JP2012107077A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire having low fuel cost, rubber strength and abrasion resistance improved in good balance.SOLUTION: There is provided the pneumatic tire produced from a rubber composition comprising a modified natural rubber having a phosphorus content of ≤200 ppm and modified butadiene rubber, wherein the modified butadiene rubber is obtained by hydrosilylating polybutadiene; the content of the modified natural rubber in 100 mass% of the rubber component is 60 to 95 mass%; and the content of the modified butadiene rubber is 5 to 40 mass%.

Description

The present invention relates to a pneumatic tire.

Conventionally, the fuel consumption of vehicles has been reduced by reducing the rolling resistance of tires and suppressing heat generation. However, in recent years, the demand for lower fuel consumption of vehicles has become increasingly strong. Excellent low heat generation (low fuel consumption) is required not only for tires but also for heavy duty tires for trucks and buses. In particular, high-load tires are required to have not only excellent fuel efficiency but also excellent wear resistance.

As a method for improving fuel efficiency, a method of replacing carbon black with silica is known. However, since silica has lower reinforcement than carbon black, replacement of carbon black with silica tends to reduce rubber strength and wear resistance.

In Patent Documents 1 to 3, modified diene rubbers such as modified butadiene rubber and modified styrene butadiene rubber are blended together with silica to further improve fuel efficiency. However, there is room for improvement in terms of improving fuel economy, rubber strength, and wear resistance in a well-balanced manner.

On the other hand, when normal natural rubber is used by removing highly purified natural rubber (modified natural rubber) with increased isoprene content by removing saponification of nitrogen impurities and phospholipids that constitute proteins It has been clarified that the fuel efficiency is improved as compared with (Patent Document 4). However, no detailed study has been made on the point of improving fuel economy, rubber strength, and wear resistance in a well-balanced manner.

JP 2001-114939 A JP 2005-126604 A JP 2005-325206 A JP 2010-138359 A

An object of the present invention is to solve the above-mentioned problems and to provide a pneumatic tire in which fuel economy, rubber strength, and wear resistance are improved in a well-balanced manner.

In order to obtain a pneumatic tire excellent in the above performance, the present inventors diligently investigated the use of the above highly purified natural rubber (modified natural rubber). As a result, when modified natural rubber is used, it has better fuel efficiency than ordinary natural rubber, but when modified natural rubber is used alone, there is a problem that sufficient wear resistance cannot be obtained. I found it. As a result of further diligent investigations on the newly generated problem, the present inventor has found that, by using a modified butadiene rubber obtained by hydrosilylating polybutadiene together with a modified natural rubber, low fuel consumption, rubber The inventors have found that the strength and wear resistance can be improved in a balanced manner, and have completed the present invention.
That is, the present invention includes a modified natural rubber having a phosphorus content of 200 ppm or less and a modified butadiene rubber, and the modified butadiene rubber is obtained by hydrosilylating polybutadiene. It relates to a pneumatic tire manufactured using a rubber composition having a modified natural rubber content of 60 to 95% by mass and a modified butadiene rubber content of 5 to 40% by mass.

The polybutadiene is preferably a polybutadiene having a 1,4-cis structure content of 80 mol% or more and a 1,2-vinyl structure content of 20 mol% or less.

The modified butadiene rubber is preferably obtained by hydrosilylating polybutadiene using a silicon-containing compound.

In the hydrosilylation of the polybutadiene, it is preferable that the vinyl group of the polybutadiene is hydrosilylated.

（式（１）中、Ｒ^１は、炭素数１〜１０の炭化水素基又はハロゲン基を表し、該炭化水素基は、水酸基、アミノ基、ハロゲン基、メルカプト基、エポキシ基、エーテル基、及びシアノ基からなる群より選択される少なくとも１種の基、又は窒素原子を有してもよく、環構造を形成してもよい。Ｒ^２は、同一若しくは異なって、炭素数１〜１０の炭化水素基又はハロゲン基を表し、該炭化水素基は、水酸基、アミノ基、ハロゲン基、及びエーテル基からなる群より選択される少なくとも１種の基、窒素原子、又はケイ素原子を有してもよく、環構造を形成してもよい。） The silicon-containing compound is preferably a compound represented by the following general formula (1).

(In the formula (1), R ¹ represents a hydrocarbon group or a halogen group having 1 to 10 carbon atoms, and the hydrocarbon group, a hydroxyl group, an amino group, a halogen group, a mercapto group, an epoxy group, an ether group and, At least one group selected from the group consisting of a cyano group, or may have a nitrogen atom and may form a ring structure, and R ² may be the same or different and is a carbon atom having 1 to 10 carbon atoms. Represents a hydrogen group or a halogen group, and the hydrocarbon group may have at least one group selected from the group consisting of a hydroxyl group, an amino group, a halogen group, and an ether group, a nitrogen atom, or a silicon atom. A ring structure may be formed.)

The modified natural rubber is obtained by saponifying natural rubber latex and washing the resulting saponified natural rubber latex until the phosphorus content in the rubber is 200 ppm or less. preferable.

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

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

According to the present invention, a rubber composition containing a specific amount of a modified natural rubber (hereinafter also referred to as HPNR) having a phosphorus content of 200 ppm or less and a modified butadiene rubber obtained by hydrosilylation of polybutadiene, By using it for each tire member such as a sidewall, it is possible to provide a pneumatic tire with improved fuel economy, rubber strength, and wear resistance in a well-balanced manner.

The pneumatic tire of the present invention comprises a rubber composition containing a specific amount of a modified natural rubber having a phosphorus content of 200 ppm or less (hereinafter also referred to as HPNR) and a modified butadiene rubber obtained by hydrosilylating polybutadiene. It is made using.

HPNR with reduced and removed phospholipids contained in natural rubber (NR) (preferably HPNR with protein and gel content removed) is less likely to generate heat. Can be achieved. Therefore, in the present invention, fuel efficiency can be improved. On the other hand, as described above, when HPNR is used alone as a rubber component, there is a problem that sufficient wear resistance cannot be obtained. However, in the present invention, by using the above modified butadiene rubber together with HPNR, Fuel economy, rubber strength, and wear resistance (especially rubber strength) can be improved in a well-balanced manner, and fuel efficiency, rubber strength, and wear resistance are extremely excellent. In particular, by using the modified butadiene rubber together with HPNR, it is possible to synergistically improve processability, rubber strength, and wear resistance (particularly rubber strength).

In addition, when the above modified butadiene rubber is used in combination with HPNR, the fuel efficiency, rubber strength, and abrasion resistance are lower than when the terminal modified butadiene rubber modified with an organosilicon compound containing an alkoxy group is used together with HPNR. Very excellent in properties.

(Rubber composition)
First, the rubber composition for producing the pneumatic tire of the present invention will be described. The rubber composition includes a specific amount of modified natural rubber (HPNR) and modified butadiene rubber as rubber components.

(Modified natural rubber (HPNR))
The modified natural rubber (HPNR) has a phosphorus content of 200 ppm or less. If it exceeds 200 ppm, the gel amount will increase during storage, and the tan δ of the vulcanized rubber will increase and the fuel efficiency will deteriorate, or the Mooney viscosity of the unvulcanized rubber will increase and the processability will tend to deteriorate. , Fuel economy, rubber strength and processability cannot be improved sufficiently. 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).

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 increases during storage and the processability tends to deteriorate, and there is a possibility that the fuel economy, rubber strength and processability cannot be improved sufficiently. . The nitrogen content can be measured by a conventional method such as Kjeldahl method. Nitrogen is derived from protein.

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 Mooney viscosity tends to increase and the processability tends to deteriorate, and the fuel efficiency, rubber strength, and processability may not be sufficiently improved. 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.

As a method for producing the modified natural rubber, for example, the production method described in JP 2010-138359 A, that is, the step (A) of obtaining a saponified natural rubber latex by saponifying the natural rubber latex, and the obtained Examples of the method include a step (B) of washing the saponified natural rubber latex until the phosphorus content in the rubber is 200 ppm or less. Specifically, first, a natural rubber latex is saponified with an alkali to prepare a saponified natural rubber latex, and then the agglomerated rubber obtained by agglomerating the saponified natural rubber latex contains phosphorus to the rubber content. A modified natural rubber (saponified natural rubber) can be produced by a method of repeatedly washing with water until the rate becomes 200 ppm or less and drying.

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 rubber composition, the content of the modified natural rubber in 100% by mass of the rubber component is 60% by mass or more, preferably 80% by mass or more. If it is less than 60% by mass, excellent fuel economy, rubber strength and processability cannot be obtained. The content of the modified natural rubber is 95% by mass or less, preferably 90% by mass or less. If it exceeds 95% by mass, the content of the modified butadiene rubber is lowered, and the fuel efficiency, rubber strength, and abrasion resistance (particularly, abrasion resistance) cannot be sufficiently improved.

(Modified butadiene rubber)
The modified butadiene rubber is obtained by hydrosilylating polybutadiene with a silicon-containing compound. The modified butadiene rubber can be produced by a known method (for example, a method described in JP 2010-168528 A). In addition, when polybutadiene is hydrosilylated using a silicon-containing compound, the reaction hardly proceeds at the double bond of the main chain of polybutadiene, and the reaction is preferentially performed at a vinyl group having a 1,2-vinyl structure as a side chain. proceed.

The polybutadiene (polybutadiene to be hydrosilylated) preferably has a 1,2-vinyl structure content of 4 to 20 mol%, more preferably 4 to 19 mol%, and more preferably 5 to 13 mol%. More preferably it is. If the content of the 1,2-vinyl structure is less than 4 mol%, hydrosilylation hardly occurs, and there is a tendency that the effect of improving low exothermicity cannot be obtained. On the other hand, if the content of the 1,2-vinyl structure exceeds 20 mol%, the glass transition point of the modified butadiene rubber increases, so that the low heat buildup and wear resistance tend to deteriorate.
In the present specification, the content of the 1,2-vinyl structure is measured by the method described in Examples described later.

The polybutadiene preferably has a 1,4-cis structure content of 80 to 95 mol%, more preferably 87 to 94 mol%. When the content of the 1,4-cis structure exceeds 95 mol%, the content of the 1,2-vinyl structure tends to be 4 mol% or less, and there is a tendency that low exothermic improvement does not easily appear. When the content of the 1,4-cis structure is less than 80 mol%, the wear resistance tends to decrease.
In the present specification, the content of the 1,4-cis structure is measured by the method described in Examples described later.

Conventionally, a butadiene rubber (low cis butadiene rubber) having a low 1,4-cis structure content obtained by a living anion polymerization method using an alkyllithium catalyst is relatively easy to modify at the end, and therefore has a low cis Attempts have been made to improve low heat build-up by modifying the end of butadiene rubber with an organosilicon compound or the like. However, low cis butadiene rubber (terminally modified low cis butadiene rubber) has a high glass transition point compared to butadiene rubber having a high 1,4-cis structure content, so that sufficient wear resistance cannot be obtained. was there.

On the other hand, when the content of the 1,2-vinyl structure and the content of the 1,4-cis structure of the polybutadiene are within the above ranges, the modified butadiene rubber obtained by hydrosilylating the polybutadiene has 1, Since the content of the 4-cis structure is high and the balance of the degree of modification to the polybutadiene main chain is suitably maintained, compared with the terminal-modified low cis-butadiene rubber in which only the molecular terminals are modified, silica and The affinity of can be further improved. Therefore, fuel economy, rubber strength, wear resistance, and processability can be further improved.

The Mooney viscosity (ML _{1 + 4} , 100 ° C.) of the polybutadiene is preferably 20 to 50, more preferably 30 to 40, and still more preferably 33 to 35. If the Mooney viscosity is lower than the above range, there will be a problem of deterioration of mechanical properties. Conversely, if the Mooney viscosity is higher than the above range, filler dispersibility at the time of kneading will be deteriorated, and sufficient performance will not be exhibited, and there will be a problem in workability. Is not preferable.
In this specification, Mooney viscosity is measured by the method as described in the below-mentioned Example.

The polybutadiene may have a monomer unit other than 1,3-butadiene. The monomer unit other than 1,3-butadiene is not particularly limited, and examples thereof include isoprene, 1,3-pentadiene, 2-ethyl-1,3-butadiene, 2,3-dimethylbutadiene, and myrcene.

The polybutadiene is preferably produced by polymerization using a catalyst comprising a metallocene complex of a transition metal compound, an ionic compound of a non-coordinating anion and a cation, and an organometallic compound. The polymerization method is not particularly limited, and bulk polymerization, solution polymerization, and the like can be applied. Examples of the solvent used for the solution polymerization include hydrocarbon solvents such as cyclohexane and toluene.

The order of addition of the catalyst components is not particularly limited, but can be performed, for example, in the following order. After the organometallic compound is added to the mixture of 1,3-butadiene and the solvent, the metallocene complex of the transition metal compound and the ionic compound are added in any order.

（式（１）中、Ｒ^１は、炭素数１〜１０の炭化水素基又はハロゲン基を表し、該炭化水素基は、水酸基、アミノ基、ハロゲン基、メルカプト基、エポキシ基、エーテル基、及びシアノ基からなる群より選択される少なくとも１種の基、又は窒素原子を有してもよく、環構造を形成してもよい。Ｒ^２は、同一若しくは異なって、炭素数１〜１０の炭化水素基又はハロゲン基を表し、該炭化水素基は、水酸基、アミノ基、ハロゲン基、及びエーテル基からなる群より選択される少なくとも１種の基、窒素原子、又はケイ素原子を有してもよく、環構造を形成してもよい。） As the silicon-containing compound, a compound represented by the following general formula (1) is preferable.

(In the formula (1), R ¹ represents a hydrocarbon group or a halogen group having 1 to 10 carbon atoms, and the hydrocarbon group, a hydroxyl group, an amino group, a halogen group, a mercapto group, an epoxy group, an ether group and, At least one group selected from the group consisting of a cyano group, or may have a nitrogen atom and may form a ring structure, and R ² may be the same or different and is a carbon atom having 1 to 10 carbon atoms. Represents a hydrogen group or a halogen group, and the hydrocarbon group may have at least one group selected from the group consisting of a hydroxyl group, an amino group, a halogen group, and an ether group, a nitrogen atom, or a silicon atom. A ring structure may be formed.)

Number of carbon atoms in the hydrocarbon group of R ¹ and ^{R 2,} 1-6 are preferred. When the number of carbon atoms exceeds 6, the hydrocarbon group is too large and the reaction activity becomes low, and the hydrophobic function for reducing the affinity for silica becomes too high, which is not preferable.

Examples of the hydrocarbon group having 1 to 10 carbon atoms of R ^1, include the following groups.
(A) An alkoxy group having 1 to 6 carbon atoms is preferred, and an ethoxy group is more preferred. (B) An alkyl group, preferably having 1 to 6 carbon atoms, more preferably a methyl group. (C) A dialkylamino group, preferably a dimethylamino group, a di-n-propylamino group, or a di-iso-propylamino group, and more preferably a diethylamino group. (D) An aminoalkyl group, preferably having 1 to 6 carbon atoms, more preferably having 1 to 3 carbon atoms, and still more preferably an aminopropyl group. (E) An aminoalkoxy group, preferably having 1 to 6 carbon atoms, more preferably having 1 to 3 carbon atoms, and still more preferably an aminoethoxy group. (F) A chloroalkoxy group, preferably having 1 to 6 carbon atoms, more preferably having 1 to 3 carbon atoms, and even more preferably a chloroethoxy group. (G) A chloroalkyl group, preferably having 1 to 6 carbon atoms, more preferably having 1 to 3 carbon atoms, and even more preferably a chloroethyl group. (H) An aromatic ring, preferably a phenyl group or a chlorophenyl group. (I) A cyanoalkyl group, preferably having 1 to 6 carbon atoms, more preferably having 1 to 3 carbon atoms, and still more preferably a cyanopropyl group. Further, (j) a mercaptoalkyl group, preferably having 1 to 6 carbon atoms, more preferably having 1 to 3 carbon atoms, and further preferably a mercaptopropyl group. (K) A hydroxyalkyl group, preferably having 1 to 6 carbon atoms, more preferably having 1 to 3 carbon atoms, and still more preferably a hydroxypropyl group. (L) A glycidoxyalkyl group, preferably having 1 to 6 carbon atoms, more preferably having 1 to 3 carbon atoms, and still more preferably a glycidoxypropyl group. (M) A nitrogen-containing cycloaliphatic group having 3 to 5 carbon atoms is preferred, and a piperidyl group is more preferred. (N) A piperidinoalkyl group, preferably having 1 to 6 carbon atoms, more preferably having 1 to 3 carbon atoms, and still more preferably a piperidinoethyl group. (O) A piperidinoalkoxy group, preferably having 1 to 6 carbon atoms, more preferably having 1 to 3 carbon atoms, and still more preferably a piperidinoethoxy group. (P) A piperazinoalkyl group, preferably having 1 to 6 carbon atoms, more preferably having 1 to 3 carbon atoms, and still more preferably a piperazinopropyl group.

The halogen group for R ¹ is preferably a chlorine group.

R ¹ is preferably an alkoxy group, an alkyl group, or a dialkylamino group, and more preferably an ethoxy group, a methyl group, or a diethylamino group.

Examples of the hydrocarbon group having 1 to 10 carbon atoms R ^2, include the following groups.
(A) An alkoxy group having 1 to 6 carbon atoms is preferred, and an ethoxy group is more preferred. (B) An alkyl group, preferably having 1 to 6 carbon atoms, more preferably a methyl group. (C) Alkylsiloxane (R ₃ SiO). Here, R is an alkyl group, preferably a methyl group. (D) A dialkylamino group, preferably a dimethyl group, a di-n-propylamino group, or a di-iso-propylamino group, and more preferably a diethylamino group. (E) An aminoalkyl group, preferably having 1 to 6 carbon atoms, more preferably having 1 to 3 carbon atoms, and even more preferably aminopropyl. (F) An aminoalkoxy group, preferably having 1 to 6 carbon atoms, more preferably having 1 to 3 carbon atoms, and still more preferably an aminoethoxy group. (G) An aromatic ring, more preferably a phenyl group or a phenyl chloride group. (H) A nitrogen-containing cycloaliphatic group having 3 to 5 carbon atoms is more preferred, and a piperidyl group is more preferred.

The halogen group for R ² is preferably a chlorine group.

R ² is preferably an alkoxy group, an alkyl group, or an alkylsiloxane group, and more preferably an ethoxy group, a methyl group, or a hexamethyltrisiloxane group.

Examples of the silicon-containing compound include triethoxysilane, 1,1,1,3,5,5,5-heptamethyltrisiloxane (1,1,1,3,5,5,5-heptamethyltrisiloxane), 1 1,1,3,3,5,5-heptamethyltrisiloxane (1,1,1,3,3,5,5-heptamethyltrisiloxane), diethylaminodimethylsilane, and the like can be suitably used. Usually, these compounds are used alone, but two or more kinds may be used in combination.

As the catalyst used for hydrosilylation of polybutadiene, those described in US Pat. No. 3,419,593 and US Pat. No. 3,715,334 can be referred to. The denaturation method performed in the steps (I) to (IV) is shown below.
(I) Polymerization of 1,3-butadiene in cyclohexane at a monomer concentration of 25-35% by weight and a temperature of 40-70 ° C., preferably 45-55 ° C. As shown below, the catalyst system used in the polymerization is composed of (a) a metallocene complex of a transition metal compound, (b) an organometallic compound, (c) an ionic compound of a non-coordinating anion and a cation. Become.
(a) A half-vanadocene (V) catalyst represented by the chemical formula (C ₅ R ₅ ) VOX ₂ Here, R = H and X = Cl.
(b) An aluminium compound represented by the chemical formula AlR ₃ . Here, R = alkyl group.
(c) Organoboric acid compound Ph ₃ CB (C ₆ F ₅ ) ₄
(II) In the hydrosilylation reaction of polybutadiene, after unreacted 1,3-butadiene monomer is released from the polymerization solution of (I), a silicon-containing compound (compound represented by the above formula (1)) and a platinum catalyst (Speier catalyst ( It is obtained by adding H ₂ PtCl ₆ )) and reacting at 40 to 80 ° C., more preferably at 50 to 60 ° C.
(III) About 1,000 ppm of antioxidant per 100 g of rubber is added to the ethanol solution to stop the reaction.
(IV) Dry the hydrosilylated cis-polybutadiene solution in cyclohexane at 100 ° C. for 1 hour under vacuum.

The solvent for performing the hydrosilylation reaction is preferably a hydrocarbon compound, and more preferably, for example, pentane, hexane, heptane, octane, cyclohexane, and aromatic hydrocarbon. More preferred are benzene, toluene and xylene, and particularly preferred is toluene.

Platinum catalysts include: (a) H ₂ PtCl _{6 in} toluene known as Speier catalyst, (b) Pt-divinyltetramethoxysilane in toluene / xylene known as Karstedt catalyst, (c) Lamoreaux catalyst (H ₂ PtCl _{6 in} n-octanol) can be used.

The amount of the platinum catalyst is preferably 0.1 to 1 mmol / mol, preferably 0.13 to 0.5 mmol / mol, as the molar ratio of platinum to the content of 1,2-vinyl structure in the polybutadiene (platinum / vinyl structure). More preferably, 0.15-0.30 mmol / mol is still more preferable, and 0.15-0.25 mmol / mol is especially preferable.

The above molar ratio is optimal to provide a sufficiently high 1,2-vinyl structure conversion (reaction rate) or hydrosilylation while avoiding excessive crosslinking due to condensation and interaction between silyl side chains. It is a condition range. When the said molar ratio is lower than the said range, there exists a tendency for a reaction rate to become low and sufficient effect not to be acquired. On the other hand, if the molar ratio is higher than the above range, it tends to be economically disadvantageous and the residual catalyst often deteriorates the physical properties of the rubber.

The hydrosilylation reaction is performed in a nitrogen atmosphere, but other inert gases such as helium and argon may be used.

Since the hydrosilylation reaction at high temperature causes a significant proportion of silane crosslinking, the reaction temperature is preferably 40-80 ° C, more preferably 45-80 ° C, and even more preferably 50-80 ° C. The reaction time is also preferably 2 to 5 hours in order to control the degree of crosslinking.

The method of hydrosilylation reaction is not particularly limited. For example, a method in which polybutadiene is dissolved in an aromatic hydrocarbon solvent such as toluene and hydrosilylation is performed using a silicon-containing compound. Examples thereof include a method of adding a compound to hydrosilylate.

In the modified butadiene rubber, the hydrosilylation product is separated by adding the hydrosilylated solution to a large volume of acetone / ethanol / methyl ethyl ketone mixture, and impurities such as unreacted silicon compounds are removed by purification. Then, the modified butadiene rubber can be obtained by drying the hydrosilylation product under vacuum at room temperature.

The weight average molecular weight (Mw) of the modified butadiene rubber is preferably 1.0 × 10 ^{5 to} 2.0 × 10 ⁶ , the lower limit is preferably 1.4 × 10 ⁵ , and the upper limit is more preferably 1.0 × 10 ⁶ .
When the weight average molecular weight is less than 1.0 × 10 ⁵ , not only is the hysteresis loss large and it is difficult to obtain sufficient fuel efficiency, but the wear resistance also tends to decrease. On the other hand, when it exceeds 2.0 × 10 ⁶ , workability tends to be lowered.
In this specification, a weight average molecular weight (Mw) is measured by the method as described in the below-mentioned Example.

The weight average molecular weight (Mw) / number average molecular weight (Mn) of the modified butadiene rubber is preferably 1.5 or more, more preferably 1.6 or more. Further, Mw / Mn is preferably 5.0 or less, more preferably 3.0 or less. When Mw / Mn is in the above range, it is possible to more suitably improve low heat buildup (low fuel consumption), rubber strength, and wear resistance.
In the present specification, the number average molecular weight (Mn) is measured by the method described in Examples described later.

The content of the silicon-containing compound in the modified butadiene rubber (ratio of hydrosilylated butadiene units to the total butadiene units) is preferably 4 mol% or more, more preferably 6 mol% or more. If it is less than 4 mol%, the reaction with silica does not proceed efficiently, and the effect tends to be difficult to obtain.
The content of the silicon-containing compound is preferably 20 mol% or less, more preferably 13 mol% or less. When it exceeds 20 mol%, reaction between rubbers occurs, gelation proceeds and workability tends to deteriorate.
In this specification, content of a silicon-containing compound is measured by the method as described in the below-mentioned Example.

In the rubber composition, the content of the modified butadiene rubber in 100% by mass of the rubber component is 5% by mass or more, preferably 10% by mass or more. If it is less than 5% by mass, fuel economy, rubber strength, and abrasion resistance (particularly, abrasion resistance) cannot be sufficiently improved.
The content of the modified butadiene rubber is 40% by mass or less, preferably 30% by mass or less. If it exceeds 40% by mass, excellent fuel efficiency, rubber strength and processability cannot be obtained.

In the rubber composition, in addition to HPNR and modified butadiene rubber, those that can be used as rubber components include natural rubber (NR), butadiene rubber (BR), styrene butadiene rubber (SBR), isoprene rubber (IR), styrene. Examples include diene rubbers such as isoprene butadiene rubber (SIBR), ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), and acrylonitrile butadiene rubber (NBR). A rubber component may be used independently and may use 2 or more types together.

The rubber composition preferably contains silica. By blending silica together with HPNR and modified butadiene rubber, good low heat buildup, high rubber strength and wear resistance can be obtained. The silica is not particularly limited, and examples thereof include dry process silica (anhydrous silicic acid), wet process silica (hydrous silicic acid), and the like, but wet process silica is preferable because of its large number of silanol groups. Silica may be used alone or in combination of two or more.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 50 m ² / g or more, and more preferably 80 m ² / g or more. If it is less than 50 m < ² > / g, there exists a tendency for a reinforcement effect to be small and for abrasion resistance to fall. The _N 2 SA of the silica is preferably 300 meters ² / g or less, more preferably 250 meters ² / g, more preferably not more than 150m ² / g. When it exceeds 300 m ² / g, the dispersibility is poor, and there is a tendency that the low exothermic property and workability are lowered.
The nitrogen adsorption specific surface area of silica is a value measured by the BET method according to ASTM D3037-81.

In the rubber composition, the content of silica is 10 parts by mass or more, preferably 30 parts by mass or more, more preferably 40 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 wear resistance may not be obtained. The content of the silica is 150 parts by mass or less, preferably 100 parts by mass or less. If it exceeds 150 parts by mass, it will be difficult to disperse silica into rubber, and the processability of rubber will deteriorate.

In the said rubber composition, it is preferable to mix | blend a silane coupling agent with a silica. Examples of the silane coupling agent include bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) trisulfide, bis (3-triethoxysilylpropyl) disulfide, and bis (2-triethoxy). Silylethyl) tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilylethyl) tetrasulfide, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyl Trimethoxysilane, 2-mercaptoethyltriethoxysilane, 3-trimethoxysilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide, 3-triethoxysilylpropyl-N, N-dimethylthiocarba Yl tetrasulfide, 2-triethoxysilylethyl-N, N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropylbenzothiazole tetrasulfide, 3-triethoxysilylpropylbenzothiazolyl tetrasulfide, 3-triethoxysilyl Propyl methacrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, bis (3-diethoxymethylsilylpropyl) tetrasulfide, 3-mercaptopropyldimethoxymethylsilane, dimethoxymethylsilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide And dimethoxymethylsilylpropylbenzothiazole tetrasulfide. Of these, bis (3-triethoxysilylpropyl) tetrasulfide and 3-trimethoxysilylpropylbenzothiazolyl tetrasulfide are preferable from the viewpoint of improving reinforcing properties. These silane coupling agents may be used alone or in combination of two or more.

In the rubber composition, the content of the silane coupling agent is preferably 1 part by mass or more and more preferably 2 parts by mass or more with respect to 100 parts by mass of the silica. If it is less than 1 part by mass, the viscosity of the unvulcanized rubber composition tends to be high and the processability tends to deteriorate. Also, rubber strength and wear resistance tend to be greatly reduced. Moreover, 20 mass parts or less are preferable with respect to 100 mass parts of silica content, and, as for content of a silane coupling agent, 15 mass parts or less are more preferable. When the amount exceeds 20 parts by mass, there is a tendency that an effect commensurate with the amount of the silane coupling agent cannot be obtained.

It is preferable to mix carbon black with the rubber composition. By blending carbon black with HPNR, modified butadiene rubber, and silica, low heat build-up (low fuel consumption), rubber strength, and wear resistance (particularly rubber strength and wear resistance) can be improved. As carbon black, GPF, HAF, ISAF, SAF, etc. can be used, for example.

When carbon black is blended, the nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 30 m ² / g or more, and more preferably 50 m ² / g or more. When N ₂ SA is less than 30 m ² / g, sufficient reinforcing properties cannot be obtained, and sufficient rubber strength and abrasion resistance tend to be not obtained. Also, _N 2 SA of carbon black is preferably 150 meters ² / g or less, 100 m ² / g or less is more preferable. When N ₂ SA is more than 150 meters ² / g, the viscosity of the unvulcanized becomes very high, processability tends to be deteriorated. In addition, fuel efficiency tends to deteriorate.
In addition, the nitrogen adsorption specific surface area of carbon black is calculated | required by A method of JISK6217.

In the rubber composition, the carbon black content is preferably 2 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 2 parts by mass, sufficient reinforcing properties cannot be obtained, and sufficient rubber strength and wear resistance may not be obtained. The content of carbon black is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, with respect to 100 parts by mass of the rubber component. When it exceeds 20 parts by mass, the heat generation tends to increase.

In addition to the above components, the rubber composition includes other reinforcing agents, vulcanizing agents, vulcanization accelerators, various oils, zinc oxide, stearic acid, various anti-aging agents, softeners, plasticizers, and the like for tires. Or various compounding agents and additives mix | blended for general rubber compositions can be mix | blended. Moreover, the content of these compounding agents and additives can also be set to general amounts.

The rubber composition 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. When natural rubber is used, before kneading and vulcanization, usually a kneading device such as a Banbury mixer is used, and rubber components such as natural rubber, peptizers (aromatic disulfide compounds, aromatic mercaptan compounds) Etc.) and the like are kneaded. By performing the mastication step, processability is improved, while natural rubber molecules are cut, resulting in a decrease in rubber strength and wear resistance. On the other hand, in the present invention, excellent processability can be obtained by using modified natural rubber (HPNR), so that the mastication step can be omitted, and the rubber strength and wear resistance are reduced as well as the productivity is improved. Can also be suppressed.

The said rubber composition can be used conveniently for each member (especially tread (cap tread, base tread), sidewall, clinch apex) of a tire.

A cap tread is a surface layer portion of a tread having a multilayer structure. For example, a tread having a two-layer structure (a surface layer (cap tread) and an inner surface layer (base tread)) is a surface layer. The base tread is an inner layer portion of a tread having a multilayer structure, and is an inner surface layer in the tread having the two-layer structure.

(Pneumatic tire)
The pneumatic tire of the present invention is produced by a usual method using the rubber composition. That is, the rubber composition containing various additives as necessary is formed into the shape of each member of the tire (particularly, tread (cap tread, base tread), sidewall, clinch apex) at an unvulcanized stage. Extruded together, molded by a normal method on a tire molding machine, bonded together with other tire members to form an unvulcanized tire, and then heated and pressurized in a vulcanizer to produce a tire be able to.

The pneumatic tire of the present invention is very excellent in low heat generation (low fuel consumption), rubber strength, and wear resistance. Moreover, the manufacturing method of the pneumatic tire of this invention does not need to perform a special mastication process. Therefore, it is excellent in productivity as well as wear resistance and rubber strength.

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 Production Examples 1 and 2 will be described together. In addition, the chemical | medical agent refine | purified according to the usual method as needed.
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.

(Production Example 1) (Synthesis of saponified natural rubber 1 (HPNR1))
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 1 (HPNR1)).

(Production Example 2) (Synthesis of saponified natural rubber 2 (HPNR2))
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 15 g of NaOH, followed by a saponification reaction 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 2 (HPNR2)).

About HPNR1 and HPNR2 which were obtained by the manufacture example, and TSR used by evaluation of the rubber composition mentioned later, nitrogen content, phosphorus content, and gel content rate were measured by the method shown 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 natural rubber 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, HPNR1 and 2 have reduced nitrogen content, phosphorus content, and gel content as compared to TSR. In addition, HPNR1 and 2 did not have a peak due to phospholipid at -3 ppm to 1 ppm.

Hereinafter, various chemicals used in Production Examples 3 to 4 will be described together. In addition, the chemical | medical agent refine | purified according to the usual method as needed.
Butadiene: 1,3-butadiene anhydrous toluene manufactured by Takachiho Chemical Industry Co., Ltd .: anhydrous toluene catalyst solution manufactured by Kanto Chemical Co., Ltd. A: Bis (cyclopentadienyl) vanadium (II) manufactured by Wako Pure Chemical Industries, Ltd. ) 18.1 mg was dissolved in 50 ml of anhydrous toluene. (Metallocene complex of transition metal compound)
TEA solution: 1M-triethylaluminum / toluene solution (organometallic compound) manufactured by Kanto Chemical Co., Inc.
Boron solution: 1M-trityltetrakis (pentafluorophenyl) borate / toluene solution (ionic compound of non-coordinating anion and cation) manufactured by Tosoh Finechem Co., Ltd.
DIBAH solution: 1M-isodibutylaluminum hydride / toluene solution (organometallic compound) manufactured by Tosoh Finechem Co., Ltd.
2,6-tert-butyl-p-cresol: 2,6-tert-butyl-p-cresol catalyst solution B manufactured by Kanto Chemical Co., Ltd. B: 2.4M-H ₂ PtCl ₆ solution manufactured by Tokyo Chemical Industry Co., Ltd. Prepared by dissolving 5 g of H ₂ PtCl _{6 in} 5 ml of i-PrOH. (Platinum catalyst (Speier catalyst))
Triethoxysilane: Triethoxysilane (silicon-containing compound (compound represented by the above formula (1))) manufactured by Tokyo Chemical Industry Co., Ltd.

The following evaluation was performed about the polymer prepared by the following manufacture examples 3-4.

(Measurement of weight average molecular weight (Mw), number average molecular weight (Mn))
Weight average molecular weight (Mw) and number average molecular weight (Mn) are gel permeation chromatograph (GPC) (GPC-8000 series, manufactured by Tosoh Corp., detector: differential refractometer, column: TSKGEL manufactured by Tosoh Corp.) It calculated | required by standard polystyrene conversion based on the measured value by SUPERMALTPORE HZ-M).

(Measurement of microstructure in polymer)
The 1,2-vinyl structure content, 1,4-cis structure content, and 1,4-trans structure content in the polymer were measured using a JNM-ECA series NMR apparatus manufactured by JEOL Ltd. And measured. 0.1 g of the obtained polymer was dissolved in 15 ml of toluene, and slowly poured into 30 ml of methanol and reprecipitated, and then measured after drying under reduced pressure.

(Content of silicon-containing compound)
The content of silicon-containing compounds (ratio of hydrosilylated butadiene units with respect to all butadiene units) was calculated as a molar basis ratio with respect to all butadiene units from the conversion rate (reaction rate) of the 1,2-vinyl structure of polybutadiene.

(Mooney viscosity)
In accordance with JIS K 6300-1 “Unvulcanized rubber—physical properties—Part 1: Determination of viscosity and scorch time using Mooney viscometer”, it was heated by preheating for 1 minute using a Mooney viscosity tester. Under the temperature condition of 100 ° C., the small rotor was rotated, and the Mooney viscosity (ML _{1 + 4} , 100 ° C.) of the diene polymer after 4 minutes was measured. The numbers after the decimal point are rounded off.

(Production Example 3) [Preparation of polymer 1 (polybutadiene)]
The inside of the reaction kettle (3 L pressure-resistant stainless steel container) was replaced with nitrogen, and 1700 ml of anhydrous toluene, 200 ml of butadiene (2.2 mol), 15 ml of TEA solution, 30 ml of boron solution, 10 ml of catalyst solution A, and 3 ml of DIBAH solution were added while stirring. The temperature was raised to 40 ° C. over 30 minutes. Further, polymerization was carried out for 4 hours while maintaining at 40 ° C. 20 ml of ethanol added with 0.1 g of 2,6-tert-butyl-p-cresol was added to terminate the polymerization. The obtained polymer solution was developed in 2 L of ethanol to obtain a white precipitate. The obtained precipitate was air-dried and then dried with a vacuum dryer to obtain 120 g of polymer 1 (polybutadiene). As a result of the analysis, Mw of the obtained polybutadiene was 85.0 × 10 ⁴ , Mw / Mn was 3.50, 1,2-vinyl structure content was 8.8 mol%, 1,4-cis structure content The amount was 89.7 mol%, the content of 1,4-trans structure was 1.5 mol%, and the Mooney viscosity (ML _{1 + 4} , 100 ° C.) was 35.

(Production Example 4) [Preparation of polymer 2 (modified butadiene rubber)]
In a reaction kettle (3 L pressure-resistant stainless steel container), 2000 g of anhydrous toluene and 80 g of polybutadiene obtained in Production Example 3 cut to approximately 5 mm square were placed, and after purging with nitrogen, dissolved with stirring for 8 hours. Further, 3.2 ml of the catalyst solution B was added, and then 27 ml (0.16 mol) of triethoxysilane was added dropwise over 1 hour. After raising the temperature to 80 ° C., the reaction was carried out for 6 hours. After cooling at room temperature, the toluene solution was poured into a large amount of a mixed solution of ethanol, acetone, and methyl ethyl ketone over 1 hour to obtain a white precipitate. The obtained precipitate was air-dried and then dried with a vacuum dryer to obtain 80 g of polymer 2 (modified butadiene rubber). As a result of analysis, Mw of the obtained modified butadiene rubber is 1.45 × 10 ⁵ , Mw / Mn is 2.5, the content of 1,2-vinyl structure in the polymer is 2.4 mol%, and modified butadiene. The content of the silicon-containing compound in the rubber was about 6.4 mol%.

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
HPNR1,2: HPNR1,2 prepared in Preparation Examples 1 and 2 above
Modified butadiene rubber: Polymer 2 prepared in Production Example 4 (modified butadiene rubber)
NR: TSR
BR: BR130B manufactured by Ube Industries, Ltd. (content of 1,4-cis structure: 96 mol%)
Carbon black: N351 (N ₂ SA: 69 m ² / g) manufactured by Cabot Japan
Silica: Zeosil 1115MP manufactured by Rhodia (CTAB specific surface area: 105 m ² / g, N ₂ SA: 115 m ² / g, average primary particle size: 25 nm)
Silane coupling agent: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by Degussa
Aroma oil: Diana Process AH-24 manufactured by Idemitsu Kosan Co., Ltd.
Wax: Sunnock N manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Anti-aging agent: Antigen 6C (N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd.
Stearic acid: Zinc oxide manufactured by NOF Corporation: Zinc oxide manufactured by Mitsui Kinzoku Mining Co., Ltd. Sulfur: Powdered sulfur vulcanization accelerator manufactured by Karuizawa Sulfur Co., Ltd .: Ouchi Shinsei Chemical Industry Co., Ltd. Noxeller CZ (N-cyclohexyl-2-benzothiazolylsulfenamide)

Examples 1-4 and Comparative Examples 1-8
In accordance with the formulation shown in Table 2, using a 1.7 L Banbury mixer, chemicals other than sulfur and vulcanization accelerator were kneaded at 150 ° C. for 3 minutes to obtain a kneaded product. Next, sulfur and a vulcanization accelerator were added to the obtained kneaded material using an open roll, and kneaded at 50 ° C. for 5 minutes to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was press vulcanized at 150 ° C. for 30 minutes to prepare a vulcanized rubber composition.
Further, the unvulcanized rubber compositions of Examples 1 and 2 and Comparative Example 4 were formed into a tread shape and bonded together with other tire members to form an unvulcanized tire. A test tire (size 195 / 65R15) was manufactured by press vulcanizing the unvulcanized tire for 10 minutes at 170 ° C.

The following evaluation was performed about the obtained unvulcanized rubber composition, the vulcanized rubber composition, and the test tire. The results are shown in Table 2.

(Processability)
About the obtained unvulcanized rubber composition, the Mooney viscosity was measured at 130 degrees according to the Mooney viscosity measuring method based on JIS K6300. The Mooney viscosity (ML _{1 + 4} ) of Comparative Example 4 was set to 100, and indexed by the following formula (Mooney viscosity index). The larger the index, the lower the Mooney viscosity and the better the workability. In addition, it is excellent in productivity by manufacturing a pneumatic tire using the rubber composition excellent in workability in the said test.
(Munii viscosity index) = (ML _{1 + 4 of} Comparative Example 4) / (ML _{1 + 4} other than Comparative Example ₄ ) × 100

(Low fuel consumption (1) (rolling resistance))
Using a viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.), the loss tangent (tan δ) of each vulcanized rubber composition was measured under the conditions of a temperature of 70 ° C., an initial strain of 10%, a dynamic strain of 2%, and a frequency of 10 Hz. Measured, and the loss tangent of Comparative Example 4 was taken as 100 and expressed as an index according to the following formula (rolling resistance index). The larger the index, the better the rolling resistance characteristics (low fuel consumption). In addition, the pneumatic tire excellent in fuel-consumption property is obtained by producing a pneumatic tire using the rubber composition excellent in fuel-consumption property in the said test.
(Rolling resistance index) = (tan δ of Comparative Example 4) / (tan δ of other than Comparative Example 4) × 100

(Rubber strength)
Using the resulting vulcanized rubber composition, a No. 3 dumbbell-shaped rubber test piece was prepared and subjected to a tensile test in accordance with JIS K6251 “How to obtain one tensile property of vulcanized rubber and thermoplastic rubber”. TB) and elongation at break (EB) were measured, and the product (TB × EB) was calculated. The rubber strength (TB × EB) of each vulcanized rubber composition was indicated by an index according to the following calculation formula. In addition, it shows that it is excellent in rubber strength, so that a rubber strength index | exponent is large. In addition, the pneumatic tire excellent in rubber strength (breaking strength) is obtained by producing a pneumatic tire using the rubber composition excellent in rubber strength in the test.
(Rubber strength index) = (TB × EB other than Comparative Example 4) / (TB × EB of Comparative Example 4) × 100

(Abrasion resistance (1))
Using a LAT tester (Laboratory Abbreviation and Skid Tester), the volume loss of each vulcanized rubber composition was measured under the conditions of a load of 50 N, a speed of 20 km / h, and a slip angle of 5 °. The volume loss amount of Comparative Example 4 was taken as 100 and displayed as an index. In addition, it shows that it is excellent in abrasion resistance, so that an index | exponent is large. In addition, the pneumatic tire excellent in abrasion resistance is obtained by producing a pneumatic tire using the rubber composition excellent in abrasion resistance in the said test.
(Abrasion resistance index) = (Volume loss amount of Comparative Example 4) / (Volume loss amount other than Comparative Example 4) × 100

(Low fuel consumption (2) (rolling resistance))
Using a rolling resistance tester, each test tire is mounted on a regular rim (22.5 × 8.25 15 ° deep rim), and the rolling resistance is measured at an internal pressure of 700 kPa, a speed of 80 km / h, and a load of 24.52 KN. The tires of Comparative Example 4 are shown as an index when the tire is 100. The smaller the value, the smaller the rolling resistance and the better.

(Abrasion resistance (2))
Wear test tires on all wheels of a vehicle (domestic FF2000cc) and run on the test track. Measure the decrease in groove depth after running 30000 km, and determine the distance traveled when the groove depth decreases by 1 mm. Calculated. And the running distance of the comparative example 4 was set to 100, and the abrasion resistance of each formulation was displayed as an index by the following formula. It shows that it is excellent in abrasion resistance, so that an index | exponent is large.
(Abrasion resistance index) = (travel distance of each formulation) / (travel distance of Comparative Example 4) × 100

In an example in which a specific amount of each of a modified natural rubber having a phosphorus content of 200 ppm or less and a modified butadiene rubber obtained by hydrosilylating polybutadiene is used, processability, low heat generation (low fuel consumption), rubber strength, Excellent wear resistance.

From Example 1 and Comparative Examples 1, 3, and 4, the combined use of modified natural rubber and modified butadiene rubber synergistically improves processability, rubber strength, and wear resistance (particularly rubber strength). I understand that

In addition, by using HPNR, there is no need for mastication, so that the processability (productivity) is excellent, and the wear resistance and rubber strength are also excellent.

Claims (8)

Including a modified natural rubber having a phosphorus content of 200 ppm or less and a modified butadiene rubber;
The modified butadiene rubber is obtained by hydrosilylating polybutadiene,
The pneumatic tire produced using the rubber composition whose content of the said modified natural rubber in 100 mass% of rubber components is 60-95 mass%, and whose content of the said modified butadiene rubber is 5-40 mass%. The pneumatic tire according to claim 1, wherein the polybutadiene is a polybutadiene having a 1,4-cis structure content of 80 mol% or more and a 1,2-vinyl structure content of 20 mol% or less. The pneumatic tire according to claim 1 or 2, wherein the modified butadiene rubber is obtained by hydrosilylating polybutadiene with a silicon-containing compound. The pneumatic tire according to any one of claims 1 to 3, wherein a vinyl group of the polybutadiene is hydrosilylated in the hydrosilylation of the polybutadiene. The pneumatic tire according to claim 3, wherein the silicon-containing compound is a compound represented by the following general formula (1).

(In the formula (1), R ¹ represents a hydrocarbon group or a halogen group having 1 to 10 carbon atoms, and the hydrocarbon group, a hydroxyl group, an amino group, a halogen group, a mercapto group, an epoxy group, an ether group and, At least one group selected from the group consisting of a cyano group, or may have a nitrogen atom and may form a ring structure, and R ² may be the same or different and is a carbon atom having 1 to 10 carbon atoms. Represents a hydrogen group or a halogen group, and the hydrocarbon group may have at least one group selected from the group consisting of a hydroxyl group, an amino group, a halogen group, and an ether group, a nitrogen atom, or a silicon atom. A ring structure may be formed.) The modified natural rubber is obtained by saponifying natural rubber latex and washing the resulting saponified natural rubber latex until the phosphorus content in the rubber is 200 ppm or less. The pneumatic tire according to any one of 1 to 5. The pneumatic tire according to any one of claims 1 to 6, wherein the nitrogen content of the modified natural rubber is 0.3 mass% or less. The pneumatic tire according to any one of claims 1 to 7, wherein the modified natural rubber has a gel content measured as a toluene insoluble content of 20% by mass or less.