JP5587842B2 - Rubber composition for tire, method for producing the same, and pneumatic tire - Google Patents

Description

The present invention relates to a tire rubber composition, a method for producing the same, and a pneumatic tire using the rubber composition.

Conventionally, it has been attempted to reduce the fuel consumption of a vehicle by reducing the rolling resistance of the tire and suppressing heat generation, but in recent years, there has been an increasing demand for a reduction in fuel consumption.

Known methods for reducing the heat generation of rubber compositions used in tires include a method using a low-reinforcing filler and a method for reducing the amount of filler. In these methods, a rubber composition is used. The reinforcing property of the object is lowered, and the breaking performance (rubber strength) is lowered. Thus, it has been difficult to achieve both low fuel consumption and rubber strength.

On the other hand, natural rubber is widely used for tires, but natural rubber has higher Mooney viscosity and poor processability compared to other synthetic rubbers, so usually adding a chelating agent and masticating, Used after decreasing Mooney viscosity. Therefore, productivity is reduced when natural rubber is used. Moreover, since the molecular chain of natural rubber is cleaved by mastication, there is a problem that the characteristics (low fuel consumption, rubber strength, etc.) of the high molecular weight polymer originally possessed are lost.

As methods for improving the processability of natural rubber, Patent Documents 1 and 2 describe a method in which natural rubber latex is added with a proteolytic enzyme and a surfactant, and in Patent Document 3, solid natural rubber swollen with a solvent is added to water. In the method of immersing in alkali oxide, in Patent Document 4, the method of adding phosphate to natural rubber latex and removing magnesium phosphate is disclosed in Patent Document 5, and in Patent Document 5, the surfactant is added to natural rubber latex and washed. Each method is disclosed. However, there is still room for improvement in terms of achieving both low fuel consumption and rubber strength.

Japanese Patent Laid-Open No. 08-12814 JP 2005-82622 A Japanese Patent Laid-Open No. 11-12306 JP 2004-250546 A Japanese Patent No. 3294901

An object of the present invention is to solve the above-mentioned problems and provide a rubber composition for a tire that can achieve both low fuel consumption and rubber strength, a method for producing the same, and a pneumatic tire using the rubber composition.

The present invention includes a rubber component containing a modified natural rubber and isoprene rubber having a phosphorus content of 200 ppm or less, and carbon black and / or a white filler, and the content of the modified natural rubber in 100% by mass of the rubber component The present invention relates to a tire rubber composition having an amount of 5% by mass or more and a content of the isoprene rubber of 5% by mass or more.

The modified natural rubber preferably has a nitrogen content of 0.3% by mass or less and a gel content measured as a toluene insoluble content of 20% by mass or less. The modified natural rubber is preferably obtained by saponifying natural rubber latex.

The modified natural rubber is a step of saponifying natural rubber latex to prepare a saponified natural rubber latex (A), and a step of alkali treating the agglomerated rubber obtained by agglomerating the saponified natural rubber latex ( B) and the step (C) of washing until the phosphorus content contained in the rubber is 200 ppm or less are preferred.

The white filler is preferably silica.

The present invention also relates to a method for producing the rubber composition that does not include a step of masticating the modified natural rubber.
The present invention also relates to a pneumatic tire produced using the rubber composition.

The present invention includes a rubber component containing a modified natural rubber and isoprene rubber having a phosphorus content of 200 ppm or less, and carbon black and / or a white filler, and the content of the modified natural rubber and the content of isoprene rubber are respectively Since it is the predetermined amount of the rubber composition for tires and the manufacturing method thereof, a pneumatic tire excellent in fuel efficiency and rubber strength can be provided.

The rubber composition for tires of the present invention contains a rubber component containing a modified natural rubber and isoprene rubber having a phosphorus content of 200 ppm or less, and carbon black and / or a white filler.

By using a modified natural rubber with reduced or removed phospholipids in natural rubber (NR) and isoprene rubber (IR) in combination, the low heat build-up can be improved synergistically. The fuel efficiency can be sufficiently improved without reducing the fuel consumption. At the same time, the rubber strength can be increased synergistically, so that both performances can be remarkably improved.

Further, the modified natural rubber also removes the deterioration-preventing components in the NR during synthesis, and the rubber deteriorates quickly, resulting in inferior performance such as wear resistance. In the present invention, the above components are used. Therefore, wear resistance and deterioration resistance can be obtained well.

Furthermore, since the unvulcanized rubber composition containing the modified natural rubber is excellent in processability, it can be sufficiently kneaded without performing a special kneading step. For this reason, it is possible to suppress the deterioration of the properties of the natural rubber due to mastication, and the above performance can be effectively enhanced.

The modified natural rubber has a phosphorus content of 200 ppm or less. If it exceeds 200 ppm, tan δ will increase and fuel economy will deteriorate, and rubber strength and processability will tend to deteriorate. The phosphorus content is preferably 150 ppm or less, more preferably 100 ppm or less, and even more preferably 80 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, more preferably 0.15% by mass or less, and further preferably 0.1% 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, or the fuel efficiency tends to deteriorate. 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 5% by mass or less. If it exceeds 20% by mass, processability tends to deteriorate, fuel economy and rubber strength tend to deteriorate. 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 free of phospholipid” 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.

The modified natural rubber can be obtained, for example, by the production method described in JP 2010-138359 A. Among them, the process (A) of preparing a saponified natural rubber latex by saponifying the natural rubber latex, A production method comprising a step (B) of subjecting the agglomerated rubber obtained by agglomerating the saponified natural rubber latex to an alkali treatment and a step (C) of washing until the phosphorus content contained in the rubber is 200 ppm or less. What is prepared is preferred. By this manufacturing method, phosphorus content, nitrogen content, etc. can be reduced effectively. Further, by using the modified natural rubber obtained by the production method, the fuel efficiency and rubber strength can be remarkably improved, and these performances can be obtained at a high level. Moreover, since the remaining acid can be neutralized by alkali treatment when agglomerated with an acid, rubber deterioration due to the acid can be suppressed.

In the production method described above, the saponification treatment can be performed by adding an alkali and, if necessary, a surfactant to natural rubber latex and allowing to stand at a predetermined temperature for a certain time. In addition, you may perform stirring etc. as needed. According to the above production method, the phosphorus content and nitrogen content of natural rubber can be suppressed.

As the natural rubber latex, conventionally known latexes such as raw latex, purified latex, and high ammonia latex can be used. Examples of the alkali used for the saponification treatment include sodium hydroxide, potassium hydroxide, calcium hydroxide, and amine compounds, and sodium hydroxide and potassium hydroxide are particularly preferable. As the surfactant, known anionic surfactants, nonionic surfactants, and amphoteric surfactants can be used. Of these, anionic surfactants are preferred, and sulfonic acid anions are preferred. A surfactant is more preferable.

In the saponification treatment, the amount of alkali added may be set as appropriate, but is preferably 0.1 to 12 parts by mass with respect to 100 parts by mass of the solid content of the natural rubber latex. The addition amount of the surfactant is preferably 0.01 to 6.0 parts by mass with respect to 100 parts by mass of the solid content of the natural rubber latex. The temperature and time of the saponification treatment may be set as appropriate, and is usually about 20 to 70 ° C. and about 1 to 72 hours.

After completion of the saponification reaction, the agglomerated rubber obtained by agglomerating the saponified natural rubber latex obtained by the reaction is crushed as necessary, and then the obtained agglomerated rubber or crushed rubber is brought into contact with an alkali. Perform alkali treatment. By the alkali treatment, the nitrogen content in the rubber can be efficiently reduced, and the effects of the present invention are further exhibited. Examples of the aggregation method include a method of adding an acid such as formic acid. The alkali treatment method is not particularly limited as long as it is a method in which rubber and alkali are brought into contact with each other, and examples thereof include a method in which agglomerated rubber and crushed rubber are immersed in alkali. Examples of the alkali that can be used for the alkali treatment include potassium carbonate, sodium carbonate, sodium hydrogen carbonate, and aqueous ammonia in addition to the alkali in the saponification treatment. Of these, sodium carbonate is preferred from the viewpoint of excellent effects of the present invention.

When the alkali treatment is performed by the above immersion, the treatment can be performed by immersing rubber (crushed rubber) in an alkaline aqueous solution having a concentration of preferably 0.1 to 5 mass%, more preferably 0.2 to 3 mass%. Thereby, the nitrogen content in the rubber can be further reduced.

When the alkali treatment is performed by the immersion, the temperature of the alkali treatment can be set as appropriate, but is usually preferably 20 to 70 ° C. The alkali treatment time depends on the treatment temperature, but is preferably 1 to 20 hours, more preferably 2 to 12 hours, considering sufficient treatment and productivity.

Phosphorus content can be reduced by performing a washing treatment after the alkali treatment. Examples of the washing treatment include a method of diluting a rubber component with water and washing, followed by a centrifugal separation treatment, and a method of leaving the rubber to stand and discharging the aqueous phase and taking out the rubber component. When centrifuging, it is first diluted with water so that the rubber content of the natural rubber latex is 5 to 40% by mass, preferably 10 to 30% by mass. Then, it may be centrifuged at 5000 to 10000 rpm for 1 to 60 minutes, and washing may be repeated until a desired phosphorus content is obtained. In addition, when the rubber is allowed to stand still, the addition of water and stirring may be repeated until the desired phosphorus content is obtained. The modified natural rubber in the present invention is obtained by drying after completion of the washing treatment.

The content of the modified natural rubber in 100% by mass of the rubber component contained in the rubber composition of the present invention is 5% by mass or more, preferably 15% by mass or more, more preferably 25% by mass or more. If it is less than 5% by mass, fuel economy and rubber strength may not be sufficiently improved. The content is preferably 95% by mass or less, more preferably 85% by mass or less, and still more preferably 75% by mass or less. If it exceeds 95% by mass, the amount of isoprene rubber is relatively reduced, and the effects of the present invention may not be sufficiently obtained.

The IR is not particularly limited, and conventionally known ones can be used as appropriate. For example, those having a cis-1,4-bond content of 90% or more and a Mooney viscosity ML _{1 + 4} (100 ° C.) of 65 to 82 can be used.

In the rubber composition of the present invention, the IR content in 100% by mass of the rubber component is 5% by mass or more, preferably 15% by mass or more, and more preferably 25% by mass or more. If it is less than 5% by mass, the fuel economy may not be sufficiently improved. The content is preferably 95% by mass or less, more preferably 85% by mass or less, and still more preferably 75% by mass or less. If it exceeds 95% by mass, the amount of the modified natural rubber is relatively reduced, and the effects of the present invention may not be sufficiently obtained, and the rubber strength may be reduced.

The total content of the modified natural rubber and IR in 100% by mass of the rubber component is preferably 80% by mass or more, more preferably 90% by mass or more, and still more preferably from the viewpoint of sufficiently improving fuel economy and rubber strength. Is 100% by mass.

In addition to the modified natural rubber and IR, examples of rubber components that can be used in the present invention include natural rubber (NR), butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), and ethylene propylene. Examples include diene rubbers such as diene rubber (EPDM), chloroprene rubber (CR), and acrylonitrile butadiene rubber (NBR).

Examples of carbon black include GPF, FEF, HAF, ISAF, and SAF, but are not particularly limited. By blending carbon black, a reinforcing effect can be obtained and good rubber strength can be obtained.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 10 m ² / g or more, and more preferably 30 m ² / g or more. If it is less than 10 m < ² > / g, there is a possibility that sufficient reinforcing effect cannot be obtained and sufficient rubber strength cannot be obtained. Further, the nitrogen adsorption specific surface area of the carbon black is preferably 300 meters ² / g or less, more preferably ^{150m 2 / g, 60m 2 /} g or less is more preferable. When it exceeds 300 m ² / g, it becomes difficult to disperse well, and there is a tendency that sufficient low fuel consumption cannot be obtained.
Incidentally, _N 2 SA of carbon black is, JIS K6217-2: determined by 2001.

As white filler, those commonly used in the rubber industry, for example, mica such as silica, calcium carbonate, sericite, aluminum hydroxide, magnesium oxide, magnesium hydroxide, clay, talc, alumina, titanium oxide Etc. can be used. Among these, silica is preferable from the viewpoint that excellent fuel economy and rubber strength can be obtained.

Examples of the silica include, but are not limited to, dry process silica (anhydrous silicic acid), wet process silica (hydrous silicic acid), and wet process silica is preferable because of its large number of silanol groups.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 50 m ² / g or more, and more preferably 160 m ² / g or more. If it is less than 50 m ² / g, the reinforcing effect is small, and there is a possibility that sufficient rubber strength cannot be obtained. The _N 2 SA of the silica is preferably 300 meters ² / g or less, more preferably 190 m ² / g. If it exceeds 300 m ² / g, the dispersibility tends to decrease and the exothermicity tends to increase.
The nitrogen adsorption specific surface area of silica is a value measured by the BET method according to ASTM D3037-81.

In the present invention, it is preferable to use a silane coupling agent together with silica.
The silane coupling agent is not particularly limited, and those conventionally used in the tire field can be used. For example, sulfide-based, mercapto-based, vinyl-based, amino-based, glycidoxy-based, nitro-based, chloro-based silane coupling Agents and the like. Among them, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide, bis (2-triethoxysilylethyl) disulfide, etc. A sulfide system can be preferably used.

The content of the silane coupling agent is preferably 2 parts by mass or more and more preferably 4 parts by mass or more with respect to 100 parts by mass of silica. If it is less than 2 parts by mass, there is a possibility that the effect of improving the fuel economy by silica blending cannot be obtained sufficiently. The content is preferably 16 parts by mass or less, and more preferably 12 parts by mass or less. When the amount exceeds 16 parts by mass, there is a tendency that the effect of improving the fuel economy and rubber strength due to the silica compound cannot be sufficiently obtained.

The total content of carbon black and white filler is preferably 10 parts by mass or more, more preferably 30 parts by mass or more, and still more preferably 40 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 10 parts by mass, sufficient rubber strength may not be obtained. The total content is preferably 150 parts by mass or less, more preferably 100 parts by mass or less, and still more preferably 60 parts by mass or less. If it exceeds 150 parts by mass, processability may be deteriorated or sufficient fuel efficiency may not be obtained.

The content of carbon black is preferably 10 parts by mass or more, more preferably 30 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 10 parts by mass, sufficient rubber strength may not be obtained. The content is preferably 150 parts by mass or less, more preferably 60 parts by mass or less. If it exceeds 150 parts by mass, sufficient fuel economy may not be obtained.

The content of the white filler is preferably 5 parts by mass or more, more preferably 25 parts by mass or more with respect to 100 parts by mass of the rubber component. The content is preferably 100 parts by mass or less, more preferably 45 parts by mass or less. Within the above range, low fuel consumption and rubber strength can be obtained satisfactorily.

The content of silica is preferably 5 parts by mass or more, more preferably 25 parts by mass or more with respect to 100 parts by mass of the rubber component. If the amount is less than 5 parts by mass, the effect of improving the fuel efficiency by silica blending may not be sufficiently obtained. The content is preferably 100 parts by mass or less, more preferably 45 parts by mass or less. If it exceeds 100 parts by mass, the workability tends to decrease.

When the rubber composition of the present invention is applied to a truck / bus tire, the oil content is preferably 3 parts by mass or less, more preferably 1 part by mass or less, with respect to 100 parts by mass of the rubber component. It does not have to be included. Thereby, sufficient rubber strength is obtained and the effects of the present invention can be obtained satisfactorily.

In addition to the above components, the rubber composition of the present invention contains compounding agents generally used in the production of rubber compositions, such as zinc oxide, stearic acid, various anti-aging agents, vulcanizing agents such as sulfur, and vulcanization. An accelerator or the like can be appropriately blended.

The rubber composition of the present invention can be produced by a general method. That is, it can be produced by a method of kneading the above components with a Banbury mixer, kneader, open roll or the like and then vulcanizing. Here, when producing a rubber composition containing natural rubber, a natural rubber mastication step is usually performed before a kneading step of each component such as a rubber component and a filler. In the present invention, since the modified natural rubber is used, the kneading step can be carried out satisfactorily without performing the kneading step, and a desired rubber composition can be produced.

The rubber composition of the present invention can be suitably used for tire members such as treads (cap treads, base treads) and sidewalls.

The pneumatic tire of the present invention can be produced by a usual method using the rubber composition. That is, a rubber composition containing various additives as required is extruded according to the shape of each member of the tire at an unvulcanized stage, and molded by a normal method on a tire molding machine, After bonding together with other tire members to form an unvulcanized tire, the tire can be manufactured by heating and pressing in a vulcanizer.

The pneumatic tire of the present invention can be suitably used for passenger cars, trucks and buses, and is particularly suitable for trucks and buses.

The present invention will be specifically described based on examples, but the present invention is not limited to these examples.
The various chemicals used in the examples are described below.
Natural rubber latex: Field latex obtained from Muhibbah Lateks is used. Surfactant: Emal-E27C (polyoxyethylene lauryl ether sodium sulfate) manufactured by Kao Corporation
NaOH: NaOH manufactured by Wako Pure Chemical Industries, Ltd.
Saponified natural rubber A: Production Example 1 below
Saponified natural rubber B: Production Example 2 below
TSR: Natural rubber TSR
IR: Nippon IR2200 made by Nippon Zeon Co., Ltd.
Carbon black: Dia Black (N ₂ SA: 50 m ² / g) manufactured by Mitsubishi Chemical Corporation
Silica: ULTRASIL VN3 (N ₂ SA: 175 m ² / g) manufactured by EVONIK-DEGUSSA
Silane coupling agent: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by EVONIK-DEGUSSA
Zinc oxide: Zinc Hana No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: Stearic acid “Kashiwa” manufactured by NOF Corporation
Anti-aging agent: Nocrack 6C (N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine) manufactured by Ouchi Shinsei Chemical Co., Ltd.
Sulfur: Sulfur powder vulcanization accelerator (NS) manufactured by Tsurumi Chemical Industry Co., Ltd .: Noxeller NS (N-tert-butyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Vulcanization accelerator (DPG): Noxeller D manufactured by Ouchi Shinsei Chemical Co., Ltd.

(Production of saponified natural rubber)
Production Example 1
After adjusting solid content concentration (DRC) of natural rubber latex to 30% (w / v), 25 g of 10% Emal-E27C aqueous solution and 50 g of 40% NaOH aqueous solution are added to 1000 g of natural rubber latex (wet state), A saponification reaction was carried out at room temperature for 48 hours to obtain a saponified natural rubber latex. 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 for aggregation.
The agglomerated rubber is pulverized, dipped in a 1% aqueous sodium carbonate solution at room temperature for 5 hours, pulled up, washed repeatedly with 1000 ml of water, and then dried at 90 ° C. for 4 hours to obtain a solid rubber (saponified natural rubber A). Obtained.

Production Example 2
A solid rubber (saponified natural rubber B) was obtained in the same manner as in Production Example 1 except that the amount of the 40% NaOH aqueous solution was changed to 25 g.

The solid content (saponified natural rubber A, B) and TSR obtained in Production Examples 1 and 2 were measured for nitrogen content, phosphorus content, and gel content 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 sample was weighed, and an 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 of the sample was determined using an ICP emission spectrometer (ICPS-8100, manufactured by Shimadzu Corporation).
In addition, ³¹ P-NMR measurement of phosphorus uses an NMR analyzer (400 MHz, AV400M, manufactured by Nippon Bruker Co., Ltd.), and uses a measurement peak of P atom in an 80% aqueous phosphoric acid solution as a reference point (0 ppm), and raw rubber with chloroform. More extracted components were purified, dissolved in CDCl ₃ and measured.

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

As shown in Table 1, the saponified natural rubbers A and B had a reduced nitrogen content, phosphorus content, and gel content as compared with TSR.
In ³¹ P-NMR measurement, the saponified natural rubbers A and B did not have a peak due to phospholipid at -3 ppm to 1 ppm.

<Examples and Comparative Examples>
According to the formulation shown in Tables 2-3, chemicals other than sulfur and a vulcanization accelerator were kneaded using 1.7 L Banbury. Next, using a roll, sulfur and a vulcanization accelerator were added to the obtained kneaded product and kneaded to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was press vulcanized at 150 ° C. for 30 minutes to obtain a vulcanized product. In Comparative Example 3 using TSR, mastication was performed in advance.

The following evaluation was performed about the obtained unvulcanized rubber composition and vulcanizate. The results are shown in Tables 2-3.

(Rolling resistance)
Loss tangent (tan δ) of each compound (vulcanized product) 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 using a viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.) The loss tangent tan δ of Comparative Examples 1 and 4 was taken as 100, and the result was expressed as an index (rolling resistance index) by the following formula. The larger the index, the better the rolling resistance characteristics.
(Rolling resistance index) = (tan δ of Comparative Examples 1 and 4) / (tan δ of each formulation) × 100

(Rubber strength)
Using the resulting vulcanized rubber sheet, a No. 3 dumbbell-shaped rubber test piece was prepared, and subjected to a tensile test according to JIS K6251 “vulcanized rubber and thermoplastic rubber—How to obtain tensile properties”. TB) and elongation at break (EB) were measured, and the product (TB × EB) was calculated. The rubber strength (TB × EB) of each compound (vulcanized product) was indicated by an index according to the following formula. In addition, it shows that it is excellent in rubber strength, so that a rubber strength index is large.
(Rubber strength index) = (TB × EB of each formulation) / (TB × EB of Comparative Examples 1 and 4) × 100

(Mooney viscosity)
About the obtained unvulcanized rubber composition, it measured at 130 degreeC according to the measuring method of the Mooney viscosity based on JISK6300. The Mooney viscosity (ML _{1 + 4} ) of Comparative Examples 1 and ₄ was set to 100, and the index was expressed by the following formula (Mooney viscosity index). The larger the index, the lower the Mooney viscosity and the better the processability.
(Mooney viscosity index) = (ML _{1 + 4} of Comparative Examples 1 and ₄ ) / (ML _{1 + 4 of} each formulation) × 100

In the examples using modified natural rubber (saponified natural rubbers A and B) and IR, the fuel efficiency and rubber strength were synergistically improved. On the other hand, in the comparative example using only the modified natural rubber and only IR, these performances were inferior. Even in the comparative example using both TSR and IR, these performances were inferior.
Moreover, although the example using saponified natural rubber was not masticated, the processability was superior to the comparative example using masticated TSR (for example, Example 1 and Comparative Example 3). ).

Claims (8)

A rubber component including a modified natural rubber and isoprene rubber having a phosphorus content of 200 ppm or less and carbon black and / or a white filler;
Wherein and the content of the modified natural rubber 100% by mass of the rubber component is 5 wt% or more state, and are content not less than 5 wt% of the isoprene rubber, the total of the modified natural rubber and the isoprene rubber tire rubber composition content of Ru der least 80 wt%. The tire rubber composition according to claim 1, wherein the nitrogen content of the modified natural rubber is 0.3 mass% or less and the gel content measured as a toluene insoluble content is 20 mass% or less. The rubber composition for a tire according to claim 1 or 2, wherein the modified natural rubber is obtained by saponifying natural rubber latex. The modified natural rubber is a step of saponifying natural rubber latex to prepare a saponified natural rubber latex (A), and a step of alkali treating the agglomerated rubber obtained by agglomerating the saponified natural rubber latex ( The tire rubber composition according to any one of claims 1 to 3, wherein the rubber composition is obtained by performing B) and a step (C) of washing until the phosphorus content contained in the rubber is 200 ppm or less. The tire rubber composition according to any one of claims 1 to 4, wherein the white filler is silica. The silica has a nitrogen adsorption specific surface area of 160 to 300 m. ² The tire rubber composition according to claim 5, which is / g. A step of saponifying natural rubber latex to prepare a saponified natural rubber latex, a step of alkali-treating the agglomerated rubber obtained by agglomerating the saponified natural rubber latex, and a phosphorus content contained in the rubber The rubber composition for tires according to any one of claims 1 to 6 , comprising a step of washing until the water content becomes 200 ppm or less to obtain a modified natural rubber, and a step of kneading the obtained modified natural rubber . Production method. The pneumatic tire produced using the rubber composition in any one of Claims 1-6 .