium metal. By using the lithium initiator as an initiator for tin-modified BR, a tin-modified BR having a high vinyl content and a low cis content can be produced.

Tin compounds include tin tetrachloride, butyltin trichloride, dibutyltin dichloride, dioctyltin dichloride, tributyltin chloride, triphenyltin chloride, diphenyldibutyltin, triphenyltin ethoxide, diphenyldimethyltin, ditolyltin chloride, diphenyltin dioctano Ate, divinyldiethyltin, tetrabenzyltin, dibutyltin distearate, tetraallyltin, p-tributyltin styrene and the like.

The content of tin atoms in the tin-modified BR is preferably 50 ppm or more, and more preferably 60 ppm or more. If it is less than 50 ppm, the effect of promoting the dispersion of carbon black in the tin-modified BR is small, and tan δ tends to increase. The tin atom content is preferably 3000 ppm or less, more preferably 2500 ppm or less, and even more preferably 250 ppm or less. If it exceeds 3000 ppm, the kneaded product is poorly organized and the edges are not aligned, so the extrudability of the kneaded product tends to deteriorate.

The molecular weight distribution (Mw / Mn) of the tin-modified BR is preferably 2 or less, and more preferably 1.5 or less. If it exceeds 2, the dispersibility of carbon black will deteriorate and tan δ will increase.

The vinyl bond amount of the tin-modified BR is preferably 5% by mass or more, and more preferably 7% by mass or more. It tends to be difficult to polymerize (manufacture) tin-modified BR of less than 5% by mass. Further, the vinyl bond amount of the tin-modified BR is preferably 50% by mass or less, and more preferably 20% by mass or less. When it exceeds 50% by mass, the dispersibility of carbon black tends to deteriorate and the tensile strength tends to decrease.

S-modified BR forms a strong bond with silica, promotes dispersion of silica at the time of kneading, and can improve elongation at break.
In the compound represented by the above formula (1), R ¹ , R ² and R ³ are the same or different and are an alkyl group, an alkoxy group, a silyloxy group, an acetal group, a carboxyl group (—COOH), a mercapto group (— SH) or derivatives thereof. As said alkyl group, C1-C4 alkyl groups, such as a methyl group, an ethyl group, n-propyl group, isopropyl group, n-butyl group, t-butyl group, etc. are mentioned, for example. Examples of the alkoxy group include alkoxy groups having 1 to 8 carbon atoms such as methoxy group, ethoxy group, n-propoxy group, isopropoxy group, n-butoxy group and t-butoxy group (preferably having 1 to 6 carbon atoms). More preferably, C1-C4) etc. are mentioned. The alkoxy group includes a cycloalkoxy group (cycloalkoxy group having 5 to 8 carbon atoms such as cyclohexyloxy group) and an aryloxy group (aryloxy group having 6 to 8 carbon atoms such as phenoxy group and benzyloxy group). ) Is also included.

Examples of the silyloxy group include a silyloxy group substituted with an aliphatic group having 1 to 20 carbon atoms and an aromatic group (trimethylsilyloxy group, triethylsilyloxy group, triisopropylsilyloxy group, diethylisopropylsilyloxy group, t- Butyldimethylsilyloxy group, t-butyldiphenylsilyloxy group, tribenzylsilyloxy group, triphenylsilyloxy group, tri-p-xylylsilyloxy group, etc.).

Examples of the acetal group include groups represented by -C (RR ')-OR "and -O-C (RR')-OR". Examples of the former include a methoxymethyl group, an ethoxymethyl group, a propoxymethyl group, a butoxymethyl group, an isopropoxymethyl group, a t-butoxymethyl group, and a neopentyloxymethyl group. The latter includes a methoxymethoxy group, an ethoxy group, and the like. Methoxy group, propoxymethoxy group, i-propoxymethoxy group, n-butoxymethoxy group, t-butoxymethoxy group, n-pentyloxymethoxy group, n-hexyloxymethoxy group, cyclopentyloxymethoxy group, cyclohexyloxymethoxy group, etc. Can be mentioned. R ¹ , R ² and R ³ are preferably alkoxy groups. Thereby, fuel efficiency can be improved, maintaining the rigidity of rubber, breaking strength, and adhesiveness with a cord.

Examples of the alkyl group for R ⁴ and R ⁵ include the same groups as the above alkyl group.

As n (integer), 1-5 are preferable. Thereby, the balance of rigidity, breaking strength, adhesiveness with a cord, and low fuel consumption can be made favorable. Furthermore, n is more preferably 2 to 4, and most preferably 3. When n is 0, it is difficult to bond a silicon atom and a nitrogen atom, and when n is 6 or more, the effect as a modifier is reduced.

Specific examples of the compound represented by the above formula (1) include 3-aminopropyldimethylmethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylethyldimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, Aminopropyldimethylethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyldimethylbutoxysilane, 3-aminopropylmethyldibutoxysilane, dimethylaminomethyltrimethoxysilane, 2-dimethyl Aminoethyltrimethoxysilane, 3-dimethylaminopropyltrimethoxysilane, 4-dimethylaminobutyltrimethoxysilane, dimethylaminomethyldimethoxymethylsilane, 2-dimethylaminoethyldimethoxy Methylsilane, 3-dimethylaminopropyldimethoxymethylsilane, 4-dimethylaminobutyldimethoxymethylsilane, dimethylaminomethyltriethoxysilane, 2-dimethylaminoethyltriethoxysilane, 3-dimethylaminopropyltriethoxysilane, 4-dimethylaminobutyl Triethoxysilane, dimethylaminomethyldiethoxymethylsilane, 2-dimethylaminoethyldiethoxymethylsilane, 3-dimethylaminopropyldiethoxymethylsilane, 4-dimethylaminobutyldiethoxymethylsilane, diethylaminomethyltrimethoxysilane, 2- Diethylaminoethyltrimethoxysilane, 3-diethylaminopropyltrimethoxysilane, 4-diethylaminobutyltrimethoxysilane, diethylamino Tildimethoxymethylsilane, 2-diethylaminoethyldimethoxymethylsilane, 3-diethylaminopropyldimethoxymethylsilane, 4-diethylaminobutyldimethoxymethylsilane, diethylaminomethyltriethoxysilane, 2-diethylaminoethyltriethoxysilane, 3-diethylaminopropyltriethoxysilane 4-diethylaminobutyltriethoxysilane, diethylaminomethyldiethoxymethylsilane, 2-diethylaminoethyldiethoxymethylsilane, 3-diethylaminopropyldiethoxymethylsilane, 4-diethylaminobutyldiethoxymethylsilane, and the like. These may be used alone or in combination of two or more.

Examples of the method for modifying the polybutadiene rubber with the compound (modifier) represented by the above formula (1) include conventionally known methods such as the methods described in JP-B-6-53768 and JP-B-6-57767. Techniques can be used. For example, the polybutadiene rubber may be brought into contact with the modifying agent, the polybutadiene rubber is polymerized, and a predetermined amount of the modifying agent is added to the polymer rubber solution, and the modifying agent is added to the polybutadiene rubber solution and reacted. Methods and the like.

The polybutadiene rubber (BR) to be modified is not particularly limited. For example, BR1220 manufactured by Nippon Zeon Co., Ltd., BR130B manufactured by Ube Industries, Ltd., BR150B, etc. BR containing a syndiotactic polybutadiene crystal such as VCR 412 and VCR 617 manufactured by Kosan Co., Ltd. can be used. BR containing syndiotactic polybutadiene crystals can provide high Hs (≈E ^* ), but tan δ is high, so it is preferable not to use it.

The vinyl bond amount of S-modified BR is preferably 35% by mass or less, more preferably 25% by mass or less, and still more preferably 20% by mass or less. When the amount of vinyl bonds exceeds 35% by mass, low heat build-up tends to be impaired. The lower limit of the vinyl bond amount is not particularly limited.
In the present specification, the vinyl bond amount (1,2-bond butadiene unit amount) can be measured by infrared absorption spectrum analysis.

The content of tin-modified BR and / or S-modified BR in 100 parts by mass of the rubber component is 5 parts by mass or more, preferably 10 parts by mass or more. If the amount is less than 5 parts by mass, the effect of low heat generation cannot be expected. Moreover, the said content is 50 mass parts or less in 100 mass parts of rubber | gum, Preferably it is 45 mass parts or less. If it exceeds 50 parts by mass, the breaking strength of the rubber tends to be insufficient.

In the present invention, high rigidity and breaking strength can be obtained by using NR and / or IR.
The rubber composition of the present invention is not particularly limited as NR and IR used as the rubber component, and those generally used in the rubber industry can be used. NR also includes epoxidized natural rubber (ENR) and deproteinized natural rubber (DPNR).

The content of NR and / or IR in 100 parts by mass of the rubber component is 50 parts by mass or more, preferably 55 parts by mass or more. If it is less than 50 parts by mass, the breaking strength decreases. Moreover, the said content is 95 mass parts or less, Preferably it is 90 mass parts or less. If it exceeds 95 parts by mass, the effect of improving tan δ cannot be obtained.

Examples of other rubber components used in the rubber composition include diene rubbers such as butadiene rubber (BR), styrene-butadiene rubber (SBR), ethylene-propylene-diene rubber (EPDM), butyl rubber (IIR), Halogenated butyl rubber (X-IIR), chloroprene rubber (CR), acrylonitrile (NBR), a halide of a copolymer of isomonoolefin and paraalkylstyrene, and the like can be used.

In the present invention, by increasing the amount of sulfur to 2.5 parts by mass or less and the filler component to 60 parts by mass or less, E ^* is increased and tan δ is decreased. Further, the modified BR has a lower adhesiveness to the cord than the NR, but the adhesiveness to the cord can be supplemented by HTS.

HTS generates {-Sx- (S- (CH ₂ ) ₆ -S) -Sy-} bonds in the process of generating and dissociating sulfur poly-S bonds, and is thermally stabilized. The reason for stabilization is that the dissociation energy between sulfur of {-Sx-Sy-} is smaller than the dissociation energy between Sx-S, S-CH ₂ and S-Sy. This thermal stabilization is accompanied by an improvement in tensile strength after heat aging. In addition, HTS has an effect of promoting the adhesion reaction by supplying an appropriate amount of H ₂ O by supplying the water-containing component when the steel cord and sulfur are bonded by an adhesion reaction.

Content of HTS is 0.1 mass part or more with respect to 100 mass parts of rubber components, Preferably it is 0.2 mass part or more, More preferably, it is 0.3 mass part or more. If the amount is less than 0.1 parts by mass, sufficient adhesion and tensile properties of the steel cord cannot be obtained. Moreover, the said content is 3 mass parts or less, Preferably it is 2.5 mass parts or less, More preferably, it is 2 mass parts or less. If the amount exceeds 3 parts by mass, the rubber hardness increases, so that the elongation decreases, and further the decrease in tensile properties due to thermal oxidative degradation increases.

As the sulfur, those generally used during vulcanization in the rubber industry can be used, but insoluble sulfur can be used because it is difficult to deposit on the rubber surface, particularly during rubber sheet extrusion or rubber sheet storage. It is preferable to use it. Here, insoluble sulfur refers to polymeric sulfur that can prevent blooming that occurs when sulfur is used in a rubber vulcanizing agent.

The sulfur content (insoluble sulfur content in the case of insoluble sulfur) is 2.5 parts by mass or more, preferably 3 parts by mass or more with respect to 100 parts by mass of the rubber component. Moreover, the said content is 7 mass parts or less, Preferably it is 6.5 mass parts or less. If it is less than 2.5 parts by mass, sulfur is not sufficiently supplied to the plated layer of the steel cord, and the peel resistance is inferior. When the amount exceeds 7 parts by mass, free sulfur that is not bonded to rubber or steel increases in the rubber composition after vulcanization, the tensile properties of the rubber composition deteriorate, and deterioration due to thermal oxidation tends to occur. The content is preferably 2.5 to 4 parts by mass for increasing the breaking strength, and 4 to 7 parts by mass for increasing the adhesiveness and tan δ.

The rubber composition of the present invention preferably contains silica. By blending silica with tin-modified BR or modified BR, low fuel consumption can be improved while maintaining the durability of rubber. Further, the modified BR has lower adhesion to the cord than NR, but the use of silica together with the aforementioned HTS can supplement the adhesion to the cord. Examples of the silica include, but are not limited to, dry method silica (anhydrous silicic acid), wet method silica (anhydrous silicic acid), and the like, and wet method silica is preferable because it has many silanol groups.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 40 m ² / g or more, and more preferably 45 m ² / g or more. If it is less than 40 m ² / g, the breaking strength tends to decrease. Further, the nitrogen adsorption specific surface area of silica is preferably 250 meters ² / g or less, more preferably 200m ² / g. When it exceeds 250 m ² / g, the exothermic property tends to deteriorate.

The content of silica is preferably 5 parts by mass or more, more preferably 10 parts by mass or more with respect to 100 parts by mass of the rubber component. If the amount is less than 5 parts by mass, there is a tendency that the effect of improving the adhesiveness to the cord and the improvement of the breaking strength due to the blending of silica cannot be obtained. The silica content is preferably 60 parts by mass or less, more preferably 55 parts by mass or less, with respect to 100 parts by mass of the rubber component. If it exceeds 60 parts by mass, the heat buildup and dispersibility tend to be poor.

The rubber composition of the present invention preferably contains a silane coupling agent. As the silane coupling agent, any silane coupling agent conventionally used in combination with silica can be used in the rubber industry. For example, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-tri Ethoxysilylethyl) tetrasulfide, bis (4-triethoxysilylbutyl) tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilylethyl) tetrasulfide, bis (4-trimethoxysilyl) Butyl) tetrasulfide, bis (3-triethoxysilylpropyl) trisulfide, bis (2-triethoxysilylethyl) trisulfide, bis (4-triethoxysilylbutyl) trisulfide, bis (3-trimethoxysilylpropyl) Trisulfi Bis (2-trimethoxysilylethyl) trisulfide, bis (4-trimethoxysilylbutyl) trisulfide, bis (3-triethoxysilylpropyl) disulfide, bis (2-triethoxysilylethyl) disulfide, bis (4 -Triethoxysilylbutyl) disulfide, bis (3-trimethoxysilylpropyl) disulfide, bis (2-trimethoxysilylethyl) disulfide, bis (4-trimethoxysilylbutyl) disulfide, 3-trimethoxysilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide, 3-triethoxysilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N, N-dimethylthiocarbamoyl tetrasulfide, 2-trime Xylylethyl-N, N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropylbenzothiazolyl tetrasulfide, 3-triethoxysilylpropylbenzothiazole tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide, 3- Sulfide type such as trimethoxysilylpropyl methacrylate monosulfide, mercapto type such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, vinyltri Vinyl series such as ethoxysilane and vinyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropyltrimethoxysila , Glycidoxy type such as γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, nitro type such as 3-nitropropyltrimethoxysilane, 3-nitropropyltriethoxysilane, 3-chloropropyl Examples include chloro-based compounds such as trimethoxysilane, 3-chloropropyltriethoxysilane, 2-chloroethyltrimethoxysilane, and 2-chloroethyltriethoxysilane. Product names include Si69, Si75, Si363 (Degussa), NXT, NXT-LV, NXT-ULV, NXT-Z (GE). Of these, bis (3-triethoxysilylpropyl) disulfide is preferable.

The content of the silane coupling agent is preferably 5 parts by mass or more and more preferably 8 parts by mass or more with respect to 100 parts by mass of the silica. If it is less than 5 mass parts, there exists a tendency for a fracture strength to fall large. Moreover, 15 mass parts or less are preferable with respect to 100 mass parts of silica content, and, as for this content, 10 mass parts or less are more preferable. When the amount exceeds 15 parts by mass, effects such as an increase in fracture strength and a reduction in rolling resistance due to the addition of the silane coupling agent tend not to be obtained.

The rubber composition of the present invention preferably contains carbon black. Thereby, Hs (≈E ^* ) of the rubber can be improved. As carbon black, GPF, HAF, ISAF, SAF, etc. can be used, for example.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 40 m ² / g or more, and more preferably 45 m ² / g or more. If it is less than 40 m < ² > / g, there exists a tendency for reinforcement property and abrasion resistance to deteriorate remarkably. Further, the nitrogen adsorption specific surface area of the carbon black (E) is preferably from 300 meters ² / g or less, more preferably 280m ² / g. When it exceeds 300 m ² / g, the dispersibility is poor, and on the contrary, the reinforcing property and the wear resistance tend to be lowered.

When the rubber composition contains silica and carbon black, the total content thereof is preferably 40 parts by mass or more, more preferably 45 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 40 parts by mass, the rubber hardness tends to be low and the breaking strength tends to be insufficient. The total content is preferably 60 parts by mass or less, more preferably 55 parts by mass or less, with respect to 100 parts by mass of the rubber component. When it exceeds 60 parts by mass, the heat build-up becomes high and the durability tends to decrease.

The rubber composition of the present invention may contain benzothiazolylsulfenamide or benzothiazolylsulfenimide represented by the following formula (2). Since this component functions as a vulcanization accelerator, the initial vulcanization speed becomes moderate, and during vulcanization, copper on the plating surface of the tire cord, sulfur and cobalt in the rubber move under moderate fluidity. , Can be combined. In addition, since the reversion is small, the formed copper-sulfur-rubber bond is not broken, and the decrease in elongation at break can be suppressed and the durability of the rubber can be improved.

R ⁶ in the above formula (2) is a linear alkyl group having a branched structure having 3 to 16 carbon atoms, and R ⁷ is a linear alkyl group having a branched structure having 3 to 16 carbon atoms or a benzothiazolyl group. A sulfide group. The linear alkyl group is composed of 3 to 16 carbon atoms, preferably 4 to 16 and more preferably 6 to 12. If it is 2 or less, the initial vulcanization speed is high and the adhesiveness is poor, and if it is 17 or more, the initial vulcanization speed is too slow and the rubber hardness is low. Preferred alkyl groups for R ⁶ and R ⁷ include t-butyl group, 2-ethylhexyl group, 2-methylhexyl group, 3-ethylhexyl group, 3-methylhexyl group, 2-ethylpropyl group, 2-ethylbutyl group, A 2-ethylpentyl group, a 2-ethylheptyl group, a 2-ethyloctyl group, and the like can be given. In addition, R ⁶ and R ⁷ are preferably the same because the number of production raw materials is reduced, the production yield is increased, the purity is increased, and the cost can be reduced.

As R ⁷ in the above formula (2), the following formula:

で表されるベンゾチアゾリルスルフィド基も挙げられる。Ｒ^７がベンゾチアゾリルスルフィド基の場合、上記式（２）で表される化合物は、ベンゾチアゾリルスルフェンイミドとなる。Ｒ^６がｔ−ブチル基の場合、Ｒ^７はベンゾチアゾリルスルフィド基であることが好ましい。

The benzothiazolyl sulfide group represented by these is also mentioned. When R ⁷ is a benzothiazolyl sulfide group, the compound represented by the above formula (2) is benzothiazolylsulfenimide. When R ⁶ is a t-butyl group, R ⁷ is preferably a benzothiazolyl sulfide group.

As the benzothiazolylsulfenamide or benzothiazolylsulfenimide represented by the above formula (2), BEHZ (N, N-di (2-ethylhexyl) -2-benzothia manufactured by Kawaguchi Chemical Industry Co., Ltd. Zolylsulfenamide), BMHZ (N, N-di (2-methylhexyl) -2-benzothiazolylsulfenamide) manufactured by Kawaguchi Chemical Co., Ltd., Santocure TBSI (N-) manufactured by Flexis Co., Ltd. tert-butyl-2-benzothiazolylsulfenimide) and the like.

The blending amount of benzothiazolylsulfenamide or benzothiazolylsulfenimide represented by the above formula (2) is 0.7 parts by mass or more, preferably 0.8 parts by mass with respect to 100 parts by mass of the rubber component. That's it. If it is less than 0.7 parts by mass, the hardness of the rubber is low and the breaking strength is low. Moreover, the said compounding quantity is 3 mass parts or less, Preferably it is 2.7 mass parts or less. When the amount exceeds 3 parts by mass, the adhesiveness with the cord decreases.

The rubber composition of the present invention may contain organic acid cobalt. Since the organic acid cobalt plays a role of cross-linking the cord and the rubber, the adhesion between the cord and the rubber can be improved by blending this component. Examples of the organic acid cobalt include cobalt stearate, cobalt naphthenate, cobalt neodecanoate, and boron 3 neodecanoate cobalt. Of these, cobalt stearate is preferable in that it functions as a processing aid (decreases the viscosity).

Content of organic acid cobalt is 0.05 mass part or more in conversion to cobalt with respect to 100 mass parts of rubber components, Preferably it is 0.1 mass part or more. If it is less than 0.05 parts by mass, the adhesion between the steel cord plating layer and the rubber is not sufficient. Moreover, this content is 0.30 mass part or less, Preferably it is 0.25 mass part or less. If it exceeds 0.30 parts by mass, the oxidative deterioration of the rubber becomes remarkable, and the breaking characteristics deteriorate.

The rubber composition of the present invention may contain a modified resorcin resin (modified resorcin condensate). Thereby, adhesiveness can be improved, without exacerbating exothermic property and elongation at break. The modified resorcin resin refers to a compound represented by the following formula (3). M in the formula is an integer. In the formula, R ⁸ is preferably an alkyl group or a hydroxyl group, and the bonding position of R ⁸ is preferably meta or para.

Examples of the modified resorcin resin include resorcin / alkylphenol / formalin copolymer, resorcin / formalin reaction product penacolite resin, RSM (a mixture of about 60% by mass resorcin and about 40% by mass stearic acid). Resorcin / alkylphenol / formalin copolymers and RSM are preferred.

The content of the modified resorcin resin is preferably 0.5 parts by mass or more and more preferably 1 part by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 0.5 part by mass, the complex elastic modulus tends not to be sufficiently improved. The content is preferably 10 parts by mass or less, and more preferably 8 parts by mass or less. If it exceeds 10 parts by mass, the breaking strength tends to decrease.

In the rubber composition of the present invention, it is preferable not to use a cresol resin because the properties of tan δ are deteriorated, and it is preferable not to use a resorcin resin because the breaking strength is lowered.

The rubber composition of the present invention can further contain a methylene donor.
Examples of the methylene donor include hexamethylenetetramine (HMT), hexamethoxymethylol melamine (HMMM), hexamethylol melamine pentamethyl ether (HMMPME), and Sumikanol 507A.

The content of the methylene donor is preferably 1 part by mass or more and more preferably 1.5 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 1 part by mass, a sufficient complex elastic modulus tends to be not obtained. The content is preferably 5 parts by mass or less, and more preferably 4 parts by mass or less. If it exceeds 5 masses, the viscosity of the rubber tends to increase and the processability tends to deteriorate.

The rubber composition for tires of the present invention includes rubber components such as tin-modified BR and S-modified BR, HTS, silica, carbon black, silane coupling agent, sulfur, benzothiazolylsulfenamide, or benzothiazolylsulfene. In addition to imide, organic acid cobalt, modified resorcin resin, methylene donor, compounding agents commonly used in the production of rubber compositions, for example, fillers such as calcium carbonate, zinc oxide, stearic acid, various anti-aging agents, Oils such as aroma oils, waxes, other vulcanizing agents and vulcanization accelerators can be appropriately blended.

The rubber composition for tires of the present invention is suitably used for breaker topping, but can also be applied to breaker edge strips and breaker lower rubber (between breaker and ply). The breaker edge strip is used for a breaker edge portion, and is disclosed in, for example, Japanese Patent Application Laid-Open No. 2004-217817. The breaker lower rubber (between the breaker and the ply) is inserted between the breaker and the ply and used for the purpose of preventing the breaker or the ply from being broken by the impact of the projection.
It can also be applied to breakers and inter-strip strips. The breaker and the case-to-case strip are used for the purpose of preventing breaker edge separation and case-to-case separation by reducing distortion.

In the pneumatic tire of the present invention, the tire cord is coated with the above rubber composition for a tire and formed into the shape of a member such as a breaker, and then bonded to another tire member to form an unvulcanized tire and vulcanized By doing so, a pneumatic tire (radial tire etc.) can be obtained.

Examples of tire cords that can be applied in the present invention include carcass cords, fillers, bands, breakers (belts), and the like. Of these, breaker cords are preferable. Examples of the tire cord include a steel cord for tire, 2 + 2 / 0.23 (a tire cord obtained by adding and twisting two cords having a wire diameter of 0.23 mm), a high tension cord with brass plating, and the like. .

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

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
Tin-modified BR: Nipol BR1250H manufactured by Nippon Zeon Co., Ltd. (lithium initiator: lithium, tin atom content: 250 ppm, Mw / Mn: 1.5, vinyl bond content: 10-13 mass%)
S-modified BR: Modified butadiene rubber manufactured by Sumitomo Chemical Co., Ltd. (vinyl bond content 15% by mass, R ¹ , R ² and R ³ = -OCH ₃ , R ⁴ and R ⁵ = -CH ₂ CH ₃ , n = 3 )
High cis BR: BR150B 1,4 high cis BR made by Ube Industries
Modified styrene butadiene rubber (modified S-SBR): HPR340 manufactured by JSR Corporation (10% by mass of bound styrene, coupled with alkoxysilane, introduced at the end)
NR: TSR20
Carbon black N326: Carbon black N326 (N ₂ SA 78 m ² / g) manufactured by Showa Cabot Co., Ltd.
Silica Z115G: Z115Gr (N ₂ SA112m ² / g) manufactured by Rhodia
Silica VN3: Nippon Silica Industry Co., Ltd. Nipsil VN3 (N ₂ SA 175 m ² / g)
Insoluble sulfur: Kristex HSOT20 (80% by weight of sulfur and 20% by weight of oil)
HTS: Duralink HTS (Hexamethylenebisthiosulfate disodium dihydrate) manufactured by Flexis Co., Ltd.
Sumikanol 620: Modified resorcin resin (resorcin / alkylphenol / formalin copolymer) manufactured by Sumitomo Chemical Co., Ltd.
Sumikanol 507A: Methylene donor (mixture of about 65% by weight methylol melamine resin with about 35% by weight silica and oil)
Zinc oxide: Silver candy R made by Toho Zinc Co., Ltd.
Cobalt stearate: cost-F (cobalt content: 9.5% by mass) manufactured by Dainippon Ink & Chemicals, Inc.
Anti-aging agent: Nocrack 6C (N- (1,3-dimethylbutyl) -N-phenyl-p-phenylenediamine) manufactured by Ouchi Shinsei Chemical Co., Ltd.
Aroma oil: Process X-140 manufactured by Japan Energy Co., Ltd.
Vulcanization accelerator DCBS: Axel DZ-G (N, N-dicyclohexylbenzothiazolylsulfenamide) manufactured by Kawaguchi Chemical Industry Co., Ltd.
Vulcanization accelerator BEHZ: BEHZ (N, N-di (2-ethylhexyl) -2-benzothiazolylsulfenamide) manufactured by Kawaguchi Chemical Industry Co., Ltd.

Examples 1-11 and Comparative Examples 1-11
In accordance with the formulation shown in Tables 1 and 2, chemicals other than insoluble sulfur and a vulcanization accelerator were kneaded for 5 minutes under a maximum temperature of 165 ° C. using a Banbury mixer to obtain a kneaded product. Next, using an open roll, insoluble sulfur and a vulcanization accelerator were added to the obtained kneaded product, and kneaded for 3 minutes under the condition of a maximum temperature of 97 ° C. to obtain an unvulcanized rubber composition. Further, the obtained unvulcanized rubber composition was rolled into a sheet and then press vulcanized with a mold at 170 ° C. for 12 minutes to obtain a vulcanized rubber sheet.

The obtained vulcanized rubber sheet was evaluated as follows. The results are shown in Tables 1-2.
(Viscoelasticity test)
A test piece of a predetermined size was prepared from a vulcanized rubber sheet, and a rubber at 30 ° C. was used under conditions of a frequency of 10 Hz, an initial strain of 10% and a dynamic strain of 2% using a viscoelastic spectrometer VES manufactured by Iwamoto Seisakusho Co., Ltd. The complex elastic modulus (E *) and loss tangent (tan δ) of the test piece were measured. In addition, it shows that it is excellent in rigidity, so that E * is large, and it is excellent in low fuel consumption, so that tan-delta is small.

(Adhesion test)
An adhesion test was carried out, and the rubber coverage (%) of the vulcanized rubber sheet was measured after the vulcanized rubber sheet had been subjected to wet heat degradation for 150 hours under conditions of a temperature of 80 ° C. and a humidity of 95%. For the rubber coverage, the ratio of the rubber covered on the peeled surface when the steel cord and the rubber were peeled was indicated by an index. 5 indicates that 100% of the entire surface is covered, and 0 indicates that the surface is not covered at all.

(Tensile test)
In accordance with JIS K 6251 “Vulcanized Rubber and Thermoplastic Rubber—How to Obtain Tensile Properties”, a tensile test was performed using a No. 3 dumbbell, and the elongation at break (EB) of the vulcanized rubber specimen was measured. In addition, it shows that it is excellent in fracture strength, so that EB is large.

In the examples, rigidity, low fuel consumption, adhesion after wet heat deterioration, and breaking strength were excellent in a well-balanced manner. From Table 1, the low fuel consumption was inferior in the comparative example 1 using high cis BR. In Comparative Examples 2 to 3 having a large amount of tin-modified BR and S-modified BR, the adhesiveness after wet heat deterioration and elongation at break were inferior. In Comparative Example 4 in which HTS was not added and Comparative Example 5 having a small amount of sulfur, the adhesiveness after wet heat deterioration was poor, and in Comparative Example 5, the rigidity was also poor.

From Table 2, in Comparative Example 6 with a large amount of sulfur, the elongation at break was inferior. In Comparative Example 7 having a small amount of HTS, the adhesiveness after wet heat deterioration was poor. In Comparative Examples 8 to 9 using modified S-SBR, the elongation at break was inferior. In Comparative Example 10 with a small amount of tin-modified BR, the fuel efficiency was inferior compared with the case where a suitable amount was used. In Comparative Example 11 in which only NR was used as the rubber component, the fuel efficiency was poor.

Claims (7)

Tin-modified polybutadiene rubber and / or the following formula (1);

(In the formula, R ¹ represents an alkoxy group, and R ² and R ³ are the same or different and each represents an alkyl group, an alkoxy group, a silyloxy group, an acetal group, a carboxyl group, a mercapto group, or a derivative thereof. R ⁴ And R ⁵ are the same or different and each represents a hydrogen atom or an alkyl group, and n represents an integer.)
100 parts by mass of a rubber component containing 5 to 50 parts by mass of a polybutadiene rubber modified with a compound represented by the following formula and 50 to 95 parts by mass of natural rubber and / or isoprene rubber:
A rubber composition for tires containing 0.1 to 3 parts by mass of hexamethylenebisthiosulfate disodium salt dihydrate and 2.5 to 7 parts by mass of sulfur ,
A rubber composition for tires used for a breaker topping, a breaker edge strip, or a breaker lower rubber between a breaker and a ply . Against rubber component 100 parts by weight, shea content 5-60 parts by weight of silica, shea silica and claim 1 tire rubber composition according the total amount of carbon black is 40 to 60 parts by weight. The tin-modified polybutadiene rubber is polymerized with a lithium initiator, the content of tin atoms is 50 to 3000 ppm, the amount of vinyl bonds is 5 to 50% by mass, and the molecular weight distribution (Mw / Mn) is 2 or less,
The rubber composition for tires according to claim 1 or 2, wherein the vinyl bond content of the polybutadiene rubber modified with the compound represented by the formula (1) is 35% by mass or less. Nitrogen adsorption specific surface area 40-280m ² The rubber composition for tires according to claim 1 or 3, comprising / g of carbon black. The rubber composition for tires according to any one of claims 1 to 4 containing organic acid cobalt. Following formula (2);

(R in Formula (2) ⁶ Is a linear alkyl group having a branched structure of 3 to 16 carbon atoms, R ⁷ Is a linear alkyl group or a benzothiazolyl sulfide group having a branched structure having 3 to 16 carbon atoms. )
Benzothiazolylsulfenamide or benzothiazolylsulfenimide represented by:
Following formula (3);

(In the formula, m is an integer. R ⁸ Is an alkyl group or a hydroxyl group. )
Modified resorcin resin represented by:
The tire rubber composition according to any one of claims 1 to 5, comprising at least one selected from the group consisting of methylene donors. A pneumatic tire having a breaker obtained by coating a breaker cord with the rubber composition according to any one of claims 1 to 6 .