JP2011231295A - Tire rubber composition and heavy-load tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tire rubber composition which achieves improvement in good fuel economy, abrasion resistance and degradation resistance with good balance, and to provide a heavy-load tire having a tread produced using the tire rubber composition.SOLUTION: The tire rubber composition contains a rubber component, silica and a compound represented by formula (2). The rubber component contains a modified natural rubber having a phosphorus content of ≤200 ppm and a modified butadiene rubber modified with a compound represented by formula (1), wherein the content of the modified natural rubber is 40-95 mass% and the content of the modified butadiene rubber is 5-60 mass%, based on 100 mass% of the rubber component. The content of the compound represented by formula (2) is 0.1-10 pts.mass and the content of the silica is 10-60 pts.mass based on 100 pts.mass of the rubber component.

Description

The present invention relates to a rubber composition for tires and a heavy duty tire using the same.

In recent years, due to soaring fuel costs and the introduction of environmental regulations, the demand for lower fuel consumption of vehicles has become stronger, and among the tire components, the rubber composition for producing treads with a high occupation ratio in tires. Therefore, excellent fuel efficiency is required.

In order to improve fuel efficiency, natural rubber or butadiene rubber is generally used as a rubber component. As a method for further improving the low fuel consumption performance, a method of using silica as a filler, a method of reducing the amount of filler, and the like are known. However, when these methods are used, the rubber strength tends to decrease and the wear resistance performance tends to deteriorate, and it has been difficult to achieve both low fuel consumption performance and wear resistance performance at a high level. Further, the rubber composition is required to have low fuel consumption performance and wear resistance performance as well as deterioration resistance performance, and a method for improving these performances in a well-balanced manner has been desired.

Patent Document 1 discloses a rubber composition using natural rubber and epoxidized natural rubber in order to increase the content ratio of non-petroleum resources. However, there is still room for improvement in terms of improving the fuel efficiency, wear resistance, and deterioration resistance in a well-balanced manner.

JP 2007-169431 A

The present invention solves the above-mentioned problems and provides a rubber composition for a tire that can improve fuel efficiency performance, wear resistance performance and degradation resistance performance in a well-balanced manner, and a heavy duty tire having a tread produced using the rubber composition. Objective.

（式（１）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、アルキル基又は環状エーテル基を表す。ｎは整数を表す。）

（式（２）において、Ａは炭素数２〜１０のアルキレン基、Ｒ^６及びＲ^７は、同一若しくは異なって、チッ素原子を含む１価の有機基を表す。） The present invention includes a rubber component, silica and a compound represented by the following formula (2), wherein the rubber component is a modified natural rubber having a phosphorus content of 200 ppm or less and a compound represented by the following formula (1) Modified butadiene rubber modified by the above, in 100% by mass of the rubber component, the content of modified natural rubber is 40 to 95% by mass, the content of modified butadiene rubber is 5 to 60% by mass, The rubber composition for tires in which the content of the compound represented by the following formula (2) is 0.1 to 10 parts by mass and the silica content is 10 to 60 parts by mass with respect to 100 parts by mass of the rubber component. Related to things.

(In the formula (1), 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 is the same or different and represents a hydrogen atom, an alkyl group or a cyclic ether group, and n represents an integer.)

(In Formula (2), A represents an alkylene group having 2 to 10 carbon atoms, and R ⁶ and R ⁷ are the same or different and each represents a monovalent organic group containing a nitrogen atom.)

The gel content measured as the toluene insoluble content of the modified natural rubber is preferably 20% by mass or less.

The modified natural rubber is preferably substantially free of phospholipids and has no peak due to phospholipid at -3 ppm to 1 ppm in ³¹ P NMR measurement of the chloroform extract.

The nitrogen content of the modified natural rubber is preferably 0.3% by mass or less.

The modified natural rubber is preferably obtained by saponifying natural rubber latex.

The rubber composition is preferably used for a tread of a heavy duty tire.

The present invention also relates to a heavy duty tire having a tread produced using the rubber composition.

According to the present invention, since it is a rubber composition for tires containing a modified natural rubber, a specific modified butadiene rubber, silica and a specific compound, by using the rubber composition in a tread of a heavy duty tire, It is possible to provide a heavy-duty tire with improved fuel efficiency, wear resistance, and deterioration resistance in a well-balanced manner.

The tire rubber composition of the present invention includes a modified natural rubber (HPNR) having a phosphorus content of 200 ppm or less, a modified butadiene rubber (modified BR) modified with a compound represented by the above formula (1), silica, and A compound represented by the above formula (2) is included. By using the modified natural rubber (HPNR) in which the protein, gel, and phospholipid contained in the natural rubber (NR) are reduced and removed, fuel consumption can be further reduced as compared with the use of NR.

However, when HPNR is synthesized by saponification of NR, etc., the degradation preventing component in NR is also removed during the synthesis, resulting in faster rubber degradation, resulting in performance such as wear resistance and degradation resistance. It is inferior to. In addition, when HPNR and silica are used in combination, the wear resistance performance tends to be reduced, although greater fuel efficiency can be realized. The use of butadiene rubber can suppress a decrease in wear resistance performance to some extent, but the effect is not sufficient in a silica compounded system.

On the other hand, in the present invention, the modified BR is used together with HPNR as the rubber component, so that the fuel efficiency can be further improved, the dispersibility of the silica can be obtained, and the wear resistance can be improved. It is possible to achieve both well. Further, by using the compound represented by the above formula (2) in combination with the above components, the rubber composition can have a CC bond having a high binding energy and a high thermal stability. It is possible to improve wear resistance and deterioration resistance while maintaining the above. As a result, low fuel consumption performance, wear resistance performance and degradation resistance performance can be improved in a well-balanced manner.

The modified natural rubber (HPNR) has a phosphorus content of 200 ppm or less. When it exceeds 200 ppm, the amount of gel increases during storage, and the tan δ of the vulcanized rubber tends to increase. The phosphorus content is preferably 150 ppm or less, and more preferably 100 ppm or less. Here, the phosphorus content can be measured by a conventional method such as ICP emission analysis. Phosphorus is derived from phospholipids (phosphorus compounds).

The gel content in the modified natural rubber is preferably 20% by mass or less, more preferably 10% by mass or less, and still more preferably 7% by mass or less. If it exceeds 20% by mass, the processability tends to decrease, for example, the Mooney viscosity increases. The gel content means a value measured as an insoluble content with respect to toluene which is a nonpolar solvent, and may be simply referred to as “gel content” or “gel content” below. The measuring method of the content rate of a gel part is as follows. First, a natural rubber sample is soaked in dehydrated toluene, light-shielded in the dark and left for 1 week, and then the toluene solution is centrifuged at 1.3 × 10 ⁵ rpm for 30 minutes to obtain an insoluble gel content and a toluene soluble content. Isolate. Methanol is added to the insoluble gel and solidified, and then dried, and the gel content is determined from the ratio between the mass of the gel and the original mass of the sample.

The modified natural rubber is preferably substantially free of phospholipids. “Substantially no phospholipid is present” represents a state in which a natural rubber sample is extracted with chloroform and a peak due to phospholipid does not exist at −3 ppm to 1 ppm in ³¹ P NMR measurement of the extract. The peak of phosphorus present at -3 ppm to 1 ppm is a peak derived from the phosphate structure of phosphorus in the phospholipid.

In the modified natural rubber, the nitrogen content is preferably 0.3% by mass or less, and more preferably 0.15% by mass or less. When the nitrogen content exceeds 0.3% by mass, the Mooney viscosity tends to increase during storage. Nitrogen is derived from proteins. The nitrogen content can be measured by a conventional method such as Kjeldahl method.

Examples of the method for producing the modified natural rubber include a method of producing natural rubber latex by saponification with alkali, washing the saponified and agglomerated rubber, and then drying. The saponification treatment is performed by adding an alkali and, if necessary, a surfactant to natural rubber latex and allowing to stand at a predetermined temperature for a predetermined time. In addition, you may perform stirring etc. as needed. According to the above production method, the phosphorus compound separated by saponification is washed away, so that the phosphorus content of the natural rubber can be suppressed. Moreover, since the protein in natural rubber is decomposed by the saponification treatment, the nitrogen content of the natural rubber can be suppressed. In the present invention, alkali can be added to natural rubber latex for saponification, but by adding it to natural rubber latex, there is an effect that saponification can be efficiently performed.

Natural rubber latex is collected as sap of heavy trees and contains rubber, water, proteins, lipids, inorganic salts, etc., and the gel content in rubber is thought to be based on the complex presence of various impurities. . In the present invention, raw latex produced by tapping a heavy tree or purified latex concentrated by centrifugation can be used. Furthermore, high ammonia latex to which ammonia is added by a conventional method may be used to prevent the progress of decay due to bacteria present in the raw rubber latex and to avoid coagulation of the latex.

Examples of the alkali used for the saponification treatment include sodium hydroxide, potassium hydroxide, calcium hydroxide, and an amine compound. From the viewpoint of the effect of the saponification treatment and the influence on the stability of the natural rubber latex, it is particularly hydroxylated. Sodium or potassium hydroxide is preferably used.

The amount of alkali added is not particularly limited, but the lower limit is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and the upper limit is 12 parts by mass or less with respect to 100 parts by mass of the solid content of natural rubber latex. Is preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and particularly preferably 5 parts by mass or less. If the amount of alkali added is less than 0.1 parts by mass, saponification may take time. Conversely, if the amount of alkali added exceeds 12 parts by mass, the natural rubber latex may be destabilized.

As the surfactant, an anionic surfactant, a nonionic surfactant, and an amphoteric surfactant can be used. Examples of the anionic surfactant include carboxylic acid-based, sulfonic acid-based, sulfate ester-based and phosphate ester-based anionic surfactants. Examples of nonionic surfactants include nonionic surfactants such as polyoxyalkylene ethers, polyoxyalkylene esters, polyhydric alcohol fatty acid esters, sugar fatty acid esters, and alkyl polyglycosides. Examples of the amphoteric surfactant include amphoteric surfactants such as amino acid type, betaine type, and amine oxide type. Among these, an anionic surfactant is preferable, and a sulfonic acid anionic surfactant is more preferable.

The addition amount of the surfactant is preferably 0.01 parts by mass or more, more preferably 0.1 parts by mass or more, and even more preferably 1.1 parts by mass or more with respect to 100 parts by mass of the solid content of the natural rubber latex. The upper limit is preferably 6.0 parts by mass or less, more preferably 5.0 parts by mass or less, and further preferably 3.5 parts by mass or less. If the addition amount of the surfactant is less than 0.01 parts by mass, the natural rubber latex may become unstable during the saponification treatment. On the other hand, if the amount of the surfactant added exceeds 6.0 parts by mass, the natural rubber latex may be overstabilized and coagulation may be difficult. Moreover, when it is 1.1 mass parts or more, the phosphorus content, the nitrogen content, and the gel content in the natural rubber can be further reduced.

The temperature of the saponification treatment can be appropriately set within a range where the saponification reaction with alkali can proceed at a sufficient reaction rate and within a range where the natural rubber latex does not undergo alteration such as coagulation, but is usually 20 to 70 ° C. Preferably, 30-70 degreeC is more preferable. Further, the treatment time is 3 to 48 hours in consideration of both sufficient treatment and productivity improvement, depending on the treatment temperature when the treatment is performed with natural rubber latex standing. Is preferable, and 3 to 24 hours is more preferable.

After completion of the saponification reaction, the agglomerated rubber is crushed and washed. Examples of the aggregation method include a method of adjusting pH by adding an acid such as formic acid. Examples of the washing treatment include a method of diluting the rubber with water and washing it, and then performing a centrifugal separation treatment to take out the rubber. When centrifuging, it is first diluted with water so that the rubber content of the natural rubber latex is 5 to 40% by mass, preferably 10 to 30% by mass. Then, it may be centrifuged at 5000 to 10000 rpm for 1 to 60 minutes, and washing may be repeated until a desired phosphorus content is obtained. After completion of the washing treatment, a saponified natural rubber latex is obtained. The modified natural rubber according to the present invention is obtained by drying the saponified natural rubber latex.

In the above production method, the saponification, washing and drying steps are preferably completed within 15 days after collecting the natural rubber latex. More preferably, it is within 10 days, and more preferably within 5 days. This is because the gel content increases if the sample is left for more than 15 days without solidification after collection.

In the tire rubber composition of the present invention, the content of the modified natural rubber in 100% by mass of the rubber component is 40% by mass or more, preferably 50% by mass or more, more preferably 60% by mass or more, and still more preferably. Is 75% by mass or more. If the amount is less than 40% by mass, excellent fuel efficiency may not be obtained. The content is 95% by mass or less, preferably 85% by mass or less. If it exceeds 95% by mass, the wear resistance and deterioration resistance may be deteriorated.

The rubber composition for tires of the present invention contains butadiene rubber (modified BR) modified with a compound represented by the following formula (1). By including the modified BR, the modified group of the modified BR is bonded to a filler such as silica, so that energy loss due to rubber movement can be reduced and fuel efficiency can be improved. Moreover, the dispersibility of a silica can be improved and abrasion resistance can also be improved.
The modified butadiene rubber may have a modifying group at the terminal or may have a modifying group in the main chain, but has a terminal modifying group from the viewpoint of easy modification. Those are preferred.

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 an alkoxy group having 1 to 8 carbon atoms (preferably 1 to 6 carbon atoms) such as a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, an n-butoxy group, and a t-butoxy group. More preferably, C1-C4) etc. are mentioned. Examples of the alkoxy group include a cycloalkoxy group (such as a cycloalkoxy group having 5 to 8 carbon atoms such as a cyclohexyloxy group) and an aryloxy group (an aryloxy group having 6 to 8 carbon atoms such as a phenoxy group and a 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, and more preferably methoxy groups. Thereby, the improvement effect of the dispersibility of a filler can be heightened.

In the compound represented by the above formula (1), R ⁴ and R ⁵ are the same or different and each represents a hydrogen atom, an alkyl group or a cyclic ether group.

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

Examples of the cyclic ether group of R ⁴ and R ⁵ include one ether bond such as an oxirane group, an oxetane group, an oxolane group, an oxane group, an oxepane group, an oxocan group, an oxonan group, an oxecan group, an oxet group, and an oxole group. A cyclic ether group having two ether bonds such as a cyclic ether group, a dioxolane group, a dioxane group, a dioxepane group and a dioxecan group, and a cyclic ether group having three ether bonds such as a trioxane group. Among these, from the point that the effect of improving the dispersibility of the filler is great, a C2-C7 cyclic ether group having one ether bond is preferable, and a C3-C5 cyclic ether group having one ether bond is preferable. More preferred. The cyclic ether group preferably has no unsaturated bond in the ring skeleton.

As R ⁴ and R ⁵ , an alkyl group (preferably having 1 to 3 carbon atoms, more preferably 1 to 2 carbon atoms) is preferable, and an ethyl group is more preferable. Thereby, the improvement effect of the dispersibility of a filler can be heightened and abrasion resistance performance can be improved.

As n (integer), 2-5 are preferable. Thereby, the improvement effect of the dispersibility of a filler can be heightened. Furthermore, n is more preferably 2 to 4, and most preferably 3. If n is 1 or less, the denaturation reaction may be inhibited, and if n is 6 or more, the effect as a denaturing agent 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, the following formulas (3) to ( And the compound represented by 10). These may be used alone or in combination of two or more. Of these, 3-diethylaminopropyltrimethoxysilane, 3-dimethylaminopropyltrimethoxysilane, and a compound represented by the following formula (3) are preferable from the viewpoint that the effect of improving the dispersibility of the filler is great.

Methods for modifying butadiene rubber with the compound represented by the above formula (1) (modifier) are described in JP-B-6-53768, JP-B-6-57767, JP-T2003-514078, and the like. Conventionally known methods such as the above method can be used. For example, the butadiene rubber may be brought into contact with the modifying agent, the butadiene 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 butadiene rubber solution and reacted. The method etc. are mentioned.

The butadiene rubber (BR) to be modified is not particularly limited, and BR having a high cis content, BR containing a syndiotactic polybutadiene crystal, or the like can be used. In addition, BR obtained by polymerization using a catalyst containing a lanthanum series rare earth-containing compound described in JP-T-2003-514078 can also be used.

The vinyl content of the 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. If the vinyl content exceeds 35% by mass, the fuel efficiency tends to deteriorate. The lower limit of the vinyl content is not particularly limited.
In the present specification, the vinyl content (1,2-bonded butadiene unit amount) of the modified BR can be measured by infrared absorption spectrum analysis.

The content of the modified BR in 100% by mass of the rubber component is 5% by mass or more, preferably 10% by mass or more, and more preferably 15% by mass or more. If it is less than 5% by mass, the fuel efficiency and wear resistance may not be sufficiently improved. The content of the modified BR is 60% by mass or less, preferably 45% by mass or less, more preferably 35% by mass or less, and still more preferably 25% by mass or less. If it exceeds 60% by mass, the blending ratio of HPNR decreases, and the desired mechanical strength may not be obtained.

The total content of HPNR and modified BR in 100% by mass of the rubber component is preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and particularly preferably 100% by mass. If it is less than 70% by mass, it may be difficult to achieve both low fuel consumption and wear resistance.

In addition to the modified natural rubber and modified butadiene rubber, examples of the rubber component used in the present invention include diene rubbers generally used in rubber compositions for tires. Specific examples of the diene rubber include natural rubber (NR) other than the modified natural rubber, styrene butadiene rubber (SBR), butadiene rubber (BR), isoprene rubber (IR), ethylene propylene diene rubber (EPDM), chloroprene. Examples include, but are not limited to, rubber (CR), acrylonitrile butadiene rubber (NBR), butyl rubber (IIR), styrene isoprene butadiene rubber (SIBR), and epoxidized natural rubber. These may be used alone or in combination of two or more.

In the present invention, silica is used. By including silica together with the modified BR, fuel efficiency can be improved. Examples of silica include dry process silica (anhydrous silica), wet process silica (hydrous silica), and wet process silica is preferred because it has many silanol groups.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 80 m ² / g or more, more preferably 100 m ² / g or more, and further preferably 120 m ² / g or more. When it is less than 80 m ² / g, since the reinforcing effect of silica is small, the wear resistance performance tends to deteriorate. Further, N ₂ SA of silica is preferably 250 m ² / g or less, more preferably 220 m ² / g or less, and further preferably 200 m ² / g or less. When it exceeds 250 m ² / g, the dispersibility of silica tends to be lowered.
The _N 2 SA of silica is a value measured by the BET method in accordance with ASTM D3037-81.

The content of silica is 10 parts by mass or more, preferably 12 parts by mass or more with respect to 100 parts by mass of the rubber component. If the amount is less than 10 parts by mass, sufficient fuel efficiency may not be obtained. The content of silica is 60 parts by mass or less, preferably 45 parts by mass or less, more preferably 25 parts by mass or less, and still more preferably 18 parts by mass or less. If it exceeds 60 parts by mass, the workability tends to decrease.

In the present invention, it is preferable to use a silane coupling agent together with silica. Examples of the silane coupling agent include sulfide-based, mercapto-based, vinyl-based, amino-based, glycidoxy-based, nitro-based, and chloro-based silane coupling agents. Among these, from the viewpoint of good processability. It is preferable to use a sulfide-based silane coupling agent. As sulfide-based silane coupling agents, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide, bis (2- Triethoxysilylethyl) disulfide, and the like. Among them, bis (3-triethoxysilylpropyl) disulfide is preferably used from the viewpoint of good workability.

When the silane coupling agent is contained, the content of the silane coupling agent is preferably 2 parts by mass or more and more preferably 4 parts by mass or more with respect to 100 parts by mass of silica. If it is less than 2 parts by mass, the wear resistance performance tends to deteriorate. Moreover, 15 mass parts or less are preferable and, as for content of a silane coupling agent, 13 mass parts or less are more preferable. When it exceeds 15 parts by mass, the effect of improving the wear resistance performance due to the blending of the silane coupling agent is not seen, and the effect commensurate with the increase in cost tends to be not obtained.

The tire rubber composition of the present invention preferably contains carbon black. By blending carbon black, it is possible to enhance the reinforcement.

If the rubber composition for a tire of the present invention contains carbon black, the nitrogen adsorption specific surface area _(N 2 SA) of carbon black is preferably not less than ^{90m 2 / g, 100m 2 /} g or more, more preferably, 105m ² / g is more preferable. If it is less than 90 m < ² > / g, there exists a possibility that sufficient reinforcement may not be obtained. Further, the nitrogen adsorption specific surface area of the carbon black is preferably 200 meters ² / g or less, more preferably 150 meters ² / g, more preferably 120 m ² / g or less. If it exceeds 200 m ² / g, it tends to be difficult to disperse carbon black well.
In addition, the nitrogen adsorption specific surface area of carbon black is calculated | required by A method of JISK6217.

When the tire rubber composition of the present invention contains carbon black, the carbon black content is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and still more preferably, with respect to 100 parts by mass of the rubber component. 30 parts by mass or more. If it is less than 10 mass parts, there exists a possibility that reinforcing property cannot fully be improved. The carbon black content is preferably 70 parts by mass or less, more preferably 50 parts by mass or less, and still more preferably 40 parts by mass or less. If it exceeds 70 parts by mass, it tends to be difficult to disperse carbon black well.

In the rubber composition of the present invention, the total content of carbon black and silica is preferably 20 parts by mass or more, more preferably 35 parts by mass or more, and further preferably 45 parts by mass or more with respect to 100 parts by mass of the rubber component. is there. The total content is preferably 130 parts by mass or less, more preferably 100 parts by mass or less, still more preferably 80 parts by mass or less, and particularly preferably 60 parts by mass or less. By setting it within the above range, good wear resistance can be obtained. In addition, good fuel efficiency can be obtained without reducing the total content.

（上記式（２）において、Ａは炭素数２〜１０のアルキレン基、Ｒ^６及びＲ^７は、同一若しくは異なって、チッ素原子を含む１価の有機基を表す。）
アルキレン基としては、特に限定されず、直鎖状、分岐状、環状のものがあげられるが、なかでも、直鎖状のアルキレン基が好ましい。 In the present invention, a compound represented by the following formula (2) is used. By compounding the compound, the rubber composition can have a CC bond having high binding energy and high thermal stability, so that it has excellent wear resistance and deterioration resistance while maintaining good fuel efficiency. Can be improved.

(In the above formula (2), A represents an alkylene group having 2 to 10 carbon atoms, and R ⁶ and R ⁷ are the same or different and represent a monovalent organic group containing a nitrogen atom.)
The alkylene group is not particularly limited, and includes linear, branched, and cyclic groups. Among them, a linear alkylene group is preferable.

2-10 are preferable and, as for carbon number of an alkylene group, 4-8 are more preferable. When the number of carbon atoms of the alkylene group is 1, the thermal stability tends to be poor, and there is a tendency that the merit obtained from the S—S bond cannot be obtained. Therefore, it tends to be difficult to replace with -S _x- .

Examples of the alkylene group satisfying the above conditions include ethylene group, trimethylene group, tetramethylene group, pentamethylene group, hexamethylene group, heptamethylene group, octamethylene group, decamethylene group and the like. Among them, a hexamethylene group is preferable because it smoothly substitutes for a polymer / polymer sulfur bridge and is thermally stable.

R ⁶ and R ⁷ are not particularly limited as long as they are monovalent organic groups containing a nitrogen atom, but those containing at least one aromatic ring are preferred, and N—C (= Those containing a linking group represented by S)-are more preferred.

R ⁶ and R ⁷ may be the same or different from each other, but are preferably the same for reasons such as ease of production.

Examples of the compound satisfying the above conditions include 1,2-bis (N, N′-dibenzylthiocarbamoyldithio) ethane, 1,3-bis (N, N′-dibenzylthiocarbamoyldithio) propane, 1, 4-bis (N, N′-dibenzylthiocarbamoyldithio) butane, 1,5-bis (N, N′-dibenzylthiocarbamoyldithio) pentane, 1,6-bis (N, N′-dibenzylthio) Carbamoyldithio) hexane, 1,7-bis (N, N′-dibenzylthiocarbamoyldithio) heptane, 1,8-bis (N, N′-dibenzylthiocarbamoyldithio) octane, 1,9-bis (N , N′-dibenzylthiocarbamoyldithio) nonane, 1,10-bis (N, N′-dibenzylthiocarbamoyldithio) decane and the like. Among these, 1,6-bis (N, N′-dibenzylthiocarbamoyldithio) hexane is preferable because it is thermally stable and has excellent polarizability.

The content of the compound represented by the above formula (2) is 0.1 parts by mass or more, preferably 0.3 parts by mass or more, more preferably 0.5 parts by mass with respect to 100 parts by mass of the rubber component. As mentioned above, More preferably, it is 0.7 mass part or more. There exists a tendency for the effect acquired by mix | blending the compound represented by the said Formula (2) that it is less than 0.1 mass part is small. The content of the compound represented by the formula (2) is 10 parts by mass or less, preferably 5 parts by mass or less, more preferably 2.5 parts by mass or less, still more preferably 2 parts by mass or less, particularly preferably. 1.5 parts by mass or less. If it exceeds 10 parts by mass, the crosslinking density becomes too high, and the wear resistance may be deteriorated.

In the present invention, sulfur is usually used.
Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur.

The sulfur content is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, and still more preferably 0.3 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 0.1 parts by mass, the vulcanization rate will be slow, and the productivity may be deteriorated. The sulfur content is preferably 2.5 parts by mass or less, more preferably 1.7 parts by mass or less, still more preferably 1.3 parts by mass or less, and particularly preferably 0.7 parts by mass or less. If the amount exceeds 2.5 parts by mass, the change in physical properties of rubber after aging may increase.

When sulfur is used in the rubber composition for tires of the present invention, the total content of sulfur and the compound represented by the above formula (2) is preferably 1 part by mass or more with respect to 100 parts by mass of the rubber component. More preferably, it is 1.2 parts by mass or more. If it is less than 1 part by mass, the vulcanization rate tends to be slow. The total content is preferably 3 parts by mass or less, more preferably 2.5 parts by mass or less, still more preferably 2 parts by mass or less, and particularly preferably 1.7 parts by mass or less. When it exceeds 3 parts by mass, the crosslinking density becomes too high, and the wear resistance may be deteriorated.

The content (mass) of the compound represented by the sulfur content (mass) / formula (2) is preferably 0.05 or more, more preferably 0.1 or more, and still more preferably 0.3 or more. If it is less than 0.05, the vulcanization rate tends to be slow. The mass ratio is preferably 2.5 or less, more preferably 1.5 or less, and still more preferably 1 or less. When it exceeds 2.5, there exists a possibility that the effect of mix | blending the compound represented by the said Formula (2) may not fully be acquired.

In the present invention, a vulcanization accelerator is usually used. Examples of the vulcanization accelerator include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N, N′-dicyclohexyl-2- Examples include benzothiazolylsulfenamide (DZ), mercaptobenzothiazole (MBT), dibenzothiazolyl disulfide (MBTS), N, N′-diphenylguanidine (DPG), and the like. Of these, sulfenamide-based vulcanization accelerators such as TBBS, CBS, and DZ are preferred, and TBBS is more preferred because the vulcanization rate can be easily controlled.

In the present invention, oil may be used. In the rubber composition for tires of the present invention, the oil content is preferably 5 parts by mass or less, more preferably 1 part by mass or less, still more preferably 0 parts by mass (substantially) with respect to 100 parts by mass of the rubber component. Not contained). Since the rubber composition for tires of the present invention can reduce Mooney viscosity by using HPNR as compared with the use of NR, the amount of oil can be reduced while maintaining good processability.

The tire rubber composition of the present invention is produced by a general method. That is, it can be produced by a method of kneading the above components with a Banbury mixer, a kneader, an open roll or the like and then vulcanizing. The rubber composition can be used for each member of a tire, and in particular, can be suitably used for a tread (cap tread) of a heavy duty tire (especially for trucks and buses).

The heavy duty tire of the present invention is produced by a usual method using the rubber composition.
That is, a rubber composition containing the above components is extruded in accordance with the shape of a tire member such as a tread at an unvulcanized stage, and is molded together with other tire members by a normal method on a tire molding machine. Thus, an unvulcanized tire is formed. By heating and pressurizing this unvulcanized tire in a vulcanizer, the heavy duty tire of the present invention can be produced.

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.
Natural rubber latex: Field latex obtained from Taitex Co., Ltd. Surfactant: Emal-E (Polyoxyethylene lauryl ether sodium sulfate) manufactured by Kao Corporation
NaOH: NaOH manufactured by Wako Pure Chemical Industries, Ltd.
NR: TSR20
HPNR (saponified natural rubber): Solid rubber BR obtained from Production Example 1 below: Nipol BR1220 (vinyl content: 1% by mass, unmodified) manufactured by Nippon Zeon Co., Ltd.
Modified BR: Modified butadiene rubber manufactured by Sumitomo Chemical Co., Ltd. (vinyl content: 15% by mass, R ¹ , R ² and R ^{3 of} formula (1) = — OCH ₃ , R ⁴ and R ⁵ = —CH ₂ CH ₃ , n = 3)
Carbon Black: Show Black N220 (N ₂ SA: 111 m ² / g) manufactured by Cabot Japan
Silica: ULTRASIL VN3 manufactured by Degussa (N ₂ SA: 175 m ² / g, average primary particle size: 15 nm)
Silane coupling agent: Si266 (bis (3-triethoxysilylpropyl) disulfide) manufactured by Degussa
Wax: Sannoc Wax anti-aging agent manufactured by Ouchi Shinsei Chemical Industry Co., Ltd .: Anti-aging agent 6C (SANTOFLEX 6PPD) manufactured by FLEXSYS Co., Ltd.
Stearic acid: Stearic acid “椿” manufactured by NOF Corporation
Zinc oxide: 2 types of zinc white VP KA9188 manufactured by Mitsui Mining & Smelting Co., Ltd .: VP KA9188 manufactured by LANXESS (1,6-bis (N, N′-dibenzylthiocarbamoyldithio) hexane)
Sulfur: Powder sulfur vulcanization accelerator manufactured by Tsurumi Chemical Industry Co., Ltd .: Noxeller NS manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

(Production of modified natural rubber with alkali)
Production Example 1
After adjusting the solid rubber latex solids concentration (DRC) to 30% (w / v), 1000 g of natural rubber latex was added with 10 g of Emal-E and 20 g of NaOH, followed by saponification at room temperature for 48 hours. Natural rubber latex was obtained. Water was added to the latex to dilute to DRC 15% (w / v), and then formic acid was added with slow stirring to adjust the pH to 4.0 to 4.5 to cause aggregation. The agglomerated rubber was pulverized, washed repeatedly with 1000 ml of water, and then dried at 110 ° C. for 2 hours to obtain a solid rubber (saponified natural rubber).

With respect to the solid rubber and TSR obtained in Production Example 1, the nitrogen content, phosphorus content, and gel content were measured by the methods described below. The results are shown in Table 1.

(Measurement of nitrogen content)
The nitrogen content was measured using CHN CORDER MT-5 (manufactured by Yanaco Analytical Industries). For the measurement, first, a calibration curve for determining the nitrogen content was prepared using antipyrine as a standard substance. Next, about 10 mg of the saponified natural rubber or TSR sample obtained in the production example was weighed, and the average value was obtained from the measurement results of three times to obtain the nitrogen content of the sample.

(Measurement of phosphorus content)
The phosphorus content was determined using an ICP emission spectrometer (ICPS-8100, manufactured by Shimadzu Corporation).
In addition, ³¹ P-NMR measurement of phosphorus uses an NMR analyzer (400 MHz, AV400M, manufactured by Nippon Bruker Co., Ltd.), and uses a measurement peak of P atom in an 80% aqueous phosphoric acid solution as a reference point (0 ppm), and raw rubber with chloroform. More extracted components were purified, dissolved in CDCl ₃ and measured.

(Measurement of gel content)
A raw rubber sample 70.00 mg cut to 1 mm × 1 mm was weighed, 35 mL of toluene was added thereto, and the mixture was allowed to stand in a cool dark place for 1 week. Subsequently, centrifugation was performed to precipitate a gel component insoluble in toluene, the soluble component of the supernatant was removed, and only the gel component was solidified with methanol, and then dried and the mass was measured. The gel content (%) was determined by the following formula.
Gel content (mass%) = [mass mg after drying / mg of initial sample] × 100

As shown in Table 1, the saponified natural rubber (HPNR) had a reduced nitrogen content, phosphorus content, and gel content as compared to TSR. Further, in the ³¹ P NMR measurement of an extract obtained by extracting from the modified natural rubber obtained in Production Example 1 it did not detect the peak due to phospholipids -3Ppm～1ppm.

<Examples and Comparative Examples>
According to the formulation shown in Table 2, using a 1.7 L Banbury mixer, chemicals other than sulfur and a vulcanization accelerator were kneaded to obtain a kneaded product. Next, using an open roll, sulfur and a vulcanization accelerator were kneaded into the obtained kneaded material to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was pressed with a 2 mm-thick mold at 150 ° C. for 30 minutes to obtain a vulcanized rubber composition. The following tests were conducted using this as a new rubber.

(Heat generation performance index)
Using a viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.), tan δ of each formulation was measured under the conditions of a temperature of 70 ° C., an initial strain of 10%, and a dynamic strain of 2%. The tan δ of each formulation was displayed as an index. A smaller value indicates less heat generation and better fuel efficiency.
(Heat generation performance index) = (tan δ of each formulation) / (tan δ of Comparative Example 3) × 100

(Abrasion resistance index)
Using a lambourne wear tester manufactured by Iwamoto Seisakusho, lambourne wear of the above vulcanized rubber composition under conditions of a surface rotation speed of 50 m / min, a load load of 3.0 kg, a sandfall of 15 g / min and a slip rate of 20%. The amount was measured. Then, the volume loss amount was calculated from the measured amount of Lambourn wear, and the volume loss amount of Comparative Example 3 was set to 100, and the volume loss amount of each formulation was displayed as an index according to the following formula. It shows that it is excellent in abrasion resistance performance, so that a numerical value is large.
(Abrasion resistance index) = (volume loss amount of Comparative Example 3) / (volume loss amount of each formulation) × 100

(Degradation resistance index)
The vulcanized rubber composition was thermally deteriorated in an oven at 80 ° C. for 7 days to obtain a deteriorated product.
A tensile test was performed according to JIS K6251 to measure the elongation at break of the deteriorated product. And the breaking elongation of the comparative example 3 was set to 100, and the breaking elongation of each formulation was indicated by an index according to the following formula. It shows that it is excellent in deterioration-resistant performance, so that a numerical value is large.
(Deterioration resistance index) = (Elongation at break for each formulation) / (Elongation at break in Comparative Example 3) × 100

From Table 2, in the examples including HPNR, modified BR, silica, and VP KA9188, the wear resistance performance, the degradation resistance performance, and the low fuel consumption performance could be improved in a balanced manner. On the other hand, the comparative example which does not use the said component together was inferior in performance compared with the Example.

Claims (7)

Including a rubber component, silica and a compound represented by the following formula (2),
The rubber component includes a modified natural rubber having a phosphorus content of 200 ppm or less and a modified butadiene rubber modified with a compound represented by the following formula (1):
In 100% by mass of the rubber component, the content of the modified natural rubber is 40 to 95% by mass, the content of the modified butadiene rubber is 5 to 60% by mass,
The rubber composition for tires in which the content of the compound represented by the following formula (2) is 0.1 to 10 parts by mass and the silica content is 10 to 60 parts by mass with respect to 100 parts by mass of the rubber component. object.

(In the formula (1), 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 is the same or different and represents a hydrogen atom, an alkyl group or a cyclic ether group, and n represents an integer.)

(In Formula (2), A represents an alkylene group having 2 to 10 carbon atoms, and R ⁶ and R ⁷ are the same or different and each represents a monovalent organic group containing a nitrogen atom.) The rubber composition for tires according to claim 1, wherein the modified natural rubber has a gel content measured as a toluene insoluble content of 20% by mass or less. 3. The tire rubber according to claim 1, wherein the modified natural rubber has no phospholipid peak at -3 ppm to 1 ppm and substantially no phospholipid in ³¹ P NMR measurement of a chloroform extract. Composition. The tire rubber composition according to any one of claims 1 to 3, wherein the modified natural rubber has a nitrogen content of 0.3 mass% or less. The rubber composition for a tire according to any one of claims 1 to 4, wherein the modified natural rubber is obtained by saponifying natural rubber latex. The tire rubber composition according to any one of claims 1 to 5, which is used for a tread of a heavy load tire. A heavy duty tire having a tread produced using the rubber composition according to claim 1.