JP2011190409A - Rubber composition for breaker topping and pneumatic tire using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for a breaker topping that achieves both rolling resistance performance and breaking strength while having good processability, and a pneumatic tire using the same. <P>SOLUTION: The rubber composition for a breaker topping includes a rubber component, carbon black and/or silica, wherein the rubber component includes modified natural rubber having a phosphorus content of 200 ppm or less, and a content of the modified natural rubber in the 100 mass% of the rubber component is 30 mass% or more. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a rubber composition for breaker topping and a pneumatic tire using the same.

In recent automobile society, tires are required to have wear resistance and low rolling resistance (LRR) performance, and various measures have been taken. On the other hand, if the wear resistance performance of the tire is improved, the period of use in the market becomes longer, so there is a concern about durability performance due to internal damage of the tire. A typical example of internal damage is breaker edge damage (BEL: BRAKER EDGELOOSENS), and various causes of BEL are known, one of which is due to a decrease in the breaking strength of the breaker topping rubber. There is.

As a technique for improving the breaking strength of a rubber composition for breaker topping, it is conventionally known to increase the amount of filler such as carbon black. However, in this method, the heat generation performance of the rubber is deteriorated and the rolling resistance performance is disadvantageous. Therefore, it is necessary to improve the breaking strength of the rubber without deteriorating the rolling resistance performance.

On the other hand, natural rubber is widely used as a rubber component for the breaker topping rubber. However, when RSS # 3 having relatively good breaking strength and rolling resistance is used, the Mooney viscosity of the unvulcanized rubber composition containing the same is used. Increases the workability. Moreover, when TSR20 is used as a natural rubber, the Mooney viscosity is lowered, but the rubber strength and low heat build-up are deteriorated. Thus, it has been difficult to improve workability, rolling resistance performance and breaking strength in a well-balanced manner.

Patent Document 1 discloses a rubber composition for cord coating containing natural rubber, carbon black and the like. However, since natural rubber such as RSS # 3 is blended and is inferior in processability, there is still room for study on improving the processability, rolling resistance performance and breaking strength at the same time.

JP 2008-69199 A

An object of the present invention is to solve the above-mentioned problems and to provide a rubber composition for a breaker topping in which workability, rolling resistance performance and breaking strength are improved in a well-balanced manner, and a pneumatic tire using the same.

The present invention includes a rubber component and carbon black and / or silica, and the rubber component includes a modified natural rubber having a phosphorus content of 200 ppm or less, and the modified natural rubber in 100% by mass of the rubber component. It is related with the rubber composition for breaker topping whose content of is 30 mass% or more.

The nitrogen content of the modified natural rubber is preferably 0.3% by mass or less. Moreover, it is preferable that the gel content rate measured as a toluene insoluble content of the said modified natural rubber is 20 mass% or less. Furthermore, the modified natural rubber is preferably obtained by saponifying natural rubber latex.

The rubber composition preferably further contains zinc oxide, sulfur and organic acid cobalt.
The present invention also relates to a pneumatic tire having a breaker manufactured using the rubber composition.

According to the present invention, since it is a rubber composition for breaker topping in which carbon black and / or silica is blended with a rubber component containing a predetermined amount of a modified natural rubber having a phosphorus content of 200 ppm or less, processability, rolling Resistance performance and breaking strength can be improved in a well-balanced manner.

The rubber composition for breaker toppings of the present invention contains a rubber component containing a predetermined amount of a modified natural rubber (hereinafter also referred to as HPNR) having a phosphorus content of 200 ppm or less, and carbon black and / or silica. In the present invention, the modified natural rubber (HPNR) in which the protein, gel, and phospholipid contained in the natural rubber (NR) are reduced and removed is used. High rubber strength and breaking strength can be obtained without increasing the amount of silica. For this reason, both low exothermic property and breaking strength can be satisfactorily achieved. In addition, because HPNR is used as a rubber component containing carbon black and silica, the increase in Mooney viscosity of the unvulcanized rubber composition is suppressed, and the processability is excellent. Strength can be improved in a well-balanced manner.

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

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

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

The gel content in the modified natural rubber is preferably 20% by mass or less, more preferably 15% by mass or less, and still more preferably 10% by mass or less. If it exceeds 20% by mass, the processability tends to decrease, for example, the Mooney viscosity increases. The gel content means a value measured as an insoluble content with respect to toluene which is a nonpolar solvent, and may be simply referred to as “gel content” or “gel content” below. The measuring method of the content rate of a gel part is as follows. First, a natural rubber sample is soaked in dehydrated toluene, light-shielded in the dark and left for 1 week, and then the toluene solution is centrifuged at 1.3 × 10 ⁵ rpm for 30 minutes to obtain an insoluble gel content and a toluene soluble content. Isolate. Methanol is added to the insoluble gel and solidified, and then dried, and the gel content is determined from the ratio between the mass of the gel and the original mass of the sample.

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

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

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

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

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

The addition amount of the surfactant is preferably 0.01 parts by mass or more, more preferably 0.1 parts by mass or more, and the upper limit is preferably 6 parts by mass or less with respect to 100 parts by mass of the solid content of the natural rubber latex. 5 mass parts or less are more preferable, 3.5 mass parts or less are more preferable, and 3 mass parts or less are especially preferable. If the addition amount of the surfactant is less than 0.01 parts by mass, the natural rubber latex may become unstable during the saponification treatment. On the other hand, if the amount of the surfactant added exceeds 6 parts by mass, the natural rubber latex is too stabilized and it may be difficult to coagulate.

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

After completion of the saponification reaction, the agglomerated rubber is crushed and washed. Examples of the aggregation method include a method of adjusting pH by adding an acid such as formic acid. Examples of the washing treatment include a method of diluting the rubber with water and washing it, and then performing a centrifugal separation treatment to take out the rubber. When centrifuging, it is first diluted with water so that the rubber content of the natural rubber latex is 5 to 40% by mass, preferably 10 to 30% by mass. Then, it may be centrifuged at 5000 to 10,000 rpm for 1 to 60 minutes. After completion of the washing treatment, a saponified natural rubber latex is obtained. The modified natural rubber according to the present invention is obtained by drying the saponified natural rubber latex.

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

In the rubber composition for breaker topping of the present invention, the content of the modified natural rubber in 100% by mass of the rubber component is 30% by mass or more, preferably 40% by mass or more, more preferably 45% by mass or more, and further preferably. It is 50 mass% or more. If the amount is less than 30% by mass, the improvement effect due to the use of HPNR may not be obtained. The upper limit of the content of the modified natural rubber is not particularly limited, and may be 100% by mass, but is preferably 90% by mass or less, more preferably 80% by mass or less, and still more preferably 70% by mass or less.

Examples of other rubber components that can be used together with the modified natural rubber (HPNR) in the rubber composition of the present invention include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), and styrene butadiene rubber (SBR). ), Butyl rubber (IIR), halogenated butyl rubber (X-IIR), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), ethylene propylene diene rubber (EPDM), copolymer of isomonoolefin and paraalkyl styrene And halides. These may be used alone or in combination of two or more. Among them, it is preferable to use NR (unmodified) in combination because good fracture characteristics (breaking strength index) can be obtained.

In the present invention, when NR (unmodified) is blended, the content of the NR in 100% by mass of the rubber component is preferably 10% by mass or more, more preferably 20% by mass or more, and further preferably 30% by mass. That's it. When the content of NR is less than 10% by mass, there is a possibility that the improvement in breaking strength cannot be obtained by using NR (unmodified) in combination. The NR content is preferably 80% by mass or less, more preferably 70% by mass or less, and still more preferably 60% by mass or less. If the NR content exceeds 80% by mass, the effects of the present invention may not be obtained.

As NR (unmodified), for example, SIR20, RSS # 3, TSR20, etc., which are common in the tire industry can be used.

Examples of carbon black include GPF, FEF, HAF, ISAF, and SAF, but are not particularly limited. By blending carbon black, a reinforcing effect is obtained, and good rubber strength and breaking strength are obtained. When used with HPNR, the effect of the present invention is obtained well.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 40 m ² / g or more, more preferably 60 m ² / g or more, and still more preferably 70 m ² / g or more. If it is less than 40 m < ² > / g, there exists a possibility that sufficient reinforcement effect may not be acquired. The nitrogen adsorption specific surface area of carbon black is preferably 150 m ² / g or less, more preferably 100 m ² / g or less, and still more preferably 90 m ² / g or less. If it exceeds 150 m ² / g, it tends to be difficult to disperse well.
In addition, the nitrogen adsorption specific surface area of carbon black is calculated | required by A method of JISK6217.

When the rubber composition contains carbon black, the carbon black content is preferably 20 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. It is. If it is less than 20 parts by mass, a sufficient reinforcing effect may not be obtained. The carbon black content is preferably 75 parts by mass or less, more preferably 65 parts by mass or less, and still more preferably 60 parts by mass or less. If it exceeds 75 parts by mass, dispersibility and workability tend to deteriorate.

The silica is not particularly limited, and for example, silica (anhydrous silicic acid) obtained by a dry method and / or silica (hydrous silicic acid) obtained by a wet method can be used. A reinforcing effect can be obtained by blending silica, and the effect of the present invention can be obtained satisfactorily when used in combination with HPNR. Among silicas, silica (hydrous silicic acid) obtained by a wet method is preferably used because of its large number of silanol groups.

The nitrogen adsorption specific surface area by the BET method of silica is preferably 30 m ² / g or more, and more preferably 100 m ² / g or more. If it is less than 30 m < ² > / g, there exists a possibility that sufficient reinforcement effect may not be acquired. Further, BET of silica is preferably 200 meters ² / g or less, more preferably 150 meters ² / g, more preferably not more than 120 m ² / g. If it exceeds 200 m ² / g, dispersibility and processability tend to deteriorate. In addition, the nitrogen adsorption specific surface area by the BET method of a silica can be measured by the method based on ASTM-D-4820-93.

The content of silica is preferably 5 parts by mass or more, more preferably 7 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, sufficient fuel efficiency may not be obtained. The silica content is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and still more preferably 20 parts by mass or less. When it exceeds 50 mass parts, there exists a tendency for workability to fall.

In the present invention, it is preferable to use a silane coupling agent together with silica. Examples of the silane coupling agent include sulfide, mercapto vinyl, amino, glycidoxy, nitro, and chloro silane coupling agents. Among them, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide, bis (2-triethoxysilylethyl) disulfide, etc. Sulfide systems are preferred, and bis (3-triethoxysilylpropyl) tetrasulfide is particularly preferred.

When the silane coupling agent is contained, the content of the silane coupling agent is preferably 2 parts by mass or more and more preferably 4 parts by mass or more with respect to 100 parts by mass of silica. If it is less than 2 parts by mass, rubber strength and wear resistance tend to deteriorate. Moreover, 15 mass parts or less are preferable and, as for content of this silane coupling agent, 13 mass parts or less are more preferable. When the amount exceeds 15 parts by mass, the effect of improving the rubber strength and wear resistance due to the blending of the silane coupling agent is not observed, and the cost tends to increase.

In the rubber composition, the total content of silica and carbon black is preferably 40 parts by mass or more, more preferably 45 parts by mass or more, and still more preferably 50 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 40 parts by mass, sufficient wear resistance may not be obtained.
The total content is preferably 80 parts by mass or less, more preferably 70 parts by mass or less, and still more preferably 65 parts by mass or less. When it exceeds 80 parts by mass, dispersibility and workability tend to deteriorate.

In addition to the components described above, the rubber composition of the present invention includes compounding agents generally used in the production of rubber compositions such as zinc oxide, stearic acid, various anti-aging agents, oils such as aroma oil, waxes, additives. A sulfurizing agent, a vulcanization accelerator, etc. can be suitably mix | blended.

The content of zinc oxide is preferably 4 parts by mass or more, more preferably 5 parts by mass or more, and still more preferably 6 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 4 mass parts, there exists a possibility that adhesive performance may deteriorate. Further, the content of zinc oxide is preferably 15 parts by mass or less, more preferably 10 parts by mass or less with respect to 100 parts by mass of the rubber component. If it exceeds 15 parts by mass, the rubber strength may be reduced.

In this invention, it is preferable to contain organic acid cobalt. Since the organic acid cobalt plays a role of cross-linking the cord and the rubber, the adhesion between the cord and the rubber can be improved by containing the organic acid cobalt. Specific examples of the organic acid cobalt include, for example, cobalt stearate, cobalt naphthenate, cobalt neodecanoate, and cobalt boron decanoate. Of these, cobalt stearate is preferable.

When the organic acid cobalt is contained, the content of the organic acid cobalt is preferably 0.02 parts by mass or more, more preferably 0.05 parts by mass or more, in terms of cobalt, with respect to 100 parts by mass of the rubber component. More preferably 1 part by mass or more. If it is less than 0.02 parts by mass, the adhesion performance may be deteriorated. Moreover, 0.8 mass part or less is preferable in conversion of cobalt, and, as for content of the said organic acid cobalt, 0.3 mass part or less is more preferable. If it exceeds 0.8 parts by mass, thermal degradation tends to occur during processing, during vulcanization and during use.

In the present invention, sulfur can be suitably used as a vulcanizing agent. Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur.
The sulfur content is preferably 2 parts by mass or more, more preferably 3 parts by mass or more, and still more preferably 4 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, a sufficient crosslinking density cannot be obtained, and the adhesion performance may be deteriorated.
Moreover, this content becomes like this. Preferably it is 10 mass parts or less, More preferably, it is 8 mass parts or less, More preferably, it is 6 mass parts or less. If it exceeds 10 parts by mass, the heat-resistant deterioration property may be deteriorated.

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

The rubber composition for breaker topping of the present invention is used for a breaker disposed inside a tread and radially outside of a carcass. Specifically, it is used for the breaker shown in FIG. 3 of JP-A-2003-94918, FIG. 1 of JP-A-2004-67027, and FIGS. 1-4 of JP-A-4-356205.

The pneumatic tire of the present invention is produced by a usual method using the rubber composition. That is, a rubber composition for breaker toppings containing the above components is extruded in accordance with the shape of the breaker 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. The unvulcanized tire is heated and pressurized in a vulcanizer to obtain a tire.

The pneumatic tire having a breaker produced using the rubber composition of the present invention is suitably used for passenger car tires, light truck tires, truck / bus tires.

The present invention will be specifically described based on examples, but the present invention is not limited to these examples.
NR (1): RSS # 3 grade NR (2): TSR20 grade HPNR (1): Production Example 1 below
HPNR (2): Production Example 2 below
Carbon black: Dia Black LH (N326, N ₂ SA: 84 m ² / g) manufactured by Mitsubishi Chemical Corporation
Silica: Silica 115Gr (N ₂ SA: 115 m ² / g) manufactured by Rhodia Japan
Silane coupling agent: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by Degussa
Oil: Diana Process Oil PS323 manufactured by Idemitsu Kosan Co., Ltd.
Anti-aging agent: NOCRACK FR manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Cobalt stearate: cost-F (cobalt content: 9.5% by mass) manufactured by Dainippon Ink & Chemicals, Inc.
Zinc oxide: Zinc Hua No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: Kristex HSOT20 manufactured by Flexis (insoluble sulfur containing 80% by mass of sulfur and 20% by mass of oil)
Vulcanization accelerator DZ: Noxeller DZ manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Natural rubber latex: Field latex obtained from Taitex Co., Ltd. Surfactant: Emal-E manufactured by Kao Corporation
NaOH: NaOH manufactured by Wako Pure Chemical Industries, Ltd.

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

The solid content, RSS, 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 natural rubber, RSS or TSR obtained in each production example 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 was determined using an ICP emission spectrometer (ICPS-8100, manufactured by Shimadzu Corporation).

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

As shown in Table 1, the saponified natural rubber 1 (HPNR1) and the saponified natural rubber 2 (HPNR2) have a reduced nitrogen content, phosphorus content, and gel content as compared to TSR and RSS.

<Examples 1-8 and Comparative Examples 1-4>
(Production of rubber test pieces and tires)
In accordance with the formulation shown in Tables 2-3, chemicals other than sulfur and a vulcanization accelerator were kneaded using a 1.7 L Banbury mixer. Next, using an open roll, sulfur and a vulcanization accelerator were added to the kneaded product and kneaded to obtain an unvulcanized rubber composition.
Next, 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 (vulcanized rubber test piece).
The obtained unvulcanized rubber composition and vulcanized rubber composition were evaluated as follows. The results are shown in Tables 2-3.

(Rolling resistance index)
The vulcanized rubber composition was measured using a viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.), and tan δ of each formulation was measured under conditions of a temperature of 70 ° C., an initial strain of 10%, and a dynamic strain of 2%. The tan δ of Example 1 or 3 was set to 100, and the index was displayed by the following calculation formula. The larger the index, the better the rolling resistance.
(Rolling resistance index) = (tan δ of Comparative Example 1 or 3) / (tan δ of each formulation) × 100

(Measurement of 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 Example 1 or 3 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 processability.
(Mooney viscosity index) = (ML _{1 + 4} of Comparative Example 1 or 3) / (ML _{1 + 4 of} each formulation) × 100

(Break strength index)
In accordance with JIS-K-6251 “How to Obtain Tensile Properties of Vulcanized Rubber and Thermoplastic Rubber”, a tensile test was conducted using a No. 3 dumbbell. The tensile strength (TB) of was measured. In addition, EBxTB of the comparative example 1 or 3 was set to 100, and EBxTB of each combination was indicated by an index according to the following calculation formula. It shows that it is excellent in breaking strength, so that an index | exponent is large.
(Breaking strength index) = (EB × TB of each formulation) / (EB × TB of Comparative Example 1 or 3) × 100

As shown in Table 2, in the formulation using only carbon black as the filler, in the examples containing saponified natural rubber (modified natural rubber) as the rubber component, rolling compared to the comparative example using RSS or TSR. Resistance performance (low fuel consumption performance), workability and breaking strength were improved in a well-balanced manner. In addition, these performances were superior when HPNR (1) having a smaller nitrogen content and phosphorus content than HPNR (2) was used.

As Table 3 shows, the same improvement effect as that of the carbon black composition shown in Table 1 was observed even when the carbon black and silica were used in combination.

Claims (6)

Including a rubber component and carbon black and / or silica;
The rubber component includes a modified natural rubber having a phosphorus content of 200 ppm or less,
A rubber composition for breaker topping, wherein the content of the modified natural rubber in 100% by mass of the rubber component is 30% by mass or more. The rubber composition for breaker topping according to claim 1, wherein the nitrogen content of the modified natural rubber is 0.3% by mass or less. The rubber composition for a breaker topping according to claim 1 or 2, wherein the modified natural rubber has a gel content measured as a toluene insoluble content of 20% by mass or less. The rubber composition for breaker topping according to any one of claims 1 to 3, wherein the modified natural rubber is obtained by saponifying natural rubber latex. The rubber composition for breaker toppings according to any one of claims 1 to 4, comprising zinc oxide, sulfur and organic acid cobalt. The pneumatic tire which has a breaker produced using the rubber composition in any one of Claims 1-5.