JP5503310B2 - Run-flat tire rubber composition and run-flat tire - Google Patents

Description

The present invention relates to a rubber composition for a run-flat tire and a run-flat tire using the same.

In recent years, run-flat tires have been developed with the aim of safely traveling a certain distance even when a tire is punctured. A run-flat tire has a sidewall reinforcement layer having a high elastic modulus and a thick wall inside the sidewall of the tire. The sidewall reinforcing layer maintains the rigidity of the tire when the tire is punctured. Therefore, even when the tire is repeatedly bent and deformed, the damage of the tire is reduced and long-distance driving is possible. As a result, there is no need to keep spare tires in the vehicle, the weight of the entire vehicle can be reduced, and fuel efficiency can be improved.

However, there is room for improvement in terms of travel speed and travel distance in run-flat running (running with air pressure lost) when the run-flat tire is punctured, and the durability of the run-flat tire is further improved. It is requested.

As an effective means for improving the durability of the run flat tire, there is a method of preventing the tire from being destroyed by suppressing the deformation of the tire by increasing the thickness of the sidewall reinforcing layer disposed inside the sidewall. However, when the sidewall reinforcing layer is thickened, the weight of the run flat tire increases as the thickness of the sidewall reinforcing layer increases. Therefore, there has been a problem that the effect of reducing the weight of the entire vehicle, which should have been obtained by using run-flat tires, is reduced.

In addition, there is a method of increasing the hardness of the reinforcing layer and suppressing the deformation of the tire by increasing the amount of reinforcing filler such as carbon black, but in the process of kneading and extrusion, the load on the kneader increases. There's a problem. Further, since the heat generated by the obtained rubber (after vulcanization) becomes large, there is a problem that the durability improving effect of the run-flat tire is not sufficient and the fuel efficiency is further deteriorated.

Patent Document 1 discloses a tire in which a thermally conductive rubber containing metal powder or diamond powder is provided on the tire lumen surface side of the bead portion, but the use of aluminum nitride has not been studied, There is room for improvement in improving the durability of run-flat tires.

Patent Document 2 discloses that a tread rubber composition containing a heat conductive material such as boron nitride or silicon carbide removes frictional heat between the tire surface and the snowy and snowy road surface generated during running, It has been disclosed that the occurrence of such a phenomenon can be suppressed and the grip performance on an icy and snowy road surface can be improved. However, use of aluminum nitride and application to a rubber composition for a run-flat tire have not been studied in detail. Even when boron nitride or silicon carbide is blended in the rubber composition for a run flat tire, there is room for improvement in improving the durability of the run flat tire.

Further, Patent Document 3 discloses a rubber composition for coating a steel belt cord having a low viscosity when not vulcanized and good workability by blending a deproteinized natural rubber. However, the phosphorus content in natural rubber and its application to a rubber composition for run-flat tires have 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-mentioned problems and to provide a rubber composition for a run-flat tire that can improve the durability and fuel efficiency of the run-flat tire in a well-balanced manner, and a run-flat tire using the same.

（式（１）中、Ｒ^１、Ｒ^２及びＲ^３は、同一若しくは異なって、アルキル基、アルコキシ基、シリルオキシ基、アセタール基、カルボキシル基、メルカプト基又はこれらの誘導体を表す。Ｒ^４及びＲ^５は、同一若しくは異なって、水素原子、アルキル基又は環状エーテル基を表す。ｎは整数を表す。） The present invention relates to a rubber composition for a run-flat tire comprising a modified natural rubber having a phosphorus content of 200 ppm or less, a modified butadiene rubber modified with a compound represented by the following formula (1), silica, and aluminum nitride. Related to things.

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

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

The modified natural rubber is preferably substantially free of phospholipids and has no peak due to phospholipid at -3 ppm to 1 ppm in ³¹ P NMR measurement of the chloroform extract.

The modified natural rubber preferably has a nitrogen content of 0.3% by mass or less. The modified natural rubber preferably has a nitrogen content of 0.15% by mass or less.

The modified natural rubber is preferably obtained by saponifying natural rubber latex.

The oxygen content of the aluminum nitride is preferably 0.4 to 5% by mass.

The content of the modified natural rubber in 100% by mass of the rubber component is 15 to 60% by mass, the content of the modified butadiene rubber is 15 to 60% by mass, and the content of styrene butadiene rubber is 15 to 60% by mass. It is preferable.

It is preferable that content of the said aluminum nitride is 10-100 mass parts with respect to 100 mass parts of rubber components.

The rubber composition for a run-flat tire is preferably used for the sidewall reinforcing layer.

The present invention also relates to a run flat tire using the rubber composition.

According to the present invention, for a run flat tire comprising a modified natural rubber having a phosphorus content of 200 ppm or less, a modified butadiene rubber modified with the compound represented by the above formula (1), silica, and aluminum nitride. Since it is a rubber composition, it can improve heat conductivity, low heat generation (low fuel consumption), rigidity, and durability in a well-balanced manner, and has excellent heat conductivity, low heat generation (low fuel consumption), rigidity and Run-flat tires with excellent durability can be provided. In this specification, the durability of the run-flat tire means the durability (also referred to as run-flat durability) when the run-flat running is performed in a state where air pressure is lost (during puncture).

The rubber composition for a run-flat tire of the present invention includes a modified natural rubber (HPNR) having a phosphorus content of 200 ppm or less, a modified butadiene rubber (modified BR) modified with a compound represented by the above formula (1), Silica and aluminum nitride.

The rubber composition of the present invention contains a modified natural rubber (HPNR) having a phosphorus content of 200 ppm or less. By using modified natural rubber (HPNR) that reduces and removes proteins, gels, and phospholipids contained in natural rubber (NR), the durability of run-flat tires and fuel efficiency are reduced compared to the use of NR. It is possible to improve the performance.

The modified natural rubber (HPNR) has a phosphorus content of 200 ppm or less. If it exceeds 200 ppm, the amount of gel increases during storage, the Mooney viscosity increases, processability tends to deteriorate, and excellent fuel efficiency tends to be not obtained. 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 gel content in the modified natural rubber is preferably 20% by mass or less, and 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.

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 gel amount increases during storage, the Mooney viscosity increases, the workability tends to deteriorate, and excellent fuel efficiency tends to be not obtained. Nitrogen is derived from proteins. The nitrogen content can be measured by a conventional method such as Kjeldahl method.

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 cause 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 sufficient treatment and improvement of productivity, depending on the treatment temperature when the treatment is performed with the 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.

The content of the modified natural rubber in 100% by mass of the rubber component is preferably 15% by mass or more, more preferably 20% by mass or more, still more preferably 25% by mass or more, and particularly preferably 28% by mass or more. If it is less than 15% by mass, excellent fuel efficiency cannot be obtained, rubber strength (rigidity) is lowered, and durability of the run-flat tire tends to be lowered. The content of the modified natural rubber is preferably 60% by mass or less, more preferably 50% by mass or less, still more preferably 40% by mass or less, and particularly preferably 35% by mass or less. If it exceeds 60% by mass, sufficient heat resistance and hardness cannot be obtained, and the durability of the run-flat tire tends to decrease.

The rubber composition of the present invention contains a modified butadiene rubber (modified BR) modified with the compound represented by the above formula (1). By using the modified BR, the Tg (glass transition temperature) of the polymer can be lowered, and the dispersibility of fillers (particularly silica) such as silica and carbon black can be improved. As a result, it is possible to improve the durability and low fuel consumption of the run-flat tire.

In the compound represented by the above formula (1), R ¹ , R ² and R ³ are the same or different and are an alkyl group, an alkoxy group, a silyloxy group, an acetal group, a carboxyl group (—COOH), a mercapto group (— SH) or derivatives thereof.

As said alkyl group, C1-C4 alkyl groups, such as a methyl group, an ethyl group, n-propyl group, isopropyl group, n-butyl group, t-butyl group, etc. are mentioned, for example.

Examples of the alkoxy group include an alkoxy group having 1 to 8 carbon atoms (preferably 1 to 6 carbon atoms) such as a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, an n-butoxy group, and a t-butoxy group. More preferably, C1-C4) etc. are mentioned. Examples of the alkoxy group include a cycloalkoxy group (such as a cycloalkoxy group having 5 to 8 carbon atoms such as a cyclohexyloxy group) and an aryloxy group (an aryloxy group having 6 to 8 carbon atoms such as a phenoxy group and a benzyloxy group). ) Is also included.

Examples of the silyloxy group include a silyloxy group substituted with an aliphatic group having 1 to 20 carbon atoms and an aromatic group (trimethylsilyloxy group, triethylsilyloxy group, triisopropylsilyloxy group, diethylisopropylsilyloxy group, t- Butyldimethylsilyloxy group, t-butyldiphenylsilyloxy group, tribenzylsilyloxy group, triphenylsilyloxy group, tri-p-xylylsilyloxy group, etc.).

Examples of the acetal group include groups represented by -C (RR ')-OR "and -O-C (RR')-OR". Examples of the former include a methoxymethyl group, an ethoxymethyl group, a propoxymethyl group, a butoxymethyl group, an isopropoxymethyl group, a t-butoxymethyl group, and a neopentyloxymethyl group. The latter includes a methoxymethoxy group, an ethoxy group, and the like. Methoxy group, propoxymethoxy group, i-propoxymethoxy group, n-butoxymethoxy group, t-butoxymethoxy group, n-pentyloxymethoxy group, n-hexyloxymethoxy group, cyclopentyloxymethoxy group, cyclohexyloxymethoxy group, etc. Can be mentioned.

R ¹ , R ² and R ³ are preferably alkoxy groups, and more preferably methoxy groups. Thereby, the improvement effect of the dispersibility of a filler can be heightened.

In the compound represented by the above formula (1), R ⁴ and R ⁵ are the same or different and each represents a hydrogen atom, an alkyl group or a cyclic ether group.

Examples of the alkyl group for R ⁴ and R ⁵ include the same groups as the above alkyl group.

Examples of the cyclic ether group of R ⁴ and R ⁵ include one ether bond such as an oxirane group, an oxetane group, an oxolane group, an oxane group, an oxepane group, an oxocan group, an oxonan group, an oxecan group, an oxet group, and an oxole group. A cyclic ether group having two ether bonds such as a cyclic ether group, a dioxolane group, a dioxane group, a dioxepane group and a dioxecan group, and a cyclic ether group having three ether bonds such as a trioxane group. Among these, a C2-C7 cyclic ether group having one ether bond is preferable, and a C3-C5 cyclic ether group having one ether bond is more preferable. The cyclic ether group preferably has no unsaturated bond in the ring skeleton.

As R ⁴ and R ⁵ , an alkyl group (preferably having 1 to 3 carbon atoms, more preferably 1 to 2 carbon atoms) is preferable, and an ethyl group is more preferable. Thereby, the improvement effect of the dispersibility of a filler can be heightened.

As n (integer), 2-5 are preferable. Thereby, the improvement effect of the dispersibility of a filler can be heightened. Furthermore, n is more preferably 2 to 4, and most preferably 3. If n is 1 or less, the denaturation reaction may be inhibited, and if n is 6 or more, the effect as a denaturing agent is reduced.

Specific examples of the compound represented by the above formula (1) include 3-aminopropyldimethylmethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylethyldimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, Aminopropyldimethylethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyldimethylbutoxysilane, 3-aminopropylmethyldibutoxysilane, dimethylaminomethyltrimethoxysilane, 2-dimethyl Aminoethyltrimethoxysilane, 3-dimethylaminopropyltrimethoxysilane, 4-dimethylaminobutyltrimethoxysilane, dimethylaminomethyldimethoxymethylsilane, 2-dimethylaminoethyldimethoxy Methylsilane, 3-dimethylaminopropyldimethoxymethylsilane, 4-dimethylaminobutyldimethoxymethylsilane, dimethylaminomethyltriethoxysilane, 2-dimethylaminoethyltriethoxysilane, 3-dimethylaminopropyltriethoxysilane, 4-dimethylaminobutyl Triethoxysilane, dimethylaminomethyldiethoxymethylsilane, 2-dimethylaminoethyldiethoxymethylsilane, 3-dimethylaminopropyldiethoxymethylsilane, 4-dimethylaminobutyldiethoxymethylsilane, diethylaminomethyltrimethoxysilane, 2- Diethylaminoethyltrimethoxysilane, 3-diethylaminopropyltrimethoxysilane, 4-diethylaminobutyltrimethoxysilane, diethylamino Tildimethoxymethylsilane, 2-diethylaminoethyldimethoxymethylsilane, 3-diethylaminopropyldimethoxymethylsilane, 4-diethylaminobutyldimethoxymethylsilane, diethylaminomethyltriethoxysilane, 2-diethylaminoethyltriethoxysilane, 3-diethylaminopropyltriethoxysilane 4-diethylaminobutyltriethoxysilane, diethylaminomethyldiethoxymethylsilane, 2-diethylaminoethyldiethoxymethylsilane, 3-diethylaminopropyldiethoxymethylsilane, 4-diethylaminobutyldiethoxymethylsilane, the following formulas (2) to ( 9) and the like. These may be used alone or in combination of two or more. Of these, 3-diethylaminopropyltrimethoxysilane, 3-dimethylaminopropyltrimethoxysilane, and a compound represented by the following formula (2) are preferable because the effect of improving the dispersibility of the filler is great.

Methods for modifying butadiene rubber with the compound represented by the above formula (1) (modifier) are described in JP-B-6-53768, JP-B-6-57767, JP-T2003-514078, and the like. Conventionally known methods such as the above method can be used. For example, the butadiene rubber may be brought into contact with the modifying agent, the butadiene rubber is polymerized, and a predetermined amount of the modifying agent is added to the polymer rubber solution, and the modifying agent is added to the butadiene rubber solution and reacted. The method etc. are mentioned.

The butadiene rubber (BR) to be modified is not particularly limited, and BR having a high cis content, BR containing a syndiotactic polybutadiene crystal, or the like can be used. In addition, BR obtained by polymerization using a catalyst containing a lanthanum series rare earth-containing compound described in JP-T-2003-514078 can also be used.

The vinyl content of the modified BR is preferably 35% by mass or less, more preferably 25% by mass or less, and still more preferably 20% by mass or less. If the vinyl content exceeds 35% by mass, the fuel efficiency tends to deteriorate. The lower limit of the vinyl content is not particularly limited.
In the present specification, the vinyl content (1,2-bonded butadiene unit amount) of the modified BR can be measured by infrared absorption spectrum analysis.

The content of the modified BR in 100% by mass of the rubber component is preferably 15% by mass or more, more preferably 20% by mass or more, still more preferably 25% by mass or more, and particularly preferably 28% by mass or more. If it is less than 15% by mass, there is a tendency that excellent fuel efficiency and durability of the run-flat tire cannot be obtained. The content of the modified BR is preferably 60% by mass or less, more preferably 50% by mass or less, still more preferably 40% by mass or less, and particularly preferably 35% by mass or less. If it exceeds 60% by mass, sufficient rubber strength (rigidity) cannot be obtained, and the durability of the run-flat tire tends to decrease.

In addition to HPNR and modified BR, rubber components that can be used in the present invention include natural rubber (NR), epoxidized natural rubber (ENR), isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), and acrylonitrile. Diene rubbers such as butadiene rubber (NBR), chloroprene rubber (CR), butyl rubber (IIR), styrene-isoprene-butadiene copolymer rubber (SIBR) may be used. These diene rubbers may be used alone or in combination of two or more. Of these, SBR is preferable because of its excellent rigidity.

The SBR is not particularly limited, and for example, emulsion polymerization styrene butadiene rubber (E-SBR), solution polymerization styrene butadiene rubber (S-SBR) and the like can be used.

The content of SBR in 100% by mass of the rubber component is preferably 15% by mass or more, more preferably 20% by mass or more, still more preferably 30% by mass or more, and particularly preferably 35% by mass or more. If it is less than 15% by mass, the heat generation of the rubber will be insufficient, the elongation (EB) of the rubber will be insufficient, and the heat resistance may be deteriorated. The SBR content is preferably 60% by mass or less, more preferably 50% by mass or less, still more preferably 45% by mass or less, and particularly preferably 42% by mass or less. If it exceeds 60% by mass, the rubber elongation (EB) tends to decrease.

The total content of HPNR, modified BR, and SBR in 100% by mass of the rubber component is preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and particularly preferably 100% by mass. . If it is less than 70% by mass, the durability and low fuel consumption of the run-flat tire may not be sufficiently improved.

The rubber composition of the present invention contains silica. By including silica together with the modified BR, good fuel economy and rubber strength (rigidity) can be obtained, and the durability and fuel efficiency of the run-flat tire can be improved. Examples of silica include dry process silica (anhydrous silica), wet process silica (hydrous silica), and wet process silica is preferred because it has many silanol groups.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 30 m ² / g or more, more preferably 100 m ² / g or more, and further preferably 150 m ² / g or more. If it is less than 30 m ² / g, the fracture strength after vulcanization tends to decrease, and the run-flat durability tends to decrease. The N ₂ SA of silica is preferably 500 m ² / g or less, more preferably 300 m ² / g or less, and still more preferably 200 m ² / g or less. If it exceeds 500 m ² / g, the processability tends to deteriorate.
The _N 2 SA of silica is a value measured by the BET method in accordance with ASTM D3037-81.

The content of silica is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and still more preferably 12 parts by mass or more with respect to 100 parts by mass of the rubber component. If the amount is less than 5 parts by mass, sufficient fuel economy may not be obtained. The content of the silica is preferably 100 parts by mass or less, more preferably 80 parts by mass or less. If it exceeds 100 parts by mass, the workability tends to decrease.

The rubber composition preferably contains a silane coupling agent together with silica.
As the silane coupling agent, any silane coupling agent conventionally used in combination with silica can be used in the rubber industry, and examples thereof include sulfide systems such as bis (3-triethoxysilylpropyl) disulfide, 3- Mercapto type such as mercaptopropyltrimethoxysilane, vinyl type such as vinyltriethoxysilane, amino type such as 3-aminopropyltriethoxysilane, glycidoxy type of γ-glycidoxypropyltriethoxysilane, 3-nitropropyltrimethoxy Examples thereof include nitro compounds such as silane and chloro compounds such as 3-chloropropyltrimethoxysilane. Among these, sulfide type is preferable, and bis (3-triethoxysilylpropyl) disulfide is more preferable.

The content of the silane coupling agent is preferably 2 parts by mass or more, more preferably 4 parts by mass or more, and still more preferably 6 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 (rigidity) and wear resistance tend to deteriorate. Further, the content of the silane coupling agent is preferably 15 parts by mass or less, more preferably 13 parts by mass or less. When it exceeds 15 parts by mass, there is a tendency that an effect commensurate with the increase in cost cannot be obtained.

The rubber composition of the present invention contains aluminum nitride. As a result, a run-flat tire excellent in thermal conductivity, low heat generation, rigidity, and run-flat durability can be obtained. For example, in the side wall reinforcing layer, a temperature rise occurs locally (locally) at a certain limited spot, and rubber destruction proceeds. In the present invention, by adding aluminum nitride, it is possible to increase the thermal conductivity, to suppress the temperature rise by diffusing locally generated heat throughout the rubber, and to suppress the progress of rubber destruction. Therefore, it is estimated that good low heat build-up (low fuel consumption) and run flat durability can be obtained.

The oxygen content of aluminum nitride is preferably 0.4% by mass or more, more preferably 0.75% by mass or more, and further preferably 0.8% by mass or more. The oxygen content is preferably 5% by mass or less, more preferably 1.5% by mass or less, still more preferably 1.3% by mass or less, and particularly preferably 1.1% by mass or less. When the oxygen content is in the above range (the surface of the aluminum nitride is oxidized so that the oxygen content is in the above range (an aluminum oxide film is formed on the surface)), thermal conductivity and low The heat generation can be improved and the durability of the run-flat tire can be improved. The oxygen content is a value measured by a combustion analysis method. For example, the amount of CO gas generated by high temperature pyrolysis of aluminum nitride in a graphite crucible using “EMGA2800” manufactured by HORIBA, Ltd. It is requested from. The oxidation treatment can be performed, for example, by treating aluminum nitride at a temperature of 500 to 900 ° C. in the presence of oxygen.

The cation impurity content of aluminum nitride is preferably 0.5% by mass or less, more preferably 0.3% by mass or less, and still more preferably 0.2% by mass or less. In particular, among the cationic impurities, the total content of Fe, Ca and Si is preferably 0.12% by mass or less (more preferably 0.08% by mass or less, and further preferably 0.05% by mass or less). . The minimum of the said content rate is not specifically limited. When the amount of cationic impurities (the above total content) is less than the specific amount, the thermal conductivity and low heat buildup can be improved, and the durability of the run-flat tire can be improved. The cation impurity concentration can be quantified by ICP emission spectroscopic analysis of the solution after aluminum nitride is melted with alkali and then neutralized with an acid. For example, it is measured using “ICPS-1000” manufactured by Shimadzu Corporation. it can. In addition, a cation impurity means a cationic substance group other than aluminum contained in aluminum nitride.

The carbon content (amount of impurity carbon) of aluminum nitride is preferably 0.1% by mass or less, more preferably 0.05% by mass or less, and still more preferably 0.04% by mass or less. The lower limit of the carbon content is not particularly limited. When the carbon content is low (0.1% by mass or less), thermal conductivity and low heat generation can be improved, and durability of the run-flat tire can be improved. The carbon content can be determined from the amount of CO and CO ₂ gas generated by firing aluminum nitride in an oxygen stream, and can be measured using, for example, “EMIA-110” manufactured by Horiba, Ltd.

The average particle diameter of aluminum nitride is preferably 0.01 μm or more, more preferably 0.1 μm or more, still more preferably 0.5 μm or more, and particularly preferably 1.0 μm or more. The average particle diameter is preferably 5 μm or less, more preferably 3.5 μm or less, still more preferably 2.5 μm or less, and particularly preferably 2.0 μm or less. When the average particle size is in the above range, thermal conductivity and low heat build-up can be improved, and durability of the run flat tire can be improved. The average particle diameter is a volume average particle diameter of aluminum nitride aggregate particles measured with a laser diffraction particle size distribution analyzer, and can be measured using, for example, “CAPA500” manufactured by Horiba, Ltd. As the aluminum nitride, aluminum nitride having an average particle diameter in the above range may be used alone, or two or more kinds of aluminum nitride having different average particle diameters may be mixed so that the average particle diameter is in the above range. May be used.

The pressed bulk density of aluminum nitride is preferably 0.2 g / cm ³ or more, more preferably 0.5 g / cm ³ or more, and further preferably 1.0 g / cm ³ or more. The pressurized bulk density is preferably 7.0 g / cm ³ or less, more preferably 3.0 g / cm ³ or less, and still more preferably 2.0 g / cm ³ or less. When the pressurized bulk density is in the above range, thermal conductivity and low heat build-up can be improved, and run-flat durability can be improved. The pressed bulk density is a value obtained by preparing an aluminum nitride pellet having a diameter of 20 mm and a thickness of 2.0 mm at a press pressure of 19.6 MPa and measuring the pellet.

The specific surface area of aluminum nitride is preferably 0.5 m ² / g or more, more preferably 1.0 m ² / g or more, and still more preferably 2.0 m ² / g or more. The specific surface area is preferably 10.0 m ² / g or less, more preferably 5.0 m ² / g or less, and still more preferably 3.0 m ² / g or less. When the specific surface area is in the above range, thermal conductivity and low heat generation can be improved, and run-flat durability can be improved. The specific surface area is a value determined by the BET method by N ₂ adsorption, for example, can be measured using "Flow Soap 2300" manufactured by Shimadzu Corporation.

The thermal conductivity of aluminum nitride is preferably 80 W / (m · K) or more, more preferably 90 W / (m · K) or more, and still more preferably 100 W / (m · K) or more. If it is less than 80 W / (m · K), sufficient fuel economy and run flat durability may not be obtained. The upper limit of the thermal conductivity of aluminum nitride is not particularly limited.
Here, the thermal conductivity of aluminum nitride is a value measured according to the thermal conductivity test method of JIS R1611-1997 “Test method of thermal diffusivity, specific heat capacity, thermal conductivity by laser flash method of fine ceramics”. It is.

The method for producing aluminum nitride is not particularly limited. For example, a reduction nitriding method (for example, a method in which aluminum oxide is brought into contact with nitrogen gas or ammonia gas in the presence of carbon under heating (for example, JP-A-2006-199541). (1)), aluminum nitride obtained by a direct nitriding method (for example, a method of treating metal aluminum with nitrogen in a nitrogen atmosphere), or a mixture thereof. Among these, aluminum nitride obtained by a reduction nitriding method is preferable because it has good thermal conductivity. Moreover, you may grind | pulverize aluminum nitride as needed, and it is preferable to grind | pulverize so that an average particle diameter may become the said range.

The content of aluminum nitride is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, still more preferably 20 parts by mass or more, and particularly 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, the effect obtained by blending aluminum nitride may not be sufficiently obtained. Further, the content is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, still more preferably 70 parts by mass or less, and particularly preferably 60 parts by mass or less with respect to 100 parts by mass of the rubber component. If it exceeds 100 parts by mass, the run-flat durability tends to decrease.

In addition to the above components, the rubber composition of the present invention includes compounding agents generally used in the production of rubber compositions, such as carbon black, white fillers (for example, mica such as calcium carbonate and sericite, hydroxylation) Reinforcing fillers such as aluminum, magnesium oxide, magnesium hydroxide, clay, talc, alumina, titanium oxide), zinc oxide, stearic acid, various anti-aging agents, antioxidants, ozone deterioration inhibitors, softeners such as oil Further, a vulcanizing agent such as wax and sulfur, a vulcanization accelerator, a vulcanization acceleration auxiliary agent and the like can be appropriately blended.

The rubber composition of the present invention preferably contains carbon black. Examples of carbon black that can be used include GPF, FEF, HAF, ISAF, and SAF, but are not particularly limited. By blending carbon black, the reinforcing property can be enhanced and the durability of the run-flat tire can be improved.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 30 m ² / g or more, and more preferably 35 m ² / g or more, from the viewpoint of obtaining sufficient reinforcement and durability of the run flat tire. Further, the nitrogen adsorption specific surface area of carbon black, from the viewpoint of excellent low heat build-up (low fuel consumption), is preferably from 100 m ² / g, more preferably not more than ^{80 m} 2 / g, more preferably ^{60 m} 2 / g or less .
In addition, the nitrogen adsorption specific surface area of carbon black is calculated | required by A method of JISK6217.

The dibutyl phthalate oil absorption (DBP) of carbon black is preferably 50 ml / 100 g or more, more preferably 80 ml / 100 g or more, from the viewpoint of obtaining sufficient reinforcement and durability of the run flat tire. Further, the DBP of carbon black is preferably 300 ml / 100 g or less, more preferably 200 ml / 100 g or less, and still more preferably 150 ml / 100 g or less, from the viewpoint of excellent fatigue resistance such as elongation at break. In addition, DBP of carbon black is calculated | required by the measuring method of JISK6217-4.

When the rubber composition contains carbon black, the carbon black content is preferably 5 parts by mass or more, more preferably 100 parts by mass with respect to 100 parts by mass of the rubber component from the viewpoint of obtaining sufficient rubber strength (rigidity). Is 20 parts by mass or more, more preferably 35 parts by mass or more. Further, the carbon black content is preferably 80 parts by mass or less, more preferably 65 parts by mass or less, from the viewpoint that the viscosity at the time of kneading is appropriately maintained and the processability is excellent.

Examples of the vulcanization accelerator include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N, N-dicyclohexyl-2. -Sulfenamide vulcanization accelerators such as benzothiazolylsulfenamide (DZ), mercaptobenzothiazole (MBT), dibenzothiazolyl disulfide (MBTS), diphenylguanidine (DPG) and the like. Of these, sulfenamide-based vulcanization accelerators are preferable, and TBBS is more preferable in terms of excellent vulcanization characteristics, low heat build-up after vulcanization, and good run flat durability.

（式中、Ｒ^６、Ｒ^７及びＲ^８は、同一若しくは異なって、炭素数５〜１２のアルキル基を示す。ｘ及びｙは、同一若しくは異なって、２〜４の整数を示す。ｍは０〜１０の整数を示す。） As the vulcanization accelerating aid, an alkylphenol / sulfur chloride condensate can be suitably used. Thereby, a rubber composition with high hardness can be obtained. Examples of the alkylphenol / sulfur chloride condensate include compounds represented by the following formula (10).

(In formula, R < ⁶ >, R < ⁷ > and R < ⁸ > are the same or different and show a C5-C12 alkyl group. X and y are the same or different and show the integer of 2-4. M is Represents an integer of 0 to 10.)

m is an integer of 0 to 10 and preferably an integer of 1 to 9 from the viewpoint of good dispersibility of the alkylphenol / sulfur chloride condensate in the rubber component. x and y are integers of 2 to 4 from the viewpoint that high hardness can be efficiently expressed (reversion suppression), and both are preferably 2. When X exceeds 4, it tends to be thermally unstable. When X is 1, the sulfur content (sulfur weight) in the alkylphenol-sulfur chloride condensate decreases. R ^{6 to} R ⁸ are alkyl groups having 5 to 12 carbon atoms, preferably alkyl groups having 6 to 9 carbon atoms, from the viewpoint of good dispersibility of the alkylphenol / sulfur chloride condensate in the rubber component.

The alkylphenol / sulfur chloride condensate can be prepared by a known method and is not particularly limited. For example, a method of reacting alkylphenol and sulfur chloride at a molar ratio of 1: 0.9 to 1.25, etc. Is mentioned.

Specific examples of the alkylphenol / sulfur chloride condensate include Takkol V200 (following formula) manufactured by Taoka Chemical Co., Ltd.

（式中、ｍは０〜１０の整数を表す。）

(In the formula, m represents an integer of 0 to 10.)

The sulfur content of the alkylphenol / sulfur chloride condensate is a ratio obtained by heating to 800 to 1000 ° C. in a combustion furnace and converting it into SO ₂ gas or SO ₃ gas, optically quantifying it from the amount of gas generated. Say.

The content of the alkylphenol / sulfur chloride condensate is 0.2 parts by mass or more, preferably 0.5 parts by mass or more, and more preferably 1.0 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 0.2 parts by mass, sufficient run-flat durability may not be obtained. Moreover, this content is 3.0 mass parts or less, Preferably it is 2.5 mass parts or less. If it exceeds 3.0 parts by mass, the run-flat performance may be reduced.

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 thermal conductivity of the rubber composition (after vulcanization) of the present invention is preferably 0.35 W / (m · K) or more, more preferably 0.36 W / (m · K) or more. If it is less than 0.35 W / (m · K), sufficient run-flat durability may not be obtained. The upper limit of the thermal conductivity is not particularly limited.
In addition, thermal conductivity is a value measured by the method as described in the below-mentioned Example.

The rubber composition of the present invention can be used for each member of a run flat tire, and in particular, can be suitably used for a sidewall reinforcing layer.
By using the rubber composition of the present invention in which HPNR, modified BR, silica and aluminum nitride are blended in the sidewall reinforcement layer, the sidewall reinforcement layer can be imparted with high thermal conductivity and low heat build-up, and rubber. Therefore, it is possible to provide a run-flat tire having excellent thermal conductivity, low heat build-up (low fuel consumption), and excellent rigidity and run-flat durability.

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-mentioned compounding agent is extruded in accordance with the shape of each member (particularly, the sidewall reinforcing layer) of the run-flat tire at an unvulcanized stage, and other tire members At the same time, 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 Examples and Comparative Examples will be described together.
NR: TSR
HPNR: HPNR (saponified natural rubber) prepared in Production Example 1 below
BR: BR150B manufactured by Ube Industries, Ltd.
Modified BR: Modified butadiene rubber manufactured by Sumitomo Chemical Co., Ltd. (vinyl content: 15% by mass, R ¹ , R ² and R ^{3 in} the above formula (1) = — OCH ₃ , R ⁴ and R ⁵ = —CH ₂ CH ₃ , n = 3)
SBR: SBR1502 manufactured by Sumitomo Chemical Co., Ltd.
Carbon black: Diamond Black E (FEF, N ₂ SA: 41 m ² / g, DBP oil absorption: 115 ml / 100 g) manufactured by Mitsubishi Chemical Corporation
Silica: ULTRASIL VN3 manufactured by Degussa (average primary particle size: 15 nm, N ₂ SA: 175 m ² / g)
Silane coupling agent: Si266 (bis (3-triethoxysilylpropyl) disulfide) manufactured by Degussa
Aluminum nitride: High-purity aluminum nitride powder made by Tokuyama Corporation H grade (aluminum nitride obtained by reduction nitriding method, specific surface area 2.59 m ² / g, average particle diameter 1.13 μm, pressurized bulk density 1.68 g / Cm ³ , oxygen content 0.83 mass%, carbon content 210 ppm, Ca content 230 ppm, Si content 43 ppm, Fe content 12 ppm, cationic impurity content: 0.15 mass%, thermal conductivity 1. 84W / (m · K))
Anti-aging agent 6C: Antigen 6C (N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd.
Anti-aging agent FR: Antigen FR manufactured by Sumitomo Chemical Co., Ltd. (A product obtained by purifying a reaction product of an amine and a ketone and having no amine residue, a quinoline-based anti-aging agent)
Zinc oxide: Two types of zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. Stearate: Sulfur sulfur manufactured by NOF Corporation: Powdered sulfur vulcanization accelerator manufactured by Karuizawa Sulfur Co., Ltd .: Ouchi Shinsei Chemical Industry Co., Ltd. NOXERA-NS (N-tert-butyl-2-benzothiazolylsulfenamide)
Vulcanization accelerating aid: Takiroll V200 manufactured by Taoka Chemical Co., Ltd.

Hereinafter, various chemicals used in the production examples will be described.
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).

With respect to the solid rubber and TSR obtained in Production Example 1, the nitrogen content, phosphorus content, and gel content were measured by the methods described below. The results are shown in Table 1.

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

(Measurement of phosphorus content)
The phosphorus content was determined using an ICP emission spectrometer (ICPS-8100, manufactured by Shimadzu Corporation).

(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

Examples 1-10 and Comparative Examples 1-4
According to the blending contents shown in Table 2, using a 1.7 L Banbury mixer, among the blended materials, materials other than sulfur, vulcanization accelerator, and vulcanization accelerator auxiliary are kneaded for 4 minutes at 150 ° C., A kneaded product was obtained. Next, sulfur, a vulcanization accelerator, and a vulcanization acceleration auxiliary agent are added to the kneaded material obtained, and kneaded for 3 minutes at 80 ° C. using an open roll to obtain an unvulcanized rubber composition. It was. The obtained unvulcanized rubber composition was press vulcanized at 160 ° C. for 20 minutes to obtain a vulcanized rubber composition.
The obtained unvulcanized rubber composition was formed into a side wall reinforcing layer shape with a thickness of 20 mm, bonded to another tire part, and vulcanized at 160 ° C. for 12 minutes to obtain a test run. A flat tire was manufactured (tire size: 215 / 45ZRI7).

The following evaluation was performed using the obtained vulcanized rubber composition and test run-flat tire. Each test result is shown in Table 2.

(Viscoelasticity test)
Using a viscoelastic spectrometer manufactured by Iwamoto Seisakusho Co., Ltd., the complex elastic modulus (E ^* ) and loss tangent (tan δ) were measured under the conditions of a measurement temperature of 70 ° C., an initial strain of 10%, a dynamic strain of ± 1%, and a frequency of 10 Hz. The measured E ^* and tan δ were expressed as an index with Comparative Example 1 as 100 (reference). The larger the E ^* index, the higher the rigidity and the better. Also, the larger the tan δ index, the less heat is generated and the better the fuel efficiency.

(Thermal conductivity)
Using a thermal conductivity measuring device (QTM-D3, manufactured by Kyoto Electronics Industry Co., Ltd.), a test piece of vulcanized rubber composition (length 100 mm × width 50 mm × thickness 10 mm) at a measurement temperature of 25 ° C. and a measurement time of 60 seconds. The thermal conductivity (W / (m · K)) of the sample was homogeneous and the measurement surface was smooth.

(Run flat durability)
The manufactured test run-flat tire was run on a drum at 80 km / h at an air pressure of 0 kPa, the running distance until the tire broke was measured, and the run-flat durability index of Comparative Example 1 was set to 100. The mileage of each formulation was displayed as an index according to the calculation formula. In addition, it shows that it is excellent in run flat durability, so that a run flat durability index | exponent is large.
(Run flat durability index) = (travel distance of each formulation) / (travel distance of Comparative Example 1) × 100

In an embodiment including a modified natural rubber (HPNR) having a phosphorus content of 200 ppm or less, a modified butadiene rubber (modified BR) modified with the compound represented by the above formula (1), silica, and aluminum nitride In addition to excellent thermal conductivity and low heat generation (low fuel consumption), it was also excellent in rigidity and run flat durability. On the other hand, Comparative Example 1 which does not contain all of HPNR, modified BR, silica, and aluminum nitride was inferior in all performances to the Examples. Further, Comparative Examples 2 and 3 in which HPNR and modified BR were not blended, respectively, were inferior in low exothermic property (low fuel consumption) and run-flat durability as compared with Examples. The comparative example 4 which did not mix | blend aluminum nitride had low heat conductivity, and its rigidity and run-flat durability were inferior compared with the Example.

Claims (10)

Seen containing a phosphorus content of less 200ppm modified natural rubber, a modified butadiene rubber modified by a compound represented by the following formula (1), and silica, and aluminum nitride,
The modified natural rubber saponifies the natural rubber latex with alkali, and the phosphorus compound separated by saponification is washed and removed repeatedly by washing the rubber agglomerated after saponification, thereby reducing the phosphorus content to 200 ppm or less. A rubber composition for run-flat tires.

(In the formula (1), R ¹ , R ² and R ³ are the same or different and each represents an alkyl group, an alkoxy group, a silyloxy group, an acetal group, a carboxyl group, a mercapto group, or a derivative thereof. R ⁴ and R ⁵ is the same or different and represents a hydrogen atom, an alkyl group or a cyclic ether group, and n represents an integer.) The run-flat tire rubber composition according to claim 1, wherein the modified natural rubber has a gel content of 20% by mass or less measured as a toluene insoluble matter. 3. The run-flat tire according to claim 1, wherein the modified natural rubber has no phospholipid peak at -3 ppm to 1 ppm and substantially no phospholipid in ³¹ P NMR measurement of a chloroform extract. Rubber composition. The run-flat tire rubber composition according to any one of claims 1 to 3, wherein the modified natural rubber has a nitrogen content of 0.3 mass% or less. The run-flat tire rubber composition according to any one of claims 1 to 4, wherein the modified natural rubber has a nitrogen content of 0.15 mass% or less. The rubber composition for a run-flat tire according to any one of claims 1 to 5 , wherein the aluminum nitride has an oxygen content of 0.4 to 5 mass%. The content of the modified natural rubber in 100% by mass of the rubber component is 15 to 60% by mass, the content of the modified butadiene rubber is 15 to 60% by mass, and the content of styrene butadiene rubber is 15 to 60% by mass. The rubber composition for run-flat tires according to any one of claims 1 to 6 . The rubber composition for a run-flat tire according to any one of claims 1 to 7 , wherein a content of the aluminum nitride is 10 to 100 parts by mass with respect to 100 parts by mass of the rubber component. The rubber composition for a run flat tire according to any one of claims 1 to 8 , which is used for a side wall reinforcing layer. A run flat tire using the rubber composition according to any one of claims 1 to 9 .