JP5992759B2 - Tire rubber composition and heavy duty tire - Google Patents

Description

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

In recent years, there has been a strong demand for lower fuel consumption due to soaring fuel costs and the introduction of environmental regulations, and excellent low fuel consumption, especially for treads that have a high occupation ratio among tire components. Sex is required.

As a technology for imparting low fuel consumption to tires, particularly heavy duty tires used in trucks and buses, etc., silica is used as a filler in tire rubber compositions, and proteins and gels contained in natural rubber as polymers, Although it is known to use modified natural rubber (HPNR) from which phospholipids have been reduced and removed, a combination of HPNR and silica has a problem that wear resistance deteriorates.

In order to solve this problem, it has been disclosed that both low fuel consumption and wear resistance can be achieved by blending a modified butadiene rubber (modified BR) (see Patent Document 1). However, a rubber composition containing HPNR, modified BR, and silica deteriorates grip performance regardless of whether it is dry or wet. Therefore, a technique for improving the above performance is required.

JP 2011-195639 A

The present invention provides a tire rubber composition that solves the above-mentioned problems and improves the fuel economy, wear resistance, wet grip performance, and dry grip performance in a well-balanced manner, and a heavy duty tire produced using the rubber composition. With the goal.

The present invention includes a rubber component and silica, and the rubber component includes a modified natural rubber having a phosphorus content of 200 ppm or less and a modified butadiene rubber, and the modified natural rubber is contained in 100% by mass of the rubber component. In the silica, the content of the modified butadiene rubber is 5 to 40% by mass, and the silica has three or more particles adjacent to one particle as branched particles A. when, branched particles are those average length _{L 1} of the branch intergranular a-a containing a is 30～400Nm, tires content of the silica to 100 parts by mass of the rubber component is 5 to 150 parts by weight Rubber composition.

The modified natural rubber preferably has a nitrogen content of 0.3% by mass or less.
The modified natural rubber is preferably obtained by saponifying natural rubber latex.

（式中、Ｒ^１、Ｒ^２及びＲ^３は、同一若しくは異なって、アルキル基、アルコキシ基、シリルオキシ基、アセタール基、カルボキシル基、メルカプト基又はこれらの誘導体を表す。Ｒ^４及びＲ^５は、同一若しくは異なって、水素原子、アルキル基又は環状エーテル基を表す。ｎは整数を表す。） The modified butadiene rubber is preferably a butadiene rubber modified with a compound represented by the following formula (1).

(Wherein R ¹ , R ² and R ³ are the same or different and each represents an alkyl group, an alkoxy group, a silyloxy group, an acetal group, a carboxyl group, a mercapto group or a derivative thereof. R ⁴ and R ⁵ are (The same or different and represents a hydrogen atom, an alkyl group or a cyclic ether group. N represents an integer.)

The rubber composition is preferably used for a tread.
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 specific amount of a specific modified natural rubber, a modified butadiene rubber, and a specific shape of silica, low fuel consumption, wear resistance, wet grip performance, and dry grip Performance can be improved in a well-balanced manner.

FIG. 2 is a schematic diagram illustrating a branched particle A. Average primary particle diameter D of the silica is a schematic diagram of the average length L ₁ of the branch intergranular A-A containing the branched particles A.

The rubber composition for tires of the present invention contains a predetermined amount of modified natural rubber, modified butadiene rubber, and silica having a specific shape with a reduced amount of phosphorus.

Although the use of modified natural rubber and modified butadiene rubber with a phosphorus content of 200 ppm or less as the rubber component of silica compounded rubber can achieve both low fuel consumption and wear resistance, grip performance of wet grip and dry grip performance Will get worse. With regard to this point, in the present invention, by using a structure silica having a specific shape as silica, the adverse grip performance is improved in both wet and dry environments without affecting fuel efficiency and wear resistance. Is demonstrated.

In particular, the silica dispersibility is significantly more pronounced when blended with modified natural rubber and modified butadiene rubber with a phosphorus content of 200 ppm or less than when blended with specific natural structure rubber and modified butadiene rubber. It improves and efficiently improves fuel efficiency, wear resistance, wet grip performance, and dry grip performance, and synergistically improves these performance balances.

In the rubber composition, the rubber component contains a predetermined amount of modified natural rubber (HPNR) and modified butadiene rubber (modified BR) having a phosphorus content of 200 ppm or less from the viewpoint that both low fuel consumption and wear resistance can be achieved.

Natural rubber (modified natural rubber) from which phospholipids contained in natural rubber (NR) have been reduced and removed (modified natural rubber, preferably from which protein and gel content have also been removed) has the property of not generating heat. Compared with the use of, further reduction in fuel consumption can be achieved. In addition, the unvulcanized rubber composition containing the modified natural rubber is excellent in processability and can be sufficiently kneaded without performing a special mastication process. Can be suppressed, and fuel efficiency, breaking strength, etc. can be effectively enhanced.

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. There is a possibility that low fuel consumption, workability, and wear resistance cannot be improved in a well-balanced manner. 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, processability, and wear resistance cannot be improved in a well-balanced manner. 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 further 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 there is a possibility that the fuel economy, processability and wear resistance cannot be improved in a well-balanced manner. 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, a step of saponifying natural rubber latex to obtain a saponified natural rubber latex and the obtained saponified natural product Examples thereof include a production method including a step of washing the rubber latex until the phosphorus content contained 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.

The content of the modified natural rubber in 100% by mass of the rubber component is 60% by mass or more, preferably 65% by mass or more, and more preferably 68% by mass or more. If the amount is less than 60% by mass, the fuel economy and wear resistance may not be improved in a well-balanced manner. The content of the modified natural rubber is 95% by mass or less, preferably 92% by mass or less, more preferably 90% by mass or less. If it exceeds 95% by mass, the content of the modified BR tends to decrease, and the wear resistance tends to deteriorate.

The modified BR is not particularly limited, and may be a BR in which either the main chain or the terminal is modified, or a BR in which both are modified. Examples of the modifying group include a nitrogen-containing group having interaction or reactivity with silica.

（式中、Ｒ^１、Ｒ^２及びＲ^３は、同一若しくは異なって、アルキル基、アルコキシ基（好ましくは炭素数１〜８、より好ましくは炭素数１〜６、さらに好ましくは炭素数１〜４のアルコキシ基）、シリルオキシ基、アセタール基、カルボキシル基（−ＣＯＯＨ）、メルカプト基（−ＳＨ）又はこれらの誘導体を表す。Ｒ^４及びＲ^５は、同一若しくは異なって、水素原子又はアルキル基（好ましくは炭素数１〜４のアルキル基）を表す。ｎは整数（好ましくは１〜５、より好ましくは２〜４、さらに好ましくは３）を表す。） One suitable example of the modified BR is butadiene rubber (S-modified BR) modified with a compound represented by the following formula (1). S-modified BR has a high effect of improving the dispersibility of the filler, and can particularly promote the dispersion of silica.

(In formula, R < ¹ >, R < ² > and R < ³ > are the same or different and are an alkyl group and an alkoxy group (preferably C1-C8, More preferably C1-C6, More preferably C1-C4 An alkoxy group), a silyloxy group, an acetal group, a carboxyl group (—COOH), a mercapto group (—SH), or a derivative thereof, and R ⁴ and R ⁵ are the same or different and represent a hydrogen atom or an alkyl group (preferably Represents an alkyl group having 1 to 4 carbon atoms, and n represents an integer (preferably 1 to 5, more preferably 2 to 4, more preferably 3).

As R ¹ , R ² and R ³ , an alkoxy group is desirable, and as R ⁴ and R ⁵ , an alkyl group is desirable. Thereby, low fuel consumption and wear resistance can be obtained.

Specific examples of the compound represented by the above formula (1) include 3-aminopropyldimethylmethoxysilane, 3-aminopropylmethyldimethoxysilane, 2-dimethylaminoethyltrimethoxysilane, 3-diethylaminopropyltrimethoxysilane, 3 -Dimethylaminopropyltrimethoxysilane etc. are mentioned. These may be used alone or in combination of two or more.

The vinyl content of the modified BR is preferably 35% by mass or less, more preferably 25% by mass or less, and further preferably 20% by mass or less. If the vinyl content exceeds 35% by mass, fuel efficiency may be reduced. Although the minimum of the said vinyl content is not specifically limited, 1 mass% or more, 5 mass% or more, 10 mass% or more may be sufficient. If it is less than 1% by mass, heat resistance and deterioration resistance may be lowered. The vinyl content (1,2-bond butadiene unit amount) can be measured by infrared absorption spectrum analysis.

Methods for modifying BR 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. A conventionally known method such as the above method can be used. For example, BR may be brought into contact with a modifying agent. After synthesizing BR by anionic polymerization, a predetermined amount of a modifying agent is added to the polymer rubber solution, and a polymerization terminal (active terminal) of BR and a modifying agent are added. And a method of reacting by adding a denaturing agent to the BR solution.

The 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 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 40% by mass or less, preferably 35% by mass or less, more preferably 32% by mass or less. When it exceeds 40% by mass, the HPNR content is decreased, and the rubber strength may be insufficient.

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, the fuel efficiency and wear resistance may not be sufficiently improved.

Other rubber components that can be used in the rubber composition of the present invention include natural rubber (NR), isoprene rubber (IR), styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), chloroprene rubber (CR), butyl rubber. (IIR) and the like.

The silica used in the present invention has three or more particles (hereinafter referred to as branched particles A) adjacent to one particle (hereinafter referred to as structure silica). The structure of the particle in contact with the branched particle A is called a branched structure. The branched particle A is a particle A among the particles in FIG. 1, which is a schematic explanatory view of a branched particle, and is in contact with three or more other particles. The structure silica includes those having a branched structure (for example, FIG. 2) and those having no branched structure. However, the structure silica having no branched structure is agglomerated immediately and is therefore substantially absent. .

The average length (L ₁ in FIG. 2) between the branched particles AA including the branched particles A of structure silica is 30 nm or more, preferably 40 nm or more. If it is less than 30 nm, the grip performance tends not to be sufficiently improved. L ₁ is 400 nm or less, preferably 200 nm or less, more preferably 100 nm or less. When it exceeds 400 nm, local distortion occurs in the rubber, the rubber strength decreases, and the wear resistance tends to deteriorate.

The average primary particle size of the structure silica (D, see FIG. 2 which is a schematic explanatory diagram of structure silica containing branched particles) is preferably 5 nm or more, more preferably 7 nm or more. If the thickness is less than 5 nm, local distortion occurs in the rubber, the rubber strength decreases, and the wear resistance tends to deteriorate. Further, D is preferably 1000 nm or less, more preferably 800 nm or less. If it exceeds 1000 nm, the grip performance tends not to be sufficiently improved.

The average aspect ratio (L ₁ / D) between the branched particles AA including the branched particles A of the structure silica is preferably 3 or more, more preferably 4 or more. If it is less than 3, there is a tendency that the grip performance cannot be sufficiently improved. L ₁ / D is preferably 100 or less, more preferably 30 or less. When L ₁ / D exceeds 100, local distortion occurs in the rubber, the rubber strength is lowered, and the wear resistance tends to deteriorate.

In the present invention, D, L ₁ and L ₁ / D of silica can be measured by observation with a transmission electron microscope of silica dispersed in a vulcanized rubber composition. For example, in FIG. 2, when the particle is a true sphere, L ₁ / D is 5.

The content of the structure silica is 5 parts by mass or more, preferably 10 parts by mass or more, more preferably 12 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 5 parts by mass, there is a tendency that a sufficient improvement effect of rolling resistance, wet grip performance and dry grip performance due to inclusion of structure silica cannot be obtained. Moreover, content of structure silica is 150 mass parts or less, Preferably it is 60 mass parts or less, More preferably, it is 45 mass parts or less, More preferably, it is 35 mass parts or less. When it exceeds 150 parts by mass, the rigidity of the rubber composition increases, and the workability and wet grip performance tend to deteriorate.

The structure silica is preferably used in combination with a silane coupling agent. The silane coupling agent is not particularly limited, and those conventionally used in combination with silica in the tire industry can be used. For example, bis (3-triethoxysilylpropyl) polysulfide, bis (2-triethoxysilylethyl) ) Polysulfide, bis (3-trimethoxysilylpropyl) polysulfide, bis (2-trimethoxysilylethyl) polysulfide, bis (4-triethoxysilylbutyl) polysulfide, bis (4-trimethoxysilylbutyl) polysulfide and the like. . These silane coupling agents may be used alone or in combination of two or more. Of these, bis (3-triethoxysilylpropyl) disulfide is preferably used because of the addition effect of the silane coupling agent and the cost.

The content of the silane coupling agent is preferably 1 part by mass or more, more preferably 2 parts by mass or more with respect to 100 parts by mass of the structure silica. If it is less than 1 part by mass, the effect of coupling with silica is small, so the rubber strength tends to decrease and the wear resistance tends to deteriorate. Further, the content of the silane coupling agent is preferably 20 parts by mass or less, more preferably 15 parts by mass or less. When it exceeds 20 parts by mass, there is a tendency that an effect commensurate with the increase in cost cannot be obtained.

In the rubber composition, in addition to the above components, compounding agents conventionally used in the rubber industry, for example, fillers such as carbon black, oils or plasticizers, antioxidants, anti-aging agents, zinc oxide, sulfur, You may contain vulcanizing agents, such as a sulfur-containing compound, a vulcanization accelerator, etc.

The rubber composition of the present invention preferably contains carbon black. Examples of carbon black that can be used include GPF, FEF, HAF, ISAF, and SAF, but are not particularly limited. By adding carbon black, the reinforcing property is enhanced, and the effect of the present invention can be obtained satisfactorily by using it together with HPNR, modified BR and structure silica.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 20 m ² / g or more, more preferably 70 m ² / g or more, and still more preferably 100 m ² / g or more. If it is less than 20 m < ² > / g, there exists a possibility that sufficient reinforcement may not be acquired. Further, the nitrogen adsorption specific surface area of the carbon black is preferably 200 meters ² / g or less, more preferably 150m ² / g. 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.

The content of carbon black is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and still more preferably 12 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 5 mass parts, there exists a possibility that reinforcing property cannot fully be improved. The carbon black content is preferably 100 parts by mass or less, more preferably 70 parts by mass or less, and still more preferably 50 parts by mass or less. When it exceeds 100 parts by mass, it tends to be difficult to disperse carbon black well. Moreover, there exists a tendency for workability to fall.

The content of carbon black in the total 100 mass% of the structure silica and carbon black is preferably 40 mass% or more, more preferably 60 mass% or more, preferably 90 mass% or less, from the viewpoint of the performance balance. More preferably, it is 80 mass% or less.

The rubber composition of the present invention is produced by a general method, and can be produced by, for example, a method of kneading the above components with a kneader such as a Banbury mixer, a kneader, or an open roll, and then vulcanizing.

In particular, the silica sol is preferably kneaded with a rubber kneading apparatus together with the rubber component and the like from the viewpoint that the rubber composition of the present invention in which structure silica is formed can be easily produced.
(I) The above rubber component, silica sol, and carbon black, silane coupling agent, zinc oxide, stearic acid, softener, anti-aging agent, wax, etc., as necessary, at 80 to 180 ° C. (preferably 90 to 170). A base kneading step of kneading for 3 to 10 minutes at
(II) a final kneading step of kneading the kneaded material obtained by the base kneading step, the vulcanizing agent, and the vulcanization accelerator at 30 to 100 ° C. (preferably 40 to 85 ° C.) for 3 to 10 minutes;
(III) A production method including a vulcanization step of vulcanizing the unvulcanized rubber composition obtained by the finish kneading step at 150 to 190 ° C. (preferably 160 to 180 ° C.) for 5 to 30 minutes is more preferable.

The preferable content of silica sol (in terms of silica) is the same as that of the above-described structure silica.

In the kneading step of forming a structure silica (such as the base kneading step), when kneading the respective components in toluene is a good solvent for rubber, for L ₁ of structure silica tends to likely too long, toluene It is preferable to knead without using.

In this specification, silica sol refers to a colloidal solution in which silica is dispersed in a solvent. The silica sol is not particularly limited, but a colloidal solution in which elongated silica is dispersed in a solvent is preferable because a structure silica can be suitably formed. A colloidal solution in which elongated silica is dispersed in an organic solvent (organo Silica sol) is more preferable. Here, the long and narrow silica means a silica (secondary particle) having a chain shape in which a plurality of primary particles such as a spherical shape and a granular shape are connected. It may be linear or branched.

The solvent for dispersing silica is not particularly limited, but alcohols such as methanol and isopropanol are preferable, and isopropanol is more preferable.

The average particle size of the primary particles was determined by visually measuring the particle size (average diameter) of 50 primary particles in a photograph taken with a transmission electron microscope JEM2100FX manufactured by JEOL Ltd. The diameter.

In addition, the average diameter of a primary particle is an average value of the thickness (diameter) measured in arbitrary 50 places of a silica (secondary particle) in an electron micrograph, when a silica (secondary particle) is elongated shape. In the case where the silica (secondary particles) is a bead with a constriction, it can be obtained as an average value of the diameters of the 50 bead in the electron micrograph. When each rosary has a major axis and a minor axis, that is, when each rosary is elongated, the minor axis is measured.

The average particle diameter of silica (secondary particles) contained in the silica sol is preferably 20 to 300 nm, more preferably 30 to 150 nm. The average particle diameter of silica (secondary particles) can be measured by a dynamic light scattering method, and specifically, can be measured by the following method.
The average particle diameter of silica (secondary particles) was measured with a laser particle analysis system ELS-8000 (cumulant analysis) manufactured by Otsuka Electronics Co., Ltd. The measurement conditions are a temperature of 25 ° C., an angle between incident light and a detector of 90 °, and an integration count of 100. The refractive index of water (1.333) is input as the refractive index of the dispersion solvent. The measurement concentration was usually about 5 × 10 ⁻³ mass%.

The silica (secondary particles) is, for example, the method described in claim 2 of the pamphlet of International Publication No. WO 00/15552 and the disclosure of the specification related thereto, Japanese Patent No. 2803134, Japanese Patent No. 2926915. It can be produced according to the method described in claim 2 of the publication and the disclosure part of the specification relating thereto.

Specific examples of the silica (secondary particles) that can be used in the present invention include “Snowtex-OUP” (average secondary particle size: 40 to 100 nm) manufactured by Nissan Chemical Industries, Ltd. "Tex-UP" (average secondary particle size: 40 to 100 nm), "Snowtex PS-M" (average secondary particle size: 80 to 150 nm), "Snowtex PS-MO" (average secondary particle size) : 80-150 nm), "Snowtex PS-S" (average secondary particle size: 80-120 nm), "Snowtex PS-SO" (average secondary particle size: 80-120 nm), "IPA-ST -UP "(average secondary particle size: 40 to 100 nm)," Quatron PL-7 "(average secondary particle size: 130 nm) manufactured by Fuso Chemical Industry Co., Ltd., and the like. Among these, IPA-ST-UP is preferable because it can form the structure silica suitably.

The rubber composition of the present invention is suitably used as a tread (cap tread) for heavy duty tires (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 the production examples will be described.
Natural rubber latex: Field latex surfactant obtained from Taitex Co., Ltd .: Emal-E manufactured by Kao Corporation
NaOH: NaOH manufactured by Wako Pure Chemical Industries, Ltd.

(Production Example 1 Preparation of saponified natural rubber with alkali)
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 (HPNR) 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 modified 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 (mass%) was determined by the following formula.
Gel content (mass%) = [mass mg after drying / mg of initial sample] × 100

As shown in Table 1, the saponification natural rubber (HPNR) had a reduced nitrogen content, phosphorus content, and gel content as compared with TSR. Further, in ³¹ P-NMR measurement, HPNR showed no peak due to phospholipid at -3 ppm to 1 ppm.

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
NR: TSR
HPNR (saponified natural rubber): Production Example 1
Non-modified BR: Nipol BR1220 (vinyl content: 1% by mass) manufactured by Nippon Zeon Co., Ltd.
Modified BR: Modified butadiene rubber manufactured by Sumitomo Chemical Co., Ltd. (S-modified BR (terminal modified), vinyl content: 15% by mass, R ¹ , R ² and R ³ = —OCH ₃ , R ⁴ and R ⁵ = —CH ₂ CH ₃ , n = 3, see the above formula (1))
Carbon Black: Show Black N220 (N ₂ SA: 111 m ² / g) manufactured by Cabot Japan
Silica A: Organosilica sol IPA-ST-UP manufactured by Nissan Chemical Industries, Ltd. (Elongated isopropanol-dispersed silica sol (average particle diameter of silica (secondary particles) measured by dynamic light scattering method: 40 to 100 nm)) Silica content: 15% by mass) (The amounts shown in Table 2 indicate the amount of silica in the organosilica sol.)
Silica B: Ultrasil VN3-G (N ₂ SA: 175 m ² / g) manufactured by Degussa
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: Zinc Hua 2 types manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: Powdered sulfur vulcanization accelerator manufactured by Tsurumi Chemical Co., Ltd .: Noxeller NS manufactured by Ouchi Shinsei Chemical Co., Ltd.

<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 the obtained vulcanized rubber composition, and the results are shown in Table 2.

(Average primary particle diameter, average length and average aspect ratio of silica)
The silica dispersed in the obtained vulcanized rubber composition was observed with a transmission electron microscope, and the average primary particle diameter (D) of silica and the average length of AA between the branched particles including the branched particles A (FIG. 2). L ₁ ), and the average aspect ratio (L ₁ / D) of AA between the branched particles including the branched particle A was measured and calculated. In addition, the numerical value was taken as the average value measured in arbitrary 50 places.

(Rubber heat generation performance index)
Using a viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.), tan δ of each vulcanized rubber composition 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 1 was set to 100, and the index was expressed by the following calculation formula. The smaller the index, the lower the heat generation and the higher the fuel efficiency.
(Rubber exothermic performance index) = (tan δ of each formulation) / (tan δ of Comparative Example 1) × 100

(Abrasion resistance index)
A test piece (vulcanized rubber composition) with a surface rotation speed of 50 m / min, a load load of 3.0 kg, and a slip rate of 15 g / min and a slip rate of 20% using a lambon abrasion tester manufactured by Iwamoto Seisakusho Co., Ltd. The wear amount of the product was measured. The reciprocal of the amount of wear was taken and indexed with Comparative Example 1 as 100. It shows that it is excellent in abrasion resistance, so that an abrasion index is large.

(Wet grip performance)
A rubber test piece molded into a cylindrical shape having a width of 20 mm and a diameter of 100 mm was prepared from the prepared vulcanized rubber composition, and the speed was measured using a flat belt friction tester (FR5010 type) manufactured by Ueshima Seisakusho Co., Ltd. Under the conditions of 20 km / h, load 4 kgf, outside air temperature 30 ° C., water temperature 25 ° C., the slip ratio of the sample with respect to the wet road surface was changed from 0 to 70%, and the maximum value of the friction coefficient detected at that time was read. . The maximum friction coefficient of Comparative Example 1 was set to 100, and the index was expressed by the following calculation formula. The larger the wet grip index, the better the wet grip performance.
(Wet grip index) = (Maximum friction coefficient of each formulation) / (Maximum friction coefficient of Comparative Example 1) × 100

(Dry grip performance)
A rubber test piece molded into a cylindrical shape having a width of 20 mm and a diameter of 100 mm was prepared from the prepared vulcanized rubber composition, and the speed was measured using a flat belt friction tester (FR5010 type) manufactured by Ueshima Seisakusho Co., Ltd. Under the conditions of 20 km / h, a load of 4 kgf, and an outside air temperature of 30 ° C., the slip ratio of the sample with respect to the dry road surface was changed from 0 to 50%, and the maximum value of the friction coefficient detected at that time was read. The maximum friction coefficient of Comparative Example 1 was set to 100, and the index was expressed by the following calculation formula. The larger the dry grip index, the better the dry grip performance.
(Dry grip index) = (Maximum friction coefficient of each formulation) / (Maximum friction coefficient of Comparative Example 1) × 100

In Comparative Examples 2 to 4 in which modified natural rubber (HPNR) and non-modified BR or modified BR are used as rubber components, compared with Comparative Example 1 in which NR, non-modified BR and carbon black are blended, low fuel consumption, All of the wear resistance, wet grip performance and dry grip performance could not be improved at the same time. On the other hand, in the example using the structure silica (silica A) as the silica of the blend containing the modified natural rubber and the modified BR, it became clear that all the performances were improved and the performance balance could be improved synergistically. .

In particular, as shown in Comparative Example 5, Example 1 and the like, the performance balance is more efficient when blended with HPNR and modified BR than when structured silica is blended with NR and modified BR. It was improved and the synergistic effect was remarkably exhibited.

A: It is called a branched particle, and means a particle having three or more particles adjacent to one particle.
D: Average primary particle diameter L ₁ : Average length of AA between branched particles including branched particles A

Claims (5)

Containing a rubber component and silica,
The rubber component includes a modified natural rubber having a phosphorus content of 200 ppm or less, and a modified butadiene rubber,
In 100% by mass of the rubber component, the content of the modified natural rubber is 60 to 95% by mass, and the content of the modified butadiene rubber is 5 to 40% by mass,
The silica is intended when the above adjacent particles are three particles branched particles A with respect to one particle, the average length L ₁ of the branch intergranular A-A containing the branched particles A of 30~400nm Yes,
A rubber composition for tires, wherein the silica content is 5 to 150 parts by mass with respect to 100 parts by mass of the rubber component. The tire rubber composition according to claim 1, wherein the modified natural rubber has a nitrogen content of 0.3 mass% or less. The modified butadiene rubber, tire rubber composition according to claim 1 or 2 is a butadiene rubber terminally modified by a compound represented by the following formula (1).

^(Wherein, R 1, ^{R 2} and ^{R 3} are the same or different, are .R ⁴ and ^{R 5} represents an an alkoxy group, the same or different, .n representing the A alkyl group represents an integer.) The rubber composition for tires according to any one of claims 1 to 3 , which is used for a tread. Heavy duty tire having a tread produced from the rubber composition according to any one of claims 1-4.

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