JP5727896B2 - Rubber composition for side wall reinforcing layer and run flat tire - Google Patents

Description

The present invention relates to a rubber composition for a sidewall reinforcing layer, and a run flat tire using the rubber composition.

In recent years, run-flat tires that can travel a predetermined distance even when the tire is punctured have been developed. A run-flat tire has a thick elastic sidewall reinforcement layer (insert) inside the sidewall of the tire, and the reinforcement layer maintains the rigidity of the tire when punctured. Can drive. As a result, there is no need to always have spare tires, and the weight of the entire vehicle can be reduced, so fuel efficiency can be improved. However, there is room for improvement in terms of travel speed and travel distance, and durability. Further improvement is required.

As a method to improve the durability of run-flat tires, a method of preventing tire destruction by increasing the thickness of the sidewall reinforcement layer is conceivable, but an increase in the weight of the tires can improve fuel efficiency. Absent. Further, although a method of increasing the hardness of the reinforcing layer by increasing the amount of reinforcing filler can be considered, the load on the kneader increases, the heat generated by the vulcanized rubber increases, and the effect of improving durability cannot be sufficiently obtained. There is a problem that fuel efficiency deteriorates. Therefore, it is generally difficult to achieve both low fuel consumption and durability in a run flat tire.

On the other hand, natural rubber is widely used for the side wall reinforcement layer, but it has poor processability compared to other synthetic rubbers and is usually used after the Mooney viscosity is lowered by mastication using a crushing agent. Is done. Therefore, there is a problem that the properties (low fuel consumption, breaking strength, etc.) of the high molecular weight polymer inherent to natural rubber are lost due to the inferior productivity and the natural rubber molecular chain being cut by mastication.

For example, in Patent Literatures 1 to 3, a tire provided with a heat conductive rubber containing metal powder or diamond powder on the tire lumen surface side of the bead portion, a heat conductive material such as boron nitride or silicon carbide was blended. A rubber composition for coating a steel belt cord containing a rubber composition for tread and a deproteinized natural rubber is disclosed. However, application to run-flat tires has not been studied in detail.

JP 2007-182095 A JP-A-2005-179617 JP 2009-24073 A

An object of the present invention is to solve the above problems and provide a rubber composition for a sidewall reinforcing layer capable of achieving both the durability and fuel efficiency of a run flat tire at a high level, and a run flat tire using the rubber composition. To do.

The present invention includes a modified natural rubber having a phosphorus content of 200 ppm or less and carbon black, and the content of the modified natural rubber in a rubber component of 100% by mass is 5% by mass or more. The present invention relates to a rubber composition.

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.

As the modified natural rubber, a step of saponifying natural rubber latex to prepare a saponified natural rubber latex (A), a step of alkali treating the agglomerated rubber obtained by agglomerating the saponified natural rubber latex What was obtained by performing (B) and the process (C) wash | cleaned until the phosphorus content contained in rubber | gum becomes 200 ppm or less is preferable.

The present invention also relates to a run flat tire having a rubber composition for a side wall reinforcing layer produced using the rubber composition described above.

According to the present invention, since it is a rubber composition for a sidewall reinforcing layer containing a modified natural rubber having a predetermined amount of phosphorus content of 200 ppm or less and carbon black, durability can be improved by using the rubber composition. In addition, it is possible to provide a run-flat tire that achieves a high level of both low fuel consumption.

The rubber composition for a side wall reinforcing layer (inspiration) of the present invention includes a modified natural rubber (HPNR) having a phosphorus content of 200 ppm or less and carbon black. HPNR with reduced and removed phospholipids contained in natural rubber (NR) (preferably HPNR with protein and gel content removed) is less likely to generate heat. Can be achieved.

In addition, HPNR has a low Mooney viscosity and excellent workability, and can be sufficiently kneaded without performing a special kneading step, so that it is possible to prevent deterioration in rubber physical properties due to mastication. As a result, the rubber properties inherent to natural rubber can be maintained, so that good fuel economy and performance such as destructive properties can be obtained. Furthermore, HPNR does not contain dust components (pebbles, wood chips, etc.) contained in TSR and the like, and does not require a removal step of the components, so that it is excellent in productivity and there is no fear of rubber destruction caused by the dust components. Therefore, the present invention can provide a run-flat tire that achieves both high fuel efficiency and durability at a high level while obtaining excellent processability (productivity).

The modified natural rubber has a phosphorus content of 200 ppm or less. If it exceeds 200 ppm, tan δ tends to increase, and there is a possibility that low fuel consumption and durability cannot be improved in a well-balanced manner. There is also a concern that phosphorus forms a network in natural rubber, leading to an increase in the amount of gel and an increase in Mooney viscosity. 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. If the nitrogen content exceeds 0.3% by mass, the fuel economy and durability may not be improved in a well-balanced manner. There is also a concern that proteins form a network in natural rubber, leading to an increase in gel amount and an increase in Mooney viscosity. The nitrogen content can be measured by a conventional method such as Kjeldahl method. Nitrogen is derived from protein.

The gel content in the modified natural rubber is preferably 20% by mass or less, more preferably 10% by mass or less, and still more preferably 7% by mass or less. If it exceeds 20% by mass, the dispersibility of the filler tends to deteriorate, or the Mooney viscosity increases and the processability tends 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 can be prepared by, for example, 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 was prepared can be used conveniently. By this manufacturing method, the amount of phosphorus can be reduced sufficiently. Moreover, after agglomerating with an acid, the remaining acid is neutralized by an alkali treatment, so that not only deterioration of the rubber due to the acid is prevented, but also the amount of nitrogen in the rubber can be further reduced. And the performance balance of low-fuel-consumption property and durability can be remarkably improved by using the obtained modified natural rubber.

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 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.

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 the lower limit is preferably 0.1 parts by mass or more and more preferably 0.3 parts by mass or more with respect to 100 parts by mass of natural rubber latex (wet state). Preferably, the upper limit is preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and still more preferably 5 parts by mass or less. The amount of the surfactant added is preferably 0.01 parts by mass or more, more preferably 0.1 parts by mass or more, and the upper limit is 6.0 parts by mass with respect to 100 parts by mass of natural rubber latex (wet state). It is preferably no greater than 5 parts by weight, more preferably no greater than 5.0 parts by weight and even more preferably no greater than 3.5 parts by weight. The temperature and time of the saponification treatment may be appropriately set, and is usually about 20 to 70 ° C. for about 1 to 72 hours, preferably about 30 to 70 ° C. for about 1 to 48 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 known methods in which an acid such as formic acid is added. 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.

In the rubber composition of the present invention, the content of the modified natural rubber in 100% by mass of the rubber component is 5% by mass or more, preferably 60% by mass or more, more preferably 75% by mass or more, and further preferably 90% by mass. That is all, and may be 100% by mass. If it is less than 5% by mass, excellent fuel efficiency cannot be obtained, rubber strength (rigidity) is lowered, and durability of the run-flat tire tends to deteriorate.

The rubber composition of the present invention may contain a rubber component other than the modified natural rubber. Examples of other rubber components include natural rubber (NR), butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), Examples thereof include diene rubbers such as acrylonitrile butadiene rubber (NBR).

The rubber composition of the present invention contains carbon black. By blending carbon black with HPNR, it is possible to enhance the reinforcement while obtaining low fuel consumption, so that both low fuel consumption and durability of the run-flat tire can be achieved. Examples of carbon black that can be used include GPF, FEF, HAF, ISAF, and SAF, but are not particularly limited.

The lower limit of the nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 50 m ² / g or more, more preferably 70 m ² / g or more, and the upper limit is 200 m from the viewpoint of achieving both low fuel consumption and durability. ² / g or less is preferable, 150 m ² / g or less is more preferable, and 120 m ² / g or less is more preferable.
In addition, the nitrogen adsorption specific surface area of carbon black is measured according to JIS K6217-2: 2001.

The dibutyl phthalate oil absorption (DBP) of carbon black is preferably 80 ml / 100 g or more, more preferably 95 ml / 100 g or more, and preferably 200 ml / 100 g or less, from the viewpoint of achieving both low fuel consumption and durability. 140ml / 100g or less is more preferable, and 120ml / 100g or less is still more preferable.
The DBP of carbon black is measured according to JIS K6217-4: 2001.

The content of carbon black is preferably 5 parts by mass or more, more preferably 20 parts by mass or more, and still more preferably 35 parts by mass with respect to 100 parts by mass of the rubber component from the viewpoint of obtaining sufficient rubber strength (rigidity). That's it. Further, the carbon black content is preferably 120 parts by mass or less, more preferably 90 parts by mass or less, and still more preferably 75 parts by mass or less from the viewpoint of excellent processability and desired rubber physical properties.

The rubber composition of the present invention preferably contains a phenolic resin. Thereby, rigidity increases and durability of the run flat tire is improved.
It does not specifically limit as a phenol-type resin, Although a well-known resin can be used, Especially a non-reactive alkylphenol resin can be used conveniently. Here, the non-reactive alkylphenol resin refers to an alkylphenol resin having no reactive sites at the ortho-position and para-position (particularly para-position) of the hydroxyl group of the benzene ring in the chain. Here, as a non-reactive alkylphenol resin, what is shown by following formula (I) or (II) can be used conveniently.

In formula (I), m is an integer. M is preferably 1 to 10 and more preferably 2 to 9 in terms of moderate bloom property. R ¹ may be the same or different and represents an alkyl group, and the number of carbon atoms is preferably 4 to 15 and more preferably 6 to 10 in terms of affinity with rubber.

In formula (II), n is an integer. In terms of moderate blooming property, n is preferably 1 to 10, and more preferably 2 to 9.

The content of the phenolic resin 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 rubber component. If it is less than 1 part by mass, sufficient hardness cannot be obtained, and durability may be reduced. The content is preferably 10 parts by mass or less, more preferably 5 parts by mass or less. If it exceeds 10 parts by mass, fuel economy and durability tend to deteriorate.

The total content of the compounds represented by the above formulas (I) and (II) is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and still more preferably with respect to 100 parts by mass of the rubber component. Is 2 parts by mass or more. If it is less than 0.5 parts by mass, sufficient hardness cannot be obtained, and durability may be lowered. The total content is preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and still more preferably 5 parts by mass or less. If it exceeds 10 parts by mass, fuel economy and durability tend to deteriorate.

The rubber composition of the present invention preferably contains oil. Examples of the oil include process oils such as aroma, naphthene, and mineral process oils; plant oils such as soybean oil, palm oil, castor oil, linseed oil, rapeseed oil, and coconut oil. Among these, it is preferable to use process oil.

The blending amount of the process oil is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more with respect to 100 parts by mass of the rubber component. On the other hand, the amount is preferably 7 parts by mass or less, more preferably 5 parts by mass or less. When adjusted to a blending amount within the above range, both low fuel consumption and durability can be satisfactorily achieved.

In the rubber composition of the present invention, in addition to the above components, compounding agents commonly used in the production of rubber compositions, such as zinc oxide, stearic acid, various anti-aging agents, antioxidants, ozone degradation inhibitors, Vulcanizing agents such as sulfur, vulcanization accelerators, vulcanization acceleration auxiliary agents, and the like can be appropriately blended.

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. 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 a modified natural rubber having excellent processability 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 is used for a side wall reinforcing layer of a side-reinforced run-flat tire. The said reinforcement layer means the lining strip layer arrange | positioned inside the sidewall of a run flat tire. The arrangement of the reinforcing rubber layer is, for example, a crescent-shaped reinforcing rubber layer that is arranged from the bead to the shoulder in contact with the inside of the carcass ply and gradually decreases in thickness in both end directions, and the carcass ply main body portion and its folded portion. Examples thereof include a reinforcing rubber layer disposed between the beads and the tread end, and two reinforcing rubber layers disposed between the plurality of carcass plies or the reinforcing plies. Specific examples of the reinforcing layer are shown in FIG. 1 of JP-A-2007-326559 and FIG. 1 of JP-A-2004-330822.

The run flat tire of the present invention is produced by a usual method using the rubber composition. That is, if necessary, the rubber composition containing the above compounding agent is extruded in accordance with the shape of the sidewall reinforcing layer (insulation) of the run flat tire at an unvulcanized stage, along with other tire members, An unvulcanized tire is formed by molding by a normal method on a tire molding machine. A run-flat tire can be obtained by heating and pressurizing the unvulcanized tire in a vulcanizer.

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 together. In addition, the chemical | medical agent refine | purified according to the usual method as needed.
Natural rubber latex: Field latex surfactant obtained from Taitex Co., Ltd .: Emal-E (sodium polyoxyethylene lauryl ether sulfate) manufactured by Kao Corporation
NaOH: NaOH manufactured by Wako Pure Chemical Industries, Ltd.

(Production Example 1: Preparation of saponified natural rubber A)
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 solid rubber (saponified natural rubber A) Obtained.

(Production Example 2: Preparation of saponified natural rubber B)
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 saponified natural rubbers A and B obtained by the above production examples 1 and 2 and the TSR used in the evaluation of the rubber composition described later are measured for nitrogen content, phosphorus content and gel content by the following methods. did. The results are shown in Table 1.

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

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

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

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
Saponified natural rubber A: Solid rubber obtained from Production Example 1 Saponified natural rubber B: Solid rubber obtained from Production Example 2 NR: TSR20
BR: BR150B manufactured by Ube Industries, Ltd.
Carbon black 1: Dia Black I manufactured by Mitsubishi Chemical Corporation (N ₂ SA: 114 m ² / g, DBP oil absorption: 114 ml / 100 g)
Carbon black 2: Dia Black HAN manufactured by Mitsubishi Chemical Corporation (N ₂ SA: 80 m ² / g, DBP oil absorption: 103 ml / 100 g)
Silica: Z115Gr made by Rhodia
Silane coupling agent: Si75 (bis (3-triethoxysilylpropyl) disulfide) manufactured by Degussa
Process oil: Vivatec 400 manufactured by H & R
Alkylphenol resin: SP1068 manufactured by Nippon Shokubai Co., Ltd. (non-reactive alkylphenol resin represented by the above formula (I): integer of m = 1 to 10, R ¹ = octyl group)
Anti-aging agent: Antigen 6C manufactured by Sumitomo Chemical Co., Ltd.
Stearic acid: NOF made by NOF Corporation
Zinc oxide: Zinc Hana 2 insoluble sulfur manufactured by Mitsui Mining & Smelting Co., Ltd .: Mucron OT (80% by mass of sulfur and 20% by mass of oil)
Vulcanization accelerator: Noxeller NS-G manufactured by Ouchi Shinsei Chemical Industry 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 (vulcanized rubber sheet). The following tests were conducted using this as a new rubber.

<Rolling resistance>
Using a viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.), tan δ of each vulcanized rubber composition was measured under conditions of a temperature of 50 ° C., an initial strain of 10%, a dynamic strain of 2%, and a frequency of 10 Hz. The smaller the numerical value, the lower the heat generation and the better the fuel efficiency. The results were evaluated in four grades, ◎, ○, Δ, and ×.

<Runflat durability>
The run flat tire for test was run on the drum at 80 km / h at an air pressure of 0 kPa, and the running distance until the tire broke was measured. The longer the mileage, the better the run-flat durability, and the results were evaluated in four stages: ◎, ○, Δ, and ×.

Compared to the comparative example using TSR in the carbon black blending system, the example using HPNR improved the fuel efficiency and run-flat durability in a well-balanced manner, and these performances were fully compatible.

Claims (2)

Saponifying natural rubber latex to prepare saponified natural rubber latex (A), alkali-treating the agglomerated rubber obtained by agglomerating the saponified natural rubber latex (B), contained in rubber The step (C) of washing until the phosphorus content is 200 ppm or less, and the step (D) of kneading the modified natural rubber obtained through the steps (A) to (C) and carbon black. A method for producing a rubber composition for a sidewall reinforcing layer. Saponifying natural rubber latex to prepare saponified natural rubber latex (A), alkali-treating the agglomerated rubber obtained by agglomerating the saponified natural rubber latex (B), contained in rubber The step (C) of washing until the phosphorus content is 200 ppm or less, and the step (D) of kneading the modified natural rubber obtained through the steps (A) to (C) and carbon black. A method for manufacturing a run-flat tire including the same.